publicationDate,title,abstract,id
2023-09-21,Lateral Solid Phase Epitaxy of Yttrium Iron Garnet,"Solid phase epitaxy is a crystallization technique used to produce high
quality thin films. Lateral solid phase epitaxy furthermore enables the
realization of non-planar structures, which are interesting, e.g., in the field
of spintronics. Here, we demonstrate lateral solid phase epitaxy of yttrium
iron garnet over an artificial edge, such that the crystallization direction is
perpendicular to the initial seed. We use single crystalline garnet seed
substrates partially covered by a \ch{SiO_x} film to study the lateral
crystallization over the \ch{SiO_x} mesa. The yttrium iron garnet layer retains
the crystal orientation of the substrate not only when in direct contact with
the substrate, but also across the edge on top of the \ch{SiO_x} mesa. By
controlling the crystallization dynamics it is possible to almost completely
suppress the formation of polycrystals and to enable epitaxial growth of single
crystalline yttrium iron garnet on top of mesas made from arbitrary materials.
From a series of annealing experiments, we extract an activation energy of
\SI{2.8}{eV} and a velocity prefactor of \SI{5.1e13}{nm/s} for the lateral
epitaxial crystallization along the <$100$> direction. Our results pave the way
to engineer single crystalline non-planar yttrium iron garnet structures with
controlled crystal orientation.",2309.12002v1
2019-01-25,Focused ion beam modification of non-local magnon-based transport in yttrium iron garnet/platinum heterostructures,"We study the impact of Ga ion exposure on the local and non-local
magnetotransport response in heterostructures of the ferrimagnetic insulator
yttrium iron garnet and platinum. In particular, we cut the yttrium iron garnet
layer in between two electrically separated wires of platinum using a Ga ion
beam, and study the ensuing changes in the magnetoresistive response. We find
that the non-local magnetoresistance signal vanishes when the yttrium iron
garnet film between the Pt wires is fully cut, although the local spin Hall
magnetoresistance signal remains finite. This observation corroborates the
notion that pure spin currents carried by magnons are crucial for the non-local
magnetotransport effects observed in magnetic insulator/metal nanostructures.",1901.08894v1
2017-12-27,Finite temperature magnon spectra in yttrium iron garnet from mean field approach in tight-binding model,"We study magnon spectra at finite temperature in yttrium iron garnet from
tight-binding model with nearest neighboring exchange interaction. The spin
reduction due to thermal magnon excitation are taken into account via the mean
field approximation to the local spin and found to be different at two sets of
iron atoms. The resulting temperature dependence of the spin wave gap shows
good agreement with experiment. We find only two magnon modes are relevant to
ferromagnetic resonance.",1712.09512v1
2023-02-21,Aluminium substituted yttrium iron garnet thin films with reduced Curie temperature,"Magnetic garnets such as yttrium iron garnet (Y$_3$Fe$_5$O$_{12}$, YIG) are
widely used in spintronic and magnonic devices. Their magnetic and
magneto-optical properties can be modified over a wide range by tailoring their
chemical composition. Here, we report the successful growth of Al-substituted
yttrium iron garnet (YAlIG) thin films via radio frequency sputtering in
combination with an ex situ annealing step. Upon selecting appropriate process
parameters, we obtain highly crystalline YAlIG films with different Al$^{3+}$
substitution levels on both, single crystalline Y$_3$Al$_5$O$_{12}$ (YAG) and
Gd$_3$Ga$_5$O$_{12}$ (GGG) substrates. With increasing Al$^{3+}$ substitution
levels, we observe a reduction of the saturation magnetisation as well as a
systematic decrease of the magnetic ordering temperature to values well below
room temperature. YAlIG thin films thus provide an interesting material
platform for spintronic and magnonic experiments in different magnetic phases.",2302.10517v2
2012-07-13,Magnetic relaxation in bilayers of yttrium iron garnet/platinum due to the dynamic coupling at the interface,"We show that in ferromagnetic (FM)/normal metal (NM) bilayers the dynamic
coupling at the interface transfers an additional magnetic relaxation from the
heavily damped motion of the conduction electron spins in the NM layer to the
FM spins. While the FM relaxation rates due to two-magnon scattering and spin
pumping decrease rapidly with increasing FM film thickness, the damping due to
the dynamic coupling does not depend on the FM film thickness. The proposed
mechanism explains the very large broadening of ferromagnetic resonance lines
in thick films of yttrium iron garnet after deposition of a Pt layer.",1207.3330v1
2013-02-28,Spin mixing conductance at a well-controlled platinum/yttrium iron garnet interface,"A platinum (Pt)/yttrium iron garnet (YIG) bilayer system with a
well-controlled interface has been developed; spin mixing conductance at the
Pt/YIG interface has been studied. Crystal perfection at the interface is
experimentally demonstrated to contribute to large spin mixing conductance. The
spin mixing conductance is obtained to be $1.3\times10^{18} \rm{m^{-2}}$ at the
well-controlled Pt/YIG interface, which is close to a theoretical prediction.",1302.7091v3
2013-09-09,Induced magneto-transport properties at palladium/yttrium iron garnet interface,"As a thin layer of palladium (Pd) is directly deposited on an yttrium iron
garnet or YIG (Y3Fe5O12) magnetic insulator film, Pd develops both low- and
high-field magneto-transport effects that are absent in standalone Pd or thick
Pd on YIG. While the low-field magnetoresistance peak of Pd tracks the coercive
field of the YIG film, the much larger high-field magnetoresistance and the
Hall effect do not show any obvious relationship with the bulk YIG
magnetization. The distinct high-field magneto-transport effects in Pd are
shown to be caused by interfacial local moments in Pd.",1309.2213v1
2016-07-12,Thermal spin dynamics of yttrium iron garnet,"Yttrium Iron Garnet is the prototypical material used to study pure spin
currents. It is a complex material with 20 magnetic atoms in the unit cell.
Almost all theories and experimental analysis approximates this complicated
material to a simple ferromagnet with a single spin wave mode. We use the
method of atomistic spin dynamics to study the temperature evolution of the
full 20 mode exchange spin wave spectrum. Our results show a strong frequency
dependence of the modes in quantitative agreement with neutron scattering
experiments. We find this causes in a reduction in the net spin pumping due to
the thermal occupation of optical modes with the opposite chirality to the FMR
mode.",1607.03263v1
2018-11-06,Parametrically squeezed states of microwave magnons in yttrium iron garnet films,"We demonstrate theoretically, and confirm experimentally, that nonlinear spin
waves excited in thin yttrium iron garnet films are good candidates for
squeezing vacuum quantum noise. The experimental demonstration is in the form
of a measurement of spin-wave induced modulation instability (IMI) conducted in
the classical regime. The experiment evidences strong phase locking of an idler
wave parametrically generated in the film with a deterministic small-signal
wave launched into the film from an external source. The theory predicts that
the same behaviour will be observed for vacuum quantum noise, resulting in
squeezing of the noise.",1811.02104v1
2002-02-10,Stable Magnetostatic Solitons in Yttrium Iron Garnet Film Waveguides for Tilted in-Plane Magnetic Fields,"The possibility of nonlinear pulses generation in Yttrium Iron Garnet thin
films for arbitrary direction between waveguide and applied static in-plane
magnetic field is considered. Up to now only the cases of in-plane magnetic
fields either perpendicular or parallel to waveguide direction have been
studied both experimentally and theoretically. In the present paper it is shown
that also for other angles (besides 0 or 90 degrees) between a waveguide and
static in-plane magnetic field the stable bright or dark (depending on
magnitude of magnetic field) solitons could be created.",0202167v1
2020-11-17,Non-local magnon-based transport in yttrium iron garnet/platinum heterostructures at high temperatures,"The spin Hall effect in a heavy metal thin film allows to probe the magnetic
properties of an adjacent magnetic insulator via magnetotransport measurements.
Here, we investigate the magnetoresistive response of yttrium iron
garnet/platinum heterostructures from room temperature to beyond the Curie
temperature $T_\mathrm{C, YIG} \approx 560\,\mathrm{K}$ of the ferrimagnetic
insulator. We find that the amplitude of the (local) spin Hall
magnetoresistance decreases monotonically from $300\,\mathrm{K}$ towards
$T_\mathrm{C}$, mimicking the evolution of the saturation magnetization of
yttrium iron garnet. Interestingly, the spin Hall magnetoresistance vanishes
around $500\,\mathrm{K}$, well below $T_\mathrm{C}$, which we attribute to the
formation of a parasitic interface layer by interdiffusion. Around room
temperature the non-local magnon-mediated magnetoresistance exhibits a power
law scaling $T^{\alpha}$ with $\alpha = 3/2$, as already reported. The exponent
decreases gradually to $\alpha \sim 1/2$ at around $420\,\mathrm{K}$, before
the non-local magnetoresistance vanishes rapidly at a similar temperature as
the spin Hall magnetoresistance. We attribute the reduced $\alpha$ at high
temperatures to the increasing thermal magnon population which leads to
enhanced scattering of the non-equilibrium magnon population and a reduced
magnon diffusion length. Finally, we find a magnetic field independent offset
voltage in the non-local signal for $T > 470\,\mathrm{K}$ which we associate
with electronic leakage currents through the normally insulating yttrium iron
garnet film. Indeed, this non-local offset voltage is thermally activated with
an energy close to the band gap.",2011.08589v1
2022-03-08,Enhancement of thermal spin pumping by orbital angular momentum of rare earth iron garnet,"In a bilayer of ferromagnetic and non-magnetic metal, spin pumping can be
generated by a thermal gradient. The spin current generation depends on the
spin mixing conductance of the interface and the magnetic properties of the
ferromagnetic layer. Due to its low intrinsic damping, rare earth iron garnet
is often used for the ferromagnetic layer in the spin Seebeck experiment.
However, it is actually a ferrimagnetic with antiferromagnetically coupled
magnetic lattices and the contribution of rare earth magnetic lattice of rare
earth iron garnet on thermal spin pumping is not well understand. Here we focus
on the effect of magnetic properties of lanthanide and show that the orbital
angular momentum of rare earth iron garnet enhances thermal spin current
generation of lanthanide substituted yttrium iron garnet.",2203.03915v2
2014-02-26,Magneto-elastic modes and lifetime of magnons in thin yttrium-iron garnet films,"We calculate the effects of the spin-lattice coupling on the magnon spectrum
of thin ferromagnetic films consisting of the magnetic insulator yttrium-iron
garnet. The magnon-phonon hybridisation generates a characteristic minimum in
the spin dynamic structure factor which quantitatively agrees with recent
Brillouin light scattering experiments. We also show that at room temperature
the phonon contribution to the magnon damping exhibits a rather complicated
momentum dependence: In the exchange regime the magnon damping is dominated by
Cherenkov type scattering processes, while in the long-wavelength dipolar
regime these processes are subdominant and the magnon damping is two orders of
magnitude smaller. We supplement our calculations by actual measurements of the
magnon relaxation in the dipolar regime. Our theory provides a simple
explanation of a recent experiment probing the different temperatures of the
magnon and phonon gases in yttrium-iron garnet.",1402.6575v2
2016-02-24,Spin Seebeck effect at microwave frequencies,"We experimentally study the transient voltage response of yttrium iron
garnet/platinum bilayer samples subject to periodic heating up to gigahertz
frequencies. We observe an intrinsic cutoff frequency of the induced
thermopower voltage, which characteristically depends on the thickness of the
yttrium iron garnet film. The cutoff frequency reaches values of up to 350 MHz
in a 50 nm thick yttrium iron garnet film, but drops to below 1 MHz for
several-micrometer-thick films. These data corroborate the notion that the
magnon spectrum responsible for the spin current emission in the spin Seebeck
effect can be shaped by tuning the thickness of the ferromagnetic layer.",1602.07442v2
2021-12-06,Accumulation of magnetoelastic bosons in yttrium iron garnet: kinetic theory and wave vector resolved Brillouin light scattering,"We derive and solve quantum kinetic equations describing the accumulation of
magnetoelastic bosons in an overpopulated magnon gas realized in a thin film of
the magnetic insulator yttrium iron garnet. We show that in the presence of a
magnon condensate, there is a non-equilibrium steady state in which incoherent
magnetoelastic bosons accumulate in a narrow region in momentum space for
energies slightly below the bottom of the magnon spectrum. The results of our
calculations agree quite well with Brillouin light scattering measurements of
the stationary non-equilibrium state of magnons and magnetoelastic bosons in
yttrium iron garnet.",2112.03310v2
2020-09-30,Electronic structure and finite temperature magnetism of yttrium iron garnet,"Yttrium iron garnet is a complex ferrimagnetic insulator with 20 magnon modes
which is used extensively in fundamental experimental studies of magnetisation
dynamics. As a transition metal oxide with moderate gap (2.8 eV), yttrium iron
garnet requires a careful treatment of electronic correlation. We have applied
quasiparticle self-consistent GW to provide a fully ab initio description of
the electronic structure and resulting magnetic properties, including the
parameterisation of a Heisenberg model for magnetic exchange interactions.
Subsequent spin dynamical modelling with quantum statistics extends our
description to the magnon spectrum and thermodynamic properties such as the
Curie temperature, finding favourable agreement with experimental measurements.
This work provides a snapshot of the state-of-the art in modelling of complex
magnetic insulators.",2009.14601v1
2018-07-02,Picosecond acoustic excitation driven ultrafast magnetization dynamics in dielectric Bi-substituted yttrium iron garnet,"Using femtosecond optical pulses, we have investigated the ultrafast
magnetization dynamics induced in a dielectric film of bismuth-substituted
yttrium iron garnet (Bi-YIG) buried below a thick Cu/Pt metallic bilayer. We
show that exciting the sample from Pt surface launches an acoustic strain pulse
propagating into the garnet film. We discovered that this strain pulse induces
a coherent magnetization precession in the Bi-YIG at the frequency of the
ferromagnetic resonance. The observed phenomena can be explain by
strain-induced changes of magnetocristalline anisotropy via the inverse
magnetostriction effect. These findings open new perspectives toward the
control of the magnetization in magnetic garnets embedded in complex
heterostructure devices.",1807.00610v1
2019-03-01,Nanoscale X-Ray Imaging of Spin Dynamics in Yttrium Iron Garnet,"Time-resolved scanning transmission x-ray microscopy (TR-STXM) has been used
for the direct imaging of spin wave dynamics in thin film yttrium iron garnet
(YIG) with spatial resolution in the sub 100 nm range. Application of this
x-ray transmission technique to single crystalline garnet films was achieved by
extracting a lamella (13x5x0.185 $\mathrm{\mu m^3}$) of liquid phase epitaxy
grown YIG thin film out of a gadolinium gallium garnet substrate. Spin waves in
the sample were measured along the Damon-Eshbach and backward volume directions
of propagation at gigahertz frequencies and with wavelengths in a range between
100~nm and 10~$\mathrm{\mu}$m. The results were compared to theoretical models.
Here, the widely used approximate dispersion equation for dipole-exchange spin
waves proved to be insufficient for describing the observed Damon-Eshbach type
modes. For achieving an accurate description, we made use of the full
analytical theory taking mode-hybridization effects into account.",1903.00498v1
2018-03-15,Synthetic antiferromagnetic coupling between ultra-thin insulating garnets,"The use of magnetic insulators is attracting a lot of interest due to a rich
variety of spin-dependent phenomena with potential applications to spintronic
devices. Here we report ultra-thin yttrium iron garnet (YIG) / gadolinium iron
garnet (GdIG) insulating bilayers on gadolinium iron garnet (GGG). From spin
Hall magnetoresistance (SMR) and X-ray magnetic circular dichroism
measurements, we show that the YIG and GdIG magnetically couple antiparallel
even in moderate in-plane magnetic fields. The results demonstrate an
all-insulating equivalent of a synthetic antiferromagnet in a garnet-based thin
film heterostructure and could open new venues for insulators in magnetic
devices. As an example, we demonstrate a memory element with orthogonal
magnetization switching that can be read by SMR.",1803.05545v1
2021-09-24,Damping in yttrium iron garnet film with an interface,"We report strong damping enhancement in a 200 nm thick yttrium iron garnet
(YIG) film due to spin inhomogeneity at the interface. The growth-induced thin
interfacial gadolinium iron garnet (GdIG) layer antiferromagnetically (AFM)
exchange couples with the rest of the YIG layer. The out-of-plane angular
variation of ferromagnetic resonance (FMR) linewidth $\Delta H$ reflects a
large inhomogeneous distribution of effective magnetization $\Delta 4 \pi
M_{eff}$ due to the presence of an exchange springlike moments arrangement in
YIG. We probe the spin inhomogeneity at the YIG-GdIG interface by performing an
in-plane angular variation of resonance field $H_{r}$, leading to a
unidirectional feature. The large extrinsic $\Delta 4\pi M_{eff}$ contribution,
apart from the inherent intrinsic Gilbert contribution, manifests enhanced
precessional damping in YIG film.",2109.12071v1
2021-07-14,Ultrafast Optomagnonics in Ferrimagnetic Multi-Sublattice Garnets,"This review discusses the ultrafast magnetization dynamics within the
gigahertz to terahertz frequency range in ferrimagnetic rare-earth iron garnets
with different substitutions. In these garnets, the roles of spin-orbit and
exchange interactions have been detected using femtosecond laser pulses via the
inverse Faraday effect. The all-optical control of spin-wave and Kaplan-Kittel
exchange resonance modes in different frequency ranges is shown. Generation and
localization of the electric field distribution inside the garnet through the
metal-bound surface plasmon-polariton strongly enhance the amplitude of the
exchange resonance modes. The exchange resonance mode in yttrium iron garnets
was observed using circularly polarized Raman spectroscopy. The results of this
study may be utilized in the development of a wide class of optomagnonic
devices in the gigahertz to terahertz frequency range.",2107.06597v1
2016-04-28,Platinum/Yttrium Iron Garnet Inverted Structures for Spin Current Transport,"30-80 nm thick yttrium iron garnet (YIG) films are grown by pulsed laser
deposition on a 5 nm thick sputtered Pt atop gadolinium gallium garnet
substrate (GGG) (110). Upon post-growth rapid thermal annealing, single crystal
YIG(110) emerges as if it were epitaxially grown on GGG(110) despite the
presence of the intermediate Pt film. The YIG surface shows atomic steps with
the root-mean-square roughness of 0.12 nm on flat terraces. Both Pt/YIG and
GGG/Pt interfaces are atomically sharp. The resulting YIG(110) films show clear
in-plane uniaxial magnetic anisotropy with a well-defined easy axis along <001>
and a peak-to-peak ferromagnetic resonance linewidth of 7.5 Oe at 9.32 GHz,
similar to YIG epitaxilly grown on GGG. Both spin Hall magnetoresistance and
longitudinal spin Seebeck effects in the inverted bilayers indicate excellent
Pt/YIG interface quality.",1604.08465v1
2019-01-08,Fabrication of yttrium-iron-garnet/Pt multilayers for the longitudinal spin Seebeck effect,"For longitudinal spin Seebeck effect (LSSE) devices, a multilayer structure
comprising ferromagnetic and nonmagnetic layers is expected to improve their
thermoelectric power. In this study, we developed the fabrication method for
alternately stacked yttrium-iron-garnet (YIG)/Pt multilayer films on a
gadolinium gallium garnet (GGG) (110) substrate, GGG/[YIG(49 nm)/Pt(4 nm)]$_n$
($n =$ 1 - 5) based on room-temperature sputtering and $ex$-$situ$
post-annealing method and we evaluated their structural and LSSE properties.
The fabricated [YIG/Pt]$_n$ samples show flat YIG/Pt interfaces and almost
identical saturation magnetization $M_{\rm s}$, although they contain
polycrystalline YIG layers on Pt layers as well as single-crystalline YIG
layers on GGG. In the samples, we observed clear LSSE signals and found that
the LSSE thermoelectric power factor (PF) increases monotonically with
increasing $n$; the PF of the [YIG/Pt]$_5$ sample is enhanced by a factor of
$\sim 28$ compared to that of [YIG/Pt]$_1$. This work may provide a guideline
for developing future multilayerbased LSSE devices.",1901.02129v1
2019-02-12,Ultra-low damping in lift-off structured yttrium iron garnet thin films,"We show that using maskless photolithography and the lift-off technique,
patterned yttrium iron garnet thin films possessing ultra-low Gilbert damping
can be accomplished. The films of 70 nm thickness were grown on (001)-oriented
gadolinium gallium garnet by means of pulsed laser deposition, and they exhibit
high crystalline quality, low surface roughness, and the effective
magnetization of 127 emu/cm3. The Gilbert damping parameter is as low as
5x10-4. The obtained structures have well-defined sharp edges which along with
good structural and magnetic film properties pave a path in the fabrication of
high-quality magnonic circuits and oxide-based spintronic devices.",1902.04605v1
2020-08-21,Integration and characterization of micron-sized YIG structures with very low Gilbert damping on arbitrary substrates,"We present a novel process that allows the transfer of monocrystalline
yttrium-iron-garnet microstructures onto virtually any kind of substrate. The
process is based on a recently developed method that allows the fabrication of
freestanding monocrystalline YIG bridges on gadolinium-gallium-garnet. Here the
bridges' spans are detached from the substrate by a dry etching process and
immersed in a watery solution. Using drop casting the immersed YIG platelets
can be transferred onto the substrate of choice, where the structures finally
can be reattached and thus be integrated into complex devices or experimental
geometries. Using time resolved scanning Kerr microscopy and inductively
measured ferromagnetic resonance we can demonstrate that the structures retain
their excellent magnetic quality. At room temperature we find a ferromagnetic
resonance linewidth of $\mu_0\Delta H_{HWHM}\approx 195\,\mu T$ and we were
even able to inductively measure magnon spectra on a single micron-sized
yttrium-iron-garnet platelet at a temperature of 5 K. The process is flexible
in terms of substrate material and shape of the structure. In the future this
approach will allow for new types of spin dynamics experiments up to now
unthinkable.",2008.09390v1
2021-12-14,Robust perpendicular magnetic anisotropy in Ce substituted yttrium iron garnet epitaxial thin films,"Cerium substituted yttrium iron garnet (Ce:YIG) epitaxial thin films are
prepared on gadolinium gallium garnet (GGG) substrate with pulsed laser
deposition (PLD). It is observed that the films grown on GGG(111) substrate
exhibit perpendicular magnetic anisotropy (PMA) as compared to films grown on
GGG(100) substrate. The developed PMA is confirmed from magneto-optical Kerr
effect, bulk magnetization and ferromagnetic resonance measurements. Further,
the magnetic bubble domains are observed in the films exhibiting PMA. The
observations are explained in terms of the growth direction of Ce:YIG films and
the interplay of various magnetic anisotropy terms. The observed PMA is found
to be tunable with thickness of the film and a remarkable temperature stability
of the PMA is observed in all the studied films of Ce:YIG deposited on GGG(111)
substrate.",2112.07264v1
2017-02-10,"Relative weight of the inverse spin Hall and spin rectification effects for metallic Py,Fe/Pt and insulating YIG/Pt bilayers estimated by angular dependent spin pumping measurements","We quantify the relative weight of inverse spin Hall and spin rectification
effects occurring in RF-sputtered polycrystalline permalloy, molecular beam
epitaxy-grown epitaxial iron and liquid phase epitaxy-grown yttrium-iron-garnet
bilayer systems with different capping materials. To distinguish the spin
rectification signal from the inverse spin Hall voltage the external magnetic
field is rotated in-plane to take advantage of the different angular
dependencies of the prevailing effects. We prove that in permalloy anisotropic
magnetoresistance is the dominant source for spin rectification while in
epitaxial iron the anomalous Hall effect has an also comparable strength. The
rectification in yttrium-iron-garnet/platinum bilayers reveals an angular
dependence imitating the one seen for anisotropic magnetoresistance caused by
spin Hall magnetoresistance.",1702.03119v1
2019-02-01,Quantum thermodynamics of complex ferrimagnets,"High-quality magnets such as yttrium iron garnet (YIG) are electrically
insulating and very complex. By implementing a quantum thermostat into
atomistic spin dynamics we compute YIG's key thermodynamic properties, viz. the
magnon power spectrum and specific heat, for a large temperature range. The
results differ (sometimes spectacularly) from simple models and classical
statistics, but agree with available experimental data.",1902.00449v1
2022-08-17,Polarization-selective magneto-optical modulation,"We study magneto-optical coupling in a ferrimagnetic sphere resonator made of
Yttrium iron garnet. We find that the resonator can be operated in the telecom
band as a polarization-selective optical modulator. Intermodulation gain can be
employed in the nonlinear regime for amplification.",2208.08148v2
2022-10-08,One Analytical Approach of Rashba-Edelstein Magnetoresistance in 2D Materials,"We study analytically the Rashba-Edelstein magnetoresistance (REMR) in a
structure made from an insulator ferromagnet, such as yttrium iron garnet
(YIG), and a 2D material (2DM) with direct and inverse Rashba-Edelstein
effects, such as SLG and MoS$_2$. Our results represent an efficient way of
analyzing the Rashba-Edelstein effects.",2210.03854v1
2024-01-17,A Distributed Magnetostatic Resonator,"This work reports the design, fabrication, and characterization of
coupling-enhanced magnetostatic forward volume wave resonators with significant
spur suppression. The fabrication is based on surface micro-machining of
yttrium iron garnet (YIG) film on a gadolinium gallium garnet (GGG) substrate
with thick gold transducers. A distributed resonator is used to excite forward
volume waves in YIG to realize a frequency dependent coupling boost. Fabricated
devices at 18 GHz and 7 GHz show coupling coefficients as high as 13$\%$ and
quality factors above 1000. Higher-order magnetostatic mode suppression is
experimentally demonstrated through a combination of transducer and YIG
geometry design. An edge-coupling filter topology is proposed and simulated
which utilizes this novel distributed magnetostatic resonator.",2401.08911v1
2019-10-07,Chiral spin-wave velocities induced by all-garnet interfacial Dzyaloshinskii-Moriya interaction in ultrathin yttrium iron garnet films,"Spin waves can probe the Dzyaloshinskii-Moriya interaction (DMI) which gives
rise to topological spin textures, such as skyrmions. However, the DMI has not
yet been reported in yttrium iron garnet (YIG) with arguably the lowest damping
for spin waves. In this work, we experimentally evidence the interfacial DMI in
a 7~nm-thick YIG film by measuring the nonreciprocal spin wave propagation in
terms of frequency, amplitude and most importantly group velocities using all
electrical spin-wave spectroscopy. The velocities of propagating spin waves
show chirality among three vectors, i.e. the film normal direction, applied
field and spin-wave wavevector. By measuring the asymmetric group velocities,
we extract a DMI constant of 16~$\mu$J/m$^{2}$ which we independently confirm
by Brillouin light scattering. Thickness-dependent measurements reveal that the
DMI originates from the oxide interface between the YIG and garnet substrate.
The interfacial DMI discovered in the ultrathin YIG films is of key importance
for functional chiral magnonics as ultra-low spin-wave damping can be achieved.",1910.02599v2
2020-12-01,Magnon hybridization in ferrimagnetic heterostructures,"We study magnon hybridization in a ferrimagnetic heterostructure consisting
of ultrathin gadolinium iron garnet and yttrium iron garnet layers and show the
localized and extended spatial profiles of the magnon modes with different
polarizations. These modes are expected to have distinct thermal excitation
properties in the presence of a temperature gradient across the
heterostructure. From a quantitative analysis of their consequences on
longitudinal spin Seebeck effect, we predict an observable shift of the
sign-changing temperature with respect to the one previously observed in
gadolinium iron garnet. Moreover, the sign-changing point of spin Seebeck
signal is found to be tunable by YIG thickness. Our results suggest the
necessity of taking into account the temperature difference between the magnon
modes in ferrimagnetic heterostructures.",2012.00576v1
2008-10-15,Magnetic susceptibility and magnetization fluctuation measurements of mixed Gadolinium-Yttrium Iron Garnets,"We study the magnetic properties of Gadolinium-Yttrium Iron Garnet
($\text{Gd}_{x}\text{Y}_{3-x}\text{Fe}_5\text{0}_{12}$, $x=3,1.8$) ferrite
ceramics. The complex initial permeability is measured in the temperature range
2 K to 295 K at frequency of 1 kHz, and in the frequency range 100 Hz to 200
MHz at temperatures 4 K, 77 K, and 295 K. The magnetic viscosity-induced
imaginary part of the permeability is observed at low frequencies. Measurements
of the magnetization noise are made at 4 K. Using the fluctuation-dissipation
theorem, we find that the observed magnetization fluctuations are consistent
with our measurements of the low-frequency imaginary part of permeability. We
discuss some implications for proposed precision measurements as well as other
possible applications.",0810.2770v1
2012-08-03,Field-dependence of magnon decay in yttrium iron garnet thin films,"We discuss threshold field-dependence of the decay rate of the uniform magnon
mode in yttrium iron garnet (YIG) thin films. We demonstrate that decays must
cease to exist in YIG films of thickness less than 1 \mu m, the lengthscale
defined by the exchange length. We show that due to the symmetry of the
three-magnon coupling the decay rate is linear in \Delta H=(Hc-H) in the
vicinity of the threshold field Hc instead of the step-like \Gamma
\Theta(\Delta H) expected from the two-dimensional character of magnon
excitations in such films. For thicker films, the decay rate should exhibit
multiple steps due to thresholds for decays into a sequence of the
two-dimensional magnon bands. For yet thicker films, such thresholds merge and
crossover to the three-dimensional single-mode behavior: \Gamma |\Delta
H|^{3/2}.",1208.0831v1
2013-01-15,Spin-Hall Magnetoresistance in Platinum on Yttrium Iron Garnet: Dependence on platinum thickness and in-plane/out-of-plane magnetization,"The occurrence of Spin-Hall Magnetoresistance (SMR) in platinum (Pt) on top
of yttrium iron garnet (YIG) has been investigated, for both in-plane and
out-of-plane applied magnetic fields and for different Pt thicknesses [3, 4, 8
and 35nm]. Our experiments show that the SMR signal directly depends on the
in-plane and out-of-plane magnetization directions of the YIG. This confirms
the theoretical description, where the SMR occurs due to the interplay of
spin-orbit interaction in the Pt and spin-mixing at the YIG/Pt interface.
Additionally, the sensitivity of the SMR and spin pumping signals on the YIG/Pt
interface conditions is shown by comparing two different deposition techniques
(e-beam evaporation and dc sputtering).",1301.3266v2
2013-02-27,Optimization of the yttrium iron garnet/platinum interface for spin pumping-based applications,"The dependence of the spin pumping efficiency and the spin mixing conductance
on the surface processing of yttrium iron garnet (YIG) before the platinum (Pt)
deposition has been investigated quantitatively. The ferromagnetic resonance
driven spin pumping injects a spin polarized current into the Pt layer, which
is transformed into an electromotive force by the inverse spin Hall effect. Our
experiments show that the spin pumping effect indeed strongly depends on the
YIG/Pt interface condition. We measure an enhancement of the inverse spin Hall
voltage and the spin mixing conductance of more than two orders of magnitude
with improved sample preparation.",1302.6697v1
2013-11-25,Spin-wave excitation and propagation in microstructured waveguides of yttrium iron garnet (YIG)/Pt bilayers,"We present an experimental study of spin-wave excitation and propagation in
microstructured waveguides patterned from a 100 nm thick yttrium iron garnet
(YIG)/platinum (Pt) bilayer. The life time of the spin waves is found to be
more than an order of magnitude higher than in comparably sized metallic
structures despite the fact that the Pt capping enhances the Gilbert damping.
Utilizing microfocus Brillouin light scattering spectroscopy, we reveal the
spin-wave mode structure for different excitation frequencies. An exponential
spin-wave amplitude decay length of 31 {\mu}m is observed which is a
significant step towards low damping, insulator based micro-magnonics.",1311.6305v1
2014-10-02,Simultaneous detection of the spin-Hall magnetoresistance and the spin-Seebeck effect in Platinum and Tantalum on Yttrium Iron Garnet,"The spin-Seebeck effect (SSE) in platinum (Pt) and tantalum (Ta) on yttrium
iron garnet (YIG) has been investigated by both externally heating the sample
(using an on-chip Pt heater on top of the device) as well as by current-induced
heating. For SSE measurements, external heating is the most common method to
obtain clear signals. Here we show that also by current-induced heating it is
possible to directly observe the SSE, separate from the also present spin-Hall
magnetoresistance (SMR) signal, by using a lock-in detection technique. Using
this measurement technique, the presence of additional 2nd order signals at low
applied magnetic fields and high heating currents is revealed. These signals
are caused by current-induced magnetic fields (Oersted fields) generated by the
used AC-current, resulting in dynamic SMR signals.",1410.0551v2
2015-07-07,Rayleigh-Jeans condensation of pumped magnons in thin film ferromagnets,"We show that the formation of a magnon condensate in thin ferromagnetic films
can be explained within the framework of a classical stochastic non-Markovian
Landau-Lifshitz-Gilbert equation where the properties of the random magnetic
field and the dissipation are determined by the underlying phonon dynamics. We
have numerically solved this equation for a tangentially magnetized
yttrium-iron garnet film in the presence of a parallel parametric pumping
field. We obtain a complete description of all stages of the nonequilibrium
time evolution of the magnon gas which is in excellent agreement with
experiments. Our calculation proves that the experimentally observed
condensation of magnons in yttrium-iron garnet at room temperature is a purely
classical phenomenon which should be called Rayleigh-Jeans rather than
Bose-Einstein condensation.",1507.01717v2
2016-02-04,Investigation of the unidirectional spin heat conveyer effect in a 200nm thin Yttrium Iron Garnet film,"We have investigated the unidirectional spin wave heat conveyer effect in
sub-micron thick yttrium iron garnet (YIG) films using lock-in thermography
(LIT). Although the effect is small in thin layers this technique allows us to
observe asymmetric heat transport by magnons which leads to asymmetric
temperature profiles differing by several mK on both sides of the exciting
antenna, respectively. Comparison of Damon-Eshbach and backward volume modes
shows that the unidirectional heat flow is indeed due to non-reciprocal
spin-waves. Because of the finite linewidth, small asymmetries can still be
observed when only the uniform mode of ferromagnetic resonance is excited. The
latter is of extreme importance for example when measuring the inverse
spin-Hall effect because the temperature differences can result in
thermovoltages at the contacts. Because of the non-reciprocity these
thermovoltages reverse their sign with a reversal of the magnetic field which
is typically deemed the signature of the inverse spin-Hall voltage.",1602.01662v1
2016-12-07,Gilbert damping of magnetostatic modes in a yttrium iron garnet sphere,"The magnetostatic mode (MSM) spectrum of a 300$\mu$m diameter single
crystalline sphere of yttrium iron garnet is investigated using broadband
ferromagnetic resonance (FMR). The individual MSMs are identified via their
characteristic dispersion relations and the corresponding mode number tuples
$(nmr)$ are assigned. Taking FMR data over a broad frequency and magnetic field
range allows to analyze both the Gilbert damping parameter~$\alpha$ and the
inhomogeneous line broadening contribution to the total linewidth of the MSMs
separately. The linewidth analysis shows that all MSMs share the same Gilbert
damping parameter $\alpha=2.7(5) \times 10^{-5}$ irrespective of their mode
index. In contrast, the inhomogeneous line broadening shows a pronounced mode
dependence. This observation is modeled in terms of two-magnon scattering
processes of the MSMs into the spin-wave manifold, mediated by surface and
volume defects.",1612.02360v1
2016-12-31,First-Principles Study of Exchange Interactions of Yttrium Iron Garnet,"Yttrium Iron Garnet is the ubiquitous magnetic insulator used for studying
pure spin currents. The exchange constants reported in the literature vary
considerably between different experiments and fitting procedures. Here we
calculate them from first-principles. The local Coulomb correction (U - J) of
density functional theory is chosen such that the parameterized spin model
reproduces the experimental Curie temperature and a large electronic band gap,
ensuring an insulating phase. The magnon spectrum calculated with our
parameters agrees reasonably well with that measured by neutron scattering. A
residual disagreement about the frequencies of optical modes indicates the
limits of the present methodology.",1701.00110v1
2017-01-03,Magnetic control of Goos-Hanchen shifts in a yttrium-iron-garnet film,"We investigate the Goos-Hanchen (G-H) shifts reflected and transmitted by a
yttrium-iron-garnet (YIG) film for both normal and oblique incidence. It is
found that the nonreciprocity effect of the MO material does not only result in
a nonvanishing reflected shift at normal incidence, but also leads to a
slab-thickness-independent term which breaks the symmetry between the reflected
and transmitted shifts at oblique incidence. The asymptotic behaviors of the
normal-incidence reflected shift are obtained in the vicinity of two
characteristic frequencies corresponding to a minimum reflectivity and a total
reflection, respectively. Moreover, the coexistence of two types of
negative-reflected-shift (NRS) at oblique incidence is discussed. We show that
the reversal of the shifts from positive to negative values can be realized by
tuning the magnitude of applied magnetic field, the frequency of incident wave
and the slab thickness as well as the incident angle. In addition, we further
investigate two special cases for practical purposes: the reflected shift with
a total reflection and the transmitted shift with a total transmission.
Numerical simulations are also performed to verify our analytical results.",1701.01462v2
2017-01-31,Lateral transport properties of thermally excited magnons in yttrium iron garnet films,"Spin information carried by magnons is attractive for computing technology
and the development of magnon-based computing circuits is of great interest.
However, magnon transport in insulators has been challenging, different from
the clear physical picture for spin transport in conductors. Here we
investigate the lateral transport properties of thermally excited magnons in
yttrium iron garnet (YIG), a model magnetic insulator. Polarity reversals of
detected spins in non-local geometry devices have been experimentally observed
and are strongly dependent on temperature, YIG film thickness, and
injector-detector separation distance. A competing two-channel transport model
for thermally excited magnons is proposed, which is qualitatively consistent
with the spin signal behavior. In addition to the fundamental significance for
thermal magnon transport, our work furthers the development of magnonics by
creating an easily accessible magnon source with controllable transport",1701.08932v1
2017-05-18,The Final Chapter In The Saga Of YIG,"The magnetic insulator Yttrium Iron Garnet can be grown with exceptional
quality, has a ferrimagnetic transition temperature of nearly 600 K, and is
used in microwave and spintronic devices that can operate at room temperature.
The most accurate prior measurements of the magnon spectrum date back nearly 40
years, but cover only 3 of the lowest energy modes out of 20 distinct magnon
branches. Here we have used time-of-flight inelastic neutron scattering to
measure the full magnon spectrum throughout the Brillouin zone. We find that
the existing model of the excitation spectrum, well known from an earlier work
titled ""The Saga of YIG"", fails to describe the optical magnon modes. Using a
very general spin Hamiltonian, we show that the magnetic interactions are both
longer-ranged and more complex than was previously understood. The results
provide the basis for accurate microscopic models of the finite temperature
magnetic properties of Yttrium Iron Garnet, necessary for next-generation
electronic devices.",1705.06594v1
2017-09-12,Direct observation of magnon-phonon coupling in yttrium iron garnet,"The magnetic insulator yttrium iron garnet (YIG) with a ferrimagnetic
transition temperature of $\sim$560 K has been widely used in microwave and
spintronic devices. Anomalous features in the spin Seeback effect (SSE)
voltages have been observed in Pt/YIG and attributed to the magnon-phonon
coupling. Here we use inelastic neutron scattering to map out low-energy spin
waves and acoustic phonons of YIG at 100 K as a function of increasing magnetic
field. By comparing the zero and 9.1 T data, we find that instead of splitting
and opening up gaps at the spin wave and acoustic phonon dispersion
intersecting points, magnon-phonon coupling in YIG enhances the hybridized
scattering intensity. These results are different from expectations of
conventional spin-lattice coupling, calling for new paradigms to understand the
scattering process of magnon-phonon interactions and the resulting
magnon-polarons.",1709.03940v1
2018-10-11,"Propagating spin waves in nanometer-thick yttrium iron garnet films: Dependence on wave vector, magnetic field strength and angle","We present a comprehensive investigation of propagating spin waves in
nanometer-thick yttrium iron garnet (YIG) films. We use broadband spin-wave
spectroscopy with integrated coplanar waveguides (CPWs) and microstrip antennas
on top of continuous and patterned YIG films to characterize spin waves with
wave vectors up to 10 rad/$\mu$m. All films are grown by pulsed laser
deposition. From spin-wave transmission spectra, parameters such as the Gilbert
damping constant, spin-wave dispersion relation, group velocity, relaxation
time, and decay length are derived and their dependence on magnetic bias field
strength and angle is systematically gauged. For a 40-nm-thick YIG film, we
obtain a damping constant of $3.5 \times 10^{-4}$ and a maximum decay length of
1.2 mm. Our experiments reveal a strong variation of spin-wave parameters with
magnetic bias field and wave vector. Spin-wave properties change considerably
up to a magnetic bias field of about 30 mT and above a field angle of
$\theta_{H} = 20^{\circ}$, where $\theta_{H} = 0^{\circ}$ corresponds to the
Damon-Eshbach configuration.",1810.04973v1
2020-09-26,Bose condensation and spin superfluidity of magnons in a perpendicularly magnetized film of yttrium iron garnet,"The formation of a Bose condensate of magnons in a perpendicularly magnetized
film of yttrium iron garnet under radio-frequency pumping in a strip line is
studied experimentally. The characteristics of nonlinear magnetic resonance and
the spatial distribution of the Bose condensate of magnons in the magnetic
field gradient are investigated. In these experiments, the Bosonic system of
magnons behaves similarly to the Bose condensate of magnons in the
antiferromagnetic superfluid 3He-B, which was studied in detail earlier.
Magnonic BEC forms a coherently precessing state with the properties of
magnonic superfluidity. Its stability is determined by the repulsive potential
between excited magnons, which compensates for the inhomogeneity of the
magnetic field.",2009.12595v1
2020-12-17,Magnetic equivalent of electric superradiance: radiative damping in yttrium-iron-garnet films,"A dense system of independent oscillators, connected only by their
interaction with the same cavity excitation mode, will radiate coherently,
which effect is termed superradiance. In several cases, especially if the
density of oscillators is high, the superradiance may dominate the intrinsic
relaxation processes. This limit can be achieved, e.g., with cyclotron
resonance in two-dimensional electron gases. In those experiments, the
cyclotron resonance is coupled to the electric field of light, while the
oscillator density can be easily controlled by varying the gate voltage.
However, in the case of magnetic oscillators, to achieve the dominance of
superradiance is more tricky, as material parameters limit the oscillator
density, and the magnetic coupling to the light wave is rather small. Here we
present quasi-optical magnetic resonance experiments on thin films of yttrium
iron garnet. Due to the simplicity of experimental geometry, the intrinsic
damping and the superradiance can be easily separated in the transmission
spectra. We show that with increasing film thickness, the losses due to
coherent radiation prevail the system's internal broadening.",2012.09440v1
2021-03-16,Spin-Phonon Interaction in Yttrium Iron Garnet,"Spin-phonon interaction is an important channel for spin and energy
relaxation in magnetic insulators. Understanding this interaction is critical
for developing magnetic insulator-based spintronic devices. Quantifying this
interaction in yttrium iron garnet (YIG), one of the most extensively
investigated magnetic insulators, remains challenging because of the large
number of atoms in a unit cell. Here, we report temperature-dependent and
polarization-resolved Raman measurements in a YIG bulk crystal. We first
classify the phonon modes based on their symmetry. We then develop a modified
mean-field theory and define a symmetry-adapted parameter to quantify
spin-phonon interaction in a phonon-mode specific way for the first time in
YIG. Based on this improved mean-field theory, we discover a positive
correlation between the spin-phonon interaction strength and the phonon
frequency.",2103.09038v1
2022-02-07,Spin-transfer-assisted parametric pumping of magnons in yttrium iron garnet,"The combination of parametric pumping and spin-transfer torque is a powerful
approach that enables high-level control over magnetic excitations in thin-film
ferromagnets. The excitation parameters, such as pumping power and external
field strength, affect the instabilities of individual magnon modes. We
theoretically explore how the simultaneous effects of parametric pumping and
spin transfer torque influence these magnetic instabilities in a thin-film
ferromagnet. Within the Landau-Lifshitz-Gilbert framework, we perform
micromagnetic simulations of magnon excitations in yttrium iron garnet by
pumping, spin transfer torque, and a combination of the two. We find that
consistent with experimental results, the magnitude and direction of the
spin-transfer torque tune the parametric instability thresholds.",2202.03247v2
2022-08-23,Reversal of nanomagnets by propagating magnons in ferrimagnetic yttrium iron garnet enabling nonvolatile magnon memory,"Despite the unprecedented downscaling of CMOS integrated circuits,
memory-intensive machine learning and artificial intelligence applications are
limited by data conversion between memory and processor. There is a challenging
quest for novel approaches to overcome this so-called von Neumann bottleneck.
Magnons are the quanta of spin waves and transport angular momenta through
magnets. They enable power-efficient computation without charge flow and would
solve the conversion problem if spin wave amplitudes could be stored directly
in a magnetic memory cell. Here, we report the reversal of ferromagnetic
nanostripes by spin waves which propagate through an underlying spin-wave bus
made from yttrium iron garnet. Thereby, the charge-free angular momentum flow
is stored after transmission over a macroscopic distance. We show that spin
waves can reverse large arrays of ferromagnetic stripes at a strikingly small
power level of nW. Combined with the already existing wave logic, our discovery
is path-breaking for the new era of magnonics-based in-memory computation and
beyond von Neumann computer architectures.",2208.10923v1
2023-06-24,Ferromagnetic levitation and harmonic trapping of a milligram-scale Yttrium Iron Garnet sphere,"We report passive magnetic levitation and three-dimensional harmonic trapping
of a 0.3 milligram, 0.5 millimeter diameter Yttrium Iron Garnet sphere at 4 K.
The gradient of an external magnetic field is used for vertical trapping, while
the finite size effect of the diamagnetic effect is used for horizontal
trapping. The dynamics of the levitated sphere was optically measured to have
trapping frequencies of up to around 600 Hz and mechanical $Q$-factors in the
order of $Q \sim 10^3$. These results were quantitatively reproduced by
three-dimensional finite element method simulations. Our results can provide a
novel system where magnetism, rigid body motions, microwaves, and optics
interact.",2306.13917v2
2023-12-14,Magnetization Reversal of 50-nm-wide Ni81Fe19 Nanostripes by Ultrashort Magnons in Yttrium Iron Garnet for Memory-Enhanced Magnonic Circuits,"Spin waves (magnons) can enable wave-based neuromorphic computing by which
one aims at overcoming limitations inherent to conventional electronics and the
von Neumann architecture. In this study, we explore the storage of magnon
signals and the magnetization switching of periodic and aperiodic arrays of
Ni81Fe19 (Py) nanostripes with widths (w) between 50 nm and 200 nm. Spin waves
excited with low microwave power in yttrium iron garnet induce the reversal of
the nanostripes of different w in a small opposing field. Exploiting
microwave-to-magnon transducers for magnon modes with ultrashort wavelengths,
we demonstrate the reversal of 50-nm-wide Py nanostripes by magnons with
wavelength ~ 100 nm after they have propagated over 25 micrometer in YIG. The
findings are important for designing a magnon-based in-memory computing device.",2312.09177v1
2024-02-07,Broadband squeezed light field by magnetostriction in an opto-magnomechanical,"We present a novel mechanism for generating a wide bandwidth squeezed optical
output field in an opto-magnomechanical system. In this system, the magnon
(mechanical) mode in the yttrium-iron-garnet crystal is coupled to the
microwave field (optical field) through magnetic dipole (radiation pressure)
interaction. The magnetostrictive force induced by the yttrium-iron-garnet
crystal causes a mechanical displacement and creates a quadrature squeezed
magnon mode. Eventually, this quadrature squeezed mechanical mode is
transferred to the output optical field through state-swap interaction. Our
results demonstrate the optimal parameter range for obtaining a stable squeezed
optical output field with a wide bandwidth. Moreover, the squeezed light field
exhibits strong robustness to environmental temperature. The new scheme we
propose has potential applications in quantum precision measurements, quantum
wireless networks, quantum radar, etc.",2402.04983v1
2009-03-17,Microscopic spin-wave theory for yttrium-iron garnet films,"Motivated by recent experiments on thin films of the ferromagnetic insulator
yttrium-iron garnet (YIG), we have developed an efficient microscopic approach
to calculate the spin-wave spectra of these systems. We model the
experimentally relevant magnon band of YIG using an effective quantum
Heisenberg model on a cubic lattice with ferromagnetic nearest neighbor
exchange and long-range dipole-dipole interactions. After a bosonization of the
spin degrees of freedom via a Holstein-Primakoff transformation and a
truncation at quadratic order in the bosons, we obtain the spin-wave spectra
for experimentally relevant parameters without further approximation by
numerical diagonalization, using efficient Ewald summation techniques to carry
out the dipolar sums. We compare our numerical results with two different
analytic approximations and with predictions based on the phenomenological
Landau-Lifshitz equation.",0903.2847v2
2012-06-28,Thermalization of magnons in yttrium-iron garnet: nonequilibrium functional renormalization group approach,"Using a nonequilibrium functional renormalization group (FRG) approach we
calculate the time evolution of the momentum distribution of a magnon gas in
contact with a thermal phonon bath. As a cutoff for the FRG procedure we use a
hybridization parameter {\Lambda} giving rise to an artificial damping of the
phonons. Within our truncation of the FRG flow equations the time evolution of
the magnon distribution is obtained from a rate equation involving
cutoff-dependent nonequilibrium self-energies, which in turn satisfy FRG flow
equations depending on cutoff-dependent transition rates. Our approach goes
beyond the Born collision approximation and takes the feedback of the magnons
on the phonons into account. We use our method to calculate the thermalization
of a quasi two-dimensional magnon gas in the magnetic insulator yttrium-iron
garnet after a highly excited initial state has been generated by an external
microwave field. We obtain good agreement with recent experiments.",1206.6689v3
2013-02-25,Phase Diagram for Magnon Condensate in Yttrium Iron Garnet Film,"Recently, magnons, which are quasiparticles describing the collective motion
of spins, were found to undergo Bose-Einstein condensation (BEC) at room
temperature in films of Yttrium Iron Garnet (YIG). Unlike other quasiparticle
BEC systems, this system has a spectrum with two degenerate minima, which makes
it possible for the system to have two condensates in momentum space. Recent
Brillouin Light scattering studies for a microwave-pumped YIG film of thickness
d=5 $\mu$m and field H=1 kOe find a low-contrast interference pattern at the
characteristic wavevector $Q$ of the magnon energy minimum. In this report, we
show that this modulation pattern can be quantitatively explained as due to
non-symmetric but coherent Bose-Einstein condensation of magnons into the two
energy minima. Our theory predicts a transition from a high-contrast symmetric
phase to a low-contrast non-symmetric phase on varying the $d$ and $H$, and a
new type of collective oscillations.",1302.6128v1
2013-02-27,Specific heat and thermal conductivity of ferromagnetic magnons in Yttrium Iron Garnet,"The specific heat and thermal conductivity of the insulating ferrimagnet
Y$_3$Fe$_5$O$_{12}$ (Yttrium Iron Garnet, YIG) single crystal were measured
down to 50 mK. The ferromagnetic magnon specific heat $C$$_m$ shows a
characteristic $T^{1.5}$ dependence down to 0.77 K. Below 0.77 K, a downward
deviation is observed, which is attributed to the magnetic dipole-dipole
interaction with typical magnitude of 10$^{-4}$ eV. The ferromagnetic magnon
thermal conductivity $\kappa_m$ does not show the characteristic $T^2$
dependence below 0.8 K. To fit the $\kappa_m$ data, both magnetic defect
scattering effect and dipole-dipole interaction are taken into account. These
results complete our understanding of the thermodynamic and thermal transport
properties of the low-lying ferromagnetic magnons.",1302.6739v1
2013-06-18,"Magnon, phonon and electron temperature profiles and the spin Seebeck effect in magnetic insulator/normal metal hybrid structures","We calculate the phonon, electron and magnon temperature profiles in yttrium
iron garnet/platinum bilayers by diffusive theory with appropriate boundary
conditions, in particular taking into account interfacial thermal resistances.
Our calculations show that in thin film hybrids, the interface magnetic heat
conductance qualitatively affects the magnon temperature. Based on published
material parameters we assess the degree of non-equilibrium at the yttrium iron
garnet/platinum interface. The magnitude of the spin Seebeck effect derived
from this approach compares well with experimental results for the longitudinal
spin Seebeck effect. Additionally we address the temperature profiles in the
transverse spin Seebeck effect.",1306.4292v2
2014-04-14,Sign of inverse spin Hall voltages generated by ferromagnetic resonance and temperature gradients in yttrium iron garnet|platinum bilayers,"We carried out a concerted effort to determine the absolute sign of the
inverse spin Hall effect voltage generated by spin currents injected into a
normal metal. We focus on yttrium iron garnet (YIG)|platinum bilayers at room
temperature, generating spin currents by microwaves and temperature gradients.
We find consistent results for different samples and measurement setups that
agree with theory. We suggest a right-hand-rule to define a positive spin Hall
angle corresponding to with the voltage expected for the simple case of
scattering of free electrons from repulsive Coulomb charges.",1404.3490v2
2014-12-12,Spin waves in micro-structured yttrium iron garnet nanometer-thick films,"We investigated the spin-wave propagation in a micro-structured yttrium iron
garnet waveguide of $40$ nm thickness. Utilizing spatially-resolved Brillouin
light scattering microscopy, an exponential decay of the spin-wave amplitude of
$(10.06 \pm 0.83)$ $\mu$m was observed. This leads to an estimated Gilbert
damping constant of $\alpha=(8.79\pm 0.73)\times 10^{-4}$, which is larger than
damping values obtained through ferromagnetic resonance measurements in
unstructured films. The theoretically calculated spatial interference of
waveguide modes was compared to the spin-wave pattern observed experimentally
by means of Brillouin light scattering spectroscopy.",1412.4032v1
2015-02-24,High Quality Yttrium Iron Garnet Grown by Room Temperature Pulsed Laser Deposition and Subsequent Annealing,"We have investigated recrystallization of amorphous Yttrium Iron Garnet (YIG)
by annealing in oxygen atmosphere. Our findings show that well below the
melting temperature the material transforms into a fully epitaxial layer with
exceptional quality, both structural and magnetic.\\ In ferromagnetic resonance
(FMR) ultra low damping and extremely narrow linewidth can be observed. For a
56 nm thick layer a damping constant of
$\alpha$=(6.63$\pm$1.50)$\cdot$10$^{-5}$ is found and the linewidth at 9.6 GHz
is as small as 1.30$\pm$0.05 Oe which are the lowest values for PLD grown thin
films reported so far. Even for a 20 nm thick layer a damping constant of
$\alpha$=(7.51$\pm$1.40)$\cdot$10$^{-5}$ is found which is the lowest value for
ultrathin films published so far. The FMR linewidth in this case is
3.49$\pm$0.10 Oe at 9.6 GHz. Our results not only present a method of
depositing thin film YIG of unprecedented quality but also open up new options
for the fabrication of thin film complex oxides or even other crystalline
materials.",1502.06724v2
2015-04-03,The effect of the magnon dispersion on the longitudinal spin Seebeck effect in yttrium iron garnets (YIG),"We study the temperature dependence of the longitudinal spin-Seebeck effect
(LSSE) in a yttrium iron garnet Y3Fe5O12 (YIG) / Pt system for samples of
different thicknesses. In this system, the thermal spin torque is
magnon-driven. The LSSE signal peaks at a specific temperature that depends on
the YIG sample thickness. We also observe freeze-out of the LSSE signal at high
magnetic fields, which we attribute to the opening of an energy gap in the
magnon dispersion. We observe partial freeze-out of the LSSE signal even at
room temperature, where kBT is much larger than the gap. This suggests that a
subset of the magnon population with an energy below kB x TC (TC about 40 K)
contribute disproportionately to the LSSE; at temperatures below TC, we label
these magnons subthermal magnons. The T-dependence of the LSSE at temperatures
below the maximum is interpreted in terms of a new empirical model that
ascribes most of the temperature dependence to that of the thermally driven
magnon flux.",1504.00895v1
2015-12-04,Magnetic field dependence of the magnon spin diffusion length in the magnetic insulator yttrium iron garnet,"We investigated the effect of an external magnetic field on the diffusive
spin transport by magnons in the magnetic insulator yttrium iron garnet (YIG),
using a non-local magnon transport measurement geometry. We observed a decrease
in magnon spin diffusion length $\lambda_m$ for increasing field strengths,
where $\lambda_m$ is reduced from 9.6$\pm1.2$ $\mu$m at 10 mT to 4.2$\pm0.6$
$\mu$m at 3.5 T at room temperature. In addition, we find that there must be at
least one additional transport parameter that depends on the external magnetic
field. Our results do not allow us to unambiguously determine whether this is
the magnon equilibrium density or the magnon diffusion constant. These results
are significant for experiments in the more conventional longitudinal spin
Seebeck geometry, since the magnon spin diffusion length sets the length scale
for the spin Seebeck effect as well and is relevant for its understanding.",1512.01410v1
2016-01-27,Observation of magnon-mediated current drag in Pt/yttrium iron garnet/Pt(Ta) trilayers,"Pure spin current, a flow of spin angular momentum without flow of any
companying net charge, is generated in two common ways. One makes use of the
spin Hall effect in normal metals (NM) with strong spin-orbit coupling, such as
Pt or Ta. The other utilizes the collective motion of magnetic moments or spin
waves with the quasi-particle excitations called magnons. A popular material
for the latter is yttrium iron garnet, a magnetic insulator (MI). Here we
demonstrate in NM/MI/NM trilayers that these two types of spin currents are
interconvertible across the interfaces, predicated as the magnon-mediated
current drag phenomenon. The transmitted signal scales linearly with the
driving current without a threshold and follows the power-law with n ranging
from 1.5 to 2.5. Our results indicate that the NM/MI/NM trilayer structure can
serve as a scalable pure spin current valve device which is an essential
ingredient in spintronics.",1601.07429v1
2016-03-31,Enhanced spin Seebeck effect signal due to spin-momentum locked topological surface states,"Spin-momentum locking in protected surface states enables efficient
electrical detection of magnon decay at a
magnetic-insulator/topological-insulator heterojunction. Here we demonstrate
this property using the spin Seebeck effect, i.e. measuring the transverse
thermoelectric response to a temperature gradient across a thin film of yttrium
iron garnet, an insulating ferrimagnet, and forming a heterojunction with
(BixSb1-x)2Te3, a topological insulator. The non-equilibrium magnon population
established at the interface can decay in part by interactions of magnons with
electrons near the Fermi energy of the topological insulator. When this decay
channel is made active by tuning (BixSb1-x)2Te3 to a bulk insulator, a large
electromotive force emerges in the direction perpendicular to the in-plane
magnetization of yttrium iron garnet. The enhanced, tunable spin Seebeck effect
which occurs when the Fermi level lies in the bulk gap offers unique advantages
over the usual spin Seebeck effect in metals and therefore opens up exciting
possibilities in spintronics.",1603.09427v1
2016-08-03,Influence of yttrium iron garnet thickness and heater opacity on the nonlocal transport of electrically and thermally excited magnons,"We studied the nonlocal transport behavior of both electrically and thermally
excited magnons in yttrium iron garnet (YIG) as a function of its thickness.
For electrically injected magnons, the nonlocal signals decrease monotonically
as the YIG thickness increases. For the nonlocal behavior of the thermally
generated magnons, or the nonlocal spin Seebeck effect (SSE), we observed a
sign reversal which occurs at a certain heater-detector distance, and it is
influenced by both the opacity of the YIG/heater interface and the YIG
thickness. Our nonlocal SSE results can be qualitatively explained by the
bulk-driven SSE mechanism together with the magnon diffusion model. Using a
two-dimensional finite element model (2D-FEM), we estimated the bulk spin
Seebeck coefficient of YIG at room temperature. The quantitative disagreement
between the experimental and modeled results indicates more complex processes
going on in addition to magnon diffusion and relaxation, especially close to
the contacts.",1608.01178v1
2016-12-06,Increased low-temperature damping in yttrium iron garnet thin films,"We report measurements of the frequency and temperature dependence of
ferromagnetic resonance (FMR) for a 15-nm-thick yttrium iron garnet (YIG) film
grown by off-axis sputtering. Although the FMR linewidth is narrow at room
temperature (corresponding to a damping coefficient $\alpha$ = (9.0 $\pm$ 0.2)
$\times 10^{-4}$), comparable to previous results for high-quality YIG films of
similar thickness, the linewidth increases strongly at low temperatures, by a
factor of almost 30. This increase cannot be explained as due to two-magnon
scattering from defects at the sample interfaces. We argue that the increased
low-temperature linewidth is due to impurity relaxation mechanisms that have
been investigated previously in bulk YIG samples. We suggest that the
low-temperature linewidth is a useful figure of merit to guide the optimization
of thin-film growth protocols because it is a particularly sensitive indicator
of impurities.",1612.01954v1
2017-03-16,Optical properties of a four-layer waveguiding nanocomposite structure in near-IR regime,"The theoretical study of the optical properties of TE- and TM- modes in a
four-layer structure composed of the magneto-optical yttrium iron garnet
guiding layer on a dielectric substrate covered by planar nanocomposite guiding
multilayer is presented. The dispersion equation is obtained taking into
account the bigyrotropic properties of yttrium-iron garnet, and an original
algorithm for the guided modes identification is proposed. The dispersion
spectra are analyzed and the energy flux distributions across the structure are
calculated. The fourfold difference between the partial power fluxes within the
waveguide layers is achieved in the wavelength range of 200 nm.",1703.05711v1
2017-03-28,Temperature dependent magnetic damping of yttrium iron garnet spheres,"We investigate the temperature dependent microwave absorption spectrum of an
yttrium iron garnet sphere as a function of temperature (5 K to 300 K) and
frequency (3 GHz to 43.5 GHz). At temperatures above 100 K, the magnetic
resonance linewidth increases linearly with temperature and shows a
Gilbert-like linear frequency dependence. At lower temperatures, the
temperature dependence of the resonance linewidth at constant external magnetic
fields exhibits a characteristic peak which coincides with a non-Gilbert-like
frequency dependence. The complete temperature and frequency evolution of the
linewidth can be modeled by the phenomenology of slowly relaxing rare-earth
impurities and either the Kasuya-LeCraw mechanism or the scattering with
optical magnons. Furthermore, we extract the temperature dependence of the
saturation magnetization, the magnetic anisotropy and the g-factor.",1703.09444v2
2017-04-28,Thermal Control of the Magnon-Photon Coupling in a Notch Filter coupled to a Yttrium-Iron-Garnet/Platinum System,"We report thermal control of mode hybridization between the ferromagnetic
resonance (FMR) and a planar resonator (notch filter) working at 4.74 GHz. The
chosen magnetic material is a ferrimagnetic insulator (Yttrium Iron Garnet:
YIG) covered by 6 nm of platinum (Pt). A current induced heating method has
been used in order to enhance the temperature of the YIG/Pt system. The device
permits us to control the transmission spectra and the magnon-photon coupling
strength at room temperature. These experimental findings reveal potentially
applicable tunable microwave filtering function.",1704.08896v3
2017-10-07,Magnon-phonon relaxation in yttrium iron garnet from first principles,"We combine the theoretical method of calculating spin wave excitation with
the finite-temperature modeling and calculate the magnon-phonon relaxation time
in the technologically important material Yttrium iron garnet (YIG) from first
principles. The finite lifetime of magnon excitation is found to arise from the
fluctuation of the exchange interaction of magnetic atoms in YIG. At room
temperature, the magnon spectra have significant broadening that is used to
extract the magnon-phonon relaxation time quantitatively. The latter is a
phenomenological parameter of great importance in YIG-based spintronics
research. We find that the magnon-phonon relaxation time for the optical magnon
is a constant while that for the acoustic magnon is proportional to $1/k^2$ in
the long-wavelength regime.",1710.02647v1
2018-03-13,Spin wave localization and guiding by magnon band structure engineering in yttrium iron garnet,"In spintronics the propagation of spin-wave excitations in magnetically
ordered materials can also be used to transport and process information. One of
the most popular materials in this regard is the ferrimagnetic insulator
yttrium-iron-garnet due its exceptionally small spin-wave damping parameter.
While the small relaxation rate allows for large propagation length of magnetic
excitations, it also leads to non-locality of the magnetic properties. By
imaging spin waves their band structure is mapped. In doing so wave vector
selection is shown to suppress dispersion effects to a large extent allowing
for local measurements of spin relaxation. Moreover we demonstrate even higher
control of magnon propagation by employing the wave vector selectivity near an
avoided crossing of different spin-wave modes where the group velocity
approaches zero. Here local engineering of the dispersion allows constructing
magnonic waveguides and at the same time reveals the local relaxation
properties.",1803.04943v3
2019-03-03,Four-layer nanocomposite structure as an effective optical waveguide switcher for near-IR regime,"We present a theoretical study of the dispersion and energy properties of the
eigenwaves (TE- and TM- modes) in a four-layer structure composed of a
magneto-optical yttrium iron garnet guiding layer on a dielectric substrate
covered by a planar nanocomposite guiding multilayer. The bigyrotropic
properties of yttrium-iron garnet are taken into account for obtaining the
dispersion equation and an original algorithm for the guided modes
identification is proposed. We demonstrated the polarization switching of TE-
and TM-modes dependent on the geometrical parameters of the guiding layers. The
dispersion diagrams and field profiles are used to illustrate the change of
propagation properties with variation of the multilayer thickness ratio of the
nanocomposite layers. The energy flux distributions across the structure are
calculated and the conditions of the optimal guiding regime are obtained. The
power switching ratio in the waveguide layers of about 6 dB for the wavelength
range of 100 nm is shown to be achieved.",1903.00854v1
2019-11-12,Parametric generation of propagating spin-waves in ultra thin yttrium iron garnet waveguides,"We present the experimental demonstration of the parallel parametric
generation of spin-waves in a microscaled yttrium iron garnet waveguide with
nanoscale thickness. Using Brillouin light scattering microscopy, we observe
the excitation of the first and second waveguide modes generated by a stripline
microwave pumping source. Micromagnetic simulations reveal the wave vector of
the parametrically generated spin-waves. Based on analytical calculations,
which are in excellent agreement with our experiments and simulations, we prove
that the spin-wave radiation losses are the determinative term of the
parametric instability threshold in this miniaturized system. The used method
enables the direct excitation and amplification of nanometer spin-waves
dominated by exchange interactions. Our results pave the way for integrated
magnonics based on insulating nano-magnets.",1911.04926v2
2020-04-20,Ultra Thin Films of Yttrium Iron Garnet with Very Low Damping: A Review,"Thin Yttrium Iron Garnet (YIG) is a promising material for integrated
magnonics. In order to introduce YIG into nanofabrication processes it is
necessary to fabricate very thin YIG films with a thickness well below 100 nm
while retaining the extraordinary magnetic properties of the material,
especially its long magnon lifetime and spin wave propagation length. Here, we
give a brief introduction into the topic and we review and discuss the various
results published over the last decade in this area. Especially for ultrathin
films it turns out that pulsed layer deposition and sputtering are the most
promising candidates. In addition, we discuss the application of room
temperature deposition and annealing for lift-off based nanopatterning and the
properties of nanostructures obtained by this method over the past years.",2004.09094v1
2020-05-08,Observation of terahertz magnon of Kaplan-Kittel exchange resonance in yttrium-iron garnet by Raman spectroscopy,"Backscattering Raman spectroscopic investigations were performed on an
yttrium-iron garnet single crystal using linearly and circularly polarized
light. A terahertz (THz) magnon of the Kaplan-Kittel (KK) exchange resonance
was discovered, which had been regarded as unobservable via optical methods.
The KK exchange resonance had a 7.8-THz frequency at 80 K, and the polarization
selection rule led to an antisymmetric Raman tensor of the $A_{2}$ mode.
Moreover, the assignment of all the Raman-active phonon modes, $3A_{1g}$,
$8E_{g}$, and $14T_{2g}$, was proposed. This study will stimulate further
investigation of the coupling of THz magnons and phonons and pave the way
toward THz optomagnonics.",2005.03852v2
2021-03-12,Double accumulation and anisotropic transport of magneto-elastic bosons in yttrium iron garnet films,"Interaction between quasiparticles of a different nature, such as magnons and
phonons in a magnetic medium, leads to the mixing of their properties and the
formation of hybrid states in the areas of intersection of individual spectral
branches. We recently reported the discovery of a new phenomenon mediated by
the magnon-phonon interaction: the spontaneous bottleneck accumulation of
magneto-elastic bosons under electromagnetic pumping of pure magnons into a
ferrimagnetic yttrium iron garnet film. Here, by studying the transport
properties of the accumulated magneto-elastic bosons, we reveal that such
accumulation occurs in two frequency-distant groups of quasiparticles:
quasi-phonons and quasi-magnons. They propagate with different speeds in
different directions relative to the magnetization field. The theoretical model
we propose qualitatively describes the double accumulation effect, and the
analysis of the two-dimensional spectrum of quasiparticles in the hybridization
region allows us to determine the wavevectors and frequencies of each of the
groups.",2103.07338v1
2021-07-12,Origin of Perpendicular Magnetic Anisotropy in Yttrium Iron Garnet Thin Films Grown on Si (100),"We report the magnetic properties of yttrium iron garnet (YIG) thin films
grown by pulsed laser deposition technique. The films were deposited on Si
(100) substrates in the range of 15-50 nm thickness. Magnetic characterizations
were investigated by ferromagnetic resonance spectra. Perpendicular magnetic
easy axis was achieved up to 50 nm thickness. We observed that the
perpendicular anisotropy values decreased by increasing the film thickness. The
origin of the perpendicular magnetic anisotropy (PMA) was attributed to the
texture and the lattice distortion in the YIG thin films. We anticipate that
perpendicularly magnetized YIG thin films on Si substrates pave the way for a
cheaper and compatible fabrication process.",2107.05591v1
2021-12-30,Giant magnon spin conductivity approaching the two-dimensional transport regime in ultrathin yttrium iron garnet films,"Conductivities are key material parameters that govern various types of
transport (electronic charge, spin, heat etc.) driven by thermodynamic forces.
Magnons, the elementary excitations of the magnetic order, flow under the
gradient of a magnon chemical potential in proportion to a magnon (spin)
conductivity $\sigma_{m}$. The magnetic insulator yttrium iron garnet (YIG) is
the material of choice for efficient magnon spin transport. Here we report an
unexpected giant $\sigma_{m}$ in record-thin YIG films with thicknesses down to
3.7 nm when the number of occupied two-dimensional (2D) subbands is reduced
from a large number to a few, which corresponds to a transition from 3D to 2D
magnon transport. We extract a 2D spin conductivity ($\approx1$ S) at room
temperature, comparable to the (electronic) spin conductivity of the
high-mobility two-dimensional electron gas in GaAs quantum wells at millikelvin
temperatures. Such high conductivities offer unique opportunities to develop
low-dissipation magnon-based spintronic devices.",2112.15165v3
2022-01-22,Dissipative generation of significant amount of photon-phonon asymmetric steering in magnomechanical interfaces,"We propose an effective approach for generating significant amount of
entanglement and asymmetric steering between photon and phonon in a cavity
magnomechanical system which consists of a microwave cavity and a yttrium iron
garnet sphere. By driving the magnon mode of the yttrium iron garnet sphere
with blue-detuned microwave field, the magnon mode can be acted as an
engineered resevoir cools the Bogoliubov modes of microwave cavity mode and
mechanical mode via beam-splitter-like interaction. In this way, the microwave
cavity mode and mechanical mode are driven to two-mode squeezed states in the
stationary limit. In particular, strong two-way and one-way asymmetric quantum
steering between the photon and phonon modes can be obtained with even equal
dissipation. It is very different from the conventional proposal of asymmetric
quantum steering, where additional unbalanced losses or noises on the two
subsystems has been imposed. Our finding may be significant to expand our
understanding of the essential physics of asymmetric steering and extend the
potential application of the cavity spintronics to device-independent quantum
key distribution.",2201.08965v1
2023-08-01,Crystallization Dynamics of Amorphous Yttrium Iron Garnet Thin Films,"Yttrium iron garnet (YIG) is a prototypical material in spintronics due to
its exceptional magnetic properties. To exploit these properties high quality
thin films need to be manufactured. Deposition techniques like sputter
deposition or pulsed laser deposition at ambient temperature produce amorphous
films, which need a post annealing step to induce crystallization. However, not
much is known about the exact dynamics of the formation of crystalline YIG out
of the amorphous phase. Here, we conduct extensive time and temperature series
to study the crystallization behavior of YIG on various substrates and extract
the crystallization velocities as well as the activation energies needed to
promote crystallization. We find that the type of crystallization as well as
the crystallization velocity depend on the lattice mismatch to the substrate.
We compare the crystallization parameters found in literature with our results
and find an excellent agreement with our model. Our results allow us to
determine the time needed for the formation of a fully crystalline film of
arbitrary thickness for any temperature.",2308.00412v1
2017-11-20,Temperature dependent relaxation of dipole-exchange magnons in yttrium iron garnet films,"Low energy consumption enabled by charge-free information transport, which is
free from ohmic heating, and the ability to process phase-encoded data by
nanometer-sized interference devices at GHz and THz frequencies are just a few
benefits of spin-wave-based technologies. Moreover, when approaching cryogenic
temperatures, quantum phenomena in spin-wave systems pave the path towards
quantum information processing. In view of these applications, the lifetime of
magnons$-$spin-wave quanta$-$is of high relevance for the fields of magnonics,
magnon spintronics and quantum computing. Here, the relaxation behavior of
parametrically excited magnons having wavenumbers from zero up to $6\cdot 10^5
\mathrm{rad~cm}^{-1}$ was experimentally investigated in the temperature range
from 20 K to 340 K in single crystal yttrium iron garnet (YIG) films
epitaxially grown on gallium gadolinium garnet (GGG) substrates as well as in a
bulk YIG crystal$-$the magnonic materials featuring the lowest magnetic damping
known so far. As opposed to the bulk YIG crystal in YIG films we have found a
significant increase in the magnon relaxation rate below 150 K$-$up to 10.5
times the reference value at 340 K$-$in the entire range of probed wavenumbers.
This increase is associated with rare-earth impurities contaminating the YIG
samples with a slight contribution caused by coupling of spin waves to the spin
system of the paramagnetic GGG substrate at the lowest temperatures.",1711.07517v1
2019-03-22,Effects of post-deposition annealing on the structure and magnetization of PLD grown Yttrium Iron Garnet films,"We report on the recrystallization of 200 nm thick as-grown Yttrium Iron
Garnet (Y_3.4 Fe_4.6 O_12) films on (111) face of Gadolinium Gallium Garnet
(GGG) single crystals by post-deposition annealing. Epitaxial conversion of the
as-grown microcrystalline YIG films was seen after annealing at 800oC for more
than 30 minutes both in ambient oxygen as well as in air. The as-grown oxygen
annealed samples at 800oC for 60 minutes crystallize epitaxially and show
excellent figure-of-merit for saturation magnetization (MS = 3.3 {\mu}B/f.u.,
comparable to bulk value) and coercivity (HC ~ 1.1 Oe). The ambient air
annealing at 800oC with a very slow rate of cooling (2oC/min) results in a
double layer structure with a thicker unstrained epitaxial top layer having the
MS and HC of 2.9 {\mu}B/f.u. and 0.12 Oe respectively. The symmetric and
asymmetric Reciprocal space maps of both the samples reveal a locking of the
in-plane lattice of the film to the in-plane lattice of substrate, indicating a
pseudomorphic growth. The residual stress calculated by sin^2 {\psi} technique
is compressive in nature. The lower layer in air annealed sample is highly
strained, whereas, the top layer has negligible compressive stress.",1903.09457v1
2014-01-20,On the theory of inhomogeneous Bose-Einstein condensation of magnons in yttrium garnet,"The Bose-Einstein condensation (BEC) of magnons created by a strong pumping
in ferromagnetic thin films of yttrium iron garnet used as systems of finite
size is considered analytically. Such a peculiarity, typical for this magnetic
material, as the presence of a minimum in the spectrum of spin waves at a
finite value of the wave vector is taken into account. The definition of
hightemperature BEC is introduced and its characteristics are discussed. A role
of boundary conditions for spin variables is analyzed, and it is shown that in
the case of free spins on the boundary the magnon lattice can form in the
system. The factors responsible for its appearance are discussed.",1401.4854v1
2016-05-30,"An integrated approach to doped thin films with strain tunable magnetic anisotropy: Powder synthesis, target preparation and pulsed laser deposition of Bi:YIG","We present a synthesis/processing method for fabricating ferrimagnetic
insulator (Bi-doped yttrium iron garnet) thin films with tunable magnetic
anisotropy. Since the desired magnetic properties rely on controllable
thickness and successful doping, we pay attention to the entire
synthesis/processing procedure (nanopowder synthesis, nanocrystalline target
preparation and pulsed laser deposition (PLD)). Atomically flat films were
deposited by PLD on (111)-orientated yttrium aluminum garnet. We show a
significant enhancement of perpendicular anisotropy in the films, caused by
strain-induced anisotropy. In addition, the perpendicular anisotropy is tunable
by decreasing the film thickness and overwhelms the shape anisotropy at a
critical thickness of 3.5 nm.",1605.09084v2
2017-03-26,Unexpected structural and magnetic depth dependence of YIG thin films,"We report measurements on yttrium iron garnet (YIG) thin films grown on both
gadolinium gallium garnet (GGG) and yttrium aluminium garnet (YAG) substrates,
with and without thin Pt top layers. We provide three principal results: the
observation of an interfacial region at the Pt/YIG interface, we place a limit
on the induced magnetism of the Pt layer and confirm the existence of an
interfacial layer at the GGG/YIG interface. Polarised neutron reflectometry
(PNR) was used to give depth dependence of both the structure and magnetism of
these structures. We find that a thin film of YIG on GGG is best described by
three distinct layers: an interfacial layer near the GGG, around 5 nm thick and
non-magnetic, a magnetic bulk phase, and a non-magnetic and compositionally
distinct thin layer near the surface. We theorise that the bottom layer, which
is independent of the film thickness, is caused by Gd diffusion. The top layer
is likely to be extremely important in inverse spin Hall effect measurements,
and is most likely Y2O3 or very similar. Magnetic sensitivity in the PNR to any
induced moment in the Pt is increased by the existence of the Y2O3 layer; any
moment is found to be less than 0.02 uB/atom.",1703.08752v1
2020-01-09,Bismuth iron garnet: ab initio study of electronic properties,"Bismuth iron garnet (BIG), i.e. Bi3Fe5O12, is a strong ferrimagnet that also
possess outstanding magneto-optical properties such as the largest known
Faraday rotation. These properties are related with the distribution of
magnetic moments on octahedral and tetrahedral sites, the presence of spin gaps
in the density of state and a strong spin-orbit coupling. In this work,
first-principles ab initio calculations are performed to study the structural,
electronic and magnetic properties of BIG using Density Functional Theory with
Hubbard+U (DFT+U) correction including spin-orbit coupling and HSE06 hybrid
functional. We found that the presence of spin gaps in the electronic structure
results from the interplay between exchange and correlation effects and the
crystal field strengths for tetrahedral and octahedral iron sublattices. The
DFT+U treatment tends to close the spin-gaps for larger U due to
over-localization effects, notably in the octahedral site. On the other hand,
the hybrid functional confirms the occurrences of three spin gaps in the iron
states of the conduction band as expected from optical measurements. A strong
exchange splitting at the top of the valence bands associated with a lone-pair
type mixture of O p and Bi s,p states is also obtained. Similar exchange
splitting was not previously observed for other iron based garnets, such as for
yttrium iron garnet. It follows that hole doping, as obtained by Ca
substitution at Bi sites, results in a full spin polarized density at the Fermi
energy. This work helps to shed more light on the theoretical comprehension of
the properties of BIG and opens the route towards the use of advanced Many Body
calculations to predict the magneto-optical coupling effects in BIG in a direct
comparison with the experimental measurements.",2001.02910v1
2018-11-29,Structural and Magnetic Study of Metallo-Organic YIG Powder Using 2-ethylhexanoate Carboxylate Based Precursors,"The crystallization and magnetic behavior of yttrium iron garnet (YIG)
prepared by metallo-organic decomposition (MOD) method are discussed. The
chemistry and physics related to synthesis of iron and yttrium carboxylates
based on 2-ethylhexanoic acid (2EHA) are studied, since no literature was found
which elucidates synthesis of metallo-organic precursor of YIG in spite of the
literatures of doped YIG samples such as Bi-YIG. Typically, the metal
carboxylates used in preparation of ceramic oxide materials are
2-ethylhexanoate (2EH) solvents. Herein, the synthesis, thermal behavior and
solubility of yttrium and iron 2EH used in synthesis of YIG powder by MOD are
reported. The crystallization and magnetic parameters, including saturation
magnetization and coercivity of these samples, smoothly change as a function of
the annealing temperature. It is observed that high sintering temperature of
1300 to 1400 {\deg}C promotes the diffraction peaks of YIG, therefore, we can
conclude that the formation of YIG in MOD method increases the crystallization
temperature. The maximum value of saturation magnetization and minimum value of
coercivity and remanence are observed for the sample sintered at 1200{\deg}C
which are 13.7 emu/g, 10.38 Oe and 1.5 emu/g, respectively. This study cites
the drawbacks in chemical synthesis of metallo-organic based YIG production.",1811.12514v1
1997-03-26,Stochastic Resonance in Chaotic Spin-Wave Dynamics,"We report the first experimental observation of noise-free stochastic
resonance by utilizing the intrinsic chaotic dynamics of the system. To this
end we have investigated the effect of an external periodic modulation on
intermittent signals observed by high power ferromagnetic resonance in yttrium
iron garnet spheres. Both the signal-to-noise ratio and the residence time
distributions show the characteristic features of stochastic resonance. The
phenomena can be explained by means of a one-dimensional intermittent map. We
present analytical results as well as computer simulations.",9703018v1
2004-11-28,Generation of spin-wave dark solitons with phase engineering,"We generate experimentally spin-wave envelope dark solitons from rectangular
high-frequency dark input pulses with externally introduced phase shifts in
yttrium-iron garnet magnetic fims. We observe the generation of both odd and
even numbers of magnetic dark solitons when the external phase shift varies.
The experimental results are in a good qualitative agreement with the theory of
the dark-soliton generation in magnetic films developed earlier [Phys. Rev.
Lett. 82, 2583 (1999)].",0411056v1
2008-05-27,Scattering of backward spin waves in a one-dimensional magnonic crystal,"Scattering of backward volume magnetostatic spin waves from a one-dimensional
magnonic crystal, realized by a grating of shallow grooves etched into the
surface of an yttrium-iron garnet film, was experimentally studied. Rejection
frequency bands were clearly observed. The rejection efficiency and the
frequency width of the rejection bands increase with increasing groove depth. A
theoretical model based on the analogy of a spin-wave film-waveguide with a
microwave transmission line was used to interpret the obtained experimental
results.",0805.4142v1
2008-09-19,Polarization proximity effect in isolator crystal pairs,"We experimentally studied the polarization dynamics (orientation and
ellipticity) of near infrared light transmitted through magnetooptic Yttrium
Iron Garnet crystal pairs using a modified balanced detection scheme. When the
pair separation is in the sub-millimeter range, we observed a proximity effect
in which the saturation field is reduced by up to 20%. 1D magnetostatic
calculations suggest that the proximity effect originates from magnetostatic
interactions between the dipole moments of the isolator crystals. This
substantial reduction of the saturation field is potentially useful for the
realization of low-power integrated magneto-optical devices.",0809.3292v1
2008-10-22,Probing of a parametrically pumped magnon gas with a non-resonant packet of traveling spin waves,"The magnon gas created by spatially localized longitudinal parametric pumping
in an yttrium-iron-garnet film is probed by a traveling packet of spin waves
non-resonant with the pumping field. The analysis of the influence of the
magnon gas on the amplitude and phase of the propagating spin waves allows to
determine characteristic properties of the parametrically pumped magnon gas. A
simple theoretical model is proposed from which the magnon density in the
pumping region is calculated.",0810.4033v1
2009-01-13,Refractive index and Snell's Law for Dipolar-Exchange Spin-Waves in a Confined Planar Structure,"We derived the analytical forms of refractive index and Snell law for
dipolar-exchange spin waves of reflection and refraction at a magnetically
heterogeneous interface in a geometrically confined planer structure composed
of different magnetic thin films from a microscopic scattering approach. A
novel behavior, the optical total reflection, was demonstrated for spin waves
with a specific interface between Yttrium iron garnet (Y3Fe5O12) and Permalloy
(Ni80Fe20), by analytical and micromagnetic numerical calculations.",0901.1700v2
2009-03-02,Magnetooptical control of light collapse in bulk Kerr media,"Magneto-optical crystals allow an efficient control of the birefringence of
light via the Cotton-Mouton and Faraday effects. These effects enable a unique
combination of adjustable linear and circular birefringence, which, in turn,
can affect the propagation of light in nonlinear Kerr media. We show
numerically that the combined birefringences can accelerate, delay, or arrest
the nonlinear collapse of (2+1)D beams, and report an experimental observation
of the acceleration of the onset of collapse in a bulk Yttrium Iron Garnet
(YIG) crystal in an external magnetic field.",0903.0373v1
2010-10-12,Linear-response theory of spin Seebeck effect in ferromagnetic insulators,"We formulate a linear response theory of the spin Seebeck effect, i.e., a
spin voltage generation from heat current flowing in a ferromagnet. Our
approach focuses on the collective magnetic excitation of spins, i.e., magnons.
We show that the linear-response formulation provides us with a qualitative as
well as quantitative understanding of the spin Seebeck effect observed in a
prototypical magnet, yttrium iron garnet.",1010.2325v2
2011-03-19,Spin transfer torque on magnetic insulators,"Recent experimental and theoretical studies focus on spin-mediated heat
currents at interfaces between normal metals and magnetic insulators. We
resolve conflicting estimates for the order of magnitude of the spin transfer
torque by first-principles calculations. The spin mixing conductance
G^\uparrow\downarrow of the interface between silver and the insulating
ferrimagnet Yttrium Iron Garnet (YIG) is dominated by its real part and of the
order of 10^14 \Omega^-1m^-2, i.e. close to the value for intermetallic
interface, which can be explained by a local spin model.",1103.3764v2
2011-06-16,Thermomagnonic spin transfer and Peltier effects in insulating magnets,"We study the coupled magnon energy transport and collective magnetization
dynamics in ferromagnets with magnetic textures. By constructing a
phenomenological theory based on irreversible thermodynamics, we describe
motion of domain walls by thermal gradients and generation of heat flows by
magnetization dynamics. From microscopic description based on magnon kinetics,
we estimate the transport coefficients and analyze the feasibility of
energy-related applications in insulating ferromagnets, such as yttrium iron
garnet and europium oxide.",1106.3135v2
2011-07-06,Spin Seebeck Effect: Amplification of Spin Waves by Thermal Torque,"We observe amplification of spin-wave packets propagating along a film of
yttrium iron garnet (YIG) subject to a transverse temperature gradient. The
amplification is attributed to a spin-transfer thermal torque created by spin
currents generated by means of the spin Seebeck effect that acts on the
magnetization and opposes the relaxation. The experimental data are interpreted
with a simple theoretical model using spin-wave theory that gives an
amplification gain in very good agreement with measurements.",1107.1271v2
2012-04-18,Domain wall heat conductance in ferromagnetic wires,"We present a theoretical study of heat transport in electrically insulating
ferromagnetic wires containing a domain wall. In the regime of validity of
continuum micromagnetism a domain wall is found to have no effect on the heat
conductance. However, spin waves are found to be reflected by domain walls with
widths of a few lattice spacings, which is associated with emergence of an
additional spin wave bound state. The resulting domain wall heat conductance
should be significant for thin films of Yttrium Iron Garnet with sharply
defined magnetic domains.",1204.4008v2
2013-09-11,Nanomechanical AC Susceptometry of an Individual Mesoscopic Ferrimagnet,"A novel method for simultaneous detection of both DC and time-dependent
magnetic signatures in individual mesoscopic structures has emerged from early
studies in spin mechanics. Multifrequency nanomechanical detection of AC
susceptibility and its harmonics highlights reversible nonlinearities in the
magnetization response of a single yttrium iron garnet (YIG) element,
separating them from hysteretic jumps in the DC magnetization.",1309.2965v1
2013-11-12,Nonreciprocity engineering in magnetostatic spin waves,"Magnetostatic surface spin waves (MSSW) excited from a coplanar waveguide
antenna travel in different directions with different amplitudes. This effect,
called nonreciprocity of MSSW, has been investigated by micromagnetic
simulations. The ratio of amplitude of two counter propagating spin waves, the
nonreciprocity parameter {\kappa}, is obtained for different ferromagnetic
materials, such as NiFe (Py), CoFeAl, yttrium iron garnet (YIG), and GaMnAs. A
device schematic has been proposed in which {\kappa} can be tuned to a large
value by varying simple geometrical parameters of the device.",1311.2686v1
2014-04-09,Current-induced spin torque resonance of magnetic insulators,"We formulate a theory of the AC spin Hall magnetoresistance (SMR) in a
bilayer system consisting of a magnetic insulator such as yttrium iron garnet
(YIG) and a heavy metal such as platinum (Pt). We derive expressions for the DC
voltage generation based on the drift-diffusion spin model and quantum
mechanical boundary condition at the interface that reveal a spin torque
ferromagnetic resonance (ST-FMR). We predict that ST-FMR experiments will
reveal valuable information on the current-induced magnetization dynamics of
magnetic insulators and AC spin Hall effect.",1404.2360v2
2014-10-05,Planar Hall effect in Y3Fe5O12(YIG)/IrMn films,"The planar Hall effect of IrMn on an yttrium iron garnet (YIG = Y3Fe5O12) was
measured in the magnetic field rotating in the film plane. The magnetic field
angle dependence of planar Hall resistance (PHR) has been observed in YIG/IrMn
bilayer at different temperatures, while the GGG/IrMn (GGG= Gd3Ga5O12) shows
constant PHR for different magnetic field angles at both 10 K and 300 K. This
provides evidence that IrMn has interfacial spins which can be led by FM in
YIG/IrMn structure. A hysteresis can be observed in PHR-magnetic field angle
loop of YIG/IrMn films at 10 K, indicating the irreversible switching of IrMn
interfacial spins at low temperature.",1410.1112v1
2014-10-07,Influence of interface condition on spin-Seebeck effects,"The longitudinal spin-Seebeck effect (LSSE) has been investigated for
Pt/yttrium iron garnet (YIG) bilayer systems. The magnitude of the voltage
induced by the LSSE is found to be sensitive to the Pt/YIG interface condition.
We observed large LSSE voltage in a Pt/YIG system with a better crystalline
interface, while the voltage decays steeply when an amorphous layer is
introduced at the interface artificially.",1410.1655v1
2014-12-03,Proximity-induced ferromagnetism in graphene revealed by anomalous Hall effect,"We demonstrate the anomalous Hall effect (AHE) in single-layer graphene
exchange-coupled to an atomically flat yttrium iron garnet (YIG) ferromagnetic
thin film. The anomalous Hall conductance has magnitude of ~0.09(2e2/h) at low
temperatures and is measurable up to ~ 300 K. Our observations indicate not
only proximity-induced ferromagnetism in graphene/YIG with large exchange
interaction, but also enhanced spin-orbit coupling which is believed to be
inherently weak in ideal graphene. The proximity-induced ferromagnetic order in
graphene can lead to novel transport phenomena such as the quantized AHE which
are potentially useful for spintronics.",1412.1521v1
2015-03-09,Magnetic spheres in microwave cavities,"We apply Mie scattering theory to study the interaction of magnetic spheres
with microwaves in cavities beyond the magnetostatic and rotating wave
approximations. We demonstrate that both strong and ultra-strong coupling can
be realized for a stand alone magnetic spheres made from yttrium iron garnet
(YIG), acting as an efficient microwave antenna. The eigenmodes of YIG spheres
with radii of the order mm's display distinct higher angular momentum character
that has been observed in experiments.",1503.02419v2
2015-06-09,Identification of spin wave modes strongly coupled to a co-axial cavity,"We demonstrate, at room temperature, the strong coupling of the fundamental
and non-uniform magnetostatic modes of an yttrium iron garnet (YIG)
ferrimagnetic sphere to the electromagnetic modes of a co-axial cavity. The
well-defined field profile within the cavity yields a specific coupling
strength for each magnetostatic mode. We experimentally measure the coupling
strength for the different magnetostatic modes and, by calculating the expected
coupling strengths, are able to identify the modes themselves.",1506.02902v1
2015-06-18,Dispersive read-out of ferromagnetic resonance for strongly coupled magnons and microwave photons,"We demonstrate the dispersive measurement of ferromagnetic resonance in a
yttrium iron garnet sphere embedded within a microwave cavity. The reduction in
the longitudinal magnetization at resonance is measured as a frequency shift in
the cavity mode coupled to the sphere. This measurement is a result of the
intrinsic non-linearity in magnetization dynamics, indicating a promising route
towards experiments in magnon cavity quantum electro-dynamics.",1506.05631v1
2015-10-22,Magneto-optical coupling in whispering gallery mode resonators,"We demonstrate that yttrium iron garnet microspheres support optical
whispering gallery modes similar to those in non-magnetic dielectric materials.
The direction of the ferromagnetic moment tunes both the resonant frequency via
the Voigt effect as well as the degree of polarization rotation via the Faraday
effect. An understanding of the magneto-optical coupling in whispering gallery
modes, where the propagation direction rotates with respect to the
magnetization, is fundamental to the emerging field of cavity optomagnonics.",1510.06661v2
2016-07-16,"Comment on ""Supercurrent in a room temperature Bose-Einstein magnon condensate""","The comment explains that the preprint arXiv:1503.0042 has not presented
persuasive theoretical or experimental arguments of existence of spin
supercurrents in a magnon condensate prepared in a room temperature
yttrium-iron-garnet magnetic film because the authors did not check known
criteria for existence of spin supercurrents in magnetically ordered materials.
Also they did not compare their supercurrent interpretation with a competing
and more realistic scenario of transport by spin diffusion.",1607.04720v2
2016-11-28,Berry curvature in magnon-phonon hybrid systems,"We theoretically study the Berry curvature of the magnon induced by the
hybridization with the acoustic phonons via the spin-orbit and dipolar
interactions. We first discuss the magnon-phonon hybridization via the dipolar
interaction, and show that the dispersions have gapless points in momentum
space, some of which form a loop. Next, when both spin-orbit and dipolar
interactions are considered, we show anisotropic texture of the Berry curvature
and its divergence with and without gap-closing. Realistic evaluation of the
consequent anomalous velocity is given for yttrium iron garnet.",1611.08993v1
2018-04-19,Damping of magnetization dynamics by phonon pumping,"We theoretically investigate pumping of phonons by the dynamics of a magnetic
film into a non-magnetic contact. The enhanced damping due to the loss of
energy and angular momentum shows interference patterns as a function of
resonance frequency and magnetic film thickness that cannot be described by
viscous (""Gilbert"") damping. The phonon pumping depends on magnetization
direction as well as geometrical and material parameters and is observable,
e.g., in thin films of yttrium iron garnet on a thick dielectric substrate.",1804.07080v2
2019-06-03,Magnon-phonon interactions in magnetic insulators,"We address the theory of magnon-phonon interactions and compute the
corresponding quasi-particle and transport lifetimes in magnetic insulators
with focus on yttrium iron garnet at intermediate temperatures from anisotropy-
and exchange-mediated magnon-phonon interactions, the latter being derived from
the volume dependence of the Curie temperature. We find in general weak effects
of phonon scattering on magnon transport and the Gilbert damping of the
macrospin Kittel mode. The magnon transport lifetime differs from the
quasi-particle lifetime at shorter wavelengths.",1906.01042v1
2019-11-12,Coherent pumping of high momentum magnons by light,"We propose to excite a large number of coherent magnons with high momentum in
optical cavities. This is achieved by two counterpropagating optical modes that
are detuned by the frequency of a selected magnon, similar to stimulated Raman
scattering. In sub-mm size yttrium iron garnet spheres, a mW laser input power
generates 10^6-10^8 coherent magnons. The large magnon population enhances
Brillouin light scattering, a probe suitable to access their quantum
properties.",1911.04728v1
2020-09-22,From Chaotic Spin Dynamics to Non-collinear Spin Textures in YIG Nano-films by Spin Current Injection,"In this article I report about a numerical investigation of nonlinear spin
dynamics in a magnetic thin-film, made of Yttrium-Iron-Garnet (YIG). This film
is exposed to a small in-plane oriented magnetic field, and strong spin
currents. The rich variety of findings encompass dynamic regimes hosting
localized, non-propagating solitons, a turbulent chaotic regime, which
condenses into a quasi-static phase featuring a non-collinear spin texture.
Eventually, at largest spin current, a homogeneously switched state is
established.",2009.10628v1
2021-02-22,A review of modelling in ferrimagnetic spintronics,"In this review we introduce computer modelling and simulation techniques
which are used for ferrimagnetic materials. We focus on models where thermal
effects are accounted for, atomistic spin dynamics and finite temperature
macrospin approaches. We survey the literature of two of the most commonly
modelled ferrimagnets in the field of spintronics--the amorphous alloy GdFeCo
and the magnetic insulator yttrium iron garnet. We look at how generic models
and material specific models have been applied to predict and understand
spintronic experiments, focusing on the fields of ultrafast magnetisation
dynamics, spincaloritronics and magnetic textures dynamics and give an outlook
for modelling in ferrimagnetic spintronics.",2102.11004v1
2021-06-10,QNMnonreciprocal_resonators: an openly available toolbox for computing the QuasiNormal Modes of nonreciprocal resonators,"QNMnonreciprocal_resonators is an extension (posted in 2021) of the QNMEig
solver of the freeware package MAN. It provides a comprehensive presentation of
the computation and normalization of electromagnetic quasinormal modes (QNMs)
of resonators composed of nonreciprocal materials. It features a theoretical
background on the topic and a COMSOL model that illustrates how to put into
practice the theory on the example of a Yttrium iron garnet wire in a
homogenous background. This document provides the necessary details on how the
model is built so that the interested readers may easily modify it for
computing QNMs of other nonreciprocal resonators.",2106.05502v1
2023-01-14,Quantum entanglement generation on magnons assisted with microwave cavities coupled to a superconducting qubit,"We present protocols to generate quantum entanglement on nonlocal magnons in
hybrid systems composed of yttrium iron garnet (YIG) spheres, microwave
cavities and a superconducting (SC) qubit. In the schemes, the YIGs are coupled
to respective microwave cavities in resonant way, and the SC qubit is placed at
the center of the cavities, which interacts with the cavities simultaneously.
By exchanging the virtual photon, the cavities can indirectly interact in the
far-detuning regime. Detailed protocols are presented to establish entanglement
for two, three and arbitrary $N$ magnons with reasonable fidelities.",2301.05820v1
2023-01-24,Direct observation of magnon BEC in an out-of-plane magnetized yttrium iron garnet film,"Bose-Einstain condensation occurs at an appropriate density of bosonic
particles, depending on their mass and temperature. We were able to
experimentally observe the transition from the spin wave regime to the magnon
Bose-Einstein condensed state (mBEC) with increasing magnon density by a
microwave pumping. We used optical methods to register the spatial distribution
of the magnon density and phase. For the first time, a coherent state of
stationary magnons was demonstrated far from the region of their excitation.",2301.10725v1
2023-02-17,Control of magnon-photon coupling by spin torque,"We demonstrate the influence of damping and field-like torques in the
magnon-photon coupling process by classically integrating the generalized
Landau-Lifshitz-Gilbert equation with RLC equation in which a phase correlation
between dynamic magnetization and microwave current through combined Amp\`ere
and Faraday effects are considered. We show that the gap between two hybridized
modes can be controlled in samples with damping parameter in the order of
$10^{-3}$ by changing the direction of the dc current density $J$ if a certain
threshold is reached. Our results suggest that an experimental realization of
the proposed magnon-photon coupling control mechanism is feasible in yttrium
iron garnet/Pt hybrid structures.",2302.08910v1
2023-05-11,Correlation-enhanced interaction of a Bose-Einstein condensate with parametric magnon pairs and virtual magnons,"Nonlinear interactions are crucial in science and engineering. Here, we
investigate wave interactions in a highly nonlinear magnetic system driven by
parametric pumping leading to Bose--Einstein condensation of spin-wave quanta
-- magnons. Using Brillouin light scattering spectroscopy in yttrium-iron
garnet films, we found and identified a set of nonlinear processes resulting in
off-resonant spin-wave excitations -- virtual magnons. In particular, we
discovered a dynamically-strong, correlation-enhanced four-wave interaction
process of the magnon condensate with pairs of parametric magnons having
opposite wavevectors and fully correlated phases.",2305.06896v1
2023-12-05,Interplay between magnetism and superconductivity in a hybrid magnon-photon bilayer system,"Spin waves in magnetic films are affected by the vicinity to a
superconductor. Here we studied a bilayer stack made of an insulating Yttrium
Iron Garnet (YIG) film and a high-$T_c$ YBCO superconducting planar resonator.
We investigated the hybridization of magnon and photon modes reporting the
temperature evolution of microwave transmission spectra. Data analysis, based
on the description of magnon modes and on the Hopfield model, shows that the
magnon-photon coupling strength and the mode frequency shift can be ultimately
related to the temperature dependence of the penetration depth of YBCO.",2312.02785v2
2015-06-19,All electrical coherent control of the magnetization in thin Yittrium Iron Garnet film,"We demonstrate coherent control of time domain ferromagnetic resonance by all
electrical excitation and detection. Using two ultrashort magnetic field steps
with variable time delay we control the induction decay in yttrium iron garnet
(YIG). By setting suitable delay times between the two steps the precession of
the magnetization can either be enhanced or completely stopped. The method
allows for a determination of the precession frequency within a few precession
periods and with an accuracy much higher than can be achieved using fast
fourier transformation. Moreover it holds the promise to massively increase
precession amplitudes in pulsed inductive microwave magnetometry (PIMM) using
low amplitude finite pulse trains. Our experiments are supported by
micromagnetic simulations which nicely confirm the experimental results.",1506.05935v1
2017-06-11,Magnetization spin dynamics in a (LuBi)3Fe5O12 (BLIG) epitaxial film,"Bismuth substituted lutetium iron garnet (BLIG) films exhibit larger Faraday
rotation, and have a higher Curie temperature than yttrium iron garnet. We have
observed magnetic stripe domains and measured domain widths of 1.4 {\mu}{\mu}m
using Fourier domain polarization microscopy, Faraday rotation experiments
yield a coercive field of 5 Oe. These characterizations form the basis of
micromagnetic simulations that allow us to estimate and compare spin wave
excitations in BLIG films. We observed that these films support thermal magnons
with a precessional frequency of 7 GHz with a line width of 400 MHz. Further,
we studied the dependence of precessional frequency on the externally applied
magnetic field. Brillouin light scattering experiments and precession
frequencies predicted by simulations show similar trend with increasing field.",1706.03340v1
2004-05-26,Microwave Magnetoelectric Effects in Single Crystal Bilayers of Yttrium Iron Garnet and Lead Magnesium Niobate-Lead Titanate,"The first observation of microwave magnetoelectric (ME) interactions through
ferromagnetic resonance (FMR) in bilayers of single crystal
ferromagnetic-piezoelectric oxides and a theoretical model for the effect are
presented. An electric field E produces a mechanical deformation in the
piezoelectric phase, resulting in a shift dHE in the resonance field for the
ferromagnet. The strength of ME coupling is obtained from data on dHE vs E.
Studies were performed at 9.3 GHz on bilayers of (111) yttrium iron garnet
(YIG) films and (001) lead magnesium niobate-lead titanate (PMN-PT). The
samples were positioned outside a TE102-reflection type cavity. Resonance
profiles were obtained for E = 0-8 kV/cm for both in-plane and out-of-plane
magnetic fields H. Important results are as follows. (i) The ME coupling in the
bilayers is an order of magnitude stronger than in polycrystalline composites
and is in the range 1-5.4 Oe cm/kOe, depending on the YIG film thickness. (ii)
The coupling strength is dependent on the magnetic field orientation and is
higher for out-of-plane H than for in-plane H. (iii) Estimated ME constant and
its dependence on volume ratio for the two phases are in good agreement with
the data.",0405622v1
2015-12-03,Cavity quantum electrodynamics with ferromagnetic magnons in a small yttrium-iron-garnet sphere,"Hybridizing collective spin excitations and a cavity with high cooperativity
provides a new research subject in the field of cavity quantum electrodynamics
and can also have potential applications to quantum information. Here we report
an experimental study of cavity quantum electrodynamics with ferromagnetic
magnons in a small yttrium-iron-garnet (YIG) sphere at both cryogenic and room
temperatures. We observe for the first time a strong coupling of the same
cavity mode to both a ferromagnetic-resonance (FMR) mode and a magnetostatic
(MS) mode near FMR in the quantum limit. This is achieved at a temperature ~ 22
mK, where the average microwave photon number in the cavity is less than one.
At room temperature, we also observe strong coupling of the cavity mode to the
FMR mode in the same YIG sphere and find a slight increase of the damping rate
of the FMR mode. These observations reveal the extraordinary robustness of the
FMR mode against temperature. However, the MS mode becomes unobservable at room
temperature in the measured transmission spectrum of the microwave cavity
containing the YIG sphere. Our numerical simulations show that this is due to a
drastic increase of the damping rate of the MS mode.",1512.00983v1
2016-08-29,Sub-micrometer yttrium iron garnet LPE films with low ferromagnetic resonance losses,"Using liquid phase epitaxy (LPE) technique (111) yttrium iron garnet (YIG)
films with thicknesses of ~100 nm and surface roughnesses as low as 0.3 nm have
been grown as a basic material for spin-wave propagation experiments in
microstructured waveguides. The continuously strained films exhibit nearly
perfect crystallinity without significant mosaicity and with effective lattice
misfits of delta a(perpendicular)/a(substrate) ~10-4 and below. The
film/substrate interface is extremely sharp without broad interdiffusion layer
formation. All LPE films exhibit a nearly bulk-like saturation magnetization of
(1800+-20) Gs and an `easy cone' anisotropy type with extremely small in-plane
coercive fields <0.2 Oe. There is a rather weak in-plane magnetic anisotropy
with a pronounced six-fold symmetry observed for saturation field <1.5 Oe. No
significant out-of-plane anisotropy is observed, but a weak dependence of the
effective magnetization on the lattice misfit is detected. The narrowest
ferromagnetic resonance linewidth is determined to be 1.4 Oe @ 6.5 GHz which is
the lowest value reported so far for YIG films of 100 nm thicknesses and below.
The Gilbert damping coefficient for investigated LPE films is estimated to be
close to 1 x 10-4.",1608.08043v1
2017-05-05,Thermographic measurements of the spin Peltier effect in metal/yttrium-iron-garnet junction systems,"The spin Peltier effect (SPE), heat-current generation due to spin-current
injection, in various metal (Pt, W, and Au single layers and Pt/Cu
bilayer)/ferrimagnetic insulator (yttrium iron garnet: YIG) junction systems
has been investigated by means of a lock-in thermography (LIT) method. The SPE
is excited by a spin current across the metal/YIG interface, which is generated
by applying a charge current to the metallic layer via the spin Hall effect.
The LIT method enables the thermal imaging of the SPE free from the
Joule-heating contribution. Importantly, we observed spin-current-induced
temperature modulation not only in the Pt/YIG and W/YIG systems but also in the
Au/YIG and Pt/Cu/YIG systems, excluding the possible contamination by anomalous
Ettingshausen effects due to proximity-induced ferromagnetism near the
metal/YIG interface. As demonstrated in our previous study, the SPE signals are
confined only in the vicinity of the metal/YIG interface; we buttress this
conclusion by reducing a spatial blur due to thermal diffusion in an infrared
emission layer on the sample surface used for the LIT measurements. We also
found that the YIG-thickness dependence of the SPE is similar to that of the
spin Seebeck effect measured in the same Pt/YIG sample, implying the reciprocal
relation between them.",1705.02094v1
2017-05-05,Neutron-scattering study of yttrium iron garnet,"The nuclear and magnetic structure and full magnon dispersions of yttrium
iron garnet Y$_3$Fe$_5$O$_{12}$ have been studied by neutron scattering. The
refined nuclear structure is distorted to a trigonal space group of $R\bar{3}$.
The highest-energy dispersion extends up to 86 meV. The observed dispersions
are reproduced by a simple model with three nearest-neighbor-exchange integrals
between 16$a$ (octahedral) and 24$d$ (tetrahedral) sites, $J_{aa}$, $J_{ad}$,
and $J_{dd}$, which are estimated to be 0.00$\pm$0.05, $-$2.90$\pm$0.07, and
$-$0.35$\pm$0.08 meV, respectively. The lowest-energy dispersion below 14 meV
exhibits a quadratic dispersion as expected from ferromagnetic magnons. The
imaginary part of $q$-integrated dynamical spin susceptibility $\chi$""($E$)
exhibits a square-root energy-dependence in the low energies. The magnon
density of state is estimated from the $\chi$""($E$) obtained on an absolute
scale. The value is consistent with a single polarization mode for the magnon
branch expected theoretically.",1705.02167v5
2017-06-14,Nonlocal magnon-polaron transport in yttrium iron garnet,"The spin Seebeck effect (SSE) is observed in magnetic insulator|heavy metal
bilayers as an inverse spin Hall effect voltage under a temperature gradient.
The SSE can be detected nonlocally as well, viz. in terms of the voltage in a
second metallic contact (detector) on the magnetic film, spatially separated
from the first contact that is used to apply the temperature bias (injector).
Magnon-polarons are hybridized lattice and spin waves in magnetic materials,
generated by the magnetoelastic interaction. Kikkawa et al. [Phys. Rev. Lett.
\textbf{117}, 207203 (2016)] interpreted a resonant enhancement of the local
SSE in yttrium iron garnet (YIG) as a function of the magnetic field in terms
of magnon-polaron formation. Here we report the observation of magnon-polarons
in \emph{nonlocal} magnon spin injection/detection devices for various
injector-detector spacings and sample temperatures. Unexpectedly, we find that
the magnon-polaron resonances can suppress rather than enhance the nonlocal
SSE. Using finite element modelling we explain our observations as a
competition between the SSE and spin diffusion in YIG. These results give
unprecedented insights into the magnon-phonon interaction in a key magnetic
material.",1706.04373v1
2018-02-09,Monocrystalline free standing 3D yttrium iron garnet magnon nano resonators,"Nano resonators in which mechanical vibrations and spin waves can be coupled
are an intriguing concept that can be used in quantum information processing to
transfer information between different states of excitation. Until now, the
fabrication of free standing magnetic nanostructures which host long lived spin
wave excitatons and may be suitable as mechanical resonators seemed elusive. We
demonstrate the fabrication of free standing monocrystalline yttrium iron
garnet (YIG) 3D nanoresonators with nearly ideal magnetic properties. The
freestanding 3D structures are obtained using a complex lithography process
including room temperature deposition and lift-off of amorphous YIG and
subsequent crystallization by annealing. The crystallization nucleates from the
substrate and propagates across the structure even around bends over distances
of several micrometers to form e.g. monocrystalline resonators as shown by
transmission electron microscopy. Spin wave excitations in individual
nanostructures are imaged by time resolved scanning Kerr microscopy. The narrow
linewidth of the magnetic excitations indicates a Gilbert damping constant of
only $\alpha = 2.6 \times 10^{-4}$ rivalling the best values obtained for
epitaxial YIG thin film material. The new fabrication process represents a leap
forward in magnonics and magnon mechanics as it provides 3D YIG structures of
unprecedented quality. At the same time it demonstrates a completely new route
towards the fabrication of free standing crystalline nano structures which may
be applicable also to other material systems.",1802.03176v2
2018-02-26,Spin Seebeck effect and ballistic transport of quasi-acoustic magnons in room-temperature yttrium iron garnet films,"We studied the transient behavior of the spin current generated by the
longitudinal spin Seebeck effect (LSSE) in a set of platinum-coated yttrium
iron garnet (YIG) films of different thicknesses. The LSSE was induced by means
of pulsed microwave heating of the Pt layer and the spin currents were measured
electrically using the inverse spin Hall effect in the same layer. We
demonstrate that the time evolution of the LSSE is determined by the evolution
of the thermal gradient triggering the flux of thermal magnons in the vicinity
of the YIG/Pt interface. These magnons move ballistically within the YIG film
with a constant group velocity, while their number decays exponentially within
an effective propagation length. The ballistic flight of the magnons with
energies above 20K is a result of their almost linear dispersion law, similar
to that of acoustic phonons. By fitting the time-dependent LSSE signal for
different film thicknesses varying by almost an order of magnitude, we found
that the effective propagation length is practically independent of the YIG
film thickness. We consider this fact as strong support of a ballistic
transport scenario - the ballistic propagation of quasi-acoustic magnons in
room temperature YIG.",1802.09593v1
2018-03-30,Nonlocal magnon spin transport in yttrium iron garnet with tantalum and platinum spin injection/detection electrodes,"We study the magnon spin transport in the magnetic insulator yttrium iron
garnet (YIG) in a nonlocal experiment and compare the magnon spin excitation
and detection for the heavy metal paramagnetic electrodes platinum (Pt|YIG|Pt)
and tantalum (Ta|YIG|Ta). The electrical injection and detection processes rely
on the (inverse) spin Hall effect in the heavy metals and the conversion
between the electron spin and magnon spin at the heavy metal|YIG interface. Pt
and Ta possess opposite signs of the spin Hall angle. Furthermore, their
heterostructures with YIG have different interface properties, i.e. spin mixing
conductances. By varying the distance between injector and detector, the magnon
spin transport is studied. Using a circuit model based on the
diffusion-relaxation transport theory, a similar magnon relaxation length of ~
10 \mu m was extracted from both Pt and Ta devices. By changing the injector
and detector material from Pt to Ta, the influence of interface properties on
the magnon spin transport has been observed. For Ta devices on YIG the spin
mixing conductance is reduced compared with Pt devices, which is quantitatively
consistent when comparing the dependence of the nonlocal signal on the
injector-detector distance with the prediction from the circuit model.",1803.11382v1
2019-01-28,Spin Hall magnetoresistance in heterostructures consisting of noncrystalline paramagnetic YIG and Pt,"The spin Hall magnetoresistance (SMR) effect arises from spin-transfer
processes across the interface between a spin Hall active metal and an
insulating magnet. While the SMR response of ferrimagnetic and
antiferromagnetic insulators has been studied extensively, the SMR of a
paramagnetic spin ensemble is not well established. Thus, we investigate herein
the magnetoresistive response of as-deposited yttrium iron garnet/platinum thin
film bilayers as a function of the orientation and the amplitude of an
externally applied magnetic field. Structural and magnetic characterization
show no evidence for crystalline order or spontaneous magnetization in the
yttrium iron garnet layer. Nevertheless, we observe a clear magnetoresistance
response with a dependence on the magnetic field orientation characteristic for
the SMR. We propose two models for the origin of the SMR response in
paramagnetic insulator/Pt heterostructures. The first model describes the SMR
of an ensemble of non-interacting paramagnetic moments, while the second model
describes the magnetoresistance arising by considering the total net moment.
Interestingly, our experimental data are consistently described by the net
moment picture, in contrast to the situation in compensated ferrimagnets or
antiferromagnets.",1901.09986v1
2019-10-19,Propagation of spin-waves packets in individual nano-sized yttrium iron garnet magnonic conduits,"Modern-days CMOS-based computation technology is reaching its fundamental
limitations. The emerging field of magnonics, which utilizes spin waves for
data transport and processing, proposes a promising path to overcome these
limitations. Different devices have been demonstrated recently on the macro-
and microscale, but the feasibility of the magnonics approach essentially
relies on the scalability of the structure feature size down to an extent of a
few 10 nm, which are typical sizes for the established CMOS technology. Here,
we present a study of propagating spin-wave packets in individual yttrium iron
garnet (YIG) conduits with lateral dimensions down to 50 nm. Space and time
resolved micro-focused Brillouin-Light-Scattering (BLS) spectroscopy is used to
characterize the YIG nanostructures and measure the spin-wave decay length and
group velocity directly. The revealed magnon transport at the scale comparable
to the scale of CMOS proves the general feasibility of a magnon-based data
processing.",1910.08801v2
2019-11-21,Low damping and microstructural perfection of sub-40nm-thin yttrium iron garnet films grown by liquid phase epitaxy,"The field of magnon spintronics is experiencing an increasing interest in the
development of solutions for spin-wave-based data transport and processing
technologies that are complementary or alternative to modern CMOS
architectures. Nanometer-thin yttrium iron garnet (YIG) films have been the
gold standard for insulator-based spintronics to date, but a potential process
technology that can deliver perfect, homogeneous large-diameter films is still
lacking. We report that liquid phase epitaxy (LPE) enables the deposition of
nanometer-thin YIG films with low ferromagnetic resonance losses and
consistently high magnetic quality down to a thickness of 20 nm. The obtained
epitaxial films are characterized by an ideal stoichiometry and perfect film
lattices, which show neither significant compositional strain nor geometric
mosaicity, but sharp interfaces. Their magneto-static and dynamic behavior is
similar to that of single crystalline bulk YIG. We found, that the Gilbert
damping coefficient alpha is independent of the film thickness and close to 1 x
10-4, and that together with an inhomogeneous peak-to-peak linewidth broadening
of delta H0|| = 0.4 G, these values are among the lowest ever reported for YIG
films with a thickness smaller than 40 nm. These results suggest, that
nanometer-thin LPE films can be used to fabricate nano- and micro-scaled
circuits with the required quality for magnonic devices. The LPE technique is
easily scalable to YIG sample diameters of several inches.",1911.09400v1
2021-06-29,Neutron Scattering Study on Yttrium Iron Garnet for Spintronics,"Spin current -- a flow of the spin degree of freedom in matter -- has vital
importance in spintronics. Propagation of the spin current ranges over a whole
momentum space; however, generated spin currents are mainly detected in the
long-wavelength limit. To facilitate practical uses of spintronics and
magnonics, microscopic understanding of the spin current is necessary. We here
address yttrium iron garnet, which is a well-employed ferrimagnet for
spintronics, and review {\it in re} the momentum- and energy-resolved
characteristics of its magnetism. Using {\it unpolarized} neutrons, we refined
its detailed crystal and magnetic structure, and examined magnetic excitations
through four decades (10~$\mu$eV-100~meV) using chopper spectrometers in
J-PARC, Japan. We also measured mode-resolved directions of the precessional
motion of the magnetic moment, i.e., magnon polarization, which carries the
spin current in insulators through {\it polarized} neutron scattering, using a
triple-axis spectrometer in ILL, France. The magnon polarization is a hitherto
untested fundamental property of magnets, affecting the thermodynamic
properties of the spin current. Our momentum- and energy-resolved experimental
findings provide an intuitive understanding of the spin current and demonstrate
the importance of neutron scattering techniques for spintronics and magnonics.",2106.15752v1
2021-08-18,Dispersionless propagation of ultra-short spin-wave pulses in ultrathin yttrium iron garnet waveguides,"We study experimentally the propagation of nanosecond spin-wave pulses in
microscopic waveguides made of nanometer-thick yttrium iron garnet films. For
these studies, we use micro-focus Brillouin light scattering spectroscopy,
which provides the possibility to observe propagation of the pulses with high
spatial and temporal resolution. We show that, for most spin-wave frequencies,
dispersion leads to broadening of the pulse by several times at propagation
distances of 10 micrometers. However, for certain frequency interval, the
dispersion broadening is suppressed almost completely resulting in a
dispersionless pulse propagation. We show that the formation of the
dispersion-free region is caused by the competing effects of the dipolar and
the exchange interaction, which can be controlled by the variation of the
waveguide geometry. These conclusions are supported by micromagnetic
simulations and analytical calculations. Our findings provide a simple solution
for the implementation of high-speed magnonic systems that require undisturbed
propagation of short information-carrying spin-wave pulses.",2108.08054v1
2021-09-10,Electrical spectroscopy of the spin-wave dispersion and bistability in gallium-doped yttrium iron garnet,"Yttrium iron garnet (YIG) is a magnetic insulator with record-low damping,
allowing spin-wave transport over macroscopic distances. Doping YIG with
gallium ions greatly reduces the demagnetizing field and introduces a
perpendicular magnetic anisotropy, which leads to an isotropic spin-wave
dispersion that facilitates spin-wave optics and spin-wave steering. Here, we
characterize the dispersion of a gallium-doped YIG (Ga:YIG) thin film using
electrical spectroscopy. We determine the magnetic anisotropy parameters from
the ferromagnetic resonance frequency and use propagating spin wave
spectroscopy in the Damon-Eshbach configuration to detect the small spin-wave
magnetic fields of this ultrathin weak magnet over a wide range of wavevectors,
enabling the extraction of the exchange constant $\alpha=1.3(2)\times10^{-12}$
J/m. The frequencies of the spin waves shift with increasing drive power, which
eventually leads to the foldover of the spin-wave modes. Our results shed light
on isotropic spin-wave transport in Ga:YIG and highlight the potential of
electrical spectroscopy to map out the dispersion and bistability of
propagating spin waves in magnets with a low saturation magnetization.",2109.05045v1
2019-05-30,Predicting New Iron Garnet Thin Films with Perpendicular Magnetic Anisotropy,"Perpendicular magnetic anisotropy (PMA) is a necessary condition for many
spintronic applications like spin-orbit torques switching, logic and memory
devices. An important class of magnetic insulators with low Gilbert damping at
room temperature are iron garnets, which only have a few PMA types such as
terbium and samarium iron garnet. More and stable PMA garnet options are
necessary for researchers to be able to investigate new spintronic phenomena.
In this study, we predict 20 new substrate/magnetic iron garnet film pairs with
stable PMA at room temperature. The effective anisotropy energies of 10
different garnet films that are lattice-matched to 5 different commercially
available garnet substrates have been calculated using shape, magnetoelastic
and magnetocrystalline anisotropy terms. Strain type, tensile or compressive
depending on substrate choice, as well as the sign and the magnitude of the
magnetostriction constants of garnets determine if a garnet film may possess
PMA. We show the conditions in which Samarium, Gadolinium, Terbium, Holmium,
Dysprosium and Thulium garnets may possess PMA on the investigated garnet
substrate types. Guidelines for obtaining garnet films with low damping are
presented. New PMA garnet films with tunable saturation moment and field may
improve spin-orbit torque memory and compensated magnonic thin film devices.",1905.13042v1
2017-04-10,Patterned growth of crystalline Y$_{3}$Fe$_{5}$O$_{12}$ nanostructures with engineered magnetic shape anisotropy,"We demonstrate patterned growth of epitaxial yttrium iron garnet (YIG) thin
films using lithographically defined templates on gadolinium gallium garnet
(GGG) substrates. The fabricated YIG nanostructures yield the desired
crystallographic orientation, excellent surface morphology, and narrow
ferromagnetic resonance (FMR) linewidth (~ 4 Oe). Shape-induced magnetic
anisotropy is clearly observed in a patterned array of nanobars engineered to
exhibit the larger coercivity (40 Oe) compared with that of continuous films.
Both hysteresis loop and angle-dependent FMR spectra measurements indicate that
the easy axis aligns along the longitudinal direction of the nanobars, with an
effective anisotropy field of 195 Oe. Our work overcomes difficulties in
patterning YIG thin films and provides an effective means to control their
magnetic properties and magnetic bias conditions.",1704.03056v2
2018-11-04,Role of gallium diffusion in the formation of a magnetically dead layer at Y3Fe5O12 / Gd3Ga5O12 epitaxial interface,"We have clarified the origin of magnetically dead interface layer formed in
yttrium iron garnet (YIG) films grown at above 700{\deg}C onto gadolinium
gallium garnet (GGG) substrate by means of laser molecular beam epitaxy. The
diffusion-assisted formation of a Ga-rich region at the YIG / GGG interface is
demonstrated by means of composition depth profiling performed by X-ray
photoelectron spectroscopy, secondary ion mass spectroscopy and X-ray and
neutron reflectometry. Our finding is in sharp contrast to the earlier
expressed assumption that Gd acts as a migrant element in the YIG/GGG system.
We further correlate the presence of Ga-rich transition layer with considerable
quenching of ferromagnetic resonance and spin wave propagation in thin YIG
films. Finally, we clarify the origin of the enigmatic low-density overlayer
that is often observed in neutron and X-ray reflectometry studies of the YIG /
GGG epitaxial system.",1811.01321v2
2019-03-05,Influence of misfit strain on the Goos-Hanchen shift upon reflection from a magnetic film on a nonmagnetic substrate,"The influence of the misfit strain on the lateral shift (Goos-Hanchen effect)
experienced by a near-infrared electromagnetic wave upon reflection from the
surface of a bilayer consisting of a magnetic, gyrotropic (i.e., whose
permittivity tensor elements depend upon magnetization) yttrium-iron garnet
film deposited on a nonmagnetic gadolinium-gallium garnet substrate is
investigated theoretically. In the geometry of the transverse magneto-optical
Kerr effect, it is shown that the mechanical strain near the geometrical
film/substrate interface can induce a significant lateral shift of the beam for
incidence angles close to normal incidence, where no shift appears in the
absence of strain. Our calculations demonstrate positive as well as negative
values of the lateral shift, depending on the incident light polarization and
on the film thickness. In contrast to that of the misfit strain, the influence
of the magnetization of the gyrotropic film on the lateral shift is more
noticeable for a TM- than for a TE-polarized wave.",1903.01948v1
2019-03-06,Microwave magnon damping in YIG films at millikelvin temperatures,"Magnon systems used in quantum devices require low damping if coherence is to
be maintained. The ferrimagnetic electrical insulator yttrium iron garnet (YIG)
has low magnon damping at room temperature and is a strong candidate to host
microwave magnon excitations in future quantum devices. Monocrystalline YIG
films are typically grown on gadolinium gallium garnet (GGG) substrates. In
this work, comparative experiments made on YIG waveguides with and without GGG
substrates indicate that the material plays a significant role in increasing
the damping at low temperatures. Measurements reveal that damping due to
temperature-peak processes is dominant above 1 K. Damping behaviour that we
show can be attributed to coupling to two-level fluctuators (TLFs) is observed
below 1 K. Upon saturating the TLFs in the substrate-free YIG at 20 mK,
linewidths of 1.4 MHz are achievable: lower than those measured at room
temperature.",1903.02527v3
2020-10-24,Octave-Tunable Magnetostatic Wave YIG Resonators on a Chip,"We have designed, fabricated, and characterized magnetostatic wave (MSW)
resonators on a chip. The resonators are fabricated by patterning
single-crystal yttrium iron garnet (YIG) film on a gadolinium gallium garnet
(GGG) substrate and excited by loop-inductor transducers. We achieved this
technology breakthrough by developing a YIG film etching process and
fabricating thick aluminum coplanar waveguide (CPW) inductor loop around each
resonator to individually address and excite MSWs. At 4.77 GHz, the 0.68 square
mm resonator achieves a quality factor Q > 5000 with a bias field of 987 Oe. We
also demonstrate YIG resonator tuning by more than one octave from 3.63 to 7.63
GHz by applying an in-plane external magnetic field. The measured quality
factor of the resonator is consistently over 3000 above 4 GHz. The
micromachining technology enables the fabrication of multiple single- and
two-port YIG resonators on the same chip with all resonators demonstrating
octave tunability and high Q .",2010.12732v1
2020-11-26,Optically-induced frequency up-conversion of the ferromagnetic resonance in an ultrathin garnet,"We perform ultrafast pump-probe measurements on a nanometer-thick crystalline
Bi-doped yttrium iron garnet film with perpendicular magnetic anisotropy.
Tuning the photon energy of the pump laser pulses above and below the
material's bandgap, we trigger ultrafast optical and spin dynamics via both
one- and two-photon absorption. Contrary to the common scenario, the
optically-induced heating of the system induces an increase up to 20% of the
ferromagnetic resonance frequency. We explain this unexpected result in terms
of a photo-induced modification of the magnetic anisotropy, i.e. of the
effective field, identifying the necessary conditions to observe this effect.
Our results disclose the possibility to optically increase the magnetic
eigenfrequency in nanometer-thick magnets.",2011.13403v1
2022-02-07,Magnetization dynamics affected by phonon pumping,"""Pumping"" of phonons by a dynamic magnetization promises to extend the range
and functionality of magnonic devices. We explore the impact of phonon pumping
on room-temperature ferromagnetic resonance (FMR) spectra of bilayers of thin
yttrium iron garnet (YIG) films on thick gadolinium gallium garnet substrates
over a wide frequency range. At low frequencies the Kittel mode hybridizes
coherently with standing ultrasound waves of a bulk acoustic resonator to form
magnon polarons that induce rapid oscillations of the magnetic susceptibility,
as reported before. At higher frequencies, the phonon resonances overlap,
merging into a conventional FMR line, but with an increased line width. The
frequency dependence of the increased line broadening follows the predictions
from phonon pumping theory in the thick substrate limit. In addition, we find
substantial magnon-phonon coupling of a perpendicular standing spin wave (PSSW)
mode. This evidences the importance of the mode overlap between the acoustic
and magnetic modes, and provides a route towards engineering the magnetoelastic
mode coupling.",2202.03331v1
2022-11-15,Nonlinear sub-switching regime of magnetization dynamics in photo-magnetic garnets,"We analyze, both experimentally and numerically, the nonlinear regime of the
photo-induced coherent magnetization dynamics in cobalt-doped yttrium iron
garnet films. Photo-magnetic excitation with femtosecond laser pulses reveals a
strongly nonlinear response of the spin subsystem with a significant increase
of the effective Gilbert damping. By varying both laser fluence and the
external magnetic field, we show that this nonlinearity originates in the
anharmonicity of the magnetic energy landscape. We numerically map the
parameter workspace for the nonlinear photo-induced spin dynamics below the
photo-magnetic switching threshold. Corroborated by numerical simulations of
the Landau-Lifshitz-Gilbert equation, our results highlight the key role of the
cubic symmetry of the magnetic subsystem in reaching the nonlinear spin
precession regime. These findings expand the fundamental understanding of
laser-induced nonlinear spin dynamics as well as facilitate the development of
applied photo-magnetism.",2211.08048v2
2023-12-17,An Edge-Coupled Magnetostatic Bandpass Filter,"This paper reports on the design, fabrication, and characterization of an
edge-coupled magnetostatic forward volume wave bandpass filter. Using
micromachining techniques, the filter is fabricated from a yttrium iron garnet
(YIG) film grown on a gadolinium gallium garnet (GGG) substrate with inductive
transducers. By adjusting an out-of-plane magnetic field, we demonstrate linear
center frequency tuning for a $4^{\text{th}}$-order filter from 4.5 GHz to 10.1
GHz while retaining a fractional bandwidth of 0.3%, an insertion loss of 6.94
dB, and a -35dB rejection. We characterize the filter nonlinearity in the
passband and stopband with IIP3 measurements of -4.85 dBm and 25.84 dBm,
respectively. When integrated with a tunable magnetic field, this device is an
octave tunable narrowband channel-select filter.",2312.10583v1
2023-12-17,Cryogenic hybrid magnonic circuits based on spalled YIG thin films,"Yttrium iron garnet (YIG) magnonics has sparked extensive research interests
toward harnessing magnons (quasiparticles of collective spin excitation) for
signal processing. In particular, YIG magnonics-based hybrid systems exhibit
great potentials for quantum information science because of their wide
frequency tunability and excellent compatibility with other platforms. However,
the broad application and scalability of thin-film YIG devices in the quantum
regime has been severely limited due to the substantial microwave loss in the
host substrate for YIG, gadolinium gallium garnet (GGG), at cryogenic
temperatures. In this study, we demonstrate that substrate-free YIG thin films
can be obtained by introducing the controlled spalling and layer transfer
technology to YIG/GGG samples. Our approach is validated by measuring a hybrid
device consisting of a superconducting resonator and a spalled YIG film, which
gives a strong coupling feature indicating the good coherence of our system.
This advancement paves the way for enhanced on-chip integration and the
scalability of YIG-based quantum devices.",2312.10660v2
2024-02-22,Laser patterning of magnonic structure via local crystallization of Yittrium Iron Garnet,"The fabrication and integration of high-quality structures of Yttrium Iron
Garnet (YIG) is critical for magnonics.Films with excellent properties are
obtained only on single crystal Gadolinium Gallium Garnet (GGG) substrates
using high-temperature processes. The subsequent realization of magnonic
structures via lithography and etching is not straightforward as it requires a
tight control of the edge roughness, to avoid magnon scattering, and
planarization in case of multilayer devices. In this work we describe a
different approach based on local laser annealing of amorphous YIG films,
avoiding the need for subjecting the entire sample to high thermal budgets and
for physical etching. Starting from amorphous and paramagnetic YIG films grown
by pulsed laser deposition at room temperature on GGG, a 405 nm laser is used
for patterning arbitrary shaped ferrimagnetic structures by local
crystallization. In thick films (160 nm) the laser induced surface corrugation
prevents the propagation of spin-wave modes in patterned conduits. For thinner
films (80 nm) coherent propagation is observed in 1.2 micron wide conduits
displaying an attenuation length of 5 micron which is compatible with a damping
coefficient of about 5e-3. Possible routes to achieve damping coefficients
compatible with state-of-the art epitaxial YIG films are discussed.",2402.14444v1
2018-11-02,Evidence for exchange Dirac gap in magneto-transport of topological insulator-magnetic insulator heterostructures,"Transport signatures of exchange gap opening because of magnetic proximity
effect (MPE) are reported for bilayer structures of Bi2Se3 thin films on
yttrium iron garnet (YIG) and thulium iron garnet (TmIG) of perpendicular
magnetic anisotropy (PMA). Pronounced negative magnetoresistance (MR) was
detected, and attributed to an emergent weak localization (WL) effect
superimposing on a weak antilocalization (WAL). Thickness-dependent study shows
that the WL originates from the time-reversal-symmetry breaking of topological
surface states by interfacial exchange coupling. The weight of WL declined when
the interfacial magnetization was aligned toward the in-plane direction, which
is understood as the effect of tuning the exchange gap size by varying the
perpendicular magnetization component. Importantly, magnetotransport study
revealed anomalous Hall effect (AHE) of square loops and anisotropic
magnetoresistance (AMR) characteristic, typifying a ferromagnetic conductor in
Bi2Se3/TmIG, and the presence of an interfacial ferromagnetism driven by MPE.
Coexistence of MPE-induced ferromagnetism and the finite exchange gap provides
an opportunity of realizing zero magnetic-field dissipation-less transport in
topological insulator/ferromagnetic insulator heterostructures.",1811.00689v1
2023-09-06,Strong magnon-magnon coupling in an ultralow damping all-magnetic-insulator heterostructure,"Magnetic insulators such as yttrium iron garnets (YIGs) are of paramount
importance for spin-wave or magnonic devices as their ultralow damping enables
ultralow power dissipation that is free of Joule heating, exotic magnon quantum
state, and coherent coupling to other wave excitations. Magnetic insulator
heterostructures bestow superior structural and magnetic properties and house
immense design space thanks to the strong and engineerable exchange interaction
between individual layers. To fully unleash their potential, realizing low
damping and strong exchange coupling simultaneously is critical, which often
requires high quality interface. Here, we show that such a demand is realized
in an all-insulator thulium iron garnet (TmIG)/YIG bilayer system. The ultralow
dissipation rates in both YIG and TmIG, along with their significant spin-spin
interaction at the interface, enable strong and coherent magnon-magnon coupling
with a benchmarking cooperativity value larger than the conventional
ferromagnetic metal-based heterostructures. The coupling strength can be tuned
by varying the magnetic insulator layer thickness and magnon modes, which is
consistent with analytical calculations and micromagnetic simulations. Our
results demonstrate TmIG/YIG as a novel platform for investigating hybrid
magnonic phenomena and open opportunities in magnon devices comprising
all-insulator heterostructures.",2309.03116v1
2019-05-02,Anomalous spin Hall angle of a metallic ferromagnet determined by a multiterminal spin injection/detection device,"We report on the determination of the anomalous spin Hall angle in the
ferromagnetic metal alloy cobalt-iron (Co$_{25}$Fe$_{75}$, CoFe). This is
accomplished by measuring the spin injection/detection efficiency in a
multiterminal device with nanowires of platinum (Pt) and CoFe deposited onto
the magnetic insulator yttrium iron garnet (Y$_3$Fe$_5$O$_{12}$, YIG). Applying
a spin-resistor model to our multiterminal spin transport data, we determine
the magnon conductivity in YIG, the spin conductance at the YIG/CoFe interface
and finally the anomalous spin Hall angle of CoFe as a function of its spin
diffusion length in a single device. Our experiments clearly reveal a negative
anomalous spin Hall angle of the ferromagnetic metal CoFe, but a vanishing
ordinary spin Hall angle. This is in contrast to the results reported for the
ferromagnetic metals Co and permalloy.",1905.00663v1
2021-12-07,Coupling function from bath density of states,"Modelling of an open quantum system requires knowledge of parameters that
specify how it couples to its environment. However, beyond relaxation rates,
realistic parameters for specific environments and materials are rarely known.
Here we present a method of inferring the coupling between a generic system and
its bosonic (e.g., phononic) environment from the experimentally measurable
density of states (DOS). With it we confirm that the DOS of the well-known
Debye model for three-dimensional solids is physically equivalent to choosing
an Ohmic bath. We further match a real phonon DOS to a series of Lorentzian
coupling functions, allowing us to determine coupling parameters for gold,
yttrium iron garnet (YIG) and iron as examples. The results illustrate how to
obtain material-specific dynamical properties, such as memory kernels. The
proposed method opens the door to more accurate modelling of relaxation
dynamics, for example for phonon-dominated spin damping in magnetic materials.",2112.04001v2
2012-05-18,Thin film growth by pulsed laser deposition and properties of 122-type iron-based superconductor AE(Fe1--xCox)2As2 (AE = alkaline earth),"This paper reports comprehensive results on thin-film growth of 122-type
iron-pnictide superconductors, AE(Fe1-xCox)2As2 (AE = Ca, Sr, and Ba,
AEFe2As2:Co) by a pulsed laser deposition method using a neodymium-doped
yttrium aluminum garnet laser as an excitation source. The most critical
parameter to produce the SrFe2As2:Co and BaFe2As2:Co phases is the substrate
temperature (Ts). It is difficult to produce highly-pure CaFe2As2:Co phase thin
film at any Ts. For BaFe2As2:Co epitaxial films, controlling Ts at 800-850
{\deg}C and growth rate to 2.8-3.3 {\AA}/s produced high-quality films with
good crystallinity, flat surfaces, and high critical current densities > 1
MA/cm2, which were obtained for film thicknesses from 100 to 500 nm. The doping
concentration x was optimized for Ba(Fe1-xCox)2As2 epitaxial films, leading to
the highest critical temperature of 25.5 K in the epitaxial films with the
nominal x = 0.075.",1205.4103v1
2017-11-01,Tunable magnetization relaxation of Fe_{2}Cr_{1-x}Co_{x}Si half-metallic Heusler alloys by band structure engineering,"We report a systematic investigation on the magnetization relaxation
properties of iron-based half-metallic Heusler alloy
Fe$_{2}$Cr$_{1-x}$Co_${x}$Si (FCCS) thin films using broadband angular-resolved
ferromagnetic resonance. Band structure engineering through Co doping (x)
demonstrated by first-principles calculations is shown to tune the intrinsic
magnetic damping over an order of magnitude, namely 0.01-0.0008. Notably, the
intrinsic damping constants for samples with high Co concentration are among
the lowest reported for Heusler alloys and even comparable to magnetic
insulator yttrium iron garnet. Furthermore, a significant reduction of both
isotropic and anisotropic contributions of extrinsic damping of the FCCS alloys
was found in the FCCS films with x=0.5-0.75, which is of particular importance
for applications. These results demonstrate a practical recipe to tailor
functional magnetization for Heusler alloy-based spintronics at room
temperature",1711.00406v1
2020-05-28,A First Principle Study on Magneto-Optical Effects and Magnetism in Ferromagnetic Semiconductors Y$_3$Fe$_5$O$_{12}$ and Bi$_3$Fe$_5$O$_{12}$,"The magneto-optical (MO) effects not only are a powerful probe of magnetism
and electronic structure of magnetic solids but also have valuable applications
in high-density data-storage technology. Yttrium iron garnet
(Y$_3$Fe$_5$O$_{12}$) (YIG) and bismuth iron garnet (Bi$_3$Fe$_5$O$_{12}$)
(BIG) are two widely used magnetic semiconductors with strong magneto-optical
effects and have also attracted the attention for fundamental physics studies.
In particular, YIG has been routinely used as a spin current injector. In this
paper, we present a thorough theoretical investigation on magnetism,
electronic, optical and MO properties of YIG and BIG, based on the density
functional theory with the generalized gradient approximation plus onsite
Coulomb repulsion. We find that both semiconductors exhibit large MO effects
with their Kerr and Faraday rotation angles being comparable to that of
best-known MO materials such as MnBi. Especially, the MO Kerr rotation angle
for bulk BIG reaches -1.2$ ^{\circ}$ at photon energy $\sim2.4$ eV, and the MO
Faraday rotation angle for BIG film reaches -74.6 $ ^{\circ}/\mu m$ at photon
energy $\sim2.7$ eV. Furthermore, we also find that both valence and conduction
bands across the MO band gap in BIG are purely spin-down states, i.e., BIG is a
single spin semiconductor. These interesting findings suggest that the iron
garnets will find valuable applications in semiconductor MO and spintronic
nanodevices. The calculated optical conductivity spectra, MO Kerr and Faraday
rotation angles agree well with the available experimental data. The main
features in the optical and MO spectra of both systems are analyzed in terms of
the calculated band structures especially by determining the band state
symmetries and the main optical transitions at the $\Gamma$ point in the
Brillouin zone.",2005.14133v2
2015-04-07,Generation of coherent spin-wave modes in Yttrium Iron Garnet microdiscs by spin-orbit torque,"Spin-orbit effects [1-4] have the potential of radically changing the field
of spintronics by allowing transfer of spin angular momentum to a whole new
class of materials. In a seminal letter to Nature [5], Kajiwara et al. showed
that by depositing Platinum (Pt, a normal metal) on top of a 1.3 $\mu$m thick
Yttrium Iron Garnet (YIG, a magnetic insulator), one could effectively transfer
spin angular momentum through the interface between these two different
materials. The outstanding feature was the detection of auto-oscillation of the
YIG when enough dc current was passed in the Pt. This finding has created a
great excitement in the community for two reasons: first, one could control
electronically the damping of insulators, which can offer improved properties
compared to metals, and here YIG has the lowest damping known in nature;
second, the damping compensation could be achieved on very large objects, a
particularly relevant point for the field of magnonics [6,7] whose aim is to
use spin-waves as carriers of information. However, the degree of coherence of
the observed auto-oscillations has not been addressed in ref. [5]. In this
work, we emphasize the key role of quasi-degenerate spin-wave modes, which
increase the threshold current. This requires to reduce both the thickness and
lateral size in order to reach full damping compensation [8] , and we show
clear evidence of coherent spin-orbit torque induced auto-oscillation in
micron-sized YIG discs of thickness 20 nm.",1504.01512v1
2017-08-06,Thermally Driven Long Range Magnon Spin Currents in Yttrium Iron Garnet due to Intrinsic Spin Seebeck Effect,"The longitudinal spin Seebeck effect refers to the generation of a spin
current when heat flows across a normal metal/magnetic insulator interface.
Until recently, most explanations of the spin Seebeck effect use the
interfacial temperature difference as the conversion mechanism between heat and
spin fluxes. However, recent theoretical and experimental works claim that a
magnon spin current is generated in the bulk of a magnetic insulator even in
the absence of an interface. This is the so-called intrinsic spin Seebeck
effect. Here, by utilizing a non-local spin Seebeck geometry, we provide
additional evidence that the total magnon spin current in the ferrimagnetic
insulator yttrium iron garnet (YIG) actually contains two distinct terms: one
proportional to the gradient in the magnon chemical potential (pure magnon spin
diffusion), and a second proportional to the gradient in magnon temperature
($\nabla T_m$). We observe two characteristic decay lengths for magnon spin
currents in YIG with distinct temperature dependences: a temperature
independent decay length of ~ 10 ${\mu}$m consistent with earlier measurements
of pure ($\nabla T_m = 0$) magnon spin diffusion, and a longer decay length
ranging from about 20 ${\mu}$m around 250 K and exceeding 80 ${\mu}$m at 10 K.
The coupled spin-heat transport processes are modeled using a finite element
method revealing that the longer range magnon spin current is attributable to
the intrinsic spin Seebeck effect ($\nabla T_m \neq 0$), whose length scale
increases at lower temperatures in agreement with our experimental data.",1708.01941v3
2017-09-21,Electrical properties of single crystal Yttrium Iron Garnet ultra-thin films at high temperatures,"We report a study on the electrical properties of 19 nm thick Yttrium Iron
Garnet (YIG) films grown by liquid phase epitaxy. The electrical conductivity
and Hall coefficient are measured in the high temperature range [300,400]~K
using a Van der Pauw four-point probe technique. We find that the electrical
resistivity decreases exponentially with increasing temperature following an
activated behavior corresponding to a band-gap of $E_g\approx 2$ eV, indicating
that epitaxial YIG ultra-thin films behave as large gap semiconductor, and not
as electrical insulator. The resistivity drops to about $5\times 10^3$~$\Omega
\cdot \text{cm}$ at $T=400$ K. We also infer the Hall mobility, which is found
to be positive ($p$-type) at 5 cm$^2$/(V$\cdot$sec) and about independent of
temperature. We discuss the consequence for non-local transport experiments
performed on YIG at room temperature. These electrical properties are
responsible for an offset voltage (independent of the in-plane field direction)
whose amplitude, odd in current, grows exponentially with current due to Joule
heating. These electrical properties also induce a sensitivity to the
perpendicular component of the magnetic field through the Hall effect. In our
lateral device, a thermoelectric offset voltage is produced by a temperature
gradient along the wire direction proportional to the perpendicular component
of the magnetic field (Righi-Leduc effects).",1709.07207v1
2018-03-02,Long lifetime of thermally-excited magnons in bulk yttrium iron garnet,"Spin currents are generated within the bulk of magnetic materials due to heat
flow, an effect called intrinsic spin-Seebeck. This bulk bosonic spin current
consists of a diffusing thermal magnon cloud, parametrized by the magnon
chemical potential ($\mu_{m}$), with a diffusion length of several microns in
yttrium iron garnet (YIG). Transient opto-thermal measurements of the
spin-Seebeck effect (SSE) as a function of temperature reveal the time
evolution of $\mu_{m}$ due to intrinsic SSE in YIG. The interface SSE develops
at times < 2 ns while the intrinsic SSE signal continues to evolve at times >
500 $\mu$s, dominating the temperature dependence of SSE in bulk YIG.
Time-dependent SSE data are fit to a multi-temperature model of coupled
spin/heat transport using finite element method (FEM), where the magnon spin
lifetime ($\tau$) and magnon-phonon thermalization time ($\tau_{mp}$) are used
as fit parameters. From 300 K to 4 K, $\tau_{mp}$ varies from 1 to 10 ns,
whereas $\tau$ varies from 2 to 60 $\mu$s with the spin lifetime peaking at 90
K. At low temperature, a reduction in $\tau$ is observed consistent with
impurity relaxation reported in ferromagnetic resonance measurements. These
results demonstrate that the thermal magnon cloud in YIG contains extremely low
frequency magnons (~10 GHz) providing spectral insight to the microscopic
scattering processes involved in magnon spin/heat diffusion.",1803.01054v3
2019-03-19,Magnetic properties and domain structure of ultrathin yttrium iron garnet/Pt bilayers,"We report on the structure, magnetization, magnetic anisotropy, and domain
morphology of ultrathin yttrium iron garnet (YIG)/Pt films with thickness
ranging from 3 to 90 nm. We find that the saturation magnetization is close to
the bulk value in the thickest films and decreases towards low thickness with a
strong reduction below 10 nm. We characterize the magnetic anisotropy by
measuring the transverse spin Hall magnetoresistance as a function of applied
field. Our results reveal strong easy plane anisotropy fields of the order of
50-100 mT, which add to the demagnetizing field, as well as weaker in-plane
uniaxial anisotropy ranging from 10 to 100 $\mu$T. The in-plane easy axis
direction changes with thickness, but presents also significant fluctuations
among samples with the same thickness grown on the same substrate. X-ray
photoelectron emission microscopy reveals the formation of zigzag magnetic
domains in YIG films thicker than 10 nm, which have dimensions larger than
several 100 $\mu$m and are separated by achiral N\'{e}el-type domain walls.
Smaller domains characterized by interspersed elongated features are found in
YIG films thinner than 10 nm.",1903.08285v1
2021-04-21,Atomic Layer Deposition of Yttrium Iron Garnet Thin Films for 3D Magnetic Structures,"A wide variety of new phenomena such as novel magnetization configurations
have been predicted to occur in three dimensional magnetic nanostructures.
However, the fabrication of such structures is often challenging due to the
specific shapes required, such as magnetic tubes and spirals. Furthermore, the
materials currently used to assemble these structures are predominantly
magnetic metals that do not allow to study the magnetic response of the system
separately from the electronic one. In the field of spintronics, the
prototypical material used for such experiments is the ferrimagnetic insulator
yttrium iron garnet (Y$_3$Fe$_5$O$_{12}$, YIG). YIG is one of the best
materials especially for magnonic studies due to its low Gilbert damping. Here,
we report the first successful fabrication of YIG thin films via atomic layer
deposition. To that end we utilize a supercycle approach based on the
combination of sub-nanometer thin layers of the binary systems Fe$_2$O$_3$ and
Y$_2$O$_3$ in the correct atomic ratio on Y$_3$Al$_5$O$_{12}$ substrates with a
subsequent annealing step. Our process is robust against typical growth-related
deviations, ensuring a good reproducibility. The ALD-YIG thin films exhibit a
good crystalline quality as well as magnetic properties comparable to other
deposition techniques. One of the outstanding characteristics of atomic layer
deposition is its ability to conformally coat arbitrarily-shaped substrates.
ALD hence is the ideal deposition technique to grant an extensive freedom in
choosing the shape of the magnetic system. The atomic layer deposition of YIG
enables the fabrication of novel three dimensional magnetic nanostructures,
which in turn can be utilized for experimentally investigating the phenomena
predicted in those structures.",2104.10293v2
2019-05-29,Coherent long-range transfer of angular momentum between magnon Kittel modes by phonons,"We report ferromagnetic resonance in the normal configuration of an
electrically insulating magnetic bilayer consisting of two yttrium iron garnet
(YIG) films epitaxially grown on both sides of a 0.5-mm-thick nonmagnetic
gadolinium gallium garnet (GGG) slab. An interference pattern is observed and
it is explained as the strong coupling of the magnetization dynamics of the two
YIG layers either in phase or out of phase by the standing transverse sound
waves, which are excited through a magnetoelastic interaction. This coherent
mediation of angular momentum by circularly polarized phonons through a
nonmagnetic material over macroscopic distances can be useful for future
information technologies.",1905.12523v3
2019-06-28,Spin transport in an insulating ferrimagnetic-antiferromagnetic-ferrimagnetic trilayer as a function of temperature,"We present a study of the transport properties of thermally generated spin
currents in an insulating ferrimagnetic-antiferromagnetic-ferrimagnetic
trilayer over a wide range of temperature. Spin currents generated by the spin
Seebeck effect (SSE) in a yttrium iron garnet (YIG) YIG/NiO/YIG trilayer on a
gadolinium gallium garnet (GGG) substrate were detected using the inverse spin
Hall effect in Pt. By studying samples with different NiO thicknesses, the NiO
spin diffusion length was determined to be 4.2 nm at room temperature.
Interestingly, below 30 K, the inverse spin Hall signals are associated with
the GGG substrate. The field dependence of the signal follows a Brillouin
function for a S=7/2 spin ($\mathrm{Gd^{3+}}$) at low temperature. Sharp
changes in the SSE signal at low fields are due to switching of the YIG
magnetization. A broad peak in the SSE response was observed around 100 K,
which we associate with an increase in the spin-diffusion length in YIG. These
observations are important in understanding the generation and transport
properties of spin currents through magnetic insulators and the role of a
paramagnetic substrate in spin current generation.",1906.12288v1
2020-08-21,Magnons Parametric Pumping in Bulk Acoustic Waves Resonator,"We report on the experimental observation of excitation and detection of
parametric spin waves and spin currents in the bulk acoustic wave resonator.
The hybrid resonator consists of ZnO piezoelectric film, yttrium iron garnet
(YIG) films on gallium gadolinium garnet substrate, and a heavy metal Pt layer.
Shear bulk acoustic waves are electrically excited in the ZnO layer due to
piezoeffect at the resonant frequencies of the resonator. The magnetoelastic
interaction in the YIG film emerges magnons (spin waves) excitation by acoustic
waves either on resonator's eigenfrequencies or the half-value frequencies at
supercritical power. We investigate acoustic pumping of magnons at the
half-value frequencies and acoustic spin pumping from parametric magnons, using
the inverse spin Hall effect in the Pt layer. The constant electric voltage in
the Pt layer, depending on the frequency, the magnetic field, and the pump
power, was systematically studied. We explain the low threshold obtained (~0.4
mW) by the high efficiency of electric power transmission into the acoustic
wave in the resonator.",2008.09520v1
2020-09-06,Enhancement of YIG$|$Pt spin conductance by local Joule annealing,"We report that Joule heating can be used to enhance the interfacial spin
conductivity between a metal and an oxide. We observe that local annealing of
the interface at about 550\,K by injecting large current densities
($>10^{12}\text{A/m}^{2}$) into a pristine 7\,nm thick Pt nanostrip evaporated
on top of yttrium iron garnet (YIG), can improve the spin transmission up to a
factor 3: a result of particular interest for interfacing ultra thin garnet
films where strong chemical etching of the surface has to be avoided. The
effect is confirmed by different methods: spin Hall magnetoresistance, spin
pumping and non-local spin transport. We use it to study the influence of the
YIG$|$Pt coupling on the non-linear spin transport properties. We find that the
cross-over current from a linear to a non-linear spin transport regime is
independent of this coupling, suggesting that the behavior of pure spin
currents circulating in the dielectric are mostly governed by the physical
properties of the bare YIG film beside the Pt nanostrip.",2009.02785v1
2020-11-15,A tunable magneto-acoustic oscillator with low phase noise,"A frequency-tunable low phase noise magneto-acoustic resonator is developed
on the base of a parallel-plate straight-edge bilayer consisting of a
yttrium-iron garnet (YIG) layer grown on a substrate of a gallium-gadolinium
garnet(GGG). When a YIG/GGG sample forms an ideal parallel plate, it supports a
series of high-quality-factor acoustic modes standing along the plate
thickness. Due to the magnetostriction of the YIG layer the ferromagnetic
resonance (FMR) mode of the YIG layer can strongly interact with the acoustic
thickness modes of the YIG/GGG structure, when the modes' frequencies match. A
particular acoustic thickness mode used for the resonance excitations of the
hybrid magneto-acoustic oscillations in a YIG/GGG bilayer is chosen by the YIG
layer FMR frequency, which can be tuned by the variation of the external bias
magnetic field. A composite magneto-acoustic oscillator, which includes an
FMR-based resonance pre-selector, is developed to guarantee satisfaction of the
Barkhausen criteria for a single-acoustic-mode oscillation regime. The
developed low phase noise composite magneto-acoustic oscillator can be tuned
from 0.84 GHz to 1 GHz with an increment of about 4.8 MHz (frequency distance
between the adjacent acoustic thickness modes in a YIG/GGG parallel plate), and
demonstrates the phase noise of -116 dBc/Hz at the offset frequency of 10 kHz.",2011.07648v1
2021-09-13,Control of magnetization dynamics by substrate orientation in YIG thin films,"Yttrium Iron Garnet (YIG) and bismuth (Bi) substituted YIG (Bi0.1Y2.9Fe5O12,
BYG) films are grown in-situ on single crystalline Gadolinium Gallium Garnet
(GGG) substrates [with (100) and (111) orientations] using pulsed laser
deposition (PLD) technique. As the orientation of the Bi-YIG film changes from
(100) to (111), the lattice constant is enhanced from 12.384 {\AA} to 12.401
{\AA} due to orientation dependent distribution of Bi3+ ions at dodecahedral
sites in the lattice cell. Atomic force microscopy (AFM) images show smooth
film surfaces with roughness 0.308 nm in Bi-YIG (111). The change in substrate
orientation leads to the modification of Gilbert damping which, in turn, gives
rise to the enhancement of ferromagnetic resonance (FMR) line width. The best
values of Gilbert damping are found to be (0.54)*10-4, for YIG (100) and
(6.27)*10-4, for Bi-YIG (111) oriented films. Angle variation measurements of
the Hr are also performed, that shows a four-fold symmetry for the resonance
field in the (100) grown film. In addition, the value of effective
magnetization (4{\pi}Meff) and extrinsic linewidth ({\Delta}H0) are observed to
be dependent on substrate orientation. Hence PLD growth can assist
single-crystalline YIG and BYG films with a perfect interface that can be used
for spintronics and related device applications.",2109.05901v1
2022-03-12,Observation of nonlinear planar Hall effect in magnetic insulator/topological insulator heterostructures,"Interfacing topological insulators (TIs) with magnetic insulators (MIs) has
been widely used to study the interaction between topological surface states
and magnetism. Previous transport studies typically interpret the suppression
of weak antilocalization or appearance of the anomalous Hall effect as
signatures of magnetic proximity effect (MPE) imposed to TIs. Here, we report
the observation of nonlinear planar Hall effect (NPHE) in Bi2Se3 films grown on
MI thulium and yttrium iron garnet (TmIG and YIG) substrates, which is an order
of magnitude larger than that in Bi2Se3 grown on nonmagnetic gadolinium gallium
garnet (GGG) substrate. The nonlinear Hall resistance in TmIG/Bi2Se3 depends
linearly on the external magnetic field, while that in YIG/Bi2Se3 exhibits an
extra hysteresis loop around zero field. The magnitude of the NPHE is found to
scale inversely with carrier density. We speculate the observed NPHE is related
to the MPE-induced exchange gap opening and out-of-plane spin textures in the
TI surface states, which may be used as an alternative transport signature of
the MPE in MI/TI heterostructures.",2203.06293v2
2022-12-05,Propagating spin-wave spectroscopy in nanometer-thick YIG films at millikelvin temperatures,"Performing propagating spin-wave spectroscopy of thin films at millikelvin
temperatures is the next step towards the realisation of large-scale integrated
magnonic circuits for quantum applications. Here we demonstrate spin-wave
propagation in a $100\,\mathrm{nm}$-thick yttrium-iron-garnet film at the
temperatures down to $45 \,\mathrm{mK}$, using stripline nanoantennas deposited
on YIG surface for the electrical excitation and detection. The clear
transmission characteristics over the distance of $10\,\mu \mathrm{m}$ are
measured and the subtracted spin-wave group velocity and the YIG saturation
magnetisation agree well with the theoretical values. We show that the
gadolinium-gallium-garnet substrate influences the spin-wave propagation
characteristics only for the applied magnetic fields beyond $75\,\mathrm{mT}$,
originating from a GGG magnetisation up to $47 \,\mathrm{kA/m}$ at $45
\,\mathrm{mK}$. Our results show that the developed fabrication and measurement
methodologies enable the realisation of integrated magnonic quantum
nanotechnologies at millikelvin temperatures.",2212.02257v3
2023-07-20,The challenges of measuring spin Seebeck noise,"Just as electronic shot noise in driven conductors results from the
granularity of charge and the statistical variation in the arrival times of
charge carriers, there are predictions for fundamental noise in magnon currents
due to angular momentum being carried by discrete excitations. The inverse spin
Hall effect as a transduction mechanism to convert spin current into charge
current raises the prospect of experimental investigations of such magnon shot
noise. Spin Seebeck effect measurements have demonstrated the electrical
detection of thermally driven magnon currents and have been suggested as an
avenue for accessing spin current fluctuations. Using spin Seebeck structures
made from yttrium iron garnet on gadolinium gallium garnet, we demonstrate the
technical challenges inherent in such noise measurements. While there is a
small increase in voltage noise in the inverse spin Hall detector at low
temperatures associated with adding a magnetic field, the dependence on field
orientation implies that this is not due to magnon shot noise. We describe
theoretical predictions for the expected magnitude of magnon shot noise,
highlighting ambiguities that exist. Further, we show that magnon shot noise
detection through the standard inverse spin Hall approach is likely impossible
due to geometric factors. Implications for future attempts to measure magnon
shot noise are discussed.",2307.11218v2
2005-04-22,Perturbation of magnetostatic modes observed by FMRFM,"Magnetostatic modes of Yttrium Iron Garnet (YIG) films are investigated by
ferromagnetic resonance force microscopy (FMRFM). A thin film ``probe'' magnet
at the tip of a compliant cantilever introduces a local inhomogeneity in the
internal field of the YIG sample. This influences the shape of the sample's
magnetostatic modes, thereby measurably perturbing the strength of the force
coupled to the cantilever. We present a theoretical model that explains these
observations; it shows that tip-induced variation of the internal field creates
either a local ``potential barrier'' or ``potential well'' for the
magnetostatic waves. The data and model together indicate that local magnetic
imaging of ferromagnets is possible, even in the presence of long-range spin
coupling, through the induction of localized magnetostatic modes predicted to
arise from sufficiently strong tip fields.",0504598v1
2007-04-24,Element-resolved x-ray ferrimagnetic and ferromagnetic resonance spectroscopy,"We report on the measurement of element-specific magnetic resonance spectra
at gigahertz frequencies using x-ray magnetic circular dichroism (XMCD). We
investigate the ferrimagnetic precession of Gd and Fe ions in Gd-substituted
Yttrium Iron Garnet, showing that the resonant field and linewidth of Gd
precisely coincide with Fe up to the nonlinear regime of parametric
excitations. The opposite sign of the Gd x-ray magnetic resonance signal with
respect to Fe is consistent with dynamic antiferromagnetic alignment of the two
ionic species. Further, we investigate a bilayer metal film,
Ni$_{80}$Fe$_{20}$(5 nm)/Ni(50 nm), where the coupled resonance modes of Ni and
Ni$_{80}$Fe$_{20}$ are separately resolved, revealing shifts in the resonance
fields of individual layers but no mutual driving effects. Energy-dependent
dynamic XMCD measurements are introduced, combining x-ray absorption and
magnetic resonance spectroscopies.",0704.3139v2
2007-12-11,Reflection-Free One-Way Edge Modes in a Gyromagnetic Photonic Crystal,"We point out that electromagnetic one-way edge modes analogous to quantum
Hall edge states, originally predicted by Raghu and Haldane in 2D gyroelectric
photonic crystals possessing Dirac point-derived bandgaps, can appear in more
general settings. In particular, we show that the TM modes in a gyromagnetic
photonic crystal can be formally mapped to electronic wavefunctions in a
periodic electromagnetic field, so that the only requirement for the existence
of one-way edge modes is that the Chern number for all bands below a gap is
non-zero. In a square-lattice gyromagnetic Yttrium-Iron-Garnet photonic crystal
operating at microwave frequencies, which lacks Dirac points, time-reversal
breaking is strong enough that the effect should be easily observable. For
realistic material parameters, the edge modes occupy a 10% band gap. Numerical
simulations of a one-way waveguide incorporating this crystal show 100%
transmission across strong defects, such as perfect conductors several lattice
constants wide, larger than the width of the waveguide.",0712.1776v2
2008-04-07,Phase reciprocity of spin-wave excitation by a microstrip antenna,"Using space-, time- and phase-resolved Brillouin light scattering
spectroscopy we investigate the difference in phase of the two
counterpropagating spin waves excited by the same microwave microstrip
transducer. These studies are performed both for backward volume magnetostatic
waves and magnetostatic surface waves in an in-plane magnetized yttrium iron
garnet film. The experiments show that for the backward volume magnetostatic
spin waves (which are reciprocal and excited symmetrically in amplitude) there
is a phase difference of $\pi$ associated with the excitation process and thus
the phase symmetry is distorted. On the contrary, for the magnetostatic surface
spin waves (which are non-reciprocal and unsymmetrical in amplitude) the phase
symmetry is preserved (there is no phase difference between the two waves
associated with the excitation). Theoretical analysis confirms this effect.",0804.1090v1
2008-12-24,Design and optimization of one-dimensional ferrite-film based magnonic crystals,"One-dimensional magnonic crystals have been implemented as gratings of
shallow grooves chemically etched into the surface of yttrium-iron garnet
films. Scattering of backward volume magnetostatic spin waves from such
structures is investigated experimentally and theoretically. Well-defined
rejection frequency bands are observed in transmission characteristics of the
magnonic crystals. The loss inserted by the gratings and the rejections bands
bandwidths are studied as a function of the film thickness, the groove depth,
the number of grooves, and the groove width. The experimental data are well
described by a theoretical model based on the analogy of a spin-wave
film-waveguide with a microwave transmission line. Our study shows that
magnonic crystals with required operational characteristics can be engineered
by adjusting these geometrical parameters.",0812.4553v1
2009-02-18,Theory of coherence in Bose-Einstein condensation phenomena in a microwave driven interacting magnon gas,"Strong experimental evidences of the formation of quasi-equilibrium
Bose-Einstein condensation (BEC) of magnons at room temperature in a film of
yttrium iron garnet (YIG) excited by microwave radiation have been recently
reported. Here we present a theory for the magnon gas driven by a microwave
field far out of equilibrium showing that the nonlinear magnetic interactions
create cooperative mechanisms for the onset of a phase transition leading to
the spontaneous generation of quantum coherence and magnetic dynamic order in a
macroscopic scale. The theory provides rigorous support for the formation of a
BEC of magnons in a YIG film magnetized in the plane. We show that the system
develops coherence only when the microwave driving power exceeds a threshold
value and that the theoretical result for the intensity of the Brillouin light
scattering from the BEC as a function of power agrees with the experimental
data. The theory also explains quantitatively experimental measurements of
microwave emission from the uniform mode generated by the confluence of BEC
magnon pairs in a YIG film when the driving power exceeds a critical value.",0902.3138v1
2009-07-16,Reverse Doppler effect in backward spin waves scattered on acoustic waves,"We report on the observation of reverse Doppler effect in backward spin waves
reflected off of surface acoustic waves. The spin waves are excited in a
yttrium iron garnet (YIG) film. Simultaneously, acoustic waves are also
generated. The strain induced by the acoustic waves in the magnetostrictive YIG
film results in the periodic modulation of the magnetic anisotropy in the film.
Thus, in effect, a travelling Bragg grating for the spin waves is produced. The
backward spin waves reflecting off of this grating exhibit a reverse Doppler
shift: shifting down rather than up in frequency when reflecting off of an
approaching acoustic wave. Similarly, the spin waves are shifted up in
frequency when reflecting from receding acoustic waves.",0907.2902v1
2009-12-16,Parametric pumping and kinetics of magnons in dipolar ferromagnets,"The time evolution of magnons subject to a time-dependent microwave field is
usually described within the so-called ""S-theory"", where kinetic equations for
the distribution function are obtained within the time-dependent Hartree-Fock
approximation. To explain the recent observation of ""Bose-Einstein condensation
of magnons"" in an external microwave field [Demokritov et al., Nature 443, 430
(2006)], we extend the ""S-theory"" to include the Gross-Pitaevskii equation for
the time-dependent expectation values of the magnon creation and annihilation
operators. We explicitly solve the resulting coupled equations within a simple
approximation where only a single condensed mode is retained. We also
re-examine the usual derivation of an effective boson model from a realistic
spin model for yttrium-iron garnet films and argue that in the parallel pumping
geometry (where both the static and the time-dependent magnetic field are
parallel to the macroscopic magnetization) the time-dependent Zeemann energy
cannot give rise to magnon condensation.",0912.3254v2
2011-03-11,Spin pumping by parametrically excited exchange magnons,"We experimentally show that exchange magnons can be detected using a
combination of spin pumping and inverse spin-Hall effect (iSHE) proving its
wavelength integrating capability down to the sub-micrometer scale. The magnons
were injected in a ferrimagnetic yttrium iron garnet film by parametric pumping
and the iSHE-induced voltage was detected in an attached Pt layer. The role of
the density, wavelength, and spatial localization of the magnons for the spin
pumping efficiency is revealed. This study opens the field of the magnon-based
information processing to magnons with nano-scale wavelengths.",1103.2229v2
2011-11-08,Time-dependent spin-wave theory,"We generalize the spin-wave expansion in powers of the inverse spin to
time-dependent quantum spin models describing rotating magnets or magnets in
time-dependent external fields. We show that in these cases, the spin operators
should be projected onto properly defined rotating reference frames before the
spin components are bosonized using the Holstein-Primakoff transformation. As a
first application of our approach, we calculate the reorganization of the
magnetic state due to Bose-Einstein condensation of magnons in the magnetic
insulator yttrium-iron garnet; we predict a characteristic dip in the
magnetization which should be measurable in experiments.",1111.2052v2
2011-12-21,Direct detection of magnon spin transport by the inverse spin Hall effect,"Conversion of traveling magnons into an electron carried spin current is
demonstrated in a time resolved experiment using a spatially separated
inductive spin-wave source and an inverse spin Hall effect (ISHE) detector. A
short spin-wave packet is excited in a yttrium-iron garnet (YIG) waveguide by a
microwave signal and is detected at a distance of 3 mm by an attached Pt layer
as a delayed ISHE voltage pulse. The delay in the detection appears due to the
finite spin-wave group velocity and proves the magnon spin transport. The
experiment suggests utilization of spin waves for the information transfer over
macroscopic distances in spintronic devices and circuits.",1112.4969v1
2012-05-20,Brillouin light scattering spectroscopy of parametrically excited dipole-exchange magnons,"The spectral distribution of parametrically excited dipole-exchange magnons
in an in-plane magnetized epitaxial film of yttrium-iron garnet was studied by
means of frequency- and wavevector-resolved Brillouin light scattering
spectroscopy. The experiment was performed in a parallel pumping geometry where
an exciting microwave magnetic field was parallel to the magnetizing field. It
was found that for both dipolar and exchange spectral areas parallel pumping
excites the lowest volume magnon modes propagating in the film plane
perpendicularly to the magnetization direction. In order to interpret the
experimental observations, we used a microscopic Heisenberg model that includes
exchange as well as dipole-dipole interactions to calculate the magnon spectrum
and construct the eigenstates. As proven in our calculations, the observed
magnons are characterized by having the highest possible ellipticity of
precession which suggests the lowest threshold of parametric generation.
Applying different pumping powers we observe modifications in the magnon
spectrum that are described theoretically by a softening of the spin stiffness.",1205.4396v1
2012-06-28,Frequency and power dependence of spin-current emission by spin pumping in a thin film YIG/Pt system,"This paper presents the frequency dependence of the spin current emission in
a hybrid ferrimagnetic insulator/normal metal system. The system is based on a
ferrimagnetic insulating thin film of Yttrium Iron Garnet (YIG, 200 nm) grown
by liquid-phase-epitaxy (LPE) coupled with a normal metal with a strong
spin-orbit coupling (Pt, 15 nm). The YIG layer presents an isotropic behaviour
of the magnetization in the plane, a small linewidth, and a roughness lower
than 0.4 nm. Here we discuss how the voltage signal from the spin current
detector depends on the frequency [0.6 - 7 GHz], the microwave power, Pin, [1 -
70 mW], and the in-plane static magnetic field. A strong enhancement of the
spin current emission is observed at low frequencies, showing the appearance of
non-linear phenomena.",1206.6671v2
2012-07-25,High cooperativity in coupled microwave resonator ferrimagnetic insulator hybrids,"We report the observation of strong coupling between the exchange-coupled
spins in gallium-doped yttrium iron garnet and a superconducting coplanar
microwave resonator made from Nb. The measured coupling rate of 450 MHz is
proportional to the square-root of the number of exchange-coupled spins and
well exceeds the loss rate of 50 MHz of the spin system. This demonstrates that
exchange coupled systems are suitable for cavity quantum electrodynamics
experiments, while allowing high integration densities due to their
extraordinary high spin densities. Our results furthermore show, that
experiments with multiple exchange-coupled spin systems interacting via a
single resonator are within reach.",1207.6039v2
2012-11-05,Investigation of induced Pt magnetic polarization in Pt/Y3Fe5O12 bilayers,"Using X-ray magnetic circular dichroism (XMCD) measurements, we explore the
possible existence of induced magnetic moments in thin Pt films deposited onto
the ferrimagnetic insulator yttrium iron garnet (Y3Fe5O12). Such a magnetic
proximity effect is well established for Pt/ferromagnetic metal
heterostructures. Indeed, we observe a clear XMCD signal at the Pt L3 edge in
Pt/Fe bilayers, while no such signal can be discerned in XMCD traces of
Pt/Y3Fe5O12 bilayers. Integrating the XMCD signals allows to estimate an upper
limit for the induced Pt magnetic polarization in Pt/Y3Fe5O12 bilayers.",1211.0916v1
2012-12-10,Heat-induced damping modification in YIG/Pt hetero-structures,"We experimentally demonstrate the manipulation of magnetization relaxation
utilizing a temperature difference across the thickness of an yttrium iron
garnet/platinum (YIG/Pt) hetero-structure: the damping is either increased or
decreased depending on the sign of the temperature gradient. This effect might
be explained by a thermally-induced spin torque on the magnetization
precession. The heat-induced variation of the damping is detected by microwave
techniques as well as by a DC voltage caused by spin pumping into the adjacent
Pt layer and the subsequent conversion into a charge current by the inverse
spin Hall effect.",1212.2073v1
2013-02-06,Theory of spin Hall magnetoresistance,"We present a theory of the spin Hall magnetoresistance (SMR) in multilayers
made from an insulating ferromagnet F, such as yttrium iron garnet (YIG), and a
normal metal N with spin-orbit interactions, such as platinum (Pt). The SMR is
induced by the simultaneous action of spin Hall and inverse spin Hall effects
and therefore a non-equilibrium proximity phenomenon. We compute the SMR in
F$|$N and F$|$N$|$F layered systems, treating N by spin-diffusion theory with
quantum mechanical boundary conditions at the interfaces in terms of the
spin-mixing conductance. Our results explain the experimentally observed spin
Hall magnetoresistance in N$|$F bilayers. For F$|$N$|$F spin valves we predict
an enhanced SMR amplitude when magnetizations are collinear. The SMR and the
spin-transfer torques in these trilayers can be controlled by the magnetic
configuration.",1302.1352v1
2013-04-08,YIG thickness and frequency dependence of the spin-charge current conversion in YIG/Pt systems,"We report the frequency dependence of the spin current emission in a hybrid
ferrimagnetic insulator/normal metal system as function of the insulating layer
thickness. The system is based on a yttrium iron garnet (YIG) film [0.2, 1, and
3 \mu m] grown by liquid-phase-epitaxy coupled with a spin current detector of
platinum [6 nm]. A strong YIG thickness dependence of the efficiency of the
spin pumping has been observed. The highest conversion factor \Delta V/P_{abs}
has been demonstrated for the thinner YIG (1.79 and 0.55 mV/mW^{-1} at 2.5 and
10 GHz, respectively) which presents an interest for the realisation of
YIG-based devices. A strong YIG thickness dependence of the efficiency of the
spin pumping has been also observed and we demonstrate the threshold frequency
dependence of the three-magnon splitting process.",1304.2190v1
2013-05-14,Exchange magnetic field torques in YIG/Pt bilayers observed by the spin-Hall magnetoresistance,"The effective field torque of an yttrium-iron-garnet film on the spin
accumulation in an attached Pt film is measured by the spin-Hall
magnetoresistance (SMR). As a result, the magnetization direction of a
ferromagnetic insulating layer can be measured electrically. Experimental
transverse and longitudinal resistances are well described by the theoretical
model of SMR in terms of the direct and inverse spin-Hall effect, for different
Pt thicknesses [3, 4, 8 and 35nm]. Adopting a spin-Hall angle of Pt
$\theta_{SH}=0.08$, we obtain the spin diffusion length of Pt
($\lambda=1.1\pm0.3$nm) as well as the real
($G_r=(7\pm3)\times10^{14}\Omega^{-1}$m$^{-2}$) and imaginary part
($G_i=(5\pm3)\times10^{13}\Omega^{-1}$m$^{-2}$) of the spin-mixing conductance
and their ratio ($G_r/G_i=16\pm4$).",1305.3117v2
2013-06-20,Experimental test of the spin mixing interface conductivity concept,"We perform a quantitative, comparative study of the spin pumping, spin
Seebeck and spin Hall magnetoresistance effects, all detected via the inverse
spin Hall effect in a series of over 20 yttrium iron garnet/Pt samples. Our
experimental results fully support present, exclusively spin current-based,
theoretical models using a single set of plausible parameters for spin mixing
conductance, spin Hall angle and spin diffusion length. Our findings establish
the purely spintronic nature of the aforementioned effects and provide a
quantitative description in particular of the spin Seebeck effect.",1306.5012v1
2013-07-29,Current-induced spin wave excitation in Pt|YIG bilayer,"We develop a self-consistent theory for current-induced spin wave excitations
in normal metal-magnetic insulator bilayer systems, thereby establishing the
relation between spin wave excitation and the experimentally controlled
parameters. We fully take into account the complex spin wave spectrum including
dipolar interactions and surface anisotropy as well as the spin-pumping at the
interface. Our results focus on the mode-dependent power close to the critical
currents for spin wave excitation. The major findings are (a) the spin transfer
torque can excite different spin-wave modes simultaneously; (b) spin pumping
counterbalances spin-transfer torque and affects the surface modes more than
the bulk modes; (c) spin pumping inhibits high frequency spin-wave modes,
thereby redshifting the excitation spectrum. We can get agreement with
experiments on yttrium iron garnet|platinum bilayers by postulating the
existence of surface anisotropy modes.",1307.7607v2
2013-09-16,Time resolved spin Seebeck effect experiments,"In this Letter, we present the results of transient thermopower experiments,
performed at room temperature on yttrium iron garnet/platinum bilayers. Upon
application of a time-varying thermal gradient, we observe a characteristic
low-pass frequency response of the ensuing thermopower voltage with cutoff
frequencies of up to 37 MHz. We interpret our results in terms of the spin
Seebeck effect, and argue that small wavevector magnons are of minor importance
for the spin Seebeck effect in our thin film hybrid structures.",1309.3986v2
2013-11-19,Observation of the spin Peltier effect,"We report the observation of the spin Peltier effect (SPE) in the
ferrimagnetic insulator Yttrium Iron Garnet (YIG), i.e. a heat current
generated by a spin current flowing through a Platinum (Pt)|YIG interface. The
effect can be explained by the spin torque that transforms the spin current in
the Pt into a magnon current in the YIG. Via magnon-phonon interactions the
magnetic fluctuations modulate the phonon temperature that is detected by a
thermopile close to the interface. By finite-element modelling we verify the
reciprocity between the spin Peltier and spin Seebeck effect. The observed
strong coupling between thermal magnons and phonons in YIG is attractive for
nanoscale cooling techniques.",1311.4772v1
2014-01-30,Temperature dependent spin transport properties of Platinum inferred from spin Hall magnetoresistance measurements,"We study the temperature dependence of the spin Hall magnetoresistance (SMR)
in yttrium iron garnet/platinum hybrid structures via magnetization orientation
dependent magnetoresistance measurements. Our experiments show a decrease of
the SMR magnitude with decreasing temperature. Using the sensitivity of the SMR
to the spin transport properties of the normal metal, we interpret our data in
terms of a decrease of the spin Hall angle in platinum from 0.11 at room
temperature to 0.075 at 10K, while the spin diffusion length and the spin
mixing conductance of the ferrimagnetic insulator/normal metal interface remain
almost constant.",1401.7787v4
2014-03-02,Generalized two-temperature model for coupled phonon-magnon diffusion,"We generalize the two-temperature model [Sanders and Walton, Phys. Rev. B,
15, 1489 (1977)] for coupled phonon-magnon diffusion to include the effect of
the concurrent magnetization flow. Working within the framework of Boltzmann
transport equation, we derive the constitutive equations for coupled
phonon-magnon transport driven by gradients of both temperature and external
magnetic fields, and the corresponding conservation laws. Our equations reduce
to the original Sanders-Walton two-temperature model under a uniform external
field, but predict a new magnon cooling effect driven by a non-uniform magnetic
field in a homogeneous single-domain ferromagnet. We estimate the magnitude of
the cooling effect in yttrium iron garnet, and show it is within current
experimental reach. With properly optimized materials, the predicted cooling
effect can potentially supplement the conventional magnetocaloric effect in
cryogenic applications in the future.",1403.0279v1
2014-03-04,Off-Resonant Manipulation of Spins in Diamond via Precessing Magnetization of a Proximal Ferromagnet,"We report the manipulation of nitrogen vacancy (NV) spins in diamond when
nearby ferrimagnetic insulator, yttrium iron garnet, is driven into precession.
The change in NV spin polarization, as measured by changes in
photoluminescence, is comparable in magnitude to that from conventional
optically detected magnetic resonance, but relies on a distinct mechanism as it
occurs at a microwave frequency far removed from the magnetic resonance
frequency of the NV spin. This observation presents a new approach to
transferring ferromagnetic spin information into a paramagnet and then
transducing the response into a robust optical signal. It also opens new
avenues for studying ferromagnetism and spin transport at the nanoscale.",1403.0656v1
2014-05-06,Hybridizing ferromagnetic magnons and microwave photons in the quantum limit,"We demonstrate large normal-mode splitting between a magnetostatic mode (the
Kittel mode) in a ferromagnetic sphere of yttrium iron garnet and a microwave
cavity mode. Strong coupling is achieved in the quantum regime where the
average number of thermally or externally excited magnons and photons is less
than one. We also confirm that the coupling strength is proportional to the
square root of the number of spins. A nonmonotonic temperature dependence of
the Kittel-mode linewidth is observed below 1 K and is attributed to the
dissipation due to the coupling with a bath of two-level systems.",1405.1913v2
2014-06-14,Electric-field coupling to spin waves in a centrosymmetric ferrite,"We experimentally demonstrate that the spin-orbit interaction can be utilized
for direct electric-field tuning of the propagation of spin waves in a
single-crystal yttrium iron garnet magnonic waveguide. Magnetoelectric coupling
not due to the spin-orbit interaction, and hence an order of magnitude weaker,
leads to electric-field modification of the spin-wave velocity for waveguide
geometries where the spin-orbit interaction will not contribute. A theory of
the phase shift, validated by the experiment data, shows that, in the exchange
spin wave regime, this electric tuning can have high efficiency. Our findings
point to an important avenue for manipulating spin waves and developing
electrically tunable magnonic devices.",1406.3675v1
2014-07-29,Motion of domain walls and the dynamics of kinks in the magnetic Peierls potential,"We study the dynamics of magnetic domain walls in the Peierls potential due
to the discreteness of the crystal lattice. The propagation of a narrow domain
wall (comparable to the lattice parameter) under the effect of a magnetic field
proceeds through the formation of kinks in its profile. We predict that,
despite the discreteness of the system, such kinks can behave like sine-Gordon
solitons in thin films of materials such as yttrium iron garnets, and we derive
general conditions for other materials. In our simulations we also observe
long-lived breathers. We provide analytical expressions for the effective mass
and limiting velocity of the kink in excellent agreement with our numerical
results.",1407.7754v1
2014-08-06,Observation of Magnonic Band Gaps in Magnonic Crystals with Nopnreciprocal Dispersion Relation,"An effect of metallization of the magnonic crystal surface on the band gaps
formation in the spectra of the surface spin wave (SSW) is studied both
theoretically and experimentally. The structures under consideration are
one-dimensional magnonic crystals based on yttrium iron garnet with an array of
etched grooves with metal screen on the top of the corrugated surface and
without it. Due to nonreciprocity of propagation of the SSW the shift of band
gap to higher frequency and from the border of the Brillouin zone in presence
of conducting overlayer was measured in transmission line experiment. Results
of numerical calculations and model analysis are in agreement with experimental
data and give further insight into origin of the band gap and properties of the
nonreciprocal SSW in metallized magnonic crystals. This gives positive answer
to the outstanding question about possibility of detection of magnonic band
gaps in the spectra of the spin waves with nonreciprocal dispersion in magnonic
crystals and creates potential for new applications and improvements of already
existing prototype magnonic devices.",1408.1221v2
2014-09-19,Perpendicularly Biased YIG Tuners for the Fermilab Recycler 52.809 MHz Cavities,"For NOvA and future experiments requiring high intensity proton beams,
Fermilab is in the process of upgrading the existing accelerator complex for
increased proton production. One such improvement is to reduce the Main
Injector cycle time, by performing slip stacking, previously done in the Main
Injector, in the now repurposed Recycler Ring. Recycler slip stacking requires
new tuneable RF cavities, discussed separately in these proceedings. These are
quarter wave cavities resonant at 52.809 MHz with a 10 kHz tuning range. The 10
kHz range is achieved by use of a tuner which has an electrical length of
approximately one half wavelength at 52.809 MHz. The tuner is constructed from
3 1/8 inch diameter rigid coaxial line, with 5 inches of its length containing
perpendicularly biased, Al doped Yttrium Iron Garnet (YIG). The tuner design,
measurements, and high power test results are presented.",1409.5762v1
2014-09-30,Spin Hall noise,"We measure the low-frequency thermal fluctuations of pure spin current in a
Platinum film deposited on yttrium iron garnet via the inverse spin Hall effect
(ISHE)-mediated voltage noise as a function of the angle $\alpha$ between the
magnetization and the transport direction. The results are consistent with the
fluctuation dissipation theorem in terms of the recently discovered spin Hall
magnetoresistance (SMR). We present a microscopic description of the $\alpha$
dependence of the voltage noise in terms of spin current fluctuations and ISHE.",1409.8513v2
2014-10-22,Spin current generation from sputtered Y3Fe5O12 films,"Spin current injection from sputtered yttrium iron garnet (YIG) films into an
adjacent platinum layer has been investigated by means of the spin pumping and
the spin Seebeck effects. Films with a thickness of 83 and 96 nanometers were
fabricated by on-axis magnetron rf sputtering at room temperature and
subsequent post-annealing. From the frequency dependence of the ferromagnetic
resonance linewidth, the damping constant has been estimated to be
$(7.0\pm1.0)\times 10^{-4}$. Magnitudes of the spin current generated by the
spin pumping and the spin Seebeck effect are of the same order as values for
YIG films prepared by liquid phase epitaxy. The efficient spin current
injection can be ascribed to a good YIG|Pt interface, which is confirmed by the
large spin-mixing conductance $(2.0\pm0.2)\times 10^{18}$ m$^{-2}$.",1410.5987v1
2014-12-07,Magnonic band gaps in YIG based magnonic crystals: array of grooves versus array of metallic stripes,"The magnonic band gaps of the two types of planar one-dimensional magnonic
crystals comprised of the periodic array of the metallic stripes on yttrium
iron garnet (YIG) film and YIG film with an array of grooves was analyzed
experimentally and theoretically. In such periodic magnetic structures the
propagating magnetostatic surface spin waves were excited and detected by
microstripe transducers with vector network analyzer and by Brillouin light
scattering spectroscopy. Properties of the magnonic band gaps were explained
with the help of the finite element calculations. The important influence of
the nonreciprocal properties of the spin wave dispersion induced by metallic
stripes on the magnonic band gap width and its dependence on the external
magnetic field has been shown. The usefulness of both types of the magnonic
crystals for potential applications and possibility for miniaturization are
discussed.",1412.2367v2
2014-12-22,Surface sensitivity of the spin Seebeck effect,"We have investigated the influence of the interface quality on the spin
Seebeck effect (SSE) of the bilayer system yttrium iron garnet (YIG) - platinum
(Pt). The magnitude and shape of the SSE is strongly influenced by mechanical
treatment of the YIG single crystal surface. We observe that the saturation
magnetic field H_{sat} for the SSE signal increases from 55.3 mT to 72.8 mT
with mechanical treatment. The change in the magnitude of H_{sat} can be
attributed to the presence of a perpendicular magnetic anisotropy due to the
treatment induced surface strain or shape anisotropy in the Pt/YIG system. Our
results show that the SSE is a powerful tool to investigate magnetic anisotropy
at the interface.",1412.7712v1
2015-01-12,Anomalous Hall effect in YIG$|$Pt bilayers,"We measure the ordinary and the anomalous Hall effect in a set of yttrium
iron garnet$|$platinum (YIG$|$Pt) bilayers via magnetization orientation
dependent magnetoresistance experiments. Our data show that the presence of the
ferrimagnetic insulator YIG leads to an anomalous Hall like signature in Pt,
sensitive to both Pt thickness and temperature. Interpretation of the
experimental findings in terms of the spin Hall anomalous Hall effect indicates
that the imaginary part of the spin mixing interface conductance
$G_{\mathrm{i}}$ plays a crucial role in YIG$|$Pt bilayers. In particular, our
data suggest a sign change in $G_{\mathrm{i}}$ between $10\,\mathrm{K}$ and
$300\,\mathrm{K}$. Additionally, we report a higher order Hall effect, which
appears in thin Pt films on YIG at low temperatures.",1501.02574v3
2015-01-14,A spin-wave logic gate based on a width-modulated dynamic magnonic crystal,"An electric current controlled spin-wave logic gate based on a
width-modulated dynamic magnonic crystal is realized. The device utilizes a
spin-wave waveguide fabricated from a single-crystal Yttrium Iron Garnet film
and two conducting wires attached to the film surface. Application of electric
currents to the wires provides a means for dynamic control of the effective
geometry of the waveguide and results in a suppression of the magnonic band
gap. The performance of the magnonic crystal as an AND logic gate is
demonstrated.",1501.03486v2
2015-02-18,Spectral shape deformation in inverse spin Hall voltage in Y3Fe5O12|Pt bilayers at high microwave power levels,"We report on the deformation of microwave absorption spectra and of the
inverse spin Hall voltage signals in thin film bilayers of yttrium iron garnet
(YIG) and platinum at high microwave power levels in a 9.45-GHz TE011 cavity.
As the microwave power increases from 0.15 to 200 mW, the resonance field
shifts to higher values, and the initially Lorentzian spectra of the microwave
absorption intensity as well as the inverse spin Hall voltage signals become
asymmetric. The contributions from opening of the magnetization precession cone
and heating of YIG cannot well reproduce the data. Control measurements of
inverse spin Hall voltages on thin-film YIG|Pt systems with a range of line
widths underscore the role of spin-wave excitations in spectral deformation.",1502.05198v1
2015-02-13,Spin-current injection and detection in strongly correlated organic conductor,"Spin-current injection into an organic semiconductor
$\rm{\kappa\text{-}(BEDT\text{-}TTF)_2Cu[N(CN)_2]Br}$ film induced by the spin
pumping from an yttrium iron garnet (YIG) film. When magnetization dynamics in
the YIG film is excited by ferromagnetic or spin-wave resonance, a voltage
signal was found to appear in the
$\rm{\kappa\text{-}(BEDT\text{-}TTF)_2Cu[N(CN)_2]Br}$ film.
Magnetic-field-angle dependence measurements indicate that the voltage signal
is governed by the inverse spin Hall effect in
$\rm{\kappa\text{-}(BEDT\text{-}TTF)_2Cu[N(CN)_2]Br}$. We found that the
voltage signal in the $\rm{\kappa\text{-}(BEDT\text{-}TTF)_2Cu[N(CN)_2]Br}$/YIG
system is critically suppressed around 80 K, around which magnetic and/or glass
transitions occur, implying that the efficiency of the spin-current injection
is suppressed by fluctuations which critically enhanced near the transitions.",1502.05244v1
2015-03-02,Supercurrent in a room temperature Bose-Einstein magnon condensate,"We report evidence for the existence of a supercurrent of magnons in a magnon
Bose-Einstein condensate prepared in a room temperature yttrium-iron-garnet
magnetic film and subject to a thermal gradient. The magnon condensate is
formed in a parametrically populated magnon gas, and its temporal evolution is
studied by time-, frequency- and wavector-resolved Brillouin light scattering
spectroscopy. It has been found that local heating in the focal point of a
probing laser beam enhances the temporal decrease in the density of the freely
evolving magnon condensate after the termination of the pumping pulse, but it
does not alter the relaxation dynamics of the gaseous magnon phase. This
phenomenon is understood as the appearance of a magnon supercurrent within the
condensate due to a temperature- and, consequently, magnetisation-gradient
induced phase gradient in the condensate wave function.",1503.00482v2
2015-04-10,Influence of magnetic surface anisotropy on spin wave reflection from the edge of ferromagnetic film,"We study propagation of the Gaussian beam of spin waves and its reflection
from the edge of thin yttrium-iron-garnet film with in-plane magnetization
perpendicular to this edge. We have performed micromagnetic simulations
supported by analytical calculations to investigate influence of the surface
magnetic anisotropy present at the film edge on the reflection, especially in
the context of the Goos-Hanchen effect. We have shown the appearance of a
negative lateral shift between reflected and incident spin wave beams' spots.
This shift is particularly sensitive to the surface magnetic anisotropy value
and is a result of the Goos-Hanchen shift which is sensitive to the magnitude
of the anisotropy and of the bending of spin wave beam. We have demonstrated
that the demagnetizing field provide graded increase of the refractive index
for spin waves, which is responsible for the bending.",1504.02668v2
2015-04-30,Magneto-optical imaging technique for hostile environment: the ghost imaging approach,"We develop a new approach in magneto-optical imaging (MOI), applying for the
first time a ghost imaging (GI) protocol to perform Faraday microscopy. MOI is
of the utmost importance for the investigation of magnetic properties of
material samples, through Weiss domains shape, dimension and dynamics analysis.
Nevertheless, in some extreme conditions such as e. g. cryogenic temperatures
or high magnetic fields application, there exists a lack of domains images due
to the difficulty in creating an efficient imaging system in such environments.
Here we present an innovative MOI technique that separates the imaging optical
path from the one illuminating the object. The technique is based on thermal
light GI and exploits correlations between light beams to retrieve the image of
magnetic domains. As a proof of principle, the proposed technique is applied to
the Faraday magneto-optical observation of the remanence domain structure of an
yttrium iron garnet sample.",1504.08239v2
2015-05-07,Formation of Bright Solitons from Wave Packets with Repulsive Nonlinearity,"Formation of bright envelope solitons from wave packets with a repulsive
nonlinearity was observed for the first time. The experiments used surface
spin-wave packets in magnetic yttrium iron garnet (YIG) thin film strips. When
the wave packets are narrow and have low power, they undergo self-broadening
during the propagation. When the wave packets are relatively wide or their
power is relatively high, they can experience self-narrowing or even evolve
into bright solitons. The experimental results were reproduced by numerical
simulations based on a modified nonlinear Schr\""odinger equation model.",1505.01882v1
2015-05-23,Long distance transport of magnon spin information in a magnetic insulator at room temperature,"The transport of spin information has been studied in various materials, such
as metals, semiconductors and graphene. In these materials, spin is transported
by diffusion of conduction electrons. Here we study the diffusion and
relaxation of spin in a magnetic insulator, where the large bandgap prohibits
the motion of electrons. Spin can still be transported, however, through the
diffusion of non-equilibrium magnons, the quanta of spin wave excitations in
magnetically ordered materials. Here we show experimentally that these magnons
can be excited and detected fully electrically in linear response, and can
transport spin angular momentum through the magnetic insulator yttrium iron
garnet (YIG) over distances as large as 40 micrometer. We identify two
transport regimes: the diffusion limited regime for distances shorter than the
magnon relaxation length, and the relaxation limited regime for larger
distances. With a model similar to the diffusion-relaxation model for electron
spin transport in (semi)conducting materials, we extract the magnon relaxation
length lambda = 9.4 micrometer in a 200 nm thin YIG film at room temperature.",1505.06325v1
2015-05-26,Observation of pure inverse spin Hall effect in ferromagnetic metals by FM/AFM exchange bias structures,"We report that the spin current generated by spin Seebeck effect (SSE) in
yttrium iron garnet (YIG) can be detected by a ferromagnetic metal (NiFe). By
using the FM/AFM exchange bias structure (NiFe/IrMn), inverse spin Hall effect
(ISHE) and planar Nernst effect (PNE) of NiFe can be unambiguously separated,
allowing us to observe a pure ISHE signal. After eliminating the in plane
temperature gradient in NiFe, we can even observe a pure ISHE signal without
PNE from NiFe itself. It is worth noting that a large spin Hall angle (0.098)
of NiFe is obtained, which is comparable with Pt. This work provides a kind of
FM/AFM exchange bias structures to detect the spin current by charge signals,
and highlights ISHE in ferromagnetic metals can be used in spintronic research
and applications.",1505.06911v2
2015-06-19,Spin superfluidity and long-range transport in thin-film ferromagnets,"In ferromagnets, magnons may condense into a single quantum state. Analogous
to superconductors, this quantum state may support transport without
dissipation. Recent works suggest that longitudinal spin transport through a
thin-film ferromagnet is an example of spin superfluidity. Although intriguing,
this tantalizing picture ignores long-range dipole interactions; we demonstrate
that such interactions dramatically affect spin transport. In single-film
ferromagnets, ""spin superfluidity"" only exists at length scales (a few hundred
nanometers in yttrium iron garnet) somewhat larger than the exchange length.
Over longer distances, dipolar interactions destroy spin superfluidity.
Nevertheless, we predict re-emergence of spin superfluidity in tri-layer
ferromagnet--normal metal--ferromagnet films of $\sim 1\, \mu$m in size. Such
systems also exhibit other types of long-range spin transport in samples
several micrometers in size.",1506.06029v1
2015-06-19,Cavity mediated coherent coupling of magnetic moments,"We demonstrate the long range strong coupling of magnetostatic modes in
spatially separated ferromagnets mediated by a microwave frequency cavity. Two
spheres of yttrium iron garnet are embedded in the cavity and their
magnetostatic modes probed using a dispersive measurement technique. We find
they are strongly coupled to each other even when detuned from the cavity
modes. We investigate the dependence of the magnet-magnet coupling on the
cavity detuning $\Delta$, and find a $1/\Delta$ dependence also characteristic
of cavity-coupled superconducting qubits. Dark states of the coupled
magnetostatic modes of the system are observed, and ascribed to mismatches
between the symmetries of the modes and the drive field.",1506.06049v2
2015-07-10,Magnon dark modes and gradient memory,"Extensive efforts have been expended in developing hybrid quantum systems to
overcome the short coherence time of superconducting circuits by introducing
the naturally long-lived spin degree of freedom. Among all the possible
materials, single-crystal yttrium iron garnet has shown up very recently as a
promising candidate for hybrid systems, and various highly coherent
interactions, including strong and even ultra-strong coupling, have been
demonstrated. One distinct advantage of these systems is that the spins are in
the form of well-defined magnon modes, which allows flexible and precise
tuning. Here we demonstrate that by dissipation engineering, a non-Markovian
interaction dynamics between the magnon and the microwave cavity photon can be
achieved. Such a process enables us to build a magnon gradient memory to store
information in the magnon dark modes, which decouple from the microwave cavity
and thus preserve a long life-time. Our findings provide a promising approach
for developing long-lifetime, multimode quantum memories.",1507.02791v1
2015-08-20,Superstrong Coupling of a Microwave Cavity to YIG Magnons,"Multiple-post reentrant 3D lumped cavity modes have been realized to design
the concept of discrete Whispering Gallery and Fabry-Perot-like Modes for
multimode microwave Quantum Electrodynamics experiments. Using a magnon
spin-wave resonance of a submillimeter-sized Yttrium-Iron-Garnet sphere at
milliKelvin temperatures and a four-post cavity, we demonstrate the
ultra-strong coupling regime between discrete Whispering Gallery Modes and a
magnon resonance with strength of 1.84 GHz. By increasing the number of posts
to eight and arranging them in a D$_4$ symmetry pattern, we expand the mode
structure to that of a discrete Fabry-Perot cavity and modify the Free Spectral
Range (FSR). We reach the superstrong coupling regime, where spin-photon
coupling strength is larger than FSR, with coupling strength in the 1.1 to 1.5
GHz range.",1508.04967v3
2015-08-25,Non-local magnetoresistance in YIG/Pt nanostructures,"We study the local and non-local magnetoresistance of thin Pt strips
deposited onto yttrium iron garnet. The local magnetoresistive response,
inferred from the voltage drop measured along one given Pt strip upon
current-biasing it, shows the characteristic magnetization orientation
dependence of the spin Hall magnetoresistance. We simultaneously also record
the non-local voltage appearing along a second, electrically isolated, Pt
strip, separated from the current carrying one by a gap of a few 100 nm. The
corresponding non-local magnetoresistance exhibits the symmetry expected for a
magnon spin accumulation-driven process, confirming the results recently put
forward by Cornelissen et al. [1]. Our magnetotransport data, taken at a series
of different temperatures as a function of magnetic field orientation, rotating
the externally applied field in three mutually orthogonal planes, show that the
mechanisms behind the spin Hall and the non-local magnetoresistance are
qualitatively different. In particular, the non-local magnetoresistance
vanishes at liquid Helium temperatures, while the spin Hall magnetoresistance
prevails.",1508.06130v1
2015-09-14,Spectral characteristics of time resolved magnonic spin Seebeck effect,"Spin Seebeck effect (SSE) holds promise for new spintronic devices with
low-energy consumption. The underlying physics, essential for a further
progress, is yet to be fully clarified. This study of the time resolved
longitudinal SSE in the magnetic insulator yttrium iron garnet (YIG) concludes
that a substantial contribution to the spin current stems from small
wave-vector subthermal exchange magnons. Our finding is in line with the recent
experiment by S. R. Boona and J. P. Heremans, Phys. Rev. B 90, 064421 (2014).
Technically, the spin-current dynamics is treated based on the
Landau-Lifshitz-Gilbert (LLG) equation also including magnons back-action on
thermal bath, while the formation of the time dependent thermal gradient is
described self-consistently via the heat equation coupled to the magnetization
dynamics",1509.04018v1
2015-10-13,Optomagnonic whispering gallery microresonators,"Magnons in ferrimagnetic insulators such as yttrium iron garnet (YIG) have
recently emerged as promising candidates for coherent information processing in
microwave circuits. Here we demonstrate optical whispering gallery modes of a
YIG sphere interrogated by a silicon nitride photonic waveguide, with quality
factors approaching $10^6$ in the telecom c-band after surface treatments.
Moreover, in contrast to conventional Faraday setup, this implementation allows
input photon polarized colinearly to the magnetization to be scattered to a
sideband mode of orthogonal polarization. This Brillouin scattering process is
enhanced through triply resonant magnon, pump and signal photon modes - all of
whispering gallery nature - within an ""optomagnonic cavity"". Our results show
the potential use of magnons for mediating microwave-to-optical carrier
conversion.",1510.03545v1
2015-11-24,Ferromagnetic Resonance of a YIG film in the Low Frequency Regime,"An improved method for characterizing the magnetic anisotropy of films with
cubic symmetry is described and is applied to an yttrium iron garnet (111)
film. Analysis of the FMR spectra performed both in-plane and out-of-plane from
0.7 to 8 GHz yielded the magnetic anisotropy constants as well as the
saturation magnetization. The field at which FMR is observed turns out to be
quite sensitive to anisotropy constants (by more than a factor ten) in the low
frequency (< 2 GHz) regime and when the orientation of the magnetic field is
nearly normal to the sample plane; the restoring force on the magnetization
arising from the magnetocrystalline anisotropy fields is then comparable to
that from the external field, thereby allowing the anisotropy constants to be
determined with greater accuracy. In this region, unusual dynamical behaviors
are observed such as multiple resonances and a switching of FMR resonance with
only a 1 degree change in field orientation at 0.7 GHz.",1511.07892v1
2015-12-01,Epitaxial patterning of nanometer-thick Y3Fe5O12 films with low magnetic damping,"Magnetic insulators such as yttrium iron garnet, Y3Fe5O12, with extremely low
magnetic damping have opened the door for low power spin-orbitronics due to
their low energy dissipation and efficient spin current generation and
transmission. We demonstrate reliable and efficient epitaxial growth and
nanopatterning of Y3Fe5O12 thin-film based nanostructures on insulating
Gd3Ga5O12 substrates. In particular, our fabrication process is compatible with
conventional sputtering and liftoff, and does not require aggressive ion
milling which may be detrimental to the oxide thin films. Structural and
magnetic properties indicate good qualities, in particular low magnetic damping
of both films and patterned structures. The dynamic magnetic properties of the
nanostructures are systematically investigated as a function of the lateral
dimension. By comparing to ferromagnetic nanowire structures, a distinct edge
mode in addition to the main mode is identified by both experiments and
simulations, which also exhbits cross-over with the main mode upon varying the
width of the wires. The non-linear evolution of dynamic modes over
nanostructural dimensions highlights the important role of size confinement to
their material properties in magnetic devices where Y3Fe5O12 nanostructures
serve as the key functional component.",1512.00286v1
2015-12-02,Bose-Einstein Condensation of Magnons Pumped by the Bulk Spin Seebeck Effect,"We propose inducing Bose-Einstein condensation of magnons in a magnetic
insulator by a heat flow oriented toward its boundary. At a critical heat flux,
the oversaturated thermal gas of magnons accumulated at the boundary
precipitates the condensate, which then grows gradually as the thermal bias is
dialed up further. The thermal magnons thus pumped by the magnonic bulk (spin)
Seebeck effect must generally overcome both the local Gilbert damping
associated with the coherent magnetic dynamics as well as the radiative
spin-wave losses toward the magnetic bulk, in order to achieve the threshold of
condensation. We quantitatively estimate the requisite bias in the case of the
ferrimagnetic yttrium iron garnet, discuss different physical regimes of
condensation, and contrast it with the competing (so-called Doppler-shift) bulk
instability.",1512.00557v1
2015-12-02,Non-equilibrium thermodynamics of the longitudinal spin Seebeck effect,"In this paper we employ non equilibrium thermodynamics of fluxes and forces
to describe magnetization and heat transport. By the theory we are able to
identify the thermodynamic driving force of the magnetization current as the
gradient of the effective field $\nabla H^*$. This definition permits to define
the spin Seebeck coefficient $\epsilon_M$ which relates $\nabla H^*$ and the
temperature gradient $\nabla T$. By applying the theory to the geometry of the
longitudinal spin Seebeck effect we are able to obtain the optimal conditions
for generating large magnetization currents. Furthermore, by using the results
of recent experiments, we obtain an order of magnitude for the value of
$\epsilon_{M} \sim 10^{-2}$ TK$^{-1}$ for yttrium iron garnet
(Y$_3$Fe$_5$O$_{12}$).",1512.00639v1
2015-12-14,Nonlocal Anomalous Hall Effect,"The anomalous Hall effect is deemed to be a unique transport property of
ferromagnetic metals, caused by the concerted action of spin polarization and
spin-orbit coupling. Nevertheless, recent experiments have shown that the
effect also occurs in a nonmagnetic metal (Pt) in contact with a magnetic
insulator (yttrium iron garnet (YIG)), even when precautions are taken to
ensure there is no induced magnetization in the metal. We propose a theory of
this effect based on the combined action of spin-dependent scattering from the
magnetic interface and the spin Hall effect in the bulk of the metal. At
variance with previous theories, we predict the effect to be of first order in
the spin-orbit coupling, just as the conventional anomalous Hall effect -- the
only difference being the spatial separation of the spin orbit interaction and
the magnetization. For this reason we name this effect \textit{nonlocal
anomalous Hall effect} and predict that its sign will be determined by the sign
of the spin Hall angle in the metal. The AH conductivity that we calculate from
our theory is in good agreement with the measured values in Pt/YIG structures.",1512.04146v1
2016-01-05,Proximity induced room-temperature ferromagnetism in graphene probed with spin currents,"The introduction and control of ferromagnetism in graphene opens up a range
of new directions for fundamental and applied studies. Several approaches have
been pursued so far, such as introduction of defects, functionalization with
adatoms, and shaping of graphene into nanoribbons with well-defined zigzag
edges. A more robust and less invasive method utilizes the introduction of an
exchange interaction by a ferromagnetic insulator in proximity with graphene.
  Here we present a direct measurement of the exchange interaction in room
temperature ferromagnetic graphene. We study the spin transport in exfoliated
graphene on a yttrium-iron-garnet substrate where the observed spin precession
clearly indicates the presence and strength of an exchange field that is an
unambiguous evidence of induced ferromagnetism. We describe the results with a
modified Bloch diffusion equation and extract an average exchange field of the
order of 0.2 T. Further, we demonstrate that a proximity induced 2D ferromagnet
can efficiently modulate a spin current by controlling the direction of the
exchange field. These results can create a building block for magnetic-gate
tuneable spin transport in one-atom-thick spintronic devices.",1601.00995v1
2016-01-21,Spin pumping in strongly coupled magnon-photon systems,"We experimentally investigate magnon-polaritons, arising in ferrimagnetic
resonance experiments in a microwave cavity with a tuneable quality factor. To
his end, we simultaneously measure the electrically detected spin pumping
signal and microwave reflection (the ferrimagnetic resonance signal) of a
yttrium iron garnet (YIG) / platinum (Pt) bilayer in the microwave cavity. The
coupling strength of the fundamental magnetic resonance mode and the cavity is
determined from the microwave reflection data. All features of the magnetic
resonance spectra predicted by first principle calculations and an input-output
formalism agree with our experimental observations. By changing the decay rate
of the cavity at constant magnon-photon coupling rate, we experimentally tune
in and out of the strong coupling regime and successfully model the
corresponding change of the spin pumping signal. Furthermore, we observe the
coupling and spin pumping of several spin wave modes and provide a quantitative
analysis of their coupling rates to the cavity.",1601.05681v1
2016-02-12,Transport and spin conversion of multi-carriers in semimetal bismuth,"In this paper, we report on the investigation of (1) the transport properties
of multi-carriers in semi-metal Bi and (2) the spin conversion physics in this
semimetal system in a ferrimagnetic insulator, yttrium-iron-garnet. Hall
measurements reveal that electrons and holes co-exist in the Bi, with electrons
being the dominant carrier. The results of a spin conversion experiment
corroborate the results of the Hall measurement; in addition, the inverse spin
Hall effect governs the spin conversion in the semimetal/insulator system. This
study provides further insights into spin conversion physics in semimetal
systems.",1602.03953v1
2016-03-02,Enhancement of Thermally Injected Spin Current through an Antiferromagnetic Insulator,"We report large enhancement of thermally injected spin current in normal
metal (NM)/antiferromagnet(AF)/yttrium iron garnet(YIG), where a thin AF
insulating layer of NiO or CoO can enhance spin current from YIG to a NM by up
to a factor of 10. The spin current enhancement in NM/AF/YIG, with a pronounced
maximum near the N\'eel temperature of the thin AF layer, has been found to
scale linearly with the spin-mixing conductance at the NM/YIG interface for NM
= 3d, 4d, and 5d metals. Calculations of spin current enhancement and spin
mixing conductance are qualitatively consistent with the experimental results.",1603.00931v2
2016-04-08,Gate-tunable spin-charge conversion and a role of spin-orbit interaction in graphene,"The small spin-orbit interaction of carbon atoms in graphene promises a long
spin diffusion length and potential to create a spin field-effect transistor.
However, for this reason, graphene was largely overlooked as a possible
spin-charge conversion material. We report electric gate tuning of the
spin-charge conversion voltage signal in a single-layer graphene. Using spin
pumping from yttrium iron garnet ferrimagnetic insulator and ionic liquid top
gate we determined that the inverse spin Hall effect is the dominant
spin-charge conversion mechanism in a single-layer graphene. From the gate
dependence of the electromotive force we showed dominance of the intrinsic over
Rashba spin-orbit interaction: a long-standing question in graphene research.",1604.02222v1
2016-04-13,Magnon spin transport driven by the magnon chemical potential in a magnetic insulator,"We develop a linear-response transport theory of diffusive spin and heat
transport by magnons in magnetic insulators with metallic contacts. The magnons
are described by a position dependent temperature and chemical potential that
are governed by diffusion equations with characteristic relaxation lengths.
Proceeding from a linearized Boltzmann equation, we derive expressions for
length scales and transport coefficients. For yttrium iron garnet (YIG) at room
temperature we find that long-range transport is dominated by the magnon
chemical potential. We compare the model's results with recent experiments on
YIG with Pt contacts [L.J. Cornelissen, et al., Nat. Phys. 11, 1022 (2015)] and
extract a magnon spin conductivity of $\sigma_{m}=5\times10^{5}$ S/m. Our
results for the spin Seebeck coefficient in YIG agree with published
experiments. We conclude that the magnon chemical potential is an essential
ingredient for energy and spin transport in magnetic insulators.",1604.03706v1
2016-04-24,Who pumps spin current into nonmagnetic-metal (NM) layer in YIG/NM multilayers at ferromagnetic resonance?,"Spin pumping in Yttrium-iron-garnet (YIG)/nonmagnetic-metal (NM) layer
systems under ferromagnetic resonance (FMR) conditions is a popular method of
generating spin current in the NM layer. A good understanding of the spin
current source is essential in extracting spin Hall angle of the NM and in
potential spintronics applications. It is widely believed that spin current is
pumped from precessing YIG magnetization into NM layer. Here, by combining
microwave absorption and DC-voltage measurements on YIG/Pt and YIG/NM1/NM2
(NM1=Cu or Al, NM2=Pt or Ta), we unambiguously showed that spin current in NM
came from the magnetized NM surface (in contact with YIG) due to the magnetic
proximity effect (MPE), rather than the precessing YIG magnetization. This
conclusion is reached through our unique detecting method where the FMR
microwave absorption of the magnetized NM surface, hardly observed in the
conventional FMR experiments, was greatly amplified when the electrical
detection circuit was switched on.",1604.07025v1
2016-04-24,Optomagnonics in Magnetic Solids,"Coherent conversion of photons to magnons, and back, provides a natural
mechanism for rapid control of interactions between stationary spins with long
coherence times and high-speed photons. Despite the large frequency difference
between optical photons and magnons, coherent conversion can be achieved
through a three-particle interaction between one magnon and two photons whose
frequency difference is resonant with the magnon frequency, as in optomechanics
with two photons and a phonon. The large spin density of a transparent
ferromagnetic insulator (such as the ferrite yttrium iron garnet) in an optical
cavity provides an intrinsic photon-magnon coupling strength that we calculate
to exceed reported optomechanical couplings. A large cavity photon number and
properly selected cavity detuning produce a predicted effective coupling
strength sufficient for observing electromagnetically induced transparency and
the Purcell effect, and even to reach the ultra-strong coupling regime.",1604.07052v2
2016-04-25,Magnon based logic in a multi-terminal YIG/Pt nanostructure,"Boolean logic is the foundation of modern digital information processing.
Recently, there has been a growing interest in phenomena based on pure spin
currents, which allow to move from charge to spin based logic gates. We study a
proof-of-principle logic device based on the ferrimagnetic insulator Yttrium
Iron Garnet (YIG), with Pt strips acting as injectors and detectors for
nonequilibrium magnons. We experimentally observe incoherent superposition of
magnons generated by different injectors. This allows to implement a fully
functional majority gate, enabling multiple logic operations (AND and OR) in
one and the same device. Clocking frequencies of the order of several GHz and
straightforward down-scaling make our device promising for applications.",1604.07262v1
2016-05-01,Magnetoelectric fields for microwave chirality discrimination in enantiomeric liquids,"Chirality discrimination is of a fundamental interest in biology, chemistry,
and metamaterial studies. In optics, near-field plasmon-resonance spectroscopy
with superchiral probing fields is effectively applicable for analyses of large
biomolecules with chiral properties. We show possibility for microwave
near-field chirality discrimination analysis based on magnon-resonance
spectroscopy. Newly developed capabilities in microwave sensing using
magnetoelectric (ME) probing fields originated from multiresonance
magnetic-dipolar-mode (MDM) oscillations in quasi-2D yttrium-iron-garnet (YIG)
disks, provide a potential for unprecedented measurements of chemical and
biological objects. We report on microwave near-field chirality discrimination
for aqueous D- and L-glucose solutions. The shown ME-field sensing is addressed
to microwave biomedical diagnostics and pathogen detection and to deepening our
understanding of microwave-biosystem interactions. It can be also important for
an analysis and design of microwave chiral metamaterials.",1605.00212v1
2016-05-17,Direct observation of dynamic modes excited in a magnetic insulator by pure spin current,"Excitation of magnetization dynamics by pure spin currents has been recently
recognized as an enabling mechanism for spintronics and magnonics, which allows
implementation of spin-torque devices based on low-damping insulating magnetic
materials. Here we report the first spatially-resolved study of the dynamic
modes excited by pure spin current in nanometer-thick microscopic insulating
Yttrium Iron Garnet disks. We show that these modes exhibit nonlinear
self-broadening preventing the formation of the self-localized magnetic bullet,
which plays a crucial role in the stabilization of the single-mode
magnetization oscillations in all-metallic systems. This peculiarity associated
with the efficient nonlinear mode coupling in low-damping materials can be
among the main factors governing the interaction of pure spin currents with the
dynamic magnetization in high-quality magnetic insulators.",1605.05211v1
2016-05-27,Combined Brillouin light scattering and microwave absorption study of magnon-photon coupling in a split-ring resonator/YIG film system,"Microfocused Brillouin light scattering (BLS) and microwave absorption (MA)
are used to study magnon-photon coupling in a system consisting of a split-ring
microwave resonator and a yttrium iron garnet (YIG) film. The split-ring
resonantor is defined by optical lithography and loaded with a 1 $\mu$m-thick
YIG film grown by liquid phase epitaxy. BLS and MA spectra of the hybrid system
are simultaneously recorded as a function of the applied magnetic field
magnitude and microwave excitation frequency. Strong coupling of the magnon and
photon modes is found with a coupling strength of $g_\text{eff}/2 \pi = 63$
MHz. The combined BLS and MA data allows to study the continuous transition of
the hybridized modes from a purely magnonic to a purely photonic mode by
varying the applied magnetic field and microwave frequency. Furthermore, the
BLS data represent an up-conversion of the microwave frequency coupling to
optical frequencies.",1605.08531v1
2016-05-28,"Magnon Waves on Chains of YIG particles: Dispersion Relations, Faraday Rotation, and Power Transmission","We calculate the dispersion relations for magnon waves on a periodic chain of
spherical or cylindrical Yttrium Iron Garnet (YIG) particles. We use the
quasistatic approximation, appropriate when $kd \ll 1$, where $k$ is the wave
number and $d$ the interparticle spacing. In this regime, because of the
magnetic dipole-dipole interaction between the localized magnetic excitations
on neighboring particles, dispersive magnon waves can propagate along the
chain. The waves are analogous to plasmonic waves generated by electric
dipole-dipole interactions between plasmons on neighboring metallic particles.
The magnon waves can be longitudinal ($L$), transverse ($T$), or elliptically
polarized. We find that a linearly polarized magnon wave undergoes a Faraday
rotation as it propagates along the chain. The amount of Faraday rotation can
be tuned by varying the off-diagonal component of the permeability tensor. We
also discuss the possibility of wireless power transmission along the chain
using these coupled magnon waves.",1605.08931v1
2016-06-10,Indirect Coupling between Two Cavity Photon Systems via Ferromagnetic Resonance,"We experimentally realize indirect coupling between two cavity modes via
strong coupling with the ferromagnetic resonance in Yttrium Iron Garnet (YIG).
We find that some indirectly coupled modes of our system can have a higher
microwave transmission than the individual uncoupled modes. Using a coupled
harmonic oscillator model, the influence of the oscillation phase difference
between the two cavity modes on the nature of the indirect coupling is
revealed. These indirectly coupled microwave modes can be controlled using an
external magnetic field or by tuning the cavity height. This work has potential
for use in controllable optical devices and information processing
technologies.",1606.03469v1
2016-07-06,Temperature dependence of the magnon spin diffusion length and magnon spin conductivity in the magnetic insulator yttrium iron garnet,"We present a systematic study of the temperature dependence of diffusive
magnon spin transport, using a non-local device geometry. In our measurements,
we detect spin signals arising from electrical and thermal magnon generation,
and we directly extract the magnon spin diffusion length $\lambda_m$ for
temperatures from 2 to 293 K. Values of $\lambda_m$ obtained from electrical
and thermal generation agree within the experimental error, with
$\lambda_m=9.6\pm0.9$ $\mu$m at room temperature to a minimum of
$\lambda_m=5.5\pm0.7$ $\mu$m at 30 K. Using a 2D finite element model to fit
the data obtained for electrical magnon generation we extract the magnon spin
conductivity $\sigma_m$ as a function of temperature, which is reduced from
$\sigma_m=5.1\pm0.2\times10^5$ S/m at room temperature to
$\sigma_m=0.7\pm0.4\times10^5$ S/m at 5 K. Finally, we observe an enhancement
of the signal originating from thermally generated magnons for low
temperatures, where a maximum is observed around $T=7$ K. An explanation for
this low temperature enhancement is however still missing and requires
additional investigations.",1607.01506v1
2016-07-08,Observation of the spin Nernst effect,"The observation of the spin Hall effect triggered intense research on pure
spin current transport. With the spin Hall effect, the spin Seebeck effect, and
the spin Peltier effect already observed, our picture of pure spin current
transport is almost complete. The only missing piece is the spin Nernst
(-Ettingshausen) effect, that so far has only been discussed on theoretical
grounds. Here, we report the observation of the spin Nernst effect. By applying
a longitudinal temperature gradient, we generate a pure transverse spin current
in a Pt thin film. For readout, we exploit the
magnetization-orientation-dependent spin transfer to an adjacent Yttrium Iron
Garnet layer, converting the spin Nernst current in Pt into a controlled change
of the longitudinal thermopower voltage. Our experiments show that the spin
Nernst and the spin Hall effect in Pt are of comparable magnitude, but differ
in sign, as corroborated by first-principles calculations.",1607.02277v2
2016-07-08,Control of magnon-photon coupling strength in a planar resonator/YIG thin film configuration,"A systematic study of the coupling at room temperature between ferromagnetic
resonance (FMR) and a planar resonator is presented. The chosen magnetic
material is a ferrimagnetic insulator (Yttrium Iron Garnet: YIG) which is
positioned on top of a stop band (notch) filter based on a stub line
capacitively coupled to a 50 $\Omega$ microstrip line resonating at 4.731 GHz.
Control of the magnon-photon coupling strength is discussed in terms of the
microwave excitation configuration and the YIG thickness from 0.2 to 41 $\mu$m.
From the latter dependence, we extract a single spin-photon coupling of
g$_{0}$/2$\pi$=162$\pm$6 mHz and a maximum of an effective coupling of 290 MHz.",1607.02358v3
2016-07-13,Surface state dominated spin-charge current conversion in topological insulator/ferromagnetic insulator heterostructures,"We report the observation of ferromagnetic resonance-driven spin pumping
signals at room temperature in three-dimensional topological insulator thin
films -- Bi2Se3 and (Bi,Sb)2Te3 -- deposited by molecular beam epitaxy on
yttrium iron garnet thin films. By systematically varying the Bi2Se3 film
thickness, we show that the spin-charge conversion efficiency, characterized by
the inverse Rashba-Edelstein effect length (lambda_IREE), increases
dramatically as the film thickness is increased from 2 quintuple layers,
saturating above 6 quintuple layers. This suggests a dominant role of surface
states in spin and charge interconversion in topological insulator/ferromagnet
heterostructures. Our conclusion is further corroborated by studying a series
of YIG/(BiSb)2Te3 heterostructures. Finally, we use the ferromagnetic resonance
linewidth broadening and the inverse Rashba-Edelstein signals to determine the
effective interfacial spin mixing conductance and lambda_IREE.",1607.03872v1
2016-07-25,Damping of parametrically excited magnons in the presence of the longitudinal spin Seebeck effect,"The impact of the longitudinal spin Seebeck effect (LSSE) on the magnon
damping in magnetic-insulator/nonmagnetic-metal bilayers was recently discussed
in several reports. However, results of those experiments can be blurred by
multimode excitation within the measured linewidth. In order to avoid possible
intermodal interference, we investigated the damping of a single magnon group
in a platinum covered Yttrium Iron Garnet (YIG) film by measurement of the
threshold of its parametric excitation. Both dipolar and exchange spin-wave
branches were probed. It turned out that the LSSE-related modification of
spin-wave damping in a micrometer-thick YIG film is too weak to be observed in
the entire range of experimentally accessible wavevectors. At the same time,
the change in the mean temperature of the YIG layer, which can appear by
applying a temperature gradient, strongly modifies the damping value.",1607.07274v1
2016-08-08,Reconstruction of an effective magnon mean free path distribution from spin Seebeck measurements in thin films,"A thorough understanding of the mean-free-path (MFP) distribution of the
energy carriers is crucial to engineer and tune the transport properties of
materials. In this context, a significant body of work has investigated the
phonon and electron MFP distribution, however, similar studies of the magnon
MFP distribution have not been carried out so far. In this work, we used
thickness-dependence measurements of the longitudinal spin Seebeck (LSSE)
effect of yttrium iron garnet films to reconstruct the cumulative distribution
of a SSE related effective magnon MFP. By using the experimental data reported
by Guo et al. [Phys. Rev. X 6, 031012 (2016)], we adapted the phonon MFP
reconstruction algorithm proposed by A.J. Minnich, [Phys. Rev. Lett. 109,
205901 (2012)] and apply it to magnons. The reconstruction showed that magnons
with different MFP contribute in different manner to the total LSSE and the
effective magnon MFP distribution spreads far beyond their typical averaged
values.",1608.02474v3
2016-09-06,Chiral charge pumping in graphene deposited on a magnetic insulator,"We demonstrate that a sizable chiral charge pumping can be achieved at room
temperature in graphene/Yttrium Iron Garnet (YIG) bilayer systems. The effect,
which cannot be attributed to the ordinary spin pumping, reveals itself in the
creation of a dc electric field/voltage in graphene as a response to the
dynamic magnetic excitations (spin waves) in an adjacent out-of-plane
magnetized YIG film. We show that the induced voltage changes its sign when the
orientation of the static magnetization is reversed, clearly indicating the
broken spatial inversion symmetry in the studied system. The strength of effect
shows a non-monotonous dependence on the spin-wave frequency, in agreement with
the proposed theoretical model.",1609.01613v2
2016-09-26,Magnon Kerr effect in a strongly coupled cavity-magnon system,"We experimentally demonstrate magnon Kerr effect in a cavity-magnon system,
where magnons in a small yttrium iron garnet (YIG) sphere are strongly but
dispersively coupled to the photons in a three-dimensional cavity. When the YIG
sphere is pumped to generate considerable magnons, the Kerr effect yields a
perceptible shift of the cavity's central frequency and more appreciable shifts
of the magnon modes. We derive an analytical relation between the magnon
frequency shift and the drive power for the uniformly magnetized YIG sphere and
find that it agrees very well with the experimental results of the Kittel mode.
Our study paves the way to explore nonlinear effects in the cavity-magnon
system.",1609.07891v2
2016-09-24,Optical manipulation of a magnon-photon hybrid system,"We demonstrate an all-optical method for manipulating the magnetization in a
1-mm YIG (yttrium-iron-garnet) sphere placed in a $\sim0.17\,$T uniform
magnetic field. An harmonic of the frequency comb delivered by a multi-GHz
infrared laser source is tuned to the Larmor frequency of the YIG sphere to
drive magnetization oscillations, which in turn give rise to a radiation field
used to thoroughly investigate the phenomenon. The radiation damping issue that
occurs at high frequency and in the presence of highly magnetizated materials,
has been overcome by exploiting magnon-photon strong coupling regime in
microwave cavities. Our findings demonstrate an effective technique for
ultrafast control of the magnetization vector in optomagnetic materials via
polarization rotation and intensity modulation of an incident laser beam. We
eventually get a second-order susceptibility value of $\sim10^{-7}$ cm$^2$/MW
for single crystal YIG.",1609.08147v1
2016-10-18,Spin transport in antiferromagnetic NiO and magnetoresistance in Y$_3$Fe$_5$O$_{12}$/NiO/Pt structures,"We have studied spin transport and magnetoresistance in yttrium iron garnet
(YIG)/NiO/Pt trilayers with varied NiO thickness. To characterize the spin
transport through NiO we excite ferromagnetic resonance in YIG with a microwave
frequency magnetic field and detect the voltage associated with the inverse
spin-Hall effect (ISHE) in the Pt layer. The ISHE signal is found to decay
exponentially with the NiO thickness with a characteristic decay length of 3.9
nm. This is contrasted with the magnetoresistance in these same structures. The
symmetry of the magnetoresistive response is consistent with spin-Hall
magnetoresistance (SMR). However, in contrast to the ISHE response, as the NiO
thickness increases the SMR signal goes towards zero abruptly at a NiO
thickness of $\simeq$ 4 nm, highlighting the different length scales associated
with the spin-transport in NiO and SMR in such trilayers.",1610.05760v1
2016-10-26,Time-resolved measurements of surface spin-wave pulses at millikelvin temperatures,"In this work, we experimentally investigate the propagation of pulsed
magnetostatic surface spin-wave (magnon) signals in an yttrium iron garnet
(YIG) waveguide at millikelvin temperatures. Our measurements are performed in
a dilution refrigerator at microwave frequencies. The excellent signal-to-noise
ratio afforded by the low-temperature environment allows the propagation of the
pulses to be observed in detail. The work gives insight both into
low-temperature magnon dynamics in YIG and the potential application of systems
of propagating magnons to solid-state quantum information processing.",1610.08402v2
2016-10-27,Spin-wave propagation in ultra-thin YIG based waveguides,"Spin-wave propagation in an assembly of microfabricated 20 nm thick, 2.5
{\mu}m wide Yttrium Iron Garnet (YIG) waveguides is studied using propagating
spin-wave spectroscopy (PSWS) and phase resolved micro-focused Brillouin Light
Scattering ({\mu}-BLS) spectroscopy. We show that spin-wave propagation in 50
parallel waveguides is robust against microfabrication induced imperfections.
Spin-wave propagation parameters are studied in a wide range of excitation
frequencies for the Damon-Eshbach (DE) configuration. As expected from its low
damping, YIG allows the propagation of spin waves over long distances (the
attenuation lengths is 25 {\mu}m at \mu$_{0}$H = 45 mT). Direct mapping of spin
waves by {\mu}-BLS allows us to reconstruct the spin-wave dispersion relation
and to confirm the multi-mode propagation in the waveguides, glimpsed by
propagating spin-wave spectroscopy.",1610.08756v1
2016-10-27,Observation of Self-Cavitating Envelope Dispersive Shock Waves in Yttrium Iron Garnet Thin Films,"The formation and properties of envelope dispersive shock wave (DSW)
excitations from repulsive nonlinear waves in a magnetic film are studied.
Experiments involve the excitation of a spin-wave step pulse in a low-loss
magnetic Y$_3$Fe$_5$O$_{12}$ thin film strip, in which the spin-wave amplitude
increases rapidly, realizing the canonical Riemann problem of shock theory.
Under certain conditions, the envelope of the spin-wave pulse evolves into a
DSW that consists of an expanding train of nonlinear oscillations with
amplitudes increasing from front to back, terminated by a black soliton. The
onset of DSW self-cavitation, indicated by a point of zero power and a
concomitant 180 phase jump, is observed for sufficiently large steps,
indicative of the bidirectional dispersive hydrodynamic nature of the DSW. The
experimental observations are interpreted with theory and simulations of the
nonlinear Schr\""odinger equation.",1610.08846v3
2016-10-29,Tailoring magnetic insulator proximity effects in graphene: First-principles calculations,"We report a systematic first-principles investigation of the influence of
different magnetic insulators on the magnetic proximity effect induced in
graphene. Four different magnetic insulators are considered: two ferromagnetic
europium chalcogenides namely EuO and EuS and two ferrimagnetic insulators
yttrium iron garnet (YIG) and cobalt ferrite (CFO). The obtained
exchange-splitting varies from tens to hundreds of meV. We also find an
electron doping induced by YIG and europium chalcogenides substrates, that
shift the Fermi level up to 0.78 eV and 1.3 eV respectively, whereas hole
doping up to 0.5 eV is generated by CFO. Furthermore, we study the variation of
the extracted exchange and tight binding parameters as a function of the EuO
and EuS thicknesses. We show that those parameters are robust to thickness
variation such that a single monolayer of magnetic insulator can induce a large
magnetic proximity effect on graphene. Those findings pave the way towards
possible engineering of graphene spin-gating by proximity effect especially in
view of recent experiments advancement.",1610.09554v1
2016-10-31,Strong coupling of magnons in a YIG sphere to photons in a planar superconducting resonator in the quantum limit,"We report measurements of a superconducting coplanar waveguide resonator
(CPWR) coupled to a sphere of yttrium-iron garnet. The non-uniform CPWR field
allows us to excite various magnon modes in the sphere. Mode frequencies and
relative coupling strengths are consistent with theory. Strong coupling is
observed to several modes even with, on average, less than one excitation
present in the CPWR. The time response to square pulses shows oscillations at
the mode splitting frequency. These results indicate the feasibility of
combining magnonic and planar superconducting quantum devices.",1610.09963v2
2016-11-18,Temporal evolution of auto-oscillations in a YIG/Pt microdisc driven by pulsed spin Hall effect-induced spin-transfer torque,"The temporal evolution of pulsed Spin Hall Effect - Spin Transfer Torque
(SHE-STT) driven auto-oscillations in a Yttrium Iron Garnet (YIG) / platinum
(Pt) microdisc is studied experimentally using time-resolved Brillouin Light
Scattering (BLS) spectroscopy. It is demonstrated that the frequency of the
auto-oscillations is different in the center and at the edge of the
investigated disc that is related to the simultaneous STT excitation of a
bullet and a non-localized spin-wave mode. Furthermore, the magnetization
precession intensity is found to saturate on a time scale of 20 ns or longer,
depending on the current density. For this reason, our findings suggest that a
proper ratio between the current and the pulse duration is of crucial
importance for future STT-based devices.",1611.06054v1
2016-12-15,Theory of the Spin Seebeck Effect at a Topological-Insulator/Ferromagnetic-Insulator Interface,"The spin-Seebeck effect refers to voltage signals induced in metals by
thermally driven spin currents in adjacent magnetic systems. We present a
theory of the spin-Seebeck signal in the case where the conductor that supports
the voltage signal is the topologically protected two-dimensional surface-state
system at the interface between a ferromagnetic insulator (FI) and a
topological insulator (TI). Our theory uses a Dirac model for the TI
surface-states and assumes Heisenberg exchange coupling between the TI
quasiparticles and the FI magnetization. The spin-Seebeck voltage is induced by
the TI surface states scattering off the nonequilibrium magnon population at
the surface of the semi-infinite thermally driven FI. Our theory is readily
generalized to spin-Seebeck voltages in any two-dimensional conductor that is
exchange-coupled to the surface of a FI. Surface-state
carrier-density-dependent signal strengths calculated using Bi$_2$Te$_3$ and
yttrium iron garnet material parameters are consistent with recent experiments.",1612.04916v3
2016-12-18,Bottleneck accumulation of hybrid magneto-elastic bosons,"It is known that an ensemble of magnons, quanta of spin waves, can be
prepared as a Bose gas of weakly interacting quasiparticles with conservation
of the particle number. Furthermore, the thermalization of the overpopulated
magnon gas can lead to the formation of a Bose-Einstein condensate at the
bottom of a spin-wave spectrum. However, magnon-phonon scattering processes can
significantly modify this scenario and new quasiparticles are formed -
magneto-elastic bosons. Our observations of a parametrically populated magnon
gas in a single-crystal film of Yttrium Iron Garnet by means of
wavevector-resolved Brillouin light scattering spectroscopy including
magneto-elastic coupling resulted in the discovery of a novel condensation
phenomenon: A spontaneous accumulation of hybrid magneto-elastic bosonic
quasiparticles at the intersection of the lowest magnon mode and a transversal
acoustic wave.",1612.05925v1
2016-12-21,Pure spin current transport in gallium doped zinc oxide,"We study the flow of a pure spin current through zinc oxide by measuring the
spin Hall magnetoresistance (SMR) in thin film trilayer samples consisting of
bismuth-substituted yttrium iron garnet (Bi:YIG), gallium-doped zinc oxide
(Ga:ZnO), and platinum. We investigate the dependence of the SMR magnitude on
the thickness of the Ga:ZnO interlayer and compare to a Bi:YIG/Pt bilayer. We
find that the SMR magnitude is reduced by almost one order of magnitude upon
inserting a Ga:ZnO interlayer, and continuously decreases with increasing
interlayer thickness. Nevertheless, the SMR stays finite even for a
$12\;\mathrm{nm}$ thick Ga:ZnO interlayer. These results show that a pure spin
current indeed can propagate through a several nm-thick degenerately doped zinc
oxide layer. We also observe differences in both the temperature and the field
dependence of the SMR when comparing tri- and bilayers. Finally, we compare our
data to predictions of a model based on spin diffusion. This shows that
interface resistances play a crucial role for the SMR magnitude in these
trilayer structures.",1612.07239v1
2016-12-15,Experimental prototype of a spin-wave majority gate,"Featuring low heat dissipation, devices based on spin-wave logic gates
promise to comply with increasing future requirements in information
processing. In this work, we present the experimental realization of a majority
gate based on the interference of spin waves in an Yttrium-Iron-Garnet-based
waveguiding structure. This logic device features a three-input combiner with
the logic information encoded in the phase of the spin waves. We show that the
phase of the output signal represents the majority of the phase of the input
signals. A switching time of about 10 ns in the prototype device provides
evidence for the ability of sub-nanosecond data processing in future
down-scaled devices.",1612.07708v1
2017-02-03,Quantitative investigation of the inverse Rashba-Edelstein effect in Bi/Ag and Ag/Bi on YIG,"The inverse Rashba-Edelstein effect (IREE) is a spin conversion mechanism
that recently attracts attention in spintronics and condensed matter physics.
In this letter, we report an investigation of the IREE in Bi/Ag by using
ferrimagnetic insulator yttrium iron garnet (YIG). We prepared two types of
samples with opposite directions of the Rashba field by changing a stacking
order of Bi and Ag. An electric current generated by the IREE was observed from
both stacks, and an efficiency of spin conversion -characterized by the IREE
length- was estimated by taking into account a number of contributions left out
in previous studies. This study provides a further insight into the IREE spin
conversion mechanism: important step towards achieving efficient spin-charge
conversion devices.",1702.00890v1
2017-02-08,Magnon-polaron transport in magnetic insulators,"We theoretically study the effects of strong magnetoelastic coupling on the
transport properties of magnetic insulators. We develop a Boltzmann transport
theory for the mixed magnon-phonon modes (magnon polarons) and determine
transport coefficients and spin diffusion length. Magnon-polaron formation
causes anomalous features in the magnetic field and temperature dependence of
the spin Seebeck effect when the disorder scattering in the magnetic and
elastic subsystems is sufficiently different. Experimental data by Kikkawa et
al. [PRL 117, 207203 (2016)] on yttrium iron garnet films can be explained by
an acoustic quality that is much better than the magnetic quality of the
material. We predict similar anomalous features in the spin and heat
conductivity and non-local spin transport experiments.",1702.02270v1
2017-02-20,Parametric pumping of spin waves by acoustic waves,"The linear and nonlinear interactions between spin waves (magnons) and
acoustic waves (phonons) in magnetostrictive materials provide an exciting
opportunity for realizing novel microwave signal processing devices and
spintronic circuits. Here we demonstrate the parametric pumping of spin waves
by acoustic waves, the possibility of which has long been theoretically
anticipated but never experimentally realized. Spin waves propagating in a thin
film of yttrium iron garnet (YIG), a magnetostrictive ferrimagnet with low spin
and acoustic wave damping, are pumped using an acoustic resonator driven at
frequencies near twice the spin wave frequency. The observation of a
counter-propagating idler wave and a distinct pump threshold that increases
quadratically with frequency non-degeneracy are evidence of a nonlinear
parametric pumping process consistent with classical theory. This demonstration
of acoustic parametric pumping lays the groundwork for developing new
spintronic and microwave signal processing devices based on amplification and
manipulation of spin waves by efficient, spatially localized acoustic
transducers.",1702.06038v1
2017-02-22,Is spin superfluidity possible in YIG films?,"Recently it was suggested that stationary spin supercurrents (spin
superfluidity) are possible in the magnon condensate observed in
yttrium-iron-garnet (YIG) magnetic films under strong external pumping. Here we
analyze this suggestion. From topology of the equilibrium order parameter in
YIG one must not expect energetic barriers making spin supercurrents
metastable. However some small barriers of dynamical origin are possible
nevertheless. The critical phase gradient (analog of the Landau critical
velocity in superfluids) is proportional to intensity of the coherent spin wave
(number of condensed magnons). The conclusion is that although spin
superfluidity in YIG films is possible in principle, the published claim of its
observation is not justified.
  The analysis revealed that the widely accepted spin-wave spectrum in YIG
films with magnetostatic and exchange interaction required revision. This led
to revision of non-linear corrections, which determine stability of the magnon
condensate with and without spin supercurrents.",1702.06994v2
2017-05-05,Nano-patterned magnonic crystals based on ultrathin YIG films,"We demonstrate a microscopic magnonic-crystal waveguide produced by
nano-patterning of a 20 nm thick film of Yttrium Iron Garnet. By using the
phase-resolved micro-focus Brillouin light scattering spectroscopy, we map the
intensity and the phase of spin waves propagating in such a periodic magnetic
structure. Based on these maps, we obtain the dispersion and the attenuation
characteristics of spin waves providing detailed information about the physics
of spin-wave propagation in the magnonic crystal. We show that, in contrast to
the simplified physical picture, the maximum attenuation of spin waves is
achieved close to the edge of the magnonic band gap, which is associated with
non-trivial reflection characteristics of spin waves in non-uniform field
potentials.",1705.02267v1
2017-05-09,Low spin wave damping in the insulating chiral magnet Cu$_{2}$OSeO$_{3}$,"Chiral magnets with topologically nontrivial spin order such as Skyrmions
have generated enormous interest in both fundamental and applied sciences. We
report broadband microwave spectroscopy performed on the insulating chiral
ferrimagnet Cu$_{2}$OSeO$_{3}$. For the damping of magnetization dynamics we
find a remarkably small Gilbert damping parameter of about $1\times10^{-4}$ at
5 K. This value is only a factor of 4 larger than the one reported for the best
insulating ferrimagnet yttrium iron garnet. We detect a series of sharp
resonances and attribute them to confined spin waves in the mm-sized samples.
Considering the small damping, insulating chiral magnets turn out to be
promising candidates when exploring non-collinear spin structures for high
frequency applications.",1705.03416v1
2017-06-06,Observation of spin superfluidity: YIG magnetic films and beyond,"From topology of the order parameter of the magnon condensate observed in
yttrium-iron-garnet (YIG) magnetic films one must not expect energetic barriers
making spin supercurrents metastable. But we show that some barriers of
dynamical origin are possible nevertheless until the gradient of the phase
(angle of spin precession) does not exceed the critical value (analog of the
Landau critical velocity in superfluids). On the other hand, recently published
claims of experimental detection of spin superfluidity in YIG films and
antiferromagnets are not justified, and spin superfluidity in magnetically
ordered solids has not yet been experimentally confirmed.",1706.01932v2
2017-06-11,Absorbing boundary layers for spin wave micromagnetics,"Micromagnetic simulations are used to investigate the effects of different
absorbing boundary layers (ABLs) on spin waves (SWs) reflected from the edges
of a magnetic nano-structure. We define the conditions that a suitable ABL must
fulfill and compare the performance of abrupt, linear, polynomial and tan
hyperbolic damping profiles in the ABL. We first consider normal incidence in a
permalloy stripe and propose a transmission line model to quantify reflections
and calculate the loss introduced into the stripe due to the ABL. We find that
a parabolic damping profile absorbs the SW energy efficiently and has a low
reflection coefficient, thus performing much better than the commonly used
abrupt damping profile. We then investigated SWs that are obliquely incident at
26.6, 45 and 63.4 degrees on the edge of a yttrium-iron-garnet film. The
parabolic damping profile again performs efficiently by showing a high SW
energy transfer to the ABL and a low reflected SW amplitude.",1706.03325v1
2017-07-20,Bistability of Cavity Magnon Polaritons,"We report the first observation of the magnon-polariton bistability in a
cavity magnonics system consisting of cavity photons strongly interacting with
the magnons in a small yttrium iron garnet (YIG) sphere. The bistable behaviors
are emerged as sharp frequency switchings of the cavity magnon-polaritons
(CMPs) and related to the transition between states with large and small number
of polaritons. In our experiment, we align, respectively, the [100] and [110]
crystallographic axes of the YIG sphere parallel to the static magnetic field
and find very different bistable behaviors (e.g., clockwise and
counter-clockwise hysteresis loops) in these two cases. The experimental
results are well fitted and explained as being due to the Kerr nonlinearity
with either positive or negative coefficient. Moreover, when the magnetic field
is tuned away from the anticrossing point of CMPs, we observe simultaneous
bistability of both magnons and cavity photons by applying a drive field on the
lower branch.",1707.06509v2
2017-09-16,Visualization of Anomalous Ettingshausen Effect in a Ferromagnetic Film: Direct Evidence of Different Symmetry from Spin Peltier Effect,"Spatial distribution of temperature modulation due to anomalous Ettingshausen
effect (AEE) is visualized in a ferromagnetic FePt thin film with in-plane and
out-of-plane magnetizations using the lock-in thermography technique. Comparing
the AEE of FePt with the spin Peltier effect (SPE) of a Pt / yttrium iron
garnet junction provides direct evidence of different symmetries of AEE and
SPE. Our experiments and numerical calculations reveal that the distribution of
heat sources induced by AEE strongly depends on the direction of magnetization,
leading to the remarkable different temperature profiles in the FePt thin film
between the in-plane and perpendicularly magnetized configurations.",1709.05449v1
2017-10-11,Approaching quantum anomalous Hall effect in proximity-coupled YIG/graphene/h-BN sandwich structure,"Quantum anomalous Hall state is expected to emerge in Dirac electron systems
such as graphene under both sufficiently strong exchange and spin-orbit
interactions. In pristine graphene, neither interaction exists; however, both
interactions can be acquired by coupling graphene to a magnetic insulator (MI)
as revealed by the anomalous Hall effect. Here, we show enhanced magnetic
proximity coupling by sandwiching graphene between a ferrimagnetic insulator
yttrium iron garnet (YIG) and hexagonal-boron nitride (h-BN) which also serves
as a top gate dielectric. By sweeping the top-gate voltage, we observe Fermi
level-dependent anomalous Hall conductance. As the Dirac point is approached
from both electron and hole sides, the anomalous Hall conductance reaches 1/4
of the quantum anomalous Hall conductance 2e2/h. The exchange coupling strength
is determined to be as high as 27 meV from the transition temperature of the
induced magnetic phase. YIG/graphene/h-BN is an excellent heterostructure for
demonstrating proximity-induced interactions in two-dimensional electron
systems.",1710.04179v1
2017-10-18,Strong Coupling of 3D Cavity Photons to Travelling Magnons At Low Temperatures,"We demonstrate strong coupling between travelling magnons in an Yttrium Iron
Garnet film and 3D microwave cavity photons at milli-Kelvin temperatures. The
coupling strength of $350$MHz or $7.3$\% of resonance frequency is observed.
The magnonic subsystem is represented by the Damon-Eshbach magnetostatic
surface wave with a distribution of wave numbers giving the linewidth of 15MHz.
The ways to improve this parameter are discussed. The energy gap in the
spectrum given by the Zeeman energy and the shape-anisotropy energy in the film
geometry give rise to a significant asymmetry of the double peak structure of
the photon-magnon avoided level crossing. A structure of two parallel YIG films
is investigated using the same re-entrant magnetostatic surface wave transducer
revealing a higher order magnon modes existing in both films. Combination of a
multi-post re-entrant cavity and multiple films is a potential base for
engineering both magnon and photon spectra.",1710.06601v1
2017-11-01,Spin current noise of the spin Seebeck effect and spin pumping,"We theoretically investigate the fluctuation of a pure spin current induced
by the spin Seebeck effect and spin pumping in a normal metal (NM)/ferromagnet
(FM) bilayer system. Starting with a simple FI--NM interface model with both
spin-conserving and spin-non-conserving processes, we derive general
expressions of the spin current and the spin-current noise at the interface
within second-order perturbation of the FI--NM coupling strength, and estimate
them for an yttrium iron garnet (YIG) --platinum interface. We show that the
spin-current noise can be used to determine the effective spin carried by a
magnon, modified by the spin-non-conserving process at the interface. In
addition, we show that it provides information on the effective spin of a
magnon, heating at the interface under spin pumping, and spin Hall angle of the
NM.",1711.00237v2
2017-11-02,Measurement of a Magnonic Crystal at Millikelvin Temperatures,"Hybrid systems combining magnons and superconducting quantum circuits have
attracted increasing interest in recent years. Magnonic crystals (MCs) are one
of the building blocks of room-temperature magnonics and can be used to create
devices with an engineered band structure. These devices, exhibiting tunable
frequency selectivity and the ability to store travelling excitations in the
microwave regime, may form the basis of a set of new tools to be used in the
context of quantum information processing. In order to ascertain the
feasibility of such plans, MCs must be demonstrated to work at the low
temperatures required for microwave-frequency quantum experiments. We report
the first measurements of the transmission of microwave signals through an MC
at 20 mK and observe a magnonic bandgap in both continuous-wave and pulsed
excitation experiments. The spin-wave damping at low temperatures in our
yttrium iron garnet MC is higher than expected, indicating that further work is
necessary before the full potential of quantum experiments using magnonic
crystals can be realised.",1711.00958v2
2017-12-07,Spin waves in coupled YIG/Co heterostructures,"We investigate yttrium iron garnet (YIG)/cobalt (Co) heterostructures using
broadband ferromagnetic resonance (FMR). We observe an efficient excitation of
perpendicular standing spin waves (PSSWs) in the YIG layer when the resonance
frequencies of the YIG PSSWs and the Co FMR line coincide. Avoided crossings of
YIG PSSWs and the Co FMR line are found and modeled using mutual spin pumping
and exchange torques. The excitation of PSSWs is suppressed by a thin aluminum
oxide (AlOx) interlayer but persists with a copper (Cu) interlayer, in
agreement with the proposed model.",1712.02561v1
2018-03-30,From Kinetic Instability to Bose-Einstein Condensation and Magnon Supercurrents,"Evolution of an overpopulated gas of magnons to a Bose-Einstein condensate
and excitation of a magnon supercurrent, propelled by a phase gradient in the
condensate wave function, can be observed at room-temperature by means of the
Brillouin light scattering spectroscopy in an yttrium iron garnet material. We
study these phenomena in a wide range of external magnetic fields in order to
understand their properties when externally pumped magnons are transferred
towards the condensed state via two distinct channels: A multistage
Kolmogorov-Zakharov cascade of the weak-wave turbulence or a one-step
kinetic-instability process. Our main result is that opening the kinetic
instability channel leads to the formation of a much denser magnon condensate
and to a stronger magnon supercurrent compared to the cascade mechanism alone.",1803.11548v1
2018-04-03,Selection rules for cavity-enhanced Brillouin light scattering from magnetostatic modes,"We experimentally identify the magnetostatic modes active for Brillouin light
scattering in the optical whispering gallery modes of a yttrium iron garnet
sphere. Each mode is identified by magnetic field dispersion of
ferromagnetic-resonance spectroscopy and coupling strength to the known field
distribution of the microwave drive antenna. Our optical measurements confirm
recent predictions that higher-order magnetostatic modes can also generate
optical scattering, according to the selection rules derived from the axial
symmetry. From this we summarize the selection rules for Brillouin light
scattering. We give experimental evidence that the optomagnonic coupling to
non-uniform magnons can be higher than that of the uniform Kittel mode.",1804.00965v2
2018-04-08,Optical cooling of magnons,"Inelastic scattering of light by spin waves generates an energy flow between
the light and magnetization fields, a process that can be enhanced and
controlled by concentrating the light in magneto-optical resonators. Here, we
model the cooling of a sphere made of a magnetic insulator, such as yttrium
iron garnet (YIG), using a monochromatic laser source. When the magnon
lifetimes are much larger than the optical ones, we can treat the latter as a
Markovian bath for magnons. The steady-state magnons are canonically
distributed with a temperature that is controlled by the light intensity. We
predict that such a cooling process can significantly reduce the temperature of
the magnetic order within current technology.",1804.02683v1
2018-04-10,Microwave cavity tuned with liquid metal and its application to Electron Paramagnetic Resonance,"This note presents a method to tune the resonant frequency $f_{0}$ of a
rectangular microwave cavity. This is achieved using a liquid metal, GaInSn, to
decrease the volume of the cavity. It is possible to shift $f_{0}$ by filling
the cavity with this alloy, in order to reduce the relative distance between
the internal walls. The resulting modes have resonant frequencies in the range
$7\div8\,$GHz. The capability of the system of producing an Electron
Paramagnetic Resonance (EPR) measurement has been tested by placing a 1 mm
diameter Yttrium Iron Garnet (YIG) sphere inside the cavity, and producing a
strong coupling between the cavity resonance and Kittel mode. This work shows
the possibility to tune a resonant system in the GHz range, which can be useful
for several applications.",1804.03443v1
2018-04-12,Spin colossal magnetoresistance in an antiferromagnetic insulator,"Colossal magnetoresistance (CMR) refers to a large change in electrical
conductivity induced by a magnetic field in the vicinity of a metal-insulator
transition and has inspired extensive studies for decades\cite{Ramirez1997,
Tokura2006}. Here we demonstrate an analogous spin effect near the N\'eel
temperature $T_{\rm{N}}$=296 K of the antiferromagnetic insulator \CrO. Using a
yttrium iron garnet \YIG/\CrO/Pt trilayer, we injected a spin current from the
YIG into the \CrO layer, and collected via the inverse spin Hall effect the
signal transmitted in the heavy metal Pt. We observed a change by two orders of
magnitude in the transmitted spin current within 14 K of the N\'eel
temperature. This transition between spin conducting and nonconducting states
could be also modulated by a magnetic field in isothermal conditions. This
effect, that we term spin colossal magnetoresistance (SCMR), has the potential
to simplify the design of fundamental spintronics components, for instance
enabling the realization of spin current switches or spin-current based
memories.",1804.04516v1
2018-04-30,Single-Nitrogen-vacancy-center quantum memory for a superconducting flux qubit mediated by a ferromagnet,"We propose a quantum memory scheme to transfer and store the quantum state of
a superconducting flux qubit (FQ) into the electron spin of a single
nitrogen-vacancy (NV) center in diamond via yttrium iron garnet (YIG), a
ferromagnet. Unlike an ensemble of NV centers, the YIG moderator can enhance
the effective FQ-NV-center coupling strength without introducing additional
appreciable decoherence. We derive the effective interaction between the FQ and
the NV center by tracing out the degrees of freedom of the collective mode of
the YIG spins. We demonstrate the transfer, storage, and retrieval procedures,
taking into account the effects of spontaneous decay and pure dephasing. Using
realistic experimental parameters for the FQ, NV center and YIG, we find that a
combined transfer, storage, and retrieval fidelity higher than 0.9, with a long
storage time of 10 ms, can be achieved. This hybrid system not only acts as a
promising quantum memory, but also provides an example of enhanced coupling
between various systems through collective degrees of freedom.",1804.11231v1
2018-05-29,Efficient injection and detection of out-of-plane spins via the anomalous spin Hall effect in permalloy nanowires,"We report a novel mechanism for the electrical injection and detection of
out-of-plane spin accumulation via the anomalous spin Hall effect (ASHE), where
the direction of the spin accumulation can be controlled by manipulating the
magnetization of the ferromagnet. This mechanism is distinct from the spin Hall
effect (SHE), where the spin accumulation is created along a fixed direction
parallel to an interface. We demonstrate this unique property of the ASHE in
nanowires made of permalloy (Py), to inject and detect out-of-plane spin
accumulation in a magnetic insulator, yttrium iron garnet (YIG). We show that
the efficiency for the injection/detection of out-of-plane spins can be up to
50% of that of in-plane spins. We further report the possibility to detect spin
currents parallel to the Py/YIG interface for spins fully oriented in the
out-of-plane direction, resulting in a sign reversal of the non-local magnon
spin signal. The new mechanisms that we have demonstrated are highly relevant
for spin torque devices and applications.",1805.11575v1
2018-06-12,Resonant spin wave excitation in magnetoplasmonic bilayers by short laser pulses,"In magnetically ordered solids a static magnetic field can be generated by
virtue of the transverse magneto-optical Kerr effect (TMOKE). Moreover, the
latter was shown to be dramatically enhanced due to the optical excitation of
surface plasmons in nanostructures with relatively small optical losses. In
this paper we suggest a new method of resonant optical excitations in a
prototypical bilayer composed of noble metal (Au) with grating and a
ferromagnet thin film of yttrium iron garnet (YIG) via frequency comb. Based on
magnetization dynamics simulations we show that for the frequency comb with the
parameters, chosen in resonant with spin-wave excitations of YIG, TMOKE is
drastically enhanced, hinting towards possible technological applications in
the optical control of spintronics systems.",1806.04764v1
2018-06-27,Boltzmann approach to the longitudinal spin Seebeck effect,"We develop a Boltzmann transport theory of coupled magnon-phonon transport in
ferromagnetic insulators. The explicit treatment of the magnon-phonon coupling
within the Boltzmann approach allows us to calculate the low-temperature
magnetic-field dependence of the spin-Seebeck voltage. Within the Boltzmann
theory we find that this magnetic field dependence shows similar features as
found by Flebus et al. [Phys. Rev. B 95, 144420 (2017)] for a strongly coupled
magnon phonon system that forms magnon-polarons, and consistent with
experimental findings in yttrium iron garnet by Kikkawa et al. [Phys. Rev.
Lett. 117, 207203 (2016)]. In addition to the anomalous magnetic-field
dependence of the spin Seebeck effect, we also predict a dependence on the
system size.",1806.10445v1
2018-07-03,Spin pinning and spin-wave dispersion in nanoscopic ferromagnetic waveguides,"Spin waves are investigated in Yttrium Iron Garnet (YIG) waveguides with a
thickness of 39 nm and widths ranging down to 50 nm, i.e., with aspect ratios
thickness over width approaching unity, using Brillouin Light Scattering
spectroscopy. The experimental results are verified by a semi-analytical theory
and micromagnetic simulations. A critical width is found, below which the
exchange interaction suppresses the dipolar pinning phenomenon. This changes
the quantization criterion for the spin-wave eigenmodes and results in a
pronounced modification of the spin-wave characteristics. The presented
semi-analytical theory allows for the calculation of spin-wave mode profiles
and dispersion relations in nano-structures.",1807.01358v3
2018-07-23,Bias dependent spin injection into graphene on YIG through bilayer hBN tunnel barriers,"We study the spin injection efficiency into single and bilayer graphene on
the ferrimagnetic insulator Yttrium-Iron-Garnet (YIG) through an exfoliated
tunnel barrier of bilayer hexagonal boron nitride (hBN). The contacts of two
samples yield a resistance-area product between 5 and 30 k$\Omega\mu$m$^2$.
Depending on an applied DC bias current, the magnitude of the non-local spin
signal can be increased or suppressed below the noise level. The spin injection
efficiency reaches values from -60% to +25%. The results are confirmed with
both spin valve and spin precession measurements. The proximity induced
exchange field is found in sample A to be (85 $\pm$ 30) mT and in sample B
close to the detection limit. Our results show that the exceptional spin
injection properties of bilayer hBN tunnel barriers reported by Gurram et al.
are not limited to fully encapsulated graphene systems but are also valid in
graphene/YIG devices. This further emphasizes the versatility of bilayer hBN as
an efficient and reliable tunnel barrier for graphene spintronics.",1807.08481v1
2018-07-24,Enhanced magnon spin transport in NiFe$_2$O$_4$ thin films on a lattice-matched substrate,"We investigate magnon spin transport in epitaxial nickel ferrite
(NiFe$_2$O$_4$, NFO) films grown on magnesium gallate spinel (MgGa$_2$O$_4$,
MGO) substrates, which have a lattice mismatch with NFO as small as 0.78%,
resulting in the reduction of antiphase boundary defects and thus in improved
magnetic properties in the NFO films. In the nonlocal transport experiments,
enhanced signals are observed for both electrically and thermally excited
magnons, and the magnon relaxation length ($\lambda_m$) of NFO is found to be
around 2.5 $\mu$m at room temperature. Moreover, at both room and low
temperatures, we present distinct features from the nonlocal spin Seebeck
signals which arise from magnon polaron formation. Our results demonstrate
excellent magnon transport properties (magnon spin conductivity, $\lambda_m$
and spin mixing conductance at the interface between Pt) of NFO films grown on
a lattice-matched substrate that are comparable with those of yttrium iron
garnet.",1807.09013v1
2018-10-01,Stabilizing Mechanism for Bose-Einstein Condensation of Interacting Magnons in Ferrimagnets and Ferromagnets,"We propose a stabilizing mechanism for the Bose-Einstein condensation (BEC)
of interacting magnons in ferrimagnets and ferromagnets. By studying the
effects of the magnon-magnon interaction on the stability of the magnon BEC in
a ferrimagnet and two ferromagnets, we show that the magnon BEC remains stable
even in the presence of the magnon-magnon interaction in the ferrimagnet and
ferromagnet with a sublattice structure, whereas it becomes unstable in the
ferromagnet without a sublattice structure. This indicates that the existence
of a sublattice structure is the key to stabilizing the BEC of interacting
magnons, and the difference between the spin alignments of a ferrimagnet and a
ferromagnet is irrelevant. Our result can resolve a contradiction between
experiment and theory in the magnon BEC of yttrium iron garnet. Our theoretical
framework may provide a starting point for understanding the physics of the
magnon BEC including the interaction effects.",1810.00584v2
2018-10-17,Conventional magnon BEC in YIG film,"The conventional magnon Bose-Einstein condensation (BEC of magnons with k =
0) is a coherent state of excited magnons described by a common wave function.
It was observed first in antiferromagnetic superfluid states of 3He. Here we
report on the discovery of a very similar magnon BEC in ferrimagnetic film at
room temperature. The experiments were performed in Yttrium Iron Garnet (YIG)
films at a magnetic field oriented perpendicular to the film. The high-density
quasiequilibrium state of excited magnon was formed by methods of pulse and/or
Continuous Waves (CW) magnetic resonance. We have observed a Long Lived
Induction Decay Signals (LLIDS), well known as a signature of spin
superfluidity. We demonstrate that the BEC state may maintain permanently by
continuous replenishment of magnons with a small radiofrequency (RF) field. Our
finding opens the way for development of potential supermagnonic applications
at an ambient conditions.",1810.08051v2
2018-10-23,Higher-order exceptional point in a cavity magnonics system,"We propose to realize the pseudo-Hermiticity in a cavity magnonics system
consisting of the Kittel modes in two small yttrium-iron-garnet spheres coupled
to a microwave cavity mode. The effective gain of the cavity can be achieved
using the coherent perfect absorption of the two input fields fed into the
cavity. With certain constraints of the parameters, the Hamiltonian of the
system has the pseudo-Hermiticity and its eigenvalues can be either all real or
one real and other two constituting a complex-conjugate pair. By varying the
coupling strengths between the two Kittel modes and the cavity mode, we find
the existence of the third-order exceptional point in the parameter space, in
addition to the usual second-order exceptional point existing in the system
with parity-time symmetry. Also, we show that these exceptional points can be
demonstrated by measuring the output spectrum of the cavity.",1810.09689v3
2018-10-27,Microwave control of thermal magnon spin transport,"We observe that an rf microwave field strongly influences the transport of
incoherent thermal magnons in yttrium iron garnet. Ferromagnetic resonance in
the nonlinear regime suppresses thermal magnon transport by 95%. The transport
is also modulated at non-resonant conditions in two cases, both related to the
magnon band minimum. Firstly, a strong enhancement of the nonlocal signal
appears at a static magnetic field below the resonance condition. This increase
only occurs at one field polarity and can be as large as 800%. We attribute
this effect to magnon kinetic processes, which give rise to band-minimum
magnons and high-energy chiral surface modes. Secondly, the signal increases at
a static field above the resonance condition, where the rf frequency coincides
with the magnon band minimum. Our study gives insight into the interplay
between coherent and incoherent spin dynamics: The rf field modifies the
occupation of relevant magnon states and, via kinetic processes, the magnon
spin transport.",1810.11667v1
2018-11-14,Tunable space-time crystal in room-temperature magnetodielectrics,"We report the experimental realization of a space-time crystal with tunable
periodicity in time and space in the magnon Bose-Einstein Condensate (BEC),
formed in a room-temperature Yttrium Iron Garnet (YIG) film by radio-frequency
space-homogeneous magnetic field. The magnon BEC is prepared to have a well
defined frequency and non-zero wavevector. We demonstrate how the crystalline
""density"" as well as the time and space textures of the resulting crystal may
be tuned by varying the experimental parameters: external static magnetic
field, temperature, thickness of the YIG film and power of the radio-frequency
field. The proposed space-time crystals provide a new dimension for exploring
dynamical phases of matter and can serve as a model nonlinear Floquet system,
that brings in touch the rich fields of classical nonlinear waves, magnonics
and periodically driven systems.",1811.05801v1
2018-11-14,Anomalous Hall-like transverse magnetoresistance in Au thin films on Y$_3$Fe$_5$O$_{12}$,"Anomalous Hall-like signals in platinum in contact with magnetic insulators
are common observations that could be explained by either proximity
magnetization or spin Hall magnetoresistance. In this work, longitudinal and
transverse magnetoresistances are measured in a pure gold thin film on the
ferrimagnetic insulator Y$_3$Fe$_5$O$_{12}$ (Yttrium Iron Garnet, YIG). We show
that both the longitudinal and transverse magnetoresistances have
quantitatively consistent scaling in YIG/Au and in a YIG/Pt reference system
when applying the Spin Hall magnetoresistance framework. No contribution of an
anomalous Hall effect due to the magnetic proximity effect is evident.",1811.05848v1
2018-12-04,Spin transport in a magnetic insulator with zero effective damping,"Applications based on spin currents strongly profit from the control and
reduction of their effective damping and their transport properties. We here
experimentally observe magnon mediated transport of spin (angular) momentum
through a 13.4 nm thin yttrium iron garnet film with full control of the
magnetic damping via spin-orbit torque. Above a critical spin-orbit torque, the
fully compensated damping manifests itself as an increase of magnon
conductivity by almost two orders of magnitude. We compare our results to
theoretical expectations based on recently predicted current induced magnon
condensates and discuss other possible origins of the observed critical
behaviour.",1812.01334v3
2019-01-08,Microscopic theory of spin transport at the interface between the superconductor and a ferromagnetic insulator,"We theoretically investigate spin transport at the interface between the
ferromagnetic insulator(FI) and a superconductor(SC). Considering a simple
FI-SC interface model, we derive formulas for the spin current and spin-current
noise induced by microwave irradiation (spin pumping) or the temperature
gradient (the spin Seebeck effect). We show how the superconducting coherence
factor affects the temperature dependence of the spin current. We also
calculate the spin-current noise in thermal equilibrium and in non-equilibrium
states induced by the spin pumping, and compare them quantitatively for an
yttrium-iron-garnet-NbN interface.",1901.02440v2
2019-01-26,Chiral excitation of spin waves in ferromagnetic films,"We theoretically investigate the interlayer dipolar and exchange couplings
for an array of metallic magnetic nanowires grown on top of an extended
ultrathin yttrium iron garnet film. The calculated interlayer dipolar coupling
agrees with observed anticrossings [Chen \emph{et al.}, Phys. Rev. Lett.
\textbf{120}, 217202 (2018)], concluding that the interlayer exchange coupling
is suppressed by a spacer layer between the nanowires and film. The Kittel mode
in the nanowire array couples chirally to spin waves in the film, even though
Damon-Eshbach surface modes do not exist. The chirality is suppressed when the
interlayer exchange coupling becomes strong.",1901.09182v1
2019-01-29,Low-impedance superconducting microwave resonators for strong coupling to small magnetic mode volumes,"Recent experiments on strongly coupled microwave and ferromagnetic resonance
modes have focused on large volume bulk crystals such as yttrium iron garnet,
typically of millimeter-scale dimensions. We extend these experiments to lower
volumes of magnetic material by exploiting low-impedance lumped-element
microwave resonators. The low impedance equates to a smaller magnetic mode
volume, which allows us to couple to a smaller number of spins in the
ferromagnet. Compared to previous experiments, we reduce the number of
participating spins by two orders of magnitude, while maintaining the strength
of the coupling rate. Strongly coupled devices with small volumes of magnetic
material may allow the use of spin orbit torques, which require high current
densities incompatible with existing structures.",1901.10395v1
2019-01-30,Surface dynamics of rough magnetic films,"The chirality of Damon-Eshbach (DE) magnons affects the transport of energy
and angular momentum at the surface of magnetic films and spheres. We calculate
the surface-disorder-limited dephasing and transport lifetimes of surface modes
of sufficiently thick high-quality magnetic films such as yttrium iron garnet.
In spite of their chirality surface magnons are not protected, but interact
strongly with smooth surface roughness. Nevertheless, for long-range disorder
the transport is much less affected by the suppressed back scattering (vertex
correction). Moreover, in the presence of roughness ferromagnetic resonance
under a \textit{uniform} microwave field can gennerate a considerable amount of
surface magnons.",1901.11046v2
2019-02-12,Characterization of spin wave propagation in (111) YIG thin films with large anisotropy,"We report on long-range spin wave (SW) propagation in nanometer-thick yttrium
iron garnet (YIG) film with an ultralow Gilbert damping. The knowledge of a
wavenumber value $|\vec{k}|$ is essential for designing SW devices. Although
determining the wavenumber $|\vec{k}|$ in experiments like Brillouin light
scattering spectroscopy is straightforward, quantifying the wavenumber in
all-electrical experiments has not been widely commented upon so far. We
analyze magnetostatic spin wave (SW) propagation in YIG films in order to
determine the SW wavenumber $|\vec{k}|$ excited by the coplanar waveguide. We
show that it is crucial to consider the influence of magnetic anisotropy fields
present in YIG thin films for precise determination of SW wavenumber. With the
proposed methods we find that experimentally derived values of $|\vec{k}|$ are
in perfect agreement with that obtained from electromagnetic simulation only if
anisotropy fields are included.",1902.04608v1
2019-03-01,Indirect observation of phase conjugate magnons from non-degenerate four-wave mixing,"A phase conjugate mirror utilising four-wave mixing in a magnetic system is
experimentally realised for the first time. Indirect evidence of
continuous-wave phase conjugation has been observed experimentally and is
supported by simulations. The experiment utilizes a pump-probe method to excite
a four-wave mixing process. Two antennae are used to pump a region of a
thin-film yttrium iron garnet waveguide with magnons of frequency $f_{1}$ to
create a spatio-temporally periodic potential. As the probe magnons of
$f_{\mathrm{p}}$ impinge on the pumped region, a signal with frequency
$f_{\mathrm{c}} = 2f_{1}-f_{\mathrm{p}}$ is observed. The amplitude of the
nonlinear signal was highly dependent on the applied magnetic field $H$. Width
modes of the probe magnons and standing wave modes of the pump magnons were
shown to affect the amplitude of the signal at $f_{\mathrm{c}}$. Experimental
data is compared with simulations and theory to suggest that $f_{\mathrm{c}}$
is a phase conjugate of $f_{\mathrm{p}}$.",1903.00400v1
2019-03-05,Optimal mode matching in cavity optomagnonics,"Inelastic scattering of photons is a promising technique to manipulate
magnons but it suffers from weak intrinsic coupling. We theoretically discuss
an idea to increase optomagnonic coupling in optical whispering gallery mode
cavities, by generalizing previous analysis to include the exchange
interaction. We predict that the optomagnonic coupling constant to surface
magnons in yttrium iron garnet (YIG) spheres with radius $300\,\mathrm{\mu}$m
can be up to $40$ times larger than that to the macrospin Kittel mode. Whereas
this enhancement falls short of the requirements for magnon manipulation in
YIG, nanostructuring and/or materials with larger magneto-optical constants can
bridge this gap.",1903.01718v2
2019-03-09,Theory of the magnon Kerr effect in cavity magnonics,"We develop a theory for the magnon Kerr effect in a cavity magnonics system,
consisting of magnons in a small yttrium iron garnet (YIG) sphere strongly
coupled to cavity photons, and use it to study the bistability in this hybrid
system. To have a complete picture of the bistability phenomenon, we analyze
two different cases in driving the cavity magnonics system, i.e., directly
pumping the YIG sphere and the cavity, respectively. In both cases, the magnon
frequency shifts due to the Kerr effect exhibit a similar bistable behavior but
the corresponding critical powers are different. Moreover, we show how the
bistability of the system can be demonstrated using the transmission spectrum
of the cavity. Our results are valid in a wide parameter regime and generalize
the theory of bistability in a cavity magnonics system.",1903.03754v1
2019-03-29,Quantum Simulation of the Fermion-Boson Composite Quasi-Particles with a Driven Qubit-Magnon Hybrid Quantum System,"We experimentally demonstrate strong coupling between the ferromagnetic
magnons in a small yttrium-iron-garnet (YIG) sphere and the drive-field-induced
dressed states of a superconducting qubit, which gives rise to the double
dressing of the superconducting qubit. The YIG sphere and the superconducting
qubit are embedded in a microwave cavity and the effective coupling between
them is mediated by the virtual cavity photons. The theoretical results fit the
experimental observations well in a wide region of the drive-field power
resonantly applied to the superconducting qubit and reveal that the driven
qubit-magnon hybrid quantum system can be harnessed to emulate a
particle-hole-symmetric pair coupled to a bosonic mode. This hybrid quantum
system offers a novel platform for quantum simulation of the composite
quasi-particles consisting of fermions and bosons.",1903.12498v1
2019-04-08,Quantum entanglement between two magnon modes via Kerr nonlinearity,"We propose a scheme to entangle two magnon modes via Kerr nonlinear effect
when driving the systems far-from-equilibrium. We consider two macroscopic
yttrium iron garnets (YIGs) interacting with a single-mode microcavity through
the magnetic dipole coupling. The Kittel mode describing the collective
excitations of large number of spins are excited through driving cavity with a
strong microwave field. We demonstrate how the Kerr nonlineraity creates the
entangled quantum states between the two macroscopic ferromagnetic samples,
when the microcavity is strongly driven by a blue-detuned microwave field. Such
quantum entanglement survives at the steady state. Our work offers new insights
and guidance to designate the experiments for observing the entanglement in
massive ferromagnetic materials. It can also find broad applications in
macroscopic quantum effects and magnetic spintronics.",1904.04167v1
2019-04-09,Ferromagnetic Resonance Studies of Strain tuned Bi:YIG Films,"Bismuth-doped Yttrium iron garnet (Bi:YIG) thin films known for large
Magneto-optical activity with low losses still needs to get probed for its
magnetization dynamics. We demonstrate a controlled tuning of
magnetocrystalline anisotropy in Bi-doped Y_3 Fe_5 O_12 (Bi:YIG) films of high
crystalline quality using growth induced epitaxial strain on [111]-oriented
Gd_3 Ga_5 O_12 (GGG) substrate. We optimize a growth protocol to get thick
highly-strained epitaxial films showing large magneto-crystalline anisotropy,
compare to thin films prepared using a different protocol. Ferromagnetic
resonance measurements establish a linear dependence of the out-of-plane
uniaxial anisotropy on the strain induced rhombohedral distortion of Bi:YIG
lattice. Interestingly, the enhancement in the magnetoelastic constant due to
an optimum substitution of Bi^(3+) ions with strong spin orbit coupling does
not strongly affect the precessional damping (~2x10^(-3) ). Large
magneto-optical activity, reasonably low damping, large magnetocrystalline
anisotropy and large magnetoelastic coupling in BiYIG are the properties that
may help BiYIG emerge as a possible material for photo-magnonics and other
spintronics applications.",1904.04800v2
2019-04-23,Current-induced switching of YIG/Pt bilayers with in-plane magnetization due to Oersted fields,"We report on the switching of the in-plane magnetization of thin yttrium iron
garnet (YIG)/Pt bilayers induced by an electrical current. The switching is
either field-induced and assisted by a dc current, or current-induced and
assisted by a static magnetic field. The reversal of the magnetization occurs
at a current density as low as $10^5$~A/cm$^{2}$ and magnetic fields of $\sim
40$~$\mu$T, two orders of magnitude smaller than in ferromagnetic metals,
consistently with the weak uniaxial anisotropy of the YIG layers. We use the
transverse component of the spin Hall magnetoresistance to sense the magnetic
orientation of YIG while sweeping the current. Our measurements and simulations
reveal that the current-induced effective field responsible for switching is
due to the Oersted field generated by the current flowing in the Pt layer
rather than by spin-orbit torques, and that the switching efficiency is
influenced by pinning of the magnetic domains.",1904.10517v1
2019-05-20,Quantum drives produce strong entanglement between YIG samples without using intrinsic nonlinearities,"We show how to generate an entangled pair of yttrium iron garnet (YIG)
samples in a cavity-magnon system without using any nonlinearities which are
typically very weak. This is against the conventional wisdom which necessarily
requires strong Kerr like nonlinearity. Our key idea, which leads to
entanglement, is to drive the cavity by a weak squeezed vacuum field generated
by a flux-driven Josephson parametric amplifier (JPA). The two YIG samples
interact via the cavity. For modest values of the squeezing of the pump, we
obtain significant entanglement. This is the principal feature of our scheme.
We discuss entanglement between macroscopic spheres using several different
quantitative criteria. We show the optimal parameter regimes for obtaining
entanglement which is robust against temperature. We also discuss squeezing of
the collective magnon variables.",1905.07884v2
2019-05-28,Broadband enhancement of the magneto-optical activity of hybrid Au loaded Bi:YIG,"We unravel the underlying near-field mechanism of the enhancement of the
magneto-optical activity of bismuth-substituted yttrium iron garnet films
(Bi:YIG) loaded with gold nanoparticles. The experimental results show that the
embedded gold nanoparticles lead to a broadband enhancement of the
magneto-optical activity with respect to the activity of the bare Bi:YIG films.
Full vectorial near- and far-field simulations demonstrate that this broadband
enhancement is the result of a magneto-optically enabled cross-talking of
orthogonal localized plasmon resonances. Our results pave the way to the
on-demand design of the magneto-optical properties of hybrid magneto-plasmonic
circuitry.",1905.11941v1
2019-05-31,Detecting Light Dark Matter with Magnons,"Scattering of light dark matter with sub-eV energy deposition can be detected
with collective excitations in condensed matter systems. When dark matter has
spin-independent couplings to atoms or ions, it has been shown to efficiently
excite phonons. Here we show that, if dark matter couples to the electron spin,
magnon excitations in materials with magnetic dipole order offer a promising
detection path. We derive general formulae for single magnon excitation rates
from dark matter scattering, and demonstrate as a proof of principle the
projected reach of a yttrium iron garnet target for several dark matter models
with spin-dependent interactions. This highlights the complementarity of
various collective excitations in probing different dark matter interactions.",1905.13744v2
2019-06-04,Thickness dependence of spin Peltier effect visualized by thermal imaging technique,"Magnon propagation length in a ferrimagnetic insulator yttrium iron garnet
(YIG) has been investigated by measuring and analyzing the YIG-thickness t_YIG
dependence of the spin Peltier effect (SPE) in a Pt/YIG junction system. By
means of the lock-in thermography technique, we measured the spatial
distribution of the SPE-induced temperature modulation in the Pt/YIG system
with the t_YIG gradation, allowing us to obtain the accurate t_YIG dependence
of SPE with high t_YIG resolution. Based on the t_YIG dependence of SPE, we
verified the applicability of several phenomenological models to estimate the
magnon diffusion length in YIG.",1906.01560v3
2019-06-11,Proximity magnetoresistance in graphene induced by magnetic insulators,"We demonstrate the existence of Giant proximity magnetoresistance (PMR)
effect in a graphene spin valve where spin polarization is induced by a nearby
magnetic insulator. PMR calculations were performed for yttrium iron garnet
(YIG), cobalt ferrite (CFO), and two europium chalcogenides EuO and EuS. We
find a significant PMR (up to 100%) values defined as a relative change of
graphene conductance with respect to parallel and antiparallel alignment of two
proximity induced magnetic regions within graphene. Namely, for high Curie
temperature (Tc) CFO and YIG insulators which are particularly important for
applications, we obtain 22% and 77% at room temperature, respectively. For low
Tc chalcogenides, EuO and EuS, the PMR is 100% in both cases. Furthermore, the
PMR is robust with respect to system dimensions and edge type termination. Our
findings show that it is possible to induce spin polarized currents in graphene
with no direct injection through magnetic materials.",1906.04469v1
2019-06-24,Macroscopic entanglement of two magnon modes via quantum correlated microwave fields,"We present a scheme to entangle two magnon modes in two macroscopic
yttrium-iron-garnet spheres. The two spheres are placed inside two microwave
cavities, which are driven by a two-mode squeezed microwave field. By using the
linear state-swap interaction between the cavity and the magnon mode in each
cavity, the quantum correlation of the two driving fields is with high
efficiency transferred to the two magnon modes. Considerable entanglement could
be achieved under experimentally achievable conditions $g \gg \kappa_a \gg
\kappa_m$, where $g$ is the cavity-magnon coupling rate and $\kappa_a$,
$\kappa_m$ are the decay rates of the cavity and magnon modes, respectively.
The entanglement is in the steady state and robust against temperature,
surviving up to hundreds of milliKelvin with experimentally accessible two-mode
squeezed source.",1906.09921v1
2019-06-30,Large spatial Schrodinger cat using a levitated ferrimagnetic nanoparticle,"The superposition principle is one of the main tenets of quantum mechanics.
Despite its counter-intuitiveness, it has been experimentally verified using
electrons, photons, atoms, and molecules. However, a similar experimental
demonstration using a nano or a micro particle is non-existent. Here in this
Letter, exploiting macroscopic quantum coherence and quantum tunneling, we
propose an experiment using levitated magnetic nanoparticle to demonstrate such
an effect. It is shown that the spatial separation between the delocalized
wavepackets of a $20~$nm ferrimagnetic yttrium iron garnet (YIG) nanoparticle
can be as large as $5~$$\mu$m. We argue that this large spatial separation can
be used to test different modifications such as collapse models to the standard
quantum mechanics. Furthermore, we show that the spatial superposition of a
core-shell structure, a YIG core and a non-magnetic silica shell, can be used
to probe quantum gravity.",1907.00415v4
2019-07-15,Tuning edge localized spin waves in magnetic microstripes by proximate magnetic structures,"The propagation of edge localized spin waves (E-SWs) in yttrium iron garnet
(YIG) microstripes with/without the proximate magnetic microstructures is
investigated by micromagnetic simulations. A splitting of the dispersion curve
with the presence of permalloy (Py) stripe is also observed. The E-SWs on the
two edges of YIG stripe have different wavelengths, group velocities, and decay
lengths at the same frequencies. The role of the Py stripe was found to be the
source of the inhomogeneous static dipolar field without dynamic coupling with
YIG. This work opens new perspectives for the design of innovative SW
interference-based logic devices.",1907.06718v1
2019-07-20,Magnon Bose-Einstein condensate and supercurrents over a wide temperature range,"Magnon Bose-Einstein Condensates (BECs) and supercurrents are coherent
quantum phenomena, which appear on a macroscopic scale in parametrically
populated solid state spinsystems. One of the most fascinating and attractive
features of these processes is the possibility of magnon condensation and
supercurrent excitation even at room temperature. At the same time, valuable
information about a magnon BEC state, such as its lifetime, its formation
threshold, and coherency, is provided by experiments at various temperatures.
Here, we use Brillouin Light Scattering (BLS) spectroscopy for the
investigation of the magnon BEC dynamics in a single-crystal film of yttrium
iron garnet in a wide temperature range from 30 K to 380 K. By comparing the
BLS results with previous microwave measurements, we re-vealed the direct
relation between the damping of the condensed and the parametrically injected
magnons. The enhanced supercurrent dynamics was detected at 180 K near the
minimum of BEC damping.",1907.08805v1
2019-08-01,Universal prethermal dynamics in Heisenberg ferromagnets,"We study the universal far from equilibrium dynamics of magnons in Heisenberg
ferromagnets. We show that such systems exhibit universal scaling in momentum
and time of the quasiparticle distribution function, with the universal
exponents distinct from those recently observed in Bose-Einstein condensates.
This new universality class originates from the SU(2) symmetry of the
Hamiltonian, which leads to a strong momentum-dependent magnon-magnon
scattering amplitude. We compute the universal exponents using the Boltzmann
kinetic equation and incoherent initial conditions that can be realized with
microwave pumping of magnons. We compare our numerical results with analytic
estimates of the scaling exponents and demonstrate the robustness of the
scaling to variations in the initial conditions. Our predictions can be tested
in quench experiments of spin systems in optical lattices and pump-probe
experiments in ferromagnetic insulators such as yttrium iron garnet.",1908.00554v2
2019-08-30,Amplitude and Phase Noise of Magnons,"The low-frequency amplitude and phase noise spectra of magnetization waves,
i.e. magnons, was measured in the yttrium iron garnet (YIG) waveguides. This
type of noise, which originates from the fluctuations of the physical
properties of the YIG crystals, has to be taken into account in the design of
YIG-based RF generators and magnonic devices for data processing, sensing and
imaging applications. It was found that the amplitude noise level of magnons
depends strongly on the power level, increasing sharply at the on-set of
nonlinear dissipation. The noise spectra of both the amplitude and phase noise
have the Lorentzian shape with the characteristic frequencies below 100 Hz.",1909.00085v1
2019-09-27,Thermally driven two-magnet nano-oscillator with large spin-charge conversion,"Next-generation spintronic applications require material properties that can
be hardly met by one material candidate. Here we demonstrate that by combining
insulating and metallic magnets, enhanced spin-charge conversion and
energy-efficient thermal spin currents can be realized. We develop a nanowire
device consisting of an yttrium iron garnet and permalloy bi-layer. An
interfacial temperature gradient drives the nanowire magnetization into
auto-oscillations at gigahertz frequencies. Interfacial spin coupling and
magnetoresistance of the permalloy layer translate spin dynamics into sizable
microwave signals. The results show prospect for energy-efficient spintronic
devices and present an experimental realization of magnon condensation in a
heterogeneous magnetic system.",1909.12445v1
2019-10-16,Spin-Wave frequency division multiplexing in an yttrium iron garnet microstripe magnetized by inhomogeneous field,"Spin waves are promising candidates for information processing and
transmission in a broad frequency range. In the realization of magnonic
devices, the frequency depended division of the spin wave frequencies is a
critical function for parallel information processing. In this work, we
demonstrate a proof-of-concept spin-wave frequency division multiplexing method
by magnetizing a homogenous magnetic microstripe with an inhomogeneous field.
The symmetry breaking additional field is introduced by a permalloy stripe
simply placed in lateral proximity to the waveguide. Spin waves with different
frequencies can propagate independently, simultaneously and separately in space
along the shared waveguide. This work brings new potentials for parallel
information transmission and processing in magnonics.",1910.07136v1
2019-10-23,Electrical manipulation of spin pumping signal through nonlocal thermal magnon transport,"We study the magnon transport in the nonlocal configuration composed of two
Pt strips on top of yttrium iron garnet, with and without the presence of RF
microwave generated by an on-chip antenna. We find that the spin-Hall induced
thermal magnon heating/cooling, the Oersted field as well as the Joule heating
generated by the a.c. current in the Pt injector can significantly influence
the spin-pumping signal measured by the Pt detector in the presence of RF
microwave, forcing the spin-pumping voltage to show up in the first and second
harmonic signals in the nonlocal magnon transport measurement. These results
indicate that nonlocal magnon transport configuration can serve as a structure
to electrically detect and manipulate the spin-pumping signal. Furthermore,
certain caution is needed when studying the interplay between incoherent magnon
and coherent magnon spin transport in the nonlocal transport configuration,
since the change in microwave-induced spin-pumping voltage can overwhelm the
incoherent magnon transport signals.",1910.10326v2
2019-10-24,Resources of nonlinear cavity magnonics for quantum information,"We theoretically explore nonlinearities of ferromagnets in microwave cavities
in the classical and quantum regimes, and assess the resources for quantum
information, i.e. fluctuation squeezing and bipartite entanglement. The
(semi-)classical analysis of the anharmonic oscillator (Duffing) model for the
Kittel mode when including all other magnon modes, reveals chaotic and
limit-cycle phases that do not survive in quantum calculations. However,
magnons with nonzero wavenumbers that are driven by the Suhl instability of the
Kittel mode, form a genuine limit cycle. We subsequently compute bounds for the
distillable entanglement, as well as entanglement of formation for the
bipartite configurations of the mixed magnon modes. The distillable
entanglement of bipartite states accessible from a covariance matrix vanishes,
but can be recovered by injection locking. The predicted magnon entanglement
can be experimentally tested with yttrium iron garnet samples under realistic
conditions.",1910.11130v1
2019-10-29,Transient response of spin Peltier effect revealed by lock-in thermoreflectance measurement,"Transient response of the spin Peltier effect (SPE) in a Pt/yttrium iron
garnet junction system has been investigated by means of a lock-in
thermoreflectance method. We applied an alternating charge current to the Pt
layer to drive SPE through the spin Hall effect, and measured the AC response
of the resultant SPE-induced temperature modulation at frequencies ranging from
10 Hz to 1 MHz. We found that the SPE-induced temperature modulation decreases
with increasing the frequency when the frequency is >1 kHz. This is a
characteristic feature of SPE revealed by the high frequency measurements based
on the lock-in thermoreflectance, while previous low frequency measurements
showed that the SPE signal is independent of the frequency. We attribute the
decrease of the temperature modulation to the length scale of the SPE-induced
heat current; by comparing the experimental results with one-dimensional heat
conduction calculations, the length scale of SPE is estimated to be 0.94
{\mu}m.",1910.13165v2
2019-10-30,Strong coupling-enabled broadband non-reciprocity,"Non-reciprocity of signal transmission enhances capacity of communication
channels and protects transmission quality against possible signal
instabilities, thus becoming an important component ensuring coherent
information processing. However, non-reciprocal transmission requires breaking
time-reversal symmetry (TRS) which poses challenges of both practical and
fundamental character hindering the progress. Here we report a new scheme for
achieving broadband non-reciprocity using a specially engineered hybrid
microwave cavity. The TRS breaking is realized via strong coherent coupling
between a selected chiral mode in the microwave cavity and a single collective
spin excitation (magnon) in a ferromagnetic yttrium iron garnet (YIG) sphere.
The non-reciprocity in transmission is observed spanning nearly a 0.5 GHz
frequency band, which outperforms by two orders of magnitude the previously
achieved bandwidths. Our findings open new directions for robust coherent
information processing in a broad range of systems in both classical and
quantum regimes.",1910.14117v2
2019-10-31,Coherent spin pumping in a strongly coupled magnon-magnon hybrid system,"We experimentally identify coherent spin pumping in the magnon-magnon hybrid
modes of permalloy/yttrium iron garnet (Py/YIG) bilayers. Using broadband
ferromagnetic resonance, an ""avoided crossing"" is observed between the uniform
mode of Py and the spin wave mode of YIG due to the fieldlike interfacial
exchange coupling. We also identify additional linewidth suppression and
enhancement for the in-phase and out-of-phase hybrid modes, respectively,
\textcolor{black}{which can be interpreted as concerted dampinglike torque from
spin pumping}. Our analysis predicts inverse proportionality of both fieldlike
and dampinglike torques to the square root of the Py thickness, which
quantitatively agrees with experiments.",1910.14470v2
2019-11-09,The magnonic superfluid droplet at room temperature,"We declare the observation of spin superfluid state in Yttrium Iron Garnet
(YIG) at room temperature. It is similar to a Homogeneous Precessing State
(HPD), observed earlier in antiferromagnetic superfluid $^3$He-B. The formation
of this state explains by the repulsive interaction between magnons, which is
required as a prior condition for the spin superfluidity. It establishes an
energy gap, which stabilizes the long range superfluid transport of
magnetization and determines the Ginzburg-Landau coherence length. This
discovery paves a way to many quantum applications of supermagnonics at room
temperature, such as magnetic Josephson effect, long distance spin transport,
Q-bit, quantum logics, magnetic sensors and others.",1911.03708v1
2019-11-26,Ultrastrong coupling between a microwave resonator and antiferromagnetic resonances of rare earth ion spins,"Quantum magnonics is a new and active research field, leveraging the strong
collective coupling between microwaves and magnetically ordered spin systems.
To date work in quantum magnonics has focused on transition metals and almost
entirely on ferromagnetic resonances in yttrium iron garnet (YIG).
Antiferromagnetic systems have gained interest as they produce no stray field,
and are therefore robust to magnetic perturbations and have narrow, shape
independent resonant linewidths. Here we show the first experimental evidence
of ultrastrong-coupling between a microwave cavity and collective
antiferromagnetic resonances (magnons) in a rare earth crystal. The combination
of the unique optical and spin properties of the rare earths and collective
antiferromagnetic order paves the way for novel quantum magnonic applications.",1911.11311v1
2019-12-15,Magnon-photon strong coupling for tunable microwave circulators,"We present a generic theoretical framework to describe non-reciprocal
microwave circulation in a multimode cavity magnonic system and assess the
optimal performance of practical circulator devices. We show that high
isolation (> 56 dB), extremely low insertion loss (< 0.05 dB), and flexible
bandwidth control can be potentially realized in high-quality-factor
superconducting cavity based magnonic platforms. These circulation
characteristics are analyzed with materials of different spin densities. For
high-spin-density materials such as yttrium iron garnet, strong coupling
operation regime can be harnessed to obtain a broader circulation bandwidth. We
also provide practical design principles for a highly integratible
low-spin-density material (vanadium tetracyanoethylene) for narrow-band
circulator operation, which could benefit noise-sensitive quantum microwave
measurements. This theory can be extended to other coupled systems and provide
design guidelines for achieving tunable microwave non-reciprocity for both
classical and quantum applications.",1912.07128v2
2020-01-15,Yttrium Iron Garnet Thickness Influence on the Spin Pumping in the Bulk Acoustic Wave Resonator,"The features of phonon-magnon interconversion in acoustic resonator determine
the efficiency of spin pumping from YIG into Pt that may be detected
electrically through the inverse spin Hall effect (ISHE). Based on the methods
developed in previous works for calculating resonator structures with a
piezoelectric (ZnO) and a magnetoelastic layer in contact with the heavy metal
(YIG/Pt), we present the results of numerical calculations of YIG film
thickness influence on acoustically driven spin waves. We obtain some YIG film
thickness regions with various behavior of dc ISHE voltage $U_{ISHE}$. At
micron and submicron thicknesses, the higher spin wave resonance (SWR) modes
(both even and odd) can be generated with efficiency comparable and even
exceeding that of the main mode. The absolute maximum of $U_{ISHE}$ is achieved
at the thickness about $s_1 \approx 208$ nm under the excitation of the first
SWR.",2001.05385v1
2020-02-11,Sub-micrometer near-field focusing of spin waves in ultrathin YIG films,"We experimentally demonstrate tight focusing of a spin wave beam excited in
extended nanometer-thick films of Yttrium Iron Garnet by a simple microscopic
antenna functioning as a single-slit near-field lens. We show that the focal
distance and the minimum transverse width of the focal spot can be controlled
in a broad range by varying the frequency/wavelength of spin waves and the
antenna geometry. The experimental data are in good agreement with the results
of numerical simulations. Our findings provide a simple solution for
implementation of magnonic nano-devices requiring local concentration of the
spin-wave energy.",2002.04284v1
2020-02-22,Bose-Einstein Condensation of Nonequilibrium Magnons in Confined Systems,"We study the formation of a room temperature magnon Bose-Einstein condensate
(BEC) in nanoscopic systems and demonstrate that its lifetime is influenced by
the spatial confinement. We predict how dipolar interactions and nonlinear
magnon scattering assist in the generation of a metastable magnon BEC in
energy-quantized nanoscopic devices. We verify our prediction by a full
numerical simulation of the Landau-Lifshitz-Gilbert equation and demonstrate
the generation of magnon BEC in confined insulating magnets of yttrium iron
garnet. We directly map out the nonlinear magnon scattering processes behind
this phase transition to show how fast quantized thermalization channels allow
the BEC formation in confined structures. Based on our results, we discuss a
new mechanism to manipulate the BEC lifetime in nanoscaled systems. Our study
greatly extends the freedom to study the dynamics of magnon BEC in realistic
systems and to design integrated circuits for BEC-based applications at room
temperature.",2002.09777v2
2020-03-12,"Tunable multiwindow magnomechanically induced transparency, Fano resonances, and slow-to-fast light conversion","We investigate the absorption and transmission properties of a weak probe
field under the influence of a strong control field in a hybrid cavity
magnomechanical system in the microwave regime. This hybrid system consists of
two ferromagnetic material yttrium iron garnet (YIG) spheres strongly coupled
to a single cavity mode. In addition to two magnon-induced transparency (MIT)
that arise due to strong photon-magnon interactions, we observe a
magnomechanically induced transparency (MMIT) due to the presence of nonlinear
phonon-magnon interaction. In addition, we discuss the emergence and tunability
of the multiple Fano resonances in our system. We find that due to strong
photon-magnon coupling the group delay of the probe field can be enhanced
significantly. The subluminal or superluminal propagation depends on the
frequency of the magnons, which can be easily tuned by an external bias
magnetic field. Besides, the group delay of the transmitted field can also be
controlled with the control field power.",2003.13760v4
2020-04-11,Brillouin Light Scattering of Spin Waves Inaccessible with Free-Space Light,"Micro-focus Brillouin light scattering is a powerful technique for the
spectroscopic and spatial characterization of elementary excitations in
materials. However, the small momentum of light limits the accessible
excitations to the center of the Brillouin zone. Here, we utilize a metallic
nanoantenna fabricated on the archetypal ferrimagnet yttrium iron garnet to
demonstrate the possibility of Brillouin light scattering from
large-wavevector, high-frequency spin wave excitations that are inaccessible
with free-space light. The antenna facilitates sub-diffraction confinement of
electromagnetic field, which enhances the local field intensity and generates
momentum components significantly larger than those of free-space light. Our
approach provides access to high frequency spin waves important for fast
nanomagnetic devices, and can be generalized to other types of excitations and
light scattering techniques.",2004.05314v1
2020-04-25,Pulse-assisted magnetization switching in magnetic nanowires at picosecond and nanosecond timescales with low energy,"Detailed understanding of spin dynamics in magnetic nanomaterials is
necessary for developing ultrafast, low-energy and high-density spintronic
logic and memory. Here, we develop micromagnetic models and analytical
solutions to elucidate the effect of increasing damping and uniaxial anisotropy
on magnetic field pulse-assisted switching time, energy and field requirements
of nanowires with perpendicular magnetic anisotropy and yttrium iron
garnet-like spin transport properties. A nanowire is initially magnetized using
an external magnetic field pulse (write) and self-relaxation. Next, magnetic
moments exhibit deterministic switching upon receiving 2.5 ns-long external
magnetic pulses in both vertical polarities. Favorable damping
({\alpha}~0.1-0.5) and anisotropy energies (10^4-10^5 J m^-3) allow for as low
as picosecond magnetization switching times. Magnetization reversal with fields
below coercivity was observed using spin precession instabilities. A
competition or a nanomagnetic trilemma arises among the switching rate, energy
cost and external field required. Developing magnetic nanowires with optimized
damping and effective anisotropy could reduce the switching energy barrier down
to 3163kBT at room temperature. Thus, pulse-assisted picosecond and low energy
switching in nanomagnets could enable ultrafast nanomagnetic logic and cellular
automata.",2004.12243v1
2020-05-10,Stationary entanglement between light and microwave via ferromagnetic magnons,"We show how to generate stationary entanglement between light and microwave
in a hybrid opto-electro-magnonical system which mainly consists of a microwave
cavity, a yttrium iron garnet (YIG) sphere and a nanofiber. The optical modes
in nanofiber can evanescently coupled to whispering gallery modes, that are
able to interact with magnon mode via spin-orbit interaction, in YIG sphere,
while the microwave cavity photons and magnons are coupled through magnetic
dipole interaction simultaneously. Under reasonable parameter regimes, pretty
amount of entanglement can be generated, and it also shows persistence against
temperature. Our work is expected to provide a new perspective for building
more advanced and comprehensive quantum networks along with magnons for
fast-developing quantum technology and for studying the macroscopic quantum
phenomena.",2005.04581v3
2020-05-20,Frequency mixing in a ferrimagnetic sphere resonator,"Frequency mixing in ferrimagnetic resonators based on yttrium and calcium
vanadium iron garnets (YIG and CVBIG) is employed for studying their nonlinear
interactions. The ferrimagnetic Kittel mode is driven by applying a pump tone
at a frequency close to resonance. We explore two nonlinear frequency mixing
configurations. In the first one, mixing between a transverse pump tone and an
added longitudinal weak signal is explored, and the experimental results are
compared with the predictions of the Landau-Zener-Stuckelberg model. In the
second one, intermodulation measurements are employed by mixing pump and signal
tones both in the transverse direction for studying a bifurcation between a
stable spiral and a stable node attractors. Our results are applicable for
developing sensitive signal receivers with high gain for both the radio
frequency and the microwave bands.",2005.09864v1
2020-06-05,Controlling the nonlinear relaxation of quantized propagating magnons in nanodevices,"Relaxation of linear magnetization dynamics is well described by the viscous
Gilbert damping processes. However, for strong excitations, nonlinear damping
processes such as the decay via magnon-magnon interactions emerge and trigger
additional relaxation channels. Here, we use space- and time-resolved
microfocused Brillouin light scattering spectroscopy and micromagnetic
simulations to investigate the nonlinear relaxation of strongly driven
propagating spin waves in yttrium iron garnet nanoconduits. We show that the
nonlinear magnon relaxation in this highly quantized system possesses
intermodal features, i.e., magnons scatter to higher-order quantized modes
through a cascade of scattering events. We further show how to control such
intermodal dissipation processes by quantization of the magnon band in
single-mode devices, where this phenomenon approaches its fundamental limit.
Our study extends the knowledge about nonlinear propagating spin waves in
nanostructures which is essential for the construction of advanced spin-wave
elements as well as the realization of Bose-Einstein condensates in scaled
systems.",2006.03400v2
2020-06-11,Nonlocal magnon entanglement generation in coupled hybrid cavity systems,"We investigate dynamical generation of macroscopic nonlocal entanglements
between two remote massive magnon-superconducting-circuit hybrid systems. Two
fiber-coupled microwave cavities are employed to serve as an interaction
channel connecting two sets of macroscopic hybrid units each containing a
magnon (hosted by a Yttrium-Iron-Garnet sphere) and a superconducting-circuit
qubit. Surprisingly, it is found that stronger coupling does not necessarily
mean faster entanglement generation. The proposed hybrid system allows the
existence of an optimal fiber coupling strength that requests the shortest
amount of time to generate a systematic maximal entanglement. Our theoretical
results are shown to be within the scope of specific parameters that can be
achieved with current technology. The noise effects on the implementation of
systems are also treated in a general environment suggesting the robustness of
entanglement generation. Our discrete-variable qubit-like entanglement theory
of magnons may lead to direct applications in various quantum information
tasks.",2006.06132v3
2020-06-25,Magnon-exciton proximity coupling at a van der Waals heterointerface,"Spin and photonic systems are at the heart of modern information devices and
emerging quantum technologies. An interplay between electron-hole pairs
(excitons) in semiconductors and collective spin excitations (magnons) in
magnetic crystals would bridge these heterogeneous systems, leveraging their
individual assets in novel interconnected devices. Here, we report the
magnon-exciton coupling at the interface between a magnetic thin film and an
atomically-thin semiconductor. Our approach allies the long-lived magnons
hosted in a film of yttrium iron garnet (YIG) to strongly-bound excitons in a
flake of a transition metal dichalcogenide, MoSe$_2$. The magnons induce on the
excitons a dynamical valley Zeeman effect ruled by interfacial exchange
interactions. This nascent class of hybrid system suggests new opportunities
for information transduction between microwave and optical regions.",2006.14257v2
2020-07-20,Sizable spin-transfer torque in Bi/Ni80Fe20 bilayer film,"The search for efficient spin conversion in Bi has attracted great attention
in spin-orbitronics. In the present work, we employ spin-torque ferromagnetic
resonance to investigate spin conversion in Bi/Ni80Fe20(Py) bilayer films with
continuously varying Bi thickness. In contrast with previous studies, sizable
spin-transfer torque (i.e., a sizable spin-conversion effect) is observed in
Bi/Py bilayer film. Considering the absence of spin conversion in
Bi/yttrium-iron-garnet bilayers and the enhancement of spin conversion in
Bi-doped Cu, the present results indicate the importance of material
combinations to generate substantial spin-conversion effects in Bi.",2007.09830v1
2020-07-27,Probing thermal magnon current mediated by coherent magnon via nitrogen-vacancy centers in diamond,"Currently, thermally excited magnons are being intensively investigated owing
to their potential in computing devices and thermoelectric conversion
technologies. We report the detection of thermal magnon current propagating in
a magnetic insulator yttrium iron garnet under a temperature gradient using a
quantum sensor: electron spins associated with nitrogen-vacancy (NV) centers in
diamond. Thermal magnon current was observed as modified Rabi oscillation
frequencies of NV spins hosted in a beam-shaped bulk diamond that resonantly
coupled with coherent magnon propagating over a long distance. Additionally,
using a nanodiamond, alteration in NV spin relaxation rates depending on the
applied temperature gradient were observed under a non-resonant NV excitation
condition. The demonstration of probing thermal magnon current mediated by
coherent magnon via NV spin states serves as a basis for creating a device
platform hybridizing spin caloritronics and spin qubits.",2007.13433v6
2020-07-30,Coherent multi-mode conversion from microwave to optical wave via a magnon-cavity hybrid system,"Coherent conversion from microwave to optical wave opens new research avenues
towards long distant quantum network covering quantum communication, computing,
and sensing out of the laboratory. Especially multi-mode enabled system is
essential for practical applications. Here we experimentally demonstrate
coherent multi-mode conversion from the microwave to optical wave via
collective spin excitation in a single crystal yttrium iron garnet (YIG,
Y3Fe5O12) which is strongly coupled to a microwave cavity mode in a
three-dimensional rectangular cavity. Expanding collective spin excitation mode
of our magnon-cavity hybrid system from Kittel to multi magnetostatic modes, we
verify that the size of YIG sphere predominantly plays a crucial role for the
microwave-to-optical multi-mode conversion efficiency at resonant conditions.
We also find that the coupling strength between multi magnetostatic modes and a
cavity mode is manipulated by the position of a YIG inside the cavity. It is
expected to be valuable for designing a magnon hybrid system that can be used
for coherent conversion between microwave and optical photons.",2007.15299v1
2020-08-04,Quantitative comparison of magnon transport experiments in three-terminal YIG/Pt nanostructures acquired via dc and ac detection techniques,"All-electrical generation and detection of pure spin currents is a promising
way towards controlling the diffusive magnon transport in magnetically ordered
insulators. We quantitatively compare two measurement schemes, which allow to
measure the magnon spin transport in a three-terminal device based on a yttrium
iron garnet thin film. We demonstrate that the dc charge current method based
on the current reversal technique and the ac charge current method utilizing
first and second harmonic lock-in detection can both efficiently distinguish
between electrically and thermally injected magnons. In addition, both
measurement schemes allow to investigate the modulation of magnon transport
induced by an additional dc charge current applied to the center modulator
strip. However, while at low modulator charge current both schemes yield
identical results, we find clear differences above a certain threshold current.
This difference originates from nonlinear effects of the modulator current on
the magnon conductance.",2008.01416v1
2020-09-09,Sub-pico-liter magneto-optical cavities,"Microwave-to-optical conversion via ferromagnetic magnons has so-far been
limited by the optical coupling rates achieved in mm-scale whispering gallery
mode resonators. Towards overcoming this limitation, we propose and demonstrate
an open magneto-optical cavity containing a thin-film of yttrium iron garnet
(YIG). We achieve a 0.1 pL (100 $\mu$m$^{3}$) optical mode volume, $\sim$50
times smaller than previous devices. From this, we estimate the magnon
single-photon coupling rate is $G\approx50$ Hz. This open cavity design offers
the prospect of wavelength scale mode volumes, small polarization splittings,
and good magneto-optical mode overlap. With achievable further improvements and
optimization, efficient microwave-optical conversion and magnon cooling devices
become a realistic possibility.",2009.04162v1
2020-09-09,Effect of dipolar interactions on cavity magnon-polaritons,"The strong photon-magnon coupling between an electromagnetic cavity and two
yttrium iron garnet (YIG) spheres has been investigated in the context of a
strong mutual dipolar interaction between the spheres. A decrease in the
coupling strength between the YIG spheres and the electromagnetic cavity is
observed, along with an increase of the total magnetic losses, as the distance
between the spheres is decreased. A model of inhomogeneous broadening of the
ferromagnetic resonance linewidth, partly mitigated by the dipolar narrowing
effect, reproduces the reduction in the coupling strength observed
experimentally. These findings have important implications for the
understanding of strongly coupled photon-magnon system involving densely packed
magnetic objects, such as ferromagnetic nanowires arrays, in which the total
coupling strength with an electromagnetic cavity might become limited due to
mutual dipolar interactions.",2009.04557v1
2020-09-30,Phase-modulated cavity magnon polaritons as a precise magnetic field probe,"We describe and operate a novel spin-magnetometer based on the phase
modulation of cavity magnon polaritons. In this scheme a rf magnetic field is
detected through the sidebands it induces on a pump, and the experimental
configuration allows for a negligible pump noise and a high frequency readout.
The demonstrator setup, based on a copper cavity coupled to an yttrium iron
garnet sphere hybrid system, reached a sensitivity of
$2.0\,\mathrm{pT/\sqrt{Hz}}$, evading the pump noise and matching the
theoretical previsions. An optimized setup can attain a rf magnetic field
sensitivity of about $8\,\mathrm{fT/\sqrt{Hz}}$ at room temperature. An orders
of magnitude improvement is expected at lower temperatures, making this
instrument one of the few magnetometers accessing the sub-fT limit. Due to its
natural applications, miniaturization and multiplexing are eventually
discussed.",2010.00093v3
2020-10-09,Einstein-Podolsky-Rosen entanglement and asymmetric steering between distant macroscopic mechanical and magnonic systems,"We propose a deterministic scheme for establishing hybrid
Einstein-Podolsky-Rosen (EPR) entanglement channel between a macroscopic
mechanical oscillator and a magnon mode in a distant yttrium-iron-garnet (YIG)
sphere across about ten gigahertz of frequency difference. The system consists
of a driven electromechanical cavity which is unidirectionally coupled to a
distant electromagnonical cavity inside which a YIG sphere is placed. We find
that far beyond the sideband-resolved regime in the electromechanical
subsystem, stationary phonon-magnon EPR entanglement can be achieved. This is
realized by utilizing the output field of the electromechanical cavity being an
intermediary which distributes the electromechanical entanglement to the
magnons, thus establishing a remote phonon-magnon entanglement. The EPR
entanglement is strong enough such that phonon-magnon quantum steering can be
attainable in an asymmetric manner. This long-distance macroscopic hybrid EPR
entanglement and steering enable potential applications not only in fundamental
tests of quantum mechanics at the macro scale, but also in quantum networking
and one-sided device-independent quantum cryptography based on magnonics and
electromechanics.",2010.04357v1
2020-10-18,Observation of magnon-polarons in a uniaxial antiferromagnetic insulator,"Magnon-polarons, a type of hybridized excitations between magnons and
phonons, were first reported in yttrium iron garnet as anomalies in the spin
Seebeck effect responses. Here we report an observation of antiferromagnetic
(AFM) magnon-polarons in a uniaxial AFM insulator Cr2O3. Despite the relatively
higher energy of magnon than that of the acoustic phonons, near the spin-flop
transition of ~ 6 T, the left-handed magnon spectrum shifts downward to
hybridize with the acoustic phonons to form AFM magnon-polarons, which can also
be probed by the spin Seebeck effect. The spin Seebeck signal is founded to be
enhanced due to the magnon-polarons at low temperatures.",2010.08926v1
2020-10-24,Enhanced sensing of weak anharmonicities through coherences in dissipatively coupled anti-PT symmetric systems,"In the last few years, the great utility of PT-symmetric systems in sensing
small perturbations has been recognized. Here, we propose an alternate method
relevant to dissipative systems, especially those coupled to the vacuum of the
electromagnetic fields. In such systems, which typically show anti-PT symmetry
and do not require the incorporation of gain, vacuum induces coherence between
two modes. Owing to this coherence, the linear response acquires a pole on the
real axis. We demonstrate how this coherence can be exploited for the enhanced
sensing of very weak anhamonicities at low pumping rates. Higher drive powers
($\sim 0.1$ W), on the other hand, generate new domains of coherences. Our
results are applicable to a wide class of systems, and we specifically
illustrate the remarkable sensing capabilities in the context of a weakly
anharmonic Yttrium Iron Garnet (YIG) sphere interacting with a cavity via a
tapered fiber waveguide. A small change in the anharmonicity leads to a
substantial change in the induced spin current.",2010.12954v1
2020-11-16,Electrically induced strong modulation of magnons transport in ultrathin magnetic insulator films,"Magnon transport through a magnetic insulator can be controlled by
current-biased heavy-metal gates that modulate the magnon conductivity via the
magnon density. Here, we report nonlinear modulation effects in 10$\,$nm thick
yttrium iron garnet (YIG) films. The modulation efficiency is larger than
40\%/mA. The spin transport signal at high DC current density (2.2$\times
10^{11}\,$A/m$^{2}$) saturates for a 400$\,$nm wide Pt gate, which indicates
that even at high current levels a magnetic instability cannot be reached in
spite of the high magnetic quality of the films.",2011.07800v1
2020-12-01,Design of an optomagnonic crystal: towards optimal magnon-photon mode matching at the microscale,"We put forward the concept of an optomagnonic crystal: a periodically
patterned structure at the microscale based on a magnetic dielectric, which can
co-localize magnon and photon modes. The co-localization in small volumes can
result in large values of the photon-magnon coupling at the single quanta
level, which opens perspectives for quantum information processing and quantum
conversion schemes with these systems. We study theoretically a simple geometry
consisting of a one-dimensional array of holes with an abrupt defect,
considering the ferrimagnet Yttrium Iron Garnet (YIG) as the basis material. We
show that both magnon and photon modes can be localized at the defect, and use
symmetry arguments to select an optimal pair of modes in order to maximize the
coupling. We show that an optomagnonic coupling in the kHz range is achievable
in this geometry, and discuss possible optimization routes in order to improve
both coupling strengths and optical losses.",2012.00760v2
2020-12-14,Effect of magnon decays on parametrically pumped magnons,"We investigate the influence of magnon decays on the non-equilibrium dynamics
of parametrically excited magnons in the magnetic insulator yttrium-iron garnet
(YIG). Our investigations are motivated by a recent experiment by Noack et al.
[Phys. Status Solidi B 256, 1900121 (2019)] where an enhancement of the spin
pumping effect in YIG was observed near the magnetic field strength where
magnon decays via confluence of magnons becomes kinematically possible. To
explain the experimental findings, we have derived and solved kinetic equations
for the non-equilibrium magnon distribution. The effect of magnon decays is
taken into account microscopically via collision integrals derived from
interaction vertices involving three powers of magnon operators. Our results
agree quantitatively with the experimental data.",2012.07870v2
2021-01-08,Compact tunable YIG-based RF resonators,"We report on the design, fabrication, and characterization of compact tunable
yttrium iron garnet (YIG) based RF resonators based on $\mu$m-sized spin-wave
cavities. Inductive antennas with both ladder and meander configurations were
used as transducers between spin waves and RF signals. The excitation of
ferromagnetic resonance and standing spin waves in the YIG cavities led to
sharp resonances with quality factors up to 350. The observed spectra were in
excellent agreement with a model based on the spin-wave dispersion relations in
YIG, showing a high magnetic field tunability of about 29 MHz/mT.",2101.02909v4
2021-01-19,Evolution of room-temperature magnon gas toward coherent Bose-Einstein condensate,"The appearance of spontaneous coherence is a fundamental feature of a
Bose-Einstein condensate and an essential requirement for possible applications
of the condensates for data processing and quantum computing. In the case of a
magnon condensate in a magnetic crystal, such computing can be performed even
at room temperature. So far, the process of coherence formation in a magnon
condensate was inaccessible. We study the evolution of magnon radiation spectra
by direct detection of microwave radiation emitted by magnons in a
parametrically driven yttrium iron garnet crystal. By using specially shaped
bulk samples, we show that the parametrically overpopulated magnon gas evolves
to a state, whose coherence is only limited by the natural magnon relaxation
into the crystal lattice.",2101.07890v1
2021-02-24,Phase-controlled pathway interferences and switchable fast-slow light in a cavity-magnon polariton system,"We study the phase controlled transmission properties in a compound system
consisting of a 3D copper cavity and an yttrium iron garnet (YIG) sphere. By
tuning the relative phase of the magnon pumping and cavity probe tones,
constructive and destructive interferences occur periodically, which strongly
modify both the cavity field transmission spectra and the group delay of light.
Moreover, the tunable amplitude ratio between pump-probe tones allows us to
further improve the signal absorption or amplification, accompanied by either
significantly enhanced optical advance or delay. Both the phase and
amplitude-ratio can be used to realize in-situ tunable and switchable fast-slow
light. The tunable phase and amplitude-ratio lead to the zero reflection of the
transmitted light and an abrupt fast-slow light transition. Our results confirm
that direct magnon pumping through the coupling loops provides a versatile
route to achieve controllable signal transmission, storage, and communication,
which can be further expanded to the quantum regime, realizing coherent-state
processing or quantum-limited precise measurements.",2102.12181v1
2021-03-05,Local heat emission due to unidirectional spin-wave heat conveyer effect observed by lock-in thermography,"Lock-in thermography measurements were performed to reveal heat source
distribution induced by the unidirectional spin-wave heat conveyer effect
(USHCE) of magnetostatic surface spin waves. When the magnetostatic surface
spin waves are excited in an yttrium iron garnet slab, the lock-in thermography
images show spatially biased sharp and complicated heating patterns, indicating
the importance of edge spin-wave dynamics for USHCE. The accessibility to the
local heat emission properties allows us to clarify a capability of remote
heating realized by USHCE; it can transfer energy for heating even through a
macro-scale air gap between two magnetic materials owing to the long-range
dipole-dipole coupling.",2103.03694v1
2021-03-19,Remote magnon entanglement between two massive ferrimagnetic spheres via cavity optomagnonics,"Recent studies show that hybrid quantum systems based on magnonics provide a
new and promising platform for generating macroscopic quantum states involving
a large number of spins. Here we show how to entangle two magnon modes in two
massive yttrium-iron-garnet (YIG) spheres using cavity optomagnonics, where
magnons couple to high-quality optical whispering gallery modes supported by
the YIG sphere. The spheres can be as large as 1 mm in diameter and each sphere
contains more than $10^{18}$ spins. The proposal is based on the asymmetry of
the Stokes and anti-Stokes sidebands generated by the magnon-induced Brillouin
light scattering in cavity optomagnonics. This allows one to utilize the Stokes
and anti-Stokes scattering process, respectively, for generating and verifying
the entanglement. Our work indicates that cavity optomagnonics could be a
promising system for preparing macroscopic quantum states.",2103.10595v2
2021-03-31,Room temperature antiferromagnetic resonance and inverse spin-Hall voltage in canted antiferromagnets,"We study theoretically and experimentally the spin pumping signals induced by
the resonance of canted antiferromagnets with Dzyaloshinskii-Moriya interaction
and demonstrate that they can generate easily observable inverse spin-Hall
voltages. Using a bilayer of hematite/heavy metal as a model system, we measure
at room temperature the antiferromagnetic resonance and an associated inverse
spin-Hall voltage, as large as in collinear antiferromagnets. As expected for
coherent spin-pumping, we observe that the sign of the inverse spin-Hall
voltage provides direct information about the mode handedness as deduced by
comparing hematite, chromium oxide and the ferrimagnet Yttrium-Iron Garnet. Our
results open new means to generate and detect spin-currents at terahertz
frequencies by functionalizing antiferromagnets with low damping and canted
moments.",2103.16872v1
2021-04-22,Theory for electrical detection of the magnon Hall effect induced by dipolar interactions,"We derive the anomalous Hall contributions arising from dipolar interactions
to diffusive spin transport in magnetic insulators. Magnons, the carriers of
angular momentum in these systems, are shown to have a non-zero Berry
curvature, resulting in a measurable Hall effect. For yttrium iron garnet (YIG)
thin films we calculate both the anomalous and magnon spin conductivities. We
show that for a magnetic field perpendicular to the film the anomalous Hall
conductivity is finite. This results in a non-zero Hall signal, which can be
measured experimentally using Permalloy strips arranged like a Hall bar on top
of the YIG thin film. We show that electrical detection and injection of spin
is possible, by solving the resulting diffusion-relaxation equation for a Hall
bar. We predict the experimentally measurable Hall coefficient for a range of
temperatures and magnetic field strengths. Most strikingly, we show that there
is a sign change of the Hall coefficient associated with increasing the
thickness of the film.",2104.11304v1
2021-04-26,Cavity magnomechanical storage and retrieval of quantum states,"We show how a quantum state in a microwave cavity mode can be transferred to
and stored in a phononic mode via an intermediate magnon mode in a
magnomechanical system. For this we consider a ferrimagnetic yttrium iron
garnet (YIG) sphere inserted in a microwave cavity, where the microwave and
magnon modes are coupled via a magnetic-dipole interaction and the magnon and
phonon modes in the YIG sphere are coupled via magnetostrictive forces. By
modulating the cavity and magnon detunings and the driving of the magnon mode
in time, a Stimulated Raman Adiabatic Passage (STIRAP)-like coherent transfer
becomes possible between the cavity mode and the phonon mode. The phononic mode
can be used to store the photonic quantum state for long periods as it
possesses lower damping than the photonic and magnon modes. Thus our proposed
scheme offers a possibility of using magnomechanical systems as quantum memory
for photonic quantum information.",2104.12323v1
2021-05-06,Spin Wave Interference Detection via Inverse Spin Hall Effect,"In this letter, we present experimental data demonstrating spin wave
interference detection using spin Hall effect (ISHE). Two coherent spin waves
are excited in a yttrium-iron garnet (YIG) waveguide by continuous microwave
signals. The initial phase difference between the spin waves is controlled by
the external phase shifter. The ISHE voltage is detected at a distance of 2 mm
and 4 mm away from the spin wave generating antennae by an attached Pt layer.
Experimental data show ISHE voltage oscillation as a function of the phase
difference between the two interfering spin waves. This experiment demonstrates
an intriguing possibility of using ISHE in spin wave logic circuit converting
spin wave phase into an electric signal",2105.02979v1
2021-05-18,Parity-symmetry-breaking quantum phase transition via parametric drive in a cavity magnonic system,"We study the parity-symmetry-breaking quantum phase transition (QPT) in a
cavity magnonic system driven by a parametric field, where the magnons in a
ferrimagnetic yttrium-iron-garnet sphere strongly couple to a microwave cavity.
With appropriate parameters, this cavity magnonic system can exhibit a rich
phase diagram, including the parity-symmetric phase, parity-symmetry-broken
phase, and bistable phase. When increasing the drive strength beyond a critical
threshold, the cavity magnonic system undergoes either a first- or second-order
nonequilibrium QPT from the parity-symmetric phase with microscopic excitations
to the parity-symmetry-broken phase with macroscopic excitations, depending on
the parameters of the system. Our work provides an alternate way to engineer
the QPT in a hybrid quantum system containing the spin ensemble in a ferri- or
ferromagnetic material with strong exchange interactions.",2105.08371v3
2021-05-22,Ferromagnetic resonance modes in the exchange dominated limit in cylinders of finite length,"We analyze the magnetic mode structure of axially-magnetized, finite-length,
nanoscopic cylinders in a regime where the exchange interaction dominates,
along with simulations of the mode frequencies of the ferrimagnet yttrium iron
garnet. For the bulk modes we find that the frequencies can be represented by
an expression given by Herring and Kittel by using wavevector components
obtained by fitting the mode patterns emerging from these simulations. In
addition to the axial, radial, and azimuthal modes that are present in an
infinite cylinder, we find localized ""cap modes"" that are ""trapped"" at the top
and bottom cylinder faces by the inhomogeneous dipole field emerging from the
ends. Semi-quantitative explanations are given for some of the modes in terms
of a one-dimensional Schrodinger equation which is valid in the exchange
dominant case. The assignment of the azimuthal mode number is carefully
discussed and the frequency splitting of a few pairs of nearly degenerate modes
is determined through the beat pattern emerging from them.",2105.10795v1
2021-05-24,Phase-resolved electrical detection of coherently coupled magnonic devices,"We demonstrate the electrical detection of magnon-magnon hybrid dynamics in
yttrium iron garnet/permalloy (YIG/Py) thin film bilayer devices. Direct
microwave current injection through the conductive Py layer excites the hybrid
dynamics consisting of the uniform mode of Py and the first standing spin wave
($n=1$) mode of YIG, which are coupled via interfacial exchange. Both the two
hybrid modes, with Py or YIG dominated excitations, can be detected via the
spin rectification signals from the conductive Py layer, providing phase
resolution of the coupled dynamics. The phase characterization is also applied
to a nonlocally excited Py device, revealing the additional phase shift due to
the perpendicular Oersted field. Our results provide a device platform for
exploring hybrid magnonic dynamics and probing their phases, which are crucial
for implementing coherent information processing with magnon excitations",2105.11057v1
2021-06-15,Nonreciprocal high-order sidebands induced by magnon Kerr nonlinearity,"We propose an effective approach for creating robust nonreciprocity of
high-order sidebands, including the first-, second- and third-order sidebands,
at microwave frequencies. This approach relies on magnon Kerr nonlinearity in a
cavity magnonics system composed of two microwave cavities and one yttrium iron
garnet (YIG) sphere. By manipulating the driving power applied on YIG and the
frequency detuning between the magnon mode in YIG and the driving field, the
effective Kerr nonlinearity can be strengthened, thereby inducing strong
transmission non-reciprocity. More interestingly, we find the higher the
sideband order, the stronger the transmission nonreciprocity marked by the
higher isolation ratio in the optimal detuning regime. Such a series of
equally-spaced high-order sidebands have potential applications in frequency
comb-like precision measurement, besides structuring high-performance on-chip
nonreciprocal devices.",2106.09542v1
2021-06-21,A low-loss ferrite circulator as a tunable chiral quantum system,"Ferrite microwave circulators allow one to control the directional flow of
microwave signals and noise, and thus play a crucial role in present-day
superconducting quantum technology. They are typically viewed as a black-box,
and their internal structure is not specified, let alone used as a resource. In
this work, we demonstrate a low-loss waveguide circulator constructed with
single-crystalline yttrium iron garnet (YIG) in a 3D cavity, and analyze it as
a multi-mode hybrid quantum system with coupled photonic and magnonic
excitations. We show the coherent coupling of its chiral internal modes with
integrated superconducting niobium cavities, and how this enables tunable
non-reciprocal interactions between the intra-cavity photons. We also probe
experimentally the effective non-Hermitian dynamics of this system and its
effective non-reciprocal eigenmodes. The device platform provides a test bed
for implementing non-reciprocal interactions in open-system circuit QED.",2106.11283v2
2021-06-24,Control of nonlocal magnon spin transport via magnon drift currents,"Spin transport via magnon diffusion in magnetic insulators is important for a
broad range of spin-based phenomena and devices. However, the absence of the
magnon equivalent of an electric force is a bottleneck. In this work, we
demonstrate the controlled generation of magnon drift currents in yttrium iron
garnet/platinum heterostructures. By performing electrical injection and
detection of incoherent magnons, we find magnon drift currents that stem from
the interfacial Dzyaloshinskii-Moriya interaction. We can further control the
magnon drift by the orientation of the magnetic field. The drift current
changes the magnon propagation length by up to $\pm$ 6 % relative to diffusion.
We generalize the magnonic spin transport theory to include a finite drift
velocity resulting from any inversion asymmetric interaction, and obtain
results consistent with our experiments.",2106.12946v1
2021-08-06,Magnon transport in $\mathrm{\mathbf{Y_3Fe_5O_{12}}}$/Pt nanostructures with reduced effective magnetization,"For applications making use of magnonic spin currents damping effects, which
decrease the spin conductivity, have to be minimized. We here investigate the
magnon transport in an yttrium iron garnet thin film with strongly reduced
effective magnetization. We show that in a three-terminal device the effective
magnon conductivity can be increased by a factor of up to six by a current
applied to a modulator electrode, which generates damping compensation above a
threshold current. Moreover, we find a linear dependence of this threshold
current on the applied magnetic field. We can explain this behavior by the
reduced effective magnetization and the associated nearly circular
magnetization precession.",2108.03263v1
2021-10-09,Single-shot imaging of ultrafast all-optical magnetization dynamics with a spatio-temporal resolution,"We present a laboratory system for single-shot magneto-optical (MO) imaging
of ultrafast magnetization dynamics with high-sensitivity of MO rotation. We
create a stack of MO images repeatedly employing a single pair of a pump and
defocused probe pulses to induce and visualize MO changes in the sample. Both
laser beams are independently wavelength-tunable allowing for a flexible,
resonant adjustable two-color pump and probe scheme. To increase the MO
contrast the probe beam is spatially filtered. We performed the all-optical
switching experiment in Co-doped yttrium iron garnet films (YIG:Co) to
demonstrate the capability of the presented method. We determine the
spatial-temporal distribution of the effective field of photo-induced
anisotropy driving the all-optical switching of the magnetization in YIG:Co
film without an external magnetic field. Moreover, using this imaging method,
we tracked the process of the laser-induced magnetization precession.",2110.04506v1
2021-10-26,Giant quadratic magneto-optical response of thin YIG films for sensitive magnetometric experiments,"We report on observation of a magneto-optical effect quadratic in
magnetization (Cotton-Mouton effect) in 50 nm thick layer of Yttrium-Iron
Garnet (YIG). By a combined theoretical and experimental approach, we managed
to quantify both linear and quadratic magneto-optical effects. We show that the
quadratic magneto-optical signal in the thin YIG film can exceed the linear
magneto-optical response, reaching values of 450 urad that are comparable with
Heusler alloys or ferromagnetic semiconductors. Furthermore, we demonstrate
that a proper choice of experimental conditions, particularly with respect to
the wavelength, is crucial for optimization of the quadratic magneto-optical
effect for magnetometry measurement.",2110.13679v1
2021-10-31,Thermally induced all-optical ferromagnetic resonance in thin YIG films,"All-optical ferromagnetic resonance (AO-FMR) is a powerful tool for local
detection of micromagnetic parameters, such as magnetic anisotropy, Gilbert
damping or spin stiffness. In this work we demonstrate that the AO-FMR method
can be used in thin films of Yttrium Iron Garnet (YIG) if a metallic capping
layer (Au, Pt) is deposited on top of the film. Magnetization precession is
triggered by heating of the metallic layer with femtosecond laser pulses. The
heating modifies the magneto-crystalline anisotropy of the YIG film and shifts
the quasi-equilibrium orientation of magnetization, which results in
precessional magnetization dynamics. The laser-induced magnetization precession
corresponds to a uniform (Kittel) magnon mode, with the precession frequency
determined by the magnetic anisotropy of the material as well as the external
magnetic field, and the damping time set by a Gilbert damping parameter. The
AO-FMR method thus enables measuring local magnetic properties, with spatial
resolution given only by the laser spot size.",2111.00586v1
2021-11-12,Classical analog of qubit logic based on a magnon Bose-Einstein condensate,"We present a classical version of several quantum bit (qubit) functionalities
using a two-component magnon Bose-Einstein condensate formed at opposite
wavevectors in a room-temperature yttrium-iron-garnet ferrimagnetic film. The
macroscopic wavefunctions of these two condensates serve as orthonormal basis
states that form a system being a classical counterpart of a single qubit.
Solving the Gross-Pitaevskii equation and employing micromagnetic numerical
simulations, we first show how to initialize the system in one of the basis
states: the application of wavevector-selective parallel parametric pumping
allows us to form only a single condensate in one of the two lowest energy
states of the magnon gas. Next, by translating the concept of Rabi-oscillations
into the wavevector domain, we demonstrate how to manipulate the magnon-BEC
system along the polar axis in the Bloch sphere representation. We also discuss
the manipulation regarding the azimuthal angle.",2111.06798v2
2021-11-16,Optical sensing of magnons via the magnetoelastic displacement,"We show how to measure a steady-state magnon population in a magnetostatic
mode of a ferromagnet or ferrimagnet, such as yttrium iron garnet. We adopt an
optomechanical approach and utilize the magnetoelasticity of the ferromagnet.
The magnetostrictive force dispersively couples magnons to the deformation
displacement of the ferromagnet, which is proportional to the magnon
population. By further coupling the mechanical displacement to an optical
cavity that is resonantly driven by a weak laser, the magnetostrictively
induced displacement can be sensed by measuring the phase quadrature of the
optical field. The phase shows an excellent linear dependence on the magnon
population for a not very large population, and can thus be used as a
`magnometer' to measure the magnon population. We further study the effect of
thermal noises, and find a high signal-to-noise ratio even at room temperature.
At cryogenic temperatures, the resolution of magnon excitation numbers is
essentially limited by the vacuum fluctuations of the phase, which can be
significantly improved by using a squeezed light.",2111.08376v2
2021-11-30,Steering light with magnetic textures,"We study the steering of visible light using a combination of magneto-optical
effects and the reconfigurability of magnetic domains in Yttrium-Iron Garnet
films. The spontaneously formed stripe domains are used as a field-controlled
optical grating, allowing for active spatiotemporal control of light. We
discuss the basic ideas behind the approach and provide a quantitative
description of the field dependence of the obtained light patterns. Finally, we
calculate and experimentally verify the efficiency of our magneto-optical
grating.",2111.15219v3
2021-12-01,Strong Long-Range Spin-Spin Coupling via a Kerr Magnon Interface,"Strong long-range coupling between distant spins is crucial for spin-based
quantum information processing. However, achieving such a strong spin-spin
coupling remains challenging. Here we propose to realize a strong coupling
between two distant spins via the Kerr effect of magnons in a
yttrium-iron-garnet nanosphere. By applying a microwave field on this
nanosphere, the Kerr effect of magnons can induce the magnon squeezing, so that
the coupling between the spin and the squeezed magnons can be exponentially
enhanced. This in turn allows the spin-magnon distance to increase from nano-
to micrometer scale. By considering the virtual excitation of the squeezed
magnons in the dispersive regime, strong spin-spin coupling mediated by the
squeezed magnons can be achieved, and a remote quantum-state transfer, as well
as the nonlocal two-qubit ISWAP gate with high fidelity becomes implementable.
Our approach offers a feasible scheme to perform quantum information processing
among distant spins.",2112.00452v3
2021-12-03,Microwave Amplification in a PT -symmetric-like Cavity Magnomechanical System,"We propose a scheme that can generate tunable magnomechanically induced
amplification in a double-cavity parity-time-(PT -) symmetric-like
magnomechanical system under a strong control and weak probe field. The system
consists of a ferromagnetic-material yttrium iron garnet (YIG) sphere placed in
a passive microwave cavity which is connected with another active cavity. We
reveal that ideally induced amplification of the microwave probe signal may
reach the maximum value 1000000 when cavity-cavity, cavity-magnon and
magnomechanical coupling strengths are nonzero simultaneously. The phenomenon
might have potential applications in the field of quantum information
processing and quantum optical devices. Besides, we also find the phenomena of
slow-light propagation. In this case, group speed delay of the light can
achieve 0.000035s, which can enhance some nonlinear effect. Moreover, due to
the relatively flat dispersion curve, the proposal may be applied to sensitive
optical switches, which plays an important role in storing photons and quantum
optical chips.",2112.01727v1
2021-12-27,Observation of magnon cross-Kerr effect in cavity magnonics,"When there is a certain amount of field inhomogeneity, the biased
ferrimagnetic crystal will exhibit the higher-order magnetostatic (HMS) mode in
addition to the uniform-precession Kittel mode. In cavity magnonics, we show
both experimentally and theoretically the cross-Kerr-type interaction between
the Kittel mode and HMS mode. When the Kittel mode is driven to generate a
certain number of excitations, the HMS mode displays a corresponding frequency
shift and vice versa. The cross-Kerr effect is caused by an exchange
interaction between these two spin-wave modes. Utilizing the cross-Kerr effect,
we realize and integrate a multi-mode cavity magnonic system with only one
yttrium iron garnet (YIG) sphere. Our results will bring new methods to
magnetization dynamics studies and pave a way for novel cavity magnonic devices
by including the magnetostatic mode-mode interaction as an operational degree
of freedom.",2112.13807v1
2022-01-11,Building instructions for a ferromagnetic axion haloscope,"A ferromagnetic haloscope is a rf spin-magnetometer used for searching Dark
Matter in the form of axions. A magnetic material is monitored searching for
anomalous magnetization oscillations which can be induced by dark matter
axions. To properly devise such instrument one first needs to understand the
features of the searched-for signal, namely the effective rf field of dark
matter axions $B_a$ acting on electronic spins. Once the properties of $B_a$
are defined, the design and test of the apparatus may start. The optimal sample
is a narrow linewidth and high spin-density material such as Yttrium Iron
Garnet (YIG), coupled to a microwave cavity with almost matched linewidth to
collect the signal. The power in the resonator is collected with an antenna and
amplified with a Josephson Parametric amplifier, a quantum-limited device
which, however, adds most of the setup noise. The signal is further amplified
with low noise HEMT and down-converted for storage with an heterodyne receiver.
This work describes how to build such apparatus, with all the experimental
details, the main issues one might face, and some solutions.",2201.04081v1
2022-01-26,Nonlinear magnon polaritons,"We experimentally and theoretically demonstrate that nonlinear spin-wave
interactions suppress the hybrid magnon-photon quasiparticle or ""magnon
polariton"" in microwave spectra of an yttrium iron garnet film detected by an
on-chip split-ring resonator. We observe a strong coupling between the Kittel
and microwave cavity modes in terms of an avoided crossing as a function of
magnetic fields at low microwave input powers, but a complete closing of the
gap at high powers. The experimental results are well explained by a
theoretical model including the three-magnon decay of the Kittel magnon into
spin waves. The gap closure originates from the saturation of the ferromagnetic
resonance above the Suhl instability threshold by a coherent back reaction from
the spin waves.",2201.10889v2
2022-02-06,Coexistence of coupling-induced transparency and absorption of transmission signals in magnon-mediated photon-photon coupling,"Coexistence of coupling-induced transparency (CIT) and absorption (CIA) of
signals in magnon-mediated photon-photon coupling was experimentally determined
in a planar hybrid structure consisting of a yttrium iron garnet (YIG) film and
three concentric inverted-split-ring resonators (ISRRs). The experimental
observation of simultaneous CIT and CIA phenomena was ascribed to
magnon-mediated photon-photon coupling between the individually decoupled
ISRRs. In order to capture the generic physics of the observed interactions, we
constructed an appropriate analytical model based on the balance between the
coherent and dissipative multiple-paths interactions, which model precisely
reproduced both the CIT and CIA experimentally observed from a single hybrid
system. This work, promisingly, can provide guidance for design of efficient,
flexible, and well-controllable photon-magnonic devices that are highly in
demand for applications to quantum technologies currently under development.",2202.02667v1
2022-04-12,Spin Peltier effect and its length scale in Pt/YIG system at high temperatures,"The temperature and yttrium-iron-garnet (YIG) thickness dependences of the
spin Peltier effect (SPE) have been investigated using a Pt/YIG junction system
at temperatures ranging from room temperature to the Curie temperature of YIG
by the lock-in thermography method. By analyzing the YIG thickness dependence
using an exponential decay model, the characteristic length of SPE in YIG is
estimated to be 0.9 $\mu$m near room temperature and almost constant even near
the Curie temperature. The high-temperature behavior of SPE is clearly
different from that of the spin Seebeck effect, providing a clue for
microscopically understanding the reciprocal relation between them.",2204.05482v1
2022-05-10,Optimal broad-band frequency conversion via a magnomechanical transducer,"Developing schemes for efficient and broad-band frequency conversion of
quantum signals is an ongoing challenge in the field of modern quantum
information. Especially the coherent conversion between microwave and optical
signals is an important milestone towards long-distance quantum communication.
In this work, we propose a two-stage conversion protocol, employing a resonant
interaction between magnetic and mechanical excitations as a mediator between
microwave and optical photons. Based on estimates for the coupling strengths
under optimized conditions for yttrium iron garnet, we predict close to unity
conversion efficiency without the requirement of matching cooperativities. We
predict a conversion bandwidth in the regions of largest efficiency on the
order of magnitude of the coupling strengths which can be further increased at
the expense of reduced conversion efficiency.",2205.05088v2
2022-06-02,Bistability in dissipatively coupled cavity magnonics,"Dissipative coupling of resonators arising from their cooperative dampings to
a common reservoir induces intriguingly new physics such as energy level
attraction. In this study, we report the nonlinear properties in a
dissipatively coupled cavity magnonic system. A magnetic material YIG (yttrium
iron garnet) is placed at the magnetic field node of a Fabry-Perot-like
microwave cavity such that the magnons and cavity photons are dissipatively
coupled. Under high power excitation, a nonlinear effect is observed in the
transmission spectra, showing bistable behaviors. The observed bistabilities
are manifested as clockwise, counterclockwise, and butterfly-like hysteresis
loops with different frequency detuning. The experimental results are well
explained as a Duffing oscillator dissipatively coupled with a harmonic one and
the required trigger condition for bistability could be determined
quantitatively by the coupled oscillator model. Our results demonstrate that
the magnon damping has been suppressed by the dissipative interaction, which
thereby reduces the threshold for conventional magnon Kerr bistability. This
work sheds light upon potential applications in developing low power
nonlinearity devices, enhanced anharmonicity sensors and for exploring the
non-Hermitian physics of cavity magnonics in the nonlinear regime.",2206.01231v1
2022-06-09,Magnetically tunable zero-index metamaterials,"Zero-index metamaterials (ZIMs) feature a uniform electromagnetic mode over a
large area in arbitrary shapes, enabling many applications including
high-transmission supercouplers with arbitrary shapes, direction-independent
phase matching for nonlinear optics, and collective emission of many quantum
emitters. However, most ZIMs reported till date are passive, with no method for
the dynamic modulation of their electromagnetic properties. Here, we design and
fabricate a magnetically tunable ZIM consisting of yttrium iron garnet (YIG)
pillars sandwiched between two copper clad laminates in the microwave regime.
By harnessing the Cotton-Mouton effect of YIG, the metamaterial was
successfully toggled between gapless and bandgap states, leading to a ""phase
transition"" between a zero-index phase and a single negative phase of the
metamaterial. Using an S-shaped ZIM supercoupler, we experimentally
demonstrated a tunable supercoupling state with a low intrinsic loss of 0.95 dB
and a high extinction ratio of up to 30.63 dB at 9 GHz. Our work enables
dynamic modulation of the electromagnetic characteristics of ZIMs, enabling
various applications in tunable linear, nonlinear, quantum and nonreciprocal
electromagnetic devices.",2206.04237v1
2022-06-26,Tripartite high-dimensional magnon-photon entanglement in PT -symmetry broken phases of a non-Hermitian hybrid system,"Hybrid systems that combine spin ensembles and superconducting circuits
provide a promising platform for implementing quantum information processing.
We propose a non-Hermitian magnoncircuit-QED hybrid model consisting of two
cavities and an yttrium iron garnet (YIG) sphere placed in one of the cavities.
Abundant exceptional points (EPs), parity-time (PT )-symmetry phases and PT
-symmetry broken phases are investigated in the parameter space. Tripartite
highdimensional entangled states can be generated steadily among modes of the
magnon and photons in PT -symmetry broken phases, corresponding to which the
stable quantum coherence exists. Results show that the tripartite
high-dimensional entangled state is robust against the dissipation of hybrid
system, independent of a certain initial state, and insensitive to the
fluctuation of magnonphoton coupling. Further, we propose to simulate the
hybrid model with an equivalent LCR circuit. This work may provide prospects
for realizing multipartite high-dimensional entangled states in the
magnon-circuit-QED hybrid system.",2206.12769v1
2022-06-29,Mechanical Bistability in Kerr-modified Cavity Magnomechanics,"Bistable mechanical vibration is observed in a cavity magnomechanical system,
which consists of a microwave cavity mode, a magnon mode, and a mechanical
vibration mode of a ferrimagnetic yttrium-iron-garnet (YIG) sphere. The
bistability manifests itself in both the mechanical frequency and linewidth
under a strong microwave drive field, which simultaneously activates three
different kinds of nonlinearities, namely, magnetostriction, magnon self-Kerr,
and magnon-phonon cross-Kerr nonlinearities. The magnon-phonon cross-Kerr
nonlinearity is first predicted and measured in magnomechanics. The system
enters a regime where Kerr-type nonlinearities strongly modify the conventional
cavity magnomechanics that possesses only a radiation-pressure-like
magnomechanical coupling. Three different kinds of nonlinearities are
identified and distinguished in the experiment. Our work demonstrates a new
mechanism for achieving mechanical bistability by combining magnetostriction
and Kerr-type nonlinearities, and indicates that such Kerr-modified cavity
magnomechanics provides a unique platform for studying many distinct
nonlinearities in a single experiment.",2206.14588v2
2022-06-30,Second order nonlinearity induced multipartite entanglement in a hybrid magnon cavity QED system,"We present a proposal to produce bipartite and tripartite entanglement in a
hybrid magnon-cavity QED system. Two macroscopic yttrium iron garnet (YIG)
spheres are coupled to a single-mode microwave cavity via magnetic dipole
interaction, while the cavity photons are generated via the two photon process
induced by a pump field. Using the mean field theory, we show that the second
order nonlinearity can result in strong bipartite entanglement between cavity
photons and magnonic modes under two conditions, i.e., $\delta_c
\delta_{m}=2g^2$ and $\delta_c=-\delta_{m}$. For the later one, we also show
the possibility for producing the bipartite entanglement between two magnonic
modes and tripartite entanglement among the cavity photons and two magnonic
modes. Combining these two conditions, we further derive a third condition,
i.e., $\delta_m^2-\phi^2+2g^2=0$, where the tripartite entanglement can be
achieved when two magnonic modes have different resonant frequencies.",2206.15326v1
2022-07-07,Experimental Demonstration of High-Performance Physical Reservoir Computing with Nonlinear Interfered Spin Wave Multi-Detection,"Physical reservoir computing, which is a promising method for the
implementation of highly efficient artificial intelligence devices, requires a
physical system with nonlinearity, fading memory, and the ability to map in
high dimensions. Although it is expected that spin wave interference can
perform as highly efficient reservoir computing in some micromagnetic
simulations, there has been no experimental verification to date. Herein, we
demonstrate reservoir computing that utilizes multidetected nonlinear spin wave
interference in an yttrium iron garnet single crystal. The subject computing
system achieved excellent performance when used for hand-written digit
recognition, second-order nonlinear dynamical tasks, and nonlinear
autoregressive moving average (NARMA). It is of particular note that normalized
mean square errors (NMSEs) for NARMA2 and second-order nonlinear dynamical
tasks were 1.81x10-2 and 8.37x10-5, respectively, which are the lowest figures
for any experimental physical reservoir so far reported. Said high performance
was achieved with higher nonlinearity and the large memory capacity of
interfered spin wave multi-detection.",2207.03216v1
2022-08-08,Effect of intense x-ray free-electron laser transient gratings on the magnetic domain structure of Tm:YIG,"Magnetic patterns can be controlled globally using fields or spin polarized
currents. In contrast, the local control of the magnetization on the nanometer
length scale remains challenging. Here, we demonstrate how magnetic domain
patterns in a Tm-doped yttrium iron garnet (Tm:YIG) thin film with
perpendicular magnetic anisotropy can be permanently and locally imprinted by
high intensity photon pulses of a hard x-ray transient grating (XTG).
Micromagnetic simulations provide a qualitative understanding of the observed
changes in the orientation of magnetic domains in Tm:YIG and XTG-induced
changes. The presented results offer a route for the local manipulation of the
magnetic state using hard XTG.",2208.04200v2
2022-09-09,A spinwave Ising machine,"We demonstrate a spin-wave-based time-multiplexed Ising Machine (SWIM),
implemented using a 5 $\mu$m thick Yttrium Iron Garnet (YIG) film and
off-the-shelf microwave components. The artificial Ising spins consist of
34--68 ns long 3.125 GHz spinwave RF pulses with their phase binarized using a
phase-sensitive microwave amplifier. Thanks to the very low spinwave group
velocity, the 7 mm long YIG waveguide can host an 8-spin MAX-CUT problem and
solve it in less than 4 $\mu$s while consuming only 7 $\mu$J. Using a real-time
oscilloscope, we follow the temporal evolution of each spin as the SWIM
minimizes its energy and find both uniform and domain-propagation-like
switching of the spin state. The SWIM has the potential for substantial further
miniaturization, scalability, speed, and reduced power consumption, and may
become a versatile platform for commercially feasible optimization problem
solvers with high performance.",2209.04291v1
2022-09-21,Interactive Entanglement in Hybrid Opto-magno-mechanics System,"We present a novel cavity opto-magno-mechanical hybrid system to generate
entanglements among multiple quantum carriers, such as magnons, mechanical
resonators, and cavity photons in both the optical and microwave domains. Two
Yttrium iron garnet (YIG) spheres are embedded in two separate microwave
cavities which are joined by a communal mechanical resonator. Because the
microwave cavities are separate, the ferromagnetic resonate frequencies of two
YIG spheres can be tuned independently, as well as the cavity frequencies. We
show that entanglement can be achieved with experimentally reachable
parameters. The entanglement is robust against environmental thermal noise,
owing to the mechanical cooling process achieved by the optical cavity. The
maximum entanglement among different carriers is achieved by optimizing the
parameters of the system. The individual tunability of the separated cavities
allows us to independently control the entanglement properties of different
subsystems and establish quantum channels with different entanglement
properties in one system. This work could provide promising applications in
quantum metrology and quantum information tasks.",2209.10120v2
2022-10-03,Chirality-induced one-way quantum steering between two waveguide-mediated ferrimagnetic microspheres,"One-way quantum steering is of importance for quantum technologies, such as
secure quantum teleportation. In this paper, we study the generation of one-way
quantum steering between two distant yttrium iron garnet (YIG) microspheres in
chiral waveguide electromagonics. We consider that the magnon mode with the
Kerr nonlinearity in each YIG sphere is chirally coupled to left- and
right-propagating guided photons in the waveguide. We find that quantum
steering between the magnon modes is absent with non-chirality but is present
merely in the form of one way (i.e., one-way steering) when the chirality
occurs. The maximal achievable steering is obviously improved as the chirality
degree increases. We further find that when the waveguide's outputs are
subjected to continuous homodyne detection, the steering can be considerably
enhanced and asymmetric steering with strong entanglement can also be achieved
by tuning the chirality. Our study shows that chirality can be explored to
effectively realize one-way quantum steering. Compared to other studies on
achieving asymmetric steering via controlling intrinsic dissipation, e.g.
cavity loss rates, our scheme merely depends on the chirality enabled via
positioning the micromagnets in the waveguide and is continuously adjustable
and experimentally more feasible.",2210.00710v1
2022-10-27,Quantum-state engineering in cavity magnomechanics formed by two-dimensional magnetic materials,"Cavity magnomechanics has become an ideal platform to explore macroscopic
quantum effects. Bringing together magnons, phonons, and photons in a system,
it opens many opportunities for quantum technologies. It was conventionally
realized by an yttrium iron garnet, which exhibits a parametric magnon-phonon
coupling $\hat{m}^\dag\hat{m}(\hat{b}^\dag+\hat{b})$, with $\hat{m}$ and
$\hat{b}$ being the magnon and phonon modes. Inspired by the recent realization
of two-dimensional (2D) magnets, we propose a cavity magnomechanical system
using a 2D magnetic material with both optical and magnetic drivings. It
features the coexisting photon-phonon radiation-pressure coupling and quadratic
magnon-phonon coupling $\hat{m}^\dag\hat{m}(\hat{b}^\dag+\hat{b})^2$ induced by
the magnetostrictive interaction. A stable squeezing of the phonon and bi- and
tri-partite entanglements among the three modes are generated in the regimes
with a suppressed phonon number. Compared with previous schemes, ours does not
require any extra nonlinear interaction and reservoir engineering and is robust
against the thermal fluctuation. Enriching the realization of cavity
magnomechanics, our system exhibits its superiority in quantum-state
engineering due to the versatile interactions enabled by its 2D feature.",2210.15519v2
2022-11-27,Entangled atomic ensemble and an yttrium-iron-garnet sphere in coupled microwave cavities,"We present a scheme to generate distant bipartite and tripartite entanglement
between an atomic ensemble and an yttrium iron garnet (YIG) sphere in coupled
microwave cavities. We consider an atomic ensemble in a single-mode microwave
cavity which is coupled with a second single-mode cavity having a YIG sphere.
Our system, therefore, has five excitation modes namely cavity-1 photons,
atomic ensemble, cavity-2 photons, a magnon and a phonon mode in the YIG
sphere. We show that significant bipartite entanglement exists between
indirectly coupled subsystems in the cavities, which is robust against
temperature. Moreover, we present suitable parameters for a significant
tripartite entanglement of ensemble, magnon, and phonon modes. We also
demonstrate the existence of tripartite entanglement between magnon and phonon
modes of the YIG sphere with indirectly coupled cavity photons. Interestingly,
this distant tripartite entanglement is of the same order as previously found
for a single-cavity system. We show that cavity-cavity coupling strength
affects both the degree and transfer of quantum entanglement between various
subsystems. Therefore, an appropriate cavity-cavity coupling optimizes the
distant entanglement by increasing the entanglement strength and its robustness
against temperature.",2211.14914v2
2022-12-02,Coherent magnon-induced domain wall motion in a magnetic insulator channel,"Advancing the development of spin-wave devices requires high-quality
low-damping magnetic materials where magnon spin currents can propagate
efficiently and interact effectively with local magnetic textures. We show that
magnetic domain walls (DW) can modulate spin-wave transport in perpendicularly
magnetized channels of Bi-doped yttrium-iron-garnet (BiYIG). Conversely, we
demonstrate that the magnon spin current can drive DW motion in the BiYIG
channel device by means of magnon spin-transfer torque. The DW can be reliably
moved over 15 um distances at zero applied magnetic field by a magnon spin
current excited by an RF pulse as short as 1 ns. The required energy for
driving DW motion is orders of magnitude smaller than those reported for
metallic systems. These results facilitate low-switching-energy magnonic
devices and circuits where magnetic domains can be efficiently reconfigured by
magnon spin currents flowing within magnetic channels.",2212.01408v1
2023-01-22,Magnon bundle in a strongly dissipative magnet,"Hybrid quantum systems based on magnetic platforms have witnessed the birth
and fast development of quantum spintronics. Until now, most of the studies
rely on magnetic excitations in low-damping magnetic insulators, particularly
yttrium iron garnet, while a large class of magnetic systems is ruled out in
this interdisciplinary field. Here we propose the generation of a magnon bundle
in a hybrid magnet-qubit system, where two or more magnons are emitted
simultaneously. By tuning the driving frequency of qubit to match the detuning
between magnon and qubit mode, one can effectively generate a magnon bundle via
super-Rabi oscillations. In contrast with general wisdom, magnetic dissipation
plays an enabling role in generating the magnon bundle, where the relaxation
time of magnons determines the typical time delay between two successive
magnons. The maximal damping that allows an antibunched magnon bundle can reach
the order of 0.1, which may break the monopoly of low-dissipation magnetic
insulators in quantum spintronics and enables a large class of magnetic
materials for quantum manipulation. Further, our finding may provide a scalable
and generic platform to study multi-magnon physics and benefit the design of
magnonic networks for quantum information processing.",2301.09095v1
2023-02-14,Switchable Superradiant Phase Transition with Kerr Magnons,"The superradiant phase transition (SPT) has been widely studied in cavity
quantum electrodynamics (CQED). However, this SPT is still subject of ongoing
debates due to the no-go theorem induced by the so-called ${\bf A}^2$ term
(AT). We propose a hybrid quantum system, consisting of a single-mode cavity
simultaneously coupled to both a two-level system and yttrium-iron-garnet
sphere supporting magnons with Kerr nonlinearity, to restore the SPT against
the AT. The Kerr magnons here can effectively introduce an additional strong
and tunable AT to counteract the intrinsic AT, via adiabatically eliminating
the degrees of freedom of the magnons. We show that the Kerr magnons induced
SPT can exist in both cases of ignoring and including the intrinsic AT. Without
the intrinsic AT, the critical coupling strength can be dramatically reduced by
introducing the Kerr magnons, which greatly relaxes the experimental conditions
for observing the SPT. With the intrinsic AT, the forbidden SPT can be
recovered with the Kerr magnons in a reversed way. Our work paves a potential
way to manipulate the SPT against the AT in hybrid systems combining CQED and
nonlinear magnonics.",2302.07163v2
2023-02-24,A Fiber-coupled Scanning Magnetometer with Nitrogen-Vacancy Spins in a Diamond Nanobeam,"Magnetic imaging with nitrogen-vacancy (NV) spins in diamond is becoming an
established tool for studying nanoscale physics in condensed matter systems.
However, the optical access required for NV spin readout remains an important
hurdle for operation in challenging environments such as millikelvin cryostats
or biological systems. Here, we demonstrate a scanning-NV sensor consisting of
a diamond nanobeam that is optically coupled to a tapered optical fiber. This
nanobeam sensor combines a natural scanning-probe geometry with high-efficiency
through-fiber optical excitation and readout of the NV spins. We demonstrate
through-fiber optically interrogated electron spin resonance and
proof-of-principle magnetometry operation by imaging spin waves in an
yttrium-iron-garnet thin film. Our scanning-nanobeam sensor can be combined
with nanophotonic structuring to control the light-matter interaction strength,
and has potential for applications that benefit from all-fiber sensor access
such as millikelvin systems.",2302.12536v1
2023-03-02,Unidirectional Microwave Transduction with Chirality Selected Short-Wavelength Magnon Excitations,"Nonreciprocal magnon propagation has recently become a highly potential
approach of developing chip-embedded microwave isolators for advanced
information processing. However, it is challenging to achieve large
nonreciprocity in miniaturized magnetic thin-film devices because of the
difficulty of distinguishing propagating surface spin waves along the opposite
directions when the film thickness is small. In this work, we experimentally
realize unidirectional microwave transduction with sub-micron-wavelength
propagating magnons in a yttrium iron garnet (YIG) thin film delay line. We
achieve a non-decaying isolation of 30 dB with a broad field-tunable band-pass
frequency range up to 14 GHz. The large isolation is due to the selection of
chiral magnetostatic surface spin waves with the Oersted field generated from
the coplanar waveguide antenna. Increasing the geometry ratio between the
antenna width and YIG thickness drastically reduces the nonreciprocity and
introduces additional magnon transmission bands. Our results pave the way for
on-chip microwave isolation and tunable delay line with short-wavelength
magnonic excitations.",2303.00936v1
2023-03-08,Nonreciprocity in Cavity Magnonics at Milikelvin Temperature,"Incorporating cavity magnonics has opened up a new avenue in controlling
non-reciprocity. This work examines a yttrium iron garnet sphere coupled to a
planar microwave cavity at milli-Kelvin temperature. Non-reciprocal device
behavior results from the cooperation of coherent and dissipative coupling
between the Kittel mode and a microwave cavity mode. The device's
bi-directional transmission was measured and compared to the theory derived
previously in the room temperature experiment. Investigations are also
conducted into key performance metrics such as isolation, bandwidth, and
insertion loss. The findings point to the coexistence of coherent and
dissipative interactions at cryogenic conditions, and one can leverage their
cooperation to achieve directional isolation. This work foreshadows the
application of a cavity magnonic isolator for on-chip readout and signal
processing in superconducting circuitry.",2303.04358v1
2023-03-20,Secondary Excitation of Spin-Waves: How Electromagnetic Cross-Talk Impacts on Magnonic Devices,"This work examines the impact of electromagnetic cross-talk in magnonic
devices when using inductive spin-wave (SW) transducers. We present detailed
electrical SW spectroscopy measurements showing the signal contributions to be
considered in magnonic device design. We further provide a rule of thumb
estimation for the cross-talk that is responsible for the secondary SW
excitation at the output transducer. Simulations and calibrated electrical
characterizations underpin this method. Additionally, we visualize the
secondary SW excitation via time-resolved MOKE imaging in the forward-volume
configuration in a 100nm Yttrium-Iron-Garnet (YIG) system. Our work is a step
towards fast yet robust joint electromagentic-micromagnetic magnonic device
design.",2303.11303v2
2023-04-04,Full quantum theory for magnon transport in two-sublattice magnetic insulators and magnon junctions,"Magnon, as elementary excitation in magnetic systems, can carry and transfer
angular momentum. Due to the absence of Joule heat during magnon transport,
researches on magnon transport have gained considerable interests over the past
decade. Recently, a full quantum theory has been employed to investigate magnon
transport in ferromagnetic insulators (FMIs). However, the most commonly used
magnetic insulating material in experiments, yttrium iron garnet (YIG), is a
ferrimagnetic insulator (FIMI). Therefore, a full quantum theory for magnon
transport in FIMI needs to be established. Here, we propose a Green's function
formalism to compute the magnon bulk and interface current in both FIMIs and
antiferromagnetic insulators (AFMIs). We investigate the spatial distribution
and temperature dependence of magnon current in FIMIs and AFMIs generated by
temperature or spin chemical potential step. In AFMIs, magnon currents
generated by temperature step in the two sublattices cancel each other out.
Subsequently, we numerically simulate the magnon junction effect using the
Green's function formalism, and result shows near 100\% magnon junction ratio.
This study demonstrates the potential for investigating magnon transport in
specific magnonic devices using a full quantum theory.",2304.01930v1
2023-04-26,Critical Cavity-Magnon Polariton Mediated Strong Long-Distance Spin-Spin Coupling,"Strong long-distance spin-spin coupling is desperately demanded for
solid-state quantum information processing, but it is still challenged. Here,
we propose a hybrid quantum system, consisting of a coplanar waveguide (CPW)
resonator weakly coupled to a single nitrogen-vacancy spin in diamond and a
yttrium-iron-garnet (YIG) nanosphere holding Kerr magnons, to realize strong
long-distance spin-spin coupling. With a strong driving field on magnons, the
Kerr effect can squeeze magnons, and thus exponentially enhance the coupling
between the CPW resonator and the squeezed magnons, which produces two
cavity-magnon polaritons, i.e., the high-frequency polariton (HP) and
low-frequency polariton (LP). When the enhanced cavity-magnon coupling
approaches to the critical value, the spin is fully decoupled from the HP,
while the coupling between the spin and the LP is significantly improved. In
the dispersive regime, a strong spin-spin coupling is achieved with accessible
parameters, and the coupling distance can be up to $\sim$cm. Our proposal
provides a promising way to manipulate remote solid spins and perform quantum
information processing in weakly coupled hybrid systems.",2304.13553v2
2023-04-26,Rapid-prototyping of microscopic thermal landscapes in Brillouin light scattering spectroscopy,"Since temperature and its spatial and temporal variations affect a wide range
of physical properties of material systems, they can be used to create
reconfigurable spatial structures of various types in physical and biological
objects. This paper presents an experimental optical setup for creating tunable
two-dimensional temperature patterns on a micrometer scale. As an example of
its practical application, we have produced temperature-induced magnetization
landscapes in ferrimagnetic yttrium iron garnet films and investigated them
using micro-focused Brillouin light scattering spectroscopy. It is shown that,
due to the temperature dependence of the magnon spectrum, temperature changes
can be visualized even for microscale thermal patterns.",2304.13658v2
2023-05-10,Proposal for optomagnonic teleportation and entanglement swapping,"A protocol for realizing discrete-variable quantum teleportation in an
optomagnonic system is provided. Using optical pulses, an arbitrary photonic
qubit state encoded in orthogonal polarizations is transferred onto the joint
state of a pair of magnonic oscillators in two macroscopic yttrium-iron-garnet
(YIG) spheres that are placed in an optical interferometer. We further show
that optomagnonic entanglement swapping can be realized in an extended
dual-interferometer configuration with a joint Bell-state detection.
Consequently, magnon Bell states are prepared. We analyze the effect of the
residual thermal occupation of the magnon modes on the fidelity in both the
teleportation and entanglement swapping protocols.",2305.05889v1
2023-05-15,Quantum interference induced magnon blockade and antibunching in a hybrid quantum system,"In this work, we study the phenomena of quantum interference assisted magnon
blockade and magnon antibunching in a weakly interacting hybrid
ferromagnet-superconductor system. The magnon excitations in two yttrium iron
garnet spheres are indirectly coupled to a superconducting qubit through
microwave cavity modes of two mutually perpendicular cavities. We find that
when one of the magnon mode is driven by a weak optical field, the destructive
interference between more than two distinct transition pathways restricts
simultaneous excitation of two magnons. We analyze the magnon correlations in
the driven magnon mode for the case of zero detunings as well as finite
detunings of the magnon modes and the qubit. We show that the magnon
antibunching can be tuned by changing the magnon-qubit coupling strength ratio
and the driving detuning. Our work proposes a possible scheme which have
significant role in the construction of single magnon generating devices.",2305.08444v1
2023-05-16,Tunable all-optical logic gates based on nonreciprocal topologically protected edge modes,"All-optical logic gates have been studied intensively for their potential to
enable broadband, low-loss, and high-speed communication. However, poor
tunability has remained a key challenge in this field. In this paper, we
propose a Y-shaped structure composed of Yttrium Iron Garnet (YIG) layers that
can serve as tunable all-optical logic gates, including, but not limited to,
OR, AND, and NOT gates, by applying external magnetic fields to magnetize the
YIG layers. Our findings demonstrate that these logic gates are based on
topologically protected one-way edge modes, ensuring exceptional robustness
against imperfections and nonlocal effects while maintaining extremely high
precision. Furthermore, the operating band of the logic gates is shown to be
tunable. In addition, we introduce a straightforward and practical method for
controlling and switching the logic gates between ""work"", ""skip"", and ""stop""
modes. These findings have important implications for the design of
high-performance and precise all-optical integrated circuits.",2305.09270v1
2023-06-07,Gain assisted controllable fast light generation in cavity magnomechanics,"We study the controllable output field generation from a cavity
magnomechanical resonator system that consists of two coupled microwave
resonators. The first cavity interacts with a ferromagnetic yttrium iron garnet
(YIG) sphere providing the magnon-photon coupling. Under passive cavities
configuration, the system displays high absorption, prohibiting output
transmission even though the dispersive response is anamolous. We replace the
second passive cavity with an active one to overcome high absorption, producing
an effective gain in the system. We show that the deformation of the YIG sphere
retains the anomalous dispersion. Further, tuning the exchange interaction
strength between the two resonators leads to the system's effective gain and
dispersive response. As a result, the advancement associated with the
amplification of the probe pulse can be controlled in the close vicinity of the
magnomechanical resonance. Furthermore, we find the existence of an upper bound
for the intensity amplification and the advancement of the probe pulse that
comes from the stability condition. These findings may find potential
applications for controlling light propagation in cavity magnomechanics.",2306.04390v1
2023-07-04,Magnonic Hong-Ou-Mandel Effect,"We carried out numerical simulations of propagation of spin waves (magnons in
quantum language) in a yttrium-iron garnet film. The numerical model is based
on an original formalism. We demonstrated that a potential barrier for magnons,
created by an Oersted field of a dc current flowing through a wire sitting on
top of the film, is able to act as an electrically controlled partly
transparent mirror for the magnons. We found that the mirror transparency can
be set to 50% by properly adjusting the current strength, thus creating a
semi-transparent mirror. A strong Hong-Ou-Mandel Effect for single magnons is
expected in this configuration. The effect must be seen as two single magnons,
launched simultaneously into the film from two transducers located from the
opposite sides of the mirror, creating a two-microwave-photon state at the
output port of one of the transducers. The probability of seeing those
two-photon states at the output port of either transducer must be the same for
both transducers.",2307.01547v1
2023-07-06,Realization of the unidirectional amplification in a cavity magnonic system,"We experimentally demonstrate the nonreciprocal microwave amplification using
a cavity magnonic system, consisting of a passive cavity (i.e., the split-ring
resonator), an active feedback circuit integrated with an amplifier, and a
ferromagnetic spin ensemble (i.e., a yttrium-iron-garnet sphere). Combining the
amplification provided by the active circuit and the nonreciprocity supported
by the cavity magnonics, we implement a nonreciprocal amplifier with the
functions of both unidirectional amplification and reverse isolation. The
microwave signal is amplified by 11.5 dB in the forward propagating direction
and attenuated in the reverse direction by -34.7 dB, giving an isolation ratio
of 46.2 dB. Such a unidirectional amplifier can be readily employed in quantum
technologies, where the device can simultaneously amplify the weak signal
output by the quantum system and isolate the sensitive quantum system from the
backscattered external noise. Also, it is promising to explore more functions
and applications using a cavity magnonic system with real gain.",2307.02826v2
2023-07-19,Zero-field spin waves in YIG nano-waveguides,"Spin-wave based transmission and processing of information is a promising
emerging nano-technology that can help overcome limitations of traditional
electronics based on the transfer of electrical charge. Among the most
important challenges for this technology is the implementation of spin-wave
devices that can operate without the need for an external bias magnetic field.
Here we experimentally demonstrate that this can be achieved using
sub-micrometer wide spin-wave waveguides fabricated from ultrathin films of
low-loss magnetic insulator - Yttrium Iron Garnet (YIG). We show that these
waveguides exhibit a highly stable single-domain static magnetic configuration
at zero field and support long-range propagation of spin waves with gigahertz
frequencies. The experimental results are supported by micromagnetic
simulations, which additionally provide information for optimization of
zero-field guiding structures. Our findings create the basis for the
development of energy-efficient zero-field spin-wave devices and circuits.",2307.09805v1
2023-07-19,Enhanced bipartite entanglement and Gaussian quantum steering of squeezed magnon modes,"We theoretically investigate a scheme to entangle two squeezed magnon modes
in a double cavitymagnon system, where both cavities are driven by a two-mode
squeezed vacuum microwave field. Each cavity contains an optical parametric
amplifier as well as a macroscopic yttrium iron garnet (YIG) sphere placed near
the maximum bias magnetic fields such that this leads to the excitation of the
relevant magnon mode and its coupling with the corresponding cavity mode. We
have obtained optimal parameter regimes for achieving the strong magnon-magnon
entanglement and also studied the effectiveness of this scheme towards the
mismatch of both the cavity-magnon couplings and decay parameters. We have also
explored the entanglement transfer efficiency including Gaussian quantum
steering in our proposed system",2307.09846v1
2023-07-31,Gating ferromagnetic resonance of magnetic insulators by superconductors via modulating electric-field radiation,"We predict that ferromagnetic resonance in insulating magnetic film with
inplane magnetization radiates electric fields polarized along the
magnetization with opposite amplitudes at two sides of the magnetic insulator,
which can be modulated strongly by adjacent superconductors. With a single
superconductor adjacent to the magnetic insulator this radiated electric field
is totally reflected with a $\pi$-phase shift, which thereby vanishes at the
superconductor side and causes no influence on the ferromagnetic resonance.
When the magnetic insulator is sandwiched by two superconductors, this
reflection becomes back and forth, so the electric field exists at both
superconductors that drives the Meissner supercurrent, which in turn shifts
efficiently the ferromagnetic resonance. We predict an ultrastrong coupling
between magnons in the yttrium iron garnet and Cooper pairs in NbN with the
frequency shift achieving tens of percent of the bare ferromagnetic resonance.",2307.16472v2
2023-08-15,Global biasing using a Hardware-based artificial Zeeman term in Spinwave Ising Machines,"A spinwave Ising machine (SWIM) is a newly proposed type of time-multiplexed
hardware solver for combinatorial optimization that employs feedback coupling
and phase sensitive amplification to map an Ising Hamiltonian into
phase-binarized propagating spin-wave RF pulses in an Yttrium-Iron-Garnet (YIG)
film. In this work, we increase the mathematical complexity of the SWIM by
adding a global Zeeman term to a 4-spin MAX-CUT Hamiltonian using a continuous
external electrical signal with the same frequency as the spin pulses and phase
locked with with one of the two possible states. We are able to induce
ferromagnetic ordering in both directions of the spin states despite
antiferromagnetic pairwise coupling. Embedding a planar antiferromagnetic spin
system in a magnetic field has been proven to increase the complexity of the
graph associated to its Hamiltonian and thus this straightforward
implementation helps explore higher degrees of complexity in this evolving
solver.",2308.07718v1
2023-08-25,Macroscopic distant magnon modes entanglement via a squeezed reservoir,"The generation of robust entanglement in quantum system arrays is a crucial
aspect of the realization of efficient quantum information processing.
Recently, the field of quantum magnonics has garnered significant attention as
a promising platform for advancing in this direction. In our proposed scheme,
we utilize a one-dimensional array of coupled cavities, with each cavity
housing a single yttrium iron garnet (YIG) sphere coupled to the cavity mode
through magnetic dipole interaction. To induce entanglement between YIGs, we
employ a local squeezed reservoir, which provides the necessary nonlinearity
for entanglement generation. Our results demonstrate the successful generation
of bipartite and tripartite entanglement between distant magnon modes, all
achieved through a single quantum reservoir. Furthermore, the steady-state
entanglement between magnon modes is robust against magnon dissipation rates
and environment temperature. Our results may lead to applications of
cavity-magnon arrays in quantum information processing and quantum
communication systems.",2308.13586v3
2023-08-28,Spin wave mode conversion in an in-plane magnetized microscale T-shaped YIG magnonic splitter,"As one of the fundamental magnonic devices, a magnonic splitter device has
been proposed and spin wave propagation in this device has been studied
numerically and experimentally. In the present work, we fabricated a T-shaped
magnonic splitter with 6 $\mu$m-wide three arms using a 100 nm-thick yttrium
iron garnet film and, using time-resolved magneto-optic Kerr microscopy,
observed that spin waves split into both, the vertical and the horizontal
direction at the junction. Analyzing the results, we found that spin wave modes
are converted into another during the splitting process and the splitting
efficiency is dominantly dependent on the 1st order of incoming spin waves.",2308.14327v1
2023-08-30,Chiral cavity-magnonic system for the unidirectional emission of a tunable squeezed microwave field,"Unidirectional photon emission is crucial for constructing quantum networks
and realizing scalable quantum information processing. In the present work an
efficient scheme is developed for the unidirectional emission of a tunable
squeezed microwave field. Our scheme is based on a chiral cavity magnonic
system, where a magnon mode in a single-crystalline yttrium iron garnet (YIG)
sphere is selectively coupled to one of the two degenerate rotating microwave
modes in a torus-shaped cavity with the same chirality. With the YIG sphere
driven by a two-color Floquet field to induce sidebands in the magnon-photon
coupling, we show that the unidirectional emission of a tunable squeezed
microwave field can be generated via the assistance of the dissipative magnon
mode and a waveguide. Moreover, the direction of the proposed one-way emitter
can be controlled on demand by reversing the biased magnetic field. Our work
opens up an avenue to create and manipulate one-way nonclassical microwave
radiation field and could find potential quantum technological applications.",2308.15826v1
2023-09-08,Programmable Real-Time Magnon Interference in Two Remotely Coupled Magnonic Resonators,"Magnon interference is a signature of coherent magnon interactions for
coherent information processing. In this work, we demonstrate programmable
real-time magnon interference, with examples of nearly perfect constructive and
destructive interference, between two remotely coupled yttrium iron garnet
spheres mediated by a coplanar superconducting resonator. Exciting one of the
coupled resonators by injecting single- and double-microwave pulse leads to the
coherent energy exchange between the remote magnonic resonators and allows us
to realize a programmable magnon interference that can define an arbitrary
state of coupled magnon oscillation. The demonstration of time-domain coherent
control of remotely coupled magnon dynamics offers new avenues for advancing
coherent information processing with circuit-integrated hybrid magnonic
networks.",2309.04289v1
2023-09-12,Anisotropy-assisted magnon condensation in ferromagnetic thin films,"We theoretically demonstrate that adding an easy-axis magnetic anisotropy
facilitates magnon condensation in thin yttrium iron garnet (YIG) films.
Dipolar interactions in a quasi-equilibrium state stabilize room-temperature
magnon condensation in YIG. Even though the out-of-plane easy-axis anisotropy
generally competes with the dipolar interactions, we show that adding such
magnetic anisotropy may even assist the generation of the magnon condensate
electrically via the spin transfer torque mechanism. We use analytical
calculations and micromagnetic simulations to illustrate this effect. Our
results may explain the recent experiment on Bi-doped YIG and open a pathway
toward applying current-driven magnon condensation in quantum spintronics.",2309.05982v3
2023-09-17,Highly-tunable and strong nonreciprocity in coupled nonlinear cavity magnonics,"Nonreciprocity, which violates Lorentz reciprocity, plays a pivotal role in
quantum information processing and networks. Nevertheless, achieving a desired
and highly-tunable level of nonreciprocity has proven to be a formidable
challenge. Here, we propose a coupled nonlinear cavity magnonic system,
consisting of two cavities, a second-order nonlinear element, and a
yttrium-iron-garnet sphere for supporting Kerr magnons, to realize this
sought-after highly-tunable nonreciprocity. We first derive the critical
condition for switching between reciprocity and nonreciprocity with undriven
magnons, then we numerically demonstrate that a strong magnonic nonreciprocity
can be obtained by breaking the critical condition. When magnons are driven, we
show that a strong magnonic nonreciprocity can also be attained within the
critical condition. Compared to previous study, the introduced nonlinear
element not only relaxes the critical condition to both the weak and strong
regimes, but also offers an alternative path to adjust the magnonic
nonreciprocity. Our work provides a promising avenue to realize highly-tunable
nonreciprocal devices with Kerr magnons.",2309.09245v2
2023-09-28,Engineering Entangled Coherent States of Magnons and Phonons via a Transmon Qubit,"We propose a scheme for generating and controlling entangled coherent states
(ECS) of magnons, i.e. the quanta of the collective spin excitations in
magnetic systems, or phonons in mechanical resonators. The proposed hybrid
circuit architecture comprises a superconducting transmon qubit coupled to a
pair of magnonic Yttrium Iron Garnet (YIG) spherical resonators or mechanical
beam resonators via flux-mediated interactions. Specifically, the coupling
results from the magnetic/mechanical quantum fluctuations modulating the qubit
inductor, formed by a superconducting quantum interference device (SQUID). We
show that the resulting radiation-pressure interaction of the qubit with each
mode, can be employed to generate maximally-entangled states of magnons or
phonons. In addition, we numerically demonstrate a protocol for the preparation
of magnonic and mechanical Bell states with high fidelity including realistic
dissipation mechanisms. Furthermore, we have devised a scheme for reading out
the prepared states using standard qubit control and resonator field
displacements. Our work demonstrates an alternative platform for quantum
information using ECS in hybrid magnonic and mechanical quantum networks.",2309.16514v1
2023-10-13,Magnon spin capacitor,"In this work we show that a magnon spin capacitor can be realized at a
junction between two exchange coupled ferromagnets. In this junction, the
buildup of magnon spin over the junction is coupled to the difference in magnon
chemical potential, realizing the magnon spin analogue of an electrical
capacitor. The relation between magnon spin and magnon chemical potential
difference directly follows from considering the magnon density-density
interaction between the two ferromagnets. We analyse the junction in detail by
considering spin injection and detection from normal metal leads, the tunneling
current across the junction and magnon decay within the ferromagnet, showing
that such a structure realizes a magnon spin capacitor in series with a spin
resistor. Choosing yttrium iron garnet as the ferromagnet, we numerically
calculate the capacitance, which ranges from picofarad to microfarad, depending
on the area of the junction. We therefore conclude that the magnon spin
capacitor could directly be of use in applications.",2310.09064v3
2023-11-17,Machine Learning Assisted Characterization of Labyrinthine Pattern Transitions,"We present a comprehensive approach to characterizing labyrinthine structures
that often emerge as a final steady state in pattern forming systems. We employ
machine learning based pattern recognition techniques to identify the types and
locations of topological defects of the local stripe ordering to augment
conventional Fourier analysis. A pair distribution function analysis of the
topological defects reveals subtle differences between labyrinthine structures
which are beyond the conventional characterization methods. We utilize our
approach to highlight a clear morphological transition between two zero-field
labyrinthine structures in single crystal Bi substituted Yttrium Iron Garnet
films. An energy landscape picture is proposed to understand the athermal
dynamics that governs the observed morphological transition. Our work
demonstrates that machine learning based recognition techniques enable novel
studies of rich and complex labyrinthine type structures universal to many
pattern formation systems.",2311.10558v1
2023-12-08,Towards an experimental proof of the magnonic Aharonov$-$Casher effect,"Controlling the phase and amplitude of spin waves in magnetic insulators with
an electric field opens the way to fast logic circuits with ultra-low power
consumption. One way to achieve such control is to manipulate the magnetization
of the medium via magnetoelectric effects. In experiments with magnetostatic
spin waves in an yttrium iron garnet film, we have obtained the first evidence
of a theoretically predicted phenomenon: The change of the spin-wave phase due
to the magnonic Aharonov$-$Casher effect$-$the geometric accumulation of the
magnon phase as these quasiparticles propagate through an electric field
region.",2312.05113v1
2024-01-03,Synthetically enhanced sensitivity using higher-order exceptional point and coherent perfect absorption,"Sensors play a crucial role in advanced apparatuses and it is persistently
pursued to improve their sensitivities. Recently, the singularity of a
non-Hermitian system, known as the exceptional point (EP), has drawn much
attention for this goal. Response of the eigenfrequency shift to a perturbation
$\epsilon$ follows the $\epsilon^{1/n}$-dependence at an $n$th-order EP,
leading to significantly enhanced sensitivity via a high-order EP. However, due
to the requirement of increasingly complicated systems, great difficulties will
occur along the path of increasing the EP order to enhance the sensitivity.
Here we report that by utilizing the spectral anomaly of the coherent perfect
absorption (CPA), the sensitivity at a third-order EP can be further enhanced
owing to the cooperative effects of both CPA and EP. We realize this
synthetically enhanced sensor using a pseudo-Hermitian cavity magnonic system
composed of two yttrium iron garnet spheres and a microwave cavity. The
detectable minimum change of the magnetic field reaches $4.2\times10^{-21}$T.
It opens a new avenue to design novel sensors using hybrid non-Hermitian
quantum systems.",2401.01613v1
2024-01-17,Giant Enhancement of Vacuum Friction in Spinning YIG Nanospheres,"Experimental observations of vacuum radiation and vacuum frictional torque
are challenging due to their vanishingly small effects in practical systems.
For example, a rotating nanosphere in free space slows down due to friction
from vacuum fluctuations with a stopping time around the age of the universe.
Here, we show that a spinning yttrium iron garnet (YIG) nanosphere near
aluminum or YIG slabs exhibits vacuum radiation eight orders of magnitude
larger than other metallic or dielectric spinning nanospheres. We achieve this
giant enhancement by exploiting the large near-field magnetic local density of
states in YIG systems, which occurs in the low-frequency GHz regime comparable
to the rotation frequency. Furthermore, we propose a realistic experimental
setup for observing the effects of this large vacuum radiation and frictional
torque under experimentally accessible conditions.",2401.09563v1
2024-01-22,Generating magnon Bell states via parity measurement,"We propose a scheme to entangle two magnon modes based on parity measurement.
In particular, we consider a system that two yttrium-iron-garnet spheres are
coupled to a $V$-type superconducting qutrit through the indirect interactions
mediated by cavity modes. An effective parity-measurement operator that can
project the two macroscopic spin systems to the desired subspace emerges when
the ancillary qutrit is projected to the ground state. Consequently,
conventional and multi-excitation magnon Bell states can be generated from any
separable states with a nonvanishing population in the desired subspace. The
target state can be distilled with a near-to-unit fidelity only by several
rounds of measurements and can be stabilized in the presence of decoherence. In
addition, a single-shot version of our scheme is obtained by shaping the
detuning in the time domain. Our scheme that does not rely on any nonlinear
effect brings insight to the entangled-state generation in massive
ferrimagnetic materials via quantum measurement.",2401.11684v1
2024-01-22,Theory of momentum-resolved magnon electron energy loss spectra: The case of Yttrium Iron Garnet,"We explore the inelastic spectra of electrons impinging in a magnetic system.
The methodology here presented is intended to highlight the charge-dependent
interaction of the electron beam in a STEM-EELS experiment, and the local
vector potential generated by the magnetic lattice. This interaction shows an
intensity $10^{-2}$ smaller than the purely spin interaction, which is taken to
be functionally the same as in the inelastic neutron experiment. On the other
hand, it shows a strong scattering vector dependence ($\kappa^{-4}$) and a
dependence with the relative orientation between the probe wavevector and the
local magnetic moments of the solid. We present YIG as a case study due to its
high interest by the community.",2401.12302v2
2024-01-30,Entropy production rate and correlations of cavity magnomechanical system,"We present the irreversibility generated by a stationary cavity
magnomechanical system composed of a yttrium iron garnet (YIG) sphere with a
diameter of a few hundred micrometers inside a microwave cavity. In this
system, the magnons, i.e., collective spin excitations in the sphere, are
coupled to the cavity photon mode via magnetic dipole interaction and to the
phonon mode via magnetostrictive force (optomechanical-like). We employ the
quantum phase space formulation of the entropy change to evaluate the
steady-state entropy production rate and associated quantum correlation in the
system. We find that the behavior of the entropy flow between the cavity photon
mode and the phonon mode is determined by the magnon-photon coupling and the
cavity photon dissipation rate. Interestingly, the entropy production rate can
increase/decrease depending on the strength of the magnon-photon coupling and
the detuning parameters. We further show that the amount of correlations
between the magnon and phonon modes is linked to the irreversibility generated
in the system for small magnon-photon coupling. Our results demonstrate the
possibility of exploring irreversibility in driven magnon-based hybrid quantum
systems and open a promising route for quantum thermal applications.",2401.16857v1
2024-02-05,Controlling magnon-photon coupling in a planar geometry,"The tunability of magnons enables their interaction with various other
quantum excitations, including photons, paving the route for novel hybrid
quantum systems. Here, we study magnon-photon coupling using a high-quality
factor split-ring resonator and single-crystal yttrium iron garnet (YIG)
spheres at room temperature. We investigate the dependence of the coupling
strength on the size of the sphere and find that the coupling is stronger for
spheres with a larger diameter as predicted by theory. Furthermore, we
demonstrate strong magnon-photon coupling by varying the position of the YIG
sphere within the resonator. Our experimental results reveal the expected
correlation between the coupling strength and the rf magnetic field. These
findings demonstrate the control of coherent magnon-photon coupling through the
theoretically predicted square-root dependence on the spin density in the
ferromagnetic medium and the magnetic dipolar interaction in a planar
resonator.",2402.03071v1
2024-02-07,Breaking surface plasmon excitation constraint via surface spin waves,"Surface plasmons in two-dimensional (2D) electron systems have attracted
great attention for their promising light-matter applications. However, the
excitation of a surface plasmon, in particular, transverse-electric (TE)
surface plasmon, remains an outstanding challenge due to the difficulty to
conserve energy and momentum simultaneously in the normal 2D materials. Here we
show that the TE surface plasmons ranging from gigahertz to terahertz regime
can be effectively excited and manipulated in a hybrid dielectric, 2D material
and magnet structure. The essential physics is that the surface spin wave
supplements an additional freedom of surface plasmon excitation and thus
greatly enhances the electric field in the 2D medium. Based on widely-used
magnetic materials like yttrium iron garnet (YIG) and manganese difluoride
($\mathrm{MnF}_2$), we further show that the plasmon excitation manifests
itself as a measurable dip in the reflection spectrum of the hybrid system
while the dip position and the dip depth can be well controlled by the electric
gating on the 2D layer and an external magnetic field. Our findings should
bridge the fields of low-dimensional physics, plasmonics and spintronics and
open a novel route to integrate plasmonic and spintronic devices.",2402.04626v1
2024-02-22,Unraveling the origin of antiferromagnetic coupling at YIG/permalloy interface,"We investigate the structural and electronic origin of antiferromagnetic
coupling in the Yttrium iron garnet (YIG) and permalloy (Py) bilayer system at
the atomic level. Ferromagnetic Resonance (FMR) reveal unique hybrid modes in
samples prepared with surface ion milling, indicative of antiferromagnetic
exchange coupling at the YIG/Py interface. Using scanning transmission electron
microscopy (STEM), we highlight significant interfacial differences introduced
by ion-milling. The observations suggests that the antiferromagnetic coupling
in YIG/Py bilayers is predominantly driven by an oxygen-mediated super-exchange
coupling mechanism on the tetrahedral Fe terminated YIG surface, which is
supported by density functional theory (DFT) calculations. This research
provides critical insight into the fundamental mechanisms governing the
efficiency of coupling in magnetic bilayers and underscores the pivotal role of
oxide surface termination in modulating magnetic interfacial dynamics.",2402.14553v2
2024-03-05,Generation of gigahertz frequency surface acoustic waves in YIG/ZnO heterostructures,"We study surface acoustic waves (SAWs) in yttrium iron garnet (YIG)/zinc
oxide (ZnO) heterostructures, comparing the results of a computationally
lightweight analytical model with time-resolved micro-focused Brillouin light
scattering data. Interdigital transducers (IDTs), with operational frequencies
in the gigahertz regime, were fabricated on 50 and 100nm thin films of YIG
prior to sputter deposition of 830nm and 890nm films of piezoelectric ZnO. We
find good agreement between our analytical model and micro-focused Brillouin
light scattering data of the IDT frequency response and SAW group velocity,
with clear differentiation between the Rayleigh and Sezawa-like modes. This
work paves the way for the study of SAW-spin wave (SW) interactions in low SW
damping YIG, with the possibility of a method for future energy-efficient SW
excitation.",2403.03006v1
2024-03-23,Spatial Control of Hybridization-Induced Spin-Wave Transmission Stop Band,"Spin-wave (SW) propagation close to the hybridization-induced transmission
stop band is investigated within a trapezoid-shaped 200\,nm thick yttrium iron
garnet (YIG) film using time-resolved magneto-optic Kerr effect (TR-MOKE)
microscopy and broadband spin wave spectroscopy, supported by micromagnetic
simulations. The gradual reduction of the effective field within the structure
leads to local variations of the SW dispersion relation and results in a SW
hybridization at a fixed position in the trapezoid where the propagation
vanishes since the SW group velocity approaches zero. By tuning external field
or frequency, spatial control of the spatial stop band position and spin-wave
propagation is demonstrated and utilized to gain transmission control over
several microstrip lines.",2403.15840v1
2024-03-28,Influence of disorder at Insulator-Metal interface on spin transport,"Motivated by experimental work showing enhancement of spin transport between
Yttrium Iron Garnet and Platinum by a thin antiferromagnetic insulator between
them, we consider spin transport through the interface of a non-magnetic metal
and compensated antiferromagnetically ordered insulator and focus on the
significance of the interface itself. The spin transport is carried by
spin-polarized electrons in the metal and by magnons in the insulator. We
compute the spin current in the presence of a spin accumulation in the metal,
cause by the spin Hall effect, and a thermal gradient using Fermi's Golden Rule
in the presence of interfacial disorder. For a perfectly clean interface, the
in-plane momentum is conserved by the electron-magnon scattering events that
govern the spin transport through the interface. We calculate how
disorder-induced broadening of scattering matrix elements with respect to the
in-plane momentum influences the spin current. As a general result, we observe
that for many experimental setups, specifically for high temperatures, one
should expect a rather small effect of interface disorder on the measured spin
current, while for small temperatures there is a significant reduction of a
spin current with increasing disorder.",2403.19277v1
2024-04-03,Enhancement of Magnon Transport by Superconductor Meissner Screening,"Recent experiments observe the spin-wave-Meissner-current modes in
ferromagnetic insulator-superconductor heterostructures, in which the
coherently excited spin waves seemingly do not decay as usual beneath the
superconductor strip [Borst et al., Science 382, 430 (2023)]. We interpret this
phenomenon by demonstrating that the stray magnetic field emitted by the
magnetization dynamics is reflected, focused, and enhanced inside the
ferromagnet by the supercurrent induced in the superconductor, such that the
group velocity of spin waves is strongly enhanced. Analytical and numerical
calculations based on this model predict that the coherent transport of magnons
is enhanced by close to 500% for yttrium iron garnet capped by superconducting
NbN with a decay length exceeding millimeters. Our finding may augment the
performance of magnons in quantum information and quantum transport processing.",2404.02598v1
2022-03-03,Optical Properties of Yttrium Gallium Garnet,"We report measurements of the reflection and transmission spectra of 2% doped
Thulium Yttrium Gallium Garnet (Tm:YGG) using variable-angle spectroscopic
ellipsometry(VASE) over a wavelength range from 210 to 1680 nm (0.73-5.9 eV).
The well-known Tm resonances are identified and separated from the aggregate
data, allowing us to calculate the previously unknown frequency dependence of
the complex refractive index of the host material. This information is
important for many applications of YGG in classical and quantum photonics,
including constructing optical cavities, laser-based applications, and quantum
information devices. A complete database of the obtained parameters is included
in the supplementary information.",2203.01689v1
2023-08-14,Investigation of Phonon Lifetimes and Magnon-Phonon Coupling in YIG/GGG Hybrid Magnonic Systems in the Diffraction Limited Regime,"Quantum memories facilitate the storage and retrieval of quantum information
for on-chip and long-distance quantum communications. Thus, they play a
critical role in quantum information processing and have diverse applications
ranging from aerospace to medical imaging fields. Bulk acoustic wave (BAW)
phonons are one of the most attractive candidates for quantum memories because
of their long lifetime and high operating frequency. In this work, we establish
a modeling approach that can be broadly used to design hybrid magnonic
high-overtone bulk acoustic wave resonator (HBAR) structures for high-density,
long-lasting quantum memories and efficient quantum transduction devices. We
illustrate the approach by investigating a hybrid magnonic system, where BAW
phonons are excited in a gadolinium iron garnet (GGG) thick film via coupling
with magnons in a patterned yttrium iron garnet (YIG) thin film. We present
theoretical and numerical analyses of the diffraction-limited BAW phonon
lifetimes, modeshapes, and their coupling strengths to magnons in planar and
confocal YIG/GGG HBAR structures. We utilize Fourier beam propagation and
Hankel transform eigenvalue problem methods and discuss the effectiveness of
the two methods to predict the HBAR phonons. We discuss strategies to improve
the phonon lifetimes, since increased lifetimes have direct implications on the
storage times of quantum states for quantum memory applications. We find that
ultra-high, diffraction-limited, cooperativities and phonon lifetimes on the
order of ~10^5 and ~10 milliseconds, respectively, could be achieved using a
CHBAR structure with 10mum lateral YIG dimension. Additionally, the confocal
HBAR structure will offer more than 100-fold improvement of integration
density. A high integration density of on-chip memory or transduction centers
is naturally desired for high-density memory or transduction devices.",2308.06896v2
2013-04-23,Quantitative study of the spin Hall magnetoresistance in ferromagnetic insulator/normal metal hybrids,"We experimentally investigate and quantitatively analyze the spin Hall
magnetoresistance effect in ferromagnetic insulator/platinum and ferromagnetic
insulator/nonferromagnetic metal/platinum hybrid structures. For the
ferromagnetic insulator we use either yttrium iron garnet, nickel ferrite or
magnetite and for the nonferromagnet copper or gold. The spin Hall
magnetoresistance effect is theoretically ascribed to the combined action of
spin Hall and inverse spin Hall effect in the platinum metal top layer. It
therefore should characteristically depend upon the orientation of the
magnetization in the adjacent ferromagnet, and prevail even if an additional,
nonferromagnetic metal layer is inserted between Pt and the ferromagnet. Our
experimental data corroborate these theoretical conjectures. Using the spin
Hall magnetoresistance theory to analyze our data, we extract the spin Hall
angle and the spin diffusion length in platinum. For a spin mixing conductance
of $4\times10^{14}\;\mathrm{\Omega^{-1}m^{-2}}$ we obtain a spin Hall angle of
$0.11\pm0.08$ and a spin diffusion length of $(1.5\pm0.5)\;\mathrm{nm}$ for Pt
in our thin film samples.",1304.6151v1
2013-08-17,Thickness and power dependence of the spin-pumping effect in Y3Fe5O12/Pt heterostructures measured by the inverse spin Hall effect,"The dependence of the spin-pumping effect on the yttrium iron garnet
(Y3Fe5O12, YIG) thickness detected by the inverse spin Hall effect (ISHE) has
been investigated quantitatively. Due to the spin-pumping effect driven by the
magnetization precession in the ferrimagnetic insulator YIG film a
spin-polarized electron current is injected into the Pt layer. This spin
current is transformed into electrical charge current by means of the ISHE. An
increase of the ISHE-voltage with increasing film thickness is observed and
compared to the theoretically expected behavior. The effective damping
parameter of the YIG/Pt samples is found to be enhanced with decreasing YIG
film thickness. The investigated samples exhibit a spin mixing conductance of
g=(7.43 \pm 0.36) \times 10^{18} m^{-2} and a spin Hall angle of theta_{ISHE} =
0.009 \pm 0.0008. Furthermore, the influence of nonlinear effects on the
generated voltage and on the Gilbert damping parameter at high excitation
powers are revealed. It is shown that for small YIG film thicknesses a
broadening of the linewidth due to nonlinear effects at high excitation powers
is suppressed because of a lack of nonlinear multi-magnon scattering channels.
We have found that the variation of the spin-pumping efficiency for thick YIG
samples exhibiting pronounced nonlinear effects is much smaller than the
nonlinear enhancement of the damping.",1308.3787v1
2014-02-15,Measurement of the intrinsic damping constant in individual nanodisks of YIG and YIG{\textbar}Pt,"We report on an experimental study on the spin-waves relaxation rate in two
series of nanodisks of diameter $\phi=$300, 500 and 700~nm, patterned out of
two systems: a 20~nm thick yttrium iron garnet (YIG) film grown by pulsed laser
deposition either bare or covered by 13~nm of Pt. Using a magnetic resonance
force microscope, we measure precisely the ferromagnetic resonance linewidth of
each individual YIG and YIG{\textbar}Pt nanodisks. We find that the linewidth
in the nanostructure is sensibly smaller than the one measured in the extended
film. Analysis of the frequency dependence of the spectral linewidth indicates
that the improvement is principally due to the suppression of the inhomogeneous
part of the broadening due to geometrical confinement, suggesting that only the
homogeneous broadening contributes to the linewidth of the nanostructure. For
the bare YIG nano-disks, the broadening is associated to a damping constant
$\alpha = 4 \cdot 10^{-4}$. A 3 fold increase of the linewidth is observed for
the series with Pt cap layer, attributed to the spin pumping effect. The
measured enhancement allows to extract the spin mixing conductance found to be
$G_{\uparrow \downarrow}= 1.55 \cdot 10^{14}~ \Omega^{-1}\text{m}^{-2}$ for our
YIG(20nm){\textbar}Pt interface, thus opening large opportunities for the
design of YIG based nanostructures with optimized magnetic losses.",1402.3630v1
2014-08-13,High Cooperativity Cavity QED with Magnons at Microwave Frequencies,"Using a sub-millimetre sized YIG (Yttrium Iron Garnet) sphere mounted in a
magnetic field-focusing cavity, we demonstrate an ultra-high cooperativity of
$10^5$ between magnon and photon modes at millikelvin temperatures and
microwave frequencies. The cavity is designed to act as a magnetic dipole by
using a novel multiple-post approach, effectively focusing the cavity magnetic
field within the YIG crystal with a filling factor of 3%. Coupling strength
(normal-mode splitting) of 2 GHz, (equivalent to 76 cavity linewidths or $0.3$
Hz per spin), is achieved for a bright cavity mode that constitutes about 10%
of the photon energy and shows that ultra-strong coupling is possible in spin
systems at microwave frequencies. With straight forward optimisations we
demonstrate that with that this system has the potential to reach
cooperativities of $10^7$, corresponding to a normal mode splitting of 5.2 GHz
and a coupling per spin approaching 1 Hz. We also observe a three-mode strong
coupling regime between a dark cavity mode and a magnon mode doublet pair,
where the photon-magnon and magnon-magnon couplings (normal-mode splittings)
are 143 MHz and 12.5 MHz respectively, with HWHM bandwidth of about 0.5 MHz.",1408.2905v3
2014-08-25,Measurements of the exchange stiffness of YIG films by microwave resonance techniques,"Measurements of the exchange stiffness $D$ and the exchange constant $A$ of
Yttrium Iron Garnet (YIG) films are presented. The YIG films with thicknesses
from 0.9 $\mu$m to 2.6 $\mu$m were investigated with a microwave setup in a
wide frequency range from 5 to 40 GHz. The measurements were performed when the
external static magnetic field was applied in-plane and out-of-plane. The
method of Schreiber and Frait, based on the analysis of the perpendicular
standing spin wave (PSSW) mode frequency dependence on the applied out-of-plane
magnetic field, was used to obtain the exchange stiffness $D$. This method was
modified to avoid the influence of internal magnetic fields during the
determination of the exchange stiffness. Furthermore, the method was adapted
for in-plane measurements as well. The results obtained using all methods are
compared and values of $D$ between $(5.18\pm0.01) \cdot 10^{-17}$T$\cdot$m$^2$
and $(5.34\pm0.02) \cdot 10^{-17}$ T$\cdot$m$^2$ were obtained for different
thicknesses. From this the exchange constant was calculated to be $A=(3.65 \pm
0.38)~$pJ/m.",1408.5772v1
2014-09-19,Study of strong photon-magnon coupling in a YIG-film split-ring resonant system,"By using the stripline Microwave Vector Network Analyzer Ferromagnetic
Resonance and Pulsed Inductive Microwave Magnetometry spectroscopy techniques,
we study a strong coupling regime of magnons to microwave photons in the planar
geometry of a lithographically formed split-ring resonator (SRR) loaded by a
single-crystal epitaxial yttrium-iron garnet (YIG) film. Strong anti-crossing
of the photon modes of SRR and of the magnon modes of the YIG film is observed
in the applied-magnetic-field resolved measurements. The coupling strength
extracted from the experimental data reaches 9 percent at 3 GHz.
  Theoretically, we propose an equivalent circuit model of an SRR loaded by a
magnetic film. This model follows from the results of our numerical simulations
of the microwave field structure of the SRR and of the magnetization dynamics
in the YIG film driven by the microwave currents in the SRR. The equivalent
circuit model is in good agreement with the experiment. It provides a simple
physical explanation of the process of mode anti-crossing.
  Our findings are important for future applications in microwave quantum
photonic devices as well as in magnetically tunable metamaterials exploiting
the strong coupling of magnons to microwave photons.",1409.5499v1
2015-02-15,Redefinition of spin Hall magnetoresistance,"Using a multi-conduction-channel model, we redefined the micromechanism of
spin Hall magnetoresistance (SMR). Four conduction channels are created by spin
accumulation of nonpolarized electron flow at top, bottom, left and right
interfaces of the film sample, which corresponds to different resistance states
of polarized electron flow with various spin directions relative to the applied
magnetic field ($\mathbf{H}$), and brings about the SMR effect finally. The
magnetic insulator layer, such as yttrium iron garnet (YIG), is not a requisite
for the observation of SMR. Instead, the SMR effect is perfectly realized, with
an order of magnitude increase, in the sample with a discontinuous layer of
isolated-Co$_2$FeAl (0.3 nm) grains covered by 2.5-nm-thick Pt layer on MgO
substrate. The model intuitively gives the typical relationship of SMR effect,
i.e. $\rho_{\parallel}\approx\rho_{\bot}>\rho_{T}$, where $\rho_{\bot}$,
$\rho_{\parallel}$ and $\rho_{T}$ are longitudinal reisitivities with applied
magnetic field ($\mathbf{H}$) direction perpendicular to the current direction
out of plane (as Z direction), parallel with and perpendicular to it in plane
(as X and Y direction), respectively. Our research reveals that the scattering
between polarized and nonpolarized conduction electrons is the origin of SMR,
and the intrinsic SMR is not constant when $\mathbf{H}$ direction rotates in XZ
plane, which is distinct from that in the reported SMR mechanism.",1502.04288v1
2015-03-20,Control of spin current by a magnetic YIG substrate in NiFe/Al nonlocal spin valves,"We study the effect of a magnetic insulator (Yttrium Iron Garnet - YIG)
substrate on the spin transport properties of Ni$_{80}$Fe$_{20}$/Al nonlocal
spin valve (NLSV) devices. The NLSV signal on the YIG substrate is about 2 to 3
times lower than that on a non magnetic SiO$_2$ substrate, indicating that a
significant fraction of the spin-current is absorbed at the Al/YIG interface.
By measuring the NLSV signal for varying injector-to-detector distance and
using a three dimensional spin-transport model that takes spin current
absorption at the Al/YIG interface into account we obtain an effective
spin-mixing conductance $G_{\uparrow\downarrow}\simeq 5 - 8\times
10^{13}~\Omega^{-1}$m$^{-2}$. We also observe a small but clear modulation of
the NLSV signal when rotating the YIG magnetization direction with respect to
the fixed spin polarization of the spin accumulation in the Al. Spin relaxation
due to thermal magnons or roughness of the YIG surface may be responsible for
the observed small modulation of the NLSV signal.",1503.06108v1
2015-03-25,Rigorous numerical study of strong microwave photon-magnon coupling in all-dielectric magnetic multilayers,"We demonstrate theoretically a strong local enhancement of the intensity of
the in-plane microwave magnetic field in multilayered structures made from a
magneto-insulating yttrium iron garnet (YIG) layer sandwiched between two
non-magnetic layers with a high dielectric constant matching that of YIG. The
enhancement is predicted for the excitation regime when the microwave magnetic
field is induced inside the multilayer by the transducer of a stripline
Broadband Ferromagnetic Resonance (BFMR) setup. By means of a rigorous
numerical solution of the Landau-Lifshitz-Gilbert equation consistently with
the Maxwell's equations, we investigate the magnetisation dynamics in the
multilayer. We reveal a strong photon-magnon coupling, which manifests itself
as anti-crossing of the ferromagnetic resonance (FMR) magnon mode supported by
the YIG layer and the electromagnetic resonance mode supported by the whole
multilayered structure. The frequency of the magnon mode depends on the
external static magnetic field, which in our case is applied tangentially to
the multilayer in the direction perpendicular to the microwave magnetic field
induced by the stripline of the BFMR setup. The frequency of the
electromagnetic mode is independent of the static magnetic field. Consequently,
the predicted photon-magnon coupling is sensitive to the applied magnetic field
and thus can be used in magnetically tuneable metamaterials based on
simultaneously negative permittivity and permeability achievable thanks to the
YIG layer. We also suggest that the predicted photon-magnon coupling may find
applications in microwave quantum information systems.",1503.07282v1
2015-04-10,Long range pure magnon spin diffusion observed in a non-local spin-Seebeck geometry,"The spin diffusion length for thermally excited magnon spins is measured by
utilizing a non-local spin-Seebeck effect measurement. In a bulk single crystal
of yttrium iron garnet (YIG) a focused laser thermally excites magnon spins.
The spins diffuse laterally and are sampled using a Pt inverse spin Hall effect
detector. Thermal transport modeling and temperature dependent measurements
demonstrate the absence of spurious temperature gradients beneath the Pt
detector and confirm the non-local nature of the experimental geometry.
Remarkably, we find that thermally excited magnon spins in YIG travel over 120
$\mu$m at 23 K, indicating that they are robust against inelastic scattering.
The spin diffusion length is found to be at least 47 $\mu$m and as high as 73
$\mu$m at 23 K in YIG, while at room temperature it drops to less than 10
$\mu$m. Based on this long spin diffusion length, we envision the development
of thermally powered spintronic devices based on electrically insulating, but
spin conducting materials.",1504.02808v2
2015-08-19,Independent tuning of electronic properties and induced ferromagnetism in topological insulators with heterostructure approach,"The quantum anomalous Hall effect (QAHE) has been recently demonstrated in
Cr- and V-doped three-dimensional topological insulators (TIs) at temperatures
below 100 mK. In those materials, the spins of unfilled d-electrons in the
transition metal dopants are exchange coupled to develop a long-range
ferromagnetic order, which is essential for realizing QAHE. However, the
addition of random dopants does not only introduce excess charge carriers that
require readjusting the Bi/Sb ratio, but also unavoidably introduces
paramagnetic spins that can adversely affect the chiral edge transport in QAHE.
In this work, we show a heterostructure approach to independently tune the
electronic and magnetic properties of the topological surface states in
(BixSb1-x)2Te3 without resorting to random doping of transition metal elements.
In heterostructures consisting of a thin (BixSb1-x)2Te3 TI film and yttrium
iron garnet (YIG), a high Curie temperature (~ 550 K) magnetic insulator, we
find that the TI surface in contact with YIG becomes ferromagnetic via
proximity coupling which is revealed by the anomalous Hall effect (AHE). The
Curie temperature of the magnetized TI surface ranges from 20 to 150 K but is
uncorrelated with the Bi fraction x in (BixSb1-x)2Te3. In contrast, as x is
varied, the AHE resistivity scales with the longitudinal resistivity. In this
approach, we decouple the electronic properties from the induced ferromagnetism
in TI. The independent optimization provides a pathway for realizing QAHE at
higher temperatures, which is important for novel spintronic device
applications.",1508.04719v1
2015-08-30,Spin-transfer torque based damping control of parametrically excited spin waves in a magnetic insulator,"The damping of spin waves parametrically excited in the magnetic insulator
Yttrium Iron Garnet (YIG) is controlled by a dc current passed through an
adjacent normal-metal film. The experiment is performed on a macroscopically
sized YIG(100nm)/Pt(10nm) bilayer of 4x2 mm^2 lateral dimensions. The spin-wave
relaxation frequency is determined via the threshold of the parametric
instability measured by Brillouin light scattering (BLS) spectroscopy. The
application of a dc current to the Pt film leads to the formation of a
spin-polarized electron current normal to the film plane due to the spin Hall
effect (SHE). This spin current exerts a spin transfer torque (STT) in the YIG
film and, thus, changes the spin-wave damping. Depending on the polarity of the
applied dc current with respect to the magnetization direction, the damping can
be increased or decreased. The magnitude of its variation is proportional to
the applied current. A variation in the relaxation frequency of +/-7.5% is
achieved for an applied dc current density of 5*10^10 A/m^2.",1508.07517v1
2016-01-08,Magnons and Phonons Optically Driven Out of Local Equilibrium in a Magnetic Insulator,"Magnons are the energy quanta of fundamental spin excitations, namely spin
waves, and they can make a considerable contribution to energy transport in
some magnetic materials in a similar manner as lattice vibration waves or
phonons. The coupling and possible non-equilibrium between magnons and other
energy carriers have been used to explain several recently discovered thermally
driven spin transport and energy conversion phenomena. Here, we report
experiments in which local non-equilibrium between magnons and phonons in a
single crystalline bulk magnetic insulator, Y3Fe5O12 (yttrium iron garnet, or
YIG), has been created optically within a focused laser spot and probed
directly with the use of micro-Brillouin light scattering (BLS). By analyzing
the experimental results with a thermally induced magnon diffusion model, we
obtain the magnon diffusion length of thermal magnons. By explicitly
establishing non-equilibrium between magnons and phonons, our studies represent
an important step toward a quantitative understanding of various spin-heat
coupling phenomena.",1601.01982v3
2016-01-21,Detection of spin pumping from YIG by spin-charge conversion in a Au/Ni$_{80}$Fe$_{20}$ spin-valve structure,"Many experiments have shown the detection of spin-currents driven by
radio-frequency spin pumping from yttrium iron garnet (YIG), by making use of
the inverse spin-Hall effect, which is present in materials with strong
spin-orbit coupling, such as Pt. Here we show that it is also possible to
directly detect the resonance-driven spin-current using Au/permalloy (Py,
Ni$_{80}$Fe$_{20}$) devices, where Py is used as a detector for the spins
pumped across the YIG/Au interface. This detection mechanism is equivalent to
the spin-current detection in metallic non-local spin-valve devices. By finite
element modeling we compare the pumped spin-current from a reference Pt strip
with the detected signals from the Au/Py devices. We find that for one series
of Au/Py devices the calculated spin pumping signals mostly match the
measurements, within 20%, whereas for a second series of devices additional
signals are present which are up to a factor 10 higher than the calculated
signals from spin pumping. We also identify contributions from thermoelectric
effects caused by the resonant (spin-related) and non-resonant heating of the
YIG. Thermocouples are used to investigate the presence of these thermal
effects and to quantify the magnitude of the Spin-(dependent-)Seebeck effect.
Several additional features are observed, which are also discussed.",1601.05605v1
2016-04-29,Spin Seebeck effect through antiferromagnetic NiO,"We report temperature-dependent spin-Seebeck measurements on Pt/YIG bilayers
and Pt/NiO/YIG trilayers, where YIG (Yttrium iron garnet, Y$_3$Fe$_5$O$_{12}$)
is an insulating ferrimagnet and NiO is an antiferromagnet at low temperatures.
The thickness of the NiO layer is varied from 0 to 10 nm. In the Pt/YIG
bilayers, the temperature gradient applied to the YIG stimulates dynamic spin
injection into the Pt, which generates an inverse spin Hall voltage in the Pt.
The presence of a NiO layer dampens the spin injection exponentially with a
decay length of $2 \pm 0.6$ nm at 180 K. The decay length increases with
temperature and shows a maximum of $5.5 \pm 0.8$ nm at 360 K. The temperature
dependence of the amplitude of the spin-Seebeck signal without NiO shows a
broad maximum of $6.5 \pm 0.5$ $\mu$V/K at 20 K. In the presence of NiO, the
maximum shifts sharply to higher temperatures, likely correlated to the
increase in decay length. This implies that NiO is most transparent to magnon
propagation near the paramagnet-antiferromagnet transition. We do not see the
enhancement in spin current driven into Pt reported in other papers when 1-2 nm
NiO layers are sandwiched between Pt and YIG.",1604.08659v2
2016-08-16,Probing current-induced magnetic fields in Au|YIG heterostructure with low-energy muon spectroscopy,"We investigated the depth dependence of current-induced magnetic fields in a
bilayer of a normal metal (Au) and a ferrimagnetic insulator (Yttrium Iron
Garnet - YIG) by using low energy muon spectroscopy (LE-muSR). This allows us
to explore how these fields vary from the Au surface down to the buried Au|YIG
interface, which is relevant to study physics like the spin-Hall effect. We
observed a maximum shift of 0.4 G in the internal field of muons at the surface
of Au film which is in close agreement to the value expected for Oersted
fields. As muons are implanted closer to the Au|YIG interface the shift is
strongly suppressed, which we attribute to the dipolar fields present at the
Au|YIG interface. Combining our measurements with modelling, we show that
dipolar fields caused by the finite roughness of the Au|YIG interface
consistently explains our observations. Our results, therefore, gauge the
limits on the spatial resolution and the sensitivity of LE-muSR to the
roughness of the buried magnetic interfaces, a prerequisite for future studies
addressing current induced fields caused by the spin-Hall effect.",1608.04584v1
2016-10-28,Insulating nanomagnets driven by spin torque,"Magnetic insulators, such as yttrium iron garnet (Y$_3$Fe$_5$O$_{12}$), are
ideal materials for ultra-low power spintronics applications due to their low
energy dissipation and efficient spin current generation and transmission.
Recently, it has been realized that spin dynamics can be driven very
effectively in micrometer-sized Y$_3$Fe$_5$O$_{12}$/Pt heterostructures by
spin-Hall effects. We demonstrate here the excitation and detection of spin
dynamics in Y$_3$Fe$_5$O$_{12}$/Pt nanowires by spin-torque ferromagnetic
resonance. The nanowires defined via electron-beam lithography are fabricated
by conventional room temperature sputtering deposition on Gd$_3$Ga$_5$O$_{12 }$
substrates and lift-off. We observe field-like and anti-damping-like torques
acting on the magnetization precession, which are due to simultaneous
excitation by Oersted fields and spin-Hall torques. The Y$_3$Fe$_5$O$_{12}$/Pt
nanowires are thoroughly examined over a wide frequency and power range. We
observe a large change in the resonance field at high microwave powers, which
is attributed to a decreasing effective magnetization due to microwave
absorption. These heating effects are much more pronounced in the investigated
nanostructures than in comparable micron-sized samples. By comparing different
nanowire widths, the importance of geometrical confinements for magnetization
dynamics becomes evident: quantized spin-wave modes across the width of the
wires are observed in the spectra. Our results are the first stepping stones
toward the realization of integrated magnonic logic devices based on
insulators, where nanomagnets play an essential role.",1610.09360v1
2016-12-22,Imaging Magnetization Structure and Dynamics in Ultrathin YIG/Pt Bilayers with High Sensitivity Using the Time-Resolved Longitudinal Spin Seebeck Effect,"We demonstrate an instrument for time-resolved magnetic imaging that is
highly sensitive to the in-plane magnetization state and dynamics of thin-film
bilayers of yttrium iron garnet (Y3Fe5O12,YIG)/Pt: the time-resolved
longitudinal spin Seebeck (TRLSSE) effect microscope. We detect the local,
in-plane magnetic orientation within the YIG by focusing a picosecond laser to
generate thermally-driven spin current from the YIG into the Pt by the spin
Seebeck effect, and then use the inverse spin Hall effect in the Pt to
transduce this spin current to an output voltage. To establish the time
resolution of TRLSSE, we show that pulsed optical heating of patterned YIG (20
nm)/Pt(6 nm)/Ru (2 nm) wires generates a magnetization-dependent voltage pulse
of less than 100 ps. We demonstrate TRLSSE microscopy to image both static
magnetic structure and gigahertz-frequency magnetic resonance dynamics with
sub-micron spatial resolution and a sensitivity to magnetic orientation below
0.3$^{\circ}/\sqrt{\text{Hz}}$ in ultrathin YIG.",1612.07610v2
2017-01-25,Hybrid nanodiamond-YIG systems for efficient quantum information processing and nanoscale sensing,"The nitrogen-vacancy (NV) center in diamond has been extensively studied in
recent years for its remarkable quantum coherence properties that make it an
ideal candidate for room temperature quantum computing and quantum sensing
schemes. However, these schemes rely on spin-spin dipolar interactions, which
require the NV centers to be within a few nanometers from each other while
still separately addressable, or to be in close proximity of the diamond
surface, where their coherence properties significantly degrade. Here we
demonstrate a method for overcoming these limitations using a hybrid yttrium
iron garnet (YIG)-nanodiamond quantum system constructed with the help of
directed assembly and transfer printing techniques. We show that YIG spin-waves
can amplify the oscillating field of a microwave source by more than two orders
of magnitude and efficiently mediate its coherent interactions with an NV
center ensemble. These results demonstrate that spin-waves in ferromagnets can
be used as quantum buses for enhanced, long-range qubit interactions, paving
the way to ultra-efficient manipulation and coupling of solid state defects in
hybrid quantum networks and sensing devices.",1701.07401v1
2017-02-17,Spin conductance of YIG thin films driven from thermal to subthermal magnons regime by large spin-orbit torque,"We report a study on spin conductance in ultra-thin films of Yttrium Iron
Garnet (YIG), where spin transport is provided by propagating spin waves, that
are generated and detected by direct and inverse spin Hall effects in two Pt
wires deposited on top. While at low current the spin conductance is dominated
by transport of thermal magnons, at high current, the spin conductance is
dominated by low-damping non-equilibrium magnons thermalized near the spectral
bottom by magnon-magnon interaction, with consequent a sensitivity to the
applied magnetic field and a longer decay length. This picture is supported by
microfocus Brillouin Light Scattering spectroscopy.",1702.05226v3
2017-04-20,Coupled mode theory for the acoustic wave and spin wave interaction in the magphonic crystals: Propagating magnetoelastic waves,"We have investigated co-directional and contra-directional couplings between
spin wave and acoustic wave in one-dimensional periodic structure (magphonic
crystal). The system consists of two ferromagnetic layers alternating in space.
We have taken into consideration materials commonly used in magnonics: yttrium
iron garnet, CoFeB, permalloy, and cobalt. The coupled mode theory (CMT)
formalism have been successfully implemented to describe magnetoelastic
interaction as a periodic perturbation in the magphonic crystal. The results of
CMT calculations have been verified by more rigorous simulations by
frequency-domain plane wave method and time-domain finite element method. The
presented resonant coupling in the magphonic crystal is an active in-space
mechanism which spatially transfers energy between propagating spin and
acoustic modes, thus creating propagating magnetoelastic wave. We have shown,
that CMT analysis of the magnetoelastic coupling is an useful tool to optimize
and design a spin wave - acoustic wave transducer based on a magphonic
crystals. The effect of spin wave damping has been included to the model to
discuss the efficiency of such a device. Our model shows that it is possible to
obtain forward conversion of the acoustic wave to the spin wave in case of
co-directional coupling and backward conversion in case of contra-directional
coupling.",1704.06118v1
2017-06-09,Negative spin Hall magnetoresistance of Pt on the bulk easy-plane antiferromagnet NiO,"We report on spin Hall magnetoresistance (SMR) measurements of Pt Hall bars
on the antiferromagnetic NiO(111) single crystal. An SMR with a sign opposite
of conventional SMR is observed over a wide range of temperatures as well as
magnetic fields stronger than 0.25T. The negative sign of the SMR can be
explained by the alignment of magnetic moments being almost perpendicular to
the external magnetic field within the easy plane (111) of the antiferromagnet.
This correlation of magnetic moment alignment and external magnetic field
direction is realized just by the easy-plane nature of the material without the
need of any exchange coupling to an additional ferromagnet. The SMR signal
strength decreases with increasing temperature, primarily due to the decrease
in N\'eel order by including fluctuations. An increasing magnetic field
increases the SMR signal strength as there are less domains and the magnetic
moments are more strongly manipulated at high magnetic fields. The SMR is
saturated at an applied magnetic field of $6$~T resulting in a spin-mixing
conductance of $\sim10^{18}~ \Omega^{-1}$m$^{-2}$, which is comparable to that
of Pt on insulating ferrimagnets such as yttrium iron garnet. An argon plasma
treatment doubles the spin-mixing conductance.",1706.03004v1
2017-06-16,Long-distance spin transport in a disordered magnetic insulator,"Spin transport through magnetic insulators via magnons has recently been
explored for a growing variety of magnetic systems with long-range order and
well-understood spin excitation spectra. Here we show dramatic effects of spin
transport through an amorphous magnetic insulator, which is both magnetically
and structurally disordered. We generate and detect spin flow though amorphous
yttrium-iron-garnet ($a$-YIG) thin films in a non-local geometry by use of the
spin Hall and inverse spin Hall effects in platinum strips separated by 10 or
more microns. By comparing non-local spin transport in $a$-YIG on suspended
micromachined thermal isolation platforms to the same experiment performed on a
bulk substrate, we show strong effects of in-plane thermal gradients on spin
transport in the disordered magnetic insulator. The resulting non-local voltage
signals are orders of magnitude larger than those seen in crystalline magnetic
insulators, with easily measurable spin signals seen even at distances in
excess of $100$ microns. In analogy to heat transport, where disordered
materials support a range of vibrational excitations that can allow large
thermal conductivities, we suggest that efficient spin transport in disordered
magnetic systems can occur via a similar spectrum of excitations that relies on
strong local exchange interactions and does not require long-range order. This
work not only opens a new area for fundamental experimental and theoretical
studies of spin transport, but also sets a new direction in materials science
for magnonic and spintronic devices.",1706.05196v1
2017-08-04,Quarter-Flux Hofstadter Lattice in Qubit-Compatible Microwave Cavity Array,"Topological- and strongly-correlated- materials are exciting frontiers in
condensed matter physics, married prominently in studies of the fractional
quantum hall effect [1]. There is an active effort to develop synthetic
materials where the microscopic dynamics and ordering arising from the
interplay of topology and interaction may be directly explored. In this work we
demonstrate a novel architecture for exploration of topological matter
constructed from tunnel-coupled, time-reversalbroken microwave cavities that
are both low loss and compatible with Josephson junction-mediated interactions
[2]. Following our proposed protocol [3] we implement a square lattice
Hofstadter model at a quarter flux per plaquette ({\alpha} = 1/4), with
time-reversal symmetry broken through the chiral Wannier-orbital of resonators
coupled to Yttrium-Iron-Garnet spheres. We demonstrate site-resolved
spectroscopy of the lattice, time-resolved dynamics of its edge channels, and a
direct measurement of the dispersion of the edge channels. Finally, we
demonstrate the flexibility of the approach by erecting a tunnel barrier
investigating dynamics across it. With the introduction of Josephson-junctions
to mediate interactions between photons, this platform is poised to explore
strongly correlated topological quantum science for the first time in a
synthetic system.",1708.01651v2
2017-08-06,Electric-field-induced extremely large change in resistance in graphene ferromagnets,"A colossal magnetoresistance ($\sim 100\times10^3\%$) and an extremely large
magnetoresistance ($\sim 1\times10^6\%$) have been previously explored in
manganite perovskites and Dirac materials, respectively. However, the
requirement of an extremely strong magnetic field (and an extremely low
temperature) makes them not applicable for realistic devices. In this work, we
propose a device that can generate even larger changes in resistance in a
zero-magnetic field and at a high temperature. The device is composed of a
graphene under two strips of yttrium iron garnet (YIG), where two gate voltages
are applied to cancel the heavy charge doping in the YIG-induced half-metallic
ferromagnets. By calculations using the Landauer-B\""{u}ttiker formalism, we
demonstrate that, when a proper gate voltage is applied on the free
ferromagnet, changes in resistance up to $305\times10^6\%$ ($16\times10^3\%$)
can be achieved at the liquid helium (nitrogen) temperature and in a zero
magnetic field. We attribute such a remarkable effect to a gate-induced
full-polarization reversal in the free ferromagnet, which results in a
metal-state to insulator-state transition in the device. We also find that, the
proposed effect can be realized in devices using other magnetic insulators such
as EuO and EuS. Our work should be helpful for developing a realistic switching
device that is energy saving and CMOS-technology compatible.",1708.01858v2
2017-09-03,Femtosecond formation dynamics of the spin Seebeck effect revealed by terahertz spectroscopy,"Understanding the transfer of spin angular momentum is essential in modern
magnetism research. A model case is the generation of magnons in magnetic
insulators by heating an adjacent metal film. Here, we reveal the initial steps
of this spin Seebeck effect with <27fs time resolution using terahertz
spectroscopy on bilayers of ferrimagnetic yttrium-iron garnet and platinum.
Upon exciting the metal with an infrared laser pulse, a spin Seebeck current
$j_\textrm{s}$ arises on the same ~100fs time scale on which the metal
electrons thermalize. This observation highlights that efficient spin transfer
critically relies on carrier multiplication and is driven by conduction
electrons scattering off the metal-insulator interface. Analytical modeling
shows that the electrons' dynamics are almost instantaneously imprinted onto
$j_\textrm{s}$ because their spins have a correlation time of only ~4fs and
deflect the ferrimagnetic moments without inertia. Applications in material
characterization, interface probing, spin-noise spectroscopy and terahertz spin
pumping emerge.",1709.00768v5
2017-09-06,Complex THz and DC inverse spin Hall effect in YIG/Cu$_{1-x}$Ir$_{x}$ bilayers across a wide concentration range,"We measure the inverse spin Hall effect of Cu$_{1-x}$Ir$_{x}$ thin films on
yttrium iron garnet over a wide range of Ir concentrations ($0.05 \leqslant x
\leqslant 0.7$). Spin currents are triggered through the spin Seebeck effect,
either by a DC temperature gradient or by ultrafast optical heating of the
metal layer. The spin Hall current is detected by, respectively, electrical
contacts or measurement of the emitted THz radiation. With both approaches, we
reveal the same Ir concentration dependence that follows a novel complex,
non-monotonous behavior as compared to previous studies. For small Ir
concentrations a signal minimum is observed, while a pronounced maximum appears
near the equiatomic composition. We identify this behavior as originating from
the interplay of different spin Hall mechanisms as well as a
concentration-dependent variation of the integrated spin current density in
Cu$_{1-x}$Ir$_{x}$. The coinciding results obtained for DC and ultrafast
stimuli show that the studied material allows for efficient spin-to-charge
conversion even on ultrafast timescales, thus enabling a transfer of
established spintronic measurement schemes into the terahertz regime.",1709.01890v1
2017-09-19,Criteria for accurate determination of the magnon relaxation length from the nonlocal spin Seebeck effect,"The nonlocal transport of thermally generated magnons not only unveils the
underlying mechanism of the spin Seebeck effect, but also allows for the
extraction of the magnon relaxation length ($\lambda_m$) in a magnetic
material, the average distance over which thermal magnons can propagate. In
this study, we experimentally explore in yttrium iron garnet (YIG)/platinum
systems much further ranges compared with previous investigations. We observe
that the nonlocal SSE signals at long distances ($d$) clearly deviate from a
typical exponential decay. Instead, they can be dominated by the nonlocal
generation of magnon accumulation as a result of the temperature gradient
present away from the heater, and decay geometrically as $1/d^2$. We emphasize
the importance of looking only into the exponential regime (i.e., the
intermediate distance regime) to extract $\lambda_m$. With this principle, we
study $\lambda_m$ as a function of temperature in two YIG films which are 2.7
and 50 $\mu$m in thickness, respectively. We find $\lambda_m$ to be around 15
$\mu$m at room temperature and it increases to 40 $\mu$m at $T=$ 3.5 K. Finite
element modeling results agree with experimental studies qualitatively, showing
also a geometrical decay beyond the exponential regime. Based on both
experimental and modeling results we put forward a general guideline for
extracting $\lambda_m$ from the nonlocal spin Seebeck effect.",1709.06321v1
2017-10-07,Dissecting spin-phonon equilibration in ferrimagnetic insulators by ultrafast lattice excitation,"To gain control over magnetic order on ultrafast time scales, a fundamental
understanding of the way electron spins interact with the surrounding crystal
lattice is required. However, measurement and analysis even of basic collective
processes such as spin-phonon equilibration have remained challenging. Here, we
directly probe the flow of energy and angular momentum in the model insulating
ferrimagnet yttrium iron garnet. Following ultrafast resonant lattice
excitation, we observe that magnetic order reduces on distinct time scales of 1
ps and 100 ns. Temperature-dependent measurements, a spin-coupling analysis and
simulations show that the two dynamics directly reflect two stages of
spin-lattice equilibration. On the 1-ps scale, spins and phonons reach
quasi-equilibrium in terms of energy through phonon-induced modulation of the
exchange interaction. This mechanism leads to identical demagnetization of the
ferrimagnet's two spin-sublattices and a novel ferrimagnetic state of increased
temperature yet unchanged total magnetization. Finally, on the much slower,
100-ns scale, the excess of spin angular momentum is released to the crystal
lattice, resulting in full equilibrium. Our findings are relevant for all
insulating ferrimagnets and indicate that spin manipulation by phonons,
including the spin Seebeck effect, can be extended to antiferromagnets and into
the terahertz frequency range.",1710.02700v2
2017-11-21,Ionic Modulation of Interfacial Magnetism through Electrostatic Doping in Pt/YIG bilayer heterostructure,"Voltage modulation of yttrium iron garnet (YIG) with compactness, high speed
response, energy efficiency and both practical/theoretical siginificances can
be widely applied to various YIG based spintronics such as spin Hall, spin
pumping, spin Seeback effects. Here we initial an ionic modulation of
interfacial magnetism process on YIG/Pt bilayer heterostructures, where the Pt
capping would influence the ferromagnetic (FMR) field position significantly,
and realize a significant magnetism enhancement in bilayer system. A large
voltage induced FMR field shifts of 690 Oe has been achieved in YIG (13 nm)/Pt
(3 nm) multilayer heterostructures under a small voltage bias of 4.5 V. The
remarkable ME tunability comes from voltage induced extra FM ordering in Pt
metal layer near the Pt/YIG interface. The first-principle theoretical
simulation reveal that the electrostatic doping induced Pt5+ ions have strong
magnetic ordering due to uncompensated d orbit electrons. The large voltage
control of FMR change pave a foundation towards novel voltage tunable YIG based
spintronics.",1711.07610v3
2017-11-27,Cavity Magnon Polaritons with Lithium Ferrite and 3D Microwave Resonators at milli-Kelvin Temperatures,"Single crystal Lithium Ferrite (LiFe) spheres of sub-mm dimension are
examined at mK temperatures, microwave frequencies and variable DC magnetic
field, for use in hybrid quantum systems and condensed matter and fundamental
physics experiments. Strong coupling regimes of the photon-magnon interaction
(cavity magnon polariton quasi-particles) were observed with coupling strength
of up to 250 MHz at 9.5 GHz (2.6\%) with magnon linewidths of order 4 MHz (with
potential improvement to sub-MHz values). We show that the photon-magnon
coupling can be significantly improved and exceed that of the widely used
Yttrium Iron Garnet crystal, due to the small unit cell of LiFe, allowing twice
more spins per unit volume. Magnon mode softening was observed at low DC fields
and combined with the normal Zeeman effect creates magnon spin wave modes that
are insensitive to first order order magnetic field fluctuations. This effect
is observed in the Kittel mode at 5.5 GHz (and another higher order mode at 6.5
GHz) with a DC magnetic field close to 0.19 Tesla. We show that if the cavity
is tuned close to this frequency, the magnon polariton particles exhibit an
enhanced range of strong coupling and insensitivity to magnetic field
fluctuations with both first order and second order insensitivity to magnetic
field as a function of frequency (double magic point clock transition), which
could potentially be exploited in cavity QED experiments.",1711.09980v2
2017-12-12,Microwave to optical photon conversion by means of travelling-wave magnons in YIG films,"In this work we study theoretically the efficiency of a travelling magnon
based microwave to optical photon converter for applications in Quantum
Information (QI). The converter employs an epitaxially grown yttrium iron
garnet (YIG) film as the medium for propagation of travelling magnons (spin
waves). The conversion is achieved through coupling of magnons to guided
optical modes of the film. The total microwave to optical photon conversion
efficiency is found to be larger than in a similar process employing a YIG
sphere by at least 4 orders of magnitude. By creating an optical resonator of a
large length from the film (such that the traveling magnon decays before
forming a standing wave over the resonator length) one will be able to further
increase the efficiency by several orders of magnitude, potentially reaching a
value similar to achieved with opto-mechanical resonators. Also, as a spin-off
result, it is shown that isolation of more that 20 dB with direct insertion
losses about 5 dBm can be achieved with YIG film based microwave isolators for
applications in Quantum Information.
  An important advantage of the suggested concept of the QI devices based on
travelling spin waves is a perfectly planar geometry and a possibility of
implementing a the device as a hybrid opto-microwave chip.",1712.04304v2
2017-12-21,Exchange-torque-induced excitation of perpendicular standing spin waves in nanometer-thick YIG films,"Spin waves in ferrimagnetic yttrium iron garnet (YIG) films with ultralow
magnetic damping are relevant for magnon-based spintronics and low-power
wave-like computing. The excitation frequency of spin waves in YIG is rather
low in weak external magnetic fields because of its small saturation
magnetization, which limits the potential of YIG films for high-frequency
applications. Here, we demonstrate how exchange-coupling to a CoFeB film
enables efficient excitation of high-frequency perpendicular standing spin
waves (PSSWs) in nanometer-thick (80 nm and 295 nm) YIG films using uniform
microwave magnetic fields. In the 295-nm-thick YIG film, we measure intense
PSSW modes up to 10th order. Strong hybridization between the PSSW modes and
the ferromagnetic resonance mode of CoFeB leads to characteristic anti-crossing
behavior in broadband spin-wave spectra. A dynamic exchange torque at the
YIG/CoFeB interface explains the excitation of PSSWs. The localized torque
originates from exchange coupling between two dissimilar magnetization
precessions in the YIG and CoFeB layers. As a consequence, spin waves are
emitted from the YIG/CoFeB interface and PSSWs form when their wave vector
matches the perpendicular confinement condition. PSSWs are not excited when the
exchange coupling between YIG and CoFeB is suppressed by a Ta spacer layer.
Micromagnetic simulations confirm the exchange-torque mechanism.",1712.08204v1
2018-01-12,Spin-Hall-Active Platinum Thin Films Grown Via Atomic Layer Deposition,"We study the magnetoresistance of yttrium iron garnet/Pt heterostructures in
which the Pt layer was grown via atomic layer deposition (ALD).
Magnetotransport experiments in three orthogonal rotation planes reveal the
hallmark features of spin Hall magnetoresistance. We estimate the spin
transport parameters by comparing the magnitude of the magnetoresistance in
samples with different Pt thicknesses. We compare the spin Hall angle and the
spin diffusion length of the ALD Pt layers to the values reported for
high-quality sputter-deposited Pt films. The spin diffusion length of 1.5nm
agrees well with platinum thin films reported in the literature, whereas the
spin Hall magnetoresistance $\Delta \rho / \rho = 2.2\times 10^{-5}$ is
approximately a factor of 20 smaller compared to that of our sputter-deposited
films. Our results demonstrate that ALD allows fabricating spin-Hall-active Pt
films of suitable quality for use in spin transport structures. This work
provides the basis to establish conformal ALD coatings for arbitrary surface
geometries with spin-Hall-active metals and could lead to 3D spintronic devices
in the future.",1801.04041v1
2018-08-17,Temperature Dependence of Magnetic Properties of an 18-nm-thick YIG Film Grown by Liquid Phase Epitaxy: Effect of a Pt Overlayer,"Liquid phase epitaxy of an 18 nm thick Yttrium Iron garnet (YIG) film is
achieved. Its magnetic properties are investigated in the 100 -- 400 K
temperature range, as well as the influence of a 3 nm thick Pt overlayer on
them. The saturation magnetization and the magnetocrystalline cubic anisotropy
of the bare YIG film behave similarly to bulk YIG. A damping parameter of only
a few $10^{-4}$ is measured, together with a low inhomogeneous contribution to
the ferromagnetic resonance linewidth. The magnetic relaxation increases upon
decreasing temperature, which can be partly ascribed to impurity relaxation
mechanisms. While it does not change its cubic anisotropy, the Pt capping
strongly affects the uniaxial perpendicular anisotropy of the YIG film, in
particular at low temperatures. The interfacial coupling in the YIG/Pt
heterostructure is also revealed by an increase of the linewidth, which
substantially grows by lowering the temperature.",1808.05785v2
2018-10-05,Magnon contribution to unidirectional spin Hall magnetoresistance,"We develop a model for the magnonic contribution to the unidirectional spin
Hall magnetoresistance (USMR) of heavy metal/ferromagnetic insulator bilayer
films. We show that diffusive transport of Holstein-Primakoff magnons leads to
an accumulation of spin near the bilayer interface, giving rise to a
magnoresistance which is not invariant under inversion of the current
direction. Unlike the electronic contribution described by Zhang and Vignale
[Phys. Rev. B 94, 140411 (2016)], which requires an electrically conductive
ferromagnet, the magnonic contribution can occur in ferromagnetic insulators
such as yttrium iron garnet. We show that the magnonic USMR is, to leading
order, cubic in the spin Hall angle of the heavy metal, as opposed to the
linear relation found for the electronic contribution. We estimate that the
maximal magnonic USMR in Pt|YIG bilayers is on the order of $10^{-8}$, but may
reach values of up to $10^{-5}$ if the magnon gap is suppressed, and can thus
become comparable to the electronic contribution in, e.g., Pt|Co. We show that
the magnonic USMR at a finite magnon gap may be enhanced by an order of
magnitude if the magnon diffusion length is decreased to a specific optimal
value that depends on various system parameters.",1810.02610v2
2018-10-16,Spin-wave-induced lateral temperature gradient in a YIG thin film/GGG system excited in an ESR cavity,"Lateral thermal gradient of an yttrium iron garnet (YIG) film under the
microwave application in the cavity of the electron spin resonance system (ESR)
was measured at room temperature by fabricating a Cu/Sb thermocouple onto it.
To date, thermal transport in YIG films caused by the Damon-Eshbach mode (DEM)
- the unidirectional spin-wave heat conveyer effect - was demonstrated only by
the excitation using coplanar waveguides. Here we show that effect exists even
under YIG excitation using the ESR cavity - tool often employed to realize spin
pumping. The temperature difference observed around the ferromagnetic resonance
(FMR) field under the 4 mW microwave power peaked at 13 mK. The observed
thermoelectric signal indicates the imbalance of the population between the
DEMs that propagate near the top and bottom surfaces of the YIG film. We
attribute the DEM population imbalance to the different magnetic damping near
the top and bottom YIG surfaces. Additionally, the spin wave dynamics of the
system were investigated using the micromagnetic simulations. The micromagnetic
simulations confirmed the existence of the DEM imbalance in the system with the
increased Gilbert damping at one of the YIG interfaces. The reported results
are indispensable for the quantitative estimation of the electromotive force in
the spin-charge conversion experiments using ESR cavities.",1810.06875v1
2018-10-16,Spin-torque oscillation in a magnetic insulator probed by a single-spin sensor,"Coherent, self-sustained oscillation of magnetization in spin-torque
oscillators (STOs) is a promising source for on-chip, nanoscale generation of
microwave magnetic fields. Such fields could be used for local excitation of
spin-wave resonances, control of spin qubits, and studies of paramagnetic
resonance. However, local characterization of fields emitted by an STO has
remained an outstanding challenge. Here, we use the spin of a single
nitrogen-vacancy (NV) defect in diamond to probe the magnetic fields generated
by an STO in a microbar of ferromagnetic insulator yttrium-iron-garnet (YIG).
The combined spectral resolution and sensitivity of the NV sensor allows us to
resolve multiple spin-wave modes and characterize their damping. When damping
is decreased sufficiently via spin injection, the modes auto-oscillate, as
indicated by a strongly reduced linewidth, a diverging magnetic power spectral
density, and synchronization of the STO frequency to an external microwave
source. These results open the way for quantitative, nanoscale mapping of the
microwave signals generated by STOs, as well as harnessing STOs as local probes
of mesoscopic spin systems.",1810.07306v1
2018-10-28,Magnetic Resonance in Defect Spins mediated by Spin Waves,"In search of two level quantum systems that implement a qubit, the
nitrogen-vacancy (NV) center in diamond has been intensively studied for years.
Despite favorable properties such as remarkable defect spin coherence times,
the addressability of NV centers raises some technical issues. The coupling of
a single NV center to an external driving field is limited to short distances,
since an efficient coupling requires the NV to be separated by only a few
microns away from the source. As a way to overcome this problem, an enhancement
of coherent coupling between NV centers and a microwave field has recently been
experimentally demonstrated using spin waves propagating in an adjacent yttrium
iron garnet (YIG) film [1]. In this paper we analyze the optically detected
magnetic resonance spectra that arise when an NV center is placed on top of a
YIG film for a geometry similar to the one in the experiment. We analytically
calculate the oscillating magnetic field of the spin wave on top of the YIG
surface to determine the coupling of spin waves to the NV center. We compare
this coupling to the case when the spin waves are absent and the NV center is
driven only with the antenna field and show that the calculated coupling
enhancement is dramatic and agrees well with the one obtained in the recent
experiment.",1810.11841v1
2018-11-29,"Effect of YIG Nanoparticle Size and Clustering in Proximity-Induced Magnetism in Graphene/YIG Composite Probed with Magnetoimpedance Sensors: Towards Improved Functionality, Sensitivity and Proximity Detection","Proximity-induced magnetism (PIM) in graphene (Gr) adjacent to magnetic
specimen has raised great fundamental interests. The subject is under debate
and yet no application is proposed and granted. In this paper, toward
accomplishment of fundamental facts, we first explore the effect of particle
size and clustering in the PIM in Gr nanoplates (GNPs)/yttrium iron garnet
(YIG) magnetic nanoparticle (MNP) composite. Microscopic analyzes suggest that
fine MNPs distributed uniformly on the GNPs have higher saturation
magnetization due to the PIM in Gr. We propose that such magnetic plates can
thus be used to shield the stray field generated on the surface of magnetic
sensors and play a role as a magnetic lens to prevent the field emanating
outside the body of magnetic specimen. The GNPs/YIG composites are coated on a
magnetic ribbon and proposed for application in magneto-impedance (MI) sensors.
We show that such planar magnetic flakes enhance the MI response against the
external applied magnetic field significantly. The suggested application can be
furthermore developed toward bio-sensing and magnetic shielding in different
magnetic sensors and devices.",1811.12317v2
2018-11-29,"High Saturation Magnetization, Low Coercivity and Fine YIG Nanoparticles Prepared by Modifying Co-Precipitation Method","Nanoparticles with their specific properties newly have drawn a great deal of
attention of researchers [1-3]Yttrium iron Garnet magnetic nanoparticles
(YIG-NPs) are promising materials with novel applications in microwave,
spintronics, magnonics, and magneto-optical devices. However, achieving stable
and remarkable magnetic YIG-NPs has been remaining as a great challenge. In
this paper, synthesized YIG-NPs by modifying co-precipitation (MCP) method is
reported. Structural and magnetic properties of final products are compared to
those of the materials prepared by citrate-nitrate (CN) method. Smaller
crystals and particle size have been found by MCP method comparing to that of
synthesized by CN method. Using a relatively low annealing temperatures for
both sets of samples (~700 {\deg}C), the final YIG samples prepared by MCP
method show more structural purity than those made by CN method. Higher
saturation magnetization (Ms) and lower coercivity (Hc) are observed in MCP YIG
sample (23.23 emu/g 36 and 30.1 Oe) than the CN prepared YIG sample (16.43
emu/g and 44.95 Oe). The Curie temperature is measured to be 569 {\deg}C for
the MCP YIG sample determined from set of Ms measurement at different
temperatures ranging from 80-600 K. These findings lead to significant
improvement in quality of synthesized (synthetic methods) of YIG-NPs.",1811.12511v1
2018-12-02,Direct detection of induced magnetic moment and efficient spin-to-charge conversion in graphene/ferromagnetic structures,"This article shows that the spin-to-charge current conversion in single-layer
graphene (SLG) by means of the inverse Rashba-Edelstein effect (IREE) is made
possible with the integration of this remarkable 2D-material with the unique
ferrimagnetic insulator yttrium iron garnet (YIG = $Y_{3}Fe_{5}O_{12}$) as well
as with the ferromagnetic metal permalloy (Py = $Ni_{81}Sb_{19}$). By means of
X-ray absorption spectroscopy (XAS) and magnetic circular dichroism (XMCD)
techniques, we show that the carbon atoms of the SLG acquires an induced
magnetic moment due to the proximity effect with the magnetic layer. The spin
currents are generated in the magnetic layer by spin pumping from microwave
driven ferromagnetic resonance and are detected by a dc voltage along the
graphene layer, at room temperature. The spin-to-charge current conversion,
occurring at the graphene layer, is explained by the extrinsic spin-orbit
interaction (SOI) induced by the proximity effect with the ferromagnetic layer.
The results obtained for the SLG/YIG and SLG/Py systems confirm very similar
values for the IREE parameter, which are larger than the values reported in
previous studies for SLG. We also report systematic investigations of the
electronic and magnetic properties of the SLG/YIG by means of scanning
tunneling microscopy (STM).",1812.00455v1
2019-01-07,Abnormal anti-crossing effect in photon-magnon coupling,"We report the experimental demonstration of an abnormal, opposite
anti-crossing effect in a photon-magnon-coupled system that consists of an
Yttrium Iron Garnet film and an inverted pattern of split-ring resonator
structure (noted as ISRR) in a planar geometry. It is found that the normal
shape of anti-crossing dispersion typically observed in photon-magnon coupling
is changed to its opposite anti-crossing shape just by changing the
position/orientation of the ISRR's split gap with respect to the microstrip
line axis along which ac microwave currents are applied. Characteristic
features of the opposite anti-crossing dispersion and its linewidth evolution
are analyzed with the help of analytical derivations based on electromagnetic
interactions. The observed opposite anti-crossing dispersion is ascribed to the
compensation of both intrinsic damping and coupling-induced damping in the
magnon modes. This compensation is achievable by controlling the relative
strength and phase of oscillating magnetic fields generated from the ISRR's
split gap and the microstrip feeding line. The position/orientation of an
ISRR's split gap provides a robust means of controlling the dispersion shape of
anti-crossing and its damping in a photon-magnon coupling, thereby offering
more opportunity for advanced designs of microwave devices.",1901.01729v2
2019-02-18,Coherent control of magnon radiative damping with local photon states,"The collective excitation of ordered spins, known as spin waves or magnons,
can in principle radiate by emitting travelling photons to an open system when
decaying to the ground state. However, in contrast to the electric dipoles,
magnetic dipoles contributed by magnons are more isolated from electromagnetic
environment with negligible radiation in the vacuum, limiting their application
in coherent communication by photons. Recently, strong interaction between
cavity standing-wave photons and magnons has been reported, indicating the
possible manipulation of magnon radiation via tailoring photon states. Here,
with loading an yttrium iron garnet sphere in a one-dimensional circular
waveguide cavity in the presence of both travelling and standing photon modes,
we demonstrate an efficient photon emissions from magnon and a significant
magnon radiative damping with radiation rate found to be proportional to the
local density of states (LDOS) of photon. By modulating the LDOS including its
magnitude and/or polarization, we can flexibly tune the photon emission and
magnon radiative damping on demand. Our findings provide a general way in
manipulating photon emission from magnon radiation for harnessing energy and
angular momentum generation, transfer and storage modulated by magnon in the
cavity and waveguide electrodynamics.",1902.06795v2
2019-03-02,Excitation of unidirectional exchange spin waves by a nanoscale magnetic grating,"Magnon spintronics is a prosperous field that promises beyond-CMOS technology
based on elementary excitations of the magnetic order that act as information
carriers for future computational architectures. Unidirectional propagation of
spin waves is key to the realization of magnonic logic devices. However,
previous efforts to enhance the Damon-Eshbach-type nonreciprocity did not
realize (let alone control) purely unidirectional propagation. Here we
experimentally demonstrate excitations of unidirectional exchange spin waves by
a nanoscale magnetic grating consisting of Co nanowires fabricated on an
ultrathin yttrium iron garnet film. We explain and model the nearly perfect
unidirectional excitation by the chirality of the magneto-dipolar interactions
between the Kittel mode of the nanowires and the exchange spin waves of the
film. Reversal of the magnetic configurations of film and nanowire array from
parallel to antiparallel changes the direction of the excited spin waves. Our
results raise the prospect of a chiral magnonic logic without the need for
fragile surface states.",1903.00638v1
2019-03-10,Magnons at low excitations: Observation of incoherent coupling to a bath of two-level-systems,"Collective magnetic excitation modes, magnons, can be coherently coupled to
microwave photons in the single excitation limit. This allows for access to
quantum properties of magnons and opens up a range of applications in quantum
information processing, with the intrinsic magnon linewidth representing the
coherence time of a quantum resonator. Our measurement system consists of a
yttrium iron garnet (YIG) sphere and a three-dimensional (3D) microwave cavity
at temperatures and excitation powers typical for superconducting quantum
circuit experiments. We perform spectroscopic measurements to determine the
limiting factor of magnon coherence at these experimental conditions. Using the
input-output formalism, we extract the magnon linewidth $\kappa_\mathrm{m}$. We
attribute the limitations of the coherence time at lowest temperatures and
excitation powers to incoherent losses into a bath of near-resonance two-level
systems (TLSs), a generic loss mechanism known from superconducting circuits
under these experimental conditions. We find that the TLSs saturate when
increasing the excitation power from quantum excitation to multi-photon
excitation and their contribution to the linewidth vanishes. At higher
temperatures, the TLSs saturate thermally and the magnon linewidth decreases as
well.",1903.03981v3
2019-05-29,A magnonic directional coupler for integrated magnonic half-adders,"Magnons, the quanta of spin waves, could be used to encode information in
beyond-Moore computing applications, and magnonic device components, including
logic gates, transistors, and units for non-Boolean computing, have already
been developed. Magnonic directional couplers, which can function as circuit
building blocks, have also been explored, but have been impractical because of
their millimetre dimensions and multi-mode spectra. Here, we report a magnonic
directional coupler based on yttrium iron garnet single-mode waveguides of 350
nm width. We use the amplitude of a spin-wave to encode information and to
guide it to one of the two outputs of the coupler depending on the signal
magnitude, frequency, and the applied magnetic field. Using micromagnetic
simulations, we also propose an integrated magnonic half-adder that consists of
two directional couplers and processes all information within the magnon domain
with aJ energy consumption.",1905.12353v3
2019-12-01,Differences in the magnon diffusion length for electrically and thermally driven magnon currents in Y$_3$Fe$_5$O$_{12}$,"Recent demonstration of efficient transport and manipulation of spin
information by magnon currents have opened exciting prospects for processing
information in devices. Magnon currents can be driven both electrically and
thermally, even in magnetic insulators, by applying charge currents in an
adjacent metal layer. Earlier reports in thin yttrium iron garnet (YIG) films
suggested that the diffusion length of magnons is independent on the biasing
method, but different values were obtained in thicker films. Here, we study the
magnon diffusion length for electrically and thermally driven magnon currents
in the linear regime in a 2-$\mu$m-thick YIG film as a function of temperature
and magnetic field. Our results show a decrease of the magnon diffusion length
with magnetic field for both biasing methods and at all temperatures from 5 to
300 K, indicating that sub-thermal magnons dominate the long-range transport.
Moreover, we demonstrate that the value of the magnon diffusion length depends
on the driving mechanism, suggesting that different non-equilibrium magnon
distributions are biased for each method. Finally, we demonstrate that the
magnon diffusion length for thermally driven magnon currents is independent of
the YIG thickness and material growth conditions, confirming that this quantity
is an intrinsic parameter of YIG.",1912.00490v2
2020-01-31,Temperature dependence of spin pinning and spin-wave dispersion in nanoscopic ferromagnetic waveguides,"The field of magnonics attracts significant attention due to the possibility
of utilizing information coded into the spin-wave phase or amplitude to perform
computation operations on the nanoscale. Recently, spin waves were investigated
in Yttrium Iron Garnet (YIG) waveguides with widths ranging down to 50 nm and
aspect ratios thickness over width approaching unity. A critical width was
found, below which the exchange interaction suppresses the dipolar pinning
phenomenon and the system becomes unpinned. Here we continue these
investigations and analyse the pinning phenomenon and spin-wave dispersions as
a function of temperature, thickness and material of choice. Higher order
modes, the influence of a finite wavevector along the waveguide and the impact
of the pinning phenomenon on the spin-wave lifetime are discussed as well as
the influence of a trapezoidal cross section and edge roughness of the
waveguides. The presented results are of particular interest for potential
applications in magnonic devices and the incipient field of quantum magnonics
at cryogenic temperatures.",2002.00003v1
2020-02-18,Mapping the intrinsic photocurrent streamlines through micromagnetic heterostructure devices,"Like air flowing over a wing, optimizing the flow of electronic charge is
essential to the operation of nanoscale devices. Unfortunately, the delicate
interplay of charge, spin, and heat in complex devices has precluded detailed
imaging of charge flow. Here, we report on the visualization of intrinsic
charge current streamlines through yttrium iron garnet micromagnetic
heterostructures. Scanning photovoltage microscopy of precisely designed
devices leads to striking spatial patterns, with prominent photovoltage
features emerging in corners and narrow constrictions. These patterns, which
evolve continuously with rotation of an external magnetic field, enable rich
spatial mapping of fluid-like flow. Taking inspiration from aerodynamic Clark Y
airfoils, we engineer micromagnetic wing shaped devices, called electrofoils,
which allow us to precisely contort, compress and decompress flowlines of
electronic charge.120 (39) e2221815120",2002.07902v3
2020-02-19,Manipulation of coupling and magnon transport in magnetic metal-insulator hybrid structures,"Ferromagnetic metals and insulators are widely used for generation, control
and detection of magnon spin signals. Most magnonic structures are based
primarily on either magnetic insulators or ferromagnetic metals, while
heterostructures integrating both of them are less explored. Here, by
introducing a Pt/yttrium iron garnet (YIG)/permalloy (Py) hybrid structure
grown on Si substrate, we studied the magnetic coupling and magnon transmission
across the interface of the two magnetic layers. We found that within this
structure, Py and YIG exhibit an antiferromagnetic coupling field as strong as
150 mT, as evidenced by both the vibrating-sample magnetometry and polarized
neutron reflectometry measurements. By controlling individual layer thicknesses
and external fields, we realize parallel and antiparallel magnetization
configurations, which are further utilized to control the magnon current
transmission. We show that a magnon spin valve with an ON/OFF ratio of ~130%
can be realized out of this multilayer structure at room temperature through
both spin pumping and spin Seebeck effect experiments. Thanks to the efficient
control of magnon current and the compatibility with Si technology, the
Pt/YIG/Py hybrid structure could potentially find applications in magnon-based
logic and memory devices.",2002.08266v1
2020-02-27,High-temperature Anomalous Hall Effect in Transition Metal Dichalcogenide-Ferromagnetic Insulator Heterostructure,"Integration of transition metal dichalcogenides (TMDs) on ferromagnetic
materials (FM) may yield fascinating physics and promise for electronics and
spintronic applications. In this work, high-temperature anomalous Hall effect
(AHE) in the TMD ZrTe2 thin film using heterostructure approach by depositing
it on ferrimagnetic insulator YIG (Y3Fe5O12, yttrium iron garnet) is
demonstrated. In this heterostructure, significant anomalous Hall effect can be
observed at temperatures up to at least 400 K, which is a record high
temperature for the observation of AHE in TMDs, and the large RAHE is more than
one order of magnitude larger than those previously reported value in
topological insulators or TMDs based heterostructures. The magnetization of
interfacial reaction-induced ZrO2 between YIG and ZrTe2 is believed to play a
crucial role for the induced high-temperature anomalous Hall effect in the
ZrTe2. These results reveal a promising system for the room-temperature
spintronic device applications, and it may also open a new avenue toward
introducing magnetism to TMDs and exploring the quantum AHE at higher
temperatures considering the prediction of nontrivial topology in ZrTe2.",2002.12068v1
2020-03-23,Physical realization of complex dynamical pattern formation in magnetic active feedback rings,"We report the clean experimental realization of cubic-quintic complex
Ginzburg-Landau physics in a single driven, damped system. Four numerically
predicted categories of complex dynamical behavior and pattern formation are
identified for bright and dark solitary waves propagating around an active
magnetic thin film-based feedback ring: (1) periodic breathing; (2) complex
recurrence; (3) spontaneous spatial shifting; and (4) intermittency. These
nontransient, long lifetime behaviors are observed in microwave spin wave
envelopes circulating within a dispersive, nonlinear yttrium iron garnet
waveguide operating in a ring geometry where the net losses are directly
compensated for via linear amplification on each round trip O(100 ns). The
behaviors exhibit periods ranging from tens to thousands of round trip times
O($\mu$ s) and are stable for 1000s of periods O(ms). We present 10
observations of these dynamical behaviors which span the experimentally
accessible ranges of attractive cubic nonlinearity, dispersion, and external
field strength that support the self-generation of backward volume spin waves
in a four-wave-mixing dominant regime. Three-wave splitting is not explicitly
forbidden and is treated as an additional source of nonlinear losses. Each of
these long lifetime behaviors of bright solitary waves was previously
numerically predicted to be observable. The dynamical pattern formation of dark
solitary waves in attractive nonlinearity, however, is entirely novel and is
reported for both the periodic breather and complex recurrence behaviors. All
behaviors are identified in the group velocity co-moving frame.",2003.10541v2
2020-05-18,The Einstein - de Haas effect at radio frequencies in and near magnetic equilibrium,"The Einstein-de Haas (EdH) effect and its reciprocal the Barnett effect are
fundamental to magnetism and uniquely yield measures of the ratio of magnetic
moment to total angular momentum. These effects, small and generally difficult
to observe, are enjoying a resurgence of interest as contemporary techniques
enable new approaches to their study. The high mechanical resonance frequencies
in nanomechanical systems offer a tremendous advantage for the observation of
EdH torques in particular. At radio frequencies, the EdH effect can become
comparable to or even exceed in magnitude conventional cross-product magnetic
torques. In addition, the RF-EdH torque is expected to be phase-shifted by 90
degrees relative to cross-product torques, provided the magnetic system remains
in quasi-static equilibrium, enabling separation in quadratures when both
sources of torque are operative. Radio frequency EdH measurements are
demonstrated through the full hysteresis range of micrometer scale,
monocrystalline yttrium iron garnet (YIG) disks. Equilibrium behavior is
observed in the vortex state at low bias field. Barkhausen-like features emerge
in the in-plane EdH torque at higher fields in the vortex state, revealing
magnetic disorder too weak to be visible through the in-plane cross-product
torque. Beyond vortex annihilation, peaks arise in the EdH torque versus bias
field, and these together with their phase signatures indicate additional
utility of the Einstein-de Haas effect for the study of RF-driven spin
dynamics.",2005.08406v1
2020-05-20,Controlling the propagation of dipole-exchange spin waves using local inhomogeneity of the anisotropy,"Spin waves are promising candidates to carry, transport, and process
information. Controlling the propagation characteristics of spin waves in
magnetic materials is an essential ingredient for designing spin-wave based
computing architectures. Here, we study the influence of surface
inhomogeneities on the spin-wave signals transmitted through thin films. We use
micromagnetic simulations to study the spin-wave dynamics in an in-plane
magnetized yttrium iron garnet thin film with a thickness in the nanometre
range in the presence of surface defects in the form of locally introduced
uniaxial anisotropies. These defects are used to demonstrate that the Backward
Volume Magnetostatic Spin Waves (BVMSW) are more responsive to backscattering
in comparison to Magnetostatic Surface Spin Waves (MSSWs). For this particular
defect type, the reason for this behavior can be quantitatively related to the
difference in the magnon band structures for the two types of spin waves. To
demonstrate this, we develop a quasi-analytical theory for the scattering
process. It shows an excellent agreement with the micromagnetic simulations,
sheds light on the backscattering processes and provides a new way to analyze
the spin-wave transmission rates in the presence of surface inhomogeneities in
sufficiently thin films, for which the role of exchange energy in the spin-wave
dynamics is significant. Our study paves the way to designing magnonic logic
devices for data processing which rely on a designed control of the spin-wave
transmission.",2005.09965v2
2020-07-31,Manipulating the photonic Hall effect with hybrid Mie-exciton resonances,"We examine the far-field optical response, under-plane wave excitation in the
presence of a static magnetic field, of core-shell nanoparticles involving a
gyroelectric component, either as the inner or the outer layer, through
analytic calculations based on appropriately extended Mie theory. We focus on
absorption and scattering of light by bismuth-substituted yttrium iron garnet
(Bi:YIG) nanospheres and nanoshells, combined with excitonic materials such as
organic-molecule aggregates or two-dimensional transition-metal
dichalcogenides, and discuss the hybrid character of the modes emerging from
the coupling of the two constituents. We observe the excitation of strong
magneto-optic phenomena and explore, in particular, the response and tunability
of a magneto-transverse light current, indicative of the photonic Hall effect.
We show how interaction between the Bi:YIG and excitonic layers leads to a pair
of narrow bands of highly directional scattering, emerging from the
aforementioned hybridization, which can be tuned at will by adjusting the
geometrical or optical parameters of the system. Our theoretical study
introduces optically anisotropic media as promising templates for strong
coupling in nanophotonics, offering a means to combine tunable magnetic and
optical properties, with potential implications both in the design of
all-dielectric photonic devices but also in novel clinical applications.",2007.16062v2
2020-12-01,Towards a quantum interface between spin waves and paramagnetic spin baths,"Spin waves have risen as promising candidate information carriers for the
next generation of information technologies. Recent experimental demonstrations
of their detection using electron spins in diamond pave the way towards
studying the back-action of a controllable paramagnetic spin bath on the spin
waves. Here, we present a quantum theory describing the interaction between
spin waves and paramagnetic spins. As a case study we consider an ensemble of
nitrogen-vacancy spins in diamond in the vicinity of an Yttrium-Iron-Garnet
thin film. We show how the back-action of the ensemble results in strong and
tuneable modifications of the spin-wave spectrum and propagation properties.
These modifications include the full suppression of spin-wave propagation and,
in a different parameter regime, the enhancement of their propagation length by
$\sim 50\%$. Furthermore, we show how the spin wave thermal fluctuations induce
a measurable frequency shift of the paramagnetic spins in the bath. This shift
results in a thermal dispersion force that can be measured optically and/or
mechanically with a diamond mechanical resonator. In addition, we use our
theory to compute the spin wave-mediated interaction between the spins in the
bath. We show that all the above effects are measurable by state-of-the-art
experiments. Our results provide the theoretical foundation for describing
hybrid quantum systems of spin waves and spin baths, and establish the
potential of quantum spins as active control, sensing, and interfacing tools
for spintronics.",2012.00540v1
2021-02-26,Control of the Bose-Einstein Condensation of Magnons by the Spin-Hall Effect,"Previously, it has been shown that rapid cooling of yttrium-iron-garnet
(YIG)/platinum (Pt) nano structures, preheated by an electric current sent
through the Pt layer, leads to overpopulation of a magnon gas and to subsequent
formation of a Bose-Einstein condensate (BEC) of magnons. The spin Hall effect
(SHE), which creates a spin-polarized current in the Pt layer, can inject or
annihilate magnons depending on the electric current and applied field
orientations. Here we demonstrate that the injection or annihilation of magnons
via the SHE can prevent or promote the formation of a rapid cooling induced
magnon BEC. Depending on the current polarity, a change in the BEC threshold of
-8% and +6% was detected. These findings demonstrate a new method to control
macroscopic quantum states, paving the way for their application in spintronic
devices.",2102.13481v2
2021-04-16,Implementing a magnonic time-delay reservoir computer model,"Recently we demonstrated experimentally that microwave oscillators based on
the time delay feedback provided by traveling spin waves could operate as
reservoir computers. In the present paper, we extend this concept by adding the
feature of time multiplexing made available by the large propagation
times/distances of traveling spin waves. The system utilizes the nonlinear
behavior of propagating magnetostatic surface spin waves in a yttrium-iron
garnet thin film and the time delay inherent in the active ring configuration
to process time dependent data streams. Higher reservoir dimensionality is
obtained through the time-multiplexing method, emulating ""virtual"" neurons as
temporally separated spin-wave pulses circulating in the active ring below the
auto-oscillation threshold. To demonstrate the efficacy of the concept, the
active ring reservoir computer is evaluated on the short-term memory and parity
check benchmark tasks, and the physical system parameters are tuned to optimize
performance. By incorporating a reference line to mix the input signal directly
onto the active ring output, both the amplitude and phase nonlinearity of the
spin waves can be exploited, resulting in significant improvement on the
nonlinear parity check task. We also find that the fading memory capacity of
the system can be easily tuned by controlling the active ring gain. Finally, we
show that the addition of a second spin-wave delay line configured to transmit
backward volume spin waves can partly compensate dispersive pulse broadening
and enhance the fading memory capacity of the active ring.",2104.07879v1
2021-04-16,Strong magnon-photon coupling with chip-integrated YIG in the zero-temperature limit,"The cross-integration of spin-wave and superconducting technologies is a
promising method for creating novel hybrid devices for future information
processing technologies to store, manipulate, or convert data in both classical
and quantum regimes. Hybrid magnon-polariton systems have been widely studied
using bulk Yttrium Iron Garnet (Y$_{3}$Fe$_{5}$O$_{12}$, YIG) and
three-dimensional microwave photon cavities. However, limitations in YIG growth
have thus far prevented its incorporation into CMOS compatible technology such
as high quality factor superconducting quantum technology. To overcome this
impediment, we have used Plasma Focused Ion Beam (PFIB) technology -- taking
advantage of precision placement down to the micron-scale -- to integrate YIG
with superconducting microwave devices. Ferromagnetic resonance has been
measured at millikelvin temperatures on PFIB-processed YIG samples using planar
microwave circuits. Furthermore, we demonstrate strong coupling between
superconducting resonator and YIG ferromagnetic resonance modes by maintaining
reasonably low loss while reducing the system down to the micron scale. This
achievement of strong coupling on-chip is a crucial step toward fabrication of
functional hybrid quantum devices that advantage from spin-wave and
superconducting components.",2104.08068v3
2021-08-25,Quantum network with magnonic and mechanical nodes,"A quantum network consisting of magnonic and mechanical nodes connected by
light is proposed. Recent years have witnessed a significant development in
cavity magnonics based on collective spin excitations in ferrimagnetic
crystals, such as yttrium iron garnet (YIG). Magnonic systems are considered to
be a promising building block for a future quantum network. However, a major
limitation of the system is that the coherence time of the magnon excitations
is limited by their intrinsic loss (typically in the order of 1 $\mu$s for
YIG). Here, we show that by coupling the magnonic system to a mechanical system
using optical pulses, an arbitrary magnonic state (either classical or quantum)
can be transferred to and stored in a distant long-lived mechanical resonator.
The fidelity depends on the pulse parameters and the transmission loss. We
further show that the magnonic and mechanical nodes can be prepared in a
macroscopic entangled state. These demonstrate the quantum state transfer and
entanglement distribution in such a novel quantum network of magnonic and
mechanical nodes. Our work shows the possibility to connect two separate fields
of optomagnonics and optomechanics, and to build a long-distance quantum
network based on magnonic and mechanical systems.",2108.11156v3
2021-12-21,Fast long-wavelength exchange spin waves in partially-compensated Ga:YIG,"Spin waves in yttrium iron garnet (YIG) nano-structures attract increasing
attention from the perspective of novel magnon-based data processing
applications. For short wavelengths needed in small-scale devices, the group
velocity is directly proportional to the spin-wave exchange stiffness constant
$\lambda_\mathrm{ex}$. Using wave vector resolved Brillouin Light Scattering
(BLS) spectroscopy, we directly measure $\lambda_\mathrm{ex}$ in Ga-substituted
YIG thin films and show that it is about three times larger than for pure YIG.
Consequently, the spin-wave group velocity overcomes the one in pure YIG for
wavenumbers $k > 4$ rad/$\mu$m, and the ratio between the velocities reaches a
constant value of around 3.4 for all $k > 20$ rad/$\mu$m. As revealed by
vibrating-sample magnetometry (VSM) and ferromagnetic resonance (FMR)
spectroscopy, Ga:YIG films with thicknesses down to 59 nm have a low Gilbert
damping ($\alpha < 10^{-3}$), a decreased saturation magnetization $\mu_0
M_\mathrm{S}~\approx~20~$mT and a pronounced out-of-plane uniaxial anisotropy
of about $\mu_0 H_{\textrm{u1}} \approx 95 $ mT which leads to an out-of-plane
easy axis. Thus, Ga:YIG opens access to fast and isotropic spin-wave transport
for all wavelengths in nano-scale systems independently of dipolar effects.",2112.11348v1
2022-01-23,Squeezed driving induced entanglement and squeezing among cavity modes and magnon mode in a magnon-cavity QED system,"We propose a scheme to generate entanglement between two cavity modes and
squeeze magnon mode in a magnon-cavity QED system, where the two microwave
cavity modes are coupled with a massive yttrium iron garnet (YIG) sphere
through magnetic dipole interaction. The nonlinearity used in our system
originates from a squeezed driving via parametric down-conversion process,
which is the reason to cause entanglement and squeezing. By using the mean
field approximation and employing experimentally feasible parameters, we
demonstrate that the system shows zero entanglement and squeezing without
squeezed driving. Meanwhile, our QED system denotes that the entanglement
between squeezed cavity mode and magnon mode can be transferred to the other
cavity mode and magnon mode via magnon-cavity coupling interaction, and then
the two cavity modes get entangled. A genuinely tripartite entangled state is
formed. We also show that magnon mode can be prepared in a squeezed state via
magnon-cavity beam-splitter interaction, which is as a result of the squeezed
field. Moreover, we show that it is a good way to enhance entanglement and
squeezing by increasing the nonlinear gain coefficient of squeezed driving. Our
results denote that magnon-cavity QED system is a powerful platform for
studying macroscopic quantum phenomena, which illustrates a new method to
photon-photon entanglement and magnon squeezing.",2201.09154v1
2022-01-26,Multi-band Bose-Einstein condensate at four-particle scattering resonance,"Superfluidity and superconductivity are macroscopic manifestations of quantum
mechanics, which have fascinated scientists since their discoveries roughly a
century ago. Ever since the initial theories of such quantum fluids were
formulated, there has been speculation as to the possibility of multi-component
quantum order. A particularly simple multi-component condensate is built from
particles occupying different quantum states, or bands, prior to condensation.
The particles in one or both bands may undergo condensation, as seen for
certain solids and anticipated for certain cold atom systems. For bulk solids,
the different bands always order simultaneously, with conventional pairing
characterized by complex order parameters describing the condensates in each
band. Another type of condensate, notably occurring at room temperature, has
been identified for magnons, the magnetic analogue of lattice vibrations,
injected by microwaves into yttrium iron garnet. Here we show that magnon
quantization for thin samples results in a new multi-band magnon condensate. We
establish a phase diagram, as a function of microwave drive power and frequency
relative to the magnon bands, revealing both single and multi-band
condensation. The most stable multi-band condensate is found in a narrow regime
favoured on account of a resonance in the scattering between two bands. Our
discovery introduces a flexible non-equilibrium platform operating at room
temperature for a well-characterised material, exploiting a Feshbach-like
resonance, for examining multi-band phenomena. It points to qualitatively new
ways to engineer and control condensates and superconducting states in
multiband systems and potential devices containing multiple interacting
condensates.",2201.11043v1
2022-02-25,Direct probing of strong magnon-photon coupling in a planar geometry,"We demonstrate direct probing of strong magnon-photon coupling using
Brillouin light scattering spectroscopy in a planar geometry. The magnonic
hybrid system comprises a split-ring resonator loaded with epitaxial yttrium
iron garnet thin films of 200 nm and 2.46 $\mu$m thickness. The Brillouin light
scattering measurements are combined with microwave spectroscopy measurements
where both biasing magnetic field and microwave excitation frequency are
varied. The cooperativity for the 200 nm-thick YIG films is 4.5, and larger
cooperativity of 137.4 is found for the 2.46 $\mu$m-thick YIG film. We show
that Brillouin light scattering is advantageous for probing the magnonic
character of magnon-photon polaritons, while microwave absorption is more
sensitive to the photonic character of the hybrid excitation. A miniaturized,
planar device design is imperative for the potential integration of magnonic
hybrid systems in future coherent information technologies, and our results are
a first stepping stone in this regard. Furthermore, successfully detecting the
magnonic hybrid excitation by Brillouin light scattering is an essential step
for the up-conversion of quantum signals from the optical to the microwave
regime in hybrid quantum systems.",2202.12696v1
2022-05-27,Magnonic Casimir Effect in Ferrimagnets,"Quantum fluctuations are the key concepts of quantum mechanics. Quantum
fluctuations of quantum fields induce a zero-point energy shift under spatial
boundary conditions. This quantum phenomenon, called the Casimir effect, has
been attracting much attention beyond the hierarchy of energy scales, ranging
from elementary particle physics to condensed matter physics together with
photonics. However, the application of the Casimir effect to spintronics has
not yet been investigated enough, particularly to ferrimagnetic thin films,
although yttrium iron garnet (YIG) is one of the best platforms for
spintronics. Here we fill this gap. Using the lattice field theory, we
investigate the Casimir effect induced by quantum fields for magnons in
insulating magnets and find that the magnonic Casimir effect can arise not only
in antiferromagnets but also in ferrimagnets including YIG thin films. Our
result suggests that YIG, the key ingredient of magnon-based spintronics, can
serve also as a promising platform for manipulating and utilizing Casimir
effects, called Casimir engineering. Microfabrication technology can control
the thickness of thin films and realize the manipulation of the magnonic
Casimir effect. Thus, we pave the way for magnonic Casimir engineering.",2205.13802v3
2022-06-27,Thermal spin current generation in the multifunctional ferrimagnet Ga$_{0.6}$Fe$_{1.4}$O$_{3}$,"In recent years, multifunctional materials have attracted increasing interest
for magnetic memories and energy harvesting applications. Magnetic insulating
materials are of special interest for this purpose, since they allow the design
of more efficient devices due to the lower Joule heat losses. In this context,
Ga$_{0.6}$Fe$_{1.4}$O$_3$ (GFO) is a good candidate for spintronics
applications, since it can exhibit multiferroicity and presents a spin Hall
magnetoresistance similar to the one observed in a yttrium iron garnet (YIG)/Pt
bilayer. Here, we explore GFO utilizing thermo-spin measurements in an on-chip
approach. By carefully considering the geometry of our thermo-spin devices we
are able to quantify the spin Seebeck effect and the spin current generation in
a GFO/Pt bilayer, obtaining a value comparable to that of YIG/Pt. This further
confirms the promises of an efficient spin current generation with the
possibility of an electric-field manipulation of the magnetic properties of the
system in an insulating ferrimagnetic material.",2206.13426v2
2022-08-29,Confinement of Bose-Einstein magnon condensates in adjustable complex magnetization landscapes,"Coherent wave states such as Bose-Einstein condensates (BECs), which
spontaneously form in an overpopulated magnon gas even at room temperature,
have considerable potential for wave-based computing and information processing
at microwave frequencies. The ability to control the transport properties of
magnon BECs plays an essential role for their practical use. Here, we
demonstrate spatio-temporal control of the BEC density distribution through the
excitation of magnon supercurrents in an inhomogeneously magnetized yttrium
iron garnet film. The BEC is created by microwave parametric pumping and probed
by Brillouin light scattering spectroscopy. The desired magnetization profile
is prepared by heating the film with optical patterns projected onto its
surface using a phase-based wavefront modulation technique. Specifically, we
observe a pronounced spatially localized magnon accumulation caused by magnon
supercurrents flowing toward each other originating in two heated regions. This
accumulation effect increases the BEC lifetime due to the constant influx of
condensed magnons into the confinement region. The shown approach to manipulate
coherent waves provides an opportunity to extend the lifetime of freely
evolving magnon BECs, create dynamic magnon textures, and study the interaction
of magnon condensates formed in different regions of the sample.",2208.13507v1
2022-09-05,Nonlocal detection of interlayer three-magnon coupling,"A leading nonlinear effect in magnonics is the interaction that splits a
high-frequency magnon into two low-frequency ones with conserved linear
momentum. Here, we report experimental observation of nonlocal three-magnon
scattering between spatially separated magnetic systems, viz. a CoFeB nanowire
and an yttrium iron garnet (YIG) thin film. Above a certain threshold power of
an applied microwave field, a CoFeB Kittel magnon splits into a pair of
counter-propagating YIG magnons that induce voltage signals in Pt electrodes on
each side, in excellent agreement with model calculations based on the
interlayer dipolar interaction. The excited YIG magnon pairs reside mainly in
the first excited (n=1) perpdendicular standing spin-wave mode. With increasing
power, the n=1 magnons successively scatter into nodeless (n=0) magnons through
a four-magnon process. Our results help to assess non-local scattering
processes in magnonic circuits that may enable quantum entanglement between
distant magnons for quantum information applications.",2209.01875v1
2022-11-12,Quantum control of a single magnon in a macroscopic spin system,"Non-classical quantum states are the pivotal features of a quantum system
that differs from its classical counterpart. However, the generation and
coherent control of quantum states in a macroscopic spin system remain an
outstanding challenge. Here we experimentally demonstrate the quantum control
of a single magnon in a macroscopic spin system (i.e., 1~mm-diameter
yttrium-iron-garnet sphere) coupled to a superconducting qubit via a microwave
cavity. By tuning the qubit frequency {\it in situ} via the Autler-Townes
effect, we manipulate this single magnon to generate its non-classical quantum
states, including the single-magnon state and the superposition state of a
single magnon and vacuum. Moreover, we confirm the deterministic generation of
these non-classical states by Wigner tomography. Our experiment offers the
first reported deterministic generation of the non-classical quantum states in
a macroscopic spin system and paves a way to explore its promising applications
in quantum engineering.",2211.06644v3
2022-11-16,Detection sensitivity enhancement of magnon Kerr nonlinearity in cavity magnonics induced by coherent perfect absorption,"We show how to enhance the detection sensitivity of magnon Kerr nonlinearity
(MKN) in cavity magnonics. The considered cavity-magnon system consists of a
three-dimensional microwave cavity containing two yttrium iron garnet (YIG)
spheres, where the two magnon modes (one has the MKN, while the other is
linear) in YIG spheres are simultaneously coupled to microwave photons. To
obtain the effective gain of the cavity mode, we feed two input fields into the
cavity. By choosing appropriate parameters, the coherent perfect absorption of
the two input fields occurs, and the cavity-magnon system can be described by
an effective non-Hermitian Hamiltonian. Under the pseudo-Hermitian conditions,
the effective Hamiltonian can host the third-order exceptional point (EP3),
where the three eigenvalues of the Hamiltonian coalesce into one. When the
magnon frequency shift $\Delta_K$ induced by the MKN is much smaller than the
linewidths $\Gamma$ of the peaks in the transmission spectrum of the cavity
(i.e., $\Delta_K\ll \Gamma$), the magnon frequency shift can be amplified by
the EP3, which can be probed via the output spectrum of the cavity. The scheme
we present provides an alternative approach to measure the MKN in the region
$\Delta_K\ll \Gamma$ and has potential applications in designing low-power
nonlinear devices based on the MKN.",2211.08922v2
2023-01-16,Crystal orientation dependent spin pumping in Bi0.1Y2.9Fe5O12/Pt interface,"Ferromagnetic resonance (FMR) based spin pumping is a versatile tool to
quantify the spin mixing conductance and spin to charge conversion (S2CC)
efficiency of ferromagnet/normal metal (FM/NM) heterostructure. The spin mixing
conductance of FM/NM interface can also be tuned by the crystal orientation
symmetry of epitaxial FM. In this work, we study the S2CC in epitaxial Bismuth
substituted Yttrium Iron Garnet (Bi0.1Y2.9Fe5O12) thin films Bi-YIG (100 nm)
interfaced with heavy metal platinum (Pt (8 nm)) deposited by pulsed laser
deposition process on different crystal orientation Gd3Ga5O12 (GGG) substrates
i.e. [100] and [111]. The crystal structure and surface roughness characterized
by X-Ray diffraction and atomic force microscopy measurements establish
epitaxial Bi-YIG[100], Bi-YIG[111] orientations and atomically flat surfaces
respectively. The S2CC quantification has been realized by two complimentary
techniques, (i) FMR-based spin pumping and inverse spin Hall effect (ISHE) at
GHz frequency and (ii) temperature dependent spin Seebeck measurements.
FMR-ISHE results demonstrate that the [111] oriented Bi-YIG/Pt sample shows
significantly higher values of spin mixing conductance ((2.31+-0.23)x10^18
m^-2) and spin Hall angle (0.01+-0.001) as compared to the [100] oriented
Bi-YIG/Pt. A longitudinal spin Seebeck measurement reveals that the [111]
oriented sample has higher spin Seebeck coefficient (106.40+-10 nV mm-1 K-1).
This anisotropic nature of spin mixing conductance and spin Seebeck coefficient
in [111] and [100] orientation has been discussed using the magnetic
environment elongation along the surface normal or parallel to the growth
direction. Our results aid in understanding the role of crystal orientation
symmetry in S2CC based spintronics devices.",2301.06477v1
2023-02-02,Ultrastrong Magnon-Photon Coupling Achieved by Magnetic Films in Contact with Superconducting Resonators,"Coherent coupling between spin wave excitations (magnons) and microwave
photons in a cavity may disclose new paths to unconventional phenomena as well
as for novel applications. Here, we present a systematic investigation on YIG
(Yttrium Iron Garnet) films on top of coplanar waveguide resonators made of
superconducting YBCO. We first show that spin wave excitations with frequency
higher than the Kittel mode can be excited by putting in direct contact a
5~$\mu$m thick YIG film with the YBCO coplanar resonator (cavity frequency
$\omega_c/2 \pi = 8.65$~GHz). With this configuration, we obtain very large
values of the collective coupling strength $\lambda/2 \pi \approx 2$~GHz and
cooperativity $C=5 \times 10^4$. Transmission spectra are analyzed by a
modified Hopfield model for which we provide an exact solution that allows us
to well reproduce spectra by introducing a limited number of free parameters.
It turns out that the coupling of the dominant magnon mode with photons exceeds
0.2 times the cavity frequency, thus demonstrating the achievement of the
ultrastrong coupling regime with this architecture. Our analysis also shows a
vanishing contribution of the diamagnetic term which is a peculiarity of pure
spin systems.",2302.00804v2
2023-02-10,Laser-induced magnonic band gap formation and control in YIG/GaAs heterostructure,"We demonstrate the laser-induced control over spin-wave (SW) transport in the
magnonic crystal (MC) waveguide formed from the semiconductor slab placed on
the ferrite film. We considered bilayer MC with periodical grooves performed on
the top of the n-type gallium arsenide slab side that oriented to the yttrium
iron garnet film. To observe the appearance of magnonic gap induced by laser
radiation, the fabricated structure was studied by the use of microwave
spectroscopy and Brillouin light-scattering. We perform detailed numerical
studies of this structure. We showed that the optical control of the magnonic
gaps (frequency width and position) is related to the variation of the charge
carriers' concentration in GaAs. We attribute these to nonreciprocity of SW
transport in the layered structure. Nonreciprocity was induced by the laser
exposure of the GaAs slab due to SWs' induced electromagnetic field screening
by the optically-generated charge carriers. We showed that SW dispersion,
nonreciprocity, and magnonic band gap position and width in the
ferrite-semiconductor magnonic crystal can be modified in a controlled manner
by laser radiation. Our results show the possibility of the integration of
magnonics and semiconductor electronics on the base of YIG/GaAs structures.",2302.05310v1
2023-03-04,Controllable magnon-induced transparency in a ferromagnetic material via cross- and self-Kerr effects,"Nonlinear interactions between optical fields and magnetic modes in cavity
magnonics constitute a rich source of various nontrivial effects in optics and
quantum information processing. In cavity magnonics, the nonlinear cross-Kerr
effect, which shifts the cavity's central frequency when a magnetic material is
pumped, causes the system to exhibit both Kittle and magnetostatic modes. Here,
we propose a new scheme for the investigation of probe fields transmission
profiles in cavity magnonic systems composed of a microwave cavity and a
ferromagnetic material (Yttrium iron garnet sphere). We report single-to-double
magnon-induced transparency (MIT) dips and a sharp magnon-induced absorption
(MIA) peak, and demonstrate how nonlinear cross- and self-Kerr interactions can
significantly enhance or suppress these phenomena. It is observed that the
splitting of the MIT window occurs when we incorporate magnon-magnon modes
coupling, which helps introducing a new degree of freedom to light-matter
interaction problems. Moreover, we investigate the propagation of group delay
in the vicinity of transparency and demonstrate how a sharp dip allows the
realization of slow light for a longer period of time. We found that both the
cavity-Kittle and magnon-magnon modes coupling parameters influence the
propagation of group delay, which demonstrates how subluminal-to-superluminal
(and vice versa) propagation phenomena may occur and transform. These findings
could pave the way for future research into nonlinear effects with novel
applications in cavity magnonics devices, which might be exploited for several
applications such as quantum computing devices and quantum memories.",2303.02332v1
2023-04-03,Observation of spin-wave moiré edge and cavity modes in twisted magnetic lattices,"We report the experimental observation of the spin-wave moir\'e edge and
cavity modes using Brillouin light scattering spectro-microscopy in a
nanostructured magnetic moir\'e lattice consisting of two twisted triangle
antidot lattices based on an yttrium iron garnet thin film. Spin-wave moir\'e
edge modes are detected at an optimal twist angle and with a selective
excitation frequency. At a given twist angle, the magnetic field acts as an
additional degree of freedom for tuning the chiral behavior of the magnon edge
modes. Micromagnetic simulations indicate that the edge modes emerge within the
original magnonic band gap and at the intersection between a mini-flatband and
a propagation magnon branch. Our theoretical estimate for the Berry curvature
of the magnon-magnon coupling suggests a non-trivial topology for the chiral
edge modes and confirms the key role played by the dipolar interaction. Our
findings shed light on the topological nature of the magnon edge mode for
emergent moir\'e magnonics.",2304.01001v1
2023-04-18,Transient non-collinear magnetic state for all-optical magnetization switching,"Resonant absorption of a photon by bound electrons in a solid can promote an
electron to another orbital state or transfer it to a neighboring atomic site.
Such a transition in a magnetically ordered material could affect the magnetic
order. While this process is an obvious road map for optical control of
magnetization, experimental demonstration of such a process remains
challenging. Exciting a significant fraction of magnetic ions requires a very
intense incoming light beam, as orbital resonances are often weak compared to
above-band-gap excitations. In the latter case, a sizeable reduction of the
magnetization occurs as the absorbed energy increases the spin temperature,
masking the non-thermal optical effects. Here, using ultrafast x-ray
spectroscopy, we were able to resolve changes in the magnetization state
induced by resonant absorption of infrared photons in Co-doped yttrium iron
garnet, with negligible thermal effects. We found that the optical excitation
of the Co ions affects the two distinct magnetic Fe sublattices differently,
resulting in a transient non-collinear magnetic state. The present results
indicate that the all-optical magnetization switching most likely occurs due to
the creation of a transient, non-collinear magnetic state followed by coherent
spin rotations of the Fe moments.",2304.08890v1
2023-04-21,Magnon squeezing by two-tone driving of a qubit in cavity-magnon-qubit systems,"We propose a scheme for preparing magnon squeezed states in a hybrid
cavity-magnon-qubit system. The system consists of a microwave cavity that
simultaneously couples to a magnon mode of a macroscopic yttrium-iron-garnet
(YIG) sphere via the magnetic-dipole interaction and to a transmon-type
superconducting qubit via the electric-dipole interaction. By far detuning from
the magnon-qubit system, the microwave cavity is adiabatically eliminated. The
magnon mode and the qubit then get effectively coupled via the mediation of
virtual photons of the microwave cavity. We show that by driving the qubit with
two microwave fields and by appropriately choosing the drive frequencies and
strengths, magnonic parametric amplification can be realized, which leads to
magnon quadrature squeezing with the noise below vacuum fluctuation. We provide
optimal conditions for achieving magnon squeezing, and moderate squeezing can
be obtained using currently available parameters. The generated squeezed states
are of a magnon mode involving more than $10^{18}$ spins and thus macroscopic
quantum states. The work may find promising applications in quantum information
processing and high-precision measurements based on magnons and in the study of
macroscopic quantum states.",2304.10760v4
2023-07-12,Quantum information diode based on a magnonic crystal,"Exploiting the effect of nonreciprocal magnons in a system with no inversion
symmetry, we propose a concept of a quantum information diode, {\it i.e.}, a
device rectifying the amount of quantum information transmitted in the opposite
directions. We control the asymmetric left and right quantum information
currents through an applied external electric field and quantify it through the
left and right out-of-time-ordered correlation (OTOC). To enhance the
efficiency of the quantum information diode, we utilize a magnonic crystal. We
excite magnons of different frequencies and let them propagate in opposite
directions. Nonreciprocal magnons propagating in opposite directions have
different dispersion relations. Magnons propagating in one direction match
resonant conditions and scatter on gate magnons. Therefore, magnon flux in one
direction is damped in the magnonic crystal leading to an asymmetric transport
of quantum information in the quantum information diode. A quantum information
diode can be fabricated from an yttrium iron garnet (YIG) film. This is an
experimentally feasible concept and implies certain conditions: low temperature
and small deviation from the equilibrium to exclude effects of phonons and
magnon interactions. We show that rectification of the flaw of quantum
information can be controlled efficiently by an external electric field and
magnetoelectric effects.",2307.06047v1
2023-07-14,Magnonic Combinatorial Memory,"In this work, we consider a type of magnetic memory where information is
encoded into the mutual arrangements of magnets. The device is an active ring
circuit comprising magnetic and electronic parts connected in series. The
electric part includes a broad-band amplifier, phase shifters, and attenuators.
The magnetic part is a mesh of magnonic waveguides with magnets placed on the
waveguide junctions. There are amplitude and phase conditions for
auto-oscillations to occur in the active ring circuit. The frequency(s) of the
auto-oscillation and spin wave propagation route(s) in the magnetic part
depends on the mutual arrangement of magnets in the mesh. The propagation route
is detected with a set of power sensors. The correlation between circuit
parameters and spin wave route is the base of memory operation. The combination
of input/output switches connecting electric and magnetic parts, and electric
phase shifters constitute the memory address. The output of power sensors is
the memory state. We present experimental data on the proof-of-the-concept
experiments on the prototype with just three magnets placed on top of a
single-crystal yttrium iron garnet Y3Fe2(FeO4)3 (YIG) film. The results
demonstrate a robust operation with On/Off ratio for route detection exceeding
35 dB at room temperature. The number of propagation routes scales factorial
with the size of the magnetic part. Coding information in propagation routes
makes it possible to drastically increase the data storage density compared to
conventional memory devices. MCM with just 25 magnets can store as much as 25!
(10 Yotta) bits. Physical limits and constraints are also discussed.",2307.07464v1
2023-08-02,Frequency Tunable Magnetostatic Wave Filters With Zero Static Power Magnetic Biasing Circuitry,"A single tunable filter simplifies complexity, reduces insertion loss, and
minimizes size compared to frequency switchable filter banks commonly used for
radio frequency (RF) band selection. Magnetostatic wave (MSW) filters stand out
for their wide, continuous frequency tuning and high-quality factor. However,
MSW filters employing electromagnets for tuning consume excessive power and
space, unsuitable for consumer wireless applications. Here, we demonstrate
miniature and high selectivity MSW tunable filters with zero static power
consumption, occupying less than 2 cc. The center frequency is continuously
tunable from 3.4 GHz to 11.1 GHz via current pulses of sub-millisecond duration
applied to a small and nonvolatile magnetic bias assembly. This assembly is
limited in the area over which it can achieve a large and uniform magnetic
field, necessitating filters realized from small resonant cavities
micromachined in thin films of Yttrium Iron Garnet. Filter insertion loss of
3.2 dB to 5.1 dB and out-of-band third order input intercept point greater than
41 dBm are achieved. The filter's broad frequency range, compact size, low
insertion loss, high out-of-band linearity, and zero static power consumption
are essential for protecting RF transceivers and antennas from interference,
thus facilitating their use in mobile applications like IoT and 6G networks.",2308.00907v3
2023-09-16,Exploring orbital-charge conversion mediated by interfaces with copper through spin-orbital pumping,"We investigated how different materials affect the orbital-charge conversion
in heterostructures with the naturally oxidized cooper capping layer. When we
added a thin layer of $CuOx(3nm)$ onto yttrium iron garnet $(YIG)/W$ stacks, we
observed a significant reduction in the charge current signal measured by means
the spin pumping effect technique. This finding contrasts with the results of a
prior study conducted on YIG/Pt/CuOx, which reported the opposite effect. On
the other hand, when we added the same $CuOx(3nm)$ layer to $YIG/Ti(4nm)$
structures, there was not much change in the spin pumping signal. This occurred
because Ti does not generate much orbital current at the $Ti/CuOx$ interface,
unlike Pt, due to its weaker spin-orbit coupling. Interestingly, when we added
the $CuOx(3nm)$ layer to $SiO_{2}/Py(5nm)/Pt(4nm)$ structures, the spin pumping
signal increased. However, in $SiO_{2}/CuOx(3nm)/Pt(4nm)/Py(5nm)$ structures,
the signal decreased. Finally, we delve into a theoretical analysis of the spin
(orbital) Hall effect in YIG/Heavy-metal systems. These findings have the
potential to advance research in the innovative field of orbitronics and
contribute to the development of new technologies based on spin-orbital
conversion.",2309.08857v2
2023-11-09,Bose-Einstein condensation in systems with flux equilibrium,"We consider flux equilibrium in dissipative nonlinear wave systems subject to
external energy pumping. In such systems, the elementary excitations, or
quasiparticles, can create a Bose-Einstein condensate. We develop a theory on
the Bose-Einstein condensation of quasiparticles for various regimes of
external excitation, ranging from weak and stationary to ultra-strong pumping,
enabling us to determine the number of quasiparticles near the bottom of the
energy spectrum and their distribution along wave vectors. We identify physical
phenomena leading to condensation in each of the regimes. For weak stationary
pumping, where the distribution of quasiparticles deviates only slightly from
thermodynamic equilibrium, we define a range of pumping parameters where the
condensation occurs and estimate the density of the condensate and the fraction
of the condensed quasiparticles. As the pumping amplitude increases, a powerful
influx of injected quasiparticles is created by the Kolmogorov-Zakharov
scattering cascade, leading to their Bose-Einstein condensation. With even
stronger pumping, kinetic instability may occur, resulting in a direct transfer
of injected quasiparticles to the bottom of the spectrum. For the case of
ultra-strong parametric pumping, we have developed a stationary nonlinear
theory of kinetic instability. The theory agrees qualitatively with
experimental data obtained using Brillouin light scattering spectroscopy during
parametric pumping of magnons in room-temperature films of yttrium-iron garnet.",2311.05315v1
2023-11-29,Nonlinear erasing of propagating spin-wave pulses in thin-film Ga:YIG,"Nonlinear phenomena are key for magnon-based information processing, but the
nonlinear interaction between two spin-wave signals requires their
spatio-temporal overlap which can be challenging for directional processing
devices. Our study focuses on a gallium-substituted yttrium iron garnet film,
which exhibits an exchange-dominated dispersion relation and thus provides a
particularly broad range of group velocities compared to pure YIG. Using time-
and space-resolved Brillouin light scattering spectroscopy, we demonstrate the
excitation of time-separated spin-wave pulses at different frequencies from the
same source, where the delayed pulse catches up with the previously excited
pulse and outruns it due to its higher group velocity. By varying the
excitation power of the faster pulse, the outcome can be finely tuned from a
linear superposition to a nonlinear interaction of both pulses, resulting in a
full attenuation of the slower pulse. Therefore, our findings demonstrate the
all-magnonic erasing process of a propagating magnonic signal, which enables
the realization of complex temporal logic operations with potential
application, e.g., in inhibitory neuromorphic functionalities.",2311.17821v2
2023-12-07,Magnon-Photon Coupling in an Opto-Electro-Magnonic Oscillator,"The opto-electronic oscillators (OEOs) hosting self-sustained oscillations by
a time delayed mechanism are of particular interest in long-haul signal
transmission and processing. On the other hand, owing to their unique
tunability and compatibility, magnons - as elementary excitations of spin waves
- are advantageous carriers for coherent signal transduction across different
platforms. In this work, we integrated an opto-electronic oscillator with a
magnonic oscillator consisting of a microwave waveguide and a yttrium iron
garnet sphere. We find that, in the presence of the magnetic sphere, the
oscillator power spectrum exhibits sidebands flanking the fundamental OEO
modes. The measured waveguide transmission reveals anti-crossing gaps, a
hallmark of the coupling between the opto-electronic oscillator modes and the
Walker modes of the sphere. Experimental results are well reproduced by a
coupled-mode theory that accounts for nonlinear magnetostrictive interactions
mediated by the magnetic sphere. Leveraging the advanced fiber-optic
technologies in opto-electronics, this work lays out a new, hybrid platform for
investigating long distance coupling and nonlinearity in coherent magnonic
phenomena.",2312.04676v2
2023-12-08,Engineering synthetic gauge fields through the coupling phases in cavity magnonics,"Cavity magnonics, which studies the interaction of light with magnetic
systems in a cavity, is a promising platform for quantum transducers, quantum
memories, and devices with non-reciprocal behaviour. At microwave frequencies,
the coupling between a cavity photon and a magnon, the quasi-particle of a spin
wave excitation, is a consequence of the Zeeman interaction between the
cavity's magnetic field and the magnet's macroscopic spin. For each
photon/magnon interaction, a coupling phase factor exists, but is often
neglected in simple systems. However, in ""loop-coupled"" systems, where there
are at least as many couplings as modes, the coupling phases become relevant
for the physics and lead to synthetic gauge fields. We present experimental
evidence of the existence of such coupling phases by considering two spheres
made of Yttrium-Iron-Garnet and two different re-entrant cavities. We predict
numerically the values of the coupling phases, and we find good agreement
between theory and the experimental data. Theses results show that in cavity
magnonics, one can engineer synthetic gauge fields, which can be useful for
cavity-mediated coupling, dark mode memories, and building nonreciprocal
devices.",2312.04915v3
2023-12-14,"Nonlocal damping of spin waves in a magnetic insulator induced by normal, heavy, or altermagnetic metallic overlayer: a Schwinger-Keldysh field theory approach","Understanding spin wave (SW) damping, and how to control it to the point of
being able to amplify SW-mediated signals, is one of the key requirements to
bring the envisaged magnonic technologies to fruition. Even widely used
magnetic insulators with low magnetization damping in their bulk, such as
yttrium iron garnet, exhibit 100-fold increase in SW damping due to inevitable
contact with metallic layers in magnonic circuits, as observed in very recent
experiments [I. Bertelli et al., Adv. Quantum Technol. 4, 2100094 (2021)]
mapping SW damping in spatially-resolved fashion. Here, we provide microscopic
and rigorous understanding of wavevector-dependent SW damping using extended
Landau-Lifshitz-Gilbert equation with nonlocal damping tensor, instead of
conventional local scalar Gilbert damping, as derived from Schwinger-Keldysh
nonequilibrium quantum field theory. In this picture, the origin of nonlocal
magnetization damping and thereby induced wavevector-dependent SW damping is
interaction of localized magnetic moments of magnetic insulator with conduction
electrons from the examined three different types of metallic overlayers --
normal, heavy, and altermagnetic. Due to spin-split energy-momentum dispersion
of conduction electrons in the latter two cases, the nonlocal damping is
anisotropic in spin and space, and it can be dramatically reduced by changing
the relative orientation of the two layers when compared to the usage of normal
metal overlayer.",2312.09140v1
2023-12-15,Magnon Bose-Einstein condensates: from time crystals and quantum chromodynamics to vortex sensing and cosmology,"Under suitable experimental conditions collective spin-wave excitations,
magnons, form a Bose-Einstein condensate (BEC) where the spins precess with a
globally coherent phase. Bose-Einstein condensation of magnons has been
reported in a few systems, including superfluid phases of $^3$He, solid state
systems such as Yttrium-iron-garnet (YIG) films, and cold atomic gases. Among
these systems, the superfluid phases of $^3$He provide a nearly ideal test
bench for coherent magnon physics owing to experimentally proven spin
superfluidity, the long lifetime of the magnon condensate, and the versatility
of the accessible phenomena. We first briefly recap the properties of the
different magnon BEC systems, with focus on superfluid $^3$He. The main body of
this review summarizes recent advances in application of magnon BEC as a
laboratory to study basic physical phenomena connecting to diverse areas from
particle physics and cosmology to new phases of condensed matter. This line of
research complements the ongoing efforts to utilize magnon BECs as probes and
components for potentially room-temperature quantum devices. In conclusion, we
provide a roadmap for future directions in the field of applications of magnon
BEC to fundamental research.",2312.10119v1
2023-12-22,Magnon-assisted magnetization reversal of Ni81Fe19 nanostripes on Y3Fe5O12 with different interfaces,"Magnetic bit writing by short-wave magnons without conversion to the
electrical domain is expected to be a game-changer for in-memory computing
architectures. Recently, the reversal of nanomagnets by propagating magnons was
demonstrated. However, experiments have not yet explored different wavelengths
and the nonlinear excitation regime of magnons required for computational
tasks. We report on the magnetization reversal of individual 20-nm-thick
Ni81Fe19 (Py) nanostripes integrated onto 113-nm-thick yttrium iron garnet
(YIG). We suppress direct interlayer exchange coupling by an intermediate layer
such as Cu and SiO2. Exciting magnons in YIG with wavelengths {\lambda} down to
148 nm we observe the reversal of the integrated ferromagnets in a small
opposing field of 14 mT. Magnons with a small wavelength of {\lambda} = 195 nm,
i.e., twice the width of the Py nanostripes, induced the reversal at an
unprecedentedly small spin precessional power of about 1 nW after propagating
over 15 {\mu}m in YIG. Considerations based on dynamic dipolar coupling explain
the observed wavelength dependence of magnon-induced reversal efficiency. For
an increased power the stripes reversed in an opposing field of only about 1
mT. Our findings are important for the practical implementation of nonvolatile
storage of broadband magnon signals in YIG by means of bistable nanomagnets
without the need of an appreciable global magnetic field.",2312.15107v1
2024-01-04,Nonreciprocal photon blockade with Kerr magnons,"Nonreciprocal devices, allowing to manipulate one-way signals, are crucial to
quantum information processing and quantum network. Here we propose a nonlinear
cavity-magnon system, consisting of a microwave cavity coupled to one or two
yttrium-iron-garnet (YIG) spheres supporting magnons with Kerr nonlinearity, to
investigate nonreciprocal photon blockade. The nonreciprocity originates from
the direction-dependent Kerr effect, distinctly different from previous
proposals with spinning cavities and dissipative couplings. For a single sphere
case, nonreciprocal photon blockade can be realized by manipulating the
nonreciprocal destructive interference between two active paths, via vary the
Kerr coefficient from positive to negative, or vice versa. By optimizing the
system parameters, the perfect and well tuned nonreciprocal photon blockade can
be predicted. For the case of two spheres with opposite Kerr effects, only
reciprocal photon blockade can be observed when two cavity-magnon coupling
strengths Kerr strengths are symmetric. However, when coupling strengths or
Kerr strengths become asymmetric, nonreciprocal photon blockade appears. This
implies that two-sphere nonlinear cavity-magnon systems can be used to switch
the transition between reciprocal and nonreciprocal photon blockades. Our study
offers a potential platform for investigating nonreciprocal photon blockade
effect in nonlinear cavity magnonics.",2401.02251v1
2024-03-20,New opportunities in condensed matter physics for nanoscale quantum sensors,"Nitrogen vacancy (NV) centre quantum sensors provide unique opportunities in
studying condensed matter systems: they are quantitative, noninvasive,
physically robust, offer nanoscale resolution, and may be used across a wide
range of temperatures. These properties have been exploited in recent years to
obtain nanoscale resolution measurements of static magnetic fields arising from
spin order and current flow in condensed matter systems. Compared with other
nanoscale magnetic-field sensors, NV centres have the unique advantage that
they can probe quantities that go beyond average magnetic fields. Leveraging
techniques from magnetic resonance, NV centres can perform high precision noise
sensing, and have given access to diverse systems, such as fluctuating
electrical currents in simple metals and graphene, as well as magnetic dynamics
in yttrium iron garnet. In this review we summarise unique opportunities in
condensed matter sensing by focusing on the connections between specific NV
measurements and previously established physical characteristics that are more
readily understood in the condensed matter community, such as correlation
functions and order parameters that are inaccessible by other techniques, and
we describe the technical frontier enabled by NV centre sensing.",2403.13710v1
2024-02-19,Magnetic anisotropy and GGG substrate stray field in YIG films down to millikelvin temperatures,"Quantum magnonics investigates the quantum-mechanical properties of magnons
such as quantum coherence or entanglement for solid-state quantum information
technologies at the nanoscale. The most promising material for quantum
magnonics is the ferrimagnetic yttrium iron garnet (YIG), which hosts magnons
with the longest lifetimes. YIG films of the highest quality are grown on a
paramagnetic gadolinium gallium garnet (GGG) substrate. The literature has
reported that ferromagnetic resonance (FMR) frequencies of YIG/GGG decrease at
temperatures below 50 K despite the increase in YIG magnetization. We
investigated a 97 nm-thick YIG film grown on 500 $\mathrm{\mu}$m-thick GGG
substrate through a series of experiments conducted at temperatures as low as
30 mK, and using both analytical and numerical methods. Our findings suggest
that the primary factor contributing to the FMR frequency shift is the stray
magnetic field created by the partially magnetized GGG substrate. This stray
field is antiparallel to the applied external field and is highly
inhomogeneous, reaching up to 40 mT in the center of the sample. At
temperatures below 500 mK, the GGG field exhibits a saturation that cannot be
described by the standard Brillouin function for a paramagnet. Including the
calculated GGG field in the analysis of the FMR frequency versus temperature
dependence allowed the determination of the cubic and uniaxial anisotropies. We
find that the total anisotropy increases more than three times with the
decrease in temperature down to 2 K. Our findings enable accurate predictions
of the YIG/GGG magnetic systems behavior at low and ultra-low millikelvin
temperatures, crucial for developing quantum magnonic devices.",2402.12112v1
2003-01-10,Enhancement of the electron electric dipole moment in gadolinium garnets,"Effects caused by the electron electric dipole moment (EDM) in gadolinium
garnets are considered. Experimental studies of these effects could improve
current upper limit on the electron EDM by several orders of magnitude. We
suggest a consistent theoretical model and perform calculations of observable
effects in gadolinium gallium garnet and gadolinium iron garnet. Our
calculation accounts for both direct and exchange diagrams.",0301133v1
2008-06-04,Electric Field Induced Transformation of Magnetic Domain Structure in Magnetoelectric Iron Garnet Films,"The room temperature magnetoelectric effect was observed in epitaxial iron
garnet films that appeared as magnetic domain wall motion induced by electric
field. The films grown on gadolinium-gallium garnet substrates with various
crystallographic orientations were examined. The effect was observed in (210)
and (110) films and was not observed in (111) films. Dynamic observation of the
domain wall motion in 400 V voltage pulses gave the value of domain wall
velocity in the range 30-50 m/s. The same velocity was achieved in magnetic
field pulse about 50 Oe.",0806.0811v1
2015-03-27,Crystal field and magnetism with Wannier functions: Rare-earth doped aluminum garnets,"Using the recently developed method we calculate the crystal field parameters
in yttrium and lutetium aluminum garnets doped with seven trivalent Kramers
rare-earth ions. We then insert calculated parameters into the atomic-like
Hamiltonian taking into account the electron-electron, spin-orbit and Zeeman
interactions and determine the multiplet splitting by the crystal field as well
as magnetic $\hat{g}$ tensors. We compare calculated results with available
experimental data.",1503.07987v2
2008-08-04,Superconductivity and Magnetism in REFeAsO1-xFx (RE=Rare Earth Elements),"Fluoride-doped iron-based oxypnictides containing rare-earth gadolinium
(GdFeAsO0.8F0.2) and co-doping with yttrium (Gd0.8Y0.2FeAsO0.8F0.2) have been
prepared via conventional solid state reaction at ambient pressure. The
non-yttrium substituted oxypnictide show superconducting transition as high as
43.9 K from temperature dependent resistance measurements with the Meissner
effect observed at a lower temperature of 40.8 K from temperature dependent
magnetization measurements. By replacing a small amount of gadolinium with
yttrium Tc was observed to be lowered by 10 K which might be caused by a change
in the electronic or magnetic structures since the crystal structure was not
altered.",0808.0289v1
2009-05-19,Orientation of Nd$^{3+}$ dipoles in yttrium aluminum garnet: A simple yet accurate model,"We report an experimental study of the 1064nm transition dipoles in neodymium
doped yttrium aluminum garnet (Nd-YAG) by measuring the coupling constant
between two orthogonal modes of a laser cavity for different cuts of the YAG
gain crystal. We propose a theoretical model in which the transition dipoles,
slightly elliptic, are oriented along the crystallographic axes. Our
experimental measurements show a very good quantitative agreement with this
model, and predict a dipole ellipticity between 2% and 3%. This work provides
an experimental evidence for the simple description in which transition dipoles
and crystallographic axes are collinear in Nd-YAG (with an accuracy better than
1 deg), a point that has been discussed for years.",0905.3125v1
2018-12-31,Vanadium in yttrium aluminum garnet: charge states and localization in the lattice,"Vanadium ions charge states and their incorporation in the yttrium aluminum
garnet Y3Al5O12 (YAG) lattice were studied by the correlated optical absorption
and electron paramagnetic resonance (EPR) measurements. In as-grown crystals,
the occupation of the V3+ at both the octahedral and tetrahedral aluminum sites
was proven. The V3+ to V4+ charge transformation was observed after annealing
in air, whereas annealing in the hydrogen atmosphere resulted exclusively in a
slight weakening of the V3+ absorption bands due to partial recharge of these
ions. Spin Hamiltonian parameters of the V3+ and V4+ ions at the tetrahedral
sites including the zero field splitting and the 51V hyperfine constants have
been determined using the high-frequency, up to 300 GHz, EPR measurements. From
the analysis of the spin Hamiltonian parameters in the framework of the crystal
field theory, the ground state energy levels splitting of the V3+ and V4+ ions
were calculated. The charge distribution over the tetrahedral V3+ and its
nearest oxygen surroundings was found to be strongly inhomogeneous whereas the
tetrahedral V4+ ion concentrated the charge with very weak participation of
surrounding ligands. Furthermore, the correlation of the optical and EPR data
allowed the proper assignment of the optical absorption peaks in YAG:V
crystals.",1812.11877v1
2021-03-03,Calibration of the scintillation of cerium-doped yttrium aluminum garnet crystals irradiated by monoenergetic 4 MeV energy electrons,"This paper presents the results of measurements of fluorescing cerium-doped
yttrium aluminum garnet crystals after being irradiated by an accelerated
electron beam with energy of around 4 MeV. The measurements were performed
using the PHIL linear accelerator at LAL (France). We observe linear dependence
of the crystal emission to the electron beam charge and the isotropy of the
photon emission. We provide the calibration coefficients of the photon emission
depending on the charge of the accelerated electron beam for two crystals
originating from two different manufacturers.",2103.02497v1
2018-05-07,Detection of the interfacial exchange field at a ferromagnetic insulator-nonmagnetic metal interface with pure spin currents,"At the interface between a nonmagnetic metal (NM) and a ferromagnetic
insulator (FI) spin current can interact with the magnetization, leading to a
modulation of the spin current. The interfacial exchange field at these FI-NM
interfaces can be probed by placing the interface in contact with the spin
transport channel of a lateral spin valve (LSV) device and observing additional
spin relaxation processes. We study interfacial exchange field in lateral spin
valve devices where Cu spin transport channel is in proximity with
ferromagnetic insulator EuS (EuS-LSV) and yttrium iron garnet
Y$_3$Fe$_5$O$_{12}$ (YIG-LSV). The spin signals were compared with reference
lateral spin valve devices fabricated on nonmagnetic Si/SiO$_2$ substrate with
MgO or AlO$_x$ capping. The nonlocal spin valve signal is about 4 and 6 times
lower in the EuS-LSV and YIG-LSV, respectively. The suppression in the spin
signal has been attributed to enhanced surface spin-flip probability at the
Cu-EuS (or Cu-YIG) interface due to interfacial spin-orbit field. Besides spin
signal suppression we also found widely observed low temperature peak in the
spin signal at $T \sim$30 K is shifted to higher temperature in the case of
devices in contact with EuS or YIG. Temperature dependence of spin signal for
different injector-detector distances reveal fluctuating exchange field at
these interfaces cause additional spin decoherence which limit spin relaxation
time in addition to conventional sources of spin relaxation. Our results show
that temperature dependent measurement with pure spin current can be used to
probe interfacial exchange field at the ferromagnetic insulator-nonmagnetic
metal interface.",1805.02433v2
2019-05-10,Experimental Implementations of Cavity-Magnon Systems: from Ultra Strong Coupling to Applications in Precision Measurement,"Several experimental implementations of cavity-magnon systems are presented.
First an Yttrium Iron Garnet (YIG) block is placed inside a re-entrant cavity
where the resulting hybrid mode is measured to be in the ultra strong coupling
regime. When fully hybridised the ratio between the coupling rate and uncoupled
mode frequencies is determined to be $g/\omega=0.46$. Next a thin YIG cylinder
is placed inside a loop gap cavity. The bright mode of this cavity couples to
the YIG sample and is similarly measured to be in the ultra strong coupling
regime with ratio of coupling rate to uncoupled mode frequencies as
$g/\omega=0.34$. A larger spin density medium such as lithium ferrite (LiFe) is
expected to improve couplings by a factor of 1.46 in both systems as coupling
strength is shown to be proportional to the square root of spin density and
magnetic moment. Such strongly coupled systems are potentially useful for
cavity QED, hybrid quantum systems and precision dark matter detection
experiments. The YIG disc in the loop gap cavity, is, in particular, shown to
be a strong candidate for dark matter detection. Finally, a LiFe sphere inside
a two post re-entrant cavity is considered. In past work it was shown that the
magnon mode in the sample has a turnover point in frequency. Additionally, it
was predicted that if the system was engineered such that it fully hybridised
at this turnover point the cavity-magnon polariton (CMP) transition frequency
would become insensitive to both first and second order magnetic bias field
fluctuations, a result useful for precision frequency applications. This work
implements such a system by engineering the cavity mode frequency to near this
turnover point, with suppression in sensitivity to second order bias magnetic
field fluctuations shown.",1905.04002v2
2019-11-26,Free-standing and positionable microwave antenna device for magneto-optical spectroscopy experiments,"Modern spectroscopic techniques for the investigation of magnetization
dynamics in micro- and nano- structures or thin films use typically microwave
antennas which are directly fabricated on top of the sample by means of
electron-beam-lithography (EBL). Following this approach, every magnetic
structure on the sample needs its own antenna, resulting in additional EBL
steps and layer deposition processes. We demonstrate a new approach for
magnetization excitation that is suitable for optical and non-optical
spectroscopy techniques. By patterning the antenna on a separated flexible
glass cantilever and insulating it electrically, we solved the before mentioned
issues. Since we use flexible transparent glass as a substrate, optical
spectroscopy techniques like Brillouin-light-scattering microscopy ({\mu}BLS),
time resolved magneto-optical Kerr effect measurements (TRMOKE) or optical
detected magnetic resonance (ODMR) measurements can be carried out at visible
laser wavelengths. As the antenna is detached from the sample it can be freely
positioned in all three dimensions to adress only the desired magnetic sample
structures and to achieve effective excitation. We demonstrate the
functionality of these antennas using {\mu}BLS and compare coherently and
thermally excited magnon spectra to show the enhancement of the signal by a
factor of about 400 due to the excitation by the antenna. Moreover, we succeed
to characterize yttrium iron garnet thin films with spatial resolution using
optical ferromagnetic resonance (FMR) experiments. We analyse the spatial
excitation profile of the antenna by measuring the magnetization dynamics in
two dimensions. The technique is furthermore applied to investigate
injection-locking of spin Hall nano-oscillators.",1911.11517v1
2020-02-02,A millimeter-wave Bell Test using a ferrite parametric amplifier and a homodyne interferometer,"A combined ferrite parametric amplifier and millimeter-wave homodyne
interferometer are proposed as an ambient temperature Bell Test. It is shown
that the non-linear magnetic susceptibility of the yttrium iron garnet (YIG)
ferrite, on account of its narrow line-width Larmor precessional resonance,
make it an ideal material for the creation of entangled photons. These can be
measured using a homodyne interferometer, as the much larger number of
thermally generated photons associated with ambient temperature emission can be
screened out. The proposed architecture may enable YIG quantum technology-based
sensors to be developed, mimicking in the millimeter-wave band the large number
of quantum optical experiments in the near-infrared and visible regions which
had been made possible by use of the nonlinear beta barium borate
ferroelectric, an analogue of YIG. It is illustrated here how the YIG
parametric amplifier can reproduce quantum optical Type I and Type II wave
interactions, which can be used to create entangled photons in the
millimeter-wave band. It is estimated that when half a cubic centimeter of YIG
crystal is placed in a magnetic field of a few Tesla and pumped with 5 Watts of
millimeter-wave radiation, approximately 0.5x10^12 entangled millimeter-wave
photon pairs per second are generated by the spin-wave interaction. This means
an integration time of only a few tens of seconds is needed for a successful
Bell Test. A successful demonstration of this will lead to novel architectures
of entanglement-based quantum technology room temperature sensors,
re-envisioning YIG as a modern quantum material.",2002.00439v3
2020-08-21,"Macroscopic, layered onion shell like magnetic domain structure generated in YIG film using ultrashort, megagauss magnetic pulses","Study of the formation and evolution of large scale, ordered structures is an
enduring theme in science. The generation, evolution and control of large sized
magnetic domains are intriguing and challenging tasks, given the complex nature
of competing interactions present in any magnetic system. Here, we demonstrate
large scale non-coplanar ordering of spins, driven by picosecond, megagauss
magnetic pulses derived from a high intensity, femtosecond laser. Our studies
on a specially designed Yttrium Iron Garnet (YIG)/dielectric/metal film
sandwich target, show the creation of complex, large, concentric, elliptical
shaped magnetic domains which resemble the layered shell structure of an onion.
The largest shell has a major axis of over hundreds of micrometers, in stark
contrast to conventional sub micrometer scale polygonal, striped or bubble
shaped magnetic domains found in magnetic materials, or the large dumbbell
shaped domains produced in magnetic films irradiated with accelerator based
relativistic electron beams. Through micromagnetic simulations, we show that
the giant magnetic field pulses create ultrafast terahertz (THz) spin waves. A
snapshot of these fast propagating spin waves is stored as the layered onion
shell shaped domains in the YIG film. Typically, information transport via spin
waves in magnonic devices occurs in the gigahertz (GHz) regime, where the
devices are susceptible to thermal disturbances at room temperature. Our
intense laser light pulse - YIG sandwich target combination, paves the way for
room temperature table-top THz spin wave devices, which operate just above or
in the range of the thermal noise floor. This dissipation-less device offers
ultrafast control of spin information over distances of few hundreds of
microns.",2008.09473v1
2020-08-29,Exploring a quantum-information-relevant magnonic material: Ultralow damping at low temperature in the organic ferrimagnet V[TCNE]x,"Quantum information science and engineering requires novel low-loss magnetic
materials for magnon-based quantum-coherent operations. The search for low-loss
magnetic materials, traditionally driven by applications in microwave
electronics near room-temperature, has gained additional constraints from the
need to operate at cryogenic temperatures for many applications in quantum
information science and technology. Whereas yttrium iron garnet (YIG) has been
the material of choice for decades, the emergence of molecule-based materials
with robust magnetism and ultra-low damping has opened new avenues for
exploration. Specifically, thin-films of vanadium tetracyanoethylene (V[TCNE]x)
can be patterned into the multiple, connected structures needed for hybrid
quantum elements and have shown room-temperature Gilbert damping ({\alpha} = 4
\times 10^-5) that rivals the intrinsic (bulk) damping otherwise seen only in
highly-polished YIG spheres (far more challenging to integrate into arrays).
Here, we present a comprehensive and systematic study of the low-temperature
magnetization dynamics for V[TCNE]x thin films, with implications for their
application in quantum systems. These studies reveal a temperature-driven,
strain-dependent magnetic anisotropy that compensates the thin-film shape
anisotropy, and the recovery of a magnetic resonance linewidth at 5 K that is
comparable to room-temperature values (roughly 2 G at 9.4 GHz). We can account
for these variations of the V[TCNE]x linewidth within the context of scattering
from very dilute paramagnetic impurities, and anticipate additional linewidth
narrowing as the temperature is further reduced.",2008.13061v3
2021-01-25,Long-range spin-wave propagation in transversely magnetized nano-scaled conduits,"Magnonics attracts increasing attention in the view of novel low-energy
computation technologies based on spin waves. Recently, spin-wave propagation
in longitudinally magnetized nano-scaled spin-wave conduits was demonstrated,
proving the fundamental feasibility of magnonics at the sub-100 nm scale.
Transversely magnetized nano-conduits, which are of great interest in this
regard as they offer a large group velocity and a potentially chirality-based
protected transport of energy, have not yet been investigated due to their
complex internal magnetic field distribution. Here, we present a study of
propagating spin waves in a transversely magnetized nanoscopic yttrium iron
garnet conduit of 50 nm width. Space and time-resolved micro-focused
Brillouin-light-scattering spectroscopy is employed to measure the spin-wave
group velocity and decay length. A long-range spin-wave propagation is observed
with a decay length of up to (8.0+-1.5) {\mu}m and a large spin-wave lifetime
of up to (44.7+-9.1) ns. The results are supported with micromagnetic
simulations, revealing a single-mode dispersion relation in contrast to the
common formation of localized edge modes for microscopic systems. Furthermore,
a frequency non-reciprocity for counter-propagating spin waves is observed in
the simulations and the experiment, caused by the trapezoidal cross-section of
the structure. The revealed long-distance spin-wave propagation on the
nanoscale is particularly interesting for an application in spin-wave devices,
allowing for long-distance transport of information in magnonic circuits, as
well as novel low-energy device architectures.",2101.10192v1
2021-05-02,Steady state entanglement of distant nitrogen-vacancy centers in a coherent thermal magnon bath,"We investigate steady-state entanglement (SSE) between two nitrogen-vacancy
(NV) centers in distant nanodiamonds on an ultrathin Yttrium Iron Garnet (YIG)
strip. We determine the dephasing and dissipative interactions of the qubits
with the quanta of spin waves (magnon bath) in the YIG depending on the qubit
positions on the strip. We show that the magnon's dephasing effect can be
eliminated, and we can transform the bath into a multimode displaced thermal
state using external magnetic fields. Entanglement dynamics of the qubits in
such a displaced thermal bath have been analyzed by deriving and solving the
master equation. An additional electric field is considered to engineer the
magnon dispersion relation at the band edge to control the Markovian character
of the open system dynamics. We determine the optimum geometrical parameters of
the system of distant qubits and the YIG strip to get SSE. Furthermore,
parameter regimes for which the shared displaced magnon bath can sustain
significant SSE against the local dephasing and decoherence of NV centers to
their nuclear spin environments have been determined. Along with SSE, we
investigate the steady-state coherence (SSC) and explain the physical mechanism
of how delayed SSE appears following a rapid generation and sudden death of
entanglement using the interplay of decoherence-free subspace states, system
geometry, displacement of the thermal bath, and enhancement of the qubit
dissipation near the magnon band edge. A non-monotonic relation between bath
coherence and SSE is found, and critical coherence for maximum SSE is
determined. Our results illuminate the efficient use of system geometry, band
edge in bath spectrum, and reservoir coherence to engineer system-reservoir
interactions for robust SSE and SSC.",2105.00519v2
2021-09-09,A low-power integrated magneto-optic modulator on silicon for cryogenic applications,"A fundamental challenge of the quantum revolution is to efficiently interface
the quantum computing systems operating at cryogenic temperatures with room
temperature electronics and media for high data-rate communication. Current
approaches to control and readout of such cryogenic computing systems use
electrical cables, which prevent scalability due to their large size, heat
conduction, and limited bandwidth1. A more viable approach is to use optical
fibers which allow high-capacity transmission and thermal isolation. A key
component in implementing photonic datalinks is a cryogenic optical modulator
for converting data from the electrical to the optical domain at high speed and
with low power consumption, while operating at temperatures of 4 K or lower.
Cryogenic modulators based on the electro-optic effect have been demonstrated
in a variety of material platforms, however they are voltage driven components
while superconducting circuits are current based, resulting in a large
impedance mismatch. Here, we present the first demonstration of an integrated
current-driven modulator based on the magneto-optic effect operating over a
wide temperature range that extends down to less than 4 K. The modulator works
at data rates up to 2 Gbps with energy consumption below 4 pJ/bit, and we show
that this figure can be reduced to less than 40 fJ/bit with optimized design
and fabrication. This modulator is a hybrid device, where a current-driven
magneto-optically active crystal (cerium substituted yttrium iron garnet, or
Ce:YIG) is bonded to a high-quality silicon microring resonator. Because of its
potential for extremely low power consumption under cryogenic conditions, the
class of magneto-optical modulators demonstrated here has the potential to
enable efficient data links in large-scale systems for quantum information
processing.",2109.04538v1
2022-10-15,Non-local magnon transconductance in extended magnetic insulating films.\\Part II: two-fluid behavior,"This review presents a comprehensive study of the spatial dispersion of
propagating magnons electrically emitted in extended yttrium-iron garnet (YIG)
films by the spin transfer effects across a YIG$\vert$Pt interface. Our goal is
to provide a generic framework to describe the magnon transconductance inside
magnetic films. We experimentally elucidate the relevant spectral contributions
by studying the lateral decay of the magnon signal. While most of the injected
magnons do not reach the collector, the propagating magnons can be split into
two-fluids: \textit{i)} a large fraction of high-energy magnons carrying energy
of about $k_B T_0$, where $T_0$ is the lattice temperature, with a
characteristic decay length in the sub-micrometer range, and \textit{ii)} a
small fraction of low-energy magnons, which are particles carrying energy of
about $\hbar \omega_K$, where $\omega_K/(2 \pi)$ is the Kittel frequency, with
a characteristic decay length in the micrometer range. Taking advantage of
their different physical properties, the low-energy magnons can become the
dominant fluid \textit{i)} at large spin transfer rates for the bias causing
the emission of magnons, \textit{ii)} at large distance from the emitter,
\textit{iii)} at small film thickness, or \textit{iv)} for reduced band
mismatch between the YIG below the emitter and the bulk due to variation of the
magnon concentration. This broader picture complements part I \cite{kohno_SD},
which focuses solely on the nonlinear transport properties of low-energy
magnons.",2210.08283v2
2023-06-28,Degenerate and non-degenerate parametric excitation in YIG nanostructures,"We study experimentally the processes of parametric excitation in microscopic
magnetically saturated disks of nanometer-thick Yttrium Iron Garnet. We show
that, depending on the relative orientation between the parametric pumping
field and the static magnetization, excitation of either degenerate or
non-degenerate magnon pairs is possible. In the latter case, which is
particularly important for applications associated with the realization of
computation in the reciprocal space, a single-frequency pumping can generate
pairs of magnons whose frequencies correspond to different eigenmodes of the
disk. We show that, depending on the size of the disk and the modes involved,
the frequency difference in a pair can vary in the range 0.1-0.8 GHz. We
demonstrate that in this system, one can easily realize a practically important
situation where several magnon pairs share the same mode. We also observe the
simultaneous generation of up to six different modes using a fixed-frequency
monochromatic pumping. Our experimental findings are supported by numerical
calculations that allow us to unambiguously identify the excited modes. Our
results open new possibilities for the implementation of reciprocal-space
computing making use of low damping magnetic insulators.",2306.16094v1
2023-08-18,"Magnon Diffusion Length and Longitudinal Spin Seebeck Effect in Vanadium Tetracyanoethylene (V[TCNE]$_x$, $x \sim 2$)","Spintronic, spin caloritronic, and magnonic phenomena arise from complex
interactions between charge, spin, and structural degrees of freedom that are
challenging to model and even more difficult to predict. This situation is
compounded by the relative scarcity of magnetically-ordered materials with
relevant functionality, leaving the field strongly constrained to work with a
handful of well-studied systems that do not encompass the full phase space of
phenomenology predicted by fundamental theory. Here we present an important
advance in this coupled theory-experiment challenge, wherein we extend existing
theories of the spin Seebeck effect (SSE) to explicitly include the
temperature-dependence of magnon non-conserving processes. This expanded theory
quantitatively describes the low-temperature behavior of SSE signals previously
measured in the mainstay material yttrium iron garnet (YIG) and predicts a new
regime for magnonic and spintronic materials that have low saturation
magnetization, $M_S$, and ultra-low damping. Finally, we validate this
prediction by directly observing the spin Seebeck resistance (SSR) in the
molecule-based ferrimagnetic semiconductor vanadium tetracyanoethylene
(V[TCNE]$_x$, $x \sim 2$). These results validate the expanded theory, yielding
SSR signals comparable in magnitude to YIG and extracted magnon diffusion
length ($\lambda_m>1$ $\mu$ m) and magnon lifetime for V[TCNE]$_x$
($\tau_{th}\approx 1-10$ $\mu$ s) exceeding YIG ($\tau_{th}\sim 10$ ns).
Surprisingly, these properties persist to room temperature despite relatively
low spin wave stiffness (exchange). This identification of a new regime for
highly efficient SSE-active materials opens the door to a new class of magnetic
materials for spintronic and magnonic applications.",2308.09752v1
2023-02-07,Sputtered terbium iron garnet films with perpendicular magnetic anisotropy for spintronic applications,"We report the structural, magnetic, and interfacial spin transport properties
of epitaxial terbium iron garnet (TbIG) ultrathin films deposited by magnetron
sputtering. High crystallinity was achieved by growing the films on gadolinium
gallium garnet (GGG) substrates either at high temperature, or at room
temperature followed by thermal annealing, above 750 {\deg}C in both cases. The
films display large perpendicular magnetic anisotropy (PMA) induced by
compressive strain, and tunable structural and magnetic properties through
growth conditions or the substrate lattice parameter choice. The ferrimagnetic
compensation temperature (TM) of selected TbIG films was measured through
temperature-dependent anomalous Hall effect (AHE) in Pt/TbIG heterostructures.
In the studied films, TM was found to be between 190-225 K, i.e., approximately
25-60 K lower than the bulk value, which is attributed to the combined action
of Tb deficiency and oxygen vacancies in the garnet lattice evidenced by x-ray
photoelectron spectroscopy measurements. Sputtered TbIG ultrathin films with
large PMA and highly tunable properties reported here can provide a suitable
material platform for a wide range of spintronic experiments and device
applications.",2302.03758v1
2008-08-03,Superconductivity in Yttrium Iron Oxyarsenide System,"Iron-based oxypnictides substituted with yttrium have been prepared via a
conventional solid state reaction. The product after first 50 hours of reaction
showed diamagnetic-like transition at around 10 K but was not superconducting,
while additional 72 hours of high temperature heat treatment was required to
yield superconducting sample which was doped with fluoride. Temperature
dependence of the susceptibility shows both screening and Meissner effect at
around 10 K, while resistance as a function of temperature displayed a drop at
around the same temperature.",0808.0288v2
2008-10-05,Electric Field Driven Magnetic Domain Wall Motion in Iron Garnet Film,"The dynamic observation of domain wall motion induced by electric field in
magnetoelectric iron garnet film is reported. Measurements in 800 kV/cm
electric field pulses gave the domain wall velocity ~45 m/s. Similar velocity
was achieved in magnetic field pulse about 50 Oe. Reversible and irreversible
micromagnetic structure transformation is demonstrated. These effects are
promising for applications in spintronics and magnetic memory.",0810.0850v1
2015-05-27,Excitation of magnetic precession in bismuth iron garnet via a polarization-independent impulsive photomagnetic effect,"A polarization-independent, nonthermal optical effect on the magnetization in
bismuth iron garnet is found, in addition to the circular
polarization-dependent inverse Faraday effect and the linear
polarization-dependent photoinduced magnetic anisotropy. Its impulsive
character is demonstrated by the field dependence of the amplitude of the
resulting precession, which cannot be explained by a long-living photo or
heat-induced anisotropy.",1505.07447v1
2023-07-04,Phonon-induced magnetization dynamics in Co-doped iron garnets,"The developing field of strain-induced magnetization dynamics offers a
promising path toward efficiently controlling spins and phase transitions.
Understanding the underlying mechanisms is crucial in finding the optimal
parameters supporting the phononic switching of magnetization. Here, we present
an experimental and numerical study of time-resolved magnetization dynamics
driven by the resonant excitation of an optical phonon mode in iron garnets.
Upon pumping the latter with an infrared pulse obtained from a free-electron
laser, we observe spatially-varying magnetization precession, with its phase
depending on the direction of an external magnetic field. Our micromagnetic
simulations effectively describe the magnetization precession and switching in
terms of laser-induced changes in the crystal's magneto-elastic energy.",2307.01907v1
2022-06-30,Origin and dynamics of umbrella states in rare-earth iron garnets,"Rare-earth iron garnets $R_{3}$Fe$_{5}$O$_{12}$ are fascinating insulators
with very diverse magnetic phases. Their strong potential in spintronic devices
has encouraged a renewal of interest in the study of their low temperature spin
structures and spin wave dynamics. A striking feature of rare-earth garnets
with $R$-ions exhibiting strong crystal-field effects like Tb-, Dy-, Ho-, and
Er-ions is the observation of low-temperature non-collinear magnetic structures
featuring ""umbrella-like"" arrangements of the rare-earth magnetic moments. In
this study, we demonstrate that such umbrella magnetic states are naturally
emerging from the crystal-field anisotropies of the rare-earth ions. By means
of a general model endowed with only the necessary elements from the crystal
structure, we show how umbrella-like spin structures can take place and
calculate the canting-angle as a result of the competition between the
exchange-interaction of the rare-earth and the iron ions as well as the
crystal-field anisotropy. Our results are compared to experimental data, and a
study of the polarised spin wave dynamics is presented. Our study improves the
understanding of umbrella-like spin structures and paves the way for more
complex spin wave calculations in rare-earth iron garnets with non-collinear
magnetic phases.",2207.00017v2
2021-04-11,Ultrafast Measurements of the Interfacial Spin Seebeck Effect in Au and Rare-Earth Iron Garnet Bilayers,"We investigate picosecond spin-currents across Au/iron-garnet interfaces in
response to ultrafast laser heating of the electrons in the Au film. In the
picoseconds after optical heating, interfacial spin currents occur due to an
interfacial temperature difference between electrons in the metal and magnons
in the insulator. We report measurements of this interfacial longitudinal spin
Seebeck effect between Au and rare-earth iron-garnet insulators, i.e. RE$_3$
Fe$_5$O$_{12}$, where RE is Y, Eu, Tb, Tm. We use time domain thermoreflectance
(TDTR) measurements to characterize the thermal response of the bilayer to
ultrafast optical heating. We use time-resolved magneto-optic Kerr effect
(TR-MOKE) measurements of the Au layer to measure the time-evolution of spin
accumulation in the Au film. We observe a spin Seebeck effect between Au/TmIG
that is three times larger than for an Au/YIG bilayer. The interfacial thermal
conductance between electrons in the Au and magnons in the TmIG layer is ~ 3
$\frac{MW}{m^2 K}$.",2104.05075v2
2018-12-31,Systematic Control of Strain-Induced Perpendicular Magnetic Anisotropy in Epitaxial Europium and Terbium Iron Garnets Thin Films,"We show tunable strain-induced perpendicular magnetic anisotropy (PMA) over a
wide range of thicknesses in epitaxial ferrimagnetic insulator Eu3Fe5O12 (EuIG)
and Tb3Fe5O12 (TbIG) thin films grown by pulsed-laser deposition on Gd3Ga5O12
with (001) and (111) orientations, respectively. The PMA field is determined by
measuring the induced anomalous Hall loops in Pt deposited on the garnet films.
Due to positive magnetostriction constants, compressive in-plane strain induces
a PMA field as large as 32.9 kOe for 4 nm thick EuIG and 66.7 kOe for 5 nm
thick TbIG at 300 K, and relaxes extremely slowly as the garnet film thickness
increases. In bilayers consisting of Pt and EuIG or Pt and TbIG, robust PMA is
revealed by squared anomalous Hall hysteresis loops in Pt, the magnitude of
which appears to be only related to the net magnetic moment of iron
sublattices. Furthermore, the magnetostriction constant is found to be
2.7x10^(-5) for EuIG and 1.35x10^(-5) for TbIG, comparable with the values for
bulk crystals. Our results demonstrate a general approach of tailoring magnetic
anisotropy of rare earth iron garnets by utilizing modulated strain via
epitaxial growth.",1812.11688v1
2019-02-16,Faraday-Rotation in Iron Garnet Films Beyond Elemental Substitutions,"In previous decades significant efforts have been devoted to increasing the
magneto-optical efficiency of iron garnet materials for the miniaturization of
nonreciprocal devices such as isolators and circulators. Elemental
substitutions or proper nano-structuring to benefit from optical resonances
have been pursued. However, all these approaches still require film thicknesses
of at least several tens of microns to deliver useful device applications, and
suffer from narrow bandwidths in the case of optical resonance effects. This
Letter reports on a newly discovered enhancement of the Faraday Effect observed
experimentally in nanoscale bismuth-substituted iron garnet films. It is shown
here that this enhancement is not due to elemental substitution or
compositional variations. Nor is it due to photon trapping or resonance
effects. Comprehensive experimental and theoretical analysis of the Faraday
rotation reveals a dramatic seven-fold amplification in the magneto-optic
gyrotropy within only 2 nm of the air-surface interface, corresponding to just
a couple of atomic monolayers as a result of symmetry-breaking at the air-film
interface. This finding opens up an avenue to the application of monolayer
magnetic garnets for the control of light.",1902.06112v1
2024-04-05,Nanometer thick magneto-optical iron garnet films,"Here we demonstrate nanometer thick iron garnet films suitable for the
magneto-optical applica-tions. Bismuth-substituted iron garnet films of
compositions Bi{_1}Y{_2}Fe{_5}O{_{12}} and Bi{_1}Tm{_2}Fe{_5}O{_{12}} deposited
on gadolinium gallium garnet substrate are fabricated and characterized. Their
thicknesses range from 2 to 10 nm, which corresponds to just a few crystal
lattice constants. Faraday rotation of the nanofilms reaches 29.7 deg/{\mu}m at
420 nm which is comparable and even a bit better than single crystal micrometer
thick films of similar composition. The film surface morphology by atomic force
microscopy gives root mean square (RMS) roughness of the nanofilms as small as
0.13 nm that is also similar to the RMS of single crystal micrometer thick
films. The Bi{_1}Tm{_2}Fe{_5}O{_{12}} films demonstrate effective uniaxial
anisotropy. These all make the fabricated nanofilms very promising for their
po-tential applications in magneto-optical devices and quantum technologies.",2404.04206v1
2004-10-14,YAG:Nd crystals as possible detector to search for double beta and alpha decay of neodymium,"Energy resolution, alpha/beta ratio, pulse-shape discrimination for gamma
rays and alpha particles, radioactive contamination were studied with neodymium
doped yttrium-aluminum garnet (YAG:Nd). Applicability of YAG:Nd scintillators
to search for double beta decay and alpha activity of natural neodymium
isotopes are discussed.",0410021v1
2008-04-16,On the solubility of Nd3+ in Y3Al5O12,"Neodymium doped yttrium aluminum garnet powders (Nd:YAG or
(Y{1-x}Nd{x})3Al5O12, x=0.15, 0.25, or 0.30, respectively) were prepared by a
sol-gel technique. By DTA measurements up to 2000 deg C eutectic and liquidus
temperatures could be determined. Exothermal peaks in the second and subsequent
DTA heating runs indicate that the crystallized DTA samples are not in
equilibrium. The section Y3Al5O12-Nd3Al5O12 of the concentration triangle
Al2O3-Nd2O3-Y2O3 is proposed on the basis of thermodynamic calculations that
allows to explain the experimental results by the balance of metastable phase
states in the previously crystallized DTA samples.",0804.2545v1
2009-11-17,Light storage protocols in Tm:YAG,"We present two quantum memory protocols for solids: A stopped light approach
based on spectral hole burning and the storage in an atomic frequency comb.
These procedures are well adapted to the rare-earth ion doped crystals. We
carefully clarify the critical steps of both. On one side, we show that the
slowing-down due to hole-burning is sufficient to produce a complete mapping of
field into the atomic system. On the other side, we explain the storage and
retrieval mechanism of the Atomic Frequency Comb protocol. This two important
stages are implemented experimentally in Tm$^{3+}$- doped
yttrium-aluminum-garnet crystal.",0911.3328v1
2017-10-04,Super-resolution microscopy of single rare-earth emitters,"We demonstrate super-resolution imaging of single rare-earth emitting
centers, namely, trivalent cerium, in yttrium aluminum garnet (YAG) crystals by
means of stimulated emission depletion (STED) microscopy. The achieved
all-optical resolution is $\approx$ 80nm. Similar results were obtained on H3
color centers in diamond with resolution of $\approx$ 60nm. In both cases, STED
resolution is improving slower than the inverse square-root of the depletion
beam intensity. This is caused by excited state absorption (ESA) and
interaction of the emitter with non-fluorescing crystal defects in its near
surrounding.",1710.01680v1
2022-10-10,Quadratic Zeeman Spectral Diffusion of Thulium Ion Population in a Yttrium Gallium Garnet Crystal,"The creation of well understood structures using spectral hole burning is an
important task in the use of technologies based on rare earth ion doped
crystals. We apply a series of different techniques to model and improve the
frequency dependent population change in the atomic level structure of Thulium
Yttrium Gallium Garnet (Tm:YGG). In particular we demonstrate that at zero
applied magnetic field, numerical solutions to frequency dependent three-level
rate equations show good agreement with spectral hole burning results. This
allows predicting spectral structures given a specific hole burning sequence,
the underpinning spectroscopic material properties, and the relevant laser
parameters. This enables us to largely eliminate power dependent hole
broadening through the use of adiabatic hole-burning pulses. Though this system
of rate equations shows good agreement at zero field, the addition of a
magnetic field results in unexpected spectral diffusion proportional to the
induced Tm ion magnetic dipole moment and average magnetic field strength,
which, through the quadratic Zeeman effect, dominates the optical spectrum over
long time scales. Our results allow optimization of the preparation process for
spectral structures in a large variety of rare earth ion doped materials for
quantum memories and other applications.",2210.05005v1
2023-01-12,Energetics of point defects in yttrium aluminum garnet doped with Mg and Si,"An influence of Mg and Si dopants on the formation energies and the
concentration of point defects in yttrium aluminum garnet (YAG) is studied
using the density functional approach. The formation energies of Mg and Si
substitutional and interstitial defects, native point defects and defect
complexes versus the oxygen chemical potential are obtained. It is shown that
in YAG doped with Mg, negatively charged Mg substitutional defects are
compensated by free carriers (holes) and positively charged oxygen vacancies,
whereas interstitial Mg ions play a minor role. The concentration of oxygen
vacancies increases under an increase in the concentration of Mg ions. In YAG
doped with Si, positively charged Si substitutional defects are compensated by
negatively changed isolated cation vacancies and complexes of Si ions and
cation vacancies. Under an increase in the concentration of Si ions most of Al
and Y vacancies bind in complexes with Si ions. As a result, the concentration
of isolated cation vacancies depends nonmonotonically on the concentration of
Si ions. The maximum of the concentration of isolated cation vacancies is
reached at $0.02 - 0.04$ at. % of Si, depending on sintering conditions. Mg -
Si complexes have very low formation energies. Due to formation of such
complexes, Si and Mg increases the solubility of each other in YAG. At the same
time Mg - Si complexes do not influence the concentration of anion and cation
vacancies. The overall concentration of vacancies in YAG codoped with Mg and Si
in equal atomic concentrations is low. At an excess concentration of Si or Mg
the concentration of vacancies increases by orders of magnitude.",2301.05170v2
2007-01-17,Gadolinium Iron Garnet as a Solid State Material for an Electron Electric Dipole Moment Search,"The possibility of a solid state electron electric dipole moment (EDM)
experiment based on Gadolinium Iron Garnet (GdIG) is investigated. GdIG appears
to exhibit superparamagnetism and this effect can be used to enhance the
electric-field-induced EDM signal at relatively a high temperatures, as
compared to a simple paramagnetic system such as Gadolinium Gallium Garnet. The
sensitivity of a GdIG based experiment might be large enough that an
improvement by over three orders of magnitude, compared to the existing
electron EDM limit, could be obtained at a modest temperature of 4 K, assuming
that the superparamagnetic effect is not suppressed at this temperature, and
that the spin relaxation time remains sufficiently rapid.",0701198v2
2021-11-30,First and second order magnetic anisotropy and damping of europium iron garnet under high strain,"Understanding and tailoring static and dynamic properties of magnetic
insulator thin films is important for spintronic device applications. Here, we
grow atomically flat epitaxial europium iron garnet (EuIG) thin films by pulsed
laser deposition on (111)-oriented garnet substrates with a range of lattice
parameters. By controlling the lattice mismatch between EuIG and the
substrates, we tune the strain in EuIG films from compressive to tensile
regime, which is characterized by X-ray diffraction. Using ferromagnetic
resonance, we find that in addition to the first-order perpendicular magnetic
anisotropy which depends linearly on the strain, there is a significant
second-order one that has a quadratic strain dependence. Inhomogeneous
linewidth of the ferromagnetic resonance increases notably with increasing
strain, while the Gilbert damping parameter remains nearly constant (~
2x10^-2). These results provide valuable insight into the spin dynamics in
ferrimagnetic insulators and useful guidance for material synthesis and
engineering of next-generation spintronics applications.",2111.15142v1
2023-04-21,Magnetic Structures and Spin-wave Excitations in Rare-Earth Iron Garnets near the Compensation Temperature,"We introduce a simple model for the ferrimagnetic non-collinear ``magnetic
umbrella"" states of rare-earth iron garnets (REIG), common when the rare-earth
moments have non-zero orbital angular momentum. The spin-wave excitations are
calculated within linear spin wave theory and temperature effects via
mean-field theory. This could be used to determine the magnetic polarization of
each mode and thereby the spin currents generated by thermal excitations
including the effects of mixed chirality. The spectra reproduce essential
features seen in more complete models, with hybridization between the rare
earth crystal field excitations and the propagating mode on the iron moments.
By the symmetry of the model, only one rare earth mode hybridizes, inducing a
gap at zero wave number and level repulsion at finite frequency. At the
compensation point, the hybridization gap closes and finally, as we approach
the N\'eel temperature, the hybridization gap appears to reopen. The chirality
of the lowest mode changes its sign around the frequency at which the level
repulsion occurs. This is important to estimate the spin current generation in
REIGs.",2304.10695v1
2018-09-12,Topological insulator Bi2Se3 films on rare earth iron garnets and their high-quality interfaces,"The integration of quantum materials like topological insulators (TIs) with
magnetic insulators (MIs) has important technological implications for
spintronics and quantum computing. Here we report excellent crystallinity of
c-axis oriented epitaxial TI films Bi2Se3 grown on MI films, a rare earth iron
garnet (ReIG), such as thulium iron garnet (Tm3Fe5O12, TmIG) by molecular beam
epitaxy (MBE) with a Se-buffered low-temperature (SBLT) growth technique. We
demonstrated a streaky reflection high-energy electron diffraction pattern
starting from the very first quintuple layer of Bi2Se3, indicating the
high-quality interface between TmIG and Bi2Se3, a prerequisite for studying
interfacial exchange coupling effects. The strong interfacial exchange
interaction was manifested by observations of anomalous Hall effect in the
Bi2Se3/TmIG bilayer and a shift of ferromagnetic resonance field of TmIG
induced by Bi2Se3. We have reproducibly grown high-quality Bi2Se3/ReIG and
interfaces using this new TI growth method, which may be applied to grow other
types of van der Waals (vdW) hetero-structures.",1809.04513v1
2023-10-09,Mapping of Spin-Wave Transport in Thulium Iron Garnet Thin Films Using Diamond Quantum Microscopy,"Spin waves, collective dynamic magnetic excitations, offer crucial insights
into magnetic material properties. Rare-earth iron garnets offer an ideal
spin-wave (SW) platform with long propagation length, short wavelength,
gigahertz frequency, and applicability to magnon spintronic platforms. Of
particular interest, thulium iron garnet (TmIG) has attracted a huge interest
recently due to its successful growth down to a few nanometers, observed
topological Hall effect and spin orbit torque-induced switching effects.
However, there is no direct spatial measurement of its SW properties. This work
uses diamond nitrogen vacancy (NV) magnetometry in combination with SW
electrical transmission spectroscopy to study SW transport properties in TmIG
thin films. NV magnetometry allows probing spin waves at the sub-micrometer
scale, seen by the amplification of the local microwave magnetic field due to
the coupling of NV spin qubits with the stray magnetic field produced by the
microwave-excited spin waves. By monitoring the NV spin resonances, the SW
properties in TmIG thin films are measured as function of the applied magnetic
field, including their amplitude, decay length (~ 50 um), and wavelength (0.8 -
2 um). These results pave the way for studying spin qubit-magnon interactions
in rare-earth magnetic insulators, relevant to quantum magnonics applications.",2310.06188v4
2013-05-08,Barium and Yttrium abundance in intermediate-age and old open clusters,"Barium is a neutron capture element, that, in open clusters, is frequently
over-abundant with respect to the Iron. A clear explanation for this is still
missing. Additionally, its gradient across the Galactic disk is poorly
constrained. We measure the abundance of yttrium and barium using the synthetic
spectrum method from UVES high-resolution spectra of eight distant open
clusters, namely Ruprecht 4, Ruprecht 7, Berkeley 25, Berkeley 73, Berkeley 75,
NGC 6192, NGC 6404, and NGC 6583. The barium abundance was estimated using NLTE
approximation. We confirm that Barium is indeed over-abundant in most clusters,
especially young clusters. Finally, we investigated the trend of yttrium and
barium abundances as a function of distance in the Galaxy and ages. Several
scenarios for the barium over-abundance are then discussed.",1305.1909v1
2013-10-08,Mechanism for Radiation Damage Resistance in Yttrium Oxide Dispersion Strengthened Steels,"ODS steels based on yttrium oxide have been suggested as potential fusion
reactor wall materials due to their observed radiation resistance properties.
Presumably this radiation resistance can be related to the interaction of the
particle with vacancies,self-interstitial atoms (SIAs) and other radiation
damage debris. Density functional theory has been used to investigate this at
the atomic scale. Four distinct interfaces, some based on HRTEM observations,
between iron and yttrium oxide were investigated. It is been shown that the
Y$_2$O$_3$-Fe interface acts as a strong trap with long-range attraction for
both interstitial and vacancy defects, allowing recombination without altering
the interface structure. The catalytic elimination of defects without change to
the microstructure explains the improved behaviour of ODS steels with respect
to radiation creep and swelling.",1310.2061v1
2018-05-05,Selection Rules for All-Optical Magnetic Recording in Iron Garnet,"Finding an electronic transition a subtle excitation of which can launch
dramatic changes of electric, optical or magnetic properties of media is one of
the long-standing dreams in the field of photo-induced phase transitions [1-5].
Therefore the discovery of the magnetization switching only by a femtosecond
laser pulse [6-10] triggered intense discussions about mechanisms responsible
for these laser-induced changes. Here we report the experimentally revealed
selection rules on polarization and wavelengths of ultrafast photo-magnetic
recording in Co-doped garnet film and identify the workspace of the parameters
(magnetic damping, wavelength and polarization of light) allowing this effect.
The all-optical magnetic switching under both single pulse and multiple-pulse
sequences can be achieved at room temperature, in narrow spectral ranges with
light polarized either along <110> or <100> crystallographic axes of the
garnet. The revealed selection rules indicate that the excitations responsible
for the coupling of light to spins are d-electron transitions in octahedral and
tetrahedral Co-sublattices, respectively.",1805.02021v1
2002-10-25,Anisotropic and incommensurate spin fluctuations in hcp iron and some other nearly magnetic metals,"We present an ab initio theoretical formalism for the static paramagnetic
spin susceptibility of metals at finite temperatures. Since relativistic
effects, e.g. spin-orbit coupling, are included, we can identify the anisotropy
or easy axes of the spin fluctuations. Our calculations find hcp-iron to be
unstable to in ab-plane, incommensurate anti-ferromagnetic (AFM) modes (linked
to nested Fermi surface) below T_N =69K for the lowest pressures under which it
is stable. T_N swiftly drops to zero as the pressure is increased. The
calculated susceptibility of yttrium is consistent with the helical,
incommensurate AFM order found in many rare-earth-dilute yttrium alloys.
Lastly, in line with experimental data, we find the easy axes of the
incommensurate AFM and ferromagnetic spin fluctuations of the normal state of
the triplet superconductor Sr2RuO4 to be perpendicular and parallel with the
crystal c-axis resepctively.",0210581v1
2014-01-27,Prospects for electron spin-dependent short-range force experiments with rare earth iron garnet test masses,"A study of the possible interactions between fermions assuming only
rotational invariance has revealed 15 forms for the potential involving the
fermion spins. We review the experimental constraints on unobserved
macroscopic, spin-dependent interactions between electrons in the range below 1
cm. An existing experiment, using 1 kHz mechanical oscillators as test masses,
has been used to constrain mass-coupled forces in this range. With suitable
modifications, including spin-polarized test masses, this experiment can be
used to explore all 15 possible spin-dependent interactions between electrons
in this range with unprecedented sensitivity. Samples of ferrimagnetic
dysprosium iron garnet have been fabricated in the suitable test mass geometry
and shown to have high spin density with very low intrinsic magnetism.",1401.6730v2
2016-09-15,Low-damping sub-10-nm thin films of lutetium iron garnet grown by molecular-beam epitaxy,"We analyze the structural and magnetic characteristics of (111)-oriented
lutetium iron garnet (Lu$_3$Fe$_5$O$_{12}$) films grown by molecular-beam
epitaxy, for films as thin as 2.8 nm. Thickness-dependent measurements of the
in- and out-of-plane ferromagnetic resonance allow us to quantify the effects
of two-magnon scattering, along with the surface anisotropy and the saturation
magnetization. We achieve effective damping coefficients of $11.1(9) \times
10^{-4}$ for 5.3 nm films and $32(3) \times 10^{-4}$ for 2.8 nm films, among
the lowest values reported to date for any insulating ferrimagnetic sample of
comparable thickness.",1609.04753v1
2017-06-26,Perpendicular magnetic anisotropy in insulating ferrimagnetic gadolinium iron garnet thin films,"We present experimental control of the magnetic anisotropy in a gadolinium
iron garnet (GdIG) thin film from in-plane to perpendicular anisotropy by
simply changing the sample temperature. The magnetic hysteresis loops obtained
by SQUID magnetometry measurements unambiguously reveal a change of the
magnetically easy axis from out-of-plane to in-plane depending on the sample
temperature. Additionally, we confirm these findings by the use of temperature
dependent broadband ferromagnetic resonance spectroscopy (FMR). In order to
determine the effective magnetization, we utilize the intrinsic advantage of
FMR spectroscopy which allows to determine the magnetic anisotropy independent
of the paramagnetic substrate, while magnetometry determines the combined
magnetic moment from film and substrate. This enables us to quantitatively
evaluate the anisotropy and the smooth transition from in-plane to
perpendicular magnetic anisotropy. Furthermore, we derive the temperature
dependent $g$-factor and the Gilbert damping of the GdIG thin film.",1706.08488v1
2018-02-13,Excitation of coherent optical phonons in iron garnet by femtosecond laser pulses,"We employed femtosecond pump probe technique to investigate the dynamics of
coherent optical phonons in iron garnet. A phenomenological symmetry-based
consideration reveals that oscillations of the terahertz T2g mode are excited.
Selective excitation by a linearly polarized pump and detection by a circularly
polarized probe confirm that impulsive stimulated Raman scattering (ISRS) is
the driving force for the coherent phonons. Experimental results obtained from
ISRS measurements reveal excellent agreement with spontaneous Raman
spectroscopy data, analyzed by considering the symmetry of the phonon modes and
corresponding excitation and detection selection rules.",1802.04515v3
2018-06-01,Optical determination of the exchange stiffness constant in an iron garnet,"Brillouin light scattering measurements were performed in the backscattering
geometry on a Bi-substituted rare earth iron garnet. We observed two different
peaks, one attributed to a surface spin wave in the dipole-exchange regime. The
other is referred to as a backscattering magnon mode, because the incident
light in this case is scattered backward by exchange-dominated spin wave inside
the material. We propose a method to estimate the exchange stiffness constant
from the frequency of the backscattering magnon mode. The obtained value is
comparable with the previously reported values for Y$ _3 $Fe$ _5 $O$ _{12} $.",1806.00228v2
2020-09-25,Experimental search for an exotic spin-spin-velocity-dependent interaction using an optically polarized vapor and a rare-earth iron garnet,"We report an experimental search for an exotic spin-spin-velocity-dependent
interaction between polarized electrons of Rb atoms and polarized electrons of
a solid-state mass, violating both the time-reversal and parity symmetries.
This search targets a minute effective magnetic field induced by the
interaction. A spin-exchange relaxation-free (SERF) magnetometer based on an
optically polarized Rb vapor is the key element for both a source of polarized
electrons and a high-sensitivity detector. A dysprosium iron garnet (DyIG)
serves as the polarized mass, with an extremely small magnetization at the
critical temperature around 240 K and a high spin density. To reduce the
magnetization, one of major systematic effects, a home-built cooling system
controls the mass temperature. To our knowledge, this is the first search for
an exotic spin-dependent interaction using the compensated ferrimagnet DyIG as
a polarized mass. The experiment set the most stringent limit on the
electron-electron coupling strength in the centimeter interaction range, in
particular $g_V^e g_V^e <10^{4}$ at $\lambda=2$ cm.",2009.12292v2
2021-03-03,THz Field-induced Spin Dynamics in Ferrimagnetic Iron Garnets,"THz magnetization dynamics is excited in ferrimagnetic thulium iron garnet
with a picosecond, single-cycle magnetic field pulse and seen as a
high-frequency modulation of the magneto-optical Faraday effect. Data analysis
combined with numerical modelling and evaluation of the effective Lagrangian
allow us to conclude that the dynamics corresponds to the exchange mode excited
by Zeeman interaction of the THz field with the antiferromagnetically coupled
spins. We argue that THz-pump IR-probe experiments on ferrimagnets offer a
unique tool for quantitative studies of dynamics and mechanisms to control
antiferromagnetically coupled spins.",2103.02449v1
2021-08-16,Magneto-optics of the 2D iron-garnet nanocylinder array with localized and lattice modes,"We experimentally show the enhancement of the Faraday and transverse
magneto-optical Kerr effects in the two-dimensional arrays of nanocylinders
made of bismuth-substituted iron-garnet and supporting both localized and
lattice modes. Simultaneous excitation of these modes makes it possible to
increase the Faraday rotation by 3 times and TMOKE by an order of magnitude
compared to the smooth magnetic film of the equal effective thickness. Both
magneto-optical effects are enhanced in wide spectral and angular ranges making
the nanocylinder array magnetic dielectric structures promising for
applications with short and tightly-focused laser pulses.",2108.07056v2
2023-12-27,Sublattice-selective inverse Faraday effect in ferrimagnetic rare-earth iron garnet,"We performed time-resolved pump--probe measurements using rare-earth iron
garnet \ce{Gd3/2Yb1/2BiFe5O12} as a two-sublattice ferrimagnet. We measured the
initial phases of the magnetic resonance modes below and above the
magnetization compensation temperature to clarify the sublattice selectivity of
the inverse Faraday effect in ferrimagnets. A comparison of the time evolution
of magnetization estimated using the equations of motion revealed that the
inverse Faraday effect occurring in ferrimagnetic materials has sublattice
selectivity. This is in striking contrast to antiferromagnets, in which the
inverse Faraday effect acts on each sublattice identically. The initial phase
analysis can be applied to other ferrimagnets with compensation temperatures.",2312.16553v1
2015-05-05,Band-gap and Band-edge Engineering of Multicomponent Garnet Scintillators: A First-principles Study,"Complex doping schemes in RE$_3$Al$_5$O$_{12}$ (RE=rare earth element) garnet
compounds have recently led to pronounced improvements in scintillator
performance. Specifically, by admixing lutetium and yttrium aluminate garnets
with gallium and gadolinium, the band-gap was altered in a manner that
facilitated the removal of deleterious electron trapping associated with cation
antisite defects. Here, we expand upon this initial work to systematically
investigate the effect of substitutional admixing on the energy levels of band
edges. Density functional theory was used to survey potential admixing
candidates that modify either the conduction band minimum (CBM) or valence band
maximum (VBM). We considered two sets of compositions based on
Lu$_3$B$_5$O$_{12}$ where B = Al, Ga, In, As, and Sb; and RE$_3$Al$_5$O$_{12}$,
where RE = Lu, Gd, Dy, and Er. We found that admixing with various RE cations
does not appreciably effect the band gap or band edges. In contrast,
substituting Al with cations of dissimilar ionic radii has a profound impact on
the band structure. We further show that certain dopants can be used to
selectively modify only the CBM or the VBM. Specifically, Ga and In decrease
the band gap by lowering the CBM, while As and Sb decrease the band gap by
raising the VBM. These results demonstrate a powerful approach to quickly
screen the impact of dopants on the electronic structure of scintillator
compounds, identifying those dopants which alter the band edges in very
specific ways to eliminate both electron and hole traps responsible for
performance limitations. This approach should be broadly applicable for the
optimization of electronic and optical performance for a wide range of
compounds by tuning the VBM and CBM.",1505.01218v1
2012-08-12,Experimental demonstration of a dual-frequency laser free from anti-phase noise,"A reduction of more than 20 dB of the intensity noise at the anti-phase
relaxation oscillation frequency is experimentally demonstrated in a
two-polarization dual-frequency solid-state laser without any optical or
electronic feedback loop. Such a behavior is inherently obtained by aligning
the two orthogonally polarized oscillating modes with the crystallographic axes
of a (100)-cut neodymium-doped yttrium aluminum garnet active medium. The
anti-phase noise level is shown to increase as soon as one departs from this
peculiar configuration, evidencing the predominant role of the nonlinear
coupling constant. This experimental demonstration opens new perspectives on
the design and realization of extremely low noise dual-frequency solid-state
lasers.",1208.2454v1
2013-01-22,Mapping spin coherence of a single rare-earth ion in a crystal onto a single photon polarization state,"We report on optical detection of a single photostable Ce3+ ion in an yttrium
aluminium garnet (YAG) crystal and on its magneto-optical properties at room
temperature. The quantum state of an electron spin of the emitting level of
cerium ion in YAG can be initialized by circularly polarized laser pulse.
Furthermore, its quantum state can be read out by observing temporal behaviour
of circularly polarized fluorescence of the ion. This implies direct mapping of
the spin quantum state of Ce3+ ion onto the polarization state of the emitted
photon and represents one-way quantum interface between a single spin and a
single photon.",1301.5215v1
2014-11-29,Evidence of Dilute Ferromagnetism in Rare-Earth doped YAG,"This work demonstrates strong coupling regime between an Erbium ion spin
ensemble and microwave Hybrid Cavity-Whispering Gallery Modes in a Yttrium
Aluminium Garnet dielectric crystal. Coupling strengths of $220$~MHz and mode
quality factors in excess of $10^6$ are demonstrated. Moreover, the magnetic
response of high-Q modes demonstrates behaviour which is unusual for
paramagnetic systems. This behaviour includes hysteresis and memory effects.
Such qualitative change of the system's magnetic field response is interpreted
as a phase transition of Rare Earth ion impurities. This phenomenon is similar
to the phenomenon of dilute ferromagnetism in semiconductors. The clear
temperature dependence of the phenomenon is demonstrated.",1412.0086v3
2015-05-07,All-optical preparation of coherent dark states of a single rare earth ion spin in a crystal,"All-optical addressing and control of single solid-state based qubits allows
for scalable architectures of quantum devices such as quantum networks and
quantum simulators. So far, all-optical addressing of qubits was demonstrated
only for color centers in diamond and quantum dots. Here, we demonstrate
generation of coherent dark state of a single rare earth ion in a solid, namely
a cerium ion in yttrium aluminum garnet (YAG). The dark state was formed under
the condition of coherent population trapping. Furthermore, high-resolution
spectroscopic studies of native and implanted single Ce ions have been
performed. They revealed narrow and spectrally stable optical transitions
between the spin sublevels of the ground and excited optical states, indicating
the feasibility of interfacing single photons with a single electron spin of a
cerium ion.",1505.01673v2
2017-04-12,High Precision Energy Measurements from the Analysis of Wide Spectral Features. Application to the fluorescence of YAG:Ce3+,"Advantage is taken of a complete and precise experimental study of the
luminescent properties of yttrium aluminium garnet doped with Ce, previously
accomplished by other authors, to confirm the accuracy of the invoked
theoretical methods for dealing with the realistic calculation of the
electromagnetic spectra of condensed phases. The fluorescent spectra at T=0 and
T=250 K of YAG:Ce(3+) were calculated with no adjustable parameter, giving
complete agreement with experiment. The energy released by the electronic
transitions was determined with precision better than 5\% the full width at
half maximum of the spectral features. Thermal quenching of the fluorescent
yield is discussed and calculated in a less accurate way, but anyway showing
good agreement with experiment.",1704.04120v1
2017-06-27,Optical and spin properties of a single praseodymium ion in a crystal,"The investigation of single atoms in solids, with both optical and nuclear
spin access is of particularly interest with applications ranging from
nanoscale sensing to quantum computation. Here, we study the optical and spin
properties of single praseodymium ions in an yttrium aluminum garnet (YAG)
crystal at cryogenic temperature. The single nuclear spin of single
praseodymium ions is detected through a background-free optical upconverting
readout technique. Single ions show stable photoluminescence (PLE) with
spectrally resolved hyperfine splitting of the praseodymium ground state. Based
on this measurement, optical Rabi and optically detected magnetic resonance
(ODMR) measurements are performed to study the spin coherence properties. Our
results reveal that the spin coherence time of single praseodymium nuclear
spins is limited by the strong spin-phonon coupling at experimental
temperature.",1706.08736v2
2019-04-17,Three-dimensional femtosecond laser nanolithography of crystals,"Nanostructuring hard optical crystals has so far been exclusively feasible at
their surface, as stress induced crack formation and propagation has rendered
high precision volume processes ineffective. We show that the inner chemical
etching reactivity of a crystal can be enhanced at the nanoscale by more than
five orders of magnitude by means of direct laser writing. The process allows
to produce cm-scale arbitrary three-dimensional nanostructures with 100 nm
feature sizes inside large crystals in absence of brittle fracture. To showcase
the unique potential of the technique, we fabricate photonic structures such as
sub-wavelength diffraction gratings and nanostructured optical waveguides
capable of sustaining sub-wavelength propagating modes inside yttrium aluminum
garnet crystals. This technique could enable the transfer of concepts from
nanophotonics to the fields of solid state lasers and crystal optics.",1904.08264v1
2019-10-15,"Generation of 3 mJ, 44 fs, 2.5 micrometer pulses from a single-stage Cr2+:ZnSe amplifier","Lasers capable of generating attosecond X-ray pulses in the water window (282
to 533 eV) through high-order harmonic generation are normally based on
inefficient, multi-stage optical parametric amplifiers or optical parametric
chirped pulse amplifiers pumped by femtosecond or picosecond lasers. Here we
report a very efficient single amplification stage laser based on traditional
chirped pulse amplification capable of producing 3 mJ, near-transform limited
44 fs (<6 cycles), 1 kHz pulses centered at 2.5 micrometer. The 68 GW peak
power is the highest value ever reached at this wavelength. In order to fully
compress the laser pulses our system is built in a nitrogen box. Our system
utilizes water cooled chromium doped zinc selenide (Cr2+:ZnSe) as the gain
medium and is pumped by a commercial nanosecond holmium doped
yttrium-aluminum-garnet (Ho:YAG) laser.",1910.06650v1
2020-08-13,Luminescence quenching via deep defect states: A recombination pathway via oxygen vacancies in Ce-doped YAG,"Luminescence quenching via non-radiative recombination channels limits the
efficiency of optical materials such as phosphors and scintillators and
therefore has implications for conversion efficiency and device lifetimes. In
materials such as Ce-doped yttrium aluminum garnet (YAG:Ce), quenching shows a
strong dependence on both temperature and activator concentration, limiting the
ability to fabricate high-intensity white-light emitting diodes with high
operating temperatures. Here, we reveal by means of first-principles
calculations an efficient recombination mechanism in YAG:Ce that involves
oxygen vacancies and gives rise to thermally activated concentration quenching.
We demonstrate that the key requirements for this mechanism to be active are
localized states with strong electron-phonon coupling. These conditions are
commonly found for intrinsic defects such as anion vacancies in wide band-gap
materials. The present findings are therefore relevant to a broad class of
optical materials and shine light on thermal quenching mechanisms in general.",2008.05830v2
2021-08-02,Spin Wave Computing using pre-recorded magnetization patterns,"We propose a novel type of a spin wave computing device, based on a bilayer
structure which includes a bias layer, made from a hard magnetic material and a
propagation layer, made from a magnetic material with low damping, for example,
Yttrium Garnet (YiG) or Permalloy. The bias layer maintains a stable
pre-recorded magnetization pattern, generating a bias field with a desired
spatial dependence, which in turn sets the equilibrium magnetization inside the
propagation layer. When an external source applies an RF field or spinwave to
the propagation layer, excited spin waves scatter on the magnetization's
inhomogenuities, resulting in a complex interference behavior. One thus has the
ability to adjust spin wave propagation properties simply by altering the
magnetization in the bias layer. We demonstrate that the phenomenon can be
utilized to perform a variety of computational operations, including Fourier
Transform, Vector-Matrix multiplication and Grover search algorithm, with the
operational parameters exceeding conventional designs by orders of magnitude.",2108.00909v1
2021-10-14,Ultrafast photonic rainbow with controllable orbital angular momentum,"Increasing any degree of freedom of light beam may open a wide application
area of this special light beam. Vortex beam with a dimension of orbital
angular momentum (OAM) as a useful light source has been widely applied in many
fields. Here, unique multicolor concentric ultrafast vortex beams (MUCU-VBs),
which are also named ultrafast photonic rainbow, with controllable orbital
angular momentum are firstly generated using cascaded four-wave mixing (CFWM)
in an yttrium aluminum garnet (YAG) plate. Up to 9 multicolor concentric
annular ultrafast vortex sidebands are generated simultaneously. The
topological charges of the sidebands, which are controllable by changing the
topological charges of the two input pump beams, are measured and in according
with the theoretical analysis very well. The novel MUCU-VBs can be manipulated
simultaneously in temporal, spatial, spectral domains and OAM state, which open
more than one new degree of freedoms of vortex light beam and will be of wide
and special applications, such as multicolor pump-probe experiments,
simultaneous microparticle manipulation and exploring, and optical
communication. Moreover, the special focusing properties of the multicolor
ultrafast sidebands, such as multi-focus of different wavelengths, may further
extend their application area.",2110.07228v1
2020-09-22,Magnon-mediated spin currents in Tm3Fe5O12/Pt with perpendicular magnetic anisotropy,"The control of pure spin currents carried by magnons in magnetic insulator
(MI) garnet films with a robust perpendicular magnetic anisotropy (PMA) is of
great interest to spintronic technology as they can be used to carry, transport
and process information. Garnet films with PMA present labyrinth domain
magnetic structures that enrich the magnetization dynamics, and could be
employed in more efficient wave-based logic and memory computing devices. In
MI/NM bilayers, where NM being a normal metal providing a strong spin-orbit
coupling, the PMA benefits the spin-orbit torque (SOT) driven magnetization's
switching by lowering the needed current and rendering the process faster,
crucial for developing magnetic random-access memories (SOT-MRAM). In this
work, we investigated the magnetic anisotropies in thulium iron garnet (TIG)
films with PMA via ferromagnetic resonance measurements, followed by the
excitation and detection of magnon-mediated pure spin currents in TIG/Pt driven
by microwaves and heat currents. TIG films presented a Gilbert damping constant
{\alpha}~0.01, with resonance fields above 3.5 kOe and half linewidths broader
than 60 Oe, at 300 K and 9.5 GHz. The spin-to-charge current conversion through
TIG/Pt was observed as a micro-voltage generated at the edges of the Pt film.
The obtained spin Seebeck coefficient was 0.54 {\mu}V/K, confirming also the
high interfacial spin transparency.",2009.10299v1
2023-02-01,Temperature-independent ferromagnetic resonance shift in Bi-doped YIG garnets through magnetic anisotropy tuning,"Thin garnet films are becoming central for magnon-spintronics and
spin-orbitronics devices as they show versatile magnetic properties together
with low magnetic losses. These fields would benefit from materials in which
heat does not affect the magnetization dynamics, an effect known as the
non-linear thermal frequency shift. In this study, low damping Bi substituted
Iron garnet (Bi:YIG) ultra-thin films have been grown using Pulsed Laser
Deposition. Through a fine tuning of the growth parameters, the precise control
of the perpendicular magnetic anisotropy allows to achieve a full compensation
of the dipolar magnetic anisotropy. Strikingly, once the growth conditions are
optimized, varying the growth temperature from 405 {\deg}C to 475 {\deg}C as
the only tuning parameter induces the easy-axis to go from out-of-plane to
in-plane. For films that are close to the dipolar compensation, Ferromagnetic
Resonance measurements yield an effective magnetization $\mu _{0}M_{eff} (T)$
that has almost no temperature dependence over a large temperature range (260 K
to 400 K) resulting in an anisotropy temperature exponent of 2. These findings
put Bi:YIG system among the very few materials in which the temperature
dependence of the magnetic anisotropy varies at the same rate than the
saturation magnetization. This interesting behavior is ascribed
phenomenologically to the sizable orbital moment of $Bi^{3+}$.",2302.00585v1
2017-07-15,Structural and magnetic properties of lightly doped M-type hexaferrites,"Vanadium substituted SrM hexaferrites (SrFe12-xVxO19 with x = 0.2, 0.4) and
Eu-substituted BaM hexaferrite (Ba0.8Eu0.2Fe12O19) were prepared by high energy
ball milling and sintering at 1200{\deg} C. X-ray diffraction measurements
revealed that the V-substituted SrM samples exhibited phase separation
resulting in the coexistence of the pure SrM magnetic phase with nonmagnetic
Sr3(VO4)2 vanadate and {\alpha}-Fe2O3 iron oxide phase. Also, the
Eu-substituted BaM hexaferrite revealed the formation of the pure BaM phase
coexisting with {\alpha}-Fe2O3 secondary phase, and Eu-garnet minor phase.
Although the magnetic properties of the samples deteriorated with respect to
pure hexaferrite properties, the magnetic parameters of the substituted samples
were found to be of potential importance for practical applications. Further,
the results of the study suggest methods for the preparation of high quality
SrM hexaferrites, and hexaferrite/garnet composites.",1707.04709v1
2020-03-11,Excitation and relaxation dynamics of spin-waves triggered by ultrafast photo-induced demagnetization in a ferrimagnetic insulator,"Excitation and propagation dynamics of spin waves in an iron-based garnet
film under out-of-plane magnetic field were investigated by time-resolved
magneto-optical imaging. The experimental results and the following data
analysis by phase-resolved spin-wave tomography reveal the excitation of spin
waves triggered by photo-induced demagnetization (PID) along the sample depth
direction. Moreover, the fast relaxation of PID accompanied by the spin
transfer due to spin-wave emission was observed. Possible scenarios of PID in
the garnet film are discussed. Finally, we develop a model for the spin-wave
excitation triggered by PID and explain the magnetic-field dependence in the
amplitude of the observed spin waves.",2003.05159v1
2023-10-27,Strain-Tunable Magnetic Compensation Temperature of Epitaxial Tb$_3$Fe$_5$O$_{12}$ Thin Films,"High-quality rare-earth iron garnet (ReIG) Tb$_3$Fe$_5$O$_{12}$ (TbIG) thin
films are epitaxially grown on a series of (111)-oriented garnet substrates
with various lattice constants. The coherent growth induces a
substrate-dependent in-plane tensile or compressive strain in the TbIG film.
Measurements of the anomalous Hall-like effect (AHLE) in TbIG/Pt
heterostructures show that the compensation temperature of TbIG films
monotonically changes with the film strain. The strain results in a variation
of the distances between magnetic atoms in the TbIG crystal and therefore the
corresponding exchange interactions. The latter is explicitly calculated as a
function of the lattice strain based on density functional theory, reproducing
the observed experimental results. This work provides a versatile way to
optimize ReIG-based spin-orbit torque devices.",2310.17841v1
2023-11-13,Magnetoresistive detection of perpendicular switching in a magnetic insulator,"Spintronics offers promising routes for efficient memory, logic, and
computing technologies. The central challenge in spintronics is electrically
manipulating and detecting magnetic states in devices. The electrical control
of magnetization via spin-orbit torques is effective in both conducting and
insulating magnetic layers. However, the electrical readout of magnetization in
the latter is inherently difficult, limiting its use in practical applications.
Here, we demonstrate magnetoresistive detection of perpendicular magnetization
reversal in an electrically insulating ferrimagnet, terbium iron garnet (TbIG).
To do so, we use TbIG|Cu|TbCo, where TbCo is a conducting ferrimagnet and
serves as the reference layer, and Cu is a nonmagnetic spacer. Current
injection through Cu|TbCo allows us to detect the magnetization reversal of
TbIG with a simple resistance readout during an external magnetic field sweep.
By examining the effect of measurement temperature, TbCo composition, and Cu
thickness on the sign and amplitude of the magnetoresistance, we conclude that
the spin-dependent electron scattering at the TbIG|Cu interface is the
underlying cause. Technologically-feasible magnetoresistive detection of
perpendicular switching in a ferrimagnetic garnet is a breakthrough, as it
opens broad avenues for novel insulating spintronic devices and concepts.",2311.07350v1
2004-07-23,Stability of Fe-based alloys with structure type C6Cr23,"Bulk metallic glass forms when liquid metal alloys solidify without
crystalization. In the search for Iron-based bulk glass-forming alloys of the
metal-metalloid type (Fe-B- and Fe-C-based), crystals based on the structural
prototype C6Cr23 often preempt the amorphous phase. Destabilizing this
competing crystal structure could enhance glass-formability. We carry out
first-principles total energy calculations of enthalpy of formation to identify
third elements that can effectively destabilize C6Cr23. Yttrium appears optimal
among transition metals, and rare earths also are suitable. Atomic size is the
dominant factor.",0407633v1
2007-11-10,Stability of Bose Einstein condensates of hot magnons in YIG,"We investigate the stability of the recently discovered room temperature
Bose-Einstein condensate (BEC) of magnons in Ytrrium Iron Garnet (YIG) films.
We show that magnon-magnon interactions depend strongly on the external field
orientation, and that the BEC in current experiments is actually metastable -
it only survives because of finite size effects, and because the BEC density is
very low. On the other hand a strong field applied perpendicular to the sample
plane leads to a repulsive magnon-magnon interaction; we predict that a
high-density magnon BEC can then be formed in this perpendicular field
geometry.",0711.1574v1
2010-01-03,Electrically stabilized magnetic vortex and antivortex states in magnetic dielectrics,"The micromagnetic distribution in a dielectric nanoparticle is theoretically
considered. It is shown that the existence of inhomogeneous magnetoelectric
interaction in magnetic dielectrics provides the possibility to stabilize the
vortex and antivortex state. The estimation of the critical voltage necessary
for vortex/antivortex nucleation in bismuth ferrite and iron garnet
nanoparticles yields a value of +/-150 V. This system can be considered as
electrically switchable two state-logic magnetic element.",1001.0391v4
2010-01-05,Ferroelectricity of Neel-type magnetic domain walls,"The chirality-dependent magnetoelectric properties of Neel-type domain walls
in iron garnet films is observed. The electrically driven magnetic domain wall
motion changes the direction to the opposite with the reversal of electric
polarity of the probe and with the chirality switching of the domain wall from
clockwise to counterclockwise. This proves that the origin of the electric
field induced micromagnetic structure transformation is inhomogeneous
magnetoelectric interaction.",1001.0672v1
2010-06-14,"Comment on ""Limit on the Electron Electric Dipole Moment in Gadolinium-Iron Garnet"" [arXiv:physics/0509106]","In the paper being commented on it is proposed a new method for the detection
of the electron EDM using the solid GdIG. There, it is argued that a sample
electric polarization appears when the sample is magnetized; the common belief
is that the electron EDM must be collinear with its magnetic moment. All this
is objected and it is suggested that the polarization of the sample can be
explained by the direct, Lorentz covariant, interaction between B^{a} and an
EDM d^{a}.",1006.4154v1
2011-07-13,Two-Dimensional Propagation of a Photoinduced Spin Wave Packet,"We report the two-dimensional propagation of photoinduced spin wave packets
in Bi-doped rare-earth iron garnet. Spin waves were excited nonthermally and
impulsively by a circularly polarized light pulse via the inverse Faraday
effect. Space- and time resolved spin waves were detected with a
magneto-optical pump-probe technique. We investigated propagation in two
directions, parallel and perpendicular to the magnetic field. Backward volume
magnetostatic waves (BVMSWs) were detected in both directions. The frequency of
BVMSWs depends on the propagation direction. The experimental results agreed
well with the dispersion relation of BVMSWs.",1107.2457v1
2016-06-27,Magnetic Bubble Domain Blowing with Electric Probe,"The problem of bubble domain generation is revisited from a new perspective
that was opened by recent findings in the field of physics of magnetic
skyrmions. The single bubble domain can be generated under the tip electrode
touching the surface of dielectric iron garnet film by positive step-like
voltage pulse and its equilibrium size can be increased with further rising of
electric potential. The theoretical analysis shows that the same mechanism can
be used to stabilize the submicron bubbles topologically equivalent to the
skyrmion.",1606.08316v2
2023-09-01,Electrical detection of parallel parametric amplification and attenuation in $\mathrm{Y}_3\mathrm{Fe}_5\mathrm{O}_{12}$/$\mathrm{Pt}$ bilayer disk,"We report a systematic quantitative evaluation of parametric amplification
gain of magnetization dynamics in ytirrium iron garnet
($\mathrm{Y}_3\mathrm{Fe}_5\mathrm{O}_{12}$) thin disk via a.c. spin pumping
and inverse spin Hall effect. We demonstrate its signature phase-dependence
where amplification and attenuation occur every $\frac{\pi}{2}$ phase shift of
the input signal. The results also show the pump-power dependence of the gain
that is explained well by our theoretical model. Finally, the optimal
conditions for the amplification is investigated by measuring the magnetic
field dependence, where we find the highest gain of 11.4 dB.",2309.00259v1
2008-10-15,The prospects for a new search for the electron electric dipole moment in solid Gadolinium iron garnet ceramics,"We address a number of issues regarding solid state electron electric dipole
moment (EDM) experiments, focusing on gadolinium iron garnet (abbreviated GdIG,
chemical formula Gd$_3$Fe$_5$O$_{12}$) as a possible sample material. GdIG
maintains its high magnetic susceptibility down to 4.2 K, which enhances the
EDM-induced magnetization of a sample placed in an electric field. We estimate
that lattice polarizability gives rise to an EDM enhancement factor of
approximately 20. We also calculate the effect of the demagnetizing field for
various sample geometries and permeabilities. Measurements of intrinsic GdIG
magnetization noise are presented, and the fluctuation-dissipation theorem is
used to compare our data with the measurements of the imaginary part of GdIG
permeability at 4.2 K, showing good agreement above frequencies of a few hertz.
We also observe how the demagnetizing field suppresses the noise-induced
magnetic flux, confirming our calculations. The statistical sensitivity of an
EDM search based on a solid GdIG sample is estimated to be on the same level as
the present experimental limit. Such a measurement would be valuable, given the
completely different methods and systematics involved. The most significant
systematics in such an experiment are the magnetic hysteresis and the
magneto-electric effect. Our analysis shows that it should be possible to
control these at the level of statistical sensitivity.",0810.2756v1
2016-12-22,Bismuth iron garnet Bi3Fe5O12: a room temperature magnetoelectric material,"The possibility to control the magnetic properties of a material with an
electric field at room temperature is highly desirable for modern applications.
Moreover, a coupling between magnetic and electric orders within a single
material presenting a wide range of exceptional physical properties, such as
bismuth iron garnet (BIG), may lead to great advances in the field of
spintronic applications. In particular, the combination of the magnetoelectric
(ME) coupling with the low damping of spin waves in BIG can allow the control
and manipulation of spin waves by an electric field in magnonic devices. Here
we report the unambiguous observation of linear magnetoelectric coupling above
300 K in BIG using ferromagnetic resonance technique with electric field
modulation. The measured coupling value is comparable with that observed for
prototypal magnetoelectric Cr2O3. On the basis of our experimental results, the
strength of this linear ME coupling is directly linked to the presence of
bismuth ions inducing strong spin orbit coupling and to the appearance of local
magnetic inhomogeneities related to the magnetic domain structure. The
unprecedented combination of magnetic, optical and magnetoelectrical properties
in BIG is expected to trigger significant interest for technological
applications as well as for theoretical studies.",1612.07531v3
2019-12-22,First-principles study of magnon-phonon interactions in gadolinium iron garnet,"We obtained the spin-wave spectrum based on a first-principles method of
exchange constants, calculated the phonon spectrum by the first-principles
phonon calculation method, and extracted the broadening of the magnon spectrum,
$\Delta \omega$, induced by magnon-phonon interactions in gadolinium iron
garnet (GdIG). Using the obtained exchange constants, we reproduce the
experimental Curie temperature and the compensation temperature from spin
models using Metropolis Monte Carlo (MC) simulations. In the lower-frequency
regime, the fitted positions of the magnon-phonon dispersion crossing points
are consistent with the inelastic neutron scattering experiment. We found that
the $\Delta \omega$ and magnon wave vector $k$ have a similar relationship in
YIG. The broadening of the acoustic spin-wave branch is proportional to
$k^{2}$, while that of the YIG-like acoustic branch and the optical branch are
a constant. At a specific $k$, the magnon-phonon thermalization time of
$\tau_{mp}$ are approximately $10^{-9}$~s, $10^{-13}$~s, and $10^{-14}$~s for
acoustic branch, YIG-like acoustic branch, and optical branch, respectively.
This research provides specific and effective information for developing a
clear understanding of the spin-wave mediated spin Seebeck effect and
complements the lack of lattice dynamics calculations of GdIG.",1912.10432v1
2020-02-25,Strain-Tuned Magnetic Anisotropy in Sputtered Thulium Iron Garnet Ultrathin Films and TIG/Au/TIG Valve Structures,"Defining the magnetic anisotropy for in-plane or out-of-plane easy axis in
ferrimagnetic insulators films by controlling the strain, while maintaining
high-quality surfaces, is desirable for spintronic and magnonic applications.
We investigate ways to tune the anisotropy of amorphous sputtered ultrathin
thulium iron garnet (TIG) films, and thus tailor their magnetic properties by
the thickness (7.5 to 60 nm), substrate choice (GGG and SGGG), and
crystallization process. We correlate morphological and structural properties
with the magnetic anisotropy of post-growth annealed films. 30 nm thick films
annealed at 600 {\deg}C show compressive strain favoring an in-plane magnetic
anisotropy (IPMA), whereas films annealed above 800 {\deg}C are under a tensile
strain leading to a perpendicular magnetic anisotropy (PMA). Air-annealed films
present a high degree of crystallinity and magnetization saturation close to
the bulk value. These results lead to successful fabrication of trilayers
TIG/Au/TIG, with coupling between the TIG layers depending on Au thickness.
These results will facilitate the use of TIG to create various in situ clean
hybrid structures for fundamental interface exchange studies, and towards the
development of complex devices. Moreover, the sputtering technique is
advantageous as it can be easily scaled up for industrial applications.",2002.10608v2
2020-09-05,Vector magneto-optical magnetometer based on the resonant all-dielectric gratings with highly anisotropic iron-garnet films,"A sensitive vector magnetometry with high spatial resolution is important for
various practical applications, such as magnetocardiography,
magnetoencephalography, explosive materials detection and many others. We
propose a magnetometer based on the magnetic iron-garnet film possessing a very
high magnetic anisotropy, placed in the rotating external magnetic field. Each
of the measured magnetic field spatial components produces different temporal
harmonics in the out-of-plane magnetization dependence. The dielectric resonant
grating placed on the top of an ultrathin film enhanced the magneto-optical
response 10 times which makes it possible to achieve 10 times higher spatial
resolution in the perpendicular to the film direction. The reported
magneto-optical magnetometer allows one to measure simultaneously all three
spatial components of the magnetic field with high spatial resolution and
sensitivity up to 100 pT/Hz$^{1/2}$.",2010.01954v1
2021-05-10,Valley polarization of trions in monolayer MoSe$_2$ interfaced with bismuth iron garnet,"Interfacing atomically thin van der Waals semiconductors with magnetic
substrates enables additional control on their intrinsic valley degree of
freedom and provides a promising platform for the development of novel
valleytronic devices for information processing and storage. Here we study
circularly polarized photoluminescence in heterostructures of monolayer
MoSe$_2$ and thin films of ferrimagnetic bismuth iron garnet. We observe strong
emission from charged excitons with negative valley polarization, which
switches sign with increasing temperature, and demonstrate contrasting response
to left and right circularly polarized excitation, associated with finite
out-of-plane magnetization in the substrate. We propose a theoretical model
accounting for magnetization-induced imbalance of charge carriers in the two
valleys of MoSe$_2$, as well as for valley-switching scattering from B to A
excitons and fast formation of trions with extended valley relaxation times,
which shows excellent agreement with the experimental data. Our results provide
new insights into valley physics in 2D semiconductors interfaced with magnetic
substrates.",2105.04327v2
2022-01-01,Giant widening of interface magnetic layer in almost compensated iron garnet,"A two-sublattice ferrimagnet undergoes a transition from a collinear to
canted magnetic phase at magnetic field oriented along an easy magnetization
direction. In this work, we study the transition by means of the
magneto-optical Faraday effect in a thin film of compensated iron garnet
(Lu$_{3-{\rm{x}}}$Bi$_{\rm{x}}$)(Fe$_{5-{\rm{y}}-{\rm{z}}}$Ga$_{\rm{y}}$Al$_{\rm{z}}$)O$_{12}$
grown on Gd$_3$Ga$_5$O$_{12}$ substrate. In the immediate vicinity of the
compensation temperature a precursor of the transition with a complex shape was
observed. Using a special sample with variable thickness we demonstrate an
interfacial origin of the precursor. Diffusion of gadolinium from the substrate
into the film forms a thin intermixed layer with enhanced magnetization. It
induces an extended inhomogeneous magnetic structure in the film. A two-step
shape of the precursor appears due to an easy-plane anisotropy of the
intermixed magnetic layer. We emphasize that an effective width of the
inhomogeneous magnetization distribution in the film grows enormously while
approaching the compensation temperature.",2201.00134v1
2023-12-26,All solution grown epitaxial magnonic crystal of thulium iron garnet thin film,"Magnonics has shown the immense potential of compatibility with CMOS devices
and the ability to be utilized in futuristic quantum computing. Therefore, the
magnonic crystals, both metallic and insulating, are under extensive
exploration. The presence of high spin-orbit interaction induced by the
presence of rare-earth elements in thulium iron garnet (TmIG) increases its
potential in magnonic applications. Previously, TmIG thin films were grown
using ultra-high vacuum-based techniques. Here, we present a cost-effective
solution-based approach that enables the excellent quality interface and
surface roughness of the epitaxial TmIG/GGG. The deposited TmIG (12.2 nm) thin
film's physical and spin dynamic properties are investigated in detail. The
confirmation of the epitaxy using X-ray diffraction in $\phi$-scan geometry
along with the X-ray reflectivity and atomic force for the thickness and
roughness analysis and topography, respectively. The epitaxial TmIG/GGG have
confirmed the perpendicular magnetic anisotropy utilizing the
polar-magneto-optic Kerr effect. Analyzing the ferromagnetic resonance study of
TmIG/GGG thin films provides the anisotropy constant K$_U$ = 20.6$\times$10$^3$
$\pm$ 0.2$\times$10$^3$ N/m$^2$ and the Gilbert damping parameter $\alpha$ =
0.0216 $\pm$ 0.0028. The experimental findings suggest that the
solution-processed TmIG/GGG thin films have the potential to be utilized in
device applications.",2312.15973v1
2021-07-19,Measurement of the Thulium Ion Spin Hamiltonian Within a Yttrium Gallium Garnet Host Crystal,"We characterize the magnetic properties for thulium ion energy levels in the
Y$_3$Ga$_5$O$_{12}$ (Tm:YGG) lattice with the goal to improve decoherence and
reduce line-width broadening caused by local host spins and crystal
imperfections. More precisely, we measure hyperfine tensors for the lowest
level of the, $^3$H$_6$, and excited, $^3$H$_4$, states using a combination of
spectral hole burning, absorption spectroscopy, and optically detected nuclear
magnetic resonance. By rotating the sample through a series of angles with an
applied external magnetic field, we measure and analyze the orientation
dependence of the Tm$^{3+}$ ion's spin-Hamiltonian. Using this
spin-Hamiltonian, we propose a set of orientations to improve material
properties that are important for light-matter interaction and quantum
information applications. Our results yield several important external field
directions: some to extend optical coherence times, another to improve spin
inhomogeneous broadening, and yet another that maximizes mixing of the spin
states for specific sets of ions, which allows improving optical pumping and
creation of lambda systems in this material.",2107.08920v1
2023-08-12,High stability white light generation in water at multi-kilohertz repetition rate,"Efficient supercontinuum (SC) generation featuring high spectral intensity
across a large bandwidth requires high peak powers of several megawatt from
pulsed lasers. Under these conditions and at multi-kilohertz (kHz) repetition
rates, the SC generated in most materials is unstable due to thermal effects.
In this work, we leverage the superior dispersion properties of water to
maximize the spectral width of the SC, while avoiding stability issues due to
thermal loading by means of a constant laminar flow of the liquid. This flow is
controlled by a differential pressure scheme that allows to precisely adjust
the fluid velocity to an optimum value for maximum stability of the SC. This
approach is successfully implemented for repetition rates of 50 kHz and 100 kHz
and two different pump wavelengths in the visible (VIS) and near infrared (NIR)
spectral region with stability of the SC signal only limited by the driving
pulses. The resulting water SC spans more than one octave covering the VIS to
NIR range. Compared to established materials, such as yttrium aluminum garnet
(YAG) and sapphire, the spectral bandwidth is increased by 60 % and 40 %
respectively. Our scheme has the potential to be implemented with other liquids
such as bromine or carbon disulfide (CS2), which promise even wider broadening
and operation up to the mid-infrared.",2308.06636v1
2007-07-20,A canonical transformation theory from extended normal ordering,"The Canonical Transformation theory of Yanai and Chan [J. Chem. Phys. 124,
194106 (2006)] provides a rigorously size-extensive description of dynamical
correlation in multireference problems. Here we describe a new formulation of
the theory based on the extended normal ordering procedure of Mukherjee and
Kutzelnigg [J. Chem. Phys. 107, 432 (1997)].
  On studies of the water, nitrogen, and iron-oxide potential energy curves,
the Linearised Canonical Transformation Singles and Doubles theory is
competitive in accuracy with some of the best multireference methods, such as
the Multireference Averaged Coupled Pair Functional, while computational
timings (in the case of the iron-oxide molecule) are two-three orders of
magnitude faster and comparable to those of Complete Active Space Second-Order
Perturbation Theory. The results presented here are greatly improved both in
accuracy and in cost over our earlier study as the result of a new numerical
algorithm for solving the amplitude equations.",0707.3128v1
2018-10-24,Electronic landscape of the P-cluster of nitrogenase as revealed through many-electron quantum wavefunctions,"The electronic structure of the nitrogenase metal cofactors is central to
nitrogen fixation. However, the P-cluster and iron molybdenum cofactor, each
containing eight irons, have resisted detailed characterization of their
electronic properties. Through exhaustive many-electron wavefunction
simulations enabled by new theoretical methods, we report on the low-energy
electronic states of the P-cluster in three oxidation states. The energy scales
of orbital and spin excitations overlap, yielding a dense spectrum with
features we trace to the underlying atomic states and recouplings. The clusters
exist in superpositions of spin configurations with non-classical spin
correlations, complicating interpretation of magnetic spectroscopies, while the
charges are mostly localized from reorganization of the cluster and its
surroundings. Upon oxidation, the opening of the P-cluster significantly
increases the density of states, which is intriguing given its proposed role in
electron transfer. These results demonstrate that many-electron simulations
stand to provide new insights into the electronic structure of the nitrogenase
cofactors.",1810.10196v2
2019-08-16,Stimulated X-ray Raman and Absorption Spectroscopy of Iron-Sulfur Dimers,"Iron-sulfur complexes play an important role in biological processes such as
metabolic electron transport. A detailed understanding of the mechanism of long
range electron transfer requires knowledge of the electronic structure of the
complexes, which has traditionally been challenging to obtain, either by theory
or by experiment, but the situation has begun to change with advances in
quantum chemical methods and intense free electron laser light sources. We
compute the signals from stimulated X-ray Raman spectroscopy (SXRS) and
absorption spectroscopy of homovalent and mixed-valence [2Fe-2S] complexes,
using the {\it ab initio} density matrix renormalization group (DMRG)
algorithm. The simulated spectra show clear signatures of the theoretically
predicted dense low-lying excited states within the d-d manifold. Furthermore,
the difference in signal intensity between the absorption-active and
Raman-active states provides a potential mechanism to selectively excite states
by a proper tuning of the excitation pump, to access the electronic dynamics
within this manifold.",1908.05802v1
2019-08-14,"The chemical compositions of the 2 new HgMn stars HD 30085 and HD 30963. Comparison to $χ$ Lupi A, $ν$ Cap and HD 174567","We report on a detailed abundance study of the fairly bright slow rotators HD
30085 (A0 IV), HD 30963 (B9 III) and HD 174567 (A0 V), hitherto reported as
normal stars and the sharp-lined chi Lupi A (B9 IV HgMn). In the spectra of HD
30085, HD 30963, the Hg II line at 3984 A line is conspicuous and numerous
lines of silicon, manganese, chromium, titanium, iron, strontium, yttrium and
zirconium appear to be strong absorbers. A comparison of the mean spectra of HD
30085 and HD 30963 with a grid of synthetic spectra for selected unblended
lines having reliable updated atomic data reveals large overabundances of
phosphorus, titanium, chromium, manganese, strontium, yttrium, and zirconium,
barium, platinum and mercury and underabundances of helium, magnesium,
scandium, nickel. The surface abundances of chi Lupi A have been rederived on
the same effective temperature scale and using the same atomic data for
consistency and comparison for HD 30085 and HD 30963. For HD 174567, milder
deficiencies and excesses are found. The abundances of sodium, magnesium and
calcium have been corrected for NLTE effects. The effective temperatures,
surface gravities, low projected rotational velocities and the peculiar
abundance patterns of HD 30085 and HD 30963 show that these stars are 2 new
HgMn stars and should be reclassified as such. HD 174567 is most likely a new
marginally Chemically Peculiar star. A list of the identifications of lines
absorbing more than 2% in the spectrum of HD 30085 is also provided.",1908.05023v1
2008-03-12,Structural stability of Fe5Si3 and Ni2Si studied by high-pressure x-ray diffraction and ab initio total-energy calculations,"We performed high-pressure angle dispersive x-ray diffraction measurements on
Fe5Si3 and Ni2Si up to 75 GPa. Both materials were synthesized in bulk
quantities via a solid-state reaction. In the pressure range covered by the
experiments, no evidence of the occurrence of phase transitions was observed.
On top of that, Fe5Si3 was found to compress isotropically, whereas an
anisotropic compression was observed in Ni2Si. The linear incompressibility of
Ni2Si along the c-axis is similar in magnitude to the linear incompressibility
of diamond. This fact is related to the higher valence-electron charge density
of Ni2Si along the c-axis. The observed anisotropic compression of Ni2Si is
also related to the layered structure of Ni2Si where hexagonal layers of Ni2+
cations alternate with graphite-like layers formed by (NiSi)2- entities. The
experimental results are supported by ab initio total-energy calculations
carried out using density functional theory and the pseudopotential method. For
Fe5Si3, the calculations also predicted a phase transition at 283 GPa from the
hexagonal P63/mcm phase to the cubic structure adopted by Fe and Si in the
garnet Fe5Si3O12. The room-temperature equations of state for Fe5Si3 and Ni2Si
are also reported and a possible correlation between the bulk modulus of iron
silicides and the coordination number of their minority element is discussed.
Finally, we report novel descriptions of these structures, in particular of the
predicted high-pressure phase of Fe5Si3 (the cation subarray in the garnet
Fe5Si3O12), which can be derived from spinel Fe2SiO4 (Fe6Si3O12).",0803.1722v1
2015-07-27,Ultrafast laser-induced changes of the magnetic anisotropy in a low-symmetry iron garnet film,"We explore a thermal mechanism of changing the anisotropy by femtosecond
laser pulses in dielectric ferrimagnetic garnets by taking a low symmetry
(YBiPrLu)3(FeGa)5O12 film grown on the (210)-oriented Gd3Ga5O12 substrate as a
model media. We demonstrate by means of spectral magneto-optical pump-probe
technique and phenomenological analysis, that the magnetization precession in
such a film is triggered by laser-induced changes of the growth-induced
magnetic anisotropy along with the well-known ultrafast inverse Faraday effect.
The change of magnetic anisotropy is mediated by the lattice heating induced by
laser pulses of arbitrary polarization on a picosecond time scale. We show that
the orientation of the external magnetic field with respect to the
magnetization easy plane noticeably affects the precession excited via the
anisotropy change. Importantly, the relative contributions from the ultrafast
inverse Faraday effect and the change of different growth-induced anisotropy
parameters can be controlled by varying the applied magnetic field strength and
direction. As a result, the amplitude and the initial phase of the excited
magnetization precession can be gradually tuned.",1507.07437v2
2023-05-12,Multireference protonation energetics of a dimeric model of nitrogenase iron-sulfur clusters,"Characterizing the electronic structure of the iron--sulfur clusters in
nitrogenase is necessary to understand their role in the nitrogen fixation
process. One challenging task is to determine the protonation state of the
intermediates in the nitrogen fixing cycle. Here, we use a dimeric iron--sulfur
model to study relative energies of protonation at C, S or Fe. Using a
composite method based on coupled cluster and density matrix renormalization
group energetics, we converge the relative energies of four protonated
configurations with respect to basis set and correlation level. We find that
accurate relative energies require large basis sets, as well as a proper
treatment of multireference and relativistic effects. We have also tested ten
density functional approximations for these systems. Most of them give large
errors in the relative energies. The best performing functional in this system
is B3LYP, which gives mean absolute and maximum errors of only 10 and 13 kJ/mol
with respect to our correlated wavefunction estimates, respectively. Our work
provides benchmark results for the calibration of new approximate electronic
structure methods and density functionals for these problems.",2305.07227v2
2022-01-11,"Single-crystal epitaxial europium iron garnet films with strain-induced perpendicular magnetic anisotropy: structural, strain, magnetic, and spin transport properties","Single-crystal europium iron garnet (EuIG) thin films epitaxially
strain-grown on gadolinium gallium garnet (GGG)(100) substrates using off-axis
sputtering have strain-induced perpendicular magnetic anisotropy (PMA). By
varying the sputtering conditions, we have tuned the europium/iron (Eu/Fe)
composition ratios in the films to tailor the film strains. The films exhibited
an extremely smooth, particle-free surface with roughness as low as 0.1 nm as
observed using atomic force microscopy. High-resolution x-ray diffraction
analysis and reciprocal space maps showed in-plane epitaxial film growth, very
smooth film/substrate interface, excellent film crystallinity with a small full
width at half maximum of 0.012$^{\circ}$ in the rocking curve scans, and an
in-plane compressive strain without relaxation. In addition, spherical
aberration-corrected scanning transmission electron microscopy showed an
atomically abrupt interface between the EuIG film and GGG. The measured
squarish out-of-plane magnetization-field hysteresis loops by vibrating sample
magnetometry in conjunction with the measurements from angle-dependent x-ray
magnetic dichroism demonstrated the PMA in the films. We have tailored the
magnetic properties of the EuIG thin films, including saturation magnetization
ranging from 71.91 to 124.51 emu/c.c. (increase with the (Eu/Fe) ratios),
coercive field from 27 to 157.64 Oe, and the strength of PMA field ($H_\bot$)
increasing from 4.21 to 18.87 kOe with the in-plane compressive strain from
-0.774 to -1.044%. We have also investigated spin transport in Pt/EuIG bi-layer
structure and evaluated the real part of spin mixing conductance to be
$3.48\times10^{14} {\Omega}^{-1}m^{-2}$. We demonstrated the current-induced
magnetization switching with a low critical switching current density of
$3.5\times10^6 A/cm^2$, showing excellent potential for low-dissipation
spintronic devices.",2201.03843v1
2022-12-31,"Electrically Sign-Reversible Topological Hall Effect in a Top-Gated Topological Insulator (Bi,Sb)2Te3 on a Ferrimagnetic Insulator Europium Iron Garnet","Topological Hall effect (THE), an electrical transport signature of systems
with chiral spin textures like skyrmions, has been observed recently in
topological insulator (TI)-based magnetic heterostructures. However, the
intriguing interplay between the topological surface state and THE is yet to be
fully understood. In this work, we report a large THE of ~10 ohm (~4
micro-ohm*cm) at 2 K with an electrically reversible sign in a top-gated 4 nm
TI (Bi0.3Sb0.7)2Te3 (BST) grown on a ferrimagnetic insulator (FI) europium iron
garnet (EuIG). Temperature, external magnetic field angle, and top gate bias
dependences of magnetotransport properties were investigated and consistent
with a skyrmion-driven THE. Most importantly, a sign change in THE was
discovered as the Fermi level was tuned from the upper to the lower parts of
the gapped Dirac cone and vice versa. This discovery is anticipated to impact
technological applications in ultralow power skyrmion-based spintronics.",2301.00213v2
2016-06-02,First-principles calculation of the stabilities of lithium garnet compositions against hydration,"A series of density functional electronic structure calculations were carried
out to better understand the crystallographic factors governing the stability
of LinA3B2O12 lithium garnet phases against hydration. The reaction studied is
H2O + LinA3B2O12 = LiOH + HnA3B2O12. Most of the compositions are stable
against pure water; the main driving force for instability in the atmosphere is
the reaction of lithium hydroxide with CO2 to make lithium carbonate. The
calculated hydration resistance scales with the Pauling bond valence on the
oxygen atom contributed by the coordinating A and B ions. In the unexchanged
Li-garnets, this bond valence must be balanced by lithium, so there is also a
good overall correlation of hydration stability with lithium stoichiometry (n):
hydration resistance increases in the order Li8-garnet < Li7-garnet <
Li6-garnet < Li5-garnet < Li3-garnet. Only Li3A3B2O12 garnets have proton
exchange energies sufficiently positive to overcome the decomposition energy of
lithium hydroxide into lithium carbonate + water; the n=3 garnets are predicted
to be stable to hydration under atmospheric conditions, in agreement with
observations (Galven et al. Chem. Mater. 2012 24, 3335-3345). At a given
lithium ion stoichiometry, hydration resistance is greater for A, B ions having
smaller ionic radii.",1606.01807v1
2005-08-05,Large Second Harmonic Kerr rotation in GaFeO3 thin films on YSZ buffered Silicon,"Epitaxial thin films of gallium iron oxide (GaFeO3) are grown on (001)
silicon by pulsed laser deposition (PLD) using yttrium-stabilized zirconia
(YSZ) buffer layer. The crystalline template buffer layer is in-situ PLD grown
through the step of high temperature stripping of the intrinsic silicon surface
oxide. The X-ray diffraction pattern shows c-axis orientation of YSZ and b-axis
orientation of GaFeO3 on Si (100) substrate. The ferromagnetic transition
temperature (TC ~ 215 K) is in good agreement with the bulk data. The films
show a large nonlinear second harmonic Kerr rotation of ~15 degrees in the
ferromagnetic state.",0508159v1
2013-03-27,"Status report on the analysis of inelastic neutron scattering from carbon, iron, yttrium and lead at 96 MeV","This work is part of an effort to provide more experimental data for the
(n,n'x) reaction. The experiments were carried out at The Svedberg Laboratory
in Uppsala, Sweden, at the quasi-mono-energetic neutron beam of 96 MeV, before
the facility was upgraded in 2004. Using an extended data analysis of data
primarily intended for measuring elastic neutron scattering only, it was found
to be possible to extract information on the inelastic scattering from several
nuclei. In the preliminary data analysis, an iterative forward-folding
technique was applied, in which a physically reasonable trial spectrum was
folded with the response function of the detector system and the output was
compared to the experimental data. As a result, double-differential cross
sections and angular distributions of inelastic neutron scattering from 12-C,
56-Fe, 89-Y and 208-Pb could be obtained. In this paper, a status update on the
efforts to improve the description of the detector response function is given.",1303.6819v1
2023-05-11,Vortex phase dynamics in yttrium superhydride YH$_6$ at megabar pressures,"A comprehensive study of the vortex phases and vortex dynamics is presented
for a recently discovered high-temperature superconductor YH$_6$ with T$_C$
(onset) of 215 K under pressure of 200 GPa.Thermal activation energy (U$_0$) is
derived in the framework of thermally activated flux flow (TAFF) theory. The
activation energy yields a power law dependence U$_0$ $\propto$ H$^\alpha$ on
magnetic field with a possible crossover at a field around 8-10 Tesla.
Furthermore, we have depicted the vortex phase transition from vortex-glass to
vortex-liquid state according to the vortex-glass theory. Finally, vortex phase
diagram is constructed for the first time for superhydrides. Very high
estimated values of flux flow barriers U$_0$(H) = 1.5-7*10$^4$ K together with
high crossover fields makes YH$_6$ a rather outstanding superconductor as
compared to most cuprates and iron-based systems. The Ginzburg number for
YH$_6$ Gi = 3-7*10$^{-3}$ indicates that thermal fluctuations are not so strong
and cannot broaden superconducting transitions in weak magnetic fields.",2305.06546v1
2011-12-17,Experimental research of double beta decay of atomic nuclei,"Results of several double beta decay experiments, performed with the help of
low background crystal scintillators, are presented. In particular, the
half-life value of the two-neutrino double beta decay of 116-Cd has been
measured as 2.9 10^{19} yr, and the new half-life limit on the neutrinoless
double beta decay of 116-Cd has been established as >1.7 10^{23} yr at 90%,
which corresponds to a restriction on the neutrino mass <1.7 eV. New half-life
bounds on the level of 10^{17}-10^{21} yr were set for double beta processes in
64-Zn, 70-Zn, 106-Cd, 108-Cd, 114-Cd, 136-Ce, 138-Ce, 142-Ce, 160-Gd, 180-W,
and 186-W by using low-background CdWO4, GSO, and ZnWO4 crystal scintillators.
The claim of discovery of the neutrinoless double beta decay of 76-Ge [Mod.
Phys. Lett. A 16 (2001) 2409] was analyzed. The demands of the future high
sensitivity double beta decay experiments, aiming to observe the neutrinoless
double beta decay or to advance restrictions on the neutrino mass to < 0.01 eV,
were considered. Requirements for their sensitivity and discovery potential
were formulated. Two projects of double beta experiments with a sensitivity on
the level of 10^{26}-10^{27} yr (CAMEO and CARVEL projects) were discussed.
Scintillation properties and radioactive contamination of CaWO4, ZnWO4, CdWO4,
PbWO4, GSO(Ce), CeF3, yttrium-aluminum garnet doped with neodymium (YAG:Nd)
crystal scintillators were studied. Applicability of these scintillators to
search for double beta decay was discussed.",1112.4067v2
2010-05-17,"Comment on ""Prospects for a new search for the electron electric-dipole moment in solid gadolinium-iron-garnet ceramics""","In a recent paper [A. O. Sushkov, S. Eckel and S. K. Lamoreaux, Phys. Rev. A
79, 022118 (2009), arXiv:0810.2756 ] the authors measured the EDM-induced
magnetization M that is given by Eq. (1) in their paper. Such an expression for
M is a consequence of the generally accepted opinion that both dipole moments,
a MDM m and an EDM d, are proportional to the spin S. Recently [T. Ivezic,
Phys. Scr. 81, 025001 (2010)] the Uhlenbeck-Goudsmit hypothesis is generalized
in a Lorentz covariant manner using the four-dimensional (4D) geometric
quantities. From the viewpoint of such formulation there is no EDM-induced
magnetization M; in the 4D spacetime the EDM d^{a} is not proportional to
S^{a}. It is argued that the induced M can come from the direct interaction
between the applied electric field E^{a} and a MDM m^{a}.",1005.3037v1
2012-11-11,Electric polarization of magnetic textures: new horizons of micromagnetism,"A common scenario of magnetoelectric coupling in multiferroics is the
electric polarization induced by spatially modulated spin structures. It is
shown in this paper that the same mechanism works in magnetic dielectrics with
inhomogeneous magnetization distribution: the domain walls and magnetic
vortexes can be the sources of electric polarization. The electric field driven
magnetic domain wall motion is observed in iron garnet films. The electric
field induced nucleation of vortex state of magnetic nanodots is theoretically
predicted and numerically simulated. From the practical point of view the
electric field control of micromagnetic structures is promising for
applications in low-power-consumption spintronic and magnonic devices.",1211.2403v1
2014-08-21,Low-energy spectrum of iron-sulfur clusters directly from many-particle quantum mechanics,"FeS clusters are a universal biological motif. They carry out electron
transfer, redox chemistry, and even oxygen sensing, in diverse processes
including nitrogen fixation, respiration, and photosynthesis. The low-lying
electronic states are key to their remarkable reactivity, but cannot be
directly observed. Here we present the first ever quantum calculation of the
electronic levels of [2Fe-2S] and [4Fe-4S] clusters free from any model
assumptions. Our results highlight limitations of long-standing models of their
electronic structure. In particular, we demonstrate that the widely used
Heisenberg-Double-Exchange model underestimates the number of states by 1-2
orders of magnitude, which can conclusively be traced to the absence of Fe
d$\rightarrow$d excitations, thought to be important in these clusters.
Further, the electronic energy levels of even the same spin are dense on the
scale of vibrational fluctuations, and this provides a natural explanation for
the ubiquity of these clusters in nature for catalyzing reactions.",1408.5080v1
2017-01-31,Tunable magnon-photon coupling in a compensating ferrimagnet - from weak to strong coupling,"We experimentally study the magnon-photon coupling in a system consitsing of
the compensating ferrimagnet gadolinium iron garnet (GdIG) and a
three-dimensional microwave cavity. The temperature is varied in order to tune
the GdIG magnetization and to observe the transition from the weak coupling
regime to the strong coupling regime. By measuring and modelling the complex
reflection parameter of the system the effective coupling rate g eff and the
magnetization M eff of the sample are extracted. Comparing g eff with the
magnon and the cavity decay rate we conclude that the strong coupling regime is
easily accessible using GdIG. We show that the effective coupling strength
follows the predicted square root dependence on the magnetization.",1701.08969v3
2017-05-09,Unidirectional control of optically induced spin waves,"Unidirectional control of optically induced spin waves in a rare-earth iron
garnet crystal is demonstrated. We observed the interference of two spin-wave
packets with different initial phases generated by circularly polarized light
pulses. This interference results in unidirectional propagation if the
spin-wave sources are spaced apart at 1/4 of the wavelength of the spin waves
and the initial phase difference is set to pi/2. The propagating direction of
the spin wave is switched by the polarization helicity of the light pulses.
Moreover, in a numerical simulation, applying more than two spin-wave sources
with a suitable polarization and spot shape, arbitrary manipulation of the spin
wave by the phased array method was replicated.",1705.03349v1
2017-08-02,Strongly exchange-coupled and surface-state-modulated magnetization dynamics in Bi2Se3/YIG heterostructures,"We report strong interfacial exchange coupling in Bi2Se3/yttrium iron garnet
(YIG) bilayers manifested as large in-plane interfacial magnetic anisotropy
(IMA) and enhancement of damping probed by ferromagnetic resonance (FMR). The
IMA and spin mixing conductance reached a maximum when Bi2Se3 was around 6
quintuple-layer (QL) thick. The unconventional Bi2Se3 thickness dependence of
the IMA and spin mixing conductance are correlated with the evolution of
surface band structure of Bi2Se3, indicating that topological surface states
play an important role in the magnetization dynamics of YIG.
Temperature-dependent FMR of Bi2Se3/YIG revealed signatures of magnetic
proximity effect of $T_c$ as high as 180 K, and an effective field parallel to
the YIG magnetization direction at low temperature. Our study sheds light on
the effects of topological insulators on magnetization dynamics, essential for
development of TI-based spintronic devices.",1708.00593v1
2018-04-13,Significant enhancement of magneto-optical effect in one-dimensional photonic crystals with magnetized epsilon-near-zero defect,"Nonreciprocal (NOR) transmission with magneto-optical materials plays a
critical role in a broad range of applications, such as optical isolation,
all-optical signal processing, and integrated photonic circuits. The underlying
mechanism is that a static magnetic field can break the time-reversal symmetry
in the presence of magneto-optical materials. However, the typical NOR devices
usually need a large size because the weak magneto-optical activity of
materials. Here, our theoretical investigations show that the NOR transmission
can be obtained in the one-dimensional photonic crystal with a magnetized
epsilon-near-zero (ENZ) defect due to strong field localization in the ENZ
medium. The inherent weak magneto-optical activity is significantly enhanced in
ENZ medium. In our configuration, the wavelength shift of transmission peaks
along two opposite incident directions can be up to 100 times higher than that
in the case that the defect layer is a normal bismuth iron garnet. Such results
will provide a new degree to design novel magneto-optical devices with small
size, and may open novel routes to exploit advanced materials for steering the
electromagnetic waves in nano-scale structures.",1804.04805v1
2018-11-08,Sensitivity enhancement for a light axion dark matter search with magnetic material,"The sensitivity of experimental searches for axion dark matter coupled to
photons is typically proportional to the strength of the applied static
magnetic field. We demonstrate how a permeable material can be used to enhance
the magnitude of this static magnetic field, and therefore improve the
sensitivity of such searches in the low frequency lumped-circuit limit. Using
gadolinium iron garnet toroids at temperature 4.2 K results in a factor of 4
enhancement compared to an air-core toroidal design. The enhancement is limited
by magnetic saturation. Correlation of signals from three such toroids allows
efficient rejection of systematics due to electromagnetic interference. The
sensitivity of a centimeter-scale axion dark matter search based on this
approach is on the order of $g_{a\gamma\gamma}\approx10^{-9}$ GeV$^{-1}$ after
8 hours of data collection for axion masses near $10^{-10}$ eV. This approach
may substantially extend the sensitivity reach of large-volume lumped element
axion dark matter searches.",1811.03231v1
2019-03-11,Exchange-enhanced Ultrastrong Magnon-Magnon Coupling in a Compensated Ferrimagnet,"The ultrastrong coupling of (quasi-)particles has gained considerable
attention due to its application potential and richness of the underlying
physics. Coupling phenomena arising due to electromagnetic interactions are
well explored. In magnetically ordered systems, the quantum-mechanical
exchange-interaction should furthermore enable a fundamentally different
coupling mechanism. Here, we report the observation of ultrastrong intralayer
exchange-enhanced magnon-magnon coupling in a compensated ferrimagnet. We
experimentally study the spin dynamics in a gadolinium iron garnet single
crystal using broadband ferromagnetic resonance. Close to the ferrimagnetic
compensation temperature, we observe ultrastrong coupling of clockwise and
anticlockwise magnon modes. The magnon-magnon coupling strength reaches more
than 30% of the mode frequency and can be tuned by varying the direction of the
external magnetic field. We theoretically explain the observed phenomenon in
terms of an exchange-enhanced mode-coupling mediated by a weak cubic
anisotropy.",1903.04330v2
2019-05-12,Peculiarities of the Faraday effect in gold-nanodisk/iron-garnet heterostructures,"In this paper, matters considering the immersion of gold nanoparticles inside
a magnetic medium are investigated experimentally and theoretically. Three
samples with periodic arrays of Au cylinders where studied: particles on a
surface of the magnetic dielectric film, inside the magnetic film and directly
under the magnetic film. The largest LSPR mediated Faraday rotation resonance
enhancement takes place for the case of the nanoparticles submerged inside the
magnetic film. Optimal place for nanoparticles is under the magnetic medium
surface at 6 nm deep in the considered configurations. It is shown that the
most influence on the Faraday rotation enhancement is produced by the magnetic
properties of the medium between the nanoantennas. The experimental results are
in good agreement with the numerical analysis.",1905.04697v1
2020-11-12,"Experimental parameters, combined dynamics, and nonlinearity of a Magnonic-Opto-Electronic Oscillator (MOEO)","We report the construction and characterization of a comprehensive
magnonic-opto-electronic oscillator (MOEO) system based on 1550-nm photonics
and yttirum iron garnet (YIG) magnonics. The system exhibits a rich and
synergistic parameter space because of the ability to control individual
photonic, electronic, and magnonic components. Taking advantage of the spin
wave dispersion of YIG, the frequency self-generation as well as the related
nonlinear processes become sensitive to the external magnetic field. Besides
being known as a narrowband filter and a delay element, the YIG delayline
possesses spin wave modes that can be controlled to mix with the optoelectronic
modes to generate higher-order harmonic beating modes. With the high
sensitivity and external tunability, the MOEO system may find usefulness in
sensing applications in magnetism and spintronics beyond optoelectronics and
photonics.",2011.06155v1
2021-11-08,A model for coupled $4f-3d$ magnetic spectra: a neutron scattering study of the Yb$-$Fe hybridisation in Yb$_3$Fe$_5$O$_{12}$,"In this work, we explore experimentally and theoretically the spectrum of
magnetic excitations of the Fe$^{3+}$ and Yb$^{3+}$ ions in ytterbium iron
garnet (Yb$_3$Fe$_5$O$_{12}$). We present a complete description of the
crystal-field splitting of the $4f$ states of Yb$^{3+}$, including the effect
of the exchange field generated by the magnetically ordered Fe subsystem. We
also consider a further effect of the Fe-Yb exchange interaction, which is to
hybridise the Yb crystal field excitations with the Fe spin-wave modes at
positions in the Brillouin zone where the two types of excitations cross. We
present detailed measurements of these hybridised excitations, and propose a
framework which can be used in the quantitative analysis of the coupled spectra
in terms of the anisotropic $4f-3d$ exchange interaction.",2111.04707v1
2022-03-29,Simulating challenging correlated molecules and materials on the Sycamore quantum processor,"Simulating complex molecules and materials is an anticipated application of
quantum devices. With strong quantum advantage demonstrated in artificial
tasks, we examine how such advantage translates into modeling physical problems
of correlated electronic structure. We simulate static and dynamical electronic
structure on a superconducting quantum processor derived from Google's Sycamore
architecture for two representative correlated electron problems: the
nitrogenase iron-sulfur molecular clusters, and $\alpha$-ruthenium trichloride,
a proximate spin-liquid material. To do so, we simplify the electronic
structure into low-energy spin models that fit on the device. With extensive
error mitigation and assistance from classically simulated data, we achieve
quantitatively meaningful results deploying about 1/5 of the gate resources
used in artificial quantum advantage experiments on a similar architecture.
This increases to over 1/2 of the gate resources when choosing a model that
suits the hardware. Our work serves to convert artificial measures of quantum
advantage into a physically relevant setting.",2203.15291v1
2023-05-04,Effective rectification of THz electromagnetic fields in a ferrimagnetic iron garnet,"It is found that single-cycle THz electromagnetic fields efficiently excite a
GHz spin resonance mode in ferrimagnetic Tm$_3$Fe$_5$O$_{12}$, despite the near
absence of GHz spectral components in the exciting THz pulse. By analyzing how
the efficiency of excitation depends on the orientation and strength of the THz
electric field, we show that it can be explained in terms of the nonlinear THz
inverse Cotton-Mouton effect. Here, the THz electric field gets effectively
rectified and acts on the ferrimagnetic spins as a uni-polar effective magnetic
field pulse. This interpretation is confirmed by a theoretical model based on
the phenomenological analysis of the effective magnetic field, combined with
the equations of motion derived from the effective Lagrangian for a
ferrimagnet. Moreover, by using the outcome of two-dimensional THz
spectroscopy, we conjecture a quantum-mechanical interpretation of the observed
effect in terms of stimulated Raman scattering of THz photons by the
crystal-field split f-f electronic transitions of Tm$^{3+}$.",2305.02971v1
2023-05-14,An ab initio correction vector restricted active space approach to the L-edge XAS and 2p3d RIXS spectra of transition metal clusters,"We describe an ab initio approach to simulate L-edge X-ray absorption (XAS)
and 2p3d resonant inelastic X-ray scattering (RIXS) spectroscopies. We model
the strongly correlated electronic structure within a restricted active space
and employ a correction vector formulation instead of sum-over-states
expressions for the spectra, thus eliminating the need to calculate a large
number of intermediate and final electronic states. We present benchmark
simulations of the XAS and RIXS spectra of the iron complexes [FeCl4]^{-1/-2}
and [Fe(SCH3)4]^{-1/-2} and interpret the spectra by deconvolving the
correction vectors. Our approach represents a step towards simulating the X-ray
spectroscopies of larger metal cluster systems that play a pivotal role in
biology.",2305.08184v2
2023-10-03,Optical excitation of multiple standing spin modes in 3D optomagnonic nanocavities,"We report the first experimental observation of multiple standing spin modes
in 3D optomagnonic nanocavity formed by nanometer-sized iron-garnet
nanocylinder. We show that launching of standing spin modes is achieved due to
a high confinement of the optically generated effective magnetic field caused
by the localized optical resonance. Quantization and spin-wave mode
inhomogeneity is achieved in each of the three spatial dimensions. The
presented approach opens new horizons of 3D optomagnonics by combining
nanophotonic and magnonic functionalities within a single nanocavity.",2310.01974v1
2023-11-27,Coherent control of photomagnetic back-switching by double-pump laser pulses,"The control of nonthermal, all-optical magnetization switching under the
regime with an independent state of laser polarization opens up new
opportunities for ultrafast magnetic recording. Here, we investigate the
photo-magnetic back-switching capabilities of the write and erase magnetic
domain pattern using double-pump pulse excitations in an iron garnet film with
pure cubic magnetocrystalline symmetry. It is essential to note that forward
and backward magnetization switching is achievable in two distinctive
scenarios: using identical linearly polarized laser pulses and with pulses
having orthogonal polarization planes. By observing the switch of magnetization
at domains independent of the initial state, one can nonthermally toggle the
magnetization, equivalent to XOR logical operation, at frequencies reaching up
to 50 GHz.",2311.16336v2
2023-12-20,Non-equilibrium criticality at the onset of time-crystalline order in $O(N)$ models,"We explore the phase transitions at the onset of time-crystalline order in
$O(N)$ models driven out-of-equilibrium. The spontaneous breaking of time
translation symmetry and its Goldstone mode are captured by an effective
description with $O(N)\times SO(2)$ symmetry. Using the renormalization group
and the $\epsilon=4-d$ expansion in a leading two-loop analysis, we identify a
new non-equilibrium universality class. Strikingly, it controls the
long-distance physics no matter how small the microscopic breaking of
equilibrium conditions is. The $O(N=2)\times SO(2)$ symmetry group is realized
for magnon condensation in pumped yttirum iron garnet (YIG) films and in
exciton-polariton systems with a polarization degree of freedom.",2312.13372v1
2020-12-17,Identifying the origin of the non-monotonic thickness dependence of spin-orbit torques and interfacial Dzyaloshinskii-Moriya interaction in a ferrimagnetic insulator heterostructure,"Electrical manipulation of magnetism via spin-orbit torques (SOTs) promises
efficient spintronic devices. In systems comprising magnetic insulators and
heavy metals, SOTs have started to be investigated only recently, especially in
systems with interfacial Dzyaloshinskii-Moriya interaction (iDMI). Here, we
quantitatively study the SOT efficiency and iDMI in a series of gadolinium
gallium garnet (GGG) / thulium iron garnet (TmIG) / platinum (Pt)
heterostructures with varying TmIG and Pt thicknesses. We find that the
non-monotonic SOT efficiency as a function of the magnetic layer thickness is
not consistent with the 1/thickness dependence expected from a simple
interfacial SOT mechanism. Moreover, considering the insulating nature of TmIG,
our results cannot be explained by the SOT mechanism established for metallic
magnets where the transverse charge spin current can inject and dephase in the
magnetic layers. Rather we can explain this non-monotonic behavior by a model
based on the interfacial spin mixing conductance that is affected by the
thickness-dependent exchange splitting energy by determining the phase
difference of the reflected spin-up and spin-down electrons at the TmIG / Pt
interface. By studying the Pt thickness dependence, we find that the effective
DMI for GGG / TmIG / Pt does not depend on the Pt thickness, which indicates
that the GGG / TmIG interface is the source of the iDMI in this system. Our
work demonstrates that SOT and DMI can originate from two different interfaces,
which enables independent optimization of DMI and SOT for advanced chiral
spintronics with low damping magnetic insulators.",2012.09358v1
2022-08-29,Machine Learning guided high-throughput search of non-oxide garnets,"Garnets, known since the early stages of human civilization, have found
important applications in modern technologies including magnetorestriction,
spintronics, lithium batteries, etc. The overwhelming majority of
experimentally known garnets are oxides, while explorations (experimental or
theoretical) for the rest of the chemical space have been limited in scope. A
key issue is that the garnet structure has a large primitive unit cell,
requiring an enormous amount of computational resources. To perform a
comprehensive search of the complete chemical space for new garnets,we combine
recent progress in graph neural networks with high-throughput calculations. We
apply the machine learning model to identify the potential (meta-)stable garnet
systems before systematic density-functional calculations to validate the
predictions. In this way, we discover more than 600 ternary garnets with
distances to the convex hull below 100~meV/atom with a variety of physical and
chemical properties. This includes sulfide, nitride and halide garnets. For
these, we analyze the electronic structure and discuss the connection between
the value of the electronic band gap and charge balance.",2208.13742v1
2014-11-03,The symmetry and magnetoelectric effects in garnet crystals and films,"The magnetoelectricity of garnets is considered by means of a symmetry and
quantum mechanical combined analysis. It is shown, that the magnetoelectric
effect is not realized in most garnets although the necessary condition of the
crystal magnetic structure antisymmetry in them is held at low temperatures.
Nevertheless, the effect can be observed in some garnets as well as other odd
effects, namely, piezomagnetic effect, magnetic field evoked piezoelectric one,
etc. It is also discovered that magnetic fields can induce specific
antiferroelectric structures in garnet crystals and produce electric
polarization in epitaxial films. The polarization can also be caused in a bulk
crystal by an inhomogeneous magnetic field.",1411.0384v1
2019-06-02,Structural and Magnetic Properties of Er3Fe5-xAlxO12 Garnets,"Er3Fe5-xAlxO12 (0.0 < x < 0.8) garnets were prepared by ball milling and
sintering at 1300 C. Rietveld refinement of the samples revealed a garnet
structure with Ia3d symmetry. The lattice parameter, cell volume, X-ray density
and magnetization of the prepared garnets decreased with the increase of Al
content (x). The coercivity of the garnets increased with x, but remained
generally low, being below 20 Oe. Low temperature magnetic measurements versus
temperature indicated that the magnetization of x = 0.0 exhibited a
compensation temperature at -186 C, however, x = 0.8 exhibited a minimum at a
higher temperature of -134 C.",1906.00405v1
2021-11-23,Enhancement of functional properties of V$_{0.6}$Ti$_{0.4}$ alloy superconductor by the addition of yttrium,"We show here that the yttrium is immiscible and precipitates with various
sizes in the body centred cubic V$_{0.6}$Ti$_{0.4}$ alloy superconductor. The
number and size of the precipitates are found to depend on the amount of
yttrium added. Precipitates with various sizes up to 30~$\mu$m are found in the
V$_{0.6}$Ti$_{0.4}$ alloy containing 5 at.\% yttrium. The large amount of line
disorders generated by the addition of yttrium in this alloy are found to be
effective in pinning the magnetic flux lines. While the superconducting
transition temperature increases with the increasing amount of yttrium in the
V$_{0.6}$Ti$_{0.4}$ alloy, the critical current density is maximum for the
alloy containing 2 at. \% yttrium, where it is more than 7.5 times the parent
alloy in fields higher than 1~T. We found that the effectiveness of each type
of defect in pinning the flux lines is dependent on the temperature and the
applied magnetic filed.",2111.11670v1
2007-01-26,Stoichiometry of Electrostatic Complexes Determined by Light Scattering,"We report on the electrostatic complexation between oppositely charged
polymers and inorganic nanoparticles investigated by static and dynamical light
scattering. The nanoparticles put under scrutiny were citrate-coated
nanocrystals of cerium oxide (CeO2, nanoceria), of iron oxide (Fe2O3,
maghemite) and of europium-doped yttrium vanadate (Eu:YVO4) with sizes in the
10 nm range. For the polymers, we have used cationic-neutral diblock copolymers
(poly(trimethylammonium ethylacrylate)-b-poly(acrylamide), hereafter referred
to as PTEA-b-PAM) with different molecular weights. For the three colloidal
dispersions, we show that the electrostatic complexation gives rise to the
formation of stable nanoparticle clusters in the 100 nm range. The complexation
was monitored by systematic measurements of the scattering intensity versus X,
the mixing ratio between nanoparticles and polymers. For 5 nanoparticle/polymer
pairs, namely CeO2/PTEA5K-b-PAM30K, Fe2O3/PTEA5K-b-PAM30K,
Fe2O3/PTEA11K-b-PAM30K, Eu:YVO4/PTEA2K-b-PAM60K and Eu:YVO4/PTEA5K-b-PAM30K, we
found a unique behavior : the scattering intensity exhibits a sharp and
prominent peak in the intermediate X-range. To account for this behavior, we
have developed a model which assumes that regardless of X, the mixed aggregates
are formed at a fixed polymer-to-nanoparticle ratio. The agreement between the
results and the model is excellent on the 5 systems. Results at different
molecular weights suggest that the stoichiometry of the mixed aggregates is
controlled by the electrostatic interactions between the opposite charges. The
model allows to derive the molecular weight and the stoichiometry of the mixed
aggregates.",0701662v1
2011-05-11,"s-Processing in the Galactic Disk. I. Super-Solar Abundances of Y, Zr, La, Ce in Young Open Clusters","In a recent study, based on homogeneous barium abundance measurements in open
clusters, a trend of increasing [Ba/Fe] ratios for decreasing cluster age was
reported. We present here further abundance determinations, relative to four
other elements hav- ing important s-process contributions, with the aim of
investigating whether the growth found for [Ba/Fe] is or not indicative of a
general property, shared also by the other heavy elements formed by slow
neutron captures. In particular, we derived abundances for yttrium, zirconium,
lanthanum and cerium, using equivalent widths measurements and the MOOG code.
Our sample includes 19 open clusters of different ages, for which the spectra
were obtained at the ESO VLT telescope, using the UVES spectrometer. The growth
previously suggested for Ba is confirmed for all the elements analyzed in our
study. This fact implies significant changes in our views of the Galactic
chemical evolution for elements beyond iron. Our results necessarily require
that very low-mass AGB stars (M < 1.5M\odot) produce larger amounts of
s-process elements (hence acti- vate the 13 C-neutron source more effectively)
than previously expected. Their role in producing neutron-rich elements in the
Galactic disk has been so far underestimated and their evolution and
neutron-capture nucleosynthesis should now be reconsidered.",1105.2208v1
2014-02-17,Neutron-Capture Nucleosynthesis in the First Stars,"Recent studies suggest that metal-poor stars enhanced in carbon but
containing low levels of neutron-capture elements may have been among the first
to incorporate the nucleosynthesis products of the first generation of stars.
We have observed 16 stars with enhanced carbon or nitrogen using the MIKE
Spectrograph on the Magellan Telescopes at Las Campanas Observatory and the
Tull Spectrograph on the Smith Telescope at McDonald Observatory. We present
radial velocities, stellar parameters, and detailed abundance patterns for
these stars. Strontium, yttrium, zirconium, barium, europium, ytterbium, and
other heavy elements are detected. In four stars, these heavy elements appear
to have originated in some form of r-process nucleosynthesis. In one star, a
partial s-process origin is possible. The origin of the heavy elements in the
rest of the sample cannot be determined unambiguously. The presence of elements
heavier than the iron group offers further evidence that zero-metallicity
rapidly-rotating massive stars and pair instability supernovae did not
contribute substantial amounts of neutron-capture elements to the regions where
the stars in our sample formed. If the carbon- or nitrogen-enhanced metal-poor
stars with low levels of neutron-capture elements were enriched by products of
zero-metallicity supernovae only, then the presence of these heavy elements
indicates that at least one form of neutron-capture reaction operated in some
of the first stars.",1402.4144v1
2016-04-19,The Solar Twin Planet Search III. The [Y/Mg] clock: estimating stellar ages of solar-type stars,"Solar twins are stars with similar stellar (surface) parameters to the Sun
that can have a wide range of ages. This provide an opportunity to analyze the
variation of their chemical abundances with age. Nissen (2015) recently
suggested that the abundances of the s-process element Y and the
$\alpha$-element Mg could be used to estimate stellar ages. This paper aims to
determine with high precision the Y, Mg, and Fe abundances for a sample of 88
solar twins that span a broad age range ($0.3-10.0$\,Gyr) and investigate their
use for estimating ages. We obtained high-quality Magellan Inamori Kyocera
Echelle (MIKE) spectra and determined Y and Mg abundances using equivalent
widths and a line-by-line differential method within a 1D LTE framework.
Stellar parameters and iron abundances were measured in Paper I of this series
for all stars, but a few (three) required a small revision. The [Y/Mg] ratio
shows a strong correlation with age. It has a slope of -0.041$\pm$0.001 dex/Gyr
and a significance of 41 $\sigma$. This is in excellent agreement with the
relation first proposed by Nissen (2015). We found some outliers that turned
out to be binaries where mass transfer may have enhanced the yttrium abundance.
Given a precise measurement of [Y/Mg] with typical error of 0.02 dex in solar
twins, our formula can be used to determine a stellar age with $\sim$0.8 Gyr
precision in the 0 to 10 Gyr range.",1604.05733v1
2019-08-13,Heavy-metal enrichment in the intermediate He-sdOB pulsator Feige 46,"The intermediate He-enriched hot subdwarf star Feige 46 was recently reported
as the second member of the V366 Aqr (or He-sdOBV) pulsating class. Feige 46 is
very similar to the prototype of the class, LS IV$-$14116, not only in terms of
pulsational properties, but also in terms of atmospheric parameters and
kinematic properties. LS IV$-$14116 is additionally characterized by a very
peculiar chemical composition, with extreme overabundances of the trans-iron
elements Ge, Sr, Y, and Zr. In this paper, we investigate the possibility that
the similitude between both pulsators extends to their chemical composition. We
retrieved archived optical and UV spectroscopic observations of Feige 46 and
perform an abundance analysis using model atmospheres and synthetic spectra
computed with TLUSTY and SYNSPEC. In total, we derive abundances for 16
metallic elements and provide upper limits for four additional elements. From
absorption lines in the optical spectrum of the star we measure an enrichment
of more than 10 000$\times$ solar for yttrium and zirconium. As for strontium,
the UV spectrum revealed it to be equally enriched. Our results confirm that
Feige 46 is not only a member of the now growing group of ""heavy-metal""
subdwarfs, but also has an abundance pattern remarkably similar to that of LS
IV$-$14116.",1908.04587v1
2021-04-19,Magnetic coupling in Y$_3$Fe$_5$O$_{12}$/Gd$_3$Fe$_5$O$_{12}$ heterostructures,"Ferrimagnetic Y$_3$Fe$_5$O$_{12}$ (YIG) is the prototypical material for
studying magnonic properties due to its exceptionally low damping. By
substituting the yttrium with other rare earth elements that have a net
magnetic moment, we can introduce an additional spin degree of freedom. Here,
we study the magnetic coupling in epitaxial
Y$_3$Fe$_5$O$_{12}$/Gd$_3$Fe$_5$O$_{12}$ (YIG/GIG) heterostructures grown by
pulsed laser deposition. From bulk sensitive magnetometry and surface sensitive
spin Seebeck effect (SSE) and spin Hall magnetoresistance (SMR) measurements,
we determine the alignment of the heterostructure magnetization through
temperature and external magnetic field. The ferromagnetic coupling between the
Fe sublattices of YIG and GIG dominates the overall behavior of the
heterostructures. Due to the temperature dependent gadolinium moment, a
magnetic compensation point of the total bilayer system can be identified. This
compensation point shifts to lower temperatures with increasing thickness of
YIG due the parallel alignment of the iron moments. We show that we can control
the magnetic properties of the heterostructures by tuning the thickness of the
individual layers, opening up a large playground for magnonic devices based on
coupled magnetic insulators. These devices could potentially control the magnon
transport analogously to electron transport in giant magnetoresistive devices.",2104.09592v1
2024-02-09,Signatures of Nuclear Isomers in Gamma-Ray Bursts from Binary Neutron Star Mergers,"Neutron star mergers are astrophysical `gold mines,' synthesizing over half
of the elements heavier than iron through rapid neutron capture
nucleosynthesis. The observation of the binary neutron star merger GW170817,
detected both in gravitational waves and electromagnetic radiation, marked a
breakthrough. One electromagnetic component of this event, the gamma ray burst
GRB 170817A, has an unresolved aspect: the characteristics of its prompt
gamma-ray emission spectrum. In this work, we propose that gamma-ray spectra in
such GRBs may be influenced by de-excitations from isomeric transitions. Our
study begins with a review of current knowledge on GRB structure and of
r-process nucleosynthesis in neutron star collisions, focusing on the role of
nuclear isomers in these settings. We then test our hypothesis by developing
criteria to select representative isomers, based on known solar element
abundances, for modeling GRB spectral characteristics. We integrate these
criteria into an interactive web page, facilitating the construction and
analysis of relevant gamma-ray spectra from isomeric transitions. Our analysis
reveals that three isomers (zirconium, lead and yttrium) stand out for their
potential to impact the prompt GRB spectrum due to their specific properties.
This information allows us to incorporate nuclear isomer data into
astrophysical simulations and calculate isomeric abundances generated by
astrophysical r-processes in neutron star mergers and their imprint on the
detected signal.",2402.06498v1
2021-03-30,"Enormous Berry-Curvature-Driven Anomalous Hall Effect in Topological Insulator (Bi,Sb)2Te3 on Ferrimagnetic Europium Iron Garnet beyond 400 K","To realize the quantum anomalous Hall effect (QAHE) at elevated temperatures,
the approach of magnetic proximity effect (MPE) was adopted to break the
time-reversal symmetry in the topological insulator (Bi0.3Sb0.7)2Te3 (BST)
based heterostructures with a ferrimagnetic insulator europium iron garnet
(EuIG) of perpendicular magnetic anisotropy. Here we demonstrate phenomenally
large anomalous Hall resistance (RAHE) exceeding 8 {\Omega} (\r{ho}AHE of 3.2
{\mu}{\Omega}*cm) at 300 K and sustaining to 400 K in 35 BST/EuIG samples,
surpassing the past record of 0.28 {\Omega} (\r{ho}AHE of 0.14
{\mu}{\Omega}*cm) at 300 K. The remarkably large RAHE as attributed to an
atomically abrupt, Fe-rich interface between BST and EuIG. Importantly, the
gate dependence of the AHE loops shows no sign change with varying chemical
potential. This observation is supported by our first-principles calculations
via applying a gradient Zeeman field plus a contact potential on BST. Our
calculations further demonstrate that the AHE in this heterostructure is
attributed to the intrinsic Berry curvature. Furthermore, for gate-biased 4 nm
BST on EuIG, a pronounced topological Hall effect (THE) coexisting with AHE is
observed at the negative top-gate voltage up to 15 K. Interface tuning with
theoretical calculations has opened up new opportunities to realize
topologically distinct phenomena in tailored magnetic TI-based
heterostructures.",2103.16487v4
2008-01-17,Towards the theory of ferrimagnetism,"Two-sublattice ferrimagnet, with spin-$s_1$ operators $\bf{S_{1i}}$ at the
sublattice $A$ site and spin-$s_2$ operators $\bf{S_{2i}}$ at the sublattice
$B$ site, is considered. The magnon of the system, the transversal fluctuation
of the total magnetization, is a complicate mixture of the transversal
fluctuations of the sublattice $A$ and $B$ spins. As a result, the magnons'
fluctuations suppress in a different way the magnetic orders of the $A$ and $B$
sublattices and one obtains two phases. At low temperature $(0,T^*)$ the
magnetic orders of the $A$ and $B$ spins contribute to the magnetization of the
system, while at the high temperature $(T^*,T_N)$, the magnetic order of the
spins with a weaker intra-sublattice exchange is suppressed by magnon
fluctuations, and only the spins with stronger intra-sublattice exchange has
non-zero spontaneous magnetization. The $T^*$ transition is a transition
between two spin-ordered phases in contrast to the transition from spin-ordered
state to disordered state ($T_N$-transition). There is no additional symmetry
breaking, and the Goldstone boson has a ferromagnetic dispersion in both
phases. A modified spin-wave theory is developed to describe the two phases.
All known Neel's anomalous $M(T)$ curves are reproduced, in particular that
with ""compensation point"". The theoretical curves are compared with
experimental ones for sulpho-spinel $MnCr2S_{4-x}Se_{x}$ and rare earth iron
garnets.",0801.2651v1
2013-11-07,Linear Response Theory for the Density Matrix Renormalization Group: Efficient Algorithms for Strongly Correlated Excited States,"Linear response theory for the density matrix renormalization group
(DMRG-LRT) was first presented in terms of the DMRG renormalization projectors
[Dorando et al., J. Chem. Phys. 130, 184111 (2009)]. Later, with an
understanding of the manifold structure of the matrix product state (MPS)
ansatz, which lies at the basis of the DMRG algorithm, a way was found to
construct the linear response space for general choices of the MPS gauge in
terms of the tangent space vectors [Haegeman et al., Phys. Rev. Lett. 107,
070601 (2011)]. These two developments led to the formulation of the
Tamm-Dancoff and random phase approximations (TDA and RPA) for MPS. This work
describes how these LRTs may be efficiently implemented through minor
modifications of the DMRG sweep algorithm, at a computational cost which scales
the same as the ground-state DMRG algorithm. In fact, the mixed canonical MPS
form implicit to the DMRG sweep is essential for efficient implementation of
the RPA, due to the structure of the second-order tangent space. We present ab
initio DMRG-TDA results for excited states of polyenes, the water molecule, and
a [2Fe-2S] iron-sulfur cluster.",1311.1646v1
2016-07-10,"Origin of Fe3+ in Fe-containing, Al-free Mantle Silicate Perovskite","We have studied the ferrous (Fe2+) and ferric (Fe3+) iron concentrations in
Al-free Fe containing Mg-silicate perovskite (Mg-Pv) at pressure (P),
temperature (T), and oxygen fugacity (fO2) conditions related to the lower
mantle using a thermodynamic model based on ab-initio calculations. We consider
the oxidation reaction and the charge disproportionation reaction, both of
which can produce Fe3+ in Mg-Pv. The model shows qualitatively good agreement
with available experimental data on Fe3+/{\Sigma}Fe ({\Sigma}Fe = total Fe in
system), spin transitions, and equations of state. We predict that under
lower-mantle conditions Fe3+/{\Sigma}Fe determined by the charge
disproportionation is estimated to be 0.01-0.07 in Al-free Mg-Pv, suggesting
that low Al Mg-Pv in the uppermost pyrolitic mantle (where majoritic garnet
contains most of the Al) and in the harzburgitic heterogeneities throughout the
lower mantle contains very little Fe3+. We find that the volume reduction by
the spin transition of the B-site Fe3+ leads to a minimum Fe3+/{\Sigma}Fe in
Mg-Pv at mid-mantle pressures. The model shows that configurational entropy is
a key driving force to create Fe3+ and therefore Fe3+ content is highly
temperature sensitive. The temperature sensitivity may lead to a maximum
Fe3+/{\Sigma}Fe in Mg-Pv in warm regions at the core-mantle boundary region,
such as Large Low Shear Velocity Provinces (LLSVPs), potentially altering the
physical (e.g., bulk modulus) and transport (e.g., thermal and electrical
conductivities) properties of the heterogeneities.",1607.02777v1
2017-05-24,Deficiency of the Bulk Spin Hall Effect Model for Spin-Orbit Torques in Magnetic Insulator/Heavy Metal Heterostructures,"Electrical currents in a magnetic insulator/heavy metal heterostructure can
induce two simultaneous effects, namely, spin Hall magnetoresistance (SMR) on
the heavy metal side and spin-orbit torques (SOTs) on the magnetic insulator
side. Within the framework of the pure spin current model based on the bulk
spin Hall effect (SHE), the ratio of the spin Hall-induced anomalous Hall
effect (SH-AHE) to SMR should be equal to the ratio of the field-like torque
(FLT) to damping-like torque (DLT). We perform a quantitative study of SMR,
SH-AHE, and SOTs in a series of thulium iron garnet/platinum or Tm3Fe5O12/Pt
heterostructures with different Tm3Fe5O12 thicknesses, where Tm3Fe5O12 is a
ferrimagnetic insulator with perpendicular magnetic anisotropy. We find the
ratio between measured effective fields of FLT and DLT is at least 2 times
larger than the ratio of the SH-AHE to SMR. In addition, the bulk SHE model
grossly underestimates the spin torque efficiency of FLT. Our results reveal
deficiencies of the bulk SHE model and also address the importance of
interfacial effects such as the Rashba and magnetic proximity effects in
magnetic insulator/heavy metal heterostructures.",1705.08919v1
2018-02-09,TMOKE as efficient tool for the magneto-optic analysis of ultra-thin magnetic films,"Ultra-thin magnetic dielectric films are of prime importance due to their
applications for nanophotonics and spintronics. Here, we propose an efficient
method for the magneto-optical investigation of ultra-thin magnetic films which
allows one to access their state of magnetization and magneto-optical
properties. It is based on the surface-plasmon-polariton-assisted transverse
magneto-optical Kerr effect (TMOKE). In our experiments, sub-100 nm-thick
bismuth-substituted lutetium iron-garnet films covered with a plasmonic gold
grating have been analyzed. The excitation of surface plasmon-polaritons
provides resonance enhancement of TMOKE up to 0.04 and makes it easily
detectable in the experiment. For films thicker than 40 nm, the TMOKE
marginally depends on the film thickness. A further decrease in the film
thickness diminishes TMOKE since for such thicknesses the surface
plasmon-polariton field partly penetrates inside the non-magnetic substrate.
Nevertheless, the TMOKE remains measurable even for few-nm-thick films, which
makes this technique unique for the magneto-optical study of ultra-thin films.
Particularly, the proposed method reveals that the off-diagonal components of
the magnetic film permittivity tensor grow slightly with the reduction of the
film thickness.",1802.04111v1
2018-02-23,Pure spin currents in magnetically ordered insulator/normal metal heterostructures,"Pure spin currents, i.e. the transport of angular momentum without an
accompanying charge current, represent a new, promising avenue in modern
spintronics from both a fundamental and an application point of view. Such pure
spin currents can not only flow in electrical conductors via mobile charge
carriers, but also in magnetically ordered electrical insulators as a flow of
spin excitation quanta. Over the course of the last years remarkable results
have been obtained in heterostructures consisting of magnetically ordered
insulators interfaced with a normal metal, where a pure spin current flows
across the interface. This topical review article deals with the fundamental
principles, experimental findings and recent developments in the field of pure
spin currents in magnetically ordered insulators. We here put our focus onto
four different manifestations of pure spin currents in such heterostructures:
The spin pumping effect, the longitudinal spin Seebeck effect, the spin Hall
magnetoresistance and the all-electrical detection of magnon transport in
non-local device concepts. In this article, we utilize a common theoretical
framework to explain all four effects and explain important material systems
(especially rare-earth iron garnets) used in the experiments. For each effect
we introduce basic measurement techniques and detection schemes and discuss
their application in the experiment. We account for the remarkable progress
achieved in each field by reporting the recent progress in each field and by
discussing research highlights obtained in our group. Finally, we conclude the
review article with an outlook on future challenges and obstacles in the field
of pure spin currents in magnetically ordered insulator / normal metal
heterostructures.",1802.08479v1
2018-05-14,Optically Pumped Floquet States of Magnetization in Ferromagnets,"Floquet states have been subject of great research interest since
Zel'dovich's pioneering work on the quasienergy of a quantum system subject to
a temporally periodic action. Nowadays periodic modulation of the system
Hamiltonian is mostly achieved by microwaves leading to novel exciting
phenomena in condensed matter physics: Floquet topological insulators, chiral
edge states etc. On the other hand, nonthermal optical control of magnetization
at picosecond time scales is currently a highly appealing research topic for
potential applications in magnetic data storage. Here we combine these two
concepts to investigate Floquet states in the system of exchange-coupled spins
in a ferromagnet. We periodically perturb the magnetization of an iron-garnet
film by a train of circularly-polarized femtosecond laser pulses hitting the
sample at 1 GHz repetition rate and monitor the magnetization dynamics behaving
like a Floquet state. An external magnetic field allows tuning of the Floquet
states leading to a pronounced increase of the precession amplitude by one
order of magnitude at the center of the Brillouin zone, i.e. when the
precession frequency is a multiple of the laser pulse repetition rate. Floquet
states might potentially allow for parametric generation of magnetic
oscillations. The observed phenomena expand the capabilities of coherent
ultrafast optical control of magnetization and pave a way for their application
in quantum computation or data processing.",1805.05822v1
2018-08-08,Low rank representations for quantum simulation of electronic structure,"The quantum simulation of quantum chemistry is a promising application of
quantum computers. However, for N molecular orbitals, the $\mathcal{O}(N^4)$
gate complexity of performing Hamiltonian and unitary Coupled Cluster Trotter
steps makes simulation based on such primitives challenging. We substantially
reduce the gate complexity of such primitives through a two-step low-rank
factorization of the Hamiltonian and cluster operator, accompanied by
truncation of small terms. Using truncations that incur errors below chemical
accuracy, we are able to perform Trotter steps of the arbitrary basis
electronic structure Hamiltonian with $\mathcal{O}(N^3)$ gate complexity in
small simulations, which reduces to $\mathcal{O}(N^2 \log N)$ gate complexity
in the asymptotic regime, while our unitary Coupled Cluster Trotter step has
$\mathcal{O}(N^3)$ gate complexity as a function of increasing basis size for a
given molecule. In the case of the Hamiltonian Trotter step, these circuits
have $\mathcal{O}(N^2)$ depth on a linearly connected array, an improvement
over the $\mathcal{O}(N^3)$ scaling assuming no truncation. As a practical
example, we show that a chemically accurate Hamiltonian Trotter step for a 50
qubit molecular simulation can be carried out in the molecular orbital basis
with as few as 4,000 layers of parallel nearest-neighbor two-qubit gates,
consisting of fewer than 100,000 non-Clifford rotations. We also apply our
algorithm to iron-sulfur clusters relevant for elucidating the mode of action
of metalloenzymes.",1808.02625v2
2019-04-15,Topological Hall effect at above room temperature in heterostructures composed of a magnetic insulator and a heavy metal,"Non-volatile memory and computing technology rely on efficient read and write
of ultra-tiny information carriers that do not wear out. Magnetic skyrmions are
emerging as a potential carrier since they are topologically robust nanoscale
spin textures that can be manipulated with ultralow current density. To date,
most of skyrmions are reported in metallic films, which suffer from additional
Ohmic loss and thus high energy dissipation. Therefore, skyrmions in magnetic
insulators are of technological importance for low-power information processing
applications due to their low damping and the absence of Ohmic loss. Moreover,
they attract fundamental interest in studying various magnon-skyrmion
interactions11. Skyrmions have been observed in one insulating material
Cu2OSeO3 at cryogenic temperatures, where they are stabilized by bulk
Dzyaloshinskii-Moriya interaction. Here, we report the observation of magnetic
skyrmions that survive above room temperature in magnetic insulator/heavy metal
heterostructures, i.e., thulium iron garnet/platinum. The presence of these
skyrmions results from the Dzyaloshinskii-Moriya interaction at the interface
and is identified by the emergent topological Hall effect. Through tuning the
magnetic anisotropy via varying temperature, we observe skyrmions in a large
window of external magnetic field and enhanced stability of skyrmions in the
easy-plane anisotropy regime. Our results will help create a new platform for
insulating skyrmion-based room temperature low dissipation spintronic
applications.",1904.07107v1
2019-06-17,Interfacial Dzyaloshinskii-Moriya interaction and chiral magnetic textures in a ferrimagnetic insulator,"The interfacial Dzyaloshinskii-Moriya interaction (DMI) in multilayers of
heavy metal and ferromagnetic metals enables the stabilization of novel chiral
spin structures such as skyrmions. Magnetic insulators, on the other hand can
exhibit enhanced dynamics and properties such as lower magnetic damping and
therefore it is of interest to combine the properties enabled by interfacial
DMI with insulating systems. Here, we demonstrate the presence of interfacial
DMI in heterostructures that include insulating magnetic layers. We use a
bilayer of perpendicularly magnetized insulating thulium iron garnet (TmIG) and
the heavy metal platinum, and find a surprisingly strong interfacial DMI that,
combined with spin-orbit torque results, in efficient switching. The
interfacial origin is confirmed through thickness dependence measurements of
the DMI, revealing the characteristic 1/thickness dependence with one order of
magnitude longer decay length compared to metallic layers. We combine chiral
spin structures and spin-orbit torques for efficient switching and identify
skyrmions that allow us to establish the GGG/TmIG interface as the origin of
the DMI.",1906.07142v3
2019-08-18,Electron g-factor engineering for non-reciprocal spin photonics,"We study the interplay of electron and photon spin in non-reciprocal
materials. Traditionally, the primary mechanism to design non-reciprocal
photonic devices has been magnetic fields in conjunction with magnetic oxides,
such as iron garnets. In this work, we present an alternative paradigm that
allows tunability and reconfigurability of the non-reciprocity through
spintronic approaches. The proposed design uses the high-spin-orbit coupling of
a narrow-band gap semiconductor (InSb) with ferromagnetic dopants. A
combination of the intrinsic and a gate-applied electric field gives rise to a
strong external Rashba spin-orbit coupling (RSOC) in a magnetically doped InSb
film. The RSOC which is gate alterable is shown to adjust the magnetic
permeability tensor via the electron g-factor of the medium. We use electronic
band structure calculations (k$\cdot$p theory) to show the gate-adjustable RSOC
manifest itself in the non-reciprocal coefficient of photon fields via shifts
in the Kerr and Faraday rotations. In addition, we show that photon spin
properties of dipolar emitters placed in the vicinity of a non-reciprocal
electromagnetic environment is distinct from reciprocal counterparts. The
Purcell factor (F$_{p}$) of a spin-polarized emitter (right-handed circular
dipole) is significantly enhanced due to a larger g-factor while a left-handed
dipole remains essentially unaffected. Our work can lead to electron spin
controlled reconfigurable non-reciprocal photonic devices.",1908.06393v2
2020-09-25,Temperature dependence of the damping parameter in the ferrimagnet Gd$_3$Fe$_5$O$_{12}$,"The damping parameter ${\alpha}_{\text{FM}}$ in ferrimagnets defined
according to the conventional practice for ferromagnets is known to be strongly
temperature dependent and diverge at the angular momentum compensation
temperature, where the net angular momentum vanishes. However, recent
theoretical and experimental developments on ferrimagnetic metals suggest that
the damping parameter can be defined in such a way, which we denote by
${\alpha}_{\text{FiM}}$, that it is free of the diverging anomaly at the
angular momentum compensation point and is little dependent on temperature. To
further understand the temperature dependence of the damping parameter in
ferrimagnets, we analyze several data sets from literature for a ferrimagnetic
insulator, gadolinium iron garnet, by using the two different definitions of
the damping parameter. Using two methods to estimate the individual sublattice
magnetizations, which yield results consistent with each other, we found that
in all the used data sets, the damping parameter ${\alpha}_{\text{FiM}}$ does
not increase at the angular compensation temperature and shows no anomaly
whereas the conventionally defined ${\alpha}_{\text{FM}}$ is strongly dependent
on the temperature.",2009.12073v2
2021-02-13,Accumulation and control of spin waves in magnonic dielectric microresonators by a comb of ultrashort laser pulses,"Spin waves in magnetic microresonators are at the core of modern magnonics.
Here we demonstrate a new method of tunable excitation of different spin wave
modes in magnetic microdisks by using a train of laser pulses coming at a
repetition rate higher than the decay rate of spin precession. The microdisks
are etched in a transparent bismuth iron garnet film and the light pulses
influence the spins nonthermally through the inverse Faraday effect. The high
repetition rate of the laser stimulus of 10 GHz establishes an interplay
between the spin wave resonances in the frequency and momentum domains. As a
result, scanning of the focused laser spot near the disk boarder changes
interference pattern of the magnons and leads to a resonant dependence of the
spin wave amplitude on the external magnetic field. Apart from that, we
achieved a switching between volume and surface spin waves by a small variation
of the external magnetic field.",2102.07021v4
2021-07-14,Sublattice spin reversal and field induced $Fe^{3+}$ spin-canting across the magnetic compensation temperature in $Y_{1.5}Gd_{1.5}Fe_{5}O_{12}$ rare-earth iron garnet,"In the present work $Fe^{3+}$ sublattice spin reversal and $Fe^{3+}$
spin-canting across the magnetic compensation temperature ($T_{Comp}$) are
demonstrated in polycrystalline $Y_{1.5}Gd_{1.5}Fe_{5}O_{12}$ (YGdIG) by means
of in-field $^{57}Fe$ M$\ddot{o}$ssbauer spectroscopy measurements.
Corroborating in-field $^{57}Fe$ M$\ddot{o}$ssbauer measurements, both
$Fe^{3+}$ & $Gd^{3+}$ sublattice spin reversal has also been manifested with
x-ray magnetic circular dichroism (XMCD) measurement in hard x-ray region.
Moreover from in-field $^{57}Fe$ M$\ddot{o}$ssbauer measurements, estimation
and analysis of effective internal hyperfine field ($H_{eff}$), relative
intensity of absorption lines in a sextet elucidated unambiguously the
signatures of $Fe^{3+}$ spin reversal, their continuous transition and field
induced spin-canting of $Fe^{3+}$ sublattices across $T_{Comp}$. Further, Fe K-
(Gd $L_{3}$-) edge XMCD signal is observed to consist of additional spectral
features, those are identified from $Gd^{3+}$ ($Fe^{3+}$) magnetic ordering,
enabling us the extraction of both the sublattices ($Fe^{3+}$ & $Gd^{3+}$)
information from a single edge analysis. The evolution of the magnetic moments
as a function of temperature for both magnetic sublattices extracted either at
the Fe K- or Gd $L_3$-edge agree quite well with values that are extracted from
bulk magnetization data of YGdIG and YIG ($Y_{3}Fe_{5}O_{12}$). These
measurements pave new avenues to investigate how the magnetic behavior of such
complex system acts across the compensation point.",2107.06508v3
2022-11-30,Unconventional spin dynamics in the non-collinear phase of a ferrimagnet,"Ferrimagnets containing several partially compensated magnetic sublattices
are considered the most promising materials for all-optical data storage and
for ultrafast communications based on spin waves. There are two magnetic phases
of the ferrimagnets: collinear and non-collinear ones. Up to now spin dynamics
in ferrimagnets has been studied mostly in the collinear state without paying
much attention to the kind of the magnetic phase. Here we investigate laser
induced ultrafast spin dynamics in a rare-earth iron garnet film in the
noncollinear phase as well. We identify a crucial influence of the magnetic
phase on the excited spin modes which allowed us to discover several prominent
effects previously overlooked. In particular, the non-collinearity makes the
quasi-antiferromagnetic mode sensitive to the external magnetic field and
brings its frequency close to the frequency of the quasiferromagnetic mode. The
latter maximizes near the magnetization compensation point and vanishes towards
the collinear phase. Spectacularly, at the phase transition the
quasiferromagnetic mode becomes soft and its amplitude significantly increases
reaching 7{\deg}. This opens new opportunities for the ultrafast control of
spins in ferrimagnets for nonthermal data storage and data processing.",2212.00085v2
2023-01-27,Field-free switching of perpendicular magnetization in an ultrathin epitaxial magnetic insulator,"For energy efficient and fast magnetic memories, switching of perpendicular
magnetization by the spin-orbit torque (SOT) appears as a very promising
solution, even more using magnetic insulators that suppress electrical
shunting. This SOT switching generally requires the assistance of an in-plane
magnetic field to break the symmetry. Here, we present experiments
demonstrating the field-free SOT switching of perpendicularly magnetized layers
of the thulium iron garnet (Tm_{3}Fe_{5}O_{12}) magnetic insulator. The
polarity of the switching loops, clockwise (CW) or counter-clockwise (CCW), is
determined by the direction of the initial current pulses, in contrast with
field-assisted switchings in which this polarity is controlled by the direction
of the field. After an independent determination of Dzyaloshinskii-Moriya
interaction (DMI), we relate the field free switching to the interplay of SOT
and DMI and the polarity of the loops to the imprint of a N\'eel domain wall
induced by the first pulse, in agreement with Kerr imaging. Our observation and
interpretation of field-free electrical switching of a magnetic insulator is an
important milestone for future low power spintronic devices.",2301.11469v1
2023-11-16,Ultrafast all-optical toggle writing of magnetic bits without relying on heat,"While in accordance with Curie's principle, one would intuitively expect that
symmetry of the cause has to be found in the symmetry of the effect, ultrafast
excitation of matter is able to violate this principle. For instance, it is
believed that heating alone, obviously not having the symmetry of a magnetic
field, cannot result in a deterministic reversal of magnetization. However, if
the heating is induced by a femtosecond laser pulse and thus ultrafast, it does
facilitate toggle switching of magnetization between stable bit-states without
any magnetic field at all. Here we show that the regime of ultrafast toggle
switching can be also realized via a mechanism without relying on any heat. The
obvious mismatch between symmetries of the cause and the response can thus be
seen as a violation of Curie's principle. In particular, ultrafast laser
excitation of iron-garnet with linearly polarized light modifies magnetic
anisotropy and thus causes toggling magnetization between two stable bit
states. In contrast to the laser-heat-induced magnetization reversal, this new
regime of 'cold' toggle switching can be observed in ferrimagnets without the
compensation point and in an exceptionally broad temperature range. The control
of magnetic anisotropy required for the toggle switching is accompanied by
lower dissipations, than in the mechanism of laser-induced-heating, but the
dissipations and the switching-time are shown to be competing parameters.",2311.10173v2
2012-01-16,Fluorine abundances in dwarf stars of the solar neighbourhood,"In spite of many observational efforts aiming to characterize the chemical
evolution of our Galaxy, not much is known about the origin of fluorine (F).
Models suggest that the F found in the Galaxy might have been produced mainly
in three different ways, namely, Type II supernovae, asymptotic giant branch
nucleosynthesis, or in the core of Wolf-Rayet stars. Only a few observational
measurements of F abundances are available in the literature and mostly for
objects whose characteristics might hamper an accurate determination of
fluorine abundance (e.g.,complex mixing and nucleosynthesis processes,
external/internal contamination). We derive the F abundances for a set of nine
cool main-sequence dwarfs in the solar neighbourhood, based on an unblended
line of the HF molecule at 2.3 microns. In addition, we study the s-process
elements of five of these stars. We acquire data using the high-resolution
IR-spectrograph CRIRES and gather FEROS data from the European Southern
Observatory archive. Several of the analysed stars seem to be slightly fluorine
enhanced with respect to the Sun, although no correlation is found between the
F abundance and the iron content. In addition, the most fluorine enriched stars
are also yttrium and zirconium enriched, which suggests that AGB fluorine
nucleosynthesis is the dominant source of fluorine production for the observed
stars. Nevertheless, the correlation between [F/Fe] and the s-elements is
rather weak and possibly masked by the uncertainties in the F abundance
measurements. Finally, we compare our derived F abundances to previous
measurements of alpha-element and iron-peak element abundances. Type II core
collapse Supernovae do not appear to be the main site of F production for our
targets, as no correlation seems to exist between the [F/Fe] and the [alpha/Fe]
ratios.",1201.3193v1
2016-11-05,Discovery of a variable lead-rich hot subdwarf: UVO 0825+15,"UVO0825+15 is a hot bright helium-rich subdwarf which lies in {\it K2} Field
5 and in a sample of intermediate helium-rich subdwarfs observed with {\it
Subaru/HDS}. The {\it K2} light curve shows low-amplitude variations, whilst
the {\it Subaru} spectrum shows Pb{\sc iv} absorption lines, indicative of a
very high lead overabundance. UVO0825+15 also has a high proper motion with
kinematics typical for a thick disk star. Analyses of ultraviolet and
intermediate dispersion optical spectra rule out a short-period binary
companion, and provide fundamental atmospheric parameters of $T_{\rm
off}=38\,900\pm270$\,K, $\log g/{\rm cm\,s^{-2}}=5.97\pm0.11$,
  $\log n_{\rm He}/n_{\rm H}=-0.57\pm0.01$, $E_{B-V}\approx0.03$, and angular
radius $\theta = 1.062\pm0.006\times10^{-11}$ radians (formal errors). The
high-resolution spectrum shows that carbon is $>2$ dex subsolar, iron is
approximately solar and all other elements heavier than argon are at least 2 --
4 dex overabundant, including germanium, yttrium and lead. Approximately 150
lines in the blue-optical spectrum remain unidentified. The chemical structure
of the photosphere is presumed to be determined by radiatively-dominated
diffusion. The {\it K2} light curve shows a dominant period around 10.8\,h,
with a variable amplitude, its first harmonic, and another period at 13.3\,h.
The preferred explanation is multi-periodic non-radial oscillation due to
g-modes with very high radial order, although this presents difficulties for
pulsation theory. Alternative explanations fail for lack of radial-velocity
evidence. UVO0825+15 represents the fourth member of a group of hot subdwarfs
having helium-enriched photospheres and 3--4 dex overabundances of trans-iron
elements, and is the first lead-rich subdwarf to show evidence of pulsations.",1611.01616v1
2009-08-24,Enhancement in transition temperature and critical current density of CeO0.8F0.2FeAs by yttrium doping,"We report significant enhancement in superconducting properties of yttrium
substituted Ce1-xYxOFFeAs superconductors. The polycrystalline samples were
prepared by two step solid state reaction technique. X-ray diffraction
confirmed tetragonal ZrCuSiAs structure with decrease in both a and c lattice
parameters on increasing yttrium substitution (with fixed F content). With
smaller ion Y in place of Ce, the transition temperature increased by 6 K.
Yttrium doping also lead to higher critical fields as well as stronger inter
and intra-granular current density. The magnetization critical current density
increased by an order of magnitude at 30 K and 1 T magnetic field.",0908.3372v1
2016-10-23,Development of Yttrium alloy ion source and its application in nanofabrication,"We present a new YAuSi Liquid Metal Alloy Ion Source (LMAIS), generating
focused ion beams of yttrium ions, and its prospective applications for
nanofabrication, sample preparation, lithographic and implantation processes.
Working parameters of the AuSiY LMAIS are similar to other gold-silicon based
LMAIS. We found anomalously high emission current of triple charged Yttrium
ions. Influence of Yttrium implantation on optical qualities of the implanted
ion-ensembles is shown in luminescence of co-implanted Erbium ions.",1610.07166v1
2020-04-02,Synthesis and $\textit{in-situ}$ characterization of photochromic yttrium oxyhydride grown by reactive $e^-$-beam evaporation,"We report on controlled growth of photochromic yttrium oxyhydride thin films
monitored by $\textit{in-situ}$ composition depth profiling. Films were grown
by reactive $e^-$-beam evaporation and subsequently oxidized, while
simultaneously tracking the oxygen and hydrogen concentrations. Sample
composition and photochromic response were characterized $\textit{in-situ}$
using non destructive ion beam analysis and image analysis, respectively - as
well as complementary $\textit{ex-situ}$ ion beam methods, X-ray diffraction
and optical spectrophotometry. We show that photochromic yttrium oxyhydride can
be grown as yttrium dihydride, which is then oxidized to O/H ratios triggering
the photochromic response.",2004.01093v2
2006-07-06,Electronic Structure and Electron-Phonon Interaction in Hexagonal Yttrium,"To understand the pressure-induced changes in the electronic structure and
the electron-phonon interaction in yttrium, we have studied hexagonal
close-packed (hcp) yttrium, stable at ambient pressure and double hexagonal
close-packed (dhcp) yttrium, stable up to around 44 GPa, using
density-functional-based methods. Our results show that as one goes from hcp
yttrium to dhcp yttrium, there is (i) a substantial charge-transfer from s->d
with extensive modifications of the d-band and a sizable reduction in the
density of states at the Fermi energy, (ii) a substantial stiffening of phonon
modes with the electron-phonon coupling covering the entire frequency range,
(iii) an increase in the electron-phonon coupling constant \lambda from 0.55 to
1.24, leading to a change in the superconducting transition temperature T_c
from 0.3 K to 15.3 K for \mu*=0.2.",0607176v3
2004-02-24,Frustrated Ising model on the garnet lattice,"We investigate a frustrated Ising spin system on the garnet lattice composed
of a specific network of corner-sharing triangles. By means of Monte Carlo
simulations with the heat bath algorithm, we discuss the magnetic properties at
finite temperatures. It is shown that the garnet spin system with the
nearest-neighbor couplings does not exhibit any magnetic transitions, yielding
the large residual entropy at zero temperature. We also investigate the effect
of the long-range dipolar interaction systematically to determine the phase
diagram of the Ising model on the garnet lattice. We find that there appear a
variety of distinct phases depending on the cutoff length of the long-range
interaction, in contrast to the pyrochlore spin-ice systems.",0402604v1
2009-09-25,The magnetic properties of the Garnet and glass forms of Mn3Al2Si3O12,"The magnetic susceptibilities and specific heats of the crystalline garnet
and glass forms of Mn3Al2Si3O12 are reported. This allows a direct comparison
of the degree of magnetic frustration of the triangle-based garnet lattice and
the structurally disordered solid at the same composition for isotropic spin
5/2 Mn^2+ (3d^5). The results show that the glass phase shows more pronounced
signs of magnetic frustration than the crystalline phase. Through comparison of
the specific heats of Ca3Al2Si3O12 (grossular) and Mn3Al2Si3O12 (spessartine)
garnets, information is provided concerning the anomalous extra specific heat
in the latter material.",0909.4720v1
2021-04-30,Current-Induced Magnetization Control in Insulating Ferrimagnetic Garnets,"The research into insulating ferrimagnetic garnets has gained enormous
momentum in the past decade. This is partly due to the improvement in the
techniques to grow high-quality ultrathin films with desirable properties and
the advances in understanding the spin transport within the ferrimagnetic
garnets and through their interfaces with conducting materials. In recent
years, we have seen remarkable progress in controlling the magnetization state
of ferrimagnetic garnets by electrical means in suitable heterostructures and
device architectures. These advances have readily placed ferrimagnetic garnets
in a favorable position for the future development of insulating spintronic
concepts. The purpose of this article is to review recent experimental results
of the current-induced magnetization control and associated phenomena in
ferrimagnetic garnets, as well as to discuss future directions in this rapidly
evolving area of spintronics.",2104.14819v1
2017-06-19,A Large-Diameter Hollow-Shaft Cryogenic Motor Based on a Superconducting Magnetic Bearing for Millimeter-Wave Polarimetry,"In this paper we present the design and measured performance of a novel
cryogenic motor based on a superconducting magnetic bearing (SMB). The motor is
tailored for use in millimeter-wave half-wave plate (HWP) polarimeters, where a
HWP is rapidly rotated in front of a polarization analyzer or
polarization-sensitive detector. This polarimetry technique is commonly used in
cosmic microwave background (CMB) polarization studies. The SMB we use is
composed of fourteen yttrium barium copper oxide (YBCO) disks and a contiguous
neodymium iron boron (NdFeB) ring magnet. The motor is a hollow-shaft motor
because the HWP is ultimately installed in the rotor. The motor presented here
has a 100 mm diameter rotor aperture. However, the design can be scaled up to
rotor aperture diameters of approximately 500 mm. Our motor system is composed
of four primary subsystems: (i) the rotor assembly, which includes the NdFeB
ring magnet, (ii) the stator assembly, which includes the YBCO disks, (iii) an
incremental encoder, and (iv) the drive electronics. While the YBCO is cooling
through its superconducting transition, the rotor is held above the stator by a
novel hold and release mechanism (HRM). The encoder subsystem consists of a
custom-built encoder disk read out by two fiber optic readout sensors. For the
demonstration described in this paper, we ran the motor at 50 K and tested
rotation frequencies up to approximately 10 Hz. The feedback system was able to
stabilize the the rotation speed to approximately 0.4%, and the measured rotor
orientation angle uncertainty is less than 0.15 deg. Lower temperature
operation will require additional development activities, which we will
discuss.",1706.05963v3
2020-07-16,The heavy-elements heritage of the falling sky,"Recent dynamical analysis based on Gaia data have revealed major accretion
events in Milky Way's history. Nevertheless, our understanding of the
primordial Galaxy is hindered because the bona fide identification of the most
metal-poor and correspondently oldest accreted stars remains challenging.
Contrary to alpha-elements, neutron-capture elements present unexplained large
abundance spreads for low metallicity stars, that could result from a mixture
of formation sites. We have analysed the abundances of yttrium, europium,
magnesium and iron in Milky Way satellite galaxies, field halo stars and
globular clusters. The chemical information has been complemented with orbital
parameters based on Gaia data. In particular, the orbit's average inclination
has been considered. The [Y/Eu] abundance behaviour with respect to the [Mg/Fe]
turnovers for satellite galaxies of different masses reveals that higher
luminosity systems, for which the [Mg/Fe] abundance declines at higher
metallicities, present enhanced [Y/Eu] abundances, particularly in the [Fe/H]
regime between -2.25 and -1.25 dex. In addition, the analysis has uncovered a
chemo-dynamical correlation for both globular clusters and field stars of the
Galactic halo, accounting for about half of the [Y/Eu] abundance spread. [Y/Eu]
under-abundances typical of protracted chemical evolutions, are preferentially
observed in polar-like orbits, pointing to a possible anisotropy in the
accretion processes. Our results strongly suggest that the observed [Y/Eu]
abundance spread in the Milky Way halo could result from a mixture of systems
with different masses. They also highlight that both nature and nurture are
relevant to the Milky Way formation, since its primordial epochs, opening new
pathways for chemical diagnostics of our Galaxy building up.",2007.08313v1
2024-01-16,Formation of yttrium oxalate phase filled by carbon clusters on the surface of yttrium oxide films,"In the current paper, we report the results of surface modification of cubic
Y2O3 films employing carbon-ion implantation. The characterization results
demonstrate the formation of a stable yttrium oxalate-based structure with
cavities filled with carbon clusters. Theoretical simulations demonstrate that
the incorporation of eighteen-atom carbon clusters into the cavities of
Y2(C2O4)3 does not lead to valuable changes in the crystal structure of yttrium
oxalate. X-ray diffraction and optical measurements demonstrate that the
subsurface bulk area of cubic yttrium oxide remains unperturbed. The oxalate
""skin"" thickness with embedded carbon clusters is estimated to be approximately
10 nm. The prospective employing the method to manage optical properties and
increase the biocompatibility of yttria and lanthanide oxides are discussed.",2401.08459v1
2017-08-25,Role of dimensional crossover on spin-orbit torque efficiency in magnetic insulator thin films,"Magnetic insulators (MIs) attract tremendous interest for spintronic
applications due to low Gilbert damping and absence of Ohmic loss. Magnetic
order of MIs can be manipulated and even switched by spin-orbit torques (SOTs)
generated through spin Hall effect and Rashba-Edelstein effect in heavy
metal/MI bilayers. SOTs on MIs are more intriguing than magnetic metals since
SOTs cannot be transferred to MIs through direct injection of electron spins.
Understanding of SOTs on MIs remains elusive, especially how SOTs scale with
the film thickness. Here, we observe the critical role of dimensionality on the
SOT efficiency by systematically studying the MI layer thickness dependent SOT
efficiency in tungsten/thulium iron garnet (W/TmIG) bilayers. We first show
that the TmIG thin film evolves from two-dimensional to three-dimensional
magnetic phase transitions as the thickness increases, due to the suppression
of long-wavelength thermal fluctuation. Then, we report the significant
enhancement of the measured SOT efficiency as the thickness increases. We
attribute this effect to the increase of the magnetic moment density in concert
with the suppression of thermal fluctuations. At last, we demonstrate the
current-induced SOT switching in the W/TmIG bilayers with a TmIG thickness up
to 15 nm. The switching current density is comparable with those of heavy
metal/ferromagnetic metal cases. Our findings shed light on the understanding
of SOTs in MIs, which is important for the future development of ultrathin
MI-based low-power spintronics.",1708.07584v2
2020-08-21,Experimental determination of ferric iron partitioning between pyroxene and melt at 100KPa,"Pyroxene is the principal host of Fe$^{3+}$ in basalt source regions, hosting
79 and 81% of the Fe$^{3+}$ in spinel and garnet lherzolite, respectively, with
opx and cpx hosting 48% and 31%, respectively, of the total Fe$^{3+}$ in spinel
peridotite. To better understand partitioning of Fe$^{3+}$ between pyroxene and
melt we conducted experiments at 100 KPa with f$_{O2}$ controlled by CO-CO$_2$
gas mixes between $\Delta$QFM -1.19 to +2.06 in a system containing andesitic
melt saturated with opx or cpx only. To produce large (100-150 $\mu$m),
homogeneous pyroxenes, we employed a dynamic cooling technique with a
5-10$\deg$C/h cooling rate, and initial and final dwell temperatures
5-10$\deg$C and 20-30$^\circ$C super and sub-liquidus, respectively. Resulting
pyroxene crystals have absolute variation in Al$_2$O$_3$ and TiO$_2$ <0.05 wt.%
and <0.02 wt.%, respectively. Fe$^{3+}$/Fe$^T$ in pyroxenes and quenched glass
were measured by XANES. We used a newly developed XANES calibration for cpx and
opx by only selecting spectra with X-ray vibrating on the optic axial plane at
$50 \pm 5^\circ$ to the crystallographic c axis. Values of DFe$^{3+}$ cpx/melt
increase from 0.03 to 0.53 as fO2 increases from $\Delta$QFM -0.44 to 2.06,
while DFe$^{3+}$ opx/melt remains unchanged at 0.26 between $\Delta$QFM -1.19
to +1.37. In comparison to natural peridotitic pyroxenes, Fe$^{3+}$/FeT in
pyroxenes crystallized in this study are lower at similar f$_{O2}$, presumably
owing to lower Al$^{3+}$ contents. This study shows that the existing
thermodynamic models implemented in pMELTS and Perple_X over-predict the
stability of Fe$^{3+}$ in pyroxenes, causing an anomalous reduced character to
spinel peridotites at calculated conditions of MORB genesis.",2008.09296v1
2022-07-28,Low-temperature nanoscale heat transport in a gadolinium iron garnet heterostructure probed by ultrafast x-ray diffraction,"Time-resolved x-ray diffraction has been used to measure the low-temperature
thermal transport properties of a Pt/Gd3Fe5O12//Gd3Ga5O12 metal/oxide
heterostructure relevant to applications in spin caloritronics. A pulsed
femtosecond optical signal produces a rapid temperature rise in the Pt layer,
followed by heat transport into the Gd3Fe5O12 (GdIG) thin film and the
Gd3Ga5O12 (GGG) substrate. The time dependence of x-ray diffraction from the
GdIG layer was tracked using an accelerator-based femtosecond x-ray source. The
ultrafast diffraction measurements probed the intensity of the GdIG (1 -1 2)
x-ray reflection in a grazing-incidence x-ray diffraction geometry. The
comparison of the variation of the diffracted x-ray intensity with a model
including heat transport and the temperature dependence of the GdIG lattice
parameter allows the thermal conductance of the Pt/GdIG and GdIG//GGG
interfaces to be determined. Complementary synchrotron x-ray diffraction
studies of the low-temperature thermal expansion properties of the GdIG layer
provide a precise calibration of the temperature dependence of the GdIG lattice
parameter. The interfacial thermal conductance of the Pt/GdIG and GdIG//GGG
interfaces determined from the time-resolved diffraction study is of the same
order of magnitude as previous reports for metal/oxide and epitaxial dielectric
interfaces. The thermal parameters of the Pt/GdIG//GGG heterostructure will aid
in the design and implementation of thermal transport devices and
nanostructures.",2207.14409v1
2023-08-14,Temperature Evolution of Magnon Propagation Length in Tm$_3$Fe$_5$O$_{12}$ Thin Films: Roles of Magnetic Anisotropy and Gilbert Damping,"The magnon propagation length ($\langle\xi\rangle$) of a ferro/ferrimagnet
(FM) is one of the key factors that controls the generation and propagation of
thermally-driven spin current in FM/heavy metal (HM) bilayer based
spincaloritronic devices. Theory predicts that for the FM layer,
$\langle\xi\rangle$ is inversely proportional to the Gilbert damping ($\alpha$)
and the square root of the effective magnetic anisotropy constant ($K_{\rm
eff}$). However, direct experimental evidence of this relationship is lacking.
To experimentally confirm this prediction, we employ a combination of
longitudinal spin Seebeck effect (LSSE), transverse susceptibility, and
ferromagnetic resonance experiments to investigate the temperature evolution of
$\langle\xi\rangle$ and establish its correlation with the effective magnetic
anisotropy field, $H_K^{\rm eff}$ ($\propto K_{\rm eff}$) and $\alpha$ in
Tm$_3$Fe$_5$O$_{12}$ (TmIG)/Pt bilayers. We observe concurrent drops in the
LSSE voltage and $\langle\xi\rangle$ below 200$^\circ$K in TmIG/Pt bilayers
regardless of TmIG film thickness and substrate choice and attribute it to the
noticeable increases in $H_K^{\rm eff}$ and $\alpha$ that occur within the same
temperature range. From the TmIG thickness dependence of the LSSE voltage, we
determined the temperature dependence of $\langle\xi\rangle$ and highlighted
its correlation with the temperature-dependent $H_K^{\rm eff}$ and $\alpha$ in
TmIG/Pt bilayers, which will be beneficial for the development of rare-earth
iron garnet-based efficient spincaloritronic nanodevices.",2308.07236v3
2017-09-20,Static Magnetization Properties Of AL800 Garnet Material,"A second harmonic tunable RF cavity is being developed for the Fermilab
Booster. This device, which promises reduction of the particle beam loss at the
injection, transition, and extraction stages, employs perpendicularly biased
garnet material for frequency tuning. The required range of the tuning is
significantly wider than in previously built and tested tunable RF devices. As
a result, the magnetic field in the garnet comes fairly close to the
gyromagnetic resonance line at the lower end of the frequency range. The chosen
design concept of a tuner for the cavity cannot ensure uniform magnetic field
in the garnet material; thus, it is important to know the static magnetic
properties of the material to avoid significant increase in the local RF loss
power density. This report summarizes studies performed at Fermilab to
understand variations in the magnetic properties of the AL800 garnet material
used to build the tuner of the cavity.",1709.07050v1
2018-01-07,Aluminum and Gallium Distribution in the Lu3(Al5-xGax)O12:Ce Multicomponent Garnet Scintillators Investigated by the Solid-State NMR and DFT calculations,"Distribution of aluminum and gallium atoms over the tetrahedral and
octahedral sites in the garnet structure was studied in the mixed
Lu3Al5-xGaxO12 crystals using the 27Al and 71Ga MAS NMR together with the
single crystal 71Ga NMR. The experimental study was accompanied by theoretical
calculations based on the density functional theory in order to predict the
tendency in substitutions of Al by Ga in the mixed garnets. Both experimental
and theoretic results show a non-uniform distribution of Al and Ga over the
tetrahedral and octahedral sites in the garnet structure, with strong
preferences for Ga, having larger ionic radius than Al, to occupy the
tetrahedral site with smaller volume in the garnet structure. The quadrupole
coupling constants and chemical shift parameters for Al and Ga nuclei have been
determined for all the studied compounds as well as electric field gradients at
Al and Ga nuclei were calculated in the framework of the density functional
theory.",1801.02223v1
2006-07-23,Prediction of Superconductivity at ~ 30 K in Compressed Body-Centered Cubic Yttrium,"Using ab initio methods, we have studied the electron-phonon interaction in
compressed, body-centered cubic (bcc) yttrium, which is predicted to be stable
at 280 GPa [Melsen et al, Phys. Rev. B 48, 15574 (1993)]. We find that
compressed, bcc yttrium has a large electron-phonon coupling with lambda=1.8,
leading to a superconducting transition temperature T_c ~ 30 K or above. Our
results indicate that the large electron-phonon coupling is due to the lattice
hardening.",0607588v2
2018-12-16,Yttrium-substituted Mg-Zn ferrites: correlation of physical properties with Yttrium content,"Yttrium (Y) substituted Mg Zn ferrites with the compositions of
Mg0.5Zn0.5YxFe2 xO4 have been synthesized by conventional standard ceramic
technique. The effect of Y3+ substitution on the structural, electrical,
dielectric and magnetic properties of Mg Zn ferrites has been studied.",1812.06370v2
2015-06-23,Atomic-scale investigation of creep behavior in nanocrystalline Mg and Mg-Y alloys,"Magnesium (Mg) and its alloys offer great potential for reducing vehicular
mass and energy consumption due to their inherently low densities.
Historically, widespread applicability has been limited by low strength
properties compared to other structural Al-, Ti- and Fe-based alloys. However,
recent studies have demonstrated high-specific-strength in a number of
nanocrystalline Mg-alloys. Even so, applications of these alloys would be
restricted to low-temperature automotive components due to microstructural
instability under high temperature creep loading. Hence, this work aims to gain
a better understanding of creep and associated deformation behavior of columnar
nanocrystalline Mg and Mg-yttrium (Y) (up to 3at.%Y(10wt.%Y)) with a grain size
of 5 nm and 10 nm. Using molecular dynamics (MD) simulations, nanocrystalline
magnesium with and without local concentrations of yttrium is subjected to
constant-stress loading ranging from 0 to 500 MPa at different initial
temperatures ranging from 473 to 723 K. In pure Mg, the analyses of the
diffusion coefficient and energy barrier reveal that at lower temperatures
(i.e., T < ~423K) the contribution of grain boundary diffusion to the overall
creep deformation is stronger that the contribution of lattice diffusion.
However, at higher temperatures (T > ~423K) lattice diffusion dominates the
overall creep behavior. Interestingly, for the first time, we have shown that
the(101-1),(101-2),(101-3) and (101-6) boundary sliding energy is reduced with
the addition of yttrium. This softening effect in the presence of yttrium
suggests that the experimentally observed high temperature beneficial effects
of yttrium addition is likely to be attributed to some combination of other
reported creep strengthening mechanisms or phenomena such as formation of
stable yttrium oxides at grain boundaries or increased forest dislocation-based
hardening.",1506.07149v1
2011-02-11,"Discovery of Yttrium, Zirconium, Niobium, Technetium, and Ruthenium Isotopes","Currently, thirty-four yttrium, thirty-five zirconium, thirty-four niobium,
thirty-five technetium, and thirty-eight ruthenium isotopes have been observed
and the discovery of these isotopes is discussed here. For each isotope a brief
synopsis of the first refereed publication, including the production and
identification method, is presented.",1102.2381v1
2002-02-17,Faraday rotation and sensitivity of (100) bismuth-substituted ferrite garnet films,"We have investigated the Faraday rotation of in-plane magnetized bismuth -
substituted ferrite garnet films grown by liquid phase epitaxy on (100)
oriented gadolinium gallium garnet substrates. The Faraday spectra were
measured for photon energies between 1.7 - 2.6 eV. To interprete the spectra,
we use a model based on two electric dipole transitions, one tetrahedral and
one octahedral. Furthermore, the Faraday rotation sensitivity was measured at
2.3 eV, and found to be in good agreement with the theoretical predicitions. In
particular, we find that the sensitivity increases linearly with the bismuth
content and nonlinearly with the gallium content.",0202281v1
2008-01-22,On the Crystallization of Terbium Aluminium Garnet,"Attempts to grow terbium aluminium garnet (Tb3Al5O12, TAG) by the Czochralski
method lead to crystals of millimeter scale. Larger crystals could not be
obtained. DTA measurements within the binary system showed that TAG melts
incongruently at 1840 deg. C. The perovskite (TbAlO3, TAP) with a congruent
melting point of 1930 deg. C is the most stable phase in this system. The
region for primary crystallization of TAP covers the chemical composition of
TAG and suppresses the primary crystallization of the terbium aluminium garnet.",0801.3317v1
2018-06-21,"Magnetic Properties of Lithium-Containing Rare Earth Garnets Li3RE3Te2O12 (RE = Y, Pr, Nd, Sm-Lu)","The synthesis, structural description, temperature dependent magnetic
susceptibilities and field dependent magnetizations of a series of rare earth
garnets of the form Li3RE3Te2O12 (RE = Y, La, Pr, Nd, Sm-Lu) are reported. The
structure of Li3Dy3Te2O12 is refined from powder X-ray diffraction data. The
field dependent magnetizations saturate for some of the members by 9 Tesla at 2
K. Of particular interest for further study in this family is the behavior of
the Pr, Tb, Dy and Yb garnets.",1806.08399v1
2023-10-02,Stuffed Rare Earth Garnets,"We report the synthesis and magnetic characterization of stuffed rare earth
gallium garnets, RE3+xGa5-xO12 (RE=Lu, Yb, Er, Dy, Gd), for x up to 0.5. The
excess rare earth ions partly fill the octahedral sites normally fully occupied
by Ga3+, forming disordered pairs of corner-shared face-sharing magnetic
tetrahedra. The Curie-Weiss constants and observed effective moments per rare
earth are smaller than are seen for the unstuffed gallium garnets. No
significant change in the field-dependent magnetization is observed but missing
entropy is seen when integrating the low-temperature heat capacity to 0.5 K.",2310.01606v1
2017-07-21,"Sensitivity of magnetic properties to chemical pressure in lanthanide garnets $Ln_3A_2X_3\text{O}_{12}$, $Ln$ = Gd, Tb, Dy, Ho, $A$ = Ga, Sc, In, Te, $X$ = Ga, Al, Li","A systematic study of the structural and magnetic properties of
three-dimensionally frustrated lanthanide garnets $Ln_3A_2X_3\text{O}_{12}$,
$Ln$ = Gd, Tb, Dy, Ho, $A$ = Ga, Sc, In, Te, $X$ = Ga, Al, Li is presented.
Garnets with $Ln$ = Gd show magnetic behaviour consistent with isotropic
Gd$^{3+}$ spins; no magnetic ordering is observed for T $\geq$ 0.4 K. Magnetic
ordering features are seen for garnets with $Ln$ = Tb, Dy, Ho in the
temperature range 0.4 < T < 2.5 K, however the nature of the magnetic ordering
varies for the different $Ln$ as well as for different combinations of $A$ and
$X$. The changes in magnetic behaviour can be explained by tuning of the
magnetic interactions and changes in the single-ion anisotropy. The change in
magnetic entropy is evaluated from isothermal magnetisation measurements to
characterise the magnetocaloric effect in these materials. Among the Gd
garnets, the maximum change in magnetic entropy per mole (15.45 J K$^{-1}$
mol$_{\text{Gd}}^{-1}$) is observed for Gd$_3$Sc$_2$Ga$_3$O$_{12}$ at 2 K, in a
field of 9 T. The performance of Dy$_3$Ga$_5$O$_{12}$ as a magnetocaloric
material surpasses the other garnets with $Ln$ = Tb, Dy, Ho.",1707.06730v1
2019-02-18,Ionic conductivity enhacements and low temperature synthesis of Li7La3Zr2O12 garnets by Bi aliovalent substitutions,"We report on a novel approach to synthesize cubic-phase fast ionic conducting
garnet-type solid state electrolytes based on Bi doped Li7La3Zr2O12 (LLZO). Bi
aliovalent substitution into LLZO utilizing the Pechini processing method is
successfully employed to synthesize Li7-xLa3Zr2-xBixO12 compounds. Ionic
conductivities up to 2.0 x 10-4 S/cm are achieved in structures not fully
densified. Cubic phase Li6La3ZrBiO12 powders are generated in the temperature
range from 650 {\deg}C to 900 {\deg}C in air. In contrast, in the absence of Bi
and under identical synthesis conditions, the cubic garnet phase of
Li7La3Zr2O12 is not formed below 700 {\deg}C while a transformation to the
tetragonal phase is observed at 900 {\deg}C for the un-doped compound. The
critical role of Bi in lowering the formation temperature of the garnet cubic
phase and the improvements in ionic conductivity is investigated in this work
through microstructural studies and AC impedance measurements. We ascribe the
effect of Bi doping in achieving these remarkable improvements to significant
enhancements at lower temperatures in the kinetics of the solid-state reaction
resulting in explosive grain growth and densification of the garnet. Moreover,
XAS is utilized to identify the specific atomic site where Bi is incorporated
in the LLZO garnet crystalline structure.",1902.06831v1
2021-12-21,Garnet pyroxenites explain high electrical conductivity in the East African deep lithosphere,"A large contrast in electrical conductivity has been observed within the
lithospheric mantle between the Tanzanian craton and the Mozambique belt at
depths > 70 km. Such contrasts are typically attributed to changes in volatiles
and/or melt content, with changes in mineralogy deemed insufficient to impact
conductivity. To test this assumption, electrical conductivity measurements
were conducted at pressure-temperature conditions relevant to the Tanzanian
lithosphere (1.5 and 3 GPa; from 400 to > 1500{\deg}C) on xenoliths from
Engorora, Northern Tanzania. I observe that, once garnet becomes stable in
fertile mantle rocks (> 60 km, 1.7 GPa), it nucleates at grain boundaries and
forms the backbone of a conductive network. At 3 GPa, the presence of
garnet-rich networks increases conductivity by a factor of 100 regardless of
temperature. Numerical models demonstrate that low (< 10^{-2} Sm^{-1}) and high
(> 10^{-1} Sm^{-1}) conductivities in the Tanzanian lithospheric mantle are
best explained by low and high degrees of garnet connectivity, respectively.
Such high electrical conductivities in cratonic roots can be explained by the
presence of connected garnet clusters, suggesting mantle refertilization. I
suggest that the garnet network represents the result of plume triggered
metasomatism due to plume impingement, and may represent an unstable structure
that will eventually lead to loss of cratonic lithosphere.",2112.11559v1
2022-01-30,GARNET: Reduced-Rank Topology Learning for Robust and Scalable Graph Neural Networks,"Graph neural networks (GNNs) have been increasingly deployed in various
applications that involve learning on non-Euclidean data. However, recent
studies show that GNNs are vulnerable to graph adversarial attacks. Although
there are several defense methods to improve GNN robustness by eliminating
adversarial components, they may also impair the underlying clean graph
structure that contributes to GNN training. In addition, few of those defense
models can scale to large graphs due to their high computational complexity and
memory usage. In this paper, we propose GARNET, a scalable spectral method to
boost the adversarial robustness of GNN models. GARNET first leverages weighted
spectral embedding to construct a base graph, which is not only resistant to
adversarial attacks but also contains critical (clean) graph structure for GNN
training. Next, GARNET further refines the base graph by pruning additional
uncritical edges based on probabilistic graphical model. GARNET has been
evaluated on various datasets, including a large graph with millions of nodes.
Our extensive experiment results show that GARNET achieves adversarial accuracy
improvement and runtime speedup over state-of-the-art GNN (defense) models by
up to 13.27% and 14.7x, respectively.",2201.12741v6
1998-09-02,Nonlocal electrical conductivity coefficient sigma sub-k,"A nonlocal functional is used to calculate superconducting properties of
barium yttrium copper oxide.",9809047v1
2007-03-22,First Principles Study on the Formation of Yttrium Nitride in Cubic and Hexagonal Phases,"We have studied the formation of yttrium nitride in which the Y-atoms were
arranged in two common close-packed stacking: The AB-stacking (hcp-symmetry) is
the ground state of metallic yttrium; while the ABC-stacking (fcc-symmetry) is
the ground state of yttrium nitride. Given the different symmetries between YN
and Y, there must be a phase transition (hcp->fcc) as N is incorporated in the
Y-lattice. By means of first principles calculations we have made a
systematical investigation where N was gradually incorporated in octahedral
interstices in AB and ABC stacking of Y. We report the heat of formation, bulk
modulus, lattice parameter and electronic structure of the resultant nitrides.
We found that both metal arrangements are physically achievable. Furthermore,
for low nitrogen incorporation the two phases may coexist. However for high
nitrogen concentration the cubic phases are favored by a 30 kJ mol-1 margin.
These results are important since fcc-YN is semiconducting and could be
utilized as active layer in electronic devices.",0703568v2
2007-09-26,Off-line studies of the laser ionization of yttrium at the IGISOL facility,"A laser ion source is under development at the IGISOL facility, Jyvaskyla, in
order to address deficiencies in the ion guide technique. The key elements of
interest are those of a refractory nature, whose isotopes and isomers are
widely studied using both laser spectroscopic and high precision mass
measurement techniques. Yttrium has been the first element of choice for the
new laser ion source. In this work we present a new coupled dye-Ti:Sapphire
laser scheme and give a detailed discussion of the results obtained from laser
ionization of yttrium atoms produced in an ion guide via joule heating of a
filament. The importance of not only gas purity, but indeed the baseline vacuum
pressure in the environment outside the ion guide is discussed in light of the
fast gas phase chemistry seen in the yttrium system. A single laser shot model
is introduced and is compared to the experimental data in order to extract the
level of impurities within the gas cell.",0709.4129v1
2020-07-08,Experimental evidence for orthorhombic Fddd crystal structure in elemental yttrium above 100 GPa,"We present electrical resistance measurements of elemental yttrium on bulk
and film samples, and both exhibit superconductivity at very high pressures. We
show that the pressure dependence of the superconducting transition temperature
above 100 GPa is in good agreement with the predicted Fddd phase by Chen et al.
[Phys. Rev. lett. 109, 157004 (2012)]. This result together with a new Rietveld
refinement made on X-ray data at 123 GPa from Samudrala et al. [J. Phys.
Condens. Matter 24, 362201 (2012)] offer strong evidence that the atomic
structure of yttrium above 100 GPa is orthorhombic Fddd. Furthermore, our
process of evaporating yttrium film directly on a diamond anvil is expected to
be a valuable asset for future synthesis of new superhydride superconductors.",2007.03969v2
2022-08-10,Synthesis and Superconductivity in Yttrium-Cerium Hydrides at Moderate Pressures,"Inspired by the high critical temperature in yttrium superhydride and the low
stabilized pressure in superconducting cerium superhydride, we carry out four
independent runs to synthesize yttrium-cerium alloy hydrides. The phases
examined by the Raman scattering and x-ray diffraction measurements. The
superconductivity is detected with the zero-resistance state at the critical
temperature in the range of 97-140 K at pressures ranging from 114 GPa to
120$\pm$4 GPa. The maximum critical temperature of the synthesized hydrides is
larger than those reported for cerium hydrides, while the corresponding
stabilized pressure is much lower than those for superconducting yttrium
hydrides. The structural analysis and theoretical calculations suggest that the
phase of Y$_{0.5}$Ce$_{0.5}$H$_9$ has the space group $P6_3/mmc$ with the
calculated critical temperature of 119 K, in fair agreement with the
experiments. These results indicate that alloying superhydrides indeed can
maintain relatively high critical temperature at modest pressures accessible by
many laboratories.",2208.05191v1
2023-05-11,Reactive pulsed direct current magnetron sputtering deposition of semiconducting yttrium oxide thin film in ultralow oxygen atmosphere: A spectroscopic and structural investigation of growth dynamics,"An experimental investigation was conducted to explore spectroscopic and
structural characterization of semiconducting yttrium oxide thin film deposited
at 623 K (+/- 5K) utilizing reactive pulsed direct current magnetron
sputtering. Based on the results obtained from both x-ray diffraction and
transmission electron microscope measurements, yttrium monoxide is very likely
formed in the transition region between {\beta}-Y2O3 and {\alpha}-Y2O3, and
accompanied by the crystalline Y2O3. Resulting from either the low energy
separation between 4d and 5s orbitals and/or different spin states of the
corresponding orbitals' sublevels, the stability of monoxide is most presumably
self-limited by the size of the crystal in thermodynamic terms. This behavior
develops a distortion in the structure of the crystal compared to the metal
oxide cubic structure and it also effectuates the arrangement in
nanocrystalline/amorphous phase. In addition to this, spectroscopic
ellipsometry denotes that the semiconducting yttrium oxide has the dominant,
mostly amorphous, formation character over crystalline Y2O3. Our purpose, by
means of the current findings, is to advance the understanding of formation
kinetics/conditions of yttrium with an unusual valency (2+).",2305.06757v1
2020-01-15,Terahertz response of gadolinium gallium garnet (GGG) and gadolinium scandium gallium garnet (SGGG),"We report the magneto-optical response of Gadolinium Gallium Garnet (GGG) and
Gadolinium Scandium Gallium Garnet (SGGG) at frequencies ranging from $300 \,
\mathrm{GHz}$ to $1 \, \mathrm{THz}$, and determine the material response
tensor. Within this frequency window, the materials exhibit nondispersive and
low-loss optical responses. At low temperatures, significant THz Faraday
rotations are found in the (S)GGG samples. Such strong gyroelectric response is
likely associated with the high-spin paramagnetic state of the Gd$^{3+}$ ions.
A model of the material response tensor is determined, together with the Verdet
and magneto-optic constants.",2001.05085v1
2021-09-16,GarNet: A Continuous Robot Vision Approach for Predicting Shapes and Visually Perceived Weights of Garments,"We present a Garment Similarity Network (GarNet) that learns geometric and
physical similarities between known garments by continuously observing a
garment while a robot picks it up from a table. The aim is to capture and
encode geometric and physical characteristics of a garment into a manifold
where a decision can be carried out, such as predicting the garment's shape
class and its visually perceived weight. Our approach features an early stop
strategy, which means that GarNet does not need to observe a garment being
picked up from a crumpled to a hanging state to make a prediction. In our
experiments, we find that GarNet achieves prediction accuracies of 92% for
shape classification and 95.5% for predicting weights and advances state-of-art
approaches by 21% for shape classification.",2109.07831v3
2023-06-20,Erbium-excess gallium garnets,"A series of garnets of formula Er3+xGa5-xO12 is described, for which we
report the crystal structures for both polycrystalline and single-crystal
samples. The x limit in the garnet phase is between 0.5 and 0.6 under our
conditions, with the Er fully occupying the normal garnet site plus
half-occupying the octahedral site at x = 0.5 in place of the Ga normally
present. Long-range antiferromagnetic order with spin ice-like frustration is
suggested by the transition temperature (TN=0.8K) being much lower than the
Curie-Weiss theta. The magnetic ordering temperature does not depend on the Er
excess, but there is increasing residual entropy as the Er excess is increased,
highlighting the potential for unusual magnetic behavior in this system.",2306.11854v1
2009-01-05,"Crystal structure of synthetic Mg3Cr2Si3O12, the high-pressure Cr end-member of the knorringite-pyrope garnet series","Knorringite, the Cr-end-member of the pyrope garnet series (Nixon et al.
1968), often occur in high proportions in kimberlite garnets and is thus used
for tracing high-pressure deep-earth conditions favorable to the formation of
diamonds, in which knorringite-rich garnet can occur as inclusions. However,
although the synthesis of knorringite is reported in the literature (Ringwood
1977; Irifune et al. 1982; Taran et al. 2004), the structure of the pure
end-member has not been yet determined from experimental data. In this study,
the crystal structure of knorringite, Mg3Cr2(SiO4)3, has been refined from high
resolution synchrotron X-ray powder diffraction data recorded under ambient
conditions on a polycrystalline sample synthesized at 12 GPa in a multi-anvil
apparatus. The structure is cubic, space group Ia-3d, a = 11.5935(1), V =
1558.27(4) {\AA}3, dcalc = 3.97 g.cm-3. The Cr-O distance of 1.957(2) {\AA} is
consistent with EXAFS results on the same sample. This short distance indicates
a substantial compression of the CrO6 octahedron, compared to ambient pressure
Cr3+-minerals such as uvarovite (<Cr-O> = 1.99 {\AA}, Andrut and Wildner 2002).
Our experimental results thus confirm early empirical predictions based on
series of high-pressure Cr-garnet end-members (Fursenko 1981), showing that the
values of the Cr-O distance and the Cr-O-Si angle decrease with the
augmentation of pressure and with the diminution of the size of the divalent
cation.",0901.0476v1
2021-07-26,"The Gaia-ESO Survey: A new approach to chemically characterising young open clusters II. Abundances of the neutron-capture elements Cu, Sr, Y, Zr, Ba, La, and Ce","Young open clusters (t<200 Myr) have been observed to exhibit several
peculiarities in their chemical compositions, from a slightly sub-solar iron
content, super-solar abundances of some atomic species (e.g. ionised chromium),
and atypical enhancements of [Ba/Fe], with values up to +0.7 dex. Regarding the
behaviour of the other $s$-process elements like yttrium, zirconium, lanthanum,
and cerium, there is general disagreement in the literature. In this work we
expand upon our previous analysis of a sample of five young open clusters
(IC2391, IC2602, IC4665, NGC2516, and NGC2547) and one star-forming region
(NGC2264), with the aim of determining abundances of different neutron-capture
elements, mainly CuI, SrI, SrII, YII, ZrII, BaII, LaII, and CeII. We analysed
high-resolution, high signal-to-noise spectra of 23 solar-type stars observed
within the \textit{Gaia}-ESO survey. We find that our clusters have solar
[Cu/Fe] within the uncertainties, while we confirm the super-solar [Ba/Fe]
values (from +0.22 to +0.64 dex). Our analysis also points to mildly enhanced
[Y/Fe] values (from 0 and +0.3 dex). For the other $s$-process elements we find
that [X/Fe] ratios are solar at all ages. It is not possible to reconcile the
anomalous behaviour of Ba and Y at young ages with standard stellar yields and
Galactic chemical evolution model predictions. Thus, we explore different
possible scenarios related to the behaviour of spectral lines, from the
sensitivity to the presence of magnetic fields to the first ionisation
potential effect. We also investigate the possibility that they may arise from
alterations of the structure of the stellar photosphere due to higher levels of
activity in such young stars. We are still unable to explain these
enhancements, but we suggest that other elements (i.e. La) might be more
reliable tracer of the $s$-process at young ages and encourage further
observations.",2107.12381v1
2019-06-20,Chemical Compositions of Field and Globular Cluster RR~Lyrae Stars: II. omega Centauri,"We present a detailed spectroscopic analysis of RR Lyrae (RRL) variables in
the globular cluster NGC 5139 (omega Cen). We collected optical (4580-5330 A),
high resolution (R = 34,000), high signal-to-noise ratio (200) spectra for 113
RRLs with the multi-fiber spectrograph M2FS at the Magellan/Clay Telescope at
Las Campanas Observatory. We also analysed high resolution (R = 26,000) spectra
for 122 RRLs collected with FLAMES/GIRAFFE at the VLT, available in the ESO
archive. The current sample doubles the literature abundances of cluster and
field RRLs in the Milky Way based on high resolution spectra. Equivalent width
measurements were used to estimate atmospheric parameters, iron, and abundance
ratios for alpha (Mg, Ca, Ti), iron peak (Sc, Cr, Ni, Zn), and s-process (Y)
elements. We confirm that omega Cen is a complex cluster, characterised by a
large spread in the iron content: -2.58 < [Fe/H] < -0.85. We estimated the
average cluster abundance as [Fe/H] = -1.80 +- 0.03, with sigma = 0.33 dex. Our
findings also suggest that two different RRL populations coexist in the
cluster. The former is more metal-poor ([Fe/H] < -1.5), with almost solar
abundance of Y. The latter is less numerous, more metal-rich, and yttrium
enhanced ([Y/Fe] > 0.4). This peculiar bimodal enrichment only shows up in the
s-process element, and it is not observed among lighter elements, whose [X/Fe]
ratios are typical for Galactic globular clusters.",1906.08550v1
2024-01-13,Iron role paradox in nerve degeneration and regeneration,"Iron accumulates in the neural tissue during peripheral nerve degeneration.
Some studies have already been suggested that iron facilitates Wallerian
degeneration (WD) events such as Schwann cell de-differentiation. On the other
hand, intracellular iron levels remain elevated during nerve regeneration and
gradually decrease. Iron enhances Schwann cell differentiation and axonal
outgrowth. Therefore, there seems to be a paradox in the role of iron during
nerve degeneration and regeneration. We explain this contradiction by
suggesting that the increase in intracellular iron concentration during
peripheral nerve degeneration is likely to prepare neural cells for the
initiation of regeneration. Changes in iron levels are the result of changes in
the expression of iron homeostasis proteins. In this review, we will first
discuss the changes in the iron/iron homeostasis protein levels during
peripheral nerve degeneration and regeneration and then explain how iron is
related to nerve regeneration. This data may help better understand the
mechanisms of peripheral nerve repair and find a solution to prevent or slow
the progression of peripheral neuropathies.",2401.07016v1
2011-11-04,Exchange-correlation effects in the monoclinic to tetragonal phase stabilization of Yttrium-doped ZrO2: a first-principles approach,"We describe, within an ab-initio approach, the stabilization of the
tetragonal phase vs. the monoclinic one in Yttrium-doped Zirconia. The process
is believed to be influenced from different mechanisms. Indeed we show that
there is a delicate balance between the change in electrostatic and kinetic
energy and exchange-correlation effects. In the tetragonal phase the
perturbation induced by doping is better screened at the price of sacrificing
correlation energy. Our work opens the opportunity to use the same approach to
predict the tetragonal phase stabilization of materials like Zirconia or
Hafnia, with different and less characterized dopants.",1111.1147v2
2014-01-29,Thermodynamic properties of yttrium cuprate,"The standard formation enthalpy and enthalpy from binary oxide of yttrium
cuprate have been determined by solution calorimetry combining the solution
enthalpies of Y2Cu2O5 and Y2O3 + 2CuO mixture in 6 M HCl at 323.15 K and
literature data. The heat capacity of Y2Cu2O5 has been measured by adiabatic
calorimetry from 8 up to 303 K. Smoothed values of heat capacities, entropies
and enthalpies were calculated on the basis of experimental data. The
thermodynamic functions (heat capacity, entropy and enthalpy) at 298.15 K have
been calculated. On the basis of obtained data it has been obtained that
above-mentioned complex oxide is thermodynamically unstable with respect to
their decomposition into binary oxides at room temperatures.",1401.7422v1
2015-12-23,Coupling of erbium dopants to yttrium orthosilicate photonic crystal cavities for on-chip optical quantum memories,"Erbium dopants in crystals exhibit highly coherent optical transitions well
suited for solid-state optical quantum memories operating in the telecom band.
Here we demonstrate coupling of erbium dopant ions in yttrium orthosilicate to
a photonic crystal cavity fabricated directly in the host crystal using focused
ion beam milling. The coupling leads to reduction of the photoluminescence
lifetime and enhancement of the optical depth in microns-long devices, which
will enable on-chip quantum memories.",1512.07389v1
2006-09-26,Genetic Regulation of Fluxes: Iron Homeostasis of Escherichia coli,"Iron is an essential trace-element for most organisms. However, because high
concentration of free intracellular iron is cytotoxic, cells have developed
complex regulatory networks that keep free intracellular iron concentration at
optimal range, allowing the incorporation of the metal into iron-using enzymes
and minimizing damage to the cell. We built a mathematical model of the network
that controls iron uptake and usage in the bacterium Escherichia coli to
explore the dynamics of iron flow. We simulate the effect of sudden decrease or
increase in the extracellular iron level on intracellular iron distribution.
Based on the results of simulations we discuss the possible roles of the small
RNA RyhB and the Fe-S cluster assembly systems in the optimal redistribution of
iron flows. We suggest that Fe-S cluster assembly is crucial to prevent the
accumulation of toxic levels of free intracellular iron when the environment
suddenly becomes iron rich.",0609042v1
2020-12-25,Superconductivity to 262 kelvin via catalyzed hydrogenation of yttrium at high pressures,"Room temperature superconductivity has been achieved under high pressure in
an organically derived carbonaceous sulfur hydride with a critical
superconducting transition temperature (Tc) of 288 kelvin. This development is
part of a new class of dense, hydrogen rich materials with remarkably high
critical temperatures. Metal superhydrides are a subclass of these materials
that provide a different and potentially more promising route to very high Tc
superconductivity. The most promising binary metal superhydrides contain
alkaline or rare earth elements, and recent experimental observations of LaH10
have shown them capable of Tc s up to 250 to 260 kelvin. Predictions have shown
yttrium superhydrides to be the most promising with an estimated Tc in excess
of 300 kelvin for YH10. Here we report the synthesis of an yttrium superhydride
that exhibits superconductivity at a critical temperature of 262 kelvin at 182
gigapascal. A palladium thin film assists the synthesis by protecting the
sputtered yttrium from oxidation and promoting subsequent hydrogenation. Phonon
mediated superconductivity is established by the observation of zero
resistance, an isotope effect and the reduction of Tc under an external
magnetic field. The upper critical magnetic field is 103 tesla at zero
temperature. We suggest YH9 is the synthesized product based on comparison of
the measured Raman spectra and Tc to calculated Raman results.",2012.13627v1
2022-07-08,Synthesis and Superconductivity in yttrium superhydrides under high pressure,"The flourishing rare earth superhydrides are a class of recently discovered
materials that possess near-room-temperature superconductivity at high
pressures, opening a new era of superconductivity research at high pressures.
Among these superhydrides, yttrium superhydrides attracted great interest owing
to their abundance of stoichiometries and excellent superconductivities. Here,
we carried out a comprehensive study of yttrium superhydrides in a wide
pressure range of 145-300 GPa. We successfully synthesized a series of
superhydrides with the compositions of YH4, YH6, YH7, and YH9, and reported
their superconducting transition temperatures of 82 K at 167 GPa, 218 K at 165
GPa, 29 K at 162 GPa, and 230 K at 300 GPa, respectively, which were evidenced
by a sharp drop of resistivity. The structure and superconductivity of YH4,
which was taken as a representative example, were also examined by X-ray
diffraction measurements and the suppression of the superconductivity under
external magnetic fields, respectively. Clathrate YH10 as a candidate of
room-temperature superconductor was not synthesized within the studied pressure
and temperature ranges of up to 300 GPa and 2000 K, respectively. The current
work created a detailed platform for further searching room-temperature
superconductors in polynary yttrium-based superhydrides.",2207.03918v1
2023-08-15,Theoretical Study of Inelastic Processes in Collisions of Y and Y$^+$ with Hydrogen Atom,"Utilizing a simplified quantum model approach, the low-energy inelastic
collision processes between yttrium atoms (ions) and hydrogen atoms have been
studied. Rate coefficients corresponding to the mutual neutralization, ion-pair
formation, excitation, and de-excitation processes for the above collision
systems have been provided in the temperature range of 1000-10000K. 3 ionic
states and 73 covalent states are considered in calculations for the collisions
of yttrium atoms with hydrogen atoms, which include 6 molecular symmetries and
4074 partial inelastic reaction processes. For the collisions of yttrium ions
with hydrogen atoms, 1 ionic state and 116 covalent states are included, which
related to 3 molecular symmetries and 13572 partial inelastic collision
processes. It is found that the rate coefficients for the mutual neutralization
process have a maximum at T = 6000K, which is an order of magnitude higher than
those of other processes. Notably, the positions of optimal windows for the
collisions of yttrium atoms and ions with hydrogen atoms are found near
electronic binding energy -2eV (Y) and -4.4eV (Y$^+$), respectively. The
scattering channels located in or near these optimal windows have
intermediate-to-large rate coefficients (greater than $10^{-12}$
cm$^3$s$^{-1}$). The reported data should be useful in the study of non-local
thermodynamic equilibrium modeling.",2308.07831v1
1999-11-01,"First Principles Study of Structural, Electronic and Magnetic Interplay in Ferroelectromagnetic Yttrium Manganite","We present results of local spin density approximation pseudopotential
calculations for the ferroelectromagnet, yttrium manganite (YMnO3). The origin
of the differences between ferroelectric and non-ferroelectric perovskite
manganites is determined by comparing the calculated properties of yttrium
manganite in its ferroelectric hexagonal and non-ferroelectric orthorhombic
phases. In addition, orthorhombic YMnO3 is compared with the prototypical
non-ferroelectric manganite, lanthanum manganite. We show that, while the
octahedral crystal field splitting of the cubic perovskite structure causes a
centro-symmetric Jahn-Teller distortion around the Mn3+ ion, the markedly
different splitting in hexagonal perovskites creates an electronic
configuration consistent with ferroelectric distortion. We explain the nature
of the distortion, and show that a local magnetic moment on the Mn3+ ion is a
requirement for it to occur.",9910524v2
2003-12-16,Electronic band structure of novel 18-K superconductor Y2C3 as compared with YC and YC2,"The electronic band structure of yttrium sesquicarbide Y2C3(Pu2C3 structural
type) reported by Akimitsu et al. (2003) as a novel 18-K superconductor is
investigated using the first-principle full-potential LMTO method and compared
with those of yttrium mono- and dicarbide: cubic YC and 4-K superconductor YC2
(CaC2 structural type). Our results show that the enhanced Tc of Y2C3 as
compared with YC2 may be interpreted by the electronic factors: the near-Fermi
DOS for Y2C3 was found to be about 70% higher that for YC2, and the
contribution from the C2p states increases. The Fermi level of the ""ideal"" bcc
Y2C3 is located near the local DOS minimum, and the superconducting properties
of Y2C3-based materials would be very sensitive to synthesis conditions and the
presence of impurities and lattice vacancies. We suppose that by changing these
factors it is possible to vary Tc for the yttrium sesquicarbide.",0312391v2
2009-03-10,Effect of the chemical pressure on superconductivity and SDW in undoped and 15%F doped La1-yYyFeAsO compounds,"We present a study concerning the partial substitution of yttrium at the
lanthanum site of the undoped LaFeAsO and superconducting LaFeAsO0.85F0.15
compounds. We prepared samples with a nominal yttrium content up to 70%
producing simultaneous shrinkage of both the a- and c-lattice parameters by
1.8% and 1.7%, respectively. The chemical pressure provided by the partial
substitution with this smaller ion size causes a lowering of the spin density
wave temperature in the undoped compounds, as well as an increase of the
superconducting transition temperatures in the doped ones. The 15%
fluorine-doped samples reach a maximum critical temperature of 40.2 K for the
50% yttrium substitution. Comparison with literature data indicates that
chemical pressure cannot be the only mechanism which tunes drastically both
TSDW and Tc in 1111 compounds. Our data suggest that structural disorder
induced by the partial substitution in the La site or by doping could play an
important role as well.",0903.1825v2
2012-05-18,Surface oxide on thin films of yttrium hydride studied by neutron reflectometry,"The applicability of standard methods for compositional analysis is limited
for H-containing films. Neutron reflectometry is a powerful, non-destructive
method that is especially suitable for these systems due to the large negative
scattering length of H. In this work we demonstrate how neutron reflectometry
can be used to investigate thin films of yttrium hydride. Neutron reflectometry
gives a strong contrast between the film and the surface oxide layer, enabling
us to estimate the oxide thickness and oxygen penetration depths. A surface
oxide layer of 5-10 nm thickness was found for unprotected yttrium hydride
films.",1205.4132v1
2012-09-24,Microwave properties of Yttrium Vanadate at cryogenic temperatures,"Yttrium Vanadate (YVO4) is a birefringent crystal material used in optical
isolators and circulators with potentials for application in cryogenic
microwave devices. As microwave properties of the YVO4 are not known, we
measured the complex permittivity at the frequency of 25 GHz, using the
Hakki-Coleman dielectric resonator technique in the temperature range from 13 K
to 80 K. The real part of relative permittivity of YVO4 turned out to be
similar to that of Sapphire - one of popular dielectric materials, used at
microwave frequencies. The measured loss tangent tang {\delta} of the YVO4 was
of the order of 10^(-6) at cryogenic temperatures. As Yttrium Vanadate (YVO4)
is easy to synthesis and machine, it may replace the expensive Sapphire in some
microwave applications.",1209.5255v1
2014-05-02,Mott insulator-to-metal transition in yttrium-doped CaIrO3,"We report on the study of insulator-to-metal transition in post-perovskite
compound CaIrO3. It is discovered that a gradual chemical substitution of
calcium by yttrium leads to the onset of strong metallic behavior in this
compound. This observation is in stark contrast to BaIrO3, which preserves its
Mott insulating behavior despite excess of charge carriers due to yttrium
doping. Magnetic measurements reveal that both compounds tend to exhibit
magnetic character irrespective of the chemical substitution of Ca or Ba. We
analyze these unusual observations in light of recent researches that suggest
that unlike BaIrO3, CaIrO3 does not necessarily possess j = 1/2 ground state
due to structural distortion. The insulator-to-metal transition in CaIrO3 will
spur new researches to explore more exotic ground state, including
superconductivity, in post-perovskite Mott insulators.",1405.0512v2
2016-09-05,New insights into the photochromic mechanism in oxygen-containing yttrium hydride thin films: an optical perspective,"Oxygen-containing yttrium hydride thin films exhibit a photochromic behavior:
transparent thin films switch from a transparent state to a photodarkened state
after being illuminated with UV or blue light. This feature has attracted much
attention in recent years due to its potential applications in smart
fenestration or in any device in which a response to intense light radiation is
needed. However, the process responsible for the reversible change of the
optical properties upon illumination is still not well understood. The
objective of the present work is to shed some light on the photochromic
mechanism by using an optical approach. On this basis, the optical properties
of oxygen-containing yttrium hydride thin films have been studied by optical
spectrophotometry and ellipsometry before (transparent state) and after UV
illumination (dark state). According to the observed results, the photochromic
optical change of the films can be explained quantitatively by the gradual
growth, under illumination, of metallic phases within the initial wide-band gap
semiconducting lattice.",1609.01054v1
2016-10-26,Synthesis of photochromic oxygen-containing yttrium hydride,"Photochromic oxygen-containing yttrium hydride has been synthesized using a
two step process. The process consists of an initial sputter deposition of
oxygen-free yttrium hydride YH$_\mathrm{x}$, followed by a controlled reaction
with air that causes incorporation of oxygen into the material. An in-situ
study of the YH$_\mathrm{x}$ as it reacted with oxygen was made possible by
applying an aluminium capping layer with a low but non-zero oxygen permeability
prior to air exposure. During the reaction, the visual appearance of the
YH$_\mathrm{x}$ went from dark and opaque to transparent and yellowish. This
transition was accredited incorporation of oxygen into the material, as shown
through analysis with energy dispersive x-ray spectroscopy (EDS) and x-ray
photoemission spectroscopy (XPS). Grazing incidence x-ray diffraction (GIXRD)
studies revealed an fcc structure both before and after oxygen exposure, with a
lattice parameter that increased from 5.2 {\AA} to 5.4 {\AA} during the
reaction. With the lattice parameter in the oxygen free YH$_\mathrm{x}$ being
equal to that reported earlier for YH$_\mathrm{2}$, our findings suggest that
the non-reacted YH$_\mathrm{x}$ in this study is in-fact YH$_\mathrm{2}$.",1610.08263v1
2019-03-12,Light-induced breathing in photochromic yttrium oxy-hydrides,"When exposed to air, metallic yttrium dihydride YH2films turn into insulating
and transparent yttrium oxy-hydride (YHO). The incorporation of oxygen causes
the lattice expansion of YH2 and the emergence of photochromic properties.
However, the oxidation of YH2 is not completely irreversible: under
illumination some oxygen atoms move towards the YHO surface, leaving behind an
oxygen-deficient bulk (responsible for the photochromic darkening and observed
lattice contraction). Under illumination, and according to experimental
evidence, some oxygen atoms can effectively leave the film, being replaced by
other oxygen atoms once the illumination has stopped, i.e., YHO ""breathes"" when
subjected to illumination/darkness cycling. Based on this ""breathing"", YHO
films become more hydrophobic under illumination conditions than when kept in
darkness. Ab-initio calculations point to the light-induced weakening of the
Y-O bond as the possible mechanism for explaining these experimental
observations.",1903.05021v1
2019-08-28,Thermal surface neutralization of Fr ions with metal foils for magneto-optical trapping of radioisotopes,"We investigate neutralization processes (especially thermal surface
neutralization), which are required for the magneto-optical trapping of
radioactive atoms. A variety of neutralization methods are first summarized:
neutral beam injection for fusion reactors, neutral atom implantation in
semiconductor processing, and the production of radioactive neutral atoms in
accelerators. We focus on thermal surface neutralization, which produces
neutral atoms in the thermal energy range for laser cooling. The experiments
were carried out with yttrium, gadolinium, and zirconium foils to neutralize
francium and rubidium ions for magneto-optical trapping. The results reconfirm
that yttrium foil is a good neutralizer (i.e., it has a neutral release
efficiency $>65\%$). In addition, the release fraction when using yttrium foil
exceeds 75\% at 1350 K, which is greater than the release fraction for the
other foils. This reconfirmation is important because few previous studies have
focused on thermal surface neutralization. Moreover, the results show that the
neutralization efficiency is strongly influenced by the experimental process
itself.",1908.10698v1
2019-11-15,Yttrium Tantalum Oxynitride Multiphases as Photoanodes for Water Oxidation,"Perovskite yttrium tantalum oxynitride is theoretically proposed as a
promising semiconductor for solar water splitting because of the predicted
bandgap and energy positions of band edges. In experiment, however, we show
here that depending on processing parameters, yttrium tantalum oxynitrides
exist in multiphases, including the desired perovskite YTaON2, defect fluorite
YTa(O,N,o)4, and N-doped YTaO4. These multiphases have bandgaps ranging between
2.13 and 2.31 eV, all responsive to visible light. The N-doped YTaO4,
perovskite main phase, and fluorite main phase derived from crystalline
fergusonite oxide precursors exhibit interesting photoelectrochemical
performances for water oxidation, while the defect fluorite derived from low
crystallized scheelite-type oxide precursors show negligible activity.
Preliminarily measurements show that loading IrOx cocatalyst on N-doped YTaO4
significantly improves its photoelectrochemical performance encouraging further
studies to optimize this new material for solar fuel production.",1911.06550v1
2019-12-23,Characterization of near-room-temperature superconductivity in yttrium superhydrides,"Recently, Troyan et al (2019 arXiv:1908.01534) and Kong et al (2019
arXiv:1909.10482) extended near-room-temperature superconductors family by new
yttrium superhydride polymorphs, YHn (n = 4,6,7,9), which exhibit
superconducting transition temperatures in the range of Tc = 210-243 K at
pressure of P = 160-255 GPa. In this paper, temperature dependent upper
critical field data, Bc2(T), for highly-compressed mixture of YH4+YH6 phases
(reported by Kong et al 2019 arXiv:1909.10482) is analysed to deduce the ratio
of Tc to the Fermi temperature, Tf. Our analysis shows that in all considered
scenarios the YH4+YH6 mixture has the ratio 0.01 < Tc/Tf < 0.04. As the result,
YH4+YH6 falls in the unconventional superconductors band in the Uemura plot. It
is also found that the characteristic temperature of the order parameter
amplitude fluctuations, Tfluc, in the YH4+YH6 mixture is only several percent
above observed Tc, and thus the superconducting transition in yttrium
superhydride polymorphs is fundamentally limited by thermodynamics
fluctuations.",1912.10941v1
2021-05-30,Systematic studies of rubidium-exposed surfaces by X-ray photoelectron spectroscopy and light-induced atom desorption,"We systematically investigated various types of surfaces on which rubidium
(Rb) atoms were deposited by X-ray photoelectron spectroscopy (XPS) and
measured the light-induced atom desorption (LIAD) from those surfaces. The main
surfaces of interest included synthetic quartz, yttrium metal, and paraffin.
The Rb atoms deposited on quartz and yttrium surfaces by exposure to Rb vapor
at room temperature were detected by XPS. Quartz is originally silicon dioxide.
The yttrium surfaces were also oxidized, and Rb atoms reacted with oxygen on
both surfaces. Conversely, Rb deposition was observed only at low temperatures
on paraffin. Specifically, Rb atoms deposited on paraffin, which is not an
oxygen compound, also formed oxygen compounds under ultrahigh vacuum conditions
by reaction with the background gas. All examined surfaces showed a similar
light wavelength or photon energy dependence, such that the LIAD rates
increased with decreasing light wavelength. We presume that some types of
compounds of alkali metal and oxygen can be ubiquitous sources for LIAD from
many types of surfaces of alkali-metal vapor cells.",2105.14451v1
2021-11-18,Light outputs of yttrium doped BaF$_2$ crystals irradiated with neutrons,"The fast luminescence component of barium fluoride (BaF$_2$) crystals with a
subnanosecond decay time can find wide application in particle physics and
nuclear physics. However, the slow luminescence component with the 630~ns decay
time could cause pile-up signals at a high rate environment. Doping of BaF$_2$
crystals with rare earth elements suppresses the slow emission component, but
at the same time the radiation hardness of the crystals deteriorates. This work
presents the results of studying crystal samples, both pure BaF$_2$ and those
doped with yttrium in a proportion of 1at.\%Y, 3at.\%Y and 5at.\%Y, irradiated
with a fast neutron fluence of about 2.3$\times$10$^{14}$~n/cm$^2$. Their light
output and decay kinetics were measured before and after irradiation. It is
found that the light output loss of a pure BaF$_2$ crystal after irradiation is
about 7\%, and the light output loss of yttrium doped samples after irradiation
is about two times higher. The measurement results demonstrate that after
irradiation the fast component of each sample has a relative light output loss
2-3\% larger than the slow one.",2111.09672v1
2023-01-28,"Structure and Dynamics of a Lattice of Tetragonal Germanates R2Ge2O7 (R = Tb-Lu, Y): Ab Initio Calculation","The crystal structure, phonon spectrum, and elastic constants of a series of
rare-earth germanates (including yttrium germanate R2Ge2O7 (R = Tb-Lu, Y)) with
a tetragonal structure have been ab initio calculated within the density
functional theory. The frequencies and types of fundamental vibrations and the
intensities of IR and Raman modes are determined. The degrees of participation
of ions in each mode are determined by analyzing the displacement vectors
obtained as a result of the ab initio calculations. The calculations have been
performed for the first time; there are no corresponding experimental data for
the entire series of compounds (except for the IR and Raman spectra of yttrium
germanate). The performed calculations made it possible to interpret and
supplement the known data in the literature on IR and Raman spectra of yttrium
germanate Y2Ge2O7.",2301.12196v1
2008-01-26,Magnetoelectric Control of Domain Walls in a Ferrite Garnet Film,"The effect of magnetic domain boundaries displacement induced by electric
field is observed in epitaxial ferrite garnet films (on substrates with the
(210) crystallographic orientation). The effect is odd with respect to the
electric field (the direction of wall displacement changes with the polarity of
the voltage) and even with respect to the magnetization in domains. The
inhomogeneous magnetoelectric interaction as a possible mechanism of the effect
is proposed.",0801.4073v1
2018-02-02,Separated quotients of Picard schemes,"We give some necessary and sufficient conditions for the existence of
N\'{e}ron models of jacobians of semistable morphisms of arbitrary relative
dimension over base schemes of arbitrary dimension. To do this, we introduce a
notion of alignment for semistable morphisms over any regular base scheme, and
show that the jacobian of an aligned projective semistable morphism admits a
separated model with the N\'{e}ron mapping property. When the Picard scheme is
smooth over the base scheme along its unit section we show that the converse
holds.",1802.00618v2
2018-06-14,Garnet Ring Measurements For The Fermilab Booster 2nd Harmonic Cavity,"A perpendicularly biased tuneable 2nd harmonic cavity is being constructed
for use in the Fermilab Booster. The cavity's tuner uses National Magnetics
AL800 garnet as the tuning media. For quality control, the magnetic properties
of the material and the uniformity of the properties within the tuner must be
assessed. We describe two tests which are performed on the rings and on their
corresponding witness samples.",1806.05716v1
2020-10-29,Miniature Annular Permanent Magnet Assembly with Fast Far Field Decay and Majority Collimated Central Field,"We report on a 3/8"" OD x 1/4"" ID x 3/8"" long NdFeB assembly of 1/16"" thick
annulars boasting half the 1/100 far field transverse decay distance compared
to an ID Helholtz-spaced pair of similar annulars; and greater than 50% of ID
collimated better than 1/1000. The device is applied to a He-3,-4 laser
spectroscopy experiment.",2011.02558v2
2021-01-10,Innovative Low Cost Laboratory Automation Environment and LabVIEW Reformation Application Case Study,"In recognition of the catalytic role of instruments, we report on an
original, low-cost, robust, LabVIEW-based automation development environment
configuration and application to reformation of a legacy laser atomic
spectroscopy system. Open source, version and configuration control, full
back-up, and remote/distributed capability characteristics make the new
environment 500% better. System reformation using reusable type definitions,
functional encapsulation, increased modularization, and polymorphism boosted
performance 983%. Both the environment configuration and reformation strategies
are transferrable to most endeavors.",2101.03637v1
2001-09-19,The Feynman Propagator from a Single Path,"We show that it is possible to construct the Feynman Propagator in one
dimension, without quantization, from a single continuous space-time path.",0109092v2
1999-07-06,Dipolar random field Ising model: an application to garnet films,"The dipolar-random field Ising model (DRFIM) recently introduced displays a
behaviour that can be connected to the magnetization of bidimensional magnetic
media. Epitaxial magnetic garnet films seem to be the ideal test material for
such a model. In this work the results of the measurements performed on garnet
samples are presented, as well as the comparisons with simulation results
obtained by the DRFIM. The results prove that a variety of hysteresis loops are
well described by the DRFIM. This capability does not derive from the fine
tuning of a great number of parameters, but by the interplay of exchange and
dipolar interactions.",9907075v1
2000-10-05,Classical Heisenberg antiferromagnet on a garnet lattice: a Monte Carlo simulation,"We have studied a classical antiferromagnet on a garnet lattice by means of
Monte Carlo simulations in an attempt to examine the role of geometrical
frustration in Gadolinium Gallium Garnet, Gd3Ga5O12 (GGG). Low-temperature
specific heat, magnetisation, susceptibility, the autocorrelation function A(t)
and the neutron scattering function S(Q) have been calculated for several
models including different types of magnetic interactions and with the presence
of an external magnetic field applied along the principal symmetry axes. A
model, which includes only nearest-neighbour exchange, J1, neither orders down
to the lowest temperature nor does it show any tendency towards forming a
short-range coplanar spin structure. This model, however, does demonstrate a
magnetic field induced ordering below T ~ 0.01 J1. In order to reproduce the
experimentally observed properties of GGG, the simulated model must include
nearest neighbour exchange interactions and also dipolar forces. The presence
of weak next-to-nearest exchange interactions is found to be insignificant. In
zero field S(Q) exhibits diffuse magnetic scattering around positions in
reciprocal space where antiferromagnetic Bragg peaks appear in an applied
magnetic field.",0010088v1
2006-07-03,Interaction between superconducting vortices and Bloch wall in ferrite garnet film,"Interaction between a Bloch wall in a ferrite-garnet film and a vortex in a
superconductor is analyzed in the London approximation. Equilibrium
distribution of vortices formed around the Bloch wall is calculated. The
results agree quantitatively with magneto-optical experiment where an in-plane
magnetized ferrite-garnet film placed on top of NbSe2 superconductor allows
observation of individual vortices. In particular, our model can reproduce a
counter-intuitive attraction observed between vortices and a Bloch wall having
the opposite polarity. It is explained by magnetic charges appearing due to
discontinuity of the in-plane magnetization across the wall.",0607043v2
2017-12-05,Deep Neural Networks for Accurate Predictions of Garnet Stability,"Predicting the stability of crystals is one of the central problems in
materials science. Today, density functional theory (DFT) calculations are the
computational tool of choice to obtain energies of crystals with quantitative
accuracy. Despite algorithmic and computing advances, DFT calculations remain
comparatively expensive and scale poorly with system size. Here we show that
deep neural networks utilizing just two descriptors - the Pauling
electronegativity and ionic radii - can predict the DFT formation energies of
C3A2D3O12 garnets with extremely low mean absolute errors of 7-8 meV/atom, an
order of magnitude improvement over previous machine learning models and well
within the limits of DFT accuracy. Further extension to mixed garnets with
little loss in accuracy can be achieved using a binary encoding scheme that
introduces minimal increase in descriptor dimensionality. Our results
demonstrate that generalizable deep-learning models for quantitative crystal
stability prediction can be built on a small set of chemically-intuitive
descriptors. Such models provide the means to rapidly transverse vast chemical
spaces to accurately identify stable compositions, accelerating the discovery
of novel materials with potentially superior properties.",1712.01908v1
2021-12-23,"Steam Degradation of Ytterbium Disilicate Environmental Barrier Coatings: Effect of Composition, Microstructure and Temperature","Recession of environmental barrier coatings (EBC) in environments containing
steam is a pressing concern that requires further research before their
implementation in gas turbine engines can be realized. In this work,
free-standing plasma sprayed Yb2Si2O7 coatings were exposed to flowing steam at
1350 {\deg}C and 1400 {\deg}C for 96 h. Three samples were investigated, one
coating with a low porosity level (< 3 %) and 1 wt.% Al2O3 representing
traditional EBCs; and two coatings with higher porosity levels (~20 %)
representing abradable EBCs. Phase composition and microstructural evolution
were studied in order to reveal the underlying mechanism for the interaction
between high temperature steam and ytterbium disilicate. The results show
depletion of Yb2SiO5 near the surface and formation of ytterbium garnet
(Yb3Al5O12) on top of all three coatings due to the reaction with gaseous
Al-containing impurities coming from the alumina furnace tubes. The 1 wt.%
Al2O3 added to the EBC sample exacerbated the formation of garnet at 1400
{\deg}C compared to the abradable samples, which presented lower quantities of
garnet. Additionally, inter-splat boundaries were visible after exposure,
indicating preferential ingress of gaseous Al-containing impurities through the
splat boundaries",2201.04939v1
2022-07-18,An Ab-initio study of the Y decorated 2D holey graphyne for hydrogen storage application,"Expanding pollution and rapid consumption of natural reservoirs (gas, oil,
and coal) led humankind to explore alternative energy fuels like hydrogen fuel.
Solid-state hydrogen storage is most desirable because of its usefulness in the
onboard vehicle. In this work, we explored the yttrium decorated ultra porous,
two-dimensional holey-graphyne for hydrogen storage. Using the first principles
DFT simulations, we predict that yttrium doped holey graphyne can adsorb up to
seven hydrogen molecules per yttrium atom resulting in a gravimetric hydrogen
weight percentage of 9.34, higher than the target of 6.5 wt% set by the US
Department of Energy (DoE). The average binding energy per H$_2$ and desorption
temperature come out to be -0.34 eV and ~ 438 K, respectively. Yttrium atom is
bonded strongly on HGY sheet due to charge transfer from Y 4d orbital to C 2p
orbital whereas the adsorption of H$_2$ molecule on Y is due to Kubas-type
interactions involving charge donation from H 1s orbital to Y 3d orbital and
back donation with net charge gain by H 1s orbital. Furthermore, sufficient
energy barriers for metal atom diffusion have been found to prevent the
clustering of transition metal (yttrium) on the HGY sheet. The stability of the
system at higher temperatures is analyzed using Ab-initio molecular dynamics
(AIMD) method and the system is found to be stable at room and the highest
desorption temperature. Stability of the system at higher temperatures,
presence of adequate diffusion energy barrier to prevent metal-metal
clustering, high gravimetric wt% of H$_2$ uptake with suitable binding energy,
and desorption temperature signifies that Y-doped HGY is a promising material
to fabricate high capacity hydrogen storage devices.",2207.08546v1
2010-11-09,First-principles modeling of the interactions of iron impurities with graphene and graphite,"Results of first principles modelling of interactions graphene and graphite
with iron impurities predict the colossal difference between these two carbon
allotropes. Insertion of the iron atoms between the planes of graphite is much
more energetically favourable than adsorption of the iron adatom at graphite or
graphene surface. High mobility of iron adatom over graphite surface and within
bulk graphite is reported. Calculated values of formation energies for the
substitutional iron impurities suggest that iron is more destructive for
graphite than for graphene. This effect caused formation of uniform carbon
environment of the iron atom inside the multilayer system. In contrast to
graphene segregation of the substitutional iron impurities in graphite at the
ambient conditions is not energetically favourable. Enhancement of interlayer
bonding in contaminated graphite and purity of graphene from iron impurities
are also reported.",1011.1950v1
2020-03-27,The Chemical Evolution of Galaxy Clusters: Dissecting the Iron Mass Budget of the Intracluster Medium,"We study the chemical evolution of galaxy clusters by measuring the iron mass
in the ICM after dissecting the abundance profiles into different components.
We use Chandra archival observations of 186 morphologically regular clusters in
the redshift range [0.04, 1.07]. For each cluster we compute the iron abundance
and gas density profiles. We aim at identifying in the iron distribution a
central peak associated with the BCG, and an approximately constant plateau
associated with early enrichment. We are able to firmly identify the two
components in a significant fraction of the sample, simply relying on the fit
of the abundance profile. We compute the iron mass included in the iron peak
and plateau, and the gas mass-weighted iron abundance out to $r_{500}$. While
the iron plateau shows no evolution, we find marginal decrease with redshift in
the iron peak. We measure that the fraction of iron peak mass is typically a
few percent (~1%) of the total iron mass within $r_{500}$. Therefore, since the
total iron mass budget is dominated by the plateau, we find consistently that
the global gas mass-weighted iron abundance does not evolve significantly. We
are also able to reproduce past claims of evolution in the global iron
abundance, which turn out to be due to the use of cluster samples with
different selection methods combined to the use of emission-weighted instead of
gas mass-weighted abundance values. Finally, while the intrinsic scatter in the
iron plateau mass is consistent with zero, the iron peak mass exhibits a large
scatter, in line with the fact that the peak is produced after the
virialization of the halo and depends on the formation of the hosting cool core
and the associated feedback processes. We conclude that only a
spatially-resolved approach can resolve the issue of the ICM iron evolution,
reconciling the contradictory results obtained in the last ten years.",2003.12426v2
2006-09-15,Fluorescence from metallic silver and iron nanoparticles prepared by exploding wire technique,"The observation of intense visible fluorescence from silver and iron
nanoparticles in different solution phases and surface capping is reported
here. Metallic silver and iron nanoparticles were obtained by exploding pure
silver and iron wires in pure water. Bovine serum albumin protein adsorption on
the silver nanoparticles showed an enhanced fluorescence. The presence of
poly-vinyl pyrrolidone polymer in the exploding medium resulted in a stabilized
growth of iron nanoparticles with enhanced fluorescence intensity. The
fluorescence was found to be surface /interface dependant. The fluorescence is
attributed to electronic transitions among characteristic interface energy
bands. The magnetic nature of iron nanoparticles was confirmed from the
hysteresis measurements.",0609369v1
2011-11-24,IrOnIc: How to Consider Hundreds of Millions of Iron-Group Lines in NLTE Model-Atmosphere Calculations,"Iron-group elements have a very high number of atomic levels and an
overwhelming number of spectral lines. No NLTE model-atmosphere code can cope
with these in a classical way. A statistical approach was developed over the
last decade to decrease the number of levels and lines to a manageable amount.
The Iron Opacity and Interface (IrOnIc) calculates sampled cross-sections and
model-atom files as input for model-atmosphere computations. IrOnIc is
presently transferred into a parallelized code to reduce the calculation time
to a reasonable value. It will be accessible by the public as a service of the
German Astrophysical Virtual Observatory.",1111.5740v1
2014-04-30,Superconducting Gaps via Raman Scattering in Iron Superconductors,"We investigate non-resonant Raman response for iron-based superconductors
using the framework of an effective S4 model that was recently proposed to
capture the essential electronic and magnetic properties of Iron based
superconductors. We compute the momentum matrix elements and the resulting
Raman vertices exactly for different polarization geometries and amazingly find
that a simple coskxcosky superconducting gap function is in good agreement with
experimental data measured in both iron-pnictides and iron-chalcogenides. The
Raman peaks are also matched quantitatively with the measured superconducting
gaps by other experimental techniques. The result strengthens the validity of
the S4 model and the dominance of the s-wave pairing for iron-based
superconductors.",1404.7745v1
2024-03-26,Suzaku observation of an iron K-shell line in the spiral galaxy NGC 6946,"An emission line at ~6.7 keV is attributable to a He-like iron K-shell
transition, which indicates existence of a thin thermal plasma with a
temperature of several keV. Using Suzaku archival data, we searched for the
iron K-line from the spiral galaxy NGC 6946, and found the iron K-line at
6.68+/-0.07 keV at the 3.1 sigma level in the central r<2.'5 region. The iron
line luminosity from the central region was estimated to be (2.3+/-1.2)x10^{37}
erg s^{-1} at a distance of 5.5 Mpc. The origin of the iron emission line is
discussed.",2403.17300v1
2013-08-27,A Computational Model of Liver Iron Metabolism,"Iron is essential for all known life due to its redox properties, however
these same properties can also lead to its toxicity in overload through the
production of reactive oxygen species. Robust systemic and cellular control are
required to maintain safe levels of iron and the liver seems to be where this
regulation is mainly located. Iron misregulation is implicated in many diseases
and as our understanding of iron metabolism improves the list of iron-related
disorders grows. Recent developments have resulted in greater knowledge of the
fate of iron in the body and have led to a detailed map of its metabolism,
however a quantitative understanding at the systems level of how its components
interact to produce tight regulation remains elusive.
  A mechanistic computational model of human liver iron metabolism, which
includes the core regulatory components, was constructed based on known
mechanisms of regulation and on their kinetic properties, obtained from several
publications. The model was then quantitatively validated by comparing its
results with previously published physiological data, and it is able to
reproduce multiple experimental findings. A time course simulation following an
oral dose of iron was compared to a clinical time course study and the
simulation was found to recreate the dynamics and time scale of the systems
response to iron challenge. A disease simulation of haemochromatosis was
created by altering a single reaction parameter that mimics a human
haemochromatosis gene (HFE) mutation. The simulation provides a quantitative
understanding of the liver iron overload that arises in this disease.
  This model supports and supplements understanding of the role of the liver as
an iron sensor and provides a framework for further modelling, including
simulations to identify valuable drug targets and design of experiments to
improve further our knowledge of this system.",1308.5826v1
2016-11-25,Thermodynamics and Charging of Interstellar Iron Nanoparticles,"Interstellar iron in the form of metallic iron nanoparticles may constitute a
component of the interstellar dust. We compute the stability of iron
nanoparticles to sublimation in the interstellar radiation field, finding that
iron clusters can persist down to a radius of $\simeq 4.5\,$\AA, and perhaps
smaller. We employ laboratory data on small iron clusters to compute the
photoelectric yields as a function of grain size and the resulting grain charge
distribution in various interstellar environments, finding that iron
nanoparticles can acquire negative charges particularly in regions with high
gas temperatures and ionization fractions. If $\gtrsim 10\%$ of the
interstellar iron is in the form of ultrasmall iron clusters, the photoelectric
heating rate from dust may be increased by up to tens of percent relative to
dust models with only carbonaceous and silicate grains.",1611.08607v1
2021-05-12,Iron-silica interaction during reduction of precipitated silica-promoted iron oxides using in situ XRD and TEM,"The effect of silica-promotion on the reduction of iron oxides in hydrogen
was investigated using in situ X-ray diffraction and aberration-corrected
transmission electron microscopy to understand the mechanism of reduction and
the identity of the iron(II) silicate phase that has historically been
designated as the cause of the iron-silica interaction in such materials. In
the absence of a silica promoter the reduction of hematite to {\alpha}-Fe
proceeds via magnetite. Silica promoted amorphous iron oxide is reduced to
{\alpha}-Fe via stable magnetite and w\""ustite phases. During reduction of
silica-promoted iron oxide, Fe0 diffuses out of the amorphous silica-promoted
iron oxide matrix upon reduction from Fe2+ and coexists with an amorphous
Fe-O-Si matrix. Certain portions of w\""ustite remain difficult to reduce to
{\alpha}-Fe owing to the formation of a protective silica-containing layer
covering the remaining iron oxide regions. Given sufficient energy, this
amorphous Fe-O-Si material forms ordered, crystalline fayalite.",2105.05620v1
2008-08-01,Measurement of diffusion coefficients of francium and rubidium in yttrium based on laser spectroscopy,"We report the first measurement of the diffusion coefficients of francium and
rubidium ions implanted in a yttrium foil. We developed a methodology, based on
laser spectroscopy, which can be applied to radioactive and stable species, and
allows us to directly take record of the diffusion time. Francium isotopes are
produced via fusion-evaporation nuclear reaction of a 100 MeV 18-O beam on a Au
target at the Tandem XTU accelerator facility in Legnaro, Italy. Francium is
ionized at the gold-vacuum interface and Fr+ ions are then transported with a 3
keV electrostatic beamline to a cell for neutralization and capture in a
magneto-optical trap (MOT). A Rb+ beam is also available, which follows the
same path as Fr+ ions. The accelerated ions are focused and implanted in a 25
um thick yttrium foil for neutralization: after diffusion to the surface, they
are released as neutrals, since the Y work function is lower than the alkali
ionization energies. The time evolution of the MOT and the vapor fluorescence
signals are used to determine diffusion times of Fr and Rb in Y as a function
of temperature.",0808.0152v1
2019-04-15,Crystal field coefficients for yttrium analogues of rare-earth/transition-metal magnets using density-functional theory in the projector-augmented wave formalism,"We present a method of calculating crystal field coefficients of
rare-earth/transition-metal (RE-TM) magnets within density-functional theory
(DFT). The principal idea of the method is to calculate the crystal field
potential of the yttrium analogue (""Y-analogue"") of the RE-TM magnet, i.e. the
material where the lanthanide elements have been substituted with yttrium. The
advantage of dealing with Y-analogues is that the methodological and conceptual
difficulties associated with treating the highly-localized 4f electrons in DFT
are avoided, whilst the nominal valence electronic structure principally
responsible for the crystal field is preserved. In order to correctly describe
the crystal field potential in the core region of the atoms we use the
projector-augmented wave formalism of DFT, which allows the reconstruction of
the full charge density and electrostatic potential. The Y-analogue crystal
field potentials are combined with radial 4f charge densities obtained in
self-interaction-corrected calculations on the lanthanides to obtain crystal
field coefficients. We demonstrate our method on a test set of 10 materials
comprising 9 RE-TM magnets and elemental Tb. We show that the calculated easy
directions of magnetization agree with experimental observations, including a
correct description of the anisotropy within the basal plane of Tb and
NdCo$_5$. We further show that the Y-analogue calculations generally agree
quantitatively with previous calculations using the open-core approximation to
treat the 4f electrons, and argue that our simple approach may be useful for
large-scale computational screening of new magnetic materials.",1904.06896v1
2001-08-17,Magnetic polarons in Ca_(1-x)Y_xMnO_3,"Experimental evidence show that in the magnetoresistive manganite Ca_(1-x)
Y_xMnO_3, ferromagnetic (FM) polarons arises in an antiferromagnetic (AF)
background, as a result of the doping with Yttrium. This hypothesis is
supported in this work by classical Monte Carlo (MC) calculations performed on
a model where FM Double Exchange (DE) and AF Superexhange (SE) compite.",0108284v1
2005-11-15,A Simple Model for Simple Aging in Glassy Yttrium-Hydrides,"A simple explanation for the logarithmic aging of the photoconductivity in
yttriumhydride is proposed. We show that the scaling (``simple'' aging) of the
relaxation response with the illumination time t_w is consistent with the
superposition of independently relaxing excitations with time offsets
distributed over a window of width t_w.",0511383v1
2008-05-28,Nernst effect of epitaxial YBCO films doped with Ca and Zn,"We report Nernst effect measurements for some crystalline films of Ca and
Zn-doped yttrium barium copper oxide grown by pulsed laser deposition. We argue
that our results and most of the published data for LSCO are consistent with
the theory of Gaussian superconducting fluctuations.",0805.4293v1
2016-06-12,The green light generation by self-frequency-doubled Yb:YCOB crystal,"Taking advantages of the broad emission bands of a Yb3+ doped calcium yttrium
oxoborate (Yb:YCOB) crystal cut along the optimized direction out of principle
planes with the maximum effective nonlinear coefficient, the
self-frequency-doubled green light based on the self-frequency-doubling
behavior of Yb:YCOB was achieved with a maximum output power of 710 mW at 523
nm.",1606.03678v1
2020-12-08,Superconductivity at 253 K in lanthanum-yttrium ternary hydrides,"Polyhydrides offer intriguing perspectives as high-temperature
superconductors. Here we report the high-pressure synthesis of a series of
lanthanum-yttrium ternary hydrides: cubic hexahydride $(La,Y)H_{6}$ with a
critical temperature $T_{C}$ = 237 +/- 5 K and decahydrides $(La,Y)H_{10}$ with
a maximum $T_{C}$ ~${253 K}$ and an extrapolated upper critical magnetic field
$B_{C2(0)}$ up to ${135 T}$ at 183 GPa. This is one of the first examples of
ternary high-$T_{C}$ superconducting hydrides. Our experiments show that a part
of the atoms in the structures of recently discovered ${Im3m}$-$YH_{6}$ and
${Fm3m}$-$LaH_{10}$ can be replaced with lanthanum (~70 %) and yttrium (~25 %),
respectively, with a formation of unique ternary superhydrides containing
incorporated $La@H_{24}$ and $Y@H_{32}$ which are specific for
${Im3m}$-$LaH_{6}$ and ${Fm3m}$-$YH_{10}$. Ternary La-Y hydrides were obtained
at pressures of 170-196 GPa via the laser heating of $P6_{3}$${/mmc}$
lanthanum-yttrium alloys in the ammonia borane medium at temperatures above
2000 K. A novel tetragonal $(La,Y)H_{4}$ was discovered as an impurity phase in
synthesized cubic $(La,Y)H_{6}$. The current-voltage measurements show that the
critical current density $J_{C}$ in $(La,Y)H_{10}$ may exceed $2500 A/mm^{2}$
at 4.2 K, which is comparable with that for commercial superconducting wires
such as ${NbTi}$, $Nb_{3}$${Sn}$. Hydrides that are unstable in a pure form may
nevertheless be stabilized at relatively low pressures in solid solutions with
superhydrides having the same structure.",2012.04787v1
2017-07-03,Lattice-Geometry Effects in Garnet Solid Electrolytes: A Lattice-Gas Monte Carlo Simulation Study,"Ionic transport in solid electrolytes can often be approximated as ions
performing a sequence of hops between distinct lattice sites. If these hops are
uncorrelated, quantitative relationships can be derived that connect
microscopic hopping rates to macroscopic transport coefficients. At non-dilute
concentrations the relationships between hopping frequency, diffusion
coefficient, and ionic conductivity deviate from the random walk case, with
this deviation quantified by single-particle and collective correlation
factors, $f$ and $f_\mathrm{I}$. These factors vary between materials, and
depend on the concentration of mobile particles, the nature of the
interactions, and the host lattice geometry. Here we study these correlation
effects for the garnet lattice using lattice-gas Monte Carlo simulations. We
find that for non-interacting particles (volume exclusion only) single-particle
correlation effects are more significant than for any previously studied
three-dimensional lattice. This is attributed to the presence of two-coordinate
lattice sites, which causes correlation effects intermediate between typical
three-dimensional and one-dimensional lattices. Including nearest-neighbour
repulsion and on-site energies produces more complex single-particle
correlations and introduces collective correlations. We predict particularly
strong correlation effects at $x_\mathrm{Li}=3$ (from site energies) and
$x_\mathrm{Li}=6$ (from nearest-neighbour repulsion). Both effects are
consequences of ordering of the mobile particles. Using these simulation data,
we consider tuning the mobile ion stoichiometry to maximise the ionic
conductivity, and show that the ""optimal"" composition is highly sensitive to
the precise nature and strength of the microscopic interactions. Finally, we
discuss the practical implications of these results in the context of lithium
garnets and other solid electrolytes.",1707.00491v2
2018-01-09,Absence of magnetic ordering and field induced phase diagram in the Gadolinium Aluminium garnet,"The robustness of spin liquids with respect to small perturbations, and the
way magnetic frustration can be lifted by slight changes in the balance between
competing magnetic interactions remains a rich and open issue. We address this
question through the study of the Gadolinium Aluminium garnet
Gd$_3$Al$_5$O$_{12}$, a related compound to the extensively studied
Gd$_3$Ga$_5$O$_{12}$. We report on its magnetic properties at very low
temperature. We show that despite a freezing at about 300 mK, no magnetic
transition is observed, suggesting the presence of a spin liquid state down to
the lowest temperatures similarly to Gd$_3$Ga$_5$O$_{12}$, in spite of a larger
ratio between exchange and dipolar interactions. Finally, the phase diagram as
a function of field and temperature is strongly reminiscent from the one
reported in Gd$_3$Ga$_5$O$_{12}$. This study reveals the robust nature of the
spin liquid phase for Gd ions on the garnet lattice in stark contrast to Gd
ions on the pyrochlore lattice for which a slight perturbation drives the
compound into a range of magnetically ordered states.",1801.02836v1
2019-05-09,Crystal fields and magnetic structure of the Ising antiferromagnet Er$_3$Ga$_5$O$_{12}$,"Rare earth garnets are an exciting playground for studying the exotic
magnetic properties of the frustrated hyperkagome lattice. Here we present a
comprehensive study of the single ion and collective magnetic properties of the
garnet Er$_3$Ga$_5$O$_{12}$. Using inelastic neutron scattering, we find a
crystal field ground state doublet for Er$^{3+}$ with strong Ising anisotropy
along local [100] axes. Magnetic susceptibility and heat capacity measurements
provide evidence for long-range magnetic ordering with $T_N$~$=$~0.8~K, and no
evidence for residual entropy is found when cooling through the ordering
transition. Neutron powder diffraction reveals that the ground state spin
configuration corresponds to the six-sublattice, Ising antiferromagnetic state
($\Gamma_3$) common to many of the rare earth garnets. However, we also found
that $\mu$SR appears to be insensitive to the ordering transition in this
material, in which a low-temperature relaxation plateau was observed with no
evidence of spontaneous muon precession. The combined muon and neutron results
may be indicative of a dynamical ground state with a relatively long
correlation time. Despite this potential complication, our work indicates that
Er$_3$Ga$_5$O$_{12}$ is an excellent model system for studying the complex
metamagnetism expected for a multi-axis antiferromagnet.",1905.03687v2
2023-04-27,"Modeling diffusion in ionic, crystalline solids with internal stress gradients","Intracrystalline diffusion is an invaluable tool for estimating timescales of
geological events. Diffusion is typically modeled using gradients in chemical
potential. However, chemical potential is derived for uniform pressure and
temperature conditions and therefore cannot be used to model diffusion when
there are gradients in stress. Internal stress variations in minerals create
gradients in strain energy which will drive diffusion. Consequently, it is
necessary to have a method that incorporates stress variations into diffusion
models. We derive a flux expression that allows diffusion to be modeled in
ionic, crystalline solids under arbitrary stress states. Our derivation
utilizes gradients in a thermodynamic potential called relative chemical
potential which quantifies changes in free energy due to the exchanges of
constituents on lattice sites under arbitrary stress conditions. We apply our
derivation to the common quaternary garnet solid solution
almandine-pyrope-grossular-spessartine. The rates and directions of divalent
cation diffusion in response to stress are determined by endmember molar volume
or lattice parameters, elastic moduli, and non-ideal activity interaction
parameters. Our results predict that internal stress variations of one hundred
MPa or more are required to shift garnet compositions by at least a few
hundredths of a mole fraction. Mineral inclusions in garnet present a potential
environment to test and apply our stress-driven diffusion approach, as stress
variations ranging from hundreds of MPa to GPa-level are observed or predicted
around such inclusions. The ability to model stress-induced diffusion may
provide new information about the magnitudes of both intracrystalline stresses
and the timescales during which they occurred, imparting a better understanding
of large-scale tectono-metamorphic processes.",2304.14330v2
2018-08-21,Spatial Distribution of Metals in the ICM: Evolution of the Iron Excess in Relaxed Galaxy Clusters,"We investigate the spatial distribution of iron in the intra-cluster medium
in a selected sample of 41 relaxed clusters in the redshift range $0.05 < z <
1.03$ using {\sl Chandra} archival data. We compute the azimuthally-averaged,
deprojected $Z_{\rm Fe}$ profile of each cluster out to $\sim 0.4r_{500}$, and
identify a peak in the distribution of iron followed by a flatter distribution
at larger radii. Due to the steep gradient both in gas density and abundance,
we find that the emission-weighted iron abundance within $0.2r_{500}$, which
entirely includes the iron peak in most of the cases, is on average $\sim$25\%
higher than the mass-weighted value, showing that spatially resolved analysis
and accurate deprojection are key to study the evolution of iron enrichment in
the very central regions of cool core clusters. We quantify the extent of the
iron distribution in each cluster with a normalized scale parameter $r_{\rm
Fe}$, defined as the radius where the iron abundance excess is half of its peak
value. We find that $r_{\rm Fe}$ increases by a factor of $\sim 3$ from $z\sim
1$ to $z\sim 0.1$, suggesting that the spatial distribution of iron in the ICM
extends with time, possibly due to the mixing with the mechanical-mode feedback
from the central galaxy. We also find that the iron mass excess within
$0.3r_{500}$, when normalized to the total baryonic mass within the same
region, does not evolve significantly, showing that this iron mass component is
already established at $z\sim 1$.",1808.06742v1
2023-09-05,"Isotopic constraints on genetic relationships among group IIIF iron meteorites, Fitzwater Pass, and the Zinder pallasite","Complex interelement trends among magmatic IIIF iron meteorites are difficult
to explain by fractional crystallization and have raised uncertainty about
their genetic relationships. Nucleosynthetic Mo isotope anomalies provide a
powerful tool to assess if individual IIIF irons are related to each other.
However, while trace-element data are available for all nine IIIF irons, Mo
isotopic data are limited to three samples. We present Mo isotopic data for all
but one IIIF irons that help assess the genetic relationships among these
irons, together with new Mo and W isotopic data for Fitzwater Pass (classified
IIIF), and the Zinder pallasite (for which a cogenetic link with IIIF irons has
been proposed). After correction for cosmic-ray exposure, the Mo isotopic
compositions of the IIIF irons are identical within uncertainty and confirm
their belonging to carbonaceous chondrite-type (CC) meteorites. The mean Mo
isotopic composition of Group IIIF overlaps those Groups IIF and IID, but a
common parent body for these groups is ruled out based on distinct trace
element systematics. The new Mo isotopic data do not argue against a single
parent body for the IIIF irons, and suggest a close genetic link among these
samples. By contrast, Fitzwater Pass has distinct Mo and W isotopic
compositions, identical to those of some non-magmatic IAB irons. The Mo and W
isotope data for Zinder indicate that this meteorite is not related to IIIF
irons, but belongs to the non-carbonaceous (NC) type and has the same Mo and W
isotopic composition as main-group pallasites.",2309.02518v1
1998-03-21,Interfaces of Modulated Phases,"Numerically minimizing a continuous free-energy functional which yields
several modulated phases, we obtain the order-parameter profiles and
interfacial free energies of symmetric and non-symmetric tilt boundaries within
the lamellar phase, and of interfaces between coexisting lamellar, hexagonal,
and disordered phases. Our findings agree well with chevron, omega, and
T-junction tilt-boundary morphologies observed in diblock copolymers and
magnetic garnet films.",9803260v1
2002-06-03,The Dirac Equation in Classical Statistical Mechanics,"The Dirac equation, usually obtained by `quantizing' a classical stochastic
model is here obtained directly within classical statistical mechanics. The
special underlying space-time geometry of the random walk replaces the missing
analytic continuation, making the model `self-quantizing'. This provides a new
context for the Dirac equation, distinct from its usual context in relativistic
quantum mechanics.",0206016v1
2002-06-14,Entwined Pairs and Schroedinger 's Equation,"We show that a point particle moving in space-time on entwined-pair paths
generates Schroedinger's equation in a static potential in the appropriate
continuum linit. This provides a new realist context for the Schroedinger
equation within the domain of classical stochastic processes. It also suggests
that self-quantizing systems may provide considerable insight into conventional
quantum mechanics.",0206095v1
2017-07-22,Gaussian and plane-wave mixed density fitting for periodic systems,"We introduce a mixed density fitting scheme that uses both a Gaussian and a
plane-wave fitting basis to accurately evaluate electron repulsion integrals in
crystalline systems. We use this scheme to enable efficient all-electron
Gaussian based periodic density functional and Hartree-Fock calculations.",1707.07114v1
2018-03-27,An efficient stochastic algorithm for the perturbative density matrix renormalization group in large active spaces,"We present an efficient stochastic algorithm for the recently introduced
perturbative density matrix renormalization group (p-DMRG) method for large
active spaces. The stochastic implementation bypasses the computational
bottleneck involved in solving the first order equation in the earlier
deterministic algorithm. We demonstrate the efficiency and accuracy of the
algorithm on the C$_2$ and Cr$_2$ molecular benchmark systems.",1803.09943v1
2018-03-27,Density Matrix Embedding Theory and Strongly Correlated Lattice Systems,"This thesis describes the development of the density matrix embedding theory
(DMET) and its applications to lattice strongly correlated electron problems,
including a review of DMET theory and algorithms (Ch 2), investigation of
finite size scaling (Ch 3), Applications to high-temperature superconductivity
(Ch 4-6), a framework for finite-temperature DMET (Ch 7).",1803.10259v1
2008-05-30,A brief comment on the chemical formulae of the rare earth iron arsenide oxide superconductors,"Just a brief comment on the chemical formulae of the rare earth iron arsenide
oxide superconductors",0805.4668v1
2010-11-08,Magnetoelastic Effects in Iron Telluride,"Iron telluride doped lightly with selenium is known to undergo a first order
magneto-structural transition before turning superconducting at higher doping.
We study the effects of magneto-elastic couplings on this transition using
symmetry considerations. We find that the magnetic order parameters are coupled
to the uniform monoclinic strain of the unit cell with one iron per cell, as
well as to the phonons at high symmetry points of the Brillouin zone. In the
magnetic phase the former gives rise to monoclinic distortion while the latter
induces dimerization of the ferromagnetic iron chains due to alternate
lengthening and shortening of the nearest-neighbour iron-iron bonds. We compare
this system with the iron arsenides and propose a microscopic magneto-elastic
Hamiltonian which is relevant for all the iron based superconductors. We argue
that this describes electron-lattice coupling in a system where
electron-electron interaction is crucial.",1011.1932v2
2015-07-23,Single solenoidal magnetic system for Iron-free detector,"We consider a single solenoidal system for possible usage in Iron-free
detectors for future linear colliders",1507.06694v1
2016-02-16,Multi-Sensor Surface Analysis for Robotic Ironing,"Robotic manipulation of deformable objects remains a challenging task. One
such task is to iron a piece of cloth autonomously. Given a roughly flattened
cloth, the goal is to have an ironing plan that can iteratively apply a regular
iron to remove all the major wrinkles by a robot. We present a novel solution
to analyze the cloth surface by fusing two surface scan techniques: a curvature
scan and a discontinuity scan. The curvature scan can estimate the height
deviation of the cloth surface, while the discontinuity scan can effectively
detect sharp surface features, such as wrinkles. We use this information to
detect the regions that need to be pulled and extended before ironing, and the
other regions where we want to detect wrinkles and apply ironing to remove the
wrinkles. We demonstrate that our hybrid scan technique is able to capture and
classify wrinkles over the surface robustly. Given detected wrinkles, we enable
a robot to iron them using shape features. Experimental results show that using
our wrinkle analysis algorithm, our robot is able to iron the cloth surface and
effectively remove the wrinkles.",1602.04918v1
2016-02-22,Iron Oxide Surfaces,"The surface science of iron oxides is comprehensively reviewed. For the full
abstract please see pdf.",1602.06774v1
2016-03-16,Magnetic Properties Controlled by Interstitial or Interlayer Cations in Iron Chalcogenides,"By applying density functional theory calculations to iron chalcogenides, we
find that magnetic order in Fe$_{1+y}$Te and magnetic instability at
$(\pi,\pi)$ in K$_y$Fe$_2$Se$_2$ are controlled by interstitial and interlayer
cations, respectively. While in Fe$_{1+y}$Te, magnetic phase transitions occur
among collinear, exotic bicollinear and plaquette-ordered antiferronmagnetic
states when the height of interstitial irons measured from iron plane or the
concentration of interstitial irons is varied, the magnetic instability at
$(\pi,\pi)$ which is believed to be responsible for the Cooper pairing in iron
pnictides is significantly enhanced when $y$ is much smaller than $1$ in
K$_y$Fe$_2$Se$_2$. Our results indicate that, similar to iron pnictides,
itinerant electrons play important roles in iron chalcogenides, even though the
fluctuating local moments become larger.",1603.04952v1
2017-06-12,Basic electronic properties of iron selenide under variation of structural parameters,"Since the discovery of high-temperature superconductivity in the thin-film
FeSe/SrTiO$_3$ system, iron selenide and its derivates have been intensively
scrutinized. Using ab initio density functional theory calculations we review
the electronic structures that could be realized in iron-selenide if the
structural parameters could be tuned at liberty. We calculate the
momentum-dependence of the susceptibility and investigate the symmetry of
electron pairing within the random phase approximation. Both the susceptibility
and the symmetry of electron pairing depend on the structural parameters in a
nontrivial way. These results are consistent with the known experimental
behavior of binary iron chalcogenides and, at the same time, reveal two
promising new ways of tuning superconducting transition temperatures in these
materials. On the one hand by expanding the iron lattice of FeSe at constant
iron-selenium distance and, on the other hand, by increasing the iron-selenium
distance with unchanged iron lattice.",1706.03543v2
2022-04-08,Nucleation and growth of iron pebbles explains the formation of iron-rich planets akin to Mercury,"The pathway to forming the iron-rich planet Mercury remains mysterious.
Mercury's core makes up 70% of the planetary mass, which implies a significant
enrichment of iron relative to silicates, while its mantle is strongly depleted
in oxidized iron. The high core mass fraction is traditionally ascribed to
evaporative loss of silicates, e.g. following a giant impact, but the high
abundance of moderately volatile elements in the mantle of Mercury is
inconsistent with reaching temperatures much above 1,000 K during its
formation. Here we explore the nucleation of solid particles from a gas of
solar composition that cools down in the hot inner regions of the
protoplanetary disc. The high surface tension of iron causes iron particles to
nucleate homogeneously (i.e., not on a more refractory substrate) under very
high supersaturation. The low nucleation rates lead to depositional growth of
large iron pebbles on a sparse population of nucleated iron nano-particles.
Silicates in the form of iron-free MgSiO$_3$ nucleate at similar temperatures
but obtain smaller sizes due to the much higher number of nucleated particles.
This results in a chemical separation of large iron particles from silicate
particles with ten times lower Stokes numbers. We propose that such conditions
lead to the formation of iron-rich planetesimals by the streaming instability.
In this view, Mercury formed by accretion of iron-rich planetesimals with a
sub-solar abundance of highly reduced silicate material. Our results imply that
the iron-rich planets known to orbit the Sun and other stars are not required
to have experienced mantle-stripping impacts. Instead their formation could be
a direct consequence of temperature fluctuations in protoplanetary discs and
chemical separation of distinct crystal species through the ensuing nucleation
process.",2204.04241v1
2023-03-21,Forming super-Mercuries: The role of stellar abundances,"Super-Mercuries, rocky exoplanets with bulk iron mass fraction of more than
60 per cent, appear to be preferentially hosted by stars with higher iron mass
fraction than the Earth. It is unclear whether these iron-rich planets can form
in the disc, or if giant impacts are necessary. Here we investigate the
formation of super-Mercuries in their natal protoplanetary discs by taking into
account their host stars' abundances (Fe, Mg, Si, S). We employ a disc
evolution model which includes the growth, drift, evaporation and
recondensation of pebbles to compute the pebble iron mass fraction. The
recondensation of outward-drifting iron vapour near the iron evaporation front
is the key mechanism that facilitates an increase in the pebble iron mass
fraction. We also simulate the growth of planetary seeds around the iron
evaporation front using a planet formation model which includes pebble
accretion and planet migration, and compute the final composition of the
planets. Our simulations are able to reproduce the observed iron compositions
of the super-Mercuries provided that all the iron in the disc are locked in
pure Fe grains and that the disc viscosity is low. The combined effects of slow
orbital migration of planets and long retention time of iron vapour in
low-viscosity discs makes it easier to form iron-rich planets. Furthermore, we
find that decreasing the stellar Mg/Si ratio results in an increase in the iron
mass fraction of the planet due to a reduction in the abundance of Mg2SiO4,
which has a very similar condensation temperature as iron, in the disc. Our
results thus imply that super-Mercuries are more likely to form around stars
with low Mg/Si, in agreement with observational data.",2303.11948v1
2023-12-14,Past and Present Dynamics of the Iron Biogeochemical Cycle,"This chapter investigates the complexities surrounding the iron
biogeochemical cycle from the Archean to present, with a focus on assessing the
balance between iron sources and sinks during long periods of Earth's history
with relatively invariable redox conditions, when steady state can be safely
assumed. Currently, the residence time of iron in the ocean may be as short as
approximately 5 years. The input flux of iron is highly sensitive to redox
cycling in sediments, while its removal primarily occurs through dispersed
processes of oxidation and precipitation. In the Archean, we find a significant
imbalance between continental and hydrothermal inputs, which collectively
contribute between 61,500 to 263,000 Gg/yr of dissolved iron to the oceans, and
the most obvious sinks such as iron formations (IFs), which sequester up to
~43,000 Gg/yr of iron. A possible solution to this imbalance involves the
dispersed abiotic precipitation and removal of iron as silicates, sulfides, and
carbonates in marine basins. Additionally, we calculate the residence time of
dissolved iron in the Archean oceans to be between 6 kyr and 3 Myr, which is
significantly longer than the ocean mixing timescale. Our estimates indicate
that under the anoxic Archean atmosphere, the iron cycle was more protracted
than today, and the isotopic compositions and concentrations of dissolved iron
were likely more uniform. Distinct water bodies were likely confined to limited
areas or specific, dynamic systems with intense iron turnover, such as regions
where deep-sea upwelling currents brought hydrothermal iron to photic zones
rich in biotic or abiotic oxidants.",2312.09044v1
1997-09-18,Magnetic excitations and structural change in the S=1/2 quasi-one-dimensional magnet Sr_{14-x}Y_{x}Cu_{24}O_{41} (0<x<1),"Neutron scattering measurements have been performed on the S=1/2
quasi-one-dimensional system Sr_{14-x}Y_{x}Cu_{24}O_{41}, which has both simple
chains and two-leg ladders of copper ions. We observed that when a small amount
of yttrium is substituted for strontium, which is expected to reduce the number
of holes, the dimerized state and the structure in the chain are changed
drastically. The inelastic peaks originating from the dimerized state of the
chain becomes broader in energy but not in momentum space. This implies that
the dimerized state becomes unstable but the spin correlations are unchanged
with yttrium substitution. Furthermore, it was observed that nuclear Bragg peak
intensities originating from the chain show strong temperature and x
dependence, which suggests that the chains slide along the c axis as
temperature and x are varied.",9709203v1
1997-11-02,"The dimpling in the CuO_2 planes of YBa_2Cu_3O_x (x=6.806-6.984, T=20-300 K) measured by yttrium EXAFS","The dimpling of the CuO_2 planes (spacing between the O2,3 and Cu2 layers) in
YBa_2Cu_3O_x has been measured as a function of oxygen concentration and
temperature by yttrium x-ray extended-fine-structure spectroscopy (EXAFS). The
relative variations of the dimpling with doping (x=6.806-6.984) and temperature
(20-300 K) are weak (within 0.05 AA), and arise mainly from displacements of
the Cu2 atoms off the O2,3 plane towards Ba. The dimpling appears to be
connected with the transition from the underdoped to the overdoped regimes at
x=6.95, and with a characteristic temperature in the normal state, T*=150 K.",9711004v1
2003-04-04,The easy axis of the magnetic response of the conduction electrons of yttrium and rare earths,"We describe a scheme for first-principles calculations of the static,
paramagnetic, spin susceptibility of metals with relativistic effects such as
spin-orbit coupling included. This gives the direction for an applied modulated
magnetic field to maximise its response. This easy axis depends on the
modulation's wave-vector q. For h.c.p. yttrium we find the peak response at a
q= (0,0,0.57)pi/c, coincident with a Fermi surface nesting vector, to have an
easy axis perpendicular to q. This is consistent with the {\it helical}
anti-ferromagnetic order found in many dilute rare earth-Yalloys. Conversely,
the easy axis for the response to a uniform magnetic field lies along the
c-axis. The conduction electrons' role in the canting of magnetic moments in
Gd-Y alloys and other rare earth materials is mooted.",0304112v1
2003-10-20,Excess Modes and Enhanced Scattering in Rare-Earth Doped Amorphous Silicon Thin Films,"We report specific heat and thermal conductivity of gadolinium- and
yttrium-doped amorphous silicon thin films measured using silicon-nitride
membrane-based microcalorimeters. Addition of gadolinium or yttrium to the
amorphous silicon network reduces the thermal conductivity over a wide
temperature range while significantly increasing the specific heat. This result
indicates that a large number of non-propagating states are added to the
vibrational spectrum that are most likely caused either by localized vibration
of the dopant atom in a Si cage, or softening of the material forming the cage
structures. High-resolution cross-sectional electron micrographs reveal
columnar features in Gd-doped material which do not appear in pure amorphous
silicon. Scattering from both the nanoscaled columns and the filled-cage
structures play a role in the reduced thermal conductivity in the rare-earth
doped amorphous semiconductor. The overall result is an amorphous solid with a
large bump in $C/T^{3}$ and no plateau in thermal conductivity.",0310463v2
2003-11-22,"The enhancement of superconducting transition temperature in yttrium sesquicarbide system, Y2C3, with the maximum Tc of Tc=18K","We discovered the enhancement of superconducting transition temperature, Tc,
in yttrium sesquicarbide system with the maximum Tc of Tc=18K and their
superconducting properties were discussed. The crystal structure of Y2C3 is the
body-centered cubic (Pu2C3-type) structure, and the lattice parameters are
varied with the heat treatment conditions. The magnetization (M-H) curves of
this compound showed a typical type-II superconducting behavior, and the lower
critical field, Hc1(0), is 3.5mT. The Tc-value in this system was changed in
the range from 15K to 18K, depending on the sintering conditions. In a previous
report by Krupka et al., maximum Tc in Y2C3 was observed at 11.5K by the
magnetic measurements. So we successfully synthesized the new high-Tc phase in
Y2C3.",0311517v1
2003-11-25,Upper Critical Field of a Novel 18-K Superconductive Phase in Metastable Yttrium Sesquicarbide Prepared Using High Pressure Technique,"The metastable phase of an yttrium sesquicarbide compound, which was vary
recently reported as a new superconductive phase with a Tc value of 18 K, was
prepared under high pressure from the nominal composition of Y2C3 and
Y2C2.9B0.1 in order to investigate this phase. We have succeeded in
reproduction, and in the transport measurement for this 18-K phase. It is
considered that the reason for the higher Tc value than the 11.5 K reported
previously is not the small amount of B as the impurity element from the BN
crucible. The Bc2 value at 0 K estimated from the resistivity data for the 18-K
phase seems to be over 30 T. It means that the Tc and Bc2 values of the 18-K
phase are as high as those of the general A15 compounds.",0311561v1
2004-11-26,Interactions between Polymers and Nanoparticles : Formation of Supermicellar Hybrid Aggregates,"When polyelectrolyte-neutral block copolymers are mixed in solutions to
oppositely charged species (e.g. surfactant micelles, macromolecules, proteins
etc), there is the formation of stable supermicellar aggregates combining both
components. The resulting colloidal complexes exhibit a core-shell structure
and the mechanism yielding to their formation is electrostatic self-assembly.
In this contribution, we report on the structural properties of supermicellar
aggregates made from yttrium-based inorganic nanoparticles (radius 2 nm) and
polyelectrolyte-neutral block copolymers in aqueous solutions. The yttrium
hydroxyacetate particles were chosen as a model system for inorganic colloids,
and also for their use in industrial applications as precursors for ceramic and
opto-electronic materials. The copolymers placed under scrutiny are the water
soluble and asymmetric poly(sodium acrylate)poly(acrylamide) diblocks. Using
static and dynamical light scattering experiments, we demonstrate the analogy
between surfactant micelles and nanoparticles in the complexation phenomenon
with oppositely charged polymers. We also determine the sizes and the
aggregation numbers of the hybrid organic-inorganic complexes. Several
additional properties are discussed, such as the remarkable stability of the
hybrid aggregates and the dependence of their sizes on the mixing conditions.",0411669v1
2006-01-10,Superconductivity at 17 K in Yttrium Metal under Nearly Hydrostatic Pressures to 89 GPa,"In an experiment in a diamond anvil cell utilizing helium pressure medium,
yttrium metal displays a superconducting transition temperature which increases
monotonically from Tc ? 3.5 K at 30 GPa to 17 K at 89.3 GPa, one of the highest
transition temperatures for any elemental superconductor. The pressure
dependence of Tc differs substantially from that observed in previous studies
under quasihydrostatic pressure to 30 GPa. Remarkably, the dependence of Tc on
relative volume V/Vo is linear over the entire pressure range above 33 GPa,
implying that higher values of Tc are likely at higher pressures. For the
trivalent metals Sc, Y, La, Lu there appears to be some correlation between Tc
and the ratio of the Wigner-Seitz radius to the ion core radius.",0601213v1
2006-06-21,Strong Electron-Phonon Coupling in Yttrium under Pressure,"Linear response methods are applied to identify the increase in
electron-phonon coupling in elemental yttrium that is responsible for its high
superconducting critical temperature Tc, which reaches nearly 20 K at 115 GPa.
While the evolution of the band structure and density of states is smooth and
seemingly modest, there is strong increase in the 4d content of the occupied
conduction states under pressure. We find that the transverse mode near the L
point of the fcc Brillouin zone, already soft at ambient pressure, becomes
unstable (in harmonic approximation) at a relative volume V/Vo=0.60 (P ~ 42
GPa). The coupling to transverse branches is relatively strong at all high
symmetry zone boundary points X, K, and L. Coupling to the longitudinal
branches is not as strong, but extends over more regions of the Brillouin zone
and involves higher frequencies. Evaluation of the electron-phonon spectral
function $\alpha^2F(\omega)$ shows a very strong increase with pressure of
coupling in the 2-7 meV range, with a steady increase also in the 7-20 meV
range. These results demonstrates strong electron-phonon coupling in this
system that can account for the observed range of Tc.",0606538v1
2008-05-12,Optical second harmonic generation in Yttrium Aluminum Borate single crystals (theoretical simulation and experiment),"Experimental measurements of the second order susceptibilities for the second
harmonic generation are reported for YAl3(BO3)4 (YAB) single crystals for the
two principal tensor components xyz and yyy. First principles calculation of
the linear and nonlinear optical susceptibilities for Yttrium Aluminum Borate
YAl3(BO3)4 (YAB) crystal have been carried out within a framework of the
full-potential linear augmented plane wave (FP-LAPW) method. Our calculations
show a large anisotropy of the linear and nonlinear optical susceptibilities.
The observed dependences of the second order susceptibilities for the static
frequency limit and for the frequency may be a consequence of different
contribution of electron-phonon interactions. The imaginary parts of the second
order SHG susceptibility chi_{123}^{(2)}(omega), chi_{112}^{(2)}(omega),
chi_{222}^{(2)}(omega), and chi_{213}^{(2)}(omega) are evaluated. We find that
the 2(omega) inter-band and intra-band contributions to the real and imaginary
parts of chi_{ijk}^{(2)}\l(omega) show opposite signs. The calculated second
order susceptibilities are in reasonably good agreement with the experimental
measurements.",0805.1671v1
2010-07-15,"Origin of Tc Enhancement Induced by Doping Yttrium and Hydrogen into LaFeAsO-based Superconductors: 57Fe, 75As, 139La, and 1H-NMR Studies","We report our extensive 57Fe-, 75As-, 139La-, and 1H-NMR studies of
La_{0.8}Y_{0.2}FeAsO_{1-y} (La_{0.8}Y_{0.2}1111) and
LaFeAsO_{1-y}H_{x}(La1111H), where doping yttrium (Y) and hydrogen (H) into
optimally doped LaFeAsO_{1-y} (La1111(OPT)) increases T_c=28 K to 34 and 32 K,
respectively. In the superconducting (SC) state, the measurements of
nuclear-spin lattice-relaxation rate 1/T_1 have revealed in terms of a multiple
fully gapped s_\pm-wave model that the SC gap and T_c in La_{0.8}Y_{0.2}1111
become larger than those in La1111(OPT) without any change in doping level. In
La1111H, the SC gap and T_c also increase slightly even though a decrease in
carrier density and some disorders are significantly introduced. As a
consequence, we suggest that the optimization of both the structural parameters
and the carrier doping level to fill up the bands is crucial for increasing T_c
among these La1111-based compounds through the optimization of the Fermi
surface topology.",1007.2514v2
2011-02-02,Transparent yttrium hydride thin films prepared by reactive sputtering,"Metal hydrides have earlier been suggested for utilization in solar cells.
With this as a motivation we have prepared thin films of yttrium hydride by
reactive magnetron sputter deposition. The resulting films are metallic for low
partial pressure of hydrogen during the deposition, and black or
yellow-transparent for higher partial pressure of hydrogen. Both metallic and
semiconducting transparent YHx films have been prepared directly in-situ
without the need of capping layers and post-deposition hydrogenation. Optically
the films are similar to what is found for YHx films prepared by other
techniques, but the crystal structure of the transparent films differ from the
well-known YH3 phase, as they have an fcc lattice instead of hcp.",1102.0450v2
2011-03-22,Shape evolution in Yttrium and Niobium neutron-rich isotopes,"The isotopic evolution of the ground-state nuclear shapes and the systematics
of one-quasiproton configurations are studied in neutron-rich odd-A Yttrium and
Niobium isotopes. We use a selfconsistent Hartree-Fock-Bogoliubov formalism
based on the Gogny energy density functional with two parametrizations, D1S and
D1M. The equal filling approximation is used to describe odd-A nuclei
preserving both axial and time reversal symmetries. Shape-transition signatures
are identified in the N=60 isotopes in both charge radii and spin-parities of
the ground states. These signatures are a common characteristic for nuclei in
the whole mass region. The nuclear deformation and shape coexistence inherent
to this mass region are shown to play a relevant role in the understanding of
the spectroscopic features of the ground and low-lying one-quasiproton states.
Finally, a global picture of the neutron-rich A=100 mass region from Krypton up
to Molybdenum isotopes is illustrated with the systematics of the nuclear
charge radii isotopic shifts.",1103.4285v1
2011-04-05,Reactive Force Field for Proton Diffusion in BaZrO3 using an empirical valence bond approach,"A new reactive force field to describe proton diffusion within the
solid-oxide fuel cell material BaZrO3 has been derived. Using a quantum
mechanical potential energy surface, the parameters of an interatomic potential
model to describe hydroxyl groups within both pure and yttrium-doped BaZrO3
have been determined. Reactivity is then incorporated through the use of the
empirical valence bond model. Molecular dynamics simulations (EVB-MD) have been
performed to explore the diffusion of hydrogen using a stochastic thermostat
and barostat whose equations are extended to the isostress-isothermal ensemble.
In the low concentration limit, the presence of yttrium is found not to
significantly influence the diffusivity of hydrogen, despite the proton having
a longer residence time at oxygen adjacent to the dopant. This lack of
influence is due to the fact that trapping occurs infrequently, even when the
proton diffuses through octahedra adjacent to the dopant. The activation energy
for diffusion is found to be 0.42 eV, in good agreement with experimental
values, though the prefactor is slightly underestimated.",1104.0773v2
2011-09-13,A new thin film photochromic material: Oxygen-containing yttrium hydride,"In this work we report on photochromism in transparent thin film samples of
oxygen-containing yttrium hydride. Exposure to visible and ultraviolet (UV)
light at moderate intensity triggers a decrease in the optical transmission of
visible and infrared (IR) light. The photo-darkening is colour-neutral. We show
that the optical transmission of samples of 500 nm thickness can be reduced by
up to 50% after one hour of illumination with light of moderate intensity. The
reaction is reversible and samples that are left in the dark return to the
initial transparent state. The relaxation time in the dark depends on the
temperature of the sample and the duration of the light exposure. The
photochromic reaction takes place under ambient conditions in the as-deposited
state of the thin-film samples.",1109.2872v1
2014-02-15,Quantifying and controlling the magnetic dipole contribution to 1.5 $μ$m light emission in erbium-doped yttrium oxide,"We experimentally quantify the contribution of magnetic dipole (MD)
transitions to the near-infrared light emission from trivalent erbium-doped
yttrium oxide (Er$^{3+}$:Y$_2$O$_3$). Using energy-momentum spectroscopy, we
demonstrate that the $^4$I$_{13/2}{\to}^4$I$_{15/2}$ emission near 1.5 $\mu$m
originates from nearly equal contributions of electric dipole (ED) and MD
transitions that exhibit distinct emission spectra. We then show how these
distinct spectra, together with the differing local density of optical states
(LDOS) for ED and MD transitions, can be leveraged to control Er$^{3+}$
emission in structured environments. We demonstrate that far-field emission
spectra can be tuned to resemble almost pure emission from either ED or MD
transitions, and show that the observed spectral modifications can be
accurately predicted from the measured ED and MD intrinsic emission rates.",1402.3717v1
2014-10-01,Effect of yttrium substitution on the superconducting properties of the system La$_{1-\textit{x}}$Y$_{\textit{x}}$O$_{0.5}$F$_{0.5}$BiS$_{2}$,"We present the effect of yttrium substitution on superconductivity in the
La$_{1-\textit{x}}$Y$_{\textit{x}}$O$_{0.5}$F$_{0.5}$BiS$_{2}$ system.
Polycrystalline samples with nominal Y concentrations up to 40% were
synthesized and characterized via electrical resistivity, magnetic
susceptibility, and specific heat measurements. Y substitution reduces the
lattice parameter \textit{a} and unit cell volume \textit{V}, and a correlation
between the lattice parameter \textit{c}, the La-O-La bond angle, and the
superconducting critical temperature $T_c$ is observed. The chemical pressure
induced by Y substitution for La produces neither the high-$T_c$
superconducting phase nor the structural phase transition seen in
LaO$_{0.5}$F$_{0.5}$BiS$_{2}$ under externally applied pressure.",1410.0084v1
2015-09-17,Nanoscale nonlinear effects in Erbium-implanted Yttrium Orthosilicate,"Doping of substrates at desired locations is a key technology for spin-based
quantum memory devices. Focused ion beam implantation is well-suited for this
task due to its high spacial resolution. In this work, we investigate ion-beam
implanted erbium ensembles in Yttrium Orthosilicate crystals by means of
confocal photoluminescence spectroscopy. The sample temperature and the
post-implantation annealing step strongly reverberate in the properties of the
implanted ions. We find that hot implantation leads to a higher activation rate
of the ions. At high enough fluences, the relation between the fluence and
final concentration of ions becomes non-linear. Two models are developed
explaining the observed behaviour.",1509.05185v1
2015-10-26,Weak ferromagnetism and magnetization reversal in YFe$_{1-x}$Cr$_x$O$_3$,"We present combined experimental and theoretical studies on the magnetic
properties of a solid solution between yttrium orthoferrite and yttrium
orthochromite systems, YFe$_{1-x}$Cr$_x$O$_3$ (0 $\leq$ x $\leq$ 1) where
Fe$^{3+}$ and Cr$^{3+}$ ions are distributed randomly at the same
crystallographic site (4b). We found that all the compositions exhibit weak
ferromagnetism below the N\'eel temperature that decreases non-linearly with
increasing $x$, while certain intermediate compositions ($x = 0.4,0.5$) show a
compensation point and magnetization reversal. This unusual behavior is
explained based on a simple model comprising the isotropic superexchange and
the antisymmetric Dzyaloshinskii-Moriya interactions. This model explains the
magnetization behavior in the entire range of doping and temperature including
the magnetization reversal which results from an interplay of various DM
interactions such as, Fe-O-Fe, Cr-O-Cr and Fe-O-Cr.",1510.07548v1
2015-12-12,High quality factor nanophotonic resonators in bulk rare-earth doped crystals,"Numerous bulk crystalline materials exhibit attractive nonlinear and
luminescent properties for classical and quantum optical applications. A
chip-scale platform for high quality factor optical nanocavities in these
materials will enable new optoelectronic devices and quantum light-matter
interfaces. In this article, photonic crystal nanobeam resonators fabricated
using focused ion beam milling in bulk insulators, such as rare-earth doped
yttrium orthosilicate and yttrium vanadate, are demonstrated. Operation in the
visible, near infrared, and telecom wavelengths with quality factors up to
27,000 and optical mode volumes close to one cubic wavelength is measured.
These devices enable new nanolasers, on-chip quantum optical memories, single
photon sources, and non-linear devices at low photon numbers based on
rare-earth ions. The techniques are also applicable to other luminescent
centers and crystals.",1512.03947v1
2017-05-23,Reducing Graphene Device Variability with Yttrium Sacrificial Layers,"Graphene technology has made great strides since the material was isolated
more than a decade ago. However, despite improvements in growth quality and
numerous 'hero' devices, challenges of uniformity remain, restricting
large-scale development of graphene-based technologies. Here we investigate and
reduce the variability of graphene transistors by studying the effects of
contact metals (with and without Ti layer), resist, and yttrium (Y) sacrificial
layers during the fabrication of hundreds of devices. We find that with optical
photolithography, residual resist and process contamination is unavoidable,
ultimately limiting device performance and yield. However, using Y sacrificial
layers to isolate the graphene from processing conditions improves the yield
(from 73% to 97%), average device performance (three-fold increase of mobility,
58% lower contact resistance), and the device-to-device variability (standard
deviation of Dirac voltage reduced by 20%). In contrast to other sacrificial
layer techniques, removal of the Y sacrificial layer with HCl does not harm
surrounding materials, simplifying large-scale graphene fabrication.",1705.09388v1
2017-06-05,Dy$^{3+}$-doped Yttrium Complex Molecular Crystals for Two-color Thermometry in Heterogeneous Materials,"We develop Dy$^{3+}$-doped yttrium complexes for use as two-color thermometry
(TCT) phosphor molecular crystals in heterogeneous materials. These complexes
include: Dy:Y(acac)$_3$(phen), Dy:Y(hfa)$_3$(DPEPO), Dy:Y(4-BBA)$_3$(TPPO),
Dy:Y(acac)$_3$, and Dy:Y(acac)$_3$(DPEPO), where the Dy/Y ratio is 1:9. We
characterize the materials' photoluminescence at different temperatures to
determine the TCT calibration parameters and the degree to which thermal
quenching influences the emission. From this data we observe a link between the
excited state lifetime at room temperature and the degree to which the material
is susceptible to thermal quenching (i.e. materials having long room
temperature lifetimes are more resistant to thermal quenching than materials
with short room temperature lifetimes). Of the five complexes tested we find
that Dy:Y(acac)$_3$(DPEPO) has the best thermal performance, with the most
likely source of improvement being DPEPO's compact rigid structure. This
rigidity helps with energy transfer to the Dy$^{3+}$ ion, suppresses
non-radiative loss modes, and reduces exciplex formation.",1706.02658v1
2017-12-01,Coherent spin dynamics of ytterbium ions in yttrium orthosilicate,"We investigate the electron and nuclear spin coherence properties of
ytterbium ($\mathrm{Yb}^{3+}$) ions with non-zero nuclear spin, within an
yttrium orthosilicate (Y$_2$SiO$_5$) crystal, with a view to their potential
application in quantum memories or repeaters. We find electron spin-lattice
relaxation times are maximised at low magnetic field ($<100$ mT) where
$g~\sim6$, reaching 5 s at 2.5 K, while coherence times are maximised when
addressing ESR transitions at higher fields where $g\sim0.7$ where a Hahn echo
measurement yields $T_2$ up to 73 $\mu$s. Dynamical decoupling (XY16) can be
used to suppress spectral diffusion and extend the coherence lifetime to over
0.5 ms, close to the limit of instantaneous diffusion. Using Davies
electron-nuclear-double-resonance (ENDOR), we performed coherent control of the
$^{173}\mathrm{Yb}^{3+}$ nuclear spin and studied its relaxation dynamics. At
around 4.5 K we measure a nuclear spin $T_1$ and $T_2$ of 4 and 0.35 ms,
respectively, about 4 and 14 times longer than the corresponding times for the
electron spin.",1712.00435v1
2018-02-12,Long spin coherence times in the ground state and an optically excited state of $^{167}$Er$^{3+}$:Y$_2$SiO$_5$ at zero magnetic field,"Spins in solids are an ideal candidate to act as a memory and interface with
superconducting qubits due to their long coherence times. We spectroscopically
investigate erbium-167-doped yttrium orthosilicate as a possible
microwave-addressed memory employing its microwave frequency transitions that
occur without applying an external magnetic field. We obtain coherence times of
380 $\mu$s in a ground state spin transition and 1.48 ms in an excited state
spin transition. This is 28 times longer compared to previous zero field
measurements, as well as 200 times longer than a previous microwave memory
demonstration in the same material. These long coherence times show that
erbium-167-doped yttrium orthosilicate has potential as a microwave-addressed
quantum memory.",1802.03862v2
2018-03-28,Critical effect of cubic phase on aging in 3 mol% yttria-stabilized zirconia ceramics for hip replacement prosthesis,"The isothermal tetragonal-to-monoclinic transformation of 3Y-TZP ceramics
sintered at two different temperatures (1450{\deg}C and 1550{\deg}C) and
duration (2 and 5 h) is investigated at 134{\deg}C in steam. Particular
attention is paid to the presence of a cubic phase and its effect on isothermal
aging. Sintering at 1550{\deg}C can result in a significant amount of large
cubic grains in the specimens, that have a detrimental impact on aging
resistance, especially for the first stage of the aging process. Cubic grains
appear to be enriched in yttrium, which in turn leads to a depletion of yttrium
in the neighboring tetragonal grains. These grains will act as nucleation sites
for tetragonal-to-monoclinic transformation. Even for specimens sintered at
lower temperature, i.e. 1450{\deg}C, the presence of a cubic phase is expected
from the phase diagram, leading to a significant effect on aging sensitivity.",1803.10480v1
2019-01-13,Superconductivity in sodalite-like yttrium hydride clathrates,"We report ab-initio calculations of the superconducting properties of two
high-Tc sodalite-like clathrate yttrium hydrides, YH6 and YH10, within the
fully anisotropic ME theory, including Coulomb corrections. For both compounds
we find almost isotropic superconducting gaps, resulting from a uniform
distribution of the electron-phonon coupling over phonon modes and electronic
states of mixed Y and H character. The Coulomb screening is rather weak,
resulting in a Morel-Anderson pseudopotential mu*= 0:11, at odds with claims of
unusually large Tc in lanthanum hydrides. The corresponding critical
temperatures at 300 GPa exceed room temperature (Tc = 290 K and 310 K for YH6
and YH10), in agreement with a previous isotropic-gap calculation. The
different response of these two compounds to external pressure, along with a
comparison to low-Tc superconducting YH3, may inspire strategies to improve the
superconducting properties of this class of hydrides.",1901.04001v1
2019-08-08,Localization of Yttrium Segregation within YSZ Grain Boundary Dislocation Cores,"Ionic conductivity blocking at grain boundaries in polycrystalline
electrolytes is one of the main obstacles that need to be overcome in order to
improve the performance of solid state fuel cells and batteries. To this aim,
harnessing the physical properties of grain boundaries in ionic conducting
materials such as yttria stabilized zirconia (YSZ) down to the atomic scale
arises as a greatly important task. Here we present a structural and
compositional analysis of a single grain boundary in a 9 mol% yttria content
YSZ bicrystal by means of aberration corrected scanning transmission electron
microscopy. Our studies combine strain and compositional atomic resolution
analysis with density-functional-theory calculations in order to find a
preferential segregation of yttrium to the expansive atomic sites at the grain
boundary dislocation cores. These results address a crucial step towards the
understanding of the physical properties of grain boundaries down to atomic
dimensions.",1908.03257v1
2020-09-15,A new class of intrinsic magnet: two-dimensional yttrium sulphur selenide,"Exploring and controlling magnetism in two-dimensional (2D) layered magnetic
crystals, as well as their inclusion in heterogeneous assemblies, provide an
unprecedented opportunity for fundamental science and technology. To date,
however, there are only a few known intrinsic 2D magnets. Here we predict a
novel 2D intrinsic magnet, yttrium sulfur selenide (YSSe), using
first-principles calculations. The magnetism of this transition metal
dichalcogenide originates from the partially-filled $3p$- and $4p$-orbitals of
the chalcogens, unlike other known intrinsic magnets where magnetism arises
from the partially-filled $3d$- and $4f$-orbitals. The unconventional magnetism
in YSSe is a result of a unique combination of its structural and electronic
properties. We further show that a lack of mirror symmetry results in
piezoelectric properties, while the broken space- and time-symmetry ensures
valley polarization. YSSe is a rare magnetic-piezoelectric material that can
enable novel spintronics, valleytronics, and quantum technologies.",2009.07232v1
2020-10-26,Optical properties of yttrium oxyhydrides: A comparative analysis with experiment,"Based on the results of computational simulations, the research addresses a
broad range of electronic and optical properties which are typical for two most
stable compositions of the yttrium oxyhydride, Y4H10O and YHO. Emphasis was
placed on characteristics of thin films of different structural phases.
Macroscopic optical properties were deduced and analyzed within the
conventional scheme that utilizes the knowledge of refractive index,
absorption, transmittance and reflectance spectra. Our major goal was two-fold:
First, to provide modeling and description of optical spectra for various
single- and bi-phase oxyhydride compositions, and second, to conduct
comparative analysis that would be powerful enough to explain the features of
the experimentally measured transmittance spectra. In the context of nonlinear
optics, for the P-43m noncentrosymmetric cubic structure of Y4H10O we evaluated
a frequency profile of the second-order susceptibility ${\chi}^{(2)}(2\omega)$
and showed that the bulk Y4H10O may exhibit a rather considerable optical
nonlinearity.",2010.13502v1
2020-12-17,High pressure computational search of trivalent lanthanide di-nitrides,"Transition metal nitrides have attracted much interest of the scientific
community for their intriguing properties and technological applications. Here
we focus on yttrium dinitride (YN$_{2}$) and its formation and structural
transition under pressure. We employed a fixed composition USPEX search to find
the most stable polymorphs. We choose yttrium as a proxy for the lanthanide
series because it has only $+3$ oxidation state, contrary to most transition
metals. We then computed thermodynamic and dynamical stability of these
structures compared to the decomposition reactions and we found that the
compound undergoes two structural transitions, the latter showing the formation
N$_{4}$ chains. A closer look into the nature of the nitrogen bonding showed
that in the first two structures, where nitrogen forms dimers, the bond length
is intermediate between that of a single bond and that of a double bond, making
it hard to rationalize the proper oxidation state configuration for YN$_{2}$.
In the latter structure where there is the formation of N$_{4}$ chains, the
bond lengths increase significantly, up to a value that can be justified as a
single bond. Finally, we also studied the electronic structure and the
dynamical stability of the structures we found.",2012.09576v1
2020-12-30,Photochromic response of encapsulated oxygen-containing yttrium hydride thin films,"Photochromic oxygen$-$containing yttrium$-$hydride thin films are synthesized
by argon$-$magnetron sputtering on microscope slides. Some of them are
encapsulated with a thin, transparent and non$-$photochromic diffusion-barrier
layer of either Al2O3 or Si3N4. Ion beam-based methods prove that these
protective diffusion barriers are stable and free from pinholes, with
thicknesses of only a few tens of nanometers. Optical spectrophotometry reveals
that the photochromic response and relaxation time for both $-$ protected and
unprotected $-$ samples are almost identical. Ageing effects in the unprotected
films lead to degradation of the photochromic performance (self$-$delamination)
while the photochromic response for the encapsulated films is stable. Our
results show that the environment does not play a decisive role for the
photochromic process and encapsulation of oxygen containing rare-earth hydride
films with transparent and non-organic thin diffusion barrier layers provides
long-time stability of the films, mandatory for applications as photochromic
coatings on e.g., smart windows.",2012.15098v1
2022-02-17,Proposal for transduction between microwave and optical photons using $\mathrm{^{167}Er}$-doped yttrium orthosilicate,"Efficient transduction devices that reversibly convert optical and microwave
quantum signals into each other are essential for integrating different
technologies. Rare-earth ions in solids, and in particular Erbium ions, with
both optical and microwave addressable transitions are promising candidates for
designing transducers. We propose a microwave-to-optical quantum transducer
scheme based on the dark state protocol in $\mathrm{^{167}Er}$ doped into
yttrium orthosilicate (YSO) at zero external magnetic fields. Zero-field
operation is beneficial for superconducting resonators that can incur extra
losses in magnetic fields. By calculating the fidelity and efficiency of the
transducer, considering the most important imperfections, we show that an
efficient conversion is possible with a high fidelity. We also investigate the
microwave transitions of $\mathrm{^{167}Er}$:YSO that can be used for the
transducer protocol.",2202.08770v2
2022-08-01,Distance calibration via Newton's rings in yttrium lithium fluoride whispering gallery mode resonators,"In this work, we analyze the first whispering gallery mode resonator (WGMR)
made from monocrystalline yttrium lithium fluoride (YLF). The disc-shaped
resonator is fabricated using single-point diamond turning and exhibits a high
intrinsic quality factor ($Q$) on the order of $10^9$. Moreover, we employ a
novel method based on microscopic imaging of Newton's rings through the back of
a trapezoidal prism. This method can be used to evanescently couple light in to
a WGMR and monitor the separation between the cavity and the coupling prism.
Accurately calibrating the distance between a coupling prism and a WGMR is
desirable as it can be used to improve experimental control and conditions,
i.e., accurate coupler gap calibration can aid in tuning into desired coupling
regimes and can be used to avoid potential damage caused by collisions between
the coupling prism and the WGMR. Here, we use two different trapezoidal prisms
together with the high-$Q$ YLF WGMR to demonstrate and discuss this method.",2208.00667v2
2024-02-22,Rare-earth doped yttrium silicate (Y2SiO5) thin films grown by chemical vapour deposition for quantum technologies,"Yttrium orthosilicate (Y2SiO5 - YSO) is one of the most promising crystals to
host rare-earth (RE) ions for quantum technologies applications. In this
matrix, they indeed exhibit narrow optical and spin linewidths that can be
exploited to develop quantum memories or quantum information processing
capabilities. In this paper, we propose a new method to grow RE doped silicate
thin films on silicon wafers based on direct liquid injection chemical vapour
deposition (DLI-CVD). We optimize the deposition and annealing conditions to
achieve formation of the high temperature X2-YSO phase. The phase purity and
crystalline quality of the films are assessed by evaluating the optical
properties of Eu3+ ions embedded in this oxide matrix. In view of the results,
we discuss the possible phase formation mechanisms, and the potential of this
new wafer-compatible form of YSO for quantum technologies applications.",2402.14445v1
2004-10-29,Magnetic properties of polypyrrole - coated iron oxide nanoparticles,"Iron oxide nanoparticles were prepared by sol -gel process. Insitu
polymerization of pyrrole monomer in the presence of oxygen in iron oxide
ethanol suspension resulted in a iron oxide - polypyrrole nanocomposite. The
structure and magnetic properties were investigated for varying pyrrole
concentrations. The presence of the gamma - iron oxide phase and polypyrrole
were confirmed by XRD and FTIR respectively. Agglomeration was found to be
comparatively much reduced for the coated samples, as shown by TEM. AC
susceptibility measurements confirmed the superparamagnetic behaviour.
Numerical simulations performed for an interacting model system are performed
to estimate the anisotropy and compare favourably with experimental results.",0410760v1
2011-12-12,Nematic orders in Iron-based superconductors,"In the newly discovered iron-based superconductors, many experiments have
demonstrated the existence of the rotational symmetry breaking nematic order,
which has been a prevailing phenomenon in many correlated electronic systems.
In this paper, we review nematic behaviors in iron-pnictides and the mechanism
behind the development of the nematic order. We discuss evidences that support
the spin-driven nematicity in iron-pnictides. Theories, results and predictions
will be discussed based on this picture. We also briefly discuss the
generalization of this theory to the nematicity in iron-chalcogenides.",1112.2713v1
2013-01-30,Properties of Liquid Iron along the Melting Line up to the Earth-core Pressures,"We report a molecular dynamics study of transport coefficients and infinite
frequency shear mod- ulus of liquid iron at high temperatures and high
pressures. We observe a simultaneous rise of both shear viscosity and diffusion
coefficient along the melting line and estimate if liquid iron can vitrify
under Earth-core conditions. We show that in frames of the model studied in our
work iron demonstrates a moderate increase of viscosity along the melting line.
It is also demonstrated that in the limit of high temperatures and high
pressures the liquid iron behaves similar to the soft spheres system with
exponent n=4.6.",1301.7158v1
2013-07-30,Synthesis of Self-assembled Iron Silicon Oxide Nanowires onto Single-crystalline Si(100),"Iron silicon oxide nanowire has been synthesized by putting single
crystalline Si(100) wafer into ammonium iron sulfate, hydrogen peroxide, and
triethylamine solution heated to from 70 to 100 degree in the air. The prepared
iron silicon oxide nanowires with diameters of about 10nm (onto non etched
Si(100) wafer) and about 75nm(onto etched Si(100) wafer) and their self
assembles were characterized. The possible mechanism that accounted for the
formation of iron silicon oxide nanowire is suggested based on experimental
evidence.",1307.7783v1
2015-12-17,Antiferromagnetism enables electron-phonon coupling in iron-based superconductors,"It is shown that a generic form of an antiferromagnetic wave function opens
strong electron-phonon coupling channels in the iron-based superconductors. In
the nonmagnetic state these channels exist locally on a single iron atom, but
are canceled out between the two iron atoms in the primitive unit cell. Our
findings are based on symmetry and the presence of an xz/yz Fermi surface near
the M point and thus should be relevant for the known iron-based pnictide or
chalcogenide superconductors.",1512.05818v2
2018-11-22,Interior structure of Mars and other rock-and-iron planetary bodies,"Here it is shown how to find the interior structure of a variety of
rock-and-iron planetary bodies by using the rock density and some aspects of
the core density as known for the Earth and using a convection principle for
the iron-rich core. Convection minimizes both the density and temperature
gradients inside the core fluid. This is achieved if the density of the core
fluid is close to pure iron melting density at the core-mantle boundary, and
the density has the smallest value possible for iron-rich melt at the inner
core boundary. The critical iron densities for both pure iron and iron with
maximal light impurities were previously obtained utilizing Landau's theory of
first order phase transitions with the most reliable experimental scaling. The
planetary interior density is found by iteratively calculating the gravity and
pressure in small radial steps. Moment of inertia factors are also calculated
and agree well for the bodies for which we have accurate measurements: Moon,
Mars and Mercury. Calculations are also made for the exoplanets Kepler-78b,
K2-229b and Kepler-10b. All show iron-rich liquid in their cores. The lighter,
solar objects are without an inner core, but the heaviest two exoplanets have a
pure iron innermost core inside the inner core. The parameter range for a
growing inner core in the radius-mass plane is calculated. The magnetic field
following the growth of an inner core protects life on Earth, and similarly for
exoplanets. This guides the selection of exoplanets to study in the search for
life.",1811.09198v1
2001-04-27,Faraday rotation spectra of bismuth-substituted ferrite garnet films with in-plane magnetization,"Single crystalline films of bismuth-substituted ferrite garnets have been
synthesized by the liquid phase epitaxy method where GGG substrates are dipped
into the flux. The growth parameters are controlled to obtain films with
in-plane magnetization and virtually no domain activity, which makes them
excellently suited for magnetooptic imaging. The Faraday rotation spectra were
measured across the visible range of wavelengths. To interprete the spectra we
present a simple model based on the existence of two optical transitions of
diamagnetic character, one tetrahedral and one octahedral. We find excellent
agreement between the model and our experimental results for photon energies
between 1.77 and 2.53 eV, corresponding to wavelengths between 700 and 490 nm.
It is shown that the Faraday rotation changes significantly with the amount of
substituted gallium and bismuth. Furthermore, the experimental results suggest
that the magnetooptic response changes linearly with the bismuth substitution.",0104536v3
2003-07-11,Photoproduction of Long-Lived Holes and Electronic Processes in Intrinsic Electric Fields Seen through Photoinduced Absorption and Dichroism in Ca_3Ga_{2-x}Mn_xGe_3O_{12} Garnets,"Long-lived photoinduced absorption and dichroism in the
Ca_3Ga_{2-x}Mn_xGe_3O_{12} garnets with x < 0.06 were examined versus
temperature and pumping intensity. Unusual features of the kinetics of
photoinduced phenomena are indicative of the underlying electronic processes.
The comparison with the case of Ca_3Mn_2Ge_3O_{12}, explored earlier by the
authors, permits one to finally establish the main common mechanisms of
photoinduced absorption and dichroism caused by random electric fields of
photoproduced charges (hole polarons). The rate of their diffusion and
relaxation through recombination is strongly influenced by the same fields,
whose large statistical straggling is responsible for a broad continuous set of
relaxation components (observed in the relaxation time range from 1 to about
1000 min). For Ca_3Ga_{2-x}Mn_xGe_3O_{12}, the time and temperature dependences
of photoinduced absorption and dichroism bear a strong imprint of structure
imperfection increasing with x.",0307273v1
2003-09-08,Absence of magnetic order in Yb3Ga5O12: relation between phase transition and entropy in geometrically frustrated materials,"From muon spin relaxation spectroscopy experiments, we show that the sharp
peak (lambda type anomaly) detected by specific heat measurements at 54 mK for
the ytterbium gallium garnet compound, Yb3Ga5O12, does not correspond to the
onset of a magnetic phase transition, but to a pronounced building up of
dynamical magnetic pair-correlations. Beside the lambda anomaly, a broad hump
is observed at higher temperature in the specific heat of this garnet and other
geometrically frustrated compounds. Comparing with other frustrated magnetic
systems we infer that a ground state with long-range order is reached only when
at least 1/4-1/3 of the magnetic entropy is released at the lambda transition.",0309185v1
2005-11-16,"Spin Hamiltonian, Competing Small Energy Scales and Incommensurate Long Range Order in the Highly Frustrated Gd3Ga5O12 Garnet Antiferromagnet","Despite the availability of a spin Hamiltonian for the Gd3Ga5O12 garnet (GGG)
for over twenty five years, there has so far been little theoretical insight
regarding the many unusual low temperature properties of GGG. Here we
investigate GGG in zero magnetic field using mean-field theory. We reproduce
the spin liquid-like correlations and, most importantly, explain the positions
of the sharp peaks seen in powder neutron diffraction experiments. We show that
it is crucial to treat accurately the long-range nature of the magnetic dipolar
interactions to allow for a determination of the small exchange energy scales
involved in the selection of the experimental ordering wave vector. Our results
show that the incommensurate order in GGG is classical in nature, intrinsic to
the microscopic spin Hamiltonian and not caused by weak disorder.",0511403v2
2006-11-20,Ill-Behaved Convergence of a Model of the Gd3Ga5O12 Garnet Antiferromagnet with Truncated Magnetic Dipole-Dipole Interactions,"Previous studies have found that calculations which consider long-range
magnetic dipolar interactions truncated at a finite cut-off distance Rc predict
spurious (unphysical) long-range ordered phases for Ising and Heisenberg
systems on the pyrochlore lattice. In this paper we show that, similar to these
two cases, calculations that use truncated dipolar interactions to model the
Gd3Ga5O12 garnet antiferromagnet also predict unphysical phases with
incommensurate ordering wave vector q_ord that is very sensitive to the dipolar
cut-off distance Rc.",0611531v1
2009-06-29,A Magnetization Sensitive Potential at Garnet-Metal Interfaces,"We investigate a magnetization-dependent voltage that appears at the
interface between garnets and various metals. The voltage is even in the
applied magnetic field and is dependent on the surface roughness and the
pressure holding the surfaces together. Large variations in the size, sign and
magnetic dependence are observed between different metal surfaces. Some
patterns have been identified in the measured voltages and a simple model is
described that can accommodate the gross features. The bulk magnetoelectric
response of one of our polycrystalline YIG samples is measured and is found to
be consistent with a term in the free energy that is quadratic in both the
electric and magnetic fields. However, the presence of such a term does not
fully explain the complex magnetization dependence of the measured voltages.",0906.5340v2
2010-06-15,Juxtaposition of Spin Freezing and Long Range Order in a Series of Geometrically Frustrated Antiferromagnetic Gadolinium Garnets,"Specific heat measurements in zero magnetic field are presented on a
homologous series of geometrically frustrated, antiferromagnetic, Heisenberg
garnet systems. Measurements of Gd3Ga5O12, grown with isotopically pure Gd,
agree well with previous results on samples with naturally abundant Gd, showing
no ordering features. In contrast, samples of Gd3Te2Li3O12 and Gd3Al5O12 are
found to exhibit clear ordering transitions at 243 mK and 175 mK respectively.
The effects of low level disorder are studied through dilution of Gd3+ with
non-magnetic Y3+ in Gd3Te2Li3O12. A thorough structural characterization, using
X-ray diffraction, is performed on all of the samples studied. We discuss
possible explanations for such diverse behavior in very similar systems.",1006.2969v2
2011-01-13,Optical identification of hybrid magnetic and electric excitations in Dy3Fe5O12 garnet,"Far-infrared spectra of magneto-dielectric Dy3Fe5O12 garnet were studied
between 13 and 100 cm-1 and at low temperatures between 5 and 80 K. A
combination of transmission, reflectivity, and rotating analyzer ellipsometry
was used to unambiguously identify the type of the dipole activity of the
infrared modes. In addition to purely dielectric and magnetic modes, we
observed several hybrid modes with a mixed magnetic and electric dipole
activity. These modes originate from the superexchange between magnetic moments
of Fe and Dy ions. Using 4x4 matrix formalism for materials with Mu=/=1, we
modeled the experimental optical spectra and determined the far-infrared
dielectric and magnetic permeability functions. The matching condition
Mu(Wh)*Se=Eps(Wh)*Sm for the oscillator strengths Se(m) explains the observed
vanishing of certain hybrid modes at Wh in reflectivity.",1101.2675v1
2011-09-29,Ratchet effects for paramagnetic beads above striped ferrite-garnet films,"We calculate the motion of a small paramagnetic bead which is manipulated by
the stripe domain pattern of a ferrite-garnet film. A model for the bead's
motion in a liquid above the film is developed and used to look for ratchet
solutions, where the bead acquires net coherent motion in one direction when
the external field is modulated periodically. We consider three cases. First,
the ratchet, where the beads all go in the same direction. Second, the height
dependent ratchet, where beads at different heights go in opposite direction.
This case can be used to separate beads of different sizes, as considered in J.
Phys. Chem. B 112, 3833 (2008). Third, we describe how the separation threshold
can be tuned by changing the amplitude of the applied field. Finally, we
describe a pseudo ratchet, where the external modulation is not periodic and
the ratchet changes direction periodically.",1109.6491v1
2013-07-26,Synchronous versus asynchronous transport of a paramagnetic particle in a modulated ratchet potential,"We present a combined experimental and theoretical study describing the
dynamical regimes displayed by a paramagnetic colloidal particle externally
driven above a stripe-patterned magnetic garnet film. A circularly polarized
rotating magnetic field modulates the stray field of the garnet film and
generates a translating periodic potential which induces particle motion.
Increasing the driving frequency, we observe a transition from a phase-locked
motion with constant speed to a sliding dynamics characterized by a lower speed
due to the loss of synchronization with the traveling potential. We explain the
experimental findings with an analytically tractable theoretical model and
interpret the particle dynamics in the presence of thermal noise. The model is
in good quantitative agreement with the experiments.",1307.7101v1
2013-11-01,Coherent Magnetism and Spin-Orbit Interaction in Garnet Films Probed with Femtosecond Magneto-Optical Four Wave Mixing,"We report about the dephasing of the spins states in a Garnet film excited by
femtosecond laser pulses. It is shown that magneto-optical four-wave-mixing
signals are efficiently generated and controlled with an external static
magnetic field. The self-diffraction of either two or three femtosecond pulses
allows us determining independently the coherent response time ($T_2$ < 50 fs)
and the population relaxation, which occurs in several steps. After the laser
induced demagnetization, the spin-lattice relaxation is the dominant mechanism
($T_{1,spin-lat}$ < 1.35 ps) and the precession of the magnetization takes
place at later times ($T_{1,prec}$ < 150 ps). The coherent response of the
spins states is modeled with a multi-level hydrogen-like system, taking into
account the fundamental relativistic quantum dynamics of the spins. Our
experimental approach is general and opens the way to investigating quantum
magnetism in ordered magnetic systems useful for applications in information
and communications technologies.",1311.0080v1
2014-01-22,Tunable interactions between paramagnetic colloidal particles driven in a modulated ratchet potential,"We study experimentally and theoretically the interactions between
paramagnetic particles dispersed in water and driven above the surface of a
stripe patterned magnetic garnet film. An external rotating magnetic field
modulates the stray field of the garnet film and generates a translating
potential landscape which induces directed particle motion. By varying the
ellipticity of the rotating field, we tune the inter-particle interactions from
net attractive to net repulsive. For attractive interactions, we show that
pairs of particles can approach each other and form stable doublets which
afterwards travel along the modulated landscape at a constant mean speed. We
measure the strength of the attractive force between the moving particles and
propose an analytically tractable model that explains the observations and is
in quantitative agreement with experiment.",1401.5754v1
2015-06-23,Effects of sublattice symmetry and frustration on ionic transport in garnet solid electrolytes,"We use rigorous group-theoretic techniques and molecular dynamics to
investigate the connection between structural symmetry and ionic conductivity
in the garnet family of solid Li-ion electrolytes. We identify new ordered
phases and order-disorder phase transitions that are relevant for conductivity
optimization. Ionic transport in this materials family is controlled by the
frustration of the Li sublattice caused by incommensurability with the host
structure at non-integer Li concentrations, while ordered phases explain
regions of sharply lower conductivity. Disorder is therefore predicted to be
optimal for ionic transport in this and other conductor families with strong Li
interaction.",1506.07142v1
2016-06-22,Garnet-free optical circulators monolithically integrated on spatially modified III-V quantum wells,"Optical circulators are indispensable components in photonic networks that
are aimed to route information in a unidirectional way among their N-ports1,2.
In general, these devices rely on magneto-optical garnets3 with appreciable
Verdet constants that are utilized in conjunction with other elements like
permanent magnets, wave-plates, birefringent crystals and/or beam splitters.
Consequently, these arrangements are typically bulky and hence not conducive to
on-chip photonic integration4-6. Of interest would be to devise strategies
through which miniaturized optical circulators can be monolithically fabricated
on light-emitting semiconductor platforms by solely relying on physical
properties that are indigenous to the material itself. By exploiting the
interplay between non-Hermiticity and nonlinearity, here we demonstrate a new
class of chip-scale circulators on spatially modified III-V quantum well
systems. These garnet-free unidirectional structures are broadband (over 2.5
THz) at 1550 nm, effectively loss-free, color-preserving, and in
proof-of-principle demonstrations have provided 23 dB isolation when used under
pulsed-mode conditions at milliwatt (mW) power levels.",1606.06949v1
2016-08-07,Ultrafast photo-magnetic recording in transparent medium,"Finding a conceptually new way to control the magnetic state of media with
the lowest possible production of heat and simultaneously at the fastest
possible time-scale is a new challenge in fundamental magnetism [1-4] as well
as an increasingly important issue in modern information technology [5]. Recent
results demonstrate that exclusively in metals it is possible to switch
magnetization between metastable states by femtosecond circularly polarized
laser pulses [6-8]. However, despite the record breaking speed of the
switching, the mechanisms in these materials are directly related to strong
optical absorption and laser-induced heating close to the Curie temperature
[9-12]. Here we report about ultrafast all-optical photo-magnetic recording in
transparent dielectrics. In ferrimagnetic garnet film a single linearly
polarized femtosecond laser pulse breaks the degeneracy between metastable
magnetic states and promotes switching of spins between them. Changing the
polarization of the laser pulse we deterministically steer the net
magnetization in the garnet, write ""0"" and ""1"" magnetic bits at will. This
mechanism operates at room temperature and allows ever fastest write-read
magnetic recording event (< 20 ps) accompanied by unprecedentedly low heat load
(< 6 J/cm3).",1609.05223v1
2017-02-14,Electromagnetic properties of terbium gallium garnet at millikelvin temperatures and single photon energy,"Electromagnetic properties of single crystal terbium gallium garnet (TGG) are
characterised from room down to millikelvin temperatures using the whispering
gallery mode method. Microwave spectroscopy is performed at low powers
equivalent to a few photons in energy and conducted as functions of the
magnetic field and temperature. A phase transition is detected close to the
temperature of 3.5 K. This is observed for multiple whispering gallery modes
causing an abrupt negative frequency shift and a change in transmission due to
extra losses in the new phase caused by a change in complex magnetic
susceptibility.",1702.04081v3
2017-05-30,"Enhanced magnetocaloric effect from Cr substitution in Ising lanthanide gallium garnets $Ln_3\text{CrGa}_4\text{O}_{12}$ ($Ln$ = Tb, Dy, Ho)","A detailed study on the crystal structure and bulk magnetic properties of Cr
substituted Ising type lanthanide gallium garnets
$Ln_3\text{CrGa}_4\text{O}_{12}$ ($Ln$ = Tb, Dy, Ho) has been carried out using
room temperature powder X-Ray and neutron diffraction, magnetic susceptibility,
isothermal magnetisation and heat capacity measurements. The magnetocaloric
effect (MCE) in $Ln_3\text{CrGa}_4\text{O}_{12}$ is compared to that of
$Ln_3\text{Ga}_5\text{O}_{12}$. In lower magnetic fields attainable by a
permanent magnet ($\leq$ 2 T), Cr substitution greatly enhances the MCE by 20%
for $Ln$ = Dy and 120% for $Ln$ = Ho compared to the unsubstituted
$Ln_3\text{Ga}_5\text{O}_{12}$. This is likely due to changes in the magnetic
ground state as Cr substitution also significantly reduces the frustration in
the magnetic lattice for the Ising type $Ln_3\text{Ga}_5\text{O}_{12}$.",1705.10547v1
2018-02-20,Comparison of the Magnetic properties of Mn3Fe2Si3O12 as a crystalline garnet and as a glass,"The crystalline garnet Mn3Fe2Si3O12 and an amorphous phase of the same
nominal composition are synthesized at high pressure. The magnetic properties
of the two forms are reported. Both phases order antiferromagnetically. The
crystalline phase exhibits a Curie-Weiss theta of -47.2 K, with a sharp
ordering transition at 12 K. The glassy phase exhibits a larger
antiferromagnetic Curie-Weiss theta, of -83.0 K, with a broad ordering
transition observed at 2.5 K. Both phases can be classified as magnetically
frustrated, although the amorphous phase shows a much higher degree of
frustration. The amorphous phase exhibits spin-glass behavior and is determined
to have an actual composition of Mn3Fe2Si3O13.",1802.07360v1
2018-08-14,"Comments on ""Amplifying magneto-optical photonic crystal, Appl. Phys. Lett. 97, 061116 (2010)""","This report concerns analytical solutions predicting the complex refractive
indices of doped crystals, based on empirical values of the refractive indices
of the dopant and the undoped crystal. An analytical approach in calculating
the refractive index of Erbium doped Gadolinium Gallium Garnet was reported by
another author previously. My first comment is related to the proposed solution
by the other author, where I have shown an alternative approach that leads to a
different solution. Although my comments are made in relation to Erbium as the
dopant and Gadolinium Gallium Garnet as the undoped lattice, the analytical
solution I propose here may be applied to any doped crystals. My second comment
concerns the limitations and mistreatment of McCumber relation in this context.",1809.04413v1
2018-11-01,Magnetodielectric effects at quantum critical fields in cobalt-containing garnets,"Here we present a comparative study of the magnetic and crystal chemical
properties of two Co2+ containing garnets, NaCa2Co2V3O12 and CaY2Co2Ge3O12.
Both phases exhibit the onset of antiferromagnetic order at 8K and 6K
respectively, as well as field-induced transitions in their magnetization at 1T
and around 11 T. We find these field-dependent transitions correspond to
quantum critical points that result in the suppression of antiferromagnetic
order and that these transitions can be clearly seen using magnetocapacitance
measurements. Finally, we perform detailed crystal chemistry analyses and
complimentary density functional theory calculations to show that changes in
the local environment of the Co-ions are responsible for differences in the two
magnetic structures and their respective properties.",1811.00165v1
2019-07-01,"Structural phase diagram and magnetic properties of Sc-substituted rare earth ferrites R1-xScxFeO3 (R=Lu, Yb, Er, and Ho)","We have studied the structural stability of Sc-substituted rare earth (R)
ferrites R1-xScxFeO3, and constructed a structural phase diagram for different
R and x. While RFeO3 and ScFeO3 adopt the orthorhombic and the bixbyite
structure respectively, the substituted compound R1-xScxFeO3 may be stable in a
different structure. Specifically, for R0.5Sc0.5FeO3, the hexagonal structure
can be stable for small R, such as Lu and Yb, while the garnet structure is
stable for larger R, such as Er and Ho. The formation of garnet structure of
the R0.5Sc0.5FeO3 compounds which requires that Sc occupies both the rare earth
and the Fe sites, is corroborated by their magnetic properties.",1907.01052v1
2019-08-09,Modeling Spin Dynamics in the Singlet Ground State Garnet Ho3Ga5O12,"Materials containing non-Kramers magnetic ions can show unusual quantum
excitations because of the exact mapping of the two-singlet crystal-field
ground state to a quantum model of Ising spins in a transverse magnetic field.
Here, we model the magnetic excitation spectrum of garnet-structured Ho3Ga5O12,
which has a two-singlet crystal-field ground state. We use a reaction-field
approximation to explain published inelastic neutron-scattering data [Zhou et
al., Phys. Rev. B 78, 140406(R) (2008)] using a three-parameter model
containing the magnetic dipolar interaction, the two-singlet crystal-field
splitting, and the nuclear hyperfine coupling. Our study clarifies the magnetic
Hamiltonian of Ho3Ga5O12, reveals that the nuclear hyperfine interaction drives
magnetic ordering in this system, and provides a framework for quantitative
analysis of magnetic excitation spectra of materials with singlet crystal-field
ground states.",1908.03530v1
2020-08-26,Hybrid Polymer-Garnet Materials for All-Solid-State Energy Storage Devices,"Hybrid electrolyte materials comprising polymer-ionic salt matrixes embedded
with garnet particles constitute a promising class of materials for the
realization of all-solid-state batteries. In addition to providing solutions to
the safety issues inherent to current liquid electrolytes, hybrid polymer
electrolytes offer advantages over other solid-state electrolytes. This is
because their functional properties such as ionic conductivity, electrochemical
stability, mechanical and thermal properties can be tailored to a particular
application by independently optimizing the properties of the constituent
materials. Thereby, providing a rational approach to solving bottlenecks
currently preventing solid-state electrolytes from practical implementation
into battery devices. This review starts with a survey of solid-state
electrolytes, focusing on their materials and ion transport limitations. Next,
we summarize the current understanding of transport mechanisms in composite
polymer electrolytes (CPEs) with the purpose of identifying materials solutions
for further improving their properties. The overall goal of the review is to
foster heightened research interest in these hybrid structures to rapidly
advance development of future all-solid-state battery devices.",2008.11855v2
2021-09-13,Model of the low temperature magnetic phases of gadolinium gallium garnet,"The magnetic behaviour of gadolinium gallium garnet in an external magnetic
field at zero temperature is considered. For high fields a classical spin model
of the gadolinium ions predicts a spin configuration that is periodic at the
level of the smallest repeating unit cell. The quantum version of the model is
treated via a truncated Holstein-Primakoff transformation with axes defined by
the classical spin configuration, and the magnon excitation bands are
calculated. The model predicts a transition in the field range of $1.9$ --
$2.1\mathrm{T}$, sensitive to the direction of the applied field, which is
caused by one or more magnon modes becoming soft as the field is decreased. In
general the soft modes occur at incommensurate wavevectors and therefore break
the periodicity of the spin configuration below the transition. One exception
occurs when the field aligns with one of the principle crystal axes, in which
case periodicity of the spin configuration is found to be maintained on a
larger crystallographic cubic cell even below the transition. This simple case
is studied in more detail. Comparisons are drawn with existing experimental
data, and further experimental tests of the model are suggested.",2109.05827v1
2023-03-18,Antiferromagnetism and Ising Ground States in the Rare-earth Garnet Nd$_3$Ga$_5$O$_{12}$,"In this paper, we investigate the low temperature magnetic properties of the
rare-earth garnet compound Nd$_3$Ga$_5$O$_{12}$ in detail by means of
magnetization, specific heat and magnetocaloric effect measurements. The
magnetic thermal properties along with the crystal field calculations reveal
that the Nd$^{3+}$ ions form into a frustrated hyper-kagome lattice with
connected triangles have an Ising-like ground state with the easy axis along
the local [100], [010] and [001] directions. Instead of a quantum spin liquid
ground state, an antiferromagnetically ordered state is found below
$T_{\mathrm{N}}=0.52~\rm K$. With applying field in the [111] direction, the
antiferromagnetic order is suppressed at the critical field of
$B_{\mathrm{c}}=0.75~\rm T$, and enhancement of the critical fluctuations with
linear crossover behaviors is observed near the critical point.",2303.10405v1
2023-11-11,Optimizing the tuning range of the Fermilab Recycler 53MHz RF cavities by exploiting the avoided crossing of the tuner and cavity modes,"The electromagnetic eigenmodes of the Fermilab Recycler RF cavities were
simulated with ACE3P running on NERSC's 'Perlmutter' supercomputer in an
attempt to optimize their tuning range to comfortably support slip-stacking. A
theory, based on coupled circuits and avoided crossings, was developed to
explain the origins of the tuning range for tuner-cavity waveguide systems.
This provided a logical, rigorous method to carry out this optimization,
although engineering problems due to high voltages in the tuner and the
operational $\mu$ range of the garnet had to be carefully implemented. It was
shown that the desired goal of 10kHz of tuning was not attainable with the
current cavity specifications. The maximum tuning range obtained was 5.59kHz
for a single tuner with a coaxial line of length 63in. A double tuner cavity
was also studied using the simulation software, although with little
improvement in the tuning range. A promising technique to improve the tuning
range involving the desynchronization of the garnets' magnetic permeabilities
is proposed.",2311.06571v1
2010-05-17,Vertical stratification of iron in atmospheres of blue horizontal-branch stars,"The aim of this study is to search for observational evidence of vertical
iron stratification in the atmosphere of fourteen blue horizontal-branch (BHB)
stars. We have found from our numerical simulations that five BHB stars: B22,
B186 in the globular cluster NGC 288, WF2-820, WF2-2692 in M13 and B203 in M15
show clear signatures of the vertical stratification of iron whose abundance
increases toward the lower atmosphere. Two other BHB stars (B334 in M15 and
B176 in M92) also show possible iron stratification in their atmosphere. A
dependence of the slope of iron stratification on the effective temperature was
also discovered. It is found that the vertical stratification of iron is
strongest in BHB stars with Teff around 11,500K. The slope of iron abundance
decreases as Teff increases and becomes negligible for the BHB stars with Teff=
14,000K. These results support the hypothesis regarding the efficiency of
atomic diffusion in the stellar atmospheres of BHB stars with Teff > 11,500K.",1005.2974v1
2011-01-04,The effect of varying Fe-content on transport properties of K intercalated iron selenide KxFe2-ySe2,"We report the successful growth of high-quality single crystals of potassium
intercalated iron selenide KxFe2-ySe2 by Bridgeman method. The effect of iron
vacancies on transport properties was investigated by electrical resistivity
and magnetic susceptibility measurements. With varying iron content, the system
passes from semiconducting/insulating to superconducting state. Comparing with
superconductivity, the anomalous ""hump"" effect in the normal state resistivity
is much more sensitive to the iron deficiency. The electrical resistivity
exhibits a perfect metallic behavior (R300K/R35K=42) for the sample with little
iron vacancies. Our results suggest that the anomalous ""hump"" effect in the
normal state resistivity may be due to the ordering process of the cation
vacancies in this non-stoichiometric compound rather than magnetic/structure
transition. A trace of superconductivity extending up to near 44 K was also
detected in some crystals of KxFe2-ySe2, which has the highest Tc of the
reported iron selenides.",1101.0789v1
2011-07-30,Phase Separation and Magnetic Order in K-doped Iron Selenide Superconductor,"Alkali-doped iron selenide is the latest member of high Tc superconductor
family, and its peculiar characters have immediately attracted extensive
attention. We prepared high-quality potassium-doped iron selenide (KxFe2-ySe2)
thin films by molecular beam epitaxy and unambiguously demonstrated the
existence of phase separation, which is currently under debate, in this
material using scanning tunneling microscopy and spectroscopy. The
stoichiometric superconducting phase KFe2Se2 contains no iron vacancies, while
the insulating phase has a \surd5\times\surd5 vacancy order. The iron vacancies
are shown always destructive to superconductivity in KFe2Se2. Our study on the
subgap bound states induced by the iron vacancies further reveals a
magnetically-related bipartite order in the superconducting phase. These
findings not only solve the existing controversies in the atomic and electronic
structures in KxFe2-ySe2, but also provide valuable information on
understanding the superconductivity and its interplay with magnetism in
iron-based superconductors.",1108.0069v1
2011-10-04,Transition metal impurity effect on charge and spin density in iron: Ab initio calculations and comparison with Mössbauer data,"Density functional theory was applied to study influence of the isolated
impurity located on the regular site of the alpha-Fe crystal on the charge and
spin density (hyperfine interactions) on the iron nucleus. Calculations were
performed by using both pseudopotential and the full potential methods. The
scalar relativistic approximation was applied. Perturbations of the charge and
spin density on iron were calculated for all d impurities soluble in iron and
additionally for Ga impurity. It was found that impurities have measurable
effect on the iron charge and spin density up to the second or third
coordination shell depending on the impurity. Hyperfine parameters of iron
adjacent to the impurity are affected by two intermixed physical mechanisms,
i.e., the volume mismatch due to the impurity and electron band mixing caused
by the electronic configuration of the impurity outer shells. Some correlations
between ab initio calculations and Moessbauer experimental results are
discussed. A table is provided with the parameters allowing calculate
Moessbauer spectrum of the binary iron alloy with d impurity or Ga. On the
other hand, provided parameters allow extraction from the Moessbauer data
information about impurity concentration and eventual order.",1110.0717v1
2013-07-23,Exploration of iron-chalcogenide superconductors,"Iron-chalcogenide compounds with FeSe(Te, S) layers did not attract much
attention until the discovery of high-Tc superconductivity (SC) in the
iron-pnictide compounds at the begining of 2008. Compared with FeAs-based
superconductors, iron-chalcogenide superconductors have aroused enormous
enthusiasm to study the relationship between SC and magnetisms with several
distinct features, such as different antiferromagnetic ground states with
relatively large moments in the parents, indicating possibly different
superconducting mechanisms, the existence of the excess Fe atoms or Fe
vacancies in the crystal lattice. Another reason is that the large single
crystals are easily grown for the iron-chalcogenide compounds. This review will
focus on our exploration for the iron-chalcogenide superconductors and
discussion on several issues, including the crystal structure, magnetic
properties, superconductivity, and phase separation. Some of them reach a
consensus but some important questions still remain to be answered.",1307.5991v1
2015-08-18,Elucidating the magnetic and superconducting phases in the alkali metal intercalated iron chalcogenides,"The complex interdigitated phases have greatly frustrated attempts to
document the basic features of the superconductivity in the alkali metal
intercalated iron chalcogenides. Here, using elastic neutron scattering,
energy-dispersive x-ray spectroscopy, and resistivity measurements, we
elucidate the relations of these phases in
Rb$_{1-\delta}$Fe$_y$Se$_{2-z}$S$_z$. We find: i) the iron content is crucial
in stabilizing the stripe antiferromagnetic (AF) phase with rhombic iron
vacancy order ($y\approx1.5$), the block AF phase with $\sqrt{5}\times
\sqrt{5}$ iron vacancy order ($y\approx1.6$), and the iron vacancy-free phase
($y\approx2$); ii) the superconducting phase ($z=0$) evolves into a metallic
phase ($z>1.5$) with sulfur substitution due to the progressive decrease of the
electronic correlation strength. Both the stripe AF phase and the block AF
phase are Mott insulators. Our data suggest that there are miscibility gaps
between these three phases. The existence of the miscibility gaps in the iron
content is the key to understanding the relationship between these complicated
phases.",1508.04482v1
2018-02-16,Manipulating surface magnetic order in iron telluride,"Control of emergent magnetic orders in correlated electron materials promises
new opportunities for applications in spintronics. For their technological
exploitation, it is important to understand the role of surfaces and interfaces
to other materials and their impact on the emergent magnetic orders. Here, we
demonstrate for iron telluride, the nonsuperconducting parent compound of the
iron chalcogenide superconductors, determination and manipulation of the
surface magnetic structure by low-temperature spin-polarized scanning tunneling
microscopy. Iron telluride exhibits a complex structural and magnetic phase
diagram as a function of interstitial iron concentration. Several theories have
been put forward to explain the different magnetic orders observed in the phase
diagram, which ascribe a dominant role either to interactions mediated by
itinerant electrons or to local moment interactions. Through the controlled
removal of surface excess iron, we can separate the influence of the excess
iron from that of the change in the lattice structure.",1802.05978v2
2022-02-17,Pressure-induced superconductivity in iron-based spin-ladder compound BaFe2+δ(S1-Sex)3,"The iron-based superconductors had a significant impact on condensed matter
physics. They have a common structural motif of a two-dimensional square iron
lattice and exhibit fruitful physical properties as a strongly correlated
electron system. During the extensive investigations, quasi-one-dimensional
iron-based spin-ladder compounds attracted much attention as a platform for
studying the interplay between magnetic and orbital ordering. In these
compounds, BaFe2S3 and BaFe2Se3 were found to exhibit superconductivity under
high pressure, having a different crystal and magnetic structure at low
temperature. We report a brief review of the iron-based spin-ladder compound
and recent studies for BaFe2+d(S1-xSex)3. BaFe2(S0.75 Se0.25)3 is in the
vicinity of the boundary of two different magnetic phases and it is intriguing
to perform high pressure experiments for studying superconductivity, since
effects of large magnetic fluctuations on superconductivity are expected. The
effect of iron stoichiometry on the interplay between magnetism and
superconductivity is also studied by changing the iron concentration in
BaFe2+dSe3.",2202.08525v1
2022-06-15,Anomalous Ettingshausen effect in iron-carbon alloys,"We have investigated the anomalous Ettingshausen effect (AEE) in iron-carbon
alloys, i.e., cast irons and steel, using the lock-in thermography. All the
alloys exhibit the clear AEE-induced temperature modulation, and their
anomalous Ettingshausen coefficient is an order of magnitude greater than that
of the pure iron at room temperature. The dimensionless figure of merit for AEE
in the ductile cast iron is 55 times greater than that in the pure iron owing
to the significant increase of the anomalous Ettingshausen coefficient. Our
result reveals a potential of iron-carbon alloys as transverse thermoelectric
materials, although the composition and microstructures optimizations are
necessary.",2206.07322v2
2003-10-29,On the Iron content in rich nearby Clusters of Galaxies,"In this paper we study the iron content of a sample of 22 nearby hot clusters
observed with BeppoSAX. We find that the global iron mass of clusters is
tightly related to the cluster luminosity and that the relatively loose
correlation between the iron mass and the cluster temperature follows from the
combination of the iron mass vs. luminosity and luminosity vs. temperature
correlations. The iron mass is found to scale linearly with the intracluster
gas mass, implying that the global iron abundance in clusters is roughly
constant. This result suggests that enrichment mechanisms operate at a similar
rate in all clusters. By employing population synthesis and chemical enrichment
models, we show that the iron mass associated to the abundance excess which is
always found in the centre of cool core clusters can be entirely produced by
the brightest cluster galaxy (BCG), which is always found at the centre of cool
core clusters. The iron mass associated to the excess, the optical magnitude of
the BCG and the temperature of the cluster are found to correlate with one
another suggesting a link between the properties of the BCG and the hosting
cluster. These observational facts lends strength to current formation theories
which envisage a strong connection between the formation of the giant BCG and
its hosting cluster.",0310828v1
2005-05-26,Thermal Evolution of Supernova Iron in Elliptical Galaxies,"In explaining the relative metal abundances observed in galaxy groups and
clusters, it is generally assumed that all metals created by supernovae are
present either in visible stars or the hot gas. We discuss here the possibility
that some of the iron expelled into the hot gas by Type Ia supernovae may have
radiatively cooled, avoiding detection by X-ray and optical observers.
Hydrodynamic models of Type Ia explosions in the hot gas inside elliptical
galaxies result in a gas of nearly pure iron that is several times hotter than
the local interstellar gas. We describe the subsequent thermal evolution of the
iron-rich gas as it radiates and thermally mixes with the surrounding gas.
There is a critical time by which the iron ions must mix into the ambient gas
to avoid rapid radiative cooling. We find that successful mixing is possible if
the iron ions diffuse with large mean free paths, as in an unmagnetized plasma.
However, in microgauss fields the Larmor radii of the iron ions are
exceptionally small, so the field geometry must be highly tangled or radial to
allow the iron to mix by diffusion faster than it cools by radiative losses.
The possibility that some of the supernova iron cools cannot be easily
discounted.",0505527v1
2005-12-16,A Magnetic and Moessbauer Spectral Study of Core/Shell Structured Fe/Au Nanoparticles,"Fe/Au nanoparticles have been chemically synthesized through a reverse
micelle reaction and investigated by both conventional and synchrotron based
x-ray diffraction and by magnetic and Moessbauer spectral studies. The powder
x-ray diffraction patterns reveal both the presence of crystalline alpha-iron
and gold and the absence of any crystalline iron oxides or other crystalline
products. First-order reversal curves, along with the major hysteresis loops of
the Fe/Au nanoparticles have been measured as a function of time in order to
investigate the evolution of their magnetic properties. The iron-57 Moessbauer
spectra of both uncoated iron nanoparticles and the Fe/Au nanoparticles have
been measured at 78 and 295 K and indicate that two major iron containing
components are present, namely the expected alpha-iron and the unexpected
amorphous Fe1-xBx alloy; several poorly crystallized ordered iron(III) oxide
components as well as paramagnetic iron(II) and iron(III) components are also
observed. These results indicate that the Fe-core/Au-shell nanoparticles
synthesized through reverse micelles are far more complex that had been
believed.",0512413v1
2006-09-15,Magnetic properties of iron nanoparticles prepared by exploding wire technique,"Nanoparticles of iron were prepared in distilled water using very thin iron
wires and sheets, by the electro-exploding wire technique. Transmission
electron microscopy reveals the size of the nanoparticles to be in the range 10
to 50 nm. However, particles of different sizes can be segregated by using
ultrahigh centrifuge. X-ray diffraction studies confirm the presence of the
cubic phase of iron. These iron nanoparticles were found to exhibit
fluorescence in the visible region in contrast to the normal bulk material. The
room temperature hysteresis measurements upto a field of 1.0 tesla were
performed on a suspension of iron particles in the solution as well as in the
powders obtained by filtration. The hysteresis loops indicate that the
particles are superparamagnetic in nature. The saturation magnetizations was ~
60 emu / gm. As these iron particles are very sensitive to oxygen a coating of
non-magnetic iron oxide tends to form around the particles giving it a core -
shell structure. The core particle size is estimated theoretically from the
magnetization measurements. Suspensions of iron nanoparticles in water have
been proposed to be used as an effective decontaminant for ground water.",0609370v1
2008-12-08,The Iron abundance in Galactic Planetary Nebulae,"We constrain the iron abundance in a sample of 33 low-ionization Galactic
planetary nebulae (PNe) using [Fe III] lines and correcting for the
contribution of higher ionization states with ionization correction factors
(ICFs) that take into account uncertainties in the atomic data. We find very
low iron abundances in all the objects, suggesting that more than 90% of their
iron atoms are condensed onto dust grains. This number is based on the solar
iron abundance and implies a lower limit on the dust-to-gas mass ratio, due
solely to iron, of M_dust/M_gas>1.3x10^{-3} for our sample. The depletion
factors of different PNe cover about two orders of magnitude, probably
reflecting differences in the formation, growth, or destruction of their dust
grains. However, we do not find any systematic difference between the gaseous
iron abundances calculated for C-rich and O-rich PNe, suggesting similar iron
depletion efficiencies in both environments. The iron abundances of our sample
PNe are similar to those derived following the same procedure for a group of 10
Galactic H II regions. These high depletion factors argue for high depletion
efficiencies of refractory elements onto dust grains both in molecular clouds
and AGB stars, and low dust destruction efficiencies both in interstellar and
circumstellar ionized gas.",0812.1578v2
2010-06-25,Missing Iron Problem and Type Ia Supernova Enrichment of Hot Gas in Galactic Spheroids,"Type Ia supernovae (Ia SNe) provide a rich source of iron for hot gas in
galactic stellar spheroids. However, the expected super-solar iron abundance of
the hot gas is not observed. Instead, X-ray observations often show decreasing
iron abundance toward galactic central regions, where the Ia SN enrichment is
expected to be the highest. We examine the cause of this missing iron problem
by studying the enrichment process and its effect on X-ray abundance
measurements of the hot gas. The evolution of Ia SN iron ejecta is simulated in
the context of galaxy-wide hot gas outflows, in both supersonic and subsonic
cases, as may be expected for hot gas in galactic bulges or elliptical galaxies
of intermediate masses. SN reverse-shock heated iron ejecta is typically found
to have a very high temperature and low density, hence producing little X-ray
emission. Such hot ejecta, driven by its large buoyancy, can quickly reach a
substantially higher outward velocity than the ambient medium, which is
dominated by mass loss from evolved stars. The ejecta is gradually and
dynamically mixed with the medium at large galactic radii. The ejecta is also
slowly diluted and cooled by {\sl insitu} mass injection from evolved stars.
These processes together naturally result in the observed positive gradient in
the average radial iron abundance distribution of the hot gas, even if
mass-weighted. This trend is in addition to the X-ray measurement bias that
tends to underestimate the iron abundance for the hot gas with a temperature
distribution.",1006.4976v1
2014-05-16,A hidden reservoir of Fe/FeS in interstellar silicates?,"The depletion of iron and sulphur into dust in the interstellar medium and
the exact nature of interstellar amorphous silicate grains is still an open
question. We study the incorporation of iron and sulphur into amorphous
silicates of olivine- and pyroxene-type and their effects on the dust
spectroscopy and thermal emission. We used the Maxwell-Garnett effective-medium
theory to construct the optical constants for a mixture of silicates, metallic
iron, and iron sulphide. We also studied the effects of iron and iron sulphide
in aggregate grains. Iron sulphide inclusions within amorphous silicates that
contain iron metal inclusions shows no strong differences in the optical
properties of the grains. A mix of amorphous olivine- and pyroxene-type
silicate broadens the silicate features. An amorphous carbon mantle with a
thickness of 10 nm on the silicate grains leads to an increase in absorption on
the short-wavelength side of the 10 $\mu$m silicate band. The assumption of
amorphous olivine-type and pyroxene-type silicates and a 10 nm thick amorphous
carbon mantle better matches the interstellar silicate band profiles. Including
iron nano-particles leads to an increase in the mid-IR extinction, while up to
5 ppm of sulphur can be incorporated as Fe/FeS nano inclusions into silicate
grains without leaving a significant trace of its presence.",1405.4208v1
2014-07-05,Fingering convection induced by atomic diffusion in stars: 3D numerical computations and applications to stellar models,"Iron-rich layers are known to form in the stellar subsurface through a
combination of gravitational settling and radiative levitation. Their presence,
nature and detailed structure can affect the excitation process of various
stellar pulsation modes, and must therefore be modeled carefully in order to
better interpret Kepler asteroseismic data. In this paper, we study the
interplay between atomic diffusion and fingering convection in A-type stars,
and its role in the establishment and evolution of iron accumulation layers. To
do so, we use a combination of three-dimensional idealized numerical
simulations of fingering convection, and one-dimensional realistic stellar
models. Using the three-dimensional simulations, we first validate the mixing
prescription for fingering convection recently proposed by Brown et al. (2013),
and identify what system parameters (total mass of iron, iron diffusivity,
thermal diffusivity, etc.) play a role in the overall evolution of the layer.
We then implement the Brown et al. (2013) prescription in the Toulouse-Geneva
Evolution code to study the evolution of the iron abundance profile beneath the
stellar surface. We find, as first discussed by Th\'eado et al. (2009), that
when the concurrent settling of helium is ignored, this accumulation rapidly
causes an inversion in the mean molecular weight profile, which then drives
fingering convection. The latter mixes iron with the surrounding material very
efficiently, and the resulting iron layer is very weak. However, taking helium
settling into account partially stabilizes the iron profile against fingering
convection, and a large iron overabundance can accumulate. The opacity also
increases significantly as a result, and in some cases ultimately triggers
dynamical convection.",1407.1437v1
2021-06-27,Pulsating iron spectral features in the emission of X-ray pulsar V0332+53,"We present results of phase- and time-resolved study of iron spectral
features in the emission of the Be/X-ray transient pulsar V0332+53, during its
type II outburst in 2004 using archival RXTE/PCA data. Coherent pulsations of
both fluorescent iron line at {\approx}6.4 keV and neutral iron K-edge at
{\approx}7.1 keV have been detected throughout the entire outburst. The
pulsating iron K-edge is reported for the first time for this object. Near the
peak of the outburst, the 3-12 keV pulse profile shows two deep, F_max / F_min
~ 2, and narrow dips of nearly identical shape, separated by exactly
{\Delta}{\phi}=0.5 in phase. The dip spectra are nearly identical to each other
and very similar in shape to the spectra outside the dips. The iron K-edge
peaks at the phase intervals corresponding to the dips, although its optical
depth {\tau}_K ~ 0.05 is by far insufficient to explain the dips. The iron line
shows pulsations with a complex pulse profile without any obvious correlation
with the total flux or optical depth of the K-edge. Accounting for the
component associated with reprocessing of the pulsar emission by the surface of
the donor star and circumstellar material, we find a very high pulsation
amplitude of the iron line flux, F_max / F_min ~ 10. We demonstrate that these
properties of V0332+53 can not be explained by contemporary emission models for
accreting X-ray pulsars and speculate about the origin of the observed iron
spectral features.",2106.14261v1
2021-09-21,Iron Rain: measuring the occurrence rate and origin of small iron meteoroids at Earth,"We report results of a four-year survey using Electron Multiplied Charged
Coupled Device (EMCCD) cameras recording 34761 two-station video meteor events
complete to a limiting magnitude of +6. The survey goal was to characterize
probable iron meteoroids. Using only physical properties of the meteor
trajectories including early peaking light curves, short luminous trajectories,
and high energies accumulated per area at beginning, we identified 1068 iron
meteors. Our iron candidates are most abundant at slow speeds < 15 km/s, where
they make up approximately 20% of the mm-sized meteoroid population. They are
overwhelmingly on asteroidal orbits, and have particularly low orbital
eccentricities and smaller semi-major axes when compared to non-irons between
10-20 km/s. Our iron population appears to be more numerous at fainter
magnitudes, comprising 15% of slow (10-15 km/s) meteors with peak brightness of
+3 with the fraction rising to 25% at +6 to +7, our survey limit. The iron
orbits are most consistent with an asteroidal source and are in highly evolved
orbits, suggesting long collisional lifetimes (107 years). Metal-rich
chondrules (nodules) found in abundance in EL Chondrites are one possible
source for this population. We also propose a possible technique using R-band
colours to more robustly identify fainter iron meteors with very high
confidence.",2109.10265v1
2010-11-21,Why the knee at 100 PeV could not be seen?,"It is shown that a ""second (iron) knee"" in cosmic ray spectrum expected at
energy about 100 PeV could not probably be found there. The reason is very
simple: the position of the ""iron knee"" depends on an answer to the questions:
""What do we see at 3-5 PeV? Is the knee seen at this energy associated with
proton or iron primaries?""",1011.4695v1
2015-04-20,Iron-Based Superconductors: current status of materials and pairing mechanism,"Since the discovery of high Tc iron-based superconductors in early 2008, more
than 15,000 papers have been published as a result of intensive research. This
paper describes the current status of iron-based superconductors (IBSC)
covering most up-to-date research progress along with the some background
research, focusing on materials (bulk and thin film) and pairing mechanism.",1504.04919v1
2021-08-05,"The electron-phonon coupling constant and the Debye temperature in polyhydrides of thorium, hexadeuteride of yttrium, and metallic hydrogen phase III","Milestone experimental discovery of superconductivity above 200 K in
highly-compressed sulphur hydride by Drozdov (Nature 525, 73 (2015)) sparked
experimental and theoretical investigations of metallic hydrides. Since then, a
dozen of superconducting binary and ternary polyhydrides have been discovered.
For instance, there are three superconducting polyhydrides of thorium: Th4H15,
ThH9, and ThH10 and four polyhydrides of yttrium: YH4, YH6, YH7, YH9. In
addition to binary and ternary hydrogen-based metallic compounds, recently
Eremets (arXiv:2109.11104) reported on the metallization of hydrogen, which
exhibits a phase transition into metallic hydrogen phase III at P>330 GPa and
T<200 K. Here we analyzed temperature-dependent resistance, R(T), in
polyhydrides of thorium, hexadeuteride of yttrium and in hydrogen phase III and
deduced the Debye temperature, $T$$_{\theta}$, and the electron-phonon coupling
constant, $\lambda_{e-ph}$, for these conductors. We found that Th4H15 phase
exhibits $\lambda_{e-ph}$ = 0.82-0.99 which is in a very good agreement with
experimental value of $\lambda_{e-ph}$ = 0.84 deduced from heat capacity
measurements (Miller, Phys. Rev. B 14, 2795 (1976)). For P63/mmc-ThH9 phase (P
= 170 GPa) we deduced $\lambda_{e-ph}$(170 GPa) = 1.46, which is in a
reasonable agreement with $\lambda_{e-ph}$ reported by Semenok (Materials Today
33, 36 (2020)). Deduced $\lambda_{e-ph}$(170 GPa) = 1.70 for Fm-3m-ThH10 is in
remarkable agreement with first-principles calculated $\lambda_{e-ph}$(174
GPa)=1.75 (Semenok, Materials Today 33, 36 (2020)). Deduced
$\lambda_{e-ph}$(172 GPa) = 1.90 for Im-3m-YD6 is also in excellent agreement
with first-principles calculated $\lambda_{e-ph}$(165 GPa)=1.80 (Troyan,
Advanced Materials 33, 2006832 (2021)). And finally, we deduced
$T$$_{\theta}$(402 GPa) = 727 K for hydrogen phase III which implies that
$\lambda_{e-ph}$(402 GPa)<1.7 in this metal.",2108.02610v4
2023-07-21,Ultra-fast yttrium hydride chemistry at high pressures via non-equilibrium states induced by x-ray free electron laser,"Controlling the formation and stoichiometric content of desired phases of
materials has become a central interest for the study of a variety of fields,
notably high temperature superconductivity under extreme pressures. The further
possibility of accessing metastable states by initiating reactions by x-ray
triggered mechanisms over ultra-short timescales is enabled with the
development of x-ray free electron lasers (XFEL). Utilizing the exceptionally
high brilliance x-ray pulses from the EuXFEL, we report the synthesis of a
previously unobserved yttrium hydride under high pressure, along with
non-stoichiometric changes in hydrogen content as probed at a repetition rate
of 4.5\,MHz using time-resolved x-ray diffraction. Exploiting non-equilibrium
pathways we synthesize and characterize a hydride with yttrium cations in an
\textit{A}15 structure type at 125\,GPa, predicted using crystal structure
searches, with a hydrogen content between 4.0--5.75 hydrogens per cation, that
is enthalpically metastable on the convex hull. We demonstrate a tailored
approach to changing hydrogen content using changes in x-ray fluence that is
not accessible using conventional synthesis methods, and reveals a new paradigm
in metastable chemical physics.",2307.11293v1
1999-06-08,Radiative Levitation in Hot Horizontal Branch Stars,"There is now considerable evidence that horizontal branch (HB) stars hotter
than about 11,500 K experience an enormous enhancement of their photospheric
iron abundance due to radiative levitation. In globular clusters, the
photospheric iron abundance can reach values of [Fe/H] ~ +0.3, or up to two
orders of magnitude higher than the cluster iron abundance. Model atmospheres
which take into account the iron overabundance are needed for understanding the
appearance of the HB in globular cluster color-magnitude diagrams (CMDs), for
the derivation of accurate luminosities, gravities and masses, and for the
ultraviolet spectral synthesis of old, metal-poor stellar populations.",9906123v1
1999-06-14,Iron line afterglows: general constraints,"The discovery of a powerful and transient iron line feature in the X-ray
afterglow spectra of gamma-ray bursts would be a major breakthrough for
understanding the nature of their progenitors, strongly suggesting the presence
of a large, iron rich, mass in the vicinity of the burst event.
Model-independent limits to the size and the mass of the the iron line emitting
region are derived and discussed. We also discuss how these results can be used
to constrain the amount of beaming or anisotropy of the burst emission.",9906234v1
1999-06-14,Iron line afterglows: how to produce them,"We discuss how a powerful iron line emission can be produced if ~1-5 iron
rich solar masses are concentrated in the close vicinity of the burst.
Recombination, thermal and fluorescent reflection are discussed. We find that
recombination suffers the high Compton temperature of the plasma while the
other two scenarios are not mutually exclusive and could account for the
claimed iron line detected in two afterglows.",9906235v1
2003-01-31,Non-collinear magnetism in iron at high pressures,"Using a first principles based, magnetic tight-binding total energy model,
the magnetization energy and moments are computed for various ordered spin
configurations in the high pressure polymorphs of iron (fcc, or $\gamma$-Fe,
and hcp, or $\epsilon$-Fe), as well ferromagnetic bcc iron ($\alpha$-Fe). For
hcp, a non-collinear, antiferromagnetic, spin configuration that minimizes
unfavorable ferromagnetic nearest neighbor ordering is the lowest energy state
and is more stable than non-magnetic $\epsilon$ iron up to about 75 GPa.
Accounting for non-collinear magnetism yields better agreement with the
experimental equation of state, in contrast to the non-magnetic equation of
state, which is in poor agreement with experiment below 50 GPa.",0301615v1
2004-01-16,Ferromagnetism in Fe-doped SnO2 thin films,"Thin films grown by pulsed-laser deposition from targets of Sn0.95Fe0.05O2
are transparent ferromagnets with Curie temperature and spontaneous
magnetization of 610 K and 2.2 Am2kg-1, respectively. The 57Fe Mossbauer
spectra show the iron is all high-spin Fe3+ but the films are magnetically
inhomogeneous on an atomic scale, with only 23 % of the iron ordering
magnetically. The net ferromagnetic moment per ordered iron ion, 1.8 Bohr
magnetons, is greater than for any simple iron oxide. Ferromagnetic coupling of
ferric ions via an electron trapped in a bridging oxygen vacancy (F center) is
proposed to explain the high Curie temperature",0401293v1
2008-07-29,The effect of pressure and spin on the isotopic composition of ferrous iron dissolved in periclase and silicate perovskite,"We perform density functional calculations of the equilibrium 57Fe/54Fe
ratios for ferrous iron dissolved in periclase and MgSiO3 perovskite at the
pressures and temperatures of the Earth's mantle. Pressure increases the
partitioning of 57Fe into both phases by a factor of three from the Earth's
surface to the core-mantle boundary. In ferropericlase, a large contribution to
this increase comes from the electronic transition from high-spin to low-spin
iron. Our calculations demonstrate that pressure-induced fractionation can play
a major role in determining planetary iron-isotope composition.",0807.4742v1
2008-08-13,Coreless Terrestrial Exoplanets,"Differentiation in terrestrial planets is expected to include the formation
of a metallic iron core. We predict the existence of terrestrial planets that
have differentiated but have no metallic core--planets that are effectively a
giant silicate mantle. We discuss two paths to forming a coreless terrestrial
planet, whereby the oxidation state during planetary accretion and
solidification will determine the size or existence of any metallic core. Under
this hypothesis, any metallic iron in the bulk accreting material is oxidized
by water, binding the iron in the form of iron oxide into the silicate minerals
of the planetary mantle. The existence of such silicate planets has
consequences for interpreting the compositions and interior density structures
of exoplanets based on their mass and radius measurements.",0808.1908v1
2009-07-01,Role of soft-iron impellers on the mode selection in the VKS dynamo experiment,"A crucial point for the understanding of the von-K\'arm\'an-Sodium (VKS)
dynamo experiment is the influence of soft-iron impellers. We present numerical
simulations of a VKS-like dynamo with a localized permeability distribution
that resembles the shape of the flow driving impellers. It is shown that the
presence of soft-iron material essentially determines the dynamo process in the
VKS experiment. % An axisymmetric magnetic field mode can be explained by the
combined action of the soft-iron disk and a rather small $\alpha$-effect
parametrizing the induction effects of unresolved small scale flow
fluctuations.",0907.0123v2
2009-08-08,A Unified Description of Cuprate and Iron Arsenide Superconductors,"We propose a unified description of cuprate and iron-based superconductivity.
Consistency with magnetic structure inferred from neutron scattering implies
significant constraints on the symmetry of the pairing gap for the iron-based
superconductors. We find that this unification requires the orbital pairing
formfactors for the iron arsenides to differ fundamentally from those for
cuprates at the microscopic level.",0908.1147v1
2009-08-27,A new 111 type iron pnictide superconductor LiFeP,"A new iron pnictide LiFeP superconductor was found. The compound crystallizes
into a Cu2Sb structure containing an FeP layer showing superconductivity with
maximum Tc of 6K. This is the first 111 type iron pnictide superconductor
containing no arsenic. The new superconductor is featured with itinerant
behavior at normal state that could helpful to understand the novel
superconducting mechanism of iron pnictide compounds.",0908.4043v1
2009-08-29,Spin-Phonon Coupling in Iron Pnictide Superconductors,"The magnetic moment in the parent phase of the iron-pnictide superconductors
varies with composition even when the nominal charge of iron is unchanged. We
propose the spin-lattice coupling due to the magneto-volume effect as the
primary origin of this effect, and formulate a Landau theory to describe the
dependence of the moment to the Fe-As layer separation. We then compare the
superconductive critical temperature of doped iron pnictides to the local
moment predicted by the theory, and suggest that the spin-phonon coupling may
play a role in the superconductivity of this compound.",0908.4361v1
2011-10-03,Calculated phonon spectra of paramagnetic iron at the alpha-gamma phase transition,"We compute lattice dynamical properties of iron at the bcc-fcc phase
transition using dynamical mean-field theory implemented with the frozen-phonon
method. Electronic correlations are found to have a strong effect on the
lattice stability of paramagnetic iron in the bcc phase. Our results for the
structural phase stability and lattice dynamical properties of iron are in good
agreement with experiment.",1110.0439v1
2013-07-22,Angle-resolved photoemission spectroscopy study on iron-based superconductors,"Angle-resolved photoemission spectroscopy (ARPES) has played an important
role in determining the band structure and the superconducting gap structure of
iron-based superconductors. Here from the ARPES perspective, we briefly review
the main results from our group in the recent years on the iron-based
superconductors and their parent compounds, and depict our current
understanding on the antiferromagnetism and superconductivity in these
materials.",1307.5754v3
2014-07-01,Explaining Mercury's Density through Magnetic Erosion,"In protoplanetary disks, dust grains rich in metallic iron can attract each
other magnetically. If they are magnetized to values near saturation, the
magnetically induced collision speeds are high enough to knock off the
non-magnetized, loosely bound silicates. This process enriches the surviving
portions of the dust grains in metallic iron, which further enhances the
magnetically mediated collisions. The magnetic enhancement to the collisional
cross-section between the iron rich dust results in rapid grain growth leading
to planetesimal formation. While this process of knocking off silicates, which
we term ""magnetic erosion"", occurs only in a very limited portion of a
protoplanetary disk, it is a possible explanation for Mercury's
disproportionately large iron core.",1407.0274v1
2015-05-22,Oxygen-annealing effects on superconductivity in polycrystalline Fe1-xTe1-ySey,"Superconductivity in anti-PbO-type iron chalcogenides Fe1-xTe1-ySey (x = 0,
0.1, y = 0.1 0.4) depends on the amount (x) of interstitial iron atoms located
between the FeTe1-ySey layers. Non-superconducting samples of nominal
Fe1.1Te1-ySey convert to superconductors with critical temperatures up to 14 K
after annealing at 300{\deg}C in an oxygen atmosphere. The process is
irreversible upon subsequent hydrogen annealing. Magnetic measurements are
consistent with the formation of iron oxides suggesting that oxygen annealing
preferably extracts interstitial iron from Fe1-xTe1-ySey which interfere with
superconductivity.",1505.06066v1
2015-10-06,Iron emission line from the spiral galaxy M101,"Archival Suzaku data of the face-on spiral galaxy M101 were analyzed. An
intense emission line at 6.72^{+0.10}_{-0.12} keV was detected in the central
region. This line is identified with a K-line from He-like iron, which
indicates the existence of a thin thermal plasma with a temperature of several
keV. The iron line luminosity within the central 5 arcmin radius region is
estimated to be (2-12)x10^{37} erg s^{-1}. The origin of the iron emission line
is discussed.",1510.01483v1
2015-10-29,Effect of antimony substitution in iron pnictide compounds,"In the present study we have examined the effect of negative chemical
pressure in iron pnictides. We have synthesized substitution series replacing
arsenic by antimony in a number of 1111- and 122-iron arsenides and present
their crystallographic and physical properties. The SDW transition temperature
in LaFeAs$_{\mathrm{1-x}}$Sb$_{\mathrm{x}}$O decreases with increasing antimony
content, while the superconducting transition temperature in
LaFeAs$_{\mathrm{1-x}}$Sb$_{\mathrm{x}}$O$_{\mathrm{0.85}}$F$_{\mathrm{0.15}}$
initially increases with Sb substitution. 1111-compounds with samarium instead
of lanthanum have a smaller unit cell volume. In these phases, no Sb solubility
is observed. There is also no apparent solubility of antimony in the 122-iron
arsenides.",1510.08665v1
2015-12-03,Non-LTE iron abundances in cool stars: The role of hydrogen collisions,"In the aim of determining accurate iron abundances in stars, this work is
meant to empirically calibrate H-collision cross-sections with iron, where no
quantum mechanical calculations have been published yet. Thus, a new iron model
atom has been developed, which includes hydrogen collisions for excitation,
ionization and charge transfer processes. We show that collisions with hydrogen
leading to charge transfer are important for an accurate non-LTE modeling. We
apply our calculations on several benchmark stars including the Sun, the
metal-rich star {\alpha} Cen A and the metal-poor star HD140283.",1512.01118v1
2016-09-14,Iron Isotope Effect in SmFeAsO0.65 and SmFeAsO0.77H0.12 Superconductors: A Raman Study,"We report the inelastic light scattering studies on SmFeAsO0.65 and
SmFeAsO0.77H0.12 with iron isotopes namely 54Fe and 57Fe. In both of these
systems under investigation we observed a significant shift in the frequency of
the phonon modes associated with the displacement of Fe atoms around ~ 200
cm-1. The observed shift in the Fe mode (B1g) for SmFeAsO0.65 is ~ 1.4 % and
lower in case of SmFeAsO0.77H0.12, which is ~ 0.65 %, attributed to the lower
percentage of isotopic substitution in case of SmFeAsO0.77H0.12. Our study
reveals the significant iron isotope effect in these systems hinting towards
the crucial role of electron-phonon coupling in the pairing mechanism of iron
based superconductors.",1609.04183v1
2017-03-31,Longitudinal modes of spin fluctuations in iron-based superconductors,"Iron-based superconductors can exhibit different magnetic ground states and
are in a critical magnetic region where frustrated magnetic interactions
strongly compete with each other. Here we investigate the longitudinal modes of
spin fluctuations in an unified effective magnetic model for iron-based
superconductors. We focus on the collinear antiferromagnetic phase (CAF) and
calculate the behavior of the longitudinal modes when different phase
boundaries are approached. The results can help to determine the nature of the
magnetic fluctuations in iron-based superconductors.",1703.10721v2
2018-01-10,The IRON Project: Photoionization of Fe ions,"The IRON Project, initiated in 1991, aims at two main objectives, i) study
the characteristics of and calculate large-scale high accuracy data for atomic
radiative and collisional processes, and ii) application in solving
astrophysical problems. It focuses on the complex iron and iron-peak elements
commonly observed in the spectra of astrophysical plasmas. The present report
will illustrate the characteristics of the dominant atomic process of
photoionization that have been established under the project and the preceding
the Opacity Project and their importance in applications.",1801.05410v1
2018-06-08,Helium-iron compounds at terapascal pressures,"We investigate the binary phase diagram of helium and iron using
first-principles calculations. We find that helium, which is a noble gas and
inert at ambient conditions, forms stable crystalline compounds with iron at
terapascal pressures. A FeHe compound becomes stable above 4 TPa, and a
FeHe$_2$ compound above 12 TPa. Melting is investigated using molecular
dynamics simulations, and a superionic phase with sublattice melting of the
helium atoms is predicted. We discuss the implications of our predicted
helium-iron phase diagram for interiors of giant (exo)planets and white dwarf
stars.",1806.03017v1
2018-11-09,Topological quantum states of matter in iron-based superconductors: From concepts to material realization,"We review recent progress in the explorations of topological quantum states
of matter in iron-based superconductors. In particular, we focus on the
nontrivial topology existing in the band structures and superconducting states
of iron's 3d orbitals. The basic concepts, models, materials and experimental
results are reviewed. The natural integration between topology and
high-temperature superconductivity in iron-based superconductors provides great
opportunities to study topological superconductivity and Majorana modes at high
temperature.",1811.03802v1
2019-02-24,Spin interactions and magnetic order in the iron oxychalcogenides BaFe2Q2O,"The ability to tune the iron chalcogenides BaFe2Q3 from Mott insulators, to
metals and then superconductors with applied pressure has renewed interest in
low-dimensional iron chalcogenides and oxychalcogenides. We report here a
combined experimental and theoretical study on the iron oxychalcogenides
BaFe2Q2O (Q=S, Se) and show that their magnetic behaviour results from
nearest-neighbour magnetic exchange interactions via oxide and selenide anions
of similar strength, with properties consistent with more localised electronic
structures than those of BaFe2Q3 systems.",1902.09035v2
2021-11-04,Sequence of superconducting states in field cooled $FeCr_2S_4$,"In the present article we discuss theoretically the emergence of
superconductivity in field cooled $FeCr_2S_4$. The chromium electrons form a
triplet $t_{2g}$ states and due to antiferromagnetic exchange with the iron
spins have Zeeman splitting. Applied, during preparation, magnetic field along
the moment of iron ions, successively compensates the Zeeman splittings. The
chromium electrons with zero Zeeman energy form Cooper pairs induced by iron
magnons. In that way, we predict theoretically the existence of sequence of
superconducting states in field cooled $FeCr_2S_4$. Actually there are three
different superconductors prepared applying, during preparation, different
magnetic fields. In these compounds superconductivity coexist with the
saturated magnetism of iron ions.",2111.02765v1
2023-07-03,Cosmic abundance of iron,"I explore a possibility to estimate an upper limit of the current iron
abundance of the barion matter. The upper limit is determined by the minimal
iron abundance, at which the gamma-ray background, produced by the decay of
$^{56}$Ni synthesised in the Universe to date, contradicts the observational
MeV gamma-ray background. I calculate the gamma-ray background from SNe~Ia and
SNe~II with the gamma-ray scattering and absorption in supernova envelope. It
is shown that the model background does not contradict the observed MeV
background, if the present day iron abundance of the barion matter is less than
15\% of the solar abundance.",2307.00944v1
2014-08-19,Soft chemical control of superconductivity in lithium iron selenide hydroxides Li1-xFex(OH)Fe1-ySe,"Hydrothermal synthesis is described of layered lithium iron selenide
hydroxides Li1-xFex(OH)Fe1-ySe (x ~ 0.2; 0.02 < y < 0.15) with a wide range of
iron site vacancy concentrations in the iron selenide layers. This iron vacancy
concentration is revealed as the only significant compositional variable and as
the key parameter controlling the crystal structure and the electronic
properties. Single crystal X-ray diffraction, neutron powder diffraction and
X-ray absorption spectroscopy measurements are used to demonstrate that
superconductivity at temperatures as high as 40 K is observed in the
hydrothermally synthesised samples when the iron vacancy concentration is low
(y < 0.05) and when the iron oxidation state is reduced slightly below +2,
while samples with a higher vacancy concentration and a correspondingly higher
iron oxidation state are not superconducting. The importance of combining a low
iron oxidation state with a low vacancy concentration in the iron selenide
layers is emphasised by the demonstration that reductive post-synthetic
lithiation of the samples turns on superconductivity with critical temperatures
exceeding 40 K by displacing iron atoms from the Li1-xFex(OH) reservoir layer
to fill vacancies in the selenide layer",1408.4350v2
1997-02-04,Roles of SNIa and SNII in ICM Enrichment,"Based on ASCA observations Mushotzky et al. (1996, ApJ 466, 686) have
recently derived the relative-abundance ratios of $\alpha$-elements to iron,
[\alpha/Fe] \simeq 0.2-0.3$, for four rich clusters, and have suggested that
the origin of metals in an intra-cluster medium (ICM) is not a type-Ia
supernovae (SNIa), but a type-II supernovae (SNII). However, these authors used
the solar photospheric iron abundance for ASCA data reduction, while the
meteoritic iron abundance is usually adopted in chemical-evolution studies. It
is true that although the photospheric and meteoritic solar abundances are
consistent for most of the elements, a serious discrepancy is known to exist
for iron; indeed, the photospheric abundance of iron is $N_{Fe}/N_H = 4.68
10^{-5}$ by number, while the meteoritic value is $3.24 10^{-5}$. The argument
concerning the relative roles of SNIa and SNII in ICM enrichment is quite
sensitive to the precise values of [\alpha/Fe], and one should use an identical
solar iron abundance in data reduction as well as in theoretical arguments. We
therefore adopt the meteoritic iron abundance, which is consistent with
chemical-evolution studies, and shift Mushotzky et al.'s ASCA data by
$\Delta[\alpha/Fe] \simeq -0.16$ dex. By comparing the corrected [\alpha/Fe]
values with theoretical nucleosynthesis prescriptions of SNIa and SNII, we
reach a conclusion that an SNIa iron contribution of 50% or higher in the ICM
enrichment could not be ruled out, and might indeed be favoured based on the
ASCA spectra.",9702036v1
2008-08-09,Iron Behaving Badly: Inappropriate Iron Chelation as a Major Contributor to the Aetiology of Vascular and Other Progressive Inflammatory and Degenerative Diseases,"The production of peroxide and superoxide is an inevitable consequence of
aerobic metabolism, and while these particular ""reactive oxygen species"" (ROSs)
can exhibit a number of biological effects, they are not of themselves
excessively reactive and thus they are not especially damaging at physiological
concentrations. However, their reactions with poorly liganded iron species can
lead to the catalytic production of the very reactive and dangerous hydroxyl
radical, which is exceptionally damaging, and a major cause of chronic
inflammation. We review the considerable and wide-ranging evidence for the
involvement of this combination of (su)peroxide and poorly liganded iron in a
large number of physiological and indeed pathological processes and
inflammatory disorders, especially those involving the progressive degradation
of cellular and organismal performance. These diseases share a great many
similarities and thus might be considered to have a common cause (i.e.
iron-catalysed free radical and especially hydroxyl radical generation). The
studies reviewed include those focused on a series of cardiovascular, metabolic
and neurological diseases, where iron can be found at the sites of plaques and
lesions, as well as studies showing the significance of iron to aging and
longevity. The effective chelation of iron by natural or synthetic ligands is
thus of major physiological (and potentially therapeutic) importance. As
systems properties, we need to recognise that physiological observables have
multiple molecular causes, and studying them in isolation leads to inconsistent
patterns of apparent causality when it is the simultaneous combination of
multiple factors that is responsible. This explains, for instance, the
decidedly mixed effects of antioxidants that have been observed, etc...",0808.1371v1
2008-11-24,The optical/X-ray connection: ICM iron content and galaxy optical luminosity in 20 galaxy clusters,"X-ray observations of galaxy clusters have shown that the intra-cluster gas
has iron abundances of about one third of the solar value. These observations
also show that part (if not all) of the intra-cluster gas metals were produced
within the member galaxies. We present a systematic analysis of 20 galaxy
clusters to explore the connection between the iron mass and the total
luminosity of early-type and late-type galaxies, and of the brightest cluster
galaxies (BCGs). From our results, the intra-cluster medium (ICM) iron mass
seems to correlate better with the luminosity of the BCGs than with that of the
red and blue galaxy populations. As the BCGs cannot produce alone the observed
amount of iron, we suggest that ram-pressure plus tidal stripping act together
to enhance, at the same time, the BCG luminosities and the iron mass in the
ICM. Through the analysis of the iron yield, we have also estimated that SN Ia
are responsible for more than 50% of the total iron in the ICM. This result
corroborates the fact that ram-pressure contributes to the gas removal from
galaxies to the inta-cluster medium, being very efficient for clusters in the
temperature range 2 < kT (keV)< 10",0811.3936v1
2009-10-25,Pair-breaking in iron-pnictides,"The puzzling features of the slopes of the upper critical field at the
critical temperature $T_c$, $H^\prime_{c2}(T_c)\propto T_c$, and of the
specific heat jump $\Delta C\propto T_c^3$ of iron-pnictides are interpreted as
caused by a strong pair-breaking.",0910.4728v1
2009-12-28,Iron pnictide superconductors: Electrons on the verge,"An optical analysis reveals that the electronic correlations in the `parent'
compounds of the iron pnictide superconductors are sufficiently strong to
significantly impede the mobility of the electrons.",0912.4989v1
2010-05-19,Rusty old stars: a source of the missing interstellar iron?,"Iron, the Universe's most abundant refractory element, is highly depleted in
both circumstellar and interstellar environments, meaning it exists in solid
form. The nature of this solid is unknown. In this Letter, we provide evidence
that metallic iron grains are present around oxygen-rich AGB stars, where it is
observationally manifest as a featureless mid-infrared excess. This
identification is made using Spitzer Space Telescope observations of evolved
globular cluster stars, where iron dust production appears ubiquitous and in
some cases can be modelled as the only observed dust product. In this context,
FeO is examined as the likely carrier for the 20-micron feature observed in
some of these stars. Metallic iron appears to be an important part of the dust
condensation sequence at low metallicity, and subsequently plays an influential
role in the interstellar medium. We explore the stellar metallicities and
luminosities at which iron formation is observed, and how the presence of iron
affects the outflow and its chemistry. The conditions under which iron can
provide sufficient opacity to drive a wind remain unclear.",1005.3489v1
2010-10-14,"Bipolaron Model of the Superconductivity of an Iron-Based Layered Compound LnO_{1-x}F_xFePn (Ln =La, Sm, Nd, Pr, Ce, Pn=P, As)","A bipolaron model is proposed as a superconductivity mechanism for iron-based
superconductivity. The results are consistent with the experiments.",1010.3026v1
2012-02-19,Spin fluctuations and superconductivity in powders of Fe_1+xTe_0.7Se_0.3 as a function of interstitial iron concentration,"Using neutron inelastic scattering, we investigate the role of interstitial
iron on the low-energy spin fluctuations in powder samples of
Fe_{1+x}Te_{0.7}Se_{0.3}. We demonstrate how combining the principle of
detailed balance along with measurements at several temperatures allows us to
subtract both temperature-independent and phonon backgrounds from S(Q,\omega)
to obtain purely magnetic scattering. For small values of interstitial iron
(x=0.009(3)), the sample is superconducting (T_{c}=14 K) and displays a spin
gap of 7 meV peaked in momentum at wave vector q_{0}=(\pi,\pi) consistent with
single crystal results. On populating the interstitial iron sites, the
superconducting volume fraction decreases and we observe a filling in of the
low-energy magnetic fluctuations and a decrease of the characteristic wave
vector of the magnetic fluctuations. For large concentrations of interstitial
iron (x=0.048(2)) where the superconducting volume fraction is minimal, we
observe the presence of gapless spin fluctuations at a wave vector of
q_{0}=(\pi,0). We estimate the absolute total moment for the various samples
and find that the amount of interstitial iron does not change the total
magnetic spectral weight significantly, but rather has the effect of shifting
the spectral weight in Q and energy. These results show that the
superconducting and magnetic properties can be tuned by doping small amounts of
iron and are suggestive that interstitial iron concentration is also a
controlling dopant in the Fe_{1+x}Te_{1-y}Se_{y} phase diagram in addition to
the Te/Se ratio.",1202.4152v1
2016-05-06,Iron: A Key Element for Understanding the Origin and Evolution of Interstellar Dust,"The origin and depletion of iron differ from all other abundant refractory
elements that make up the composition of the interstellar dust. Iron is
primarily synthesized in Type Ia supernovae (SNe Ia) and in core collapse
supernovae (CCSN), and is present in the outflows from AGB stars. Only the
latter two are observed to be sources of interstellar dust, since searches for
dust in SN~Ia have provided strong evidence for the absence of any significant
mass of dust in their ejecta. Consequently, more than 65% of the iron is
injected into the ISM in gaseous form. Yet, ultraviolet and X-ray observations
along many lines of sight in the ISM show that iron is severely depleted in the
gas phase compared to expected solar abundances. The missing iron, comprising
about 90% of the total, is believed to be locked up in interstellar dust. This
suggests that most of the missing iron must have precipitated from the ISM gas
by cold accretion onto preexisting silicate, carbon, or composite grains. Iron
is thus the only element that requires most of its growth to occur outside the
traditional stellar condensation sources. This is a robust statement that does
not depend on our evolving understanding of the dust destruction efficiency in
the ISM. Reconciling the physical, optical, and chemical properties of such
composite grains with their many observational manifestations is a major
challenge for understanding the nature and origin of interstellar dust.",1605.01957v1
2018-06-25,Fermi surface pockets in electron-doped iron superconductor by Lifshitz transition,"The Fermi surface pockets that lie at the corner of the two-iron Brillouin
zone in heavily electron-doped iron selenide superconductors are accounted for
by an extended Hubbard model over the square lattice of iron atoms that
includes the principal 3d xz and 3d yz orbitals. At half filling, and in the
absence of intra-orbital next-nearest neighbor hopping, perfect nesting between
electron-type and hole-type Fermi surfaces at the the center and at the corner
of the one-iron Brillouin zone is revealed. It results in hidden magnetic order
in the presence of magnetic frustration within mean field theory. An
Eliashberg-type calculation that includes spin-fluctuation exchange finds that
the Fermi surfaces undergo a Lifshitz transition to electron/hole Fermi surface
pockets centered at the corner of the two-iron Brillouin zone as on-site
repulsion grows strong. In agreement with angle-resolved photoemission
spectroscopy on iron selenide high-temperature superconductors, only the two
electron-type Fermi surface pockets remain after a rigid shift in energy of the
renormalized band structure by strong enough electron doping. At the limit of
strong on-site repulsion, a spin-wave analysis of the hidden-magnetic-order
state finds a ""floating ring"" of low-energy spin excitations centered at the
checkerboard wavenumber (pi,pi). This prediction compares favorably with recent
observations of low-energy spin resonances around (pi,pi) in intercalated iron
selenide by inelastic neutron scattering.",1806.09322v2
2021-10-22,Thermal conductivity of oxide scale and its components in the range from 0 C to 1300 C: Generalized estimates with account for movability of phase transitions,"The data of different authors on the thermal conductivity of wustite Fe1-xO,
magnetite F3O4, hematite Fe2O3 and pure iron are systematized. The generalized
values are described by piecewise smooth functions containing as varying
parameters the temperatures of magnetiv and polymorphic (for iron)
transformations as well as the thermodynamic stability boundary (for wustite).
At polymorphic transformation a finite break of the thermal conductivity
function is envisaged, at othet critical points only a break of its temperature
derivative is acceptable. The proposed formulas are presented in two forms: the
general form that allow varying the values of critical temperatures and the
particular form corresponding to their basic values: the boundary of
thermodynamic stability of wustite - 570 C, the Curie points of magnetite - 575
C, hematite - 677 C, iron - 770 C and polymorphic transformation temperature of
iron - 912 C. To calculate the thermal conductivity of oxide scale as a whole,
it is proposed to take into account separately metallic iron and composite
matrix of iron oxides. Model computations using the proposed formulas shows
that the true thermal conductivity of oxide scale (without pores), depending on
the temperature may be from 3 to 6 W / (m K) in the absence of metallic iron
and up to 15 W / (m K) if free iron is released in the eutectoid decay of
wustite. The effective thermal conductivity of oxide scale, taking into account
its real porosity, may be lower by 15-35%. The obtained dependencies are
recommended for use in mathematical simulation of production and processing of
steel products in the presence of oxide scale on their surface.",2110.11632v1
2021-10-28,A Quantitative Analysis of the Ignition Characteristics of Fine Iron Particles,"Ignition of iron particles in an oxidizing environment marks the onset of a
self-sustained combustion. The objective of the current study is to
quantitatively examine the ignition characteristics of fine iron particles
governed by the kinetics of solid-phase iron oxidation. The oxidation rates are
inversely proportional to the thickness of the oxide layer and calibrated using
the experimentally measured growth of iron-oxide layers over time. Steady-state
and unsteady analysis have been performed to probe the dependence of the
critical gas temperature required to trigger a thermal runaway (namely, the
ignition temperature $T_\mathrm{ign}$) on particle size, initial thickness of
oxide layer, inert gas species, radiative heat loss, and the collective heating
effect in a suspension of particles. Both analyses indicate that
$T_\mathrm{ign}$ depends on $\delta_0$, i.e., the ratio between the initial
oxide layer thickness and particle size, regardless of the absolute size of the
particle. The unsteady analysis predicts that, for $\delta_0 \lesssim 0.003$,
$T_\mathrm{ign}$ becomes independent of $\delta_0$. Under standard conditions
in air, $T_\mathrm{ign}$ is approximately 1080 K for any particle size greater
than 5 microns. Radiative heat loss has a minor effect on $T_\mathrm{ign}$. The
collective effect of a suspension of iron particles in reducing
$T_\mathrm{ign}$ is demonstrated. The transition behavior between
kinetic-controlled and external-diffusion-controlled combustion regimes of an
ignited iron particle is systematically examined. The influences of initial
oxide-layer thickness and particle temperature on the ignition delay time,
$\tau_\mathrm{ign}$, of iron particles are parametrically probed. A $d^2$-law
scaling between $\tau_\mathrm{ign}$ and particle size is identified.",2110.15461v2
1996-08-23,NMR in copper-Oxide Metals,"The anomalous part of the NMR relaxation rate of coppernuclei in the normal
state of copper-oxide metals is calculated using the orbital magnetic parts of
the fluctuations derived in a recent theory to explain the long wavelength
transport anomalies. Oxygen and Yttrium reside on lattice sites at which the
anomalous contribution is absent at all hole densities. The frequency, momentum
dependence, and the form-factor of the fluctuations is predicted,which is
verifiable by inelastic neutron scattering experiments.",9608109v1
1996-12-09,From microscopic description to statistical mechanics of Cu-O chain fragments in the high-Tc superconductors REBa_2Cu_3O_{6+x},"The oxygen deficient CuO_x planes of the high-Tc superconductors
REBa_2Cu_3O_{6+x} (RE denotes a rare-earth atom or yttrium) are studied.
Starting from the Emery model for the Cu-O chain fragments, an extended ASYNNNI
model is proposed to describe the statistical mechanics of the CuO_x planes.
The model is analysed by using Monte Carlo techniques, computing especially the
charge transfer to the CuO$_2$ planes regulating the high-Tc superconductivity,
and the concentration of differently coordinated Cu ions.Results are compared
to experimental data for various RE cases.",9612072v1
1998-09-03,Fermi Surface as the Driving Mechanism for Helical Antiferromagnetic Ordering in Gd-Y Alloys,"The first direct experimental evidence for the Fermi surface (FS) driving the
helical antiferromagnetic ordering in a gadolinium-yttrium alloy is reported.
The presence of a FS sheet capable of nesting is revealed, and the nesting
vector associated with the sheet is found to be in excellent agreement with the
periodicity of the helical ordering.",9809063v1
1999-03-04,Parameter-free expression for superconducting Tc in cuprates,"A parameter-free expression for the superconducting critical temperature of
layered cuprates is derived which allows us to express Tc in terms of
experimentally measured parameters. It yields Tc values observed in about 30
lanthanum, yttrium and mercury-based samples for different levels of doping.
This remarkable agreement with the experiment as well as the unusual critical
behaviour and the normal-state gap indicate that many cuprates are close to the
Bose-Einstein condensation regime.",9903071v1
1999-06-11,Induced spin polarisation in a ferromagnetic gadolinium-yttrium alloy,"The first direct evidence of an induced spin moment in Gd(62.4)Y(37.6) is
presented. This additional moment, of 0.16 +/- 0.03 Bohr magnetons, arises from
polarisation of Y electrons in the alloy. The moment was detected in a Compton
scattering experiment via the measurement of the one dimensional projection of
the momentum space electron spin density in Gd and in the alloy. The result is
consistent with theoretical predictions calculated using the LMTO method within
the local spin density approximation.",9906171v1
2001-06-18,"Disorder induced hexagonal-orthorhombic transition in (Y,Gd)MnO3","We show that the transition in AMnO3 from the orthorhombic perovskite phase
to the hexagonal phase is promoted by inducing disorder on the A-site. The gap
between the orthorhombic and the hexagonal phase is widened for disordered,
mixed yttrium-gadolinium manganite samples. At the cost of the orthorhombic
phase a two phase region emerges. The phase separation exhibits very unusual
thermodynamical behaviour. We also show that high pressure synthesis favours
the orthorhombic phase. YMnO3 is formed in the orthorhombic phase at 15 kbar.",0106335v1
2002-02-09,Fermi surface of yttrium,"Electron-positron momentum densities in Y, reconstructed from two-dimensional
angular correlation of annihilation radiation spectra, are compared with the
theoretical predictions of fully-relativistic augmented plane-wave
calculations. Knowledge of the theoretical densities and of the effects on them
of certain symmetry selection rules has allowed us to separate two hole Fermi
sur-faces in the third and fourth bands and to establish some Fermi momenta for
each of them.",0202157v2
2002-07-29,Electronic Structure of the YH3 Phase from Angle-Resolved Photoemission Spectroscopy,"Yttrium can be loaded with hydrogen up to high concentrations causing
dramatic structural and electronic changes of the host lattice. We report on
angle-resolved photoemission experiments of the Y trihydride phase. Most
importantly, we find the absence of metal d-bands at the Fermi level and a set
of flat, H-induced bands located at much higher binding energy than predicted,
indicating an increased electron affinity at H sites.",0207680v1
2002-09-10,On the reliability of various enhancement theories for a description of electron-positron densities in metals,"Four theoretical approaches to calculate momentum densities of
electron-positron annihilation pairs (MDAP) in crystalline solids are
confronted with 3D densities reconstructed from two-dimensional angular
correlation (2D-ACAR) data for copper, chromium, and yttrium. It is shown that
the Bloch-modified ladder theory, in contrast to other approaches, is able to
describe - at least qualitatively - the MDAP profiles for all metals
investigated.",0209235v1
2004-01-28,Effects of Substituting Calcium for Yttrium on the Superconducting Properties of YBa2Cu3Oz Bulk Samples,"We report systematic studies of AC magnetic susceptibility and transport
properties of Y(1-x)Ca(x)Ba2Cu3Oz bulk samples with 0\leq x\leq 0.4. Single
phase materials, reduction of carrier concentration and decrease of Tc to 85 K
were obtained at doping levels up to 20%. For Y0.7Ca0.3Ba2Cu3Oz sample the
improvement of grains boundary transport and screening capabilities has been
observed as a result of the optimal ratio between carrier concentration and
impurity phase BaCuO2 presence. The appearence of bulk pinning and nonlinear
effects starting at the highest temperature were detected also.",0401584v1
2011-11-10,High-Temperature Superconductivity Mechanism for Cuprates,"Egorov and March plotted the product of resistivity and the copper
spin-lattice relaxation time vs. temperature for yttrium barium copper oxide
finding a minimum at temperature T greater than the superconducting
temperature, heralding an electronic phase change which can be interpreted as
the formation of a ""preformed"" pair. In this context we propose a
superconducting mechanism based on the notion that the preformed pair is a
""soft"" boson (a localized, different type of Cooper pair) which dissociates
above the classical BKT transition temperature, resulting in two circular
charge density waves. The model suggests explanations for considerable
experimental work and offers a physical explanation for the basis of the
Uemura-Homes law.",1111.2560v1
2013-09-04,Unexpected colloid-like supernatant from liquid-phase ball-milling graphite using miscible solutions as solvents: a failure analysis,"Ball-milling graphite was conducted in miscible solutions with the purpose to
exfoliate graphene. Colloid-like stable supernatants were unexpectedly
obtained. Followed were the characterizations with Scanning electronic
microscopy, Thermogravimetric analysis, X-ray diffraction and Elemental
dispersive X-ray mapping to recognize them. As a result, strongly against the
initial judgments, the components of colloid were mainly impurities of mixture
of zirconia, silicate and yttrium oxide, other than nano-graphite.",1309.1056v2
2014-11-25,Simulation study of negative thermal expansion in yttrium tungstate Y2W3O12,"A simulation study of negative thermal expansion in Y2W3O12 was carried out
using calculations of phonon dispersion curves through the application of
density functional perturbation theory. The mode eigenvectors were mapped onto
flexibility models and results compared with calculations of the mode Gruneisen
parameters. It was found that many lower-frequency phonons contribute to
negative thermal expansion in Y2W3O12, all of which can be described in terms
of rotations of effectively rigid WO4 tetrahedra and Y-O rods. The results are
strikingly different from previous phonon studies of higher-symmetry materials
that show negative thermal expansion.",1411.7071v1
2015-11-21,Theoretical description of slow non-monotonic relaxation processes in Al-Y melts,"The slow non-monotonic relaxation processes, which have been recently fixed
in Al-Y melts, are described theoretically. The theoretical description is
based on the Cahn-Hilliard theory and functional methods of non-equilibrium
dynamics. In terms of the suggested approach the reasons of this relaxation
kinetics are non-linearity of the system near to the liquidus line, which
sharply increases with Y concentration, and strong initial heterogeneity of the
melt on the concentration of Y atoms. According to our analysis one can
conclude that the non-monotonic temporal dependence of viscosity is caused by
the Ostwald ripening processes in the rich in yttrium areas.",1511.06908v1
2016-11-17,Thin Film growth of Solid State materials,"Magnetron sputtering has also been used to deposit thin films of some
materials and it has significant technological importance. A modeling on
deposition of epitaxial thin films of Yttrium Stabilized Zirconia (YSZ) was
done the diffusion of adatom on the surface were studies. There exists a strong
interaction of ions formed in the plasma during the sputtering process. Cu thin
films were deposited on Si. Nanocomposite thin film of SiCN showed dendritic
growth.",1611.07926v1
2018-08-23,"Bond relaxation, electronic and magnetic behavior of 2D metals structures Y on Li(110) surface","We investigated the bond, electronic and magnetic behavior of adsorption
Yttrium atoms on Lithium (110) surface using a combination of
Bond-order-length-strength(BOLS) correlation and density-functional
theory(DFT). We found that adsorption Y atoms on Li(110) surfaces form
two-dimensional (2D) geometric structures of hexagon, nonagon, solid hexagonal,
quadrangle and triangle. The consistent with the magnetic moment are
6.66{\mu}B, 5.54{\mu}B, 0.28{\mu}B, 1.04{\mu}B, 2.81{\mu}B, respectively. In
addition, this work could pave the way for design new 2D metals electronic and
magnetic properties.",1809.03407v1
2019-01-16,Structure and dielectric properties of Ba$_2$Cu$_x$Y$_{1-x}$TaO$_{6-y}$ double perovskite,"In this paper, we reported the effect of Cu doping on the structural and
dielectric properties of Ba$_2$Y$_{1-x}$Cu$_x$TaO$_{6-y}$ (0.00 $\leq$ x $\leq$
0.50) ceramics at room temperature. The Copper for Yttrium substitution reduces
the sintering temperature and leads to structural changes in the Ba$_2$YTaO$_6$
rock-salt crystalline structure. Dielectric permittivity and complex impedance
spectroscopy measurements suggested enhancement of the dielectric constant and
occurrence of interfacial Maxwell-Wagner polarization.",1901.05548v2
2020-03-23,Chemical characterization of dislocation in yttria-stabilized zirconia,"This study demonstrates that a space charge layer is formed on dislocation
during mechanical deformation at elevated temperature. High density of
dislocation lines is generated in bulk single crystalline Y2O3 stabilized ZrO2
(YSZ) by uniaxial compression at elevated temperature. The creation of
dislocation is proven with transmission electron microscopy (TEM). Then,
energy-dispersive X-ray spectroscopy (EDS) and electron energy loss
spectroscopy (EELS) are used to explore the changes in the composition on and
away from the dislocation lines. Also, it is clarified that segregation of
dopant atoms (yttrium) on the dislocation line is induced by high temperature
annealing. Comparing the compositional variations with and without thermal
annealing, we study the space charge layer formed on dislocation lines in a
doped system.",2003.10093v1
2020-04-02,Optical spectra of rare-earth nickelates,"Based on the electronic band structure obtained from first principles DFT
calculations, the opticalspectra of yttrium and neodymium nickelates are
computed. We show that the results are in fairagreement with available
experimental data. We clarify the electronic transitions at the origin of
thefirst two peaks, highlighting the important role of transitions from t2g
states neglected in previousmodels. We discuss the evolution of the optical
spectra from small to large rare-earth cations andrelate the changes to the
electronic band structure.",2004.01100v1
2022-06-25,High cooperativity coupling of rare earth spins with planar superconducting resonator,"Interfacing superconducting microwave resonator with rare earth doped
crystals presents a promising hybrid quantum system for applications including
spin-assisted transducers and memories. The coupling strength between spins of
rare earth ions and the microwave photons is characterized by the
cooperativity. Here we report an ultra-high cooperativity $C \sim$ 650 between
rare earth spins and a planar superconducting microwave resonator that features
a highly uniform magnetic field for harnessing the strong anisotropic coupling
strength of erbium doped yttrium orthosilicate. This cooperativity rivals that
from a bulk dielectric resonator and paves a path for efficiently coupling of
spins with microwave photons on an integrated platform.",2206.12646v1
2022-12-27,Study on the hydrogen behavior in Y and Co doped barium-zirconate,"Hydrogen release behavior from mixed-perovskite oxide, yttrium and cobalt
doped barium-zirconate, BaZr$_{0.955}$Y$_{0.03}$Co$_{0.015}$O$_{3-a}$ (BZYC)
exposed to D$_2$ or D$_2$O atmosphere was studied by thermal desorption
spectroscopy (TDS) detecting deuterium gas (D$_2$) and heavy water vapor
(D$_2$O) separately. The release of hydrogen appeared at around 1000 K.
Hydrogen solubility was higher in the BZYC sample exposed to the D$_2$O.",2301.02522v1
2024-02-04,A critical assessment of the dislocation-driven model for superplasticity in yttria tetragonal zirconia polycrystals,"In this paper, the origin of the threshold stress in pure 3 mol %-yttria
tetragonal zirconia polycrystals (YTZP) is analysed in detail. At this regard,
the two explanations reported in literature are discussed thoroughly. One of
them invokes dislocation activity as the origin for such quantity, whereas the
other one is based upon yttrium segregation at the grain boundaries. Crirical
assessment for both of them is performed, and it has allowed concluding that
the dislocation activity observed by Morita and Hiraga is just an artifact
created during sample preparation. Thence, segregation at the grain boundaries
seems to be the only mechanism accounting for a threshold stress and its
temperature and grain size dependence.",2402.04015v1
2000-06-23,ORFEUS II echelle spectra: On the influence of iron-group line blanketing in the Far-UV spectral range of hot subdwarfs,"We present an analysis of the subdwarf O star Feige 67 with a fully
metal-line blanketed NLTE model atmosphere based on high-resolution Far-UV
(912-2000 A) and Near-UV (2000-3400 A) spectra from new ORFEUS II echelle
observations and the IUE final archive. The Far-UV spectra are heavily
blanketed by iron and nickel lines, preventing the detection of the stellar
continuum and complicating the abundance analysis.
  Important points concerning the account for blanketing by millions of
iron-group lines and for an accurate determination of iron and nickel
abundances are discussed: The usage of all theoretically and experimentally
known line opacities of the iron-group elements, the consideration of a broad
wavelength range for a reliable determination of the stellar continuum flux,
and the role of interstellar reddening. This paper outlines a basic approach
for spectral analysis of future high-resolution Far-UV spectra of hot compact
stars. During this study we re-analyzed the iron and nickel abundance of our
exemplary object Feige 67 and confirm their extraordinarily amount.",0006341v1
2002-05-04,"Iron abundance in hot hydrogen-deficient central stars and white dwarfs from FUSE, HST, and IUE spectroscopy","We present a first systematic investigation of the iron abundance in very hot
(Teff>50,000K) hydrogen-deficient post-AGB stars. Our sample comprises 16
PG1159 stars and four DO white dwarfs. We use recent FUSE observations as well
as HST and IUE archival data to perform spectral analyses with line blanketed
NLTE model atmospheres. Iron is not detected in any PG1159 star. In most cases
this is compatible with a solar iron abundance due to limited quality of HST
and IUE data, although the tendency to an iron underabundance may be
recognized. However, the absence of iron lines in excellent FUSE spectra
suggests an underabundance by at least 1 dex in two objects (K1-16 NGC 7094). A
similar result has been reported recently in the [WC]-PG1159 transition object
Abell 78 (Werner et al. 2002). We discuss dust fractionation and s-process
neutron-captures as possible origins. We also announce the first identification
of sulfur in PG1159 stars.",0205058v1
2001-10-18,Suppression of Tc in the (Y0.9Ca0.1)Ba2Cu4-xFexO8 system,"In this paper, the effects produced by the iron substitutions in the
(Y0.9Ca0.1)Ba2Cu4-xFexO8 system on the superconducting and structural
properties are studied. The Rietveld fit of the crystal structure and Mossbauer
spectroscopy results of (Y0.9Ca0.1)Ba2Cu4-xFexO8 samples indicate that, the
iron atoms occupy the Cu(1) sites of the (Cu-O)2 double chain in fivefold
coordination at low iron concentrations. Besides at high iron concentrations
the iron atoms occupy the Cu(1) sites of single Cu-O chainss and Cu(2) sites in
the CuO2 planes of the (Y0.9Ca0.1)Ba2Cu4-xFexO8 phase with structural defects.
Simultaneouly, as iron concentration increases, a faster decrease of Tc is
observed in this material comapred with the YBa2Cu3-xFexO7-y system. According
to the charge transfer model proposed for YBa2Cu4O8 under pressure, the
decrease in the Cu(1)-O(4) bond length in parallel to the increase in the
Cu(2)-O(4) bond length may affect the charge transfer mechanism leading to the
suppression of Tc.",0110388v1
1995-06-30,Structural and Magnetic Properties of Trigonal Iron,"First principles calculations of the electronic structure of trigonal iron
were performed using density function theory. The results are used to predict
lattice spacings, magnetic moments and elastic properties; these are in good
agreement with experiment for both the bcc and fcc structures. We find however,
that in extracting these quantities great care must be taken in interpreting
numerical fits to the calculated total energies. In addition, the results for
bulk iron give insight into the properties of thin iron films. Thin films grown
on substrates with mismatched lattice constants often have non-cubic symmetry.
If they are thicker than a few monolayers their electronic structure is similar
to a bulk material with an appropriately distorted geometry, as in our trigonal
calculations. We recast our bulk results in terms of an iron film grown on the
(111) surface of an fcc substrate, and find the predicted strain energies and
moments accurately reflect the trends for iron growth on a variety of
substrates.",9506009v1
2007-12-05,Vertical stratification of iron abundance in atmospheres of blue horizontal-branch stars,"The observed slow rotation and abundance peculiarities of certain blue
horizontal branch (BHB) stars suggests that atomic diffusion can be important
in their stellar atmospheres and can lead to vertical abundance stratification
of chemical species in the atmosphere. To verify this hypothesis, we have
undertaken an abundance stratification analysis in the atmospheres of six BHB
stars, based on recently acquired McDonald-CE spectra. Our numerical
simulations show that the iron abundance is vertically stratified in the
atmospheres of two stars in M15: B267 and B279. One star WF2-2541 in M13 also
appears to have vertically stratified iron abundance, while for WF4-3085 the
signatures of iron stratification are less convincing. In all cases the iron
abundances increase towards the lower atmosphere. The other two stars in our
sample, WF4-3485 and B84, do not show any significant variation of iron with
atmospheric depth. Our results support the idea that atomic diffusion dominates
other hydrodynamic processes in the atmospheres of BHB stars.",0712.0809v1
2009-09-03,A Mechanism for the Oxygen and Iron Bimodal Radial Distribution Formation in the Disc of our Galaxy,"Recently it has been proposed that there are two types of SN Ia progenitors
-- short-lived and long-lived. On the basis of this idea, we develope a theory
of a unified mechanism for the formation of the bimodal radial distribution of
iron and oxygen in the Galactic disc. The underlying cause for the formation of
the fine structure of the radial abundance pattern is the influence of spiral
arms, specifically, the combined effect of the corotation resonance and
turbulent diffusion. From our modelling we conclude that to explain the bimodal
radial distributions simultaneously for oxygen and iron and to obtain
approximately equal total iron output from different types of supernovae, the
mean ejected iron mass per supernova event should be the same as quoted in
literature if maximum mass of stars, that eject heavy elements, is $50
M_{\odot}$. For the upper mass limit of $70 M_{\odot}$ the production of iron
by a supernova II explosion should be increased by about 1.5 times.",0909.0626v1
2011-03-23,Magnetic Frustration and Iron-Vacancy Ordering in Iron-Chalcogenide,"We show that the magnetic and vacancy orders in the 122
$(A_{1-y}Fe_{2-x}Se_2)$ iron-chalcogenides can be naturally derived from the
$J_1-J_2-J_3$ model with $J_1$ being the ferromagnetic (FM) nearest neighbor
exchange coupling and $J_{2}, J_3$ being the antiferromagnetic (AFM) next and
third nearest neighbor ones respectively, previously proposed to describe the
magnetism in the 11(FeTe/Se) systems. In the 11 systems, the magnetic exchange
couplings are extremely frustrated in the ordered bi-collinear
antiferromagnetic state so that the magnetic transition temperature is low. In
the 122 systems, the formation of iron vacancy order reduces the magnetic
frustration and significantly increases the magnetic transition temperature and
the ordered magnetic moment. The pattern of the 245 iron-vacancy order
($\sqrt{5}\times \sqrt{5}$) observed in experiments is correlated to the
maximum reduction of magnetic frustration. The nature of the iron-vacancy
ordering may hence be electronically driven. We explore other possible vacancy
patterns and magnetic orders associated with them. We also calculate the spin
wave excitations and their novel features to test our model.",1103.4599v2
2011-09-01,Iron and nickel diffusion in subdwarf B stars,"Pulsations in subdwarf B stars are attributed to radiative levitation of
iron-group elements in the stellar envelope. Until now, only iron diffusion is
accounted for in stellar models used for sdB seismology. However, nickel has
also been suggested as a contributor to the opacity bump that drives the
pulsation modes. Stellar models including time-dependent atomic diffusion, as
we compute here, are needed to evaluate the importance of different iron-group
elements for mode driving. We perform detailed calculations of radiative
accelerations of H, He, C, N, O, Ne, Mg, Fe and Ni and include these in
Burgers' diffusion equations. We compute the evolution and non-adiabatic
pulsations of a typical subdwarf B star. We show that, despite its lower
initial abundance, nickel accumulates to comparable mass fractions as iron in
the sdB envelope. For accurate determination of pulsation frequencies and mode
instability, it is essential that diffusion of both metals are included in
stellar models. The role of other iron-group elements remain to be evaluated.",1109.0121v1
2012-06-20,Mössbauer study of the '11' iron-based superconductors parent compound Fe(1+x)Te,"57Fe Moessbauer spectroscopy was applied to investigate the superconductor
parent compound Fe(1+x)Te for x=0.06, 0.10, 0.14, 0.18 within the temperature
range 4.2 K - 300 K. A spin density wave (SDW) within the iron atoms occupying
regular tetrahedral sites was observed with the square root of the mean square
amplitude at 4.2 K varying between 9.7 T and 15.7 T with increasing x. Three
additional magnetic spectral components appeared due to the interstitial iron
distributed over available sites between the Fe-Te layers. The excess iron
showed hyperfine fields at approximately 16 T, 21 T and 49 T for three
respective components at 4.2 K. The component with a large field of 49 T
indicated the presence of isolated iron atoms with large localized magnetic
moment in interstitial positions. Magnetic ordering of the interstitial iron
disappeared in accordance with the fallout of the SDW with the increasing
temperature.",1206.4439v1
2013-02-20,Absence of strong magnetic fluctuations in the iron phosphide superconductors LaFePO and Sr2ScO3FeP,"We report neutron inelastic scattering measurements on polycrystalline LaFePO
and Sr2ScO3FeP, two members of the iron phosphide families of superconductors.
No evidence is found for any magnetic fluctuations in the spectrum of either
material in the energy and wavevector ranges probed. Special attention is paid
to the wavevector at which spin-density-wave-like fluctuations are seen in
other iron-based superconductors. We estimate that the magnetic signal, if
present, is at least a factor of four (Sr2ScO3FeP) or seven (LaFePO) smaller
than in the related iron arsenide and chalcogenide superconductors. These
results suggest that magnetic fluctuations are not as influential on the
electronic properties of the iron phosphide systems as they are in other
iron-based superconductors.",1302.5057v2
2013-04-23,Theoretical study of solid iron nanocrystal movement inside a carbon nanotube,"We use a first-principles based kinetic Monte Carlo simulation to study the
movement of a solid iron nanocrystal inside a carbon nanotube driven by the
electrical current. The origin of the iron nanocrystal movement is the
electromigration force. Even though the iron nanocrystal appears to be moving
as a whole, we find that the core atoms of the nanocrystal is completely
stationary, and only the surface atoms are moving. Movement in the contact
region with the carbon nanotube is driven by electromigration forces, and the
movement on the remaining surfaces is driven by diffusion. Results of our
calculations also provide a simple model which can predict the center of mass
speed of the iron nanocrystal over a wide range of parameters. We find both
qualitative and quantitative agreement of the iron nanocrystal center of mass
speed with experimental data.",1304.6438v1
2014-04-14,Structure and composition of the superconducting phase in alkali iron selenide K$_y$Fe$_{1.6+x}$Se$_2$,"We use neutron diffraction to study the temperature evolution of the average
structure and local lattice distortions in insulating and superconducting
potassium iron selenide K$_y$Fe$_{1.6+x}$Se$_2$. In the high temperature
paramagnetic state, both materials have a single phase with crystal structure
similar to that of the BaFe$_2$As$_2$ family of iron pnictides. While the
insulating K$_y$Fe$_{1.6+x}$Se$_2$ forms a $\sqrt{5}\times\sqrt{5}$ iron
vacancy ordered block antiferromagnetic (AF) structure at low-temperature, the
superconducting compounds spontaneously phase separate into an insulating part
with $\sqrt{5}\times\sqrt{5}$ iron vacancy order and a superconducting phase
with chemical composition of K$_z$Fe$_{2}$Se$_2$ and BaFe$_2$As$_2$ structure.
Therefore, superconductivity in alkaline iron selenides arises from alkali
deficient K$_z$Fe$_{2}$Se$_2$ in the matrix of the insulating block AF phase.",1404.3715v1
2014-08-05,Effect of the iron valence in the two types of layers in LiFeO$_2$Fe$_2$Se$_2$,"We perform electronic structure calculations for the recently synthesized
iron-based superconductor LiFeO$_2$Fe$_2$Se$_2$. In contrast to other
iron-based superconductors, this material comprises two different iron atoms in
3$d^5$ and 3$d^6$ configurations. In band theory, both contribute to the
low-energy electronic structure. Spin-polarized density functional theory
calculations predict an antiferromagnetic metallic ground state with different
moments on the two Fe sites. However, several other almost degenerate magnetic
configurations exist. Due to their different valences, the two iron atoms
behave very differently when local quantum correlations are included through
the dynamical mean-field theory. The contributions from the half-filled 3$d^5$
atoms in the LiFeO$_2$ layer are suppressed and the 3$d^6$ states from the FeSe
layer restore the standard iron-based superconductor fermiology.",1408.0960v2
2014-12-16,Raman-assisted crystallography reveals end-on peroxide intermediates in a nonheme iron enzyme,"Iron-peroxide intermediates are central in the reaction cycle of many
iron-containing biomolecules. We trapped iron(III)-(hydro)peroxo species in
crystals of superoxide reductase (SOR), a nonheme mononuclear iron enzyme that
scavenges superoxide radicals. X-ray diffraction data at 1.95 angstrom
resolution and Raman spectra recorded in crystallo revealed iron-(hydro)peroxo
intermediates with the (hydro)peroxo group bound end-on. The dynamic SOR active
site promotes the formation of transient hydrogen bond networks, which
presumably assist the cleavage of the iron-oxygen bond in order to release the
reaction product, hydrogen peroxide.",1412.5040v1
2015-01-05,Reversed anisotropy of the in-plane resistivity in the antiferromagnetic phase of iron tellurides,"We systematically investigated the anisotropic in-plane resistivity of the
iron telluride including three kinds of impurity atoms: excess Fe, Se
substituted for Te, and Cu substituted for Fe. Sizable resistivity anisotropy
was found in the magneto-structurally ordered phase whereas the sign is
opposite ($\rho_a$ $>$ $\rho_b$, where the $b$-axis parameter is shorter than
the $a$-axis one) to that observed in the transition-metal doped iron arsenides
($\rho_a$ $<$ $\rho_b$). On the other hand, our results demonstrate that the
magnitude of the resistivity anisotropy in the iron tellurides is correlated
with the amount of impurities, implying that the resistivity anisotropy
originates from an exotic impurity effect like that in the iron arsenides. This
suggests that the anisotropic carrier scattering by impurities is a universal
phenomenon in the magneto-structurally ordered phase of the iron-based
materials.",1501.00774v1
2015-03-24,Iron spin crossover and its influence on post-perovskite transitions in MgSiO$_3$ and MgGeO$_3$,"MgGeO$_3$-perovskite is known to be a low-pressure analog of
MgSiO$_3$-perovskite in many respects, but especially in regard to the
post-perovskite transition. As such, investigation of spin state changes in
Fe-bearing MgGeO$_3$ might help to clarify some aspects of this type of state
change in Fe-bearing MgSiO$_3$. Using DFT+U calculations, we have investigated
pressure induced spin state changes in Fe$^{2+}$ and Fe$^{3+}$ in MgGeO$_3$
perovskite and post-perovskite. Owing to the relatively larger atomic size of
germanium compared to silicon, germanate phases have larger unit cell volume
and inter-atomic distances than equivalent silicate phases at same pressures.
As a result, all pressure induced state changes in iron occur at higher
pressures in germanate phases than in the silicate ones, be it a spin state
change or position change of (ferrous) iron in the perovskite cage. We showed
that iron state transitions occur at particular average Fe-O bond-length
irrespective of mineral composition (silicate or germanate) or functionals
(LDA+U$_{sc}$ or GGA+U$_{sc}$). Ferrous iron substitution decreases the
perovskite to post-perovskite (PPv) transition pressure while coupled ferric
iron substitution increases it noticeably.",1503.07194v1
2015-05-20,An equatorial ultra iron-poor star identified in BOSS,"We report the discovery of SDSS J131326.89-001941.4, an ultra iron-poor red
giant star ([Fe/H] ~ -4.3) with a very high carbon abundance ([C/Fe]~ +2.5).
This object is the fifth star in this rare class, and the combination of a
fairly low effective temperature (Teff ~ 5300 K), which enhances line
absorption, with its brightness (g=16.9), makes it possible to measure the
abundances of calcium, carbon and iron using a low-resolution spectrum from the
Sloan Digital Sky Survey. We examine the carbon and iron abundance ratios in
this star and other similar objects in the light of predicted yields from
metal-free massive stars, and conclude that they are consistent. By way of
comparison, stars with similarly low iron abundances but lower carbon-to-iron
ratios deviate from the theoretical predictions.",1505.05555v1
2015-07-21,Pressure-induced Superconductivity in the Iron-based Ladder Material BaFe2S3,"All the iron-based superconductors identified to date share a square lattice
composed of Fe atoms as a common feature, despite having different crystal
structures. In copper-based materials, the superconducting phase emerges not
only in square lattice structures but also in ladder structures. Yet iron-based
superconductors without a square lattice motif have not been found despite
being actively sought out. Here, we report the discovery of pressure-induced
superconductivity in the iron-based spin-ladder material BaFe2S3, a Mott
insulator with striped-type magnetic ordering below ~120 K. On the application
of pressure this compound exhibits a metal-insulator transition at about 11
GPa, followed by the appearance of superconductivity below Tc = 14 K, right
after the onset of the metallic phase. Our findings indicate that iron-based
ladder compounds represent promising material platforms, in particular for
studying the fundamentals of iron-based superconductivity.",1507.05864v1
2016-10-27,Non-trivial role of interlayer cation states in iron-based superconductors,"Unconventional superconductivity in iron pnictides and chalcogenides has been
suggested to be controlled by the interplay of low-energy antiferromagnetic
spin fluctuations and the particular topology of the Fermi surface in these
materials. Based on this premise, one would also expect the large class of
isostructural and isoelectronic iron germanide compounds to be good
superconductors. As a matter of fact, they, however, superconduct at very low
temperatures or not at all. In this work we establish that superconductivity in
iron germanides is suppressed by strong ferromagnetic tendencies, which
surprisingly do not originate from changes in bond-angles or -distances with
respect to iron pnictides and chalcogenides, but are due to changes in the
electronic structure in a wide range of energies happening upon substitution of
atom species (As by Ge and the corresponding spacer cations). Our results
indicate that superconductivity in iron-based materials may not always be fully
understood based on $d$ or $dp$ model Hamiltonians only.",1610.08626v1
2017-01-12,Interplay of iron and rare-earth magnetic order in rare-earth iron pnictide superconductors under magnetic field,"The magnetic properties of iron pnictide superconductors with magnetic
rare-earth ions under strong magnetic field are investigated based on the
cluster self-consistent field method. Starting from an effective Heisenberg
model, we present the evolution of magnetic structures on magnetic field in
RFeAsO (R=Ce, Pr, Nd, Sm, Gd and Tb) and RFe2As2 (R=Eu) compounds. It is found
that spin-flop transition occurs in both rare-earth and iron layers under
magnetic field, in good agreement with the experimental results. The interplay
between rare-earth and iron spins plays a key role in the magnetic-field-driven
magnetic phase transition, which suggests that the rare-earth layers can
modulate the magnetic behaviors of iron layers. In addition, the factors that
affect the critical magnetic field for spin-flop transition are also discussed.",1701.03258v1
2018-09-13,In situ soft x-ray absorption spectroscopic study of Fe/MgO interfaces,"Interfacial reaction between iron and MgO has been studied in situ during
deposition of iron on MgO surface, using soft x-ray absorption spectroscopy.
High sensitivity of the technique which is capable of detecting even a sub
monolayer of a given phase, combined with in situ measurements as a function of
iron layer thickness, allowed one to make a quantitative estimate of
interfacial phases. Two different substrates namely, MgO (001) single crystal,
and a polycrystalline MgO film on Si substrate have been used in order to
elucidate the role of the state of MgO surface in controlling the interface
structure. It is found that at the interface of iron and MgO film, about two
monolayers of Fe3O4 is formed. Fe3O4 being the oxide of iron with the highest
heat of formation, the reaction appears to be controlled thermodynamically. On
the other hand, on the interface with MgO (001) surface, FeO is formed,
suggesting that the reaction is limited by the availability of oxygen atoms.
Magnetic behaviour of the FeO layer gets modified significantly due to
proximity effect of the bulk ferromagnetic iron layer.",1809.04782v2
2019-01-30,"Tidally-Distorted, Iron-Enhanced Exoplanets Closely Orbiting Their Stars","The transiting planet candidate KOI 1843.03 ($0.6 R_\oplus$ radius, 4.245
hour orbital period, $0.46 M_\odot$ host star) has the shortest orbital period
of any planet yet discovered. Here we show, using the first three-dimensional
interior structure simulations of ultra-short-period tidally distorted rocky
exoplanets, that KOI 1843.03 may be shaped like an American football, elongated
along the planet-star axis with an aspect ratio of up to 1.79. Furthermore, for
KOI 1843.03 to have avoided tidal disruption (wherein the planet is pulled
apart by the tidal gravity of its host star) on such a close-in orbit, KOI
1843.03 must be as iron-rich as Mercury (about 66% by mass iron compared to
Mercury's 70% by mass iron, Hauck et al. 2013). Of the ultra-short-period
($P_\mathrm{orb} \lesssim 1$ day) planets with physically-meaningful
constraints on their densities characterized to date, just under half (4 out of
9) are iron-enhanced. As more are discovered, we will better understand the
diversity of rocky planet compositions and the variety of processes that lead
to planetary iron enhancement.",1901.10666v2
2019-09-25,Globular Cluster Intrinsic Iron Abundance Spreads: I. Catalog,"We present an up-to-date catalog of intrinsic iron abundance spreads in the
55 Milky Way globular clusters for which sufficiently precise spectroscopic
measurements are available. Our method combines multiple datasets when possible
to improve the statistics, taking into account the fact that different methods
and instruments can lead to systematically offset metallicities. Only high
spectral resolution (R>14,000) studies that measure the equivalent widths of
individual iron lines are found to have uncertainties on the metallicities of
the individual stars that can be calibrated sufficiently well for the intrinsic
dispersion to be separated cleanly from random measurement error. The median
intrinsic iron spread is found to be 0.045 dex, which is small but
unambiguously measured to be non-zero in most cases. There is large variation
between clusters, but more luminous globular clusters, above 10^5 L_sun, have
increasingly large iron spreads on average; no trend between iron spread and
metallicity is found.",1909.11731v1
2020-04-07,Electronic correlations and transport in iron at Earth's core conditions,"The transport properties of iron under Earth's inner core conditions are
essential input for the geophysical modelling but are poorly constrained
experimentally. Here we show that the thermal and electrical conductivity of
iron at those conditions remains high even if the electron-electron-scattering
(EES) is properly taken into account. This result is obtained by ab initio
simulations taking into account consistently both thermal disorder and
electronic correlations. Thermal disorder suppresses the non-Fermi-liquid
behavior of the body-centered cubic iron phase, hence, reducing the EES; the
total calculated thermal conductivity of this phase is 220 Wm$^{-1}$K$^{-1}$
with the EES reduction not exceeding 20%. The EES and electron-lattice
scattering are intertwined resulting in breaking of the Matthiessen's rule with
increasing EES. In the hexagonal close-packed iron the EES is also not
increased by thermal disorder and remains weak. Our main finding thus holds for
the both likely iron phases in the inner core.",2004.03700v2
2021-07-10,Phase separation near the charge neutrality point in FeSe$_{1-x}$Te$_{x}$ crystals with x $<$ 0.15,"Our study of FeSe$ _ {1-x}$Te$ _ {x}$ crystals with x $<$ 0.15 shows that the
phase separation in these compositions occurs into phases with a different
stoichiometry of iron. This phase separation may indicate structural
instability of the iron plane in the studied range of compositions. To explain
it, we discuss the bond polarity and the peculiarity of the direct $d$ exchange
in the iron plane in the framework of the basic phenomenological description
such as the Bethe-Slater curve. With this approach, when the distance between
iron atoms is close to the value at which the sign of the magnetic exchange for
some $d$ orbitals changes, structural and electronic instability can occur.
Anomalies in the crystal field near the point of charge neutrality can also be
a significant component of this instability. A similar instability of the iron
plane may also be an important factor for other series of iron-based
superconductors.",2107.04793v2
2021-10-27,Synthesis and Characterisation of Iron Oxide Nanoparticles with Tunable Sizes by Hydrothermal Method,"The present study investigates the effect of different reaction times on the
crystallinity, surface morphology and size of iron oxide nanoparticles. In this
synthetic system, aqueous iron (III) nitrate (Fe(NO$_3$)$_3\cdot9$H$_2$O)
nonahydrate, provided the iron source and triethylamine was the precipitant and
alkaline agent. The as-synthesised iron oxide nanoparticles were characterised
by X-ray diffraction (XRD), Rietveld analysis, Scanning Electron Microscopy
(SEM) and Fourier transform infrared spectroscopy (FTIR). Prolonged reaction
times indicated the change on nanoparticle shape from elongated nanorods to
finally distorted nanocubes. Analysis on the crystallinity of the iron oxide
nanoparticles suggest that the samples mainly consist of two phases, which are
Goethite ($\alpha$-FeOOH) and Hematite $(\alpha$-Fe$_2$O$_3$), respectively.",2110.14774v1
2022-07-29,Structural investigation of Ayurveda Lauha (Iron) Bhasma,"In Ayurveda, Lauha (Iron) bhasma is primarily used to cure diseases related
with iron deficiency in humans. It is produced from purified raw metallic iron
using a combination of multi-step traditional preparation processes described
in the Ayurveda literature. Here, we present results of structural
investigation performed on the medicinal grade Lauha bhasma using various X-ray
based techniques. Our results indicate that after several rounds of heating and
cooling in specific conditions following the Ayurvedic preparation procedure,
metallic iron eventually converts to a natural iron-oxide mineral belonging to
the Magnetite group. Scanning electron microscopy (SEM) and X-ray standing wave
assisted fluorescence measurements carried out on powdered bhasma specimen
reveal that the Magnetite micro-particles in the bhasma specimen are usually
present in the form of agglomerates of nano-particles. We anticipate that the
Ayurvedic Lauha Bhasma has great potential for noninvasive localized target
killing of cancer cells, particularly in sensitive parts of the human body such
as brain, spinal cord, and lungs, via necrosis by application of an alternating
external magnetic field or photo electron generation through X-rays.",2207.14615v3
2022-10-18,Impact of Electronic Correlations on High-Pressure Iron: Insights from Time-Dependent Density Functional Theory,"We present a comprehensive investigation of the electrical and thermal
conductivity of iron under high pressures at ambient temperature, employing the
real-time formulation of time-dependent density functional theory (RT-TDDFT).
Specifically, we examine the influence of a Hubbard correction (+\textit{U}) to
account for strong electron correlations. Our calculations based on RT-TDDFT
demonstrate that the evaluated electrical conductivity for both high-pressure
body-centered cubic (BCC) and hexagonal close-packed (HCP) iron phases agrees
well with experimental data. Furthermore, we explore the anisotropy in the
thermal conductivity of HCP iron under high pressure, and our findings are
consistent with experimental observations. Interestingly, we find that the
incorporation of the +\textit{U} correction significantly impacts the ground
state and linear response properties of iron at pressures below 50 GPa, with
its influence diminishing as pressure increases. This study offers valuable
insights into the influence of electronic correlations on the electronic
transport properties of iron under extreme conditions.",2210.10132v3
2023-01-16,The fate of water in hydrogen-based iron oxide reduction,"Gas-solid reactions are cornerstones of many catalytic and redox processes
that will underpin the energy and sustainability transition. The specific case
of hydrogen-based iron oxide reduction is the foundation to render the global
steel industry fossil-free, an essential target as iron production is the
largest single industrial emitter of carbon dioxide. Our perception of
gas-solid reactions has not only been limited by the availability of
state-of-the-art techniques which can delve into the reacted solids in great
structural and chemical detail, but we continue to miss an important reaction
partner that defines the thermodynamics and kinetics of gas phase reactions:
the gas molecules. In this investigation, we use the latest development in
cryogenic atom probe tomography to study the quasi in-situ evolution of gas
phase heavy water at iron-iron oxide interfaces resulting from the direct
reduction of iron oxide by deuterium gas at 700{\deg}C. The findings provide
new insights into the formation kinetics and location of water formed during
hydrogen-based reduction of FeO, an its interaction with the ongoing redox
reaction.",2301.06391v1
2024-04-04,The economic consequences of geopolitical fragmentation: Evidence from the Cold War,"The Cold War was the defining episode of geopolitical fragmentation in the
twentieth century. Trade between East and West across the Iron Curtain (a
symbolical and physical barrier dividing Europe into two distinct areas) was
restricted, but the severity of these restrictions varied over time. We
quantify the trade and welfare effects of the Iron Curtain and show how the
difficulty of trading across the Iron Curtain fluctuated throughout the Cold
War. Using a novel dataset on trade between the two economic blocs and a
quantitative trade model, we find that while the Iron Curtain at its height
represented a tariff equivalent of 48% in 1951, trade between East and West
gradually became easier until the fall of the Berlin Wall in 1989. Despite the
easing of trade restrictions, we estimate that the Iron Curtain roughly halved
East-West trade flows and caused substantial welfare losses in the Eastern bloc
countries that persisted until the end of the Cold War. Conversely, the Iron
Curtain led to an increase in intra-bloc trade, especially in the Eastern bloc,
which outpaced the integration of Western Europe in the run-up to the formation
of the European Union.",2404.03508v1
2010-10-25,"An extremely peculiar hot subdwarf with a ten-thousand-fold excess of zirconium, yttrium, and strontium","Helium-rich subdwarf B (He-sdB) stars represent a small group of low-mass hot
stars with luminosities greater than those of conventional subdwarf B stars,
and effective temperatures lower than those of subdwarf O stars. By measuring
their surface chemistry, we aim to explore the connection between He-sdB stars,
He-rich sdO stars and normal sdB stars. LS IV-14 116 is a relatively
intermediate He-sdB star, also known to be a photometric variable.
High-resolution blue-optical spectroscopy was obtained with the
Anglo-Australian Telescope. Analysis of the spectrum shows LS IV-14 116 to have
effective temperature Teff = 34 000 +/- 500 K, surface gravity log g = 5.6 +/-
0.2, and surface helium abundance nHe = 0.16 +/- 0.03 by number. This places
the star slightly above the standard extended horizontal branch, as represented
by normal sdB stars. The magnesium and silicon abundances indicate the star to
be metal poor relative to the Sun. A number of significant but unfamiliar
absorption lines were identified as being due to germanium, strontium, yttrium
and zirconium. After calculating oscillator strengths (for Ge, Y and Zr), the
photospheric abundances of these elements were established to range from 3 dex
(Ge) to 4 dex (Sr, Y and Zr) above solar. The most likely explanation is that
these overabundances are caused by radiatively-driven diffusion forming a
chemical cloud layer in the photosphere. It is conjectured that this cloud
formation could be mediated by a strong magnetic field.",1010.5146v1
2013-02-19,Structure and dynamics in yttrium-based molten rare earth alkali fluorides,"The transport properties of molten LiF-YF3 mixtures have been studied by
pulsed field gradient nuclear magnetic resonance spectroscopy, potentiometric
experiments, and molecular dynamics simulations. The calculated diffusion
coefficients and electric conductivities compare very well with the
measurements accross a wide composition range. We then extract static (radial
distribution functions, coordination numbers distributions) and dynamic (cage
correlation functions) quantities from the simulations. Then, we discuss the
interplay between the microscopic structure of the molten salts and their
dynamic properties. It is often considered that variations in the diffusion
coefficient of the anions are mainly driven by the evolution of its
coordination with the metallic ion (Y3+ here). We compare this system with
fluorozirconate melts and demonstrate that the coordination number is a poor
indicator of the evolution of the diffusion coefficient. Instead, we propose to
use the ionic bonds lifetime. We show that the weak Y-F ionic bonds in LiF-YF3
do not induce the expected tendency of the fluoride diffusion coefficient to
converge toward the one of yttrium cation when the content in YF3 increases.
Implications on the validity of the Nernst-Einstein relation for estimating the
electrical conductivity are discussed.",1302.4563v2
2018-10-24,Radiation Damage and Thermal Recovery of Perovskite Superconductor Yttrium Barium Copper Oxide,"High temperature superconducting materials are being considered to generate
the magnetic fields required for the confinement of plasma in fusion reactors.
The present study aims to assess the microstructural degradation resulting from
ion implantation at room temperature under two implantation conditions in
Yttrium Barium Copper Oxide (YBCO) tapes. Xray Diffraction (XRD) and high
resolution characterisation techniques including Atom Probe Tomography (APT)
and Transmission Electron Microscopy (TEM) analyses were used to correlate
alterations in superconducting behaviour measured using a Magnetic Properties
Measurement System (MPMS) to amorphization and recovery caused by ion
implantation. TEM analysis was performed to depth profile the degree of
crystallinity (or lack thereof) on irradiated samples. SRIM predicted the
damage depth at 900 nm below the sample surface of the 2 MeV Xe implanted
sample and 450 nm beneath the surface of the 0.6 MeV Xe implanted sample. 2 MeV
Xe implantation caused the superconducting temperature to decrease by 10 K and
the critical current density to display a 10 fold reduction. Post irradiation
heat treatments up to 600C caused recrystallisation of the irradiated layer,
but also oxygen loss and alterations in grain size. The recrystallised grain
orientation was random in TEM lamellae, however, bulk samples re-grew along the
original crystal orientation provided that some of the original material was
not amorphized (ie if they nucleated on crystalline YBCO). This is extremely
promising for the thermal recovery of tokamak components.",1810.10477v3
2019-01-10,High-cooperativity coupling of a rare-earth spin ensemble to a superconducting resonator using yttrium orthosilicate as a substrate,"Yttrium orthosilicate (Y$_2$SiO$_5$, or YSO) has proved to be a convenient
host for rare-earth ions used in demonstrations of microwave quantum memories
and optical memories with microwave interfaces, and shows promise for coherent
microwave--optical conversion owing to its favourable optical and spin
properties. The strong coupling required by such microwave applications could
be achieved using superconducting resonators patterned directly on
Y$_2$SiO$_5$, and hence we investigate here the use of Y$_2$SiO$_5$ as an
alternative to sapphire or silicon substrates for superconducting hybrid device
fabrication. A NbN resonator with frequency 6.008 GHz and low power quality
factor $Q \approx 400000$ was fabricated on a Y$_2$SiO$_5$ substrate doped with
isotopically enriched Nd$^{145}$. Measurements of dielectric loss yield a
loss-tangent $\tan\delta = 4 \times 10^{-6}$, comparable to sapphire. Electron
spin resonance (ESR) measurements performed using the resonator show the
characteristic angular dependence expected from the anisotropic Nd$^{145}$
spin, and the coupling strength between resonator and electron spins is in the
high cooperativity regime ($C = 30$). These results demonstrate Y$_2$SiO$_5$ as
an excellent substrate for low-loss, high-Q microwave resonators, especially in
applications for coupling to optically-accessible rare earth spins.",1901.03262v2
2019-04-05,"Osmium-Nitrosyl Oxalato-Bridged Lanthanide-Centered Pentanuclear Complexes - Synthesis, Crystal Structures and Magnetic Properties","A series of pentanuclear heterometallic coordination compounds of the general
formula (Bu 4 N) 5 [Ln{Os(NO)($\mu$-ox)-Cl 3 } 4 (H 2 O) n ] [Ln = Y (for 2)
and Dy (for 3) when n = 0; Ln = Dy (for 3), Tb (for 4), and Gd (for 5) when n =
1] were synthesized by the reaction of the precursor (Bu 4 N) 2 [Os(NO)(ox)-Cl
3 ] (1) with the respective lanthanide(III) (Gd, Tb, Dy) or yttrium(III)
chloride. For the five new complexes, the coordination numbers eight or nine
are found for the central metal ion. The compounds were fully characterized by
elemental analysis, IR spectroscopy, single-crystal X-ray diffraction analysis,
magnetic susceptibility measurements, and ESI mass spectrometry. In addition,
compound 1 was studied by UV/Vis spectroscopy and cyclic voltammetry. The X-ray
dif-fraction analyses revealed that the anionic complexes consist of a
lanthanide or yttrium core bridged through oxalato li-gands to four octahedral
osmium-nitrosyl moieties. This picture , in which the central ion is
eight-coordinate, holds for",1904.02913v1
2019-09-23,Superconductivity up to 243 K in yttrium hydrides under high pressure,"The discovery of high-temperature conventional superconductivity in H3S with
a critical temperature of Tc=203 K was followed by the recent record of Tc ~250
K in the face-centered cubic (fcc) lanthanum hydride LaH10 compound. It was
realized in a new class of hydrogen-dominated compounds having a clathrate-like
crystal structure in which hydrogen atoms form a 3D framework and surround a
host atom of rare earth elements. Yttrium hydrides are predicted to have even
higher Tc exceeding room temperature. In this paper, we synthesized and refined
the crystal structure of new hydrides: YH4, YH6, and YH9 at pressures up to 237
GPa finding that YH4 crystalizes in the I4/mmm lattice, YH6 in Im-3m lattice
and YH9 in P63/mmc lattice in excellent agreement with the calculations. The
observed very high-temperature superconductivity is comparable to that found in
fcc-LaH10: the pressure dependence of Tc for YH9 also displays a ""dome like
shape"" with the highest Tc of 243 K at 201 GPa. We also observed a Tc of 227 K
at 237 GPa for the YH6 phase. However, the measured Tcs are notably lower by
~30 K than predicted. Evidence for superconductivity includes the observation
of zero electrical resistance, a decrease of Tc under an external magnetic
field and an isotope effect. The theoretically predicted fcc YH10 with the
promising highest Tc>300 K was not stabilized in our experiments under
pressures up to 237 GPa.",1909.10482v1
2020-05-23,Hyperfine interaction and coherence time of praseodymium ions at the site 2 in yttrium orthosilicate,"Praseodymium (Pr$^{3+}$) ions doped in the site 1 of yttrium orthosilicate
(Y$_2$SiO$_5$) has been widely employed as the photonic quantum memory due to
their excellent optical coherence and spin coherence. While praseodymium ions
occupying the site 2 in Y$_2$SiO$_5$ crystal have better optical coherence as
compared with those at site 1, which may enable better performance in quantum
memory. Here we experimentally characterize the hyperfine interactions of the
ground state $^3$H$_4$ and excited state $^1$D$_2$ of Pr$^{3+}$ at site 2 in
Y$_2$SiO$_5$ using Raman heterodyne detected nuclear magnetic resonance. The
Hamiltonians for the hyperfine interaction are reconstructed for both ground
state $^3$H$_4$ and excited state $^1$D$_2$ based on the Raman heterodyne
spectra in 201 magnetic fields. The two-pulse spin-echo coherence lifetime for
the ground state is measured to be 2.6$\pm$0.1 ms at site 2 with zero magnetic
field, which is more than five times longer than that at site 1. The magnetic
fields with zero first order Zeeman shift in the hyperfine transition for
Pr$^{3+}$ at site 2 in Y$_2$SiO$_5$ are identified.",2005.11543v1
2021-03-09,Chemical physics of superconductivity in layered yttrium carbide halides from first principles,"We perform a thorough first-principles study on superconductivity in yttrium
carbide halide Y$_2$$X_2$C$_2$ ($X$=Cl, Br, I) whose maximum transition
temperature ($T_{\rm c}$) amounts to $\sim$10 K. A detailed analysis on the
optimized crystal structures reveals that the Y$_2$C$_2$ blocks are compressed
uniaxially upon the halogen substitution from Cl, Br to I, contrary to the
monotonic expansion of the lattice vectors. With a nonempirical method based on
the density functional theory for superconductors within the conventional
phonon mechanism, we successfully reproduce the halogen dependence of $T_{\rm
c}$. Anomalously enhanced coupling of one C$_2$ libration mode is observed in
Y$_2$I$_2$C$_2$, which imply possible departure from the conventional pairing
picture. Utilizing the Wannier representation of the electron-phonon coupling,
we show that the halogen electronic orbitals and ionic vibrations scarcely
contribute to the superconducting pairing. The halogen dependence of this
system is hence an indirect effect of the halogen ions through the uniaxial
compressive force on the superconducting Y$_2$C$_2$ blocks. We thus establish a
quantitatively reliable picture of the superconducting physics of this system,
extracting a unique effect of the atomic substitution which is potentially
applicable to other superconductors.",2103.05312v1
2022-04-05,Potential high-$T_{c}$ superconductivity in YCeH$_{x}$ and LaCeH$_{x}$ under pressure,"Lanthanum, yttrium, and cerium hydrides are the three most well-known
superconducting binary hydrides (La-H, Y-H, and Ce-H systems), which have
gained great attention in both theoretical and experimental studies. Recent
studies have shown that ternary hydrides composed of lanthanum and yttrium can
achieve high superconductivity around 253 K. In this study we employ the
evolutionary-algorithm-based crystal structure prediction (CSP) method and
first-principles calculations to investigate the stability and
superconductivity of ternary hydrides composed of (Y, Ce) and (La, Ce) under
high pressure. Our calculations show that there are multiple stable phases in
Y-Ce-H and La-Ce-H systems, among which $P4/mmm$-YCeH$_{8}$,
$P\bar{6}m2$-YCeH$_{18}$, $R\bar{3}m$-YCeH$_{20}$, $P4/mmm$-LaCeH$_{8}$, and
$R\bar{3}m$-LaCeH$_{20}$ possessing H$_{18}$, H$_{29}$ and H$_{32}$ clathrate
structures can maintain both the thermodynamic and lattice-dynamic stabilities.
In addition, we also find that these phases also maintain a strong resistance
to decomposition at high temperature. Electron-phonon coupling calculations
show that only three of these five phases can exhibit high-temperature
superconductivity. The superconducting transition temperatures ($T_\mathrm{c}$)
of $R\bar{3}m$-YCeH$_{20}$, $R\bar{3}m$-LaCeH$_{20}$, and
$P\bar{6}m2$-YCeH$_{18}$ are predicted using the Allen-Dynes-modified McMillan
formula to be 122 K at 300 GPa, 116 K at 250 GPa, and 173 K at 150 GPa,
respectively. Moreover, the pressure to stabilize $P\bar{6}m2$-YCeH$_{18}$ can
be lowered to 150 GPa, suggesting an accessible condition for its high-pressure
synthesis.",2204.01921v2
2022-06-29,Optical properties of oxygen-containing yttrium hydride thin films during and after the deposition,"The synthesis of the photochromic YHO films is based on the oxidation of
deposited yttrium hydride in ambient conditions. The actual state of the films
during the deposition process, which is influenced by the deposition pressure
and the oxidation caused by the residual gases, is not completely known. We
report on the YHxOy thin films deposited by reactive pulsed-DC magnetron
sputtering. Since the visible light transmittance is closely related to the
phase and chemical composition of the films, in-situ transmittance measurements
during and after deposition are performed. Ex-situ spectroscopic ellipsometry
is used to determine the optical constants of YHxOy throughout the film
thickness. In order to obtain metallic YH2-x films, the densest possible
structure with a high deposition rate is required, otherwise the films could
already be partially transparent during the deposition. The transmittance is
higher if deposition pressure is increased. This is because of the oxidation
promoted by more porous growth of the microstructure that is observed at the
surface and cross-section images of the films. The films exhibit a refractive
index gradient perpendicular to the substrate surface, which is related to the
porosity and variation of the chemical composition.",2206.14644v1
2023-07-25,Computational design of new superconducting materials and their targeted experimental synthesis,"In the last six years (2015-2021), many superconducting hydrides with
critical temperatures $\textit{T}$$_C$ of up to 253 K, a record for today, have
been discovered. Now, a special field of hydride superconductivity at ultrahigh
pressures has developed. For the most part, the properties of superhydrides are
well described by the Migdal-Eliashberg theory of strong electron-phonon
interaction, especially when anharmonicity of phonons is taken into account.
The isotope effect, the effect of the magnetic field (up to 60-70 T) on the
critical temperature and critical current in the hydride samples, the
dependence of $\textit{T}$$_C$ on the pressure and degree of doping - all data
indicate that polyhydrides are conventional superconductors, the theory of
which was created by Bardeen, Cooper, and Schrieffer in 1957.
  This work presents a retrospective analysis of data for 2015-2021 and
describes the main directions for future research in the field of hydride
superconductivity. The thesis consists of six chapters devoted to the study of
the structure and superconductivity of binary and ternary superhydrides of
thorium (ThH$_9$ and ThH$_{10}$), yttrium (YH$_6$ and YH$_9$), europium and
other lanthanides (Ce, Pr, Nd), and lanthanum-yttrium (La-Y). This work
describes the physical properties of cubic decahydrides, hexahydrides, and
hexagonal metal nonahydrides, demonstrates high efficiency of evolutionary
algorithms and density functional methods in predicting the formation of
polyhydrides under high-pressure and high-temperature conditions. We proposed a
theoretical-experimental algorithm for analyzing the superconducting properties
of hydrides, which makes it possible to systematize the accumulated
experimental data. In general, this research is a vivid example of the
effectiveness and synergy of modern methods for studying the condensed state of
matter under high pressures.",2307.13313v1
2023-08-08,ExoMol line lists -- LIII: Empirical Rovibronic spectra of Yttrium Oxide (YO),"Empirical line lists for the open shell molecule $^{89}$Y$^{16}$O (yttrium
oxide) and its isotopologues are presented. The line lists cover the 6 lowest
electronic states: $X {}^{2}\Sigma^{+}$, $A {}^{2}\Pi$, $A' {}^{2}\Delta$, $B
{}^{2}\Sigma^{+}$, $C {}^{2}\Pi$ and $D {}^{2}\Sigma^{+}$ up to 60000 cm$^{-1}$
($<0.167$ $\mu$m) for rotational excitation up to $J = 400.5$. An \textit{ab
initio} spectroscopic model consisting of potential energy curves (PECs),
spin-orbit and electronic angular momentum couplings is refined by fitting to
experimentally determined energies of YO, derived from published YO
experimental transition frequency data. The model is complemented by empirical
spin-rotation and $\Lambda$-doubling curves and \textit{ab initio} dipole
moment and transition dipole moment curves computed using MRCI. The \textit{ab
initio} PECs computed using the complete basis set limit extrapolation and the
CCSD(T) method with its higher quality provide an excellent initial
approximation for the refinement. Non-adiabatic coupling curves for two pairs
of states of the same symmetry $A$/$C$ and $B$/$D$ are computed using a
state-averaged CASSCF and used to built diabatic representations for the $A
{}^{2}\Pi$, $C {}^{2}\Pi$, $B {}^{2}\Sigma^{+}$ and $D {}^{2}\Sigma^{+}$
curves. Calculated lifetimes of YO are tuned to agree well with the experiment,
where available. The BRYTS YO line lists for are included into the ExoMol data
base (www.exomol.com).",2308.04173v3
2001-08-01,Conformal lattice of magnetic bubble domains in garnet film,"We report experimental observations of magnetic bubble domain arrays with no
apparent translational symmetry. Additionally the results of comparative
numerical studies are discussed. Our goal is to present experimental evidence
for natural occurence of conformal structures.",0108009v1
2002-10-13,Enhanced magnetocaloric effect in frustrated magnets,"The magnetothermodynamics of strongly frustrated classical Heisenberg
antiferromagnets on kagome, garnet, and pyrochlore lattices is examined. The
field induced adiabatic temperature change (dT/dH)_S is significantly larger
for such systems compared to ordinary non-frustrated magnets and also exceeds
the cooling rate of an ideal paramagnet in a wide range of fields. An
enhancement of the magnetocaloric effect is related to presence of a
macroscopic number of soft modes in frustrated magnets below the saturation
field. Theoretical predictions are confirmed with extensive Monte Carlo
simulations.",0210288v1
2003-12-24,Subatomic movements of a domain wall in the Peierls potential,"Movements of individual domain walls in a ferromagnetic garnet were studied
with angstrom resolution. The measurements reveal that domain walls can be
locked between adjacent crystallographic planes and propagate by distinct steps
matching the lattice periodicity. Domain walls are found to be weakly mobile
within valleys of the atomic washboard but become unexpectedly flexible on
Peierls ridges, where they can be kept in a bi-stable state by ac magnetic
field. We describe the latter observation in terms of a single magnetic kink
propagating along a domain wall.",0312631v1
2006-03-27,Modeling transient absorption and thermal conductivity in a simple nanofluid,"Molecular dynamics simulations are used to simulate the thermal properties of
a model fluid containing nanoparticles (nanofluid). By modelling transient
absorption experiments, we show that they provide a reliable determination of
interfacial resistance between the particle and the fluid. The flexibility of
molecular simulation allows us to consider separately the effect of
confinement, particle mass and Brownian motion on the thermal transfer between
fluid and particle. Finally, we show that in the absence of collective effects,
the heat conductivity of the nanofluid is well described by the classical
Maxwell Garnet equation model.",0603704v1
2003-06-16,"Energy levels and lifetimes of Nd IV, Pm IV, Sm IV, and Eu IV","To address the shortage of experimental data for electron spectra of
triply-ionized rare earth elements we have calculated energy levels and
lifetimes of 4f{n+1} and 4f{n}5d configurations of Nd IV (n=2), Pm IV (n=3), Sm
IV (n=4), and Eu IV (n=5) using Hartree-Fock and configuration interaction
methods. To control the accuracy of our calculations we also performed similar
calculations for Pr III, Nd III and Sm III, for which experimental data are
available. The results are important, in particular, for physics of magnetic
garnets.",0306141v1
2002-06-17,Energy levels and lifetimes of Gd IV and enhancement of the electron dipole moment,"We have calculated energy levels and lifetimes of 4f7 and 4f6 5d
configurations of Gd IV using Hartree-Fock and configuration interaction
methods. This allows us to reduce significantly the uncertainty of the
theoretical determination of the electron electric dipole moment (EDM)
enhancement factor in this ion and, correspondingly, in gadolinium-containing
garnets for which such measurements were recently proposed. Our new value for
the EDM enhancement factor of Gd+3 is -2.2 +- 0.5. Calculations of energy
levels and lifetimes for Eu~III are used to control the accuracy.",0206047v1
1995-11-28,A Supersymmetric Treatment of a Particle Subjected to a Ring-shaped Potential,"The ring-shaped Hartmann potential $V = \eta \sigma^{2} \epsilon_{0} \left(
\frac{2 a_{0}}{r} - \frac{\eta a_{0}^{2}}{r^{2} sin^{2} \theta} \right)$ was
introduced in quantum chemistry to describe ring-shaped molecules like benzene.
In this article, fundamental concepts of supersymmetric quantum mechanics
(SUSYQM) are discussed.
  The energy eigenvalues and (radial) eigenfunctions of the Hartmann potential
are subsequently rederived using the techniques of SUSYQM.",9511040v1
2003-05-12,Comment on Repulsive Casimir Forces,"A recent theoretical calculation shows that the Casimir force between two
parallel plates can be repulsive for plates with nontrivial magnetic properties
(O. Kenneth et al., Phys. Rev. Lett. 89, 033001 (2002)). According to the
authors, the effect may be observed with known materials, such as ferrites and
garnets, and it might be possible to engineer micro- or nanoelectromechanical
systems (MEMS or NEMS) that could take advantage of a short range repulsive
force. Here we show that on the contrary the Casimir force between two parallel
plates in vacuum at micron and submicron distance is always attractive.",0305065v1
2004-10-31,A physical basis for the phase in Feynman path integration,"In the path integral formulation of quantum mechanics, the phase factor
Exp[iS(x[t])] is associated with every path x[t]. Summing this factor over all
paths yields Feynman's propagator as a sum-over-paths. In the original
formulation, the complex phase was a mathematical device invoked to extract
wave behaviour in a particle framework. In this paper we show that the phase
itself can have a physical origin in time reversal, and that the propagator can
be drawn by a single deterministic path.",0411005v1
2008-04-10,Density Matrix Renormalization Group Lagrangians,"We introduce a Lagrangian formulation of the Density Matrix Renormalization
Group (DMRG). We present Lagrangians which when minimised yield the optimal
DMRG wavefunction in a variational sense, both within the general matrix
product ansatz, as well as within the canonical form of the matrix product that
is constructed within the DMRG sweep algorithm. Some of the results obtained
are similar to elementary expressions in Hartree-Fock theory, and we draw
attention to such analogies. The Lagrangians introduced here will be useful in
developing theories of analytic response and derivatives in the DMRG.",0804.1755v1
2008-10-27,Macroscopic signature of protected spins in a dense frustrated magnet,"The inability of systems of interacting objects to satisfy all constraints
simultaneously leads to frustration. A particularly important consequence of
frustration is the ability to access certain protected parts of a system
without disturbing the others. For magnets such ""protectorates"" have been
inferred from theory and from neutron scattering, but their practical
consequences have been unclear. We show that a magnetic analogue of optical
hole-burning can address these protected spin clusters in a well-known,
geometrically frustrated Heisenberg system, gadolinium gallium garnet. Our
measurements additionally provide a resolution of a famous discrepancy between
the bulk magnetometry and neutron diffraction results for this magnetic
compound.",0810.4744v1
2009-01-20,Analytic response theory for the density matrix renormalization group,"We propose an analytic response theory for the density matrix renormalization
group whereby response properties correspond to analytic derivatives of density
matrix renormalization group observables with respect to the applied
perturbations. Both static and frequency-dependent response theories are
formulated and implemented. We evaluate our pilot implementation by calculating
static and frequency dependent polarizabilities of short oligo-di-acetylenes.
The analytic response theory is competitive with dynamical density matrix
renormalization group methods and yields significantly improved accuracies when
using a small number of density matrix renormalization group states. Strengths
and weaknesses of the analytic approach are discussed.",0901.3166v1
2009-01-22,Perfect Reflection of Chiral Fermions in Gated Graphene Nanoribbons,"We describe the results of a theoretical study of transport through gated
metallic graphene nanoribbons using a non-equilibrium Green function method.
Although analogies with quantum field theory predict perfect transmission of
chiral fermions through gated regions in one dimension, we find \emph{perfect
reflection} of chiral fermions in armchair ribbons for specific configurations
of the gate. This effect should be measurable in narrow graphene constrictions
gated by a charged carbon nanotube.",0901.3407v1
2010-12-15,Giant transversal particle diffusion in a longitudinal magnetic ratchet,"We study the transversal motion of paramagnetic particles on a uniaxial
garnet film, exhibiting a longitudinal ratchet effect in the presence of an
oscillating magnetic field. Without the field, the thermal diffusion
coefficient obtained by video microscopy is $D_{0}\approx 3\times 10^{-4}$ $\mu
m^2/s$. With the field, the transversal diffusion exhibits a giant enhancement
by almost four decades and a pronounced maximum as a function of the driving
frequency. We explain the experimental findings with a theoretical
interpretation in terms of random disorder effects within the magnetic film.",1012.3343v1
2011-03-10,"Analytic Time Evolution, Random Phase Approximation, and Green Functions for Matrix Product States","Drawing on similarities in Hartree-Fock theory and the theory of matrix
product states (MPS), we explore extensions to time evolution, response theory,
and Green functions. We derive analytic equations of motion for MPS from the
least action principle, which describe optimal evolution in the small time-step
limit. We further show how linearized equations of motion yield a MPS random
phase approximation, from which one obtains response functions and excitations.
Finally we analyze the structure of site-based Green functions associated with
MPS, as well as the structure of correlations introduced via the
fluctuation-dissipation theorem.",1103.2155v1
2012-03-24,4f and 5d levels of Ce3+ in D2 eightfold oxygen coordination,"The effects on the 4f and 5d levels of Ce3+ of its first coordination shell
geometry in Ce-doped oxides with a D2 8-fold site, like garnets, are studied
with embedded cluster, wave function based ab initio methods. The only
deformations of a CeO8 cube that are found to shift the lowest 4f-5d transition
to the red are the symmetric Ce-O bond compression and the tetragonal symmetric
bond bending. These results are analyzed in terms of centroid and ligand field
stabilization energy differences. The splittings of the upper 5d levels and of
the 4f levels are also discussed.",1203.5391v1
2012-10-19,"Magnetization, Magnetic Susceptibility and ESR in Tb3Ga5O12","We report on the measurement of the magnetic susceptibility and of ESR
transitions in the garnet substance Tb$_3$Ga$_5$O$_{12}$ (TGG). The results are
compared with a calculation in the framework of crystal field theory for the
orthorhombic surroundings of the six inequivalent Tb ions of TGG. We also
present a calculation of the magnetization for the three main crystal
directions.",1210.5350v1
2012-11-06,"Deep trapping states in Cerium doped (Lu,Y,Gd)3(Ga,Al)5O12 single crystal scintillators","We study deep trapping states in Ce3+-doped garnet crystals with the
composition (Lu,Y,Gd)3(Ga,Al)5O12, recently shown as having remarkably high
light yield. We use thermally stimulated luminescence (TSL) technique above
room temperature and determine the composition Gd3Ga3Al2O12 as the host showing
the lowest concentration of traps. This host consistently manifest very low
afterglow comparable to that of the standard BGO crystal. We also perform TSL
glow peak analysis based on the initial rise technique to evaluate trap depth
and other characteristics associated with TSL peaks.",1211.1256v1
2014-02-14,Nonlinearity management of photonic composites and observation of spatial-modulation instability due to quintic nonlinearity,"We present a procedure for nonlinearity management of metal-dielectric
composites. Varying the volume fraction occupied by silver nanoparticles
suspended in acetone we could cancel the refractive index related to the
third-order susceptibility, $\chi_{eff}^{(3)}$, and the nonlinear refraction
behavior was due to the fifth-order susceptibility, $\chi_{eff}^{(5)}$. Hence,
in a cross-phase modulation experiment, we demonstrated for the first time the
effect of spatial-modulation- instability due to $\chi_{eff}^{(5)}$. The
results are corroborated with numerical calculations based on a generalized
Maxwell-Garnet model.",1402.3345v1
2014-02-23,The intermediate and spin-liquid phase of the half-filled honeycomb Hubbard model,"We obtain the phase-diagram of the half-filled honeycomb Hubbard model with
density matrix embedding theory, to address recent controversy at intermediate
couplings. We use clusters from 2-12 sites and lattices at the thermodynamic
limit. We identify a paramagnetic insulating state, with possible hexagonal
cluster order, competitive with the antiferromagnetic phase at intermediate
coupling. However, its stability is strongly cluster and lattice size
dependent, explaining controver- sies in earlier work. Our results support the
paramagnetic insulator as being a metastable, rather than a true, intermediate
phase, in the thermodynamic limit.",1402.5622v1
2014-07-03,Origin of the Phonon Hall Effect in Rare-Earth Garnets,"The phonon Hall effect has been observed in the paramagnetic insulator,
Tb3Gd5O12. A magnetic field applied perpendicularly to a heat current induces a
temperature gradient that is perpendicular to both the field and the current.
We show that this effect is due to resonant skew scattering of phonons from the
crystal field states of superstoichiometric Tb^3+ ions. This scattering
originates from the coupling between the quadrupole moment of Tb^3+ ions and
the lattice strain. The estimated magnitude of the effect is consistent with
experimental observations at T=5 K, and can be significantly enhanced by
increasing temperature.",1407.0802v2
2015-02-16,Correct quantum chemistry in a minimal basis from effective Hamiltonians,"We describe how to create ab-initio effective Hamiltonians that qualitatively
describe correct chemistry even when used with a minimal basis. The
Hamiltonians are obtained by folding correlation down from a large parent basis
into a small, or minimal, target basis, using the machinery of canonical
transformations. We demonstrate the quality of these effective Hamiltonians to
correctly capture a wide range of excited states in water, nitrogen, and
ethylene, and to describe ground and excited state bond-breaking in nitrogen
and the chromium dimer, all in small or minimal basis sets.",1502.04698v1
2015-02-26,Excited state geometry optimization with the density matrix renormalization group as applied to polyenes,"We describe and extend the formalism of state-specific analytic density
matrix renormalization group (DMRG) energy gradients, first used by Liu et al
(J. Chem. Theor.Comput. 9, 4462 (2013)). We introduce a DMRG wavefunction
maximum overlap following technique to facilitate state-specific DMRG excited
state optimization. Using DMRG configuration interaction (DMRG-CI) gradients we
relax the low-lying singlet states of a series of trans-polyenes up to C20H22.
Using the relaxed excited state geometries as well as correlation functions, we
elucidate the exciton, soliton, and bimagnon (""single-fission"") character of
the excited states, and find evidence for a planar conical intersection.",1502.07731v2
2015-12-31,A time-dependent formulation of multi-reference perturbation theory,"We discuss the time-dependent formulation of perturbation theory in the
context of the interacting zeroth-order Hamiltonians that appear in
multi-reference situations. As an example, we present a time-dependent
formulation and implementation of second-order n-electron valence perturbation
theory. The resulting t-NEVPT2 method yields the fully uncontracted n-electron
valence perturbation wavefunction and energy, but has a lower computational
scaling than the usual contracted variants, and also avoids the construction of
high-order density matrices and the diagonalization of metrics. We present
results of t-NEVPT2 for the water, nitrogen, carbon, and chromium molecules,
and outline directions for the future.",1512.09213v2
2016-02-12,Density matrix embedding theory for interacting electron-phonon systems,"We describe the extension of the density matrix embedding theory (DMET)
framework to coupled interacting fermion-boson systems. This provides a
frequency-independent, entanglement embedding formalism to treat bulk
fermion-boson problems. We illustrate the concepts within the context of the
one-dimensional Hubbard-Holstein model, where the phonon bath states are
obtained from the Schmidt decomposition of a self-consistently adjusted
coherent state. We benchmark our results against accurate density matrix
renormalization group calculations.",1602.04195v1
2016-05-16,The degree of commutativity and lamplighter groups,"The degree of commutativity of a group $G$ measures the probability of
choosing two elements in $G$ which commute. There are many results studying
this for finite groups. In [AMV17], this was generalised to infinite groups. In
this note, we compute the degree of commutativity for wreath products of the
form $\mathbb{Z}\wr \mathbb{Z}$ and $F\wr \mathbb{Z}$ where $F$ is any finite
group.",1605.04829v2
2016-06-03,Difference of Convex Functions Programming Applied to Control with Expert Data,"This paper reports applications of Difference of Convex functions (DC)
programming to Learning from Demonstrations (LfD) and Reinforcement Learning
(RL) with expert data. This is made possible because the norm of the Optimal
Bellman Residual (OBR), which is at the heart of many RL and LfD algorithms, is
DC. Improvement in performance is demonstrated on two specific algorithms,
namely Reward-regularized Classification for Apprenticeship Learning (RCAL) and
Reinforcement Learning with Expert Demonstrations (RLED), through experiments
on generic Markov Decision Processes (MDP), called Garnets.",1606.01128v2
2017-01-17,Gaussian-based coupled-cluster theory for the ground state and band structure of solids,"We present the results of Gaussian-based ground-state and excited-state
equation-of-motion coupled-cluster theory with single and double excitations
for three-dimensional solids. We focus on diamond and silicon, which are
paradigmatic covalent semiconductors. In addition to ground-state properties
(the lattice constant, bulk modulus, and cohesive energy), we compute the
quasiparticle band structure and band gap. We sample the Brillouin zone with up
to 64 k-points using norm-conserving pseudopotentials and polarized double- and
triple-zeta basis sets, leading to canonical coupled-cluster calculations with
as many as 256 electrons in 2,176 orbitals.",1701.04832v1
2017-09-07,The conjugacy ratio of groups,"In this paper we introduce and study the conjugacy ratio of a finitely
generated group, which is the limit at infinity of the quotient of the
conjugacy and standard growth functions. We conjecture that the conjugacy ratio
is $0$ for all groups except the virtually abelian ones, and confirm this
conjecture for certain residually finite groups of subexponential growth,
hyperbolic groups, right-angled Artin groups, and the lamplighter group.",1709.02152v1
2017-10-03,Lowering of the complexity of quantum chemistry methods by choice of representation,"The complexity of the standard hierarchy of quantum chemistry methods is not
invariant to the choice of representation. This work explores how the scaling
of common quantum chemistry methods can be reduced using real-space,
momentum-space, and time-dependent intermediate representations without
introducing approximations. We find the scalings of exact Gaussian basis
Hartree--Fock theory, second-order M{\o}ller-Plesset perturbation theory, and
coupled cluster theory (specifically, linearized coupled cluster doubles and
the distinguishable cluster approximation with doubles) to be
$\mathcal{O}(N^3)$, $\mathcal{O}(N^3)$, and $\mathcal{O}(N^5)$ respectively,
where $N$ denotes system size. These scalings are not asymptotic and hold over
all ranges of $N$.",1710.01004v1
2017-11-20,Electron paramagnetic resonance g-tensors from state interaction spin-orbit coupling density matrix renormalization group,"We present a state interaction spin-orbit coupling method to calculate
electron paramagnetic resonance (EPR) $g$-tensors from density matrix
renormalization group wavefunctions. We apply the technique to compute
$g$-tensors for the \ce{TiF3} and \ce{CuCl4^2-} complexes, a [2Fe-2S] model of
the active center of ferredoxins, and a \ce{Mn4CaO5} model of the S2 state of
the oxygen evolving complex. These calculations raise the prospects of
determining $g$-tensors in multireference calculations with a large number of
open shells.",1711.07195v3
2018-03-27,The fate of atomic spin in atomic scattering off surfaces,"We explore model electron dynamics of an atom scattering off a surface within
the time-dependent complete active space self consistent field (TD-CASSCF)
approximation. We focus especially on the scattering of a hydrogen atom and its
resulting spin-dynamics starting from an initially spin-polarized state. Our
results reveal competing electronic time-scales that are governed by the
electronic structure of the surface as well as the character of the atom. The
timescales and nonadiabaticity of the dynamics are reported on by the final
spin-polarization of the scattered atom, which may be probed in future
experiments.",1803.09895v1
2018-10-08,"Comment on ""Numerical Evidence Falsifying Finite-Temperature Many-Body Perturbation Theory""","In this comment we address the preprint of Jha and Hirata (arXiv:1809.10316
[physics.chem-ph]) which claims ""Numerical Evidence Falsifying
Finite-Temperature Many-Body Perturbation Theory."" We agree that finite
difference differentiation of the exact grand potential is the correct way to
verify the terms in the perturbation expansion. However, it is our suspicion
that theoretical errors, uncontrolled numerical errors, and/or errors in their
implementation have led Jha and Hirata to incorrectly conclude that finite
temperature perturbation theory is incorrect. We show numerical evidence from
finite difference differentiation of the grand potential that supports the
correctness of finite-temperature perturbation theory.",1810.03653v2
2019-04-24,Layered optomagnonic structures: Time Floquet scattering-matrix approach,"A fully dynamic theoretical approach to layered optomagnonic structures,
based on a time Floquet scattering-matrix method, is developed. Its
applicability is demonstrated on a simple design of a dual photonic-magnonic
cavity, formed by sandwiching a magnetic garnet thin film between two
dielectric Bragg mirrors, subject to continuous excitation of a perpendicular
standing spin wave. Some remarkable phenomena, including nonlinear
photon-magnon interaction effects and enhanced inelastic light scattering in
the strong-coupling regime, fulfilling a triple-resonance condition, are
analyzed and the limitations of the quasistatic adiabatic approximation are
established.",1904.10714v1
2019-05-02,Projected Density Matrix Embedding Theory with Applications to the Two-Dimensional Hubbard Model,"Density matrix embedding theory (DMET) is a quantum embedding theory for
strongly correlated systems. From a computational perspective, one bottleneck
in DMET is the optimization of the correlation potential to achieve
self-consistency, especially for heterogeneous systems of large size. We
propose a new method, called projected density matrix embedding theory
(p-DMET), which achieves self-consistency without needing to optimize a
correlation potential. We demonstrate the performance of p-DMET on the
two-dimensional Hubbard model.",1905.00886v2
2019-07-26,Time-dependent coupled cluster theory on the Keldysh contour for non-equilibrium systems,"We leverage the Keldysh formalism to extend our implementation of finite
temperature coupled cluster theory [\textit{J. Chem. Theory Comput.} 2018,
\textit{14}, 5690-5700] to thermal systems that have been driven out of
equilibrium. The resulting Keldysh coupled cluster theory is discussed in
detail. We describe the implementation of the equations necessary to perform
Keldysh coupled cluster singles and doubles calculations of finite temperature
dynamics, and we apply the method to some simple systems including a Hubbard
model with a Peierls phase and an {\it ab initio} model of warm-dense silicon
subject to an ultrafact XUV pulse.",1907.11695v1
2020-01-09,Theoretical Prediction of Magnetic Exchange Coupling Constants from Broken-Symmetry Coupled Cluster Calculations,"Exchange coupling constants ($J$) are fundamental to the understanding of
spin spectra of magnetic systems. Here we investigate the broken-symmetry (BS)
approaches of Noodleman and Yamaguchi in conjunction with coupled cluster (CC)
methods to obtain exchange couplings. $J$ values calculated from CC in this
fashion converge smoothly towards the FCI result with increasing level of CC
excitation. We compare this BS-CC scheme to the complementary EOM-CC approach
on a selection of bridged molecular cases and give results from a few other
methodologies for context.",2001.03226v1
2020-03-06,Dynamical Phase Transitions in a 2D Classical Nonequilibrium Model via 2D Tensor Networks,"We demonstrate the power of 2D tensor networks for obtaining large deviation
functions of dynamical observables in a classical nonequilibrium setting. Using
these methods, we analyze the previously unstudied dynamical phase behavior of
the fully 2D asymmetric simple exclusion process with biases in both the x and
y directions. We identify a dynamical phase transition, from a jammed to a
flowing phase, and characterize the phases and the transition, with an estimate
of the critical point and exponents.",2003.03050v2
2022-07-28,Differentiable quantum chemistry with PySCF for molecules and materials at the mean-field level and beyond,"We introduce an extension to the PySCF package which makes it automatically
differentiable. The implementation strategy is discussed, and example
applications are presented to demonstrate the automatic differentiation
framework for quantum chemistry methodology development. These include orbital
optimization, properties, excited-state energies, and derivative couplings, at
the mean-field level and beyond, in both molecules and solids. We also discuss
some current limitations and directions for future work.",2207.13836v2
2022-11-07,Multi-site Reaction Dynamics Through Multi-fragment Density Matrix Embedding,"The practical description of disordered chemical reactions, where reactions
involve multiple species at multiple sites, is presently challenge using
correlated electronic structure methods. Here we describe the gradient theory
of multi-fragment density matrix embedding theory, which potentially provides a
minimal computational framework to model such processes at the correlated
electron level. We present the derivation and implementation of the gradient
theory, its validation on model systems and chemical reactions using density
matrix embedding, and its application to a molecular dynamics simulation of
proton transport in a small water cluster, a simple example of multi-site
reaction dynamics.",2211.03728v1
2023-06-28,Fast classical simulation of evidence for the utility of quantum computing before fault tolerance,"We show that a classical algorithm based on sparse Pauli dynamics can
efficiently simulate quantum circuits studied in a recent experiment on 127
qubits of IBM's Eagle processor [Nature 618, 500 (2023)]. Our classical
simulations on a single core of a laptop are orders of magnitude faster than
the reported walltime of the quantum simulations, as well as faster than the
estimated quantum hardware runtime without classical processing, and are in
good agreement with the zero-noise extrapolated experimental results.",2306.16372v1
2023-08-24,Non-reciprocal coherent all-optical switching between magnetic multi-states,"We present experimental and computational findings of the laser-induced
non-reciprocal motion of magnetization during ultrafast photo-magnetic
switching in garnets. We found distinct coherent magnetization precession
trajectories and switching times between four magnetization states, depending
on both directions of the light linear polarization and initial magnetic state.
As a fingerprint of the topological symmetry, the choice of the switching
trajectory is governed by an interplay of the photo-magnetic torque and
magnetic anisotropy. Our results open a plethora of possibilities for designing
energy-efficient magnetization switching routes at arbitrary energy landscapes.",2308.12771v1
2016-10-04,Planck's Dusty GEMS. II. Extended [CII] emission and absorption in the Garnet at z=3.4 seen with ALMA,"We present spatially resolved ALMA [CII] observations of the bright (flux
density S=400 mJy at 350 microns), gravitationally lensed, starburst galaxy
PLCK G045.1+61.1 at z=3.427, the ""Garnet"". This source is part of our set of
""Planck's Dusty GEMS"", discovered with the Planck's all-sky survey. Two
emission-line clouds with a relative velocity offset of ~600 km/s extend
towards north-east and south-west, respectively, of a small, intensely
star-forming clump with a star-formation intensity of 220 Msun/yr/kpc^2, akin
to maximal starbursts. [CII] is also seen in absorption, with a redshift of
+350 km/s relative to the brightest CO component. [CII] absorption has
previously only been found in the Milky Way along sightlines toward bright
high-mass star-forming regions, and this is the first detection in another
galaxy. Similar to Galactic environments, the [CII] absorption feature is
associated with [CI] emission, implying that this is diffuse gas shielded from
the UV radiation of the clump, and likely at large distances from the clump.
Since absorption can only be seen in front of a continuum source, the gas in
this structure can definitely be attributed to gas flowing towards the clump.
The absorber could be part of a cosmic filament or merger debris being accreted
onto the galaxy. We discuss our results also in light of the on-going debate of
the origin of the [CII] deficit in dusty star-forming galaxies.",1610.01169v1
2017-03-09,Magnon mode selective spin transport in compensated ferrimagnets,"We investigate the generation of magnonic thermal spin currents and their
mode selective spin transport across interfaces in insulating, compensated
ferrimagnet/normal metal bilayer systems. The spin Seebeck effect signal
exhibits a non-monotonic temperature dependence with two sign changes of the
detected voltage signals. Using different ferrimagnetic garnets, we demonstrate
the universality of the observed complex temperature dependence of the spin
Seebeck effect. To understand its origin, we systematically vary the interface
between the ferrimagnetic garnet and the metallic layer, and by using different
metal layers we establish that interface effects play a dominating role. They
do not only modify the magnitude of the spin Seebeck effect signal but in
particular also alter its temperature dependence. By varying the temperature,
we can select the dominating magnon mode and we analyze our results to reveal
the mode selective interface transmission probabilities for different magnon
modes and interfaces. The comparison of selected systems reveals
semi-quantitative details of the interfacial coupling depending on the
materials involved, supported by the obtained field dependence of the signal.",1703.03218v2
2017-10-13,Relieving the frustration through Mn$^{3+}$ substitution in Holmium Gallium Garnet,"We present a study on the impact of Mn$^{3+}$ substitution in the
geometrically frustrated Ising garnet Ho$_3$Ga$_5$O$_{12}$ using bulk magnetic
measurements and low temperature powder neutron diffraction. We find that the
transition temperature, $T_N$ = 5.8 K, for Ho$_3$MnGa$_4$O$_{12}$ is raised by
almost 20 when compared to Ho$_3$Ga$_5$O$_{12}$. Powder neutron diffraction on
Ho$_3$Mn$_x$Ga$_{5-x}$O$_{12}$ ($x$ = 0.5, 1) below $T_N$ shows the formation
of a long range ordered ordered state with $\mathbf{k}$ = (0,0,0). Ho$^{3+}$
spins are aligned antiferromagnetically along the six crystallographic axes
with no resultant moment while the Mn$^{3+}$ spins are oriented along the body
diagonals, such that there is a net moment along [111]. The magnetic structure
can be visualised as ten-membered rings of corner-sharing triangles of
Ho$^{3+}$ spins with the Mn$^{3+}$ spins ferromagnetically coupled to each
individual Ho$^{3+}$ spin in the triangle. Substitution of Mn$^{3+}$ completely
relieves the magnetic frustration with $f = \theta_{CW}/T_N \approx 1.1$ for
Ho$_3$MnGa$_4$O$_{12}$.",1710.05083v1
2018-11-27,GarNet: A Two-Stream Network for Fast and Accurate 3D Cloth Draping,"While Physics-Based Simulation (PBS) can accurately drape a 3D garment on a
3D body, it remains too costly for real-time applications, such as virtual
try-on. By contrast, inference in a deep network, requiring a single forward
pass, is much faster. Taking advantage of this, we propose a novel architecture
to fit a 3D garment template to a 3D body. Specifically, we build upon the
recent progress in 3D point cloud processing with deep networks to extract
garment features at varying levels of detail, including point-wise, patch-wise
and global features. We fuse these features with those extracted in parallel
from the 3D body, so as to model the cloth-body interactions. The resulting
two-stream architecture, which we call as GarNet, is trained using a loss
function inspired by physics-based modeling, and delivers visually plausible
garment shapes whose 3D points are, on average, less than 1 cm away from those
of a PBS method, while running 100 times faster. Moreover, the proposed method
can model various garment types with different cutting patterns when parameters
of those patterns are given as input to the network.",1811.10983v3
2021-03-17,Ionic conductivity optimization of composite polymer electrolytes through filler particle chemical modification,"The addition of filler particles to polymer electrolytes is known to
increment their ionic conductivity (IC). A detailed understanding of how the
interactions between the constituent materials are responsible for the
enhancement, remains to be developed. A significant contribution is ascribed to
an increment of the polymer amorphous fraction, induced by the fillers,
resulting in the formation of higher ionic conductivity channels in the polymer
matrix. However, the dependence of IC on the particle weight load and its
composition on the polymer morphology is not fully understood. This work
investigates Li ion transport in composite polymer electrolytes (CPE)
comprising Bi-doped LLZO particles embedded in PEO: LiTFSI matrixes. We find
that the IC optimizes for very low particle weight loads (5 to 10%) and that
both its magnitude and the load required, strongly depend on the garnet
particle composition. Based on structural characterization results and
electrochemical impedance spectroscopy, a mechanism is proposed to explain
these findings. It is suggested that the Li-molar content in the garnet
particle controls its interactions with the polymer matrix, resulting at the
optimum loads reported, in the formation of high ionic conductivity channels.
We propose that filler particle chemical manipulation of the polymer morphology
is a promising avenue for the further development of composite polymer
electrolytes.",2103.09887v1
2021-04-30,A numerical exploration of signal detector arrangement in a spin-wave reservoir computing device,"This paper studies numerically how the signal detector arrangement influences
the performance of reservoir computing using spin waves excited in a
ferrimagnetic garnet film. This investigation is essentially important since
the input information is not only conveyed but also transformed by the spin
waves into high-dimensional information space when the waves propagate in the
film in a spatially distributed manner. This spatiotemporal dynamics realizes a
rich reservoir-computational functionality. First, we simulate spin waves in a
rectangular garnet film with two input electrodes to obtain spatial
distributions of the reservoir states in response to input signals, which are
represented as spin vectors and used for a machine-learning waveform
classification task. The detected reservoir states are combined through readout
connection weights to generate a final output. We visualize the spatial
distribution of the weights after training to discuss the number and positions
of the output electrodes by arranging them at grid points, equiangularly
circular points or at random. We evaluate the classification accuracy by
changing the number of the output electrodes, and find that a high accuracy
($>$ 90\%) is achieved with only several tens of output electrodes regardless
of grid, circular or random arrangement. These results suggest that the spin
waves possess sufficiently complex and rich dynamics for this type of tasks.
Then we investigate in which area useful information is distributed more by
arranging the electrodes locally on the chip. Finally, we show that this device
has generalization ability for input wave-signal frequency in a certain
frequency range. These results will lead to practical design of spin-wave
reservoir devices for low-power intelligent computing in the near future.",2104.14915v1
2021-08-30,Bright and dark states of two distant macrospins strongly coupled by phonons,"We study the collective dynamics of two distant magnets coherently coupled by
acoustic phonons that are transmitted through an intercalated crystal. By
tuning the ferromagnetic resonances of the two magnets to an acoustic resonance
of the crystal, we control a coherent three levels system. We show that the
parity of the phonon mode governs the nature of the indirect coupling between
the magnets: the resonances with odd / even phonon modes correspond to
out-of-phase / in-phase lattice displacements at the magnets, leading to bright
/ dark states in response to uniform microwave magnetic fields, respectively.
The sample is a tri-layer garnet consisting of two thin magnetic layers
epitaxially grown on both sides of a half-millimeter thick non-magnetic single
crystal. In spite of the relatively weak magneto-elastic interaction, the long
lifetimes of the magnon and phonon modes in the sample are the key to unveil
this long range strong coupling. This demonstrates that garnets are a great
platform to study multi-partite hybridization process between magnon and
phonons at microwave frequencies.",2108.13272v2
2022-02-06,Enhancing Perpendicular Magnetic Anisotropy in Garnet Ferrimagnet by Interfacing with Few-Layer WTe2,"Engineering magnetic anisotropy in a ferro- or ferrimagnetic (FM) thin film
is crucial in spintronic device. One way to modify the magnetic anisotropy is
through the surface of the FM thin film. Here, we report the emergence of a
perpendicular magnetic anisotropy (PMA) induced by interfacial interactions in
a heterostructure comprised of a garnet ferrimagnet, Y3Fe5O12 (YIG), and the
low-symmetry, high spin orbit coupling (SOC) transition metal dichalcogenide,
WTe2. At the same time, we also observed an enhancement in Gilbert damping in
the WTe2 covered YIG area. Both the magnitude of interface-induced PMA and the
Gilbert damping enhancement have no observable WTe2 thickness dependence down
to single quadruple-layer, indicating that the interfacial interaction plays a
critical role. The ability of WTe2 to enhance the PMA in FM thin film, combined
with its previously reported capability to generate out-of-plane damping like
spin torque, makes it desirable for magnetic memory applications.",2202.02834v1
2022-06-23,An Investigation into the Kinetics of $Li^+$ Ion Migration in Garnet-Type Solid State Electrolyte: $Li_7La_3Zr_2O_{12}$,"An all solid-state thin film lithium ion battery has been touted the holy
grail for energy storage technology ever since the inception of the first one
in 1986 by Keiichi Kanehori. Solid-state batteries provide the distinct
advantage of outperforming current technology by having a simpler composition,
being easier and cheaper to manufacture, safer and having a higher theoretical
gravimetric and volumetric energy density. The commercialization of this
technology however, is plagued by its own set of challenges, primarily low
ionic conductivity and interfacial stability of the solid-state electrolyte
separating the anode and cathode, a small electrochemical window and sub-par
mechanical properties. In the last decade considerable progress has been made
in remedying these issues with garnet-type electrolytes, especially
Li7La3Zr2O12 (LLZO), having emerged the leading contender. This has prompted
renewed effects into the field of solid-state ionic's and maximizing the ionic
conductivity of LLZO by modifying its properties, primarily by means of doping
with a varying degree of success. Carving a clear road ahead requires an
in-depth understanding of the origin of the high Li+ ion conductivity, the
primary means of investigating which is by first-principle methods. In this
term paper we try to gain insight into the origin of mechanisms at play that
drive the collective migration of Li+ ions in LLZO using a first-principles
approach, to gain a deeper understanding and appreciation for optimizing its
properties for use in next-generation energy storage systems.",2206.11435v1
2024-02-06,Magnon mediated spin pumping by coupled ferrimagnetic garnets heterostructure,"Spin pumping has significant implications for spintronics, providing a
mechanism to manipulate and transport spins for information processing.
Understanding and harnessing spin currents through spin pumping is critical for
the development of efficient spintronic devices. The use of a magnetic
insulator with low damping, enhances the signal-to-noise ratio in crucial
experiments such as spin-torque ferromagnetic resonance (FMR) and spin pumping.
A magnetic insulator coupled with a heavy metal or quantum material offers a
more straight forward model system, especially when investigating spin-charge
interconversion processes to greater accuracy. This simplicity arises from the
absence of unwanted effects caused by conduction electrons unlike in
ferromagnetic metals. Here, we investigate the spin pumping in coupled
ferrimagnetic (FiM) Y3Fe5O12 (YIG)/Tm3Fe5O12 (TmIG) bilayers combined with
heavy-metal (Pt) using the inverse spin Hall effect (ISHE). It is observed that
magnon transmission occurs at both of the FiMs FMR positions. The enhancement
of spin pumping voltage (Vsp) in the FiM garnet heterostructures is attributed
to the strong interfacial exchange coupling between FiMs. The modulation of Vsp
is achieved by tuning the bilayer structure. Further, the spin mixing
conductance for these coupled systems is found to be 10^18 m^-2. Our findings
describe a novel coupled FiM system for the investigation of magnon coupling
providing new prospects for magnonic devices.",2402.03734v1
2024-03-04,"Double magnetic transition, complex field-induced phases, and large magnetocaloric effect in the frustrated garnet compound Mn$_{3}$Cr$_{2}$Ge$_{3}$O$_{12}$","A detailed study of the magnetic and magnetocaloric properties of a garnet
compound Mn$_{3}$Cr$_{2}$Ge$_{3}$O$_{12}$ is carried out using x-ray
diffraction, magnetization, heat capacity, and neutron diffraction measurements
as well as \textit{ab initio} band-structure calculations. This compound
manifests two successive magnetic transitions at $T_{\rm N1} \simeq 4.5$ K and
$T_{\rm N2} \simeq 2.7$ K. Neutron powder diffraction experiments reveal that
these two transitions correspond to the collinear and non-collinear
antiferromagnetic ordering of the nonfrustrated Cr$^{3+}$ and frustrated
Mn$^{2+}$ sublattices, respectively. The interactions within each of the Cr and
Mn sublattices are antiferromagnetic, while the inter-sublattice interactions
are ferromagnetic. The $H-T$ phase diagram is quite complex and displays
multiple phases under magnetic field, which can be attributed to the frustrated
nature of the spin lattice. Mn$_{3}$Cr$_{2}$Ge$_{3}$O$_{12}$ shows a large
magnetocaloric effect with a maximum value of isothermal entropy change $\Delta
S_{\rm m} \simeq -23$ J/kg-K and adiabatic temperature change $\Delta T_{\rm
ad} \simeq 9$ K for a field change of 7 T. Further, a large value of the
relative cooling power ($RCP \simeq 360$ J/kg) demonstrates the promise of
using this compound in magnetic refrigeration.",2403.02082v2
2024-03-22,UV- and X-ray-activated broadband NIR garnet-type Ca3Ga2Sn3O12:Fe3+ phosphors with efficient persistent luminescence,"Near-infrared phosphor-converted light-emitting diodes (NIR pc-LEDs) are
compact light sources of great interest for NIR spectroscopy applications.
Beyond typical Cr3+-activated NIR-emitting phosphors, there exists a strong
demand for Cr3+-free alternatives with high efficiency and broadband emission
to rich the landscape of NIR luminescent materials and extend their range of
application fields. Here, we report a series of Fe3+-activated Ca3Ga2Sn3O12
garnet-type phosphors exhibiting broadband NIR emission in the 650-1000 nm
range attributed to 4T1(G)-->6A1(S) transition, with a maximum at 754 nm and a
FWHM of 89 nm upon UV excitation. The spectroscopic results were analyzed
according to the Tanabe-Sugano theory from which the crystal field parameter Dq
and Racah parameters B and C were obtained for the octahedrally coordinated
Fe3+ ion. Notably, the NIR persistent luminescence lasting over 1 h was
detected following UV or X-ray irradiation. The possible mechanism involving
electron traps was proposed to explain the observed persistent luminescence.
Furthermore, a NIR pc-LED was fabricated by coating synthesized phosphor on a
UV chip, and its performance was evaluated to assess its potential suitability
as a NIR light source. Our discovery of novel type of nontoxic Fe3+-activated
broadband NIR luminescence phosphors with efficient NIR persistent luminescence
paves the way for discovering Cr3+-free multifunctional NIR luminescence
materials, thereby expanding their application possibilities.",2403.15168v1
2001-04-19,An Empirical Ultraviolet Template for Iron Emission in Quasars as Derived from I Zw 1,"We present an empirical template spectrum suitable for fitting/subtracting
and studying the FeII and FeIII line emission in the restframe UV spectra of
active galatic nuclei (AGNs), the first empirical UV iron template to cover the
full 1250 - 3090 A range. Iron emission is often a severe contaminant in
optical--UV spectra of AGNs. Its presence complicates and limits the accuracy
of measurements of both strong and weak emission lines and the continuum
emission, affecting studies of line and continuum interrelations, the
ionization structure, and elemental abundances in AGNs. Despite the wealth of
work on modeling the AGN FeII emission and the need to account for it in
observed AGN spectra, there is no UV template electronically available to aid
this process. The iron template we present is based on HST spectra of the
Narrow Line Seyfert 1, IZw1. Its intrinsic narrow lines (~900 km/s) and rich
iron spectrum make the template particularly suitable for use with most AGN
spectra. The iron emission spectrum and the line identifications and
measurements are presented and compared with the work of Laor et al. We
illustrate the application of the derived FeII and FeIII templates by fitting
and subtracting the iron emission from UV spectra of four high-z quasars and of
the nearby quasar, 3C273. We briefly discuss the small discrepancies between
this observed iron emission and the UV template, and compare the template with
previously published ones. We discuss the advantages and limitations of the
templates and of the template fitting method. We conclude that the templates
work sufficiently well to be a valuable and important tool for eliminating and
studying the iron emission in AGNs, at least until accurate theoretical iron
emission models are developed. (Abridged)",0104320v1
2008-10-01,Galactic abundance gradients from Cepheids : On the iron abundance gradient around 10-12 kpc,"Context: Classical Cepheids can be adopted to trace the chemical evolution of
the Galactic disk since their distances can be estimated with very high
accuracy. Aims: Homogeneous iron abundance measurements for 33 Galactic
Cepheids located in the outer disk together with accurate distance
determinations based on near-infrared photometry are adopted to constrain the
Galactic iron gradient beyond 10 kpc. Methods: Iron abundances were determined
using high resolution Cepheid spectra collected with three different
observational instruments: ESPaDOnS@CFHT, Narval@TBL and FEROS@2.2m ESO/MPG
telescope. Cepheid distances were estimated using near-infrared (J,H,K-band)
period-luminosity relations and data from SAAO and the 2MASS catalog. Results:
The least squares solution over the entire data set indicates that the iron
gradient in the Galactic disk presents a slope of -0.052+/-0.003 dex/kpc in the
5-17 kpc range. However, the change of the iron abundance across the disk seems
to be better described by a linear regime inside the solar circle and a
flattening of the gradient toward the outer disk (beyond 10 kpc). In the latter
region the iron gradient presents a shallower slope, i.e. -0.012+/-0.014
dex/kpc. In the outer disk (10-12 kpc) we also found that Cepheids present an
increase in the spread in iron abundance. Current evidence indicates that the
spread in metallicity depends on the Galactocentric longitude. Finally, current
data do not support the hypothesis of a discontinuity in the iron gradient at
Galactocentric distances of 10-12 kpc. Conclusions: The occurrence of a spread
in iron abundance as a function of the Galactocentric longitude indicates that
linear radial gradients should be cautiously treated to constrain the chemical
evolution across the disk.",0810.0205v1
2011-11-09,Galactic restrictions on iron production by various Types of supernovae,"We propose a statistical method for decomposition of contributions to iron
production from various sources: supernovae Type II and the subpopulations of
supernovae Type Ia -- prompt (their progenitors are short-lived stars of ages
less then $\sim$100 Myr) and tardy (whose progenitors are long-lived stars of
ages $>$100 Myr). To do that, we develop a theory of oxygen and iron synthesis
which takes into account the influence of spiral arms on amount of the above
elements synthesized by both the supernovae Type II and prompt supernovae Ia.
We solve this task without of any preliminary suppositions about the ratio
among the portions of iron synthesized by the above sources.
  The relative portion of iron synthesized by tardy supernovae Ia for the
life-time of the Galaxy is $\sim$35 per cent (in the present ISM this portion
is $\sim$50 per cent). Correspondingly, the total portion of iron supplied to
the disc by supernovae Type II and prompt supernovae Ia is $\sim$65 per cent
(in the present ISM this portion is $\sim$50 per cent).
  The above result slightly depends on the adopted mass of oxygen and iron
synthesized during one explosion of supernovae and the shape (bimodal or
smooth) of the so-called Delay Time Distribution function.
  The portions of iron mass distributed between the short-lived supernovae are
usually as follows: depending on the ejected masses of oxygen or iron during
one supernovae Type II event the relative portion of iron, supplied to the
Galactic disc for its age, varies in the range 12 - 32 per cent (in the present
ISM 9-25 per cent); the portion supplied by prompt supernovae Ia to the
Galactic disc is 33 - 53 per cent (in ISM 26 - 42 per cent).",1111.2152v1
2018-08-27,Why Are Some Gamma-Ray Bursts Hosted by Oxygen-rich Galaxies?,"Theoretically long gamma-ray bursts (GRBs) are expected to happen in
low-metallicity environments, because in a single massive star scenario, low
iron abundance prevents loss of angular momentum through stellar wind,
resulting in ultra-relativistic jets and the burst. In this sense, not just a
simple metallicity measurement but also low iron abundance ([Fe/H]<-1.0) is
essentially important. Observationally, however, oxygen abundance has been
measured more often due to stronger emission. In terms of oxygen abundance,
some GRBs have been reported to be hosted by high-metallicity star-forming
galaxies, in tension with theoretical predictions. Here we compare iron and
oxygen abundances for the first time for GRB host galaxies (GRB 980425 and
080517) based on the emission-line diagnostics. The estimated total iron
abundances, including iron in both gas and dust, are well below the solar
value. The total iron abundances can be explained by the typical value of
theoretical predictions ([Fe/H]<-1.0), despite high oxygen abundance in one of
them. According to our iron abundance measurements, the single massive star
scenario still survives even if the oxygen abundance of the host is very high,
such as the solar value. Relying only on oxygen abundance could mislead us on
the origin of the GRBs. The measured oxygen-to-iron ratios, [O/Fe], can be
comparable to the highest values among the iron-measured galaxies in the Sloan
Digital Sky Survey. Possible theoretical explanations of such high [O/Fe]
include the young age of the hosts, top-heavy initial mass function, and
fallback mechanism of the iron element in supernova explosions.",1808.08969v1
2021-03-25,Thermodynamic Analysis of Titanium Removal from Molten iron Smelted with Large Amounts of Sodium Additives,"High purity iron is obtained from vanadium-titanium magnetite (VTM) by
one-step coal-based direct reduction-smelting process with coal as reductant
and sodium carbonate (Na2CO3) as additives. Industrial experiments show that
the process of treating molten iron with a large amount of Na2CO3 is effective
in removing titanium from molten iron. However, the studies are rarely
conducted in thermodynamic relationship between titanium and other components
of molten iron, under the condition of a large amount of Na2CO3 additives. In
this study, through the thermodynamic database software Factsage8.0, the
effects of melting temperature, sodium content and oxygen content on the
removal of titanium from molten iron are studied. The results of thermodynamic
calculation show that the removal of titanium from molten iron needs to be
under the condition of oxidation, and the temperature should be below the
critical temperature of titanium removal (the highest temperature at which
titanium can be removed). Relatively low temperature and high oxygen content
contribute to the removal of titanium from molten iron. The high oxygen content
is conducive to the simultaneous removal of titanium and phosphorus from molten
iron. In addition, from a thermodynamic point of view, excessive sodium
addition inhibits the removal of titanium from molten iron.",2103.13572v1
2021-08-17,"Nigral diffusivity, but not free water, correlates with iron content in Parkinson's disease","The loss of melanized neurons in the substantia nigra pars compacta is a
primary feature in Parkinson's disease (PD). Iron deposition occurs in
conjunction with this loss. Loss of nigral neurons should remove barriers for
diffusion and increase diffusivity of water molecules in regions undergoing
this loss. In metrics from single-compartment diffusion tensor imaging models,
these changes should manifest as increases in mean diffusivity and the free
water compartment as well as and reductions in fractional anisotropy. However,
studies examining nigral diffusivity changes from PD with single-compartment
models have yielded inconclusive results and emerging evidence in control
subjects indicates that iron corrupts diffusivity metrics derived from
single-compartment models.
  Iron-sensitive data and diffusion data were analyzed in two cohorts. The
effect of iron on diffusion measures from single- and bi-compartment models was
assessed in both cohorts.
  Measures sensitive to the free water compartment and iron content were found
to increase in substantia nigra of the PD group in both cohorts. However,
diffusion markers derived from the single-compartment model were not replicated
across cohorts. Correlations were seen between single-compartment diffusion
measures and iron markers in the discovery cohort and validation cohort but no
correlation was observed between a measure from the bi-compartment model
related to the free water compartment and iron markers in either cohort.
  The variability of single-compartment nigral diffusion metrics in PD may be
attributed to competing influences of increased iron content, which drives
diffusivity down, and increases in the free water compartment, which drives
diffusivity up. In contrast to diffusion metrics derived from the
single-compartment model, no relationship was seen between iron and the free
water compartment in substantia nigra.",2108.07864v1
2024-01-30,Carrier-phase DNS of ignition and combustion of iron particles in a turbulent mixing layer,"Three-dimensional CP-DNS of reacting iron particle dust clouds in a turbulent
mixing layer are conducted. The simulation approach considers the Eulerian
transport equations for the reacting gas phase and resolves all scales of
turbulence, whereas the particle boundary layers are modelled employing the
Lagrangian point-particle framework for the dispersed phase. The CP-DNS employs
an existing sub-model for iron particle combustion that considers the oxidation
of iron to FeO and that accounts for both diffusion- and kinetically-limited
combustion. At first, the particle sub-model is validated against experimental
results for single iron particle combustion considering various particle
diameters and ambient oxygen concentrations. Subsequently, the CP-DNS approach
is employed to predict iron particle cloud ignition and combustion in a
turbulent mixing layer. The upper stream of the mixing layer is initialised
with cold particles in air, while the lower stream consists of hot air flowing
in the opposite direction. Simulation results show that turbulent mixing
induces heating, ignition and combustion of the iron particles. Significant
increases in gas temperature and oxygen consumption occur mainly in regions
where clusters of iron particles are formed. Over the course of the oxidation,
the particles are subjected to different rate-limiting processes. While
initially particle oxidation is kinetically-limited it becomes
diffusion-limited for higher particle temperatures and peak particle
temperatures are observed near the fully-oxidised particle state. Comparing the
present non-volatile iron dust flames to general trends in volatile-containing
solid fuel flames, non-vanishing particles at late simulation times and a
stronger limiting effect of the local oxygen concentration on particle
conversion is found for the present iron dust flames in shear-driven
turbulence.",2401.16944v1
1998-09-10,Abundances of UV bright stars in globular clusters. I. ROA 5701 in omega Centauri and Barnard 29 in M 13,"Two UV brights stars in globular clusters, ROA 5701 (omega Cen) and Barnard
29 (M 13) are analysed from high-resolution UV and optical spectra. The main
aim is the measurement of iron abundances from UV spectra obtained with the
HST-GHRS. In addition atmospheric parameters and abundances for He, C, N, O,
and Si are derived from optical spectra (ESO CASPEC) for ROA 5701 or taken from
literature for Barnard 29. Both stars are found to be post-asymptotic giant
branch stars. Surprisingly, their iron abundances lie significantly below the
cluster abundance in both cases. Barnard 29 lies 0.5 dex below the iron
abundance derived for giant stars in M 13 and the iron abundance of ROA 5701 is
the lowest of any star in omega Cen analysed so far. Barnard 29 shows the same
abundance pattern as the red giant stars in M 13, except for its stronger iron
deficiency. The iron depletion could be explained by gas-dust separation in the
AGB progenitor's atmosphere, if iron condensed into dust grains which were then
removed from the atmosphere by a radiatively driven wind. The interpretation of
the abundance pattern for ROA 5701 is hampered by the star-to-star abundance
variations seen in omega Cen, but its abundance pattern appears to be
consistent with the gas-dust separation scenario.",9809128v1
2002-02-05,Iron Features in the XMM-Newton spectrum of NGC 4151,"We present a detailed analysis of the hard X-ray (>2.5 keV) EPIC spectra from
the first observations of NGC 4151 made by XMM-Newton. We fit the spectra with
a model consisting of a power-law continuum modified by line-of-sight
absorption (arising in both partially photoionized and neutral gas) plus
additional iron-K emission and absorption features. This model provides an
excellent overall fit to the EPIC spectra. The iron K-alpha line is well
modelled as a narrow Gaussian component. In contrast to several earlier studies
based on data from ASCA, a relativistically broadened iron K-alpha emission
feature is not required by the XMM-Newton data. The upper limit on the flux
contained in any additional broad line is ~8% of that in the narrow line. The
measured intrinsic line width (sigma =32+_7 eV) may be ascribed to (i) the
doublet nature of the iron K-alpha line and (ii) emission from low ionization
states of iron, ranging from neutral up to ~FeXVII. The additional iron
absorption edge arises in cool material and implies factor ~2 overabundance of
iron in this component.",0202093v1
2004-04-21,Ultra-Low Iron Abundances in Distant Hot Gas in Galaxy Groups,"A new XMM observation of the outer regions of the galaxy group NGC 5044
indicates hot gas iron abundances of only ~0.15 solar between r=0.2 - 0.4
r_vir. While the total baryon mass within the virial radius may be close to the
cosmic mean value observed in rich clusters, the ratio of total iron mass to
optical light in NGC 5044 is about 3 times lower than that in rich clusters.
The remarkably low iron abundance over a large volume of the intergroup gas in
the outer regions of NGC 5044 cannot be easily understood in terms of the
outflow of enriched gas in a group wind during its early history or by the long
term enrichment by the group member galaxies that currently occupy this region.
It is possible that the stars in NGC 5044 did not produce iron with the same
efficiency as in clusters, or the iron resides in non-luminous clouds or stars,
or the entropy of the iron-enriched gas created in early galactic starburst
winds was too high to penetrate the group gas of lower entropy.",0404430v1
2004-12-28,Model atmospheres and X-ray spectra of iron-rich bursting neutron stars. II. Iron rich Comptonized Spectra,"This paper presents the set of plane-parallel model atmosphere equations for
a very hot neutron star (X-ray burst source). The model equations assume both
hydrostatic and radiative equilibrium, and the equation of state of an ideal
gas in local thermodynamic equilibrium (LTE). The equation of radiative
transfer includes terms describing Compton scattering of photons on free
electrons in fully relativistic thermal motion, for photon energies approaching
m_e *c^2. Model equations take into account many bound-free and free-free
energy-dependent opacities of hydrogen, helium, and the iron ions, and also a
dozen bound-bound opacities for the highest ions of iron. We solve model
equations by partial linearisation and the technique of variable Eddington
factors. Large grid of H-He-Fe model atmospheres of X-ray burst sources has
been computed for 10^7 < T_eff < 3*10^7 K, a wide range of surface gravity, and
various iron abundances. We demonstrate that the spectra of X-ray bursters with
iron present in the accreting matter differ significantly from pure H-He
spectra (published in an earlier paper), and also from blackbody spectra.
Comptonized spectra with significant iron abundance are generally closer to
blackbody spectra than spectra of H-He atmospheres. The ratio of color to
effective temperatures in our grid always remains in the range 1.2 < T_c/T_eff
< 1.85. The present grid of model atmospheres and theoretical X-ray spectra
will be used to determine the effective temperatures, radii and M/R ratios of
bursting neutron stars from observational data.",0412644v1
2005-08-24,Iron Fluorescent Line Emission from Black Hole Accretion Disks with Magnetic Reconnection-Heated Corona,"We investigate the iron K$\alpha$ fluorescent line produced by hard X-ray
photons from magnetic reconnection-heated corona. The hot corona with
temperature being about $10^9$K can irradiate the underlying disk with a
continuum X-ray spectrum produced via thermal Comptonization. Then the iron
atoms in the disk photoelectrically absorb X-ray photons and radiate K$\alpha$
line photons. Therefore, the activity of corona is responsible to the iron line
emission from the underlying disk. In previous studies, oversimplified X-ray
photon sources are often assumed above the disk in order to compute the iron
line profile or power-law line emissivity profiles are assumed with an index
being a free parameter. We adopt the more realistic corona model constructed by
Liu et al. in which the corona is heated by magnetic energy released through
the reconnection of magnetic flux loops and which has no free parameter. Then
the accretion energy is dominantly dissipated in the corona, in which X-ray
photons are efficiently produced and irradiate the underlying disk. We find the
local emmisivity of iron line on the disk is approximated as $F_{{\rm
K}\alpha}(r)\propto r^{-5}$. The iron line profiles derived from this model
give excellent fits to the observational data of MCG-6-30-15 with the profiles
derived theoretically for $i\sim 30^{\circ}$ for energy band 4-7keV. Possible
origins of line variability are briefly discussed.",0508507v1
2008-04-15,UV and FUV spectroscopy of the hybrid PG 1159-type central star NGC 7094,"Previous studies aiming at the iron-abundance determination in three PG 1159
stars (K 1-16, PG 1159-035, NGC 7094) and a [WC]-PG 1159 transition star (Abell
78) have revealed that no object shows any iron line in the UV spectrum. The
stars are iron-deficient by at least 1 dex, typically. A possible explanation
is that iron nuclei were transformed by neutron captures into heavier elements
(s-process), however, the extent of the iron-destruction would be much stronger
than predicted by AGB star models. But if n-captures are the right explanation,
then we should observe an enrichment of trans-iron elements. In this paper we
report on our search for a possible nickel overabundance in one of the four Fe
deficient PG 1159 stars, namely the central star NGC 7094. We are unable to
identify any nickel line in HST and FUSE spectra and conclude that Ni is not
overabundant. It is conceivable that iron was transformed into even heavier
elements, but their identification suffers from the lack of atomic data.",0804.2372v1
2013-06-07,Orbital-dependent effects of electron correlations in microscopic models for iron-based superconductors,"The bad metal behavior in the normal state of the iron-based superconductors
suggests an intimate connection between the superconductivity and a proximity
to a Mott transition. At the same time, there is strong evidence for the
multi-orbital nature of the electronic excitations. It is then important to
understand the orbital-dependent effects of electron correlations. In this
paper we review the recent theoretical progresses on the metal-to-insulator
transition in multiorbital models for the iron-based superconductors. These
include studies of models that contain at least the 3d xy and 3d xz/yz models,
using a slave-spin technique. For commensurate filling corresponding to that of
the parent iron pnictides and chalcogenideds, a Mott transition generally
exists in all these models. Near the Mott transition, a strongly correlated
metal exhibiting bad metal features and strong orbital selectivity is
stabilized due to the interplay of Hund's coupling and orbital-degeneracy
breaking. Particularly for the alkaline iron selenides, the ordered vacancies
effectively reduce the kinetic energy, thereby pushing the system further into
the Mott-insulating regime; in the metallic state, there exists an
orbital-selective Mott phase in which the iron 3d xy orbital is Mott localized
while the other 3d orbitals are still itinerant. An overall phase diagram for
the alkaline iron selenides has been proposed, in which the orbital-selective
Mott phase connects between the superconducting phase and the Mott-insulating
parent state.",1306.1697v1
2013-06-18,Magnetic anisotropy and lattice dynamics in FeAs studied by Mössbauer spectroscopy,"Iron mono-arsenide in the powder form has been investigated by transmission
57Fe Moessbauer spectroscopy in the temperature range 4.2 - 1000 K. Additional
spectra have been obtained at 20 K and 100 K applying external magnetic field
of 7 T. It was found that the spin spiral propagating along the c-axis leads to
the complex variation of the hyperfine magnetic field amplitude with the spin
orientation varying in the a-b plane. The magnitude of the hyperfine field
pointing in the direction of the local magnetic moment depends on the
orientation of this moment in the a-b plane. Patterns are vastly different for
iron located in the [0 k 0] positions and for iron in the [0 k+1/2 0] positions
within the orthorhombic cell set to the Pnma symmetry. Lattice softens upon
transition to the paramagnetic state at 69.2 K primarily in the a-c plane as
seen by iron atoms. This effect is quite large considering lack of the
structural transition. Two previously mentioned iron sites are discernible in
the paramagnetic region till 300 K by different electron densities on the iron
nuclei. The anisotropy of the iron vibrations developed at the transition to
the paramagnetic state increases with the temperature in accordance with the
harmonic approximation, albeit tends to saturation at high temperatures
indicating gradual onset of the quasi-harmonic conditions. It seems that
neither hyperfine fields nor magnetic moments are correct order parameters in
light of the determined static critical exponents. Sample starts to loose
arsenic at about 1000 K and under vacuum.",1306.4170v3
2014-06-22,Using iron line reverberation and spectroscopy to distinguish Kerr and non-Kerr black holes,"The iron K$\alpha$ line commonly observed in the X-ray spectrum of both
stellar-mass and supermassive black hole candidates is produced by the
illumination of a cold accretion disk by a hot corona. In this framework, the
activation of a new flaring region in the hot corona imprints a time variation
on the iron line spectrum. Future X-ray facilities with high time resolution
and large effective areas may be able to measure the so-called 2-dimensional
transfer function; that is, the iron line profile detected by a distant
observer as a function of time in response to an instantaneous flare from the
X-ray primary source. This work is a preliminary study to determine if and how
such a technique can provide more information about the spacetime geometry
around the compact object than the already possible measurements of the
time-integrated iron line profile. Within our simplified model, we find that a
measurement of iron line reverberation can improve constraints appreciably
given a sufficiently strong signal, though that most of the information is
present in the time-integrated spectrum. Our aim is to test the Kerr metric. We
find that current X-ray facilities and data are unable to provide strong tests
of the Kerr nature of supermassive black hole candidates. We consider an
optimistic case of $10^5$ iron line photons from a next-generation data set.
With such data, the reverberation model improves upon the spectral constraint
by an order of magnitude.",1406.5677v3
2014-10-01,Millihertz quasi-periodic oscillations and broad iron line from LMC X-1,"We study the temporal and energy spectral characteristics of the persistent
black hole X-ray binary LMC X-1 using two XMM-Newton and a Suzaku observation.
We report the discovery of low frequency (~ 26-29 mHz) quasi-periodic
oscillations (QPOs). We also report the variablity of the broad iron K-alpha
line studied earlier with Suzaku. The QPOs are found to be weak with fractional
rms amplitude in the ~ 1-2 % range and quality factor Q~2-10 . They are
accompanied by weak red noise or zero-centered Lorentzian components with rms
variability at the ~ 1-3 % level. The energy spectra consists of three varying
components - multicolour disk blackbody (kT_{in} ~ 0.7-0.9 keV), high energy
power-law tail (Gamma ~ 2.4 - 3.3) and a broad iron line at 6.4-6.9 keV. The
broad iron line, the QPO and the strong power-law component are not always
present. The QPOs and the broad iron line appear to be clearly detected in the
presence of a strong power-law component. The broad iron line is found to be
weaker when the disk is likely truncated and absent when the power-law
component almost vanished. These results suggest that the QPO and the broad
iron line together can be used to probe the dynamics of the accretion disk and
the corona.",1410.0135v2
2014-11-08,Melting of iron close to Earth's inner core boundary conditions and beyond,"Several important geophysical features such as heat flux at the Core-Mantle
Boundary or geodynamo production are intimately related with the temperature
profile in the Earth's core. However, measuring the melting curve of iron at
conditions corresponding to the Earth inner core boundary under pressure of 330
GPa has eluded scientists for several decades. Significant discrepancies in
previously reported iron melting temperatures at high pressure have called into
question the validity of dynamic measurements. We report measurements made with
a novel approach using X-ray absorption spectroscopy using an X-ray free
electron laser source coupled to a laser shock experiment. We determine the
state of iron along the shock Hugoniot up to 420 GPa (+/- 50) and 10800 K (+/-
1390) and find an upper boundary for the melting curve of iron by detecting
solid iron at 130 GPa and molten at 260, 380 and 420 GPa along the shock
Hugoniot. Our result establishes unambiguous agreement between dynamic
measurement and recent extrapolations from static data thus resolving the
long-standing controversy over the reliability of using dynamic compression to
study the melting of iron at conditions close to the Earth's inner core
boundary and beyond.",1411.2074v1
2015-07-06,Unconventional superconductivity in the layered iron germanide YFe$_2$Ge$_2$,"Since the discovery of superconductivity in LaFePO in 2006, numerous
iron-based superconductors have been identified within diverse structure
families, all of which combine iron with a group-V (pnictogen) or group-VI
(chalco- gen) element. Unconventional superconductivity is extremely rare among
transition metal compounds outside these layered iron systems and the cuprates,
and it is almost universally associated with highly anisotropic electronic
properties and nearly 2D Fermi surface geometries. The iron-based intermetallic
YFe$_2$Ge$_2$ features a 3D Fermi surface and a strongly enhanced low
temperature heat capacity, which signals strong electronic correlations. We
present data from a new generation of high quality samples of YFe$_2$Ge$_2$,
which show superconducting transition anomalies below 1.8 K in thermodynamic as
well as transport measurements, establishing that superconductivity is
intrinsic in this layered iron compound outside the known superconducting iron
pnictide or chalcogenide families. The Fermi surface geometry of YFe$_2$Ge$_2$
resembles that of KFe$_2$As$_2$ in the high pressure collapsed tetragonal
phase, in which superconductivity at temperatures as high as 10 K has recently
been reported, suggesting an underlying connection between the two systems.",1507.01436v2
2015-09-15,Search for New Superconductors: An Electro-Magnetic Phase Transition in an Iron Meteorite Inclusion at 117 K,"The discovery of superconductivity in pnictides and iron chalcogenides
inspires the search for new iron based superconducting phases. Iron-rich
meteorites present a unique opportunity for this search, because they contain a
broad range of compounds produced under extreme growth conditions. We
investigated a natural iron sulfide based materials (Troilite) inclusion with
its associated minerals in the iron meteorite Tlacotepec. Tlacotepec formed in
an asteroidal core under high pressure and at high temperature over millions of
years, while insoluble sulfur rich materials segregated into inclusions during
cooling along with included minerals. The search for superconductivity in these
heterogeneous materials requires a technique capable of detecting minute
amounts of a superconducting phase embedded in a non-superconducting matrix. We
used Magnetic Field Modulated Microwave Spectroscopy (MFMMS), a very sensitive,
selective, and non-destructive technique, to search for superconductivity in
heterogeneous systems. Here, we report the observation of an electro-magnetic
phase transition at 117 K that causes a MFMMS-response typical of a
superconductor. A pronounced and reproducible peak together with isothermal
magnetic field sweeps prove the appearance of a new electromagnetic phase below
117 K. This is very similar to the characteristic response due to flux trapping
in a granular superconductor with a short coherence length. Although the
compound responsible for the peak in the MFMMS-spectra was not identified, it
is possibly an iron sulfide based phase, or another material heterogeneously
distributed over the inclusion.",1509.04452v2
2017-04-04,Iron Partitioning between Ferropericlase and Bridgmanite in the Earth's Lower Mantle,"Earth's lower mantle is generally believed to be seismically and chemically
homogeneous because most of the key seismic parameters can be explained using a
simplified mineralogical model at expected press-temperature conditions.
However, recent high-resolution tomographic images have revealed seismic and
chemical stratification in the middle-to-lower parts of the lower mantle. Thus
far, the mechanism for the compositional stratification and seismic
inhomogeneity, especially their relationship with the speciation of iron in the
lower mantle, remains poorly understood. We have built a complete and
integrated thermodynamic model of iron and aluminum chemistry for lower mantle
conditions, and from this model has emerged a stratified picture of the
valence, spin and composition profile in the lower mantle. Within this picture
the lower mantle has an upper region with Fe3+ enriched bridgmanite with
high-spin ferropericlase and metallic Fe, and a lower region with low-spin,
iron-enriched ferropericlase coexisting with iron-depleted bridgmanite and
almost no metallic Fe. The transition between the regions occurs at a depth of
around 1600km and is driven by the spin transition in ferropericlase, which
significantly changes the iron partitioning and speciation to one that favors
Fe2+ in ferropericlase and suppresses Fe3+ and metallic iron formation These
changes lead to lowered bulk sound velocity by 3-4% around the mid-lower mantle
and enhanced density by ~1% toward the lowermost mantle. The predicted
chemically and seismically stratified lower mantle differs dramatically from
the traditional homogeneous model.",1704.01140v1
2018-03-05,Iron and silicate dust growth in the Galactic interstellar medium: clues from element depletions,"The interstellar abundances of refractory elements indicate a substantial
depletion from the gas phase, that increases with gas density. Our recent model
of dust evolution, based on hydrodynamic simulations of the lifecycle of giant
molecular clouds (GMCs) proves that the observed trend for [Si$_{gas}$/H] is
driven by a combination of dust growth by accretion in the cold diffuse
interstellar medium (ISM) and efficient destruction by supernova (SN) shocks
(Zhukovska et al. 2016). With an analytic model of dust evolution, we
demonstrate that even with optimistic assumptions for the dust input from stars
and without destruction of grains by SNe it is impossible to match the observed
[Si$_{gas}$/H]$-n_H$ relation without growth in the ISM. We extend the
framework developed in our previous work for silicates to include the evolution
of iron grains and address a long-standing conundrum: ``Where is the
interstellar iron?'. Much higher depletion of Fe in the warm neutral medium
compared to Si is reproduced by the models, in which a large fraction of
interstellar iron (70%) is locked as inclusions in silicate grains, where it is
protected from sputtering by SN shocks. The slope of the observed
[Fe$_{gas}$/H]$-n_H$ relation is reproduced if the remaining depleted iron
resides in a population of metallic iron nanoparticles with sizes in the range
of 1-10nm. Enhanced collision rates due to the Coulomb focusing are important
for both silicate and iron dust models to match the observed slopes of the
relations between depletion and density and the magnitudes of depletion at high
density.",1803.01929v2
2018-08-31,Insight of the thermal conductivity of $ε-$iron at Earth's core conditions from the newly developed direct $ab~initio$ methodology,"The electronic thermal conductivity of iron at Earth's core conditions is an
extremely important physical property in geophysics field. However, the exact
value of electronic thermal conductivity of iron under extreme pressure and
temperature still remains poorly known both experimentally and theoretically. A
few recent experimental studies measured the value of the electronic thermal
conductivity directly and some theoretical works have predicted the electronic
thermal conductivity of iron at Earth's core conditions based on the
Kubo-Greenwood method. However, these results differ largely from each other. A
very recent research has confirmed that for iron at Earth's core conditions the
strength of electron-electron scattering could be comparable to that for
electron-phonon scattering, meaning that the electron-electron scattering
should also be considered when evaluating the electronic thermal conductivity
in the Earth's core situations. Here, by utilizing a newly developed
methodology based on direct non-equilibrium $ab~initio$ molecular dynamics
simulation coupled with the concept of electrostatic potential oscillation, we
predict the electronic thermal conductivity of iron in h.c.p phase. Our
methodology inherently includes the electron-phonon and electron-electron
interactions under extreme conditions. Our results are comparable to the
previous theoretical and experimental studies. More importantly, our
methodology provides a new physical picture to describe the heat transfer
process in $\epsilon-$iron at Earth's core conditions from the electrostatic
potential oscillation point of view and offers a new approach to study thermal
transport property of pure metals in planet's cores with different temperature
and pressures.",1808.10860v1
2019-06-05,"Small Planets in the Galactic Context: Host Star Kinematics, Iron, and $α$ Element Enhancement","We explored the occurrence rate of small close-in planets among
$\textit{Kepler}$ target stars as a function of the iron abundance and the
stellar total velocity $V_\mathrm{tot}$. We estimated the occurrence rate of
those planets by combining information from LAMOST and the
California-$\textit{Kepler}$ Survey (CKS) and found that iron-poor stars
exhibit an increase in the occurrence with $V_\mathrm{tot}$ from $f < 0.2$
planets per star at $ V_\mathrm{tot} < 30\ \mathrm{km~s}^{-1}$ to $f \sim 1.2$
at $V_\mathrm{tot} > 90\ \mathrm{km~s}^{-1}$. We suggest this planetary
profusion may be a result of a higher abundance of $\alpha$ elements associated
with iron-poor, high-velocity stars. Furthermore, we have identified an
increase in small planet occurrence with iron abundance, particularly for the
slower stars ($V_\mathrm{tot} < 30\ \mathrm{km~s}^{-1}$), where the occurrence
increased to $f \sim 1.1$ planets per star in the iron-rich domain. Our results
suggest there are two regions in the
$([\mathrm{Fe}/\mathrm{H}],[\alpha/\mathrm{Fe}])$ plane in which stars tend to
form and maintain small planets. We argue that analysis of the effect of
overall metal content on planet occurrence is incomplete without including
information on both iron and $\alpha$ element enhancement.",1906.01982v2
2020-06-02,Study of iron complexes in visceral organs and brain from a ${}^57$Fe enriched $β$-thalassaemia mouse model via Mössbauer Spectroscopy,"The hearts, kidneys, livers, spleens and brains of ${}^57$Fe enriched
wild-type and heterozygous $\beta$-thalassaemic mice at 1, 3, 6 and 9 months of
age were studied by means of M\""ossbauer Spectroscopy at 80K. Ferritin-like
iron depositions in the heart and the brain of the thalassaemic mice were found
to be slightly increased while significant amounts of Ferritin-like iron were
found in the kidneys, liver and spleen. The ferritin-like iron doublet, found
in the organs, could be further separated into two sub-doublets representing
the inner and surface structures of ferritin mineral core. Surface iron sites
were found to be predominant in the hearts and brains of all mice and in the
kidneys of the wild-type animals. Ferritin rich in inner iron sites was
predominant in the kidneys of the thalassaemic mice, as well as in the livers
and in the spleens. The inner-to-surface iron sites ratio was elevated in all
thalassaemic samples indicating that besides ferritin amount, the disease can
also affect ferritin mineral core structure.",2006.01511v1
2021-03-05,Ferromagnetic Composite Self-Arrangement in Iron-Implanted Epitaxial Palladium Thin Films,"We report on the formation of the dilute $Pd_{1-x}Fe_x$ compositions with
tunable magnetic properties under an ion-beam implantation of epitaxial Pd thin
films. Binary $Pd_{1-x}Fe_x$ alloys with a mean iron content $x$ of $0.025$,
$0.035$ or $0.075$ were obtained by the implantation of $40 keV$ $Fe^+$ ions
into the palladium films on MgO (001) substrate to the doses of
$0.5\cdot10^{16}, 1.0\cdot10^{16}$ and $3.0\cdot10^{16}$ $ions/cm^2$,
respectively. Structural and magnetic studies have shown that iron atoms occupy
regular fcc-lattice Pd-sites without the formation of any secondary
crystallographic phase. All the iron implanted Pd films reveal ferromagnetism
at low temperatures (below $200 K$) with both the Curie temperature and
saturation magnetization determined by the implanted iron dose. In contrast to
the magnetic properties of the molecular beam epitaxy grown $Pd_{1-x}Fe_x$
alloy films with the similar iron contents, the Fe-implanted Pd films possess
weaker in-plane magnetocrystalline anisotropy, and, accordingly, a lower
coercivity. The observed multiple ferromagnetic resonances in the implanted
$Pd_{1-x}Fe_x$ films indicate a formation of a magnetically inhomogeneous state
due to spinodal decomposition into regions, presumably layers, with identical
crystal symmetry but different iron contents. The multiphase magnetic structure
is robust with respect to the vacuum annealing at $770 K$, though develops
towards well-defined local $Pd-Fe$ compositions.",2103.03562v1
2021-09-30,Nucleosynthetic Pt isotope anomalies and the Hf-W chronology of core formation in inner and outer solar system planetesimals,"The 182Hf-182W chronology of iron meteorites provides crucial information on
the timescales of accretion and differentiation of some of the oldest
planetesimals of the Solar System. Determining accurate Hf-W model ages of iron
meteorites requires correction for cosmic ray expo-sure (CRE) induced
modifications of W isotope compositions, which can be achieved using in-situ
neutron dosimeters such as Pt isotopes. Until now it has been assumed that all
Pt isotope variations in meteorites reflect CRE, but here we show that some
ungrouped iron meteorites display small nucleosynthetic Pt isotope anomalies.
These provide the most appropriate starting composition for the correction of
CRE-induced W isotope variations in iron meteorites from all major chemical
groups, which leads to a ~1 Ma upward revision of previously reported Hf-W
model ages. The revised ages indicate that core formation in non-carbonaceous
(NC) iron meteorite parent bodies occurred at ~1-2 Ma after CAI formation,
whereas most carbonaceous (CC) iron meteorite parent bodies underwent core
formation ~2 Ma later. We show that the younger CC cores have lower Fe/Ni
ratios than the earlier-formed NC cores, indicating that core formation under
more oxidizing conditions occurred over a more protracted timescale. Thermal
modeling of planetesimals heated by 26Al-decay reveals that this protracted
core formation timescale is consistent with a higher fraction of water ice in
CC compared to NC planetesimals, implying that in spite of distinct core
formation timescales, NC and CC iron meteorite parent bodies accreted about
contemporaneously within ~1 Ma after CAI formation, but at different radial
locations in the disk.",2109.15250v1
2021-10-01,Q-Net: A Quantitative Susceptibility Mapping-based Deep Neural Network for Differential Diagnosis of Brain Iron Deposition in Hemochromatosis,"Brain iron deposition, in particular deep gray matter nuclei, increases with
advancing age. Hereditary Hemochromatosis (HH) is the most common inherited
disorder of systemic iron excess in Europeans and recent studies claimed high
brain iron accumulation in patient with Hemochromatosis. In this study, we
focus on Artificial Intelligence (AI)-based differential diagnosis of brain
iron deposition in HH via Quantitative Susceptibility Mapping (QSM), which is
an established Magnetic Resonance Imaging (MRI) technique to study the
distribution of iron in the brain. Our main objective is investigating
potentials of AI-driven frameworks to accurately and efficiently differentiate
individuals with Hemochromatosis from those of the healthy control group. More
specifically, we developed the Q-Net framework, which is a data-driven model
that processes information on iron deposition in the brain obtained from
multi-echo gradient echo imaging data and anatomical information on T1-Weighted
images of the brain. We illustrate that the Q-Net framework can assist in
differentiating between someone with HH and Healthy control (HC) of the same
age, something that is not possible by just visualizing images. The study is
performed based on a unique dataset that was collected from 52 subjects with HH
and 47 HC. The Q-Net provides a differential diagnosis accuracy of 83.16% and
80.37% in the scan-level and image-level classification, respectively.",2110.00203v1
2021-10-12,Earth's accretion inferred from iron isotopic anomalies of supernova nuclear statistical equilibrium origin,"Nucleosynthetic Fe isotopic anomalies in meteorites may be used to
reconstruct the early dynamical evolution of the solar system and to identify
the origin and nature of the material that built planets. Using high-precision
iron isotopic data of 23 iron meteorites from nine major chemical groups we
show that all iron meteorites show the same fundamental dichotomy between
non-carbonaceous (NC) and a carbonaceous (CC) meteorites previously observed
for other elements. The Fe isotopic anomalies are predominantly produced by
variation in 54Fe, where all CC iron meteorites are characterized by an excess
in 54Fe relative to NC iron meteorites. This excess in 54Fe is accompanied by
an excess in 58Ni observed in the same CC meteorite groups. Together, these
overabundances of 54Fe and 58Ni are produced by nuclear statistical equilibrium
either in type Ia supernovae or in the Si/S shell of core-collapse supernovae.
The new Fe isotopic data reveal that Earth's mantle plots on or close to
correlations defined by Fe, Mo, and Ru isotopic anomalies in iron meteorites,
indicating that throughout Earth's accretion, the isotopic composition of its
building blocks did not drastically change. While Earth's mantle has a similar
Fe isotopic composition to CI chondrites, the latter are clearly distinct from
Earth's mantle for other elements (e.g., Cr and Ni) whose delivery to Earth
coincided with Fe. The fact that CI chondrites exhibit large Cr and Ni isotopic
anomalies relative to Earth's mantle, therefore, demonstrates that CI
chondrites are unlikely to have contributed significant Fe to Earth.",2110.06045v1
2022-01-23,Large Impacts onto the Early Earth: Planetary Sterilization and Iron Delivery,"Late accretion onto the Hadean Earth included large impacts that could have
influenced early habitability, either by sterilizing the planet or
alternatively catalyzing the origin of life by delivering iron required to
create a reducing environment/atmosphere. We present 3D numerical simulations
of 1500-3400 km diameter impacts on the early Earth in order to quantify their
effects on planetary habitability. We find sterilizing impact events require
larger projectiles than previously assumed, with a 2000-2700 km diameter
impactor required to completely melt Earth's surface and an extrapolated >700
km diameter impactor required for ocean-vaporization. We also find that
reducing environments are less likely to arise following large impacts than
previously suggested, because >70% of the projectile iron is deposited in the
crust and upper mantle where it is not immediately available to reduce surface
water and contribute to forming a reducing atmosphere. Although the largest
expected late accretion impacts (~1 lunar mass) delivered sufficient iron to
the atmosphere to have reduced an entire ocean mass of water, such impacts
would also have melted the entire surface, potentially sequestering condensing
iron that is not oxidized quickly. The hypothesis that life emerged in the
aftermath of large impacts requires an efficient mechanism of harnessing the
reducing power of iron sequestered in the crust/mantle, or an origin of life
pathway that operates in more weakly-reducing post-impact environments that
require smaller quantities of impact-delivered iron.",2201.09349v1
2022-04-10,Effect of iron vacancies on the magnetic order and spin dynamics of the spin ladder BaFe$_{2-δ}$S$_{1.5}$Se$_{1.5}$,"Quasi-one-dimensional iron chalcogenides possess various magnetic states
depending on the lattice distortion, electronic correlations, and presence of
defects. We present neutron diffraction and inelastic neutron scattering
experiments on the spin ladder compound BaFe$_{2-\delta}$S$_{1.5}$Se$_{1.5}$
with $\sim$6% iron vacancies. The data reveal that long-range magnetic order is
absent, while the characteristic magnetic excitations that correspond to both
the stripe- and block-type antiferromagnetic correlations are observed.
First-principles calculations support the existence of both stripe and
block-type antiferromagnetic short-range order in the experimental sample. The
disappearance of long-range magnetic order may be due to the competition
between these two magnetic orders, which is greatly enhanced for a certain
concentration of iron vacancies, which we calculate to be about 6%, consistent
with the measured iron vacancy concentration. Our results highlight how iron
vacancies in the iron-based spin ladder system strongly influence the magnetic
ground state.",2204.04697v1
2022-04-20,Experimental Simulations of Shock Textures in BCC Iron: Implications for Iron Meteorites,"Neumann band in iron meteorites, which is deformation twins in kamacite
(Fe-Ni alloy), has been known to be a characteristic texture indicating ancient
collisions on parent bodies of meteorites. We conducted a series of shock
recovery experiments on bcc iron with the projectile velocity at 1.5 km/sec at
various initial temperatures, room temperature, 670 K, and 1100 K, and
conducted an annealing experiment on the shocked iron. We also conducted
numerical simulations with the iSALE-2D code to investigate peak pressure and
temperature distributions in the nontransparent targets. The effects of
pressure and temperature on the formation and disappearance of the twins
(Neumann band) were explored based on laboratory and numerical experiments. The
twin was formed in the run products of the experiments conducted at room
temperature and 670 K, whereas it was not observed in the run product formed by
the impact at 1100 K. The present experiments combined with the numerical
simulations revealed that the twin was formed by impacts with various shock
pressures from 1.5-2 GPa to around 13 GPa. The twin in iron almost disappeared
by annealing at 1070 K. The iron meteorites with Neumann bands were shocked at
this pressure range and temperatures at least up to 670 K, and were not heated
to the temperatures above 1070 K after the Neumann band formation.",2204.09195v1
2022-09-11,Correlation-corrected band topology and topological surface states in iron-based superconductors,"Iron-based superconductors offer an ideal platform for studying topological
superconductivity and Majorana fermions. In this paper, we carry out a
comprehensive study of the band topology and topological surface states of a
number of iron-based superconductors using a combination of density functional
theory (DFT) and dynamical mean field theory. We find that the strong
electronic correlation of Fe 3d electrons plays a crucial role in determining
the band topology and topological surface states of iron-based superconductors.
Electronic correlation not only strongly renormalizes the bandwidth of Fe 3d
electrons, but also shifts the band positions of both Fe 3d and As/Se p
electrons. As a result, electronic correlation moves the DFT-calculated
topological surface states of many iron-based superconductors much closer to
the Fermi level, which is crucial for realizing topological superconducting
surface states and observing Majorana zero modes as well as achieving practical
applications, such as quantum computation. More importantly, electronic
correlation can change the band topology and make some iron-based
superconductors topologically nontrivial with topological surface states
whereas they have trivial band topology and no topological surface states in
DFT calculations. Our paper demonstrates that it is important to take into
account electronic correlation effects in order to accurately determine the
band topology and topological surface states of iron-based superconductors and
other strongly correlated materials.",2209.04776v1
2023-04-26,Assessment of sol-gel derived iron oxide substituted 45S5 bioglass-ceramics for biomedical applications,"Magnetic bioactive glass ceramic (MGC) powders have been synthesized by sol
gel route by systematically substituting silicon dioxide with iron oxide in the
45S5 glass composition. Powder x-ray diffraction studies revealed a variation
in the percentage of combeite (Ca$_2$Na$_2$Si$_3$O$_9$), magnetite
(Fe$_3$O$_4$), and hematite (Fe$_2$O$_3$) nanocrystalline phases in MGC powders
as a function of composition. Zeta potential measurements showed that MGC
containing up to 10 wt.% iron oxide formed stable suspensions. Saturation
magnetization and heat generation capacity of MGC fluids increased with
increase in iron oxide content. Degradation of MGC powders was investigated in
phosphate buffer saline (PBS). In vitro bioactivity of the MGC powders taken in
pellet form was confirmed by observing the pH variation as well as
hydroxyapatite layer (HAp) formation upon soaking in modified simulated body
fluid. These studies showed a decrement in overall bioactivity in samples with
high iron oxide content due to the proportional decrease in silanol group.
Monitoring the proliferation of MG-63 osteoblast cell in Dulbecco's Modified
Eagle Medium (DMEM) revealed that MGC with up to 10 wt.% iron oxide exhibited
acceptable viability. The systematic study revealed that the MGC with 10 wt.%
iron oxide exhibited optimal cell viability, magnetic properties and induction
heating capacity which were better than those of FluidMag-CT, which is used for
hyperthermia treatment.",2304.13437v1
2023-11-02,Studying the variability of fluorescence emission and the presence of clumpy wind in HMXB GX 301$-$2 using XMM-Newton,"We present the results from an analysis of data from an \textit{XMM-Newton}
observation of the accreting high mass X-ray binary pulsar GX 301$-$2. Spectral
analysis in the non-flaring segment of the observation revealed that the
equivalent width of the iron fluorescence emission is correlated with the
observed absorption column density and the ratio of the iron K$\beta$ and
K$\alpha$ line strength varied with the flux of the source. Coherent pulsations
were detected with the spin period of the pulsar of 687.9$\pm$0.1 s, and a
secondary pulsation was also detected with a period of 671.8$\pm$0.2 s, most
prominent in the energy band of the iron line. At the spin period of the
neutron star, the pulsation of the iron line has a low amplitude and the
profile is different from the continuum. Pulse phase-resolved spectroscopy also
revealed pulsations of the iron emission line during the non-flaring segment of
the light curve. At the secondary period, both the iron line and the continuum
have nearly identical pulse fraction and pulse profile. The additional
periodicity can be attributed to the beat frequency between the spin of the
neutron star and the Keplerian frequency of a stellar wind clump in retrograde
motion around the neutron star. Reprocessed X-ray emissions originating from
the clump can produce the observed secondary pulsations both in the continuum
and the iron fluorescence line. The clump rotating around the neutron star is
estimated to be approximately five lt-s away from the neutron star.",2311.01176v1
2019-01-15,"Dust-depletion sequences in damped Ly-α absorbers II. The composition of cosmic dust, from low-metallicity systems to the Galaxy","We aim at assessing what are the most dominant dust species or types,
including silicate and iron oxide grains present in the ISM, by using recent
observations of dust depletion of galaxies at various evolutionary stages. We
use the observed elemental abundances in dust of several metals (O, S, Si, Mg,
and Fe) in different environments, considering systems with different
metallicities and dust content, namely damped Lyman-{\alpha} absorbers (DLAs)
towards quasars and the Galaxy. We derive a possible dust composition by
computationally finding the statistically expected elemental abundances in dust
assuming a set of key dust species with the iron content as a free parameter.
Carbonaceous dust is not considered in the present study. Metallic iron (likely
in the form of inclusions in silicate grains) and iron oxides is an important
component of the mass composition of carbon-free dust. Iron oxides make up a
significant mass fraction (~1/4 in some cases) of the oxygen-bearing dust and
there are good reasons to believe that metallic iron constitutes a similar mass
fraction of dust. W\""ustite (FeO) could be a simple explanation for the
depletion of iron and oxygen because it is easily formed. There appears to be
no silicate species clearly dominating the silicate mass, but rather a mix of
iron-poor as well as iron-rich olivine and pyroxene. To what extent sulphur
depletion is due to sulfides remains unclear. In general, there seems to be
little evolution of the dust composition (not considering carbonaceous dust)
from low-metallicity systems to the Galaxy.",1901.04710v3
2023-04-28,A comparison of mechanistic models for the combustion of iron microparticles and their application to polydisperse iron-air suspensions,"Metals can serve as carbon-free energy carriers, e. g. in innovative
metal-metal oxide cycles as proposed by Bergthorson (Prog. Energy Combust.
Sci., 2018). Iron powder is a suitable candidate since it can be oxidized with
air. Nevertheless, the combustion of iron powder in air is challenging
especially with respect to flame stabilization which depends on the particle
size distribution among other factors. Models for the prediction of reaction
front speed in iron-air suspensions can contribute to overcoming this
challenge. To this end, three different models for iron particle oxidation are
integrated into a laminar flame solver for simulating reaction fronts. The
scientific objective of this work is to elucidate the influence of
polydispersity on the reaction front speed, which is still not satisfactorily
understood. In a systematic approach, cases with successively increasing
complexity are considered: From single particle combustion to iron-air
suspensions prescribing binary particle size distributions (PSDs), generic
PSDs, and a PSD measured for a real iron powder sample. The simulations show
that, dependent on the PSD, particles undergo thermochemical conversion in a
sequential manner according to their size and every particle fraction exhibits
an individual combustion environment. The local environment can be leaner or
richer than the overall iron-to-air ratio would suggest and can be very
different from single particle experiments. The contribution of individual
particle fractions to the overall reaction front speed depends on its ranking
within the PSD. The study further demonstrates, that although the three
particle models show good agreement for single particle combustion, they lead
to very different reaction front speeds. This is due to the different ignition
behavior predicted by the particle models, which is shown to strongly influence
the reaction front characteristics.",2304.14927v2
1994-10-05,Influence of Cooling Flow and Galactic Motion on the Iron Distribution in Clusters of Galaxies,"Iron abundance distribution is now known for 12 clusters of galaxies. For
some clusters (e.g. Centaurus) the observed abundance increases toward the
cluster center, while for the others (e.g. Coma and Hydra-A) no significant
inhomogeneity was observed. In order to understand this difference, we
investigate the influence of cooling flow and turbulence produced by galactic
motion on the iron abundance distribution by simple spherical models. We show
that the cooling flow has a significant effect to flatten the iron abundance
distribution if the flow velocity is sufficiently large. Further, by applying
our analysis to the above clusters we show that we can give a systematic
account for the observed variety of the iron abundance distribution
qualitatively.",9410014v1
1999-11-19,Evolution of iron core white dwarfs,"Recent measurements made by Hipparcos (Provencal et al. 1998) present
observational evidence supporting the existence of some white dwarf (WD) stars
with iron - rich, core composition. In this connection, the present paper is
aimed at exploring the structure and evolution of iron - core WDs by means of a
detailed and updated evolutionary code. In particular, we examine the evolution
of the central conditions, neutrino luminosity, surface gravity,
crystallization, internal luminosity profiles and ages. We find that the
evolution of iron - rich WDs is markedly different from that of their carbon -
oxygen counterparts. In particular, cooling is strongly accelerated as compared
with the standard case. Thus, if iron WDs were very numerous, some of them
would have had time enough to evolve at lower luminosities than that
corresponding to the fall - off in the observed WD luminosity function.",9911371v1
1999-11-19,"Gas, Iron and Gravitational Mass in Galaxy Clusters: The General Lack of Cluster Evolution at z < 1.0","We have analyzed the ASCA data of 29 nearby clusters of galaxies
systematically, and obtained temperatures, iron abundances, and X-ray
luminosities of their intracluster medium (ICM). We also estimate ICM mass
using the beta model, and then evaluate iron mass contained in the ICM and
derive the total gravitating mass. This gives the largest and most homogeneous
information about the ICM derived only by the ASCA data. We compare these
values with those of distant clusters whose temperatures, abundances, and
luminosities were also measured with ASCA, and find no clear evidence of
evolution for the clusters at z<1.0. Only the most distant cluster at z=1.0,
AXJ2019.3+1127, has anomalously high iron abundance, but its iron mass in the
ICM may be among normal values for the other clusters, because the ICM mass may
be smaller than the other clusters. This may suggest a hint of evolution of
clusters at z ~ 1.0.",9911388v1
1999-12-15,On the influence of resonant absorption on the iron emission line profiles from accreting black holes,"The fluorescent iron K$\alpha$ emission line profile provides an excellent
probe of the innermost regions of active galactic nuclei. Fe XXV and Fe XXVI in
diffuse plasma above the accretion disc can affect the X-ray spectrum by iron
K$\alpha$ resonant absorption. This in turn can influence the interpretation of
the data and the estimation of the accretion disc and black hole parameters. We
embark on a fully relativistic computation of this effect and calculate the
iron line profile in the framework of a specific model in which rotating,
highly ionized and resonantly-absorbing plasma occurs close to the black hole.
This can explain the features seen in the iron K$\alpha$ line profile recently
obtained by Nandra et al. (1999) for the Seyfert 1 galaxy NGC 3516. We show
that the redshift of this feature can be mainly gravitational in origin and
accounted for without the need to invoke fast accretion of matter onto the
black hole. New X-ray satellites such as XMM, ASTRO-E and Chandra provide
excellent opportunities to test the model against high quality observational
data.",9912321v1
2000-02-17,The Iron Project,"Recent advances in theoretical atomic physics have enabled large-scale
calculation of atomic parameters for a variety of atomic processes with high
degree of precision. The development and application of these methods is the
aim of the Iron Project. At present the primary focus is on collisional
processes for all ions of iron, Fe I- FeXXVI, and other iron-peak elements; new
work on radiative processes has also been initiated. Varied applications of the
Iron Project work to X-ray astronomy are discussed, and more general
applications to other spectral ranges are pointed out. The IP work forms the
basis for more specialized projects such as the RMaX Project, and the work on
photoionization/recombination, and aims to provide a comprehensive and
self-consistent set of accurate collsional and radiative cross sections, and
transition probabilities, within the framework of relativistic close coupling
formulation using the Breit-Pauli R-Matrix method. An illustrative example is
presented of how the IP data may be utilised in the formation of X-ray spectra
of the K$\alpha$ complex at 6.7 keV from He-like Fe XXV.",0002356v1
2000-09-29,X-ray iron line variability: constraints on the inner accretion disk,"After reviewing the basic physics of X-ray reflection in AGN, we present
three case studies which illustrate the current state of X-ray reflection
studies. For the low-luminosity AGN NGC4258, we find that the iron line is much
narrower than is typically found in higher luminosity AGN. We argue that this
is evidence for either a truncated cold accretion disk (possibly due to a
transition to an advection dominate accretion flow at r ~ 100GM/c^2) or a large
r ~ 100GM/c^2 X-ray emitting corona surrounding the accretion disk. We also
present results for the higher luminosity Seyfert nuclei in NGC5548 and
MCG-6-30-15. In both of these sources, RXTE shows that the iron line equivalent
width decreases with increasing luminosity. Furthermore, the iron line
equivalent width is found to be anticorrelated with the relative strength of
the reflection continuum, contrary to all simple reflection models. It is
proposed that continuum-flux correlated changes in the ionization of the
accretion disk surface can explain this spectral variability. Finally, we
address the issue of X-ray iron line reverberation in the light of these
complicating factors.",0009503v1
2001-06-27,An Empirical Ultraviolet Iron Spectrum Template Applicable to Active Galaxies,"Iron emission is often a severe contaminant in optical-ultraviolet spectra of
active galaxies. Its presence complicates emission line studies. A viable
solution, already successfully applied at optical wavelengths, is to use an
empirical iron emission template. We have generated FeII and FeIII templates
for ultraviolet active galaxy spectra based on HST archival 1100 - 3100 A
spectra of IZw1. Their application allows fitting and subtraction of the iron
emission in active galaxy spectra. This work has shown that in particular CIII]
lambda 1909 can be heavily contaminated by other line emission, including iron
transitions. Details of the data processing, generation, and use of the
templates, are given by Vestergaard & Wilkes (2001).",0106510v1
2002-02-01,Temperature Scale and Iron Abundances of Very Hot Central Stars of Planetary Nebulae,"The determination of effective temperatures of very hot central stars
(Teff>70000K) by model atmosphere analyses of optical H and He line profiles is
afflicted with considerable uncertainty, primarily due to the lack of neutral
helium lines. Ionization balances of metals, accessible only with UV lines,
allow more precise temperature estimates. The potential of iron lines is
pointed out. At the same time iron and other metal abundances, hardly
investigated until today, may be derived from UV spectra. We describe recent
HST spectroscopy performed for this purpose.
  A search for iron lines in FUV spectra of the hottest H-deficient central
stars (PG1159-type, Teff>100000K) taken with FUSE was unsuccessful. The derived
deficiency is interpreted in terms of iron depletion due to n-capture
nucleosynthesis in intershell matter, which is now exposed at the stellar
surface as a consequence of a late He shell flash.",0202012v1
2002-03-14,Cerenkov Line Emission as a Possible Mechanism of X-ray Lines in Gamma-ray Bursts,"The recent discoveries of X-ray lines in the afterglows of gamma-ray bursts
(GRBs) provide significant clues to the nature of GRB progenitors and central
environments. However, the iron line interpretation by fluorescence or
recombination mechanism requires a large amount of iron material. We argue that
the very strong iron line could be attributed to an alternative mechanism:
Cerenkov line emission since relativistic electrons and dense medium exist near
GRB sites. Therefore, the broad iron lines are expected, and line intensity
will be nearly independent of the iron abundance, the medium with the
anomalously high Fe abundance is not required.",0203222v2
2003-05-13,Iron and Nickel properties in the X-ray reflecting region of the Circinus Galaxy,"We discuss the iron and nickel properties in the nuclear X-ray reflecting
region of the Circinus Galaxy, studied with XMM-Newton. The main results are:
a) from the depth of the Fe Kalpha edge, a value of A_Fe=1.7 in number with
respect to the cosmic value (as for Anders & Grevesse 1989) is measured, if the
(not directly visible) illuminating spectrum is assumed to be that measured by
BeppoSAX. If the slope of the primary power law is left free to vary, a steeper
spectrum and a lower iron abundance (about 1.2) are found. b) From the Ni to Fe
Kalpha lines flux ratio, a nickel-to-iron abundance ratio of 0.055-0.075 is
found. c) The Fe Kbeta/Kalpha flux ratio is slightly lower than expected,
possibly due to a mild ionization of iron (which however cannot be much more
ionized than X). d) The presence of the Fe Kalpha Compton Shoulder, already
discovered by Chandra, is confirmed, its relative flux implying Compton-thick
matter. This further supports the identification of the reflecting region with
the absorber.",0305217v1
2003-06-25,Iron K features in the hard X-ray XMM-Newton spectrum of NGC 4151,"Recent XMM-Newton observations have measured the hard (2.5-12 keV) X-ray
spectrum of the well-known Seyfert galaxy NGC 4151 with a signal-to-noise
unprecedented for this source. We find that a spectral model, developed to fit
previous Beppo-SAX and ASCA observations of NGC 4151, provides an excellent
description of the XMM-Newton EPIC data. The results support the view that it
is the level of the continuum that is the main driver of the complex spectral
variability exhibited by NGC 4151. We focus on the iron K features in the NGC
4151 spectrum. There is no requirement for a relativistically broadened iron Ka
line, in contrast to several earlier studies. The iron Ka line profile is well
modelled by a narrow Gaussian, the intensity of which varies by ~25% on
timescales of about a year. There is also a strong suggestion that the cold
media present in the active nucleus of NGC 4151 have an iron abundance that is
at least twice the solar value.",0306540v1
2003-08-11,Theoretical UBVRI colors of iron core white dwarfs,"We explore photometric properties of hypothetical iron core white dwarfs and
compute their expected colors in UBVRI Johnson broadband system. Atmospheres of
iron core WDs in this paper consist of pure iron covered by a pure hydrogen
layer of an arbitrary column mass. LTE model atmospheres and theoretical
spectra are calculated on the basis of Los Alamos TOPS opacities and the
equation of state from the OPAL project, suitable for nonideal Fe and H gases.
We have also computed UBVRI colors of the models and determined an area on the
B-V vs. U-B and U-B vs. V-I planes, occupied by both pure Fe, and pure H model
atmospheres of WD stars. Finally, we search for iron core white dwarf
candidates in the available literature.",0308184v2
2006-09-12,Discoveries of Diffuse Iron Line Sources from the Sgr B Region,"The radio complex Sgr B region is observed with the X-Ray Imaging
Spectrometers (XIS) on board Suzaku. This region exhibits diffuse iron lines at
6.4, 6.7 and 6.9 keV, which are K$\alpha$ lines of Fe \emissiontype{I} (neutral
iron), Fe\emissiontype{XXV} (He-like iron) and Fe\emissiontype{XXVI} (H-like
iron), respectively. The high energy resolving power of the XIS provides the
separate maps of the K-shell transition lines from Fe\emissiontype{I} (6.4 keV)
and Fe\emissiontype{XXV} (6.7 keV). Although the 6.7 keV line is smoothly
distributed over the Sgr B region, a local excess is found near at $(l, b) =
(\timeform {0D.61}, \timeform{0D.01})$, possibly a new SNR. The plasma
temperature is \textit{kT} $\sim$3 keV and the age is estimated to be around
several$\times10^{3}$ years. The 6.4 keV image is clumpy with local excesses
nearby Sgr B2 and at $(l, b) = (\timeform{0D.74}, -\timeform{0D.09})$. Like Sgr
B2, this excess may be another candidate of an X-ray reflection nebula (XRN).",0609310v1
2006-07-08,Magnetic Magnetoelectric and Magnetoelastic Properties of new multiferroic material NdFe3(BO3)4,"Complex experimental and theoretical study of the magnetic, magnetoelectric,
and magnetoelastic properties of neodymium iron borate NdFe3(BO3)4 along
various crystallographic directions have been carried out in strong pulsed
magnetic fields up to 230 kOe in a temperature range of 4.2-50 K. It has been
found that neodymium iron borate, as well as gadolinium iron borate, is a
multiferroic. It has much larger (above 3 10^(-4) C/m^2) electric polarization
controlled by the magnetic field and giant quadratic magnetoelectric effect.
The exchange field between the rare-earth and iron subsystems (~50 kOe) has
been determined for the first time from experimental data. The theoretical
analysis based on the magnetic symmetry and quantum properties of the Nd ion in
the crystal provides an explanation of an unusual behavior of the
magnetoelectric and magnetoelastic properties of neodymium iron borate in
strong magnetic fields and correlation observed between them.",0607217v1
2005-09-14,Role of proton irradiation and relative air humidity on iron corrosion,"This paper presents a study of the effects of proton irradiation on iron
corrosion. Since it is known that in humid atmospheres, iron corrosion is
enhanced by the double influence of air and humidity, we studied the iron
corrosion under irradiation with a 45% relative humidity. Three proton beam
intensities (5, 10 and 20 nA) were used. To characterise the corrosion layer,
we used ion beam methods (Rutherford Backscattering Spectrometry (RBS), Elastic
Recoil Detection Analysis (ERDA)) and X-ray Diffraction (XRD) analysis. The
corrosion kinetics are plotted for each proton flux. A diffusion model of the
oxidant species is proposed, taking into account the fact that the flux through
the surface is dependent on the kinetic factor K. This model provides evidence
for the dependence of the diffusion coefficient, D, and the kinetic factor, K,
on the proton beam intensity. Comparison of the values for D with the diffusion
coefficients for thermal oxygen diffusion in iron at 300 K suggests an
enhancement due to irradiation of 6 orders of magnitude.",0509116v1
2005-09-14,Origin of the hydrogen involved in iron corrosion under irradiation,"In the perspective of long term geological storage, high level nuclear wastes
will be overpacked in low carbon steel containers. In that context, we have
studied the influence of oxygen dissolved in water on iron corrosion.
Therefore, leaching experiments were performed in desaerated D$\_2$O and in
aerated H$\_2$O and a kinetic study of iron corrosion under proton irradiation
was lead in aqueous media with two different dissolved oxygen concentrations.
The leaching experiments underline the major role of dissolved oxygen in
oxydoreduction reactions which take place as far as iron is in contact with
water. But the kinetic study of iron corrosion under irradiation put in
evidence the balance between the oxydoreduction reactions and the corrosion
rate induced by radicals species generated by water radiolysis. In addition, to
check if, in the atomic % concentration range, hydrogen diffuse from the air/Fe
interface through the foil an irradiation experiment was performed in argon. It
proved that no hydrogen permeation occurs at a concentration level of the
atomic percent.",0509117v1
2005-09-14,Use ion beam techniques to study the coupling between air and its relative humidity on iron corrosion under irradiation,"In this paper, the role of air humidity on the iron corrosion under
irradiation is studied in the context of geological disposal of nuclear wastes.
The irradiation experiments are performed at room temperature using a 3 MeV
extracted proton beam with a 10 nA intensity. Different atmospheres are
studied: Humid air with a relative humidity (RH) fixed at 45 %, dry air and a
$^{15}N\_2$ atmosphere (45% RH). The hydrogen and oxygen distribution profiles
at the iron surface in contact with atmosphere are measured by using
respectively ERDA (Elastic Recoil Detection Analysis) and RBS (Rutherford
Backscattering Spectrometry) analysis. From these experiments it is clearly
demonstrated that the coupling of O$\_2$+H$\_2$O enhances iron oxidation
whereas for iron hydrogenation, humidity is sufficient whatever the atmosphere.
An interpretation is given, which is based on the reaction mechanisms and the
species formed by air ionisation.",0509120v1
2007-10-25,Nuclear PDFs from neutrino deep inelastic scattering,"We study nuclear effects in charged current deep inelastic neutrino-iron
scattering in the frame-work of a chi^2 analysis of parton distribution
functions. We extract a set of iron PDFs and show that under reasonable
assumptions it is possible to constrain the valence, light sea and strange
quark distributions. Our iron PDFs are used to compute x_{Bj}-dependent and
Q^2-dependent nuclear correction factors for iron structure functions which are
required in global analyses of free nucleon PDFs. We compare our results with
nuclear correction factors from neutrino-nucleus scattering models and
correction factors for charged lepton-iron scattering. We find that, except for
very high x_{Bj}, our correction factors differ in both shape and magnitude
from the correction factors of the models and charged-lepton scattering.",0710.4897v2
2007-10-25,Topology of the Spin-polarized Charge Density in bcc and fcc Iron,"We investigate the topology of the spin-polarized charge density in bcc and
fcc iron. While the total spin-density is found to possess the topology of the
non-magnetic prototypical structures, in some cases the spin-polarized
densities are characterized by unique topologies; for example, the
spin-polarized charge densities of bcc and high-spin fcc iron are atypical of
any known for non-magnetic materials. In these cases, the two spin-densities
are correlated: the spin-minority electrons have directional bond paths with
deep minima in the minority density, while the spin-majority electrons fill
these holes, reducing bond directionality. The presence of two distinct spin
topologies suggests that a well-known magnetic phase transition in iron can be
fruitfully reexamined in light of these topological changes. We show that the
two phase changes seen in fcc iron (paramagnetic to low-spin and low-spin to
high-spin) are different. The former follows the Landau symmetry-breaking
paradigm and proceeds without a topological transformation, while the latter
also involves a topological catastrophe.",0710.4942v2
2007-11-19,XMM-Newton and Broad Iron Lines,"Iron line emission is common in the X-ray spectra of accreting black holes.
When the line emission is broad or variable then it is likely to originate from
close to the black hole. X-ray irradiation of the accretion flow by the
power-law X-ray continuum produces the X-ray 'reflection' spectrum which
includes the iron line. The shape and variability of the iron lines and
reflection can be used as a diagnostic of the radius, velocity and nature of
the flow. The inner radius of the dense flow corresponds to the innermost
stable circular orbit and thus can be used to determine the spin of the black
hole. Studies of broad iron lines and reflection spectra offer much promise for
understanding how the inner parts of accretion flows (and outflows) around
black holes operate. There remains great potential for XMM-Newton to continue
to make significant progress in this work. The need for high quality spectra
and thus for long exposure times is paramount.",0711.2976v1
2008-03-26,Supernova progenitors and iron density evolution from SN rate evolution measurements,"Using an extensive compilation of literature supernova rate data we study to
which extent its evolution constrains the star formation history, the
distribution of the type Ia supernova (SNIa) progenitor's lifetime, the mass
range of core-collapse supernova (CCSN) progenitors, and the evolution of the
iron density in the field.
  We find that the diagnostic power of the cosmic SNIa rate on their progenitor
model is relatively weak. More promising is the use of the evolution of the
SNIa rate in galaxy clusters. We find that the CCSN rate is compatible with a
Salpeter IMF, with a minimum mass for their progenitors > 10 Msun. We estimate
the evolution in the field of the iron density released by SNe and find that in
the local universe the iron abundance should be ~ 0.1 solar. We discuss the
difference between this value and the iron abundance in clusters.",0803.3793v2
2008-07-01,"Light matter in the core of the Earth: its identity, quantity and temperature using tricritical phenomena","Light elements in the iron-rich core of the Earth are important indicators
for the evolution of our planet. Their amount and distribution, and the
temperature in the core, are essential for understanding how the core and the
mantle interact and for modelling the geodynamo which generates the planetary
magnetic field. However, there is a longstanding controversy surrounding the
identity and quantity of the light elements. Here, the theory of tricritical
phenomena is employed as a precise theoretical framework to study
solidification at the high pressures and temperatures where both experimental
and numerical methods are complicated to implement and have large uncertainties
in their results. Combining the theory with the most reliable iron melting data
and the Preliminary Reference Earth Model (PREM) seismic data, one obtains the
solidification temperature at the inner core boundary (ICB) for both pure iron
and for the alloy of iron and light elements in the actual core melt. One also
finds a value of about 2.5 mole% for the amount of light matter. In addition,
the density of both solid and liquid pure iron at its melting temperature is
found. This allows one to obtain the density of the light matter and thus to
identify it to be MgSiO3.",0807.0187v1
2008-08-15,Relativistic Iron Line Emission from the Neutron Star Low-mass X-ray Binary 4U 1636-536,"We present an analysis of XMM-Newton and RXTE data from three observations of
the neutron star LMXB 4U 1636-536. The X-ray spectra show clear evidence of a
broad, asymmetric iron emission line extending over the energy range 4-9 keV.
The line profile is consistent with relativistically broadened Fe K-alpha
emission from the inner accretion disk. The Fe K-alpha line in 4U 1636-536 is
considerably broader than the asymmetric iron lines recently found in other
neutron star LMXBs, which indicates a high disk inclination. We find evidence
that the broad iron line feature is a combination of several K-alpha lines from
iron in different ionization states.",0808.2214v2
2009-02-11,Temperature of the inner-core boundary of the Earth: Melting of iron at high pressure from first-principles coexistence simulations,"The Earth's core consists of a solid ball with a radius of 1221 Km,
surrounded by a liquid shell which extends up to 3480 Km from the centre of the
planet, roughly half way towards the surface (the mean radius of the Earth is
6373 km). The main constituent of the core is iron, and therefore the melting
temperature of iron at the pressure encountered at the boundary between the
solid and the liquid (the ICB) provides an estimate of the temperature of the
core. Here I report the melting temperature of Fe at pressures near that of the
ICB, obtained with first principles techniques based on density functional
theory. The calculations have been performed by directly simulating solid and
liquid iron in coexistence, and show that and at a pressure of $\sim 328$ GPa
iron melts at $\sim 6370\pm 100$ K. These findings are in good agreement with
earlier simulations, which used exactly the same quantum mechanics techniques,
but obtained melting properties from the calculation of the free energies of
solid and liquid Fe",0902.1831v1
2009-05-23,Kinetic Magnetism and Orbital Order in Iron Telluride,"Iron telluride (FeTe), a relative of the iron based high temperature
superconductors, displays unusual magnetic order and structural transitions.
Here we explore the idea that strong correlations may play an important role in
these materials. We argue that the unusual orders observed in FeTe can be
understood from a picture of correlated local moments with orbital degeneracy,
coupled to a small density of itinerant electrons. A component of the
structural transition is attributed to orbital, rather than magnetic ordering,
introducing a strongly anisotropic character to the system along the diagonal
directions of the iron lattice. Double exchange interactions couple the
diagonal chains leading to the observed ordering wavevector. The incommensurate
order in samples with excess iron arises from electron doping in this scenario.
The strong anisotropy of physical properties in the ordered phase should be
detectable by transport in single domains. Predictions for ARPES, inelastic
neutron scattering and hole/electron doping studies are also made.",0905.3782v1
2009-07-02,Moessbauer spectroscopy evidence for the lack of iron magnetic moment in superconducting FeSe,"Superconducting FeSe has been investigated by measurements of the magnetic
susceptibility versus temperature and Moessbauer spectroscopy at various
temperatures including strong external magnetic fields applied to the absorber.
It was found that isomer shift exhibits sharply defined increase at about 105 K
leading to the lowering of the electron density on iron nucleus by 0.02
electron/a.u.^3. Above jump in the electron density is correlated with the
transition from the P4/nmm to the Cmma structure, while decreasing temperature.
Moessbauer measurements in the external magnetic field and for temperatures
below transition to the superconducting state revealed null magnetic moment on
iron atoms. Hence, the compound exhibits either Pauli paramagnetism or
diamagnetic behavior. The principal component of the electric field gradient on
the iron nucleus was found as negative on the iron site.",0907.0383v2
2010-06-19,High resolution spectroscopic study of red clump stars in the Galaxy: iron group elements,"The main atmospheric parameters and abundances of the iron group elements
(vanadium, chromium, iron, cobalt and nickel) are determined for 62 red giant
""clump"" stars revealed in the Galactic field by the Hipparcos orbiting
observatory. The stars form a homogeneous sample with the mean value of
temperature T=4750 +- 160K, of surface gravity log g = 2.41 +- 0.26 and the
mean value of metallicity [Fe/H] = -0.04 +- 0.15 dex. A Gaussian fit to the
[Fe/H] distribution produces the mean [Fe/H] = -0.01 dex and dispersion of
[Fe/H] = 0.08 dex. The near-solar metallicity and small dispersion of [Fe/H] of
clump stars of the Galaxy obtained in this work confirm the theoretical model
of the Hipparcos clump by Girardi & Salaris (2001). This suggests that nearby
clump stars are (in the mean) relatively young objects, reflecting mainly the
near-solar metallicities developed in the local disk during the last few Gyrs
of its history. We find iron group element to iron abundance ratios in clump
giants to be close to solar.",1006.3857v1
2010-07-19,Can an underestimation of opacity explain B-type pulsators in the SMC?,"Slowly Pulsating B and $\beta$ Cephei are $\kappa$ mechanism driven pulsating
B stars. That $\kappa$ mechanism works since a peak in the opacity due to a
high number of atomic transitions from iron-group elements occurs in the area
of $\log T \approx 5.3$. Theoretical results predict very few SPBs and no
$\beta$ Cep to be encountered in low metallicity environments such as the Small
Magellanic Cloud. However recent variability surveys of B stars in the SMC
reported the detection of a significant number of SPB and $\beta$ Cep
candidates. Though the iron content plays a major role in the excitation of
$\beta$ Cep and SPB pulsations, the chemical mixture representative of the SMC
B stars such as recently derived does not leave room for a significant increase
of the iron abundance in these stars. Whilst abundance of iron-group elements
seems reliable, is the opacity in the iron-group elements bump underestimated?
We determine how the opacity profile in B-type stars should change to excite
SPB and $\beta$ Cep pulsations in early-type stars of the SMC.",1007.3088v1
2010-11-12,"Spin waves in the $(π,0)$ magnetically ordered iron chalcogenide Fe$_{1.05}$Te","We use inelastic neutron scattering to show that the spin waves in the iron
chalcogenide Fe$_{1.05}$Te display novel dispersion clearly different from
those in the related iron pnictide systems. By fitting the spin waves to a
Heisenberg Hamiltonian, we extract magnetic exchange couplings that are
dramatically different from both predictions by density functional calculations
and measurements on the iron pnictide CaFe$_2$As$_2$. While the
nearest-neighbor exchange couplings in CaFe$_2$As$_2$ and Fe$_{1.05}$Te are
quite different, their next-nearest-neighbor exchange couplings are similar.
These results suggest that superconductivity in the pnictides and chalcogenides
share a common magnetic origin that is intimately associated with the
next-nearest-neighbor magnetic coupling between the irons.",1011.2930v2
2010-12-02,Interstitial Iron Controlled Superconductivity in Fe1+xTe0.7Se0.3,"The superconducting series, Fe(Te,Se), has a complex structural and magnetic
phase diagram that is dependent on composition and occupancy of a secondary
interstitial Fe site. In this letter, we show that superconductivity in
Fe1+xTe0.7Se0.3 can be enhanced by topotactic deintercalation of the
interstitial iron, demonstrating the competing roles of the two iron sites.
Neutron diffraction reveals a flattening of the Fe(Te,Se)4 tetrahedron on Fe
removal of iron and an increase in negative thermal expansion within the ab
plane that correlates with increased lattice strain. Inelastic neutron
scattering shows that a gapped excitation at 6 meV, evolves into gapless
paramagnetic scattering with increasing iron; similar to the fluctuations
observed for non-superconducting Fe1+xTe itself.",1012.0590v1
2010-12-31,Binary and nonbinary description of hypointensity in human brain MR images,"Accumulating evidence has shown that iron is involved in the mechanism
underlying many neurodegenerative diseases, such as Alzheimer's disease,
Parkinson's disease and Huntington's disease. Abnormal (higher) iron
accumulation has been detected in the brains of most neurodegenerative
patients, especially in the basal ganglia region. Presence of iron leads to
changes in MR signal in both magnitude and phase. Accordingly, tissues with
high iron concentration appear hypo-intense (darker than usual) in MR
contrasts. In this report, we proposed an improved binary hypointensity
description and a novel nonbinary hypointensity description based on principle
components analysis. Moreover, Kendall's rank correlation coefficient was used
to compare the complementary and redundant information provided by the two
methods in order to better understand the individual descriptions of iron
accumulation in the brain.",1101.0242v1
2011-01-25,Quantum criticality in the iron pnictides and chalcogenides,"Superconductivity in the iron pnictides and chalcogenides arises at the
border of antiferromagnetism, which raises the question of the role of quantum
criticality. In this topical review, we describe the theoretical work that led
to the prediction for a magnetic quantum critical point arising out of a
competition between electronic localization and itinerancy, and the proposal
for accessing it by using isoelectronic P substitution for As in the undoped
iron pnictides. We go on to compile the emerging experimental evidence in
support of the existence of such a quantum critical point in
isoelectronically-tuned iron pnictides. We close by discussing the implications
of these results for the physics of the iron pnictides and chalcogenides.",1101.4701v1
2011-02-22,Magneto-elastic quantum fluctuations and phase transitions in the iron superconductors,"We examine the relevance of magneto-elastic coupling to describe the complex
magnetic and structural behaviour of the different classes of the iron
superconductors. We model the system as a two-dimensional metal whose magnetic
excitations interact with the distortions of the underlying square lattice.
Going beyond mean field we find that quantum fluctuation effects can explain
two unusual features of these materials that have attracted considerable
attention. First, why iron telluride orders magnetically at a non-nesting
wave-vector $(\pi/2, \pi/2)$ and not at the nesting wave-vector $(\pi, 0)$ as
in the iron arsenides, even though the nominal band structures of both these
systems are similar. And second, why the $(\pi, 0)$ magnetic transition in the
iron arsenides is often preceded by an orthorhombic structural transition.
These are robust properties of the model, independent of microscopic details,
and they emphasize the importance of the magneto-elastic interaction.",1102.4622v2
2012-12-05,Progress in wire fabrication of iron-based superconductors,"Iron-based superconductors, with Tc values up to 55 K, are of great interest
for applications, due to their lower anisotropies and ultrahigh upper critical
fields. In the past 4 years, great progress has been made in the fabrication of
iron-based superconducting wires and tapes using the powder-in-tube (PIT)
processing method, including main three types of 122, 11, and 1111 iron-based
parent compounds. In this article, an overview of the current state of
development of iron-based superconducting wires and tapes is presented. We
focus on the fabrication techniques used for 122 pnictide wires and tapes, with
an emphasis on their meeting the critical current requirements for making
high-performance conductors, such as a combination of using Ag sheath, addition
element and optimized heat treatment to realize high Jc, ex situ process
employed to reduce non-superconducting phases and to obtain a high relative
density, and a texture control to improve grain connectivity. Of particular
interest is that so far transport Jc values above 10^4 A/cm^2 at 4.2 K and 10 T
are obtained in 122 type tapes, suggesting that they are prospective candidates
for high-field applications. Finally, a perspective and future development of
PIT pnictide wires are also given.",1212.1207v1
2013-05-30,Searching for the missing iron in the core of the Centaurus cluster,"We re-analyse a combined 198 ks Chandra observation of NGC4696, the brightest
galaxy of the Centaurus cluster. We extract temperature and metallicity
profiles from the data, and we confirm the presence of a sharp drop in iron
abundance, from ~1.8 Zsolar to ~0.4 Zsolar, within the central 5 kpc of the
cluster. We estimate that this abundance drop corresponds to a total ""missing""
iron mass of 1.4e06 Msolar. We propose that part of this missing iron is locked
up in cool (~19 K) far-IR emitting dust, as found by Spitzer and Herschel
observations. This can occur if the iron injected by stellar mass loss in the
central region is in grains, which remain in that form as the injected dusty
cold gas mixes and joins the cold dusty filamentary nebula observed within the
same region. The bubbling feedback process observed in the cluster core then
drags filaments outward and dumps them at 10-20 kpc radius, where the
metallicity is high.",1305.7046v3
2013-08-13,The unique electronic structure of Ca10(Pt4As8)(Fe2-xPtxAs2)5 with metallic Pt4As8 layers,"We studied the low-lying electronic structure of the newly discovered
iron-platinum-arsenide superconductor, Ca10(Pt4As8)(Fe2-xPtxAs2)5 (Tc=22 K)
with angle-resolved photoemission spectroscopy. We found that the Pt4As8 layer
contributes to a small electron-like Fermi surface, indicative of metallic
charge reservoir layers that are rare for iron based superconductors. Moreover,
the electronic structure of the FeAs-layers resembles those of other prototype
iron pnictides to a large extent. However, there is only dxy-orbital originated
hole-like Fermi surface near the zone center, which is rather unique for an
iron pnictide superconductor with relatively high superconducting transition
temperature; and the dxz and dyz originated bands are not degenerate at the
zone center. Furthermore, all bands near the Fermi energy show negligible kz
dependence, indicating the strong two-dimensional nature of this material. Our
results indicate this material possesses rather unique electronic structure,
which enriches our current knowledge of iron based superconductors.",1308.3105v1
2013-12-03,Disk emission and atmospheric absorption lines in black hole candidate 4U 1630-472,"We re-analyzed SUZAKU data of the black hole candidate 4U 1630-472 being in
the high/soft state. We show that the continuum X-ray spectrum of 4U 1630-472
with iron absorption lines can be satisfactorily modeled by the spectrum from
an accretion disk atmosphere. Absorption lines of highly ionized iron
originating in hot accretion disk atmosphere can be an alternative or
complementary explanation to the wind model usually favored for these type of
sources. We model continuum and line spectra using a single model. Absorption
lines of highly ionized iron can origin in upper parts of the disk atmosphere
which is intrinsically hot due to high disk temperature. Iron line profiles
computed with natural, thermal and pressure broadenings match very well
observations. We showed that the accretion disk atmosphere can effectively
produce iron absorption lines observed in 4U 1630-472 spectrum. Absorption line
arising in accretion disk atmosphere is the important part of the observed line
profile, even if there are also other mechanisms responsible for the absorption
features. Nevertheless, the wind theory can be an artifact of the fitting
procedure, when the continuum and lines are fitted as separate model
components.",1312.0922v1
2014-05-22,Electronic structure of iron-based superconductors: from pnictides to chalcogenides and other similar systems,"This review discusses and compares electronic spectra of new iron-based
high-temperature superconductors (HTSC), as well as a number of chemically
similar compounds. Particular attention is payed to iron chalcogenide
K_{1-x}Fe_{2-y}Se_2, which is isostructural to BaFe_2As_2 (122) pnictide. It is
shown, that Fermi surfaces of K_{1-x}Fe_{2-y}Se_2 are essentially different
from those for pnictides. Using LDA+DMFT and LDA'+DMFT calculations we show,
that electronic correlations in K_{1-x}Fe_{2-y}Se_2 influence the electronic
structure much more significantly, than in the most studied 122 system. We also
discuss the electronic structure of several multiple-band superconductors,
chemically similar to iron-based HTSC, with relatively small values of $T_c$,
such as SrPt_{2}As_{2}, APt_{3}P, (Sr,Ca)Pd_2As_2, and non superconducting
compound BaFe_2Se_3. It is shown, that electronic structure of these systems is
very different from previously studies iron pnictides and chalcogenides. The
value of T_c in these systems can be understood within the simple BCS model.",1405.5677v1
2014-05-26,Dynamic transition in supercritical iron,"Recent advance in understanding the supercritical state posits the existence
of a new line above the critical point separating two physically distinct
states of matter: rigid liquid and non-rigid gas-like fluid. The location of
this line, the Frenkel line, remains unknown for important real systems. Here,
we map the Frenkel line on the phase diagram of supercritical iron using
molecular dynamics simulations. On the basis of our data, we propose a general
recipe to locate the Frenkel line for any system, the recipe that importantly
does not involve system-specific detailed calculations and relies on the
knowledge of the melting line only. We further discuss the relationship between
the Frenkel line and the metal-insulator transition in supercritical liquid
metals. Our results enable predicting the state of supercritical iron in
several conditions of interest. In particular, we predict that liquid iron in
the Jupiter core is in the ""rigid liquid"" state and is highly conducting. We
finally analyse the evolution of iron conductivity in the core of smaller
planets such as Earth and Venus as well as exoplanets: as planets cool off, the
supercritical core undergoes the transition to the rigid-liquid conducting
state at the Frenkel line.",1405.6491v1
2014-06-13,Effect of dopants on thermal stability and self-diffusion in iron nitride thin films,"We studied the effect of dopants (Al, Ti, Zr) on the thermal stability of
iron nitride thin films prepared using a dc magnetron sputtering technique.
Structure and magnetic characterization of deposited samples reveal that the
thermal stability together with soft magnetic properties of iron nitride thin
films get significantly improved with doping. To understand the observed
results, detailed Fe and N self-diffusion measurements were performed. It was
observed that N self-diffusion gets suppressed with Al doping whereas Ti or Zr
doping results in somewhat faster N diffusion. On the other hand Fe
self-diffusion seems to get suppressed with any dopant of which heat of nitride
formation is significantly smaller than that of iron nitride. Importantly, it
was observed that N self-diffusion plays only a trivial role, as compared to Fe
self-diffusion, in affecting the thermal stability of iron nitride thin films.
Based on the obtained results effect of dopants on self-diffusion process is
discussed.",1406.3446v1
2014-06-14,Emergence of magnetism and controlling factors of superconductivity in Li/Na-ammonia co-intercalated FeSe1-zTez,"The discovery of superconductivity in alkali-ammonia co-intercalated FeSe has
generated intensive interest because of their highest Tc (~ 45 K) among
iron-chalcogenide superconductors with bulk form. Here, we report the phase
diagrams of two series of Li/Na-ammonia co-intercalated FeSe1-zTez. When
superconductivity is suppressed by Te doping, the magnetic ordering states are
emergent. Moreover, a novel phase Lix(NH3)yFe2-{\delta}Te2 with possible
antiferromagnetism is discovered. This strongly indicates the intimate relation
between superconductivity and magnetism in these materials, like in other
iron-based superconductors. On the other hand, comparative structure analysis
with FeSe1-zTez suggests that although there is remarkable similarity in phase
diagrams for both iron-chalcogenide and iron-pnictide superconductors, the
different types of anions with different charges lead to the dissimilar
controlling factors in superconductivity for both classes of materials. This
opens up an opportunity to tune the superconductivity in iron-chalcogenide
superconductors in more ways than just one.",1406.3733v2
2014-07-18,Magnetism and Superconductivity in Iron-based Superconductors Decided by Condensed Particle-hole Excitations away from the Fermi Level,"The origin of magnetism and superconductivity in iron-based superconductors
is still unclear. Here, by investigating the momentum-dependent particle-hole
excitations which quantify the tendency of itinerant electrons towards various
magnetic states or superconducting phases, we unravel a novel origin to account
for the variety of physical properties of iron-based compounds. We show that
condensation of particle-hole excitations away from the Fermi surface in
momentum space is the underlying mechanism in deciding the magnetic and
superconducting properties of iron-based materials. The applicability of this
scenario to the whole family of iron-based superconductors suggests that
inclusion of the orbital degrees of freedom, which may lead to competing
tendencies towards different magnetically ordered states, is more crucial than
taking into account the strong correlations. Our findings further indicate that
in order to properly model these materials, the electronic states away from the
Fermi level have to be considered.",1407.4888v1
2015-01-08,The origin of the spurious iron spread in the globular cluster NGC 3201,"NGC 3201 is a globular cluster suspected to have an intrinsic spread in the
iron content. We re-analysed a sample of 21 cluster stars observed with
UVES-FLAMES at the Very Large Telescope and for which Simmerer et al. found a
0.4 dex wide [Fe/H] distribution with a metal-poor tail. We confirmed that when
spectroscopic gravities are adopted, the derived [Fe/H] distribution spans ~0.4
dex. On the other hand, when photometric gravities are used, the metallicity
distribution from Fe I lines remains large, while that derived from Fe II lines
is narrow and compatible with no iron spread. We demonstrate that the
metal-poor component claimed by Simmerer et al. is composed by asymptotic giant
branch stars that could be affected by non local thermodynamical equilibrium
effects driven by iron overionization. This leads to a decrease of the Fe I
abundance, while leaving the Fe II abundance unaltered. A similar finding has
been already found in asymptotic giant branch stars of the globular clusters M5
and 47 Tucanae. We conclude that NGC 3201 is a normal cluster, with no evidence
of intrinsic iron spread.",1501.01968v1
2015-03-08,Antiferromagnetic order and spin dynamics in iron-based superconductors,"High-transition temperature (high-$T_c$) superconductivity in the iron
pnictides/chalcogenides emerges from the suppression of the static
antiferromagnetic order in their parent compounds, similar to copper oxides
superconductors. This raises a fundamental question concerning the role of
magnetism in the superconductivity of these materials. Neutron scattering, a
powerful probe to study the magnetic order and spin dynamics, plays an
essential role in determining the relationship between magnetism and
superconductivity in high-$T_c$ superconductors. The rapid development of
modern neutron time-of-flight spectrometers allows a direct determination of
the spin dynamical properties of iron-based superconductors throughout the
entire Brillouin zone. In this review, we present an overview of the neutron
scattering results on iron-based superconductors, focusing on the evolution of
spin excitation spectra as a function of electron/hole-doping and isoelectronic
substitution. We compare spin dynamical properties of iron-based
superconductors with those of copper oxide and heavy fermion superconductors,
and discuss the common features of spin excitations in these three families of
unconventional superconductors and their relationship with superconductivity.",1503.02340v2
2015-09-05,Iron abundance in the atmosphere of Arcturus,"Abundance of iron in the atmosphere of Arcturus has been determined from the
profiles or regions of the profiles of the weak lines sensitive to iron
abundance. The selected lines of Fe I and Fe II were synthesized with the MARCS
theoretical models of the atmosphere. From the observed profiles of lines
available with a high spectral resolution in the atlas by Hinkle and Wallace
(2005), the values of the iron abundance $A = 6.95 \pm 0.03$ and the
radial-tangential macroturbulent velocity $5.6 \pm 0.2$ km/s were obtained for
Arcturus. The same physical quantities were found for the Sun as a star; they
are $7.42 \pm 0.02$ and $3.4 \pm 0.3$ km/s, respectively. For Arcturus, the
iron abundance relative to the solar one was determined with the differential
method as [Fe/H] $=-0.48 \pm 0.02$.",1509.01700v1
2015-10-22,Internal structure of Pluto and Charon with an iron core,"Pluto has been observed by the New Horizons space probe to have some
relatively fresh ice on the old ices covering most of the surface. Pluto was
thought to consist of only a rocky core below the ice. Here I show that Pluto
can have an iron core, as can also its companion Charon, which has recently
been modelled to have one. The presence of an iron core means the giant impact
origin calculations should be redone to include iron and thus higher
temperatures. An iron core leads to the possibility of a different geology. An
originally molten core becomes solid later, with contraction and a release of
latent heat. The space vacated allows the upper rock layers to flow downwards
at some locations at the surface of the core, and some of the ice above the
rock to descend, filling the spaces left by the rock motion downwards. These
phenomena can lead to the forces recently deforming the icy surface of Pluto,
and in a lesser way, of Charon.",1510.06604v1
2016-01-05,Testing the Kerr nature of black hole candidates using iron line reverberation mapping in the CPR framework,"The iron K$\alpha$ line commonly observed in the X-ray spectrum of black hole
candidates is produced by X-ray fluorescence of the inner accretion disk. This
line can potentially be quite a powerful tool to probe the spacetime geometry
around these objects and test the Kerr black hole hypothesis. In a previous
paper, we studied the ability to constrain possible deviations from the Kerr
solution from the standard time-integrated iron line spectrum within the
Cardoso-Pani-Rico framework. In the present work, we expand on that study and
consider iron line reverberation mapping in the CPR framework. That is, we
consider the time-evolution of the iron line profile in response to
fluctuations in the X-ray primary source. Our simulations clearly show that the
time information in reverberation mapping can better constrain the background
metric than the time-integrated approach, and this is true, notably, for the
deformation parameter $\epsilon^r_3$, which is only weakly informed by a
time-integrated observation.",1601.00838v2
2016-01-27,Particle-Hole Transformation in Strongly-Doped Iron-Based Superconductors,"An exact particle-hole transformation is discovered in a local-moment model
for a single layer of heavily electron-doped FeSe. The model harbors hidden
magnetic order between the iron d_xz and d_yz orbitals at the wavenumber
(pi,pi). It potentially is tied to the magnetic resonances about the very same
Neel ordering vector that have been recently discovered in intercalated FeSe.
Upon electron doping, the local-moment model successfully accounts for the
electron-pocket Fermi surfaces observed experimentally at the corner of the
two-iron Brillouin zone in electron-doped FeSe, as well as for isotropic Cooper
pairs. Application of the particle-hole transformation predicts a surface-layer
iron-based superconductor at strong hole doping that exhibits high T_c, and
that shows hole-type Fermi-surface pockets at the center of the two-iron
Brillouin zone.",1601.07479v3
2016-02-13,Origin of the Broad Iron Line Feature and the Soft X-ray Variation in Seyfert Galaxies,"Many Seyfert galaxies are known to exhibit significant X-ray spectral
variations and seemingly broad iron K-emission line features. In this paper, we
show that the ""variable partial covering model"", which has been successfully
proposed for MCG-6.30-15 (Miyakawa, Ebisawa & Inoue 2012) and 1H0707.495
(Mizumoto, Ebisawa & Sameshima 2014), can also explain the spectral variations
in 2-10 keV as well as the broad iron line features in 20 other Seyfert
galaxies observed with Suzaku. In this model, the absorbed spectral component
through the optically-thick absorbing clouds has a significant iron K-edge,
which primarily accounts for the observed seemingly broad iron line feature.
Fluctuation of the absorbing clouds in the line of sight of the extended X-ray
source results in variation of the partial covering fraction, which causes an
anti-correlation between the direct (not covered) spectral component and the
absorbed (covered) spectral component below ~10 keV. Observed spectral
variation in 2-10 keV in a timescale of less than ~day is primarily explained
by such variations of the partial covering fraction, while the intrinsic soft
X-ray luminosity is hardly variable.",1602.04284v1
2016-03-10,Ferromagnetism and particle collisions: applications to protoplanetary disks and the meteoritical record,"The meteoritical record shows both iron partitioning and tungsten isotopic
partitioning between matrix and chondrules. Tungsten is not abundant enough to
have driven its own isotopic partitioning, but if tungsten were correlated with
iron, then ferromagnetic interactions grains could help explain both
observations. We derive a practical parameterization for the increase in
particle-particle collision rates caused by mutually attracting particle
magnetic dipole moments. While the appropriate magnetic parameters remain
uncertain, we show that ambient magnetic fields in protoplanetary disks are
expected to be strong enough to magnetize iron metal bearing dust grains
sufficiently to drive large increases in their collision rates. Such increased
collision rates between iron metal rich grains could help preserve primordial
iron and W isotopic inhomogeneities; and would help explain why the
meteoritical record shows their partitioning in the solar nebula. The
importance of magnetic interactions for larger grains whose growth is balanced
by fragmentation is less clear, and will require future laboratory or numerical
studies.",1603.03326v1
2016-04-28,Mössbauer parameters of Fe-related defects in group-IV semiconductors: first principles calculations,"We employ a combination of pseudopotential and all-electron density
functional calculations, to relate the structure of defects in supercells to
the isomer shifts and quadrupole splittings observed in M\""ossbauer
spectroscopy experiments. The methodology is comprehensively reviewed and
applied to the technologically relevant case of iron-related defects in
silicon, and to other group-IV hosts to a lesser degree. Investigated defects
include interstitial and substitutional iron, iron-boron pairs, iron-vacancy
and iron-divacancy. We find that in general, agreement between the calculations
and M\""ossbauer data is within a 10% error bar. Nonetheless, we show that the
methodology can be used to make accurate assignments, including to separate
peaks of similar defects in slightly different environments.",1604.08425v2
2016-05-13,Crystal Chemistry and Structural Design of Iron-Based Superconductors,"The second class of high-temperature superconductors (HTSCs), iron-based
pnictides and chalcogenides, necessarily contain Fe$_2$$X_2$ (""$X$"" refers to a
pnictogen or a chalcogen element) layers, just like the first class of HTSCs
which possess the essential CuO$_2$ sheets. So far, dozens of iron-based HTSCs,
classified into nine groups, have been discovered. In this article, the
crystal-chemistry aspects of the known iron-based superconductors are reviewed
and summarized by employing ""hard and soft acids and bases (HSAB)"" concept.
Based on these understandings, we propose an alternative route to exploring new
iron-based superconductors via rational structural design.",1605.04179v1
2016-06-14,Ab-initio perspective on structural and electronic properties of iron-based superconductors,"The discovery of iron pnictides and iron chalcogenides as a new class of
unconventional superconductors in 2008 has generated an enourmous amount of
experimental and theoretical work that identifies these materials as correlated
metals with multiorbital physics, where magnetism, nematicity and
superconductivity are competing phases that appear as a function of pressure
and doping. A microscopic understanding of the appearance of these phases is
crucial in order to determine the nature of superconductivity in these systems.
Here we review our recent theoretical efforts to describe and understand from
first principles the properties of iron pnictides and chalcogenides with
special focus on (i) pressure dependence, (ii) effects of electronic
correlation and (iii) origin of magnetism and superconductivity.",1606.04411v1
2016-12-07,Direct observation of dispersive lower Hubbard band in iron-based superconductor FeSe,"Electronic correlations were long suggested not only to be responsible for
the complexity of many novel materials, but also to form essential
prerequisites for their intriguing properties. Electronic behavior of
iron-based superconductors is far from conventional, while the reason for that
is not yet understood. Here we present a combined study of the electronic
spectrum in the iron-based superconductor FeSe by means of angle-resolved
photoemission spectroscopy (ARPES) and dynamical mean field theory (DMFT). Both
methods in unison reveal strong deviations of the spectrum from single-electron
approximation for the whole 3$d$ band of iron: not only the well separated
coherent and incoherent parts of the spectral weight are observed, but also a
noticeable dispersion of the lower Hubbard band (LHB) is clearly present. This
way we demonstrate correlations of the most puzzling intermediate coupling
strength in iron superconductors.",1612.02313v1
2017-01-10,Orbital-driven two-dome superconducting phases in iron-based superconductors,"Recent several experiments revealed that novel bipartite
magnetic/superconducting phases widely exist in iron pnictides and
chalcogenides. Nevertheless, the origin of the two-dome superconducting phases
in iron-based compounds still remains unclear. Here we theoretically
investigated the electronic structures, magnetic and superconducting properties
of three representative iron-based systems, i.e. LaFeAsO1-xHx, LaFeAs1-xPxO and
KFe2As2. We found that in addition to the degenerate in-plane anisotropic xz/yz
orbitals, the quasi-degenerate in-plane isotropic orbitals drive these systems
entering into the second parent phase. Moreover, the second superconducting
phase is contributed by the isotropic orbitals rather than the anisotropic ones
in the first superconducting phase, indicating an orbital-selective pairing
state. These results imply an orbital-driven mechanism and shed light on the
understanding of the two-dome magnetic/superconducting phases in iron-based
compounds.",1701.02500v1
2017-01-31,SANS contrast variation study of magnetoferritin structure at various iron loading,"Magnetoferritin, a synthetic derivate of iron storage protein - ferritin, has
been synthesized with different iron oxide loading values. Small-angle neutron
scattering experiments were applied to study the structure of magnetoferritin
solutions using contrast variation method by varying the light to heavy water
ratio of the solvent. Higher iron loading leads to increasing of the neutron
scattering length density of magnetoferritin and also to the increase of the
polydispersity of complexes. The formation of the magnetic core and the
variation of the protein shell structure upon iron loading are concluded.",1701.09174v1
2017-01-30,Effect of iron oxide loading on magnetoferritin structure in solution as revealed by SAXS and SANS,"Synthetic biological macromolecule of magnetoferritin containing an iron
oxide core inside a protein shell (apoferritin) is prepared with different
content of iron. Its structure in aqueous solution is analyzed by small-angle
synchrotron X-ray (SAXS) and neutron (SANS) scattering. The loading factor (LF)
defined as the average number of iron atoms per protein is varied up to LF=800.
With an increase of the LF, the scattering curves exhibit a relative increase
in the total scattered intensity, a partial smearing and a shift of the match
point in the SANS contrast variation data. The analysis shows an increase in
the polydispersity of the proteins and a corresponding effective increase in
the relative content of magnetic material against the protein moiety of the
shell with the LF growth. At LFs above ~150, the apoferritin shell undergoes
structural changes, which is strongly indicative of the fact that the shell
stability is affected by iron oxide presence.",1702.00350v1
2017-03-09,Transport properties of iron at the Earth's core conditions: the effect of spin disorder,"The electronic and thermal transport properties of the Earth's core are
crucial for many geophysical models such as the geodynamo model of the Earth's
magnetic field and of its reversals. Here we show, by considering bcc-iron and
iron-rich iron-silicon alloy as a representative of the Earth's core
composition and applying the first-principles modeling that the spin disorder
at the Earth's core conditions provides an essential contribution, of order
20~$\mu\Omega$\,cm, to the electrical resistivity. This value is comparable in
magnitude with the electron-phonon and with the recently estimated
electron-electron scattering contributions. The origin of the spin-disorder
resistivity (SDR) consists in the existence of fluctuating local moments that
are stabilized at high temperatures by the magnetic entropy even at pressures
at which the ground state of iron is non-magnetic. We find that electron-phonon
and SDR contributions are not additive at high temperatures. We thus observe a
large violation of the Matthiessen rule, not common in conventional metallic
alloys at ambient conditions.",1703.03205v3
2017-03-19,Surface anisotropy of iron oxide nanoparticles and slabs from first principles : influence of coatings and ligands as a test of the Heisenberg model,"We performed ab initio computations of the magnetic properties of simple iron
oxide clusters and slabs. We considered an iron oxide cluster functionalized by
a molecule or glued to a gold cluster of the same size. We also considered a
magnetite slab coated by cobalt oxide or a mixture of iron oxide and cobalt
oxide. The changes in magnetic behavior were explored using constrained
magnetic calculations. A possible value for the surface anisotropy was
estimated from the fit of a classical Heisenberg model on ab initio results.
The value was found to be compatible with estimations obtained by other means,
or inferred from experimental results. The addition of a ligand, coating, or of
a metallic nanoparticle to the systems degraded the quality of the description
by the Heisenberg Hamiltonian. Proposing a change in the anisotropies allowing
for the proportion of each transition atom we could get a much better
description of the magnetism of series of hybrid cobalt and iron oxide systems.",1703.06414v1
2017-06-16,Robotic Ironing with 3D Perception and Force/Torque Feedback in Household Environments,"As robotic systems become more popular in household environments, the
complexity of required tasks also increases. In this work we focus on a
domestic chore deemed dull by a majority of the population, the task of
ironing. The presented algorithm improves on the limited number of previous
works by joining 3D perception with force/torque sensing, with emphasis on
finding a practical solution with a feasible implementation in a domestic
setting. Our algorithm obtains a point cloud representation of the working
environment. From this point cloud, the garment is segmented and a custom
Wrinkleness Local Descriptor (WiLD) is computed to determine the location of
the present wrinkles. Using this descriptor, the most suitable ironing path is
computed and, based on it, the manipulation algorithm performs the
force-controlled ironing operation. Experiments have been performed with a
humanoid robot platform, proving that our algorithm is able to detect
successfully wrinkles present in garments and iteratively reduce the
wrinkleness using an unmodified iron.",1706.05340v1
2017-07-20,"Abundances in Galactic Bulge planetary nebulae from optical, ultraviolet and infrared observations","Iron suffers from high levels of depletion in the highly ionized environments
of planetary nebulae, making the direct determination of undepleted elemental
iron abundances difficult. Zinc, which does not suffer from the same depletion
effects as iron, may be used as a surrogate element to measure iron abundances
as there is an approximately constant zinc-to-iron ratio across a wide range of
metallicities. In this paper, we report zinc abundances of six Galactic Bulge
planetary nebulae determined from new observations taken with ISAAC on the Very
Large Telescope, Chile, prior to the instrument's decommissioning as well as a
further three based upon literature observations. UVES data of the sample
planetary nebulae are presented and have been used to derive abundances,
temperatures and densities of a variety of elements and ions. The abundances
derived from the UVES data agree well with results from the literature. [Zn/H],
determined from the ISAAC observations, is found to be generally sub-solar and
[O/Zn] is found to be either consistent or enriched with respect to Solar.",1707.06672v1
2018-05-09,Graphene-Supported Silver-Iron Carbon Nitride Derived from Thermal Decomposition of Silver Hexacyanoferrate as Effective Electrocatalyst for the Oxygen Reduction Reaction in Alkaline Media,"Silver-iron carbon nitride has been obtained by pyrolysis (under inert
atmosphere) of silver hexacyanoferrate(II), precipitated on graphene
nanoplatelets, and examined as electrocatalyst for oxygen reduction reaction in
alkaline media in comparison to silver nanoparticles and iron carbon nitride
(prepared separately in a similar manner on graphene nanoplatelets). The
catalytic materials have been studied in 0.1 M potassium hydroxide electrolyte
using such electrochemical diagnostic techniques as cyclic voltammetry and
rotating ring-disk electrode voltammetry. Upon application of graphene
nanoplateletssupported mixed silver-iron carbon nitride catalyst, the reduction
of oxygen proceeds at more positive potentials and the amounts of hydrogen
peroxide (generated during reduction of oxygen at potentials more positive than
0.3 V) are lower relative to silver nanoparticles and iron carbon nitride
(supported on graphene nanoplatelets) examined separately. Promoting effect is
ascribed to high activity of silver toward the reduction/decomposition of H2O2
in basic medium. Additionally, it has been observed that the systems based on
carbon nitrides show considerable stability due to strong fixation of metal
complexes to CN shells.",1805.03439v1
2018-12-13,Seeding the Formation of Mercurys: An Iron-sensitive Bouncing Barrier in Disk Magnetic Fields,"The inner part of protoplanetary disks can be threaded by strong magnetic
fields. In laboratory levitation experiments, we study how magnetic fields up
to 7 mT influence the aggregation of dust by observing the self-consistent
collisional evolution of particle ensembles. As dust samples we use mixtures of
iron and quartz in different ratios. Without magnetic fields, particles in all
samples grow into a bouncing barrier. These aggregates reversibly form larger
clusters in the presence of magnetic fields. The size of these clusters depends
on the strength of the magnetic field and the ratio between iron and quartz.
The clustering increases the size of the largest entities by a factor of a few.
If planetesimal formation is sensitive to the size of the largest aggregates,
e.g., relying on streaming instabilities, then planetesimals will
preferentially grow iron-rich in the inner region of protoplanetary disks. This
might explain the iron gradient in the solar system and the formation of dense
Mercury-like planets.",1812.05338v1
2019-06-19,The Modulating Optical Depth of Photoelectric Absorption Edge with Pulse Phase in Accretion-Powered X-ray Pulsars,"We report the first discovery of pulse phase modulating optical depths at the
iron K-edge in accretion-powered X-ray pulsars, from Suzaku observations. A
significant modulating optical depth of the iron K-edge is detected for Vela
X-1 and GX 1+4. Similar trends are seen in GX 301-2 and OAO 1657-415, though
with poor statistical significance. The observed iron K-edge exhibits a maximum
optical depth, when the X-ray continuum dims, and there is no significant pulse
phase variation in the ionization state of iron. The revealed changes in the
optical depth with pulse phase can be explained as being due to the accreting
matter captured by the magnetic field lines of the pulsar, which co-rotates
with the neutron star spin and is responsible for photoelectric absorption.
Based on the above interpretation, we propose that the accreting matter within
the Alfv\'en radius contains iron with an ionization state of Fe$_{\rm
V\hspace{-0.1em}I-X\hspace{-0.1em}I}$ with a particle density of $10^{17}$
cm$^{-3}$ and has a shape flattened along the azimuthal direction, such as an
accretion curtain.",1906.08037v2
2019-08-19,Reverse chemistry of iron in the deep Earth,"In this work, we demonstrate a remarkable change of chemical trend of Iron
under high pressure that is of great importance for understanding the
distribution of elements in the Earth's mantle and core. Using first principles
crystal structure search method, we conduct a systematic study of the
propensity of p block elements to chemically bind with iron under high
pressures ranging from ambient conditions to that of Earth's core. We show that
under increasing pressure, iron tends to reverse its chemical nature, changing
from an electron donor (reductant) to an electron acceptor, and oxidizes
p-block elements in many compounds. Such reverse chemistry has a significant
impact on the stoichiometries, bond types and strengths, structures and
properties of iron compounds under deep planetary conditions.",1908.06569v1
2019-12-16,Iron telluride ladder compounds: Predicting the structural and magnetic properties of BaFe$_2$Te$_3$,"Since the discovery of pressure-induced superconductivity in the two-leg
ladder system BaFe$_2X_3$ ($X$=S, Se), with the 3$d$ iron electronic density $n
= 6$, the quasi-one-dimensional iron-based ladders have attracted considerable
attention. Here, we use Density Functional Theory (DFT) to predict that the
novel $n = 6$ iron ladder BaFe$_2$Te$_3$ could be stable with a similar crystal
structure as BaFe$_2$Se$_3$. Our results also indicate that BaFe$_2$Te$_3$ will
display the complex 2$\times$2 Block-type magnetic order. Due to the magnetic
striction effects of this Block order, BaFe$_2$Te$_3$ should be a magnetic
noncollinear ferrielectric system with a net polarization $0.31$ $\mu$C/cm$^2$.
Compared with the S- or Se-based iron ladders, the electrons of the Te-based
ladders are more localized, implying that the degree of electronic correlation
is enhanced for the Te case which may induce additional interesting properties.
The physical and structural similarity with BaFe$_2$Se$_3$ also suggests that
BaFe$_2$Te$_3$ could become superconducting under high pressure.",1912.07749v1
2020-02-25,"Heavily Hydride-ion-doped 1111-type Iron-based Superconductors: Synthesis, Physical Properties and Electronic Structure","Iron-based superconductors have grown to be a new continent of high Tc
superconductors comparable to cuprates. The optimal critical temperature (Tc)
of 56 K in electron-doped 1111-type iron oxypnictides attracts considerable
attention of physicists and chemists. Carrier doping is not only essential to
induce superconductivity but also is a critical parameter that governs the
electronic, magnetic, and crystallographic properties of ground states in
high-Tc superconductors. Hydride ion (H-) which is an anionic state of hydrogen
acts as an efficient electron donor in the 1111-type, leading to several
important discoveries such as two-dome structure of superconducting phase and
bipartite parent phase. This article summarizes the synthesis, physical
properties, and electronic structure of the H- bearing 1111-type iron-based
superconductors along with the relevant phenomena of other superconductors. We
show several common characteristics of iron-based superconductors with high-Tc
over 50 K and suggest a way to achieve higher Tc.",2002.11218v1
2020-02-22,Hemolithin: a Meteoritic Protein containing Iron and Lithium,"This paper characterizes the first protein to be discovered in a meteorite.
Amino acid polymers previously observed in Acfer 086 and Allende meteorites
[1,2] have been further characterized in Acfer 086 via high precision MALDI
mass spectrometry to reveal a principal unified structure of molecular weight
2320 Daltons that involves chains of glycine and hydroxy-glycine residues
terminated by iron atoms, with additional oxygen and lithium atoms.
Signal-to-noise ratios up to 135 have allowed the quantification of iron and
lithium in the various MALDI fragments via the isotope satellites due to their
respective minority isotopic masses 54Fe and 6Li. Analysis of the complete
spectrum of isotopes associated with each molecular fragment shows 2H
enhancements above terrestrial averaging 25,700 parts per thousand (sigma =
3,500, n=15), confirming extra-terrestrial origin and hence the existence of
this molecule within the asteroid parent body of the CV3 meteorite class. The
molecule is tipped by an iron-oxygen-iron grouping that in other terrestrial
contexts has been proposed to be capable of absorbing photons and splitting
water into hydroxyl and hydrogen moieties.",2002.11688v1
2020-07-01,Orbital selectivity in electron correlations and superconducting pairing of iron-based superconductors,"Electron correlations play a central role in iron-based superconductors. In
these systems, multiple Fe $3d$-orbitals are active in the low-energy physics,
and they are not all degenerate. For these reasons, the role of
orbital-selective correlations has been an active topic in the study of the
iron-based systems. In this paper, we survey the recent developments on the
subject. For the normal state, we emphasize the orbital-selective Mott physics
that has been extensively studied, especially in the iron chalcogenides, in the
case of electron filling $n \sim 6$. In addition, the interplay between orbital
selectivity and electronic nematicity is addressed. For the superconducting
state, we summarize the initial ideas for orbital-selective pairing, and
discuss the recent explosive activities along this direction. We close with
some perspectives on several emerging topics. These include the evolution of
the orbital-selective correlations, magnetic and nematic orders and
superconductivity as the electron filling factor is reduced from $6$ to $5$, as
well as the interplay between electron correlations and topological
bandstructure in iron-based superconductors.",2007.00181v1
2021-06-24,Polymers' surface interactions with molten iron: a theoretical study,"Environmental concerns are the chief drive for more innovative recycling
techniques for end-of-life polymeric products. One attractive option is taking
advantage of C and H content of polymeric waste in steelmaking industry. In
this work, we examined the interaction of two high production polymers, i.e.,
polyurethane and polysulfide with molten iron using ab initio molecular
dynamics simulation. We demonstrate that both polymers can be used as
carburizers for molten iron. Additionally, we found that light weight H$_2$ and
CH$_x$ molecules were released as by-products of the polymer-molten iron
interaction. The outcomes of this study will have applications in the
carburization of molten iron during ladle metallurgy and waste plastic
injection in electric arc furnace.",2106.12722v1
2021-10-28,Influence of spin fluctuations on structural phase transitions of iron,"The effect of spin fluctuations on the $\alpha$ (bcc) - $\gamma$ (fcc) -
$\delta$ (bcc) structural phase transitions in iron is investigated with a
tight-binding (TB) model. The orthogonal $d$-valent TB model is combined with
thermodynamic integration, spin-space averaging and Hamiltonian Monte Carlo to
compute the temperature-dependent free-energy difference between bcc and fcc
iron. We demonstrate that the TB model captures experimentally observed phonon
spectra of bcc iron at elevated temperatures. Our calculations show that spin
fluctuations are crucial for both, the $\alpha$ - $\gamma$ and the $\gamma$ -
$\delta$ phase transitions but they enter through different mechanisms. Spin
fluctuations impact the $\alpha$ - $\gamma$ phase transition mainly via the
magnetic/electronic free-energy difference between bcc and fcc iron. The
$\gamma$ - $\delta$ phase transition, in contrast, is influenced by spin
fluctuations only indirectly via the spin-lattice coupling. Combining the two
mechanisms, we obtain both, the $\alpha$ - $\gamma$ and the $\gamma$ - $\delta$
phase transitions with our TB model. The calculated transition temperatures are
in very good agreement with experimental values.",2110.15003v2
2022-02-22,Many body study of iron(III) bound human serum transferrin,"Transferrins are proteins responsible for transporting metal ions in all
vertebrates. However, the iron binding properties of transferrins remain poorly
understood. Iron, as a transition metal, forms ions with partially-occupied 3d
subshells. The electrons within the 3d orbitals of iron-bound transferrin are
therefore highly localized, and interact with one another in a complex manner
that cannot be fully characterized by considering each electron separately. In
this work, we make use of dynamical mean field theory, a technique that
accounts for the strong interactions between these electrons. This is a higher
level of theory than has ever been used to study transferrins. We present novel
data on the effective spin, multiplet states and optical spectra of iron-bound
human serum transferrin.",2202.10818v1
2022-04-05,IRON: Inverse Rendering by Optimizing Neural SDFs and Materials from Photometric Images,"We propose a neural inverse rendering pipeline called IRON that operates on
photometric images and outputs high-quality 3D content in the format of
triangle meshes and material textures readily deployable in existing graphics
pipelines. Our method adopts neural representations for geometry as signed
distance fields (SDFs) and materials during optimization to enjoy their
flexibility and compactness, and features a hybrid optimization scheme for
neural SDFs: first, optimize using a volumetric radiance field approach to
recover correct topology, then optimize further using edgeaware physics-based
surface rendering for geometry refinement and disentanglement of materials and
lighting. In the second stage, we also draw inspiration from mesh-based
differentiable rendering, and design a novel edge sampling algorithm for neural
SDFs to further improve performance. We show that our IRON achieves
significantly better inverse rendering quality compared to prior works. Our
project page is here: https://kai-46.github.io/IRON-website/",2204.02232v1
2022-07-18,Study of Thin Iron Films for Polarization Analysis of Ultracold Neutrons,"The TUCAN (TRIUMF Ultra-Cold Advanced Neutron) collaboration aims to search
for the neutron electric dipole moment (nEDM) with unprecedented precision. One
of the essential elements for the nEDM measurement is a polarization analyzer
of ultracold neutrons (UCNs), whose main component is a magnetized thin iron
film. Several thin iron films were deposited on aluminum and silicon ubstrates
and were characterized by vibrating sample magnetometry and cold-neutron
reflectometry. A magnetic field required to saturate the iron film is $\sim$12
kA/m for those on the aluminum substrates and 6.4 kA/m for the silicon
substrates. The magnetic potential of the iron films on the Si substrate was
estimated to be 2 T by the neutron reflectometry, which is sufficient
performance for an UCN polarization analyzer of the nEDM measurement.",2207.08441v1
2022-09-17,Theoretical predictions of melting behaviors of hcp iron up to 4000 GPa,"The high-pressure melting diagram of iron is a vital ingredient for the
geodynamic modeling of planetary interiors. Nonetheless, available data for
molten iron show an alarming discrepancy. Herein, we propose an efficient
one-phase approach to capture the solid-liquid transition of iron under extreme
conditions. Our basic idea is to extend the statistical moment method to
determine the density of iron in the TPa region. On that basis, we adapt the
work-heat equivalence principle to appropriately link equation-of-state
parameters with melting properties. This strategy allows explaining
cutting-edge experimental and ab initio results without massive computational
workloads. Our theoretical calculations would be helpful to constrain the
chemical composition, internal dynamics, and thermal evolution of the Earth and
super-Earths.",2209.08220v1
2022-10-24,Electronic properties and surface states of RbNi$_2$Se$_2$,"Iron-based superconductors, with the ThCr$_{2}$Si$_{2}$-type tetragonal
structure (122 family), due to the iron arsenide/selenide layers exhibit
several characteristic electronic properties. For example, multiband character
mosty associated with the $d$-orbitals of iron and the quasi-two-dimensional
(2D) cylindrical Fermi surface. Moreover, external hydrostatic pressure leads
to the isostructural phase transition from the tetragonal to
collapsed-tetragonal phase. In this paper, in relation to the iron-based
superconductors, we discuss the electronic properties of novel 122-family
member RbNi$_{2}$Se$_{2}$ [Liu H. et al., Phys. Rev. B 106, 094511 (2022)]. We
show that the two Fermi pockets exhibit quasi-2D character. Calculation of the
surface spectral function for the (001) surface shows that the surface states
are realized independently on the surface termination. Additionally, contrary
to the iron-based 122 compounds, RbNi$_{2}$Se$_{2}$ exhibits extraordinary
multiple isostructural phase transitions under pressure. Moreover, the Lifshizt
transition occurs under external pressure, which results into a strong
modification of the shapes of the Fermi pockets.",2210.13280v2
2023-06-08,Iron Oxide Nanoparticles as a Contrast Agent for Synchrotron Imaging of Sperm,"Fast phase-contrast imaging offered by modern synchrotron facilities opens
the possibility of imaging dynamic processes of biological material such as
cells. Cells are mainly composed of carbon and hydrogen, which have low X-ray
attenuation, making cell studies with X-ray tomography challenging. At specific
low energies, cells provide contrast, but cryo-conditions are required to
protect the sample from radiation damage. Thus, non-toxic labelling methods are
needed to prepare living cells for X-ray tomography at higher energies. We
propose using iron oxide nanoparticles due to their proven compatibility in
other biomedical applications. We show how to synthesize and attach iron oxide
nanoparticles and demonstrate that cell-penetrating peptides facilitate iron
oxide nanoparticle uptake into sperm cells. We show results from the TOMCAT
Nanoscope (Swiss Light Source), showing that iron oxide nanoparticles allow the
heads and midpiece of fixed sperm samples to be reconstructed from X-ray
projections taken at 10 keV.",2309.03908v1
2023-12-05,Iron and gold thin films: first-principles study,"Using density functional theory, we carried out systematic calculations for a
series of ultrathin iron layers with thicknesses ranging from one atomic
monolayer to eleven monolayers (up to about 1.5 nm). We considered three cases:
(1) iron layers both on a gold substrate and coated with gold, (2) iron layers
on a gold substrate but without coverage, and (3) freestanding iron layers
adjacent to a vacuum. For our models, we chose initial bcc Fe(001) surfaces and
fcc Au(001) substrates. Based on the calculations, we determined the details of
the geometry and magnetic properties of the systems. We calculate lattice
parameters, magnetic moments, Curie temperatures and magnetocrystalline
anisotropy energies. From the thickness dependence, we determined the volume
and surface contributions to the magnetic anisotropy constant. The further
analysis allowed us to determine the thickness ranges of the occurrence of
perpendicular magnetic anisotropy, as well as the effect of thickness and the
presence of a substrate and cap layer on the direction of the magnetization
easy axis.",2312.02701v1
2024-01-11,Boundary-induced phase in epitaxial iron layers,"We report the discovery of a boundary-induced body-centered tetragonal (bct)
iron phase in thin films deposited on MgAl$_{2}$O$_{4}$ ($001$) substrates. We
present evidence for this phase using detailed x-ray analysis and ab-initio
density functional theory calculations. A lower magnetic moment and a rotation
of the easy magnetisation direction are observed, as compared to body-centered
cubic (bcc) iron. Our findings expand the range of known crystal and magnetic
phases of iron, providing valuable insights for the development of
heterostructure devices using ultra-thin iron layers.",2401.05990v1
2024-02-05,Influence of graphene on the electronic and magnetic properties of an iron(III) porphyrin chloride complex,"Although iron-based catalysts are regarded as a promising alternative to
precious metal catalysts, their precise electronic structures during catalysis
still pose challenges for computational descriptions. A particularly urgent
question is the influence of the environment on the electronic structure, and
how to describe this properly with computational methods. Here, we study an
iron porphyrin chloride complex adsorbed on a graphene sheet using density
functional theory calculations to detail how much the electronic structure is
influenced by the presence of a graphene layer. Our results indicate that weak
interactions due to van der Waals forces dominate between the porphyrin complex
and graphene, and only a small amount of charge is transferred between the two
entities. Furthermore, the interplay of the ligand field environment, strong
$p$ $-$ $d$ hybridization, and correlation effects within the complex are
strongly involved in determining the spin state of the iron ion. By bridging
molecular chemistry and solid state physics, this study provides first steps
towards a joint analysis of the properties of iron-based catalysts from first
principles.",2402.03544v1
1998-05-14,An RXTE Observation of the Seyfert 1 Galaxy MCG-6-30-15 : X-ray Reflection and the Iron Abundance,"We report on a 50 ks observation of the bright Seyfert 1 galaxy MCG--6-30-15
with the Rossi X-ray Timing Explorer. The data clearly show the broad
fluorescent iron line (equivalent width ~ 250 eV), and the Compton reflection
continuum at higher energies. A comparison of the iron line and the reflection
continuum has enabled us to constrain reflective fraction and the elemental
abundances in the accretion disk. Temporal studies provide evidence that
spectral variability is due to changes in both the amount of reflection seen
and the properties of the primary X-ray source itself.",9805198v1
2002-03-12,Ionized iron Kαlines in AGN X-ray spectra,"The Equivalent Widths (EW) of the He- and H-like iron lines produced in
photoionized, circumnuclear matter of AGN are calculated with respect to both
the reflected and the total continua. We found that the EWs with respect tothe
total continuum may be as large as a few tens of eV, making them observable in
bright Seyfert 1s by instruments on board Chandra and XMM-Newton. We apply our
calculations to the XMM-Newton spectrum of NGC 5506 and found a good agreement
with the data at the expense of a modest iron overabundance.",0203178v1
2004-09-14,Spectroscopic Equilibrium of Iron in Metal-Rich Dwarfs,"We analyze twenty five nearby metal-rich G and late-F dwarfs in order to
verify whether the spectroscopic equilibrium (LTE) of iron lines satisfy the
observational constraints imposed by the Infrared Flux Method (angular
diameters) and Hipparcos parallaxes. The atmospheric parameters derived from
iron lines (assuming LTE and employing 1D Kurucz model atmospheres) do not
satisfy simultaneously both observational constraints, probably because
classical modeling fails to reproduce the detailed line formation of FeI lines.",0409347v1
2004-12-16,On the thermal behaviour of small iron grains,"The optical properties of small spherical iron grains are derived using a
Kramers-Kronig-consistent model of the dielectric function including its
dependence on temperature and size. Especially discussed is the effect of the
size dependence, which results from the limitation of the free path of the free
electrons in the metal by the size of the grain, on the absorption behaviour of
small iron spheres and spheroids. The estimated absorption properties are
applied to study the temperature behaviour of spherical and spheroidal grains
which are heated by the interstellar radiation field.",0412425v2
2006-11-30,Instability strips of main sequence B stars: a parametric study of iron enhancement,"The discovery of beta Cephei stars in low metallicity environments, as well
as the difficulty to theoretically explain the excitation of the pulsation
modes observed in some beta Cephei and SPB stars, suggest that the iron opacity
``bump'' provided by standard models could be underestimated. We investigate,
by means of a parametric study, the effect of a local iron enhancement on the
location of the beta Cephei and SPB instability strips.",0611944v1
1998-06-02,The stabilizing role of itinerant ferromagnetism in inter-granular cohesion in iron,"We present a simple, general energy functional for ferromagnetic materials
based upon a local spin density extension to the Stoner theory of itinerant
ferromagnetism. The functional reproduces well available ab initio results and
experimental interfacial energies for grain boundaries in iron. The model shows
that inter-granular cohesion along symmetric tilt boundaries in iron is
dependent upon strong magnetic structure at the interface, illuminates the
mechanisms underlying this structure, and provides a simple explanation for
relaxation of the atomic structure at these boundaries.",9806034v1
2001-10-15,Superconductivity in compressed iron: Role of spin fluctuations,"The recent discovery of superconductivity in hexagonal iron under pressure
poses a question about whether it is of conventional (phonon) or unconventional
(magnetic?) origin. We present first-principles calculations of the
electron-phonon coupling in iron at $P\agt 15$ GPa, and argue that a
conventional mechanism can explain the appearance of superconductivity, but not
its rapid disappearance at $P\agt 30$ GPa. We suggest that spin fluctuations,
ferro- and/or antiferromagnetic, play a crucial role in superconductivity in
this case.",0110297v1
2004-04-15,High-field magnetoresistance of Fe/GaAs/Fe tunnel junctions,"We investigate transport through 6 to 10 nm thin epitaxial GaAs(001) barriers
sandwiched between polycrystalline iron films. Apart from a pronounced
tunneling magnetoresistance effect (TMR) at low magnetic fields we observe a
distinct negative magnetoresistance (MR) at low and a positive MR at higher
temperatures. We show that the negative MR contribution is only observed for
the ferromagnetic iron contacts but is absent if iron is replaced by copper or
gold electrodes. Possible explanations of the negative MR involve suppression
of spin-flip scattering or Zeeman splitting of the tunneling barrier.",0404351v1
2004-06-16,Development of an interatomic potential for phosphorus impurities in iron,"We present the derivation of an interatomic potential for the iron phosphorus
system based primarily on {\it ab initio} data. Transferrability in this system
is extremely problematic, and the potential is intended specifically to address
the problem of radiation damage and point defects in iron containing low
concentrations of phosphorus atoms. Some preliminary molecular dynamics
calculations show that P strongly affects point defect migration.",0406356v1
2006-12-30,Low relaxation rate in a low-Z alloy of iron,"The longest relaxation time and sharpest frequency content in ferromagnetic
precession is determined by the intrinsic (Gilbert) relaxation rate \emph{$G$}.
For many years, pure iron (Fe) has had the lowest known value of $G=\textrm{57
Mhz}$ for all pure ferromagnetic metals or binary alloys. We show that an
epitaxial iron alloy with vanadium (V) possesses values of $G$ which are
significantly reduced, to 35$\pm$5 Mhz at 27% V. The result can be understood
as the role of spin-orbit coupling in generating relaxation, reduced through
the atomic number $Z$.",0701004v1
1998-01-21,Total and Parity-Projected Level Densities of Iron-Region Nuclei by the Shell Model Monte Carlo Method,"Total and parity-projected level densities of iron-region nuclei are
calculated microscopically by using Monte Carlo methods for the nuclear shell
model in the complete $(pf+0g_{9/2})$-shell. The calculated total level density
is found to be in good agreement with the experimental level density. The Monte
Carlo calculations offer a significant improvement over the thermal
Hartree-Fock approximation. Contrary to the Fermi gas model, it is found that
the level density has a significant parity-dependence in the neutron resonance
region. The systematics of the level density parameters (including shell
effects) in the iron region is presented.",9801042v1
2001-08-01,Hybrid Rings of Fixed 8T Superconducting Magnets and Iron Magnets Rapidly Cycling between -2T and +2T for a Muon Collider,"Two 2200m radius hybrid rings of fixed superconducting magnets and iron
magnets ramping at 200 Hz and 330 Hz are used to accelerate muons. Muons are
given 25 GeV of RF energy per orbit. Acceleration is from 250 GeV/c to 2400
GeV/c and requires a total of 86 orbits in both rings; 82% of the muons
survive. The total power consumption of the iron dipoles is 4 megawatts.
Stranded copper conductors and thin Metglas laminations are used to reduce
power losses.",0108001v1
2008-01-06,A comparison of the magnetic properties of Proton- and Iron-implanted graphite,"In this work we have investigated the changes of the magnetic properties of
highly oriented pyrolytic graphite samples after irradiation either with $\sim
3 \times 10^{14}$ protons or $ 3.5 \times 10^{13} ... 3.5 \times 10^{14}$ iron
ions with energies in the MeV range. Our results show that iron and proton
irradiations can produce similar paramagnetic contributions depending on the
implantation temperature. However, only protons induce a ferromagnetic effect.",0801.0850v1
2008-05-22,Iron nanoparticle formation in a metal-organic matrix: from ripening to gluttony,"A simple method for the fabrication of metal nanoparticles is introduced.
Heating metal-organic crystals in vacuum results in the formation of well
defined metal particles embedded in a carbon matrix. The method is demonstrated
for iron-phthalocyanine. At 500C homogeneously distributed iron nanoparticles
with a reasonably narrow size distribution form by nucleation and ripening.
After this initial phase the formation kinetics changes drastically. The
particles move in the matrix to incorporate material. The ""gluttony"" phase
shows astonishing similarities with the search for nutrition of living
micro-organisms. Particle formation, ripening and gluttony are followed in-situ
by transmission electron microscopy.",0805.3416v1
2008-08-14,Synthesis and superconducting properties of the iron oxyarsenide TbFeAsO0.85,"The iron oxyarsenide TbFeAsO0.85 was synthesized by a high-pressure method. A
high-quality polycrystalline sample was obtained and characterized by
measurements of magnetic susceptibility and electrical resistivity. Bulk
superconductivity with Tc of 42 K was clearly established without an F doping
usually conducted to tune on superconductivity in the iron oxypnictide.",0808.1948v1
2008-11-11,Theory of Andreev reflection in junctions with iron-based High-$T_c$ superconductors,"We construct a theory for low-energy quantum transport in
normal$\mid$superconductor junctions involving the recently discovered
iron-based high-$T_c$ superconductors. We properly take into account both
Andreev bound surface states and the complex Fermi surface topology in our
approach, and investigate the signatures of the possible order parameter
symmetries for the FeAs-lattice. Our results could be helpful in determining
the symmetry of the superconducting state in the iron-pnicitide
superconductors.",0811.1775v1
2008-11-17,Effect of hybridization on structural and magnetic properties of iron-based superconductors,"We show that the strong hybridization between the iron 3d and the arsenic 4p
orbitals, in the newly discovered iron-based high-T$_{c}$ superconductors,
leads to an explanation of certain experimental observations that are presently
not well understood. The existence of a lattice distortion, the smallness of
the Fe magnetic moment in the undoped systems, and the suppression of both the
lattice distortion and the magnetic order upon doping with fluorine, are all
shown to result from this hybridization.",0811.2716v1
2008-12-17,Phase-Sensitive measurements on the corner junction of iron-based superconductor BaFe1.8Co0.2As2,"We have made a phase-sensitive measurement on the corner junction of the
iron-based superconductor BaFe1.8Co0.2As2, and observed the typical
Fraunhofer-like diffraction pattern. The result suggests that there is no phase
shift between the a-c face and b-c face of a crystal, which indicates that the
superconducting wavefunction of the iron based superconductor is different from
that of a cuprate superconductor.",0812.3295v1
2009-02-19,Is the nature of magnetic order in copper-oxides and in iron-pnictides different?,"We use the results of first-principles electronic structure calculations and
a strong coupling perturbation approach, together with general theoretical
arguments, to illustrate the differences in super-exchange interactions between
the copper-oxides and iron-pnictides. We show that the two magnetic ground
states can be understood in a simple manner within the same theoretical
foundation. Contrary to the emerging view that magnetic order in the
iron-pnictides is of itinerant nature, we argue that the observed magnetic
moment is small because of frustration introduced by the electrons of the Fe
orbitals as they compete to impose their preferred magnetic ordering.",0902.3450v1
2009-03-06,On the mechanism of high-temperature superconductivity in the iron based pnictides,"The recent discovery of superconductivity at moderately high temperature (26
K to 55 K) in doped iron-based pnictides (LnO_{1-x}F_xFeAs, where Ln = La, Ce,
Sm, Pr, Nd, etc.), having layered-structure-like cuprates, has triggered
renewed challenge towards understanding the pairing mechanism.
  After reviewing the current findings on these systems, a theoretical model of
a combined mechanism is suggested in which the phonon-mediated and
distortion-field-mediated pairing processes give the right order of
superconducting critical temperature T_c. The distortion-field modes arise from
Jahn-Teller or pseudo Jahn-Teller effects due to degenerate or near-degenerate
iron 3d_{xz} and 3d_{yz} orbitals.",0903.1181v1
2009-03-25,Exchange Constants and Neutron Spectra of Iron Pnictide Materials,"We show that the neutron scattering spectra observed in CaFe$_2$As$_2$ by
Zhao et al (arXiv:0903.2686v1) and the highly unusual spatially anisotropic
exchange constants in the iron pnictides derived by Han et al (Phys. Rev. Lett.
102, 107003 (2009)), using electronic structure calculations, can be explained
by assuming a role for orbital order in these materials. We write down a simple
model Hamiltonian with tertagonal symmetry, whose spin-wave spectra describes
the observed dispersion relations. We further argue that these materials have
orbital selective Mott transition, which is driven by superexchange between
neighboring iron atoms. We suggest that reduced spin and quasi-one
dimensionality and not frustration are responsible for the reduced moments in
these materials.",0903.4408v1
2009-06-11,To What Extent Iron-Pnictide New Superconductors Have Been Clarified: A Progress Report,"In this review, the authors present a summary of experimental reports on
newly discovered iron-based superconductors as they were known at the end of
2008. At the same time, this paper is intended to be useful for experimenters
to know the current status of these superconductors. The authors introduce
experimental results that reveal basic physical properties in the normal and
superconducting states. The similarities and differences between iron-pnictide
superconductors and other unconventional superconductors are also discussed.",0906.2045v1
2009-09-08,Is Fermi-surface nesting the origin of superconductivity in iron pnictides?: A fluctuation-exchange-approximation study,"We study whether Fermi-surface (FS) nesting can give rise to high-temperature
superconductivity in iron pnictides. Starting with ab initio construction of an
effective four-orbital model, we employ the fluctuation-exchange approximation
to show that FS does not necessarily favor the stripe antiferromagnetic order
observed in experiments, especially for realistic electronic correlations. If
superconductivity in iron pnictides is magnetically mediated and has
fully-gapped sign-reversing s-wave symmetry, our results suggest that the
pairing interaction does not arise only from FS nesting and exchange
interactions between local moments in the Fe 3d orbitals may play a crucial
role.",0909.1413v1
2009-10-14,Magnetic Excitations of Undoped Iron Oxypnictides,"We study the magnetic excitations of undoped iron oxypnictides using a
three-dimensional Heisenberg model with single-ion anisotropy. Analytic forms
of the spin wave dispersion, velocities, and structure factor are given. Aside
from quantitative comparisons which can be made to inelastic neutron scattering
experiments, we also give qualitative criteria which can distinguish various
regimes of coupling strength. The magnetization reduction due to quantum zero
point fluctuations shows clear dependence on the c-axis coupling.",0910.2528v1
2010-04-17,Looking at the superconducting gap of iron pnictides,"THz and infrared spectroscopy is widely utilized to investigate the
electrodynamic properties of the novel iron-based superconductors in the normal
and superconducting states. Besides electronic excitations and correlations,
electron-phonon coupling and the influence of magnetism, the experiments yield
important information on low-lying excitations and help to clarify the number
and symmetry of superconducting gaps. While the experimental data of different
groups converge, the interpretation is still under debate. Here we review the
status of optical investigations on the superconducting state for the 122 and
11 family of iron pnictides.",1004.2962v1
2010-04-27,Magnetic Ordering in Blocking Layer and Highly Anisotropic Electronic Structure of High-Tc Iron-based Superconductor Sr2VFeAsO3: LDA+U Studies,"We calculate electronic structures of a high-Tc iron-based superconductor
Sr2VFeAsO3 by LDA+U method. We assume a checker-board antiferromagnetic order
on blocking layers including vanadium and strong correlation in d-orbits of
vanadium through the Hubbard U. While the standard LDA brings about metallic
blocking layers and complicated Fermi surface as in the previous literatures,
our calculation changes the blocking layer into insulating one and the Fermi
surface becomes quite similar to those of other iron-based superconductors.
Moreover, the appearance of the insulating blocking layers predicts high
anisotropy on quasi-particle transports and new types of intrinsic Josephson
effects.",1004.4741v1
2010-06-11,"First Homologous Series of Iron Pnictide Oxide Superconductors (Fe2As2)(Can+1(Sc,Ti)nOy) [n = 3,4,5] with Extremely Thick Blocking Layers","We have discovered first homologous series of iron pnictide oxide
superconductors (Fe2As2)(Can+1(Sc,Ti)nOy) [n = 3,4,5]. These compounds have
extremely thick blocking layers up to quintuple perovskite oxide layers
sandwiched by the Fe2As2 layers. These samples exhibited bulk superconductivity
with relatively high Tc up to 42 K. The relationship between Tc and the
iron-plane interlayer distance suggested that superconductivity due to the mono
Fe2As2 layer is substantially 40 K-class.",1006.2355v2
2010-08-09,Electronic structure and total energy of interstitial hydrogen in iron: Tight binding models,"An application of the tight binding approximation is presented for the
description of electronic structure and interatomic force in magnetic iron,
both pure and containing hydrogen impurities. We assess the simple canonical
d-band description in comparison to a non orthogonal model including s and d
bands. The transferability of our models is tested against known properties
including the segregation energies of hydrogen to vacancies and to surfaces of
iron. In many cases agreement is remarkably good, opening up the way to quantum
mechanical atomistic simulation of the effects of hydrogen on mechanical
properties.",1008.1499v4
2010-08-25,Electronic correlations at the alpha-gamma structural phase transition in paramagnetic iron,"We compute the equilibrium crystal structure and phase stability of iron at
the alpha(bcc)-gamma(fcc) phase transition as a function of temperature, by
employing a combination of ab initio methods for calculating electronic band
structures and dynamical mean-field theory. The magnetic correlation energy is
found to be an essential driving force behind the alpha-gamma structural phase
transition in paramagnetic iron.",1008.4342v2
2010-10-20,Templated self-assembly of iron oxide nanoparticles,"We report on self-assembled iron oxide nanoparticle films on silicon
substrates. In addition to homogeneously assembled layers, we fabricated
patterned trenches of 40-1000 nm width using electron beam lithography for the
investigation of assisted self-assembly. The nanoparticles with a diameter of
20 nm +/- 7% were synthesized by thermal decomposition of iron oleate complexes
in trioctylamine in presence of oleic acid. Samples with different track widths
and nanoparticle concentration were characterized by scanning electron
microscopy and by superconducting quantum interference device magnetometry.",1010.4166v1
2011-04-08,Spin fluctuations in LiFeAs observed by neutron scattering,"We report neutron inelastic scattering measurements on the stoichiometric
iron-based superconductor LiFeAs. We find evidence for (i) magnetic scattering
consistent with strong antiferromagnetic fluctuations, and (ii) an increase in
intensity in the superconducting state at low energies, similar to the resonant
magnetic excitation observed in other iron-based superconductors. The results
do not support a recent theoretical prediction of spin-triplet p-wave
superconductivity in LiFeAs, and instead suggest that the mechanism of
superconductivity is similar to that in the other iron-based superconductors.",1104.1609v1
2011-06-02,Cubic to hexagonal iron phase transition promoted by interstitial hydrogen,"Using ab-initio density functional theory we study the role of interstitial
hydrogen on the energetics of the phase transformation of iron from bcc to hcp
along Bain's pathway. The impurity creates an internal stress field that can be
released through a tetragonal distortion of the lattice, promoting the bcc
(ferromagnetic) $\rightarrow$ fcc (frustrated antiferromagnetic) $\rightarrow$
hcp (ferromagnetic) transition. The transformation between crystal systems is
accompanied by a drastic magnetic reorganization and sudden variations of the
unit cell volume, that can be one of the reasons for embrittlement and
mechanical failure of iron upon hydrogen adsorption.",1106.0386v1
2011-09-19,Local Quantum Criticality of an Iron-Pnictide Tetrahedron,"Motivated by the close correlation between transition temperature ($T_c$) and
the tetrahedral bond angle of the As-Fe-As layer observed in the iron-based
superconductors, we study the interplay between spin and orbital physics of an
isolated iron-arsenide tetrahedron embedded in a metallic environment. Whereas
the spin Kondo effect is suppressed to low temperatures by Hund's coupling, the
orbital degrees of freedom are expected to quantum mechanically quench at high
temperatures, giving rise to an overscreened, non-Fermi liquid ground-state.
Translated into a dense environment, this critical state may play an important
role in the superconductivity of these materials.",1109.4131v2
2011-11-02,Thin Film Growth and Device Fabrication of Iron-Based Superconductors,"Iron-based superconductors have received much attention as a new family of
high-temperature superconductors owing to their unique properties and distinct
differences from cuprates and conventional superconductors. This paper reviews
progress in thin film research on iron-based superconductors since their
discovery for each of five material systems with an emphasis on growth,
physical properties, device fabrication, and relevant bulk material properties.",1111.0358v1
2011-11-15,The Pressure Effects on Electronic Structure of Iron Chalcogenide Superconductors FeSe$_{1-x}$Te$_x$,"We study the electronic structure of iron-based superconductors
FeSe$_{1-x}$Te$_x$ within the density functional theory. We pay particular
attention to the pressure effects on the Fermi surface (FS) topology, which
seem to be correlated with a critical superconducting temperature TC of iron
chalcogenides and pnictides. A reduction of the FS nesting between hole and
electron cylinders with increasing pressure is observed, which can lead to
higher values of TC . The tellurium substitution into selenium sites yields FS
changes similar to the pressure effect.",1111.3523v2
2012-05-15,Magnetic softness in iron-based superconductors,"We examine the relevance of several major material-dependent parameters to
the magnetic softness in iron-base superconductors by first-principles
electronic structure analysis of their parent compounds. The results are
explained in the spin-fermion model where localized spins and orbitally
degenerate itinerant electrons coexist and are coupled by Hund's rule coupling.
We found that the difference in the strength of the Hund's rule coupling term
is the major material-dependent microscopic parameter for determining the
ground-state spin pattern. The magnetic softness in iron-based superconductors
is essentially driven by the competition between the double-exchange
ferromagnetism and the superexchange antiferromagnetism.",1205.3509v1
2012-10-10,Raman scattering in iron-based superconductors,"Iron-based superconducting layered compounds have the second highest
transition temperature after cuprate superconductors. Their discovery is a
milestone in the history of high-temperature superconductivity and will have
profound implications for high-temperature superconducting mechanism as well as
industrial applications. Raman scattering has been extensively applied to
correlated electron systems including the new superconductors due to its unique
ability to probe multiple primary excitations and their coupling. In this
review, we will give a brief summary of the existing Raman experiments in the
iron-based materials and their implication for pairing mechanism in particular.
And we will also address some open issues from the experiments.",1210.2889v1
2013-03-25,TAO pairing: a fully gapped pairing scenario for the Iron-Based Superconductors,"Motivated by the fully gapped superconductivity in iron-based superconductors
with uncompensated electron pockets, we propose a spin singlet, but orbital
triplet analogue of the superfluid phase of He-3B. We show that orbital
triplets with a nominal d-wave symmetry at the iron sites can transform as
s-wave pairs under rotations about the selenium sites. Linear combinations of
such d$_{xy}$ and d$_{x^{2}-y^{2}}$ triplets form a fully gapped, topological
superconductor. Raman-active excitations are predicted to develop below the
superconducting transition temperature.",1303.6325v4
2013-11-16,Coexisting Itinerant and Localized Electrons in Iron-Based Superconductors,"The surprising discovery of high-$T_c$ superconductivity in iron-based
compounds has prompted an intensive investigation on the role of interaction
and magnetism in the these materials. Based on the general features of
multi-bands and intermediate coupling strengths, a phenomenological theory of
coexisting itinerant and localized electrons has been proposed to describe the
low-energy physics in iron-based superconductors. It provides a unified
framework to understand magnetic, superconducting, and normal phases, subject
to further microscopic justification and experimental verification.",1311.4094v2
2014-01-14,Unconventional superconductivity in iron-base superconductors in a three-band model,"Iron-base superconductors exhibits features of systems where the
Fulde-Ferrel-Larkin-Ovchinnikov (FFLO) phase, a superconducting state with
non-zero total momentum of Cooper pairs, is actively sought. Experimental and
theoretical evidence points strongly to the FFLO phase in these materials above
the Pauli limit. In this article we discuss the ground state of iron-base
superconductors near the critical magnetic field and the full $h-T$ phase
diagram for pnictides in case of intra-band pairing, in a three-band model with
$s_{\pm}$ symmetry.",1401.3066v1
2014-02-28,Antiferromagnetism in Iron-Based Superconductors: Selection of Magnetic Order and Quasiparticle Interference,"The recent discovery of superconductivity in the iron-based layered pnictides
with T_c ranging between 26 and 56K generated enormous interest in the physics
of these materials. Here, we review some of the peculiarities of the
antiferromagnetic order in the iron pnictides, including the selection of the
stripe magnetic order and the formation of the Ising-nematic state in the
unfolded BZ within an itinerant description. In addition we analyze the
properties of the quasiparticle interference spectrum in the parent
antiferromagnetic phase.",1402.7206v1
2014-08-18,Relativistic configuration-interaction calculation of $Kα$ transition energies in beryllium-like iron,"We perform relativistic configuration-interaction calculations of the energy
levels of the low-lying and core-excited states of beryllium-like iron,
Fe$^{22+}$. The results include the QED contributions calculated by two
different methods, the model QED operator approach and the screening-potential
approach. The uncertainties of theoretical energies are estimated
systematically. The predicted wavelengths of the K\alpha transitions in
beryllium-like iron improve previous theoretical results and compare favorably
with the experimental data.",1408.3949v1
2015-05-19,Electromagnetic acceleration of permanent magnets,"We consider the acceleration of the permanent magnets, consisting of
neodymium iron boron by means of the running magnetic field gradient. It is
shown that the specific magnetic moment per nucleon in neodymium iron boron is
determined by the remained magnetization of the substance. The maximum
accessable gradient of the magnetic field accelerating the permanent magnets is
determined by the coercive force thirty kilogauss. For the neodymium iron boron
magnets this gradient is equal to twenty kilogauss divided by one centimeter.
The finite velocity of the magnets six kilometers per second, the length of
acceleration is six hundred thirty-seven meters.",1508.04078v1
2016-02-17,On the analysis of stage I in the resistivity recovery of electron irradiated iron,"The experimental results of Takaki et al. [1] on the stage I resistivity
recovery of electron irradiated iron are analyzed using the analytical theory
of diffusion annealing formulated by Simpson & Sossin [2] and Schroeder [3]
taking into account the recent first-principles calculations of Fu et al. [4]
regarding the mobility of interstitials. Excellent agreement between theory and
experiment is obtained by a minimal set of adjustable parameters. The results
show that the diffusion annealing equations can be successfully employed for
the analysis of recovery experiments in iron.",1602.05449v2
2017-09-11,Magnetic order and phase transition in the iron oxysulfide La2O2Fe2OS2,"The Mott-insulating iron oxychalcogenides exhibit complex magnetic behaviour
and we report here a neutron diffraction investigation into the magnetic
ordering in La2O2Fe2OS2. This quaternary oxysulfide adopts the
anti-Sr2MnO2Sb2-type structure and orders antiferromagnetically below TN = 105
K. We consider both its long-range magnetic structure and its magnetic
microstructure, and the onset of magnetic order. It adopts the multi-k vector
""2k"" magnetic structure (k = (0.5 0 0.5) and k = (0 0.5 0.5) and has
similarities with related iron oxychalcogenides, illustrating the robust nature
of the ""2k"" magnetic structure.",1709.03323v1
2018-03-05,Using electron irradiation to probe iron - based superconductors,"High energy electron irradiation is an efficient way to create
vacancy-interstitial Frenkel pairs in crystal lattice, thereby inducing
controlled non-magnetic point - like scattering centers. In combination with
London penetration depth and resistivity measurements, the irradiation was
particularly useful as a phase - sensitive probe of the superconducting order
parameter in iron - based superconductors lending strongest support to sign -
changing $s_{\pm}$ pairing. Here we review the key results on the effect of
electron irradiation in iron-based superconductors.",1803.01956v1
2019-03-30,Shot Noise as a probe for the pairing symmetry of Iron pnictide superconductors,"One of the outstanding problems in Iron pnictide research is the unambiguous
detection of its pairing symmetry. The most probable candidates are the
two-band s$++$ and sign reversed s$\pm$ wave pairing. In this work, the Andreev
conductance and shot noise are used as a probe for the pairing symmetry of Iron
pnictide superconductors. Clear differences emerge in both the zero bias
differential conductance and the shot noise in the tunneling limit for the two
cases enabling an effective distinction between the two.",1904.00201v2
2022-04-07,Editorial on Research Topic: High-Tc Superconductivity in Electron-Doped Iron Selenide and Related Compounds,"In this editorial, we first give a brief survey of the field of iron-selenide
superconductivity, both in the case of bulk FeSe characterized by the
co-existence of superconductivity and nematic order, and in the case of
electron-doped FeSe characterized by high-temperature superconductivity. We
next review the 8 contributions to the Frontiers in Physics research topic
""High-Tc Superconductivity in Electron-Doped Iron Selenide and Related
Compounds"".",2204.03735v2
2022-08-25,Persistent homology analysis with nonnegative matrix factorization for 3D voxel data of iron ore sinters,"This paper proposes a data analysis method using persistent homology and
nonnegative matrix factorization. A concatenated persistence image technique is
used to extract coexisting structures from the persistence diagrams of
different dimensions hidden behind the data. To demonstrate the potential of
our method, we apply the method to 3D voxel data of iron ore sinters obtained
by X-ray computed tomography. The analysis successfully captures the
coexistence structures in these iron ore sinters.",2208.11943v1
2023-02-20,"Triplet pairing, orbital selectivity and correlations in Iron-based superconductors","We use a slave-boson approach to study the band renormalization and pair
susceptibility in the normal state of Iron-based superconductors in presence of
strong Coulomb repulsion and Hund's interaction. Our results show orbital
selectivity toward localization of $xy$ orbitals and its interplay with
superconductivity. We also compare the recently proposed triplet resonating
valence bond theory of superconductivity in Iron-based superconductors with the
more conventional $s_\pm$ pairing and show that both favor a superconductivity
when the $xy$ orbital is delocalized.",2302.09702v1
1996-07-03,ASCA observations of the iron K complex of Circinus X-1 near zero phase: spectral evidence for partial covering,"We report on ASCA energy spectra of Cir X-1 taken near its zero phase on 1994
August 4-5. The ASCA SIS detectors allow a more detailed study of the iron K
complex than has been possible before. We find that prior to a sudden upward
flux transition the dominant iron K feature appears to consist of a large edge
from neutral or nearly-neutral iron. The depth of the edge corresponds to an
absorption column of about 1.5E24 cm^{-2}, while little absorption over that
expected from the Galaxy is seen at lower X-ray energies. The differential
absorption at high and low X-ray energies combined with the iron edge energy
are strong evidence that partial covering is a crucial determinant of the
behaviour observed from Cir X-1. The continuum spectral variability observed by
ASCA can also be understood naturally in terms of partial covering column
changes. There is evidence for a relatively weak emission line from neutral
iron with an equivalent width of only about 65 eV. After the flux transition,
the strength of the edge feature is greatly reduced, suggesting a large
reduction in the amount of partial covering. For a large region of
statistically acceptable chi-squared parameter space, the luminosity of Cir
X-1, after correction for partial covering, need not change during the
transition. We discuss models for the partial covering and suggest that X-ray
scattering by electrons may be important. Aspects of the Cir X-1 spectrum are
very similar to those of Seyfert 2 galaxies with Compton-thin tori.",9607018v1
1997-05-19,Iron fluorescence from within the innermost stable orbit of black hole accretion disks,"The fluorescent iron Ka line is a powerful observational probe of the inner
regions of black holes accretion disks. Previous studies have assumed that only
material outside the radius of marginal stability can contribute to the
observed line emission. Here, we show that fluorescence by material inside the
radius of marginal stability, which is in the process of spiralling towards the
event horizon, can have a observable influence on the iron line profile and
equivalent width. For concreteness, we consider the case of a geometrically
thin accretion disk, around a Schwarzschild black hole, in which fluorescence
is excited by an X-ray source placed at some height above the disk and on the
axis of the disk. Fully relativistic line profiles are presented for various
source heights and efficiencies. It is found that the extra line flux generally
emerges in the extreme red wing of the iron line, due to the large
gravitational redshift experienced by photons from the region within the radius
of marginal stability. We apply our models to the variable iron line seen in
the ASCA spectrum of the Seyfert nucleus MCG-6-30-15. It is found that the
change in the line profile, equivalent width, and continuum normalization, can
be well explained as being due to a change in the height of the source above
the disk. We discuss the implications of these results for distinguishing
rapidly-rotating black holes from slowly rotating holes using iron line
diagnostics.",9705136v2
2002-02-22,The continuum variability of MCG--6-30-15: A detailed analysis of the long 1999 ASCA observation,"We report on an analysis in the 3--10 keV X-ray band of the long 1999 ASCA
observation of MCG--6-30-15. The time-averaged broad iron K line is
well-described by disk emission near a Schwarzschild black hole, confirming the
results of earlier analyses on the ASCA 1994 and 1997 data. The time-resolved
iron-line profile is remarkably stable over a factor of three change in source
flux, and the line and continuum fluxes are uncorrelated. Detailed fits to the
variable iron-line profile suggest that the active region (parametrized by the
best-fit inner and outer radii of the accretion disk) responsible for iron line
emission actually narrows with increasing flux to a region around 4--5 r_g. In
contrast to the iron line, the power-law continuum exhibits significant
variability during the 1999 observation. Time-resolved spectral analysis
reveals a new feature in the well-known photon index (Gamma) vs. flux
correlation: Gamma appears to approach a limiting value of Gamma ~ 2.1 at high
flux. Two models are proposed to explain both the new feature in the Gamma vs.
flux correlation and the uncorrelated iron-line flux: a phenomenological two
power-law model, and the recently proposed ``thundercloud'' model of Merloni &
Fabian (2001). Both models are capable of reproducing the data well, but
because they are poorly constrained by the observed Gamma vs. flux relation,
they cannot at present be tested meaningfully by the data. The various
implications and the physical interpretation of these models are discussed.",0202432v1
2002-09-09,The X-ray spectrum of the Seyfert I galaxy Mrk 766: Dusty Warm Absorber or Relativistic Emission Lines?,"Competing models for broad spectral features in the soft X-ray spectrum of
the Seyfert I galaxy Mrk766 are tested against data from a 130 ks XMM-Newton
observation. A model including relativistically broadened Ly-alpha emission
lines of OVIII, NVII and CVI is a better fit to 0.3-2 keV XMM RGS data than a
dusty warm absorber. Moreover, the measured depth of neutral iron absorption
lines in the spectrum is inconsistent with the magnitude of the iron edge
required to produce the continuum break at 17-18Angstroms in the dusty warm
absorber model. The relativistic emission line model can reproduce the
broad-band (0.1-12 keV) XMM-EPIC data with the addition of a fourth line to
represent emission from ionized iron at 6.7 keV and an excess due to reflection
at energies above the iron line. The profile of the 6.7 keV iron line is
consistent with that measured for the low energy lines. There is evidence in
the RGS data at the 3sigma level for spectral features that vary with source
flux. The covering fraction of warm absorber gas is estimated to be ~12%. Iron
in the warm absorber is found to be overabundant with respect to CNO compared
to solar values.",0209145v1
2005-11-19,Thermal X-Ray Iron Line Emission from the Galactic Center Black Hole Sagittarius A*,"We model thermal X-ray emission from the accreting supermassive black hole
Sagittarius A* at the Galactic Center. For the region inside
$1.^{\prime\prime}5$ of the center, we use a {generalized} radiatively
inefficient accretion flow (RIAF) model, and for the region out to
$10^{\prime\prime}$ we use published models of the ambient hot gas. We
calculate the equivalent widths of Hydrogen-like and Helium-like emission lines
of various elements, notably iron. We predict that a strong Helium-like iron
line with an equivalent width $\sim1$ keV should be emitted by both the
external medium and the RIAF. The equivalent width in the external medium is
sensitive to the metallicity $Z$ of the gas as well as the mean temperature.
For reasonable choices of these parameters, the calculated results agree with
Chandra's detection of an iron line with an equivalent width of 1.3 keV within
$10^{\prime\prime}$. The emission from within $1.^{\prime\prime}5$ is not
sensitive to the external temperature, but is sensitive to the density and,
especially, temperature profile inside the Bondi radius. For the range of
profiles we consider, we calculate the equivalent width of the iron line to be
$\sim0.6-1.5 (Z/Z_\odot)$ keV, where $Z_\odot$ is the solar metallicity. We
present a new Chandra spectrum of the quiescent emission within
$1.^{\prime\prime}5$ of Sgr A*. The measured equivalent width of the iron line
is 0.7 keV. Although this measurement has a large uncertainty, it is consistent
with our predictions, provided the metallicity of the gas is approximately
solar.",0511590v1
2006-06-23,Fe-bump instability: the excitation of pulsations in subdwarf B and other low-mass stars,"We consider the excitation of radial and non-radial oscillations in low-mass
B stars by the iron-bump opacity mechanism. The results are significant for the
interpretation of pulsations in subdwarf B stars, helium-rich subdwarfs and
extreme helium stars, including the EC14026 and PG1716 variables. We
demonstrate that, for radial oscillations, the driving mechanism becomes
effective by increasing the contrast between the iron-bump opacity and the
opacity from other sources. The location of the iron-bump instability boundary
depends on the mean molecular weight in the envelope and also on the radial
order of the oscillation. A bluer instability boundary is provided by
increasing the iron abundance alone, explaining the observed EC14026 variables,
and by higher radial order oscillations. We show that the coolest EC14026
variables may vary in the fundamental radial mode, but the hottest variables
must be of higher radial order. In considering non-radial oscillations, we
demonstrate that g-modes of high radial order and low spherical degree (l<4)
may be excited in some blue horizontal branch stars with near-normal
composition (Z=0.02). Additional iron enhancement extends the g-mode
instability zone to higher effective temperatures and also creates a p-mode
instability zone. With sufficient iron, the p-mode and g-mode instability zones
overlap, allowing a small region where the EC14026 and PG1716-type variability
can be excited simultaneously. However its location is roughly 5000 K too low
compared with the observed boundary between EC14026 and PG1716 variables.",0606594v2
2008-03-03,Constraints on grain size and stable iron phases in the uppermost Inner Core from multiple scattering modeling of seismic velocity and attenuation,"We propose to model the uppermost inner core as an aggregate of randomly
oriented anisotropic ``patches''. A patch is defined as an assemblage of a
possibly large number of crystals with identically oriented crystallographic
axes. This simple model accounts for the observed velocity isotropy of short
period body waves, and offers a reasonable physical interpretation for the
scatterers detected at the top of the inner core. From rigorous multiple
scattering modeling of seismic wave propagation through the aggregate, we
obtain strong constraints on both the size and the elastic constants of iron
patches. We perform a systematic search for iron models compatible with
measured seismic velocities and attenuations. An iron model is characterized by
its symmetry (cubic or hexagonal), elastic constants, and patch size.
Independent of the crystal symmetry, we infer a most likely size of patch of
the order of 400 m. Recent {\it bcc} iron models from the literature are in
very good agreement with the most probable elastic constants of cubic crystals
found in our inversion. Our study (1) suggests that the presence of melt may
not be required to explain the low shear wavespeeds in the inner core and (2)
supports the recent experimental results on the stability of cubic iron in the
inner core, at least in its upper part.",0803.0264v1
2008-06-24,A BLR origin for the iron K$α$ line in NGC7213,"The X-ray spectrum of NGC7213 is known to present no evidence for Compton
reflection, a unique result among bright Seyfert 1s. The observed neutral iron
K$\alpha$ line, therefore, cannot be associated with a Compton-thick material,
like the disc or the torus, but is due to Compton-thin gas, with the Broad Line
Region (BLR) as the most likely candidate. To check this hypothesis, a long
Chandra HETG observation, together with a quasi-simultaneous optical
spectroscopic observation at the ESO NTT EMMI were performed. We found that the
iron line is resolved with a FWHM=$2 400^{+1 100}_{-600}$ km/s, in perfect
agreement with the value measured for the broad component of the H$\alpha$,
$2640^{+110}_{-90}$ km/s. Therefore, NGC7213 is the only Seyfert 1 galaxy whose
iron K$\alpha$ line is unambiguously produced in the BLR. We also confirmed the
presence of two ionised iron lines and studied them in greater detail than
before. The resonant line is the dominant component in the Fe XXV triplet,
therefore suggesting an origin in collisionally ionised gas. If this is the
case, the blueshift of around 1000 km/s of the two ionised iron lines could be
the first measure of the velocity of a starburst wind from its X-ray emission.",0806.3876v1
2008-08-04,Iron pnictides as a new setting for quantum criticality,"Two major themes in the physics of condensed matter are quantum critical
phenomena and unconventional superconductivity. These usually occur in the
context of competing interactions in systems of strongly-correlated electrons.
All this interesting physics comes together in the behavior of the recently
discovered iron pnictide compounds that have generated enormous interest
because of their moderately high-temperature superconductivity. The ubiquity of
antiferromagnetic ordering in their phase diagrams naturally raises the
question of the relevance of magnetic quantum criticality, but the answer
remains uncertain both theoretically and experimentally. Here we show that the
undoped iron pnictides feature a novel type of magnetic quantum critical point,
which results from a competition between electronic localization and
itinerancy. Our theory provides a mechanism to understand the
experimentally-observed variation of the ordered moment among the undoped iron
pnictides. We suggest P substitution for As in the undoped iron pnictides as a
means to access this new example of magnetic quantum criticality in an unmasked
fashion. Our findings point to the iron pnictides as a much-needed new setting
for quantum criticality, one that offers a new set of control parameters.",0808.0305v3
2008-09-18,A search for iron emission lines in the Chandra X-ray spectra of neutron star low-mass X-ray binaries,"While iron emission lines are well studied in black hole systems, both in
X-ray binaries and Active Galactic Nuclei, there has been less of a focus on
these lines in neutron star low-mass X-ray binaries (LMXBs). However, recent
observations with Suzaku and XMM-Newton have revealed broad asymmetric iron
line profiles in 4 neutron star LMXBs, confirming an inner disk origin for
these lines in neutron star systems. Here, we present a search for iron lines
in 6 neutron star LMXBs. For each object we have simultaneous Chandra and RXTE
observations at 2 separate epochs, allowing for both a high resolution
spectrum, as well as broadband spectral coverage. Out of the six objects in the
survey, we only find significant iron lines in two of the objects, GX 17+2 and
GX 349+2. However, we cannot rule out that there are weak, broad lines present
in the other sources. The equivalent width of the line in GX 17+2 is consistent
between the 2 epochs, while in GX 349+2 the line equivalent width increases by
a factor of ~3 between epochs as the source flux decreases by a factor of 1.3.
This suggests that the disk is highly ionized, and the line is dominated by
recombination emission. We find that there appears to be no specific locations
in the long-term hardness-intensity diagrams where iron emission lines are
formed, though more sources and further observations are required.",0809.3171v1
2009-04-01,The nature of the light variability of the silicon star HR 7224,"Although photometric variations of chemically peculiar (CP) stars are
frequently used to determine their rotational periods, the detailed mechanism
of their light variability remains poorly understood. We simulate the light
variability of the star HR 7224 using the observed surface distribution of
silicon and iron. We used the TLUSTY model atmospheres calculated for the
appropriate silicon and iron abundances to obtain the emergent flux and to
predict the rotationally modulated light curve of the star. We also obtained
additional photometric measurements and employed our own regression procedure
to derive a more precise estimate of the light elements. We show that the light
variation of the star can be explained as a result of i) the uneven surface
distribution of the elements, ii) the flux redistribution from the ultraviolet
to the visible part of the spectrum, and iii) rotation of the star. We show
that the silicon bound-free transitions and iron bound-bound transitions
provide the main contribution to the flux redistribution, although an
additional source of opacity is needed. We confirm that numerous iron lines
significantly contribute to the well-known depression at 5200 A and discuss the
connection between iron abundance and the value of peculiarity index a. The
uneven surface distribution of silicon and iron is able to explain most of the
rotationally modulated light variation in the star HR 7224.",0904.0231v1
2011-01-03,Thermal X-ray iron line emission from the advection dominated accretion flow in the galactic binary GX 339-4,"We explore thermal X-ray iron line emission from the galactic X-ray binary GX
339-4 in the off state, using the models of the advection dominated accretion
flow (ADAF) without or with outflows. The equivalent widths of hydrogen-like
and helium-like thermal iron lines are calculated with different model
parameters including viscosity parameter $\alpha$, mass accretion rate at the
outer radius of the ADAF $\dot{m}_{\rm out}$ and outflow strength parameter
$p$. Our calculations show that the equivalent widths of thermal iron lines
emitted from the pure ADAF, i.e., the ADAF without outflows, should be very
small, assuming a solar metallicity for the accreting gas in the accretion
flow. Strong thermal iron lines are expected to be emitted from the ADAF with
relatively strong outflows. {For reasonable choice of parameters, the total
equivalent width of the He-like and H-like thermal iron lines reaches to
$\gtrsim 500$ eV for accreting gas with solar metallicity. The observation of
strong thermal X-ray lines from GX 339-4 at the off state may give a clue to
the accretion mode of the source and provide evidence for the presence of
outflows/winds in the accretion flow around the black hole in GX 339-4. It is
found that the values of $\dot{m}_{\rm out}$ and $p$ are degenerate, i.e., the
observed X-ray continuum spectrum can be fairly well reproduced with different
sets of the parameters $\dot{m}_{\rm out}$ and $p$. Such {degeneracy} can be
broken when the thermal X-ray line emission data is available. We also compare
our results with those in the previous similar work.}",1101.0507v1
2011-08-24,The effects of aggregation and protein corona on the cellular internalization of iron oxide nanoparticles,"Engineered inorganic nanoparticles are essential components in the
development of nanotechnologies. For applications in nanomedicine, particles
need to be functionalized to ensure a good dispersibility in biological fluids.
In many cases however, functionalization is not sufficient : the particles
become either coated by a corona of serum proteins or precipitate out of the
solvent. In the present paper, we show that by changing the coating of iron
oxide nanoparticles from a low-molecular weight ligand (citrate ions) to small
carboxylated polymers (poly(acrylic acid)), the colloidal stability of the
dispersion is improved and the adsorption/internalization of iron towards
living mammalian cells is profoundly affected. Citrate-coated particles are
shown to destabilize in all fetal-calf-serum based physiological conditions
tested, whereas the polymer coated particles exhibit an outstanding
dispersibility as well as a structure devoid of protein corona. The
interactions between nanoparticles and human lymphoblastoid cells are
investigated by transmission electron microscopy and flow cytometry. Two types
of nanoparticle/cell interactions are underlined. Iron oxides are found either
adsorbed on the cellular membranes, or internalized into membrane-bound
endocytosis compartments. For the precipitating citrate-coated particles, the
kinetics of interactions reveal a massive and rapid adsorption of iron oxide on
the cell surfaces. The quantification of the partition between adsorbed and
internalized iron was performed from the cytometry data. The results highlight
the importance of resilient adsorbed nanomaterials at the cytoplasmic membrane.",1108.4779v1
2011-09-02,A first-principles study of helium storage in oxides and at oxide--iron interfaces,"Density-functional theory calculations based on conventional as well as
hybrid exchange-correlation functionals have been carried out to study the
properties of helium in various oxides (Al2O3, TiO2, Y2O3, YAP, YAG, YAM, MgO,
CaO, BaO, SrO) as well as at oxide-iron interfaces. Helium interstitials in
bulk oxides are shown to be energetically more favorable than substitutional
helium, yet helium binds to existing vacancies. The solubility of He in oxides
is systematically higher than in iron and scales with the free volume at the
interstitial site nearly independently of the chemical composition of the
oxide. In most oxides He migration is significantly slower and He--He binding
is much weaker than in iron. To quantify the solubility of helium at oxide-iron
interfaces two prototypical systems are considered (Fe|MgO, Fe|FeO|MgO). In
both cases the He solubility is markedly enhanced in the interface compared to
either of the bulk phases. The results of the calculations allow to construct a
schematic energy landscape for He interstitials in iron. The implications of
these results are discussed in the context of helium sequestration in oxide
dispersion strengthened steels, including the effects of interfaces and lattice
strain.",1109.0433v2
2012-08-21,Evolution of precipitate morphology during heat treatment and its implications for the superconductivity in KxFe1.6+ySe2 single crystals,"We study the relationship between precipitate morphology and
superconductivity in KxFe1.6+ySe2 single crystals grown by self-flux method.
Scanning electron microscopy (SEM) measurements revealed that superconducting
phase forms a network in the samples quenched above iron vacancy order-disorder
transition temperature Ts. For the samples obtained by natural cooling down to
room temperature in the furnace, referred to as furnace cooling,
superconducting phase aggregates into micrometer-sized rectangular bars and
aligns as disconnected chains. Accompanying this change in morphology the
superconducting shielding fraction is strongly reduced in the furnace-cooling
samples. By post-annealing above Ts followed by quenching in room temperature
water, the network recovers with superconducting shielding fraction approaching
80%. A reversible change from network to bar chains was realized by a secondary
heat treatment in annealed samples showing large shielding fraction, i.e.,
heating above Ts followed by slow cooling across Ts. The large shielding
fraction observed in KxFe1.6+ySe2 single crystals actually results from a
uniform and contiguous distribution of superconducting phase. Through the
measurements of temperature dependent x-ray diffraction, it is found that the
reflection corresponding to superconducting phase merges into that from iron
vacancy ordered phase upon warming. It is a solid solution above Ts, where iron
atoms randomly occupy the both Fe1 and Fe2 sites in iron vacancy disordering
status. By cooling across Ts, superconducting phase precipitates while iron
vacancy ordered phase forms together, suggesting that phase separation in
KxFe1.6+ySe2 single crystals is driven by the iron vacancy order-disorder
transition.",1208.4159v2
2012-10-24,The Unexpected Properties of Alkali Metal Iron Selenide Superconductors,"The iron-based superconductors that contain FeAs layers as the fundamental
building block in the crystal structures have been rationalized in the past
using ideas based on the Fermi Surface nesting of hole and electron pockets
when in the presence of weak Hubbard $U$ interactions. This approach seemed
appropriate considering the small values of the magnetic moments in the parent
compounds and the clear evidence based on photoemission experiments of the
required electron and hole pockets. However, recent results in the context of
alkali metal iron selenides, with generic chemical composition
$A_x$Fe$_{2-y}$Se$_2$ ($A$ = alkali element), have drastically challenged those
previous ideas since at particular compositions $y$ the low-temperature ground
states are insulating and display antiferromagnetic magnetic order with large
iron magnetic moments. Moreover, angle resolved photoemission studies have
revealed the absence of hole pockets at the Fermi level in these materials. The
present status of this exciting area of research, with the potential to alter
conceptually our understanding of the iron-based superconductors, is here
reviewed, covering both experimental and theoretical investigations. Other
recent related developments are also briefly reviewed, such as the study of
selenide two-leg ladders and the discovery of superconductivity in a single
layer of FeSe. The conceptual issues considered established for the alkali
metal iron selenides, as well as the several issues that still require further
work, are discussed in the text.",1210.6501v1
2013-02-08,X-ray diagnostics of chemical composition of the accretion disk and donor star in ultra-compact X-ray binaries,"Non-solar composition of the donor star in ultra-compact X-ray binaries may
have a pronounced effect on the fluorescent lines appearing in their spectra
due to reprocessing of primary radiation by the accretion disk and the white
dwarf surface. We show that the most dramatic and easily observable consequence
of the anomalous C/O abundance, is the significant, by more than an order of
magnitude, attenuation of the Ka line of iron. It is caused by screening of the
presence of iron by oxygen - in the C/O dominated material the main interaction
process for a E ~ 7keV photon is absorption by oxygen rather than by iron,
contrary to the solar composition case. Ionization of oxygen at high mass
accretion rates adds a luminosity dependence to this behavior - the iron line
is significantly suppressed only at low luminosity, log(LX) less than 37-37.5,
and should recover its nominal strength at higher luminosity. The increase of
the EW of the Ka lines of carbon and oxygen, on the other hand, saturates at
rather moderate values. Screening by He is less important, due to its low
ionization threshold and because in the accretion disk it is mostly ionized.
Consequently, in the case of the He-rich donor, the iron line strength remains
close to its nominal value, determined by the iron abundance in the accretion
disk. This opens the possibility of constraining the nature of donor stars in
UCXBs by means of X-ray spectroscopy with moderate energy resolution.",1302.2070v2
2013-03-26,Superconductivity and Crystal Structure of the Palladium-Iron-Arsenides Ca10(Fe1-xPdxAs)10Pd3As8,"The palladium-iron-arsenides Ca10(Fe1-xPdxAs)10(Pd3As8) were synthesized by
solid state methods and characterized by X-ray powder and single crystal
diffraction. The triclinic crystal structure (space group P-1) is isotypic to
the homologue platinum 1038 type superconductors with alternating FeAs4/4- and
Pd3As8-layers, each separated by layers of calcium atoms. Iron is tetrahedral
and palladium is planar coordinated by four arsenic atoms. As2-dimers (dAs-As =
250 pm) are present in the Pd3As8-layer. Even though each layer itself has a
fourfold rotational symmetry, the shifted layer stacking causes the triclinic
space group. Resistivity measurements of La-doped samples show the onset of
superconductivity at 17 K and zero resistivity below 10 K. The magnetic
shielding fraction is about 20 % at 3.5 K. 57Fe-M\""ossbauer spectra exhibit one
absorption line and show no hint to magnetic ordering. The electronic structure
is very similar to the known iron-arsenides with cylinder-like Fermi surfaces
and partial nesting between hole- and electron-like sheets. Our results show
that superconductivity in the palladium-iron-compounds is present but
complicated by too high substitution of iron by palladium in the active
FeAs-layers. Since the electronic preconditions are satisfied, we expect higher
critical temperatures in Pd1038-compounds with lower or even without Pd-doping
in the FeAs-layer.",1303.6579v1
2013-05-22,Iron abundance correlations and an occurrence distribution discrepancy from ongoing planet migration,"Whether the higher occurrence of giant planets being hosted by metal-rich
versus metal-poor stars results from formation or from ""pollution"" has been a
question of intense debate. We present new patterns that emerge when
planet/star systems are separated by stellar [Fe/H], and when systems with
stellar companions are separated out. These differences can best be explained
if the onset of high eccentricity planet migration is also a time when planet
are sent into merge with the star. Planet migration into the star is likely a
complementary explanation to the view that systems with higher initial iron
abundance form more planets, and that more crowded planets are more likely to
scatter into eccentric orbits. Planets of iron-rich single stars have
eccentricity distributions that are higher than planets of iron-poor single
stars (where ""rich"" and ""poor"" are stars whose [Fe/H] is above and below solar,
respectively). Stars with planets that have a stellar companion comprise a
third population of systems in which the stars are preferentially iron-rich. We
describe new patterns that are best explained by eccentric planet migration
being associated with other planets migrating into the star. Though medium
planets are more numerous than giant planets at periods greater than three
days, giant planets are more numerous than medium planets at the shortest
periods. Since giant planets migrate into the star faster, we show this as
evidence of giant planet migration. Planet migration into the star is certain
to be an important part of planetary system evolution.",1305.5197v2
2013-11-05,Spin dynamics and an orbital-antiphase pairing symmetry in iron-based superconductors,"The symmetry of the wave function describing the Cooper pairs is one of the
most fundamental quantities in a superconductor but its measurement in the
iron-based superconductors has proved to be very difficult. The complex
multi-band nature of these materials makes the interplay of superconductivity
with spin and orbital dynamics very intriguing, leading to very material
dependent magnetic excitations, and pairing symmetries. Here we use
first-principles many-body method, including ab initio determined two-particle
vertex function, to study the spin dynamics and superconducting pairing
symmetry in a large number of iron-based superconductors. In iron compounds
with high transition temperature, we find both the dispersive high-energy spin
excitations, and very strong low energy commensurate or nearly commensurate
spin response, suggesting that these low energy spin excitations play the
dominate role in cooper pairing. We find three closely competing types of
pairing symmetries, which take a very simple form in the space of active iron
$3d$ orbitals, and differ only in the relative quantum mechanical phase of the
$xz$, $yz$ and $xy$ orbital contributions. The extensively discussed s$^{+-}$
symmetry appears when contributions from all orbitals have equal sign, while
the opposite sign in $xz$ and $yz$ orbitals leads to the $d$ wave symmetry. A
novel orbital antiphase $s^{+-}$ symmetry emerges when $xy$ orbital has
opposite sign to $xz$ and $yz$ orbitals. We propose that this orbital-antiphase
pairing symmetry explains the puzzling variation of the experimentally observed
superconducting gaps on all the Fermi surfaces of LiFeAs. This novel symmetry
of the order parameter may be realized in other iron superconductors.",1311.1188v1
2013-12-04,Mössbauer studies of the peculiar magnetism in parent compounds of the iron-based superconductors,"A review of the magnetism in the parent compounds of the iron-based
superconductors is given based on the transmission Moessbauer spectroscopy of
57Fe and 151Eu. It was found that the 3d magnetism is of the itinerant
character with varying admixture of the spin-polarized covalent bonds. For the
122 compounds a longitudinal spin density wave (SDW) develops. In the case of
the EuFe2As2 a divalent europium orders antiferromagnetically at much lower
temperature as compared to the onset of SDW. These two magnetic systems remain
almost uncoupled one to another. For the non-stoichiometric Fe(1+x)Te parent of
the 11 family one has a transversal SDW and magnetic order of the interstitial
iron with relatively high and localized magnetic moments. These two systems are
strongly coupled one to another. For the grand parent of the iron-based
superconductors FeAs one observes two mutually orthogonal phase-related
transversal SDW on the iron sites. There are two sets of such spin arrangements
due to two crystallographic iron sites. The FeAs exhibits the highest covalency
among compounds studied, but it has still a metallic character.",1312.1152v1
2014-02-25,"C/O abundance ratios, iron depletions, and infrared dust features in Galactic planetary nebulae","We study the dust present in 56 Galactic planetary nebulae (PNe) through
their iron depletion factors, their C/O abundance ratios (in 51 objects), and
the dust features that appear in their infrared spectra (for 33 objects). Our
sample objects have deep optical spectra of good quality, and most of them also
have ultraviolet observations. We use these observations to derive the iron
abundances and the C/O abundance ratios in a homogeneous way for all the
objects. We compile detections of infrared dust features from the literature
and we analyze the available Spitzer/IRS spectra. Most of the PNe have C/O
ratios below one and show crystalline silicates in their infrared spectra. The
PNe with silicates have C/O < 1, with the exception of Cn 1-5. Most of the PNe
with dust features related to C-rich environments (SiC or the 30 {\mu}m feature
usually associated to MgS) have C/O $\gtrsim$ 0.8. PAHs are detected over the
full range of C/O values, including 6 objects that also show silicates. Iron
abundances are low in all the objects, implying that more than 90% of their
iron atoms are deposited into dust grains. The range of iron depletions in the
sample covers about two orders of magnitude, and we find that the highest
depletion factors are found in C-rich objects with SiC or the 30 {\mu}m feature
in their infrared spectra, whereas some of the O-rich objects with silicates
show the lowest depletion factors.",1402.6376v1
2014-12-12,Electronic structure of ruthenium-doped iron chalcogenides,"The structural and electronic properties of hypothetical Ru$_x$Fe$_{1-x}$Se
and Ru$_x$Fe$_{1-x}$Te systems have been investigated from first principles
within the density functional theory (DFT). Reasonable values of lattice
parameters and chalcogen atomic positions in the tetragonal unit cell of iron
chalcogenides have been obtained with the use of norm-conserving
pseudopotentials. The well known discrepancies between experimental data and
DFT-calculated results for structural parameters of iron chalcogenides are
related to the semicore atomic states which were frozen in the used here
approach. Such an approach yields valid results of the electronic structures of
the investigated compounds. The Ru-based chalcogenides exhibit the same
topology of the Fermi surface (FS) as that of FeSe, differing only in subtle FS
nesting features. Our calculations predict that the ground states of RuSe and
RuTe are nonmagnetic, whereas those of the solid solutions Ru$_x$Fe$_{1-x}$Se
and Ru$_x$Fe$_{1-x}$Te become the single- and double-stripe antiferromagnetic,
respectively. However, the calculated stabilization energy values are
comparable for each system. The phase transitions between these magnetic
arrangements may be induced by slight changes of the chalcogen atom positions
and the lattice parameters $a$ in the unit cell of iron selenides and
tellurides. Since the superconductivity in iron chalcogenides is believed to be
mediated by the spin fluctuations in single-stripe magnetic phase, the
Ru$_x$Fe$_{1-x}$Se and Ru$_x$Fe$_{1-x}$Te systems are good candidates for new
superconducting iron-based materials.",1412.3961v1
2015-04-08,Testing the Kerr Nature of Black Hole Candidates using Iron Line Spectra in the CPR Framework,"The iron K$\alpha$ line commonly observed in the X-ray spectrum of both
stellar-mass and supermassive black hole candidates originates from X-ray
fluorescence of the inner accretion disk. Accordingly, it can be used to map
the spacetime geometry around these objects. In this paper, we extend previous
work using the iron K$\alpha$ line to test the Kerr black hole hypothesis. We
adopt the Cardoso-Pani-Rico parametrization and we test the possibility of
constraining possible deviations from the Kerr solution that can be obtained
from observations across the range of black hole spins and inclination angles.
We confirm previous claims that the iron K$\alpha$ line is potentially a quite
powerful probe for testing the Kerr metric given sufficiently high quality data
and with systematics under control, especially in the case of fast-rotating
black holes and high inclination angles since both conditions serve to maximize
relativistic effects. We find that some geometric perturbations from Kerr
geometry manifest more strongly in the iron line profile than others. While the
perturbation parameter $\epsilon^t_3$ can be well constrained by the iron line
profile, an orthogonal data set is necessary to constrain departures from Kerr
geometry in $\epsilon^r_3$.",1504.01970v2
2015-06-10,Structural disorder in Li(x)[C5H5N](y)Fe(2-z)Se2 and Cs(x)Fe(2-z)Se2 superconductors studied by Mössbauer spectroscopy,"Two iron-chalcogenide superconductors Li(x)[C5H5N](y)Fe(2-z)Se2 and
Cs(x)Fe(2-z)Se2 in the as-prepared and annealed state have been investigated by
means of the Moessbauer spectroscopy versus temperature. Multi-component
spectra are obtained. One can see a non-magnetic component due to iron located
in the unperturbed Fe-Se sheets responsible for superconductivity. Remaining
components are magnetically ordered even at room temperature. There is some
magnetically ordered iron in Fe-Se sheets perturbed by presence of the iron
vacancies. Additionally, one can see iron dispersed between sheets in the form
of magnetically ordered high spin trivalent ions, some clusters of above ions,
and in the case of pyridine intercalated compound in the form of alpha-Fe
precipitates. Pyridine intercalated sample shows traces of superconductivity in
the as-prepared state, while cesium intercalated sample in the as-prepared
state does not show any superconductivity. Superconductors with transition
temperatures being 40 K and 25 K, respectively, are obtained upon annealing.
Annealing leads to removal/ordering of the iron vacancies within Fe-Se sheets,
while clusters of alpha-Fe grow in the pyridine intercalated sample.",1506.03390v2
2015-12-02,"The iron dispersion of the globular cluster M 2, revised","M 2 has been claimed to posses three distinct stellar components that are
enhanced in iron relative to each other. We use equivalent width measurements
from 14 red giant branch stars from which Yong et al. detect a $\sim$0.8 dex
wide, trimodal iron distribution to redetermine the metallicity of the cluster.
In contrast to Yong et al., which derive atmospheric parameters following only
the classical spectroscopic approach, we perform the chemical analysis using
three different methods to constrain effective temperatures and surface
gravities. When atmospheric parameters are derived spectroscopically, we
measure a trimodal metallicity distribution, that well resembles that by Yong
et al. We find that the metallicity distribution from Fe II lines strongly
differs from the distribution obtained from Fe I features when photometric
gravities are adopted. The Fe I distribution mimics the metallicity
distribution obtained using spectroscopic parameters, while the Fe II shows the
presence of only two stellar groups with metallicity [Fe/H]$\simeq$-1.5 and
-1.1 dex, which are internally homogeneous in iron. This finding, when coupled
with the high-resolution photometric evidence, demonstrates that M 2 is
composed by a dominant population ($\sim$99%) homogeneous in iron and a
minority component ($\sim$1%) enriched in iron with respect to the main cluster
population.",1512.00691v1
2016-02-16,Role of Arsenic in Iron-based Superconductivity at Atomic Scale,"In iron-based superconductors, a unique tri-layer Fe-As (Se, Te, P) plays an
essential role in controlling the electronic properties, especially the Cooper
pairing interaction. Here we use scanning tunneling microscopy/spectroscopy
(STM/S) to investigate the role of arsenic atom in superconducting
Ba0.4K0.6Fe2As2 by directly breaking and restoring the Fe-As structure at
atomic scale. After the up-As-layer peeled away, the tunneling spectrum of the
exposed iron surface reveals a shallow incoherent gap, indicating a severe
suppression of superconductivity without arsenic covering. When a pair of
arsenic atoms is placed on such iron surface, a localized topographic feature
is formed due to Fe-As orbital hybridization, and the superconducting coherent
peaks recover locally with the gap magnitude the same as that on the iron-layer
fully covered by arsenic. These observations unravel the Fe-As interactions on
an atomic scale and imply its essential roles in the iron-based
superconductivity.",1602.04956v2
2016-08-03,High-temperature miscibility of iron and rock during terrestrial planet formation,"The accretion of a terrestrial body and differentiation of its silicate/oxide
mantle from iron core provide abundant energy for heating its interior to
temperatures much higher than the present day Earth. The consequences of
differentiation on the structure and composition of planets are typically
addressed considering only the interaction of molten iron with an immiscible
`rocky' phase. We demonstrate that mixing in a representative system of liquid
or solid MgO and liquid iron to a single homogeneous liquid occurs at
sufficiently low temperature to be present in the aftermath of a giant impact.
Applying the thermodynamic integration technique to density functional theory
molecular dynamics simulations, we determine the solvus closure temperature for
the Fe-MgO system for pressures up to 400 GPa. Solvus closure occurs at
$\sim$4000 K at low pressure, and has a weak positive pressure dependence, such
that its gradient with respect to depth is less steep than an adiabatic
temperature profile. This predicts a new mode of core-mantle differentiation
following the most energetic giant impacts, with exsolution of iron from the
mixture beginning in the outer layers of the planet. We demonstrate that
high-temperature equilibration results in delivery of nominally insoluble
Mg-rich material to the early core. Since MgO is the least soluble major mantle
component in iron at low temperatures, these results may represent an upper
bound on temperature for mixing in terrestrial planets.",1608.01295v1
2017-11-27,Solar abundance ratios of the iron-peak elements in the Perseus Cluster,"The metal abundance of the hot plasma that permeates galaxy clusters
represents the accumulation of heavy elements produced by billions of
supernovae. Therefore, X-ray spectroscopy of the intracluster medium provides
an opportunity to investigate the nature of supernova explosions integrated
over cosmic time. In particular, the abundance of the iron-peak elements
(chromium, manganese, iron and nickel) is key to understanding how the
progenitors of typical type Ia supernovae evolve and explode. Recent X-ray
studies of the intracluster medium found that the abundance ratios of these
elements differ substantially from those seen in the Sun, suggesting
differences between the nature of type Ia supernovae in the clusters and in the
Milky Way. However, because the K-shell transition lines of chromium and
manganese are weak and those of iron and nickel are very close in photon
energy, high-resolution spectroscopy is required for an accurate determination
of the abundances of these elements. Here we report observations of the Perseus
cluster, with statistically significant detections of the resonance emission
from chromium, manganese and nickel. Our measurements, combined with the latest
atomic models, reveal that these elements have near-solar abundance ratios with
respect to iron, in contrast to previous claims. Comparison between our results
and modern nucleosynthesis calculations disfavours the hypothesis that type Ia
supernova progenitors are exclusively white dwarfs with masses well below the
Chandrasekhar limit (about 1.4 times the mass of the Sun). The observed
abundance pattern of the iron-peak elements can be explained by taking into
account a combination of near- and sub-Chandrasekhar-mass type Ia supernova
systems, adding to the mounting evidence that both progenitor types make a
substantial contribution to cosmic chemical enrichment.",1711.10035v1
2017-12-15,"Tunable polymorphism of epitaxial iron oxides in the four-in-one ferroic-on-GaN system with magnetically ordered α-, γ-, ε-Fe2O3 and Fe3O4 layers","Hybridization of semiconducting and magnetic materials into a single
heterostructure is believed to be potentially applicable to the design of novel
functional spintronic devices. In the present work we report epitaxial
stabilization of four magnetically ordered iron oxide phases (Fe3O4,
{\gamma}-Fe2O3, {\alpha}-Fe2O3 and most exotic metastable {\epsilon}-Fe2O3) in
the form of nanometer sized single crystalline films on GaN(0001) surface. The
epitaxial growth of as many as four distinctly different iron oxide phases is
demonstrated within the same single-target Laser MBE technological process on a
GaN semiconductor substrate widely used for electronic device fabrication. The
discussed iron oxides belong to a family of simple formula magnetic materials
exhibiting a rich variety of outstanding physical properties including peculiar
Verwey and Morin phase transitions in Fe3O4 and {\alpha}-Fe2O3 and multiferroic
behavior in metastable magnetically hard {\epsilon}-Fe2O3 ferrite. The physical
reasons standing behind the nucleation of a particular phase in an epitaxial
growth process deserve interest from the fundamental point of view. The
practical side of the presented study is to exploit the tunable polymorphism of
iron oxides for creation of ferroic-on-semiconductor heterostructures usable in
novel spintronic devices. By application of a wide range of experimental
techniques the surface morphology, crystalline structure, electronic and
magnetic properties of the single phase iron oxide epitaxial films on GaN have
been studied. A comprehensive comparison has been made to the properties of the
same ferrite materials in the bulk and nanostructured form reported by other
research groups.",1712.05632v1
2018-05-02,The Problem of the High Iron Abundance in Accretion Disks around Black Holes,"In most accreting black-hole systems the copious X-rays commonly observed
from the inner-most regions are accompanied by a reflection spectrum. The
latter is the signature of energetic photons reprocessed by the optically thick
material of an accretion disk. Given their abundance and fluorescence yield,
the iron K-shell lines are the most prominent features in the X-ray reflected
spectrum. Their line profiles can be grossly broadened and skewed by Doppler
effects and gravitational redshift. Consequently, modeling the reflection
spectrum provides one of the best methods to measure, among other physical
quantities, the black-hole spin. At present the accuracy of the spin estimates
is called into question because the data fits require very high iron
abundances: typically several times the solar value. Concurrently no plausible
physical explanation has been proffered for these black-hole systems to be so
iron rich. The most likely explanation for the supersolar iron abundances is
model shortfall at very high densities ($>10^{18}$ cm$^{-3}$) due to atomic
data shortcomings in this regime. We review the current observational evidence
for the iron supersolar abundance in many black-hole systems, and show the
effects of high density in state-of-the-art reflection models. We also briefly
discuss our current efforts to produce new atomic data for high-density
plasmas, which are required to refine the photoionization models.",1805.00581v1
2018-10-25,"Limits on stable iron in Type$\,$Ia supernovae from NIR spectroscopy","We obtained optical and near-infrared spectra of Type$\,$Ia supernovae
(SNe$\,$Ia) at epochs ranging from 224 to 496 days after the explosion. The
spectra show emission lines from forbidden transitions of singly ionised iron
and cobalt atoms. We used non-local thermodynamic equilibrium (NLTE) modelling
of the first and second ionisation stages of iron, nickel, and cobalt to fit
the spectra using a sampling algorithm allowing us to probe a broad parameter
space. We derive velocity shifts, line widths, and abundance ratios for iron
and cobalt. The measured line widths and velocity shifts of the singly ionised
ions suggest a shared emitting region. Our data are fully compatible with
radioactive $^{56}$Ni decay as the origin for cobalt and iron. We compare the
measured abundance ratios of iron and cobalt to theoretical predictions of
various SN$\,$Ia explosion models. These models include, in addition to
$^{56}$Ni, different amounts of $^{57}$Ni and stable $^{54,56}$Fe. We can
exclude models that produced only $^{54,56}$Fe or only $^{57}$Ni in addition to
$^{56}$Ni. If we consider a model that has $^{56}$Ni, $^{57}$Ni, and
$^{54,56}$Fe then our data imply that these ratios are $^{54,56}$Fe / $^{56}$Ni
$=0.272\pm0.086$ and $^{57}$Ni / $^{56}$Ni $=0.032\pm0.011$.",1810.10781v1
2019-02-06,Partial order induced superconductivity in $Fe^{2+}$ iron,"In this letter, we address a novel mechanism for iron based superconductors.
We study $F^{2+}$ state of iron with six 3d electrons. Five of them are
localized with ferromagnetic order, while the sixth one is itinerant
antiparallel with the localized ones. We consider spin-fermion model of 3d
electrons and show that one can fix the parameters in the theory so that the
calculated magnetization to match the experimentally measured one. With these
parameters in mind we show that the sixth 3d electrons have well defined Fermi
surfaces, therefore the material is metal.
  Further on we consider an iron prepared by means of applied external magnetic
field upon a cooling. We assume that the applied magnetic field is along the
magnetic order of localized 3d electrons and antiparallel to the magnetic order
of the itinerant sixth electron. Therefore the applied field decreases the
Zeeman splitting of spin-up and spin-down sixth electrons. We focus on quantum
partial order (QPO) state which is obtained when the applied field compensates
the Zeeman splitting so that the sixth 3d electrons do not contribute the
magnetism of iron and magnetic order is formed by means of localized 3d
electrons. We obtain an effective Hamiltonian for iron in (QPO) state and show
that it posses a spin triplet superconductivity with $T_{1u}$ configuration.",1902.02290v2
2020-05-27,Prediction of exotic magnetic states in the alkali metal quasi-one-dimensional iron selenide compound Na$_2$FeSe$_2$,"The magnetic and electronic phase diagram of a model for the
quasi-one-dimensional alkali metal iron selenide compound Na$_2$FeSe$_2$ is
presented. The novelty of this material is that the valence of iron is
Fe$^{2+}$ contrary to most other iron-chain compounds with valence Fe$^{3+}$.
Using first-principles techniques, we developed a three-orbital tight-binding
model that reproduces the {\it ab initio} band structure near the Fermi level.
Including Hubbard and Hund couplings and studying the model via the density
matrix renormalization group and Lanczos methods, we constructed the ground
state phase diagram. A robust region where the block state $\uparrow \uparrow
\downarrow \downarrow \uparrow \uparrow \downarrow \downarrow$ is stabilized
was unveiled. The analog state in iron ladders, employing 2$\times$2
ferromagnetic blocks, is by now well-established, but in chains a block
magnetic order has not been observed yet in real materials. The phase diagram
also contains a large region of canonical staggered spin order $\uparrow
\downarrow \uparrow \downarrow \uparrow \downarrow \uparrow$ at very large
Hubbard repulsion. At the block to staggered transition region, a novel phase
is stabilized with a mixture of both states: an inhomogeneous orbital-selective
charge density wave with the exotic spin configuration $\uparrow \uparrow
\downarrow \uparrow \downarrow \downarrow \uparrow \downarrow$. Our predictions
for Na$_2$FeSe$_2$ may guide crystal growers and neutron scattering
experimentalists towards the realization of block states in one-dimensional
iron-selenide chain materials.",2005.13132v1
2020-10-01,Molecular Dynamics Simulation for the Analysis of Mechanical Properties and Effect of Stone-Wales and BiVacancy Defect on Carbon Nanotube Reinforced Iron Composites,"Carbon nanotube (CNT) reinforced metal matrix composites (MMCs) are gaining
the attention of the researchers because of their demand in space and
automobile industries for having low weight and high mechanical properties.
Iron is the most used metal in all engineering fields. Therefore, reinforcing
iron with CNT can reduce its required amount, which might have a positive
economic impact due to the reduced cost of production. However, before the
industrial application of any material the mechanical properties under
different conditions must be known. In this study, the mechanical properties of
iron reinforced separately with single, double and triple wall CNTs are
investigated by Molecular Dynamics (MD) simulation. The study revealed that the
strength and stiffness of pure iron could be enhanced up to 80.4 % and 57.4 %,
respectively, by adding CNTs into iron. We also investigated the effect of
fiber volume percentage and temperature on the mechanical properties of the
composite having single, double and triplewalled carbon nanotubes individually.
As the stone-wales and bi-vacancy defects are inherently introduced in CNTs
during manufacturing, their effect on mechanical properties are also
investigated in the present study",2010.00275v1
2021-01-19,"Quantitative analysis of iron sand mineral content from the south coast of Cidaun, West Java using rietveld refinement method","Iron sand is one of the abundant natural resources in Indonesia, especially
on the south coast of Cidaun; West Java which is the basic material for
building and metal industry. Iron mineral content is generally metal oxide such
as magnetite, hematite and silica/quartz. Sand with iron content used in this
study is derived from beach sand Desa Kertajadi, Kecamatan Cidaun, Kabupaten
Cianjur, Jawa Barat. Then mass of 2 kg sand was separated using a magnetic
separator in order to obtain magnetic and nonmagnetic mineral content. After
nine rounds of separation takes two different types of samples that are no
separation sand (TS) sample and concentrate in the third separation (S3)
sample. The sample is then examined by X-Ray Diffraction (XRD) measurement and
analyzed quantitatively using MAUD software to determine the content of Fe3O4
(magnetite) by using the Rietveld refinement method from XRD data. As the
analysis result, the magnetite content contained in iron sand is counted
quantitatively for each different sample. For iron sand samples (TS) yielding a
24.27 percent of magnetite and a third concentrate separation sample (S3)
yields 61.98 percent.",2101.10442v1
2021-10-20,"Manifestations of Spinodal Decomposition into Dilute Pd$_{1-x}$Fe$_{x}$ ""Phases"" in Iron-Implanted Palladium Films: FMR Study","Palladium-iron alloys produced by high-dose implantation of iron ions into
epitaxial palladium films were investigated with the ferromagnetic resonance
(FMR) and vibrating sample magnetometry (VSM) techniques. The samples reveal
distinct multiple FMR responses depending on the dose of iron ion implantation.
The post-implantation annealing at 770 K does not bring the implanted films to
a homogeneous solid solution state, as might be expected from the Pd-Fe phase
diagram. On the contrary, the system approaches a stable state composed of
several magnetic phases. FMR spectra exhibit an angular behavior specific for a
stack of interacting magnetic layers. This observation, correlated with the
magnetometry data, indicates that the palladium-iron binary alloy has a
previously unknown tendency towards spinodal decomposition into isostructural
phases with well-defined iron concentrations and, accordingly, with different
temperatures of ferromagnetic ordering and saturation magnetizations.",2110.10397v1
2021-11-02,Structure and motifs of iron oxides from 1 to 3 TPa,"Iron oxides are fundamental components of planet-forming materials.
Understanding the Fe-O system's behavior and properties under high pressure can
help us identify many new phases and states possible in exoplanetary interiors,
especially terrestrial ones. Using the adaptive genetic algorithm (AGA), we
investigate the structure of iron oxides for a wide range of stoichiometries
($0.25\leq x_O \leq 0.8$) at 1, 2, and 3 TPa. Five unreported ground-state
structures with Fe$_2$O, FeO, Fe$_3$O$_5$, FeO$_2$, and FeO$_4$ compositions
are identified. The calculated density of states (DOS) suggests that, except
for FeO$_4$, all phases are metallic, but their carrier densities decrease with
increasing pressure and oxygen content. The cluster alignment analysis of
stable and metastable phases shows that several motifs may co-exist in a
structure of iron oxides with low O content. In contrast, most iron oxides with
high O content adopt a simple BCC motif at TPa pressures. Our results provide a
crystal structure database of iron oxides for modeling and understanding the
interiors of exoplanets.",2111.01305v2
2022-01-07,Online 3-Axis Magnetometer Hard-Iron and Soft-Iron Bias and Angular Velocity Sensor Bias Estimation Using Angular Velocity Sensors for Improved Dynamic Heading Accuracy,"This article addresses the problem of dynamic on-line estimation and
compensation of hard-iron and soft-iron biases of 3-axis magnetometers under
dynamic motion in field robotics, utilizing only biased measurements from a
3-axis magnetometer and a 3-axis angular rate sensor. The proposed magnetometer
and angular velocity bias estimator (MAVBE) utilizes a 15-state process model
encoding the nonlinear process dynamics for the magnetometer signal subject to
angular velocity excursions, while simultaneously estimating 9 magnetometer
bias parameters and 3 angular rate sensor bias parameters, within an extended
Kalman filter framework. Bias parameter local observability is numerically
evaluated. The bias-compensated signals, together with 3-axis accelerometer
signals, are utilized to estimate bias compensated magnetic geodetic heading.
Performance of the proposed MAVBE method is evaluated in comparison to the
widely cited magnetometer-only TWOSTEP method in numerical simulations,
laboratory experiments, and full-scale field trials of an instrumented
autonomous underwater vehicle in the Chesapeake Bay, MD, USA. For the proposed
MAVBE, (i) instrument attitude is not required to estimate biases, and the
results show that (ii) the biases are locally observable, (iii) the bias
estimates converge rapidly to true bias parameters, (iv) only modest instrument
excitation is required for bias estimate convergence, and (v) compensation for
magnetometer hard-iron and soft-iron biases dramatically improves dynamic
heading estimation accuracy.",2201.02449v1
2022-10-19,GRB 180325A: dust grain-size distribution and interstellar iron nanoparticles contribution,"We modelled dust grain-size distributions for carbonaceous and silicates
dust, as well as for free-flying iron nanoparticles in the environment of a
$\gamma$-ray burst (GRB) afterglow, GRB 180325A. This GRB, at $z=2.2486$, has
an unambiguous detection of the 2175 \r{A} extinction feature with $R_V=4.58$
and $A_V=1.58$. In addition to silicates, polycyclic aromatic hydrocarbons
(PAH), and graphite, we used iron nanoparticles grain-size distributions for
the first time to model the observed extinction curve of GRB 180325A. We fit
the observed extinction for four model permutations, using 232 sets of
silicates, graphite, carbon abundance in hydrocarbon molecules ($b_C$), and
fraction of iron abundance in free-flying nanoparticles ($b_{\text{Fe}}$).
These four different permutations were chosen to test iron nanoparticles
significance and carbon abundance in hydrocarbons. Our results indicate that
iron nanoparticles contribution is insignificant and there is a degeneracy of
carbon abundances, with the range $(0.0 \leq b_C \leq 0.7)\times10^{-5}$
providing the best-fit to the observed extinction curve of GRB 180325A. We
therefore favour the simplest model of silicates and polycyclic aromatic
hydrocarbons. The silicates are dominant and contribute to the entire
wavelength range of the GRB extinction curve while graphite contributes towards
both the 2175 \r{A} bump and the UV extinction. The afterglow peak luminosity
($1.5\times10^{51}$ ergs/s) indicates dust destruction may have taken place. We
conclude that further investigations into other potential contributors of
extinction are warranted, particularly for steep UV extinction.",2210.10423v1
2023-01-30,The Curie line in protoplanetary disks and the formation of Mercury-like planets,"In laboratory experiments, we heated chondritic material up to 1400K in a
hydrogen atmosphere. Moessbauer spectroscopy and magnetometry reveal that, at
high temperatures, metallic iron forms from silicates. The transition
temperature is about 1200K after 1 h of tempering, likely decreasing to about
1000K for longer tempering. This implies that in a region of high temperatures
within protoplanetary disks, inward drifting solids will generally be a
reservoir of metallic iron. Magnetic aggregation of iron-rich matter then
occurs within the magnetic field of the disk. However, the Curie temperature of
iron, 1041 K, is a rather sharp discriminator that separates the disk into a
region of strong magnetic interactions of ferromagnetic particles and a region
of weak paramagnetic properties. We call this position in the disk the Curie
line. Magnetic aggregation will be turned on and off here. On the outer,
ferromagnetic side of the Curie line, large clusters of iron-rich particles
grow and might be prone to streaming instabilities. To the inside of the Curie
line, these clusters dissolve, but that generates a large number density that
might also be beneficial for planetesimal formation by gravitational
instability. One way or the other, the Curie line may define a preferred region
for the formation of iron-rich bodies.",2301.12910v1
2023-02-28,Correlating Chemical Reaction and Mass Transport in Hydrogen-based Direct Reduction of Iron Oxide,"Steelmaking contributes 8% to the total CO2 emissions globally, primarily due
to coal-based iron ore reduction. Clean hydrogen-based ironmaking has variable
performance because the dominant gas-solid reduction mechanism is set by the
defects and pores inside the mm-nm sized oxide particles that change
significantly as the reaction progresses. While these governing dynamics are
essential to establish continuous flow of iron and its ores through reactors,
the direct link between agglomeration and chemistry is still contested due to
missing measurements. In this work, we directly measure the connection between
chemistry and agglomeration in the smallest iron oxides relevant to magnetite
ores. Using synthesized spherical 10-nm magnetite particles reacting in H2, we
resolve the formation and consumption of w\""ustite (FeO) - the step most
commonly attributed to agglomeration. Using X-ray scattering and microscopy, we
resolve crystallographic anisotropy in the rate of the initial reaction, which
becomes isotropic as the material sinters. Complementing with imaging, we
demonstrate how the particles self-assemble, subsequently react and sinter into
~100x oblong grains. Our insights into how morphologically uniform iron oxide
particles react and agglomerate H2 reduction enable future size-dependent
models to effectively describe the multiscale iron ore reduction.",2302.14215v2
2023-04-26,The width-flux relation of the broad iron line during the state transition of the black hole X-ray binaries,"The observation of varying broad iron lines during the state transition of
the black hole X-ray binaries (BHXBs) have been accumulating.In this work, the
relation between the normalized intensity and the width of iron lines is
investigated, in order to understand better the variation of iron lines and
possibly its connection to state transition. Considering the uncertainties due
to ionization and illuminating X-rays, only the effects of geometry and gravity
are taken into account. Three scenarios were studied, i.e., the continuous disk
model, innermost annulus model, and the cloud model. As shown by our
calculations, at given iron width, the line flux of the cloud model is smaller
than that of the continuous disk model; while for the innermost annulus model,
the width is almost unrelated with the flux. The range of the line strength
depends on both the BH spin and the inclination of the disk. We then apply to
the observation of MAXI J1631-479 by NuSTAR during its decay from the soft
state to the intermediate state. We estimated the relative line strength and
width according to the spectral fitting results by Xu et al.(2020), and then
compared with our theoretical width-flux relation. It was found that the cloud
model was more favored. We further modeled the iron line profiles, and found
that the cloud model can explain both the line profile and its variation with
reasonable parameters.",2304.13358v1
2023-05-09,Reproduction Experiments of Radial Pyroxene Chondrules Using a Gas-jet Levitation System under Reduced Conditions,"Reproduction experiments of radial pyroxene (RP) chondrules were carried out
using an Ar-$\mathrm{H_2}$ or Ar gas-jet levitation system in a reducing
atmosphere in order to simulate chondrule formation in the protoplanetary disk.
The experiments reproduced RP-chondrule textures, consisting of sets of thin
pyroxene crystals and mesostasis glass between crystals. However, iron
partition coefficients between pyroxene and glassy mesostasis ($\rm{D_{Fe}}$ =
Fe mol$\rm{\%_{pyroxene}}$ / Fe mol$\rm{\%_{mesostasis}}$) in natural RP
chondrules were much higher than that in experimentally reproduced RP
chondrules. The high $\rm{D_{Fe}}$ in natural RP chondrules suggest that iron
was removed from the mesostasis melt at high temperatures after the growth of
pyroxene crystals. We found that many small iron-metal inclusions had formed in
the mesostasis glass, indicating that FeO in the high-temperature melt of
mesostasis was reduced to metallic iron, and iron in the mesostasis diffused
into the newly formed metal inclusions. The formation of the iron-metal
inclusions in the mesostasis was reproduced by our experiments in a reducing
atmosphere, confirming that $\rm{D_{Fe}}$ in natural RP chondrules increased
after the growth of RP crystals. Therefore, the $\rm{D_{Fe}}$ of RP chondrules
can be an indicator to constrain cooling rates and redox states during
chondrule formation.",2305.05787v4
2023-07-31,Trading oxygen for iron I: the [O/Fe] -- specific star formation rate relation of galaxies,"Our current knowledge of star-forming metallicity relies primarily on
gas-phase oxygen abundance measurements. This may not allow one to accurately
describe differences in stellar evolution and feedback driven by variations in
iron abundance. $\alpha$-elements (such as oxygen) and iron are produced by
sources that operate on different timescales and the link between them is not
straightforward. We explore the origin of the [O/Fe] - specific SFR (sSFR)
relation, linking chemical abundances to galaxy formation timescales. This
relation is followed by star-forming galaxies across redshifts according to
cosmological simulations and basic theoretical expectations. Its apparent
universality makes it suitable for trading the readily available oxygen for
iron abundance. The relation is determined by the relative iron production
efficiency of core-collapse and type Ia supernovae and the delay time
distribution of the latter -- uncertain factors that could be constrained
empirically with the [O/Fe]-sSFR relation. We compile and homogenise a
literature sample of star-forming galaxies with observational iron abundance
determinations to place first constraints on the [O/Fe]-sSFR relation over a
wide range of sSFR. The relation shows a clear evolution towards lower [O/Fe]
with decreasing sSFR and a flattening above log(sSFR/yr)>-9. The result is
broadly consistent with expectations, but better constraints are needed to
inform the models. We independently derive the relation from old Milky Way
stars and find a remarkable agreement between the two, as long as the
recombination-line absolute oxygen abundance scale is used in conjunction with
stellar metallicity measurements.",2308.00023v1
2023-08-28,"R-Matrix calculations for opacities.II. Photoionization and oscillator strengths of iron ions FeXVII, FeXVIII and FeXIX","Iron is the dominant heavy element that plays an important role in radiation
transport in stellar interiors. Owing to its abundance and large number of
bound levels and transitions, iron ions determine the opacity more than any
other astrophysically abundant element. A few iron ions constitute the
abundance and opacity of iron at the base of the convection zone (BCZ) at the
boundary between the solar convection and radiative zones, and are the focus of
the present study. Together, FeXVII, FeXVIII and FeXIX contribute 85\% of iron
ion fractions 20\%, 39\% and 26\% respectively, at the BCZ physical conditions.
We report heretofore the most extensive R-matrix atomic calculations for these
ions for bound-bound and bound-free transitions, the two main processes of
radiation absorption. We consider wavefunction expansions with 218 target or
core ion fine structure levels of FeXVIII for FeXVII, 276 levels of FeXIX for
FeXVIII, in the Breit-Pauli R-matrix (BPRM) approximation, and 180 LS terms
(equivalent to 415 fine structure levels) of FeXX for FeXIX calculations. These
large target expansions which includes core ion excitations to n=2,3,4
complexes enable accuracy and convergence of photoionization cross sections, as
well as inclusion of high lying resonances. Photoionization cross sections have
obtained for all bound fine structure levels of FeXVII and FeXVIII, and for 900
bound LS states of FeXIX. Selected results demonstrating prominent
characteristic features of photoionization are presented, particularly the
strong Seaton PEC (photoexcitation-of-core) resonances formed via high-lying
core excitations with $\Delta n=1$ that significantly impact bound-free
opacity.",2308.14854v1
2023-09-05,"Calculated iron $L_{2,3}$ x-ray absorption and XMCD of spin-crossover Fe(phen)$_{2}$(NCS)$_{2}$ molecule adsorbed on Cu(001) surface","The PAW method has been used to compute the iron L$_{2,3}$ edges of x-ray
absorption spectra (XAS) and x-ray magnetic circular dichroism (XMCD) of the
spin-crossover Fe(phen)$_{2}$(NCS)$_{2}$ molecule when adsorbed on Cu(001)
surface and in the gas phase, for both the high spin (HS) and low spin (LS)
states. It is found that the calculated XAS and XMCD with the static core hole
or the Slater transition state half hole are in less good agreement with
experiment than those using the so called initial state. This disagreement is
due to the reduction of the iron spin magnetic moment caused by the static
screening of the core hole by the photo-electron. The L$_{2,3}$ XAS formula is
found to be directly related to the unoccupied $3d$ density of states (DOS),
and hence the symmetry broken $e_g$ and the $t_{2g}$ iron DOS are used to
explain the XAS and XMCD results. It is demonstrated that the dependence of the
HS XMCD on the direction of incident x-ray circularly polarized light with
respect to the magnetization direction can be used to determine the iron
octahedron deformation, while the XMCD for various magnetization directions is
directly related to the anisotropy of the orbital magnetic moment and the
magneto-crystalline energy. It is also shown that the magnetic dipole moment
$T_z$ is very large due to the strong distortion of the iron octahedron and is
necessary for an accurate determination of the sum rule computed spin magnetic
moment.",2309.02078v1
2024-01-29,Pulsed Iron line Emission from the First Galactic Ultraluminous X-ray Pulsar Swift J0243.6+6124,"We report the phase-resolved spectral results of the first Galactic Pulsating
Ultra-Luminous X-ray source (PULX) Swift J0243.6+6124, modeling at its
2017-2018 outburst peak using data collected by the Hard X-ray Modulation
Telescope (Insight-HXMT). The broad energy coverage of Insight-HXMT allows us
to obtain more accurate spectral continuum to reduce the coupling of broad iron
line profiles with other components. We use three different continuum spectrum
models but obtain similar iron line results. For the first time, we detected
the pulse characteristics of the broad iron line in a PULX. The variation in
width and intensity of this iron line with $\sigma \sim 1.2-1.5$\,keV has a
phase offset of about 0.25 from the pulse phase. We suggest that the uneven
irradiation of the thick inner disk by the accretion column produces the
modulated variation of the broad iron line. In addition, the non-pulsed narrow
line is suggested to come from the outer disk region.",2401.15992v1
1996-09-06,The Iron Discrepancy in Elliptical Galaxies after ASCA,"We present estimates for the iron content of the stellar and diffused
components of elliptical galaxies, as derived respectively from integrated
optical spectra and from ASCA X-ray observations. A macroscopic discrepancy
emerges between the expected iron abundances in the hot interstellar medium
(ISM) and what is indicated by the X-ray observations, especially when
allowance is made for the current iron enrichment by Type Ia supernovae. This
strong discrepancy, that in some extreme instances may be as large as a factor
of $\sim 20$, calls into question our current understanding of supernova
enrichment and chemical evolution of galaxies. We discuss several astrophysical
implications of the inferred low iron abundances in the ISM, including the
chemical evolution of galaxies and cluster of galaxies, the evolution of gas
flows in ellipticals, and the heating of the intracluster medium. Some of the
consequences appear hard to accept, and in the attempt to avoid some of these
difficulties we explore ways of hiding or diluting iron in the ISM of
ellipticals. None of these possibilities appears astrophysically plausible, and
we alternatively rise the question of the reliability of iron-L line
diagonostic tools. Various thin plasma emission models are shown to give iron
abundances that may differ significantly, especially at low temperatures ($kT
\lsim 1$ keV). From a collection of ASCA and other X-ray observatory data, it
is shown that current thin plasma codes tend to give very low iron abundances
when the temperature of the objects is below $\sim 1$ keV. We conclude that --
besides rethinking the chemical evolution of galaxies -- one should also
consider the possibility that existing thin plasma models may incorporate
inaccurate atomic physics for the ions responsible for the iron-L complex.",9609046v1
2002-08-22,How the BAL quasars are quiet,"All properties of the quasars known by the author (quietness of the BAL
quasars, Lyman forest, iron in the high-z quasars...) are explained supposing
that the kernel of the quasar is surrounded by a halo containing an accretion
disk and magnetic satellites (no dark matter or fast jet, no variation of the
fine structure constant, no strange source of iron...). The key is taking into
account the coherent light-matter interactions.",0208405v1
2003-10-23,The Iron Project and the RmaX Project,"Ongoing activities under an international collaboration of atomic physicists
and astrophysicists under the Iron Project and the RmaX Project, with
applications to X-ray astronomy, are briefly described.",0310700v1
2004-12-14,Live Fe-60 in the Early Solar System,"The latest finding by Hester et al. supports the view of "". . . iron cores of
the inner planets, iron meteorites, and the core of the sun as likely
condensation products from the supernova core."" [Science 195, 209 (14 January
1977)]",0412349v2
2005-06-03,A Chandra HETGS Spectral Study of the Iron K Bandpass in MCG-6-30-15: A Narrow View of the Broad Iron Line,"We present a high resolution X-ray spectrum of the iron K bandpass in
MCG-6-30-15 based on a 522 ksec observation with Chandra's High Energy
Transmission Grating Spectrometer. The Chandra spectrum is consistent with the
presence of a relativistically broadened, highly redshifted iron K alpha
emission line with a similar profile to previous observations. A number of
narrow features are detected above 2 keV, including a narrow Fe K alpha
emission line and narrow absorption lines from H- and He-like Fe, H-like S and
H-like Si. This absorption is well described by a photoionized plasma with a
column density log N_H = 23.2 and an ionization parameter log xi = 3.6,
assuming the iron abundance has the Solar value and a velocity dispersion
parameter b = 100 km/s. Applying this absorption model to a high fidelity
XMM-Newton EPIC-pn spectrum we find that a broad iron line is still required
with emission extending to within 1.9 gravitational radii of the black hole. If
the iron line comes from an accretion disk truncated at the innermost stable
circular orbit, this indicates that the black hole must be spinning rapidly
with a>0.95. Ionized absorption models attempting to explain the 3-6 keV
spectral curvature without strong gravity predict absorption lines in the
6.4-6.6 keV range that are inconsistent with the Chandra spectrum. The H- and
He-like iron absorption lines in the Chandra spectrum are blueshifted by 2.0
(+0.7/-0.9) x 10^3 km/s compared to the source frame, and may originate in a
high velocity, high ionization component of the warm absorber outflow. This
high ionization component may dominate the energy budget of the outflow, and
account for a significant fraction of the outflowing mass. (Abstract
truncated).",0506082v1
2006-10-13,Suzaku Observations of Iron Lines and Reflection in AGN,"Initial results on the iron K-shell line and reflection component in several
AGN observed as part of the Suzaku Guaranteed time program are reviewed. This
paper discusses a small sample of Compton-thin Seyferts observed to date with
Suzaku; namely MCG -5-23-16, MCG -6-30-15, NGC 4051, NGC 3516, NGC 2110, 3C 120
and NGC 2992. The broad iron K$\alpha$ emission line appears to be present in
all but one of these Seyfert galaxies, while the narrow core of the line from
distant matter is ubiquitous in all the observations. The iron line in MCG
-6-30-15 shows the most extreme relativistic blurring of all the objects, the
red-wing of the line requires the inner accretion disk to extend inwards to
within 2.2Rg of the black hole, in agreement with the XMM-Newton observations.
Strong excess emission in the Hard X-ray Detector (HXD) above 10 keV is
observed in many of these Seyfert galaxies, consistent with the presence of a
reflection component from reprocessing in Compton-thick matter (e.g. the
accretion disk). Only one Seyfert galaxy (NGC 2110) shows neither a broad iron
line nor a reflection component. The spectral variability of MCG -6-30-15, MCG
-5-23-16 and NGC 4051 is also discussed. In all 3 cases, the spectra appear
harder when the source is fainter, while there is little variability of the
iron line or reflection component with source flux. This agrees with a simple
two component spectral model, whereby the variable emission is the primary
power-law, while the iron line and reflection component remain relatively
constant.",0610436v1
2006-11-28,Iron line and diffuse hard X-ray emission from the starburst galaxy M82,"We examine the properties of the diffuse hard X-ray emission in the classic
starburst galaxy M82. We use new Chandra ACIS-S observations in combination
with reprocessed archival Chandra ACIS-I and XMM-Newton observations. We find
E~6.7 keV Fe He-alpha emission is present in the central |r| < 200 pc, |z| <
100 pc of M82 in all datasets at high statistical significance, in addition to
a possibly non-thermal X-ray continuum and marginally significant E=6.4 keV Fe
K-alpha line emission. No statistically significant Fe emission is found in the
summed X-ray spectra of the point-like X-ray sources or the ULX in the two
epochs of Chandra observation. The total nuclear region iron line fluxes in the
2004 April 21 XMM-Newton observation are consistent with those of the
Chandra-derived diffuse component, but in the 2001 May 6 XMM-Newton observation
they are significantly higher and also both E=6.4 and E=6.9 keV iron lines are
detected. We attribute the excess iron line emission to the Ultra-Luminous
X-ray source in its high state. In general the iron K-shell luminosity of M82
is dominated by the diffuse component. The total X-ray luminosity of the
diffuse hard X-ray emission (corrected for emission by unresolved low
luminosity compact objects) is L_X ~ 4.4 x 10^39 erg/s in the E=2-8 keV energy
band, and the 6.7 keV iron line luminosity is L_X ~ (1.1 -- 1.7) x 10^38 erg/s.
The 6.7 keV iron line luminosity is consistent with that expected from the
previously unobserved metal-enriched merged supernova ejecta that is thought to
drive the larger-scale galactic superwind. The iron line luminosity implies a
thermal pressure within the starburst region of P/k ~ 2 x 10^7 K/cm^3, which is
consistent with independent observational estimates of the starburst region
pressure [Abstract abridged].",0611859v1
2006-12-08,Iron Air collision with high density QCD,"The color glass condensate approach describes successfully heavy ion
collisions at RHIC. We investigate Iron-air collisions within this approach and
compare results to event generators commonly used in air shower simulations. We
estimate uncertainties in the extrapolation to GZK energies and discuss
implications for air shower simulations.",0612218v1
2004-09-03,Helicoidal ordering in iron perovskites,"We consider magnetic ordering in materials with negative charge transfer
energy, such as iron perovskite oxides. We show that for a large weight of
oxygen holes in conduction bands, the double exchange mechanism favors a
helicoidal rather than ferromagnetic spin ordering both in metals, e.g. SrFeO_3
and insulators with a small gap, e.g. CaFeO_3. We discuss the magnetic
excitation spectrum and effects of pressure on magnetic ordering in these
materials.",0409068v1
2009-09-01,Discovery of the Iron Isotopes,"Twenty-eight iron isotopes have so far been observed; the discovery of these
isotopes is discussed. For each isotope a brief summary of the first refereed
publication, including the production and identification method, is presented.",0909.0091v1
2010-01-05,"Response to I. I. Mazin's correspondence on ""Electronic correlations in the iron pnictides""","We discuss the discrepancy between the measured optical Drude weight and band
structure calculations in LaFePO and other iron-based superconductors. This
discrepancy is mostly due to mass renormalization arising from electronic
correlation effects.",1001.0643v1
2010-06-07,Screening of the Raman response in multiband superconductors -- application to iron-pnictides,"We performed model calculations of Raman responses for multiband 2D
superconductors. The multiband effects of screening in the A_{1g} symmetry
channel were investigated analytically and numerically for a band structure
model mimicing ARPES data on iron-pnictide materials. An acceptable agreement
between our model calculations and recent experimental data is demonstrated by
modification of the band structure parameters.",1006.1333v1
2010-10-13,Atomic structure and electronic properties of nanotubes of layered iron-based superconductors,"The atomic models of nanotubes for layered FeSe, LiFeAs, SrFe2As2, and
LnFeAsO - the parent phases of so-called 11, 111, 122, and 1111 groups of newly
discovered family of iron-based high temperature superconductors are proposed.
On example of SrFe2As2 the electronic properties of predicted nanotubes are
examined and discussed in comparison with those for the corresponding single
layer and the crystal.",1010.2624v1
2010-11-09,Iron lines in model disk spectra of galactic black hole binaries,"We present angle-dependent, broad-band intensity spectra from accretion disks
around black holes of 10 M$_\odot$. In our computations disks are assumed to be
slim, which means that the radial advection is taken into account while
computing effective temperature of the disk. We attempt to reconstruct
continuum and line spectra of X-ray binaries in soft state, i.e. dominated by
the disk component of multitemperature shape.
  We follow how the iron line complex depends on the external irradiation, an
accretion rate and a black hole spin. Full radiative transfer is solved
including effects of Compton scattering, free-free and all important bound-free
transitions of 10 main elements. Moreover, we include here the fundamental
series of iron lines from helium-like and hydrogen-like ions, and fluorescent
K$_{\alpha}$ and K$_{\beta}$ lines from low ionized iron. We consider two
cases: non-rotating black hole, and black hole rotating with almost maximum
spin a=0.98, and obtain spectra for five accretion disks from hard X-rays to
the infrared. In non irradiated disks, resonance lines from He-like and H-like
iron appear mostly in absorption. Such disk spectra exhibit limb-darkening in
the whole energy range. External irradiation causes that iron resonance lines
appear in emission. Furthermore, depending on disk effective temperature,
fluorescent iron K$_{\alpha}$ and K$_{\beta}$ lines are present in disk
emitting spectra.All models with irradiation exhibit limb-brightening in their
X-ray reflected continua. We show, that the disk around stellar black hole
itself is hot enought to produce strong absorption resonance lines of iron.
Emission lines can be observed only if heating by external X-rays dominates
over thermal processess in hot disk atmosphere. Irradiated disks are usually
brighter in X-ray continuum when seen edge on, and fainter when seen face on.",1011.2061v1
2010-12-15,"Reply to Comment on ""Violation of Anderson's Theorem for the sign-reversing s-wave state of Iron-Pnictide Superconductors"" [arXiv:1012.0414] by Y. Bang","We explain that the study of impurity effect in iron pnictides are correctly
calculated based on the T-matrix approximation, contrary to the Comment by
Bang. The replacement T with T-I proposed by Bang breaks the perturbation
theory and is therefore erroneous.",1012.3307v1
2011-01-05,Pressure study of the new iron-based superconductor K0.8Fe2Se2,"We investigated pressure effects on transition temperature (Tc) of the new
iron-based superconductor K0.8Fe2Se2 using a BeCu/NiCrAl hybrid-type clamped
piston-cylinder cell. The Tc(onset) was 33K at 0.85 GPa. With increasing
pressure, Tc(onset) gradually increased and reached 36.6 K at 2.03 GPa.",1101.0896v1
2011-03-15,Dirac cone in iron-based high Tc superconductors,"The band structure of iron-based superconductors gives rise to yet another
scenario for the appearance of Dirac fermions. A viewpoint on ""Observation of
Dirac cone electronic dispersion in BaFe2As2"" (Richard et.al., PRL 104, 137001
(2010)).",1103.2946v1
2012-02-10,"A perspective of superconductivity as multiband phenomena: Cuprate, iron and aromatic systems","A theoretical overview of the classes of superconductors encompassing (a)
high-Tc cuprate, (b) iron-based and (c) aromatic superconductors is given.
Emphasis is put on the multiband natures of all the three classes, where the
differences in the multiorbits and their manifestations in the electronic
structures and pairing are clarified. From these, future directions and
prospects are discussed.",1202.2170v1
2012-05-05,The mechanism of anisotropic exchange interaction in superconducting iron arsenides,"Using a combination of linear response theory and constrained orbital
hybridization approach, we study the mechanism of magnetic exchange interaction
of iron-based superconductor. We reproduce the observed highly anisotropic
exchange interaction, and our constrain-orbital calculation unambiguously
identifies that the anisotropic feature of exchange interaction is not
sensitive to the unequal d$_{xz}$/d$_{yz}$ orbital population.",1205.1109v1
2013-12-18,Strongly magnetized iron white dwarfs and the total lepton number violation,"The influence of a neutrinoless electron to positron conversion on a cooling
of strongly magnetized iron white dwarfs is studied.",1312.5343v1
2014-06-30,Magnetic anisotropy in FeSb studied by 57Fe Mössbauer spectroscopy,"The Fe(1+x)Sb compound has been synthesized close to stoichiometry with x =
0.023(8). The compound was investigated by 57Fe M\""ossbauer spectroscopy in the
temperature range 4.2 - 300 K. The antiferromagnetic ordering temperature was
found as 232 K i.e. much higher than for the less stoichiometric material.
Regular iron was found to occupy two different positions in proportion 2:1.
They differ by the electric quadrupole coupling constants and both of them
exhibit extremely anisotropic electric field gradient tensor (EFG) with the
asymmetry parameter equal one. The negative component of both EFGs is aligned
with the c-axis of the hexagonal unit cell, while the positive component is
aligned with the <120> direction. Hence, a model describing deviation from the
NiAs P63/mmc symmetry group within Fe-planes has been proposed. Spectra in the
magnetically ordered state could be explained by introduction of the
incommensurate spin spirals propagating through the iron atoms in the direction
of the c-axis with a complex pattern of the hyperfine magnetic fields
distributed within a-b plane. Hyperfine magnetic field pattern of spirals due
to major regular iron is smoothed by the spin polarized itinerant electrons,
while the minor regular iron exhibits hyperfine field pattern characteristic of
the highly covalent bonds to the adjacent antimony atoms. The excess
interstitial iron orders magnetically at the same temperature as the regular
iron, and magnetic moments of these atoms are likely to form two-dimensional
spin glass with moments lying in the a-b plane. The upturn of the hyperfine
field for minor regular iron and interstitial iron is observed below 80 K.
Magneto-elastic effects are smaller than for FeAs, however the recoilless
fraction increases significantly upon transition to the magnetically ordered
state.",1406.7767v2
2014-07-18,Iron-free detectors for future linear colliders,"We continue consideration of Iron-free magnetic systems for possible
application in detectors for high energy collider. In particular we suggest a
new type of magnetic system with the multiple flux-return solenoids. This
system allows reaching higher field level at IP compared with traditional ones.",1407.5056v1
2014-11-27,The critical relaxation of the model of iron-vanadium magnetic superlattice,"The critical relaxation of iron-vanadium magnetic superlattice in case of the
equality between interlayer and intralayer exchange interactions is
investigated. The dynamic and static critical exponents of the model are
calculated. A value of the critical temperature is evaluated.",1411.7505v1
2015-08-26,Nuclear Reactions For Nucleosynthesis Beyond Fe,"Many more nuclear transitions have to be known in the determination of
stellar reactivities for trans-iron nucleosynthesis than for reactions of light
nuclei. This requires different theoretical and experimental approaches. Some
of the issues specific for trans-iron nucleosynthesis are discussed.",1508.06569v1
2015-10-06,Local Stellar Kinematics from RAVE data - VI. Metallicity Gradients Based on the F-G Main-sequence Stars,"We estimated iron and metallicity gradients in the radial and vertical
directions with the F and G type dwarfs taken from the RAVE DR4 database. The
sample defined by the constraints Zmax<=825 pc and ep<=0.10 consists of stars
with metal abundances and space velocity components agreeable with the
thin-disc stars. The radial iron and metallicity gradients estimated for the
vertical distance intervals 0<Zmax<=500 and 500<Zmax<=800 pc are
d[Fe/H]/dRm=-0.083(0.030) and d[Fe/H]/dRm=-0.048(0.037 )dex/kpc; and
d[M/H]/dRm=-0.063(0.011) and d[M/H]/dRm=-0.028(0.057) dex/kpc, respectively,
where Rm is the mean Galactocentric distance. The iron and metallicity
gradients for less number of stars at further vertical distances,
800<Zmax<=1500 pc, are mostly positive. Compatible iron and metallicity
gradients could be estimated with guiding radius (Rg) for the same vertical
distance intervals 0<Zmax<=500 and 500<Zmax<=800 pc, i.e.
d[Fe/H]/dRg=-0.083(0.030) and d[Fe/H]/dRg=-0.065(0.039) dex/kpc;
d[M/H]/dRg=-0.062(0.018) and d[M/H]/dRg=-0.055(0.045) dex/kpc. F and G type
dwarfs on elongated orbits show a complicated radial iron and metallicity
gradient distribution in different vertical distance intervals. Significant
radial iron and metallicity gradients could be derived neither for the
sub-sample stars with Rm<=8 kpc, nor for the ones at larger distances, Rm>8
kpc. The range of the iron and metallicity abundance for the F and G type
dwarfs on elongated orbits, [-0.13, -0.01), is similar to the thin-disc stars,
while at least half of their space velocity components agree better with those
of the thick-disc stars. The vertical iron gradients estimated for the F and G
type dwarfs on circular orbits are d[Fe/H]/dZmax=-0.176(0.039) dex/kpc and
d[Fe/H]/dZmax=-0.119(0.036) dex/kpc for the intervals Zmax<= 825 and Zmax<=1500
pc, respectively.",1510.01749v1
2016-04-23,M(H) dependence and size distribution of SPIONs measured by atomic magnetometry,"We demonstrate that the quasistatic recording of the magnetic excitation
function M(H) of superparamagnetic iron oxide magnetic nanoparticle (SPION)
suspensions by an atomic magnetometer allows a precise determination of the
sample's iron mass content mFe and the particle size distribution.",1604.06882v1
2016-06-03,"Energy Losses of Magnetic Monopoles in Aluminum, Iron and Copper","The Energy Losses and Ranges of magnetic monopoles with magnetic charges
$1g_{D}$, $2g_{D}$, $3g_{D}$, $6g_{D}$ and $9g_{D}$ in Aluminum, Iron and in
Copper are computed, in the different regimes of velocities. The Restricted
Energy Losses of monopoles with magnetic charges $1g_{D}$, $2g_{D}$ and
$3g_{D}$ in Nuclear Track Detector is also given.",1606.01220v1
2022-10-11,Oxygen and iron in interstellar dust: an X-ray investigation,"Understanding the chemistry of the interstellar medium (ISM) is fundamental
for the comprehension of the Galactic and stellar evolution. X-rays provide an
excellent way to study the dust chemical composition and crystallinity along
different sight-lines in the Galaxy. In this work we study the dust grain
chemistry in the diffuse regions of the interstellar medium in the soft X-ray
band (<1 keV). We use newly calculated X-ray dust extinction cross sections,
obtained from laboratory data, in order to investigate the oxygen K and iron L
shell absorption. We explore the XMM-Newton and Chandra spectra of 5 low-mass
X-ray binaries located in the Galactic plane, and we model the gas and dust
features of oxygen and iron simultaneously. The dust samples used for this
study include silicates with different Mg:Fe ratios, sulfides, iron oxides and
metallic iron. Most dust samples are in both amorphous and crystalline lattice
configuration. The extinction cross sections have been computed using Mie
scattering approximation and assuming a power law dust size distribution. We
find that the Mg-rich amorphous pyroxene (Mg0.75Fe0.25SiO3) represents the
largest fraction of dust towards most of the X-ray sources, about 70% on
average. Additionally, we find that ~15% of the dust column density in our
lines of sight is in Fe metallic. We do not find strong evidence for
ferromagnetic compounds, such as Fe3O4 or iron sulfides (FeS, FeS2). Our study
confirms that the iron is heavily depleted from the gas phase into solids; more
than 90% of iron is in dust. The depletion of neutral oxygen is mild, between
10-20% depending on the line of sight.",2210.05778v1
2023-07-05,Heterophased grain boundary-rich superparamagnetic Iron Oxides/carbon composite for Cationic and Anionic Dye Removal,"Iron oxide-based nanostructures receive significant attention as an efficient
adsorbent for organic dyes removal. The removal properties have strong
dependency on the stoichiometry, phases, reactive edges, defect states etc
present in the iron-oxides nanostructures. Herein, iron oxide/carbon composite
with well-defined heterophased grain boundaries is synthesized by simple
precipitation method and followed by calcination. The local structure, spin
dynamics and magnetic properties of heterophased iron oxides/carbon composite
are thoroughly investigated to explore its cationic and anionic dye removal
capability. To validate the effectivity of the presence of heterogeneous grain
boundaries, iron oxide/carbon nanocomposite with homogeneous grain boundaries
is also examined. It was found that the hetero-phased iron oxide/carbon showed
removal capacity of 35.45 mg g-1 and 45.84 mg g-1 for cationic (Crystal Violet)
and anionic (Congo Red) dyes, respectively as compared to that of
as-synthesised imidazole-capped superparamagnetic {\alpha}-Fe2O3 (25.11 mg g-1
and 40.44 mg g-1, respectively) and homophased iron oxide/carbon nanocomposite
(9.41 mg g-1 and 5.43 mg g-1, respectively). The plausible mechanism on the
local structural evolution of the heterophase in the course of calcination and
increase of the removal capacity is discussed. A detailed dye adsorption
investigation is presented including the adsorption kinetic study. The
pseudo-second order kinetic model is found to be an appropriate one and
suggests that the chemisorption is dominant factor leading to adsorption of
dyes. Whereas Weber-Morris model indicate the strong influence of boundary
layers of nanocomposite on the adsorption process.",2307.02142v1
2007-07-15,Linear and nonlinear low frequency electrodynamics of the surface superconducting states in an yttrium hexaboride a single crystal,"We report the low-frequency and tunneling studies of yttrium hexaboride
single crystal. Ac susceptibility at frequencies 10 - 1500 Hz has been measured
in parallel to the crystal surface DC felds, H0. We found that in the DC feld
H0 > Hc2 DC magnetic moment completely disappears while the ac response
exhibited the presence of superconductivity at the surface. Increasing of the
DC field from Hc2 revealed the enlarging of losses with a maximum in the feld
between Hc2 and Hc3. Losses at the maximum were considerably larger than in the
mixed and in the normal states. The value of the DC field, where loss peak was
observed, depends on the amplitude and frequency of the ac feld. Close to Tc
this peak shifts below Hc2 which showed the coexistence of surface
superconducting states and Abrikosov vortices. We observed a logarithmic
frequency dependence of the in-phase component of the susceptibility. Such
frequency dispersion of the inphase component resembles the response of
spin-glass systems, but the out-of-phase component also exhibited frequency
dispersion that is not a known feature of the classic spin-glass response.
Analysis of the experimental data with Kramers-Kronig relations showed the
possible existence of the loss peak at very low frequencies (< 5 Hz). We found
that the amplitude of the third harmonic was not a cubic function of the ac
amplitude even at considerably weak ac felds. This does not leave any room for
treating the nonlinear effects on the basis of perturbation theory. We show
that the conception of surface vortices or surface critical currents could not
adequately describe the existing experimental data. Consideration of a model of
slow relaxing nonequilibrium order parameter permits one to explain the partial
shielding and losses of weak ac field for H0 > Hc2.",0707.2211v1
2013-09-18,The spin-state crossover and low-temperature magnetic state in yttrium doped Pr$_{0.7}$Ca$_{0.3}$CoO$_3$,"The structural and magnetic properties of two mixed-valence cobaltites with
formal population of 0.30 Co$^{4+}$ ions per f.u.,
(Pr$_{1-y}$Y$_{y}$)$_{0.7}$Ca$_{0.3}$CoO$_3$ ($y=0$ and 0.15), have been
studied down to very low temperatures by means of the high-resolution neutron
diffraction, SQUID magnetometry and heat capacity measurements. The results are
interpreted within the scenario of the spin-state crossover from a
room-temperature mixture of the intermediate spin Co$^{3+}$ and low spin
Co$^{4+}$ (IS/LS) at the to the LS/LS mixture in the sample ground states. In
contrast to the yttrium free $y=0$ that retains the metallic-like character and
exhibits ferromagnetic ordering below 55 K, the doped system $y=0.15$ undergoes
a first-order metal-insulator transition at 132 K, during which not only the
crossover to low spin states but also a partial electron transfer from
Pr$^{3+}$ 4f to cobalt 3d states take place simultaneously. Taking into account
the non-magnetic character of LS Co$^{3+}$, such valence shift electronic
transition causes a magnetic dilution, formally to 0.12 LS Co$^{4+}$ or 0.12
$t_{2g}$ hole spins per f.u., which is the reason for an insulating, highly
non-uniform magnetic ground state without long-range order. Nevertheless, even
in that case there exists a relatively strong molecular field distributed over
all the crystal lattice. It is argued that the spontaneous FM order in $y=0$
and the existence of strong FM correlations in $y=0.15$ apparently contradict
the single $t_{2g}$ band character of LS/LS phase. The explanation we suggest
relies on a model of the defect induced, itinerant hole mediated magnetism,
where the defects are identified with the magnetic high-spin Co$^{3+}$ species
stabilized near oxygen vacancies.",1309.4812v1
2016-08-31,Lattice instability and enhancement of superconductivity in YB$_6$,"The superconducting and normal state characteristics of yttrium hexaboride
(YB$_6$) have been investigated for the single crystals with a transition
temperatures $T_c$ ranging between 6 K and 7.6 K. The extracted set of
microscopic parameters [the coherence length $\xi$(0) $\sim$ 320$\div$340
${\AA}$, the penetration depth $\lambda$(0) $\sim$ 1100$\div$1600 ${\AA}$ and
the mean free path of charge carriers $l$ = 31$\div$58 ${\AA}$, the
Ginzburg-Landau-Maki parameters $\kappa$$_{1,2}$(0) $\sim$ 3.3$\div$4.8 and the
superconducting gap $\Delta$(0) $\sim$ 10.3$\div$14.8 K] confirms the type II
superconductivity in ""dirty limit"" ($\xi$$\gg$ $l$) with a medium to strong
electron-phonon interaction (the electron-phonon interaction constant
$\lambda_{e-ph}$ = 0.93$\div$0.96) and $s$-type pairing of charge carriers in
this compound [2$\Delta$(0)$/k_BT_c$ $\approx$ 4]. The comparative analysis of
charge transport (resistivity, Hall and Seebeck coefficients) and thermodynamic
(heat capacity, magnetization) properties in the normal state in YB$_6$ allowed
to detect a transition into the cage-glass state at $T^*$ $\sim$ 50 K with a
static disorder in the arrangement of the Y$^{3+}$ ions. We argue that the
significant $T_c$ variations in the YB$_6$ single crystals are determined by
two main factors: (i) the superconductivity enhancement is related with the
increase of the number of isolated vacancies, both at yttrium and boron sites,
which leads to the development of an instability in the hexaboride lattice;
(ii) the $T_c$ depression is additionally stimulated by the spin polarization
of conduction electrons emerged and enhanced by the magnetic field in the
vicinity of defect complexes in the YB$_6$ matrix.",1608.08902v1
2019-08-05,Anomalous high-temperature superconductivity in YH$_6$,"Pressure-stabilized hydrides are a new rapidly growing class of
high-temperature superconductors which is believed to be described within the
conventional phonon-mediated mechanism of coupling. Here we report the
synthesis of yttrium hexahydride Im3m-YH$_6$ that demonstrates the
superconducting transition with T$_c$ = 224 K at 166 GPa, much lower than the
theoretically predicted (>270 K). The measured upper critical magnetic field
B$_c$$_2$(0) of YH$_6$ was found to be 116-158 T, which is 2-2.5 times larger
than the calculated value. A pronounced shift of T$_c$ in yttrium deuteride
YD$_6$ with the isotope coefficient 0.4 supports the phonon-assisted
superconductivity. Current-voltage measurements showed that the critical
current I$_c$ and its density J$_c$ may exceed 1.75 A and 3500 A/mm$^2$ at 0 K,
respectively, which is comparable with the parameters of commercial
superconductors, such as NbTi and YBCO. The superconducting density functional
theory (SCDFT) and anharmonic calculations suggest unusually large impact of
the Coulomb repulsion in this compound. The results indicate notable departures
of the superconducting properties of the discovered YH$_6$ from the
conventional Migdal-Eliashberg and Bardeen-Cooper-Schrieffer theories.",1908.01534v2
2020-02-23,Spectroscopy of YO from first principles,"We report an ab initio study on the spectroscopy of the open-shell diatomic
molecule yttrium oxide, YO. The study considers the six lowest doublet states,
$X\,{}^{2}\Sigma^{+}$, $A\,{}^{2}\Pi$, $C\,{}^{2}\Pi$, $A'\,{}^{2}\Delta$,
$B\,{}^{2}\Sigma^{+}$, $D\,{}^{2}\Sigma^{+}$ and a few higher-lying quartet
states using high levels of electronic structure theory and accurate nuclear
motion calculations. The coupled cluster singles, doubles, and perturbative
triples, CCSD(T), and multireference configuration interaction (MRCI) methods
are employed in conjunction with a relativistic pseudopotential on the yttrium
atom and a series of correlation-consistent basis sets ranging in size from
triple-$\zeta$ to quintuple-$\zeta$ quality. Core-valence correlation effects
are taken into account and complete basis set limit extrapolation is performed
for CCSD(T). Spin-orbit coupling is included through the use of both MRCI
state-interaction with spin-orbit (SI-SO) approach and four-component
relativistic equation-of-motion CCSD calculations. Using the ab initio data for
bond lengths ranging from 1.0 to 2.5 A, we compute 6 potential energy, 12
spin-orbit, 8 electronic angular momentum, 6 electric dipole moment and 12
transition dipole moment (4 parallel and 8 perpendicular) curves which provide
a complete description of the spectroscopy of the system of six lowest doublet
states. The Duo nuclear motion program is used to solve the coupled nuclear
motion Schr\""{o}dinger equation for these six electronic states. The spectra of
$^{89}$Y$^{16}$O simulated for different temperatures are compared with several
available high resolution experimental studies; good agreement is found once
minor adjustments are made to the electronic excitation energies.",2002.09994v1
2020-07-30,Solid-state laser refrigeration of nanodiamond quantum sensors,"The negatively-charged nitrogen vacancy (NV$^-$) centre in diamond is a
remarkable optical quantum sensor for a range of applications including,
nanoscale thermometry, magnetometry, single photon generation, quantum
computing, and communication. However, to date the performance of these
techniques using NV$^-$ centres has been limited by the thermally-induced
spectral wandering of NV$^-$ centre photoluminescence due to detrimental
photothermal heating. Here we demonstrate that solid-state laser refrigeration
can be used to enable rapid (ms) optical temperature control of nitrogen
vacancy doped nanodiamond (NV$^-$:ND) quantum sensors in both atmospheric and
\textit{in vacuo} conditions. Nanodiamonds are attached to ceramic
microcrystals including 10\% ytterbium doped yttrium lithium fluoride
(Yb:LiYF$_4$) and sodium yttrium fluoride (Yb:NaYF$_4$) by van der Waals
bonding. The fluoride crystals were cooled through the efficient emission of
upconverted infrared photons excited by a focused 1020 nm laser beam. Heat
transfer to the ceramic microcrystals cooled the adjacent NV$^-$:NDs by 10 and
27 K at atmospheric pressure and $\sim$10$^{-3}$ Torr, respectively. The
temperature of the NV$^-$:NDs was measured using both Debye-Waller factor (DWF)
thermometry and optically detected magnetic resonance (ODMR), which agree with
the temperature of the laser cooled ceramic microcrystal. Stabilization of
thermally-induced spectral wandering of the NV$^{-}$ zero-phonon-line (ZPL) is
achieved by modulating the 1020 nm laser irradiance. The demonstrated cooling
of NV$^-$:NDs using an optically cooled microcrystal opens up new possibilities
for rapid feedback-controlled cooling of a wide range of nanoscale quantum
materials.",2007.15247v1
2021-12-14,Exploring yttrium doped C$_{24}$ fullerene as a high-capacity reversible hydrogen storage material: DFT investigations,"By employing the state-of-the-art density functional theory, we report the
hydrogen storage capability of yttrium decorated C$_{24}$ fullerene. Single Y
atom attached on C$_{24}$ fullerene can reversibly adsorb a maximum number of 6
H$_2$ molecules with average adsorption energy -0.37 eV and average desorption
temperature 477 K, suitable for fuel cell applications. The gravimetric weight
content of hydrogen is 8.84 %, which exceeds the target value of 6.5 wt % H by
the department of energy (DoE) of the United States. Y atom is strongly bonded
to C$_{24}$ fullerene with a binding energy of -3.4 eV due to a charge transfer
from Y-4d and Y-5s orbitals to the C-2p orbitals of C$_{24}$ fullerene. The
interaction of H$_2$ molecules with the Y atom is due to the Kubas type
interaction involving a charge donation from the metal d orbital to H 1s
orbital, and back donation causing slight elongation of H-H bond length. The
stability of the system at the highest desorption temperature is confirmed by
ab-initio molecular dynamics simulations, and the metal-metal clustering
formation has been investigated by computing the diffusion energy barrier for
the movement of Y atoms. We have corrected all the calculated energies for the
van der Waals (vdW) interactions by applying the dispersion energy corrections,
in addition to the contribution of the GGA exchange-correlation functional. The
C$_{24}$+Y system is stable at room temperature, and at the highest desorption
temperature, the presence of a sufficient diffusion energy barrier prevents
metal-metal clustering. Furthermore, binding energies of H$_2$ are within the
target value by DoE (-0.2-0.7 eV/H$_2$ ), while H$_2$ uptake (8.84 % H) is
higher than DoE's criteria. Therefore, we propose that Y decorated C$_{24}$
fullerene can be tailored as a practically viable potential hydrogen storage
candidate.",2112.07151v2
2023-09-04,NLTE analysis for Y I and Y II in atmospheres of F-G-K stars,"The non-local thermodynamical equilibrium (NLTE) line formation of Y I and Y
II is considered in 1D LTE model atmospheres of F-G-K-type stars. The model
atom was constructed with the most up-to-date atomic data, including quantum
cross sections and rate coefficients for transitions in inelastic collisions of
Y I and Y II with hydrogen atoms. For seven reference stars, we obtained an
agreement between NLTE abundances inferred from the two ionization stages,
while the difference in LTE abundance (Y I - Y II) can reach up to -0.31 dex.
In the atmospheres of F-G-K-type stars, for both Y I and Y II lines, the NLTE
abundance corrections are positive. In solar metallicity stars, the NLTE
abundance corrections for Y II lines do not exceed 0.12 dex, while in
atmospheres of metal-poor stars they do not exceed 0.21 dex. For Y I lines, the
NLTE abundance corrections can reach up to 0.5 dex. We determined the yttrium
NLTE abundances for a sample of 65 F and G dwarfs and subgiants in the
-2.62~$\leq$~[Fe/H]~$\leq$~+0.24 metallicity range, using high-resolution
spectra. For stars with [Fe/H]~$\leq$~-1.5, [Y/Fe] versus [Fe/H] diagram
reveals positive trend with an average value of [Y/Fe]~$\simeq$~0. For
metal-poor stars, among Sr, Y, and Zr, the arrangement [Sr/Fe] < [Y/Fe] <
[Zr/Fe] remains consistent. The current study is useful for the Galactic
chemical evolution research. The model atom will be applied for NLTE yttrium
abundance determination in very metal-poor stars studied with LAMOST and
Subaru.",2309.01402v1
2023-10-13,"Compound-tunable embedding potential method to model local electronic excitations on $f$-element ions in solids: Pilot relativistic coupled cluster study of Ce and Th impurities in yttrium orthophosphate, YPO$_4$","A method to simulate local properties and processes in crystals with
impurities via constructing cluster models within the frame of the
compound-tunable embedding potential (CTEP) and highly-accurate {\it ab initio}
relativistic molecular-type electronic structure calculations is developed and
applied to the Ce and Th-doped yttrium orthophosphate crystals, YPO$_4$, having
xenotime structure. Two embedded cluster models are considered, the ""minimal""
one, YO$_8$@CTEP$_{\rm min}$, consisting of the central Y$^{3+}$ cation and its
first coordination sphere of eight O$^{2-}$ anions (i.~e.\ with broken P--O
bonds), and its extended counterpart, Y(PO$_4$)$_6$@CTEP$_{\rm ext}$, implying
the full treatment of all atoms of the PO$_4^{3-}$ anions nearest to the
central Y$^{3+}$ cation. CTEP$_{\rm min,ext}$ denote here the corresponding
cluster environment described within the CTEP method. The relativistic
Fock-space coupled cluster (FS RCC) theory is applied to the minimal cluster
model to study electronic excitations localized on Ce$^{3+}$ and Th$^{3+}$
impurity ions. Calculated transition energies for the cerium-doped xenotime are
in a good agreement with the available experimental data (mean absolute
deviation of ca.0.3 eV for $4f{\to}5d$ type transitions). For the thorium-doped
crystal the picture of electronic states is predicted to be quite complicated,
the ground state is expected to be of the $6d$ character. The uncertainty for
the excitation energies of thorium-doped xenotime is estimated to be within
0.35 eV. Radiative lifetimes of excited states are calculated at the FS RCC
level for both doped crystals. The calculated lifetime of the lowest $5d$ state
of Ce$^{3+}$ differs from the experimentally measured one by no more than
twice.",2310.09240v2
2017-12-19,"Influence of gallium content on Ga3+ position and photo- and thermally stimulated luminescence in Ce3+ - doped multicomponent (Y,Lu,)3GaxAl5-xO12 garnets","Photoluminescence, thermally stimulated luminescence (TSL) and EPR
characteristics of the Ce3+ doped single crystals of multicomponent
Y1Lu2GaxAl5-xO12 and Lu3GaxAl5-xO12 garnets with different Ga contents (x = 0,
1, 2, 3, 4, 5) excited in the Ce3+ - related absorption bands are investigated
in the 9 - 500 K temperature range. The distribution of Ga3+ and Al3+ ions in
the crystal lattice is determined by the NMR method. The relative number of
Ga3+ ions in the tetrahedral crystal lattice sites, the maxima positions of the
TSL glow curve peaks and the corresponding trap depths are found to decrease
linearly with the increasing Ga content. At the same time, the reduction of the
activation energy Ea of the TSL glow curve peaks creation under irradiation in
the 4f - 4d1 absorption band of Ce3+ is strongly nonlinear. To explain this
effect, the suggestion is made that Ea is the energy distance between the
excited 5d1 level of Ce3+ and a defect level located between the 5d1 level and
the bottom of the conduction band and arising from the Ga3+ ion perturbed by
the nearest neighboring Ce3+ ion. The electrons thermally released from the
excited Ce3+ ions are suggested to be trapped at the perturbed Ga3+ ions
resulting in the appearance of electron Ga2+ centers. In spite of the fact that
the paramagnetic Ga2+ ions were not detected by EPR, the described above
process was found for Fe3+ impurity ions, namely the electron transfer from the
5d1 excited levels of Ce3+ to Fe3+ was directly detected by EPR.",1712.06925v1
2018-08-06,Lithium Metal Penetration Induced by Electrodeposition through Solid Electrolytes: Example in Single-Crystal Li6La3ZrTaO12 Garnet,"Solid electrolytes are considered a potentially enabling component in
rechargeable batteries that use lithium metal as the negative electrode, and
thereby can safely access higher energy density than available with today's
lithium ion batteries. To do so, the solid electrolyte must be able to suppress
morphological instabilities that lead to poor coulombic efficiency and, in the
worst case, internal short circuits. In this work, lithium electrodeposition
experiments were performed using single-crystal Li6La3ZrTaO12 garnet as solid
electrolyte layers to investigate the factors that determine whether lithium
penetration occurs through brittle inorganic solid electrolytes. In these
single crystals, grain boundaries are excluded as possible paths for lithium
metal propagation. However, Vickers microindentation was used to introduce
sharp surface flaws of known size. Using operando optical microscopy, it was
found that lithium metal penetration sometimes initiates at these controlled
surface defects, and when multiple indents of varying size were present,
propagates preferentially from the largest defect. However, a second class of
flaws was found to be equally or more important. At the perimeter of surface
current collectors, an enhanced electrodeposition current density causes
lithium metal filled cracks to initiate and grow to penetration, even when the
large Vickers defects are in close proximity. Modeling the electric field
concentration for the experimental configurations, it was shown that a factor
of 5 enhancement in field can readily occur within 10 micrometers of current
collector discontinuities, which we interpret as the origin of
electrochemomechanical stresses leading to failure. Such field amplification
may determine the sites where supercritical surface defects dominate lithium
metal propagation during electrodeposition, overriding the presence of larger
defects elsewhere.",1808.02105v1
2018-12-31,Oxygen-vacancy centers in Y3Al5O12 garnet crystals: electron paramagnetic resonance and dielectric spectroscopy study,"F+ center, an electron trapped at oxygen vacancy (VO), was investigated in
the oxygen deficient Y3Al5O12 (YAG) crystals by EPR. The measurements were
performed at temperatures 5-450 K and frequencies 9.4-350 GHz with using both
the continue wave and pulse EPR technique. The pulse electron-nuclear double
resonance was applied to resolve the hyperfine interaction of the trapped
electron with surrounding nuclei. The measurements show that at low
temperatures, T < 50 K, EPR spectrum of the F+ center is anisotropic with g
factors in the range 1.999-1.988 and originates from three magnetically
inequivalent positions of the center in garnet lattice according to different
directions of the Al(IV)-VO-Al(VI) chains, where Al(IV) and Al(VI) are the
tetrahedral and octahedral Al sites, respectively. As the temperature
increases, the EPR spectrum becomes isotropic suggesting a motional averaging
of the anisotropy due to motion of electron between neighboring oxygen
vacancies. With further increase of the temperature to T > 200 K, we observed
delocalization of the electron into the conduction band with the activation
energy about 0.4-0.5 eV that resulted in substantial narrowing of the EPR
spectral line with simultaneous change of its shape from the Gaussian to
Lorentzian due to diminish up to zero of the Fermi contact hyperfine field at
27Al and 89Y nuclei. Such temperature behavior of the F+-center electron in YAG
is completely similar to behavior of a donor electron in a semiconductor. Our
findings is further supported by measurements of the conductivity and
dielectric properties. In particular, these data show that the conduction
electrons are not homogeneously distributed in the crystal: there are
high-conductive regions separated by poorly-conductive dielectric layers. This
leads to the so-called Maxwell-Wagner dielectric relaxation with huge apparent
dielectric constant at low frequencies.",1812.11873v2
2022-01-23,H$_2$O and CO$_2$ Surface Contamination of the Lithium-Stuffed Garnet,"Understanding the reactivity of ubiquitous molecules on complex oxides has
broad impacts in energy applications and catalysis. The garnet-type
Li$_7$La$_3$Zr$_2$O$_{12}$ is a promising solid-state electrolyte for
lithium(Li)-ion batteries, and it readily reacts with H$_2$O and CO$_2$ when
exposed to ambient air. Such reactions form a contamination layer on
Li$_7$La$_3$Zr$_2$O$_{12}$ that is detrimental to the battery operations. The
strong interactions of Li$_7$La$_3$Zr$_2$O$_{12}$ with H$_2$O and CO$_2$,
however, make Li$_7$La$_3$Zr$_2$O$_{12}$ a promising support to catalyze H$_2$O
dissociation and CO$_2$ adsorption. Here, using first-principles calculations,
we investigate the adsorption and reactions of H$_2$O and CO$_2$ on a
Li$_7$La$_3$Zr$_2$O$_{12}$ surface. We show that H$_2$O reacts through the
exchange of proton and Li$^{+}$ and produces metal hydroxide species. At high
H$_2$O coverage, half of the H$_2$O molecules dissociate while the other half
remain intact. CO$_2$ reacts with the Li$_7$La$_3$Zr$_2$O$_{12}$ surface
directly to produce carbonate species. We clarify that the individual reactions
of H$_2$O and CO$_2$ with Li$_7$La$_3$Zr$_2$O$_{12}$ are more thermodynamically
favorable than the co-adsorption of H$_2$O and CO$_2$. Finally, we demonstrate
that low temperature and high partial pressure promote the reactions of H$_2$O
and CO$_2$ with Li$_7$La$_3$Zr$_2$O$_{12}$. For energy storage application of
Li$_7$La$_3$Zr$_2$O$_{12}$, our study guides processing conditions to minimize
surface contamination. From a catalysis point of view, our findings reveal the
potential of using complex oxides, such as Li$_7$La$_3$Zr$_2$O$_{12}$ as a
support for reactions requiring H$_2$O dissociation and strong CO$_2$
adsorption.",2201.09348v1
2023-03-03,Comparative study of magnetocaloric properties for Gd$^{3+}$ compounds with different frustrated lattice geometries,"As materials with suppressed ordering temperatures and enhanced ground state
entropies, frustrated magnetic oxides are ideal candidates for cryogenic
magnetocaloric refrigeration. While previous materials design has focused on
tuning the magnetic moments, their interactions, and density of moments on the
lattice, there has been relatively little attention to frustrated lattices.
Prior theoretical work has shown that the magnetocaloric cooling rate at the
saturation field is proportional to a macroscopic number of soft mode
excitations that arise due to the classical ground state degeneracy. The number
of these modes is directly determined by the geometry of the frustrating
lattice. For corner-sharing geometries, the pyrochlore has 50\% more modes than
the garnet and kagome lattices, whereas the edge-sharing \emph{fcc} has only a
subextensive number of soft modes. Here, we study the role of soft modes in the
magnetocaloric effect of four large-spin Gd$^{3+}$ ($L=0$, $J=S=7/2$)
Heisenberg antiferromagnets on a kagome, garnet, pyrochlore, and \emph{fcc}
lattice. By comparing measurements of the magnetic entropy change $\Delta S_m$
of these materials at fields up to $9$~T with predictions using mean-field
theory and Monte Carlo simulations, we are able to understand the relative
importance of spin correlations and quantization effects. We observe that
tuning the value of the nearest neighbor coupling has a more dominant
contribution to the magnetocaloric entropy change in the liquid-He cooling
regime ($2$-$20$~K), rather than tuning the number of soft mode excitations.
Our results inform future materials design in terms of dimensionality, degree
of magnetic frustration, and lattice geometry.",2303.01773v1
1995-10-04,X-ray reflection in Galactic Black Hole Candidates: smeared edge profiles and resonant Auger destruction,"We consider the spectra of Thomson-thick, geometrically-thin accretion discs
around Galactic black hole candidates in the reflection model and compute their
iron K edges and iron K$\alpha$ lines. We compare the smeared iron K edge
profiles that we compute with observation and find them to be a satisfactory
description of the data. We find that a combination of Doppler broadening and
resonant Auger destruction of line photons can make iron K$\alpha$ lines very
difficult to detect in highly ionized inclined discs. We detail the physics of
resonant Auger destruction at the level it is currently understood and point
out its implications.",9510022v1
1997-06-04,The Galaxy Cluster Luminosity-Temperature Relationship and Iron Abundances - A Measure of Formation History ?,"Both the X-ray luminosity-temperature (L-T) relationship and the iron
abundance distribution of galaxy clusters show intrinsic dispersion. Using a
large set of galaxy clusters with measured iron abundances we find a
correlation between abundance and the relative deviation of a cluster from the
mean L-T relationship. We argue that these observations can be explained by
taking into account the range of cluster formation epochs expected within a
hierarchical universe. The known relationship of cooling flow mass deposition
rate to luminosity and temperature is also consistent with this explanation.
From the observed cluster population we estimate that the oldest clusters
formed at z>~2. We propose that the iron abundance of a galaxy cluster can
provide a parameterization of its age and dynamical history.",9706041v1
1997-11-28,ICM masses in nearby and distant clusters of galaxies,"We compile X-ray data of clusters of galaxies at a wide range of redshift
$z=0.0\sim1.0$ and compare X-ray luminosities, gas masses, iron abundances and
iron masses of nearby clusters and those of distant clusters as a function of
plasma temperature. All the date presented in this paper have been obtained
only with \ASCA and/or \ROSAT. No evidence for a change in the \KT -\LX\
relationship or \KT - iron abundance at $z<0.6$ is found. No significant change
in \KT -\LX relationship at $z>0.6$ is seen, either. However, the gas masses of
very distant clusters at $z\sim0.8-1.0$ and some clusters around $z\sim0.6$ are
significantly lower than those of nearby clusters, which indicates a hint of
evolution. The iron masses of the two very distant clusters at $z\sim0.8-1.0$
are significantly different from each other, which suggests that the epoch of
the metal injection into ICM is different from cluster to cluster.",9711353v1
1999-06-16,Iron line in the afterglow: a key to the progenitor,"The discovery of a powerful and transient iron line feature in the X-ray
afterglow spectrum of GRB 970508 and GRB 970828, if confirmed, would be a major
breakthrough for understanding the nature the progenitor of gamma-ray bursts.
We show that a large mass of iron very close to the burster is necessary to
produce the emission line. This in itself strongly limits the possible
progenitor of the gamma-ray event, suggesting the former explosion of a
supernova, as predicted in the Supranova model (Vietri & Stella 1998). The line
emission process and the line intensity depend strongly on the age, density and
temperature of the remnant. The simultaneous observation of the iron line and
of a power-law optical afterglow lasted for one year strongly suggest that the
burst emission is isotropic. Recent observations of GRB 990123 are also
discussed.",9906268v1
1999-07-25,Constraints on Type Ia Supernova Models from X-ray Spectra of Galaxy Clusters,"We present constraints on theoretical models of Type Ia supernovae using
spatially resolved ASCA X-ray spectroscopy of three galaxy clusters: Abell 496,
Abell 2199 and Abell 3571. All three clusters have central iron abundance
enhancements; an ensemble of abundance ratios are used to show that most of the
iron in the central regions of the clusters comes from SN Ia. These
observations are consistent with the suppressed galactic wind scenario proposed
by Dupke and White (1999). At the center of each cluster, simultaneous analysis
of spectra from all ASCA instruments shows that the nickel to iron abundance
ratio (normalized by the solar ratio) is Ni/Fe ~ 4. We use the nickel to iron
ratio as a discriminator between SN Ia explosion models: the Ni/Fe ratio of
ejecta from the ""Convective Deflagration"" model W7 is consistent with the
observations, while those of ""delayed detonation"" models are not consistent at
the 90% confidence level.",9907343v1
1999-09-29,Mass-radius relations for white dwarf stars of different internal compositions,"The purpose of this work is to present accurate and detailed mass-radius
relations for white dwarf (WD) models with helium, carbon, oxygen, silicon and
iron cores, by using a fully updated stellar evolutionary code. We considered
masses from 0.15 to 0.5 Mo for the case of helium core, from 0.45 to 1.2 Mo for
carbon, oxygen and silicon cores and from 0.45 to 1.0 Mo for the case of an
iron core. In view of recent measurements made by Hipparcos that strongly
suggest the existence of WDs with an iron-dominated core, we focus our
attention mainly on the finite-temperature, mass-radius relations for WD models
with iron interiors. Furthermore, we explore the effects of gravitational,
chemical and thermal diffusion on low-mass helium WD models with hydrogen and
helium envelopes.",9909499v1
1999-10-08,Iron line reverberation mapping with Constellation-X,"The broad X-ray iron line seen in the spectra of many AGN is thought to
originate from the inner regions of the putative black hole accretion disk, and
hence provides a rare probe of that central region. In principle, future high
throughput X-ray spectrometers should be able to examine the temporal response
of this fluorescent line to flares in the X-ray continuum source (which
energizes this emission line) - i.e. iron line reverberation mapping will be
possible. It has been previously found that there are robust reverberation
signatures of the black hole spin, mass and the X-ray flare location above the
accretion disk. Here, we simulate observations of a bright Seyfert nucleus with
the proposed NASA mission Constellation-X and demonstrate the feasibility of
detecting these reverberation signatures with this mission. Hence, starting
with XMM in 1999, and maturing with Constellation-X in c2010, iron line
reverberation will open a new window on the innermost regions of AGN.",9910168v1
2000-04-26,Broad iron lines in Active Galactic Nuclei,"An intrinsically narrow line emitted by an accretion disk around a black hole
appears broadened and skewed as a result of the Doppler effect and
gravitational redshift. The fluorescent iron line in the X-ray band at
6.4-6.9keV is the strongest such line and is seen in the X-ray spectrum of many
active galactic nuclei and, in particular, Seyfert galaxies. It is an important
diagnostic with which to study the geometry and other properties of the
accretion flow very close to the central black hole. The broad iron line
indicates the presence of a standard thin accretion disk in those objects,
often seen at low inclination. The broad iron line has opened up strong
gravitational effects around black holes to observational study with
wide-reaching consequences for both astrophysics and physics.",0004366v1
2000-06-23,The iron abundance in hot central stars of planetary nebulae derived from IUE spectra,"We present the first attempt to determine the iron abundance in hot central
stars of planetary nebulae. We perform an analysis with fully metal-line
blanketed NLTE model atmospheres for a sample of ten stars (T_eff >= 70.000 K)
for which high-resolution UV spectra are available from the IUE archive. In all
cases lines of Fe VI or Fe VII can be identified. As a general trend, the iron
abundance appears to be subsolar by 0.5-1 dex, however, the S/N of the IUE
spectra is not sufficient to exclude a solar abundance in any specific case.
Improved spectroscopy by either FUSE or HST is necessary to verify the
possibility of a general iron deficiency in central stars. The suspected
deficiency may be the result of gravitational settling in the case of three
high-gravity objects. For the other stars with low gravity and high luminosity
dust fractionation during the previous AGB phase is a conceivable origin.",0006338v1
2001-04-04,Iron line emission in X-ray afterglows,"Recent observations of X-ray afterglows reveal the presence of a redshifted
Kalpha iron line in emission in four bursts. In GRB 991216, the line was
detected by the low energy grating of Chandra, which showed the line to be
broad, with a full width of ~15,000 km/s. These observations indicate the
presence of a >1 solar mass of iron rich material in the close vicinity of the
burst, most likely a supernova remnant. The fact that such strong lines are
observed less than a day after the trigger strongly limits the size of the
remnant, which must be very compact. If the remnant had the observed velocity
since the supernova explosion, its age would be less than a month. In this case
nickel and cobalt have not yet decayed into iron. We show how to solve this
paradox.",0104086v1
2001-08-31,The complex iron line of NGC 5506,"The bright Narrow Emission Line Galaxy, NGC 5506, has been observed
simultaneously by XMM-Newton and BeppoSAX. The iron line is complex, with at
least two components: one narrow and corresponding to neutral iron, the second
one broad and corresponding to ionized iron. The latter line is equally well
fitted by a truly broad line or by a blend of He- and H-like narrow lines. The
bulk of the Compton reflection continuum originates in neutral matter, and is
therefore associated with the narrow line: they are most likely emitted in
distant matter. The origin of the ionized line(s) is less certain, but the
solution in terms of a blend of narrow lines from photoionized matter seems to
be preferable to emission from an ionized, relativistic accretion disc.",0108508v1
2001-10-09,The intracluster iron distribution around 4C+55.16,"We report on the metal distribution in the intracluster medium around the
radio galaxy 4C+55.16 (z=0.24) observed with the Chandra X-ray Observatory. The
radial metallicity profile shows a dramatic change at 10 arcsec (~50 kpc) in
radius from half solar to twice solar at inner radii. Also found was a
plume-like feature located at ~3 arcsec to the south-west of the centre of the
galaxy, which is mostly accounted for by a strong enhancement of iron L
emission. The X-ray spectrum of the plume is characterized by the metal
abundance pattern of Type Ia supernovae (SNeIa), i.e., large ratios of Fe to
alpha-elements, with the iron metallicity being unusually high at 7.9(+24/-5.0)
solar (90 per cent error). How the plume has been formed is not entirely clear.
The inhomogeneous iron distribution suggested in this cluster provides
important clues to understanding the metal enrichment process of the cluster
medium.",0110216v1
2002-05-19,Delayed Nickel Decay in Gamma Ray Bursts,"Recently observed emission lines in the X-ray afterglow of gamma ray bursts
suggest that iron group elements are either produced in the gamma ray burst, or
are present nearby. If this material is the product of a thermonuclear burn,
then such material would be expected to be rich in Nickel-56. If the nickel
remains partially ionized, this prevents the electron capture reaction normally
associated with the decay of Nickel-56, dramatically increasing the decay
timescale. Here we examine the consequences of rapid ejection of a fraction of
a solar mass of iron group material from the center of a collapsar/hypernova.
The exact rate of decay then depends on the details of the ionization and
therefore the ejection process. Future observations of iron, nickel and cobalt
lines can be used to diagnose the origin of these elements and to better
understand the astrophysical site of gamma ray bursts. In this model, the X-ray
lines of these iron-group elements could be detected in suspected hypernovae
that did not produce an observable gamma ray burst due to beaming.",0205321v1
2002-05-21,The complex iron line in NGC 7469 observed by BeppoSAX,"In this letter we present analysis of BeppoSAX data from a long look at the
Seyfert 1 galaxy NGC 7469. The presence of a soft excess below 0.8 keV is
confirmed by our analysis and no warm absorber component is required to fit the
spectrum. A complex iron emission line and the Compton reflection hump are
clearly detected. The profile of the line is too broad to associate this
feature with distant matter. In addition, the observed soft excess and the
energy of the iron line E_{Fe}=6.8 keV strongly support a scenario in which the
hard X-rays are reprocessed by a photoionized accretion disc. This hypothesis
was tested fitting the BeppoSAX spectrum with the ionized disc reflection model
of Ross & Fabian. A second narrow line component, in addition to that produced
in the disc, is also required to fit the observed iron line profile. A high
energy cut-off around 150 keV is clearly detected in the spectrum.",0205347v1
2002-09-19,Cosmic Needles versus Cosmic Microwave Background Radiation,"It has been suggested by a number of authors that the 2.7K cosmic microwave
background (CMB) radiation might have arisen from the radiation from Population
III objects thermalized by conducting cosmic graphite/iron needle-shaped dust.
Due to lack of an accurate solution to the absorption properties of exceedingly
elongated grains, in existing literature which studies the CMB thermalizing
process they are generally modelled as (1) needle-like spheroids in terms of
the Rayleigh approximation; (2) infinite cylinders; and (3) the antenna theory.
We show here that the Rayleigh approximation is not valid since the Rayleigh
criterion is not satisfied for highly conducting needles. We also show that the
available intergalactic iron dust, if modelled as infinite cylinders, is not
sufficient to supply the required opacity at long wavelengths to obtain the
observed isotropy and Planckian nature of the CMB. If appealing to the antenna
theory, conducting iron needles with exceedingly large elongations (10^4)
appear able to provide sufficient opacity to thermalize the CMB within the iron
density limit. But the applicability of the antenna theory to exceedingly thin
needles of nanometer/micrometer in thickness needs to be justified.",0209386v1
2002-11-18,XMM-Newton Observations of AGN Iron Line Profiles,"XMM-Newton observations of type I AGN are presented. The properties of the
iron K emission line are reviewed, the majority of AGN observed by XMM-Newton
show narrow, unresolved (by XMM) iron lines at 6.4 keV from cold matter that
must originate far from the inner accretion disc, perhaps in the putative torus
or outer broad line region. The strength of this narrow line appears to
decrease with luminosity, implying a reduction in the covering fraction of this
material in the more luminous quasars. Few examples of the broad, relativistic
iron line profile have been found by XMM-Newton, although in MCG -6-30-15, the
extreme breadth of the broad line component may imply a Kerr metric for the
central black hole. Generally, relativistic Fe K line profiles are not required
in a number of other Seyfert 1 X-ray spectra.",0211381v1
2003-07-08,The origin of the iron lines in NGC 7213,"The analysis of a simultaneous XMM-Newton/BeppoSAX plus three previous
BeppoSAX observations revealed that NGC 7213 is a rather peculiar Seyfert 1. No
significant Compton reflection component was observed, while an iron line
complex, best explained in terms of three narrow lines, is clearly apparent in
the data. Due to the absence of the reflection component, the neutral iron line
is likely not produced in a Compton-thick material, but current data do not
allow to choose between a Compton-thin torus and the BLR. The two ionized iron
lines from \ion{Fe}{xxv} and \ion{Fe}{xxvi} may be produced in a photoionized
gas with a column density of a few 10$^{23}$ cm$^{-2}$, in analogy with the
case of NGC 5506.",0307143v1
2003-07-09,The lack of variability of the iron line in MCG-6-30-15: general relativistic effects,"The spectrum and variability of the Seyfert galaxy MCG-6-30-15 can be
decomposed into two apparently disconnected components: a highly variable power
law and an almost constant component which contains a broad and strong iron
line. We explore a possible explanation of the puzzling lack of variability of
the iron line, by assuming that the variations of the power law component are
due to changes in the height of the primary source in the near vicinity of a
rotating black hole. Due to the bending of light in the strong field of the
central black hole, the apparent brightness of the power-law component can vary
by about a factor 4 according to its position, while the total iron line flux
variability is less than 20 percent. This behaviour is obtained if the primary
source is located within 3-4 gravitational radii ($r_{\rm g}$) from the
rotation axis with a variable height of between $\sim$ 3 and 8 $r_{\rm g}$.
These results revive the possibility that future X-ray observations of
MCG-6-30-15 can map out the strong gravity regime of accreting black holes.",0307163v1
2003-11-13,The reprocessing features in the X-ray spectrum of the NELG MCG-5-23-16,"We present results from the spectral analysis of the Seyfert 1.9 galaxy
MCG-5-23-16, based on ASCA, BeppoSAX, Chandra and XMM-Newton observations. The
spectrum of this object shows a complex iron Kalpha emission line, which is
best modeled by a superposition of a narrow and a broad (possibly relativistic)
iron line, together with a Compton reflection component. Comparing results from
all (six) available observations, we do not find any significant variation in
the flux of both line components. The moderate flux continuum variability
(about 25% difference between the brightest and faintest states), however, does
not permit us to infer much about the location of the line-emitting material.
The amount of Compton reflection is lower than expected from the total iron
line EW, implying either an iron overabundance or that one of the two line
components (most likely the narrow one) originates in Compton-thin matter.",0311316v1
2003-11-27,The Iron Unresolved Transition Array in Active Galactic Nuclei,"The unresolved transition array (UTA) of iron M-shell ions is a prominent
absorption feature in the X-ray spectrum of many active galactic nuclei (AGNs).
Modeling photoionized plasmas in attempt to match the observed silicon and
oxygen lines fail to predict the level of ionization of iron as inferred by
this feature. It is suggested that the discrepancy is due to underestimation of
the low-temperature dielectronic recombination rates for iron M-shell ions.
Modified ionization balance calculations, based on new (guessed) atomic data,
support this idea. The results are shown and compared to the global properties
of several observed UTAs. Implications for AGN absorbing gas are discussed
including an analysis of the ionization parameter distribution in such sources.
The need for real calculations of such atomic data is stressed.",0311604v1
2004-03-10,Handling of Atomic Data,"State-of-the-art NLTE model-atmosphere codes have arrived at a high level of
numerical sophistication and are now useful tools to analyze high-quality
spectra from the infrared to the X-ray wavelength range. The capacity of
current computers permit calculations which include line spectra from all
elements from hydrogen up to the iron group. The lack of reliable atomic data
has become a critical problem for further progress.
  We summarize available sources of atomic data, and discuss how these are
implemented in the Tuebingen Model-Atmosphere Package TMAP. We describe our
Iron Opacity Interface IrOnIc which is used to calculate opacities of
iron-group elements from Kurucz's and the Opacity Project's data.
  We propose general use of the Tuebingen Model-Atom Database TMAD, which would
allow an easy exchange of ready-to-use model atoms between all model-atmosphere
groups. The comparison of model-atmosphere calculations would then be much
easier, and would save a great deal of manpower that is presently consumed
preparing suitable model atoms for spectral analyses.",0403239v1
2004-03-19,Extragalactic UHE proton spectrum and prediction for iron-nuclei flux at 10^8 - 10^9 GeV,"We investigate the problem of transition from Galactic cosmic rays to
extragalactic ultra high energy cosmic rays. Using the model for extragalactic
ultra high energy cosmic rays and observed all-particle cosmic ray spectrum, we
calculate the galactic spectrum of iron nuclei in the energy range $10^8 -
10^9$ GeV. The flux and spectrum predicted at lower energies agree well with
the KASCADE data. The transition from Galactic to extragalactic cosmic rays is
distinctly seen in spectra of protons and iron nuclei, when they are measured
separately. The shape of predicted iron spectrum agrees with the Hall
diffusion.",0403477v2
2004-04-15,X-ray reprocessing in Seyfert Galaxies: simultaneous XMM-Newton/BeppoSAX observations,"We selected a sample of eight bright unobscured (at least at the iron line
energy) Seyfert Galaxies observed simultaneously by XMM-Newton and BeppoSAX,
taking advantage of the complementary characteristics of the two missions. The
main results of our analysis can be summarized as follows: narrow neutral iron
lines are confirmed to be an ubiquitous component in Seyfert spectra; none of
the analyzed sources shows unambiguously a broad relativistic iron line; all
the sources of our sample (with a single exception) show the presence of a
Compton reflection component; emission lines from ionized iron are observed in
some sources; peculiar weak features around 5-6 keV (possibly arising from
rotating spots on the accretion disk) are detected in two sources. The scenario
emerging from these results strongly requires some corrections for the
classical model of reprocessing from the accretion disk. As for materials
farther away from the Black Hole, our results represent a positive test for the
Unification Model, suggesting the presence of the torus in (almost) all
sources, even if unobscured.",0404308v1
2004-10-23,Why the Model of a Hydrogen-Filled Sun Is Obsolete,"Isotope analyses on meteorites, planets, lunar samples, the solar wind, and
solar flares show that heterogeneous debris of a supernova (SN) that exploded
here 5 Gy ago formed the solar system. The Sun formed on the collapsed SN core.
Iron meteorites and the iron cores of the terrestrial planets formed out of
iron-rich material surrounding the SN core. Giant gaseous planets formed out of
the light-weight elements in the outer SN layers. Mass separation enriches
light elements like H and He at the solar surface, but the bulk Sun consists
almost entirely of the same seven, even-numbered elements that comprise 99% of
ordinary meteorites - iron (Fe), oxygen (O), nickel (Ni), silicon (Si),
magnesium (Mg), sulfur (S) and calcium (Ca).",0410569v1
2004-11-22,The influence of chemical composition on the properties of Cepheid stars I - Period-Luminosity relation vs iron abundance,"We have assessed the influence of the stellar iron content on the Cepheid
Period-Luminosity (PL) relation by relating the V band residuals from the
Freedman et al (2001) PL relation to [Fe/H] for 37 Galactic and Magellanic
Clouds Cepheids. The iron abundances were measured from FEROS and UVES
high-resolution and high-signal to noise optical spectra. Our data indicate
that the stars become fainter as metallicity increases, until a plateau or
turnover point is reached at about solar metallicity. Our data are incompatible
with both no dependence of the PL relation on iron abundance, and with the
linearly decreasing behavior often found in the literature (e.g. Kennicutt et
al 1998, Sakai et al 2004). On the other hand, non-linear theoretical models of
Fiorentino et al (2002) provide a fairly good description of the data.",0411594v2
2005-01-25,The Iron Line Background,"We investigate the presence of iron line emission among faint X-ray sources
identified in the 1Ms Chandra Deep Field South and in the 2Ms Chandra Deep
Field North. Individual source spectra are stacked in seven redshift bins over
the range z=0.5-4. We find that iron line emission is an ubiquitous property of
X-ray sources up to z~3. The measured line strengths are in good agreement with
those expected by simple pre-Chandra estimates based on X-ray background
synthesis models. The average rest frame equivalent width of the iron line does
not show significant changes with redshift.",0501542v1
2005-10-20,Truncated disc versus extremely broad iron line in XTE J1650-500,"There is growing evidence from both spectral and timing properties that there
is a truncated inner accretion disc in low mass accretion rate Galactic black
hole systems. The detection of extremely smeared relativistic iron lines in
some of these systems is the only current piece of evidence which conflicts
with this geometrical interpretation of the low/hard state. Here we show that
the line width in the BeppoSAX data of a bright low/hard state of the transient
black hole XTE J1650-500 is indeed consistent with extreme relativistic
effects. However, the relativistic smearing can be significantly reduced if
there is also resonance iron K line absorption from an outflowing disc wind.
The iron line smearing is then completely compatible with a truncated disc, so
gives no information on the black hole spin.",0510614v2
2006-03-06,Relativistic Iron lines at high redshifts,"The shape and the intensity of the 6.4 keV iron line bring unique information
on the geometrical and physical properties of the supermassive black hole and
the surrounding accreting gas at the very center of Active Galactic Nuclei.
While there are convincing evidences of a relativistically broadened iron line
in a few nearby bright objects, their properties at larger distances are
basically unknown. We have searched for the presence of iron line by fully
exploiting Chandra observations in the deep fields. The line is clearly
detected in the average spectra of about 250 sources stacked in several
redshift bins over the range z=0.5-4.0. We discuss their average properties
with particular enphasys on the presence and intensity of a broad component.",0603139v1
2006-08-24,Non-LTE modeling of supernova-fallback disks,"We present a first detailed spectrum synthesis calculation of a
supernova-fallback disk composed of iron. We assume a geometrically thin disk
with a radial structure described by the classical alpha-disk model. The disk
is represented by concentric rings radiating as plane-parallel slabs. The
vertical structure and emission spectrum of each ring is computed in a fully
self-consistent manner by solving the structure equations simultaneously with
the radiation transfer equations under non-LTE conditions. We describe the
properties of a specific disk model and discuss various effects on the emergent
UV/optical spectrum.
  We find that strong iron-line blanketing causes broad absorption features
over the whole spectral range. Limb darkening changes the spectral distribution
up to a factor of four depending on the inclination angle. Consequently, such
differences also occur between a blackbody spectrum and our model. The overall
spectral shape is independent of the exact chemical composition as long as iron
is the dominant species. A pure iron composition cannot be distinguished from
silicon-burning ash. Non-LTE effects are small and restricted to few spectral
features.",0608529v1
2006-09-15,A Short Review of Relativistic Iron Lines from Stellar-Mass Black Holes,"In this contribution, I briefly review recent progress in detecting and
measuring the properties of relativistic iron lines observed in stellar-mass
black hole systems, and the aspects of these lines that are most relevant to
studies of similar lines in Seyfert-1 AGN. In particular, the lines observed in
stellar-mass black holes are not complicated by complex low-energy absorption
or partial-covering of the central engine, and strong lines are largely
independent of the model used to fit the underlying broad-band continuum flux.
Indeed, relativistic iron lines are the most robust diagnostic of black hole
spin that is presently available to observers, with specific advantages over
the systematics-plagued disk continuum. If accretion onto stellar-mass black
holes simply scales with mass, then the widespread nature of lines in
stellar-mass black holes may indicate that lines should be common in Seyfert-1
AGN, though perhaps harder to detect.",0609447v1
2006-11-14,Chandra Detection of Fe XVII in Absorption: Iron Abundance in the Hot Gaseous Interstellar Medium,"The iron depletion level and the gas-phase iron abundance in the hot ~10^6 K
interstellar medium (ISM) is critical to the understanding of its energy
balance as well as the thermal sputtering, cooling, and heating processes of
dust grains. Here we report on the first detection of the Fe XVII absorption
line at 15.02 A from the hot ISM in the spectrum of the low mass X-ray binary
4U~1820-303 observed with Chandra X-Ray Observatory. By jointly analyzing this
absorption line with those from OVII, OVIII, and NeIX ions in the same
spectrum, we obtain an abundance ratio as Fe/Ne=0.8(0.4, 2.1) in units of the
Anders & Grevesse solar value (90% confidence intervals). We find that the
result is robust with respect to different assumed gas temperature
distributions. The obtained Fe/Ne abundance ratio, albeit with large
uncertainties, is consistent with the solar value, indicating that there is
very little or no iron depleted into dust grains, i.e., most of or all of the
dust grains have been destroyed in the hot ISM.",0611446v2
2006-11-21,Discovery of Variable Iron Fluorescence from Reflection Nebulae in the Galactic Center,"Based on three years of deep observations of the Galactic center with the
Chandra X-ray Observatory, we report the discovery of changes in the
intensities and morphologies of two hard X-ray nebulosities. The nebulosities
are dominated by fluorescent iron emission, and are coincident with molecular
clouds. The morphological changes are manifest on parsec scales, which requires
that these iron features are scattered X-rays from a 2 or 3-year-long outburst
of a point source (either Sgr A* or an X-ray binary) with a luminosity of at
least 1e37 erg/s. The variability precludes the hypotheses that these nebulae
either are produced by keV electrons bombarding molecular clouds, or are
iron-rich ejecta from supernovae. Moreover, the morphologies of the reflection
nebulae implies that the dense regions of the clouds are filamentary, with
widths of ~0.3 pc and lengths of ~2 pc.",0611651v1
2007-01-17,Galactic Basins of Helium and Iron around the Knee Energy,"The differential energy spectrum of cosmic rays exhibits a change of slope,
called ""knee"" of the spectrum, around the nominal energy of 3 x 10^15 eV, and
individual ""knees"" for single ions, at different energies. The present work
reports a detailed account of the characteristics and the origin of the knees
for Helium and Iron. Current observational data regarding the magnetic field,
the insterstellar matter density, the size of the Galaxy and the galactic wind,
are incorporated in appropriate algorithms which allow to simulate millions of
cosmic-ion trajectories in the disk. Bundles of ion trajectories define
galactic regions called basins utilized in the present analysis of the knees.
The fundamental role of the nuclear cross sections in the origin of the helium
and iron knees is demonstrated and highlighted.
  The results of the calculation are compared with the experimental data in the
energy interval 10^12 eV - 5 x 10^17 eV. There is a fair agreement between the
computed and measured energy spectra of Helium and Iron; rather surprisingly
their relative intensities are also in accord with those computed here. The
results suggest that acceleration mechanisms in the disk are extraneous to the
origin of the ""knees"".",0701498v1
1999-05-21,Structure and Dynamics of Liquid Iron under Earth's Core Conditions,"First-principles molecular dynamics simulations based on density-functional
theory and the projector augmented wave (PAW) technique have been used to study
the structural and dynamical properties of liquid iron under Earth's core
conditions. As evidence for the accuracy of the techniques, we present PAW
results for a range of solid-state properties of low- and high-pressure iron,
and compare them with experimental values and the results of other
first-principles calculations. In the liquid-state simulations, we address
particular effort to the study of finite-size effects, Brillouin-zone sampling
and other sources of technical error. Results for the radial distribution
function, the diffusion coefficient and the shear viscosity are presented for a
wide range of thermodynamic states relevant to the Earth's core. Throughout
this range, liquid iron is a close-packed simple liquid with a diffusion
coefficient and viscosity similar to those of typical simple liquids under
ambient conditions.",9905319v1
2001-05-11,Magnetization Process of Nanoscale Iron Cluster,"Low-temperature magnetization process of the nanoscale iron cluster in
linearly sweeped fields is investigated by a numerical analysis of
time-dependent Schr$\ddot{\rm o}$dinger equation and the quantum master
equation. We introduce an effective basis method extracting important states,
by which we can obtain the magnetization process effectively. We investigate
the structure of the field derivative of the magnetization. We find out that
the antisymmetric interaction determined from the lattice structure reproduces
well the experimental results of the iron magnets and that this interaction
plays an important role in the iron cluster. Deviations from the adiabatic
process are also studied. In the fast sweeping case, our calculations indicate
that the nonadiabatic transition dominantly occurs at the level crossing for
the lowest field. In slow sweeping case, due to the influence of the thermal
environment to the spin system, the field derivative of the magnetization shows
an asymmetric behavior, the magnetic F$\ddot{\rm o}$hn effect, which explains
the substructure of the experimental results in the pulsed field.",0105227v1
2001-11-26,Evidence of local magnetic order in hcp iron from Raman mode splitting,"Experimental measurements of Raman spectra for hcp iron at high pressure show
two modes over a considerable pressure range in contrast to the prediction of
one doubly degenerate mode for the hcp lattice. We use density functional
theory to investigate the influence of magnetic order on the Raman active modes
of hcp iron. We find an antiferromagnetic state that lifts the degeneracy of
the transverse optical mode, and yields stable antiferromagnetic moments up to
approximately 60 GPa (55 Bohr$^3$). The resulting frequencies of the two
transverse optical modes are in good agreement with the experimental Raman
shifts, lending support to the existence of local antiferromagnetic order in
hcp iron.",0111487v1
2003-10-22,Unconventional superconductivity and normal state properties of epsilon-iron at high pressure,"Following the discovery of superconductivity in epsilon-iron, subsequent
experiments hinted at non-Fermi liquid behaviour of the normal phase and
sensitive dependence of the superconducting state on disorder, both signatures
of unconventional pairing. We report further resistive measurements under
pressure of samples of iron from multiple sources. The normal state resistivity
of epsilon-iron varied as rho_0+AT^{5/3} at low temperature over the entire
superconducting pressure domain. The superconductivity could be destroyed by
mechanical work, and was restored by annealing, demonstrating sensitivity to
the residual resistivity rho_0. There is a strong correlation between the rho_0
and A coefficients and the superconducting critical temperature T_c. Within the
partial resistive transition there was a significant current dependence, with
V(I)=a(I-I_0)+bI^2, with a >> b, possibly indicating flux-flow resistivity,
even in the absence of an externally applied magnetic field.",0310519v1
2004-05-19,Dynamics of the magnetic and structural a -> e phase transition in Iron,"We have studied the high-pressure iron bcc to hcp phase transition by
simultaneous X-ray Magnetic Circular Dichroism (XMCD) and X-ray Absorption
Spectroscopy (XAS) with an X-ray dispersive spectrometer. The combination of
the two techniques allows us to obtain simultaneously information on both the
structure and the magnetic state of Iron under pressure. The magnetic and
structural transitions simultaneously observed are sharp. Both are of first
order in agreement with theoretical prediction. The pressure domain of the
transition observed (2.4 $\pm$ 0.2 GPa) is narrower than that usually cited in
the literature (8 GPa). Our data indicate that the magnetic transition slightly
precedes the structural one, suggesting that the origin of the instability of
the bcc phase in iron with increasing pressure is to be attributed to the
effect of pressure on magnetism as predicted by spin-polarized full potential
total energy calculations.",0405439v4
2005-01-17,Electronic structure of nanoscale iron oxide particles measured by scanning tunneling and photoelectron spectroscopies,"We have investigated the electronic structure of nano-sized iron oxide by
scanning tunnelling microscopy (STM) and spectroscopy (STS) as well as by
photoelectron spectroscopy. Nano particles were produced by thermal treatment
of Ferritin molecules containing a self-assembled core of iron oxide. Depending
on the thermal treatment we were able to prepare different phases of iron oxide
nanoparticles resembling gamma-Fe2O3, alpha-Fe2O3, and a phase which apparently
contains both gamma-Fe2O3 and alpha-Fe2O3. Changes to the electronic structure
of these materials were studied under reducing conditions. We show that the
surface band gap of the electronic excitation spectrum can differ from that of
bulk material and is dominated by surface effects.",0501377v1
2006-01-30,Iron self-diffusion in FeZr/$^{57}$FeZr multilayers measured by neutron reflectometry: Effect of applied compressive stress,"Iron self-diffusion in nano-composite FeZr alloy has been investigated using
neutron reflectometry technique as a function of applied compressive stress. A
composite target of (Fe+Zr) and (57Fe+Zr) was alternatively sputtered to
deposit chemically homogeneous multilayer (CHM) structure,
[Fe75Zr25/57Fe75Zr25]10. The multilayers were deposited on to a bent Si wafer
using a 3-point bending device. Post-deposition, the bending of the substrate
was released which results in an applied compressive stress on to the
multilayer. In the as-deposited state, the alloy multilayer forms an amorphous
phase, which crystallizes into a nano-composite phase when heated at 373 K.
Bragg peaks due to isotopic contrast were observed from CHM, when measured by
neutron reflectivity, while x-ray reflectivity showed a pattern corresponding
to a single layer. Self-diffusion of iron was measured with the decay of the
intensities at the Bragg peaks in the neutron reflectivity pattern after
thermal annealing at different temperatures. It was found that the
self-diffusion of iron slows down with an increase in the strength of applied
compressive stress.",0601646v1
2007-01-12,Iron melting curve with a tricritical point,"Solidification as a first order phase transition is described in the Landau
theory by the same equation as tricritical phenomena. Here, the solidification
or melting temperature against pressure curve is modelled to end at a
tricritical point. The model gives the phase transition temperature's
dependence on pressure up to the quadratic term with a definite expression for
the coefficients. This formula is expected to be generally valid for pure
materials having melting curves with dT/dP approaching zero at very high P.
Excellent experimental agreement is obtained for iron, the material having the
most high pressure data which rather accurately determines the value of the
coefficient defining the curvature. The geophysically interesting iron
solidification temperatures at the Earth's core pressures are obtained. In
addition, the general formulae for entropy change, latent heat and volume
contraction in solidification are found and calculated for iron as functions of
pressure and temperature.",0701283v1
2004-09-21,The axial ratio of hcp iron at the conditions of the Earth's inner core,"We present ab initio calculations of the high-temperature axial c/a ratio of
hexagonal-close-packed (hcp) iron at Earth's core pressures, in order to help
interpret the observed seismic anisotropy of the inner core. The calculations
are based on density functional theory, which is known to predict the
properties of high-pressure iron with good accuracy. The temperature dependence
of c/a is determined by minimising the Helmholtz free energy at fixed volume
and temperature, with thermal contributions due to lattice vibrations
calculated using harmonic theory. Anharmonic corrections to the harmonic
predictions are estimated from calculations of the thermal average stress
obtained from ab initio molecular dynamics simulations of hcp iron at the
conditions of the inner core. We find a very gradual increase of axial ratio
with temperature. This increase is much smaller than found in earlier
calculations, but is in reasonable agreement with recent high-pressure,
high-temperature diffraction measurements. This result casts doubt on an
earlier interpretation of the seismic anisotropy of the inner core.",0409109v1
2007-10-29,Muon content of ultra-high-energy air showers: Yakutsk data versus simulations,"We analyse a sample of 33 extensive air showers (EAS) with estimated primary
energies above 2\cdot 10^{19} eV and high-quality muon data recorded by the
Yakutsk EAS array. We compare, event-by-event, the observed muon density to
that expected from CORSIKA simulations for primary protons and iron, using
SIBYLL and EPOS hadronic interaction models. The study suggests the presence of
two distinct hadronic components, ``light'' and ``heavy''. Simulations with
EPOS are in a good agreement with the expected composition in which the light
component corresponds to protons and the heavy component to iron-like nuclei.
With SYBILL, simulated muon densities for iron primaries are a factor of \sim
1.5 less than those observed for the heavy component, for the same
electromagnetic signal. Assuming two-component proton-iron composition and the
EPOS model, the fraction of protons with energies E>10^{19} eV is
0.52^{+0.19}_{-0.20} at 95% confidence level.",0710.5508v2
2007-11-03,"Inner-shell Annihilation of Positrons in Argon, Iron and Copper Atoms","The annihilation parameters of positrons with electrons in different shells
of Argon, Iron and Copper atoms are calculated below the positronium (Ps)
formation thresholds. Quite accurate ab initio calculations of the bound state
wavefunctions of Argon, Iron and Copper orbitals are obtained from Cowan
computer code. A least-squares variational method (LSVM) is used for
determining the wavefunction of the positrons. The program is employed for
calculating the s-wave partial cross sections of positrons scattered by Iron
and Copper atoms. Our results of the effective charge are compared with
available experimental and theoretical ones. --",0711.0453v1
2008-04-06,Carbon nanotube-sharp tips and carbon nanotube-soldering irons,"We report on the nano-electron beam assisted fabrication of atomically sharp
iron-based tips and on the creation of a nano-soldering iron for
nano-interconnects using Fe-filled multiwalled carbon nanotubes (MWCNTs). High
energy electron beam machining has been proven a powerful tool to modify
desired nanostructures for technological applications and to form molecular
junctions and interconnections between carbon nanotubes. Recent studies showed
the high degree of complexity in the creation of direct interconnections
between multiwalled and CNTs having dissimilar diameters. Our technique allows
for carving a MWCNT into a nanosoldering iron that was demonstrated capable of
joining two separated halves of a tube. This approach could easily be extended
to the interconnection of two largely dissimilar CNTs, between a CNT and a
nanowire or between two nanowires.",0804.0929v1
2008-05-06,Coherence-incoherence crossover in the normal state of iron-oxypnictides and importance of the Hund's rule coupling,"A new class of high temperature superconductors based on iron and arsenic was
recently discovered, with superconducting transition temperature as high as 55
K. Here we show, using microscopic theory, that the normal state of the iron
pnictides at high temperatures is highly anomalous, displaying a Curie Weiss
susceptibility and a linear temperature dependence of the resistivity. Below a
coherence scale T*, the resistivity sharply drops and susceptibility crosses
over to Pauli-like temperature dependence. Remarkably, the
coherence-incoherence crossover temperature is a very strong function of the
strength of the Hund's rule coupling J_Hund. On the basis of the normal state
properties, we estimate J_Hund to be 0.35-0.4 eV. In the atomic limit, this
value of J_Hund leads to the critical ratio of the exchange constants
J_1/J_2~2. While normal state incoherence is in common to all strongly
correlated superconductors, the mechanism for emergence of the incoherent state
in iron-oxypnictides, is unique due to its multiorbital electronic structure.",0805.0722v2
2008-05-27,Spin density wave anomaly at 140 K in the ternary iron arsenide BaFe2As2,"The ternary iron arsenide BaFe2As2 with the tetragonal ThCr2Si2-type
structure exhibits a spin density wave (SDW) anomaly at 140 K, very similar to
LaFeAsO, the parent compound of the iron arsenide superconductors. BaFe2As2 is
a poor Pauli-paramagnetic metal and undergoes a structural and magnetic phase
transition at 140 K, accompanied by strong anomalies in the specific heat,
electrical resistance and magnetic susceptibility. In the course of this
transition, the space group symmetry changes from tetragonal (I4/mmm) to
orthorhombic (Fmmm). 57Fe Moessbauer spectroscopy experiments show a single
signal at room temperature and full hyperfine field splitting below the phase
transition temperature (5.2 T at 77 K). Our results suggest that BaFe2As2 can
serve as a new parent compound for oxygen-free iron arsenide superconductors.",0805.4021v2
2008-05-29,Superconductivity at 38 K in the iron arsenide (Ba1-xKx)Fe2As2,"The ternary iron arsenide BaFe2As2 becomes superconducting by hole doping,
which was achieved by partial substitution of the barium site with potassium.
We have discovered bulk superconductivity up to Tc = 38 K in (Ba1-xKx)Fe2As2
with x = 0.4. The parent compound BaFe2As2 as well as KFe2As2 both crystallize
in the tetragonal ThCr2Si2-type structure, which consists of (FeAs)- iron
arsenide layers separated by barium or potassium ions. BaFe2As2 is a poor metal
and exhibits a SDW anomaly at 140 K. By substituting Ba2+ for K+ ions we have
introduced holes in the (FeAs)- layers, which suppress the SDW anomaly and
induce superconductivity. This scenario is very similar to the recently
discovered arsenide-oxide superconductors. The Tc of 38 K in (Ba1-xKx)Fe2As2 is
the highest observed critical temperature in hole doped iron arsenide
superconductors so far. Therefore, we were able to expand this class of
superconductors by oxygen-free compounds with the ThCr2Si2-type structure. Our
results suggest, that superconductivity in these systems essentially evolves
from the (FeAs)- layers and may occur in other related compounds.",0805.4630v2
2008-06-04,Parton distribution function uncertainties & nuclear corrections for the LHC,"We study nuclear effects of charged current deep inelastic neutrino-iron
scattering in the framework of a chi^2 analysis of parton distribution
functions (PDFs). We extract a set of iron PDFs which are used to compute
x_Bj-dependent and Q^2-dependent nuclear correction factors for iron structure
functions which are required in global analyses of free nucleon PDFs. We
compare our results with nuclear correction factors from neutrino-nucleus
scattering models and correction factors for charged lepton-iron scattering. We
find that, except for very high x_Bj, our correction factors differ in both
shape and magnitude from the correction factors of the models and
charged-lepton scattering.",0806.0723v1
2008-08-06,Kondo Effect and Spin Glass Behavior of Dilute Iron Clusters in Silver Studied by Mössbauer Spectroscopy and Resistivity,"Thin films of silver containing 0.3 - 1.5 at % Fe have been prepared by vapor
co-deposition. Depending on substrate temperature and iron concentration we
could systematically follow the formation of nanometer size clusters of iron
from initially dilute iron monomers. samples were characterized via X-ray
diffraction, resistivity and M\""{o}ssbauer spectroscopic measurements. The
magnetic behavior derived from M\""{o}ssbauer data can be best described with an
ensemble of ferromagnetic mono-domain particles. The magnetic freezing observed
at low temperatures, is controlled via the inter-particle interactions mediated
via conduction electron polarization, i.e. RKKY interaction. The interaction of
the cluster magnetic moments with the conduction electron sea is best
quantified by the electrical resistivity data. For all studied concentrations
we find a non-monotonic variation with temperature which can be understood by
competing shielding of the cluster moments by conduction electron spin
scattering due to Kondo effect and the magnetic coupling.",0808.0929v1
2008-08-19,Telescopes versus Microscopes: the puzzle of Iron-60,"The discovery that the short-lived radionucleide iron-60 was present in the
oldest meteorites suggests that the formation of the Earth closely followed the
death of a massive star. I discuss three astrophysical origins: winds from an
AGB star, injection of supernova ejecta into circumstellar disks, and induced
star formation on the boundaries of HII regions. I show that the first two fail
to match the solar system iron-60 abundance in the vast majority of star
forming systems. The cores and pillars on the edges of HII regions are
spectacular but rare sites of star formation and larger clumps with masses
1e3-1e4 solar masses at tens of parsec from a supernova are a more likely birth
environment for our Sun. I also examine gamma-ray observations of iron-60 decay
and show that the Galactic background could account for the low end of the
range of meteoritic measurements if the massive star formation rate was at
least a factor of 2 higher 4.6 Gyr ago.",0808.2506v1
2008-09-30,Effect of the tetrahedral distortion on the electronic properties of iron-pnictides,"We study the dependence of the electronic structure of iron pnictides on the
angle formed by the arsenic-iron bonds. Within a Slater-Koster tight binding
model which captures the correct symmetry properties of the bands, we show that
the density of states and the band structure are sensitive to the distortion of
the tetrahedral environment of the iron atoms. This sensitivity is extremely
strong in a two-orbital (d_xz, d_yz) model due to the formation of a flat band
around the Fermi level. Inclusion of the d_xy orbital destroys the flat band
while keeping a considerable angle dependence in the band structure.",0810.0019v2
2008-10-13,"Synthesis, crystal structure and spin-density-wave anomaly of the iron arsenide-fluoride SrFeAsF","The new quaternary iron arsenide-fluoride SrFeAsF with the tetragonal
ZrCuSiAs-type structure was synthesized and the crystal structure was
determined by X-ray powder diffraction (P4/nmm, a = 399.30(1), c = 895.46(1)
pm). SrFeAsF undergoes a structural and magnetic phase transition at 175 K,
accompanied by strong anomalies in the specific heat, electrical resistance and
magnetic susceptibility. In the course of this transition, the space group
symmetry changes from tetragonal (P4/nmm) to orthorhombic (Cmme). 57Fe
Moessbauer spectroscopy experiments show a single signal at room temperature at
an isomer shift of 0.30(1) mm/s and magnetic hyperfine-field splitting below
the phase transition temperature. Our results clearly show that SrFeAsF
exhibits a spin density wave (SDW) anomaly at 175 K very similar to LaFeAsO,
the parent compound of the iron arsenide-oxide superconductors and thus SrFeAsF
may serve as a further parent compound for oxygen-free iron arsenide
superconductors.",0810.2120v1
2008-11-22,A simple theory of the Invar effect in iron-nickel alloys,"Certain alloys of iron and nickel (so-called 'Invar' alloys) exhibit almost
no thermal expansion over a wide range of temperature. It is clear that this is
the result of an anomalous contraction upon heating which counteracts the
normal thermal expansion arising from the anharmonicity of lattice vibrations.
This anomalous contraction seems to be related to the alloys' magnetic
properties, since the effect vanishes at a temperature close to the Curie
temperature. However, despite many years of intensive research, a widely
accepted microscopic theory of the Invar effect in face-centered-cubic Fe-Ni
alloys is still lacking. Here we present a simple theory of the Invar effect in
these alloys based on Ising magnetism, ab initio total energy calculations, and
the Debye-Gruneisen model. We show that this theory accurately reproduces
several well known properties of these materials, including Guillaume's famous
plot1 of the thermal expansion coefficient as a function of the concentration
of nickel. Within the same framework, we are able to account in a
straightforward way for experimentally observed deviations from Vegard's law.
Our approach supports the idea that the lattice constant is governed by a few
parameters, including the fraction of iron-iron nearest-neighbour pairs.",0811.3673v1
2008-12-17,Nuclear Parton Distribution Functions,"We study nuclear effects of charged current deep inelastic neutrino-iron
scattering in the framework of a chi^2 analysis of parton distribution
functions (PDFs). We extract a set of iron PDFs which are used to compute
x_Bj-dependent and Q^2-dependent nuclear correction factors for iron structure
functions which are required in global analyses of free nucleon PDFs. We
compare our results with nuclear correction factors from neutrino-nucleus
scattering models and correction factors for charged-lepton--iron scattering.
We find that, except for very high x_Bj, our correction factors differ in both
shape and magnitude from the correction factors of the models and
charged-lepton scattering.",0812.3370v1
2008-12-26,Normal State Spin Dynamics of Five-band Model for Iron-pnictides,"Normal state spin dynamics of the recently discovered iron-pnictide
superconductors is discussed by calculating spin structure factor S(q, omega)
in an itinerant five-band model within RPA approximation. Due to the
characteristic Fermi surface structure of iron-pnictide, column like response
is found at (pi, 0) in extended Brillouin zone in the undoped case, which is
consistent with the recent neutron scattering experiment. This indicates that
the localized spin model is not necessary to explain the spin dynamics of this
system. Furthermore, we show that the temperature dependence of inelastic
neutron scattering intensity can be well reproduced in the itinerant model. We
also study NMR 1/T_1T in the same footing calculation and show that the
itinerant model can capture the magnetic property of iron-pnictide
superconductors.",0812.4664v1
2009-05-11,Antiferromagnetically Driven Electronic Correlation in Iron Pnictides and Cuprates,"The iron pnictides and the cuprates represent two families of materials,
where strong antiferromagnetic correlation drives three other distinct ordering
tendencies: (1) superconducting pairing, (2) Fermi surface distortion, and (3)
orbital current order. We propose that (1)-(3) and the antiferromagnetic
correlation are the hallmarks of a class of strongly correlated materials to
which the cuprates and pnictides belong. In this paper we present the results
of the functional renormalization group studies to support the above claim. In
addition, we show that as a function of the interlayer hopping parameter, the
double layer Hubbard model nicely interpolates between the cuprate and the iron
pnictide physics. Finally, as a check, we will present the renormalization
group study of a ladder version of the iron pnictide, and compare the results
to those of the two-dimensional model.",0905.1711v2
2009-06-30,New extended atomic data in cool star model atmospheres - Using Kurucz's new iron data in MAFAGS-OS models,"Context. Cool star model atmospheres are a common tool for the investigation
of stellar masses, ages and elemental abundance composition. Theoretical
atmospheric models strongly depend on the atomic data used when calculating
them. Aims. We present the changes in flux and temperature stratification when
changing from iron data computed by R.L. Kurucz in the mid 90s to the Kurucz
2009 iron computations. Methods. MAFAGS-OS opacity sampling atmospheres were
recomputed with Kurucz 2009 iron atomic data as implemented in the VALD
database by Ryabchikova. Temperature stratification and emergent flux
distribution of the new version, called MAFAGS-OS9, is compared to the former
version and to solar flux measurements. Results. Using the Kurucz line lists
converted into the VALD format and new bound-free opacities for Mg i and Al i
leads to changes in the solar temperature stratification by not more than 28 K.
At the same time, the calculated solar flux distribution shows significantly
better agreement between observations and theoretical solar models. These
changes in the temperature stratification of the corresponding models are
small, but nevertheless of a magnitude that affects stellar parameter
determinations and abundance analysis.",0906.5449v1
2009-07-04,Angle-Resolved Photoemission Spectroscopy of Iron-Chalcogenide Superconductor Fe1.03Te0.7Se0.3 : Strong-Coupling Superconductivity and Universality of Inter-Band Scattering,"We have performed high-resolution angle-resolved photoemission spectroscopy
of iron-chalcogenide superconductor Fe1.03Te0.7Se0.3 (Tc = 13 K) to investigate
the electronic structure relevant to superconductivity. We observed a hole- and
an electron-like Fermi surfaces at the Brillouin zone center and corner,
respectively, which are nearly nested by the Q~(pi, pi) wave vector. We do not
find evidence for the nesting instability with Q~(pi+delta, 0) reminiscent of
the antiferromagnetic order in the parent compound Fe1+yTe. We have observed an
isotropic superconducting gap along the hole-like Fermi surface with the gap
size Delta of ~4 meV (2Delta/kBTc~7), demonstrating the strong-coupling nature
of the superconductivity. The observed similarity of low-energy electronic
excitations between iron-chalcogenide and iron-arsenide superconductors
strongly suggests that common interactions which involve Q~(pi, pi) scattering
are responsible for the superconducting pairing.",0907.0763v1
2009-08-19,Sr$_2$VO$_3$FeAs: A Nanolayered Bimetallic Iron Pnictide Superconductor,"One of the unifying concepts in the iron-pnictide superconductors, both for
the mechanism of magnetic ordering and of unconventional order parameter
character, has been the electron and hole Fermi surfaces that are approximately
nested. Using the density functional methods that have predicted Fermi surfaces
correctly in SrFe$_2$P$_2$, we find that the recently reported superconducting
Sr$_2$VO$_3$FeAs, with $T_c$=37 K and no apparent competition between magnetism
and superconductivity, possesses different Fermi surface geometry and character
than previous classes of iron pnictides. The intervening layer (a V bilayer)
gives rise to bands that cross the Fermi level. Coupling to the FeAs layer is
small except for interaction along the zone boundary, however that coupling
degrades the Fermi surface nesting. Sr$_2$VO$_3$FeAs, with its alternating
layers of open shell atoms, deserves further close study that should help to
understand the origin of the properties of iron pnictide compounds.",0908.2698v3
2009-09-02,Electronic correlations in the iron pnictides,"In correlated metals derived from Mott insulators, the motion of an electron
is impeded by Coulomb repulsion due to other electrons. This phenomenon causes
a substantial reduction in the electron's kinetic energy leading to remarkable
experimental manifestations in optical spectroscopy. The high-Tc
superconducting cuprates are perhaps the most studied examples of such
correlated metals. The occurrence of high-Tc superconductivity in the iron
pnictides puts a spotlight on the relevance of correlation effects in these
materials. Here we present an infrared and optical study on single crystals of
the iron pnictide superconductor LaFePO. We find clear evidence of electronic
correlations in metallic LaFePO with the kinetic energy of the electrons
reduced to half of that predicted by band theory of nearly free electrons.
Hallmarks of strong electronic many-body effects reported here are important
because the iron pnictides expose a new pathway towards a correlated electron
state that does not explicitly involve the Mott transition.",0909.0312v1
2009-10-05,Universal magnetic and structural behaviors in the iron arsenides,"Commonalities among the order parameters of the ubiquitous antiferromagnetism
present in the parent compounds of the iron arsenide high temperature
superconductors are explored. Additionally, comparison is made between the well
established two-dimensional Heisenberg-Ising magnet, K$_2$NiF$_4$ and iron
arsenide systems residing at a critical point whose structural and magnetic
phase transitions coincide. In particular, analysis is presented regarding two
distinct classes of phase transition behavior reflected in the development of
antiferromagnetic and structural order in the three main classes of iron
arsenide superconductors. Two distinct universality classes are mirrored in
their magnetic phase transitions which empirically are determined by the
proximity of the coupled structural and magnetic phase transitions in these
materials.",0910.0489v1
2009-10-12,Orbital selective local moment formation in iron: first principle route to an effective model,"We revisit a problem of theoretical description of alpha-iron. By performing
LDA+DMFT calculations in the paramagnetic phase we find that Coulomb
interaction and, in particular Hund exchange, yields the formation of local
moments in e_g electron band, which can be traced from imaginary time
dependence of the spin-spin correlation function. This behavior is accompanied
by non-Fermi-liquid behavior of e_g electrons and suggests using local moment
variables in the effective model of iron. By investigating orbital-selective
contributions to the Curie-Weiss law for Hund exchange I=0.9 eV we obtain an
effective value of local moment of e_g electrons 2p=1.04 mu_B. The effective
bosonic model, which allows to describe magnetic properties of iron near the
magnetic phase transition, is proposed.",0910.2161v1
2009-12-01,A common magnetic origin for the Invar effects in fcc iron-based ferromagnets,"Using first-principles calculations, in conjunction with Ising magnetism, we
undertake a theoretical study to elucidate the origin of the experimentally
observed Invar effects in disordered fcc iron-based ferromagnets. First, we
show that our theory can account for the Invar effects in iron-nickel alloys,
the anomalies being driven by the magnetic contributions to the average free
energies. Second, we present evidence indicating that the relationship between
thermal expansion and magnetism is essentially the same in all the studied
alloys, including those which display the Invar effect and those which do not.
Hence we propose that magnetism plays a crucial role in determining whether a
system exhibits normal thermal expansion, the Invar effect, or something else.
The crucial determining factor is the rate at which the relative orientation of
the local magnetic moments of nearest-neighbor iron atoms fluctuates as the
system is heated.",0912.0215v4
2009-12-29,London penetration depth and strong pair-breaking in iron-based superconductors,"The low temperature variation of the London penetration depth for a number of
iron-pnictide and iron-chalcogenide superconductors is nearly quadratic,
$\Delta \lambda(T) = \beta T^n$ with $n\approx 2$. The coefficient in this
dependence shows a robust scaling, $\beta \propto 1/T_c^3$ across different
families of these materials. We associate the scaling with a strong
pair-breaking. The same mechanism have recently been suggested to explain the
scalings of the specific heat jump, $\Delta C \propto T_c^3$, and of the slopes
of the upper critical field, $dH_{c2}/dT\propto T_c$ in these materials. This
suggests that thermodynamic and electromagnetic properties of the iron-based
superconductors can be described within a strong pair-breaking scenario.",0912.5346v1
2010-01-08,Effect of time and storing conditions on iron forms in ferrous gluconate and Ascofer,"Antianemic medicament Ascofer and ferrous gluconate, its basic iron bearing
ingredient, were studied with the use of Mossbauer spectroscopy. Room
temperature spectra gave a clear evidence that two phases of iron were present
viz. ferrous (Fe2+) as a major one with a contribution of 85+-5%, and ferric
(Fe3+) whose contribution was found to be 15+-5%. However, the actual values of
the contributions of the two kind of the iron ions in Ascofer depend on
sample's age: the abundance of Fe2+ ions increases with time by 10% after 51
months, while that of Fe3+ decreases by the same amount. This means that an
internal reduction of Fe3+ ions takes place. Ferrous ions were shown to occupy
at least two different sites. In Ascofer, the relative abundance of the two
sites does not depend on the age of sample, while in the gluconate the
population of site 1 increases and that of site 2 decreases with the age of the
sample.",1001.1218v1
2010-02-08,Evidence for a full energy gap for nickel-pnictide LaNiAsO_{1-x}F_x superconductors by ^{75}As nuclear quadrupole resonance,"We report systematic ^{75}As-NQR and ^{139}La-NMR studies on nickel-pnictide
superconductors LaNiAsO_{1-x}F_x (x=0, 0.06, 0.10 and 0.12). The spin lattice
relaxation rate 1/T_1 decreases below T_c with a well-defined coherence peak
and follows an exponential decay at low temperatures. This result indicates
that the superconducting gap is fully opened, and is strikingly different from
that observed in iron-pnictide analogs. In the normal state, 1/T_1T is constant
in the temperature range T_c \sim 4 K < T <10 K for all compounds and up to
T=250 K for x=0 and 0.06, which indicates weak electron correlations and is
also different from the iron analog. We argue that the differences between the
iron and nickel pnictides arise from the different electronic band structure.
Our results highlight the importance of the peculiar Fermi-surface topology in
iron-pnictides.",1002.1506v1
2010-02-09,Iron line emission from X-ray pulsars: physical conditions and geometry of the system,"We present here the preliminary results of the study of the fluorescent iron
line emission from X-ray pulsars with Be companions. We propose to use
properties of this emission to investigate the spatial distribution and
physical conditions of the matter around the compact object as well as in the
binary system as a whole. Using data of the RXTE observatory the iron line
behavior in the transient X-ray pulsar V 0332+53 spectrum was studied during
the powerful type II outburst in 2004-2005. Particularly, we investigated a
variability of the iron line equivalent width on different time scales (pulse
period, orbital period, outburst phase) and searched for its correlation with
the continuum flux, spectral parameters, etc.",1002.1898v1
2010-02-12,Low magnetization and anisotropy in the antiferromagnetic state of undoped iron pnictides,"We examine the magnetic phase diagram of iron pnictides using a five band
model. For the intermediate values of the interaction expected to hold in the
iron pnictides, we find a metallic low moment state characterized by
antiparallel orbital magnetic moments. The anisotropy of the interorbital
hopping amplitudes is the key to understanding this low moment state. This
state accounts for the small magnetization measured in undoped iron pnictides
and leads to the strong exchange anisotropy found in neutron experiments.
Orbital ordering is concomitant with magnetism and produces the large zx
orbital weight seen at Gamma in photoemission experiments.",1002.2584v2
2010-04-06,Anion height dependence of Tc and density of states in iron based superconductors,"Systematic ab initio LDA calculations were performed for all the typical
representatives of recently discovered class of iron based high-temperature
superconductors: REOFe(As,P) (RE=La,Ce,Nd,Sm,Tb), Ba2Fe2As, (Sr,Ca)FFeAs,
Sr4Sc2O6Fe2P2, LiFeAs and Fe(Se,Te). Non-monotonic behavior of total density of
states at the Fermi level is observed as a function of anion height relative to
Fe layer with maximum at about Dz_a~1.37A, attributed to changing Fe - As
(P,Se,Te) hybridization. This leads to a similar dependence of superconducting
transition temperature Tc as observed in the experiments. The fit of this
dependence to elementary BCS theory produces semiquantitative agreement with
experimental data for Tc for the whole class of iron based superconductors. The
similar fit to Allen - Dynes formula underestimates Tc in the vicinity of the
maximum, signifying the possible importance of non - phonon pairing in this
region. These results unambiguously demonstrate that the main effect of Tc
variation between different types of iron based superconductors is due to the
corresponding variation of the density of states at the Fermi level.",1004.0801v1
2010-06-11,"New Iron Arsenide Oxides (Fe2As2)(Sr4(Sc,Ti)3O8), (Fe2As2)(Ba4Sc3O7.5), and (Fe2As2)(Ba3Sc2O5)","We synthesized new layered iron arsenide oxides
(Fe2As2)(Sr4(Sc,Ti)3O8),(Fe2As2)(Ba4Sc3O7.5), and (Fe2As2)(Ba3Sc2O5). The
crystal structures of these compounds are tetragonal with a space group of
I4/mmm. The structure of (Fe2As2)(Sr4(Sc,Ti)3O8) and (Fe2As2)(Ba4Sc3O7.5)
consists of the alternate stacking of antifluorite Fe2As2 layers and triple
perovskite-type oxide layers. The interlayer distance between the Fe planes of
(Fe2As2)(Ba4Sc3O7.5) is ~18.7 A. Moreover, the a-axis of (Fe2As2)(Ba3Sc2O5) is
the longest among the layered iron pnictides, indicating the structural
flexibility of the layered iron pnictide containing perovskite-type layers. The
bulk sample of (Fe2As2)(Sr4(Sc0.6Ti0.4)3O8) exhibited diamagnetism up to 28 K
in susceptibility measurements.",1006.2353v1
2010-07-13,Phase transitions and iron-ordered moment form factor in LaFeAsO,"Elastic neutron scattering studies of an optimized LaFeAsO single crystal
reveal that upon cooling, an onset of the tetragonal (T)-to-orthorhombic (O)
structural transition occurs at $T_\texttt{S} \approx 156$ K, and it exhibits a
sharp transition at $T_\texttt{P} \approx 148$ K. We argue that in the
temperature range $T_\texttt{S}$ to $T_\texttt{P}$, T and O structures may
dynamically coexist possibly due to nematic spin correlations recently proposed
for the iron pnictides, and we attribute $T_\texttt{P}$ to the formation of
long-range O domains from the finite local precursors. The antiferromagnetic
structure emerges at $T_\texttt{N} \approx 140$ K, with the iron moment
direction along the O \emph{a} axis. We extract the iron magnetic form factor
and use the tabulated $\langle j_0\rangle$ of Fe, Fe$^{2+}$ and Fe$^{3+}$ to
obtain a magnetic moment size of $\sim$0.8 $\mu_\texttt{B}$ at 9.5 K.",1007.2197v1
2010-08-10,Development of Powder-in-Tube Processed Iron Pnictide Wires and Tapes,"The development of the PIT fabrication process of iron pnictide
superconducting wires and tapes has been carried out in order to enhance their
transport properties. Silver was found to be the best sheath material, since no
reaction layer was observed between the silver sheath and the superconducting
core. The grain connectivity of iron pnictide wires and tapes has been markedly
improved by employing Ag or Pb as dopants. At present, critical current
densities in excess of 3750 A/cm^2 (Ic = 37.5 A) at 4.2 K have been achieved on
Ag-sheathed SrKFeAs wires prepared with the above techniques, which is the
highest in iron-based wires and tapes so far. Moreover, Ag-sheathed Sm-1111
superconducting tapes were successfully prepared by PIT method at temperatures
as low as 900C, instead of commonly used temperatures of 1200C. These results
demonstrate the feasibility of producing superconducting pnictide composite
wires, even grain boundary properties require much more attention.",1008.1735v2
2010-08-10,"Orbital Fluctuation Theory in Iron Pnictides: Effects of As-Fe-As Bond Angle, Isotope Substitution, and $Z^2$-Orbital Pocket on the Superconductivity","We study the pairing mechanism in iron pnictide superconductors based on the
five-orbital Hubbard-Holstein model. Due to Fe-ion oscillations, the s-wave
superconducting (SC) state without sign reversal (s_{++}-wave state) is induced
by orbital fluctuations by using realistic model parameters. The virtue of the
present theory is that the famous empirical relation between Tc and the
As-Fe-As bond angle is automatically explained, since the electron-phonon
(e-ph) coupling that creates the orbital fluctuations is the strongest when the
As$_4$-tetrahedron is regular. The negative iron isotope effect is also
reproduced. In addition, the magnitude of the SC gap on hole-pockets is
predicted to be rather insensitive to the corresponding d-orbital (xz/yz- or
z^2-orbital), which is consistent with the recent bulk-sensitive angle-resolved
photoemission spectroscopy (ARPES) measurement for (Ba,K)Fe$_2$As$_2$ and
BaFe$_2$(As,P)$_2$. These obtained results indicate that the
orbital-fluctuation-mediated s_{++}-wave state is a plausible candidate for
iron pnictides.",1008.1765v3
2010-09-20,Iron Depletion into Dust Grains in Galactic Planetary Nebulae,"We present preliminary results of an analysis of the iron depletion factor
into dust grains for a sample of 20 planetary nebulae (PNe) from the Galactic
bulge. We compare these results with the ones we obtained in a prior analysis
of 28 Galactic disk PNe and 8 Galactic H II regions. We derive high depletion
factors in all the objects, suggesting that more than 80% of their iron atoms
are condensed into dust grains. The range of iron depletions in the sample PNe
covers about two orders of magnitude, and we explore here if the differences
are related to the PN morphology. However, we do not find any significant
correlation.",1009.3945v1
2010-10-25,The melting curve of iron at extreme pressures: implications for planetary cores,"Exoplanets with masses similar to that of Earth have recently been discovered
in extrasolar systems. A first order question for understanding their dynamics
is to know whether they possess Earth like liquid metallic cores. However, the
iron melting curve is unknown at conditions corresponding to planets of several
times the Earth's mass (over 1500 GPa for planets with 10 times the Earth's
mass (ME)). In the density-temperature region of the cores of those
super-Earths, we calculate the iron melting curve using first principle
molecular dynamics simulations based on density functional theory. By comparing
this melting curve with the calculated thermal structure of Super Earths, we
show that planets heavier than 2ME, have solid cores, thus precluding the
existence of an internal metallic-core driven magnetic field. The iron melting
curve obtained in this study exhibits a steeper slope than any calculated
planetary adiabatic temperature profile rendering the presence of molten
metallic cores less likely as sizes of terrestrial planets increase.",1010.5133v1
2010-11-01,Quantitative magnetic force microscopy on permalloy dots using an iron filled carbon nanotube probe,"We have characterized a new Magnetic Force Microscopy (MFM) probe based on an
iron filled carbon nanotube (FeCNT) using MFM imaging on permalloy (Py) disks
saturated in a high magnetic field perpendicular to the disk plane. The
experimental data are accurately modeled by describing the FeCNT probe as
having a single magnetic monopole at its tip whose effective magnetic charge is
determined by the diameter of the iron wire enclosed in the carbon nanotube and
its saturation magnetization 4 \pi M_s ~ 2.2 x 10^4 G. A magnetic monopole
probe enables quantitative measurements of the magnetic field gradient close to
the sample surface. The lateral resolution is defined by the diameter of the
iron wire ~15 nm and the probe-sample separation. As a demonstration, the
magnetic field gradients close to the surface of a Py dot in domain and vortex
states were imaged.",1011.0389v1
2010-11-29,Antiferromagnetic order in multi-band Hubbard models for iron-pnictides,"We investigate multi-band Hubbard models for the three iron 3$d$-$t_{2g}$
bands and the two iron 3$d$-$e_g$ bands in ${\rm La O Fe As}$ by means of the
Gutzwiller variational theory. Our analysis of the paramagnetic ground state
shows that neither Hartree--Fock mean-field theories nor effective spin models
describe these systems adequately. In contrast to Hartree--Fock-type
approaches, the Gutzwiller theory predicts that antiferromagnetic order
requires substantial values of the local Hund's-rule exchange interaction. For
the three-band model, the antiferromagnetic moment fits experimental data for a
broad range of interaction parameters. However, for the more appropriate
five-band model, the iron $e_g$ electrons polarize the $t_{2g}$ electrons and
they substantially contribute to the ordered moment.",1011.6219v1
2010-12-13,Rigidity dependence of cosmic ray escape length in the Galaxy obtained from a comparison of proton and iron spectra in the range 3-3000 GV,"The simple leaky-box model of propagation of cosmic rays in the Galaxy is
quite suitable for handling data on cosmic ray nuclei energy spectra and
composition at E ? 1 GeV [1,2]. In the leakybox model a full information about
cosmic ray propagation in Galaxy is compressed to the single parameter - escape
length, Xe, characterizing mean grams of a matter passed by cosmic rays from
sources to the Earth. In this paper we analyze the world data on proton and
iron cosmic ray spectra collected in the past (HEAO, CRN et al.) and in series
of recent electronic experiments (ATIC, CREAM, MS, BESS, Tracer et al.) and
obtain the rigidity dependence of escape length, Xe(R) = R^(-0.47\pm-0.03),
from the measured rigidity dependence of the protons/iron ratio. It quite
agrees with the one stimated in standard manner from the secondary/primary
nuclei ratio. But at R > 300 GV the behavior of Xe(R)distinctly changes, that
can (variant of explanation)point out to the change of proton/iron ratio in
cosmic ray sources.",1012.2722v1
2010-12-30,Pressure-Driven Quantum Criticality in An Iron-Selenide Superconductor,"The discovery of superconductivity of about 30 K in iron selenides with very
large magnetic moments simulates the examination of completing orders. Here we
report a finding of pressure- induced suppression of the superconducting
transition temperature Tc and enhancement of the temperature of the resistance
hump TH through charge transfer between two iron sites with different
occupancies. The activation energy for the electric transport of the
high-temperature resistance is observed to go to zero at a critical pressure of
8.7 GPa, at which superconductivity tends to disappear and the
semiconductor-to-metal transition takes place. Beyond the critical point, the
resistance exhibits a metallic behavior over the whole temperature range
studied. All these features indicate the existence of quantum criticality in
iron-selenide superconductors.",1101.0092v3
2011-01-05,Dust production and mass loss in the Galactic globular cluster 47 Tucanae,"Dust production among post-main-sequence stars is investigated in the
Galactic globular cluster 47 Tucanae (NGC 104) based on infrared photometry and
spectroscopy. We identify metallic iron grains as the probable dominant opacity
source in these winds. Typical evolutionary timescales of AGB stars suggest the
mass-loss rates we report are too high. We suggest that this is because the
iron grains are small or elongated and/or that iron condenses more efficiently
than at solar metallicity. Comparison to other works suggests metallic iron is
observed to be more prevalent towards lower metallicities. The reasons for this
are explored, but remain unclear. Meanwhile, the luminosity at which dusty mass
loss begins is largely invariant with metallicity, but its presence correlates
strongly with long-period variability. This suggests that the winds of low-mass
stars have a significant driver that is not radiation pressure, but may be
acoustic driving by pulsations.",1101.1096v1
2011-01-20,Spin-state crossover and hyperfine interactions of ferric iron in MgSiO$_3$ perovskite,"Using density functional theory plus Hubbard $U$ calculations, we show that
the ground state of (Mg,Fe)(Si,Fe)O$_3$ perovskite, a major mineral phase in
the Earth's lower mantle, has high-spin ferric iron ($S=5/2$) at both the
dodecahedral (A) and octahedral (B) site. As the pressure increases, the B-site
iron undergoes a spin-state crossover to the low-spin state ($S=1/2$), while
the A-site iron remains in the high-spin state. Our calculation shows that the
B-site spin-state crossover in the pressure range of 40-70 GPa is accompanied
by a noticeable volume reduction and an increase in quadrupole splitting,
consistent with recent X-ray diffraction and M\""ossbauer spectroscopy
measurements. The volume reduction leads to a significant softening in the bulk
modulus, which suggests a possible source of seismic velocity anomalies in the
lower mantle.",1101.3819v2
2011-03-09,Interstitial iron tuning of the spin fluctuations in Fe1+xTe,"Using neutron inelastic scattering, we investigate the low-energy spin
fluctuations in Fe1+xTe as a function of both temperature and interstitial iron
concentration. For Fe1.057(7)Te the magnetic structure is defined by a
commensurate wavevector of (1/2,0,1/2). The spin fluctuations are gapped with a
sharp onset at 7 meV and are three dimensional in momentum transfer, becoming
two dimensional at higher energy transfers. On doping with interstitial iron,
we find in Fe1.141(5)Te the ordering wavevector is located at the (0.38, 0,
1/2) position and the fluctuations are gapless with the intensity peaked at an
energy transfer of 4 meV. These results show that the spin fluctuations in the
Fe1+xTe system a can be tuned not only through selenium doping, but also with
interstitial iron. We also compare these results with superconducting
concentrations and in particular the resonance mode in the Fe_1+xTe_1-ySe_y
system.",1103.1811v2
2011-03-18,First-principles Studies for the Hydrogen Doping Effects on Iron-based Superconductors,"We study hydrogen doping effects in an iron-based superconductor
LaFeAsO_(1-y) by using the first-principles calculation and explore the reason
why the superconducting transition temperature is remarkably enhanced by the
hydrogen doping. The present calculations reveal that a hydrogen cation stably
locating close to an iron atom attracts a negatively-charged FeAs layer and
results in structural distortion favorable for further high temperature
transition. In fact, the lattice constant a averaged over the employed
supercell shrinks and then the averaged As-Fe-As angle approaches 109.74
degrees with increasing the hydrogen doping amount. Moreover, the calculations
clarify electron doping effects of the solute hydrogen and resultant
Fermi-level shift. These insights are useful for design of high
transition-temperature iron-based superconductors.",1103.3560v1
2011-04-18,Optimized Orthogonal Basis Tight Binding. Application to Iron,"The formal link between the linear combination of atomic orbitals approach to
density functional theory and two-center Slater-Koster tight-binding models is
used to derive an orthogonal $d$-band tight-binding model for iron with only
two fitting parameters. The resulting tight-binding model correctly predicts
the energetic ordering of the low energy iron-phases, including the
ferromagnetic BCC, antiferromagnetic FCC, HCP and topologically close-packed
structures. The energetics of test structures that were not included in the fit
are equally well reproduced as those included, thus demonstrating the
transferability of the model. The simple model also gives a good description of
the vacancy formation energy in the nonmagnetic FCC and ferromagnetic BCC iron
lattices.",1104.3598v1
2011-05-26,"Iron abundance in the prototype PG1159 star, GW Vir pulsator PG1159-035, and related objects","We performed an iron abundance determination of the hot, hydrogen deficient
post-AGB star PG1159-035, which is the prototype of the PG1159 spectral class
and the GW Vir pulsators, and of two related objects (PG1520+525, PG1144+005),
based on the first detection of Fe VIII lines in stellar photospheres. In
another PG1159 star, PG1424+535, we detect Fe VII lines. In all four stars,
each within Teff = 110,000 - 150,000 K, we find a solar iron abundance. This
result agrees with our recent abundance analysis of the hottest PG1159 stars
(Teff = 150,000 - 200,000 K) that exhibit Fe X lines. On the whole, we find
that the PG1159 stars are not significantly iron deficient, in contrast to
previous notions.",1105.5276v1
2011-06-02,Ab-initio molecular dynamics simulation of hydrogen diffusion in $α$-iron,"First-principles atomistic molecular dynamics simulation in the
micro-canonical and canonical ensembles has been used to study the diffusion of
interstitial hydrogen in $\alpha$-iron. Hydrogen to Iron ratios between
$\theta=1/16 and 1/2 have been considered by locating interstitial hydrogen
atoms at random positions in a $2 \times 2 \times 2$ supercell. We find that
the average optimum absorption site and the barrier for diffusion depend on the
concentration of interestitials. Iron Debye temperature decreases monotonically
for increasing concentration of interstitial hydrogen, proving that iron-iron
interatomic potential is significantly weakened in the presence of a large
number of diffusing hydrogen atoms.",1106.0464v1
2011-07-11,Impairment of double exchange mechanism in electron transport of iron pnictides,"Double exchange mechanism is believed to favor transport along ferromagnetic
directions, the failure of which in explaining the unusual resistivity
anisotropy in iron pnictides is investigated. Several factors intrinsic to the
microscopic mechanism of transport in iron pnictides are identified and
analyzed, including the moderate Hund's coupling, low local moment, and
presence of two anisotropic degenerate orbitals xz and yz. In particular, the
substantial second neighbor hoppings are found to be decisive in giving results
opposite to the double exchange picture. In high temperature nonmagnetic phase,
orbital ordering is shown to give the right trend of resistivity anisotropy as
observed experimentally, advocating its essential role in electron transport of
iron pnictides.",1107.1952v1
2011-07-12,Revealing the dual nature of magnetism in iron pnictides and iron chalcogenides using x-ray emission spectroscopy,"We report Fe K beta x-ray emission spectroscopy study of local magnetic
moments in various iron based superconductors in their paramagnetic phases.
Local magnetic moments are found in all samples studied: PrFeAsO,
Ba(Fe,Co)2As2, LiFeAs, Fe1+x(Te,Se), and A2Fe4Se5 (A=K, Rb, and Cs). The moment
size varies significantly across different families. Specifically, all iron
pnictides samples have local moments of about 1 $\mu_B$/Fe, while FeTe and
K2Fe4Se5 families have much larger local moments of ~2$\mu_B$/Fe,
~3.3$\mu_B$/Fe, respectively. In addition, we find that neither carrier doping
nor temperature change affects the local moment size.",1107.2211v1
2011-08-13,Imaging the coexistence of superconductivity and a charge density modulation in K0.73Fe1.67Se2 superconductor,"We report scanning tunneling microscopy studies of the local structural and
electronic properties of the iron selenide superconductor K0.73Fe1.67Se2 with
TC = 32K. On the atomically resolved FeSe surface, we observe well-defined
superconducting gap and the microscopic coexistence of a charge density
modulation with root2*root2 periodicity with respect to the original Se
lattice. We propose that a possible origin of the pattern is the electronic
superstructure caused by the block antiferromagnetic ordering of the iron
moments. The widely expected iron vacancy ordering is not observed, indicating
that it is not a necessary ingredient for superconductivity in the intercalated
iron selenides.",1108.2798v1
2011-10-03,Block Antiferromagnetism and Checkerboard Charge Ordering in Alkali-doped Iron Selenides $R$$_{1-x}$Fe$_{2-y}$Se$_2$,"By performing first-principles electronic structure calculations and
analyzing effective magnetic model of alkali-doped iron selenides, we show that
the materials without iron vacancies should approach a novel checkerboard phase
in which each four Fe sites group together in tetragonal structure. The
checkerboard phase is the ground state with a block antiferromagnetic (AFM)
order and a small charge density wave order in the absence of
superconductivity. Both of them can also coexist with superconductivity. The
results explain mysterious $2\times 2$ ordered patterns and hidden orders
observed in various different experiments, clarify the missing link between AFM
and superconducting phases, suggest that the block-AFM state is the parent
state, and unify the understanding of various observed phases in alkali-doped
iron selenides.",1110.0372v1
2011-11-25,Growth and electronic and magnetic structure of iron oxide films on Pt(111),"Ultrathin (111)-oriented polar iron oxide films were grown on a Pt(111)
single crystal either by the reactive deposition of iron or oxidation of
metallic iron monolayers. These films were characterized using low energy
electron diffraction, scanning tunneling microscopy and conversion electron
Mossbauer spectroscopy. The reactive deposition of Fe led to the island growth
of Fe3O4, in which the electronic and magnetic properties of the bulk material
were modulated by superparamagnetic size effects for thicknesses below 2 nm,
revealing specific surface and interface features. In contrast, the oxide films
with FeO stoichiometry, which could be stabilized as thick as 4 nm under
special preparation conditions, had electronic and magnetic properties that
were very different from their bulk counterpart, w\""ustite. Unusual long range
magnetic order appeared at room temperature for thicknesses between three and
ten monolayers, the appearance of which requires severe structural modification
from the rock-salt structure.",1111.5938v2
2011-12-07,Relativistic iron K X-ray Reverberation in NGC 4151,"Recent X-ray observations have enabled the study of reverberation delays in
AGN for the first time. All the detections so far are in sources with a strong
soft excess, and the measured delay is between the hard (1-3 keV) direct
continuum and the soft excess (0.5-1 keV), interpreted as the reflection
continuum smeared by relativistic effects. There is however an inherent
ambiguity in identifying and studying the details of the lines in the soft
excess. Here we report the first detection of reverberation in the iron K band
in any AGN. Using XMM-Newton observations of NGC 4151, we find delays of order
2000 s on time-scales of 10e5 s between the 5-6 keV band and 2-3 and 7-8 keV
bands, with a broad lag profile resembling a relativistically-broadened iron
line. The peak of the lag spectra shifts to lower energies at higher
frequencies, consistent with the red wing of the line being emitted at smaller
radii, as expected from reflection off the inner accretion disk. This is a
first detection of a broad iron line using timing studies.",1112.1717v2
2012-02-06,Unconventional superconducting gap via spin fluctuations in iron-vacancy ordered A$_{y}$Fe$_{2-x}$Se$_{2}$,"Based on an effective 12-orbital tight-binding model, we examine the
superconducting states induced by the antiferromagnetic fluctuations for
iron-vacancy-ordered A$_{y}$Fe$_{2-x}$Se$_{2}$. It is shown that due to the
broken reflection symmetry induced by the iron vacancies, new superconducting
states with $C_{4h}$ symmetry emerge. In particular, we show that in the
$C_{4h}$ symmetry, symmetric axes of the pairing momenta do not need to
coincide with axes of the unit cell. As a result, in addition to the magnitude
of the pairing gap, the relative orientation of the pairing wave function to
the lattice forms another degree of freedom for characterizing the
superconducting gap and can further help in gaining the condensation energy.
Nonetheless, similar to other iron-based superconductors, the singlet ground
state is still dominated by s-wave or d-wave, which are nearly degenerate with
anisotropic gaps. Furthermore, s-wave and d-wave superconducting states are
separated by a quantum critical point controlled by the Hund's rule coupling
$J_{H}$.",1202.1063v2
2012-02-17,Electronic and Magnetic Structures of Chain Structured Iron Selenide Compounds,"Electronic and magnetic structures of iron selenide compounds Ce2O2FeSe2
(2212\ast) and BaFe2Se3(123\ast) are studied by the first-principles
calculations. We find that while all these compounds are composed of
one-dimensional (1D) Fe chain (or ladder) structures, their electronic
structures are not close to be quasi-1D. The magnetic exchange couplings
between two nearest-neighbor (NN) chains in 2212\ast and between two NN
two-leg-ladders in 123\ast are both antiferromagnetic (AFM), which is
consistent with the presence of significant third NN AFM coupling, a common
feature shared in other iron-chalcogenides, FeTe (11\ast) and KyFe2-xSe2
(122\ast). In magnetic ground states, each Fe chain of 2212\ast is
ferromagnetic and each two-leg ladder of 123\ast form a block-AFM structure. We
suggest that all magnetic structures in iron-selenide compounds can be unified
into an extended J1-J2-J3 model. Spin-wave excitations of the model are
calculated and can be tested by future experiments on these two systems.",1202.4016v1
2012-03-11,Iron-Based Superconductors: $S_4$ Symmetry Superconductors,"I elaborate the construction of the recent two-orbital model for iron-based
superconductors\cite{hu-hao} and discuss the properties of superconducting(SC)
phases based on the $S_4$ symmetry. I demonstrate further that the underlining
electronic structure is an almost decoupled two-orbital model obeying the $S_4$
symmetry. I discuss the classification of the SC states according to the $S_4$
symmetry, which leads to a natural prediction that there are two different
phases even in the proposed $A_{1g}$ s-wave SC state of iron-based
superconductors and the sign change in the SC state should be hidden between
the upper and lower As(Se) layer in a single Fe-(As)Se layer, an analogy of the
sign change under the $90^\circ$ degree rotation in the d-wave SC state of
cuprates. The $S_4$ symmetry makes iron-based superconductors a unique class of
superconductors with promising device applications.",1203.2304v3
2012-06-27,Quantum Monte Carlo Study of Pairing Symmetry and Correlation in Iron-based Superconductors,"We perform a systematic quantum Monte Carlo study of the pairing correlation
in the $S_4$ symmetric microscopic model for iron-based superconductors. It is
found that the pairing with an extensive s-wave symmetry robustly dominates
over other pairings at low temperature in reasonable parameter region. The
pairing susceptibility, the effective pairing interaction and the
$(\pi,0)$antiferromagnetic correlation strongly increase as the on-site Coulomb
interaction increases, indicating the importance of the effect of
electron-electron correlation. Our non-biased numerical results provide a
unified understanding of superconducting mechanism in iron-pnictides and
iron-chalcogenides and demonstrate that the superconductivity is driven by
strong electron-electron correlation effects.",1206.6277v2
2012-07-23,A general moment NRIXS approach to the determination of equilibrium Fe isotopic fractionation factors: application to goethite and jarosite,"We measured the reduced partition function ratios for iron isotopes in
goethite FeO(OH), potassium-jarosite KFe3(SO4)2(OH)6, and hydronium-jarosite
(H3O)Fe3(SO4)2(OH)6, by Nuclear Resonant Inelastic X-Ray Scattering (NRIXS,
also known as Nuclear Resonance Vibrational Spectroscopy -NRVS- or Nuclear
Inelastic Scattering -NIS) at the Advanced Photon Source. These measurements
were made on synthetic minerals enriched in 57Fe. A new method (i.e., the
general moment approach) is presented to calculate {\beta}-factors from the
moments of the NRIXS spectrum S(E). The first term in the moment expansion
controls iron isotopic fractionation at high temperature and corresponds to the
mean force constant of the iron bonds, a quantity that is readily measured and
often reported in NRIXS studies.",1207.5559v1
2012-08-28,Orbital-selective Mott Phase in Multiorbital Models for Alkaline Iron Selenides K(1-x)Fe(2-y)Se2,"We study a multiorbital model for the alkaline iron selenides
K(1-x)Fe(2-y)Se2 using a slave-spin method. With or without ordered vacancies,
we identify a metal-to-Mott-insulator transition at the commensurate filling of
six 3d electrons per iron ion. For Hund's couplings beyond a threshold value,
this occurs via an intermediate orbital-selective Mott phase, in which the 3d
xy orbital is Mott localized while the other 3d orbitals remain itinerant. This
phase is still stabilized over a range of carrier dopings. Our results lead to
an overall phase diagram for the alkaline iron selenides, which provides a
unified framework to understand the interplay between the strength of vacancy
order and carrier doping. In this phase diagram, the orbital-selective Mott
phase provides a natural link between the superconducting K(1-x)Fe(2-y)Se2 and
its Mott-insulating parent compound.",1208.5547v1
2012-08-30,A Short Review of the $S_4$ Symmetric Microscopic Model for Iron-Based High Temperature Superconductors,"We briefly review the recently constructed two orbital microscopic model for
iron-based superconductors based on $S_4$ symmetry (PRX 2 021009(2012)). With
this faithful representation of the kinematics of the tri-layer FeAs or FeSe
structure, the model provides answers and physical pictures to fundamental
questions related to the robustness of superconductivity and pairing symmetry,
unifies different families of iron-based superconductors, casts new insight
into the connections to the other high $T_c$ superconductors, cuprates, and
reveals why an s-wave pairing can be stabilized by repulsive interactions.
Further progresses include that the model provides a clean understanding of
band reconstruction observed in magnetically ordered states, which is a strong
support to the kinematics of the $S_4$ model, and captures the essential low
energy physics of iron-based superconductors based on numerical results from
unbiased quantum Monte Carlo simulation.",1208.6201v1
2012-12-17,The first-principles study of thermodynamical properties of random magnetic overlayers on fcc-Cu(001) substrate,"We present the theoretical study of thermodynamical properties of fcc-Cu(001)
substrate covered by iron-cobalt monolayer as well as by incomplete iron layer.
The effective two-dimensional Heisenberg Hamiltonian is constructed from first
principles and properties of exchange interactions are investigated. The Curie
temperatures are estimated using the Monte-Carlo (MC) simulations and compared
with a simplified approach using the random-phase approximation (RPA) in
connection with the virtual-crystal approach (VCA) to treat randomness in
exchange integrals. Calculations indicate a weak maximum of the Curie
temperature as a function of composition of the iron-cobalt overlayer. While a
good quantitative agreement between RPA-VCA and MC was found for iron-cobalt
monolayer, the RPA-VCA approach fails quantitatively for low coverage due to
the magnetic percolation effect. We also present the study of the effect of
alloy disorder on the shape of magnon spectra of random overlayers.",1212.4057v1
2013-02-22,Nematicity driven by hybridization in iron-based superconductors,"In this paper we study an effective model for the normal state of iron-based
superconductors. It has separate, but interacting itinerant and localized
degrees of freedom, originating from the d_xz and d_yz, and from d_xy iron
orbitals respectively. At low temperatures, below a mean-field phase
transition, these different states condense together in an excitonic order
parameter. We show that at even lower temperature, after another phase
transition, this ordered state can spontaneously break the C_4 lattice symmetry
and become nematic. We propose this mechanism as an explanation of the tendency
towards nematicity observed in several iron-based compounds.",1302.5739v2
2013-03-04,Broad K$α$ iron line from accretion disks around traversable wormholes,"It has been proposed that the supermassive black hole candidates at the
centers of galaxies might be wormholes formed in the early Universe and
connecting our Universe with other sister Universes. The analysis of the
profile of the relativistic K$\alpha$ iron line is currently the only available
approach to probe the spacetime geometry around these objects. In this paper, I
compute the expected K$\alpha$ iron line in some wormhole spacetimes and I
compare the results with the line produced around Kerr black holes. The line
produced in accretion disks around non-rotating or very slow-rotating wormholes
is relatively similar to the one expected around Kerr black holes with mid or
high value of spin parameter and current observations are still marginally
compatible with the possibility that the supermassive black hole candidates in
galactic nuclei are these objects. For wormholes with spin parameter $a_*
\gtrsim 0.02$, the associated K$\alpha$ iron line is instead quite different
from the one produced around Kerr black holes, and their existence may already
be excluded.",1303.0624v2
2013-03-11,Mechanism for Odd Parity Superconductivity in Iron-Based Superconductors,"Under the assumption that superconducting pairing is driven by local d-p
hybridization, we show that the superconducting state in iron-based
superconductors is classified as an odd parity s-wave spin-singlet pairing
state in a single trilayer FeAs/Se, the building block of the materials. In a
low energy effective model with only d-orbitals in an iron square bipartite
lattice, the superconducting order parameter in this state is a combination of
a s-wave normal pairing between two sublattices and a s-wave $\eta$-pairing
within the sublattices. Parity conservation was violated in proposed
superconducting states in the past. The results demonstrate iron-based
superconductors being a new quantum state of matter and suggest that a
measurement of odd parity can establish fundamental principles related to high
temperature superconducting mechanism.",1303.2624v2
2013-03-25,Upturn observed in heavy nuclei to iron ratios by the ATIC-2 experiment,"The ratios of fluxes of heavy nuclei from sulfur (Z=16) to chromium (Z=24) to
the flux of iron were measured by the ATIC-2 experiment. The ratios are
decreasing functions of energy from 5 GeV/n to approximately 80 GeV/n, as
expected. However, an unexpected sharp upturn in the ratios are observed for
energies above 100 GeV/n for all elements from Z=16 to Z=24. Similar upturn but
with lower amplitude was also discovered in the ATIC-2 data for the ratio of
fluxes of abundant even nuclei (C, O, Ne, Mg, Si) to the flux of iron.
Therefore the spectrum of iron is significantly different from the spectra of
other abundant even nuclei.",1303.6108v1
2013-04-08,Spin states of iron impurities in magnesium oxide under pressure: A possible intermediate state,"Ferropericlase (Mg,Fe)O is a major lower mantle mineral, and studying its
properties is a fundamental step toward understanding the Earth's interior.
Here, we performed a first-principles investigation on the properties of iron
as an isolated impurity in magnesium oxide, which is the condition of
ferropericlase under which iron-iron interactions could be neglected. The
calculations were carried using the all-electron full-potential linearized
augmented plane wave method within the density functional theory in the
generalized gradient approximation plus the on-site Hubbard correction. We
present the electronic and magnetic properties, electric and magnetic hyperfine
splitting of this impurity in high and low spin states for several charge
states at zero pressure, which were then extended to high pressures. For the
impurity in the neutral charge state, our results indicated that there is a
metastable intermediate spin state (S=1), in addition to the high (S=2) and low
(S=0) spin states. Those results were discussed in the context of an
intermediate spin state, experimentally identified in ferrosilicate perovskite.",1304.2227v1
2013-05-15,Iron impurities in gold and silver: Comparison of transport measurements to numerical renormalization group calculations exploiting non-Abelian symmetries,"We consider iron impurities in the noble metals gold and silver and compare
experimental data for the resistivity and decoherence rate to numerical
renormalization group results. By exploiting non-Abelian symmetries we show
improved numerical data for both quantities as compared to previous
calculations [Costi et al., Phys. Rev. Lett. 102, 056802 (2009)], using the
discarded weight as criterion to reliably judge the quality of convergence of
the numerical data. In addition we also carry out finite-temperature
calculations for the magnetoresistivity of fully screened Kondo models with S =
1/2, 1 and 3/2, and compare the results with available measurements for iron in
silver, finding excellent agreement between theory and experiment for the
spin-3/2 three-channel Kondo model. This lends additional support to the
conclusion of Costi et al. that the latter model provides a good effective
description of the Kondo physics of iron impurities in gold and silver.",1305.3551v2
2013-07-08,K$α$ iron line profile from accretion disks around regular and singular exotic compact objects,"The nature of the super-massive black hole candidates in galactic nuclei can
be tested by analyzing the profile of the K$\alpha$ iron line observed in their
X-ray spectrum. In this paper, we consider the possibility that the spacetime
in the immediate vicinity of these objects may be described by some non vacuum
exact solutions of Einstein's equations resulting as the end-state of
gravitational collapse. The vacuum far away portion of the spacetime is
described by the Schwarzschild metric, while the interior part may be either
regular or have a naked singularity at the center. The iron line generated
around this class of objects has specific features, which can be used to
distinguish such objects from Kerr black holes. In particular, their iron line
cannot have the characteristic low-energy tail of the line generated from
accretion disks around fast-rotating Kerr black holes. We can thus conclude
that the super-massive black hole candidates whose spin parameter has been
estimated to be close to 1 assuming the Kerr background cannot be this kind of
objects.",1307.2106v2
2013-07-18,Iron Line Variability of Discoseismic Corrugation Modes,"Using a fast semi-analytic raytracing code, we study the variability of
relativistically broadened iron lines due to discoseismic oscillations
concentrated in the inner-most regions of accretion discs around black holes.
The corrugation mode, or c-mode, is of particular interest as its natural
frequency corresponds well to the ~0.1-15Hz range observed for low-frequency
quasi-periodic oscillations (LFQPOs) for lower spins. Comparison of the
oscillation phase dependent variability and QPO-phase stacked iron line
observations will allow such discoseismic models to be confirmed or ruled out
as a source of particular LFQPOs. The spectral range and frequency of the
variability of the iron line due to corrugation modes can also potentially be
used to constrain the black hole spin if observed with sufficient temporal and
spectral resolution.",1307.4971v1
2013-07-31,Determination of the iron content of Cepheids from the shape of their light curves,"We present the study of the metallicity dependence of the Fourier amplitude
ratios R_21 and R_31 for the light curves of short-period Galactic classical
Cepheids in B, V, R_C and I_C bands. Based on the available photometric and
spectroscopic data we determined the relations between the atmospheric iron
abundance, [Fe/H], and the Fourier parameters. Using these relations we
calculated the photometric [Fe/H] values of all program Cepheids with an
average accuracy of 0.15 dex. No spectroscopic iron abundance was known before
for 14 of these stars. These empirical results provide an alternate method to
determine the iron abundance of classical Cepheids too faint for spectroscopic
observations. We also checked whether the metal-poor Cepheids of both
Magellanic Clouds follow the same relationships, and a good agreement was
found.",1307.8275v1
2013-08-19,Broad iron lines in neutrons stars: dynamical broadening or wind scattering?,"Broad iron emission lines are observed in many accreting systems from black
holes in AGN and X-ray binaries to neutron star low-mass X-ray binaries. The
origin of the line broadening is often interpreted as due to dynamical
broadening and relativistic effects. However, alternative interpretations have
been proposed, included broadening due to Compton scattering in a wind or
accretion disk atmosphere. Here we explore the observational signatures
expected from broadening in a wind, in particular that the iron line width
should increase with an increase in the column density of the absorber (due to
an increase in the number of scatterings). We study the data from three neutron
star low-mass X-ray binaries where both a broad iron emission line and
absorption lines are seen simultaneously, and show that there is no significant
correlation between line width and column density. This favors an inner disk
origin for the line broadening rather than scattering in a wind.",1308.4023v1
2013-09-17,A Chandra view of the clumpy reflector at the heart of the Circinus galaxy,"We present a spectral and imaging analysis of the X-ray reflecting structure
at the heart of the Circinus galaxy, investigating the innermost regions
surrounding the central black hole. By studying an archival 200 ks Chandra
ACIS-S observation, we are able to image the extended clumpy structure
responsible for both cold reflection of the primary radiation and neutral iron
Ka line emission. We measure an excess of the equivalent width of the iron Ka
line which follows an axisymmetric geometry around the nucleus on a hundred pc
scale. Spectra extracted from different regions confirm a scenario in which the
dominant mechanism is the reflection of the nuclear radiation from
Compton-thick gas. Significant differences in the equivalent width of the iron
Ka emission line (up to a factor of 2) are found. It is argued that these
differences are due to different scattering angles with respect to the line of
sight rather than to different iron abundances.",1309.4456v1
2013-10-15,Atomic structure of grain boundaries in iron modeled using the atomic density function,"A model based on the continuous atomic density function (ADF) approach is
applied to predict the atomic structure of grain boundaries (GBs) in iron.
Symmetrical [100] and [110] tilt GBs in bcc iron are modeled with the ADF
method and relaxed afterwards in molecular dynamics (MD) simulations. The shape
of the GB energy curve obtained in the ADF model reproduces well the
peculiarities of the angles of 70.53 deg. [$\Sigma$ 3(112)] and 129.52 deg.
[$\Sigma$ 11(332)] for [110] tilt GBs. The results of MD relaxation with an
embedded-atom method potential for iron confirm that the atomic GB
configurations obtained in ADF modeling are very close to equilibrium ones. The
developed model provides well-localized atomic positions for GBs of various
geometries.",1310.3964v2
2013-12-17,Ground state pairing correlations in the $S_4$ symmetric microscopic model for iron-based superconductors,"We present the ground state pairing correlations in the $S_4$ symmetric
microscopic model for iron-based superconductors, computed with the
constrained-path Monte Carlo method. For various electron fillings and
interaction strengths, we find that the $s_{xy}$ pairing dominates over other
pairing correlations and is positive when the pair separation exceeds several
lattice constants, whatever for iron pnictides and iron chlcogenides. These
ground state properties, especially the long range part pairing correlations
re-confirm the previous finite temperature results published in Phys. Rev.
Lett. 110, 107002(2013). We further our study by including the nearest
neighbour interaction $V$ and it is found that the $s_{xy}$ pairing correlation
is slightly suppressed by the increasing $V$.",1312.4777v2
2014-03-05,Electrical and optical properties of fluid iron from compressed to expanded regime,"Using quantum molecular dynamics simulations, we show that the electrical and
optical properties of fluid iron change drastically from compressed to expanded
regime. The simulation results reproduce the main trends of the electrical
resistivity along isochores and are found to be in good agreement with
experimental data. The transition of expanded fluid iron into a nonmetallic
state takes place close to the density at which the constant volume derivative
of the electrical resistivity on internal energy becomes negative. The study of
the optical conductivity, absorption coefficient, and Rosseland mean opacity
shows that, quantum molecular dynamics combined with the Kubo-Greenwood
formulation provides a powerful tool to calculate and benchmark the electrical
and optical properties of iron from expanded fluid to warm dense region.",1403.1030v1
2014-06-07,Optical conductivity of iron-based superconductors,"The new family of unconventional iron-based superconductors discovered in
2006 immediately relieved their copper-based high-temperature predecessors as
the most actively studied superconducting compounds in the world. The
experimental and theoretical effort made in order to unravel the mechanism of
superconductivity in these materials has been overwhelming. Although our
understanding of their microscopic properties has been improving steadily, the
pairing mechanism giving rise to superconducting transition temperatures up to
55 K remains elusive. And yet the hope is strong that these materials, which
possess a drastically different electronic structure but similarly high
transition temperatures compared to the copper-based compounds, will shed
essential new light onto the several-decade-old problem of unconventional
superconductivity. In this work we review the current understanding of the
itinerant-charge-carrier dynamics in the iron-based superconductors and parent
compounds largely based on the optical-conductivity data the community has
gleaned over the past seven years using such experimental techniques as
reflectivity, ellipsometry, and terahertz transmission measurements and analyze
the implications of these studies for the microscopic properties of the
iron-based materials as well as the mechanism of superconductivity therein.",1406.1879v1
2014-06-09,Manipulation of gap nodes by uniaxial strain in iron-based superconductors,"In the iron pnictides and chalcogenides, multiple orbitals participate in the
superconducting state, enabling different gap structures to be realized in
distinct materials. Here we argue that the spectral weights of these orbitals
can in principle be controlled by a tetragonal symmetry-breaking uniaxial
strain, due to the enhanced nematic susceptibility of many iron-based
superconductors. By investigating multi-orbital microscopic models in the
presence of orbital order, we show that not only $T_{c}$ can be enhanced, but
pairs of accidental gap nodes can be annihilated and created in the Fermi
surface by an increasing external strain. We explain our results as a mixture
of nearly-degenerate superconducting states promoted by strain, and show that
the annihilation and creation of nodes can be detected experimentally via
anisotropic penetration depth measurements. Our results provide a promising
framework to externally control the superconducting properties of iron-based
materials.",1406.2388v2
2014-07-24,Parallax diagnostics of radiation source geometric dilution for iron opacity experiments,"Experimental tests are in progress to evaluate the accuracy of the modeled
iron opacity at solar interior conditions [J.E. Bailey et al., Phys. Plasmas
16, 058101 (2009)]. The iron sample is placed on top of the Sandia National
Laboratories z-pinch dynamic hohlraum (ZPDH) radiation source. The samples are
heated to 150 - 200 eV electron temperatures and 7e21 - 4e22 e/cc electron
densities by the ZPDH radiation and backlit at its stagnation [T. Nagayama et
al., Phys. Plasmas 21, 056502 (2014)]. The backlighter attenuated by the heated
sample plasma is measured by four spectrometers along +/- 9 degree with respect
to the z-pinch axis to infer the sample iron opacity. Here we describe
measurements of the source-to-sample distance that exploit the parallax of
spectrometers that view the half-moon-shaped sample from +/-9 degree. The
measured sample temperature decreases with increased source-to-sample distance.
This distance must be taken into account for understanding the sample heating.",1407.6645v1
2014-09-23,Superconductivity and its mechanism in an ab initio model for electron-doped LaFeAsO,"Two families of high temperature superconductors whose critical temperatures
are higher than 50K are known. One is the copper oxides and the other is the
iron-based superconductors. Comparisons of mechanisms between these two in
terms of common ground as well as distinctions will greatly help in searching
for higher Tc superconductors. However, studies on mechanisms for the iron
family based on first principles calculations are few. Here we first show that
the superconductivity emerges in the state-of-the-art numerical calculations
for an ab initio multi-orbital model of an electron-doped iron-based
superconductor LaFeAsO, in accordance with experimental observations. Then the
mechanism of the superconductivity is identified as enhanced uniform density
fluctuations by one-to-one correspondence with the instability toward
inhomogeneity driven by first-order antiferromagnetic and nematic transitions.
Despite many differences, certain common features with the copper oxides are
also figured out in terms of the underlying orbital selective Mottness found in
the iron family.",1409.6536v1
2014-10-14,Entangled Orbital Triplet Pairs in Iron-Based Superconductors,"A key question in high temperature iron-based superconductivity is the
mechanism by which the paired electrons minimize their strong mutual Coulomb
repulsion. While electronically paired superconductors generally avoid the
Coulomb interaction through the formation of nodal, higher angular momentum
pairs, iron based superconductors appear to form singlet s-wave (s$^{\pm}$)
pairs. By taking the orbital degrees of freedom of the iron atoms into account,
here we argue that the s$^{\pm}$ state in these materials possesses internal
d-wave structure, in which a relative d-wave ($L=2$) motion of the pairs
entangles with the ($I=2$) internal angular momenta of the d-orbitals to form a
low spin $J=L+I=0$ singlet. We discuss how the recent observation of a nodal
gap with octahedral structure in KFe$_{2}$As$_{2}$ can be understood as a high
spin ($J=L+I=4$) configuration of the orbital and isospin angular momenta; the
observed pressure-induced phase transition into a fully gapped state can then
interpreted as a high-to-low spin phase transition of the Cooper pairs.",1410.3554v1
2014-10-27,First-principles study of intermediate-spin ferrous iron in the Earth's lower mantle,"Spin crossover of iron is of central importance in solid Earth geophysics. It
impacts all physical properties of minerals that altogether constitute $\sim
95$ vol\% of the Earth's lower mantle: ferropericlase [(Mg,Fe)O] and Fe-bearing
magnesium silicate (MgSiO$_3$) perovskite. Despite great strides made in the
past decade, the existence of intermediate-spin (IS) state in ferrous iron
(Fe$^{2+}$) (with total electron spin $S=1$) and its possible role in the
pressure-induced spin crossover in these lower-mantle minerals still remain
controversial. Using density functional theory $+$ self-consistent Hubbard $U$
(DFT$+U_{sc}$) calculations, we investigate all possible types of IS states of
Fe$^{2+}$ in (Mg,Fe)O and (Mg,Fe)SiO$_3$ perovskite. Among the possible IS
states in these minerals, the most probable IS state has an electronic
configuration that significantly reduces the electron overlap and the iron
nuclear quadrupole splitting (QS). These most probable IS states, however, are
still energetically disfavored, and their QSs are inconsistent with
M\""{o}ssbauer spectra. We therefore conclude that IS Fe$^{2+}$ is highly
unlikely in the Earth's lower mantle.",1410.7200v1
2014-12-04,"Magnetism of the Fe$^{2+}$ and Ce$^{3+}$ sublattices in Ce$_{2}$O$_{2}$FeSe$_{2}$: a combined neutron powder diffraction, inelastic neutron scattering and density functional study","The discovery of superconductivity in the 122 iron selenide materials above
30 K necessitates an understanding of the underlying magnetic interactions. We
present a combined experimental and theoretical investigation of magnetic and
semiconducting Ce$_{2}$O$_{2}$FeSe$_{2}$ composed of chains of edge-linked iron
selenide tetrahedra. The combined neutron diffraction and inelastic scattering
study and density functional calculations confirm the ferromagnetic nature of
nearest-neighbour Fe -- Se -- Fe interactions in the ZrCuSiAs-related iron
oxyselenide Ce$_{2}$O$_{2}$FeSe$_{2}$. Inelastic measurements provide an
estimate of the strength of nearest-neighbor Fe -- Fe and Fe -- Ce
interactions. These are consistent with density functional theory calculations,
which reveal that correlations in the Fe--Se sheets of
Ce$_{2}$O$_{2}$FeSe$_{2}$ are weak. The Fe on-site repulsion $U_{Fe}$ is
comparable to that reported for oxyarsenides and K$_{1-x}$Fe$_{2-y}$Se$_{2}$,
which are parents to iron-based superconductors.",1412.1773v1
2014-12-23,"Atomic, electronic and magnetic structure of graphene/iron and nickel interfaces: theory and experiment","First-principles calculations of the effect of carbon coverage on the atomic,
electronic and magnetic structure of nickel and iron substrates demonstrate
insignificant changes in the interatomic distances and magnetic moments on the
atoms of the metallic substrates. The coverage of the iron surface by mono- and
few-layer graphene induces significant changes in the orbital occupancies and
exchange interactions between the layers in contrast to the case of a nickel
substrate for which changes in the orbital ordering and exchange interactions
are much smaller. Experimental measurements demonstrate the presence of
ferromagnetic fcc-iron in Fe@C nanoparticles and the superparamagnetic behavior
of Ni@C nanoparticles.",1412.7291v1
2015-03-20,Thermoelasticity of Fe2+-bearing bridgmanite,"We present LDA+U calculations of high temperature elastic properties of
bridgmanite with composition (Mg$_{(1-x)}$Fe$_{x}^{2+}$)SiO$_3$ for
$0\le{x}\le0.125$. Results of elastic moduli and acoustic velocities for the
Mg-end member (x=0) agree very well with the latest high pressure and high
temperature experimental measurements. In the iron-bearing system, we focus
particularly on the change in thermoelastic parameters across the state change
that occurs in ferrous iron above $\sim$30 GPa, often attributed to a high-spin
(HS) to intermediate spin (IS) crossover but explained by first principles
calculations as a lateral displacement of substitutional iron in the perovskite
cage. We show that the measured effect of this change on the equation of state
of this system can be explained by the lateral displacement of substitutional
iron, not by the HS to IS crossover. The calculated elastic properties of
(Mg$_{0.875}$Fe$_{0.125}^{2+}$)SiO$_3$ along an adiabatic mantle geotherm,
somewhat overestimate longitudinal velocities but produce densities and shear
velocities quite consistent with Preliminary Reference Earth Model data
throughout most of the lower mantle.",1503.05983v1
2015-05-07,Type Ia Supernova Remnants: Shaping by Iron Bullets,"Using 2D numerical hydrodynamical simulations of type Ia supernova remnants
(SNR Ia) we show that iron clumps few times denser than the rest of the SN
ejecta might form protrusions in an otherwise spherical SNR. Such protrusions
exist in some SNR Ia, e.g., SNR 1885 and Tycho. Iron clumps are expected to
form in the deflagration to detonation explosion model. In SNR Ia where there
are two opposite protrusions, termed ears, such as Kepler's SNR and SNR
G1.9+0.3, our scenario implies that the dense clumps, or iron bullets, were
formed along an axis. Such a preferred axis can result from a rotating white
dwarf progenitor. If our claim holds, this offers an important clue to the SN
Ia explosion scenario.",1505.02034v2
2015-07-13,Electronic and magnetic properties of orthorhombic iron selenide (FeSe),"Iron orbitals in orthorhombic iron selenide (FeSe) can produce charge-like
multipoles that are polar (parity-odd). Orbitals in question include Fe(3d),
Fe(4p) and p-type ligands that participate in transport properties and bonding.
The polar multipoles may contribute weak, space-group forbidden Bragg spots to
diffraction patterns collected with x-rays tuned in energy to a Fe atomic
resonance (Templeton & Templeton scattering). Ordering of conventional, axial
magnetic dipoles does not accompany the tetragonal-orthorhombic structural
phase transition in FeSe, unlike other known iron-based superconductors. We
initiate a new line of inquiry for this puzzling property of orthorhombic FeSe,
using a hidden magnetic-order that belongs to the m'm'm' magnetic
crystal-class. It is epitomized by the absence of ferromagnetism and axial
magnetic dipoles, and the appearance of magnetic monopoles and magneto-electric
quadrupoles. A similar magnetic order occurs in cuprate superconductors, YBCO &
Hg1201, where it was unveiled with the Kerr effect and in Bragg diffraction
patterns revealed by polarized neutrons. PACS number 75.25.-j",1507.03449v3
2015-07-16,Feasibility of pulsed inflector for g-2ring (1),"We revise a possibility of usage iron-free fast pulsed magnet as inflector
for g-2 ring, coming to conclusion that it is a feasible option.",1507.04796v1
2015-08-06,Charge Nematicity and Electronic Raman Scattering in Iron-based Superconductors,"We review the recent developments in electronic Raman scattering measurements
of charge nematic fluctuations in iron-based superconductors. A simple
theoretical framework of a $d$-wave Pomeranchuk transition is proposed in order
to capture the salient features of the spectra. We discuss the available Raman
data in the normal state of 122 iron-based systems, particularly Co doped
BaFe$_2$As$_2$, and we show that the low energy quasi-elastic peak, the
extracted nematic susceptibility and the scattering rates are consistent with
an electronic driven structural phase transition. In the superconducting state
with a full gap the quasi-elastic peak transforms into a finite frequency
nematic resonance, evidences for which are particularly strong in the electron
doped systems. A crucial feature of the analysis is the fact that the
electronic Raman signal is unaffected by the acoustic phonons. This makes Raman
spectroscopy a unique probe of electronic nematicity.",1508.01319v2
2015-08-29,Competing Magnetic Fluctuations in Iron Pnictide Superconductors: Role of Ferromagnetic Spin Correlations Revealed by NMR,"In the iron pnictide superconductors, theoretical calculations have
consistently shown enhancements of the static magnetic susceptibility at both
the stripe-type antiferromagnetic (AFM) and in-plane ferromagnetic (FM)
wavevectors. However, the possible existence of FM fluctuations has not yet
been examined from a microscopic point of view. Here, using $^{75}$As NMR data,
we provide clear evidence for the existence of FM spin correlations in both the
hole- and electron-doped BaFe$_2$As$_2$ families of iron-pnictide
superconductors. These FM fluctuations appear to compete with superconductivity
and are thus a crucial ingredient to understanding the variability of $T_{\rm
c}$ and the shape of the superconducting dome in these and other iron-pnictide
families.",1508.07506v1
2015-12-23,Giant biquadratic interaction induced magnetic anisotropy in the iron-based superconductor AxFe2-ySe2,"The emergence of the electron-pocket only iron-based superconductor
AxFe2-ySe2 (A = alkali metal) challenges the Fermi-surface nesting picture
established in iron-pnictides. It was widely believed that magnetism is
correlated with the superconductivity in AxFe2-ySe2. Unfortunately, the highly
anisotropic exchange parameters and the disagreement between theoretical
calculations and experimental results triggered a fierce debate on the nature
of magnetism in AxFe2-ySe2. Here we find that the strong magnetic anisotropy is
from the anisotropic biquadratic interaction. In order to accurately obtain the
magnetic interaction parameters, we propose a universal method, which does not
need including other high energy configurations as did in conventional energy
mapping method. We show that our model successfully captures the magnetic
interactions in AxFe2-ySe2 and correctly predicts the spin wave spectrum, in
quantitative agreement with the experimental observation. These results suggest
that the local moment picture, including the biquadratic term, can describe
accurately the magnetic properties and spin excitations in AxFe2-ySe2, which
sheds new light on the future study of the high-Tc iron-based superconductors.",1512.07327v1
2016-01-08,Isotropic Cooper Pairs with Emergent Sign Changes in Single-Layer Iron Superconductor,"We model a single layer of heavily electron-doped FeSe by spin-1/2 moments
over a square lattice of iron atoms that include the 3d xz and 3d yz orbitals,
at strong on-site Coulomb repulsion. Above half filling, we find emergent hole
bands below the Fermi level at the center of the one-iron Brillouin zone in a
half metal state characterized by hidden magnetic order and by electron-type
Fermi surface pockets at wavenumbers that double the unit cell along the
principal axes. ""Replicas"" of the emergent hole bands exist at lower energy in
the two-iron Brillouin zone. Exact calculations with two mobile electrons find
evidence for isotropic Cooper pairs that alternate in sign between the electron
bands and the emergent hole bands.",1601.01860v3
2016-03-18,Stability mechanisms of high current transport in iron-chalcogenides superconducting films,"The improvement in the fabrication techniques of iron-based superconductors
have made these materials real competitors of high temperature superconductors
and MgB$_2$. In particular, iron-chalcogenides have proved to be the most
promising for the realization of high current carrying tapes. But their use on
a large scale cannot be achieved without the understanding of the current
stability mechanisms in these compounds. Indeed, we have recently observed the
presence of flux flow instabilities features in Fe(Se,Te) thin films grown on
CaF$_2$. Here we present the results of current-voltage characterizations at
different temperatures and applied magnetic fields on Fe(Se,Te) microbridges
grown on CaF$_2$. These results will be analyzed from the point of view of the
most validated models with the aim to identify the nature of the flux flow
instabilities features (i.e., thermal or electronic), in order to give a
further advance to the high current carrying capability of iron-chalcogenide
superconductors.",1603.05980v1
2016-05-15,Nonlocal correlations in the vicinity of the $α$-$γ$ phase transition in iron within a DMFT plus spin-fermion model approach,"We consider nonlocal correlations in iron in the vicinity of the
$\alpha$-$\gamma$ phase transition within the spin-rotationally-invariant
dynamical mean-field theory (DMFT) approach, combined with the recently
proposed spin-fermion model of iron. The obtained nonlocal corrections to DMFT
yield a decrease of the Curie temperature of the $\alpha$ phase, leading to an
agreement with its experimental value. We show that the corresponding nonlocal
corrections to the energy of the $\alpha$ phase are crucially important to
obtain the proximity of energies of $\alpha$ and $\gamma$ phases in the
vicinity of the iron $\alpha$-$\gamma$ transformation.",1605.04589v2
2016-06-01,Quasi-particle bands and structural phase transition of iron from Gutzwiller Density-Functional Theory,"We use the Gutzwiller Density Functional Theory to calculate ground-state
properties and bandstructures of iron in its body-centered-cubic (bcc) and
hexagonal-close-packed (hcp) phases. For a Hubbard interaction $U=9\, {\rm eV}$
and Hund's-rule coupling $J=0.54\, {\rm eV}$ we reproduce the lattice
parameter, magnetic moment, and bulk modulus of bcc iron. For these parameters,
bcc is the ground-state lattice structure at ambient pressure up to a pressure
of $p_{\rm c}=41\, {\rm GPa}$ where a transition to the non-magnetic hcp
structure is predicted, in qualitative agreement with experiment ($p_{\rm
c}^{\rm exp}=10\ldots 15\, {\rm GPa}$). The calculated bandstructure for bcc
iron is in good agreement with ARPES measurements. The agreement improves when
we perturbatively include the spin-orbit coupling.",1606.00307v1
2016-08-03,Moiré-free ultrathin iron oxide film: FeO(111) on Ag(111),"Ultrathin iron oxide films epitaxially grown on the (111)- and
(0001)-oriented metal single crystal supports exhibit unique electronic,
catalytic and magnetic properties not observed for the corresponding bulk
oxides. These properties originate mainly from the presence of Moir\'e
superstructures which, in turn, disqualify ultrathin films as model systems
imitating bulk materials. We present a route for the preparation of a
close-packed Moir\'e-free ultrathin iron oxide film, namely FeO(111) on
Ag(111). Experimental scanning tunneling microscopy (STM), low energy electron
diffraction (LEED) and x-ray photoelectron spectroscopy (XPS) results confirm
perfect structural order in the film. Density functional theory (DFT)-based
calculations suggest full relaxation of the oxide layer that adopts the atomic
lattice of the crystalline support and exhibits properties similar to those of
a free-standing FeO. The results open new pathways for model-type studies of
electronic, catalytic and magnetic properties of fully-relaxed iron oxide films
and related systems.",1608.01376v2
2016-08-21,Coexistence of antiferromagnetic and ferromagnetic spin correlations in Ca(Fe1-xCox)2As2 revealed by 75As nuclear magnetic resonance,"Recent nuclear magnetic resonance (NMR) measurements revealed the coexistence
of stripe-type antiferromagnetic (AFM) and ferromagnetic (FM) spin correlations
in both the hole- and electron-doped BaFe$_2$As$_2$ families of iron-pnictide
superconductors by a Korringa ratio analysis. Motivated by the NMR work, we
investigate the possible existence of FM fluctuations in another iron pnictide
superconducting family, Ca(Fe$_{1-x}$Co$_x$)$_2$As$_2$. We re-analyzed our
previously reported data in terms of the Korringa ratio and found clear
evidence for the coexistence of stripe-type AFM and FM spin correlations in the
electron-doped CaFe$_2$As$_2$ system. These NMR data indicate that FM
fluctuations exist in general in iron-pnictide superconducting families and
thus must be included to capture the phenomenology of the iron pnictides.",1608.05952v1
2016-08-29,Frustrated magnetism and bicollinear antiferromagnetic order in FeTe,"Iron chalcogenides display a rich variety of electronic orders in their phase
diagram. A particularly enigmatic case is FeTe, a metal which possesses
co-existing hole and electron Fermi surfaces as in the iron pnictides but has a
distinct ($\pi$/2,$\pi/2$) bicollinear antiferromagnetic order in the Fe square
lattice. While local-moment physics has been recognized as essential for
understanding the electronic order, it has been a long-standing challenge to
understand how the bicollinear antiferromagnetic ground state emerges in a
proper quantum spin model. We show here that a bilinear-biquadratic spin-$1$
model on a square lattice with nonzero ring-exchange interactions exhibits the
bicollinear antiferromagnetic order over an extended parameter space in its
phase diagram. Our work shows that frustrated magnetism in the quantum spin
model provides a unified description of the electronic orders in the iron
chalcogenides and iron pnictides.",1608.08206v1
2016-09-12,Spin excitations in hole-overdoped iron-based superconductors,"Understanding the overall features of magnetic excitation is essential for
clarifying the mechanism of Cooper pair formation in iron-based
superconductors. In particular, clarifying the relationship between magnetism
and superconductivity is a central challenge because magnetism may play a key
role in their exotic superconductivity. BaFe2As2 is one of ideal systems for
such investigation because its superconductivity can be induced in several
ways, allowing a comparative examination. Here we report a study on the spin
fluctuations of the hole-overdoped iron-based superconductors Ba1-xKxFe2As2 (x
= 0.5 and 1.0; Tc = 36 K and 3.4 K, respectively) over the entire Brillouin
zone using inelastic neutron scattering. We find that their spin spectra
consist of spin wave and chimney-like dispersions. The chimney-like dispersion
can be attributed to the itinerant character of magnetism. The band width of
the spin wave-like dispersion is almost constant from the non-doped to
optimum-doped region, which is followed by a large reduction in the overdoped
region. This suggests that the superconductivity is suppressed by the reduction
of magnetic exchange couplings, indicating a strong relationship between
magnetism and superconductivity in iron-based superconductors.",1609.03335v1
2016-09-21,Nematicity at the Hund's metal crossover in iron superconductors,"The theoretical understanding of the nematic state of iron-based
superconductors and especially of FeSe is still a puzzling problem. Although a
number of experiments calls for a prominent role of local correlations and
place iron superconductors at the entrance of a Hund metal state, the effect of
the electronic correlations on the nematic state has been theoretically poorly
investigated. In this work we study the nematic phase of iron superconductors
accounting for local correlations, including the effect of the Hund's coupling.
We show that Hund's physics strongly affects the nematic properties of the
system. It severely constraints the precise nature of the feasible
orbital-ordered state and induces a differentiation in the effective masses of
the zx=yz orbitals in the nematic phase. The latter effect leads to distinctive
signatures in different experimental probes, so far overlooked in the
interpretation of experiments. As notable examples the splittings between zx
and yz bands at Gamma and M points are modified, with important consequences
for ARPES measurements.",1609.06672v2
2016-10-27,Influence of multiorbitals and anisotropic Coulomb interactions on isotope effect coefficient in doped Fe-based superconductors,"The present work describes the theoretical analysis of isotope effect
coefficient as a function of transition temperature in two orbital per site
model Hamiltonian in iron based superconducting system. The expression of
isotope effect coefficient has been computed numerically and self-consistently
by employing Green's function technique within the BCS-mean-field
approximation. It is observed that the isotope effect coefficient increases
with the increase of the hybridization while with the increase in Coulomb
interaction it starts decreasing. On increasing the carrier density per site in
two orbital per site iron pnictide system, isotope effect coefficient
($\alpha$) exhibits large values (much higher than BCS limit) at lower
temperatures. While in the underdoped case, isotope effect coefficient shows
minimum value in superconducting states of the iron based systems. Furthermore,
it has been found that the large value of the isotope effect coefficient is the
indication of the fact that the contribution of phonon alone is inadequate as
the origin of superconductivity in these systems. Finally, the obtained
theoretical results have been compared with experimental and existing
theoretical observations in iron based superconductors.",1610.08888v1
2016-11-01,Missing Fe: hydrogenated iron nanoparticles,"Although it was found that the FeH lines exist in the spectra of some stars,
none of the spectral features in the ISM have been assigned to this molecule.
We suggest that iron atoms interact with hydrogen and produce Fe-H
nanoparticles which sometimes contain many H atoms. We calculate infrared
spectra of hydrogenated iron nanoparticles using density functional theory
methods and find broad, overlapping bands. Desorption of H2 could induce
spinning of these small Fe-H dust grains. Some of hydrogenated iron
nanoparticles posses magnetic and electric moments and should interact with
electromagnetic fields in the ISM. Fe_nH_m nanoparticles could contribute to
the polarization of the ISM and the anomalous microwave emission. We discuss
the conditions required to form FeH and Fe_nH_m in the ISM.",1611.00309v1
2016-11-25,Modeling the Anomalous Microwave Emission with Spinning Nanoparticles: No PAHs Required,"In light of recent observational results indicating an apparent lack of
correlation between the Anomalous Microwave Emission (AME) and mid-infrared
emission from polycyclic aromatic hydrocarbons (PAHs), we assess whether
rotational emission from spinning silicate and/or iron nanoparticles could
account for the observed AME without violating observational constraints on
interstellar abundances, ultraviolet extinction, and infrared emission. By
modifying the SpDust code to compute the rotational emission from these grains,
we find that nanosilicate grains could account for the entirety of the observed
AME, whereas iron grains could be responsible for only a fraction, even for
extreme assumptions on the amount of interstellar iron concentrated in
ultrasmall iron nanoparticles. Given the added complexity of contributions from
multiple grain populations to the total spinning dust emission, as well as
existing uncertainties due to the poorly-constrained grain size, charge, and
dipole moment distributions, we discuss generic, carrier-independent
predictions of spinning dust theory and observational tests that could help
identify the AME carrier(s).",1611.08597v1
2017-01-18,Phase-separation control of K$_x$Fe$_{2-y}$Se$_2$ superconductor through rapid-quenching process,"K$_x$Fe$_{2-y}$Se$_2$ exhibits an iron-vacancy ordering at $T_{\rm s}
{\sim}270{\deg}$C and separates into two phases: a minor superconducting
(iron-vacancy-disordered) phase and a major non-superconducting
(iron-vacancy-ordered) phase. The microstructural and superconducting
properties of this intermixture can be tuned by an appropriate control of the
quenching process through $T_{\rm s}$. A faster quenching rate leads to a finer
microstructure and a suppression of formation of the non-superconducting phase
by up to 50%. Nevertheless, such a faster cooling rate does induce a monotonic
reduction in the superconducting transition temperature (from 30.7 K down to
26.0 K) and, simultaneously, a decrease in the iron content within the
superconducting phase such that the compositional ratio changed from
K$_{0.35}$Fe$_{1.83}$Se$_2$ to K$_{0.58}$Fe$_{1.71}$Se$_2$.",1701.04911v2
2017-05-19,The phonon softening due to melting of the ferromagnetic order in elemental iron,"We study the fundamental question of the lattice dynamics of a metallic
ferromagnet in the regime where the static long range magnetic order is
replaced by the fluctuating local moments embedded in a metallic host. We use
the \textit{ab initio} Density Functional Theory(DFT)+embedded Dynamical
Mean-Field Theory(eDMFT) functional approach to address the dynamic stability
of iron polymorphs and the phonon softening with increased temperature. We show
that the non-harmonic and inhomogeneous phonon softening measured in iron is a
result of the melting of the long range ferromagnetic order, and is unrelated
to the first order structural transition from the BCC to the FCC phase, as is
usually assumed. We predict that the BCC structure is dynamically stable at all
temperatures at normal pressure, and is only thermodynamically unstable between
the BCC-$\alpha$ and the BCC-$\delta$ phase of iron.",1705.06877v2
2017-06-21,"Emergent phases in iron pnictides: Double-Q antiferromagnetism, charge order and enhanced nematic correlations","Electron correlations produce a rich phase diagram in the iron pnictides.
Earlier theoretical studies on the correlation effect demonstrated how quantum
fluctuations weaken and concurrently suppress a $C_2$-symmetric single-Q
antiferromagnetic order and a nematic order. Here we examine the emergent
phases near the quantum phase transition. For a $C_4$-symmetric collinear
double-Q antiferromagnetic order, we show that it is accompanied by both a
charge order and an enhanced nematic susceptibility. Our results provide
understanding for several intriguing recent experiments in hole-doped iron
arsenides, and bring out common physics that underlies the different magnetic
phases of various iron-based superconductors.",1706.07087v2
2017-09-26,Timing and Charge measurement of single gap Resistive Plate Chamber Detectors for INO-ICAL Experiment,"The recently approved India-based Neutrino Observatory will use the world's
largest magnet to study atmospheric muon neutrinos. The 50 kiloton Iron
Calorimeter consists of iron alternating with single-gap resistive plate
chambers. A uniform magnetic field of $\sim$1.5 T is produced in the iron using
toroidal-shaped copper coils. Muon neutrinos interact with the iron target to
produce charged muons, which are detected by the resistive plate chambers, and
tracked using orthogonal pick up strips. Timing information for each layer is
used to discriminate between upward and downward traveling muons. The design of
the readout electronics for the detector depends critically on an accurate
model of the charge induced by the muons, and the dependence on bias voltages.
In this paper, we present timing and charge response measurements using
prototype detectors under different operating conditions. We also report the
effect of varying gas mixture, particularly $SF_6$, on the timing response.",1709.08946v1
2018-01-03,Distinguishing black holes and naked singularities with iron line spectroscopy,"It is commonly thought that the final product of gravitational collapse is a
black hole. Nevertheless, theoretical studies have not yet provided a final
answer to the question whether black holes are the only possible outcome or
whether naked singularities are also allowed. Observational tests may thus
represent a complementary approach. In the present paper, we consider the
Janis-Newman-Winicour metric, which describes a rotating source with a
surface-like naked singularity. We calculate iron line shapes in the reflection
spectrum of a putative disk around a Janis-Newman-Winicour singularity and we
compare our results with the iron line shapes expected in the spectrum of a
Kerr black hole. While it is difficult to distinguish the two spacetimes from
the iron line shape in general, it seems that Janis-Newman-Winicour
singularities cannot mimic fast-rotating Kerr black holes observed at a low or
moderate inclination angle. Our analysis thus suggests that available
observations of specific sources can already constrain the possible existence
of Janis-Newman-Winicour singularities in the Universe.",1801.00867v2
2018-01-24,Evidence for a neutral iron line generated by MeV protons from supernova remnants interacting with molecular clouds,"Supernova remnants (SNRs) have been prime candidates for Galactic cosmic-ray
accelerators. When low-energy cosmic-ray protons (LECRp) collide with
interstellar gas, they ionize neutral iron atoms and emit the neutral iron line
(Fe I K$\alpha$) at 6.40keV. We search for the iron K-shell line in seven SNRs
from the Suzaku archive data of the Galactic plane in the $6^{\circ} \lesssim l
\lesssim 40^{\circ}, |b| < 1^{\circ}$ region. All these SNRs interact with
molecular clouds. We discover Fe I K$\alpha$ line emissions from five SNRs
(W28, Kes 67, Kes 69, Kes 78, and W44). The spectra and morphologies suggest
that the Fe I K$\alpha$ line is produced by interactions between LECRp and the
adjacent cold gas. The proton energy density is estimated to be $\gtrsim$
10-100 eV cm$^{-3}$, which is more than 10 times higher than that in the
ambient interstellar medium.",1801.07881v1
2018-02-11,Two-dimensional Iron Monocarbide with Planar Hypercoordinate Iron and Carbon,"We report on the theoretical discovery of Iron monocarbide binary sheets
stabilized at two-dimensional confined space, which we call tetragonal-FeC
(t-FeC) and orthorhombic-FeC (o-FeC), respectively. From the energy viewpoint,
the proposed t-FeC is the global minimum configuration in the 2D space, and
each carbon atom is four-coordinated with ambient four Iron atoms. Strikingly,
the o-FeC monolayer is an orthorhombic phase with planar pentacoordinate carbon
moiety and planar seven-coordinate Fe moiety. To our knowledge, this monolayer
is the first example of a simultaneously pentacoordinate carbon and planar
seven-coordinate Fe-containing material. State-of-the-art theoretical
calculations confirm that all these monolayers have significantly dynamic,
mechanical, and thermal stabilities. Among these two monolayers, t-FeC
monolayer shows a higher theoretical capacity (395 mAh g-1 ), and can stably
adsorb Li up to t-FeCLi3 . Low migration energy barrier is predicted as small
as 0.26 eV for Li, which result in the fast diffusion of Li atom on this
monolayer. Moreover, electron-phonon calculations coupled with
Bardeen-Cooper-Schrieffer arguments suggest t-FeC can be potential
two-dimensional superconductors with 6.77 K superconducting transition
temperature.",1802.03673v1
2018-03-01,Strong electronic correlations and Fermi surface reconstruction in the quasi-one dimensional iron superconductor BaFe2S3,"BaFe2S3 is a special iron superconductor with two-leg ladder structure which
can help to unravel the role played by the electronic correlations in high-Tc
superconductivity. At zero pressure it is insulating with stripe
antiferromagnetic (AF) order and superconductivity emerges under pressure. We
use a slave-spin technique to analyze the strength of the local correlations in
BaFe2S3. We find that at the pressure at which the superconductivity appears
the electronic correlations in BaFe2S3 are similar to the ones measured in
other iron superconductors. However, at zero pressure the strength of the
correlations is strongly enhanced, being particularly severe for the two
orbitals with the largest weight at the Fermi level what invalidates nesting as
the mechanism for AF. The system is not a Mott insulator at zero temperature,
but these two orbitals with mass enhancements m* ~ 12-15 will become incoherent
at higher temperatures. Different from what happens in other iron
superconductors, at both pressures, the Fermi surface is reconstructed by the
electronic correlations.",1803.00282v1
2018-03-28,Iron line spectroscopy with Einstein-dilaton-Gauss-Bonnet black holes,"Einstein-dilaton-Gauss-Bonnet gravity is a well-motivated alternative theory
of gravity that emerges naturally from string theory. While black hole
solutions have been known in this theory in numerical form for a while, an
approximate analytical metric was obtained recently by some of us, which allows
for faster and more detailed analysis. Here we test the accuracy of the
analytical metric in the context of X-ray reflection spectroscopy. We analyze
innermost stable circular orbits (ISCO) and relativistically broadened iron
lines and find that both the ISCO and iron lines are determined sufficiently
accurately up to the limit of the approximation. We also find that, though the
ISCO increases by about 7% as dilaton coupling increases from zero to extremal
values, the redshift at ISCO changes by less than 1%. Consequently, the shape
of the iron line is much less sensitive to the dilaton charge than expected.",1803.10819v1
2018-04-13,Subsurface Cation Vacancy Stabilization of the Magnetite (001) Surface,"Iron oxides play an increasingly prominent role in heterogeneous catalysis,
hydrogen production, spintronics and drug delivery. The surface or material
interface can be performance limiting in these applications, so it is vital to
determine accurate atomic-scale structures for iron oxides and understand why
they form. Using a combination of quantitative low-energy electron diffraction,
scanning tunneling microscopy, and density functional theory calculations, we
show that an ordered array of subsurface iron vacancies and interstitials
underlies the well-known (rt2xrt2)R45{\deg} reconstruction of Fe3O4(001). This
hitherto unobserved stabilization mechanism occurs because the iron oxides
prefer to redistribute cations in the lattice in response to oxidizing or
reducing environments. Many other metal oxides also achieve stoichiometric
variation in this way, so such surface structures are likely commonplace.",1804.04836v1
2018-04-21,Iron line spectroscopy of black holes in asymptotically safe gravity,"We study the iron line shape expected in the reflection spectrum of accretion
disks around black holes in asymptotically safe gravity. We compare the results
of our simulations with the iron line shapes expected in the reflection
spectrum of accretion disks around Kerr black holes to see if the technique of
iron line spectroscopy can be used as a tool to test asymptotically safe
gravity. Our analysis shows that current X-ray facilities are surely unable to
distinguish black holes in asymptotically safe gravity from black holes in
Einstein's gravity. In the case of the next generation of X-ray missions, which
promise to provide unprecedented high quality data, the question remains open
because it cannot be addressed within our simplified model.",1804.07955v2
2018-04-30,New iron-based multiferroics with improper ferroelectricity,"In this contribution to the special issue on magnetoelectrics and their
applications, we focus on some single phase multiferroics theoretically
predicted and/or experimentally discovered by the authors in recent years. In
these materials, iron is the common core element. However, these materials are
conceptually different from the mostly-studied BiFeO$_3$, since their
ferroelectricity is improper. Our reviewed materials are not simply repeating
one magnetoelectric mechanism, but cover multiple branches of improper
ferroelectricity, including the magnetism-driven ferroelectrics, geometric
ferroelectric, as well as electronic ferroelectric driven by charge ordering.
In this sense, these iron-based improper ferroelectrics can be an encyclopaedic
playground to explore the comprehensive physics of multiferroics and
magnetoelectricity. Furthermore, the unique characteristics of iron's $3d$
orbitals make some of their magnetoelectric properties quite prominent,
comparing with the extensively-studied Mn-based improper multiferroics. In
addition, these materials establish the crossover between multiferroics and
other fields of functional materials, which enlarges the application scope of
multiferroics.",1804.11125v1
2018-05-23,Single-crystal growth of iron-based superconductor La$_{0.34}$Na$_{0.66}$Fe$_2$As$_2$,"We report single-crystal growth of La$_{0.34}$Na$_{0.66}$Fe$_2$As$_2$
iron-based superconductor with the size of several millimeters. The samples
were accidentally obtained in trying to grow LaFeAsO$_{1-y}$F$_y$ ( $y \geq$
0.8 ) single crystals with NaAs and NaF flux. The sample shows both
antiferromagnetic and structural transitions at 106 K. The superconducting
transition temperature is about 27 K with the superconducting anisotropy of
about 1.9. These values and the temperature dependence of the Hall coefficient
suggest that La$_{0.34}$Na$_{0.66}$Fe$_2$As$_2$ belongs to hole-doped ""122""
families of iron pnictides with the doping level slightly lower than optimal
doping. Compared with previous reports on the polycrystalline samples, our
results suggest that either $T_c$ of the this system can be further increased,
or the superconducting dome may not be well formed in this system. In either
case, the La$_{0.5-x}$Na$_{0.5+x}$Fe$_2$As$_2$ system provides a new platform
to study the antiferromagnetic and superconducting properties of iron-based
superconductors.",1805.08923v2
2018-06-16,Iron Line Spectroscopy of Black Holes in Vector-Tensor Galileons Modified Gravity,"Recently, a rotating black hole solution was found in Vector-Tensor Galileons
modified gravity that has some significant differences from the Kerr black hole
solution. We study the iron line shape that is part of the reflection spectrum
of accretion disks around black holes in this new black hole solution. We
simulate and compare the iron lines of this solution with those of the Kerr
solution to see if the technique of iron line spectroscopy can be used as a
tool to test Vector-Tensor Galileons modified gravity. Our analysis shows that
current X-ray facilities can, in principle, be used to test and place
constraints on Vector-Tensor Galileons modified gravity in the strong coupling
and ultraspinning regimes.",1806.06240v2
2018-08-07,Forming Mercury by Giant Impacts,"The origin of Mercury's high iron-to-rock ratio is still unknown. In this
work we investigate Mercury's formation via giant impacts and consider the
possibilities of a single giant impact, a hit-and-run, and multiple collisions
in one theoretical framework. We study the standard collision parameters
(impact velocity, mass ratio, impact parameter), along with the impactor's
composition and the cooling of the target. It is found that the impactor's
composition affects the iron distribution within the planet and the final mass
of the target by up to 15\%, although the resulting mean iron fraction is
similar. We suggest that an efficient giant impact requires to be head-on with
high velocities, while in the hit-and-run case the impact can occur closer to
the most probable collision angle (45$^{\circ}$). It is also shown that
Mercury's current iron-to-rock ratio can be a result of multiple-collisions,
with their exact number depending on the collision parameters. Mass loss is
found to be more significant when the collisions are tight in time.",1808.02448v1
2018-08-26,Realization of continuously electron doping in bulk iron selenides and identification of a new superconducting zone,"It is known that iron selenide superconductors exhibit unique characteristics
distinct from iron pnicitides, especially in the electron-doped region.
However, acomprehensive study of continuous carrier doping ang the
corresponding crystal structures of FeSe is still lacking, mainly due to the
difficulties in controlling the carrier density in bulk materials. Here, we
report the successful synthesis of a new family of bulk Lix(C3H10N2)0.37FeSe,
which features a continue superconducting dome harboring Lifshitz transition
within the wide range of 0.06~0.68. We demonstrate that with electron-doped,
the anion height of FeSe layers deviates lineraly away from the optimized
values of pnictides and pressurized FeSe. This feature leads to anew
superconducting zone with unique doping dependence of the electronic structures
and strong orbital-selective electronic correlation. Optimal superconductivity
is achieved when the Fe 3d t2g orbitals have almost the same intermediate
electronic correlation strength, with moderate mass enhancement between 3~4 in
the two separate superconducting zone. Our result shed light on archieving
unified mechanism of superconductivity in iron-based materials.",1808.08501v1
2018-09-13,Dendritic Oxide Growth in Zero-Valent Iron Nanofilms Revealed by Atom Probe Tomography,"Atom probe tomography (APT) analysis of chemically pure nanofilms of
zero-valent iron (Fe(0), or ZVI) and their thermal oxide nano-overlayers
reveals the presence of dendritic iron oxide features that extend from the
oxide nano-overlayer surface into the ZVI bulk. The dendrites are observed by
APT to be in the 5 nm x 10 nm size range and form quickly under natural
atmospheric conditions. Their growth into the ZVI lalyer is, within the limit
of our three-month long study, self-limiting (i.e. their initial growth appears
to quickly discontinue). The atomistic views presented here shed first light on
the atmospheric corrosion process of Fe(0)-bearing engineered nanostructures
and their surfaces in the limit of low bulk impurities. Possible roles of the
newly identified oxidized iron dendrites are also discussed in the context of
passivation processes limiting technological applications of Fe(0).",1809.04909v2
2018-10-28,A mathematical and experimental study on iron rings formation in porous stones,"In this interdisciplinary paper, we study the formation of iron precipitates
- the so-called Liesegang rings - in Lecce stones in contact with iron source.
These phenomena are responsible of exterior damages of lapideous artifacts, but
also in the weakening of their structure. They originate in presence of water,
determining the flow of carbonate compunds mixing with the iron ions and then,
after a sequence of reactions and precipitation, leading to the formation of
Liesegang rings. In order to model these phenomena observed in situ and in
laboratory experiments, we propose a modification of the classical
Keller-Rubinow model and show the results obtained with some numerical
simulations, in comparison with the experimental tests. Our model is of
interest for a better understanding of damage processes in monumental stones.",1810.11825v1
2019-01-10,A topology optimized switchable permanent magnet system,"The design of a magnetic field source that can switch from a high field to a
low field configuration by rotation by $90^\circ$ of a set of iron pieces is
investigated using topology optimization. A Halbach cylinder is considered as
the magnetic field source and iron inserts are placed in the air gap of the
Halbach cylinder. The ideal shape of these iron inserts is determined as
function of the field generated by the Halbach cylinder and as function of the
size of the iron segments. The topology optimized structures are parabolic
shaped pieces and have a difference in flux density between the high and low
positions that is on average 1.29 times higher than optimized regular pole
pieces. The maximum increase is a factor of 2.08 times higher than the regular
pole pieces.",1901.03110v1
2019-01-10,Topological Vortex Phase Transitions in Iron-Based Superconductors,"We study topological vortex phases in iron-based superconductors. Besides the
previously known vortex end Majorana zero modes (MZMs) phase stemming from the
existence of a three dimensional (3D) strong topological insulator state, we
show that there is another topologically nontrivial phase as iron-based
superconductors can be doped superconducting 3D weak topological insulators
(WTIs). The vortex bound states in a superconducting 3D WTI exhibit two
different types of quantum states, a robust nodal superconducting phase with
pairs of bulk MZMs and a full-gap topologically nontrivial superconducting
phase which has single vortex end MZM in a certain range of doping level.
Moreover, we predict and summarize various topological phases in iron-based
superconductors, and find that carrier doping and interlayer coupling can drive
systems to have phase transitions between these different topological phases.",1901.03120v1
2019-01-28,Surface passivation by graphene in the lubrication of iron: A comparison with bronze,"It has been recently reported that graphene is able to significantly reduce
the friction coefficient of steel-on-steel sliding contacts. The microscopic
origin of this behavior has been attributed to the mechanical action of load
carrying capacity. However, a recent work highlighted the importance of the
chemical action of graphene. According to this work graphene reduces the
adhesion of iron interfaces by reducing the surface energy thanks to a
passivation effect. The aim of the present work is to clarify the still debated
lubricating behavior of graphene flakes. We perform pin-on-disc experiments
using liquid dispersed graphene solution as a lubricant. Two different
materials, pure iron and bronze are tested against 100Cr6 steel. Raman
spectroscopy is used to analyze the surfaces after the friction tests. The
results of these tests prove that graphene flakes have a beneficial effect on
the friction coefficient. At the same time they show a tendency of graphene to
passivate the native iron surfaces that are exposed during sliding as a
consequence of wear.",1901.09616v1
2019-03-19,First performance test of 30 mm iron-based superconductor single pancake coil under 24 T background field,"The iron-based superconductor (IBS) single pancake coil (SPC) with 30 mm
inner diameter was firstly fabricated and tested under 24 T background field.
This SPC was successfully made using the 7-filamentary Ba1-xKxFe2As2 (Ba122)
tape by wind-and-react method. This IBS coil show the highest Ic value at
magnetic field reported so far. For example, the transport critical current of
this Ba122 SPC achieved 35 A at 4.2 K and 10 T, which is about half of that of
short sample. This indicates that the non-insulation winding process together
with the stainless-steel tape is suitable to the iron-based superconductor.
Even more encouraging is the fact that the Ic of this SPC is still as high as
26 A under 24 T background field, which is still about 40% of that at zero
external magnetic field. These results clearly demonstrate that the iron-based
superconductors are very promising for high-field magnet applications.",1903.07960v1
2019-03-29,Nematic and Antiferromagnetic Quantum Criticality in a Multi-Orbital Hubbard Model for Iron Pnictides,"The extent to which quantum criticality drives the physics of iron pnictides
is a central question in the field. Earlier theoretical considerations were
based on an effective field theory, and the proposed realization in P-doped
iron arsenides has received extensive experimental evidence. To connect the
quantum critical behavior with the underlying electronic physics, it is
important to analyze it within microscopic models. Here, we do so for a
multi-orbital model containing both Hubbard and Hund's interactions, by a
variational Monte Carlo method based on Jastrow-Slater wave functions that
allow for a non-perturbative treatment of electron correlations. We find strong
evidence for the existence of a unique quantum critical point, where both
nematic and $(\pi,0)$ antiferromagnetic orders develop together, in the
bad-metal regime of the phase diagram. Implications of our results for the
iron-based superconductivity are discussed.",1903.12625v1
2019-04-08,High-energy spin fluctuation in low-$T_{\rm c}$ iron-based superconductor LaFePO$_{0.9}$,"Spin fluctuations are widely believed to play an important role in the
superconducting mechanisms of unconventional high-temperature superconductors.
Spin fluctuations have been observed in iron-based superconductors as well.
However, in some iron-based superconductors such as LaFePO$_{0.9}$, they have
not been observed by inelastic neutron scattering (INS). LaFePO$_{0.9}$ is an
iron-based superconductor with a low superconducting transition temperature
($T_{\rm c}$= 5 K), where line nodes are observed in the superconducting gap
function. The line-node symmetry typically originates from sign reversal of the
order parameter in spin-fluctuation-mediated superconductivity. This
contradiction has been a long-standing mystery of this superconductor. Herein,
spin fluctuations were found at high energies such as 30$-$50 meV with
comparable intensities to an optimally doped LaFeAs(O,F). Based on this
finding, the line-node symmetry can be explained naturally as
spin-fluctuation-mediated superconductivity.",1904.03854v1
2019-06-04,Pairing symmetry and topological surface state in iron-chalcogenide superconductors,"The symmetries of superconducting gap functions remain an important question
of iron-based superconductivity. Motivated by the recent angle-resolved
photoemission spectroscopic measurements on iron-chalcogenide superconductors,
we investigate the influence of pairing symmetries on the topological surface
state. If the surface Dirac cone becomes gapped in the superconducting phase,
it implies magnetization induced from time-reversal symmetry breaking pairing
via spin-orbit coupling. Based on the crystalline symmetry constraints on the
Ginzburg-Landau free energy, the gap function symmetries are among the
possibilities of $A_{1g(u)}\pm iA_{2g(u)}$, $B_{1g(u)}\pm iB_{2g(u)}$, or,
$E_{g(u)}\pm i E_{g(u)}$. This time-reversal symmetry breaking effect can exist
in the normal state very close to $T_c$ with the relative phase between two gap
functions locked at $\pm \frac{\pi}{2}$. The coupling between magnetization and
superconducting gap functions is calculated based on a three-orbital model for
the band structure of iron-chalcogenides. This study provides the connection
between the gap function symmetries and topological properties of the surface
state.",1906.01754v3
2019-06-20,Effects of spin-orbit coupling on the neutron spin resonance in iron-based superconductors,"The so-called neutron spin resonance consists of a prominent enhancement of
the magnetic response at a particular energy and momentum transfer upon
entering the superconducting state of unconventional superconductors. In the
case of iron-based superconductors, the neutron resonance has been extensively
studied experimentally, and a peculiar spin-space anisotropy has been
identified by polarized inelastic neutron scattering experiments. Here we
perform a theoretical study of the energy- and spin-resolved magnetic
susceptibility in the superconducting state with $ s_{+-} $-wave order
parameter, relevant to iron-pnictide and iron-chalcogenide superconductors. Our
model is based on a realistic bandstructure including spin-orbit coupling with
electronic Hubbard-Hund interactions included at the RPA level. Spin-orbit
coupling is taken into account both in the generation of spin-fluctuation
mediated pairing, as well as the numerical computation of the spin
susceptibility in the superconducting state. We find that spin-orbit coupling
and superconductivity in conjunction can reproduce the salient experimentally
observed features of the magnetic anisotropy of the neutron resonance. This
includes the possibility of a double resonance, the tendency for a $c$-axis
polarized resonance, and the existence of enhanced magnetic anisotropy upon
entering the superconducting phase.",1906.08566v1
2019-08-26,"New thermodynamic constraints on internal, thermal and magnetic states of terrestrial-like Super-Earths","Ascertaining rocky exoplanets dynamic evolution requires better understanding
of key internal thermophysical processes that shaped their geological surfaces,
heat fluxes, volatiles and atmospheric content. New high-pressure experiments
on iron and silicates compressible, melting and transport properties are
providing new constraints that demand reassessments of super-Earths thermal and
magnetic evolution models. We examine the interior structure, temperature
distribution, thermal states and dynamo action of these planets with masses
ranging from 1-10 ME. We show that the shallow adiabaticity of iron-alloys and
perovskite or stishovite silicates compared to their liquidus at high pressure
would allow for deep basal magma oceans, and frozen iron cores in planets
larger than 4 ME. The presence and partitioning of MgO may alter this scenario.
For the more massive planets, the dramatic reduction in liquid silicates
viscosity should ensure a vigorous convection in the lower mantle, while the
rise of iron thermal conductivity under high pressures, is shown to keep the
internal cores of planets more massive than 2.5 ME subadiabatic and
non-convicting. This will preclude the dynamo action in the more massive
super-Earths (SE). Our results could allow a new mineral physics centered
classification of terrestrial-like superEarths.",1908.09871v1
2019-11-03,Interpreting Verbal Irony: Linguistic Strategies and the Connection to the Type of Semantic Incongruity,"Human communication often involves the use of verbal irony or sarcasm, where
the speakers usually mean the opposite of what they say. To better understand
how verbal irony is expressed by the speaker and interpreted by the hearer we
conduct a crowdsourcing task: given an utterance expressing verbal irony, users
are asked to verbalize their interpretation of the speaker's ironic message. We
propose a typology of linguistic strategies for verbal irony interpretation and
link it to various theoretical linguistic frameworks. We design computational
models to capture these strategies and present empirical studies aimed to
answer three questions: (1) what is the distribution of linguistic strategies
used by hearers to interpret ironic messages?; (2) do hearers adopt similar
strategies for interpreting the speaker's ironic intent?; and (3) does the type
of semantic incongruity in the ironic message (explicit vs. implicit) influence
the choice of interpretation strategies by the hearers?",1911.00891v3
2020-03-27,Phonon dispersions throughout the iron spin crossover in ferropericlase,"Ferropericlase (Fp), (Mg$_\mathrm{1-x}$Fe$_\mathrm{x}$)O, is the second most
abundant phase in the Earths lower mantle. At relevant pressure-temperature
conditions, iron in Fp undergoes a high spin (HS), S=2, to low spin (LS), S=0,
state change. The nature of this phenomenon is quite well understood now, but
there are still basic questions regarding the structural stability and the
existence of soft phonon modes during this iron state change. General theories
exist to explain the volume reduction, the significant thermo-elastic
anomalies, and the broad nature of this HS-LS crossover. These theories make
extensive use of the quasi-harmonic approximation (QHA). Therefore, dynamical
and structural stability is essential to their validity. Here, we investigate
the vibrational spectrum of Fp throughout this spin-crossover using $\textit{ab
initio}$ DFT+Usc calculations. We address vibrational modes associated with
isolated and (2nd) nearest neighbor iron ions undergoing the HS-LS state
change. As expected, acoustic modes of this solid solution are resilient while
optical modes are the most affected. We show that there are no soft phonon
modes across this HS-LS crossover, and Fp is dynamically stable at all relevant
pressures.",2003.12348v1
2020-06-11,Embracing defects and disorder in magnetic nanoparticles,"Iron oxide nanoparticles have tremendous scientific and technological
potential in a broad range of technologies, from energy applications to
biomedicine. To improve their performance, single-crystalline and defect-free
nanoparticles have thus far been aspired. However, in several recent studies
defect-rich nanoparticles outperform their defect-free counterparts in magnetic
hyperthermia and magnetic particle imaging. Here, an overview on the
state-of-the-art of design and characterization of defects and resulting spin
disorder in magnetic nanoparticles is presented with a focus on iron oxide
nanoparticles. The beneficial impact of defects and disorder on intracellular
magnetic hyperthermia performance of magnetic nanoparticles for drug delivery
and cancer therapy is emphasized. Defect-engineering in iron oxide
nanoparticles emerges to become an alternative approach to tailor their
magnetic properties for biomedicine, as it is already common practice in
established systems such as semiconductors and emerging fields including
perovskite solar cells. Finally, perspectives and thoughts are given on how to
deliberately induce defects in iron oxide nanoparticles and their potential
implications for magnetic tracers to monitor cell therapy and immunotherapy by
magnetic particle imaging.",2006.06474v1
2020-11-20,An Investigation of Commercial Iron Oxide Nanoparticles: Advanced Structural and Magnetic Properties Characterization,"Magnetic nanoparticles (MNPs) have been extensively used as tiny heating
sources in magnetic hyperthermia therapy, contrast agents in magnetic resonance
imaging (MRI), tracers in magnetic particle imaging (MPI), carriers for
drug/gene delivery, etc. There have emerged many magnetic
nanoparticle/microbeads suppliers since the last decade, such as Ocean
NanoTech, Nanoprobes, US Research Nanomaterials, Miltenyi Biotec, micromod
Partikeltechnologie GmbH, and nanoComposix, etc. In this paper, we report the
physical and magnetic characterizations on iron oxide nanoparticle products
from Ocean NanoTech. Standard characterization tools such as Vibrating-Sample
Magnetometer (VSM), X-Ray Diffraction (XRD), Dynamic Light Scattering (DLS),
Transmission Electron Microscopy (TEM), and Zeta Potential Analyzer are used to
provide magnetic nanoparticle customers and researchers with an overview of
these iron oxide nanoparticle products. In addition, the dynamic magnetic
responses of these iron oxide nanoparticles in aqueous solutions are
investigated under low and high frequency alternating magnetic fields, giving a
standardized operating procedure for characterizing the MNPs from Ocean
NanoTech, thereby yielding the best of magnetic nanoparticles for different
applications.",2011.10215v1
2020-11-23,A Learning-based Optimization Algorithm:Image Registration Optimizer Network,"Remote sensing image registration is valuable for image-based navigation
system despite posing many challenges. As the search space of registration is
usually non-convex, the optimization algorithm, which aims to search the best
transformation parameters, is a challenging step. Conventional optimization
algorithms can hardly reconcile the contradiction of simultaneous rapid
convergence and the global optimization. In this paper, a novel learning-based
optimization algorithm named Image Registration Optimizer Network (IRON) is
proposed, which can predict the global optimum after single iteration. The IRON
is trained by a 3D tensor (9x9x9), which consists of similar metric values. The
elements of the 3D tensor correspond to the 9x9x9 neighbors of the initial
parameters in the search space. Then, the tensor's label is a vector that
points to the global optimal parameters from the initial parameters. Because of
the special architecture, the IRON could predict the global optimum directly
for any initialization. The experimental results demonstrate that the proposed
algorithm performs better than other classical optimization algorithms as it
has higher accuracy, lower root of mean square error (RMSE), and more
efficiency. Our IRON codes are available for further
study.https://www.github.com/jaxwangkd04/IRON",2011.11365v1
2021-02-01,Confirmation of Asymmetric Iron Absorption in WASP-76b with HARPS,"Hot Jupiters are predicted to have hot, clear daysides and cooler, cloudy
nightsides. Recently, an asymmetric signature of iron absorption has been
resolved in the transmission spectrum of WASP-76b using ESPRESSO on ESO's Very
large Telescope. This feature is interpreted as being due to condensation of
iron on the nightside, resulting in a different absorption signature from the
evening than from the morning limb of the planet. It represents the first time
that a chemical gradient has been observed across the surface of a single
exoplanet. In this work, we confirm the presence of the asymmetric iron feature
using archival HARPS data of four transits. The detection shows that such
features can also be resolved by observing multiple transits on smaller
telescopes. By increasing the number of planets where these condensation
features are detected, we can make chemical comparisons between exoplanets and
map condensation across a range of parameters for the first time.",2102.01095v1
2021-03-07,IRON: Invariant-based Highly Robust Point Cloud Registration,"In this paper, we present IRON (Invariant-based global Robust estimation and
OptimizatioN), a non-minimal and highly robust solution for point cloud
registration with a great number of outliers among the correspondences. To
realize this, we decouple the registration problem into the estimation of
scale, rotation and translation, respectively. Our first contribution is to
propose RANSIC (RANdom Samples with Invariant Compatibility), which employs the
invariant compatibility to seek inliers from random samples and robustly
estimates the scale between two sets of point clouds in the meantime. Once the
scale is estimated, our second contribution is to relax the non-convex global
registration problem into a convex Semi-Definite Program (SDP) in a certifiable
way using Sum-of-Squares (SOS) Relaxation and show that the relaxation is
tight. For robust estimation, we further propose RT-GNC (Rough Trimming and
Graduated Non-Convexity), a global outlier rejection heuristic having better
robustness and time-efficiency than traditional GNC, as our third contribution.
With these contributions, we can render our registration algorithm, IRON.
Through experiments over real datasets, we show that IRON is efficient, highly
accurate and robust against as many as 99% outliers whether the scale is known
or unknown, outperforming the existing state-of-the-art algorithms.",2103.04357v2
2021-03-11,Flatband-Induced Itinerant Ferromagnetism in RbCo$_2$Se$_2$,"$A$Co$_2$Se$_2$ ($A$=K,Rb,Cs) is a homologue of the iron-based
superconductor, $A$Fe$_2$Se$_2$. From a comprehensive study of RbCo$_2$Se$_2$
via measurements of magnetization, transport, neutron diffraction,
angle-resolved photoemission spectroscopy, and first-principle calculations, we
identify a ferromagnetic order accompanied by an orbital-dependent
spin-splitting of the electronic dispersions. Furthermore, we identify the
ordered moment to be dominated by a $d_{x^2-y^2}$ flatband near the Fermi
level, which exhibits the largest spin splitting across the ferromagnetic
transition, suggesting an itinerant origin of the ferromagnetism. In the
broader context of the iron-based superconductors, we find this $d_{x^2-y^2}$
flatband to be a common feature in the band structures of both
iron-chalcogenides and iron-pnictides, accessible via heavy electron doping.",2103.06528v1
2021-04-20,Bulk superconductivity in FeTe$_{1-x}$Se$_{x}$ via physicochemical pumping of excess iron,"The iron-based superconductor FeTe$_{1-x}$Se$_{x}$ has attracted considerable
attention as a candidate topological superconductor owing to a unique
combination of topological surface states and bulk high-temperature
superconductivity. The superconducting properties of as-grown single crystals,
however, are highly variable and synthesis dependent due to excess interstitial
iron impurities incorporated during growth. Here we report a novel
physicochemical process for pumping this interstitial iron out of the
FeTe$_{1-x}$Se$_{x}$ matrix and achieving bulk superconductivity. Our method
should have significant value for the synthesis of high-quality single crystals
of FeTe$_{1-x}$Se$_{x}$ with large superconducting volume fractions.",2104.10145v1
2021-05-26,Prenatal stress perturbs fetal iron homeostasis in a sex-specific manner,"What is the influence of chronic maternal prenatal stress (PS) on fetal iron
homeostasis? In a prospective case-control study in 164 pregnant women, we show
that cord blood transferrin saturation is lower in male stressed neonates. The
total effect of PS exposure on fetal ferritin revealed a decrease of 15.4%
compared with controls. Electrocardiogram-based Fetal Stress Index (FSI)
identified affected fetuses non-invasively during the third trimester of
gestation. FSI-based timely detection of fetuses affected by PS can support
early individualized iron supplementation and neurodevelopmental follow-up to
prevent long-term sequelae due to PS-exacerbated impairment of the iron
homeostasis.",2105.12809v3
2021-06-02,Effective exchange interaction for terahertz spin waves in iron layers,"The exchange stiffness is a central material parameter of all ferromagnetic
materials. Its value controls the Curie temperature as well as the dynamic
properties of spin waves to a large extend. Using ultrashort spin current
pulses we excite perpendicular standing spin waves (PSSW) in ultrathin
epitaxial iron layers at frequencies of up to 2.4 THz. Our analysis shows that
for the PSSWs the observed exchange stiffness of iron is about 20% smaller
compared to the established iron bulk value. In addition, we find an
interface-related reduction of the effective exchange stiffness for layers with
the thickness below 10 nm. To understand and discuss the possible mechanisms of
the exchange stiffness reduction we develop an analytical 1D-model. In doing so
we find that the interface induced reduction of the exchange stiffness is
mode-dependent.",2106.01066v1
2021-06-08,Topological Superconductivity in an s-wave Superconductor and Its Implication to Iron-based Superconductors,"In the presence of both space and time reversal symmetries, an s-wave A1g
superconducting state is usually topologically trivial. Here we demonstrate
that an exception can take place in a type of nonsymmorphic lattice structures.
We specify the demonstration in a system with a centrosymmetric space group
P4/nmm, the symmetry group that governs iron-based superconductors, by showing
the existence of a second-order topological state protected by a mirror
symmetry. The topological superconductivity is featured by 2Z degenerate Dirac
cones on the (1,0) edge, and Z pairs of Majorana modes at the intersection
between the (1,1) and (1,-1) edges. The topological invariance and Fermi
surface criterion for the topological state are provided. Moreover, we point
out that the previously proposed s-wave state in iron-based superconductors,
which features a sign-changed superconducting order parameter between two
electron pockets, is such a topological state. Thus, these results not only
open a new route to pursue topological superconductivity, but also establish a
measurable quantity to settle one long-lasting debate on the pairing nature of
iron-based superconductors.",2106.04200v1
2021-08-10,Metallic nature and site-selective magnetic collapse in iron oxide Fe4O5 at the extreme conditions of Earth's deep interior,"Properties of iron oxides at the extreme conditions are of essential
importance in condensed matter physics and Geophysics. The recent discovery of
a new type of iron oxide, Fe4O5, at high pressure and high temperature of
Earth's deep interior attracts great interests. In this paper, we report the
electronic structure and the magnetic properties of Fe4O5 predicted by the
density functional theory plus dynamic mean field theory (DFT+DMFT) approach.
We find that Fe4O5 stays metallic from ambient pressure to high pressure. The
magnetic moments of iron atoms at the three different crystallographic
positions of Fe4O5 undergo position-dependent collapse as being compressed.
Such site-selective magnetic moment collapse originates from the shift of
energy levels and the consequent charge transfer among the Fe-3d orbits under
compression.",2108.04477v1
2021-11-30,Early differentiation of magmatic iron meteorite parent bodies from Mn-Cr chronometry,"Magmatic iron meteorite groups such as IIAB, IIIAB and IVA, represent the
largest sampling of extraterrestrial core material from the earliest accreted
distinct planetary bodies in the solar system. Chromium isotope compositions of
chromite/daubreelite from seven samples, translated into 53Cr/52Cr model ages,
provide robust time information on planetary core formation. These ages range
within 1.5 Ma after formation of calcium-aluminium-rich inclusions (CAIs) and
define the time of metal core formation in the respective parent bodies,
assuming metal-silicate separation was an instantaneous event that induced
strong chemical fractionation of Mn from the more siderophile Cr. The early
core formation ages support accretion and differentiation of the magmatic iron
meteorite parent bodies to have occurred prior to the chondrule formation
interval. The calibration of Mn-Cr ages with established Hf-W ages of samples
from the same magmatic iron meteorite groups constrains the initial E53Cr of
the solar system to -0.30, and thus lower than previously estimated.",2111.15291v1
2022-08-18,"Role of strain on the stability of B, C, N, and O in Iron","The preference for the occupation of solute atoms like B, C, N, and O at
various sites in iron is generally explained by the size of the solute and the
volume available for the solute atoms to occupy. Such an explanation based on
the size of solute atoms and available space at the occupation site assumes
that distortion alone dictates the stability of solute atoms. Using
first-principles density functional theory (DFT), we separately calculate the
distortion energy (DE) and electronic binding energy (EBE) of solute atoms in
iron. We show that electronic binding dictates the relative stability of O
rather than distortion. In contrast, the relative stability of B, C, and N is
dictated by the distortion it exerts on iron atoms. Contribution to the
relative stability of B atoms is dictated mostly by distortion. It suggests
that B could occupy a large volume region like grain boundaries. The same
agrees with experiments indicating B segregates at grain boundaries and planar
defects. Such conclusions could not have been drawn from the formation energy
calculation, which shows that B is stable at the substitution site.",2208.08680v1
2022-11-09,Quantitative Susceptibility Mapping in Cognitive Decline: A Review of Technical Aspects and Applications,"In the human brain, essential iron molecules for proper neurological
functioning exist in transferrin (tf) and ferritin (Fe3) forms. However, its
unusual increment manifests iron overload, which reacts with hydrogen peroxide.
This reaction will generate hydroxyl radicals, and irons higher oxidation
states. Further, this reaction causes tissue damage or cognitive decline in the
brain and also leads to neurodegenerative diseases. The susceptibility
difference due to iron overload within the volume of interest (VOI) responsible
for field perturbation of MRI and can benefit in estimating the neural
disorder. The quantitative susceptibility mapping (QSM) technique can estimate
susceptibility alteration and assist in quantifying the local tissue
susceptibility differences. It has attracted many researchers and clinicians to
diagnose and detect neural disorders such as Parkinsons, Alzheimers, Multiple
Sclerosis, and aging. The paper presents a systematic review illustrating QSM
fundamentals and its processing steps, including phase unwrapping, background
field removal, and susceptibility inversion. Using QSM, the present work
delivers novel predictive biomarkers for various neural disorders. It can
strengthen new researchers fundamental knowledge and provides insight into its
applicability for cognitive decline disclosure. The paper discusses the future
scope of QSM processing stages and their applications in identifying new
biomarkers for neural disorders.",2211.04764v1
2022-11-15,The Dissipation of the Solar Nebula Constrained by Impacts and Core Cooling in Planetesimals,"Rapid cooling of planetesimal cores has been inferred for several iron
meteorite parent bodies based on metallographic cooling rates, and linked to
the loss of their insulating mantles during impacts. However, the timing of
these disruptive events is poorly constrained. Here, we used the short-lived
107Pd / 107Ag decay system to date rapid core cooling by determining Pd-Ag ages
for iron meteorites. We show closure times for the iron meteorites equate to
cooling in the timeframe ~7.8 to 11.7 Myr after CAI, and indicate that an
energetic inner Solar System persisted at this time. This likely results from
the dissipation of gas in the protoplanetary disk, after which the damping
effect of gas drag ceases. An early giant planet instability between 5 and 14
Myr after CAI could have reinforced this effect. This correlates well with the
timing of impacts recorded by the Pd Ag system for iron meteorites.",2211.08306v1
2023-01-02,Enhance the Field Strength by Adding Soft Iron in the Hybrid Permanent magnet,"Permanent magnet has a small and compact structure, is especially suitable
for a narrow space. With the aid of soft iron, the magnetic field can be
increased much more and the field uniformity can be well controlled. Most
Permanent magnets have a symmetry structure; the soft iron can be selected as
the float magnet pole to keep its constant scalar potential, and take roles as
media to collect the direct flux from the permanent blocks, then release
indirect flux in magnet aperture and to the nearby return yoke. This paper
presents the magnetic flux method to design and fabricate a hybrid permanent
dipole by using axially and radially magnetized permanent blocks. A variable
gradient permanent quadrupole and a variable gradient sextupole are designed as
the extend design examples . They all consist of two nested hybrid permanent
rings, where the iron poles are used to control the field quality, collect the
magnetic flux from the outer ring, block the skew quadrupole and high order
harmonics.",2301.00532v1
2023-05-22,Ion-selective scattering studied by the variable-energy electron irradiation of Ba$_{0.2}$K$_{0.8}$Fe$_2$As$_2$ superconductor,"Low-temperature variable-energy electron irradiation was used to induce
non-magnetic disorder in a single crystal of hole-doped iron-based
superconductor, Ba$_{1-x}$K$_x$Fe$_2$As$_2$, $x=$0.80. To avoid systematic
errors, the beam energy was adjusted non-consequently for five values between
1.0 and 2.5 MeV, whence sample resistance was measured in-situ at 22 K. For all
energies, the resistivity raises linearly with the irradiation fluence
suggesting the creation of uncorrelated dilute point-like disorder (confirmed
by simulations). The rate of the resistivity increase peaks at energies below
1.5 MeV. Comparison with calculated partial cross-sections points to the
predominant creation of defects in the iron sublattice. Simultaneously,
superconducting $T_c$, measured separately between the irradiation runs, is
monotonically suppressed as expected since it depends on the total scattering
rate, hence total cross-section, which is a monotonically increasing function
of energy. Our work confirms experimentally an often-made assumption of the
dominant role of the iron sub-lattice in iron-based superconductors.",2305.13217v1
2024-01-16,Detection of the neutral iron line from the supernova remnant W49B with Suzaku,"Recent studies of supernova remnants (SNRs) have revealed that some SNRs
exhibit a neutral iron line emission at 6.4 keV. This line has been proposed to
originate from the interaction of high-energy particles formed in the SNR shell
with the surrounding cold matter. We searched for the neutral iron line
emission in the SNR W49B. Significant detection of the 6.4 keV line is found in
the northwest region, close to the molecular cloud interacting with the SNR
shell. In addition, an excess emission at 8-9 keV, in which K_gamma, K_delta,
and K_epsilon lines of He-like iron exist, is also significantly found in the
region where the radio shell is not bright. We discuss the origin of the 6.4
keV line and the excess emission at 8-9 keV.",2401.08234v1
1999-07-26,First Constraints on Iron Abundance versus Reflection Fraction from the Seyfert~1 Galaxy MCG--6-30-15,"We report on a joint ASCA and RXTE observation spanning an $\sim$ 400~ks time
interval of the bright Seyfert~1 galaxy MCG--6-30-15. The data clearly confirm
the presence of a broad skewed iron line ($W_{K\alpha} \sim$ 266 eV) and
Compton reflection continuum at higher energies reported in our previous paper.
We also investigate whether the gravitational and Doppler effects that affect
the iron line may also be manifest in the reflected continuum. The uniqueness
of this data set is underlined by the extremely good statistics that we obtain
from the approximately four million photons that make up the 2-20 keV RXTE PCA
spectrum alone. This, coupled with the high energy coverage of HEXTE and the
spectral resolution of ASCA in the iron line regime has allowed us to constrain
the relationship between abundance and reflection fraction for the first time
at the 99 per cent confidence level. The reflection fraction is entirely
consistent with a flat disk, i.e. the cold material subtends $\rm 2 \pi$ sr at
the source, to an accuracy of 20 per cent. Monte Carlo simulations show that
the observed strong iron line intensity is explained by an overabundance of
iron by a factor of $\sim$ 2 and an underabundance of the lower-Z elements by a
similar factor. By considering non-standard abundances, a clear and consistent
picture can be made in which both the iron line and reflection continuum come
from the same material such as e.g. an accretion disk.",9907352v1
1999-12-01,On the lack of X-ray iron line reverberation in MCG-6-30-15: Implications for the black hole mass and accretion disk structure,"We use the method of Press, Rybicki & Hewitt (1992) to search for time lags
and time leads between different energy bands of the RXTE data for MCG-6-30-15.
We tailor our search in order to probe any reverberation signatures of the
fluorescent iron Kalpha line that is thought to arise from the inner regions of
the black hole accretion disk. In essence, an optimal reconstruction algorithm
is applied to the continuum band (2-4keV) light curve which smoothes out noise
and interpolates across the data gaps. The reconstructed continuum band light
curve can then be folded through trial transfer functions in an attempt to find
lags or leads between the continuum band and the iron line band (5-7keV). We
find reduced fractional variability in the line band. The spectral analysis of
Lee et al. (1999) reveals this to be due to a combination of an apparently
constant iron line flux (at least on timescales of few x 10^4s), and flux
correlated changes in the photon index. We also find no evidence for iron line
reverberation and exclude reverberation delays in the range 0.5-50ksec. This
extends the conclusions of Lee et al. and suggests that the iron line flux
remains constant on timescales as short as 0.5ksec. The large black hole mass
(>10^8Msun) naively suggested by the constancy of the iron line flux is
rejected on other grounds. We suggest that the black hole in MCG-6-30-15 has a
mass of M_BH~10^6-10^7Msun and that changes in the ionization state of the disk
may produce the puzzling spectral variability. Finally, it is found that the
8-15keV band lags the 2-4keV band by 50-100s. This result is used to place
constraints on the size and geometry of the Comptonizing medium responsible for
the hard X-ray power-law in this AGN.",9912001v1
2003-10-29,The XMM-Newton Iron Line Profile of NGC 3783,"We report on observations of the iron K line in the nearby Seyfert 1 galaxy,
NGC 3783, obtained in a long, 2 orbit (240 ks) XMM-Newton observation. The line
profile obtained exhibits two strong narrow peaks at 6.4 keV and at 7.0 keV,
with measured line equivalent widths of 120 and 35 eV respectively. The 6.4 keV
emission is the K-alpha line from near neutral Fe, whilst the 7.0 keV feature
probably originates from a blend of the neutral Fe K-beta line and the H-like
line of Fe at 6.97 keV. The relatively narrow velocity width of the K-alpha
line (<5000 km/s), its lack of response to the continuum emission on short
timescales and the detection of a neutral Compton reflection component are all
consistent with a distant origin in Compton-thick matter such as the putative
molecular torus. A strong absorption line from highly ionized iron (at 6.67
keV) is detected in the time-averaged iron line profile, whilst the depth of
the feature appears to vary with time, being strongest when the continuum flux
is higher. The iron absorption line probably arises from the highest ionization
component of the known warm absorber in NGC 3783, with an ionization of logxi=3
and column density of 5x10^{22}cm{-2} and may originate from within 0.1pc of
the nucleus. A weak red-wing to the iron K line profile is also detected below
6.4 keV. However when the effect of the highly ionized warm absorber on the
underlying continuum is taken into account, the requirement for a relativistic
iron line component from the inner disk is reduced.",0310820v1
2006-09-25,Tracing the evolution in the iron content of the ICM,"We present a Chandra analysis of the X-ray spectra of 56 clusters of galaxies
at z>0.3, which cover a temperature range 3<kT<15 keV. Our analysis is aimed at
measuring the iron abundance in the intra-cluster medium (ICM) out to the
highest redshift probed to date. We made use of combined spectral analysis
performed over five redshift bins at 0.3<z<1.3 to estimate the average emission
weighted iron abundance. We find that the emission weighted iron abundance
measured within (0.15-0.3)R_vir in clusters below 5 keV is, on average, a
factor of ~2 higher than in hotter clusters, following Z(T) = 0.88 T^{-0.47}
Z_o, confirming the trend seen in local samples. We also find a constant
average iron abundance Z_{Fe}~0.25Z_o as a function of redshift, but only for
clusters at z>0.5. The emission weighted iron abundance is significantly higher
(Z_{Fe}~0.4 Z_o) in the redshift range z~0.3-0.5, approaching the value
measured locally in the inner 0.15 R_{vir} radii for a mix of cool-core and non
cool-core clusters at 0.1<z<0.3. The decrease in metallicity with redshift can
be parametrized by a power law of the form ~(1+z)^{-1.25}. The observed
evolution implies that the average iron content of the ICM at present epoch is
a factor of ~2 larger than at z~1.2. We confirm that the ICM is already
significantly enriched (Z_{Fe} ~ 0.25 Z_o) at a look-back time of 9 Gyr. Our
data provide significant constraints on the time scales and physical processes
which drive the chemical enrichment of the ICM. (abridged)",0609664v3
2006-10-31,Tracing the evolution in the iron content of the ICM,"We present a Chandra analysis of the X-ray spectra of 56 clusters of galaxies
at z>0.3, which cover a temperature range of 3>kT>15 keV. Our analysis is aimed
at measuring the iron abundance in the ICM out to the highest redshift probed
to date. We find that the emission-weighted iron abundance measured within
(0.15-0.3)R_vir in clusters below 5 keV is, on average, a factor of ~2 higher
than in hotter clusters, following Z(T)~0.88T^-(0.47)Z_o, which confirms the
trend seen in local samples. We made use of combined spectral analysis
performed over five redshift bins at 0.3>z>1.3 to estimate the average emission
weighted iron abundance. We find a constant average iron abundance Z_Fe~0.25Z_o
as a function of redshift, but only for clusters at z>0.5. The
emission-weighted iron abundance is significantly higher (Z_Fe~0.4Z_o) in the
redshift range z~0.3-0.5, approaching the value measured locally in the inner
0.15R_vir radii for a mix of cool-core and non cool-core clusters in the
redshift range 0.1<z<0.3. The decrease in Z_Fe with redshift can be
parametrized by a power law of the form ~(1+z)^(-1.25). The observed evolution
implies that the average iron content of the ICM at the present epoch is a
factor of ~2 larger than at z=1.2. We confirm that the ICM is already
significantly enriched (Z_Fe~0.25Z_o) at a look-back time of 9 Gyr. Our data
provide significant constraints on the time scales and physical processes that
drive the chemical enrichment of the ICM.",0610940v1
2007-03-12,Evolution in the iron abundance of the ICM,"We present a Chandra analysis of the X-ray spectra of 56 clusters of galaxies
at $z>0.3$, which cover a temperature range of $3> kT > 15$ keV. Our analysis
is aimed at measuring the iron abundance in the ICM out to the highest redshift
probed to date. We find that the emission-weighted iron abundance measured
within $(0.15-0.3) R_{vir}$ in clusters below 5 keV is, on average, a factor of
$\sim2$ higher than in hotter clusters, following $Z(T)\simeq 0.88 T^{-0.47}
Z_\odot$, which confirms the trend seen in local samples. We made use of
combined spectral analysis performed over five redshift bins at $0.3> z > 1.3$
to estimate the average emission weighted iron abundance. We find a constant
average iron abundance $Z_{Fe}\simeq 0.25 Z_\odot$ as a function of redshift,
but only for clusters at $z>0.5$. The emission-weighted iron abundance is
significantly higher ($Z_{Fe}\simeq0.4 Z_\odot$) in the redshift range
$z\simeq0.3-0.5$, approaching the value measured locally in the inner $0.15
R_{vir}$ radii for a mix of cool-core and non cool-core clusters in the
redshift range $0.1<z<0.3$. The decrease in $Z_{Fe}$ with $z$ can be
parametrized by a power law of the form $\sim(1+z)^{-1.25}$. The observed
evolution implies that the average iron content of the ICM at the present epoch
is a factor of $\sim2$ larger than at $z\simeq 1.2$. We confirm that the ICM is
already significantly enriched ($Z_{Fe}\simeq0.25 Z_\odot$) at a look-back time
of 9 Gyr. Our data provide significant constraints on the time scales and
physical processes that drive the chemical enrichment of the ICM.",0703261v1
2009-06-17,Fabrication and characterization of iron pnictide wires and bulk materials through the powder-in-tube method,"The recent discovery of superconductivity in the iron based superconductors
with very high upper critical fields presents a new possibility for practical
applications, but fabricating fine-wire is a challenge because of mechanically
hard and brittle powders and the toxicity and volatility of arsenic. In this
paper, we report the synthesis and the physical characterization of iron
pnictide wires and bulks prepared by the powder-in-tube method (PIT). A new
class of high-Tc iron pnictide composite wires, such as LaFeAsO1-xFx,
SmFeAsO1-xFx and Sr1-xKxFeAs, has been fabricated by the in situ PIT technique
using Fe, Ta and Nb tubes. Microscopy and x-ray analysis show that the
superconducting core is continuous, and retains phase composition after wire
drawing and heat treatment. Furthermore, the wires exhibit a very weak Jc-field
dependence behavior even at high temperatures. The upper critical field Hc2(0)
value can exceed 100 T, surpassing those of MgB2 and all the low temperature
superconductors and indicating a strong potential for applications requiring
very high field. These results demonstrate the feasibility of producing
superconducting pnictide composite wire. We also applied the one step PIT
method to synthesize the iron-based bulks, due to its convenience and safety.
In fact, by using this technique, we have successfully discovered
superconductivity at 35 K and 15 K in Eu0.7Na0.3Fe2As2 and SmCoFeAsO compounds,
respectively. These clearly suggest that the one-step PIT technique is unique
and versatile and hence can be tailored easily for other rare earth derivatives
of novel iron-based superconductors.",0906.3114v1
2012-04-20,The Carina Project. V. The impact of NLTE effects on the iron content,"We have performed accurate iron abundance measurements for 44 red giants
(RGs) in the Carina dwarf spheroidal (dSph) galaxy. We used archival,
high-resolution spectra (R~38,000) collected with UVES at ESO/VLT either in
slit mode (5) or in fiber mode (39, FLAMES/GIRAFFE-UVES). The sample is more
than a factor of four larger than any previous spectroscopic investigation of
stars in dSphs based on high-resolution (R>38,000) spectra. We did not impose
the ionization equilibrium between neutral and singly-ionized iron lines. The
effective temperatures and the surface gravities were estimated by fitting
stellar isochrones in the V, B-V color-magnitude diagram. To measure the iron
abundance of individual lines we applied the LTE spectrum synthesis fitting
method using MARCS model atmospheres of appropriate metallicity. We found
evidence of NLTE effects between neutral and singly-ionized iron abundances.
Assuming that the FeII abundances are minimally affected by NLTE effects, we
corrected the FeI stellar abundances using a linear fit between FeI and FeII
stellar abundance determinations.
  We found that the Carina metallicity distribution based on the corrected FeI
abundances (44 RGs) has a weighted mean metallicity of [Fe/H]=-1.80 and a
weighted standard deviation of sigma=0.24 dex. The Carina metallicity
distribution based on the FeII abundances (27 RGs) gives similar estimates
([Fe/H]=-1.72, sigma=0.24 dex). The current weighted mean metallicities are
slightly more metal poor when compared with similar estimates available in the
literature. Furthermore, if we restrict our analysis to stars with the most
accurate iron abundances, ~20 FeI and at least three FeII measurements (15
stars), we found that the range in iron abundances covered by Carina RGs (~1
dex) agrees quite well with similar estimates based on high-resolution spectra.",1204.4612v2
2014-08-15,Protected Fe valence in quasi-two dimensional $α$-FeSi$_2$,"We report the first comprehensive study of the high temperature form
($\alpha$-phase) of iron disilicide. Measurements of the magnetic
susceptibility, magnetization, heat capacity and resistivity were performed on
well characterized single crystals. With a nominal iron $d^6$ configuration,
and a quasi-two dimensional crystal structure that strongly resembles that of
LiFeAs, $\alpha$-FeSi$_2$ is a potential candidate for unconventional
superconductivity. Akin to LiFeAs, $\alpha$-FeSi$_2$ does not develop any
magnetic order, and we confirm its metallic state down to the lowest
temperatures ($T$=1.8 K). However, our experiments reveal that paramagnetism
and electronic correlation effects in $\alpha$-FeSi$_2$ are considerably weaker
than in the pnictides. Band theory calculations yield small Sommerfeld
coefficients of the electronic specific heat $\gamma=C_e/T$ that are in
excellent agreement with experiment. Additionally, realistic many-body
calculations further corroborate that quasi-particle mass enhancements are only
modest in $\alpha$-FeSi$_{2}$ .
  Remarkably, we find that the natural tendency to vacancy formation in the
iron sublattice has little influence on the iron valence and the density of
states at the Fermi level. Moreover, Mn doping does not significantly change
the electronic state of the Fe ion. This suggests that the iron valence is
protected against hole doping, and indeed the substitution of Co for Fe causes
a rigid-band like response of the electronic properties. As a key difference
from the pnictides, we identify the smaller inter-iron layer spacing, which
causes the active orbitals near the Fermi level to be of a different symmetry
in $\alpha$-FeSi$_2$. This change in orbital character might be responsible for
the lack of superconductivity in this system, providing constraints on pairing
theories in the iron based pnictides and chalcogenides.",1408.3606v2
2016-07-04,Origin of the Characteristic X-ray Spectral Variations of IRAS 13224$-$3809,"The Narrow-line Seyfert 1 galaxy (NLS1) IRAS 13224$-$3809 is known to exhibit
significant X-ray spectral variation, a sharp spectral drop at $\sim$ 7 keV,
strong soft excess emission, and a hint of iron L-edge feature, which is very
similar to the NLS1 1H 0707$-$495. We have proposed the ""Variable Double
Partial Covering (VDPC) model"" to explain the energy spectra and spectral
variability of 1H 0707$-$495 (Mizumoto, Ebisawa and Sameshima 2014, PASJ, 66,
122). In this model, the observed flux/spectral variations below 10 keV within
a $\sim$day are primarily caused by change of the partial covering fraction of
patchy clouds composed by double absorption layers in the line of sight. In
this paper, we apply the VDPC model to IRAS 13224$-$3809. Consequently, we have
found that the VDPC model can explain the observed spectral variations of IRAS
13224$-$3809 in the 0.5$-$10 keV band. In particular, we can explain the
observed Root Mean Square (RMS) spectra (energy dependence of the fractional
flux variation) in the entire 0.5$-$10 keV band. In addition to the well-known
significant drop in the iron K-band, we have found intriguing iron L-peaks in
the RMS spectra when the iron L-edge is particularly deep. This feature, which
is also found in 1H 0707$-$495, is naturally explained with the VDPC model,
such that the RMS variations increase at the energies where optical depths of
the partial absorbers are large. The absorbers have a larger optical depth at
the iron L-edge than in the adjacent energy bands, thus a characteristic iron
L-peak appears. On the other hand, just below the iron K-edge, the optical
depth is the lowest and the RMS spectrum has a broad dip.",1607.00879v1
2017-08-05,Nematic Fluctuations in Iron-Oxychalcogenide Mott Insulators,"Nematic fluctuations occur in a wide range of physical systems from liquid
crystals to biological molecules to solids such as exotic magnets, cuprates and
iron-based high-$T_c$ superconductors. Nematic fluctuations are thought to be
closely linked to the formation of Cooper-pairs in iron-based superconductors.
It is unclear whether the anisotropy inherent in this nematicity arises from
electronic spin or orbital degrees of freedom. We have studied the iron-based
Mott insulators La$_{2}$O$_{2}$Fe$_{2}$O$M$$_{2}$ $M$ = (S, Se) which are
structurally similar to the iron pnictide superconductors. They are also in
close electronic phase diagram proximity to the iron pnictides. Nuclear
magnetic resonance (NMR) revealed a critical slowing down of nematic
fluctuations as observed by the spin-lattice relaxation rate ($1/T_1$). This is
complemented by the observation of a change of electrical field gradient over a
similar temperature range using M\""ossbauer spectroscopy. The neutron pair
distribution function technique applied to the nuclear structure reveals the
presence of local nematic $C_2$ fluctuations over a wide temperature range
while neutron diffraction indicates that global $C_{4}$ symmetry is preserved.
Theoretical modeling of a geometrically frustrated spin-$1$ Heisenberg model
with biquadratic and single-ion anisotropic terms provides the interpretation
of magnetic fluctuations in terms of hidden quadrupolar spin fluctuations.
Nematicity is closely linked to geometrically frustrated magnetism, which
emerges from orbital selectivity. The results highlight orbital order and spin
fluctuations in the emergence of nematicity in Fe-based oxychalcogenides. The
detection of nematic fluctuation within these Mott insulator expands the group
of iron-based materials that show short-range symmetry-breaking.",1708.01693v4
2020-01-22,Superconductivity by Hidden Spin Fluctuations in Electron-Doped Iron Selenide,"Berg, Metlitski and Sachdev, Science 338, 1606 (2012), have shown that the
exchange of hidden spin fluctuations by conduction electrons with two orbitals
can result in high-temperature superconductivity in copper-oxide materials. We
introduce a similar model for high-temperature iron-selenide superconductors
that are electron doped. Conduction electrons carry the minimal 3d xz and 3d yz
iron-atom orbitals. Low-energy hidden spin fluctuations at the checkerboard
wavevector Q_AF result from nested Fermi surfaces at the center and at the
corner of the unfolded (one-iron) Brillouin zone. Magnetic frustration from
super-exchange interactions via the selenium atoms stabilize hidden spin
fluctuations at Q_AF versus true spin fluctuations. At half filling, Eliashberg
theory based purely on the exchange of hidden spin fluctuations reveals a
Lifshitz transition to electron/hole Fermi surface pockets at the corner of the
folded (two-iron) Brillouin zone, but with vanishing spectral weights. The
underlying hidden spin-density wave groundstate is therefore a Mott insulator.
Upon electron doping, Eliashberg theory finds that the spectral weights of the
hole Fermi surface pockets remain vanishingly small, while the spectral weights
of the larger electron Fermi surface pockets become appreciable. This
prediction is therefore consistent with the observation of electron Fermi
surface pockets alone in electron-doped iron selenide by angle-resolved
photoemission spectroscopy (ARPES). Eliashberg theory also finds an instability
to S+- superconductivity at electron doping, with isotropic Cooper pairs that
alternate in sign between the visible electron Fermi surface pockets and the
faint hole Fermi surface pockets. Comparison with the isotropic energy gaps
observed in electron-doped iron selenide by ARPES and by scanning tunneling
microscopy (STM) is consistent with short-range hidden magnetic order.",2001.07908v3
2020-04-25,Reconciliation of experiments and theory on transport properties of iron and the geodynamo,"The amount of heat transport from the core, which constrains the dynamics and
thermal evolution of the region, depends on the transport properties of iron.
Ohta et al.(2016) and Konopkova et al.(2016) measured electrical resistivity
and thermal conductivity of iron, respectively, in laser-heated diamond anvil
cells (DACs) at relevant Earth's core pressure-temperature (P-T) conditions,
and obtained dramatically contradictory results. Here we measure the electrical
resistivity of hcp-iron up to ~170 GPa and ~3,000 K using a four-probe van der
Pauw method coupled with homogeneous flat-top laser-heating in a DAC. We also
compute its electrical and thermal conductivity by first-principles methods
including electron-phonon and electron-electron scattering. We find that the
measured resistivity of hcp-iron increases almost linearly with increasing
temperature, and is consistent with current first-principles computations. The
proportionality coefficient between resistivity and thermal conductivity (the
Lorenz number) in hcp-iron differs from the ideal value (2.44*10^-8 W Omega
K^-2), so a non-ideal Lorenz number of ~(2.0-2.1)*10^-8 W Omega K^-2 is used to
convert the experimental resistivity to the thermal conductivity of hcp-Fe at
high P-T. The results constrain the resistivity and thermal conductivity of
hcp-iron to ~80(5) u Omega cm and ~100(10) W/mK, respectively, at conditions
near core-mantle boundary. Our results indicate an adiabatic heat flow of
~10(1) TW through the core-mantle boundary for a liquid Fe alloy outer core,
supporting a present-day geodynamo driven by thermal convection through the
core's secular cooling and by compositional convection through the latent heat
and gravitational energy during the inner core's solidification.",2004.12035v1
2020-09-29,The iron record of asteroidal processes in carbonaceous chondrites,"The valence of iron has been used in terrestrial studies to trace the
hydrolysis of primary silicate rocks. Here, we use a similar approach to
characterize the secondary processes, namely thermal metamorphism and aqueous
alteration, that have affected carbonaceous chondrites. X-ray absorption
near-edge structure spectroscopy at the Fe-K- edge was performed on a series of
36 CM, 9 CR, 10 CV, and 2 CI chondrites. Among the four carbonaceous chondrites
groups studied, a correlation between the iron oxidation index (IOI = [2
((Fe2+) + 3(Fe3+))/FeTOT) and the hydrogen content is observed. However, within
the CM group, for which a progressive alteration sequence has been defined, a
conversion of Fe3+ to Fe2+ is observed with increasing degree of aqueous
alteration. This reduction of iron can be explained by an evolution in the
mineralogy of the secondary phases. In the case of the few CM chondrites that
experienced some thermal metamorphism, in addition to aqueous alteration, a
redox memory of the aqueous alteration is present: a significant fraction of 3+
2+ 0 Fe is present, together with Fe and sometimes Fe. From our data set, the
CR chondrites show a wider range of IOI from 1.5 to 2.5. In all considered CR
chondrites, the three oxidation states of iron coexist. Even in the
least-altered CR chondrites, the fraction of Fe3+ can be high (30% for MET
00426). This observation confirms that oxidized iron has been integrated during
formation of fine-grained amorphous material in the matrix. Last, the IOI of CV
chondrites does not reflect the reduced/oxidized classification based on metal
and magnetite proportions, but is strongly correlated with petrographic types.
The valence of iron in CV chondrites therefore appears to be most closely
related to thermal history, rather than aqueous alteration, even if these
processes can occur together .",2009.13950v2
2020-09-30,DEEPMIR: A DEEP neural network for differential detection of cerebral Microbleeds and IRon deposits in MRI,"Lobar cerebral microbleeds (CMBs) and localized non-hemorrhage iron deposits
in the basal ganglia have been associated with brain aging, vascular disease
and neurodegenerative disorders. Particularly, CMBs are small lesions and
require multiple neuroimaging modalities for accurate detection. Quantitative
susceptibility mapping (QSM) derived from in vivo magnetic resonance imaging
(MRI) is necessary to differentiate between iron content and mineralization. We
set out to develop a deep learning-based segmentation method suitable for
segmenting both CMBs and iron deposits. We included a convenience sample of 24
participants from the MESA cohort and used T2-weighted images, susceptibility
weighted imaging (SWI), and QSM to segment the two types of lesions. We
developed a protocol for simultaneous manual annotation of CMBs and
non-hemorrhage iron deposits in the basal ganglia. This manual annotation was
then used to train a deep convolution neural network (CNN). Specifically, we
adapted the U-Net model with a higher number of resolution layers to be able to
detect small lesions such as CMBs from standard resolution MRI. We tested
different combinations of the three modalities to determine the most
informative data sources for the detection tasks. In the detection of CMBs
using single class and multiclass models, we achieved an average sensitivity
and precision of between 0.84-0.88 and 0.40-0.59, respectively. The same
framework detected non-hemorrhage iron deposits with an average sensitivity and
precision of about 0.75-0.81 and 0.62-0.75, respectively. Our results showed
that deep learning could automate the detection of small vessel disease lesions
and including multimodal MR data (particularly QSM) can improve the detection
of CMB and non-hemorrhage iron deposits with sensitivity and precision that is
compatible with use in large-scale research studies.",2010.00148v3
2022-01-31,Green steel at its crossroads: hybrid hydrogen-based reduction of iron ores,"Iron- and steelmaking cause ~7% of the global CO2 emissions, due to the use
of carbon for the reduction of iron ores. Replacing carbon by hydrogen as the
reductant offers a pathway to reduce emissions. However, production of hydrogen
using renewable energy will remain a bottlenecks, because making the annual
crude steel production of 1.8 billion tons sustainable requires a minimum
amount of ~97 million tons of green hydrogen per year. Another fundamental
aspect to make ironmaking sector more sustainable lies in an optimal
utilization of green hydrogen and energy, thus reducing efforts for costly
in-process hydrogen recycling. We therefore demonstrate here how the efficiency
in hydrogen and energy consumption during iron ore reduction can be
dramatically improved by the knowledge-based combination of two technologies:
partially reducing the ore at low temperature via solid-state direct reduction
(DR) to a kinetically defined degree, and subsequently melting and completely
transforming it to iron under a reducing plasma (i.e. via hydrogen plasma
reduction, HPR). Results suggest that an optimal transition point between these
two technologies occurs where their efficiency in hydrogen utilization is
equal. We found that the reduction of hematite through magnetite into wustite
via DR is clean and efficient, but it gets sluggish and inefficient when iron
forms at the outermost layers of the iron ore pellets. Conversely, HPR starts
violent and unstable with arc delocalization, but proceeds smoothly and
efficiently when processing semi-reduced oxides. We performed hybrid reduction
experiments by partially reducing hematite pellets via DR at 700{\deg}C to 38%
global reduction (using a standard thermogravimetry system) and subsequently
transferring them to HPR, conducted with a gas mixture of Ar-10%H2 in an
arc-melting furnace, to achieve conversion into liquid iron.",2201.13356v1
2022-03-09,Accounting for iron-related off-target binding effects of 18F-AV1451 PET in the evaluation of cognition and microstructure in APOE-e4+ MCI,"The pathology of Alzheimer's disease (AD) and mild cognitive impairment (MCI)
is characterized by the presence of beta-amyloid extracellular plaques and
neurofibrillary tangles containing hyper-phosphorylated tau. Individuals
carrying the apolipoprotein E-e4 (APOE-e4) allele are at increased risk of
cognitive decline and developing AD pathology. The development of positron
emission tomography (PET) radioligands sensitive to tau neurofibrillary
tangles, such as 18F-AV1451, has allowed for visualization and assessment of AD
pathology in vivo. The radioligand used in 18F-AV1451 binds with iron in
addition to tau neurofibrillary tangles. We employ multimodal neuroimaging
analyses, combining iron-sensitive measures from MRI with 18F-AV1451 PET, to
examine off-target binding effects in cohorts of 20 APOE-e4 negative, 20
APOE-e4 positive MCI, and 29 control participants. Increased tau pathology,
after controlling for tissue susceptibility, was found in the temporal lobe and
hippocampus of APOE-e4+ MCI participants as compared to APOE-e4 negative MCI
and control participants. Tau pathology in the hippocampus was significantly
related to memory, but only in APOE-e4+ participants. Correlations between
hippocampal 18F-AV1451 PET uptake and cognitive correlations did not
significantly differ when correcting for the influence of iron on 18F-AV1451
PET signal. However, controlling for susceptibility was found to influence
correlations between tau-PET uptake and diffusion metrics and the change in
this interaction may be due to the influence of iron on diffusivity. Taken
together, these results suggest that iron does not need to be accounted for in
group comparisons of tau-PET uptake or correlations between cognitive measures
and tau-PET SUVR. However, iron should be taken into account in correlations
between diffusion measures and tau-PET uptake.",2203.16444v1
2022-12-13,On the surface chemisorption of oxidizing fine iron particles: insights gained from molecular dynamics simulations,"Molecular dynamics (MD) simulations are performed to investigate the thermal
and mass accommodation coefficients (TAC and MAC, respectively) for the
combination of iron(-oxide) and air. The obtained values of TAC and MAC are
then used in a point-particle Knudsen model to investigate the effect of
chemisorption and the Knudsen transition regime on the combustion behavior of
(fine) iron particles. The thermal accommodation for the interactions of
$\mathrm{Fe}$ with $\mathrm{N_2}$ and $\mathrm{Fe_xO_y}$ with $\mathrm{O_2}$ is
investigated for different surface temperatures, while the mass accommodation
coefficient for iron(-oxide) with oxygen is investigated for different initial
oxidation stages $Z_\mathrm{O}$, which represents the molar ratio of
$\mathrm{O}/\left(\mathrm{O} + \mathrm{Fe}\right)$, and different surface
temperatures. The MAC decreases fast from unity to 0.03 as $Z_\mathrm{O}$
increases from 0 to 0.5 and then diminishes as $Z_\mathrm{O}$ further increases
to 0.57. By incorporating the MD-informed accommodation coefficients into the
single iron particle combustion model,a new temperature evolution for single
iron particles is observed compared to results obtained with previously
developed continuum models. Specifically, results of the present simulations
show that the oxidation process continues after the particle reaching the peak
temperature, while previous models predicting that the maximum temperature was
attained when the particle is oxidized to $Z_\mathrm{O} = 0.5$. Since the rate
of oxidation slows down as the MAC decreases with an increasing oxidation
stage, the rate of heat loss exceeds the rate of heat release upon reaching the
maximum temperature, while the particle is not yet oxidized to $Z_\mathrm{O} =
0.5$. Finally, the effect of transition-regime heat and mass transfer on the
combustion behavior of fine iron particles is investigated and discussed.",2212.06432v2
1995-06-20,On the Bilayer Coupling in the Yttrium-Barium Family of High Temperature Superconductors,"We present and solve a model for the susceptibility of two CuO2 planes
coupled by an interplane coupling J_perp and use the results to analyze a
recent ""cross-relaxation"" NMR experiment on Y2Ba4Cu7O15. We deduce that in this
material the product of J_perp and the maximum value of the in-plane
susceptibility chi_max varies from approximately 0.2 at T = 200 K to 0.4 at T =
120 K and that this implies the existence of a temperature dependent in-plane
spin correlation length. Using estimates of chi_max from the literature we find
5 meV < J_perp < 20 meV. We discuss the relation of the NMR results to neutron
scattering results which have been claimed to imply that in YBa2Cu3O_{6+x} the
two planes of a bilayer are perfectly anticorrelated. We also propose that the
recently observed 41 meV excitation in YBa2Cu3O7 is an exciton pulled down
below the superconducting gap by J_perp.",9506088v1
1996-06-04,On the Bilayer Coupling in the Yttrium-Barium Family of High Temperature Superconductors,"We derive the expressions needed to interpret experiments relating to
interplane magnetic coupling in YBa$_{2}$Cu$_{3}$O$_{6+x}$ and related
materials, and use the results to interpret measurements of the optical magnon
energy in YBa_{2}Cu_{3}O_{6.2} and of the NMR ``cross-relaxation"" rate in
Y_2Ba_{4}Cu_{7}O_{15}. We estimate $J_{\perp}\sim 14$ meV in both materials,
and $\chi_{max}/\mu^2_{B} \sim 100$ {states}/{eV}-Cu in Y_2Ba_4Cu_7O_{15} at
T=100K. We show that there is at present no obvious contradiction between the
results of a widely-used analysis of NMR experiments and the results of neutron
scattering experiments in the Y-Ba system. We argue that the 41 meV excitation
observed in superconducting YBa_{2}Cu_{3}O_{7} is a collective mode pulled down
below the superconducting gap by interactions, and that the observed
antisymmetry under interchange of planes follows from the non-negligible value
of $J_{\perp}$.",9606008v2
1997-01-29,Local structure studies of the underdoped-overdoped transition in YBa_2Cu_3O_x. Measurement of the yttrium y-ray absorption fine structure,"We have measured the extended x-ray absorption-fine-structure (EXAFS) at the
Y-K edge of YBa_2Cu_3O_x for x=6.801, 6.947, 6.968, 6.984 at T=20-300 K. Across
the underdoped-overdoped transition the Y-Cu2 pairs exhibit harmonic vibrations
which freeze out in the superconducting phase, whereas the Y-O2,3 pairs exhibit
strong anharmonicities with a singularity at T_c. In the underdoped regime the
average spacing O2,3-Cu2 increases with x due to displacements of Cu2 towards
Ba, but the average position of O2,3 along c is almost unaffected. Optimum
doping is a notable point in the x-T phase diagram, also concerning the lattice
degrees of freedom. Here the O2,3-Cu2 spacing (buckling) is largest, and in the
superconducting phase the Cu2 position along the c-axis is independent on
temperature. In the overdoped regime increasing x displaces the Cu2 along c
further towards Ba, but the O2,3 layer starts to shift in the same direction,
thus decreasing the O2,3-Cu2 spacing.",9701208v1
2000-10-06,Magnetic relaxation phenomena and cluster glass properties of La{0.7-x}Y{x}Ca{0.3}MnO{3} manganites,"The dynamic magnetic properties of the distorted perovskite system
La{0.7-x}Y{x}Ca{0.3}MnO{3} (0 <= x <= 0.15) have been investigated by
ac-susceptibility and dc magnetization measurements, with emphasis on
relaxation and aging studies. They evidence for x >= 0.10 the appearance of a
metallic cluster glass phase, that develops just below the ferromagnetic
transition temperature. The clusters grow with decreasing temperature down to a
temperature T(f0) at which they freeze due to severe intercluster frustration.
The formation of these clusters is explained by the presence of yttrium induced
local structural distortions that create localized spin disorder in a magnetic
lattice where double-exchange ferromagnetism is dominant.",0010110v2
2001-04-22,Nonadiabatiic superconductivity in MgB2 and cuprates,"The Fermi energy, Ef of newly discovered high-Tc superconductor MgB2 and
cuprates is estimated from the measured London penetration depth using a
parameter-free expression. Ef of MgB2 and more than 30 lanthanum, yttrium and
mercury-based cuprates appears to be about or below 100 meV, depending on
doping. There is every evidence that the remarkable low value of Ef and the
strong coupling of carriers with high-frequency phonons is the cause of high Tc
in all newly discovered superconductors. Taking into account that the carriers
mainly reside on oxygen in cuprates, on boron in magnesium diborade, and on
carbon in doped fullerenes, these superconductors form what is essentially
$nonadiabatic$ 'metallic' oxygen, boron and carbon, respectively. The boron
isotope effect on the carrier mass in magnesium-diboride similar to the oxygen
isotope effect on the supercarrier mass observed by Guo-meng Zhao et al. in
cuprates is predicted.",0104413v1
2001-05-07,Possibility of the investigation of the X-ray diffraction patterns for yttrium ceramic YBa2Cu3Ox having different oxygen stoichiometry on the basis of the mixed-layer crystal model,"In view of the strong anisotropy of oxygen diffusion in high-Tc ceramic
YBa2Cu3Ox, it is supposed that a polycrystalline sample of this material can be
presented as consisting of crystal grains where each grain was formed by a
certain sequence of layers with tetragonal or orthorhombic phase structure. The
theory of scattering by mixed-layer crystals was taken as a basis for
calculating theoretical X-ray patterns for different sequences of the layers.
Some modifications were made in the theory due to crystal structure features of
the YBa2Cu3Ox phases. The results obtained agreed quantitatively with data
published in many papers and can be used for interpreting the X-ray patterns
from ceramics with different oxygen stoichiometry.",0105133v1
2002-09-12,Electron momentum density in yttrium,"A simultaneous analysis of high-resolution directional Compton profiles and
two-dimensional angular correlation of positron annihilation experimental data
has been performed by studying both a directional anisotropy of measured
spectra and reconstructed densities. The results were compared with theoretical
fully-relativistic augmented plane-wave calculations with and without including
correlation effects. Estimated symmetry selection rules have allowed us to
establish some values of Fermi momenta. Both experiments show exactly the same
shape of the anisotropy of the momentum densities, in agreement with the band
structure results. In the positron annihilation data electron-positron
correlations are not seen while in both experiments electron-electron
correlations are observed.",0209297v1
2003-06-23,Disorder effects at low temperatures in La_{0.7-x}Y_{x}Ca_{0.3}MnO_{3} manganites,"With the aim of probing the effect of magnetic disorder in the
low-temperature excitations of manganites, specific-heat measurements were
performed in zero field, and in magnetic fields up to 9 T in polycrystalline
samples of La_{0.7-x}Y_{x}Ca_{0.3}MnO_{3}, with Y concentrations x=0, 0.10, and
0.15. Yttrium doping yielded the appearance of a cluster-glass state, giving
rise to unusual low-temperature behavior of the specific-heat. The main feature
observed in the results is a strong enhancement of the specific-heat linear
term, which is interpreted as a direct consequence of magnetic disorder. The
analysis was further corroborated by resistivity measurements in the same
compounds.",0306582v1
2004-10-01,Magnetic Properties of Cuprate Perovskites,"The magnetic susceptibility of underdoped yttrium and lanthanum cuprates is
interpreted based on the self-consistent solution of the t-J model of a Cu-O
plane. The calculations reproduce correctly the frequency dependencies of the
susceptibility in YBa2Cu3O_{7-y} and La_{2-x}Sr_xCuO4 attributing their
dissimilarity to the difference in the damping of spin excitations. In
YBa2Cu3O_{7-y} these excitations are well defined at the antiferromagnetic wave
vector Q=(\pi,\pi) even in the normal state which manifests itself in a
pronounced maximum -- the resonance peak -- in the susceptibility. In
La_{2-x}Sr_xCuO4 the spin excitations are overdamped which leads to a broad
low-frequency feature in the susceptibility. The low-frequency
incommensurability in the magnetic response is attributed to a dip in the
magnon damping at Q. The calculated concentration and temperature dependencies
of the incommensurability parameter conform with experimental observations.
Generally the incommensurate magnetic response is not accompanied with an
inhomogeneity of the carrier density.",0410009v1
2005-02-18,Accuracy of ab initio methods in predicting the crystal structures of metals: review of 80 binary alloys,"Predicting and characterizing the crystal structure of materials is a key
problem in materials research and development. We report the results of ab
initio LDA/GGA computations for the following systems: AgAu, AgCd, AgMg, AgMo*,
AgNa, AgNb*, AgPd, AgRh*, AgRu*, AgTc*, AgTi, AgY, AgZr, AlSc, AuCd, AuMo*,
AuNb, AuPd, AuPt*, AuRh*, AuRu*, AuSc, AuTc*, AuTi, AuY, AuZr, CdMo*, CdNb*,
CdPd, CdPt, CdRh, CdRu*, CdTc*, CdTi, CdY, CdZr, CrMg*, MoNb, MoPd, MoPt, MoRh,
MoRu, MoTc*, MoTi, MoY*, MoZr, NbPd, NbPt, NbRh, NbRu, NbTc, NbY*, NbZr*, PdPt,
PdRh*, PdRu*, PdTc, PdTi, PdY, PdZr, PtRh, PtRu, PtY, PtTc, PtTi, PtZr, RhRu,
RhTc, RhTi, RhY, RhZr, RuTi, RuTc, RuY, RuZr, TcTi, TcY, TcZr, TiZr*, YZr* (*=
systems in which the ab initio method predicts that no compounds are stable). A
detailed comparison to experimental data confirms the high accuracy with which
ab initio methods can predict ground states.
  Keywords: Binary Alloys, Ab initio, Intermetallics, Transition Metals,
StructureAluminum, Cadmium, Gold, Magnesium, Molybdenum, Niobium, Palladium,
Platinum, Rhodium, Ruthenium, Scandium, Silver, Sodium, Titanium, Technetium,
Yttrium, Zirconium.",0502465v1
2005-08-27,The thermodynamic stability and hydration enthalpy of strontium cerate doped by yttrium,"The standard molar enthalpy of formation of SrY0.05Ce0.95O2.975 has been
derived by combining the enthalpy of solution of this compound in 1 M HCl + 0.1
KI obtained by us and auxiliary literature data. The following value has been
derived: DfH (SrY0.05Ce0.95O2.975, s, 298.15 K) = -1720.4 (3.4) kJ/mol. The
obtained value has been used to obtain the formation enthalpy of
SrY0.05Ce0.95O2.975 from the mixture of binary oxides (DoxH (298.15 K) = -45.9
(3.4) kJ/mol) and formation enthalpy of reaction of SrY0.05Ce0.95O2.975 with
water forming Sr(OH)2, CeO2, Y2O3 (DrH (298.15 K) = -85.5 (3.4) kJ/mol). Data
obtained by solution calorimetry and additional information on the entropies of
different substances have shown that SrY0.05Ce0.95O2.975 is thermodynamically
stable with respect to a mixture of SrO, Y2O3, CeO2 and that the reaction of
SrY0.05Ce0.95O2.975 with water is thermodynamically favourable.",0508654v1
2005-10-21,"Superconductivity mediated by a soft phonon mode: specific heat, resistivity, thermal expansion and magnetization of YB6","The superconductor YB6 has the second highest critical temperature Tc among
the boride family MBn. We report measurements of the specific heat,
resistivity, magnetic susceptibility and thermal expansion from 2 to 300 K,
using a single crystal with Tc = 7.2 K. The superconducting gap is
characteristic of medium-strong coupling. The specific heat, resistivity and
expansivity curves are deconvolved to yield approximations of the phonon
density of states, the spectral electron-phonon scattering function and the
phonon density of states weighted by the frequency-dependent Grueneisen
parameter respectively. Lattice vibrations extend to high frequencies >100 meV,
but a dominant Einstein-like mode at ~8 meV, associated with the vibrations of
yttrium ions in oversized boron cages, appears to provide most of the
superconducting coupling and gives rise to an unusual temperature behavior of
several observable quantities. A surface critical field Hc3 is also observed.",0510572v3
2006-07-07,Polymer-Nanoparticle Complexes : from Dilute Solution to Solid State,"We report on the formation and the structural properties of supermicellar
aggregates also called electrostatic complexes, made from mineral nanoparticles
and polyelectrolyte-neutral block copolymers in aqueous solutions. The mineral
particles put under scrutiny are ultra-fine and positively charged yttrium
hydroxyacetate nanoparticles. Combining light, neutron and x-ray scattering
experiments, we have characterized the sizes and the aggregation numbers of the
organic-inorganic complexes. We have found that the hybrid aggregates have
typical sizes in the range 100 nm and exhibit a remarkable colloidal stability
with respect to ionic strength and concentration variations. Solid films with
thicknesses up to several hundreds of micrometers were cast from solutions,
resulting in a bulk polymer matrix in which nanoparticle clusters are dispersed
and immobilized. It was found in addition that the structure of the complexes
remains practically unchanged during film casting.",0607182v1
2006-12-01,Two types of Hc2(T) dependences in Bi_2Sr_2Ca_(1-x)Y_xCu_2O_(8+delta) with different Yttrium content,"We reanalyze the magnetization data collected on
Bi_2Sr_2Ca_(1-x)Y_xCu_2O_(8+y) samples (Kim at al, Phys. Rev. B 72, 64525
(2005)) and argue that the method, which was used for the analysis of
equilibrium magnetization data, is not adequate to the experimental situation.
As a result, the temperature dependencies of the upper critical field Hc2(T)
and the magnetic field penetration depth lambda (T), obtained in this work, are
misinterpreted. Using a different approach to analysis, we demonstrate that the
normalizedHc2(T) curves are rather different from those presented in the
original publication and do not follow predictions of the
Werthamer-Helfand-Hohenberg theory. Another important observation is that the
Hc2(T) dependencies for two samples with different levels of doping are
qualitatively different.",0612031v1
2007-03-20,"Steric quenching of the switchable mirror effect Phys. Rev. B 75, 104109 (2007)","Scandium was substituted for yttrium to observe the effect of unit cell size
on the optical metal-to-insulator (MIT) transition in the Y_(1-z)Sc_(z)H_(x)
alloy system. The optical transmittance decreases significantly for z>0.10.
Simultaneous electrical resistivity measurements confirm the transition from
trihydride to dihydride behavior with increasing z. These observations imply a
quenching of the MIT when the unit cell volume falls below a critical level
that is consistent with the boundary between trihydride and non-trihydride
forming rare-earth elements. A combinatoric model reveals this formation
boundary corresponds to two or more Sc per unit cell.",0703521v1
2003-04-07,Search for quantum transducers between electromagnetic and gravitational radiation: A measurement of an upper limit on the transducer conversion efficiency of yttrium barium copper oxide,"A minimal coupling rule for the coupling of the electron spin to curved
spacetime in general relativity suggests the possibility of a coupling between
electromagnetic and gravitational radiation mediated by means of a quantum
fluid. Thus quantum transducers between these two kinds of radiation fields
might exist. We report here on the first attempt at a Hertz-type experiment, in
which a high-$\rm{T_c}$ superconductor (YBCO) was the sample material used as a
possible quantum transducer to convert EM into GR microwaves, and a second
piece of YBCO in a separate apparatus was used to back-convert GR into EM
microwaves. An upper limit on the conversion efficiency of YBCO was measured to
be $1.6\times10^{-5}$ at liquid nitrogen temperature.",0304026v1
2007-07-24,Terahertz spectroscopy of electromagnons in Eu_{1-x}Y_xMnO_3,"Dielectric permittivity spectra of yttrium-doped EuMnO$_3$ in the composition
range 0 =< x =< 0.5 have been investigated in the terahertz frequency range.
Magnetoelectric contributions to the permittivity were observed in all
compositions for ac electric fields parallel to the crystallographic a-axis.
Well defined electromagnons exist for x >= 0.2 close to \nu ~ 20 cm^{-1} and
with dielectric strength strongly increasing on doping. In addition to
electromagnons, a broad contribution of magnetoelectric origin is observed for
all compositions. For Eu_{0.8}Y_{0.2}MnO_3 the electromagnons can be suppressed
by external magnetic fields which induce a canted antiferromagnetic phase.
Magnetoelectric effects in the different doping regimes are discussed in
detail.",0707.3614v1
2007-11-10,Ab initio calculations of the electronic structure of cuprates using large scale cluster techniques,"The local electronic structures of La2CuO4, three members of the
Yttrium-family (YBa2Cu3O6, YBa2Cu3O7, and YBa2Cu4O8), and to some extent of
Nd2CuO4 have been determined using all-electron ab-initio cluster calculations
for clusters comprising up to thirteen planar copper atoms associated with
their nearest planar and apical oxygen atoms. Spin-polarized calculations in
the framework of density functional theory have enabled an estimation of the
superexchange couplings J. Electric field gradients at the planar copper sites
are determined and their dependence on the occupation of the various atomic
orbitals are investigated in detail. The changes of the electronic field
gradient and of the occupation of orbitals upon doping are studied and
discussed. Furthermore, magnetic hyperfine fields are evaluated and
disentangled into on-site and transferred contributions, and the chemical
shifts at the copper nucleus are calculated. In general the results are in good
agreement with values deduced from experiments except for the value of the
chemical shift with applied field perpendicular to the CuO2-plane.",0711.1606v1
2009-01-16,Surface superconducting states in yttrium hexaboride single crystal in a tilted magnetic field,"We present the results of an experimental study of the nucleation of
superconductivity at the surface of a single crystal YB$_6$ in a tilted dc
magnetic field. A recently developed experimental technique allowed us to
determine $H_{c3}$ at each side of the sample as a function of the angle
between the dc magnetic field and the surface. Experiment shows that the ratio
$H_{c3}/ H_{c2}\approx 1.28 $ in the direction perpendicular to the surface dc
field while according to the theory this ratio should be equal to 1. This sharp
distinction cannot be ascribed to the surface roughness.",0901.2544v2
2009-12-23,The effect of anomalous adsorption of H2O and CO2 by pre-hydrated YBa_2Cu_3O_{6.53},"The results of a comprehensive study on the YBa_2Cu_3O_{6.53} oxide subjected
to ""mild"" hydration (exposure at small values of pH2O) by a special technique
have been reported. The material modified in this way acquires an interesting
property; namely, in natural conditions it intensively absorbs large quantities
of components (H2O and CO2) comprising the gas atmosphere. Arguments have been
adduced that at least the water enters the crystal lattice of the
yttrium-barium cuprate. This lattice is in the two-phase (tetragonal and
orthorhombic) state: testing of the magnetic properties of the oxide has
revealed the presence of antiferromagnetic and diamagnetic regions in this
material.",0912.4601v1
2011-03-23,Numerical Simulation of Magnetic Interactions in Polycrystalline YFeO3,"The magnetic behavior of polycrystalline yttrium orthoferrite was studied
from the experimental and theoretical points of view. Magnetization
measurements up to 170 kOe were carried out on a single-phase YFeO3 sample
synthesized from heterobimetallic alkoxides. The complex interplay between
weak-ferromagnetic and antiferromagnetic interactions, observed in the
experimental M(H) curves, was successfully simulated by locally minimizing the
magnetic energy of two interacting Fe sublattices. The resulting values of
exchange field (H_E = 5590 kOe), anisotropy field (H_A = 0.5 kOe) and
Dzyaloshinsky-Moriya antisymmetric field (H_D = 149 kOe) are in good agreement
with previous reports on this system.",1103.4462v1
2011-04-07,Electrostatic Control of the Evolution from Superconductor to Insulator in Ultrathin Films of Yttrium Barium Copper Oxide,"The electrical transport properties of ultrathin YBCO films have been
modified using an electric double layer transistor configuration employing an
ionic liquid. The films were grown on SrTiO3 substrates using high pressure
oxygen sputtering. A clear evolution from superconductor to insulator was
observed in nominally 7 unit cell thick films. Using a finite size scaling
analysis, curves of resistance versus temperature, R(T), over the temperature
range from 6K to 22K were found to collapse onto a single scaling function,
which suggests the the presence of a quantum critical point. However the
scaling failed at the lowest temperatures suggesting the presence of an
additional phase between the superconducting and insulating regimes.",1104.1357v1
2011-08-22,Adler-Bell-Jackiw anomaly in Weyl semi-metals: Application to Pyrochlore Iridates,"Weyl semimetals are three dimensional analogs of graphene where the energy of
the excitations are a linear function of their momentum. Pyrochlore Iridates
$(A_{2}Ir_{2}O_{7})$ with A =yttrium or lanthanide element) are conjectured to
be examples of such a system, with the low energy physics described by twenty
four Weyl nodes. An intriguing possibility is that these materials provide a
physical realization of the Adler-Bell-Jackiw anomaly. In this letter we
investigate the properties of pyrochlore iridates in an applied magnetic field.
We find that the dispersion of the lowest landau level depends on the direction
of the applied magnetic field. As a consequence the magneto-conductivity in an
electric field, applied parallel to the magnetic field is highly anisotropic,
providing a detectable signature of the semi-metallic state.",1108.4426v2
2012-01-19,Quantum storage of polarization qubits in birefringent and anisotropically absorbing materials,"Storage of quantum information encoded into true single photons is an
essential constituent of long-distance quantum communication based on quantum
repeaters and of optical quantum information processing. The storage of
photonic polarization qubits is, however, complicated by the fact that many
materials are birefringent and have polarization-dependent absorption. Here we
present and demonstrate a simple scheme that allows compensating for these
polarization effects. The scheme is demonstrated using a solid-state quantum
memory implemented with an ensemble of rare-earth ions doped into a biaxial
yttrium orthosilicate ($Y_2SiO_5$) crystal. Heralded single photons generated
from a filtered spontaneous parametric downconversion source are stored, and
quantum state tomography of the retrieved polarization state reveals an average
fidelity of $97.5 \pm 0.4%$, which is significantly higher than what is
achievable with a measure-and-prepare strategy.",1201.4097v3
2012-04-16,Nonlinear Induction Detection of Electron Spin Resonance,"We present a new approach to the induction detection of electron spin
resonance (ESR) signals exploiting the nonlinear properties of a
superconducting resonator. Our experiments employ a yttrium barium copper oxide
(YBCO) superconducting stripline microwave (MW) resonator integrated with a
microbridge. A strong nonlinear response of the resonator is thermally
activated in the microbridge when exceeding a threshold in the injected MW
power. The responsivity factor characterizing the ESR-induced change in the
system's output signal is about 100 times larger when operating the resonator
near the instability threshold, compared to the value obtained in the linear
regime of operation. Preliminary experimental results, together with a
theoretical model of this phenomenon are presented. Under appropriate
conditions nonlinear induction detection of ESR can potentially improve upon
the current capabilities of conventional linear induction detection ESR.",1204.3588v2
2012-06-27,Effect of lattice volume and strain on the conductivity of BaCeY-oxide ceramic proton conductors,"In-situ electrochemical impedance spectroscopy was used to study the effect
of lattice volume and strain on the proton conductivity of the yttrium-doped
barium cerate proton conductor by applying the hydrostatic pressure up to 1.25
GPa. An increase from 0.62 eV to 0.73 eV in the activation energy of the bulk
conductivity was found with increasing pressure during a unit cell volume
change of 0.7%, confirming a previously suggested correlation between lattice
volume and proton diffusivity in the crystal lattice. One strategy worth trying
in the future development of the ceramic proton conductors could be to expand
the lattice and potentially lower the activation energy under tensile strain.",1206.6287v1
2012-09-18,Magneto-optical trapping of diatomic molecules,"The development of the magneto-optical trap revolutionized the fields of
atomic and quantum physics by providing a simple method for the rapid
production of ultracold, trapped atoms. A similar technique for producing a
diverse set of dense, ultracold diatomic molecular species will likewise
transform the study of strongly interacting quantum systems, precision
measurement, and physical chemistry. We demonstrate one- and two-dimensional
transverse laser cooling and magneto-optical trapping of the polar molecule
yttrium (II) oxide (YO). Using a quasicycling optical transition we observe
transverse Doppler cooling of a YO molecular beam to a temperature of 5 mK,
limited by interaction time. With the addition of an oscillating magnetic
quadrupole field we demonstrate a transverse magneto-optical trap and achieve
temperatures of 2 mK.",1209.4069v1
2013-03-06,Crystal field with Wannier functions: Application to rare-earth aluminates,"A method to calculate the crystal field parameters {\it ab initio} is
proposed and applied to trivalent rare earth impurities in yttrium aluminate
and to Tb$^{3+}$ ion in TbAlO$_3$. To determine crystal field parameters local
Hamiltonian expressed in basis of Wannier functions is expanded in a series of
spherical tensor operators. Wannier functions are obtained by transforming the
Bloch functions calculated using the density functional theory based program.
The results show that the crystal field is continuously decreasing as the
number of $4f$ electrons increases and that the hybridization of $4f$ states
with the states of oxygen ligands is important. Theory is confronted with
experiment for Nd$^{3+}$ and Er$^{3+}$ ions in YAlO$_3$ and for Tb$^{3+}$ ion
in TbAlO$_3$ and a fair agreement is found.",1303.1281v3
2013-03-29,Point-contact spectroscopy of the phononic mechanism of superconductivity in YB6,"Lortz et al. [Phys. Rev. B 73, 024512 (2006)] have utilized specific heat and
resistivity measurements as ""thermal spectroscopies"" to deconvolve the spectrum
of the electron-phonon interaction in YB$_6$ assuming a major role of the low
frequency phonon mode in mediating superconductivity. Here, we present direct
point-contact spectroscopy studies of the superconducting interaction in this
system. As a result the normalized superconducting gap reveals a strong
coupling with $2\Delta/k_BT_c = 4$ and moreover the spectra contain
nonlinearities typical of the electron-phonon interaction at energies around 8
meV. The in-magnetic-field measurements evidence that the phonon features found
in the second derivative of the current-voltage characteristics are due to the
energy dependence of the superconducting energy gap as their energy position
shrinks equally as the gap is closing. This is a direct proof that the
superconducting coupling in the system is due to the low energy Einstein-like
phonon mode associated with the yttrium ion vibrations in a perfect agreement
with determinations from bulk measurements.",1303.7321v1
2013-07-23,Solution calorimetry investigations of new phase BaCe0.6Y0.3In0.1O2.8,"The preparation of BaCeO3 doped by yttrium and indium oxides
(BaCe0.6Y0.3In0.1O2.8) has been performed by solid-state reaction from BaCO3,
CeO2, Y2O3, In2O3. The compound BaCe0.6Y0.3In0.1O2.8 has been synthesized for
the first time. The X-ray measurements have showed that BaCe0.6Y0.3In0.1O2.8
has an orthorhombic structure (space group Pmcn). The standard formation
enthalpies of BaCe0.6Y0.3In0.1O2.8 have been determined by solution calorimetry
combining the solution enthalpies of BaCe0.6Y0.3In0.1O2.8 and BaCl2 + 0.6CeCl3
+ 0.3YCl3 + 0.1InCl3 mixtures in 1 M HCl with 0.1 M KI at 298.15 K and
literature data. It has been obtained that above-mentioned mixed oxide is
thermodynamically stable with respect to their decomposition into binary oxides
at room temperatures. It has been also shown that BaCe0.6Y0.3In0.1O2.8 has been
more thermodynamically favored than BaCe0.9In0.1O2.95.",1307.5940v1
2013-08-27,Nuclear beta decay with Lorentz violation,"We consider the possibility of Lorentz-invariance violation in weak-decay
processes. We present a general approach that entails modifying the W-boson
propagator by adding a Lorentz-violating tensor to it. We describe the effects
of Lorentz violation on nuclear beta decay in this scenario. In particular we
show the expression for a first-forbidden transition with a spin change of two.
Using data from an old experiment on the rotational invariance of yttrium-90,
we derive several bounds on the Lorentz-violating parameters of the order of
10^(-6)-10^(-8).",1308.5829v2
2013-09-16,Results on damage induced by high-energy protons in LYSO calorimeter crystals,"Lutetium-Yttrium Orthosilicate doped with Cerium (LYSO:Ce), as a bright
scintillating crystal, is a candidate for calorimetry applications in strong
ionizing-radiation fields and large high-energy hadron fluences as are expected
at the CERN Large Hadron Collider after the planned High-Luminosity upgrade.
There, proton-proton collisions will produce fast hadron fluences up to
~5E14/cm^2 in the large-rapidity regions of the calorimeters. The performance
of LYSO:Ce has been investigated, after exposure to different fluences of 24
GeV/c protons. Measured changes in optical transmission as a function of proton
fluence are presented, and the evolution over time due to spontaneous recovery
at room temperature is studied. The activation of materials will also be an
issue in the described environment. Studies of the ambient dose induced by LYSO
and its evolution with time, in comparison with other scintillating crystals,
have also been performed through measurements and FLUKA simulations.",1309.3872v2
2013-10-14,Element spots in HgMn stars,"A fraction of late B-type stars, the so-called HgMn stars, exhibit enhanced
absorption lines of certain chemical elements, notably Hg and Mn, combined with
an underabundance of He. For about a decade now the elements with anomalously
high abundances in HgMn stars are known to be distributed inhomogeneously over
the stellar surface. Temporal evolution of these elemental spots have been
reported in a few HgMn stars, first secular evolution of the mercury spots in
alpha And, and recently also a fast evolution of yttrium and strontium spots in
HD 11753. The fast evolution of spots in HD 11753 is combined with a slower
change in the overall abundance of the affected elements. In this paper I
review what is known of elemental spots in HgMn stars and their secular and
fast temporal evolution.",1310.3686v1
2013-11-12,Feasibility Study on SRF Cavity Improvement by Doping Method,"In this article a new idea is proposed by PKU group to improve the RF
superconductive property of niobium cavity. Rare earth elements like scandium
and yttrium are doped into ingot niobium during the smelting processes. A
series of experiments have been done since 2010, and the preliminary testing
results show that the magnetic property of niobium materials has been changed
with different doping elements and proportions while the superconductive
transition temperature almost does not change. Then a large ingot niobium doped
with scandium was melted. RRR and mechanical properties were measured. This
method may increase the superheating magnetic field and decrease surface
resistance of niobium so as to improve the performance of niobium cavity which
is a key component of SRF accelerators. A single-cell cavity made of Sc-doped
niobium has been fabricated.",1311.2710v1
2013-12-12,Commissioning of the Francium Trapping Facility at TRIUMF,"We report on the successful commissioning of the Francium Trapping Facility
at TRIUMF. Large laser-cooled samples of francium are produced from a francium
ion beam delivered by the ISAC radioactive ion beam facility. The ion beam is
neutralized on an yttrium foil, which is subsequently heated to transfer the
atoms into the magneto-optical trapping region. We have successfully trapped
$^{207}$Fr, $^{209}$Fr and $^{221}$Fr, with a maximum of $2.5 \times 10^5$
$^{209}$Fr atoms. The neutral cold atoms will be used in studies of the weak
interaction through measurements of atomic parity non-conservation.",1312.3562v1
2014-04-11,Rotated stripe order and its competition with superconductivity in La$_{1.88}$Sr$_{0.12}$CuO$_4$,"We report the observation of a bulk charge modulation in
La$_{1.88}$Sr$_{0.12}$CuO$_4$ (LSCO) with a characteristic in-plane wave-vector
of (0.236, $\pm \delta$), with $\delta$=0.011 r.l.u. The transverse shift of
the ordering wave-vector indicates the presence of rotated charge-stripe
ordering, demonstrating that the charge ordering is not pinned to the Cu-O bond
direction. On cooling through the superconducting transition, we find an abrupt
change in the growth of the charge correlations and a suppression of the charge
order parameter indicating competition between the two orderings. Orthorhombic
LSCO thus helps bridge the apparent disparities between the behavior previously
observed in the tetragonal ""214"" cuprates and the orthorhombic yttrium and
bismuth-based cuprates and thus lends strong support to the idea that there is
a common motif to charge order in all cuprate families.",1404.3193v2
2014-04-21,Wide-angle energy-momentum spectroscopy,"Light emission is defined by its distribution in energy, momentum, and
polarization. Here, we demonstrate a method that resolves these distributions
by means of wide-angle energy-momentum spectroscopy. Specifically, we image the
back focal plane of a microscope objective through a Wollaston prism to obtain
polarized Fourier-space momentum distributions, and disperse these
two-dimensional radiation patterns through an imaging spectrograph without an
entrance slit. The resulting measurements represent a convolution of individual
radiation patterns at adjacent wavelengths, which can be readily deconvolved
using any well-defined basis for light emission. As an illustrative example, we
use this technique with the multipole basis to quantify the intrinsic emission
rates for electric and magnetic dipole transitions in europium-doped yttrium
oxide (Eu$^{3+}$:Y$_{2}$O$_{3}$) and chromium-doped magnesium oxide
(Cr$^{3+}$:MgO). Once extracted, these rates allow us to reconstruct the full,
polarized, two-dimensional radiation patterns at each wavelength.",1404.5109v1
2014-06-20,Photoluminescence of focused ion beam implanted Er$^{3+}$:Y$_{2}$SiO$_{5}$ crystals,"Erbium doped low symmetry Y$_2$SiO$_5$ crystals attract a lot of attention in
perspective of quantum information applications. However, only doping of the
samples during growth is available up to now, which yields a quite homogeneous
doping density. In the present work, we deposit Er$^{3+}$-ions by the focused
ion beam technique at Yttrium sites with several fluences in one sample. With a
photoluminescence study of these locally doped Er$^{3+}$:Y$_2$SiO$_5$ crystals,
we are able to evaluate the efficiency of the implantation process and develop
it for the highest efficiency possible. We observe the dependence of the ion
activation after the post-implantation annealing on the fluence value.",1406.5371v1
2014-10-21,Radial velocity measurements of the pulsating zirconium star: LS IV -14 116,"The helium-rich hot subdwarf LS IV -14 116 shows remarkably high surface
abundances of zirconium, yttrium, strontium, and germanium, indicative of
strong chemical stratification in the photosphere. It also shows photometric
behaviour indicative of non-radial g-mode pulsations, despite having surface
properties inconsistent with any known pulsational instability zone. We have
conducted a search for radial velocity variability. This has demonstrated that
at least one photometric period is observable in several absorption lines as a
radial velocity variation with a semi-amplitude in excess of 5 km s$^{-1}$. A
correlation between line strength and pulsation amplitude provides evidence
that the photosphere pulsates differentially. The ratio of light to velocity
amplitude is too small to permit the largest amplitude oscillation to be
radial.",1410.5732v1
2015-01-09,Coherent frequency up-conversion of microwaves to the optical telecommunications band in an Er:YSO crystal,"The ability to convert quantum states from microwave photons to optical
photons is important for hybrid system approaches to quantum information
processing. In this paper we report the up-conversion of a microwave signal
into the optical telecommunications wavelength band using erbium dopants in a
yttrium orthosilicate crystal via stimulated Raman scattering. The microwaves
were applied to the sample using a 3D copper loop-gap resonator and the
coupling and signal optical fields were single passed. The conversion
efficiency was low, in agreement with a theoretical analysis, but can be
significantly enhanced with an optical resonator.",1501.02014v2
2015-01-20,Rotational state microwave mixing for laser cooling of complex diatomic molecules,"We demonstrate the mixing of rotational states in the ground electronic state
using microwave radiation to enhance optical cycling in the molecule yttrium
(II) monoxide (YO). This mixing technique is used in conjunction with a
frequency modulated and chirped continuous wave laser to slow longitudinally a
cryogenic buffer gas beam of YO. We generate a measurable flux of YO below
10~m/s, directly loadable into a three-dimensional magneto-optical trap. This
technique opens the door for laser cooling of molecules with more complex
structure.",1501.04683v1
2015-03-17,The Hubbard model in strong magnetic field: Low-frequency quantum oscillations due to strong electron correlations,"The density of states of the two-dimensional fermionic Hubbard model in the
perpendicular homogeneous magnetic field is calculated using the strong
coupling diagram technique. The density of states at the Fermi level as a
function of the inverse magnetic induction oscillates, and the frequency of
these oscillations increases by an order of magnitude with the change of the
deviation from half-filling from small to moderate values. This frequency
variation is caused by the change of Landau subbands contributing to the
density -- in the former case they are at the periphery of the Landau spectrum,
while in the latter case the dominant contribution is provided by bands near
its center. With changing induction these groups of bands behave differently.
For small deviations from half-filling the calculated oscillation frequency is
comparable to that observed in quantum oscillation experiments in yttrium
cuprates.",1503.04934v1
2015-03-25,Cold Brownian motion in aqueous media via anti-Stokes photoluminescence,"Advances in cryogenic sciences have enabled several observations of new
low-temperature physical phenomena including superconductivity, superfluidity,
and Bose-Einstein condensates. Heat transfer is also critical in numerous
applications including thermal management within integrated microelectronics
and the regulation of plant-growth and development. Here we demonstrate that
single-beam laser-trapping can be used to induce and quantify the local
refrigeration of aqueous media through analysis of the cold Brownian dynamics
of individual Yb3+-doped yttrium lithium fluoride (YLF) crystals in an
inhomogeneous temperature field via forward light scattering and
back-focal-plane interferometry. A tunable, NIR continuous-wave laser is used
to optically trap individual YLF crystals with an irradiance on the order of 1
MW/cm2. Heat is transported out of the crystal lattice (across the solid /
liquid interface) by anti-Stokes photoluminescence following upconversion of
Yb3+ excited states mediated by optical-phonon absorption. The cold Brownian
motion (CBM) analysis of individual YLF crystals indicates local cooling by >21
C below ambient conditions suggesting a range of potential future applications.",1503.07265v1
2015-04-03,High-resolution spectroscopy of single Pr$^{3+}$ ions on the $^3$H$_4$-$^1$D$_2$ transition,"Rare earth ions in crystals exhibit narrow spectral features and
hyperfine-split ground states with exceptionally long coherence times. These
features make them ideal platforms for quantum information processing in the
solid state. Recently, we reported on the first high-resolution spectroscopy of
single Pr$^{3+}$ ions in yttrium orthosilicate (YSO) nanocrystals. While in
that work we examined the less explored $^3$H$_4$-$^3$P$_0$ transition at a
wavelength of 488 nm, here we extend our investigations to the
$^3$H$_4$-$^1$D$_2$ transition at 606 nm. In addition, we present measurements
of the second-order autocorrelation function, fluorescence lifetime, and
emission spectra of single ions as well as their polarization dependencies on
both transitions; these data were not within the reach of the first experiments
reported earlier. Furthermore, we show that by a proper choice of the
crystallite, one can obtain narrower spectral lines and, thus, resolve the
hyperfine levels of the excited state. We expect our results to make single-ion
spectroscopy accessible to a larger scientific community.",1504.00857v1
2015-07-03,Nanophotonic coherent light-matter interfaces based on rare-earth-doped crystals,"Quantum light-matter interfaces (QLMIs) connecting stationary qubits to
photons will enable optical networks for quantum communications, precise global
time keeping, photon switching, and studies of fundamental physics.
Rare-earth-ion (REI) doped crystals are state-of-the-art materials for optical
quantum memories and quantum transducers between optical photons, microwave
photons and spin waves. Here we demonstrate coupling of an ensemble of
neodymium REIs to photonic nano-cavities fabricated in the yttrium
orthosilicate host crystal. Cavity quantum electrodynamics effects including
Purcell enhancement (F=42) and dipole-induced transparency are observed on the
highly coherent 4I9/2-4F3/2 optical transition. Fluctuations in the cavity
transmission due to statistical fine structure of the atomic density are
measured, indicating operation at the quantum level. Coherent optical control
of cavity-coupled REIs is performed via photon echoes. Long optical coherence
times (T2~100 microseconds) and small inhomogeneous broadening are measured for
the cavity-coupled REIs, thus demonstrating their potential for on-chip
scalable QLMIs.",1507.00977v1
2015-10-19,Ferroelectric polarization switching with a remarkably high activation-energy in orthorhombic GaFeO3 thin films,"Orthorhombic GaFeO3 (o-GFO) with the polar Pna21 space group is a prominent
ferrite by virtue of its piezoelectricity and ferrimagnetism, coupled with
magneto-electric effects. Herein, we unequivocally demonstrate a large
ferroelectric remanent polarization in undoped o-GFO thin films by adopting
either a hexagonal strontium titanate (STO) or a cubic yttrium-stabilized
zirconia (YSZ) substrate. The polarization-electric-field hysteresis curves of
the polar c-axis-grown o-GFO film on a SrTiO3/STO substrate show the net
switching polarization of ~35 {\mu}C/cm2 with an unusually high coercive field
of +-1400 kV/cm at room temperature. The PUND measurement also demonstrates the
switching polarization of ~26 {\mu}C/cm2. The activation energy for the
polarization switching, as obtained by density-functional theory calculations,
is remarkably high, 1.05 eV per formula unit. This high value accounts for the
observed stability of the polar Pna21 phase over a wide range of temperature up
to 1368 K.",1510.05359v1
2015-10-29,Controlled emission and coupling of small-size YAG:Ce3+ nanocrystals to gold nanowire,"We report a controlled emission of Ce3+ ions inside single Yttrium Aluminum
Gar- net Y3Al5O12 (YAG:Ce3+) nanocrystals with a diameter of 22 +- 10 nm as a
result of a coupling of a surface plasmon mode propagating along single gold
nanowire (NW). From the PL images, the intensity for single YAG:Ce3+
nanocrystals in the proximity of the single gold NW increases by a factor of
two in comparison with that without the NW. Also, we observe a maximum of
3.8-fold emission rate en- hancements for the single nanocrystal close to the
single gold NW. The emission rate enhancements of YAG:Ce3+ nanocrystals are two
folds the enhancements of 100-nm fluorescent nanospheres. This value is in
agreement with the calculation of a combi- nation from the analytical
scattering model and boundary element method (BEM). We also confirm that the
small size light sources are more efficient for the emission rate enhancements.
Thus, the controlled emission of small YAG:Ce3+ nanocrystals with the perfect
photostabilities will pave the way for the ultimate efficient nanoscale light
sources.",1510.08769v1
2015-12-11,Coupling erbium spins to a three-dimensional superconducting cavity at zero magnetic field,"We experimentally demonstrate the coupling at zero magnetic field of an
isotopically pure erbium doped yttrium orthosilicate crystal ($^{167}$Er:YSO)
to a three-dimensional superconducting cavity with a $Q$ factor of $10^5$. A
tunable loop-gap resonator is used, and its resonance frequency is tuned to
observe the hyperfine transitions of the erbium sample. The observed spectrum
differs from what is predicted by the published spin Hamiltonian parameters.
The narrow cavity linewidth also enables the observation of asymmetric line
shapes for these hyperfine transitions. Such a broadly tunable superconducting
cavity (from 1.6 GHz to 4.0 GHz in the current design) is a promising device
for building hybrid quantum systems.",1512.03606v2
2016-02-08,Phase separated behavior in Yttrium doped CaMnO3,"The effect of electron doping on the structural, transport, and magnetic
properties of Mn (IV) - rich Ca1-xYxMnO3 (x < 0.2) samples have been
investigated using neutron diffraction, neutron depolarization, magnetization
and resistivity techniques. The temperature dependence of resistivity follows
the small polaron model and the activation energy exhibits a minimum for x=0.1
sample. A phase separated magnetic ground state consisting of ferromagnetic
domains (~7microns) embedded in G-type antiferromagnetic matrix is observed in
the sample, x = 0.1. The transition to the long range magnetically ordered
state in this sample is preceded by a Griffiths phase. On lowering temperature
below 300K a structural transition from orthorhombic structure (Pnma) to a
monoclinic structure (P21/m) is observed in the case of x=0.2 sample. The
ferromagnetic behavior in this case is suppressed and the antiferromagnetic
ordering is described by coexisting C-type and G-type magnetic structures
corresponding to the monoclinic and orthorhombic phases, respectively.<",1602.02479v1
2016-07-05,Effects of intense optical phonon pumping on the structure and electronic properties of yttrium barium copper oxide,"We investigate the structural modulations induced by optical excitation of a
polar phonon mode in YBa$_2$Cu$_3$O$_7$, using first-principles calculations
based on density functional theory. We focus on the intense-excitation regime
in which we expect that fourth-order phonon-phonon coupling terms dominate, and
model the structural modulations induced by pulses of such intensity. Our
calculations of the phonon-phonon anharmonicities confirm that the cubic
coupling between modes, shown in earlier work to cause a quasi-static change in
the apical O - Cu distance and a buckling of the CuO$_2$ planes, is the leading
contribution at moderate pump strengths. At higher pump strengths ($\sim$10
MV/cm) the previously neglected quartic couplings become relevant and produce
an additional shearing of the CuO$_2$ planes. Finally, we analyze the changes
in the electronic and magnetic properties associated with the induced
structural changes.",1607.01180v2
2017-02-08,Low-Temperature Microwave Properties of Biaxial YAlO3,"Low-loss crystals with defects due to paramagnetic or rare earth impurity
ions is a major area of investigation for quantum hybrid systems at both
optical and microwave frequencies. In this work we examine the single crystal
yttrium aluminium perovskite, YAlO$_3$ using the Whispering Gallery Mode
Technique. Multiple resonant microwave modes were measured from room
temperature to 20 mK allowing precise characterization of the permittivity
tensor at microwave frequencies. We show that it is biaxial and characterize
the tensor as a function of temperature with estimated uncertainties below
0.26%. Electron spin resonance spectroscopy was also performed at 20 mK, with
new transitions identified with Zero-Field splittings of 16.72 and 9.92 GHz.
Spin-photon couplings of order 4.2 and 8.4 MHz were observed for residual
levels of concentration, which are stronger than the photon cavity linewidths
of 116 kHz but the same order of the linewidths of the discovered spin
transitions.",1702.02288v2
2017-12-22,Magnetoresistance in YBi and LuBi semimetals due to nearly perfect carrier compensation,"Monobismuthides of yttrium and lutetium are shown as new representatives of
materials which exhibit extreme magnetoresistance and magnetic-field-induced
resistivity plateau. At low temperatures and in magnetic field of 9T the
magnetoresistance attains the order of magnitude of 10,000% and 1,000%, on YBi
and LuBi, respectively. Our thorough examination of electron transport
properties of both compounds show that observed features are the consequence of
nearly perfect carrier compensation rather than of possible nontrivial topology
of electronic states. The field-induced plateau of electrical resistivity can
be explained with Kohler scaling. Anisotropic multi-band model of electronic
transport describes very well the magnetic field dependence of electrical
resistivity and Hall resistivity. Data obtained from the Shubnikov-de Haas
oscillations analysis also confirm that Fermi surface of each compound contains
almost equal amounts of holes and electrons. First-principle calculations of
electronic band structure are in a very good agreement with the experimental
data.",1712.08433v3
2018-03-20,Optically addressing single rare-earth ions in a nanophotonic cavity,"We demonstrate optical probing of spectrally resolved single Nd rare-earth
ions in yttrium orthovanadate. The ions are coupled to a photonic crystal
resonator and show strong enhancement of the optical emission rate via the
Purcell effect, resulting in near radiatively limited single photon emission.
The measured high coupling cooperativity between a single photon and the ion
allows for the observation of coherent optical Rabi oscillations. This could
enable optically controlled spin qubits, quantum logic gates, and spin-photon
interfaces for future quantum networks.",1803.07520v2
2018-08-03,3-D Magneto-Optical Trap of Yttrium Monoxide,"We report three-dimensional trapping of an oxide molecule (YO), using a
radio-frequency magneto-optical trap (MOT). The total number of molecules
loaded is $\sim$1.5$\times10^4$ , with a temperature of 7(1)~mK. This
diversifies the frontier of molecules that are laser coolable and paves the way
for the second-stage narrow-line cooling in this molecule to the microkelvin
regime. Futhermore, the new challenges of creating a 3-D MOT of YO resolved
here indicate that MOTs of more complex non-linear molecules should be feasible
as well.",1808.01067v1
2018-08-21,Superconductivity at 215 K in lanthanum hydride at high pressures,"We synthesized lanthanum hydride (LaHx) by laser heating of lanthanum in
hydrogen atmosphere at pressure P = 170 GPa. The sample shows a superconducting
step at 209 K and 170 GPa and temperature dependence of resistance. By
releasing the pressure to 150 GPa, the superconducting transition temperature
Tc increases to 215 K - the record Tc. This finding supports a way of achieving
Tc higher than the one in H3S (203 K) in hydrides with sodalite-like
structures, first proposed for CaH6 (Tc=245 K) and later for yttrium and
lanthanum hydrides where higher, room temperature superconductivity is
expected.",1808.07039v1
2018-10-06,Ultrafast negative thermal expansion driven by spin-disorder,"We measure the transient strain profile in a nanoscale multilayer system
composed of Yttrium, Holmium and Niobium after laser excitation using ultrafast
X-ray diffraction. The strain propagation through each layer is determined by
transient changes of the material-specific Bragg angles. We experimentally
derive the exponentially decreasing stress profile driving the strain wave and
show that it closely matches the optical penetration depth. Below the Neel
temperature of Ho, the optical excitation triggers negative thermal expansion,
which is induced by a quasi-instantaneous contractive stress, and a second
contractive stress contribution rising on a 12 ps timescale. These two
timescales have recently been measured for the spin-disordering in Ho [Rettig
et al, PRL 116, 257202 (2016)]. As a consequence we observe an unconventional
bipolar strain pulse with an inverted sign travelling through the
heterostructure.",1810.03036v1
2018-10-30,Magnetic field sensing with the kinetic inductance of a high-$T_\mathrm{c}$ superconductor,"We carry out an experimental feasibility study of a magnetic field sensor
based on the kinetic inductance of the high-$T_\mathrm{c}$ superconductor
yttrium barium copper oxide. We pattern thin superconducting films into
radio-frequency resonators that feature a magnetic field pick-up loop. At 77 K
and for film thicknesses down to 75 nm, we observe the persistence of screening
currents that modulate the loop kinetic inductance. According to the
experimental results the device concept appears attractive for sensing
applications in ambient magnetic field environments. We report on a device with
a magnetic field sensitivity of 4 pT/Hz${}^{1/2}$, an instantaneous dynamic
range of 11 $\mu$T, and operability in magnetic fields up to 28 $\mu$T.",1810.12725v1
2018-11-14,Observation of Optical Refrigeration in a Holmium-doped Crystal,"We report the first demonstration of solid-state optical refrigeration of a
Ho-doped material. A 1 mol% Ho-doped Yttrium Lithium Fluoride (YLF) crystal is
cooled by mid-IR laser radiation, and its external quantum efficiency and
parasitic background absorption are evaluated. Using detailed
temperature-dependent spectroscopic analysis the minimum achievable temperature
of a 1% Ho:YLF sample is estimated. Owing to its narrower ground- and
excited-state manifolds, larger absorption cross-section, and coincidence of
optimum cooling wavelength of 2070 nm with commercially available high-power
and highly efficient Tm-fiber lasers, Ho^3+-doped crystals are superior to
Tm^3+-doped systems for mid-IR optical refrigeration. With further improvement
in material purity and increased doping concentration, they offer great
potential towards enhancing the cooling efficiency nearly two-fold over the
best current Yb:YLF systems, achieving lower temperatures as well as for
realization of eye-safe mid-IR high-power radiation balanced lasers.",1811.05745v1
2018-12-05,Influence of composition and heating schedules on compatibility of FeCrAl alloys with high-temperature steam,"FeCrAl alloys are proposed and being intensively investigated as alternative
accident tolerant fuel (ATF) cladding for nuclear fission application. Herein,
the influence of major alloy elements (Cr and Al), reactive element effect and
heating schedules on the oxidation behavior of FeCrAl alloys in steam up to
1500{\deg}C was examined. In case of transient ramp tests, catastrophic
oxidation, i.e. rapid and complete consumption of the alloy, occurred during
temperature ramp up to above 1200{\deg}C for specific alloys. The maximum
compatible temperature of FeCrAl alloys in steam increases with raising Cr and
Al content, decreasing heating rates during ramp period and doping of yttrium.
Isothermal oxidation resulted in catastrophic oxidation at 1400{\deg}C for all
examined alloys. However, formation of a protective alumina scale at
1500{\deg}C was ascertained despite partial melting. The occurrence of
catastrophic oxidation seems to be controlled by dynamic competitive mechanisms
between mass transfer of Al from the substrate and transport of oxidizing gas
through the scale both toward the metal/oxide scale interface.",1812.01850v1
2018-12-21,Deep and persistent spectral holes in Tm-doped yttrium orthosilicate for imaging applications,"With their optical wavelength in the near infrared (790-800nm) and their
unique spectroscopic properties at cryogenic temperatures, thulium-doped
crystals are at the center of many architectures linked to classical signal
processing and quantum information. In this work, we focus on Tm-doped YSO, a
compound that was left aside in the mid-1990s due to its rather short optical
coherence lifetime. By means of time-resolved hole-burning spectroscopy, we
investigate the anisotropic enhanced nuclear Zeeman effect and demonstrate
deep, sub-MHz, persistent spectral hole burning under specific magnetic field
orientation and magnitude. By estimating the experimental parameters
corresponding to a real-scale ultrasound optical tomography setup using Tm:YSO
as a spectral filter, we validate Tm:YSO as a promising compound for medical
imaging in the human body.",1812.10369v2
2019-04-17,Nanophotonic quantum storage at telecommunications wavelength,"Quantum memories for light are important components for future long distance
quantum networks. We present on-chip quantum storage of telecommunications band
light at the single photon level in an ensemble of erbium-167 ions in an
yttrium orthosilicate photonic crystal nanobeam resonator. Storage times of up
to 10 $\mu$s are demonstrated using an all-optical atomic frequency comb
protocol in a dilution refrigerator under a magnetic field of 380 mT. We show
this quantum storage platform to have high bandwidth, high fidelity, and
multimode capacity, and we outline a path towards an efficient erbium-167
quantum memory for light.",1904.08052v1
2019-04-17,Aqueous metal-organic solutions for YSZ thin film inkjet deposition,"Inkjet printing of 8% Y2O3-stabilized ZrO2 (YSZ) thin films is achieved by
designing a novel water-based reactive ink for Drop-on-Demand (DoD) inkjet
printing. The ink formulation is based on a novel chemical strategy that
consists of a combination of metal oxide precursors (zirconium alkoxide and
yttrium salt), water and a nucleophilic agent, i.e. n-methyldiethanolamine
(MDEA). This chemistry leads to metal-organic complexes with long term ink
stability and high precision printability. Ink rheology and chemical reactivity
are analyzed and controlled in terms of metal-organic interactions in the
solutions. Thin dense nanocrystalline YSZ film below 150 nm are obtained by low
temperature calcination treatments (400-500 {\deg}C), making the deposition
suitable for a large variety of substrates, including silicon, glass and
metals. Thin films and printed patterns achieve full densification with no
lateral shrinkage and high ionic conductivity.",1904.08143v1
2019-07-28,Coherent control and single-shot readout of a rare-earth ion embedded in a nanophotonic cavity,"Quantum networks based on optically addressable spin qubits promise to enable
secure communication, distributed quantum computing, and tests of fundamental
physics. Scaling up quantum networks based on solid-state luminescent centers
requires coherent spin and optical transitions coupled to photonic resonators.
Here we investigate single $\mathrm{{}^{171}Yb^{3+}}$ ions in yttrium
orthovanadate coupled to a nanophotonic cavity. These ions possess optical and
spin transitions that are first-order insensitive to magnetic field
fluctuations, enabling optical linewidths less than 1 MHz and spin coherence
times exceeding 30 ms for cavity-coupled ions. The cavity-enhanced optical
emission rate facilitates efficient spin initialization and conditional
single-shot readout with fidelity greater than 95%. These results showcase a
solid-state platform based on single coherent rare-earth ions for the future
quantum internet.",1907.12161v1
2019-08-18,Pressure induced electronic structure transformation of topological semimetal,"We study the electronic structure change of yttrium trihydride
$\mathrm{YH_3}$ by applying a hydrostatic pressure. At zero pressure,
$\mathrm{YH_3}$ has the structure with energy favored symmetry group
$P\bar{3}c1$ (165). From first principle calculation, we argue that the band
crossings are caused by overlapping of an electron- and hole-like bands.
Besides the space inversion symmetry ($\mathcal{I}$) and the time reversal
symmetry, the band structure also exhibits an approximate particle-hole
symmetry. Thus, $\mathrm{YH_3}$ can be viewed as a pseudo nodal surface
semimetal belongs to class BDI of the ten-fold AZ+ $\mathcal{I}$
classifications of gapless topological matter. As pressure increases, the
approximate particle-hole symmetry is gradually broken and the pseudo nodal
surface turns into a nodal ring belonging to the class AI with fewer
non-spatial symmetries. Also, the nodal ring is shrinking in the process. At
about $31$ GPa, which is higher than the reported structure phase transition
pressure $21$ GPa, the nodal ring shrinks to a nodal point. When above $31$
GPa, all band crossings are gapped out and $\mathrm{YH_3}$ becomes a trivial
insulator eventually.",1908.06494v2
2019-08-28,Alkali ion-to-neutral atom converter for the magneto-optical trap of a radioactive isotope,"We have developed a unique neutralizer device that uses an yttrium target
surrounded by a platinum wall to magneto-optically trap radioactive atoms. In
general, the radioactive nucleus produced in a nuclear reaction is extracted
and transported in ion form. For the magneto-optical trap, thermal
neutralization must occur on the surface of a metal with a small work function.
The converter can produce a neutral atomic beam with small angular divergence
that, given the recycling of atoms and ions, converts ions into neutral atoms
with remarkable efficiency. We demonstrated the ion neutralization process
using stable rubidium and confirmed $10^6$ neutralized atoms in the
magneto-optical trap. Additionally, the experiment using francium demonstrated
the obtaining of neutralized francium atoms.",1908.10686v1
2019-09-26,Coherent charge and magnetic ordering in Ho/Y superlattice revealed by element-selective x-ray scattering,"Magnetic rare-earth / non-magnetic metal superlattices are well-known to
display chiral spin helices in the rare-earth layers that propagate coherently
across the non-magnetic layers. However, the underlying mechanism that
preserves the magnetic phase and chirality coherence across the non-magnetic
layers has remained elusive. In this Letter, we use resonant and
element-specific x-ray scattering to evidence directly the formation of two
fundamentally different long-range modulations in a Holmium/Yttrium (Ho/Y)
multilayer: the known Ho chiral spin helix with periodicity 25 {\AA}, and a
newly observed charge density wave with periodicity 16 {\AA} that propagates
through both the Ho and non-magnetic Y layer. With x-ray circular magnetic
dichroism measurements ruling out the existence of a magnetic proximity effect
induced moment in the non-magnetic Y layers, we propose that the charge density
wave is also chiral, thus providing the means for the transmittance of magnetic
chirality coherence between Ho layers.",1909.12372v2
2019-10-04,Solid-state laser refrigeration of a semiconductor optomechanical resonator,"Photothermal heating represents a major constraint that limits the
performance of many nanoscale optoelectronic and optomechanical devices
including nanolasers, quantum optomechanical resonators, and integrated
photonic circuits. Although radiation-pressure damping has been reported to
cool an individual vibrational mode of an optomechanical resonator to its
quantum ground state, to date the internal material temperature within an
optomechanical resonator has not been reported to cool via laser excitation.
Here we demonstrate the direct laser refrigeration of a semiconductor
optomechanical resonator >20K below room temperature based on the emission of
upconverted, anti-Stokes photoluminescence of trivalent ytterbium ions doped
within a yttrium-lithium-fluoride (YLF) host crystal. Optically-refrigerating
the lattice of a dielectric resonator has the potential to impact several
fields including scanning probe microscopy, the sensing of weak forces, the
measurement of atomic masses, and the development of radiation-balanced
solid-state lasers. In addition, optically refrigerated resonators may be used
in the future as a promising starting point to perform motional cooling for
exploration of quantum effects at mesoscopic length scales,temperature control
within integrated photonic devices, and solid-state laser refrigeration of
quantum materials",1910.02153v1
2019-10-20,A search for heavy-metal stars: abundance analyses of hot subdwarfs with Subaru,"The discovery of extremely zirconium- and lead-rich surfaces amongst a small
subgroup of hot subdwarfs has provoked questions pertaining to chemical
peculiarity in hot star atmospheres and about their evolutionary origin. With
only three known in 2014, a limited search for additional `heavy-metal'
subdwarfs was initiated with the Subaru telescope. Five hot subdwarfs having
intermediate to high surface enrichment of helium were observed at
high-resolution and analyzed for surface properties and abundances. This paper
reports the analyses of four of these stars. PG1559+048 and FBS 1749+373,
having only intermediate helium enrichment, show strong lines of triply ionized
lead. PG1559+048 also shows a strong overabundance of germanium and yttrium.
With more helium-rich surfaces, Ton 414 and J17554+5012, do not show evidence
of heavy-metal enrichment. This limited survey suggests that extreme enrichment
of `heavy metals' by selective radiative levitation in hot subdwarf atmospheres
is suppressed if the star is too helium-rich.",1910.08947v1
2019-10-31,Optically unstable phase from ion-ion interactions in an erbium doped crystal,"We demonstrate an optical unstable phase for a laser driven erbium ion
ensemble. The transmitted light through an erbium-doped yttrium orthosillicate
crystal becomes dynamically unstable when illuminated by a strong
continuous-wave laser. Transient net gain was recorded if the light passes the
sample twice. The experimental results are understood in the framework of a
many-body system interacting with a classical field, where the ion-ion
interaction becomes significant as a result of the high erbium concentration. A
Bloch-equation model that includes the excitation-induced frequency-shift is
introduced to discuss the conditions of the instabilities.",1910.14298v2
2019-12-08,On-chip coherent microwave-to-optical transduction mediated by ytterbium in YVO$_4$,"Optical networks that distribute entanglement among quantum technologies will
form a powerful backbone for quantum science but are yet to interface with
leading quantum hardware such as superconducting qubits. Consequently, these
systems remain isolated because microwave links at room temperature are noisy
and lossy. Building connectivity requires interfaces that map quantum
information between microwave and optical fields. While preliminary
microwave-to-optical (M2O) transducers have been realized, developing
efficient, low-noise devices that match superconducting qubit frequencies
(gigahertz) and bandwidths (10 kHz - 1 MHz) remains a challenge. Here we
demonstrate a proof-of-concept on-chip M2O transducer using
$^{171}\mathrm{Yb}^{3+}$-ions in yttrium orthovanadate (YVO) coupled to a
nanophotonic waveguide and a microwave transmission line. The device's
miniaturization, material, and zero-magnetic-field operation are important
advances for rare-earth ion magneto-optical devices. Further integration with
high quality factor microwave and optical resonators will enable efficient
transduction and create opportunities toward multi-platform quantum networks.",1912.03671v1
2019-12-16,The nature of the photometric variability of HgMn stars: A test of simulated light curves of φ Phe against the TESS data,"The inhomogeneous surface distribution of heavy elements is known to cause
periodic light variability of magnetic chemically peculiar stars. It is unclear
to what extent the same paradigm applies to mercury-manganese (HgMn) stars. We
aim to model the photometric variability of the HgMn star {\phi}Phe using
abundance maps obtained from high-resolution spectroscopy and to study how this
variability evolves with time.
  We compute a grid of ATLAS12 model atmospheres and the corresponding SYNSPEC
synthetic spectra. Interpolating within this grid and integrating the specific
intensity over the visible stellar surface at different rotational phases, we
obtain theoretical light curves of the star.
  We predict the variability of {\phi} Phe in the ultraviolet and in the
visible spectral regions with amplitude of the order of millimagnitudes, mainly
caused by absorption in lines of yttrium, chromium, and titanium. We also show
how this variability is affected by changes of the distribution of the heavy
elements over time.
  The main characteristics of the predicted light variability of {\phi} Phe
correspond roughly to the variability of the star observed with the TESS
satellite.",1912.07265v1
2020-01-15,Stability and superconductivity of lanthanum and yttrium decahydrides,"Rare-earth hydrides can exhibit high-temperature superconductivity under high
pressure. Here, we apply a crystal structure prediction method to the current
record-holding $T_c$ material, LaH$_{10}$, and a candidate for even higher
$T_c$, YH$_{10}$. We find a pressure-induced phase transition from the
experimentally observed cubic LaH$_{10}$ phase to a new hexagonal phase at
around 420 GPa. This hexagonal phase could explain experimental observations of
hcp impurities in fcc samples. We find that YH$_{10}$ forms similar structures
to LaH$_{10}$ and discuss the sensitivity of superconductivity calculations to
the computational parameters used.",2001.05305v3
2020-01-31,Sub-Doppler Cooling and Compressed Trapping of YO Molecules at $μ$K Temperatures,"Complex molecular structure demands customized solutions to laser cooling by
extending its general set of principles and practices. Yttrium monoxide (YO)
has unique intramolecular interactions. The Fermi-contact interaction dominates
over the spin-rotation coupling, resulting in two manifolds of closely spaced
states, with one of them possessing a negligible Land\'e g-factor. This unique
energy level structure favors dual-frequency DC magneto-optical trapping (MOT)
and gray molasses cooling (GMC). We report exceptionally robust cooling of YO
at 4 $\mu$K over a wide range of laser intensity, detunings (one and
two-photon), and magnetic field. The magnetic insensitivity enables the spatial
compression of the molecular cloud by alternating GMC and MOT under the
continuous operation of the quadrupole magnetic field. A combination of these
techniques produces a laser-cooled molecular sample with the highest phase
space density in free space.",2002.00056v1
2020-05-27,Demonstration of site-selective angular-resolved absorption spectroscopy of the $^{4}I_{15/2} \rightarrow $$^{4}I_{13/2}$ erbium transition in the monoclinic crystal Y$_2$SiO$_5$,"We study the angular dependence in polarized light of the optical absorption
for the Er$^{3+}$ transition $^{4}I_{15/2} \rightarrow $$^{4}I_{13/2}$ in
Y$_2$SiO$_5$, revealing thus the associated anisotropy and the orientation of
the related absorption principal directions in the dielectric plan
perpendicular to the monoclinic axis b. The measurements are performed at low
temperature. This allows us to isolate the lowest crystal field levels in the
ground and excited states. We spectrally resolve and independently characterize
the two yttrium substitution sites in the Y$_2$SiO$_5$ matrix. The absorption
tensor components cannot be unambiguously determined yet while only considering
the investigated dielectric plane. Still, measurements remarkably demonstrate
that this transition of interest well resolved at low temperature is not only a
magnetic-dipole allowed transition but indeed a hybrid electric-magnetic
transition.",2005.13626v2
2020-08-25,Multifunctional on-chip storage at telecommunication wavelength for quantum networks,"Quantum networks will enable a variety of applications, from secure
communication and precision measurements to distributed quantum computing.
Storing photonic qubits and controlling their frequency, bandwidth and
retrieval time are important functionalities in future optical quantum
networks. Here we demonstrate these functions using an ensemble of erbium ions
in yttrium orthosilicate coupled to a silicon photonic resonator and controlled
via on-chip electrodes. Light in the telecommunication C-band is stored,
manipulated and retrieved using a dynamic atomic frequency comb protocol
controlled by linear DC Stark shifts of the ion ensemble's transition
frequencies. We demonstrate memory time control in a digital fashion in
increments of 50 ns, frequency shifting by more than a pulse-width ($\pm39$
MHz), and a bandwidth increase by a factor of three, from 6 MHz to 18 MHz.
Using on-chip electrodes, electric fields as high as 3 kV/cm were achieved with
a low applied bias of 5 V, making this an appealing platform for rare earth
ions, which experience Stark shifts of the order of 10 kHz/(V/cm).",2008.10795v1
2020-09-02,Peculiarities of Abundances of Selected Elements in Metal-Rich Field RR Lyrae Stars,"We use the data of our extended catalog of spectroscopic determinations of
elemental abundances in the atmospheres of Galactic-field RR Lyrae type
variables to show that metal-rich RR Lyraes ($\rm{[Fe/H]} > -1.0$) have
anomalous abundances of some elements. In particular, the relative abundances
of scandium, titanium, and yttrium in metal-rich RR Lyrae type variables are
lower than the corresponding abundances in field stars of similar metallicity
beyond the errors. We discuss the errors of the determination of the abundances
of the above elements and point out the fact that no europium, zirconium, and
lanthanum abundance determinations are available for metal-rich RR Lyrae type
variables. We also analyze various possible causes of the observed
peculiarities of the chemical composition of metal-rich RR Lyrae type
variables.",2009.00906v1
2020-09-29,Distal edge determination precision for a multi-slat promptgamma camera: a comprehensive simulation and optimization of the detection system,"Multi-slat prompt-gamma camera is a promising tool for range monitoring
during proton therapy. We report the results of a comprehensive simulation
study analyzing the precision which is possible to reach with this camera in
determination of the position of the distal edge of the Bragg peak. For the
first time we include simulation of optical photons. The proton beam (single
pencil beam, 130 MeV, 10 ns bunch period, total of 10^8 protons) is interacting
with a polymethyl methacrylate (PMMA) phantom, which is a cylinder of 200 mm in
diameter and length. The prompt gamma rays generated in the phantom are
collimated with a multi-slat collimator and detected using a combination of
yttrium aluminum perovskite (YAP) scintillators, installed in the collimator
apertures, and light sensors. Two scintillator packing schemes, with one and
with two scintillator plates per aperture, are considered. The collimator
configuration (the septal thickness, aperture and height), resulting in the
best precision, is determined using two methods of detector optimization.
Precision of 2.1 mm (full width at half maximum) in the edge position
determination is demonstrated.",2009.14154v2
2020-11-03,Strongly correlated bistable sublattice and temperature hysteresis of elastic and thermal crystal properties,"It is shown that in crystal lattices with a basis the cooperative behavior of
a certain type of atoms performing optical long-wavelength vibrations in a
double-well potential of the field of the matrix lattice may lead to the
formation of a bistable sublattice. As a result of the interaction of the
metastable states of such a sublattice with the vibrational states of the
matrix lattice, the elastic and thermal properties of the crystal acquire
anomalous, hysteresis-like, temperature curves. The concepts developed in the
paper make it possible to obtain a qualitative interpretation, which agrees
with the experimental data, of the hysteresis-like temperature dependence of
the speed and absorption of ultrasonic waves, the specific heat, and the
thermal conductivity in superconducting yttrium and bismuth cuprates.",2011.01594v1
2020-12-11,Local-mean preserving post-processing step for non-negativity enforcement in PET imaging: application to $^{90}$Y-PET,"In a low-statistics PET imaging context, the positive bias in regions of low
activity is a burning issue. To overcome this problem, algorithms without the
built-in non-negativity constraint may be used. They allow negative voxels in
the image to reduce, or even to cancel the bias. However, such algorithms
increase the variance and are difficult to interpret, since negative
radioactive concentrations have no physical meaning. Here, we propose a
post-processing strategy to remove negative intensities while preserving the
local mean activities. Our idea is to transfer the negative intensities to
neighboring voxels, so that the mean of the image is preserved. The proposed
post-processing algorithm solves a linear programming problem with a specific
symmetric structure, and the solution can be computed in a very efficient way.
Acquired data from an yttrium-90 phantom show that on images produced by a
non-constrained algorithm, a much lower variance in the cold area is obtained
after the post-processing step.",2012.06432v1
2021-02-03,Evolutionary search for cobalt-rich compounds in the yttrium-cobalt-boron system,"Modern high-performance permanent magnets are made from alloys of rare earth
and transition metal elements, and large magnetization is achieved in the
alloys with high concentration of transition metals. We applied evolutionary
search scheme based on first-principles calculations to the Y-Co-B system and
predicted 37 cobalt-rich compounds with high probability of being stable.
Focusing on remarkably cobalt-rich compounds, YCo$_{16}$ and YCo$_{20}$, we
found that, although they are metastable phases, the phase stability is
increased with increase of temperature due to the contribution of vibrational
entropy. The magnetization and Curie temperature are higher by 0.22 T and 204 K
in YCo$_{16}$ and by 0.29 T and 204 K in YCo$_{20}$ than those of
Y$_{2}$Co$_{17}$ which has been well studied as strong magnetic compounds.",2102.02097v1
2021-04-03,Characterization of Er$^{3+}$:YVO$_{4}$ for microwave to optical transduction,"Quantum transduction between microwave and optical frequencies is important
for connecting superconducting quantum platforms in a quantum network.
Ensembles of rare-earth ions are promising candidates to achieve this
conversion due to their collective coherent properties at microwave and optical
frequencies. Erbium ions are of particular interest because of their telecom
wavelength optical transitions that are compatible with fiber communication
networks. Here, we report the optical and electron spin properties of erbium
doped yttrium orthovanadate (Er$^{3+}$:YVO$_{4}$), including high-resolution
optical spectroscopy, electron paramagnetic resonance studies and an initial
demonstration of microwave to optical conversion of classical fields. The
highly absorptive optical transitions and narrow ensemble linewidths make
Er$^{3+}$:YVO$_{4}$ promising for magneto-optic quantum transduction.",2104.01501v1
2021-04-09,Polarons formation in Bi-deficient BaBiO$_3$,"BaBiO$_3$ is a charged ordered Peierls-like perovskite well known for its
superconducting properties upon K or Pb doping. We present a study on the
transport and electronic properties of BaBiO$_3$ perovskite with strong
Bi-deficiency. We show that it is possible to synthesize BaBiO$_3$ thin layers
with Bi-vacancies above 8-10% by depositing an yttrium-stabilized zirconia
capping layer. By combining transport measurements with ab initio calculations
we propose an scenario where the Bi-vacancies give rise to the formation of
polarons and suggest that the electrical transport is dominated by the
migration of these polarons trapped at Bi$^{3+}$ sites. Our work shows that
cation vacancies engineering -- hardly explored to date -- appears as a
promising pathway to tune the electronic and functional properties of
perovskites.",2104.04573v1
2021-05-12,Probing Strong Coupling between a Microwave Cavity and a Spin Ensemble with Raman Heterodyne Spectroscopy,"Raman heterodyne spectroscopy is a powerful tool for characterizing the
energy and dynamics of spins. The technique uses an optical pump to transfer
coherence from a spin transition to an optical transition where the coherent
emission is more easily detected.
  Here Raman heterodyne spectroscopy is used to probe an isotopically purified
ensemble of erbium dopants, in a yttrium orthosilicate (Y$_2$SiO$_5$) crystal
coupled to a microwave cavity. Because the erbium electron spin transition is
strongly coupled to the microwave cavity, we observed Raman heterodyne signals
at the resonant frequencies of the hybrid spin-cavity modes (polaritons) rather
than the bare erbium spin transition frequency. Using the coupled system, we
made saturation recovery measurements of the ground state spin relaxation time
T$_1$ = 10$\pm$3 seconds, and also observed Raman heterodyne signals using an
excited state spin transition. We discuss the implications of these results for
efforts towards converting microwave quantum states to optical quantum states.",2105.05387v1
2021-06-06,Prediction of half-metallicity and spin-gapless semiconducting behavior in the new series of FeCr-based quaternary Heusler alloys: an ab initio study,"This paper presents a detailed investigation of FeCr-based quaternary Heusler
alloys. By using ultrasoft pseudopotential, electronic and magnetic properties
of the compounds are studied within the framework of Density Functional Theory
(DFT) by using the Quantum Espresso package. The thermodynamic, mechanical, and
dynamical stability of the compounds is established through the comprehensive
study of different mechanical parameters and phonon dispersion curves. The
meticulous study of elastic parameters such as bulk, Young's, shear moduli,
etc. is done to understand different mechanical properties. The FeCr-based
compounds containing also Yttrium are studied to redress the contradictory
electronic and magnetic properties observed in the literature. The interesting
properties like half-metallicity and spin-gapless semiconducting (SGS) behavior
are realized in the compounds under study.",2106.03026v1
2021-07-13,High Phase-Space Density of Laser-Cooled Molecules in an Optical Lattice,"We report laser cooling and trapping of yttrium monoxide (YO) molecules in an
optical lattice. We show that gray molasses cooling remains exceptionally
efficient for YO molecules inside the lattice with a molecule temperature as
low as 6.1(6) $\mu$K. This approach has produced a trapped sample of 1200
molecules, with a peak spatial density of $\sim1.2\times10^{10}$ cm$^{-3}$, and
a peak phase-space density of $\sim3.1\times10^{-6}$. By adiabatically ramping
down the lattice depth, we cool the molecules further to 1.0(2) $\mu$K, twenty
times colder than previously reported for laser-cooled molecules in a trap.",2107.06422v2
2021-08-11,Optical excitation and probing of the antiferromagnetic modes with non-uniform in-depth distribution in birefringent antiferromagnetic crystals,"Optical pump-probe setups are commonly used for excitation and investigation
of the spin dynamics in various types of magnetic materials. However, usually
the spatially homogeneous excitation is considered. In the present study we
describe an approach for optical excitation of the nonuniform THz spin dynamics
and for probing its spatial distribution inside a magnetic crystal. We propose
to illuminate a crystal with laser pulses of properly adjusted polarization to
benefit from a strong optical birefringence inherent to the crystal. It results
in an unusual behavior of the effective magnetic field generated by the pulses
due to the inverse Faraday effect and the peculiar sign-changing dependence of
the direct Faraday effect inside the crystal. The study is performed exemplary
for yttrium orthoferrite crystal although the proposed approach is applicable
for various magnetic materials with optical anisotropy.",2108.05443v2
2022-01-29,Vibrational fingerprints of ferroelectric hafnia,"Hafnia (HfO2) is a promising material for emerging chip applications due to
its high-k dielectric behaviour, suitability for negative capacitance
heterostructures, scalable ferroelectricity, and silicon compatibility. The
lattice dynamics along with phononic properties such as thermal conductivity,
contraction, and heat capacity are under-explored, primarily due to the absence
of high quality single crystals. Herein, we report the vibrational properties
of a series of HfO2 crystals stabilized with yttrium (chemical formula HfO2:xY,
where x = 20, 12, 11, 8, and 0%) and compare our findings with a symmetry
analysis and lattice dynamics calculations. We untangle the effects of Y by
testing our calculations against the measured Raman and infrared spectra of the
cubic, antipolar orthorhombic, and monoclinic phases and then proceed to reveal
the signature modes of polar orthorhombic hafnia. This work provides a
spectroscopic fingerprint for several different phases of HfO2 and paves the
way for an analysis of mode contributions to high-k dielectric and
ferroelectric properties for chip technologies.",2201.12643v1
2022-06-22,An improved smart meta-superconductor MgB2,"Increasing and improving the critical transition temperature (Tc), current
density (Jc) and Meissner effect (Hc) of conventional superconductors are the
most important problems in superconductivity research, but progress has been
slow for many years. In this study, by introducing the p-n junction
electroluminescent inhomogeneous phase with red wavelength to realize energy
injection, we found the improved property of smart meta-superconductors MgB2,
the critical transition temperature Tc increases by 0.8K, the current density
Jc increases by 37%, and the diamagnetism of Meissner effect Hc also
significantly improved, compared with pure MgB2. Compared with previous yttrium
oxide inhomogeneous phase, p-n junction has higher luminescence intensity,
longer stable life and simpler external field requirements. The coupling
between superconducting electrons and surface plasmon polaritons may be explain
this phenomenon. The realization of smart meta-superconductor by this
electroluminescent inhomogeneous phase provides a new way to improve the
performance of superconductors.",2206.10940v1
2022-07-05,Proposal for spin squeezing in rare-earth ion-doped crystals with a four-color scheme,"Achieving spin squeezing within solid-state devices is a long standing
research goal, due to the promise of their particularities, for instance their
long coherence times, the possibility of low-temperature experiments or
integration of entanglement-assisted sensors on-chip. In this work, we
investigate an interferometer-free four-color scheme to achieve spin squeezing
of rare-earth ion-doped crystals. The proposal relies on an analytic derivation
that starts from a Tavis-Cummings model for light-matter interaction, providing
microscopic insights onto spin-squeezing generation. We evidence spin squeezing
signature in the light intensity variance. We consider the two particular cases
of europium- and praseodymium-doped yttrium orthosilicates, workhorses of
quantum technology developments. We show that up to 8 dB of spin squeezing can
be obtained with readily accessible experimental resources, including noise due
to photon scattering. Our results for rare-earth ion-doped crystals add to
promising properties of these platforms for manipulating many-body entangled
states and for high-precision measurements.",2207.02169v2
2022-08-22,Magnetically Tuned Continuous Transition from Weak to Strong Coupling in Terahertz Magnon Polaritons,"Depending on the relative rates of coupling and dissipation, a light-matter
coupled system is either in the weak- or strong-coupling regime. Here, we
present a unique system where the coupling rate continuously increases with an
externally applied magnetic field while the dissipation rate remains constant,
allowing us to monitor a weak-to-strong coupling transition as a function of
magnetic field. We observed a Rabi splitting of a terahertz magnon mode in
yttrium orthoferrite above a threshold magnetic field of ~14 T. Based on a
microscopic theoretical model, we show that with increasing magnetic field the
magnons transition into magnon polaritons through an exceptional point, which
will open up new opportunities for in situ control of non-Hermitian systems.",2208.10030v1
2022-08-29,Frequency Response Analysis of Backside Illuminated Free-Membrane Type IR Superconducting Bolometer,"The IR response of a backside illuminated type Yttrium Barium Copper Oxide
(YBCO) transition-edge bolometer (TEB) in a free-membrane configuration is
measured and analyzed. The analysis is based on a comprehensive equivalent
circuit model for the bolometer structure considering all the thermal
parameters of the device. The detector is made using a 450nm superconductive
YBCO thin film grown on about 100 um thick crystalline SrTiO3 (STO) substrate
using an optimized low cost Metal Organic Deposition (MOD) technique. The
backside illuminated structure provided a basis for freely utilizing different
IR absorber materials and structures on the backside of the bolometer in order
to get wide band high radiation absorption coefficient for the device, while
also avoiding any negative effect of the deposition of the absorber layer on
the YBCO thin film properties. The obtained analytical and experimental results
for the backside illuminated bolometer were also compared with the results of
the previously reported front-side illuminated bolometers.",2208.13711v1
2022-10-08,"Valence and magnetism in $\rm EuPd_3S_4$ and $\rm (Y,La)_xEu_{1-x}Pd_3S_4$","$^{151}$Eu M\""ossbauer spectroscopy shows that yttrium substitution in
mixed-valent $\rm EuPd_3S_4$ drives the initial 50:50 mix of Eu$^{3+}$ and
Eu$^{2+}$ towards pure Eu$^{2+}$, whereas lanthanum substitution has the
opposite effect, but only for substitution levels above 50\%. We find that
total valence electron count and chemical pressure effects cannot account for
the observed behaviour, however conserving the cell volume provides a
consistent description of the changes in the Eu$^{2+}$:Eu$^{3+}$ ratio.
Remarkably, lanthanum substitution also leads to a clear transition from static
mixed-valent behavior at lower temperatures to dynamic mixed valent behavior at
higher temperatures, with the onset temperature monotonically increasing with
Eu content and extrapolating to a value of $\sim$340~K for the pure $\rm
EuPd_3S_4$ compound. Magnetic order persists at least as far as x=0.875 in both
series, despite the drastic reduction in the amount of moment-carrying
Eu$^{2+}$ ions.",2210.03860v1
2022-11-04,In-plane anisotropy of electrical transport in Y$_{0.85}$Tb$_{0.15}$Ba$_2$Cu$_3$O$_{7-x}$ films,"We fabricate high-quality c-axis oriented epitaxial YBa$_2$Cu$_3$O$_{7-x}$
films with 15% of yttrium atoms replaced by terbium (YTBCO) and study their
electrical properties. The Tb substitution reduces the charge carrier density
resulting in increased resistivity and decreased critical current density
compared to the pure YBa$_2$Cu$_3$O$_{7-x}$ films. The electrical properties of
the YTBCO films show an in-plane anisotropy in both the superconducting and
normal state providing evidence for the twin-free film. Unexpectedly, the
resistive transition of the bridges also demonstrates the in-plane anisotropy
that can be explained within the framework of Tinkham's model of the resistive
transition and the Berezinskii-Kosterlitz-Thouless (BKT) model depending on the
sample parameters. We consider YTBCO films to be a promising platform for both
the fundamental research on the BKT transition in the cuprate superconductors
and for the fabrication of devices with high kinetic inductance.",2211.02564v2
2022-12-03,Microstructure Evolution of Solid Oxide Fuel Cell Anodes Characterized by Persistent Homology,"Uncovering microstructure evolution mechanisms that accompany the long-term
operation of solid oxide fuel cells is a fundamental challenge in designing a
more durable energy system for the future. To date, the study of fuel cell
stack degradation has focused mainly on electrochemical performance and, more
rarely, on averaged microstructural parameters. Here we show an alternative
approach in which an evolution of three-dimensional microstructural features is
studied using electron tomography coupled with topological data analysis. The
latter produces persistent images of microstructure before and after long-term
operation of electrodes. Those images unveil a new insight into the degradation
process of three involved phases: nickel, pores, and yttrium-stabilized
zirconium.",2212.01576v1
2023-02-02,Superconducting phases of YH9 under pressure,"Yttrium superhydrides has attracted much attention due to their multiple
stoichiometries and excellent superconductivities under high pressure.
Especially, YH9 have a Tc of 243 K, which is the second highest Tc among all
binary hydrides. It exhibits a positive pressure dependence of Tc below 200
GPa, contrary to the results of theoretical prediction. In order to explore the
origin of Tc at low pressure, we extensively investigated the crystal structure
of YH9 at different pressure, and found a distorted cage structure with a
symmetry of Pnma. This phase has the lowest enthalpy at pressure below 220 GPa,
and its X-ray diffraction patterns is consistent with experimental data. Most
importantly, the pressure dependence of Tc in phase Pnma is in line with the
experimental results. Further calculations show the structural distortion
strongly affect the lattice vibration and electron-phonon coupling, leads to
the Pnma phase exhibiting a positive pressure dependence of Tc.",2302.01122v2
2023-06-26,Discovery of a 760 nm P Cygni line in AT2017gfo: Identification of yttrium in the kilonova photosphere,"Neutron star mergers are believed to be a major cosmological source of rapid
neutron-capture elements. The kilonovae associated with neutron star mergers
have to date yielded only a single well-identified spectral signature: the P
Cygni line of Sr$^+$ at about 1$\mu$m in the spectra of the optical transient,
AT2017gfo. Such P Cygni lines are important, because they provide significant
information not just potentially on the elemental composition of the merger
ejecta, but also on the velocity, geometry, and abundance stratification of the
explosion. In this paper we show evidence for a previously unrecognised P Cygni
line in the spectra of AT2017gfo that emerges several days after the explosion,
located at $\lambda \approx 760\,$nm. We show that the feature is
well-reproduced by 4d$^2$-4d5p transitions of Y$^+$, which have a weighted mean
wavelength around 760-770 nm, with the most prominent line at 788.19 nm. While
the observed line is weaker than the Sr$^+$ feature, the velocity
stratification of the new line provides an independent constraint on the
expansion rate of the ejecta similar to the constraints from Sr$^+$.",2306.14942v1
2023-09-25,Simultaneous High-Speed and Low-Dose 4-D STEM Using Compressive Sensing Techniques,"Here we show that compressive sensing allow 4-dimensional (4-D) STEM data to
be obtained and accurately reconstructed with both high-speed and low fluence.
The methodology needed to achieve these results compared to conventional 4-D
approaches requires only that a random subset of probe locations is acquired
from the typical regular scanning grid, which immediately generates both higher
speed and the lower fluence experimentally. We also consider downsampling of
the detector, showing that oversampling is inherent within convergent beam
electron diffraction (CBED) patterns, and that detector downsampling does not
reduce precision but allows faster experimental data acquisition. Analysis of
an experimental atomic resolution yttrium silicide data-set shows that it is
possible to recover over 25dB peak signal-to-noise in the recovered phase using
0.3% of the total data.",2309.14055v3
2023-10-10,Optical assembly of nanostructures mediated by surface roughness,"Rigorous understanding of the self-assembly of colloidal nanocrystals is
crucial to the development of tailored nanostructured materials. Despite
extensive studies, a mechanistic understanding of self-assembly under
non-equilibrium driven by an external field remains an ongoing challenge. We
demonstrate self-assembly by optical tweezers imposing an external attractive
field for cubic-phase sodium yttrium fluoride nanocrystals. We show that
surface roughness of the nanocrystals is a decisive factor for contact leading
to assembly between the nanocrystals, manifested by the roughness-dependent
hydrodynamic resistivity. This provides direct evidence that dynamics are
equally important to energetics in understanding self-assembly. These results
have implications in a wide variety of different fields, such as in
understanding the factors that mediate oriented attachment-based crystal growth
or in interpreting the structure of binding sites on viruses.",2310.06774v1
2023-11-28,Spectral Multiplexing of Rare-earth Emitters in a Co-doped Crystalline Membrane,"The spectral addressing of many individual rare-earth dopants in optical
resonators offers great potential for realizing distributed quantum information
processors. To this end, it is required to understand and control the spectral
properties of the emitters in micron-scale devices. Here, erbium emitters are
investigated in a Fabry-Perot resonator which contains a ten-micrometer-thin
membrane of crystalline yttrium orthosilicate that is co-doped with europium.
The co-doping allows for tailoring the inhomogeneous distribution of the
emitter frequency, which enables high-fidelity spectral multiplexing of more
than 360 qubits with Purcell factors exceeding 35. At the same time, the
optical coherence is preserved up to 0.62(3) ms under dynamical decoupling.
Without decoupling, the coherence still reaches the lifetime limit for the
emitters with the strongest Purcell enhancement that leads up to a 110-fold
lifetime reduction, down to 0.104(9) ms. Future work may combine this with
long-lived nuclear spin memories, which makes the investigated co-doped
membranes a promising platform for quantum repeaters and distributed quantum
computers.",2311.16875v2
2024-01-21,Levitodynamic spectroscopy for single nanoparticle characterisation,"Fast detection and characterization of single nanoparticles such as viruses,
airborne aerosols and colloidal particles are considered to be particularly
important for medical applications, material science and atmospheric physics.
In particular, non-intrusive optical characterization, which can be carried out
in isolation from other particles, and without the deleterious effects of a
substrate or solvent, is seen to be particularly important. Optical
characterization via the scattering of light does not require complicated
sample preparation and can in principle be carried out in-situ. We describe the
characterization of single nanoparticle shape based on the measurement of their
rotational and oscillatory motion when optically levitated within vacuum. Using
colloidally grown yttrium lithium fluoride nanocrystals of different sizes,
trapped in a single-beam optical tweezer, we demonstrate the utility of this
method which is in good agreement with simulations of the dynamics. Size
differences as small as a few nanometers could be resolved using this technique
offering a new optical spectroscopic tool for non-contact characterization of
single nanoparticles in the absence of a substrate.",2401.11551v1
2024-02-04,High temperature deformation mechanisms in monolithic 3YTZP and 3YTZP containing single wall carbon nanotubes,"Monolithic 3YTZP and 3YTZP containing 2.5 vol.% of single-walled carbon
nanotubes (SWCNT) were fabricated by Spark Plasma Sintering (SPS) at 1250 C.
Microstructural characterization of the as-fabricated 3YTZP/SWCNTs composite
shows a homogeneous CNTs dispersion throughout of ceramic matrix. The specimens
have been crept at temperatures between 1100 and 1200 C in order to investigate
the influence of the SWCNTs addition on high temperature deformation mechanisms
in zirconia. Slightly higher stress exponent values are found for 3YTZP/SWCNTs
nanocomposites (n~2.5) compared to monolithic 3YTZP (n~2.0). However, the
activation energy in 3YTZP (Q = 715 +- 60 kJ/mol) experiences a reduction of
about 25% by the addition of 2.5 vol.% of SWCNTs (Q = 540 +- 40 kJ/mol).
Scanning electron microscopy studies indicate that there is no microstructural
evolution in crept specimens, and Raman spectroscopy measurements show that
SWCNTs preserved their integrity during the creep tests. All these results seem
to indicate that the high temperature deformation mechanism is grain boundary
sliding (GBS) accommodated by grain-boundary diffusion, which is influenced by
yttrium segregation and the presence of SWCNTs at the grain boundary.",2402.06651v1
1998-04-06,Detection of an iron K Emission Line from the LINER NGC 4579,"We present the results of an ASCA observation of the LINER NGC 4579. A
point-like X-ray source is detected at the nucleus with a 2-10 keV luminosity
of 1.5x10^41 ergs/s assuming a distance of 16.8 Mpc. The X-ray spectrum is
represented by a combination of a power-law with a photon index of ~1.7 and
soft thermal component with kT~0.9 keV. An iron K emission line is detected at
6.73+/-0.13 keV (rest frame) with an equivalent width of 490 +180/-190 eV and
is statistically significant at more than 99.9 % confidence. The line center
energy is consistent with Helium-like iron and is significantly higher than 6.4
keV which is expected from fluorescence by ""cold"" (or a lower ionization state
of) iron. The iron line profile shows no significant red tail in contrast to
Seyfert 1 galaxies although the statistics are limited. The line center energy,
equivalent width, and profile are consistent with an origin in an ionized
accretion disk. However the large mass accretion rate necessary to ionize the
accretion disk is not consistent with the observed luminosity and normal
accretion models.",9804054v1
1998-10-01,Compton reflection and iron fluorescence in AGN and GBHCs,"Any cold, optically-thick matter in the vicinity of an accreting black hole,
such as the accretion disk, can intercept and reprocess some fraction of the
hard X-ray continuum emission, thereby imprinting atomic features into the
observed spectrum. This process of `X-ray reflection' primarily gives rise to a
broad reflection `hump' peaking at 30keV and an iron emission line at 6.4keV.
In this review, I briefly describe the physics of this process before reviewing
the observations of these features in active galactic nuclei (AGN) and Galactic
black hole candidates (GBHCs). In some AGN, Seyfert galaxies in particular, the
iron line is found to be very broad and asymmetric. It is believed that such
lines arise from the innermost regions of the accretion disk, with
mildly-relativistic Doppler shifts and gravitational redshifts combining to
produce the line profile. Hence, such lines give us a direct observational
probe of the region within several gravitational radii of the black hole. The
complications that plague similar studies of GBHCs, such as disk ionization and
the possibly of inner disk disruption, are also addressed. I conclude with a
discussion of iron line reverberation, i.e. temporal changes of the iron line
as `echos' of large X-ray flares sweep across the accretion disk. It is shown
that interesting reverberation effects, such as a definitive signature of
extremal Kerr geometry, is within reach of high throughput spectrometers such
as Constellation-X.",9810018v1
2000-10-24,XMM-Newton observation of an unusual iron line in the quasar Markarian 205,"XMM-Newton observations of the low luminosity, radio-quiet quasar Markarian
205 have revealed a unique iron K emission line profile. In marked contrast to
the broad and redshifted iron K line commonly seen in ASCA observations of
Seyfert 1 galaxies, we find that a substantial amount of the line flux in Mrk
205 occurs above the neutral line energy of 6.4 keV. Furthermore, we find that
the iron line emission has two distinct components, a narrow, unresolved
neutral line at 6.4 keV and a broadened line centred at 6.7 keV. We suggest
that the most likely origin of the 6.7 keV line is from X-ray reflection off
the surface of a highly ionised accretion disk, whilst the 6.4 keV component
may arise from neutral matter distant from the black hole, quite possibly in
the putative molecular torus. Overall this observation underlines the potential
of XMM-Newton for using the iron K line as a diagnostic of matter in the
innermost regions of AGN.",0010490v1
2001-11-02,Spectroscopic Signatures of Convection in the Spectrum of Procyon. Fundamental Parameters and Iron Abundance,"We have observed the spectrum of Procyon A (F5IV) from 4559 to 5780 A with a
S/N of ~ 1e3 and a resolving power of 2e5. We have measured the line bisectors
and relative line shifts of a large number of Fe I and Fe II lines, comparing
them to those found in the Sun. A three-dimensional(3D) hydrodynamical model
atmosphere has been computed and is tested against observations. The model
reproduces in detail most of the features observed, although we identify some
room for improvement. At all levels, the comparison of the 3D time-dependent
calculations with the observed spectral lines shows a much better agreement
than for classical homogeneous models, making it possible to refine previous
estimates of the iron abundance, the projected rotational velocity, the
limb-darkening, and the systemic velocity of the Procyon binary system.
  The difference between the iron abundance determined with the 3D model and
its
  1D counterpart is <~ 0.05 dex. We find consistency between the iron abundance
derived from Fe I and Fe II lines, suggesting that departures from LTE in the
formation of the studied lines are relatively small. The scatter in the iron
abundance determined from different lines still exceeds the expectations from
the uncertainties in the atomic data, pointing out that one or more components
in the modeling can be refined further.",0111055v1
2002-01-09,Dust and the spectral energy distribution of the OH/IR star OH 127.8+0.0: Evidence for circumstellar metallic iron,"We present a fit to the spectral energy distribution of OH 127.8+0.0, a
typical asymptotic giant branch star with an optically thick circumstellar dust
shell. The fit to the dust spectrum is achieved using non-spherical grains
consisting of metallic iron, amorphous and crystalline silicates and water ice.
Previous similar attempts have not resulted in a satisfactory fit to the
observed spectral energy distributions, mainly because of an apparent lack of
opacity in the 3--8 micron region of the spectrum. Non-spherical metallic iron
grains provide an identification for the missing source of opacity in the
near-infrared. Using the derived dust composition, we have calculated spectra
for a range of mass-loss rates in order to perform a consistency check by
comparison with other evolved stars. The L-[12 micron] colours of these models
correctly predict the mass-loss rate of a sample of AGB stars, strengthening
our conclusion that the metallic iron grains dominate the near-infrared flux.
We discuss a formation mechanism for non-spherical metallic iron grains.",0201128v1
2002-04-09,Short Timescale Correlations Between Line and Continuum Fluxes in Cygnus X-1,"We present the results of 16-s time scale spectral fits for Cygnus X-1 in the
soft state and in the transition state, using a Comptonised blackbody plus an
iron line. On these timescales, we find that that the continuum source flux can
vary by factors 2-3 and that the iron line intensity appears to track these
changes well, i.e., the inferred equivalent width of the line remains constant
to within the errors. We also find no significant changes in the seed
(blackbody) photon temperature, while the properties of the Comptonising corona
clearly do vary, with the spectral hardness and flux generally being
correlated. The corona therefore seems to be the overall driver for the rapid
timescale variability observed in the soft and transition states. These results
are consistent with the Fourier resolved spectroscopy results of Gilfanov et
al. (2000) that indicate the iron line shows rapid flux variations while the
blackbody component does not and suggest that the iron line flux in fact tracks
continuum changes down to very short timescales. We extend this work by showing
that not only the variability amplitudes, but also the {\it phases} of the iron
line and continuum components are identical. We note that the short timescale
variability properties of the soft and transition states are actually not very
different from those of the hard state, suggesting that the corona is the main
cause of rapid variability in that state too, and hence that the mechanism
responsible for the corona is similar in all three states.",0204160v2
2002-10-11,Iron abundances and heating of the ICM in hydrodynamical simulations of galaxy clusters,"Results from a large set of hydrodynamical SPH simulations of galaxy clusters
in a flat LCDM cosmology are used to investigate the metal enrichment and
heating of the ICM. The physical modeling of the gas includes radiative
cooling, star formation, energy feedback and metal enrichment that follow from
the explosions of SNe of type II and Ia. The metallicity dependence of the
cooling function is also taken into account. For a fiducial set of model
prescriptions the results indicate radial iron profiles in broad agreement with
observations; global iron abundances are also consistent with data. It is found
that the iron distribution in the ICM is critically dependent on the shape of
the metal deposition profile. For low temperatu re clusters simulations yield
iron abundances below the allowed observational range, unless it is introduced
a minimum diffusion length of metals in the ICM. The simulated
emission-weighted radial temperature profiles are in good agreement with data
for cooling flow clusters, but at very small distances from the cluster centres
($\sim 2%$ of the virial radii) the temperatures are a factor $\sim$ two higher
than the measured spectral values. The luminosity-temperature relation is in
excellent agreement with the data, cool clusters ($T_X\sim 1keV$) have a core
excess entropy of $\sim 200 keVcm^2$ and their X-ray properties are unaffected
by the amount of feedback energy that has heated the ICM. The fraction of hot
gas $f_g$ at the virial radius increases with $T_X$ and the distribution
obtained from the simulated cluster sample is consistent with the observational
ranges.",0210263v2
2003-07-12,Early star formation traced by the highest redshift quasars,"The iron abundance relative to alpha-elements in the circumnuclear region of
quasars is regarded as a clock of the star formation history and, more
specifically, of the enrichment by SNIa. We investigate the iron abundance in a
sample of 22 quasars in the redshift range 3.0<z<6.4 by measuring their rest
frame UV FeII bump, which is shifted into the near-IR, and by comparing it with
the MgII 2798 flux. The observations were performed with a device that can
obtain near-IR spectra in the range 0.8-2.4 um in one shot, thereby enabling an
optimal removal of the continuum underlying the FeII bump. We detect iron in
all quasars including the highest redshift (z=6.4) quasar currently known. The
uniform observational technique and the wide redshift range allows a reliable
study of the trend of the FeII/MgII ratio with redshift. We find the FeII/MgII
ratio is nearly constant at all redshifts, although there is marginal evidence
for a higher FeII/MgII ratio in the quasars at z~6. If the FeII/MgII ratio
reflects the Fe/alpha abundance, this result suggests that the z~6 quasars have
already undergone a major episode of iron enrichment. We discuss the possible
implications of this finding for the star formation history at z>6. We also
detect a population of weak iron emitters at z~4.5, which are possibly hosted
in systems that evolved more slowly. Alternatively, the trend of the FeII/MgII
ratio at high redshift may reflect significantly different physical conditions
of the circumnuclear gas in such high redshift quasars.",0307264v2
2003-07-16,Abundance Analysis of Planetary Host Stars I. Differential Iron Abundances,"We present atmospheric parameters and iron abundances derived from
high-resolution spectra for three samples of dwarf stars: stars which are known
to host close-in giant planets (CGP), stars for which radial velocity data
exclude the presence of a close-in giant planetary companion (no-CGP), as well
as a random sample of dwarfs with a spectral type and magnitude distribution
similar to that of the planetary host stars (control). All stars have been
observed with the same instrument and have been analyzed using the same model
atmospheres, atomic data and equivalent width modeling program. Abundances have
been derived differentially to the Sun, using a solar spectrum obtained with
Callisto as the reflector with the same instrumentation. We find that the iron
abundances of CGP dwarfs are on average by 0.22 dex greater than that of no-CGP
dwarfs. The iron abundance distributions of both the CGP and no-CGP dwarfs are
different than that of the control dwarfs, while the combined iron abundances
have a distribution which is very similar to that of the control dwarfs. All
four samples (CGP, no-CGP, combined, control) have different effective
temperature distributions. We show that metal enrichment occurs only for CGP
dwarfs with temperatures just below solar and approximately 300 K higher than
solar, whereas the abundance difference is insignificant at Teff around 6000 K.",0307321v1
2004-02-06,A Two-Dimensional Hydrostatically Equilibrium Atmosphere of a Neutron Star with Given Differential Rotation,"An analytic solution has been found in the Roche approximation for the
axially symmetric structure of a hydrostatically equilibrium atmosphere of a
neutron star produced by collapse. A hydrodynamic (quasione-dimensional) model
for the collapse of a rotating iron core in a massive star gives rise to a
heterogeneous rotating protoneutron star with an extended atmosphere composed
of matter from the outer part of the iron core with differential rotation
(Imshennik and Nadyozhin, 1992). The equation of state of a completely
degenerate iron gas with an arbitrary degree of relativity is taken for the
atmospheric matter. We construct a family of toroidal model atmospheres with
total masses $M \approx 0.1 \div 0.2 M_{\odot}$ and total angular momenta $J
\approx (1 \div 5.5) \cdot 10^{49} erg \cdot s$, which are acceptable for the
outer part of the collapsed iron core, in accordance with the hydrodynamic
model, as a function of constant parameters $\omega_{0} and r_{0}$ of the
specified differential rotation law $\Omega =
\omega_{0}\exp{\Big[-\frac{(r\sin{\Theta})^{2}}{r_{0}^{2}}\Big]}$ in spherical
coordinates. The assumed rotation law is also qualitatively consistent with the
hydrodynamic model for the collapse of an iron core.",0402151v1
2005-04-25,A New Model for Iron Emission Lines and Re-Burst in GRB X-Ray Afterglows,"Recently iron emission features have been observed in several X-ray
afterglows of GRBs. It is found that the energy obtained from the illuminating
continuum which produces the emission lines is much higher than that of the
main burst.The observation of SN-GRB association indicates a fallback disk
should be formed after the supernovae explosion. The disk is optically thick
and advection-dominated and dense. We suggest that the delayed injection energy
after the initial main burst, much higher than energy of the main burst, causes
the re-burst appearance in GRB afterglow and illuminates the region of the disk
surface with $\tau\approx1$($\tau$ is the optical depth for the Thomson scatter
) and produces the iron emission line whose luminosity can be up to $10^{45}$
erg$s^{-1}$. The duration of the iron line emission can be $10^{4}-10^{5}$ s.
This model can explain the appearance of re-burst and emission lines in GRB
afterglow and disappearance of the iron emission lines, and also can naturally
solve the problem of higher energy of the illuminating continuum than that of
the main burst. This scenario is different from the models put forward to
explain the emission lines before, that can be tested by SWIFT satellite.",0504533v2
2006-05-26,High-Resolution X-ray Spectroscopy of the Interstellar Medium II: Neon and Iron Absorption Edges,"We present high-resolution spectroscopy of the neon K-shell and iron L-shell
interstellar absorption edges in nine X-ray binaries using the High Energy
Transmission Grating Spectrometer (HETGS) onboard the Chandra X-ray
Observatory. We found that the iron absorption is well fit by an experimental
determination of the cross-section for metallic iron, although with a slight
wavelength shift of ~20 mA. The neon edge region is best fit by a model that
includes the neutral neon edge and three Gaussian absorption lines. We identify
these lines as due to the 1s-2p transitions from Ne II, Ne III, and Ne IX. As
we found in our oxygen edge study, the theoretical predictions for neutral and
low-ionization lines all require shifts of ~20 mA to match our data. Combined
with our earlier oxygen edge study, we find that a best fit O/Ne ratio of
5.4+/-1.6, consistent with standard interstellar abundances. Our best fit Fe/Ne
ratio of 0.20+/-0.03 is significantly lower than the interstellar value. We
attribute this difference to iron depletion into dust grains in the
interstellar medium. We make the first measurement of the neon ionization
fraction in the ISM. We find Ne II/Ne I ~ 0.3 and Ne III/Ne I ~ 0.07. These
values are larger than is expected given the measured ionization of
interstellar helium. For Ne IX, our results confirm the detection of the hot
ionized interstellar medium of the Galaxy.",0605674v1
2007-06-21,The nature of the fluorescent iron line in V 1486 Ori,"The fluorescent 6.4 keV iron line provides information on cool material in
the vicinity of hard X-ray sources as well as on the characteristics of the
X-ray sources themselves. First discovered in the X-ray spectra of the flaring
Sun, X-ray binaries and active galactic nuclei (AGN), the fluorescent line was
also observed in a number of stellar X-ray sources. The young stellar object
(YSO) V1486 Ori was observed in the framework of the Chandra Ultra Deep Project
(COUP) as the source COUP 331. We investigate its spectrum, with emphasis on
the strength and time variability of the fluorescent iron K-alpha line, derive
and analyze the light curve of COUP 331 and proceed with a time-resolved
spectral analysis of the observation. The light curve of V 1486 Ori shows two
major flares, the first one lasting for (approx) 20 ks with a peak X-ray
luminosity of 2.6*10^{32} erg/s (dereddened in the 1-10 keV band) and the
second one -- only partially observed -- for >60 ks with an average X-ray
luminosity of 2.4*10^{31} erg/s (dereddened). The spectrum of the first flare
is very well described by an absorbed thermal model at high temperature, with a
pronounced 6.7 keV iron line complex, but without any fluorescent K-alpha line.
The X-ray spectrum of the second flare is characterized by even higher
temperatures (>= 10 keV) without any detectable 6.7 keV Fe XXV feature, but
with a very strong fluorescent iron K-alpha line appearing predominantly in the
20 ks rise phase of the flare. Preliminary model calculations indicate that
photoionization is unlikely to account for the entire fluorescent emission
during the rise phase.",0706.3097v1
2007-10-04,New Insights on Interstellar Gas-Phase Iron,"In this paper, we report on the gas-phase abundance of singly-ionized iron
(Fe II) for 51 lines of sight, using data from the Far Ultraviolet
Spectroscopic Explorer (FUSE). Fe II column densities are derived by measuring
the equivalent widths of several ultraviolet absorption lines and subsequently
fitting those to a curve of growth. Our derivation of Fe II column densities
and abundances creates the largest sample of iron abundances in moderately- to
highly-reddened lines of sight explored with FUSE, lines of sight that are on
average more reddened than lines of sight in previous Copernicus studies. We
present three major results. First, we observe the well-established correlation
between iron depletion and <n_H> and also find trends between iron depletion
and other line of sight parameters (e.g. f(H_2), E_(B-V), and A_V), and examine
the significance of these trends. Of note, a few of our lines of sight probe
larger densities than previously explored and we do not see significantly
enhanced depletion effects. Second, we present two detections of an extremely
weak Fe II line at 1901.773 A in the archival STIS spectra of two lines of
sight (HD 24534 and HD 93222). We compare these detections to the column
densities derived through FUSE spectra and comment on the line's f-value and
utility for future studies of Fe II. Lastly, we present strong anecdotal
evidence that the Fe II f-values derived empirically through FUSE data are more
accurate than previous values that have been theoretically calculated, with the
probable exception of f_1112.",0710.1062v1
2008-06-20,Bandwidth and Fermi surface of Iron-Oxypnictides: covalency and sensitivity to structural changes,"Some important aspects of the electronic structure of the iron oxypnictides
depend very sensitively on small changes in interatomic distances and bond
angles within the iron-pnictogen subunit. Using first-principles full-potential
electronic structure calculations, we investigate this sensitive dependence,
contrasting in particular LaOFeAs and LaOFeP. The width of the Fe-bands is
significantly larger for LaOFeP, indicating a better metal and weaker
electronic correlations. When calculated at their experimental crystal
structure these two materials have significantly different low-energy band
structure. The topology of the Fermi surface changes when going from LaOFeP to
LaOFeAs, with a three-dimensional hole pocket present in the former case
transforming into a tube with two-dimensional dispersion. We show that the
low-energy band structure of LaOFeAs evolves towards that of LaOFeP as the As
atom is lowered closer to the Fe plane with respect to its experimental
position. The physical origin of this sensitivity to the iron-pnictogen
distance is the covalency of the iron-pnictogen bond, leading to strong
hybridization effects. To illustrate this, we construct Wannier functions,
which are found to have a large spatial extension when the energy window is
restricted to the bands with dominant iron character. Finally, we show that the
Fe bandwidth slightly increases as one moves along the rare-earth series in
ReOFeAs and discuss the physical origin of this effect.",0806.3285v1
2008-07-24,The Unprecedented Giant Coupling of Fe-spin State and the As-As Hybridization in Iron-Pnictide,"From first principles calculations we unravel surprisingly strong
interactions between arsenic ions in iron-pnictides, the strength of which is
controlled by the Fe-spin state. Reducing the Fe-magnetic moment, weakens the
Fe-As bonding, and in turn, increases As-As interactions, causing giant
reduction in the c-axis. For CaFe$_2$As$_2$ system, this reduction is as large
as 1.4 \AA. Since the large c-reduction has been recently observed only under
high-pressure\cite{cTphase}, our results suggest that the iron magnetic moment
should be present in Fe-pnictides at all times at ambient pressure. Finally,
the conventional electron-phonon coupling in the collapsed phase of
CaFe$_2$As$_2$ gives a maximum $T_c$ of 0.6 K and can not explain the $\sim12$
K superconductivity observed in some experiments. Implications of these
findings on the mechanism of superconductivity in iron-pnictides are discussed.",0807.3936v3
2008-12-12,Experimental determination of the microscopic origin of magnetism in parent iron pnictides,"Like high Tc cuprates, the newly discovered iron based superconductors lie in
close proximity to a magnetically ordered parent phase. However, while the
magnetic order in parent cuprates is known to derive from a spin-spin local
superexchange interaction, a plethora of experiments including neutron
scattering have so far been unable to conclusively resolve whether a local
moment Heisenberg description applies in parent iron based compounds, or
whether magnetism arises from a collective SDW order instability. These two
alternatives can in principle be distinguished by measuring the low energy
momentum-resolved bulk-representative electronic structure of the magnetically
ordered phase. Using a combination of polarization dependent ARPES and STM, we
have isolated the complete low-lying bulk representative electronic structure
of magnetic SrFe2As2 with d-orbital symmetry specificity for the first time.
Our results show that while multiple bands with different iron d-orbital
character indeed contribute to charge transport, only one pair of bands with
opposite mirror symmetries microscopically exhibit an itinerant SDW instability
with energy scales on the order of 50 meV. The orbital resolved band topology
below T_SDW point uniquely to a nesting driven band hybridization mechanism of
the observed antiferromagnetism in the iron pnictides, and is consistent with
an unusual anisotropic nodal-density-wave state. In addition, these results
place strong constraints on many theories of pnictide superconductivity that
require a strict local moment magnetism starting point.",0812.2289v1
2009-01-27,Correlation effects in the iron pnictides,"One of the central questions about the iron pnictides concerns the extent to
which their electrons are strongly correlated. Here we address this issue
through the phenomenology of the charge transport and dynamics, single-electron
excitation spectrum, and magnetic ordering and dynamics. We outline the
evidence that the parent compounds, while metallic, have electron interactions
that are sufficiently strong to produce incipient Mott physics. In other words,
in terms of the strength of electron correlations compared to the kinetic
energy, the iron pnictides are closer to intermediately-coupled systems lying
at the boundary between itinerancy and localization, such as V2O3 or Se-doped
NiS2, rather than to simple antiferromagnetic metals like Cr. This level of
electronic correlations produces a new small parameter for controlled
theoretical analyses, namely the fraction of the single-electron spectral
weight that lies in the coherent part of the excitation spectrum. Using this
expansion parameter, we construct the effective low-energy Hamiltonian and
discuss its implications for the magnetic order and magnetic quantum
criticality. Finally, this approach sharpens the notion of magnetic frustration
for such a metallic system, and brings about a multiband matrix t-J1-J2 model
for the carrier-doped iron pnictides.",0901.4112v2
2010-09-14,"Comment on ""Isotope effect in multi-band and multi-channel attractive systems and inverse isotope effect in iron-based superconductors"" by T. Yanagisawa, et al","In a recent paper Yanagisawa et al. [1] claim from a theoretical analysis of
a multi-channel multi-band superconductor model that an inverse isotope
exponent on the superconducting transition temperature Tc can be realized in
iron-based superconductors. Simultaneously, a subgroup of the authors of Ref. 1
performed the corresponding isotope effect experiment on (Ba, K)Fe2As2 by
investigating the iron isotope exchange effect on Tc [2]. In accordance with
their theoretical analysis they indeed report an unusually large sign reversed
isotope exponent of {\alpha} \simeq -0.18(3) which is in strong contrast to
previous experiments on the nominally same system with the same composition in
Ba, K content, namely Ba0.6K0.4Fe2As2 [3], where the exponent was determined to
be {\alpha} \simeq 0.37(3). This conflict remains unsolved until now with the
exception of Ref. 4 where the iron isotope exponent has been determined for
FeSe. In accordance with the results of Ref. 3 a large positive isotope
exponent has been seen thus questioning the outcome of Ref. 1 and implicitly
the findings of Ref. 2. Here, we do not comment on the controversial
experimental situation but address the theoretical analysis of Ref. 1, where a
variety of misleading assumptions have led to the conclusion that a sign
reversed isotope exponent can be realized in a multi-band and multi-channel
attractive model for iron based superconductors.",1009.2590v1
2010-12-23,"Fe-based high temperature superconductivity with Tc=31K bordering an insulating antiferromagnet in (Tl,K)FexSe2 Crystals","Up to now, there have been two material families, the cuprates and the
iron-based compounds with high-temperature superconductivity (HTSC). An
essential open question is whether the two classes of materials share the same
essential physics. In both, superconductivity (SC) emerges when an
antiferromagnetical (AFM) ordered phase is suppressed. However, in cuprates,
the repulsive interaction among the electrons is so strong that the parent
compounds are ""Mott insulators."" By contrast, all iron-based parents are
metallic. One perspective is that the iron-based parents are weakly correlated
and that the AFM arises from a strong ""nesting"" of the Fermi surfaces. An
alternative view is that the electronic correlations in the parents are still
sufficiently strong to place the system close to the boundary between
itinerancy and electronic localization. A key strategy to differentiate theses
views is to explore whether the iron-based system can be tuned into a Mott
insulator. Here we identify an insulating AFM in (Tl,K)FexSe2 by introducing
Fe-vacancies and creating superconductivity in the Fe-planar. With the
increasing Fe-content, the AFM order is reduced. When the magnetism is
eliminated, a superconducting phase with Tc as high as 31K (and a Tc onset as
high as 40K) is induced. Our findings indicate that the correlation effect
plays a crucial role in the iron-based superconductors. (Tl,K)FexSe2,
therefore, represents the first Fe-based high temperature superconductor near
an insulating AFM.",1012.5236v1
2011-01-17,Modeling the iron oxides and oxyhydroxides for the prediction of environmentally sensitive phase transformations,"Iron oxides and oxyhydroxides are challenging to model computationally as
competing phases may differ in formation energies by only several kJ/mol, they
undergo magnetization transitions with temperature, their structures may
contain partially occupied sites or long-range ordering of vacancies, and some
loose structures require proper description of weak interactions such as
hydrogen bonding and dispersive forces. If structures and transformations are
to be reliably predicted under different chemical conditions, each of these
challenges must be overcome simultaneously, while preserving a high level of
numerical accuracy and physical sophistication. Here we present comparative
studies of structure, magnetization, and elasticity properties of iron oxides
and oxyhydroxides using density functional theory calculations with plane-wave
and locally-confined-atomic-orbital basis sets, which are implemented in VASP
and SIESTA packages, respectively. We have selected hematite, maghemite,
goethite, lepidocrocite, and magnetite as model systems from a total of 13
known iron oxides and oxyhydroxides; and use same convergence criteria and
almost equivalent settings in order to make consistent comparisons. Our results
show both basis sets can reproduce the energetic stability and magnetic
ordering, and are in agreement with experimental observations. There are
advantages to choosing one basis set over the other, depending on the intended
focus. In our case, we find the method using PW basis set most appropriate, and
combine our results to construct the first phase diagram of iron oxides and
oxyhydroxides in the space of competing chemical potentials, generated entirely
from first principles",1101.3105v1
2011-08-03,Origin of conductivity cross over in entangled multi-walled carbon nanotube network filled by iron,"A realistic transport model showing the interplay of the hopping transport
between the outer shells of iron filled entangled multi-walled carbon nanotubes
(MWNT) and the diffusive transport through the inner part of the tubes, as a
function of the filling percentage, is developed. This model is based on
low-temperature electrical resistivity and magneto-resistance (MR)
measurements. The conductivity at low temperatures showed a crossover from
Efros-Shklovski (E-S) variable range hopping (VRH) to Mott VRH in 3 dimensions
(3D) between the neighboring tubes as the iron weight percentage is increased
from 11% to 19% in the MWNTs. The MR in the hopping regime is strongly
dependent on temperature as well as magnetic field and shows both positive and
negative signs, which are discussed in terms of wave function shrinkage and
quantum interference effects, respectively. A further increase of the iron
percentage from 19% to 31% gives a conductivity crossover from Mott VRH to 3D
weak localization (WL). This change is ascribed to the formation of long iron
nanowires at the core of the nanotubes, which yields a long dephasing length
(e.g. 30 nm) at the lowest measured temperature. Although the overall transport
in this network is described by a 3D WL model, the weak temperature dependence
of inelastic scattering length expressed as L_phi ~T^-0.3 suggests the
possibility for the presence of one-dimensional channels in the network due to
the formation of long Fe nanowires inside the tubes, which might introduce an
alignment in the random structure.",1108.0881v1
2011-10-17,Testing the sign-changing superconducting gap in iron-based superconductors with quasiparticle interference and neutron scattering,"We present a phenomenological calculation of the quasiparticle-interference
(QPI) pattern and inelastic Neutron scattering (INS) spectra in iron-pnictide
and layered iron-selenide compounds by using materials specific band-structure
and superconducting (SC) gap properties. As both the QPI and the INS spectra
arise due to scattering of the Bogolyubov quasiaprticles, they exibit an
one-to-one correspondence of the scattering vectors and the energy scales. We
show that these two spectroscopies complement each other in such a way that a
comparative study allows one to extract the quantitative and unambiguous
information about the underlying pairing structure and the phase of the SC gap.
Due to the nodeless and isotropic nature of the SC gaps, both the QPI and INS
maps are concentrated at only two energies in pnictide (two SC gaps) and one
energy in iron-selenide, while the associated scattering vectors q for
scattering of sign-changing and same-sign of the SC gaps change between these
spectroscopies. The results presented, particularly for newly iron-selenide
compounds, can be used to test the nodeless d-wave pairing in this class of
high temperature superconductors.",1110.3834v2
2012-02-27,$S_4$ Symmetric Microscopic Model for Iron-Based Superconductors,"Although iron-based superconductors are multi-orbital systems with
complicated band structures, we demonstrate that the low energy physics which
is responsible for high-$T_c$ superconductivity is essentially governed by one
effective Hamiltonianwith two almost decoupled orbitals near half filling. This
underlining electronic structure is protected by the $S_4$ symmetry. With
repulsive or strong next nearest neighbor antiferromagnetic exchange
interactions, each single-orbital effective Hamiltonian results in a robust
$A_{1g}$ s-wave pairing which can be exactly mapped to the d-wave pairing
observed in cuprates. The classification of the superconducting(SC) states
according to the $S_4$ symmetry leads to a natural prediction of the existence
of two different phases named A and B phases. In the B phase, the
superconducting order has an overall sign change along c-axis between the top
and bottom As(Se) planes in a single Fe-(As)Se trilayer structure, which is an
analogy of the sign change under the $90^\circ$ degree rotation in the d-wave
SC state of cuprates. Our derivation provides a unified understanding of
iron-pnictides and iron-chalcogenides, and suggests that cuprates and
iron-based superconductors share identical high-$T_c$ superconducting
mechanism.",1202.5881v5
2012-04-24,Microstructural analysis of phase separation in iron chalcogenide superconductors,"The interplay between superconductivity, magnetism and crystal structure in
iron-based superconductors is a topic of great interest amongst the condensed
matter physics community as it is thought to be the key to understanding the
mechanisms responsible for high temperature superconductivity. Alkali metal
doped iron chalcogenide superconductors exhibit several unique characteristics
which are not found in other iron-based superconducting materials such as
antiferromagnetic ordering at room temperature, the presence of ordered iron
vacancies and high resistivity normal state properties. Detailed
microstructural analysis is essential in order to understand the origin of
these unusual properties. Here we have used a range of complementary scanning
electron microscope based techniques, including high-resolution electron
backscatter di raction mapping, to assess local variations in composition and
lattice parameter with high precision and sub-micron spatial resolution. Phase
separation is observed in the Csx Fe2-ySe2 crystals, with the minor phase
distributed in a plate-like morphology throughout the crystal. Our results are
consistent with superconductivity occurring only in the minority phase.",1204.5472v4
2012-04-25,A Monte Carlo Markov Chain based investigation of black hole spin in the active galaxy NGC3783,"The analysis of relativistically broadened X-ray spectral features from the
inner accretion disk provides a powerful tool for measuring the spin of
supermassive black holes (SMBH) in active galactic nuclei (AGN). However, AGN
spectra are often complex and careful analysis employing appropriate and
self-consistent models are required if one is to obtain robust results. In this
paper, we revisit the deep July-2009 Suzaku observation of the Seyfert galaxy
NGC3783 in order to study in a rigorous manner the robustness of the inferred
black hole spin parameter. Using Monte Carlo Markov Chain (MCMC) techniques, we
identify a (partial) modeling degeneracy between the iron abundance of the disk
and the black hole spin parameter. We show that the data for NGC3783 strongly
require both supersolar iron abundance (Z_Fe=2-4Zsun) and a rapidly spinning
black hole (a>0.88). We discuss various astrophysical considerations that can
affect the measured abundance. We note that, while the abundance enhancement
inferred in NGC3783 is modest, the X-ray analysis of some other objects has
found extreme iron abundances. We introduce the hypothesis that the radiative
levitation of iron ions in the innermost regions of radiation-dominated AGN
disks can enhance the photospheric abundance of iron. We show that radiative
levitation is a plausible mechanism in the very inner regions of high accretion
rate AGN disks.",1204.5747v2
2012-09-19,Orbital and spin magnetic moments of transforming 1D iron inside metallic and semiconducting carbon nanotubes,"The orbital and spin magnetic properties of iron inside transforming metallic
and semiconducting 1D carbon nanotube hybrids are studied by means of local
x-ray magnetic circular dichroism (XMCD) and bulk superconducting quantum
interference device (SQUID) measurements. Nanotube hybrids are initially
ferrocene filled single-walled carbon nanotubes (SWCNT) of different
metallicities. After a high temperature nanochemical reaction ferrocene
molecules react with each other to form iron nano clusters. We show that the
ferrocenes molecular orbitals interact differently with the SWCNT of different
metallicities without significant XMCD response. This XMCD at various
temperatures and magnetic fields reveals that the orbital and/or spin magnetic
moments of the encapsulated iron are altered drastically as the transformation
to 1D Fe nanoclusters takes place. The orbital and spin magnetic moments are
both found to be larger in filled semiconducting nanotubes than in the metallic
sample. This could mean that the magnetic polarizations of the encapsulated
material is dependent on the metallicity of the tubes. From a comparison
between the iron 3d magnetic moments and the bulk magnetism measured by SQUID,
we conclude that the delocalized magnetisms dictate the magnetic properties of
these 1D hybrid nanostructures.",1209.4265v1
2013-03-12,Démixtion et ségrégation superficielle dans les alliages fer-chrome,"Ferritic steels possibly strengthened by oxide dispersion are candidates as
structural materials for generation IV and fusion nuclear reactors. Their use
is limited by incomplete knowledge of the iron-chromium phase diagram at low
temperatures and of the phenomena inducing preferential segregation of one
element at grain boundaries or at surfaces. In this context, this work
contributes to the multi-scale study of the model iron-chromium alloy and their
free surfaces by numerical simulations. This study begins with ab initio
calculations of properties related to the mixture of atoms of iron and
chromium. We highlight complex dependency of the magnetic moments of the
chromium atoms on their local chemical environment. Surface properties are also
proving sensitive to magnetism. This is the case of impurity segregation of
chromium in iron and of their interactions near the surface. In a second step,
we construct a simple energy model for high numerical efficiency. It is based
on pair interactions on a rigid lattice to which are given local chemical
environment and temperature dependencies. With this model, we reproduce the ab
initio results at zero temperature and experimental results at high
temperature. We also deduce the solubility limits at all intermediate
temperatures with mean field approximations that we compare to Monte Carlo
simulations. The last step of our work is to introduce free surfaces in our
model. We then study the effect of ab initio calculated bulk and surface
properties on surface segregation. Finally, we calculate segregation isotherms.
We therefore propose an evolution model of surface composition of iron-chromium
alloys as a function of bulk composition.",1303.2938v1
2013-03-29,A magnetic origin for high temperature superconductivity in iron pnictides,"In conventional Bardeen-Cooper-Schrieffer (BCS) superconductors,
superconductivity occurs when electrons form coherent Cooper pairs below the
superconducting transition temperature Tc. Although the kinetic energy of
paired electrons increases in the superconducting state relative to the normal
state, the reduction in the ion lattice energy is sufficient to give the
superconducting condensation energy. For iron pnictide superconductors derived
from electron or hole doping of their antiferromagnetic (AF) parent compounds,
the microscopic origin for supercnductivity is unclear. Here we use neutron
scattering to show that high-Tc superconductivity only occurs for iron
pnictides with low-energy itinerant electron-spin excitation coupling and high
energy spin excitations. Since our absolute spin susceptibility measurements
for optimally hole-doped iron pnictide reveal that the change in magnetic
exchange energy below and above Tc can account for the superconducting
condensation energy, we conclude that the presence of both high-energy spin
excitations giving rise to a large magnetic exchange coupling J and low-energy
spin excitations coupled to the itinerant electrons is essential for high-Tc
superconductivity in iron pnictides.",1303.7339v1
2013-05-03,Photophoretic separation of metals and silicates: the formation of Mercury like planets and metal depletion in chondrites,"Mercury's high uncompressed mass density suggests that the planet is largely
composed of iron, either bound within metal (mainly Fe-Ni), or iron sulfide.
Recent results from the MESSENGER mission to Mercury imply a low temperature
history of the planet which questions the standard formation models of impact
mantle stripping or evaporation to explain the high metal content. Like
Mercury, the two smallest extrasolar rocky planets with mass and size
determination, CoRoT-7b and Kepler-10b, were found to be of high density. As
they orbit close to their host stars this indicates that iron rich inner
planets might not be a nuisance of the solar system but be part of a general
scheme of planet formation. From undifferentiated chondrites it is also known
that the metal to silicate ratio is highly variable which must be ascribed to
pre-planetary fractionation processes. Due to this fractionation most
chondritic parent bodies - most of them originated in the asteroid belt - are
depleted in iron relative to average solar system abundances. The astrophysical
processes leading to metal silicate fractionation in the solar nebula are
essentially unknown. Here, we consider photophoretic forces. As these forces
particularly act on irradiated solids, they might play a significant role for
the composition of planetesimals forming at the inner edge of protoplanetary
discs. Photophoresis can separate high thermal conductivity materials (iron)
from lower thermal conductivity solids (silicate). We suggest that the
silicates are preferentially pushed into the optical thick disk. Subsequent
planetesimal formation at the edge moving outwards leads to metal rich
planetesimals close to the star and metal depleted planetesimals further out in
the nebula.",1305.0689v1
2013-07-03,Galactic Constraints on Supernova Progenitor Models,"We undertake a statistical analysis of the radial abundance distributions in
the Galactic disk within a theoretical framework for Galactic chemical
evolution which incorporates the influence of spiral arms. 1) The mean mass of
oxygen ejected per core-collapse SNe (CC SNe) event (which are concentrated
within spiral arms) is $\sim$0.27 M$_{\odot}$; 2) the mean mass of iron ejected
by `tardy' Type Ia SNe (SNeIa; progenitors of whom are older/longer-lived stars
with ages $\simgt$100 Myr and up to several Gyr, which do not concentrate
within spiral arms) is $\sim$0.58 M$_{\odot}$; 3) the upper mass of iron
ejected by prompt SNeIa (SNe whose progenitors are younger/shorter-lived stars
with ages $\simlt$100 Myr, which are concentrated within spiral arms) is
$\leq$0.23 M$_{\odot}$ per event; 4) the corresponding mean mass of iron
produced by CC SNe is $\leq$0.04 M$_{\odot}$ per event; (v) short-lived SNe
(core-collapse or prompt SNeIa) supply $\sim$85% of the Galactic disk's iron.
  The inferred low mean mass of oxygen ejected per CC SNe event implies a low
upper mass limit for the corresponding progenitors of $\sim$23 M$_{\odot}$,
otherwise the Galactic disk would be overabundant in oxygen.
  The low mean mass of iron ejected by prompt SNeIa, relative to the mass
produced by tardy SNeIa ($\sim$2.5 times lower), prejudices the idea that both
sub-populations of SNeIa have the same physical nature. We suggest that,
perhaps, prompt SNeIa are more akin to CC SNe, and discuss the implications of
such a suggestion.",1307.0928v1
2013-09-16,Superconductivity in LiFeO2Fe2Se2 with anti-PbO-type Spacer Layers,"Superconductivity has been found in the iron-arsenides with different
structures by alternative stacking of the conducting Fe2As2 layers and spacer
layers including alkali- or alkali-earth metal ions and PbO- or perovskite-type
oxides blocks. So far, no spacer layer could be intercalated in between the
neutral Fe2Se2 layers similar in structure to Fe2As2 layers except for
alkali-metal ions in AxFe2-ySe2. The superconducting phase in AxFe2-ySe2 with
transition temperature of 32 K is always inter-grown with the insulating phase
which exhibits an antiferromagnetic order with extremely high Neel temperature
of ~560 K and the order of Fe vacancies. Such inhomogeneity makes the
investigation on the underlying physics in AxFe2-ySe2 complicated. Here we
report the synthesis of a novel superconductor LiFeO2Fe2Se2 by hydrothermal
method, exhibiting superconductivity at ~43 K, in which anti-PbO-type spacer
layers of LiFeO2 have been successfully intercalated between anti-PbO-type
Fe2Se2 layers. This finding demonstrates that superconductivity can be realized
in the iron selenide with a novel spacer layer of anti-PbO-type, which is not
found in the iron arsenides, and expands the category of the iron-based
superconductors. Such a new synthetic method paves a new way to search for
possible novel superconductors with different spacer layers, which is helpful
to further study the underlying physics in iron-based high-Tc superconductors.",1309.3833v3
2014-01-24,Effect of correlations and doping on the spin susceptibility of iron pnictides: the case of KFe2As2,"The temperature dependence of the paramagnetic susceptibility of the iron
pnictide superconductor KFe2As2 and its connection with the spectral properties
of that material is investigated by a combination of density functional theory
(DFT) in the local density approximation and dynamical mean-field theory
(DMFT). Unlike other iron pnictide parent compounds where the typical oxidation
state of iron is 2, the formal valence of Fe in KFe2As2 is 2.5, corresponding
to an effective doping with 0.5 hole per iron atom compared to, for example,
BaFe2As2. This shifts the chemical potential and thereby reduces the distance
between the peaks in the spectral functions of KFe2As2 and the Fermi energy as
compared to BaFe2As2. The shift, which is clearly seen on the level of DFT as
well as in DMFT, is further enhanced by the strong electronic correlations in
KFe2As2. In BaFe2As2 the presence of these peaks results [Phys. Rev. B 86,
125124 (2012)] in a temperature increase of the susceptibility up to a maximum
at ~1000 K. While the temperature increase was observed experimentally the
decrease at even higher temperatures is outside the range of experimental
observability. We predict that in KFe2As2 the situation is different. Namely,
the reduction of the distance between the peaks and the Fermi level due to
doping is expected to shift the maximum in the susceptibility to much lower
temperatures, such that the decrease of the susceptibility should become
visible in experiment.",1401.6291v3
2014-02-12,Electric double-layer transistor using layered iron selenide Mott insulator TlFe1.6Se2,"A1-xFe2-ySe2 (A = K, Cs, Rb, Tl) are recently discovered iron-based
superconductors with critical temperatures (Tc) ranging up to 32 K. Their
parent phases have unique properties when compared with other iron-based
superconductors; e.g., their crystal structures include ordered Fe vacancies,
their normal states are antiferromagnetic (AFM) insulating phases, and they
have extremely high N\'eel transition temperatures. However, control of carrier
doping into the parent AFM insulators has been difficult due to their intrinsic
phase separation. Here, we fabricated an Fe-vacancy-ordered TlFe1.6Se2
insulating epitaxial film with an atomically flat surface and examined its
electrostatic carrier doping using an electric double-layer transistor (EDLT)
structure with an ionic liquid gate. The positive gate voltage gave conductance
modulation of three orders of magnitude at 25 K, and further induced and
manipulated a phase transition; i.e., delocalized carrier generation by
electrostatic doping is the origin of the phase transition. This is the first
demonstration, to the authors' knowledge, of an EDLT using a Mott insulator
iron-selenide channel and opens a way to explore high-Tc superconductivity in
iron-based layered materials, where carrier doping by conventional chemical
means is difficult.",1402.2767v2
2014-03-24,Discovery of Enhanced Radiative Recombination Continua of He-like Iron and Calcium from IC 443 and Its Implications,"We present deep observations of the Galactic supernova remnant IC 443 with
the {\it Suzaku X-ray satellite}. We find prominent K-shell lines from iron and
nickel, together with a triangle residual at 8--10~keV, which corresponds to
the energy of the radiative recombination continuum (RRC) of He-like iron. In
addition, the wavy residuals have been seen at $\sim$5.1 and $\sim$5.5~keV. We
confirm that the residuals show the first enhanced RRCs of He- and H-like
calcium found in supernova remnants. These facts provide robust evidence for
the recombining plasma. We reproduce the plasma in the 3.7--10~keV band using a
recombining plasma model at the electron temperature 0.65~keV. The
recombination parameter $n_{\rm e}t$ ($n_{\rm e}$ is electron density and $t$
is elapsed time after formation of a recombining plasma) and abundances of iron
and nickel are strongly correlated, and hence the errors are large. On the
other hand, the ratio of nickel to iron relative to the solar abundances is
well constrained to 11$^{+4}_{-3}$ (1$\sigma$). A possibility is that the large
abundance ratio is a result of an asymmetric explosion of the progenitor star.",1403.5850v1
2014-04-18,Faint Population III supernovae as the origin of the most iron-poor stars,"The most iron-deficient stars in the Milky Way provide important
observational constraints on the nature of astrophysical objects that have
enriched the primordial gas with heavy elements from which these stars were
formed. Among them, the recently discovered iron-deficient star SMSS
J031300.36-670839.3 shows a remarkable chemical composition with non-detection
of iron ([Fe/H]$<-7.1$) and large enhancement of carbon and magnesium relative
to calcium. We investigate the supernova yields of metal-free (Population III)
stars to interpret the observed abundance pattern for this star. We report that
the high [C/Ca] and [C/Mg] ratios and upper limits determined for other
elemental abundances are well reproduced with the yields of core-collapse
supernovae (that have normal kinetic energies of explosion $E$ of
$E_{51}=E/10^{51}$erg$=1$) or hypernovae ($E_{51}\geq 10$) of the Population
III 25$M_{\odot}$ or 40$M_{\odot}$ stars. The best-fit model assumes that the
explosion of the Population III progenitor undergoes extensive matter mixing
and fallback, leaving behind a black hole remnant. In these models, Ca is
produced by static/explosive O burning and incomplete Si burning in the
Population III supernova/hypernova, in contrast to the suggestion that Ca is
originated from the hot CNO cycle during the presupernova evolution. Among the
five most iron-poor stars with [Fe/H]$<-4.5$, four carbon-enhanced stars are
consistent with the faint supernova models with the ejected mass of $^{56}$Ni
less than 10$^{-3}M_{\odot}$.",1404.4817v3
2014-04-27,Extraordinary quasiparticle scattering and bandwidth-control by dopants in iron-based superconductors,"The diversities in crystal structures and ways of doping result in extremely
diversified phase diagrams for iron-based superconductors. With angle-resolved
photoemission spectroscopy (ARPES), we have systematically studied the effects
of chemical substitution on the electronic structure of various series of
iron-based superconductors. In addition to the control of Fermi surface
topology by heterovalent doping, we found two more extraordinary effects of
doping: 1. the site and band dependencies of quasiparticle scattering; and more
importantly 2. the ubiquitous and significant bandwidth-control by both
isovalent and heterovalent dopants in the iron-anion layer. Moreover, we found
that the bandwidth-control could be achieved by either applying the chemical
pressure or doping electrons, but not by doping holes. Together with other
findings provided here, these results complete the microscopic picture of the
electronic effects of dopants, which facilitates a unified understanding of the
diversified phase diagrams and resolutions to many open issues of various
iron-based superconductors.",1404.6716v1
2014-04-28,Relativistic iron K alpha line detection in the Suzaku spectra of IC 4329A,"We present an analysis of five Suzaku observations of the bright Seyfert1
galaxy IC 4329A. The broad energy band and high signal-to-noise ratio of the
data give new constraints on the iron K alpha line profile and its relationship
with the Compton hump at higher energies. The Fe K bandpass is dominated by a
narrow core (EW=57 eV) at 6.4 keV consistent with neutral material. Using a
physically-motivated model, our analysis also reveals the presence of a broad
Iron K alpha line (EW=124 eV), most likely produced in the inner part of the
accretion disk and blurred by general relativistic effects. This component is
not immediately evident from the individual spectra, but is clearly present in
the stacked residuals of all five observations, and has high statistical
significance. This highlights the difficulty in identifying broad iron lines in
AGN, even in data with very high signal-to-noise ratio, as they are difficult
to disentangle from the continuum. The data are consistent with the narrow and
broad iron line components tracking the Compton Hump, but do not provide clear
evidence that this is the case. An additional narrow FeXXVI emission line at
6.94 keV is also seen, suggesting the presence of ionized material relatively
distant from the central region. There is also a hint of variability, so the
precise origin of this line remains unclear.",1404.7126v1
2014-05-15,"Control and diagnosis of temperature, density, and uniformity in x-ray heated iron/magnesium samples for opacity measurements","Experimental tests are in progress to evaluate the accuracy of the modeled
iron opacity at solar interior conditions, in particular to better constrain
the solar abundance problem [S. Basu and H.M. Antia, Physics Reports 457, 217
(2008)]. Here we describe measurements addressing three of the key requirements
for reliable opacity experiments: control of sample conditions, independent
sample condition diagnostics, and verification of sample condition uniformity.
The opacity samples consist of iron/magnesium layers tamped by plastic. By
changing the plastic thicknesses, we have controlled the iron plasma conditions
to reach i) Te=167+/-3 eV and ne=(7.1+/-1.5)e21 e/cc, ii) Te=170+/-2 eV and
ne=(2.0+/-0.2)e22 e/cc, and iii) Te=196+/-6 eV and ne=(3.8+/-0.8)e22 e/cc,
which were measured by magnesium tracer K-shell spectroscopy. The opacity
sample non-uniformity was directly measured by a separate experiment where Al
is mixed into the side of the sample facing the radiation source and Mg into
the other side. The iron condition was confirmed to be uniform within their
measurement uncertainties by Al and Mg K-shell spectroscopy. The conditions are
suitable for testing opacity calculations needed for modeling the solar
interior, other stars, and high energy density plasmas.",1405.4012v1
2014-07-03,A Clumpy Stellar Wind and Luminosity-Dependent Cyclotron Line Revealed by The First Suzaku Observation of the High-Mass X-ray Binary 4U 1538-522,"We present results from the first Suzaku observation of the high-mass X-ray
binary 4U 1538-522. The broad-band spectral coverage of Suzaku allows for a
detailed spectral analysis, characterizing the cyclotron resonance scattering
feature at $23.0 \pm 0.4$ keV and the iron K$\alpha$ line at $6.426 \pm 0.008$
keV, as well as placing limits on the strengths of the iron K$\beta$ line and
the iron K edge. We track the evolution of the spectral parameters both in time
and in luminosity, notably finding a significant positive correlation between
cyclotron line energy and luminosity. A dip and spike in the lightcurve is
shown to be associated with an order-of-magnitude increase in column density
along the line of sight, as well as significant variation in the underlying
continuum, implying the accretion of a overdense region of a clumpy stellar
wind. We also present a phase-resolved analysis, with most spectral parameters
of interest showing significant variation with phase. Notably, both the
cyclotron line energy and the iron K$\alpha$ line intensity vary significantly
with phase, with the iron line intensity significantly out-of-phase with the
pulse profile. We discuss the implications of these findings in the context of
recent work in the areas of accretion column physics and cyclotron resonance
scattering feature formation.",1407.1028v1
2014-12-23,Phase diagram of (Li1-xFex)OHFeSe: a bridge between iron selenide and arsenide superconductors,"Previous experimental results have shown important differences between iron
selenide and arsenide superconductors, which seem to suggest that the high
temperature superconductivity in these two subgroups of iron-based family may
arise from different electronic ground states. Here, we report the complete
phase diagram of a newly synthesized superconducting (SC) system
(Li1-xFex)OHFeSe with a similar structure to FeAs-based superconductors. In the
non-SC samples, an antiferromagnetic (AFM) spin-density-wave (SDW) transition
occurs at ~127 K. This is the first example to demonstrate such an SDW phase in
FeSe-based superconductor system. Transmission electron microscopy (TEM) shows
that a well-known sqrr(5) x sqrr(5) iron vacancy ordered state, resulting in an
AFM order at ~ 500K in AyFe2-xSe2 (A = metal ions) superconductor system, is
absent in both non-SC and SC samples, but a unique superstructure with a
modulation wave vector q=1/2(1, 1, 0), identical to that seen in SC phase of
KyFe2-xSe2, is dominant in the optimal SC sample (with an SC transition
temperature Tc = 40 K). Hence, we conclude that the high-Tc superconductivity
in (Li1-xFex)OHFeSe stems from the similarly weak AFM fluctuations as
FeAs-based superconductors, suggesting a universal physical picture for both
iron selenide and arsenide superconductors.",1412.7236v1
2015-06-12,Observation of universal strong orbital-dependent correlation effects in iron chalcogenides,"Establishing the appropriate theoretical framework for unconventional
superconductivity in the iron-based materials requires correct understanding of
both the electron correlation strength and the role of Fermi surfaces. This
fundamental issue becomes especially relevant with the discovery of the iron
chalcogenide (FeCh) superconductors, the only iron-based family in proximity to
an insulating phase. Here, we use angle-resolved photoemission spectroscopy
(ARPES) to measure three representative FeCh superconductors, FeTe0.56Se0.44,
K0.76Fe1.72Se2, and monolayer FeSe film grown on SrTiO3. We show that, these
FeChs are all in a strongly correlated regime at low temperatures, with an
orbital-selective strong renormalization in the dxy bands despite having
drastically different Fermi-surface topologies. Furthermore, raising
temperature brings all three compounds from a metallic superconducting state to
a phase where the dxy orbital loses all spectral weight while other orbitals
remain itinerant. These observations establish that FeChs display universal
orbital-selective strong correlation behaviors that are insensitive to the
Fermi surface topology, and are close to an orbital-selective Mott phase
(OSMP), hence placing strong constraints for theoretical understanding of
iron-based superconductors.",1506.03888v2
2015-07-22,Mott localization in a pure stripe antiferromagnet Rb$_{1-δ}$Fe$_{1.5-σ}$S$_2$,"A combination of neutron diffraction and angle-resolved photoemission
spectroscopy measurements on a pure antiferromagnetic stripe
Rb$_{1-\delta}$Fe$_{1.5-\sigma}$S$_2$ is reported. A neutron diffraction
experiment on a powder sample shows that a 98$\%$ volume fraction of the sample
is in the antiferromagnetic stripe phase with rhombic iron vacancy order and a
refined composition of Rb$_{0.66}$Fe$_{1.36}$S$_{2}$, and that only 2$\%$ of
the sample is in the block antiferromagnetic phase with $\sqrt{5}\times
\sqrt{5}$ iron vacancy order. Furthermore, a neutron diffraction experiment on
a single crystal shows that there is only a single phase with the stripe
antiferromagnetic order with the refined composition of
Rb$_{0.78}$Fe$_{1.35}$S$_2$, while the phase with block antiferromagnetic order
is absent. Angle-resolved photoemission spectroscopy measurements on the same
crystal with the pure stripe phase reveal that the electronic structure is
gapped at the Fermi level with a gap larger than 0.325 eV. The data
collectively demonstrates that the extra 10$\%$ iron vacancies in addition to
the rhombic iron vacancy order effectively impede the formation of the block
antiferromagnetic phase; the data also suggest that the stripe
antiferromagnetic phase with rhombic iron vacancy order is a Mott insulator.",1507.06062v2
2015-09-18,A disk wind interpretation of the strong Fe Kα features in 1H 0707-495,"1H 0707-495 is the most convincing example of a supermassive black hole with
an X-ray spectrum being dominated by extremely smeared, relativistic
reflection, with the additional requirement of strongly supersoler iron
abundance. However, here we show that the iron features in its 2--10 keV
spectrum are rather similar to the archetypal wind dominated source, PDS 456.
We fit all the 2--10 keV spectra from 1H 0707-495 using the same wind model as
used for PDS 456, but viewed at higher inclination so that the iron absorption
line is broader but not so blueshifted. This gives a good overall fit to the
data from 1H 0707-495, and an extrapolation of this model to higher energies
also gives a good match to the NuSTAR data. Small remaining residuals indicate
that the iron line emission is stronger than in PDS 456. This is consistent
with the wider angle wind expected from a continuum driven wind from the
super-Eddington mass accretion rate in 1H 0707-495, and/or the presence of
residual reflection from the underlying disk though the presence of the
absorption line in the model removes the requirement for highly relativistic
smearing, and highly supersoler iron abundance. We suggest that the spectrum of
1H 0707-495 is sculpted more by absorption in a wind than by extreme
relativistic effects in strong gravity.",1509.05645v3
2015-09-29,The Impact of Enhanced Iron Opacity on Massive Star Pulsations: Updated Instability Strips,"Recently, Bailey et al. (2015) made a direct measurement of the Iron opacity
at the physical conditions of the solar tachocline. They found that the
wavelength-integrated Iron opacity is roughly 75% higher that what the OP and
OPAL models predict. Here, we compute new opacity tables with enhanced Iron and
Nickel contributions to the Rosseland mean opacity by 75% each, and compute
three dense MESA grids of evolutionary models for Galactic O- and B-type stars
covering from 2.5 to 25 M$_\odot$ from ZAMS until $T_{\rm eff}=10\,000$ K after
the core hydrogen exhaustion. We carry out non-adiabatic mode stability
analysis with GYRE, and update the extension of the instability strips of
heat-driven p- and g-mode pulsators, and the hybrid pulsating SPB - $\beta$ Cep
stars. We compare the position of two confirmed late O-type $\beta$ Cep and
eight confirmed hybrid B-type pulsators with the new instability domains, and
justify that $\sim$75% enhancement, only in Iron opacity, is sufficient to
consistently reproduce the observed position of these stars on the $\log T_{\rm
eff}$ versus $\log g$ plane. We propose that this improvement in opacities be
incorporated in the input physics of new stellar models.
  To reproduce the results, all software, opacity tables and the new
instability strips are freely available for download at the following URL:
https://fys.kuleuven.be/ster/Projects/ASAMBA.",1509.08652v1
2015-10-28,Variability of the X-ray Broad Iron Spectral Features in Active Galactic Nuclei and Black-hole Binaries,"The ""broad iron spectral features"" are often seen in X-ray spectra of Active
Galactic Nuclei (AGN) and black-hole binaries (BHB). These features may be
explained either by the ""relativistic disc reflection"" scenario or the ""partial
covering"" scenario: It is hardly possible to determine which model is valid
from time-averaged spectral analysis. Thus, X-ray spectral variability has been
investigated to constrain spectral models. To that end, it is crucial to study
iron structure of BHBs in detail at short time-scales, which is, for the first
time, made possible with the Parallel-sum clocking (P-sum) mode of XIS
detectors on board Suzaku. This observational mode has a time-resolution of
7.8~ms as well as a CCD energy-resolution. We have carried out systematic
calibration of the P-sum mode, and investigated spectral variability of the BHB
GRS 1915+105. Consequently, we found that the spectral variability of GRS
1915+105 does not show iron features at sub-seconds. This is totally different
from variability of AGN such as 1H0707--495, where the variation amplitude
significantly drops at the iron K-energy band. This difference can be naturally
explained in the framework of the ""partial covering"" scenario.",1510.08189v1
2015-11-24,Origin of the X-ray Broad Iron Spectral Feature in GRS 1915+105,"The X-ray spectrum of GRS 1915+105 is known to have a ``broad iron spectral
feature'' in the spectral hard state. Similar spectral features are often
observed in Active Galactic Nuclei (AGNs) and other black-hole binaries (BHBs),
and several models have been proposed for explaining it. In order to
distinguish spectral models, time variation provides an important key. In AGNs,
variation amplitude has been found to drop significantly at the iron K-energy
band at timescales of ~10 ks. If spectral variations of black-holes are
normalized by their masses, the spectral variations of BHBs at timescales of
sub-seconds should exhibit similar characteristics to those of AGNs. In this
paper, we investigated spectral variations of GRS 1915+105 at timescales down
to ~10 ms. This was made possible for the first time with the Suzaku XIS
Parallel-sum clocking (P-sum) mode, which has the CCD energy-resolution as well
as a time-resolution of 7.8 ms. Consequently, we found that the variation
amplitude of GRS 1915+105 does not drop at the iron K-energy band at any
timescales from 0.06 s to 63000 s, and that the entire X-ray flux and the iron
feature are independently variable at timescales of hours. These are naturally
understood in the framework of the ``partial covering'' model, in which
variation timescales of the continuum flux and partial absorbers are
independent. The difference of energy dependence of the variation amplitude
between AGN and BHB is presumably due to different mechanisms of the outflow
winds, i.e., the partial absorbers are due to UV-line driven winds (AGN) or
thermally-driven winds (BHB).",1511.07630v1
2016-01-11,Investigation of iron emission lines in the eclipsing high mass X-ray binary pulsar OAO 1657-415,"We present the results obtained from timing and spectral studies of high mass
X-ray binary pulsar OAO 1657-415 using a Suzaku observations in 2011 September.
X-ray pulsations were detected in the light curves up to $\sim$70 keV. The
continuum spectra during the high- and low-flux regions in light curves were
well described by high energy cutoff power-law model along with a blackbody
component and iron fluorescent lines at 6.4 keV and 7.06 keV. Time resolved
spectroscopy was carried out by dividing the entire observations into 18 narrow
segments. Presence of additional dense matter at various orbital phases was
confirmed as the cause of low-flux regions in the observations. Presence of
additional matter at several orbital phases of the pulsar was interpreted as
due to the inhomogeneously distributed clumps of matter around the neutron
star. Using clumpy wind hypothesis, the physical parameters of the clumps
causing the high- and low-flux episodes in the pulsar light curve were
estimated. The equivalent width of iron emission lines was found to be
significantly large at certain orbital phases of low-flux segments. We
investigated the iron line emitting regions and suggest the existence of
neutral and ionized iron atoms in emission sites that are located within the
accretion radius.",1601.02345v1
2016-01-25,Iron Opacity Bump Changes the Stability and Structure of Accretion Disks in Active Galactic Nuclei,"Accretion disks around supermassive black holes have regions where the
Rosseland mean opacity can be much larger than the electron scattering opacity
primarily due to the large number of bound-bound transitions in iron. We study
the effects of this iron opacity ""bump"" on the thermal stability and vertical
structure of radiation pressure dominated accretion disks, utilizing three
dimensional radiation magneto-hydrodynamic simulations in the local shearing
box approximation. The simulations self-consistently calculate the heating due
to MHD turbulence caused by magneto-rotational instability and radiative
cooling by using the radiative transfer module based on a variable Eddington
tensor in Athena. For a $5\times 10^8$ solar mass black hole with $\sim 3\%$ of
the Eddington luminosity, a model including the iron opacity bump maintains its
structure for more than $10$ thermal times without showing significant signs of
thermal runaway. In contrast, if only electron scattering and free-free opacity
are included as in the standard thin disk model, the disk collapses on the
thermal time scale. The difference is caused by a combination of 1) an
anti-correlation between the total optical depth and the temperature, and 2)
enhanced vertical advective energy transport. These results suggest that the
iron opacity bump may have a strong impact on the stability and structure of
AGN accretion disks, and may contribute to a dependence of AGN properties on
metallicity. Since this opacity is relevant primarily in UV emitting regions of
the flow, it may help to explain discrepancies between observation and theory
that are unique to AGNs.",1601.06836v1
2016-02-09,Quantum states entanglement in hemoglobin molecule active center,"An ab initio study of the electronic and spin configuration for the iron ion
in the active center of the human hemoglobin molecule is presented. It is well
known that the iron ion, being surrounded by the porphyrin ring and the
ligands, plays the key role in the realization of the basic oxygen-transport
functions of the molecule. This work is focused on the investigation the
features of the 3$d$-shell electronic states of the iron ion located inside the
active center of the hemoglobin molecule. Also in this paper we study in detail
the changes in these states occurring during the oxidation process. We use a
combination of the Density Functional Theory (DFT) method and the Dynamical
Mean Field Theory (DMFT) approach. This method allows to consider dynamic
correlation effects that are important in the description of systems containing
transition metal ions. It was found that the state of the valence electrons of
the iron ion of the active center of hemoglobin molecule is the entangled
quantum state. This state is a mixture of several electronic states with
comparable statistical probability. Furthermore, it was found that the process
of the bond formation between the iron-porphyrin complex and the oxygen
molecule is more complex than a simple high-spin to low-spin state of the Fe
ion transition. The transition metal ion oxidation is accompanied by
substantial redistribution of the states probabilities and the increasing of
the entanglement degree. This process also leads to the reduction of the total
spin moment from $s\approx$2.1 for the FeP(Im) to $s\approx$1.7 for the
FeP(Im)(O$_2$).",1602.02963v2
2016-03-29,"Spin crossover in (Mg,Fe$^{3+}$)(Si,Fe$^{3+}$)O$_3$ bridgmanite: effects of disorder, iron concentration, and temperature","The spin crossover of iron in Fe$^{3+}$-bearing bridgmanite, the most
abundant mineral of the Earth's lower mantle, is by now a well-established
phenomenon, though several aspects of this crossover remain unclear. Here we
investigate effects of disorder, iron concentration, and temperature on this
crossover using ab initio LDA + U$_{sc}$ calculations. The effect of
concentration and disorder are addressed using complete statistical samplings
of coupled substituted configurations in super-cells containing up to 80 atoms.
Vibrational/thermal effects on the crossover are addressed within the
quasiharmonic approximation. The effect of disorder seems quite small, while
increasing iron concentration results in considerable increase in crossover
pressure. Our calculated compression curves for iron-free, Fe$^{2+}$-, and
Fe$^{3+}$-bearing bridgmanite compare well with the latest experimental
measurements. The comparison also suggests that in a close system, Fe$^{2+}$
present in the sample may transform into Fe$^{3+}$ by introduction of Mg and O
vacancies with increasing pressure. As in the spin crossover in ferropericlase,
this crossover in bridgmanite is accompanied by a clear volume reduction and an
anomalous softening of the bulk modulus throughout the crossover pressure
range. These effects reduce significantly with increasing temperature. Though
the concentration of [Fe$^{3+}$]$_{Si}$ in bridgmanite may be small, related
elastic anomalies may impact the interpretation of radial and lateral velocity
structures of the Earth's lower mantle.",1603.08947v1
2016-04-28,On the evolution of the inner disk radius with flux in the neutron star low-mass X-ray binary Serpens X-1,"We analyze the latest \emph{Suzaku} observation of the bright neutron star
low-mass X-ray binary Serpens X-1 taken in 2013 October and 2014 April. The
observation was taken using the burst mode and only suffered mild pile-up
effects. A broad iron line is clearly detected in the X-ray spectrum. We test
different models and find that the iron line is asymmetric and best interpreted
by relativistic reflection. The relativistically broadened iron line is
generally believed to originate from the innermost regions of the accretion
disk, where strong gravity causes a series of special and general relativistic
effects. The iron line profile indicates an inner radius of $\sim8$ $R_{\rm
G}$, which gives an upper limit on the size of the neutron star. The asymmetric
iron line has been observed in a number of previous observations, which gives
several inner radius measurements at different flux states. We find that the
inner radius of Serpens X-1 does not evolve significantly over the range of
$L/L_{\rm Edd}\sim0.4-0.6$, and the lack of flux dependence of the inner radius
implies that the accretion disk may be truncated outside the innermost stable
circular orbit by the boundary layer rather than the stellar magnetic field.",1604.08626v2
2016-06-08,A critical look at the merger scenario to explain multiple populations and rotation in iron-complex globular clusters,"Merging has been proposed to explain multiple populations in globular
clusters (GCs) where there is a spread in iron abundance (hereafter,
iron-complex GCs). By means of N-body simulations, we investigate if merging is
consistent with the observations of sub-populations and rotation in
iron-complex GCs. The key parameters are the initial mass and density ratios of
the progenitors. When densities are similar, the more massive progenitor
dominates the central part of the merger remnant and the less massive
progenitor forms an extended rotating population. The low-mass progenitor can
become the majority population in the central regions of the merger remnant
only if its initial density is higher by roughly the mass ratio. To match the
radial distribution of multiple populations in two iron-complex GCs ({\omega}
Cen and NGC 1851), the less massive progenitor needs to be four times as dense
as the larger one. Our merger remnants show solid-body rotation in the inner
parts, becoming differential in the outer parts. Rotation velocity V and
ellipticity {\epsilon} are in agreement with models for oblate rotators with
isotropic dispersion. We discuss several kinematic signatures of a merger with
a denser lower mass progenitor that can be tested with future observations.",1606.02743v1
2016-07-30,Observation of the anisotropic Dirac cone in the band dispersion of 112-structured iron-based superconductor Ca0.9La0.1FeAs2,"CaFeAs2 is a parent compound of recently discovered 112-type iron-based
superconductors. It is predicted to be a staggered intercalation compound that
naturally integrates both quantum spin Hall insulating and superconducting
layers and an ideal system for the realization of Majorana modes. We performed
a systematical angle-resolved photoemission spectroscopy and first-principle
calculation study of the slightly electron-doped CaFeAs2. We found that the
zigzag As chain of 112-type iron-based superconductors play a considerable role
in the low-energy electronic structure, resulting in the characteristic
Dirac-cone like band dispersion as the prediction. Our experimental results
further confirm that these Dirac cones only exists around the X but not Y
points in the Brillouin zone, breaking the S4 symmetry at iron sites. Our
findings present the compelling support to the theoretical prediction that the
112-type iron-based superconductors might host the topological nontrivial edge
states. The slightly electron doped CaFeAs2 would provide us a unique
opportunity to realize and explore Majorana fermion physics.",1608.00072v1
2016-11-23,High-Tc superconductivity in FeSe at high pressure: Dominant hole carriers and enhanced spin fluctuations,"The importance of electron-hole interband interactions is widely acknowledged
for iron-pnictide superconductors with high transition temperatures (Tc).
However, high-Tc superconductivity without hole carriers has been suggested in
FeSe single-layer films and intercalated iron-selenides, raising a fundamental
question whether iron pnictides and chalcogenides have different pairing
mechanisms. Here, we study the properties of electronic structure in the
high-Tc phase induced by pressure in bulk FeSe from magneto-transport
measurements and first-principles calculations. With increasing pressure, the
low-Tc superconducting phase transforms into high-Tc phase, where we find the
normal-state Hall resistivity changes sign from negative to positive,
demonstrating dominant hole carriers in striking contrast to other FeSe-derived
high-Tc systems. Moreover, the Hall coefficient is remarkably enlarged and the
magnetoresistance exhibits anomalous scaling behaviors, evidencing strongly
enhanced interband spin fluctuations in the high-Tc phase. These results in
FeSe highlight similarities with high-Tc phases of iron pnictides, constituting
a step toward a unified understanding of iron-based superconductivity.",1611.07973v1
2017-03-09,Orbital selective pairing and superconductivity in iron selenides,"An important challenge in condensed matter physics is understanding
iron-based superconductors. Among these systems, the iron selenides hold the
record for highest superconducting transition temperature and pose especially
striking puzzles regarding the nature of superconductivity. The pairing state
of the alkaline iron selenides appears to be of $d$-wave type based on the
observation of a resonance mode in neutron scattering, while it seems to be of
$s$-wave type from the nodeless gaps observed everywhere on the Fermi surface
(FS). Here we propose an orbital-selective pairing state, dubbed $s \tau_{3}$,
as a natural explanation of these disparate properties. The pairing function,
containing a matrix $\tau_{3}$ in the basis of $3d$-electron orbitals, does not
commute with the kinetic part of the Hamiltonian. This dictates the existence
of both intraband and interband pairing terms in the band basis. A spin
resonance arises from a $d$-wave-type sign change in the intraband pairing
component whereas the quasiparticle excitation is fully gapped on the FS due to
an $s$-wave-like form factor associated with the addition in quadrature of the
intraband and interband pairing terms. We demonstrate that this pairing state
is energetically favored when the electron correlation effects are orbitally
selective. More generally, our results illustrate how the multiband nature of
correlated electrons affords unusual types of superconducting states, thereby
shedding new light not only on the iron-based materials but also on a broad
range of other unconventional superconductors such as heavy fermion and organic
systems.",1703.03170v1
2017-04-18,Unified phase diagram for iron-based superconductors,"High-temperature superconductivity is closely adjacent to a long-range
antiferromagnet, which is called a parent compound. In cuprates, all parent
compounds are alike and carrier doping leads to superconductivity, so a unified
phase diagram can be drawn. However, the properties of parent compounds for
iron-based superconductors show significant diversity and both carrier and
isovalent dopings can cause superconductivity, which casts doubt on the idea
that there exists a unified phase diagram for them. Here we show that the
ordered moments in a variety of iron pnictides are inversely proportional to
the effective Curie constants of their nematic susceptibility. This unexpected
scaling behavior suggests that the magnetic ground states of iron pnictides can
be achieved by tuning the strength of nematic fluctuations. Therefore, a
unified phase diagram can be established where superconductivity emerges from a
hypothetical parent compound with a large ordered moment but weak nematic
fluctuations, which suggests that iron-based superconductors are strongly
correlated electron systems.",1704.05182v2
2017-07-04,Optical properties of non-stoichiometric amorphous silicates with application to circumstellar dust extinction,"Optical constants of non-stoichiometric amorphous magnesium-iron silicates
are determined. It is demonstrated that these can well reproduce the observed
mid-infrared emission spectra of evolved stars. Stoichiometric and
non-stoichiometric amorphous magnesium-iron silicate films are fabricated by
pulsed laser deposition. Transmittance and ellipsometry measurements are
performed in the wavelength range between 2 and 200 $\mu$m and 1.7 and 33
$\mu$m, respectively. Optical constants are derived from transmittance and
ellipsometric $\Psi$ and $\Delta$ spectra by means of oscillator models. The
optical constants are applied in radiative transfer models for examining
reproducibility of the observed spectral features of circumstellar dust shells
around supergiants. The spectra of four selected supergiants are dominated by
amorphous silicate dust emission in the wavelength range of 9 and 25 $\mu$m. To
obtain a good fit to the observed spectra, we take into account amorphous
corundum and metallic iron particles as additional dust components to account
for dust emission at $\lambda<8 \mu$m and in between the two silicate features.
For each of the objects, a set of model parameters (dust mass, condensation
temperature) is derived by an automated optimization procedure which well
reproduces the observation. Consequently, our model spectra using the new
optical data find that the silicate bands at $\approx 10$ and $\approx 18 \mu$m
depend on the magnesium and iron ratio in the silicate system, and that a good
fit requires a significant iron content of the amorphous silicate dust
component to reproduce the observed peak positions and shape of the silicate
bands.",1707.00903v1
2017-10-05,Whether it is possible to stabilize the 1144-phase pnictides with tri-valence cations?,"The 1144 iron arsenide (e.g. CaKFe4As4) has recently been discovered and
inspired a tide of search for superconductors. Such far, the discovered
compounds are confined to iron arsenides (ABFe4As4), where A and B are either
alkali metals or alkaline earth elements. In this work, we propose two
directions in searching 1144 structures: (i) using tri-valence cations for A;
(ii) substituting the transition metal, e.g. replacing Fe by Co. Following the
two directions, we employ density functional theory to study stability and
electronic structures of 1144 pnictides of various tri-valence cations (La, Y,
In, Tl, Sm and Gd), as well as cobalt arsenides. For LaAFe4As4, the 1144 phase
can be stabilized in three systems: LaKFe4As4, LaRbFe4As4 and LaCsFe4As4, which
show quasi-two-dimensional semi-metal features similar to the iron pnictide
superconductors: hole-type Fermi surface at Gama point and electron-type Fermi
surface at M point in B.Z. In addition, LaKFe4As4 feature an extra bubble
shaped Fermi surface sheets, distinct from the other two peers. Y does not
support any 1144 phase within our search. For In and Tl, substitute Fe by Co
and two unknown compounds of the 122 phase are stabilized: InCo2As2 and
TlCo2As2. The two cobalt arsenides have Fermi surfaces of similar topology as
iron arsenides, but the Fermi surfaces are all electron-type, showing
potentials to be undiscovered superconductors. Stable 1144 phases are also
found in InKCo4As4 and InRbCo4As4. For Sm and Gd, most 1144 and 122 iron
arsenides are found unstable.",1710.01868v2
2018-02-28,The Coulomb problem in iron based superconductors,"We discuss the role of strong Coulomb interactions in iron-based
superconductors (FeSCs). The presumed $s^{\pm}$ character of these
superconductors means that the condensate is not symmetry protected against
Coulomb repulsion. Remarkably, the transition temperatures and the excitation
gap are quite robust across the large family of iron based superconductors,
despite drastic changes in Fermi surface geometry. The Coulomb problem is to
understand how these superconductors avoid the strong onsite Coulomb
interaction at the iron atoms, while maintaining a robust transition
temperature. Within the dominant space of $t_{2g}$ orbitals, on-site repulsion
in the FeSCs enforces two linearly independent components of the condensate to
vanish. This raises the possibility that iron-based superconductors might adapt
their condensate to the Coulomb constraints by rotating the pairing state
within the large manifold of entangled, extended s-wave gap functions with
different orbital and momentum space structure. We examine this ""orbital and
k-space flexibility"" (OKF) mechanism using both Landau theory and microscopic
calculations within a multi-orbital t-J model. Based on our results, we
conclude that OKF necessitates a large condensate degeneracy. One interesting
possibility raised by our results, is that a resolution to the Coulomb problem
in FeSC might require a reconsideration of triplet pairing.",1802.10580v3
2018-03-02,"Direct observation of multiple topological phases in the iron-based superconductor Li(Fe,Co)As","Topological insulators/semimetals and unconventional iron-based
superconductors have attracted major attentions in condensed matter physics in
the past 10 years. However, there is little overlap between these two fields,
although the combination of topological states and superconducting states will
produce more exotic topologically superconducting states and Majorana bound
states (MBS), a promising candidate for realizing topological quantum
computations. With the progress in laser-based spin-resolved and angle-resolved
photoemission spectroscopy (ARPES) with very high energy- and
momentum-resolution, we directly resolved the topological insulator (TI) phase
and topological Dirac semimetal (TDS) phase near Fermi level ($E_F$) in the
iron-based superconductor Li(Fe,Co)As. The TI and TDS phases can be separately
tuned to $E_F$ by Co doping, allowing a detailed study of different
superconducting topological states in the same material. Together with the
topological states in Fe(Te,Se), our study shows the ubiquitous coexistence of
superconductivity and multiple topological phases in iron-based
superconductors, and opens a new age for the study of high-Tc iron-based
superconductors and topological superconductivity.",1803.00846v1
2018-06-06,First-principles calculations of iron-hydrogen reactions in silicon,"Controlling the contamination of silicon materials by iron, especially
dissolved interstitial iron (Fe$_{\mathrm{i}}$), is a longstanding problem with
recent developments and several open issues. Among these we have the question
whether hydrogen can assist iron diffusion, or if significant amounts of
substitutional iron (Fe$_{\mathrm{s}}$) can be created. Using density
functional calculations we explore the structure, formation energies, binding
energies, migration, and electronic levels of several FeH complexes in Si. We
find that a weakly bound Fe$_{\mathrm{i}}$H pair has a migration barrier close
to that of isolated Fe$_{\mathrm{i}}$ and a donor level at
$E_{\mathrm{v}}+0.5$~eV. Conversely, Fe$_{\mathrm{i}}$H$_{2}(0/+)$ is estimated
at $E_{\mathrm{v}}+0.33$~eV. These findings suggest that the hole trap at
$E_{\mathrm{v}}+0.32$~eV measured by capacitance measurements should be
assigned to Fe$_{\mathrm{i}}$H$_{2}$ . Fe$_{\mathrm{s}}$H-related complexes
show only deep acceptor activity and are expected to have little effect on
minority carrier life-time in $p$-type Si. The opposite conclusion can be drawn
for $n$-type Si. We find that while in H-free material Fe$_{\mathrm{i}}$
defects have lower formation energy than Fe$_{\mathrm{s}}$, in hydrogenated
samples Fe$_{\mathrm{s}}$-related defects become considerably more stable. This
would explain the observation of an EPR signal attributed to a
Fe$_{\mathrm{s}}$H-related complex in hydrogenated Si, which was quenched from
above 1000$^{\circ}$C to iced-water temperature.",1806.02249v2
2018-08-16,Atomic iron and titanium in the atmosphere of the exoplanet KELT-9b,"The chemical composition of an exoplanet is a key ingredient in constraining
its formation history. Iron is the most abundant transition metal, but has
never been directly detected in an exoplanet due to its highly refractory
nature. KELT-9b (HD 195689b) is the archetype of the class of ultra-hot
Jupiters that straddle the transition between stars and gas-giant exoplanets
and serve as distinctive laboratories for studying atmospheric chemistry,
because of its high equilibrium temperature of 4050 +/- 180 K. These properties
imply that its atmosphere is a tightly constrained chemical system that is
expected to be nearly in chemical equilibrium and cloud-free. It was previously
predicted that the spectral lines of iron will be detectable in the visible
range of wavelengths. At these high temperatures, iron and several other
transition metals are not sequestered in molecules or cloud particles and exist
solely in their atomic forms. Here, we report the direct detection of atomic
neutral and singly-ionized iron (Fe and Fe+), and singly-ionized titanium (Ti+)
in KELT-9b via the cross-correlation technique applied to high-resolution
spectra obtained during the primary transit of the exoplanet.",1808.05653v1
2019-04-15,Using the infrared iron lines to probe solar subsurface convection,"Studying the properties of the solar convection using high-resolution
spectropolarimetry began in the early 90's with the focus on observations in
the visible wavelength regions. Its extension to the infrared (IR) remains
largely unexplored. The IR iron lines around 15600\,$\rm{\AA}$, most commonly
known for their high magnetic sensitivity, also have a non-zero response to
line-of-sight velocity below $\log (\tau)=0.0$. In this paper we aim to tap
this potential to explore the possibility of using them to measure sub-surface
convective velocities. By assuming a snapshot of a three-dimensional
magnetohydrodynamic simulation to represent the quiet Sun, we investigate how
well the iron IR lines can reproduce the LOS velocity in the cube and up to
what depth. We use the recently developed spectropolarimetric inversion code
SNAPI and discuss the optimal node placements for the retrieval of reliable
results from these spectral lines. We find that the IR iron lines can measure
the convective velocities down to $\log (\tau)=0.5$, below the photosphere, not
only at original resolution of the cube but also when degraded with a
reasonable spectral and spatial PSF and stray light. Meanwhile, the commonly
used Fe~{\sc i} 6300\,\AA{} line pair performs significantly worse. Our
investigation reveals that the IR iron lines can probe the subsurface
convection in the solar photosphere. This paper is a first step towards
exploiting this diagnostic potential.",1904.07306v1
2019-05-21,Impact of the fac/mer isomerism on the excited states dynamics of pyridyl-carbene Fe(II) complexes,"The control of photophysical properties of iron complexes and especially of
their excited states decay is a great challenge in the search for sustainable
alternatives to noble metals in photochemical applications. Herein we report
the synthesis and investigations of the photophysics of mer and fac iron
complexes bearing bidentate pyridyl-NHC ligands, coordinating the Fe with three
ligand-field enhancing carbene bonds. Ultrafast transient absorption
spectroscopy reveals two distinct excited state populations for both mer and
fac forms, ascribed to the populations of the T1 and the T2 states,
respectively, which decay to the ground state via parallel pathways. We find
3-4 ps and 15-20 ps excited state lifetimes, with respective amplitudes
depending on the isomer. The longer lifetime exceeds the one reported for iron
complexes with tridentate ligands analogues involving four iron-carbene bonds.
By combining experimental and computational results, a mechanism based on the
differential trapping of the triplet states in spin-crossover regions is
proposed for the first time to explain the impact of the fac/mer isomerism on
the overall excited-state lifetimes. Our results clearly highlight the impact
of bidentate Pyridyl-NHC ligands on the photophysics of iron complexes,
especially the paramount role of fac/mer isomerism in modulating the overall
decay process, which can be potentially exploited in the design of new
Fe(II)-based photoactive compound.",1905.08858v1
2019-10-03,Decoupling of Lattice and Orbital Degrees of Freedom in an Iron-Pnictide Superconductor,"The interplay of structural and electronic phases in iron-based
superconductors is a central theme in the search for the superconducting
pairing mechanism. While electronic nematicity, defined as the breaking of
four-fold symmetry triggered by electronic degrees of freedom, is competing
with superconductivity, the effect of purely structural orthorhombic order is
unexplored. Here, using x-ray diffraction (XRD), we reveal a new structural
orthorhombic phase with an exceptionally high onset temperature
($T_\mathrm{ort} \sim 250$ K), which coexists with superconductivity
($T_\mathrm{c} = 25$ K), in an electron-doped iron-pnictide superconductor far
from the underdoped region. Furthermore, our angle-resolved photoemission
spectroscopy (ARPES) measurements demonstrate the absence of electronic nematic
order as the driving mechanism, in contrast to other underdoped iron pnictides
where nematicity is commonly found. Our results establish a new, high
temperature phase in the phase diagram of iron-pnictide superconductors and
impose strong constraints for the modeling of their superconducting pairing
mechanism.",1910.01639v2
2020-02-05,Spin Resonances in Iron-Selenide High-Tc Superconductors by Proximity to Hidden Spin Density Wave,"Recent inelastic neutron scattering studies by Pan et al., Nature
Communications 8, 123 (2017), find evidence for spin excitations at energies
above the quasi-particle gap in an iron-selenide high-Tc superconductor. The
momenta of the spin excitations form a diamond around the checkerboard
wavevector, Q_AF, that is associated with the square lattice of iron atoms that
makes up the system. It has been suggested that such a ""hollowed-out""
spin-excitation spectrum is due to hidden Neel order. We study such a hidden
spin-density wave (hSDW) state that results from nested Fermi surfaces at the
center and at the corner of the unfolded Brillouin zone. It emerges within mean
field theory from an extended Hubbard model over a square lattice of iron atoms
that contain the minimal d_xz and d_yz orbitals. Opposing Neel order exists
over the isotropic d+ = d_xz + i d_yz and d- = d_xz - i d_yz orbitals. The
dynamical spin susceptibility of the hSDW is computed within the random phase
approximation, at perfect nesting. Unobservable Goldstone modes that disperse
acoustically are found at Q_AF. A threshold is found in the spectrum of
observable spin excitations that forms a ""floating ring"" at Q_AF also. The ring
threshold moves down in energy toward zero with increasing Hund's Rule
coupling, while it moves up in energy with increasing magnetic frustration.
Comparison with the normal-state features of the spin-excitation spectrum shown
by electron-doped iron selenide is made. Also, recent predictions of a Lifshitz
transition from the nested Fermi surfaces to Fermi surface pockets at the
corner of the folded Brillouin zone will be discussed.",2002.01732v2
2020-10-01,A Molecular Dynamics Investigation of Mechanical Properties of Graphene Reinforced Iron Composite and The Effect of Vacancy Defect Distance from the Matrix-Fiber Interface,"Graphene is a material of excellent mechanical properties, which make it an
ideal fiber for reinforcing metal. Since iron is the most used metal in the
world, reinforcing iron with graphene can reduce the overall requirement of
material in any application where strength is demanded. However, the effect of
graphene reinforcement on the mechanical properties of iron needs to be known
before the industrial application of the composite. In this paper, we have
investigated the mechanical properties of graphene-reinforced iron composite by
Molecular Dynamics (MD) method for various conditions. The properties were
investigated by applying uniaxial tension on a modeled representative volume
element (RVE). The effect of temperature on the mechanical property of the
composite was also studied because the knowledge is required for manufacturing
products with the composite operating at a wide temperature range. MD analysis
also revealed that the initiation of fracture is from the matrix-fiber
interface. We also investigated how the distance of vacancy defects from the
matrix-fiber interface affects the mechanical properties of the composite,
which can be used to select a suitable manufacturing process. The results
obtained from this study show that vacancy defects lower the strength at a
greater extent as it gets closer to the interface.",2010.00274v1
2021-06-04,Magnetic states of quasi-one-dimensional iron chalcogenide Ba$_2$FeS$_3$,"Quasi-one-dimensional iron-based ladders and chains, with the 3$d$ iron
electronic density $n = 6$, are attracting considerable attention. Recently, a
new iron chain system Ba$_2$FeS$_3$, also with $n = 6$, was prepared under
high-pressure and high-temperature conditions. Here, the magnetic and
electronic phase diagrams are theoretically studied for this
quasi-one-dimensional compound. Based on first-principles calculations, a
strongly anisotropic one-dimensional electronic band behavior near the Fermi
level was observed. In addition, a three-orbital electronic Hubbard model for
this chain was constructed. Introducing the Hubbard and Hund couplings and
studying the model via the density matrix renormalization group (DMRG) method,
we studied the ground-state phase diagram. A robust staggered
$\uparrow$-$\downarrow$-$\uparrow$-$\downarrow$ AFM region was unveiled in the
chain direction, consistent with our density functional theory (DFT)
calculations. Furthermore, at intermediate Hubbard $U$ coupling strengths, this
system was found to display an orbital selective Mott phase (OSMP) with one
localized orbital and two itinerant metallic orbitals. At very large $U/W$ ($W$
= bandwidth), the system displays Mott insulator characteristics, with two
orbitals half-filled and one doubly occupied. Our results for high pressure
Ba$_2$FeS$_3$ provide guidance to experimentalists and theorists working on
this one-dimensional iron chalcogenide chain material.",2106.02753v2
2021-07-29,Modelling disease progression with multi-level electronic health records data and informative observation times: an application to treating iron deficiency anaemia in primary care of the UK,"Modelling disease progression of iron deficiency anaemia (IDA) following oral
iron supplement prescriptions is a prerequisite for evaluating the
cost-effectiveness of oral iron supplements. Electronic health records (EHRs)
from the Clinical Practice Research Datalink (CPRD) provide rich longitudinal
data on IDA disease progression in patients registered with 663 General
Practitioner (GP) practices in the UK, but they also create challenges in
statistical analyses. First, the CPRD data are clustered at multi-levels (i.e.,
GP practices and patients), but their large volume makes it computationally
difficult to implement estimation of standard random effects models for
multi-level data. Second, observation times in the CPRD data are irregular and
could be informative about the disease progression. For example, shorter/longer
gap times between GP visits could be associated with deteriorating/improving
IDA. Existing methods to address informative observation times are mostly based
on complex joint models, which adds more computational burden. To tackle these
challenges, we develop a computationally efficient approach to modelling
disease progression with EHRs data while accounting for variability at
multi-level clusters and informative observation times. We apply the proposed
method to the CPRD data to investigate IDA improvement and treatment
intolerance following oral iron prescriptions in primary care of the UK.",2107.13956v1
2021-10-27,Globular Cluster Intrinsic Iron Abundance Spreads: II. Protocluster Metallicities and the Age-Metallicity Relations of Milky Way Progenitors,"Intrinsic iron abundance spreads in globular clusters, although usually
small, are very common, and are signatures of self enrichment: some stars
within the cluster have been enriched by supernova ejecta from other stars
within the same cluster. We use the Bailin (2018) self enrichment model to
predict the relationship between properties of the protocluster -- its mass and
the metallicity of the protocluster gas cloud -- and the final observable
properties today -- its current metallicity and the internal iron abundance
spread. We apply this model to an updated catalog of Milky Way globular
clusters where the initial mass and/or the iron abundance spread is known to
reconstruct their initial metallicities. We find that with the exception of the
known anomalous bulge cluster Terzan 5 and three clusters strongly suspected to
be nuclear star clusters from stripped dwarf galaxies, the model provides a
good lens for understanding their iron spreads and initial metallicities. We
then use these initial metallicities to construct age-metallicity relations for
kinematically-identified major accretion events in the Milky Way's history. We
find that using the initial metallicity instead of the current metallicity does
not alter the overall picture of the Milky Way's history, since the difference
is usually small, but does provide information that can help distinguish which
accretion event some individual globular clusters with ambiguous kinematics
should be associated with, and points to potential complexity within the
accretion events themselves.",2110.14571v1
2021-12-08,Prediction of orbital selective Mott phases and block magnetic states in the quasi-one-dimensional iron chain Ce$_2$O$_2$FeSe$_2$ under hole and electron doping,"The recent detailed study of quasi-one-dimensional iron-based ladders, with
the $3d$ iron electronic density $n = 6$, has unveiled surprises, such as
orbital-selective phases. However, similar studies for $n=6$ iron chains are
still rare. Here, a three-orbital electronic Hubbard model was constructed to
study the magnetic and electronic properties of the quasi-one-dimensional $n=6$
iron chain Ce$_2$O$_2$FeSe$_2$, with focus on the effect of doping.
Specifically, introducing the Hubbard $U$ and Hund $J_{H}$ couplings and
studying the model via the density matrix renormalization group, we report the
ground-state phase diagram varying the electronic density away from $n=6$. For
the realistic Hund coupling $J_{H}/U = 1/4$, several electronic phases were
obtained, including a metal, orbital-selective Mott, and Mott insulating
phases. Doping away from the parent phase, the competition of many tendencies
leads to a variety of magnetic states, such as ferromagnetism, as well as
several antiferromagnetic and magnetic ""block"" phases. In the hole-doping
region, two different interesting orbital-selective Mott phases were found:
OSMP1 (with one localized orbital and two itinerant orbitals) and OSMP2 (with
two localized orbitals and one itinerant orbital). Moreover, charge
disproportionation phenomena were found in special doping regions. We argue
that our predictions can be tested by simple modifications in the original
chemical formula of Ce$_2$O$_2$FeSe$_2$.",2112.04049v1
2022-01-07,First-principles study on the solute-induced low diffusion and self-trapping of helium in fcc iron,"The addition of alloying elements plays an essential role in helium (He)
behaviours produced by transmutation in metal alloys. Effects of solutes (Ni,
Cr, Ti, P, Si, C) on the behaviours of He and He-He pair in face-centred cube
(fcc) iron have been investigated using first-principles calculations based on
density functional theory (DFT). For the interactions of solutes and He, we
found that Ti, P, Si, and C attracts He is more potent than Ni and Cr in fcc
iron. We have determined the most stable configuration for the He-He pair,
which is the Hesub-Hetetra pair with a binding energy of 1.60 eV. In
considering the effect of solutes on the stability of the He-He pair, we have
proposed a unique definition of binding energy. By applying the definition, we
suggest that Ti and P could weaken He self-trapping, and Cr and C are
beneficial for He self-trapping, while Ni is similar to the matrix Fe itself.
For the diffusion of He, which is the necessary process of forming the He
bubble, we determined that the most stable interstitial He is in a tetrahedral
site and could migrate with the energy barrier of 0.16 eV in pure fcc iron. We
further found that Ti and Si can increase the barrier to 0.18 and 0.20 eV; on
the contrary, Cr and P decrease the barrier to 0.10 and 0.06 eV, respectively.
Summarizing the calculations, we conclude that Ti decreases while Cr increases
the diffusion and self-trapping of He in fcc iron.",2201.02423v1
2022-02-17,Helium absorption in exoplanet atmospheres is connected to stellar coronal abundances,"Transit observations in the helium triplet around 10830 Angstrom are a
successful tool to study exoplanetary atmospheres and their mass loss. Forming
those lines requires ionisation and recombination of helium in the exoplanetary
atmosphere. This ionisation is caused by stellar photons at extreme
ultra-violet (EUV) wavelengths; however, no currently active telescopes can
observe this part of the stellar spectrum. The relevant part of the stellar EUV
spectrum consists of individual emission lines, many of them being formed by
iron at coronal temperatures. The stellar iron abundance in the corona is often
observed to be depleted for high-activity low-mass stars due to the first
ionisation potential (FIP) effect. I show that stars with high versus low
coronal iron abundances follow different scaling laws that tie together their
X-ray emission and the narrow-band EUV flux that causes helium ionisation. I
also show that the stellar iron to oxygen abundance ratio in the corona can be
measured reasonably well from X-ray CCD spectra, yielding similar results to
high-resolution X-ray observations. Taking coronal iron abundance into account,
the currently observed large scatter in the relationship of EUV irradiation
with exoplanetary helium transit depths can be reduced, improving the target
selection criteria for exoplanet transmission spectroscopy. In particular,
previously puzzling non-detections of helium for Neptunic exoplanets are now in
line with expectations from the revised scaling laws.",2202.08838v1
2022-05-24,Iron as a sustainable chemical carrier of renewable energy: Analysis of opportunities and challenges for retrofitting coal-fired power plants,"As a result of the 2021 United Nations Climate Change Conference (COP26),
several countries committed to phasing down coal electricity as soon as
possible, deactivating hundreds of power plants in the near future. CO$_2$-free
electricity can be generated in these plants by retrofitting them for iron
combustion. Iron oxides produced during the process can be collected and
reduced back to metallic iron using H$_2$, in a circular process where it
becomes an energy carrier. Using clean energy in the recycling process enables
storage and distribution of excess generated in periods of abundance. This
concept uses and scales up existing dry metal cycle technologies, which are the
focus of extensive research worldwide. Retrofitting is evaluated here to
determine feasibility of adding these material requirements to markets, in the
context of current plans for decarbonization of steel industry, and policies on
hydrogen and renewable electricity. Results indicate that not only for a single
power plant, but also on larger scales, the retrofitting plan is viable,
promoting and supporting advancements in sustainable electricity, steel
industry and hydrogen production, converging necessary technological and
construction efforts. The maturation and first commercial-scale application of
iron combustion technology by 2030, together with developing necessary
reduction infrastructure over the next decades, would pave the way for
large-scale retrofitting and support the phasing out of coal in many regions.
The proposed plan represents a feasible solution that takes advantage of
existing assets, creates a long-lasting legacy for the industry and establishes
circular energy economies that increase local energy security.",2205.11944v1
2022-11-10,Inferring Type II-P Supernova Progenitor Masses from Plateau Luminosities,"Connecting observations of core-collapse supernova explosions to the
properties of their massive star progenitors is a long-sought, and challenging,
goal of supernova science. Recently, Barker et al. (2022) presented bolometric
light curves for a landscape of progenitors from spherically symmetric
neutrino-driven core-collapse supernova (CCSN) simulations using an effective
model. They find a tight relationship between the plateau luminosity of the
Type II-P CCSN light curve and the terminal iron core mass of the progenitor.
Remarkably, this allows us to constrain progenitor properties with photometry
alone. We analyze a large observational sample of Type II-P CCSN light curves
and estimate a distribution of iron core masses using the relationship of
Barker et al 2022. The inferred distribution matches extremely well with the
distribution of iron core masses from stellar evolutionary models, and namely,
contains high-mass iron cores that suggest contributions from very massive
progenitors in the observational data. We use this distribution of iron core
masses to infer minimum and maximum mass of progenitors in the observational
data. Using Bayesian inference methods to locate optimal initial mass function
parameters, we find M$_{\mathrm{min}}=9.8^{+0.37}_{-0.27}$ and
M$_{\mathrm{max}}=24.0^{+3.9}_{-1.9}$ solar masses for the observational data.",2211.05789v2
2022-12-13,Antiferromagnetic iron based magnetoelectric compounds,"The Landau free-energy of a compound that benefits from a linear coupling of
an electric field and a magnetic field includes a product of the two fields,
one polar and time-even and one axial and time-odd. In ME compounds,
expectation values of some atomic magnetic tensors are invariant with respect
to anti-inversion. An invariance shared by the Dirac monopole (an element of
charge allowed in Maxwell's equations that has not been observed) and a
Zeldovich anapole, also known as a Dirac dipole. From the science of materials
perspective, it has been established that Dirac multipoles contribute to the
diffraction of x-rays and neutrons. We identify Dirac monopoles in bulk
magnetic properties of iron tellurate (Fe2TeO6) and a spin ladder (SrFe2S2O).
Both cited compounds present a simple antiferromagnetic configuration of axial
dipoles, and their different magnetic crystal classes allow a linear ME effect.
However, the Kerr effect is symmetry allowed in the spin ladder and forbidden
in iron tellurate. Anapoles are forbidden in iron tellurate and allowed in the
spin ladder compound, a difference evident in diffraction patterns fully
informed by symmetry. More generally, we identify a raft of Dirac multipoles,
and axial multipoles beyond dipoles, visible in future experiments using
standard techniques with beams of neutrons or x-rays tuned in energy to an iron
atomic resonance. ME invariance imposes a phase relationship between nuclear
(charge) and magnetic contributions to neutron (x-ray) diffraction amplitudes.
In consequence, intensities of Bragg spots in an x-ray pattern do not change
when helicity in the primary beam is reversed. A like effect occurs in the
magnetic diffraction of polarized neutrons.",2212.06403v1
2022-12-20,Numerical modeling of pulverized iron flames in a multidimensional hot counterflow burner,"Pulverized iron flames stabilized in a multidimensional hot counterflow
burner are simulated using a numerical model, which is extended from the
state-of-the-art model developed by Hazenberg and van Oijen (PCI, 2021)
considering unsteady effects. The results are compared to available
experimental data (McRae et al., PCI, 2019), including particle image
velocimetry measurements, a direct flame photo, the flow field velocity and the
flame speed for different iron and oxygen concentrations. The comparison shows
that the particle dynamics and flame shape can be reasonably well predicted.
The flow field velocity and flame speed also show quantitative agreement
between the simulation and the experiment. Based on the validated simulation
results, the iron combustion characteristics, including the thermal structures
and the multidimensional effects, are analyzed for different oxidizer
environments. The analysis shows that the iron particles undergo a transition
from kinetic-controlled regime (up to ignition) to a diffusion-controlled
regime (burning) at the central axis for both environments with the particle
temperature being higher than the gas temperature at the flame front, which is
indicated by the Damk\""ohler number. For the hot counterflow burner, there
exist multidimensional effects, i.e., the temperature and Damk\""ohler number
change along the radial direction.",2212.10226v1
2023-02-27,Searching for iron nanoparticles with a general-purpose Gaussian approximation potential,"We present a general-purpose machine learning Gaussian approximation
potential (GAP) for iron that is applicable to all bulk crystal structures
found experimentally under diverse thermodynamic conditions, as well as
surfaces and nanoparticles (NPs). By studying its phase diagram, we show that
our GAP remains stable at extreme conditions, including those found in the
Earth's core. The new GAP is particularly accurate for the description of NPs.
We use it to identify new low-energy NPs, whose stability is verified by
performing density functional theory calculations on the GAP structures. Many
of these NPs are lower in energy than those previously available in the
literature up to $N_\text{atoms}=100$. We further extend the convex hull of
available stable structures to $N_\text{atoms}=200$. For these NPs, we study
characteristic surface atomic motifs using data clustering and low-dimensional
embedding techniques. With a few exceptions, e.g., at magic numbers
$N_\text{atoms}=59$, $65$, $76$ and $78$, we find that iron tends to form
irregularly shaped NPs without a dominant surface character or characteristic
atomic motif, and no reminiscence of crystalline features. We hypothesize that
the observed disorder stems from an intricate balance and competition between
the stable bulk motif formation, with bcc structure, and the stable surface
motif formation, with fcc structure. We expect these results to improve our
understanding of the fundamental properties and structure of low-dimensional
forms of iron, and to facilitate future work in the field of iron-based
catalysis.",2302.13722v2
2023-03-07,The potential of retrofitting existing coal power plants: a case study for operation with green iron,"Storing electrical energy for long periods and transporting it over long
distances is an essential task of the necessary transition to a CO$_2$-free
energy economy. An oxidation-reduction cycle based on iron and its oxides
represents a very promising technology in this regard. The present work
assesses the potential of converting an existing modern coal-fired power plant
to operation with iron. For this purpose, a systematic retrofit study is
carried out, employing a model that balances all material and energy fluxes in
a state-of-the-art coal-fired power plant. Particular attention is given to
components of the burner system and the system$'$s heat exchanger. The analysis
provides evidence that main components such as the steam generator and steam
cycle can be reused with moderate modifications. Major modifications are
related to the larger amounts of solids produced during iron combustion, for
instance in the particle feeding and removal systems. Since the high particle
densities and lower demand for auxiliary systems improve the heat transfer, the
net efficiencies of iron operation can be one to two percentage points better
than coal operation, depending on operating conditions. This new insight can
significantly accelerate the introduction of this innovative technology by
guiding future research and the development of the retrofit option.",2303.04000v2
2023-04-14,Performance of TES X-Ray Microcalorimeters Designed for 14.4-keV Solar Axion Search,"A 57Fe nucleus in the solar core could emit a 14.4-keV monochromatic axion
through the M1 transition if a hypothetical elementary particle, axion, exists
to solve the strong CP problem. Transition edge sensor (TES) X-ray
microcalorimeters can detect such axions very efficiently if they are again
converted into photons by a 57Fe absorber. We have designed and produced a
dedicated TES array with 57Fe absorbers for the solar axion search. The iron
absorber is set next to the TES, keeping a certain distance to reduce the
iron-magnetization effect on the spectroscopic performance. A gold thermal
transfer strap connects them. A sample pixel irradiated from a 55Fe source
detected 698 pulses. In contrast to thermal simulations, we consider that the
pulses include either events produced in an iron absorber or gold strap at a
fraction dependent on the absorption rate of each material. Furthermore,
photons deposited on the iron absorber are detected through the strap as
intended. The identification of all events still needs to be completed.
However, we successfully operated the TES with the unique design under iron
magnetization for the first time.",2304.07068v2
2023-04-10,Pourable and Destroyable Cosmic Ray Radiation Shield for Spacecraft,"Historically, materials such as lead, tungsten, and iron have been used in
spacecraft to shield scientific detectors from Cosmic Rays. These materials
work well when reentry to Earth is not an issue. The typical strategy is to
have a controlled descent of the spacecraft or to have extremely limited
shielding, if any, due to the NASA requirement that all impacting parts must
impact with no greater than 15J of energy. Given the nature of this mission
neither a controlled descent nor having no shielding was not an option. This is
the issue Wichita State University nuSOL team is facing for its 3U CubeSat
demonstrator.
  The CubeSat will be equipped with scientific equipment with the purpose of
detecting solar neutrinos, and the less background noise from Cosmic Rays the
better the study will be. Through simulations, density tests, and burn tests,
WSU was able to develop an epoxy based shield doped with either iron or
tungsten powder. The simulations were conducted by firing electrons, protons,
alpha particles, and oxygen and iron nuclei into the shield material with
energies ranging from 1MeV until consistent failure rate using Geant4. The
standards for these simulations are the base epoxy at 1.15g per cc to solid
steel at 8g per cc . Mixing tests have determined for iron, a density of 4g per
cc is achievable, which is 53 percent iron by volume. Tungsten epoxy with a
density of 7.5g per cc is more easily achieved, and results in 40 percent
tungsten by volume. These ratios are concrete in texture, pourable, and
homogeneous.",2304.09177v1
2023-04-19,Fabrication of a 64-Pixel TES Microcalorimeter Array with Iron Absorbers Uniquely Designed for 14.4-keV Solar Axion Search,"If a hypothetical elementary particle called an axion exists, to solve the
strong CP problem, a 57Fe nucleus in the solar core could emit a 14.4-keV
monochromatic axion through the M1 transition. If such axions are once more
transformed into photons by a 57Fe absorber, a transition edge sensor (TES)
X-ray microcalorimeter should be able to detect them efficiently. We have
designed and fabricated a dedicated 64-pixel TES array with iron absorbers for
the solar axion search. In order to decrease the effect of iron magnetization
on spectroscopic performance, the iron absorber is placed next to the TES while
maintaining a certain distance. A gold thermal transfer strap connects them. We
have accomplished the electroplating of gold straps with high thermal
conductivity. The residual resistivity ratio (RRR) was over 23, more than eight
times higher than a previous evaporated strap. In addition, we successfully
electroplated pure-iron films of more than a few micrometers in thickness for
absorbers and a fabricated 64-pixel TES calorimeter structure.",2304.09539v1
2023-09-22,Decoding 122-Type Iron-Based Superconductors: A Comprehensive Simulation of Phase Diagrams and Transition Temperatures,"Iron-based superconductors, a cornerstone of low-temperature physics, have
been the subject of numerous theoretical models aimed at deciphering their
complex behavior. In this study, we present a comprehensive approach that
amalgamates several existing models and incorporates experimental data to
simulate the superconducting phase diagrams of the principal 122-type
iron-based compounds. Our model considers a multitude of factors including the
momentum dependence of the superconducting gap, spin-orbital coupling,
antiferromagnetism, spin density wave, induced XY potential on the tetrahedral
structure, and electron-phonon coupling. We have refined the electron-phonon
scattering matrix using experimental angle-resolved photoemission spectroscopy
(ARPES) data, ensuring that all electrons pertinent to iron-based
superconductivity are accounted for. This innovative approach allows us to
calculate theoretical critical temperature Tc values for Ba1-xKxFe2As2,
CaFe2As2 and SrFe2As2 as functions of pressure. These calculated values exhibit
remarkable agreement with experimental findings. Furthermore, our model
predicts that MgFe2As2 remains non-superconducting irrespective of the applied
pressure. Given that 122-type superconductivity at low pressure or low doping
concentration has been experimentally validated, our combined model serves as a
powerful predictive tool for generating superconducting phase diagrams at high
pressure. This study underscores that the high transition temperatures and the
precise doping and pressure dependence of iron-based superconductors are
intrinsically linked to an intertwined mechanism involving a strong interplay
between structural, magnetic and electronic degrees of freedom.",2309.12615v1
2023-10-09,Detecting Iron Oxidation States in Liquids with the VOXES Bragg Spectrometer,"Determining the oxidation states of metals assumes great importance in
various applications because a variation in the oxidation number can
drastically influence the material properties. As an example, this becomes
evident in edible liquids like wine and oil, where a change in the oxidation
states of the contained metals can significantly modify both the overall
quality and taste. To this end, here we present the MITIQO project, which aims
to identify oxidation states of metals in edible liquids utilizing X-ray
emission with Bragg spectroscopy. This is achieved using the VOXES crystal
spectrometer, developed at INFN National Laboratories of Frascati (LNF),
employing mosaic crystal (HAPG) in the Von Hamos configuration. This
combination allow us to work with effective source sizes of up to a few
millimeters and improves the typical low efficiency of Bragg spectroscopy, a
crucial aspect when studying liquids with low metal concentration. Here we
showcase the concept behind MITIQO, for a liquid solution containing oxidized
iron. We performed several high-resolution emission spectra measurements, for
the liquid and for different powdered samples containing oxidized and pure
iron. By looking at the spectral features of the iron's K$\beta$ emission
lineshape, we were able to obtain, for a liquid, a result consistent with the
oxidized iron powders and successfully quantifying the effect of oxidation.",2310.06062v1
2024-03-05,"Elemental abundances in the diffuse ISM from joint FUV and X-ray spectroscopy: iron, oxygen, carbon and sulfur","In this study, we investigate interstellar absorption lines along the line of
sight toward the galactic low-mass X-ray binary Cygnus X-2. We combine
absorption line data obtained from high-resolution X-ray spectra collected with
Chandra and XMM-Newton satellites, along with Far-UV absorption lines observed
by the Hubble Space Telescope's (HST) Cosmic Origins Spectrograph (COS)
Instrument. Our primary objective is to understand the abundance and depletion
of oxygen, iron, sulfur, and carbon. To achieve this, we have developed an
analysis pipeline that simultaneously fits both the UV and X-ray datasets. This
novel approach takes into account the line spread function (LSF) of HST/COS,
enhancing the precision of our results. We examine the absorption lines of
FeII, SII, CII, and CI present in the FUV spectrum of Cygnus X-2, revealing the
presence of at least two distinct absorbers characterized by different
velocities. Additionally, we employ Cloudy simulations to compare our findings
concerning the ionic ratios for the studied elements. We find that gaseous iron
and sulfur exist in their singly ionized forms, Fe II and S II, respectively,
while the abundances of CII and CI do not agree with the Cloudy simulations of
the neutral ISM. Finally, we explore discrepancies in the X-ray atomic data of
iron and discuss their impact on the overall abundance and depletion of iron.",2403.02664v1
1999-07-06,Hysteresis properties at zero temperature in the Dipolar-Random Field Ising Model,"We present a modified two-dimensional random field Ising model, where a
dipolar interaction term is added to the classic random field Hamiltonian. In a
similar model it was already verified that the system state can exhibit domains
in the form of stripe patterns, typical of thin materials with strong
perpendicular anisotropy. In this work we show that the hysteresis loops
obtained at zero temperature can display a strict similarity with the loops
obtained in thin magnetic materials such as garnet films. In our model the
processes of domain nucleation and domain wall motion are well separated in
time as the system evolves. This remarkable fact allowed us to better
understand the nucleation process in this family of spin systems.",9907074v1
2000-03-21,Field induced ordering in highly frustrated antiferromagnets,"We predict that an external field can induce a spin order in highly
frustrated classical Heisenberg magnets. We find analytically stabilization of
collinear states by thermal fluctuations at a one-third of the saturation field
for kagome and garnet lattices and at a half of the saturation field for
pyrochlore and frustrated square lattices. This effect is studied numerically
for the frustrated square-lattice antiferromagnet by Monte Carlo simulations
for classical spins and by exact diagonalization for $S=1/2$. The field induced
collinear states have a spin gap and produce magnetization plateaus.",0003343v2
2001-10-10,Modeling Two Dimensional Magnetic Domain Patterns,"Two-dimensional magnetic garnets exhibit complex and fascinating magnetic
domain structures, like stripes, labyrinths, cells and mixed states of stripes
and cells. These patterns do change in a reversible way when the intensity of
an externally applied magnetic field is varied. The main objective of this
contribution is to present the results of a model that yields a rich pattern
structure that closely resembles what is observed experimentally. Our model is
a generalized two-dimensional Ising-like spin-one Hamiltonian with long-range
interactions, which also incorporates anisotropy and Zeeman terms. The model is
studied numerically, by means of Monte Carlo simulations. Changing the model
parameters stripes, labyrinth and/or cellular domain structures are generated.
For a variety of cases we display the patterns, determine the average size of
the domains, the ordering transition temperature, specific heat, magnetic
susceptibility and hysteresis cycle. Finally, we examine the reversibility of
the pattern evolution under variations of the applied magnetic field. The
results we obtain are in good qualitative agreement with experiment.",0110208v1
2003-07-28,Low temperature spin fluctuations in geometrically frustrated Yb3Ga5O12,"In the garnet structure compound Yb3Ga5O12, the Yb3+ ions (ground state
effective spin S' = 1/2) are situated on two interpenetrating corner sharing
triangular sublattices such that frustrated magnetic interactions are possible.
Previous specific heat measurements evidenced the development of short range
magnetic correlations below 0.5K and a lambda-transition at 54mK (Filippi et
al. J. Phys. C: Solid State Physics 13 (1980) 1277). From 170-Yb M""ossbauer
spectroscopy measurements down to 36mK, we find there is no static magnetic
order at temperatures below that of the lambda-transition. Below 0.3K, the
fluctuation frequency of the short range correlated Yb3+ moments progressively
slows down and as the temperature tends to 0, the frequency tends to a
quasi-saturated value of 3 x 10^9 s^-1. We also examined the Yb3+ paramagnetic
relaxation rates up to 300K using 172-Yb perturbed angular correlation
measurements: they evidence phonon driven processes.",0307676v1
2006-06-05,Multireference Correlation in Long Molecules with the Quadratic Scaling Density Matrix Renormalization Group,"We have devised and implemented a local ab initio Density Matrix
Renormalization Group (DMRG) algorithm to describe multireference nondynamic
correlations in large systems. For long molecules that are extended in one of
their spatial dimensions, this method allows us to obtain an exact
characterisation of correlation, in the given basis, with a cost that scales
only quadratically with the size of the system. The reduced scaling is achieved
solely through integral screening and without the construction of correlation
domains. We demonstrate the scaling, convergence, and robustness of the
algorithm in polyenes and hydrogen chains. We converge to exact correlation
energies (with 1-10 microhartree precision) in all cases and correlate up to
100 electrons in 100 active orbitals. We further use our algorithm to obtain
exact energies for the metal-insulator transition in hydrogen chains and
compare and contrast our results with those from conventional quantum chemical
methods.",0606115v3
2004-05-10,Manifestations of nuclear anapole moments in solid state NMR,"We suggest to use insulating garnets doped by rare earth ions for
measurements of nuclear anapole moments. A parity violating shift of the NMR
frequency arises due to the combined effect of the lattice crystal field and
the anapole moment of the rare-earth nucleus.
  We show that there are two different observable effects related to frequency:
1) A shift of the NMR frequency in an external electric field applied to the
solid. The value of the shift is about \Delta \nu_1 ~ 10^{-5} Hz with E = 10
kV/cm; 2) A splitting of the NMR line into two lines. The second effect is
independent of the external electric field. The value of the splitting is about
\Delta \nu_2 ~ 0.5 Hz and it depends on the orientation of the crystal with
respect to magnetic field. Both estimates are presented for a magnetic field of
about 10 tesla.
  We also discuss a radiofrequency electric field and a static macroscopic
magnetization caused by the nuclear anapole moment.",0405043v1
2006-06-22,Band Edge Effects and Normal Mode Propagation in Waveguide Magnetophotonic Crystals,"A study of band edge phenomena in ridge waveguide magnetophotonic crystals is
presented. Normal mode analysis is used to examine the near-band edge and Bragg
center-wavelength group velocities and their relation to the polarization.
Large polarization departures from the input are observed in Bragg gratings
patterned by focused-ion-beam milling on liquid-phase-epitaxial (LPE) BiLuIG
films on (111) gadolinium gallium garnet (GGG) substrates. Transfer matrix
analysis of the spectral response in the photonic crystals allows the
determination of the phase of the elliptically polarized normal modes from
measured transmittances and polarization rotation. Unlike non-birefringent
Faraday rotators a non-linear-relation exists between polarization rotation and
the normal mode phase difference. Large phase differences between right- and
left-elliptically polarized normal modes and optical slow-down are found near
the band edges and at the resonant cavity center-wavelength. Standing-wave
photon trapping and optical slow-down are analyzed and compared for these
systems.",0606199v2
1996-02-08,Supersymmetry and the Hartmann Potential of Theoretical Chemistry,"The ring-shaped Hartmann potential $ V = \eta \sigma^{2} \epsilon_{0} \left(
\frac{2 a_{0}}{r} - \frac{\eta a_{0}^{2}}{r^{2} sin^{2} \theta} \right) $ was
introduced in quantum chemistry to describe ring-shaped molecules like benzene.
In this article, the supersymmetric features of the Hartmann potential are
discussed. We first review the results of a previous paper in which we
rederived the eigenvalues and radial eigenfunctions of the Hartmann potential
using a formulation of one-dimensional supersymmetric quantum mechanics
(SUSYQM) on the half-line $\left[ 0, \infty \right)$. A reformulation of SUSYQM
in the full line $\left( -\infty, \infty \right)$ is subsequently developed. It
is found that the second formulation makes a connection between states having
the same quantum number $L$ but different values of $\eta \sigma^{2}$ and
quantum number $N$. This is in contrast to the first formulation, which relates
states with identical values of the quantum number $N$ and $\eta \sigma^{2}$
but different values of the quantum number $L$.",9602005v1
2002-08-01,"Entwined Paths, Difference Equations and the Dirac Equation","Entwined space-time paths are bound pairs of trajectories which are traversed
in opposite directions with respect to macroscopic time. In this paper we show
that ensembles of entwined paths on a discrete space-time lattice are simply
described by coupled difference equations which are discrete versions of the
Dirac equation. There is no analytic continuation, explicit or forced, involved
in this description. The entwined paths are `self-quantizing'. We also show
that simple classical stochastic processes that generate the difference
equations as ensemble averages are stable numerically and converge at a rate
governed by the details of the stochastic process. This result establishes the
Dirac equation in one dimension as a phenomenological equation describing an
underlying classical stochastic process in the same sense that the Diffusion
and Telegraph equations are phenomenological descriptions of stochastic
processes.",0208004v2
2007-07-20,The radical character of the acenes: A density matrix renormalization group study,"We present a detailed investigation of the acene series using high-level
wavefunction theory. Our ab-initio Density Matrix Renormalization Group
algorithm has enabled us to carry out Complete Active Space calculations on the
acenes from napthalene to dodecacene correlating the full pi-valence space.
  While we find that the ground-state is a singlet for all chain-lengths,
examination of several measures of radical character, including the natural
orbitals, effective number of unpaired electrons, and various correlation
functions, suggests that the longer acene ground-states are polyradical in
nature.",0707.3120v1
2007-07-20,Targeted Excited State Algorithms,"To overcome the limitations of the traditional state-averaging approaches in
excited state calculations, where one solves for and represents all states
between the ground state and excited state of interest, we have investigated a
number of new excited state algorithms. Building on the work of van der Vorst
and Sleijpen (SIAM J. Matrix Anal. Appl., 17, 401 (1996)), we have implemented
Harmonic Davidson and State-Averaged Harmonic Davidson algorithms within the
context of the Density Matrix Renormalization Group (DMRG). We have assessed
their accuracy and stability of convergence in complete active space DMRG
calculations on the low-lying excited states in the acenes ranging from
naphthalene to pentacene. We find that both algorithms offer increased accuracy
over the traditional State-Averaged Davidson approach, and in particular, the
State-Averaged Harmonic Davidson algorithm offers an optimal combination of
accuracy and stability in convergence.",0707.3121v1
2007-10-23,Structural relaxation around substitutional Cr3+ in pyrope garnet,"The structural environment of substitutional Cr3+ ion in a natural pyrope
Mg3Al2Si3O12 has been investigated by Cr K-edge Extended X-ray Absorption Fine
Structure (EXAFS) and X-ray Absorption Near Edge Structure (XANES) coupled with
first-principles computations. The Cr-O distance is close to that in
knorringite Mg3Cr2Si3O12, indicating a full relaxation of the first neighbors.
The local C3i symmetry of the octahedral Y site is retained during Cr-Al
substitution. The second and third shells of neighbors (Mg and Si) relax only
partially. Site relaxation is accommodated by strain-induced bond buckling,
with angular tilts of the Si-centered tetrahedra around the Cr-centered
octahedron, and by a radial deformation of the Mg-centered dodecahedra.",0710.4189v1
2007-11-09,An Introduction to the Density Matrix Renormalization Group Ansatz in Quantum Chemistry,"The Density Matrix Renormalisation Group (DMRG) is an electronic structure
method that has recently been applied to ab-initio quantum chemistry. Even at
this early stage, it has enabled the solution of many problems that would
previously have been intractable with any other method, in particular,
multireference problems with very large active spaces. Historically, the DMRG
was not originally formulated from a wavefunction perspective, but rather in a
Renormalisation Group (RG) language. However, it is now realised that a
wavefunction view of the DMRG provides a more convenient, and in some cases
more powerful, paradigm. Here we provide an expository introduction to the DMRG
ansatz in the context of quantum chemistry.",0711.1398v1
2007-12-14,"Orbital Optimization in the Density Matrix Renormalization Group, with applications to polyenes and β-carotene","In previous work we have shown that the Density Matrix Renormalization Group
(DMRG) enables near-exact calculations in active spaces much larger than are
possible with traditional Complete Active Space algorithms. Here, we implement
orbital optimisation with the Density Matrix Renormalization Group to further
allow the self-consistent improvement of the active orbitals, as is done in the
Complete Active Space Self-Consistent Field (CASSCF) method. We use our
resulting DMRGCASSCF method to study the low-lying excited states of the
all-trans polyenes up to C24H26 as well as \beta-carotene, correlating with
near-exact accuracy the optimised complete \pi-valence space with up to 24
active electrons and orbitals, and analyse our results in the light of the
recent discovery from Resonance Raman experiments of new optically dark states
in the spectrum.",0712.2475v2
2008-06-03,Site symmetry and crystal symmetry: a spherical tensor analysis,"The relation between the properties of a specific crystallographic site and
the properties of the full crystal is discussed by using spherical tensors. The
concept of spherical tensors is introduced and the way it transforms under the
symmetry operations of the site and from site to site is described in detail.
The law of spherical tensor coupling is given and illustrated with the example
of the electric dipole and quadrupole transitions in x-ray absorption
spectroscopy. The main application of the formalism is the reduction of
computation time in the calculation of the properties of crystals by band
structure methods. The general approach is illustrated by the examples of
substitutional chromium in spinel and substitutional vanadium in garnet.",0806.0438v1
2009-07-27,Approximating strongly correlated spin and fermion wavefunctions with correlator product states,"We explore correlator product states for the approximation of correlated
wavefunctions in arbitrary dimensions. We show that they encompass many
interesting states including Laughlin's quantum Hall wavefunction, Huse and
Elser's frustrated spin states, and Kitaev's toric code. We further establish
their relation to common families of variational wavefunctions, such as matrix
and tensor product states and resonating valence bond states. Calculations on
the Heisenberg and spinless Hubbard models show that correlator product states
capture both two-dimensional correlations (independent of system width) as well
as non-trivial fermionic correlations (without sign problems). In
one-dimensional simulations, correlator product states appear competitive with
matrix product states with a comparable number of variational parameters,
suggesting they may eventually provide a route to practically generalise the
density matrix renormalisation group to higher dimensions.",0907.4646v3
2010-02-27,Embedding theory for excited states with inclusion of self-consistent environment screening,"We present a general embedding theory of electronic excitations of a
relatively small, localized system in contact with an extended, chemically
complex environment. We demonstrate how to include the screening response of
the environment into highly accurate electronic structure calculation of the
localized system by means of an effective interaction between the electrons,
which contains only screening processes occurring in the environment. For the
common case of a localized system which constitutes an inhomogeneity in an
otherwise homogeneous system, such as a defect in a crystal, we show how matrix
elements of the environment-screened interaction can be calculated from
density-functional calculations of the homogeneous system only. We apply our
embedding theory to the calculation of excitation energies in crystalline
ethylene.",1003.0102v1
2010-05-15,Coupling between magnon and ligand-field excitations in magnetoelectric Tb3Fe5O12 garnet,"The spectra of far-infrared transmission in Tb3Fe5O12 magnetoelectric single
crystals have been studied in the range between 15 and 100 cm-1, in magnetic
fields up to 10 T, and for temperatures between 5 and 150 K. We attribute some
of the observed infrared-active excitations to electric-dipole transitions
between ligand-field split states of Tb3+ ions. Anticrossing between the
magnetic exchange excitation and the ligand-field transition occurs at the
temperature between 60 and 80 K. The corresponding coupling energy for this
interaction is 6 cm-1. Temperature-induced softening of the hybrid IR
excitation correlates with the increase of the static dielectric constant. We
discuss the possibility for hybrid excitations of magnons and ligand-field
states and their possible connection to the magnetoelectric effect in
Tb3Fe5O12.",1005.2705v1
2010-08-29,Tensor factorizations of local second-order Møller Plesset theory,"Efficient electronic structure methods can be built around efficient tensor
representations of the wavefunction. Here we describe a general view of tensor
factorization for the compact representation of electronic wavefunctions. We
use these ideas to construct low-complexity representations of the doubles
amplitudes in local second order M{\o}ller-Plesset perturbation theory. We
introduce two approximations - the direct orbital specific virtual
approximation and the full orbital specific virtual approximation. In these
approximations, each occupied orbital is associated with a small set of
correlating virtual orbitals. Conceptually, the representation lies between the
projected atomic orbital representation in Pulay-Saeb{\o} local correlation
theories and pair natural orbital correlation theories. We have tested the
orbital specific virtual approximations on a variety of systems and properties
including total energies, reaction energies, and potential energy curves.
Compared to the Pulay-Saeb{\o} ansatz, we find that these approximations
exhibit favourable accuracy and computational times, while yielding smooth
potential energy curves.",1008.4943v1
2010-08-29,Further developments in correlator product states: deterministic optimization and energy evaluation,"Correlator product states (CPS) are a class of tensor network wavefunctions
applicable to strongly correlated problems in arbitrary dimensions. Here, we
present a method for optimizing and evaluating the energy of the CPS
wavefunction that is non-variational but entirely deterministic. The
fundamental assumption underlying our technique is that the CPS wavefunction is
an exact eigenstate of the Hamiltonian, allowing the energy to be obtained
approximately through a projection of the Schr\""odinger equation. The validity
of this approximation is tested on two dimensional lattices for the spin-1/2
antiferromagnetic Heisenberg model, the spinless Hubbard model, and the full
Hubbard model. In each of these models, the projected method reproduces the
variational CPS energy to within 1%. For fermionic systems, we also demonstrate
the incorporation of a Slater determinant reference into the ansatz, which
allows CPS to act as a generalization of the Jastrow-Slater wavefunction.",1008.4945v1
2010-12-16,Dynamical mean-field theory from a quantum chemical perspective,"We investigate the dynamical mean-field theory (DMFT) from a quantum chemical
perspective. Dynamical mean-field theory offers a formalism to extend quantum
chemical methods for finite systems to infinite periodic problems within a
local correlation approximation. In addition, quantum chemical techniques can
be used to construct new ab-initio Hamiltonians and impurity solvers for DMFT.
Here we explore some ways in which these things may be achieved. First, we
present an informal overview of dynamical mean-field theory to connect to
quantum chemical language. Next we describe an implementation of dynamical
mean-field theory where we start from an ab-initio Hartree- Fock Hamiltonian
that avoids double counting issues present in many applications of DMFT. We
then explore the use of the configuration interaction hierarchy in DMFT as an
approximate solver for the impurity problem. We also investigate some numerical
issues of convergence within DMFT. Our studies are carried out in the context
of the cubic hydrogen model, a simple but challenging test for correlation
methods. Finally we finish with some conclusions for future directions.",1012.3609v1
2011-01-18,Uniform Peak Optical Conductivity in Single-Walled Carbon Nanotubes,"Recent measurements in single-walled carbon nanotubes show that, on
resonance, all nanotubes display the same peak optical conductivity of
approximately 8 $e^2/h$, independent of radius or chirality [Joh \emph{et al.},
\emph{Nature Nanotechnology} \textbf{6}, 51 (2011)]. We show that this uniform
peak conductivity is a consequence of the relativistic band structure and
strength of the Coulomb interaction in carbon nanotubes. We further construct a
minimalist model of exciton dynamics that describes the general phenomenology
and provides an accurate prediction of the numerical value of the peak optical
conductivity. The work illustrates the need for careful treatment of relaxation
mechanisms in modeling the optoelectronic properties of carbon nanotubes.",1101.3546v1
2011-04-22,New Experimental Limit on the Electric Dipole Moment of the Electron in a Paramagnetic Insulator,"We report results of an experimental search for the intrinsic Electric Dipole
Moment (EDM) of the electron using a solid-state technique. The experiment
employs a paramagnetic, insulating gadolinium gallium garnet (GGG) that has a
large magnetic response at low temperatures. The presence of the eEDM would
lead to a small but non-zero magnetization as the GGG sample is subject to a
strong electric field. We search for the resulting Stark-induced magnetization
with a sensitive magnetometer. Recent progress on the suppression of several
sources of background allows the experiment to run free of spurious signals at
the level of the statistical uncertainties. We report our first limit on the
eEDM of $(-5.57 \pm 7.98 \pm 0.12)\times$10$^{-25}$e$\cdot$cm with 5 days of
data averaging.",1104.4391v2
2012-03-30,A correlator product state study of molecular magnetism in the giant Keplerate Mo72Fe30,"We have studied the properties of the giant Keplerate molecular magnet
Mo72Fe30, as a function of applied magnetic field, using the correlator product
state (CPS) tensor network ansatz. The magnet is modeled with an S = 5/2
antiferromagnetic Heisenberg Hamiltonian on the 30-site icosidodecahedron
lattice, a model for which exact diagonalization is infeasible. The CPS ansatz
produces significant improvements in variational energies relative to previous
studies using the density matrix renormalization group, a result of its
superior ability to handle strong correlation in two dimensional spin systems.
The CPS results reaffirm that the ground state energies adhere qualitatively to
the parabolic progression of the rotational band model (RBM), but show
important deviations near 1/3 of the saturation field. These deviations predict
anomalous behavior in the differential magnetization and heat capacity that
cannot be explained by the RBM alone. Finally, we show that these energetic
deviations originate from a qualitative change in the ground state that
resembles a finite size analogue of a phase transition.",1203.6883v1
2012-04-12,Analytical modeling for the heat transfer in sheared flows of nanofluids,"We developed a model for the enhancement of the heat flux by spherical and
elongated nano- particles in sheared laminar flows of nano-fluids. Besides the
heat flux carried by the nanoparticles the model accounts for the contribution
of their rotation to the heat flux inside and outside the particles. The
rotation of the nanoparticles has a twofold effect, it induces a fluid
advection around the particle and it strongly influences the statistical
distribution of particle orientations. These dynamical effects, which were not
included in existing thermal models, are responsible for changing the thermal
properties of flowing fluids as compared to quiescent fluids. The proposed
model is strongly supported by extensive numerical simulations, demonstrating a
potential increase of the heat flux far beyond the Maxwell-Garnet limit for the
spherical nanoparticles. The road ahead which should lead towards robust
predictive models of heat flux enhancement is discussed.",1204.2694v1
2012-04-25,Density matrix embedding: A simple alternative to dynamical mean-field theory,"We introduce DMET, a new quantum embedding theory for predicting ground-state
properties of infinite systems. Like dynamical mean-field theory (DMFT), DMET
maps the the bulk interacting system to a simpler impurity model and is exact
in the non-interacting and atomic limits. Unlike DMFT, DMET is formulated in
terms of the frequency-independent local density matrix, rather than the local
Green's function. In addition, it features a finite, algebraically
constructible bath of only one bath site per impurity site, which exactly
embeds ground-states at a mean-field level with no bath discretization error.
Frequency independence and the minimal bath make DMET a computationally simple
and very efficient method. We test the theory in the 1D and 2D Hubbard models
at and away from half-filling, and we find that compared to benchmark data,
total energies, correlation functions, and paramagnetic metal-insulator
transitions are well reproduced, at a tiny computational cost.",1204.5783v2
2012-09-04,Origin of the structural phase transition in Li7La3Zr2O12,"Garnet-type Li7La3Zr2O12 (LLZO) is a solid electrolyte material with a
low-conductivity tetragonal and a high-conductivity cubic phase. Using
density-functional theory and variable cell shape molecular dynamics
simulations, we show that the tetragonal phase stability is dependent on a
simultaneous ordering of the Li ions on the Li sublattice and a
volume-preserving tetragonal distortion that relieves internal structural
strain. Supervalent doping introduces vacancies into the Li sublattice,
increasing the overall entropy and reducing the free energy gain from ordering,
eventually stabilizing the cubic phase. We show that the critical temperature
for cubic phase stability is lowered as Li vacancy concentration (dopant level)
is raised and that an activated hop of Li ions from one crystallographic site
to another always accompanies the transition. By identifying the relevant
mechanism and critical concentrations for achieving the high conductivity
phase, this work shows how targeted synthesis could be used to improve
electrolytic performance.",1209.0690v1
2012-10-04,Striped spin liquid crystal ground state instability of kagome antiferromagnets,"The Dirac spin liquid ground state of the spin 1/2 Heisenberg kagome
antiferromagnet has potential instabilities[1-4]. This has been suggested as
the reason why it is not strongly supported in large-scale numerical
calculations[5]. However, previous attempts to observe these instabilities have
failed. We report on the discovery of a projected BCS state with lower energy
than the projected Dirac spin liquid state which provides new insight into the
stability of the ground state of the kagome antiferromagnet. The new state has
three remarkable features. First, it breaks both spatial symmetry in an unusual
way that may leave spinons deconfined along one direction. Second, it breaks
the U(1) gauge symmetry down to $Z_2$. Third, it has the spatial symmetry of a
previously proposed ""monopole"" suggesting that it is an instability of the
Dirac spin liquid. The state described herein also shares a remarkable
similarity to the distortion of the kagome lattice observed at low Zn
concentrations in Zn-Paratacamite suggesting it may already be realized in
these materials.",1210.1585v1
2012-10-05,"Excited States, Dynamic Correlation Functions and Spectral Properties from Full Configuration Interaction Quantum Monte Carlo","In this communication, we propose a method for obtaining isolated excited
states within the Full Configuration Interaction Quantum Monte Carlo framework.
This method allows for stable sampling with respect to collapse to lower energy
states and requires no uncontrolled approximations. In contrast with most
previous methods to extract excited state information from Quantum Monte Carlo
methods, this results from a modification to the underlying propagator, and
does not require explicit orthogonalization, analytic continuation, transient
estimators or restriction of the Hilbert space via a trial wavefunction.
Furthermore, we show that the propagator can directly yield frequency-domain
correlation functions and spectral functions such as the density of states
which are difficult to obtain within a traditional Quantum Monte Carlo
framework. We demonstrate this approach with pilot applications to the neon
atom and beryllium dimer.",1210.1650v1
2012-11-05,Exact asymptotic behavior of magnetic stripe domain arrays,"The classical problem of magnetic stripe domain behavior in films and plates
with uniaxial magnetic anisotropy is treated. Exact analytical results are
derived for the stripe domain widths as function of applied perpendicular
field, $H$, in the regime where the domain period becomes large. The stripe
period diverges as $(H_c-H)^{-1/2}$, where $H_c$ is the critical (infinite
period) field, an exact result confirming a previous conjecture. The
magnetization approaches saturation as $(H_c-H)^{1/2}$, a behavior which
compares excellently with experimental data obtained for a $4 \mu$m thick
ferrite garnet film. The exact analytical solution provides a new basis for
precise characterization of uniaxial magnetic films and plates, illustrated by
a simple way to measure the domain wall energy. The mathematical approach is
applicable for similar analysis of a wide class of systems with competing
interactions where a stripe domain phase is formed.",1211.1366v1
2012-12-12,Density matrix embedding: A strong-coupling quantum embedding theory,"We extend our density matrix embedding theory (DMET) [Phys. Rev. Lett. 109
186404 (2012)] from lattice models to the full chemical Hamiltonian. DMET
allows the many-body embedding of arbitrary fragments of a quantum system, even
when such fragments are open systems and strongly coupled to their environment
(e.g., by covalent bonds). In DMET, empirical approaches to strong coupling,
such as link atoms or boundary regions, are replaced by a small, rigorous
quantum bath designed to reproduce the entanglement between a fragment and its
environment. We describe the theory and demonstrate its feasibility in strongly
correlated hydrogen ring and grid models; these are not only beyond the scope
of traditional embeddings, but even challenge conventional quantum chemistry
methods themselves. We find that DMET correctly describes the notoriously
difficult symmetric dissociation of a 4x3 hydrogen atom grid, even when the
treated fragments are as small as single hydrogen atoms. We expect that DMET
will open up new ways of treating of complex strongly coupled, strongly
correlated systems in terms of their individual fragments.",1212.2679v1
2013-04-15,Off-policy Learning with Eligibility Traces: A Survey,"In the framework of Markov Decision Processes, off-policy learning, that is
the problem of learning a linear approximation of the value function of some
fixed policy from one trajectory possibly generated by some other policy. We
briefly review on-policy learning algorithms of the literature (gradient-based
and least-squares-based), adopting a unified algorithmic view. Then, we
highlight a systematic approach for adapting them to off-policy learning with
eligibility traces. This leads to some known algorithms - off-policy
LSTD(\lambda), LSPE(\lambda), TD(\lambda), TDC/GQ(\lambda) - and suggests new
extensions - off-policy FPKF(\lambda), BRM(\lambda), gBRM(\lambda),
GTD2(\lambda). We describe a comprehensive algorithmic derivation of all
algorithms in a recursive and memory-efficent form, discuss their known
convergence properties and illustrate their relative empirical behavior on
Garnet problems. Our experiments suggest that the most standard algorithms on
and off-policy LSTD(\lambda)/LSPE(\lambda) - and TD(\lambda) if the feature
space dimension is too large for a least-squares approach - perform the best.",1304.3999v1
2013-12-11,Cs2NaAl1-xCrxF6: A family of compounds presenting magnetocaloric effect,"In this paper we explore the magnetocaloric effect (MCE) of chromium-doped
elpasolite Cs$_2$NaAl$_{1-x}$Cr$_x$F$_6$ (x = 0.01 and 0.62) single crystals.
Our magnetization and heat capacity data show the magnetocaloric potentials to
be comparable to those of garnets, perovskites and other fluorides, producing
magnetic entropy changes of 0.5 J/kg$\cdot$K (x = 0.01) and 11 J/kg$\cdot$K (x
= 0.62), and corresponding adiabatic temperature changes of 4 K and 8 K,
respectively. These values are for a magnetic field change of 5 T at a
temperature around 3 K. A clear Schottky anomaly below 10 K, which becomes more
apparent when an external magnetic field is applied, was observed and related
to the splitting of the Cr$^{3+}$ energy levels. These results hint at a new
family of materials with potential wide use in cryorefrigeration.",1312.3014v2
2014-05-04,Quasi-three-level laser emission of neodymium doped disordered crystal waveguides,"This paper reports on the quasi-three-level continuous wave laser operation
based on waveguide structures in neodymium doped calcium niobium gallium garnet
disordered crystal. Laser wavelength selection through the waveguide cross
section was observed. Waveguide structures with different cross sections were
fabricated by the ultrafast laser inscription, which have propagation losses
around 1 dB/cm. With suitable pumping conditions, laser emissions were observed
at the low-wavelengths of ~930 nm and ~890 nm. The lasing threshold for the
low-wavelength emission was around 50 mW, which is far below the threshold of
several watts reported in the bulk laser system. In addition, it was found the
laser generation at the wavelength of ~890 nm has direct relationship with the
volume of the waveguide structure. The results suggest advantages of the
waveguide platforms over the bulk systems on the low-wavelength laser emission.",1405.0704v1
2014-08-21,A flexible multi-reference perturbation theory by minimizing the Hylleraas functional with matrix product states,"We describe a formulation of multi-reference perturbation theory that obtains
a rigorous upper bound to the second order energy by minimizing the Hylleraas
functional in the space of matrix product states (MPS). The first order
wavefunctions so obtained can also be used to compute the third order energy
with little overhead. Our formulation has several advantages including (i)
flexibility with respect to the choice of zeroth order Hamiltonian, (ii)
recovery of the exact uncontracted multi-reference perturbation theory energies
in the limit of large MPS bond dimension, (iii) no requirement to compute high
body density matrices, (iv) an embarrassingly parallel algorithm (scaling up to
the number of virtual orbitals, squared, processors). Preliminary numerical
examples show that the MPS bond dimension required for accurate first order
wavefunctions scales sub-linearly with the size of the basis.",1408.5092v1
2014-10-26,Twisted Conjugacy in Houghton's groups,"For a fixed $n\ge2$, the Houghton group $H_n$ consists of bijections of
$X_n=\{1,\ldots,n\} \times \mathbb{N}$ that are `eventually translations' of
each copy of $\mathbb{N}$. The Houghton groups have been shown to have solvable
conjugacy problem. In general solvable conjugacy problem does not imply that
all finite extensions and finite index subgroups have solvable conjugacy
problem. Our main theorem is that a stronger result holds: for any $n\ge2$ and
any group $G$ commensurable to $H_n$, $G$ has solvable conjugacy problem.",1410.7051v6
2014-11-01,A transformed framework for dynamic correlation in multireference problems,"We describe how multirefence dynamic correlation theories can be naturally
obtained as single-reference correlation theories in a canonically transformed
frame. Such canonically transformed correlation theories are very simple and
involve identical expressions to their single-reference counterparts. The
corresponding excitations involve quasiparticles rather than the bare particles
of the system. High-order density matrices (or their approximations) and the
numerical metric instabilities common to multireference correlation theories do
not appear. As an example, we formulate the Bogoliubov canonically transformed
version of second-order M{\o}ller-Plesset perturbation theory and demonstrate
its performance in hydrogen, water, nitrogen, and BeH$_2$ bond dissociation.",1411.0067v4
2015-01-14,Dispersionless spin waves in Gadolinium Gallium Garnet,"We report the results of neutron scattering on a powder sample of Gd3Ga5O12
at high magnetic fields. We find that in high fields (B>1.8 T) the system is
not fully polarized, but has a small canting of the moments induced by the
dipolar interaction. We show that the degree of canting is accurately predicted
by the standard Hamiltonian which includes the dipolar interaction. The
inelastic scattering is dominated at large momentum transfers by a band of
almost dispersionless excitations. We show that these correspond to the spin
waves localized on ten site rings, expected for a system described by a nearest
neighbor interaction, and that the spectrum at high fields B>1.8 T is
well-described by a spin wave theory. The phase for fields <1.8 T is
characterized by an antiferromagnetic Bragg peak at (210) and an incommensurate
peak.",1501.03493v1
2015-01-28,Interplay of disorder and geometrical frustration in doped Gadolinium Gallium Garnet,"The geometrically-frustrated, triangular antiferromagnet GGG exhibits a rich
mix of short-range order and isolated quantum states. We investigate the
effects of up to 1% Neodymium substitution for Gallium on the ac magnetic
response at temperatures below 1 K in both the linear and nonlinear regimes.
Substitutional disorder actually drives the system towards a more perfectly
frustrated state, apparently compensating for the effect of imperfect
Gadolinium/Gallium stoichiometry, while at the same time more closely
demarcating the boundaries of isolated, coherent clusters composed of hundreds
of spins. Optical measurements of the local Nd environment substantiate the
picture of an increased frustration index with doping.",1501.07229v1
2015-04-02,Search for exotic short-range interactions using paramagnetic insulators,"We describe a proposed experimental search for exotic spin-coupled
interactions using a solid-state paramagnetic insulator. The experiment is
sensitive to the net magnetization induced by the exotic interaction between
the unpaired insulator electrons with a dense, non-magnetic mass in close
proximity. An existing experiment has been used to set limits on the electric
dipole moment of the electron by probing the magnetization induced in a
cryogenic gadolinium gallium garnet sample on application of a strong electric
field. With suitable additions, including a movable source mass, this
experiment can be used to explore ""monopole-dipole"" forces on polarized
electrons with unique or unprecedented sensitivity. The solid-state,
non-magnetic construction, combined with the low-noise conditions and extremely
sensitive magnetometry available at cryogenic temperatures could lead to a
sensitivity over ten orders of magnitude greater than exiting limits in the
range below 1 mm.",1504.00552v2
2015-04-08,Ground-state phase diagram of the square lattice Hubbard model from density matrix embedding theory,"We compute the ground-state phase diagram of the Hubbard and frustrated
Hubbard models on the square lattice with density matrix embedding theory using
clusters of up to 16 sites. We provide an error model to estimate the
reliability of the computations and complexity of the physics at different
points in the diagram. We find superconductivity in the ground-state as well as
competition between inhomogeneous charge, spin, and pairing states at low
doping. The estimated errors in the study are below T$_c$ in the cuprates and
on the scale of contributions in real materials that are neglected in the
Hubbard model.",1504.01784v3
2015-07-07,Fast and rewritable colloidal assembly via field synchronized particle swapping,"We report a technique to realize reconfigurable colloidal crystals by using
the controlled motion of particle defects above an externally modulated
magnetic substrate. The transport of particles is induced by applying a uniform
rotating magnetic field to a ferrite garnet film characterized by a periodic
lattice of magnetic bubbles. For filling factor larger than one colloid per
bubble domain, the particle current arises from propagating defects where
particles synchronously exchange their position when passing from one occupied
domain to the next. The amplitude of an applied alternating magnetic field can
be used to displace the excess particles via a swapping mechanism, or to
mobilize the entire colloidal system at a predefined speed.",1507.01964v1
2015-12-14,Spectral Functions of the Uniform Electron Gas via Coupled-Cluster Theory and Comparison to the $GW$ and Related Approximations,"We use, for the first time, ab initio coupled-cluster theory to compute the
spectral function of the uniform electron gas at a Wigner-Seitz radius of
$r_\mathrm{s}=4$. The coupled-cluster approximations we employ go significantly
beyond the diagrammatic content of state-of-the-art $GW$ theory. We compare our
calculations extensively to $GW$ and $GW$-plus-cumulant theory, illustrating
the strengths and weaknesses of these methods in capturing the quasiparticle
and satellite features of the electron gas. Our accurate calculations further
allow us to address the long-standing debate over the occupied bandwidth of
metallic sodium. Our findings indicate that the future application of
coupled-cluster theory to condensed phase material spectra is highly promising.",1512.04556v2
2015-12-26,"N-electron valence state perturbation theory based on a density matrix renormalization group reference function, with applications to the chromium dimer and poly-p-phenylene vinylene oligomer","The strongly-contracted variant of second order N -electron valence state
perturbation theory (NEVPT2) is an efficient perturbative method to treat
dynamic correlation without the problems of intruder states or level shifts,
while the density matrix renormalization group (DMRG) provides the capability
to tackle static correlation in large active spaces. We present a combination
of the DMRG and strongly-contracted NEVPT2 (DMRG-SC-NEVPT2) that uses an
efficient algorithm to compute high order reduced density matrices from DMRG
wave functions. The capabilities of DMRG-SC-NEVPT2 are demonstrated on
calculations of the chromium dimer potential energy curve at the basis set
limit, and the excitation energies of poly-p-phenylene vinylene trimer
(PPV(n=3)).",1512.08137v4
2016-03-21,Hybrid graphene/silicon integrated optical isolators with photonic spin-orbit interaction,"Optical isolators are an important building block in photonic computation and
communication. In traditional optics, isolators are realized with
magneto-optical garnets. However, it remains challenging to incorporate such
materials on an integrated platform because of the difficulty in material
growth and bulky device footprint. Here, we propose an ultracompact integrated
isolator by exploiting graphene's magneto-optical property on a
silicon-on-insulator platform. The photonic nonreciprocity is achieved because
the cyclotrons in graphene experiencing different optical spin exhibit
different response to counterpropagating light. Taking advantage of cavity
resonance effects, we have numerically optimized a device design, which shows
excellent isolation performance with the extinction ratio over 45 dB and the
insertion loss around 12 dB at a wavelength near 1.55 um. Featuring graphene's
CMOS compatibility and substantially reduced device footprint, our proposal
sheds light to monolithic integration of nonreciprocal photonic devices.",1603.06332v1
2016-03-28,A practical guide to density matrix embedding theory in quantum chemistry,"Density matrix embedding theory (DMET) provides a theoretical framework to
treat finite fragments in the presence of a surrounding molecular or bulk
environment, even when there is significant correlation or entanglement between
the two. In this work, we give a practically oriented and explicit description
of the numerical and theoretical formulation of DMET. We also describe in
detail how to perform self-consistent DMET optimizations. We explore different
embedding strategies with and without a self-consistency condition in hydrogen
rings, beryllium rings, and a sample S$_{\text{N}}$2 reaction. The source code
for the calculations in this work can be obtained from
\url{https://github.com/sebwouters/qc-dmet}.",1603.08443v2
2016-03-31,Five years of density matrix embedding theory,"Density matrix embedding theory (DMET) describes finite fragments in the
presence of a surrounding environment. In contrast to most embedding methods,
DMET explicitly allows for quantum entanglement between both. In this chapter,
we discuss both the ground-state and response theory formulations of DMET, and
review several applications. In addition, a proof is given that the local
density of states can be obtained by working with a Fock space of bath
orbitals.",1605.05547v1
2016-05-27,The Effect of Tetrahedral versus Octahedral Network-Blocking Atom Substitutions on Lithium Ion Conduction in LLZO Garnet,"Molecular dynamics calculations are carried out on pure, Al-substituted, and
In-substituted LLZO. The calculations show that the tendency of Al to occupy
the 24d sites in LLZO lithium ion conductors is hypothesized here to negatively
impact ionic conductivity. The room-temperature ionic conductivity of In-LLZO,
in which the In resides at the 48g sites, is predicted to be an order of
magnitude higher than Al-LLZO. Consideration of the simple tetrahedral topology
of the lithium ion conduction network suggests that the increased conductivity
arises because the 48g site sits at a bridge in the lithium ion conduction
network. An immobile ion residing in this location blocks fewer lithium
conduction pathways than an ion, such as Al, that preferentially occupies the
24d site located at a node within the network. In addition, the electronic
structure calculations presented here indicate no large difference in the
stabilities of tetragonal and cubic phases for the aluminum-substituted and
indium-substituted compounds. In both cases, the cubic phase is more stable
than the tetragonal phase. This indicates that it should be possible to make a
cubic In-LLZO phase with significant conductivity enhancement over the cubic
Al-LLZO phase.",1605.08598v1
2016-06-18,Enhanced diffusion and anomalous transport of magnetic colloids driven above a two-state flashing potential,"We combine experiment and theory to investigate the diffusive and
subdiffusive dynamics of paramagnetic colloids driven above a two-state
flashing potential. The magnetic potential was realized by periodically
modulating the stray field of a magnetic bubble lattice in a uniaxial ferrite
garnet film. At large amplitudes of the driving field, the dynamics of
particles resembles an ordinary random walk with a frequency-dependent
diffusion coefficient. However, subdiffusive and oscillatory dynamics at short
time scales is observed when decreasing the amplitude. We present a persistent
random walk model to elucidate the underlying mechanism of motion, and perform
numerical simulations to demonstrate that the anomalous motion originates from
the dynamic disorder in the structure of the magnetic lattice, induced by
slightly irregular shape of bubbles.",1606.05783v1
2016-07-19,Electrical detection of spiral spin structures in Pt|Cu_2OSeO_3 heterostructures,"The interaction between the itinerant spins in metals and localized spins in
magnetic insulators thus far has only been explored in collinear spin systems,
such as garnets. Here, we report the spin-Hall magnetoresistance (SMR)
sensitive to the surface magnetization of the spin-spiral material, Cu_2OSeO_3.
We experimentally demonstrate that the angular dependence of the SMR changes
drastically at the transition between the helical spiral and the conical spiral
phases. Furthermore, the sign and magnitude of the SMR in the conical spiral
state are controlled by the cone angle. We show that this complex behaviour can
be qualitatively explained within the SMR theory initially developed for
collinear magnets. In addition, we studied the spin Seebeck effect (SSE), which
is sensitive to the bulk magnetization. It originates from the conversion of
thermally excited low-energy spin waves in the magnet, known as magnons, into
the spin current in the adjacent metal contact (Pt). The SSE displays
unconventional behavior where not only the magnitude but also the phase of the
SSE vary with the applied magnetic field.",1607.05630v1
2016-08-03,Automatic numerical evaluation of vacancy-mediated transport for arbitrary crystals: Onsager coefficients in the dilute limit using a Green function approach,"A general solution for vacancy-mediated diffusion in the
dilute-vacancy/dilute-solute limit for arbitrary crystal structures is derived
from the master equation. A general numerical approach to the vacancy lattice
Green function reduces to the sum of a few analytic functions and numerical
integration of a smooth function over the Brillouin zone for arbitrary
crystals. The Dyson equation solves for the Green function in the presence of a
solute with arbitrary but finite interaction range to compute the transport
coefficients accurately, efficiently and automatically, including cases with
very large differences in solute-vacancy exchange rates. The methodology takes
advantage of the space group symmetry of a crystal to reduce the complexity of
the matrix inversion in the Dyson equation. An open-source implementation of
the algorithm is available, and numerical results are presented for the
convergence of the integration error of the bare vacancy Green function, and
tracer correlation factors for a variety of crystals including wurtzite
(hexagonal diamond) and garnet.",1608.01252v2
2016-08-11,Cluster size convergence of the density matrix embedding theory and its dynamical cluster formulation: a study with an auxiliary-field quantum Monte Carlo solver,"We investigate the cluster size convergence of the energy and observables
using two forms of density matrix embedding theory (DMET): the original cluster
form (CDMET) and a new formulation motivated by the dynamical cluster
approximation (DCA-DMET). Both methods are applied to the half-filled one- and
two-dimensional Hubbard models using a sign-problem free auxiliary-field
quantum Monte Carlo (AFQMC) impurity solver, which allows for the treatment of
large impurity clusters of up to 100 sites. While CDMET is more accurate at
smaller impurity cluster sizes, DCA- DMET exhibits faster asymptotic
convergence towards the thermodynamic limit (TDL). We use our two formulations
to produce new accurate estimates for the energy and local moment of the
two-dimensional Hubbard model for U/t = 2, 4, 6. These results compare
favourably with the best data available in literature, and help resolve earlier
uncertainties in the moment for U/t = 2.",1608.03316v1
2016-10-14,Bidirectional particle transport and size selective sorting of Brownian particles in a flashing spatially periodic energy landscape,"We demonstrate a size sensitive experimental scheme which enables
bidirectional transport and fractionation of paramagnetic colloids in a fluid
medium. It is shown that two types of magnetic colloidal particles with
different sizes can be simultaneously transported in opposite directions, when
deposited above a stripe-patterned ferrite garnet film subjected to a
square-wave magnetic modulation. Due to their different sizes, the particles
are located at distinct elevations above the surface, and they experience two
different energy landscapes, generated by the modulated magnetic substrate. By
combining theoretical arguments and numerical simulations, we reveal such
energy landscapes, which fully explain the bidirectional transport mechanism.
The proposed technique does not require pre-imposed channel geometries such as
in conventional microfluidics or lab-on-a-chip systems, and permits remote
control over the particle motion, speed and trajectory, by using relatively low
intense magnetic fields.",1610.04380v1
2016-10-26,A general second order complete active space self-consistent-field solver for large-scale systems,"We present a new second order complete active space self-consistent field
implementation to converge wavefunctions for both large active spaces and large
atomic orbital (AO) bases. Our algorithm decouples the active space
wavefunction solver from the orbital optimization in the microiterations, and
thus may be easily combined with various modern active space solvers. We also
introduce efficient approximate orbital gradient and Hessian updates, and step
size determination. We demonstrate its capabilities by calculating the
low-lying states of the Fe(\Roman{2})-porphine complex with modest resources
using a density matrix renormalization group solver in a CAS(22,27) active
space and a 3000 AO basis.",1610.08394v2
2016-12-02,Tiny adiabatic-demagnetization refrigerator for a commercial superconducting quantum interference device magnetometer,"A tiny adiabatic-demagnetization refrigerator (T-ADR) has been developed for
a commercial superconducting quantum interference device magnetometer [Magnetic
Property Measurement System (MPMS) from Quantum Design]. The whole T-ADR system
is fit in a cylindrical space of the diameter $8.5$ mm and the length $250$ mm,
and can be inserted into the narrow sample tube of MPMS. A sorption pump is
self-contained in T-ADR, and hence no complex gas handling system is necessary.
With the single crystalline Gd$_3$Ga$_5$O$_{12}$ garnet ($\sim 2$ grams) used
as a magnetic refrigerant, the routinely achievable lowest temperature is $\sim
0.56$ K. The lower detection limit for a magnetization anomaly is $\sim 1
\times 10^{-7}$ emu, estimated from fluctuation of the measured magnetization.
The background level is $\sim 5 \times 10^{-5}$ emu below 2 K at $H = 100$ Oe,
which is largely attributable to a contaminating paramagnetic signal from the
magnetic refrigerant.",1612.01376v1
2016-12-31,Stripe order in the underdoped region of the two-dimensional Hubbard model,"Competing inhomogeneous orders are a central feature of correlated electron
materials including the high-temperature superconductors. The two- dimensional
Hubbard model serves as the canonical microscopic physical model for such
systems. Multiple orders have been proposed in the underdoped part of the phase
diagram, which corresponds to a regime of maximum numerical difficulty. By
combining the latest numerical methods in exhaustive simulations, we uncover
the ordering in the underdoped ground state. We find a stripe order that has a
highly compressible wavelength on an energy scale of a few Kelvin, with
wavelength fluctuations coupled to pairing order. The favored filled stripe
order is different from that seen in real materials. Our results demonstrate
the power of modern numerical methods to solve microscopic models even in
challenging settings.",1701.00054v3
2017-01-27,The Python-based Simulations of Chemistry Framework (PySCF),"PySCF is a general-purpose electronic structure platform designed from the
ground up to emphasize code simplicity, both to aid new method development, as
well as for flexibility in computational workflow. The package provides a wide
range of tools to support simulations of finite size systems, extended systems
with periodic boundary conditions, low dimensional periodic systems, and custom
Hamiltonians, using mean-field and post-mean-field methods with standard
Gaussian basis functions. To ensure easy of extensibility, PySCF uses the
Python language to implement almost all its features, while computationally
critical paths are implemented with heavily optimized C routines. Using this
combined Python/C implementation, the package is as efficient as the best
existing C or Fortran based quantum chemistry programs. In this paper we
document the capabilities and design philosophy of the current version of the
PySCF package.",1701.08223v2
2017-03-31,Time-dependent N-electron valence perturbation theory with matrix product state reference wavefunctions for large active spaces and basis sets: Applications to the chromium dimer and all-trans polyenes,"In earlier work [J. Chem. Phys. 144, 064102 (2016)], we introduced a
time-dependent formulation of the second-order N-electron valence perturbation
theory (t-NEVPT2) which (i) had a lower computational scaling than the usual
internally-contracted perturbation formulation, and (ii) yielded the fully
uncontracted NEVPT2 energy. Here, we present a combination of t-NEVPT2 with a
matrix product state (MPS) reference wavefunction (t-MPS-NEVPT2) that allows to
compute uncontracted dynamic correlation energies for large active spaces and
basis sets, using the time-dependent density matrix renormalization group
(td-DMRG) algorithm. In addition, we report a low-scaling MPS-based
implementation of strongly-contracted NEVPT2 (sc-MPS-NEVPT2) that avoids
computation of the four-particle reduced density matrix. We use these new
methods to compute the dissociation energy of the chromium dimer and to study
the low-lying excited states in all-trans polyenes (C$_4$H$_6$ to
C$_{24}$H$_{26}$), incorporating dynamic correlation for reference
wavefunctions with up to 24 active electrons and orbitals.",1703.10830v3
2017-05-16,Bloch line dynamics within moving domain walls in 3D ferromagnets,"We study field-driven magnetic domain wall dynamics in garnet strips by
large-scale three-dimensional micromagnetic simulations. The domain wall
propagation velocity as a function of the applied field exhibits a low-field
linear part terminated by a sudden velocity drop at a threshold field
magnitude, related to the onset of excitations of internal degrees of freedom
of the domain wall magnetization. By considering a wide range of strip
thicknesses from 30 nm to 1.89 $\mu$m, we find a non-monotonic thickness
dependence of the threshold field for the onset of this instability, proceeding
via nucleation and propagation of Bloch lines within the domain wall. We
identify a critical strip thickness above which the velocity drop is due to
nucleation of horizontal Bloch lines, while for thinner strips and depending on
the boundary conditions employed, either generation of vertical Bloch lines, or
close-to-uniform precession of the domain wall internal magnetization takes
place. For strips of intermediate thicknesses, the vertical Bloch lines assume
a deformed structure due to demagnetizing fields at the strip surfaces,
breaking the symmetry between the top and bottom faces of the strip, and
resulting in circulating Bloch line dynamics along the perimeter of the domain
wall.",1705.05642v1
2017-06-29,Time-step targeting time-dependent and dynamical density matrix renormalization group algorithms with ab initio Hamiltonians,"We study the dynamical density matrix renormalization group (DDMRG) and
time-dependent density matrix renormalization group (td-DMRG) algorithms in the
ab initio context, to compute dynamical correlation functions of correlated
systems. We analyze the strengths and weaknesses of the two methods in small
model problems, and propose two simple improved formulations, DDMRG$^{++}$ and
td-DMRG$^{++}$, that give increased accuracy at the same bond dimension, at a
nominal increase in cost. We apply DDMRG$^{++}$ to obtain the oxygen
core-excitation energy in the water molecule in a quadruple-zeta quality basis,
which allows us to estimate the remaining correlation error in existing coupled
cluster results. Further, we use DDMRG$^{++}$ to compute the local density of
states and gaps, and td-DMRG$^{++}$ to compute the complex polarization
function, in linear hydrogen chains with up to 50 H atoms, to study metallicity
and delocalization as a function of bond-length.",1706.09537v2
2017-08-01,Importance sampling large deviations in nonequilibrium steady states. I,"Large deviation functions contain information on the stability and response
of systems driven into nonequilibrium steady states, and in such a way are
similar to free energies for systems at equilibrium. As with equilibrium free
energies, evaluating large deviation functions numerically for all but the
simplest systems is difficult, because by construction they depend on
exponentially rare events. In this first paper of a series, we evaluate
different trajectory-based sampling methods capable of computing large
deviation functions of time integrated observables within nonequilibrium steady
states. We illustrate some convergence criteria and best practices using a
number of different models, including a biased Brownian walker, a driven
lattice gas, and a model of self-assembly. We show how two popular methods for
sampling trajectory ensembles, transition path sampling and diffusion Monte
Carlo, suffer from exponentially diverging correlations in trajectory space as
a function of the bias parameter when estimating large deviation functions.
Improving the efficiencies of these algorithms requires introducing guiding
functions for the trajectories.",1708.00459v2
2017-08-13,Experimental study of antiferromagnetic resonance in noncollinear antiferromagnet Mn$_{3}$Al$_{2}$Ge$_{3}$O$_{12}$,"We have measured antiferromagnetic resonance (AFMR) frequency-field
dependences for aluminum-manganese garnet Mn$_{3}$Al$_{2}$Ge$_{3}$O$_{12}$ at
frequencies from 1 to 125 GHz and at the fields up to 60 kOe. Three AFMR modes
were observed for all orientations, their zero field gaps are about 40 and 70
GHz. Andreev-Marchenko hydrodynamic theory [Sov. Phys. Usp. 130, 39 (1980)]
well describes experimental frequency-field dependences. We have observed
hysteresis of resonance absorption as well as history dependence of resonance
absorption near gap frequencies below 10 kOe in all three measured field
orientations, which are supposedly due to the sample domain structure.
Observation of the AFMR signal at the frequencies from 1 to 5 GHz allows to
estimate repulsion of nuclear and electron modes of spin precession in the
vicinity of spin-reorientation transition at H||[100].",1708.03961v1
2017-08-16,Anisotropic phase diagram and spin fluctuations of the hyperkagome magnet Gd3Ga5O12 as revealed by sound velocity measurements,"Sound velocity and attenuation measurements on the frustrated garnet material
Gd3Ga5O12 (GGG) are presented as a function of field and temperature, using two
different acoustic modes and with two different magnetic field orientations:
[100] and [110]. We demonstrate that the phase diagram is highly anisotropic,
with two distinct field-induced ordered phases for H||[110] and only one for
H||[100]. Extensive lattice softening is found to occur at low fields, which
can be associated with spin fluctuations. However, deep within the spin liquid
phase a low-temperature stiffening of the lattice and reduced attenuation
provides evidence for a spin gap which may be related to short-range
antiferromagnetic correlations over minimal 10-spin loops.",1708.04916v2
2017-08-30,Exact fluctuations of nonequilibrium steady states from approximate auxiliary dynamics,"We describe a framework to significantly reduce the computational effort to
evaluate large deviation functions of time integrated observables within
nonequilibrium steady states. We do this by incorporating an auxiliary dynamics
into trajectory based Monte Carlo calculations, through a transformation of the
system's propagator using an approximate guiding function. This procedure
importance samples the trajectories that most contribute to the large deviation
function, mitigating the exponentially complexity of such calculations. We
illustrate the method by studying driven diffusions and interacting lattice
models in one and two dimensions. Our work offers an avenue to calculate large
deviation functions for high dimensional systems driven far from equilibrium.",1708.09482v4
2017-09-06,Superposition as a Relativistic Filter,"By associating a binary signal with the relativistic worldline of a particle,
a binary form of the phase of non-relativistic wavefunctions is naturally
produced by time dilation. An analog of superposition also appears as a Lorentz
filtering process, removing paths that are relativistically inequivalent. In a
model that includes a stochastic component, the free-particle Schr\""{o}dinger
equation emerges from a completely relativistic context in which its origin
{\em and function} is known. The result establishes the fact that the phase of
wavefunctions in Schr\""{o}dinger's equation and the attendant superposition
principle may both be considered remnants of time dilation. This strongly
argues that quantum mechanics has its origins in special relativity.",1709.02022v1
2017-10-23,Frequency and wavenumber selective excitation of spin waves through coherent energy transfer from elastic waves,"Using spin-wave tomography (SWaT), we have investigated the excitation and
the propagation dynamics of optically-excited magnetoelastic waves, i.e.
hybridized modes of spin waves and elastic waves, in a garnet film. By using
time-resolved SWaT, we reveal the excitation dynamics of magnetoelastic waves
through coherent-energy transfer between optically-excited pure-elastic waves
and spin waves via magnetoelastic coupling. This process realizes frequency and
wavenumber selective excitation of spin waves at the crossing of the dispersion
relations of spin waves and elastic waves. Finally, we demonstrate that the
excitation mechanism of the optically-excited pure-elastic waves, which are the
source of the observed magnetoelastic waves, is dissipative in nature.",1710.08087v2
2017-10-27,Nuclear Magnetic Resonance in Noncollinear Antiferromagnet Mn3Al2Ge3O12,"The 55Mn nuclear magnetic resonance spectrum of noncollinear 12-sublattice
antiferromagnet Mn3Al2Ge3O12 has been studied in the frequency range of 200 -
640 MHz in the external magnetic field H || [001]} at T=1.2 K. Three absorption
lines have been observed in fields less than the field of the reorientation
transition Hc at the polarization h||H of the rf field. Two lines have been
observed at H > Hc and h_|_H. The spectral parameters indicate that the
magnetic structure of manganese garnet differs slightly from the exchange
triangular 120-degree structure. The anisotropy of the spin reduction and (or)
weak antiferromagnetism that are allowed by the crystal symmetry lead to the
difference of approximately 3% in the magnetization of sublattices in the field
H < Hc. When the spin plane rotates from the orientation perpendicular to the
C3 axis to the orientation perpendicular to the C4 axis, all magnetic moments
of the electronic subsystem decrease by approximately 2% from the average value
in the zero field.",1710.10048v1
2017-11-13,Quantum Simulation of Electronic Structure with Linear Depth and Connectivity,"As physical implementations of quantum architectures emerge, it is
increasingly important to consider the cost of algorithms for practical
connectivities between qubits. We show that by using an arrangement of gates
that we term the fermionic swap network, we can simulate a Trotter step of the
electronic structure Hamiltonian in exactly $N$ depth and with $N^2/2$
two-qubit entangling gates, and prepare arbitrary Slater determinants in at
most $N/2$ depth, all assuming only a minimal, linearly connected architecture.
We conjecture that no explicit Trotter step of the electronic structure
Hamiltonian is possible with fewer entangling gates, even with arbitrary
connectivities. These results represent significant practical improvements on
the cost of most Trotter based algorithms for both variational and phase
estimation based simulation of quantum chemistry.",1711.04789v2
2017-12-04,Phase-resolved Spin-Wave Tomography,"The propagation dynamics of spin waves are represented by their dispersion
relations. Recently, we have developed a method, called spin-wave tomography
(SWaT), to obtain dispersion relation of spin waves in the long wavelength
regime, so-called pure magnetostatic waves. In our previous studies on SWaT,
phase information of spin waves was disregarded. In this report, we demonstrate
an advanced SWaT analysis, called phase-resolved spin-wave tomography (PSWaT),
to realize the direct observation of the amplitude and the phase of spin waves.
The PSWaT spectra are obtained by separating the real and the imaginary
components of the complex Fourier transform in the SWaT analysis. We
demonstrate the PSWaT spectra of spin waves excited by the photo-induced
demagnetization in a Bi-doped garnet film, reflecting the characteristic
features of the complex dynamical susceptibility affected by magnetostatic
coupling in the film.",1712.00927v2
2017-12-05,Surface plasmon-mediated nanoscale localization of laser-driven sub-THz spin dynamics in magnetic dielectrics,"Ultrafast all-optical control of spins with femtosecond laser pulses is one
of the hot topics at the crossroads of photonics and magnetism with a direct
impact on future magnetic recording. Unveiling light-assisted recording
mechanisms for an increase of the bit density beyond the diffraction limit
without excessive heating of the recording medium is an open challenge. Here we
show that surface plasmon-polaritons in hybrid metal-dielectric structures can
provide spatial confinement of the inverse Faraday effect, mediating the
excitation of localized coherent spin precession with 0.41 THz frequency. We
demonstrate a two orders of magnitude enhancement of the excitation efficiency
at the surface plasmon resonance within the 100 nm layer in dielectric garnet.
Our findings broaden the horizons of ultrafast spin-plasmonics and open
pathways towards non-thermal opto-magnetic recording at the nano-scale.",1712.01617v1
2017-12-27,Progress on the design of a perpendicularly biased 2nd harmonic cavity for the Fermilab Booster,"A perpendicularly biased 2nd harmonic cavity is being designed and built for
the Fermilab Booster. Its purpose is to flatten the bucket at injection and
thus change the longitudinal beam distribution to decrease space charge
effects. It can also help at extraction. The cavity frequency range is 76 - 106
MHz. The power amplifier will be built using the Y567B tetrode, which is also
used for the fundamental mode cavities in the Fermilab Booster. We discuss
recent progress on the cavity, the biasing solenoid design and plans for
testing the tuner's garnet material.",1712.09637v1
2018-03-21,180-degree phase shift of magnetoelastic waves observed by phase-resolved spin-wave tomography,"We have investigated optically-excited magnetoelastic waves by phase-resolved
spin-wave tomography (PSWaT). PSWaT reconstructs dispersion relation of spin
waves together with their phase information by using time-resolved
magneto-optical imaging for spin-wave propagation followed by an analysis based
on the convolution theorem and a complex Fourier transform. In PSWaT spectra
for a Bi-doped garnet film, we found a 180 degree phase shift of magnetoelastic
waves at around the crossing of the dispersion relations of spin and elastic
waves. The result is explained by a coupling between spin waves and elastic
waves through magnetoelastic interaction. We also propose an efficient way for
phase manipulation of magnetoelastic waves by rotating the orientation of
magnetization less than 10 degree.",1803.07697v1
2018-04-14,Particle Morphology and Lithium Segregation to Surfaces of the Li$_7$La$_3$Zr$_2$O$_{12}$ Solid Electrolyte,"Solid electrolytes for solid-state Li-ion batteries are stimulating
considerable interest for next-generation energy storage applications. The
Li$_7$La$_3$Zr$_2$O$_{12}$ garnet-type solid electrolyte has received
appreciable attention as a result of its high ionic conductivity. However,
several challenges for the successful application of solid-state devices based
on Li$_7$La$_3$Zr$_2$O$_{12}$ remain, such as dendrite formation and
maintaining physical contact at interfaces over many Li
intercalation/extraction cycles. Here, we apply first-principles density
functional theory to provide insights into the Li$_7$La$_3$Zr$_2$O$_{12}$
particle morphology under various physical and chemical conditions. Our
findings indicate Li segregation at the surfaces, suggesting Li-rich grain
boundaries at typical synthesis and sintering conditions. On the basis of our
results, we propose practical strategies to curb Li segregation at the
Li$_7$La$_3$Zr$_2$O$_{12}$ interfaces. This approach can be extended to other
Li-ion conductors for the design of practical energy storage devices.",1804.05165v1
2018-06-19,Time-Dependent Density Matrix Renormalization Group Algorithms for Nearly Exact Absorption and Fluorescence Spectra of Molecular Aggregates at Both Zero and Finite Temperature,"We implement and apply time-dependent density matrix renormalization group
(TD-DMRG) algorithms at zero and finite temperature to compute the linear
absorption and fluorescence spectra of molecular aggregates. Our implementation
is within a matrix product state/operator framework with an explicit treatment
of the excitonic and vibrational degrees of freedom, and uses the locality of
the Hamiltonian in the zero-exciton space to improve the efficiency and
accuracy of the calculations. We demonstrate the power of the method by
calculations on several molecular aggregate models, comparing our results
against those from multi-layer multiconfiguration time- dependent Hartree and
n-particle approximations. We find that TD-DMRG provides an accurate and
efficient route to calculate the spectrum of molecular aggregates.",1806.07443v2
2018-07-22,Efficient representation of long-range interactions in tensor network algorithms,"We describe a practical and efficient approach to represent physically
realistic long-range interactions in two-dimensional tensor network algorithms
via projected entangled-pair operators (PEPOs). We express the long-range
interaction as a linear combination of correlation functions of an auxiliary
system with only nearest-neighbor interactions. To obtain a smooth and radially
isotropic interaction across all length scales, we map the physical lattice to
an auxiliary lattice of expanded size. Our construction yields a long-range
PEPO as a sum of ancillary PEPOs, each of small, constant bond dimension. This
representation enables efficient numerical simulations with long-range
interactions using projected entangled pair states.",1807.08378v2
2018-07-26,A time-dependent formulation of coupled cluster theory for many-fermion systems at finite temperature,"We present a time-dependent formulation of coupled cluster theory. This
theory allows for direct computation of the free energy of quantum systems at
finite temperature by imaginary time integration and is closely related to the
thermal cluster cumulant theory of Mukherjee and co-workers. Our derivation
highlights the connection to perturbation theory and zero-temperature coupled
cluster theory. We show explicitly how the finite-temperature coupled cluster
singles and doubles amplitude equations can be derived in analogy with the
zero-temperature theory and how response properties can be efficiently computed
using a variational Lagrangian. We discuss the implementation for realistic
systems and showcase the potential utility of the method with calculations of
the exchange correlation energy of the uniform electron gas at warm dense
matter conditions.",1807.09961v2
2018-08-28,The FNAL Booster 2nd Harmonic RF Cavity,"A second harmonic RF cavity which uses perpendicularly biased garnet for
frequency tuning is currently being constructed for use in the Fermilab
Booster. The cavity will operate at twice the fundamental RF frequency, from
~76 - 106 MHz, and will be turned on only during injection, and transition or
extraction. Its main purpose is to reduce beam loss as required by Fermilab's
Proton Improvement Plan (PIP). After three years of optimization and study, the
cavity design has been finalized and all constituent parts have been received.
We discuss the design aspects of the cavity and its associated systems,
component testing, and status of the cavity construction.",1808.09513v1
2018-09-27,The electronic complexity of the ground-state of the FeMo cofactor of nitrogenase as relevant to quantum simulations,"We report that a recent active space model of the nitrogenase FeMo cofactor,
proposed in the context of quantum simulations, is not representative of the
electronic structure of the FeMo cofactor ground-state. Although quantum
resource estimates, outside of the cost of adiabatic state preparation, will
not be much affected, conclusions should not be drawn from the complexity of
classical simulations of the electronic structure of this system in this active
space. We provide a different model active space for the FeMo cofactor that
contains the basic open-shell qualitative character, which may be useful as a
benchmark system for making classical and quantum resource estimates.",1809.10307v1
2018-10-03,Efficient ab initio auxiliary-field quantum Monte Carlo calculations in Gaussian bases via low-rank tensor decomposition,"We describe an algorithm to reduce the cost of auxiliary-field quantum Monte
Carlo (AFQMC) calculations for the electronic structure problem. The technique
uses a nested low-rank factorization of the electron repulsion integral (ERI).
While the cost of conventional AFQMC calculations in Gaussian bases scales as
$\mathcal{O}(N^4)$ where $N$ is the size of the basis, we show that
ground-state energies can be computed through tensor decomposition with reduced
memory requirements and sub-quartic scaling. The algorithm is applied to
hydrogen chains and square grids, water clusters, and hexagonal BN. In all
cases we observe significant memory savings and, for larger systems, reduced,
sub-quartic simulation time.",1810.01549v2
2018-11-14,Enhancing nanoparticle diffusion on a unidirectional domain wall magnetic ratchet,"The performance of nanoscale magnetic devices is often limited by the
presence of thermal fluctuations, while in micro-nanofluidic applications the
same fluctuations may be used to spread reactants or drugs. Here we demonstrate
the controlled motion and the enhancement of diffusion of magnetic
nanoparticles that are manipulated and driven across a series of Bloch walls
within an epitaxially grown ferrite garnet film. We use a rotating magnetic
field to generate a traveling wave potential that unidirectionally transports
the nanoparticles at a frequency tunable speed. Strikingly, we find an
enhancement of diffusion along the propulsion direction and a frequency
dependent diffusion coefficient that can be precisely controlled by varying the
system parameters. To explain the reported phenomena, we develop a theoretical
approach that shows a fair agreement with the experimental data enabling an
exact analytical expression for the enhanced diffusivity above the magnetically
modulated periodic landscape. Our technique to control thermal fluctuations of
driven magnetic nanoparticles represents a versatile and powerful way to
programmably transport magnetic colloidal matter in a fluid, opening the doors
to different fluidic applications based on exploiting magnetic domain wall
ratchets.",1811.05762v1
2019-01-17,Statistical Mechanics and the Ghosts of Departed Quantities,"Quantum mechanics appears to contain ghosts from both classical statistical
mechanics and special relativity. On one hand, both the Dirac and
Schr\""{o}dinger equations have classical analogs that emerge directly from
classical statistical mechanics, unimpeded by major problems of interpretation.
On the other hand, the formal analytic continuation that takes these classical
equations to the quantum version introduces a velocity dependent phase.
However, among classical theories, only in relativistic mechanics does one find
path-dependent phase in the form of relativistic time dilation. This paper
explores the idea that if we start with statistical mechanics and special
relativity we can discover a version of the quantum algorithm and show that at
least some of the resulting ghosts are direct descendants of those connected
with the birth of the differential calculus.",1901.11066v1
2019-01-25,Monolithic integration of broadband optical isolators for polarization-diverse silicon photonics,"Integrated optical isolators have been a longstanding challenge for photonic
integrated circuits (PIC). An ideal integrated optical isolator for PIC should
be made by a monolithic process, have a small footprint, exhibit broadband and
polarization-diverse operation, and be compatible with multiple materials
platforms. Despite significant progress, the optical isolators reported so far
do not meet all these requirements. In this article we present monolithically
integrated broadband magneto-optical isolators on silicon and silicon nitride
(SiN) platforms operating for both TE and TM modes with record high
performances, fulfilling all the essential characteristics for PIC
applications. In particular, we demonstrate fully-TE broadband isolators by
depositing high quality magneto-optical garnet thin films on the sidewalls of
Si and SiN waveguides, a critical result for applications in TE-polarized
on-chip lasers and amplifiers. This work demonstrates monolithic integration of
high performance optical isolators on chip for polarization-diverse silicon
photonic systems, enabling new pathways to impart nonreciprocal photonic
functionality to a variety of integrated photonic devices.",1902.01236v1
2019-03-09,Conversion of projected entangled pair states into a canonical form,"We propose an algorithm to convert a projected entangled pair state (PEPS)
into a canonical form, analogous to the well-known canonical form of a matrix
product state. Our approach is based on a variational gauging ansatz for the QR
tensor decomposition of PEPS columns into a matrix product operator and a
finite depth circuit of unitaries and isometries. We describe a practical
initialization scheme that leads to rapid convergence in the QR optimization.
We explore the performance and stability of the variational gauging algorithm
in norm calculations for the transverse-field Ising and Heisenberg models on a
square lattice. We also demonstrate energy optimization within the PEPS
canonical form for the transverse-field Ising and Heisenberg models. We expect
this canonical form to open up improved analytical and numerical approaches for
PEPS.",1903.03843v4
2019-04-15,Dynamical phase behavior of the single- and multi-lane asymmetric simple exclusion process via matrix product states,"We analyze the dynamical phases of the current-biased 1D and multi-lane open
asymmetric simple exclusion processes (ASEP), using matrix product states and
the density matrix renormalization group (DMRG) algorithm. In the 1D ASEP, we
present a systematic numerical study of the current cumulant generating
function and its derivatives, which serve as dynamical phase order parameters.
We further characterize the microscopic structure of the phases from local
observables and the entanglement spectrum. In the multi-lane ASEP, which may be
viewed as finite width 2D strip, we use the same approach and find the
longitudinal current-biased dynamical phase behavior to be sensitive to
transverse boundary conditions. Our results serve to illustrate the potential
of tensor networks in the simulation of classical nonequilibrium statistical
models.",1904.07336v1
2019-05-01,Hamiltonian symmetries in auxiliary-field quantum Monte Carlo calculations for electronic structure,"We describe how to incorporate symmetries of the Hamiltonian into
auxiliary-field quantum Monte Carlo calculations (AFQMC). Focusing on the case
of Abelian symmetries, we show that the computational cost of most steps of an
AFQMC calculation is reduced by $N_k^{-1}$, where $N_k$ is the number of
irreducible representations of the symmetry group. We apply the formalism to a
molecular system as well as to several crystalline solids. In the latter case,
the lattice translational group provides increasing savings as the number of k
points is increased, which is important in enabling calculations that approach
the thermodynamic limit. The extension to non-Abelian symmetries is briefly
discussed.",1905.00511v1
2019-05-28,Coupled-cluster impurity solvers for dynamical mean-field theory,"We describe the use of coupled-cluster theory as an impurity solver in
dynamical mean-field theory (DMFT) and its cluster extensions. We present
numerical results at the level of coupled-cluster theory with single and double
excitations (CCSD) for the density of states and self-energies of cluster
impurity problems in the one- and two-dimensional Hubbard models. Comparison to
exact diagonalization shows that CCSD produces accurate density of states and
self-energies at a variety of values of $U/t$ and filling fractions. However,
the low cost allows for the use of many bath sites, which we define by a
discretization of the hybridization directly on the real frequency axis. We
observe convergence of dynamical quantities using approximately 30 bath sites
per impurity site, with our largest 4-site cluster DMFT calculation using 120
bath sites. We suggest coupled cluster impurity solvers will be attractive in
ab initio formulations of dynamical mean-field theory.",1905.12050v2
2019-08-14,A Tuneable Magnetic Domain Wall Conduit Regulating Nanoparticle Diffusion,"We demonstrate a general and robust method to confine on a plane strongly
diffusing submicrometer particles in water by using size tunable magnetic
channels. These virtual conduits are realized with pairs of movable Bloch walls
(BWs) located within an epitaxially grown ferrite garnet film. We show that,
once inside the magnetic conduit, the particles experience an effective local
parabolic potential in the transverse direction, while freely diffusing along
the conduit. The stiffness of the magnetic potential is determined as a
function of field amplitude which varies the width of the magnetic channel, and
precise control of the degree of confinement is demonstrated by tuning the
applied field. The magnetic conduit is then used to realize single files of
non-passing particles and to induce periodic condensation of an ensemble of
particles into parallel stripes in a completely controllable and reversible
manner.",1908.05039v1
2019-09-18,Efficient Formulation of Ab Initio Quantum Embedding in Periodic Systems: Dynamical Mean-Field Theory,"We present an efficient ab initio dynamical mean-field theory (DMFT)
implementation for quantitative simulations in solids. Our DMFT scheme employs
ab initio Hamiltonians defined for impurities comprising the full unit cell or
a supercell of atoms and for realistic quantum chemical basis sets. We avoid
double counting errors by using Hartree-Fock as the low-level theory. Intrinsic
and projected atomic orbitals (IAO+PAO) are chosen as the local embedding
basis, facilitating numerical bath truncation. Using an efficient integral
transformation and coupled-cluster Green's function (CCGF) impurity solvers, we
are able to handle embedded impurity problems with several hundred orbitals. We
apply our ab initio DMFT approach to study a hexagonal boron nitride monolayer,
crystalline silicon, and nickel oxide in the antiferromagnetic phase, with up
to 104 and 78 impurity orbitals in spin-restricted and unrestricted cluster
DMFT calculations and over 100 bath orbitals. We show that our scheme produces
accurate spectral functions compared to both benchmark periodic coupled-cluster
computations and experimental spectra.",1909.08592v2
2019-09-18,Efficient Implementation of Ab Initio Quantum Embedding in Periodic Systems: Density Matrix Embedding Theory,"We describe an efficient quantum embedding framework for realistic ab initio
density matrix embedding (DMET) calculations in solids. We discuss in detail
the choice of orbitals and mapping to a lattice, treatment of the virtual space
and bath truncation, and the lattice-to embedded integral transformation. We
apply DMET in this ab initio framework to a hexagonal boron nitride monolayer,
crystalline silicon, and nickel monoxide in the antiferromagnetic phase, using
large embedded clusters with up to 300 embedding orbitals. We demonstrate our
formulation of ab initio DMET in the computation of ground-state properties
such as the total energy, equation of state, magnetic moment and correlation
functions.",1909.08596v2
2019-09-24,First principles coupled cluster theory of the electronic spectrum of the transition metal dichalcogenides,"The electronic properties of two-dimensional transition metal dichalcogenides
(2D TMDs) have attracted much attention during the last decade. We show how a
diagrammatic ab initio coupled cluster singles and doubles (CCSD) treatment
paired with a careful thermodynamic limit extrapolation in two dimensions can
be used to obtain converged bandgaps for monolayer materials in the MoS2
family. We find general agreement between CCSD and previously reported GW
simulations in terms of the band structure, but predict slightly higher band
gap values and effective hole masses compared to previous reports. We also
investigate the ability of CCSD to describe trion states, finding reasonable
qualitative structure, but poor excitation energies due to the lack of
screening of three-particle excitations in the effective Hamiltonian. Our study
provides an independent high-level benchmark of the role of many-body effects
in 2D TMDs and showcases the potential strengths and weaknesses of diagrammatic
coupled cluster approaches for realistic materials.",1909.10886v1
2019-09-25,Constructing Auxiliary Dynamics for Nonequilibrium Stationary States by Variance Minimization,"We present a strategy to construct guiding distribution functions (GDFs)
based on variance minimization. Auxiliary dynamics via GDFs mitigates the
exponential growth of variance as a function of bias in Monte Carlo estimators
of large deviation functions. The variance minimization technique exploits the
exact properties of eigenstates of the tilted operator that defines the biased
dynamics in the nonequilibrium system. We demonstrate our techniques in two
classes of problems. In the continuum, we show that GDFs can be optimized to
study interacting driven diffusive systems where the efficiency is
systematically improved by incorporating higher correlations into the GDF. On
the lattice, we use a correlator product state ansatz to study the 1D WASEP. We
show that with modest resources we can capture the features of the
susceptibility in large systems that marks the phase transition from uniform
transport to a traveling wave state. Our work extends the repertoire of tools
available to study nonequilibrium properties in realistic systems.",1909.11283v3
2019-10-22,Exact Parameterization of Fermionic Wave Functions via Unitary Coupled Cluster Theory,"A formal analysis is conducted on the exactness of various forms of unitary
coupled cluster (UCC) theory based on particle-hole excitation and
de-excitation operators. Both the conventional single exponential UCC
parameterization and a disentangled (factorized) version are considered. We
formulate a differential cluster analysis to determine the UCC amplitudes
corresponding to a general quantum state. The exactness of conventional UCC
(ability to represent any state) is explored numerically and it is formally
shown to be determined by the structure of the critical points of the UCC
exponential mapping. A family of disentangled UCC wave functions are shown to
exactly parameterize any state, thus showing how to construct
Trotter-error-free parameterizations of UCC for applications in quantum
computing. From these results, we derive an exact disentangled UCC
parameterization that employs an infinite sequence of particle-hole or general
one- and two-body substitution operators.",1910.10130v1
2019-11-18,Finite temperature density matrix embedding theory,"We describe a formulation of the density matrix embedding theory at finite
temperature. We present a generalization of the ground-state bath orbital
construction that embeds a mean-field finite-temperature density matrix up to a
given order in the Hamiltonian, or the Hamiltonian up to a given order in the
density matrix. We assess the performance of the finite-temperature density
matrix embedding on the 1D Hubbard model both at half-filling and away from it,
and the 2D Hubbard model at half-filling, comparing to exact data where
available, as well as results from finite-temperature density matrix
renormalization group, dynamical mean-field theory, and dynamical cluster
approximations. The accuracy of finite-temperature density matrix embedding
appears comparable to that of the ground-state theory, with at most a modest
increase in bath size, and competitive with that of cluster dynamical
mean-field theory.",1911.07439v1
2019-12-27,Ferromagnetic state above room temperature in a proximitized topological Dirac semimetal,"We report an above-room-temperature ferromagnetic state realized in a
proximitized Dirac semimetal, which is fabricated by growing typical Dirac
semimetal Cd$_3$As$_2$ films on a ferromagnetic garnet with strong
perpendicular magnetization. Observed anomalous Hall conductivity with
substantially large Hall angles is found to be almost proportional to
magnetization and opposite in sign to it. Theoretical calculations based on
first-principles electronic structure also demonstrate that the Fermi-level
dependent anomalous Hall conductivity reflects the Berry curvature originating
in the split Weyl nodes. The present Dirac-semimetal/ferromagnetic-insulator
heterostructure will provide a novel platform for exploring Weyl-node transport
phenomena and spintronic functions lately proposed for topological semimetals.",1912.11964v1
2020-01-01,Exploring the magnetic properties of the largest single molecule magnets,"The giant $\{ \mathrm{Mn}_{70} \}$ and $\{ \mathrm{Mn}_{84} \}$ wheels are
the largest nuclearity single-molecule magnets synthesized to date and
understanding their magnetic properties poses a challenge to theory. Starting
from first principles calculations, we explore the magnetic properties and
excitations in these wheels using effective spin Hamiltonians. We find that the
unusual geometry of the superexchange pathways leads to weakly coupled $\{
\mathrm{Mn}_{7} \}$ subunits carrying an effective $S=2$ spin. The spectrum
exhibits a hierarchy of energy scales and massive degeneracies, with the lowest
energy excitations arising from Heisenberg-ring-like excitations of the $\{
\mathrm{Mn}_{7} \}$ subunits around the wheel, at energies consistent with the
observed temperature dependence of the magnetic susceptibility. We further
suggest an important role for weak longer-range couplings in selecting the
precise spin ground-state of the $\mathrm{Mn}$ wheels out of the nearly
degenerate ground-state band.",2001.00247v2
2020-01-14,Invariable generation and wreath products,"Invariable generation is a topic that has predominantly been studied for
finite groups. In 2014, Kantor, Lubotzky, and Shalev produced extensive tools
for investigating invariable generation for infinite groups. Since their paper,
various authors have investigated the property for particular infinite groups
or families of infinite groups.
  A group is invariably generated by a subset $S$ if replacing each element of
$S$ with any of its conjugates still results in a generating set for $G$. In
this paper we investigate how this property behaves with respect to wreath
products. Our main work is to deal with the case where the base of $G\wr_X H$
is not invariably generated. We see both positive and negative results here
depending on $H$ and its action on $X$.",2001.04748v3
2020-04-03,Finite-temperature coupled cluster: Efficient implementation and application to prototypical systems,"We discuss the theory and implementation of the finite temperature coupled
cluster singles and doubles (FT-CCSD) method including the equations necessary
for an efficient implementation of response properties. Numerical aspects of
the method including the truncation of the orbital space and integration of the
amplitude equations are tested on some simple systems, and we provide some
guidelines for applying the method in practice. The method is then applied to
the 1D Hubbard model, the uniform electron gas at warm, dense conditions, and
some simple materials. The performance on model systems at high temperatures is
encouraging: for the 1-dimensional Hubbard model FT-CCSD provides a
qualitatively accurate description of finite-temperature correlation effects
even at $U = 8$, and it allows for the computation of systematically improvable
exchange-correlation energies of the warm, dense UEG over a wide range of
conditions. We highlight the obstacles that remain in using the method for
realistic {\it ab initio} calculations on materials.",2004.01729v1
2020-04-18,Novel algorithms and high-performance cloud computing enable efficient fully quantum mechanical protein-ligand scoring,"Ranking the binding of small molecules to protein receptors through
physics-based computation remains challenging. Though inroads have been made
using free energy methods, these fail when the underlying classical mechanical
force fields are insufficient. In principle, a more accurate approach is
provided by quantum mechanical density functional theory (DFT) scoring, but
even with approximations, this has yet to become practical on drug
discovery-relevant timescales and resources. Here, we describe how to overcome
this barrier using algorithms for DFT calculations that scale on widely
available cloud architectures, enabling full density functional theory, without
approximations, to be applied to protein-ligand complexes with approximately
2500 atoms in tens of minutes. Applying this to a realistic example of 22
ligands binding to MCL1 reveals that density functional scoring outperforms
classical free energy perturbation theory for this system. This raises the
possibility of broadly applying fully quantum mechanical scoring to real-world
drug discovery pipelines.",2004.08725v1
2020-05-07,Minimal matrix product states and generalizations of mean-field and geminal wavefunctions,"Simple wavefunctions of low computational cost but which can achieve
qualitative accuracy across the whole potential energy surface (PES) are of
relevance to many areas of electronic structure as well as to applications to
dynamics. Here, we explore a class of simple wavefunctions, the minimal matrix
product state (MMPS), that generalizes many simple wavefunctions in common use,
such as projected mean-field wavefunctions, geminal wavefunctions, and
generalized valence bond states. By examining the performance of MMPSs for PESs
of some prototypical systems, we find that they yield good qualitative behavior
across the whole PES, often significantly improving on the aforementioned
ans\""atze.",2005.03703v2
2020-05-18,Optical properties of YAG:Ce and GGG:Ce scintillation crystals irradiated with a high fluence proton beam,"In this paper, we report on the study of the optical properties of YAG:Ce and
GGG:Ce garnet crystals after irradiation in a 660~MeV proton beam with a
fluence up to 8.9$\times$10$^{14}$ protons/cm$^2$. We found that the
transparency of both crystals fell by no more than 7\% in the region of their
own luminescence. The light yield of a YAG:Ce sample, measured one year after
irradiation, dropped by about 35\%.",2005.09087v1
2020-07-03,Invariable generation and the Houghton groups,"The Houghton groups $H_1, H_2, \ldots$ are a family of infinite groups. In
1975 Wiegold showed that $H_3$ was invariably generated (IG) but $H_1\le H_3$
was not. A natural question is then whether the groups $H_2, H_3, \ldots$ are
all IG. Wiegold also ends by saying that, in the examples he had found of an IG
group with a subgroup that is not IG, the subgroup was never of finite index.
Another natural question is then whether there is a subgroup of finite index in
$H_3$ that is not IG. In this note we prove, for each $n\in \{2, 3, \ldots\}$,
that $H_n$ and all of its finite index subgroups are IG.
  The independent work of Minasyan and Goffer-Lazarovich in June 2020 frames
this note quite nicely: they showed that an IG group can have a finite index
subgroup that is not IG.",2007.01626v1
2020-08-24,Numerical continuum tensor networks in two dimensions,"We describe the use of tensor networks to numerically determine wave
functions of interacting two-dimensional fermionic models in the continuum
limit. We use two different tensor network states: one based on the numerical
continuum limit of fermionic projected entangled pair states obtained via a
tensor network formulation of multi-grid, and another based on the combination
of the fermionic projected entangled pair state with layers of isometric
coarse-graining transformations. We first benchmark our approach on the
two-dimensional free Fermi gas then proceed to study the two-dimensional
interacting Fermi gas with an attractive interaction in the unitary limit,
using tensor networks on grids with up to 1000 sites.",2008.10566v1
2020-08-25,Short-range Thermal Magnon Diffusion in Magnetic Garnet,"Using the spin Seebeck effect (SSE), we study the propagation distance of
thermal spin currents inside a magnetic insulator thin film in the short-range
regime. We disambiguate spin currents driven by temperature and chemical
potential gradients by comparing the SSE signal before and after adding a
thermalization capping layer on the same device. We report that the measured
spin decay behavior near the heat source is well accounted for by a diffusion
model where the magnon diffusion length is in submicron range, \textit{i.e.}
two orders of magnitude smaller than previous estimates inferred from the
long-range behavior. Our results highlight the caveat in applying a diffusive
theory to describe thermal magnon transport, where a single decay length may
not capture the behavior on all length scales.",2008.10942v1
2020-09-08,Quantum Computation of Finite-Temperature Static and Dynamical Properties of Spin Systems Using Quantum Imaginary Time Evolution,"Developing scalable quantum algorithms to study finite-temperature physics of
quantum many-body systems has attracted considerable interest due to recent
advancements in quantum hardware. However, such algorithms in their present
form require resources that exceed the capabilities of current quantum
computers except for a limited range of system sizes and observables. Here, we
report calculations of finite-temperature properties including energies, static
and dynamical correlation functions, and excitation spectra of spin
Hamiltonians with up to four sites on five-qubit IBM Quantum devices. These
calculations are performed using the quantum imaginary time evolution (QITE)
algorithm and made possible by several algorithmic improvements, including a
method to exploit symmetries that reduces the quantum resources required by
QITE, circuit optimization procedures to reduce circuit depth, and error
mitigation techniques to improve the quality of raw hardware data. Our work
demonstrates that the ansatz-independent QITE algorithm is capable of computing
diverse finite-temperature observables on near-term quantum devices.",2009.03542v1
2020-09-28,A coupled cluster framework for electrons and phonons,"We describe a coupled cluster framework for coupled systems of electrons and
phonons. Neutral and charged excitations are accessed via the
equation-of-motion version of the theory. Benchmarks on the Hubbard-Holstein
model allow us to assess the strengths and weaknesses of different coupled
cluster approximations which generally perform well for weak to moderate
coupling. Finally, we report progress towards an implementation for {\it ab
initio} calculations on solids, and present some preliminary results on
finite-size models of diamond. We also report the implementation of
electron-phonon coupling matrix elements from crystalline Gaussian type
orbitals (cGTO) within the PySCF program package.",2009.13568v2
2020-10-26,Ultrafast phononic switching of magnetization,"Identifying an efficient pathway to change the order parameter via a subtle
excitation of the coupled high-frequency mode is the ultimate goal of the field
of ultrafast phase transitions. This is an especially interesting research
direction in magnetism, where the coupling between spin and lattice excitations
is required for magnetization reversal. Despite several attempts however, the
switching between magnetic states via resonant pumping of phonon modes has not
yet been demonstrated. Here we show how an ultrafast resonant excitation of the
longitudinal optical phonon modes in magnetic garnet films switches
magnetization into a peculiar quadrupolar magnetic domain pattern,
unambiguously revealing the magneto-elastic mechanism of the switching. In
contrast, the excitation of strongly absorbing transverse phonon modes results
in thermal demagnetization effect only.",2010.13671v1
2021-01-14,Constructing Tensor Network Influence Functionals for General Quantum Dynamics,"We describe an iterative formalism to compute influence functionals that
describe the general quantum dynamics of a subsystem beyond the assumption of
linear coupling to a quadratic bath. We use a space-time tensor network
representation of the influence functional and investigate its approximability
in terms of the bond dimensions and time-like entanglement in the tensor
network description. We study two numerical models, the spin-boson model and a
model of interacting hard-core bosons in a 1D harmonic trap. We find that the
influence functional and the intermediates involved in its construction can be
efficiently approximated by low bond dimension tensor networks in certain
dynamical regimes, which allows the quantum dynamics to be accurately computed
for longer times than with direct time evolution methods. However, as one
iteratively integrates out the bath, the correlations in the influence
functional can first increase before decreasing, indicating that the final
compressibility of the influence functional is achieved via non-trivial
cancellation.",2101.05466v3
2021-01-28,On the finite index subgroups of Houghton's groups,"An erratum has been added to resolve an issue raised by Professor Derek Holt.
This appears after the original paper, and also includes two new results.
  Original abstract: Houghton's groups $H_2, H_3, \ldots$ are certain infinite
permutation groups acting on a countably infinite set; they have been studied,
among other things, for their finiteness properties. In this note we describe
all of the finite index subgroups of each Houghton group, and their isomorphism
types. Using the standard notation that $d(G)$ denotes the minimal size of a
generating set for $G$ we then show, for each $n\in \{2, 3,\ldots\}$ and $U$ of
finite index in $H_n$, that $d(U)\in\{d(H_n), d(H_n)+1\}$ and characterise when
each of these cases occurs.",2101.12116v5
2021-02-07,Characterization and identification of Au pathfinder minerals from an artisanal mine site using X-ray diffraction,"Gold-associated pathfinder minerals have been investigated by identifying
host minerals of Au for samples collected from an artisanal mining site near a
potential gold mine (Kubi Gold Project) in Dunkwa-On-Offin in the central
region of Ghana. We find that for each composition of Au powder (impure) and
the residual black hematite/magnetite sand that remains after gold panning,
there is a unique set of associated diverse indicator minerals. These indicator
minerals are identified as SiO2 (quartz), Fe3O4 (magnetite), and Fe2O3
(hematite), while contributions from pyrite, arsenopyrites, iridosmine,
scheelite, tetradymite, garnet, gypsum, and other sulfate materials are
insignificant. This constitutes a confirmative identification of Au pathfinding
minerals in this particular mineralogical area. The findings suggest that X-ray
diffraction could also be applied in other mineralogical sites to aid in
identifying indicator minerals of Au and the location of ore bodies at reduced
environmental and exploration costs.",2102.03744v1
2021-02-25,Externally corrected CCSD with renormalized perturbative triples (R-ecCCSD(T)) and density matrix renormalization group and selected configuration interaction external sources,"We investigate the renormalized perturbative triples correction together with
the externally corrected coupled-cluster singles and doubles (ecCCSD) method.
We take the density matrix renormalization group (DMRG) and heatbath CI (HCI)
as external sources for the ecCCSD equations. The accuracy is assessed for the
potential energy surfaces of H2O, N2, and F2. We find that the triples
correction significantly improves on ecCCSD and we do not see any instability
of the renormalized triples with respect to dissociation. We explore how to
balance the cost of computing the external source amplitudes with respect to
the accuracy of the subsequent CC calculation. In this context, we find that
very approximate wavefunctions (and their large amplitudes) serve as an
efficient and accurate external source. Finally, we characterize the domain of
correlation treatable using the externally corrected method and renormalized
triples combination studied in this work via a well-known wavefunction
diagnostic.",2102.12703v1
2021-03-18,Low communication high performance ab initio density matrix renormalization group algorithms,"There has been recent interest in the deployment of ab initio density matrix
renormalization group computations on high performance computing platforms.
Here, we introduce a reformulation of the conventional distributed memory ab
initio DMRG algorithm that connects it to the conceptually simpler and
advantageous sum of sub-Hamiltonians approach. Starting from this framework, we
further explore a hierarchy of parallelism strategies, that includes (i)
parallelism over the sum of sub-Hamiltonians, (ii) parallelism over sites,
(iii) parallelism over normal and complementary operators, (iv) parallelism
over symmetry sectors, and (v) parallelism over dense matrix multiplications.
We describe how to reduce processor load imbalance and the communication cost
of the algorithm to achieve higher efficiencies. We illustrate the performance
of our new open-source implementation on a recent benchmark ground-state
calculation of benzene in an orbital space of 108 orbitals and 30 electrons,
with a bond dimension of up to 6000, and a model of the FeMo cofactor with 76
orbitals and 113 electrons. The observed parallel scaling from 448 to 2800 CPU
cores is nearly ideal.",2103.09976v3
2021-04-02,Surface plasmon-enhanced photo-magnetic excitation of spin dynamics in Au/YIG:Co magneto-plasmonic crystals,"We report strong amplification of photo-magnetic spin precession in Co-doped
YIG employing a surface plasmon excitation in a metal-dielectric
magneto-plasmonic crystal. Plasmonic enhancement is accompanied by the
localization of the excitation within the 300~nm-thick layer inside the
transparent dielectric garnet. Experimental results are nicely reproduced by
numerical simulations of the photo-magnetic excitation. Our findings
demonstrate the magneto-plasmonic concept of subwavelength localization and
amplification of the photo-magnetic excitation in dielectric YIG:Co and open up
a path to all-optical magnetization switching below diffraction limit with
energy efficiency approaching the fundamental limit for magnetic memories.",2104.01250v1
2021-04-14,Spin waves propagating through a stripe magnetic domain structure and their applications to reservoir computing,"Spin waves propagating through a stripe domain structure and reservoir
computing with their spin dynamics have been numerically studied with focusing
on the relation between physical phenomena and computing capabilities. Our
system utilizes a spin-wave-based device that has a continuous magnetic garnet
film and 1-input/72-output electrodes on the top. To control
spatially-distributed spin dynamics, a stripe magnetic domain structure and
amplitude-modulated triangular input waves were used. The spatially-arranged
electrodes detected spin vector outputs with various nonlinear characteristics
that were leveraged for reservoir computing. By moderately suppressing
nonlinear phenomena, our system achieves 100$\%$ prediction accuracy in
temporal exclusive-OR (XOR) problems with a delay step up to 5. At the same
time, it shows perfect inference in delay tasks with a delay step more than 7
and its memory capacity has a maximum value of 21. This study demonstrated that
our spin-wave-based reservoir computing has a high potential for edge-computing
applications and also can offer a rich opportunity for further understanding of
the underlying nonlinear physics.",2104.06794v1
2021-04-28,The Fermionic Quantum Emulator,"The fermionic quantum emulator (FQE) is a collection of protocols for
emulating quantum dynamics of fermions efficiently taking advantage of common
symmetries present in chemical, materials, and condensed-matter systems. The
library is fully integrated with the OpenFermion software package and serves as
the simulation backend. The FQE reduces memory footprint by exploiting number
and spin symmetry along with custom evolution routines for sparse and dense
Hamiltonians, allowing us to study significantly larger quantum circuits at
modest computational cost when compared against qubit state vector simulators.
This release paper outlines the technical details of the simulation methods and
key advantages.",2104.13944v2
2021-06-04,Conservation laws in coupled cluster dynamics at finite-temperature,"We extend the finite-temperature Keldysh non-equilibrium coupled cluster
theory (Keldysh-CC) [{\it J. Chem. Theory Comput.} \textbf{2019}, 15,
6137-6253] to include a time-dependent orbital basis. When chosen to minimize
the action, such a basis restores local and global conservation laws
(Ehrenfest's theorem) for all one-particle properties, while remaining energy
conserving for time-independent Hamiltonians. We present the time-dependent
orbital-optimized coupled cluster doubles method (Keldysh-OCCD) in analogy with
the formalism for zero-temperature dynamics, extended to finite temperatures
through the time-dependent action on the Keldysh contour. To demonstrate the
conservation property and understand the numerical performance of the method,
we apply it to several problems of non-equilibrium finite-temperature dynamics:
a 1D Hubbard model with a time-dependent Peierls phase, laser driving of
molecular H$_2$, driven dynamics in warm-dense silicon, and transport in the
single impurity Anderson model.",2106.02691v1
2021-06-08,Implications of PREX--2 data on the electron--neutrino opacity in dense matter,"Motivated by the recent measurement of the neutron distribution radius of
${}^{208}$Pb from the PREX--2 data, I study the effects of the new G3(M)
parameter set constrained by PREX--2 data on the electron--neutrino scattering
in dense matter using the extended relativistic mean field (E--RMF) model. I
employ the G3(M) parameter set to describe the nuclear matter. The obtained
equation of state for the G3(M) parameter set has an excellent agreement with
experimental data and the chiral effective field theory calculation with
N$^3$LO 3N forces. I analyze both differential cross section of
electron--neutrino and electron--neutrino mean free path to observe their
sensitivity to the G3(M) parameter set. One finds that the differential cross
sections of electron--neutrino for different baryon densities have higher
values compared with that obtained for the TM1e and FSU Garnet parameter sets.
The higher cross section decreases the electron--neutrino mean free path.",2106.04474v2
2021-07-03,The Variational Power of Quantum Circuit Tensor Networks,"We characterize the variational power of quantum circuit tensor networks in
the representation of physical many-body ground-states. Such tensor networks
are formed by replacing the dense block unitaries and isometries in standard
tensor networks by local quantum circuits. We explore both quantum circuit
matrix product states and the quantum circuit multi-scale entanglement
renormalization ansatz, and introduce an adaptive method to optimize the
resulting circuits to high fidelity with more than $10^4$ parameters. We
benchmark their expressiveness against standard tensor networks, as well as
other common circuit architectures, for the 1D/2D Heisenberg and 1D
Fermi-Hubbard models. We find quantum circuit tensor networks to be
substantially more expressive than other quantum circuits for these problems,
and that they can even be more compact than standard tensor networks.
Extrapolating to circuit depths which can no longer be emulated classically,
this suggests a region of advantage in quantum expressiveness in the
representation of physical ground-states.",2107.01307v2
2021-09-22,Matrix product states with large sites,"We explore various ways to group orbitals into clusters in a matrix product
state (MPS). We explain how a generic cluster MPS can often lead to an increase
in computational cost and instead propose a special cluster structure,
involving only the first and last orbitals/sites, with a wider scope for
computational advantage. This structure is a natural formalism to describe
correlated multireference (MR) theories. We demonstrate the flexibility and
usefulness of this approach by implementing various uncontracted MR
configuration interaction, perturbation and linearized coupled cluster theories
using an MPS with large cluster sites. Applications to the nitrogen dimer, the
chromium dimer, and benzene, including up to triple excitations in the external
space, demonstrate the utility of an MPS with up to two large sites. We use our
results to analyze the quality of different multireference approximations.",2109.11036v2
2021-10-18,On the pure state $v$-representability of density matrix embedding theory,"Density matrix embedding theory (DMET) formally requires the matching of
density matrix blocks obtained from high-level and low-level theories, but this
is sometimes not achievable in practical calculations. In such a case, the
global band gap of the low-level theory vanishes, and this can require
additional numerical considerations. We find that both the violation of the
exact matching condition and the vanishing low-level gap are related to the
assumption that the high-level density matrix blocks are non-interacting
pure-state $v$-representable (NI-PS-V), which assumes that the low-level
density matrix is constructed following the Aufbau principle. In order to relax
the NI-PS-V condition, we develop an augmented Lagrangian method to match the
density matrix blocks without referring to the Aufbau principle. Numerical
results for 2D Hubbard and hydrogen model systems indicate that in some
challenging scenarios, the relaxation of the Aufbau principle directly leads to
exact matching of the density matrix blocks, which also yields improved
accuracy.",2110.09558v2
2021-11-23,Quantum harmonic free energies for biomolecules and nanomaterials,"Obtaining the free energy of large molecules from quantum mechanical energy
functions is a longstanding challenge. We describe a method that allows us to
estimate, at the quantum mechanical level, the harmonic contributions to the
thermodynamics of molecular systems of large size, with modest cost. Using this
approach, we compute the vibrational thermodynamics of a series of diamond
nanocrystals, and show that the error per atom decreases with system size in
the limit of large systems. We further show that we can obtain the vibrational
contributions to the binding free energies of prototypical protein-ligand
complexes where the exact computation is too expensive to be practical. Our
work raises the possibility of routine quantum mechanical estimates of
thermodynamic quantities in complex systems.",2111.12200v2
2021-12-17,Systematic electronic structure in the cuprate parent state from quantum many-body simulations,"The quantitative description of correlated electron materials remains a
modern computational challenge. We demonstrate a numerical strategy to simulate
correlated materials at the fully ab initio level beyond the solution of
effective low-energy models, and apply it to gain a detailed microscopic
understanding across a family of cuprate superconducting materials in their
parent undoped states. We uncover microscopic trends in the electron
correlations and reveal the link between the material composition and magnetic
energy scales via a many-body picture of excitation processes involving the
buffer layers. Our work illustrates a path towards a quantitative and reliable
understanding of more complex states of correlated materials at the ab initio
many-body level.",2112.09735v3
2021-12-20,Realizing symmetry-protected topological phases in a spin-1/2 chain with next-nearest neighbor hopping on superconducting qubits,"The realization of novel phases of matter on quantum simulators is a topic of
intense interest. Digital quantum computers offer a route to prepare
topological phases with interactions that do not naturally arise in analog
quantum simulators. Here, we report the realization of symmetry-protected
topological (SPT) phases of a spin-{1/2} Hamiltonian with next-nearest-neighbor
hopping on up to 11 qubits on a programmable superconducting quantum processor.
We observe clear signatures of the two distinct SPT phases, such as excitations
localized to specific edges and finite string order parameters. Our work
advances ongoing efforts to realize novel states of matter with exotic
interactions on digital near-term quantum computers.",2112.10333v1
2021-12-20,Holographic simulation of correlated electrons on a trapped ion quantum processor,"We develop holographic quantum simulation techniques to prepare correlated
electronic ground states in quantum matrix product state (qMPS) form, using far
fewer qubits than the number of orbitals represented. Our approach starts with
a holographic technique to prepare a compressed approximation to electronic
mean-field ground-states, known as fermionic Gaussian matrix product states
(GMPS), with a polynomial reduction in qubit- and (in select cases gate-)
resources compared to existing techniques. Correlations are then introduced by
augmenting the GMPS circuits in a variational technique which we denote GMPS+X.
We demonstrate this approach on Quantinuum's System Model H1 trapped-ion
quantum processor for 1$d$ models of correlated metal and Mott insulating
states. Focusing on the $1d$ Fermi-Hubbard chain as a benchmark, we show that
GMPS+X methods faithfully capture the physics of correlated electron states,
including Mott insulators and correlated Luttinger liquid metals, using
considerably fewer parameters than problem-agnostic variational circuits.",2112.10810v3
2022-01-10,Entanglement in the quantum phases of an unfrustrated Rydberg atom array,"We report on the ground state phase diagram of interacting Rydberg atoms in
the unfrustrated square lattice array. Using new tensor network algorithms, we
scale to large systems in two dimensions while including all long-range
interactions, revealing the phases in the bulk and their analogs in accessible
finite arrays. We find a greatly altered phase diagram from earlier numerical
and experimental studies, and in particular, we uncover an emergent entangled
quantum nematic phase that appears in the absence of frustration. Broadly our
results yield a conceptual guide for future experiments, while our techniques
provide a blueprint for converging numerical studies in other lattices.",2201.03189v1
2022-06-14,Hyper-optimized approximate contraction of tensor networks with arbitrary geometry,"Tensor network contraction is central to problems ranging from many-body
physics to computer science. We describe how to approximate tensor network
contraction through bond compression on arbitrary graphs. In particular, we
introduce a hyper-optimization over the compression and contraction strategy
itself to minimize error and cost. We demonstrate that our protocol outperforms
both hand-crafted contraction strategies in the literature as well as recently
proposed general contraction algorithms on a variety of synthetic and physical
problems on regular lattices and random regular graphs. We further showcase the
power of the approach by demonstrating approximate contraction of tensor
networks for frustrated three-dimensional lattice partition functions, dimer
counting on random regular graphs, and to access the hardness transition of
random tensor network models, in graphs with many thousands of tensors.",2206.07044v2
2022-06-21,The chromium dimer: closing a chapter of quantum chemistry,"The complex electronic structure and unusual potential energy curve of the
chromium dimer have fascinated scientists for decades, with agreement between
theory and experiment so far elusive. Here, we present a new ab initio
simulation of the potential energy curve and vibrational spectrum that
significantly improves on all earlier estimates. Our data support a shift in
earlier experimental assignments of a cluster of vibrational frequencies by one
quantum number. The new vibrational assignment yields an experimentally derived
potential energy curve in quantitative agreement with theory across all bond
lengths and across all measured frequencies. By solving this long-standing
problem, our results raise the possibility of quantitative quantum chemical
modeling of transition metal clusters with spectroscopic accuracy.",2206.10738v2
2022-07-06,A comparison between the one- and two-step spin-orbit coupling approaches based on the ab initio Density Matrix Renormalization Group,"The efficient and reliable treatment of both spin-orbit coupling (SOC) and
electron correlation is essential for understanding f-element chemistry. We
analyze two approaches to the problem, the one-step approach where both effects
are treated simultaneously, and the two-step state interaction approach. We
report an implementation of the ab initio density matrix renormalization group
(DMRG) with a one-step treatment of the SOC effect which can be compared to
prior two-step treatments on an equal footing. Using a dysprosium octahedral
complex and bridged dimer as benchmark systems, we identify characteristics of
problems where the one-step approach is beneficial for obtaining the low-energy
spectrum.",2207.02435v2
2022-09-07,Testing the Gallium Anomaly,"We study the online detection by gallium capture of mono-energetic neutrinos
produced by a $^{51}$Cr radioactive source in a scintillation experiment. We
find that cerium-doped gadolinium aluminum gallium garnet (GAGG) is a suitable
scintillator which contains about 21% of gallium per weight and has a high mass
density and light yield. Combined with a highly efficient light detection
system this allows tagging of the subsequent germanium decay and thus a clean
distinction of gallium capture and elastic neutrino electron scattering events.
With 1.5 tons of scintillator and 10 source runs of 3.4MCi, each, we obtain
about 760 gallium capture events with a purity of 85% and 680,000 neutrino
electron scattering events, where the latter provide a precise normalization
independent of any nuclear physics. This configuration would allow to test the
gallium anomaly at more than $5\sigma$ in an independent way.",2209.02885v3
2022-08-16,"Arithmetic circuit tensor networks, multivariable function representation, and high-dimensional integration","Many computational problems can be formulated in terms of high-dimensional
functions. Simple representations of such functions and resulting computations
with them typically suffer from the ""curse of dimensionality"", an exponential
cost dependence on dimension. Tensor networks provide a way to represent
certain classes of high-dimensional functions with polynomial memory. This
results in computations where the exponential cost is ameliorated or in some
cases, removed, if the tensor network representation can be obtained. Here, we
introduce a direct mapping from the arithmetic circuit of a function to
arithmetic circuit tensor networks, avoiding the need to perform any
optimization or functional fit. We demonstrate the power of the circuit
construction in examples of multivariable integration on the unit hypercube in
up to 50 dimensions, where the complexity of integration can be understood from
the circuit structure. We find very favorable cost scaling compared to
quasi-Monte-Carlo integration for these cases, and further give an example
where efficient quasi-Monte-Carlo cannot be theoretically performed without
knowledge of the underlying tensor network circuit structure.",2209.07410v1
2022-11-18,Real time evolution of Anderson impurity models via tensor network influence functionals,"In this work we present and analyze two tensor network-based influence
functional approaches for simulating the real-time dynamics of quantum impurity
models such as the Anderson model. Via comparison with recent numerically exact
simulations, we show that such methods accurately capture the long-time
non-equilibrium quench dynamics. The two parameters that must be controlled in
these tensor network influence functional approaches are a time discretization
(Trotter) error and a bond dimension (tensor network truncation) error. We show
that the actual numerical uncertainties are controlled by an intricate
interplay of these two approximations which we demonstrate in different
regimes. Our work opens the door to using these tensor network influence
functional methods as general impurity solvers.",2211.10430v2
2022-11-25,Asymmetric Faraday Effect in a Magnetophotonic Crystal,"It is widely known that the magneto-optical Faraday effect is linear in
magnetization and therefore the Faraday angles for the states with opposite
magnetizations are of opposite sign but equal in modulus. Here we
experimentally study propagation of light through a one-dimensional all-garnet
magnetophotonic crystal to demonstrate an asymmetric Faraday effect (AFE) for
which Faraday angles for opposite magnetic states differ not only in sign but
in the absolute value as well. AFE appears in the vicinity of the cavity
resonance for an oblique incidence of light which plane of polarization is
inclined to the incidence plane. Under proper incidence and polarization angles
the magnitude of AFE could be very large reaching 30% of the absolute value of
the Faraday effect. The effect originates from the difference in Q-factors for
p- and s- polarized cavity modes that breaks the symmetry between the two
opposite directions of polarization rotation. The discovered AFE is of prime
importance for nanoscale magnonics and optomagnetism.",2211.14355v2
2022-12-18,Exact relationships between the GW approximation and equation-of-motion coupled-cluster theories through the quasi-boson formalism,"We describe the relationship between the GW approximation and various
equation-of-motion (EOM) coupled-cluster (CC) theories. We demonstrate the
exact equivalence of the G$_0$W$_0$ approximation and the propagator theory for
an electron-boson problem in a particular excitation basis. From there, we
establish equivalence within the quasi-boson picture to the IP+EA-EOM unitary
coupled-cluster propagator. We analyze the incomplete description of screening
provided by the standard similarity-transformed IP+EA-EOM-CC and the recently
introduced G$_0$W$_0$ Tamm-Dancoff approximation. We further consider the
approximate decoupling of IP and EA sectors in EOM-CC treatments and devise the
analogous particle-hole decoupling approach for the G$_0$W$_0$ approximation.
Finally, we numerically demonstrate the exact relationships and magnitude of
the approximations in calculations of a set of molecular ionization potentials
and electron affinities.",2212.08982v1
2023-02-20,Optimizing the magnon-phonon cooperativity in planar geometries,"Optimizing the cooperativity between two distinct particles is an important
feature of quantum information processing. Of particular interest is the
coupling between spin and phonon, which allows for integrated long range
communication between gates operating at GHz frequency. Using local light
scattering, we show that, in magnetic planar geometries, this attribute can be
tuned by adjusting the orientation and strength of an external magnetic field.
The coupling strength is enhanced by about a factor of 2 for the out-of-plane
magnetized geometry where the Kittel mode is coupled to circularly polarized
phonons, compared to the in-plane one where it couples to linearly polarized
phonons. We also show that the overlap between magnon and phonon is maximized
by matching the Kittel frequency with an acoustic resonance that satisfies the
half-wave plate condition across the magnetic film thickness. Taking the
frequency dependence of the damping into account, a maximum cooperativity of
about 6 is reached in garnets for the normal configuration near 5.5 GHz.",2302.09936v2
2023-05-04,Quantum Enhanced Probes of Magnetic Circular Dichroism,"Magneto-optical microscopies, including optical measurements of magnetic
circular dichroism, are increasingly ubiquitous tools for probing spin-orbit
coupling, charge-carrier g-factors, and chiral excitations in matter, but the
minimum detectable signal in classical magnetic circular dichroism measurements
is fundamentally limited by the shot-noise limit of the optical readout field.
Here, we use a two-mode squeezed light source to improve the minimum detectable
signal in magnetic circular dichroism measurements by 3 dB compared with
state-of-the-art classical measurements, even with relatively lossy samples
like terbium gallium garnet. We also identify additional opportunities for
improvement in quantum-enhanced magneto-optical microscopies, and we
demonstrate the importance of these approaches for environmentally sensitive
materials and for low temperature measurements where increased optical power
can introduce unacceptable thermal perturbations.",2305.02904v1
2023-06-07,Simulating quantum circuit expectation values by Clifford perturbation theory,"The classical simulation of quantum circuits is of central importance for
benchmarking near-term quantum devices. The fact that gates belonging to the
Clifford group can be simulated efficiently on classical computers has
motivated a range of methods that scale exponentially only in the number of
non-Clifford gates. Here, we consider the expectation value problem for
circuits composed of Clifford gates and non-Clifford Pauli rotations, and
introduce a heuristic perturbative approach based on the truncation of the
exponentially growing sum of Pauli terms in the Heisenberg picture. Numerical
results are shown on a Quantum Approximate Optimization Algorithm (QAOA)
benchmark for the E3LIN2 problem and we also demonstrate how this method can be
used to quantify coherent and incoherent errors of local observables in
Clifford circuits. Our results indicate that this systematically improvable
perturbative method offers a viable alternative to exact methods for
approximating expectation values of large near-Clifford circuits.",2306.04797v2
2023-06-09,"Fermionic reduced density low-rank matrix completion, noise filtering, and measurement reduction in quantum simulations","Fermionic reduced density matrices summarize the key observables in fermionic
systems. In electronic systems, the two-particle reduced density matrix (2-RDM)
is sufficient to determine the energy and most physical observables of
interest. Here, we consider the possibility of using matrix completion to
reconstruct the two-particle reduced density matrix to chemical accuracy from
partial information. We consider the case of noiseless matrix completion, where
the partial information corresponds to a subset of the 2-RDM elements, as well
as noisy completion, where the partial information corresponds to both a subset
of elements, as well as statistical noise in their values. Through experiments
on a set of 24 molecular systems, we find that the 2-RDM can be efficiently
reconstructed from a reduced amount of information. In the case of noisy
completion, this results in multiple orders of magnitude reduction in the
number of measurements needed to determine the 2-RDM to chemical accuracy.
These techniques can be readily applied to both classical and quantum
algorithms for quantum simulations.",2306.05640v1
2023-06-18,Study of Ge Doped Garnet Type Li$_7$La$_3$Zr$_2$O$_{12}$ as Solid Electrolyte for Li-ion Battery Application,"Li$_{7-4x}$Ge$_x$La$_3$Zr$_2$O$_{12}$ has been synthesized using the
conventional solid-state reaction method by substituting Germanium (Ge) at the
Li site, which increases the Li-ion vacancies and leads to an increase in
conductivity with $x$ varying from 0.05-0.20. The formation of cubic phase is
confirmed by using XRD analysis. The surface morphology and elemental
distribution have been studied using SEM characterization which gives the
average particle size of the sample. The densities of the samples were
calculated. For the confirmation of functional groups present within the
sample, IR spectroscopy has been studied. The modulus and ac conductivity
studies have also been studied. A complex impedance study has been done in the
frequency range 20Hz-20MHz. Increase in ionic conductivity by one order has
been observed in the sample with $x=0.10$. The minimum value of 0.56 eV
activation energy is associated with the highest conductivity value of 7.23 x
10$^{-6}$ S/cm at room temperature. Thus increment in ionic conductivity at
room temperature makes this material a promising solid electrolyte for future
sustainable energy storage devices.",2306.10483v1
2023-06-28,Ab initio quantum many-body description of superconducting trends in the cuprates,"Using a systematic ab initio quantum many-body approach that goes beyond
low-energy models, we directly compute the superconducting pairing order of
several doped cuprate materials and structures. We find that we can correctly
capture two well-known trends: the pressure effect, where pairing order
increases with intra-layer pressure, and the layer effect, where the pairing
order varies with the number of copper-oxygen layers. From these calculations,
we observe that the strength of superexchange and the covalency at optimal
doping are the best descriptors of the maximal pairing order. Our microscopic
analysis further identifies short-range copper spin fluctuations, together with
multi-orbital charge fluctuations, as central to the pairing trends. Our work
illustrates the possibility of a quantitative computational understanding of
unconventional high-temperature superconducting materials.",2306.16561v2
2023-08-07,Adiabatic quantum imaginary time evolution,"We introduce an adiabatic state preparation protocol which implements quantum
imaginary time evolution under the Hamiltonian of the system. Unlike the
original quantum imaginary time evolution algorithm, adiabatic quantum
imaginary time evolution does not require quantum state tomography during its
runtime, and unlike standard adiabatic state preparation, the final Hamiltonian
is not the system Hamiltonian. Instead, the algorithm obtains the adiabatic
Hamiltonian by integrating a classical differential equation that ensures that
one follows the imaginary time evolution state trajectory. We introduce some
heuristics that allow this protocol to be implemented on quantum architectures
with limited resources. We explore the performance of this algorithm via
classical simulations in a one-dimensional spin model and highlight essential
features that determine its cost, performance, and implementability for longer
times. We find competitive performance when compared to the original quantum
imaginary time evolution, and argue that the rapid convergence of this protocol
and its low resource requirements make it attractive for near-term state
preparation applications.",2308.03292v1
2023-08-09,Fast and converged classical simulations of evidence for the utility of quantum computing before fault tolerance,"A recent quantum simulation of observables of the kicked Ising model on 127
qubits implemented circuits that exceed the capabilities of exact classical
simulation. We show that several approximate classical methods, based on sparse
Pauli dynamics and tensor network algorithms, can simulate these observables
orders of magnitude faster than the quantum experiment, and can also be
systematically converged beyond the experimental accuracy. Our most accurate
technique combines a mixed Schr\""{o}dinger and Heisenberg tensor network
representation with the Bethe free entropy relation of belief propagation to
compute expectation values with an effective wavefunction-operator sandwich
bond dimension >16,000,000, achieving an absolute accuracy, without
extrapolation, in the observables of <0.01, which is converged for many
practical purposes. We thereby identify inaccuracies in the experimental
extrapolations and suggest how future experiments can be implemented to
increase the classical hardness.",2308.05077v3
2023-08-13,Measurement of the non-linearity in the gamma-ray response of the GAGG:Ce inorganic scintillator,"A characteristic of every inorganic scintillator crystal is its light yield,
i.e., the amount of emitted scintillation photons per unit of energy deposited
in the crystal. Light yield is known to be usually non-linear with energy,
which impacts the spectroscopic properties of the scintillator. Cerium-doped
gadolinium-aluminium-gallium garnet (GAGG:Ce) is a recently developed
scintillator with several interesting properties, which make it very promising
for space-based gamma-ray detectors, such as in the HERMES nanosatellite
mission. In this paper we report an accurate measurement of the GAGG:Ce
non-linearity in the 20-662 keV gamma-ray energy interval, using a setup
composed of three samples of GAGG:Ce crystals read out by Silicon Drift
Detectors (SDDs).",2308.06759v1
2023-08-15,Enhancement in Li-ion Conductivity through Co-doping of Ge and Ta in Garnet Li$_7$La$_3$Zr$_2$O$_{12}$ Solid Electrolyte,"For being used as an electrolyte in All Solid State Batteries (ASSB), a solid
electrolyte must possess ionic conductivity comparable to that of conventional
liquid electrolytes. To achieve this conductivity range, the series
Li$_{6.8-y}$Ge$_{0.05}$La$_3$Zr$_{2-y}$Ta$_y$O$_{12}$ ($y = 0, 0.15, 0.25,
0.35, 0.45$) has been synthesized using solid-state reaction method and studied
using various characterization techniques. The highly conducting cubic phase is
confirmed from XRD analysis. Structural information was collected using SEM and
density measurements. The prepared ceramic sample containing 0.25 Ta, sintered
at 1050$^\circ$C for 7.30 hrs shows the maximum ionic conductivity of 6.61 x
10$^{-4}$ S/cm at 25$^\circ$C. The air stability of the same ceramic has also
been evaluated after exposure for 5 months. The minimum activation energy
associated with the maximum conductivity of 0.25 Ta is 0.25 eV. The DC
conductivity measurements were done to confirm the ionic nature of conductivity
for all ceramic samples. The stable result of ionic conductivity makes the 0.25
Ta containing ceramic sample a promising candidate for solid electrolytes for
ASSB applications.",2308.07716v1
2023-10-05,Block2: a comprehensive open source framework to develop and apply state-of-the-art DMRG algorithms in electronic structure and beyond,"Block2 is an open source framework to implement and perform density matrix
renormalization group and matrix product state algorithms. Out-of-the-box it
supports the eigenstate, time-dependent, response, and finite-temperature
algorithms. In addition, it carries special optimizations for ab initio
electronic structure Hamiltonians and implements many quantum chemistry
extensions to the density matrix renormalization group, such as dynamical
correlation theories. The code is designed with an emphasis on flexibility,
extensibility, and efficiency, and to support integration with external
numerical packages. Here we explain the design principles and currently
supported features and present numerical examples in a range of applications.",2310.03920v2
2023-11-23,Invariable generation of certain branch groups,"We investigate invariable generation among key examples of branch groups. In
particular, we prove that all generating sets of the torsion Grigorchuk groups,
of the branch Grigorchuk-Gupta-Sidki groups and of the torsion multi-EGS groups
(which are natural generalisations of the Grigorchuk-Gupta-Sidki groups) are
invariable generating sets. Furthermore, for the first Grigorchuk group and the
torsion Grigorchuk-Gupta-Sidki groups, every finitely generated subgroup has a
finite invariable generating set. We also show that a branch
Grigorchuk-Gupta-Sidki group is almost $\frac32$-generated, that the diameter
of its generating subgraph $\Delta(G)$ is 2 and its total domination number is
2. Some of our results apply to groups for which every maximal subgroup is
normal. This class, known as $\mathcal{MN}$, includes all nilpotent groups.",2311.14022v1
2023-11-30,AB-G$_0$W$_0$: A practical G$_0$W$_0$ method without frequency integration based on an auxiliary boson expansion,"Common G$_0$W$_0$ implementations rely on numerical or analytical frequency
integration to determine the G$_0$W$_0$ self-energy, which results in a variety
of practical complications. Recently, we demonstrated an exact connection
between the G$_0$W$_0$ approximation and equation-of-motion (EOM) quantum
chemistry approaches [J. Chem. Phys., 158, 124123 (2023)]. Based on this
connection, we propose a new method to determine G$_0$W$_0$ quasiparticle
energies which completely avoids frequency integration and its associated
problems. To achieve this, we make use of an auxiliary boson (AB) expansion. We
name the new approach AB-G$_0$W$_0$ and demonstrate its practical applicability
in a range of molecular problems.",2311.18304v1
2024-01-04,Effect of Ca doping on Li ion conductivity of Ge and Ta doped garnet LLZO,"The series Li6.55+xGe0.05La3-xCaxZr1.75Ta0.25O12 ( x= 0, 0.05, 0.10, 0.15,
0.20 ) was prepared by conventional solid state reaction method with the
sintering temperature of 10500C for 7.30 hr by substituting Ca at the La site
to increase the Li ion conductivity. The synergistic effects of Ca
incorporation on Li6.55Ge0.05La3Zr1.75Ta0.25O12 were studied using various
structural and electrochemical analyses. X-ray diffraction, scanning electron
microscopy, and Impedance analysis were used to determine the crystal
structure, morphology, and AC conductivity of the prepared ceramic samples,
respectively. The highest conductivity of 9.95 x 10-4 S/cm was obtained for a
0.05 Ca ceramic sample with minimum activation energy of 0.23 eV. The DC
polarization measurements confirmed the dominance of ionic conduction in 0.05
Ca ceramic. The results obtained make the 0.05 Ca ceramic sample a promising
candidate as solid electrolytes for all solid state Li-ion batteries (ASSLIBs).",2401.02359v1
2024-01-23,"Tensor network influence functionals in the continuous-time limit: connections to quantum embedding, bath discretization, and higher-order time propagation","We describe two developments of tensor network influence functionals (in
particular, influence functional matrix product states (IF-MPS)) for quantum
impurity dynamics within the fermionic setting of the Anderson impurity model.
The first provides the correct extension of the IF-MPS to continuous time by
introducing a related mathematical object, the boundary influence functional
MPS. The second connects the dynamics described by a compressed IF-MPS to that
of a quantum embedding method with a time-dependent effective bath undergoing
non-unitary dynamics. Using these concepts, we implement higher-order time
propagators for the quench dynamics of the Anderson impurity model within the
boundary IF-MPS formalism. The calculations illustrate the ability of the
current formulation to efficiently remove the time-step error in standard
discrete-time IF-MPS implementations as well as to interface with state-vector
propagation techniques. They also show the advantages of IF-MPS dynamics, with
its associated highly compact effective bath dynamics, over state-vector
propagation with a static bath discretization.",2401.12460v1
2024-02-19,Image Super-resolution Inspired Electron Density Prediction,"Drawing inspiration from the domain of image super-resolution, we view the
electron density as a 3D grayscale image and use a convolutional residual
network to transform a crude and trivially generated guess of the molecular
density into an accurate ground-state quantum mechanical density. We find that
this model outperforms all prior density prediction approaches. Because the
input is itself a real-space density, the predictions are equivariant to
molecular symmetry transformations even though the model is not constructed to
be. Due to its simplicity, the model is directly applicable to unseen molecular
conformations and chemical elements. We show that fine-tuning on limited new
data provides high accuracy even in challenging cases of exotic elements and
charge states. Our work suggests new routes to learning real-space physical
quantities drawing from the established ideas of image processing.",2402.12335v1
2024-02-27,Fast Lithium Ion Diffusion in Brownmillerite $\mathrm{Li}_{x}\mathrm{{Sr}_{2}{Co}_{2}{O}_{5}}$,"Ionic conductors have great potential for interesting tunable physical
properties via ionic liquid gating and novel energy storage applications such
as all-solid-state lithium batteries. In particular, low migration barriers and
high hopping attempt frequency are the keys to achieve fast ion diffusion in
solids. Taking advantage of the oxygen-vacancy channel in
$\mathrm{Li}_{x}\mathrm{{Sr}_{2}{Co}_{2}{O}_{5}}$, we show that migration
barriers of lithium ion are as small as 0.28~0.17eV depending on the lithium
concentration rates. Our first-principles calculation also investigated hopping
attempt frequency and concluded the room temperature ionic diffusivity and ion
conductivity is high as ${10}^{-7}\sim{10}^{-6}~\mathrm{{cm}^{2}~s^{-1}}$ and
${10}^{-3}\sim{10}^{-2}~\mathrm{S\cdot{cm}^{-1}}$ respectively, which
outperform most of perovskite-type, garnet-type and sulfide Li-ion solid-state
electrolytes. This work proves
$\mathrm{Li}_{x}\mathrm{{Sr}_{2}{Co}_{2}{O}_{5}}$ as a promising solid-state
electrolyte.",2402.17557v2
2024-04-02,Understanding spin currents from magnon dispersion and polarization: Spin-Seebeck effect and neutron scattering study on Tb3Fe5O12,"Magnon spin currents in the ferrimagnetic garnet Tb3Fe5O12 with 4f electrons
were examined through the spin-Seebeck effect and neutron scattering
measurements. The compound shows a magnetic compensation, where the
spin-Seebeck signal reverses above and below Tcomp = 249.5(4) K. Unpolarized
neutron scattering unveils two major magnon branches with finite energy gaps,
which are well-explained in the framework of spin-wave theory. Their
temperature dependencies and the direction of the precession motion of magnetic
moments, i.e. magnon polarization, defined using polarized neutrons, explain
the reversal at Tcomp and decay of the spin-Seebeck signals at low
temperatures. We illustrate an example that momentum- and energy-resolved
microscopic information is a prerequisite to understanding the magnon spin
current.",2404.01603v1
2024-04-04,Performant Automatic Differentiation of Local Coupled Cluster Theories: Response Properties and Ab Initio Molecular Dynamics,"In this work, we introduce a differentiable implementation of the local
natural orbital coupled cluster (LNOCC) method within the automatic
differentiation framework of the PySCFAD package. The implementation is
comprehensively tuned for enhanced performance, which enables the calculation
of first-order static response properties on medium-sized molecular systems
using coupled cluster theory with single, double, and perturbative triple
excitations [CCSD(T)]. We evaluate the accuracy of our method by benchmarking
it against the canonical CCSD(T) reference for nuclear gradients, dipole
moments, and geometry optimizations. In addition, we demonstrate the
possibility of property calculations for chemically interesting systems through
the computation of bond orders and M\""ossbauer spectroscopy parameters for a
[NiFe]-hydrogenase active site model, along with the simulation of infrared
(IR) spectra via ab initio LNO-CC molecular dynamics for a protonated water
hexamer.",2404.03129v2
1998-03-17,The Soft X-ray Spectrum of Scattering--Dominated AGN,"This paper discusses the properties of scattering--dominated active galactic
nuclei (AGN). We define these to be AGN for which the direct line-of-sight to
the continuum source is obscured by Compton-thick material. The aim is to
construct, for the first time, a model consistent with X-ray line luminosities,
line ratios and various luminosity indicators. The ASCA spectra of six such
sources show several X-ray lines that can be reliably measured, mostly due to
highly ionized magnesium, silicon sulphur and iron. These enable us to
investigate the physical conditions of the scattering material. The sources
show evidence of He-like and H-like iron lines that are likely to be produced
in hot (T approx 10^6 K) photoionized gas. By measuring the EW of the lines,
and by constructing a diagnostic line-ratio diagram, we demonstrate that the
silicon and magnesium lines are produced by the same gas emitting the highly
ionized iron lines. The properties of this gas are rather different from the
properties of warm absorbers in type I AGN. Neutral 6.4 keV iron lines are also
detected, originating in a different component which can be either Compton-thin
or Compton-thick. The best measured iron lines suggest an enhancement of
n_{Fe}/n_H by a factor approx 2 compared to solar, in both the hot and cool
Compton-thin components. We further show that in four of the sources, the Fe
Kalpha(6.4keV)/Hbeta (lambda 4861Ang) line ratio is consistent with that
predicted for typical narrow line region clouds, and the reddening corrected
Hbeta is known, provided the column density is larger than approx
10^{22.5}/cm^2, alpha_{ox} is smaller than 1.3. For some sources, this is a
viable alternative to the commonly assumed Compton thick medium as the origin
of the 6.4 keV iron line.",9803205v1
2001-06-15,The effects of relativistic bulk motion of X-ray flares in the corona on the iron Kalpha line in Seyfert 1 galaxies,"We study the effects of the bulk motion of X-ray flares on the shape and
equivalent width of the iron Kalpha line from an untruncated cold disk around a
Kerr black hole using fully relativistic calculations. The flares are located
above a cold accretion disk -- either on or off the rotation axis. For on- or
off-axis flares, the upward/outward bulk motion causes a reduction of the iron
Kalpha line width. To a distant observer with a low inclination angle (\theta_o
\simlt 30deg.), larger upward/outward bulk velocities decrease the extension of
the red wing, with little change in the location of the blue `edge'. In
contrast, an observer at a large inclination angle (e.g. \theta_o=60deg.) sees
both the red wing and the blue `edge' change with the bulk velocity. The
equivalent width of the iron Kalpha line decreases rapidly with increasing bulk
velocity of flares. However, the `narrower' line profiles observed in some
objects (e.g. IC4329A and NGC4593) are difficult to produce using the
out-flowing magnetic flare model with an appropriate equivalent width unless
the X-ray emission is concentrated in an outer region with a radius of several
tens of r_g=GM/c^2 or more. An important result is that the iron Kalpha line
intensity is found to be constant even though the continuum flux varies
significantly, which is true for out-flowing magnetic flares with different
bulk velocities but similar intrinsic luminosities when located close to the
central black hole. We find that fluctuations in the bulk velocities of
out-flowing low-height flares located at the inner region (r\simlt 15r_g) can
account for a constant iron Kalpha line and significant continuum variation as
observered in MCG-6-30-15 and NGC5548. (Abridged)",0106290v2
2004-10-20,The impact of non-LTE effects and granulation inhomogeneities on the derived iron and oxygen abundances in metal-poor halo stars,"This paper presents the results of a detailed theoretical investigation of
the impact of non-LTE effects and of granulation inhomogeneities on the derived
iron and oxygen abundances in the metal-poor halo subgiant HD140283. Our
analysis is based on both the `classical' one-dimensional (1D) stellar
atmosphere models and on the new generation of three-dimensional (3D)
hydrodynamical models. We find that the non-LTE effects on the iron abundance
derived from Fe {\sc i} lines are very important, amounting to ${\sim}0.9$ dex
and to ${\sim}0.6$ dex in the 3D and 1D cases, respectively. On the other hand,
we find that non-LTE and 3D effects have to be taken into account for a
reliable determination of the iron abundance from weak Fe {\sc ii} lines,
because the significant overexcitation of their upper levels in the granular
regions tend to produce emission features. As a result such Fe {\sc ii} lines
are weaker than in LTE and the abundance correction amounts to ${\sim}0.4$ dex
for the 3D case. We derive also the oxygen-to-iron abundance ratio in the
metal-poor star HD140283 by using the O {\sc i} triplet at 7772--5 \AA and the
forbidden [O {\sc i}] line at 6300 \AA. Interestingly, when both non-LTE and 3D
effects are taken into account there still remains significant discrepancies in
the iron abundances derived from Fe {\sc i} and Fe {\sc ii} lines, as well as
in the oxygen abundances inferred from the O {\sc i} and [O {\sc i}] lines. We
conclude that the metalicity of this type of metal-poor stars could be
significantly larger than previously thought, which may have far-reaching
implications in stellar astrophysics.",0410475v1
2005-03-29,The XMM-Newton view of Mrk3 and IXO30,"We present the analysis of the XMM-Newton EPIC pn spectrum of the Seyfert 2
galaxy, Mrk3. We confirm that the source is dominated by a pure Compton
reflection component and an iron K$\alpha$ line, both produced as reflection
from a Compton-thick torus, likely responsible also for the large column
density which is pierced by the primary powerlaw only at high energies. A low
inclination angle and an iron underabundance, suggested by the amount of
reflection and the depth of the iron edge, are consistent with the iron
K$\alpha$ line EW with respect to the Compton reflection component. Moreover,
the iron line width, if interpreted in terms of Doppler broadening due to the
Keplerian rotation of the torus, puts an estimate to the inner radius of the
latter, $r=0.6^{+1.3}_{-0.3} \sin^2{i}$ pc. Finally, two different photoionised
reflectors are needed to take into account a large number of soft X-ray
emission lines from N, O, Ne, Mg, Si, Fe L and the FeXXV emission line. RGS
spectra show that the soft X-ray spectrum is dominated by emission lines, while
the underlying continuum is best fitted by an unabsorbed powerlaw with the same
photon index of the primary continuum, produced as reflection by a photoionised
material with a column density of a few $10^{22}$ cm$^{-2}$. We also present
the first X-ray spectrum of ROSAT source IXO30, which shows a huge iron line
and is well represented either by an absorbed powerlaw or bremsstrahlung
emission. Its spectral properties point to a likely identification in terms of
a weak Galactic Cataclysmic Variable, but the lack of any optical counterpart
precludes excluding other possibilities, like an ULX at the distance of Mrk3.",0503623v1
2007-05-30,Numerical Study on Stellar Core Collapse and Neutrino Emission: Probe into the Spherically Symmetric Black Hole Progenitors with 3 - 30Msun Iron Cores,"The existence of various anomalous stars, such as the first stars in the
universe or stars produced by stellar mergers, has been recently proposed. Some
of these stars will result in black hole formation. In this study, we
investigate iron core collapse and black hole formation systematically for the
iron-core mass range of 3 - 30Msun, which has not been studied well so far.
Models used here are mostly isentropic iron cores that may be produced in
merged stars in the present universe but we also employ a model that is meant
for a Population III star and is obtained by evolutionary calculation. We solve
numerically the general relativistic hydrodynamics and neutrino transfer
equations simultaneously, treating neutrino reactions in detail under spherical
symmetry. As a result, we find that massive iron cores with ~10Msun
unexpectedly produce a bounce owing to the thermal pressure of nucleons before
black hole formation. The features of neutrino signals emitted from such
massive iron cores differ in time evolution and spectrum from those of ordinary
supernovae. Firstly, the neutronization burst is less remarkable or disappears
completely for more massive models because the density is lower at the bounce.
Secondly, the spectra of neutrinos, except the electron type, are softer owing
to the electron-positron pair creation before the bounce. We also study the
effects of the initial density profile, finding that the larger the initial
density gradient is, the more steeply the neutronization burst declines.
Further more, we suggest a way to probe into the black hole progenitors from
the neutrino emission and estimate the event number for the currently operating
neutrino detectors.",0705.4350v1
2011-05-24,Spin Waves and magnetic exchange interactions in insulating Rb$_{0.89}$Fe$_{1.58}$Se$_2$,"The discovery of alkaline iron selenide $A$Fe$_{1.6+x}$Se$_2$ ($A=$ K, Rb,
Cs) superconductors has generated considerable excitement in the condensed
matter physics community because superconductivity in these materials may have
a different origin from the sign reversed s-wave electron pairing mechanism, a
leading candidate proposed for all other Fe-based superconductors. Although
$A$Fe$_{1.6+x}$Se$_2$ are isostructural with the metallic antiferromagnetic
(AF) iron pnictides such as (Ba,Ca,Sr)Fe$_2$As$_2$, they are insulators near
$x=0$ and form a $\sqrt{5}\times\sqrt{5}$ blocked AF structure (Fig. 1a)
completely different from the iron pnictides. If magnetism is responsible for
superconductivity of all iron-based materials, it is important to determine
their common magnetic features. Here we use neutron scattering to map out spin
waves in the AF insulating Rb$_{0.89}$Fe$_{1.58}$Se$_2$. We find that although
Rb$_{0.89}$Fe$_{1.58}$Se$_2$ has a N$\rm \acute{e}$el temperature ($T_N=475$ K)
much higher than that of the iron pnictides ($T_N\leq 220$ K), spin waves for
both classes of materials have similar zone boundary energies. A comparison of
the fitted effective exchange couplings using a local moment Heisenberg
Hamiltonian in Rb$_{0.89}$Fe$_{1.58}$Se$_2$, (Ba,Ca,Sr)Fe$_2$As$_2$, and iron
chalcogenide Fe$_{1.05}$Te reveals that their next nearest neighbor (NNN)
exchange couplings are similar. Therefore, superconductivity in all Fe-based
materials may have a common magnetic origin that is intimately associated with
the NNN magnetic exchange interactions, even though they have metallic or
insulating ground states, different AF orders and electronic band structures.",1105.4675v1
2012-10-08,Magnetic fluctuations and effective magnetic moments in γ-iron due to electronic structure peculiarities,"Applying the local density and dynamical mean field approximations to
paramagnetic \gamma-iron we revisit the problem of theoretical description of
magnetic properties in a wide temperature range. We show that contrary to
\alpha-iron, the frequency dependence of the electronic self-energy has a
quasiparticle form for both, t_{2g} and e_g states. In the temperature range
T=1200-1500 K, where \gamma-iron exist in nature, this substance can be
nevertheless characterized by temperature-dependent effective local moments,
which yield relatively narrow peaks in the real part of the local magnetic
susceptibility. At the same time, at low temperatures \gamma-iron (which is
realized in precipitates) is better described in terms of itinerant picture. In
particular, the nesting features of the Fermi surfaces yield maximum of the
static magnetic susceptibility at the incommensurate wave vector q_{max}
belonging the direction q_X-q_W (q_X=(2\pi/a)(1,0,0),q_W=(2\pi/a)(1,1/2,0), a
is a lattice parameter) in agreement with the experimental data. This state is
found however to compete closely with the states characterized by magnetic wave
vectors along the directions q_X-q_L-q_K, where q_L=(2\pi/a)(1/2,1/2,1/2),
q_K=(2\pi/a)(3/4,3/4,0). From the analysis of the uniform magnetic
susceptibility we find that contrary to \alpha-iron, the Curie-Weiss law is not
fulfilled in a broad temperature range, although the inverse susceptibility is
nearly linear in the moderate-temperature region (1200-1500 K). The
non-linearity of the inverse uniform magnetic susceptibility in a broader
temperature range is due to the density of states peak located close to the
Fermi level. The effective exchange integrals in the paramagnetic phase are
estimated on the base of momentum dependent susceptibility.",1210.2188v2
2012-10-18,Electron Correlation and Spin Dynamics in Iron Pnictides and Chalcogenides,"Superconductivity in the iron pnictides and chalcogenides is closely
connected to a bad-metal normal state and a nearby antiferromagnetic order.
Therefore, considerable attention has been focused on the role of electron
correlations and spin dynamics. In this article, we summarize some key
experiments that quite directly imply strong electron correlations in these
materials, and discuss aspects of the recent theoretical studies on these
issues. In particular, we outline a $w$-expansion, which treats the correlation
effects using the Mott transition as the reference point. For the parent
systems, it gives rise to an effective J1-J2 model that is coupled to the
itinerant electrons in the vicinity of the Fermi energy; this model yields an
isoelectronically-tuned quantum critical point, and allows a study of the
distribution of the spin spectral weight in the energy and momentum space in
the paramagnetic phase. Within the same framework, we demonstrate the Mott
insulating phase in the iron oxychalcogenides as well as the alkaline iron
selenides; for the latter system, we also consider the role of an
orbital-selective Mott phase. Finally, we discuss the singlet superconducting
pairing driven by the short-range J1-J2 interactions. Our considerations
highlight the iron pnictides and chalcogenides as exemplifying
strongly-correlated electron systems at the boundary of electronic localization
and itinerancy.",1210.5017v2
2014-02-06,"A single low-energy, iron-poor supernova as the source of metals in the star SMSS J 031300.36-670839.3","The element abundance ratios of four low-mass stars with extremely low
metallicities indicate that the gas out of which the stars formed was enriched
in each case by at most a few, and potentially only one low-energy, supernova.
Such supernovae yield large quantities of light elements such as carbon but
very little iron. The dominance of low-energy supernovae is surprising, because
it has been expected that the first stars were extremely massive, and that they
disintegrated in pair-instability explosions that would rapidly enrich galaxies
in iron. What has remained unclear is the yield of iron from the first
supernovae, because hitherto no star is unambiguously interpreted as
encapsulating the yield of a single supernova. Here we report the optical
spectrum of SMSS J031300.36- 670839.3, which shows no evidence of iron (with an
upper limit of 10^-7.1 times solar abundance). Based on a comparison of its
abundance pattern with those of models, we conclude that the star was seeded
with material from a single supernova with an original mass of ~60 Mo (and that
the supernova left behind a black hole). Taken together with the previously
mentioned low-metallicity stars, we conclude that low-energy supernovae were
common in the early Universe, and that such supernovae yield light element
enrichment with insignificant iron. Reduced stellar feedback both chemically
and mechanically from low-energy supernovae would have enabled first-generation
stars to form over an extended period. We speculate that such stars may perhaps
have had an important role in the epoch of cosmic reionization and the chemical
evolution of early galaxies.",1402.1517v1
2015-04-09,A three-dimensional hydrodynamical line profile analysis of iron lines and barium isotopes in HD140283,"Heavy-elements, i.e. those beyond the iron peak, mostly form via two neutron
capture processes: the s- and r-process. Metal-poor stars should contain fewer
isotopes that form via the s-process, according to currently accepted theory.
It has been shown in several investigations that theory and observation do not
agree well, raising questions on the validity of either the methodology or the
theory. We analyse the metal-poor star HD140283, for which we have a high
quality spectrum. We test whether a 3D LTE stellar atmosphere and spectrum
synthesis code permits a more reliable analysis of the iron abundance and
barium isotope ratio than a 1D LTE analysis. Using 3D model atmospheres, we
examine 91 iron lines of varying strength and formation depth. This provides us
with the star's rotational speed. With this, we model the barium isotope ratio
by exploiting the hyperfine structure of the singly ionised 4554 resonance
line, and study the impact of the uncertainties in the stellar parameters.
HD140283's vsini = 1.65 +/- 0.05 km/s. Barium isotopes under the 3D paradigm
show a dominant r-process signature as 77 +/- 6 +/- 17% of barium isotopes form
via the r-process, where errors represent the assigned random and systematic
errors, respectively. We find that 3D LTE fits reproduce iron line profiles
better than those in 1D, but do not provide a unique abundance (within the
uncertainties). However, we demonstrate that the isotopic ratio is robust
against this shortcoming. Our barium isotope result agrees well with currently
accepted theory regarding the formation of the heavy-elements during the early
Galaxy. The improved fit to the asymmetric iron line profiles suggests that the
current state of 3D LTE modelling provides excellent simulations of fluid
flows. However, the abundances they provide are not yet self-consistent. This
may improve with NLTE considerations and higher resolution models.",1504.02353v1
2015-06-12,Identification of prototypical Brinkman-Rice Mott physics in a class of iron chalcogenides superconductors,"The 122$^{*}$ series of iron-chalcogenide superconductors, for example
K$_x$Fe$_{2-y}$Se$_{2}$, only possesses electron Fermi pockets. Their
distinctive electronic structure challenges the picture built upon iron
pnictide superconductors, where both electron and hole Fermi pockets coexist.
However, partly due to the intrinsic phase separation in this family of
compounds, many aspects of their behavior remain elusive. In particular, the
evolution of the 122$^{*}$ series of iron-chalcogenides with chemical
substitution still lacks a microscopic and unified interpretation. Using
angle-resolved photoemission spectroscopy, we studied a major fraction of
122$^{*}$ iron-chalcogenides, including the isovalently `doped'
K$_x$Fe$_{2-y}$Se$_{2-z}$S$_z$, Rb$_x$Fe$_{2-y}$Se$_{2-z}$Te$_z$ and
(Tl,K)$_x$Fe$_{2-y}$Se$_{2-z}$S$_z$. We found that the bandwidths of the low
energy Fe \textit{3d} bands in these materials depend on doping; and more
crucially, as the bandwidth decreases, the ground state evolves from a metal to
a superconductor, and eventually to an insulator, yet the Fermi surface in the
metallic phases is unaffected by the isovalent dopants. Moreover, the
correlation-driven insulator found here with small band filling may be a novel
insulating phase. Our study shows that almost all the known 122$^{*}$-series
iron chalcogenides can be understood {\it via} one unifying phase diagram which
implies that moderate correlation strength is beneficial for the
superconductivity.",1506.04018v3
2015-11-30,Iron Fluorescent Line Emission from the mCvs and Hard X-ray Emitting Symbiotic Stars as a Source of the Iron Fluorescent Line Emission from the Galactic Ridge,"The Galactic Ridge X-ray Emission (GRXE) spectrum has strong iron emission
lines at 6.4, 6.7, and 7.0~keV, each corresponding to the neutral (or
low-ionized), He-like, and H-like iron ions. The 6.4~keV fluorescence line is
due to irradiation of neutral (or low ionized) material (iron) by hard X-ray
sources, indicating uniform presence of the cold matter in the Galactic plane.
In order to resolve origin of the cold fluorescent matter, we examined the
contribution of the 6.4~keV line emission from white dwarf surfaces in the hard
X-ray emitting symbiotic stars (hSSs) and magnetic cataclysmic variables (mCVs)
to the GRXE. In our spectral analysis of 4~hSSs and 19~mCVs observed with
Suzaku, we were able to resolve the three iron emission lines. We found that
the equivalent-widths (EWs) of the 6.4~keV lines of hSSs are systematically
higher than those of mCVs, such that the average EWs of hSSs and mCVs are
$179_{-11}^{+46}$~eV and $93_{-3}^{+20}$~eV, respectively. The EW of hSSs
compares favorably with the typical EWs of the 6.4~keV line in the GRXE of
90--300~eV depending on Galactic positions. Average 6.4~keV line luminosities
of the hSSs and mCVs are $9.2\times 10^{39}$ and $1.6\times
10^{39}$~photons~s$^{-1}$, respectively, indicating that hSSs are intrinsically
more efficient 6.4~keV line emitters than mCVs. We compare expected
contribution of the 6.4 keV lines from mCVs with the observed GRXE 6.4 keV line
flux in the direction of $(l,b) \approx (28.5\arcdeg, 0\arcdeg$). We conclude
that almost all the 6.4 keV line flux in GRXE may be explained by mCVs within
current undertainties of the stellar number densities, while contribution from
hSSs may not be negligible.",1511.09424v2
2016-06-16,Broadband X-ray emission and the reality of the broad iron line from the Neutron Star - White Dwarf X-ray binary 4U 1820-30,"Broad relativistic iron lines from neutron star X-ray binaries are important
probes of the inner accretion disk. The X-ray reflection features can be
weakened due to strong magnetic fields or very low iron abundances such as is
possible in X-ray binaries with low mass, first generation stars as companions.
Here we investigate the reality of the broad iron line detected earlier from
the neutron star low mass X-ray binary 4U~1820--30 with a degenerate helium
dwarf companion. We perform a comprehensive, systematic broadband spectral
study of the atoll source using \suzaku{} and simultaneous \nustar{} \&
\swift{} observations. We have used different continuum models involving
accretion disk emission, thermal blackbody and thermal Comptonization of either
disk or blackbody photons. The \suzaku{} data show positive and negative
residuals in the region of iron K band. These features are well described by
two absorption edges at $7.67\pm0.14\kev$ and $6.93\pm0.07\kev$ or partial
covering photoionized absorption or by blurred reflection. Though, the
simultaneous \swift{} and \nustar{} data do not clearly reveal the emission or
absorption features, the data are consistent with the presence of either
absorption or emission features. Thus, the absorption based models provide an
alternative to the broad iron line or reflection model. The absorption features
may arise in winds from the inner accretion disk. The broadband spectra appear
to disfavour continuum models in which the blackbody emission from the neutron
star surface provides the seed photons for thermal Comptonization. Our results
suggest emission from a thin accretion disk ($kT_{disk} \sim 1\kev$),
Comptonization of disk photons in a boundary layer most likely covering a large
fraction of the neutron star surface and innermost parts of the accretion disk,
and blackbody emission ($kT_{bb} \sim 2\kev$) from the polar regions.",1606.05307v1
2020-01-09,Near-ultraviolet Transmission Spectroscopy of HD 209458b: Evidence of Ionized Iron Beyond the Planetary Roche Lobe,"The inflated transiting hot Jupiter HD 209458b is one of the best studied
objects since the beginning of exoplanet characterization. Transmission
observations of this system between the mid infrared and the far ultraviolet
have revealed the signature of atomic, molecular, and possibly aerosol species
in the lower atmosphere of the planet, as well as escaping hydrogen and metals
in the upper atmosphere. From a re-analysis of near-ultraviolet (NUV)
transmission observations of HD 209458b, we detect ionized iron (Fe II)
absorption in a 100 A-wide range around 2370 A, lying beyond the planetary
Roche lobe. However, we do not detect absorption of equally strong Fe II lines
expected to be around 2600 A. Further, we find no evidence for absorption by
neutral magnesium (Mg I), ionized magnesium (Mg II), nor neutral iron (Fe I).
These results avoid the conflict with theoretical models previously found by
Vidal-Madjar et al. (2013), which detected Mg I but did not detect Mg II from
this same data set. Our results indicate that hydrodynamic escape is strong
enough to carry atoms as heavy as iron beyond the planetary Roche lobe, even
for planets less irradiated than the extreme ultra-hot-Jupiters such as
WASP-12b and KELT-9b. The detection of iron and non-detection of magnesium in
the upper atmosphere of HD 209458b can be explained by a model in which the
lower atmosphere forms (hence, sequesters) primarily magnesium-bearing
condensates, rather than iron condensates. This is suggested by current
microphysical models. The inextricable synergy between upper- and
lower-atmosphere properties highlights the value of combining observations that
probe both regions.",2001.03126v1
2020-03-22,Formation of embryos of the Earth and the Moon from the common rarefied condensation and their subsequent growth,"Embryos of the Moon and the Earth may have formed as a result of contraction
of a common parental rarefied condensation. The required angular momentum of
this condensation could largely be acquired in a collision of two rarefied
condensations producing the parental condensation. With the subsequent growth
of embryos of the Moon and the Earth taken into account, the total mass of
as-formed embryos needed to reach the current angular momentum of the
Earth-Moon system could be below 0.01 of the Earth mass. For the low lunar iron
abundance to be reproduced with the growth of originally iron-depleted embryos
of the Moon and the Earth just by the accretion of planetesimals, the mass of
the lunar embryo should have increased by a factor of 1.3 at the most. The
maximum increase in the mass of the Earth embryo due to the accumulation of
planetesimals in a gas-free medium is then threefold, and the current
terrestrial iron abundance is not attained. If the embryos are assumed to have
grown just by accumulating solid planetesimals (without the ejection of matter
from the embryos), it is hard to reproduce the current lunar and terrestrial
iron abundances at any initial abundance in the embryos. For the current lunar
iron abundance to be reproduced, the amount of matter ejected from the Earth
embryo and infalling onto the Moon embryo should have been an order of
magnitude larger than the sum of the overall mass of planetesimals infalling
directly on the Moon embryo and the initial mass of the Moon embryo, which had
formed from the parental condensation, if the original embryo had the same iron
abundance as the planetesimals. The greater part of matter incorporated into
the Moon embryo could be ejected from the Earth in its multiple collisions with
planetesimals (and smaller bodies).",2003.09925v1
2020-07-01,Cobalt and copper abundances in 56 Galactic bulge red giants,"The Milky Way bulge is an important tracer of the early formation and
chemical enrichment of the Galaxy. The abundances of different iron-peak
elements in field bulge stars can give information on the nucleosynthesis
processes that took place in the earliest supernovae. Cobalt (Z=27) and copper
(Z=29) are particularly interesting.We aim to identify the nucleosynthesis
processes responsible for the formation of the iron-peak elements Co and Cu.
Methods. We derived abundances of the iron-peak elements cobalt and copper in
56 bulge giants, 13 of which were red clump stars. High-resolution spectra were
obtained using FLAMES-UVES at the ESO Very Large Telescope by our group in
2000-2002, which appears to be the highest quality sample of high-resolution
data on bulge red giants obtained in the literature to date. Over the years we
have derived the abundances of C, N, O, Na, Al, Mg; the iron-group elements Mn
and Zn; and neutron-capture elements. In the present work we derive abundances
of the iron-peak elements cobalt and copper. We also compute chemodynamical
evolution models to interpret the observed behaviour of these elements as a
function of iron. The sample stars show mean values of [Co/Fe]~0.0 at all
metallicities, and [Cu/Fe]~0.0 for [Fe/H]>-0.8 and decreasing towards lower
metallicities with a behaviour of a secondary element. We conclude that [Co/Fe]
varies in lockstep with [Fe/H], which indicates that it should be produced in
the alpha-rich freezeout mechanism in massive stars. Instead [Cu/Fe] follows
the behaviour of a secondary element towards lower metallicities, indicating
its production in the weak s-process nucleosynthesis in He-burning and later
stages. The chemodynamical models presented here confirm the behaviour of these
two elements (i.e. [Co/Fe] vs. [Fe/H]~constant and [Cu/Fe] decreasing with
decreasing metallicities).",2007.00397v1
2021-05-23,Decomposing the Iron Cross-Correlation Signal of the Ultra-Hot Jupiter WASP-76b in Transmission using 3D Monte-Carlo Radiative Transfer,"Ultra-hot Jupiters are tidally locked gas giants with dayside temperatures
high enough to dissociate hydrogen and other molecules. Their atmospheres are
vastly non-uniform in terms of chemistry, temperature and dynamics, and this
makes their high-resolution transmission spectra and cross-correlation signal
difficult to interpret. In this work, we use the SPARC/MITgcm global
circulation model to simulate the atmosphere of the ultra-hot Jupiter WASP-76b
under different conditions, such as atmospheric drag and the absence of TiO and
VO. We then employ a 3D Monte-Carlo radiative transfer code, HIRES-MCRT, to
self-consistently model high-resolution transmission spectra with iron (Fe I)
lines at different phases during the transit. To untangle the structure of the
resulting cross-correlation map, we decompose the limb of the planet into four
sectors, and we analyse each of their contributions separately. Our experiments
demonstrate that the cross-correlation signal of an ultra-hot Jupiter is
primarily driven by its temperature structure, rotation and dynamics, while
being less sensitive to the precise distribution of iron across the atmosphere.
We also show that the previously published iron signal of WASP-76b can be
reproduced by a model featuring iron condensation on the leading limb.
Alternatively, the signal may be explained by a substantial temperature
asymmetry between the trailing and leading limb, where iron condensation is not
strictly required to match the data. Finally, we compute the $K_{p}-V_{sys}$
maps of the simulated WASP-76b atmospheres, and we show that rotation and
dynamics can lead to multiple peaks that are displaced from zero in the
planetary rest frame.",2105.11034v2
2021-07-13,How many explosions does one need? -- Quantifying supernovae in globular clusters from iron abundance spreads,"Many globular clusters (GCs) are known to host multiple populations
distinguishable by their light-element content. Less common are GCs displaying
iron abundance spreads which are seen as evidence for enrichment through core
collapse supernovae (SNe). We present a simple analytical method to estimate
the number of SNe required to have occurred in a GC from its metallicity and
iron abundance spread. We then use this result to estimate how long star
formation (SF) lasted to build the GC. We apply our method to up-to-date
measurements and find that, assuming the correctness of these measurements,
multiple SNe (up to $10^5$) are required in most GCs with iron abundance
spreads. The number of SNe events which contributed to the enrichment of the
GCs studied here is typically a factor of 10 less than the expected number of
SNe in a canonical initial mass function (IMF). This indicates that gas
expulsion from the forming GC occurred after the first 10 per cent of SNe
exploded. We compute that for the GCs typically SF ends after only a few Myr
(extending up to $\approx 30 ~\rm Myr$ in a few cases). We also discuss
possible improvements of this method and especially its sensitivity to the
error of iron abundance measurements of individual stars of a GC. The method
presented here can quickly give an estimate for the number of SNe required to
explain the iron abundance spread in a GC without the requirement of any
hydrodynamical simulations.",2107.06240v3
2021-11-22,Chemo-Mechanical Phase-Field Modeling of Iron Oxide Reduction with Hydrogen,"The reduction of iron ore with carbon-carriers is one of the largest sources
of greenhouse gas emissions in the industry, motivating global activities to
replace the coke-based blast furnace reduction by hydrogen-based direct
reduction (HyDR). Iron oxide reduction with hydrogen has been widely
investigated both experimentally and theoretically. The process includes
multiple types of chemical reactions, solid state and defect-mediated diffusion
(by oxygen and hydrogen species), several phase transformations, as well as
massive volume shrinkage and mechanical stress buildup. In this work, a
chemo-mechanically coupled phase-field (PF) model has been developed to explore
the interplay between phase transformation, chemical reaction, species
diffusion, large elasto-plastic deformation and microstructure evolution.
Energetic constitutive relations of the model are based on the system free
energy which is calibrated with the help of a thermodynamic database. The model
has been first applied to the classical core-shell (w\""ustite-iron) structure.
Simulations show that the phase transformation from w\""ustite to alpha-iron can
result in high stress and rapidly decelerating reaction kinetics. Mechanical
stresses can contribute elastic energy to the system, making phase
transformation difficult. Thus slow reaction kinetics and low metallization are
observed. However, if the stress becomes comparatively high, it can shift the
shape of the free energy from a double-well to a single-well case and speed up
the transformation. The model has been further applied to simulate an actual
iron oxide specimen with its complex microstructure, characterized by electron
microscopy. The simulation results show that isolated pores in the
microstructure are filled with water vapor during reduction, an effect which
influences the local reaction atmosphere and dynamics.",2111.11538v1
2021-11-30,A New Iron Emission Template for Active Galactic Nuclei. I. Optical Template for the H$β$ region,"We present a new empirical template for iron emission in active galactic
nuclei (AGN) covering the $4000-5600$ A range. The new template is based on a
spectrum of the narrow-line Seyfert 1 galaxy Mrk 493 obtained with the Hubble
Space Telescope. In comparison with the canonical iron template object I Zw 1,
Mrk 493 has narrower broad-line widths, lower reddening, and a less extreme
Eddington ratio, making it a superior choice for template construction. We
carried out a multicomponent spectral decomposition to produce a template
incorporating all permitted and forbidden lines of Fe II identified in the Mrk
493 spectrum over this wavelength range, as well as lines from Ti II, Ni II,
and Cr II. We tested the template by fitting it to AGN spectra spanning a broad
range of iron emission properties, and we present a detailed comparison with
fits using other widely used monolithic and multi-component iron emission
templates. The new template generally provides the best fit (lowest $\chi^2$)
compared to other widely used monolithic empirical templates. In addition, the
new template yields more accurate spectral measurements including a
significantly better match of the derived Balmer line profiles (H$\beta$,
H$\gamma$, H$\delta$), in contrast with results obtained using the other
templates. Our comparison tests show that the choice of iron template can
introduce a systematic bias in measurements of the H$\beta$ line width, which
consequently impacts single-epoch black hole mass estimates by $\sim0.1$ dex on
average and possibly up to $\sim0.3-0.5$ dex individually.",2111.15118v2
2022-10-03,Physical Modeling of Dust Polarization from Magnetically Enhanced Radiative Torque (MRAT) Alignment in Protostellar Cores with POLARIS,"Magnetic fields ($\textbf{B}$) are an important factor that controls the star
formation process. The leading method to observe $\textbf{B}$ is using
polarized thermal emission from dust grains aligned with $\textbf{B}$. However,
in dense environments such as protostellar cores, dust grains may have
inefficient alignment due to strong gas randomizations, so that using dust
polarization to trace $\textbf{B}$ is uncertain. Hoang $\&$ Lazarian (2016)
demonstrated that the grain alignment by RAdiative Torques is enhanced if dust
grains contain embedded iron inclusions. Here we extend POLARIS code to study
the effect of iron inclusions on grain alignment and thermal dust polarization
toward a protostellar core, assuming uniform magnetic fields. We found that
paramagnetic grains produce a low polarization degree of $p \sim 1\%$ in the
envelope and negligible $p \ll 1\%$ in the central region due to the loss of
grain alignment. In contrast, grains with a high level of iron inclusions can
have perfect alignment and produce high $p \sim 40\%$ in the envelope and low
$p \leq 10\%$ in the central region. Grains with a moderate level of iron
inclusions induce the polarization flipping from $\textbf{P}$ $\parallel$
$\textbf{B}$ at millimeter to $\textbf{P}$ $\perp$ $\textbf{B}$ at
submillimeter due to the change in the internal alignment caused by slow
internal relaxation. The weak alignment of very large grains of $a \geq 10\mu
m$ reduces the polarization by dichroic extinction at submillimeter
wavelengths. We found a positive correlation between p and the level of iron
inclusions, which opens a new window to constrain the abundance of irons locked
in dust through dust polarimetry.",2210.01036v3
2022-10-05,The magnetic properties of the iron phthalocyanine molecule grafted to the Ti$_2$C MXene layer,"The magnetic tetrapyrrole molecules (such as porphyrins and phthalocyanines)
with an active transition metal atom in their centre are currently intensively
studied as prosperous potential elements of devices for high-density
information storage and processing. It has been recently proved that by means
of external factors one could induce two stable fully controllable molecular
states. Therefore, hybrid systems consisting of such magnetic molecules and
suitable carriers from the family of two-dimensional materials are often
considered as promising highly scalable spintronic systems that could in the
near future lead to novel industrial applications. Here, we perform the spin
polarised density functional theory (DFT) studies of the hybrid system, which
is the iron phthalocyanine molecule (FePc) on the top of the titanium carbide
Ti$_2$C MXene layer. The most relevant issue in this part is the interaction
between magnetic atoms: Ti from MXene substrate and iron from FePc. Four
various magnetic configurations of FePc/Ti$_2$C were considered. The
significant ferromagnetic interaction between the iron atom and the upper
titanium layer plays important role in the reorientation of the iron atom's
magnetic moment. We also analyse a model of the system in which the FePc
molecule is in a quintet state (the ground state of an isolated molecule is a
triplet). To get a better understanding of the physics of the FePc/Ti$_2$C
hybrid system, we studied the hybrid systems with a single iron atom and
non-magnetic H$_2$Pc on the Ti$_2$C layer, Fe/Ti$_2$C and H$_2$Pc/Ti$_2$C,
respectively, which nicely explains the role of the Pc ligand in the
FePc/Ti$_2$C hybrid system.",2210.02141v1
2022-12-07,Nodal s$_\pm$ Pairing Symmetry in an Iron-Based Superconductor with only Hole Pockets,"The origin of the high temperature superconductivity in the iron-based
superconductors remains elusive after being extensively studied for more than a
decade. Determination of the pairing symmetry is essential in understanding the
superconductivity mechanism. In the iron-based superconductors that have hole
pockets around the Brillouin zone center and electron pockets around the zone
corners, the pairing symmetry is generally considered to be s$_\pm$, endowing a
sign change in the superconducting gap between the hole and electron pockets.
For the iron-based superconductors with only hole pockets, however, a couple of
pairing scenarios have been proposed but the exact symmetry is still highly
controversial. Here we report our determination of the pairing symmetry in
KFe$_2$As$_2$ which is a prototypical iron-based superconductor with hole
pockets both around the zone center and around the zone corners. By taking
laser-based angle resolved photoemission measurements with super-high
resolution and at ultra-low temperature, we have precisely determined the
superconducting gap distribution and identified the locations of the gap nodes
on all the Fermi surface around the zone center and the zone corners. The
complete superconducting gap structure, in combination with the observation of
the spin resonance in neutron scattering, provides strong evidence on the
s$_\pm$ pairing symmetry in KFe$_2$As$_2$ with a gap sign reversal between the
hole pockets around the zone center and the hole pockets around the zone
corners. These results unify the pairing symmetry in the hole-doped iron-based
superconductors and point to the spin fluctuation as the pairing glue in
generating superconductivity.",2212.03472v1
2023-03-20,Machine learning assisted phase and size-controlled synthesis of iron oxides,"The controllable synthesis of iron oxides particles is a critical issue for
materials science, energy storage, biomedical applications, environmental
science, and earth science. However, synthesis of iron oxides with desired
phase and size are still a time-consuming and trial-and-error process. This
study presents solutions for two fundamental challenges in materials synthesis:
predicting the outcome of a synthesis from specified reaction parameters and
correlating sets of parameters to obtain products with desired outcomes. Four
machine learning algorithms, including random forest, logistic regression,
support vector machine, and k-nearest neighbor, were trained to predict the
phase and particle size of iron oxide based on experimental conditions. Among
the models, random forest exhibited the best performance, achieving 96% and 81%
accuracy when predicting the phase and size of iron oxides in the test dataset.
Premutation feature importance analysis shows that most models (except logistic
regression) rely on known features such as precursor concentration, pH, and
temperature to predict the phases from synthesis conditions. The robustness of
the random forest models was further verified by comparing prediction and
experimental results based on 24 randomly generated methods in additive and
non-additive systems not included in the datasets. The predictions of product
phase and particle size from the models are in good agreement with the
experimental results. Additionally, a searching and ranking algorithm was
developed to recommend potential synthesis parameters for obtaining iron oxide
products with desired phase and particle size from previous studies in the
dataset.",2303.11244v1
1997-02-17,Lack of Evolution in the Iron Abundance in Clusters of Galaxies and Implications for the Global Star Formation Rate at High Redshift,"We present the first large sample of accurate iron abundances and
temperatures for clusters at redshifts greater than 0.14. We find that the Fe
abundance shows little or no evolution out to redshift 0.3. This and the early
formation epoch of elliptical galaxies in clusters indicate that most of the
enrichment of the intracluster medium occurred at redshifts greater than 1. If
clusters represent fair samples of the universe, then global metal production
is 2-5 times greater than is inferred from recent studies of galaxies at low
and high redshifts.",9702149v1
1997-02-21,Reply to ``Roles of SNIa and SNII in ICM Enrichment'' by Y. Ishimaru and N. Arimoto,"We address a number of misunderstandings and misstatements contained in the
paper ``Roles of SNIa and SNII in ICM Enrichment'' by Y. Ishimaru and N.
Arimoto with regard to the papers by Mushotzky et al. (1996, ApJ, 466, 686) and
Loewenstein and Mushotzky (1996, ApJ, 466, 695). In particular, we emphasize
that comparison between observations and models in these papers were made
self-consistently assuming a particular (photospheric) value for the solar iron
abundance. We also briefly revisit the question of the contribution of Type Ia
supernovae to the iron enrichment of the intracluster medium.",9702190v1
1998-02-03,Iron Kalpha line widths in magnetic cataclysmic variables,"Following a recent report that AO Psc has broad iron Kalpha emission lines we
have looked at the ASCA spectra of 15 magnetic cataclysmic variables. We find
that half of the systems have Kalpha lines broadened by ~200 eV, while the
remainder have narrow lines. We argue that the Doppler effect is insufficient
to explain the finding and propose that the lines originate in accretion
columns on the verge of optical thickness, where Compton scattering of
resonantly-trapped line photons broadens the profile. We suggest that the
broadening is a valuable diagnostic of conditions in the accretion column.",9802040v1
1998-05-19,Multi-Element Doppler Imaging of the Ap star epsilon Ursae Majoris,"The surface distribution of five elements: iron, chromium, titanium,
magnesium and manganese on the magnetic A0pCr star epsilon UMa, have been
calculated using the Doppler imaging technique. We found that iron, chromium
and manganese are correlated with the assumed dipole magnetic field geometry of
this star, which is apparently not the case of magnesium and titanium.",9805244v1
1998-10-30,Spinning Black Holes in Active Galactic Nuclei,"Recent X-ray spectroscopy made with ASCA have shown broad, skewed iron line
emission from Seyfert-1 galaxies. The large extent of the red tail allows
probing of the innermost regions of the black hole's accretion disc. A model of
line emission has been developed and very strong evidence for the presence of a
rapidly rotating Kerr black hole has been established in the case of
MCG--6-30-15. Issues related to the observed line equivalent width and the
position/geometry of the primary source are discussed. Both the continuum and
the reflected iron line are computed, in a consistent manner, for a source
located on the axis of rotation.",9810494v1
2000-11-10,The formation of life,"The formation of life is an automatic stage in the consolidation of rocky or
""terrestrial"" planets. The organic (=carbonaceous) matter, light elements,
gases, and water must ""float"" toward the surface and the heavier metals must
sink toward the center. Random processes in the molecular soup that fills
microfractures in unmelted crust eventually produce self-replicating
microtubules. In an appendix I suggest that some primordial crust remains
because there is not enough consolidation energy to melt the whole planet.
Energy is lost when iron planetesimals first partially melt and then coalesce
to form the molten iron planetary core. Stony planetesimals accrete onto the
surface of an already consolidated core.",0011209v1
2001-09-17,Iron line profiles from black hole accretion discs with spiral velocity structure,"We calculate the iron line profiles from accretion discs with spiral velocity
structures around Schwarzschild black holes. We find that quasi-periodic bumps
appear in the the profiles, thereby providing a test for spiral wave patterns.
This study is motivated by recent work showing that spiral density waves can
result from MHD instabilities even in non-self-gravitating discs, and by
improved spectral resolution of forthcoming X-ray missions.",0109243v1
2002-01-12,"On the origin of the broad, relativistic iron line of MCG-6-30-15 observed by XMM-Newton","The relativistic iron line profile recently observed by XMM-Newton in the
spectrum of the Seyfert 1 galaxy MCG--6-30-15 (Wilms et al., 2001) is discussed
in the framework of the lamp-post model. It is shown that the steep disc
emissivity, the large line equivalent width and the amount of Compton
reflection can be self- consistently reproduced in this scenario.",0201192v1
2002-01-17,FUSE observations of the central star of Abell 78,"FUSE high resolution spectra of two PG1159 type central stars (K1-16 and NGC
7094) have revealed an unexpected iron deficiency of at least 1 or 2 dex (Miksa
et al. 2002). Here we present early results of FUSE spectroscopy of the CSPN
Abell 78. It is shown that iron is strongly deficient in this star, too.",0201280v1
2002-02-07,Fe-deficiency in H-deficient post-AGB stars due to n-capture nucleosynthesis,"H-deficient post-AGB objects, e.g. PG1159 type star K1-16 and born-again AGB
star Sakurai's object, have been reported to be significantly iron-deficient.
We find that the iron deficiencies expected due to neutron-capture
nucleosynthesis during either the progenitor AGB evolution and/or the neutron
burst that occurs as a result of the rapid burning of protons during a post-AGB
He-flash are generally in line with observations.",0202143v1
2002-08-28,Metal abundances in PG1159 stars from Chandra and FUSE spectroscopy,"We investigate FUSE spectra of three PG1159 stars and do not find any
evidence for iron lines. From a comparison with NLTE models we conclude a
deficiency of 1-1.5 dex. We speculate that iron was transformed into heavier
elements. A soft X-ray Chandra spectrum of the unique H- and He-deficient star
H1504+65 is analyzed. We find high neon and magnesium abundances and confirm
that H1504+65 is the bare core of either a C-O or a O-Ne-Mg white dwarf.",0208505v1
2002-11-06,Iron abundances in hydrodynamical simulations of galaxy clusters,"Hydrodynamical SPH simulations of galaxy clusters are used to investigate the
metal enrichment of the intracluster medium. The final metallicity abundances
of the simulated clusters are determined according to the numerical resolution
and a number of model parameters. For a fiducial set of model prescriptions the
results of the simulations indicate iron abundances in broad agreement with
data. Final X-ray properties are not sensitive to the heating of the ICM. This
supports a scenario where the ICM evolution of cool clusters is driven by
radiative cooling.",0211111v1
2003-02-18,The recent X-ray history of NGC 5506,"We present a detailed discussion of the spectral and spatial components of
NGC 5506, based on XMM-Newton, Chandra and BeppoSAX observations. The overall
picture consists of a nucleus absorbed by cold gas with column density of
$\approx10^{22}$ cm$^{-2}$ and surrounded by a Compton-thick torus, whose
existence is inferred by a cold reflection component and an iron K$\alpha$
line. On a much larger scale, a photoionized gas extended on $\approx350$ pc
reprocesses the nuclear radiation, producing a soft excess and ionized iron
lines. Noteworthy, we find no evidence for the presence of the accretion disc.",0302349v1
2003-11-03,Iron Emission in z ~ 6 QSOs and its Possible Implications,"We have obtained low-resolution near-infrared spectra of five SDSS QSOs at
5.3 < z < 6.3 using the NICMOS instrument of the Hubble Space Telescope. We
find evidence of emission in the Fe II complex centered near 2500 A (rest) in
all five objects. We estimate Fe II / Mg II 2800 A flux ratios comparable to
those measured in QSOs at lower redshifts, which indicate metallicities near or
above the solar level. We discuss the possible implications of this result
assuming the iron enrichment to have been produced mainly in Type Ia
supernovae.",0311043v1
2004-02-12,Accurate Modelling of Relativistic Iron Lines from Accretion Discs,"Observations of fluorescent iron lines from accreting black holes provide one
of the best tests of strong field gravity available to date, and the only
current observational tool to probe black hole spacetime. However, the two most
widely used models for spectral fitting (diskline, laor) are over a decade old
and have significant limitations. We present a new code for calculating these
effects which will be incorporated within the XSPEC package",0402279v1
2004-06-10,The sharp drop in the flux striking the accretion disk,"In this paper,We present a simple relativistic approach to analyze the flux
striking the disk which is possibly from a source up the Black hole.The X-ray
source is locate above an accretion disc orbiting around the black hole,this
assumption is invoked by recent studies about iron k$\alpha$. we compute and
arguing that due to the light bending effect near black hole, the flux striking
the disk surface may be very concentrated,which will undoubtable change the
disk's ionization state hence change the iron line's ionization state and
emissivity.Also,Our model may explain the steep power law when modelling the
lines.",0406258v1
2004-10-29,Chemical abundances of RGB-Tip stars in the Sagittarius dwarf Spheroidal galaxy,"We present preliminary iron abundances and $\alpha$ element (Ca, Mg)
abundance ratios for a sample of 22 Red Giant Branch (RGB) Stars in the
Sagittarius dwarf spheroidal galaxy (Sgr), selected near the RGB-Tip. The
sample is representative of the Sgr dominant population. The mean iron
abundance is [Fe/H]=-0.49. The $\alpha$ element abundance ratios are slightly
subsolar, in agreement with the results recently prensented by Bonifacio et
al.(2004, A&A, 414, 503).",0410749v1
2004-11-06,Surface Evidence of an Iron-Rich Solar Interior and a Neutron-Rich Solar Core,"Quantitative data on the solar wind, solar magnetic fields, solar eruptions,
solar neutrinos, and on the planetary material orbiting the Sun all indicate
the presence of an iron-rich solar interior and a neutron star at the core of
the Sun. Solar magnetic fields are deep-seated remnants from the core and/or
Bose-Einstein condensation of Fe-rich material into a rotating superconductor.
Neutron emission from the core triggers a series of reactions that produce
solar luminosity, the H carrier gas that maintains mass separation in the Sun,
and an outpouring of 3 E43 H+ ions per year in the solar wind.",0411163v1
2005-01-31,Resonant Auger Destruction and Iron K-Alpha Spectra in Compact X-ray Sources,"We examine the effects of resonant Auger destruction in modifying the
intensities and flux distributions of K-alpha spectra from iron L-shell ions.
Applications include X-ray irradiated stellar winds in X-ray binaries and
accretion disk atmospheres. Using detailed atomic models, we find that resonant
Auger destruction is selective, in that only a subset of the emitted K-alpha
lines is highly attenuated. We also show that that the local excitation
conditions can have a dramatic effect on the K-alpha emissivity spectrum.",0502002v1
2007-01-24,Photospheric magnetic field and chromospheric emission,"We present a statistical analysis of network and internetwork properties in
the photosphere and the chromosphere. For the first time we simultaneously
observed (a) the four Stokes parameters of the photospheric iron line pair at
630.2 nm and (b) the intensity profile of the Ca II H line at 396.8 nm. The
vector magnetic field was inferred from the inversion of the iron lines. We aim
at an understanding of the coupling between photospheric magnetic field and
chromospheric emission.",0701681v1
1996-02-11,Theory on the Itinerant Ferromagnetism in the $3d$-transition metal systems,"Keeping nickel, cobalt and iron in mind, we investigate the origin of the
itinerant ferromagnetism. In so doing, we generalize the Gutzwiller
approximation. In that,we take account of the effect of the band degeneracy and
the Hund's-rule coupling in addition to the on-site repulsion. After the
discussion on nickel, the condition for the incomplete ferromagnetism, observed
in cobalt and iron, is argued. Phase diagrams, which show the interplay between
the band shape peculiarity and the Hund's-rule coupling, are given. It is found
that for the $3d$-transition metal systems, both of the Hund's-rule coupling
and the special feature of the density of states are necessary to explain the
itinerant ferromagnetism.",9602058v1
1999-12-14,Hall cross size scaling and its application to measurements on nanometer-size iron particle arrays,"Hall crosses were used to measure the magnetic properties of arrays of
ferromagnetic, nanometer-scale iron particles. The arrays typically consist of
several hundred particles of 9 -- 20 nm in diameter. It is shown that the
sensitivity of the measurements can be improved by matching the areas of the
Hall cross and the array grown onto it by at least an order of magnitude. We
predict that single particles of diameter as small as 10 nm can be measured if
grown onto a Hall cross of appropriate size.",9912266v1
2000-08-15,"Electronic structure, hyperfine interactions and disordering effects in iron nitride Fe4N","Iron nitride Fe4N is studied by full-potential LAPW method. Structure
parameters, electronic and magnetic properties as well as hyperfine interaction
parameters are obtained. We observe perfect agreement with experimental
results. Hypothetical Fe4N structure was also calculated to study the influence
of disordering effects on parameters of Moessbauer spectra. We performed
detailed analysis of EFG formation on Fe nuclei including magnetization
effects. We show that the formation of N-Fe-N local configuration is
energetically favourable in nitrogen austenites.",0008214v1
2001-12-20,Ferromagnetic and antiferromagnetic spin fluctuations and superconductivity in the hcp-phase of Fe,"High purity iron, which transforms into the hcp phase under pressure, has
recently been reported to be superconducing in the pressure range 150-300 kBar
[shim]. The electronic structure and the electron-phonon coupling
($\lambda_{ph}$) are calculated for hcp iron at different volumes. A
parameter-free theory for calculating the coupling constants $\lambda_{sf}$
from ferromagnetic (FM) and antiferromagnetic (AFM) spin fluctuations is
developed. The calculated $\lambda_{sf}$ are sufficiently large to explain
superconductivity especially from FM fluctuations. The results indicate that
superconductivity mediated by spin fluctuations is more likely than from
electron-phonon interaction.",0112382v1
2002-05-29,Influence of nonstoichiometry and iron doping on optical absorption in KNbO3 single crystal,"Single crystals of KNbO3 and KNbO3 : Fe have been grown using the flux method
at various technological conditions. The investigations of optical absorption
of these crystals were carried out. Marked influence of technological
conditions and doping with iron on optical absorption has been found. Observed
changes of the absorption spectra are associated with lattice defects arising
due to nonstoichiometry and/or doping.",0205611v1
2002-11-12,Magneto-Optical Kerr Effect of Iron Thin Films on Paramagnetic Substrates,"First principles calculations of the magnetic properties and the
magneto-optical Kerr effect (MOKE) of iron thin films epitaxially grown on the
[001] surface of paramagnetic metals: copper, silver, gold, palladium, and
platinum are presented. The role of hybridization with the substrate is
investigated and it is shown how the relaxation effects influence the complex
Kerr angle. The results are obtained by means of the relativistic
full-potential linear muffin-tin method, and the film is modeled using a slab
geometry within a supercell technique.",0211234v1
2004-06-18,First principles simulations of the magnetic and structural properties of Iron,"We have implemented non-collinear GGA and a generalized Bloch's theorem to
simulate unconmensurate spiral arrangements of spins in a Density Functional
Theory code based on localized wave functions. We have subsequently performed a
thorough study of the different states of bulk Iron. We determine the minimal
basis set required to obtain reliable orderings of ground and excited states.
We find that the most stable fcc phase is a spiral with an equilibrium lattice
constant 3.56 A.",0406424v1
2004-07-27,Composition dependent magnetic properties of iron oxide - polyaniline nanoclusters,"Gamma - Iron Oxide prepared by sol -gel process was used to produce
nanocomposites with polyaniline of varying aniline concentrations. TEM shows
the presence of chain like structure for lower polyaniline concentration. The
room temperature hysteresis curves show finite coercivity of 160 Oe for all the
composites while the saturation magnetization was found to decrease with
increasing polymer content. ZFC - FC magnetisation measurements indicate high
blocking temperatures. It is believed that this indicates a strongly
interacting system, which is also shown by our TEM results. Monte Carlo
simulations performed on a random anisotropy model with dipolar and exchange
inteactions match well with experimental results.",0407693v1
2005-10-31,Fe3O4(001) films on Fe(001) - termination and reconstruction of iron rich surfaces,"High-quality and impurity-free magnetite surfaces with (sqrt2xsqrt2)R45o
reconstruction have been obtained for the Fe3O4(001) epitaxial films deposited
on Fe(001). Based on atomically resolved STM images for both negative and
positive sample polarity and Density Functional Theory calculations, a model of
the magnetite (001) surface terminated with Fe ions forming dimers on the
reconstructed (sqrt2xsqrt2)R45o octahedral iron layer is proposed.",0510821v2
2006-06-16,An iron(III) phosphonate cluster containing a nonanuclear ring,"This communication reports the first example of cyclic ferric clusters with
an odd number of iron atoms capped by phosphonate ligands, namely,
[Fe9(m-OH)7(m-O)2(O3PC6H9)8-(py)12]. The magnetic studies support a S = 1/2
ground state with an exchange coupling constant of about J = -30 K.",0606452v1
2006-12-12,First-principles thermoelasticity of bcc iron under pressure,"We investigate the elastic and isotropic aggregate properties of
ferromagnetic bcc iron as a function of temperature and pressure by computing
the Helmholtz free energies for the volume-conserving strained structures using
the first-principles linear response linear-muffin-tin-orbital method and the
generalized-gradient approximation. We include the electronic excitation
contributions to the free energy from the band structures, and phonon
contributions from quasi-harmonic lattice dynamics. We make detailed
comparisons between our calculated elastic moduli and their temperature and
pressure dependences with available experimental and theoretical data.",0612308v1
2007-01-10,Computational approach to finite size and shape effects in iron nanomagnets,"We develop and validate a computational approach to nanomagnets. It is built
on the spin wave approximation to a Heisenberg ferromagnet whose parameters can
be calculated from a first principles theory (e.g. density functional theory).
The method can be used for high throughput analysis of a variety of
nanomagnetic materials. We compute the dependence of the magnetization of an
iron nanomagnet on temperature, size and shape. The approach is applied to
nanomagnets in the range of 432 atoms to 59 million atoms, a size which is
several orders of magnitude beyond the scalability of density functional
theory.",0701225v1
2007-02-05,"Theory of Layered Iron Oxide on Frustrated Geometry: Electric Polarization, Magnetoelectric Effect and Orbital State","A layered iron oxide \rfeo ($R$: rare-earth elements) is an exotic dielectric
material with charge-order (CO) driven electric polarization and
magnetoelectric effect caused by spin-charge coupling. In this paper, a theory
of electronic structure and dielectric property in \rfeo is presented. Charge
frustration in paired-triangular lattices allows a charge imbalance without
inversion symmetry. Spin frustration induces reinforcement of this polar CO by
a magnetic ordering. We also analyze an orbital model for the Fe ion which does
not show a conventional long-range order.",0702087v2
1999-03-22,Electron Response and e/h Ratio of Iron-Scintillator Hadron Prototype Calorimeter with Longitudinal Tile Configuration,"The detailed information about electron response, electron energy resolution
and e/h ratio as a function of incident energy E, impact point Z and incidence
angle $\Theta$ of iron-scintillator hadron prototype calorimeter with
longitudinal tile configuration is presented. These results are based on
electron and pion beams data of E = 20, 50, 100, 150, 300 GeV at $\Theta =
10^o, 20^o, 30^o$, which were obtained during test beam period in July 1995.
The obtained calibration constant is used for muon response converting from pC
to GeV. The results are compared with existing experimental data and with some
Monte Carlo calculations.",9903050v1
1999-03-22,Non-Compensation of the Barrel Tile Hadron Module-0 Calorimeter,"The detailed experimental information about the electron and pion responses,
the electron energy resolution and the e/h ratio as a function of incident
energy E, impact point Z and incidence angle $\Theta$ of the Module-0 of the
iron-scintillator barrel hadron calorimeter with the longitudinal tile
configuration is presented. The results are based on the electron and pion
beams data for E = 10, 20, 60, 80, 100 and 180 GeV at $\eta$ = -0.25 and -0.55,
which have been obtained during the test beam period in 1996. The results are
compared with the existing experimental data of TILECAL 1m prototype modules,
various iron-scintillator calorimeters and with some Monte Carlo calculations.",9903054v1
2000-10-17,Possible Observation of a Second Kind of Light,"According to classical electrodynamics, sunlight that is passed through an
iron layer can be detected with the naked eye only if the thickness of the
layer is less than 170nm. However, in an old experiment, August Kundt was able
to see the sunlight with the naked eye even when it had passed an iron layer
with thickness greater than 200nm. To explain this observation, we propose a
second kind of light which was introduced in a different context by Abdus
Salam. A tabletop experiment can verify this possibility.",0010040v1
2003-01-10,Modeling skin effect in large magnetized iron detectors,"The experimental problem of the calibration of magnetic field in large iron
detectors is discussed. Emphasis is laid on techniques based on ballistic
measurements as the ones employed by MINOS or OPERA.In particular, we provide
analytical formulas to model the behavior of the apparatus in the transient
regime, keeping into account eddy current effects and the finite penetration
velocity of the driving fields. These formulas ease substantially the design of
the calibration apparatus.Results are compared with experimental data coming
from a prototype of the OPERA spectrometer.",0301015v1
2004-01-26,"Local density and the RPA corrections in charge current quasielastic neutrino on Oxygen, Argon and Iron scattering","Numerical computations of cross sections for quasielastic charge current
scattering of neutrino on Oxygen, Argon and Iron in Local Density Approximation
(LDA) are presented. We consider processes for a few GeV neutrino energy. We
include corrections from nucleon re-interaction in nucleus described by
relativistic Random Phase Approximation (RPA). We adopt the relativistic Fermi
gas model of nucleus with and without taking into account the effective mass of
nucleons.",0401053v2
2007-04-13,Towards understanding of birds magnetoreceptor mechanism,"In the present letter we suggest a new theoretical model for a quantitative
description of the magnetoreception mechanism in birds. The considered
mechanism involves two types of iron minerals (magnetite and maghemite) which
were found in subcellular compartments within sensory dendrites of the upper
beak of several bird species. The analysis of forces acting between the iron
particles shows that the orientation of the external geomagnetic field can
significantly change the probability of the mechanosensitive ion channels
opening and closing. The performed theoretical analysis shows that the
suggested magnetoreceptor system might be a sensitive biological magnetometer
providing an essential part of the magnetic map for navigation.",0704.1763v1
2007-05-29,A Challenge to Control Gravity via Applying Electromagnetic Low-Frequency Radiation - Theory and Proposed Model Experiments,"Including Vaidya metric into the model of Expansive Nondecelerative Universe
allows to localize the energy of gravitational field. A term of effective
gravitational range is introduced and classic Newton potential is substituted
for Yukawa-type potential. It allows to allocate a typical frequency value to
each gravitational field. Derived theoretical conclusions led us to investigate
the effect of electromagnetic field with a precisely predetermined frequency
and intensity on iron. We believe that under certain circumstances a decrease
in iron gravitational mass should be observed. Two model experiments verifying
the theoretical conclusions are proposed.",0705.4143v2
2007-09-06,Muon Identification without Iron,"Muons can be identified with high efficiency and purity and reconstructed
with high precision is a detector with a dual readout calorimeter and a dual
solenoid to return the flux without iron. We shown CERN test beam data for the
calorimeter and calculations for the magnetic fields and the track
reconstruction. For isolated tracks, the rejection of pions against muons
ranges from $10^3$ at 20 GeV/c to $10^5$ at 300 GeV/c.",0709.0768v1
2007-11-28,Evidence for Two Current Conduction in Iron,"Measurements of resistivities of dilute iron based alloys show strong
deviations from Matthiessen's rule. These deviations can be explained by a
model in which spin up and spin down electrons conduct in parallel. The results
are consistent with the theory of impurity shielding in these alloys. [This
1967 paper provides the first experimental demonstration of two current
conduction at low temperatures in a ferromagnetic metal. One direct consequence
of this property is the Giant Magnetoresistance discovered in 1988 by the
groups of Albert Fert and of Peter Gr\""unberg].",0711.4478v1
2008-04-03,Orbital Degeneracy and the Microscopic Model of the FeAs Plane in the Iron-Based Superconductors,"A microscopic model for the FeAs plane in the newly discovered Iron-based
superconductors is proposed with the emphasis on the role of the orbital
degeneracy between the Fe $3d_{xz}$ and $3d_{yz}$ orbital in the crystal field
environment. The model predicts commensurate antiferromagnetic ordered ground
state for the parent compounds and a d-wave superconducting ground state at
finite doping. Inter-orbital couplings plays an interesting role in enhancing
both orders. Correlated variational wave functions are proposed for both
ordered phases.",0804.0536v1
2008-04-10,Spin-triplet p-wave pairing in a 3-orbital model for iron pnictide superconductors,"We examine the possibility that the superconductivity in the newly discovered
FeAs materials may be caused by the Coulomb interaction between d-electrons of
the iron atoms. We find that when the Hund's rule ferromagnetic interaction is
strong enough, the leading pairing instability is in spin-triplet p-wave
channel in the weak coupling limit. The resulting superconducting gap has nodal
lines on the 3D Fermi surfaces. The k dependent hybridization of several
orbitals around a Fermi pocket is the key for the appearance of the
spin-triplet p-wave pairing.",0804.1739v3
2008-05-06,The minimum model for the iron-based superconductors,"A single band $t$-$U$-$J_1$-$J_2$ model is proposed as the minimum model to
describe the superconductivity of the newly discovered iron-based
superconductors $R(O_{1-x}F_x)FeAs$ and $RO_{1-x}FeAs$ ($R=La, Ce, Sm, Pr,
Nd,Gd$). With the mean-field approach, it is found that the pairing occurs in
the d-wave channel. In the likely parameter region of the real materials, by
lowering temperature, the system enters firstly the $d_{xy}$ superconducting
phase with $D_{4h}$-symmetry and then enters the time-reversal-symmetry-broken
$d_{xy}+id_{x^2-y^2}$ superconducting phase with $C_{4h}$-symmetry.",0805.0644v1
2008-05-07,Design Methodology and Manufacture of a Microinductor,"Potential core materials to supersede ferrite in the 0.5-10 MHz frequency
range are investigated. The performance of electrodeposited nickel-iron,
cobalt-iron-copper alloys and the commercial alloy Vitrovac 6025 have been
assessed through their inclusion within a custom-made solenoid microinductor.
Although the present inductor, at 500 KHz, achieves 77% power efficiency for
24.7W/cm3 power density, an optimized process predicts a power efficiency of
97% for 30.83W/cm3 power density. The principle issues regarding microinductor
design and performance are discussed.",0805.0859v1
2008-06-10,Synthesis and Microstructural Studies of Iron Based LaO1-xFxFeAs Superconducting Materials,"We report on the synthesis and microstructural studies of fluorine based iron
doped superconductors. We have successfully synthesized the fluorine based new
superconducting material LaO1-xFxFeAs by choosing comparatively lower
temperature and longer synthesis duration. The superconducting transition
temperature that we have achieved is 27.5 K which is observed at doping level
of x=0.2. The structural microstructural characterizations have been done by
employing XRD, SEM and TEM techniques. The SEM and TEM micrographs reveal the
layered structure.",0806.1661v1
2008-06-17,Large Seebeck coefficients in Iron-oxypnictides : a new route towards n-type thermoelectric materials,"The iron-oxypnictide compounds, recently reported as a new class of
superconductors when appropriately doped, exhibit large Seebeck coefficients,
of the order of -100 microV/K, while keeping good electrical conductivity.
Their power factor shows a peak at low temperatures, suggesting possible
applications of these materials in thermoelectric cooling modules in the liquid
nitrogen temperature range.",0806.2751v1
2008-06-19,Possible unconventional superconductivity in iron-based layered compound LaFePO: Study of heat capacity,"Heat capacity measurements were performed on recently discovered iron based
layered superconductors, non doped LaFePO and fluorine doped LaFePO. A
relatively large electronic heat capacity coefficient and a small normalized
heat capacity jump at Tc = 3.3 K were observed in LaFePO. LaFePO0.94F0.06 had a
smaller electronic heat capacity coefficient and a larger normalized heat
capacity jump at Tc = 5.8 K. These values indicate that these compounds have
strong electron electron correlation and magnetic spin fluctuation, which are
the signatures of unconventional superconductivity mediated by spin
fluctuation.",0806.3139v1
2008-06-30,The superconductivity at 18 K in LiFeAs system,"A new iron arsenide superconducting system LiFeAs was found that crystallizes
into a tetragonal structure with space group P4/nmm. The superconductivity with
Tc up to 18 K was observed in the compounds. This simple 111 type layered iron
arsenide superconductor can be viewed as an analogue of the infinite layer
structure of copper oxides.",0806.4688v3
2008-07-04,Lattice dynamical calculations of infinite layer iron oxides SrFeO2 and CaFeO2,"We report extensive lattice dynamical calculations of the newly discovered
infinite-layer iron oxides SrFeO2 and CaFeO2. For SrFeO2, the parameters of the
interatomic potential have been determined to reproduce the zone-centre phonon
frequencies reported using ab-initio calculations. Further we have extended the
potential model for calculations of CaFeO2. The potential parameters are found
to be transferable between the two compounds, and are used to calculate the
phonon spectra in the whole Brillouin zone and several thermodynamic properties
for these compounds. The calculations show fair agreement with the available
experimental data of structure, thermal expansion, and mean-squared amplitudes
of the atoms.",0807.0716v1
2008-07-28,Multiple Gaps and Superfluid Density from Interband Pairing in Iron Oxypnictides,"We study a four-band model for the iron oxypnictides, in which the
superconducting properties are assumed to be determined by the interband
coupling between hole-like and electron-like Fermi sheets. We show that
reasonable parameters can account for the angle-resolved photoemission spectra
showing multiple gaps in Ba$_{1-x}$K$_x$Fe$_2$As$_2$, and for the temperature
dependence of the superfluid density. At the same time, the zero-temperature
value of the superfluid density shows a conventional scaling with the number of
carriers.",0807.4408v1
2008-08-09,Transport and Magnetic Properties of FexVse2 (x = 0 - 0.33),"We present our results of the effect of Fe intercalation on the structural,
transport and magnetic properties of 1T-VSe2. Intercalation of iron, suppresses
the 110K charge density wave (CDW) transition of the 1T-VSe2. For the higher
concentration of iron, formation of a new kind of first order transition at
160K takes place, which go on stronger for the 33% Fe intercalation.
Thermopower of the FexVSe2 compounds (x = 0 - 0.33), however do not show any
anomaly around the transition. The intercalation of Fe does not trigger any
magnetism in the weak paramagnetic 1T-VSe2, and Fe is the low spin state of
Fe3+.",0808.1333v1
2008-08-24,Theory for Superconductivity in Iron Pnictides at Large Coulomb U Limit,"Superconductivity in iron pnictides is studied by using a two-orbital Hubbard
model in the large U limit. The Coulomb repulsion induces an orbital-dependent
pairing between charge carriers. The pairing is found mainly from the
scattering within the same Fermi pocket. The inter-pocket pair scatterings
determine the symmetry of the superconductivity, which is extended s-wave at
small Hund's coupling, and d-wave at large Hund's coupling and large U. The
former is consistent with recent experiments of ARPES and Andreev reflection
spectroscope.",0808.3234v2
2008-08-27,Charge dynamics in the normal state of the iron oxypnictide superconductor LaFePO,"We present the first infrared and optical study in the normal state of
ab-plane oriented single crystals of the iron-oxypnictide superconductor
LaFePO. We find that this material is a low carrier density metal with a
moderate level of correlations and exhibits signatures of electron-boson
coupling. The data is consistent with the presence of coherent quasiparticles
in LaFePO.",0808.3748v1
2008-09-04,Impurity states in antiferromagnetic Iron Arsenides,"We explore theoretically impurity states in the antiferromagnetic
spin-density wave state of the iron arsenide. Two types of impurity models are
employed: one has only the intraband scattering while the other has both the
intraband and interband scattering with the equal strength. Interestingly, the
impurity bound state is revealed around the impurity site in the energy gap for
both models. However, the impurity state is doubly degenerate with respect to
spin for the first case; while the single impurity state is observed in either
the spin-up or spin-down channel for the second one. The impurity-induced
variations of the local density of states are also examined.",0809.0795v1
2008-09-22,"High-Tc Superconductivity in some Heavy Rare-earth Iron-arsenide REFeAsO1-delta(RE = Ho, Y, Dy and Tb) Compounds","New iron-arsenide superconductors of REFeAsO1-delta (RE = Ho, Y, Dy and Tb)
were successfully synthesized by a high pressure synthesizing method with a
special rapid quenching process, with the onset superconducting critical
temperatures at 50.3 K, 46.5 K, 52.2K and 48.5 K for RE = Ho, Y, Dy and Tb
respectively.",0809.3582v1
2008-10-13,Antiferromagnetic Correlation and the Pairing Mechanism of the Cuprates and Iron Pnictides : a View From the Functional Renormalization Group Studies,"We compare the one-loop functional renormalization group results for the
cuprates and the iron pnictides. Interestingly a coherent picture suggesting
that antiferromagnetic correlation causes pairing for both materials emerges.",0810.2320v2
2008-10-17,"Structure, antiferromagnetism and superconductivity of the layered iron arsenide NaFeAs","A new layered iron arsenide NaFeAs isostructural with the superconducting
lithium analogue, displays evidence for the coexistence of superconductivity
and magnetic ordering.",0810.3214v2
2008-10-28,Enhanced low-energy spin dynamics with diffusive character in the iron-based superconductor (La0.87Ca0.13)FePO: Analogy with high Tc cuprates (A short note),"In a recent NMR investigation of the iron-based superconductor
(La0.87Ca0.13)FePO [Phys. Rev. Lett. 101, 077006 (2008)] Y. Nakai et al.
reported an anomalous behavior of the nuclear spin-lattice relaxation of 31P
nuclei in the superconducting state: The relaxation rate 1/T1 strongly depends
on the measurement frequency and its T dependence does not show the typical
decrease expected for the superconducting state. In this short note, we point
out that these two observations bear similarity with the situation is some of
the high Tc cuprates.",0810.5135v1
2008-11-05,Superconductivity in S-substituted FeTe,"We have successfully synthesized a new superconducting phase of FeTe1-xSx
with a PbO-type structure. It has the simplest crystal structure in iron-based
superconductors. Superconducting transition temperature is about 10 K at x =
0.2. The upper critical field Hc2 was estimated to be ~70 T. The coherent
length was calculated to be ~2.2 nm. Because FeTe1-xSx is composed of nontoxic
elements, this material is a candidate for applications and will activate more
and more research on iron-based superconductor.",0811.0711v2
2008-12-01,High - Temperature Superconductivity in Iron Based Layered Compounds,"We present a review of basic experimental facts on the new class of high -
temperature superconductors - iron based layered compounds like REOFeAs
(RE=La,Ce,Nd,Pr,Sm...), AFe_2As_2 (A=Ba,Sr...), AFeAs (A=Li,...) and FeSe(Te).
We discuss electronic structure, including the role of correlations, spectrum
and role of collective excitations (phonons, spin waves), as well as the main
models, describing possible types of magnetic ordering and Cooper pairing in
these compounds.",0812.0302v1
2008-12-31,Experimental Detection of Sign-Reversal Pairing in Iron-Based Superconductors,"We propose a modified Josephson corner-junction experiment which can test
whether the order parameter in the iron pnictides changes sign between the
electron and hole pockets of the Fermi surface.",0901.0038v3
2009-01-19,Possible Kondo effect in the iron arsenides,"The normal state of the iron arsenides shows the poor metallic behavior mixed
with strong magnetic fluctuations. In particular, some FeAs-1111 and FeAs-122
compounds show the linear-T dependence of susceptibility above the spin-density
wave (SDW) transition and the logarithmic upturn of resistivity at low
temperatures. We suggest that this is due to the spin-flip scattering between
the charge carriers and the local moments in the undoped FeAs layer where Kondo
effect coexists with the SDW. This scenario is also accounted for the change of
the magnetoresistance from positive to negative in the Sr3Sc2O5Fe2As2 compound.",0901.2787v2
2009-02-21,Unconventional pairing originating from disconnected Fermi surfaces in the iron-based superconductor,"For the iron-based high $T_c$ superconductor LaFeAsO$_{1-x}$F$_x$, we
construct a minimal model, where all of the five Fe $d$ bands turn out to be
involved. We then investigate the origin of superconductivity with a five-band
random-phase approximation by solving the Eliashberg equation. We conclude that
the spin fluctuation modes arising from the nesting between the disconnected
Fermi pockets realise, basically, an extended s-wave pairing, where the gap
changes sign across the nesting vector.",0902.3691v1
2009-03-11,Pairing in the iron arsenides: a functional RG treatment,"We study the phase diagram of a microscopic model for the superconducting
iron arsenides by means of a functional renormalization group. Our treatment
establishes a connection between a strongly simplified two-patch model by
Chubukov et al. and a five-band- analysis by Wang et al.. For a wide parameter
range, the dominant pairing instability occurs in the extended s-wave channel.
The results clearly show the relevance of pair scattering between electron and
hole pockets. We also give arguments that the phase transition between the
antiferromagnetic phase for the undoped system and the superconducting phase
may be first order.",0903.1963v1
2009-03-22,Anomalous Magnetic Susceptibility in Iron Pnictides: Paramagnetic Phase,"Observation of an anomalous temperature dependence of the spin
susceptibility, along with a spin gap in NMR, in the quantum paramagnetic
normal state of Iron Pnictides is a signature of an unusual metallic state. We
argue that both these anomalous features are associated with a wide
fluctuational regime dominated by dynamical, short-ranged and frustrated spin
correlations in a strongly correlated metal. Using LDA+DMFT, we show that both
these features can be quantitatively undertstood in the doped Fe-pnictides. We
argue that such spin correlations naturally arise in a Mottness scenario, where
an effective, dualistic description involves coexisting renormalized
quasiparticles and effectively localized moments, arising from the same set of
d bands.",0903.3732v1
2009-03-24,Band structure of new layered 17 K superconductor Sr4Sc2Fe2P2O6 in comparison with hypothetical Sr4Sc2Fe2As2O6,"The results of the ab initio FLAPW-GGA calculations of the band structure of
the newly synthesized tetragonal (space group P4/nmm) layered iron
phosphide-oxide: 17K superconductor Sr4Sc2Fe2P2O6 are presented. For
Sr4Sc2Fe2P2O6 the optimized structural data, the energy bands, total and
partial densities of states, Fermi surface topology, low-temperature electron
specific heat and molar Pauli paramagnetic susceptibility have been determined
and discussed in comparison with hypothetical isostructural iron arsenide-oxide
phase Sr4Sc2Fe2As2O6 and related layered FeAs and FeP superconductors.",0903.4038v1
2009-04-01,Electronic structure of Ti-doped Sr4Sc2Fe2As2O6,"First principle FLAPW-GGA calculations have been performed with the purpose
to understand the electronic properties for the newly synthesized tetragonal
(space group P4/nmm) layered iron arsenide-oxide: Sr4Sc2Fe2As2O6 doped with
titanium. The total and partial densities of states, low-temperature electron
specific heat and molar Pauli paramagnetic susceptibility have been obtained
and discussed for Sr4ScTiFe2As2O6 in comparison with parent phase
Sr4Sc2Fe2As2O6.
  Our results show that the insertion of Ti into Sc sublattice of iron
arsenide-oxide phase Sr4Sc2Fe2As2O6 leads to principal change of its electronic
structure; in result the insulating so-called ""charge reservoirs', i.e.
perovskite-based [Sr4Sc2O6] blocks became conducting. This situation differs
essentially from the known picture for all others Fe-As superconductors where
the conducting [Fe2As2] blocks are separated by isolating blocks.",0904.0117v1
2009-04-07,Evidence for polarons in iron pnictides of the Ln-1111 and AE-122 families,"Examination of the electrical resistivities of iron pnictides shows that they
can be accounted by conduction by polarons. Their activation energies show a
linear behaviour with the critical temperatures of the spin density waves
(SDW), T*, as both vary with pressure. The slope matches the ratio SDW gap to
T*, while the intercept can be related to the transition temperature of the
lattice distortion, T0. An adapted Landau free energy predicts the observed
order of the transitions, according to which is higher, T* or T0. Simple
arguments favour combined Jahn-Teller antiferromagnetic bipolarons.",0904.1173v1
2009-05-26,Analysis of transport properties of iron pnictides: spin-fluctuation scenario,"We present a phenomenological theory of quasiparticle scattering and
transport relaxation in the normal state of iron pnictides based on the
simplified two-band model coupled via spin fluctuations. In analogy with
anomalous properties of cuprates it is shown that a large and anomalous
normal-state resistivity and thermopower can be interpreted as the consequence
of strong coupling to spin fluctuations. The generalization to the
superconducting phase is also discussed.",0905.4153v2
2009-05-29,Tight-binding models for the new iron based superconductor materials,"The rich novel materials class of iron based superconductors turned out to
exhibit a very complex electronic structure, despite of the simplicity of their
crystal structures. For various approaches to study the instability against
magnetic order or superconductivity, a real space description of the electronic
structure is required. Here, the bonding situation and the orbital structure of
the electronic state are analyzed and minimum tight-binding models
quantitatively correctly describing the low-energy electronic structure are
provided.",0905.4844v2
2009-07-01,The Stoichiometry of FeSe,"Tetragonal iron selenide, FeSe, the layered parent compound of the recently
discovered superconducting arsenide family, has previously been shown to be non
magnetic and superconducting with a critical temperature near 8 K. There has,
however, been a lack of consensus as to whether selenium vacancies present due
to large deviations from ideal stoichiometry are required to give rise to the
superconductivity. Here we describe the results of experiments that demonstrate
simply that superconducting iron selenide can only be synthesized as a pure
material when near stoichiometric (i.e. FeSe). Significant selenium deficiency
or excess gives rise to secondary magnetic phases, and a suppression of the
superconductivity.",0907.0174v1
2009-09-07,Modeling Antiferromagnetic Phase in Iron Pnictides: Weakly Ordered State,"We examine electronic states of antiferromagnetic phase in iron pnictides by
mean-field calculations of the optical conductivity. We find that a five-band
model exhibiting a small magnetic moment, inconsistent with the
first-principles calculations, reproduces well the excitation spectra
characterized by a multi-peak structure emerging below the N\'{e}el temperature
at low energy, together with an almost temperature-independent structure at
high energy. Investigating the interlayer magnetoresistance for this model, we
also predict its characteristic field dependence reflecting the Fermi surface.",0909.1081v2
2009-09-07,First-principles-based $\pm s$-wave modelling for iron-based superconductors:Studies for specific heat and nuclear magnetic relaxation rate,"In order to consistently explain controversial experimental results on
superconducting states observed by different probes in typical iron-based
superconductors, we construct a realistic multi-band $\pm s$-wave pairing model
by combining the quasiclassical formalism with the first-principles
calculation. The model successfully resolves the controversies in contrast to
the fact that simplified models such as two-band $\pm s$-wave one fail to do. A
key in the model is the existence of relatively small gaps which leads to
material-dependent peculiarities.",0909.1195v1
2009-09-15,Bulk Superconductivity at 2.6 K in Undoped RbFe_2As_2,"The iron arsenide RbFe_2As_2 with the ThCr_2Si_2-type structure is found to
be a bulk superconductor with T_c=2.6 K. The onset of diamagnetism was used to
estimate the upper critical field H_c2(T), resulting in dH_c2/dT=-1.4 T/K and
an extrapolated H_c2(0)=2.5 T. As a new representative of iron pnictide
superconductors, superconducting RbFe_2As_2 contrasts with BaFe_2As_2, where
the Fermi level is higher and a magnetic instability is observed. Thus, the
solid solution series (Rb,Ba)Fe_2As_2 is a promising system to study the
crossover from superconductivity to magnetism.",0909.2740v1
2009-11-16,Simple Real-Space Picture of Nodeless and Nodal s-wave Gap Functions in Iron Pnictide Superconductors,"We propose a simple way to parameterize the gap function in iron pnictides.
The key idea is to use orbital representation, not band representation, and to
assume real-space short-range pairing. Our parameterization reproduces fairly
well the structure of gap function obtained in microscopic calculation. At the
same time the present parameterization is simple enough to obtain an intuitive
picture and to develop a phenomenological theory. We also discuss
simplification of the treatment of the superconducting state.",0911.2959v2
2009-11-16,Nuclear Magnetic Relaxation Rate in Iron-Pnictide Superconductors,"Nuclear magnetic relaxation rate 1/T_1 in iron-pnictide superconductors is
calculated using the gap function obtained in a microscopic calculation. Based
on the obtained results, we discuss the issues such as the rapid decrease of
1/T_1 just below the transition temperature and the difference between nodeless
and nodal s-wave gap functions. We also investigate the effect of Coulomb
interaction on 1/T_1 in the random phase approximation and show its importance
in interpreting the experimental results.",0911.2963v1
2009-12-09,FERO (Finding Extreme Relativistic Objects): relativistic Iron K alpha lines in type 1 AGN,"The observational evidence for AGN relativistic Iron lines is very much
debated. To address this topic, the FERO project makes use of the largest
sample of X-ray spectra of radio quiet Type 1 AGN available in the XMM-Newton
archive. We perform a systematic fit of the individual sources using a full
relativistic code. Results on the first part of the project are presented here.",0912.1889v1
2009-12-16,Anomalous normal-state properties of iron pnictides: phenomenological theory,"We employ the phenomenological theory of the quasiparticle relaxation based
on the simplified two-band description and the spin-fluctuation induced
interband coupling to analyze recent normal-state transport data in
electron-doped iron pnictides, in particular the Ba(Fe_1-x Co_x)_2As_2 family.
Temperature dependence of the resistivity, thermopower and the Hall constant
are evaluated. It is shown that their anomalous behavior emerging from
experiments can be consistently described within the same framework assuming
also non-Fermi-liquid spin fluctuations.",0912.3122v2
2010-01-26,On spatial non-homogeneity in iron pnictides: formation of stripes,"The heterogeneous coexistence of antiferromagnetism (SDW) and
superconductivity on a mesoscopic scale was observed in iron-pnictides in many
recent experiments. We suggest and discuss the scenario in which the
heterogeneity is caused by formation of domain walls inherent to the SDW state
of pnictides at a proper doping or under applied pressure. Superconductivity
would emerge from the modulated SDW structure. The phenomenon is akin to the
FFLO-phase in superconductors.",1001.4641v2
2010-02-13,Spin and Charge Dynamics Ruled by Antiferromagnetic Order in Iron Pnictides,"We examine the spin and charge excitations in antiferromagnetic iron
pnictides by mean-field calculations with a random phase approximation in a
five-band itinerant model. The calculated excitation spectra reproduce well
spin-wave dispersions observed in inelastic neutron scattering, with a
realistic magnetic moment for CaFe$_2$As$_2$. A particle-hole gap is found to
be crucial to obtain consistent results; we predict the spin wave in LaFeAsO
disappears at a lower energy than in CaFe$_2$As$_2$. We analyze that the charge
dynamics to make predictions for resonant inelastic x-ray scattering spectra.",1002.2701v2
2010-02-17,Evidence for an electron nematic phase transition in underdoped iron pnictide superconductors,"Electrical resistivity measurements of detwinned single crystals of the
representative iron arsenide Ba(Fe$_{1-x}$Co$_x$)$_2$As$_2$ reveal a dramatic
in-plane anisotropy associated with the tetragonal-to-orthorhombic structural
transition that precedes the onset of long-range antiferromagnetic order. These
results indicate that the structural transition in this family of compounds is
fundamentally electronic in origin.",1002.3364v2
2010-03-03,Relationship between Colours of Ochre from Roussillon and Content of Iron-Bearing Minerals,"Nine samples of ochre originating from the Sentier des Ocres near Roussillon,
France, were studied with Mossbauer spectroscopy and Spectro-photo-colorimetry.
The former yielded a quantitative phase analysis of iron containing minerals
(goethite, hematite and kaolin), and the latter enabled determination of the
CIE-L*a*b* colorimetric coefficients. Based on the results obtained it is shown
that both a* and b* coordinates are responsible for the colour of the
investigated ochres.",1003.0760v1
2010-03-10,Dichotomy between large local and small ordered magnetic moment in Iron-based superconductors,"We study a four band model for iron-based superconductors within local
density approximation + dynamical mean field theory (LDA+DMFT). This
successfully reproduces the results of models which take As p degrees of
freedom explicitly into account and has several physical advantages over the
standard five d-band model. Our findings reveal that the new superconductors
are more strongly correlated than their single-particle properties suggest.
Two-particle correlation functions unveil the dichotomy between local and
ordered magnetic moments in these systems, calling for further experiments to
better resolve the short time scale spin dynamics.",1003.2162v1
2010-03-19,Gamma ray production in inelastic scattering of neutrons produced by cosmic muons in $^{56}$Fe,"We report on the study of the intensities of several gamma lines emitted
after the inelastic scattering of neutrons in $^{56}$Fe. Neutrons were produced
by cosmic muons passing the 20t massive iron cube placed at the Earth's surface
and used as a passive shield for the HPGe detector. Relative intensities of
detected gamma lines are compared with the results collected in the same iron
shield by the use of $^{252}$Cf neutrons. Assessment against the published data
from neutron scattering experiments at energies up to 14 MeV is also provided.",1003.3890v1
2010-05-06,Self consistent GW determination of the interaction strength: application to the iron arsenide superconductors,"We introduce a first principles approach to determine the strength of the
electronic correlations based on the fully self consistent GW approximation.
The approach provides a seamless interface with dynamical mean field theory,
and gives good results for well studied correlated materials such as NiO.
Applied to the recently discovered iron arsenide materials, it accounts for the
noticeable correlation features observed in optics and photoemission while
explaining the absence of visible satellites in X-ray absorption experiments
and other high energy spectroscopies.",1005.0885v1
2010-06-11,Structural Features of Layered Iron Pnictide Oxides (Fe2As2)(Sr4M2O6),"Structural features of newly found perovskite-based iron pnictide oxide
system have been systematically studied. Compared to REFePnO system,
perovskite-based system tend to have lower Pn-Fe-Pn angle and higher pnictogen
height owing to low electronegativity of alkaline earth metal and small
repulsive force between pnictogen and oxygen atoms. As-Fe-As angles of
(Fe2As2)(Sr4Cr2O6), (Fe2As2)(Sr4V2O6) and (Fe2Pn2)(Sr4MgTiO6) are close to
ideal tetrahedron and those pnictogen heights of about 1.40 A are close to
NdFeAsO with optimized carrier concentration. These structural features of this
system may leads to realization of high Tc superconductivity.",1006.2351v1
2010-06-21,Phase Field Crystal Study of Symmetric Tilt Grain Boundaries of Iron,"We apply the phase field crystal model to study the structure and energy of
symmetric tilt grain boundaries of bcc iron in 3D. The parameters for the model
are obtained by using a recently developed eight-order fitting scheme [A.
Jaatinen et al., Phys. Rev. B 80, 031602 (2009)]. The grain boundary free
energies we obtain from the model are in good agreement with previous results
from molecular dynamics simulations and experiments.",1006.5405v1
2010-06-28,Eliashberg Analysis of Optical Spectra Reveals Strong Coupling of Charge Carriers to Spin Fluctuations in Superconducting Iron Pnictides,"The temperature and frequency dependences of the optical conductivity of Co
and Ni-doped BaFe2As2 are analyzed and the electron-boson spectral density
a2F(w) extracted using Eliashberg's formalism. The characteristic energy of a
large peak in the spectrum around 10 meV coincide with the resonance peak in
the spin excitation spectra, giving compelling evidence that in iron-based
superconductors spin fluctuations strongly couple to the charge carriers and
mediate superconductivity. In addition the spectrum is found to evolve with
temperature towards a less structured background at higher energies as in the
spin susceptibility.",1006.5468v1
2010-07-15,The electronic instabilities of the Iron-based superconductors: a variational Monte-Carlo study,"We report the first variational Monte Carlo (VMC) study of the iron-based
superconductors. We use realistic band structures, and the ordering
instabilities/variational ansatzs are suggested by previous functional
renormalization group calculations. We examine antiferromagnetism,
superconducting pairing, normal state fermi surface distortion, and orbital
order in the antiferromagnetic state.",1007.2643v4
2010-08-03,Rescaled potential for transition metal solutes in a-iron,"We present empirical potentials for dilute transition metal solutes in
a-iron. It is in the Finnis-Sinclair form and is therefore suitable for billion
atom molecular dynamics simulations. First principles calculation shows that
there are clear trends across the transition metal series which enable us to
relate the rescaling parameters to principal quantum number and number of d
electrons. The potential has been developed using a rescaling technique to
provide solute-iron and solute-solute interactions from an existing iron
potential.",1008.0508v1
2010-08-17,Domain Walls in Normal and Superconducting States of Iron Pnictides,"The electronic and magnetic structures in the normal and superconducting
states of iron pnictides are investigated by solving self-consistently the
Bogoliubov-de Gennes equation. It is shown that strong electron correlations
can induce domain walls, which separate regions with different spin density
wave orders. At zero or low electron doping, $90^\circ$ domain walls are formed
while anti-phase domain walls are produced at higher electron doping. On the
domain walls, larger electron densities are always present. The results agree
qualitatively with recent observations of scanning tunneling microscopy and
superconducting quantum interference device microscopy.",1008.2981v1
2010-09-02,Toroidal Carbon Nanotubes with Encapsulated Atomic Metal Loops,"Toroidal carbon nanotubes can serve as hosts for encapsulated loops of atomic
metal wires. Such composite structures have been analyzed using density
functional theory for a semiconducting C$_{120}$ torus encapsulating chains of
Fe, Au and Cu atoms. The sheathed metal necklaces form a zigzag structure and
drops the HOMO/LUMO bandgap to less than 0.1 eV. The iron composite is
ferromagnetic with a magnetic moment essentially the same as that of bcc iron.
The azimuthal symmetry of these toroidal composites suggests that they may
offer novel elecromagnetic properties not associated with straight,
metal-encapsulated carbon nanotubes.",1009.0442v1
2010-09-20,Non-Fermi-Liquid-Like Behaviors and Superconductivity Driven by Orbital Fluctuations in Iron Pnictides: Analysis by Fluctuation-Exchange Approximation,"We study the five-orbital Hubbard-Holstein model for iron pnictides with
small electron-phonon interaction due to Fe-ion Einstein oscillators. Using the
fluctuation-exchange (FLEX) approximation, orbital fluctuations evolve
inversely proportional to the temperature, and therefore the resistivity shows
linear or convex T-dependence for wide range of temperatures. We also analyze
the Eliashberg gap equation, and show that s-wave superconducting state without
sign reversal (s_{++}-wave state) emerges when the orbital fluctuations
dominate the spin fluctuations. When both fluctuations are comparable, their
competition gives rise to a nodal s-wave state. The present study offers us a
unified explanation for both the normal and superconducting states.",1009.3882v1
2010-09-29,Phase Separation and Chemical Inhomogeneity in the Iron Chalcogenide Superconductor Fe1+yTexSe1-x,"We report investigation on Fe1+yTexSe1-x single crystals by using scanning
transmission electron microscopy (STEM) and electron energy loss spectroscopy
(EELS). Both nonsuperconducting samples with excess iron and superconducting
samples demonstrate nanoscale phase separation and chemical inhomogeneity of
Te/Se content, which we attribute to a miscibility gap. The line scan EELS
technique indicates ~20% or less fluctuation of Te concentration from the
nominal compositions.",1009.6010v1
2010-12-02,"Comment on ""Violation of Anderson's Theorem for the sign-reversing s-wave state of Iron-Pnictide Superconductors"" by Onari et al., Phys. Rev. Lett. 103, 177001(2009)[1]","We pointed out that the main claim of Ref.[1] that the presence of the
orbital degree of freedom is essential to describe the correct impurity effects
for Iron-based superconductors is incorrect and demonstrated the equivalent
results of Tc suppression due to impurities by both the band basis model and
the orbital basis model.",1012.0414v1
2011-01-05,77Se NMR study of pairing symmetry and spin dynamics in KyFe2-xSe2,"We present a 77Se NMR study of the newly discovered iron selenide
superconductor KyFe2-xSe2, in which Tc = 32 K. Below Tc, the Knight shift 77K
drops sharply with temperature, providing strong evidence for singlet pairing.
Above Tc, Korringa-type relaxation indicates Fermi-liquid behavior. Our
experimental results set strict constraints on the nature of possible theories
for the mechanism of high-Tc superconductivity in this iron selenide system.",1101.1017v2
2011-01-06,"Comment on ""Orbital Order, Structural Transition and Superconductivity in Iron Pnictides"" [arXiv:1010.0129] by Yanagi et al","In contrast to the claim by Yanagi et al. in Ref. [1], the development of
orbital fluctuations at $q ~ 0$ due to the ""orthorhombic phonon"" is unable to
explain the high-Tc superconductivity in iron pnictides. The reason is that the
orthorhombic-phonon is acoustic with the energy $\omega_q \propto q$, although
the authors in Ref. [1] treated it as optical phonon ($\omega_o=0.02 eV$)
inconsistently.",1101.1157v3
2011-01-18,Temperature-dependent spin resonance energy in iron pnictides and multiband s\pm Eliashberg theory,"The phenomenology of iron-pnictides superconductors can be explained in the
framework of a three bands s\pm wave Eliashberg theory with only two free
parameters plus a feedback effect i.e. the effect of the condensate on the
antiferromagnetic spin fluctuactions responsible of the superconductivity in
these compounds. I have examined the experimental data of four materials:
LaFeAsO1-xFx, SmFeAsO1-xFx, Ba1-xKxFe2As2, and Ba(FexCo1-x)2As2 and I have
found that it is possible to reproduce the experimental critical temperature
and gap values in a moderate strong-coupling regime: ltot about 1.7-2.0.",1101.3473v2
2011-02-18,Maximizing Fermi surface multiplicity optimizes superconductivity in iron pnictides,"We study the condition for optimizing superconductivity in the iron pnictides
from the lattice structure point of view. Studying the band structure of the
hypothetical lattice structure of LaFeAsO, the hole Fermi surface multiplicity
is found to be maximized around the Fe-As-Fe bond angle regime where the
arsenic atoms form a regular tetrahedron. Superconductivity is optimized within
this three hole Fermi surface regime, while the stoner factor of the
antiferromagnetism has an overall tendency of increasing upon decreasing the
bond angle. Combining also the effect of the varying the Fe-As bond length, we
provide a guiding principle for obtaining high $T_c$.",1102.3765v1
2011-03-10,From density functional theory to the functional renormalization group: superconductivity in the iron pnictide LiFeAs,"A combined density functional theory and functional renormalization group
method is introduced which takes into account orbital-dependent interaction
parameters to derive the effective low-energy theory of weakly to
intermediately correlated Fermi systems. As an application, the competing
fluctuations in LiFeAs are investigated, which is the main representative of
the 111 class of iron pnictides displaying no magnetic order, but
superconductivity, for the parent compound. The superconducting order parameter
is found to be of s+- type driven by collinear antiferromagnetic fluctuations.
They eventually exceed the ferromagnetic fluctuations stemming from the small
hole pocket at the Gamma point, as the system flows to low energies.",1103.2101v1
2011-04-07,Detection of melting by in-situ observation of spherical-drop formation in laser-heated diamond-anvil cells,"A simple method for detection of melting event in laser-heated diamond anvil
cells (DACs) is introduced. The melting is registered optically by the
formation of spherical drops of the investigated material as heated in an inert
pressure transmitting medium. Feasibility of the method is demonstrated on the
examples of metal (iron and gold) and iron oxide (Fe2O3), materials molten at
pressures over 40 GPa employing a portable laser heating system.",1104.1304v1
2011-04-26,Specific heat jump at superconducting transition in the presence of Spin-Density-Wave in iron-pnictides,"We analyze the magnitude of the specific heat jump \Delta C at the
superconducting transition temperature T_c in the situation when
superconductivity develops in the pre-existing antiferromagnetic phase. We show
that \Delta C/T_c differs from the BCS value and is peaked at the tri-critical
point where this coexistence phase first emerges. Deeper in the magnetic phase,
the onset of coexistence, T_c, drops and \Delta C/T_c decreases, roughly as
\Delta C/T_c \propto T^2_c at intermediate T_c and exponentially at the lowest
T_c, in agreement with the observed behavior of \Delta C/T_c in iron-based
superconductors.",1104.5037v1
2011-04-28,Spin and Orbital Characters of Excitations in Iron Arsenide Superconductors Revealed by Simulated Fe L-Edge RIXS,"We theoretically examine the orbital excitations coupled to the spin degree
of freedom in the parent state of the iron-arsenide superconductor, based on
the calculation in a five-band itinerant model. The calculated Fe $L_3$-edge
resonant inelastic x-ray scattering (RIXS) spectra disclose the presence of
spin-flip excitations involving several specific orbitals. Magnon excitations
predominantly composed of a single orbital component can be seen in
experiments, although its spectral weight is smaller than spin-flipped
interorbital high-energy excitations. The detailed polarization and momentum
dependence is also discussed with predictions for the experiments.",1104.5424v2
2011-05-10,Consistent picture for the electronic structure around a vortex core in iron-based superconductors,"Based on a two-orbital model and taking into account the presence of the
impurity, we studied theoretically the electronic structure in the vortex core
of the iron-Pnictide superconducting materials. The vortex is pinned when the
impurity is close to the vortex core. The bound states shows up for the
unpinned vortex and are wiped out by a impurity. Our results are in good
agreement with recent experiments and present a consistent explanation for the
different electronic structure of vortex core revealed by experiments on
different materials.",1105.1851v1
2011-05-19,Differential conductance of point contacts between an iron-based superconductor and a normal metal,"We present a theoretical description of the differential conductance of point
contacts between a normal metal and a multi-band superconductor with extended
s\pm pairing symmetry. We demonstrate that the interband impurity scattering
broadens the coherent peak near the superconducting gap and significantly
reduces its height even at relatively low scattering rates. This broadening is
consistent with a number of recent experiments performed for both tunnel
junctions and larger diffusive contacts. Our theory helps to better evaluate
the energy gap of iron-based superconductors from point contact Andreev
spectroscopy measurements.",1105.3926v2
2011-05-26,Orbital-spin ordering in the striped antiferromagnetic state of iron-based superconductors,"The magnetic properties of iron-arsenides are investigated using the LSDA+U
approach. In addition to one high moment state, we find that a positive U also
produces two low moment states with m~0.4 $\mu_{B}$ and m~1.0 $\mu_{B}$. The
electronic structures indicate that the low moment states originate in the
strong orbital hybridization between antiferromagnetic Fe neighbors. Therefore,
the geometry of the FeAs4 tetrahedron is crucial to the low moment states,
which is the key to understand the negative pressure coefficient of Tc in
LiFeAs. Finally, our theory suggests that the superconducting phase is an
orbital-spin ordered state, where the orbital spin-moments cancel each other.",1105.5412v1
2011-06-12,Anomalies in the Multicritical Behavior of Staggered Magnetic and Direct Magnetic Susceptibilities of Iron Group Dihalides,"In this study, the temperature dependencies of magnetic response functions of
the anhydrous dihalides of iron-group elements are examined in the neighborhood
of multi-critical points (tricritical, critical end point, double critical end
point) and first order transition temperatures within molecular field
approximation. Our findings reveal the fact that metamagnetic Ising system
exhibits anomalies in the temperature dependence of the magnetic response
functions for r<0.3. In addition, we extensively investigated how an inter- and
intra-layer exchange interaction ratio can influence magnetic response
properties of these systems. Finally, a comparison is made with related works.",1106.2308v1
2011-06-22,Magnetic excitations in iron pnictides,"Spin wave dispersion and damping are investigated in the metallic SDW state
of different itinerant electron models including a small interlayer hopping.
Magnetic excitations in iron pnictides are shown to be well understood in terms
of physical mechanisms characteristic of metallic magnets, such as
carrier-induced ferromagnetic spin couplings, intra-band particle-hole
excitations, and the spin-charge coupling mechanism, which is also important in
ferromagnetic manganites.",1106.4421v1
2011-07-04,"Reply to Comment on ""Neutron-Inelastic-Scattering Peak by Dissipationless Mechanism in the $s_{++}$-wave State in Iron-based Superconductors"" [arXiv:1106.2376] by Y. Nagai and K. Kuroki","This article is a reply to the comment by Nagai and Kuroki [arXiv:1106.2376]
for our unpublished paper in arXiv [arXiv:1105.6233]. Contrary to their claim,
we certainly obtain a large hump structure at $q=(\pi,0)$ in the $s_{++}$-wave
state in iron pnictides due to the ``dissipationless mechanism'', even when
similar parameters used by Nagai and Kuroki are employed.",1107.0748v1
2011-11-15,First principles study of iron-based molecule grafted on graphene,"Motivated by recent experimental studies on single molecular magnets grafted
on graphene and single walled carbon nanotubes, we investigate the structural,
electronic, and magnetic properties of an iron based magnetic molecule grafted
on a graphene sheet using \textit{ab initio} calculations.
  In particular, the induced charge transfer and magnetization are described in
terms of the coupling between the molecule and the graphene orbitals.
  This interaction and its effects on graphene electronic properties are
determined and discussed in view of the potential utilization of graphene in
spintronics.",1111.3516v1
2011-11-30,Electronic and Magnetic Structure of Possible Iron Based Superconductor BaFe2Se3,"We present results of LDA calculations (band structure, densities of states,
Fermi surfaces) for possible iron based superconductor BaFe2Se3 (Ba123) in
normal (paramagnetic) phase. Results are briefly compared with similar data on
prototype BaFe2As2 and (K,Cs)Fe2Se2 superconductors. Without doping this system
is antiferromagnetic with T_N^{exp}~250K and rather complicated magnetic
structure. Neutron diffraction experiments indicated the possibility of two
possible spin structures (antiferromagnetically ordered ""plaquettes"" or
""zigzags""), indistinguishable by neutron scattering. Using LSDA calculated
exchange parameters we estimate Neel temperatures for both spin structures
within the molecular field approximation and show \tau_1 (""plaquettes"") spin
configuration to be more favorable than \tau_2 (""zigzags"").",1111.7046v1
2011-12-20,Ab initio Evidence for Strong Correlation Associated with Mott Proximity in Iron-based Superconductors,"We predict that iron-based superconductors discovered near d6 configuration
(5 Fe 3d orbitals filled by 6 electrons) is located on the foot of an
unexpectedly large dome of correlated electron matter centered at the Mott
insulator at d5 (namely, half filling). This is based on the many-variable
variational Monte-Carlo results for ab initio low-energy models derived by the
downfolding. The d5 Mott proximity extends to subsequent emergence of
incoherent metals, orbital differentiations due to the Mott physics and
Hund's-rule coupling, followed by antiferromagnetic quantum criticality, in
quantitative accordance with available experiments.",1112.4682v1
2011-12-21,Dislocation core field. II. Screw dislocation in iron,"The dislocation core field, which comes in addition to the Volterra elastic
field, is studied for the <111> screw dislocation in alpha-iron. This core
field, evidenced and characterized using ab initio calculations, corresponds to
a biaxial dilatation, which we modeled within the anisotropic linear
elasticity. We show that this core field needs to be considered when extracting
quantitative information from atomistic simulations, such as dislocation core
energies. Finally, we look at how dislocation properties are modified by this
core field, by studying the interaction between two dislocations composing a
dipole, as well as the interaction of a screw dislocation with a carbon atom.",1112.4936v1
2011-12-31,Brief review on iron-based superconductors: are there clues for unconventional superconductivity?,"Study of superconductivity in layered iron-based materials was initiated in
2006 by Hosono's group, and boosted in 2008 by the superconducting transition
temperature, Tc, of 26 K in LaFeAsO1-xFx. Since then, enormous researches have
been done on the materials, with Tc reaching as high as 55 K. Here, we review
briefly experimental and theoretical results on atomic and electronic
structures and magnetic and superconducting properties of FeAs-based
superconductors and related compounds. We seek for clues for unconventional
superconductivity in the materials.",1201.0237v1
2012-01-26,Effect of uniaxial pressure on the magneto-structural transitions of iron arsenide superconductors,"We study theoretically the variation of the magnetic and the structural
transition temperatures of the iron arsenide superconductors with external
uniaxial stress. We show that the increase of the transition temperatures
reported in recent experiments is compatible with a simple magneto-elastic
model in which the physical origin of this variation is linked to the fact that
antiferromagnetic bonds are longer than the ferromagnetic ones in the magnetic
phase. We make predictions which can be verified in order to test the relevance
of this model.",1201.5594v2
2012-03-05,Iron-platinum-arsenide superconductors Ca10(PtnAs8)(Fe2-xPtxAs2)5,"An overview of the crystal structures and physical properties of the recently
discovered iron-platinum-arsenide superconductors, Ca10(PtnAs8)(Fe2-xPtxAs2)5
(n = 3 and 4), which have a superconducting transition temperature up to 38 K,
is provided. The crystal structure consists of superconducting Fe2As2 layers
alternating with platinum-arsenic layers, PtnAs8. The upper critical field Hc2,
hydrostatic pressure dependence of superconducting transition temperature Tc,
and normal-state magnetic susceptibility are reported.",1203.0821v1
2012-03-15,Divergent nematic susceptibility in an iron arsenide superconductor,"Within the Landau paradigm of continuous phase transitions, ordered states of
matter are characterized by a broken symmetry. Although the broken symmetry is
usually evident, determining the driving force behind the phase transition is
often a more subtle matter due to coupling between otherwise distinct order
parameters. In this paper we show how measurement of the divergent nematic
susceptibility of an iron pnictide superconductor unambiguously distinguishes
an electronic nematic phase transition from a simple ferroelastic distortion.
These measurements also reveal an electronic nematic quantum phase transition
at the composition with optimal superconducting transition temperature.",1203.3239v1
2012-04-07,Rotationally-Invariant Exchange Interaction: The Case of Paramagnetic Iron,"We present a generalization of the spin-fluctuation theory of magnetism which
allows us to treat the full rotational invariance of the exchange interaction.
The approach is formulated in terms of the local density approximation plus
dynamical mean-field theory (LDA+DMFT), providing a systematic many-body
treatment of the effect of spin-density fluctuations. This technique is
employed to study the electronic and magnetic properties of paramagnetic
$\alpha$ iron. Our result for the Curie temperature is in good agreement with
experiment, while the calculations with the Ising-type exchange interaction
yield almost twice overestimated value.",1204.1636v1
2012-05-29,Ab initio study of helium and hydrogen interactions in $α$-Fe,"Density Functional Theory (DFT) calculations show a weak interaction between
hydrogen and helium in iron, in contrast to previous reports of a strong
trapping of hydrogen at helium. The strong preference of He and H to occupy
regions with low electronic density (such as vacancies) explains this
discrepancy, with vacancy-He and vacancy-H binding forces concealing the
repulsive interaction between He and H. Furthermore, Rate Theory simulations
based on our DFT-calculated V$_n$He$_m$H$_p$ cluster energetics predict, as it
is observed in some experiments, that synergetic effects could be expected
between H and He in iron under irradiation.",1205.6374v2
2012-05-30,"Multiple Superconducting Gaps, Anisotropic Spin Fluctuations and Spin-Orbit Coupling in Iron-Pnictides","This article reviews the NMR and NQR studies on iron-based high-temperature
superconductors by the IOP/Okayama group. It was found that the electron pairs
in the superconducting state are in the spin-singlet state with multiple
fully-opened energy gaps. The antiferromagnetic spin fluctuations in the normal
state are found to be closely correlated with the superconductivity. Also the
antiferromagnetic spin fluctuations are anisotropic in the spin space, which is
different from the case in copper oxide superconductors. This anisotropy
originates from the spin-orbit coupling and is an important reflection of the
multiple-bands nature of this new class of superconductors.",1205.6589v1
2012-06-11,Chemical Bonds and Spin State Splittings in Spin Crossover Complexes. A DFT and QTAIM Analysis,"Density functional theory (DFT) calculations have been performed for the
high-spin (HS) and low-spin (LS) isomers of a series of iron(II) spin crossover
complexes with nitrogen ligands. The calculated charge densities have been
analyzed in the framework of the quantum theory of atoms in molecules (QTAIM).
For a number of iron(II) complexes with substituted tris(pyrazolyl) ligands the
energy difference between HS and LS isomers, the spin state splitting, has been
decomposed into atomic contributions in order to rationalize changes of the
spin state splitting due to substituent effects.",1206.2136v1
2012-06-13,Nuclear Resonance Vibrational Spectroscopy of Iron Sulfur Proteins,"Nuclear inelastic scattering in conjunction with density functional theory
(DFT) calculations has been applied for the identification of vibrational modes
of the high-spin ferric and the high-spin ferrous iron-sulfur center of a
rubredoxin-type protein from the thermophylic bacterium Pyrococcus abysii.",1206.2788v1
2012-10-26,Finite-size effect of antiferromagnetic transition and electronic structure in LiFePO4,"The finite-size effect on the antiferromagnetic (AF) transition and
electronic configuration of iron has been observed in LiFePO4. Determination of
the scaling behavior of the AF transition temperature (TN) versus the
particle-size dimension (L) in the critical regime 1-TN(L)/TN(XTL)\simL^-1
reveals that the activation nature of the AF ordering strongly depends on the
surface energy. In addition, the effective magnetic moment that reflects the
electronic configuration of iron in LiFePO4 is found to be sensitive to the
particle size. An alternative structural view based on the polyatomic ion
groups of (PO4)3- is proposed.",1210.7167v1
2012-12-07,Molecular Dynamics and OKMC Study of Radiation Induced Motion of Voids and He Bubbles in BCC Iron,"We show that voids adjacent to radiation damage cascades can be moved in
their entirety by several lattice spacings. This is done using molecular
dynamics cascade simulations in iron at energies of 1-5 keV. The effect of this
mechanism is studied further using an OKMC code and shows enhancement of void
diffusion by 2 orders of magnitude from 1x10^-22 cm^2/s to 3x10^-20 cm^2/s.
Repeating the study on He bubbles shows that the movement is damped by the
presence of helium in the void.",1212.1652v2
2012-12-13,Consequence of total lepton number violation in strongly magnetized iron white dwarfs,"The influence of neutrinoless electron to positron conversion on cooling of
strongly magnetized iron white dwarfs is studied. It is shown that they can be
good candidates for soft gamma-ray repeaters and anomalous X-ray pulsars.",1212.3155v4
2013-01-08,Mechanism for the α -> ε phase transition in iron,"The mechanism of the {\alpha}-{\epsilon} transition in iron is reconsidered.
A path in the Burgers description of the bcc/hcp transition different from
those previously considered is proposed. It relies on the assumption that shear
and shuffle are decoupled and requires some peculiar magnetic order, different
from that of {\alpha} and {\epsilon} phases as found in Density-Functional
Theory. Finally, we put forward an original mechanism for this transition,
based on successive shuffle motion of layers, which is akin to a
nucleation-propagation process rather than to some uniform motion.",1301.1623v1
2013-03-06,Mixed-State Effect on the Low-Energy Spin Dynamics in Optimally-doped Iron Pnictide Superconductors,"Based on a phenomenological model with $s_{\pm}$ or s-wave pairing symmetry,
the mixed-state effect on the low-energy spin dynamics in optimally-doped iron
pnictide superconductors is studied by solving Bogoliubov-de Gennes equations.
Our results of the spin susceptibility at $\mathbf{q}=\mathbf{Q}$ in the
normal, superconducting and mixed states agree qualitatively with recent
neutron scattering experiments. We also propose that the field-induced
intensity change shows different behaviors between the $s_{\pm}$ and s-wave
symmetries in both momentum and real space, thus it can be used to distinguish
these two pairing symmetries.",1303.1557v1
2013-03-15,van der Waals interaction in iron-chalcogenide superconductors,"We demonstrate that the inclusion of van der Waals dispersive interaction
sensibly improves the prediction of lattice constants by density functional
theory in iron-chalcogenides (FeCh) superconductor compounds, namely FeSe and
FeTe. We show how generalized gradient approximation (GGA) for the exchange
correlation potential overestimates the out-of-plane lattice constants in both
compounds when compared with experiments. In addition, GGA predicts a too weak
bonding between the neutral FeCh layers, with a sensible underestimation of the
bulk modulus. van der Waals corrected simulations completely solve both
problems, reconciling theoretical results with experiments. These findings must
be considered when dealing with theoretical predictions in FeCh compounds.",1303.3747v2
2013-03-25,To the interpretation of the upturn observed by ATIC in heavy nuclei to iron ratios,"It is argued that the upturn observed in heavy nuclei to iron ratios as
measured in the ATIC experiment could be understood within the model of closed
galaxy with embedded local regions containing the sources of CR (Peters,
Westergaard, 1977). The universal upturn near the energies of 200-300 GeV/n in
the spectra of abundant primary nuclei is also predicted by this model, but it
also predicts the source spectral index to be near 2.5.",1303.6102v1
2013-04-29,Bulk Synthesis of Iron-based Superconductors,"Exploratory synthesis efforts for iron-based superconductors (FeSC) have been
driven by hopes of improving superconducting critical temperatures (TCs),
providing high-quality samples for in-depth studies of intrinsic properties,
and exploring potential superconductivity in similar families of materials.
This manuscript summarizes the synthesis routes that are used for producing
FeSC and their undoped parents, in single crystal and polycrystalline forms. A
few of the materials challenges are summarized.",1304.7708v1
2013-05-03,"Fermiology, Orbital Order, Orbital Fluctuation and Cooper Pairing in Iron-based Superconductors","We address two important issues that arise in recent studies of iron-based
superconductivity. (1) Why are the T_c of A_xFe_{2-y}Se_2 and the single unit
cell FeSe on SrTiO$_3$ so high despite both only have electron pockets? (2)
What (if any) are the effects of orbital order and orbital fluctuation on the
Cooper pairing. Our conclusions are summarized in the third paragraph of the
paper.",1305.0605v3
2013-05-08,Topological Surface States in Paramagnetic and Antiferromagnetic Iron Pnictides,"The electronic structure of iron pnictides is topologically nontrivial,
leading to the appearance of Dirac cones in the band structure for the
antiferromagnetic phase. Motivated by the analogy with Dirac cones in graphene,
we explore the possible existence of topologically protected surface states.
Surprisingly, bands of surface states exist even in the paramagnetic state. A
realistic five-orbital model predicts two such bands. In the antiferromagnetic
phase, these surface bands survive but split. We obtain the bulk and surface
dispersion from exact diagonalization of two- and five-orbital models in a
strip geometry and discuss the results based on topology.",1305.1770v2
2013-05-15,Nematic susceptibility of hole- and electron-doped BaFe2As2 iron-based superconductors from shear modulus measurements,"The nematic susceptibility of hole-doped Ba1-xKxFe2As2 and electron-doped
Ba(Fe1-xCox)2As2 iron-based superconductors is obtained from measurements of
the elastic shear modulus using a three-point bending setup in a capacitance
dilatometer. Nematic fluctuations, although weakened by doping, extend over the
whole superconducting dome in both systems, suggesting their close tie to
superconductivity. Evidence for quantum critical behavior of the nematic
susceptibility is, surprisingly, only found for Ba(Fe1-xCox)2As2, the system
with the lower maximal Tc value.",1305.3515v2
2013-07-04,Unusual band renormalization in the simplest iron based superconductor,"The electronic structure of the iron chalcogenide superconductor FeSe_{1-x}
was investigated by high- resolution angle-resolved photoemission spectroscopy
(ARPES). The results were compared to DFT calculations showing some significant
differences between the experimental electronic structure of FeSe_{1-x}, DFT
calculations and existing data on FeSe_{x}Te_{1-x}. The bands undergo a
pronounced orbital dependent renormalization, different from what was observed
for FeSe_{x}Te_{1-x} and any other pnictides.",1307.1280v1
2013-09-25,Superconductivity in 1111-type CaFeAsF1-xHx induced by selective hydrogen elimination,"The difference in thermal stability of F- and H- in 1111-type iron based
superconductors, allows selective hydrogen elimination from non-superconductive
CaFeAsF0.8H0.2 by thermal annealing. The analyzed chemical composition of the
resulting samples indicates that incorporated hydrogen was selectively
eliminated by thermal annealing at 553 K for 72 hours. The resulting
hydrogen-eliminated sample shows bulk superconductivity with Tc = 29 K. This
technique may be used for indirect electron doping for AeFeAeF (Ae;
alkali-earth metal) iron based superconductor described by CaFeAsF1-xHx =>
CaFeAsF1-x + xe- + 1/2xH2.",1309.6398v2
2013-10-03,Raman scattering as a probe of charge nematic fluctuations in iron based superconductors,"We report Raman scattering measurement of charge nematic fluctuations in the
tetragonal phase of BaFe$_2$As$_2$ and Sr(Fe$_{1-x}$Co$_x$)$_2$As$_2$ (x=0.04)
single crystals. In both systems, the observed nematic fluctuations are found
to exhibit divergent Curie-Weiss like behavior with very similar characteristic
temperature scales, indicating a universal tendency towards charge nematic
order in 122 iron-based superconductors.",1310.0934v2
2013-12-17,Nesting Induced Large Magnetoelasticity in the Iron Arsenide Systems,"A novel feature of the iron arsenides is the magnetoelastic coupling between
the long wavelength in-plane strains of the lattice and the collective spin
fluctuations of the electrons near the magnetic ordering wavevectors. Here, we
study its microscopic origin from an electronic model with nested Fermi pockets
and a nominal interaction. We find the couplings diverge with a power-law as
the system is tuned to perfect nesting. Furthermore, the theory reveals how
nematicity is boosted by nesting. These results are relevant for other systems
with nesting driven density wave transitions.",1312.4968v3
2014-01-15,X-ray absorption spectroscopy characterization of iron-oxide nanoparticles synthesized by high temperature plasma processing,"Iron-oxide nanoparticles have been synthesized by high temperature arc plasma
route with different plasma currents and characterized for their structure,
morphology and local atomic order. Fe K-edge x-ray absorption spectra reveal
distinct local structure of the samples grown with different plasma currents.
We have shown that the local disorder is higher for the higher plasma current
grown samples that also have a larger average particle-size. The results
provide useful information to control structural and morphological properties
of nanoparticles grown by high temperature plasma synthesis process.",1401.3655v1
2014-01-17,Globular clusters: a chemical roadmap between anomalies and homogeneity,"For several decades, globular clusters have been considered the best example
of simple stellar populations, hosting coeval and chemical homogeneous stars.
The last decade of spectroscopic and photometric studies has revealed a more
complex view of their chemical composition, with a high level of homogeneity in
their iron content but star-to-star variations in some light elements. This
contribution summarizes the main evidence about the chemical anomalies in the
stellar content of the globular clusters, discussing also some peculiar objects
with intrinsic dispersions in their iron content.",1401.4323v1
2014-03-25,Functional Renormalization Group Analysis of $η$-Pairing in Iron-based Superconductors,"Using functional renormalization group (FRG) approach, we analyze the $\eta$
pairing in a five d-orbital model for iron-pncitides. We find that the $\eta$
pairing between two hole pockets is a leading instability at low energy when
the two hole pockets are close to a nesting condition. The result suggests that
the system can spontaneously enter into a superconducting state with both
normal pairing and $\eta$ paring and the $\eta$ pairing is driven by the
inter-orbital antiferromagnetic exchange coupling while the normal pairing is
driven by the intra-orbital antiferromagnetic ones. An effective model at low
energy is proposed to account for the $\eta$ pairing instability.",1403.6240v1
2014-03-31,Evaluation of the Debye temperature for iron cores in human liver ferritin and its pharmaceutical analogue Ferrum Lek using Mossbauer spectroscopy,"An iron polymaltose complex Ferrum Lek used as antianemic drug and considered
as a ferritin analogue and human liver ferritin were investigated in the
temperature range from 295K to 90K by means of 57Fe Mossbauer spectroscopy with
a high velocity resolution i.e. in 4096 channels. The Debye temperatures equal
to 502K for Ferrum Lek and to 461K for human liver ferritin were determined
from the temperature dependence of the center shift obtained using two
different fitting procedures.",1403.7900v1
2014-09-17,"Electronic structure, spin excitations, and orbital ordering in a three-orbital model for iron pnictides","A three-orbital itinerant-electron model involving d_{xz}, d_{yz} and d_{xy}
Fe 3d orbitals is proposed for iron pnictides towards understanding the (\pi,0)
ordered magnetism and magnetic excitations in these materials. It is shown that
this model at half filling yields a gapped (\pi,0) magnetic state with high
degree of robustness and stability, and simultaneously reproduces several
experimentally observed features such as the electronic structure, spin
excitations, as well as the ferro orbital order between the d_{xz} and d_{yz}
orbitals.",1409.4984v2
2014-10-18,Structural and magnetic characterisation of iron oxyselenides Ce2O2Fe2OSe2 and Nd2O2Fe2OSe2,"We present here an investigation of the magnetic ordering in the Mott
insulating oxyselenide materials Ln2O2Fe2OSe2 (Ln = Ce, Nd). Neutron powder
diffraction data are consistent with a non-collinear multi-k ordering on the
iron sublattice structure and analysis indicates a reduced magnetic correlation
length perpendicular to the [Fe2O]2+ layers. The magnetic role of the Ln3+
cations is investigated and Ce3+ moments are found to order for T < 16 K.",1410.4990v1
2014-11-21,Spontaneous appearance of nonzero momentum Cooper pairing: Possible application to the iron-pnictides,"We suggest that an inhomogeneous (non-zero momentum) paired phase can appear
in the absence of an external magnetic field in the system with a predominant
interband pairing and with separate Fermi-surface sheets. The Fermi wave vector
mismatch which appears in such situation can be compensated by nonzero
center-of-mass momentum of the Cooper pairs, what can lead to a spontaneous
appearance of the Fulde-Ferrell type of superconducting state. The idea is
examined using a tight-binding model which emulates the hole-like and the
electron-like bands of iron based superconductor. The state can appear for the
case of both spin-singlet and -triplet pairing channels.",1411.5882v1
2015-01-28,Synthesis of endohedral iron-fullerenes by ion implantation,"In this paper, we discuss the results of our study of the synthesis of
endohedral iron-fullerenes. A low energy Fe+ ion beam was irradiated to C60
thin film by using a deceleration system. Fe+-irradiated C60 thin film was
analyzed by high performance liquid chromatography and laser
desorption/ionization time-of-flight mass spectrometry. We investigated the
performance of the deceleration system for using a Fe+ beam with low energy. In
addition, we attempted to isolate the synthesized material from a
Fe+-irradiated C60 thin film by high performance liquid chromatography.",1501.07022v1
2015-06-30,Orbital-selective electronic excitations in iron arsenides revealed by simulated nonresonant inelastic x-ray scattering,"Nonresonant inelastic x-ray scattering (NIXS) is a possible tool to detect
charge excitations in electron systems. In addition, multipole transitions at
high-momentum-transfer region open a new possibility to determine
orbital-selective electronic excitations in multi-orbital itinerant 3d electron
systems. As a theoretical example, we chose the antiferromagnetic state of iron
arsenides and demonstrate that the orbital-selective excitations are detectable
by choosing appropriate momentum transfer in NIXS. We propose that both NIXS
and resonant inelastic x-ray scattering are complementary to each other for
fully understanding the nature of orbital excitations in multi-orbital
itinerant electron systems.",1506.08972v1
2015-07-05,Magneto-orbital coupling in iron pnictides,"A magneto-orbital coupling mechanism is proposed to account for the weak
energy gap at the Fermi energy in the $(\pi,0)$ ordered SDW state of a
realistic three band model for iron pnictides involving $d_{xz}$, $d_{yz}$, and
$d_{xy}$ Fe orbitals. The orbital mixing terms between the $d_{xy}$ and
$d_{xz}/d_{yz}$ orbitals, which are important in reproducing the orbital
composition of the elliptical electron pockets at $(\pm \pi,0)$ and $(0,\pm
\pi)$, are shown to play a key role in the energy gap formation in the SDW
state.",1507.01189v1
2015-08-11,Multiple phase transitions in Pauli limited iron-based superconductors,"Specific heat measurements have been successfully used to probe
unconventional superconducting phases in one-band heavy-fermion and organic
superconductors. We extend the method to study successive phase transitions in
multi-band materials such as iron based superconductors. The signatures are
multiple peaks in the specific heat, at low temperatures and high magnetic
field, which can lead the experimental verification of unconventional
superconducting states with non-zero total momentum.",1508.02740v2
2015-09-16,"Structural transition and superconductivity in hydrothermally synthesized FeX (X = S, Se)","Tetragonal beta-FeSe obtained by hydrothermal reaction is not superconducting
and transforms to a triclinic structure at 60 K unlike superconducting FeSe
from solid state synthesis, which becomes orthorhombic at 90 K. In contrast,
tetragonal iron sulphide FeS from hydrothermal synthesis is superconducting at
4.8 K but undergoes no structural transition. Our results suggest that the
absence of superconductivity in hydrothermally synthesized FeSe may be
associated to the low-temperature structure with zigzag chains of iron atoms,
which is different from the known orthorhombic Cmme structure of
superconducting FeSe.",1509.04851v1
2015-11-21,Ironing in the Dark,"This paper presents the first polynomial-time algorithm for position and
matroid auction environments that learns, from samples from an unknown bounded
valuation distribution, an auction with expected revenue arbitrarily close to
the maximum possible. In contrast to most previous work, our results apply to
arbitrary (not necessarily regular) distributions and the strongest possible
benchmark, the Myerson-optimal auction. Learning a near-optimal auction for an
irregular distribution is technically challenging because it requires learning
the appropriate ""ironed intervals,"" a delicate global property of the
distribution.",1511.06918v1
2015-11-24,Testing the no-hair theorem with the continuum-fitting and the iron line methods: a short review,"The continuum-fitting and the iron line methods are leading techniques
capable of probing the spacetime geometry around astrophysical black hole
candidates and testing the no-hair theorem. In the present paper, we review the
two approaches, from the astrophysical models and their assumptions, to the
constraining power with present and future facilities.",1511.07587v2
2016-05-06,Investigation of magnetic phases in parent compounds of Iron-chalcogenides via quasiparticle scattering interference,"We employ a five-orbital tight-binding model to develop the mean field
solution for various possible spin density wave states in the
iron-chalcogenides. The quasiparticle interference (QPI) technique is applied
to detect signatures of these states due to scatterings arising from
non-magnetic impurities. Apart from the experimentally observed double striped
structure with ordering vector $(\pi/2,\pi/2)$, the QPI method is investigated
for the extended-stripe as well as the orthogonal double stripe phase. We
discuss QPI as a possible tool to detect and classify various magnetic
structures with different electronic structure reconstruction within framework
of the Fe$_{1+y}$Te compound.",1605.01798v1
2016-05-11,Vibrational and thermoelastic properties of bcc iron from selected EAM potentials,"A comprehensive, critical study of the vibrational, thermodynamic and
thermoelastic properties of bcc iron is presented, using well established
semi-empirical embedded-atom method potentials available in the literature.
Classical molecular dynamics simulations are used to address temperature
effects, where dynamical matrices are constructed as a time average of the
second moment of the atomic displacements. The $C_{11}, C_{44}, C'$ elastic
constants are then obtained from the sound velocities along high symmetry
directions in reciprocal space. Results are compared to ultrasonic measurements
and highlight the limitations of the potentials considered here in describing
thermoelastic properties.",1605.03334v2
2016-07-25,Evidences of Mott physics in iron pnictides from x-ray spectroscopy,"X-ray emission and absorption spectroscopies are jointly used as fast probes
to determine the evolution as a function of doping of the fluctuating local
magnetic moments in K- and Cr- hole-doped BaFe2As2. An increase in the local
moment with hole-doping is found, supporting the theoretical scenario in which
a Mott insulating state that would be realized for half-filled conduction bands
has an influence throughout the phase diagram of these iron-pnictides.",1607.07417v1
2016-12-21,Unconventional superconductors: Iron-based diversity,"Nine years ago, superconductors based on the magnetic element iron were
discovered. A flurry of research activity has revealed an unprecedented
diversity of chemical structures and physical properties. Similarly to other
unconventional superconductors, stripe-type antiferromagnetism seems to play an
important role. Particularly interesting is its strong coupling to the crystal
lattice. The systematic comparison of different compounds may allow to identify
key elements in the mechanism of superconductivity and provide guidelines for
the search for new and better superconductors.",1612.07356v1
2017-03-09,Spin-wave excitations in the SDW state of iron pnictides: a comparison between the roles of interaction parameters,"We investigate the role of Hund's coupling in the spin-wave excitations of
the ($\pi, 0$) ordered magnetic state within a five-orbital tight-binding model
for iron pnictides. To differentiate between the roles of intraorbital Coulomb
interaction and Hund's coupling, we focus on the self-consistently obtained
mean-field SDW state with a fixed magnetic moment obtained by using different
sets of interaction parameters. We find that the Hund's coupling is crucial for
the description of various experimentally observed characteristics of the
spin-wave excitations including the anisotropy, energy-dependent behavior, and
spin-wave spectral weight distribution.",1703.03228v2
2017-04-13,Roles of anisotropic and unequal gaps in the quasiparticle interference of superconducting iron pnictides,"We investigate the role of gap characteristics such as anisotropy and
inequality of the gaps in the quasiparticle interferences of iron pnictides
using a five-orbital tight-binding model. We examine how the difference in the
sensitivities exhibited by the sign-changing and -preserving $s$-wave
superconductivity in an annular region around ($\pi, 0$), which can be used to
determine the sign change of the superconducting gap, gets affected when the
gaps are unequal on the electron and hole pocket. In addition, we also discuss
how robust these differentiating features are on changing the quasiparticle
energy or when the gap is anisotropic.",1704.04069v1
2017-04-18,Tilting the balance towards d-wave in iron-based superconductors,"The intricate interplay of interactions and Fermiology can give rise to a
close competition between nodeless (e.g. s-wave) and nodal (e.g. d-wave) order
in electronically driven unconventional superconductors. We analyze how such a
scenario is affected by a Zeeman magnetic field $H_{\text{Z}}$ and temperature
$T$. In the neighborhood of a zero temperature first order critical point
separating a nodal from a nodeless phase, the phase boundary at low
$H_{\text{Z}}$ and/or low $T$ has a universal line shape cubic in
$H_{\text{Z}}$ or $T$, such that the nodal state is stabilized at the expense
of the nodeless. We calculate this line shape for a model of competing
s_\pm-wave and d-wave pairing in iron-based superconductors.",1704.05525v1
2017-06-27,Orbital mismatch boosting nematic instability in iron-based superconductors,"We derive the effective action for the collective spin modes in iron-based
superconductors. We show that, due to the orbital-selective nature of spin
fluctuations, the magnetic and nematic instabilities are controlled by the
degrees of orbital nesting between electron and hole pockets. Within a
prototypical three-pockets model the hole-electron orbital mismatch is found to
boost spin-nematic order. This explains the enhancement of the nematic order in
FeSe as compared to 122 compounds, and its suppression under pressure, where
the emergence of the second hole pocket compensates the orbital mismatch of the
three-pockets configuration.",1706.08953v2
2017-07-08,Quasi-2D behavior of 112-type iron-based superconductors,"Fluctuation magnetoconductivity and magnetization above the superconducting
transition temperature (Tc) are measured on the recently discovered 112 family
of iron-based superconductors (IBS), Ca$_{1-x}$La$_x$Fe$_{1-y}$Ni$_y$As$_2$,
which presents an extra As-As chain spacer-layer. The analysis in terms of a
generalization of the Lawrence-Doniach (LD) approach to finite applied magnetic
fields indicates that these compounds are among the most anisotropic IBS
($\gamma$ up to ~30), and provides a compelling evidence of a
quasi-two-dimensional behavior for doping levels near the optimal one.",1707.02470v1
2017-08-29,A compact cosmic muon veto detector and possible use with the Iron Calorimeter detector for neutrinos,"The motivation for a cosmic muon veto (CMV) detector is to explore the
possibility of locating the proposed large Iron Calorimeter (ICAL) detector at
the India based Neutrino Observatory (INO) at a shallow depth. An initial
effort in that direction, through the assembly and testing of a $\sim$ 1 m
$\times$ 1 m $\times$ 0.3 m plastic scintillator based detector, is described.
The plan for making a CMV detector for a smaller prototype mini-ICAL is also
outlined.",1708.08597v2
2017-11-13,A possible explanation of the void discovered in the pyramid of Khufu on the basis of the pyramid texts,"A recent exploration has shown the presence of a significant void in the
pyramid of Khufu at Giza. A possible explanation of this space, interpreted as
a chamber connected to the lower north channel and aimed to contain a specific
funerary equipment is tentatively proposed. According to the Pyramid Texts,
this equipment might consist of a Iron throne, actually a wooden throne endowed
with meteoritic Iron sheets.",1711.04617v2
2018-01-16,Iron single crystal growth from a lithium-rich melt,"\alpha-Fe single crystals of rhombic dodecahedral habit were grown from a
melt of Li$_{84}$N$_{12}$Fe$_{\sim 3}$. Crystals of several millimeter along a
side form at temperatures around $T \approx 800^\circ$C. Upon further cooling
the growth competes with the formation of Fe-doped Li$_3$N. The b.c.c.
structure and good sample quality of \alpha-Fe single crystals were confirmed
by X-ray and electron diffraction as well as magnetization measurements and
chemical analysis. A nitrogen concentration of 90\,ppm was detected by means of
carrier gas hot extraction. Scanning electron microscopy did not reveal any
sign of iron nitride precipitates.",1801.05287v1
2018-03-21,Self-assembly of magnetic iron oxide nanoparticles into cuboidal superstructures,"This chapter describes the synthesis and some characteristics of magnetic
iron oxide nanoparticles, mainly nanocubes, and focus on their self-assembly
into crystalline cuboids in dispersion. The influence of external magnetic
fields, the concentration of particles, and the temperature on the assembly
process is experimentally investigated.",1803.07922v1
2018-04-14,"""With 1 follower I must be AWESOME :P"". Exploring the role of irony markers in irony recognition","Conversations in social media often contain the use of irony or sarcasm, when
the users say the opposite of what they really mean. Irony markers are the
meta-communicative clues that inform the reader that an utterance is ironic. We
propose a thorough analysis of theoretically grounded irony markers in two
social media platforms: $Twitter$ and $Reddit$. Classification and frequency
analysis show that for $Twitter$, typographic markers such as emoticons and
emojis are the most discriminative markers to recognize ironic utterances,
while for $Reddit$ the morphological markers (e.g., interjections, tag
questions) are the most discriminative.",1804.05253v1
2018-12-02,Novel Magnetic Block States in Low-Dimensional Iron-Based Superconductors,"Inelastic neutron scattering recently confirmed the theoretical prediction of
a $\uparrow\uparrow\downarrow\downarrow$-magnetic state along the legs of
quasi-one-dimensional (quasi-1D) iron-based ladders in the orbital-selective
Mott phase (OSMP). We show here that electron-doping of the OSMP induces a
whole class of novel block-states with a variety of periodicities beyond the
previously reported $\pi/2$ pattern. We discuss the magnetic phase diagram of
the OSMP regime that could be tested by neutrons once appropriate quasi-1D
quantum materials with the appropriate dopings are identified.",1812.00325v2
2019-01-25,Polarized neutron reflectometry study from iron oxide nanoparticles monolayer,"We report on the polarized neutron reflectometry investigation of monolayer
of magnetic iron oxide nanoparticles assembled by the Langmuir-Schaefer method.
After deposition onto a solid substrate the polarized neutron reflectometry
measurements in the external magnetic field were carried out. Thickness,
density, roughness and in-depth resolved magnetization profile of the resulted
layer were obtained from accurate fitting routine.",1901.08819v1
2019-10-09,Electric-field control of magnetism in iron oxide nanoparticle / BaTiO3 film composites,"We study composites of monodisperse ferrimagnetic nanoparticles (NPs)
embedded into ferroelectric barium titanate (BTO) films. The BTO films were
prepared by pulsed laser deposition. The composite consists of a stack of two
BTO films sandwiching one monolayer of iron oxide NPs. We observe a
magnetoelectric coupling due to strain and interface charge co-mediation
between the BTO and the NPs. This is demonstrated by measurements of the
magnetization as function of DC and AC electric fields.",1910.04127v1
2019-11-20,Suppression of superconductivity by spin fluctuations in iron-based superconductors,"We study the superconducting instability mediated by spin fluctuations in the
Eliashberg theory for a minimal two-band model of iron-based superconductors.
While antiferromagnetic spin fluctuations can drive superconductivity (SC) as
is well established, we find that spin fluctuations necessarily contain a
contribution to suppress SC even though SC can eventually occur at lower
temperatures. This self-restraint effect stems from a general feature of the
spin-fluctuation mechanism, namely the repulsive pairing interaction, which
leads to phase frustration of the pairing gap and consequently the suppression
of SC.",1911.09009v3
2020-02-08,Atomic diffusion in alpha-iron across the Curie point: an effcient and transferable ab-initio-based modelling approach,"An accurate prediction of atomic diffusion in Fe alloys is challenging due to
thermal magnetic excitations and magnetic transitions. We propose an effcient
approach to address these properties via Monte Carlo simulation, using
ab-initio based effective interaction models. The temperature evolution of
self- and Cu diffusion coeffcients in alpha-iron are successfully predicted,
particularly the diffusion acceleration around the Curie point, which requires
a quantum treatment of spins. We point out a dominance of magnetic disorder
over chemical effects on diffusion in the very dilute systems.",2002.03126v2
2020-03-23,Inverse heat source problem and experimental design for determining iron loss distribution,"Iron loss determination in the magnetic core of an electrical machine, such
as a motor or a transformer, is formulated as an inverse heat source problem.
The sensor positions inside the object are optimized in order to minimize the
uncertainty in the reconstruction in the sense of the A-optimality of Bayesian
experimental design. This paper focuses on the problem formulation and an
efficient numerical solution of the discretized sensor optimization and source
reconstruction problems. A semirealistic linear model is discretized by finite
elements and studied numerically.",2003.10395v2
2020-04-10,Baby MIND detector first physics run,"Baby MIND is a Magnetized Iron Neutrino Detector, serving as a downstream
magnetized muon range detector for WAGASCI on the T2K beam line in Japan. The
first physics run of Baby MIND together with other WAGASCI sub-detectors took
place in the period from November 2019 to February 2020 (T2K run10), where a
total of $4.8 \times 10^{20}$ Protons on target (POT) was delivered.
Preliminary results showing Baby MIND data quality, detector performance and
examples of neutrino interactions on iron during the first physics run are
presented.",2004.05245v1
2020-09-03,Measurements of sub-nT dynamic magnetic field shielding with soft iron and mu-metal for use in linear colliders,"There is an increasing need to shield beams and accelerator elements from
stray magnetic fields. The application of magnetic shielding in linear
colliders is discussed. The shielding performance of soft iron and mu-metal is
measured for magnetic fields of varying amplitude and frequency. Special
attention is given to characterise the shielding performance for very
small-amplitude magnetic fields.",2009.01519v2
2020-10-18,Some comments on events associated with falling terrestrial rocks and iron from the sky,"Some examples of the events associated with falls of rocks and iron
terrestrial origin from the sky are considered (in scientific publications they
are often called as meteor-wrongs or pseudo-meteorites). Their possible
connections with other natural phenomena (like a whirlwind and a
ball-lightning) are considered. Some compilation of info connected with the
event in the US town of Elma in 2003 is presented. Also some possible parallels
with the 1908 Tunguska event are given. The author hopes to draw attention to
the need for more detailed research of such phenomena.",2012.00686v1
2021-04-15,Surface orbital order and chemical potential inhomogeneity of the iron-based superconductor FeTe0.55Se0.45 investigated with special STM tips,"The atomically clean surface of the iron-based superconductor FeTe0.55Se0.45
is investigated by low-temperature STM with different tip apex states. By
manipulating a single Fe atom onto the tip apex, signatures of the orbital
nature of the subsurface Fe layer of FeTe0.55Se0.45 can be identified. By
preparing a charged tip state, the intrinsic spatial inhomogeneity of the
chemical potential of FeTe0.55Se0.45 can be revealed. As a result, three
different types of vortex bound states originating from locally varying
topological properties of the FeTe0.55Se0.45 surface are observed by scanning
tunneling spectroscopy.",2104.07418v1
2021-05-23,Ab initio investigation of impurity ferromagnetism in the Pd1-xFex alloys: concentration and position dependence,"We present the ab initio results of the structural and magnetic properties of
the Pd host matrix implanted with Fe solute atoms at various concentrations. By
means of density functional theory we confirm that iron impurities are able to
initialize significant magnetization of the Pd atoms, when the impurity
consentation exceeds 3 at.%. Besides, we demonstrate that the imposed
magnetization depends on impurity positions in the host matrix, in particular,
there is a maximum of magnetization for a uniform distribution of the iron
impurity.",2105.10918v1
2021-09-20,Quantile Regression for positive data using a general class of distributions,"This paper presents a general class of quantile regression models for
positive continuous data. In this class of models we consider that the response
variable has a IRON distribution. We provide inference and diagnostic tools for
this class of models. An R package, called IRON, was implemented. This package
provides estimation and inference for the parameters and tools useful to check
the fit of models. The methods are also illustrated with an application to
modeling household income in Chile.",2109.09281v1
2021-09-26,Monte Carlo simulation of ultrafast nonequilibrium spin and charge transport in iron,"Spin transport and spin dynamics after femtosecond laser pulse irradiation of
iron (Fe) are studied using a kinetic Monte Carlo model. This model simulates
spin dependent dynamics by taking into account two interaction processes during
nonequilibrium: Elastic electron - lattice scattering, where only the direction
of the excited electrons changes neglecting the energy loss, and inelastic
electron - electron interaction, where secondary electrons are generated. An
analysis of the particle kinetics inside the material shows that a smaller
elastic scattering time affects the spin dynamics by leading to a larger
spatial spread of electrons in the material, whereas generation of secondary
electrons affects the spin transport with a larger time of propagation of
homogeneous spin polarization.",2109.12578v1
2021-11-22,"Electron and Superconducting Properties of the AFeAs (A= Li, Na) Family Alkali-Metal Pnictides: Current Stage of the Research (mini-review)","The review is focused on one of the most exotic families of iron-based
superconductors belonging to the AFeAs structural type, where A is alkali
metal. We briefly concern physical and electron properties of the typical
members of this family, LiFeAs and NaFeAs, discuss the theoretical models
describing the multiple-gap superconducting state, and the experimental data
available in literature. As well, we specify the main unsolved problems, that
seem crucial for both the AFeAs family and for iron-based superconductors in
general.",2111.11122v1
2022-03-11,Electrical Conductivity of Iron in Earth's Core from Microscopic Ohm's Law,"Understanding the electronic transport properties of iron under high
temperatures and pressures is essential for constraining geophysical processes.
The difficulty of reliably measuring these properties under Earth-core
conditions calls for sophisticated theoretical methods that can support
diagnostics. We present results of the electrical conductivity within the
pressure and temperature ranges found in Earth's core from simulating
microscopic Ohm's law using time-dependent density functional theory. Our
predictions provide a new perspective on resolving discrepancies in recent
experiments.",2203.06025v1
2022-07-18,Direct observation of the spin exciton in Andreev spectroscopy of iron-based superconductors,"Quasiparticle excitations provide viable information on the physics of
unconventional superconductors. Higgs and Leggett modes are some of the classic
examples. Another important bosonic excitation is the spin exciton originating
from the sign-changing superconducting gap structure. Here we report a direct
observation of the temperature-dependent spin exciton in the Andreev spectra of
iron-based superconductors. Combined with the other experimental evidence, our
observation confirms the extended $s$-wave ($s_\pm$) order parameter symmetry
and indirectly proves the spin-fluctuation mechanism of Cooper pairing.",2207.08493v2
2023-01-11,Mathematical and Physical Properties of Three-Band s+- Eliashberg Theory for Iron Pnictides,"The phenomenology of the iron pnictide superconductor can be described by the
threeband s+- Eliashberg theory in which the mechanism of superconducting
coupling is mediated by antiferromagnetic spin fluctuations and whose
characteristic energy W0 scales with Tc according to the empirical law W0 =
4.65kBTc. This model presents the universal characteristics that are
independent of the critical temperature, such as the link between the two free
parameters l13 and l23 and the ratio Di/kBTc.",2301.04557v1
2023-05-04,"Iron-based superconductors: teenage, complex, challenging","The advent of iron-based superconductors in 2008 came as a complete surprise
to the condensed matter community. Now 15 years later, they are beginning to
impart some of their new-found wisdom on a slew of emerging superconductors
that boast similar traits.",2305.03035v1
2023-08-26,Multivariate Majorization in Principal-Agents Models,"We introduce a definition of multivariate majorization that is new to the
economics literature. Our majorization technique allows us to generalize Mussa
and Rosen's (1978) ""ironing"" to a broad class of multivariate principal-agents
problems. Specifically, we consider adverse selection problems in which agents'
types are one dimensional but informational externalities create a
multidimensional ironing problem. Our majorization technique applies to
discrete and continuous type spaces alike and we demonstrate its usefulness for
contract theory and mechanism design. We further show that multivariate
majorization yields a natural extension of second-order stochastic dominance to
multiple dimensions and derive its implications for decision making under
multivariate risk.",2308.13804v1
2023-10-10,Ab initio description of bcc iron with correlation matrix renormalization theory,"We applied the ab initio spin-polarized Correlation Matrix Renormalization
Theory (CMRT) to the ferromagnetic state of the bulk BCC iron. We showed that
it was capable of reproducing the equilibrium physical properties and the
pressure-volume curve in good comparison with experiments. We then focused on
the analysis of its local electronic correlations. By exploiting different
local fluctuation-related physical quantities as measures of electronic
correlation within target orbits, we elucidated the different roles of $t_{2g}$
and $e_g$ states in both spin channels and presented compelling evidence to
showcase this distinction in their electronic correlation.",2310.06942v1
1994-06-07,Abundances of four very metal-poor stars of the BPS survey,"High resolution CASPEC and EMMI spectra (R$\approx$10$^4$) of the faint
metal- deficient candidates CS 22891--209, CS 22897--8, CS 22948--66 and CS
22968--14 taken from the survey of Beers, Preston and Shectman (1985, BPS) are
analyzed for abundances. The fine analysis with LTE model atmospheres gives an
iron metallicity for the four stars between $-$3.15 and $-$3.45 in good
agreement with the abundances inferred from CaII K index by Beers et al.
(1992). These four objects considerably augment the number of spectroscopically
studied stars at the low metallicity extreme. We found the $\alpha$-elements
Mg, Ca, Si, and Ti enhanced, and the iron-peak elements Sc, Mn and Cr tracking
closely iron with the typical pattern of the more metallic halo stars. Aluminum
results deficient with respect both to iron and to magnesium showing a strong
{\it odd-even\/} effect, but for [Fe/H] $\leq$ $-$3.0 [Al/Mg] levels out into a
plateau around $-$1.0, showing a primary behaviour. [Na/Fe] is $\approx$ $-$0.2
and only compared to magnesium it shows a mild odd-even effect. The heavy
elements Sr and Ba show a large scatter which is not observed for other
elements and cannot be due to observational errors only. In the case of CS
22891--209 they are particularly overabundant with [Sr,Ba/Fe] $\approx$ 0.9.
The spread might reflect the presence of strong inhomogeneities in the
interstellar gas at the earliest stages of Galaxy formation. This might be an
important signature of the still elusive processes of the early formation of
these elements observed in old stars.",9406018v1
1995-03-14,CHEMICAL ABUNDANCES IN CLUSTERS OF GALAXIES,"We study the origin of iron and alpha-elements (O, Mg, Si) in clusters of
galaxies. In particular, we discuss the [O/Fe] ratio and the iron
mass-to-luminosity ratio in the intracluster medium (ICM) and their link to the
chemical and dynamical evolution of elliptical and lenticular galaxies. We
adopt a detailed model of galactic evolution incorporating the development of
supernovae- driven galactic winds which pollute the ICM with enriched ejecta.
We demonstrate \it quantitatively \rm the crucial dependence upon the assumed
stellar initial mass function in determining the evolution of the mass and
abundances ratios of heavy elements in typical model ICMs. We show that
completely opposite behaviours of [alpha/Fe] ratios (\ie positive versus
negative ratios) can be obtained by varying the initial mass function without
altering the classic assumptions regarding type Ia supernovae progenitors or
their nucleosynthesis. Our results indicate that models incorporating somewhat
flatter-than-Salpeter initial mass functions (ie x approx 1, as opposed to
x=1.35) are preferred, provided the intracluster medium iron mass-to-luminosity
ratio, preliminary [alpha/Fe]>0 ASCA results, and present-day type Ia
supernovae rates, are to be matched. A simple Virgo cluster simulation which
adheres to these constraints shows that approx 70% of the measured ICM iron
mass has its origin in type II supernovae, with the remainder being synthesized
in type Ia systems.",9503057v1
1995-07-24,Good Abundances from Bad Spectra: I. Techniques,"We have developed techniques to extract true iron abundances and surface
gravities from spectra of the type provided by the multiple-object fibre-fed
spectroscopic radial-velocity surveys underway with 2dF, HYDRA, NESSIE, and the
forthcoming Sloan survey. Our method is optimised for low S/N, intermediate
resolution blue spectra of G stars. Spectroscopic indices sensitive to iron
abundance and gravity are defined from a set of narrow (few Angstrom)
wavelength intervals, and calibrated using synthetic spectra. We have also
defined a single abundance indicator which is able to provide useful iron
abundance information from spectra having S/N ratios as low as 10 per Angstrom.
The theoretical basis and calibration using synthetic spectra are described in
this paper. The empirical calibration of these techniques by application to
observational data is described in Jones, Wyse and Gilmore (PASP July 1995).
The technique provides precise iron abundances, with zero-point correct to
$\sim 0.1$ dex, and is reliable, with typical uncertainties being $\approxle
0.2$ dex. A derivation of the {\it in situ\/} thick disk metallicity
distribution using these techniques is presented by Gilmore, Wyse and Jones (AJ
1995 v109 p1095).",9507091v1
1997-06-09,Iron as a tracer in galaxy clusters and groups,"Available X-ray data are collected and organized concerning the iron and gas
content of galaxy clusters and groups, together with the optical luminosity,
mass and iron abundance of cluster galaxies. Several astrophysical inferences
are then drawn, including the evidence for rich clusters having evolved without
much baryon exchange with their surrondings, and having experienced very
similar star formation histories. Groups are much gas-poor compared to
clusters, and appear instead to have shed a major fraction of their original
cosmic share of baryons, which indicates that galaxy clusters cannot have
formed by assembling groups similar to the present day ones. It is argued that
this favors low-$\Omega$ universes, in which the growth of rich clusters is
virtually complete at high redshifts. It is also argued that elemental
abundance ratios in clusters are nearly solar, which is consistent with a
similar proportion of supernovae of Type Ia and Type II having enriched both
the solar neghborhood as well clusters as a whole. Much of the iron in clusters
appears to reside in the intracluster medium rather than inside galaxies. It
appears that the baryon to star conversion in clusters has been nearly as
efficient as currently adopted for the universe as a whole. Yet the metallicity
of the clusters is $\sim 5$ times higher than the global metallicity adopted
for the nearby universe. It is concluded that the intergalactic medium should
have a metallicity $\sim 1/3$ solar if stellar nucleosynthesis has proceeded in
stars within field galaxies with the same efficiency as in stars within
clusters of galaxies.",9706083v1
1997-10-07,Ionization Structure and Spectra of Iron in Gaseous Nebulae},"The emission spectra and the ionization structure of the low ionization
stages of iron, Fe I--IV, in gaseous nebulae are studied. This work includes:
(i) new atomic data: photoionization cross sections, total e-ion recombination
rates, excitation collision strengths, and transition probabilities; (ii)
detailed study of excitation mechanisms for the [Fe II], [Fe III], and [Fe IV]
emission, and spectroscopic analysis of the observed IR, optical, and UV
spectra; (iii) study of the physical structure and kinematics of the nebulae
and their ionization fronts. Spectral analysis of the well observed Orion
nebula is carried out as a test case, using extensive collisional-radiative and
photoionization models. It is shown that the [Fe II] emission from the Orion
nebula is predominantly excited via electron collisions in high density
partially ionized zones; radiative fluorescence is relatively less effective.
Further evidence for high density zones is derived from the [O I] and [Ni II]
spectral lines, as well as from the kinematic measurements of ionic species in
the nebula. The ionization structure of iron in Orion is modeled using the
newly calculated atomic data, showing some significant differences from
previous models. The new model suggests a fully ionized H II region at
densities on the order of $10^3$ cm$^{-3}$, and a dynamic partially ionized H
II/H I region at densities of $10^5-10^7$ \cm3. Photoionization models also
indicate that the optical [O I] and [Fe II] emission originates in high density
partially ionized regions within ionization fronts. The gas phase iron
abundance in Orion is estimated from observed spectra.",9710073v1
1999-06-24,X-ray iron line variability for the model of an orbiting flare above a black hole accretion disc,"The broad X-ray iron line, detected in many active galactic nuclei, is likely
to be produced by fluorescence from the X-ray illuminated central parts of an
accretion disc close to a supermassive black hole. The time-averaged shape of
the line can be explained most naturally by a combination of special and
general relativistic effects. Such line profiles contain information about the
black hole spin and the accretion disc as well as the geometry of the emitting
region and may help to test general relativity in the strong gravity regime. In
this paper we embark on the computation of the temporal response of the line to
the illuminating flux. Previous studies concentrated on the calculation of
reverberation signatures from static sources illuminating the disc. In this
paper we focus on the more physically justified case of flares located above
the accretion disc and corotating with it. We compute the time dependent iron
line taking into account all general relativistic effects and show that its
shape is of very complex nature, and also present light curves accompanying the
iron line variability. We suggest that future X-ray satellites like XMM or
Constellation-X may be capable of detecting features present in the computed
reverberation maps.",9906397v1
1999-07-26,Model Photospheres for Late-Type Stars from the Inversion of High-Resolution Spectroscopic Observations. Groombridge 1830 and Epsilon Eridani,"An inversion technique to recover LTE one-dimensional model photospheres for
late-type stars, which was previously applied to the Sun (Allende Prieto et al.
1998), is now employed to reconstruct, semi-empirically, the photospheres of
cooler dwarfs: the metal-poor Gmb1830 and the active star of solar-metallicity
Eps Eri. The model atmospheres we find reproduce satisfactorily all the
considered weak-to-moderate neutral lines of metals, satisfying in detail the
excitation equilibrium of iron, the wings of strong lines, and the slope of the
optical continuum. The retrieved models show a slightly steeper temperature
gradient than flux-constant model atmospheres in the layers where log tau <=
-0.5. We argue that these differences should reflect missing ingredients in the
flux-constant models and point to granular-like inhomogeneities as the best
candidate.
  The iron ionization equilibrium is well satisfied by the model for Gmb1830,
but not for Eps Eri, for which a discrepancy of 0.2 dex between the logarithmic
iron abundance derived from neutral and singly ionized lines may signal
departures from LTE. The chemical abundances of calcium, titanium, chromium,
and iron derived with the empirical models from neutral lines do not differ
much from previous analyses based on flux-constant atmospheric structures.",9907368v1
1999-12-17,Discovery of a red and blue shifted iron disk line in the galactic jet source GRO J1655-40,"We report the discovery of emission features in the X-ray spectrum of GRO
J1655-40 obtained with RXTE during the observation of 1997, Feb 26. We have
fitted the features firstly by two Gaussian lines which in four spectra
analysed have average energies of 5.85 +/- 0.08 keV and 7.32 +/- 0.13 keV,
strongly suggestive that these are the red and blue shifted wings of an iron
disk line. These energies imply a velocity of ~0.33 c. The blue wing is less
bright than in the calculated profiles of disk lines near a black hole subject
to Doppler boosting, however known Fe absorption lines in GRO J1655-40 at
energies between ~7 and 8 keV can reduce the apparent brightness of the blue
wing. Secondly, we have fitted the spectra using the disk line model of Laor
based on a full relativistic treatment plus an absorption line, and show that
good fits are obtained. This gives a restframe energy of the disk line between
6.4 and 6.8 keV indicating that the line is iron K_alpha emission probably of
significantly ionized material. The Laor model shows that the line originates
in a region of the accretion disk extending from ~10 Schwarzschild radii from
the black hole outwards. The line is direct evidence for the black hole nature
of the compact object and is the first discovery of a highly red and blue
shifted iron disk line in a Galactic source.",9912389v2
2000-03-07,The Chandra Iron-L X-Ray Line Spectrum of Capella,"An analysis of the iron L-shell emission in the publicly available spectrum
of the Capella binary system, as obtained by the High Energy Transmission
Grating Spectrometer on board the Chandra X-ray Observatory, is presented. The
atomic-state model, based on the HULLAC code, is shown to be especially
adequate for analyzing high-resolution x-ray spectra of this sort. Almost all
of the spectral lines in the 10 - 18 Angstrom wavelength range are identified.
It is shown that, for the most part, these lines can be attributed to emission
from L-shell iron ions in the Capella coronae. Possibilities for electron
temperature diagnostics using line ratios of Fe16+ are demonstrated. It is
shown that the observed iron-L spectrum can be reproduced almost entirely by
assuming a single electron temperature of kTe= 600 eV. This temperature is
consistent with both the measured fractional ion abundances of iron and with
the temperature derived from ratios of Fe16+ lines. A volume emission measure
of 1053 cm-3 is calculated for the iron L-shell emitting regions of the Capella
coronae indicating a rather small volume of 1029 cm3 for the emitting plasma if
an electron density of 1012 cm-3 is assumed.",0003099v3
2000-03-27,Atomic data from the Iron Project.XLIV. Transition probabilities and line ratios for Fe VI with fluorescent excitation in planetary nebulae,"Relativistic atomic structure calculations for electric dipole E1, electric
quadrupole E2 and magnetic dipole M1 transition probabilities among the first
80 fine-structure levels of Fe VI, dominated by configurations 3d^3, 3d^24s,
and 3d^24p, are carried out using the Breit-Pauli version of the code
Superstructure. Experimental energies are used to improve the accuracy of these
transition probabilities. Employing the 80-level collision-radiative (CR) model
with these dipole and forbidden transition probabilities, and Iron Project
R-matrix collisional data, we present a number of [Fe VI] line ratios
applicable to spectral diagnostics of photoionized H II regions. It is shown
that continuum fluorescent excitation needs to be considered in CR models in
order to interpret the observed line ratios of optical [Fe VI] lines in
planetary nebulae NGC 6741, IC 351, and NGC 7662. The analysis leads to
parametrization of line ratios as function of, and as constraints on, the
electron density and temperature, as well as the effective radiation
temperature of the central source and a geometrical dilution factor. The
spectral diagnostics may also help ascertain observational uncertainties. The
method may be generally applicable to other objects with intensive background
radiation fields, such as novae and active galactic nuclei. The extensive new
Iron Project radiative and collisional calculations enable a consistent
analysis of many line ratios for the complex iron ions.",0003410v1
2000-06-13,Hot HB stars in globular clusters - Physical parameters and consequences for theory. V. Radiative levitation versus helium mixing,"Atmospheric parameters (effective temperature Teff, surface gravity log g),
masses and helium abundances are derived for 42 hot horizontal branch (HB)
stars in the globular cluster NGC 6752. For 19 stars we derive magnesium and
iron abundances as well and find that iron is enriched by a factor of 50 on
average with respect to the cluster abundance whereas the magnesium abundances
are consistent with the cluster abundance. Radiation pressure may levitate
heavy elements like iron to the surface of the star in a diffusive process.
Taking into account the enrichment of heavy elements in our spectroscopic
analyses we find that high iron abundances can explain part, but not all, of
the problem of anomalously low gravities along the blue HB. The blue HB stars
cooler than about 15,100 K and the sdB stars (Teff > 20,000 K) agree well with
canonical theory when analysed with metal-rich ([M/H] = +0.5) model
atmospheres, but the stars in between these two groups remain offset towards
lower gravities and masses. Deep Mixing in the red giant progenitor phase is
discussed as another mechanism that may influence the position of the blue HB
stars in the (Teff, log g)-plane but not their masses.",0006182v2
2000-12-13,XMM-Newton observation of the Tycho Supernova Remnant,"We present the observation of the Tycho supernova remnant obtained with the
EPIC and RGS instruments onboard the XMM-Newton satellite. We compare images
and azimuthally averaged radial profiles in emission lines from different
elements (silicon and iron) and different transition lines of iron (Fe L and Fe
K). While the Fe XVII L line and Si XIII K line images are globally spatially
coincident, the Fe K emission clearly peaks at a smaller radius, indicating a
higher temperature toward the reverse shock. This is qualitatively the profile
expected when the reverse shock, after travelling through the outer power-law
density profile, has entered the central plateau of the ejecta. The high energy
continuum map has an overall smooth distribution, with a similar extent to the
radio emission. Its radial profile peaks further out than the lines emission.
Brighter and harder continuum regions are observed with a rough bipolar
symmetry in the eastern and western edges. The spectral analysis of the
southeastern knots supports spatial variations of the relative abundance of
silicon and iron, which implies an incomplete mixing of the silicon and iron
layers.",0012288v1
2001-01-25,Evolution of Iron K$_α$ Line Emission in the Black Hole Candidate GX 339-4,"GX 339-4 was regularly monitored with RXTE during a period (in 1999) when its
X-ray flux decreased significantly (from 4.2$\times 10^{-10}$ erg cm$^{-2}
s^{-1}$ to 7.6$\times 10^{-12}$ erg cm$^{-2}$s$^{-1}$ in the 3--20 keV band),
as the source settled into the ``off state''. Our spectral analysis revealed
the presence of a prominent iron K$_{\alpha}$ line in the observed spectrum of
the source for all observations. The line shows an interesting evolution: it is
centered at $\sim$6.4 keV when the measured flux is above 5$\times 10^{-11}$
erg cm$^{-2} s^{-1}$, but is shifted to $\sim$6.7 keV at lower fluxes. The
equivalent width of the line appears to increase significantly toward lower
fluxes, although it is likely to be sensitive to calibration uncertainties.
While the fluorescent emission of neutral or mildly ionized iron atoms in the
accretion disk can perhaps account for the 6.4 keV line, as is often invoked
for black hole candidates, it seems difficult to understand the 6.7 keV line
with this mechanism, because the disk should be less ionized at lower fluxes
(unless its density changes drastically). On the other hand, the 6.7 keV line
might be due to recombination cascade of hydrogen or helium like iron ions in
an optically thin, highly ionized plasma. We discuss the results in the context
of proposed accretion models.",0101459v1
2001-04-03,On the absorption feature in the prompt X-ray spectrum of GRB 990705,"The absorption feature detected in the prompt X-ray emission of GRB 990705
bears important consequences. We investigate different production mechanisms
and we conclude that the absorbing material cannot be very close to the burster
and is likely to be moderately clumped. These properties challenge any model in
which the burst explodes in coincidence with the core-collapse of a massive
rotating star. We show that the straightforward interpretation of the
absorption feature as a photoionization K edge of neutral iron faces a severe
problem in that it requires a huge amount of iron in the close vicinity of the
burster. We then discuss an alternative scenario, in which iron ions are kept
in a high ionization state by the burst flux, and the absorption feature is
produced by resonant scattering from hydrogen-like iron, broadened by a range
outflow velocities. In this case the physical conditions and geometry of the
absorbing material are fully consistent with the presence of a young supernova
remnant surrounding the burst site at a radius R ~ 10^{16} cm. We finally
discuss how this remnant might affect the generation of afterglows with a
standard power-law flux decay.",0104062v1
2001-06-17,Are Stars with Planets Polluted?,"We compare the metallicities of stars with radial velocity planets to the
metallicity of a sample of field dwarfs. We confirm recent work indicating that
the stars-with-planet sample as a whole is iron rich. However, the lowest mass
stars tend to be iron poor, with several having [Fe/H]<-0.2, demonstrating that
high metallicity is not required for the formation of short period Jupiter-mass
planets. We show that the average [Fe/H] increases with increasing stellar mass
(for masses below 1.25 solar masses) in both samples, but that the increase is
much more rapid in the stars-with-planet sample. The variation of metallicity
with stellar age also differs between the two samples. We examine possible
selection effects related to variations in the sensitivity of radial velocity
surveys with stellar mass and metallicity, and identify a color cutoff
(B-V>0.48) that contributes to but does not explain the mass-metallicity trend
in the stars-with-planets sample. We use Monte Carlo models to show that adding
an average of 6.5 Earth masses of iron to each star can explain both the
mass-metallicity and the age-metallicity relations of the stars-with-planets
sample. However, for at least one star, HD 38529, there is good evidence that
the bulk metallicity is high. We conclude that the observed metallicities and
metallicity trends are the result of the interaction of three effects;
accretion of about 6 Earth masses of iron rich material, selection effects, and
in some cases, high intrinsic metallicity.",0106294v1
2002-01-16,An X-ray view of the active nucleus in NGC 4258,"XMM-Newton observed the Seyfert 1.9 galaxy NGC 4258 in December 2000. At
energies above 2 keV a hard nuclear point source is resolved that can be fitted
by a highly absorbed power-law spectrum (NH = (8.0+-0.4)x10^22 cm^-2, photon
index 1.64+-0.08) with an unabsorbed luminosity of 7.5x10^40erg/s in the 2-10
keV band. No narrow iron Kalpha emission line is detected (90% upper limit of
equivalent width EW ~40 eV). The nuclear emission flux was observed to remain
constant over the observation. A short archival Chandra observation taken in
March 2000 further constrains the hard emission to a point source coincident
with the radio nucleus. A point source ~3"" southwest of the nucleus does not
contribute significantly. Spectral results of the Chandra nuclear source are
comparable (within the limited statistics) to the XMM-Newton parameters. The
comparison of our iron line upper limit with reported detections indicates
variability of the line EW. These results can be explained by the relatively
low nuclear absorption of NGC 4258 (which is in the range expected for its
intermediate Seyfert type) and some variability of the absorbing material.
Reflection components as proposed to explain the large iron line EW of highly
absorbed Seyfert 2 galaxies and/or variations in the accretion disk are however
imposed by the time variability of the iron line flux.",0201267v1
2003-01-13,Spectral variations of the X-ray binary pulsar LMC X-4 during its long period intensity variation and a comparison with Her X-1,"We present spectral variations of the binary X-ray pulsar LMC X-4 using the
RXTE/PCA observations at different phases of its 30.5 day long super-orbital
period. Only out of eclipse data were used for this study. During the high
state of the super-orbital period of LMC X-4, the spectrum is well described by
a high energy cut-off power-law with a photon index in the range of 0.7-1.0 and
an iron emission line. In the low state, the spectrum is found to be flatter
with power-law photon index in the range 0.5-0.7. A direct correlation is
detected between the continuum flux in 7-25 keV energy band and the iron
emission line flux. The equivalent width of the iron emission line is found to
be highly variable during low intensity state, whereas it remains almost
constant during the high intensity state of the super-orbital period. It is
observed that the spectral variations in LMC X-4 are similar to those of Her
X-1 (using RXTE/PCA data). These results suggest that the geometry of the
region where the iron line is produced and its visibility with respect to the
phase of the super-orbital period is similar in LMC X-4 and Her X-1. A
remarkable difference between these two systems is a highly variable absorption
column density with phase of the super-orbital period that is observed in Her
X-1 but not in LMC X-4.",0301208v1
2003-02-13,The variability of accretion onto Schwarzschild black holes from turbulent magnetized discs,"We use global magnetohydrodynamic simulations, in a pseudo-Newtonian
potential, to investigate the temporal variability of accretion discs around
Schwarzschild black holes. We use the vertically-averaged magnetic stress in
the simulated disc as a proxy for the rest-frame dissipation, and compute the
observed emission by folding this through the transfer function describing the
relativistic beaming, light bending and time delays near a non-rotating black
hole. The temporal power spectrum of the predicted emission from individual
annuli in the disc is described by a broken power law, with indices of -3.5 at
high frequency and 0 to -1 at low frequency. Integrated over the disc, the
power spectrum is approximated by a single power law with an index of -2.
Increasing inclination boosts the relative power at frequencies of around 0.3
times the orbital frequency at the marginally stable orbit, but no evidence is
found for sharp quasi-periodic oscillations in the lightcurve. Assuming that
fluorescent iron line emission locally tracks the continuum flux, we compute
simulated broad iron line profiles. We find that relativistic beaming of the
non-axisymmetric emission profile, induced by turbulence, produces
high-amplitude variability in the iron line profile. We show that this
substructure within the broad iron line profile can survive averaging over a
number of orbital periods, and discuss the origin of the anomalous X-ray
spectral features, recently reported by Turner et al. (2002) for the Seyfert
galaxy NGC3516, in the context of turbulent disc models.",0302271v1
2003-03-06,Iron K alpha line profiles and the inner boundary condition of accretion flows,"Recent X-ray observations have shown evidence for exceptionally broad and
skewed iron K alpha emission lines from several accreting black hole systems.
The lines are assumed to be due to fluorescence of the accretion disk
illuminated by a surrounding corona and require a steep emissivity profile
increasing in to the innermost radius. This appears to question both standard
accretion disc theory and the zero torque assumption for the inner boundary
condition, both of which predict a much less extreme profile. Instead it argues
that a torque may be present due to magnetic coupling with matter in the
plunging region or even to the spinning black hole itself. Discussion so far
has centered on the torque acting on the disc. However the crucial determinant
of the iron line profile is the radial variation of the power radiated in the
corona. Here we study the effects of different inner boundary conditions on the
coronal emissivity and on the profiles of the observable Fe K alpha lines. We
argue that in the extreme case where a prominent highly redshifted component of
the iron line is detected, requiring a steep emissivity profile in the
innermost part and a flatter one outside, energy from the gas plunging into the
black hole is being fed directly to the corona.",0303143v1
2003-05-13,Iron abundance in the ICM at high redshift,"We present the analysis of the X-ray spectra of 18 distant clusters of
galaxies with redshift 0.3 < z < 1.3. Most of them were observed with the
Chandra satellite in long exposures ranging from 36 ks to 180 ks. For two of
the z>1 clusters we also use deep XMM-Newton observations. Overall, these
clusters probe the temperature range 3<kT<8 keV. Our analysis is aimed at
deriving the iron abundance in the Intra Cluster Medium (ICM) out to the
highest redshifts probed to date. Using a combined spectral fit of cluster
subsamples in different redshift bins, we investigate the evolution of the mean
ICM metallicity with cosmic epoch. We find that the mean Fe abundance at <z>
=0.8 is Z =0.25 +0.04 -0.06 Zo, consistent with the local canonical metallicity
value, Z ~0.3 Zo, within 1sigma confidence level. Medium and low temperature
clusters (kT <5 keV) tend to have larger iron abundances than hot clusters. At
redshift <z>~1.2 (4 clusters at z>1) we obtain a statistically significant
detection of the Fe-K line only in one cluster (Z>0.10 Zo at the 90% c.l.).
Combining all the current data set from Chandra and XMM at z>1, the average
metallicity is measured to be <Z> = 0.21 +0.10 -0.05 Zo (1sigma error), thus
suggesting no evolution of the mean iron abundance out to z~1.2.",0305223v1
2003-08-15,The impact of pollution on stellar evolution models,"An approach is introduced for incorporating the concept of stellar pollution
into stellar evolution models. The approach involves enhancing the metal
content of the surface layers of stellar models. In addition, the surface
layers of stars in the mass range of 0.5-2.0 Solar masses are mixed to an
artificial depth motivated by observations of lithium abundance. The behavior
of polluted stellar evolution models is explored assuming the pollution occurs
after the star has left the fully convective pre main sequence phase. Stellar
models polluted with a few Earth masses of iron are significantly hotter than
stars of the same mass with an equivalent bulk metallicity. Polluted stellar
evolution models can successfully reproduce the metal-rich, parent star tau
Bootis and suggest a slightly lower mass than standard evolution models.
Finally, the possibility that stars in the Hyades open cluster have accreted an
average of 0.5 Earth masses of iron is explored. The results indicate that it
is not possible to rule out stellar pollution on this scale from the scatter of
Hyades stars on a color-magnitude diagram. The small amount of scatter in the
observational data set does rule out pollution on the order of 1.5 Earth masses
of iron. Pollution effects at the low level of 0.5 Earth masses of iron do not
produce substantial changes in a star's evolution.",0308267v1
2003-09-23,Does the Iron K$_α$ Line of Active Galactic Nuclei Arise from the Cerenkov Line-like Radiation?,"When thermal relativistic electrons with isotropic distribution of velocities
move in a gas region, or impinge upon the surface of a cloud that consists of a
dense gas or doped dusts, the Cerenkov effect produces peculiar atomic or ionic
emission lines -- the Cerenkov line-like radiation. This newly recognized
emission mechanism may find wide applications in high-energy astrophysics. In
this paper, we tentatively adopt this new line emission mechanism to discuss
the origin of iron K$_{\alpha}$ feature of AGNs. Motivation of this research is
to attempt a solution to a problem encountered by the ``disk-fluorescence
line'' model, i.e. the lack of temporal response of the observed iron
K$_{\alpha}$ line flux to the changes of the X-ray continuum flux. If the
Cerenkov line emission is indeed responsible significantly for the iron
K$_{\alpha}$ feature, the conventional scenario around the central supermassive
black holes of AGNs would need to be modified to accommodate more energetic,
more violent and much denser environments than previously thought.",0309604v1
2003-09-29,The Type-Ia Supernova Rate in z < 1 Galaxy Clusters: Implications for Progenitors and the Source of Cluster Iron,"The iron mass in galaxy clusters is about 6 times larger than could have been
produced by core-collapse supernovae (SNe), assuming the stars in the cluster
formed with a standard initial mass function (IMF). SNe Ia have been proposed
as the alternative dominant iron source. Different SN Ia progenitor models
predict different ``delay functions'' between the formation of a stellar
population and the explosion of some of its members as SNe Ia. We use our
previous measurements of the cluster SN Ia rate at high redshift to constrain
SN Ia progenitor models and the star-formation epoch in clusters. The low
observed rate of cluster SNe Ia at z ~ 0 - 1 means that, if SNe Ia produced the
observed amount of iron, they must have exploded at even higher z. This puts a
>95% upper limit on the mean SN Ia delay time of tau <2 Gyr (<5 Gyr) if the
stars in clusters formed at redshift z<2 (z<3), assuming Ho=70 km/s/Mpc. In a
companion paper (astro-ph/0309796), we show that, for some current versions of
cosmic (field) star formation history (SFH), observations of field SNe Ia place
a lower bound on the delay time, tau>3 Gyr. If these SFHs are confirmed, the
entire range of tau will be ruled out. Cluster enrichment by core-collapse SNe
from a top-heavy IMF will then remain the only viable option.",0309797v1
2004-02-25,Oxygen Overabundance in the Extremely Iron-Poor Star CS29498-043,"An abundance analysis for the carbon-enhanced, extremely iron-poor ([Fe/H]
-3.5) star CS29498-043 has been obtained using new high-resolution, high
signal-to-noise spectra from the Subaru Telescope. The [O I] forbidden line at
6300A and the O I triplet feature at 7771-7776A are both clearly detected. The
overabundance of oxygen is significant ([O/Fe]>2). In addition, Na, Co, and Ni
abundances have been newly measured. The abundance pattern from C to Ni of this
object is quite similar to that of CS 22949--037, another extremely metal-poor
star with large excesses of C, N, O, and the alpha-elements. The abundance
patterns of these two stars suggest the existence of supernovae progenitors
that ejected relatively little material fromtheir iron cores during the very
early era of nucleosynthesis in the Galaxy. Themetallicity in these objects,
when one includes the elements C, N, and O in the tally of total metals, is not
as low as in the most metal-poor stars, suggesting the existence of quite
different formation processes for these iron-deficient objects than pertain to
the bulk of other metal-deficient stars.",0402585v1
2004-05-11,Photoionization Modeling and the K Lines of Iron,"We calculate the efficiency of iron K line emission and iron K absorption in
photoionized models using a new set of atomic data. These data are more
comprehensive than those previously applied to the modeling of iron K lines
from photoionized gases, and allow us to systematically examine the behavior of
the properties of line emission and absorption as a function of the ionization
parameter, density and column density of model constant density clouds. We show
that, for example, the net fluorescence yield for the highly charged ions is
sensitive to the level population distribution produced by photoionization, and
these yields are generally smaller than those predicted assuming the population
is according to statistical weight. We demonstrate that the effects of the many
strongly damped resonances below the K ionization thresholds conspire to smear
the edge, thereby potentially affecting the astrophysical interpretation of
absorption features in the 7-9 keV energy band. We show that the centroid of
the ensemble of K$\alpha$ lines, the K$\beta$ energy, and the ratio of the
K$\alpha_1$ to K$\alpha_2$ components are all diagnostics of the ionization
parameter of our model slabs",0405210v1
2004-07-17,Time-dependent Circulation Flows: Iron Enrichment in Cooling Flows with Heated Return Flows,"We describe a new type of dynamical model for hot gas in galaxy groups and
clusters in which gas moves simultaneously in both radial directions.
Circulation flows are consistent with (1) the failure to observe cooling gas in
X-ray spectra, (2) multiphase gas observed near the centers of these flows and
(3) the accumulation of iron in the hot gas from Type Ia supernovae in the
central galaxy. Dense inflowing gas cools, producing a positive central
temperature gradient, as in normal cooling flows. Bubbles of hot, buoyant gas
flow outward. Circulation flows eventually cool catastrophically if the outward
flowing gas transports mass but no heat; to maintain the circulation both mass
and energy must be supplied to the inflowing gas over a large volume, extending
to the cooling radius. The rapid radial recirculation of gas produces a flat
central core in the gas iron abundance, similar to many observations. We
believe the circulation flows described here are the first gasdynamic,
long-term evolutionary models that are in good agreement with all essential
features observed in the hot gas: little or no gas cools as required by XMM
spectra, the gas temperature increases outward near the center, and the gaseous
iron abundance is about solar near the center and decreases outward.",0407367v1
2004-10-28,Hydrodynamic model atmospheres for WR stars: Self-consistent modeling of a WC star wind,"We present the first non-LTE atmosphere models for WR stars that incorporate
a self-consistent solution of the hydrodynamic equations. The models account
for iron-group line-blanketing and clumping, and compute the hydrodynamic
structure of a radiatively driven wind consistently with the non-LTE radiation
transport in the co-moving frame. We construct a self-consistent wind model
that reproduces all observed properties of an early-type WC star (WC5). We find
that the WR-type mass-loss is initiated at high optical depth by the so-called
`Hot Iron Bump' opacities (Fe IX-XVI). The acceleration of the outer wind
regions is performed by iron-group ions of lower excitation in combination with
C and O. Consequently, the wind structure shows two acceleration regions, one
close to the hydrostatic wind base in the optically thick part of the
atmosphere, and another farther out in the wind. In addition to the radiative
acceleration, the `Iron Bump' opacities are responsible for an intense heating
of deep atmospheric layers. We find that the observed narrow OVI-emissions in
the optical spectra of WC stars originate from this region. By their dependence
on the clumping factor we gain important information about the location where
the density inhomogeneities in WR-winds start to develop.",0410697v1
2005-06-13,Brief history of the metal accumulation in the intracluster medium,"We use models of the rates of Type Ia supernovae (SNe Ia) and core-collapse
supernovae, built in such a way that both are consistent with recent
observational constraints at z<1.6 and can reproduce the measured cosmic star
formation rate, to recover the history of the metals accumulation in the
intra-cluster medium. We show that these SN rates, in unit of SN number per
comoving volume and rest-frame year, provide on average a total amount of Iron
that is marginally consistent with the value measured in galaxy clusters in the
redshift range 0-1, and a relative evolution with redshift that is in agreement
with the observational constraints up to z~1.2. Moreover, we verify that the
predicted metals to Iron ratios reproduce the measurements obtained in nearby
clusters through X-ray analysis, implying that (1) about half of the Iron mass
and >75 per cent of the Nickel mass observed locally are produced by SN Ia
ejecta, (2) the SN Ia contribution to the metal budget decreases steeply with
redshift and by z~1 is already less than half of the local amount and (3) a
transition in the abundance ratios relative to the Iron is present between
redshifts ~0.5 and 1.4, with core-collapse SN products becoming dominant at
higher redshifts.",0506272v2
2006-10-03,The iron K feature in Narrow Line Seyfert 1's: evidence for a P Cygni profile?,"Narrow Line Seyfert 1 galaxies are generally accreting at high fractions of
the Eddington limit. They can show complex X-ray spectra, with a strong `soft
excess' below 2 keV and a sharp drop at ~7 keV. There is strong evidence
linking the soft excess to either reflection or absorption from relativistic,
partially ionized material close to the black hole. The reflection models can
also simultaneously produce the 7 keV feature from fluorescent iron Ka line
emission from the disc. Here we show that absorption can also produce a sharp
feature at 7 keV from the P Cygni profile which results from
absorption/scattering/emission of He- and H-like iron Ka resonance lines in the
wind. We demonstrate this explicitly by fitting the iron feature seen in
XMM-Newton data from 1H 0707-495 to a P Cygni profile. The resulting column and
ionization required to produce this feature are probably larger than those
needed to produce the soft excess. Nonetheless, the absorbing material could
still be a single structure with stratified ionization such as that produced by
the ionization instability.",0610078v1
2006-11-21,The origin of the strong soft excess and puzzling iron line complex in Mkn 841,"Mkn 841 has been observed during 3 different periods (January 2001, January
2005 and July 2005) by XMM-Newton for a total cumulated exposure time of ~108
ks. We present in this paper a broad band spectral analysis of the complete
EPIC-pn data sets. These observations confirm the presence of the strong soft
excess and complex iron line profile known to be present in this source since a
long time. They also reveal their extreme and puzzling spectral and temporal
behaviors. Indeed, the 0.5-2 keV soft X-ray flux decreases by a factor 3
between 2001 and 2005 and the line shape appears to be a mixed of broad and
narrow components, both variable but on differen timescales. The broad-band
0.5-10 keV spectra are well described by a model including a primary power law
continuum, a blurred photoionized reflection and a narrow iron line, the
blurred reflection fitting self-consistently the soft excess and the broad line
component. The origin and nature of the narrow component is unclear.",0611665v1
2007-03-16,On the Iwasawa-Taniguchi effect of radio-quiet AGN,"The existence of an anti-correlation between the Equivalent Width (EW) of the
neutral narrow core of the iron Kalpha emission line and the 2-10 keV
luminosity (the so-called `X-ray Baldwin' or `Iwasawa-Taniguchi' effect) has
been debated in the last years. We aim at testing this claim on the largest
catalogue of radio quiet AGN high-quality X-ray spectra ever published. The
final sample comprises 157 objects. We search for a relation of the iron line
EW not only with the X-ray luminosity, but also with the Black Hole mass, the
Eddington ratio and the cosmological distance. The data presented here were
analyzed homogeneously, all spectra are from the same instrument and with high
Signal-to-Noise Ratio. A linear censored fit on the EW versus 2-10 keV
luminosity is highly significant and yields $\log(EW_{Fe}) = (1.73\pm0.03) +
(-0.17\pm0.03) \log(L_{X,44})$, where $EW_{Fe}$ is the EW of the neutral iron
Kalpha line in eV and $L_{x,44}$ is the 2-10 keV X-ray luminosity in units of
$10^{44}$ erg s$^{-1}$. The anti-correlation with the Eddington ratio is also
very significant, while no dependence of the iron EW on the BH mass is
apparent.",0703433v1
2005-12-26,Anisotropic Correlations in Epitaxial Iron Silicide: Contribution of Surface and Bulk States,Scanning tunneling microscopy,0512643v2
1999-03-22,Effect on a Hadron Shower Leakage on the Energy Response and Resolution of Hadron TILE Calorimeter,"The hadronic shower longitudinal and lateral leakages and its effect on the
pion response and energy resolution of iron-scintillator barrel hadron
prototype calorimeter with longitudinal tile configuration with a thickness of
9.4 nuclear interaction lengths have been investigated. The results are based
on 100 GeV pion beam data at incidence angle $\Theta = 10^o$ at impact point Z
in the range from - 36 to 20 cm which were obtained during test beam period in
May 1995 with setup equipped scintillator detector planes placed behind and
back of the calorimeter. The fraction of the energy of 100 GeV pions at $\Theta
= 10^o$ leaking out at the back of this calorimeter amounts to 1.8 % and agrees
with the one for a conventional iron-scintillator calorimeter. Unexpected
behaviour of the energy resolution as a function of leakage is observed: 6 %
lateral leakage lead to 18 % improving of energy resolution in compare with the
showers without leakage. The measured values of longitudinal punchthrough
probability $(18 \pm 1) %$ and $(20 \pm 1) %$ for two different hit definitions
of leaking events agree with the earlier measurement for our calorimeter and
with the one for a conventional iron-scintillator calorimeter with the same
nuclear interaction length thickness respectively. Due to more soft cut for hit
definition in the leakage detectors the measured value of longitudinal
punchthrough probability more corresponds to the calculated iron equivalent
length $L_{Fe} = 158 cm$.",9903051v1
2007-10-15,Transition from galactic to extragalactic cosmic rays,"The transition from galactic to extragalactic cosmic rays is discussed. One
of critical indications for transition is given by the Standard Model of
Galactic cosmic rays, according to which the maximum energy of acceleration for
iron nuclei is of order of $E_{\rm Fe}^{\rm max} \approx 1\times 10^{17}$ eV.
At $E > E_{\rm Fe}^{\rm max}$ the spectrum is predicted to be very steep and
thus the Standard Model favours the transition at energy not much higher than
$E_{\rm Fe}^{\rm max}$. As observations are concerned there are two signatures
of transition: change of energy spectra and elongation rate (depth of shower
maximum in the atmosphere $X_{\rm max}$ as function of energy). Three models of
transition are discussed: dip-based model, mixed composition model and ankle
model. In the latter model the transition occurs at the observed spectral
feature, ankle, which starts at $E_a \approx 1\times 10^{19}$ eV and is
characterised by change of mass compostion from galactic iron to extragalactic
protons. In the dip model the transition occures at the second knee observed at
energy $(4 -8)\times 10^{17}$ eV and is characterised by change of mass
composition from galactic iron to extragalactic protons. The mixed composition
model describes transition at $E \sim 3\times 10^{18}$ eV with mass composition
changing from galactic iron to extragactic mixed composition of different
nuclei. These models are confronted with observational data on spectra and
elongation rates from different experiments, including Auger.",0710.2750v2
2008-01-10,On why the Iron K-shell absorption in AGN is not a signature of the local Warm/Hot Intergalactic Medium,"We present a comparison between the 2001 XMM-Newton and 2005 Suzaku
observations of the quasar, PG1211+143 at z=0.0809. Variability is observed in
the 7 keV iron K-shell absorption line (at 7.6 keV in the quasar frame), which
is significantly weaker in 2005 than during the 2001 XMM-Newton observation.
From a recombination timescale of <4 years, this implies an absorber density
n>0.004 particles/cm3, while the absorber column is 5e22<N_H <1 1e24
particles/cm2. Thus the sizescale of the absorber is too compact (pc scale) and
the surface brightness of the dense gas too high (by 9-10 orders of magnitude)
to arise from local hot gas, such as the local bubble, group or Warm/Hot
Intergalactic Medium (WHIM), as suggested by McKernan et al. (2004, 2005).
Instead the iron K-shell absorption must be associated with an AGN outflow with
mildly relativistic velocities. Finally we show that the the association of the
absorption in PG1211+143 with local hot gas is simply a coincidence, the
comparison between the recession and iron K absorber outflow velocities in
other AGN does not reveal a one to one kinematic correlation.",0801.1587v1
2008-02-01,The iron abundance of the Magellanic Bridge,"High-resolution HST ultra-violet spectra for five B-type stars in the
Magellanic Bridge and in the Large and Small Magellanic Clouds have been
analysed to estimate their iron abundances. Those for the Clouds are lower than
estimates obtained from late-type stars or the optical lines in B-type stars by
approximately 0.5 dex. This may be due to systematic errors possibly arising
from non-LTE effects or from errors in the atomic data as similar low Fe
abundances having previously been reported from the analysis of the
ultra-violet spectra of Galactic early-type stars. The iron abundance estimates
for all three Bridge targets appear to be significantly lower than those found
for the SMC and LMC by approximately -0.5 dex and -0.8 dex respectively and
these differential results should not be affected by any systematic errors
present in the absolute abundance estimates. These differential iron abundance
estimates are consistent with the underabundances for C, N, O, Mg and Si of
approximately -1.1 dex relative to our Galaxy previously found in our Bridge
targets. The implications of these very low metal abundances for the Magellanic
Bridge are discussed in terms of metal deficient material being stripped from
the SMC.",0802.0132v1
2008-07-28,Nature of Magnetic Interactions and Inelastic Neutron Scattering as a Probe of Magnetic Excitations in Iron-Pnictide Superconductors,"This submission has been withdrawn by the arXiv admins because it is an
abstract only, which is against arXiv policy.",0807.4351v2
2008-08-29,What will be the maximum Tc in the iron-based superconductors?,"Using the newly developed real space vortex-lattice based theory of
superconductivity, we study the maximum superconducting transition temperature
(T_{c}^{\max}) in the iron-based superconductors. We find that all the reported
FeAs superconductors can be divided into two basic classes (c/a=3 and c/a=5/2)
depending on the lattice constants, where a is the Fe-Fe distance in the
xy-plane and c is the Fe-Fe layer distance along the z-axis. Our results
suggest that the former class has a maximum T_{c}^{\max}<60K, while the latter
class has a lower T_{c}^{\max}\leq 40K. Our investigations further indicate
that, in order to enhance T_{c}^{\max} in this family of compounds, new class
of superconductors with a larger ratio of c/a should be synthesized. It is
likely that their T_{c}^{\max} values could be raised into the liquid nitrogen
range (77K) and 100K, supposing the new analogues with c/a=5 (approximately
c>13A, if a=2.750A) and c/a=11 (c>31A) can be experimentally achieved,
respectively. For the new FeSe series, our mechanism predicts that their
T_{c}^{\max} is impossible to exceed 30 K due to a relatively shorter c-axis
lattice constant (c/a=2). Finally, based on the new experimental results
(arXiv:0811.0094 and arXiv:0811.2205), the possible ways to raise the Tc of the
iron-based superconductors into 70 K are also suggested.",0808.4093v3
2008-09-01,Spin Fluctuation Dynamics and Multiband Superconductivity in Iron Pnictides,"Multiband superconductivity, involving resonant pair scattering between
different bands, has emerged as a possible explanation of some of the main
characteristics of the recently discovered iron pnictides. A key feature of
such interband pairing mechanism is that it can generate or enhance
superconducting pairing irrespective of whether it is attractive or repulsive.
The latter case typically leads to the superconducting gap switching its sign
among different sections of the Fermi surface. In iron pnictides, the natural
scenario is that the gap changes sign between the hole and the electron Fermi
surfaces. However, the macroscopic symmetry of such an extended s'-wave state
still belongs to the general s-wave category, raising the question of how to
distinguish it from an ordinary s-wave. In such a quest, it is essential to use
experimental techniques that have a momentum space resolution and can probe
momenta of order M, the wavevector that separates the hole and the electron
Fermi surfaces in the Brillouin zone. Here we study experimental signatures in
the spin fluctuation dynamics of the fully-gapped s- and s'-wave
superconducting states, as well as those of the nodal d- and p-wave. The
coupling between spin fluctuations of the incipient nearly-nested spin
density-wave (SDW) and the Bogoliubov-deGennes quasiparticles of the
superconducting state leads to the Landau-type damping of the former. The
intrinsic structure of the superconducting gap leaves a distinctive signature
in the form of this damping, allowing it to be used to diagnose the nature of
iron-based superconductivity in neutron scattering and other experiments
sensitive to spin fluctuations in momentum space. We also discuss the
coexistence between superconductivity and SDW order.",0809.0014v1
2008-10-15,A Large Iron Isotope Effect in SmFeAsO1-xFx and Ba1-xKxFe2As2,"The recent discovery of superconductivity in oxypnictides with the critical
temperature (TC) higher than McMillan limit of 39 K (the theoretical maximum
predicted by Bardeen-Cooper-Schrieffer (BCS) theory) has generated great
excitement. Theoretical calculations indicate that the electron-phonon
interaction is not strong enough to give rise to such high transition
temperatures, while strong ferromagnetic/antiferromagnetic fluctuations have
been proposed to be responsible. However, superconductivity and magnetism in
pnictide superconductors show a strong sensitivity to the lattice, suggesting a
possibility of unconventional electron-phonon coupling. Here we report the
effect of oxygen and iron isotopic mass on Tc and the spin-density wave (SDW)
transition temperature (TSDW) in SmFeAsO1-xFx and Ba1-xKxFe2As2 systems. The
results show that oxygen isotope effect on TC and TSDW is very little, while
the iron isotope exponent alpha=-dlnTc/dlnM is about 0.35, being comparable to
0.5 for the full isotope effect. Surprisingly, the iron isotope exchange shows
the same effect on TSDW as TCc These results indicate that electron-phonon
interaction plays some role in the superconducting mechanism, but simple
electron-phonon coupling mechanism seems to be rather unlikely because a strong
magnon-phonon coupling is included. Sorting out the interplay between the
lattice and magnetic degrees of freedom is a key challenge for understanding
the mechanism of high-TC superconductivity.",0810.2694v2
2009-01-12,Electrodynamics in Iron and Steel,"In order to calculate the reflected EM fields at low amplitudes in iron and
steel, more must be understood about the nature of long wavelength excitations
in these metals. A bulk piece of iron is a very complex material with
microstructure, a split band structure, magnetic domains and crystallographic
textures that affect domain orientation. Probing iron and other bulk
ferromagnetic materials with weak reflected and transmitted inductive low
frequency fields is an easy operation to perform but the responses are
difficult to interpret because of the complexity and variety of the structures
affected by the fields. First starting with a simple single coil induction
measurement and classical EM calculation to show the error is grossly under
estimating the measured response. Extending this experiment to measuring the
transmission of the induced fields allows the extraction of three dispersion
curves which define these internal fields. One dispersion curve yielded an
exceedingly small effective mass of 1.8 10^{-39}kg (1.3 10^{-9} m_e) for those
spin waves. There is a second distinct dispersion curve more representative of
the density function of a zero momentum bound state rather than a propagating
wave. The third dispersion curve describes a magneto-elastic coupling to a very
long wave length propagating mode. These experiments taken together display the
characteristics of a high temperature Bose-Einstein like condensation that can
be initiated by pumping two different states. A weak time dependent field
drives the formation of coupled J=0 spin wave pairs with the reduced effective
mass reflecting the increased size of the coherent state. These field can
dominate induction measurements well past the Curie temperature.",0901.1631v2
2009-03-16,Spin Waves and Magnetic Exchange Interactions in CaFe2As2,"Antiferromagnetism is relevant to high temperature (high-Tc)
superconductivity because copper oxide and iron arsenide high-Tc
superconductors arise from electron- or hole-doping of their antiferromagnetic
(AF) ordered parent compounds. There are two broad classes of explanation for
the phenomenon of antiferromagnetism: in the local moment picture, appropriate
for the insulating copper oxides, AF interactions are well described by a
Heisenberg Hamiltonian; while in the itinerant model, suitable for metallic
chromium, AF order arises from quasiparticle excitations of a nested Fermi
surface. There has been contradictory evidence regarding the microscopic origin
of the AF order in iron arsenide materials, with some favoring a localized
picture while others supporting an itinerant point of view. More importantly,
there has not even been agreement about the simplest effective ground state
Hamiltonian necessary to describe the AF order. Here we report inelastic
neutron scattering mapping of spin-wave excitations in CaFe2As2, a parent
compound of the iron arsenide family of superconductors. We find that the spin
waves in the entire Brillouin zone can be described by an effective
three-dimensional local moment Heisenberg Hamiltonian, but the large in-plane
anisotropy cannot. Therefore, magnetism in the parent compounds of iron
arsenide superconductors is neither purely local nor purely itinerant; rather
it is a complicated mix of the two.",0903.2686v1
2009-04-02,The layered iron arsenides Sr2CrO3FeAs and Ba2ScO3FeAs,"Polycrystalline samples of the layered iron arsenides Sr2CrO3FeAs and
Ba2ScO3FeAs were synthesized by high temperature solid state reactions and
their crystal structures determined by the X-ray powder diffraction. Their
structures are tetragonal (P4/nmm; Sr2CrO3FeAs: a = 391.12(1) pm, c =
1579.05(3) pm; Ba2ScO3FeAs: a = 412.66(5) pm, c = 1680.0(2) pm, Z = 2) and
isotypic to Sr2ScO3CuS. Iron arsenide layers are sandwiched between
perowskite-like oxide blocks and separated by ~1600 pm, which is much larger
compared to the 1111 iron arsenide superconductors. The bond length and angles
within the FeAs layers are adapted to the space requirements of the oxide
blocks. Measurements of the magnetic susceptibility and electrical resistivity
show no hint for a SDW-like anomaly in both compounds. Sr2CrO3FeAs shows
Curie-Weiss paramagnetism above 160 K with an effective magnetic moment of
3.83(3) muB in good agreement with the theoretical value of 3.87 muB for Cr3+.
Antiferromagnetic ordering was detected below TN ~ 31 K. 57Fe Moessbauer
spectra of Sr2CrO3FeAs show a single signal that broadens below the magnetic
ordering temperature due to a small transferred hyperfine field induced by the
magnetic ordering of the chromium atoms. 57Fe-Moessbauer spectra of Ba2ScO3FeAs
show single signals at 298, 77, and 4.2 K which are only subject to weak
quadrupole splitting.",0904.0479v2
2009-05-21,Integer and half-integer flux-quantum transitions in a niobium/iron-pnictide loop,"The recent discovery of iron-based superconductors challenges the existing
paradigm of high-temperature superconductivity. Owing to their unusual
multi-orbital band structure, magnetism, and electron correlation, theories
propose a unique sign reversed s-wave pairing state, with the order parameter
changing sign between the electron and hole Fermi pockets. However, because of
the complex Fermi surface topology and material related issues, the predicted
sign reversal remains unconfirmed. Here we report a novel phase-sensitive
technique for probing unconventional pairing symmetry in the polycrystalline
iron-pnictides. Through the observation of both integer and half-integer
flux-quantum transitions in composite niobium/iron-pnictide loops, we provide
the first phase-sensitive evidence of the sign change of the order parameter in
NdFeAsO0.88F0.12, lending strong support for microscopic models predicting
unconventional s-wave pairing symmetry. These findings have important
implications on the mechanism of pnictide superconductivity, and lay the
groundwork for future studies of new physics arising from the exotic order in
the FeAs-based superconductors.",0905.3571v2
2009-05-25,A double stellar generation in the Globular Cluster NGC6656 (M 22). Two stellar groups with different iron and s-process element abundance,"AIMS. In this paper we present the chemical abundance analysis from high
resolution UVES spectra of seventeen bright giant stars of the Globular Cluster
M~22. RESULTS. We obtained an average iron abundance of [Fe/H]=-1.76\pm0.02
(internal errors only) and an \alpha enhancement of 0.36\pm0.04 (internal
errors only). Na and O, and Al and O follow the well known anti-correlation
found in many other GCs. We identified two groups of stars with significantly
different abundances of the s-process elements Y, Zr and Ba. The relative
numbers of the two group members are very similar to the ratio of the stars in
the two SGBs of M22 recently found by Piotto (2009). Y and Ba abundances do not
correlate with Na, O and Al. The s-element rich stars are also richer in iron
and have higher Ca abundances. The results from high resolution spectra have
been further confirmed by lower resolution GIRAFFE spectra of fourteen
additional M22 stars. GIRAFFE spectra show also that the Eu -- a pure r-process
element -- abundance is not related to the iron content. We discuss the
chemical abundance pattern of M22 stars in the context of the multiple stellar
populations in GC scenario.",0905.4058v1
2009-06-29,A novel wear-resistant magnetic thin film material based on a $Ti_{1-x}Fe_xC_{1-y}$ nanocomposite alloy,"In this study we report on the film growth and characterization of thin
(approximately 50 nm thick) Ti-Fe-C films deposited on amorphous quartz. The
experimental studies have been complemented by first principles density
functional theory (DFT) calculations. Upon annealing of as-prepared films, the
composition of the metastable Ti-Fe-C film changes. An iron-rich phase is first
formed close to the film surface, but with increasing annealing time this phase
is gradually displaced toward the film-substrate interface where its position
stabilizes. Both the magnetic ordering temperature and the saturation
magnetization changes significantly upon annealing. The DFT calculations show
that the critical temperature and the magnetic moment both increase with
increasing Fe and C-vacancy concentration. The formation of the metastable
iron-rich Ti-Fe-C compound is reflected in the strong increase of the magnetic
ordering temperature. Eventually, after enough annealing time ($\geq 10$
minutes), nano-crystalline $\alpha$-Fe starts to precipitate and the amount and
size of these precipitates can be controlled by the annealing procedure; after
20 minutes of annealing, the experimental results indicate a nano-crystalline
iron-film embedded in a wear resistant TiC compound. This conclusion is further
supported by transmission electron microscopy studies on epitaxial Ti-Fe-C
films deposited on single crystalline MgO substrates where, upon annealing, an
iron film embedded in TiC is formed. Our results suggest that annealing of
metastable Ti-Fe-C films can be used as an efficient way of creating a
wear-resistant magnetic thin film material.",0906.5386v1
2009-09-02,A homogeneous spectroscopic analysis of host stars of transiting planets,"The analysis of transiting extra-solar planets provides an enormous amount of
information about the formation and evolution of planetary systems. A precise
knowledge of the host stars is necessary to derive the planetary properties
accurately. The properties of the host stars, especially their chemical
composition, are also of interest in their own right. Information about planet
formation is inferred by, among others, correlations between different
parameters such as the orbital period and the metallicity of the host stars.
The stellar properties studied should be derived as homogeneously as possible.
The present work provides new, uniformly derived parameters for 13 host stars
of transiting planets. Effective temperature, surface gravity, microturbulence
parameter, and iron abundance were derived from spectra of both high
signal-to-noise ratio and high resolution by assuming iron excitation and
ionization equilibria. For some stars, the new parameters differ from previous
determinations, which is indicative of changes in the planetary radii. A
systematic offset in the abundance scale with respect to previous assessments
is found for the TrES and HAT objects. Our abundance measurements are
remarkably robust in terms of the uncertainties in surface gravities. The iron
abundances measured in the present work are supplemented by all previous
determinations using the same analysis technique. The distribution of iron
abundance then agrees well with the known metal-rich distribution of planet
host stars. To facilitate future studies, the spectroscopic results of the
current work are supplemented by the findings for other host stars of
transiting planets, for a total dataset of 50 objects.",0909.0285v1
2009-10-20,The Distribution and Cosmic Density of Relativistic Iron Lines in Active Galactic Nuclei,"X-ray observations of several active galactic nuclei show prominent iron
K-shell fluorescence lines that are sculpted due to special and general
relativistic effects. These observations are important because they probe the
space-time geometry close to distant black holes. However, the intrinsic
distribution of Fe line strengths in the cosmos has never been determined. This
uncertainty has contributed to the controversy surrounding the relativistic
interpretation of the emission feature. Now, by making use of the latest
multi-wavelength data, we show theoretical predictions of the cosmic density of
relativistic Fe lines as a function of their equivalent width and line flux. We
are able to show unequivocally that the most common relativistic iron lines in
the universe will be produced by neutral iron fluorescence in Seyfert galaxies
and have equivalent widths < 100 eV. Thus, the handful of very intense lines
that have been discovered are just the bright end of a distribution of line
strengths. In addition to validating the current observations, the predicted
distributions can be used for planning future surveys of relativistic Fe lines.
Finally, the predicted sky density of equivalent widths indicate that the X-ray
source in AGNs can not, on average, lie on the axis of the black hole.",0910.3947v1
2010-03-09,A comparison of hard X-ray photon indices and iron \ka emission lines in X-ray luminous narrow- and broad-line Seyfert 1 galaxies,"We use publicly available XMM-Newton data to systematically compare the hard
X-ray photon indices, $\Gamma_{\rm 2-10\ keV}$ and the iron K$\alpha$ emission
lines of narrow-line (NL) and broad-line Seyfert 1 (BLS1) galaxies. We compile
a flux-limited ($f_{\rm 2-10\ keV} \geq 1 \times 10^{-12}$ erg s$^{-1}$
cm$^{-2}$) sample including 114 radio-quiet objects, with the 2-10 keV
luminosity ranging from 10$^{41}$ to 10$^{45}$ erg s$^{-1}$. Our main results
are: 1) NLS1s and BLS1s show similar luminosity distributions; 2) The weighted
mean of $\Gamma_{\rm 2-10\ keV}$ of NLS1s, BLS1s and the total sample is
$2.04\pm0.04$, $1.74\pm0.02$, $1.84\pm0.02$, respectively; a significant
anti-correlation between \ga and FWHMH$\beta$ suggests that $\Gamma_{\rm 2-10\
keV} > 2.0$ may be taken to indicate X-ray luminous NLS1 type; 3) The 6.4 keV
narrow iron K$\alpha$ lines from NLS1s are generally weaker than that from
BLS1s; this would indicate a smaller covering factor of the dusty tori in
NLS1s, if the line emission originates from the inner boundary region of the
dusty torus in an AGN; 4) all the broadened iron K$\alpha$ lines with intrinsic
width $\sigma>0.5$ keV correspond to FWHM\hb $\leq 4000 ~\kms$.",1003.1772v2
2010-04-08,The final verdict by XMM-Newton: the X-ray obscured Seyfert galaxy NGC5506 has a broad Fe K-alpha line,"We present the first unambiguous evidence of a broad (Gaussian width ~330 eV)
component of the iron K-alpha fluorescent emission line in the X-ray obscured
Narrow Line Seyfert 1 Galaxy NGC5506. This is the main results of a
spectroscopic monitoring campaign on this source performed with the XMM-Newton
observatory between February 2001 and January 2009. The broad line lacks
extreme redwards skewness. If modelled with a relativistic component, the
profile of the line is consistent with a flat emissivity radial dependence
(alpha~1.9). The disk inclination (~40 degrees) is nominally larger then
typically observed in unobscured AGN, in agreement with most measurements of
broadened iron lines in Seyfert 2 galaxies. The quality of the data allows us
to decompose the full iron emission line complex, and to study its long-term
(timescales of weeks to years) variability pattern. The intensity of the
neutral and narrow iron K-alpha core remains constant during the monitoring
campaign. This indicates that the optically thick gas responsible for the
non-relativistic reprocessing of the primary AGN continuum in NGC5506 is
probably located in the torus rather than in the optical Broad Line Region.",1004.1442v1
2010-06-11,Mott Transition in Multi-Orbital Models for Iron Pnictides,"The bad-metal behavior of the iron pnictides has motivated a theoretical
description in terms of a proximity to Mott localization. Since the parent
compounds of the iron pnictides contain an even number of 3d-electrons per Fe,
it is important to determine whether a Mott transition robustly exists and the
nature of the possible Mott insulating phases. We address these issues in a
minimal two-orbital model and a more realistic four-orbital model for the
parent iron pnictides using a slave-spin approach. In the two-orbital model
with two electrons per Fe, we identify a transition from metal to Mott
insulator. The critical coupling, $U_c$, is greatly reduced by the Hund's
coupling. Depending on the ratio between the inter- and intra-orbital Coulomb
repulsions, the insulating state can be either a spin-Mott insulator or an
orbital-Mott insulator. In the four-orbital model with four electrons per Fe,
we find an orbitally selective metal-to-insulator transition in the case of
zero Hund's coupling; the transition to a Mott insulator in the $xz$ and $yz$
orbitals takes place at the same critical coupling as the transition to a band
insulator in the $xy$ and $x^2-y^2$ orbitals. In the presence of a finite
Hund's coupling, however, the localization transition is into a spin-Mott
state.",1006.2337v3
2010-07-29,Looking into the inner black hole accretion disc with relativistic models of iron line,"We discuss black hole spin measurements employing the relativistic iron line
profiles in the X-ray domain. We investigate the iron line band for two
representative sources -- MCG -6-30-15 (active galaxy) and GX 339-4 (X-ray
binary). We compare two models of the broad iron line, LAOR and KYRLINE. We
realise that the spin is currently determined entirely from the position of the
marginally stable orbit while the effect of the spin on the overall line shape
would be resolvable with higher resolution X-ray missions. We show that the
precision of the spin measurements depends on an unknown angular distribution
of the disc emission. We study how sensitive the spin determination is to the
assumptions about the intrinsic angular distribution of the emitted photons. We
find that the uncertainty of the directional emission distribution translates
to 20% uncertainty in the determination of the radius of marginally stable
orbit. We perform radiation transfer computations of an X-ray irradiated disc
atmosphere (NOAR code) to determine the directionality of outgoing X-rays in
the 2-10 keV energy band. Based on these computations, we find that from the
simple formulae for the directionality, the isotropic case reproduces the
simulated data with the best accuracy. The most frequently used limb-darkening
law favours higher values of spin and, in addition, a steeper radial emissivity
profile. Furthermore, we present a spectral analysis of an XMM-Newton
observation of a Seyfert 1.5 galaxy IRAS 05078+1626 being the first X-ray
spectroscopic study of this source. The lack of the significant relativistic
blurring of the reflection model component suggests the accretion disc to be
truncated at a farther radius.",1007.5196v2
2010-08-16,Pulse-phase resolved spectroscopy of continuum and reflection in SAX J1808.4-3658,"We perform phase-resolved spectroscopy of the accreting millisecond pulsar,
SAX J1808.4-3658, during the slow-decay phase of the 2002 outburst. Simple
phenomenological fits to RXTE PCA data reveal a pulsation in the iron line at
the spin frequency of the neutron star. However, fitting more complex spectral
models reveals a degeneracy between iron-line pulsations and changes in the
underlying hotspot blackbody temperature with phase. By comparing with the
variations in reflection continuum, which are much weaker than the iron line
variations, we infer that the iron-line is not pulsed. The observed spectral
variations can be explained by variations in blackbody temperature associated
with rotational Doppler shifts at the neutron star surface. By allowing
blackbody temperature to vary in this way, we also find a larger phase-shift
between the pulsations in the Comptonised and blackbody components than has
been seen in previous work. The phase-shift between the pulsation in the
blackbody temperature and normalisation is consistent with a simple model where
the Doppler shift is maximised at the limb of the neutron star, ~90 degrees
prior to maximisation of the hot-spot projected area.",1008.2708v2
2011-04-04,Interplay between magnetism and superconductivity in iron-chalcogenide superconductors: crystal growth and characterizations,"In this review, we present a summary of the results on single crystal growth
of two types of iron-chalcogenide superconductors, Fe(1+y)Te(1-x)Se(x) (11),
and A(x)Fe(2-y)Se(2) (A= K, Rb, Cs, Tl, Tl/K, Tl/Rb), using Bridgman,
zone-melting, vapor self-transport, and flux techniques. The superconducting
and magnetic properties (the latter gained mainly from neutron scattering
measurements) of these materials are reviewed to demonstrate the connection
between magnetism and superconductivity. It will be shown that for the 11
system, while static magnetic order around the reciprocal lattice position
(0.5, 0) competes with superconductivity, spin excitations centered around
(0.5, 0.5) are closely coupled to the materials' superconductivity; this is
made evident by the strong correlation between the spectral weight around (0.5,
0.5) and the superconducting volume fraction. The observation of a spin
resonance below the superconducting temperature, Tc, and the magnetic-field
dependence of the resonance, emphasize the important role spin excitations play
in the superconductivity. Generally, these results illustrate the similarities
between the iron-based and cuprate superconductors. In A(x)Fe(2-y)Se(2),
superconductivity with Tc ~ 30 K borders an antiferromagnetic insulating phase;
this is closer to the behavior observed in the cuprates but differs from that
in other iron-based superconductors.",1104.0695v2
2011-04-18,Kinetic frustration and the nature of the magnetic and paramagnetic states in iron pnictides and iron chalcogenides,"The iron pnictide and chalcogenide compounds are a subject of intensive
investigations due to their high temperature superconductivity.\cite{a-LaFeAsO}
They all share the same structure, but there is significant variation in their
physical properties, such as magnetic ordered moments, effective masses,
superconducting gaps and T$_c$. Many theoretical techniques have been applied
to individual compounds but no consistent description of the trends is
available \cite{np-review}. We carry out a comparative theoretical study of a
large number of iron-based compounds in both their magnetic and paramagnetic
states. We show that the nature of both states is well described by our method
and the trends in all the calculated physical properties such as the ordered
moments, effective masses and Fermi surfaces are in good agreement with
experiments across the compounds. The variation of these properties can be
traced to variations in the key structural parameters, rather than changes in
the screening of the Coulomb interactions. Our results provide a natural
explanation of the strongly Fermi surface dependent superconducting gaps
observed in experiments\cite{Ding}. We propose a specific optimization of the
crystal structure to look for higher T$_c$ superconductors.",1104.3454v1
2011-04-26,Electronic and magnetic phase diagram in K$_x$Fe$_{2-y}$Se$_2$ superconductors,"The correlation and competition between antiferromagnetism and
superconductivity are one of the most fundamental issues in all of high
temperature superconductors. The superconductivity in high temperature cuprate
superconductors arises from suppressing an antiferromagnetic (AFM) Mott
insulator phase by doping1 while that in iron-pnictide high temperature
superconductors arises from AFM semimetals and can coexist with AFM orders2-9.
This key difference marked in their phase diagrams has raised many intriguing
debates about whether the two materials can be placed in the same category to
understand the mechanism of superconductivity. Recently, superconductivity at
32 K has been reported in iron-chalcogenide superconductors AxFe2-ySe2 (A=K,
Rb, and Cs)10-12, which have the same structure as that of iron-pnictide
AFe2As2 (A=Ba, Sr, Ca and K)13-15. Here, we report electronic and magnetic
phase diagram of KxFe2-ySe2 system as a function of Fe valence. We find two AFM
insulating phases and reveal that the superconducting phase is sandwiched
between them, and give direct evidence that the superconductivity in AxFe2-ySe2
originates from the AFM insulating parent compounds. The two insulating phases
are characterized by two distinct superstructures caused by Fe vacancy orders
with modulation wave vectors of q1=(1/5, 3/5, 0) and q2=(1/4, 3/4, 0),
respectively. These experimental results strongly indicate that iron-based
superconductors and cuprates share a common origin and mechanism of
superconductivity.",1104.4941v1
2011-05-13,First Principles Calculations of Defects in Unstable Crystals: Austenitic Iron,"First principles calculations have given a new insight into the energies of
point defects in many different materials, information which cannot be readily
obtained from experiment. Most such calculation are done at zero Kelvin, with
the assumption that finite temperature effects on defect energies and barriers
are small. In some materials, however, the stable crystal structre of interest
is mechanically unstable at 0K. In such cases, alternate approaches are needed.
Here we present results of first principles calculations of austenitic iron
using the VASP code. We determine an appropriate reference state for collinear
magnetism to be the antiferromagnetic double-layer (AFM-d) which is both stable
and lower in energy than other possible models for the low temperature limit of
paramagnetic fcc iron. We then consider the energetics of dissolving typical
alloying impurities (Ni, Cr) in the materials, and their interaction with point
defects typical of the irradiated environment. We show that using standard
methods there is a very strong dependence of calculated defect formation
energies on the reference state chosen. Furthermore, there is a correlation
between local free volume magnetism and energetics. The effect of
substitutional Ni and Cr on defect properties is weak, rarely more than tenths
of eV, so it is unlikely that small amounts of Ni and Cr will have a
significant effect on the radiation damage in austenitic iron at high
temperatures.",1105.2663v1
2011-05-16,On the apparent absence of broad iron lines in Seyfert galaxies,"We present an analysis of XMM-Newton observations of eleven Seyfert galaxies
that appear to be missing a broad iron K alpha line. These objects represent a
challenge to the established paradigm for active galactic nuclei, where a
relatively cold accretion disc feeds the central black hole. In that paradigm,
X-ray illumination of the accretion disc should lead to continuum and
fluorescence emission from iron which is broadened and shifted by relativistic
effects close the hole. We extend the work of Nandra et al. (2007), who found
no evidence for such a component in an earlier analysis of these objects, by
testing a variety of more complex relativistic reflection models. Specifically,
we consider the possibility that the disc is highly ionised, and/or that the
the reflection is heavily blurred by strong relativistic effects in a Kerr
geometry. We find that in 8/11 of the observations with no apparent broad iron
line, the fit is significantly improved when an ionised or strongly blurred
reflector is included, and that all 11 observations allow for such a component.
The disc inclinations are found generally to be around 60 degrees, which when
combined with a steep emissivity profile results in strong relativistic
blurring of the reflection, rendering the K alpha line difficult to distinguish
from the underlying continuum. Nevertheless, relativistic reflection does
appear to be present, and the strength of the smeared reflection is similar to
that expected from a flat disc illuminated by a point source. Such blurred
reflection and the associated steep radial emissivity profiles are consistent
with the gravitational light bending of the continuum photons close to the
black hole.",1105.3065v1
2011-07-26,Interplay between magnetism and superconductivity in EuFe(2-x)Co(x)As2 studied by 57Fe and 151Eu Mössbauer spectroscopy,"The compound EuFe(2-x)Co(x)As2 was investigated by means of the 57Fe and
151Eu Moessbauer spectroscopy versus temperature (4.2 - 300 K) for x=0
(parent), x=0.34 - 0.39 (superconductor) and x=0.58 (overdoped). It was found
that spin density wave (SDW) is suppressed by Co-substitution, however it
survives in the region of superconductivity, but iron spectra exhibit some
non-magnetic component in the superconducting region. Europium orders
anti-ferromagnetically regardless of the Co concentration with the spin
re-orientation from the a-axis in the parent compound toward c-axis with the
increasing replacement of iron by cobalt. The re-orientation takes place close
to the a-c plane. Some trivalent europium appears in EuFe(2-x)Co(x)As2 versus
substitution due to the chemical pressure induced by Co-atoms and it
experiences some transferred hyperfine field from Eu2+. Iron experiences some
transferred field due to the europium ordering for substituted samples in the
SDW and non-magnetic state both, while the transferred field is undetectable in
the parent compound. Superconductivity coexists with the 4f-europium magnetic
order within the same volume. It seems that superconductivity has some
filamentary character in EuFe(2-x)Co(x)As2 and it is confined to the
non-magnetic component seen by the iron Moessbauer spectroscopy.",1107.5271v2
2011-07-26,Superconductivity up to 35 K in the iron-platinum arsenides (CaFe1-xPtxAs)10Pt4-yAs8 with layered structures,"We report the synthesis and crystal structures of three new superconducting
iron-platinum arsenides (CaFe1-xPtxAs)10Pt4-yAs8 (x = 0-0.15, y = 0-0.4). The
structures are stacking variants of FeAs- and slightly puckered Pt4-yAs8-layers
with square coordinated platinum separated by calcium-layers, respectively.
Arsenic atoms in the Pt4-yAs8-layers form (As2)4- dumbbells according to
Zintl's concept, providing charge balance in (Ca2+Fe2+As3-)10(Pt2+)3[(As2)4-]4.
Superconductivity was observed at 13-35 K. We suggest that the highest Tc above
30 K occurs in the 1048 phase with clean FeAs-layers that are indirectly
electron-doped according to (Ca2+Fe2+As3-)10(Pt2+)4[(As2)4-]4*2e-. We also
suggest that the lower critical temperatures occur in the 1038- and a-1048
phases due to Pt-doping at the Fe-site. DFT band structure calculations
indicate that the contribution of the Pt4-yAs8-layers to the Fermi surface is
small and that the Fermi energy is slightly either below or above a quasi-gap
in the Pt-states. The new platinum-iron compounds represent the first
iron-based superconductors with so far unknown structure types and can serve as
a new platform for further studies that go beyond the known systems.",1107.5320v1
2011-08-02,Weak-interaction mediated rates on iron isotopes for presupernova evolution of massive stars,"During the presupernova evolution of massive stars, the isotopes of iron,
$^{54,55,56}$Fe, are advocated to play a key role inside the cores primarily
decreasing the electron-to-baryon ratio ($Y_{e}$) mainly via electron capture
processes thereby reducing the pressure support. Electron decay and positron
capture on $^{55}$Fe, on the other hand, also has a consequential role in
increasing the lepton ratio during the silicon burning phases of massive stars.
The neutrinos and antineutrinos produced, as a result of these weak-interaction
reactions, are transparent to the stellar matter and assist in cooling the core
thereby reducing the entropy. The structure of the presupernova star is altered
both by the changes in $Y_{e}$ and the entropy of the core material. The aim of
this paper is to report the improved microscopic calculation of Gamow-Teller
(GT$_{\pm}$) strength distributions of these key isotopes of iron using the
pn-QRPA theory. The main improvement comes from the incorporation of
experimental deformation values for these nuclei. Additionally six different
weak-interaction rates, namely electron & positron capture, electron & positron
decay, and, neutrino & antineutrino cooling rates, were also calculated in
presupernova matter. The calculated electron capture and neutrino cooling rates
due to isotopes of iron are in good agreement with the large-scale shell model
(LSSM) results. The calculated beta decay rates, however, are suppressed by
three to five orders of magnitude.",1108.0507v1
2011-08-24,Energy spectra of primary and secondary cosmic-ray nuclei measured with TRACER,"The TRACER cosmic-ray detector, first flown on long-duration balloon (LDB) in
2003 for observations of the major primary cosmic-ray nuclei from oxygen (Z=8)
to iron (Z=26), has been upgraded to also measure the energies of the lighter
nuclei, including the secondary species boron (Z=5). The instrument was used in
another LDB flight in 2006. The properties and performance of the modified
detector system are described, and the analysis of the data from the 2006
flight is discussed. The energy spectra of the primary nuclei carbon (Z=6),
oxygen, and iron over the range from 1 GeV amu$^{-1}$ to 2 TeV amu$^{-1}$ are
reported. The data for oxygen and iron are found to be in good agreement with
the results of the previous TRACER flight. The measurement of the energy
spectrum of boron also extends into the TeV amu$^{-1}$ region. The relative
abundances of the primary nuclei, such as carbon, oxygen, and iron, above
$\sim10$ GeV amu$^{-1}$ are independent of energy, while the boron abundance,
i.e. the B/C abundance ratio, decreases with energy as expected. However, there
is an indication that the previously reported $E^{-0.6}$ dependence of the B/C
ratio does not continue to the highest energies.",1108.4838v1
2011-10-10,X-ray Diagnostics of Giant Molecular Clouds in the Galactic Center Region and Past Activity of Sgr A*,"Strong iron fluorescence at 6.4 keV and hard-X-ray emissions from giant
molecular clouds in the Galactic center region have been interpreted as
reflections of a past outburst of the Sgr A* supermassive black hole. Careful
treatment of multiple interactions of photons in a complicated geometry is
essential to modeling the reprocessed emissions from the dense clouds. We
develop a new calculation framework of X-ray reflection from molecular clouds
based on Monte Carlo simulations for accurate interpretation of high-quality
observational data. By utilizing this simulation framework, we present the
first calculations of morphologies and spectra of the reflected X-ray emission
for several realistic models of Sgr B2, which is the most massive molecular
cloud in our Galaxy. The morphology of scattered hard X-rays above 20 keV is
significantly different from that of iron fluorescence due to their large
penetrating power into dense regions of the cloud, probing the structure of the
cloud. High-resolution spectra provide quantitative evaluation of the iron line
including its Compton shoulder to constrain the mass and the chemical
composition of the cloud as well as the luminosity of the illuminating source.
These predictions can be checked in the near future with future X-ray missions
such as NuStar (hard X-rays) and ASTRO-H (both iron lines and hard X-rays).",1110.1936v1
2011-10-12,Reemerging superconductivity at 48 K across quantum criticality in iron chalcogenides,"Pressure plays an essential role in the induction1 and control2,3 of
superconductivity in iron-based superconductors. Substitution of a smaller
rare-earth ion for the bigger one to simulate the pressure effects has
surprisingly raised the superconducting transition temperature Tc to the record
high 55 K in these materials4,5. However, Tc always goes down after passing
through a maximum at some pressure and the superconductivity eventually tends
to disappear at sufficiently high pressures1-3. Here we show that the
superconductivity can reemerge with a much higher Tc after its destruction upon
compression from the ambient-condition value of around 31 K in newly discovered
iron chalcogenide superconductors. We find that in the second superconducting
phase the maximum Tc is as high as 48.7 K for K0.8Fe1.70Se2 and 48 K for
(Tl0.6Rb0.4)Fe1.67Se2, setting the new Tc record in chalcogenide
superconductors. The presence of the second superconducting phase is proposed
to be related to pressure-induced quantum criticality. Our findings point to
the potential route to the further achievement of high-Tc superconductivity in
iron-based and other superconductors.",1110.2600v3
2011-11-02,Structural quantum criticality and superconductivity in iron-based superconductor Ba(Fe1-xCox)2As2,"We investigated the elastic properties of the iron-based superconductor
Ba(Fe1-xCox)2As2 with eight Co concentrations. The elastic constant C66 shows
large elastic softening associated with the structural phase transition. The
C66 was analyzed base on localized and itinerant pictures of Fe-3d electrons,
which shows the strong electron-lattice coupling and a possible mass
enhancement in this system. The results resemble those of unconventional
superconductors, where the properties of the system are governed by the quantum
fluctuations associated with the zero-temperature critical point of the
long-range order; namely, the quantum critical point (QCP). In this system, the
inverse of C66 behaves just like the magnetic susceptibility in the magnetic
QCP systems. While the QCPs of these existing superconductors are all ascribed
to antiferromagnetism, our systematic studies on the canonical iron-based
superconductor Ba(Fe1-xCox)2As2 have revealed that there is a signature of
""structural quantum criticality"" in this material, which is so far without
precedent. The elastic constant anomaly is suggested to concern with the
emergence of superconductivity. These results highlight the strong
electron-lattice coupling and effect of the band in this system, thus
challenging the prevailing scenarios that focus on the role of the iron
3d-orbitals.",1111.0366v1
2011-12-05,Pairing symmetries of several families of iron-based superconductors and some similarities with cuprates and heavy-fermions,"We show that, by using unit-cell transformation between 1 Fe per unit cell to
2 Fe per unit cell, one can qualitatively understand the pairing symmetry of
several families of iron-based superconductors. In iron-pnictides and
iron-chalcogenides, the nodeless s+- pairing and the resulting magnetic
resonance mode transform nicely between the two unit cells, while retaining all
physical properties unchanged. However, when the electron-pocket disappears
from the Fermi surface with complete doping in KFe2As2, we find that the
unit-cell invariant requirement prohibits the occurrence of s+- pairing
symmetry (caused by inter-hole-pocket nesting). However, the intra-pocket
nesting is compatible here, which leads to a nodal d-wave pairing. The
corresponding Fermi surface topology and the pairing symmetry are similar to
Ce-based heavy-fermion superconductors. Furthermore, when the Fermi surface
hosts only electron-pockets in KyFe2-xSe2, the inter-electron-pocket nesting
induces a nodeless and isotropic d-wave pairing. This situation is analogous to
the electron-doped cuprates, where the strong antiferromagnetic order creates
similar disconnected electron-pocket Fermi surface, and hence nodeless d-wave
pairing appears. The unit-cell transformation in KyFe2-xSe2 exhibits that the
d-wave pairing breaks the translational symmetry of the 2 Fe unit cell, and
thus cannot be realized unless a vacancy ordering forms to compensate for it.
These results are consistent with the coexistence picture of a competing order
and nodeless d-wave superconductivity in both cuprates and KyFe1.6Se2.",1112.1004v1
2012-02-29,Muon Background Reduction in CLIC,"We report on a study concerning the reduction of muon backgrounds in CLIC
using magnetised iron.",1202.6628v1
2012-03-30,The role of different negatively charged layers in Ca10(Fe1-xPtxAs)10(Pt3+yAs8) and superconductivity at 30 K in electron-doped (Ca0.8La0.2)10(FeAs)10(Pt3As8),"The recently discovered compounds Ca10(Fe1-xPtxAs)10(Pt3+yAs8) exhibit
superconductivity up to 38 K, and contain iron arsenide (FeAs) and platinum
arsenide (Pt3+yAs8) layers separated by layers of Ca atoms. We show that high
Tc's above 15 K only emerge if the iron-arsenide layers are at most free of
platinum-substitution (x \rightarrow 0) in contrast to recent reports. In fact
Pt-substitution is detrimental to higher Tc, which increases up to 38 K only by
charge doping of pure FeAs layers. We point out, that two different negatively
charged layers [(FeAs)10]n- and (Pt3+yAs8)m- compete for the electrons provided
by the Ca2+ ions, which is unique in the field of iron-based superconductors.
In the parent compound Ca10(FeAs)10(Pt3As8), no excess charge dopes the
FeAs-layer, and superconductivity has to be induced by Pt-substitution, albeit
below 15 K. In contrast, the additional Pt-atom in the Pt4As8layer shifts the
charge balance between the layers equivalent to charge doping by 0.2 electrons
per FeAs. Only in this case Tc raises to 38 K, but decreases again if
additionally platinum is substituted for iron. This charge doping scenario is
supported by our discovery of superconductivity at 30 K in the electron-doped
La-1038 compound (Ca0.8La0.2)10(FeAs)10(Pt3As8) without significant
Pt-substitution.",1203.6767v1
2012-04-11,"Strong pairing at iron $3d_{xz,yz}$ orbitals in hole-doped BaFe$_2$As$_2$","Among numerous hypotheses, recently proposed to explain superconductivity in
iron-based superconductors [1-9], many consider Fermi surface (FS) nesting [2,
4, 8, 10] and dimensionality [4, 9] as important contributors. Precise
determination of the electronic spectrum and its modification by
superconductivity, crucial for further theoretical advance, were hindered by a
rich structure of the FS [11-17]. Here, using the angle-resolved photoemission
spectroscopy (ARPES) with resolution of all three components of electron
momentum and electronic states symmetry, we disentangle the electronic
structure of hole-doped BaFe2As2, and show that nesting and dimensionality of
FS sheets have no immediate relation to the superconducting pairing.
Alternatively a clear correlation between the orbital character of the
electronic states and their propensity to superconductivity is observed: the
magnitude of the superconducting gap maximizes at 10.5 meV exclusively for iron
3dxz;yz orbitals, while for others drops to 3.5 meV. Presented results reveal
similarities of electronic response to superconducting and magneto-structural
transitions [18, 19], implying that relation between these two phases is more
intimate than just competition for FS, and demonstrate importance of orbital
physics in iron superconductors.",1204.2432v1
2012-06-01,Error estimates for binomial approximations of game put options,"We construct algorithms via binomial approximations for computation of prices
of game put options and obtain estimates of approximation errors.",1206.0153v2
2012-07-03,Suzaku Observation of Strong Fluorescent Iron Line Emission from the Young Stellar Object V1647 Ori during Its New X-ray Outburst,"The Suzaku X-ray satellite observed the young stellar object V1647 Ori on
2008 October 8 during the new mass accretion outburst reported in August 2008.
During the 87 ksec observation with a net exposure of 40 ks, V1647 Ori showed a
high level of X-ray emission with a gradual decrease in flux by a factor of 5
and then displayed an abrupt flux increase by an order of magnitude. Such
enhanced X-ray variability was also seen in XMM-Newton observations in 2004 and
2005 during the 2003-2005 outburst, but has rarely been observed for other
young stellar objects. The spectrum clearly displays emission from Helium-like
iron, which is a signature of hot plasma (kT ~5 keV). It also shows a
fluorescent iron Kalpha line with a remarkably large equivalent width of ~600
eV. Such a large equivalent width suggests that a part of the incident X-ray
emission that irradiates the circumstellar material and/or the stellar surface
is hidden from our line of sight. XMM-Newton spectra during the 2003-2005
outburst did not show a strong fluorescent iron Kalpha line, so that the
structure of the circumstellar gas very close to the stellar core that absorbs
and re-emits X-ray emission from the central object may have changed in between
2005 and 2008. This phenomenon may be related to changes in the infrared
morphology of McNeil's nebula between 2004 and 2008.",1207.0774v1
2012-07-18,MARS Star Density Results for Shielding Applications,"Comparison of MARS 15.09 star density results in thick shielding to the star
density distribution in iron and concrete rule-of-thumb expectations.",1207.4457v1
2012-07-24,"From d-wave to s-wave pairing in the iron-pnictide superconductor (Ba,K)Fe2As2","The nature of the pairing state in iron-based superconductors is the subject
of much debate. Here we argue that in one material, the stoichiometric iron
pnictide KFe2As2, there is overwhelming evidence for a d-wave pairing state,
characterized by symmetry-imposed vertical line nodes in the superconducting
gap. This evidence is reviewed, with a focus on thermal conductivity and the
strong impact of impurity scattering on the critical temperature Tc. We then
compare KFe2As2 to Ba0.6K0.4Fe2As2, obtained by Ba substitution, where the
pairing symmetry is s-wave and the Tc is ten times higher. The transition from
d-wave to s-wave within the same crystal structure provides a rare opportunity
to investigate the connection between band structure and pairing mechanism. We
also compare KFe2As2 to the nodal iron-based superconductor LaFePO, for which
the pairing symmetry is probably not d-wave, but more likely s-wave with
accidental line nodes.",1207.5719v1
2012-07-27,The Gutzwiller Density Functional Theory,"In this tutorial presentation, we give a comprehensive introduction into the
Gutzwiller variational approach and its merger with the density functional
theory. The merits of this method are illustrated by a discussion of results
for two-band Hubbard models and realistic multi-band Hamiltonians for
iron-pnictide systems.",1207.6456v1
2012-08-24,Conformity of spin fluctuations in alkali-metal iron selenide superconductors inferred from the observation of a magnetic resonant mode in K(x)Fe(2-y)Se(2),"Spin excitations stemming from the metallic phase of the ferrochalcogenide
superconductor K(0.77)Fe(1.85)Se(2) (T_c=32 K) were mapped out in the ab plane
by means of the time-of-flight neutron spectroscopy. We observed a magnetic
resonant mode at Q_res=(1/2 1/4), whose energy and in-plane shape are almost
identical to those in the related compound Rb(0.8)Fe(1.6)Se(2). This lets us
infer that there is a unique underlying electronic structure of the bulk
superconducting phase K(x)Fe(2)Se(2), which is universal for all alkali-metal
iron selenide superconductors and stands in contrast to the doping-tunable
phase diagrams of the related iron pnictides. Furthermore, the spectral weight
of the resonance on the absolute scale, normalized to the volume fraction of
the superconducting phase, is several times larger than in optimally doped
BaFe(2-x)Co(x)As(2). We also found no evidence for any additional low-energy
branches of spin excitations away from Q_res. Our results provide new input for
theoretical models of the spin dynamics in iron based superconductors.",1208.5033v1
2012-09-26,Overview on the physics and materials of the new superconductor KxFe2-ySe2,"Since the discovery of high temperature superconductivity in iron pnictides
in early 2008, many iron-based superconductors with different structures have
been discovered, with the highest transition temperature to date being 57 K. By
the end of 2010, another kind of new superconductor, the Fe-based chalcogenide
K1-xFe2-ySe2 was discovered. A naive counting of the electrons in the system
would lead to a conclusion that the system is heavily electron overdoped (~0.4
e/Fe). Band structure calculations further support this speculation and predict
that the hole pockets which are found in the iron pnictides may be missing.
This greatly challenges the widely perceived picture that the superconducting
pairing is established by exchanging anti-ferromagnetic spin fluctuations and
the electrons are scattered between the electron and hole pockets. Later, it
was found that both potassium and iron might be deficient in K1-xFe2-ySe2,
yielding to a picture of phase separation. In this picture the superconducting
phase and the antiferromagnetic (AF) phase may phase separate spatially into
different regions. This generates further curiosity about what is the real
superconducting phase, what is the relationship between the superconducting
phase and the AF phase, and what is the parent state for the superconducting
phase. We propose a ""spider web"" model for the phase separation, which can
explain both the transport and magnetic data. In this paper, we review the
status of research in this rapidly growing field and list the important and
unsettled issues as perspectives for future research.",1209.5945v1
2012-10-05,Rapid Microwave-Assisted Synthesis of Dextran-Coated Iron Oxide Nanoparticles for Magnetic Resonance Imaging,"Currently, magnetic iron oxide nanoparticles are the only nano-sized magnetic
resonance imaging (MRI) contrast agents approved for clinical use, yet
commercial manufacturing of these agents has been limited or discontinued.
Though there is still widespread demand for these particles both for clinical
use and research, they are difficult to obtain commercially, and complicated
syntheses make in-house preparation infeasible for most biological research
labs or clinics. To make commercial production viable and increase
accessibility of these products, it is crucial to develop simple, rapid, and
reproducible preparations of biocompatible iron oxide nanoparticles. Here, we
report a rapid, straightforward microwave-assisted synthesis of
superparamagnetic dextran-coated iron oxide nanoparticles. The nanoparticles
were produced in two hydrodynamic sizes with differing core morphologies by
varying the synthetic method as either a two-step or single step process. A
striking benefit of these methods is the ability to obtain swift and consistent
results without the necessity for air, pH, or temperature sensitive techniques;
therefore, reaction times and complex manufacturing processes are greatly
reduced as compared to conventional synthetic methods. This is a great benefit
for cost-effective translation to commercial production. The nanoparticles are
found to be superparamagnetic and exhibit properties consistent for use in MRI.
In addition, the dextran coating imparts the water-solubility and
biocompatibility necessary for in vivo utilization.",1210.1827v1
2013-02-19,Improper s-wave symmetry for the electronic pairing in iron-based superconductors by first-principles calculation,"By means of space-group symmetry arguments, we argue that the electronic
pairing in iron-based high temperature superconductors shows a structure which
is a linear combination of planar s-wave and d-wave symmetry channels, both
preserving the 3-dimensional A_1g irreducible representation of the
corresponding crystal point-group. We demonstrate that the s- and d-wave
channels are determined by the parity under reflection of the electronic
orbitals through the iron planes, and by improper rotations around the iron
sites. We provide evidence of these general properties by performing accurate
quantum Monte Carlo ab-initio calculations of the pairing function, for a FeSe
lattice with tetragonal experimental geometry at ambient pressure. We find that
this picture survives even in the FeSe under pressure and at low temperatures,
when the tetragonal point-group symmetry is slightly broken. In order to
achieve a higher resolution in momentum space we introduce a BCS model that
faithfully describes our QMC variational pairing function on the simulated 4x4
FeSe unit cell. This allows us to provide a k-resolved image of the pairing
function, and show that non-isotropic contributions in the BCS gap function are
related to the improper s-wave symmetry. Our theory can rationalize and explain
a series of contradictory experimental findings, such as the observation of
twofold symmetry in the FeSe superconducting phase, the anomalous drop of T_c
with Co-impurity in LaFeAsO_(1-x)F_x, the s-to-d-wave gap transition in
BaFe_2As_2 under K doping, and the nodes appearing in the LiFeAs
superconducting gap upon P isovalent substitution.",1302.4748v2
2013-02-25,Highly Correlated Electron State and High-Temperature Superconductivity in Iron Pnictides,"It is shown that the qualitative model of the high-temperature
superconductivity suggested earlier for cuprates and doped picene and based on
the idea that the valence electron state depends on the character of the
chemical bonds they form and on the Coulomb interaction between the electrons
is not only confirmed by the experimental data on iron pnictides but is also
improved. From the chemical point of view, the high-temperature
superconductivity is associated with additional $\pi$ bonding along chains of
covalently bonded ions via a delocalized $\pi$ orbital, just like in cuprates.
From the physical point of view, as the data on iron pnictides show, the
superconductivity is associated with a FeAs layer transition into the state
similar to a macroscopic quantum system characterized by a highly correlated
electron state, formation of two-dimensional crystals of electron pairs with
quantized energy levels, and a strong Coulomb interaction between these
crystals. Superconductivity in such a system is accomplished by a
two-dimensional Wigner crystal consisting of one-dimensional Wigner crystals
formed by bosons, i.e., singlet electron pairs that are in the same
quasi-one-dimensional state extending along the ion chain, which corresponds to
a delocalized $\pi$ orbital in chemistry. The model applicability to three
different classes of materials (cuprates, picene, iron pnictides) indicates
that it can prove useful for development of the theory of superconductivity
taking into consideraion the highly correlated state of valence electrons and
strong Coulomb interactions between the electrons.",1302.6002v4
2013-03-27,Solubility of Iron in Metallic Hydrogen and Stability of Dense Cores in Giant Planets,"The formation of the giant planets in our solar system, and likely a majority
of giant exoplanets, is commonly explained by the accretion of nebular hydrogen
and helium onto a large core of terrestrial-like composition. The fate of this
core has important consequences for the evolution of the interior structure of
the planet. It has recently been shown that H2O, MgO and SiO2 dissolve in
liquid metallic hydrogen at high temperature and pressure. In this study, we
perform ab initio calculations to study the solubility of an innermost metallic
core. We find dissolution of iron to be strongly favored above 2000 K over the
entire pressure range (0.4-4 TPa) considered. We compare with and summarize the
results for solubilities on other probable core constituents. The calculations
imply that giant planet cores are in thermodynamic disequilibrium with
surrounding layers, promoting erosion and redistribution of heavy elements.
Differences in solubility behavior between iron and rock may influence
evolution of interiors, particularly for Saturn-mass planets. Understanding the
distribution of iron and other heavy elements in gas giants may be relevant in
understanding mass-radius relationships, as well as deviations in transport
properties from pure hydrogen-helium mixtures.",1303.6743v1
2013-05-16,Pseudogap formation above the superconducting dome in iron-pnictides,"The nature of the pseudogap in high transition temperature (high-Tc)
superconducting cuprates has been a major issue in condensed matter physics. It
is still unclear whether the high-Tc superconductivity can be universally
associated with the pseudogap formation. Here we provide direct evidence of the
existence of the pseudogap phase via angle-resolved photoemission spectroscopy
in another family of high-Tc superconductor, iron-pnictides. Our results reveal
a composition dependent pseudogap formation in the multi-band electronic
structure of BaFe2(As1-xPx)2. The pseudogap develops well above the
magnetostructural transition for low x, persists above the nonmagnetic
superconducting dome for optimal x and is destroyed for x ~ 0.6, thus showing a
notable similarity with cuprates. In addition, the pseudogap formation is
accompanied by inequivalent energy shifts in xz/yz orbitals of iron atoms,
indicative of a peculiar iron orbital ordering which breaks the four-fold
rotational symmetry.",1305.3875v2
2013-09-13,Separation of antiferromagnetism and high-temperature superconductivity in Ca$_{1-x}$La$_x$Fe$_2$As$_2$ under pressure,"We report the effect of applied pressures on magnetic and superconducting
order in single crystals of the aliovalent La-doped iron pnictide material
Ca$_{1-x}$La$_{x}$Fe$_{2}$As$_{2}$. Using electrical transport, elastic neutron
scattering and resonant tunnel diode oscillator measurements on samples under
both quasi-hydrostatic and hydrostatic pressure conditions, we report a series
of phase diagrams spanning the range of substitution concentrations for both
antiferromagnetic and superconducting ground states that include
pressure-tuning through the antiferromagnetic (AFM) quantum critical point. Our
results indicate that the observed superconducting phase with maximum
transition temperature of $T_{c}$=47 K is intrinsic to these materials,
appearing only upon suppression of magnetic order by pressure tuning through
the AFM critical point. In contrast to all other intermetallic iron-pnictide
superconductors with the ThCr$_2$Si$_2$ structure, this superconducting phase
appears to exist only exclusively from the antiferromagnetic phase in a manner
similar to the oxygen- and fluorine-based iron-pnictide superconductors with
the highest transition temperatures reported to date. The unusual dichotomy
between lower-$T_{c}$ systems with coexistent superconductivity and magnetism
and the tendency for the highest-$T_{c}$ systems to show non-coexistence
provides an important insight into the distinct transition temperature limits
in different members of the iron-based superconductor family.",1309.3576v1
2013-12-27,Fe-vacancy order and superconductivity in PbO-type tetragonal β-Fe1-xSe,"Several superconducting transition temperatures in the range of 30-40 K were
reported in the recently discovered intercalated FeSe sytem (A1-xFe2-ySe2, A =
K, Rb, Cs, Tl). Although the superconducting phases were not yet conclusively
decided, more than one magnetic phase with particular orders of iron vacancy
and/or potassium vacancy were identified, and some were argued to be the parent
phase. Here we show the discovery of the presence and ordering of iron vacancy
in nonintercalated FeSe (PbO-type tetragonal {\beta}-Fe1-xSe). Three types of
iron-vacancy order were found through analytical electron microscopy, and one
was identified to be nonsuperconducting and magnetic at low temperature. This
discovery suggests that the rich-phases found in A1-xFe2-ySe2 are not exclusive
in Fe-Se related superconductors. In addition, the magnetic {\beta}-Fe1-xSe
phases with particular iron-vacancy orders are more likely to be the parent
phase of FeSe superconducting system, instead of the previously assigned
{\beta}-Fe1+{\delta}Te.",1312.7255v1
2014-02-11,Iron-line and continuum variations in the XMM-Newton and Suzaku spectra of the neutron-star low-mass X-ray binary 4U 1636-53,"We used six simultaneous XMM-Newton and Rossi X-ray Timing Explorer plus five
Suzaku observations to study the continuum spectrum and the iron emission line
in the neutron-star low-mass X-ray binary 4U 1636-53. We modelled the spectra
with two thermal components (representing the accretion disc and boundary
layer), a Comptonised component (representing a hot corona), and either a
Gaussian or a relativistic line component to model an iron emission line at
about 6.5 keV. For the relativistic line component we used either the diskline,
laor or kyrline model, the latter for three different values of the spin
parameter. The fitting results for the continuum are consistent with the
standard truncated disc scenario. We also find that the flux and equivalent
width of the iron line first increase and then decrease as the flux of the
Comptonised component increases. This could be explained either by changes in
the ionisation state of the accretion disc where the line is produced by
reflection, or by light bending of the emission from the Comptonised component
if the height at which this component is produced changes with mass accretion
rate.",1402.2350v1
2014-06-16,Simulation Studies for Electromagnetic Design of INO ICAL Magnet and its Response to Muons,"The iron calorimeter (ICAL) detector at the India-based Neutrino Observatory
(INO) will be used to measure neutrino mass hierarchy. The magnet in the ICAL
detector will be used to distinguish the {\mu^-} and {\mu^+} events induced by
{\nu_{\mu}} and {\bar{\nu_{\mu}}}, respectively. Due to the importance of the
magnet in ICAL, an electromagnetic simulation has been carried out to study the
B-field distribution in iron using various designs. The simulation shows better
uniformity in the portion of the iron layer between the coils, which is bounded
by regions which have lesser field strength as we move to the periphery of the
iron layer. The ICAL magnet was configured to have a tiling structure that gave
the minimum reluctance path while keeping a reasonably uniform field
pattern.This translates into less Ampere-turns needed for generation of the
required magnetic field. At low Ampere-turns, a larger fractional area with
\vert B \vert \ge 1 Tesla (T) can be obtained by using a soft magnetic
material. A study of the effect of the magnetic field on muon trajectories has
been carried out using GEANT4. For muons up to 20 GeV, the energy resolution
improves as the magnetic field increases from 1.1T to 1.8T. The charge
identification efficiency for muons was found to be more than 90\% except for
large zenith angles.",1406.3965v3
2014-08-20,Nuclear inputs of key iron isotopes for core-collapse modeling and simulation,"From the modeling and simulation results of presupernova evolution of massive
stars, it was found that isotopes of iron, $^{54,55,56}$Fe, play a significant
role inside the stellar cores, primarily decreasing the electron-to-baryon
ratio ($Y_{e}$) mainly via electron capture processes thereby reducing the
pressure support. The neutrinos produced, as a result of these capture
processes, are transparent to the stellar matter and assist in cooling the core
thereby reducing the entropy. The structure of the presupernova star is altered
both by the changes in $Y_{e}$ and the entropy of the core material. Here we
present the microscopic calculation of Gamow-Teller strength distributions for
isotopes of iron. The calculation is also compared with other theoretical
models and experimental data. Presented also are stellar electron capture rates
and associated neutrino cooling rates, due to isotopes of iron, in a form
suitable for simulation and modeling codes. It is hoped that the nuclear inputs
presented here should assist core-collapse simulators in the process of
fine-tuning of the $Y_{e}$ parameter during various phases of presupernova
evolution of massive stars. A reliable and accurate time evolution of this
parameter is a possible key to generate a successful explosion in modeling of
core-collapse supernovae.",1408.4534v1
2014-09-08,Electronic structure in one-Fe Brillouin zone of iron-pnictide superconductor CsFe$_2$As$_2$,"The multiband nature of iron-pnictide superconductors is one of the keys to
the understanding of their intriguing behavior. The electronic and magnetic
properties heavily rely on the multiband interactions between different
electron and hole pockets near the Fermi level. At the fundamental level,
though many theoretical models were constructed on the basis of the so-called
1-Fe Brillouin zone (BZ) with an emphasis of the basic square lattice of iron
atoms, most electronic structure measurements were interpreted in the 2-Fe BZ.
Whether the 1-Fe BZ is valid in a real system is still an open question. Using
angle-resolved photoemission spectroscopy (ARPES), here we show in an extremely
hole-doped iron-pnictide superconductor CsFe$_2$As$_2$ that the distribution of
electronic spectral weight follows the 1-Fe BZ, and that the emerging band
structure bears some features qualitatively different from theoretical band
structures of the 1-Fe BZ. Our analysis suggests that the interlayer separation
is an important tuning factor for the physics of FeAs layers, the increase of
which can reduce the coupling between Fe and As and lead to the emergence of
the electronic structure in accord with the 1-Fe symmetry of the Fe square
lattice. Our finding puts strong constraints on the theoretical models
constructed on the basis of the 1-Fe BZ.",1409.2300v2
2014-11-20,Significant contribution of As 4p orbitals to the low-lying electronic structure of 112-type iron-based superconductor Ca0.9La0.1FeAs2,"We report a systematic polarization-dependent angle-resolved photoemission
spectroscopy study of the three-dimensional electronic structure of the
recently discovered 112-type iron-based superconductor Ca1-xLaxFeAs2 (x = 0.1).
Besides the commonly reported three hole-like and two electron-like bands in
iron-based superconductors, we resolve one additional hole-like band around the
zone center and one more fast-dispersing band near the X point in the vicinity
of Fermi level. By tuning the polarization and the energy of incident
photons,we are able to identify the specific orbital characters and the kz
dependence of all bands. Combining with band calculations, we find As 4pz and
4px (4py) orbitals contribute significantly to the additional three-dimensional
hole-like band and the narrow band, respectively. Also, there are considerable
hybridization between the As 4p zand Fe 3d orbitals in the additional hole-like
band, which suggests the strong coupling between the unique arsenic zigzag bond
layers and the FeAs layers therein. Our findings provide a comprehensive
picture of the orbital characters of the low-lying band structure of 112-type
iron-based superconductors, which can be a starting point for the further
understanding of their unconventional superconductivity.",1411.5525v1
2015-01-23,Tensile strain-induced softening of iron at high temperature,"In weakly ferromagnetic materials, already small changes in the atomic
configuration triggered by temperature or chemistry can alter the magnetic
interactions responsible for the non-random atomic-spin orientation. Different
magnetic states, in turn, can give rise to substantially different macroscopic
properties. A classical example is iron, which exhibits a great variety of
properties as one gradually removes the magnetic long-range order by raising
the temperature towards and beyond its Curie point of
$T_{\text{C}}^{0}=1043$\,K. Using first-principles theory, here we demonstrate
that uniaxial tensile strain can also destabilize the magnetic order in iron
and eventually lead to a ferromagnetic to paramagnetic transition at
temperatures far below $T_{\text{C}}^{0}$. In consequence, the intrinsic
strength of the ideal single-crystal body-centered cubic iron dramatically
weakens above a critical temperature of $\sim 500$\,K. The discovered
strain-induced magneto-mechanical softening provides a plausible atomic-level
mechanism behind the observed drop of the measured strength of Fe whiskers
around $300-500$\,K. Alloying additions which have the capability to partially
restore the magnetic order in the strained Fe lattice, push the critical
temperature for the strength-softening scenario towards the magnetic transition
temperature of the undeformed lattice. This can result in a surprisingly large
alloying-driven strengthening effect at high temperature as illustrated here in
the case of Fe-Co alloy.",1501.05774v2
2015-01-23,Quasiparticles in Iron Silicides: GW versus LDA,"The angle-resolved photoemission spectroscopy, ARPES, is able to measure both
the spectra and spectral weights of the quasiparticles in solids. Although it
is common to interpret the band structure obtained within the
density-functional-theory based methods as quasi-particle spectra, these
methods are not able to provide the changes in spectral weights of the electron
excitations. We use Vienna Ab initio Simulation Package, VASP, for evaluation
of the quasiparticle spectra and their spectral weights within Hedin GW
approximation for Fe3Si and FeSi2, providing, thus, a prediction for the ARPES
experiments. Comparison of the band structures shows that both theories reflect
peculiarities of the crystal structures in similar shape of the bands in
certain k-directions, however, in general the difference is quite noticeable.
We find that the spectral weight of quasiparticles in these compounds deviates
from unity everywhere and shows non-monotonic behavior in those parts of bands
where the delocalized states contribute to their formation. Both methods lead
to the same conclusion: those of iron ions in Fe3Si which occupy the positions,
where they are surrounded by only Fe ions, have the d-electrons localized and
large magnetic moment whereas Fe ions with the Si nearest neighbors have
d-electrons delocalized and the magnetic moments quenched. The Si influence on
the Fe ion state is even more pronounced in the FeSi2 where all iron ions have
the Si ions as nearest neighbors: both approaches produce zero moment on iron
ions. The advantages and disadvantages of both approaches are discussed.",1501.05898v3
2015-01-27,Direct observation of nanoscale interface phase in the superconducting chalcogenide K$_{x}$Fe$_{2-y}$Se$_2$ with intrinsic phase separation,"We have used scanning micro x-ray diffraction to characterize different
phases in superconducting K$_{x}$Fe$_{2-y}$Se$_2$ as a function of temperature,
unveiling the thermal evolution across the superconducting transition
temperature (T$_c\sim$32 K), phase separation temperature (T$_{ps}\sim$520 K)
and iron-vacancy order temperature (T$_{vo}\sim$580 K). In addition to the
iron-vacancy ordered tetragonal magnetic phase and orthorhombic metallic
minority filamentary phase, we have found a clear evidence of the interface
phase with tetragonal symmetry. The metallic phase is surrounded by this
interface phase below $\sim$300 K, and is embedded in the insulating texture.
The spatial distribution of coexisting phases as a function of temperature
provides a clear evidence of the formation of protected metallic percolative
paths in the majority texture with large magnetic moment, required for the
electronic coherence for the superconductivity. Furthermore, a clear
reorganization of iron-vacancy order around the T$_{ps}$ and T$_c$ is found
with the interface phase being mostly associated with a different iron-vacancy
configuration, that may be important for protecting the percolative
superconductivity in K$_{x}$Fe$_{2-y}$Se$_2$.",1501.06745v1
2015-02-26,"Strong Interplay between Stripe Spin Fluctuations, Nematicity and Superconductivity in FeSe","Elucidating the microscopic origin of nematic order in iron-based
superconducting materials is important because the interactions that drive
nematic order may also mediate the Cooper pairing. Nematic order breaks
fourfold rotational symmetry in the iron plane, which is believed to be driven
by either orbital or spin degrees of freedom. However, as the nematic phase
often develops at a temperature just above or coincides with a stripe magnetic
phase transition, experimentally determining the dominant driving force of
nematic order is difficult. Here, we use neutron scattering to study
structurally the simplest iron-based superconductor FeSe, which displays a
nematic (orthorhombic) phase transition at $T_s=90$ K, but does not order
antiferromagnetically. Our data reveal substantial stripe spin fluctuations,
which are coupled with orthorhombicity and are enhanced abruptly on cooling to
below $T_s$. Moreover, a sharp spin resonance develops in the superconducting
state, whose energy (~4 meV) is consistent with an electron boson coupling mode
revealed by scanning tunneling spectroscopy, thereby suggesting a spin
fluctuation-mediated sign-changing pairing symmetry. By normalizing the dynamic
susceptibility into absolute units, we show that the magnetic spectral weight
in FeSe is comparable to that of the iron arsenides. Our findings support
recent theoretical proposals that both nematicity and superconductivity are
driven by spin fluctuations.",1502.07544v1
2015-03-18,Broad Iron Emission from Gravitationally Lensed Quasars Observed by Chandra,"Recent work has demonstrated the potential of gravitationally lensed quasars
to extend measurements of black hole spin out to high-redshift with the current
generation of X-ray observatories. Here we present an analysis of a large
sample of 27 lensed quasars in the redshift range 1.0<z<4.5 observed with
Chandra, utilizing over 1.6 Ms of total observing time, focusing on the
rest-frame iron K emission from these sources. Although the X-ray
signal-to-noise (S/N) currently available does not permit the detection of iron
emission from the inner accretion disk in individual cases in our sample, we
find significant structure in the stacked residuals. In addition to the narrow
core, seen almost ubiquitously in local AGN, we find evidence for an additional
underlying broad component from the inner accretion disk, with a clear red wing
to the emission profile. Based on simulations, we find the detection of this
broader component to be significant at greater than the 3-sigma level. This
implies that iron emission from the inner disk is relatively common in the
population of lensed quasars, and in turn further demonstrates that, with
additional observations, this population represents an opportunity to
significantly extend the sample of AGN spin measurements out to high-redshift.",1503.05255v1
2015-05-12,Experimental Observation of Incoherent-Coherent Crossover and Orbital Dependent Band Renormalization in Iron Chalcogenide Superconductors,"The level of electronic correlation has been one of the key questions in
understanding the nature of superconductivity. Among the iron-based
superconductors, the iron chalcogenide family exhibits the strongest electron
correlations. To gauge the correlation strength, we performed systematic
angle-resolved photoemission spectroscopy study on the iron chalcogenide series
Fe$_{1+y}$Se$_x$Te$_{1-x}$ (0$<$x$<$0.59), a model system with the simplest
structure. Our measurement reveals an incoherent to coherent crossover in the
electronic structure as the selenium ratio increases and the system evolves
from the weakly localized to more itinerant state. Furthermore, we found that
the effective mass of bands dominated by the d$_{xy}$ orbital character
significantly decreases with increasing selenium ratio, as compared to the
d$_{xz}$/d$_{yz}$ orbital-dominated bands. The orbital dependent change in the
correlation level agrees with theoretical calculations on the band structure
renormalization, and may help to understand the onset of superconductivity in
Fe$_{1+y}$Se$_x$Te$_{1-x}$.",1505.03074v1
2015-06-02,Development of high-performance iron-based superconducting wires and tapes,"Conventional powder-in-tube (PIT) method has been the most effective
technique for fabricating iron-based superconducting wires and tapes.
Tremendous advances have been made during the last few years, especially for
122 family pnictide tapes. Here we review some of the most recent and
significant developments in making high-performance iron-based tapes by the
ex-situ PIT process, paying particular attention to several fabrication
techniques to realize high-field Jc performance in terms of increase of core
density and improvement of texture. At 4.2 K, the practical level transport Jc
up to 0.12 MA/cm2 in 10 T and 0.1 MA/cm2 in 14 T have been achieved in the
K-doped 122/Ag tapes. As for multifilamentary 122 iron-based wires and tapes,
the highest Jc values reached so far are 61 kA/cm2 and 35 kA /cm2 at 4.2 K and
10 T, respectively for 7- and 19-core Sr-122 tapes. Recently, high Jc
Cu-cladded and stainless steel/Ag double-sheathed 122 tapes have also been
produced in order to improve either mechanical properties or thermal stability.
More importantly, the scalable rolling process has been used for the first time
to demonstrate high Jc values in 122 conductor tapes of 11 m in length.",1506.00792v2
2015-07-06,A chemical trompe-l'œil: no iron spread in the globular cluster M22,"We present the analysis of high-resolution spectra obtained with UVES and
UVES-FLAMES at the Very Large Telescope of 17 giants in the globular cluster
M22, a stellar system suspected to have an intrinsic spread in the iron
abundance. We find that when surface gravities are derived spectroscopically
(by imposing to obtain the same iron abundance from FeI and FeII lines) the
[Fe/H] distribution spans ~0.5 dex, according to previous analyses. However,
the gravities obtained in this way correspond to unrealistic low stellar masses
(0.1-0.5 Msun) for most of the surveyed giants. Instead, when photometric
gravities are adopted, the [FeII/H] distribution shows no evidence of spread at
variance with the [FeI/H] distribution. This difference has been recently
observed in other clusters and could be due to non-local thermodynamical
equilibrium effects driven by over-ionization mechanisms, that mainly affect
the neutral species (thus providing lower [FeI/H]) but leave [FeII/H]
unaltered. We confirm that the s-process elements show significant star-to-star
variations and their abundances appear to be correlated with the difference
between [FeI/H] and [FeII/H]. This puzzling finding suggests that the peculiar
chemical composition of some cluster stars may be related to effects able to
spuriously decrease [FeI/H]. We conclude that M22 is a globular cluster with no
evidence of intrinsic iron spread, ruling out that it has retained the
supernovae ejecta in its gravitational potential well.",1507.01596v1
2015-07-09,O and Fe abundance correlations and distributions inferred for the thick and thin disk,"A linear [Fe/H]-[O/H] relation is found for different stellar populations in
the Galaxy (halo, thick disk, thin disk) from a data sample obtained in a
recent investigation (Ram{\'\i}rez et al. 2013). These correlations support
previous results inferred from poorer samples: stars display a ""main sequence""
expressed as [Fe/H] = $a$[O/H$]+b\mp\Delta b$ where a unit slope, $a=1$,
implies a constant [O/Fe] abundance ratio. Oxygen and iron empirical abundance
distributions are then determined for different subsamples, which are well
explained by the theoretical predictions of multistage closed-(box+reservoir)
(MCBR) chemical evolution models by taking into account the found correlations.
The interpretation of these distributions in the framework of MCBR models gives
us clues about inflow/outflow rates in these different Galactic regions and
their corresponding evolution. Outflow rate for the thick and the thin disks
are lower than the halo outflow rate. Moreover if the thin disk built up from
the thick disk, both systems result of comparable masses. Besides that, the
iron-to-oxygen yield ratio and the primary to not primary contribution ratio
for the iron production are obtained from the data, resulting consistent with
SNII progenitor nucleosynthesis and with the iron production from SNIa
supernova events.",1507.02405v1
2015-08-07,Spin reorientation driven by the interplay between spin-orbit coupling and Hund's rule coupling in iron pnictides,"In most magnetically-ordered iron pnictides, the magnetic moments lie in the
FeAs planes, parallel to the modulation direction of the spin stripes. However,
recent experiments in hole-doped iron pnictides have observed a reorientation
of the magnetic moments from in-plane to out-of-plane. Interestingly, this
reorientation is accompanied by a change in the magnetic ground state from a
stripe antiferromagnet to a tetragonal non-uniform magnetic configuration.
Motivated by these recent observations, here we investigate the origin of the
spin anisotropy in iron pnictides using an itinerant microscopic electronic
model that respects all the symmetry properties of a single FeAs plane. We find
that the interplay between the spin-orbit coupling and the Hund's rule coupling
can account for the observed spin anisotropies, including the spin
reorientation in hole-doped pnictides, without the need to invoke orbital or
nematic order. Our calculations also reveal an asymmetry between the magnetic
ground states of electron- and hole-doped compounds, with only the latter
displaying tetragonal magnetic states.",1508.01763v4
2015-08-26,Spatial competition of the ground states in 1111 iron pnictides,"Using nuclear quadrupole resonance, the phase diagram of 1111
$R$FeAsO$_{1-x}$F$_x$ ($R$$=$La, Ce, Sm) iron pnictides is constructed as a
function of the local charge distribution in the paramagnetic state, which
features low-doping-like (LD-like) and high-doping-like (HD-like) regions.
Compounds based on magnetic rare earths (Ce, Sm) display a unified behavior,
and comparison with La-based compounds reveals the detrimental role of static
iron $3d$ magnetism on superconductivity, as well as a qualitatively different
evolution of the latter at high doping. It is found that the LD-like regions
fully account for the orthorhombicity of the system, and are thus the origin of
any static iron magnetism. Orthorhombicity and static magnetism are not
hindered by superconductivity but limited by dilution effects, in agreement
with 2D (respectively 3D) nearest-neighbor square lattice site percolation when
the rare earth is nonmagnetic (respectively magnetic). The LD-like regions are
not intrinsically supportive of superconductivity, on the contrary of the
HD-like regions, as evidenced by the well-defined Uemura relation between the
superconducting transition temperature and the superfluid density when
accounting for the proximity effect. This leads us to propose a complete
description of the interplay of ground states in 1111 pnictides, where
nanoscopic regions compete to establish the ground state through suppression of
superconductivity by static magnetism, and extension of superconductivity by
proximity effect.",1508.06532v1
2015-10-04,To the measurement of the radius via an electron scattering,"We propose an experiment for an accurate measurement of the proton radius. A
key feature of our proposal is an iron-free magnetic spectrometer. Projected
systematics uncertainties will allow a 1% level accuracy for the $r_p$ value.",1510.00890v1
2015-10-28,Superconducting state in Fe-based materials and spin-fluctuation theory of pairing,"Short review of the spin-fluctuation theory of superconductive pairing in
iron-based pnictides and chalcogenides.",1510.08279v1
2015-11-02,Comment on 'A new nanoscale metastable iron phase in carbon steels',"We show that the selected area diffraction patterns presented in a recent
paper (T. Liu et al. Sci. Rep. 2015 5, 15331) do not prove the existence of a
new hexagonal phase in martensitic steels. They can be actually simulated by
twin effects.",1511.00591v1
2015-12-08,Photodisintegrated gamma rays and neutrinos from heavy nuclei in the gamma-ray burst jet of GRB 130427A,"Detection of ~ 0.1-70 GeV prompt gamma-ray emission from the exceptionally
bright gamma-ray burst (GRB) 130427A by the Fermi-Large Area Telescope provides
an opportunity to explore the physical processes of GeV gamma-ray emission from
the GRB jets. In this work we discuss interactions of Iron and Oxygen nuclei
with observed keV-MeV photons in the jet of GRB 130427A in order to explain an
additional, hard spectral component observed during 11.5-33 second after
trigger. The photodisintegration time scale for Iron nuclei is comparable to or
shorter than this duration. We find that gamma rays resulting from the Iron
nuclei disintegration can account for the hard power-law component of the
spectra in the 1-70 GeV range, before the gamma-gamma to electron-positron pair
production with low-energy photons severely attenuates emission of higher
energy photons. Electron antineutrinos from the secondary neutron decay, on the
other hand, can be emitted with energies up to 2 TeV. The flux of these
neutrinos is low and consistent with non-detection of GRB 130427A by the
IceCube Neutrino Observatory. The required total energy in the Iron nuclei for
this hadronic model for GeV emission is approximately 10 times the observed
total energy released in the prompt keV-MeV emission.",1512.02434v3
2015-12-10,Robust Zero Energy Bound States Localized at Magnetic Impurities in Iron-based Superconductors,"We investigate the effect of spin-orbit coupling on the in-gap bound states
localized at magnetic impurities in multi-band superconductors with
unconventional (sign-changed) and conventional (sign-unchanged) $s$-wave
pairing symmetry, which may be relevant to iron-based superconductors. Without
spin-orbit coupling, for spin-singlet superconductors it is known that such
bound states cross zero energy at a critical value of the impurity scattering
strength and acquire a finite spin-polarization. Moreover, the degenerate,
spin-polarized, zero energy bound states are unstable to applied Zeeman fields
as well as deviation of the impurity scattering strength away from criticality.
Using a T-matrix formalism as well as analytical arguments, we show that, in
the presence of spin-orbit coupling, the zero-energy bound states localized at
magnetic impurities in unconventional, sign-changed, $s$-wave superconductors
acquire surprising robustness to applied Zeeman fields and variation in the
impurity scattering strength, an effect which is absent in the conventional,
sign-unchanged, $s$-wave superconductors. Given that the iron-based multi-band
superconductors may possess a substantial spin-orbit coupling as seen in recent
experiments, our results may provide one possible explanation to the recent
observation of surprisingly robust zero bias scanning tunneling microscope
peaks localized at magnetic impurities in iron-based superconductors provided
the order parameter symmetry is sign changing $s_{+-}$-wave.",1512.03450v2
2015-12-18,Seismic waves damping with arrays of inertial resonators,"We investigate the elastic stop band properties of a theoretical cubic array
of iron spheres connected to a bulk of concrete via iron or rubber ligaments.
Each sphere can move freely within a surrounding air cavity, but ligaments
couple it to the bulk and further facilitate bending and rotational motions.
Associated low frequency local resonances are well predicted by an asymptotic
formula. We find complete stop bands (for all wave-polarizations) in the
frequency range $[16,21]$ Hertz (resp. $[6,11]$ Hertz) for $7.4$-meter (resp.
$0.74$-meter) diameter iron spheres with a $10$-meter (resp. $1$-meter)
center-to-center spacing, when they are connected to concrete via steel (resp.
rubber) ligaments. The scattering problem shows that only bending modes are
responsible for damping and that rotational modes are totally overwritten by
bending modes. Regarding seismic applications, we further consider soil as a
bulk medium, in which case the relative bandwidth of the low frequency stop
band can be enlarged through ligaments of different sizes that allow for well
separated bending and rotational modes. We finally achieve some damping of
elastodynamic waves from $8$ to $49$ Hertz (relative stop band of $143$
percent) for iron spheres $0.74$-meter in diameter that are connected to soil
with six rubber ligaments of optimized shapes. These results represent a
preliminary step in the design of seismic shields placed around, or underneath,
the foundations of large civil infrastructures.",1512.06078v2
2016-04-13,Magnetic properties and pairing tendencies of the iron-based superconducting ladder BaFe$_2$S$_3$: combined ab initio and density matrix renormalization group study,"The recent discovery of superconductivity under high pressure in the two-leg
ladder compound BaFe$_2$S$_3$ [H. Takahashi et al., Nature Materials 14, 1008
(2015)] opens a broad avenue of research, because it represents the first
report of pairing tendencies in a quasi one-dimensional iron-based high
critical temperature superconductor. Similarly as in the case of the cuprates,
ladders and chains can be far more accurately studied using many-body
techniques and model Hamiltonians than their layered counterparts, particularly
if several orbitals are active. In this publication, we derive a two-orbital
Hubbard model from first principles that describes individual ladders of
BaFe$_2$S$_3$. The model is studied with the density matrix renormalization
group. These first reported results are exciting for two reasons: (i) at
half-filling, ferromagnetic order emerges as the dominant magnetic pattern
along the rungs of the ladder, and antiferromagnetic order along the legs, in
excellent agreement with neutron experiments; (ii) pairs form in the strong
coupling regime, as found by studying the binding energy of two holes doped on
the half-filled system. In addition, Orbital Selective Mott Phase
characteristics develop with doping, with only one Wannier orbital receiving
the hole carriers while the other remains half-filled. These results suggest
that the analysis of models for iron-based two-leg ladders could clarify the
origin of pairing tendencies and other exotic properties of iron-based high
critical temperature superconductors.",1604.03621v2
2016-05-10,A unified model of grain alignment: radiative alignment of interstellar grains with magnetic inclusions,"The radiative torque (RAT) alignment of interstellar grains with ordinary
paramagnetic susceptibilities has been supported by earlier studies. The
alignment of such grains depends on the so-called RAT parameter $q^{\max}$ that
is determined by the grain shape. In this paper, we elaborate our model of RAT
alignment for grains with enhanced magnetic susceptibility due to iron
inclusions, such that RAT alignment is magnetically enhanced for which we term
MRAT mechanism. Such grains can get aligned with high angular momentum at the
so-called high-J attractor points, achieving a high degree of alignment. Using
our analytical model of RATs we derive the critical value of the magnetic
relaxation parameter $\delta_{m}$ to produce high-J attractor points as
functions of $q^{\max}$ and the anisotropic radiation angle relative to the
magnetic field $\psi$. We find that if about $10\%$ of total iron abundance
present in silicate grains are forming iron clusters, it is sufficient to
produce high-J attractor points for all reasonable values of $q^{\max}$. To
calculate the degree of grain alignment, we carry out numerical simulations of
MRAT alignment by including stochastic excitations from gas collisions and
magnetic fluctuations. We show that large grains can achieve perfect alignment
when the high-J attractor point is present, regardless of the values of
$q^{\max}$. Our obtained results pave the way for physical modeling of
polarized thermal dust emission as well as magnetic dipole emission. We also
find that millimeter-sized grains in accretion disks may be aligned with the
magnetic field if they are incorporated with iron nanoparticles.",1605.02828v2
2016-06-08,Observation of a Hidden Hole-Like Band Approaching the Fermi Level in K-Doped Iron Selenide Superconductor,"One of the ultimate goals of the study of iron-based superconductors is to
identify the common feature that produces the high critical temperature (Tc).
In the early days, based on a weak-coupling viewpoint, the nesting between
hole- and electron-like Fermi surfaces (FSs) leading to the so-called $s\pm$
state was considered to be one such key feature. However, this theory has faced
a serious challenge ever since the discovery of alkali-metal-doped FeSe (AFS)
superconductors, in which only electron-like FSs with a nodeless
superconducting gap are observed. Several theories have been proposed, but a
consistent understanding is yet to be achieved. Here we show experimentally
that a hole-like band exists in KxFe2-ySe2, which presumably forms a hole-like
Fermi surface. The present study suggests that AFS can be categorized in the
same group as iron arsenides with both hole- and electron-like FSs present.
This result provides a foundation for a comprehensive understanding of the
superconductivity in iron-based superconductors.",1606.02405v1
2016-06-27,Coordinated Analysis of Two Graphite Grains from the CO3.0 LAP 031117 Meteorite: First Identification of a CO Nova Graphite and a Presolar Iron Sulfide Subgrain,"Presolar grains constitute remnants of stars that existed before the
formation of the solar system. In addition to providing direct information on
the materials from which the solar system formed, these grains provide
ground-truth information for models of stellar evolution and nucleosynthesis.
Here we report the in-situ identification of two unique presolar graphite
grains from the primitive meteorite LaPaz Icefield 031117. Based on these two
graphite grains, we estimate a bulk presolar graphite abundance of 5(-3)(+7)
ppm in this meteorite. One of the grains (LAP-141) is characterized by an
enrichment in 12C and depletions in 33,34S, and contains a small iron sulfide
subgrain, representing the first unambiguous identification of presolar iron
sulfide. The other grain (LAP-149) is extremely 13C-rich and 15N-poor, with one
of the lowest 12C/13C ratios observed among presolar grains. Comparison of its
isotopic compositions with new stellar nucleosynthesis and dust condensation
models indicates an origin in the ejecta of a low-mass CO nova. Grain LAP-149
is the first putative nova grain that quantitatively best matches nova model
predictions, providing the first strong evidence for graphite condensation in
nova ejecta. Our discovery confirms that CO nova graphite and presolar iron
sulfide contributed to the original building blocks of the solar system.",1606.08310v1
2016-07-05,Delayed hepatic uptake of multi-phosphonic acid poly(ethylene glycol) coated iron oxide measured by real-time Magnetic Resonance Imaging,"We report on the synthesis, characterization, stability and pharmacokinetics
of novel iron based contrast agents for magnetic resonance imaging (MRI).
Statistical copolymers combining multiple phosphonic acid groups and
poly(ethylene glycol) (PEG) were synthesized and used as coating agents for 10
nm iron oxide nanocrystals. In vitro, protein corona and stability assays show
that phosphonic acid PEG copolymers outperform all other coating types
examined, including low molecular weight anionic ligands and polymers. In vivo,
the particle pharmacokinetics is investigated by monitoring the MRI signal
intensity from mouse liver, spleen and arteries as a function of the time,
between one minute and seven days after injection. Iron oxide particles coated
with multi-phosphonic acid PEG polymers are shown to have a blood circulation
lifetime of 250 minutes, i.e. 10 to 50 times greater than that of recently
published PEGylated probes and benchmarks. The clearance from the liver takes
in average 2 to 3 days and is independent of the core size, coating and
particle stability. By comparing identical core particles with different
coatings, we are able to determine the optimum conditions for stealth MRI
probes.",1607.01656v1
2016-07-11,A quasi-periodic modulation of the iron line centroid energy in the black hole binary H 1743-322,"Accreting stellar-mass black holes often show a `Type-C' quasi-periodic
oscillation (QPO) in their X-ray flux, and an iron emission line in their X-ray
spectrum. The iron line is generated through continuum photons reflecting off
the accretion disk, and its shape is distorted by relativistic motion of the
orbiting plasma and the gravitational pull of the black hole. The physical
origin of the QPO has long been debated, but is often attributed to
Lense-Thirring precession, a General Relativistic effect causing the inner flow
to precess as the spinning black hole twists up the surrounding space-time.
This predicts a characteristic rocking of the iron line between red and blue
shift as the receding and approaching sides of the disk are respectively
illuminated. Here we report on XMM-Newton and NuSTAR observations of the black
hole binary H 1743-322 in which the line energy varies systematically over the
~4 s QPO cycle (3.70 sigma significance), as predicted. This provides strong
evidence that the QPO is produced by Lense-Thirring precession, constituting
the first detection of this effect in the strong gravitation regime. There are
however elements of our results harder to explain, with one section of data
behaving differently to all the others. Our result enables the future
application of tomographic techniques to map the inner regions of black hole
accretion disks.",1607.02866v1
2016-12-20,Magnetism of PrFeAsO parent compound for iron-based superconductors: Mössbauer spectroscopy study,"Moessbauer spectroscopy measurements were performed for the temperature range
between 4.2 K and 300 K in a transmission geometry applying 14.41-keV resonant
line in 57Fe for PrFeAsO the latter being a parent compound of the iron-based
superconductors belonging to the '1111' family. It was found that an itinerant
3d magnetic order develops at about 165 K and it is accompanied by an
orthorhombic distortion of the chemical unit cell. A complete longitudinal 3d
incommensurate spin density wave (SDW) order develops at about 140 K.
Transferred hyperfine magnetic field generated by the praseodymium magnetic
order on iron nuclei is seen at 12.8 K and below, i.e., below magnetic order of
praseodymium magnetic moments. It is oriented perpendicular to the field of SDW
on iron nuclei. The shape of SDW is almost rectangular at low temperatures and
it transforms into roughly triangular form around 'nematic' transition at about
140 K. Praseodymium magnetic order leads to the substantial enhancement of SDW
due to the large orbital contribution to the magnetic moment of praseodymium. A
transferred field indicates presence of strong magnetic susceptibility
anisotropy in the [b-c] plane while following rotation of praseodymium magnetic
moments in this plane with lowering temperature. It was found that 'nematic'
phase region is a region of incoherent spin density wavelets typical for a
critical region.",1612.06776v3
2017-04-06,Towards Picogram Detection of Superparamagnetic Iron-Oxide Particles Using a Gradiometric Receive Coil,"Superparamagnetic iron-oxide nanoparticles can be used in a variety of
medical applications like vascular or targeted imaging. Magnetic particle
imaging (MPI) is a promising tomographic imaging technique that allows
visualizing the 3D nanoparticle distribution concentration in a non-invasive
manner. The two main strengths of MPI are high temporal resolution and high
sensitivity. While the first has been proven in the assessment of dynamic
processes like cardiac imaging, it is unknown how far the detection limit of
MPI can be lowered. Within this work, we will present a highly sensitive
gradiometric receive-coil unit combined with a noise-matching network tailored
for the measurement of mice. The setup is capable of detecting 5 ng of iron in
vitro at 2.14 sec acquisition time. In terms of iron concentration we are able
to detect 156 {\mu}g/L marking the lowest value that has been reported for an
MPI scanner so far. In vivo MPI mouse images of a 512 ng bolus at 21.5 ms
acquisition time allow for capturing the flow of an intravenously injected
tracer through the heart of a mouse. Since it has been rather difficult to
compare detection limits across MPI publications we propose guidelines
improving the comparability of future MPI studies.",1704.01789v2
2017-07-10,Diagnosing the kinematics of the tori in active galactic nuclei with the velocity-resolved reverberation mapping of the narrow iron K$α$ line,"The properties of the dusty tori in active galactic nuclei (AGNs) have been
investigated in detail, mainly focusing on the geometry and components;
however, the kinematics of the torus is still not clear. The narrow iron
K$\alpha$ line at 6.4 keV is thought to be produced by the X-ray reflection
from the torus. Thus, the velocity-resolved reverberation mapping of it is able
to constrain the kinematics of the torus. Such effort is limited by the
spectral resolution of current CCD detectors and should be possible with the
microcalorimeter on the next generation X-ray satellite. In this paper, we
first construct the response functions of the torus under a uniform inflow, a
Keplerian rotation, and a uniform outflow. Then the energy-dependent light
curve of the narrow iron K$\alpha$ line is simulated according to the
performance of the X-ray Integral Field Unit in Athena. Finally, the
energy-dependent cross-correlation function is calculated to reveal the
kinematic signal. According to our results, one hundred observations with 5 ks
exposure of each are sufficient to distinguish the above three velocity fields.
Although the real geometry and velocity field of the torus could be more
complex than we assumed, the present result proves the feasibility of the
velocity-resolved reverberation mapping of the narrow iron K$\alpha$ line. The
combination of the dynamics of the torus with those of the broad line region
and the host galaxy is instructive for the understanding of the feeding and
feedback process of AGNs.",1707.02665v1
2017-08-15,Effects of ultrasound waves intensity on the removal of Congo red color from the textile industry wastewater by Fe3O4@TiO2 core-shell nanospheres,"Environmental pollutants, such as colors from the textile industry, affect
water quality indicators like color, smell, and taste. These substances in the
water cause the obstruction of filters and membranes and thereby reduce the
efficiency of advanced water treatment processes. In addition, they are harmful
to human health because of reaction with disinfectants and production of
by-products. Iron oxide nanoparticles are considered effective absorbents for
the removal of pollutants from aqueous environments. In order to increase the
stability and dispersion, nanospheres with iron oxide core and titanium dioxide
coating were used in this research and their ability to absorb Congo red color
was evaluated. Iron oxide-titanium oxide nanospheres were prepared based on the
coprecipitation method and then their physical properties were determined using
a tunneling electron microscope (TEM) and an X-ray diffraction device.
Morphological investigation of the absorbent surface showed that iron
oxide-titanium oxide nanospheres sized about 5 to 10 nm. X-ray dispersion
survey also suggested the high purity of the sample. In addition, the
absorption rate was measured in the presence of ultrasound waves and the
results indicated that the capacity of the synthesized sample to absorb Congo
red is greatly dependent on the intensity power of ultrasound waves, as the
absorption rate reaches 100% at powers above 30 watts.",1708.04683v2
2017-09-21,Orbital loop currents in iron-based superconductors,"We show that the antiferromagnetic state commonly observed in the phase
diagrams of the iron-based superconductors necessarily triggers loop currents
characterized by charge transfer between different Fe $ 3d $ orbitals. This
effect is rooted on the glide-plane symmetry of these materials and on the
existence of an atomic spin-orbit coupling that couples states at the $X$ and
$Y$ points of the 1-Fe Brillouin zone. In the particular case in which the
magnetic moments are aligned parallel to the magnetic ordering vector direction
which is the moment configuration most commonly found in the iron-based
superconductors these loop currents involve the $d_{xy}$ orbital and either the
$d_{yz}$ orbital (if the moments point along the $y$ axis) or the $d_{xz}$
orbitals (if the moments point along the $x$ axis). We show that the two main
manifestations of the orbital loop currents are the emergence of magnetic
moments in the pnictide/chalcogen site and an orbital-selective band splitting
in the magnetically ordered state, both of which could be detected
experimentally. Our results highlight the unique intertwining between orbital
and spin degrees of freedom in the iron-based superconductors, and reveal the
emergence of an unusual correlated phase that may impact the normal state and
superconducting properties of these materials.",1709.07266v2
2017-10-13,A Suzaku View of Accretion Powered X-ray Pulsar GX 1+4,"We present results obtained from a Suzaku observation of the accretion
powered X-ray pulsar GX 1+4. Broad-band continuum spectrum of the pulsar was
found to be better described by a simple model consisting of a blackbody
component and an exponential cutoff power-law than the previously used compTT
continuum model. Though the pulse profile had a sharp dip in soft X-rays ($<$10
keV), phase-resolved spectroscopy confirmed that the dimming was not due to
increase in photoelectric absorption. Phase-sliced spectral analysis showed the
presence of a significant spectral modulation beyond 10 keV except for the dip
phase. A search for the presence of cyclotron resonance scattering feature in
the Suzaku spectra yielded a negative result. Iron K-shell (K$_\alpha$ and
K$_\beta$) emission lines from nearly neutral iron ions ($<$Fe III) were
clearly detected in the source spectrum. A significant K$_\alpha$ emission line
from almost neutral Ni atoms was detected for the first time in this source. We
estimated the iron abundance of $\sim$80 % of the solar value and Ni/Fe
abundance ratio of about two times of the solar value. We searched for a iron
Ly$_\alpha$ emission line and found a significant improvement in the spectral
fitting by inclusion of this line.",1710.04820v2
2017-12-13,Quantum effects on dislocation motion from Ring-Polymer Molecular Dynamics,"Quantum motion of atoms known as zero-point vibrations is recognized to be
important at low temperatures in condensed matter systems comprised of light
atoms or ions, affecting such properties and behaviors as proton-transfer
reactions, vibrational spectra of water and ice, and mechanical properties of
low temperature helium. Recently, quantum motion of atoms was proposed to
explain a long-standing discrepancy between theoretically computed and
experimentally measured low-temperature resistance (Peierls stress) to
dislocation motion in iron and possibly other metals with high atomic masses.
Here we report the first direct simulations of quantum motion of screw
dislocations in iron within the exact formalism of Ring-Polymer Molecular
Dynamics (RPMD) that rigorously accounts for quantum effects on the statistics
of condensed-phase systems. Our quantum RPMD simulations predict only a modest
($\approx\!13\%$) reduction in the Peierls stress in iron compared to its fully
classical prediction. Our simulations confirm that reduction in the Peierls
stress solely due to the zero-point energy is close to $50\%$ predicted
earlier, but its effect is substantially offset by an increase in the effective
atom size with decreasing temperature, an effect known as quantum dispersion.
Thus, quantum motion of atoms does not resolve the notorious discrepancy
between theoretical and experimental values of the Peierls stress in iron.",1712.04629v2
2017-12-19,Cysteine and cystine adsorption on FeS$_{2}$(100),"Iron pyrite (FeS$_{2}$) is the most abundant metal sulfide on Earth. Owing to
its reactivity and catalytic activity, pyrite has been studied in various
research fields such as surface science, geochemistry, and prebiotic chemistry.
Importantly, native iron-sulfur clusters are typically coordinated by cysteinyl
ligands of iron-sulfur proteins. In the present paper, we study the adsorption
of L-cysteine and its oxidized dimer, L-cystine, on the FeS$_{2}$ surface,
using electronic structure calculations based density functional theory and
Raman spectroscopy measurements. Our calculations suggest that sulfur-deficient
surfaces play an important role in the adsorption of cysteine and cystine. In
the thiol headgroup adsorption on the sulfur-vacancy site, dissociative
adsorption is found to be energetically favorable compared with molecular
adsorption. In addition, the calculations indicate that, in the cystine
adsorption on the defective surface under vacuum conditions, the formation of
the S-Fe bond is energetically favorable compared with molecular adsorption.
Raman spectroscopic measurements suggest the formation of cystine molecules
through the S-S bond on the pyrite surface in aqueous solution. Our results
might have implications for chemical evolution at mineral surfaces on the early
Earth and the origin of iron-sulfur proteins, which are believed to be one of
the most ancient families of proteins.",1712.06785v1
2018-01-18,"Iron-peak elements Sc, V, Mn, Cu and Zn in Galactic bulge globular clusters","Globular clusters are tracers of the history of star formation and chemical
enrichment in the early Galaxy. Their abundance pattern can help understanding
their chemical enrichment processes. In particular, the iron-peak elements have
been relatively little studied so far in the Galactic bulge. The abundances of
iron-peak elements are derived for the sample clusters, and compared with bulge
field, and thick disk stars. We derive abundances of the iron-peak elements Sc,
V, Mn, Cu, and Zn in individual stars of five bulge globular clusters (NGC
6528, NGC 6553, NGC 6522, NGC 6558, HP1), and of the reference thick disk/inner
halo cluster 47 Tucanae (NGC 104). High resolution spectra were obtained with
the UVES spectrograph at the Very Large Telescope over the years. The sample
globular clusters studied span metallicities in the range -1.2<Fe/H]<0.0. V and
Sc appear to vary in lockstep with Fe, indicating that they are produced in the
same supernovae as Fe. We find that Mn is deficient in metal-poor stars,
confirming that it is underproduced in massive stars; Mn-over-Fe steadily
increases at the higher metallicities due to a metallicity-dependent enrichment
by supernovae of type Ia. Cu behaves as a secondary element, indicating its
production in a weak-s process in massive stars. Zn has an alpha-like behaviour
at low metallicities, which can be explained in terms of nucleosynthesis in
hypernovae. At the metal-rich end, Zn decreases with increasing metallicity,
similarly to the alpha-elements.",1801.06157v1
2018-02-17,J0023+0307: A mega metal-poor dwarf star from SDSS/BOSS,"Only a handful of stars have been identified with an iron abundance
[Fe/H]<-5, and only one at [Fe/H]<-7. These stars have very large
carbon-to-iron ratios, with A(C)~7.0, most likely due to fallback in
core-collapse supernovae, which makes their total metallicity Z much higher
than their iron abundances. The failure to find population III stars, those
with no metals, has been interpreted, with support from theoretical modeling,
as the result of a top-heavy initial mass function. With zero or very low metal
abundance limiting radiative cooling, the formation of low-mass stars could be
inhibited. Currently, the star SDSS J1029+1729 sets the potential metallicity
threshold for the formation of low-mass stars at log Z/Z_0~-5. We have
identified SDSS J0023+0307, a primitive star with T_eff =6188+-84 K, and log
g=4.9+-0.5, an upper limit [Fe/H]< -6.6, and a carbon abundance A(C)< 6.3. In
our quest to push down the metallicity threshold we find J0023+0307 to be one
of the two most iron-poor stars known, and it exhibits less carbon that most of
stars at [Fe/H]< -5.",1802.06240v2
2018-03-26,"The chemical composition of NGC5824, a globular cluster without iron spread but with an extreme Mg-Al anticorrelation","NGC5824 is a massive Galactic globular cluster suspected to have an intrinsic
spread in its iron content, according to the strength of the calcium triplet
lines. We present chemical abundances of 117 cluster giant stars using
high-resolution spectra acquired with the multi-object spectrograph FLAMES. The
metallicity distribution of 87 red giant branch stars is peaked at
[Fe/H]=-2.11+-0.01 dex, while that derived from 30 asymptotic giant branch
stars is peaked at [Fe/H]=-2.20+-0.01 dex. Both the distributions are
compatible with a null spread, pointing out that this cluster did not retain
the ejecta of supernovae. The small iron abundance offset between the two
groups of stars is similar to those already observed among red and asymptotic
giant branch stars in other clusters. The lack of intrinsic iron spread rules
out the possibility that NGC5824 is the remnant of a disrupted dwarf galaxy, as
previously suggested. We also find evidence of the chemical anomalies usually
observed in globular clusters, namely the Na-O and the Mg-Al anticorrelations.
In particular, NGC5824 exhibits a huge range of [Mg/Fe] abundance, observed
only in a few metal-poor and/or massive clusters. We conclude that NGC5824 is a
normal globular cluster, without spread in [Fe/H] but with an unusually large
spread in [Mg/Fe], possibly due to an efficient self-enrichment driven by
massive asymptotic giant branch stars.",1803.09759v1
2018-04-30,X-ray short-time lags in the Fe-K energy band produced by scattering clouds in active galactic nuclei,"X-rays illuminating the accretion disc in active galactic nuclei give rise to
an iron K line and its associated reflection spectrum which are lagged behind
the continuum variability by the light-travel time from the source to the disc.
The measured lag timescales in the iron band can be as short as $\sim R_g/c$,
where $R_g$ is the gravitational radius, which is often interpreted as evidence
for a very small continuum source close to the event horizon of a rapidly
spinning black hole. However, the short lags can also be produced by reflection
from more distant material, because the primary photons with no time-delay
dilute the time-lags caused by the reprocessed photons. We perform a
Monte-Carlo simulation to calculate the dilution effect in the X-ray
reverberation lags from a half-shell of neutral material placed at $100\,R_g$
from the central source. This gives lags of $\sim2\,R_g/c$, but the iron line
is a distinctly narrow feature in the lag-energy plot, whereas the data often
show a broader line. We show that both the short lag and the line broadening
can be reproduced if the scattering material is outflowing at $\sim0.1c$. The
velocity structure in the wind can also give shifts in the line profile in the
lag-energy plot calculated at different frequencies. Hence we propose that the
observed broad iron reverberation lags and shifts in profile as a function of
frequency of variability can arise from a disc wind at fairly large distances
from the X-ray source.",1805.00046v1
2018-07-16,Revisiting the iron abundance in the hyper iron-poor star HE$~$1327-2326 with UV COS/$HST$ data,"We present a new iron abundance analysis of the hyper metal-poor star
HE$~$1327-2326, based on Fe II lines detected in its UV spectral range for the
first time. In a Cosmic Origins Spectrograph (COS) spectrum, five new Fe II
lines could be measured. A Si I line was also detected for the first time. We
determine a 1D Local Thermodynamic Equilibrium (LTE) Fe II abundance of [Fe
II/H] = -5.99$\pm$0.25. We also investigate departures from LTE for both Fe I
and Fe II lines. Guided by 3D Non-LTE (NLTE) analyses of other well-studied
metal-poor stars, we identify potential ""residual"" 3D effects in HE$~$1327-2326
arising from the absence of full 3D NLTE Fe calculations. Accordingly, we
employ measurements of 10 weak Fe I lines previously detected in an optical
spectrum of HE$~$1327-2326, as no Fe I lines are detectable in our UV spectrum.
Following our previous work, we adopt the 1D NLTE Fe I abundance of [Fe/H] =
-5.20$\pm$0.12 for HE$~$1327-2326. Adopting a value based on the optical Fe I
rather than UV lines was heavily informed by our extensive investigation of
model atmosphere and radiative transfer effects on different lines accross the
entire UV-optical wavelength range. An iron abundance of [Fe/H] =
-5.20$\pm$0.12 is only 0.2 dex higher than what was used in previous studies.
Accordingly, no previous conclusions regarding the nature of the star are
affected.",1807.06153v1
2019-02-13,Strain Controlling Catalytic Efficiency of Water Oxidation for Ni1-xFexOOH alloy,"A catalyst surface may be exposed to strain due to application of load or
interfacing with a substrate with large lattice mismatch. In order to test the
effect of strain on catalytic efficiency, we use Density Functional Theory +U
(DFT+U) to model water oxidation on expanded and contracted surfaces of the
Ni1-xFexOOH alloy, one of the best known catalysts for water splitting. We find
that a low amount of iron content has a similar effect as of applying
compressive strain. Due to high oxidation state of Fe4+ at the active site, the
Fe-O bond is shorter than in pure FeOOH, which is beneficial for extracting
electrons from states delocalized on Fe and Ni atoms. At 33% of Fe content the
efficiency is even better since Fe3+ is at the active site and can easily
change oxidation state during the reaction. However, the efficiency drops at
higher iron percentages since the surface is unstable and may form FeOOH
aggregates. We find that the best performance is obtained at 33% iron content
and 5% expansion. Therefore, in addition to changing iron content, strain can
also be used as a control handle for improving water splitting catalysis.",1902.04788v1
2019-03-27,"Design, Fabrication and Characterization of FeAl-based Metallic-Intermetallic Laminate (MIL) Composites","FeAl-based MIL composites of various iron alloys were fabricated with an
innovative 'multiple-thin-foil' configuration and 'two-stage reaction'
strategy.",1903.11724v1
2019-04-02,"The Wolf-Rayet Stellar Response To The Iron Opacity Bump: Envelope Inflation, Winds, and Microturbulence","Early-type Wolf-Rayet(WR) stellar models harbor a super-Eddington layer in
their outer envelopes due to a prominent iron opacity bump. In the past few
decades, one-dimensional hydrostatic and time-steady hydrodynamic models have
suggested a variety of WR responses to a super-Eddington force including
envelope inflation and optically thick winds. In this paper, I study these
responses using semianalytical estimates and WR models from both MESA and Ro &
Matzner; four conclusions are present. First, early-type WR stars do not harbor
inflated envelopes because they have either strong winds or insufficient
luminosities. Second, the condition for an opacity bump to harbor a sonic point
is expressible as a minimum mass-loss rate, $\dot{M}_{\rm sp}(L_*)$. In
agreement with Grassitelli et al. and Ro, the majority of galactic early-type
WR stars can harbor sonic points at the iron opacity bump. However, about half
of those in the Large Magellanic Cloud cannot given typical wind parameters.
Third, WR winds driven by the iron opacity bump must have mass-loss rates that
exceed a global minimum of $10^{-5.8}-10^{-6}M_\odot\,{\rm yr}^{-1}$. Lastly,
the observed early-type WR distribution follows a simple mass-loss relation
derived here if the radiation-to-gas pressure ratio is approximately $p_r/p_g
\sim 145$ in the wind; a value consistent with studies by Grafener et al. and
Nakauchi & Saio.",1904.01703v1
2019-04-30,Scalable Majorana vortex modes in iron-based superconductors,"A vortex in an s-wave superconductor with a surface Dirac cone can trap a
Majorana bound state with zero energy leading to a zero-bias peak (ZBP) of
tunneling conductance. The iron-based superconductor FeTe$_x$Se$_{1-x}$ is one
of the material candidates hosting these Majorana vortex modes. It has been
observed by recent scanning tunneling spectroscopy measurement that the
fraction of vortex cores possessing ZBPs decreases with increasing magnetic
field on the surface of this iron-based superconductor. We construct a
three-dimensional tight-binding model simulating the physics of over a hundred
Majorana vortex modes in FeTe$_x$Se$_{1-x}$ with realistic physical parameters.
Our simulation shows that the Majorana hybridization and disordered vortex
distribution can explain the decreasing fraction of the ZBPs observed in the
experiment. Furthermore, we find the statistics of the energy peaks off zero
energy in our simulation with the Majorana physics in agreement with the
analyzed peak statistics in the vortex cores from the experiment. This
agreement and the explanation of the decreasing ZBP fraction lead to an
important indication of scalable Majorana vortex modes in the iron-based
superconductor. Thus, FeTe$_x$Se$_{1-x}$ can be one promising platform
possessing scalable Majorana qubits for quantum computing. In addition, we
further show the interplay of the ZBP presence and the vortex locations
qualitatively agrees with our additional experimental observation and predict
the universal spin signature of the hybridized multiple Majorana vortex modes.",1904.13374v3
2019-06-18,X-ray reprocessing: Through the eclipse spectra of high mass X-ray binaries with XMM-Newton,"The study of X-ray reprocessing is one of the key diagnostic tools to probe
the environment in X-ray binary systems. One difficult aspect of studying X-ray
reprocessing is the presence of much brighter primary radiation from the
compact star together with the reprocessed radiation. In contrast for eclipsing
systems, the X-rays we receive during eclipse are only those produced by
reprocessing of the emission from the compact star by the surrounding medium.
We report results from a spectral study of the X-ray emission during eclipse
and outside eclipse (when available) in 9 high mass X-ray binaries (HMXBs) with
XMM- Newton EPIC pn to investigate different aspects of the stellar wind in
these HMXBs. During eclipse the continuum component of the spectrum is reduced
by a factor of $\sim$8-237, but the count-rate for 6.4 keV Iron emission line
or complex of Iron emission lines in HMXBs are reduced by a smaller factor
leading to large equivalent widths of the Iron emission lines. This indicates a
large size for the line emission region, comparable to or larger than the
companion star in these HMXB systems. However there are significant system to
system differences. 4U 1538$-$52, in spite of having a large absorption column
density, shows a soft emission component with comparable flux during the
eclipse and out-of-eclipse phases. Emission from Hydrogen-like Iron has been
observed in LMC X-4 for the first time, in the out-of-eclipse phase in one of
the observations. Overall, we find significant differences in the eclipse
spectrum of different HMXBs and also in their eclipse spectra against
out-of-eclipse spectra.",1906.07739v1
2019-11-13,Superparamagnetic iron oxide nanoparticles conjugated with doxorubicin for targeting breast cancer,"Development of the next generations of cancer therapy modalities is currently
a crucial requirement of oncology. Advances in nanotechnology are bringing us
closer to the development of dual and multifunctional nanoparticles that are
challenging the traditional distinction between diagnostic and treatment
agents. The chase of innovative, multifunctional, more efficient, and safer
treatments is a major challenge in preclinical nanoparticle-mediated
thermotherapeutic research for breast cancer. Here, we report that iron oxide
nanoparticles have the dual capacity to act as both magnetic and drug delivery
agents. The aim of this work was to investigate the in vitro effect of the
loading of doxorubicin (DOX) on negatively charged polycarboxylic iron-oxide
nanoparticles (SPIONs) and Rhodamine B functionalized SPIONs on breast
carcinoma cell lines. For proper analysis and understanding of cell behavior
after administration of DOX-SPIONs compared with free DOX, a complex set of in
vitro tests, including production of MTT assay, cell cycle determination, and
cellular uptake, were utilized. In summary, we have developed a magnetic
nanoparticle-based drug delivery system that sequentially delivers the
cytotoxic drug doxorubicin to breast cancer cells (MCF-7 and MDA-MB-231). The
drug-coated nanoparticles, DOX-NPs, were assembled stepwise, with doxorubicin
adsorbed to bare iron oxide nanoparticles first, by electrostatic reaction and
allowed for the complexation of doxorubicin. In contrast, they were
internalized to a much greater extent in MCF-7 and MDA-MB-231 cells and were
cytotoxic due to the synergistic action of the two drugs and the effects of
hyperthermia. The drug-coated particles were able to inhibit growth and
proliferation of breast cancer cells in vitro, indicating that the system has
potential to act as an antimetastatic chemothermotherapeutic agent.",1911.05378v1
2020-03-06,Mössbauer parameters of $^{57}$Fe substituents in the topological insulator $Bi_2Se_3$,"$^{57}$Fe M\""ossbauer spectroscopy can probe several \emph{local} structural,
electronic and magnetic properties of Fe-containing systems. However, to
establish a direct relationship between these properties and a system's
geometric structure, the experimental M\""ossbauer parameters need to be
analyzed \emph{via} electronic structure calculations. Herein, structural,
electronic and magnetic effects of iron substituents in the topological
insulator $Bi_2Se_3$, as uniquely probed by $^{57}$Fe M\""ossbauer spectroscopy,
have been determined \emph{via} spin-polarized electronic structure
calculations. The iron ion substituents, of \emph{nominal} Fe$^{3+}(S = 5/2)$
oxidation and spin state, are unequivocally shown to substitute Bi$^{3+}$ sites
in epitaxial $Bi_2Se_3$ thin-films used for M\""ossbauer measurements.
Concomitant with iron substitution, \emph{localized} structural rearrangements
take place whereby the longer Bi-Se bonds of the native system are replaced by
significantly shorter Fe-Se counterparts in the Fe-containing system. The
resulting distorted-octahedral environment about substituent iron ions gives
rise to characteristic M\""ossbauer parameters ($\delta_{Fe} \approx$ 0.51 mm/s,
$\Delta E_{Q} \approx$ 0.20 mm/s) which have been calculated in excellent
agreement with measured values for Fe-doped $Bi_2Se_3$ thin films. Consistent
with a substituent Fe$^{3+}$ ion's \emph{nominal} high-spin electronic
configuration ($t_{2g}^{\uparrow \uparrow \uparrow} e_g^{\uparrow \uparrow}$),
an Fe-centered spin density has been established which, nevertheless, extends
towards neighboring Se atoms \emph{via} direct Fe-Se bonding and concomitant
Fe(d)-Se(p) hybridization.",2003.03458v1
2020-04-01,Phase transitions and spin-state of iron in FeO at the conditions of Earth's deep interior,"Iron-bearing oxides undergo a series of pressure-induced electronic, spin and
structural transitions that can cause seismic anomalies and dynamic
instabilities in Earth's mantle and outer core. We employ x-ray diffraction and
x-ray emission spectroscopy along with state-of-the-art density functional plus
dynamical mean-field theory (DFT+DMFT) to characterize the electronic structure
and spin states, and crystal-structural properties of w\""ustite (Fe$_{1-x}$O)
-- a basic oxide component of Earth's interior -- at high pressure-temperature
conditions up to 140 GPa and 2100 K. We find that FeO exhibits complex
polymorphism under pressure, with abnormal compression behavior associated with
electron-spin and crystallographic phase transitions, and resulting in a
substantial change of bulk modulus. Our results reveal the existence of a
high-pressure phase characterized by a metallic high-spin state of iron at
about the pressure-temperature conditions of Earth's core-mantle boundary. The
presence of high-spin metallic iron near the base of the mantle can
significantly influence the geophysical and geochemical properties of Earth's
deep interior.",2004.00652v2
2020-06-05,Planetary mass-radius relations across the galaxy,"Planet formation theory suggests that planet bulk compositions are likely to
reflect the chemical abundance ratios of their host star's photosphere.
Variations in the abundance of particular chemical species in stellar
photospheres between different galactic stellar populations demonstrate that
there are differences among the expected solid planet bulk compositions. We aim
to present planetary mass-radius relations of solid planets for kinematically
differentiated stellar populations, namely, the thin disc, thick disc, and
halo. Using two separate internal structure models, we generated synthetic
planets using bulk composition inputs derived from stellar abundances. We
explored two scenarios, specifically iron-silicate planets at 0.1 AU and
silicate-iron-water planets at 4 AU. We show that there is a persistent
statistical difference in the expected mass-radius relations of solid planets
among the different galactic stellar populations. At 0.1 AU for silicate-iron
planets, there is a 1.51 to 2.04\% mean planetary radius difference between the
thick and thin disc stellar populations, whilst for silicate-iron-water planets
past the ice line at 4 AU, we calculate a 2.93 to 3.26\% difference depending
on the models. Between the halo and thick disc, we retrieve at 0.1 AU a 0.53 to
0.69\% mean planetary radius difference, and at 4 AU we find a 1.24 to 1.49\%
difference depending on the model. Future telescopes (such as PLATO) will be
able to precisely characterize solid exoplanets and demonstrate the possible
existence of planetary mass-radius relationship variability between galactic
stellar populations.",2006.03601v2
2020-10-01,Near L-Edge Single and Multiple Photoionization of Doubly Charged Iron Ions,"Using the photon-ion merged-beams technique at a synchrotron light source, we
have measured relative cross sections for single and up to five-fold
photoionization of Fe$^{2+}$ ions in the energy range 690--920 eV. This range
contains thresholds and resonances associated with ionization and excitation of
$2p$ and $2s$ electrons. Calculations were performed to simulate the total
absorption spectra. The theoretical results show very good agreement with the
experimental data, if overall energy shifts of up to 2.5 eV are applied to the
calculated resonance positions and assumptions are made about the initial
experimental population of the various levels of the Fe$^{2+}$([Ar]$3d^6$)
ground configuration. Furthermore, we performed extensive calculations of the
Auger cascades that result when an electron is removed from the $2p$ subshell
of Fe$^{2+}$. These computations lead to a better agreement with the measured
product-charge-state distributions as compared to earlier work. We conclude
that the $L$-shell absorption features of low-charged iron ions are useful for
identifying gas-phase iron in the interstellar medium and for discriminating
against the various forms of condensed-phase iron bound to composite
interstellar dust grains.",2010.00473v1
2020-10-13,Chemical Fingerprints of Formation in Rocky Super-Earths' Data,"The composition of rocky exoplanets in the context of stars' composition
provides important constraints to formation theories. In this study, we select
a sample of exoplanets with mass and radius measurements with an uncertainty
<25% and obtain their interior structure. We calculate compositional markers,
ratios of iron to magnesium and silicon, as well as core-mass fractions (cmf)
that fit the planetary parameters, and compare them to the stars'. We find four
key results that successful planet formation theories need to predict: (1) In a
population sense, the composition of rocky planets spans a wider range than
stars. The stars' Fe/Si distribution is close to a Gaussian distribution
$1.63^{+0.91}_{-0.85}$, while the planets' distribution peaks at lower values
and has a longer tail, $1.15^{+1.43}_{-0.76}$. It is easier to see the
discrepancy in cmf space, where primordial stellar composition is
$0.32^{+0.14}_{-0.12}$, while rocky planets' follow a broader distribution
$0.24^{+0.33}_{-0.18}$. (2) We introduce uncompressed density
($\overline{\rho_0}$ at reference pressure/temperature) as a metric to compare
compositions. With this, we find what seems to be the maximum iron enrichment
that rocky planets attain during formation ($\overline{\rho_0}$ ~ 6 and cmf ~
0.8). (3) Highly irradiated planets exhibit a large range of compositions. If
these planets are the result of atmospheric evaporation, iron enrichment and
perhaps depletion must happen before gas dispersal. And (4), we identify a
group of highly-irradiated planets that, if rocky, would be 2-fold depleted in
Fe/Si with respect to the stars. Without a reliable theory for forming
iron-depleted planets, these are interesting targets for follow up.",2010.06480v1
2020-11-16,Role of anion in the pairing interaction of iron-based superconductivity,"High-temperature iron-based superconductivity develops in a structure with
unusual lattice-orbital geometry, based on a planar layer of Fe atoms with 3d
orbitals and tetrahedrally coordinated by anions. Here we elucidate the
electronic role of anions in the iron-based superconductors utilizing
state-of-the-art scanning tunneling microscopy. By measuring the local
electronic structure, we find that As anion in Ba0.4K0.6Fe2As2 has a striking
impact on the electron pairing. The superconducting electronic feature can be
switched off/on by removing/restoring As atoms on Fe layer at the atomic scale.
Our analysis shows that this remarkable atomic switch effect is related to the
geometrical cooperation between anion mediated hopping and unconventional
pairing interaction. Our results uncover that the local Fe-anion coupling is
fundamental for the pairing interaction of iron-based superconductivity, and
promise the potential of bottom-up engineering of electron pairing.",2011.07701v1
2020-11-26,Oxidising and carburising catalyst conditioning for the controlled growth and transfer of large crystal monolayer hexagonal boron nitride,"Hexagonal boron nitride (h-BN) is well-established as a requisite support,
encapsulant and barrier for 2D material technologies, but also recently as an
active material for applications ranging from hyperbolic metasurfaces to room
temperature single-photon sources. Cost-effective, scalable and high quality
growth techniques for h-BN layers are critically required. We utilise
widely-available iron foils for the catalytic chemical vapour deposition (CVD)
of h BN and report on the significant role of bulk dissolved species in h-BN
CVD, and specifically, the balance between dissolved oxygen and carbon. A
simple pre-growth conditioning step of the iron foils enables us to tailor an
error-tolerant scalable CVD process to give exceptionally large h-BN monolayer
domains. We also develop a facile method for the improved transfer of as-grown
h-BN away from the iron surface by means of the controlled humidity oxidation
and subsequent rapid etching of a thin interfacial iron oxide; thus, avoiding
the impurities from the bulk of the foil. We demonstrate wafer-scale (2 inch)
production and utilise this h-BN as a protective layer for graphene towards
integrated (opto) electronic device fabrication.",2011.13176v1
2020-12-23,Hot electron relaxation in normal state of iron pnictides: memory function approach,"This study leads to the investigation of the non-equilibrium electron
relaxation in the normal state of iron pnictides. Here we consider the
relaxation of electrons due to their coupling with magnons and phonons in the
metallic state of iron pnictides using the memory function approach. In the
present model, electrons live at a higher temperature than that of the phonon
and magnon baths, mimicking a non-equilibrium steady state situation. Further
we analyze theoretically the generalized Drude scattering rate within the
framework of Two Temperature Model and study the full frequency and temperature
behavior for it. In zero frequency regime, the rate of electron-magnon
scattering and electron-phonon scattering shows a linear temperature dependence
at higher temperature values greater than Bloch-Gr\""{u}neisen temperature.
Whereas at lower temperature values, $T\ll\Theta_{BG}$, corresponding
scattering rates follow the temperature behavior as ($1/\tau_{e-p} \varpropto
T^3$) and ($1/\tau_{e-m} \varpropto T^{3/2}$), respectively. In the AC regime,
we compute that $1/\tau \propto \omega^2$ for $\omega\ll\omega_{BG}$ and for
the values greater than the Bloch-Gr\""{u}neisen frequency, it is
$\omega$-independent. Also, in lower frequency and zero temperature limit, we
have observed the different frequency scale of electron-magnon and
electron-phonon scattering i.e ($1/\tau \propto \omega^{3/2}$) and
($1/\tau\propto \omega^{3}$). These results can be viewed with the pump-probe
experimental setting for the normal state of iron pnictides.",2012.12650v1
2021-02-10,Influence of microstructure and atomic-scale chemistry on iron ore reduction with hydrogen at 700°C,"With 1.85 billion tons produced per year, steel is the most important
material class in terms of volume and environmental impact. While steel is a
sustainability enabler, for instance through lightweight design, magnetic
devices, and efficient turbines, its primary production is not. For 3000 years,
iron has been reduced from ores using carbon. Today 2.1 tons CO2 are produced
per ton of steel, causing 30% of the global CO2 emissions in the manufacturing
sector, which translates to 6.5% of the global CO2 emissions. These numbers
qualify iron- and steel-making as the largest single industrial greenhouse gas
emission source. The envisaged future industrial route to mitigate these CO2
emissions targets green hydrogen as a reductant. Although this reaction has
been studied for decades, its kinetics is not well understood, particularly
during the wustite reduction step which is dramatically slower than the
hematite reduction. Many rate-limiting factors of this reaction are set by the
micro- and nanostructure as well as the local chemistry of the ores. Their
quantification allows knowledge-driven ore preparation and process optimization
to make the hydrogen-based reduction of iron ores commercially viable, enabling
the required massive CO2 mitigation to ease global warming. Here, we report on
a multi-scale structure and composition analysis of iron reduced from hematite
with pure H2, reaching down to near-atomic scale.",2102.05654v1
2021-04-06,Early volatile depletion on planetesimals inferred from C-S systematics of iron meteorite parent bodies,"During the formation of terrestrial planets, volatile loss may occur through
nebular processing, planetesimal differentiation, and planetary accretion. We
investigate iron meteorites as an archive of volatile loss during planetesimal
processing. The carbon contents of the parent bodies of magmatic iron
meteorites are reconstructed by thermodynamic modelling. Calculated
solid/molten alloy partitioning of C increases greatly with liquid S
concentration and inferred parent body C concentrations range from 0.0004 to
0.11 wt.%. Parent bodies fall into 2 compositional clusters characterized by
cores with medium, and low C/S. Both of these require significant planetesimal
degassing, as metamorphic devolatilization on chondrite-like precursors is
insufficient to account for their C depletions. Planetesimal core formation
models, ranging from closed system extraction to degassing of a wholly molten
body, show that significant open system silicate melting and volatile loss is
required to match medium and low C/S parent body core compositions. Greater
depletion in C relative to S is the hallmark of silicate degassing, indicating
that parent body core compositions record processes that affect composite
silicate/iron planetesimals. Degassing of bare cores stripped of their silicate
mantles would deplete S with negligible C loss, and could not account for
inferred parent body core compositions. Devolatilization during small-body
differentiation is thus a key process in shaping the volatile inventory of
terrestrial planets derived from planetesimals and planetary embryos.",2104.02706v1
2021-05-15,Two-step nucleation of the Earth's inner core,"It has long been assumed the Earth's solid inner core started to grow when
molten iron cooled to its melting point. However, the nucleation mechanism,
which is a necessary step of crystallization, has not been well understood.
Recent studies found it requires an unrealistic degree of undercooling to
nucleate the stable hexagonal close-packed (hcp) phase of iron, which can never
be reached under the actual Earth's core conditions. This contradiction leads
to the inner core nucleation paradox [1]. Here, using a persistent-embryo
method and molecular dynamics simulations, we demonstrate that the metastable
body-centered cubic (bcc) phase of iron has a much higher nucleation rate than
the hcp phase under inner-core conditions. Thus, the bcc nucleation is likely
to be the first step of inner core formation instead of direct nucleation of
the hcp phase. This mechanism reduces the required undercooling of iron
nucleation, which provides a key factor to solve the inner-core nucleation
paradox. The two-step nucleation scenario of the inner core also opens a new
avenue for understanding the structure and anisotropy of the present inner
core.",2105.07296v2
2021-06-04,Disentangling Dense Multi-Cable Knots,"Disentangling two or more cables requires many steps to remove crossings
between and within cables. We formalize the problem of disentangling multiple
cables and present an algorithm, Iterative Reduction Of Non-planar Multiple
cAble kNots (IRON-MAN), that outputs robot actions to remove crossings from
multi-cable knotted structures. We instantiate this algorithm with a learned
perception system, inspired by prior work in single-cable untying that given an
image input, can disentangle two-cable twists, three-cable braids, and knots of
two or three cables, such as overhand, square, carrick bend, sheet bend, crown,
and fisherman's knots. IRON-MAN keeps track of task-relevant keypoints
corresponding to target cable endpoints and crossings and iteratively
disentangles the cables by identifying and undoing crossings that are critical
to knot structure. Using a da Vinci surgical robot, we experimentally evaluate
the effectiveness of IRON-MAN on untangling multi-cable knots of types that
appear in the training data, as well as generalizing to novel classes of
multi-cable knots. Results suggest that IRON-MAN is effective in disentangling
knots involving up to three cables with 80.5% success and generalizing to knot
types that are not present during training, with cables of both distinct or
identical colors.",2106.02252v1
2021-09-17,Quantum hardware calculations of periodic systems with partition-measurement symmetry verification: simplified models of hydrogen chain and iron crystals,"Running quantum algorithms on real hardware is essential for understanding
their strengths and limitations, especially in the noisy intermediate scale
quantum (NISQ) era. Herein we focus on the practical aspect of quantum
computational calculations of solid-state crystalline materials based on theory
developed in our group by using real quantum hardware with a novel noise
mitigation technique referred to as partition-measurement symmetry
verification, which performs post-selection of shot counts based on $Z_{2}$ and
$U_{1}$ symmetry verification. We select two periodic systems with different
level of complexity for these calculations. One of them is the distorted
hydrogen chain as an example of very simple systems, and the other one is iron
crystal in the BCC and FCC phases as it is considered to be inaccessible by
using classical computational wavefunction methods. The ground state energies
are evaluated based on the translational quantum subspace expansion (TransQSE)
method for the hydrogen chain, and periodic boundary condition adapted VQE for
our iron models. By applying these techniques for the simplest 2 qubit iron
model systems, the correlation energies obtained by the hardware calculations
agree with those of the state-vector simulations within $\sim$5 kJ/mol.
Although the quantum computational resources used for those experiments are
still limited, the techniques applied to obtain our simplified models will be
applicable in essentially the same manner to more complicated cases as quantum
hardware matures.",2109.08401v4
2021-09-23,Large Exotic Spin Torques in Antiferromagnetic Iron Rhodium,"Spin torque is a promising tool for driving magnetization dynamics for novel
computing technologies. These torques can be easily produced by spin-orbit
effects, but for most conventional spin source materials, a high degree of
crystal symmetry limits the geometry of the spin torques produced. Magnetic
ordering is one way to reduce the symmetry of a material and allow exotic
torques, and antiferromagnets are particularly promising because they are
robust against external fields. We present spin torque ferromagnetic resonance
measurements and second harmonic Hall measurements characterizing the spin
torques in antiferromagnetic iron rhodium alloy. We report extremely large,
strongly temperature-dependent exotic spin torques with a geometry apparently
defined by the magnetic ordering direction. We find the spin torque efficiency
of iron rhodium to be (330$\pm$150) % at 170 K and (91$\pm$32) % at room
temperature. We support our conclusions with theoretical calculations showing
how the antiferromagnetic ordering in iron rhodium gives rise to such exotic
torques.",2109.11108v1
2021-12-29,"Composition of super-Earths, super-Mercuries, and their host stars","Because of their common origin, it was assumed that the composition of planet
building blocks should, to a first order, correlate with stellar atmospheric
composition, especially for refractory elements. In fact, information on the
relative abundance of refractory and major rock-forming elements such as Fe,
Mg, Si has been commonly used to improve interior estimates for terrestrial
planets. Recently Adibekyan et al. (2021) presented evidence of a tight
chemical link between rocky planets and their host stars. In this study we add
six recently discovered exoplanets to the sample of Adibekyan et al and
re-evaluate their findings in light of these new data. We confirm that i)
iron-mass fraction of rocky exoplanets correlates (but not a 1:1 relationship)
with the composition of their host stars, ii) on average the iron-mass fraction
of planets is higher than that of the primordial iron-mass fraction of the
protoplanetary disk, iii) super-Mercuries are formed in disks with high iron
content. Based on these results we conclude that disk-chemistry and planet
formation processes play an important role in the composition, formation, and
evolution of super-Earths and super-Mercuries.",2112.14512v1
2022-01-06,Ironing out the details of unconventional superconductivity,"Superconductivity is a remarkably widespread phenomenon observed in most
metals cooled down to very low temperatures. The ubiquity of such conventional
superconductors, and the wide range of associated critical temperatures, is
readily understood in terms of the celebrated Bardeen-Cooper-Schrieffer (BCS)
theory. Occasionally, however, unconventional superconductors are found, such
as the iron-based materials, which extend and defy this understanding in new
and unexpected ways. In the case of the iron-based superconductors, this
includes a new appreciation of the ways in which the presence of multiple
atomic orbitals can manifest in unconventional superconductivity, giving rise
to a rich landscape of gap structures that share the same dominant pairing
mechanism. Besides superconductivity, these materials have also led to new
insights into the unusual metallic state governed by the Hund's interaction,
the control and mechanisms of electronic nematicity, the impact of magnetic
fluctuations and quantum criticality, and the significance of topology in
correlated states. Over the thirteen years since their discovery, they have
proven to be an incredibly fruitful testing ground for the development of new
experimental tools and theoretical approaches, both of which have extensively
influenced the wider field of quantum materials.",2201.02095v1
2022-03-21,White Dwarf Photospheric Abundances in Cataclysmic Variables -- II. White Dwarfs With and Without a Mask,"Taking advantage of the now available Gaia EDR3 parallaxes, we carry out an
archival {\it Hubble Space Telescope} (HST) far ultraviolet spectroscopic
analysis of 10 cataclysmic variable systems, including 5 carefully selected
eclipsing systems. We obtain accurate white dwarf (WD) masses and temperatures,
in excellent agreement with the masses for 4 of the eclipsing systems. For
three systems in our sample, BD Pav, HS 2214, and TT Crt, we report the first
robust masses for their WDs. We modeled the absorption lines to derive the WD
chemical abundances and rotational velocities for each of the ten systems. As
expected, for five higher inclination ($i \gtrsim 75^{\circ}$) systems, the
model fits are improved with the inclusion of a cold absorbing slab (an iron
curtain masking the WD) with $N_{\rm H} \approx 10^{20}-10^{22}$cm$^{-2}$.
Modeling of the metal lines in the HST spectra reveals that 7 of the 10 systems
have significant subsolar carbon abundance, and six have subsolar silicon
abundance, thereby providing further evidence that CV WDs exhibit subsolar
abundances of carbon and silicon. We suggest that strong aluminum absorption
lines (and iron absorption features) in the spectra of some CV WDs (such as IR
Com) may be due to the presence of a {\it thin} iron curtain ($N_{\rm H}\approx
10^{19}$cm$^{-2}$) rather than to suprasolar aluminum and iron abundances in
the WD photosphere. The derived WD (projected) rotational velocities all fall
in the range $\approx 100-400$~km/s, all sub-Keplerian similar to the values
obtained in earlier studies.",2203.11020v1
2022-04-11,Forming Iron-rich Planets with Giant Impacts,"We investigate mantle stripping giant impacts (GI) between super-Earths with
masses between 1 M$_{\oplus}$ and 20 M$_{\oplus}$. We infer new scaling laws
for the mass of the largest fragment and its iron mass fraction, as well as
updated fitting coefficients for the critical specific impact energy for
catastrophic disruption, $Q_{RD}^{*}$. With these scaling laws, we derive
equations that relate the impact conditions, i.e., target mass, impact velocity
and impactor-to-target mass ratio, to the mass and iron mass fraction of the
largest fragment. This allows one to predict collision outcomes without
performing a large suite of simulations. Using these equations we present the
maximum and minimum planetary iron mass fraction as a result of collisional
stripping of its mantle for a given range of impact conditions. We also infer
the radius for a given mass and composition using interior structure models and
compare our results to observations of metal-rich exoplanets. We find good
agreement between the data and the simulated planets suggesting that GI could
have played a key role in their formation. Furthermore, using our scaling laws
we can further constrain the impact conditions that favour their masses and
compositions. Finally, we present a flexible and easy-to-use tool that allows
one to predict mass and composition of a planet after a GI for an arbitrary
range of impact conditions which in turn allows to assess the role of GI in
observed planetary systems.",2204.04925v3
2023-01-11,Evolution of the spin dynamics during freezing in the spin-glass Fe$_{x}$Cr$_{1-x}$,"In the iron--chromium system, Fe$_{x}$Cr$_{1-x}$, a wide dome of spin-glass
behavior emerges when the ferromagnetism of iron is suppressed and the
antiferromagnetism of chromium emerges as a function of increasing iron content
$x$. As both, the high-temperature state and the characteristic cluster size
vary as a function of $x$, different regimes of spin-glass behavior may be
compared in a single, isostructural material system. Here, we report a study of
the spin dynamics across the freezing process into the spin-glass state for
different iron concentrations ($x = 0.145$, $0.175$, $0.21$) using Modulation
of IntEnsity with Zero Effort (MIEZE) spectroscopy. In the parameter range
studied, the relaxation process observed experimentally may be described well
in terms of a stretched exponential. In the reentrant cluster-glass regime, $x
= 0.145$, this behavior persists up to high temperatures. In comparison, in the
superparamagnetic regime, $x = 0.175$ and $x = 0.21$, a single relaxation time
at elevated temperatures is observed. For all samples studied, the spin
relaxation exhibits a momentum dependence consistent with a power law,
providing evidence of a dispersive character of the spin relaxation.",2301.04495v1
2023-03-12,Competing Magnetic Interactions and Field-Induced Metamagnetic Transition in Highly Crystalline Phase-Tunable Iron Oxide Nanorods,"The inherent existence of multi phases in iron oxide nanostructures
highlights the significance of them being investigated deliberately to
understand and possibly control the phases. Here, the effects of annealing at
250 0C with a variable duration on the bulk magnetic and structural properties
of high aspect ratio bi-phase iron oxide nanorods with ferrimagnetic Fe3O4 and
antiferromagnetic alpha-Fe2O3 is explored. Increasing annealing time under a
free flow of oxygen enhanced the alpha-Fe2O3 volume fraction, and improved the
crystallinity of the Fe3O4 phase, identified in changes in the magnetization as
a function of annealing time. A critical annealing time of approximately 3
hours maximized the presence of both phases, as observed via an enhancement in
the magnetization and an interfacial pinning effect. This is attributed to
disordered spins separating the magnetically distinct phases which tend to
align with the application of a magnetic field at high temperatures. The
increased antiferromagnetic phase can be distinguished due to the field-induced
metamagnetic transitions observed in structures annealed for more than 3 hours
and was especially prominent in the 9-hour annealed sample. Our controlled
study in determining the changes in volume fractions with annealing time will
enable precise control over phase tunability in iron oxide nanorods, allowing
custom-made phase volume fractions in different applications ranging from
spintronics to biomedical applications.",2303.06684v1
2023-03-24,Early phases of the Galaxy from the chemical imprint on the iron-poor stars J0815+4729 and J0023+0307,"We have been exploring large spectroscopic databases such as SDSS to search
for unique stars with extremely low iron content with the goal of extracting
detailed information from the early phases of the Galaxy. We recently
identified two extremely iron-poor dwarf stars J0815+4729 (Aguado et al. 2018a)
and J0023+0307 (Aguado et al. 2018b) from SDSS/BOSS database and confirmed from
high-quality spectra taken with ISIS and OSIRIS spectrographs at the 4.2m WHT
and 10.4m GTC telescopes, respectively, located in La Palma (Canary Islands,
Spain). We have also acquired high-resolution spectroscopy with UVES at 8.2m
VLT telescope (Paranal, ESO, Chile) and HIRES at the 10m KeckI telescope (Mauna
Kea, Hawaii, USA), uncovering the unique abundance pattern of these stars, that
reveal e.g. the extreme CNO abundances in J0815+4729 with ratios [X/Fe]~$> 4$
(Gonz\'alez Hern\'andez et al. 2020). In addition, we are able to detect Li at
the level of the lithium plateau in J0023+0307 (Aguado et al. 2019a), whereas
we are only able to give a Li upper-limit 0.7 dex below the lithium plateau in
J0815+4729, thus adding more complexity to the cosmological lithium problem.
New upcoming surveys such as WEAVE, 4MOST and DESI will likely allow us to
discover new interesting extremely iron-poor stars, that will certainly
contribute to our understanding of the Early Galaxy, and the properties of the
first stars and the first supernovae.",2303.14142v1
2023-10-27,Emergent spin-glass state in the doped Hund's metal CsFe2As2,"Hund's metal is one kind of correlated metal, in which the electronic
correlation is strongly influenced by the Hund's interaction. At high
temperatures, while the charge and orbital degrees of freedom are quenched, the
spin degrees of freedom can persist in terms of frozen moments. As temperature
decreases, a coherent electronic state with characteristic orbital
differentiation always emerges at low temperatures through an
incoherent-to-coherent crossover, which has been widely observed in iron-based
superconductors (e.g., iron selenides and AFe2As2 (A = K, Rb, Cs)).
Consequently, the above frozen moments are ""screened"" by coupling to orbital
degrees of freedom, leading to an emergent Fermi-liquid state. In contrast, the
coupling among frozen moments should impede the formation of the Fermi-liquid
state by competitive magnetic ordering, which is still unexplored in Hund's
metal. Here, in the iron-based Hund's metal CsFe2As2, we adopt a chemical
substitution at iron sites by Cr/Co atoms to explore the competitive magnetic
ordering. By a comprehensive study of resistivity, magnetic susceptibility,
specific heat and nuclear magnetic resonance, we demonstrate that the
Fermi-liquid state is destroyed in Cr-doped CsFe2As2 by a spinfreezing
transition below T_g ~ 22 K. Meanwhile, the evolution of charge degrees of
freedom measured by angle-resolved photoemission spectroscopy also supports the
competition between the Fermi-liquid state and spin-glass state.",2310.17858v1
2023-11-07,Direct reduction of iron-ore with hydrogen in fluidized beds: A coarse-grained CFD-DEM-IBM study,"Hydrogen metallurgy technology uses hydrogen as the reducing agent instead of
carbon reduction, which is one of the important ways to reduce carbon dioxide
emissions and ensure the green and sustainable development of iron and steel
industry. Due to the advantages of high gas-solid contact efficiency and
outstanding mass and heat transfer, direct reduction of iron ore in fluidized
beds has attracted much attention. In this study, a coarse-grained CFD-DEM-IBM
solver based on hybrid CPU-GPU computing is developed to simulate the direct
reduction process of two kinds of iron ore with hydrogen in fluidized beds,
where an unreacted shrinking core model based on multiple reaction paths is
used to model the reduction reactions, a coarse-grained model and multiple GPUs
enable the significant acceleration of particle computation, and the immersed
boundary method (IBM) enables the use of simple mesh even in complex geometries
of reactors. The predicted results of particle reduction degree are in good
agreement with the experimental values, which proves the correctness of the
CFD-DEM-IBM solver. In addition, the effects of reaction kinetic parameters and
operating temperature on particle reduction degree are also investigated.
Present study provides a method for digital design, optimization and scale-up
of ironmaking reactors.",2311.03908v1
2023-12-22,Broken inversion symmetry in van der Waals topological ferromagnetic metal iron germanium telluride,"Inversion symmetry breaking is critical for many quantum effects and
fundamental for spin-orbit torque, which is crucial for next-generation
spintronics. Recently, a novel type of gigantic intrinsic spin-orbit torque has
been established in the topological van-der-Waals (vdW) magnet iron germanium
telluride. However, it remains a puzzle because no clear evidence exists for
interlayer inversion symmetry breaking. Here, we report the definitive evidence
of broken inversion symmetry in iron germanium telluride directly measured by
the second harmonic generation (SHG) technique. Our data show that the crystal
symmetry reduces from centrosymmetric P63/mmc to noncentrosymmetric polar P3m1
space group, giving the three-fold SHG pattern with dominant out-of-plane
polarization. Additionally, the SHG response evolves from an isotropic pattern
to a sharp three-fold symmetry upon increasing Fe deficiency, mainly due to the
transition from random defects to ordered Fe vacancies. Such SHG response is
robust against temperature, ensuring unaltered crystalline symmetries above and
below the ferromagnetic transition temperature. These findings add crucial new
information to our understanding of this interesting vdW metal, iron germanium
telluride: band topology, intrinsic spin-orbit torque and topological vdW polar
metal states.",2312.14384v1
2024-01-05,The Fate of Primary Iron Sulfides in the CM1 Carbonaceous Chondrites: Effects of Advanced Aqueous Alteration on Primary Components,"We have carried out a SEM-EPMA-TEM study to determine the textures and
compositions of relict primary iron sulfides and their alteration products in a
suite of moderately to heavily-altered CM1 carbonaceous chondrites. We observed
four textural groups of altered primary iron sulfides: 1)
pentlandite+phyllosilicate (2P) grains, characterized by pentlandite with
submicron lenses of phyllosilicates, 2) pyrrhotite+pentlandite+magnetite (PPM)
grains, characterized by pyrrhotite-pentlandite exsolution textures with
magnetite veining and secondary pentlandite, 3) pentlandite+serpentine (PS)
grains, characterized by relict pentlandite exsolution, serpentine, and
secondary pentlandite, and 4) pyrrhotite+pentlandite+magnetite+serpentine
(PPMS) grains, characterized by features of both the PPM and PS grains.
  We have determined that all four groups were initially primary iron sulfides,
which formed from crystallization of immiscible sulfide melts within silicate
chondrules in the solar nebula. The fact that such different alteration
products could result from the same precursor sulfides within even the same
meteorite sample further underscores the complexity of the aqueous alteration
environment for the CM chondrites. The different alteration reactions for each
textural group place constraints on the mechanisms and conditions of alteration
with evidence for acidic environments, oxidizing environments, and changing
fluid compositions (Ni-bearing and Si-Mg-bearing).",2401.02932v1
2024-02-19,"Breaks in the Hall-Petch Relationship after Severe Plastic Deformation of Magnesium, Aluminum, Copper, and Iron","Strengthening by grain refinement via the Hall-Petch mechanism and softening
by nanograin formation via the inverse Hall-Petch mechanism have been the
subject of argument for decades, particularly for ultrafine-grained materials.
In this study, the Hall-Petch relationship is examined for ultrafine-grained
magnesium, aluminum, copper, and iron produced by severe plastic deformation in
the literature. Magnesium, aluminum, copper, and their alloys follow the
Hall-Petch relationship with a low slope, but an up-break appears when the
grain sizes are reduced below 500-1000 nm. This extra strengthening, which is
mainly due to the enhanced contribution of dislocations, is followed by a
down-break for grain sizes smaller than 70-150 nm due to the diminution of the
dislocation contribution and an enhancement of thermally-activated phenomena.
For pure iron with a lower dislocation mobility, the Hall-Petch breaks are not
evident, but the strength at the nanometer grain size range is lower than the
expected Hall-Petch trend in the submicrometer range. The strength of
nanograined iron can be increased to the expected trend by stabilizing grain
boundaries via impurity atoms. Detailed analyses of the data confirm that grain
refinement to the nanometer level is not necessarily a solution to achieve
extra strengthening, but other strategies such as microstructural stabilization
by segregation or precipitation are required.",2402.11798v1
2024-02-19,Ironing allocations,"I propose a new approach to solving standard screening problems when the
monotonicity constraint binds. A simple geometric argument shows that when
virtual values are quasi-concave, the optimal allocation can be found by
appropriately truncating the solution to the relaxed problem. I provide a
simple algorithm for finding this optimal truncation when virtual values are
concave.",2402.11881v1
1994-01-24,The Contribution of the Obscuring Torus to the X--Ray Spectrum of Seyfert Galaxies: A Test for the Unification Model,"The presence of an obscuring torus around the nucleus of Seyfert galaxies, as
supposed in the popular unification scheme, can strongly modify the X--ray
spectrum for both type 1 and 2 Seyfert galaxies. We find that if the torus is
Compton thick, it can scatter at small angles a significant fraction of the
nuclear radiation, and contribute to the continuum of Seyfert 1 galaxies above
$\sim$10 keV, and to the fluorescence iron line at 6.4 keV. At large
inclination angles and for large torus column densities, the spectrum is
attenuated by photoabsorption and Compton scattering, while the iron
fluorescence line produced by the torus can have large equivalent widths. Even
after dilution by the continuum scattered by the warm material outside the
torus, this iron line could be strong enough to explain the ``cold"" component
in the spectrum of NGC 1068. We stress that the complex pattern of the
predicted variability can be a powerful tool for constraining the parameters of
the model, such as the column density of the torus, its inclination and the
amount of warm scattering material.",9401044v1
1996-08-26,Variability of the iron K-emission line in the Seyfert 1 galaxy NGC 3516,"We present strong evidence for variability of the flux of the iron K$\alpha$
emission line in the Seyfert 1 galaxy, NGC 3516. Two ASCA observations,
separated by $\sim 1$~yr, showed a marked decrease in continuum flux by $\sim
60$~per cent. The flux in the broad, iron K$\alpha$ line decreased by the same
factor in this time period, with no evidence for changes in the line profile.
The line variability is significant at $>99$~per cent confidence and rules out
models in which the line is produced in a molecular torus located at $>1$~pc
from the nucleus. An accretion disk is considerably more likely.",9608171v1
1997-03-25,The iron K line complex in NGC1068: implications for X-ray reflection in the nucleus,"We report a new analysis of ASCA data on the iron K line complex in NGC1068.
The line complex basically consists of three components, as previously
reported. A weak red wing of the 6.4 keV fluoresence iron K line is found. A
plausible explanation is Compton scattering in optically thick, cold matter
which can be identified with an obscuring torus or cold gas in the host galaxy.
We also show that this `Compton shoulder' should be observable with ASCA using
a simulated reflection spectrum. In order to explain the two higher energy
lines as well as the cold 6.4 keV line, we fit the ASCA data with a composite
model of cold and warm reflection. This shows that cold reflection dominates
the observed X-ray emission above 4 keV. The two higher energy lines have large
equivalent width with respect to the warm-scattered continuum, suggesting that
efficient resonant scattering operates. The line energies are systematically
lower than those expected from resonant lines for FeXXV and FeXXVI by 100 eV.
The redshifts may be due to either the ionized gas of the warm mirror receding
at a radial velocity of 4000-5000 km/s, or effects of Compton scattering in a
complicated geometry.",9703159v1
1997-07-07,Special relativistic effects on the strength of the fluorescent K-alpha iron line from black hole accretion disks,"The broad iron K$\alpha$ emission line, commonly seen in the X-ray spectrum
of Seyfert nuclei, is thought to originate when the inner accretion disk is
illuminated by an active disk-corona. We show that relative motion between the
disk and the X-ray emitting material can have an important influence on the
observed equivalent width (EW) of this line via special relativistic aberration
and Doppler effects. We suggest this may be relevant to understanding why the
observed EW often exceeds the prediction of the standard X-ray reflection
model. Several observational tests are suggested that could disentangle these
special relativistic effects from iron abundance effects.",9707082v1
1998-02-05,How Abundant is Iron in the Core of the Perseus Cluster?,"The analysis of Perseus data collected with the Medium Energy Concentrator
Spectrometer (MECS) on board Beppo-SAX shows that the ratio of the flux of the
8 keV line complex (dominated by Fe K$_{\beta}$ emission) over the 6.8 keV line
complex (dominated by Fe K$_{\alpha}$ emission) is significantly larger than
predicted by standard thermal emission codes. Moreover the analysis of
spatially resolved spectra shows that the above ratio decreases with increasing
cluster radius. We find that, amongst the various explanations we consider, the
most likely requires the plasma to be optically thick for resonant scattering
at the energy of the Fe K$_{\alpha}$ line. We argue that if this is the case,
then measures of the iron abundance made using standard thermal emission codes,
that assume optically thin emission, can significantly underestimate the true
iron abundance. In the case of the core of Perseus we estimate the true
abundance to be $\sim$ 0.9 solar in a circular region with radius of $\sim 60$
kpc and centered on NGC 1275. Finally we speculate that similar results may
hold for the core of other rich clusters.",9802067v1
1999-02-18,The contribution of AGN to the X-ray background: the effect of iron features,"The contribution of the iron emission line, commonly detected in the X-ray
spectra of Seyfert (Sey) galaxies, to the cosmic X-ray background (XRB)
spectrum is evaluated in the framework of the XRB synthesis models based on AGN
unification schemes. To derive the mean line properties, we have carried out a
search in the literature covering a sample of about 70 AGN. When adopting line
parameters in agreement with the observations, it turns out that the maximum
contribution of the iron line to the XRB is less than 7% at a few keV. This is
still below the present uncertainties in the XRB spectrum measurements.",9902256v1
1999-06-21,Galactic Ultra-High-Energy Cosmic Rays,"The absence of the expected GZK cutoff strongly challenges the notion that
the highest-energy cosmic rays are of distant extragalactic origin. We discuss
the possibility that these ultra-high-energy events originate in our Galaxy and
propose that they may be due to iron nuclei accelerated from young, strongly
magnetic neutron stars. Newly formed pulsars accelerate ions from their surface
through relativistic MHD winds. We find that pulsars whose initial spin periods
are shorter than $\sim 4 (B_S/10^{13}{\rm G})$ ms, where $B_S$ is the surface
magnetic field, can accelerate iron ions to greater than $10^{20} eV$. These
ions can pass through the remnant of the supernova explosion that produced the
pulsar without suffering significant spallation reactions. Depending on the
structure of the galactic magnetic field, the trajectories of the iron ions
from galactic sources can be consistent with the observed arrival directions of
the highest energy events.",9906338v1
1999-08-25,Reprocessed emission from warped accretion discs with application to X-ray iron line profiles,"Flourescent iron line profiles currently provide the best diagnostic for
active galactic nuclei (AGN) engine geometries. Here we construct a method for
calculating the relativistic iron line profile from an arbitrarily warped
accretion disc, illuminated from above and below by hard X-ray sources. This
substantially generalises previous calculations of reprocessing by accretion
discs by including non-axisymmetric effects. We include a relativistic
treatment of shadowing by ray-tracing photon paths along Schwarzchild
geodesics. We apply this method to two classes of warped discs, and generate a
selection of resulting line profiles. New profile features include the
possibility of sharper red, and softer blue fall-offs, a time varying line
profile if the warp precesses about the disc, and some differences between
`twisted' and `twist-free' warps. We discuss some qualitative implications of
the line profiles in the context of Type I and II Seyfert AGN.",9908275v1
1999-11-19,Revised Stroemgren metallicity calibration for red giants,"A new calibration of the Stroemgren (b-y),m_1 diagram in terms of iron
abundance of red giants is presented. This calibration is based on a
homogeneous sample of giants in the globular clusters omega Centauri, M22, and
M55 as well as field giants from the list of Anthony-Twarog & Twarog (1998).
Towards high metallicities, the new calibration is connected to a previous
calibration by Grebel & Richtler (1992), which was unsatisfactory for iron
abudances lower than -1.0 dex. The revised calibration is valid for
CN-weak/normal red giants in the abundance range of -2.0 < [Fe/H]r $< 0.0 dex,
and a color range of 0.5 < (b-y) < 1.1 mag. As shown for red giants in $\omega$
Centauri, CN-weak stars with Stroemgren metallicities higher than -1.0 dex
cannot be distinguished in the (b-y),m_1 diagram from stars with lower iron
abundances but higher CN band strengths.",9911387v1
1999-12-01,Line emission from gamma-ray burst environments,"The time and angle dependent line and continuum emission from a dense torus
around a cosmological gamma-ray burst source is simulated, taking into account
photoionization, collisional ionization, recombination, and electron heating
and cooling due to various processes. The importance of the hydrodynamical
interaction between the torus and the expanding blast wave is stressed. Due to
the rapid deceleration of the blast wave as it interacts with the dense torus,
the material in the torus will be illuminated by a drastically different photon
spectrum than observable through a low-column-density line of sight, and will
be heated by the hydrodynamical interaction between the blast wave and the
torus. A model calculation to reproduce the Fe K-alpha line emission observed
in the X-ray afterglow of GRB 970508 is presented. The results indicate that ~
10^{-4} solar masses of iron must be concentrated in a region of less than
10^{-3} pc. The illumination of the torus material due to the hydrodynamic
interaction of the blast wave with the torus is the dominant heating and
ionization mechanism leading to the formation of the iron line. These results
suggest that misaligned GRBs may be detectable as X-ray flashes with pronounced
iron emission line features.",9912030v2
1999-12-10,Ultra-High Energy Cosmic Rays from Young Neutron Star Winds,"The long-held notion that the highest-energy cosmic rays are of distant
extragalactic origin is challenged by observations that events above $\sim
10^{20}$ eV do not exhibit the expected high-energy cutoff from photopion
production off the cosmic microwave background. We suggest that these
unexpected ultra-high-energy events are due to iron nuclei accelerated from
young strongly magnetized neutron stars through relativistic MHD winds. We find
that neutron stars whose initial spin periods are shorter than $\sim 4
(B_S/10^{13}{\rm G})^{1/2}$ ms, where $B_S$ is the surface magnetic field, can
accelerate iron cosmic rays to greater than $\sim 10^{20}$ eV. These ions can
pass through the remnant of the supernova explosion that produced the neutron
star without suffering significant spallation reactions. For plausible models
of the Galactic magnetic field, the trajectories of the iron ions curve
sufficiently to be consistent with the observed arrival directions of the
highest energy events.",9912240v2
2000-01-19,Observing the effects of strong gravity with future X-ray missions,"Spectroscopy of the broad iron iron with ASCA and BeppoSAX has up opened the
innermost regions of accreting black hole systems to detailed study. In this
contribution, I discuss how observations with future X-ray missions will extend
these studies and all us to observationally address issues which are currently
only in the realm of the theorists. In particular, high-throughput spectroscopy
with XMM and, eventually, Constellation-X will allow the full diagnostic power
of iron line variability to be realized. Instabilities of the inner accretion
flow, the geometry of the variable X-ray source, and the black hole mass and
spin will all be open to study. Eventually, X-ray interferometry will allow
direct imaging of the black hole region in nearby active galaxies, thereby
providing the ultimate probe of black hole astrophysics.",0001324v1
2000-10-11,Discovery of a redshifted Iron K-line in the X-ray afterglow of GRB 000214,"We report the detection (3 sigma significance level) of a strong iron
emission line in the X-ray spectrum of the afterglow of GRB 000214
(``Valentine's Day Burst'') observed by BeppoSAX. An emission line feature was
observed with a centroid energy of 4.7+/-0.2 keV which, if interpreted as
K-alpha emission from hydrogen-like iron, corresponds to a redshift of z=0.47.
The observed intensity (EW ~2 keV) and duration (tens of hours) of the line
give information on the distance, from the burst region, of the emitting
material (R>3x10^15 cm) and its mass (M>1.4 solar mass). These results are not
easily reconciled with the binary merger and hypernova models for gamma ray
bursts.",0010221v1
2000-10-20,First XMM-Newton observations of a cataclysmic variable II: the X-ray spectrum of OY Car,"We present XMM-Newton X-ray spectra of the disc accreting cataclysmic
variable OY Car, which were obtained during the performance verification phase
of the mission. These data were taken 4 days after a short outburst. In the
EPIC spectra we find strong iron Kalpha emission with weaker iron Kbeta
emission together with silicon and sulphur lines. The spectra are best fitted
with a three temperature plasma model with a partial covering absorber.
Multiple temperature emission is confirmed by the emission lines seen in the
RGS spectrum and the H/He like intensity ratio for iron and sulphur which imply
temperatures of ~7keV and ~3keV respectively.",0010416v1
2000-10-20,XMM-Newton observations of the cluster of galaxies Sersic 159-03,"The cluster of galaxies Sersic 159-03 was observed with the XMM-Newton X-ray
observatory as part of the Guaranteed Time program. X-ray spectra taken with
the EPIC and RGS instruments show no evidence for the strong cooling flow
derived from previous X-ray observations. There is a significant lack of cool
gas below 1.5 keV as compared to standard isobaric cooling flow models. While
the oxygen is distributed more or less uniformly over the cluster, iron shows a
strong concentration in the center of the cluster, slightly offset from the
brightness center but within the central cD galaxy. This points to enhanced
type Ia supernova activity in the center of the cluster. There is also an
elongated iron-rich structure extending to the east of the cluster, showing the
inhomogeneity of the iron distribution. Finally, the temperature drops rapidly
beyond 4 arcmin from the cluster center.",0010423v2
2000-10-25,The unique rapid variabilities of the iron K$α$ line profiles in NGC 4151,"We present a detailed analysis of the iron K$\alpha$ line variabilities in
NGC 4151 by using long ASCA observation data obtained in May 1995. Despite the
relatively small amplitude variations in the continuum flux, the iron K$\alpha$
line flux and profile show dramatic variations. Particularly, the line profile
changes from single peak to seeming double peaks and back in time scales of a
few 10$^4$ sec. The seemingly double-peaked profiles can be well interpreted as
line emission from a Keplerian ring around a massive black hole. An absorption
line at around 5.9 keV is also marginnaly detected. We discussed current Fe K
line models, but none of them can well explain the observed line and continuum
variations.",0010524v1
2000-11-28,Stellar Pollution in the Solar Neighborhood,"We study spectroscopically determined iron abundances of 642 solar-type stars
to search for the signature of accreted iron-rich material. We find that the
metallicity [Fe/H] of a subset of 466 main sequence stars, when plotted as a
function of stellar mass, mimics the pattern seen in lithium abundances in open
clusters. Using Monte Carlo models we find that, on average, these stars have
accreted about 0.4 Earth masses of iron while on the main sequence. A much
smaller sample of 19 stars in the Hertzsprung gap, which are slightly evolved
and whose convection zones are significantly more massive, have lower average
[Fe/H], and their metallicity shows no clear variation with stellar mass. These
findings suggest that terrestrial-type material is common around solar type
stars.",0011530v1
2001-03-23,A Measurement of the Flux of Cosmic Ray Iron at 5 x 10^13 eV,"We present results from the initial flight of our Balloon Air CHerenkov
(BACH) payload. BACH detects air Cherenkov radiation from cosmic ray nuclei as
coincident flashes in two optical modules. The flight (dubbed PDQ BACH) took
place on April 22, 1998 from Ft. Sumner, New Mexico. During an exposure of 2.75
hours, with a typical threshold energy for iron nuclei of 2.2$\times10^{13}$
eV, we observed several events cleanly identifiable as iron group nuclei.
Analysis of the data yields a new flux measurement that is fully consistent
with that reported by other investigations.",0103397v1
2001-07-18,Non-Equilibrium Ionization States of GRB Environments,"Iron spectral features are thought to be the best tracer of a progenitor of
gamma-ray bursts (GRBs). The detections of spectral features such as an iron
line and/or a Radiative Recombination edge and Continuum (RRC) were reported in
four X-ray afterglows of GRBs. However their properties were different each
other burst by burst. For example, Chandra observation of GRB 991216 reported
both the strong H-like iron line together with its RRC. On the contrary,
Yoshida et al. (2001) report only a detection of the strong RRC in GRB 970828
with ASCA. Since it is difficult to produce the strong RRC, we have to consider
special condition for the line and/or the RRC forming region. In this paper, we
point out a possibility of a ``non-equilibrium ionization state'' for the line
and the RRC forming region.",0107330v1
2001-09-13,High Redshift Quasars and Star Formation in the Early Universe,"In order to derive information on the star formation history in the early
universe we observed 6 high-redshift (z=3.4) quasars in the near-infrared to
measure the relative iron and \mgii emission strengths. A detailed comparison
of the resulting spectra with those of low-redshift quasars show essentially
the same FeII/MgII emission ratios and very similar continuum and line spectral
properties, indicating a lack of evolution of the relative iron to magnesium
abundance of the gas since z=3.4 in bright quasars. On the basis of current
chemical evolution scenarios of galaxies, where magnesium is produced in
massive stars ending in type II SNe, while iron is formed predominantly in SNe
of type Ia with a delay of ~1 Gyr and assuming as cosmological parameters H_o =
72 km/s Mpc, Omega_M = 0.3, and Omega_Lambda = 0.7$, we conclude that major
star formation activity in the host galaxies of our z=3.4 quasars must have
started already at an epoch corresponding to z_f ~= 10, when the age of the
universe was less than 0.5 Gyrs.",0109208v1
2002-03-29,The shape of the relativistic iron K-alpha line from MCG6--6-30-15 measured with the Chandra HETGS and RXTE,"We confirm the detection of the relativistically broadened iron K-alpha
emission at 6.4 keV with simultaneous Chandra HETGS and RXTE PCA observations.
Heavily binned HETGS data show a disk line profile with parameters very similar
to those previously seen by ASCA. We observe a resolved narrow component with a
velocity width ~4700 km/s (FWHM ~ 11,000 km/s), that is most prominent, and
narrower (FWHM ~ 3600 km/s) when the continuum flux is high. It plausibly is
just the blue wing of the broad line. We obtain a stringent limit on the
equivalent width of an intrinsically narrow line in the source of 16 eV,
indicating little or no contribution due to fluoresence from distant material
such as the molecular torus. Variability studies of the narrow component show a
constant iron line flux and variable width indicating the line may be
originating from different kinematic regions of the disk.",0203523v2
2002-06-07,X-ray spectral diagnostics of the immediate environment of GRB 991216,"The recent report of iron line features in the afterglow of the gamma-ray
burst (GRB) 991216 has important implications for the properties of the
radiating material and hence the nature of the immediate burst environment. We
argue that the putative strong Fe emission line can be attributed to the
reflected emission from Thomson-thick matter which is illuminated by a
power-law continuum. The ionization parameter of the material (i.e., the flux
to density ratio) is around 10^3, resulting in a Fe K line from He-like iron. A
supersolar abundance of iron is not required by the data. Interestingly, the
ionizing continuum must be harder than the observed one. We interpret this as
due to the fact that the observed continuum is dominated by the standard blast
wave emission, while the line is produced by reprocessing material located at
much smaller radii.",0206116v1
2002-07-08,Sulphur and iron abundances in halo stars,"From equivalent widths of the SI lines at 8694 A, Israelian & Rebolo (2001)
and Takada-Hidai et al. (2002) have derived a surprisingly high sulphur-to-iron
ratio ([S/Fe] = 0.5 to 0.7) in six halo stars with [Fe/H] ~ -2.0 suggesting
perhaps that hypernovae made a significant contribution to the formation of
elements in the early Galaxy. To investigate this problem we have used
high-resolution spectra obtained with the ESO VLT/UVES spectrograph to
determine the S/Fe ratio in 19 main-sequence and subgiant stars ranging in
[Fe/H] from -3.2 to -0.7. The sulphur abundances are determined from SI lines
at 8694 A and 9212 - 9237 A, and the iron abundances from about 20 FeII lines.
S/Fe ratios as derived from 1D model atmospheres are presented and possible 3D
effects are discussed. The initial results from our survey do not confirm the
high values of [S/Fe] quoted above; instead we find that the ratio [S/Fe]
remains constant at about 0.35 dex for metallicities -3 < [Fe/H] -1.",0207163v1
2002-07-29,The iron Kalpha Compton Shoulder in transmitted and reflected spectra,"We calculate the Equivalent Widht of the Core and the centroid energy and
relative flux of the 1st order Compton Shoulder of the iron Kalpha emission
line from neutral matter. The calculations are performed with Monte Carlo
simulations. We explore a large range of column densities for both transmitted
and reflected spectra, and study the dependence on the iron abundance. The
Compton Shoulder is now becoming observable in many objects thanks to the
improved sensitivity and/or energy resolution of XMM-Newton and Chandra
satellites, and the present work aims to provide a tool to derive informations
on the geometry and element abundances of the line emitting matter from Compton
Shoulder measurements.",0207615v1
2003-01-03,Implementing TOPbase/Iron Project: Continuous Absorption from Fe II,"We discuss implementation of TOPbase and Iron Project opacities for stellar
spectral codes. We use a technique employed by Peach, where a
Boltzmann-averaged cross section is calculated for selected temperatures, and
the opacity obtained from double interpolation in temperature and wavelength.
It is straightforward to include {\it all} levels for which cross sections have
been calculated. Boltzmann-averaged cross sections for Fe II show a local
maximum between 1700 and 2000[A]. We suggest this feature arises from 3d^5 4snl
to 3d^5 4pnl transitions within Fe II. IUE spectra of iron-rich CP stars show
local minima in this region. Theoretical calculations of a representative
stellar continuum demonstrate that Fe II photoionization contributes
significantly to the observed minima.",0301045v1
2003-01-14,Relics of subluminous supernovae in metal-poor stars,"The unique elemental abundance pattern of the carbon-rich stars CS29498-043
and CS22949-037 is characterized by a large excess of magnesium and silicon in
comparison with iron. This excess is investigated in the context of a
supernova-induced star formation scenario, and it is concluded that these stars
were born from the matter swept up by supernova remnants containing little iron
and that such supernovae are similar to the least-luminous SNe ever observed,
SNe 1997D and 1999br. Comparison of the observed abundance pattern in
iron-group elements of subluminous supernovae with those of other supernovae
leads to an intriguing implication for explosion, nucleosynthesis, and mixing
in supernovae. The observed invariance of these ratios can not be accounted for
by a spherically symmetric supernova model.",0301236v1
2003-03-04,Preparation of enriched cosmic ray mass groups with KASCADE,"The KASCADE experiment measures a high number of EAS observables with a large
degree of sampling of the electron-photon, muon, and hadron components. It
provides accurate data for an event-by-event analysis of the primary cosmic ray
flux in the energy range around the knee. The possibility of selecting samples
of enriched proton and iron induced extensive air showers by applying the
statistical techniques of multivariate analyses is scrutinized using detailed
Monte Carlo simulations of three different primaries. The purity and efficiency
of the proton and iron classified events is investigated. After obtaining
enriched samples from the measured data by application of the procedures the
reconstructed number of hadrons, hadronic energy and other parameters are
investigated in the primary energy range 1-10 PeV. By comparing these shower
parameters for purified proton and iron events, respectively, with simulated
distributions an attempt is made to check the validity of strong interaction
models at high energies.",0303070v1
2003-05-21,Ratio of color and effective temperatures in X-ray burst spectra,"We present model atmospheres and theoretical spectra for X-ray bursters. Our
models include the effects of Compton scattering on free electrons. The
atmospheres have compositions that are mixtures of hydrogen, helium, and iron.
For our models the ratio of color temperature, $T_c$, to effective temperature,
$T_{eff}$, is in the range 1.2 - 1.8. This ratio depends on $T_{eff}$, surface
gravity, and iron abundance. For fixed $T_{eff}$ and surface gravity, models
with non-zero iron abundance exhibit values of $T_c/T_{eff}$ that are slightly
lower than pure hydrogen-helium models.",0305391v1
2003-08-29,The Iron Abundance and Density Structure of the Inner Ring around SN 1987A,"We present a spectroscopic study of the inner circumstellar ring around SN
1987A. The aim is to determine the elemental abundances and density structure,
with particular emphasis on the abundance of iron. We acquired and analysed
optical spectra at the Anglo-Australian Telescope (AAT) between 1400 and 4300
days post-explosion. We also assembled from the literature all available
optical/near-IR line fluxes of the inner ring. The observed line light curves
were then compared with a photoionisation model for the inner ring. This
indicates an iron abundance of (0.20+-0.08) x solar which is lower than that
generally seen in the Large Magellanic Cloud (LMC).",0308533v1
2003-09-16,"The hard X-ray spectrum of the Seyfert galaxy IRAS 18325-5926: cool corona, reflection from an ionized disk and variable iron K emission","We report our analysis of X-ray spectra of the Seyfert galaxy IRAS 18325-5926
(=Fairall 49) obtained from various X-ray observatories prior to XMM-Newton,
including new results from two RXTE and one BeppoSAX observations. A relatively
steep continuum slope (photon-index of ~2.2) in the 2-15 keV band is confirmed.
The continuum spectrum observed with the BeppoSAX PDS shows a possible
roll-over at energies above 30 keV, indicating a Comptonizing corona cooler
than in other Seyfert nuclei. The X-ray spectrum above 2 keV is best explained
with a model including reflection from a highly ionized disk with significant
relativistic blurring. The iron K-alpha emission feature is then mainly due to
FeXXV. The recent seven observations shows that the iron K emission flux
appears to follow the continuum between the observations separated by a few
months to years, although some exceptions suggest that the line strength may be
determined in a more complex way.",0309432v1
2003-09-17,A new Method to Constrain the Iron Abundance from Cooling Delays in Coronal Loops,"Recent observations with TRACE reveal that the time delay between the
appearance of a cooling loop in different EUV temperature filters is
proportional to the loop length, dt_12 ~ L. We model this cooling delay in
terms of radiative loss and confirm this linear relationship theoretically. We
derive an expression that can be used to constrain the coronal iron enhancement
alpha_Fe=A_Fe^cor/A_Fe^Ph relative to the photospheric value as function of the
cooling delay dt_12, flux F_2, loop width w, and filling factor q_w < 1. With
this relation we find upper limits on the iron abundance enhancement of
alpha_Fe < 4.8+/-1.7 for 10 small-scale nanoflare loops, and alpha_Fe <
1.4+/-0.4 for 5 large-scale loops, in the temperature range of T~1.0-1.4 MK.
This result supports the previous finding that low-FIP elements, including Fe,
are enhanced in the corona. The same relation constitutes also a lower limit
for the filling factor, which is q_w > 0.2+/-0.1 and q_w > 0.8+/-0.2 for the
two groups of coronal loops.",0309506v1
2003-10-17,The high energy emission line spectrum of NGC 1068,"We present and discuss the high energy (E>4 keV) XMM-Newton spectrum of the
Seyfert 2 galaxy, NGC 1068. Possible evidence for flux variability in both the
neutral and ionized reflectors with respect to a BeppoSAX observation taken 3.5
years before is found. Several Fe and Ni emission lines, from both neutral and
highly ionized material, are detected. The intensity of the iron K$\alpha$
Compton shoulder implies that the neutral reflector is Compton--thick, likely
the visible inner wall of the $N_H > 10^{25}$ cm$^{-2}$ absorber. From the
equivalent width of the ionized iron lines a column density of a few $\times
10^{21}$ cm$^{-2}$ is deduced for the hot ionized reflector. Finally, an iron
(nickel) overabundance, when compared to solar values, of about 2 (4) with
respect to lower Z elements, is found.",0310492v1
2003-10-27,Constraints on SN Ia Progenitors and ICM enrichment from field and cluster SN rates,"The iron mass in galaxy clusters is about 6 times larger than could have been
produced by core-collapse SNe, assuming the stars in cluster galaxies formed
with a standard IMF. Type-Ia SNe have been proposed as the alternative dominant
iron source. We use our HST measurements of the cluster SN-Ia rate at high
redshift to study the cluster iron enrichment scenario. The measurements can
constrain the star-formation epoch and the SN-Ia progenitor models via the mean
delay time between the formation of a stellar population and the explosion of
some of its members as SNe-Ia. The low observed rate of cluster SNe-Ia at z~1
pushes back the star-formation epoch in clusters to z>2, and implies a short
delay time. We also show a related analysis for high-z field SNe which implies,
under some conditions, a long SN-Ia delay time. Thus, cluster enrichment by
core-collapse SNe from a top-heavy IMF may remain the only viable option.",0310768v1
2004-02-04,Relativistic Iron Lines in Galactic Black Holes: Recent Results and Lines in the ASCA Archive,"Recent observations with Chandra and XMM-Newton, aided by broad-band spectral
coverage from RXTE, have revealed skewed relativistic iron emission lines in
stellar-mass Galactic black hole systems. Such systems are excellent
laboratories for testing General Relativity, and relativistic iron lines
provide an important tool for making such tests. In this contribution to the
Proceedings of the 10th Annual Marcel Grossmann Meeting on General Relativity,
we briefly review recent developments and present initial results from fits to
archival ASCA observations of Galactic black holes. It stands to reason that
relativistic effects, if real, should be revealed in many systems (rather than
just one or two); the results of our archival work have borne-out this
expectation. The ASCA spectra reveal skewed, relativistic lines in XTE
J1550-564, GRO J1655-40, GRS 1915+105, and Cygnus X-1.",0402101v1
2004-04-08,Iron Line Spectroscopy of NGC4593 with XMM-Newton: Where is the Black Hole Accretion Disk?,"We present an analysis of the 2-10keV XMM-Newton/EPIC-pn spectrum of the
Seyfert-1 galaxy NGC4593. Apart from the presence of two narrow emission lines
corresponding to the Kalpha lines of cold and hydrogen-like iron, this spectrum
possesses a power-law form to within 3-5%. There is a marked lack of spectral
features from the relativistic regions of the black hole accretion disk. We
show that the data are, however, consistent with the presence of a
radiatively-efficient accretion disk extending right down to the radius of
marginal stability if it possesses low iron abundance, an appropriately ionized
surface, a very high inclination, or a very centrally concentrated emission
pattern (as has been observed during the Deep Minimum State of the Seyfert
galaxy MCG-6-30-15). Deeper observations of this source are required in order
to validate or reject these models.",0404187v1
2004-06-28,Iron Abundance Diagnostics in High-Redshift QSOs,"The abundance of alpha-process elements such as magnesium and carbon relative
to iron measured from the broad emission lines of QSOs can serve as a
diagnostic of the star formation and chemical enrichment histories of their
host galaxies.
  We investigate the relationship between Fe/Mg and Fe/C abundance ratios and
the resulting Fe II / Mg II 2800A and Fe II / 1900A-blend flux ratios, both of
which have been measured in QSOs out to redshifts of approximately six. Using a
galactic chemical evolution model based on a starburst in a giant elliptical
galaxy, we find that these flux ratios are good tracers of the chemical
enrichment of the nuclei. However, the values of these ratios measured in
objects at redshifts of approximately six suggest that iron enrichment has
occurred more rapidly in these objects than predicted by the assumed elliptical
starburst model, under currently favored cosmologies.",0406630v1
2004-07-07,The Additional Line Component within the Iron KαProfile in MCG-6-30-15: Evidence for Blob Ejection?,"The EPIC data of MCG -6-30-15 observed by XMM-Newton were analyzed for the
complexities of the iron K-alpha line. Here we report that the additional line
component (ALC) at 6.9 keV undoubtedly appears within the broad iron Kalpha;
line profile at the high state, whereas it disappears at the low state. These
state-dependent behaviors exclude several possible origins and suggest an
origin of the ALC in matter being ejected from the vicinity of the black hole.
At the low state, the newborn blob ejected from the accretion disk is so
Thomson-thick that hard X-rays are blocked from ionizing the old blobs, leading
to the disappearance of the ALC. When the blob becomes Thomson-thin as a result
of expansion, the hard X-ray will penetrate it and ionize the old ones,
emitting the ALC at the high state. The blob ejection is the key to switching
the ALC on or off.",0407124v1
2004-09-08,Atomic data from the Iron Project.LVIII. New radiative transition probabilities for Fe IV including fine structure,"We present new calculations for transition probabilities of Fe IV, with much
more extensive datasets than heretofore available. The large-scale close
coupling R-matrix calculations yield 1,798 LS bound states with n $\leq$ 11 and
$l \leq$ 9, and corresponding transition probabilities for 138,121 dipole
allowed transitions in the form of oscillator strengths $f$, line strengths
$S$, and A-coeffficients for a variety of applications. This represents the
largest R-matrix dataset in LS coupling for any ion under either the Opacity
Project or the Iron Project. Through algebraic transformation of the LS
multiplets, a total of 712,120 dipole allowed fine structure transitions for Fe
IV are obtained. Observed transition energies are used together with the energy
independent line strengths to derive the $f$- and the $A$-values; the adopted
algorithm used calculated energies for the remainder. Present results show
significantly better accuracy for the important low-lying states than previous
calculations. Monochromatic and mean opacities for Fe IV are computed and
compared with those obtained using the Opacity Project data. We find
differences which could have important consequences for several astrophysical
applications involving low ionization stages of iron.",0409202v1
2004-11-01,The absorption spectrum of V838 Mon in 2002 February - March. I. Atmospheric parameters and iron abundance,"We present a determination of the effective temperatures, iron abundances,
and microturbulent velocities for the pseudophotosphere of V838 Mon on 2002
February 25, and March 2 and 26. Physical parameters of the line forming region
were obtained in the framework of a self-consistent approach, using fits of
synthetic spectra to observed spectra in the wavelength range 5500-6700A. We
obtained Tef = 5330, 5540 and 4960 K, for February 25, March 2, and March 26,
respectively. The iron abundance log N(Fe)=-4.7 does not appear to change in
the atmosphere of V838 Mon from February 25 to March 26, 2002.",0411032v1
2004-11-22,"Fe XXV and Fe XXVI lines from low velocity, photoionised gas in the X-ray spectra of AGN","We have calculated the equivalent widths of the absorption lines produced by
Fe XXV and Fe XXVI in a Compton-thin, low-velocity photoionised material
illuminated by the nuclear continuum in AGN. The results, plotted against the
ionisation parameter and the column density of the gas, are a complement to
those presented by Bianchi & Matt 2002 for the emission lines from the same
ionic species. As an extension to the work by Bianchi & Matt 2002, we also
present a qualitative discussion on the different contributions to the He-like
iron emission line complex in the regimes where recombination or resonant
scattering dominates, providing a useful diagnostic tool to measure the column
density of the gas. Future high resolution missions (e.g., Astro-E2) will allow
us to fully take advantage of these plasma diagnostics. In the meantime, we
compare our results with an up-to-date list of Compton-thick and unobscured (at
least at the iron line energy) Seyfert galaxies with emission and/or absorption
lines from H- and He-like iron observed with Chandra and XMM-Newton.",0411603v1
2004-11-22,The iron $K_α$ lines as a tool for magnetic field estimations in non-flat accretion flows,"Observations of AGNs and microquasars by ASCA, RXTE, Chandra and XMM-Newton
indicate the existence of broad X-ray emission lines of ionized heavy elements
in their spectra. Such spectral lines were discovered also in X-ray spectra of
neutron stars and X-ray afterglows of GRBs. Recently, Zakharov et al. (MNRAS,
2003, 342, 1325) described a procedure to estimate an upper limit of the
magnetic fields in regions from which X-ray photons are emitted. The authors
simulated typical profiles of the iron $K_\alpha$ line in the presence of
magnetic field and compared them with observational data in the framework of
the widely accepted accretion disk model. Here we further consider typical
Zeeman splitting in the framework of a model of non-flat accretion flows, which
is a generalization of previous consideration into non-equatorial plane motion
of particles emitting X-ray photons.
  Using perspective facilities of space borne instruments (e.g. Constellation-X
mission) a better resolution of the blue peak structure of iron $K_\alpha$ line
will allow to evaluate the magnetic fields with higher accuracy.",0411608v1
2004-12-09,Broad Iron Lines in AGN and X-ray Binaries,"Several AGN and black hole X-ray binaries show a clear very broad iron line
which is strong evidence that the black holes are rapidly spinning. Detailed
analysis of these objects shows that the emission line is not significantly
affected by absorption and that the source variability is principally due to
variation in amplitude of a power-law. Underlying this is a much less variable,
relativistically-smeared, reflection-dominated, component which carries the
imprint of strong gravity at a few gravitational radii. The strong
gravitational light bending in these regions then explains the power-law
variability as due to changes in height of the primary X-ray source above the
disc. The reflection component, in particular its variability and the profile
of the iron line, enables us to study the innermost regions around an
accreting, spinning, black hole.",0412224v2
2005-02-16,A changing inner radius in the accretion disc of Q0056-363?,"Q0056-363 is the most powerful X-ray quasar known to exhibit a broad, likely
relativistic iron line (Porquet & Reeves 2003). It has been observed twice by
XMM-$Newton$, three and half years apart (July 2000 and December 2003). In the
second observation, the UV and soft X-ray fluxes were fainter, the hard X-ray
power law flatter, and the iron line equivalent width (EW) smaller than in the
2000 observation. These variations can all be explained, at least
qualitatively, if the disc is truncated in the second observation. We report
also on the possible detection of a transient, redshifted iron absorption line
during the 2003 observation.",0502323v1
2005-09-28,Isotopes Tell Origin and Operation of the Sun,"The Iron Sun formed on the collapsed core of a supernova and now acts as a
magnetic plasma diffuser, as did the precursor star, separating ions by mass.
This process covers the solar surface with lightweight elements and with
lighter isotopes of each element. Running difference images expose rigid,
iron-rich structures below the fluid photosphere made of lightweight elements.
The energy source for the Sun and ordinary stars seems to be neutron-emission
and neutron-decay, with partial fusion of the decay product, rather than simple
fusion of hydrogen into helium or heavier elements. Neutron-emission from the
solar core and neutron-decay generate about sixty five percent of solar
luminosity and H-fusion generates about thirty-five percent. The upward flow of
H ions maintains mass-separation in the Sun. Only about one percent of this
neutron decay product survives its upward journey to depart as solar-wind
hydrogen.",0510001v1
2005-10-18,The Metallicity Dependence of the Cepheid Period-Luminosity Relation,"We have assessed the influence of the stellar iron content on the Cepheid
Period-Luminosity (PL) relation by relating the V band residuals from the
Freedman et al (2001) PL relation to [Fe/H] for 68 Galactic and Magellanic
Cloud Cepheids. The iron abundances were measured from FEROS and UVES
high-resolution and high signal-to-noise optical spectra. Our data indicate
that the stars become fainter as metallicity increases, until a plateau or
turnover point is reached at about solar metallicity. This behavior appears at
odds both with the PL relation being independent from iron abundance and with
Cepheids becoming monotonically brighter as metallicity increases (e.g.
Kennicutt et al 1998, Sakai et al 2004).",0510521v1
2005-10-21,Resolving the Fe xxv Triplet with Chandra in Cen X-3,"We present the results of a 45 ks Chandra observation of the high-mass X-ray
binary Cen X--3 at orbital phases between 0.13 and 0.40 (in the eclipse
post-egress phases). Here we concentrate on the study of discrete features in
the energy spectrum at energies between 6 and 7 keV, i.e. on the iron
K$_\alpha$ line region, using the High Energy Transmission Grating Spectrometer
on board the Chandra satellite. We clearly see a K$_\alpha$ neutral iron line
at $\sim 6.40$ keV and were able to distinguish the three lines of the
\ion{Fe}{25} triplet at 6.61 keV, 6.67 keV, and 6.72 keV, with an equivalent
width of 6 eV, 9 eV, and 5 eV, respectively. The equivalent width of the
K$_\alpha$ neutral iron line is 13 eV, an order of magnitude lower than
previous measures. We discuss the possibility that the small equivalent width
is due to a decrease of the solid angle subtended by the reflector.",0510645v1
2005-11-02,The Iron K-shell features of MXB 1728-34 from a Simultaneous Chandra-RXTE Observation,"We report on a simultaneous Chandra and RossiXTE observation of the low-mass
X-ray binary atoll bursting source MXB 1728-34 performed on 2002 March 3-5. We
fit the 1.2-35 keV continuum spectrum with a blackbody plus a Comptonized
component. Large residuals at 6-10 keV can be fitted by a broad (FWHM ~ 2 keV)
Gaussian emission line or, alternatively, by two absorption edges associated
with lowly ionized iron and Fe XXV/XXVI at ~7.1 keV and ~9 keV, respectively.
In this interpretation, we find no evidence of broad, or narrow, emission lines
between 6 and 7 keV. We test our alternative modelling of the iron K shell
region by reanalysing a previous BeppoSAX observation of MXB 1728-34, finding a
general agreement with our new spectral model.",0511072v1
2005-11-14,A prominent relativistic iron line in the Seyfert 1 MCG-02-14-009,"I report the discovery of a prominent broad and asymmetrical feature near 6.4
keV in the Seyfert 1 MCG-02-14-009 (z=0.028) with XMM-Newton/EPIC. The present
short X-ray observation (PN net exposure time ~5 ks) is the first one above 2
keV for MCG-02-14-009. The feature can be explained by either a relativistic
iron line around either a Schwarzschild (non-rotating) or a Kerr (rotating)
black hole. If the feature is a relativistic iron line around a Schwarzschild
black hole, the line energy is 6.51 (+0.21,-0.12) keV with an equivalent width
of 631 (+259,-243) eV and that the inclination angle of the accretion disc
should be less than 43 degrees. A relativistically blurred photoionized disc
model gives a very good spectral fit over the broad band 0.2-12keV energy
range. The spectrum is reflection dominated and this would indicate that the
primary source in MCG-02-14-009 is located very close to the black hole, where
gravitational light bending effect is important (about 3-4 Rg), and that the
black hole may rapidly rotate.",0511387v1
2005-11-16,Oxygen and Iron Abundances in Nearby Galaxies Using Ultraluminous X-ray Sources,"We determined oxygen and iron abundances of the interstellar medium (ISM)
using K-shell (O) and L-shell (Fe) X-ray photo-ionization edges towards Ultra
luminous X-ray sources (ULXs). We determine the hydrogen column densities (n_H)
towards the ULXs from XMM-Newton archival spectra of 14 ULX sources. We compare
our X-ray values with those obtained from radio HI observations for 8 of the
sources. The X-ray model n_H values are in good agreement with the HI n_H
values, implying that the hydrogen absorption towards the ULX is not local to
the source, with the exception of M81 X-1. Oxygen abundances and iron
abundances are roughly solar for the host galaxies.",0511493v1
2005-11-23,Iron depletion in the hot bubbles in planetary nebulae,"We have searched for the emission from \fex and \fexiv that is expected from
the gas emitting in diffuse X-rays in \bd, NGC 6543, NGC 7009, and NGC 7027.
Neither line was detected in any object. Models that fit the X-ray spectra of
these objects indicate that the \fex emission should be below our detection
thresholds, but the predicted \fexiv emission exceeds our observed upper limits
(one sigma) by factors of at least 3.5 to 12. The best explanation for the
absence of \fexiv is that the X-ray plasma is depleted in iron. In principle,
this result provides a clear chemical signature that may be used to determine
the origin of the X-ray gas in either the nebular gas or the stellar wind. At
present, though various lines of evidence appear to favour a nebular origin,
the lack of atmospheric and nebular iron abundances in the objects studied here
precludes a definitive conclusion.",0511681v1
2006-01-12,Permitted Oxygen Abundances and the Temperature Scale of Metal-Poor Turn-Off Stars,"We use high quality VLT/UVES published data of the permitted OI triplet and
FeII lines to determine oxygen and iron abundances in unevolved (dwarfs,
turn-off, subgiants) metal-poor halo stars. The calculations have been
performed both in LTE and NLTE, employing effective temperatures obtained with
the new infrared flux method (IRFM) temperature scale by Ramirez & Melendez,
and surface gravities from Hipparcos parallaxes and theoretical isochrones. A
new list of accurate transition probabilities for FeII lines, tied to the
absolute scale defined by laboratory measurements, has been used. We find a
plateau in the oxygen-to-iron ratio over more than two orders of magnitude in
iron abundance (-3.2 < [Fe/H] < -0.7), with a mean [O/Fe] = 0.5 dex (sigma =
0.1 dex), independent of metallicity, temperature and surface gravity.
According to the new IRFM Teff scale, the temperatures of turn-off halo stars
strongly depend on metallicity, a result that is in excellent qualitative and
quantitative agreement with stellar evolution calculations, which predict that
the Teff of the turn-off at [Fe/H] = -3 is about 600-700 K higher than that at
[Fe/H] = -1.",0601256v1
2006-03-02,Abundance studies of sdB stars using UV echelle HST/STIS spectroscopy,"Aims: We test the hypothesis that the pulsations in sdB stars are correlated
with the surface abundances of iron-group elements. Any correlation might
explain why, when given two spectroscopically similar stars, one will pulsate
while the other will not. Methods: We have obtained high-resolution ultraviolet
spectra two pulsating and three non-pulsating sdB stars using the Space
Telescope Imaging Spectrograph onboard the Hubble Space Telescope. We
determined abundances for 25 elements including the iron group and even heavier
elements such as tin and lead using LTE curve-of-growth and spectrum synthesis
techniques. Results: We find no clear correlation between pulsations and metal
abundances, and we comment on the resulting implications, including whether it
is possible to determine the difference between a pulsating and a non-pulsating
sdB spectroscopically. In addition to the main goal of our observations, we
have also investigated the effect of supersolar metallicity on fundamental
parameter determination, possible trends with iron abundance, and the
hypothesis that weak winds may be selectively removing elements from the
stellar envelopes. These effects provide challenges to stellar atmosphere
modelling and diffusion models for sdB stars.",0603069v1
2006-04-27,A Likelihood Method for Measuring the Ultrahigh Energy Cosmic Ray Composition,"Air fluorescence detectors traditionally determine the dominant chemical
composit ion of the ultrahigh energy cosmic ray flux by comparing the averaged
slant depth of the shower maximum, $X_{max}$, as a function of energy to the
slant depths expect ed for various hypothesized primaries. In this paper, we
present a method to make a direct measurement of the expected mean number of
protons and iron by comparing the shap es of the expected $X_{max}$
distributions to the distribution for data. The advantages of this method
includes the use of information of the full distribution and its ability to
calculate a flux for various cosmic ray compositi ons. The same method can be
expanded to marginalize uncertainties due to choice of spectra, hadronic models
and atmospheric parameters. We demonstrate the technique with independent
simulated data samples from a parent sample of protons and iron. We accurately
predict the number of protons and iron in the parent sample and show that the
uncertainties are meaningful.",0604558v2
2006-08-20,Iron in Hot DA White Dwarfs,"We present a study of the iron abundance pattern in hot hydrogen-rich (DA)
white dwarfs. The study is based on new and archival far ultraviolet
spectroscopy of a sample of white dwarfs in the temperature range 30,000 K <
T_eff < 64,000 K. The spectra obtained with the Far Ultraviolet Spectroscopic
Explorer along with spectra obtained with the Hubble Space Telescope Imaging
Spectrograph and the International Ultraviolet Explorer sample FeIII to FeVI
absorption lines enabling a detailed iron abundance analysis over a wider range
of effective temperatures than previously afforded. The measurements reveal
abundance variations in excess of two orders of magnitude between the highest
and the lowest temperatures probed, but also show considerable variations (over
one order of magnitude) between objects with similar temperatures and surface
gravities. Such variations in cooler objects may be imputed to accretion from
unseen companions or so-called circumstellar debris although the effect of
residual mass-loss and selective radiation pressure in the hottest objects in
the sample remain dominant.",0608416v1
2006-12-15,"Strong gravity effects: X-ray spectra, variability and polarimetry","Accreting black holes often show iron line emission in their X-ray spectra.
When this line emission is very broad or variable then it is likely to
originate from close to the black hole. The theory and observations of such
broad and variable iron lines are briefly reviewed here. In order for a clear
broad line to be found, one or more of the following have to occur: high iron
abundance, dense disk surface and minimal complex absorption. Several excellent
examples are found from observations of Seyfert galaxies and Galactic Black
Holes. In some cases there is strong evidence that the black hole is rapidly
spinning. Further examples are expected as more long observations are made with
XMM-Newton, Chandra and Suzaku. The X-ray spectra show evidence for the strong
gravitational redshifts and light bending expected around black holes.",0612435v1
2001-09-17,Improvement of critical current in MgB2/Fe wires by a ferromagnetic sheath,"Transport critical current (Ic) was measured for Fe-sheathed MgB2 round
wires. A critical current density of 5.3 x 10^4 A/cm^2 was obtained at 32K.
Strong magnetic shielding by the iron sheath was observed, resulting in a
decrease in Ic by only 15% in a field of 0.6T at 32K. In addition to shielding,
interaction between the iron sheath and the superconductor resulted in a
constant Ic between 0.2 and 0.6T. This was well beyond the maximum field for
effective shielding of 0.2T. This effect can be used to substantially improve
the field performance of MgB2/Fe wires at fields at least 3 times higher than
the range allowed by mere magnetic shielding by the iron sheath. The dependence
of Ic on the angle between field and current showed that the transport current
does not flow straight across the wire, but meanders between the grains.",0109283v1
2002-05-09,Self-assembly of Nanometer-scale Magnetic Dots with Narrow Size Distributions on an Insulating Substrate,"The self-assembly of iron dots on the insulating surface of NaCl(001) is
investigated experimentally and theoretically. Under proper growth conditions,
nanometer-scale magnetic iron dots with remarkably narrow size distributions
can be achieved in the absence of a wetting layer Furthermore, both the
vertical and lateral sizes of the dots can be tuned with the iron dosage
without introducing apparent size broadening, even though the clustering is
clearly in the strong coarsening regime. These observations are interpreted
using a phenomenological mean-field theory, in which a coverage-dependent
optimal dot size is selected by strain-mediated dot-dot interactions.",0205205v1
2002-05-28,Magnetic properties of alpha-iron(II) phthalocyanine,"We report on the magnetic properties of the supra-molecular compound iron(II)
phthalocyanine in its alpha-form. dc- and ac-susceptometry measurements and
Mossbauer experiments show that the iron atoms are strongly magnetically
coupled into ferromagnetic Ising chains with very weak antiferromagnetic
interchain coupling. The transition to 3D magnetic ordering below 10 K is
hindered by the presence of impurities or other defects, by which the
domain-wall arrangements along individual chains become gradually
blocked/frozen, leading to a disordered 3D distribution of ferromagnetic chain
segments. Below 5 K, field-cooled and zero-field-cooled magnetization
measurements show strong irreversible behavior, attributed to pinning of the
domain-walls by the randomly distributed defects in combination with the
interchain coupling. High-field magnetization experiments reveal a canted
arrangement of the moments in adjacent ferromagnetic chains.",0205587v1
2002-07-31,Magnetic shielding in MgB2/Fe superconducting wires,"Transport critical current (Ic) was measured for MgB2/Fe round wires, with
magnetic field oriented perpendicular to the wire and parallel to it.
Measurements were made on a wire with pure MgB2 core and another wire where
MgB2 core was doped with nano-size SiC. This doping strongly improved the
vortex pinning in MgB2. The field dependence of Ic was strongly improved due to
the presence of the iron sheath. At 30K, Ic did not depend on the field for
fields between 0.09 and 0.7T. At lower temperatures, Ic increased with the
field, after initial decrease, resembling a ""peak effect"". This effect was
extended to higher fields as the temperature went down: at 10K the peak
appeared at 3.5T. This improvement was not due to mere magnetic shielding by
iron, but more likely to an interaction between the iron sheath and
superconductor. Improvement of vortex pinning did not affect the range of
fields within which this effect was observed.",0207727v1
2003-07-31,"The valence state of iron in the Sr2Fe(Mo,W,Ta)O6.0 double-perovskite system: An Fe K-edge and L2,3-edge XANES study","Here we employ both Fe K and L2,3 edge x-ray absorption near-edge structure
(XANES) spectroscopy techniques to clarify that iron in the B-site ordered
double-perovskite halfmetal, Sr2FeMoO6.0, possesses a mixed-valence state,
FeII/III, and accordingly molybdenum a mixed MoV/VI valence state. A reliable
interpretation of the spectral features has been made possible by using a
series of samples of the Sr2Fe(Mo,W/Ta)O6.0 system. Replacing MoV/VI gradually
with WVI causes increasing amount of Fe to adopt the FeII state, whereas TaV
substitution shifts the valence of iron towards FeIII. As the valence of Fe
increases from II to III in the Sr2Fe(Mo,W/Ta)O6.0 system, the absorption
energy at the Fe K-edge gradually shifts towards the higher energy side.
Similarly, in the L2,3-edge XANES spectra intermediate spectral features are
revealed for the Sr2FeMoO6.0 sample in comparison with those for samples
heavily substituted with either W or Ta.",0307755v1
2004-10-27,Matrix Assisted Formation of Ferrihydrite Nanoparticles in a Siloxane/Poly(Oxyethylene) Nanohybrid,"Matrix-assisted formation of ferrihydrite, an iron oxide hydroxide analogue
of the protein ferritin-core, in a sol-gel derived organic-inorganic hybrid is
reported. The hybrid network (named di-ureasil) is composed of
poly(oxyethylene) chains of different average polymer molecular weights grafted
to siloxane domains by means of urea cross-linkages and accommodates
ferrihydrite nanoparticles. Magnetic measurements, Fourier transform infrared
and nuclear magnetic resonance spectroscopy reveal that the controlled
modification of the polymer molecular weight allows the fine-tuning of the
ability of the hybrid matrix to assist and promote iron coordination at the
organic-inorganic interface and subsequent nucleation and growth of the
ferrihydrite nanoparticles whose core size (2-4 nm) is tuned by the amount of
iron incorporated. The polymer chain length, its arrangement and crystallinity,
are key factors on the anchoring and formation of the ferrihydrite particles.",0410695v1
2005-02-17,Evidence for differentiation in the iron-helicoidal-chain in GdFe$_{3}$(BO$_{3}$)$_{4}$,"We report on a single-crystal X-ray structure study of $GdFe_{3}(BO_{3})_{4}$
at room temperature and at T=90 K. At room temperature $GdFe_{3}(BO_{3})_{4}$
crystallizes in a trigonal space group R32 (No. 155), the same as found for
other members of iron-borate family $RFe_{3}(BO_{3})_{4}$. At 90 K the
structure of $GdFe_{3}(BO_{3})_{4}$ has transformed to the space group
$P3_{1}2_{1}$ (No. 152). The low-temperature structure determination gives new
insight into the weakly first-order structural phase transition at 156 K and
into the related Raman phonon anomalies. The discovery of two inequivalent iron
chains in the low temperature structure provide new point of view on the
low-temperature magnetic properties.",0502423v2
2005-04-27,The nature of iron-oxygen vacancy defect centers in PbTiO3,"The iron(III) center in ferroelectric PbTiO3 together with an oxygen vacancy
forms a charged defect associate, oriented along the crystallographic c-axis.
Its microscopic structure has been analyzed in detail comparing results from a
semi-empirical Newman superposition model analysis based on finestructure data
and from calculations using density functional theory.
  Both methods give evidence for a substitution of Fe3+ for Ti4+ as an acceptor
center. The position of the iron ion in the ferroelectric phase is found to be
similar to the B-site in the paraelectric phase. Partial charge compensation is
locally provided by a directly coordinated oxygen vacancy.
  Using high-resolution synchrotron powder diffraction, it was verified that
lead titanate remains tetragonal down to 12 K, exhibiting a c/a-ratio of
1.0721.",0504728v1
2005-07-22,Interaction between superconductor and ferromagnetic domains in iron sheath: peak effect in MgB2/Fe wires,"Interaction between the superconductor and ferromagnet in MgB2/Fe wires
results in either a plateau or a peak effect in the field dependence of
transport critical current, Ic(H). This is in addition to magnetic shielding of
external field. Current theoretical models cannot account for the observed peak
effect in Ic(H). This paper shows that the theoretical explanation of the peak
effect should be sought in terms of interaction between superconductor and
magnetic domain structure, obtained after re-magnetization of the iron sheath
by the self-field of the current. There is a minimum value of critical current,
below which the re-magnetization of the iron sheath and peak effect in Ic(H)
are not observed.",0507510v1
2006-02-13,Magnetic properties of polymerized C$_{60}$ with Fe,"We provide evidence that high-pressure high-temperature (2.5 GPa and 1040 K)
treatment of mixtures of iron with fullerene powders leads to the complete
transformation of iron into iron carbide Fe$_3$C. The comparison of the
magnetic properties (Curie temperature and magnetic moment) of the here studied
samples and those for the ferromagnetic polymer Rh-C$_{60}$ indicates that the
main ferromagnetic signal reported in those samples is due to Fe$_3$C and not
related to the ferromagnetism of carbon as originally interpreted. Taking into
account the results obtained in this study the original paper on ``Magnetic
carbon"" (Nature {\bf 413}, 716 (2001)) was recently retracted.",0602306v3
2006-06-01,Microstructural characterization and kinetics modelling of vermicular cast irons,"Several experimental techniques are used for phase identification and
microstructure characterization of austempered vermicular cast irons (XRD, SEM,
TEM and Mossbauer spectroscopy). Acicular structures were found to be composed
by ferrite and austenite with average sizes compatible with those reported for
bainitic ferrite in steels and Austempered Ductile Iron. An assessment of the
free energy change involved in the austenite to bainite transformation assuming
a plate-like nucleation shape for bainite gave an average characteristic length
close to the observed from statistical length distributions. The kinetics of
the transformation was modelled in the Avrami framework; both the diffusion
controlled and the diffusionless growth hypothesis were considered in order to
elucidate the mechanism underlying the austempering phase transformation.
Results indicated that diffusion of C is the responsible of the nucleation
process of the bainite sheaves, that appear as a consequence of a localized
displacive transformation when the C concentration is adequate, but further
growth of the bainite plates is almost suppressed.",0606031v2
1999-04-29,Hadronic Shower Development in Iron-Scintillator Tile Calorimetry,"The lateral and longitudinal profiles of hadronic showers detected by a
prototype of the ATLAS Iron-Scintillator Tile Hadron Calorimeter have been
investigated. This calorimeter uses a unique longitudinal configuration of
scintillator tiles. Using a fine-grained pion beam scan at 100 GeV, a detailed
picture of transverse shower behavior is obtained. The underlying radial energy
densities for four depth segments and for the entire calorimeter have been
reconstructed. A three-dimensional hadronic shower parametrization has been
developed. The results presented here are useful for understanding the
performance of iron-scintillator calorimeters, for developing fast simulations
of hadronic showers, for many calorimetry problems requiring the integration of
a shower energy deposition in a volume and for future calorimeter design.",9904032v1
1999-10-07,Hadronic Shower Development in Tile Iron-Scintillator Calorimetry,"The lateral and longitudinal profiles of hadronic showers detected by a
prototype of the ATLAS Iron-Scintillator Tile Hadron Calorimeter have been
investigated. This calorimeter uses a unique longitudinal configuration of
scintillator tiles. Using a fine-grained pion beam scan at 100 GeV, a detailed
picture of transverse shower behavior is obtained. The underlying radial energy
densities for four depth segments and for the entire calorimeter have been
reconstructed. A three-dimensional hadronic shower parametrization has been
developed. The results presented here are useful for understanding the
performance of iron-scintillator calorimeters, for developing fast simulations
of hadronic showers, for many calorimetry problems requiring the integration of
a shower energy deposition in a volume and for future calorimeter design.",9910015v1
2002-07-30,Commissioning of SLAC SLD 45-Degree Chambers,"The SLD experiment at the Stanford Linear Accelerator Center had a
significant gap in its muon tracking coverage, provided by the Warm Iron
Calorimeter. Supplemental planes of limited streamer tube chambers were added
to improve the coverage in the vicinity of the gap at 0.65 < |cos(theta)|<
0.85. A software effort to upgrade the tracking software for this system is
detailed. The commissioning of the forty-five degree chamber region of the SLAC
SLD Warm Iron Calorimeter is presented. This task involved the completion of
the forty-five degree chamber region geometry for the Warm Iron Calorimeter's
fitter and swimmer and the changing of the way multiple scattering effects are
treated in the fitter algorithm.",0207099v1
2002-08-08,Accelerating Muons to 2400 GeV/c with Dogbones Followed by Interleaved Fast Ramping Iron and Fixed Superconducting Magnets,"The first acceleration stage for this muon collider scenario includes twenty
passes through a single two GeV Linac. Teardrop shaped arcs of 1.8 Tesla fixed
field magnets are used at each end of the Linac. This dogbone geometry
minimizes muon decay losses because muons pass through shorter arcs when their
gamma boost is low. Two 2200 meter radius hybrid rings of fixed superconducting
magnets and iron magnets ramping at 200 Hz and 330 Hz are used as part of the
second stage of muon acceleration. Muons are given 25 GeV of RF energy per
orbit. Acceleration is from 250 GeV/c to 2400 GeV/c and requires a total of 86
orbits in both rings; 82% of the muons survive. The total power consumption of
the iron dipoles is 4 megawatts. Stranded copper conductors and thin magnetic
laminations are used to reduce power losses.",0208010v1
2002-04-18,Physical Properties of Iron in the Inner Core,"The Earth's inner core plays a vital role in the dynamics of our planet and
is itself strongly exposed to dynamic processes as evidenced by a complex
pattern of elastic structure. To gain deeper insight into the nature of these
processes we rely on a characterization of the physical properties of the inner
core which are governed by the material physics of its main constituent, iron.
Here we review recent research on structure and dynamics of the inner core,
focusing on advances in mineral physics. We will discuss results on core
composition, crystalline structure, temperature,and various aspects of
elasticity. Based on recent computational results, we will show that aggregate
seismic properties of the inner core can be explained by temperature and
compression effects on the elasticity of pure iron, and use single crystal
anisotropy to develop a speculative textural model of the inner core that can
explain major aspects of inner core anisotropy.",0204055v1
2007-05-09,RBS1423 - a new QSO with relativistic reflection from an ionised disk,"We present the analysis and results of a 20 ks XMM-Newton observation of
RBS1423. X-ray spectral analysis is used to establish a significantly broadened
relativistic iron K-alpha line from a highly ionised disk. A QSO at z=2.262 was
considered to be the optical counterpart of this ROSAT Bright Survey X-ray
source. Based on the improved XMM-Newton source position we identified a
z=0.208 QSO as optical counterpart to RBS1423. The 0.2-12 keV X-ray luminosity
of this radio-quiet QSO is 6x10^{44} erg/s. The XMM-EPIC spectra are well
described by a power law with a significantly broadened iron K-alpha line. Disk
line models for both Schwarzschild and Kerr black holes require hydrogen-like
iron ions to fit the measured line profile. Significant ionisation of the
reflection disk is confirmed by model fits with ionised disk models, resulting
in an ionisation parameter xi~2000.",0705.1267v1
2007-05-18,Simulation of Heme using DFT+U: a step toward accurate spin-state energetics,"We investigate the DFT+U approach as a viable solution to describe the
low-lying states of ligated and unligated iron heme complexes. Besides their
central role in organometallic chemistry, these compounds represent a
paradigmatic case where LDA, GGA, and common hybrid functionals fail to
reproduce the experimental magnetic splittings. In particular, the imidazole
pentacoordinated heme is incorrectly described as a triplet by all usual DFT
flavors. In this study we show that a U parameter close to 4 eV leads to spin
transitions and molecular geometries in quantitative agreement with
experiments, and that DFT+U represents an appealing tool in the description of
iron porphyrin complexes, at a much reduced cost compared to correlated
quantum-chemistry methods. The possibility of obtaining the U parameter from
first-principles is explored through a self-consistent linear-response
formulation. We find that this approach, which proved to be successful in other
iron systems, produces in this case some overestimation with respect to the
optimal values of U.",0705.2743v1
2007-07-12,The First Detailed Abundances for M giants in the inner Bulge from Infrared Spectroscopy,"We report the first abundance analysis of 17 M giant stars in the inner
Galactic bulge at $(l,b)=(0\deg,-1\deg)$, based on $R=25,000$ infrared
spectroscopy $(1.5-1.8 ~\mu \rm m)$ using NIRSPEC at the Keck telescope. Based
on their luminosities and radial velocities, we identify these stars with a
stellar population older than 1 Gyr. We find the iron abundance $\rm < [Fe/H] >
= -0.22 \pm 0.03$, with a $1\sigma$ dispersion of $0.14\pm 0.024$. We also find
the bulge stars have enhanced [$\rm alpha$/Fe] abundance ratio at the level of
+0.3 dex relative to the Solar stars, and low $\rm <^{12}C/^{13}C>\approx
6.5\pm 0.3$. The derived iron abundance and composition for this inner bulge
sample is indistinguishable from that of a sample of M giants our team has
previously studied in Baade's Window $(l,b)=(0.9,-4)$. We find no evidence of
any major iron abundance or abundance ratio gradient between this inner field
and Baade's window.",0707.1855v1
2007-07-26,P-V-T equation of state of epsilon iron and its densities at core conditions,"The author's new p-V-T Equation of State is tested against the available
experiments of epsilon iron. The root-mean-square-deviations (RMSD) of the
molar volume, pressure, and temperature are 0.021 cm3, 2.0 GPa and 144.9 K
respectively. Separating the experiments into 200 K ranges the new EoS was
compared to the most widely used finite strain, interatomic potential, and
empirical isothermal EoSs such as the Burch-Murnaghan, the Vinet, and the
Roy-Roy respectively. Correlation coefficients, RMSDs of the residuals and
Akaike Information Criteria were used for evaluating the fittings. Based on
these fitting parameters the new p-V-T EoS is equal or better than the
conventional isothermal EoSs. The newly defined parameters were used to
calculate the density of the inner core. The calculated densities are
significantly lower than the current consensus indicating that it might be too
early excluding the possibility of a pure iron-nickel core with no light
elements.",0707.3960v1
2007-09-21,Composition of UHECR and the Pierre Auger Observatory Spectrum,"We fit the recently published Pierre Auger ultra-high energy cosmic ray
spectrum assuming that either nucleons or nuclei are emitted at the sources. We
consider the simplified cases of pure proton, or pure oxygen, or pure iron
injection. We perform an exhaustive scan in the source evolution factor, the
spectral index, the maximum energy of the source spectrum Z E_{max}, and the
minimum distance to the sources. We show that the Pierre Auger spectrum agrees
with any of the source compositions we assumed. For iron, in particular, there
are two distinct solutions with high and low E_{max} (e.g. 6.4 10^{20} eV and 2
10^{19} eV) respectively which could be distinguished by either a large
fraction or the near absence of proton primaries at the highest energies. We
raise the possibility that an iron dominated injected flux may be in line with
the latest composition measurement from the Pierre Auger Observatory where a
hint of heavy element dominance is seen.",0709.3390v2
2007-10-17,Iron abundances from optical Fe III absorption lines in B-type stellar spectra,"The role of optical Fe III absorption lines in B-type stars as iron abundance
diagnostics is considered. To date, ultraviolet Fe lines have been widely used
in B-type stars, although line blending can severely hinder their diagnostic
power. Using optical spectra, covering a wavelength range ~ 3560 - 9200 A, a
sample of Galactic B-type main-sequence and supergiant stars of spectral types
B0.5 to B7 are investigated. A comparison of the observed Fe III spectra of
supergiants, and those predicted from the model atmosphere codes TLUSTY
(plane-parallel, non-LTE), with spectra generated using SYNSPEC (LTE), and
CMFGEN (spherical, non-LTE), reveal that non-LTE effects appear small. In
addition, a sample of main-sequence and supergiant objects, observed with
FEROS, reveal LTE abundance estimates consistent with the Galactic environment
and previous optical studies. Based on the present study, we list a number of
Fe III transitions which we recommend for estimating the iron abundance from
early B-type stellar spectra.",0710.3252v1
2007-10-26,Neutrons from Piezonuclear Reactions,"We report the results obtained by cavitating water solutions of iron salts
(iron chloride and iron nitrate) with different concentrations at different
ultrasound powers. In all cases we detected a neutron radiation well higher
than the background level. The neutron production is perfectly reproducible and
can at some extent be controlled. These evidences for neutron emission
generated by cavitation support some preliminary clues for the possibility of
piezonuclear reactions (namely nuclear reactions induced by pressure and shock
waves) obtained in the last ten years. We have been able for the first time to
state some basic features of such a neutron emission induced by cavitation,
namely: 1) a marked threshold behavior in power, energy and time; 2) its
occurring without a concomitant production of gamma radiation.",0710.5115v3
2007-11-27,Broad iron K-alpha emission lines as a diagnostic of black hole spin,"We address the ability of broad iron emission lines from black hole accretion
disks to diagnose the spin of the black hole. Using a high-resolution
3-dimensional MHD simulation of a geometrically-thin accretion disk in a
Pseudo-Newtonian potential, we show that both the midplane density and the
vertical column density of the accretion flow drop dramatically over a narrow
range of radii close to the innermost stable circular orbit (ISCO). We argue
that this drop of density is accompanied by a sharp increase in the ionization
parameter of the X-ray photosphere, and that the resulting imprint of the ISCO
on the X-ray reflection spectrum can be used to constrain spin. Motivated by
this simulation, we construct a simplified toy-model of the accretion flow
within the ISCO of a Kerr black hole, and use this model to estimate the
systematic error on inferred black hole spin that may result from slight
bleeding of the iron line emission to the region inside of the ISCO. We find
that these systematic errors can be significant for slowly spinning black holes
but become appreciably smaller as one considers more rapidly rotating black
holes.",0711.4158v1
2008-01-24,Tracing the distribution and evolution of Iron in the IntraCluster Medium,"Emission lines in X-ray spectra of clusters of galaxies reveal the presence
of heavy elements in the diffuse hot plasma (ICM) in virial equilibrium in the
dark matter potential well. Thanks to the X-ray satellites Chandra and
XMM-Newton we are now able to measure with good accuracy the distribution and
evolution of Iron up to redshift z ~ 1.3. The capability of studying the
chemical and thermodynamical properties of the ICM in high redshift clusters is
an efficient tool to constrain the interaction processes between the cluster
galaxies and the surrounding medium. We confirm that the ICM is already
significantly enriched at a look-back time of 9 Gyr, and find that the Iron
abundance change with redshift as (1+z)^(-1.25), implying an increase of a
factor of ~2 with respect to z=1.3. This result can be explained by a prompt
enrichment by star formation processes in massive ellipticals at z>2, followed
by a slower release of enriched gas from disk galaxies into the ICM, associated
to a morphological transition from disk to S0.",0801.3756v1
2008-04-25,Magnetic Excitations in the High Tc Iron Pnictides,"We calculate the expected finite frequency neutron scattering intensity based
on the two-sublattice collinear antiferromagnet found by recent neutron
scattering experiments as well as by theoretical analysis on the iron
oxypnictide LaOFeAs. We consider two types of superexchange couplings between
Fe atoms: nearest-neighbor coupling J1 and next-nearest-neighbor coupling J2.
We show how to distinguish experimentally between ferromagnetic and
antiferromagnetic J1. Whereas magnetic excitations in the cuprates display a
so-called resonance peak at (pi,pi) (corresponding to a saddlepoint in the
magnetic spectrum) which is at a wavevector that is at least close to nesting
Fermi-surface-like structures, no such corresponding excitations exist in the
iron pnictides. Rather, we find saddlepoints near (pi,pi/2) and (0,pi/2)(and
symmetry related points). Unlike in the cuprates, none of these vectors are
close to nesting the Fermi surfaces.",0804.4115v4
2008-05-15,Orbital fluctuation mechanism for superconductivity in iron-based compounds,"We propose orbital fluctuations in a multi-band ground state as the
superconducting pairing mechanism in the new iron-based materials. We develop a
general SU(4) theoretical framework for studying a two-orbital model and
discuss a number of scenarios that may be operational within this orbital
fluctuation paradigm. The orbital and spin symmetry of the superconducting
order parameter is argued to be highly non-universal and dependent on the
details of the underlying band structure. We introduce a minimal two-orbital
model for the Fe-pnictides characterized by non-degenerate orbitals that
strongly mix with each other. They correspond to the iron ""d_xy"" orbital and to
an effective combination of ""d_zx"" and ""d_zy"", respectively. Using this
effective model we perform RPA calculations of susceptibilities and effective
pairing interactions. We find that spin and orbital fluctuations are,
generally, strongly coupled and we identify the parameters that control this
coupling as well as the relative strength of various channels.",0805.2150v2
2008-06-04,"RXTE determination of the intermediate polar status of XSS J00564+4548, IGR J17195-4100, and XSS J12270-4859","Aims: We determine the nature of the intermediate polar candidates XSS
J00564+4548, IGR J17195-4100, and XSS J12270-4859.
  Methods: Pointed RXTE observations searched for intermediate polar
characteristics in these candidate systems.
  Results: XSS J00564+4548 exhibits a period of 465.68+-0.07 s, which we
interpret as the spin period, an energy dependent modulation depth, and a
spectrum that is fit by a 22 keV photoelectrically absorbed bremsstrahlung with
an iron line profile. IGR J17195-4100 shows several candidate periodicities and
a spectrum that is fit by a power law with an iron line. XSS J12270-4859
exhibits a candidate spin period of 859.57+-0.64 s and a spectrum that is fit
by a power law with no evidence of an iron line.
  Conclusions: XSS J00564+4548 is confirmed to be an intermediate polar. IGR
J17195-4100 and XSS J12270-4859 both show some properties of intermediate
polars, but cannot be confirmed as definite members of the class here.",0806.0751v1
2008-07-04,Magnetic Order of the Iron Spins in NdOFeAs,"Polarized and unpolarized neutron diffraction measurements have been carried
out to investigate the iron magnetic order in undoped NdOFeAs.
Antiferromagnetic order is observed below 141(6) K, which is in close proximity
to the structural distortion observed in this material. The magnetic structure
consists of chains of parallel spins that are arranged antiparallel between
chains, which is the same in-plane spin arrangement as observed in all the
other iron oxypnictide materials. Nearest-neighbor spins along the c-axis are
antiparallel like LaOFeAs. The ordered moment is 0.25(7) muB, which is the
smallest moment found so far in these systems.",0807.0662v2
2008-07-10,Neutron diffraction on antiferromagnetic ordering in single-crystal BaFe2As2,"Neutron diffraction experiments have been carried out on a Sn-flux grown
BaFe2As2 single crystal, the parent compound of the A-122 family of FeAs-based
high-Tc superconductors. A tetragonal to orthorhombic structural phase
transition and a three dimensional long-range antiferromagnetic ordering of the
iron moment, with a unique magnetic propagation wavevector k = (1, 0, 1), have
been found to take place at ~90 K. The magnetic moments of iron are aligned
along the long a axis in the low temperature orthorhombic phase (Fmmm with
b<a<c). Our results thus demonstrate that the magnetic structure of BaFe2As2
single crystal is the same as those in other A-122 iron pnictides compounds. We
argue that the tin incorporation in the lattice is responsible for a smaller
orthorhombic splitting and lower Neel temperature T_N observed in the
experiment.",0807.1743v3
2008-08-14,Determination of the single-ion anisotropy energy in a S = 5/2 kagome antiferromagnet using X-ray absorption spectroscopy,"We report x-ray absorption and x-ray linear dichroism measurements at the Fe
L2,3 edges of the geometrically frustrated systems of potassium and hydronium
iron jarosite. Comparison with simulated spectra, involving ligand-field
multiplet calculations modelling the 3d-2p hybridization between the iron ion
and the oxygen ligands, has yielded accurate estimates for the ligand metal-ion
hybridization and the resulting single-ion crystal field anisotropy energy.
Using this method we provide an experimentally verified scenario for the
appearance of a single-ion anisotropy in this nominally high-spin 3d5 orbital
singlet 6S system, which accounts for features of the spin-wave dispersion in
the long-range ordered ground state of potassium iron jarosite.",0808.1969v2
2008-09-18,Metallicity in the Galactic Center: The Quintuplet cluster,"We present a measurement of metallicity in the Galactic center Quintuplet
Cluster made using quantitative spectral analysis of two Luminous Blue
Variables (LBVs). The analysis employs line-blanketed NLTE wind/atmosphere
models fit to high-resolution near-infrared spectra containing lines of H, HeI,
SiII, MgII, and FeII. We are able to break the H/He ratio vs. mass-loss rate
degeneracy found in other LBVs and to obtain robust estimates of the He content
of both objects. Our results indicate solar iron abundance and roughly twice
solar abundance in the alpha-elements. These results are discussed within the
framework of recent measurements of oxygen and carbon composition in the nearby
Arches Cluster and iron abundances in red giants and supergiants within the
central 30 pc of the Galaxy. The relatively large enrichment of alpha-elements
with respect to iron is consistent with a history of more nucleosynthesis in
high mass stars than the Galactic disk.",0809.3185v1
2008-11-11,Extreme Sensitivity of Superconductivity to Stoichiometry in FeSe (Fe1+dSe),"The recently discovered iron arsenide superconductors, which display
superconducting transition temperatures as high as 55 K, appear to share a
number of general features with high-Tc cuprates, including proximity to a
magnetically ordered state and robustness of the superconductivity in the
presence of disorder. Here we show that superconductivity in Fe1+dSe, the
parent compound of the superconducting arsenide family, is destroyed by very
small changes in stoichiometry. Further, we show that non-superconducting
Fe1+dSe is not magnetically ordered down to low temperatures. These results
suggest that robust superconductivity and immediate instability against an
ordered magnetic state should not be considered as intrinsic characteristics of
iron-based superconducting systems, and that Fe1+dSe may present a unique
opportunity for determining which materials characteristics are critical to the
existence of superconductivity in high Tc iron arsenide superconductors and
which are not.",0811.1613v2
2008-11-20,A novel non-Fermi-liquid state in the iron-pnictide FeCrAs,"We report transport and thermodynamic properties of stoichiometric single
crystals of the hexagonal iron-pnictide FeCrAs. The in-plane resistivity shows
an unusual ""non-metallic"" dependence on temperature T, rising continuously with
decreasing T from ~ 800 K to below 100 mK. The c-axis resistivity is similar,
except for a sharp drop upon entry into an antiferromagnetic state at T_N 125
K. Below 10 K the resistivity follows a non-Fermi-liquid power law, rho(T) =
rho_0 - AT^x with x<1, while the specific heat shows Fermi liquid behaviour
with a large Sommerfeld coefficient, gamma ~ 30 mJ/mol K^2. The high
temperature properties are reminiscent of those of the parent compounds of the
new layered iron-pnictide superconductors, however the T -> 0 properties
suggest a new class of non-Fermi liquid.",0811.3439v1
2008-12-03,Novel properties in Josephson junctions involving the cos(kx)cos(ky)-pairing state in iron-pnictides,"We propose a trilayer $\pi$-junction that takes advantage of the
unconventional $s_{x^2 y^2}=\cos k_x \cos k_y$ pairing symmetry which changes
sign between electron and hole Fermi pockets in the iron pnictides. In
addition, we also present theoretical results for Andreev bound states in thin
superconductor-normal metal (or insulator) iron-pnictide junctions. The
presence of nontrivial in-gap states, which uniquely appear in this
unconventional pairing state, is a distinct feature in comparison to other
singlet pairing states.",0812.0661v2
2008-12-05,Electronic and lattice dynamical properties of the iron-based superconductors LiFeAs and NaFeAs,"The electronic structure and lattice vibrational frequencies of the newly
discovered superconductors, LiFeAs and NaFeAs, are calculated within density
functional theory. We show that in the vicinity of the Fermi energy, the
density of states is dominated by contributions from Fe 3d states. We also
calculate the electron-phonon coupling strength and show that it is too weak to
account for the observed values of the superconducting transition temperatures.
This seems to indicate that the iron-based superconductors are not of the
conventional type.",0812.1215v1
2008-12-09,An analysis of electron distributions in galaxy clusters by means of the flux ratio of iron lines FeXXV and XXVI,"The interpretation of hard X-ray emission from galaxy clusters is still
ambiguous and different models proposed can be probed using various
observational methods. Here we explore a new method based on Fe line
observations.
  Spectral line emissivities have usually been calculated for a Maxwellian
electron distribution. In this paper a generalized approach to calculate the
iron line flux for a modified Maxwellian distribution is considered.
  We have calculated the flux ratio of iron lines for the various possible
populations of electrons that have been proposed to account for measurements of
hard X-ray excess emission from the clusters A2199 and Coma. We found that the
influence of the suprathermal electron population on the flux ratio is more
prominent in low temperature clusters (as Abell 2199) than in high temperature
clusters (as Coma).",0812.1650v1
2009-01-20,Probing the Ground State Properties of Iron-based Superconducting Pnictides and Related Systems by Muon-Spin Spectroscopy,"In this short review, we attempt to give a comprehensive discussion of
studies performed to date by muon-spin spectroscopy (more precisely the
relaxation and rotation technique, also know as \muSR technique) on the
recently discovered layered iron-based superconductors. On one side, \muSR has
been used to characterized the magnetic state of different families of layered
iron-based systems. Similarly the subtle interplay of the magnetic state and
the structural transition present in some families has been investigated. We
will also discuss the information provided by this technique on the interaction
between the magnetic state and the superconducting phase. Finally the \muSR
technique has been used to investigate the magnetic penetration depth of the
superconducting ground state. The study of its absolute value, temperature and
magnetic field dependence provides crucial tests for investigating possible
unconventional superconducting states in such systems.",0901.3139v2
2009-01-22,Magnon-Mediated Pairing and Isotope Effect in Iron-based Superconductors,"Within a minimal model for the iron-based superconductors in which itinerant
electrons interact with a band of local moments, we derive a a general
conclusion for multi-band superconductivity. In a multi-band superconductor,
due to the Adler theorem, the inter-band scattering dominates the intra-band
scattering at the long wave length limit as long as both interactions are
induced by Goldstone boson (which is magnon in our case) and the transfered
momentum is nonzero. Such kind of interaction leads to a well-known
sigh-reversing superconductivity even if the inter-band and intra-band
interaction are repulsive. This effect can be modeled as arising from an
internal Josephson link between the Fermi surface sheets. Our model is also
consistent with the recently discovered coexistence of superconductivity and
magnetic order in iron-pnictides. Although the experimentally observed isotope
effect is large, $\alpha=0.4$, we show that it is consistent with a
non-phononic mechanism in which it is the isotope effects result in a change in
the lattice constant and as a consequence the zero-point motion of the Fe
atoms.",0901.3538v2
2009-01-23,Anisotropic London Penetration Depth and Superfluid Density in Single Crystals of Iron-based Pnictide Superconductors,"In- and out-of-plane magnetic penetration depths were measured in three
iron-based pnictide superconducting systems. All studied samples of both 122
systems show a robust power-law behavior, $\lambda (T) T^n$, with the
sample-dependent exponent n=2-2.5, which is indicative of unconventional
pairing. This scenario could be possible either through scattering in a $s_{\pm
}$ state or due to nodes in the superconducting gap. In the Nd-1111 system, the
interpretation of data may be obscured by the magnetism of rare-earth ions. The
overall anisotropy of the pnictide superconductors is small. The 1111 system is
about two times more anisotropic than the 122 system. Our data and analysis
suggest that the iron-based pnictides are complex superconductors in which a
multiband three-dimensional electronic structure and strong magnetic
fluctuations play important roles.",0901.3698v2
2009-01-28,Both accurate and precise gf-values for FeII lines,"We present a new set of oscillator strengths for 142 FeII lines in the
wavelength range 4000-8000 A. Our gf-values are both accurate and precise,
because each multiplet was globally normalized using laboratory data
(accuracy), while the relative gf-values of individual lines within a given
multiplet were obtained from theoretical calculations (precision). Our line
list was tested with the Sun and high-resolution (R ~ 10^5), high-S/N
(~700-900) Keck+HIRES spectra of the metal-poor stars HD 148816 and HD 140283,
for which line-to-line scatter (sigma) in the iron abundances from FeII lines
as low as 0.03, 0.04, and 0.05 dex are found, respectively. For these three
stars the standard error in the mean iron abundance from FeII lines is
negligible (sigma_mean <= 0.01 dex). The mean solar iron abundance obtained
using our gf-values and different model atmospheres is A_Fe = 7.45 (sigma =
0.02).",0901.4451v2
2009-02-02,Density Functional Study of the Over-Doped Iron Chalcogenide: TlFe$_{2}$Se$_{2}$ with ThCr$_{2}$Si$_{2}$ structure,"We report density functional calculations of electronic structure and
magnetic properties of ternary iron chalcogenide TlFe$_{2}$Se$_{2}$, which
occurs in the ThCr$_{2}$Si$_{2}$ structure and discuss the results in relation
to the iron-based superconductors. The ground state is antiferromagnetic with
checkerboard order and Fe moment $\sim$ 1.90 $\mu$B. There is strong
magnetoelastic coupling similar to the Fe-based superconductors, reflected in a
sensitivity of the Se position to magnetism. Tl is monovalent in this compound,
providing heavy electron-doping of 0.5 additional carriers per Fe relative to
the parent compounds of the Fe-based superconductors. Other than the change in
electron count, the electronic structure is rather similar to those materials.
In particular, the Fermi surface is closely related to those of the Fe-based
superconductors, except that the electron cylinders are larger, and the hole
sections are suppressed. This removes the tendency towards a spin density wave.",0902.0265v1
2009-02-04,Evidence for Three-Dimensionality in the Fermi Surface Topology of Layered Electron Doped Ba(Fe1-XCox)2As2 Iron Superconductors,"The electronic structure of electron doped iron-arsenide superconductors
Ba(Fe1- xCox)2As2 has been measured with Angle Resolved Photoemission
Spectroscopy. The data reveal a marked photon energy dependence of points in
momentum space where the bands cross the Fermi energy, a distinctive and direct
signature of three-dimensionality in the Fermi surface topology. By providing a
unique example of high temperature superconductivity hosted in layered
compounds with three-dimensional electronic structure, these findings suggest
that the iron-arsenides are unique materials, quite different from the cuprates
high temperature superconductors.",0902.0756v3
2009-02-21,Inelastic Neutron Scattering Studies of the Spin and Lattice Dynamics in Iron Arsenide Compounds,"Neutrons have played an important role in advancing our understanding of the
pairing mechanism and the symmetry of the superconducting energy gap in the
iron arsenide compounds. Neutron measurements of the phonon density-of-state
are in good agreement with ab initio calculations, provided the magnetism of
the iron atoms is taken into account. However, the predicted superconducting
transition temperatures are less than 1 K, making a conventional phononic
mechanism for superconductivity highly unlikely. Measurements of the spin
dynamics within the spin density wave phase of the parent compounds show
evidence of strongly dispersive spin waves with exchange interactions
consistent with the observed magnetic order. Antiferromagnetic fluctuations
persist in the normal phase of the superconducting compounds, but they are more
diffuse. Below Tc, there is evidence compounds that these fluctuations condense
into a resonant spin excitation at the antiferromagnetic wavevector with an
energy that scales with Tc, consistent with unconventional superconductivity of
extended-s+/- wave symmetry.",0902.3760v1
2009-04-15,"Direct imaging of the structural domains in iron pnictides AFe2As2 (A = Ca, Sr, Ba)","The parent compounds of recently discovered iron-arsenide superconductors,
$A$Fe$_2$As$_2$ with alkaline earth $A$=Ca, Sr, Ba, undergo simultaneous
structural and magnetic phase transitions at a temperature $T_{SM}$. Using a
combination of polarized light microscopy and spatially resolved high-energy
synchrotron X-ray diffraction we show that the orthorhombic distortion leads to
the formation of 45$^o$-type structural domains in all parent compounds.
Domains penetrate through the sample thickness in the $c$- direction and are
not affected by crystal defects such as growth terraces. The domains form
regular stripe patterns in the plane with a characteristic dimension of 10 to
50 $\mu m$. The direction of the stripes is fixed with respect to the
tetragonal (100) and (010) directions but can change by 90$^o$ on thermal
cycling through the transition. This domain pattern may have profound
implications for intrinsic disorder and anisotropy of iron arsenides.",0904.2337v2
2009-04-26,The orbital characters of bands in iron-based superconductor BaFe1.85Co0.15As2,"The unconventional superconductivity in the newly discovered iron-based
superconductors is intimately related to its multi-band/multi-orbital nature.
Here we report the comprehensive orbital characters of the low-energy
three-dimensional electronic structure in BaFe$_{1.85}$Co$_{0.15}$As$_2$ by
studying the polarization and photon energy dependence of angle-resolved
photoemission data. While the distributions of the $d_{xz}$, $d_{yz}$, and
$d_{3z^2-r^2}$ orbitals agree with the prediction of density functional theory,
those of the $d_{xy}$ and $d_{x^2-y^2}$ orbitals show remarkable disagreement
with theory. Our results point out the inadequacy of the existing band
structure calculations, and more importantly, provide a foundation for
constructing the correct microscopic model of iron pnictides.",0904.4022v3
2009-04-29,Discovery of Red-Skewed K_alpha iron line in Cyg X-2 with Suzaku,"We report on the Suzaku observation of neutron star low-mass X-ray binary
Cygnus X-2 which reveals a presence of the iron K_alpha emission line. The line
profile shows a significant red wing. This discovery increases the number of
neutron star sources where red-skewed iron lines were observed and strongly
suggests that this phenomenon is common not only in black holes but also in
other types of accreting compact objects. We examine the line profile in terms
of models which attribute its production to the relativistic effects due to
reflection of X-ray radiation from a cold accretion disk and also as a result
of the line formation in the extended wind/outflow configuration. Both models
are able to adequately represent the observed line profile. We consider the
results of line modeling in the context of subsecond variability. While we were
unable to conclusively disqualify one of the models, we find that the wind
paradigm has several advantages over the relativistic disk reflection model.",0904.4682v1
2009-05-09,Low ordered magnetic moment by off-diagonal frustration in undoped parent compounds to iron-based high-Tc superconductors,"A Heisenberg model over the square lattice recently introduced by Si and
Abrahams to describe local-moment magnetism in the new class of Fe-As high-Tc
superconductors is analyzed in the classical limit and on a small cluster by
exact diagonalization. In the case of spin-1 iron atoms, large enough
Heisenberg exchange interactions between neighboring spin-1/2 moments on
different iron 3d orbitals that frustrate true magnetic order lead to hidden
magnetic order that violates Hund's rule. It accounts for the low ordered
magnetic moment observed by elastic neutron diffraction in an undoped parent
compound to Fe-As superconductors. We predict that low-energy spin-wave
excitations exist at wavenumbers corresponding to either hidden Neel or hidden
ferromagnetic order.",0905.1359v2
2009-05-11,The Microstrain-Doping Phase Diagram of the Iron Pnictides Heterostructures at Atomic Limit,"The 3D phase diagram of iron pnictides where the critical temperature depends
on charge density and microstrain in the active FeAs layers is proposed. The
iron pnictides superconductors are shown to be a practical realization of a
heterostructure at the atomic limit made of a superlattice of FeAs layers
intercalated by spacer layers. We have focussed our interest on the A 1-x
BxFe2As2 (122) families and we show that FeAs layers have a tensile microstrain
due to the misfit strain between the active layers and the spacers. We have
identified the critical range of doping and microstrain where the critical
temperature gets amplified to its maximum value.",0905.1631v1
2009-05-11,Orbital-Ordering Induces Structural Phase Transition and the Resistivity Anomaly in Iron Pnictides,"We attribute the structural phase transition (SPT) in the parent compounds of
the iron pnictides to orbital ordering. Due to the anisotropy of the $d_{xz}$
and $d_{yz}$ orbitals in the $xy$ plane, a ferro-orbital ordering makes the
orthorhombic structure more energetically favorable, thus inducing the SPT. In
this orbital-ordered system, the sites with orbitals that do not order have
higher energies. Scattering of the itinerant electrons by these localized
two-level systems causes a resistivity anomaly upon the onset of the SPT. The
proposed orbital ordering also leads to the stripe-like anti-ferromagnetism and
anisotropy of the magnetic exchanges. This model is quantitatively consistent
with available experimental observations.",0905.1704v2
2009-05-18,Superconductivity in Multi-orbital t-J1-J2 Model and its Implications for Iron Pnictides,"Motivated by the bad metal behavior of the iron pnictides, we study a
multi-orbital $\mathrm{t-J_1-J_2}$ model and investigate possible singlet
superconducting pairings. Magnetic frustration by itself leads to a large
degeneracy in the pairing states. The kinetic energy breaks this into a
quasi-degeneracy among a reduced set of pairing states. For small electron and
hole Fermi pockets, an $A_{1g}$ state dominates over the phase diagram but a
$B_{1g}$ state has close-by energy. In addition to the nodeless $A_{1g}$
$s_{x^2y^2}$ channel, the nodal $A_{1g}$ $s_{x^2+y^2}$ and $B_{1g}$
$d_{x^2-y^2}$ channels are also competitive in the magnetically frustrated $J_1
\sim J_2$ parameter regime. An $A_{1g}+i B_{1g}$ state, which breaks
time-reversal symmetry, occurs at low temperatures in part of the phase
diagram. Implications for the experiments in the iron pnictides are discussed.",0905.2634v3
2009-05-18,Ferro-Orbital Order and Strong Magnetic Anisotropy in the Parent Compounds of Iron-Pnictide Superconductors,"The puzzling nature of magnetic and lattice phase transitions of iron
pnictides is investigated via a first-principles Wannier function analysis of
representative parent compound LaOFeAs. A rare ferro-orbital ordering is found
to give rise to the recently observed highly anisotropic magnetic coupling, and
drive the phase transitions--without resorting to widely employed frustration
or nesting picture. The revealed necessity of the additional orbital physics
leads to a correlated electronic structure fundamentally distinct from that of
the cuprates. In particular, the strong coupling to the magnons advocates
active roles of light orbitons in spin dynamics and electron pairing in iron
pnictides.",0905.2957v2
2009-05-19,Strength of correlations in pnictides and its assessment by theoretical calculations and spectroscopy experiments,"LDA+DMFT (Local Density Approximation combined with Dynamical Mean-Field
Theory) computation scheme has been used to calculate spectral properties of
LaFeAsO -- the parent compound of the new high-T_c iron oxypnictides. The
average Coulomb repulsion U=3-4 eV and Hund's exchange J=0.8 eV parameters for
iron 3d electrons were calculated using the first principles constrained
density functional theory scheme in the Wannier functions formalism. DMFT
calculations using these parameters result in moderately correlated electronic
structure with effective electron mass enhancement m^*~2 that is in agreement
with the experimental X-ray and photoemission spectra. Conclusion of moderate
correlations strength is confirmed by the observation that pnictides
experimental spectra agree well with corresponding spectra for metallic iron
while being very different with Mott insulator FeO spectra.",0905.3038v1
2009-06-12,Violation of Anderson's Theorem for Sign-Reversing s-Wave State of Iron-Pnictide Superconductors,"Based on the five-orbital model, we study the effect of local impurity in
iron pnictides, and find that the interband impurity scattering is promoted by
the d-orbital degree of freedom. This fact means that the fully-gapped
sign-reversing s-wave state, which is predicted by spin fluctuation theories,
is very fragile against impurities. In the BCS theory, only 1% impurities with
intermediate strength induce huge pair-breaking, resulting in the large in-gap
state and prominent reduction in Tc, contrary to the prediction based on simple
orbital-less models. The present study provides a stringent constraint on the
pairing symmetry and the electronic states in iron pnictides.",0906.2269v4
2009-06-12,Interplay of inequivalent atomic positions in resonant x-ray diffraction of Fe3BO6,"'Forbidden' Bragg reflections of iron orthoborate Fe3BO6 were studied
theoretically and experimentally in the vicinity of the iron K edge. Their
energy spectra are explained as resulting from the interference of x-rays
scattered from two inequivalent crystallographic sites occupied by iron ions.
This particular structure property gives rise to complex azimuthal dependences
of the reflection intensities in the pre-edge region as they result from the
interplay of site specific dipole-quadrupole and quadrupole-quadrupole resonant
scattering. Also evidenced is an isotropic character of the absorption
spectrum. Self-absorption correction to the diffraction data, as well as
possible contributions of thermal vibrations and magnetic order, are discussed.
Particular care is given to extracting clean spectra from the data, and it is
demonstrated that excellent results can be obtained even from measurements that
appear corrupted by several effects such as poor crystal quality and multiple
scattering.",0906.2338v1
2009-07-26,Josephson effect between electron-doped and hole-doped iron pnictide single crystals,"We have observed the Josephson effect in junctions formed between single
crystals of SrFe1.74Co0.26As2 and Ba0.23K0.77Fe2As2. I-V curves showed
resistively-shunted junction characteristics, and the ac Josephson effect was
observed under microwave irradiation. By applying an in-plane magnetic field,
the critical current is completely modulated and shows a relatively symmetric
diffraction pattern, consistent with the intermediate junction limit. The
observation of the Josephson effect in the p-n bicrystal structure not only has
significant implications for designing phase-sensitive junctions to probe the
pairing symmetry of iron pnictide superconductors, but also represents an
important step in developing all iron pnictide devices for applications.",0907.4456v1
2009-08-06,Resonance as a probe of the electron superconducting gap in BaFe1.9Ni0.1As2,"The discovery of high-transition temperature (high-Tc) superconductivity near
antiferromagnetism in iron arsenides raised the possibility of an
unconventional superconducting mechansim1-8. The observation of clear Fermi
surfaces and nodeless superconducting gaps by angle resolved photoemission9-12
suggests that electron pairing in these materials may be mediated by
quasiparticle excitations between sign reversed hole and electron Fermi
pockets5-8. Although the presence of a 'resonance' in the spin excitation
spectrum found by inelastic neutron scattering13-17 is consistent with this
picture18-20, there has been no direct evidence connecting the resonance to the
superconducting gap energy. Here we show that for the optimally electron doped
BaFe1.9Ni0.1As2 (Tc =20 K, Fig. 1c) iron arsenide superconductor, application
of a magnetic field that suppresses the superconductivity and superconducting
gap energy also reduces the intensity and energy of the resonance. These
results suggest that the energy of the resonance is proportional to the
electron pairing energy, and thus indicate that spin fluctuations are
intimately related to the mechanism of superconductivity in iron arsenides.",0908.0954v1
2009-08-11,Influence of thermohaline convection on diffusion-induced iron accumulation in A stars,"Atomic diffusion may lead to heavy element accumulation inside stars in
certain specific layers. Iron accumulation in the Z-bump opacity region has
been invoked by several authors to quantitatively account for abundance
anomalies observed in some stars, or to account for stellar oscillations
through the induced $\kappa$-mechanism. These authors however never took into
account the fact that such an accumulation creates an inverse $\mu$-gradient,
unstable for thermohaline convection. Here, we present results for A-F stars,
where abundance variations are computed with and without this process. We show
that iron accumulation is still present when thermohaline convection is taken
into account, but much reduced compared to when this physical process is
neglected. The consequences of thermohaline convection for A-type stars as well
as for other types of stars are presented",0908.1534v1
2009-09-07,Spin excitations in the excitonic spin-density-wave state of the iron pnictides,"Motivated by the iron pnictides, we examine the spin excitations in an
itinerant antiferromagnet where a spin-density wave (SDW) originates from an
excitonic instability of nested electron-like and hole-like Fermi pockets.
Using the random phase approximation (RPA), we derive the Dyson equation for
the transverse susceptibility in the excitonic SDW state. The Dyson equation is
solved for two different two-band models, describing an antiferromagnetic
insulator and metal, respectively. We determine the collective spin-wave
dispersions and also consider the single-particle continua. The results for the
excitonic models are compared with each other and also contrasted with the
well-known SDW state of the Hubbard model. Despite the qualitatively different
SDW states in the two excitonic models, their magnetic response shows many
similarities. We conclude with a discussion of the relevance of the excitonic
SDW scenario to the iron pnictides.",0909.1222v2
2009-09-25,The inverse iron-bias in action in Abell 2028,"Recent work based on a global measurement of the ICM properties find evidence
for an increase of the iron abundance in galaxy clusters with temperature
around 2-4 keV. We have undertaken a study of the metal distribution in nearby
clusters in this temperature range, aiming at resolving spatially the metal
content of the ICM. The XMM observation of the first object of the sample, the
cluster Abell 2028, reveals a complex structure of the cluster over scale of ~
300 kpc, showing an interaction between two sub-clusters in a ``cometary''
configuration. We show that a naive one-component fit for the core of Abell
2028 returns a biased high metallicity. This is due to the inverse iron-bias,
which is not related to the presence in the spectrum of both Fe-L and Fe-K
emission lines but to the behavior of the fitting code in shaping the Fe-L
complex of a one temperature component to adjust to the multi-temperature
structure of the projected spectrum.",0909.4679v1
2009-10-02,Broad iron L-line and X-ray reverberation in 1H0707-495,"A detailed analysis of a long XMM-Newton observation of the Narrow Line
Seyfert 1 galaxy 1H0707-495 is presented, including spectral fitting, spectral
variability and timing studies. The two main features in the spectrum are the
drop at ~ 7 keV and a complex excess below 1 keV. These are well described by
two broad, K and L, iron lines. Alternative models based on absorption,
although they may fit the high energy drop, cannot account for the 1 keV
complexity and the spectrum as a whole. Spectral variability shows that the
spectrum is composed of at least two components, which are interpreted as a
power-law dominating between 1-4 keV, and a reflection component outside this
range. The high count rate at the iron L energies has enabled us to measure a
significant soft lag of ~ 30 s between 0.3-1 and 1-4 keV, meaning that the
direct hard emission leads the reflected emissions. We interpret the lag as a
reverberation signal originating within a few gravitational radii of the black
hole.",0910.0367v1
2009-10-08,Local density of states and superconducting gap in the iron chalcogenide superconductor Fe$_{1+δ}$Se$_{1-x}$Te$_{x}$ observed by scanning tunneling spectroscopy,"We report on the first investigation of the quasiparticle local density of
states and superconducting gap in the iron chalcogenide superconductor
Fe$_{1+\delta}$Se$_{1-x}$Te$_{x}$ ($T_{\mathrm{c}} \sim 14$ K). The surface of
a cleaved crystal revealed an atomic square lattice, superimposed on the
inhomogeneous background, with a lattice constant of $\sim 3.8$ \AA without any
reconstruction. Tunneling spectra measured at 4.2 K exhibit the superconducting
gap, which completely disappears at 18 K, with a magnitude of $\sim 2.3$ meV,
corresponding to $2\Delta / k_{\mathrm{B}}T_{\mathrm{c}}=3.8$.In stark contrast
to the cuprate superconductors, the value of the observed superconducting gap
is relatively homogeneous, following a sharp distribution with a small standard
deviation of 0.23 meV. Conversely, the normal-state local density of states
observed above $T_{\mathrm{c}}$ shows spatial variation over a wide energy
range of more than 1 eV, probably due to the excess iron present in the
crystal.",0910.1485v3
2009-10-09,Spin-waves in the $J_{1a}-J_{1b}-J_{2}$ orthorombic square-lattice Heisenberg models: Application to the iron pnictide materials,"Motivated by the observation of spatially anisotropic exchange constants in
the iron pnictide materials, we study the spin-wave spectra of the
$J_{1a}-J_{1b}-J_{2}$ Heisenberg models on a square-lattice with nearest
neighbor exchange $J_{1a}$ along x and $J_{1b}$ along y axis and a second
neighbor exchange $J_2$. We focus on the regime, where the spins order at
($\pi,0$), and compute the spectra by systematic expansions around the Ising
limit. We study both spin-half and spin-one Heisenberg models as well as a
range of parameters to cover various cases proposed for the iron pnictide
materials. The low-energy spectra have anisotropic spin-wave velocities and are
renormalized with respect to linear spin-wave theory by up to 20 percent,
depending on parameters. Extreme anisotropy, consisting of a ferromagnetic
$J_{1b}=- |J_F|$, is best distinguished from a weak anisotropy ($J_{1a}\approx
J_{1b}=J_1$, $J_2>J_1/2$) by the nature of the spin-waves near the wavevectors
($0,\pi$) or ($\pi,\pi$). The reported spectra for the pnictide material
CaFe$_2$As$_2$ clearly imply such an extreme anisotropy.",0910.1793v1
2009-10-17,Suzaku Discovery of the Strong Radiative Recombination Continuum of Iron from the Supernova Remnant W49B,"We present a hard X-ray spectrum of unprecedented quality of the Galactic
supernova remnant W49B obtained with the Suzaku satellite. The spectrum
exhibits an unusual structure consisting of a saw-edged bump above 8 keV. This
bump cannot be explained by any combination of high-temperature plasmas in
ionization equilibrium. We firmly conclude that this bump is caused by the
strong radiative recombination continuum (RRC) of iron, detected for the first
time in a supernova remnant. The electron temperature derived from the
bremsstrahlung continuum shape and the slope of the RRC is 1.5 keV. On the
other hand, the ionization temperature derived from the observed intensity
ratios between the RRC and K-alpha lines of iron is 2.7 keV. These results
indicate that the plasma is in a highly overionized state. Volume emission
measures independently determined from the fluxes of the thermal and RRC
components are consistent with each other, suggesting the same origin of these
components.",0910.3302v1
2009-10-19,Structure of Neutron-Scattering Peak in both s++ wave and s+- wave states of an Iron pnictide Superconductor,"We study the neutron scattering spectrum in iron pnictides based on the
random-phase approximation in the five-orbital model, for fully-gapped s-wave
states with sign reversal (s+-) and without sign reversal (s++). In the s++
wave state, we find that a prominent hump structure appears just above the
spectral gap, by taking account of the quasiparticle damping gamma due to
strong electron-electron correlation: As the superconductivity develops, the
reduction in gamma gives rise to the large overshoot in the spectrum above the
gap. The obtained hump structure looks similar to the resonance peak in the s+-
wave state, although the height and weight of the peak in the latter state is
much larger. In the present study, experimentally observed broad spectral peak
in iron pnictides is naturally reproduced by assuming the s++ wave state.",0910.3472v2
2009-10-29,A Theoretical Study on a Reaction of Iron(III) Hydroxide with Boron Trichloride by Ab Initio Calculation,"We investigate a reaction of boron trichloride (BCl3) with iron(III)
hydroxide (Fe(OH)3) by ab initio quantum chemical calculation as a simple model
for a reaction of iron impurities in BCl3 gas. We also examine a reaction with
water. We find that compounds such as Fe(Cl)(OBCl2)2(OHBCl2) and
Fe(Cl)2(OBCl2)(OHBCl2) are formed while producing HCl and reaction paths to
them are revealed. We also analyze the stabilization mechanism of these paths
using newly-developed interaction energy density derived from electronic stress
tensor in the framework of the Regional DFT (Density Functional Theory) and
Rigged QED (Quantum ElectroDynamics).",0910.5633v1
2009-11-03,Coherence effect in a two-band superconductor: Application to iron pnictides,"From a theoretical point of view, we propose an experimental method to
determine the pairing symmetry of iron pnictides. We focus on two kinds of
pairing symmetries, $s_{+-}$ and $s_{++}$, which are strong candidates for the
pairing symmetry of iron pnictides. For each of these two symmetries, we
calculate both the density and spin response functions by using the two-band
BCS model within the one-loop approximation. As a result, a clear difference is
found between the $s_{+-}$- and $s_{++}$-wave states in the temperature
dependence of the response functions at nesting vector $\bf{Q}$, which connects
the hole and electron Fermi surfaces. We point out that this difference comes
from the coherence effect in the two-band superconductor. We suggest that the
pairing symmetry could be clarified by observing the temperature dependence of
both the density and spin structure factors at the nesting vector $\bf{Q}$ in
neutron scattering measurements.",0911.0528v2
2009-11-27,Unconventional pairing in the iron arsenide superconductors,"We use magnetic long range order as a tool to probe the Cooper pair wave
function in the iron arsenide superconductors. We show theoretically that
antiferromagnetism and superconductivity can coexist in these materials only if
Cooper pairs form an unconventional, sign-changing state. The observation of
coexistence in Ba(Fe$_{1-x}$Co$_{x}$)$_{2}$As$_{2}$ then demonstrates
unconventional pairing in this material. The detailed agreement between theory
and neutron diffraction experiments, in particular for the unusual behavior of
the magnetic order below $T_{c}$, demonstrates the robustness of our
conclusions. Our findings strongly suggest that superconductivity is
unconventional in all members of the iron arsenide family.",0911.5183v3
2009-12-24,"Band Narrowing and Mott Localization in Iron Oxychalcogenides La2O2Fe2O(Se,S)2","Bad metal properties have motivated a description of the parent iron
pnictides as correlated metals on the verge of Mott localization. What has been
unclear is whether interactions can push these and related compounds to the
Mott insulating side of the phase diagram. Here we consider the iron
oxychalcogenides La2O2Fe2O(Se,S)2, which contain an Fe square lattice with an
expanded unit cell. We show theoretically that they contain enhanced
correlation effects through band narrowing compared to LaOFeAs, and we provide
experimental evidence that they are Mott insulators with moderate charge gaps.
We also discuss the magnetic properties in terms of a Heisenberg model with
frustrating J1-J2-J2' exchange interactions on a ""doubled"" checkerboard
lattice.",0912.4741v2
2009-12-30,Three-band superconductivity and the order parameter that breaks time-reversal symmetry,"We consider a model of multiband superconductivity, inspired by iron
pnictides, in which three bands are connected via repulsive pair-scattering
terms. Generically, three distinct superconducting states arise within such a
model. Two of them are straightforward generalizations of the two-gap order
parameter while the third one corresponds to a time-reversal symmetry breaking
order parameter, altogether absent within the two-band model. Potential
observation of such a genuinely frustrated state would be a particularly vivid
manifestation of the repulsive interactions being at the root of iron-based
high temperature superconductivity. We construct the phase diagram of this
model and discuss its relevance to the iron pnictides family of high
temperature superconductors. We also study the case of the Josephson coupling
between a two-band s' (or extended s-wave) superconductor and a single-gap
s-wave superconductor, and the associated phase diagram.",0912.5214v2
2009-12-30,Nanoscale electronic order in iron pnictides,"The charge distribution in RFeAsO$_{1-x}$F$_x$ (R=La, Sm) iron pnictides is
probed using As nuclear quadrupole resonance. Whereas undoped and
optimally-doped or overdoped compounds feature a single charge environment, two
charge environments are detected in the underdoped region. Spin-lattice
relaxation measurements show their coexistence at the nanoscale. Together with
the quantitative variations of the spectra with doping, they point to a local
electronic order in the iron layers, where low- and high-doping-like regions
would coexist. Implications for the interplay of static magnetism and
superconductivity are discussed.",0912.5495v2
2010-01-12,"London penetration depth and superfluid density in single crystals of Fe(Te,Se) and Fe(Te,S) superconductors","The in-plane London penetration depth, $\lambda(T)$, was measured in single
crystals of the iron-chalcogenide superconductors
Fe$_{1.03}$(Te$_{0.63}$Se$_{0.37}$) and Fe$_{1.06}$(Te$_{0.88}$S$_{0.14}$) by
using a radio-frequency tunnel diode resonator. As is also the case for the
iron-pnictides, these iron-chalcogenides exhibit a nearly quadratic temperature
variation of $\lambda(T)$ at low temperatures. The absolute value of the
penetration depth in the $T \to 0$ limit was determined for
Fe$_{1.03}$(Te$_{0.63}$Se$_{0.37})$ by using an Al coating technique, giving
$\lambda(0)\approx560 \pm 20$ nm. The superfluid density
$\rho_s(T)=\lambda^2(0)/\lambda^2(T)$ was fitted with a self-consistent two-gap
$\gamma-$model. While two different gaps are needed to describe the full-range
temperature variation of $\rho_s(T)$, a non-exponential behavior at low
temperatures requires additional factors, such as scattering and/or significant
gap anisotropy.",1001.2042v1
2010-01-20,The magnetic form factor of iron in SrFe2As2,"The iron magnetic form factor in SrFe2As2 has been determined by neutron
diffraction and by density functional theory (DFT). As noted previously, the
magnitude of the calculated moment using DFT is sensitive to the Fe-As
distance. However, the shape of the calculated form factor is practically
insensitive to the Fe-As distance, and further we show that the form factor
closely resembles that of bcc iron, and agrees well with experiment. The spin
density exhibits some anisotropy due to geometry and As hybridization.",1001.3658v1
2010-02-18,Why some Iron-based superconductors are nodal while others are nodeless,"The symmetry of the order parameter in iron-based superconductors, especially
the presence or absence of nodes, is still a question of debate. While
contradictory experiments can be explained by appropriately tuned theories of
nodeless superconductivity in the iron-arsenide compounds, for LaOFeP all
experiments clearly point to a nodal order parameter. We put forward a scenario
that naturally explains the difference between the order-parameter character in
these two sets of compounds, and use functional renormalization group (fRG)
techniques to analyze it in detail. Our results show that, due to the orbital
content of the electron and hole bands, nodal superconductivity on the electron
pockets (hole pocket gaps are always nodeless) can naturally appear when the
third hole pocket which lies at wavevector (pi,pi) in the unfolded Brillouin
zone is absent, as is the case in LaOFeP. When present, the third hole pocket
has overwhelming d_{xy} orbital character, and the intra-orbital interaction
with the d_{xy} dominated part of the electron Fermi surface is enough to drive
the superconductivity nodeless (of s^+- form). However, in its absence, pair
hopping, inter-orbital, and electron-electron intra-orbital interactions render
the gap on the electron pockets softly nodal.",1002.3599v1
2010-03-02,Unified Picture for Magnetic Correlations in Iron-Based Superconductors,"The varying metallic antiferromagnetic correlations observed in iron-based
superconductors are unified in a model consisting of both itinerant electrons
and localized spins. The decisive factor is found to be the sensitive
competition between the superexchange antiferromagnetism and the
orbital-degenerate double-exchange ferromagnetism. Our results reveal the
crucial role of Hund's rule coupling for the strongly correlated nature of the
system and suggest that the iron-based superconductors are closer kin to
manganites than cuprates in terms of their diverse magnetism and incoherent
normal-state electron transport. This unified picture would be instrumental for
exploring other exotic properties and the mechanism of superconductivity in
this new class of superconductors.",1003.0512v2
2010-03-26,Strong carrier-scattering in iron-pnictide superconductors with highest Tc obtained from charge transport experiments,"Characteristic normal-state charge transport is found in the oxygen-deficient
iron-arsenides LnFeAsO1-y (Ln: La and Nd) with the highest Tc's among known
Fe-based superconductors. The effect of ""doping"" in this system is mainly on
the carrier scattering, quite distinct from that in high-Tc cuprates. In the
superconducting regime of the La system with maximum Tc = 28 K, the
low-temperature resistivity is dominated by a T^2 term. On the other hand, in
the Nd system with Tc higher than 40 K, the carriers are subject to stronger
scattering showing T-linear resistivity and small magnetoresistance. Such
strong scattering appears crucial for high-Tc superconductivity in the
iron-based system.",1003.5039v1
2010-04-10,$^{75}$As NQR and NMR studies of superconductivity and electron correlations in iron arsenide Li$_{x}$FeAs,"We report the $^{75}$As-NQR and NMR studies on the iron arsenide
superconductor Li$_{x}$FeAs with $T_{\rm c} \sim 17$ K. The spin lattice
relaxation rate, $1/T_{1}$, decreases below $T_{\rm c}$ without a coherence
peak, and can be fitted by gaps with s$^{\pm}$-wave symmetry in the presence of
impurity scattering. In the normal state, both $1/T_{1}T$ and the Knight shift
decrease with decreasing temperature but become constant below $T \leq 50 K$.
Estimate of the Korringa ratio shows that the spin correlations are weaker than
that in other families of iron arsenides, which may account for the lower
$T_{\rm c}$ in this material.",1004.1688v5
2010-04-28,Single Impurity Problem in Iron-Pnictide Superconductors,"Single impurity problem in iron-pnictide superconductors is investigated by
solving Bogoliubov-de Gennes (BdG) equation in the five-orbital model, which
enables us to distinguish s$_{+-}$ and s$_{++}$ superconducting states. We
construct a five-orbital model suitable to BdG analysis. This model reproduces
the results of random phase approximation in the uniform case. Using this
model, we study the local density of states around a non-magnetic impurity and
discuss the bound-state peak structure, which can be used for distinguishing
s$_{+-}$ and s$_{++}$ states. A bound state with nearly zero-energy is found
for the impurity potential $I\sim 1.0$ eV, while the bound state peaks stick to
the gap edge in the unitary limit. Novel multiple peak structure originated
from the multi-orbital nature of the iron pnictides is also found.",1004.5093v1
2010-05-07,Importance of Itinerancy and Quantum Fluctuations for the Magnetism in Iron Pnictides,"By applying density functional theory, we find strong evidence for an
itinerant nature of magnetism in two families of iron pnictides. Furthermore,
by employing dynamical mean field theory with continuous time quantum Monte
Carlo as an impurity solver, we observe that the antiferromagnetic metal with
small magnetic moment naturally arises out of coupling between unfrustrated and
frustrated bands. Our results point to a possible scenario for magnetism in
iron pnictides where magnetism originates from a strong instability at the
momentum vector ($\pi$, $\pi$, $\pi$) while it is reduced by quantum
fluctuations due to the coupling between weakly and strongly frustrated bands.",1005.1170v2
2010-06-03,Nodes vs. minima in the energy gap of iron-pnictides from field-induced anisotropy,"We develop the formalism for computing the oscillations of the specific heat
and thermal transport under rotated magnetic field in multiband superconductors
with anisotropic gap and apply it to iron-pnictides. We show that these
oscillations change sign at low temperatures and fields, which strongly
influences the conclusions about the gap structure based on experiment. We find
that recent measurements of the specific heat oscillations indicate that the
iron-based superconductors possess an anisotropic gap with deep minima or nodes
close to the line connecting electron and hole pockets. We make predictions for
the behavior of the thermal conductivity that will help distinguish between
these cases.",1006.0738v2
2010-06-11,"Superconductivity Above 40 K Observed in a New Iron Arsenide Oxide (Fe2As2)(Ca4(Mg,Ti)3Oy)","A new layered iron arsenide oxide (Fe2As2)(Ca4(Mg,Ti)3Oy) was discovered. Its
crystal structure is tetragonal with a space group of I4/mmm consisted of the
anti-fluorite type FeAs layer and blocking layer of triple perovskite cells and
is identical with (Fe2As2)(Sr4(Sc,Ti)3O8) discovered in our previous study. The
lattice constants of (Fe2As2)(Ca4(Mg,Ti)3Oy) are a = 3.877 A and c = 33.37 A.
This compound exhibited bulk superconductivity up to 43 K in susceptibility
measurement without intentional carrier doping. A resistivity drop was observed
at ~47 K and zero resistance was achieved at 42 K. These values correspond to
the second highest Tc among the layered iron-based superconductors after
REFeAsO system.",1006.2367v2
2010-06-15,Quantum Dielectric Fluctuation in an Electronic Ferroelectricity studied by Variational Monte-Carlo Method,"Electronic structure and dielectric property in an electronic
ferroelectricty, where electric polarization is driven by an electronic charge
order without inversion symmetry, are studied. Motivated from layered iron
oxides, roles of quantum fluctuation on ferroelectricity in a paired-triangular
lattice are focused on. Three types of the extended V-t model are examined by
the variational Monte-Carlo method with the Gutzwiller-type correlation factor.
It is shown that electron transfer between the triangular layers corresponding
to the inter-layer polarization fluctuation promotes the three-fold charge
order associated with an electric polarization. This result is in highly
contrast to the usual manner of quantum fluctuation in the hydrogen-bond type
ferroelectricities and the quantum paraelectric oxides. Spin degree of freedom
of electron and a realistic crystal structure for the layered iron oxides
further stabilize the polar charge ordered state. Implications of the numerical
results for layered iron oxides are discussed.",1006.2889v1
2010-06-16,Sub-monolayers of carbon on alpha-iron facets: an ab-initio study,"Motivated by recent in situ studies of carbon nanotube growth from large
transition-metal nanoparticles, we study various alpha-iron (ferrite) facets at
different carbon concentrations using ab initio methods. The studied (110),
(100) and (111) facets show qualitatively different behaviour when carbon
concentration changes. In particular, adsorbed carbon atoms repel each other on
the (110) facet, resulting in carbon dimer and graphitic material formation.
Carbon on the (100) facet forms stable structures at concentrations of about
0.5 monolayer and at 1.0 monolayer this facet becomes unstable due to a
frustration of the top layer iron atoms. The stability of the (111) facet is
weakly affected by the amount of adsorbed carbon and its stability increases
further with respect to the (100) facet with increasing carbon concentration.
The exchange of carbon atoms between the surface and sub-surface regions on the
(111) facet is easier than on the other facets and the formation of carbon
dimers is exothermic. These findings are in accordance with a recent in situ
experimental study where the existence of graphene decorated (111) facets is
related to increased carbon concentration.",1006.3187v1
2010-06-23,High-temperature superconductivity in iron-based materials,"The surprising discovery of superconductivity in layered iron-based
materials, with transition temperatures climbing as high as 55 K, has lead to
thousands of publications on this subject over the past two years. While there
is general consensus on the unconventional nature of the Cooper pairing state
of these systems, several central questions remain - including the role of
magnetism, the nature of chemical and structural tuning, and the resultant
pairing symmetry - and the search for universal properties and principles
continues. Here we review the progress of research on iron-based
superconducting materials, highlighting the major experimental benchmarks that
have been so far reached and the important questions that remain to be
conclusively answered.",1006.4618v2
2010-07-09,Contrasted role of disorder for magnetic properties in an original mixed valency iron Phosphate,"We have measured the magnetic properties of a mixed valency iron phosphate.
It presents an original structure with crossed chains containing Fe II and
orthogonal to the longest direction of the crystallites. Microstructural
investigations using electron microscopy show the presence of random
nano-twinning. The ac susceptibility measurements demonstrate similarities with
the kinetics of a disordered magnetic, spin-glass like, state but are shown to
be essentially due to this peculiar disorder. Scaling properties are
characteristics of 3D second order transition implying that this disorder at a
small scale does not influence significantly long range magnetic ordering. At
low temperature, a decrease of the spontaneous magnetization and an
irreversible metamagnetic transition is observed, and is attributed to a
canting of the spins in the iron chain.",1007.1607v1
2010-08-13,Anion height as a controlling parameter for the superconductivity in iron pnictides and cuprates,"Both families of high $T_c$ superconductors, iron pnictides and cuprates,
exhibit material dependence of superconductivity. Here, we study its origin
within the spin fluctuation pairing theory based on multiorbital models that
take into account realistic band structures. For pnictides, we show that the
presence and absence of Fermi surface pockets is sensitive to the pnictogen
height measured from the iron plane due to the multiorbital nature of the
system, which is reflected to the nodeless/nodal form of the superconducting
gap and $T_c$. Surprisingly, even for the cuprates, which is conventionally
modeled by a single orbital model, the multiorbital band structure is shown to
play a crucial role in the material dependence of superconductivity. In fact,
by adopting a two orbital model that considers the $d_{z^2}$ orbital on top of
the $d_{x^2-y^2}$ orbital, we can resolve a long standing puzzle of why the
single layered Hg cuprate have much higher $T_c$ than the La cuprate.
Interestingly, here again the apical oxygen height measured from the CuO$_2$
plane plays an important role in determining the relative energy difference
between $d_{x^2-y^2}$ and $d_{z^2}$ orbitals, thereby strongly affecting the
superconductivity.",1008.2286v1
2010-08-25,Detailed abundances of Red Giants in the Globular Cluster NGC~1851: C+N+O and the Origin of Multiple Populations,"We present chemical abundance analysis of a sample of 15 red giant branch
(RGB) stars of the Globular Cluster NGC~1851 distributed along the two RGBs of
the (v, v-y) CMD. We determined abundances for C+N+O, Na, $\alpha$, iron-peak,
and s-elements. We found that the two RGB populations significantly differ in
their light (N,O,Na) and s-element content. On the other hand, they do not show
any significant difference in their $\alpha$ and iron-peak element content.
More importantly, the two RGB populations do not show any significant
difference in their total C+N+O content. Our results do not support previous
hypotheses suggesting that the origin of the two RGBs and the two subgiant
branches of the cluster is related to a different content of either $\alpha$
(including Ca) or iron-peak elements, or C+N+O abundance, due to a second
generation polluted by SNeII.",1008.4372v1
2010-09-03,Pnicogen-bridged antiferromagnetic superexchange interactions in iron pnictides,"The first-principles electronic structure calculations made substantial
contribution to study of high $T_c$ iron-pnictide superconductors. By the
calculations, LaFeAsO was first predicted to be an antiferromagnetic semimetal,
and the novel bi-collinear antiferromagnetic order was predicted for
$\alpha$-FeTe. Moreover, based on the calculations the underlying mechanism was
proposed to be Arsenic-bridged antiferromagnetic superexchange interaction
between the next-nearest neighbor Fe moments. In this article, this physical
picture is further presented and discussed in association with the elaborate
first-principles calculations on LaFePO. The further discussion of origin of
the magnetism in iron-pnictides and in connection with superconductivity is
presented as well.",1009.0726v1
2010-09-06,Spin Dynamics of a $J_1-J_2$ Antiferromagnet and its Implications for Iron Pnictides,"Motivated by the recent observation of antiferromagnetic correlations in the
paramagnetic phase of iron pnictides, we study the finite-temperature spin
dynamics of a two-dimensional $J_1-J_2$ antiferromagnet. We consider the
paramagnetic phase in the $J_2>J_1$ regime of a $(\pi,0)$ collinear ground
state, using the modified spin wave theory. Below the mean-field Ising
transition temperature, we identify short-range anisotropic antiferromagnetic
correlations. We show that the dynamical structure factor
$\mathcal{S}(\mathbf{q},\omega)$ contains elliptic features in the momentum
space, and determine its variation with temperature and energy. Implications
for the spin-dynamical experiments in the iron pnictides are discussed.",1009.1111v3
2010-09-29,Superconductivity-induced optical anomaly in an iron arsenide,"One of the central tenets of conventional theories of superconductivity,
including most models proposed for the recently discovered iron-pnictide
superconductors, is the notion that only electronic excitations with energies
comparable to the superconducting energy gap are affected by the transition.
Here we report the results of a comprehensive spectroscopic ellipsometry study
of a high-quality crystal of superconducting
$\textrm{Ba}_{0.68}\textrm{K}_{0.32}\textrm{Fe}_2\textrm{As}_2$ that challenges
this notion. We observe a superconductivity-induced suppression of an
absorption band at an energy of $2.5\ \textrm{eV}$, two orders of magnitude
above the superconducting gap energy $2\Delta\sim 20\ \textrm{meV}$. Based on
density-functional calculations, this band can be assigned to transitions from
As-p to Fe-d orbitals crossing the Fermi surface. We identify a related effect
at the spin-density-wave transition in parent compounds of the 122 family. This
suggests that As-p states deep below the Fermi level contribute to the
formation of the superconducting and spin-density-wave states in the iron
arsenides.",1009.5915v1
2010-10-01,"Orbital Order, Structural Transition and Superconductivity in Iron Pnictides","We investigate the 16-band d-p model for iron pnictide superconductors in the
presence of the electron-phonon coupling g with the orthorhombic mode which is
crucial for reproducing the recently observed ultrasonic softening. Within the
RPA, we obtain the ferro-orbital order below TQ which induces the
tetragonal-orthorhombic structural transition at Ts = TQ, together with the
stripe-type antiferromagnetic order below TN. Near the phase transitions, the
system shows the s++ wave superconductivity due to the orbital fluctuation for
a large g case with TQ > TN, while the s+- wave due to the magnetic fluctuation
for a small g case with TQ < TN. The former case is consistent with the phase
diagram of doped iron pnictides with Ts > TN.",1010.0129v3
2010-10-02,The layered compound CaClFeP is an Arsenic-free high $T_c$ iron-pnictide,"We first analyze why the iron pnictides with high $T_c$ superconductivity so
far are As-based, by the Hund's rule correlation picture, then examine the
P-based and Sb-based cases, respectively. Consequently, we propose that CaClFeP
with ZrCuSiAs-type structure is an As-free high $T_c$ iron-pnictide. The
subsequent density functional theory calculations show that the ground state of
CaClFeP is of a collinearly antiferromagnetic order on Fe moments with
structural distortion, resulting from the interplay between the strong nearest
and next-nearest neighbor antiferromagnetic superexchange interactions bridged
by P atoms, similar as the As-based pnictides. The other P-based pnictides are
either nonmagnetic or magnetic but with weak exchange interactions. The
Sb-based pnictides unlikely show high $T_c$ superconductivity because of the
existence of robust ferromagnetic order.",1010.0342v1
2010-10-18,Quasiparticle interference in an iron-based superconductor,"We develop a model for the effect of a magnetic field on quasiparticle
interference in an iron-based superconductor. Recently, scanning tunneling
experiments have been performed on Fe(Se,Te) to determine the relative sign of
the superconducting gap from the magnetic-field dependence of quasiparticle
scattering amplitudes. Using a simple two-band BCS model, we study three
different cases of scattering in a spin-split spectrum. The dominant effect of
a magnetic field in iron-based superconductors is caused by the Pauli limiting
of conduction electrons. Thereby time reversal odd scattering is induced which
enhances the sign-preserving and depresses the sign-reversing peaks in the
quasiparticle interference patterns.",1010.3545v3
2010-11-10,Theory of Valley-Density Wave and Hidden Order in Iron-Pnictides,"In the limit of perfect nesting, the physics of iron-pnictides is governed by
the density wave formation at the zone-edge vector M. At high energies, various
spin- (SDW), charge- (CDW), orbital/pocket- (PDW) density waves, and their
linear combinations, all appear equally likely, unified within the unitary
order parameter of U(4)XU(4) symmetry. Nesting imperfections and low-energy
interactions reduce this symmetry to that of real materials. Nevertheless, the
generic ground state preserves a distinct signature of its highly symmetric
origins: a SDW along one axis of the iron lattice is predicted to coexist with
a perpendicular PDW, accompanied by weak charge currents. This ""hidden"" order
induces the structural transition in our theory, naturally insures T_s >= T_N,
and leads to orbital ferromagnetism and other observable consequences.",1011.2499v3
2010-12-04,Epitaxial Growth of Superconducting Ba(Fe1-xCox)2As2 Thin Films on Technical IBAD-MgO Substrates,"The biaxially textured growth of superconducting Co-doped BaFe2As2 (Ba-122)
thin films has been realized on ion beam assisted deposition (IBAD) MgO coated
conductor templates by employing an iron buffer architecture. The iron pnictide
coated conductor showed a superconducting transition temperature of 21.5 K,
which is slightly lower than that of Co-doped Ba-122 films on single
crystalline MgO substrates. A self-field critical current density of over 10^5
A/cm2 has already been achieved even at 8 K. The current experiment highlights
the potential of possible coated conductor applications of the iron-based
superconductors.",1012.0894v1
2010-12-12,S-wave superconductivity with orbital dependent sign change in the checkerboard models of iron-based superconductors,"We study three different multi-orbital models for iron-based superconductors
(iron-SCs) in the solvable limit of weakly coupled square plaquettes. The
strongest superconducting (SC) pairing is in the $A_{1g}$ $s$-wave channel and
its development is correlated with the emergence of the next-nearest-neighbour
antiferromagnetism (NNN-AFM). For the models with more than three orbitals,
this study suggests that the signs of the intra-orbital pairing order
parameters of the $d_{xy}$ and the $d_{xz}$ (or $d_{yz}$) orbitals must be {\it
opposite}. Such sign difference stems from the intrinsic symmetry properties of
inter-orbital hoppings and might, ultimately, lead to the sign-change of the SC
orders between the hole Fermi pockets at the $\Gamma$ point and produce
anisotropic or even gapless SC gaps in the electron Fermi pockets around the
$M$ point in reciprocal space, as restoring back to the homogeneous limit.",1012.2566v1
2010-12-19,Bistability of Free Cobalt and Iron Clusters,"The cobalt and iron clusters CoN, FeN (20 < N < 150) measured in a cryogenic
molecular beam are found to be bistable with magnetic moments per atom both
{\mu}N/N 2{\mu}B in the ground states and {\mu}N */N {\mu}B in the metastable
excited states (for iron clusters, {\mu}N ~3N{\mu}B and {\mu}N* N{\mu}B). This
energy gap between the two states vanish for large clusters, which explains the
rapid convergence of the magnetic moments to the bulk value and suggests that
ground state for the bulk involves a superposition of the two, in line with the
fluctuating local orders in the bulk itinerant ferromagnetism.",1012.4133v1
2010-12-23,Electronic structure and Fermi surface of new K intercalated iron selenide superconductor KxFe2Se2,"Using the ab initio FLAPW-GGA method we examine the electronic band
structure, densities of states, and the Fermi surface topology for a very
recently synthesized ThCr2Si2-type potassium intercalated iron selenide
superconductor KxFe2Se2. We found that the electronic state of the
stoichiometric KFe2Se2 is far from that of the isostructural iron pnictide
superconductors. Thus the main factor responsible for experimentally observed
superconductivity for this material is the deficiency of potassium, i.e. the
hole doping effect. On the other hand, based on the results obtained, we
conclude that the tuning of the electronic system of the new KxFe2Se2
superconductor in the presence of K vacancies is achieved by joint effect owing
to structural relaxations and hole doping, where the structural factor is
responsible for the modification of the band topology, whereas the doping level
determines their filling.",1012.5164v1
2010-12-23,Discovery of Iron in PG1159 Stars,"The lack of FeVII lines in PG1159 stars had led to the conclusion that in
some objects iron must be strongly depleted. We have now detected FeX lines in
FUSE spectra of the very hottest PG1159 stars Teff=150,000 - 200,000 K;
RXJ2117.1+3412, K1-16, NGC 246, Longmore 4). Surprisingly, we derive a solar
iron abundance. It is conspicuous that they are among the most massive PG1159
stars (0.71-0.82 Msun), in contrast to those objects for which strongest
Fe-deficiency was claimed (0.53-0.56 Msun). Based on new FeVIII line
identifications in SOHO/SUMER UV spectra of the Sun, we were able to detect
these lines in FUSE spectra of several ""cooler"" (Teff<150,000 K) objects, among
them is the prototype PG1159-035. An abundance analysis is in progress.",1012.5228v1
2010-12-29,"Heavily electron-doped electronic structure and isotropic superconducting gap in AxFe2Se2 (A=K,Cs)","The low energy band structure and Fermi surface of the newly discovered
superconductor, AxFe2Se2 (A=K,Cs), have been studied by angle-resolved
photoemission spectroscopy. Compared with iron pnictide superconductors,
AxFe2Se2 (A=K,Cs) is the most heavily electron-doped with Tc~30 K. Only
electron pockets are observed with an almost isotropic superconducting gap of
~10.3 meV, while there is no hole Fermi surface near the zone center, which
indicates the inter-pocket hopping or Fermi surface nesting is not a necessary
ingredient for the unconventional superconductivity in iron-based
superconductors. Thus, the sign changed s$_\pm$ pairing symmetry, a leading
candidate proposed for iron-based superconductors, becomes conceptually
irrelevant in describing the superconducting state here. A more conventional
s-wave pairing is a better description.",1012.5980v1
2011-01-17,"Mott transition in Modulated Lattices and Parent Insulator of (K,Tl)yFexSe2 Superconductors","The degree of electron correlations remains a central issue in the iron-based
superconductors. The parent iron pnictides are antiferromagnetic, and their
bad-metal behavior has been interpreted in terms of proximity to a Mott
transition. We study such a transition in multi-orbital models on modulated
lattices containing an ordered pattern of iron vacancies, using a slave-rotor
method. We show that the ordered vacancies lead to a band-narrowing, which
pushes the system to the Mott insulator side. This effect is proposed to
underlie the insulating behavior observed in the parent compounds of the newly
discovered (K,Tl)yFexSe2 superconductors.",1101.3307v2
2011-02-13,Orbital magnetic moment and extrinsic spin Hall effect for iron impurity in gold,"We report electronic structure calculations of an iron impurity in gold host.
The spin, orbital and dipole magnetic moments were investigated using the
LDA+$U$ correlated band theory. We show that the {\em
around-mean-field}-LDA+$U$ reproduces the XMCD experimental data well and does
not lead to formation of a large orbital moment on the Fe atom. Furthermore,
exact diagonalization of the multi-orbital Anderson impurity model with the
full Coulomb interaction matrix and the spin-orbit coupling is performed in
order to estimate the spin Hall angle. The obtained value $\gamma_S \approx
0.025$ suggests that there is no giant extrinsic spin Hall effect due to
scattering on iron impurities in gold.",1102.2614v1
2011-02-16,Ionization structure and Fe K$α$ energy for irradiated accretion disks,"We study the radial ionization structure at the surface of an X-ray
illuminated accretion disk. We plot the expected iron K$\alpha$ line energy as
a function of the Eddington ratio and of the distance of the emitting matter
from the central source, for a non-rotating and a maximally-rotating black
hole. We compare the predicted disk line energies with those measured in an
archival sample of active galactic nuclei observed with {\it Chandra}, {\it
XMM-Newton} and {\it Suzaku}, and discuss whether the line energies are
consistent with the radial distances inferred from reverberation studies. We
also suggest using rapidly-variable iron K$\alpha$ lines to estimate the
viscosity parameter of an accretion disk. There is a forbidden region in the
line energy versus Eddington ratio plane, at low Eddington ratios, where an
accretion disk cannot produce highly-ionized iron K$\alpha$ lines. If such
emission is observed in low-Eddington-ratio sources, it is either coming from a
highly-ionized outflow, or is a blue-shifted component from fast-moving neutral
matter.",1102.3327v1
2011-02-22,Superconductivity mediated by the antiferromagnetic spin-wave in chalcogenide iron-base superconductors,"The ground state of K$_{0.8+x}$Fe$_{1.6+y}$Se$_2$ and other iron-based
selenide superconductors are doped antiferromagnetic semiconductors. There are
well defined iron local moments whose energies are separated from those of
conduction electrons by a large band gap in these materials. We propose that
the low energy physics of this system is governed by a model Hamiltonian of
interacting electrons with on-site ferromagnetic exchange interactions and
inter-site superexchange interactions. We have derived the effective pairing
potential of electrons under the linear spin-wave approximation and shown that
the superconductivity can be driven by mediating coherent spin wave excitations
in these materials. Our work provides a natural account for the coexistence of
superconducting and antiferromagnetic long range orders observed by neutron
scattering and other experiments.",1102.4575v1
2011-03-03,Electron correlation induced small anisotropy in iron-based superconductors,"We have investigated the electron correlation effect on the electronic
structures and transport properties of the iron-based superconductors using the
density functional theory (DFT) and dynamical mean field theory (DMFT). By
considering the Fe 3d electron correlation using the DMFT, the bandwidth near
the Fermi level is substantially suppressed compared to the conventional DFT
calculation. Because of the different renormalization factors of each 3d
orbital, the DMFT gives considerably reduced electrical anisotropy compared to
the DFT results, which explains the unusually small anisotropic resistivity and
superconducting property observed in the iron-based superconductors. We suggest
that the electron correlation effect should be considered to explain the
anisotropic transport properties of the general d/f valence electron system.",1103.0678v2
2011-03-10,Iron Depletion in ionized Nebulae of the Large Magellanic Cloud,"We present here preliminary results of an analysis of the iron abundance in
the ionized gas of three planetary nebulae and one H II region of the Large
Magellanic Cloud (LMC). These results are compared with the ones we obtain for
a sample of Galactic and extragalactic nebulae. We find that the amounts of
iron depletion into dust grains in LMC nebulae are similar to those found in
Galactic nebulae. Objects with lower metallicities show lower depletions, but a
larger sample of objects is needed to explore the reasons behind this trend.",1103.2158v1
2011-03-13,Topological insulators with perfect vacancy superstructure and possible implications for iron chalcogenide superconductors,"Motivated by the newly-discovered intercalated iron chalcogenide
superconductors, we construct a single orbital tight-binding model for
topological insulators on the square lattice with a perfect vacancy
superstructure. We find that such lattice structure naturally accommodates a
non-vanishing geometry phase associated with the next-nearest-neighbor
spin-orbit interaction. By calculating the bulk band structures and the finite
stripe edge states, we show that the topological insulator phases can be tuned
at certain electron fillings in a wide range of the model parameters. The
possible implications of these results for the iron deficient compounds
$(A,Tl)_{y}Fe_{2-x}Se_2$ have been discussed.",1103.2538v2
2011-03-25,Local spin fluctuations in iron-based superconductors: 77Se and 87Rb NMR measurements of Tl0.47Rb0.34Fe1.63Se2,"We report nuclear magnetic resonance (NMR) studies of the intercalated iron
selenide superconductor (Tl, Rb)$_{y}$Fe$_{2-x}$Se$_2$ ($T_c = 32$ K).
Single-crystal measurements up to 480 K on both $^{77}$Se and $^{87}$Rb nuclei
show a superconducting phase with no magnetic order. The Knight shifts $K$ and
relaxation rates $1/T_1T$ increase very strongly with temperature above $T_c$,
before flattening at 400 K. The quadratic $T$-dependence and perfect
proportionality of both $K$ and $1/T_1T$ data demonstrate their origin in
paramagnetic moments. A minimal model for this pseudogap-like response is not a
missing density of states but two additive contributions from the itinerant
electronic and local magnetic components, a framework unifying the $K$ and
$1/T_1 T$ data in many iron-based superconductors.",1103.4960v5
2011-04-10,Interplay of orbital and spin ordering in the iron pnictides,"A number of recent experiments exhibit electronic anisotropy in the iron
pnictides, and there is a growing body of experimental evidence that its origin
is related to orbital ordering in Fe d_{xz} and d_{yz} orbitals. We examine
this problem in the parent compounds of the iron pnictides by a combination of
ab initio band theory calculations, phenomenological Ginzburg-Landau theory of
coupled orbital and magnetic order parameters, and a microscopic mean-field
study of the Kugel-Khomskii model. We find that orbital ordering is sufficient
to explain a number of key experimental observations, in particular a linear
correlation between the orthorhombic lattice distortion and the magnetic
ordered moment. We predict that orbital polarization should scale as a square
of magnetic moment close to T_N. Mediated by orbital polarization, the
effective spin-spin exchange interactions develop anisotropy in the ab-plane,
in accord with recent neutron scattering measurements.",1104.1747v1
2011-04-18,"New ternary ThCr2Si2-type iron-selenide superconducting materials: synthesis, properties and simulations","Very recently (November, 2010, PRB, 82, 180520R), the first ThCr2Si2-type
ternary superconductor K0.8Fe2Se2 with enhanced TC ~ 31 K has been discovered.
This finding has stimulated much activity in search for related materials and
triggered intense studies of their properties. Indeed, very soon
superconductivity (TC ~ 28-32 K) was also found in the series of related
ternary systems (so-called 122 phases) such as CsxFe2-ySe2, RbxFe2-ySe2,
(TlK)xFeySe2, (TlRb)xFeySe2 etc., which formed a new group of superconducting
iron-based materials without toxic As. In this paper the recent progress in
synthesis of 122-like iron-selenide systems and in experimental research of
their properties is reviewed. Available theoretical data on electronic,
magnetic, and elastic properties of this newest group of superconducting
materials are also discussed.",1104.3400v1
2011-05-04,Structural Phase Transformations in Iron-Chalcogen under High Pressures,"We report high pressure structural phase transformation sequence in a layered
Iron-based superconducting compound FeSe0.3Te0.7 to 31 GPa at room temperature.
The ambient pressure PbO type tetragonal phase (Space Group - P4/nmm)
transforms to a monoclinic phase (Space group - P21/m) at a pressure of 7.3 \pm
0.9 GPa. This monoclinic phase is similar to the one observed below 100 K at
ambient pressure. On further increase of pressure above 12 GPa, a
transformation to an amorphous phase is observed that is completed by 20 GPa.
The amorphous phase is found to be stable to the highest pressure of 31 GPa.
This structural sequence of tetragonal \to monoclinic \to amorphous phase
transformation appears to be a common feature of iron-based layered
superconductors under compression. The pressure induced structural phase
transformations are likely to play a key role in the superconductivity in these
materials at high pressures.",1105.0908v1
2011-05-05,Robustness of s-wave Pairing in Electron-Overdoped $\text{A}_{1-y}\text{Fe}_{2-x}\text{Se}_2$,"Using self consistent mean field and functional renormalization group
approaches we show that s-wave pairing symmetry is robust in the heavily
electron-doped iron chalcogenides $(\text{K, Cs}) \text{Fe}_{2-x}\text{Se}_2 $.
This is because in these materials the leading antiferromagnetic (AFM) exchange
coupling is between next-nearest-neighbor (NNN) sites while the nearest
neighbor (NN) magnetic exchange coupling is ferromagnetic (FM). This is
different from the iron pnictides, where the NN magnetic exchange coupling is
AFM and leads to strong competition between s-wave and d-wave pairing in the
electron overdoped region. Our finding of a robust s-wave pairing in $(\text{K,
Cs}) \text{Fe}_{2-x}\text{Se}_2$ differs from the d-wave pairing result
obtained by other theories where non-local bare interaction terms and the NNN
$J_2$ term are underestimated. Detecting the pairing symmetry in $(\text{K,
Cs}) \text{Fe}_{2-x}\text{Se}_2 $ may hence provide important insights
regarding the mechanism of superconducting pairing in iron based
superconductors.",1105.1135v1
2011-05-09,Anomalous Tail Effect on Resistivity Transition and Weak-link Behavior of Iron Based Superconductor,"Temperature dependent resistivity of the iron-based superconductor
NdFeAsO0.88F0.12 was measured under different applied fields and excitation
currents. Arrhenius plot shows an anomalous tail effect, which contains obvious
two resistivity dropping stages. The first is caused by the normal
superconducting transition, and the second is supposed to be related to the
weak-link between the grains. A model for the resistivity dropping related to
the weak-link behavior is proposed, which is based on the Josephson junctions
formed by the impurities in grain boundaries like FeAs, Sm2O3 and cracks
together with the adjacent grains. These Josephson junctions can be easily
broken by the applied fields and the excitations currents, leading to the
anomalous resistivity tail in many polycrystalline iron-based superconductors.
The calculated resistivity dropping agrees well with the experimental data,
which manifests the correctness of the explanation of the obtained anomalous
tail effect.",1105.1648v1
2011-05-24,Unidirectional Electronic Structure in the Parent State of Iron-Chalcogenide Superconductor Fe$_{1+δ}$Te,"We use scanning tunnelling microscopy and spectroscopy to explore the
electronic structure of Fe$_{1.07}$Te which is the parent compound of the
iron-chalcogenide superconductors. A unidirectional electronic structure with a
period of $a_{0}$ (where $a_{0}$ is the lattice constant) along the a-axis is
observed. The unidirectional pattern is visible within an energy range from
approximately -200 to +130 meV. Since the direction of the unidirectional
electronic structure coincides with those of the underlying antiferromagnetic
and the predicted orbital orders, it is presumable that the observed
unidirectional structure is closely tied to these orders and is peculiar to the
parent state in iron-based superconductors.",1105.4754v2
2011-05-31,"Role of Hund's coupling in stabilization of the (0,pi) ordered SDW state within the minimal two-band model for iron pnictides","Spin wave excitations and stability of the (0,pi) ordered SDW state are
investigated within the minimal two-band model for iron pnictides including a
Hund's coupling term. The SDW state is shown to be stable in two distinct
doping regimes --- finite hole doping in the lower SDW band for small second
neighbour hoppings, and small electron doping in the upper SDW band for
comparable first and second neighbour hoppings. In both cases, Hund's coupling
strongly stabilizes the SDW state due to generation of additional ferromagnetic
spin couplings involving the inter-orbital part of the particle-hole
propagator. Spin wave energies for the two-band model are very similar to the
one-band t-t' Hubbard model results obtained earlier, and are in agreement with
inelastic neutron scattering studies of iron pnictides.",1105.6191v1
2011-05-31,Neutron-Inelastic-Scattering Peak by Dissipationless Mechanism in the s++ -wave State in Iron-based Superconductors,"We investigate the neutron scattering spectrum in iron pnictides based on the
random-phase approximation in the five-orbital model with a realistic
superconducting (SC) gap, Delta=5meV. In the normal state, the neutron spectrum
is suppressed by large inelastic quasi-particle (QP) scattering rate gamma* ~
Delta. In the fully-gapped s-wave state without sign reversal (s++), a
hump-shaped enhancement appears in the neutron spectrum just above 2Delta,
since the inelastic QP scattering is prohibited by the SC gap. That is, the
hump structure is produced by the dissipationless QPs for Ek<3Delta. The
obtained result is more consistent with experimental spectra, compared to the
results of our previous paper with Delta=50meV. On the other hand, both height
and weight of the resonance peak in the fully-gapped s-wave states with sign
reversal (s+-) are much larger than those observed in experiments. We conclude
that experimentally observed broad spectral peak in iron pnictides is created
by the present ""dissipationless mechanism"" in the s++ -wave state.",1105.6233v3
2011-06-13,Iron-chalcogenide FeSe$_{0.5}$Te$_{0.5}$ coated superconducting tapes for high field applications,"The high upper critical field characteristic of the recently discovered
iron-based superconducting chalcogenides opens the possibility of developing a
new type of non-oxide high-field superconducting wires. In this work, we
utilize a buffered metal template on which we grow a textured
FeSe$_{0.5}$Te$_{0.5}$ layer, an approach developed originally for high
temperature superconducting coated conductors. These tapes carry high critical
current densities (>1$\times10^{4}$A/cm$^{2}$) at about 4.2K under magnetic
field as high as 25 T, which are nearly isotropic to the field direction. This
demonstrates a very promising future for iron chalcogenides for high field
applications at liquid helium temperatures. Flux pinning force analysis
indicates a point defect pinning mechanism, creating prospects for a
straightforward approach to conductor optimization.",1106.2466v1
2011-06-14,Fermi surfaces of iron-pnictide high-Tc superconductors from the limit of local magnetic moments,"A 2-orbital t-J model over the square lattice that describes low-energy
electronic excitations in iron-pnictide high-Tc superconductors is analyzed
with Schwinger-boson-slave-fermion meanfield theory and by exact numerical
diagonalization on a finite system. A quantum critical point (QCP) is
identified that separates a commensurate spin-density wave (cSDW) state at
strong Hund's rule coupling from a hidden half-metal state at weak Hund's rule
coupling when inter-orbital hole hopping is suppressed. Low-energy spinwaves
that disperse anisotropically from cSDW momenta are predicted at the QCP.
Nested Fermi surfaces similar to those observed experimentally in iron-pnictide
materials are also predicted in such case.",1106.2600v3
2011-06-25,An unified minimum effective model of magnetism in iron-based superconductors,"Since 2008, many new families of iron-based high temperature (high-$T_c$)
superconductors have been discovered \cite{Hosono,ChenXH,FeTe,ChenXL}. Unlike
all parent compounds of cuprates that share a common antiferromagnetically (AF)
ordered ground state, those of iron-based superconductors exhibit many
different AF ordered ground states, including collinear-AF (CAF) state in
ferropnictides \cite{caf}, bicollinear-AF (BCAF) state in 11-ferrochalcogenide
$FeTe$ \cite{bcaf,bcaf2}, and block-AF (BAF) state in 122-ferrochalcogenide
$K_{0.8}Fe_{1.6}Se_2$ \cite{baf}. While the universal presence of
antiferromagnetism suggests that superconductivity is strongly interrelated
with magnetism, the diversity of the AF ordered states obscures their
interplay. Here we show that all magnetic phases can be unified within an
effective magnetic model. This model captures three incommensurate magnetic
phases, two of which have been observed experimentally. The model characterizes
the nature of phase transitions between the different magnetic phases and
explains a variety of magnetic properties, such as spin-wave spectra and
electronic nematism. Most importantly, by unifying the understanding of
magnetism, we cast new insight on the key ingredients of magnetic interactions
which are critical to the occurrence of superconductivity.",1106.5169v1
2011-06-27,Lattice expansion from isotope substitution in the Iron based superconductors,"We estimate the changes in lattice parameters due to iron isotope
substitution in the iron-based high temperature superconductors using a
variational calculation based on the anharmonicity of the Fe-As(Se) bond. For
BaFe2As2 and 57Fe to 54$Fe substitution we find a c-axis expansion of 1
10^{-3}{\AA} and in-plane a-axis contraction of 1 10^{-5}{\AA} at 250K in good
agreement with experimental values on (Ba,K)Fe2As2 for which a negative isotope
exponent \alpha=-\frac{d\ln T_c}{d\ln m}<0 was found [P.M. Shirage et al.,
Phys. Rev. Lett. 103, 257003 (2009)]. For FeSe in contrast we find an expansion
for both a and c lattice parameters. We discuss the relevance of these isotope
induced changes of lattice parameters to the isotope effect in light of the
well established sensitivity to the Fe-As(Se) coordination.",1106.5332v1
2011-06-29,Mechanism for a Pairing State with Time-Reversal Symmetry Breaking in Iron-Based Superconductors,"The multipocket Fermi surfaces of iron-based superconductors promote pairing
states with both s_{+-}-wave and d_{x^2-y^2}-wave symmetry. We argue that the
competition between these two order parameters could lead to a
time-reversal-symmetry breaking state with s+id-pairing symmetry in the
iron-based superconductors, and propose serveral scenarios in which this phase
may be found. To understand the emergence of such a pairing state on a more
rigorous footing, we start from a microscopic 5-orbital description
representative for the pnictides. Using a combined approach of functional
renormalization group and mean-field analysis, we identify the microscopic
parameters of the s+id-pairing state. There, we find the most promising region
for s+id-pairing in the electron doped regime with an enhanced pnictogen
height.",1106.5964v1
2011-07-11,Magnetotransport properties of iron microwires fabricated by focused electron beam induced autocatalytic growth,"We have prepared iron microwires in a combination of focused electron beam
induced deposition (FEBID) and autocatalytic growth from the iron
pentacarbonyl, Fe(CO)5, precursor gas under UHV conditions. The electrical
transport properties of the microwires were investigated and it was found that
the temperature dependence of the longitudinal resistivity (rhoxx) shows a
typical metallic behaviour with a room temperature value of about 88
micro{\Omega} cm. In order to investigate the magnetotransport properties we
have measured the isothermal Hall-resistivities in the range between 4.2 K and
260 K. From these measurements positive values for the ordinary and the
anomalous Hall coefficients were derived. The relation between anomalous Hall
resistivity (rhoAN) and longitudinal resistivity is quadratic, rhoAN rho^2 xx,
revealing an intrinsic origin of the anomalous Hall effect. Finally, at low
temperature in the transversal geometry a negative magnetoresistance of about
0.2 % was measured.",1107.2014v1
2011-08-11,"Excitation functions and isotopic effects in (n,p) reactions for stable iron isotopes from reaction threshold to 20 MeV","The excitation functions for (n,p) reactions from reaction threshold to 20
MeV on four stable Iron isotopes viz; 54Fe,56Fe,57Fe and 58Fe were calculated
using Talys-1.2 nuclear model code, this essentially involves fitting a set of
global parameters. An excellent agreement between the calculated and
experimental data is obtained with minimal effort on parameter fitting and only
one free parameter called 'Shell damping factor' has been adjusted. This is
very importance to the validation of nuclear model approaches with increased
predictive power. The systematic decrease in (n, p) cross-sections with
increasing neutron number in reactions induced by neutrons on isotopes of iron
is explained in terms of the pre-equilibrium model. The compound nucleus and
pre-equilibrium reaction mechanism as well as the isotopic effects were also
studied extensively.",1108.2661v1
2011-08-15,Iron Displacements and Magnetoelastic Coupling in the Spin-Ladder Compound BaFe2Se3,"We report long-range ordered antiferromagnetism concomitant with local iron
displacements in the spin-ladder compound BaFe$_2$Se$_3$. Short-range magnetic
correlations, present at room temperature, develop into long-range
antiferromagnetic order below T$_N$ = 256 K, with no superconductivity down to
1.8 K. Built of ferromagnetic Fe$_4$ plaquettes, the magnetic ground state
correlates with local displacements of the Fe atoms. These iron displacements
imply significant magnetoelastic coupling in FeX$_4$-based materials, an
ingredient hypothesized to be important in the emergence of superconductivity.
This result also suggests that knowledge of these local displacements is
essential for properly understanding the electronic structure of these systems.
As with the copper oxide superconductors two decades ago, our results highlight
the importance of reduced dimensionality spin ladder compounds in the study of
the coupling of spin, charge, and atom positions in superconducting materials.",1108.2928v2
2011-08-24,Effective tight-binding model for the iron vacancy ordered A$_{y}$Fe$%_{1.6}$Se$_{2}$,"We investigate the electronic structure of the ternary iron selenide K$_{y}$%
Fe$_{1.6}$Se$_{2}$ by considering the spatial symmetry of the $\sqrt{5}% \times
\sqrt{5}$ vacancy ordered structure. Based on three orbitals of $% t_{2g}$,
which are believed to play major physics in iron-based superconductors, an
effective two-dimensional tight binding Hamiltonian is constructed with the
vacancy ordered structure being explicitly included. It is shown that the
constructed band model, when combined with generalized Hubbard interactions,
yields a spin susceptibility which exhibits both the block-checkerboard
antiferromagnetism instability and the stripe antiferromagnetism instability.
In particular, for large Hund's rule couplings, the block-checkerboard
antiferromagnetism wins over the stripe antiferromagnetism, in agreement with
the observation in experiments. We argue that such a model with correct
symmetry and Fermi surface structures should be the starting point to model
K$_{y}$Fe$_{1.6}$Se$_{2}$. The spin fluctuations at $\mathbf{q}$=($\pi ,\pi $)
suggest that interblock fluctuations of spins might play an important role in
the mechanism of superconductivity occurring in this system.",1108.4787v3
2011-09-09,C/O Abundance Ratios and Dust Features in Galactic Planetary Nebulae,"The iron depletion factors found in Galactic planetary nebulae (PNe) span
over two orders of magnitude, suggesting that there are differences in the
grain formation and destruction processes from object to object. We explore
here the relation between the iron depletions, the infrared dust features, and
the C/O abundance ratios in a sample of Galactic PNe. We find that those
objects with C/O < 1 show a trend of increasing depletions for higher values of
C/O, whereas PNe with C/O > 1 break the trend and cover all the range of
depletions. Most of the PNe with C/O < 1 show silicate features, but several
PNe with C-rich features have C/O < 1, probably reflecting the uncertainties
associated with the derivation of C/O. PAHs are distributed over the entire
range of iron depletions and C/O values.",1109.1867v1
2011-09-13,Formation of iron nitride thin films with Al and Ti additives,"In this work we investigate the process of iron nitride (Fe-N) phase
formation using 2 at.% Al or 2 at.% Ti as additives. The samples were prepared
with a magnetron sputtering technique using different amount of nitrogen during
the deposition process. The nitrogen partial pressure (\pn) was varied between
0-50% (rest Argon) and the targets of pure Fe, [Fe+Ti] and [Fe+Al] were
sputtered. The addition of small amount of Ti or Al results in improved
soft-magnetic properties when sputtered using \pn $\leq$ 10\p. When \pn is
increased to 50\p non-magnetic Fe-N phases are formed. We found that iron
mononitride (FeN) phases (N at% $\sim$50) are formed with Al or Ti addition at
\pn =50% whereas in absence of such addition \eFeN phases (N\pat$\sim$30) are
formed. It was found that the overall nitrogen content can be increased
significantly with Al or Ti additions. On the basis of obtained result we
propose a mechanism describing formation of Fe-N phases Al and Ti additives.",1109.2725v1
2011-10-03,Enhancement of the upper critical field in codoped iron-arsenic high-temperature superconductors,"We present the first study of codoped iron-arsenide superconductors of the
122 family (Sr/Ba)_(1-x)K_xFe_(2-y)Co_yAs_2 with the purpose to increase the
upper critical field H_c2 compared to single doped (Sr/Ba)Fe_2As_2 materials.
H_c2 was investigated by measuring the magnetoresistance in high pulsed
magnetic fields up to 64 T. We find, that H_c2 extrapolated to T = 0 is indeed
enhanced significantly to ~ 90 T for polycrystalline samples of
Ba_0.55K_0.45Fe_1.95Co_0.05As_2 compared to ~75 T for Ba_0.55K_0.45Fe_2As_2 and
BaFe_1.8Co_0.2As_2 single crystals. Codoping thus is a promising way for the
systematic optimization of iron-arsenic based superconductors for
magnetic-field and high-current applications.",1110.0478v1
2011-10-04,Inter-layer Superconducting Pairing Induced c-axis Nodal Lines in Iron-based Superconductors,"A layered superconductor with a full pairing energy gap can be driven into a
nodal superconducting (SC) state by inter-layer pairing when the SC state
becomes more quasi-3D. We propose that this mechanism is responsible for the
observed nodal behavior in a class of iron-based SCs. We show that the intra-
and inter-layer pairings generally compete and the gap nodes develop on one of
the {\em hole} Fermi surface pockets as they become larger in the
iron-pnictides. Our results provide a natural explanation of the c-axis gap
modulations and gap nodes observed by angle resolved photoemission
spectroscopy. Moreover, we predict that an anti-correlated c-axis gap
modulations on the hole and electron pockets should be observable in the
$S^{\pm}$-wave pairing state.",1110.0695v1
2011-10-05,Phase diagram of iron-pnictides if doping acts as a disorder,"We obtain and analyze the phase diagram of doped iron-pnictides under the
assumption that doping adds non-magnetic impurities to the system but does not
change the densities of carriers. We show that the phase diagram is quite
similar to the one obtained under the opposite rigid band assumption. In both
cases, there is a phase where extended s+- superconductivity and
antiferromagnetism co-exist. We evaluate the jump of the specific heat at the
superconducting transition across the phase diagram and show that the jump is
non-monotonic, with the maximum at the onset of the co-existence phase. Our
results are in quantitative agreement with experiments on some iron-pnictides.",1110.0972v2
2011-10-06,Quantum oscillation studies of the Fermi surface of iron-pnictide superconductors,"This paper reviews quantum oscillation studies of iron-pnictide
superconductors and related materials. These measurements give unique
information regarding the full three dimensional topology of the Fermi surfaces
and the renormalisation of the quasi-particle masses. The review will cover
measurements of the 122 arsenide end members, XFe_2As_2 (X = Ba, Sr, Ca) which
have a spin density wave ground state, but will concentrate on the phosphide
end members (LaFePO and XFe2P2) which have a paramagnetic ground state and a
Fermi surface topology which is similar to the higher Tc superconducting
iron-pnictides. All three of the 122 phosphides become superconducting when P
is partially substituted by As, and for the BaFe2(As1-xPx)2 series de Haas-van
Alphen oscillations are observable for 0:42 \leq x \leq 1 with Tc up to 25 K.
The results show the changes in the Fermi surface topology and the increase in
the mass renormalisation as the correlations which induce superconductivity
develop.",1110.1326v1
2011-10-11,Impurity-Induced Electronic Nematic State in Iron-Pnictide Superconductors,"We propose that impurity-induced electronic nematic state is realized above
the orthorhombic structure transition temperature $T_S$ in iron-pnictide
superconductors. In the presence of strong orbital fluctuations near $T_S$, it
is theoretically revealed that a single impurity induces non-local orbital
order with $C_2$-symmetry, consistently with recent STM/STS measurements. Each
impurity-induced $C_2$ orbital order aligns along a-axis by applying tiny
uniaxial pressure along b-axis. In this impurity-induced nematic phase, the
resistivity shows sizable in-plane anisotropy ($\rho_b/\rho_a \sim 2$) even
above $T_S$, actually observed in various ""detwinned"" samples. The present
study indicates the existence of strong orbital fluctuations in iron-pnictide
superconductors.",1110.2401v2
2011-10-20,First-Principles Study on the Mobility of Screw Dislocations in BCC Iron,"The fully two-dimensional Peierls barrier map of screw dislocations in BCC
iron has been calculated using the first principles method to identify the
migration path of a dislocation core. An efficient method to correct the effect
of the finite size cell used in the first principles method on the energy of a
lattice defect was devised to determine the accurate barrier profile. We find
that the migration path is close to a straight line which is confined in a
$\{110\}$ plane and the Peierls barrier profile is single-humped. This result
clarifies a reason that the existing empirical potentials of BCC iron fail to
predict the correct mobility path. A line tension model, incorporating these
first principles calculation results, is used to predict the kink activation
energy to be 0.73 eV in agreement with experiment.",1110.4487v4
2011-10-21,Fermi surface topology and low-lying electronic structure of a new iron-based superconductor Ca10(Pt3As8)(Fe2As2)5,"We report a first study of low energy electronic structure and Fermi surface
topology for the recently discovered iron-based superconductor
Ca10(Pt3As8)(Fe2As2)5 (the 10-3-8 phase, with Tc = 8K), via angle-resolved
photoemission spectroscopy (ARPES). Despite its triclinic crystal structure,
ARPES results reveal a fourfold symmetric band structure with the absence of
Dirac-cone-like Fermi dots (related to magnetism) found around the Brillouin
zone corners in other iron-based superconductors. Considering that the
triclinic lattice and structural supercell arising from the Pt3As8 intermediary
layers, these results indicate that those layers couple only weakly to the FeAs
layers in this new superconductor, which has implications for the determination
of its potentially novel pairing mechanism.",1110.4687v1
2011-10-20,Hydrogen Geysers: Explanation for Observed Evidence of Geologically Recent Volatile-Related Activity on Mercury's Surface,"High resolution images of Mercury's surface, from the MESSENGER spacecraft,
reveal many bright deposits associated with irregular, shallow, rimless
depressions whose origins were attributed to volatile-related activity, but
absent information on the nature and origin of that volatile matter. Here I
describe planetary formation, unlike the cited models, and show that primordial
condensation from an atmosphere of solar composition at pressures of one
atmosphere or above will lead to iron condensing as a liquid and dissolving
copious amounts of hydrogen, which is subsequently released as Mercury's core
solidifies and escapes from the surface, yielding the observed pit-like
features with associated highly-reflecting matter. The exiting hydrogen
chemically reduces some iron compound, probably iron sulfide, to the metal,
which accounts for the bright deposits.",1110.5796v2
2011-12-01,Simulation of Proton and Iron Induced Extensive Air Showers,"The reliable simulation of extensive air showers induced by different primary
particles (e. g. proton, iron, gamma etc.) is of great importance in high
energy cosmic ray research. The CORSIKA is a standard Monte-Carlo simulation
package to simulate the four dimensional evolution of Extensive Air Shower
(EAS) in the atmosphere initiated by gamma, hadrons and nuclei. CORSIKA has
different high energy interaction models like DPMJET, QGSJET, NEXUS, SIBYLL,
VENUS and EPOS which are based on different theoretical frameworks. The
influence of different hadronic interaction models, viz., QGSJET and DPMJET on
the lateral distribution functions (LDF) and muon to electron ratio of cosmic
ray EAS induced by 10^17 eV to 10^20 eV proton and iron primaries are explored
in this work.",1112.0356v1
2012-01-12,Universal behavior of the upper critical field in iron based superconductors,"The newly discovered iron-based high temperature superconductors have
demonstrated rich physical properties. Here we give a brief review on the
recent studies of the upper critical field and its anisotropy in a few typical
series of the iron-based superconductors (FeSCs). In spite of their characters
of a layered crystal structure, all the FeSCs possess an extremely large upper
critical field and a weak anisotropy of superconductivity, being unique among
the layered superconductors. These particular properties indicate potential
applications of the FeSCs in the future. Based on the experimental facts of the
FeSCs, we will discuss the possible mechanisms of pair breaking in high
magnetic fields and its restrictions on the theoretical analysis of the
superconducting pairing mechanisms.",1201.2548v1
2012-01-13,The Solar Flare Iron Abundance,"The abundance of iron is measured from emission line complexes at 6.65 keV
(Fe line) and 8 keV (Fe/Ni line) in {\em RHESSI} X-ray spectra during solar
flares. Spectra during long-duration flares with steady declines were selected,
with an isothermal assumption and improved data analysis methods over previous
work. Two spectral fitting models give comparable results, viz. an iron
abundance that is lower than previous coronal values but higher than
photospheric values. In the preferred method, the estimated Fe abundance is
$A({\rm Fe}) = 7.91 \pm 0.10$ (on a logarithmic scale, with $A({\rm H}) = 12$),
or $2.6 \pm 0.6$ times the photospheric Fe abundance. Our estimate is based on
a detailed analysis of 1,898 spectra taken during 20 flares. No variation from
flare to flare is indicated. This argues for a fractionation mechanism similar
to quiet-Sun plasma. The new value of $A({\rm Fe})$ has important implications
for radiation loss curves, which are estimated.",1201.2875v1
2012-03-12,Pairing Symmetry in Iron-Pnictide Superconductor KFe$_2$As$_2$,"The pairing symmetry is one of the major issues in the study of iron-based
superconductors. We adopt a low-energy effective kinetic model based on the
first-principles band structure calculations combined with the $J_1$-$J_2$
model for KFe$_2$As$_2$, the phase diagram of pairing symmetries is
constructed. Putting the values of $J_1$ and $J_2$ of the $J_1$-$J_2$ model
obtained by the first-principles calculations into this phase diagram, we find
that the pairing symmetry for KFe$_2$As$_2$ is a nodal $d_{xy}$-wave in the
folded Brillouin zone with two iron atoms per unit cell. This is in good
agreement with experiments observed a nodal order parameter.",1203.2581v4
2012-03-14,Enhancement of $T_{c}$ by disorder in underdoped iron pnictides,"We analyze how disorder affects the transition temperature $T_{c}$ of the
$s^{+-}$superconducting state in the iron pnictides. The conventional wisdom is
that $T_{c}$ should rapidly decrease with increasing inter-band non-magnetic
impurity scattering, but we show that this behavior holds only in the overdoped
region of the phase diagram. In the underdoped regime, where superconductivity
emerges from a pre-existing magnetic state, disorder gives rise to two
competing effects: breaking of the Cooper pairs, which tends to reduce $T_{c}$,
and suppression of the itinerant magnetic order, which tends to bring $T_{c}$
up. We show that for a wide range of parameters the second effect wins, leading
to an increase of $T_{c}$ with disorder in the coexistence state. Our results
explain several recent experimental findings and provide another evidence for
$s^{+-}$-pairing in the iron pnictides.",1203.3012v2
2012-04-02,Red Supergiant Stars as Cosmic Abundance Probes: NLTE Effects in J-band Iron and Titanium Lines,"Detailed non-LTE calculations for red supergiant stars are presented to
investigate the influence of NLTE on the formation of atomic iron and titanium
lines in the J-band. With their enormous brightness at J-band red supergiant
stars are ideal probes of cosmic abundances. Recent LTE studies have found that
metallicities accurate to 0.15 dex can be determined from medium resolution
spectroscopy of individual red supergiants in galaxies as distant as 10 Mpc.
The non-LTE results obtained in this investigation support these findings.
Non-LTE abundance corrections for iron are smaller than 0.05 dex for effective
temperatures between 3400K to 4200K and 0.1 dex at 4400K. For titanium the
non-LTE abundance corrections vary smoothly between -0.4 dex and +0.2 dex as a
function of effective temperature. For both elements, the corrections also
depend on stellar gravity and metallicity. The physical reasons behind the
non-LTE corrections and the consequences for extragalactic J-band abundance
studies are discussed.",1204.0511v1
2012-04-08,"Least momentum space frustration as a condition for ""high $T_c$ sweet spot"" in the iron-based superconductors","In the present paper, we describe how the band structure and the Fermi
surface of the iron-based superconductors vary as the Fe-As-Fe bond angle
changes. We discuss how these Fermi surface configurations affect the
superconductivity mediated by spin fluctuations, and show that in several
situations, frustration in the sign of the gap function arises due to the
repulsive pairing interactions that requires sign change of the order
parameter. Such a frustration can result in nodes or very small gaps, and
generally works destructively against superconductivity. Conversely, we propose
that the optimal condition for superconductivity is realized for the Fermi
surface configuration that gives the least frustration while maximizing the
Fermi surface multiplicity. This is realized when there are three hole Fermi
surfaces, where two of them have $d_{XZ/YZ}$ orbital character and one has
$d_{X^2-Y^2}$ {\it for all $k_z$} in the three dimensional Brillouin zone.
Looking at the band structures of various iron-based superconductors, the
occurrence of such a ""sweet spot"" situation is limited to a narrow window.",1204.1717v1
2012-05-02,Evidence of a spin resonance mode in the iron-based superconductor Ba$_{0.6}$K$_{0.4}$Fe$_{2}$As$_{2}$ from scanning tunneling spectroscopy,"We used high-resolution scanning tunneling spectroscopy to study the
hole-doped iron pnictide superconductor Ba$_{0.6}$K$_{0.4}$Fe$_{2}$As$_{2}$
($T_c=38$ K). Features of a bosonic excitation (mode) are observed in the
measured quasiparticle density of states. The bosonic features are intimately
associated with the superconducting order parameter and have a mode energy of
$\sim$14 meV, similar to the spin resonance measured by inelastic neutron
scattering. These results indicate a strong electron-spin excitation coupling
in iron pictnide superconductors, similar to that in high-$T_c$ copper oxide
superconductors.",1205.0352v1
2012-05-08,Anisotropy of strong pinning in multi-band superconductors,"The field-angular dependence and anisotropy of the critical current density
in iron-based superconductors is evaluated using a phenomenological approach
featuring distinct anisotropy factors for the penetration depth and the
coherence length. Both the weak collective pinning limit, and the strong
pinning limit relevant for iron-based superconductors at low magnetic fields
are considered. It is found that in the more anisotropic materials, such as
SmFeAsO and NdFeAsO, the field-angular dependence is completely dominated by
the coherence-length (upper-critical field) anisotropy, thereby explaining
recent results on the critical current in these materials. In less anisotropic
superconductors, strong pinning can lead to an apparent inversion of the
anisotropy. Finally, it is shown that, under all circumstances, the ratio of
c-axis and ab-plane critical current densities for magnetic field along the
ab-plane directly yields the coherence length anisotropy factor
{\epsilon}{\xi}.",1205.1741v3
2012-05-11,Anisotropic Energy Gaps of Iron-based Superconductivity from Intra-band Quasiparticle Interference in LiFeAs,"If strong electron-electron interactions between neighboring Fe atoms mediate
the Cooper pairing in iron-pnictide superconductors, then specific and distinct
anisotropic superconducting energy gaps \Delta_i(k) should appear on the
different electronic bands i. Here we introduce intra-band Bogoliubov
quasiparticle scattering interference (QPI) techniques for determination of
\Delta_i(k) in such materials, focusing on LiFeAs. We identify the three
hole-like bands assigned previously as \gamma, \alpha_2 and \alpha_1, and we
determine the anisotropy, magnitude and relative orientations of their
\Delta_i(k). These measurements will advance quantitative theoretical analysis
of the mechanism of Cooper pairing in iron-based superconductivity.",1205.2673v1
2012-05-15,A relativistic iron emission line from the neutron star low-mass X-ray binary GX 3+1,"We present the results of a spectroscopic study of the Fe K{\alpha} emission
of the persistent neutron-star atoll low-mass X-ray binary and type I X-ray
burster GX 3+1 with the EPIC-PN on board XMM-Newton. The source shows a flux
modulation over several years and we observed it during its fainter phase,
which corresponds to an X-ray luminosity of Lx~10^37 ergs/s. When fitted with a
two-component model, the X-ray spectrum shows broad residuals at \sim6-7 keV
that can be ascribed to an iron K{\alpha} fluorescence line. In addition, lower
energy features are observed at \sim3.3 keV, \sim3.9 keV and might originate
from Ar XVIII and Ca XIX. The broad iron line feature is well fitted with a
relativistically smeared profile. This result is robust against possible
systematics caused by instrumental pile-up effects. Assuming that the line is
produced by reflection from the inner accretion disk, we infer an inner disk
radius of \sim25 Rg and a disk inclination of 35{\deg} < i < 44{\deg}.",1205.3348v1
2012-05-23,Superfluid density in the $s_{\pm}$-wave state of clean iron-based superconductors,"Based on a phenomenological model and the Kubo formula, we investigate the
superfluid density $\rho_s(T)$ and then the penetration depth $\lambda(T)$ of
the iron-based superconductors in the coexistence region of the
spin-density-wave(SDW) and superconductivity, and also in the over-doped
region. Our calculations show a dramatic increase of $\lambda(0)$ with the
decrease of the doping concentration $x$ below $x=0.1$. This result is
consistent with the experimental observations. At low temperatures, $\rho(T)$
shows an exponential-law behavior, while at higher temperatures, the
linear-in-$T$ behavior is dominant before it trends to vanish. The evolution of
$\Delta\lambda(T)$ can be roughly fitted by a exponential function at overdoped
levels while in other doping range it is a power-law function with the exponent
depending on the doping concentration. We show that the Uemura relation holds
for the iron-based superconductors only at very low doping levels.",1205.5086v2
2012-05-23,"Dimer Impurity Scattering, ""Reconstructed"" Nesting and Density-Wave Diagnostics in Iron Pnictides","While the impurity-induced nanoscale electronic disorder has been extensively
reported in the underdoped iron pnictides, its microscopic origins remain
elusive. Recent scanning tunneling microscopy (STM) measurements reveal a
dimer-type resonant structure induced by cobalt doping. These dimers are
randomly distributed but uniformly aligned with the antiferromagnetic a axis. A
theory of the impurity-induced quasiparticle interference patterns is presented
that shows the local density of states developing an oscillatory pattern
characterized by both geometry and orbital content of the {\em reconstructed}
Fermi pockets, occasioned by the pocket density-wave (PoDW) order along the b
axis. This pattern breaks the $C_4$ symmetry and its size and orientation
compare well with the dimer resonances found in the STM experiments, hinting at
the presence of a ""hidden"" PoDW order. More broadly, our theory spotlights such
nanoscale structures as a useful diagnostic tool for various forms of order in
iron pnictides.",1205.5280v3
2012-06-05,The effect of spin fluctuations on the electronic structure in iron based superconductors,"Magnetic inelastic neutron scattering (INS) studies of iron-based
superconductors reveal a strongly temperature-dependent spin-fluctuation
spectrum in the normal conducting state, which develops a prominent low-energy
resonance feature when entering the superconducting state. Angle-resolved
photoemission spectroscopy (ARPES) and scanning tunneling spectroscopy (STS)
allow to study the fingerprints of fluctuation modes via their interactions
with electronic quasiparticles. We calculate such fingerprints in 122 iron
pnictides using an experimentally motivated spin-fluctuation spectrum and make
a number of predictions that can be tested in ARPES and STS experiments. This
includes discussions of the quasiparticle scattering rate and the
superconducting order parameter. In quantitative agreement with experiment we
reproduce the quasiparticle dispersions obtained from momentum distribution
curves as well as energy distribution curves. We discuss the relevance of the
coupling between spin fluctuations and electronic excitations for the
superconducting mechanism.",1206.0904v2
2012-07-02,Consequences of extended $s_\pm$-wave pairing in iron-based superconductors,"Motivated by a recent experiment of Song \emph{et al.} [Science {\bf 332},
1410 (2011)], we theoretically study the spin dynamics, charge dynamics, and
point-contact Andreev-reflection spectroscopy (PCARS) of two-band iron-based
superconductors of a possible extended $s_\pm$-wave pairing symmetry. We
consider the case of a dominant $s_\pm$ gap blended by a secondary extended $s$
component in which gap nodes can develop in the Fermi pockets near zone corner
and/or boundary. Due to the strong nesting effect associated with nodal
regions, dynamical spin and charge susceptibilities can exhibit strong peaks at
momenta near $(\pm\pi/2,0)$, $(\pm\pi,\pm\pi/2)$, as well as $(\pm\pi,0)$ in
the unfolded Brillouin zone. For PCARS, considering an anisotropic band effect
induced by an applied voltage, [100] differential conductance can exhibit a
$V$-shape behavior manifesting a gap node occurring in such direction. It is
highly suggested that the above features can be experimentally investigated to
help sorting out the pairing symmetry of iron-based superconductors.",1207.0270v1
2012-07-10,Deviating band symmetries and many-body interactions in a model hole doped iron pnictide superconductor,"We present a polarization resolved study of the low energy band structure in
the optimally doped iron pnictide superconductor
Ba$_{0.6}$K$_{0.4}$Fe$_2$As$_2$ (T$_c$=37K) using angle resolved photoemission
spectroscopy. Polarization-contrasted measurements are used to identify and
trace all three low energy hole-like bands predicted by local density
approximation (LDA) calculations. The photoemitted electrons reveal an
inconsistency with LDA-predicted symmetries along the $\Gamma$-X high symmetry
momentum axis, due to unexpectedly strong rotational anisotropy in electron
kinetics. We evaluate many-body effects such as Mott-Hubbard interactions that
are likely to underlie the anomaly, and discuss how the observed deviations
from LDA band structure affect the energetics of iron pnictide Cooper pairing
in the hole doped regime.",1207.2221v2
2012-09-11,Many-body effects in iron pnictides and chalcogenides -- non-local vs dynamic origin of effective masses,"We apply the quasi-particle self-consistent GW (QSGW) approximation to some
of the iron pnictide and chalcogenide superconductors. We compute Fermi
surfaces and density of states, and find excellent agreement with experiment,
substantially improving over standard band-structure methods. Analyzing the
QSGW self-energy we discuss non-local and dynamic contributions to effective
masses. We present evidence that the two contributions are mostly separable,
since the quasi-particle weight is found to be essentially independent of
momentum. The main effect of non locality is captured by the static but
non-local QSGW effective potential. Moreover, these non-local self-energy
corrections, absent in e.g. dynamical mean field theory (DMFT), can be
relatively large. We show, on the other hand, that QSGW only partially accounts
for dynamic renormalizations at low energies. These findings suggest that QSGW
combined with DMFT will capture most of the many-body physics in the iron
pnictides and chalcogenides.",1209.2213v1
2012-10-17,Superconductivity in a single layer alkali-doped FeSe: a weakly coupled two-leg ladder system,"We prepare single layer potassium-doped iron selenide (110) film by molecular
beam expitaxy. Such a single layer film can be viewed as a two-dimensional
system composed of weakly coupled two-leg iron ladders. Scanning tunneling
spectroscopy reveals that superconductivity is developed in this two-leg ladder
system. The superconducting gap is similar to that of the multi-layer films.
However, the Fermi surface topology given by first-principles calculation is
remarkably different from that of the bulk materials. Our results suggest that
superconducting pairing is very short-ranged or takes place rather locally in
iron-chalcogenides. The superconductivity is most likely driven by
electron-electron correlation effect and is insensitive to the change of Fermi
surfaces.",1210.4619v1
2012-11-15,LDA'+DMFT Investigation of Electronic Structure of K{1-x}Fe{2-y}Se2 Superconductor,"We investigate electronic structure of the new iron chalcogenide high
temperature superconductor K{1-x}Fe{2-y}Se2 (hole doped case with x=0.24,
y=0.28) in the normal phase using the novel LDA'+DMFT computational approach.
We show that this iron chalcogenide is more correlated in a sense of bandwidth
renormalization (energy scale compression by factor about 5 in the interval
+/-1.5 eV), than typical iron pnictides (compression factor about 2), though
the Coulomb interaction strength is almost the same in both families. Our
results for spectral densities are in general agreement with recent ARPES data
on this system. It is found that all Fe-3d(t2g) bands crossing the Fermi level
have equal renormalization, in contrast to some previous interpretations.
Electronic states at the Fermi level are of predominantly xy symmetry. Also we
show that LDA'+DMFT results are in better agreement with experimental spectral
function maps, than the results of conventional LDA+DMFT. Finally we make
predictions for photoemission spectra lineshape for K{0.76}Fe{1.72}Se2.",1211.3499v1
2012-11-20,$a-b$ Plane Point Contact Spectroscopy measurements of optimally Cobalt doped Ba-122 iron-pnictide superconductors,"Point contact spectroscopy (PCS) is a technique which can reveal the size and
symmetry of a superconducting gap ($\Delta$) and is especially useful for new
materials such as the iron-based superconductors. PCS is usually employed in
conjunction with the extended Blonder-Tinkham-Klapwijk (BTK) model which is
used to extract information such as the existence of nodes in $\Delta$ from PCS
data obtained on unconventional superconductors. The BTK model uses a
dimensionless parameter $Z$ to quantify the barrier strength across a normal
metal - superconductor junction. We have used a unique feature of PCS which
allows variation of $Z$ to obtain crucial information about $\Delta$. We report
our $Z$-dependent, $a-b$ plane PCS measurements on single crystals of the
iron-based superconductor BaFe$_{2-x}$Co$_{x}$As$_{2}$. Our measurements show
that BaFe$_{2-x}$Co$_{x}$As$_{2}$ ($x$=0.148) is a superconductor with two gaps
which does not contain any nodes. The $Z$ dependent point contact spectra rule
out a pure $d$ symmetry and the gaps at optimal doping have negligible
anisotropy.",1211.4659v1
2012-12-05,Investigation of variability of iron emission lines in Centaurus X-3,"We present the results obtained from a study of the variability of iron
emission lines in the high mass X-ray binary pulsar Cen X-3 during the eclipse,
eclipse-egress and out-of-eclipse phases using XMM-Newton observations. Three
iron emission lines at 6.4 keV, 6.7 keV, and 6.97 keV are clearly detected in
the spectrum of the pulsar during the entire observations, irrespective of
different binary phases. The properties of these emission lines are
investigated at different intensity levels. The flux level and equivalent width
of the emission lines change during the eclipse, eclipse-egress and
out-of-eclipse orbital phases. Based on the results obtained from the time
resolved spectral analysis, it is understood that the most probable emitting
region of 6.4 keV fluorescent line is very close to the neutron star whereas
the other two lines are produced in a region that is far from the neutron star,
probably in the highly photo-ionized wind of the companion star or in the
accretion disk corona.",1212.0949v1
2012-12-20,Pairing insights in iron-based superconductors from scanning tunneling microscopy,"Scanning tunneling microscopy (STM) has made tremendous progress in the study
and understanding of both classical and unconventional superconductors. This
has motivated a rapidly growing effort to apply the same techniques to the
iron-based high-Tc superconductors since their discovery in 2008. Five years
have brought exciting advances in imaging and spectroscopic investigation of
this new class of materials. In this review, we focus on several recent STM
contributions to the identification of the gap symmetry and pairing glue. We
highlight the unique capabilities and challenges still ahead for STM studies of
iron-based superconductors.",1212.5164v2
2013-01-18,Unusual persistence of superconductivity against high magnetic fields in the strongly-correlated iron-chalcogenide film FeTe:O$_{x}$,"We report an unusual persistence of superconductivity against high magnetic
fields in the iron chalcogenide film FeTe:O$_{x}$ below ~ 2.5 K. Instead of
saturating like a mean-field behavior with a single order parameter, the
measured low-temperature upper critical field increases progressively,
suggesting a large supply of superconducting states accessible via magnetic
field or low-energy thermal fluctuations. We demonstrate that superconducting
states of finite momenta can be realized within the conventional theory,
despite its questionable applicability. Our findings reveal a fundamental
characteristic of superconductivity and electronic structure in the
strongly-correlated iron-based superconductors.",1301.4487v3
2013-01-27,Iron-Based Superconductors as Parity Odd Superconductors,"Parity is a fundamental quantum number to classify a state of matter.
Materials rarely possess ground states with odd parity. We show that the
superconducting state in iron-based superconductors is classified as an odd
parity s-wave spin-singlet pairing state in a single trilayer FeAs/Se, the
building block of the materials. In a low energy effective model constructed on
the Fe square bipartite lattice, the superconducting order parameter in this
state is a combination of a s-wave normal pairing between two sublattices and a
s-wave $\eta$-pairing within the sublattices. Parity conservation was violated
in proposed superconducting states in the past. The state has a fingerprint
with a real space sign inversion between the top and bottom As/Se layers. The
results demonstrate iron-based superconductors being a new quantum state of
matter and suggest that the measurement of the odd parity can establish
fundamental principles related to high temperature superconducting mechanism.",1301.6342v5
2013-01-28,Evolution of the multiband RKKY interaction: Application to iron pnictides and chalcogenides,"The indirect RKKY interaction in iron pnictide and chalcogenide metals is
calculated for a simplified four bands Fermi surface (FS) model. We investigate
the specific multi-band features and show that distinct length scales of the
RKKY oscillations appear. For the regular lattice of the local moments, the
generalized RKKY interaction is defined in momentum space. We consider its
momentum dependence in paramagnetic and spin density wave (SDW) phases, discuss
its implications for the possible type of magnetic order and compare it to the
results obtained from more realistic tight-binding type Fermi surface model.
Our finding can give important clues on the magnetic ordering of the 4f- iron
based superconductors.",1301.6497v1
2013-02-22,Surface Atom Motion to Move Iron Nanocrystals through Constrictions in Carbon Nanotubes under the Action of an Electric Current,"Under the application of electrical currents, metal nanocrystals inside
carbon nanotubes can be bodily transported. We examine experimentally and
theoretically how an iron nanocrystal can pass through a constriction in the
carbon nanotube with a smaller cross-sectional area than the nanocrystal
itself. Remarkably, through in situ transmission electron imaging and
diffraction, we find that, while passing through a constriction, the
nanocrystal remains largely solid and crystalline and the carbon nanotube is
unaffected. We account for this behavior by a pattern of iron atom motion and
rearrangement on the surface of the nanocrystal. The nanocrystal motion can be
described with a model whose parameters are nearly independent of the
nanocrystal length, area, temperature, and electromigration force magnitude. We
predict that metal nanocrystals can move through complex geometries and
constrictions, with implications for both nanomechanics and tunable synthesis
of metal nanoparticles.",1302.5709v2
2013-03-25,Elementary Excitations due to Orbital Degrees of Freedom in Iron Based Superconductors,"One central issue under intense debate in the study of the iron based
superconductors is the origin of the structural phase transition that changes
the crystal lattice symmetry from tetragonal to orthorhombic. This structural
phase transition, occurring universally in almost every family of the
iron-based superconductors, breaks the lattice $C_4$ rotational symmetry and
results in an anisotropy in a number of physical properties. Due to the unique
topology of the Fermi surface, both orbital- and spin-based scenarios have been
proposed as the driving force. In this review, we focus on theories from the
orbital-based scenario and discuss several related experiments. It is pointed
out that although both scenarios lead to the same macroscopic phases and are
not distinguishable in bulk measurements of the thermodynamic properties, the
elementary excitations could be fundamentally different, and provide us with
the possibility to resolve this long-standing debate between orbital- and
spin-based theories.",1303.6295v1
2013-04-04,Study of the itinerant electron magnetism of Fe-based superconductors by the proximity effect,"We used the proximity effect as a tool to achieve an ideal (barrier - free)
NS boundary for quantitative evaluation of transport phenomena that accompany
converting dissipative current into supercurrent in NS systems with
unconventional superconductors, single - crystal chalcogenide FeSe and
granulated pnictide LaO(F)FeAs. Using features (limitations) of Andreev
reflection in the NS systems with dispersion of the electron spin subbands, we
revealed direct evidence for spin - polarized nature of transport and the
absence of residual magnetization in iron - based superconductors in the normal
state: In heterocontacts with single - crystal FeSe and granular LaO(F)FeAs, we
detected a spin-dependent contribution to the efficiency of the Andreev
reflection associated with the spin accumulation at the NS boundary, and a
hysteresis of conductivity of FeSe in the ground state in low external magnetic
fields. Based on our findings, we conclude that in iron-based superconductors,
the itinerant electron magnetism is predominant, magnetism of iron atoms being
localized.",1304.1418v1
2013-04-08,Electronic phase separation in iron pnictides,"A mechanism for electronic phase separation in iron pnictides is proposed. It
is based on the competition between commensurate and incommensurate
spin-density-wave phases in a system with an imperfect doping-dependent nesting
of a multi-sheeted Fermi surface. We model the Fermi surface by two elliptical
electron pockets and three circular hole pockets. The interaction between a
charge carrier in a hole band and a carrier in an electron band leads to the
formation of spin-density-wave order. The commensurate spin density wave in the
parent compound transforms to the incommensurate phase when doping is
introduced. We show that, for certain parameter values, the uniform state is
unstable with respect to phase separation. The resulting inhomogeneous state
consists of regions of commensurate and incommensurate spin-density-wave
phases. Our results are in qualitative agreement with recent observations of
incommensurate spin density waves and electronic inhomogeneity in iron
pnictides.",1304.2175v2
2013-04-18,Discovery of a superhard iron tetraboride superconductor,"Single crystals of novel orthorhombic (space group Pnnm) iron tetraboride
FeB4 were synthesised at pressures above 8 GPa and high temperatures. Magnetic
susceptibility measurements demonstrated bulk superconductivity below 2.9 K.
The putative isotope effect on the superconducting critical temperature
indicates that FeB4 is likely a phonon-mediated superconductor, which is
unexpected in the light of previous knowledge on Fe-based superconductors. The
discovered iron tetraboride is highly incompressible and has the
nanoindentation hardness of 65(5) GPa, thus, it opens a new class of highly
desirable materials combining advanced mechanical properties and
superconductivity.",1304.5106v1
2013-04-23,Quantum critical point lying beneath the superconducting dome in iron-pnictides,"Whether a quantum critical point (QCP) lies beneath the superconducting dome
has been a long-standing issue that remains unresolved in many classes of
unconventional superconductors, notably cuprates, heavy fermion compounds and
most recently iron-pnictides. The existence of a QCP may offer a route to
understand: the origin of their anomalous non-Fermi liquid properties, the
microscopic coexistence between unconventional superconductivity and magnetic
or some exotic order, and ultimately the mechanism of superconductivity itself.
The isovalent substituted iron-pnictide BaFe$_2$(As$_{1-x}$P$_x$)$_2$ offers a
new platform for the study of quantum criticality, providing a unique
opportunity to study the evolution of the electronic properties in a wide range
of the phase diagram. Recent experiments in BaFe$_2$(As$_{1-x}$P$_x$)$_2$ have
provided the first clear and unambiguous evidence of a second order quantum
phase transition lying beneath the superconducting dome.",1304.6387v1
2013-05-08,Functional renormalization group study of the pairing symmetry and pairing mechanism in iron-selenide superconductors,"In iron selenide superconductors only electron-like Fermi pockets survive,
challenging the $S^{\pm}$ pairing based on the quasi-nesting between the
electron and hole Fermi pockets (as in iron arsenides). By functional
renormalization group study we show that an in-phase $S$-wave pairing on the
electron pockets ($S^{++}_{ee}$) is realized. The pairing mechanism involves
two competing driving forces: The strong C-type spin fluctuations cause
attractive pair scattering between and within electron pockets via Cooperon
excitations on the virtual hole pockets, while the G-type spin fluctuations
cause repulsive pair scattering. The latter effect is however weakened by the
hybridization splitting of the electron pockets. The resulting
$S^{++}_{ee}$-wave pairing symmetry is consistent with experiments. We further
propose that the quasiparticle interference pattern in scanning tunneling
microscopy and the Andreev reflection in out-of-plane contact tunneling are
efficient probes of in-phase versus anti-phase $S$-wave pairing on the electron
pockets.",1305.1806v2
2013-05-22,Odd parity pairing and nodeless anti-phase $s^\pm$ in Iron-Based Superconductors,"We discuss the sign change of superconducting order parameters in both real
and reciprocal spaces when the odd parity spin singlet pairing proposed
recently in\cite{huoddparity} is allowed. We show that in this case an nodeless
anti-phase $s^\pm$ can be generated. In a 2-Fe Brilliouin zone (BZ), sign
change exists between two hole pockets and between two electron pockets. In a
1-Fe BZ which includes two 2-Fe BZs, the sign change is between two 2-Fe BZs,
which leads to a d-wave type sign distribution on the electron pockets, namely,
an anti-phase $s^\pm$ state with no symmetry protected gapless node on the
electron pockets. This sign change character consistently explains experimental
results related to sign change properties measured on both iron-pnictides and
iron-chalcogenides.",1305.5034v2
2013-05-30,Observation of isosceles triangular electronic structure around excess iron atoms in Fe$_{1+δ}$Te,"We present scanning tunneling microscopy and spectroscopy studies around an
individual excess Fe atom, working as a local perturbation, in the parent
material of the iron-chalcogenide superconductor Fe$_{1+\delta}$Te.
Spectroscopic imaging reveals a novel isosceles triangular electronic structure
around the excess Fe atoms. Its spatial symmetry reects the underlying
bicollinear antiferromagnetic spin state and the structural monoclinic
symmetry. These findings provide important clues to understand the role of the
excess Fe atoms, which complicate the understanding of the phenomena occurring
in iron-chalcogenide materials.",1305.7206v1
2013-06-05,Nematicity as a probe of superconducting pairing in iron-based superconductors,"In several families of iron-based superconducting materials, a d-wave pairing
instability may compete with the leading s-wave instability. Here we show that
when both states have comparable free energies, superconducting and nematic
degrees of freedom are strongly coupled. While nematic order causes a sharp
non-analytic increase in $T_{c}$, nematic fluctuations can change the character
of the s-wave to d-wave transition, favoring an intermediate state that does
not break time-reversal symmetry but does break tetragonal symmetry. The
coupling between superconductivity and nematicity is also manifested in the
strong softening of the shear modulus across the superconducting transition.
Our results show that nematicity can be used as a diagnostic tool to search for
unconventional pairing states in iron pnictides and chalcogenides.",1306.1125v2
2013-06-18,"Orbital-selective superconductivity, gap anisotropy and spin resonance excitations in a multiorbital t-J1-J2 model for iron pnictides","We study the orbital-dependent superconducting pairing in a five-orbital
t-J1-J2 model for iron pnictides. Depending on the orbital selectivity of
electron correlations and the orbital characters along the Fermi surface, the
superconducting gap in an A_{1g} pairing state may exhibit anisotropy. This
anisotropy varies with the degree of J1-J2 magnetic frustration. We have also
calculated the dynamical spin susceptibility in the superconducting state. The
frequency dependence of the susceptibility at the antiferromagnetic wavevector
(\pi,0) shows a resonance, whose width is enhanced by the orbital dependence of
the superconducting gap; when the latter is sufficiently strong, the resonance
peak may be split into two. We discuss the implications of our results on the
recent angle-resolved photoemission and neutron-scattering measurements in
several superconducting iron pnictides.",1306.4184v1
2013-06-25,Photo-Disintegration of the Iron Nucleus in Fractured Magnetite Rocks with Magnetostriction,"There has been considerable interest in recent experiments on iron nuclear
disintegrations observed when rocks containing such nuclei are crushed and
fractured. The resulting nuclear transmutations are particularly strong for the
case of magnetite rocks, i.e. loadstones. We argue that the fission of the iron
nucleus is a consequence of photo-disintegration. The electro-strong coupling
between electromagnetic fields and nuclear giant dipole resonances are central
for producing observed nuclear reactions. The large electron energies produced
during the fracture of piezomagnetic rocks are closely analogous to the
previously discussed case of the fracture of piezoelectric rocks. In both cases
electro-weak interactions can produce neutrons and neutrinos from energetic
protons and electrons thus inducing nuclear transmutations. The electro-strong
condensed matter coupling discussed herein represents new many body collective
nuclear photo-disintegration effects.",1306.6286v1
2013-07-29,Review of nuclear magnetic resonance studies on iron-based superconductors,"The newly discovered iron-based superconductors have triggered renewed
enormous research interest in the condensed matter physics community. Nuclear
magnetic resonance (NMR) is a low-energy local probe for studying strongly
correlated electrons, and particularly important for high-$T_{\rm C}$
superconductors. In this paper, we review NMR studies on the structural
transition, antiferromagnetic order, spin fluctuations, and superconducting
properties of several iron-based high-$T_{\rm C}$ superconductors, including
LaFeAsO$_{1-x}$F$_x$, LaFeAsO$_{1-x}$, BaFe$_2$As$_2$,
Ba$_{1-x}$K$_x$Fe$_2$As$_2$, Ca$_{0.23}$Na$_{0.67}$Fe$_2$As$_2$,
BaFe$_2$(As$_{1-x}$P$_x$)$_2$, Ba(Fe$_{1-x}$Ru$_x$)$_2$As$_2$,
Ba(Fe$_{1-x}$Co$_x$)$_2$As$_2$, Li$_{1+x}$FeAs, LiFe$_{1-x}$Co$_x$As, NaFeAs,
NaFe$_{1-x}$Co$_x$As, K$_y$Fe$_{2-x}$Se$_2$, and (Tl,Rb)$_y$Fe$_{2-x}$Se$_2$.",1307.7528v1
2013-08-12,The substitution effects on electronic structure of iron selenide superconductors,"The influence of a partial substitution with S, Te, Co, Ni and Cu atoms on
the electronic structure of the FeSe superconductor has been investigated
within the density functional theory. The results of the supercell calculations
reveal distinct changes of electronic structures of the substituted FeSe
systems, which can be responsible for their superconducting properties. The
replacement of Se atoms by Te or S ones yields imperfect nesting between the
holelike and electronlike Fermi surface (FS) sheets, which enhances magnetic
fluctuations responsible for superconducting pairing, thus leading to higher
values of the superconducting critical temperatures. Meanwhile, the
substitutions with transition-metal atoms for iron sites make more substantial
changes of the FSs topology, since the holelike cylinders shrink at the cost of
an enlargement of the electronlike ones. Thus, the superconducting pairing,
driven by the nesting between these sheets, weakens and superconductivity
disappears for a small percentage of dopants. The results support the idea of
spin-fluctuation mediated superconductivity in iron chalcogenides.",1308.2508v1
2013-09-19,Investigation of atomic and electronic structures of MgOFeSe studied by the first-principles calculations,"In order to assist the search of new superconductors in iron selenide
materials by intercalation, we calculate the crystal and electronic structures
of MgOFeSe using the first-principles density functional theory. MgOFeSe is
isotructural to the parent compound of iron pnictide superconductor LaOFeAs. In
LaOFeAs, the anion O$^{2-}$ is located at the center of each LaO tetrahedra.
But for MgOFeSe, we find that the crystal structure with the cation Mg$^{2+}$
as the tetrahedral center in the MgO layer is energetically more stable. The
low energy band structures around the Fermi surfaces of MgOFeSe are contributed
mainly by Fe 3$d$ orbitals. The ground state of MgOFeSe is collinearly
antiferromagnetically ordered. The height of Se atoms above the Fe-Fe layer is
about 1.38 \AA, which is close to the height of As from the Fe-Fe layer in the
iron pnictide superconductors with optimal superconducting transition
temperatures.",1309.5079v2
2013-09-27,Constrained non-collinear magnetism in disordered Fe and Fe-Cr alloys,"The development of quantitative models for radiation damage effects in iron,
iron alloys and steels, particularly for the high temperature properties of the
alloys, requires understanding of magnetic interactions, which control the
phase stability of ferritic-martensitic, ferritic, and austenitic steels. In
this work, disordered magnetic configurations of pure iron and Fe-Cr alloys are
investigated using Density Functional Theory (DFT) formalism, in the form of
constrained non-collinear magnetic calculations, with the objective of creating
a database of atomic magnetic moments and forces acting between the atoms. From
a given disordered atomic configuration of either pure Fe or Fe-Cr alloy, a
penalty contribution to the usual spin-polarized DFT total energy has been
calculated by constraining the magnitude and direction of magnetic moments. An
extensive database of non-collinear magnetic moment and force components for
various atomic configurations has been generated and used for interpolating the
spatially-dependent magnetic interaction parameters, for applications in
large-scale spin-lattice dynamics and magnetic Monte-Carlo simulations.",1309.7183v1
2013-10-23,The non-magnetic collapsed tetragonal phase of CaFe2As2 and superconductivity in the iron pnictides,"The relationship between antiferromagnetic spin fluctuations and
superconductivity has become a central topic of research in studies of
superconductivity in the iron pnictides. We present unambiguous evidence of the
absence of magnetic fluctuations in the non-superconducting collapsed
tetragonal phase of CaFe2As2 via inelastic neutron scattering time-of-flight
data, which is consistent with the view that spin fluctuations are a necessary
ingredient for unconventional superconductivity in the iron pnictides. We
demonstrate that the collapsed tetragonal phase of CaFe2As2 is non-magnetic,
and discuss this result in light of recent reports of high-temperature
superconductivity in the collapsed tetragonal phase of closely related
compounds.",1310.6346v1
2013-11-11,Model of the Electronic Structure of Electron-Doped Iron-Based Superconductors: Evidence for Enhanced Spin Fluctuations by Diagonal Electron Hopping,"We present a theoretical understanding of the superconducting phase diagram
of the electron-doped iron pnictides. We show that, besides the Fermi surface
nesting, a peculiar motion of electrons, where the next nearest neighbor
(diagonal) hoppings between iron sites dominate over the nearest neighbor ones,
plays an important role in the enhancement of the spin fluctuation and thus
superconductivity. In the highest $T_c$ materials, the crossover between the
Fermi surface nesting and this ""prioritized diagonal motion"" regime occurs
smoothly with doping, while in relatively low $T_c$ materials, the two regimes
are separated and therefore results in a double dome $T_c$ phase diagram.",1311.2413v2
2013-11-23,Thirty Femtograms Detection of Iron in Mammalian Cells,"Inorganic nanomaterials and particles with enhanced optical, mechanical or
magnetic attributes are currently being developed for a wide range of
applications. Safety issues have been formulated however concerning their
potential cyto- and genotoxicity. For in vivo and in vitro experimentations,
recent developments have heightened the need of simple and facile methods to
measure the amount of nanoparticles taken up by cells or tissues. In this work,
we present a rapid and highly sensitive method for quantifying the uptake of
iron oxide nanoparticles in mammalian cells. Our approach exploits the
digestion of incubated cells with concentrated hydrochloric acid reactant and a
colorimetric based UV-Visible absorption technique. The technique allows the
detection of iron in cells over 4 decades in masses, from 0.03 to 300 picograms
per cell. Applied on particles of different surface chemistry and sizes, the
protocol demonstrates that the coating is the key parameter in the
nanoparticle/cell interactions. The data are corroborated by scanning and
transmission electron microscopy and stress the importance of resiliently
adsorbed nanoparticles at the plasma membrane.",1311.6019v1
2013-12-20,Enhancing the three-dimensional electronic structure in 1111-type iron arsenide superconductors by H-substitution,"The 1111-type iron arsenide hydride CaFe1-xCoxAsH was synthesized by
high-pressure solid-state reaction, and its electronic structure and
superconducting properties were investigated. Bulk superconductivity was
observed at x = 0.07-0.26. A maximum superconducting critical temperature Tcmax
of 23 K was observed at x = 0.07. These values are in agreement with those of
CaFe1-xCoxAsF. The calculated Fermi surface of CaFeAsH has a small
three-dimensional 3D hole pocket around the Gamma point. This is a result of
weak covalent bonding between the As 4p and H 1s orbitals. No such covalency
exists in CaFeAsF, because the energy level of the F 2p orbital is sufficiently
deep to inhibit overlap with the As 4p orbital. The similar superconducting
properties of CaFe1-xCoxAsH and CaFe1-xCoxAsF are explained on the nesting
scenario. The small 3D hole pocket of CaFe1-xCoxAsH does not significantly
contribute to electron excitation. These findings encourage exploration of
hydrogen-containing 1111-type iron-based materials with lower anisotropies and
higher Tc applicable to superconducting wires and tapes.",1312.5818v2
2013-12-20,Band antiferromagnetism in a two-band model for iron pnictides,"In this work I investigate a two-band Hubbard model using the Gutzwiller
wavefunction. The tight-binding part of the model was constructed to have a
gapless spin-density wave state which leads to Dirac points in the
bandstructure, a common feature of many iron-pnictide compounds. For quarter,
half and three-quarter fillings I show that the Hund's rule coupling has a
large impact on the metal-insulator transition in the paramagnetic phase. For
the half-filled model in the antiferromagnetic phase, the magnetism evolves in
a Stoner-like behavior and the size of the ordered moment is mainly determined
by the Hubbard interaction. As the Hund's coupling plays a minor role in this
state, the model does not describe a Hund's metal which is in contrast to more
realistic models for iron-pnictide compounds.",1312.5902v2
2013-12-29,Electron capture of iron group nuclei in magnetars,"Using the theory of relativity in superstrong magnetic fields (SMFs) and
nuclear shell model, we carry out estimation for electron capture (EC) rates on
iron group nuclei in SMFs. The rates of change of electronic abundance (RCEA)
due to EC are also investigated in SMFs. It is concluded that the EC rates of
most iron group nuclides are increased greatly by SMFs and even exceeded by
nine orders of magnitude. On the other hand, RCEA is influenced greatly by SMFs
and even reduced by more than eight orders of magnitude in the EC reaction.We
also compare our results with those of Fuller et al.(FFN) and Aufderheide et
al.(AUFD) in the case with and without SMFs. The results show that our results
are in good agreement with AUFD's, but the rates of FFN's are about close to
one order of magnitude bigger than ours in the case without SMFs. On the
contrary, our calculated rates for most nuclides in SMFs are increased and even
exceeded as much as for nine and eight orders of magnitude of compared to FFN's
and AUFD's results, which is in the case without SMFs, respectively.",1312.7552v1
2014-02-17,Electronic Nematicity Revealed by Torque Magnetometry in Iron Arsenide EuFe$_2$(As$_{1-x}$P$_x$)$_2$,"Electronic nematics, an electron orientational order which breaks the
underlying rotational symmetry, have been observed in iron pnictide
superconductors several years after their discovery. However, the universality
of the doping dependence of this phase and its relation to other
symmetry-breaking orders (such as superconductivity) in distinct families of
iron pnictides, remain outstanding questions. Here we use torque magnetometry
as a probe to study the rotational symmetry breaking in
EuFe$_2$(As$_{1-x}$P$_x$)$_2$ without introducing external pressure. The
nematic phase is found to proliferate well above the structural transition and
to persist into the superconducting regime at optimal doping, after which it
becomes absent or very weak, in sharp contrast to the behaviour observed in
BaFe$_2$(As$_{1-x}$P$_x$)$_2$. These measurements suggest a putative quantum
nematic transition near optimal doping under the superconducting dome.",1402.4124v1
2014-03-01,Doping dependence of the anisotropic quasiparticle interference in NaFe1-xCoxAs iron-based superconductors,"We use scanning tunneling microscopy to investigate the doping dependence of
quasiparticle interference (QPI) in NaFe1-xCoxAs iron-based superconductors.
The goal is to study the relation between nematic fluctuations and Cooper
pairing. In the parent and underdoped compounds, where four-fold rotational
symmetry is broken macroscopically, the QPI patterns reveal strong rotational
anisotropy. At optimal doping, however, the QPI patterns are always four-fold
symmetric. We argue this implies small nematic susceptibility and hence
insignificant nematic fluctuation in optimally doped iron pnictides. Since Tc
is the highest this suggests nematic fluctuation is not a prerequistite for
strong Cooper pairing.",1403.0090v1
2014-03-07,The origin of low [alpha/Fe] ratios in extremely metal-poor stars,"We show that the low ratios of $\alpha$ elements (Mg, Si, and Ca) to Fe
recently found for a small fraction of extremely metal-poor stars can be
naturally explained with the nucleosynthesis yields of core-collapse
supernovae, i.e., $13-25M_\odot$ supernovae, or hypernovae. For the case
without carbon enhancement, the ejected iron mass is normal, consistent with
observed light curves and spectra of nearby supernovae. On the other hand, the
carbon enhancement requires much smaller iron production, and the low
[$\alpha$/Fe] of carbon enhanced metal-poor stars can also be reproduced with
$13-25M_\odot$ faint supernovae or faint hypernovae. Iron-peak element
abundances, in particular Zn abundances, are important to put further
constraints on the enrichment sources from galactic archaeology surveys.",1403.1796v1
2014-03-07,Iron based high transition temperature superconductors,"In a superconductor electrons form pairs and electric transport becomes
dissipation-less at low temperatures. Recently discovered iron based
superconductors have the highest superconducting transition temperature next to
copper oxides. In this article, we review material aspects and physical
properties of iron based superconductors. We discuss the dependence of
transition temperature on the crystal structure, the interplay between
antiferromagnetism and superconductivity by examining neutron scattering
experiments, and the electronic properties of these compounds obtained by angle
resolved photoemission spectroscopy in link with some results from scanning
tunneling microscopy/spectroscopy measurements. Possible microscopic model for
this class of compounds is discussed from a strong coupling point of view.",1403.2612v1
2014-03-24,Majorana edge states and topological properties in 1D/2D Rashba semiconductor proximity coupled to iron-based superconductor,"We study Majorana edge states and their topological properties of
one-dimensional(1D) and two-dimensional(2D) Rashba semiconductor deposited on
iron-based superconductor under the applied Zeeman field for various
directions. Using the recursive Green's function method, we calculate the local
density of states(LDOS) both for $s_{\pm}$ and $s_{++}$-wave pairings. We
elucidate that it shows anisotropic response to the applied Zeeman field
specific to Majorana edge states. This anisotropy can be understood by the
winding number, which shows whether the present system is topological or not.
The resulting LDOS and winding numbers for $s_{\pm}$ and $s_{++}$-wave pairings
are significantly different at the lower Zeeman field. These results serve as a
guide to determine the pairing symmetry of iron-pnictide.",1403.5857v2
2014-03-25,Electronic correlations determine the phase stability of iron up to the melting temperature,"We present theoretical results on the high-temperature phase stability and
phonon spectra of paramagnetic bcc iron which explicitly take into account
many-body effects. Several peculiarities, including a pronounced softening of
the [110] transverse (T$_1$) mode and a dynamical instability of the bcc
lattice in harmonic approximation are identified. We relate these features to
the ${\alpha}$-to-${\gamma}$ and ${\gamma}$-to-${\delta}$ phase transformations
in iron. The high-temperature bcc phase is found to be highly anharmonic and
appears to be stabilized by the lattice entropy.",1403.6497v1
2014-04-24,A Tentative Size-Luminosity Relation for the Iron Emission-Line Region in Quasars,"New reverberation mapping measurements of the size of the optical iron
emission-line region in quasars are provided, and a tentative size-luminosity
relation for this component is reported. Combined with lag measurements in
low-luminosity sources, the results imply an emission-region size that is
comparable to and at most twice that of the H$\beta$ line, and is characterized
by a similar luminosity dependence. This suggests that the physics underlying
the formation of the optical iron blends in quasars may be similar to that of
other broad emission lines.",1404.6142v1
2014-05-14,"Observations of MCG-5-23-16 with Suzaku, XMM-Newton and NuSTAR: Disk tomography and Compton hump reverberation","MCG-5-23-16 is one of the first AGN where relativistic reverberation in the
iron K line originating in the vicinity of the supermassive black hole was
found, based on a short XMM-Newton observation. In this work, we present the
results from long X-ray observations using Suzaku, XMM-Newton and NuSTAR
designed to map the emission region using X-ray reverberation. A relativistic
iron line is detected in the lag spectra on three different time-scales,
allowing the emission from different regions around the black hole to be
separated. Using NuSTAR coverage of energies above 10 keV reveals a lag between
these energies and the primary continuum, which is detected for the first time
in an AGN. This lag is a result of the Compton reflection hump responding to
changes in the primary source in a manner similar to the response of the
relativistic iron K line.",1405.3674v1
2014-05-22,Intrinsic Josephson junctions in the iron-based multi-band superconductor (V2Sr4O6)Fe2As2,"In layered superconductors, Josephson junctions may be formed within the unit
cell due to sufficiently low interlayer coupling. These intrinsic Josephson
junction (iJJ) systems have attracted considerable interest for their
application potential in quantum computing as well as efficient sources of THz
radiation, closing the famous ""THz gap"". So far, iJJ have been demonstrated in
single-band, copper-based high-Tc superconductors, mainly in Ba-Sr-Ca-Cu-O.
Here we report clear experimental evidence for iJJ behavior in the iron-based
superconductor (V2Sr4O6)Fe2As2. The intrinsic junctions are identified by
periodic oscillations of the flux flow voltage upon increasing a well aligned
in-plane magnetic field. The periodicity is well explained by commensurability
effects between the Josephson vortex lattice and the crystal structure, which
is a hallmark signature of Josephson vortices confined into iJJ stacks. This
finding adds (V2Sr4O6)Fe2As2 as the first iron-based, multi-band superconductor
to the copper-based iJJ materials of interest for Josephson junction
applications, and in particular novel devices based on multi-band Josephson
coupling may be realized.",1405.5693v1
2014-05-27,Disorder-induced topological change of the superconducting gap structure in iron pnictides,"In superconductors with unconventional pairing mechanisms, the energy gap in
the excitation spectrum often has nodes, which allow quasiparticle excitations
at low energies. In many cases, e.g. $d$-wave cuprate superconductors, the
position and topology of nodes are imposed by the symmetry, and thus the
presence of gapless excitations is protected against disorder. Here we report
on the observation of distinct changes in the gap structure of iron-pnictide
superconductors with increasing impurity scattering. By the successive
introduction of nonmagnetic point defects into BaFe$_2$(As$_{1-x}$P$_x$)$_2$
crystals via electron irradiation, we find from the low-temperature penetration
depth measurements that the nodal state changes to a nodeless state with fully
gapped excitations. Moreover, under further irradiation the gapped state
evolves into another gapless state, providing bulk evidence of unconventional
sign-changing $s$-wave superconductivity. This demonstrates that the topology
of the superconducting gap can be controlled by disorder, which is a strikingly
unique feature of iron pnictides.",1405.6951v2
2014-06-03,Magnetic spectra in the tridiminished-icosahedron \{Fe$_9$\} nano-cluster by inelastic neutron scattering,"Inelastic neutron scattering (INS) experiments under applied magnetic field
at low temperatures show detailed low lying magnetic excitations in the so
called tridiminshed iron icosahedron magnetic molecule. The magnetic molecule
consists of nine iron Fe$^{3+}$ ($s = 5/2$) and three phosphorous atoms that
are situated on the twelve vertices of a nearly perfect icosahedron. The three
phosphorous atoms form a plane that separates the iron cluster into two weakly
coupled three- and six-ion fragments, \{Fe$_3$\} and \{Fe$_6$\}, respectively.
The magnetic field INS results exhibit an $S=1/2$ ground state expected from a
perfect equilateral triangle of the \{Fe$_3$\} triad with a powder averaged
$g$-value $=2.00$. Two sets of triplet excitations whose temperature and
magnetic field dependence indicate an $S=0$ ground state with two
non-degenerate $S=1$ states are attributed to the \{Fe$_6$\} fragment. The
splitting may result from a finite coupling between the two fragments,
single-ion anisotropy, antisymmetric exchange couplings, or from magnetic
frustration of its triangular building blocks.",1406.0889v1
2014-06-19,Magnetic and Ising quantum phase transitions in a model for isoelectronically tuned iron pnictides,"Considerations of the bad-metal behavior led to an early proposal for a
quantum critical point under a P for As doping in the iron pnictides, which has
since been experimentally observed. We study here an effective model for the
isoelectronically tuned pnictides using a large-$N$ approach. The model
contains antiferromagnetic and Ising-nematic order parameters appropriate for
$J_1$-$J_2$ exchange-coupled local moments on an Fe square lattice, and a
damping caused by coherent itinerant electrons. The zero-temperature magnetic
and Ising transitions are concurrent and essentially continuous. The
order-parameter jumps are very small, and are further reduced by the
inter-plane coupling; quantum criticality hence occurs over a wide dynamical
range. Our results provide the basis for further studies on the quantum
critical properties in the P-doped iron arsenides.",1406.5136v2
2014-06-30,Laboratories of Oligarchy? How the Iron Law Extends to Peer Production,"Peer production projects like Wikipedia have inspired voluntary associations,
collectives, social movements, and scholars to embrace open online
collaboration as a model of democratic organization. However, many peer
production projects exhibit entrenched leadership and deep inequalities,
suggesting that they may not fulfill democratic ideals. Instead, peer
production projects may conform to Robert Michels' ""iron law of oligarchy,""
which proposes that democratic membership organizations become increasingly
oligarchic as they grow. Using exhaustive data of internal processes from a
sample of 683 wikis, we construct empirical measures of participation and test
for increases in oligarchy associated with growth. In contrast to previous
studies, we find support for Michels' iron law and conclude that peer
production entails oligarchic organizational forms.",1407.0323v1
2014-07-05,Nematic state stabilized by off-site Coulomb interaction in iron-based superconductors,"Using a variational Monte Carlo method, we investigate the nematic state in
iron-base superconductors based on a three-band Hubbard model. Our results
demonstrate that the nematic state, formed by introducing an anisotropic
hopping order into the projected wave function, can arise in the underdoped
regime when a realistic off-site Coulomb interaction $V$ is considered. {\color
{red} We demonstrate that the off-site Coulomb interaction $V$, which is
neglected so far in the analysis of iron-base superconductors, make a dominant
contribution to the stabilization of nematic state. We calculate the doping
dependencies of the anisotropic properties such as the unequal occupation of
$d_{xz}$ and $d_{yz}$ orbitals, anisotropies of kinetic energy and spin
correlations, and show that they are all suppressed upon electron doping, which
are consistent with the intrinsic anisotropies observed by optical spectrum
measurement and ARPES experiments.",1407.1411v1
2014-07-25,"Correlation, doping and interband effects on the optical conductivity of iron superconductors","Electronic interactions in multiorbital systems lead to non-trivial features
in the optical spectrum. In iron superconductors the Drude weight is strongly
suppressed with hole-doping. We discuss why the common association of the
renormalization of the Drude weight with that of the kinetic energy, used in
single band systems, does not hold in multi-orbital systems. This applies even
in a Fermi liquid description when each orbital is renormalized differently, as
it happens in iron superconductors. We estimate the contribution of interband
transitions at low energies. We show that this contribution is strongly
enhanced by interactions and dominates the coherent part of the spectral weight
in hole-doped samples at frequencies currently used to determine the Drude
weight.",1407.6935v2
2014-07-31,Superconducting Gap and Symmetry in FeSe_1-x_Te_x_ Studied by Specific Heat in Magnetic Fields,"In order to investigate details of the superconducting (SC) gap in the
iron-chalcogenide superconductors, the specific heat, C, of FeSe_1-x_Te_x_ with
x=0.6-1 has been measured in magnetic fields. Using the two-gap model, it has
been found that the smaller SC gap is significantly depressed by the
application of magnetic field, resulting in the increase of the slope of the
C/T vs T^2^ plot at low temperatures. From the specific-heat measurements at
very low temperatures down to 0.4 K, it has been found that the enhancement of
the residual electronic-specific-heat-coefficient in the ground state,
gamma_0_, by the application of magnetic field is much smaller than that
expected for superconductors with the typical s-wave or d-wave SC paring
symmetry, which is in sharp contrast to the significant enhancement of gamma_0
observed in the iron-pnictide superconductors. These results are discussed in
relation to the multi-band effect in the iron-based superconductors.",1407.8266v1
2014-08-01,Charge-Stripe Order in a Parent Compound of Iron-based Superconductors,"Charge ordering is one of the most intriguing and extensively studied
phenomena in correlated electronic materials because of its strong impact on
electron transport properties including superconductivity. Despite its
ubiquitousness in correlated systems, the occurrence of charge ordering in
iron-based superconductors is still unresolved. Here we use scanning tunneling
microscopy to reveal a long-range charge-stripe order and a highly anisotropic
dispersion of electronic states in the ground state of stoichiometric FeTe, the
parent compound of the Fe(Te, Se, S) superconductor family. The formation of
charge order in a strongly correlated electron system with integer nominal
valence (here Fe$^{2+}$) is unexpected and suggests that the iron-based
superconductors may exhibit more complex charge dynamics than originally
expected. We show that the present observations can be attributed to the
surpassing of the role of local Coulomb interaction by the poorly screened
longer-range Coulomb interactions, facilitated by large Hund's rule coupling.",1408.0057v1
2014-08-06,Orbital Nematic Order and Interplay with Magnetism in the Two-Orbital Hubbard Model,"Motivated by the recent angle-resolved photoemission spectroscopy (ARPES) on
FeSe and iron pnictide families of iron-based superconductors, we have studied
the orbital nematic order and its interplay with antiferromagnetism within the
two-orbital Hubbard model. We used random phase approximation (RPA) to
calculate the dependence of the orbital and magnetic susceptibilities on the
strength of interactions and electron density (doping). To account for strong
electron correlations not captured by RPA, we further employed non-perturbative
variational cluster approximation (VCA) capable of capturing symmetry broken
magnetic and orbitally ordered phases. Both approaches show that the electron
and hole doping affect the two orders differently. While hole doping tends to
suppress both magnetism and orbital ordering, the electron doping suppresses
magnetism faster. Crucially, we find a realistic parameter regime for moderate
electron doping that stabilizes orbital nematicity in the absence of long-range
antiferromagnetic order. This is reminiscent of the non-magnetic orbital
nematic phase observed recently in FeSe and a number of iron pnictide materials
and raises the possibility that at least in some cases, the observed electronic
nematicity may be primarily due to orbital rather than magnetic fluctuations.",1408.1408v2
2014-08-27,Tunable Band gap of Iron-Doped Lanthanum-Modified Bismuth Titanate Synthesized by the Thermal Decomposition of a Secondary Phase,"The photoelectric properties of complex oxides have prompted interest in
materials with a tunable band gap, because the absorption The substitution of
iron atoms in La-modified bismuth titanate (BLT) can lead to dramatic
improvements in the band gap, however, the substitution of iron atoms in BLT
without forming a BiFeO3 secondary phase is quite challenging. Therefore, a
series of Fe-doped BLT (Fe-BLT) samples were characterized using a solid
reaction at various calcination temperatures (300~900{\deg}C) to remove the
secondary phase. The structural and optical properties were analyzed by X-ray
diffraction and ultraviolet-visible absorption spectroscopy. This paper reports
a new route to synthesize a pure Fe-BLT phase with a reduced optical band gap
by high temperature calcination due to the thermal decomposition of BiFeO3
during high temperature calcination. This simple route to reduce the second
phase can be adapted to other complex oxides for use in emerging oxide
optoelectronic devices.",1408.6294v1
2014-08-28,Persistent detwinning of iron pnictides by small magnetic fields,"Our comprehensive study on EuFe$_2$As$_2$ reveals a dramatic reduction of
magnetic detwinning fields compared to other AFe$_2$As$_2$ (A = Ba, Sr, Ca)
iron pnictides by indirect magneto-elastic coupling of the Eu$^{2+}$ ions. We
find that only 0.1T are sufficient for persistent detwinning below the local
Eu$^{2+}$ ordering; above $T_\text{Eu}$ = 19K, higher fields are necessary.
Even after the field is switched off, a significant imbalance of twin domains
remains constant up to the structural and electronic phase transition (190K).
This persistent detwinning provides the unique possibility to study the low
temperature electronic in-plane anisotropy of iron pnictides without applying
any symmetrybreaking external force.",1408.6666v1
2014-09-05,Electronic structure and Fermi surface of iron-based superconductors R2Fe3Si5 (R = Lu;Y;Sc) from first principles,"Electronic structures of three superconducting rare-earth iron silicides
(Lu;Y;Sc)2Fe3Si5 and non-superconducting Lu2Ru3Si5, adopting a tetragonal
crystal structure (P4/mnc), have been calculated employing the full-potential
local-orbital method within the density functional theory. The investigations
were focused particularly on the band structures and Fermi surfaces, existing
in four bands and containing rather three-dimensional electronlike and holelike
sheets. They support an idea of unconventional multi-band superconductivity in
these ternaries, proposed earlier by other authors for Lu2Fe3Si5, based on
heat-capacity, resistivity, electromagnetic and muon spin rotation
measurements. Finally, a discussion on differences in the electronic structures
between the investigated here and other common families of iron-based
superconductors is carried out.",1409.1870v1
2014-09-17,Depth of Maximum of Air-Shower Profiles at the Pierre Auger Observatory: Composition Implications,"Using the data taken at the Pierre Auger Observatory between December 2004
and December 2012, we have examined the implications of the distributions of
depths of atmospheric shower maximum (Xmax), using a hybrid technique, for
composition and hadronic interaction models. We do this by fitting the
distributions with predictions from a variety of hadronic interaction models
for variations in the composition of the primary cosmic rays and examining the
quality of the fit. Regardless of what interaction model is assumed, we find
that our data are not well described by a mix of protons and iron nuclei over
most of the energy range. Acceptable fits can be obtained when intermediate
masses are included, and when this is done consistent results for the proton
and iron-nuclei contributions can be found using the available models. We
observe a strong energy dependence of the resulting proton fractions, and find
no support from any of the models for a significant contribution from iron
nuclei. However, we also observe a significant disagreement between the models
with respect to the relative contributions of the intermediate components.",1409.5083v1
2014-09-21,Quantum oscillations and upper critical magnetic field of the iron-based superconductor FeSe,"Shubnikov-de Haas (SdH) oscillations and upper critical magnetic field
($H\_{c2}$) of the iron-based superconductor FeSe ($T\_c$ = 8.6 K) have been
studied by tunnel diode oscillator-based measurements in magnetic fields of up
to 55 T and temperatures down to 1.6 K. Several Fourier components enter the
SdH oscillations spectrum with frequencies definitely smaller than predicted by
band structure calculations indicating band renormalization and reconstruction
of the Fermi surface at low temperature, in line with previous ARPES data. The
Werthamer-Helfand-Hohenberg model accounts for the temperature dependence of
$H\_{c2}$ for magnetic field applied both parallel (\textbf{H} $\|$ $ab$) and
perpendicular (\textbf{H} $\|$ $c$) to the iron conducting plane, suggesting
that one band mainly controls the superconducting properties in magnetic fields
despite the multiband nature of the Fermi surface. Whereas Pauli pair breaking
is negligible for \textbf{H} $\|$ $c$, a Pauli paramagnetic contribution is
evidenced for \textbf{H} $\|$ $ab$ with Maki parameter $\alpha$ = 2.1,
corresponding to Pauli field $H\_{P}$ = 36.5 T",1409.6003v2
2014-10-03,CuFeAs: A New Member in the 111-Family of Iron-Pnictides,"We have synthesized CuFeAs, a new iron-pnictide compound with a layered
tetragonal Cu2Sb type structure (space group P4/nmm: a = b = 3.7442(2) {\AA}
and c = 5.8925(4) {\AA}) that is identical to that of 111-type iron-based
superconductors. Our measurements suggest that in low applied magnetic field it
undergoes an antiferromagnetic transition below TN ~ 9 K. When compared with
the ground state of CuFeSb, recently reported 111-type ferromagnetic material
(TC ~ 375 K), it has important implication with regard to the nature of Fe-Fe
magnetic interaction in Fe-As materials. CuFeAs does not exhibit
superconductivity down to 2 K.",1410.0805v1
2014-10-09,Pair breaking due to orbital magnetism in iron-based superconductors,"We consider superconductivity in the presence of impurities in a two-band
model suited for the description of iron-based superconductors. We analyze the
effect of interband scattering processes on superconductivity, allowing for
orbital, i.e., nonspin-magnetic but time-reversal symmetry-breaking impurities.
Pair breaking in such systems is described by a nontrivial phase in an
interband-scattering matrix element. We find that the transition temperature of
conventional superconductors can be suppressed due to interband scattering,
whereas unconventional superconductors may be unaffected. We also discuss the
stability of density wave phases in the presence of impurities. As an example,
we consider impurities associated with imaginary charge density waves that are
of interest for iron-based superconductors.",1410.2555v2
2014-10-29,Effective Exchange Interactions for Bad Metals and Implications for Iron-based Superconductors,"The experimentally observed bad metal behavior in parent iron pnictides and
chalcogenides suggests that these systems contain strong electronic
correlations and are on the verge of a metal-to-insulator transition. The
magnetic excitations in this bad-metal regime mainly derive from the incoherent
part of the electronic spectrum away from the Fermi energy. We present a
microscopic study of the exchange interactions in such a regime within a slave
rotor approach. We find that the exchange interaction is maximized near the
Mott transition. Generalizations to the multi-orbital case are discussed, as
are the implications for the strength of superconducting pairing amplitude in
the iron-based superconductors.",1410.8118v2
2014-10-30,Spin-orbital interplay and topology in the nematic phase of iron pnictides,"The origin of the nematic state is an important puzzle to be solved in iron
pnictides. Iron superconductors are multiorbital systems and these orbitals
play an important role at low energy. The singular $C_4$ symmetry of $d_{zx}$
and $d_{yz}$ orbitals has a profound influence at the Fermi surface since the
$\Gamma$ pocket has vortex structure in the orbital space and the X/Y electron
pockets have $yz$/$zx$ components respectively. We propose a low energy theory
for the spin--nematic model derived from a multiorbital Hamiltonian. In the
standard spin--nematic scenario the ellipticity of the electron pockets is a
necessary condition for nematicity. In the present model nematicity is
essentially due to the singular $C_4$ symmetry of $yz$ and $zx$ orbitals. By
analyzing the ($\pi, 0$) spin susceptibility in the nematic phase we find
spontaneous generation of orbital splitting extending previous calculations in
the magnetic phase. We also find that the ($\pi, 0$) spin susceptibility has an
intrinsic anisotropic momentum dependence due to the non trivial topology of
the $\Gamma$ pocket.",1410.8488v4
2014-11-26,Electronic and Magnetic Properties of the New Iron -- Based Superconductor [Li$_{1-x}$Fe$_x$OH]FeSe,"We present the results of paramagnetic LDA band structure calculations: band
dispersions, densities of states and Fermi surfaces, for the new iron based
high-temperature superconductor LiOHFeSe. Main structural motif providing bands
in the vicinity of the Fermi level is FeSe layer which is isostructural to the
bulk FeSe prototype superconductor. The bands crossing the Fermi level and
Fermi surfaces of the new compound are typical for other iron based
superconductors. Experimentally it was shown that introduction of Fe ions into
LiOH layer gives rise to ferromagnetic ordering of the Fe ions at T$_C$=10K. To
study magnetic properties of [Li$_{0.8}$Fe$_{0.2}$OH]FeSe system we have
performed LSDA calculations for $\sqrt 5 \times \sqrt 5$ superlattice and found
ferromagnetism within the Li$_4$Fe(OH) layer. To estimate the Curie temperature
we obtained Fe-Fe exchange interaction parameters for Heisenberg model from our
LSDA calculations, leading to theoretical value of Curie temperature 10.4K in
close agreement with experiment.",1411.7194v1
2014-11-27,The critical dynamics of the models of iron-vanadium magnetic superlattice,"We report the results of a numerical investigation of static and dynamic
critical behavior of the anisotropic easy-plane Heisenberg model which is used
as a model for iron-vanadium magnetic superlattices. Models of iron-vanadium
magnetic superlattice investigated with different values of intralayer and
interlayer exchange interactions ratio. Numerical experiment technique, based
on the dynamic finite-size scaling theory. Basic features of the time evolution
of dynamic parameters for the researched systems are studied. The effect of
interlayer exchange interaction value on a character of the critical dynamics
is determined. It is confirmed the possibility of application of the
Hamiltonian with strong easy-plane anisotropy for investigation both static and
dynamic critical behavior of complex planar magnetic models.",1411.7509v1
2014-12-22,"Interplay between tetragonal magnetic order, stripe magnetism, and superconductivity in iron-based materials","Motivated by recent experiments in Ba$_{1-x}$K$_{x}$Fe$_{2}$As$_{2}$ {[}A. E.
B\""ohmer \textit{et al}, to be published{]}, we analyze the type of
spin-density wave (SDW) order in doped iron-pnictides and the discontinuities
of the superconducting transition temperature $T_{c}$ in the coexistence phase
with SDW magnetism. By tracking the magnetic transition line $T_{N}(x)$ towards
optimal doping within an itinerant fermionic model, we find a sequence of
transitions from the stripe-orthorhombic ($C_{2}$) SDW order to the tetragonal
($C_{4}$) order and then back to the $C_{2}$ order. We argue that the
superconducting $T_{c}$ has two discontinuities -- it jumps to a smaller value
upon entering the coexistence region with the $C_{4}$ magnetic phase, and then
jumps to a larger value inside the SDW state when it crosses the boundary
between the $C_{4}$ and $C_{2}$ SDW orders. The full agreement with the
experimental phase diagram provides a strong indication that the itinerant
approach is adequate to describe the physics of weakly/moderately doped
iron-pnictides.",1412.7079v2
2015-01-07,Structure of superoxide reductase bound to ferrocyanide and active site expansion upon X-ray-induced photo-reduction,"Some sulfate-reducing and microaerophilic bacteria rely on the enzyme
superoxide reductase (SOR) to eliminate the toxic superoxide anion radical
(O2*-). SOR catalyses the one-electron reduction of O2*- to hydrogen peroxide
at a nonheme ferrous iron center. The structures of Desulfoarculus baarsii SOR
(mutant E47A) alone and in complex with ferrocyanide were solved to 1.15 and
1.7 A resolution, respectively. The latter structure, the first ever reported
of a complex between ferrocyanide and a protein, reveals that this
organo-metallic compound entirely plugs the SOR active site, coordinating the
active iron through a bent cyano bridge. The subtle structural differences
between the mixed-valence and the fully reduced SOR-ferrocyanide adducts were
investigated by taking advantage of the photoelectrons induced by X-rays. The
results reveal that photo-reduction from Fe(III) to Fe(II) of the iron center,
a very rapid process under a powerful synchrotron beam, induces an expansion of
the SOR active site.",1501.01472v1
2015-01-29,"Link between local iron coordination, Fe 2p XPS core level line shape and Mg segregation into thin magnetite films grown on MgO(001)","A well ordered Fe(001) ultra thin film epitaxially grown on MgO(001) has been
oxidized by post deposition annealing in oxygen atmosphere. LEED patterns
indicate the formation of magnetite (Fe$_3$O$_4$) after one hour of oxygen
exposure. The LEED pattern remains stable despite annealing the sample for
further four hours. In contrast X-ray Photoelectron Spectroscopy (XPS) of the
Fe $2p$ core levels suggests the formation of an iron oxide comprising mostly
of merely trivalent iron. This discrepancy is analyzed and discussed employing
charge transfer multiplet calculations for the Fe $2p$ XPS spectra. We find
that Mg ion segregation from the substrate into the magnetite thin film
replacing octahedrally coordinated Fe$^{2+}$ ions and the excess occupation of
octahedral sites which are unoccupied in the ideal inverse spinel structure are
driving forces for the altered shape of the Fe $2p$ XPS spectra. Different
potential models which might explain the nature of the Mg ion segregation into
the magnetite films are discussed.",1501.07443v1
2015-02-04,Disordered Fe vacancies and superconductivity in potassium-intercalated iron selenide (K2-xFe4+ySe5),"The parent compound of an unconventional superconductor must contain unusual
correlated electronic and magnetic properties of its own. In the high-Tc
potassium intercalated FeSe, there has been significant debate regarding what
the exact parent compound is. Our studies unambiguously show that the
Fe-vacancy ordered K2Fe4Se5 is the magnetic, Mott insulating parent compound of
the superconducting state. Non-superconducting K2Fe4Se5 becomes a
superconductor after high temperature annealing, and the overall picture
indicates that superconductivity in K2-xFe4+ySe5 originates from the Fe-vacancy
order to disorder transition. Thus, the long pending question whether magnetic
and superconducting state are competing or cooperating for cuprate
superconductors may also apply to the Fe-chalcogenide superconductors. It is
believed that the iron selenides and related compounds will provide essential
information to understand the origin of superconductivity in the iron-based
superconductors, and possibly to the superconducting cuprates.",1502.01116v2
2015-02-09,[NiFe] dithiolene diphosphine complex for hydrogen gas activation: a Theoretic Insight,"A diphosphino-nickel-iron dithiolene complex, [Ni(bdt)(dppf)] (bdt =
1,2-benzenedithiolate, dppf = 1,1-bis(diphenylphosphino)ferrocene), has been
recently found to be reasonably active on proton reduction to dihydrogen (J.
Am. Chem. Soc. 2015, 137, 1109). Interestingly, this exceptional complex was
found to be also reactive towards dihydrogen activation as indicated by the
electrochemical investigation. However, a pure nickel dithiolene diphosphine
theoretical mode, excluding the contributions from iron moiety, was applied to
attribute the experimental catalytic observation. We have re-visited the
theoretical approach in details for this [NiFe] catalyst and compared it with
the non-active nickel dithiolene diphosphine complexes. We found that both
nickel and iron moieties in this newly developed complex were imperative for
the observed catalytic per-formance, particularly towards the activation of
dihydrogen.",1502.02706v1
2015-02-18,Theoretical study on the correlation between the spin fluctuation and $T_c$ in the isovalent-doped 1111 iron-based superconductors,"Motivated by recent experiments on isovalent-doped 1111 iron-based
superconductors LaFeAs$_{1-{x}}$P$_{x}$O$_{1-{y}}$F$_{y}$ and the theoretical
study that followed, we investigate, within the five orbital model, the
correlation between the spin fluctuation and the superconducting transition
temperature, which exhibits a double dome feature upon varying the Fe-As-Fe
bond angle. Around the first dome with higher $T_c$, the low energy spin
fluctuation and $T_c$ are not tightly correlated because the finite energy spin
fluctuation also contributes to superconductivity. On the other hand, the
strength of the low-energy spin fluctuation originating from the $d_{xz/yz}$
orbital is correlated with $T_c$ in the second dome with lower $T_c$. These
calculation results are consistent with recent NMR study, and hence strongly
suggest that the pairing in the iron-based superconductors is predominantly
caused by the multi-orbital spin fluctuation.",1502.05144v1
2015-03-07,The Three Dimensional Evolution to Core Collapse of a Massive Star,"We present the first three dimensional (3D) simulation of the final minutes
of iron core growth in a massive star, up to and including the point of core
gravitational instability and collapse. We self-consistently capture the
development of strong convection driven by violent Si burning in the shell
surrounding the iron core. This convective burning builds the iron core to its
critical (Chandrasekhar) mass and collapse ensues, driven by electron capture
and photodisintegration. The non-spherical structure and motion (turbulent
fluctuations) generated by 3D convection is substantial at the point of
collapse. We examine the impact of such physically-realistic 3D initial
conditions on the core-collapse supernova mechanism using 3D simulations
including multispecies neutrino leakage. We conclude that non-spherical
progenitor structure should not be ignored, and has a significant and favorable
impact on the likelihood for neutrino-driven explosions.",1503.02199v2
2015-03-13,Magnetic interactions in iron superconductors: A review,"High temperature superconductivity in iron pnictides and chalcogenides
emerges when a magnetic phase is suppressed. The multi-orbital character and
the strength of correlations underlie this complex phenomenology, involving
magnetic softness and anisotropies, with Hund's coupling playing an important
role. We review here the different theoretical approaches used to describe the
magnetic interactions in these systems. We show that taking into account the
orbital degree of freedom allows us to unify in a single phase diagram the main
mechanisms proposed to explain the (\pi,0) order in iron pnictides: the
nesting-driven, the exchange between localized spins, and the Hund induced
magnetic state with orbital differentiation. Comparison of theoretical
estimates and experimental results helps locate the Fe superconductors in the
phase diagram. In addition, orbital physics is crucial to address the magnetic
softness, the doping dependent properties, and the anisotropies.",1503.04223v2
2015-03-30,Magnon contribution to the magnetoresistance of iron nanowires deposited using pulsed electrodeposition,"Iron nanowires with a square cross section are grown by pulsed
electrodeposition within a newly developed nanochannel template that allows for
easy characterization. Measurements of the magnetoresistance as a function of
magnetic field and temperature are performed within a large parameter window
allowing for the investigation of the magnonic contribution to the
magnetoresistance of electrodeposited iron nanowires. Values for the
temperature dependent magnon stiffness D(T) are extracted.",1503.08595v1
2015-04-17,Nematic resonance in the Raman response of iron-based superconductors,"In a fully-gapped superconductor the electronic Raman response has a
pair-breaking peak at twice the superconducting gap $\Delta$, if the Bogoliubov
excitations are uncorrelated. Motivated by the iron based superconductors, we
study how this peak is modified if the superconducting phase hosts a
nematic-structural quantum critical point. We show that, upon approaching this
point by tuning, e.g., doping, the growth of nematic correlations between the
quasiparticles transforms the pair-breaking peak into a nematic resonance. The
mode energy is below 2$\Delta$, and stays finite at the quantum critical point,
where its spectral weight is sharply enhanced. The latter is consistent with
recent experiments on electron-doped iron based superconductors and provides
direct evidence of nematic correlations in their superconducting phases.",1504.04570v2
2015-05-03,The Role of Temperature and Magnetic Effects on the Stacking-fault Energy in Austenitic Iron,"We have investigated the role of temperature and magnetic effects on the
stacking-fault energy (SFE) in pure austenitic iron based on Density Functional
Theory (DFT) calculations. Using the axial next-nearest-neighbor Ising (ANNNI)
model, the SFE is expanded in terms of the free energiesof bulk with
face-centered cubic (fcc), hexagonal close-packed (hcp), and double-hcp (dhcp)
structures. The free-energy calculations require the lattice constant and the
local magnetic moments at various temperatures. The earlier is obtained from
the available experimental data, while the later is calculated by accounting
for the thermal magnetic excitations using the Monte-Carlo tech- niques. Our
results demonstrate a strong dependence of the SFE on the magnetic effects in
pure iron. Moreover, we found that the SFE increases with temperature.",1505.00431v2
2015-05-14,Ab initio Studies of Magnetism in the Iron Chalcogenides FeTe and FeSe,"The iron chalcogenides FeTe and FeSe belong to the family of iron-based
superconductors. We study the magnetism in these compounds in the normal state
using the ab initio downfolding scheme developed for strongly correlated
electron systems. In deriving ab initio low-energy effective models, we employ
the constrained GW method to eliminate the double counting of electron
correlations originating from the exchange correlations already taken into
account in the density functional theory. By solving the derived ab initio
effective models, we reveal that the elimination of the double counting is
important in reproducing the bicollinear antiferromagnetic order in FeTe, as is
observed in experiments. We also show that the elimination of the double
counting induces a unique degeneracy of several magnetic orders in FeSe, which
may explain the absence of the magnetic ordering. We discuss the relationship
between the degeneracy and the recently found puzzling phenomena in FeSe as
well as the magnetic ordering found under pressure.",1505.03730v2
2015-07-07,The most iron-deficient stars as the polluted population III stars,"We investigate the origin of the most iron-poor stars including SMSS
J031300.36-670839.3 with [Fe/H] < -7.52. We compute the change of surface
metallicity of stars with the accretion of interstellar matter (ISM) after
their birth using the chemical evolution model within the framework of the
hierarchical galaxy formation. The predicted metallicity distribution function
agrees very well with that observed from extremely metal-poor stars. In
particular, the lowest metallicity tail is well reproduced by the Population
III stars whose surfaces are polluted with metals through ISM accretion. This
suggests that the origin of iron group elements is explained by ISM accretion
for the stars with [Fe/H]$\lesssim -5$. The present results give new insights
into the nature of the most metal-poor stars and the search for Population III
stars with pristine abundances.",1507.01664v1
2015-07-20,Electronic nematic correlations in the stress free tetragonal state of BaFe$_{2-x}$Ni$_{x}$As$_{2}$,"We use transport and neutron scattering to study electronic, structural, and
magnetic properties of the electron-doped BaFe$_{2-x}$Ni$_x$As$_2$ iron
pnictides in the external stress free detwinned state. Using a specially
designed in-situ mechanical detwinning device, we demonstrate that the in-plane
resistivity anisotropy observed in the uniaxial strained tetragonal state of
BaFe$_{2-x}$Ni$_x$As$_2$ below a temperature $T^\ast$, previously identified as
a signature of the electronic nematic phase, is also present in the stress free
tetragonal phase below $T^{\ast\ast}$ ($<T^\ast$). By carrying out neutron
scattering measurements on BaFe$_2$As$_2$ and BaFe$_{1.97}$Ni$_{0.03}$As$_2$,
we argue that the resistivity anisotropy in the stress free tetragonal state of
iron pnictides arises from the magnetoelastic coupling associated with
antiferromagnetic order. These results thus indicate that the local lattice
distortion and nematic spin correlations are responsible for the resistivity
anisotropy in the tetragonal state of iron pnictides.",1507.05423v1
2015-07-21,Ab initio downfolding study of the iron-based ladder superconductor BaFe$_2$S$_3$,"Motivated by the recent discovery of superconductivity in the iron-based
ladder compound BaFe$_2$S$_3$ under high pressure, we derive low-energy
effective Hamiltonians from first principles. We show that the complex band
structure around the Fermi level is represented only by the Fe 3$d_{xz}$ (mixed
with 3$d_{xy}$) and 3$d_{x^2-y^2}$ orbitals. The characteristic band degeneracy
allows us to construct a four-band model with the band unfolding approach. We
also estimate the interaction parameters and show that the system is more
correlated than the 1111 family of iron-based superconductors. Provided the
superconductivity is mediated by spin fluctuations, the $3d_{xz}$-like band
plays an essential role, and the gap function changes its sign between the
Fermi surface around the $\Gamma$ point and that around the Brillouin-zone
boundary.",1507.05715v2
2015-07-22,The Effects of Stoichiometry and Substitution in quasi-one-dimensional iron-chalcogenide BaFe$_{2}$S$_{3}$,"The effects of off-stoichiometry and elemental substitution on electronic
properties of iron-based ladder compound BaFe$_{2}$S$_{3}$ are investigated.
Resistivity and magnetization are revealed to be quite sensitive to the
stoichiometry of Fe atoms, and 10 \% deficiency at Fe sites reduces the
antiferromagnetic transition temperature by 40 K. The antiferromagnetic
transition temperature decreases even faster and collapse to zero with hole
doping through 10 \% K substitution at Ba site, while the antiferromagnetic
ordering phase remains with electron doping through 20 \% Co substitution at Fe
site. Such electron-hole asymmetry is opposite to two-dimensional iron-based
superconductors, and can be explained on the basis of both itinerant and
localized electronic pictures.",1507.06047v1
2015-07-29,"Constraining planet structure from stellar chemistry: the cases of CoRoT-7, Kepler-10, and Kepler-93","We explore the possibility that the stellar relative abundances of different
species can be used to constrain the bulk abundances of known transiting rocky
planets. We use high resolution spectra to derive stellar parameters and
chemical abundances for Fe, Si, Mg, O, and C in three stars hosting low mass,
rocky planets: CoRoT-7, Kepler-10, and Kepler-93. These planets follow the same
line along the mass-radius diagram, pointing toward a similar composition. The
derived abundance ratios are compared with the solar values. With a simple
stoichiometric model, we estimate the iron mass fraction in each planet,
assuming stellar composition. We show that in all cases, the iron mass fraction
inferred from the mass-radius relationship seems to be in good agreement with
the iron abundance derived from the host star's photospheric composition. The
results suggest that stellar abundances can be used to add constraints on the
composition of orbiting rocky planets.",1507.08081v1
2015-07-31,Elastic Properties of FeC and FeN Martensites,"Single crystal elastic constants of bcc iron and bct FeC and FeN alloys,
martensites, have been evaluated by ab initio calculations based on the density
functional theory. The energy of a strained crystal has been computed using the
supercell method at several values of the strain intensity, and the stiffness
coefficient has been determined from the slope of the energy versus square of
strain relation. Some of the third order elastic constants have also been
evaluated. The absolute magnitudes of the calculated values for bcc iron are in
fair agreement with experiment, including the third order constants, although
the computed elastic anisotropy is much weaker than measured. The tetragonally
distorted dilute FeC and FeN alloys exhibit lower stiffness than bcc iron,
particularly in the tensor component C33, while the elastic anisotropy is
virtually the same. Average values of elastic moduli for polycrystalline
aggregates are also computed. Youngs modulus and the rigidity modulus, as well
as the bulk modulus, are decreased by about 10 per cent by the addition of C or
N to 3.7 atomic per cent, which agrees with the experimental data for FeC
martensite.",1508.00521v1
2015-08-17,Spectroscopic Study of the Envelope of the Hybrid Nova V458 Vul and Surrounding Nebula,"Spectroscopic observations of the hybrid V458 Vul obtained between days 9 and
778 after the brightness maximum are analyzed. Short-period, daily profile
variations of forbidden [FeVII] iron lines were detected in the nebular phase,
as well as a long-period (about 60-day) cyclic variation that was correlated
with the photometric and X-ray cycles. The abundances of helium, neon, and iron
in the nova's envelope have been estimated. The helium, neon, and iron
abundances exceed the solar values by factors of 4.4, 4.8, and 3.7. The
envelope mass is 1.4$\times$ 10$^{-5}$M$_{\odot}$. The electron temperatures
and number densities have been calculated for the Northwestern and Southeastern
knots of the planetary nebula. The temperature derived for the Northwestern
knot is Te = 10 000 K and the electron number density, n$_{e}$ = 600 cm $^{-3}$
for the Southeastern knot, Te = 13 000 K and n$_{e}$ = 750 cm$^{-3}$.",1508.03990v1
2015-11-16,Tracing the $s_\pm$-symmetry in iron pnictides by controlled disorder,"Consecutive proton irradiation of iron pnictides reduces the superconducting
transition temperature to decrease monotonically. Our systematic optical THz
investigations of Ba(Fe$_{0.9}$Co$_{0.1}$)$_2$As$_2$ thin films reveal,
however, that the low-energy superconducting gap is first suppressed, but
recovers for higher irradiation doses. At the same time the decrease of the
superfluid density with disorder comes to a halt. These observations are in
excellent agreement with theoretical calculations, which predict a
disorder-induced transition of the order parameter from $s_{\pm}$ to $s_{++}$
symmetry. Thereby we solve the longstanding puzzle of the iron pnictides gap
symmetry in favor of $s_{\pm}$-symmetry and demonstrate THz spectroscopy as a
tool to determine the symmetry of the superconducting order parameter.",1511.05017v2
2015-11-20,Impact of ordering competition on the global phase diagram of iron pnictides,"We consider the impact of the competition among superconductivity, spin
density wave, and nematic order in iron pnictides, and show that the ordering
competition substantially reshapes the global phase diagram. We perform a
detailed renormalization group analysis of an effective field theory of iron
pnictides and derive the flow equations of all the physical parameters. Using
these results, we find that superconductivity can be strongly suppressed by the
ordering competition, and also extract the $T$-dependence of superfluid
density. Moreover, the phase transitions may become first order. Interestingly,
our RG analysis reveal that the nematic order exists only in an intermediate
temperature region $T_{m}< T < T_{n}$, but is destroyed at $T > T_{n}$ by
thermal fluctuation and at $T < T_{m}$ by ordering competition. This anomalous
existence of nematic order leads to a back-bending of the nematic transition
line on the phase diagram, consistent with the observed reentrance of
tetragonal structure at low temperatures. A modified phase diagram is obtained
based on the RG results.",1511.06517v1
2015-11-24,Nodal superconductivity in FeS: Evidence from quasiparticle heat transport,"We report low-temperature heat transport measurements on superconducting iron
sulfide FeS with $T_c \approx$ 5 K, which has the same crystal structure and
similar electronic band structure to the superconducting iron selenide FeSe. In
zero magnetic field, a significant residual linear term $\kappa_0/T$ is
observed. At low field, $\kappa_0/T$ increases rapidly with the increase of
field. These results provide strong evidence for nodal superconducting gap in
FeS. We compare it with the sister compound FeSe, and other iron-based
superconductors with nodal gap.",1511.07717v3
2016-01-13,Hybrid Crystals of Cuprates and Iron-Based Superconductors,"We propose two possible new compounds, Ba$_2$CuO$_2$Fe$_2$As$_2$ and
K$_2$CuO$_2$Fe$_2$Se$_2$, which hybridize the building blocks of two high
temperature superconductors, cuprates and iron-based superconductors. These
compounds consist of square CuO$_2$ layers and antifluorite-type Fe$_2$X$_2$
(X=As,Se) layers separated by Ba/K. The calculations of binding energies and
phonon spectrums indicate that they are dynamically stable, which ensures that
they may be experimentally synthesized. The Fermi surfaces and electronic
structures of the two compounds inherit the characteristics of both cuprates
and iron-based superconductors. These compounds can be superconductors with
intriguing physical properties to help to determine pairing mechanisms of high
$T_c$ superconductivity.",1601.03220v1
2016-01-28,Effects of Pnictogen Atmosphere Annealing in Fe$_{1+y}$Te$_{0.6}$Se$_{0.4}$,"It has been clarified that bulk superconductivity in
Fe$_{1+y}$Te$_{0.6}$Se$_{0.4}$ can be induced by annealing in an appropriate
atmosphere to remove the harmful effects of excess iron. In order to clarify
the details of the annealing process, we studied the changes in the physical
properties and reaction products of Fe$_{1+y}$Te$_{0.6}$Se$_{0.4}$ annealed in
pnictogen (P, As, Sb) atmospheres. Crystals annealed in a pnictogen atmosphere
show bulk superconductivity and the values of $T_{c}$ and $J_{c}$ are about
$14~$K and 2-4 $\times 10{^5}~$A/cm$^2$ ($2~$K, self-field), respectively. It
is also found that the reaction rate increases with the increase in the
saturated vapor pressure of the pnictogen. Unexpectedly, the reaction products
of Fe$_{1+y}$Te$_{0.6}$Se$_{0.4}$ after annealing in a P atmosphere mainly
consist of FeTe$_2$. In addition, the amount of P required to obtain the
optimal $T_{c}$ is much smaller than the amount of excess iron, which is
similar to the case of oxygen annealing. P, oxygen, and to some extent As could
serve as catalysts to form FeTe$_2$ to remove excess iron.",1601.07703v1
2016-02-16,Orbital selectivity of layer resolved tunneling on iron superconductor Ba0.6K0.4Fe2As2,"We use scanning tunneling microscopy/spectroscopy (STM/S) to elucidate the
Cooper pairing of the iron pnictide superconductor Ba0.6K0.4Fe2As2. By a
cold-cleaving technique, we obtain atomically resolved termination surfaces
with different layer identities. Remarkably, we observe that the low-energy
tunneling spectrum related to superconductivity has an unprecedented dependence
on the layer-identity. By cross-referencing with the angle-revolved
photoemission results and the tunneling data of LiFeAs, we find that tunneling
on each termination surface probes superconductivity through selecting distinct
Fe-3d orbitals. These findings imply the real-space orbital features of the
Cooper pairing in the iron pnictide superconductors, and propose a new and
general concept that, for complex multi-orbital material, tunneling on
different terminating layers can feature orbital selectivity.",1602.04949v2
2016-02-16,Extreme abundance ratios in the polluted atmosphere of the cool white dwarf NLTT19868,"We present an analysis of intermediate-dispersion spectra and photometric
data of the newly identified cool, polluted white dwarf NLTT19868. The spectra
obtained with X-shooter on the Very Large Telescope (VLT)-Melipal show strong
lines of calcium, and several lines of magnesium, aluminium and iron. We use
these spectra and the optical-to-near infrared spectral energy distribution to
constrain the atmospheric parameters of NLTT19868. Our analysis shows that
NLTT19868 is iron poor with respect to aluminium and calcium. A comparison with
other cool, polluted white dwarfs shows that the Fe to Ca abundance ratio
(Fe/Ca) varies by up to approximately two orders of magnitudes over a narrow
temperature range with NLTT19868 at one extremum in the Fe/Ca ratio and, in
contrast, NLTT888 at the other extremum. The sample shows evidence of extreme
diversity in the composition of the accreted material: In the case of NLTT888,
the inferred composition of the accreted matter is akin to iron-rich planetary
core composition, while in the case of NLTT19868 it is close to mantle or
bulk-Earth composition depleted by subsequent chemical separation at the bottom
of the convection zone.",1602.05000v1
2016-02-17,"Magnetism, superconductivity, and spontaneous orbital order in iron-based superconductors: who comes first and why?","Magnetism and nematic order are the two non-superconducting orders observed
in iron-based superconductors. To elucidate the interplay between them and
ultimately unveil the pairing mechanism, several models have been investigated.
In models with quenched orbital degrees of freedom, magnetic fluctuations
promote stripe magnetism which induces orbital order. In models with quenched
spin degrees of freedom, charge fluctuations promote spontaneous orbital order
which induces stripe magnetism. Here we develop an unbiased approach, in which
we treat magnetic and orbital fluctuations on equal footing. Key to our
approach is the inclusion of the orbital character of the low-energy electronic
states into renormalization group analysis. Our results show that in systems
with large Fermi energies, such as BaFe2As2, LaFeAsO, and NaFeAs, orbital order
is induced by stripe magnetism. However, in systems with small Fermi energies,
such as FeSe, the system develops a spontaneous orbital order, while magnetic
order does not develop. Our results provide a unifying description of different
iron-based materials.",1602.05503v1
2016-03-05,Phase transitions in a frustrated biquadratic Heisenberg model with coupled orbital degree of freedom for iron-based superconductors,"In this work, we study a biquadratic Heisenberg model with coupled orbital
degree of freedom using Monte Carlo simulation in order to investigate the
phase transitions in iron-based superconductors. The antiferro-quadrupolar
state, which may be related to the magnetism of FeSe [Phys. Rev. Lett. 115,
116401 (2015)], is stabilized by the anisotropic biquadratic interaction
induced by a ferro-orbital-ordered state. It is revealed that the orbital and
nematic transitions occur at the same temperature for all the cases, supporting
the mechanism of the orbital-driven nematicity as revealed in most recent
experiments [Nat. Mater. 14, 210 (2015)]. In addition, it is suggested that the
orbital interaction may lead to the separation of the structural and magnetic
phase transitions as observed in many families of iron pnictides.",1603.01669v1
2016-03-10,Spin and quadrupolar orders in the spin-1 bilinear-biquadratic model for iron-based superconductors,"Motivated by recent experimental and theoretical progresses of the magnetic
properties of iron-based superconductors, we provide a comprehensive analysis
of the spin-1 bilinear-biquadratic (BBQ) model on the square lattice. Using
variational approach in the mean-field level, we identify the existence of
various magnetic phases, including conventional spin dipolar orderings (ferro-
or antiferromagnet), novel quadrupolar (spin nematic) orderings and mixed
dipolar-quadrupolar orderings. In contrast to the usual Heisenberg model, the
elementary excitations of the spin-1 BBQ model are described by the flavor-wave
theory within the SU(3) representation. By fitting the experimental spin-wave
dispersion, we determine the refined exchange couplings corresponding to the
collinear antiferromagnetic iron pnictides. We also present the dynamic
structure factors of both spin dipolar and quadrupolar components with
connections to the future experiments.",1603.03273v2
2016-03-14,A study for testing the Kerr metric with AGN iron line eclipses,"Recently, two of us have studied iron line reverberation mapping to test
black hole candidates, showing that the time information in reverberation
mapping can better constrain the Kerr metric than the time-integrated approach.
Motivated by this finding, here we explore the constraining power of another
time-dependent measurement: an AGN iron line eclipse. An obscuring cloud passes
between the AGN and the distant observer, covering different parts of the
accretion disk at different times. Similar to the reverberation measurement, an
eclipse might help to better identify the relativistic effects affecting the
X-ray photons. However, this is not what we find. In our study, we employ the
Johannsen-Psaltis parametrisation, but we argue that our conclusions hold in a
large class of non-Kerr metrics. We explain our results pointing out an
important difference between reverberation and eclipse measurements.",1603.04115v2
2016-03-15,Testing the Kerr black hole hypothesis: comparison between the gravitational wave and the iron line approaches,"The recent announcement of the detection of gravitational waves by the
LIGO/Virgo collaboration has opened a new window to test the nature of
astrophysical black holes. Konoplya & Zhidenko have shown how the LIGO data of
GW 150914 can constrain possible deviations from the Kerr metric. In this
letter, we compare their constraints with those that can be obtained from
accreting black holes by fitting their reflected X-ray spectrum, the so-called
iron line method. We simulate observations with eXTP, a next generation X-ray
mission, finding constraints much stronger than those obtained by Konoplya &
Zhidenko. Our results can at least show that, contrary to what is quite
commonly believed, it is not obvious that gravitational waves are the most
powerful approach to test strong gravity. In the presence of high quality data
and with the systematics under control, the iron line method may provide
competitive constraints.",1603.04720v2
2016-04-12,High Temperature Superconductivity in Iron Pnictides and Chalcogenides,"Superconductivity develops in metals upon the formation of a coherent
macroscopic quantum state of electron pairs. Iron pnictides and chalcogenides
are materials that have high superconducting transition temperatures. In this
Review, we describe the advances in the field that have led to higher
superconducting transition temperatures in iron-based superconductors and the
wide range of materials that form them. We summarize both the essential aspects
of the normal state and the mechanism for superconductivity. We emphasize the
degree of electron-electron correlations and their manifestation in properties
of the normal state. We examine the nature of magnetism, analyse its role in
driving the electronic nematicity, and discuss quantum criticality at the
border of magnetism in the phase diagram. Finally, we review the amplitude and
structure of the superconducting pairing, and survey the potential settings for
optimizing superconductivity.",1604.03566v1
2016-04-24,Vanishing Absorption and Blueshifted Emission in FeLoBAL Quasars,"We study the dramatic decrease in iron absorption strength in the iron
low-ionization broad absorption line quasar SDSS J084133.15+200525.8. We report
on the continued weakening of absorption in the prototype of this class of
variable broad absorption line quasar, FBQS J140806.2+305448. We also report a
third example of this class, SDSS J123103.70+392903.6; unlike the other two
examples, it has undergone an increase in observed continuum brightness (at
3000~\AA\ rest-frame) as well as a decrease in iron absorption strength. These
changes could be caused by absorber transverse motion or by ionization
variability. We note that the \mgii\ and UV \feii\ lines in several FeLoBAL
quasars are blueshifted by thousands of \kms\ relative to the \Hb\ emission
line peak. We suggest that such emission arises in the outflowing winds
normally seen only in absorption.",1604.06977v1
2016-05-09,A global look at X-ray time lags in Seyfert Galaxies,"X-ray reverberation, where light-travel time delays map out the compact
geometry around the inner accretion flow in supermassive black holes, has been
discovered in several of the brightest, most variable and well-known Seyfert
galaxies. In this work, we expand the study of X-ray reverberation to all
Seyfert galaxies in the XMM-Newton archive above a nominal rms variability and
exposure level (a total of 43 sources). 50 per cent of source exhibit iron K
reverberation, in that the broad iron K emission line responds to rapid
variability in the continuum. We also find that on long timescales, the hard
band emission lags behind the soft band emission in 85 per cent of sources.
This `low-frequency hard lag' is likely associated with the coronal emission,
and so this result suggests that most sources with X-ray variability show
intrinsic variability from the nuclear region. We update the known iron K lag
amplitude vs. black hole mass relation, and find evidence that the height or
extent of the coronal source (as inferred by the reverberation time delay)
increases with mass accretion rate.",1605.02631v1
2016-05-31,Thermoelectric properties of iron-based superconductors and parent compounds,"Herewith, we review the available experimental data of thermoelectric
transport properties of iron-based superconductors and parent compounds. We
discuss possible physical mechanisms into play in determining the Seebeck
effect, from whence one can extract information about Fermi surface
reconstruction and Lifshitz transitions, multiband character, coupling of
charge carriers with spin excitations and its relevance in the unconventional
superconducting pairing mechanism, nematicity, quantum critical fluctuations
close to the optimal doping for superconductivity, correlation. Additional
information is obtained from the analysis of the Nernst effect, whose
enhancement in parent compounds must be related partially to multiband
transport and low Fermi level, but mainly to the presence of Dirac cone bands
at the Fermi level. In the superconducting compounds, large Nernst effect in
the normal state is explained in terms of fluctuating precursors of the spin
density wave state, while in the superconducting state it mirrors the usual
vortex liquid dissipative regime. A comparison between the phenomenology of
thermoelectric behavior of different families of iron-based superconductors and
parent compounds allows to evidence the key differences and analogies, thus
providing clues on the rich and complex physics of these fascinating
unconventional superconductors.",1605.09577v1
2016-06-03,"Synthesis, phase stability, structural and physical properties of 11-type iron chalcogenides","This article reviews recent experimental investigations on two binary
Fe-chalcogenides: FeSe and Fe$_{1+y}$Te. The main focus is on synthesis, single
crystal growth, chemical composition, as well as on the effect of excess iron
on structural, magnetic, and transport properties of these materials. The
structurally simplest Fe-based superconductor Fe$_{1+x}$Se with a critical
temperature $T_c \approx$ 8.5 K undergoes a tetragonal to orthorhombic phase
transition at a temperature $T_s \approx$ 87 K. No long-range magnetic order is
observed down to the lowest measured temperature in Fe$_{1+x}$Se. On the other
hand, isostructural Fe$_{1+y}$Te displays a complex interplay of magnetic and
structural phase transitions in dependence on the tuning parameter such as
excess amount of Fe or pressure, but it becomes a superconductor only when Te
is substituted by a sufficient amount of Se. We summarize experimental evidence
for different competing interactions and discuss related open questions.",1606.01012v1
2016-06-05,Enhanced critical-current in P-doped BaFe2As2 thin films on metal substrates arising from poorly aligned grain boundaries,"Thin films of the iron-based superconductor BaFe2(As1-xPx)2 (Ba122:P) were
fabricated on polycrystalline metal-tape substrates with two kinds of in-plane
grain boundary alignments (well aligned (4 deg.) and poorly aligned (8 deg.))
by pulsed laser deposition. The poorly aligned substrate is not applicable to
cuprate-coated conductors because the in-plane alignment >4 deg. results in
exponential decay of the critical current density (Jc). The Ba122:P film
exhibited higher Jc at 4 K when grown on the poorly aligned substrate than on
the well-aligned substrate even though the crystallinity was poorer. It was
revealed that the misorientation angles of the poorly aligned samples were less
than 6 deg., which are less than the critical angle of an iron-based
superconductor, cobalt-doped BaFe2As2 (~9 deg.), and the observed strong
pinning in the Ba122:P is attributed to the high-density grain boundaries with
the misorientation angles smaller than the critical angle. This result reveals
a distinct advantage over cuprate-coated conductors because well-aligned
metal-tape substrates are not necessary for practical applications of the
iron-based superconductors.",1606.01477v2
2016-07-09,Orientation of the electric field gradient and ellipticity of the magnetic cycloid in multiferroic BiFeO3,"The paper deals with the hyperfine interactions observed on the 57Fe nucleus
in multiferroic BiFeO3 by means of the 14.41-keV resonant transition in 57Fe,
and for transmission geometry applied to the random powder sample. Spectra were
obtained at 80 K, 190 K and at room temperature. It was found that iron occurs
in the high spin trivalent state. Hyperfine magnetic field follows distribution
due to the elliptic-like distortion of the magnetic cycloid. The long axis of
the ellipse is oriented along <111> direction of the rhombohedral unit cell.
The hyperfine magnetic field in this direction is about 1.013 of the field in
the perpendicular direction at room temperature. This ratio diminishes to 1.010
at 80 K. Axially symmetric electric field gradient (EFG) on the iron atoms has
the principal axis oriented in the same direction and the main component of the
EFG is positive. Our results are consistent with the finding that iron magnetic
moments are confined to the [1-21] crystal plane.",1607.02601v3
2016-07-11,An Iron K Component to the Ultrafast Outflow in NGC 1313 X-1,"We present the detection of an absorpton feature at $E=8.77^{+0.05}_{-0.06}$
keV in the combined X-ray spectrum of the ultraluminous X-ray source NGC 1313
X-1 observed with XMM-Newton and NuSTAR, significant at the 3$\sigma$ level. If
associated with blueshifted ionized iron, the implied outflow velocity is
~0.2$c$ for Fe XXVI, or ~0.25$c$ for Fe XXV. These velocities are similar to
the ultrafast outflow seen in absorption recently discovered in this source at
lower energies by XMM-Newton, and we therefore conclude that this is an iron
component to the same outflow. Photoionization modeling marginally prefers the
Fe XXV solution, but in either case the outflow properties appear to be
extreme, potentially supporting a super-Eddington hypothesis for NGC 1313 X-1.",1607.03124v1
2016-07-19,Relativistic iron lines in accretion disks: the contribution of higher order images in the strong deflection limit,"The shapes of relativistic iron lines observed in spectra of candidate black
holes carry the signatures of the strong gravitational fields in which the
accretion disks lie. These lines result from the sum of the contributions of
all images of the disk created by gravitational lensing, with the direct and
first-order images largely dominating the overall shapes. Higher order images
created by photons tightly winding around the black holes are often neglected
in the modeling of these lines, since they require a substantially higher
computational effort. With the help of the strong deflection limit, we present
the most accurate semi-analytical calculation of these higher order
contributions to the iron lines for Schwarzschild black holes. We show that two
regimes exist depending on the inclination of the disk with respect to the line
of sight. Many useful analytical formulae can be also derived in this
framework.",1607.05365v2
2016-07-19,Spin resonance in the superconducting state of Li$_{1-x}$Fe$_{x}$ODFe$_{1-y}$Se observed by neutron spectroscopy,"We have performed inelastic neutron scattering measurements on a powder
sample of the superconductor lithium iron selenide hydroxide
Li$_{1-x}$Fe$_{x}$ODFe$_{1-y}$Se ($x \simeq 0.16, y \simeq 0.02$, $T_{\rm c} =
41$\,K). The spectrum shows an enhanced intensity below $T_{\rm c}$ over an
energy range $0.64\times2\Delta < E < 2\Delta$, where $\Delta$ is the
superconducting gap, with maxima at the wave vectors $Q_1 \simeq
1.46$\,\AA$^{-1}$ and $Q_2 \simeq 1.97$\,\AA$^{-1}$. The behavior of this
feature is consistent with the spin resonance mode found in other
unconventional superconductors, and strongly resembles the spin resonance
observed in the spectrum of the molecular-intercalated iron selenide,
Li$_{0.6}$(ND$_{2}$)$_{0.2}$(ND$_{3}$)$_{0.8}$Fe$_{2}$Se$_{2}$. The signal can
be described with a characteristic two-dimensional wave vector $(\pi, 0.67\pi)$
in the Brillouin zone of the iron square lattice, consistent with the nesting
vector between electron Fermi sheets.",1607.05588v2
2016-07-19,Synthesis of strontium ferrite/iron oxide exchange coupled nano-powders with improved energy product for rare earth free permanent magnet applications,"We present a simple, scalable synthesis route for producing exchange coupled
soft/hard magnetic composite powder that outperforms pure soft and hard phase
constituents. Importantly, the composites is iron oxide based (SrFe12O19 and
Fe3O4) and contain no rare earth or precious metal. The two step synthesis
process consists of first precipitating, an Iron oxide/hydroxide precursor
directly on top of SrFe12O19 nano-flakes, ensuring a very fine degree of mixing
between the hard and the soft magnetic phases. We then use a second step that
serves to reduce the precursor to create the proper soft magnetic phase and
create the intimate interface necessary for exchange coupling. We establish a
clear processing window; at temperatures below this window the desired soft
phase is not produced, while higher temperatures result in deleterious reaction
at the soft/hard phase interfaces, causing an improper ratio of soft to hard
phases. Improvements of Mr, Ms, and (BH)max are 42%, 29% and 37% respectively
in the SrFe12O19/Fe3O4 composite compared to pure hard phase (SrFe12O19). We
provide evidence of coupling (exchange spring behavior) with hysteresis curves,
first order reversal curve (FORC) analysis and recoil measurements.",1607.05689v1
2016-08-11,Collective magnetic excitations of $C_{4}$ symmetric magnetic states in iron-based superconductors,"We study the collective magnetic excitations of the recently discovered
$C_{4}$ symmetric spin-density wave states of iron-based superconductors with
particular emphasis on their orbital character based on an itinerant
multiorbital approach. This is important since the $C_{4}$ symmetric
spin-density wave states exist only at moderate interaction strengths where
damping effects from a coupling to the continuum of particle-hole excitations
strongly modifies the shape of the excitation spectra compared to predictions
based on a local moment picture. We uncover a distinct orbital polarization
inherent to magnetic excitations in $C_{4}$ symmetric states, which provide a
route to identify the different commensurate magnetic states appearing in the
continuously updated phase diagram of the iron-pnictide family.",1608.03493v1
2016-11-08,Superconductivity and magnetism in Iron Sulfides Intercalated by Metal Hydroxides,"Inspired by naturally occurring sulfide minerals, we present a new family of
iron-based superconductors. A metastable form of FeS known as the mineral
mackinawite forms two-dimensional sheets that can be readily intercalated by
various cationic guest species. Under hydrothermal conditions using alkali
metal hydroxides, we prepare three different cation and metal
hydroxide-intercalated FeS phases including (Li$_{1-x}$Fe$_x$OH)FeS,
[(Na$_{1-x}$Fe$_x$)(OH)$_2$]FeS, and K$_x$Fe$_{2-y}$S$_2$. Upon successful
intercalation of the FeS layer, the superconducting critical temperature $T_c$
of mackinawite is enhanced from 5 K to 8 K for the
(Li$_{1-x}$Fe$_x$OH)$^{\delta+}$ intercalate. Layered heterostructures of
[(Na$_{1-x}$Fe$_x$)(OH)$_2$]FeS resemble the natural mineral tochilinite, which
contains an iron square lattice interleaved with a hexagonal hydroxide lattice.
Whilst heterostructured [(Na$_{1-x}$Fe$_x$)(OH)$_2$]FeS displays long-range
magnetic ordering near 15 K, K$_x$Fe$_{2-y}$S$_2$ displays short range
antiferromagnetism.",1611.02383v2
2016-11-11,Antiferromagnetic order in epitaxial FeSe films on SrTiO3,"Single monolayer FeSe film grown on Nb-doped SrTiO$_3$(001) substrate shows
the highest superconducting transition temperature (T$_C$ $\sim$ 100 K) among
the iron-based superconductors (iron-pnictide), while T$_C$ of bulk FeSe is
only $\sim$ 8 K. Antiferromagnetic spin fluctuations were believed to be
crucial in iron-pnictides, which has inspired several proposals to understand
the FeSe/SrTiO$_3$ system. Although bulk FeSe does not show the
antiferromagnetic order, calculations suggest that the parent FeSe/SrTiO$_3$
films are AFM. Experimentally, due to lacking of direct probe, the magnetic
state of FeSe/SrTiO$_3$ films remains mysterious. Here, we report the direct
evidences of the antiferromagnetic order in the parent FeSe/SrTiO$_3$ films by
the magnetic exchange bias effect measurements. The phase transition
temperature is $\geq$ 140 K for single monolayer film. The AFM order disappears
after electron doping.",1611.03603v2
2016-12-30,Exchange Bias Effects in Iron Oxide-Based Nanoparticle Systems,"The exploration of exchange bias (EB) on the nanoscale provides a novel
approach to improving the anisotropic properties of magnetic nanoparticles for
prospective applications in nanospintronics and nanomedicine. However, the
physical origin of EB is not fully understood. Recent advances in chemical
synthesis provide a unique opportunity to explore EB in a variety of iron
oxide-based nanostructures ranging from core/shell to hollow and hybrid
composite nanoparticles. Experimental and atomistic Monte Carlo studies have
shed light on the roles of interface and surface spins in these nanosystems.
This review paper aims to provide a thorough understanding of the EB and
related phenomena in iron oxide-based nanoparticle systems, knowledge of which
is essential to tune the anisotropic magnetic properties of exchange-coupled
nanoparticle systems for potential applications.",1612.09455v1
2017-01-10,Size-dependent frequency bands in the ferromagnetic resonance of a Fe-nanocube,"Using full micromagnetic simulations we calculate the spectra of
ferromagnetic resonance (FMR) for an iron (core-shell) nanocube and show that
the FMR characteristics are strongly size dependent. For instance, for a
$40~$nm it is found that, in contrast to a macrospin picture, the spectrum of
the iron nanocube possesses two bands centered around $0.4~$T and $\approx
0.1~$T. The peaks originate from the surface anisotropy induced by the strong
demagnetizing fields (DMFs) of iron. Further simulations reveal that for
$\approx 20~$nm nanocubes the macrospin model becomes viable. Above $40~$nm we
find a broad band for FMR absorption. Our results point to possible
interpretations of existing FMR experimental observations for the system
studied here.",1701.02503v1
2017-02-08,Magnetic Lifshitz transition and its consequences in multi-band iron-based superconductors,"In this paper we address Lifshitz transition induced by applied external
magnetic field in a case of iron-based superconductors, in which a difference
between the Fermi level and the edges of the bands is relatively small. We
introduce and investigate a two-band model with intra-band pairing in the
relevant parameters regime to address a generic behaviour of a system with
hole-like and electron-like bands in external magnetic field. Our results show
that two Lifshitz transitions can develop in analysed systems and the first one
occurs in the superconducting phase and takes place at approximately constant
magnetic field. The chosen sets of the model parameters can describe
characteristic band structure of iron-based superconductors and thus the
obtained results can explain the experimental observations in FeSe and Co-doped
BaFe$_{2}$As$_{2}$ compounds.",1702.02612v1
2017-03-13,Various arsenic network structures in 112-type Ca1-xLaxFe1-yPdyAs2 revealed by synchrotron x-ray diffraction experiments,"Two novel 112-type palladium doped iron arsenides were synthesized and
identified using comprehensive studies involving synchrotron x-ray diffraction
and x-ray absorption near edge structure (XANES) experiments. Whereas in-plane
arsenic zigzag chains were found in 112-type superconducting iron arsenide,
Ca1-xLaxFeAs2 with maximum Tc = 34 K, deformed arsenic network structures
appeared in 112-type materials such as longitudinal arsenics zigzag chains in
CaFe1-yPdyAs2 (y ~ 0.51) and arsenic square sheets constructed via hypervalent
bonding in Ca1-xLaxFe1-yPdyAs2 (x ~ 0.31, y ~ 0.30). As K-edge XANES spectra
clarified the similar oxidization states around FeAs4 tetrahedrons, expecting
us the possible parents for high Tc 112-type iron arsenide superconductors.",1703.04204v1
2017-04-07,Spin wave propagation and spin polarized electron transport in single crystal iron films,"The technique of propagating spin wave spectroscopy is applied to a 20 nm
thick Fe/MgO (001) film. The magnetic parameters extracted from the position of
the resonance peaks are very close to those tabulated for bulk iron. From the
propagating waveforms, a group velocity of 4 km/s and an attenuation length of
about 6 micrometers are extracted for 1.6 micrometers-wavelength spin-wave at
18 GHz. From the measured current-induced spin-wave Doppler shift, we also
extract a surprisingly high degree of spin-polarization of the current of 83%.
This set of results makes single-crystalline iron a promising candidate for
building devices utilizing high frequency spin-waves and spin-polarized
currents.",1704.02217v1
2017-04-11,Possible Bicollinear Nematic State with Monoclinic Lattice Distortions in Iron Telluride Compounds,"Iron telluride FeTe is known to display bicollinear magnetic order at low
temperatures together with a monoclinic lattice distortion. Because the
bicollinear order can involve two different wavevectors $(\pi/2,\pi/2)$ and
$(\pi/2,-\pi/2)$, symmetry considerations allow for the possible stabilization
of a nematic state with short-range bicollinear order coupled to monoclinic
lattice distortions at a $T_S$ higher than the temperature $T_N$ where
long-range bicollinear order fully develops. As a concrete example, the
three-orbitals spin-fermion model for iron telluride is studied with an
additional coupling $\tilde\lambda_{12}$ between the monoclinic lattice strain
and an orbital-nematic order parameter with $B_{2g}$ symmetry. Monte Carlo
simulations show that with increasing $\tilde\lambda_{12}$ the first-order
transition characteristic of FeTe splits and bicollinear nematicity is
stabilized in a (narrow) temperature range. In this new regime the lattice is
monoclinically distorted and short-range spin and orbital order breaks
rotational invariance. A discussion of possible realizations of this exotic
state is provided.",1704.03495v2
2017-04-28,Strong anisotropy effect in iron-based superconductor CaFe$_{0.882}$Co$_{0.118}$AsF,"The anisotropy of the Fe-based superconductors is much smaller than that of
the cuprates and the theoretical calculations. A credible understanding for
this experimental fact is still lacking up to now. Here we experimentally study
the magnetic-field-angle dependence of electronic resistivity in the
superconducting phase of iron-based superconductor
CaFe$_{0.882}$Co$_{0.118}$AsF, and find the strongest anisotropy effect of the
upper critical field among the iron-based superconductors based on the
framework of Ginzburg-Landau theory. The evidences of energy band structure and
charge density distribution from electronic structure calculations demonstrate
that the observed strong anisotropic effect mainly comes from the strong ionic
bonding in between the ions of Ca$^{2+}$ and F$^-$, which weakens the
interlayer coupling between the layers of FeAs and CaF. This finding provides a
significant insight into the nature of experimentally observed strong
anisotropic effect of electronic resistivity, and also paves an avenue to
design exotic two dimensional artificial unconventional superconductors in
future.",1704.08791v1
2017-05-31,Crystal growth and phase diagram of 112-type iron pnictide superconductor Ca1-yLayFe1-xNixAs2,"We report a systematic crystal growth and characterization of
Ca$_{1-y}$La$_{y}$Fe$_{1-x}$Ni$_{x}$As$_{2}$, the newly discovered 112-type
iron-based superconductor. After substituting Fe by a small amount of Ni, bulk
superconductivity is successfully obtained in high quality single crystals
sized up to 6 mm. Resistivity measurements indicate common features for
transport properties in this 112-type iron pnictide, suggest strong scattering
from chemical dopants. Together with the superconducting transition temperature
$T_c$, and the Neel temperature $T_N$ determined by the elastic neutron
scattering, we sketch a three-dimensional phase diagram in the combination of
both Ni and La dopings.",1705.11144v1
2017-06-06,Detailed opacity calculations for astrophysical applications,"Nowadays, several opacity codes are able to provide data for stellar
structure models, but the computed opacities may show significant differences.
In this work, we present state-of-the-art precise spectral opacity
calculations, illustrated by stellar applications. The essential role of
laboratory experiments to check the quality of the computed data is underlined.
We review some X-ray and XUV laser and Z-pinch photo-absorption measurements as
well as X-ray emission spectroscopy experiments involving hot dense plasmas
produced by ultra-high-intensity laser irradiation. The measured spectra are
systematically compared with the fine-structure opacity code SCO-RCG. Focus is
put on iron, due to its crucial role in understanding asteroseismic
observations of $\beta$ Cephei-type and Slowly Pulsating B stars, as well as of
the Sun. For instance, in $\beta$ Cephei-type stars, the iron-group opacity
peak excites acoustic modes through the ""kappa-mechanism"". A particular
attention is paid to the higher-than-predicted iron opacity measured at the
Sandia Z-machine at solar interior conditions. We discuss some theoretical
aspects such as density effects, photo-ionization, autoionization or the
""filling-the-gap"" effect of highly excited states.",1706.01761v1
2017-06-10,Local orthorhombicity in the magnetic $C_4$ phase of the hole-doped iron-arsenide superconductor Sr$_{1-x}$Na$_{x}$Fe$_2$As$_2$,"We report temperature-dependent pair distribution function measurements of
Sr$_{1-x}$Na$_{x}$Fe$_2$As$_2$, an iron-based superconductor system that
contains a magnetic phase with reentrant tetragonal symmetry, known as the
magnetic $C_4$ phase. Quantitative refinements indicate that the instantaneous
local structure in the $C_4$ phase is comprised of fluctuating orthorhombic
regions with a length scale of $\sim$2 nm, despite the tetragonal symmetry of
the average static structure. Additionally, local orthorhombic fluctuations
exist on a similar length scale at temperatures well into the paramagnetic
tetragonal phase. These results highlight the exceptionally large nematic
susceptibility of iron-based superconductors and have significant implications
for the magnetic $C_4$ phase and the neighboring $C_2$ and superconducting
phases.",1706.03279v2
2017-06-16,Observation of topological superconductivity on the surface of an iron-based superconductor,"Topological superconductors, whose edge hosts Majorana bound states or
Majorana fermions that obey non-Abelian statistics, can be used for
low-decoherence quantum computations. Most of the proposed topological
superconductors are realized with spin-helical states through proximity effect
to BCS superconductors. However, such approaches are difficult for further
studies and applications because of the low transition temperatures and
complicated hetero-structures. Here by using high-resolution spin-resolved and
angle-resolved photoelectron spectroscopy, we discover that the iron-based
superconductor FeTe1-xSex (x = 0.45, Tc = 14.5 K) hosts Dirac-cone type
spin-helical surface states at Fermi level, which open an s-wave SC gap below
Tc. Our study proves that the surface states of FeTe0.55Se0.45 are 2D
topologically superconducting, and thus provides a simple and possibly high-Tc
platform for realizing Majorana fermions.",1706.05163v2
2017-06-23,Dynamic Simulation of Structural Phase Transitions in Magnetic Iron,"The occurrence of bcc-fcc ($\alpha$-$\gamma$) and fcc-bcc ($\gamma$-$\delta$)
phase transitions in magnetic iron stems from the interplay between magnetic
excitations and lattice vibrations. However, this fact has never been proven by
a direct dynamic simulation, treating non-collinear magnetic fluctuations and
dynamics of atoms, and their coupling at a finite temperature. Starting from a
large set of data generated by ab initio simulations, we derive non-collinear
magnetic many-body potentials for bcc and fcc iron describing fluctuations in
the vicinity of near perfect lattice positions. We then use spin-lattice
dynamics simulations to evaluate the difference between free energies of bcc
and fcc phases, assessing their relative stability within a unified dynamic
picture. We find two intersections between the bcc and fcc free energy curves,
which correspond to $\alpha$-$\gamma$ bcc-fcc and $\gamma$-$\delta$ fcc-bcc
phase transitions. The maximum fcc-bcc free energy difference over the
temperature interval between the two phase transition points is 2 meV, in
agreement with other experimental and theoretical estimates.",1706.07635v1
2017-07-12,Local magnetic moments in iron and nickel at ambient and Earth's core conditions,"Some Bravais lattices have a particular geometry that can slow down the
motion of Bloch electrons by pre-localization due to the band-structure
properties. Another known source of electronic localization in solids is the
Coulomb repulsion in partially filled d- or f-orbitals, which leads to the
formation of local magnetic moments. The combination of these two effects is
usually considered of little relevance to strongly correlated materials. Here
we show that it represents, instead, the underlying physical mechanism in two
of the most important ferromagnets: nickel and iron. In nickel, the van Hove
singularity has an unexpected impact on the magnetism. As a result, the
electron-electron scattering rate is linear in temperature, in violation of the
conventional Landau theory of metals. This is true even at Earth's core
pressures, at which iron is instead a good Fermi liquid. The importance of
nickel in models of geomagnetism may have therefore to be reconsidered.",1707.03789v1
2017-07-19,On local sensing of spin Hall effect in tungsten films by using STM-based measurements,"The spin Hall effect in tungsten films has been experimentally studied by
using STM-based measurements. These measurements have been performed by using
tungsten and iron coated tungsten tips. In the case of tungsten tips, it has
been observed that the current flow through the tungsten film results in an
appreciable asymmetry in the tunneling current with respect to the change in
the polarity of the tunneling voltage. It is reasoned that the cause of this
asymmetry is the accumulation of spin polarized electrons on the tungsten film
surface due to the spin Hall effect. This asymmetry is not affected by the
change of the direction of the bias current through the film. However, in the
case of iron coated tungsten tips, it has been observed that a change in the
direction of the bias current does lead to an additional asymmetry in the
tunneling current. It is thus experimentally demonstrated that this asymmetry
is caused by the SHE and spin-dependent density of states of iron-coated tips.",1707.06116v2
2017-09-18,Magnetism and superconductivity in the layered hexagonal transition metal pnictides,"We investigate the electronic and magnetic structures of the 122
(AM$_2$B$_2$) hexagonal transition-metal pnictides with A=(Sr, Ca), M=(Cr, Mn,
Fe, Co, Ni) and B=(As, P, Sb). It is found that the family of materials share
critical similarities with those of tetragonal structures that include the
famous iron-based high temperature superconductors. In both families, the next
nearest neighbor(NNN) effective antiferromagnetic(AFM) exchange couplings reach
the maximum value in the iron-based materials. While the NNN couplings in the
latter are known to be responsible for the C-type AFM state and to result in
the extended s-wave superconducting state upon doping, they cause the former to
be extremely frustrated magnetic systems and can lead to an time reversal
symmetry broken $d+id$ superconducting state upon doping. The iron-based
compounds with the hexagonal structure, thus if synthesized, can help us to
determine the origin of high temperature superconductivity.",1709.05736v1
2017-10-09,Appearance of a Domain Structure and its Electronic states in Iron Doped 1$T$-TaS$_2$ Observed using Scanning Tunneling Microscopy and Spectroscopy,"In this paper, we report on scanning tunneling microscopy and spectroscopy
(STM/STS) measurements on iron doped 1$T$-Ta$_{1-x}$Fe$_x$S$_2$. A novel domain
structure composed of the domains with localized nature divided by the walls is
observed in Ta$_{0.99}$Fe$_{0.01}$S$_2$, where the Mott transition is
completely suppressed. This indicates that the melting of the Mott state
accompanies the appearance of the domain structure. Since the number of walls
increase in superconducting Ta$_{0.98}$Fe$_{0.02}$S$_2$, the domain walls seem
to be responsible for superconductivity in iron doped 1$T$-TaS$_2$.",1710.02979v1
2017-11-07,Spin-Orbit Coupling and Magnetic Anisotropy in Iron-Based Superconductors,"We determine theoretically the effect of spin-orbit coupling on the magnetic
excitation spectrum of itinerant multi-orbital systems, with specific
application to iron-based superconductors. Our microscopic model includes a
realistic ten-band kinetic Hamiltonian, atomic spin-orbit coupling, and
multi-orbital Hubbard interactions. Our results highlight the remarkable
variability of the resulting magnetic anisotropy despite constant spin-orbit
coupling. At the same time, the magnetic anisotropy exhibits robust universal
behavior upon changes in the bandstructure corresponding to different materials
of iron-based superconductors. A natural explanation of the observed
universality emerges when considering optimal nesting as a resonance
phenomenon. Our theory is also of relevance to other itinerant system with
spin-orbit coupling and nesting tendencies in the bandstructure.",1711.02460v1
2017-11-15,Anisotropy of the Seebeck and Nernst coefficients in parent compounds of the iron-based superconductors,"In-plane longitudinal and transverse thermoelectric phenomena in two parent
compounds of iron-based superconductors are studied. Namely, the Seebeck (S)
and Nernst (n) coefficients were measured in the temperature range 10 - 300 K
for BaFe2As2 and CaFe2As2 single crystals that were detwinned in-situ. The
thermoelectric response shows sizeable anisotropy in the spin density wave
state (SDW) for both compounds, while some dissimilarities in the vicinity of
the SDW transition can be attributed to the different nature of the phase
change in BaFe2As2 and CaFe2As2. Temperature dependences of S and n can be
described within a two-band model that contains a contribution from highly
mobile, probably Dirac, electrons. The Dirac band seems to be rather isotropic,
whereas most of the anisotropy in the transport phenomena could be attributed
to ""regular"" hole-like charge carriers. We also observe that the off-diagonal
element of the Peltier tensor axy is not the same for the a and b orthorhombic
axes, which indicates that the widely used Mott formula is not applicable to
the SDW state of iron-based superconductors.",1711.05831v2
2017-12-19,Emergent magnetic degeneracy in iron pnictides due to the interplay between spin-orbit coupling and quantum fluctuations,"Recent experiments in iron pnictide superconductors reveal that, as the
putative magnetic quantum critical point is approached, different types of
magnetic order coexist over a narrow region of the phase diagram. Although
these magnetic configurations share the same wave-vectors, they break distinct
symmetries of the lattice. Importantly, the highest superconducting transition
temperature takes place close to this proliferation of near-degenerate magnetic
states. In this paper, we employ a renormalization group calculation to show
that such a behavior naturally arises due to the effects of spin-orbit coupling
on the quantum magnetic fluctuations. Formally, the enhanced magnetic
degeneracy near the quantum critical point is manifested as a stable Gaussian
fixed point with a large basin of attraction. Implications of our findings to
the superconductivity of the iron pnictides are also discussed.",1712.07188v4
2018-01-22,Excitation and charge transfer in low-energy hydrogen atom collisions with neutral iron,"Data for inelastic processes due to hydrogen atom collisions with iron are
needed for accurate modelling of the iron spectrum in late-type stars.
Excitation and charge transfer in low-energy Fe+H collisions is studied
theoretically using a previously presented method based on an asymptotic
two-electron linear combination of atomic orbitals (LCAO) model of
ionic-covalent interactions in the neutral atom-hydrogen-atom system, together
with the multi-channel Landau-Zener model. An extensive calculation including
166 covalent states and 25 ionic states is presented and rate coefficients are
calculated for temperatures in the range 1000 - 20000 K. The largest rates are
found for charge transfer processes to and from two clusters of states around
6.3 and 6.6 eV excitation, corresponding in both cases to active 4d and 5p
electrons undergoing transfer. Excitation and de-excitation processes among
these two sets of states are also significant.",1801.07050v1
2018-02-26,Iron-based trinuclear metal-organic nanostructures on a surface with local charge accumulation,"Coordination chemistry relies on harnessing active metal sites within organic
matrices. Polynuclear complexes - consisting of organic ligands binding to
clusters of several metal atoms are of particular interest, owing to their
electronic/magnetic properties and potential for functional reactivity
pathways. However, their synthesis remains challenging; only a limited number
of geometries and configurations have been achieved. Here, we synthesise - via
supramolecular chemistry on a noble metal surface - one-dimensional
metal-organic nanostructures composed of terpyridine (tpy)-based molecules
coordinated with well-defined polynuclear iron clusters. By a combination of
low-temperature scanning probe microscopy techniques and density functional
theory, we demonstrate that the coordination motif consists of coplanar tpy's
linked via a linear tri-iron node in a mixed (positive) valence, metal-metal
bond configuration. This unusual linkage is stabilized by a local accumulation
of electrons at the interface between cations, ligand and surface. The latter,
enabled by the bottom-up on-surface synthesis, hints at a chemically active
metal centre, and opens the door to the engineering of nanomaterials with novel
catalytic and magnetic functionalities.",1802.09146v1
2018-03-02,Nonlinear uniaxial pressure dependence of $T_c$ in iron-based superconductors,"We have systematically studied the effects of in-plane uniaxial pressure $p$
on the superconducting transition temperature $T_c$ in many iron-based
superconductors. The change of $T_c$ with $p$ is composed of linear and
nonlinear components. The latter can be described as a quadratic term plus a
much smaller fourth-order term. In contrast to the linear component, the
nonlinear $p$ dependence of $T_c$ displays a pronounced in-plane anisotropy,
which is similar to the anisotropic response of the resistivity to $p$. As a
result, it can be attributed to the coupling between the superconducting and
nematic orders, in accordance with the expectations of a phenomenological
Landau theory. Our results provide direct evidences for the interplay between
nematic fluctuations and superconductivity, which may be a common behavior in
iron-based superconductors.",1803.00717v2
2018-04-11,Fe intercalation under graphene and hexagonal boron nitride in-plane heterostructure on Pt(111),"Metal nanostructures confined between sp2 hybridized 2D materials and solid
supports are attracting attention for their potential application in new
nanotechnologies. Model studies under well-defined conditions are valuable for
understanding the fundamental aspects of the phenomena under 2D covers. In this
work we investigate the intercalation of iron atoms through a single layer of
mixed graphene and hexagonal boron nitride on Pt(111) using a combination of
spectroscopic and microscopic techniques. Thermally activated diffusion of iron
proceeds preferentially under graphene and only partially under hexagonal boron
nitride areas. When oxygen is coadsorbed with iron, the intercalation rate is
higher, and formation of B2O3 and oxygenated B-C species is observed. Our
results suggest the possibility of confining ferromagnetic layers under
heterostructures of graphene and hexagonal boron nitride with potential
technological implications in the fields of spintronics, magnetic data storage
or chemistry under 2D covers.",1804.04240v1
2018-04-13,Experimental evidence of a body centered cubic iron at the Earth's core condition,"The crystal structure of iron in the Earth's inner core remains debated. Most
recent experiments suggest a hexagonal-close-packed (hcp) phase. In
simulations, it has been generally agreed that the hcp-Fe is stable at inner
core pressures and relatively low temperatures. At high temperatures, however,
several studies suggest a body-centered-cubic (bcc) phase at the inner core
condition. We have examined the crystal structure of iron at high pressures
over 2 million atmospheres (>200GPa) and at high temperatures over 5000 kelvin
in a laser-heated diamond cell using microstructure analysis combined with
$\textit{in-situ}$ x-ray diffraction. Experimental evidence shows a bcc-Fe
appearing at core pressures and high temperatures, with an hcp-bcc transition
line in pressure-temperature space from about 95$\pm$2GPa and 2986$\pm$79K to
at least 222$\pm$6GPa and 4192$\pm$104K. The trend of the stability field
implies a stable bcc-Fe at the Earth's inner core condition, with implications
including a strong candidate for explaining the seismic anisotropy of the
Earth's inner core.",1804.05109v1
2018-04-19,Anisotropy of the DC conductivity due to orbital-selective spin fluctuations in the nematic phase of iron superconductors,"We study the dc conductivity of iron-based superconductors within the
orbital-selective spin fluctuation scenario. Within this approach, the
anisotropy of spin fluctuations below the spin-nematic transition at T$_S$ is
also responsible for the orbital ordering, induced by nematic self-energy
corrections to the quasiparticle dispersion. As a consequence, the anisotropy
of the dc conductivity below T$_S$ is determined not only by the anisotropy of
the scattering rates as expected within a spin-nematic scenario, but also by
the modification of the Fermi velocity due to the orbital reconstruction. More
interestingly, it turns out that these two effects contribute to the
dc-conductivity anisotropy with opposite signs. By using realistic
band-structure parameters we compute the conductivity anisotropy for both 122
and FeSe compounds, discussing the possible origin of the different
dc-conductivity anisotropy observed experimentally in these two families of
iron-based superconductors.",1804.07293v4
2018-05-09,Superconducting joint between iron-based superconductor tapes,"Superconducting joints are essential for iron-based superconductor's
applications in future. In this study, a process for fabricating
superconducting joints between Sr1-xKxFe2As2 (Sr-122) tapes is developed for
the first time. The Ag sheath was peeled off from one side of each sample. The
exposed superconducting parts of the two tapes were joined and wrapped again
with Ag foil. The diffusion bonding of the iron-based superconducting joint was
achieved by hot-pressing process in Argon atmosphere. The superconducting
properties, microstructures and the elements distribution of the joint regions
had been investigated. The pressure and pressing times were optimized in order
to enhance the transport current of the joints. At 4.2 K and 10 T, a transport
critical current Ic of 57 A for the joint was obtained, which is approximately
63.3% of the current capacity of the tapes themselves. Furthermore, the joint
resistances dV/dI were estimated from the V-I curve of the joints and the
calculated joint resistances values are below 10^-9 Ohm. These results
demonstrate that the hot pressing was useful for fabricating the
superconducting joint samples.",1805.03399v1
2018-06-28,Fe3O4@astragalus polysaccharide core-shell nanoparticles for iron deficiency anemia therapy and magnetic resonance imaging in vivo,"Fe3O4@astragalus polysaccharide core-shell nanoparticles (Fe3O4@APS NPs) were
demonstrated to be an efficient therapeutic drug for treating iron deficiency
anemia (IDA) in vivo. The Fe3O4@APS NPs have been synthesized using a two steps
approach involving hydrothermal synthesis and subsequent esterification.
Transmission electron microscopy (TEM) and Fourier transform infrared (FTIR)
spectroscopy studies show that APS are attached on the surfaces of the highly
monodisperse Fe3O4 NPs. Dynamic light scatting (DLS) and magnetic
characterizations reveal that the Fe3O4@APS NPs have outstanding water
solubility and stability. Cytotoxicity assessment using Hela cells and
pathological tests in mice demonstrate their good biocompatibility and low
toxicity. The IDA treatment in rats shows that they have efficient therapeutic
effect, which is contributed to both the iron element supplement from Fe3O4 and
the APS-stimulated hematopoietic cell generation. Moreover, the Fe3O4@APS NPs
are superparamagnetic and thus able to be used for magnetic resonance imaging
(MRI). This study has demonstrated the potential of nanocomposites involving
purified natural products from Chinese herb medicine for biomedical
applications.",1806.10740v1
2018-07-25,Interplay between nematic fluctuation and superconductivity in the two-orbital Hubbard model: A quantum Monte Carlo study,"To understand the interplay between nematic fluctuation and superconductivity
in iron-based superconductors, we performed a systematic study of the realistic
two-orbital Hubbard model by using the constrained-path quantum Monte Carlo
method. Our numerical results showed that the on-site nematic interaction
induces a strong enhancement of nematic fluctuations at various momentums,
especially at ($\pi$,$\pi$). Simultaneously, it was found that the on-site
nematic interaction suppresses the ($\pi$,0)/(0,$\pi$) antiferromagnetic order
and long-range electron pairing correlations for dominant pairing channels in
iron-based superconductors. Our findings suggest that nematic fluctuation seems
to compete with superconductivity in iron-based superconductors.",1807.09457v1
2018-08-17,Local Magnetic States of the Weakly Ferromagnetic Iron-Based Superconductor Sr$_2$VFeAsO$_{3-δ}$ Studied by X-ray Magnetic Circular Dichroism,"We have performed x-ray magnetic circular dichroism (XMCD) measurements on
the iron-based superconductor Sr$_2$VFeAsO$_{3-\delta}$ to study the origin of
weak ferromagnetism (WFM) reported for this compound. While Fe 3$d$ electrons
show a magnetic response similar to the other iron pnictides, signals from V
3$d$ electrons remain finite at zero magnetic field and may be responsible for
the WFM.",1808.05715v3
2018-08-30,Selective Aggregation Experiments on Planetesimal Formation and Mercury-Like Planets,"Much of a planet's composition could be determined right at the onset of
formation. Laboratory experiments can constrain these early steps. This
includes static tensile strength measurements or collisions carried out under
Earth's gravity and on various microgravity platforms. Among the variety of
extrasolar planets which eventually form are (Exo)-Mercury, terrestrial planets
with high density. If they form in inner protoplanetary disks, high temperature
experiments are mandatory but they are still rare. Beyond the initial process
of hit-and-stick collisions, some additional selective processing might be
needed to explain Mercury. In analogy to icy worlds, such planets might, e.g.,
form in environments which are enriched in iron. This requires methods to
separate iron and silicate at early stages. Photophoresis might be one viable
way. Mercury and Mercury-like planets might also form due to the ferromagnetic
properties of iron and mechanisms like magnetic aggregation in disk magnetic
fields might become important. This review highlights some of the mechanisms
with the potential to trigger Mercury formation.",1808.10246v1
2018-09-10,Hedgehog Spin-vortex Crystal Antiferromagnetic Quantum Criticality in CaK(Fe1-xNix)4As4 Revealed by NMR,"Two ordering states, antiferromagnetism and nematicity, have been observed in
most iron-based superconductors (SCs). In contrast to those SCs, the newly
discovered SC CaK(Fe$_{1-x}$Ni$_x$)$_4$As$_4$ exhibits an antiferromagnetic
(AFM) state, called hedgehog spin-vortex crystal structure, without nematic
order, providing the opportunity for the investigation into the relationship
between spin fluctuations and SC without any effects of nematic fluctuations.
Our $^{75}$As nuclear magnetic resonance studies on
CaK(Fe$_{1-x}$Ni$_x$)$_4$As$_4$ (0$\le x\le$ 0.049) revealed that
CaKFe$_4$As$_4$ is located close to a hidden hedgehog SVC AFM quantum-critical
point (QCP). The magnetic QCP without nematicity in
CaK(Fe$_{1-x}$Ni$_x$)$_4$As$_4$ highlights the close connection of spin
fluctuations and superconductivity in iron-based SCs. The advantage of
stoichiometric composition also makes CaKFe$_4$As$_4$ an ideal platform for
further detailed investigation of the relationship between magnetic QCP and
superconductivity in iron-based SCs without disorder effects.",1809.03354v1
2018-11-06,First study on iron complexes in blood and organ samples from thalassaemic and normal laboratory mice using Moessbauer spectroscopy,"In this paper, blood and tissues samples from one normal and one thalassaemic
lab-mice were studied using 57Fe Mossbauer spectroscopy at 78K for the first
time. In contrast to human patients, these laboratory mice did not receive any
medical treatment, thus the iron components present in the samples are not
altered. The measured Moessbauer spectra of the blood, liver and spleen samples
of the thalassaemic mouse were found to be different in the shape and iron
content as compared to the corresponding spectra of the normal mouse. This
result demonstrates the further exploitation of the thalassaemic mouse model to
study thalassaemia in more details by means of Moessbauer spectroscopy.",1811.02594v1
2018-12-16,Strong electron-boson coupling in the iron-based superconductor BaFe1.9Pt0.1As2 revealed by infrared spectroscopy,"Understanding the formation of Cooper pairs in iron-based superconductors is
one of the most important topics in condensed matter physics. In conventional
superconductors, the electron-phonon interaction leads to the formation of
Cooper pairs. In conventional strong-coupling superconductors like lead (Pb),
the features due to electron-phonon interaction are evident in the infrared
absorption spectra. Here we investigate the infrared absorption spectra of the
iron arsenide superconductor BaFe1.9Pt0.1As2. We find that this superconductor
has fully gapped (nodeless) Fermi surfaces, and we observe the strong-coupling
electron-boson interaction features in the infrared absorption spectra. Through
modeling with the Eliashberg function based on Eliashberg theory, we obtain a
good quantitative description of the energy gaps and the strong-coupling
features. The full Eliashberg equations are solved to check the
self-consistency of the electron-boson coupling spectrum, the largest energy
gap, and the transition temperature (Tc). Our experimental data and analysis
provide compelling evidence that superconductivity in BaFe1.9Pt0.1As2 is
induced by the coupling of electrons to a low-energy bosonic mode that does not
originate solely from phonons.",1812.06546v1
2018-12-26,Helical Hinge Majoranas in Iron-Based Superconductors,"Motivated by recent experiments on FeTe$_{1-x}$Se$_{x}$, we construct an
explicit minimal model of an iron-based superconductor with band inversion at
the $Z$ point and non-topological bulk $s_{\pm}$ pairing. While there has been
considerable interest in Majorana zero modes localized at vortices in such
systems, we find that our model - without any vortices - intrinsically supports
1D helical Majorana modes localized at the hinges between (001) and (100) or
(010) surfaces, suggesting that this is a viable platform for observing
""higher-order"" topological superconductivity. We provide a general theory for
these hinge modes and discuss their stability and experimental manifestation.
Our work indicates the possible experimental observability of hinge Majoranas
in iron-based topological superconductors.",1812.10493v2
2019-01-01,A strongly inhomogeneous superfluid in an iron-based superconductor,"Among the mysteries surrounding unconventional, strongly correlated
superconductors is the possibility of spatial variations in their superfluid
density. We use atomic-resolution Josephson scanning tunneling microscopy to
reveal a strongly inhomogeneous superfluid in the iron-based superconductor
FeTe0.55Se0.45. By simultaneously measuring the topographic and electronic
properties, we find that this inhomogeneity in the superfluid density is not
caused by structural disorder or strong inter-pocket scattering, and does not
correlate with variations in Cooper pair-breaking gap. Instead, we see a clear
spatial correlation between superfluid density and quasiparticle strength,
putting the iron-based superconductors on equal footing with the cuprates and
demonstrating that locally, the quasiparticles are sharpest when the
superconductivity is strongest. When repeated at different temperatures, our
technique could further help elucidate what local and global mechanisms limit
the critical temperature in unconventional superconductors.",1901.00149v1
2019-01-29,Interaction between Molecular Clouds and MeV-TeV Cosmic-ray Protons Escaped from Supernova Remnants,"Recent discovery of the X-ray neutral iron line (Fe I K\alpha at 6.40 keV)
around several supernova remnants (SNRs) show that MeV cosmic-ray (CR) protons
are distributed around the SNRs and are interacting with neutral gas there. We
propose that these MeV CRs are the ones that have been accelerated at the SNRs
together with GeV-TeV CRs. In our analytical model, the MeV CRs are still
confined in the SNR when the SNR collides with molecular clouds. After the
collision, the MeV CRs leak into the clouds and produce the neutral iron line
emissions. On the other hand, GeV-TeV CRs had already escaped from the SNRs and
emit gamma-rays through interaction with molecular clouds surrounding the SNRs.
We apply this model to the SNRs W28 and W44 and show that it can reproduce the
observations of the iron line intensities and the gamma-ray spectra. This can
be another support of a hadronic scenario for the gamma-ray emissions from
these SNRs.",1901.10477v3
2019-03-01,"Broken mirror symmetry, incommensurate spin correlations, and $B_{2g}$ nematic order in iron pnictides","Motivated by growing indications for a distinct form of nematic correlations
in the extremely hole doped iron pnictide compounds $A$Fe$_2$As$_2$
($A$=K,Rb,Cs), we consider spin-driven nematic order in the general case of
incommensurate magnetic fluctuations. We classify the nematic order parameters
by broken mirror symmetries of the tetragonal $D_{4h}$ point group, and use
this scheme to construct a general Ginzburg-Landau theory that links the
nematic order to spatial pattern of magnetic fluctuations. Our analysis points
to incommensurate magnetic fluctuations of wavevector $(q,q)$ as underlying a
$B_{2g}$ nematic order in $A$Fe$_2$As$_2$. We substantiate this idea by
microscopic calculations of the nematic order based on 3-sublattice
$(2\pi/3,2\pi/3)$ spin correlations in an extended bilinear-biquadratic
Heisenberg model. We summarize the existing evidence in support of the proposed
mechanism, suggest ways to further test it in future experiments, and discuss
the implications of our results for iron-based high temperature
superconductivity.",1903.00375v2
2019-03-12,Epsilon-iron as a spin-smectic state,"Using x-ray emission spectroscopy, we find appreciable local magnetic moments
until 30-40 GPa in the high-pressure phase of iron, however no magnetic order
is detected with neutron powder diffraction down to 1.8 K contrary to previous
predictions. Our first-principles calculations reveal a ""spin-smectic"" state
lower in energy than previous results. This state forms antiferromagnetic
bilayers separated by null spin bilayers, which allows a complete relaxation of
the inherent frustration of antiferromagnetism on a hexagonal close-packed
lattice. The magnetic bilayers are likely orientationally disordered, owing to
the soft interlayer excitations and the near-degeneracy with other smectic
phases. This possible lack of long-range correlation agrees with the null
results from neutron powder diffraction. An orientationally-disordered,
spin-smectic state resolves previously perceived contradictions in high
pressure iron and could be integral to explaining its puzzling
superconductivity.",1903.04792v2
2019-03-15,"Plasma environment effects on K lines of astrophysical interest. II. Ionization potentials, K thresholds, radiative rates and Auger widths in Ne- through He-like iron ions (Fe xvii - Fe xxv)","Aims. In the context of accretion disks around black holes, we estimate
plasma-environment effects on the atomic parameters associated with the decay
of K-vacancy states in highly charged iron ions, namely Fe xvii - Fe xxv.
Methods. Within the relativistic multiconfiguration Dirac-Fock (MCDF)
framework, the electron-nucleus and electron-electron plasma screenings are
approximated with a time-averaged Debye-Huckel potential. Results. Modified
ionization potentials, K thresholds, wavelengths, radiative emission rates and
Auger widths are reported for astrophysical plasmas characterized by electron
temperatures and densities respectively in the ranges 1E5 - 1E7 K and 1E18 -
1E22 cm-3 . Conclusions. We conclude that the high-resolution
micro-calorimeters onboard future X-ray missions such as XRISM and ATHENA are
expected to be sensitive to the lowering of the iron K edge due to the extreme
plasma conditions occurring in accretion disks around compact objects.",1903.06458v1
2019-04-11,Strain tuning and anisotropic spin correlations in iron-based systems,"Nematic order in the iron-based superconductors is closely tied to a lattice
distortion and a structural transition from tetragonal to orthorhombic
symmetry. External stress of the appropriate symmetry acts as a conjugate field
of the nematic order parameter and can be utilized to detwin nematic domains
but also smears an otherwise sharp nematic transition. On the other hand,
applying stress in proper symmetry channels allows one to tune the nematic
phase transition. Recent experiments analyzed the stress-induced changes of the
nematic and magnetic phase transition temperature. Here we show that the
observed trends can be understood in terms of spin-induced nematicity. The
strain sensitivity is shown to be a fluctuation effect. The strong sensitivity
to antisymmetric strain is a consequence of the anisotropic nature of the
magnetic excitation spectrum. The formalism presented here can be naturally
generalized to determine the strain-sensitivity of vestigial phases related to
other magnetic states that have been observed in the iron-based systems, such
as e.g.\ the spin-charge density wave and the spin-vortex crystals.",1904.05583v2
2019-04-27,Neutron star radius measurement from the ultraviolet and soft X-ray thermal emission of PSR J0437-4715,"We analyzed the thermal emission from the entire surface of the millisecond
pulsar PSR J0437-4715 observed in the ultraviolet and soft X-ray bands. For
this, we calculated non-magnetized, partially ionized atmosphere models of
hydrogen, helium, and iron compositions and included plasma frequency effects
that may affect the emergent spectrum. This is particularly true for the
coldest atmospheres composed of iron (up to a few percent changes in the soft
X-ray flux). Employing a Markov chain Monte Carlo method, we found that the
spectral fits favour a hydrogen atmosphere, disfavour a helium composition and
rule out iron atmosphere and blackbody models. By using a Gaussian prior on the
dust extinction, based on the latest 3D map of Galactic dust, and accounting
for the presence of hot polar caps found in previous work, we found that the
hydrogen atmosphere model results in a well-constrained neutron star radius
$R_\mathrm{NS} = 13.6^{+0.9}_{-0.8}~\mathrm{km}$ and bulk surface temperature
$T^{\infty}_\mathrm{eff}=\left(2.3\pm0.1\right)\times10^5~\mathrm{K}$. This
relatively large radius favours a stiff equation of state and disfavours a
strange quark composition inside neutron stars.",1904.12114v2
2019-05-01,p-Wave Superconductivity in Iron-based Superconductors,"The possibility of p-wave pairing in superconductors has been proposed more
than five decades ago, but has not yet been convincingly demonstrated. One
difficulty is that some p-wave states are thermodynamically indistinguishable
from s-wave, while others are very similar to d-wave states. Here we studied
the self-field critical current of NdFeAs(O,F) thin films in order to extract
absolute values of the London penetration depth, the superconducting energy
gap, and the relative jump in specific heat at the superconducting transition
temperature, and find that all the deduced physical parameters strongly
indicate that NdFeAs(O,F) is a bulk p-wave superconductor. Further
investigation revealed that single atomic layer FeSe also shows p-wave pairing.
In an attempt to generalize these findings, we re-examined the whole inventory
of superfluid density measurements in iron-based superconductors show quite
generally that most of the iron-based superconductors are p-wave
superconductors.",1905.00183v3
2019-06-21,Topological Crystalline Superconductivity in Dirac Semimetal Phase of Iron-based Superconductors,"In iron-based superconductors, band inversion of $d$- and $p$-orbitals yields
Dirac semimetallic states. We theoretically investigate their topological
properties in normal and superconducting phases, based on the tight-binding
model involving full symmetry of the materials. We demonstrate that a Cooper
pair between electrons with $d$- and $p$-orbitals relevant to the band
structure yields odd-parity superconductivity. Moreover, we present the typical
surface states by solving the Bogoliubov-de Gennes equation and characterize
them by topological invariants defined with crystal symmetry. It is found that
there appear various types of Majorana fermions such as surface flat band,
Majorana quartet and M\""{o}bius twisted surface state. Our theoretical results
show that iron-based superconductors are promising platforms to realize rich
topological crystalline phases.",1906.09286v1
2019-08-30,Magnetic states of iron-based two-leg ladder tellurides,"The recent discovery of superconductivity at high pressure in the two-leg
ladder compounds BaFe$_2X_3$ ($X$=S, Se) started the novel field of
quasi-one-dimensional iron-based superconductors. In this publication, we use
Density Functional Theory (DFT) to predict that the previously barely explored
ladder compound RbFe$_2$Te$_3$ should be magnetic with a CX-type arrangement
involving ferromagnetic rungs and antiferromagnetic legs, at the realistic
density of $n=5.5$ electrons per iron. The magnetic state similarity with
BaFe$_2$S$_3$ suggests that RbFe$_2$Te$_3$ could also become superconducting
under pressure. Moreover, at $n=6.0$ our DFT phase diagrams (with and without
lattice tetramerization) reveal that the stable magnetic states could be either
a 2$\times$2 magnetic Block-type, as for $X$=Se, or a previously never observed
before CY-type state, with ferromagnetic legs and antiferromagnetic rungs. In
the Te-based studies, electrons are more localized than in S, implying that the
degree of electronic correlation is enhanced for the Te case.",1908.11765v2
2019-09-10,Anisotropic magnetic excitations of a frustrated bilinear-biquadratic spin model -- Implications for spin waves of detwinned iron pnictides,"Elucidating the nature of spin excitations is important to understanding the
mechanism of superconductivity in the iron pnictides. Motivated by recent
inelastic neutron scattering measurements in the nearly 100% detwinned
BaFe$_{2}$As$_{2}$, we study the spin dynamics of an $S=1$ frustrated
bilinear-biquadratic Heisenberg model in the antiferromagnetic phase with
wavevector $(\pi,0)$. The biquadratic interactions are treated in a dynamical
way using a flavor-wave theory in an $SU(3)$ representation. Besides the magnon
(dipolar) excitations, the biquadratic interactions give rise to quadrupolar
excitations at high energies. We find that the quadrupolar wave significantly
influences, in an energy dependent way, the anisotropy between the spin
excitation spectra along the $(\pi,0)$ and $(0,\pi)$ directions in the wave
vector space. Our theoretical results capture the essential behavior of the
spin dynamics measured in the antiferromagnetic phase of the detwinned
BaFe$_2$As$_2$. More generally, our results underscore the importance of
electron correlation effects for the microscopic physics of the iron pnictides.",1909.04555v2
2019-09-21,Dynamical stability of radiation-induced C15 clusters in iron,"Density functional theory predicts clusters in the form of the C15 Laves
phase to be the most stable cluster of self-interstitials in iron at small
sizes. The C15 clusters can form as a result of irradiation, but their
prevalence and survival in harsh irradiation conditions have not been
thoroughly studied. Using a new bond-order potential optimised for molecular
dynamics simulations of radiation damage, we explore the dynamical stability of
the C15 clusters in iron under irradiation conditions. We find that small C15
clusters make up 5-20% of the interstitial clusters formed directly in
cascades. In continuous irradiation, C15 clusters are frequently formed, after
which they remain highly stable and grow by absorbing nearby single
interstitial atoms. Growth of C15 clusters ultimately leads to collapse into
dislocation loops, most frequently into 1/2<111> loops and only rarely
collapsing into <100> loops at low temperatures. The population, size, and
collapse of C15 clusters during continuous irradiation correlates well with
their formation energies relative to dislocation loops calculated at zero
Kelvin.",1909.09818v1
2019-10-31,Quantum critical nematic fluctuations and spin excitation anisotropy in iron pnictides,"Quantum criticality in iron pnictides involves both the nematic and
antiferromagnetic degrees of freedom, but the relationship between the two
types of fluctuations has yet to be clarified. Here we study this problem in
the presence of a small external uniaxial potential, which breaks the
$C_4$-symmetry in the B$_{1g}$ sector. We establish an identity that connects
the spin excitation anisotropy, which is the difference of the dynamical spin
susceptibilities at $\vec{Q}_1=\left(\pi,0\right)$ and
$\vec{Q}_2=\left(0,\pi\right)$, with the dynamical magnetic susceptibility and
static nematic susceptibility. Using this identity, we introduce a scaling
procedure to determine the dynamical nematic susceptibility in the quantum
critical regime, and illustrate the procedure for the case of the optimally
Ni-doped BaFe$_2$As$_2$[Y. Song \textit{et al.}, Phys. Rev. B 92, 180504
(2015)]. The implications of our results for the overall physics of the
iron-based superconductors are discussed.",1910.14597v4
2019-12-11,Hypothetical hyperbolic encounters between Venus and proto-Mercury that partially \ stripped away proto-Mercury's mantle,"Mercury has an unusually large metal core comprising ~70% of its mass
comparing to all other terrestrial planets in the solar system. Giant impacts
can remove a significant fraction of the silicate mantle of a chondritic
proto-Mercury and form the iron rich present-day Mercury. However, such
high-temperature giant impacts seem at odds with the retainment of moderately
volatile elements on present-day Mercury (Peplowski et al. 2011). We simulated
a series of hyperbolic encounters between proto-Mercury and proto-Venus, which
may occur in the chaotic early solar system. Tidal disruption of proto-Mercury
always removes part of its silicate mantle while its iron core remains intact.
We find, in favourable cases, four close encounters with fast spinning
projectiles (resulting from previous encounters) can lead to present-day
Mercury iron fraction. More encounters are needed when the spin and orbital
angular momentum are not always aligned. These hyperbolic encounters have
various outcomes, such as orbital decay, binary planets and change of spin
rates. These results suggest the importance of proper treatment of close
encounters in N-body simulations of planetary accretion.",1912.05219v1
2019-12-12,X-ray reverberation lags from the 1.5 Seyfert galaxy NGC 5273,"We present the results of X-ray spectral-timing analysis of a 90ks XMM-Newton
observation of the nearby, broad line, early-type AGN NGC5273. The X-ray
spectrum revealed the clear presence of a reflection component at high
energies, with a clear signature of a narrow iron line at 6.4 keV, consistent
with distant reflection. Applying a relativistic reflection model, we found
only marginal evidence for a broader relativistic line component. However,
cross-spectral analysis revealed that, between 4 and 6 $\times 10^{-4}$ Hz, the
5-8 keV band lagged the 2-3 keV band, implying reflection of the iron line from
material close to the black hole. From the analysis of the lag-energy spectrum,
we found a broad, but skewed line with a peak of $\approx$ 1000s at 7.5 keV
relative to the continuum, which we interpret as the iron line in the
reverberation spectrum from an illuminated accretion disc. From the asymmetry
in the shape of lag-energy spectrum, we also found that the source is
consistent with having an inclination $\geq 45^\circ$.",1912.06196v1
2020-02-18,Low work function in the 122-family of iron-based superconductors,"We determine the work functions of the iron arsenic compounds $A$Fe$_2$As$_2$
($A=\mathrm{Ca, Ba, Cs}$) using photoemission spectroscopy to be 2.7 eV for
CaFe$_2$As$_2$, 1.8 eV for BaFe$_2$As$_2$, and 1.3 eV for CsFe$_2$As$_2$. The
work functions of these 122 iron-based superconductors track those of the
elementary metal $A$ but are substantially smaller. The most likely explanation
of this observation is that the cleaving surface exposes only half an
$A$-layer. The low work function and good photoemission cross section of
BaFe$_2$As$_2$ and CsFe$_2$As$_2$ enable photoemission even from a common white
LED light.",2002.07924v1
2020-02-21,Iron Line Tomography of General Relativistic Hydrodynamic Accretion around Kerr Black Holes,"We consider a temporal response of relativistically broadened line spectrum
of iron from black hole accretion irradiated by an X-ray echo under strong
gravity. The physical condition of accreting gas is numerically calculated in
the context of general relativistic hydrodynamics under steady-state,
axisymmetry in Kerr geometry. With the onset of a point-like X-ray flare of a
short finite duration just above the accretion surface, the gas is assumed to
be ionized to produce a neutral iron fluorescent line. Using a fully
relativistic ray-tracing approach, the response of line photons due to the
X-ray illumination is traced as a function of time and energy for different
source configurations around \sw and Kerr black holes. Our calculations show
that the X-ray echo on the accretion surface clearly imprints a characteristic
time-variability in the line spectral features depending on those parameters.
Simulated line profiles, aimed for the future microcalorimeter missions of
large collecting area such as {\it Athena}/X-IFU for typical radio-quiet
Seyfert galaxies, are presented to demonstrate that state-of-the-art new
observations could differentiate various source parameters by such an X-ray
tomographic line reverberation.",2002.09550v1
2020-02-22,Molecular static simulation of edge dislocation core in bcc iron,"We simulate the dislocation core structure in bcc iron using the modified
Molecular Static method. A feature of this method is the application of an
iterative procedure in which the atomic structure in the vicinity of the defect
and the constants that determine the displacements of atoms immersed in the
elastic continuum are calculated in a self-consistent manner. Following the
mentioned approach, we develop a model for calculating the atomic structure of
edge dislocations, taking into account the anisotropy of the elastic medium
surrounding the main calculation cell. Anisotropy is taken into account by
introducing an explicit angular dependence for the parameters of the elastic
field created by the dislocation: magnitude of Burgers vector and Poisson's
ratio. Simulation is carried out for a split dislocation with Burgers vector
along [100]. The convergence of the iterative algorithm is shown and the
influence of the computational cell size on the results is considered.
Calculated results are: atomic structure of dislocation in bcc iron, angular
dependence of the parameters describing the elastic dislocation field at large
distances from the dislocation line, and the strain tensor components in the
entire simulation area.",2002.09601v2
2020-02-25,A Type Ia supernova at the heart of superluminous transient SN 2006gy,"Superluminous supernovae radiate up to 100 times more energy than normal
supernovae. The origin of this energy and the nature of their stellar
progenitors are poorly understood. We identify neutral iron lines in the
spectrum of one such transient, SN 2006gy, and show that they require a large
mass of iron (>~0.3 Msun) expanding at 1500 km/s. We demonstrate that a model
of a standard Type Ia supernova hitting a shell of circumstellar material
produces a light curve and late-time iron-dominated spectrum that match SN
2006gy. In such a scenario, common envelope evolution of the progenitor system
can synchronize envelope ejection and supernova explosion and may explain these
bright transients.",2002.10768v1
2020-05-07,In the Pursuit of Majorana Modes in Iron-based High-$T_c$ Superconductors,"Majorana zero mode is an exotic quasi-particle excitation with non-Abelian
statistics in topological superconductor systems, and can serve as the
cornerstone for topological quantum computation, a new type of fault-tolerant
quantum computation architecture. This review paper highlights recent progress
in realizing Majorana modes in iron-based high-temperature superconductors. We
begin with the discussion on topological aspect of electronic band structures
in iron-based superconductor compounds. Then we focus on several concrete
proposals for Majorana modes, including the Majorana zero modes inside the
vortex core on the surface of Fe(Te,Se), helical Majorana modes at the hinge of
Fe(Te,Se), the Majorana zero modes at the corner of the Fe(Te,Se)/FeTe
heterostructure or the monolayer Fe(Te,Se) under an in-plane magnetic field. We
also review the current experimental stage and provide the perspective and
outlook for this rapidly developing field.",2005.03603v1
2020-05-11,Simplified ResNet approach for data driven prediction of microstructure-fatigue relationship,"The heterogeneous microstructure in metallic components results in locally
varying fatigue strength. Metal fatigue strongly depends on size and shape of
non-metallic inclusions and pores, commonly referred to as ""defects"". Nodular
cast iron (NCI) contains graphite inclusions (nodules) whose shape and
frequency influence the fatigue strength. Fatigue strength can be simulated by
micromechanical finite element models. The drawback of these models are the
large computational costs. Therefore, we employ a data-driven machine learning
methodology. More precisely, we utilize the simplified residual neural network
(SimResNet) which was recently introduced (Herty et al., Kinetic Theory for
Residual Neural Networks, 2020) to predict fatigue strength from metallographic
data. For the training, we use fatigue data which is simulated with a
micromechanical model and the shakedown theorem. The micromechanical models are
derived directly from micrographs of nodular cast iron, respectively. The
application of SimResNet shows a good performance to predict fatigue strength
by local microstructures of nodular cast iron. We show several test cases. The
simplified character of SimResNet enables fast predictions of fatigue by
microstructures, even in comparision to classical residual neural networks.",2005.06615v1
2020-06-05,Observation of Two-dimensional Superconductivity in an Ultrathin Iron-Arsenic Superconductor,"Two-dimensional (2D) superconductors supply important platforms for exploring
new quantum physics and high-$T_c$ superconductivity. The intrinsic
superconducting properties in the 2D iron-arsenic superconductors are still
unknown owing to the difficulties in the preparation of ultrathin samples. Here
we report the fabrication and physical investigations of the high quality
single-crystalline ultrathin films of the iron-arsenic superconductor
KCa$_2$Fe$_4$As$_4$F$_2$. For the sample with the thickness of 2.6$\sim$5 nm
(1$\sim$2 unit cells), a sharp superconducting transition at around 30 K (onset
point) is observed. Compare with the bulk material, the ultrathin sample
reveals a relatively lower $T_c$, wider transition width, and broader flux
liquid region under the in-plane field. Moreover, the angle dependent upper
critical field follows the Tinkham model, demonstrating the two-dimensional
superconductivity in ultrathin KCa$_2$Fe$_4$As$_4$F$_2$.",2006.03338v1
2020-06-24,Composition and Size Dependent Sorting in Preplanetary Growth: Seeding the Formation of Mercury-like Planets,"In an earlier work, we found that large metallic iron fractions in dust
aggregates and strong magnetic fields boost preplanetary growth. This sets an
initial bias for the formation of Mercury-like planets in the inner part of
protoplanetary disks. We extended these experiments here by adding pure quartz
aggregates to the iron-rich aggregates. Magnetic boost still leads to the
formation of larger clusters of aggregates. These clusters now include silicate
aggregates, which can also be connecting bridges between chains. However, at
least a certain fraction of iron-rich aggregates are needed to trigger magnetic
boost. Without a magnetic field, the sticking properties of the aggregates and
their constituents determine the composition of clusters of a given size. This
introduces a new fractionation and sorting mechanism by cluster formation at
the bouncing barrier.",2006.13692v1
2020-07-14,In-plane p-wave coherence length in iron-based superconductors,"High-temperature superconductivity in iron-based layered compounds discovered
by Hosono group (Kamihara et al 2006 J. Am. Chem. Soc. 128 10012) is
fascinating physical phenomenon which still has many unanswered questions. One
of these questions is the superconducting gap symmetry in iron-based
superconductors (IBS), for which the most agreed concept is multiple-band
$s$-wave symmetry. Recently, an alternative concept of single-band $p$-wave
symmetry has been proposed. To disprove/reaffirm the latter concept, in this
paper we analyse temperature dependent in-plane coherence length in FeSe,
FeSe1-xTex, Ba(Fe1-x(Co,Ni)x)2As2 and Ca10(Pt4As8)((Fe,Pt)2As2)5 in order to
extract the gap-to-critical-temperature ratio, 2$\Delta$(0)/$k$$_B$$T$$_c$, and
the specific-heat-jump ratio, $\Delta$C/C,in these compounds. In the result, we
report that deduced ratios are in a good agreement with the concept of
single-band $p$-wave superconductivity in these materials.",2007.07110v1
2020-08-20,Canted Antiferromagnetism in the Quasi-1D Iron Chalcogenide BaFe$_{2}$Se$_{4}$,"We report the synthesis and physical properties studies of quais-1D iron
chalcogenide $\rm BaFe_2Se_4$ which shares the $\rm FeSe_4$ tetrahedra building
motif commonly seen in the iron chalcogenide superconductors. A high-quality
polycrystalline sample was achieved by solid-state reaction method and
characterized by X-ray diffraction, electrical resistivity, magnetic
susceptibility and neutron diffraction measurements. $\rm BaFe_2Se_4$ is a
narrow gap semiconductor that magnetically orders at $\sim$ 310 K. Both neutron
powder diffraction results and isothermal M-H loops suggest a canted
antiferromagnetic structure where Fe sublattice are antiferromagnetically
ordered along the c-axis quasi-1D chain direction, resulting in a net
ferromagnetic moment in the perpendicular direction along the a-axis with
tilted angle of 18.7$^\circ$ towards the b-axis.",2008.08809v1
2020-09-04,Strong enhancement of magnetic order from bulk to stretched monolayer FeSe as Hund's metals,"Despite of the importance of magnetism in possible relation to other key
properties in iron-based superconductors, its understanding is still far from
complete especially for FeSe systems. On one hand, the origin of the absence of
magnetic orders in bulk FeSe is yet to be clarified. On the other hand, it is
still not clear how close monolayer FeSe on SrTiO$_3$, with the highest
transition temperature among iron-based superconductors, is to a magnetic
instability. Here we investigate magnetic properties of bulk and monolayer FeSe
using dynamical mean-field theory combined with density-functional theory. We
find that suppressed magnetic order in bulk FeSe is associated with the
reduction of inter-orbital charge fluctuations, an effect of Hund's coupling,
enhanced by a larger crystal field splitting. Meanwhile, spatial isolation of
Fe atoms in expanded monolayer FeSe leads into a strong magnetic order, which
is completely destroyed by a small electron doping. Our work provides a
comprehensive understanding of the magnetic order in iron-based superconductors
and other general multi-orbital correlated systems as Hund's metals.",2009.02024v1
2020-09-24,Probing redox potential for Iron sulfur clusters in photosystem I,"Photosystem I is a light-driven electron transfer device. Available X-ray
crystal structure from Thermosynechococcus elongatus, showed that electron
transfer pathways consist of two nearly symmetric branches of cofactors
converging at the first iron sulfur cluster FX, which is followed by two
terminal iron sulfur clusters FA and FB. Experiments have shown that Fx has
lower oxidation potential than FA and FB, which facilitate the electron
transfer reaction. Here, we use Density Functional Theory and Multi-Conformer
Continuum Electrostatics to explain the differences in the midpoint Em
potentials of the Fx, FA and FB clusters. Our calculations show that Fx has the
lowest oxidation potential compared to FA and FB due strong pair-wise
electrostatic interactions with surrounding residues. These interactions are
shown to dominated by the bridging sulfurs and cysteine ligands, which may be
attributed to the shorter average bond distances between the oxidized Fe ion
and ligating sulfurs for FX compared to FA and FB. Moreover, the electrostatic
repulsion between the 4Fe-4S clusters and the positive potential of the
backbone atoms is least for FX compared to both of FA and FB. These results
agree with the experimental measurements from the redox titrations of
low-temperature EPR signals and of room temperature recombination kinetics.",2009.11681v1
2020-10-11,Electrical properties of thermal oxide scales on pure iron in liquid lead-bismuth eutectic,"The impedance behavior of pre-oxidized iron in liquid lead-bismuth eutectic
(LBE) at 200 oC is studied using electrochemical impedance spectroscopy. The
structures and resistance of oxide grown on iron oxidized in air at different
temperatures and durations are compared. The results show that the resistance
of the oxide film increases with increasing oxidizing temperature, due to the
formation of a thicker scale and fewer defects. At the same temperature (600
oC), increasing the oxidation time can also reduce the defect concentration in
the oxide film and improve the impedance of the oxide scale in LBE.",2010.05372v1
2020-10-15,"Anomalous thermal properties and spin crossover of ferromagnesite (Mg,Fe)CO3","Ferromagnesite (Mg,Fe)CO3, also referred to as magnesiosiderite at high iron
concentration, is a solid solution of magnesite (MgCO3) and siderite (FeCO3).
Ferromagnesite is believed to enter the Earth's lower mantle via subduction and
is considered a major carbon carrier in the Earth's lower mantle, playing a key
role in the Earth's deep carbon cycle. Experiments have shown that
ferromagnesite undergoes a pressure-induced spin crossover, accompanied by
volume and elastic anomalies, in the lower-mantle pressure range. In this work,
we investigate thermal properties of (Mg,Fe)CO3 using first-principles
calculations. We show that nearly all thermal properties of ferromagnesite are
drastically altered by iron spin crossover, including anomalous reduction of
volume, anomalous softening of bulk modulus, and anomalous increases of thermal
expansion, heat capacity, and Guneisen parameter. Remarkably, the anomaly of
heat capacity remains prominent (up to 40%) at high temperature without
smearing out, which suggests that iron spin crossover may significantly affect
the thermal properties of subducting slabs and the Earth's deep carbon cycle.",2010.07720v2
2020-11-11,Electron doping of the iron-arsenide superconductor CeFeAsO controlled by hydrostatic pressure,"In the iron-pnictide material CeFeAsO not only the Fe moments, but also the
local 4f moments of the Ce order antiferromagnetically at low temperatures. We
elucidate on the peculiar role of the Ce on the emergence of superconductivity.
While application of pressure suppresses the iron SDW ordering temperature
monotonously up to 4 GPa, the Ce-4f magnetism is stabilized, until both types
of magnetic orders disappear abruptly and a narrow SC dome develops. With
further increasing pressure characteristics of a Kondo-lattice system become
more and more apparent in the electrical resistivity. This suggests a
connection of the emergence of superconductivity with the extinction of the
magnetic order and the onset of Kondo-screening of the Ce-4f moments.",2011.05665v1
2020-11-17,Dichotomy Between Orbital and Magnetic Nematic Instabilities in BaFe2S3,"Nematic orders emerge nearly universally in iron-based superconductors, but
elucidating their origins is challenging because of intimate couplings between
orbital and magnetic fluctuations. The iron-based ladder material BaFe2S3,
which superconducts under pressure, exhibits antiferromagnetic order below TN ~
117K and a weak resistivity anomaly at T* ~ 180K, whose nature remains elusive.
Here we report angle-resolved magnetoresistance (MR) and elastoresistance (ER)
measurements in BaFe2S3, which reveal distinct changes at T*. We find that MR
anisotropy and ER nematic response are both suppressed near T*, implying that
an orbital order promoting isotropic electronic states is stabilized at T*.
Such an isotropic state below T* competes with the antiferromagnetic order,
which is evidenced by the nonmonotonic temperature dependence of nematic
fluctuations. In contrast to the cooperative nematic orders in spin and orbital
channels in iron pnictides, the present competing orders can provide a new
platform to identify the separate roles of orbital and magnetic fluctuations.",2011.08600v1
2020-11-25,Expansion and Age of the Supernova Remnant G350.1-0.3: High-Velocity Iron Ejecta from a Core-Collapse Event,"We report Chandra observations of the highly asymmetric core-collapse
supernova remnant G350.1-0.3. We document expansion over 9 years away from the
roughly stationary central compact object, with sky-plane velocities up to
$5000 d_{4.5}$ km s$^{-1}$ ($d_{4.5}$ is the distance in units of 4.5 kpc),
redshifts ranging from 900 km s$^{-1}$ to 2600 km s$^{-1}$, and
three-dimensional space velocities approaching 6000 km s$^{-1}$. Most of the
bright emission comes from heavy-element ejecta particularly strong in iron.
Iron-enhanced ejecta are seen at 4000 - 6000 km s$^{-1}$, strongly suggesting
that the supernova was not a common Type IIP event. While some fainter regions
have roughly solar abundances, we cannot identify clear blast-wave features.
Our expansion proper motions indicate that G350.1-0.3 is no more than about 600
years old, independent of distance: the third youngest known core-collapse
supernova in the Galaxy, and one of the most asymmetric.",2011.12977v2
2020-12-18,Efficient Analytical Approach for High-Pressure Melting Properties of Iron,"Iron represents the principal constituent of the Earth's core, but its
high-pressure melting diagram remains ambiguous. Here we present a simple
analytical approach to predict the melting properties of iron under deep-Earth
conditions. In our model, anharmonic free energies of the solid phase are
directly determined by the moment expansion technique in quantum statistical
mechanics. This basis associated with the Lindemann criterion for a vibrational
instability can deduce the melting temperature. Moreover, we correlate the
thermal expansion process with the shear response to explain a discontinuity of
atomic volume, enthalpy, and entropy upon melting. Our numerical calculations
are quantitatively consistent with recent experiments and simulations. The
obtained results would improve understanding of the Earth's structure,
dynamics, and evolution.",2012.10023v1
2021-02-19,Thermodynamic electric quadrupole moments of nematic phases from first-principles calculation,"The electronic nematic phase emerging with spontaneous rotation symmetry
breaking is a central issue of modern condensed matter physics. In particular,
various nematic phases in iron-based superconductors and high-$T_{\rm c}$
cuprate superconductors are extensively studied recently. Electric quadrupole
moments (EQMs) are one of the order parameters characterizing these nematic
phases in a unified way, and elucidating EQMs is a key to understanding these
nematic phases. However, the quantum-mechanical formulation of the EQMs in
crystals is a nontrivial issue because the position operators are non-periodic
and unbound. Recently, the EQMs have been formulated by local thermodynamics,
and such {\it thermodynamic EQMs} may be used to characterize the fourfold
rotation symmetry breaking in materials. In this paper, we calculate the
thermodynamic EQMs in iron-based superconductors LaFeAsO and FeSe as well as a
cuprate superconductor La$_2$CuO$_4$ by a first-principles calculation. We show
that owing to the orbital degeneracy the EQMs in iron-based superconductors are
mainly determined by the geometric properties of wave functions. This result is
in sharp contrast to the cuprate superconductor, in which the EQMs are
dominated by distortion of the Fermi surface.",2102.09783v1
2021-03-16,Accretion geometry of the black hole binary MAXI J1820+070 probed by frequency-resolved spectroscopy,"The geometry of the inner accretion flow in the hard and hard-intermediate
states of X-ray binaries remains controversial. Using NICER observations of the
black hole X-ray binary MAXI J1820+070 during the rising phase of its 2018
outburst, we study the evolution of the timing properties, in particular the
characteristic variability frequencies of the prominent iron K$\alpha$ line.
Using frequency-resolved spectroscopy, we find that reflection occurs at large
distances from the Comptonizing region in the bright hard state. During the
hard- to soft transition, the variability properties suggest the reflector
moves closer to the X-ray source. In parallel, the peak of the iron line shifts
from 6.5 to ~7 keV, becoming consistent with that expected of from a highly
inclined disc extending close to the black hole. We additionally find
significant changes in the dependence of the root-mean-square (rms) variability
on both energy and Fourier frequency as the source softens. The evolution of
the rms-energy dependence, the line profile, and the timing properties of the
iron line as traced by the frequency-resolved spectroscopy all support the
picture of a truncated disc/inner flow geometry.",2103.08795v1
2021-03-16,Emerging symmetric strain response and weakening nematic fluctuations in strongly hole-doped iron-based superconductors,"Electronic nematicity is often found in unconventional superconductors,
suggesting its relevance for electronic pairing. In the strongly hole-doped
iron-based superconductors, the symmetry channel and strength of the nematic
fluctuations, as well as the possible presence of long-range nematic order,
remain controversial. Here, we address these questions using transport
measurements under elastic strain. By decomposing the strain response into the
appropriate symmetry channels, we demonstrate the emergence of a giant in-plane
symmetric contribution, associated with the growth of both strong electronic
correlations and the sensitivity of these correlations to strain. We find
weakened remnants of the nematic fluctuations that are present at optimal
doping, but no change in the symmetry channel of nematic fluctuations with hole
doping. Furthermore, we find no evidence for a nematic-ordered state in the
AFe$_2$As$_2$(A = K, Rb, Cs) superconductors. These results revise the current
understanding of nematicity in hole-doped iron-based superconductors.",2103.08972v1
2021-05-25,Dynamics of particles with cubic magnetic anisotropy in a viscous liquid,"The specific absorption rate (SAR) of a dilute assembly of spherical iron
nanoparticles with cubic anisotropy distributed in a viscous liquid is
calculated using the solution of stochastic Landau - Lifshitz equation for unit
magnetization vector and stochastic equations for multiple particle directors
that specify the spatial orientation of the nanoparticle in a liquid. The
viscous and magnetic magnetization reversal modes of particles are revealed at
low and sufficiently high amplitudes of alternating magnetic field,
respectively. The SAR of iron nanoparticle assembly is shown to exceed
significantly that of iron oxide nanoparticles with uniaxial anisotropy at the
same amplitudes and frequencies of applied magnetic field. The linear response
theory is shown to be valid only at small magnetic field amplitudes, H0 < 50 -
70 Oe.",2105.11916v1
2021-06-06,Testing the Kerr black hole hypothesis with GRS 1716-249 by combining the continuum-fitting and the iron-line methods,"The continuum-fitting and the iron-line methods are currently the two leading
techniques for measuring the spins of accreting black holes. In the past few
years, these two methods have been developed for testing fundamental physics.
In the present work, we employ state-of-the-art models to test black holes
through the continuum-fitting and the iron-line methods and we analyze three
NuSTAR observations of the black hole binary GRS 1716-249 during its outburst
in 2016-2017. In these three observations, the source was in a
hard-intermediate state and the spectra show both a strong thermal component
and prominent relativistic reflection features. Our analysis confirms the Kerr
nature of the black hole in GRS 1716-249 and provides quite stringent
constraints on possible deviations from the predictions of general relativity.",2106.03086v2
2021-06-21,Testing the Kerr black hole hypothesis with the continuum-fitting and the iron line methods: the case of GRS 1915+105,"The continuum-fitting and the iron line methods are currently the two leading
techniques for probing the strong gravity region around accreting black holes.
In the present work, we test the Kerr black hole hypothesis with the
stellar-mass black hole in GRS 1915+105 by analyzing five disk-dominated RXTE
spectra and one reflection-dominated Suzaku spectrum. The combination of the
constraints from the continuum-fitting and the iron line methods has the
potential to provide more stringent tests of the Kerr metric. Our constraint on
the Johannsen deformation parameter $\alpha_{13}$ is $-0.15 < \alpha_{13} <
0.14$ at 3$\sigma$, where the Kerr metric is recovered when $\alpha_{13} = 0$.",2106.10982v2
2021-06-24,Artificial neural network molecular mechanics of iron grain boundaries,"This study reports grain boundary (GB) energy calculations for 46
symmetric-tilt GBs in alpha-iron using molecular mechanics based on an
artificial neural network (ANN) potential and compares the results with
calculations based on the density functional theory (DFT), the embedded atom
method (EAM), and the modified EAM (MEAM). The results by the ANN potential are
in excellent agreement with those of the DFT (5% on average), while the EAM and
MEAM significantly differ from the DFT results (about 27% on average). In a
uniaxial tensile calculation of Sigma 3 (1-12) GB, the ANN potential reproduced
the brittle fracture tendency of the GB observed in the DFT while the EAM and
MEAM showed mistakenly showed ductile behaviors. These results demonstrate the
effectiveness of the ANN potential in grain boundary calculations of iron as a
fast and accurate simulation highly in demand in the modern industrial world.",2106.12745v1
2021-08-12,Polarized neutron scattering studies of magnetic excitations in iron-selenide superconductor (Li$_{0.8}$Fe$_{0.2}$)ODFeSe ($T_c$ = 41 K),"We report polarized neutron scattering measurements of the low energy spin
fluctuations of the iron-selenide superconductor Li$_{0.8}$Fe$_{0.2}$ODFeSe
below and above its superconducting transition temperature $T_c=41$ K. Our
experiments confirmed that the resonance mode near 21 meV is magnetic.
Moreover, the spin excitations are essentially isotropic in spin space at
5$\leq E\leq$ 29 meV in the superconducting and normal states. Our results
suggest that the resonance mode in iron-based superconductors becomes isotropic
when the influence of spin-orbit coupling and magnetic/nematic order is
minimized, similar to those observed in cuprate superconductors.",2108.05832v1
2021-08-25,Cooling Delays from Iron Sedimentation and Iron Inner Cores in White Dwarfs,"Do white dwarfs have inner cores made of iron? Neutron rich nuclei like
$^{56}$Fe experience a net gravitational force and sediment toward the core.
Using new phase diagrams and molecular dynamics simulations, we show that
$^{56}$Fe should separate into mesoscopic Fe-rich crystallites due to its large
charge relative to the background. At solar abundances, these crystallites
rapidly precipitate and form an inner core of order 100 km and $10^{-3}
M_\odot$ that may be detectable with asteroseismology. Associated cooling
delays could be up to a Gyr for low mass white dwarfs but are only $\sim$0.1
Gyr for massive white dwarfs, so while this mechanism may contribute to the
Q-branch the heating is insufficient to fully explain it.",2108.11389v1
2021-09-10,Interference Effect of Beam Splitter Current in Iron-Pnictide Superconductors,"We consider a Cooper pair beam splitter for Iron-Pnictide superconductor and
calculate the entangled electron-hole current. We investigate the interplay of
various physical parameters such as doping at electron and hole pockets as well
as non-zero nesting between the electron and hole pocket. We find that in the
absence of magnetic order, the current due to hole pocket and electron pocket
add up ordinarily. However in the presence of magnetic ordering the two
currents take part in characteristic interference effect to modify the
resultant current significantly. This interference effect manifests itself in
non-monotonous and oscillatory nature of beam splitter current. We investigate
in details this non-monotonicity with the chemical potential as well as nesting
vectror $|\bf q|$. We also investigate the evolution of density of states with
system parameters and correlate it with the beam-splitter current. Further we
enumerate the relevant parameter space where the efficiency of such beam
splitter set up is enhanced. Our finding can be useful in experimental
determination or verification of co-existence phase in Iron-Pnictide
superconductors and has potential applications in realizing quantum gates or
switches.",2109.04796v2
2021-09-19,Data analysis of $ab$ $initio$ effective Hamiltonians in iron-based superconductors $\unicode{x2014}$ Construction of predictors for superconducting critical temperature,"High-temperature superconductivity occurs in strongly correlated materials
such as copper oxides and iron-based superconductors. Numerous experimental and
theoretical works have been done to identify the key parameters that induce
high-temperature superconductivity. However, the key parameters governing the
high-temperature superconductivity remain still unclear, which hamper the
prediction of superconducting critical temperatures ($T_\text{c}$s) of strongly
correlated materials. Here by using data-science techniques, we clarified how
the microscopic parameters in the $ab$ $initio$ effective Hamiltonians
correlate with the experimental $T_\text{c}$s in iron-based superconductors. We
showed that a combination of microscopic parameters can characterize the
compound-dependence of $T_\text{c}$ using the principal component analysis. We
also constructed a linear regression model that reproduces the experimental
$T_\text{c}$ from the microscopic parameters. Based on the regression model, we
showed a way for increasing $T_\text{c}$ by changing the lattice parameters.
The developed methodology opens a new field of materials informatics for
strongly correlated electron systems.",2109.09121v2
2021-10-01,Iron-rich Fe-O compounds with closest-packed layers at core pressures,"Oxygen solubility in solid iron is extremely low, even at high pressures and
temperatures. Thus far, no Fe-O compounds between Fe and FeO endmembers have
been reported experimentally. We observed chemical reactions of Fe with FeO or
Fe$_2$O$_3$ $in\ situ$ x-ray diffraction experiments at 220-260 GPa and
3,000-3,500 K. The refined diffraction patterns are consistent with a series of
Fe$_n$O (n $>$ 1) compounds (e.g., Fe$_{25}$O$_{13}$ and Fe$_{28}$O$_{14}$)
identified using the adaptive genetic algorithm. Like $\epsilon$-Fe in the
hexagonal close-packed (hcp) structure, the structures of Fe$_n$O compounds
consist of oxygen-only close-packed monolayers distributed between iron-only
layers. $Ab\ initio$ calculations show systematic electronic properties of
these compounds that have ramifications for the physical properties of Earth's
inner core.",2110.00524v1
2021-11-22,Oxygen-driven enhancement of electron correlation in hexagonal iron at Earth's inner core conditions,"Earth's inner core consists of mainly iron with a bit of light elements.
Understanding of its structure and related physical properties has been elusive
for both experiment and theory due to its required extremely high pressure and
temperature conditions. Here, using density functional theory plus dynamical
mean field theory, we demonstrate that oxygen atoms energetically stabilize
hexagonal structured iron at the inner core condition. Electrical resistivity
is much enhanced compared with pure hcp-Fe, supporting the conventional thermal
convection model. Moreover, our calculated seismic velocity shows a
quantitative match with geologically observed Preliminary Reference Earth Model
data.",2111.11033v1
2021-12-01,Comparison of hydrogen diffusivities measured by electrochemical permeation and temperature-programmed desorption in cold-rolled pure iron,"The diffusivity of hydrogen in cold-rolled pure iron is investigated using
permeation and desorption methods. Electrochemical charging, electro-permeation
and thermal desorption spectroscopy (TDS) experiments are conducted. Firstly,
the relation between the charging current and the hydrogen concentration is
established. Secondly, permeation experiments are conducted at 22, 40 and
67{\deg}C to quantify the diffusivity dependence on temperature. Finally, the
diffusivity is estimated by using two types of desorption experiments and
Fick's law: (i) a `rest time' method, by which we measure the hydrogen content
of samples held at room temperature for different times, and (ii) isothermal
desorption experiments at temperatures ranging from 22 to 80{\deg}C, fitting
the resulting desorption rate versus time curves. Good agreement is obtained
between the isothermal desorption and permeation approaches, with observed
differences discussed and rationalised. Moreover, measured diffusivity values
for cold-rolled pure iron are also found to be comparable to those reported in
the literature. This work demonstrates that isothermal desorption experiments
are a convenient approach to determine hydrogen diffusivity over a wide range
of temperatures, as facilitated by new TDS systems with fast heating rates.",2112.00589v1
2022-01-27,FeSe and the missing electron pocket problem,"The nature and origin of electronic nematicity remains a significant
challenge in our understanding of the iron-based superconductors. This is
particularly evident in the iron chalcogenide, FeSe, where it is currently
unclear how the experimentally determined Fermi surface near the M point
evolves from having two electron pockets in the tetragonal state to exhibiting
just a single electron pocket in the nematic state. This has posed a major
theoretical challenge, which has become known as the missing electron pocket
problem of FeSe, and is of central importance if we wish to uncover the secrets
behind nematicity and superconductivity in the wider iron-based
superconductors. Here, we review the recent experimental work uncovering this
nematic Fermi surface of FeSe from both ARPES and STM measurements, as well as
current theoretical attempts to explain this missing electron pocket of FeSe,
with a particular focus on the emerging importance of incorporating the
$d_{xy}$ orbital into theoretical descriptions of the nematic state.
Furthermore, we will discuss the consequence this missing electron pocket has
on the theoretical understanding of superconductivity in this system and
present several remaining open questions and avenues for future research.",2201.11702v1
2022-02-01,Ubiquitous enhancement of nematic fluctuations across the phase diagram of iron based superconductors probed by the Nernst effect,"The role of nematic fluctuations for unconventional superconductivity has
been subject of intense discussions for many years. In iron-based
superconductors, the most established probe for electronic-nematic
fluctuations, i.e. the elastoresistivity seems to imply that superconductivity
is reinforced by electronic-nematic fluctuations, since the elastoresistivity
amplitude peaks at or close to optimal $T_C$. However, on the over-doped side
of the superconducting dome, the diminishing elastoresistivity suggests a
negligible importance in the mechanism of superconductivity. Here we introduce
the Nernst coefficient as a genuine probe for electronic nematic fluctuations,
and we show that the amplitude of the Nernst coefficient tracks the
superconducting dome of two prototype families of iron-based superconductors,
namely Rh-doped $BaFe_{2}As_{2}$ and Co-doped $LaFeAsO$. Our data thus provide
fresh evidence that in these systems nematic fluctuations foster the
superconductivity throughout the phase diagram.",2202.00485v1
2022-02-14,"Hydrothermal synthesis, structure, and antibacterial studies of a nanosized iron zeolite","The present research explores the effects of Percentage Fe incorporation on
the structure and antibacterial activity of Fe ZSM 5. Silica extracted from
local rice husk straw (white particles) by applying NaOH and HCl solutions for
consecutive chemical treatment was used for hydrothermal synthesis of FeZSM 5
with constant Si(Fe plus Al) ratios. The chemical and physical changes of ZSM 5
and Fe ZSM 5 surfaces were investigated by X ray diffraction analysis (XRD),
scanning electron microscopy (SEM), Fourier transform infrared spectroscopy
(FTIR), UV Vis spectroscopy, differential scanning calorimetry (DSC), and pore
structure analysis by N2 adsorption at 196 . XRD analysis revealed the typical
ZSM 5 structure with new diffraction lines attributed to the iron silicate
phase. FTIR spectral analysis of ZSM 5 samples containing iron display a new
band at 656 cm that is ascribed to the SiOFe group. The antibacterial activity
of such coatings towards different kinds of bacteria, such as S. pneumonia, B.
subtilis, E. coli and P. aeruginosa, and fungi, such as A. fumigatus and C.
albicans, for investigated ZSM 5 and Fe (20 and 100 percentages) samples showed
selective antibacterial actions.",2202.06900v1
2022-03-01,Ultrafast Melting of Superconductivity in an Iron-Based Superconductor,"Intense debate has recently arisen regarding the photoinduced changes to the
iron-chalcogenide superconductors, including the enhancement of
superconductivity and a metastable state. Here, by employing high energy
resolution, we directly observe the melting of superconductivity on ultrafast
timescales. We demonstrate a distinctly nonequilibrium response on short
timescales, where the gap fills in prior to the destruction of the
superconducting peak, followed by a metastable response. We propose that the
former is due to pair phase decoherence and speculate that the latter is due to
the increase in double stripe correlations that are known to compete with
superconductivity. Our results add to exciting new developments on the
iron-based superconductors, indicating that the photoinduced metastable state
possibly competes with superconductivity.",2203.00678v2
2022-03-26,Ferromagnetic Impurity Induced Majorana Zero Mode in Iron-Based Superconductor,"Recent experiments reported the puzzling zero energy modes associated with
ferromagnetic impurities in some iron-based superconductors with topological
band structures. Here, we show that the sufficiently strong exchange coupling
between a ferromagnetic impurity and substrate can trigger a quantum phase
transition, beyond which, the phase of the topological surface superconducting
order parameter around the impurity acquires a sign-change. In such a case, we
prove that a Kramers degenerate pair of Majorana modes can be induced at the
boundary separating the two sign-change regimes and trapped around the impurity
in the topological surface superconducting state. Furthermore, we show that our
theory can explain the controversial observations and confusing features of the
zero energy modes from recent experiments in some iron-based superconductors.",2203.14017v3
2022-04-14,Orbital memory from individual Fe atoms on black phosphorus,"Bistable valency in individual atoms presents a new approach toward
single-atom memory, as well as a building block to create tunable and
stochastic multi-well energy landscapes. Yet, this concept of orbital memory
has thus far only been observed for cobalt atoms on the surface of black
phosphorus, which are switched using tip-induced ionization. Here, we show that
individual iron atoms on the surface of black phosphorus exhibit orbital memory
using a combination of scanning tunneling microscopy and spectroscopy with ab
initio calculations based on density functional theory. Unlike cobalt, the iron
orbital memory can be switched in its non-ionized ground state. Based on
calculations, we confirm that each iron valency has a distinct magnetic moment
that is characterized by a distinguishable charge distribution due to the
different orbital population. By studying the stochastic switching of the
valency with varying tunneling conditions, we propose that the switching
mechanism is based on a two-electron tunneling process.",2204.06915v1
2022-04-19,Recycling End-of-life Polycarbonate in Steelmaking; $\textit{Ab Initio}$ Study of Carbon Dissolution in Molten Iron,"The scarcity of fossil fuels as carbon resources has motivated the
steelmaking industry to search for new carbon sources such as end-of-life
polymeric products. Using $\textit{ab initio}$ molecular dynamics simulation,
we demonstrate that 41% of polycarbonate's carbon content is readily dissolved
in molten iron's interface at $T$ = 1823 K which is comparable to graphite with
$\sim$ 58% carbon content dissolution. More importantly, we demonstrate that
polycarbonate's hydrogen content does not dissolve in molten iron but rather
escape in gaseous form. Therefore, waste polycarbonate constitutes a feasible
carbon source for steelmaking.",2204.08706v1
2022-04-20,Control of magnetic susceptibility of probiotic strain Lactobacillus Rhamnosus GG,"The paper investigates the increase in the natural magnetically controlled
properties of probiotic microorganisms Lactobacillus rhamnosus GG (LGG) and
their ability to form magnetic sensitive inclusions (MsI). The magnetic
susceptibility of LGG was increased by modifying the nutrient medium
composition and by cultivating the probiotic culture in a constant magnetic
field. Therefore, this study can be useful for their further use as
magnetically controlled vectors, since it is being extensively researched for
the use in targeted drug delivery in cancer treatment, for the prevention of
chemotherapy complications, etc. The results of this study indicate that
growing microorganisms with natural magnetically-guided properties in a
modified medium with iron chelate and in an external magnetic field leads to an
increase in the magnetic susceptibility of LGG by 1,8 and 2,6 times,
respectively, compared with the control. The best magnetic susceptibility was
recorded for LGG suspensions, which were grown in a constant magnetic field and
cultured in modified medium with iron chelate. The LGG suspension, grown both
in a constant magnetic field and on a modified medium with iron chelate, had
the highest magnetic susceptibility and was 4.8 times larger than the control.",2204.09338v1
2022-04-27,On the possibility of incorporation of the iron impurity into $A$ sites in SrTiO$_3$,"The local environment and oxidation state of the Fe impurity in strontium
titanate are studied using XAFS spectroscopy. The influence of annealing
temperature and deviation from stoichiometry on the possibility of
incorporation of the impurity into the $A$ and $B$ sites of the perovskite
structure is studied. The results obtained from the X-ray diffraction, XANES
spectra, and EXAFS spectra suggest that at high annealing temperature the iron
atoms, at least partially (up to 30%), enter the $A$ sites in SrTiO$_3$. The
obtained results agree with results of first-principles calculations, according
to which the iron at the $A$ site exhibits strong off-centering (the
displacement of $\sim$1 {\AA}), similar to that previously established in
SrTiO$_3$ samples doped with Mn and Co.",2204.12775v2
2022-05-04,Ab initio melting temperatures of bcc and hcp iron under the Earth's inner core condition,"There has been a long debate on the stable phase of iron under the Earth's
inner core conditions. Because of the solid-liquid coexistence at the inner
core boundary, the thermodynamic stability of solid phases directly relates to
their melting temperatures, which remains considerable uncertainty. In the
present study, we utilized a semi-empirical potential fitted to
high-temperature ab initio data to perform a thermodynamic integration from
classical systems described by this potential to ab initio systems. This method
provides a smooth path for thermodynamic integration and significantly reduces
the uncertainty caused by the finite-size effect. Our results suggest the hcp
phase is the stable phase of pure iron under the inner core conditions, while
the free energy difference between the hcp and bcc phases is tiny, on the order
of 10s meV/atom near the melting temperature.",2205.02290v2
2022-08-03,Magnetic biophysical characterization of biomimetic polyeth-ylenimine-coated nanoparticles on in vitro silico model,"Understanding the biophysical and magnetic interactions of nanoparticles
(NPs) with cell mem-branes is critical for developing effective nanocarrier
systems for drug delivery applications and targeted nanophysics applications.
Recent discoveries in nanomedicine can be used to test an in vitro system that
reproduce a similar tumor model. Iron-oxide nanoparticles can be used for
diagnosis, as well as a good carrier of drugs and induced therapeutic for
magnetic hyperthermia. In the present study, we engineered
polyethylenimine-conjugated superparamagnetic iron-oxide nanoparticles (SPIONs)
for the targeted delivery of chemotherapeutics on in vitro silico model.
Doxorubicin is used to treat numerous types of tumors including breast cancer.
The drug-coated mul-ti-functionalized nanoparticles, were assembled stepwise,
with doxorubicin adsorbed to polyeth-ylenimine-iron oxide nanoparticles first,
by electrostatic reaction and allowed for the complexation of doxorubicin.. The
drug-coated particles were able to inhibit growth and proliferation of
resistant cancer cells in vitro, indicating that the system has potential to
act as an antimetastatic chemo-thermotherapeutic agent. Here, we demonstrated a
sophisticated strategy to kill in a precise way only cancer cells by
conjugating a magnetic nanoparticle to chemotherapeutic.",2208.02838v1
2022-09-29,Exploring Supernova Gravitational Waves with Machine Learning,"Core-collapse supernovae (CCSNe) emit powerful gravitational waves (GWs).
Since GWs emitted by a source contain information about the source, observing
GWs from CCSNe may allow us to learn more about CCSNs. We study if it is
possible to infer the iron core mass from the bounce and early ring-down GW
signal. We generate GW signals for a range of stellar models using numerical
simulations and apply machine learning to train and classify the signals. We
consider an idealized favourable scenario. First, we use rapidly rotating
models, which produce stronger GWs than slowly rotating models. Second, we
limit ourselves to models with four different masses, which simplifies the
selection process. We show that the classification accuracy does not exceed
~70%, signifying that even in this optimistic scenario, the information
contained in the bounce and early ring-down GW signal is not sufficient to
precisely probe the iron core mass. This suggests that it may be necessary to
incorporate additional information such as the GWs from later post-bounce
evolution and neutrino observations to accurately measure the iron core mass.",2209.14542v2
2022-11-03,Magnetism in Two-Dimensional Ilmenenes: Intrinsic Order and Strong Anisotropy,"Iron ilmenene is a new two-dimensional material that has recently been
exfoliated from the naturally-occurring iron titanate found in ilmenite ore, a
material that is abundant on earth surface. In this work, we theoretically
investigate the structural, electronic and magnetic properties of 2D
transition-metal-based ilmenene-like titanates. The study of magnetic order
reveals that these ilmenenes usually present intrinsic antiferromagnetic
coupling between the 3d magnetic metals decorating both sides of the Ti-O
layer. Furthermore, the ilmenenes based on late 3d brass metals, such as
CuTiO$_3$ and ZnTiO$_3$, become ferromagnetic and spin compensated,
respectively. Our calculations including spin-orbit coupling reveal that the
magnetic ilmenenes have large magnetocrystalline anisotropy energies when the
3d shell departs from being either filled or half-filled, with their spin
orientation being out-of-plane for elements below half-filling of 3d states and
in-plane above. These interesting magnetic properties of ilmenenes make them
useful for future spintronic applications because they could be synthesized as
already realized in the iron case.",2211.01732v1
2023-02-03,Effect of iron thicknesses on spin transport in a Fe/Au bilayer system,"This paper is concerned with a theoretical analysis of the behavior of
optically excited spin currents in bilayer and multilayer systems of
ferromagnetic and normal metals. As the propagation, control and manipulation
of the spin currents created in ferromagnets by femtosecond optical pulses is
of particular interest, we examine the influence of different thicknesses of
the constituent layers for the case of electrons excited several electronvolts
above the Fermi level. Using a Monte-Carlo simulation framework for such highly
excited electrons, we first examine the spatio-temporal characteristics of the
spin current density driven in a Fe layer, where the absorption profile of the
light pulses plays an important role. Further, we examine how the combination
of light absorption profiles, spin-dependent transmission probabilities, and
iron layer thicknesses affect spin current density in a Fe/Au bilayer system.
For high-energy electrons studied here, the interface and secondary electron
generation have a small influence on spin transport in the bilayer system.
However, we find that spin injection from one layer to another is most
effective within a certain range of iron layer thicknesses.",2302.01472v1
2023-06-13,Origin of superionic state in Earth's inner core,"Earth's inner core (IC) serves as a reservoir for volatile elements, which
significantly affects its behavior and properties. Recent studies suggest that
superionicity can be observed in ice and iron hydrides under high-pressure and
temperature conditions, providing an alternative understanding of the planet's
interior. In this study, we demonstrated that electride formation drives the
superionic state in iron hydride under IC pressure conditions. The electride
stabilizes the iron lattice and provides a pathway for volatile diffusion. The
coupling between lattice stability and superionicity is triggered near 100 GPa
and enhanced at higher pressures. The electride-driven superionicity can also
be generalized for volatiles in other rocky planetary cores. These findings
provide new insights into the mechanisms of core formation and evolution of
rocky planets.",2306.07534v1
2023-06-14,Slope of the upper critical field at $T_{c}$ in two-band superconductors with non-magnetic disorder: $s_{++}$ superconductivity in $\textrm{Ba}_{1-x}\textrm{K}_{x}\textrm{Fe}_{2}\textrm{As}_{2}$,"A recent theory of the disorder-dependent slope of the upper critical field,
$H_{c2}$, at the superconducting transition temperature, $T_{c}$, is extended
to multiband superconductors aiming at iron-based superconductors, considering
two constant gaps of different magnitude and, potentially, different signs. The
result shows that there is only a narrow domain inside the $s_{\pm}$ pairing
state where the slope increases with the increase of transport (non-magnetic)
scattering rate, $P$. In most phase space, the slope should decrease in an
$s_{\pm}$ state and increase in the $s_{++}$ pairing state. The experiment
shows that in an archetypal iron-based superconductor,
$\textrm{Ba}_{1-x}\textrm{K}_{x}\textrm{Fe}_{2}\textrm{As}_{2}$ (BaK122),
non-magnetic disorder induced by electron irradiation increases the slope $S$
across the superconducting ``dome,'' at different $x$. This implies that
$\textrm{Ba}_{1-x}\textrm{K}_{x}\textrm{Fe}_{2}\textrm{As}_{2}$ is likely an
$s_{++}$ superconductor with two (or more) gaps of different magnitudes. This
work reopens a decade-long discussion of the nature of the superconducting
order parameter in iron pnictides.",2306.08703v2
2023-06-22,Data-Driven Update of B(H) Curves of Iron Yokes in Normal Conducting Accelerator Magnets,"Constitutive equations are used in electromagnetic field simulations to model
a material response to applied fields or forces. The $B(H)$ characteristic of
iron laminations depends on thermal and mechanical stresses that may have
occurred during the manufacturing process. Data-driven modelling and updating
of the $B(H)$ characteristic are therefore well known necessities. In this work
the $B(H)$ curve of an iron yoke of an accelerator magnet is updated based on
observed magnetic flux density data by solving a non-linear inverse problem.
The inverse problem is regularized by restricting the solution to the function
space that is spanned by the truncated Karhunen Loeve expansion of a stochastic
$B(H)$-curve model based on material measurements. It is shown that this method
is able to retrieve a previously selected ground truth $B(H)$-curve. With the
update of the $B(H)$ characteristic, the numerical model gains predictive
capacities for excitation currents that were not included in the data.",2306.12872v1
2023-09-30,High gas pressure and high-temperature synthesis (HP-HTS) technique and its impact on iron-based superconductors,"The high-pressure growth technique generally plays an important role in the
improvement of the sample quality and the enhancement of various physical and
magnetic properties of materials. The high gas pressure technique provides a
large sample space (10-15 cm) to grow various kinds of materials. In this
paper, we introduce the high gas pressure and high-temperature synthesis
(HP-HTS) technique that is present at our institute and is applied to the
growth process of different kinds of superconducting materials, particularly
iron-based superconductors. More details and the working principle of this
HP-HTS technique are discussed. We have also demonstrated the current results
based on the iron-based superconductors by using this unique HP-HTS technique.
These results demonstrate the enhancement of the superconducting properties
with the improved sample quality compared to the conventional synthesis process
at ambient pressure.",2310.00282v1
2023-10-09,Detection of Iron in Nanoclustered Cytochrome C Proteins Using Nitrogen-Vacancy Magnetic Relaxometry,"Nitrogen-vacancy (NV) magnetometry offers an alternative tool to detect iron
levels in neurons and cells with a favorable combination of magnetic
sensitivity and spatial resolution. Here we employ NV-T1 relaxometry to detect
Fe in cytochrome C (Cyt-C) nanoclusters. Cyt-C is a water-soluble protein that
contains a single heme group and plays a vital role in the electron transport
chain of mitochondria. Under ambient conditions, the heme group remains in the
Fe+3 paramagnetic state. We perform NV-T1 relaxometry on a functionalized
diamond chip and vary the concentration of Cyt-C from 6 uM to 54 uM, resulting
in a decrease of T1 from 1.2 ms to 150 us, respectively. This reduction is
attributed to spin-noise originating from the Fe spins present within the
Cyt-C. We perform relaxometry imaging of Cyt-C proteins on a nanostructured
diamond chip by varying the density of adsorbed iron from 1.44 x 10^6 to 1.7 x
10^7 per um^2.",2310.08605v2
2023-11-10,Machine Learning-Driven Structure Prediction for Iron Hydrides,"We created a computational workflow to analyze the potential energy surface
(PES) of materials using machine-learned interatomic potentials in conjunction
with the minima hopping algorithm. We demonstrate this method by producing a
versatile machine-learned interatomic potential for iron hydride via a neural
network using an iterative training process to explore its energy landscape
under different pressures. To evaluate the accuracy and comprehend the
intricacies of the PES, we conducted comprehensive crystal structure
predictions using our neural network-based potential paired with the minima
hopping approach. The predictions spanned pressures ranging from ambient to 100
GPa. Our results reproduce the experimentally verified global minimum
structures such as \textit{dhcp}, \textit{hcp}, and \textit{fcc}, corroborating
previous findings. Furthermore, our in-depth exploration of the iron hydride
PES at different pressures has revealed complex alterations and stacking faults
in these phases, leading to the identification of several new low-enthalpy
structures. This investigation has not only confirmed the presence of regions
of established FeH configurations but has also highlighted the efficacy of
using data-driven, extensive structure prediction methods to uncover the
multifaceted PES of materials.",2311.06010v1
2023-11-15,Probing Iron in Earth's Core With Molecular-Spin Dynamics,"Dynamic compression of iron to Earth-core conditions is one of the few ways
to gather important elastic and transport properties needed to uncover key
mechanisms surrounding the geodynamo effect. Herein a new machine-learned
ab-initio derived molecular-spin dynamics (MSD) methodology with explicit
treatment for longitudinal spin-fluctuations is utilized to probe the dynamic
phase-diagram of iron. This framework uniquely enables an accurate resolution
of the phase-transition kinetics and Earth-core elastic properties, as
highlighted by compressional wave velocity and adiabatic bulk moduli
measurements. In addition, a unique coupling of MSD with time-dependent density
functional theory enables gauging electronic transport properties, critically
important for resolving geodynamo dynamics.",2311.08737v1
2023-11-21,Speciation controls the kinetics of iron hydroxide precipitation and transformation,"The formation of energetically favourable and metastable mineral phases
within the Fe-H2O system controls the long-term mobility of iron complexes as
well as other aqueous phase constituents in natural aquifers, soils and other
environmentally and industrially relevant systems. The fundamental mechanism
controlling the formation of these solid phases has remained enigmatic. Here,
we develop a general state-of-the-art partial equilibrium model and succeed in
predicting the rate of amorphous 2-line ferrihydrite precipitation, dissolution
and overall transformation to crystalline goethite at alkaline pH. All
mechanistic steps constituting the transformation mechanism accurately predict
the experimentally measured solid and aqueous phase composition over time,
involving only a single kinetic rate constant each. It is found that the
precipitation of goethite (i) occurs from solution and (ii) is limited by the
comparatively slow dissolution of the first forming amorphous phase 2-line
ferrihydrite. A generalised transformation mechanism applicable to near-neutral
and mildly acidic pH further illustrates that differences in the kinetics of
Fe(III) precipitation are controlled by the coordination environment of the
predominant Fe(III) hydrolysis product. Findings provide a framework for the
modelling of other iron(bearing) phases across a broad range of aqueous phase
compositions.",2311.12464v1
2024-01-04,Exploring the Unconventional Electron Distribution Patterns in Iron-based Superconductors,"For more than a decade, the unusual distribution of electrons observed in
ARPES (angle-resolved photoemission spectroscopy) data within the energy range
of ~30meV to ~300meV below the Fermi level, known as the ARPES range, has
remained a puzzle in the field of iron-based superconductivity. However, in
this study, we have made a noteworthy observation: although the electron-phonon
coupling alone is insufficient to account for the observed ARPES pattern, our
analysis reveals that when the instantaneous electron-phonon coupling occurring
in selective phonon channel is enhanced by the coexistence of antiferromagnetic
spin density wave and charge density wave phenomena, the amplified interaction
becomes comparable to the ARPES range. This finding suggests that the
instantaneous interplay between these intricate phenomena should play a crucial
role in generating the observed energy range in ARPES. Our work may provide a
valuable clue towards achieving a deeper understanding of the complex
relationship between electronic correlations, lattice structure, and
superconductivity in iron-based materials for uncovering the origin of the
unconventional ARPES pattern.",2401.02140v1
2024-01-16,Unusually weak irradiation effects in anisotropic iron-based superconductor RbCa2Fe4As4F2,"We report on the effects of 3.5 MeV proton irradiation in
RbCa$_2$Fe$_4$As$_4$F$_2$, an iron-based superconductor with unusual properties
in between those of the pnictides and of the cuprate high-temperature
superconductors. We studied how structural disorder introduced by ion
bombardment affects the critical temperature, superfluid density and gap values
by combining a coplanar waveguide resonator technique, electric transport
measurements and point-contact Andreev-reflection spectroscopy. We find an
unusually weak dependence of the superconducting properties on the amount of
disorder in this material when compared to other iron-based superconductors
under comparable irradiation conditions. The nodal multigap state exhibited by
pristine RbCa$_2$Fe$_4$As$_4$F$_2$ is also robust against proton irradiation,
with a two-band $d-d$ model being the one that best fits the experimental data.",2401.08279v1
2024-01-18,X-ray Iron absorption line in Swift J1858.6-0814,"We present the spectral analysis of bright steady states in an outburst of
the transient neutron star low-mass X-ray binary (NS-LMXB) Swift J1858.6-0814
observed with NICER. We detected an ionized iron K absorption line (H-like Fe)
at 6.97keV in the spectrum. We estimated the photoionization parameter using
the ratio of the equivalent widths (EWs) of the FeXXVI (H-like) (17+\-5eV) and
FeXXV (He-like) (<3eV) and discuss the origin of the iron absorption line. The
irradiated gas producing the absorption line would locate within (3-6)*1E9cm
from the X-ray source. We suggest that the observed H-like Fe absorption line
originates from the highly-ionized gas in the inner accretion disk in Swift
J1858.6-0814.",2401.09664v1
2024-01-31,Tailoring magnetic and hyperthermia properties of biphase iron oxide nanocubes through post-annealing,"Tailoring the magnetic properties of iron oxide nanosystems is essential to
expand their biomedical applications. In this study, the 34 nm iron oxide
nanocubes with two phases consisting of Fe3O4 and alpha-Fe2O3 were annealed for
2 hours in the presence of O2, N2, He, and Ar to tune the respective phase
volume fractions and control the magnetic properties. X-ray diffraction and
magnetic measurements were carried out post-treatment to evaluate the changes
of the treated samples compared to the as-prepared, which showed an enhancement
of the alpha-Fe2O3 phase in the samples annealed with O2, while the others
indicated Fe3O4 enhancement. Furthermore, the latter samples indicated
enhancements in the crystallinity and saturation magnetization while coercivity
enhancement was most significant in the samples annealed with O2, resulting in
the highest specific absorption rates (up to 1000 W/g) in all the applied
fields of 800, 600, and 400 Oe in agar during magnetic hyperthermia
measurements. The general enhancement in the specific absorption rate
post-annealing underscores the importance of the annealing atmosphere in the
enhancement of the magnetic and structural properties of nanostructures.",2401.18009v1
2024-03-19,Growth of metal catalyst nanoparticles in hydrocarbon-rich atmosphere of arc discharge for synthesis of carbon nanotubes,"A direct current (DC) arc discharge is a widely used method for
industrial-scale production of single-walled carbon nanotubes (SWCNT). A
high-selectivity synthesis of SWCNT requires ultra-fine, typically a few
nanometers in diameter, catalyst particles, which is challenging to achieve in
harsh arc environments involving high temperatures, ablation of electrode
materials, convection, and instabilities. Here, we explore how the size of
metal catalyst nanoparticles is affected by a hydrocarbon-rich atmosphere of
the DC arc. In this arc, iron nanoparticles are produced by the evaporation of
an anode, made from low-carbon steel. Methane admixture into argon gas serves
as a carbon source. Electron microscopy and elemental analysis suggest that
hydrocarbons decompose on iron clusters forming a carbon shell, which limits
further iron particle growth. Experimental observations are explained using an
aerosol growth model. The results demonstrate the potential to manipulate the
catalyst particle size in hydrocarbon arc environments.",2403.12700v1
2004-08-18,Heavy elements and chemical enrichment in globular clusters,"High resolution (R > 40 000) and high S/N spectra have been acquired with
UVES on the VLT-Kueyen (Paranal Observatory, ESO Chile) for several main
sequence turnoff stars (V ~ 17 mag) and subgiants at the base of the Red Giant
Branch (V ~ 16 mag) in three globular clusters (NGC 6397, NGC 6752 and 47
Tuc/NGC 104) at different metallicities (respectively [Fe/H] = -2.0; -1.5;
-0.7$). Spectra for a sample of 25 field halo subdwarves have also been taken
with equal resolution, but higher S/N. These data have been used to determine
the abundances of several neutron-capture elements in these three clusters:
strontium, yttrium, barium and europium. This is the first abundance
determination of these heavy elements for such unevolved stars in these three
globular clusters. These values, together with the [Ba/Eu] and [Sr/Ba]
abundance ratios, have been used to test the self-enrichment scenario. A
comparison is done with field halo stars and other well known Galactic globular
clusters in which heavy elements have already been measured in the past, at
least in bright giants (V > 11-12 mag). Our results show clearly that globular
clusters have been uniformly enriched by r- and s-process syntheses, and that
most of them seem to follow exactly the same abundance patterns as field halo
stars, which discards the ``classical'' self-enrichment scenario for the origin
of metallicities and heavy elements in globular clusters.",0408330v1
1993-11-15,Spin Gaps and Bilayer Coupling in YBa$_2$Cu$_3$O$_{7-δ}$ and YBa$_2$Cu$_4$O$_8$,"We investigate the relevance to the physics of underdoped
YBa$_2$Cu$_3$O$_{\rm 6+x}$ and YBa$_2$Cu$_4$O$_8$ of the quantum critical point
which occurs in a model of two antiferromagnetically coupled planes of
antiferromagnetically correlated spins. We use a Schwinger boson mean field
theory and a scaling analysis to obtain the phase diagram of the model and the
temperature and frequency dependence of various susceptibilities and relaxation
rates. We distinguish between a low $\omega ,T$ coupled-planes regime in which
the optic spin excitations are frozen out and a high $\omega ,T$
decoupled-planes regime in which the two planes fluctuate independently. In the
coupled-planes regime the yttrium nuclear relaxation rate at low temperatures
is larger relative to the copper and oxygen rates than would be naively
expected in a model of uncorrelated planes. Available data suggest that in
YBa$_2$Cu$_4$O$_8$ the crossover from the coupled to the decoupled planes
regime occurs at $T 700K$ or $T \sim 200K$. The predicted correlation length is
of order 6 lattice constants at $T=200K$. Experimental data related to the
antiferromagnetic susceptibility of YBa$_2$Cu$_4$O$_8$ may be made consistent
with the theory, but available data for the uniform susceptibility are
inconsistent with the theory.",9311035v1
1998-07-04,Theory for Metal Hydrides with Switchable Optical Properties,"Recently it has been discovered that lanthanum, yttrium, and other metal
hydride films show dramatic changes in the optical properties at the
metal-insulator transition. Such changes on a high energy scale suggest the
electronic structure is best described by a local model based on negatively
charged hydrogen (H$^-$) ions. We develop a many-body theory for the strong
correlation in a H$^-$ ion lattice. The metal hydride is described by a large
$U$-limit of an Anderson lattice model. We use lanthanum hydride as a prototype
of these compounds, and find LaH$_3$ is an insulator with a substantial gap
consistent with experiments. It may be viewed either as a Kondo insulator or a
band insulator due to strong electron correlation. A H vacancy state in LaH$_3$
is found to be highly localized due to the strong bonding between the electron
orbitals of hydrogen and metal atoms. Unlike the impurity states in the usual
semiconductors, there is only weak internal optical transitions within the
vacancy. The metal-insulator transition takes place in a band of these vacancy
states.",9807062v1
1998-12-01,Physical origin of the buckling in CuO$_2$: Electron-phonon coupling and Raman spectra,"It is shown theoretically that the buckling of the CuO$_{2}$ planes in
certain cuprate systems can be explained in terms of an electric field across
the planes which originates from different valences of atoms above and below
the plane. This field results also in a strong coupling of the Raman-active
out-of-phase vibration of the oxygen atoms ($B_{1g}$ mode) to the electronic
charge transfer between the two oxygens in the CuO$_{2}$ plane. Consequently,
the electric field can be deduced from the Fano-type line shape of the $B_{1g}$
phonon. Using the electric field estimated from the electron-phonon coupling
the amplitude of the buckling is calculated and found to be in good agreement
with the structural data. Direct experimental support for the idea proposed is
obtained in studies of YBa$_{2}$Cu$_{3}$O$_{6+x}$ and
Bi$_{2}$Sr$_{2}$(Ca$_{1-x}$Y$_{x}$)Cu$_{2}$O$_{8}$ with different oxygen and
yttrium doping, respectively, including antiferromagnetic samples. In the
latter compound, symmetry breaking by replacing Ca partially by Y leads to an
enhancement of the electron-phonon coupling by an order of magnitude.",9812014v1
2003-10-25,Characterization of the electronic properties of YB$_4$ and YB$_6$ using $^{11}$B NMR and first-principles calculations,"Two compounds, tetragonal YB$_4$ and cubic YB$_6$, have been investigated by
electric-field gradient (EFG) and Knight shift measurements at the boron sites
using the $^{11}$B nuclear magnetic resonance (NMR) technique and by performing
first-principles calculations. In YB$_6$ $^{11}$B ($I=3/2$) NMR spectra reveal
patterns typical for an axially symmetric field gradient with a quadrupole
coupling frequency of $\nu_Q=600\pm15$ kHz. In the second boride (YB$_4$) three
different EFGs were observed corresponding to the three inequivalent
crystallographic sites for the boron atoms ($4h$, $4e$, and $8j$). They
correspond to: $\nu_Q(4h)=700\pm30$ kHz with an asymmetry parameter
$\eta=0.02\pm0.02$, $\nu_Q(4e)=515\pm30$ kHz, $\eta=0.00+0.02/-0.00$, and
$\nu_Q(8j)=515\pm40$ kHz, $\eta=0.46\pm0.08$. The Knight shifts measured by
Magic-Angle Spinning (MAS) NMR at room temperature are very small being
$0.6\pm8$ ppm and $-1\pm8$ ppm for YB$_4$ and YB$_6$, respectively. For the
theoretical calculations structure optimizations were performed as a first
step. For the obtained structural parameters the EFGs were computed within the
local-density approximation. Very satisfactory agreement between experimental
and theoretical results is obtained both for the structural parameters and the
B EFGs thus confirming the underlying structural models. In addition to the
EFGs, band structures, densities of states, and valence-electron densities are
presented and the bonding situation in the two yttrium borides is discussed.
The band-structure results are compatible with the very low values for the
Knight shifts mentioned above.",0310602v1
2005-02-02,Analysis of NMR Spin-Lattice Relaxation Rates in Cuprates,"We investigate nuclear spin-lattice relaxation data in the normal state of
optimally doped YBaCuO_7 by analyzing the contributions to the relaxation rate
of the copper, planar oxygen and yttrium along the directions perpendicular to
the applied field. In this new picture there is no contrasting temperature
dependence of the copper and oxygen relaxation. We use the model of fluctuating
fields to express the rates in terms of hyperfine interaction energies and an
effective correlation time tau_eff characterizing the dynamics of the spin
fluid. The former contain the effects of the antiferromagnetic static spin
correlations, which cause the hyperfine field constants to be added coherently
at low temperature and incoherently at high temperature. The degree of
coherency is therefore controlled by the spin-spin correlations. The model is
used to determine the temperature-dependent correlation lengths. The
temperature-dependent effective correlation time is found to be made up of a
linear and a constant contribution that can be related to scattering and spin
fluctuations of localized moments respectively. The extrapolation of our
calculation at higher temperature fits the data also very well at those
temperatures. The underdoped compounds YBaCuO_6.63 and YBaCuO_8 are studied in
the limit of the data available with some success by modifying the effective
correlation time with a gap parameter. The copper data of the LaSrCuO series
are then discussed in terms of the interplay between the two contributions to
tau_eff.",0502075v2
2010-03-09,"Dynamical evolution of titanium, strontium, and yttrium spots on the surface of the HgMn star HD 11753","Aims. We gathered about 100 high-resolution spectra of three typical HgMn
(mercury-manganese) stars, HD 11753, HD 53244, and HD 221507, to search for
slowly pulsating B-like pulsations and surface inhomogeneous distribution of
various chemical elements. Methods. Classical frequency analysis methods were
used to detect line profile variability and to determine the variation period.
Doppler imaging reconstruction was performed to obtain abundance maps of
chemical elements on the stellar surface. Results. For HD 11753, which is the
star with the most pronounced variability, distinct spectral line profile
changes were detected for Ti, Sr, Y, Zr, and Hg, whereas for HD 53244 and HD
221507 the most variable line profiles belong to the elements Hg and Y,
respectively. We derived rotation periods for all three stars from the
variations of radial velocities and equivalent widths of spectral lines
belonging to inhomogeneously distributed elements: P_rot (HD 11753)=9.54 d,
P_rot (HD 53244)=6.16 d, and P_rot (HD 221507)=1.93 d. For HD 11753 the Doppler
imaging technique was applied to derive the distribution of the most variable
elements Ti, Sr, and Y using two datasets separated by ~65 days. Results of
Doppler imaging reconstruction revealed noticeable changes in the surface
distributions of TiII, SrII, and YII between the datasets, indicating the
hitherto not well understood physical processes in stars with radiative
envelopes that cause a rather fast dynamical chemical spot evolution.",1003.1902v1
2010-04-23,Metal-insulator transition and the Pr$^{3+}$/Pr$^{4+}$ valence shift in (Pr$_{1-y}$Y$_{y}$)$_{0.7}$Ca$_{0.3}$CoO$_3$,"The magnetic, electric and thermal properties of the
($Ln_{1-y}$Y$_{y}$)$_{0.7}$Ca$_{0.3}$CoO$_3$ perovskites ($Ln$~=~Pr, Nd) were
investigated down to very low temperatures. The main attention was given to a
peculiar metal-insulator transition, which is observed in the praseodymium
based samples with $y=0.075$ and 0.15 at $T_{M-I}=64$ and 132~K, respectively.
The study suggests that the transition, reported originally in
Pr$_{0.5}$Ca$_{0.5}$CoO$_3$, is not due to a mere change of cobalt ions from
the intermediate- to the low-spin states, but is associated also with a
significant electron transfer between Pr$^{3+}$ and Co$^{3+}$/Co$^{4+}$ sites,
so that the praseodymium ions occur below $T_{M-I}$ in a mixed
Pr$^{3+}$/Pr$^{4+}$ valence. The presence of Pr$^{4+}$ ions in the insulating
phase of the yttrium doped samples (Pr$_{1-y}$Y$_{y}$)$_{0.7}$Ca$_{0.3}$CoO$_3$
is evidenced by Schottky peak originating in Zeeman splitting of the ground
state Kramers doublet. The peak is absent in pure Pr$_{0.7}$Ca$_{0.3}$CoO$_3$
in which metallic phase, based solely on non-Kramers Pr$^{3+}$ ions, is
retained down to the lowest temperature.",1004.4100v2
2010-07-07,The Chemical Evolution of the Monoceros Ring/Galactic Anticenter Stellar Structure,"The origin of the Galactic Anticenter Stellar Structure (GASS) or ""Monoceros
ring"" --- a low latitude overdensity at the edge of the Galactic disk spanning
at least the second and third Galactic quadrants --- remains controversial.
Models for the origin of GASS fall generally into scenarios where it is either
a part (e.g., warp) of the Galactic disk or it represents tidal debris from the
disruption of a Milky Way (MW) satellite galaxy. To further constrain models
for the origin of GASS, we derive chemical abundance patterns from high
resolution spectra for 21 M giants spatially and kinematically identified with
it. The abundances of the (mostly) $\alpha$ element titanium and s-process
elements yttrium and lanthanum for these GASS stars are found to be lower at
the same [Fe/H] than those for MW stars, but similar to those of stars in the
Sagittarius stream, other dwarf spheroidal galaxies, and the Large Magellanic
Cloud. This demonstrates that GASS stars have a chemical enrichment history
typical of dwarf galaxies --- and unlike those of typical MW stars (at least MW
stars near the Sun). Nevertheless, these abundance results cannot definitively
rule out the possibility that GASS was dynamically created out of a previously
formed, outer MW disk because $\Lambda$CDM-based structure formation models
show that galactic disks grow outward by accretion of dwarf galaxies. On the
other hand, the chemical patterns seen in GASS stars do provide striking
verification that accretion of dwarf galaxies has indeed happened at the edge
of the MW disk.",1007.1056v1
2010-09-17,"First-principles studies of Ce-doped RE2M2O7 (RE=Y,La;M=Ti,Zr,Hf): A class of non-scintillators","Lanthanum and yttrium compounds with composition RE2M2O7 (RE=Y, La; M = Ti,
Zr, Hf) have high density and high Z and can be doped with Ce onto the La and Y
sites. This makes these compounds good candidates for Ce activated scintillator
gamma-ray detectors particularly for the hafnate systems which have a very high
density. There is disagreement in the literature concerning La2Hf2O7:Ce as it
has been reported to show both bright as well as no Ce activated luminescence
by different experimental groups. We have performed first-principles electronic
structure calculations of these compounds doped with Ce using the
pseudopotential method based on the generalized gradient approximation in
density functional theory. The positions of the Ce 4f states relative to the
valence band maximum and the position of the Ce 5d states relative to the
conduction band minimum (CBM) of the host material are determined. We find,
unlike Ce activated La and Y compounds where the CBM is typically of La 5d or Y
4d character, that, in these systems the CBM is predominately of d character on
the Ti, Zr, Hf atoms. For all these compounds we also find that the Ce 5d state
lies above the CBM which would prevent any luminescence from the Ce site.",1009.3381v1
2010-12-05,The solar photospheric abundance of zirconium,"Zirconium (Zr), together with strontium and yttrium, is an important element
in the understanding of the Galactic nucleosynthesis. In fact, the triad
Sr-Y-Zr constitutes the first peak of s-process elements. Despite its general
relevance not many studies of the solar abundance of Zr were conducted. We
derive the zirconium abundance in the solar photosphere with the same CO5BOLD
hydrodynamical model of the solar atmosphere that we previously used to
investigate the abundances of C-N-O. We review the zirconium lines available in
the observed solar spectra and select a sample of lines to determine the
zirconium abundance, considering lines of neutral and singly ionised zirconium.
We apply different line profile fitting strategies for a reliable analysis of
Zr lines that are blended by lines of other elements. The abundance obtained
from lines of neutral zirconium is very uncertain because these lines are
commonly blended and weak in the solar spectrum. However, we believe that some
lines of ionised zirconium are reliable abundance indicators. Restricting the
set to Zr II lines, from the CO5BOLD 3D model atmosphere we derive
A(Zr)=2.62+/-0.06, where the quoted error is the RMS line-to-line scatter.",1012.1038v1
2011-06-06,"Protons in lattice confinement: Static pressure on the Y-substituted, hydrated BaZrO3 ceramic proton conductor decreases proton mobility","Yttrium substituted BaZrO3, with nominal composition BaZr0.9Y0.1O3, a ceramic
proton conductor, was subject to impedance spectroscopy for temperatures 300 K
< T < 715 K at mechanical pressures 1 GPa < p < 2 GPa. The activation energies
Ea of bulk and grain boundary conductivity from two perovskites synthesized by
solid-state reaction and sol-gel method were determined under high pressures.
At high temperature, the bulk activation energy increases with pressure by 5%
for sol-gel derived sample and by 40% for solid-state derived sample. For the
sample prepared by solid-state reaction, there is a large gap of 0.17 eV
between the activation energy at 1.0 GPa and > 1.2 GPa. The grain boundary
activation energy is around a factor two times as that of the bulk, and it
reaches a maximum at 1.25 - 1.5 GPa, and then decrease as the pressure
increases, indicating higher proton mobility in the grain boundaries at higher
pressure. Since this effect is not reversible, it is suggested that the grain
boundary resistance decreases as a result of pressure induced sintering. The
steady increase of the bulk resistivity upon pressurizing suggests that the
proton mobility depends on the space available in the lattice. In return, an
expanded lattice with a/a0 > 1 should thus have a lower activation energy,
suggesting that thin films expansive tensile strain could have a larger proton
conductivity with desirable properties for applications.",1106.1091v1
2012-05-11,Novel multifunctional 90Y-labelled albumin magnetic microspheres for cancer therapy,"We present in vitro and in vivo studies of yttrium-90 (90Y)-labelled human
serum albumin magnetic microspheres (HSAMMS) as multifunctional agent for
bimodal radionuclide-hyperthermia cancer therapy. The HSAMMS were produced
using a modified emulsification-heat stabilization technique and contained
10-nm magnetite nanoparticles coated with citric acid, distributed as
inhomogeneous clusters within the albumin microspheres. The average particle
size of the complete HSAMMS was 20 (mu)m, and they exhibited superparamagnetic
behavior at room temperature. The stability of the 90^Y-labelled HSAMMS was
investigated in vitro (in saline and human serum) and in vivo by analyzing
their biodistribution in normal Wistar rats. The in vitro experiments revealed
the high stability of the labelled HSAMMS in saline and human serum after 72 h.
Following the intravenous administration of the 90^Y-HSAMMS in rats, 88.81% of
the activity localizes in the lungs after 1 h, with 82.67% remaining after 72
h. These data on 90Y-HSAMMS provide good evidence for their potential use in
bimodal radionuclide-hyperthermia cancer therapy.",1205.2440v1
2013-07-17,Temperature-driven Phase Transformation in Y_3Co: Neutron Scattering and First-principles Studies,"Contrary to previous studies that identified the ground state crystal
structure of the entire R_3Co series (R is a rare earth) as orthorhombic Pnma,
we show that Y_3Co undergoes a structural phase transition at T_t=160K. Single
crystal neutron diffraction data reveal that at T_t the trigonal prisms formed
by a cobalt atom and its six nearest-neighbor yttrium atoms experience
distortions accompanied by notable changes of the Y-Co distances. The formation
of the low-temperature phase is accompanied by a pronounced lattice distortion
and anomalies seen in heat capacity and resistivity measurements. Density
functional theory calculations reveal a dynamical instability of the Pnma
structure of Y_3Co. In particular, a transversal acoustic phonon mode along the
(00z) direction has imaginary frequencies at z<1/4. Employing inelastic neutron
scattering measurements we find a strong damping of the (00z) phonon mode below
a critical temperature T_t. The observed structural transformation causes the
reduction of dimensionality of electronic bands and decreases the electronic
density of states at the Fermi level that identifies Y_3Co as a system with the
charge density wave instability.",1307.4736v1
2013-07-18,Numerical response of the magnetic permeability as a funcion of the frecuency of NiZn ferrites using Genetic Algorithm,"The magnetic permeability of a ferrite is an important factor in designing
devices such as inductors, transformers, and microwave absorbing materials
among others. Due to this, it is advisable to study the magnetic permeability
of a ferrite as a function of frequency.
  When an excitation that corresponds to a harmonic magnetic field \textbf{H}
is applied to the system, this system responds with a magnetic flux density
\textbf{B}; the relation between these two vectors can be expressed as
\textbf{B}=$\mu(\omega)$ \textbf{H} . Where $\mu$ is the magnetic permeability.
  In this paper, ferrites were considered linear, homogeneous, and isotropic
materials. A magnetic permeability model was applied to NiZn ferrites doped
with Yttrium.
  The parameters of the model were adjusted using the Genetic Algorithm. In the
computer science field of artificial intelligence, Genetic Algorithms and
Machine Learning does rely upon nature's bounty for both inspiration nature's
and mechanisms. Genetic Algorithms are probabilistic search procedures which
generate solutions to optimization problems using techniques inspired by
natural evolution, such as inheritance, mutation, selection, and crossover.
  For the numerical fitting usually is used a nonlinear least square method,
this algorithm is based on calculus by starting from an initial set of variable
values. This approach is mathematically elegant compared to the exhaustive or
random searches but tends easily to get stuck in local minima. On the other
hand, random methods use some probabilistic calculations to find variable sets.
They tend to be slower but have greater success at finding the global minimum
regardless of the initial values of the variables",1307.5007v1
2013-08-12,Diamond Magnetometry of Superconducting Thin Films,"In recent years diamond magnetometers based on the nitrogen-vacancy (NV)
center have been of considerable interest for magnetometry applications at the
nanoscale. An interesting application which is well suited for NV centers is
the study of nanoscale magnetic phenomena in superconducting materials. We
employ the magnetic sensitivity of NV centers in diamond to interrogate the
magnetic properties of a thin-layer yttrium barium copper oxide (YBCO)
superconductor. Using fluorescence-microscopy methods and samples integrated
with an NV sensor on a microchip, we measure the temperature of phase
transition in the layer to be 70.0(2) K, and the penetration field of vortices
to be 46(4) G. We observe the pinning of the vortices in the layer at 65 K, and
estimate their density after cooling the sample in a ~ 10 G field to be 0.45(1)
\mu m^{-2}. These measurements are done with a 10 nm thick NV layer, so that
high spatial resolution may be enabled in the future. Based on these results,
we anticipate that this magnetometer could be useful for imaging the structure
and dynamics of vortices. As an outlook, we present a fabrication method for a
superconductor chip designed for this purpose.",1308.2689v3
2014-01-22,Dzyaloshinskii-Moriya nature of ferroelectric ordering in magnetoelectric Gd$_{1-x}$Y$_{x}$MnO$_{3}$ system,"This work reports on magnetic, dielectric, thermodynamic and magnetoelectric
properties of Gd$_{1-x}$Y$_{x}$MnO$_{3}$, with 0 \leq x \leq 0.4, with emphasis
on the (x, T) phase diagram, towards unraveling the role of the driving
mechanisms in stabilizing both magnetic and ferroelectric orderings. The (x, T)
phase diagram reflects the effect of lattice distortions induced by the
substitution of $Gd^{3+}$ ion by smaller $Y^{3+}$ ion, which gradually
unbalances the antiferromagnetic against the ferromagnetic exchange
interactions, enabling the emergence of ferroelectricity for higher
concentrations of yttrium. For $x \leq 0.1$, the paramagnetic phase is followed
by a presumably incommensurate collinear antiferromagnetic phase, then a weak
ferromagnetic canted A-type antiferromagnetic ordering is established at lower
temperatures.For $0.2 \leq x \leq 0.4$, a different phase sequence is obtained.
The canted A-type antiferromagnetic arrangement is no more stable, and instead
a pure antiferromagnetic ordering is stabilized below T$_{lock}$ $\approx$ 14 -
17 K, with an improper ferroelectric character. From these results, a cycloid
modulated spin arrangement at low temperatures is proposed, accordingly to the
inverse Dzyaloshinskii Moriya model. Anomalous temperature dependence of the
dipolar relaxation energy and magnetization evidence for structural and
magnetic changes occurring at $T* \approx 22 - 28 K$, for $0.1 \leq x \leq
0.4$.",1401.5718v2
2014-01-29,Nucleosynthesis in helium-enriched asymptotic giant branch models: Implications for Heavy Element Enrichment in Omega Centauri,"We investigate the effect of helium enrichment on the evolution and
nucleosynthesis of low-mass asymptotic giant branch (AGB) stars of 1.7Msun and
2.36Msun with a metallicity of Z=0.0006 ([Fe/H] = -1.4). We calculate
evolutionary sequences with the primordial helium abundance (Y = 0.24) and with
helium-enriched compositions (Y = 0.30, 0.35, 0.40). For comparison we
calculate models of the same mass but at a lower metallicity Z=0.0003 ([Fe/H] =
-1.8) with Y=0.24. Post-processing nucleosynthesis calculations are performed
on each of the evolutionary sequences to determine the production of elements
from hydrogen through to bismuth. Elemental surface abundance predictions and
stellar yields are presented for each model. The models with enriched helium
have shorter main sequence and AGB lifetimes, and enter the AGB with a more
massive hydrogen exhausted core than the primordial helium model. The main
consequences are 1) low-mass AGB models with enhanced helium will evolve more
than twice as fast, giving them the chance to contribute sooner to the chemical
evolution of the forming globular clusters, and 2) the stellar yields will be
strongly reduced relative to their primordial helium counterparts. An increase
of Delta Y = 0.10 at a given mass decreases the yields of carbon by up to ~60%,
of fluorine by up to 80%, and decreases the yields of the s-process elements
barium and lanthanum by about 45%. While the yields of first s-process peak
elements strontium, yttrium and zirconium decrease by up to 50%, the yields of
rubidium either do not change or increase.",1401.7479v1
2014-03-19,Pt-based nanowire networks with enhanced oxygen-reduction activity,"Pt-Al and Pt-Y-Al thin film electrodes on yttria-stabilised zirconia
electrolytes were prepared by dealloying of co-sputtered Pt-Al or Pt-Y-Al
films. The selective dissolution of Al from the Pt-alloy compound causes the
formation of a highly porous nanowire network with a mean branch thickness
below 25 nm and a pore intercept length below 35 nm. The oxygen reduction
capability of the resulting electrodes was analysed in a micro-solid oxide fuel
cell setup at elevated temperatures (598-873 K). Here, we demonstrate that
these nanoporous thin films excel ""state-of-the-art"" fuel cell electrodes in
terms of catalytic activity and thermal stability. The nanoporous Pt electrodes
exhibit exchange current densities that are up to 13 times higher than
conventional Pt electrodes, measured at 648 K. It is shown that the enhanced
catalytic activity of these Pt electrodes is achieved through the engineering
of the materials d-bands due to the addition of yttrium as ternary constituent.",1403.4665v4
2014-05-23,Proof-of-principle of a new geometry for sampling calorimetry using inorganic scintillator plates,"A novel geometry for a sampling calorimeter employing inorganic scintillators
as an active medium is presented. To overcome the mechanical challenges of
construction, an innovative light collection geometry has been pioneered, that
minimises the complexity of construction. First test results are presented,
demonstrating a successful signal extraction. The geometry consists of a
sampling calorimeter with passive absorber layers interleaved with layers of an
active medium made of inorganic scintillating crystals. Wavelength-shifting
(WLS) fibres run along the four long, chamfered edges of the stack,
transporting the light to photodetectors at the rear. To maximise the amount of
scintillation light reaching the WLS fibres, the scintillator chamfers are
depolished. It is shown herein that this concept is working for cerium fluoride
(CeF$_3$) as a scintillator. Coupled to it, several different types of
materials have been tested as WLS medium. In particular, materials that might
be sufficiently resistant to the High-Luminosity Large Hadron Collider
radiation environment, such as cerium-doped Lutetium-Yttrium Orthosilicate
(LYSO) and cerium-doped quartz, are compared to conventional plastic WLS
fibres. Finally, an outlook is presented on the possible optimisation of the
different components, and the construction and commissioning of a full
calorimeter cell prototype is presented.",1405.6202v1
2014-07-29,Discovery of extremely lead-rich subdwarfs: does heavy metal signal the formation of subdwarf B stars?,"Hot subdwarfs represent a group of low-mass helium-burning stars formed
through binary-star interactions and include some of the most
chemically-peculiar stars in the Galaxy. Stellar evolution theory suggests that
they should have helium-rich atmospheres but, because radiation causes hydrogen
to diffuse upwards, a majority are extremely helium poor. Questions posed
include: when does the atmosphere become chemically stratified and at what
rate?
  The existence of several helium-rich subdwarfs suggests further questions;
are there distinct subgroups of hot subdwarf, or do hot subdwarfs change their
surface composition in the course of evolution? Recent analyses have revealed
remarkable surface chemistries amongst the helium-rich subgroup. In this paper,
we analyse high-resolution spectra of nine intermediate helium-rich hot
subdwarfs. We report the discovery that two stars, HE 2359-2844 and HE
1256-2738, show an atmospheric abundance of lead which is nearly ten thousand
times that seen in the Sun. This is measured from optical Pb IV absorption
lines never previously seen in any star. The lead abundance is ten to 100 times
that measured in normal hot subdwarf atmospheres from ultraviolet spectroscopy.
HE 2359-2844 also shows zirconium and yttrium abundances similar to those in
the zirconium star LS IV-14 116. The new discoveries are interpreted in terms
of heavily stratified atmospheres and the general picture of a surface
chemistry in transition from a new-born helium-rich subdwarf to a normal
helium-poor subdwarf.",1407.7668v1
2015-04-28,High-precision abundances of elements in solar twin stars: Trends with stellar age and elemental condensation temperature,"HARPS spectra with S/N > 600 for 21 solar twin stars are used to determine
very precise (sigma ~ 0.01 dex) differential abundances of C, O, Na, Mg, Al,
Si, S, Ca, Ti, Cr, Fe, Ni, Zn, and Y in order to see how well [X/Fe] is
correlated with elemental condensation temperature, Tc. In addition, precise
(sigma < 0.8 Gyr) stellar ages are obtained by interpolating between
Yonsei-Yale isochrones in the logg - Teff diagram. It is confirmed that the
ratio between refractory and volatile elements is lower in the Sun than in most
of the solar twins, but for many stars, the relation between [X/Fe] and Tc is
not well defined. For several elements there is, instead, an astonishingly
tight correlation between [X/Fe] and stellar age with amplitudes up to 0.2 dex
over an age interval of 8 Gyr in contrast to the lack of correlation between
[Fe/H] and age. While [Mg/Fe] increases with age, the s-process element yttrium
shows the opposite behavior so that [Y/Mg] can be used as a sensitive
chronometer for Galactic evolution. [Na/Fe] and [Ni/Fe] are not well correlated
with stellar age, but define a tight Ni-Na relation similar to that previously
found for more metal-poor stars. These results provide new constraints on
supernovae yields and Galactic evolution. Furthermore, it is found that the C/O
ratio evolves very little with time, which is of interest for discussions of
the composition of exoplanets.",1504.07598v1
2015-06-18,Short intense ion pulses for materials and warm dense matter research,"We have commenced experiments with intense short pulses of ion beams on the
Neutralized Drift Compression Experiment-II at Lawrence Berkeley National
Laboratory, by generating beam spots size with radius r < 1 mm within 2 ns FWHM
and approximately 10^10 ions/pulse. To enable the short pulse durations and
mm-scale focal spot radii, the 1.2 MeV Li+ ion beam is neutralized in a
1.6-meter drift compression section located after the last accelerator magnet.
An 8-Tesla short focal length solenoid compresses the beam in the presence of
the large volume plasma near the end of this section before the target. The
scientific topics to be explored are warm dense matter, the dynamics of
radiation damage in materials, and intense beam and beam-plasma physics
including selected topics of relevance to the development of heavy-ion drivers
for inertial fusion energy. Here we describe the accelerator commissioning and
time-resolved ionoluminescence measurements of yttrium aluminium perovskite
using the fully integrated accelerator and neutralized drift compression
components.",1506.05839v1
2015-09-15,Measurement of time resolution of the Mu2e LYSO calorimeter prototype,"In this paper we present the time resolution measurements of the
Lutetium-Yttrium Oxyorthosilicate (LYSO) calorimeter prototype for the Mu2e
experiment. The measurements have been performed using the $e^-$ beam of the
Beam Test Facility (BTF) in Frascati, Italy in the energy range from 100 to 400
MeV. The calorimeter prototype consisted of twenty five 30x30x130 mm$^3$, LYSO
crystals read out by 10x10 mm$^2$ Hamamatsu Avalanche Photodiodes (APDs). The
energy dependence of the measured time resolution can be parametrized as
$\sigma_{t}(E)=a/\sqrt{E/\mathrm{GeV}} \oplus b$, with the stochastic and
constant terms $a=(51\pm1)$ ps and $b=(10\pm4)$ ps, respectively. This
corresponds to the time resolution of ($162\pm4$) ps at 100 MeV.",1509.04468v2
2015-11-16,The evolved pulsating CEMP star HD112869,"Radial velocity measurements, $BVR_C$ photometry, and high-resolution
spectroscopy in the wavelength region from blue to near infrared are employed
in order to clarify the evolutionary status of the carbon-enhanced metal-poor
star HD112869 with unique ratio of carbon isotopes in the atmosphere. An LTE
abundance analysis was carried out using the method of spectral synthesis and
new self consistent 1D atmospheric models. The radial velocity monitoring
confirmed semiregular variations with a peak-to-peak amplitude of about 10 km
$s^{-1}$ and a dominating period of about 115 days. The light, color and radial
velocity variations are typical of the evolved pulsating stars. The atmosphere
of HD112869 appears to be less metal-poor than reported before, [Fe/H] = -2.3
$\pm$0.2 dex. Carbon to oxygen and carbon isotope ratios are found to be
extremely high, C/O $\simeq$ 12.6 and $^{12}C/^{13}C \gtrsim$ 1500,
respectively. The s-process elements yttrium and barium are not enhanced, but
neodymium appears to be overabundant. The magnesium abundance seems to be lower
than the average found for CEMP stars, [Mg/Fe] < +0.4 dex. HD112869 could be a
single low mass halo star in the stage of asymptotic giant branch evolution",1511.04953v2
2016-02-18,Hole-doping-induced melting of spin-state ordering in PrBaCo2O5.5+x,"The layered perovskite cobaltite RBaCo$_2$O$_{5.5}$ (R: rare-earth elements
or Yttrium) exhibits an abrupt temperature-induced metal$-$insulator transition
(MIT) and has been attributed to spin-state ordering (SSO) of Co$^{3+}$ ions.
Here we investigated the hole doping member of PrBaCo$_2$O$_{5.5+x}$ ($0 \le x
\le 0.24$) with multiple techniques. The analysis on crystal and magnetic
structures by electron and neutron diffraction confirm the SSO in the
insulating phase of undoped PrBaCo$_2$O$_{5.5}$, which is melted by increasing
the temperature across the MIT. In addition, we discovered that hole doping to
PrBaCo$_2$O$_{5.5}$ also melts the SSO in conjunction with an insulator-metal
transition. The experimental results from electron/neutron diffraction and soft
x-ray absorption spectroscopy (XAS) all lead to the conclusion that hole-doping
induced MIT occurs is in the same manner as the temperature-induced MIT.
Therefore, we propose a unified mechanism that dominates the temperature- and
hole-doping-induced MITs in the PrBaCo$_2$O$_{5.5+x}$ system. Specifically,
this mechanism involves symmetry breaking coupled with a SSO in the
paramagnetic phase.",1602.05687v2
2016-03-22,Polaronic contributions to oxidation and hole conductivity in acceptor-doped BaZrO$_3$,"Acceptor-doped perovskite oxides like BaZrO$_3$ are showing great potential
as materials for renewable energy technologies where hydrogen acts an energy
carrier, such as solid oxide fuel cells and hydrogen separation membranes.
While ionic transport in these materials has been investigated intensively, the
electronic counterpart has received much less attention and further exploration
in this field is required. Here, we use density functional theory (DFT) to
study hole polarons and their impact on hole conductivity in Y-doped BaZrO$_3$.
Three different approaches have been used to remedy the self-interaction error
of local and semi-local exchange-correlation functionals: DFT$+U$, pSIC-DFT and
hybrid functionals. Self-trapped holes are found to be energetically favorable
by about $-$0.1 eV and the presence of yttrium results in further
stabilization. Polaron migration is predicted to occur through intraoctahedral
transfer and polaron rotational processes, which are associated with adiabatic
barriers of about 0.1 eV. However, the rather small energies associated with
polaron formation and migration suggest that the hole becomes delocalized and
band-like at elevated temperatures. These results together with an endothermic
oxidation reaction [A. Lindman et al., Phys. Rev. B 91, 245114 (2015)] yield a
picture that is consistent with experimental data for the hole conductivity.
The results we present here provide new insight into hole transport in
acceptor-doped BaZrO$_3$ and similar materials, which will be of value in the
future development of sustainable technologies.",1603.06728v2
2017-01-20,Ultrafast X-ray Diffraction Thermometry Measures the Influence of Spin Excitations on the Heat Transport through nanolayers,"We investigate the heat transport through a rare earth multilayer system
composed of Yttrium (Y), Dysprosium (Dy) and Niobium (Nb) by ultrafast X-ray
diffraction. This is an example of a complex heat flow problem on the
nanoscale, where several different quasi-particles carry the heat. The Bragg
peak positions of each layer represent layer-specific thermometers that measure
the energy flow through the sample after excitation of the Y top-layer with
fs-laser pulses. In an experiment-based analytic solution to the nonequilibrium
heat transport problem, we derive the individual contributions of the spins and
the coupled electron-lattice system to the heat conduction. The full
characterization of the spatiotemporal energy flow at different starting
temperatures reveals that the spin excitations of antiferromagnetic Dy speed up
the heat transport into the Dy layer at low temperatures, whereas the heat
transport through this layer and further into the Y and Nb layers underneath is
slowed down. The experimental findings are compared to the solution of the heat
equation using macroscopic temperature-dependent material parameters without
separation of spin- and phonon contributions to the heat. We explain, why the
simulated energy density matches our experiment-based derivation of the heat
transport, although the simulated thermoelastic strain in this simulation is
not even in qualitative agreement.",1701.05918v1
2017-10-24,Hyperfine interactions of $\text{Er}^{3+}$ ions in $\text{Y}_2\text{SiO}_{5}$: electron paramagnetic resonance in a tunable microwave cavity,"The hyperfine structure of the ground state of erbium doped yttrium
orthosilicate is analyzed with the use of electron paramagnetic resonance
experiments in a tunable microwave resonator. This work was prompted by the
disagreement between the measurements made in zero magnetic field [Phys. Rev.
B, 94, 075117, (2016)] and a previously published spin Hamiltonian, which is
derived from standard EPR measurements at 9.5 GHz [Phys. Rev. B, 74, 214409,
(2006)].
  The ability to vary magnetic field strength, resonator frequency, and the
orientation of our sample enabled us to monitor how the frequencies of
hyperfine transitions change as a function of a vector magnetic field. Compared
to [Phys. Rev. B, 74, 214409, (2006)], we arrived at a different set of spin
Hamiltonian parameters, which are also broadly consistent with their data. We
discuss the reliability of our new spin Hamiltonian parameters to make
predictions outside the magnetic field and frequency regimes of our data. We
also discuss why it proved to be difficult to determine spin Hamiltonian
parameters for this material, and present data collection strategies that
improve the model reliability.",1710.09014v2
2017-11-06,A Raman-Heterodyne Study of the Hyperfine Interaction of the Optically-Excited State $^5$D$_0$ of Eu$^{3+}$:Y$_2$SiO$_5$,"The spin coherence time of $^{151}$Eu$^{3+}$ which substitutes the yttrium at
site 1 in Y$_2$SiO$_5$ crystal has been extended to 6 hours in a recent work
[\textit{Nature} \textbf{517}, 177 (2015)]. To make this long-lived spin
coherence useful for optical quantum memory applications, we experimentally
characterize the hyperfine interaction of the optically-excited state $^5$D$_0$
using Raman-heterodyne-detected nuclear magnetic resonance. The effective spin
Hamiltonians for excited and ground state are fitted based on the experimental
spectra obtained in 200 magnetic fields with various orientations. To show the
correctness of the fitted parameters and potential application in quantum
memory protocols, we also characterize the ground-state hyperfine interaction
and predict the critical magnetic field which produces the 6-hour-long
coherence time. The complete energy level structure for both the $^7$F$_0$
ground state and $^5$D$_0$ excited state at the critical magnetic field are
obtained. These results enable the design of quantum memory protocols and the
optimization of optical pumping strategy for realization of photonic quantum
memory with hour-long lifetime.",1711.01814v2
2017-11-16,Anisotropy and phonon modes from analysis of the dielectric function tensor and inverse dielectric function tensor of monoclinic yttrium orthosilicate,"We determine the frequency dependence of the four independent Cartesian
tensor elements of the dielectric function for monoclinic symmetry Y$_2$SiO$_5$
using generalized spectroscopic ellipsometry from 40-1200 cm$^{-1}$. Three
different crystal cuts, each perpendicular to a principle axis, are
investigated. We apply our recently described augmentation of lattice
anharmonicity onto the eigendielectric displacement vector summation approach
[A. Mock et al., Phys. Rev. B 95, 165202 (2017)], and we present and
demonstrate the application of an eigendielectric displacement loss vector
summation approach with anharmonic broadening. We obtain excellent match
between all measured and model calculated dielectric function tensor elements
and all dielectric loss function tensor elements. We obtain 23 A$_{\mathrm{u}}$
and 22 B$_{\mathrm{u}}$ symmetry long wavelength active transverse and
longitudinal optical mode parameters including their eigenvector orientation
within the monoclinic lattice. We perform density functional theory
calculations and obtain 23 A$_{\mathrm{u}}$ symmetry and 22 B$_{\mathrm{u}}$
transverse and longitudinal optical mode parameters and their orientation
within the monoclincic lattice. We compare our results from ellipsometry and
density functional theory and find excellent agreement. We also determine the
static and above reststrahlen spectral range dielectric tensor values and find
a recently derived generalization of the Lyddane-Sachs-Teller relation for
polar phonons in monoclinic symmetry materials satisfied [M. Schubert, Phys.
Rev. Lett. 117, 215502 (2016)].",1711.06336v1
2017-12-29,Origins and dissociation of pyramidal <c + a> dislocations in magnesium and its alloys,"Alloying magnesium (Mg) with rare earth elements such as yttrium (Y) has been
reported to activate the pyramidal <c + a> slip systems and improve the
plasticity of Mg at room temperature. However, the origins of such dislocations
and their dissociation mechanisms remain poorly understood. Here, we
systematically investigate these mechanisms using dispersion-inclusive density
functional theory, in combination with molecular dynamics simulations. We find
that <c + a> dislocations form more readily on the pyramidal I plane than on
the pyramidal II plane in Mg. The addition of Y atoms in Mg facilitates the
dissociation of <c + a> dislocations on pyramidal II, leading to the easier
formation of the pyramidal II than pyramidal I in Mg-Y alloy. Importantly, in
pyramidal II slip plane, a flat potential-energy surface (PES) exists around
the position of stable stacking fault energy (SFE), which allows cooperative
movement of atoms within the slip plane. Alloying Mg with Y atoms increases the
range of the PES, and ultimately promotes different sliding pathways in the
Mg-Y alloy. These findings are consistent with experimentally observed
activation of the pyramidal II <c + a> slip system in Mg-Y alloys, and provide
important insight into the relationship between dislocation structure and
macroscopic enhancement of plasticity.",1712.10098v1
2018-01-10,Study of a Prototype VP-PET Imaging System Based on highly Pixelated CdZnTe Detectors,"We are investigating a prototype virtual pinhole positron emission tomography
(VP-PET) system for small animal imaging applications. The PET detector modules
were made up of 1.3 mm lutetium-yttrium oxyorthosilicate (LYSO) arrays, and the
insert detectors consists of 0.6 mm pixelated Cadmium Zinc Telluride (CdZnTe).
To validate the imaging experiment, we conducted a Monte Carlo simulation for
the VP-PET system in Geant4 Application for Emission Tomography (GATE). For a
point source of Na-22 with 0.5 mm diameter, the filtered back-projection (FBP)
algorithm reconstructed PET image shows a resolution of 0.7 mm
full-width-at-half-maximum (FWHM). The system sensitivity is 0.46 cps/kBq at
the center of field view (CFOV) of the PET system with a source activity of
0.925 MBq and an energy resolution of 350-650 keV. A rod source phantom and a
Derenzo phantom with F-18 were also simulated to investigate the PET imaging
capability. GATE simulation indicated that two point sources with 0.5 mm
diameter 2 mm apart could be clearly separated using 0.6 mm pixelated CdZnTe
detectors as insert devices in a VP-PET system.",1801.03225v1
2018-01-11,"Nano-machining, surface analysis and emittance measurements of a copper photocathode at SPARC_LAB","R\&D activity on Cu photocathodes is under development at the SPARC\_LAB test
facility to fully characterize each stage of the photocathode ""life"" and to
have a complete overview of the photoemission properties in high brightness
photo-injectors. The nano(n)-machining process presented here consists in
diamond milling, and blowing with dry nitrogen. This procedure reduces the
roughness of the cathode surface and prevents surface contamination introduced
by other techniques, such as polishing with diamond paste or the machining with
oil. Both high roughness and surface contamination cause an increase of
intrinsic emittance and consequently a reduction of the overall electron beam
brightness. To quantify these effects, we have characterized the photocathode
surface in terms of roughness measurement, and morphology and chemical
composition analysis by means of Scanning Electron Microscopy (SEM), Energy
Dispersive Spectroscopy (EDS), and Atomic Force Microscopy (AFM) techniques.
The effects of n-machining on the electron beam quality have been also
investigated through emittance measurements before and after the surface
processing technique. Finally, we present preliminary emittance studies of
yttrium thin film on Cu photocathodes.",1801.03823v1
2018-02-17,Controlling rare-earth ions in a nanophotonic resonator using the ac Stark shift,"On-chip nanophotonic cavities will advance quantum information science and
measurement because they enable efficient interaction between photons and
long-lived solid-state spins, such as those associated with rare-earth ions in
crystals. The enhanced photon-ion interaction creates new opportunities for
all-optical control using the ac Stark shift. Toward this end, we characterize
the ac Stark interaction between off-resonant optical fields and Nd$^{3+}$-ion
dopants in a photonic crystal resonator fabricated from yttrium orthovanadate
(YVO$_4$). Using photon echo techniques, at a detuning of 160 MHz we measure a
maximum ac Stark shift of 2$\pi\times$12.3 MHz per intra-cavity photon, which
is large compared to both the homogeneous linewidth ($\Gamma_h =$100 kHz) and
characteristic width of isolated spectral features created through optical
pumping ($\Gamma_f \approx$3 MHz). The photon-ion interaction strength in the
device is sufficiently large to control the frequency and phase of the ions for
quantum information processing applications. In particular, we discuss and
assess the use of the cavity enhanced ac Stark shift to realize all-optical
quantum memory and detection protocols. Our results establish the ac Stark
shift as a powerful added control in rare-earth ion quantum technologies.",1802.06172v1
2018-03-05,Widefield imaging of superconductor vortices with electron spins in diamond,"Understanding the mechanisms behind high-$T_{c}$ Type-II superconductors (SC)
is still an open task in condensed matter physics. One way to gain further
insight into the microscopic mechanisms leading to superconductivity is to
study the magnetic properties of the SC in detail, for example by studying the
properties of vortices and their dynamics. In this work we describe a new
method of wide-field imaging magnetometry using nitrogen-vacancy (NV) centers
in diamond to image vortices in an yttrium barium copper oxide (YBCO) thin
film. We demonstrate quantitative determination of the magnetic field strength
of the vortex stray field, the observation of vortex patterns for different
cooling fields and direct observation of vortex pinning in our disordered YBCO
film. This method opens prospects for imaging of the magnetic-stray fields of
vortices at frequencies from DC to several megahertz within a wide range of
temperatures which allows for the study of both high-$T_{C}$ and low-$T_{C}$
SCs. The wide temperature range allowed by NV center magnetometry also makes
our approach applicable for the study of phenomena like island
superconductivity at elevated temperatures (e.g. in metal nano-clusters).",1803.01957v1
2018-08-22,Evidence against anomalous compositions for giants in the Galactic Nuclear Star Cluster,"Very strong Sc I lines have been found recently in cool M giants in the
Nuclear Star Cluster in the Galactic Center. Interpreting these as anomalously
high scandium abundances in the Galactic Center would imply a unique
enhancement signature and chemical evolution history for nuclear star clusters,
and a potential test for models of chemical enrichment in these objects. We
present high resolution K-band spectra (NIRSPEC/Keck II) of cool M giants
situated in the solar neighborhood and compare them with spectra of M giants in
the Nuclear Star Cluster. We clearly identify strong Sc I lines in our solar
neighborhood sample as well as in the Nuclear Star Cluster sample. The strong
Sc I lines in M giants are therefore not unique to stars in the Nuclear Star
Cluster and we argue that the strong lines are a property of the line formation
process that currently escapes accurate theoretical modeling. We further
conclude that for giant stars with effective temperatures below approximately
3800 K these Sc I lines should not be used for deriving the scandium abundances
in any astrophysical environment until we better understand how these lines are
formed. We also discuss the lines of vanadium, titanium, and yttrium identified
in the spectra, which demonstrate a similar striking increase in strength below
3500 K effective temperature.",1808.07489v1
2018-11-21,Position Sensitive Alpha Detector for an Associate Particle Imaging System,"Associated Particle Imaging (API) is a nuclear technique that allows for the
nondestructive determination of 3D isotopic distributions. The technique is
based on the detection of the alpha particles associated with the neutron
emitted in the deuterium-tritium (DT) fusion reaction, which provides
information regarding the direction and time of the emitted 14 MeV neutron.
Inelastic neutron scattering leads to characteristic gamma-ray emission from
certain isotopes, for example C-12, that can be correlated with the neutron
interaction location. An API system consisting of a sealed-type neutron
generator, gamma detectors, and a position-sensitive alpha detector is under
development for the nondestructive quantification of carbon distribution in
soils. This paper describes the design of the alpha detector, detector response
simulations, and first experimental results. The alpha detector consists of a
Yttrium Aluminum Perovskite (YAP) scintillator mounted on the inside of a
neutron generator tube. The scintillation light propagates through a sapphire
window to a position-sensitive photomultiplier tube mounted on the outside. The
16x16 output signals are connected through a resistive network for a 4-corner
readout. The four readout channels are amplified, filtered, and then digitized
for the calculation of the alpha position. First test results demonstrate that
an excellent alpha position resolution, better than the 1 mm FWHM required by
the application, can be achieved with this detector design.",1811.08591v1
2019-02-12,High Quality Factor High-Temperature Superconducting Microwave Cavity Development for the Dark Matter Axion Search in a Strong Magnetic Field,"We demonstrate a superconducting (SC) microwave (mw) cavity that can
accelerate the dark matter search by maintaining superconductivity in a high DC
magnetic field. We used high-temperature superconductor (HTSC) yttrium barium
copper oxide (YBCO) with a phase transition temperature of 90K to prevent SC
failure by the magnetic field. Since the direct deposition of HTSC film on the
metallic mw cavity is very difficult, we used the commercial HTSC tapes which
are flexible metallic tapes coated with HTSC thin films. We fabricated
resonating cavity ($f_{TM010}$ ~ 6.89 GHz) with a third of the inner wall
covered by YBCO tapes and measured the quality factor (Q factor) at 4K
temperature, varying the DC magnetic field from 0 to 8 tesla. There was no
significant quality (Q) factor drop and the superconductivity was well
maintained even in 8 tesla magnetic field. This implies the possibility of good
performance of HTSC mw resonant cavity under a strong magnetic field for axion
detection.",1902.04551v3
2019-03-04,Ionization-density-dependent Scintillation Pulse Shape and Mechanism of Luminescence Quenching in LaBr3:Ce,"Pulse-shape discrimination (PSD) is usually achieved using the different fast
and slow decay components of inorganic scintillators, such as BaF2, CsI:Tl,
etc. However, LaBr3:Ce is considered to not possess different components at
room temperature, but has been proved to have the capability of discriminating
{\gamma} and {\alpha} events using fast digitizers. In this paper,
ionization-density-dependent transport and rate equations are used to
quantitatively model the competing processes in a particle track. With one
parameter set, the model reproduces the nonproportionality response of
electrons or {\alpha} particles, and explains the measured {\alpha} and
{\gamma} pulse-shape difference well. In particular, the nonlinear quenching of
excited dopant ions, Ce3+, is confirmed herein to mainly contribute observable
ionization {\alpha} and {\gamma} pulse-shape differences. Further study of the
luminescence quenching can also help to better understand the fundamental
physics of nonlinear quenching and thus improve the crystal engineering.
Moreover, based on the mechanism of dopant quenching, the
ionization-density-dependent pulse-shape differences in other fast
single-decay-component inorganic scintillators, such as lutetium yttrium
oxyorthosilicate, Lu2(1-x)Y2xSiO5:Ce (LYSO) and CeBr3, are also predicted and
verified with experiments.",1903.01452v3
2020-01-26,The Spectral and Magnetic Properties of Er$^{3+}$ and Yb$^{3+}$ Ions in Y$_{2}$Ti$_{2}$O$_{7}$ Crystals with a Pyrochlore Structure,"Cubic Y$_{2}$Ti$_{2}$O$_{7}$ single crystals doped with Er$^{3+}$ and
Yb$^{3+}$ ions have been studied by the methods of electron spin resonance
(ESR) and selective laser spectroscopy. ESR spectra exhibit signals from
rare-earth ions that substitute for yttrium ions in sites with local trigonal
symmetry. The $g$ tensor components are determined. The results of optical
investigations indicate that impurity centers of several types are formed; the
sublevel energies of the ground and excited multiplets of these centers are
found. Among the great variety of detected optical centers, the centers that
dominate in the formation of ESR spectra are discriminated. An analysis of the
experimental data using the exchange-charge model have made it possible to
determine the sets of parameters of the crystal field for Er$^{3+}$ and
Yb$^{3+}$ ions substituting Y$^{3+}$ ions in regular crystallographic sites in
pyrochlore Y$_{2}$Ti$_{2}$O$_{7}$.",2001.09447v1
2020-02-20,Reliable coherent optical memory based on a laser-written waveguide,"$\mathrm {^{151}Eu^{3+}}$-doped yttrium silicate ($\mathrm
{^{151}Eu^{3+}:Y_2SiO_5}$ ) crystal is a unique material that possesses
hyperfine states with coherence time up to 6 h. Many efforts have been devoted
to the development of this material as optical quantum memories based on the
bulk crystals, but integrable structures (such as optical waveguides) that can
promote $\mathrm {^{151}Eu^{3+}:Y_2SiO_5}$-based quantum memories to practical
applications, have not been demonstrated so far. Here we report the fabrication
of type 2 waveguides in a $\mathrm {^{151}Eu^{3+}:Y_2SiO_5}$ crystal using
femtosecond-laser micromachining. The resulting waveguides are compatible with
single-mode fibers and have the smallest insertion loss of $4.95\ dB$.
On-demand light storage is demonstrated in a waveguide by employing the
spin-wave atomic frequency comb (AFC) scheme and the revival of silenced echo
(ROSE) scheme. We implement a series of interference experiments based on these
two schemes to characterize the storage fidelity. Interference visibility of
the readout pulse is $0.99\pm 0.03$ for the spin-wave AFC scheme and $0.97\pm
0.02$ for the ROSE scheme, demonstrating the reliability of the integrated
optical memory.",2002.08780v1
2020-02-21,Sensing individual nuclear spins with a single rare-earth electron spin,"Rare-earth related electron spins in crystalline hosts are unique material
systems, as they can potentially provide a direct interface between telecom
band photons and long-lived spin quantum bits. Specifically, their optically
accessible electron spins in solids interacting with nuclear spins in their
environment are valuable quantum memory resources. Detection of nearby
individual nuclear spins, so far exclusively shown for few dilute nuclear spin
bath host systems such as the NV center in diamond or the silicon vacancy in
silicon carbide, remained an open challenge for rare-earths in their host
materials, which typically exhibit dense nuclear spin baths. Here, we present
the electron spin spectroscopy of single Ce$^{3+}$ ions in a yttrium
orthosilicate host, featuring a coherence time of $T_{2}=124\,\mu$s. This
coherent interaction time is sufficiently long to isolate proximal $^{89}$Y
nuclear spins from the nuclear spin bath of $^{89}$Y. Furthermore, it allows
for the detection of a single nearby $^{29}$Si nuclear spin, native to the host
material with ~5% abundance. This study opens the door to quantum memory
applications in rare-earth ion related systems based on coupled environmental
nuclear spins, potentially useful for quantum error correction schemes.",2002.09357v2
2020-04-06,Successful production of Solution Blow Spun YBCO+Ag complex ceramics,"YBCO fabrics composed of nanowires, produced by solution blow spinning (SBS)
are so brittle that the Lorentz force produced by induced currents can be
strong enough to damage them. On the other hand, it is known that silver
addition improves the mechanical and flux pinning properties of ceramic
superconductors. Thus, in this work, we show how we successfully obtained a
polymeric precursor solution containing YBCO$+$Ag salts, which can be spun by
the SBS route to produce ceramic samples. Yttrium, barium, copper, and silver
metal acetates, and polyvinylpyrrolidone (PVP) (in a ratio of 5:1wt
[PVP:acetates]) were dissolved in a solution with 61.5 wt\% of methanol, 12
wt\% of propionic acid, and 26.5 wt\% of ammonium hydroxide, together with 6
wt\% of PVP in solution. Three different amounts of silver (10 wt\%, 20 wt\%,
and 30 wt\%) were used in YBa$_2$Cu$_3$O$_{7-x}$. The TGA characterizations
revealed a lowering of crystallization and partial melting temperatures by
about \SI{30}{\celsius}. SEM images show that after burning out the polymer, a
fabric composed of nanowires of diameters up to \SI{380}{\nano \metre} is
produced. However, after the sintering process at \SI{925}{\celsius} for
\SI{1}{\hour}, the nanowires shrink into a porous-like sample.",2004.07287v2
2020-04-15,Experimental observation of magnetic dimers in diluted Yb:YAlO$_3$,"We present a comprehensive experimental investigation of Yb magnetic dimers
in Yb$_{0.04}$Y$_{0.96}$AlO$_3$, an Yb-doped Yttrium Aluminum Perovskite (YAP)
YAlO$_3$ by means of specific heat, magnetization and high-resolution inelastic
neutron scattering (INS) measurements. In our sample, the Yb ions are randomly
distributed over the lattice and $\sim 7$\% of Yb ions form quantum dimers due
to nearest-neighbor antiferromagnetic coupling along the $c$-axis. At zero
field, the dimer formation manifests itself in an appearance of an inelastic
peak at $\Delta \approx 0.2$~meV in the INS spectrum and a Schottky-like
anomaly in the specific heat. The structure factor of the INS peak exhibits a
cosine modulation along the $L$ direction, in agreement with the $c$-axis
nearest-neighbor intra-dimer coupling. A careful fitting of the low-temperature
specific heat shows that the excited state is a degenerate triplet, which
indicates a surprisingly small anisotropy of the effective Yb-Yb exchange
interaction despite the low crystal symmetry and anisotropic magnetic dipole
contribution, in agreement with previous reports for the Yb parent compound,
YbAlO$_3$ [arXiv:1904.11513, arXiv:1902.04112], and in contrast to
Yb$_2$Pt$_2$Pb [arXiv:1606.01309, arXiv:1907.01067]. The obtained results are
precisely reproduced by analytical calculations for the Yb dimers.",2004.07325v1
2020-04-28,Al-dependent electronic and magnetic properties of YCrO$_3$ with magnetocaloric application: an ab-initio and Monte-Carlo approach,"In this paper, a theoretical journey from electronic to magneto-caloric
effect has been shown through the magnetic properties of aluminium induced
yttrium chromate. The ground state electronic band structure and density of
states have been studied using first principle calculations under GGA+U
schemes. From the energy minimization, the ferromagnetic structure is more
stable than the antiferromagnetic one. The interaction constant as well as the
magnetic moment, have been determined from mean-field theory and DFT,
respectively. The Monte-Carlo simulation under Metropolis algorithm has been
employed to determine the critical temperature ($T_C$), which is nearly same as
the experimental value. The temperature-dependent magnetization shows that
these materials exhibit a paramagnetic to ferromagnetic phase transition at
~136 K, 130 K, 110 K, and 75 K respectively. The two inherent properties named
the isothermal entropy change ($\Delta S_M$) and the adiabatic temperature
change ($\Delta T_{ad}$) as a function of temperature for different applied
magnetic fields have been determined to measure the magnetocaloric efficiency
of these materials. The relative cooling power (RCP), which is calculated
around $T_C$, changes from 4.7 J/Kg to 2.5 J/Kg with the decreasing
Cr-concentration.",2004.13456v2
2020-05-21,Local distortions and dynamics in hydrated Y-doped BaZrO$_3$,"Y-doped BaZrO$_3$ is a promising proton conductor for intermediate
temperature solid oxide fuel cells. In this work, a combination of static DFT
calculations and DFT based molecular dynamics (DFT-MD) was used to study proton
conduction in such a material. Geometry optimisations of 100 structures with a
12.5% dopant concentration allowed us to identify a clear correlation between
the bending of the metal-oxygen-metal angle and the energies of the simulated
cells. Depending on the type of bending, two configurations, designated as
inwards bending and outwards bending, were defined. The results demonstrate
that a larger bending decreases the energy and that the lowest energies are
observed for structures combining inwards bending with protons being close to
the dopant atoms. These lowest energy structures are the ones with the
strongest hydrogen bonds. DFT-MD simulations in cells with different yttrium
distributions provide complementary microscopic information on proton diffusion
as they capture the dynamic distortions of the lattice caused by thermal
motion. A careful analysis of the proton jumps between different environments
confirmed that the inwards and outwards bending states are relevant for the
understanding of proton diffusion. Indeed, intra-octahedral jumps were shown to
only occur starting from an outwards configuration while the inwards
configuration seems to favor rotations around the oxygen. On average, in the
DFT-MD simulations, the hydrogen bond lengths are shorter for the outwards
configuration which facilitates the intraoctahedral jumps. Diffusion
coefficients and activation energies were also determined and compared to
previous theoretical and experimental data showing a good agreement with
previous data corresponding to local proton motion.",2005.10877v1
2020-09-14,An all-digital associated particle imaging system for the 3D determination of isotopic distributions,"Associated particle imaging (API) is a non-destructive nuclear technique for
the 3D determination of isotopic distributions. By detecting the alpha particle
associated with the emitted neutron in the deuterium-tritium fusion reaction
with a position- and time-resolving detector, the direction of the 14.1 MeV
neutron and its time of emission can be determined. Employing this method,
isotope characteristic gamma rays emitted in inelastic neutron scattering
events can be correlated with the neutron interaction location. An API system
consisting of a sealed-type neutron generator, gamma detectors, and a
position-sensitive alpha detector was designed, constructed, and characterized.
The system was tested with common soil elements and shown to be sensitive to
12C, 16O, 28Si, 27Al, and 56Fe. New aspects of our approach are the use of a
yttrium-aluminum-perovskite (YAP) scintillator, using a sapphire window instead
of a fiber-optic faceplate for light transport to the photomultiplier, and the
all-digital data acquisition system. We present a description of the system
with simulations and experimental results that show a position resolution on
the alpha detector of 1 mm, a depth resolution using a LaBr3 detector of 6.2
cm, and an angular resolution of 4.5 degrees. Additionally, we present
single-element gamma response measurements for the elements mentioned above
together with a comparison to Monte Carlo simulations (MCNP6).",2009.06768v2
2020-11-15,A single-projection three-dimensional reconstruction algorithm for scanning transmission electron microscopy data,"Increasing interest in three-dimensional nanostructures adds impetus to
electron microscopy techniques capable of imaging at or below the nanoscale in
three dimensions. We present a reconstruction algorithm that takes as input a
focal series of four-dimensional scanning transmission electron microscopy
(4D-STEM) data. We apply the approach to a lead iridate, Pb$_2$Ir$_2$O$_7$, and
yttrium-stabilized zirconia,Y$_{0.095}$Zr$_{0.905}$O$_2$ , heterostructure from
data acquired with the specimen in a single plan-view orientation, with the
epitaxial layers stacked along the beam direction. We demonstrate that Pb-Ir
atomic columns are visible in the uppermost layers of the reconstructed volume.
We compare this approach to the alternative techniques of depth sectioning
using differential phase contrast scanning transmission electron microscopy
(DPC-STEM) and multislice ptychographic reconstruction.",2011.07652v2
2020-12-09,Kinetically-stabilized Ferroelectricity in Bulk Singlecrystalline HfO2:Y without Wake-up Effects,"HfO2, a simple binary oxide, holds ultra-scalable ferroelectricity integrable
into silicon technology. Polar orthorhombic (Pbc21) form in ultra-thin-films
ascribes as the plausible root-cause of the astonishing ferroelectricity, which
has thought not attainable in bulk crystals. Though, perplexities remain
primarily due to the polymorphic nature and the characterization challenges at
small-length scales. Herein, utilizing a state-of-the-art Laser-Diode-heated
Floating Zone technique, we report ferroelectricity in bulk single-crystalline
HfO2:Y as well as the presence of anti-polar Pbca phase at different Y
concentrations. Neutron diffraction and atomic imaging demonstrate (anti-)polar
crystallographic signatures and abundant 90o/180o ferroelectric domains in
addition to the switchable polarization with little wake-up effects.
Density-functional theory calculations suggest that the Yttrium doping and
rapid cooling are the key factors for the desired phase. Our observations
provide new insights into the polymorphic nature and phase controlling of HfO2,
remove the upper size limit for ferroelectricity, and also pave a new road
toward the next-generation ferroelectric devices.",2012.05289v1
2021-02-08,"Improvement of reversible H storage capacity by fine tuning of the composition in the pseudo-binary systems A2-xLaxNi7 (A = Gd, Sm, Y, Mg)","A2B7 compounds (A = rare earth or Mg, B = transition metal) are widely
studied as active materials for negative electrode in Ni-MH batteries. By
playing on the substitution rate of both A and B elements, it is possible to
prepare various compositions. This strategy will help to improve the
properties, for example get a higher reversible hydrogen capacity and a
well-adapted hydrogen sorption pressure. Indeed, A can be almost all light rare
earths (La to Gd), yttrium and alkaline earth metals (Mg or Ca), whereas B can
contain various late transition metals (Mn to Ni). To understand the effects of
composition on the physicochemical properties of La2Ni7-based compound, various
pseudo-binary systems have been investigated: Gd2 xLaxNi7 (x = 0, 0.6, 1, 1.5),
Sm2-xLaxNi7 (x = 0, 0.5, 1, 1.5), Y2-xLaxNi7 (x = 0, 0.4, 0.5, 0.6, 0.8, 1,
1.5, 1.75) and A0.5La1.1Mg0.4Ni7 (A = Sm, Gd and Y). To determine their
crystallographic properties, X-ray diffraction analysis was performed followed
by Rietveld refinement. Thermodynamic properties regarding reversible hydrogen
sorption were investigated at room temperature. Quaternary compounds present
drastically improved sorption properties in the frame of practical energy
storage applications with reversible capacity equivalent to 400 mAh/g for the
compound La1.1Sm0.5Mg0.4Ni7.",2102.04161v1
2021-03-06,Spectroscopic Evidence for the Superconductivity of Elemental Metal Y under Pressure,"Very high applied pressure induces superconductivity with the transition
temperature ($T_c$) exceeding 19 K in elemental yttrium, but relatively little
is known about the nature of that superconductivity. From point-contact
spectroscopy (PCS) measurements in a diamond anvil cell (DAC), a strong
enhancement in the differential conductance is revealed near the zero-biased
voltage owing to Andreev reflection, a hallmark of the superconducting (SC)
phase. Analysis of the PCS spectra based on the extended
Blonder-Tinkham-Klapwijk (BTK) model indicates two SC gaps at 48.6 GPa, where
the large gap $\Delta_L$ is 3.63 meV and the small gap $\Delta_S$ is 0.46 meV.
When scaled against a reduced temperature, both small and large SC gaps
collapse on a single curve that follows the prediction from BCS theory. The SC
gap-to-$T_c$ ratio is 8.2 for the larger gap, and the initial slope of the
upper critical field is -1.9 T/K, indicating that Y belongs to a family of
strongly coupled BCS superconductors. The successful application of PCS to Y in
DAC environments demonstrates its utility for future research on other
pressure-induced high-$T_c$ superconductors.",2103.04070v3
2021-03-18,An antisite defect mechanism for room temperature ferroelectricity in orthoferrites,"Single-phase multiferroic materials that allow the coexistence of
ferroelectric and magnetic ordering above room temperature are highly
desirable, motivating an ongoing search for mechanisms for unconventional
ferroelectricity in magnetic oxides. Here, we report an antisite defect
mechanism for room temperature ferroelectricity in epitaxial thin films of
yttrium orthoferrite, YFeO3, a perovskite-structured canted antiferromagnet. A
combination of piezoresponse force microscopy, atomically resolved elemental
mapping with aberration corrected scanning transmission electron microscopy and
density functional theory calculations reveals that the presence of YFe
antisite defects facilitates a non-centrosymmetric distortion promoting
ferroelectricity. This mechanism is predicted to work analogously for other
rare earth orthoferrites, with a dependence of the polarization on the radius
of the rare earth cation. Furthermore, a vertically aligned nanocomposite
consisting of pillars of a magnetoelastic oxide CoFe2O4 embedded epitaxially in
the YFeO3 matrix exhibits both robust ferroelectricity and ferrimagnetism at
room temperature, as well as a noticeable strain-mediated magnetoelectric
coupling effect. Our work uncovers the distinctive role of antisite defects in
providing a novel mechanism for ferroelectricity in a range of magnetic
orthoferrites and further augments the functionality of this family of complex
oxides for multiferroic applications.",2103.10338v1
2021-06-08,"Superconducting microresonators for electron spin resonance, the good, the bad, and the future","The field of electron spin resonance is in constant need to improve its
capabilities. Among other things, this means having better resonators which
would provide improved spin sensitivity, as well as enable larger microwave
magnetic field power conversion factors. Surface micro resonators, made of
small metallic patches on a dielectric substrate, provide very good absolute
spin sensitivity and high conversion factors due to their very small mode
volume. However, such resonators suffer from having a relatively low quality
factor, which offsets some of their significant potential advantages. The use
of superconducting patches to replace the metallic layer seems like a
reasonable and straightforward solution to the quality factor issue, at least
for measurements carried out at cryogenic temperatures. Nevertheless,
superconducting materials are not easily incorporated into setups requiring
high magnetic fields, due to electric current vortices generated in the
latter's surface. This makes the transition from normal conducing materials to
superconductors highly nontrivial. Here we present the design, fabrication, and
testing results of surface micro resonators made of yttrium barium copper oxide
(YBCO) superconducting material. We show that with a unique experimental setup,
these resonators can be made to operate well even at high fields of about 1.2
T. Furthermore, we analyze the effect of current vortices on the ESR signal and
the spins' coherence times. Finally, we provide a head to head comparison of
YBCO vs copper resonators of the same dimensions, which clearly shows their
pros and cons and directs us to future potential developments and improvements
in this field.",2106.04163v2
2021-08-29,Nuclear spin-wave quantum register for a solid state qubit,"Solid-state nuclear spins surrounding individual, optically addressable
qubits provide a crucial resource for quantum networks, computation and
simulation. While hosts with sparse nuclear spin baths are typically chosen to
mitigate qubit decoherence, developing coherent quantum systems in nuclear
spin-rich hosts enables exploration of a much broader range of materials for
quantum information applications. The collective modes of these dense nuclear
spin ensembles provide a natural basis for quantum storage, however, utilizing
them as a resource for single spin qubits has thus far remained elusive. Here,
by using a highly coherent, optically addressed 171Yb3+ qubit doped into a
nuclear spin-rich yttrium orthovanadate crystal, we develop a robust quantum
control protocol to manipulate the multi-level nuclear spin states of
neighbouring 51V5+ lattice ions. Via a dynamically-engineered spin exchange
interaction, we polarise this nuclear spin ensemble, generate collective spin
excitations, and subsequently use them to implement a long-lived quantum
memory. We additionally demonstrate preparation and measurement of maximally
entangled 171Yb--51V Bell states. Unlike conventional, disordered nuclear spin
based quantum memories, our platform is deterministic and reproducible,
ensuring identical quantum registers for all 171Yb qubits. Our approach
provides a framework for utilising the complex structure of dense nuclear spin
baths, paving the way for building large-scale quantum networks using single
rare-earth ion qubits.",2108.12723v1
2021-09-11,Dzyaloshinskii interaction and exchange-relativistic effects in orthoferrites,"We present an overview of the microscopic theory of the Dzyaloshinskii-Moriya
(DM) coupling and related exchange-relativistic effects such as exchange
anisotropy, electron-nuclear antisymmetric supertransferred hyperfine
interactions, antisymmetric magnetogyrotropic effects, and antisymmetric
magnetoelectric coupling in strongly correlated 3$d$ compounds focusing on
orthoferrites RFeO$_3$ (R is a rare-earth ion or yttrium Y). % Particular
emphasis will be placed on the role of crystal field effects, the sense and
direction of the Dzyaloshinskii vector, its dependence on the superexchange
bonding geometry, and other subtle features of exchange-relativistic effects.
Most attention in the paper centers around the derivation of the Dzyaloshinskii
vector, its value, orientation, and sense (sign) under different types of the
(super)exchange interaction and crystal field. Microscopically derived
expression for the dependence of the Dzyaloshinskii vector on the superexchange
geometry allows one to find all the overt and hidden canting angles in
orthoferrites RFeO$_3$ as well as corresponding contribution to magnetic
anisotropy. Being based on the theoretical predictions regarding the sign of
the Dzyaloshinskii vector we have predicted and study in detail a novel
magnetic phenomenon, {\it weak ferrimagnetism} in mixed weak ferromagnets with
competing signs of the Dzyaloshinskii vectors. The ligand NMR measurements in
weak ferromagnets are shown to be an effective tool to inspect the effects of
DM coupling in an external magnetic field. Along with orthoferrites RFeO$_3$
and weak ferrimagnets RFe$_{1-x}$Cr$_x$O$_3$, although to a lesser extent, we
address such typical weak ferromagnets as $\alpha$-Fe$_2$O$_3$, FeBO$_3$, and
FeF$_3$.",2109.05326v1
2021-11-20,Trivalent ion overcharging on electrified graphene,"The structure of the electrical double layer (EDL) formed near graphene in
aqueous environments strongly impacts its performance for a plethora of
applications, including capacitive deionization. In particular, adsorption and
organization of multivalent counterions near the graphene interface can promote
nonclassical behaviors of EDL including overcharging followed by co-ion
adsorption. In this paper, we characterize the EDL formed near an electrified
graphene interface in dilute aqueous $YCl_3$ solution using in situ high
resolution x-ray reflectivity (also known as crystal truncation rod (CTR)) and
resonant anomalous x-ray reflectivity (RAXR). These interfacial-specific
techniques reveal the electron density profiles with molecular-scale
resolution. We find that yttrium ions ($Y^{3+}$) readily adsorb to the
negatively charged graphene surface to form an extended ion profile. This ion
distribution resembles a classical diffuse layer but with a significantly high
ion coverage, i.e., 1 $Y^{3+}$ per 11.4 $\pm$ 1.6 A$^2$, compared to the value
calculated from the capacitance measured by cyclic voltammetry (1 $Y^{3+}$ per
~240 A$^2$). Such overcharging can be explained by co-adsorption of chloride
that effectively screens the excess positive charge. The adsorbed $Y^{3+}$
profile also shows a molecular-scale gap ($\geq$5 A) from the top graphene
surfaces, which is attributed to the presence of intervening water molecules
between the adsorbents and adsorbates as well as the lack of inner-sphere
surface complexation on chemically inert graphene. We also demonstrate
controlled adsorption by varying the applied potential and reveal consistent
$Y^{3+}$ ion position with respect to the surface and increasing cation
coverage with decreasing applied potential.",2111.10516v2
2021-12-09,Comparative studies of hydrogen dissolution and release behavior in zirconate oxides by TDS and TMAP4 analysis,"Proton-conducting oxides are potential materials for electrochemical devices
such as fuel cells, hydrogen pumps, hydrogen sensors, and the tritium
purification and recovery system in nuclear fusion reactors. The hydrogen
concentration in oxide materials is important, but its precise measurement is
difficult. In this study, thermal desorption spectroscopy (TDS) was used to
investigate hydrogen dissolution and release behavior in proton-conducting
oxides, yttrium (Y), and cobalt (Co) doped barium-zirconates in the temperature
range of 673-1273 K using deuterium (D2) and heavy water (D2O). Specimens were
prepared with conventional powder metallurgy: the powder of three zirconates,
BaZr0.9Y0.1O3-a (BZY), BaZr0.955Y0.03Co0.015O3-a (BZYC), and CaZr0.9In0.1O2.95
(CZI) was pressed into discs and fired in the air at 1873 K for 20 h. The
densities of the sintered BZY, BZYC, and CZI specimens were 98 percent, 99.7
percent, and 99.5 percent of the theoretical densities respectively. XRD, SEM,
and EDX were performed for the structural and morphological analysis of the
sintered samples. From TDS measurement, a similar trend of
temperature-dependent hydrogen solubility was obtained for all samples compared
to the tritium imaging plate (TIP) methods literature data of HT- and
DTO-exposed samples. To compare the experimental results of the deuterium
desorption profile derived by TDS analysis, the simulation code of the tritium
migration analysis program, version 4 (TMAP4) was employed.",2112.04649v1
2022-07-06,Robust millisecond coherence times of erbium electron spins,"Erbium-doped solids are prime candidates for optical quantum communication
networks due to erbium's telecom C-band emission. A long-lived electron spin of
erbium with millisecond coherence time is highly desirable for establishing
entanglement between adjacent quantum repeater nodes while long-term storage of
the entanglement could rely on transferring to erbium's second-long coherence
nuclear spins. Here we report GHz-range electron spin transitions of
$^{167}\mathrm{Er}^{3+}$ in yttrium oxide ($\mathrm{Y_2O_3}$) matrix with
coherence times that are consistently longer than a millisecond. Instead of
addressing field-specific Zero First-Order Zeeman transitions, we probe weakly
mixed electron spins with the field orientation along the lower g-factors.
Using pulsed electron spin resonance spectroscopy, we find paramagnetic
impurities are the dominant source of decoherence, and by polarizing them we
achieve a Hahn echo spin $\mathrm{T_2}$ up to 1.46 ms, and a coherence time up
to 7.1 ms after dynamical decoupling. These coherence lifetimes are among the
longest found in crystalline hosts especially those with nuclear spins. We
further enhance the coherence time beyond conventional dynamical decoupling,
using customized sequences to simultaneously mitigate spectral diffusion and
Er-Er dipolar interactions. Despite nuclear and impurity spins in the host,
this work shows that long-lived erbium spins comparable to non-nuclear spin
hosts can be achieved. Our study not only establishes $^{167}\mathrm{Er}^{3+}$:
$\mathrm{Y_2 O_3}$ as a significantly promising quantum memory platform but
also provides a general guideline for engineering long-lived erbium spins in a
variety of host materials for quantum technologies.",2207.02708v1
2022-09-15,"Yttrium incorporation in Cr2AlC: On the metastable phase formation and decomposition of (Cr,Y)2AlC MAX phase thin films","Herein we report on the synthesis of a metastable (Cr,Y)2AlC MAX phase solid
solution by co-sputtering from a composite Cr-Al-C and elemental Y target, at
room temperature, followed by annealing. While direct high-temperature
synthesis resulted in multiphase films, as evidenced by X-ray diffraction
analyses, room temperature depositions, followed by annealing to 760 {\deg}C
led to the formation of phase pure (Cr,Y)2AlC by diffusion. Higher annealing
temperatures caused decomposition of the metastable phase into Cr2AlC, Y5Al3 ,
and Cr-carbides. In contrast to pure Cr2AlC, the Y-containing phase
crystallizes directly in the MAX phase structure instead of first forming a
disordered solid solution. Furthermore, the crystallization temperature was
shown to be Y-content dependent and was increased by ~200 {\deg}C for 5 at.% Y
compared to Cr2AlC. Calculations predicting the metastable phase formation of
(Cr,Y)2AlC and its decomposition are in excellent agreement with the
experimental findings.",2209.07119v1
2022-11-29,Comparative Analysis of the Electronic Energy Structure of Nanocrystalline Polymorphs of Y2O3 Thin Layers: Theory and Experiments,"The results of fabrication and characterization of atomic structure of
nanocrystalline thin layers of Y2O3 in cubic and monoclinic phases is reported.
Experimental data demonstrate crystalline ordering in nanocrystalline films
with average grain size of ~10-14 nm both for cubic and monoclinic studied
structures. Density Functional Theory (DFT) based simulations demonstrate
insignificant differences of electronic structure of these phases in the bulk
and on the surfaces. Theoretical modeling also pointed out the significant
broadening of valence and conductive bands caused by means of energy levels
splitting in agreement with experimental data (X-ray photoelectron and
photoluminescence spectra). The presence of various intrinsic and extrinsic
defects (including surface adsorption of carbon mono- and dioxide) does not
promote visible changes in electronic structure of Y2O3 surface for both
studied phases. Optical absorption and luminescence measurements indicate
insignificant bandgap reduction of Y2O3 nanocrystalline layers and the very
little contribution from defect states. Simulation of extrinsic compression and
expanding demonstrate stability of the electronic structure of nanocrystalline
Y2O3 even under significant strain. Results of comprehensive studies
demonstrate that yttrium oxide based nanocrystalline layers are prospective for
various optical applications as a stable material.",2211.16004v1
2023-01-18,Stripe Symmetry of Short-range Charge Density Waves in Cuprate Superconductors,"The omnipresence of charge density waves (CDWs) across almost all cuprate
families underpins a common organizing principle. However, a longstanding
debate of whether its spatial symmetry is stripe or checkerboard remains
unresolved. While CDWs in lanthanum- and yttrium-based cuprates possess a
stripe symmetry, distinguishing these two scenarios has been challenging for
the short-range CDW in bismuth-based cuprates. Here, we employed
high-resolution resonant inelastic x-ray scattering to uncover the spatial
symmetry of the CDW in Bi$_2$Sr$_{2-x}$La$_{x}$CuO$_{6+\delta}$. Across a wide
range of doping and temperature, anisotropic CDW peaks with elliptical shapes
were found in reciprocal space. Based on Fourier transform analysis of
real-space models, we interpret the results as evidence of unidirectional
charge stripes, hosted by mutually 90$^\circ$-rotated anisotropic domains. Our
work paves the way for a unified symmetry and microscopic description of CDW
order in cuprates.",2301.07637v1
2023-04-28,Phantom study for 90Y post-treatment dosimetry with a long axial field-of-view PET/CT,"Purpose: The physical properties of yttrium-90 (90Y) allow for imaging with
positron emission tomography/computed tomography (PET/CT). The increased
sensitivity of long axial field-of-view (LAFOV) PET/CT scanners possibly allows
to overcome the small branching ratio for positron production from 90Y decays
and to improve for the post-treatment dosimetry of 90Y of selective internal
radiation therapy.
  Methods: For the challenging case of an image quality body phantom, we
compare a full Monte Carlo (MC) dose calculation with the results from the two
commercial software packages Simplicit90Y and Hermes. The voxel dosimetry
module of Hermes relies on the 90Y images taken with a LAFOV PET/CT, while the
MC and Simplicit90Y dose calculations are image independent.
  Results: The resulting doses from the MC calculation and Simplicit90Y agree
well within the error margins. The image-based dose calculation with Hermes,
however, consistently underestimates the dose. This is due to the mismatch of
the activity distribution in the PET images and the size of the volume of
interest. Furthermore, there are likely limitations of Hermes' dose calculation
algorithm for 90Y. We found that only for the smallest phantom sphere there is
a statistically significant dependence of the Hermes dose on the image
reconstruction parameters and scan time.
  Conclusion: Our study shows that Simplicit90Y's local deposition model can
provide a reliable dose estimate. On the other hand, the image based dose
calculation requires further benchmarks and verification in order to take full
advantage of LAFOV PET/CT systems.",2304.14797v2
2023-08-29,KilonovAE: Exploring Kilonova Spectral Features with Autoencoders,"Kilonovae are likely a key site of heavy r-process element production in the
Universe, and their optical/infrared spectra contain insights into both the
properties of the ejecta and the conditions of the r-process. However, the
event GW170817/AT2017gfo is the only kilonova so far with well-observed
spectra. To understand the diversity of absorption features that might be
observed in future kilonovae spectra, we use the TARDIS Monte Carlo radiative
transfer code to simulate a suite of optical spectra spanning a wide range of
kilonova ejecta properties and r-process abundance patterns. To identify the
most common and prominent absorption lines, we perform dimensionality reduction
using an autoencoder, and we find spectra clusters in the latent space
representation using a Bayesian Gaussian Mixture model. Our synthetic kilonovae
spectra commonly display strong absorption by strontium Sr II, yttrium Y II,
and zirconium Zr I - II, with strong lanthanide contributions at low electron
fractions (Ye < 0.25). When a new kilonova is observed, our machine learning
framework will provide context on the dominant absorption lines and key ejecta
properties, helping to determine where this event falls within the larger 'zoo'
of kilonovae spectra.",2308.15657v2
2023-09-11,Topological phase transition and tunable surface states in YBi,"A unique co-existence of extremely large magnetoresistance (XMR) and
topological characteristics in non-magnetic rare-earth monopnictides
stimulating intensive research on these materials. Yttrium monobismuthide (YBi)
has been reported to exhibit XMR up to 105% but its Topological properties
still need clarification. Here we use the hybrid density functional theory to
probe the structural, electronic and topological properties of YBi in detail.
We observe that YBi is topologically trivial semimetal at ambient pressure
which is in accordance with reported experimental results. The topological
phase transitions i.e., trivial to non-trivial are obtained with volumetric
pressure of 6.5 GPa and 3% of epitaxial strain. This topological phase
transitions are well within the structural phase transition of YBi (24.5 GPa).
The topological non-trivial state is characterized by band inversions among Y-d
band and Bi-p band near {\Gamma}- and X-point in the Brillouin zone. This is
further verified with the help of surface band structure along (001) plane. The
Z2 topological invariants are calculated with the help of product of parities
and evolution of Wannier charge centers. The occurrence of non-trivial phase in
YBi with a relatively small epitaxial strain, which a thin film geometry can
naturally has, might make it an ideal candidate to probe inter-relationship
between XMR and non-trivial topology.",2309.05553v1
2023-12-12,Origin of correlated diffuse scattering in the hexagonal manganites,"We use a combination of first-principles density functional calculations and
spin-dynamics simulations to explain the unusual diffuse inelastic neutron
scattering in the hexagonal multiferroic yttrium manganite, YMnO$_3$. Using
symmetry considerations, we construct a model spin Hamiltonian with parameters
derived from our density functional calculations and show that it captures the
measured behavior. We then show that the observed directionality in the
structured diffuse scattering in momentum space is a hallmark of the triangular
geometry, and that its persistence across a wide range of temperatures, both
above and below the N\'eel temperature, T$_\text{N}$, is a result of the strong
magnetic frustration. We predict that this diffuse scattering exists in a
yet-to-be-observed modulated continuum of energies, that its associated spin
excitations have distinct in-plane and out-of-plane character and that the
frustration influences the magnetism below the N\'eel temperature. Finally, we
show that visualizing the magnetic order in terms of composite trimer
magnetoelectric monopoles and toroidal moments, rather than individual spins,
provides insight into the real space fluctuations, revealing clusters of
emerging order in the paramagnetic state, as well as collective short-range
excitations in the ordered antiferromagnetic phase. Our understanding of this
directional diffuse scattering in such a wide temperature range, both below and
above T$_\text{N}$, provides new insight into the magnetic phase transitions in
frustrated systems.",2312.07449v2
2023-12-21,The Numerical Equivalence of Diabatic and Adiabatic Representations in Diatomic Molecules,"The (stationary) Schr\""{o}dinger equation for atomistic systems is solved
using the adiabatic potential energy curves (PECs) and the associated adiabatic
approximation. Despite being very simplistic, this approach is very powerful
and used in nearly all practical applications. In cases when interactions
between electronic states become important, the associated non-adiabatic
effects are taken into account via the derivative couplings (DDRs), also known
as non-adiabatic couplings (NACs). For diatomic molecules, the corresponding
PECs in the adiabatic representation are characterized by avoided crossings.
The alternative to the adiabatic approach is the diabatic representation,
obtained via a unitary transformation of the adiabatic states by minimizing the
DDRs. For diatomics, the diabatic representation has zero DDR and non-diagonal
diabatic couplings (DCs) ensue. The two representations are fully equivalent
and so should be the rovibronic energies and wavefunctions which result from
the solution of the corresponding Schr\""{o}dinger equations.
  We demonstrate (for the first time), the numerical equivalence between the
adiabatic and diabatic rovibronic calculations of diatomic molecules, using the
ab initio curves of yttrium oxide (YO) and carbon monohydride (CH) as examples
of two-state systems, where YO is characterized by a strong NAC, while CH has a
strong diabatic coupling. Rovibronic energies and wavefunctions are computed
using a new diabatic module implemented in variational rovibronic code DUO. We
show that it is important to include both the Diagonal Born-Oppenheimer
Correction (DBOC) and non-diagonal DDRs. We also show that convergence of the
vibronic energy calculations can strongly depend on the representation of
nuclear motion used and that no one representation is best in all cases.",2312.13895v1
2024-01-24,3D NLTE modelling of Y and Eu. Centre-to-limb variation and solar abundances,"Context. Abundances of s- and r-process elements in Sun-like stars constrain
nucleosynthesis in extreme astrophysical events, such as compact binary mergers
and explosions of highly magnetised rapidly rotating massive stars.
  Aims. We measure solar abundances of yttrium (Y) and europium (Eu) using 3D
non-local thermal equilibrium (NLTE) models. We use the model to determine the
abundance of Y, and also explore the model's ability to reproduce the solar
centre-to-limb variation of its lines. In addition, we determine the Eu
abundance using solar disc-centre and integrated flux spectra.
  Methods. We developed an NLTE model of Eu and updated our model of Y with
collisional data from detailed quantum-mechanical calculations. We used the IAG
spatially resolved high-resolution solar spectra to derive the solar abundances
of Y across the solar disc and of Eu for integrated flux and at disc centre
using a set of carefully selected lines and a 3D radiation-hydrodynamics model
of the solar atmosphere.
  Results. We find 3D NLTE solar abundances of A(Y)$_{\textrm{3D NLTE}}$=$2.30
\pm 0.03_{\textrm{stat}} \pm 0.07_{\textrm{syst}}$ dex based on observations at
all angles and A(Eu)$_{\textrm{3D NLTE}}$=$0.57 \pm 0.01_{\textrm{stat}} \pm
0.06_{\textrm{syst}}$ dex based on the integrated flux and disc-centre
intensity. 3D NLTE modelling offers the most consistent abundances across the
solar disc, and resolves the problem of severe systematic bias in Y and Eu
abundances inherent to 1D LTE, 1D NLTE, and 3D LTE modelling.",2401.13450v1
2024-01-26,Engineering strong magnetoelectricity using a hexagonal 2D material on electron-doped hexagonal LuFeO$_3$,"Cubic perovskite-structure ABO$_3$ and A$_{1-x}$A$^{\prime}$$_x$BO$_3$-type
oxides have been investigated extensively while their hexagonal-structure
versions have received minimal attention, even though they are multiferroic and
can form heterostructures with the manifold hexagonal two-dimensional
materials. Hexagonal ferrites of the form RFeO$_3$, where R is yttrium or a
rare-earth element such as Lu, Yb, etc., feature coupled ferroelectricity (FE)
and weak-ferromagnetism (wFM), exhibiting linear magnetoelectricity. Their only
drawback is weak ferromagnetism. In this paper, we employ
density-functional-theory (DFT) calculations on hexagonal LuFeO$_3$ ($h$-LFO),
targeting its magnetic ordering by electron doping,anticipating
spin-disproportionation of the Fe sublattices. Indeed, we show that
spin-disproportionation in heavily-electron-doped versions
Lu$_{1-x}$Hf$_x$FeO$_3$ ($h$-LHFO), especially for x=1/3 and 1/2, leads to
robust out-of-plane collinear ferrimagnetism that is stable at room
temperature. Furthermore, the robust ferroelectricity of $h$-LFO persists via a
Jahn-Teller metal-to-insulator transition. Finally, we construct a
$h$-LHFO/$h$-2D heterostructure, where $h$-2D stands for the FE/FM monolayer
MnSTe, and demonstrate strong magnetoelectric coupling, namely manipulation of
magnetic skyrmions in MnSTe by an external electric field through the $h$-LHFO
polarization, opening up a new realm for magnetoelectric applications.",2401.15053v1
2006-12-14,On Site Raman Analysis of Iznik Pottery Glazes and Pigments,"On site Raman analyses were performed at the Mus\'{e}e national de
C\'{e}ramique, S\`{e}vres, France, on rare Iznik (former Nicaea) pottery
produced from ~1480 to ~1620. A comparison is made with a series of shards. The
town of production of these potteries was highly disputed in the 80's and many
questions still remain. The potential of glaze on-site analyses as a
classification/datating tool is evaluated. The structure of the silicate glaze
does not change with the sample (index of polymerisation ~ 0.5-0.8, indicating
a lead silicate composition; characteristic Si-O stretching mode doublet at
\~985 and 1030-1050 cm-1). By contrast the corresponding signature of most of
the ""K\""{u}tahya"" wares peaks at ~1070-1090 cm-1. The lowest index is measured
for a brilliant overglazed red bole, according to a lower temperature of
(post)firing. The different crystalline phases identified in the glaze are
&#61537;-quartz, haematite, spinel, cassiterite, uvarovite garnet and zircon.
White colour arises from &#61537;-quartz slip in most samples studied.
Cassiterite (SnO2) opacifier is only present in some early blue-and-white
ceramics (Master of the Knots and Baba Nakkas style, ca. 1510-1530) and we do
not have other evidence of its intentional use as an opacifier. Intentional
addition of tin oxide is likely for colour lightening in some red, blue and in
clear green boles. At least two types of red glazes and two types of
Cr-containing green pigments are evidenced.",0612375v1
2006-01-24,Trapping atoms on a transparent permanent-magnet atom chip,"We describe experiments on trapping of atoms in microscopic magneto-optical
traps on an optically transparent permanent-magnet atom chip. The chip is made
of magnetically hard ferrite-garnet material deposited on a dielectric
substrate. The confining magnetic fields are produced by miniature magnetized
patterns recorded in the film by magneto-optical techniques. We trap Rb atoms
on these structures by applying three crossed pairs of counter-propagating
laser beams in the conventional magneto-optical trapping (MOT) geometry. We
demonstrate the flexibility of the concept in creation and in-situ modification
of the trapping geometries through several experiments.",0601163v2
2008-10-14,Field induced magnetic order in the frustrated magnet Gadolinium Gallium Garnet,"Gd3Ga5O12, (GGG), has an extraordinary magnetic phase diagram, where no long
range order is found down to 25 mK despite \Theta_CW \approx 2 K. However, long
range order is induced by an applied field of around 1 T. Motivated by recent
theoretical developments and the experimental results for a closely related
hyperkagome system, we have performed neutron diffraction measurements on a
single crystal sample of GGG in an applied magnetic field. The measurements
reveal that the H-T phase diagram of GGG is much more complicated than
previously assumed. The application of an external field at low T results in an
intensity change for most of the magnetic peaks which can be divided into three
distinct sets: ferromagnetic, commensurate antiferromagnetic, and
incommensurate antiferromagnetic. The ferromagnetic peaks (e.g. (112), (440)
and (220)) have intensities that increase with the field and saturate at high
field. The antiferromagnetic reflections have intensities that grow in low
fields, reach a maximum at an intermediate field (apart from the (002) peak
which shows two local maxima) and then decrease and disappear above 2 T. These
AFM peaks appear, disappear and reach maxima in different fields. We conclude
that the competition between magnetic interactions and alternative ground
states prevents GGG from ordering in zero field. It is, however, on the verge
of ordering and an applied magnetic field can be used to crystallise ordered
components. The range of ferromagnetic and antiferromagnetic propagation
vectors found reflects the complex frustration in GGG.",0810.2410v1
2010-08-06,Photon Self-Induced Spin to Orbital Conversion in TGG crystal at high laser power,"In this paper, we present experimental evidence of a newly discovered
third-order nonlinear optical process Self-Induced Spin-to-Orbital Conversion
(SISTOC) of the photon angular momentum. This effect is the physical mechanism
at the origin of the depolarization of very intense laser beams propagating in
isotropic materials. The SISTOC process, like self-focusing, is triggered by
laser heating leading to a radial temperature gradient in the medium. In this
work we tested the occurrence of SISTOC in a terbium gallium garnet (TGG) rod
for an impinging laser power of about 100~W. To study the SISTOC process we
used different techniques: polarization analysis, interferometry and tomography
of the photon orbital angular momentum. Our results confirm, in particular,
that the apparent depolarization of the beam is due to the occurrence of
maximal entanglement between the spin and orbital angular momentum of the
photons undergoing the SISTOC process. This explanation of the true nature of
the depolarization mechanism could be of some help in finding novel methods to
reduce or to compensate for this usually unwanted depolarization effect in all
cases where very high laser power and good beam quality are required.",1008.1283v1
2011-08-03,Optimizing large parameter sets in variational quantum Monte Carlo,"We present a technique for optimizing hundreds of thousands of variational
parameters in variational quantum Monte Carlo. By introducing iterative Krylov
subspace solvers and by multiplying by the Hamiltonian and overlap matrices as
they are sampled, we remove the need to construct and store these matrices and
thus bypass the most expensive steps of the stochastic reconfiguration and
linear method optimization techniques. We demonstrate the effectiveness of this
approach by using stochastic reconfiguration to optimize a correlator product
state wavefunction with a pfaffian reference for four example systems. In two
examples on the two dimensional Hubbard model, we study 16 and 64 site
lattices, recovering energies accurate to 1% in the smaller lattice and
predicting particle-hole phase separation in the larger. In two examples
involving an ab initio Hamiltonian, we investigate the potential energy curve
of a symmetrically dissociated 4x4 hydrogen lattice as well as the
singlet-triplet gap in free base porphin. In the hydrogen system we recover 98%
or more of the correlation energy at all geometries, while for porphin we
compute the gap in a 24 orbital active space to within 0.02eV of the exact
result. The numbers of variational parameters in these examples range from
4x10^3 to 5x10^5, demonstrating an ability to go far beyond the reach of
previous formulations of stochastic reconfiguration.",1108.0900v1
2012-03-08,Truncated Configuration Interaction expansions as solvers for correlated quantum impurity models and dynamical mean field theory,"The development of polynomial cost solvers for correlated quantum impurity
models, with controllable errors, is a central challenge in quantum many-body
physics, where these models find applications ranging from nano-science to the
dynamical mean-field theory (DMFT). Here we describe how configuration
interaction (CI) approximations to exact diagonalization (ED) may be used as
solvers in DMFT. CI approximations retain the main advantages of ED, such as
the ability to treat general interactions and off-diagonal hybridizations and
to obtain real spectral information, but are of polynomial cost. Furthermore,
their errors can be controlled by monitoring the convergence of physical
quantities as a function of the CI hierarchy. Using benchmark DMFT
applications, such as single-site DMFT of the 1D Hubbard model and $2\times 2$
cluster DMFT of the 2D Hubbard model, we show that CI approximations allow us
to obtain near-exact ED results for a tiny fraction of the cost. This is true
over the entire range of interaction strengths including ""difficult"" regimes,
such as in the pseudogap phase of the 2D Hubbard model. We use the ability of
CI approximations to treat large numbers of orbitals to demonstrate convergence
of the bath representation in the $2\times 2$ cluster DMFT using a 24 bath
orbital representation. CI approximations thus form a promising route to extend
ED to problems that are currently difficult to study using other solvers such
as continuous-time quantum Monte Carlo, including impurity models with large
numbers of orbitals and general interactions.",1203.1914v1
2013-02-10,Efficient Tree Tensor Network States (TTNS) for Quantum Chemistry: Generalizations of the Density Matrix Renormalization Group Algorithm,"We investigate tree tensor network states for quantum chemistry. Tree tensor
network states represent one of the simplest generalizations of matrix product
states and the density matrix renormalization group. While matrix product
states encode a one-dimensional entanglement structure, tree tensor network
states encode a tree entanglement structure, allowing for a more flexible
description of general molecules. We describe an optimal tree tensor network
state algorithm for quantum chemistry. We introduce the concept of
half-renormalization which greatly improves the efficiency of the calculations.
Using our efficient formulation we demonstrate the strengths and weaknesses of
tree tensor network states versus matrix product states. We carry out benchmark
calculations both on tree systems (hydrogen trees and \pi-conjugated
dendrimers) as well as non-tree molecules (hydrogen chains, nitrogen dimer, and
chromium dimer). In general, tree tensor network states require much fewer
renormalized states to achieve the same accuracy as matrix product states. In
non-tree molecules, whether this translates into a computational savings is
system dependent, due to the higher prefactor and computational scaling
associated with tree algorithms. In tree like molecules, tree network states
are easily superior to matrix product states. As an ilustration, our largest
dendrimer calculation with tree tensor network states correlates 110 electrons
in 110 active orbitals.",1302.2298v2
2013-05-08,The Thouless theorem for matrix product states and subsequent post-density matrix renormalization group methods,"The similarities between Hartree-Fock (HF) theory and the density-matrix
renormalization group (DMRG) are explored. Both methods can be formulated as
the variational optimization of a wave-function ansatz. Linearization of the
time-dependent variational principle near a variational minimum allows to
derive the random phase approximation (RPA). We show that the non-redundant
parametrization of the matrix product state (MPS) tangent space [J. Haegeman et
al., Phys. Rev. Lett. 107, 070601 (2011)] leads to the Thouless theorem for
MPS, i.e. an explicit non-redundant parametrization of the entire MPS manifold,
starting from a specific MPS reference. Excitation operators are identified,
which extends the analogy between HF and DMRG to the Tamm-Dancoff approximation
(TDA), the configuration interaction (CI) expansion, and coupled cluster
theory. For a small one-dimensional Hubbard chain, we use a CI-MPS ansatz with
single and double excitations to improve on the ground state and to calculate
low-lying excitation energies. For a symmetry-broken ground state of this
model, we show that RPA-MPS allows to retrieve the Goldstone mode. We also
discuss calculations of the RPA-MPS correlation energy. With the long-range
quantum chemical Pariser-Parr-Pople Hamiltonian, low-lying TDA-MPS and RPA-MPS
excitation energies for polyenes are obtained.",1305.1761v3
2013-09-09,Spectral functions of strongly correlated extended systems via an exact quantum embedding,"Density matrix embedding theory (DMET) [Phys. Rev. Lett., 109, 186404
(2012)], introduced a new approach to quantum cluster embedding methods,
whereby the mapping of strongly correlated bulk problems to an impurity with
finite set of bath states was rigorously formulated to exactly reproduce the
entanglement of the ground state. The formalism provided similar physics to
dynamical mean-field theory at a tiny fraction of the cost, but was inherently
limited by the construction of a bath designed to reproduce ground state,
static properties. Here, we generalize the concept of quantum embedding to
dynamic properties and demonstrate accurate bulk spectral functions at
similarly small computational cost. The proposed spectral DMET utilizes the
Schmidt decomposition of a response vector, mapping the bulk dynamic
correlation functions to that of a quantum impurity cluster coupled to a set of
frequency dependent bath states. The resultant spectral functions are obtained
on the real-frequency axis, without bath discretization error, and allows for
the construction of arbitrary dynamic correlation functions. We demonstrate the
method on the 1D and 2D Hubbard model, where we obtain zero temperature,
thermodynamic limit spectral functions, and show the trivial extension to
two-particle Green functions. This advance therefore extends the scope and
applicability of DMET in condensed matter problems as a computationally
tractable route to correlated spectral functions of extended systems, and
provides a competitive alternative to dynamical mean-field theory for dynamic
quantities.",1309.2320v2
2014-03-12,Projector quantum Monte Carlo with matrix product states,"We marry tensor network states (TNS) and projector quantum Monte Carlo (PMC)
to overcome the high computational scaling of TNS and the sign problem of PMC.
Using TNS as trial wavefunctions provides a route to systematically improve the
sign structure and to eliminate the bias in fixed-node and constrained-path
PMC. As a specific example, we describe phaseless auxiliary-field quantum Monte
Carlo with matrix product states (MPS-AFQMC). MPS-AFQMC improves significantly
on the DMRG ground-state energy. For the J1-J2 model on two-dimensional square
lattices, we observe with MPS-AFQMC an order of magnitude reduction in the
error for all couplings, compared to DMRG. The improvement is independent of
walker bond dimension, and we therefore use bond dimension one for the walkers.
The computational cost of MPS-AFQMC is then quadratic in the bond dimension of
the trial wavefunction, which is lower than the cubic scaling of DMRG. The
error due to the constrained-path bias is proportional to the variational error
of the trial wavefunction. We show that for the J1-J2 model on two-dimensional
square lattices, a linear extrapolation of the MPS-AFQMC energy with the
discarded weight from the DMRG calculation allows to remove the
constrained-path bias. Extensions to other tensor networks are briefly
discussed.",1403.3125v2
2014-08-21,A spin-adapted Density Matrix Renormalization Group algorithm for quantum chemistry,"We extend the spin-adapted density matrix renormalization group (DMRG)
algorithm of McCulloch and Gulacsi [Europhys. Lett.57, 852 (2002)] to quantum
chemical Hamiltonians. This involves two key modifications to the
non-spin-adapted DMRG algorithm: the use of a quasi-density matrix to ensure
that the renormalised DMRG states are eigenvalues of $S^2$ , and the use of the
Wigner-Eckart theorem to greatly reduce the overall storage and computational
cost. We argue that the advantages of the spin-adapted DMRG algorithm are
greatest for low spin states. Consequently, we also implement the
singlet-embedding strategy of Nishino et al [Phys. Rev. E61, 3199 (2000)] which
allows us to target high spin states as a component of a mixed system which is
overall held in a singlet state. We evaluate our algorithm on benchmark
calculations on the Fe$_2$S$_2$ and Cr$_2$ transition metal systems. By
calculating the full spin ladder of Fe$_2$S$_2$ , we show that the spin-adapted
DMRG algorithm can target very closely spaced spin states. In addition, our
calculations of Cr$_2$ demonstrate that the spin-adapted algorithm requires
only roughly half the number of renormalised DMRG states as the
non-spin-adapted algorithm to obtain the same accuracy in the energy, thus
yielding up to an order of magnitude increase in computational efficiency.",1408.5039v1
2014-08-21,Spectroscopic accuracy directly from quantum chemistry: application to ground and excited states of beryllium dimer,"We combine explicit correlation via the canonical transcorrelation approach
with the density matrix renormalization group and initiator full configuration
interaction quantum Monte Carlo methods to compute a near-exact beryllium dimer
curve, {\it without} the use of composite methods. In particular, our direct
density matrix renormalization group calculations produce a well-depth of
$D_e$=931.2 cm$^{-1}$ which agrees very well with recent experimentally derived
estimates $D_e$=929.7$\pm 2$~cm$^{-1}$ [Science, 324, 1548 (2009)] and
$D_e$=934.6~cm$^{-1}$ [Science, 326, 1382 (2009)]], as well the best composite
theoretical estimates, $D_e$=938$\pm 15$~cm$^{-1}$ [J. Phys. Chem. A, 111,
12822 (2007)] and $D_e$=935.1$\pm 10$~cm$^{-1}$ [Phys. Chem. Chem. Phys., 13,
20311 (2011)]. Our results suggest possible inaccuracies in the functional form
of the potential used at shorter bond lengths to fit the experimental data
[Science, 324, 1548 (2009)]. With the density matrix renormalization group we
also compute near-exact vertical excitation energies at the equilibrium
geometry. These provide non-trivial benchmarks for quantum chemical methods for
excited states, and illustrate the surprisingly large error that remains for
1$^1\Sigma^-_g$ state with approximate multi-reference configuration
interaction and equation-of-motion coupled cluster methods. Overall, we
demonstrate that explicitly correlated density matrix renormalization group and
initiator full configuration interaction quantum Monte Carlo methods allow us
to fully converge to the basis set and correlation limit of the
non-relativistic Schr\""odinger equation in small molecules.",1408.5090v1
2015-12-16,Hilbert space renormalization for the many-electron problem,"Renormalization is a powerful concept in the many-body problem. Inspired by
the highly successful density matrix renormalization group (DMRG) algorithm,
and the quantum chemical graphical representation of configuration space, we
introduce a new theoretical tool: Hilbert space renormalization, to describe
many-electron correlations. While in DMRG, the many-body states in nested Fock
subspaces are successively renormalized, in Hilbert space renormalization,
many-body states in nested Hilbert subspaces undergo renormalization. This
provides a new way to classify and combine configurations. The underlying
wavefunction ansatz, namely the Hilbert space matrix product state (HS-MPS),
has a very rich and flexible mathematical structure. It provides low-rank
tensor approximations to any configuration interaction (CI) space through
restricting either the 'physical indices' or the coupling rules in the HS-MPS.
Alternatively, simply truncating the 'virtual dimension' of the HS-MPS leads to
a family of size-extensive wave function ansaetze that can be used efficiently
in variational calculations. We make formal and numerical comparisons between
the HS-MPS, the traditional Fock-space MPS used in DMRG, and traditional CI
approximations. The analysis and results shed light on fundamental aspects of
the efficient representation of many-electron wavefunctions through the
renormalization of many-body states.",1512.05218v1
2016-03-21,From plane waves to local Gaussians for the simulation of correlated periodic systems,"We present a simple, robust and black-box approach to the implementation and
use of local, periodic, atom-centered Gaussian basis functions within a plane
wave code, in a computationally efficient manner. The procedure outlined is
based on the representation of the Gaussians within a finite bandwidth by their
underlying plane wave coefficients. The core region is handled within the
projected augment wave framework, by pseudizing the Gaussian functions within a
cut-off radius around each nucleus, smoothing the functions so that they are
faithfully represented by a plane wave basis with only moderate kinetic energy
cutoff. To mitigate the effects of the basis set superposition error and
incompleteness at the mean-field level introduced by the Gaussian basis, we
also propose a hybrid approach, whereby the complete occupied space is first
converged within a large plane wave basis, and the Gaussian basis used to
construct a complementary virtual space for the application of correlated
methods. We demonstrate that these pseudized Gaussians yield compact and
systematically improvable spaces with an accuracy comparable to their
non-pseudized Gaussian counterparts. A key advantage of the described method is
its ability to efficiently capture and describe electronic correlation effects
of weakly bound and low-dimensional systems, where plane waves are not
sufficiently compact or able to be truncated without unphysical artefacts. We
investigate the accuracy of the pseudized Gaussians for the water dimer
interaction, neon solid and water adsorption on a LiH surface, at the level of
second-order M\{o}ller--Plesset perturbation theory.",1603.06457v3
2016-04-05,Simulation of White Light Generation and Near Light Bullets Using a Novel Numerical Technique,"An accurate and efficient simulation has been devised, employing a new
numerical technique to simulate the derivative generalised non-linear
Schr\""odinger equation in all three spatial dimensions and time. The simulation
models all pertinent effects such as self-steepening and plasma for the
non-linear propagation of ultrafast optical radiation in bulk material.
Simulation results are compared to published experimental spectral data of an
example ytterbium aluminum garnet system at 3.1um radiation and fits to within
a factor of 5. The simulation shows that there is a stability point near the
end of the 2 mm crystal where a quasi-light bullet (spatial temporal soliton)
is present. Within this region, the pulse is collimated at a reduced diameter
(factor of ~2) and there exists a near temporal soliton at the spatial center.
The temporal intensity within this stable region is compressed by a factor of
~4 compared to the input. This study shows that the simulation highlights new
physical phenomena based on the interplay of various linear, non-linear and
plasma effects that go beyond the experiment and is thus integral to achieving
accurate designs of white light generation systems for optical applications. An
adaptive error reduction algorithm tailor made for this simulation will also be
presented in appendix.",1604.01140v3
2016-05-09,"Matrix Product Operators, Matrix Product States, and ab initio Density Matrix Renormalization Group algorithms","Current descriptions of the ab initio DMRG algorithm use two superficially
different languages: an older language of the renormalization group and
renormalized operators, and a more recent language of matrix product states and
matrix product operators. The same algorithm can appear dramatically different
when written in the two different vocabularies. In this work, we carefully
describe the translation between the two languages in several contexts. First,
we describe how to efficiently implement the ab-initio DMRG sweep using a
matrix product operator based code, and the equivalence to the original
renormalized operator implementation. Next we describe how to implement the
general matrix product operator/matrix product state algebra within a pure
renormalized operator-based DMRG code. Finally, we discuss two improvements of
the ab initio DMRG sweep algorithm motivated by matrix product operator
language: Hamiltonian compression, and a sum over operators representation that
allows for perfect computational parallelism. The connections and
correspondences described here serve to link the future developments with the
past, and are important in the efficient implementation of continuing advances
in ab initio DMRG and related algorithms.",1605.02611v2
2016-07-05,Transport and selective chaining of bidisperse particles in a travelling wave potential,"We combine experiments, theory and numerical simulation to investigate the
dynamics of a binary suspension of paramagnetic colloidal particles dispersed
in water and transported above a stripe patterned magnetic garnet film. The
substrate generates a one-dimensional periodic energy landscape above its
surface. The application of an elliptically polarized rotating magnetic field
causes the landscape to translate, inducing direct transport of paramagnetic
particles placed above the film. The ellipticity of the applied field can be
used to control and tune the interparticle interactions, from net repulsive to
net attractive. When considering particles of two distinct sizes, we find that,
depending on their elevation above the surface of the magnetic substrate, the
particles feel effectively different potentials, resulting in different
mobilities. We exploit this feature to induce selective chaining for certain
values of the applied field parameters. In particular, when driving two types
of particles, we force only one type to condense into travelling parallel
chains. These chains confine the movement of the other non-chaining particles
within narrow colloidal channels. This phenomenon is explained by considering
the balance of pairwise magnetic forces between the particles and their
individual coupling with the travelling landscape.",1607.01131v1
2016-09-24,A real-time extension of density matrix embedding theory for non-equilibrium electron dynamics,"We introduce real-time density matrix embedding theory (DMET), a dynamical
quantum embedding theory for computing non-equilibrium electron dynamics in
strongly correlated systems. As in the previously developed static DMET,
real-time DMET partitions the system into an impurity corresponding to the
region of interest coupled to the surrounding environment, which is efficiently
represented by a quantum bath of the same size as the impurity. In this work,
we focus on a single-impurity time-dependent theory as a first step towards a
full multi-impurity theory. The equations of motion of the coupled impurity and
bath embedding problem in real-time DMET are then derived using the
time-dependent variational principle. The accuracy of real-time DMET is
compared to that of time-dependent complete active space self-consistent field
(TD-CASSCF) theory and time-dependent Hartree-Fock (TDHF) theory for a variety
of quantum quenches in the single impurity Anderson model (SIAM), in which the
Hamiltonian is suddenly changed (quenched) to induce a non-equilibrium state.
Real-time DMET shows a marked improvement over the meanfield TDHF, converging
to the exact answer even in the non-trivial Kondo regime of the SIAM. However,
as in static DMET, the increased dynamic flexibility of TD-CASSCF in comparison
to real-time DMET using a single impurity leads to faster convergence with
respect to active space size. Our results demonstrate that real-time DMET is an
efficient method well suited for the simulation of non-equilibrium electron
dynamics in which strong electron correlation plays an important role.",1609.07678v2
2016-10-07,"Polarizers, optical bridges and Sagnac interferometers for nanoradian polarization rotation measurements","The ability to measure nanoradian polarization rotations, $\theta_F$, in the
photon shot noise limit is investigated for partially crossed polarizers (PCP),
a static Sagnac interferometer and an optical bridge, each of which can in
principal be used in this limit with near equivalent figures-of-merit (FOM). In
practice a bridge to PCP/Sagnac source noise rejection ratio of $1/4\theta_F^2$
enables the bridge to operate in the photon shot noise limit even at high light
intensities. The superior performance of the bridge is illustrated via the
measurement of a 3 nrad rotation arising from an axial magnetic field of 0.9 nT
applied to a terbium gallium garnet. While the Sagnac is functionally
equivalent to the PCP in terms of the FOM, unlike the PCP it is able to
discriminate between rotations with different time ($T$) and parity ($P$)
symmetries. The Sagnac geometry implemented here is similar to that used
elsewhere to detect non-reciprocal ($\overline{T}P$) rotations like those due
to the Faraday effect. Using a Jones matrix approach, novel Sagnac geometries
uniquely sensitive to non-reciprocal $\overline{TP}$ (e.g. magneto-electric or
magneto-chiral) rotations, as well as to reciprocal rotations (e.g. due to
linear birefringence, $TP$, or to chirality, $T\overline{P}$) are proposed.",1610.02297v3
2016-12-08,Quantum embedding theories,"In complex systems, it is often the case that the region of interest forms
only one part of a much larger system. The idea of joining two different
quantum simulations - a high level calculation on the active region of
interest, and a low level calculation on its environment - formally defines a
quantum embedding. While any combination of techniques constitutes an
embedding, several rigorous formalisms have emerged that provide for exact
feedback between the embedded system and its environment. These three
formulations: it density functional embedding, Green's function embedding, and
density matrix embedding, respectively use the single-particle density,
single-particle Green's function, and single-particle density matrix as the
quantum variables of interest. Many excellent reviews exist covering these
methods individually. However, a unified presentation of the different
formalisms is so far lacking. Indeed, the various languages commonly used:
functional equations for density functional embedding; diagrammatics for
Green's function embedding; and entanglement arguments for density matrix
embedding, make the three formulations appear vastly different. In this
account, we introduce the basic equations of all three formulations in such a
way as to highlight their many common intellectual strands. While we focus
primarily on a straightforward theoretical perspective, we also give a brief
overview of recent applications, and possible future developments.",1612.02576v2
2017-01-18,Excitation of magnon accumulation by laser clocking as a source of long-range spin waves in transparent magnetic films,"Optical tools are of great promise for generation of spin waves due to the
possibility to manipulate on ultrashort time scales and to provide local
excitation. However, a single laser pulse can inject spin waves only with a
broad frequency spectrum, resulting in a short propagation distance and low
amplitude. Here we excite a magnetic garnet film by a train of fs-laser pulses
with 1 GHz repetition rate so that pulse separation is smaller than decay time
of the magnetic modes which allows to achieve collective photonic impact on
magnetization. It establishes a quasi-stationary source of SWs, namely a
coherent magnon accumulation (""magnon cloud""). This approach has several
appealing features: (i) the source is tunable; (ii) the SW amplitude can be
significantly enhanced; (iii) the spectrum of the generated SWs is quite narrow
that provides longer propagation distance; (iv) the periodic pumping results in
almost constant in time SW amplitude up to 100 um away from the source; and (v)
the SW emission shows a pronounced directionality. These results expand the
capabilities of ultrafast coherent optical control of magnetization and pave a
way for applications in data processing, including the quantum regime. The
quasi-stationary magnon accumulation might be also of interest for the problem
of magnon Bose-Einstein condensate.",1701.05109v1
2017-01-26,Automated construction of molecular active spaces from atomic valence orbitals,"We introduce the atomic valence active space (AVAS), a simple and
well-defined automated technique for constructing active orbital spaces for use
in multi-configuration and multireference (MR) electronic structure
calculations. Concretely, the technique constructs active molecular orbitals
capable of describing all relevant electronic configurations emerging from a
targeted set of atomic valence orbitals (e.g., the metal d orbitals in a
coordination complex). This is achieved via a linear transformation of the
occupied and unoccupied orbital spaces from an easily obtainable
single-reference wavefunction (such as from a Hartree-Fock or Kohn-Sham
calculations) based on projectors to targeted atomic valence orbitals. We
discuss the premises, theory, and implementation of the idea, and several of
its variations are tested. To investigate the performance and accuracy, we
calculate the excitation energies for various transition metal complexes in
typical application scenarios. Additionally, we follow the homolytic bond
breaking process of a Fenton reaction along its reaction coordinate. While the
described AVAS technique is not an universal solution to the active space
problem, its premises are fulfilled in many application scenarios of transition
metal chemistry and bond dissociation processes. In these cases the technique
makes MR calculations easier to execute, easier to reproduce by any user, and
simplifies the determination of the appropriate size of the active space
required for accurate results.",1701.07862v2
2017-05-01,Towards the solution of the many-electron problem in real materials: equation of state of the hydrogen chain with state-of-the-art many-body methods,"We present numerical results for the equation of state of an infinite chain
of hydrogen atoms. A variety of modern many-body methods are employed, with
exhaustive cross-checks and validation. Approaches for reaching the continuous
space limit and the thermodynamic limit are investigated, proposed, and tested.
The detailed comparisons provide a benchmark for assessing the current state of
the art in many-body computation, and for the development of new methods. The
ground-state energy per atom in the linear chain is accurately determined
versus bondlength, with a confidence bound given on all uncertainties.",1705.01608v2
2017-05-31,Low Depth Quantum Simulation of Electronic Structure,"Quantum simulation of the electronic structure problem is one of the most
researched applications of quantum computing. The majority of quantum
algorithms for this problem encode the wavefunction using $N$ Gaussian
orbitals, leading to Hamiltonians with ${\cal O}(N^4)$ second-quantized terms.
We avoid this overhead and extend methods to the condensed phase by utilizing a
dual form of the plane wave basis which diagonalizes the potential operator,
leading to a Hamiltonian representation with ${\cal O}(N^2)$ second-quantized
terms. Using this representation we can implement single Trotter steps of the
Hamiltonians with linear gate depth on a planar lattice. Properties of the
basis allow us to deploy Trotter and Taylor series based simulations with
respective circuit depths of ${\cal O}(N^{7/2})$ and $\widetilde{\cal
O}(N^{8/3})$ for fixed charge densities - both are large asymptotic
improvements over all prior results. Variational algorithms also require
significantly fewer measurements to find the mean energy in this basis,
ameliorating a primary challenge of that approach. We conclude with a proposal
to simulate the uniform electron gas (jellium) using a low depth variational
ansatz realizable on near-term quantum devices. From these results we identify
simulations of low density jellium as a promising first setting to explore
quantum supremacy in electronic structure.",1706.00023v3
2017-12-19,Hole self-trapping in the Y3Al5O12 and Lu3Al5O12 garnet crystals,"The processes of hole localization in the Y3Al5O12 and Lu3Al5O12 single
crystals were investigated by electron paramagnetic resonance (EPR) and
thermally stimulated luminescence (TSL). It was found that holes created by
x-ray irradiation at 77 K are predominantly self-trapped at regular oxygen ions
forming O- hole center. This self-trapped hole (STH) center is thermally stable
to about 100 K in both YAG and LuAG crystals. At higher temperatures, thermally
liberated holes are retrapped at oxygen ions in the vicinity of an acceptor ion
such as Mg2+ and Al_{Y} or Al_{Lu} antisite ion that leads to increase of the
thermal stability of the trapped hole to app. 150 K. TSL measurements show two
composite glow peaks in the temperature range of 77 - 280 K, the temperature
positions of which well correlate with the thermal stability of the O- centers.
The hole thermal ionization energy was determined from a numerical fit of the
TSL peaks within the model of second order kinetics. It is in the range of 0.25
- 0.26 eV for the O- STH center, and increases to 0.41 - 0.45 eV for O- center
stabilized by the acceptor. Revealed O- centers can be attributed to O- small
polarons formed mainly due to the hole stabilization by short-range interaction
with the surrounding lattice.",1712.06928v1
2018-03-19,A Perturbative Density Matrix Renormalization Group Algorithm for Large Active Spaces,"We describe a low cost alternative to the standard variational DMRG (density
matrix renormalization group) algorithm that is analogous to the combination of
selected configuration interaction plus perturbation theory (SCI+PT). We denote
the resulting method p-DMRG (perturbative DMRG) to distinguish it from the
standard variational DMRG. p-DMRG is expected to be useful for systems with
very large active spaces, for which variational DMRG becomes too expensive.
Similar to SCI+PT, in p-DMRG a zeroth-order wavefunction is first obtained by a
standard DMRG calculation, but with a small bond dimension. Then, the residual
correlation is recovered by a second-order perturbative treatment. We discuss
the choice of partitioning for the perturbation theory, which is crucial for
its accuracy and robustness. To circumvent the problem of a large bond
dimension in the first-order wavefunction, we use a sum of matrix product
states (MPS) to expand the first-order wavefunction, yielding substantial
savings in computational cost and memory. We also propose extrapolation schemes
to reduce the errors in the zeroth- and first-order wavefunctions. Numerical
results for Cr 2 with a (28e,76o) active space and 1,3-butadiene with a
(22e,82o) active space reveal that p-DMRG provides ground state energies of a
similar quality to variational DMRG with very large bond dimensions, but at a
significantly lower computational cost. This suggests that p-DMRG will be an
efficient tool for benchmark studies in the future.",1803.07150v2
2018-05-02,Pseudo-Goldstone gaps and order-by-quantum-disorder in frustrated magnets,"In systems with competing interactions, continuous degeneracies can appear
which are accidental, in that they are not related to any symmetry of the
Hamiltonian. Accordingly, the pseudo-Goldstone modes associated with these
degeneracies are also unprotected. Indeed, through a process known as
""order-by-quantum-disorder"", quantum zero-point fluctuations can lift the
degeneracy and induce a gap for these modes. We show that this gap can be
exactly computed at leading order in $1/S$ in spin-wave theory from the mean
curvature of the classical and quantum zero-point energies - without the need
to consider any spin-wave interactions. We confirm this equivalence through
direct calculations of the spin-wave spectrum to $O(1/S^2)$ in a wide variety
of theoretically and experimentally relevant quantum spin models. We prove this
equivalence through the use of an exact sum rule that provides the required
mixing of different orders of $1/S$. Finally, we discuss some implications for
several leading order-by-quantum-disorder candidate materials, clarifying the
expected pseudo-Goldstone gap sizes in Er$_2$Ti$_2$O$_7$ and
Ca$_3$Fe$_2$Ge$_3$O$_{12}$.",1805.00947v2
2018-12-12,Potential jumps at transport bottlenecks cause instability of nominally ionic solid electrolytes in electrochemical cells,"Normal operations of electrochemical devices such as solid oxide fuel cells
(SOFC), solid oxide electrolyzer cells (SOEC) and lithium ion batteries (LIB)
sometimes fail because of unexpected formation of internal phases. These phases
include oxygen bubbles at grain boundaries inside the zirconia electrolyte of
SOEC, isolated Li metal islands inside the (garnet type) Li7La3Zr2O12
electrolyte of all-solid-state LIB, and similar Na metal islands inside the
Na-beta-alumina and NASICON electrolytes of Na-S batteries. Remarkably,
although the devices can operate in both polarities, the propensity for failure
depends on the polarity. Here we explain these and other phenomena in nominally
ionic solid electrolytes and mixed-conducting electrodes in simple
thermodynamic and kinetic terms: the unexpected internal phases are caused by a
large potential jump that is needed to push a constant ion or electron flow
through its internal transport bottleneck. Definite rules for internal phase
formation including its polarity dependence are formulated to help predict and
mitigate it, which leads to microstructural instability, efficiency
deterioration and breakdown.",1812.05187v5
2019-01-23,Determining eigenstates and thermal states on a quantum computer using quantum imaginary time evolution,"The accurate computation of Hamiltonian ground, excited, and thermal states
on quantum computers stands to impact many problems in the physical and
computer sciences, from quantum simulation to machine learning. Given the
challenges posed in constructing large-scale quantum computers, these tasks
should be carried out in a resource-efficient way. In this regard, existing
techniques based on phase estimation or variational algorithms display
potential disadvantages; phase estimation requires deep circuits with ancillae,
that are hard to execute reliably without error correction, while variational
algorithms, while flexible with respect to circuit depth, entail additional
high-dimensional classical optimization. Here, we introduce the quantum
imaginary time evolution and quantum Lanczos algorithms, which are analogues of
classical algorithms for finding ground and excited states. Compared to their
classical counterparts, they require exponentially less space and time per
iteration, and can be implemented without deep circuits and ancillae, or
high-dimensional optimization. We furthermore discuss quantum imaginary time
evolution as a subroutine to generate Gibbs averages through an analog of
minimally entangled typical thermal states. Finally, we demonstrate the
potential of these algorithms via an implementation using exact classical
emulation as well as through prototype circuits on the Rigetti quantum virtual
machine and Aspen-1 quantum processing unit.",1901.07653v3
2019-02-21,Learning representations of irregular particle-detector geometry with distance-weighted graph networks,"We explore the use of graph networks to deal with irregular-geometry
detectors in the context of particle reconstruction. Thanks to their
representation-learning capabilities, graph networks can exploit the full
detector granularity, while natively managing the event sparsity and
arbitrarily complex detector geometries. We introduce two distance-weighted
graph network architectures, dubbed GarNet and GravNet layers, and apply them
to a typical particle reconstruction task. The performance of the new
architectures is evaluated on a data set of simulated particle interactions on
a toy model of a highly granular calorimeter, loosely inspired by the endcap
calorimeter to be installed in the CMS detector for the High-Luminosity LHC
phase. We study the clustering of energy depositions, which is the basis for
calorimetric particle reconstruction, and provide a quantitative comparison to
alternative approaches. The proposed algorithms provide an interesting
alternative to existing methods, offering equally performing or less
resource-demanding solutions with less underlying assumptions on the detector
geometry and, consequently, the possibility to generalize to other detectors.",1902.07987v2
2019-04-17,Graphene Induced Large Shift of Surface Plasmon Resonances of Gold Films: Effective Medium Theory for Atomically Thin Materials,"Despite successful modeling of graphene as a 0.34-nm thick optical film
synthesized by exfoliation or chemical vapor deposition (CVD), graphene induced
shift of surface plasmon resonance (SPR) of gold films has remained
controversial. Here we report the resolution of this controversy by developing
a clean CVD graphene transfer method and extending Maxwell-Garnet effective
medium theory (EMT) to 2D materials. A SPR shift of 0.24 is obtained and it
agrees well with 2D EMT in which wrinkled graphene is treated as a 3-nm
graphene/air layered composite, in agreement with the average roughness
measured by atomic force microscope. Because the anisotropic built-in boundary
condition of 2D EMT is compatible with graphene's optical anisotropy, graphene
can be modelled as a film thicker than 0.34-nm without changing its optical
property; however, its actual roughness, i.e., effective thickness will
significantly alter its response to strong out-of-plane fields, leading to a
larger SPR shift.",1904.08308v1
2019-05-30,A Test of Bolometric Properties of Tm-containing Crystals as a Perspective Detector for the Solar Axion Search,"The $^{169}$Tm nuclide has first nuclear level at 8.41 keV with magnetic type
transition to the ground state and, therefore, can be used as a target nucleus
for the search of resonant absorption of solar axions. We plan to use a
Tm-containing crystal of a garnet family Tm$_3$Al$_5$O$_{12}$ as a bolometric
detector in order to search for the excitation of the first nuclear level of
$^{169}$Tm via the resonant absorption of solar axions. With this perspective
in mind, a sample of the Tm$_3$Al$_5$O$_{12}$ crystal was grown and tested for
its bolometric and optical properties. Measurements of chemical and/or
radioactive contaminations were performed as well. In this paper we present the
test results and estimate the requirements for a future low-background
experimental setup.",1905.12952v1
2019-07-13,On the generalization of the exponential basis for tensor network representations of long-range interactions in two and three dimensions,"In one dimension (1D), a general decaying long-range interaction can be fit
to a sum of exponential interactions $e^{-\lambda r_{ij}}$ with varying
exponents $\lambda$, each of which can be represented by a simple matrix
product operator (MPO) with bond dimension $D=3$. Using this technique,
efficient and accurate simulations of 1D quantum systems with long-range
interactions can be performed using matrix product states (MPS). However, the
extension of this construction to higher dimensions is not obvious. We report
how to generalize the exponential basis to 2D and 3D by defining the basis
functions as the Green's functions of the discretized Helmholtz equation for
different Helmholtz parameters $\lambda$, a construction which is valid for
lattices of any spatial dimension. Compact tensor network representations can
then be found for the discretized Green's functions, by expressing them as
correlation functions of auxiliary fermionic fields with nearest neighbor
interactions via Grassmann Gaussian integration. Interestingly, this analytic
construction in 3D yields a $D=4$ tensor network representation of correlation
functions which (asymptotically) decay as the inverse distance ($r^{-1}_{ij}$),
thus generating the (screened) Coulomb potential on a cubic lattice. These
techniques will be useful in tensor network simulations of realistic materials.",1907.06018v1
2019-08-27,The relationship between the redox activity and electrochemical stability of solid electrolytes for solid-state batteries,"All-solid-state Li-ion batteries promise safer electrochemical energy storage
with larger volumetric and gravimetric energy densities. A major concern is the
limited electrochemical stability of solid electrolytes and related detrimental
electrochemical reactions, especially because of our restricted understanding.
Here we demonstrate for the argyrodite, garnet and NASICON type solid
electrolytes, that the favourable decomposition pathway is indirect rather than
direct, via (de)lithiated states of the solid electrolyte, into the
thermodynamically stable decomposition products. The consequence is that the
electrochemical stability window of the solid electrolyte is significantly
larger than predicted for direct decomposition, rationalizing the observed
stability window. The observed argyrodite metastable (de)lithiated solid
electrolyte phases contribute to the (ir)reversible cycling capacity of
all-solid-state batteries, in addition to the contribution of the decomposition
products, comprehensively explaining solid electrolyte redox activity. The
fundamental nature of the proposed mechanism suggests this is a key aspect for
solid electrolytes in general, guiding interface and material design for
all-solid-state batteries.",1908.10144v1
2019-09-30,Direct comparison of many-body methods for realistic electronic Hamiltonians,"A large collaboration carefully benchmarks 20 first principles many-body
electronic structure methods on a test set of 7 transition metal atoms, and
their ions and monoxides. Good agreement is attained between the 3
systematically converged methods, resulting in experiment-free reference
values. These reference values are used to assess the accuracy of modern
emerging and scalable approaches to the many-electron problem. The most
accurate methods obtain energies indistinguishable from experimental results,
with the agreement mainly limited by the experimental uncertainties. Comparison
between methods enables a unique perspective on calculations of many-body
systems of electrons.",1910.00045v2
2019-10-05,Electronic structure of bulk manganese oxide and nickel oxide from coupled cluster theory,"We describe the ground- and excited-state electronic structure of bulk MnO
and NiO, two prototypical correlated electron materials, using coupled cluster
theory with single and double excitations (CCSD). As a corollary, this work
also reports the first implementation of unrestricted periodic ab initio
equation-of motion CCSD. Starting from a Hartree-Fock reference, we find
fundamental gaps of 3.46 eV and 4.83 eV for MnO and NiO respectively for the 16
unit supercell, slightly overestimated compared to experiment, although
finite-size scaling suggests that the gap is more severely overestimated in the
thermodynamic limit. From the character of the correlated electronic bands we
find both MnO and NiO to lie in the intermediate Mott/charge-transfer insulator
regime, although NiO appears as a charge transfer insulator when only the
fundamental gap is considered. While the lowest quasiparticle excitations are
of metal 3d and O 2p character in most of the Brillouin zone, near the {\Gamma}
point, the lowest conduction band quasiparticles are of s character. Our study
supports the potential of coupled cluster theory to provide high level
many-body insights into correlated solids.",1910.02191v2
2019-10-18,Magnetic order and single-ion anisotropy in Tb$_3$Ga$_5$O$_{12}$,"Terbium gallium garnet (TGG), Tb$_3$Ga$_5$O$_{12}$, is well known for its
applications in laser optics, but also exhibits complex low-temperature
magnetism that is not yet fully understood. Its low-temperature magnetic order
is determined by means of time-of-flight neutron powder diffraction. It is
found to be a multiaxial antiferromagnet with magnetic Tb$^{3+}$ ions forming
six sublattices of magnetic moments aligned parallel and anti-parallel to the
$\langle100\rangle$ crystallographic directions of the cubic unit cell. The
structure displays strong easy-axis anisotropy with respect to a two-fold axis
of symmetry in the local orthorhombic environment of the Tb$^{3+}$ sites. The
crystal-field splitting within the single-ion ground-state manifold is
investigated by inelastic neutron scattering on powder samples. A strong
temperature dependence of the quasidoublet ground-state is observed and revised
parameters of the crystal-field Hamiltonian are given. The results of bulk
magnetic susceptibility and magnetisation measurements are in good agreement
with values based on the crystal-field model down to 20~K, where the onset of
magnetic correlations is observed.",1910.08570v1
2019-11-05,"Ground-state properties of the hydrogen chain: insulator-to-metal transition, dimerization, and magnetic phases","Accurate and predictive computations of the quantum-mechanical behavior of
many interacting electrons in realistic atomic environments are critical for
the theoretical design of materials with desired properties, and require
solving the grand-challenge problem of the many-electron Schrodinger equation.
An infinite chain of equispaced hydrogen atoms is perhaps the simplest
realistic model for a bulk material, embodying several central themes of modern
condensed matter physics and chemistry, while retaining a connection to the
paradigmatic Hubbard model. Here we report a combined application of
cutting-edge computational methods to determine the properties of the hydrogen
chain in its quantum-mechanical ground state. Varying the separation between
the nuclei leads to a rich phase diagram, including a Mott phase with quasi
long-range antiferromagnetic order, electron density dimerization with
power-law correlations, an insulator-to-metal transition and an intricate set
of intertwined magnetic orders.",1911.01618v2
2019-11-11,A simplified and improved approach to tensor network operators in two dimensions,"Matrix product states (MPS) and matrix product operators (MPOs) are one
dimensional tensor networks that underlie the modern density matrix
renormalization group (DMRG) algorithm. The use of MPOs accounts for the high
level of generality and wide range of applicability of DMRG. However, current
algorithms for two dimensional (2D) tensor network states, known as projected
entangled-pair states (PEPS), rarely employ the associated 2D tensor network
operators, projected entangled-pair operators (PEPOs), due to their
computational cost and conceptual complexity. To lower these two barriers, we
describe how to reformulate a PEPO into a set of tensor network operators that
resemble MPOs by considering the different sets of local operators that are
generated from sequential bipartitions of the 2D system. The expectation value
of a PEPO can then be evaluated on-the-fly using only the action of MPOs and
generalized MPOs at each step of the approximate contraction of the 2D tensor
network. This technique allows for the simpler construction and more efficient
energy evaluation of 2D Hamiltonians that contain finite-range interactions,
and provides an improved strategy to encode long-range interactions that is
orders of magnitude more accurate and efficient than existing schemes.",1911.04592v1
2020-01-10,Quantum algorithms for quantum chemistry and quantum materials science,"As we begin to reach the limits of classical computing, quantum computing has
emerged as a technology that has captured the imagination of the scientific
world. While for many years, the ability to execute quantum algorithms was only
a theoretical possibility, recent advances in hardware mean that quantum
computing devices now exist that can carry out quantum computation on a limited
scale. Thus it is now a real possibility, and of central importance at this
time, to assess the potential impact of quantum computers on real problems of
interest. One of the earliest and most compelling applications for quantum
computers is Feynman's idea of simulating quantum systems with many degrees of
freedom. Such systems are found across chemistry, physics, and materials
science. The particular way in which quantum computing extends classical
computing means that one cannot expect arbitrary simulations to be sped up by a
quantum computer, thus one must carefully identify areas where quantum
advantage may be achieved. In this review, we briefly describe central problems
in chemistry and materials science, in areas of electronic structure, quantum
statistical mechanics, and quantum dynamics, that are of potential interest for
solution on a quantum computer. We then take a detailed snapshot of current
progress in quantum algorithms for ground-state, dynamics, and thermal state
simulation, and analyze their strengths and weaknesses for future developments.",2001.03685v2
2020-01-17,An interlayer with low solubility for lithium enhances tolerance to dendrite growth in solid state electrolytes,"All solid state Li-ion batteries employing metallic lithium as an anode offer
higher energy densities while also being safer than conventional liquid
electrolyte based Li-ion batteries. However, the growth of tiny filaments of
lithium (dendrites) across the solid state electrolyte layer leads to premature
shorting of cells and limits their practical viability. The microscopic
mechanisms that lead to lithium dendrite growth in solid state cells are still
unclear. Using garnet based lithium ion conductor as a model solid state
electrolyte, we show that interfacial void growth during lithium dissolution
precedes dendrite nucleation and growth. Using a simple electrostatic model, we
show that current density at the edges of the voids could be amplified by as
much as four orders of magnitude making the cells highly susceptible to
dendrite growth after void formation. We propose the use of metallic
interlayers with low solubility and high nucleation overpotential for lithium
to delay void growth. These interlayers increase dendrite growth tolerance in
solid state electrolytes without the undue necessity for high stack pressures.",2001.06276v1
2020-03-03,Ab Initio Full Cell GW+DMFT for Correlated Materials,"Quantitative prediction of electronic properties in correlated materials
requires simulations without empirical truncations and parameters. We present a
method to achieve this goal through a new ab initio formulation of dynamical
mean-field theory (DMFT). Instead of using small impurities defined in a
low-energy subspace, which require complicated downfolded interactions which
are often approximated, we describe a full cell $GW$+DMFT approach, where the
impurities comprise all atoms in a unit cell or supercell of the crystal. Our
formulation results in large impurity problems, which we treat here with
efficient quantum chemistry impurity solvers that work on the real-frequency
axis, combined with a one-shot $G_0W_0$ treatment of long-range interactions.
We apply our full cell approach to bulk Si, two antiferromagnetic correlated
insulators NiO and $\alpha$-Fe$_2$O$_3$, and the paramagnetic correlated metal
SrMoO$_3$, with impurities containing up to 10 atoms and 124 orbitals. We find
that spectral properties, magnetic moments, and two-particle spin correlation
functions are obtained in good agreement with experiments. In addition, in the
metal oxide insulators, the balanced treatment of correlations involving all
orbitals in the cell leads to new insights into the orbital character around
the insulating gap.",2003.01349v2
2020-03-12,Genesis of primitive Hawaiian rejuvenated-stage lavas: Evidence for carbonatite metasomatism and implications for ancient eclogite source,"To constrain a contribution of deep carbonated mantle, to fractionation of Hf
relative to rare earth elements (REE) in volcanic series, we examine available
high-quality data on major, trace element and Nd-Hf isotope compositions of
primitive lavas and glasses erupted during preshield, postshield and mostly
rejuvenated stage of the Hawaiian hot spot (Pacific Ocean). Strong variations
of Hf/Sm, Zr/Sm, Ti/Eu, K/Th, Nb/Th, La/K and Ba/K in the lavas are not
features of the melt equilibration with residual amphibole or phlogopite, and
cannot be due to variable degrees of batch or dynamic melting of uncarbonated
lherzolite source. Enrichment in REE, Th and Ba relative to K, Hf, Zr, Ti and
Nb together and low Si, high Na, K and Ca contents in the Hawaiian lavas are
compositional features of carbonated mantle lithospheric to asthenospheric
peridotite source affected by carbonatite metasomatism. In contrast, major and
trace element signatures of most primitive preshield- and postshield-stage
magmas require pyroxenite source.
  The available data infer that Salt Lake Crater garnet pyroxenite xenoliths
hosted by the Koolau volcano lavas on Oahu, Hawaii, were derived from deep
eclogite source likely generating the carbonatite melts within the Hawaiian
plume. Highly radiogenic Hf and decoupled Nd-Hf isotope systematics recorded in
the Salt Lake Crater mantle xenolith series on Oahu may be explained by strong
Hf fractionation relative to REE owing to ancient event of carbonatite
metasomatism, which is likely related to partial melting of the deeply
subducted carbonated eclogite within the Hawaiian plume.",2003.05705v1
2020-07-07,All-electron Gaussian-based $G_0W_0$ for Valence and Core Excitation Energies of Periodic Systems,"We describe an all-electron $G_0W_0$ implementation for periodic systems with
$k$-point sampling implemented in a crystalline Gaussian basis. Our
full-frequency $G_0W_0$ method relies on efficient Gaussian density fitting
integrals and includes both analytic continuation and contour deformation
schemes. Due to the compactness of Gaussian bases, no virtual state truncation
is required as is seen in many plane-wave formulations. Finite size corrections
are included by taking the $q \to 0$ limit of the Coulomb divergence. Using our
implementation, we study quasiparticle energies and band structures across a
range of systems including molecules, semiconductors, rare gas solids, and
metals. We find that the $G_0W_0$ band gaps of traditional semiconductors
converge rapidly with respect to the basis size, even for the conventionally
challenging case of ZnO. Using correlation-consistent bases of polarized
triple-zeta quality, we find the mean absolute relative error of the
extrapolated $G_0W_0$@PBE band gaps to be only 5.2% when compared to
experimental values. For core excitation binding energies (CEBEs), we find that
$G_0W_0$ predictions improve significantly over those from DFT if the $G_0W_0$
calculations are started from hybrid functionals with a high percentage of
exact exchange.",2007.03148v3
2020-07-16,Automatic transformation of irreducible representations for efficient contraction of tensors with cyclic group symmetry,"Tensor contractions are ubiquitous in computational chemistry and physics,
where tensors generally represent states or operators and contractions express
the algebra of these quantities. In this context, the states and operators
often preserve physical conservation laws, which are manifested as group
symmetries in the tensors. These group symmetries imply that each tensor has
block sparsity and can be stored in a reduced form. For nontrivial
contractions, the memory footprint and cost are lowered, respectively, by a
linear and a quadratic factor in the number of symmetry sectors.
State-of-the-art tensor contraction software libraries exploit this opportunity
by iterating over blocks or using general block-sparse tensor representations.
Both approaches entail overhead in performance and code complexity. With
intuition aided by tensor diagrams, we present a technique, irreducible
representation alignment, which enables efficient handling of Abelian group
symmetries via only dense tensors, by using contraction-specific reduced forms.
This technique yields a general algorithm for arbitrary group symmetric
contractions, which we implement in Python and apply to a variety of
representative contractions from quantum chemistry and tensor network methods.
As a consequence of relying on only dense tensor contractions, we can easily
make use of efficient batched matrix multiplication via Intel's MKL and
distributed tensor contraction via the Cyclops library, achieving good
efficiency and parallel scalability on up to 4096 Knights Landing cores of a
supercomputer.",2007.08056v4
2020-08-31,Finite and Infinite Matrix Product States for Gutzwiller Projected Mean-Field Wavefunctions,"Matrix product states (MPS) and `dressed' ground states of quadratic mean
fields (e.g. Gutzwiller projected Slater Determinants) are both important
classes of variational wave-functions. This latter class has played important
roles in understanding superconductivity and quantum spin-liquids. We present a
novel method to obtain both the finite and infinite MPS (iMPS) representation
of the ground state of an arbitrary fermionic quadratic mean-field Hamiltonian,
(which in the simplest case is a Slater determinant and in the most general
case is a Pfaffian). We also show how to represent products of such states
(e.g. determinants times Pfaffians). From this representation one can project
to single occupancy and evaluate the entanglement spectra after Gutzwiller
projection. We then obtain the MPS and iMPS representation of Gutzwiller
projected mean-field states that arise from the variational slave-fermion
approach to the $S=1$ Bilinear-Biquadratic (BLBQ) quantum spin chain. To
accomplish this, we develop an approach to orthogonalize degenerate iMPS to
find all the states in the degenerate ground-state manifold. We find the
energies of the MPS and iMPS states match the variational energies closely
indicating the method is accurate and there is minimal loss due to truncation
error. We then present the first exploration of the entanglement spectra of
projected slave-fermion states exploring their qualitative features and finding
good qualitative agreement with the respective exact ground state spectra found
from DMRG.",2009.00064v1
2020-12-22,On the spread of infinite groups,"A group is $\frac32$-generated if every non-trivial element is part of a
generating pair. In 2019, Donoven and Harper showed that many Thompson groups
are $\frac32$-generated and posed five questions. The first of these is whether
there exists a 2-generated group with every proper quotient cyclic that is not
$\frac32$-generated. This is a natural question given the significant work in
proving that no finite group has this property, but we show that there is such
an infinite group. The groups we consider are a family of finite index
subgroups of the Houghton group $\text{FSym}(\mathbb{Z})\rtimes\mathbb{Z}$. We
then show that the first two groups in our family are $\frac32$-generated, and
investigate the related notion of spread for these groups. We are able to show
that they have finite spread which is greater than 2. These are therefore the
first infinite groups to be shown to have finite positive spread, and the first
to be shown to have spread greater than 2 (other than $\mathbb{Z}$ and the
Tarski monsters, which have infinite spread).",2012.12197v3
2021-04-05,"Analyser-free, intensity-based wide-field magneto-optical microscopy","In conventional Kerr- and Faraday microscopy the sample is illuminated with
plane-polarised light and a magnetic domain contrast is generated by an
analyser making use of the Kerr- or Faraday rotation. In this paper we
demonstrate possibilities of analyser-free magneto-optical microscopy based on
magnetisation-dependent intensity modulations of the light: (i) The transverse
Kerr effect can be applied for in-plane magnetised material, demonstrated for
an FeSi sheet. (ii) Illuminating the same sample with circularly polarised
light leads to a domain contrast with a different symmetry as the conventional
Kerr contrast. (iii) Circular polarisation can also be used for perpendicularly
magnetised material, demonstrated for a garnet film and an ultrathin CoFeB
film. (iv) Plane-polarised light at a specific angle can be employed for both,
in-plane and perpendicular media. (v) Perpendicular light incidence leads to a
domain contrast on in-plane materials that is quadratic in the magnetisation
and to a domain boundary contrast. (vi) Domain contrast can even be obtained
without polariser. In cases (ii) and (iii), the contrast is generated by MCD
(Magnetic Circular Dichroism), while MLD (Magnetic Linear Dichroism) is
responsible for the contrast in case (v). The domain boundary contrast is due
to the magneto-optical gradient effect in metallic samples. A domain boundary
contrast can also arise due to interference of phase-shifted magneto-optical
amplitudes. An explanation of these contrast phenomena is provided in terms of
Maxwell-Fresnel theory.",2104.01831v2
2021-05-20,Spin dynamics of the quantum dipolar magnet Yb$_3$Ga$_5$O$_{12}$ in an external field,"We investigate ytterbium gallium garnet Yb$_{3}$Ga$_{5}$O$_{12}$ in the
paramagnetic phase above the supposed magnetic transition at $T_{\lambda}
\approx 54$ mK. Our study combines susceptibility and specific heat
measurements with neutron scattering experiments and theoretical calculations.
Below 500 mK, the elastic neutron response is strongly peaked in the momentum
space. Along with that the inelastic spectrum develops flat excitation modes.
In magnetic field, the lowest energy branch follows a Zeeman shift in
accordance with the field-dependent specific heat data. An intermediate state
with spin canting away from the field direction is evidenced in small magnetic
fields. In the field of 2 T, the total magnetization almost saturates and the
measured excitation spectrum is well reproduced by the spin-wave calculations
taking into account solely the dipole-dipole interactions. The small positive
Curie-Weiss temperature derived from the susceptibility measurements is also
accounted for by the dipole spin model. Altogether, our results suggest that
Yb$_{3}$Ga$_{5}$O$_{12}$ is a quantum dipolar magnet.",2105.09817v1
2021-12-06,Space applications of GAGG:Ce scintillators: a study of afterglow emission by proton irradiation,"We discuss the results of a proton irradiation campaign of a GAGG:Ce
(Cerium-doped Gadolinium Aluminium Gallium Garnet) scintillation crystal,
carried out in the framework of the HERMES-TP/SP (High Energy Rapid Modular
Ensemble of Satellites -- Technological and Scientific Pathfinder) mission. A
scintillator sample was irradiated with 70 MeV protons, at levels equivalent to
those expected in equatorial and sun-synchronous low-Earth orbits over orbital
periods spanning 6 months to 10 years. The data we acquired are used to
introduce an original model of GAGG:Ce afterglow emission. Results from this
model are applied to the HERMES-TP/SP scenario, aiming at an upper-bound
estimate of the detector performance degradation resulting from afterglow
emission.",2112.02897v3
2022-01-28,Using hyper-optimized tensor networks and first-principles electronic structure to simulate experimental properties of the giant {Mn84} torus,"The single-molecule magnet {Mn84} is a challenge to theory due to its high
nuclearity. Building on our prior work which characterized the structure of the
spectrum of this magnet, we directly compute two experimentally accessible
observables, the field-dependent magnetization up to 75 T and the
temperature-dependent heat capacity, using parameter free theory. In
particular, we use first principles calculations to derive short- and
long-range exchange interactions, while we compute the exact partition function
of the resulting classical Potts and Ising spin models for all 84 Mn $S=2$
spins to obtain the observables. The latter computation is possible because of
a simulation methodology that uses hyper-optimized tensor network contraction,
borrowing from recent techniques developed to simulate quantum supremacy
circuits. We also synthesize the magnet and measure its heat capacity and
field-dependent magnetization. We observe good qualitative agreement between
theory and experiment, identifying an unusual peak in the heat capacity in
both, as well as a plateau in the magnetization. Our work also identifies some
limitations of current theoretical modeling in large magnets, such as the
sensitivity to small, long-range, exchange couplings.",2201.11979v1
2022-03-10,Cavity-Dumping a Single Infrared Pulse from a Free-Electron Laser for Two-Color Pump-Probe Experiments,"Electromagnetic radiation in the mid- to far-infrared spectral range
represents an indispensable tool for the study of numerous types of collective
excitations in solids and molecules. Short and intense pulses in this THz
spectral range are, however, difficult to obtain. While wide
wavelength-tunability is easily provided by free-electron lasers, the energies
of individual pulses are relatively moderate, on the order of microjoules. Here
we demonstrate a setup that uses cavity-dumping of a free-electron laser to
provide single, picosecond-long pulses in the mid- to far-infrared frequency
range. The duration of the Fourier-limited pulses can be varied by cavity
detuning, and their energy was shown to exceed 100 {\mu}J. Using the
aforementioned infrared pulse as a pump, we have realized a two-color
pump-probe setup facilitating single-shot time-resolved imaging of
magnetization dynamics. We demonstrate the capabilities of the setup first on
thermally-induced demagnetization and magnetic switching of a GdFeCo thin film
and second by showing a single-shot time-resolved detection of resonant
phononic switching of the magnetization in a magnetic garnet.",2203.05348v1
2022-03-20,Deposition temperature dependence of thermo-spin and magneto-thermoelectric conversion in Co$_2$MnGa films on Y$_3$Fe$_5$O$_{12}$ and Gd$_3$Ga$_5$O$_{12}$,"We have characterized Co$_2$MnGa (CMG) Heusler alloy films grown on
Y$_3$Fe$_5$O$_{12}$ (YIG) and Gd$_3$Ga$_5$O$_{12}$ (GGG) substrates at
different deposition temperatures and investigated thermo-spin and
magneto-thermoelectric conversion properties by means of a lock-in thermography
technique. X-ray diffraction, magnetization, and electrical transport
measurements show that the deposition at high substrate temperatures induces
the crystallized structures of CMG while the resistivity of the CMG films on
YIG (GGG) prepared at and above 500 {\deg}C (550 {\deg}C) becomes too high to
measure the thermo-spin and magneto-thermoelectric effects due to large
roughness, highlighting the difficulty of fabricating highly ordered continuous
CMG films on garnet structures. Our lock-in thermography measurements show that
the deposition at high substrate temperatures results in an increase in the
current-induced temperature change for CMG/GGG and a decrease in that for
CMG/YIG. The former indicates the enhancement of the anomalous Ettingshausen
effect in CMG through crystallization. The latter can be explained by the
superposition of the anomalous Ettingshausen effect and the spin Peltier effect
induced by the positive (negative) charge-to-spin conversion for the amorphous
(crystallized) CMG films. These results provide a hint to construct
spin-caloritronic devices based on Heusler alloys.",2203.10566v2
2022-04-04,"Magnetocaloric properties of $R_3$Ga$_5$O$_{12}$ ($R$ = Tb,Gd,Nd,Dy)","We report the characteristic magnetic properties of several members of the
rare-earth garnet family, Gd$_3$Ga$_5$O$_{12}$ (GGG), Dy$_3$Ga$_5$O$_{12}$
(DGG), Tb$_3$Ga$_5$O$_{12}$ (TGG), and Nd$_3$Ga$_5$O$_{12}$ (NGG), and compare
their relative potential utility for magnetocaloric cooling, including their
minimal adiabatic demagnetization refrigeration (ADR) temperatures and relative
cooling parameters. A main objective of this work concerns the identification
of potential improvements over the magnetocaloric properties of GGG for use in
low temperature ADR cryostats. Using Tb$^{+3}$ and Dy$^{+3}$ in the rare-earth
site offers, in principle, a higher saturation magnetization and Nd$^{+3}$
gives a lower de Gennes factor and therefore potentially reduced magnetic
transition temperatures, limiting the useful temperature range. Our results
show that Dy$_3$Ga$_5$O$_{12}$ yields an optimal relative cooling parameter
($RCP$) at low applied fields and low limiting temperatures, which would allow
for the design of more efficient ADR cryostats.",2204.01752v2
2022-05-05,Performance of a spaghetti calorimeter prototype with tungsten absorber and garnet crystal fibres,"A spaghetti calorimeter (SPACAL) prototype with scintillating crystal fibres
was assembled and tested with electron beams of energy from 1 to 5 GeV. The
prototype comprised radiation-hard Cerium-doped Gd$_3$Al$_2$Ga$_3$O$_{12}$
(GAGG:Ce) and Y$_3$Al$_5$O$_{12}$ (YAG:Ce) embedded in a pure tungsten
absorber. The energy resolution was studied as a function of the incidence
angle of the beam and found to be of the order of $10\% / \sqrt{E} \oplus1\%$,
in line with the LHCb Shashlik technology. The time resolution was measured
with metal channel dynodes photomultipliers placed in contact with the fibres
or coupled via a light guide, additionally testing an optical tape to glue the
components. Time resolution of a few tens of picosecond was achieved for all
the energies reaching down to (18.5 $\pm$ 0.2) ps at 5 GeV.",2205.02500v3
2022-08-03,Is there evidence for exponential quantum advantage in quantum chemistry?,"The idea to use quantum mechanical devices to simulate other quantum systems
is commonly ascribed to Feynman. Since the original suggestion, concrete
proposals have appeared for simulating molecular and materials chemistry
through quantum computation, as a potential ``killer application''. Indications
of potential exponential quantum advantage in artificial tasks have increased
interest in this application, thus, it is critical to understand the basis for
potential exponential quantum advantage in quantum chemistry. Here we gather
the evidence for this case in the most common task in quantum chemistry,
namely, ground-state energy estimation. We conclude that evidence for such an
exponential advantage across chemical space has yet to be found. While quantum
computers may still prove useful for quantum chemistry, it may be prudent to
assume exponential speedups are not generically available for this problem.",2208.02199v3
2022-09-01,Growth parameters of Bi0.1Y2.9Fe5O12 thin films for high frequency applications,"The growth and characterization of Bismuth (Bi) substituted YIG (Bi-YIG,
Bi0.1Y2.9Fe5O12) thin films are reported. Pulsed laser deposited (PLD) films
with thicknesses ranging from 20 to 150 nm were grown on Gadolinium Gallium
Garnet substrates. Two substrate orientations of (100) and (111) were
considered. The enhanced distribution of Bi3+ ions at dodecahedral site along
(111) is observed to lead to an increment in lattice constant from 12.379
angstrom in (100) to 12.415 angstrom in (111) oriented films. Atomic force
microscopy images showed decreasing roughness with increasing film thickness.
Compared to (100) grown films, (111) oriented films showed an increase in
ferromagnetic resonance linewidth and consequent increase in Gilbert damping.
The lowest Gilbert damping values are found to be (1.06) * 10E-4 for (100) and
(2.30) * 10E-4 for (111) oriented films with thickness of 150 nm. The observed
values of extrinsic linewidth, effective magnetization, and anisotropic field
are related to thickness of the films and substrate orientation. In addition,
the in-plane angular variation established four-fold symmetry for the (100)
deposited films unlike the case of (111) deposited films. This study prescribes
growth conditions for PLD grown single-crystalline Bi-YIG films towards desired
high frequency and magneto-optical device applications.",2209.00558v1
2022-09-21,Performance enhancement of a spin-wave-based reservoir computing system utilizing different physical conditions,"The authors have numerically studied how to enhance reservoir computing
performance by thoroughly extracting their spin-wave device potential for
higher-dimensional information generation. The reservoir device has a 1-input
exciter and 120-output detectors on the top of a continuous magnetic garnet
film for spin-wave transmission. For various nonlinear and fading-memory
dynamic phenomena distributing in the film space, small in-plane magnetic
fields were used to prepare stripe domain structures and various damping
constants at the film sides and bottom were explored. The ferromagnetic
resonant frequency and relaxation time of spin precession clearly characterized
the change in spin dynamics with the magnetic field and damping constant. The
common input signal for reservoir computing was a 1 GHz cosine wave with random
6-valued amplitude modulation. A basic 120-dimensional reservoir output vector
was obtained from time-series signals at the 120 output detectors under each of
the three magnetic field conditions. Then, 240- and 360-dimensional reservoir
output vectors were also constructed by concatenating two and three basic ones,
respectively. In nonlinear autoregressive moving average (NARMA) prediction
tasks, the computational performance was enhanced as the dimension of the
reservoir output vector becomes higher and a significantly low prediction error
was achieved for the 10th-order NARMA using the 360-dimensional vector and
optimum damping constant. The results are clear evidence that the collection of
diverse output signals efficiently increases the dimensionality effective for
reservoir computing, i.e., reservoir-state richness. This paper demonstrates
that performance enhancement through various configuration settings is a
practical approach for on-chip reservoir computing devices with small numbers
of real output nodes.",2209.10123v1
2022-10-14,The Surprisingly Straightforward Scene Text Removal Method With Gated Attention and Region of Interest Generation: A Comprehensive Prominent Model Analysis,"Scene text removal (STR), a task of erasing text from natural scene images,
has recently attracted attention as an important component of editing text or
concealing private information such as ID, telephone, and license plate
numbers. While there are a variety of different methods for STR actively being
researched, it is difficult to evaluate superiority because previously proposed
methods do not use the same standardized training/evaluation dataset. We use
the same standardized training/testing dataset to evaluate the performance of
several previous methods after standardized re-implementation. We also
introduce a simple yet extremely effective Gated Attention (GA) and
Region-of-Interest Generation (RoIG) methodology in this paper. GA uses
attention to focus on the text stroke as well as the textures and colors of the
surrounding regions to remove text from the input image much more precisely.
RoIG is applied to focus on only the region with text instead of the entire
image to train the model more efficiently. Experimental results on the
benchmark dataset show that our method significantly outperforms existing
state-of-the-art methods in almost all metrics with remarkably higher-quality
results. Furthermore, because our model does not generate a text stroke mask
explicitly, there is no need for additional refinement steps or sub-models,
making our model extremely fast with fewer parameters. The dataset and code are
available at this https://github.com/naver/garnet.",2210.07489v2
2022-11-04,GARNet: Global-Aware Multi-View 3D Reconstruction Network and the Cost-Performance Tradeoff,"Deep learning technology has made great progress in multi-view 3D
reconstruction tasks. At present, most mainstream solutions establish the
mapping between views and shape of an object by assembling the networks of 2D
encoder and 3D decoder as the basic structure while they adopt different
approaches to obtain aggregation of features from several views. Among them,
the methods using attention-based fusion perform better and more stable than
the others, however, they still have an obvious shortcoming -- the strong
independence of each view during predicting the weights for merging leads to a
lack of adaption of the global state. In this paper, we propose a global-aware
attention-based fusion approach that builds the correlation between each branch
and the global to provide a comprehensive foundation for weights inference. In
order to enhance the ability of the network, we introduce a novel loss function
to supervise the shape overall and propose a dynamic two-stage training
strategy that can effectively adapt to all reconstructors with attention-based
fusion. Experiments on ShapeNet verify that our method outperforms existing
SOTA methods while the amount of parameters is far less than the same type of
algorithm, Pix2Vox++. Furthermore, we propose a view-reduction method based on
maximizing diversity and discuss the cost-performance tradeoff of our model to
achieve a better performance when facing heavy input amount and limited
computational cost.",2211.02299v1
2022-12-21,Towards Neural Variational Monte Carlo That Scales Linearly with System Size,"Quantum many-body problems are some of the most challenging problems in
science and are central to demystifying some exotic quantum phenomena, e.g.,
high-temperature superconductors. The combination of neural networks (NN) for
representing quantum states, coupled with the Variational Monte Carlo (VMC)
algorithm, has been shown to be a promising method for solving such problems.
However, the run-time of this approach scales quadratically with the number of
simulated particles, constraining the practically usable NN to - in machine
learning terms - minuscule sizes (<10M parameters). Considering the many
breakthroughs brought by extreme NN in the +1B parameters scale to other
domains, lifting this constraint could significantly expand the set of quantum
systems we can accurately simulate on classical computers, both in size and
complexity. We propose a NN architecture called Vector-Quantized Neural Quantum
States (VQ-NQS) that utilizes vector-quantization techniques to leverage
redundancies in the local-energy calculations of the VMC algorithm - the source
of the quadratic scaling. In our preliminary experiments, we demonstrate VQ-NQS
ability to reproduce the ground state of the 2D Heisenberg model across various
system sizes, while reporting a significant reduction of about ${\times}10$ in
the number of FLOPs in the local-energy calculation.",2212.11296v1
2022-12-22,Spin wave dispersion of ultra-low damping hematite ($α\text{-Fe}_2\text{O}_3$) at GHz frequencies,"Low magnetic damping and high group velocity of spin waves (SWs) or magnons
are two crucial parameters for functional magnonic devices. Magnonics research
on signal processing and wave-based computation at GHz frequencies focussed on
the artificial ferrimagnetic garnet Y$_3$Fe$_5$O$_{12}$ (YIG) so far. We report
on spin-wave spectroscopy studies performed on the natural mineral hematite
($\alpha\text{-Fe}_2\text{O}_3$) which is a canted antiferromagnet. By means of
broadband GHz spectroscopy and inelastic light scattering, we determine a
damping coefficient of $1.1\times10^{-5}$ and magnon group velocities of a few
10 km/s, respectively, at room temperature. Covering a large regime of wave
vectors up to $k\approx 24~{\rm rad}/\mu$m, we find the exchange stiffness
length to be relatively short and only about 1 \r{A}. In a small magnetic field
of 30 mT, the decay length of SWs is estimated to be 1.1 cm similar to the best
YIG. Still, inelastic light scattering provides surprisingly broad and partly
asymmetric resonance peaks. Their characteristic shape is induced by the large
group velocities, low damping and distribution of incident angles inside the
laser beam. Our results promote hematite as an alternative and sustainable
basis for magnonic devices with fast speeds and low losses based on a stable
natural mineral.",2212.11887v2
2023-01-18,Hierarchical Clifford transformations to reduce entanglement in quantum chemistry wavefunctions,"The performance of computational methods for many-body physics and chemistry
is strongly dependent on the choice of basis used to cast the problem; hence,
the search for better bases and similarity transformations is important for
progress in the field. So far, tools from theoretical quantum information have
been not thoroughly explored for this task. Here we take a step in this
direction by presenting efficiently computable Clifford similarity
transformations for quantum chemistry Hamiltonians, which expose bases with
reduced entanglement in the corresponding molecular ground states. These
transformations are constructed via block diagonalization of a hierarchy of
truncated molecular Hamiltonians, preserving the full spectrum of the original
problem. We show that the bases introduced here allow for more efficient
classical and quantum computation of ground state properties. First, we find a
systematic reduction of bipartite entanglement in molecular ground states as
compared to standard problem representations. This entanglement reduction has
implications in classical numerical methods such as ones based on the density
matrix renormalization group. Then, we develop variational quantum algorithms
that exploit the structure in the new bases, showing again improved results
when the hierarchical Clifford transformations are used.",2301.07726v1
2023-02-28,CHGNet: Pretrained universal neural network potential for charge-informed atomistic modeling,"The simulation of large-scale systems with complex electron interactions
remains one of the greatest challenges for the atomistic modeling of materials.
Although classical force fields often fail to describe the coupling between
electronic states and ionic rearrangements, the more accurate
\textit{ab-initio} molecular dynamics suffers from computational complexity
that prevents long-time and large-scale simulations, which are essential to
study many technologically relevant phenomena, such as reactions, ion
migrations, phase transformations, and degradation.
  In this work, we present the Crystal Hamiltonian Graph neural Network
(CHGNet) as a novel machine-learning interatomic potential (MLIP), using a
graph-neural-network-based force field to model a universal potential energy
surface. CHGNet is pretrained on the energies, forces, stresses, and magnetic
moments from the Materials Project Trajectory Dataset, which consists of over
10 years of density functional theory static and relaxation trajectories of
$\sim 1.5$ million inorganic structures. The explicit inclusion of magnetic
moments enables CHGNet to learn and accurately represent the orbital occupancy
of electrons, enhancing its capability to describe both atomic and electronic
degrees of freedom. We demonstrate several applications of CHGNet in
solid-state materials, including charge-informed molecular dynamics in
Li$_x$MnO$_2$, the finite temperature phase diagram for Li$_x$FePO$_4$ and Li
diffusion in garnet conductors. We critically analyze the significance of
including charge information for capturing appropriate chemistry, and we
provide new insights into ionic systems with additional electronic degrees of
freedom that can not be observed by previous MLIPs.",2302.14231v2
2023-07-06,Spin transport from order to disorder,"Schwinger boson mean-field theory (SBMFT) is a non-perturbative approach
which treats ordered and disordered phases of magnetic systems on equal
footing. We leverage its versatility to evaluate the spin correlators which
determine thermally-induced spin transport (the spin Seebeck effect) in
Heisenberg ferromagnets (FMs) and antiferromagnets (AFs), at arbitrary
temperatures. In SBMFT, the spin current, $J_s$, is made up of
particle-hole-like excitations which carry integral spin angular momentum. Well
below the ordering temperature, $J_s$ is dominated by a magnonic contribution,
reproducing the behavior of a dilute-magnon gas. Near the transition
temperature, an additional, paramagnetic-like contribution becomes significant.
In the AF, the two contributions come with opposite signs, resulting in a
signature, rapid inversion of the spin Seebeck coefficient as a function of
temperature. Ultimately, at high temperatures, the low-field behavior of the
paramagnetic SSE reduces to Curie-Weiss physics. Analysis based on our theory
confirms that in recent experiments on gadolinium gallium garnet, the low-field
spin Seebeck coefficient $\mathcal{S}(T) \propto \chi(T)$, the spin
susceptibility, down to the Curie-Weiss temperature. At lower temperatures in
the disordered phase, our theory shows a deviation of $\mathcal{S}(T)$ relative
to $\chi(T)$ in both FMs and AFs, which increases with decreasing temperature
and arises due to a paramagnetic liquid phase in our theory. These results
demonstrate that the SSE can be a probe of the short-ranged magnetic
correlations in disordered correlated spin systems and spin liquids.",2307.02734v1
2023-12-10,Radiation resistance of fine-grained ceramics Y2.5Nd0.5Al5O12 under Xe-ions irradiation,"Oxide Y2.5Nd0.5Al5O12 (YAG:Nd) with garnet structure was synthesized in the
powder and ceramics forms. Fine-grained YAG:Nd ceramics with a relative density
of ~99% were obtained by the Spark Plasma Sintering method (SPS). The radiation
resistance of ceramics was studied under irradiation with swift Xe-ions (E =
146 MeV). A gradient defect structure is formed in irradiated ceramics, varying
from layer to layer. The strained YAG phase formed as a result of Xe ions
irradiation is localized in a near-surface layer with a thickness of ~5 {\mu}m.
Full amorphization of the samples was observed under irradiation with a fluence
of 1x10^13 cm-2. The calculated critical fluence was 6.5x10^12 cm-2, which
corresponded to 0.03 dpa. The microhardness of the surface layers of irradiated
ceramics is less than the central layers, and, in general, decreases with
increasing ion fluence.",2312.05820v1
2023-12-29,Fast emulation of fermionic circuits with matrix product states,"We describe a matrix product state (MPS) extension for the Fermionic Quantum
Emulator (FQE) software library. We discuss the theory behind symmetry adapted
matrix product states for approximating many-body wavefunctions of spin-1/2
fermions, and we present an open-source, MPS-enabled implementation of the FQE
interface (MPS-FQE). The software uses the open-source pyblock3 and block2
libraries for most elementary tensor operations, and it can largely be used as
a drop-in replacement for FQE that allows for more efficient, but approximate,
emulation of larger fermionic circuits. Finally, we show several applications
relevant to both near-term and fault-tolerant quantum algorithms where
approximate emulation of larger systems is expected to be useful:
characterization of state preparation strategies for quantum phase estimation,
the testing of different variational quantum eigensolver Ans\""atze, the
numerical evaluation of Trotter errors, and the simulation of general quantum
dynamics problems. In all these examples, approximate emulation with MPS-FQE
allows us to treat systems that are significantly larger than those accessible
with a full statevector emulator.",2312.17657v3
1997-12-17,Late Spectral Evolution of SN 1987A: II. Line Emission,"Using the temperature and ionization calculated in our previous paper, we
model the spectral evolution of SN 1987A. The IR-catastrophe is seen in the
metal lines as a transition from thermal to non-thermal excitation, most
clearly in the [O I] 6300, 6364 lines. The distribution of the different zones,
and therefore the gamma-ray deposition, is determined from the line profiles of
the most important lines, where possible. We find the total mass of
hydrogen-rich gas to be ~7.7 Msun. The helium mass derived from the line fluxes
is sensitive to assumptions about the degree of redistribution in the line. The
mass of the helium dominated zone is consistent with ~1.9 Msun, with a further
~3.9 Msun of helium residing in the hydrogen component. Because of
uncertainties in the modeling of the non-thermal excitation of the [O I] lines,
the uncertainty in the oxygen mass is considerable. In addition, masses of
nitrogen, neon, magnesium, iron and nickel are estimated. The dominant
contribution to the line luminosity often originates in a different zone from
where most of the newly synthesized material resides. This applies to e.g.
carbon, calcium and iron. The [C I] lines, mainly arising in the helium zone,
indicate a substantially lower abundance of carbon mixed with helium than
stellar evolution models give, and a more extended zone with CNO processed gas
is indicated. The [Fe II] lines have in most phases a strong contribution from
primordial iron, and at t > 600 - 800 days this component dominates the [Fe II]
lines. The wings of the [Fe II] lines may therefore come from primordial iron,
rather than synthesized iron mixed to high velocity. Lines from ions with low
ionization potential indicate that the UV field below at least 1600 AA is
severely quenched by dust absorption and resonance scattering.",9712224v1
2001-07-09,Implications of O and Mg abundances in metal-poor halo stars for stellar iron yields,"Inhomogeneous chemical evolution models of galaxies which try to reproduce
the scatter seen in element-to-iron ratios of metal-poor halo stars are heavily
dependent on theoretical nucleosynthesis yields of core-collapse supernovae.
Hence inhomogeneous models present themselves as a test for stellar nucleosyn-
thesis calculations. Applying an inhomogeneous chemical evolution model to our
Galaxy reveals a number of shortcomings of existing theoretical nucleosynthesis
yields. One problem is the predicted scatter in [O/Fe] and [Mg/Fe] which is too
large compared to the one observed in metal-poor halo stars. This can be either
due to the O or Mg yields or due to the Fe yields (or both). However, O and Mg
are alpha-elements that are produced mainly during hydrostatic burning and thus
are not affected by the theoretical uncertainties afflicting the collapse and
explosion of a massive star. Stellar iron yields, on the other hand, depend
heavily on the choice of the mass-cut between ejecta and proto neutron star and
are therefore very uncertain. We present Fe yield distributions as function of
progenitor mass that are consistent with the abundance distribution of metal-
poor halo stars and are in agreement with observed Ni yields of SNe II with
known progenitor masses. The iron yields of lower-mass SNe II (in the range
10-20 Msol) are well constrained by those observations. Present observations,
however, do not allow to determine a unique solution for higher-mass SNe.
Nevertheless, the main dependence of the stellar iron yield as function of
progenitor mass may be derived and can be used as constraint for future
supernova/hypernova models. The results are of importance for the earliest
stages of galaxy formation when the ISM is dominated by chemical
inhomogeneities and the instantaneous mixing approximation is not valid.",0107153v2
2001-08-07,Heavy Element Diffusion in Metal Poor Stars,"Stellar evolution models which include the effect of helium and heavy element
diffusion have been calculated for initial iron abundances of [Fe/H] = -2.3,
-2.1, -1.9 and -1.7. These models were calculated for a large variety of masses
and three separate mixing lengths, \alpha = 1.50, 1.75 and 2.00 (with \alpha =
1.75 being the solar calibrated mixing length). The change in the surface iron
abundance for stars of different masses was determined for the ages 11, 13 and
15 Gyr. Iron settles out of the surface convection zone on the main sequence;
this iron is dredged back up when the convection zone deepens on the giant
branch. In all cases, the surface [Fe/H] abundance in the turn-off stars was at
least 0.28 dex lower than the surface [Fe/H] abundance in giant-branch stars of
the same age. However, recent high dispersion spectra of stars in the globular
cluster NGC 6397 found that the turn-off and giant branch stars had identical
(within a few percent) iron abundances of [Fe/H] =-2.03 (Gratton et al. 2001).
These observations prove that heavy element diffusion must be inhibited in the
surface layers of metal-poor stars. When diffusion is inhibited in the outer
layers of a stellar model, the predicted temperatures of the models are similar
to models evolved without diffusion, while the predicted lifetimes are similar
to stars in which diffusion is not inhibited. Isochrones constructed from the
models in which diffusion is inhibited fall half-way between isochrones without
diffusion, and isochrones with full diffusion. As a result, absolute globular
cluster ages which are based upon the absolute magnitude of the turn-off are 4%
larger than ages inferred from full diffusion isochrones, and 4% smaller than
ages inferred from no diffusion isochrones.",0108119v1
2002-06-18,Multi-wavelength study of the Seyfert 1 galaxy NGC 3783 with XMM-Newton,"We present the analysis of multi-wavelength XMM-Newton data from the Seyfert
galaxy NGC 3783, including UV imaging, X-ray and UV lightcurves, the 0.2-10 keV
X-ray continuum, the iron K-alpha emission line, and high-resolution
spectroscopy and modelling of the soft X-ray warm absorber. The 0.2-10 keV
spectral continuum can be well reproduced by a power-law at higher energies; we
detect a prominent Fe K-alpha emission line, with both broad and narrow
components, and a weaker emission line at 6.9 keV which is probably a
combination of Fe K-beta and Fe XXVI. We interpret the significant deficit of
counts in the soft X-ray region as being due to absorption by ionised gas in
the line of sight. This is demonstrated by the large number of narrow
absorption lines in the RGS spectrum from iron, oxygen, nitrogen, carbon, neon,
argon, magnesium, silicon and sulphur. The wide range of iron states present in
the spectrum enables us to deduce the ionisation structure of the absorbing
medium. We find that our spectrum contains evidence of absorption by at least
two phases of gas: a hotter phase containing plasma with a log ionisation
parameter xi (where xi is in erg cm/s) of 2.4 and greater, and a cooler phase
with log xi centred around 0.3. The gas in both phases is outflowing at speeds
of around 800 km/s. The main spectral signature of the cold phase is the
Unresolved Transition Array (UTA) of M-shell iron, which is the deepest yet
observed; its depth requires either that the abundance of iron, in the cold
phase, is several times that of oxygen, with respect to solar abundances, or
that the absorption lines associated with this phase are highly saturated. The
cold phase is associated with ionisation states that would also absorb in the
UV.",0206316v2
2003-01-29,The iron line in MCG-6-30-15 from XMM-Newton: evidence for gravitational light-bending?,"The lack of variability of the broad iron line seen in the Seyfert 1 galaxy
MCG-6-30-15 is studied using the EPIC pn data obtained from a 2001 observation
of 325 ks, during which the count rate from the source varied by a factor of 5.
The spectrum of 80 ks of data from when the source was bright, using the the
lowest 10 ks as background, is well fitted over the 3-10 keV band with a simple
power-law of photon index Gamma=2.11. The source spectrum can therefore be
decomposed into an approximately constant component, containing a strong iron
emission line, and a variable power law component. Assuming that the power-law
continuum extends down to 0.5 keV enables us to deduce the absorption acting on
the nucleus. A simple model involving Galactic absorption and 2 photoelectric
edges (at 0.72 and 0.86 keV) is adequate for the EPIC spectrum above 1 keV. It
still gives a fair representation of the spectrum at lower energies where
absorption lines, UTAs etc are expected. Applying the absorption model to the
low flux spectrum enables us to characterize it as reflection-dominated with
iron about 3 times Solar. Fitting this model, with an additional power-law
continuum, to 32 x 10 ks spectra of the whole observation reveals that Gamma
lies mostly between 2 and 2.3 and the normalization of the reflection-dominated
component varies by up to 25 per cent. The breadth of the iron line suggests
that most of the illumination originates from about 2 gravitational radii.
Gravitational light bending will be very strong there, causing the observed
continuum to be a strong function of the source height and much of the
continuum radiation to return to the disk. Together these effects can explain
the otherwise puzzling disconnectedness of the continuum and reflection
components of MCG-6-30-15.",0301588v1
2005-01-10,Massive elliptical galaxies in X-rays: the role of late gas accretion,"We present a new chemical evolution model meant to be a first step in the
self-consistent study of both optical and X-ray properties of elliptical
galaxies. Detailed cooling and heating processes in the interstellar medium are
taken into account using a mono-phase one-zone treatment which allows a more
reliable modelling of the galactic wind regime with respect to previous work.
The model successfully reproduces simultaneously the mass-metallicity,
colour-magnitude, the L_X - L_B and the L_X - T relations, as well as the
observed trend of the [Mg/Fe] ratio as a function of sigma, by adopting the
prescriptions of Pipino & Matteucci (2004) for the gas infall and star
formation timescales. We found that a late secondary accretion of gas from the
environment plays a fundamental role in driving the L_X - L_B and L_X - T
relations and can explain their large observational scatter. The iron
discrepancy, namely the too high predicted iron abundance in X-ray haloes of
ellipticals compared to observations, still persists. On the other hand, we
predict [O/Fe] in the ISM which is in good agreement with the most recent
observations. We suggest possible mechanisms acting on a galactic scale which
may solve the iron discrepancy. In particular, mixing of gas driven by AGNs may
preserve the gas mass (and thus the X-ray luminosity) while diluting the iron
abundance. New predictions for the amounts of iron, oxygen and energy ejected
into the intracluster medium (ICM) are presented and we conclude that Type Ia
supernovae (SNe Ia) play a fundamental role in the ICM enrichment. SNe Ia
activity, in fact, may power a galactic wind lasting for a considerable amount
of the galactic lifetime, even in the case for which the efficiency of energy
transfer into the ISM per SN Ia event is less than unity.",0501149v1
2005-02-17,Lifting the Iron Curtain : Toward an Understanding of the Iron Stars XX Oph and AS 325,"We present new optical, near infrared, and archival ultraviolet observations
of XX Ophiuchi and AS 325, two proposed iron stars. These unusual stars have
optical spectra dominated by emission lines arising from hydrogen as well as
ionized metals such as iron, chromium, and titanium. Both stars have been
classified as iron stars and a number of exotic models have been presented for
their origin. Using two years of moderately high resolution optical
spectroscopy, the first high signal-to-noise K-band spectroscopy of these
sources (which reveals stellar photospheric absorption lines), and new
near-infrared interferometric observations, we confirm that both systems are
composed of two stars, likely binaries, containing a hot Be star with an
evolved late-type secondary. The hydrogen emission features arise in the hot
wind from the Be star while the corresponding P-Cygni absorption lines are
produced from dense material in the expanding, radiation driven, wind around
each system. The optical FeII emission lines are pumped by ultraviolet FeII
absorption lines through fluorescence. Contrary to some claims in the
literature, the spectral features of XX Oph and AS 325 are quite similar,
evidence that they are comparable systems. We examine the variability of the
spectral morphology and radial velocity motions of both sources. We also study
the variability of XX Oph during a major photometric event and find that the
spectral nature of the system varies during the event. A comparison of the
velocity of the absorption line components in our new spectra with those in the
literature show that the structure of the stellar wind from XX Oph has changed
since the system was observed in 1951.",0502336v1
2005-03-24,High resolution X-ray spectrum of the accreting binary X-ray pulsar GX 1+4,"We present here high resolution X-ray spectrum of the accreting binary X-ray
pulsar GX 1+4 obtained with the High Energy Transmission Grating (HETG)
instrument of the Chandra X-ray Observatory. This was supplemented by a
simultaneous observation with the Proportional Counter Array (PCA) of the Rossi
X-ray Timing Explorer (RXTE). During this observation, the source was in a
somewhat low intensity state and the pulse profile with both Chandra and RXTE
shows a narrow dip, characteristic of GX 1+4 in medium and low intensity
states. The continuum X-ray spectrum obtained with the HETG and PCA can be
fitted well with a high energy cutoff power-law model with line of sight
absorption. Interestingly, we find that this low state is accompanied by a
relatively small absorption column density. A 6.4 keV narrow emission line with
an equivalent width of 70 eV is clearly detected in the HETG spectrum. The
fluorescence iron line, or at least part of it is produced in the neutral or
lowly ionized iron in the circumstellar material that also causes most of the
line of sight absorption. In the HETG spectrum, we have found evidence for a
weak (equivalent width ~30 eV) emission line at 6.95 keV. This line is
identified as Ly_alpha emission line from hydrogen-like iron and the spectrum
does not show emission lines from helium-like iron. We discuss various emission
regions for the hydrogen-like iron emission line, like gas diffused into the
Alfven sphere or an accretion curtain flowing from the inner accretion disk to
the magnetic poles.",0503530v1
2005-06-12,Chandra Observation of the Cluster of Galaxies MS 0839.9+2938 at z=0.194: the Central Excess Iron and SN Ia Enrichment,"We present the Chandra study of the intermediately distant cluster of
galaxies MS 0839.9+2938. By performing both the projected and deprojected
spectral analyses, we find that the gas temperature is approximately constant
at about 4 keV in 130-444h_70^-1 kpc. In the inner regions, the gas temperature
descends towards the center, reaching <~ 3 keV in the central 37h_70^-1 kpc.
This infers that the lower and upper limits of the mass deposit rate are 9-34
M_sun yr^-1 and 96-126 M_sun yr^-1, respectively within 74h_70^-1 kpc where the
gas is significantly colder. Along with the temperature drop, we detect a
significant inward iron abundance increase from about 0.4 solar in the outer
regions to about 1 solar within the central 37h_70^-1 kpc. Thus MS 0839.9+2938
is the cluster showing the most significant central iron excess at z>~ 0.2. We
argue that most of the excess iron should have been contributed by SNe Ia. By
utilizing the observed SN Ia rate and stellar mass loss rate, we estimate that
the time needed to enrich the central region with excess iron is 6.4-7.9 Gyr,
which is similar to those found for the nearby clusters. Coinciding with the
optical extension of the cD galaxy (up to about 30h_70^-1 kpc), the observed
X-ray surface brightness profile exhibits an excess beyond the distribution
expected by either the beta model or the NFW model, and can be well fitted with
an empirical two-beta model that leads to a relatively flatter mass profile in
the innermost region.",0506260v1
2005-07-13,XMM-Newton spectral properties of the Ultraluminous IRAS Galaxy Mrk 273,"We present a 23 ks XMM-Newton observation of the ULIRG Mrk 273. The hard
X-ray spectrum can be modeled by a highly absorbed power law plus an Fe Kalpha
emission line. The iron line is broad, suggesting possible superposition of a
neutral iron line at 6.4 keV, and a blend of ionized iron lines from Fe XXV and
Fe XXVI. Given the relatively short exposure, the three line components can not
be singularly resolved with high statistical significance: the neutral
component is detected at ~2.5sigma and the Fe XXV line at ~2sigma c.l., while
for the Fe XXVI line we can only estimate an upper limit. The broad band
spectrum requires, in addition to a highly absorbed power law, at least three
collisionally ionized plasma components, which may be associated with
star-forming regions. The temperatures of the three plasmas are about 0.3, 0.8
and 6 keV, where the highest of the three is sufficient to produce ionized iron
emission lines. An alternative interpretation for the origin of the soft
emission might also be given in terms of reflection off some photoionized gas,
as has been observed in a number of nearby Compton-thick Seyfert 2 galaxies. A
hot gas, photoionized by the primary, continuum can also produce ionized iron
lines. Unfortunately, given the limited statistics and the lack of high
resolution spectroscopy, it is not possible to distinguish between the two
models investigated. We further compare the XMM-Newton findings with the
Chandra data obtaining consistent spectral results. The absorption corrected
hard X-ray (2-10 keV) luminosity of Mrk 273 corresponds to ~0.2% of the far-IR
luminosity, similar to typical values found in pure starbursts. The thermal
contribution to the soft X-ray luminosity is ~0.2-0.7x10^42 erg s^-1,
comparable to those found in NGC 6240 and other starburst dominated ULIRGs.",0507321v1
2005-08-22,The Spin Periods and Rotational Profiles of Neutron Stars at Birth,"We present results from an extensive set of one- and two-dimensional
radiation-hydrodynamic simulations of the supernova core collapse, bounce, and
postbounce phases, and focus on the protoneutron star (PNS) spin periods and
rotational profiles as a function of initial iron core angular velocity, degree
of differential rotation, and progenitor mass. For the models considered, we
find a roughly linear mapping between initial iron core rotation rate and PNS
spin. The results indicate that the magnitude of the precollapse iron core
angular velocities is the single most important factor in determining the PNS
spin. Differences in progenitor mass and degree of differential rotation lead
only to small variations in the PNS rotational period and profile. Based on our
calculated PNS spins, at ~ 200-300 milliseconds after bounce, and assuming
angular momentum conservation, we estimate final neutron star rotation periods.
We find periods of one millisecond and shorter for initial central iron core
periods of below ~ 10 s. This is appreciably shorter than what previous studies
have predicted and is in disagreement with current observational data from
pulsar astronomy. After considering possible spindown mechanisms that could
lead to longer periods we conclude that there is no mechanism that can robustly
spin down a neutron star from ~ 1 ms periods to the ""injection"" periods of tens
to hundreds of milliseconds observed for young pulsars. Our results indicate
that, given current knowledge of the limitations of neutron star spindown
mechanisms, precollapse iron cores must rotate with periods around 50-100
seconds to form neutron stars with periods generically near those inferred for
the radio pulsar population.",0508462v2
2006-10-19,High-resolution ultraviolet spectroscopy of PG1159-035 with HST and FUSE,"PG1159-035 is the prototype of the PG1159 spectral class which consists of
extremely hot hydrogen-deficient (pre-) white dwarfs. It is also the prototype
of the GW Vir variables, which are non-radial g-mode pulsators. The study of
PG1159 stars reveals insight into stellar evolution and nucleosynthesis during
AGB and post-AGB phases. We perform a quantitative spectral analysis of
PG1159-035 focusing on the abundance determination of trace elements. We have
taken high-resolution ultraviolet spectra of PG1159-035 with the Hubble Space
Telescope and the Far Ultraviolet Spectroscopic Explorer. They are analysed
with non-LTE line blanketed model atmospheres. We confirm the high effective
temperature with high precision (Teff=140,000+/-5000 K) and the surface gravity
of logg=7. For the first time we assess the abundances of silicon, phosphorus,
sulfur, and iron. Silicon is about solar. For phosphorus we find an upper limit
of solar abundance. A surprisingly strong depletion of sulfur (2% solar) is
discovered. Iron is not detected, suggesting an upper limit of 30% solar. This
coincides with the Fe deficiency found in other PG1159 stars. We redetermine
the nitrogen abundance and find it to be lower by one dex compared to previous
analyses. The sulfur depletion is in contradiction with current models of AGB
star intershell nucleosynthesis. The iron deficiency confirms similar results
for other PG1159 stars and is explained by the conversion of iron into heavier
elements by n-capture in the s-processing environment of the precursor AGB
star. However, the extent of the iron depletion is stronger than predicted by
evolutionary models. The relatively low nitrogen abundance compared to other
pulsating PG1159 stars weakens the role of nitrogen as a distinctive feature of
pulsators and non-pulsators in the GW Vir instability strip.",0610592v2
2007-08-09,An XMM-Newton survey of broad iron lines in Seyfert galaxies,"We present an analysis of the X-ray spectra of a sample of 37 observations of
26 Seyfert galaxies observed by XMM-Newton in order to characterize their iron
K emission. All objects show evidence for iron line emission in the 6-7 keV
band. A narrow core at 6.4 keV is seen almost universally in the spectra, and
we model this using a neutral Compton reflection component, assumed to be
associated with distant, optically thick material such as the molecular torus.
Once this, and absorption by a zone of ionized gas in the line-of-sight is
accounted for, less than half of the sample observations show an acceptable
fit. Approximately 2/3 of the sample shows evidence for further, broadened
emission in the iron K-band. When modeled with a Gaussian, the inferred energy
is close to that expected for neutral iron, with a slight redshift, with an
average velocity width of ~0.1c. The mean parameters are consistent with
previous ASCA results and support the idea that the broad components can be
associated with the accretion disk. Before proceeding to that conclusion, we
test an alternative model comprising a blend of 3-4 narrow, unshifted emission
lines (including the 6.4 keV core), together with 1-2 zones of highly ionized
gas in the line-of-sight. Around 1/3 of the objects are not adequately fit by
this model, and in general better fits are obtained with a relativistic disk
line model, which has fewer free parameters. Nonetheless we find that
absorption by ionized gas affects the spectrum above 2.5 keV in approximately
half the sample. There is evidence for multiple ionized zones in at least 3
objects, but in all those cases a blurred reflector is required in addition to
the complex absorption. (truncated)",0708.1305v1
2008-09-30,Tools for Dissecting Supernova Remnants Observed with Chandra: Methods and Application to the Galactic Remnant W49B,"We introduce methods to quantify the X-ray morphologies of supernova remnants
observed with the Chandra X-ray Telescope. These include a power-ratio
technique to measure morphological asymmetries, correlation-length analysis to
probe chemical segregation and distribution, and wavelet-transform analysis to
quantify X-ray substructure. We demonstrate the utility and accuracy of these
techniques on relevant synthetic data. Additionally, we show the methods'
capabilities by applying them to the 55-ks Chandra ACIS observation of the
galactic supernova remnant W49B. We analyze the images of prominent emission
lines in W49B and use the results to discern physical properties. We find that
the iron morphology is very distinct from the other elements: it is
statistically more asymmetric, more segregated, and has 25% larger emitting
substructures than the lighter ions. Comparatively, the silicon, sulfur, argon,
and calcium are well-mixed, more isotropic, and have smaller, equally-sized
emitting substructures. Based on fits of XMM-Newton spectra in regions
identified as iron rich and iron poor, we determine that the iron in W49B must
have been anisotropically ejected. We measure the abundance ratios in many
regions, and we find that large, local variations are persistent throughout the
remnant. We compare the mean, global abundance ratios to those predicted by
spherical and bipolar core-collapse explosions; the results are consistent with
a bipolar origin from a 25 solar mass progenitor. We calculate the filling
factor of iron from the volume of its emitting substructures, enabling more
precise mass estimates than previous studies. Overall, this work is a first
step toward rigorously describing the physical properties of supernova remnants
for comparison within and between sources.",0810.0009v2
2009-04-21,A relativistically smeared spectrum in the neutron star X-ray Binary 4U 1705-44: Looking at the inner accretion disc with X-ray spectroscopy,"Iron emission lines at 6.4-6.97 keV, identified with fluorescent Kalpha
transitions, are among the strongest discrete features in the X-ray band. These
are therefore one of the most powerful probes to infer the properties of the
plasma in the innermost part of the accretion disc around a compact object. In
this paper we present a recent XMM observation of the X-ray burster 4U 1705-44,
where we clearly detect a relativistically smeared iron line at about 6.7 keV,
testifying with high statistical significance that the line profile is
distorted by high velocity motion in the accretion disc. As expected from disc
reflection models, we also find a significant absorption edge at about 8.3 keV;
this feature appears to be smeared, and is compatible with being produced in
the same region where the iron line is produced. From the line profile we
derive the physical parameters of the inner accretion disc with large
precision. The line is identified with the Kalpha transition of highly ionised
iron, Fe XXV, the inner disc radius is Rin = (14 \pm 2) R_g (where R_g is the
Gravitational radius, GM/c^2), the emissivity dependence from the disc radius
is r^{-2.27 \pm 0.08}, the inclination angle with respect to the line of sight
is i = (39 \pm 1) degrees. Finally, the XMM spectrum shows evidences of other
low-energy emission lines, which again appear broad and their profiles are
compatible with being produced in the same region where the iron line is
produced.",0904.3318v2
2009-06-08,"On the Non-relativistic Origin of Red-skewed Iron Lines in CV, Neutron Star and Black Hole Sources","We perform the analysis of the iron K_alpha lines detected in three sources
representing of three types of accreting compact sources: cataclysmic variable
(CV) GK Per, neutron star (NS) Serpens X-1 and black hole (BH) GX 339-4. We
find, using data from Epic-PN Camera on-board XMM-Newton observatory,that the
iron K_alpha emission line in GK Per has a noticeable red-skewed profile. We
compare the GK Per asymmetric line with the red-skewed lines observed by
XMM-Newton in Serpens X-1 and GX 339-4. The observation of the K_alpha emission
with red-skewed features in CV GK Per cannot be related to the redshift effects
of General Relativity (GR). Therefore, if the mechanism of the K_alpha-line
formation is the same in CVs, NSs and BHs then it is evident that the GR
effects would be ruled out as a cause of red skewness of K_alpha line. The line
reprocessing in an outflowing wind has been recently suggested an alternative
model for a broad red-shifted iron line formation. In the framework of the
outflow scenario the red-skewed iron line is formed in the strong extended wind
due to its illumination by the radiation emanating from the innermost part of
the accreting material. In this Paper we demonstrate that the asymmetric shapes
of the lines detected from these CV, NS and BH sources are well described with
the wind (outflow) model. While this fact is hard to reconcile with the
relativistic models, it is consistent with the outflowing gas washing out high
frequency modulations of the radiation presumably originated in the innermost
part of the source.",0906.1490v1
2010-01-13,X-ray spectral study of the hot gas in three Clusters of Galaxies,"We study the physical properties of three clusters of galaxies, selected from
a BeppoSAX Wide Field Camera (WFC) survey. These sources are identified as 1RXS
J153934.7-833535, 1RXS J160147.6-754507, and 1RXS J081232.3-571423 in the ROSAT
All-Sky Survey catalogue. We obtained XMM-Newton follow-up observations for
these three clusters. We fit single and multi-temperature models to spectra
obtained from the EPIC-pn camera to determine the temperature, the chemical
composition of the gas and their radial distribution. Since two observations
are contaminated by a high soft-proton background, we develop a new method to
estimate the effect of this background on the data. For the first time, we
present the temperature and iron abundance of two of these three clusters. The
iron abundance of 1RXS J153934.7-33535 decreases with radius. The fits to the
XMM-Newton and Chandra data show that the radial temperature profile within 3'
towards the centre either flattens or lowers. A Chandra image of the source
suggests the presence of X-ray cavities. The gas properties in 1RXS
J160147.6-754507 are consistent with a flat radial distribution of iron and
temperature within 2' from the centre. 1RXS J081232.3-571423 is a relatively
cool cluster with a temperature of about 3 keV. The radial temperature and iron
profiles suggest that 1RXS J153934.7-833535 is a cool core cluster. The Chandra
image shows substructure which points toward AGN feedback in the core. The flat
radial profiles of the temperature and iron abundance in 1RXS J160147.6-754507
are similar to the profiles of non-cool-core clusters.",1001.2222v2
2010-06-10,Rms variability properties of the iron K alpha line in Seyfert galaxies,"We present an analysis of the rms variability spectra of a sample of 18
observations of 14 Seyfert galaxies observed by XMM-Newton, which exhibit
sufficient variability and signal-to-noise ratio to examine the variations in
the iron K-band. The narrow core of the K alpha line at 6.4 keV, seen
universally in Seyferts, shows minimal evidence for variability and is always
less variable than the continuum, supporting an origin in distant material such
as the torus. At least half the observations do show evidence for variations in
the wider iron K-band, however, and in at least 5 cases the excess line
variations appear to be broad. The simplest prediction -- that the broad
emission line is as variable as the continuum -- is generally not confirmed as
only two observations show this type of behaviour. In four cases, the red wing
of the line is more variable than the power-law continuum and extends down to
energies of ~ 5 keV. Three observations show strong variability blueward of the
line core that could also be from the disk, but alternatively might be due to
emission or absorption by other hot or photoionised gas close to the nucleus.
In cases where this excess blue variability is present, it is not always seen
in the time-averaged spectrum. Six observations possess a broad iron line in
the time-averaged spectra but with an invariant red wing, and three of these
six show no variability across the entire iron line region. This suggests a
decoupling of the continuum and reflection component, perhaps due to light
bending or other anisotropic effects as has been suggested for MCG-6-30-15 and
other narrow-line Seyfert 1s. A key result is that the rms spectra of objects
such as NGC 3516 do not agree with complex absorption effects mimicking the
broad red wing.",1006.1982v1
2010-07-28,The Suzaku Hard X-ray Survey on the Galactic Center Region,"Diffuse X-rays from the Galactic center (GC) region were found to exhibit
many K-shell lines from iron and nickel atoms in the 6--9 keV band. The strong
emission lines seen in the spectrum are neutral iron K$\alpha$ at 6.4~keV,
He-like iron K$\alpha$ at 6.7~keV, H-like iron Ly$\alpha$ at 6.9~keV, and
He-like iron K$\beta$ at 7.8~keV. Among them, the 6.4~keV emission line is a
probe of non-thermal phenomena. We have detected strong 6.4~keV emission in
several giant molecular clouds, some of which were newly discovered by Suzaku.
All the spectra exhibit large equivalent widths of 1-2~keV and absorption
columns of $2-10\times 10^{23}\{\rm H\ cm}^{-2}$. We found time variability of
diffuse 6.4~keV emission in the Sgr B2 region comparing the maps and spectra
obtained from 1994 to 2005 with ASCA, Chandra, XMM-Newton and Suzaku. We also
report discovery of K$\alpha$ lines of neutral argon, calcium, chrome, and
manganese atoms in the Sgr~A region. We show that the equivalent width of the
6.4~keV emission line detected in X-ray faint region against the 6.4
keV-associated continuum (power-law component) is $\sim 800\ {\rm eV}$. These
features are naturally explained by the X-ray reflection nebula scenario rather
than the low energy cosmic-ray electrons scenario. On the other hand, a 6.4~keV
clump, G~0.162$-$0.217, discovered at the south end of the Radio Arc has a
small equivalent width of 6.4~keV emission line of $\sim200\ {\rm eV}$. The
Radio Arc is a site of relativistic electrons. Thus, it is conceivable that the
X-rays of G~0.162$-$0.217 are due to low energy cosmic-ray electrons",1007.4863v1
2011-01-25,Broad iron emission lines in Seyfert Galaxies - re-condensation of gas onto an inner disk below the ADAF,"Recent observations of Seyfert 1 AGN with Chandra, XMM-Newton and Suzaku
revealed broad iron K_alpha emission lines, some relativistically blurred. For
galactic black hole X-ray binaries XMM-Newton spectra during hard state also
reveal the presence of a relativistic iron emission line and a thermal
component, interpreted as an indication for a weak inner cool accretion disk
underneath a hot corona. These thermal components were found after the
transition from soft to hard spectral state and can be understood as sustained
by re-condensation of gas from an advection-dominated flow (ADAF) onto the
disk. In view of the similarity of accretion flows around stellar mass and
supermassive black holes we discuss whether the broad iron emission lines in
Seyfert 1 AGN can be understood as arising from a similar accretion flow
geometry. We derive Eddington-scaled accretion rates for Seyfert galaxies with
strong lines in samples of Miller (2007) and Nandra et al. (2007). For the
evaluation we use the observed X-ray luminosity, bolometric corrections and
black hole masses from literature, most values taken from Fabian and Vasudevan
(2009). Rates derived are less than 0.1 of the Eddington rate for more than
half of the sources. For 10^7 to 10^8 solar mass black holes in Seyfert 1 AGN
this limit corresponds to 0.01 to 0.2 solar masses per year. Our investigation
shows that for quite a number of Seyfert AGN in hard spectral state iron
emission lines can arise from an inner weak disk surrounded by an ADAF as
predicted by the re-condensation model. Some of the remaining sources with
higher accretion rates may be in a spectral state comparable to the ""very high""
state of LMXBs. (abridged)",1101.4854v1
2011-03-07,Modelling the high mass accretion rate spectra of GX 339-4: Black hole spin from reflection?,"We extract all the XMM-Newton EPIC pn burst mode spectra of GX 339-4,
together with simultaneous/contemporaneous RXTE data. These include three disc
dominated and two soft intermediate spectra, and the combination of broad
bandpass/moderate spectral resolution gives some of the best data on these
bright soft states in black hole binaries. The disc dominated spectra span a
factor three in luminosity, and all show that the disc emission is broader than
the simplest multicolour disc model. This is consistent with the expected
relativistic smearing and changing colour temperature correction produced by
atomic features in the newest disc models. However, these models do not match
the data at the 5 per cent level as the predicted atomic features are not
present in the data, perhaps indicating that irradiation is important even when
the high energy tail is weak. Whatever the reason, this means that the data
have smaller errors than the best physical disc models, forcing use of more
phenomenological models for the disc emission. We use these for the soft
intermediate state data, where previous analysis using a simple disc continuum
found an extremely broad residual, identified as the red wing of the iron line
from reflection around a highly spinning black hole. However, the iron line
energy is close to where the disc and tail have equal fluxes, so using a
broader disc continuum changes the residual 'iron line' profile dramatically.
With a broader disc continuum model, the inferred line is formed outside of 30
${\rm{R_g}}$, so cannot constrain black hole spin. We caution that a robust
determination of black hole spin from the iron line profile is very difficult
where the disc makes a significant contribution at the iron line energy i.e. in
most bright black hole states.",1103.1256v2
2011-06-13,Size of the group IVA iron meteorite core: Constraints from the age and composition of Muonionalusta,"The group IVA fractionally crystallized iron meteorites display a diverse
range of metallographic cooling rates. These have been attributed to their
formation in a metallic core, approximately 150 km in radius, that cooled to
crystallization in the absence of any appreciable insulating mantle. Here we
build upon this formation model by incorporating several new constraints. These
include (i) a recent U-Pb radiometric closure age of <2.5 Myr after solar
system formation for the group IVA iron Muonionalusta, (ii) new measurements
and modeling of highly siderophile element compositions for a suite of IVAs,
and (iii) consideration of the thermal effects of heating by the decay of the
short-lived radionuclide 60Fe. Our model for the thermal evolution of the IVA
core suggests that it was approximately 50 - 110 km in radius after being
collisionally exposed. This range is due to uncertainties in the initial
abundance of live 60Fe incorporated into the IVA core. Our models define a
relationship between cooling rate and closure age, which is used to make
several predictions that can be tested with future measurements. In general,
our results show that diverse cooling rates and early U-Pb closure ages can
only coexist on mantle-free bodies and that energy released by the decay of
60Fe reduces the core size necessary to produce diverse metallographic cooling
rates. The influence of 60Fe on cooling rates has largely been neglected in
previous core formation models; accounting for this heat source can affect size
estimates for other iron meteorite cores that cooled to crystallization in the
presence of live 60Fe. Candidates for such a scenario of early, mantle-free
formation include the iron IIAB, IIIAB and IVB groups.",1106.2479v1
2014-01-28,Electronic Evidence of an Insulator-Superconductor Transition in Single-Layer FeSe/SrTiO3 Films,"In high temperature cuprate superconductors, it is now generally agreed that
the parent compound is a Mott insulator and superconductivity is realized by
doping the antiferromagnetic Mott insulator. In the iron-based superconductors,
however, the parent compound is mostly antiferromagnetic metal, raising a
debate on whether an appropriate starting point should go with an itinerant
picture or a localized picture. It has been proposed theoretically that the
parent compound of the iron-based superconductors may be on the verge of a Mott
insulator, but so far no clear experimental evidence of doping-induced Mott
transition has been available. Here we report an electronic evidence of an
insulator-superconductor transition observed in the single-layer FeSe films
grown on the SrTiO3 substrate. By taking angle-resolved photoemission
measurements on the electronic structure and energy gap, we have identified a
clear evolution of an insulator to a superconductor with the increasing doping.
This observation represents the first example of an insulator-superconductor
transition via doping observed in the iron-based superconductors. It indicates
that the parent compound of the iron-based superconductors is in proximity of a
Mott insulator and strong electron correlation should be considered in
describing the iron-based superconductors.",1401.7115v1
2014-04-02,X-ray diagnostics of chemical composition of the accretion disk and donor star in UCXBs II: XMM-Newton observations,"We search for the Fe K${\alpha}$ line in spectra of Ultra Compact X-ray
Binaries (UCXBs). For this purpose we have analyzed XMM-Newton observations of
five confirmed UCXBs. We find that the object 2S 0918-549 - whose optical
spectrum bears tentative signatures of a C/O accretion disk - is devoid of any
emission features in the 6-7 keV range, with an upper limit of less than 10 eV
for the equivalent width (EW) of the iron line. 4U 1916-05 - whose optical
spectrum is consistent with reflection from a He-rich accretion disk - exhibits
a bright broad iron emission line. This behavior is in agreement with the
theoretical predictions presented in Koliopanos, Gilfanov and Bildsten (2013).
Namely, we expect strong suppression of the Fe K${\alpha}$ emission line in
spectra originating in moderately bright (LogLx less than $\approx$ 37.5) UCXBs
with C/O or O/Ne/Mg-rich donors. On the other hand the EW of the iron line in
spectra from UCXBs with He-rich donors is expected to retain its nominal value
of $\approx$ 100 eV. Our analysis also reveals a strong Fe K${\alpha}$ line in
the spectrum of 4U 0614+091. This detection points towards a He-rich donor and
seems to be at odds with the source's classification as C/O-rich. Nevertheless,
a He-rich donor would explain the bursting activity reported for this system.
Lastly, based on our theoretical predictions, we attribute the lack of a strong
iron emission line - in the two remaining UCXB sources in our sample (XTE
J1807-294, 4U 0513-40) - as an indication of a C/O or O/Ne/Mg white dwarf
donor. From the upper limits of the Fe K${\alpha}$ line EW in 4U 0513-40, 2S
0918-549 and XTE J1807-294 we obtain a lower limit on the oxygen-to-iron
ratio,O/Fe$\ge$ 10$\times$[O/Fe]$_{\odot}$.",1404.0617v2
2014-10-08,A metal-rich elongated structure in the core of the group NGC4325,"We used X-ray 2D spectrally resolved maps to resolve structure in temperature
and metal abundance. To perform stellar population analysis we applied the
spectral fitting technique with STARLIGHT to the optical spectrum of the
central galaxy. We simulated the chemical evolution of the central galaxy.
While the temperature, pseudo-pressure, and pseudo-entropy maps showed no
inhomogeneities, the iron spatial distribution shows a filamentary structure in
the core of this group, which is spatially correlated with the central galaxy,
suggesting a connection between the two. The analysis of the optical spectrum
of the central galaxy showed no contribution by any recent AGN activity. Using
the star formation history as input to chemical evolution models, we predicted
the iron and oxygen mass released by supernovae (SNe) winds in the central
galaxy up to the present time. Comparing the predicted amount of mass released
by the NGC4325 galaxy to the ones derived through X-ray analysis we conclude
that the winds from the central galaxy alone play a minor role in the IGM metal
enrichment of this group inside r2500. The SNe winds are responsible for no
more than 3% of it and of the iron mass and 21% of the oxygen mass enclosed
within r2500. Our results suggest that oxygen has been produced in the early
stages of the group formation, becoming well mixed and leading to an almost
flat profile. Instead, the iron distribution is centrally peaked, indicating
that this element is still being added to the IGM specifically in the core by
the SNIa. A possible scenario to explain the elongated iron-rich structure in
the core of the NGC4325 is a past AGN activity, in which our results suggest an
episode older than ~10^7-10^8 yrs and younger than 5x10^8.",1410.2294v2
2014-10-24,Magnetic order without tetragonal-symmetry-breaking in iron arsenides: microscopic mechanism and spin-wave spectrum,"Most iron-based superconductors undergo a transition to a magnetically
ordered state characterized by staggered stripes of parallel spins. With
ordering vectors $(\pi,0)$ or $(0,\pi)$, this magnetic state breaks the
high-temperature tetragonal symmetry of the system, which is manifested by a
splitting of the lattice Bragg peaks. Remarkably, recent experiments in
hole-doped iron arsenides reported an ordered state that displays magnetic
Bragg peaks at $(\pi,0)$ and $(0,\pi)$ but remains tetragonal. Despite being
inconsistent with a magnetic stripe configuration, this unusual magnetic phase
can be described in terms of a double-$\mathbf{Q}$ magnetic structure
consisting of an equal-weight superposition of the ordering vectors $(\pi,0)$
and $(0,\pi)$. Here we show that a non-collinear double-$\mathbf{Q}$ magnetic
configuration, dubbed \emph{orthomagnetic}, arises naturally within an
itinerant three-band microscopic model for the iron pnictides. In particular,
we find that strong deviations from perfect nesting and residual interactions
between the electron pockets favor the orthomagnetic over the stripe magnetic
state. Using an effective low-energy model, we also calculate the spin-wave
spectrum of the orthomagnetic state. In contrast to the stripe state, there are
three Goldstone modes, manifested in all diagonal and one off-diagonal
component of the spin-spin correlation function. The total magnetic structure
factor displays two anisotropic spin-wave branches emerging from both $(\pi,0)$
and $(0,\pi)$ momenta, in contrast to the case of domains of stripe order,
where only one spin-wave branch emerges from each momentum. We propose that
these unique features of the orthomagnetic state can be used to unambiguously
distinguish it from the stripe state via neutron scattering experiments, and
discuss the implications of its existence to the nature of the magnetism of the
iron arsenides.",1410.6789v2
2014-11-21,Relative Mobility of Human Transferrin Domains Accounts for Its Efficient Recognition and Recycling,"Human serum transferrin (hTf) transports ferric ions in the blood stream and
inflamed mucosal surfaces with high affinity and delivers them to cells via
receptor mediated endocytosis. A typical hTf is folded into two homologous
lobes; each lobe is further divided into two similar sized domains. Three
different crystal structures of hTf delineate large conformational changes
involved in iron binding/dissociation. However, whether the release process
follows the same trend at serum (~7.4) and endosomal (~5.6) pH remains
unanswered. The specialized role of the two lobes and if communication between
them leads to efficient and controlled release is also debated. Here, we study
the dynamics of the full structure as well as the separate lobes in different
closed, partially open, and open conformations under the nearly neutral pH
conditions in the blood serum and the more acidic one in the endosome. The
results corroborate experimental observations and underscore the distinguishing
effect of pH on the dynamics of hTf. Furthermore, in a total of 2 {\mu}s
molecular dynamics simulation of different forms of hTf, residue fluctuations
elucidate the cross talk between the two lobes correlated by the peptide linker
bridging the two lobes at serum pH, while their correlated motions is lost
under endosomal conditions. At serum pH, the presence of even a single iron on
either lobe leads C-lobe fluctuations to subside, making it the target for
recognition by human cells or hostile bacteria seeking iron sequestration. The
N-lobe, on the other hand, has a propensity to open, making iron readily
available when needed at regions of serum pH. At endosomal pH, both lobes
readily open, making irons available for delivery. The interplay between the
relative mobility of the lobes renders efficient mechanism for the recognition
and release of hTf at the cell surface, and therefore its recycling in the
organism.",1411.5954v1
2014-12-01,Magnetised accretion discs in Kerr spacetimes,"We study the effect caused by external magnetic fields on the observed
thermal spectra and iron line profiles of thin accretion discs formed around
Kerr black holes and naked singularities. We aim to provide a tool that can be
used to estimate the presence of magnetic fields in the neighbourhood of a
compact object and to probe the cosmic censorship conjecture in these
particular astrophysical environments. We developed a numerical scheme able to
calculate thermal spectra of magnetised Page-Thorne accretion discs formed
around rotating black holes and naked singularities as seen by an arbitrary
distant observer. We incorporated two different magnetic field configurations:
uniform and dipolar, using a perturbative scheme in the coupling constant
between matter and magnetic field strength. Under the same assumptions, we
obtained observed synthetic line profiles of the 6.4 keV fluorescent iron line.
We show that an external magnetic field produces potentially observable
modifications on the thermal energy spectrum and the fluorescent iron line
profile. Thermal energy spectra of naked singularities are harder and brighter
than those from black holes, and in addition, peak and cut-off energies are
affected by the external magnetic field. Moreover, iron line profiles of slowly
rotating black holes suffer more changes by a uniform magnetic field, while
nearly extremal black holes and naked singularities are more altered in the
dipolar case. Based on our calculations, we discard the possibility of
modelling the archetypal black-hole candidate in Cygnus X-1 as a naked
singularity. Comparison of our models with observational data can be used to
probe the cosmic censorship conjecture and to estimate the existence and global
geometry of magnetic fields around compact objects by fitting the thermal
energy spectra and iron line profiles of X-ray binaries.",1412.0557v1
2015-05-15,Orbital selectivity and emergent superconducting state from quasi-degenerate $s-$ and $d-$wave pairing channels in iron-based superconductors,"A major puzzle about the nature of the iron-based superconductivity appears
in the case of the alkaline iron selenides. Compared to the iron pnictides,
these systems have only electron Fermi pockets (i.e. no hole Fermi pockets) but
comparable superconducting transition temperatures. The challenge lies in
reconciling the two basic experimental features of their superconducting state:
a node-less gap and the existence of a resonance in the spin excitation
spectrum. We propose a mechanism based on reconstructing two quasi-degenerate
pairing states, one in an $s$-wave $A_{1g}$ channel that is fully gapped, and
the other in a $d$-wave $B_{1g}$ channel whose pairing function changes sign
across the electron Fermi pockets at the Brillouin-zone boundary. The resulting
intermediate pairing state, which we call an orbital-selective $s \times
\tau_3$ state, incorporates both of the above two properties. When the leading
spin-singlet pairing is in the $d_{xz}, d_{yz}$ orbital subspace, this state
retains the $s$-wave form factor but has a $B_{1g}$ symmetry due to an internal
$\tau_3$ structure in the orbital space. Within a five-orbital $t-J_{1}-J_{2}$
model with orbital-selective exchange couplings, we show that the proposed
pairing state is energetically competitive over a finite range of control
parameters. We calculate the dynamical spin susceptibility in the
orbital-selective $s \times \tau_3$ superconducting state and show that a spin
resonance arises and has the characteristics of observed by inelastic neutron
experiments in the alkaline iron selenides. More generally, the formation of
the orbital-selective $s \times \tau_3$ state represents a novel means of
relieving the quasi-degeneracy between $s-$ and $d-$wave pairing states, which
is a hitherto unsuspected alternative to the conventional route of linearly
superposing the two into a time-reversal symmetry breaking $s+id$ state.",1505.04170v1
2015-10-21,On the neutron-capture elements across the Galactic thin disk using Cepheids,"We present new accurate abundances for five neutron-capture (Y, La, Ce, Nd,
Eu) elements in 73 classical Cepheids located across the Galactic thin disk.
Individual abundances are based on high spectral resolution (R ~ 38,000) and
high signal-to-noise ratio (S/N ~ 50-300) spectra collected with UVES at ESO
VLT for the DIONYSOS project. Taking account for similar Cepheid abundances
provided either by our group (111 stars) or available in the literature, we end
up with a sample of 435 Cepheids covering a broad range in iron abundances
(-1.6 < [Fe/H] < 0.6). We found, using homogeneous individual distances and
abundance scales, well defined gradients for the above elements. However, the
slope of the light s-process element (Y) is at least a factor of two steeper
than the slopes of heavy s- (La, Ce, Nd) and r- (Eu) process elements. The s to
r abundance ratio ([La/Eu]) of Cepheids shows a well defined anticorrelation
with of both Eu and Fe. On the other hand, Galactic field stars attain an
almost constant value and only when they approach solar iron abundance display
a mild enhancement in La. The [Y/Eu] ratio shows a mild evidence of a
correlation with Eu and, in particular, with iron abundance for field Galactic
stars. We also investigated the s-process index - [hs/ls] - and we found a well
defined anticorrelation, as expected, between [La/Y] and iron abundance.
Moreover, we found a strong correlation between [La/Y] and [La/Fe] and, in
particular, a clear separation between Galactic and Sagittarius red giants.
Finally, the comparison between predictions for low-mass asymptotic giant
branch stars and the observed [La/Y] ratio indicate a very good agreement over
the entire metallicity range covered by Cepheids. However, the observed spread,
at fixed iron content, is larger than predicted by current models.",1510.06314v1
2015-10-28,NIR spectroscopy of the Sun and HD20010 - Compiling a new linelist in the NIR,"Context: Effective temperature, surface gravity, and metallicity are basic
spectroscopic stellar parameters necessary to characterize a star or a
planetary system. Reliable atmospheric parameters for FGK stars have been
obtained mostly from methods that relay on high resolution and high
signal-to-noise optical spectroscopy. The advent of a new generation of high
resolution near-IR spectrographs opens the possibility of using classic
spectroscopic methods with high resolution and high signal-to-noise in the NIR
spectral window. Aims: We aim to compile a new iron line list in the NIR from a
solar spectrum to derive precise stellar atmospheric parameters, comparable to
the ones already obtained from high resolution optical spectra. The spectral
range covers 10 000 {\AA} to 25 000 {\AA}, which is equivalent to the Y, J, H,
and K bands. Methods: Our spectroscopic analysis is based on the iron
excitation and ionization balance done in LTE. We use a high resolution and
high signal-to-noise ratio spectrum of the Sun from the Kitt Peak telescope as
a starting point to compile the iron line list. The oscillator strengths (log
gf) of the iron lines were calibrated for the Sun. The abundance analysis was
done using the MOOG code after measuring equivalent widths of 357 solar iron
lines. Results: We successfully derived stellar atmospheric parameters for the
Sun. Furthermore, we analysed HD20010, a F8IV star, from which we derived
stellar atmospheric parameters using the same line list as for the Sun. The
spectrum was obtained from the CRIRES- POP database. The results are compatible
with the ones found in the literature, confirming the reliability of our line
list. However, due to the quality of the data we obtain large errors.",1510.08273v1
2016-07-04,NaFe$_{0.56}$Cu$_{0.44}$As: A pnictide insulating phase induced by on-site Coulomb interaction,"In the studies of iron-pnictides, a key question is whether their bad-metal
state from which the superconductivity emerges lies in close proximity with a
magnetically ordered insulating phase. Recently it was found that at low
temperatures, the heavily Cu-doped NaFe$_{1-x}$Cu$_x$As ($x > 0.3$)
iron-pnictide is an insulator with long-range antiferromagnetic order, similar
to the parent compound of cuprates but distinct from all other iron-pnictides.
Using angle-resolved photoemission spectroscopy, we determined the
momentum-resolved electronic structure of NaFe$_{1-x}$Cu$_x$As ($x = 0.44$) and
identified that its ground state is a narrow-gap insulator. Combining the
experimental results with density functional theory (DFT) and DFT+U
calculations, our analysis reveals that the on-site Coulombic (Hubbard) and
Hund's coupling energies play crucial roles in formation of the band gap about
the chemical potential. We propose that at finite temperatures charge carriers
are thermally excited from the Cu-As-like valence band into the conduction
band, which is of Fe $3d$-like character. With increasing temperature, the
number of electrons in the conduction band becomes larger and the hopping
energy between Fe sites increases, and finally the long-range antiferromagnetic
order is destroyed at $T > T_\mathrm{N}$. Our study provides a basis for
investigating the evolution of the electronic structure of a Mott insulator
transforming into a bad metallic phase, and eventually forming a
superconducting state in iron-pnictidesa superconducting state in
iron-pnictides.",1607.00770v1
2016-07-19,Detecting supernova neutrinos with iron and lead detectors,"Supernova (SN) neutrinos can excite the nuclei of various detector materials
beyond their neutron emission thresholds through charged current (CC) and
neutral current (NC) interactions. The emitted neutrons, if detected, can be a
signal for the supernova event. Here we present the results of our study of SN
neutrino detection through the neutron channel in lead ($^{208} {\rm Pb}$) and
iron ($^{56} {\rm Fe}$) detectors for realistic neutrino fluxes and energies
given by the recent Basel/Darmstadt simulations for a 18 solar mass progenitor
SN at a distance of 10 kpc. We find that, in general, the number of neutrons
emitted per kTon of detector material for the neutrino luminosities and average
energies of the different neutrino species as given by the Basel/Darmstadt
simulations are significantly lower than those estimated in previous studies
based on the results of earlier SN simulations. At the same time, we highlight
the fact that, although the total number of neutrons produced per kTon in a
iron detector is more than an order of magnitude lower than that for lead, the
dominance of the flavor blind NC events in the case of iron, as opposed to
dominance of $\nu_e$ induced CC events in the case of lead, offers a
complementarity between the two detector materials so that simultaneous
detection of SN neutrinos in a lead and a sufficiently large iron detector
suitably instrumented for neutron detection may allow estimating the fraction
of the total $\mu$ and $\tau$ flavored neutrinos in the SN neutrino flux and
thereby probing the emission mechanism as well as flavor oscillation scenarios
of the SN neutrinos.",1607.05591v2
2016-09-13,A new galactic chemical evolution model with dust: results for dwarf irregular galaxies and DLA systems,"We present a galactic chemical evolution model which adopts updated
prescriptions for all the main processes governing the dust cycle. We follow in
detail the evolution of the abundances of several chemical species (C, O, S,
Si, Fe and Zn) in the gas and dust of a typical dwarf irregular galaxy. The
dwarf irregular galaxy is assumed to evolve with a low but continuous level of
star formation and experience galactic winds triggered by supernova explosions.
We predict the evolution of the gas to dust ratio in such a galaxy and discuss
critically the main processes involving dust, such as dust production by AGB
stars and Type II SNe, destruction and accretion (gas condensation in clouds).
We then apply our model to Damped Lyman-Alpha systems which are believed to be
dwarf irregulars, as witnessed by their abundance patterns. Our main
conclusions are: i) we can reproduce the observed gas to dust ratio in dwarf
galaxies. ii) We find that the process of dust accretion plays a fundamental
role in the evolution of dust and in certain cases it becomes the dominant
process in the dust cycle. On the other hand, dust destruction seems to be a
negligible process in irregulars. iii) Concerning Damped Lyman-Alpha systems,
we show that the observed gas-phase abundances of silicon, normalized to
volatile elements (zinc and sulfur), are in agreement with our model. iv) The
abundances of iron and silicon in DLA systems suggest that the two elements
undergo a different history of dust formation and evolution. Our work casts
light on the nature of iron-rich dust: the observed depletion pattern of iron
is well reproduced only when an additional source of iron dust is considered.
Here we explore the possibility of a contribution from Type Ia SNe as well as
an efficient accretion of iron nano-particles.",1609.03833v1
2017-03-08,"Pressure-driven phase transition from antiferromagnetic semiconductor to nonmagnetic metal in two-leg ladders $A$Fe$_2$$X$$_3$ ($A$=Ba or K, $X$=S or Se)","The recent discovery of superconductivity in BaFe$_2$S$_3$ [Takahashi {\it et
al.}, Nat. Mater. {\bf 14}, 1008 (2015)] has stimulated considerable interest
in 123-type iron chalcogenides. This material is the first reported iron-based
two-leg ladder superconductor, as opposed to the prevailing two-dimensional
layered structures of the iron superconductors family. Once the hydrostatic
pressure exceeds $11$ GPa, BaFe$_2$S$_3$ changes from a semiconductor to a
superconductor below $24$~K. Although previous calculations correctly explained
its ground state magnetic state and electronic structure, the pressure induced
phase transition was not successfully reproduced. In this work, our first
principles calculations find that with increasing pressure the lattice
constants as well as local magnetic moments are gradually suppressed, followed
by a first-order magnetic transition at a critical pressure, with local
magnetic moments dropping to zero suddenly. Our calculations suggests that the
self-doping caused by electrons transferred from S to Fe may play a key role in
this transition. The development of a nonmagnetic metallic phase at high
pressure may pave the way to superconductivity. As extensions of this effort,
two other 123-type iron chalcogenides, KFe$_2$S$_3$ and KFe$_2$Se$_3$, have
also been investigated. KFe$_2$S$_3$ also displays a first-order transition
with increasing pressure, but KFe$_2$Se$_3$ shows instead a second-order, or
weakly first-order, transition. The required pressures for KFe$_2$S$_3$ and
KFe$_2$Se$_3$ to quench the magnetism are higher than for BaFe$_2$S$_3$.
Further experiments can confirm the predicted first-order nature of the
transition in BaFe$_2$S$_3$ and KFe$_2$S$_3$, as well as the possible
metallic/superconductivity state in other 123-type iron chalcogenides under
high pressure.",1703.03071v1
2017-03-13,"Star formation, supernovae, iron, and alpha: consistent cosmic and Galactic histories","Recent versions of the observed cosmic star-formation history (SFH) have
resolved an inconsistency with the stellar mass density history. We show that
the revised SFH also scales up the delay-time distribution (DTD) of Type Ia
supernovae (SNe Ia), as determined from the observed volumetric SN Ia rate
history, aligning it with other field-galaxy SN Ia DTD measurements. The
revised-SFH-based DTD has a $t^{-1.1 \pm 0.1}$ form and a
Hubble-time-integrated production efficiency of $N/M_\star=1.3\pm0.1$ SNe Ia
per $1000~{\rm M_\odot}$ of formed stellar mass. Using these revised histories
and updated empirical iron yields of the various SN types, we re-derive the
cosmic iron accumulation history. Core-collapse SNe and SNe Ia have contributed
about equally to the total mass of iron in the Universe today. We find the
track of the average cosmic gas element in the [$\alpha$/Fe] vs. [Fe/H]
abundance-ratio plane. The track is broadly similar to the observed main locus
of Galactic stars in this plane, indicating a Milky Way (MW) SFH similar in
form to the cosmic one. We easily find a simple MW SFH that makes the track
closely match this stellar locus. Galaxy clusters appear to have a
higher-normalization DTD. This cluster DTD, combined with a short-burst MW SFH
peaked at $z=3$, produces a track that matches remarkably well the observed
""high-$\alpha$"" locus of MW stars, suggesting the halo/thick-disk population
has had a galaxy-cluster-like formation mode. Thus, a simple two-component SFH,
combined with empirical DTDs and SN iron yields, suffices to closely reproduce
the MW's stellar abundance patterns.",1703.04540v5
2017-04-18,Ejection of iron-bearing giant-impact fragments and the dynamical and geochemical influence of the fragment re-accretion,"The Earth was born in violence. Many giant collisions of protoplanets are
thought to have occurred during the terrestrial planet formation. Here we
investigated the giant impact stage by using a hybrid code that consistently
deals with the orbital evolution of protoplanets around the Sun and the details
of processes during giant impacts between two protoplanets. A significant
amount of materials (up to several tens of percent of the total mass of the
protoplanets) is ejected by giant impacts. We call these ejected fragments the
giant-impact fragments (GIFs). In some of the erosive hit-and-run and
high-velocity collisions, metallic iron is also ejected, which comes from the
colliding protoplanets' cores. From ten numerical simulations for the giant
impact stage, we found that the mass fraction of metallic iron in GIFs ranges
from ~ 1wt% to ~ 25wt%. We also discussed the effects of the GIFs on the
dynamical and geochemical characteristics of formed terrestrial planets. We
found that the GIFs have the potential to solve the following dynamical and
geochemical conflicts: (1) The Earth, currently in a near circular orbit, is
likely to have had a highly eccentric orbit during the giant impact stage. The
GIFs are large enough in total mass to lower the eccentricity of the Earth to
its current value via their dynamical friction. (2) The concentrations of
highly siderophile elements (HSEs) in the Earth's mantle are greater than what
was predicted experimentally. Re-accretion of the iron-bearing GIFs onto the
Earth can contribute to the excess of HSEs. In addition, the estimated amount
of iron-bearing GIFs provides significant reducing agent that could transform
primitive CO2-H2O atmosphere and ocean into more reducing H2-bearing
atmosphere. Thus, GIFs are important for the origin of Earth's life and its
early evolution.",1704.05251v1
2018-01-08,"Search for trans-iron elements in hot, helium-rich white dwarfs with the HST Cosmic Origins Spectrograph","The metal abundances in the atmospheres of hot white dwarfs (WDs) entering
the cooling sequence are determined by the preceding Asymptotic Giant Branch
(AGB) evolutionary phase and, subsequently, by the onset of gravitational
settling and radiative levitation. In this paper, we investigate three hot
He-rich WDs, which are believed to result from a late He-shell flash. During
such a flash, the He-rich intershell matter is dredged up and dominates the
surface chemistry. Hence, in contrast to the usual H-rich WDs, their spectra
allow direct access to s-process element abundances in the intershell that were
synthesized during the AGB stage. In order to look for trans-iron group
elements (atomic number Z>29), we performed a non-local thermodynamic
equilibrium model atmosphere analysis of new ultraviolet spectra taken with the
Cosmic Origins Spectrograph aboard the Hubble Space Telescope. One of our
program stars is of PG1159 spectral type; this star, PG1707+427, has effective
temperature Teff=85,000 K, and surface gravity logg=7.5. The two other stars
are DO white dwarfs: WD0111+002 has Teff=58,000 K and logg=7.7, and PG0109+111
has Teff=70,000 K and logg=8.0. These stars trace the onset of element
diffusion during early WD evolution. While zinc is the only trans-iron element
we could detect in the PG1159 star, both DOs exhibit lines from Zn, Ga, Ge, Se;
one additionally exhibits lines from Sr, Sn, Te, and I and the other from As.
Generally, the trans-iron elements are very abundant in the DOs, meaning that
radiative levitation must be acting. Most extreme is the almost six orders of
magnitude oversolar abundance of tellurium in PG0109+111. In terms of mass
fraction, it is the most abundant metal in the atmosphere. The two DOs join the
hitherto unique hot DO RE0503-289, in which 14 trans-iron elements had even
been identified.",1801.02414v1
2018-01-11,TOPoS: IV. Chemical abundances from high-resolution observations of seven EMP stars,"Extremely metal-poor stars provide us with indirect information on the first
generations of massive stars. The TOPoS survey has been designed to increase
the census of these stars and to provide a chemical inventory that is as
detailed as possible. Seven of the most iron-poor stars have been observed with
the UVES spectrograph at the ESO VLT Kueyen 8.2m telescope to refine their
chemical composition. We analysed the spectra based on 1D LTE model
atmospheres, but also used 3D hydrodynamical simulations of stellar
atmospheres. We measured carbon in six of the seven stars: all are
carbon-enhanced and belong to the low-carbon band, defined in the TOPoS II
paper. We measured lithium (A(Li)=1.9) in the most iron-poor star (SDSS
J1035+0641, [Fe/H] < -5.2 ). We were also able to measure Li in three stars at
[Fe/H]~ -4.0, two of which lie on the Spite plateau. We confirm that SDSS
J1349+1407 is extremely rich in Mg, but not in Ca. It is also very rich in Na.
Several of our stars are characterised by low alpha-to-iron ratios. The lack of
high-carbon band stars at low metallicity can be understood in terms of
evolutionary timescales of binary systems. The detection of Li in SDSS
J1035+0641 places a strong constraint on theories that aim at solving the
cosmological lithium problem. The Li abundance of the two warmer stars at
[Fe/H]~ -4.0 places them on the Spite plateau, while the third, cooler star,
lies below. We argue that this suggests that the temperature at which Li
depletion begins increases with decreasing [Fe/H]. SDSS J1349+1407 may belong
to a class of Mg-rich EMP stars. We cannot assess if there is a scatter in
alpha-to-iron ratios among the EMP stars or if there are several discrete
populations. However, the existence of stars with low alpha-to-iron ratios is
supported by our observations.",1801.03935v1
2018-05-26,A new ab initio equation of state of hcp-Fe and its implication on the interior structure and mass-radius relations of rocky super-Earths,"More than a third of all exoplanets can be classified as super-Earths based
on radius (1-2 $R_{\bigoplus}$) and mass (< 10 $M_{\bigoplus}$). Here we model
mass-radius relations based on silicate mantle and iron core equations of state
to infer to first order the structure and composition range of rocky
super-Earths assuming insignificant gas envelopes. We develop a new equation of
state of hexagonal close packed (hcp) iron for super-Earth conditions (SEOS)
based on density functional theory results for pressures up to 137~TPa. A
comparison of SEOS and extrapolated equations of state for iron from the
literature reveals differences in density of up to 4% at 1~TPa and up to 20% at
10~TPa. Such density differences change the derived mass by up to 10\% for
Earth-like super-Earths (core radius fraction of 0.5) and 20% for Mercury-like
super-Earths (core radius fraction of 0.8). We find that the effect of
temperature on mass (< 5%) is smaller than that resulting from the
extrapolation of the equations of state of iron and lower mantle temperatures
are too low to allow for rock and iron miscibility for R<1.75 $R_{\bigoplus}$.
We find that modeling uncertainties dominate over observational uncertainties
for many observed super-Earths. We illustrate these uncertainties explicitly
for Kepler-36b with well-constrained mass and radius. Assuming a core
composition of 0.8$\rho$ Fe (equivalent to 50 mol% S) instead of pure Fe leads
to an increase of the core radius fraction from 0.53 to 0.64. Using a mantle
composition of Mg$_{0.5}$Fe$_{0.5}$SiO$_3$ instead of MgSiO$_3$ leads to a
decrease of the core radius fraction to 0.33. Effects of thermal structure and
the choice of equation of state for the core material on the core radius of
Kepler-36b are small but non-negligible, reaching 2% and 5%, respectively.",1805.10530v1
2018-09-11,Chemical analysis of NGC 6528: one of the most metal-rich bulge globular cluster,"The Bulge Globular Clusters (GCs) are key tracers of this central ancient
component of our Galaxy. It is essential to understand their formation and
evolution to study that of the bulge, as well as their relationship with the
other Galactic GC systems (halo and disk GCs). Our main goals are to obtain
detailed abundances for a sample of seven red giant members of NGC 6528 in
order to characterize its chemical composition and study the relationship of
this GC with the bulge, and with other bulge, halo and disk GCs. Moreover, we
analyze this cluster$'$s behavior associated with the Multiple Populations
(MPs) phenomenon. We obtained the stellar parameters and chemical abundances of
light elements (Na, Al), iron-peak elements (V, Cr, Mn, Fe, Co, Ni, Cu),
{\alpha}-elements (O, Mg, Si, Ca, Ti) and heavy elements (Zr, Ba, Eu) in seven
red giant members of NGC 6528 using high resolution spectroscopy from
FLAMES-UVES. We obtained in six stars of our sample a mean iron content of
[Fe/H]=-0.14+/-0.03 dex, in good agreement with other studies. We found no
significant internal iron spread. We detected one candidate variable star,
which was excluded from the mean in iron content, we derived a metallicity in
this star of [Fe/H]=-0.55+/-0.04 dex. Moreover, we found no extended O-Na
anticorrelation but instead only an intrinsic Na spread. In addition, NGC 6528
does not exhibit a Mg-Al anticorrelation, and no significant spread in either
Mg or Al. The {\alpha} and iron-peak elements show good agreement with the
bulge field star trend. The heavy elements are slightly dominated by the
r-process. The chemical analysis suggests an origin and evolution similar to
that of typical old Bulge field stars. Finally, we find remarkable agreement in
the chemical patterns of NGC 6528 and another bulge GC, NGC 6553, suggesting a
similar origin and evolution.",1809.04164v1
2019-02-14,Quantum magnetic imaging of iron biomineralisation in teeth of the chiton Acanthopleura hirtosa,"Iron biomineralisation is critical for life. Nature capitalises on the
physical attributes of iron biominerals for a variety of functional, structural
and sensory applications. Although magnetism is an integral property of iron
biominerals, the role it plays in their nano-assembly remains a fundamental,
unanswered question. This is well exemplified by the magnetite-bearing radula
of chitons. Chitons, a class of marine mollusc, create the hardest biomineral
of any animal in their abrasion-resistant, self-sharpening teeth4. Despite this
system being subjected to a range of high resolution imaging studies, the
mechanisms that drive mineral assembly remain unresolved. However, the advent
of quantum imaging technology provides a new avenue to probe magnetic
structures directly. Here we use quantum magnetic microscopy, based on
nitrogen-vacancy centres in diamond, to attain the first subcellular magnetic
profiling of a eukaryotic system. Using complementary magnetic imaging
protocols, we spatially map the principal mineral phases (ferrihydrite and
magnetite) in the developing teeth of Acanthopleura hirtosa with submicron
resolution. The images reveal previously undiscovered long-range magnetic
order, established at the onset of magnetite mineralisation. This is in
contrast to electron microscopy studies that show no strong common
crystallographic orientation. The quantum-based magnetic profiling techniques
presented in this work have broad application in biology, earth science,
chemistry and materials engineering and can be applied across the range of
systems for which iron is vital.",1902.09637v2
2019-09-18,Electronic correlations in dense iron: from moderate pressure to Earth's core conditions,"We discuss the role of dynamical many-electron effects in the physics of iron
and iron-rich solid alloys under applied pressure on the basis of recent ab
initio studies employing the dynamical mean-field theory (DMFT). Electronic
correlations in iron in the moderate pressure range up to 60 GPa are discussed
in the first section. DMFT-based methods predict an enhancement of electronic
correlations at the pressure-induced transition from body-centered cubic (bcc)
alpha-Fe to hexagonal close-packed (hcp) epsilon-Fe. In particular, the
electronic effective mass, scattering rate and electron-electron contribution
to the electrical resistivity undergo a step-wise increase at the transition
point. One also finds a significant many-body correction to the epsilon-Fe
equation of state, thus clarifying the origin of discrepancies between previous
DFT studies and experiment. An electronic topological transition is predicted
to be induced in epsilon-Fe by many-electron effects; its experimental
signatures are analyzed. Next section focuses on the geophysically relevant
pressure-temperature regime of the Earth's inner core (EIC) corresponding to
the extreme pressure of 360 GPa combined with temperatures up to 6000 K. The
three iron allotropes (bcc, hcp and face-centered-cubic) previously proposed as
possible stable phases at such conditions are found to exhibit qualitatively
different many-electron effects as evidenced by a strongly non-Fermi-liquid
metallic state of bcc-Fe and an almost perfect Fermi liquid in the case of
hcp-Fe. A recent active discussion on the electronic state and transport
properties of hcp-Fe at the EIC conditions is reviewed in details. We also
discuss the impact of a Ni admixture, which is expected to be present in the
core matter. We conclude by outlining some limitation of the present DMFT-based
framework and perspective directions for further development.",1909.08482v1
2021-01-11,"Iron Mobility During Diagenesis at Vera Rubin Ridge, Gale Crater, Mars","The Curiosity rover investigated a topographic structure known as Vera Rubin
ridge, associated with a hematite signature in orbital spectra. There,
Curiosity encountered mudstones interpreted as lacustrine deposits, in
continuity with the 300 m-thick underlying sedimentary rocks of the Murray
formation at the base of Mount Sharp. While the presence of hematite
($\alpha$-Fe2O3) was confirmed insitu by both Mastcam and ChemCam spectral
observations and by the CheMin instrument, neither ChemCam nor APXS observed
any significant increase in FeO$_T$ (total iron oxide) abundances compared to
the Murray formation. Instead, Curiosity discovered dark-toned diagenetic
features displaying anomalously high FeO$_T$ abundances, commonly observed in
association with light-toned Ca-sulfate veins but also as crystal pseudomorphs
in the host rock. These iron-rich diagenetic features are predominantly
observed in ""grey"" outcrops on the upper part of the ridge, which lack the
telltale ferric signature of other Vera Rubin ridge outcrops. Their composition
is consistent with anhydrous Fe-oxide, as the enrichment in iron is not
associated with enrichment in any other elements, nor with detections of
volatiles. The lack of ferric absorption features in the ChemCam reflectance
spectra and the hexagonal crystalline structure associated with dark-toned
crystals points toward coarse ""grey"" hematite. In addition, the host rock
adjacent to these features appears bleached and show low-FeO$_T$ content as
well as depletion in Mn, indicating mobilization of these redox-sensitive
elements during diagenesis. Thus, groundwater fluid circulations could account
for the remobilization of iron and recrystallization as crystalline hematite
during diagenesis as well as color variations observed in the Vera Rubin ridge
outcrops.",2101.03767v1
2021-01-29,A discovery of a low-energy excess in cosmic-ray iron: an evidence of the past supernova activity in the Local Bubble,"Since its launch, the Alpha Magnetic Spectrometer - 02 (AMS-02) has delivered
outstanding quality measurements of the spectra of cosmic-ray (CR) species,
$\bar{p}$, $e^{\pm}$, and nuclei, $_1$H-$_8$O, $_{10}$Ne, $_{12}$Mg, $_{14}$Si,
which resulted in a number of breakthroughs. One of the latest long awaited
surprises is the spectrum of $_{26}$Fe just published by AMS-02. Because of the
large fragmentation cross section and large ionization energy losses, most of
CR iron at low energies is local, and may harbor some features associated with
relatively recent supernova (SN) activity in the solar neighborhood. Our
analysis of new iron spectrum together with Voyager 1 and ACE-CRIS data reveals
an unexpected bump in the iron spectrum and in the Fe/He, Fe/O, and Fe/Si
ratios at 1-2 GV, while a similar feature in the spectra of He, O, Si, and in
their ratios is absent, hinting at a local source of low-energy CRs. The found
excess fits well with recent discoveries of radioactive $^{60}$Fe deposits in
terrestrial and lunar samples, and in CRs. We provide an updated local
interstellar spectrum (LIS) of iron in the energy range from 1 MeV
nucleon$^{-1}$ to $\sim$10 TeV nucleon$^{-1}$. Our calculations employ the
GalProp-HelMod framework that is proved to be a reliable tool in deriving the
LIS of CR $\bar{p}$, $e^{-}$, and nuclei $Z\le28$.",2101.12735v2
2021-04-21,Chandra Observations of Excess Fe K$α$ Line Emission in Galaxies with High Star Formation Rates: X-ray Reflection on Galaxy Scales?,"In active galactic nuclei (AGN), fluorescent Fe K$\alpha$ (iron) line
emission is generally interpreted as originating from obscuring material around
a supermassive black hole (SMBH) on the scale of a few parsecs (pc). However,
recent Chandra studies indicate the existence of iron line emission extending
to kpc scales in the host galaxy. The connection between iron line emission and
large-scale material can be spatially resolved directly only in nearby
galaxies, but could be inferred in more distant AGNs by a connection between
line emission and star-forming gas and dust that is more extended than the
pc-scale torus. Here we present the results from a stacking analysis and X-ray
spectral fitting performed on sources in the Chandra Deep Field South (CDFS) 7
Ms observations. From the deep stacked spectra, we select sources with stellar
mass $\log(M_*/M_\odot)>10$ at $0.5<z<2$, obtaining 25 sources with high
infrared luminosity ($ {\rm SFR}_{\rm FIR} \geq 17\;M_{\odot}\;{\rm yr}^{-1}$)
and 32 sources below this threshold. We find that the equivalent width of the
iron line EW(Fe) is a factor of three higher with 3$\sigma$ significance for
high infrared luminosity measured from Herschel observations, indicating a
connection between iron line emission and star-forming material on galaxy
scales. We show that there is no significant dependence in EW(Fe) on $M_*$ or
X-ray luminosity, suggesting the reflection of AGN X-ray emission over large
scales in their host galaxies may be widespread.",2104.10702v1
2021-08-29,Emergent vortex Majorana zero mode in iron-based superconductors,"The vortex of iron-based superconductors is emerging as a promising platform
for Majorana zero mode, owing to a magic integration among intrinsic vortex
winding, non-trivial band topology, strong electron-electron correlations,
high-Tc superconductivity and the simplification of single material. It
overcomes many difficulties suffered in heterostructure-based Majorana
platforms, including small topological gap, interfacial contamination, lattice
imperfections, and etc. Isolated zero-bias peaks have been found in vortex of
several iron-based superconductors. So far, studies from both experimental and
theoretical aspects strongly indicate the realization of vortex Majorana zero
mode, with a potential to be applied to topological quantum computation. By
taking Fe(Te,Se) superconductor as an example, here we review original idea and
research progress of Majorana zero modes in this new platform. After
introducing the identifications of topological band structure and real zero
modes in vortex, we summarize the physics behaviors of vortex Majorana zero
modes systematically. Firstly, relying on the behavior of the zero mode wave
function and evidence of quasiparticle poisoning, we analyze the mechanism of
emergence of vortex Majorana zero modes. Secondly, assisted with some
well-established theories, we elaborate the measurements on Majorana symmetry
and topological nature of vortex Majorana zero modes. After that, we switch
from quantum physics to quantum engineering, and analyze the performance of
vortex Majorana zero mode under real circumstances, which may potentially
benefit the exploration of practical applications in the future. This review
follows the physics properties of vortex Majorana zero modes, especially
emphasizes the link between phenomena and mechanisms. It provides a chance to
bridge the gap between the well-established theories and the newly discovered
iron home of Majoranas.",2108.12850v1
2022-01-21,A Detailed Investigation of the Onion Structure of Exchanged Coupled Magnetic Fe(3-delta)O4@CoFe2O4@Fe(3-delta)O4 Nanoparticles,"Nanoparticles (NPs) which combine several magnetic phases offer wide
perspectives for cutting edge applications because of the high modularity of
their magnetic properties. Besides the addition of the magnetic characteristics
intrinsic to each phase, the interface that results from core-shell and,
further, from onion structures leads to synergistic properties such as magnetic
exchange coupling. Such a phenomenon is of high interest to overcome the
superparamagnetic limit of iron oxide NPs which hampers potential applications.
In this manuscript, we report on the design of NPs with an onion-like structure
which have been scarcely reported yet. These NPs consist in a Fe(3_delta)O4
core covered by a first shell of CoFe2O4 and a second shell of Fe(3-delta)O4.
They were synthesized by a multi-step seed mediated growth approach. Although
TEM micrographs clearly show the growth of each shell from the iron oxide core,
core sizes and shell thicknesses markedly differ from what is suggested by the
size increase. We investigated very precisely the structure of NPs in
performing high resolution (scanning) TEM imaging and GPA. The chemical
composition and spatial distribution of atoms were studied by EELS. The
chemical environment and oxidation state of cations were investigated by
M\""ossbauer spectrometry, soft XAS and XMCD. These techniques allowed us to
estimate the increase of Fe2+ content in the iron oxide core of the core@shell
structure and the increase of the cobalt ferrite shell thickness in the
core@shell@shell one, while the iron oxide shell appears to be much thinner
than expected. Thus, the modification of the chemical composition as well as
the size of the Fe(3-delta)O4 core and the thickness of the cobalt ferrite
shell have a high impact on the magnetic properties. Furthermore, the growth of
the iron oxide shell also markedly modifies the magnetic properties of the
core-shell NPs.",2201.08923v1
2022-01-23,Improving Time and Position Resolution of RPC detectors using Time Over Threshold Information,"INO-ICAL is a proposed underground particle physics experiment to study the
neutrino oscillation parameters by detecting neutrinos produced in the
atmospheric air showers. Iron CALorimeter (ICAL) is to have 151 layers of iron
stacked vertically, with active detector elements in between the iron layers.
The iron layers will be magnetized to enable the measurement of momentum and
charge of the $\mu^-$ (or $\mu^+$) produced by $\nu_\mu$ (or $\bar{\nu}_\mu$)
interactions. Resistive Plate Chambers (RPCs) have been chosen as the active
detector elements due to their large area coverage, uncompromised sensitivity,
consistent performance for decades, as well as cost effectiveness. The major
factors that decide the physics potential of the ICAL experiment are
efficiency, position resolution and time resolution of the large area RPCs. A
prototype detector called miniICAL (with 11 iron layers) was commissioned to
understand the engineering challenges in building the large scale magnet and
its ancillary systems, and also to study the performance of the RPC detectors
and readout electronics developed by the INO collaboration. As part of the
performance study of the RPC detectors, an attempt is made to improve the
position and time resolution of them. Even a small improvement in the position
and time resolution will help to improve the measurements of momentum and
directionality of the neutrinos in ICAL. The Time-over-Threshold (ToT) of the
RPC pulses (signals) is recorded by the readout electronics. ToT is a measure
of the pulse width and consequently the amplitude. This information is used to
improve the time and position resolution of the RPCs and consequently INO
physics potential.",2201.09279v2
2022-04-21,Reduced atmospheres of post-impact worlds: The early Earth,"Impacts may have had a significant effect on the atmospheric chemistry of the
early Earth. Reduced phases in the impactor (e.g., metallic iron) can reduce
the planet's H$_2$O inventory to produce massive atmospheres rich in H$_2$.
Whilst previous studies have focused on the interactions between the impactor
and atmosphere in such scenarios, we investigate two further effects, 1) the
distribution of the impactor's iron inventory during impact between the target
interior, target atmosphere, and escaping the target, and 2) interactions
between the post-impact atmosphere and the impact-generated melt phase. We find
that these two effects can potentially counterbalance each other, with the
melt-atmosphere interactions acting to restore reducing power to the atmosphere
that was initially accreted by the melt phase. For a $\sim10^{22}\,\mathrm{kg}$
impactor, when the iron accreted by the melt phase is fully available to reduce
this melt, we find an equilibrium atmosphere with H$_2$ column density
$\sim10^4\,\mathrm{moles\,cm^{-2}}$
($p\mathrm{H2}\sim120\,\mathrm{bars}\mathrm{,}~X_\mathrm{H2}\sim0.77$),
consistent with previous estimates. However, when the iron is not available to
reduce the melt (e.g., sinking out in large diameter blobs), we find
significantly less H$_2$ ($7\times10^2-5\times10^3\,\mathrm{moles\,cm^{-2}}$,
$p\mathrm{H2}\lesssim60\,\mathrm{bars}\mathrm{,}~X_\mathrm{H2}\lesssim0.41$).
These lower H$_2$ abundances are sufficiently high that species important to
prebiotic chemistry can form (e.g., NH3, HCN), but sufficiently low that the
greenhouse heating effects associated with highly reducing atmospheres, which
are problematic to such chemistry, are suppressed. The manner in which iron is
accreted by the impact-generated melt phase is critical in determining the
reducing power of the atmosphere and re-solidified melt pool in the aftermath
of impact.",2204.09946v1
2022-04-24,Nematic fluctuations in the non-superconducting iron pnictide BaFe$_{1.9-x}$Ni$_{0.1}$Cr$_{x}$As$_{2}$,"The main driven force of the electronic nematic phase in iron-based
superconductors is still under debate. Here, we report a comprehensive study on
the nematic fluctuations in a non-superconducting iron pnictide system
BaFe$_{1.9-x}$Ni$_{0.1}$Cr$_{x}$As$_{2}$ by electronic transport,
angle-resolved photoemission spectroscopy (ARPES) and inelastic neutron
scattering (INS) measurements. Previous neutron diffraction and transport
measurements suggested that the collinear antiferromagnetism persists to
$x=0.8$, with similar N\'{e}el temperature $T_N$ and structural transition
temperature $T_s$ around 32 K, but the charge carriers change from electron
type to hole type around $x=$ 0.5. In this study, we have found that the
in-plane resistivity anisotropy also highly depends on the Cr dopings and the
type of charge carriers. While ARPES measurements suggest possibly weak orbital
anisotropy onset near $T_s$ for both $x=0.05$ and $x=0.5$ compounds, INS
experiments reveal clearly different onset temperatures of low-energy spin
excitation anisotropy, which is likely related to the energy scale of spin
nematicity. These results suggest that the interplay between the local spins on
Fe atoms and the itinerant electrons on Fermi surfaces is crucial to the
nematic fluctuations of iron pnictides, where the orbital degree of freedom may
behave differently from the spin degree of freedom, and the transport
properties are intimately related to the spin dynamics.",2204.11204v1
2022-05-31,Galactic chemical evolution of exoplanet host stars: Are high-mass planetary systems young?,"The imprints of stellar nucleosynthesis and chemical evolution of the galaxy
can be seen in different stellar populations, with older generation stars
showing higher $\alpha$-element abundances while the later generations becoming
enriched with iron-peak elements. The evolutionary connections and chemical
characteristics of circumstellar disks, stars, and their planetary companions
can be inferred by studying the interdependence of planetary and host star
properties. Numerous studies in the past have confirmed that high-mass giant
planets are commonly found around metal-rich stars, while the stellar hosts of
low-mass planets have a wide range of metallicity. In this work, we analyzed
the detailed chemical abundances for a sample of $>900$ exoplanet hosting stars
drawn from different radial velocity and transit surveys. We correlate the
stellar abundance trends for $\alpha$ and iron-peak elements with the planets'
mass. We find the planet mass-abundance correlation to be primarily negative
for $\alpha$-elements and marginally positive or zero for the iron-peak
elements, indicating that stars hosting giant planets are relatively younger.
This is further validated by the age of the host stars obtained from isochrone
fitting. The later enrichment of protoplanetary material with iron and
iron-peak elements is also consistent with the formation of the giant planets
via the core accretion process. A higher metal fraction in the protoplanetary
disk is conducive to rapid core growth, thus providing a plausible route for
the formation of giant planets. This study, therefore, indicates the observed
trends in stellar abundances and planet mass are most likely a natural
consequence of Galactic chemical evolution.",2205.15793v2
2022-07-20,Anatomy of rocky planets formed by rapid pebble accretion I. How icy pebbles determine the core fraction and FeO contents,"We present a series of papers dedicated to modelling the accretion and
differentiation of rocky planets that form by pebble accretion within the
lifetime of the protoplanetary disc. In this first paper, we focus on how the
accreted ice determines the distribution of iron between the mantle (oxidized
FeO and FeO$_{1.5}$) and the core (metallic Fe and FeS). We find that an
initial primitive composition of ice-rich material leads, upon heating by the
decay of $^{26}$Al, to extensive water flow and the formation of clay minerals
inside planetesimals. Metallic iron dissolves in liquid water and precipitates
as oxidized magnetite Fe$_3$O$_4$. Further heating by $^{26}$Al destabilizes
the clay at a temperature of around 900 K. The released supercritical water
ejects the entire water content from the planetesimal. Upon reaching the
silicate melting temperature of 1,700 K, planetesimals further differentiate
into a core (made mainly of iron sulfide FeS) and a mantle with a high fraction
of oxidized iron. We propose that the asteroid Vesta's significant FeO fraction
in the mantle is a testimony of its original ice content. We consider Vesta to
be a surviving member of the population of protoplanets from which Mars, Earth,
and Venus grew by pebble accretion. We show that the increase in the core mass
fraction and decrease in FeO contents with increasing planetary mass (in the
sequence Vesta -- Mars -- Earth) is naturally explained by the growth of
terrestrial planets outside of the water ice line through accretion of pebbles
containing iron that was dominantly in metallic form with an intrinsically low
oxidation degree.",2207.09795v2
2023-02-13,The ignition of fine iron particles in the Knudsen transition regime,"A theoretical model is considered to predict the minimum ambient gas
temperature at which fine iron particles can undergo thermal runaway--the
ignition temperature. The model accounts for Knudsen transition transport
effects, which become significant when the particle size is comparable to, or
smaller than, the molecular mean free path of the surrounding gas. Two kinetic
models for the high-temperature solid-phase oxidation of iron are analyzed. The
first model (parabolic kinetics) considers the inhibiting effect of the iron
oxide layers at the particle surface on the rate of oxidation, and a kinetic
rate independent of the gaseous oxidizer concentration. The ignition
temperature is solved as a function of particle size and initial oxide layer
thickness with an unsteady analysis considering the growth of the oxide layers.
In the small-particle limit, the thermal insulating effect of transition heat
transport can lead to a decrease of ignition temperature with decreasing
particle size. However, the presence of the oxide layer slows the reaction
kinetics and its increasing proportion in the small-particle limit can lead to
an increase of ignition temperature with decreasing particle size. This effect
is observed for sufficiently large initial oxide layer thicknesses. The
continuum transport model is shown to predict the ignition temperature of iron
particles exceeding an initial diameter of 30 $\mu$m to a difference of 3% (30
K) or less when compared to the transition transport model. The second kinetic
model (first-order kinetics) considers a porous, non-hindering oxide layer, and
a linear dependence of the kinetic rate of oxidation on the gaseous oxidizer
concentration. The ignition temperature is resolved as a function of particle
size with the transition and continuum transport models, and the differences
between the ignition characteristics predicted by the two models are discussed.",2302.06704v1
2023-03-01,Techno-economic assessment of long-distance supply chains of energy carriers: Comparing hydrogen and iron for carbon-free electricity generation,"Effective usage of renewable energy requires ways of storage and delivery to
balance energy demand and availability divergences. Carbon-free chemical energy
carriers are proposed solutions, converting clean electricity into stable media
for storage and long-distance energy trade. Hydrogen (H$_2$) is the subject of
significant investment and research. Metal fuels, such as iron (Fe), are
promising solutions for a clean energy supply, but establishing an
interconnected ecosystem still requires considerable research and development.
A model is proposed to assess the supply chain of hydrogen and iron as clean,
carbon-free energy carriers and then examines case studies of possible trade
routes between the potential energy exporters Morocco, Saudi Arabia, and
Australia and importers Germany and Japan. The work comprehends the assessment
of economic (levelized cost of electricity - LCOE), energetic (thermodynamic
efficiency) and environmental (CO$_2$ emissions) aspects, quantified by the
comprehensive model accounting for the most critical processes in the supply
chain. Sensitivity and uncertainty analyses identify the main drivers for
energy costs. Iron is shown to be lower-cost and more efficient to transport in
longer routes and for long-term storage, but potentially more expensive and
less efficient than H$_2$ to produce and convert. Uncertainties related to the
supply chain specifications and the sensitivity to the used variables indicate
that the path to viable energy carriers fundamentally depends on efficient
synthesis, conversion, storage, and transport. A break-even analysis
demonstrated that clean energy carriers could be competitive with conventional
energy carriers at low renewable energy prices, while carbon taxes might be
needed to level the playing field. Thereby, green iron is an important
potential energy carrier for long-distance trade in a globalized clean energy
market.",2303.00681v2
2023-09-02,Simulation of RPC responses in mini-Iron Calorimeter for cosmic ray muon studies,"A Prototype of the Iron Calorimeter for the India-based Neutrino Observatory
is currently running in Madurai, India. This consists of twenty large area
single gap Resistive Plate Chambers (RPCs) of size, $\sim$ 185\,cm $\times$
175\,cm sandwiched between 11 layers of iron plates of thickness 5.6\,cm. The
total size of the mini-Iron Calorimeter(mini-ICAL) is
4\,m$\times$4\,m$\times$1.2\,m and having a weight of 85\,tons is a (1/600)
scaled-down version of the ICAL detector of INO~\cite{ichep2018}. The detector
is magnetized using iron plates and two sets of copper coils, each coil has 18
turns. The central region of the mini-ICAL, where the RPCs are placed, has a
nearly uniform magnetic field of 1.4\,T, similar to the magnetic field in the
final ICAL detector. This prototype serves as the basis for the design of the
demonstrators, which closely mimics the characteristics of a future ICAL. This
detector is built to test the final electronics in the fringe field of the
magnet and also to develop the experience to construct the ICAL detector.
  The mini-ICAL has been operational since 2018 and collects cosmic muon data
with different configurations of RPC, and electronics, which are continuously
changing for various R\&D efforts. Dedicated efforts are made in parallel to
measure the momentum and azimuthal angle of $\mu^+$ and $\mu^-$ independently,
which could be an important input to the cosmic neutrino event generators. To
improve the precision of those measurements a dedicated simulation effort was
made, particularly in the digitisation of the RPC signal for a real detector
simulation, where efficiency, noise rate, strip multiplicity, etc. were matched
with the real data collected during runs at mini-ICAL.",2309.00992v2
2013-05-13,On the metallicity distribution of classical Cepheids in the Galactic inner disk,"We present homogeneous and accurate iron abundances for almost four dozen
(47) of Galactic Cepheids using high-spectral resolution (R$\sim$40,000) high
signal-to-noise ratio (S/N $\ge$ 100) optical spectra collected with UVES at
VLT. A significant fraction of the sample (32) is located in the inner disk (RG
$le$ 6.9 kpc) and for half of them we provide new iron abundances. Current
findings indicate a steady increase in iron abundance when approaching the
innermost regions of the thin disk. The metallicity is super-solar and ranges
from 0.2 dex for RG $\sim$ 6.5 kpc to 0.4 dex for RG $\sim$ 5.5 kpc. Moreover,
we do not find evidence of correlation between iron abundance and distance from
the Galactic plane. We collected similar data available in the literature and
ended up with a sample of 420 Cepheids. Current data suggest that the mean
metallicity and the metallicity dispersion in the four quadrants of the
Galactic disk attain similar values. The first-second quadrants show a more
extended metal-poor tail, while the third-fourth quadrants show a more extended
metal-rich tail, but the bulk of the sample is at solar iron abundance.
Finally, we found a significant difference between the iron abundance of
Cepheids located close to the edge of the inner disk ([Fe/H]$\sim$0.4) and
young stars located either along the Galactic bar or in the nuclear bulge
([Fe/H]$\sim$0). Thus suggesting that the above regions have had different
chemical enrichment histories. The same outcome applies to the metallicity
gradient of the Galactic bulge, since mounting empirical evidence indicates
that the mean metallicity increases when moving from the outer to the inner
bulge regions.",1305.2742v2
1993-09-29,A Simulation of the Intracluster Medium with Feedback from Cluster Galaxies,"The formation and evolution of an X--ray cluster is studied using a 3--D
N-body + hydrodynamical simulation which includes feedback of energy and iron
from cluster galaxies. The differences in evolution and final state between the
simulation and a similar run without feedback are highlighted. We address the
energetics of cluster gas; the distribution of dark matter, gas, and galaxies;
the thermodynamic state of cluster gas, the beta model, and the beta
discrepancy; x-ray evolution; the validity of estimates of the binding mass and
of the baryon fraction of the cluster; dynamics of the galaxy population and
velocity bias; and of the evolution of the iron abundance distribution in the
cluster. We find that preheating by galactic winds results in a lower core
density for the ICM, which in turn makes the simulated cluster fainter at high
redshift and undergo rapid luminosity evolution to the present. A strong iron
abundance gradient is present, even at high redshift. Velocity bias is present
in the galaxy population; this bias combined with the preheating from winds
drives the value of $\beta_{spec}\,=\,\sigma^{2}/\left(kT/\mu m_{p}\right)$ to
values less than one. The two fluid simulation, modelling infall only, predicts
$\beta_{spec}\,\geq\,1$, less in line with observation.",9309050v1
1994-04-20,A New Multiplet Table for Fe,"We have recorded spectra of iron-neon and iron-argon hollow cathode lamps in
the region 1700A -- 5um (59000 -- 2000cm-1), with Fourier transform (FT)
spectrometers at the National Solar Observatory, Tucson, Arizona, U.S.A. and
Imperial College, London, U.K., and with a high resolution grating spectrograph
at the National Institute of Standards and Technology, Gaithersburg, U.S.A. The
uncertainty of the strongest lines in the FT spectra is <0.002cm-1 (0.2mA at
3000A; 8mA at 2um). Pressure and current-dependent shifts are <0.001cm-1 for
transitions between low lying levels, increasing to 0.006 cm-1 for transitions
between the most highly excited levels. We report 28 new energy levels of Fe I
and revised values of another 818 levels. We have identified 9501 lines as due
to 9759 transitions in Fe I, and these are presented in the form of a new
multiplet table and finding list. This compares with the 5500 lines due to 467
energy levels in the multiplet tables of Moore (1950, 1959). The biggest
increase is in the near ultraviolet and near infra-red, and many of the new
lines are present in the solar spectrum. Experimental log(gf) values are
included where available. A further 125 unidentified lines due to Fe I are
given.",9404049v1
1995-11-19,Silicon Burning I: Neutronization and the Physics of Quasi-Equilibrium,"As the ultimate stage of stellar nucleosynthesis, and the source of the iron
peak nuclei, silicon burning is important to our understanding of the evolution
of massive stars and supernovae. Our reexamination of silicon burning, using
results gleaned from simulation work done with a large nuclear network (299
nuclei and more than 3000 reactions) and from independent calculations of
equilibrium abundance distributions, offers new insights into the
quasi-equilibrium mechanism and the approach to nuclear statistical
equilibrium. We find that the degree to which the matter has been neutronized
is of great importance, not only to the final products but also to the rate of
energy generation and the membership of the quasi-equilibrium groups. A small
increase in the global neutronization results in much larger free neutron
fluences, increasing the abundances of more neutron-rich nuclei. As a result,
incomplete silicon burning results in neutron richness among the isotopes of
the iron peak much larger than the global neutronization would indicate.
Finally, we briefly discuss the limitations and pitfalls of models for silicon
burning currently employed within hydrodynamic models. In a forthcoming paper
we will present a new approximation to the full nuclear network which preserves
the most important features of the large nuclear network calculations at a
significant improvement in computational speed. Such improved methods are
ideally suited for hydrodynamic calculations which involve the production of
iron peak nuclei, where the larger network calculation proves unmanageable.",9511088v1
1996-04-13,Model neutron star atmospheres with low magnetic fields. 1. Atmospheres in radiative equilibrium,"We present a detailed investigation of neutron star atmospheres with low
magnetic fields, $B < 10^8 -10^{10}$ G, which do not affect opacities and
equation of state of the atmospheric matter. We compute the atmospheric
structure, emergent spectral fluxes and specific intensities for hydrogen,
helium and iron atmospheres in a wide domain of effective temperatures and
gravitational accelerations expected for neutron stars. The iron atmospheres
are computed with the opacities and equations of state from the OPAL opacity
library. We show that the model atmosphere spectra are substantially different
from the blackbody spectra. For light element atmospheres, the flux is greater
than the blackbody flux, and the spectrum is harder, at high photon energies,
whereas at low energies the spectral flux follows the Rayleigh-Jeans law with a
(surface) temperature lower than the effective temperature. The spectra of iron
atmospheres display prominent spectral features in the soft X-ray range. The
emergent specific intensity is anisotropic, with the anisotropy depending on
energy. These properties of the atmospheric radiation should be taken into
account for the proper interpretation of the thermal component of the neutron
star radiation detectable at X-ray through UV energies. In particular, fitting
of the thermal component with the blackbody model may result in substantially
incorrect parameters of the radiating regions. We discuss an application of our
atmosphere models to the nearby millisecond pulsar PSR J0437-4715.",9604072v1
1996-10-23,Spectral Variability and iron line emission in the ASCA Observations of the Seyfert 1 Galaxy NGC4051,"We present the results of an extensive analysis of the ``ASCA'' AO2
observation of the Seyfert 1 galaxy NGC4051. The target exhibits broadband
[0.5--10 keV] variability by a factor $\sim 8$ on time scales $\sim 10^4 s$,
with a typical doubling time $\sim 500 s$. The spectrum is characterized by a
strong emission excess over the extrapolated power law at energies $E \le 1
keV$. Absorption edges due to ionized oxygen species OVII and OVIII are
detected together with an emission-like feature at $E \sim 0.93 keV$. The OVII
edge undergoes significant variability on a timescale as low as $\sim 10^4 s$,
whilst no contemporary variability of the OVIII feature is detected. Typical
variability time scales place constraints on the location and the density of
the absorbing matter. In the self-consistent hypothesis of a high energy ($E
\ge 2.3 keV$) power law reflected by an infinite plane-parallel cold slab, a
photon index change ($\Delta \Gamma = 0.4$) has also been observed; a natural
explanation can be found in the framework of non-thermal Comptonization models.
The iron line is redshifted (centroid energy $E \sim 6.1 keV$) and broad
($\sigma > 0.2 keV$); multicomponent structure is suggestive of emission from a
relativistic accretion disk; however if the disk is not ionized a contribution
by a molecular torus or an iron overabundance by a factor $\sim 1.5$ are
required.",9610180v1
1997-05-12,ASCA observations of type-2 Seyfert galaxies: II. The Importance of X-ray Scattering and Reflection,"We discuss the importance of X-ray scattering and Compton reflection in
type-2 Seyfert galaxies, based upon the analysis of ASCA observations of 25
such sources. Consideration of the iron Kalpha, [O III] line and X-ray
variability suggest that NGC 1068, NGC 4945, NGC 2992, Mrk 3, Mrk 463E and Mrk
273 are dominated by reprocessed X-rays. We examine the properties of these
sources in more detail.
  We find that the iron Kalpha complex contains significant contributions from
neutral and high-ionization species of iron. Compton reflection, hot gas and
starburst emission all appear to make significant contributions to the observed
X-ray spectra.
  Mrk 3 is the only source in this subsample which does not have a significant
starburst contamination. The ASCA spectrum below 3 keV is dominated by hot
scattering gas with U_X ~ 5, N_H ~ 4 x 10^23 cm^-2. This material is more
highly ionized than the zone of material comprising the warm absorber seen in
Seyfert~1 galaxies, but may contain a contribution from shock-heated gas
associated with the jet. Estimates of the X-ray scattering fraction cover 0.25
- 5%. The spectrum above 3 keV appears to be dominated by a Compton reflection
component although there is evidence that the primary continuum component
becomes visible close to 10 keV.",9705087v1
1997-05-29,Is UU Herculis a post-AGB star?,"In order to understand the evolutionary status of the anomalous supergiant
UUHer, the prototype of the class of variable supergiants located at high
galactic latitudes, we obtained several high-resolution spectra of this star,
with the 6m telescope, over 5 years. This material was used for a search of
possible temporal variations of the radial velocity at the different depths in
the photosphere and for studying the chemical composition. The average radial
velocity Vr approximately 130 km/sec suggests that UUHer belongs to the old
population of the Galaxy. No systematic dependence of the velocity on depth of
the line formation layer or on ionization and excitation potential is observed.
The radial velocity of the H_alpha absorption differs strongly from the average
photospheric velocity. The iron abundance in the photosphere of UUHer is
significantly lower than that of the Sun: [Fe/H]=-1.32. The enhancement of
nitrogen relatively to iron content [N/Fe]=+0.40 in combination with the carbon
underabundance [C/Fe]=-0.30 suggests that only a first dredge-up episode
occurred. The Na content is normal relatively to iron, therefore there is no
evidence for dredging-up of Ne-Na cycle products. The heavy s-process metals Y,
Ba are depleted relative to H and Fe, which again implies that the third
dredge-up did not occur.",9705230v1
1997-06-15,Supernovae Types Ia/II and Intracluster Medium Enrichment,"We re-examine the respective roles played by supernovae (SNe) Types Ia and II
in enriching the intracluster medium (ICM) of galaxy clusters, in light of the
recent downward shift of the ASCA abundance ratios of alpha-elements to iron
favoured by Ishimaru & Arimoto (1997, PASJ, 49, 1). Because of this shift,
Ishimaru & Arimoto conclude that >50% of the ICM iron must have originated from
within Type Ia SNe progenitors. A point not appreciated in their study, nor in
most previous analyses, is the crucial dependence of such a conclusion upon the
adopted massive star physics. Employing several alternative Type II SN yield
compilations, we demonstrate how uncertainties in the treatment of convection
and mass-loss can radically alter our perception of the relative importance of
Type Ia and II SNe as ICM polluters. If mass-loss of the form favoured by
Maeder (1992, A&A, 264, 105) or convection of the form favoured by Arnett
(1996, Supernovae and Nucleosynthesis) is assumed, the effect upon the oxygen
yields would lead us to conclude that Type Ia SNe play no part in polluting the
ICM, in contradiction with Ishimaru & Arimoto. Apparent dichotomies still exist
(e.g. the mean ICM neon-to-iron ratio implies a 100% Type II Fe origin, while
the mean sulphur ratio indicates a 100% Type Ia origin) that cannot be
reconciled with the currently available yield tables.",9706138v1
1997-07-07,"Rosat, Asca and Osse Observations of the Broad Line Radio Galaxy 3C120","We present simultaneous observations of the superluminal radio galaxy 3C120
performed with the ASCA and GRO (OSSE) satellites on February-March 1994, as
well as an analysis of all the ROSAT archival data. The ASCA spectrum of this
object can be described by an absorbed (N_H=1.6e^21 cm^-2) power law with
photon index Gamma_ASCA=2 and a very broad sigma>0.8 keV intense iron line
(EW>400 eV) at ~ 6 keV. The combined ASCA--OSSE data do not exclude the
presence of a narrower (sigma=0.4 keV) and less intense (EW<300 eV) iron line
plus a hard component, corresponding either to reflection from an accretion
disk or to a flatter power law from a jet. However a single power law plus
broad Fe line is preferred from a statistical point of view by the ASCA data.
The ROSAT data yield a column density in excess of the Galactic value. The
spectral slopes, ranging from Gamma_ROSAT=2.5 to 3.3, are steeper than that
measured by ASCA, suggesting the presence of a soft excess. The 0.1-2 keV
power-law slope is variable and softer at higher intensity. These results show
that the combined soft and hard X-ray spectrum of 3C120 is rather complex. The
intrinsic absorption, the soft excess, and the iron line indicate that the
X-ray emission from this blazar-like radio galaxy is dominated by a
Seyfert-like component, at least in the 0.1-10keV energy band. The jet
contribution, if present, becomes important only at higher energies.",9707078v1
1997-07-10,Infrared and Optical Spectroscopy of Type Ia Supernovae in the Nebular Phase,"We present near-infrared (NIR) spectra for Type Ia supernovae at epochs of 13
to 338 days after maximum blue light. Some contemporary optical spectra are
also shown. All the NIR spectra exhibit considerable structure throughout the
J-, H- and K-bands. In particular they exhibit a flux `deficit' in the J-band
which persists as late as 175 days. This is responsible for the well-known red
J-H colour. To identify the emission features and test the $^{56}$Ni hypothesis
for the explosion and subsequent light curve, we compare the NIR and optical
nebular-phase data with a simple non-LTE nebular spectral model. We find that
many of the spectral features are due to iron-group elements and that the
J-band deficit is due to a lack of emission lines from species which dominate
the rest of the IR/optical spectrum. Nevertheless, some emission is unaccounted
for, possibly due to inaccuracies in the cobalt atomic data. For some
supernovae, blueshifts of 1000--3000 km/s are seen in infrared and optical
features at 3 months. We suggest this is due to clumping in the ejecta. The
evolution of the cobalt/iron mass ratio indicates that $^{56}$Co-decay
dominates the abundances of these elements. The absolute masses of iron-group
elements which we derive support the basic thermonuclear explosion scenario for
Type Ia supernovae. A core-collapse origin is less consistent with our data.",9707119v1
1997-08-20,Further constraints on white dwarf galactic halos,"The suggestion that roughly half the mass of the galactic halo might be in
the form of white dwarfs, together with the limits on the infrared background
light and on the initial metallicity of the galactic disk, would set strong
constraints on the initial mass function (IMF) of the halo. Particular IMFs
have been proposed to cut off both the numbers of low-mass stars contributing
to the infrared background and of high-mass stars which contribute to the
growth of metallicity when they promptly explode as gravitational-collapse
(Type II and Type Ib/c) supernovae. Here we examine the further contribution to
metallicity from the Type Ia (thermonuclear) supernovae which would later be
produced from the halo white dwarf population. We find that, for most of the
evolutionary scenarios for the Type Ia supernova progenitor systems proposed so
far, the constraints on the white dwarf mass fraction in the halo from the
predicted production of iron would be extremely severe. When the predicted iron
excess is not so large, then the exceedingly high Type Ia supernova rate
predicted for the present time would also exclude a major contribution of white
dwarfs to the halo mass. The white dwarf contribution, in all cases, should be
below 5-10%. Besides, for the IMFs considered, the duration of the halo burst
should be shorter than 1 Gyr in order to avoid too large a spread in the iron
abundances of Population II halo dwarfs, and the predicted halo $[O/Fe]$ ratio
would be at odds with observations.",9708178v1
1997-11-14,Simultaneous ASCA And RXTE Observations of Cygnus X--1 During Its 1996 State Transition,"We report results from simultaneous ASCA and RXTE observations of Cyg X-1
when the source made a rare transition from the hard (= low) state to the soft
(= high) state in 1996. These observations together cover a broad energy range
~0.7--50 keV with a moderate energy resolution at the iron K-band, thus make it
possible to disentangle various spectral components. The low-energy spectrum is
dominated by an ultra-soft component, which is likely to be the emission from
the hottest inner portion of the accretion disk around the black hole. At high
energies, the X-ray spectrum can be described by a Comptonized spectrum with a
reflection component. The Compton corona, which upscatters soft ``seed
photons'' to produce the hard X-ray emission, is found to have a y-parameter
~0.28. The hard X-ray emission illuminates the accretion disk and the
re-emitted photons produce the observed ``reflection bump''. We show that the
reflecting medium subtends only a small solid angle ($\sim 0.15\times 2\pi$),
but has a large ionization parameter such that iron is ionized up to
\ion{Fe}{24}-\ion{Fe}{26}. The presence of a broad iron line at $6.58\pm0.04$
keV is also consistent with a highly ionized disk, if we take into account the
gravitational and Doppler shift of the line energy. These results imply a
geometry with a central corona surrounding the black hole and the reflection
occurring in the innermost region of the disk where matter is highly ionized.",9711164v1
1997-12-17,Complex Absorption and Reflection of a Multi-temperature Cyclotron-Bremsstrahlung X-ray Cooling Shock in BY Cam,"We re-analyse the ASCA and GINGA X-ray data from BY Cam, a slightly
asynchronous magnetic accreting white dwarf. The spectra are strongly affected
by complex absorption, which we model as a continuous (power law) distribution
of covering fraction and column of neutral material. This absorption causes a
smooth hardening of the spectrum below 3 keV, and is probably produced by
material in the preshock column which overlies the X-ray emission region. The
ASCA data show that the intrinsic emission from the shock is not consistent
with a single temperature plasma. Significant iron L emission co-existing with
iron K shell lines from H and He-like iron clearly shows that there is a wide
range of temperatures present, as expected from a cooling shock structure. The
GINGA data give the best constraints on the maximum temperature emission in the
shocked plasma, with kT(max)=21(+18,-4) keV. Cyclotron cooling should also be
important, which supresses the highest temperature bremsstrahlung components,
so the X-ray data only give a lower limit on the mass of the white dwarf of M>
0.5 solar masses. Reflection of the multi-temperature bremsstrahlung emission
from the white dwarf surface is also significantly detected.
  We stress the importance of modelling ALL these effects in order to gain a
physically self-consistent picture of the X-ray spectra from polars in general
and BY Cam in particular.",9712226v1
1998-06-24,X-ray iron line reverberation from black hole accretion disks,"The relativistically broad X-ray iron line seen in many AGN spectra is
thought to originate from the central regions of the putative black hole
accretion disk. Both the line profile and strength will vary in response to
rapid variability of the primary X-ray continuum source. The temporal response
of the line contains information on the accretion disk structure, the X-ray
source geometry, and the spin of the black hole. Since the X-ray source will
have a size comparable to the fluorescing region of the accretion disk, the
general reverberation problem is not invertible. However, progress can be made
since, empirically, AGN light curves are seen to undergo dramatic short
timescale variability which presumably corresponds to the creation of a single
new active region within the distributed X-ray source. The iron line response
to these individual events can be described using linear transfer theory. We
consider the line response to the activation/flaring of a new X-ray emitting
region. Most of our detailed calculations are performed for the case of an
X-ray source on the symmetry axis and at some height above the disk plane
around a Kerr black hole. We also present preliminary calculations for off-axis
flares. We suggest ways in which future, high-throughput X-ray observatories
such as XMM and the Constellation X-ray Mission may use these reverberation
signatures to probe both the mass and spin of AGN black holes, as well as the
X-ray source geometry.",9806327v2
1998-07-08,Nitrogen Abundances in Damped Ly alpha Galaxies,"Nitrogen abundances have been derived in Damped Ly alpha (DLA) galaxies at
Zabs = 2.309, 2.827 and 3.025 toward the QSOs 0100+1300, 1425+6039 and
0347-3819 respectively. The behaviour of nitrogen relative to iron-peak and
alpha-elements has been investigated by considering all the extant NI
determinations for a total of 9 DLA galaxies. We have estimated the fraction of
iron locked into dust grains to convert the observed [N/Fe] ratios into overall
(dust plus gas) relative abundances, [N/Fe]corr. The ratios [N/alpha] have been
mostly determined by using sulphur as a tracer of alpha-elements which is
unaffected by dust. The [N/Fe] and [N/alpha] ratios show high dispersions, of
one order of magnitude or more, which have no equivalent in other
element-to-element ratios in DLAs. The lowest values of the [N/Fe]corr and
[N/alpha] ratios are at variance with the values measured in Galactic halo
stars of similar metallicity suggesting that part of the DLA galaxies do not
follow the chemical evolution of the Milky Way. The DLA nitrogen abundances and
their dispersion show some similarities with those observed in dwarf galaxies.
The behaviour of nitrogen abundance ratios can be ascribed, in general to the
delayed release of nitrogen in the course of evolution. However it is difficult
to conciliate this interpretation with the lowest [N/alpha] values measured,
since an expected enhancement of alpha-elements respect to the iron-peak
elements is not observed simultaneously in these DLA galaxies. In two cases,
relatively high [N/alpha] values are observed which require also a more complex
chemical evolution to be explained.",9807082v1
1998-08-05,Observation of Cen A by the Rossi X-ray Timing Explorer,"The Rossi X-ray Timing Explorer made a short (10 ks) observation of the radio
galaxy Centaurus A on 14 August 1996. Analysis of the combined 2.5-240 keV
spectrum has revealed a heavily absorbed(NH=9.42+/-0.24 e22 cm-2) primary power
law (index=1.86+/-0.015) and an iron line due to fluorescence of cold matter
(EW=162+/-25 eV). Flux from either a jet, primary flux scattered into the line
of sight, or primary flux seen through a partial absorber was not required. The
iron line width is unresolved at the 95% confidence level (sigma < 0.54 keV).
No significant variability in the iron line flux is seen from measurements over
the last two decades, while the overall continuum flux varied by more than a
factor of four, which implies that the line emission region is distant from
that of the primary emission. While radio-quiet Seyfert galaxies exhibit
spectral components attributable to Compton reflection from cold matter, Cen A
reveals no such component (exposed solid angle ratio < 0.09). This supports
unified models of active galaxies that have little difference between Seyfert 2
and low luminosity radio galaxies",9808042v1
1998-08-10,Iron line profiles including emission from within the innermost stable orbit of a black hole accretion disc,"Reynolds & Begelman (1997) have recently proposed a model in which the broad
and extremely redshifted iron line seen during a deep minimum of the light
curve of the Seyfert 1 galaxy MCG-6-30-15 originates from matter spiralling
into a Schwarzschild black hole, contrary to previous claims that the black
hole may be spinning rapidly (Iwasawa et al 1996; Dabrowski et al 1997). Here
we calculate in detail the X-ray spectrum produced by their model using the
full reflected continuum emission, including absorption features. This
calculation takes into account the doppler and relativistic effects. For the
range of parameters we consider, we find that the spectrum should show a large
photoelectric absorption edge of iron, which is not seen in the data. The
absorption edge is a consequence of the line emitting matter within the
innermost stable orbit being highly ionized, and is largely independent of the
parameters chosen for their model. If we restrict our attention to the 3-10 keV
band we may effectively remove this absorption edge by fitting a steeper power
law, but this results in a significant underprediction of the 0.4-0.5 keV flux.
We conclude that the data on MCG-6-30-15 are more consistent with the Kerr than
the Schwarzschild model.",9808089v1
1999-01-20,BeppoSAX Observations of the Radio Galaxy Centaurus A,"We present preliminary results from two observations of the radio galaxy
Centaurus A performed by the BeppoSAX satellite. We did not detect any spectral
variation of the nuclear continuum in spite of the long-term flux change (by a
factor 1.3) between the two observations. At both epochs, the nuclear
point-like emission was well fitted with a strongly absorbed power law with an
exponential cutoff at high energies (E_cutoff>200 keV). We also observed a
significant flux variation of the iron line between the two observations. The
flux of the line and of the continuum changed in the opposite sense. The line
is more intense at the first epoch, when the nuclear source was at the lower
intensity level. The implied delay between the continuum and line variations
strongly suggests that the cold material responsible for the iron line
production is not located very near to the primary X-ray source. There is also
evidence that the line profile changed between the two epochs, being broader
and slightly blueshifted when the source was fainter. It is possible that the
emission feature is a blend of cold and ionized iron lines produced in separate
regions surrounding the nuclear source.",9901266v1
1999-02-01,"The X-ray afterglow of the Gamma-ray burst of May 8, 1997: spectral variability and possible evidence of an iron line","We report the possible detection (99.3% of statistical significance) of
redshifted Fe iron line emission in the X-ray afterglow of Gamma-ray burst
GRB970508 observed by BeppoSAX. Its energy is consistent with the redshift of
the putative host galaxy determined from optical spectroscopy. The line
disappeared about 1 day after the burst. We have also analyzed the spectral
variability during the outburst event that characterizes the X-ray afterglow of
this GRB. The spectrum gets harder during the flare, turning to steep when the
flux decreases. The variability, intensity and width of the line indicate that
the emitting region should have a mass approximately greater than 0.5 solar
masses (assuming the iron abundance similar to its solar value), a size of
about 3 times 10^15 cm, be distributed anisotropically, and be moving with
sub-relativistic speed. In contrast to the fairly clean environment expected in
the merging of two neutron stars, the observed line properties would imply that
the site of the burst is embedded in a large mass of material, consistent with
pre-explosion ejecta of a very massive star. This material could be related
with the outburst observed in the afterglow 1 day after the GRB and with the
spectral variations measured during this phase.",9902013v1
1999-02-03,Iron line in the afterglow: a key to unveil Gamma-Ray Burst progenitors,"The discovery of a powerful and transient iron line feature in the X-ray
afterglow spectra of gamma-ray bursts would be a major breakthrough for
understanding the nature of their progenitors. Piro et al. (1999) and Yoshida
et al. (1999) report such a detection in the afterglow of GRB 970508 and GRB
970828, respectively. We discuss how such a strong line could be produced in
the various scenarios proposed for the event progenitor. We show that the
observed line intensity requires a large iron mass, concentrated in the
vicinity of the burst. The previous explosion of a supernova, predicted in the
Supranova scenario, is the most straightforward way to account for such a large
amount of matter. We discuss three different physical processes that could
account for the line: recombination, reflection and thermal emission. Among
these, reflection and thermal emission may explain the observed line features:
reflection should be important if the remnant is optically thick, while thermal
lines can be produced only in a thin plasma. The recombination process requires
extremely high densities to efficiently reprocess the burst photons, whereas
this process could work during the X-ray afterglow. Future key observations for
discriminating the actual radiating process are discussed.",9902058v1
1999-06-27,Stellar Iron Abundances: non-LTE Effects,"We report new statistical equilibrium calculations for Fe I and Fe II in the
atmosphere of Late-Type stars. We used atomic models for Fe I and Fe II having
respectively 256 and 190 levels, as well as 2117 and 3443 radiative
transitions. Photoionization cross-sections are from the Iron Project. These
atomic models were used to investigate non-LTE effects in iron abundances of
Late-Type stars with different atmospheric parameters.
  We found that most Fe I lines in metal-poor stars are formed in conditions
far from LTE. We derived metallicity corrections of about 0.3 dex with respect
to LTE values, for the case of stars with [Fe/H] ~ -3.0. Fe II is found not to
be affected by significant non-LTE effects. The main non-LTE effect invoked in
the case of Fe I is overionization by ultraviolet radiation, thus classical
ionization equilibrium is far to be satisfied. An important consequence is that
surface gravities derived by LTE analysis are in error and should be corrected
before final abundances corrections.
  This apparently solves the observed discrepancy between spectroscopic surface
gravities derived by LTE analyses and those derived from Hipparcos parallaxes.
A table of non-LTE [Fe/H] and log g values for a sample of metal-poor late-type
stars is given.",9906433v1
1999-11-22,The First Five Minutes of a Core Collapse Supernova: Multidimensional Hydrodynamic Models,"We present results of high-resolution two-dimensional simulations which
follow the first five minutes of a core collapse supernova explosion in a 15
solar mass blue supergiant progenitor. The computations start shortly after
core bounce and include neutrino-matter interactions by using a light-bulb
approximation for the neutrinos, and a treatment of the nucleosynthesis due to
explosive silicon and oxygen burning. We find that newly formed iron-group
elements are distributed throughout a significant fraction of the stellar
helium core by the concerted action of convective and Rayleigh-Taylor
instabilities. Fast moving nickel mushrooms with velocities up to 4000 km/s are
observed. A continuation of the calculations to later times, however,
indicates, that the iron velocities observed in SN 1987 A cannot be reproduced
due to a strong deceleration of the clumps during their interaction with the
dense shell left behind by the shock at the He/H interface. Therefore, we
cannot confirm the claim that convective ""premixing"" of the nickel in the early
phases of the explosion solves the problem of the high iron velocities.",9911407v1
2000-03-13,X-ray emitting-absorbing media in Seyfert 1 galaxies,"Seyfert galaxies have been shown to exhibit a large variety of features in
their X-ray spectra from which the environment of the central engine can be
deduced. We focus on the two following aspects: the Warm Absorber, mainly
responsible of the soft X-ray properties, and the reprocessing/reflecting
plasma medium at the origin of the iron Kalpha fluorescent line. The physical
parameters and the location of the so-called Warm Absorber (WA), a photoionized
medium along the line of sight to the nuclear region, are more strongly
constrained by optical coronal lines than by the oxygen edges observed in the
soft X-rays and produced by the WA. The photoionization models also predict the
intensities of the X-ray emission lines which are going to be detected with the
new generation of X-ray satellites. An alternative model to the relativistic
accretion disc is proposed to explain the profile of the X-ray iron Kalpha line
observed in the Seyfert 1. This line can be formed in the framework of a
quasi-spherical accretion of optically thick clouds. An optically thick
photoionization code coupled with a Monte-Carlo code has been developed to
compute the entire spectrum from the IR to the hard X-rays for a close geometry
with a large covering factor. The multiple Compton reflections allow to
reproduce the redshifted broad iron line as detected in several Seyfert 1
galaxies and in MCG-6-30-15.",0003168v1
2000-03-14,SN Ia Enrichment in Virgo Early-Type Galaxies from ROSAT and ASCA Observations,"We analyzed nine X-ray bright Virgo early-type galaxies observed by both ASCA
and ROSAT. Through spatially resolved spectroscopy, we determined the radial
temperature profile and abundances of Mg, Si and Fe for six galaxies. The
temperature profiles are consistent with isothermal temperatures outside of a
cooler region at the galaxy center. We present new evidence for iron abundance
gradients in NGC4472 and NGC4649 and confirm the previous results on NGC4636.
Mg and Si abundance gradients on average are flatter compared to those of iron
and correspond to an underabundance of alpha-process elements at high Fe
values, while at low iron, the element ratios favor enrichment by type II SNe.
We explain the observed trend by the metallicity dependence of SN Ia metal
production and present constraints on the available theoretical modeling for
low-metallicity inhibition of SNe Ia (Kobayashi et al. 1998). Our results imply
a cut-off metallicity in the range 0.07-0.3 solar and require a lower limit of
0.3 solar on the Fe contribution of SN Ia. We estimate an SN Ia rate at the
centers of the brightest galaxies in our sample of ~0.08 (h_75)^3 SNu
(supernova units). The rates inferred from optical searches should be corrected
for the presence of `faint' SN Ia events, since these release limited metals
and therefore do not contribute significantly to the measured metallicity in
the X-ray gas. With this correction the present-epoch SN Ia rate in early-type
galaxies is 0.10+/-0.06 (h_75)^2 SNu (Cappellaro et al. 1997) and is therefore
comparable with the X-ray estimates. Abridged.",0003202v1
2000-04-05,A deep X-ray observation of NGC 4258 and its surrounding field,"We present a deep X-ray observation of the low-luminosity active galactic
nucleus in NGC4258 (M106) using ASCA. The soft X-ray spectrum <2keV is
dominated by thermal emission from optically-thin plasma with kT~0.5keV. The
hard X-ray emission is clearly due to a power-law component with photon index
Gamma=1.8 absorbed by a column density of N_H=8x10^22/cm^2. The power-law is
readily identified with primary X-ray emission from the AGN central engine. We
also clearly detect a narrow iron K-alpha emission line at 6.4keV. No broad
component is detected. We suggest that the bulk of this narrow line comes from
the accretion disk and, furthermore, that the power-law X-ray source which
excites this line emission (which is typically identified with a disk corona)
must be at least 100GM/c^2 in extent. This is in stark contrast to many
higher-luminosity Seyfert galaxies which display a broad iron line indicating a
small 10 GM/c^2 X-ray emitting region. It must be stressed that this study
constrains the size of the X-ray emitting corona rather than the
presence/absence of a radiatively efficient accretion disk in the innermost
regions. If, instead, a substantial fraction of the observed narrow line
originates from material not associated with the accretion disk, limits can be
placed on the parameter space of possible allowed relativistically broad iron
lines. By comparing our data with previous ASCA observations, we find marginal
evidence for a change in absorbing column density through to the central
engine, and good evidence for a change in the AGN flux.",0004068v1
2000-05-31,Ionization physics evidence for magnetic flare origin of X-rays in AGN,"We present full disk X-ray reflection spectra for two currently popular
accretion flow geometries for AGN -- the lamppost model frequently used to
discuss the iron line reverberation in AGN, and the model where the X-rays are
produced in magnetic flares above a cold accretion disk (AD). The lamppost
spectra contain several spectroscopic features characteristic of highly ionized
material that are not seen in the X-ray spectra of most AGN. The magnetic flare
model, on the other hand, produces reflected spectra that are roughly a
super-position of a power-law and a {\em neutral-like} reflection and iron
K$\alpha$ line, and are thus more in line with typical AGN X-ray spectra.
Furthermore, because of the difference in the ionization structure of the
illuminated material in the two models, the line equivalent width increases
with the X-ray luminosity, $L_x$, for the lamppost, and decreases with $L_x$
for the flare model. In light of these theoretical insights, recent iron line
reverberation studies of AGN, the X-ray Baldwin effect, and the general lack of
X-ray reflection features in distant quasars all suggest that, for high
accretion rates, the cold accretion disk is covered by a Thomson thick,
completely ionized skin. Because the latter is only possible when the X-rays
are concentrated to small emitting regions, we believe that this presents a
strong evidence for the magnetic flare origin of X-rays in AGN.",0005603v1
2000-09-10,The Temperature of Nonspherical Circumstellar Dust Grains,"The temperatures of prolate and oblate spheroidal dust grains in the
envelopes of stars of various spectral types are calculated. Homogeneous
particles with aspect ratios {\small $a/b \le 10$} composed of amorphous
carbon, iron, dirty ice, various silicates, and other materials are considered.
The temperatures of spherical and spheroidal particles were found to vary
similarly with particle size, distance to the star, and stellar temperature.
The temperature ratio {\small $T_{\rm d}({\rm spheroid})/T_{\rm d}({\rm
sphere}) $} depends most strongly on the grain chemical composition and shape.
Spheroidal grains are generally colder than spherical particles of the same
volume; only iron spheroids can be slightly hotter than iron spheres. At
{\small $a/b \approx 2$}, the temperature differences do not exceed 10 %. If
{\small $a/b \ga 4$}, the temperatures can differ by 30-40 %. For a fixed dust
mass in the medium, the fluxes at wavelengths {\small $\lambda \ga 100 \mkm$}
are higher if the grains are nonspherical, which gives over estimated dust
masses from millimeter observations. The effect of grain shape should also be
taken into account when modeling Galactic-dust emission properties, which are
calculated when searching for fluctuations of the cosmic microwave background
radiation in its Wien wing.",0009149v1
2000-09-20,The Chandra High Energy Transmission Grating Observation of an X-ray Ionization Cone in Markarian 3,"We present a preliminary analysis of the first high-resolution X-ray spectrum
of a Seyfert 2 galaxy, Mkn 3, obtained with the High Energy Transmission
Grating Spectrometer onboard the Chandra X-ray Observatory. The high-energy
spectrum (lambda < 4 Ang) is dominated by reflection of the AGN continuum
radiation in a cold optically thick medium and contains bright K-alpha
fluorescent lines from iron and silicon, as well as weak, blended lines from
sulfur and magnesium. The soft X-ray emission (4 < lambda < 23 Ang) is
spatially extended along the [O III] ionization cone and shows discrete
signatures of emission following recombination and photoexcitation produced in
a warm photoionized region. The measured iron L line fluxes indicate that
emission from collisionally ionized plasma is almost completely negligible, and
does not contribute significantly to the total energy budget of the X-ray
emission. We find that significant fractions of the H- and He-like resonance
lines, as well as the observed iron L lines are produced through re-emission
from the warm absorbing medium observed in Seyfert 1 galaxies. Its X-ray
spectral properties are qualitatively consistent with those of a typical
Seyfert 1 galaxy viewed at a different orientation, and provide further
convincing evidence for the existence of an obscured Seyfert 1 nucleus in Mkn
3.",0009323v1
2001-04-02,RXTE monitoring of Centaurus A,"We report on the analysis from ~110 ks of X-ray observations of Centaurus A
carried out with the Proportional Counter Array (PCA) and the High Energy X-ray
Timing Experiment (HEXTE) instruments on Rossi X-ray Timing Explorer (RXTE)
during three monitoring campaigns over the last 4 years (10 ks in 1996, 74 ks
in 1998, and 25 ks in 2000). The joint PCA/HEXTE X-ray spectrum can be well
described by a heavily absorbed power law with photon index 1.8 and a narrow
iron line due to fluorescence of cold matter. The measured column depth
decreased by about 30% between 1996 and 2000, while the detected 2-10 keV
continuum flux remained constant between 1996 and 1998, but increased by 60% in
2000. Since in all three observations the iron line flux did not vary, a
corresponding decrease in equivalent width was noted. No appreciable evidence
for a reflection continuum in the spectrum was detected. We present the
interpretation of the iron line strength through Monte Carlo computations of
various geometries. No significant temporal variability was found in Cen A at
time scales from days to tens of minutes.",0104018v2
2001-04-02,Quasar Evolution and the Baldwin Effect in the Large Bright Quasar Survey,"From a large homogeneous sample of optical/UV emission line measurements for
993 quasars from the Large Bright Quasar Survey (LBQS), we study correlations
between emission line equivalent width and both restframe ultraviolet
luminosity (i.e., the Baldwin Effect) and redshift. Our semi-automated spectral
fitting accounts for absorption lines, fits blended iron emission, and provides
upper limits to weak emission lines. Use of a single large, well-defined sample
and consistent emission line measurements allows us to sensitively detect many
correlations, most of which have been previously noted. A new finding is a
significant Baldwin Effect in UV iron emission. Further analysis reveals that
the primary correlation of iron emission strength is probably with redshift,
implying an evolutionary rather than a luminosity effect. We show that for most
emission lines with a significant Baldwin Effect, and for some without,
evolution dominates over luminosity effects. This may reflect evolution in
abundances, in cloud covering factors, or overall cloud conditions such as
density and ionization. We find that in our sample, a putative correlation
between Baldwin Effect slope and the ionization potential is not significant.
Uniform measurements of other large quasar samples will extend the luminosity
and redshift range of such spectral studies and provide even stronger tests of
spectral evolution.",0104029v1
2001-10-16,XMM-Newton discovery of a sharp spectral feature at ~7 keV in the Narrow-Line Seyfert 1 galaxy 1H 0707-495,"We report the first detection of a sharp spectral feature in a Narrow-Line
Seyfert 1 galaxy. Using XMM-Newton we have observed 1H0707-495 and find a drop
in flux by a factor of more than 2 at a rest-frame energy of ~7 keV without any
detectable narrow Fe K alpha line emission. The energy of this feature suggests
a connection with the neutral iron K photoelectric edge, but the lack of any
obvious absorption in the spectrum at lower energies makes the interpretation
challenging. We explore two alternative explanations for this unusual spectral
feature: (i) partial covering absorption by clouds of neutral material and (ii)
ionised disc reflection with lines and edges from different ionisation stages
of iron blurred together by relativistic effects. We note that both models
require an iron overabundance to explain the depth of the feature. The X-ray
light curve shows strong and rapid variability, changing by a factor of four
during the observation. The source displays modest spectral variability which
is uncorrelated with flux.",0110367v1
2001-10-30,Iron K Lines from Gamma Ray Bursts,"We present models for reprocessing of an intense flux of X-rays and gamma
rays expected in the vicinity of gamma ray burst sources. We consider the
transfer and reprocessing of the energetic photons into observable features in
the X-ray band, notably the K lines of iron. Our models are based on the
assumption that the gas is sufficiently dense to allow the microphysical
processes to be in a steady state, thus allowing efficient line emission with
modest reprocessing mass and elemental abundances ranging from solar to
moderately enriched. We show that the reprocessing is enhanced by
down-Comptonization of photons whose energy would otherwise be too high to
absorb on iron, and that pair production can have an effect on enhancing the
line production. Both ""distant"" reprocessors such as supernova or wind remnants
and ""nearby"" reprocessors such as outer stellar envelopes can reproduce the
observed line fluxes with Fe abundances 30-100 times above solar, depending on
the incidence angle. The high incidence angles required arise naturally only in
nearby models, which for plausible values can reach Fe line to continuum ratios
close to the reported values.",0110654v3
2002-04-02,Boron in the Small Magellanic Cloud: A Novel Test of Light Element Production,"Hubble Space Telescope STIS observations of the B III resonance line at 2066A
have been obtained and analyzed for two Small Magellanic Cloud (SMC) B-type
stars. While boron is not detected in either star, upper limits to the boron
abundance are set, with 12+log(B/H) le 1.6 for both AV 304 and NGC 346-637. The
upper limits are consistent with the relationship between boron and oxygen
previously reported for Galactic disk stars. The SMC upper limits are discussed
in light of that galaxy's star formation history, present oxygen abundance, and
its present cosmic ray flux.
  The UV spectrum has also been used to determine the iron-group abundances in
the SMC stars. For AV 304, [Fe/H]=-0.6 pm 0.2, from both an absolute and a
differential analysis (with respect to the Galactic B-type star HD 36591). This
is consistent with results from A-F supergiants in the SMC. A lower iron
abundance is found for NGC 346-637, [Fe/H]=-1.0 pm 0.3, but this is in good
agreement with the supergiant iron abundances in NGC 330,another young SMC
cluster. We propose NGC 346-637 may be an unrecognized binary though, which
complicates its spectral analysis.",0204026v1
2002-05-03,Compton reflection and iron fluorescence in BeppoSAX observations of Seyfert type 1 galaxies,"A sample of nine bright Seyfert 1 and NELG type galaxies, observed with
BeppoSAX, is analyzed to assess on a truly broad band basis (0.1-200 keV) the
issue of the spectral contributions of Compton reflection and iron line
fluorescence from circumnuclear gas. The empirical description adopted for the
direct continuum is the commonly used power law with an exponential cut-off.
The most direct test of the theoretical predictions, namely that the equivalent
width of the line, Walpha, and the strength R of the reflection relative to the
direct continuum are closely related to each other, gives a substantially
positive result, that is their mean ratio is very close to expectation, and
only a modest spread in the iron abundance seems implied. The existence of a
steep correlation between R and the slope Gamma of the power law is not
confirmed. A weak evidence is found that the existence of a very shallow trend
to increase on average with Gamma cannot be altogether excluded in both R and
Walpha, but needs to be tested with a larger sample. The energy Ef in the
exponential cut-off spans a range from about 80 to more than 300 keV. A
possible correlation is found, with Ef increasing on average with Gamma: if
ignored, for instance by keeping Ef at a fixed value in a sample study, it
could be cause of artificial steepening in a correlation between R and Gamma.",0205045v1
2002-06-06,A long hard look at MCG-6-30-15 with XMM-Newton,"We present first results from a 325 ks observation of the Seyfert 1 galaxy
MCG-6-30-15 with XMM-Newton and BeppoSAX. The strong, broad, skewed iron line
is clearly detected and is well characterised by a steep emissivity profile
within 6r_g (i.e. 6GM/c^2) and a flatter profile beyond. The inner radius of
the emission appears to lie at about 2r_g, consistent with results reported
from both an earlier XMM-Newton observation of MCG-6-30-15 by Wilms et al. and
part of an ASCA observation by Iwasawa et al. when the source was in a lower
flux state. The radius and steep emissivity profile do depend however on an
assumed incident power-law continuum and a lack of complex absorption above 2.5
keV. The blue wing of the line profile is indented, either by absorption at
about 6.7 keV or by a hydrogenic iron emission line. The broad iron line flux
does not follow the continuum variations in a simple manner.",0206095v1
2002-11-13,A stellar relic from the early Milky Way,"The chemical composition of the most metal-deficient stars reflects the
composition of the gas from which they formed. These old stars provide crucial
clues to the star formation history and the synthesis of chemical elements in
the early Universe. They are the local relics of epochs otherwise observable
only at very high redshifts; if totally metal-free (``population III'') stars
could be found, this would allow the direct study of the pristine gas from the
Big Bang. Earlier searches for such stars found none with an iron abundance
less than 1/10,000 that of the Sun, leading to the suggestion that low-mass
stars could only form from clouds above a critical iron abundance. Here we
report the discovery of a low-mass star with an iron abundance as low as
1/200,000 of the solar value. This discovery suggests that population III stars
could still exist, that is, that the first generation of stars also contained
long-lived low-mass objects. The previous failure to find them may be an
observational selection effect.",0211274v1
2002-11-24,The influence of microlensing on the shape of the AGN Fe K-alpha line,"We study the influence of gravitational microlensing on the AGN Fe K-alpha
line confirming that unexpected enhancements recently detected in the iron line
of some AGNs can be produced by this effect. We use a ray tracing method to
study the influence of microlensing in the emission coming from a compact
accretion disc considering both geometries, Schwarzschild and Kerr.
  Thanks to the small dimensions of the region producing the AGN Fe K-alpha
line, the Einstein Ring Radii associated to even very small compact objects
have size comparable to the accretion disc hence producing noticeable changes
in the line profiles. Asymmetrical enhancements contributing differently to the
peaks or to the core of the line are produced by a microlens, off-centered with
respect to the accretion disc.
  In the standard configuration of microlensing by a compact object in an
intervening galaxy, we found that the effects on the iron line are two orders
of magnitude larger than those expected in the optical or UV emission lines. In
particular, microlensing can satisfactorily explain the excess in the iron line
emission found very recently in two gravitational lens systems, H 1413+117 and
MG J0414+0534.
  Exploring other physical {scenario} for microlensing, we found that compact
objects (of the order of one Solar mass) which belong to {the bulge or the
halo} of the host galaxy can also produce significant changes in the Fe
K$_\alpha$ line profile of an AGN. However, the optical depth estimated for
this type of microlensing is {very small, $\tau\sim 0.001$, even in a favorable
case.",0211523v1
2002-12-13,Chandra Analysis of Abell 496 - No Chemical Gradients Across Cold Fronts,"We present the results of a spatially-resolved spectroscopic analysis of the
galaxy cluster Abell 496 with the S3 chip on-board the Chandra satellite. We
confirm the presence of a central positive temperature gradient consistent with
a cooling flow, but with a minimum gas temperature of ~0.5-0.9 keV. The cluster
also exhibits sharp edges in gas density and temperature which are consistent
with ""cold front"" substructures. The iron abundance profile is not radially
symmetric relative to the cluster center. Towards the direction of the most
prominent (northerly) cold front, the iron abundance is roughly flat, with
nearly solar values. In the opposite (southerly) direction from the center, the
iron abundance distribution shows an ""off-center"" peak. Various abundance
ratios suggest that the heavy elements in the central regions of the cluster
are dominated by SN Ia ejecta. However, for radii greater than 100 kpc, the
abundance ratios vary in such a way that different abundance ratios provide
very different estimates of the proportion of SN Ia/II ejecta. Nonetheless,
observed abundances and abundance ratios are continuous across the cold fronts,
which suggests that the cold fronts are not likely to be the result of a
subcluster merger. We suggest instead that the cold fronts in A496 are caused
by ""sloshing"" of the central cooling flow gas, induced by the motion of the cD
about the cluster center.",0212332v1
2003-01-15,Feedback Heating in Cluster and Galactic Cooling Flows,"Cluster cooling flow models that include both thermal conduction and AGN
heating have lower overall mass cooling rates and simultaneously sustain
density and temperature profiles similar to those observed with no ad hoc mass
dropout. To achieve this agreement, the thermal conductivity must be about 0.35
+/- 0.10 of the Spitzer value, similar to that advocated by Narayan & Medvedev.
However, when applied to galaxy/group scales the synergistic combination of AGN
heating and conduction is less satisfactory. When the computed density profile
and the global cooling rate are lowered by AGN heating to match observations of
these smaller scale flows, the gas temperatures within about 10 kpc are too
large. In addition, best-fitting flows in galaxy/groups with AGN heating and
thermal conduction require larger conductivities, about 0.5 - 1.0 of the
Spitzer value. When the gas density in galaxy/group flows is lowered by
heating, the iron enrichment by Type Ia supernovae is more effective and the
hot gas iron abundance greatly exceeds observed values. Consequently,
galactic/group flows with central heating and conduction require an additional
process that removes the iron: failure of Type Ia ejecta to go into the hot
phase, selective cooling, etc.",0301283v1
2003-01-16,First-generation black-hole-forming supernovae and the metal abundance pattern of a very iron-poor star,"It has been proposed theoretically that the first generation of stars in the
Universe (population III) would be as massive as 100 solar masses (100Mo),
because of inefficient cooling of the precursor gas clouds. Recently, the most
iron-deficient (but still carbon-rich) low-mass star -- HE0107-5240 -- was
discovered. If this is a population III that gained its metals (elements
heavier than helium) after its formation, it would challenge the theoretical
picture of the formation of the first stars. Here we report that the patterns
of elemental abundance in HE0107-5240 (and other extremely metal-poor stars)
are in good accord with the nucleosynthesis that occurs in stars with masses of
20-130Mo when they become supernovae if, during the explosions, the ejecta
undergo substantial mixing and fall-back to form massive black holes. Such
supernovae have been observed. The abundance patterns are not, however,
consistent with enrichment by supernovae from stars in the range 130-300 Mo. We
accordingly infer that the first-generation supernovae came mostly from
explosions of ~ 20-130Mo stars; some of these produced iron-poor but carbon-
and oxygen-rich ejecta. Low-mass second-generation stars, like HE0107-5240,
could form because the carbon and oxygen provided pathways for gas to cool.",0301315v3
2003-01-21,3-D Simulations of the Chemical and Dynamical Evolution of the Galactic Bulge,"A three-dimensional hydrodynamical N-body model for the formation of the
Galaxy is presented with special attention to the formation of the bulge
component. Starting with cosmologically motivated initial conditions, we obtain
a qualitatively similar stellar system to the Galaxy. Then we analyze the
chemical and kinematic properties of the bulge stars in our model and find
qualitative agreement with observational data. The early evolution of our model
has revealed that most bulge stars form during the sub-galactic merger (merger
component of the bulge stars). Because of the strong star burst induced by the
merger, the metallicity distribution function of such stars becomes as wide as
observed. We find that another group of the bulge stars forms later in the
inner region of the disk (non-merger component of the bulge stars). Because of
the difference in the formation epoch, the main source of iron for this group
of stars is different from the merger component. Iron in the merger and
non-merger components comes mainly from Type II and Type Ia supernovae,
respectively. Since a Type Ia supernova ejects $\sim$ 10 times more iron than a
Type II supernova, [Fe/H] of the non-merger component tends to be higher than
that of the merger component, which widens the metallicity distribution
function. From these results, we suggest that the Galactic bulge consists of
two chemically different components; one has formed quickly through the
sub-galactic clump merger in the proto-galaxy and the other has formed
gradually in the inner disk.",0301404v1
2003-06-27,FeII/MgII Emission Line Ratio in High Redshift Quasars,"We present results of the analysis of near infrared spectroscopic
observations of 6 high-redshift quasars (z > 4), emphasizing the measurement of
the ultraviolet FeII/MgII emission line strength in order to estimate the
beginning of intense star formation in the early universe. To investigate the
evolution of the FeII/MgII ratio over a wider range in cosmic time, we measured
this ratio for composite quasar spectra which cover a redshift range of 0 < z <
5 with nearly constant luminosity, as well as for those which span ~6 orders of
magnitude in luminosity. A detailed comparison of the high-redshift quasar
spectra with those of low-redshift quasars with comparable luminosity shows
essentially the same FeII/MgII emission ratios and very similar continuum and
line spectral properties, i.e. a lack of evolution of the relative iron to
magnesium abundance of the gas in bright quasars since z=5. Current
nucleosynthesis and stellar evolution models predict that alpha-elements like
magnesium are produced in massive stars ending in type II SNe, while iron is
formed predominantly in SNe of type Ia with intermediate mass progenitors. This
results in an iron enrichment delay of 0.2 to 0.6 Gyr. We conclude that intense
star formation activity in the host galaxies of z>4 quasars must have started
already at an epoch corresponding to z_f = 6 to 9, when the age of the universe
was ~0.5 Gyr (H_o = 72 km/s/Mpc, Omega_M = 0.3, Omega_Lambda = 0.7). This epoch
corresponds well to the re-ionization era of the universe.",0306584v1
2003-07-07,A Massive X-Ray Outflow from the Quasar PDS 456,"We report on XMM-Newton spectroscopic observations of the luminous,
radio-quiet quasar PDS 456. The hard X-ray spectrum of PDS 456 shows a deep
absorption trough (constituting 50% of the continuum) at energies above 7 keV
in the quasar rest frame, which can be attributed to a series of blue-shifted
K-shell absorption edges due to highly ionized iron. The higher resolution soft
X-ray RGS spectrum exhibits a broad absorption line feature near 1 keV, which
can be modeled by a blend of L-shell transitions from highly ionized iron (Fe
XVII-XXIV). An extreme outflow velocity of 50000 km/s is required to model the
K and L shell iron absorption present in the XMM-Newton data. Overall, a large
column density ($N_{H}=5\times10^{23}$cm$^{-2}$) of highly ionized gas
(logxi=2.5) is required in PDS 456. A high mass outflow rate of 10 solar masses
per year (assuming a conservative outflow covering factor of 0.1 steradian) is
derived, which is of the same order as the overall mass accretion rate in PDS
456. The kinetic energy of the outflow represents a substantial fraction (10%)
of the quasar energy budget, whilst the large column and outflow velocity place
PDS 456 towards the extreme end of the broad absorption line quasar population.",0307127v1
2003-07-31,Iron Emission in the z=6.4 Quasar SDSS J114816.64+525150.3,"We present near-infrared J and K-band spectra of the z = 6.4 quasar SDSS
J114816.64+525150.3 obtained with the NIRSPEC spectrograph at the Keck-II
telescope, covering the rest-frame spectral regions surrounding the C IV 1549
and Mg II 2800 emission lines. The iron emission blend at rest wavelength
2900-3000 A is clearly detected and its strength appears nearly
indistinguishable from that of typical quasars at lower redshifts. The Fe II /
Mg II ratio is also similar to values found for lower-redshift quasars,
demonstrating that there is no strong evolution in Fe/alpha broad-line emission
ratios even out to z=6.4. In the context of current models for iron enrichment
from Type Ia supernovae, this implies that the SN Ia progenitor stars formed at
z > 10. We apply the scaling relations of Vestergaard and of McLure & Jarvis to
estimate the black hole mass from the widths of the C IV and Mg II emission
lines and the ultraviolet continuum luminosity. The derived mass is in the
range (2-6)x10^9 solar masses, with an additional uncertainty of a factor of 3
due to the intrinsic scatter in the scaling relations. This result is in
agreement with the previous mass estimate of 3x10^9 solar masses by Willott,
McLure, & Jarvis, and supports their conclusion that the quasar is radiating
close to its Eddington luminosity.",0308005v1
2003-08-19,Modeling the NeIX Triplet Spectral Region of Capella with the Chandra and XMM-Newton Gratings,"High resolution X-ray spectroscopy with the diffraction gratings of Chandra
and XMM-Newton offers new chances to study a large variety of stellar coronal
phenomena. A popular X-ray calibration target is Capella, which has been
observed with all gratings with significant exposure times. We gathered
together all available data of the HETGS (155ks), LETGS (219ks), and RGS (53ks)
for comparative analysis focusing on the NeIX triplet at around 13.5A, a region
that is severely blended by strong iron lines. We identify 18 emission lines in
this region of the HEG spectrum, including many from FeXIX, and find good
agreement with predictions from a theoretical model constructed using the
Astrophysical Plasma Emission Code (APEC). The model uses an emission measure
distribution derived from FeXV to FeXXIV lines. While these 18 emission lines
cannot be isolated in the LETGS or RGS spectra, their wavelengths and fluxes as
measured with HEG are consistent with the lower resolution spectra. In the
Capella model for HEG, the weak intercombination line of NeIX is significantly
blended by iron lines, which contribute about half the flux. After accounting
for blending in the He-like diagnostic lines, we find the density to be
consistent with the low density limit (n_e<2 10^10 cm^-3); however, the
electron temperature indicated by the NeIX G-ratio is surprisingly low (~2MK)
compared with the peak of the emission measure distribution (~6MK). Models show
that the NeIX triplet is less blended in cooler plasmas and in plasmas with an
enhanced neon-to-iron abundance ratio.",0308317v1
2003-09-12,Detection of a Fully-resolved Compton Shoulder of the Iron K-alpha Line in the Chandra X-ray Spectrum of GX 301-2,"We report the detection of a fully-resolved, Compton-scattered emission line
in the X-ray spectrum of the massive binary GX 301-2 obtained with the High
Energy Transmission Grating Spectrometer onboard the Chandra X-ray Observatory.
The iron K-alpha fluorescence line complex observed in this system consists of
an intense narrow component centered at an energy of E = 6.40 keV and a redward
shoulder that extends down to ~6.24 keV, which corresponds to an energy shift
of a Compton back-scattered iron K-alpha photon. From detailed Monte Carlo
simulations and comparisons with the observed spectra, we are able to directly
constrain the physical properties of the scattering medium, including the
electron temperature and column density, as well as an estimate for the metal
abundance.",0309344v1
2003-12-19,XMM-Newton observations of Sagittarius A East,"We present an analysis of a recent XMM-Newton observation of Sgr A East, a
supernova remnant located close to the Galactic Centre. Very high quality X-ray
spectra reveal many emission lines from highly ionized atoms consistent with a
multi-temperature thin thermal plasma in ionization equilibrium. We use a
two-temperature model to fit the spectra and derive temperatures of 1 keV and 4
keV. There is significant concentration of iron towards the centre of the X-ray
source such that the iron abundance varies from ~4 times solar in the core down
to ~0.5 solar in the outer regions, which contrasts with the rather uniform
distribution of other metals such as sulfur, argon and calcium, which have
abundances in the range 1--3. The derived total energy, mass, and the abundance
pattern are consistent with a single supernova event, either of type-Ia or
type-II origin, involving a relatively low-mass progenitor star. A weak 6.4-keV
neutral iron fluorescence line is also detected, the illumination source most
likely being Sgr A East itself. The morphology and spectral characteristics of
Sgr A East show no clear linkage to putative past activity in Sgr A*.",0312541v1
2004-02-06,The Possibility of Emersion of the Outer Layers in a Massive Star Simultaneously with Iron-Core Collapse: A Hydrodynamic Model,"We analyze the behavior of the outer envelope in a massive star during and
after the collapse of its iron core into a protoneutron star (PNS) in terms of
the equations of one-dimensional spherically symmetric ideal hydrodynamics. The
profiles obtained in the studies of the evolution of massive stars up to the
final stages of their existence, immediately before a supernova explosion
(Boyes et al. 1999), are used as the initial data for the distribution of
thermodynamic quantities in the envelope.We use a complex equation of state for
matter with allowances made for arbitrary electron degeneracy and relativity,
the appearance of electron-positron pairs, the presence of radiation, and the
possibility of iron nuclei dissociating into free nucleons and helium nuclei.
We performed calculations with the help of a numerical scheme based on
Godunov's method. These calculations allowed us to ascertain whether the
emersion of the outer envelope in a massive star is possible through the
following two mechanisms: first, the decrease in the gravitational mass of the
central PNS through neutrino-signal emission and, second, the effect of hot
nucleon bubbles, which are most likely formed in the PNS corona, on the
envelope emersion. We show that the second mechanism is highly efficient in the
range of acceptable masses of the nucleon bubbles ($\leq 0.01M_\odot$)
simulated in our hydrodynamic calculations in a rough, spherically symmetric
approximation.",0402153v1
2004-02-13,Iron Kalpha emission from the low-luminosity Active Galaxies M81 and NGC 4579,"We report on XMM-Newton spectroscopy of the low-luminosity active galaxies
(LLAGN) M81 and NGC4579 both of which have known black hole masses and
well-sampled spectral energy distributions (SED). The iron Kalpha line profiles
from both the LLAGN can be described in terms of two components - a narrow line
at 6.4 keV and a moderately broad line (FWHM = 20000 km/s) arising from highly
ionized, He-like or H-like species (E \sim 6.8 keV). We interpret the broad
lines arising from an accretion disk the inner edge of which is restricted to
large radii (r_{in} \sim 100 r_g). However, the Eddington ratio, {L}/{L_{Edd}},
of these sources, is 3 - 4 orders of magnitude lower than that required to
photo-ionize a cold disk to He-like iron. We suggest that the lines can be
explained as collisionally ionized X-ray lines arising from the transition
region between a hot (radiatively inefficient) flow in the inner regions and a
cold disk outside r \sim 100r_g. The accretion flow geometry probed by our
XMM-Newton observations is consistent with the truncated disk models proposed
to explain the SED of LLAGNs.",0402327v1
2004-05-28,The soft X-ray absorption lines of the Seyfert 1 galaxy MCG--6-30-15,"The absorption lines in the soft X-ray spectrum of MCG--6-30-15 are studied
using the Reflection Grating Spectrometer data from the 2001 XMM-Newton 320 ks
observation. A line search of the full time-averaged spectrum reveals 51
absorption lines and one emission line. The equivalent widths of the lines are
measured and the majority of the lines identified. We find lines produced by a
broad range of charge states for several elements, including almost all the
charge states oxygen and iron, suggesting a broad range of ionization
parameters is present in the warm absorber. The equivalent widths of the lines
are broadly consistent with the best fitting warm absorber models from Turner
et al (2003). The equivalent widths of the absorption lines allow confidence
limits on the column density of the species to be determined. For OVII a column
density of 10^18.36-10^18.86 cm^-2 is found. This column density of OVII, when
combined with the inferred FeI absorption, is sufficient to explain the drop in
flux at 0.7 keV as being due to absorption from the warm absorber. Fitting OI
K-edge absorption to the spectrum reveals a column of 10^17.51-10^17.67 cm^-2
of OI, suggesting an Fe:O ratio of ~1:2, consistent with the neutral iron being
in the form of iron oxide dust. Variability is seen in a few absorption lines,
but the majority of the absorption features, including the prominent absorption
edges, stay constant throughout the observation despite variability in the
continuum flux.",0405570v1
2004-06-29,"Nucleosynthesis in Fast Expansions of High-Entropy, Proton Rich Matter","We demonstrate that nucleosynthesis in rapid, high-entropy expansions of
proton-rich matter from high temperature and density can result in a wider
variety of abundance patterns than heretofore appreciated. In particular, such
expansions can produce iron-group nuclides, p-process nuclei, or even heavy,
neutron-rich isotopes. Such diversity arises because the nucleosynthesis enters
a little explored regime in which the free nucleons are not in equilibrium with
the abundant alpha particles. This allows nuclei significantly heavier than
iron to form in t he presence of abundant free nucleons early in the expansion.
As the temperature drops, nucleons increasingly assemble into alpha particles
and heavier nuclei. If the assembly is efficient, the resulting depletion of
free neutrons allows disintegrat ion flows to drive nuclei back down to iron
and nickel. If this assembly is inefficient, then the large abundance of free
nucleons prevents the disintegration flows and leaves a distribution of heavy
nuclei after reaction freezeout. For cases in between, an intermediate
abundance distribution, enriched in p-process isotopes, is frozen out. These
last expansions may contribute to the solar system's supply of the p-process
nuclides if mildly proton-rich, high-entropy matter is ejected from
proto-neutron stars winds or other astrophysical sites. Also sign ificant is
the fact that, because the nucleosynthesis is primary, the signature of this
nucleosyn thesis may be evident in metal poor stars.",0406659v1
2004-09-24,Detection of hard X-ray pulsations and a strong iron K_beta emission line during an extended low state of GX 1+4,"We present here results obtained from a detailed timing and spectral analysis
of three BeppoSAX observations of the binary X-ray pulsar GX 1+4 carried out in
August 1996, March 1997, and August 2000. In the middle of the August 2000
observation, the source was in a rare low intensity state that lasted for about
30 hours. Though the source does not show pulsations in the soft X-ray band
(1.0-5.5 keV) during the extended low state, pulsations are detected in
5.5-10.0 keV energy band of the MECS detector and in hard X-ray energy bands
(15-150 keV) of the PDS instrument. Comparing the 2-10 keV flux during this low
state with the previously reported low states in GX 1+4, we suggest that the
propeller regime in GX 1+4 occurs at a lower mass accretion rate than reported
earlier. Broad-band (1.0-150 keV) pulse averaged spectroscopy reveals that the
best-fit model comprises of a Comptonized continuum along with an iron K_alpha
emission line. A strong iron K_beta emission line is detected for the first
time in GX 1+4 during the extended low state of 2000 observation with
equivalent width of ~550 eV. The optical depth and temperature of the
Comptonizing plasma are found to be identical during the high and low intensity
states whereas the hydrogen column density and the temperature of the seed
photons are higher during the low state. We also present results from pulse
phase resolved spectroscopy during the high and low flux episodes.",0409587v1
2004-12-20,"Ultrahigh Energy Nuclei Propagation in a Structured, Magnetized Universe","We compare the propagation of iron and proton nuclei above 10^19 eV in a
structured Universe with source and magnetic field distributions obtained from
a large scale structure simulation and source densities about 10^(-5) Mpc^(-3).
All relevant cosmic ray interactions are taken into account, including
photo-disintegration and propagation of secondary products. Iron injection
predicts spectral shapes different from proton injection which disagree with
existing data below about 30 EeV. Injection of light nuclei or protons must
therefore contribute at these energies. However, at higher energies, existing
data are consistent with injection of pure iron with spectral indices between 2
and 2.4. This allows a significant recovery of the spectrum above roughly 100
EeV, especially in the case of large deflections. Significant auto-correlation
and anisotropy, and considerable cosmic variance are also predicted in this
energy range. The mean atomic mass A fluctuates considerably between different
scenarios. At energies below 60 EeV, if the observed A > 35, magnetic fields
must have a negligible effect on propagation. At the highest energies the
observed flux will be dominated by only a few sources whose location may be
determined by next generation experiments to within 10-20 degrees even if
extra-galactic magnetic fields are important.",0412525v1
2004-12-23,Iron Fluorescent Line Emission from Young Stellar Objects in the Orion Nebula,"We present the result of a systematic search for the iron Kalpha fluorescent
line at 6.4 keV among 1616 X-ray sources detected by ultra-deep Chandra
observations of the Orion Nebula Cluster and the obscured Orion Molecular Cloud
1 population as part of the Chandra Orion Ultra-deep Project (COUP). Seven
sources are identified to have an excess emission at 6.4 keV among 127 control
sample sources with significant counts in the 6.0-9.0 keV band. These seven
sources are young stellar objects (YSOs) characterized by intense flare-like
flux variations, thermal spectra, and near-infrared (NIR) counterparts. The
observed equivalent widths of the line cannot be attributed to the fluorescence
by interstellar or circumstellar matter along the line of sight. The X-ray
spectral fits and NIR colors of the 6.4 keV sources show that these sources
have X-ray absorption of > 1x10^22 cm^(-2) and NIR excess emission, which is
not expected when the fluorescence occurs at the stellar photosphere. We
therefore conclude that the iron fluorescent line of YSOs arises from
reflection off of circumstellar disks, which are irradiated by the hard X-ray
continuum emission of magnetic reconnection flares.",0412608v2
2005-03-09,A broad iron line in the Chandra/HETG spectrum of 4U 1705-44,"We present the results of a Chandra 30 ks observation of the low mass X-ray
binary and atoll source 4U 1705-44. Here we concentrate on the study of
discrete features in the energy spectrum at energies below 3 keV, as well as on
the iron Kalpha line, using the HETG spectrometer on board of the Chandra
satellite. Below 3 keV, three narrow emission lines are found at 1.47, 2.0, and
2.6 keV. The 1.47 and 2.6 keV are probably identified with Ly-alpha emission
from Mg XII and S XVI, respectively. The identification of the feature at 2.0
keV is uncertain due to the presence of an instrumental feature at the same
energy. The iron Kalpha line at ~6.5 keV is found to be intrinsically broad
(FWHM ~ 1.2 keV); its width can be explained by reflection from a cold
accretion disk extending down to 15 km from the neutron star center or by
Compton broadening in the external parts of a hot (~2 keV) Comptonizing corona.
We finally report here precise X-ray coordinates of the source.",0503224v1
2005-04-26,Axisymmetric collapse simulations of rotating massive stellar cores in full general relativity: Numerical study for prompt black hole formation,"We perform axisymmetric simulations for gravitational collapse of a massive
iron core to a black hole in full general relativity. The iron cores are
modeled by $\Gamma = 4/3$ equilibrium polytrope for simplicity and a parametric
equation of state is adopted during the collapse. Performing simulations for a
wide variety of initial conditions changing the mass, the angular momentum, the
rotational velocity profile of the core, and the parameters of the equations of
state (which are chosen so that the maximum mass of the cold spherical
polytrope is $\approx 1.6M_{\odot}$), a criterion for the prompt black hole
formation is clarified in terms of them. It is found that (i) with the increase
of the thermal energy generated by shocks, the threshold mass for the prompt
black hole formation is increased by 20--40%, (ii) the rotational centrifugal
force increases the threshold mass by $\alt 25%$, (iii) with the increase of
the degree of differential rotation, the threshold mass is also increased, and
(iv) the amplification factors shown in the results (i)--(iii) depend
sensitively on the equation of state. We also find that the collapse dynamics
and the structure of the shock formed at the bounce depend strongly on the
stiffness of the adopted equation of state. In particular, as a new feature, a
strong bipolar explosion is observed for the collapse of rapidly rotating iron
cores with an equation of state which is stiff in subnuclear density and soft
in supranuclear density. Gravitational waves are computed in terms of a
quadrupole formula. It is also found that the waveform depends sensitively on
the equations of state.",0504567v1
2005-06-10,X-ray Spectral Evolution of Her X-1 in a Low State and the Following Short High State,"We analyzed spectral variations of $\sim 8.5$ days long RXTE monitoring
observations of Her X-1 in December 2001. This set of observations enables, for
the first time, frequent continuous monitoring (111 pointings in $\sim 8.5$
days) of the source with RXTE including $\sim 1.7$ days long low state part and
the following $\sim 6.8$ days long short high state part. We used absorbed
power law model with iron line energy complex modeled as a Gaussian to fit both
the 3-60 keV PCA-HEXTE overall short high state spectrum and 3-20 keV
individual PCA spectra. Additional partial cold absorber model was used for
both cases. Using 3-20 keV individual PCA spectra, absorption in anomalous dips
and preeclipse dips in short high state were compared. Decreasing ratio of
unabsorbed flux to absorbed flux with increasing unabsorbed flux in anomalous
and preeclipse dips was interpreted as an evidence of the fact that the regions
causing opaque obscuration and soft absorption are not geometrically far away
from each other. Higher iron line peak energies in low state and short high
state ($\sim 6.6-6.9$ keV) were interpreted as a clue of the presence of iron
line components other than K$\alpha$ emission line.",0506227v1
2005-09-11,Evidence for Gravitational Infall of Matter onto the Super-Massive Black Hole in the quasar PG 1211+143?,"We report the detection of redshifted iron K-alpha absorption lines in the
Chandra LETG spectrum of the narrow-line quasar, PG 1211+143. The absorption
lines are observed at 4.22 keV and 4.93 keV in the quasar spectrum,
corresponding to 4.56 keV and 5.33 keV in the rest frame of PG 1211+143. From
Monte Carlo simulations, the chance probability of both lines being false
detections is low at 1.36e-04. Highly redshifted ionized iron K-alpha (Fe XXV
or Fe XXVI) is the most plausible identification for the lines at their
observed energies. If identified with H-like iron K-alpha at 6.97 keV, then the
relativistic velocity shifts required are 0.40c and 0.26c. The extreme
velocities can be explained by pure gravitational redshift if the matter exists
in a stable orbit within 6 gravitational radii of the black hole. This would
require a Kerr metric for the black hole. Alternatively the absorption may be
the result of matter infalling directly onto the black hole, with a maximum
observed velocity of 0.38c at 6Rg in the Schwarzschild metric. This matter may
originate in a failed outflow or jet, which does not escape the gravitational
potential of the black hole.",0509280v1
2005-09-22,A Compton reflection dominated spectrum in a peculiar accreting neutron star,"We report on a puzzling event occurred during a long BeppoSAX observation of
the slow-rotating binary pulsar GX 1+4. During this event, lasting about 1 day,
the source X-ray flux was over a factor 10 lower than normal. The low-energy
pulsations disappeared while at higher energies they were shifted in phase. The
spectrum taken outside this low-intensity event was well fitted by an absorbed
cut-off power law, and exhibited a broad iron line at ~6.5 keV probably due to
the blending of the neutral (6.4 keV) and ionised (6.7 keV) K_alpha iron lines.
The spectrum during the event was Compton reflection dominated and it showed
two narrow iron lines at ~6.4 keV and ~7.0 keV, the latter never revealed
before in this source. We also present a possible model for this event in which
a variation of the accretion rate thickens a torus-like accretion disc which
hides for a while the direct neutron star emission from our line of sight. In
this scenario the Compton reflected emission observed during the event is well
explained in terms of emission reflected by the side of the torus facing our
line of sight.",0509692v1
2006-08-03,The Galactic WN stars: Spectral analyses with line-blanketed model atmospheres versus stellar evolution models with and without rotation,"CONTEXT: Very massive stars pass through the Wolf-Rayet (WR) stage before
they finally explode. Details of their evolution have not yet been safely
established, and their physics are not well understood. Their spectral analysis
requires adequate model atmospheres, which have been developed step by step
during the past decades and account in their recent version for line blanketing
by the millions of lines from iron and iron-group elements. However, only very
few WN stars have been re-analyzed by means of line-blanketed models yet.
  AIMS: The quantitative spectral analysis of a large sample of Galactic WN
stars with the most advanced generation of model atmospheres should provide an
empirical basis for various studies about the origin, evolution, and physics of
the Wolf-Rayet stars and their powerful winds.
  METHODS: We analyze a large sample of Galactic WN stars by means of the
Potsdam Wolf-Rayet (PoWR) model atmospheres, which account for iron line
blanketing and clumping. The results are compared with a synthetic population,
generated from the Geneva tracks for massive star evolution. RESULTS: We obtain
a homogeneous set of stellar and atmospheric parameters for the Galactic WN
stars, partly revising earlier results.
  CONCLUSIONS: Comparing the results of our spectral analyses of the Galactic
WN stars with the predictions of the Geneva evolutionary calculations, we
conclude that there is rough qualitative agreement. However, the quantitative
discrepancies are still severe, and there is no preference for the tracks that
account for the effects of rotation. It seems that the evolution of massive
stars is still not satisfactorily understood.",0608078v1
2006-08-25,Fundamental Parameters and Abundances of Metal-Poor Stars: The SDSS Standard BD +17 4708,"The atmospheric parameters and iron abundance of the Sloan Digital Sky Survey
(SDSS) spectrophotometric standard star BD +17 4708 are critically examined
using up-to-date Kurucz model atmospheres, LTE line formation calculations, and
reliable atomic data. We find Teff = 6141+-50 K, log g = 3.87+-0.08, and
[Fe/H]=-1.74+-0.09. The line-of-sight interstellar reddening, bolometric flux,
limb-darkened angular diameter, stellar mass, and the abundances of Mg, Si, and
Ca are also obtained. This star is a unique example of a moderately metal-poor
star for which the effective temperature can be accurately constrained from the
observed spectral energy distribution (corrected for reddening). Such analysis
leads to a value that is higher than most spectroscopic results previously
reported in the literature (~5950 K). We find that the ionization balance of Fe
lines is satisfied only if a low Teff (~5950 K) is adopted. With our preferred
Teff (6141 K), the mean iron abundance we obtain from the FeII lines is lower
by about 0.15 dex than that from the FeI lines, and therefore, the discrepancy
between the mean iron abundance from FeI and FeII lines cannot be explained by
overionization by UV photons as the main non-LTE effect. We also comment on
non-LTE effects and the importance of inelastic collisions with neutral H atoms
in the determination of oxygen abundances in metal-poor stars from the 777 nm
OI triplet. (Abridged)",0608559v1
2006-10-05,XMM-Newton observation of the NLS1 Galaxy Ark 564: I. Spectral analysis of the time-average spectrum,"We use the data from a recent, 100 ksec XMM-Newton observation of the Narrow
Line Seyfert 1 galaxy Ark 564 to obtain its time average, X-ray spectrum. The
3-11 keV spectrum is well fitted by a power-law of slope 2.43. We detect a weak
(equivalent width ~80 eV) emission line at ~6.7 keV, which implies emission
from ionized iron. There is no compelling evidence for significant broadening
of the line.We also detect a possible Doppler shifted absorption line at 8.1
keV. At energies lower than 2 keV, the spectrum is dominated by a smooth soft
excess component which can be well fitted either by a two black body components
(kT~0.15 and 0.07 keV) or by a black body plus a relativistically blurred
photoionized disc reflection model. We detect a broad, shallow flux deficit in
the 0.65-0.85 keV band, reminiscent of the iron unresolved transition array
(UTA) features. We do not detect neither a strong absorption edge around 0.7
keV nor an emission line around 1 keV. The soft excess emission is consistent
with being reflected emission from a geometrically flat disc, with solar
abundances, illuminated by an isotropic source. The weakness of the iron line
emission can be explained by relativistic blurring. The UTA feature implies the
presence of warm material with a column density of 2-5*10^{20} cm^{-2}. If the
absorption line at 8.1 keV corresponds to FeXXVI Kalpha, it suggests the
presence of a highly ionized absorbing material with N_H > 10^{23} cm^{-2},
outflowing at a high velocity of ~0.17c.",0610154v1
2007-03-13,"Gamma ray bursts, supernovae and metallicity in the intergalactic medium","The mean iron abundance observed in the intergalactic medium (IGM) within
galaxy clusters and without galaxy clusters is consistent with the mean amount
of iron per unit volume in the Universe which has been produced by standard
supernova (SN) explosions with a rate proportional to the cosmic star-formation
rate. If most SNe took place inside galaxies, then the IGM could have been
enriched with their metals by galactic winds and jets that swept most of the
galactic gas with the SNe ejecta into the IGM. A significant fraction of the
early SNe, however, could have taken place outside galaxies or within dwarf
galaxies, which were later disrupted by tidal interactions, and/or mass loss
through fast winds, SN ejecta and jets. Little is known about such
intergalactic SNe at high red-shifts. They could have occurred primarily in
highly obscured environments, avoiding detection. Supporting evidence for
intergalactic SNe is provided by SNe associated with gamma ray bursts (GRBs)
without a host galaxy and from the ratio of well localized GRBs with and
without a host galaxy. A direct test of whether a significant contribution to
the iron abundance in the IGM came from intergalactic SNe would require the
measurement of their rate per comoving unit volume as function of red-shift.
This may be feasible with IR telescopes, such as the Spitzer Space Telescope.",0703293v3
1995-08-10,Structure and Magnetism of Fe/Si Multilayers Grown by Ion-Beam Sputtering,"Ion-beam sputtering has been used to prepare Fe/Si multilayers on a variety
of substrates and over a wide range of temperatures. Small-angle x-ray
diffraction and transmission electron microscopy experiments show that the
layers are heavily intermixed although a composition gradient is maintained.
When the spacer layer is an amorphous iron silicide, the magnetic properties of
the multilayers are similar to those of bulk Fe. When the spacer layer is a
crystalline silicide with the B2 or DO$_3$ structure, the multilayers show
antiferromagnetic interlayer coupling like that observed in
ferromagnet/paramagnet multilayers such as Fe/Cr and Co/Cu. Depending on the
substrate type and the growth temperature, the multilayers grow in either the
(011) or (001) texture. The occurrence of the antiferromagnetic interlayer
coupling is dependent on the crystallinity of the iron and iron silicide
layers, but does not seem to be strongly affected by the perfection of the
layering or the orientation of the film. Since the B2- and DO$_3$-structure
Fe$\rm _x$Si$\rm _{1-x}$ compounds are known to be metallic, antiferromagnetic
interlayer coupling in Fe/Si multilayers probably originates from the same
quantum-well and Fermi surface effects as in Fe/Cr and Co/Cu multilayers.",9508032v1
2000-04-06,Electronic structure and magnetism of equiatomic FeN,"In order to investigate the phase stability of equiatomic FeN compounds and
the structure-dependent magnetic properties, the electronic structure and total
energy of FeN with NaCl, ZnS and CsCl structures and various magnetic
configurations are calculated using the first-principles TB-LMTO-ASA method.
Among all the FeN phases considered, the antiferromagnetic NaCl structure with
q=(00pi) is found to have the lowest energy at the theoretical equilibrium
volume. However, the FM NaCl phase lies only 1mRyd higher. The estimated
equilibrium lattice constant for nonmagnetic ZnS-type FeN agrees quite well
with the experimental value, but for the AFM NaCl phase the estimated value is
6.7% smaller than that observed experimentally. For ZnS-type FeN, metastable
magnetic states are found for volumes larger than the equilibrium value. On the
basis of an analysis of the atom- and orbital-projected density of states and
orbital-projected Crystal Orbital Hamilton Population, the iron-nitrogen
interactions in NM ZnS, AFM NaCl and FM CsCl structures are discussed. The
leading Fe-N interactions is due to the d-p iron-nitrogen hybridization, while
considerable s-p and p-p hybridizations are also observed in all three phases.
The iron magnetic moment in FeN is found to be highly sensitive to the
nearest-neighboring Fe-N distance. In particular, the magnetic moment shows an
abrupt drop from a value of about 2 muB to zero with the reduction of the Fe-N
distance for the ZnS and CsCl structures.",0004091v1
2003-06-04,Interaction of superconductor with magnetic sheath as a way for improvement of critical current in MgB2/Fe superconductor,"Magnesium diboride superconducting wires give the largest critical current
density (Jc) when produced with iron sheath. Because iron is ferromagnetic, it
is expected to improve the field dependence of Jc by shielding of the external
field for low magnetic fields. However, transport and magnetic measurements of
Jc reveal that Jc in MgB2/Fe is improved far beyond the effect of simple
magnetic shielding. The transport measurements in external field show that Jc
initially decreases with the field. This is followed by an increase for
intermediate fields and again a decrease for high fields, resembling the ?peak
effect?. The value of Jc in the field range of this peak effect is higher than
the Jc without iron sheath. The field range of improved Jc widens with
decreasing the temperature, shifting to the higher values of the field. The
explanation of this phenomenon is suggested in terms of a model predicting the
occurrence of overcritical state, as a result of interaction between partly
vortex filled superconductor and a magnet. In this model, the currents are
pushed into vortex-free volume of the superconductor, effectively increasing
its value of loss-free current. The occurrence of the overcritical state is
supported by magnetic measurements of Jc.",0306083v1
2003-07-11,Ab initio Simulations of Fe-based Ferric Wheels,"Based on first-principles density-functional theory calculations we
investigate the electronic structure of hexanuclear ""ferric wheels"" M
Fe_6[N(CH_2 CH_2 O)_3]_6 Cl (M = Li, Na) in their antiferromagnetic ground
state. The electronic structure is presented in form of spin- and site-resolved
local densities of states. The latter clearly indicate that the magnetic moment
is distributed over several sites. The local moment at the iron site is still
the largest one with about 4 mu_B, thus indicating the valence state of iron to
be closer to Fe(II) than to commonly accepted Fe(III). The local spin of S=5/2
per iron site, following from magnetization measurements, is perfectly
reproduced if one takes the moments on the neighbor atoms into account. The
largest magnetic polarization is found on the apical oxygen atom, followed by
nitrogen bridging oxygens. These findings are confirmed by a map of spatial
spin density. A further goal of the present study has been a comparative test
of two different DFT implementations, Siesta and NRLMOL. They yield a very good
agreement down to small details in the electronic structure.",0307292v2
2005-09-21,Effect of iron-doping on spin-state transition and ferromagnetism in Pr$_{0.5}$Ca$_{0.5}$CoO$_{3-δ}$ cobalt oxides,"Resistivity and dc magnetization measurements were performed for the
polycrystalline Pr$_{0.5}$Ca$_{0.5}$Co$_{1-x}$Fe$_{x}$O$_{3-\delta}$ ($x$ = 0,
0.05, 0.10 and 0.15) samples. The as-fabricated samples exhibit ferromagnetic
(FM) transition and the transition temperature increases with increasing the
iron doping level. Annealing under high oxygen pressure induces a spin-state
transition of Co ions in the \emph{iron-free} sample and such transition is
reinforced with increasing the annealing oxygen pressure, while the annealing
under high oxygen pressure suppresses the ferromagnetic ordering. Contrary to
the case of the \emph{iron-free} sample, no spin-state transition is induced by
the annealing under high oxygen pressure for the \emph{iron-doped} samples, and
the ferromagnetic transition temperature is nearly independent of the annealing
procedures. The enhancement of the spin-state transition in the
\emph{iron-free} sample after annealing under high oxygen pressure should be
attributed to the reduction of the cell volume. The suppression of the
spin-state transition by the Fe doping is related to the enlargement of the
cell volume and the stronger Fe-O bonds than Co-O bonds. The enhancement of the
ferromagnetism by the iron-doping might arise from the ferromagnetic exchange
interaction between Fe$^{3+}$ and Co$^{4+}$ through oxygen
(Fe$^{3+}$-O-Co$^{4+}$).",0509533v1
2006-01-25,The wave model of martensite growth for the FCC-BCC transformation of iron-based alloys,"This book is the first monograph in the scientific literature, dedicated to
the FCC-BCC transformation in iron-based alloys, in which the dynamical
approach is used for the explanation of the martensite growth stage.
  The rapid growth of a cooling martensite crystal is considered as a
self-organized process controlled by the quasi-longitudinal lattice
displacement waves (DW). The regime of the DW initial excitation is rigid. DW
have the frequencies ~$10^{10} sec^{-1}$ from the hypersound band and the
amplitudes providing the level of deformation ~$10^{-3}$. The conditions that
are necessary for the generation of DW by non-equilibrium d-electrons are
analyzed.
  A wide range of questions (from peculiarities of the electronic spectrum to
macroscopic morphological indicators), connected with the physical
interpretation of the FCC-BCC martensitic transformation in iron-based alloys,
is discussed.
  The short review of results having fundamental meaning for the creation of a
physical model describing the martensite nucleation process is given in the
monograph's conclusion. It is shown, that processes of the heterogeneous
nucleation and wave growth have the genetic connection to the FCC-BCC
martensitic transformation. The short review of the last author's results
revealing features of the physical mechanisms controlling processes of
martensite crystal formation for all alternatives of the FCC-BCC martensitic
transformation is given in the monograph's epilogue.",0601569v4
2006-03-06,Magnetism of iron: from the bulk to the monoatomic wire,"The magnetic properties of iron (spin and orbital magnetic moments,
magnetocrystalline anisotropy energy) in various geometries and
dimensionalities are investigated by using a parametrized tight-binding model
in an $s$, $p$ and $d$ atomic orbital basis set including spin polarization and
the effect of spin-orbit coupling. The validity of this model is well
established by comparing the results with those obtained by using an ab-initio
code. This model is applied to the study of iron in bulk bcc and fcc phases,
$(110)$ and $(001)$ surfaces and to the monatomic wire, at several interatomic
distances. New results are derived. The variation of the component of the
orbital magnetic moment on the spin quantization axis has been studied as a
function of depth, revealing a significant enhancement in the first two layers,
especially for the $(001)$ surface. It is found that the magnetic anisotropy
energy is drastically increased in the wire and can reach several meV. This is
also true for the orbital moment, which in addition is highly anisotropic.
Furthermore it is shown that when the spin quantization axis is neither
parallel nor perpendicular to the wire the average orbital moment is not
aligned with the spin quantization axis. At equilibrium distance the easy
magnetization axis is along the wire but switches to the perpendicular
direction under compression. The success of this model opens up the possibility
of obtaining accurate results on other elements and systems with much more
complex geometries.",0603121v1
1998-09-24,Oxygen in the Earth's core: a first principles study,"First principles electronic structure calculations based on density
functional theory have been used to study the thermodynamic, structural and
transport properties of solid solutions and liquid alloys of iron and oxygen at
Earth's core conditions. Aims of the work are to determine the oxygen
concentration needed to account for the inferred density in the outer core, to
probe the stability of the liquid against phase separation, to interpret the
bonding in the liquid, and to find out whether the viscosity differs
significantly from that of pure liquid iron at the same conditions. It is shown
that the required concentration of oxygen is in the region 25-30 mol percent,
and evidence is presented for phase stability at these conditions. The Fe-O
bonding is partly ionic, but with a strong covalent component. The viscosity is
lower than that of pure liquid iron at Earth's core conditions. It is shown
that earlier first-principles calculations indicating very large enthalpies of
formation of solid solutions may need reinterpretation, since the assumed
crystal structures are not the most stable at the oxygen concentration of
interest.",9809036v1
2007-07-18,Chemical Abundances of Luminous Cool Stars in the Galactic Center from High-Resolution Infrared Spectroscopy,"We present chemical abundances in a sample of luminous cool stars located
within 30 pc of the Galactic Center. Abundances of carbon, nitrogen, oxygen,
calcium, and iron were derived from high-resolution infrared spectra in the H-
and K-bands. The abundance results indicate that both [O/Fe] and [Ca/Fe] are
enhanced respectively by averages of +0.2 and +0.3 dex, relative to either the
Sun or the Milky Way disk at near solar Fe abundances. The Galactic Center
stars show a nearly uniform and nearly solar iron abundance. The mean value of
A(Fe) = 7.59 +- 0.06 agrees well with previous work. The total range in Fe
abundance among Galactic Center stars, 0.16 dex, is significantly narrower than
the iron abundance distributions found in the literature for the older bulge
population. Our snapshot of the current-day Fe abundance within 30 pc of the
Galactic Center samples stars with an age less than 1 Gyr; a larger sample in
time (or space) may find a wider spread in abundances.",0707.2610v1
2007-07-19,Mass-Radius Relationships for Solid Exoplanets,"We use new interior models of cold planets to investigate the mass-radius
relationships of solid exoplanets, considering planets made primarily of iron,
silicates, water, and carbon compounds. We find that the mass-radius
relationships for cold terrestrial-mass planets of all compositions we
considered follow a generic functional form that is not a simple power law:
$\log_{10} R_s = k_1 + 1/3 \log_{10}(M_s) - k_2 M_s^{k_3}$ for up to $M_p
\approx 20 M_{\oplus}$, where $M_s$ and $R_s$ are scaled mass and radius
values. This functional form arises because the common building blocks of solid
planets all have equations of state that are well approximated by a modified
polytrope of the form $\rho = \rho_0 + c P^n$.
  We find that highly detailed planet interior models, including temperature
structure and phase changes, are not necessary to derive solid exoplanet bulk
composition from mass and radius measurements. For solid exoplanets with no
substantial atmosphere we have also found that: with 5% fractional uncertainty
in planet mass and radius it is possible to distinguish among planets composed
predominantly of iron or silicates or water ice but not more detailed
compositions; with $\sim$~5% uncertainty water ice planets with $\gtrsim 25%$
water by mass may be identified; the minimum plausible planet size for a given
mass is that of a pure iron planet; and carbon planet mass-radius relationships
overlap with those of silicate and water planets due to similar zero-pressure
densities and equations of state. We propose a definition of ""super Earths''
based on the clear distinction in radii between planets with significant gas
envelopes and those without.",0707.2895v1
2007-08-27,Evidence of a Broad Relativistic Iron Line from the Neutron Star Low-Mass X-ray Binary Serpens X-1,"We report on an analysis of XMM-Newton data from the neutron star low mass
X-ray binary (LMXB) Serpens X-1 (Ser X-1). Spectral analysis of EPIC PN data
indicates that the previously known broad iron K$\alpha$ emission line from
this source has a significantly skewed structure with a moderately extended red
wing. The asymmetric shape of the line is well described with the laor and
diskline models in XSPEC and strongly supports an inner accretion disk origin
of the line. To our knowledge this is the first strong evidence of a
relativistic line in a neutron star LMXB. This finding suggests that the broad
lines seen in other neutron star LMXBs likely originate from the inner disk as
well. Detailed study of such lines opens up a new way to probe neutron star
parameters and their strong gravitational fields. The red wing of the iron line
from Ser X-1 is not as broad as that observed from some black hole systems.
This is not unreasonable for a neutron star system, as the accretion disk has
to terminate at or before the hard stellar surface. Finally, the inferred
source inclination angle in the approximate range 40 degree to 60 degree is
consistent with the lack of dips and eclipses from Ser X-1.",0708.3648v1
2007-10-29,Search for vertical stratification of metals in atmospheres of blue horizontal-branch stars,"The observed abundance peculiarities of many chemical species relative to the
expected cluster metallicity in blue horizontal-branch (BHB) stars presumably
appear as a result of atomic diffusion in the photosphere. The slow rotation
(typically $v\sin{i}<$ 10 km s$^{-1}$) of BHB stars with effective temperatures
$T_{\rm eff}>$ 11,500 K supports this idea since the diffusion mechanism is
only effective in a stable stellar atmosphere. In this work we search for
observational evidence of vertical chemical stratification in the atmospheres
of six hot BHB stars: B84, B267 and B279 in M15 and WF2-2541, WF4-3085 and
WF4-3485 in M13. We undertake an abundance stratification analysis of the
stellar atmospheres of the aforementioned stars, based on acquired Keck HIRES
spectra. We have found from our numerical simulations that three stars (B267,
B279 and WF2-2541) show clear signatures of the vertical stratification of iron
whose abundance increases toward the lower atmosphere, while the other two
stars (B84 and WF4-3485) do not. For WF4-3085 the iron stratification results
are inconclusive. B267 also shows a signature of titanium stratification. Our
estimates for radial velocity, $v\sin{i}$ and overall iron, titanium and
phosphorus abundances agree with previously published data for these stars
after taking the measurement errors into account. The results support the
hypothesis regarding the efficiency of atomic diffusion in the stellar
atmospheres of BHB stars with $T_{\rm eff}>$ 11,500 K.",0710.5330v2
2008-03-19,A Laboratory Study of the Reduction of Iron Oxides by Hydrogen,"To reduce the emission of greenhouse gases by the steel industry,
particularly for ironmaking, the production of DRI (Direct Reduced Iron) using
hydrogen as the reducing gas instead of carbon monoxide is being considered. In
this context, the reduction of pure hematite by hydrogen was studied at the
laboratory scale, varying the experimental conditions and observing the rate
and the course of the reaction. All the reduction experiments were performed in
a thermobalance and supplementary characterization methods were used like
scanning and transmission electron microscopy, X-ray diffraction, and
M\""ossbauer spectrometry. The influence of rising temperature in the range
550-900 degrees C is to accelerate the reaction; no slowing down was observed,
contrary to some literature conclusions. A series of experiments consisted in
interrupting the runs before complete conversion, thus enabling the
characterization of partially reduced samples. Interpretation confirms the
occurrence of three successive and rather separate reduction steps, through
magnetite and wustite to iron, and illustrates a clear structural evolution of
the samples. Finally, the influence of the sample type was revealed comparing a
regular powder, a nanopowder and a sintered sample. The regular powder proved
to be the most reactive despite its larger grain size, due to a more porous
final structure.",0803.2831v1
2008-04-01,Studying the X-ray hysteresis in GX 339-4: the disc and iron line over one decade,"We report on a comprehensive and consistent investigation into the X-ray
emission from GX 339-4. All public observations in the 11 year RXTE archive
were analysed. Three different types of model - single powerlaw, broken
powerlaw and a disc + powerlaw - were fitted to investigate the evolution of
the disc, along with a fixed gaussian component at 6.4 keV to investigate any
iron line in the spectrum. We show that the relative variation in flux and
X-ray colour between the two best sampled outbursts are very similar. The decay
of the disc temperature during the outburst is clearly seen in the soft state.
The expected decay is S_Disc \propto T^4; we measure T^4.75\pm0.23. This
implies that the inner disc radius is approximately constant in the soft state.
We also show a significant anti-correlation between the iron line significant
width and the X-ray flux in the soft state while in the hard state the EW is
independent of the flux. This results in hysteresis in the relation between
X-ray flux and both line flux and EW. To compare the X-ray binary outburst to
the behaviour seen in AGN, we construct a Disc Fraction Luminosity Diagram for
GX 339-4, the first for an X-ray binary. The shape qualitatively matches that
produced for AGN. Linking this with the radio emission from GX 339-4 the change
in radio spectrum between the disc and power-law dominated states is clearly
visible.",0804.0148v1
2008-04-25,The chemical composition of red giant stars in four intermediate-age clusters of the Large Magellanic Cloud,"This paper presents the chemical abundance analysis of a sample of 27 red
giant stars located in 4 popolous intermediate-age globular clusters in the
Large Magellanic Cloud, namely NGC 1651, 1783, 1978 and 2173. This analysis is
based on high-resolution (R ~ 47000) spectra obtained with the UVES@VLT
spectrograph. For each cluster we derived up to 20 abundance ratios sampling
the main chemical elemental groups, namely light odd-Z, alpha, iron-peak and
neutron-capture elements. All the analysed abundance patterns behave similarly
in the 4 clusters and also show negligible star-to-star scatter within each
cluster. We find [Fe/H]=-0.30+-0.03, -0.35+-0.02, -0.38+-0.02 and -0.51+-0.03
dex for NGC 1651, 1783, 1978 and 2173, respectively. The measurement of light
odd-Z nuclei gives slightly subsolar [Na/Fe] and a more significant [Al/Fe]
depletion (~ -0.50 dex). The [alpha / Fe] abundance ratios are nearly solar,
while the iron-peak elements well trace that one of the iron. s-process
elements behave in a peculiar way: light s-elements give subsolar [Y/Fe] and
[Zr/Fe] abundance ratios, while heavy s-elements give enhanced [Ba/Fe], [La/Fe]
and [Nd/Fe] with respect to the solar values. Also, the [Eu/Fe] abundance ratio
turns out to be enhanced (~ 0.4 dex).",0804.4061v1
2008-05-08,The Metal Content of Bulge Field Stars from FLAMES-GIRAFFE Spectra. I. Stellar parameters and Iron Abundances,"We determine the iron distribution function (IDF) for bulge field stars, in
three different fields along the Galactic minor axis and at latitudes b=-4 deg,
b=-6 deg, and b=-12 deg. A fourth field including NGC6553 is also included in
the discussion. About 800 bulge field K giants were observed with the GIRAFFE
spectrograph of FLAMES@VLT at spectral resolution R~20,000. Several of them
were observed again with UVES at R~45,000 to insure the accuracy of the
measurements. The LTE abundance analysis yielded stellar parameters and iron
abundances that allowed us to construct an IDF for the bulge that, for the
first time, is based on high-resolution spectroscopy for each individual star.
The IDF derived here is centered on solar metallicity, and extends from [Fe/H]~
-1.5 to [Fe/H]~ +0.5. The distribution is asymmetric, with a sharper cutoff on
the high-metallicity side, and it is narrower than previously measured. A
variation in the mean metallicity along the bulge minor axis is clearly between
b=-4 deg and b=-6 deg ([Fe/H] decreasing by ~ 0.6 dex per kpc). The field at
b=-12 deg is consistent with the presence of a gradient, but its quantification
is complicated by the higher disk/bulge fraction in this field. Our findings
support a scenario in which both infall and outflow were important during the
bulge formation, and then suggest the presence of a radial gradient, which
poses some challenges to the scenario in which the bulge would result solely
from the vertical heating of the bar.",0805.1218v1
2008-05-13,Nature and distribution of iron sites in a sodium silicate glass investigated by neutron diffraction and EPSR simulation,"The short and medium range structure of a NaFeSi2O6 (NFS) glass has been
investigated by high-resolution neutron diffraction with Fe isotopic
substitution, combined with Empirical Potential Structure Refinement (EPSR)
simulations. The majority (~60%) of Fe is 4-coordinated ([4]Fe) and corresponds
only to ferric iron, Fe3+, with a distance d[4]Fe3+-O=1.87$\pm$0.01{\AA} . This
is at variance with the 3D-structure predicted by glass stoichiometry. The
existence of a majority of [4]Fe3+ sites illustrates a glass structure that
differs from the structure of crystalline NaFeSi2O6, which contains only
octahedral Fe3+. The EPSR modeling of glass structure shows that [4]Fe3+ is
randomly distributed in the silicate network and shares corner with silicate
tetrahedra. The existence of a majority of [4]Fe3+ sites differs from the
structure of the corresponding crystalline phase, which contains only
octahedral Fe3+. The network-forming behavior of [4]Fe3+, coupled with the
presence of Na+ ions acting as charge-compensators, is at the origin of
peculiar physical properties of Fe-bearing glasses, such as the increase of the
elastic modulus of sodium silicate glasses with increasing Fe-concentration.
Our data provide also direct evidence for 5-coordinated Fe, with an average
distance d[5]Fe-O=2.01$\pm$0.01{\AA}. This second Fe population concerns both
Fe2+ and Fe3+. 5-coordinated Fe atoms tend to segregate by sharing mainly
edges. The direct structural evidence of the dual role of ferric iron in NFS
glass provides support for understanding the peculiar properties of NFS glass,
such as magnetic, optical, electronic or thermodynamic properties.",0805.1850v1
2008-05-13,Enrichment and Pre-Heating in Intragroup Gas from Galactic Outflows,"We examine metal and entropy content in galaxy groups having T_X~0.5-2 keV in
cosmological hydrodynamic simulations. Our simulations include a
well-constrained prescription for galactic outflows following momentum-driven
wind scalings, and a sophisticated chemical evolution model. Our simulation
with no outflows reproduces observed iron abundances in X-ray emitting gas, but
the oxygen abundance is too low; including outflows yields iron and oxygen
abundances in good agreement with data. X-ray measures of [O/Fe] primarily
reflect metal distribution mechanisms into hot gas, not the ratio of Type Ia to
Type II supernovae within the group. Iron abundance increases by x2 from z=1-0
independent of group size, consistent with that seen in clusters, while [O/Fe]
drops by ~30%. Core entropy versus temperature is elevated over self-similar
predictions regardless of outflows due to radiative cooling removing
low-entropy gas, but outflows provide an additional entropy contribution below
1 keV. This results in a noticeable break in the L_X-T_X relation below 1 keV,
as observed. Importantly, outflows serve to reduce the stellar content of
groups to observed levels. Radial profiles from simulations are in broad
agreement with observations, but there remain non-trivial discrepancies that
may reflect an excess of late-time star formation in central group galaxies in
our simulations. Our model with outflows suggests a connection between physical
processes of galaxy formation and both pre-heating and enrichment in intragroup
gas, though more definitive conclusions must await a model that simultaneously
suppresses cooling flows as observed.",0805.1938v2
2008-06-04,Evidence for two distinct scales of current flow in polycrystalline Sm and Nd iron oxypnictides,"Early studies have found quasi-reversible magnetization curves in
polycrystalline bulk rare-earth iron oxypnictides that suggest either
wide-spread obstacles to intergranular current or very weak vortex pinning. In
the present study of polycrystalline samarium and neodymium rare-earth iron
oxypnictide samples made by high pressure synthesis, the hysteretic
magnetization is significantly enhanced. Magneto optical imaging and study of
the field dependence of the remanent magnetization as a function of particle
size both show that global currents over the whole sample do exist but that the
intergranular and intragranular current densities have distinctively different
temperature dependences and differ in magnitude by about 1000. Assuming that
the highest current density loops are restricted to circulation only within
grains leads to values of ~5 MA/cm2 at 5 K and self field, while whole-sample
current densities, though two orders of magnitude lower are 1000-10000 A/cm2,
some two orders of magnitude higher than in random polycrystalline cuprates. We
cannot yet be certain whether this large difference in global and intragrain
current density is intrinsic to the oxypnictides or due to extrinsic barriers
to current flow, because the samples contain significant second phase, some of
which wets the grain boundaries and produces evidences of SNS proximity effect
in the whole sample critical current.",0806.0816v1
2008-07-13,Electronic structure of the iron-based superconductor LaOFeP,"The recent discovery of superconductivity in the so-called iron-oxypnictide
family of compounds has generated intense interest. The layered crystal
structure with transition metal ions in planar square lattice form and the
discovery of spin-density-wave order near 130 K seem to hint at a strong
similarity with the copper oxide superconductors. A burning current issue is
the nature of the ground state of the parent compounds. Two distinct classes of
theories have been put forward depending on the underlying band structures:
local moment antiferromagnetic ground state for strong coupling approach and
itinerant ground state for weak coupling approach. The local moment magnetism
approach stresses on-site correlations and proximity to a Mott insulating state
and thus the resemblance to cuprates; while the latter approach emphasizes the
itinerant electron physics and the interplay between the competing
ferromagnetic and antiferromagnetic fluctuations. Such a controversy is partly
due to the lack of conclusive experimental information on the electronic
structures. Here we report the first angle-resolved photoemission spectroscopy
(ARPES) investigation of LaOFeP (Tc = 5.9 K), the first reported iron-based
superconductor. Our results favor the itinerant ground state, albeit with band
renormalization. In addition, our data reveal important differences between
these and copper based superconductors.",0807.2009v1
2008-07-20,"Nearly Isotropic superconductivity in (Ba,K)Fe2As2","Superconductivity was recently observed in the iron-arsenic-based compounds
with a superconducting transition temperature (Tc) as high as 56K [1-7],
naturally raising comparisons with the high Tc copper oxides. The copper oxides
have layered crystal structures with quasi-two-dimensional electronic
properties, which led to speculations that reduced dimensionality (that is,
extreme anisotropy) is a necessary prerequisite for superconductivity at
temperatures above 40 K [8,9]. Early work on the iron-arsenic compounds seemed
to support this view [7,10]. Here we report measurements of the electrical
resistivity in single crystals of (Ba,K)Fe2As2 in a magnetic field up to 60 T.
We find that the superconducting properties are in fact quite isotropic, being
rather independent of the direction of the applied magnetic fields at low
temperature. Such behaviour is strikingly different from all previously-known
layered superconductors [9,11], and indicates that reduced dimensionality in
these compounds is not a prerequisite for high-temperature superconductivity.
We suggest that this situation arises because of the underlying electronic
structure of the iron-arsenide compounds, which appears to be much more three
dimensional than that of the copper oxides. Extrapolations of low-field
single-crystal data incorrectly suggest a high anisotropy and a greatly
exaggerated zero-temperature upper critical field.",0807.3137v4
2008-12-05,XMM-Newton detects a relativistically broadened iron line in the spectrum of the ms X-ray pulsar SAX J1808.4-3658,"We report on a 63-ks long XMM-Newton observation of the accreting millisecond
pulsar SAX J1808.4-3658 during the latest X-ray outburst which started on
September 21st 2008. The pn spectrum shows a highly significant emission line
in the energy band where the iron K-alpha line is expected, and which we
identify as emission from neutral (or mildly ionized) iron. The line profile
appears to be quite broad (more than 1 keV FWHM) and asymmetric; the most
probable explanation for this profile is Doppler and relativistic broadening
from the inner accretion disc. From a fit with a diskline profile we find an
inner radius of the disc of 8.7^(+3.7)_(-2.7) R_g, corresponding to
18.0^(+7.6)_(-5.6) km for a 1.4 Msun neutron star. The disc therefore appears
truncated inside the corotation radius (31 km for SAX J1808.4-3658) in
agreement with the fact that the source was still showing pulsations during the
XMM-Newton observation.",0812.1149v2
2008-12-19,Fermi surface nesting induced strong pairing in iron-based superconductors,"The discovery of high-temperature superconductivity in iron pnictides raised
the possibility of an unconventional superconducting mechanism in multiband
materials. The observation of Fermi-surface(FS)-dependent nodeless
superconducting gaps suggested that inter-FS interactions may play a crucial
role in superconducting pairing. In the optimally hole-doped
Ba$_{0.6}$K$_{0.4}$Fe$_2$As$_2$, the pairing strength is enhanced
simultaneously (2$\Delta$/Tc$\sim$7) on the nearly nested FS pockets, i.e. the
inner holelike ($\alpha$) FS and the two hybridized electronlike FSs, while the
pairing remains weak (2$\Delta$/Tc$\sim$3.6) in the poorly-nested outer
hole-like ($\beta$) FS. Here we report that in the electron-doped
BaFe$_{1.85}$Co$_{0.15}$As$_2$ the FS nesting condition switches from the
$\alpha$ to the $\beta$ FS due to the opposite size changes for hole- and
electron-like FSs upon electron doping. The strong pairing strength
(2$\Delta$/Tc$\sim$6) is also found to switch to the nested $\beta$ FS,
indicating an intimate connection between FS nesting and superconducting
pairing, and strongly supporting the inter-FS pairing mechanism in the
iron-based superconductors.",0812.3704v2
2008-12-30,Anisotropy of the Optimally-Doped Iron Pnictide Superconductor Ba(Fe0.926Co0.074)2As2,"Anisotropies of electrical resistivity, upper critical field, London
penetration depth and critical currents have been measured in single crystals
of the optimally doped iron pnictide superconductor
Ba(Fe$_{1-x}$Co$_x$)$_2$As$_2$, $x$=0.074 and $T_c \sim$23 K. The normal state
resistivity anisotropy was obtained by employing both the Montgomery technique
and direct measurements on samples cut along principal crystallographic
directions. The ratio $\gamma_{\rho} = \rho_c /\rho_a$ is about 4$\pm$1 just
above $T_c$ and becomes half of that at room temperature. The anisotropy of the
upper critical field, $\gamma_{H} = H_{c2,ab} /H_{c2,c} $, as determined from
specific heat measurements close to $T_c$, is in the range of 2.1 to 2.6,
depending on the criterion used. A comparable low anisotropy of the London
penetration depth, $\gamma_{\lambda}=\lambda_{c}/\lambda_{ab}$, was recorded
from TDR measurements and found to persist deep into the superconducting state.
An anisotropy of comparable magnitude was also found in the critical currents,
$\gamma_j=j_{c,ab}/j_{c,c}$, as determined from both direct transport
measurements ($\sim$1.5) and from the analysis of the magnetization data
($\sim$3). Overall, our results show that iron pnictide superconductors
manifest anisotropies consistent with essentially three-dimensional
intermetallic compound and bear little resemblance to cuprates.",0812.4991v1
2009-01-06,Comparison of Relativistic Iron Line Models,"The analysis of the broad iron line profile in the X-ray spectra of active
galactic nuclei and black hole X-ray binaries allows us to constrain the spin
parameter of the black hole. We compare the constraints on the spin value for
two X-ray sources, MCG-6-30-15 and GX 339-4, with a broad iron line using
present relativistic line models in XSPEC - LAOR and KYRLINE. The LAOR model
has the spin value set to the extremal value a=0.9982, while the KYRLINE model
enables direct fitting of the spin parameter. The spin value is constrained
mainly by the lower boundary of the broad line, which depends on the inner
boundary of the disc emission where the gravitational redshift is maximal. The
position of the inner disc boundary is usually identified with the marginally
stable orbit which is related to the spin value. In this way the LAOR model can
be used to estimate the spin value. We investigate the consistency of the LAOR
and KYRLINE models. We find that the spin values evaluated by both models agree
within the general uncertainties when applied on the current data. However, the
results are apparently distinguishable for higher quality data, such as those
simulated for the International X-ray Observatory (IXO) mission. We find that
the LAOR model tends to overestimate the spin value and furthermore, it has
insufficient resolution which affects the correct determination of the
high-energy edge of the broad line.",0901.0670v1
2009-01-30,Variable partial covering and a relativistic iron line in NGC 1365,"We present a complete analysis of the hard X-ray (2-10 keV) properties of the
Seyfert galaxy NGC 1365, based on a 60 ks XMM-Newton observation performed in
January 2004. The two main results are: 1) We detect an obscuring cloud with
N_H~3.5x10^23 cm^(-2) crossing the line of sight in ~25 ks. This implies a
dimension of the X-ray source not larger than a few 10^13 cm and a distance of
the obscuring cloud of the order of 10^16 cm. Adopting the black hole mass
M(BH) estimated from the M(BH)-velocity dispersion relation, the source size is
D_S<20 R_G and the distance and density of the obscuring clouds are
R~3000-10000 R_G and n~10^(10) cm^(-3), i.e. typical values for broad line
region clouds. 2) An iron emission line with a relativistic profile is detected
with high statistical significance. A time integrated fit of the line+continuum
reflection components suggests a high iron abundance (~3 times solar) and an
origin of these components in the inner part (~10 R_G) of the accretion disk,
in agreement with the small source size inferred from the analysis of the
absorption variability.",0901.4809v1
2009-06-08,"Enhanced magnetism, memory and aging in Gold-Iron oxide nanoparticle composites","In this report we present systematic magnetic studies of pure iron oxide
nanoparticles and gold iron oxide nanocomposite with increasing Au particle
size/content. For the magnetic studies of these samples we have measured: (1)
zero field cooled (ZFC) and field cooled (FC) magnetization, (2) ac
susceptibility, (3) magnetization vs field at various temperatures, (4)
thermoremanant magnetization relaxation (TRM) and zero field cooled
magnetization relaxation (ZFCM) at fixed temperature for various wait times tw
for studying the aging effect, (5) magnetization memory effect and (6) exchange
bias as a function of cooling field. The detailed magnetic measurement analysis
indicates that the pure Fe3O4 nanoparticles sample behaves like a
superparamagnet and on incorporation of gold (Au) nanoparticles the
nanocomposite system slowly evolves from superparamagnetic to superspin glass
state. The memory and aging effect enhances with the increase of the Au
nanoparticle size/content. The most important observation in this study is the
enhancement of magnetization with the incorporation of Au nanoparticles. The
enhancement increases with the increase in the Au content in the nanocomposite.
We have explained the cause of this enhancement of magnetization as due to
large orbital magnetic moment formation at the Au/magnetic particle interface.",0906.1497v2
2009-07-21,Normal-State Spin Dynamics and Temperature-Dependent Spin Resonance Energy in an Optimally Doped Iron Arsenide Superconductor,"The proximity of superconductivity and antiferromagnetism in the phase
diagram of iron arsenides, the apparently weak electron-phonon coupling and the
""resonance peak"" in the superconducting spin excitation spectrum have fostered
the hypothesis of magnetically mediated Cooper pairing. However, since most
theories of superconductivity are based on a pairing boson of sufficient
spectral weight in the normal state, detailed knowledge of the spin excitation
spectrum above the superconducting transition temperature Tc is required to
assess the viability of this hypothesis. Using inelastic neutron scattering we
have studied the spin excitations in optimally doped BaFe1.85Co0.15As2 (Tc = 25
K) over a wide range of temperatures and energies. We present the results in
absolute units and find that the normal state spectrum carries a weight
comparable to underdoped cuprates. In contrast to cuprates, however, the
spectrum agrees well with predictions of the theory of nearly antiferromagnetic
metals, without complications arising from a pseudogap or competing
incommensurate spin-modulated phases. We also show that the temperature
evolution of the resonance energy follows the superconducting energy gap, as
expected from conventional Fermi-liquid approaches. Our observations point to a
surprisingly simple theoretical description of the spin dynamics in the iron
arsenides and provide a solid foundation for models of magnetically mediated
superconductivity.",0907.3632v1
2009-08-18,Dense Iron Ejecta and Core-collapse Supernova Explosion in the Young Supernova Remnant G11.2-0.3,"We present the results of near-infrared spectroscopic observations of dense
($\simgt$ 10$^3$ cm$^{-3}$) iron ejecta in the young core-collapse supernova
remnant G11.2-0.3. Five ejecta knots projected to be close to its center show a
large dispersion in their Doppler shifts: two knots in the east are blueshifted
by more than 1,000 \kms, while three western knots have relatively small
blueshifts of 20-60 \kms. This velocity discrepancy may indicate that the
western knots have been significantly decelerated or that there exists a
systematic velocity difference among the knots. One ejecta filament in the
northwestern boundary, on the other hand, is redshifted by $\simgt$ 200 \kms,
while opposite filament in the southeastern boundary shows a negligible radial
motion. Some of the knots and filaments have secondary velocity components, and
one knot shows a bow shock-like feature in the velocity structure. The iron
ejecta appear to be devoid of strong emission from other heavy elements, such
as S, which may attest to the alpha-rich freezeout process in the explosive
nucleosynthesis of the core-collapse supernova explosion close to its center.
The prominent bipolar distribution of the Fe ejecta in the northwestern and
southeastern direction, along with the elongation of the central pulsar wind
nebula in the perpendicular direction, is consistent with the interpretation
that the supernova exploded primarily along the northwestern and southeastern
direction.",0908.2613v1
2009-10-05,Intrinsic iron spread and a new metallicity scale for Globular Clusters,"We have collected spectra of about 2000 red giant branch (RGB) stars in 19
Galactic globular clusters (GC) using FLAMES@VLT (about 100 star with GIRAFFE
and about 10 with UVES, respectively, in each GC). These observations provide
an unprecedented, precise, and homogeneous data-set of Fe abundances in GCs. We
use it to study the cosmic scatter of iron and find that, as far as Fe is
concerned, most GCs can still be considered mono-metallic, since the upper
limit to the scatter in iron is less than 0.05 dex, meaning that the degree of
homogeneity is better than 12%. The scatter in Fe we find seems to have a
dependence on luminosity, possibly due to the well-known inadequacies of
stellar atmospheres for upper-RGB stars and/or to intrinsic variability. It
also seems to be correlated with cluster properties, like the mass, indicating
a larger scatter in more massive GCs which is likely a (small) true intrinsic
scatter. The 19 GCs, covering the metallicity range of the bulk of Galactic
GCs, define an accurate and updated metallicity scale. We provide
transformation equations for a few existing scales. We also provide new values
of [Fe/H], on our scale, for all GCs in the Harris' catalogue.",0910.0675v1
2009-10-14,Debye temperature of disordered bcc-Fe-Cr alloys,"Debye temperature, TD, of Fe100-xCrx disordered alloys with 0<x<99.9 was
determined from the temperature dependence of the centre shift of 57Fe
Mossbauer spectra recorded in the temperature range of 80-300K. Its
compositional dependence shows an interesting non-monotonous behaviour. For
0<x<~45 as well as for ~75<x<~95 the Debye temperature is enhanced relative to
its value of a metallic iron, and at x=~3 there is a local maximum having a
relative height of ~12% compared to a pure iron. For ~45<x<~75 and for x>~95
the Debye temperature is smaller than the one for the metallic iron, with a
local minimum at x=~55 at which the relative decrease of TD amounts to ~12%.
The first maximum coincides quite well with that found for the spin-waves
stiffness coefficient, D0, while the pretty steep decrease observed for x>~95
which is indicative of a decoupling of the probe Fe atoms from the underlying
chromium matrix is likely related to the spin-density waves which constitute
the magnetic structure of chromium in that interval of composition. The
harmonic force constant calculated from the Debye temperature of the least
Fe-concentrated alloy (x>99.9) amounts to only 23% of the one characteristic of
a pure chromium.",0910.2544v1
2009-10-30,Spectroscopic properties of cool Ursa Major group members,"Until now, most members of the Ursa Major (UMa) group of stars have been
identified by means of kinematic criteria. However, in many cases kinematic
criteria alone are insufficient to ascertain, whether an individual star is
really a member of this group. Since photometric criteria are ineffective in
the case of cool dwarf members, one must use spectroscopic criteria.
Nevertheless, resulting membership criteria are inconclusive. We reanalyse
spectroscopic properties of cool UMa group dwarfs. In particular, we study the
distribution of iron abundance, the strength of the Li I absorption at 6708 A
and the Li abundance, and the infilling of the core of the H alpha line.
Twenty-five cool and northern bona-fide members are carefully selected from the
literature. Homogeneously measured stellar parameters and iron abundances are
given for all Sun-like stars selected, based on spectra of high resolution and
high signal-to-noise ratio. In addition, we measure the Li equivalent width and
abundance as well as the relative intensity of the H alpha core and the
corresponding chromospheric flux. The studied stars infer an average Ursa Major
group iron abundance of -0.03+-0.05 dex, which is higher by about 0.06 dex than
determined elsewhere. The Li abundance derived of Ursa Major group dwarf stars
is higher than in the Hyades at effective temperatures cooler than the Sun, but
lower than in the younger Pleiades, a result which is independent of the exact
value of the effective temperature adopted. The Sun-like and cooler dwarfs also
display chromospheric infilling of the H alpha core. We present spectroscopic
criteria that may be used to exclude non-members.",0910.5913v1
2009-11-06,Black hole accretion disks in the canonical low-hard state,"Stellar-mass black holes in the low-hard state may hold clues to jet
formation and basic accretion disk physics, but the nature of the accretion
flow remains uncertain. A standard thin disk can extend close to the innermost
stable circular orbit, but the inner disk may evaporate when the mass accretion
rate is reduced. Blackbody-like continuum emission and dynamically-broadened
iron emission lines provide independent means of probing the radial extent of
the inner disk. Here, we present an X-ray study of eight black holes in the
low-hard state. A thermal disk continuum with a colour temperature consistent
with $L \propto T^{4}$ is clearly detected in all eight sources, down to
$\approx5\times10^{-4}L_{Edd}$. In six sources, disk models exclude a
truncation radius larger than 10rg. Iron-ka fluorescence line emission is
observed in half of the sample, down to luminosities of
$\approx1.5\times10^{-3}L_{Edd}$. Detailed fits to the line profiles exclude a
truncated disk in each case. If strong evidence of truncation is defined as (1)
a non-detection of a broad iron line, {\it and} (2) an inner disk temperature
much cooler than expected from the ${\rm L} \propto {\rm T}^{4}$ relation, none
of the spectra in this sample offer strong evidence of disk truncation. This
suggests that the inner disk may evaporate at or below
$\approx1.5\times10^{-3}L_{Edd}$.",0911.1151v1
2009-11-11,Truncation of the Inner Accretion Disk around a Black Hole at Low Luminosity,"Most black hole binaries show large changes in X-ray luminosity caused
primarily by variations in mass accretion rate. An important question for
understanding black hole accretion and jet production is whether the inner edge
of the accretion disk recedes at low accretion rate. Measurements of the
location of the inner edge (Rin) can be made using iron emission lines that
arise due to fluorescence of iron in the disk, and these indicate that Rin is
very close to the black hole at high and moderate luminosities (near 1% of the
Eddington luminosity, Ledd). Here, we report on X-ray observations of the black
hole GX 339-4 in the hard state by Suzaku and the Rossi X-ray Timing Explorer
(RXTE) that extend iron line studies to 0.14% Ledd and show that Rin increases
by a factor of >27 over the value found when GX 339-4 was bright. The exact
value of Rin depends on the inclination of the inner disk (i), and we derive
90% confidence limits of Rin > 35 Rg at i = 0 degrees and Rin > 175 Rg at i =
30 degrees. This provides direct evidence that the inner portion of the disk is
not present at low luminosity, allowing for the possibility that the inner disk
is replaced by advection- or magnetically-dominated accretion flows.",0911.2240v1
2009-11-23,Magnetic anisotropy determination and magnetic hyperthermia properties of small Fe nanoparticles in the superparamagnetic regime,"We report on the magnetic and hyperthermia properties of iron nanoparticles
synthesized by organometallic chemistry. They are 5.5 nm in diameter and
display a saturation magnetization close to the bulk one. Magnetic properties
are dominated by the contribution of aggregates of nanoparticles with respect
to individual isolated nanoparticles. Alternative susceptibility measurements
are been performed on a low interacting system obtained after eliminating the
aggregates by centrifugation. A quantitative analysis using the Gittleman s
model allow a determination of the effective anisotropy Keff = 1.3 * 10^5
J.m^{-3}, more than two times the magnetocristalline value of bulk iron.
Hyperthermia measurements are performed on agglomerates of nanoparticles at a
magnetic field up to 66 mT and at frequencies in the range 5-300 kHz. Maximum
measured SAR is 280 W/g at 300 kHz and 66 mT. Specific absorption rate (SAR)
displays a square dependence with the magnetic field below 30 mT but deviates
from this power law at higher value. SAR is linear with the applied frequency
for mu_0H=19 mT. The deviations from the linear response theory are discussed.
A refined estimation of the optimal size of iron nanoparticles for hyperthermia
applications is provided using the determined effective anisotropy value.",0911.4413v1
2009-12-01,The cluster Terzan 5 as a remnant of a primordial building block of the Galactic bulge,"Globular star clusters are compact and massive stellar systems old enough to
have witnessed the entire history of our Galaxy, the Milky Way. Although recent
results suggest that their formation may have been more complex than previously
thought, they still are the best approximation to a stellar population formed
over a relatively short time scale (less than 1 Gyr) and with virtually no
dispersion in the iron content. Indeed, only one cluster-like system (omega
Centauri) in the Galactic halo is known to have multiple stellar populations
with a significant spread in iron abundance and age4,5. Similar findings in the
Galactic bulge have been hampered by the obscuration arising from thick and
varying layers of interstellar dust. Here we report that Terzan 5, a
globular-cluster-like system in the Galactic bulge, has two stellar populations
with different iron content and ages. Terzan 5 could be the surviving remnant
of one of the primordial building blocks that are thought to merge and form
galaxy bulges.",0912.0192v1
2009-12-23,Linking dwarf galaxies to halo building blocks with the most metal-poor star in Sculptor,"Current cosmological models indicate that the Milky Way's stellar halo was
assembled from many smaller systems. Based on the apparent absence of the most
metal-poor stars in present-day dwarf galaxies, recent studies claimed that the
true Galactic building blocks must have been vastly different from the
surviving dwarfs. The discovery of an extremely iron-poor star (S1020549) in
the Sculptor dwarf galaxy based on a medium-resolution spectrum cast some doubt
on this conclusion. However, verification of the iron-deficiency and
measurements of additional elements, such as the alpha-element Mg, are
mandatory for demonstrating that the same type of stars produced the metals
found in dwarf galaxies and the Galactic halo. Only then can dwarf galaxy stars
be conclusively linked to early stellar halo assembly. Here we report
high-resolution spectroscopic abundances for 11 elements in S1020549,
confirming the iron abundance of less than 1/4000th that of the Sun, and
showing that the overall abundance pattern mirrors that seen in low-metallicity
halo stars, including the alpha-elements. Such chemical similarity indicates
that the systems destroyed to form the halo billions of years ago were not
fundamentally different from the progenitors of present-day dwarfs, and
suggests that the early chemical enrichment of all galaxies may be nearly
identical.",0912.4734v1
2010-01-06,Electronic structure of Fe1.04(Te0.66Se0.34),"We report the electronic structure of the iron-chalcogenide superconductor,
Fe1.04(Te0.66Se0.34), obtained with high resolution angle-resolved
photoemission spectroscopy and density functional calculations. In
photoemission measurements, various photon energies and polarizations are
exploited to study the Fermi surface topology and symmetry properties of the
bands. The measured band structure and their symmetry characters qualitatively
agree with our density function theory calculations of Fe(Te0.66Se0.34),
although the band structure is renormalized by about a factor of three. We find
that the electronic structures of this iron-chalcogenides and the
iron-pnictides have many aspects in common, however, significant differences
exist near the Gamma-point. For Fe1.04(Te0.66Se0.34), there are clearly
separated three bands with distinct even or odd symmetry that cross the Fermi
energy (EF) near the zone center, which contribute to three hole-like Fermi
surfaces. Especially, both experiments and calculations show a hole-like
elliptical Fermi surface at the zone center. Moreover, no sign of spin density
wave was observed in the electronic structure and susceptibility measurements
of this compound.",1001.0855v1
2010-01-20,"Atmospheric Chemistry in Giant Planets, Brown Dwarfs, and Low-Mass Dwarf Stars III. Iron, Magnesium, and Silicon","We use thermochemical equilibrium calculations to model iron, magnesium, and
silicon chemistry in the atmospheres of giant planets, brown dwarfs, extrasolar
giant planets (EGPs), and low-mass stars. The behavior of individual Fe-, Mg-,
and Si-bearing gases and condensates is determined as a function of
temperature, pressure, and metallicity. Our results are thus independent of any
particular model atmosphere. The condensation of Fe metal strongly affects iron
chemistry by efficiently removing Fe-bearing species from the gas phase.
Monatomic Fe is the most abundant Fe-bearing gas throughout the atmospheres of
EGPs and L dwarfs and in the deep atmospheres of giant planets and T dwarfs.
Mg- and Si-bearing gases are effectively removed from the atmosphere by
forsterite (Mg2SiO4) and enstatite (MgSiO3) cloud formation. Monatomic Mg is
the dominant magnesium gas throughout the atmospheres of EGPs and L dwarfs and
in the deep atmospheres of giant planets and T dwarfs. Silicon monoxide (SiO)
is the most abundant Si-bearing gas in the deep atmospheres of brown dwarfs and
EGPs, whereas SiH4 is dominant in the deep atmosphere of Jupiter and other gas
giant planets. Several other Fe-, Mg-, and Si-bearing gases become increasingly
important with decreasing effective temperature. In principle, a number of Fe,
Mg, and Si gases are potential tracers of weather or diagnostic of temperature
in substellar atmospheres.",1001.3639v1
2010-03-29,"From (pi, 0) magnetic order to superconductivity with (pi, pi) magnetic resonance in Fe1.02(Te1-xSex)","The iron chalcogenide Fe1+y(Te1-xSex) is structurally the simplest of the
Fe-based superconductors. Although the Fermi surface is similar to iron
pnictides, the parent compound Fe1+yTe exhibits antiferromagnetic order with
in-plane magnetic wave-vector (pi, 0). This contrasts the pnictide parent
compounds where the magnetic order has an in-plane magnetic wave-vector (pi,
pi) that connects hole and electron parts of the Fermi surface. Despite these
differences, both the pnictide and chalcogenide Fe-superconductors exhibit
superconducting spin resonances around (pi, pi), suggesting a common symmetry
for their superconducting order parameter. A central question in this
burgeoning field is therefore how (pi, pi) superconductivity can emerge from a
(pi, 0) magnetic instability. Here, we report that the magnetic soft mode
evolving from the (pi, 0)-type magnetic long-range order is associated with
weak charge carrier localization. Bulk superconductivity occurs only as the
magnetic mode at (pi, pi) becomes dominant upon doping. Our results suggest a
common magnetic origin for superconductivity in iron chalcogenide and pnictide
superconductors.",1003.5647v1
2010-04-06,Anisotropic superconducting properties of single-crystalline FeSe0.5Te0.5,"Iron-chalcogenide single crystals with the nominal composition
FeSe$_{0.5}$Te$_{0.5}$ and a transition temperature of $T_{c}\simeq14.6$ K were
synthesized by the Bridgman method. The structural and anisotropic
superconducting properties of those crystals were investigated by means of
single crystal X-ray and neutron powder diffraction, SQUID and torque
magnetometry, and muon-spin rotation. Room temperature neutron powder
diffraction reveals that 95% of the crystal volume is of the same tetragonal
structure as PbO. The structure refinement yields a stoichiometry of
Fe_1.045Se_0.406Te_0.594. Additionally, a minor hexagonal Fe_7Se_8 impurity
phase was identified. The magnetic penetration depth \lambda at zero
temperature was found to be 491(8) nm in the ab-plane and 1320(14) nm along the
c-axis. The zero-temperature value of the superfluid density \rho_s(0)
\lambda^-2(0) obeys the empirical Uemura relation observed for various
unconventional superconductors, including cuprates and iron-pnictides. The
temperature dependences of both \lambda_ab and \lambda_c are well described by
a two-gap s+s-wave model with the zero-temperature gap values of
\Delta_S(0)=0.51(3) meV and \Delta_L(0)=2.61(9) meV for the small and the large
gap, respectively. The magnetic penetration depth anisotropy parameter
\gamma_\lambda(T)=\lambda_c(T)/\lambda_{ab}(T) increases with decreasing
temperature, in agreement with \gamma_\lambda(T) observed in the iron-pnictide
superconductors.",1004.0812v1
2010-04-09,Evidence of a universal and isotropic 2Δ/kBTC ratio in 122-type iron pnictide superconductors over a wide doping range,"We have systematically investigated the doping and the directional dependence
of the gap structure in the 122-type iron pnictide superconductors by point
contact Andreev reflection spectroscopy. The studies were performed on single
crystals of Ba1-xKxFe2As2 (x = 0.29, 0.49, and 0.77) and SrFe1.74Co0.26As2 with
a sharp tip of Pb or Au pressed along the c-axis or the ab-plane direction. The
conductance spectra obtained on highly transparent contacts clearly show
evidence of a robust superconducting gap. The normalized curves can be well
described by the Blonder-Tinkham-Klapwijk model with a lifetime broadening. The
determined gap value scales very well with the transition temperature, giving
the 2{\Delta}/kBTC value of ~ 3.1. The results suggest the presence of a
universal coupling behavior in this class of iron pnictides over a broad doping
range and independent of the sign of the doping. Moreover, conductance spectra
obtained on c-axis junctions and ab-plane junctions indicate that the observed
gap is isotropic in these superconductors.",1004.1445v2
2010-08-16,"Second Homologous Series of Iron Pnictide Oxide Superconductors (Fe2As2)(Can+2(Al,Ti)nOy)[n = 2,3,4]","We have discovered a new homologous series of iron pnictide oxides
(Fe2As2)(Can+2(Al,Ti)nOy)[n = 2,3,4]. These compounds have perovskite-like
blocking layers between Fe2As2 layers. The structure of new compounds are
tetragonal with space groups of P4/nmm for n = 2 and 4 and P4mm for n = 3,
which are similar to those of (Fe2As2)(Can+1(Sc,Ti)nOy)[n = 3,4,5] found in our
previous study. Compounds with n = 3 and 4 have new crystal structures with 3
and 4 sheets of perovskite layers, respectively, including a rock salt layer in
each blocking layer. The a-axis lengths of the three compounds are
approximately 3.8 A, which are close to those of FeSe and LiFeAs.
(Fe2As2)(Ca6(Al,Ti)4Oy) exhibited bulk superconductivity in magnetization
measurement with Tc(onset)~36 K and resistivity drop was observed at ~39 K.
(Fe2As2)(Ca5(Al,Ti)3Oy) also showed large diamagnetism at low temperatures.
These new compounds indicate considerable rooms are still remaining for new
superconductors in layered iron pnictides.",1008.2582v4
2010-09-06,Electron-capture supernovae as the origin of elements beyond iron,"We examine electron-capture supernovae (ECSNe) as sources of elements heavier
than iron in the solar system and in Galactic halo stars. Nucleosynthesis
calculations are performed on the basis of thermodynamic histories of mass
elements from a fully self-consistent, two-dimensional (2D) hydrodynamic
explosion model of an ECSN. We find that neutron-rich convective lumps with an
electron fraction down to Ye,min=0.40, which are absent in the one-dimensional
(1D) counterpart, allow for interesting production of elements between the iron
group and N=50 nuclei (from Zn to Zr, with little Ga) in nuclear
(quasi-)equilibrium. Our models yield very good agreement with the Ge, Sr, Y,
and Zr abundances of r-process deficient Galactic halo stars and constrain the
occurrence of ECSNe to ~4% of all stellar core-collapse events. If tiny amounts
of additional material with slightly lower Ye,min down to ~0.30-0.35 were also
ejected - which presently cannot be excluded because of the limitations of
resolution and two-dimensionality of the model -, a weak r-process can yield
elements beyond N=50 up to Pd, Ag, and Cd as observed in the r-process
deficient stars.",1009.1000v2
2010-10-08,Chemical pattern across the young associations ONC and OB1b,"Context. Abundances of iron-peak and alpha-elements are poorly known in
Orion, and the available measurements yield contradictory results. Aims. We
measure accurate and homogeneous elemental abundances of the Orion subgroups
ONC and OB1b, and search for abundance differences across the Orion complex.
Methods. We present FLAMES/UVES spectroscopic observations of 20 members of the
ONC and OB1b. We measured radial velocity, veiling, effective temperature using
two spectroscopic methods, and determined the chemical abundances of Fe, Na,
Al, Si, Ca, Ti, and Ni using the code MOOG. We also performed a new consistent
analysis of spectra previously analyzed by our group. Results. We find three
new binaries in the ONC, two in OB1b, and three non-members in OB1b (two of
them most likely being OB1a/25 Ori members). Veiling only affects one target in
the ONC, and the effective temperatures derived using two spectroscopic
techniques agree within the errors. The ONC and OB1b are characterized by a
small scatter in iron abundance, with mean [Fe/H] values of -0.11+/-0.08 and
-0.05+/-0.05, respectively. We find a small scatter in all the other elemental
abundances. We confirm that P1455 is a metal-rich star in the ONC. Conclusions.
We conclude that the Orion metallicity is not above the solar value. The OB1b
group might be slightly more metal-rich than the ONC; on the other hand, the
two subgroups have similar almost solar abundances of iron-peak and
alpha-elements with a high degree of homogeneity.",1010.1658v1
2010-11-07,Interactions between sub-10 nm iron and cerium oxide nanoparticles and 3T3 fibroblasts : the role of the coating and aggregation state,"Recent nanotoxicity studies revealed that the physico-chemical
characteristics of engineered nanomaterials play an important role in the
interactions with living cells. Here, we report on the toxicity and uptake of
the cerium and iron oxide sub-10 nm nanoparticles by NIH/3T3 mouse fibroblasts.
Coating strategies include low-molecular weight ligands (citric acid) and
polymers (poly(acrylic acid), MW = 2000 g mol-1). Electrostatically adsorbed on
the surfaces, the organic moieties provide a negatively charged coating in
physiological conditions. We find that most particles were biocompatible, as
exposed cells remained 100% viable relative to controls. Only the bare and the
citrate-coated nanoceria exhibit a slight decrease of the mitochondrial
activity for cerium concentrations above 5 mM (equivalent to 0.8 g L-1). We
also observe that the citrate-coated particles are internalized by the cells in
large amounts, typically 250 pg per cell after a 24 h incubation for iron
oxide. In contrast, the polymer-coated particles are taken up at much lower
rates (< 30 pg per cell). The strong uptake shown by the citrate-coated
particles is related to the destabilization of the dispersions in the cell
culture medium and their sedimentation down to the cell membranes. In
conclusion, we show that the uptake of nanomaterials by living cells depends on
the coating of the particles and on its ability to preserve the colloidal
nature of the dispersions.",1011.1670v1
2011-01-04,Structural Analysis on Iron-Based Superconductor Pr1111 System with Oxygen Deficiency and Flourine Substitution,"We have performed structural analyses on iron-based superconductors,
PrFeAsO$_{1-y}$ and PrFeAsO$_{1-x}$F$_x$, systematically, by means of Rietveld
method on neutron powder diffraction data. The shifts of iron ion valence from
+2, $\delta$, are accurately determined from the occupancies of O and
O$_{1-x}$F$_x$ sites obtained by the Rietveld analysis and F-concentration
obtained by secondary ion-microprobe mass spectrometry. $T_\textrm{c}$-$\delta$
curve of PrFeAsO$_{1-y}$ is different from the curve of PrFeAsO$_{1-x}$F$_x$,
indicating that $\delta$ is not a principal parameter for $T_\textrm{c}$ in
so-called 1111 system. Structural parameters of the FeAs layers, for example,
As-Fe-As bond angle and As-height from Fe layer, are different between both
systems with similar $\delta$-values. Their parent compounds are also found to
have different structural parameters, possibly due to the different synthetic
conditions. These results suggest that the difference of structural parameters
of FeAs layer is the origin of the discrepancy of $T_\textrm{c}$-$\delta$
curves of both systems and the $T_\textrm{c}$-value in the 1111 system is
sensitive to the structural parameters. It may be attribute to an energy
balance of the conducting bands contributing to the superconductivity.",1101.0636v1
2011-01-05,X-ray reflected spectra from accretion disk models.II. Diagnostic tools for X-ray observations,"We present a comprehensive study of the emission spectra from accreting
sources. We use our new reflection code to compute the reflected spectra from
an accretion disk illuminated by X-rays. This set of models covers different
values of ionization parameter, solar iron abundance and photon index for the
illuminating spectrum. These models also include the most complete and recent
atomic data for the inner-shell of the iron and oxygen isonuclear sequences. We
concentrate our analysis to the 2-10 keV energy region, and in particular to
the iron K-shell emission lines. We show the dependency of the equivalent width
(EW) of the Fe K$\alpha$ with the ionization parameter. The maximum value of
the EW is $\sim 800$ eV for models with log $\xi\sim 1.5$, and decreases
monotonically as $\xi$ increases. For lower values of $\xi$ the Fe K$\alpha$ EW
decreases to a minimum near log $\xi\sim 0.8$. We produce simulated CCD
observations based on our reflection models. For low ionized, reflection
dominated cases, the 2-10 keV energy region shows a very broad, curving
continuum that cannot be represented by a simple power-law. We show that in
addition to the Fe K-shell emission, there are other prominent features such as
the Si and S L$\alpha$ lines, a blend of Ar {\sc viii-xi} lines, and the Ca
{\sc x} K$\alpha$ line. In some cases the S {\sc xv} blends with the He-like Si
RRC producing a broad feature that cannot be reproduced by a simple Gaussian
profile. This could be used as a signature of reflection.",1101.1115v1
2011-01-27,"Electronic band structure, Fermi surface and elastic properties of polymorphs of new 5.2K iron-free superconductor SrPt2As2 from first principles calculations","By means of the first-principles calculations, we have studied in details the
structural, elastic and electronic properties of the new tetragonal
CaBe2Ge2-type 5.2K superconductor SrPt2As2 in comparison with two hypothetical
SrPt2As2 polymorphs with ThCr2Si2-type structures which differ by atomic
configurations of [Pt2As2] (or [Pt2As2]) blocks. We have found that
CaBe2Ge2-type SrPt2As2 is a quite unique system with complicated 2D-3D
character of near-Fermi bands, and the ""intermediate"" type of the Fermi
surface, which consists of electronic pockets having cylinder-like (2D)
topology (typical for 122 FeAs phases) together with 3D-like electronic and
hole pockets, which are characteristic for ThCr2Si2-like iron-free low-Tc
superconductors. Our analysis reveals that against ThCr2Si2-like 122 phases,
the other features for CaBe2Ge2-like SrPt2As2 are: (1). The essential
differences of contributions of states from [Pt2As2] and [Pt2As2] blocks into
near-Fermi region when the conduction is expected to be anisotropic and
happening mainly in [Pt2As2] blocks; (2). The formation of the 3D system of
strong covalent Pt-As bonds (inside and between of [Pt2As2]/[As2Pt2] blocks)
which is responsible for enhanced stability of this polymorph, and (3). the
essential charge anisotropy between the adjacent [Pt2As2] and [As2Pt2] blocks.
We have predicted also that CaBe2Ge2-like SrPt2As2 is mechanically stable,
relatively soft material with high compressibility and will behave in a ductile
manner. On the contrary the ThCr2Si2-type SrPt2As2 polymorphs which contain
only [Pt2As2] or [As2Pt2] blocks, are less stable, their Fermi surfaces adopt a
multi-sheet three-dimensional type - similar to ThCr2Si2-like iron-free 122
phases, and these polymorphs will be ductile materials with high elastic
anisotropy.",1101.5253v1
2011-02-04,A Novel Large Moment Antiferromagnetic Order in K0.8Fe1.6Se2 Superconductor,"The discovery of cuprate high Tc superconductors has inspired searching for
unconventional su- perconductors in magnetic materials. A successful recipe has
been to suppress long-range order in a magnetic parent compound by doping or
high pressure to drive the material towards a quantum critical point, which is
replicated in recent discovery of iron-based high TC superconductors. The
long-range magnetic order coexisting with superconductivity has either a small
magnetic moment or low ordering temperature in all previously established
examples. Here we report an exception to this rule in the recently discovered
potassium iron selenide. The superconducting composition is identified as the
iron vacancy ordered K0.8Fe1.6Se2 with Tc above 30 K. A novel large moment 3.31
{\mu}B/Fe antiferromagnetic order which conforms to the tetragonal crystal
symmetry has the unprecedentedly high an ordering temperature TN = 559 K for a
bulk superconductor. Staggeredly polarized electronic density of states thus is
suspected, which would stimulate further investigation into superconductivity
in a strong spin-exchange field under new circumstance.",1102.0830v1
2011-02-08,Sodium-oxygen anticorrelation and neutron capture elements in Omega Centauri stellar populations,"Omega Centauri is no longer the only globular cluster known to contain
multiple stellar populations, yet it remains the most puzzling. Due to the
extreme way in which the multiple stellar population phenomenon manifests in
this cluster, it has been suggested that it may be the remnant of a larger
stellar system. In this work, we present a spectroscopic investigation of the
stellar populations hosted in the globular cluster Omega Centauri to shed light
on its, still puzzling, chemical enrichment history. With this aim we used
FLAMES+GIRAFFE@VLT to observe 300 stars distributed along the multimodal red
giant branch of this cluster, sampling with good statistics the stellar
populations of different metallicities. We determined chemical abundances for
Fe, Na, O, and n-capture elements Ba and La. We confirm that Omega Centauri
exhibits large star-to-star variations in iron with [Fe/H] ranging from ~ -2.0
to ~ -0.7 dex. Barium and lanthanum abundances of metal poor stars are
correlated with iron, up to [Fe/H] -1.5, while they are almost constant (or at
least have only a moderate increase) in the more metal rich populations. There
is an extended Na-O anticorrelation for stars with [Fe/H]<~ -1.3 while more
metal rich stars are almost all Na-rich. Sodium was found to midly increase
with iron over all the metallicity range.",1102.1653v1
2011-02-09,Iron vacancy superstructure and possible room temperature antiferromagnetic order in superconducting Cs_{y}Fe_{2-x}Se_2,"Neutron and x-ray powder and single crystal synchrotron diffraction of
CsyFe2-xSe2 show the presence of superstructure reflections with propagation
vector k=[2/5, 1/5, 1] with respect to the average crystal structure I4/mmm (a
= 4, c = 15A). The propagation vector star corresponds to the 5 times bigger
unit cell given by transformation A=2a+b, B= -a+2b, C= c. A solution for the
atomic structure is found in the space groups P42/n and I4/m with an ordered
pattern of iron vacancies corresponding to the iron deficiency x = 0.29 and Cs
stoichiometry y = 0.83. The superstructure satellites are more pronounced in
the neutron diffraction patterns suggesting that they can have some magnetic
contribution. We have sorted out possible symmetry adapted magnetic
configurations and found that the presence of AFM ordering with the ordered
magnetic moment of Fe with 2{\mu}B does not contradict to the experimental
data. However, the solutions space is highly degenerate and we cannot choose a
specific solution. Instead we propose possible magnetic configurations with the
Fe magnetic moments in (ab)-plane or along c-axis. The superstructure is
destroyed above Ts ~ 500 K by a first-order-like transition.",1102.1919v2
2011-02-11,Quasiparticle states around a nonmagnetic impurity in electron-doped iron-based superconductors with spin-density-wave order,"The quasiparticle states around a nonmagnetic impurity in electron-doped
iron-based superconductors with spin-density-wave (SDW) order are investigated
as a function of doping and impurity scattering strength. In the undoped
sample, where a pure SDW state exists, two impurity-induced resonance peaks are
observed around the impurity site and they are shifted to higher (lower)
energies as the strength of the positive (negative) scattering potential (SP)
is increased. For the doped samples where the SDW order and the superconducting
order coexist, the main feature is the existence of sharp in-gap resonance
peaks whose positions and intensity depend on the strength of the SP and the
doping concentration. In all cases, the local density of states exhibits clear
$C_2$ symmetry. We also note that in the doped cases, the impurity will divide
the system into two sublattices with distinct values of magnetic order. Here we
use the band structure of a two-orbital model, which considers the asymmetry of
the As atoms above and below the Fe-Fe plane. This model is suitable to study
the properties of the surface layers in the iron-pnictides and should be more
appropriate to describe the scanning tunneling microscopy experiments.",1102.2401v1
2011-02-16,"Room temperature antiferromagnetic order in superconducting X_yFe_{2-x}Se_ 2, (X= Rb, K): a powder neutron diffraction study","Magnetic and crystal structures of superconducting X yFe 2-xSe 2 (X= Rb and K
with Tc=31.5 K and 29.5 K) have been studied by neutron powder diffraction at
room temperature. Both crystals show ordered iron vacancy pattern and the
crystal structure is well described in the I4/m space group with the lattice
constants a=8.799, c=14.576 and a=8.730, c=14.115 A, and the refined
stoichiometry x=0.30(1), y=0.83(2) and x=0.34(1), y=0.83(1) for Rb- and
K-crystals respectively. The structure contains one fully occupied iron
position and one almost empty vacancy position. Assuming that the iron moment
is ordered only on the fully occupied site we have sorted out all eight
irreducible representations (irreps) for the propagation vector k=0 and have
found that irreps tau_2 and tau_7 well fit the experimental data with the
moments along c-axis. The moment amplitudes amounted to 2.15(3) mu_B, 2.55(3)
mu_B for tau_2 and 2.08(6) mu_B, 2.57(3) mu_B for tau_7 for Rb- and K-crystals
respectively. Irrep tau_2 corresponds to the Shubnikov group I4/m' and gives a
constant moment antiferromagnetic configuration, whereas tau_7 does not have
Shubnikov counterpart and allows two different magnetic moments in the
structure.",1102.3380v1
2011-03-05,Orbital magnetic response and the anisotropy of magnetic susceptibility in the Iron-based superconductors,"We propose that the orbital angular momentum of the conduction electrons in
the Iron-based superconductors is activated in their low energy physics. Using
a five-band tight-binding model derived from fitting the LDA band structure, we
find that the orbital magnetic susceptibility of the conduction electrons in
such a multi-orbital system is several times larger than the Pauli spin
susceptibility and is comparable in magnitude to the observed total magnetic
susceptibility. The orbital magnetic susceptibility in the Fe-As
plane($\chi^{x}_{L}$) is found to be larger than that perpendicular to the
Fe-As plane($\chi^{z}_{L}$) by a factor about two and the total magnetic
susceptibility in the normal state can be fitted with formula
$\chi(T,\theta)\approx \chi_{s}(T)+\chi_{L}(\theta)$, where $\chi_{s}(T)$ is
the temperature dependent isotropic part due to spin and $\chi_{L}(\theta)$ is
the temperature independent anisotropic part due to orbital. In the
superconducting state, $\chi^{x}_{L}$ is found to be significantly reduced as
the pairing gap develops, while $\chi^{z}_{L}$ is almost not affected by the
superconducting transition. We argue the large anisotropy observed in the bulk
magnetic susceptibility and the Knight shift in the Iron-based superconductors
should be attributed to the orbital magnetic response of their conduction
electrons.",1103.1056v2
2011-03-10,Weighing Super-Massive Black Holes with Narrow Fe K$α$ Line,"It has been suggested that the narrow cores of the Fe K$\alpha$ emission
lines in Active Galactic Nuclei (AGNs) are likely produced in the torus, the
inner radius of which can be measured by observing the lag time between the $V$
and $K$ band flux variations. In this paper we compare the virial products of
the infrared time lags and the narrow Fe K$\alpha$ widths for 10 type 1 AGNs
with the black hole masses from other techniques. We find the narrow Fe
K$\alpha$ line width is in average 2.6$^{+0.9}_{-0.4}$ times broader than
expected assuming an isotropic velocity distribution of the torus at the
distance measured by the infrared lags. We propose the thick disk model of the
torus could explain the observed larger line width. Another possibility is the
contamination by emission from the broad line region or the outer accretion
disk. Alternatively, the narrow iron line might originate from the inner most
part of the obscuring torus within the sublimation radius, while the infrared
emission from outer cooler part. We note the correlation between the black hole
masses based on this new technique and those based on other known techniques is
statistically insignificant. We argue that this could be attributed to the
small sample size and the very large uncertainties in the measurements of iron
K line widths. The next generation of X-ray observatories could help verify the
origin of the narrow iron K$\alpha$ line and the reliability of this new
technique.",1103.1927v2
2011-03-14,"AGN feedback and iron enrichment in the powerful radio galaxy, 4C+55.16","We present a detailed X-ray analysis of 4C+55.16, an unusual and interesting
radio galaxy, located at the centre of a cool core cluster of galaxies.
4C+55.16 is X-ray bright (L(cluster)~10^45 erg/s), radio powerful, and shows
clear signs of interaction with the surrounding intracluster medium. By
combining deep Chandra (100 ks) with 1.4 GHz VLA observations, we find evidence
of multiple outbursts from the central AGN, providing enough energy to offset
cooling of the ICM (P_bubbles=6.7x10^44 erg/s). Furthermore, 4C+55.16 has an
unusual intracluster iron distribution showing a plume-like feature rich in Fe
L emission that runs along one of the X-ray cavities. The excess of iron
associated with the plume is around 10^7M_sol. The metal abundances are
consistent with being Solar-like, indicating that both SNIa and SNII contribute
to the enrichment. The plume and southern cavity form a region of cool
metal-rich gas, and at the edge of this region, there is a clear discontinuity
in temperature (from kT~2.5 keV to kT~5.0 keV), metallicity (from ~0.4 solar to
0.8 solar), and surface brightness distribution, consistent with it being
caused by a cold front. However, we also suggest that this discontinuity could
be caused by cool metal-rich gas being uplifted from the central AGN along one
of its X-ray cavities.",1103.2585v2
2011-03-16,Superconductivity at the Border of Electron Localization and Itinerancy,"The superconducting state of iron pnictides and chalcogenides exists at the
border of antiferromagnetic order. Consequently, these materials could provide
clues about the relationship between magnetism and unconventional
superconductivity. One explanation, motivated by the so-called bad-metal
behaviour of these materials, proposes that magnetism and superconductivity
develop out of quasi-localized magnetic moments which are generated by strong
electron-electron correlations. Another suggests that these phenomena are the
result of weakly interacting electron states that lie on nested Fermi surfaces.
Here we address the issue by comparing the newly discovered alkaline iron
selenide superconductors, which exhibit no Fermi-surface nesting, to their iron
pnictide counterparts. We show that the strong-coupling approach leads to
similar pairing amplitudes in these materials, despite their different Fermi
surfaces. We also find that the pairing amplitudes are largest at the boundary
between electronic localization and itinerancy, suggesting that new
superconductors might be found in materials with similar characteristics.",1103.3259v2
2011-03-17,"Origin of Orthorhombic Transition, Magnetic Transition, and Shear Modulus Softening in Iron Pnictide Superconductors: Analysis based on the Orbital Fluctuation Theory","The main features in iron-pnictide superconductors are summarized as (i) the
orthorhombic transition accompanied by remarkable softening of shear modulus,
(ii) high-Tc superconductivity close to the orthorhombic phase, and (iii)
stripe-type magnetic order induced by orthorhombicity. To present a unified
explanation for them, we analyze the multiorbital Hubbard-Holstein model with
Fe-ion optical phonons based on the orbital fluctuation theory. In the
random-phase-approximation (RPA), a small electron-phonon coupling constant
($\lambda ~ 0.2$) is enough to produce large orbital (=charge quadrupole)
fluctuations. The most divergent susceptibility is the
$O_{xz}$-antiferro-quadrupole (AFQ) susceptibility, which causes the s-wave
superconductivity without sign reversal (s_{++}-wave state). At the same time,
divergent development of $O_{x2-y2}$-ferro-quadrupole (FQ) susceptibility is
brought by the ""two-orbiton process"" with respect to the AFQ fluctuations,
which is absent in the RPA. The derived FQ fluctuations cause the softening of
$C_{66}$ shear modulus, and its long-range-order not only triggers the
orthorhombic structure transition, but also induces the instability of
stripe-type antiferro-magnetic state. In other words, the condensation of
composite bosons made of two orbitons gives rise to the FQ order and structure
transition. The theoretically predicted multi-orbital-criticality presents a
unified explanation for abovementioned features of iron pnictide
superconductors.",1103.3360v3
2011-03-25,Unconventional temperature enhanced magnetism in iron telluride,"Highly energetic magnetic fluctuations, discovered in high-temperature
superconductors (HTSC) by inelastic neutron scattering (INS), are now widely
believed to be vital for the superconductivity. In two competing scenarios,
they either originate from local atomic spins, or are a property of cooperative
spin-density-wave (SDW) behavior of conduction electrons. Both assume clear
partition into localized electrons, giving rise to local spins, and itinerant
ones, occupying well-defined, rigid conduction bands. Here, by performing an
INS study of spin dynamics in iron telluride, a parent material of one of the
iron-based HTSC families, we have discovered that this very assumption fails,
and that conduction and localized electrons are fundamentally entangled. We
find that the real-space structure of magnetic correlations can be explained by
a simple local-spin plaquette model. However, the effective spin implicated in
such a model, appears to increase with the increasing temperature. Thus, we
observe a remarkable redistribution of magnetism between the two groups of
electrons, which occurs in the temperature range relevant for the
superconductivity. The analysis of magnetic spectral weight shows that the
effective spin per Fe at T \approx 10 K, in the antiferromagnetic phase,
corresponds to S \approx 1, consistent with the recent analyses that emphasize
importance of Hund's intra-atomic exchange. However, it grows to S \approx 3/2
in the disordered phase, a result that profoundly challenges the picture of
rigid bands, broadly accepted for HTSC.",1103.5073v1
2011-04-12,Isotropic three-dimensional gap in the iron-arsenide superconductor LiFeAs from directional heat transport measurements,"The thermal conductivity k of the iron-arsenide superconductor LiFeAs (Tc ~
18K) was measured in single crystals at temperatures down to T~50mK and in
magnetic fields up to H=17T, very close to the upper critical field Hc2~18T.
For both directions of the heat current, parallel and perpendicular to the
tetragonal c-axis, a negligible residual linear term k/T is found as T ->0,
revealing that there are no zero-energy quasiparticles in the superconducting
state. The increase in k with magnetic field is the same for both current
directions and it follows closely the dependence expected for an isotropic
superconducting gap. There is no evidence of multi-band character, whereby the
gap would be different on different Fermi-surface sheets. These findings show
that the superconducting gap in LiFeAs is isotropic in 3D, without nodes or
deep minima anywhere on the Fermi surface. Comparison with other iron-pnictide
superconductors suggests that a nodeless isotropic gap is a common feature at
optimal doping (maximal Tc).",1104.2209v2
2011-05-06,"Effect of iron content and potassium substitution in A$_{0.8}$Fe$_{1.6}$Se$_2$ (A = K, Rb, Tl) superconductors: a Raman-scattering investigation","We have performed Raman-scattering measurements on high-quality single
crystals of the superconductors K$_{0.8}$Fe$_{1.6}$Se$_2$ ($T_c$ = 32 K),
Tl$_{0.5}$K$_{0.3}$Fe$_{1.6}$Se$_2$ ($T_c$ = 29 K), and
Tl$_{0.5}$Rb$_{0.3}$Fe$_{1.6}$Se$_2$ ($T_c$ = 31 K), as well as of the
insulating compound KFe$_{1.5}$Se$_2$. To interpret our results, we have made
first-principles calculations for the phonon modes in the ordered iron-vacancy
structure of K$_{0.8}$Fe$_{1.6}$Se$_2$. The modes we observe can be assigned
very well from our symmetry analysis and calculations, allowing us to compare
Raman-active phonons in the AFeSe compounds. We find a clear frequency
difference in most phonon modes between the superconducting and
non-superconducting potassium crystals, indicating the fundamental influence of
iron content. By contrast, substitution of K by Tl or Rb in
A$_{0.8}$Fe$_{1.6}$Se$_2$ causes no substantial frequency shift for any modes
above 60 cm$^{-1}$, demonstrating that the alkali-type metal has little effect
on the microstructure of the FeSe layer. Several additional modes appear below
60 cm$^{-1}$ in Tl- and Rb-substituted samples, which are vibrations of heavier
Tl and Rb ions. Finally, our calculations reveal the presence of ""chiral""
phonon modes, whose origin lies in the chiral nature of the
K$_{0.8}$Fe$_{1.6}$Se$_2$ structure.",1105.1198v2
2011-05-10,Magnetic-crystallographic phase diagram of superconducting parent compound Fe$_{1+x}$Te,"hrough neutron diffraction experiments, including spin-polarized
measurements, we find a collinear incommensurate spin-density wave with
propagation vector $ \mathbf k = $ ($0.4481(4) \, \,0 \, \, \frac1 2$) at base
temperature in the superconducting parent compound Fe$_{1+x}$Te. This critical
concentration of interstitial iron corresponds to $x \approx 12%$ and leads
crystallographic phase separation at base temperature. The spin-density wave is
short-range ordered with a correlation length of 22(3) \AA, and as the ordering
temperature is approached its propagation vector decreases linearly in the
H-direction and becomes long-range ordered. Upon further populating the
interstitial iron site, the spin-density wave gives way to an incommensurate
helical ordering with propagation vector $ \mathbf k =$ ($0.3855(2) \, \,0 \,
\, \frac1 2$) at base temperature. For a sample with $x \approx 9(1) %$, we
also find an incommensurate spin-density wave that competes with the
bicollinear commensurate ordering close to the N\'eel point. The shifting of
spectral weight between competing magnetic orderings observed in several
samples is supporting evidence for the phase separation being electronic in
nature, and hence leads to crystallographic phase separation around the
critical interstitial iron concentration of 12%. With results from both powder
and single crystal samples, we construct a magnetic-crystallographic phase
diagram of Fe$_{1+x}$Te for $ 5% < x <17%$",1105.1937v1
2011-05-20,Orbital-Selective Superconductivity and the Effect of Lattice Distortion in Iron-Based Superconductors,"The superconducting (SC) state of iron-based compounds in both tetragonal and
orthorhombic phases is studied on the basis of an effective Hamiltonian
composed of the kinetic energy including the five Fe 3d-orbitals, the
orthorhombic crystalline electric field (CEF) energy, and the two-orbital
Kugel'-Khomski\u{i}-type superexchange interaction. Our basic assumption is
that the antiferromagnetic (AF) state in the parent compounds can be described
by the $d_{xz}$ and $d_{yz}$ orbitals, and that the electrons in these orbitals
have relatively strong electron correlation in the vicinity of the AF state. In
order to study the physical origin of the structure-sensitive SC transition
temperature, the effect of orthorhombic distortion is taken into account as the
energy-splitting, $\Delta_{\textrm{ortho.}}$, between the $d_{xz}$ and $d_{yz}$
orbitals. We find that the eigenvalue of the linearized gap equation decreases
accompanied with the reduction of the partial density of states for the
$d_{xz}$ and $d_{yz}$ orbitals as $\Delta_{\textrm{ortho.}}$ increases, and
that the dominant pairing symmetry is an unconventional fully gapped
$s_{+-}$-wave pairing. We also find large anisotropy of the SC gap function in
the orthorhombic phase. We propose that the CEF energy plays an important role
in controlling $T_{\textrm{c}}$ and the SC gap function, and that
orbital-selective superconductivity is a key feature in iron-based
superconductors, which causes the structure-sensitive $T_{\textrm{c}}$.",1105.4028v1
2011-06-10,Electron doped Ca10(Pt3As8)(Fe2As2)5 and Ca10(Pt4As8)(Fe2As2)5 - High Tc superconductors with skutterudite intermediary layers,"It has been argued that the very high transition temperatures of the highest
Tc cuprate superconductors are facilitated by enhanced CuO2 plane coupling
through the (Bi,Tl,Hg)-O intermediary layers. Whether enhanced coupling through
intermediary layers can also influence Tc in the iron arsenide superconductors
has never been tested due the lack of appropriate systems for study. Here we
report the crystal structures and properties of two iron arsenide
superconductors, Ca10(Pt3As8)(Fe2As2)5 (the 10-3-8 phase) and
Ca10(Pt4As8)(Fe2As2)5 (the 10-4-8 phase). Based on -Ca-(PtnAs8)-Ca-Fe2As2-
layer stacking, the most important difference in the structures lies in the
structural and electronic characters of the intermediary platinum arsenide
layers. Electron doping through partial substitution of Pt for Fe in the Fe2As2
layers leads to Tc of 11 K in the 10-3-8 phase and 25 K in the 10-4-8 phase.
Using the chemical concepts of Zintl ion electron counting and the stability of
Pt in the 5d8 configuration we argue that the dramatic difference in Tc arises
because the intermediary layer is semiconducting in the 10-3-8 phase but
metallic in the 10-4-8 phase, leading to enhanced interlayer coupling in the
10-4-8 phase. The results suggest that metallic intermediary layers may offer a
new road to higher Tc in iron arsenide superconductors.",1106.2111v1
2011-06-12,Upper critical field and thermally activated flux flow in single crystalline Tl$_{0.58}$Rb$_{0.42}$Fe$_{1.72}$Se$_2$,"The upper critical field $\mu_0H_{c2}(T_c)$ of
Tl$_{0.58}$Rb$_{0.42}$Fe$_{1.72}$Se$_2$ single crystals has been determined by
means of measuring the electrical resistivity in both a pulsed magnetic field
($\sim$60T) and a DC magnetic field ($\sim$14T). It is found that $H_{c2}$
linearly increases with decreasing temperature for $\textbf{H}$$\parallel$$c$,
reaching $\mu_0H_{c2}^{\textbf{H}\parallel c}(0\textrm{K})\simeq60$ T. On the
other hand, a larger $\mu_0H_{c2}(0\textrm{K})$ with a strong convex curvature
is observed for $\textbf{H}$$\perp$$c$ ($\mu_0H_{c2}^{\textbf{H}\perp
c}$(18K)$\simeq$60T). This compound shows a moderate anisotropy of the upper
critical field around $T_c$, but decreases with decreasing temperature.
Analysis of the upper critical field based on the Werthamer-Helfand-Hohenberg
(WHH) method indicates that $\mu_0H_{c2}(0\textrm{K})$ is orbitally limited for
$\textbf{H}$$\parallel$$c$, but the effect of spin paramagnetism may play an
important role on the pair breaking for $\textbf{H}$$\perp$$c$. All these
experimental observations remarkably resemble those of the iron pnictide
superconductors, suggesting a unified scenario for the iron-based
superconductors. Moreover, the superconducting transition is significantly
broadened upon applying a magnetic field, indicating strong thermal fluctuation
effects in the superconducting state of
Tl$_{0.58}$Rb$_{0.42}$Fe$_{1.72}$Se$_2$. The derived thermal activation energy
for vortex motion is compatible with those of the 1111-type iron pnictides.",1106.2283v2
2011-06-16,"Modulated superconductivity due to vacancy and magnetic order in $A_x$Fe$_{2-x/2}$Se$_2$ [$A=$Cs, K, (Tl,Rb), (Tl,K)] iron-selenide superconductors","We present a calculation of a 'modulated' superconducting state in
iron-selenide superconductors. The zero-momentum $d-$wave pairing breaks the
translational symmetry of the conventional BaFe$_2$Se$_2$-like crystal of
$I4/mmm$ space group. This pairing state becomes compatible when the Fe
vacancies form an ordered state and the crystal symmetry changes to a
low-temperature $I4/m$ one. For the specific case of an incommensurate vacancy
order at $Q_v=(1/5, 3/5)$ in K$_{0.82(2)}$Fe$_{1.626(3)}$Se$_2$, we find that
it induces a block checkerboard antiferromagnetic phase at wavevector ${\bf
Q}_m=4{\bf Q}_v$. The coexistence of vacancy order and magnetic order leads to
a reconstructed ground state which naturally couples to the $d-$wave
superconductivity in a uniform phase in what we propose will be a general
coupling for all iron-selenide superconductors. Our results agree with numerous
experimental data available to date. We thus suggest that the
incommensurability leads to uniform coexistence of multiple phases as a viable
alternative to a nanoscale phase separation in high-$T_c$ superconductors and
play an important role in the enhancement of superconductivity.",1106.3289v1
2011-07-04,Comparative studies of the scanning tunneling spectra in cuprate and iron-arsenide superconductors,"We report scanning tunneling spectroscopic studies of cuprate and
iron-arsenic superconductors, including YBa_2Cu_3O_{7-\delta} (Y-123, T_c = 93
K), Sr_{0.9}La_{0.1}CuO_2 (La-112, T_c = 43 K), and the ""122"" compounds
Ba(Fe_{1-x}Co_x)_2As_2 (Co-122 with x = 0.06, 0.08, 0.12 for T_c = 14, 24, 20
K). For H > 0, pseudogap (\Delta_{PG}) features are revealed inside the
vortices, with \Delta_{PG} = [(\Delta_{eff})^2+(\Delta_{SC})^2]^{1/2} >
\Delta_{SC} in Y-123 and \Delta_{PG} < \Delta_{SC} in La-112, suggesting that
the physical origin of \Delta_{PG} is a competing order coexisting with
superconductivity. Additionally, Fourier transformation (FT) of the Y-123
spectra exhibits two types of spectral peaks, one type is associated with
energy (\omega)-dependent quasiparticle interference (QPI) wave-vectors and the
other consists of \omega-independent wave-vectors due to competing orders and
(\pi,\pi) magnetic resonances. For the multi-band Co-122 compounds, two-gap
superconductivity is found for all doping levels. Magnetic resonant modes that
follow the temperature dependence of the superconducting gaps are also
identified. These findings, together with the \omega- and x-dependent QPI
spectra, are consistent with a sign-changing s-wave pairing symmetry in the
Co-122 iron arsenides. Our comparative studies suggest that the commonalities
among the cuprate and the ferrous superconductors include the proximity to
competing orders, antiferromagnetic (AFM) spin fluctuations and magnetic
resonances in the superconducting (SC) state, and the unconventional pairing
symmetries with sign-changing order parameters on different parts of the Fermi
surface.",1107.0697v1
2011-08-19,Structure and magnetic properties of nanostructured Pd-Fe thin films produced by pulse electrodeposition,"Nanostructured Pd-Fe thin films with varied Fe content were prepared by
electrodeposition technique from organic electrolytes on Cu and brass
substrates. The structure and the magnetic properties of the films were
investigated prior to post-deposition annealing. The structure of the Pd1-xFex
thin films with x = 0.14, 0.24, and 0.52 was determined by X-ray diffraction
(XRD) and transmission electron microscopy (TEM) as a solid solution of iron in
palladium face-centered cubic lattice with the (111) orientation of nanograins
relatively to the substrate surface. The films with higher iron concentration,
x = 0.74, 0.91, have structure of a solid solution based on the body-centered
cubic lattice. The average grain size determined by the scanning electron
microscopy (SEM) for the first two alloys is 7-10 nm, and for the latter ones
it is about 120 nm. The saturation magnetization of the films has linear
dependence on the iron content, but coercivity has non-monotonic dependence on
x, i.e. the films with x = 0.68 show highest coercivity. The magnetic
anisotropy of the samples is studied by ferromagnetic resonance (FMR)
spectroscopy.",1108.3888v1
2011-09-07,Solar Cycle Variations in the Elemental Abundance of Helium and Fractionation of Iron in the Fast Solar Wind - Indicators of an Evolving Energetic Release of Mass from the Lower Solar Atmosphere,"We present and discuss the strong correspondence between evolution of the
emission length scale in the lower transition region and in situ measurements
of the fast solar wind composition during this most recent solar minimum. We
combine recent analyses demonstrating the variance in the (supergranular)
network emission length scale measured by SOHO (and STEREO) with that of the
Helium abundance (from WIND) and the degree of Iron fractionation in the solar
wind (from the ACE and Ulysses). The net picture developing is one where a
decrease in the Helium abundance and the degree of Iron fractionation
(approaching values expected of the photosphere) in the fast wind indicate a
significant change in the process loading material into the fast solar wind
during the recent solar minimum. This result is compounded by a study of the
Helium abundance during the space age using the NASA OMNI database which shows
a slowly decaying amount of Helium being driven into the heliosphere over the
course of the several solar cycles.",1109.1408v1
2011-09-22,Self-Diffusion of Iron in L10 FePd films Upon He-irradiation (alternative title: An alternative for diffusion studies in isotopic FePd multilayers),"The continuous need towards improving the capacity of magnetic storage
devices requires materials with strong perpendicular magnetic anisotropy. FePd,
CoPd and their Co(Fe)Pt counterparts very attractive candidate for such
purposes. The magnetic properties of these films are largely dependent on the
orientation and local distribution of the L10 FePd phase fraction which are
mainly controlled by diffusion processes and involve diffusion paths of a few
angstroms. Highly ordered as well as disordered epitaxial isotope-periodic
57FePd/natFePd (001) thin films were prepared by molecular-beam epitaxy on
MgO(001) substrate. Short range diffusion of different phases in FePd thin film
induced by room temperature 130 keV He+ irradiation was investigated at
fluences up to 30\times1015 ions/cm2. Conversion electron M\""ossbauer
spectroscopy and synchrotron M\""ossbauer reflectivity experiments showed that
the inter-atomic diffusion across 57FePd/natFePd interface occur mainly via the
iron rich regions. The ratio of the diffusion length in the L10, fcc and iron
rich structure are 1:1.4:5.6 respectively. Assuming that the diffusion
coefficient in the fcc phase is between the diffusion coefficient of the L10
phase in the crystallographic c direction and perpendicular to it, the
diffusion coefficient in the c-direction of the L10 phase is found more than
1.9 times lower than in the a-b plane.",1109.4742v1
2011-10-26,Non-Fermi Liquid due to Orbital Fluctuations in Iron Pnictide Superconductors,"We study the influence of quantum fluctuations on the electron self energy in
the normal state of iron-pnictide superconductors using a five orbital tight
binding model with generalized Hubbard on-site interactions. Within a one-loop
treatment, we find that an overdamped collective mode develops at low frequency
in channels associated with quasi-1D $d_{xz}$ and $d_{yz}$ bands. When the
critical point for the $C_4$ symmetry broken phase (structural phase
transition) is approached, the overdamped collective modes soften, and acquire
increased spectral weight, resulting in non-Fermi liquid behavior at the Fermi
surface characterized by the frequency dependence of the imaginary part of
electron self energy of the form $\omega^\lambda$, $0<\lambda<1$. We argue that
this non-Fermi liquid behavior is responsible for the recently observed
zero-bias enhancement in the tunneling signal in quantum point contact
spectroscopy. A key experimental test of this proposal is the absence of the
non-Fermi liquid behaviour in the hole-doped materials. Our result suggests
that quantum criticality plays an important role in understanding the normal
state properties of iron-pnictide superconductors.",1110.5917v4
2011-10-27,Analysing the Suzaku Spectra of the Broad-Line Seyfert 1 Galaxy CBS 126,"We analysed new simultaneous \emph{Suzaku} and \emph{Swift} data of the Broad
Line Seyfert 1 (BLS1) galaxy CBS 126. A clear Fe emission line and a strong
soft excess are present in the source spectra. We fit the spectra with a
relativistic reflection model and find the model tends to fit the data with a
high iron abundance possibly due to the large soft excess present. By checking
the difference and the RMS spectra, we find there is likely an absorption edge
at $\sim$ 0.89 keV, which might be caused by oxygen or neon. We also produced
an analysis of the time-resolved spectra in order to examine the existence of
the edge. Although high iron abundance is required more in the time-resolved
spectra, a model of solar iron abundance together with an absorption edge gives
a more physical explanation. Variation of the ionisation parameter is an
alternative, plausible explanation for the excess seen in the difference
spectra. It is difficult to know if there are warm absorbers in this source
from the current data. To further investigate the presence of possible warm
absorbers, higher signal-to-noise low-energy data are needed. The work
presented here tentatively suggests that the spectra of a BLS1 can be explained
by a relativistic reflection model similar to that often seen in their
narrow-line cousins.",1110.6047v2
2011-12-01,Observational studies of Cepheid amplitudes. II Metallicity dependence of pulsation amplitudes,"Physical and phenomenological properties (radius, luminosity, shape of the
light curve, etc.) of Cepheids strongly depend on the pulsation period, with
the exception of the pulsation amplitude. A possible factor causing a wide
range of pulsation amplitudes might be the different atmospheric metallicities
of individual Cepheids.
  We studied the influence exerted by the atmospheric iron content, [Fe/H], on
the pulsational amplitude of Galactic Cepheids. We searched for correlations
between the [Fe/H] value and both the observed amplitudes and amplitude related
parameters.
  The amplitude of the Cepheid pulsation slightly decreases with increasing
iron abundance. This effect is more pronounced for the radial velocity
variations and for the shorter pulsation periods. The wavelength dependence of
photometric amplitudes is also found to be sensitive to the metallicity. Some
of these effects are not consequences of differential line blanketing. Based on
the calibrations of the metallicity sensitivity relationships, we derived
photometric iron abundance for 21 Galactic Cepheids. The dichotomic behaviour
dividing Galactic Cepheids that pulsate in the fundamental mode into short- and
long-period groups at the period of 10.47 d can be noticed in some diagrams
that show metallicity-related dependences.
  We confirm that variety in atmospheric metallicity in Cepheids contributes to
the finite range of pulsation amplitudes at a given period. Effects of
metallicity on the amplitudes revealed from observational data and the
occurrence of the dichotomy also derived from phenomenological data have to be
confirmed by appropriate theoretical models of stellar structure and pulsation.",1112.0115v1
2012-01-25,Newly-born pulsars as sources of ultrahigh energy cosmic rays,"Newly-born pulsars offer favorable sites for the injection of heavy nuclei,
and for their further acceleration to ultrahigh energies. Once accelerated in
the pulsar wind, nuclei have to escape from the surrounding supernova envelope.
We examine this escape analytically and numerically, and discuss the pulsar
source scenario in light of the latest ultrahigh energy cosmic ray (UHECR)
data. Our calculations show that, at early times, when protons can be
accelerated to energies E>10^20 eV, the young supernova shell tends to prevent
their escape. In contrast, because of their higher charge, iron-peaked nuclei
are still accelerated to the highest observed energies at later times, when the
envelope has become thin enough to allow their escape. Ultrahigh energy iron
nuclei escape newly-born pulsars with millisecond periods and dipole magnetic
fields of ~10^(12-13) G, embedded in core-collapse supernovae. Due to the
production of secondary nucleons, the envelope crossing leads to a transition
of composition from light to heavy elements at a few EeV, as observed by the
Auger Observatory. The escape also results in a softer spectral slope than that
initially injected via unipolar induction, which allows for a good fit to the
observed UHECR spectrum. We conclude that the acceleration of iron-peaked
elements in a reasonably small fraction (< 0.01%) of extragalactic
rotation-powered young pulsars would reproduce satisfactorily the current UHECR
data. Possible signatures of this scenario are also discussed.",1201.5197v1
2012-02-28,U(1) Slave-spin theory and its application to Mott transition in a multi-orbital model for iron pnictides,"A U(1) slave-spin representation is introduced for multi-orbital Hubbard
models. As with the $Z_2$ form of L. de'Medici et al. (Phys. Rev. B 72, 205124
(2005)), this approach represents a physical electron operator as the product
of a slave spin and an auxiliary fermion operator. For non-degenerate
multi-orbital models, our U(1) approach is advantageous in that it captures the
non-interacting limit at the mean-field level. For systems with either a single
orbital or degenerate multiple orbitals, the U(1) and $Z_2$ slave-spin
approachs yield the same results in the slave-spin-condensed phase. In general,
the U(1) slave-spin approach contains a U(1) gauge redundancy, and properly
describes a Mott insulating phase. We apply the U(1) slave-spin approach to
study the metal-to-insulator transition in a five-orbital model for parent iron
pnictides. We demonstrate a Mott transition as a function of the interactions
in this model. The nature of the Mott insulating state is influenced by the
interplay between the Hund's rule coupling and crystal field splittings. In the
metallic phase, when the Hund's rule coupling is beyond a threshold, there is a
crossover from a weakly correlated metal to a strongly correlated one, through
which the quasiparticle speactral weight rapidly drops. The existence of such a
strongly correlated metallic phase supports the incipient Mott picture of the
parent iron pnictides. In the parameter regime for this phase and in the
vicinity of the Mott transition, we find that an orbital selective Mott state
has nearly as competitive a ground state energy.",1202.6115v1
2012-02-29,The s-process nucleosynthesis in massive stars: current status and uncertainties due to convective overshooting,"Context: It is well known that the so-called s-process is responsible for the
production of neutron-rich trans-iron elements, that form the bulk of the
""heavy nuclides"" (i.e. nuclides more massive than the iron-group nuclei) in the
solar-system composition, considered as ""standard of reference"" dataset for
cosmic abundances. In particular, the s-process produces about half of all the
trans-iron isotopes by moving along the ""valley of stability"" through a series
of neutron capture reactions and beta decays. More than one s-process
""component"" (i.e. a nucleosynthesis event with a single set of physical
conditions like neutron exposure, initial abundances and neutron density) is
required in order to explain the observed solar distribution of s-nuclei
abundances. Current views on the subject suggest the existence of several
components that, in terms of stellar environments, correspond to distinct
categories of stars in different evolutionary phases. Aims: The purpose of the
chapter is to review the s-process nucleosynthesis occurring in massive stars
(so-called weak component of s-process), pointing particular attention on the
recent studies devoted to analyze how the uncertainties due to stellar
evolution modeling and, specifically, due to convective overshooting affect the
efficiency of this nucleosynthesis process.",1202.6577v2
2012-03-20,"Orbital fluctuation theory in iron-based superconductors: s-wave superconductivity, structure transition, and impurity-induced nematic order","The main features in iron-based superconductors would be (i) the orthorhombic
transition accompanied by remarkable softening of shear modulus, (ii) high-Tc
superconductivity close to the orthorhombic phase, and (iii) nematic transition
in the tetragonal phase. In this paper, we present a unified explanation for
them, based on the orbital fluctuation theory, considering both the e-ph and
the Coulomb interaction. It is found that a small e-ph coupling constant
($\lambda ~ 0.2$) is enough to produce large orbital (=charge quadrupole
$O_{xz/yz}$) fluctuations, which causes the s-wave superconductivity without
sign reversal ($s_{++}$-wave state). The derived orbital fluctuations also
cause the instability toward the structure transition due to the bound state
formation of two orbitons with opposite momenta, which is called the
""two-orbiton process"". Moreover, impurity-induced non-local orbital order with
$C_2$-symmetry is obtained when the orbital fluctuations are strong. This
""impurity-induced nematic state"" explains the in-plane anisotropy of
resistivity in detwinned samples. We stress that (i)-(iii) are reproducible
only when orbital fluctuations with respect to $O_{xz}$ and $O_{yz}$ charge
quadrupoles are the most divergent. This fact ensures the reliability of the
present model Hamiltonian and calculation.",1203.4602v2
2012-03-22,Magnetic hour-glass dispersion and its relation to high-temperature superconductivity in iron-tuned Fe$_{1+y}$Te$_{0.7}$Se$_{0.3}$,"High-temperature superconductivity remains arguably the largest outstanding
enigma of condensed matter physics. The discovery of iron-based
high-temperature superconductors has renewed the importance of understanding
superconductivity in materials susceptible to magnetic order and fluctuations.
Intriguingly they show magnetic fluctuations reminiscent of the superconducting
(SC) cuprates, including a 'resonance' and an 'hour-glass' shaped dispersion,
which provide an opportunity to new insight to the coupling between spin
fluctuations and superconductivity. Here we report inelastic neutron scattering
data on Fe$_{1+y}$Te$_{0.7}$Se$_{0.3}$ using excess iron concentration to tune
between a SC ($y=0.02$) and a non-SC ($y=0.05$) ground states. We find
incommensurate spectra in both samples but discover that in the one that
becomes SC, a constriction towards a commensurate hourglass shape develop well
above $T_c$. Conversely a spin-gap and concomitant spectral weight shift happen
below $T_c$. Our results imply that the hourglass shaped dispersion is most
likely a pre-requisite for superconductivity, whereas the spin-gap and shift of
spectral weight are consequences of superconductivity. We explain this
observation by pointing out that an inwards dispersion towards the commensurate
wave-vector is needed for the opening of a spin gap to lower the magnetic
exchange energy and hence provide the necessary condensation energy for the SC
state to emerge.",1203.4974v2
2012-03-28,"Geometric and disorder -- type magnetic frustration in ferrimagnetic ""114"" Ferrites: Role of diamagnetic Li+ and Zn2+ cation substitution","The comparative study of the substitution of zinc and lithium for iron in the
""114"" ferrites, YBaFe4O7 and CaBaFe4O7, shows that these diamagnetic cations
play a major role in tuning the competition between ferrimagnetism and magnetic
frustration in these oxides. The substitution of Li or Zn for Fe in the cubic
phase YBaFe4O7 leads to a structural transition to a hexagonal phase
YBaFe4-xMxO7, for M = Li (0.30 < x < 0.75) and for M = Zn (0.40 < x < 1.50). It
is seen that for low doping values i.e. x = 0.30 (for Li) and x = 0.40 (for
Zn), these diamagnetic cations induce a strong ferrimagnetic component in the
samples, in contrast to the spin glass behaviour of the cubic phase. In all the
hexagonal phases, YBaFe4-xMxO7 and CaBaFe4-xMxO7 with M = Li and Zn, it is seen
that in the low doping regime (x ~ 0.3 to 0.5), the competition between
ferrimagnetism and 2 D magnetic frustration is dominated by the average valency
of iron. In contrast, in the high doping regime (x ~ 1.5), the emergence of a
spin glass is controlled by the high degree of cationic disorder, irrespective
of the iron valency.",1203.6220v1
2012-04-17,"Manifestations of nematic degrees of freedom in the magnetic, elastic, and superconducting properties of the iron pnictides","We investigate how emergent nematic order and nematic fluctuations affect
several macroscopic properties of both the normal and superconducting states of
the iron pnictides. Due to its magnetic origin, long-range nematic order
enhances magnetic fluctuations, leaving distinctive signatures in the
spin-lattice relaxation rate, the spin-spin correlation function, and the
uniform magnetic susceptibility. This enhancement of magnetic excitations is
also manifested in the electronic spectral function, where a pseudogap can open
at the hot spots of the Fermi surface. In the nematic phase, electrons are
scattered by magnetic fluctuations that are anisotropic in momentum space,
giving rise to a non-zero resistivity anisotropy whose sign changes between
electron-doped and hole-doped compounds. We also show that due to the
magneto-elastic coupling, nematic fluctuations soften the shear modulus in the
normal state, but harden it in the superconducting state. The latter effect is
an indirect consequence of the competition between magnetism and
superconductivity, and also causes a suppression of the orthorhombic distortion
below T_{c}. We also demonstrate that ferro-orbital fluctuations enhance the
nematic susceptibility, cooperatively promoting an electronic tetragonal
symmetry-breaking. Finally, we argue that T_{c} in the iron pnictides might be
enhanced due to nematic fluctuations of magnetic origin.",1204.3694v3
2012-04-19,Evolution from unconventional spin density wave to superconductivity and a novel gap-like phase in NaFe1-xCoxAs,"Similar to the cuprate high TC superconductors, the iron pnictide
superconductors also lie in close proximity to a magnetically ordered phase. A
central debate concerning the superconducting mechanism is whether the local
magnetic moments play an indispensable role or the itinerant electron
description is sufficient. A key step for resolving this issue is to acquire a
comprehensive picture regarding the nature of various phases and interactions
in the iron compounds. Here we report the doping, temperature, and spatial
evolutions of the electronic structure of NaFe1-xCoxAs studied by scanning
tunneling microscopy. The spin density wave gap in the parent state is observed
for the first time, which shows a strongly asymmetric lineshape that is
incompatible with the conventional Fermi surface nesting scenario. The
optimally doped sample exhibits a single, symmetric energy gap, but in the
overdoped regime another asymmetric gap-like feature emerges near the Fermi
level. This novel gap-like phase coexists with superconductivity in the ground
state, persists deep into the normal state, and shows strong spatial
variations. The characteristics of the three distinct low energy states, in
conjunction with the peculiar high energy spectra, suggest that the coupling
between the local moments and itinerant electrons is the fundamental driving
force for the phases and phase transitions in the iron pnictides.",1204.4237v1
2012-04-25,Fermi surface evolution and checker-board block-spin antiferromagnetism in $A_x$Fe$_{2-y}$Se$_{2}$,"We develop an effective multiorbital mean-field t-J Hamiltonian with
realistic tight-binding and exchange parameters to describe the electronic and
magnetic structures of iron-selenide based superconductors
$A_x$Fe$_{2-y}$Se$_2$ for iron vacancy doping in the range $0 \leq y \leq 0.4$.
The Fermi surface topology extracted from the spectral function of
angle-resolved photoemission spectroscopy (ARPES) experiments is adequately
accounted for by a tight-binding lattice model with random vacancy disorder.
Since introducing iron vacancies breaks the lattice periodicity of the
stochiometric compound, it greatly affects the electronic band structure. With
changing vacancy concentration the electronic band structure evolves, leading
to a reconstruction of the Fermi surface topology. For intermediate doping
levels, the realized stable electronic structure is a compromise between the
solutions for the perfect lattice with $y=0$ and the vacancy stripe-ordered
lattice with $y=0.4$, which results in a competition between vacancy random
disorder and vacancy stripe order. A multiorbital hopping model is
parameterized by fitting Fermi surface topologies to ARPES experiments, from
which we construct a mean-field t-J lattice model to study the paramagnetic and
antiferromagnetic (AFM) phases of K$_{0.8}$Fe$_{1.6}$Se$_2$. In the AFM phase
the calculated spin magnetization of the t-J model leads to a checker-board
block-spin structure in good agreement with neutron scattering experiments and
{\it ab}-{\it initio} calculations.",1204.5768v1
2012-05-01,Shielding Experiments Under JASMIN Collaboration at Fermilab(III) - Measurement of High-Energy Neutrons Penetrating a Thick Iron Shield from the Antiproton Production Target by AU Activation Method,"In an antiproton production (Pbar) target station of the Fermi National
Accelerator Laboratory (FNAL), the secondary particles produced by bombarding a
target with 120-GeV protons are shielded by a thick iron shield. In order to
obtain experimental data on high-energy neutron transport at more than
100-GeV-proton accelerator facilities, we indirectly measured more than 100-MeV
neutrons at the outside of the iron shield at an angle of 50{\deg} in the Pbar
target station. The measurement was performed by using the Au activation method
coupled with a low-background {\gamma}-ray counting system. As an indicator for
the neutron flux, we determined the production rates of 8 spallation nuclides
(196-Au, 188-Pt, 189-Ir, 185-Os, 175-Hf, 173-Lu, 171-Lu, and 169-Yb) in the Au
activation detector. The measured production rates were compared with the
theoretical production rates calculated using PHITS. We proved that the Au
activation method can serve as a powerful tool for indirect measurements of
more than 100-MeV neutrons that play a vital role in neutron transport. These
results will be important for clarifying the problems in theoretical
calculations of high-energy neutron transport.",1205.0265v1
2012-05-15,Magnetic States of the Two-Leg Ladder Alkali Metal Iron Selenides $A$Fe$_2$Se$_3$,"Recent neutron scattering experiments addressing the magnetic state of the
two-leg ladder selenide compound BaFe$_2$Se$_3$ have unveiled a dominant spin
arrangement involving ferromagnetically ordered 2$\times$2 iron-superblocks,
that are antiferromagnetically coupled among them (the ""block-AFM"" state).
Using the electronic five-orbital Hubbard model, first principles techniques to
calculate the electronic hopping amplitudes between irons, and the real-space
Hartree-Fock approximation to handle the many-body effects, here it is shown
that the exotic block-AFM state is indeed stable at realistic electronic
densities close to $n \sim 6.0$. Another state (the ""CX"" state) with parallel
spins along the rungs and antiparallel along the legs of the ladders is close
in energy. This state becomes stable in other portions of the phase diagrams,
such as with hole doping, as also found experimentally via neutron scattering
applied to KFe$_2$Se$_3$. In addition, the present study unveils other
competing magnetic phases that could be experimentally stabilized varying
either $n$ chemically or the electronic bandwidth by pressure. Similar results
were obtained using two-orbital models, studied here via Lanczos and DMRG
techniques. A comparison of the results obtained with the realistic selenides
hoppings amplitudes for BaFe$_2$Se$_3$ against those found using the hopping
amplitudes for pnictides reveals several qualitative similarities, particularly
at intermediate and large Hubbard couplings.",1205.3239v3
2012-06-06,The role of oxygen vacancies on the structure and the density of states of iron doped zirconia,"In this paper we study, both with theoretical and experimental approach, the
effect of iron doping in zirconia. Combining density functional theory (DFT)
simulations with the experimental characterization of thin films, we show that
iron is in the Fe3+ oxidation state and accordingly that the films are rich in
oxygen vacancies (VO). VO favor the formation of the tetragonal phase in doped
zirconia (ZrO2:Fe) and affect the density of state at the Fermi level as well
as the local magnetization of Fe atoms. We also show that the Fe(2p) and Fe(3p)
energy levels can be used as a marker for the presence of vacancies in the
doped system. In particular the computed position of the Fe(3p) peak is
strongly sensitive to the VO to Fe atoms ratio. A comparison of the theoretical
and experimental Fe(3p) peak position suggests that in our films this ratio is
close to 0.5. Besides the interest in the material by itself, ZrO2:Fe
constitutes a test case for the application of DFT on transition metals
embedded in oxides. In ZrO2:Fe the inclusion of the Hubbard U correction
significantly changes the electronic properties of the system. However the
inclusion of this correction, at least for the value U = 3.3 eV chosen in the
present work, worsen the agreement with the measured photo-emission valence
band spectra.",1206.1197v4
2012-06-07,Effect of inelastic scattering on the nuclear magnetic relaxation rate 1/T1T in iron-based superconductors,"We present a microscopic study of the nuclear magnetic relaxation rate 1/T1
based on the five-orbital model for iron-based superconductors. We mainly
discuss the effect of the ""inelastic"" quasi-particle damping rate {\gamma} due
to many-body interaction on the size of the coherence peak, for both s++ and
s+- wave superconducting states. We focus on Ba(Fe1-xCox)2As2, and
systematically evaluate {\gamma} in the normal state from the experimental
resistivity, from optimally to over-doped compounds. Next, {\gamma} in the
superconducting state is calculated microscopically based on the second order
perturbation theory. In optimally doped compounds (Tc ~ 30 K), it is revealed
that the coherence peak on 1/T1T is completely suppressed due to large {\gamma}
for both s++ and s+- wave states. On the other hand, in heavily over doped
compounds with Tc < 10 K, the coherence peak could appear for both pairing
states, since {\gamma} at Tc is quickly suppressed in proportion to Tc^2. By
making careful comparison between theoretical and experimental results, we
conclude that it is difficult to discriminate between s++ and s+- wave states
from the present experimental results.",1206.1399v2
2012-06-11,Metastable superconducting state in quenched KxFe2-ySe2,"By direct quenching or post-annealing followed by quenching, we have
successfully obtained a series of KxFe2-ySe2 samples with different properties.
It is found that the samples directly quenched in the cooling process of growth
show superconductivity and the one cooled with furnace is insulating even
though their stoichiometries are similar. The sample cooled with furnace can be
tuned from insulating to superconducting by post-annealing and then quenching.
Based on the two points mentioned above, we conclude that the superconducting
state in KxFe2-ySe2 is metastable, and quenching is the key point to achieve
the superconducting state. The similar stoichiometries of all the
non-superconducting and superconducting samples indicate that the iron valence
doesn't play a decisive role in determining whether a KxFe2-ySe2 sample is
superconducting. Combining with the result got in the KxFe2-ySe2 thin films
prepared by molecular beam epitaxy (MBE), we argue that our superconducting
sample partly corresponds to the phase without iron vacancies as evidenced by
scanning tunnelling microscopy (STM) and the insulating sample mainly
corresponds to the phase with the $\sqrt{5}\times\sqrt{5}$ vacancy order.
Quenching may play a role of freezing the phase without iron vacancies.",1206.2191v1
2012-08-08,"Composition Structure of Interplanetary Coronal Mass Ejections From Multispacecraft Observations, Modeling, and Comparison with Numerical Simulations","We present an analysis of the ionic composition of iron for two
interplanetary coronal mass ejections observed in May 21-23 2007 by the ACE and
STEREO spacecraft in the context of the magnetic structure of the ejecta flux
rope, sheath region, and surrounding solar wind flow. This analysis is made
possible due to recent advances in multispacecraft data interpolation,
reconstruction, and visualization as well as results from recent modeling of
ionic charge states in MHD simulations of magnetic breakout and flux
cancellation CME initiation. We use these advances to interpret specific
features of the ICME plasma composition resulting from the magnetic topology
and evolution of the CME. We find that in both the data and our MHD
simulations, the flux ropes centers are relatively cool, while charge state
enhancements surround and trail the flux ropes. The magnetic orientation of the
ICMEs are suggestive of magnetic breakout-like reconnection during the eruption
process, which could explain the spatial location of the observed iron
enhancements just outside the traditional flux rope magnetic signatures and
between the two ICMEs. Detailed comparisons between the simulations and data
were more complicated, but a sharp increase in high iron charge states in the
ACE and STEREO-A data during the second flux rope corresponds well to similar
features in the flux cancellation results. We discuss the prospects of this
integrated in-situ data analysis and modeling approach to advancing our
understanding of the unified CME-to-ICME evolution.",1208.1791v3
2012-08-31,Radiative properties of magnetic neutron stars with metallic surfaces and thin atmospheres,"The goal of this work is to develop a simple analytic description of the
emission properties (spectrum and polarization) of the condensed, strongly
magnetized surface of neutron stars. We have improved the method of van
Adelsberg et al. (2005) (arXiv:astro-ph/0406001) for calculating the spectral
properties of condensed magnetized surfaces. Using the improved method, we
calculate the reflectivity of an iron surface at magnetic field strengths B
\sim (10^{12} - 10^{14}) G, with various inclinations of the magnetic field
lines and radiation beam with respect to the surface and each other. We
construct analytic expressions for the emissivity of this surface as functions
of the photon energy, magnetic field strength, and the three angles that
determine the geometry of the local problem. Using these expressions, we
calculate X-ray spectra for neutron stars with condensed iron surfaces covered
by thin partially ionized hydrogen atmospheres. We develop simple analytic
descriptions of the intensity and polarization of radiation emitted or
reflected by condensed iron surfaces of neutron stars with strong magnetic
fields typical for isolated neutron stars. This description provides boundary
conditions at the bottom of a thin atmosphere, which are more accurate than
previously used approximations. The spectra calculated with this improvement
show absorption features different from those in simplified models. The
approach developed in this paper yields results that can facilitate modeling
and interpretation of the X-ray spectra of isolated, strongly magnetized,
thermally emitting neutron stars.",1208.6582v2
2012-09-18,Active galaxy 4U 1344-60: did the relativistic line disappear?,"X-ray bright active galactic nuclei represent a unique astrophysical
laboratory for studying accretion physics around super-massive black holes. 4U
1344-60 is a bright Seyfert galaxy which revealed relativistic reflection
features in the archival XMM-Newton observation. We present the spectroscopic
results of new data obtained with the Suzaku satellite and compare them with
the previous XMM-Newton observation. The X-ray continuum of 4U 1344-60 can be
well described by a power-law component with the photon index ~ 1.7 modified by
a fully and a partially covering local absorbers. We measured a substantial
decrease of the fraction of the partially absorbed radiation from around 45% in
the XMM-Newton observation to less than 10% in the Suzaku observation while the
power-law slope remains constant within uncertainties. The iron line in the
Suzaku spectrum is relatively narrow, $\sigma=(0.08 \pm 0.02)$ keV, without any
suggestion for relativistic broadening. Regarding this, we interpret the iron
line in the archival XMM-Newton spectrum as a narrow line of the same width
plus an additional red-shifted emission around 6.1 keV. No evidence of the
relativistic reflection is present in the Suzaku spectra. The detected
red-shifted iron line during the XMM-Newton observation could be a temporary
feature either due to locally enhanced emission or decreased ionisation in the
innermost accretion flow.",1209.4068v1
2012-10-05,"Rapid Size-Controlled Synthesis of Dextran-Coated, 64Cu-Doped Iron Oxide Nanoparticles","Research into developing dual modality probes enabled for magnetic resonance
imaging (MRI) and positron emission tomography (PET) has been on the rise
recently due to the potential to combine the high resolution of MRI and the
high sensitivity of PET. Current synthesis techniques for developing multimodal
probes is largely hindered in part by prolonged reaction times during
radioisotope incorporation - leading to a weakening of the radioactivity. Along
with a time-efficient synthesis, the resulting products must fit within a
critical size range (between 20-100nm) to increase blood retention time. In
this work, we describe a novel, rapid, microwave-based synthesis technique to
grow dextran-coated iron oxide nanoparticles doped with copper (DIO/Cu).
Traditional methods for coprecipitation of dextran-coated iron oxide
nanoparticles require refluxing for 2 hours and result in approximately 50 nm
diameter particles. We demonstrate that microwave synthesis can produce 50 nm
nanoparticles with 5 minutes of heating. We discuss the various parameters used
in the microwave synthesis protocol to vary the size distribution of DIO/Cu,
and demonstrate the successful incorporation of 64Cu into these particles with
the aim of future use for dual-mode MR/PET imaging.",1210.1823v1
2012-10-18,Specific Heat vs Field of LiFe1-xCuxAs,"LiFeAs is one of the new class of iron superconductors with a bulk onset Tc
in the 15-17 K range. We report on the specific heat characterization of single
crystal material prepared from self-flux growth techniques with significantly
improved properties, including a much decreased residual gamma (proportional to
C/T as T->0) in the superconducting state. Thus, in contrast to previous
explanations of a finite residual gamma in LiFeAs being due to intrinsic states
in the superconducting gap, the present work shows that such a finite residual
gamma in LiFeAs is instead a function of sample quality. Further, since LiFeAs
has been characterized as nodeless with multiple superconducting gaps, we
report here on its specific heat properties in zero and applied magnetic fields
to compare to similar results on nodal iron superconductors. For comparison, we
also investigate LiFe0.98Cu0.02As, which has the reduced Tc of 9 K and Hc2 of
15 T. Interestingly, although presumably both LiFeAs and LiFe0.98Cu0.02As are
nodeless, they clearly show a non-linear dependence of the electronic density
of states (proportional to the specific heat gamma) at the Fermi energy in the
mixed state with applied field similar to the Volovik effect for nodal
superconductors. However, rather than nodal behavior, the satisfactory
comparison with a recent theory for gamma(H) for a two isotropic gap
superconductor in the presence of impurities argues for nodeless behavior.
Thus, in terms of specific heat in magnetic field, LiFeAs can serve as the
prototypical multiband, nodeless iron superconductor.",1210.4995v1
2012-11-12,Testing the space-time geometry around black hole candidates with the analysis of the broad K$α$ iron line,"Astrophysical black hole candidates are thought to be the Kerr black holes
predicted by General Relativity, but there is not yet clear evidence that the
geometry of the space-time around these objects is really described by the Kerr
metric. In order to confirm the Kerr black hole hypothesis, we have to observe
strong gravity features and check that they are in agreement with the ones
predicted by General Relativity. In this paper, I study the broad K$\alpha$
iron line, which is often seen in the X-ray spectrum of both stellar-mass and
super-massive black hole candidates and whose shape is supposed to be strongly
affected by the space-time geometry. As found in previous studies in the
literature, there is a strong correlation between the spin parameter and the
deformation parameter; that is, the line emitted around a Kerr black hole with
a certain spin can be very similar to the one coming from the space-time around
a non-Kerr object with a quite different spin. Despite that, the analysis of
the broad K$\alpha$ iron line is potentially more powerful than the
continuum-fitting method, as it can put an interesting bound on possible
deviations from the Kerr geometry independently of the value of the spin
parameter and without additional measurements.",1211.2513v2
2012-12-19,Emergent Nesting of the Fermi Surface from Local-Moment Description of Iron-Pnictide High-Tc Superconductors,"We uncover the low-energy spectrum of a t-J model for electrons on a square
lattice of spin-1 iron atoms with 3dxz and 3dyz orbital character by applying
Schwinger-boson-slave-fermion mean-field theory and by exact diagonalization of
one hole roaming over a 4 x 4 x 2 lattice. Hopping matrix elements are set to
produce hole bands centered at zero two-dimensional (2D) momentum in the
free-electron limit. Holes can propagate coherently in the t-J model below a
threshold Hund coupling when long-range antiferromagnetic order across the d+ =
3d(x+iy)z and d- = 3d(x-iy)z orbitals is established by magnetic frustration
that is off-diagonal in the orbital indices. This leads to two hole-pocket
Fermi surfaces centered at zero 2D momentum. Proximity to a commensurate
spin-density wave (cSDW) that exists above the threshold Hund coupling results
in emergent Fermi surface pockets about cSDW momenta at a quantum critical
point (QCP). This motivates the introduction of a new Gutzwiller wavefunction
for a cSDW metal state. Study of the spin-fluctuation spectrum at cSDW momenta
indicates that the dispersion of the nested band of one-particle states that
emerges is electron-type. Increasing Hund coupling past the QCP can push the
hole-pocket Fermi surfaces centered at zero 2D momentum below the Fermi energy
level, in agreement with recent determinations of the electronic structure of
mono-layer iron-selenide superconductors.",1212.4619v3
2012-12-20,Measurement of Coherent Polarons in the Strongly Coupled Antiferromagnetically Ordered Iron-Chalcogenide Fe1.02Te using Angle-Resolved Photoemission Spectroscopy,"The nature of metallicity and the level of electronic correlations in the
antiferromagnetically ordered parent compounds are two important open issues
for the iron-based superconductivity. We perform a temperature-dependent
angle-resolved photoemission spectroscopy study of Fe1.02Te, the parent
compound for iron chalcogenide superconductors. Deep in the antiferromagnetic
state, the spectra exhibit a ""peak-dip-hump"" line shape associated with two
clearly separate branches of dispersion, characteristics of polarons seen in
manganites and lightly-doped cuprates. As temperature increases towards the
Neel temperature (T_N), we observe a decreasing renormalization of the peak
dispersion and a counterintuitive sharpening of the hump linewidth, suggestive
of an intimate connection between the weakening electron-phonon (e-ph) coupling
and antiferromagnetism. Our finding points to the highly-correlated nature of
Fe1.02Te ground state featured by strong interactions among the charge, spin
and lattice and a good metallicity plausibly contributed by the coherent
polaron motion.",1212.4946v1
2013-03-02,Signs of atmospheric inhomogeneities in cool stars from 1D-NLTE analysis of iron lines,"For the well studied halo star HD 122563 and the four stars in the globular
cluster NGC 6397, we determine NLTE abundances of iron using classical
plane-parallel model atmospheres. Each star reveals a discrepancy in abundances
between the Fe I lines arising from the ground state and the other Fe I lines,
in qualitative agreement with the 3D-LTE line formation predictions, however,
the magnitude of the observed effect is a factor of 2 smaller compared with the
predicted one. When ignoring the Fe I low-excitation lines, the NLTE abundances
from the two ionization stages, Fe I and Fe II, are consistent in each
investigated star. For the subgiants in NGC 6397, this is only true when using
the cooler effective temperature scale of Alonso et al. (1999). We also present
full 3D-LTE line formation calculations for some selected iron lines in the
solar and metal-poor 4480/2/-3 models and NLTE calculations with the
corresponding spatial and temporal average <3D> models. The use of the <3D>
models is justified only for particular Fe I lines in particular physical
conditions. Our NLTE calculations reproduce well the centre-to-limb variation
of the solar Fe I 7780 A line, but they are unsuccessful for Fe I 6151 A. The
metal-poor <3D> model was found to be adequite for the strong Fe I 5166 A (Eexc
= 0) line, but inadequite in all other investigated cases.",1303.0357v1
2013-03-04,"Orbital selective correlations between nesting/scattering/Lifshitz transition and the superconductivity in AFe1-xCoxAs (A=Li, Na)","The correlations between the superconductivity in iron pnictides and their
electronic structures are elusive and controversial so far. Here through
angle-resolved photoemission spectroscopy measurements, we show that such
correlations are rather distinct in AFe$_{1-x}$Co$_x$As (A=Li, Na), but only
after one realizes that they are orbital selective. We found that the
superconductivity is enhanced by the Fermi surface nesting, but only when it is
between $d_{xz}/d_{yz}$ Fermi surfaces, while for the $d_{xy}$ orbital, even
nearly perfect Fermi surface nesting could not induce superconductivity.
Moreover, the superconductivity is completely suppressed just when the
$d_{xz}/d_{yz}$ hole pockets sink below Fermi energy and evolve into an
electron pocket. Our results thus establish the orbital selective relation
between the Fermiology and the superconductivity in iron-based superconductors,
and substantiate the critical role of the $d_{xz}/d_{yz}$ orbitals.
Furthermore, around the zone center, we found that the $d_{xz}/d_{yz}$-based
bands are much less sensitive to impurity scattering than the $d_{xy}$-based
band, which explains the robust superconductivity against heavy doping in
iron-based superconductors.",1303.0682v2
2013-03-11,Magnetically-Driven Suppression of Nematic Order in an Iron-Based Superconductor,"A theory of superconductivity in the iron-based materials requires an
understanding of the phase diagram of the normal state. In these compounds,
superconductivity emerges when stripe spin density wave (SDW) order is
suppressed by doping, pressure or atomic disorder. This magnetic order is often
pre-empted by nematic order, whose origin is yet to be resolved. One scenario
is that nematic order is driven by orbital ordering of the iron 3d-electrons
that triggers stripe SDW order. Another is that magnetic interactions produce a
spin-nematic phase, which then induces orbital order. In this article, we
report the observation by neutron powder diffraction of an additional four-
fold-symmetric phase in Ba1-xNaxFe2As2 close to the suppression of SDW order,
which is consistent with the predictions of magnetically-driven models of
nematic order.",1303.2647v2
2013-03-12,Change of pairing symmetry in the iron-based superconductor KFe2As2,"The pairing mechanism in iron-based superconductors is the subject of ongoing
debate. Proximity to an antiferromagnetic phase suggests that pairing is
mediated by spin fluctuations, but orbital fluctuations have also been invoked.
The former typically favour a pairing state of extended s-wave symmetry with a
gap that changes sign between electron and hole Fermi surfaces (s+-), while the
latter yield a standard s-wave state without sign change (s++). Here we show
that applying pressure to KFe2As2 induces a change of pairing state. The
critical temperature Tc decreases with pressure initially, and then suddenly
increases, above a critical pressure Pc. The constancy of the Hall coefficient
through Pc rules out a change in the Fermi surface. There is compelling
evidence that the pairing state below Pc is d-wave, from bulk measurements at
ambient pressure. Above Pc, the high sensitivity to disorder argues for a
particular kind of s+- state. The change from d-wave to s-wave is likely to
proceed via an unusual s + id state that breaks time-reversal symmetry. The
proximity of two distinct pairing states found here experimentally is natural
given the near degeneracy of d-wave and s+- states found theoretically. These
findings make a compelling case for spin-fluctuation-mediated superconductivity
in this key iron-arsenide material.",1303.2961v3
2013-04-11,Sign-reversal of the in-plane resistivity anisotropy in iron pnictides,"The concept of an electronically-driven breaking of the rotational symmetry
of a crystal, without involving magnetic order, has found experimental support
in several systems, from semiconductor heterostructures and ruthenates, to
cuprate and iron-pnictide superconductors. In the pnictide BaFe$_{2}$As$_{2}$,
such an ""electronic nematic state"" appears above the magnetic transition dome,
over a temperature range that can be controlled by external strain. Here, by
measuring the in-plane resistivity anisotropy, we probe the electronic
anisotropy of this material over the entire nematic/magnetic dome, whose end
points coincide with the optimal superconducting transition temperatures.
Counter-intuitively, we find that, unlike other materials, the resistivity
anisotropy in BaFe$_{2}$As$_{2}$ changes sign across the doping phase diagram,
even though the signs of the magnetic, nematic, and orthorhombic order
parameters are kept fixed. This behavior is explained by the Fermi surface
reconstruction in the magnetic phase and spin-fluctuation scattering in the
nematic phase. The unique behavior of the transport anisotropy unveils that the
primary role is played by magnetic scattering in the normal state transport
properties of the iron pnictides, suggesting a close connection between
magnetism, nematicity, and unconventional superconductivity.",1304.3490v1
2013-04-12,"Space group symmetry, spin-orbit coupling and the low energy effective Hamiltonian for iron based superconductors","We construct the symmetry adapted low energy effective Hamiltonian for the
electronic states in the vicinity of the Fermi level in iron based
superconductors. We use Luttinger's method of invariants, expanding about Gamma
and M points in the Brillouin zone corresponding to two iron unit cell, and
then matching the coefficients of the expansion to the 5- and 8-band models. We
then use the method of invariants to study the effects of the spin-density wave
order parameters on the electronic spectrum, with and without spin-orbit
coupling included. Among the results of this analysis is the finding that the
nodal spin-density wave is unstable once spin-orbit coupling is included.
Similar analysis is performed for the A_{1g} spin singlet superconducting
state. Without spin-orbit coupling there is one pairing invariant near the
Gamma point, but two near the M point. This leads to an isotropic spectral gap
at the hole Fermi surface near Gamma, but anisotropic near M. The relative
values of these three parameters determine whether the superconducting state is
s_{++}, s_{+-}, or nodal. Inclusion of spin-orbit coupling leads to additional
mixing of spin triplet pairing, with one additional pairing parameter near
Gamma and one near M. This leads to an anisotropic spectral gap near both hole
and electron Fermi surfaces, the latter no longer cross, but rather split.",1304.3723v1
2013-05-23,Measuring the Kerr spin parameter of a non-Kerr compact object with the continuum-fitting and the iron line methods,"Under the assumption that astrophysical black hole candidates are the Kerr
black holes of general relativity, the continuum-fitting method and the
analysis of the K$\alpha$ iron line are today the only available techniques
capable of providing a relatively reliable estimate of the spin parameter of
these objects. If we relax the Kerr black hole hypothesis and we try to test
the nature of black hole candidates, we find that there is a strong correlation
between the measurement of the spin and possible deviations from the Kerr
solution. The properties of the radiation emitted in a Kerr spacetime with spin
parameter $a_*$ are indeed very similar, and practically indistinguishable,
from the ones of the radiation emitted around a non-Kerr object with different
spin. In this paper, I address the question whether measuring the Kerr spin
with both the continuum-fitting method and the K$\alpha$ iron line analysis of
the same object can be used to claim the Kerr nature of the black hole
candidate in the case of consistent results. In this work, I consider two
non-Kerr metrics and it seems that the answer does depend on the specific
background. The two techniques may either provide a very similar result (the
case of the Bardeen metric) or show a discrepancy (Johannsen-Psaltis
background).",1305.5409v2
2013-06-05,BeppoSAX and XMM-Newton spectral study of 4U 1735-44,"Low-mass X-ray binary systems consist of a neutron star and a main-sequence
companion star. The compact object accretes matter via Roche-lobe overflow,
which leads to an accretion disk. In addition to a broad-band continuum
emission of a thermal component and a Comptonization part, evidence for a broad
iron K{\alpha} line is found in several sources. Some of them show an
asymmetric line profile as well, which could originate from relativistic
effects. To understand the spectral behavior of the system 4U 1735-44, we study
the broad-band spectrum and especially the iron line feature between 6.4 and
6.97 keV. The shape of the line allows one to determine the region where the
line is produced. Together with the continuum models, a geometrical model of
the source can be proposed. Furthermore, the effects of pile-up in the
XMM-Newton observation are investigated. We analyzed data obtained with the
X-ray satellites BeppoSAX and XMM-Newton. The XMM-Newton data were analyzed,
specifically taking into account pile-up effects. With the help of the data of
these two satellites, we performed a detailed spectral study in an energy range
from 0.2-24 keV. During the observations, the source was in the so-called
banana state of an atoll source. Fitting the BeppoSAX data, we found line
features that we were able to model with a reflection model, whereas the
continuum was modeled with a combination of a thermal component and a
Comptonization part. The analysis of the XMM-Newton data gave evidence for a
broad but not asymmetric iron line. We found no broadening or asymmetry of the
line because of pile-up.",1306.1040v1
2013-06-22,A Toroidal Magnetised Iron Neutrino Detector (MIND) for a Neutrino Factory,"A neutrino factory has unparalleled physics reach for the discovery and
measurement of CP violation in the neutrino sector. A far detector for a
neutrino factory must have good charge identification with excellent background
rejection and a large mass. An elegant solution is to construct a magnetized
iron neutrino detector (MIND) along the lines of MINOS, where iron plates
provide a toroidal magnetic field and scintillator planes provide 3D space
points. In this report, the current status of a simulation of a toroidal MIND
for a neutrino factory is discussed in light of the recent measurements of
large $\theta_{13}$. The response and performance using the 10 GeV neutrino
factory configuration are presented. It is shown that this setup has equivalent
$\delta_{CP}$ reach to a MIND with a dipole field and is sensitive to the
discovery of CP violation over 85% of the values of $\delta_{CP}$.",1306.5327v2
2013-07-18,Steady state rheological behaviour of multi-component magnetic suspensions,"In this paper we study the rheological behaviour (in the absence of magnetic
field and upon its application) of multi-component magnetic suspensions that
consist of a mixture of magnetic (iron) and non-magnetic (PMMA) particles
dispersed in a liquid carrier. These suspensions exhibit considerably higher
viscosity and yield stress in the absence of magnetic field than
single-component suspensions of the same solid fraction, as a consequence of
the adsorption of the iron particles on the PMMA ones. The adsorbed layer of
iron particles on the PMMA ones is observed through optical microscopy of
dilute samples and confirmed by attenuated total reflectance. Microscopic
observations also show that the resulting non-magnetic-core-magnetic-shell
composites move upon magnetic field application and aggregate into particle
structures aligned with the applied field. These structures, which consist of
both types of particles, give rise to high values of the static and dynamic
yield stresses upon field application. Actually, both quantities are much
higher than those of a suspension with the same volume fraction of magnetic
particles, and increase when the amount of non-magnetic ones increases. These
trends are adequately predicted by a theoretical model that considers that the
main contribution to the yield stress is the change of the suspension magnetic
permeability when particle chains are deformed by the shear.",1307.4975v1
2013-08-05,Physics picture from neutron scattering study on Fe-based superconductors,"Neutron scattering, with its ability to measure the crystal structure, the
magnetic order, and the structural and magnetic excitations, plays an active
role in investigating various families of Fe-based high-Tc superconductors.
Three different types of antiferromag- netic orders have been discovered in the
Fe plane, but two of them cannot be explained by the spin-density-wave (SDW)
mechanism of nesting Fermi surfaces. Noticing the close relation between
antiferromagnetic order and lattice distortion in orbital ordering from
previous studies on manganites and other oxides, we have advocated orbital or-
dering as the underlying common mechanism for the structural and
antiferromagnetic transitions in the 1111, 122 and 11 parent compounds. We
observe the coexistence of antiferromagnetic order and superconductivity in the
(Ba,K)Fe2 As2 system, when its phase separation is generally accepted. Optimal
Tc is proposed to be controlled by the local FeAs4 tetrahedron from our
investigation on the 1111 materials. The Bloch phase coherence of the Fermi
liquid is found crucial to the occurrence of bulk superconductiv- ity in iron
chalcogenides of both the 11 and the 245 families. Iron chalcogenides carry a
larger staggered magnetic moment (> 2{\mu}B /Fe) than that in iron pnictides (<
1{\mu}B /Fe) in the antiferromagnetic order. Normal state magnetic excitations
in the 11 supercon- ductor are of the itinerant nature while in the 245
superconductor the spin-waves of localized moments. The observation of
superconducting resonance peak provides a cru- cial piece of information in
current deliberation of the pairing symmetry in Fe-based superconductors.",1308.1040v1
2013-08-28,Strong electronic correlations in iron pnictides: Comparison of the optical spectra for BaFe2As2-related compounds,"We carried out combined transport and optical measurements for BaFe2As2 and
five isostructural transition-metal (TM) pnictides. The low-energy optical
conductivity spectra of these compounds are, to a good approximation,
decomposed into a narrow Drude (coherent) component and an incoherent
component. The iron arsenides, BaFe2As2 and KFe2As2, are distinct from other
pnictides in their highly incoherent charge dynamics or bad metallic behavior
with the coherent Drude component occupying a tiny fraction of the low-energy
spectral weight. The fraction of the coherent spectral weight or the degree of
coherence is shown to be well correlated with the TM-pnictogen bond angle and
the electron filling of TM 3d orbitals, which are measures of the strength of
electronic correlations. The iron arsenides are thus strongly correlated
systems, and the doping into BaFe2As2 controls the strength of electronic
correlations. This naturally explains a remarkable asymmetry in the charge
dynamics of electron- and hole-doped systems, and the unconventional
superconductivity appears to emerge when the correlations are fairly strong.",1308.6113v1
2013-09-06,Investigation of the Puzzling Abundance Pattern in the Stars of the Fornax Dwarf Spheroidal Galaxy,"Many works have found unusual characteristics of elemental abundances in
nearby dwarf galaxies. This implies that there is a key factor of galactic
evolution that is different from that of the Milky Way (MW). The chemical
abundances of the stars in the Fornax dwarf spheroidal galaxy (Fornax dSph)
provide excellent information for setting constraints on the models of the
galactic chemical evolution. In this work, adopting the five-component
approach, we fit the abundances of the Fornax dSph stars, including $\alpha$
elements, iron group elements and neutron-capture elements. For most sample
stars, the relative contributions from the various processes to the elemental
abundances are not usually in the MW proportions. We find that the
contributions from massive stars to the primary $\alpha$ elements and iron
group elements increase monotonously with increasing [Fe/H]. This means that
the effect of the galactic wind is not strong enough to halt star formation and
the contributions from massive stars to $\alpha$ elements did not halted for
[Fe/H]$\lesssim$-0.5. The average contributed ratios of various processes
between the dSph stars and the MW stars monotonously decrease with increasing
progenitor mass. This is important evidence of a bottom-heavy initial mass
function (IMF) for the Fonax dSph, compared to the MW. Considering a
bottom-heavy IMF for the dSph, the observed relations of [$\alpha$/Fe] versus
[Fe/H], [iron group/Fe] versus [Fe/H] and [neutron-capture/Fe] versus [Fe/H]
for the dSph stars can be explained.",1309.1519v1
2013-10-04,The soft component and the iron line as signatures of the disc inner radius in Galactic black hole binaries,"The inner radius of the accretion disc around a black hole in the low/hard
state can be measured in one of two ways. Firstly, via the extent of broadening
of the iron emission line, and secondly, from the luminosity and temperature of
the weak soft component seen in this state, assuming it is the disc. We use
both of these methods on all the low/hard state spectra taken in timing mode of
XMM-Newton's EPIC-pn. We find that the two methods are not consistent with each
other, and the difference is not always in a single direction. The two methods
are neither model independent, nor are they independent of current calibration
issues. We find that the remaining small residuals in the EPIC-pn timing mode
response at the <3% level can have a dramatic effect on the fit parameters for
the reflected spectrum. There is also a mismatch in cross-calibration with
RXTE, which makes it difficult to use simultaneous data to extend the bandpass
of the spectral fits. Nonetheless, it is clear from the data that the iron line
is noticeably broader and stronger at higher L/LEdd, which is consistent with
the truncated disc models. We also show that it is likely that the soft
component changes character, from a stable component consistent with a
truncated disc at high L/LEdd, to a variable one with much smaller radius at
low L/LEdd. This adds to growing evidence for a complex soft component in the
low/hard state, possibly resulting from clumps torn from the edge of the
truncated disc.",1310.1219v1
2013-11-14,Electric field gradient wave (EFGW) in iron-based superconductor Ba(0.6)K(0.4)Fe2As2 studied by Mössbauer spectroscopy,"The optimally doped 122 iron-based superconductor Ba(0.6)K(0.4)Fe2As2 has
been studied by 57Fe Moessbauer spectroscopy versus temperature ranging from
4.2 K till 300 K with particular attention paid to the superconducting
transition around 38 K. The spectra do not contain magnetic components and they
exhibit quasi-continuous distribution of quadrupole split doublets. A
distribution follows the electric field gradient (EFG) spatial modulation
(wave) - EFGW. The EFGW is accompanied by some charge density wave (CDW) having
about an order of magnitude lesser influence on the spectrum. The EFGW could be
modeled as widely separated narrow sheets with the EFG increasing from small
till maximum value almost linearly and subsequently dropping back to the
original value in a similar fashion - across the sheet. One encounters very
small and almost constant EFG between sheets. The EFGW shape and amplitude as
well as the amplitude of CDW are strongly affected by a superconducting
transition. All modulations are damped significantly at transition (38 K) and
recover at a temperature being about 14 K lower. The maximum quadrupole
splitting at 4.2 K amounts to about 2.1 mm/s, while the dispersion of CDW seen
on the iron nuclei could be estimated far away from the superconducting gap
opening and at low temperature as 0.5 el./a.u.^3. It drops to about 0.3
el./a.u.^3 just below transition to the superconducting state.",1311.3503v4
2013-11-22,A first-principles study of the electronic structure of Iron-Selenium; Implications for electron-phonon superconductivity,"We have performed density functional theory (DFT) calculations using the
linearized augmented plane wave method (LAPW) with the local density
approximation (LDA) functional to study the electronic structure of the
iron-based superconductor Iron-Selenium (FeSe). In our study, we have performed
a comprehensive set of calculations involving structural, atomic, and spin
configurations. All calculations were executed using the tetragonal lead-oxide
or P4/nmm structure, with various volumes, c/a ratios and internal parameters.
Furthermore, we investigated the spin polarization using the LDA functional to
assess ferromagnetism in this material. The paramagnetic LDA calculations find
the equilibrium configuration of FeSe in the P4/nmm structure to have a volume
of 472.5au$^3$ with a c/a ratio of 1.50 and internal parameter of 0.255, with
the ferromagnetic having comparable results to the paramagnetic case. In
addition, we calculated total energies for FeSe using a pseudopotential method,
and found comparable results to the LAPW calculations. Superconductivity
calculations were done using the Gaspari-Gyorffy and the McMillan formalism and
found substantial electron-phonon coupling. Under pressure, our calculations
show that the superconductivity critical temperature continues to rise, but
underestimates the measured values.",1311.5914v2
2014-02-04,"Spin and orbital magnetic moments of size-selected iron, cobalt, and nickel clusters and their link to the bulk phase diagrams","Spin and orbital magnetic moments of cationic iron, cobalt, and nickel
clusters have been determined from x-ray magnetic circular dichroism
spectroscopy. In the size regime of $n = 10 - 15$ atoms, these clusters show
strong ferromagnetism with maximized spin magnetic moments of 1~$\mu_B$ per
empty $3d$ state because of completely filled $3d$ majority spin bands. The
only exception is $\mathrm{Fe}_{13}^+$ where an unusually low average spin
magnetic moment of $0.73 \pm 0.12$~$\mu_B$ per unoccupied $3d$ state is
detected; an effect, which is neither observed for $\mathrm{Co}_{13}^+$ nor
$\mathrm{Ni}_{13}^+$.\@ This distinct behavior can be linked to the existence
and accessibility of antiferromagnetic, paramagnetic, or nonmagnetic phases in
the respective bulk phase diagrams of iron, cobalt, and nickel. Compared to the
experimental data, available density functional theory calculations generally
seem to underestimate the spin magnetic moments significantly. In all clusters
investigated, the orbital magnetic moment is quenched to $5 - 25$\,\% of the
atomic value by the reduced symmetry of the crystal field. The magnetic
anisotropy energy is well below 65 $\mu$eV per atom.",1402.0701v1
2014-02-07,"Modelling a new, low CO2 emissions, hydrogen steelmaking process","In an effort to develop breakthrough technologies that enable drastic
reduction in CO2 emissions from steel industry (ULCOS project), the reduction
of iron ore by pure hydrogen in a direct reduction shaft furnace was
investigated. After experimental and modelling studies, a 2D, axisymmetrical
steady-state model called REDUCTOR was developed to simulate a counter-current
moving bed reactor in which hematite pellets are reduced by pure hydrogen. This
model is based on the numerical solution of the local mass, energy and momentum
balances of the gas and solid species by the finite volume method. A single
pellet sub-model was included in the global furnace model to simulate the
successive reactions (hematite->magnetite ->wustite->iron) involved in the
process, using the concept of additive reaction times. The different steps of
mass transfer and possible iron sintering at the grain scale were accounted
for. The kinetic parameters were derived from reduction experiments carried out
in a thermobalance furnace, at different conditions, using small hematite cubes
shaped from industrial pellets. Solid characterizations were also performed to
further understand the microstrutural evolution. First results have shown that
the use of hydrogen accelerates the reduction in comparison to CO reaction,
making it possible to design a hydrogen-operated shaft reactor quite smaller
than current MIDREX and HYL. Globally, the hydrogen steelmaking route based on
this new process is technically and environmentally attractive. CO2 emissions
would be reduced by more than 80%. Its future is linked to the emergence of the
hydrogen economy.",1402.1715v1
2014-02-15,Identifying the `Fingerprint' of Antiferromagnetic Spin-Fluctuations on Iron-Pnictide Superconductivity,"Cooper pairing in the iron-based high-Tc superconductors is often conjectured
to involve bosonic fluctuations. Among the candidates are antiferromagnetic
spin-fluctuations and d-orbital fluctuations amplified by phonons. Any such
electron-boson interaction should alter the electron's `self-energy', and then
become detectable through consequent modifications in the energy dependence of
the electron's momentum and lifetime. Here we introduce a
theoretical/experimental approach aimed at identifying the relevant
fluctuations of iron-based superconductors by measuring effects of their
self-energy. We use quasiparticle interference (QPI) imaging techniques in
LiFeAs to reveal strongly momentum-space anisotropic self-energy signatures
that are focused along the Fe-Fe (interband scattering) direction, where the
spin fluctuations of LiFeAs are concentrated. These effects coincide in energy
with perturbations to the density-of-states N(\omega) usually associated with
the Cooper pairing interaction. We show that all the measured phenomena
comprise the predicted QPI `fingerprint' of a self-energy due to
antiferromagnetic spin-fluctuations, thereby distinguishing them as the
predominant electron-boson interaction.",1402.3714v2
2014-02-17,Pressure decoupled magnetic and structural transitions of the parent compound of iron based 122 superconductors BaFe2As2,"The recent discovery of iron ferropnictide superconductors has received
intensive concerns on magnetic involved superconductors. Prominent features of
ferropnictide superconductors are becoming apparent: the parent compounds
exhibit antiferromagnetic (AFM) ordered spin density wave (SDW) state; the
magnetic phase transition is always accompanied to a crystal structural
transition; superconductivity can be induced by suppressing the SDW phase via
either chemical doping or applied external pressure to the parent state. These
features generated considerable interests on the interplay between magnetism
and structure in chemical doped samples, showing crystal structure transitions
always precedes to or coincide with magnetic transition. Pressure tuned
transition on the other hand would be more straightforward to superconducting
mechanism studies since there are no disorder effects caused by chemical
doping; however, remarkably little is known about the interplay in the parent
compounds under controlled pressure due to the experimental challenge of in
situ measuring both of magnetic & crystal structure evolution at high pressure
& low temperatures. Here we show from combined synchrotron Mossbauer and x-ray
diffraction at high pressures that the magnetic ordering surprisingly precedes
the structural transition at high pressures in the parent compound BaFe2As2, in
sharp contrast to the chemical doping case. The results can be well understood
in terms of the spin fluctuations in the emerging nematic phase before the long
range magnetic order that sheds new light on understanding how parent compound
evolves from a SDW state to a superconducting phase, a key scientific inquiry
of iron based superconductors.",1402.4086v1
2014-03-05,The chemical composition of a regular halo globular cluster: NGC 5897,"We report for the first time on the chemical composition of the halo cluster
NGC 5897 (R=12.5 kpc), based on chemical abundance ratios for 27 alpha-,
iron-peak, and neutron-capture elements in seven red giants. From our
high-resolution, high signal-to-noise spectra obtained with the Magellan/MIKE
spectrograph, we find a mean iron abundance from the neutral species of [Fe/H]
= -2.04 +/- 0.01 (stat.) +/- 0.15 (sys.), which is more metal-poor than implied
by previous photometric and low-resolution spectroscopic studies. NGC 5897 is
alpha-enhanced (to 0.34 +/- 0.01 dex) and shows Fe-peak element ratios typical
of other (metal-poor) halo globular clusters (GCs) with no overall, significant
abundance spreads in iron nor in any other heavy element. Like other GCs, NGC
5897 shows a clear Na-O anti-correlation, where we find a prominent primordial
population of stars with enhanced O abundances and ~Solar Na/Fe ratios, while
two stars are Na-rich, providing chemical proof of the presence of multiple
populations in this cluster. Comparison of the heavy element abundances with
the Solar-scaled values and the metal poor GC M15 from the literature confirms
that NGC 5897 has experienced only little contribution from s-process
nucleosynthesis. One star of the first generation stands out in that it shows
very low La and Eu abundances. Overall, NGC 5897 is a well-behaved GC showing
archetypical correlations and element-patterns, with little room for surprises
in our data. We suggest that its lower metallicity could explain the unusually
long periods of RR Lyr that were found in NGC 5897.",1403.1262v1
2014-03-14,Spin-dependent conductivity of iron-based superconductors in a magnetic field,"We report the results of a study of magnetic field features of electron
transport in heterojunctions with NS boundary inside iron-based
superconductors, represented by a binary phase of $\alpha$ - FeSe and
oxyarsenide pnictide LaO(F)FeAs. We used the ability of self magnetic field of
the transport current to partially destroy superconductivity, no matter how low
the field may be, in the NS interface area, where, due to the proximity effect,
the superconducting order parameter, $\Delta$, disperses from 1 to 0 within the
scale of the Ginzburg-Landau coherence length. The following features of
transport were found:(i) at $T<T_{c}$, magnetoresistance in systems with
different superconductors has different sign;(ii) sign and magnitude of the
magnetoresistance depend on the magnitude of current and temperature, and (iii)
in all operating modes where the contribution from Andreev reflection is
suppressed ($(T + eV) \gtrsim \Delta$),the hysteresis of the magnetoresistance
is present. Based on the results of the experiment and analysis it has been
concluded that there is along-range magnetic order in th eground normal state
of the iron-based superconductors studied, in the presence of itinerant
magnetism of conduction electrons which determines the possibility of
anisotropic spin-dependent exchange interaction with the local magnetic moments
of the ions.",1403.3549v1
2014-03-24,Bipartite magnetic parent phases in the iron-oxypnictide superconductor,"High-temperature (high-$T_{\rm c}$) superconductivity appears as a
consequence of the carrier-doping of an undoped parent compound exhibiting
antiferromagnetic order; thereby, ground-state properties of the parent
compound are closely relevant to the superconducting state. On the basis of the
concept, a spin-fluctuation has been addressed as an origin of pairing of the
superconducting electrons in cuprates. Whereas, there is growing interest in
the pairing mechanism such as an unconventional spin-fluctuation or an advanced
orbital-fluctuation due to the characteristic multi-orbital system in
iron-pnictides. Here, we report the discovery of an antiferromagnetic order as
well as a unique structural transition in electron-overdoped
LaFeAsO$_{1-x}$H$_x$ ($x$ ~ 0.5), whereby another parent phase was uncovered,
albeit heavily doped. The unprecedented two-dome superconducting phases
observed in this material can be interpreted as a consequence of the
carrier-doping starting from the original at $x\sim0$ and advanced at
$x\sim0.5$ parent phases toward the intermediate region. The bipartite parent
phases with distinct physical properties in the second magnetic phase provide
us with an interesting example to illustrate the intimate interplay among the
magnetic interaction, structural change and orbital degree of freedom in
iron-pnictides.",1403.6021v1
2014-04-01,Magnetic states of the five-orbital Hubbard model for one-dimensional iron-based superconductors,"The magnetic phase diagrams of models for quasi one-dimensional compounds
belonging to the iron-based superconductors family are presented. The
five-orbital Hubbard model and the real-space Hartree-Fock approximation are
employed, supplemented by density functional theory to obtain the hopping
amplitudes. Phase diagrams are constructed varying the Hubbard $U$ and Hund $J$
couplings and at zero temperature. The study is carried out at electronic
density (electrons per iron) $n = 5.0$, which is of relevance for the already
known material TlFeSe$_2$, and also at $n = 6.0$, where representative
compounds still need to be synthesized. At $n = 5.0$ there is a clear dominance
of staggered spin order along the chain direction. At $n = 6.0$ and the
realistic Hund coupling $J/U = 0.25$, the phase diagram is far richer including
a variety of ``block'' states involving ferromagnetic clusters that are
antiferromagnetically coupled, in qualitative agreement with recent Density
Matrix Renormalization Group calculations for the three-orbital Hubbard model
in a different context. These block states arise from the competition between
ferromagnetic order (induced by double exchange, and prevailing at large $J/U$)
and antiferromagnetic order (dominating at small $J/U$). The density of states
and orbital compositions of the many phases are also provided.",1404.0069v1
2014-04-01,High-resolution abundance analysis of very metal-poor r-I stars,"Moderately r-process-enriched stars (r-I) are at least four times as common
as those that are greatly enriched in r-process elements (r-II), and the
abundances in their atmospheres are important tools for obtaining a better
understanding of the nucleosynthesis processes responsible for the origin of
the elements beyond the iron peak. The main aim of this work is to derive
abundances for a sample of seven metal-poor stars with classified as r-I stars,
to understand the role of these stars for constraining the astrophysical
nucleosynthesis event(s) that is(are) responsible for the production of the
r-process, and to investigate whether they differ, in any significant way, from
the r-II stars. We carried out a detailed abundance analysis based on
high-resolution spectra obtained with the VLT/UVES spectrograph. The OSMARCS
LTE 1D model atmosphere grid was employed, along with the spectrum synthesis
code Turbospectrum. We have derived abundances of light elements Li, C, and N,
alpha-elements, odd-Z elements, iron-peak elements, and the trans-iron elements
from the first peak, the second peak, the third peak, and the actinides
regions. The results are compared with values for these elements for r-II and
normal very and extremely metal-poor stars reported in the literature, ages
based on radioactive chronometry are explored using different models, and a
number of conclusions about the r-process and the r-I stars are presented.
Hydrodynamical models were used for some elements, and general behaviors for
the 3D corrections were presented.",1404.0234v1
2014-04-03,Dynamics and mechanism of oxygen annealing in Fe$_{1+y}$Te$_{0.6}$Se$_{0.4}$ single crystal,"Iron chalcogenide Fe(Te,Se) attracted much attention due to its simple
structure, which is favorable for probing the superconducting mechanism. Its
less toxic nature compared with iron arsenides is also advantageous for
applications of iron-based superconductors. By intercalating spacer layers,
superconducting transition temperature has been raised over 40 K. On the other
hand, the presence of excess Fe is almost unavoidable in Fe(Te,Se) single
crystals, which hinders the appearance of bulk superconductivity and causes
strong controversies over its fundamental properties. Here we report a
systematical study of O$_2$-annealing dynamics in Fe$_{1+y}$Te$_{1-x}$Se$_{x}$
by controlling the amount of O$_2$, annealing temperature, and time. Bulk
superconductivity can be gradually induced by increasing the amount of O$_2$
and annealing time at suitable temperatures. The optimally annealed crystals
can be easily obtained by annealing with ~ 1.5% molar ratio of oxygen at 400
$^{\circ}$C for more than 1 hour. Superconductivity was witnessed to evolve
mainly from the edge of the crystal to the central part. After the optimal
annealing, the complete removal of excess Fe was demonstrated via STM
measurements. Some fundamental properties were recharacterized and compared
with those of as-grown crystals to discuss the influence of excess Fe.",1404.0916v1
2014-04-10,Space weathering simulations through controlled growth of iron nanoparticles on olivine,"Airless planetary bodies are directly exposed to space weathering. The main
spectral effects of space weathering are darkening, reduction in intensity of
silicate mineral absorption bands, and an increase in the spectral slope
towards longer wavelengths (reddening). Production of nanophase metallic iron
(npFe$^{0}$) during space weathering plays major role in these spectral
changes. A laboratory procedure for the controlled production of npFe$^{0}$ in
silicate mineral powders has been developed. The method is based on a two-step
thermal treatment of low-iron olivine, first in ambient air and then in
hydrogen atmosphere. Through this process, a series of olivine powder samples
was prepared with varying amounts of npFe$^{0}$ in the 7-20 nm size range. A
logarithmic trend is observed between amount of npFe$^{0}$ and darkening,
reduction of 1 {\mu}m olivine absorption band, reddening, and 1 {\mu}m band
width. Olivine with a population of physically larger npFe$^{0}$ particles
follows spectral trends similar to other samples, except for the reddening
trend. This is interpreted as the larger, ~40-50 nm sized, npFe$^{0}$ particles
do not contribute to the spectral slope change as efficiently as the smaller
npFe$^{0}$ fraction. A linear trend is observed between the amount of
npFe$^{0}$ and 1 {\mu}m band center position, most likely caused by Fe$^{2+}$
disassociation from olivine structure into npFe$^{0}$ particles.",1404.2956v2
2014-07-02,Connection between ambient-pressure and pressure-induced superconducting phases in alkaline iron selenide superconductors,"A unique platform for investigating the correlation between the
antiferromagnetic (AFM) and superconducting (SC) states in high temperature
superconductors is created by the discovery of alkaline iron selenide
superconductors which are composed of an AFM insulating phase and a SC phase
separated spatially. Our previous studies showed that pressure can fully
suppress the superconductivity of ambient-pressure superconducting phase (SC-I)
and AFM order simultaneously, then induce another superconducting phase (SC-II)
at higher pressure. Consequently, the connection between the two
superconducting phases becomes an intriguing issue. In this study, on the basis
of observing pressure-induced reemergence of superconductivity in
Rb0.8Fe2-ySe2-xTex (x=0, 0.19 and 0.28) superconductors, we find that the
superconductivity of the SC-I and SC-II phases as well as the AFM ordered state
can be synchronously tuned by Te doping and disappear together at the doping
level of x=0.4. We propose that the two superconducting phases are connected by
the AFM phase, in other words, the state of long-ranged AFM order plays a role
in giving rise to superconductivity of the SC-I phase, while the fluctuation
state of the suppressed AFM phase drives the emergence of SC-II phase. These
results comprehensively demonstrate the versatile roles of AFM states in
stabilizing and developing superconductivity in the alkaline iron selenide
superconductors.",1407.0589v2
2014-07-24,Preventing corona effects: multi-phosphonic acid poly(ethylene glycol) copolymers for stable stealth iron oxide nanoparticles,"When disperse in biological fluids, engineered nanoparticles are selectively
coated with proteins, resulting in the formation of a protein corona. It is
suggested that the protein corona is critical in regulating the conditions of
entry into the cytoplasm of living cells. Recent reports describe this
phenomenon as ubiquitous and independent of the nature of the particle. For
nanomedicine applications however, there is a need to design advanced and
cost-effective coatings that are resistant to protein adsorption and that
increase the biodistribution in vivo. In this study, phosphonic acid
poly(ethylene glycol) copolymers were synthesized and used to coat iron oxide
particles. The copolymer composition was optimized to provide simple and
scalable protocols as well as long-term stability in culture media. It is shown
that polymers with multiple phosphonic acid functionalities and PEG chains
outperform other types of coating, including ligands, polyelectrolytes and
carboxylic acid functionalized PEG. PEGylated particles exhibit moreover
exceptional low cellular uptake, of the order of 100 femtograms of iron per
cell. The present approach demonstrates that the surface chemistry of
engineered particles is a key parameter in the interactions with cells. It also
opens up new avenues for the efficient functionalization of inorganic surfaces.",1407.6411v1
2014-08-05,Two spatially separated phases in semiconducting Rb$_{0.8}$Fe$_{1.5}$S$_2$,"We report neutron scattering and transport measurements on semiconducting
Rb$_{0.8}$Fe$_{1.5}$S$_2$, a compound isostructural and isoelectronic to the
well-studied $A_{0.8}$Fe$_{y}$Se$_2 (A=$ K, Rb, Cs, Tl/K) superconducting
systems. Both resistivity and DC susceptibility measurements reveal a magnetic
phase transition at $T=275$ K. Neutron diffraction studies show that the 275 K
transition originates from a phase with rhombic iron vacancy order which
exhibits an in-plane stripe antiferromagnetic ordering below 275 K. In
addition, interdigitated mesoscopically with the rhombic phase is an ubiquitous
phase with $\sqrt{5}\times\sqrt{5}$ iron vacancy order. This phase has a
magnetic transition at $T_N=425$ K and an iron vacancy order-disorder
transition at $T_{S}=600$ K. These two different structural phases are closely
similar to those observed in the isomorphous Se materials. Based on the close
similarities of the in-plane antiferromagnetic structures, moments sizes, and
ordering temperatures in semiconducting Rb$_{0.8}$Fe$_{1.5}$S$_2$ and
K$_{0.81}$Fe$_{1.58}$Se$_2$, we argue that the in-plane antiferromagnetic order
arises from strong coupling between local moments. Superconductivity,
previously observed in the $A_{0.8}$Fe$_{y}$Se$_{2-z}$S$_z$ system, is absent
in Rb$_{0.8}$Fe$_{1.5}$S$_2$, which has a semiconducting ground state. The
implied relationship between stripe/block antiferromagnetism and
superconductivity in these materials as well as a strategy for further
investigation is discussed in this paper.",1408.0842v1
2014-08-10,Unfolding of the electronic structure through the induced representations of space groups: Application to Fe-based superconductors,"We revisit the problem that relevant parts of bandstructures for a given cell
choice can reflect exact or approximate higher symmetries of subsystems in the
cell and can therefore be significantly simplified by an unfolding procedure
that recovers the higher symmetry. We show that bandstructure unfolding can be
understood as projection onto induced irreducible representations of a group
obtained by extending the original group of translations with a number of
additional symmetry operations. The resulting framework allows us to define a
generalized unfolding procedure which includes the point group operations and
can be applied to any quantity in the reciprocal space. The unfolding of the
Brillouin zone follows naturally from the properties of the induced irreducible
representations. In this context, we also introduce a procedure to derive
tight-binding models of reduced dimensionality by making use of point group
symmetries. Further, we show that careful consideration of unfolding has
important consequences on the interpretation of angle resolved photoemission
experiments. Finally, we apply the unfolding procedure to various
representative examples of Fe-based superconductor compounds and show that the
one iron picture arises as an irreducible representation of the glide mirror
group and we comment on the consequences for the interpretation of one-iron
versus two-iron Brillouin zone representations.",1408.2258v2
2014-08-19,Neutrino and anti-neutrino energy loss rates due to iron isotopes suitable for core-collapse simulations,"Accurate estimate of neutrino energy loss rates are needed for the study of
the late stages of the stellar evolution, in particular for cooling of neutron
stars and white dwarfs. The energy spectra of neutrinos and antineutrinos
arriving at the Earth can also provide useful information on the primary
neutrino fluxes as well as neutrino mixing scenario (it is to be noted that
these supernova neutrinos are emitted after the supernova explosion which is a
much later stage of stellar evolution than that considered in this paper).
Recently an improved microscopic calculation of weak-interaction mediated rates
for iron isotopes was introduced using the proton-neutron quasiparticle random
phase approximation (pn-QRPA) theory. Here I present for the first time the
fine-grid calculation of the neutrino and anti-neutrino energy loss rates due
to $^{54,55,56}$Fe in stellar matter. In the core of massive stars isotopes of
iron, $^{54,55,56}$Fe, are considered to be key players in decreasing the
electron-to-baryon ratio ($Y_{e}$) mainly via electron capture on these
nuclide. Core-collapse simulators may find this calculation suitable for
interpolation purposes and for necessary incorporation in the stellar evolution
codes. The calculated cooling rates are also compared with previous
calculations.",1408.4321v1
2014-08-19,Stellar $β^{\pm}$ decay rates of iron isotopes and its implications in astrophysics,"$\beta$-decay and positron decay are believed to play a consequential role
during the late phases of stellar evolution of a massive star culminating in a
supernova explosion. Recently the microscopic calculation of weak-interaction
mediated rates on key isotopes of iron was introduced using the proton-neutron
quasiparticle random phase approximation (pn-QRPA) theory with improved model
parameters. Here I discuss in detail the improved calculation of $\beta^{\pm}$
decay rates for iron isotopes ($^{54,55,56}$Fe) in stellar environment. The
pn-QRPA theory allows a microscopic ""state-by-state"" calculation of stellar
rates as explained later in text. Excited state Gamow-Teller distributions are
much different from ground state and a microscopic calculation of decay rates
from these excited states greatly increases the reliability of the total decay
rate calculation specially during the late stages of stellar evolution. The
reported decay rates are also compared with earlier calculations. The positron
decay rates are in reasonable agreement with the large-scale shell model
calculation. The main finding of this work includes that the stellar
$\beta$-decay rates of $^{54,55,56}$Fe are around 3 -- 5 orders of magnitude
smaller than previously assumed and hence irrelevant for the determination of
the evolution of $Y_{e}$ during the presupernova phase of massive stars. The
current work discourages the inclusion of $^{55,56}$Fe in the list of key
stellar $\beta$-decay nuclei as suggested by former simulation results.",1408.4407v1
2014-09-10,Interpretation of the X-ray Spectral Variation of 1H0707-495 with a Variable Double Partial Covering Model,"The Narrow-line Seyfert 1 galaxy 1H0707-495 is known to exhibit significant
X-ray spectral variations. Its X-ray energy spectrum is characterized by a
strong soft excess emission, an extremely deep iron K-edge structure at ~7 keV,
and a putative iron L-line/edge feature at ~1 keV. We have found that the
energy spectrum of 1H0707-495 in 0.5-10 keV is successfully explained by a
""variable double partial covering model"" where the original continuum spectrum,
which is composed of the soft multi-color disk blackbody component and the hard
power-law component, is partially covered by two ionized absorption layers with
different ionization states and the same partial covering fraction. The
lower-ionized and thicker absorption layer primarily explains the iron K-edge
feature, and the higher-ionized and thinner absorption layer explains the
L-edge feature. We have discovered that the observed significant
intensity/spectral variation within a ~ day is mostly explained by only
variation of the partial covering fraction. In our model, the intrinsic
luminosity and spectral shape are hardly variable within a ~ day, while some
intrinsic variability above 3 keV is recognized. This is consistent with the
picture that the multi-color disk blackbody spectrum is almost invariable in
this timescale, and the hard power-law component is more variable. We propose
that the observed spectral variation of 1H0707-495 is caused by three
physically independent variations with different timescales; (1) intrinsic
luminosity variation over days, (2) variation of partial covering fraction at a
timescale of hours, and (3) small intrinsic hard component variation above 3
keV in a timescale of hours or less.",1409.3019v1
2014-09-14,Correlation-induced self-doping in intercalated iron-pnictide superconductor Ba2Ti2Fe2As4O,"The electronic structure of the intercalated iron-based superconductor
Ba2Ti2Fe2As4O (Tc - 21.5 K) has been investigated by using angle-resolved
photoemission spectroscopy and combined local density approximation and
dynamical mean field theory calculations. The electronic states near the Fermi
level are dominated by both the Fe 3d and Ti 3d orbitals, indicating that the
spacing layers separating different FeAs layers are also metallic. By counting
the enclosed volumes of the Fermi surface sheets, we observe a large
self-doping effect, i.e. 0.25 electrons per unit cell are transferred from the
FeAs layer to the Ti2As2O layer, leaving the FeAs layer in a hole-doped state.
This exotic behavior is successfully reproduced by our dynamical mean field
calculations, in which the self-doping effect is attributed to the electronic
correlations in the Fe 3d shell. Our work provides an alternative route of
effective doping without element substitution for iron-based superconductors.",1409.4090v1
2014-09-29,MD Simulations of Compression of Nanoscale Iron Pillars,"It is now possible to create perfect crystal nanowires of many metals. The
deformation of such objects requires a good understanding of the processes
involved in plasticity at the nanoscale. Isotropic compression of such
nanometre scale micropillars is a good model system to understand the
plasticity. Here we investigate these phenomena using Molecular Dynamics (MD)
simulations of nanometre scale single crystal BCC iron pillars in compression.
  We find that pillars with large length to width ratio may buckle under high
strain rates. The type of buckling behaviour depends sensitively on the
boundary conditions used: periodic boundary conditions allow for rotation at
top and bottom of the pillar, and result in an S shaped buckle, by contrast
fixed boundaries enforce a C shape. Pillars with a length to width ratio closer
to that used in experimental micropillar compression studies show deformation
behaviour dominated by slip, in agreement with the experiments. For
micropillars oriented along <100>, slip occurs on <110> planes and localized
slip bands are formed. Pillars of this size experience higher stresses than
bulk materials before yielding takes place. One might expect that this may be
in part due to the lack of nucleation sites needed to induce slip. However,
further simulations with possible dislocation sources: a shorter iron pillar
containing a spherical grain boundary, and a similar pillar containing jagged
edges did not show a decreased yield strength.",1409.8328v1
2014-10-14,NLTE effects on AGB stars in 47 Tucanae,"We present the iron abundance of 24 asymptotic giant branch (AGB) stars
members of the globular cluster 47 Tucanae, obtained with high-resolution
spectra collected with the FEROS spectrograph at the MPG/ESO-2.2m Telescope. We
find that the iron abundances derived from neutral lines (with mean value [Fe
I/H] = -0.94 +/- 0.01, {\sigma} = 0.08 dex) are systematically lower than those
derived from single ionized lines ([Fe II/H] = -0.83 +/- 0.01, {\sigma} = 0.05
dex). Only the latter are in agreement with those obtained for a sample of red
giant branch (RGB) cluster stars, for which Fe I and Fe II lines provide the
same iron abundance. This finding suggests that Non Local Thermodynamical
Equilibrium (NLTE) effects driven by overionization mechanisms are present in
the atmosphere of AGB stars and significantly affect Fe I lines, while leaving
Fe II features unaltered. On the other hand, the very good ionization
equilibrium found for RGB stars indicates that these NLTE effects may depend on
the evolutionary stage. We discuss the impact of this finding both on the
chemical analysis of AGB stars, and on the search for evolved blue stragglers.",1410.3841v1
2014-10-21,A Study on the time resolution of Glass RPC,"The 50~kton Iron Calorimeter (ICAL) detector at the underground India based
Neutrino Observatory (INO) will make measurements on atmospheric neutrinos.
Muons produced in charged current (CC) interactions of muon neutrinos with the
iron are tracked spatially and temporally through the signals that they produce
in the Resistive Plate Chambers~(RPCs) that are interleaved with iron layers.
Since the RPCs will be operated in the avalanche mode the signal rise-time is
$\sim~1~\rm{nsec}$ resulting in a fast time response. While the muon track is
derived from the X and Y hit information of the RPCs and the layer number (Z),
the upward or downward direction is obtained by using the time information from
the detector. Such a capability can be examined by analysing the timing
information from $1~\rm{m}~\times~1~\rm{m}$ glass RPCs, with $3~\rm{cm}$ wide
X- and Y- pick-up strips, in a $12$ layer RPC stack that measures cosmic muon
events. The present study looks at the pixel-wise time response of these RPCs
in order to improve the relative time distribution and hence the up-down
discrimination capability. After including the effect of propagation delay in
the cable and pick-up panel the time resolution improves, in some cases, to
$\leq~1~\rm{nsec}$ whereas in some cases there is no significant change. These
results will help in significantly improving on the extraction of the
directionality of muons produced in CC interactions of $\nu_{\mu}$ and
$\bar{\nu}_{\mu}$.",1410.5532v1
2014-11-16,Distinguishing spin-orbit coupling and nematic order in the electronic spectrum of iron-based superconductors,"The low-energy electronic states of the iron-based superconductors are
strongly affected by both spin-orbit coupling and, when present, by the nematic
order. These two effects have different physical origins, yet they can lead to
similar gap features in the electronic spectrum. Here we show how to
disentangle them experimentally in the iron superconductors with one Fe plane
per unit cell. Although the splitting of the low energy doublet at the
Brillouin zone center ($\Gamma$-point) can be due to either the spin-orbit
coupling or the nematic order, or both, the degeneracy of each of the doublet
states at the zone corner ($M$-point) is protected by the space group symmetry
even when spin-orbit coupling is taken into account. Therefore, any splitting
at $M$ must be due to lowering of the crystal symmetry, such as due to the
nematic order. We further analyze a microscopic tight-binding model with two
different contributions to the nematic order: $d_{xz}/d_{yz}$ onsite energy
anisotropy and the $d_{xy}$ hopping anisotropy. We find that a precise
determination of the former, which has been widely used to characterize the
nematic phase, requires a simultaneous measurement of the splittings of the
$\Gamma$-point doublet and at the two low-energy $M$-point doublets. We also
discuss the impact of twin domains and show how our results shed new light on
ARPES measurements in the normal state of these materials.",1411.4303v1
2014-12-04,High transport Jc in magnetic fields up to 28 T of stainless steel/Ag double sheathed Ba122 tapes fabricated by scalable rolling process,"The recently discovered iron-based superconductors with very high upper
critical field and small anisotropy have been regarded as a potential candidate
material for high field applications. However, enhancements of superconducting
properties are still needed to boost the successful use of iron-based
superconductors in such applications. Here, we propose a new sheath
architecture of stainless steel (SS)/Ag double sheath and investigate its
influence on the microstructures and Jc-H property. We found that the transport
Jc-H curves for rolled and pressed tapes both show extremely small magnetic
field dependence and exceed 3*10^4A/cm^2 under 28 T, which are much higher than
those of low-temperature superconductors. More interestingly, 12 cm long rolled
tape shows very high homogeneity and sustains Jc as high as 7.7*10^4 A/cm^2 at
10 T. These are the highest values reported so far for iron-based
superconducting wires fabricated by scalable rolling process. The
microstructure investigations indicate that such high Jc was achieved by higher
density of the core and uniform deformation resulting better texturing. These
results indicate that our process is very promising for fabricating long Ba122
wires for high field magnet, i.e. above 20 T.",1412.1580v1
2014-12-12,Magnetism of BaFe2Se3 studied by Mössbauer spectroscopy,"The compound BaFe2Se3 (Pnma) has been synthesized in the form of single
crystals with the average composition Ba0.992Fe1.998Se3. The Moessbauer
spectroscopy used for investigation of the valence states of Fe in this
compound at temperature ranging from 4.2 K till room temperature revealed the
occurrence of mixed-valence state for iron. The spectrum is characterized by
sharply defined electric quadrupole doublet above magnetic ordering at about
250 K. For the magnetically ordered state one sees four iron sites at least and
each of them is described by separate axially symmetric electric field gradient
tensor with the principal component making some angle with the hyperfine
magnetic field. They form two groups occurring in equal abundances. It is
likely that each group belongs to separate spin ladder with various tilts of
the FeSe4 tetrahedral units along the ladder. Two impurity phases are found,
i.e., superconducting FeSe and some other unidentified iron-bearing phase being
magnetically disordered above 80 K. Powder form of BaFe2Se3 is unstable in
contact with the air and decomposes slowly to this unidentified phase
exhibiting almost the same quadrupole doublet as BaFe2Se3 above magnetic
transition temperature.",1412.4024v2
2015-01-27,The Compton hump and variable blue wing in the extreme low-flux NuSTAR observations of 1H0707-495,"The Narrow-line Seyfert I galaxy, 1H0707-495, has been well observed in the
0.3-10 keV band, revealing a dramatic drop in flux in the iron K alpha band, a
strong soft excess, and short timescale reverberation lags associated with
these spectral features. In this paper, we present the first results of a deep
250 ks NuSTAR observation of 1H0707-495, which includes the first sensitive
observations above 10 keV. Even though the NuSTAR observations caught the
source in an extreme low-flux state, the Compton hump is still significantly
detected. NuSTAR, with its high effective area above 7 keV, clearly detects the
drop in flux in the iron K alpha band, and by comparing these observations with
archival XMM-Newton observations, we find that the energy of this drop
increases with increasing flux. We discuss possible explanations for this, the
most likely of which is that the drop in flux is the blue wing of the
relativistically broadened iron K alpha emission line. When the flux is low,
the coronal source height is low, thus enhancing the most gravitationally
redshifted emission.",1501.06849v2
2015-01-29,Superconducting properties of sulfur-doped iron selenide,"The recent discovery of high-temperature superconductivity in single-layer
iron selenide has generated significant experimental interest for optimizing
the superconducting properties of iron-based superconductors through the
lattice modification. For simulating the similar effect by changing the
chemical composition due to S doping, we investigate the superconducting
properties of high-quality single crystals of FeSe$_{1-x}$S$_{x}$ ($x$=0, 0.04,
0.09, and 0.11) using magnetization, resistivity, the London penetration depth,
and low temperature specific heat measurements. We show that the introduction
of S to FeSe enhances the superconducting transition temperature $T_{c}$,
anisotropy, upper critical field $H_{c2}$, and critical current density
$J_{c}$. The upper critical field $H_{c2}(T)$ and its anisotropy are strongly
temperature dependent, indicating a multiband superconductivity in this system.
Through the measurements and analysis of the London penetration depth $\lambda
_{ab}(T)$ and specific heat, we show clear evidence for strong coupling two-gap
$s$-wave superconductivity. The temperature-dependence of $\lambda _{ab}(T)$
calculated from the lower critical field and electronic specific heat can be
well described by using a two-band model with $s$-wave-like gaps. We find that
a $d$-wave and single-gap BCS theory under the weak-coupling approach can not
describe our experiments. The change of specific heat induced by the magnetic
field can be understood only in terms of multiband superconductivity.",1501.07346v1
2015-02-25,Crossover of the pairing symmetry from $s$- to $d$-wave in iron pnictide superconductors,"One of the major themes in the physics of condensed matter is unconventional
superconductivity in correlated electronic systems. The symmetry structure of
Cooper pairs is thought to be the key to the understanding of the pairing
mechanism of their superconductivity. In iron pnictide superconductors, the
precise symmetry of the order parameter as well its evolution with doping
remains highly controversial. There is no general consensus on the nature of
pairing in iron-based superconductors leaving the perspectives ranging from
$s^{++}$ wave, to $s^{\pm}$, and $d$ wave. Here we show that doping induced a
sudden change of the pairing symmetry from the $s^{++}$- to $d$-wave in the
BaFe$_{2-x}$Ni$_{x}$As$_{2}$ system with an $s^{\pm}$ state near the crossover
boundary at $x=0.15$. The presence of the $s^{\pm}$ state is of particular
scientific interest because an intermediate phase breaks the pairing symmetry
when the $s$- and $d$-wave phases come together to interfere. For $x <$ 0.15,
the temperature dependence of the London penetration depth, lower critical
field, and specific heat in the superconducting (SC) state provides strong
evidence for a two-band $s$-wave order parameter. Upon doping for $x >$ 0.15,
we find the temperature and magnetic-field contributions to the specific heat
in $T^{2}$ and $\sqrt{H}$, respectively, indicating line nodes in the SC gap.
These findings thus clarify the symmetry nature as well as the evolution of the
SC order parameter with doping in pnictide superconductors.",1502.07130v1
2015-04-20,A Mott insulator continuously connected to iron pnictide superconductors,"Iron-based superconductivity develops near an antiferromagnetic order and out
of a bad metal normal state, which has been interpreted as originating from a
proximate Mott transition. Whether an actual Mott insulator can be realized in
the phase diagram of the iron pnictides remains an open question. Here we use
transport, transmission electron microscopy, X-ray absorption spectroscopy, and
neutron scattering to demonstrate that NaFe$_{1-x}$Cu$_x$As near $x\approx 0.5$
exhibits real space Fe and Cu ordering, and are antiferromagnetic insulators
with the insulating behavior persisting above the N\'eel temperature,
indicative of a Mott insulator. Upon decreasing $x$ from $0.5$, the
antiferromagnetic ordered moment continuously decreases, yielding to
superconductivity around $x=0.05$. Our discovery of a Mott insulating state in
NaFe$_{1-x}$Cu$_x$As thus makes it the only known Fe-based material in which
superconductivity can be smoothly connected to the Mott insulating state,
highlighting the important role of electron correlations in the high-$T_{\rm
c}$ superconductivity.",1504.05116v2
2015-04-26,Manifestation of nematic degrees of freedom in the Raman response function of iron pnictides,"We establish a relation between the Raman response function in the $B_{1g}$
channel and the electronic contribution to the nematic susceptibility within
the spin-driven approach to electron nematicity of the iron based
superconductors. The spin-driven nematic phase, characterized by the broken
$C_4$ symmetry, but unbroken $O(3$) spin-rotational symmetry, is generated by
the presence of magnetic fluctuations associated with the striped phase. It
occurs as a separate phase between $T_N$ and $T_s$ in systems where the
structural and magnetic phase transitions are separated. Detecting the presence
of nematic degrees of freedom in iron-based superconductors is a difficult
task, since it involves measuring higher order spin correlation functions. We
show that the nematic degrees of freedom manifest themselves in the
experimentally measurable Raman response function. We calculate the Raman
response function in tetragonal phase in the large $N$ limit by considering
Aslamazov-Larkin type of diagrams that contain a series of inserted fermionic
boxes that resemble the nematic coupling constant of the theory. These diagrams
effectively account for collisions between spin fluctuations. By summing an
infinite number of such higher order diagrams, we demonstrate that the
electronic Raman response function shows a clear maximum at the structural
phase transition in the $B_{1g}$ channel. Hence, the Raman response function
can be used to probe nematic degrees of freedom.",1504.06841v2
2015-05-19,Direct observation of a Fermi liquid-like normal state in an iron-pnictide superconductor,"There are two prerequisites for understanding high-temperature (high-T$_c$)
superconductivity: identifying the pairing interaction and a correct
description of the normal state from which superconductivity emerges. The
nature of the normal state of iron-pnictide superconductors, and the role
played by correlations arising from partially screened interactions, are still
under debate. Here we show that the normal state of carefully annealed
electron-doped BaFe$_{2-x}$Co$_{x}$As$_2$ at low temperatures has all the
hallmark properties of a local Fermi liquid, with a more incoherent state
emerging at elevated temperatures, an identification made possible using
bulk-sensitive optical spectroscopy with high frequency and temperature
resolution. The frequency dependent scattering rate extracted from the optical
conductivity deviates from the expected scaling
$M_{2}(\omega,T)\propto(\hbar\omega)^{2}+(p\pi k_{B}T)^{2}$ with $p\approx$
1.47 rather than $p$ = 2, indicative of the presence of residual elastic
resonant scattering. Excellent agreement between the experimental results and
theoretical modeling allows us to extract the characteristic Fermi liquid scale
$T_{0}\approx$ 1700 K. Our results show that the electron-doped iron-pnictides
should be regarded as weakly correlated Fermi liquids with a weak mass
enhancement resulting from residual electron-electron scattering from thermally
excited quasi-particles.",1505.05139v1
2015-05-22,Interaction-induced singular Fermi surface in a high-temperature oxypnictide superconductor,"In the family of iron-based superconductors, LaFeAsO-type materials possess
the simplest electronic structure due to their pronounced two-dimensionality.
And yet they host superconductivity with the highest transition temperature
Tc=55K. Early theoretical predictions of their electronic structure revealed
multiple large circular portions of the Fermi surface with a very good
geometrical overlap (nesting), believed to enhance the pairing interaction and
thus superconductivity. The prevalence of such large circular features in the
Fermi surface has since been associated with many other iron-based compounds
and has grown to be generally accepted in the field. In this work we show that
a prototypical compound of the 1111-type, SmFe0.92Co0.08AsO, is at odds with
this description and possesses a distinctly different Fermi surface, which
consists of two singular constructs formed by the edges of several bands,
pulled to the Fermi level from the depths of the theoretically predicted band
structure by strong electronic interactions. Such singularities dramatically
affect the low-energy electronic properties of the material, including
superconductivity. We further argue that occurrence of these singularities
correlates with the maximum superconducting transition temperature attainable
in each material class over the entire family of iron-based superconductors.",1505.06152v1
2015-05-22,Double-Q spin-density wave in iron arsenide superconductors,"Elucidating the nature of the magnetic ground state of iron-based
superconductors is of paramount importance in unveiling the mechanism behind
their high temperature superconductivity. Until recently, it was thought that
superconductivity emerges only from an orthorhombic antiferromagnetic stripe
phase, which can in principle be described in terms of either localized or
itinerant spins. However, we recently reported that tetragonal symmetry is
restored inside the magnetically ordered state of a hole-doped BaFe2As2. This
observation was interpreted as indirect evidence of a new double-Q magnetic
structure, but alternative models of orbital order could not be ruled out.
Here, we present Mossbauer data that show unambiguously that half of the iron
sites in this tetragonal phase are non-magnetic, establishing conclusively the
existence of a novel magnetic ground state with a non-uniform magnetization
that is inconsistent with localized spins. We show that this state is naturally
explained as the interference between two spin-density waves, demonstrating the
itinerant character of the magnetism of these materials and the primary role
played by magnetic over orbital degrees of freedom.",1505.06175v1
2015-05-29,"Tables of phase functions, opacities, albedos, equilibrium temperatures, and radiative accelerations of dust grains in exoplanets","There has been growing observational evidence for the presence of condensates
in the atmospheres and/or comet-like tails of extrasolar planets. As a result,
systematic and homogeneous tables of dust properties are useful in order to
facilitate further observational and theoretical studies. In this paper we
present calculations and analysis of non-isotropic phase functions, asymmetry
parameter (mean cosine of the scattering angle), absorption and scattering
opacities, single scattering albedos, equilibrium temperatures, and radiative
accelerations of dust grains relevant for extrasolar planets. Our assumptions
include spherical grain shape, Deirmendjian particle size distribution, and Mie
theory. We consider several species: corundum/alumina, perovskite, olivines
with 0\% and 50\% iron content, pyroxenes with 0\%, 20\% and 60\% iron content,
pure iron, carbon at two different temperatures, water ice, liquid water, and
ammonia. The presented tables cover the wavelength range of 0.2 to 500 micron
and modal particle radii from 0.01 micron to 100 micron. Equilibrium
temperatures and radiative accelerations assume irradiation by a non-black-body
source of light with temperatures from 7000K to 700K seen at solid angles from
2$\pi$ to $10^{-6}$ sr. The tables are provided to the community together with
a simple code which allows for an optional, finite, angular dimension of the
source of light (star) in the phase function.",1505.08013v2
2015-06-02,Enhancement of the 6.4 keV line in the inner Galactic ridge: Proton-induced fluorescence?,"A common idea for the origin of the Galactic diffuse X-ray emission,
particularly that of the iron lines from neutral and highly ionized atoms, is a
superposition of many cataclysmic variables and coronally active binaries. In
this scenario, the flux should symmetrically distribute between the east and
west on the plane with respect to Sagittarius A$^*$ because the stellar mass
distribution determined by infrared observations is nearly symmetric. This
symmetry is confirmed for the highly ionized iron line as well as the continuum
emission. However, a clear excess of the neutral iron line in the near east of
the Galactic center compared to the near-west side is found. The flux
distribution of the excess emission well correlates with molecular column
density. The X-ray spectrum of the excess emission is described by a power-law
continuum plus a 6.4 keV line with the large equivalent width of $\sim1.3$ keV,
which is hardly explained by the low-energy electron bombardment scenario. The
longitudinal and latitudinal distribution of the excess emission disfavors the
X-ray irradiation, neither by Sagittarius A$^*$ nor by nearby X-ray binaries.
Then the low-energy proton bombardment is the most probable origin although the
high energy density $\sim 80$ eV cm$^{-3}$ in 0.1-1000 MeV is required and
there is no conventional proton source in the vicinity.",1506.00759v1
2015-06-02,Localization and Orbital Selectivity in Iron-Based Superconductors with Cu Substitution,"We study an inhomogeneous three-orbital Hubbard model for the Cu-substituted
iron pnictides using an extended real-space Green's function method combined
with density functional calculations. We find that the onsite interactions of
the Cu ions are the principal determinant of whether an electron dopant or a
hole dopant is caused by the Cu substitution. It is found that the Cu
substitution could lead to a hole doping when its onsite interactions are
smaller than a critical value, as opposed to an electron doping when the
interactions of Cu ions are larger than the critical value, which may explain
why the effects of Cu substitution on the carrier density are entirely
different in NaFe$_{1-x}$Cu$_x$As and Ba(Fe$_{1-x}$Cu$_x$)$_2$As$_2$. We also
find that the effect of a doping-induced disorder is considerable in the
Cu-substituted iron pnictides, and its cooperative effect with electron
correlations contributes to the orbital-selective insulating phases in
NaFe$_{1-x}$Cu$_x$As and Ba(Fe$_{1-x}$Cu$_x$)$_2$As$_2$.",1506.00767v3
2015-06-06,Spectroscopic Studies of Quasiparticle Low-Energy Excitations in Cuprate and Iron-Based High-Temperature Superconductors,"Recent development in the physics of high-temperature superconductivity is
reviewed, with special emphasis on the studies of the low-energy excitations of
cuprate and iron-based superconductors. For cuprate superconductors, a
phenomenology based on coexisting competing orders with superconductivity in
the ground state of these doped Mott insulators is shown to provide a
consistent account for a wide range of experimental findings. In the case of
iron-based superconductors, studies of the low-energy excitations reveal
interesting similarities and differences when compared with cuprate
superconductors. In contrast to the single-band cuprate superconductivity with
an insulating parent state, the ferrous superconductors are multi-band
materials with a semi-metallic parent state and exhibit two-gap
superconductivity when doped. On the other hand, both systems exhibit strong
antiferromagnetic correlation and Fermi-surface distortion, leading to
unconventional pairing symmetries with sign-changing order parameters on
different parts of the Fermi surface. These findings suggest that the pairing
potentials in both the cuprate and the ferrous superconductors are generally
repulsive, thus favor a pairing mechanism that is electronically driven and a
pairing strength that is closely related to the electronic correlation. The
physical implications of the unified phenomenology based on antiferromagnetic
correlations and remaining open issues associated with the cuprate and ferrous
superconductivity are discussed.",1506.02091v1
2015-06-09,"Better Alternative to ""Astronomical Silicate"": Laboratory-Based Optical Functions of Chondritic/Solar Abundance Glass With Application to HD161796","""Astronomical"" or ""circumstellar"" silicate optical functions (real and
imaginary indices of refraction n and k have been previously derived from
compositionally and structurally disparate samples; past values were compiled
from different sources in the literature, and are essentially kluges of
observational, laboratory, and extrapolated or interpolated values. These
synthetic optical functions were created because astronomers lack the
quantitative data on amorphous silicates at all wavelengths needed for
radiative transfer modeling. This paper provides optical functions that (1) are
created with a consistent methodology, (2) use the same sample across all
wavelengths, and (3) minimize interpolation and extrapolation wherever
possible. We present electronic data tables of optical functions derived from
mid-ultraviolet to far-infrared laboratory transmission spectra for two
materials: iron-free glass with chondritic/solar atmospheric abundances, and
metallic iron. We compare these optical functions to other popular n, k data
used to model amorphous silicates (e.g., ""astronomical"" or ""circumstellar""
silicate), both directly and in application to a simple system: the dust shell
of the post-AGB star HD161796. Using the new optical functions, we find that
the far-IR profile of model SEDs are significantly affected by the ratio of
glass to iron. Our case study on HD161796 shows that modeling with our new
optical functions, the mineralogy is markedly different from that derived using
synthetic optical functions and suggests a new scenario of crystalline silicate
formation.",1506.03110v1
2015-06-18,Unusual Sensitivity of Superconductivity to Strain in Iron-Based 122 Superconductors,"Co-doped BaFe2As2 has been previously shown to have an unusually significant
improvement of Tc (up to 2 K, or almost 10%) with annealing 1-2 weeks at 700 or
800 C, where such annealing conditions are insufficient to allow significant
atomic diffusion. While confirming similar behavior in optimally Co-doped
SrFe2As2 samples, the influence on Tc of strain induced by grinding to ~50
micron sized particles, followed by pressing the powder into a pellet using 10
kbar pressure, was found to increase the annealed transition width of 1.5 K by
approximately a factor of ten. Also, the bulk discontinuity in the specific
heat at Tc, deltaC, on the same pellet sample was completely suppressed by
grinding. This evidence for a strong sensitivity of superconductivity to strain
was used to optimize single crystal growth of Co-doped BaFe2As2. This strong
dependence (both positive via annealing and negative via grinding) of
superconductivity on strain in these two iron based 122 structure
superconductors is compared to the unconventional heavy Fermion superconductor
UPt3, where grinding is known to completely suppress superconductivity, and to
recent reports of strong sensitivity of Tc to damage induced by
electron-irradiation-induced point defects in other 122 structure iron-based
superconductors, Ba(Fe0.76Ru0.24)2As2 and Ba1-xKxFe2As2. Both the electron
irradiation and the introduction of strain by grinding are believed to only
introduce non-magnetic defects, and argue for unconventional superconducting
pairing.",1506.05735v1
2015-06-18,Robustness of s-wave pairing symmetry in iron-based superconductors and its implications to fundamentals on magnetically-driven high temperature superconductivity,"Under the assumption that the superconducting state belongs to a single
irreducible representation of lattice symmetry, we argue that the pairing
symmetry in all measured iron-based superconductors is universally consistent
with the A_{1g} s-wave. The robust s-wave pairing throughout the different
families of iron-based superconductors at different doping regions signals two
fundamental principles behind high T_c superconducting mechanisms: (1) the
correspondence principle: the short range magnetic exchange interactions and
the Fermi surfaces act collaboratively to achieve high T_c superconductivity
and determine pairing symmetries; (2) the magnetic selection pairing rule: the
superconductivity is only induced by the magnetic exchange couplings from the
superexchange mechanism through cation-anion-cation chemical bondings. These
principles explain why the unconventional high T_c superconductivity appears to
be such a rare but robust phenomena with its strict requirement on electronic
environment. The robust s-wave pairing also reveals that the current standard
effective models with only onsite interactions are not sufficient and a minimum
microscopic model must include strong nearest neighbor repulsive interactions
resulted from the d-d direct bondings to serves as a s-wave symmetry
stabilizer. Finally, the sign distribution of the superconducting order
parameters in the reciprocal space is simply a consequence of the form factors
given by the leading short-range pairings. The sign change of superconducting
order parameters on Fermi surfaces is not a necessary requirement in
repulsive-interaction-driven high T_c mechanism. The results will guide us to
search for new electronic structure that supports high T_c superconductivity.",1506.05791v1
2015-07-07,"SD 1313-0019 -- Another second-generation star with [Fe/H] = -5.0, observed with the Magellan Telescope","We present a Magellan/MIKE high-resolution (R ~ 35,000) spectrum of the
ancient star SD 1313-0019 which has an iron abundance of [Fe/H] = -5.0, paired
with a carbon enhancement of [C/Fe] ~ 3.0. The star was initially identified by
Allende Prieto et al. in the BOSS survey. Its medium-resolution spectrum
suggested a higher metallicity of [Fe/H] = -4.3 due to the CaII K line blending
with a CH feature which is a common issue related to the search for the most
iron-poor stars. This star joins several other, similar stars with [Fe/H] <
-5.0 that all display a combination of low iron and high carbon abundances.
Other elemental abundances of SD 1313-0019 follow that of more metal-rich halo
stars. From fitting the abundance pattern with yields of Population III
supernova, we conclude that SD 1313-0019 had only one massive progenitor star
with 20 - 30 M_sun that must have undergone a mixing and fallback episode.
Overall, there are now five stars known with [Fe/H] < -5.0 (1D LTE abundances).
This population of second-generation stars strongly suggests massive first
stars that almost exclusively produced large amounts of carbon through stellar
winds and/or their mixing and fallback supernova explosions. As a consequence,
their natal clouds -- presumably some early minihalo structures -- contained
ample amounts of carbon and oxygen that likely facilitated the formation of
these first low-mass stars.",1507.01973v2
2015-07-15,Impact of Uniaxial Pressure on Structural and Magnetic Phase Transitions in Electron-Doped Iron Pnictides,"We use neutron resonance spin echo and Larmor diffraction to study the effect
of uniaxial pressure on the tetragonal-to-orthorhombic structural ($T_s$) and
antiferromagnetic (AF) phase transitions in iron pnictides
BaFe$_{2-x}$Ni$_{x}$As$_{2}$ ($x=0,0.03,0.12$), SrFe$_{1.97}$Ni$_{0.03}$As$_2$,
and BaFe$_2$(As$_{0.7}$P$_{0.3}$)$_2$. In antiferromagnetically ordered
BaFe$_{2-x}$Ni$_{x}$As$_{2}$ and SrFe$_{1.97}$Ni$_{0.03}$As$_2$ with $T_N$ and
$T_s$ ($T_N\leq T_s$), a uniaxial pressure necessary to detwin the sample also
increases $T_N$, smears out the structural transition, and induces an
orthorhombic lattice distortion at all temperatures. By comparing temperature
and doping dependence of the pressure induced lattice parameter changes with
the elastoresistance and nematic susceptibility obtained from transport and
ultrasonic measurements, we conclude that the in-plane resistivity anisotropy
found in the paramagnetic state of electron underdoped iron pnictides depends
sensitively on the nature of the magnetic phase transition and a strong
coupling between the uniaxial pressure induced lattice distortion and
electronic nematic susceptibility.",1507.04191v2
2015-08-24,Critical current density and microstructure of iron sheathed multifilamentary Sr1-xKxFe2As2/Ag composite conductors,"Iron-based superconductors have been considered to be very promising in
high-field applications, for which multifilamentary wire and tape conductors
with high mechanical strength are essential. In this work, 7-,19- and
114-filament Sr0.6K0.4Fe2As2 (Sr-122) superconducting wires and tapes with
silver as matrix and iron as outer reinforcing sheath were produced by the ex
situ powder-in-tube method. The mass densities of Sr-122 phase in 7- and
19-filament conductors were investigated by microhardness characterization,
which revealed a positive correlation between hardness and transport critical
current density (Jc) in round wires and flat tapes with various thicknesses.
For Sr-122/Ag/Fe 114-filament conductors, in which an average cross-sectional
filament size smaller than 50 microns was achieved by drawing into round wires
of 2.0 mm in diameter, the transport Jc can be significantly enhanced by flat
rolling, as for the 7- and 19-filament conductors. The highest transport Jc of
the 7-,19- and 114-filament Sr-122/Ag/Fe tapes reached 1.4x10^4, 8.4x10^3 and
6.3x10^3 A cm-2 (4.2 K, 10 T), respectively, showing a Jc degradation with the
increase of filament number. This Jc degradation can be ascribed to the sausage
effect for filaments in longitudinal direction and the grain refinement in
these very fine filaments.",1508.05781v1
2015-09-29,Chemical analysis of Asymptotic Giant Branch stars in M62,"We have collected UVES-FLAMES high-resolution spectra for a sample of 6
asymptotic giant branch (AGB) and 13 red giant branch (RGB) stars in the
Galactic globular cluster M62 (NGC6266). Here we present the detailed abundance
analysis of iron, titanium, and light-elements (O, Na, Al and Mg). For the
majority (5 out 6) of the AGB targets we find that the abundances, of both iron
and titanium, determined from neutral lines are significantly underestimated
with respect to those obtained from ionized features, the latter being,
instead, in agreement with those measured for the RGB targets. This is similar
to recent findings in other clusters and may suggest the presence of Non-Local
Thermodynamical Equilibrium (NLTE) effects. In the O-Na, Al-Mg and Na-Al
planes, the RGB stars show the typical correlations observed for globular
cluster stars. Instead, all the AGB targets are clumped in the regions where
first generation stars are expected to lie, similarly to what recently found
for the AGB population of NGC6752. While the sodium and aluminum abundance
could be underestimated as a consequence of the NLTE bias affecting iron and
titanium, the used oxygen line does not suffer from the same effects and the
lack of O-poor AGB stars therefore is solid. We can thus conclude that none of
the investigated AGB stars belong to the second stellar generation of M62. We
also find a RGB star with extremely high sodium abundance ([Na/Fe] = +1.08
dex).",1509.08917v1
2015-11-08,Magnetic ground state of FeSe,"Elucidating the nature of the magnetism of a high-temperature superconductor
is crucial for establishing its pairing mechanism. The parent compounds of the
cuprate and iron-pnictide superconductors exhibit N\'eel and stripe magnetic
order, respectively. However, FeSe, the structurally simplest iron-based
superconductor, shows nematic order (Ts = 90 K), but not magnetic order in the
parent phase, and its magnetic ground state is intensely debated. Here, we
report inelastic neutron-scattering experiments that reveal both stripe and
N\'eel spin fluctuations over a wide energy range at 110 K. On entering the
nematic phase, a substantial amount of spectral weight is transferred from the
N\'eel to the stripe spin fluctuations. Moreover, the total fluctuating
magnetic moment of FeSe is ~ 60% larger than that in the iron pnictide
BaFe2As2. Our results suggest that FeSe is a novel S = 1 nematic
quantum-disordered paramagnet interpolating between the N\'eel and stripe
magnetic instabilities.",1511.02485v2
2015-11-13,Spin nematic susceptibility studied by inelastic neutron scattering in FeSe,"Mechanism of unconventional superconductivity in FeSe has been intensely
scrutinized recently because of a variety of exotic properties unprecedented
for other iron-based superconductors. A central unanswered question concerns
the origin of the interaction that causes the nematic transition at $T_s=90\,K$
without accompanying magnetic order. Elucidating the nature of spin excitations
in the normal state is a key to addressing this issue. Here we report, from
inelastic neutron-scattering measurements in FeSe single crystals, that
high-energy spin excitation spectra of FeSe exhibit characteristic energy
dependence with missing intensity at around 70-80$\,$meV, which are very
different from other iron-based superconductors. Despite of the strongest
electron correlations among the iron-based superconductor family, the spectra
are qualitatively at variance with the local moment model and can be
essentially described by the itinerant electron picture. Moreover, the
dynamical spin susceptibility above $T_s$ is only weakly temperature dependent,
which is in stark contrast to the Curie-Weiss behavior of the electronic
nematic susceptibility, suggesting that the nematic transition is not likely
driven by spin but by orbital degrees of freedom.",1511.04267v4
2015-12-08,Interface control by homoepitaxial growth in pulsed laser deposited iron chalcogenide thin ilms,"Thin film growth of iron chalcogenides by pulsed laser deposition (PLD) is
still a delicate issue in terms of simultaneous control of stoichiometry,
texture, substrate/film interface properties, and superconducting properties.
The high volatility of the constituents sharply limits optimal deposition
temperatures to a narrow window and mainly challenges reproducibility for
vacuum based methods. In this work we demonstrate the beneficial introduction
of a semiconducting FeSe$_{1\text{--}x}$Te$_x$ seed layer for subsequent
homoepitaxial growth of superconducting FeSe$_{1\text{--}x}$Te$_x$ thin film on
MgO substrates. MgO is one of the most favorable substrates used in
superconducting thin film applications, but the controlled growth of iron
chalcogenide thin films on MgO has not yet been optimized and is the least
understood. The large mismatch between the lattice constants of MgO and
FeSe$_{1\text{--}x}$Te$_x$ of about 11% results in thin films with a mixed
texture, that prevents further accurate investigations of a correlation between
structural and electrical properties of FeSe$_{1\text{--}x}$Te$_x$. Here we
present an effective way to significantly improve epitaxial growth of
superconducting FeSe$_{1\text{--}x}$Te$_x$ thin films with reproducible high
critical temperatures ($\geq$ 17 K) at reduced deposition temperatures (200
{\deg}C - 320 {\deg}C) on MgO using PLD. This offers a broad scope of various
applications.",1512.02524v1
2015-12-19,What makes the Tc of monolayer FeSe on SrTiO3 so high: a sign-problem-free quantum Monte Carlo study,"Monolayer FeSe films grown on SrTiO3 (STO) substrate show superconducting
gap-opening temperatures (Tc) which are almost an order of magnitude higher
than those of the bulk FeSe and are highest among all known Fe-based
superconductors. Angle-resolved photoemission spectroscopy (ARPES) observed
""replica bands"" suggesting the importance of the interaction between FeSe
electrons and STO phonons. These facts rejuvenated the quest for Tc enhancement
mechanisms in iron-based, especially iron-chalcogenide, superconductors. Here,
we perform the first numerically-exact sign-problem-free quantum Monte Carlo
simulations to iron-based superconductors. We (i) study the electronic pairing
mechanism intrinsic to heavily electron doped FeSe films, and (ii) examine the
effects of electron-phonon interaction between FeSe and STO as well as nematic
fluctuations on Tc. Armed with these results, we return to the question ""what
makes the Tc of monolayer FeSe on SrTiO3 so high?"" in the conclusion and
discussions.",1512.06179v4
2016-01-11,High-temperature superconductivity from fine-tuning of Fermi-surface singularities in iron oxypnictides,"In the family of the iron-based superconductors, the $RE$FeAsO-type compounds
(with $RE$ being a rare-earth metal) exhibit the highest bulk superconducting
transition temperatures ($T_{\mathrm{c}}$) up to $55\ \textrm{K}$ and thus hold
the key to the elusive pairing mechanism. Recently, it has been demonstrated
that the intrinsic electronic structure of SmFe$_{0.92}$Co$_{0.08}$AsO
($T_{\mathrm{c}}=18\ \textrm{K}$) is highly nontrivial and consists of multiple
band-edge singularities in close proximity to the Fermi level. However, it
remains unclear whether these singularities are generic to the $RE$FeAsO-type
materials and if so, whether their exact topology is responsible for the
aforementioned record $T_{\mathrm{c}}$. In this work, we use angle-resolved
photoemission spectroscopy (ARPES) to investigate the inherent electronic
structure of the NdFeAsO$_{0.6}$F$_{0.4}$ compound with a twice higher
$T_{\mathrm{c}}=38\ \textrm{K}$. We find a similarly singular Fermi surface and
further demonstrate that the dramatic enhancement of superconductivity in this
compound correlates closely with the fine-tuning of one of the band-edge
singularities to within a fraction of the superconducting energy gap $\Delta$
below the Fermi level. Our results provide compelling evidence that the
band-structure singularities near the Fermi level in the iron-based
superconductors must be explicitly accounted for in any attempt to understand
the mechanism of superconducting pairing in these materials.",1601.02686v1
2016-01-20,Orbital Order and Spin Nematicity in the Tetragonal Phase of Electron-doped Iron-Pnictides NaFe$_{1-x}$Co$_{x}$As,"In copper-oxide and iron-based high temperature (high-$T_{\rm c}$)
superconductors, many physical properties exhibit in-plane anisotropy, which is
believed to be caused by a rotational symmetry-breaking nematic order, whose
origin and its relationship to superconductivity remain elusive. In many
iron-pnictides, a tetragonal-to-orthorhombic structural transition temperature
$T_{\rm s}$ coincides with the magnetic transition temperature $T_{\rm N}$,
making the orbital and spin degrees of freedom highly entangled. NaFeAs is a
system where $T_{\rm s}$ = 54 K is well separated from $T_{\rm N}$ = 42 K,
which helps simplify the experimental situation. Here we report nuclear
magnetic resonance (NMR) measurements on NaFe$_{1-x}$Co$_x$As (0 $\leq x \leq$
0.042) that revealed orbital and spin nematicity occurring at a temperature
$T^{\rm *}$ far above $T_{\rm s}$ in the tetragonal phase. We show that the NMR
spectra splitting and its evolution can be explained by an incommensurate
orbital order that sets in below $T^{\rm *}$ and becomes commensurate below
$T_{\rm s}$, which brings about the observed spin nematicity.",1601.05293v1
2016-01-29,Weak-coupling superconductivity in a strongly correlated iron pnictide,"Iron-based superconductors have been found to exhibit an intimate interplay
of orbital, spin, and lattice degrees of freedom, dramatically affecting their
low-energy electronic properties, including superconductivity. Albeit the
precise pairing mechanism remains unidentified, several candidate interactions
have been suggested to mediate the superconducting pairing, both in the orbital
and in the spin channel. Here, we employ optical spectroscopy (OS),
angle-resolved photoemission spectroscopy (ARPES), ab initio band-structure,
and Eliashberg calculations to show that nearly optimally doped
NaFe$_{0.978}$Co$_{0.022}$As exhibits some of the strongest orbitally selective
electronic correlations in the family of iron pnictides. Unexpectedly, we find
that the mass enhancement of itinerant charge carriers in the strongly
correlated band is dramatically reduced near the $\Gamma$ point and attribute
this effect to orbital mixing induced by pronounced spin-orbit coupling.
Embracing the true band structure allows us to describe all low-energy
electronic properties obtained in our experiments with remarkable consistency
and demonstrate that superconductivity in this material is rather weak and
mediated by spin fluctuations.",1601.08195v1
2016-02-16,Surface terminations and layer-resolved spectroscopy in 122 iron pnictide superconductors,"The surface terminations of 122-type alkaline earth metal iron pnictides
AEFe2As2 (AE = Ca, Ba) are investigated with scanning tunneling
microscopy/spectroscopy (STM/STS). Cleaving these crystals at a cryogenic
temperature yields a large majority of terminations with atomically resolved
square-root-two (rt2) or 1*2 lattice, as well as the very rare terminations
with 1*1 symmetry. By means of lattice alignment and chemical marking, we
identify these terminations as rt2-AE, 1*2-As, and rt2-Fe surfaces,
respectively. Layer-resolved spectroscopy on these terminating surfaces reveals
a well-defined superconducting gap on the As terminations, while the gap
features become weaker and absent on AE and Fe terminations respectively. The
local gap features are hardly affected by the surface reconstruction on As or
AE surface, whereas a suppression of them along with the in-gap states can be
induced by As vacancies. The emergence of two impurity resonance peaks at +-2
meV is consistent with the sign-reversal pairing symmetry. The definite
identification of surface terminations and their spectroscopic signatures shall
provide a more comprehensive understanding of the high-temperature
superconductivity in multilayered iron pnictides.",1602.04937v1
2016-02-25,ARPES view of orbitally resolved quasiparticle lifetimes in iron pnictides,"We study with ARPES the renormalization and quasiparticle lifetimes of the
$d_{xy}$ and $d_{xz}$/$d_{yz}$ orbitals in two iron pnictides, LiFeAs and
Ba(Fe$_{0.92}$Co$_{0.08}$)$_2$As$_2$ (Co8). We find that both quantities depend
on orbital character rather than on the position on the Fermi Surface (for
example hole or electron pocket). In LiFeAs, the renormalizations are larger
for $d_{xy}$, while they are similar on both types of orbitals in Co8. The most
salient feature, which proved robust against all the ARPES caveats we could
think of, is that the lifetimes for $d_{xy}$ exhibit a markedly different
behavior than those for $d_{xz}$/$d_{yz}$. They have smaller values near $E_F$
and exhibit larger $\omega$ and temperature dependences. While the behavior of
$d_{xy}$ is compatible with a Fermi liquid description, it is not the case for
$d_{xz}$/$d_{yz}$. This situation should have important consequences for the
physics of iron pnictides, which have not been considered up to now. More
generally, it raises interesting questions on how a Fermi liquid regime can be
established in a multiband system with small effective bandwidths.",1602.07986v1
2016-03-07,The intercalation chemistry of layered iron chalcogenide superconductors,"The iron chalcogenides FeSe and FeS are superconductors composed of
two-dimensional sheets held together by van der Waals interactions, which makes
them prime candidates for the intercalation of various guest species. We review
the intercalation chemistry of FeSe and FeS superconductors and discuss their
synthesis, structure, and physical properties. Before we review the latest work
in this area, we provide a brief background on the intercalation chemistry of
other inorganic materials that exhibit enhanced superconducting properties upon
intercalation, which include the transition metal dichalcogenides, fullerenes,
and layered cobalt oxides. From past studies of these intercalated
superconductors, we discuss the role of the intercalates in terms of charge
doping, structural distortions, and Fermi surface reconstruction. We also
briefly review the physical and chemical properties of the host
materials---mackinawite-type FeS and $\beta$-FeSe. The three types of
intercalates for the iron chalcogenides can be placed in three categories: 1.)
alkali and alkaline earth cations intercalated through the liquid ammonia
technique; 2.) cations intercalated with organic amines such as
ethylenediamine; and 3.) layered hydroxides intercalated during hydrothermal
conditions. A recurring theme in these studies is the role of the intercalated
guest in electron doping the chalcogenide host and in enhancing the
two-dimensionality of the electronic structure by spacing the FeSe layers
apart. We end this review discussing possible new avenues in the intercalation
chemistry of transition metal monochalcogenides, and the promise of these
materials as a unique set of new inorganic two-dimensional systems.",1603.02334v1
2016-03-15,Iron in galaxy groups and clusters: Confronting galaxy evolution models with a newly homogenised dataset,"We present an analysis of the iron abundance in the hot gas surrounding
galaxy groups and clusters. To do this, we first compile and homogenise a large
dataset of 79 low-redshift (|z| = 0.03) systems (159 individual measurements)
from the literature. Our analysis accounts for differences in aperture size,
solar abundance, and cosmology, and scales all measurements using customised
radial profiles for the temperature (T), gas density, and iron abundance (Z).
We then compare this dataset to groups and clusters in the L-Galaxies galaxy
evolution model.
  Our homogenised dataset reveals a tight T-Z relation for clusters, with a
scatter in Z of only 0.10 dex and a slight negative gradient. After examining
potential measurement biases, we conclude that at least some of this negative
gradient has a physical origin. Our model suggests greater accretion of
hydrogen in the hottest systems, via stripping of gas from infalling
satellites, as a cause. At lower temperatures, L-Galaxies over-estimates Z in
groups, indicating that metal-rich gas removal (via e.g. AGN feedback) is
required.
  L-Galaxies provides a reasonable match to the observed Z in the intracluster
medium (ICM) of the hottest clusters from at least z ~ 1.3 to 0.3. This is
achieved without needing to modify any of the galactic chemical evolution (GCE)
model parameters. However, the Z in intermediate-temperature clusters appears
to be under-estimated in our model at z = 0. The merits and problems with
modifying the GCE modelling to correct this are discussed.",1603.04858v1
2016-03-16,Tracing the electronic pairing glue in unconventional superconductors via inelastic Scanning Tunneling Spectroscopy,"The origin of Cooper pairing in high-temperature superconductors, such as the
copper-oxide and iron-based system, is still under debate. High transition
temperatures together with unconventional pairing states support the picture of
an electronic pairing glue in the cuprates, where superconductivity is mediated
by collective bosonic excitations of the electron fluid. In other materials,
most importantly iron based systems with only hole or only electron pockets,
the microscopic origin is hotly debated. Scanning tunneling microscopy (STM)
has been shown to be a powerful experimental probe to detect electronic
excitations and further allows to deduce some fingerprints of bosonic
collective modes. Here, we demonstrate that the inclusion of inelastic tunnel
events is crucial for the interpretation of tunneling spectra and allows to
directly probe bosonic excitations via STM. We develop a model describing both
the elastic tunneling current, which displays the electronic spectral function,
and the inelastic current, that contains the information about the bosonic
spectrum, in the superconducting state. Adopting this extended tunneling
formalism we can naturally reproduce the tunneling spectra of various
unconventional superconductors and trace the occurring features back to an
opening of a spin gap in the superconducting state. More generally, our
approach is a strong argument in favour of a collective mode mediating the
pairing state in particular in iron-based systems. In particular, we conclude
that the debated pairing mechanism in LiFeSe is also of electronic origin with
sign-changing pairing symmetry.",1603.05288v3
2016-04-26,Surface Nematic Order in Iron Pnictides,"Electronic nematicity plays important role in iron-based superconductors.
These materials have layered structure and theoretical description of their
magnetic and nematic transitions has been well established in two-dimensional
approximation, i.e., when the layers can be treated independently. However, the
interaction between iron layers mediated by electron tunneling may cause
non-trivial three-dimensional behavior. Starting from the simplest model for
orbital nematic in a single layer, we investigate the influence of interlayer
tunneling on bulk nematic order and possible preemptive state where this order
is only formed near the surface.
  We found that the interlayer tunneling suppresses the bulk nematicity which
makes favorable formation of a surface nematic above the bulk transition
temperature. The purely electronic tunneling Hamiltonian, however, favors
alternating from layer-to-layer nematic order parameter in the bulk. The
uniform bulk state typically observed experimentally may be stabilized by the
coupling with the elastic lattice deformation. Depending on strength of this
coupling, we found three regimes: (i) surface nematic and alternating bulk
order, (ii) surface nematic and uniform bulk order, and (iii) uniform bulk
order without the intermediate surface phase. The intermediate surface-nematic
state may resolve the current controversy about the existence of the weak
""meta-nematic transition"" in the compound BaFe$_2$As$_{2-x}$P$_{x}$.",1604.07757v3
2016-05-28,"Hubbard interactions in iron-based pnictides and chalcogenides: Slater parametrization, screening channels and frequency dependence","We calculate the strength of the frequency-dependent on-site electronic
interactions in the iron pnictides LaFeAsO, BaFe2As2, BaRu2As2, and LiFeAs and
the chalcogenide FeSe from first principles within the constrained random phase
approximation. We discuss the accuracy of an atomic-like parametrization of the
two-index density-density interaction matrices based on the calculation of an
optimal set of three independent Slater integrals, assuming that the angular
part of the Fe-d localized orbitals can be described within spherical harmonics
as for isolated Fe atoms. We show that its quality depends on the ligand-metal
bonding character rather than on the dimensionality of the lattice: it is
excellent for ionic-like Fe-Se (FeSe) chalcogenides and a more severe
approximation for more covalent Fe-As (LaFeAsO, BaFe2As2) pnictides. We
furthermore analyze the relative importance of different screening channels,
with similar conclusions for the different pnictides but a somewhat different
picture for the benchmark oxide SrVO3: the ligand channel does not appear to be
dominant in the pnictides, while oxygen screening is the most important process
in the oxide. Finally, we analyze the frequency dependence of the interaction.
In contrast to simple oxides, in iron pnictides its functional form cannot be
simply modeled by a single plasmon, and the actual density of modes enters the
construction of an effective Hamiltonian determining the low-energy properties.",1605.08918v1
2016-06-15,Iron K$α$ line of Kerr black holes with scalar hair,"Recently, a family of hairy black holes in 4-dimensional Einstein gravity
minimally coupled to a complex, massive scalar field was discovered~\cite{hbh}.
Besides the mass $M$ and spin angular momentum $J$, these objects are
characterized by a Noether charge $Q$, measuring the amount of scalar hair,
which is not associated to a Gauss law and cannot be measured at spatial
infinity. Introducing a dimensionless scalar hair parameter $q$, ranging from 0
to 1, we recover (a subset of) Kerr black holes for $q=0$ and a family of
rotating boson stars for $q=1$. In the present paper, we explore the
possibility of measuring $q$ for astrophysical black holes with current and
future X-ray missions. We study the iron K$\alpha$ line expected in the
reflection spectrum of such hairy black holes and we simulate observations with
Suzaku and eXTP. As a proof of concept, we point out, by analyzing a sample of
hairy black holes, that current observations can already constrain the scalar
hair parameter $q$, because black holes with $q$ close to 1 would have iron
lines definitively different from those we observe in the available data. We
conclude that a detailed scanning of the full space of solutions, together with
data from the future X-ray missions, like eXTP, will be able to put relevant
constraints on the astrophysical realization of Kerr black holes with scalar
hair.",1606.04654v2
2016-07-05,Two new parent compounds for FeSe-based superconducting phases,"It is well established that the occurrence of superconductivity in iron
pnictides is closely related to the tetragonal to orthorhombic structural and
antiferromagnetic (AFM) phase transitions. It, however, has not been clear
whether the same scenario is appropriate for iron chalcogenide counterparts due
to the absence of parent compounds for the latter family of superconductors.
Here, we report the synthesis and structure determination of two novel phases
in ethylenediamine intercalated FeSe, one is tetragonal and the other
orthorhombic in room temperature, which can be stabilized with neutral spacer
layers. Both phases can be regarded as the parent compounds for
superconductivity as they are non-superconducting (non-SC) in pristine form and
superconducting (SC) with Tc up to 38K and 46K, respectively after Na doping,
and the switch between SC and no-SC is reversible. Moreover, the two non-SC
parent compounds show no evidence of long-range magnetic ordering down to 2K,
only with dynamic spin fluctuations at low temperatures, suggesting that no
competition between SC and AFM ordering. Our results reveal that undoped iron
selenides are quantum paramagnetic in ground state, implying that they are
distinct from their pnictide counterparts in pairing mechanism.",1607.01103v1
2016-07-11,Effect of local environment on moment formation in iron silicides,"The effect of local environment on the formation of magnetic moments on Fe
atoms in iron silicides are studied by combination of ab initio and model
calculations. The suggested model includes all Fe d- and Si p-orbitals,
intra-atomic Coulomb interactions, inter-atomic Fe-Fe exchange and hopping of
electrons to nearest and next nearest neighboring atoms and takes into account
all symmetries within the Slater-Koster scheme. The parameters of the model are
found from the requirement that self-consistent moments on atoms and density of
states found from ab initio and model calculations within the Hartree-Fock
approximation are close to each other as much as possible. Contrary to the
commonly accepted statement that an increase of the Si concentration within
nearest environment of Fe atoms in the ordered Fe3Si and FexSi1-x alloys leads
to a decrease of Fe magnetic moment we find that a crucial role in the
formation of magnetic moments is played by second coordination sphere of Fe
atoms. Particularly, the Fe atoms have higher magnetic moments in amorphous
films compared to the epitaxial ones due to decrease in the number of
iron-atoms in the next nearest environment. Both our model and ab initio
calculations confirm existence of known spin crossover with pressure and
predict second crossover at higher pressure",1607.02856v2
2016-07-12,"Simulation study of the correlation ($X_{max}^μ$, $N^μ$) in view of obtaining information on primary mass of the UHECRs","In this paper we study, using Monte Carlo simulations, the possibility to
discriminate the mass of the Ultra High Energy Cosmic Rays (UHECRs) by
combining information obtained from the maximum $X_{max}^{\mu}$ of the muon
production rate longitudinal profile of Extensive Air Showers (EAS) and the
number of muons, $N^{\mu}$, which hit an array of detectors located in the
horizontal plane. We investigate the sensitivity of the 2D distribution
$X_{max}^{\mu}$ versus $N^{\mu}$ to the mass of the primary particle generating
the air shower. To this purpose we analyze a set of CORSIKA showers induced by
protons and iron nuclei at energies of $10^{19}$eV and $10^{20}$eV, at five
angles of incidence, $0^{\circ}$, $37^{\circ}$, $48^{\circ}$, $55^{\circ}$ and
$60^{\circ}$. Using the simulations we obtain the 2D Probability Functions
$Prob(X_{max}^{\mu},N^{\mu} \ | \ p)$ and $Prob(X_{max}^{\mu},N^{\mu} \ | \
Fe)$ which give the probability that a shower induced by a proton or iron
nucleus contributes to a specific point on the plane ($X_{max}^{\mu}$,
$N^{\mu}$). Then we construct the probability functions $Prob(p\ | \
X_{max}^{\mu},N^{\mu})$ and $Prob(Fe \ | \ X_{max}^{\mu},N^{\mu})$ which give
the probability that a certain point on the plane ($X_{max}^{\mu}$, $N^{\mu}$)
corresponds to a shower initiated by a proton or an iron nucleus, respectively.
Finally, a test of this procedure using a Bayesian approach, confirms an
improved accuracy of the primary mass estimation in comparison with the results
obtained using only the $X_{max}^{\mu}$ distributions.",1607.03244v1
2016-07-17,Testing the Kerr metric with the iron line and the KRZ parametrization,"The spacetime geometry around astrophysical black holes is supposed to be
well approximated by the Kerr metric, but deviations from the Kerr solution are
predicted in a number of scenarios involving new physics. Broad iron K$\alpha$
lines are commonly observed in the X-ray spectrum of black holes and originate
by X-ray fluorescence of the inner accretion disk. The profile of the iron line
is sensitively affected by the spacetime geometry in the strong gravity region
and can be used to test the Kerr black hole hypothesis. In this paper, we
extend previous work in the literature. In particular: i) as test-metric, we
employ the parametrization recently proposed by Konoplya, Rezzolla, and
Zhidenko, which has a number of subtle advantages with respect to the existing
approaches; ii) we perform simulations with specific X-ray missions, and we
consider NuSTAR as a prototype of current observational facilities and eXTP as
an example of the next generation of X-ray observatories. We find a significant
difference between the constraining power of NuSTAR and eXTP. With NuSTAR, it
is difficult or impossible to constrain deviations from the Kerr metric. With
eXTP, in most cases we can obtain quite stringent constraints (modulo we have
the correct astrophysical model).",1607.04893v2
2016-08-19,Optical observation of spin-density-wave fluctuations in Ba122 iron-based superconductors,"In iron-based superconductors, a spin-density-wave (SDW) magnetic order is
suppressed with doping and unconventional superconductivity appears in close
proximity to the SDW instability. The optical response of the SDW order shows
clear gap features: substantial suppression in the low-frequency optical
conductivity, alongside a spectral weight transfer from low to high
frequencies. Here, we study the detailed temperature dependence of the optical
response in three different series of the Ba122 system
[Ba$_{1-x}$K$_{x}$Fe$_{2}$As$_{2}$, Ba(Fe$_{1-x}$Co$_{x}$)$_{2}$As$_{2}$ and
BaFe$_{2}$(As$_{1-x}$P$_{x}$)$_{2}$]. Intriguingly, we found that the
suppression of the low-frequency optical conductivity and spectral weight
transfer appear at a temperature $T^{\ast}$ much higher than the SDW transition
temperature $T_{SDW}$. Since this behavior has the same optical feature and
energy scale as the SDW order, we attribute it to SDW fluctuations.
Furthermore, $T^{\ast}$ is suppressed with doping, closely following the doping
dependence of the nematic fluctuations detected by other techniques. These
results suggest that the magnetic and nematic orders have an intimate
relationship, in favor of the magnetic-fluctuation-driven nematicity scenario
in iron-based superconductors.",1608.05474v1
2016-08-23,Non-LTE line formation of Fe in late-type stars - III. 3D non-LTE analysis of metal-poor stars,"As one of the most important elements in astronomy, iron abundance
determinations need to be as accurate as possible. We investigate the accuracy
of spectroscopic iron abundance analyses using archetypal metal-poor stars. We
perform detailed 3D non-LTE radiative transfer calculations based on 3D
hydrodynamic Stagger model atmospheres, and employ a new model atom that
includes new quantum-mechanical neutral hydrogen collisional rate coefficients.
With the exception of the red giant HD122563, we find that the 3D non-LTE
models achieve Fe i/Fe ii excitation and ionization balance as well as not
having any trends with equivalent width to within modelling uncertainties of
0.05 dex, all without having to invoke any microturbulent broadening; for
HD122563 we predict that the current best parallax-based surface gravity is
over-estimated by 0.5 dex. Using a 3D non-LTE analysis, we infer iron
abundances from the 3D model atmospheres that are roughly 0.1 dex higher than
corresponding abundances from 1D MARCS model atmospheres; these differences go
in the same direction as the non-LTE effects themselves. We make available
grids of departure coefficients, equivalent widths and abundance corrections,
calculated on 1D MARCS model atmospheres and horizontally- and
temporally-averaged 3D Stagger model atmospheres.",1608.06390v2
2016-09-04,Iron K$α$ line of boson stars,"The present paper is a sequel to our previous work [Y. Ni et al., JCAP 1607,
049 (2016)] in which we studied the iron K$\alpha$ line expected in the
reflection spectrum of Kerr black holes with scalar hair. These metrics are
solutions of Einstein's gravity minimally coupled to a massive, complex scalar
field. They form a continuous bridge between a subset of Kerr black holes and a
family of rotating boson stars depending on one extra parameter, the
dimensionless scalar hair parameter $q$, ranging from 0 (Kerr black holes) to 1
(boson stars). Here we study the limiting case $q=1$, corresponding to rotating
boson stars. For comparison, spherical boson stars are also considered. We
simulate observations with XIS/Suzaku. Using the fact that current observations
are well fit by the Kerr solution and thus requiring that acceptable
alternative compact objects must be compatible with a Kerr fit, we find that
some boson star solutions are relatively easy to rule out as potential
candidates to explain astrophysical black holes, while other solutions, which
are neither too dilute nor too compact are more elusive and we argue that they
cannot be distinguished from Kerr black holes by the analysis of the iron line
with current X-ray facilities.",1609.00901v2
2016-10-13,TOPoS: III. An ultra iron-poor multiple CEMP system,"One of the primary objectives of the TOPoS survey is to search for the most
metal-poor stars. Our search has led to the discovery of one of the most
iron-poor objects known, SDSS\,J092912.32+023817.0. This object is a multiple
system, in which two components are clearly detected in the spectrum. We have
analysed 16 high-resolution spectra obtained using the UVES spectrograph at the
ESO 8.2m VLT telescope to measure radial velocities and determine the chemical
composition of the system. Cross correlation of the spectra with a synthetic
template yields a double-peaked cross-correlation function (CCF) for eight
spectra, and in one case there is evidence for the presence of a third peak.
Chemical analysis of the spectrum obtained by averaging all the spectra for
which the CCF showed a single peak found that the iron abundance is
[Fe/H]=-4.97. The system is also carbon enhanced with [C/Fe]=+3.91 (A(C)=7.44).
From the permitted oxygen triplet we determined an upper limit for oxygen of
[O/Fe]<+3.52 such that C/O>1.3. We are also able to provide more stringent
upper limits on the Sr and Ba abundances ([Sr/Fe]<+0.70, and [Ba/Fe]<+1.46,
respectively).",1610.04106v1
2016-11-01,Experimental evidence for the importance of Hund's exchange interaction for the incoherence of the charge carriers in iron-based superconductors,"Angle-resolved photoemission spectroscopy (ARPES) is used to study the
scattering rates of charge carriers from the hole pockets near Gamma in the
iron-based high-Tc hole doped superconductors KxBa1-xFe2As2 x=0.4 and
KxEu1-xFe2As2 x=0.55$ and the electron doped compound Ba(Fe1-xCox)2As2 x=0.075.
The scattering rate for any given band is found to depend linearly on energy,
indicating a non-Fermi liquid regime. The scattering rates in the hole-doped
compound are considerably larger than those in the electron-doped compounds. In
the hole-doped systems the scattering rate of the charge carriers of the inner
hole pocket is about three times bigger than the binding energy indicating that
the spectral weight is heavily incoherent. The strength of the scattering rates
and the difference between electron and hole doped compounds signals the
importance of Hund's exchange coupling for correlation effects in these
iron-based high-Tc superconductors. The experimental results are in qualitative
agreement with theoretical calculations in the framework of combined density
functional dynamical mean-field theory.",1611.00239v1
2016-11-10,A new migration mechanism for oversized solutes in cubic lattices: correlation effects,"Recent ab-initio calculations showed that oversized solute atoms (OSA) in BCC
and FCC iron exhibit a very strong attraction with a nearby vacancy (V) at
first neighbour distance (1NN). The attraction it is so large that the 1NN pair
OSA+V is no longer stable and relaxes spontaneously towards a new configuration
where the OSA sits in the middle of the bond, the two ends of which are
decorated with two half-vacancies (V/2). Taking into account the formation of
this complex V/2+OSA+V/2 in the migration process has never been done before:
it requires a new formulation of correlation effects. This is the aim of the
present contribution which establishes the expression of the diffusion
coefficient of the OSA and evaluates exactly the correlation factor in BCC and
FCC lattices, thanks to the introduction of macrojumps. The formalism is
applied to the case of Y in BCC iron and its results are compared to those
obtained by previous authors. It is shown that the smallness of the correlation
factor is not due to the transport mechanism of the OSA but only to the jump
frequencies of the vacancy in the vicinity of the OSA. This smallness of the
correlation factor is however overcompensated by a large macrojump frequency,
and, as a result, the Y atom diffuses more rapidly than iron at all
temperatures by orders of magnitude in the two structures.",1611.03230v2
2016-11-10,Lattice Parameters Guide Superconductivity in Iron-Arsenides,"The discovery of superconducting materials has led to their use in
technological marvels such as magnetic-field sensors in MRI machines, powerful
research magnets, short transmission cables, and high-speed trains. Despite
such applications, the uses of superconductors are not widespread because they
function much below room-temperature, hence the costly cooling. Since the
discovery of Cu- and Fe-based high-temperature superconductors (HTS), much
intense effort has tried to explain and understand the superconducting
phenomenon. While no exact explanations are given, several trends are reported
in relation to the materials basis in magnetism and spin excitations. In fact,
most HTS have antiferromagnetic undoped 'parent' materials that undergo a
superconducting transition upon small chemical substitutions in them. As it is
currently unclear which 'dopants' can favor superconductivity, this manuscript
investigates crystal structure changes upon chemical substitutions, to find
clues in lattice parameters for the superconducting occurrence. We review the
chemical substitution effects on the crystal lattice of iron-arsenide-based
crystals (2008 to present). We note that (a) HTS compounds have nearly
tetragonal structures with a-lattice parameter close to 4 A, and (b)
superconductivity can depend strongly on the c-lattice parameter changes with
chemical substitution. For example, a decrease in c-lattice parameter is
required to induce 'in-plane' superconductivity. The review of lattice
parameter trends in iron-arsenides presented here should guide synthesis of new
materials and provoke theoretical input, giving clues for HTS.",1611.03400v1
2016-12-01,Spin anisotropy due to spin-orbit coupling in optimally hole-doped Ba$_{0.67}$K$_{0.33}$Fe$_{2}$As$_{2}$,"We use polarized inelastic neutron scattering to study the temperature and
energy dependence of spin space anisotropies in the optimally hole-doped iron
pnictide Ba$_{0.67}$K$_{0.33}$Fe$_{2}$As$_{2}$ ($T_{{\rm c}}=38$ K). In the
superconducting state, while the high-energy part of the magnetic spectrum is
nearly isotropic, the low-energy part displays a pronouced anisotropy,
manifested by a $c$-axis polarized resonance. We also observe that the spin
anisotropy in superconducting Ba$_{0.67}$K$_{0.33}$Fe$_{2}$As$_{2}$ extends to
higher energies compared to electron-doped BaFe$_{2-x}TM_{x}$As$_{2}$ ($TM=$Co,
Ni) and isovalent-doped BaFe$_{2}$As$_{1.4}$P$_{0.6}$, suggesting a connection
between $T_{\rm c}$ and the energy scale of the spin anisotropy. In the normal
state, the low-energy spin anisotropy for optimally hole- and electron-doped
iron pnictides onset at temperatures similar to the temperatures at which the
elastoresistance deviate from Curie-Weiss behavior, pointing to a possible
connection between the two phenomena. Our results highlight the relevance of
the spin-orbit coupling to the superconductivity of the iron pnictides.",1612.00379v2
2016-12-22,Unravelling incommensurate magnetism and its emergence in iron-based superconductors,"We focus on a broad class of tetragonal itinerant systems sharing a tendency
towards the spontaneous formation of incommensurate magnetism with ordering
wavevectors $\mathbf{Q}_{1,2}=(\pi-\delta,0)/(0,\pi-\delta)$ or
$\mathbf{Q}_{1,2}=(\pi,\delta)/(-\delta,\pi)$. Employing a Landau approach, we
obtain the generic magnetic phase diagram and identify the leading
instabilities near the paramagnetic-magnetic transition. Nine distinct magnetic
phases exist that either preserve or violate the assumed $C_4$-symmetry of the
paramagnetic phase. These are single- and double-$\mathbf{Q}$ phases consisting
of magnetic stripes, helices and whirls, either in an individual or coexisting
manner. These nine phases can be experimentally distinguished by polarized
neutron scattering, or, for example, by combining measurements of the induced
charge order and magnetoelectric coupling. Within two representative
five-orbital models, suitable for BaFe$_2$As$_2$ and LaFeAsO, we find that the
incommensurate magnetic phases discussed here are accessible in iron-based
superconductors. Our investigation unveils a set of potential candidates for
the unidentified $C_2$-symmetric magnetic phase that was recently observed in
Ba$_{1-x}$Na$_x$Fe$_{2}$As$_{2}$. Among the phases stabilized we find a
spin-whirl crystal, which is a textured magnetic $C_4$-symmetric phase. The
possible experimental observation of textured magnetic orders in iron-based
superconductor, opens new directions for realizing intrinsic topological
superconductors.",1612.07633v3
2017-01-04,Origin of the Galactic Diffuse X-ray Emission: Iron K-shell Line Diagnostics,"This paper reports detailed K-shell line profiles of iron (Fe) and nickel
(Ni) of the Galactic Center X-ray Emission (GCXE), Galactic Bulge X-ray
Emission (GBXE), Galactic Ridge X-ray Emission (GRXE), magnetic Cataclysmic
Variables (mCVs), non-magnetic Cataclysmic Variables (non-mCVs), and coronally
Active Binaries (ABs). For the study of the origin of the GCXE, GBXE, and GRXE,
the spectral analysis is focused on equivalent widths of the Fe K$\alpha$, Fe
He$\alpha$, and Fe Ly$\alpha$ lines. The global spectrum of the GBXE is
reproduced by a combination of the mCVs, non-mCVs, and ABs spectra. On the
other hand, the GRXE spectrum shows significant data excesses at the Fe
K$\alpha$ and Fe He$\alpha$ line energies. This means that additional
components other than mCVs, non-mCVs, and ABs are required, which have
symbiotic phenomena of cold gas and very high-temperature plasma. The GCXE
spectrum shows larger excesses than those found in the GRXE spectrum at all the
K-shell lines of iron and nickel. Among them the largest ones are the Fe
K$\alpha$, Fe He$\alpha$, Fe Ly$\alpha$, and Fe Ly$\beta$ lines. Together with
the fact that the scale heights of the Fe K$\alpha$, Fe He$\alpha$, and Fe
Ly$\alpha$ lines are similar to that of the central molecular zone (CMZ), the
excess components would be related to high-energy activity in the extreme
envelopment of the CMZ.",1701.00884v1
2017-02-07,Supernova of 1006 (G327.6+14.6),"SN 1006 (G327.6+14.6) was the brightest supernova (SN) witnessed in human
history. As of one thousand years later, it stands out as an ideal laboratory
to study Type Ia SNe and shocks in supernova remnants (SNRs). The present state
of knowledge about SN 1006 is reviewed in this article. No star consistent with
a surviving companion expected in the traditional single-degenerate scenario
has been found, which favors a double-degenerate scenario for the progenitor of
SN 1006. Both unshocked and shocked SN ejecta have been probed through
absorption lines in ultraviolet spectra of background sources and thermal X-ray
emission, respectively. The absorption studies suggest that the amount of iron
is < 0.16 M_sun, which is significantly less than the range for normal SNe Ia.
On the other hand, analyses of X-ray data reveal the distribution of shocked
ejecta to be highly asymmetric especially for iron. Therefore, most of iron
might have escaped from the ultraviolet background sources. Another important
aspect with SN 1006 is that it was the first SNR in which synchrotron X-ray
emission was detected from shells of the remnant, providing evidence that
electrons are accelerated up to ~100 TeV energies at forward shocks. The
bilateral symmetry of the synchrotron emission (bright in northeastern and
southwestern limbs) is likely due to a polar cap geometry. The broadband
(radio, X-ray, and gamma-ray) spectral energy distribution suggests that the
gamma-ray emission is predominantly leptonic. At the northwestern shock,
evidence for extreme, but less than mass proportional, temperature
non-equilibration has been found by optical, ultraviolet, and X-ray
observations.",1702.02054v1
2017-02-13,Electron-Capture and Low-Mass Iron-Core-Collapse Supernovae: New Neutrino-Radiation-Hydrodynamics Simulations,"We present new 1D (spherical) and 2D (axisymmetric) simulations of
electron-capture (EC) and low-mass iron-core-collapse supernovae (SN). We
consider six progenitor models: the ECSN progenitor from Nomoto (1984, 1987);
two ECSN-like low-mass low-metallicity iron core progenitors from Heger
(private communication); and the 9-, 10-, and 11-$M_\odot$ (zero-age main
sequence) progenitors from Sukhbold et al. (2016). We confirm that the ECSN and
ESCN-like progenitors explode easily even in 1D with explosion energies of up
to a 0.15 Bethes ($1 {\rm B} \equiv 10^{51}\ {\rm erg}$), and are a viable
mechanism for the production of very low-mass neutron stars. However, the 9-,
10-, and 11-$M_\odot$ progenitors do not explode in 1D and are not even
necessarily easier to explode than higher-mass progenitor stars in 2D. We study
the effect of perturbations and of changes to the microphysics and we find that
relatively small changes can result in qualitatively different outcomes, even
in 1D, for models sufficiently close to the explosion threshold. Finally, we
revisit the impact of convection below the protoneutron star (PNS) surface. We
analyze, 1D and 2D evolutions of PNSs subject to the same boundary conditions.
We find that the impact of PNS convection has been underestimated in previous
studies and could result in an increase of the neutrino luminosity by up to
factors of two.",1702.03927v2
2017-02-25,Serum protein resistant behavior of multisite-bound poly(ethylene glycol) chains onto iron oxide surfaces,"Recent surveys have shown that the number of nanoparticle-based formulations
actually used at the clinical level is significantly lower than expected a
decade ago. One reason for this is that the nanoparticle physicochemical
properties fall short for handling the complexity of biological environments
and for preventing nonspecific protein adsorption. In this study, we address
the issue of the interactions of plasma proteins with polymer coated surfaces.
To this aim, we use a non-covalent grafting-to method to functionalize iron
oxide sub-10 nm nanoparticles and iron oxide flat substrates, and compare their
protein responses. The functionalized copolymers consist in alternating
poly(ethylene glycol) (PEG) chains and phosphonic acid grafted on the same
backbone. Quartz Crystal Microbalance with dissipation was used to monitor the
polymer adsorption kinetics and to evaluate the resistance to protein
adsorption. On flat substrates, functionalized PEG copolymers adsorb and form a
brush in the moderate or in the highly stretched regimes, with density between
0.15 and 1.5 nm-2. PEG layers using phosphonic acid as linkers exhibit
excellent protein resistance. In contrast, layers prepared with carboxylic acid
as grafting agent exhibit mitigated protein responses and layer
destructuration. The present study establishes a correlation between the
long-term stability of PEG coated particles in biofluids and the protein
resistance of surfaces coated with the same polymers.",1702.07857v1
2017-03-11,Non-LTE line formation of Fe in late-type stars IV: Modelling of the solar centre-to-limb variation in 3D,"Our ability to model the shapes and strengths of iron lines in the solar
spectrum is a critical test of the accuracy of the solar iron abundance, which
sets the absolute zero-point of all stellar metallicities. We use an extensive
463-level Fe atom with new photoionisation cross-sections for FeI as well as
quantum mechanical calculations of collisional excitation and charge transfer
with neutral hydrogen; the latter effectively remove a free parameter that has
hampered all previous line formation studies of Fe in non-local thermodynamic
equilibrium (NLTE). For the first time, we use realistic 3D NLTE calculations
of Fe for a quantitative comparison to solar observations. We confront our
theoretical line profiles with observations taken at different viewing angles
across the solar disk with the Swedish 1-m Solar Telescope. We find that 3D
modelling well reproduces the observed centre-to-limb behaviour of spectral
lines overall, but highlight aspects that may require further work, especially
cross-sections for inelastic collisions with electrons. Our inferred solar iron
abundance is log(eps(Fe))=7.48+-0.04.",1703.04027v1
2017-03-25,Electronic structure of FeS,"Here we report the electronic structure of FeS, a recently identified
iron-based superconductor. Our high-resolution angle-resolved photoemission
spectroscopy studies show two hole-like ($\alpha$ and $\beta$) and two
electron-like ($\eta$ and $\delta$) Fermi pockets around the Brillouin zone
center and corner, respectively, all of which exhibit moderate dispersion along
$k_z$. However, a third hole-like band ($\gamma$) is not observed, which is
expected around the zone center from band calculations and is common in
iron-based superconductors. Since this band has the highest renormalization
factor and is known to be the most vulnerable to defects, its absence in our
data is likely due to defect scattering --- and yet superconductivity can exist
without coherent quasiparticles in the $\gamma$ band. This may help resolve the
current controversy on the superconducting gap structure of FeS. Moreover, by
comparing the $\beta$ bandwidths of various iron chalcogenides, including FeS,
FeSe$_{1-x}$S$_x$, FeSe, and FeSe$_{1-x}$ Te$_x$, we find that the $\beta$
bandwidth of FeS is the broadest. However, the band renormalization factor of
FeS is still quite large, when compared with the band calculations, which
indicates sizable electron correlations. This explains why the unconventional
superconductivity can persist over such a broad range of isovalent substitution
in FeSe$_{1-x}$Te$_{x}$ and FeSe$_{1-x}$S$_{x}$.",1703.08682v1
2017-04-03,Nucleosynthesis in thermonuclear supernovae,"The explosion energy of thermonuclear (Type Ia) supernovae is derived from
the difference in nuclear binding energy liberated in the explosive fusion of
light 'fuel' nuclei, predominantly carbon and oxygen, into more tightly bound
nuclear 'ash' dominated by iron and silicon group elements. The very same
explosive thermonuclear fusion event is also one of the major processes
contributing to the nucleosynthesis of the heavy elements, in particular the
iron-group elements. For example, most of the iron and manganese in the sun and
its planetary system were produced in thermonuclear supernovae. Here, we review
the physics of explosive thermonuclear burning in carbon-oxygen white dwarf
material and the methodologies utilized in calculating predicted
nucleosynthesis from hydrodynamic explosion models. While the dominant
explosion scenario remains unclear, many aspects of the nuclear combustion and
nucleosynthesis are common to all models and must occur in some form in order
to produce the observed yields. We summarize the predicted nucleosynthetic
yields for existing explosion models, placing particular emphasis on
characteristic differences in the nucleosynthetic signatures of the different
suggested scenarios leading to Type Ia supernovae. Following this, we discuss
how these signatures compare with observations of several individual
supernovae, remnants, and the composition of material in our galaxy and galaxy
clusters.",1704.00415v1
2017-04-07,High Radiation Pressure on Interstellar Dust Computed by Light-Scattering Simulation on Fluffy Agglomerates of Magnesium-silicate Grains with Metallic-iron Inclusions,"Recent space missions have provided information on the physical and chemical
properties of interstellar grains such as the ratio $\beta$ of radiation
pressure to gravity acting on the grains in addition to the composition,
structure, and size distribution of the grains. Numerical simulation on the
trajectories of interstellar grains captured by Stardust and returned to Earth
constrained the $\beta$ ratio for the Stardust samples of interstellar origin.
However, recent accurate calculations of radiation pressure cross sections for
model dust grains have given conflicting stories in the $\beta$ ratio of
interstellar grains. The $\beta$ ratio for model dust grains of so-called
""astronomical silicate"" in the femto-kilogram range lies below unity, in
conflict with $\beta \sim 1$ for the Stardust interstellar grains. Here, I
tackle this conundrum by re-evaluating the $\beta$ ratio of interstellar grains
on the assumption that the grains are aggregated particles grown by coagulation
and composed of amorphous MgSiO$_{3}$ with the inclusion of metallic iron. My
model is entirely consistent with the depletion and the correlation of major
rock-forming elements in the Local Interstellar Cloud surrounding the Sun and
the mineralogical identification of interstellar grains in the Stardust and
Cassini missions. I find that my model dust particles fulfill the constraints
on the $\beta$ ratio derived from not only the Stardust mission but also the
Ulysses and Cassini missions. My results suggest that iron is not incorporated
into silicates but exists as metal, contrary to the majority of interstellar
dust models available to date.",1704.02066v2
2017-05-05,X-ray Magnetic and Natural Circular Dichroism from first principles: Calculation of K- and L1-edge spectra,"An efficient first principles approach to calculate X-ray magnetic circular
dichroism (XMCD) and X-ray natural circular dichroism (XNCD) is developed and
applied in the near edge region at the K-and L1-edges in solids. Computation of
circular dichroism requires precise calculations of X-ray absorption spectra
(XAS) for circularly polarized light. For the derivation of the XAS cross
section, we used a relativistic description of the photon-electron interaction
that results in an additional term in the cross-section that couples the
electric dipole operator with an operator $\mathbf{\sigma}\cdot
(\mathbf{\epsilon} \times \mathbf{r})$ that we name spin-position. The
numerical method relies on pseudopotentials, on the gauge including projected
augmented wave method and on a collinear spin relativistic description of the
electronic structure. We apply the method to the calculations of K-edge XMCD
spectra of ferromagnetic iron, cobalt and nickel and of I L1-edge XNCD spectra
of $\alpha$-LiIO3, a compound with broken inversion symmetry. For XMCD spectra
we find that, even if the electric dipole term is the dominant one, the
electric quadrupole term is not negligible (8% in amplitude in the case of
iron). The term coupling the electric dipole operator with the spin-position
operator is significant (28% in amplitude in the case of iron). We obtain a
sum-rule relating this new term to the spin magnetic moment of the p-states. In
$\alpha$-LiIO3 we recover the expected angular dependence of the XNCD spectra.",1705.02192v1
2017-05-05,Constraining The Single-Degenerate Channel of Type Ia Supernovae With Stable Iron-Group Elements in SNR 3C 397,"Recent Suzaku X-ray spectra of SNR 3C 397 indicate enhanced stable iron-group
element abundances of Ni, Mn, Cr, and Fe. Seeking to address key questions
about the progenitor and explosion mechanism of 3C 397, we compute
nucleosynthetic yields from a suite of multidimensional hydrodynamics models in
the near-Chandrasekhar mass, single-degenerate paradigm for supernova Type Ia.
Varying the progenitor white dwarf internal structure, composition, ignition,
and explosion mechanism, we find the best match to the observed iron-peak
elements of 3C 397 are dense (central density $\ge$ 6$\times$10$^{9}$ g
cm$^{-3}$), low-carbon white dwarfs that undergo a weak, centrally-ignited
deflagration, followed by a subsequent detonation. The amount of $^{56}$Ni
produced is consistent with a normal or bright normal supernova Type Ia. A pure
deflagration of a centrally-ignited, low central density ($\simeq$
2$\times$10$^{9}$ g cm$^{-3}$) progenitor white dwarf, frequently considered in
the literature, is also found to produce good agreement with 3C 397
nucleosynthetic yields, but leads to a subluminous SN Ia event, in conflict
with X-ray linewidth data. Additionally, in contrast to prior work which
suggested a large super-solar metallicity for the white dwarf progenitor for
SNR 3C 397, we find satisfactory agreement for solar and sub-solar metallicity
progenitors. We discuss a range of implications our results have for the
single-degenerate channel.",1705.02339v1
2017-05-09,Chemical abundances in the nucleus of the Sagittarius dwarf spheroidal galaxy,"We present Iron, Magnesium, Calcium, and Titanium abundances for 235 stars in
the central region of the Sagittarius dwarf spheroidal galaxy (within 9.0
arcmin ~70 pc from the center) from medium-resolution Keck/DEIMOS spectra. All
the considered stars belong to the massive globular cluster M54 or to the
central nucleus of the galaxy (Sgr,N). In particular we provide abundances for
109 stars with [Fe/H] > -1.0, more than doubling the available sample of
spectroscopic metallicity and alpha-elements abundance estimates for Sgr dSph
stars in this metallicity regime. Also, we find the first confirmed member of
the Sagittarius dwarf spheroidal with [Fe/H]< -2.0 based on analysis of iron
lines. We find for the first time a metallicity gradient in the Sgr,N
population, whose peak iron abundance goes from [Fe/H]=-0.38 for R < 2.5 arcmin
to [Fe/H]=-0.57 for 5.0 < R < 9.0 arcmin. On the other hand the trends of
[Mg/Fe], [Ca/Fe], and [Ti/Fe] with [Fe/H] are the same over the entire region
explored by our study. We reproduce the observed chemical patterns of the
Sagittarius dwarf spheroidal as a whole with a chemical evolution model
implying a high mass progenitor ( M_(DM)=6 X 10^{10} Msun ) and a significant
event of mass-stripping occurred a few Gyr ago, presumably starting at the
first peri-Galactic passage after infall.",1705.03251v1
2017-05-12,Orbital-selective Mott phase in multiorbital models for iron pnictides and chalcogenides,"There is increasing recognition that the multiorbital nature of the 3d
electrons is important to the proper description of the electronic states in
the normal state of the iron-based superconductors. Earlier studies of the
pertinent multiorbital Hubbard models identified an orbital-selective Mott
phase, which anchors the orbital-selective behavior seen in the overall phase
diagram. An important characteristics of the models is that the orbitals are
kinetically coupled -- i.e. hybridized -- to each other, which makes the
orbital-selective Mott phase especially nontrivial. A U(1) slave-spin method
was used to analyze the model with nonzero orbital-level splittings. Here we
develop a Landau free-energy functional to shed further light on this issue. We
put the microscopic analysis from the U(1) slave-spin approach in this
perspective, and show that the intersite spin correlations are crucial to the
renormalization of the bare hybridization amplitude towards zero and the
concomitant realization of the orbital-selective Mott transition. Based on this
insight, we discuss additional ways to study the orbital-selective Mott physics
from a dynamical competition between the interorbital hybridization and
collective spin correlations. Our results demonstrate the robustness of the
orbital-selective Mott phase in the multiorbital models appropriate for the
iron-based superconductors.",1705.04541v1
2017-07-04,Apparent Trend of the Iron Abundance in NGC 3201: the Same Outcome with Different Data,"We further study the unusual trend we found at statistically significant
levels in some globular clusters, including NGC 3201: a decreasing iron
abundance in red giants towards the cluster centers. We first show that
recently published new estimates of iron abundance in the cluster reproduce
this trend, in spite of the authors' statement about no metallicity spread due
to a low scatter achieved in the [FeII/H] ratio. The mean of [FeII/H] within $R
\sim 2'$ from the cluster center is lower, by $\Delta$[FeII/H] = 0.05$\pm$0.02
dex, than in the outer region, in agreement with our original estimate for a
much larger sample size within $R \approx 9'$. We found that an older dataset
traces the trend to a much larger radial distance, comparable with the cluster
tidal radius, at $\Delta$[Fe/H]$\sim$0.2 dex due to higher metallicity of
distant stars. We conclude the trend is reproduced by independent datasets and
find that it is accompanied with both a notable same-sign trend of oxygen
abundance which can vary by up to $\Delta$[O/Fe]$\sim$0.3 dex within $R \approx
9'$, and opposite-sign trend of sodium abundance.",1707.00786v1
2017-07-05,Switching Magnetism and Superconductivity with Spin-Polarized Current in Iron-Based Superconductor,"We have explored a new mechanism for switching magnetism and
superconductivity in a magnetically frustrated iron-based superconductor using
spin-polarized scanning tunneling microscopy (SPSTM). Our SPSTM study on single
crystal Sr$_2$VO$_3$FeAs shows that a spin-polarized tunneling current can
switch the Fe-layer magnetism into a non-trivial $C_4$ (2$\times$2) order, not
achievable by thermal excitation with unpolarized current. Our tunneling
spectroscopy study shows that the induced $C_4$ (2$\times$2) order has
characteristics of plaquette antiferromagnetic order in Fe layer and strongly
suppressed superconductivity. Also, thermal agitation beyond the bulk Fe spin
ordering temperature erases the $C_4$ state. These results suggest a new
possibility of switching local superconductivity by changing the symmetry of
magnetic order with spin-polarized and unpolarized tunneling currents in
iron-based superconductors.",1707.01191v2
2017-07-10,Explosive nucleosynthesis of ultra-stripped Type Ic supernovae: application to light trans-iron elements,"We investigate the explosive nucleosynthesis during two dimensional
neutrino-driven explosion of ultra-stripped Type Ic supernovae evolved from
1.45 and 1.5 M$_\odot$ CO stars. These supernovae explode with the explosion
energy of $\sim 10^{50}$ erg and release $\sim 0.1$ M$_\odot$ ejecta. The light
trans-iron elements Ga-Zr are produced in the neutrino-irradiated ejecta. The
abundance distribution of these elements has a large uncertainty because of the
uncertainty of the electron fraction of the neutrino-irradiated ejecta. The
yield of the elements will be less than 0.01 M$_\odot$. Ultra-stripped
supernova and core-collapse supernova evolved from a light CO core can be main
sources of the light trans-iron elements. They could also produce neutron-rich
nuclei $^{48}$Ca. The ultra-stripped supernovae eject $^{56}$Ni of $\sim$ 0.006
- 0.01 M$_\odot$. If most of neutrino-irradiated ejecta is proton-rich,
$^{56}$Ni will be produced more abundantly. The light curves of these
supernovae indicate sub-luminous fast decaying explosion with the peak
magnitude of about $-15$ - $-16$. Future observations of ultra-stripped
supernovae could give a constraint to the event rate of a class of neutron star
mergers.",1707.02685v1
2017-07-26,Shock-darkening in ordinary chondrites: determination of the pressure-temperature conditions by shock physics mesoscale modeling,"We determined the shock-darkening pressure range in ordinary chondrites using
the iSALE shock physics code. We simulated planar shock waves on a mesoscale in
a sample layer at different nominal pressures. Iron and troilite grains were
resolved in a porous olivine matrix in the sample layer. We used equations of
state (Tillotson EoS and ANEOS) and basic strength and thermal properties to
describe the material phases. We used Lagrangian tracers to record peak shock
pressures in each material unit. The post-shock temperatures (and the fractions
of tracers experiencing temperatures above the melting point) for each material
were estimated after the passage of the shock wave and after reflections of the
shock at grain boundaries in the heterogeneous materials. The results showed
that shock-darkening, associated with troilite melt and the onset of olivine
melt, happened between 40 and 50 GPa - with 52 GPa being the pressure at which
all tracers in the troilite material reach the melting point. We demonstrate
the difficulties of shock heating in iron and also the importance of porosity.
Material impedances, grain shapes and the porosity models available in the
iSALE code are discussed. We also discussed possible not-shock-related triggers
for iron melt.",1707.08422v1
2017-08-03,Orbital-selective spin excitation of a magnetic porphyrin,"Scattering of electrons by localized spins is the ultimate process enabling
electrical detection and control of the magnetic state of a spin-doped
material. At the molecular scale, this scattering is mediated by the electronic
orbitals hosting the spin. Here we report the selective excitation of a
molecular spin by electrons tunneling through different molecular orbitals.
Spatially-resolved tunneling spectra on iron porphyrins on Au(111) reveal that
the inelastic spin excitation extends beyond the iron site. The inelastic
features also change shape and symmetry along the molecule. Combining DFT
simulations with a phenomenological scattering model, we show that the
extension and lineshape variations of the inelastic signal are due to
excitation pathways assisted by different frontier orbitals, each of them with
a different degree of hybridization with the surface. By selecting the
intramolecular site for electron injection, the relative weight of iron and
pyrrole orbitals in the tunneling process is modified. In this way, the spin
excitation mechanism, reflected by its spectral lineshape, changes depending on
the degree of localization and energy alignment of the chosen molecular
orbital.",1708.01268v2
2017-08-09,Measurement of the Iron Spectrum in Cosmic Rays with VERITAS,"The elemental energy spectra of cosmic rays play an important role in
understanding their acceleration and propagation. Most current results are
obtained either from direct measurements by balloon or satellite detectors, or
from indirect measurements by air shower detector arrays on the Earth's
surface. Imaging Air Cherenkov Telescopes (IACTs), used primarily for gamma-ray
astronomy, can also be used for cosmic-ray physics. They are able to measure
Cherenkov light emitted both by heavy nuclei and by secondary particles
produced in their air showers, and are thus sensitive to the charge and energy
of cosmic ray particles with energies of tens to hundreds of TeV.
  A measurement of the energy spectrum of iron nuclei, based on 71 hours of
data taken by the VERITAS array of IACTs between 2009 and 2012, will be
presented. The energy and other properties of the primary particle are
reconstructed using a template-based likelihood fit. The event selection makes
use of direct Cherenkov light, which is emitted by the primary particle before
starting the air shower. A multivariate method is used to estimate the
remaining background. Using these methods, the iron spectrum was measured in
the energy range from 20 TeV to 500 TeV.",1708.02960v2
2017-09-05,On the Iron Abundance Anomaly in K-dwarf and Hyades Stars,"Using standard 1D-LTE model atmosphere analysis, we provide an in-depth
investigation of iron abundance as derived from neutral and singly ionization
iron lines (Fe {\scriptsize{I, II}}) in nearby star clusters. Specifically, we
replicate the discrepancy regarding $\Delta$[Fe/H], wherein the difference of
Fe {\scriptsize{II}} - Fe {\scriptsize{I}} increases for stars of the same
cluster with decreasing $T_\mathrm{eff}$, reaching an astonishing 1.0 dex at
$T_\mathrm{eff}$ $\thicksim$ 4000 K. Previous studies have investigated this
anomaly in the Pleiades and Hyades clusters with no concrete solution. In this
analysis, we probe two samples: 63 wide binary field stars where the primary
star is of sun-like temperatures and the secondary is a K-dwarf, ranging from
4231 K $\leq$ $T_\mathrm{eff}$ $\leq$ 6453 K, and 33 Hyades stars of
temperatures 4268 K $\leq$ $T_\mathrm{eff}$ $\leq$ 6072 K. Previous studies
have found discrepancies on the order of 1.0 dex. However, we find that these
studies have neglected line-blending effects of certain Fe {\scriptsize{II}}
lines, namely $\lambda$ = \{4508.29 \AA, 4993.34 \AA, 5197.58 \AA, 5325.55 \AA,
5425.26 \AA, 6456.38 \AA\}. When these lines are removed from the line-list, we
find $\Delta$[Fe/H] decreases to $\thicksim$ 0.6 dex in the field binaries and
$\thicksim$ 0.3 dex in the Hyades. The reason for this remaining trend is
investigated by probing NLTE effects, as well as age and activity
considerations using Ca {\scriptsize{II}} H+K emission and Li absorption, but
these results appear to be small to negligible.",1709.01244v1
2017-09-21,Analysis of Ultra High Energy Muons at the INO-ICAL Using Pair-Meter Technique,"The proposed ICAL detector at INO is a large sized underground magnetized
iron detector. ICAL is designed to reconstruct muon momentum using magnetic
spectrometers. Energy measurement using magnets fail for muons in TeV range,
since the angular deflection of the muon in the magnetic field is negligible
and the muon tracks become nearly straight. A new technique for measuring the
energy of muons in the TeV range is used by the CCFR neutrino detector, known
as the Pair-Meter technique. This technique estimates muon energy from
measurements of the energy deposited by the muon in many layers of an
iron-calorimeter through e$^+$ and e$^-$ pair production. In this work we have
performed Geant4 based preliminary analysis for iron plates and have
demonstrated the observational feasibility of very high energy muons
(1TeV-1000TeV) in a large mass underground detector operating as a pair-meter.
This wide range of energy spectrum will be helpful for studying the cosmic rays
in the Knee region and an understanding of the atmospheric neutrino flux for
the present and future ultra high-energy atmospheric neutrino experiments.",1709.07445v1
2017-10-04,Pop III $\textit{i}$-process Nucleosynthesis and the Elemental Abundances of SMSS J0313-6708 and the Most Iron-Poor Stars,"We have investigated a highly energetic H-ingestion event during shell He
burning leading to H-burning luminosities of $\log(L_\mathrm{H}/\mathrm{\Lsun})
\sim 13$ in a $45 \Msun$ Pop III massive stellar model. In order to track the
nucleosynthesis which may occur in such an event, we run a series of
single-zone nucleosynthesis models for typical conditions found in the stellar
evolution model. Such nucleosynthesis conditions may lead to
$\textit{i}-$process neutron densities of up to $ \sim 10^{13}
\mathrm{cm}^{-3}$. The resulting simulation abundance pattern, where Mg comes
from He burning and Ca from the $\textit{i}$ process, agrees with the general
observed pattern of the most iron-poor star currently known, SMSS
J031300.36-670839.3. However, Na is also efficiently produced in these $i$
process conditions, and the prediction exceeds observations by $\sim 2.5
\unitstyle{dex}$. While this probably rules out this model for SMSS
J031300.36-670839.3, the typical $\textit{i}-$process signature of combined He
burning and $\textit{i}$ process of higher than solar [Na/Mg], [Mg/Al] and low
[Ca/Mg] is reproducing abundance features of the two next most iron-poor stars
HE\,1017-5240 and HE\,1327-2326 very well. The $i$ process does not reach Fe
which would have to come from a low level of additional enrichment.
$\textit{i}$ process in hyper-metal poor or Pop III massive stars may be able
to explain certain abundance patterns observed in some of the most-metal poor
CEMP-no stars.",1710.01763v4
2017-10-07,Simulations of Electron Capture and Low-Mass Iron Core Supernovae,"The evolutionary pathways of core-collapse supernova progenitors at the
low-mass end of the spectrum are beset with major uncertainties. In recent
years, a variety of evolutionary channels has been discovered in addition to
the classical electron capture supernova channel of super-AGB stars. The few
available progenitor models at the low-mass end have been studied with great
success in supernova simulations as the peculiar density structure makes for
robust neutrino-driven explosions in this mass range. Detailed nucleosynthesis
calculations have been conducted both for models of electron capture supernovae
and low-mass iron core supernovae and revealed an interesting production of the
lighter trans-iron elements (such as Zn, Sr, Y, Zr) as well as rare isotopes
like Ca-48 and Fe-60. We stress the need to explore the low-mass end of the
supernova spectrum further and link various observables to understand the
diversity of explosions in this regime.",1710.02641v1
2017-10-24,Recent advances in iron-based superconductors toward applications,"Iron with a large magnetic moment was widely believed to be harmful to the
emergence of superconductivity because of the competition between the static
ordering of electron spins and the dynamic formation of electron pairs (Cooper
pairs). Thus, the discovery of a high critical temperature (Tc) iron-based
superconductor (IBSC) in 2008 was accepted with surprise in the condensed
matter community and rekindled extensive study globally. IBSCs have since grown
to become a new class of high-Tc superconductors next to the high-Tc cuprates
discovered in 1986. The rapid research progress in the science and technology
of IBSCs over the past decade has resulted in the accumulation of a vast amount
of knowledge on IBSC materials, mechanisms, properties, and applications with
the publication of more than several tens of thousands of papers. This article
reviews recent progress in the technical applications (bulk magnets, thin
films, and wires) of IBSCs in addition to their fundamental material
characteristics. Highlights of their applications include high-field bulk
magnets workable at 15-25 K, thin films with high critical current density (Jc)
> 1 MA/cm2 at ~10 T and 4 K, and an average Jc of 1.3*104 A/cm2 at 10 T and 4 K
achieved for a 100-m-class-length wire. These achievements are based on the
intrinsically advantageous properties of IBSCs such as the higher
crystallographic symmetry of the superconducting phase, higher critical
magnetic field, and larger critical grain boundary angle to maintain high Jc.
These properties also make IBSCs promising for applications using high magnetic
fields.",1710.08574v1
2017-10-24,Mössbauer study of Eu0.57Ca0.43Fe2As2 and Eu0.73Ca0.27(Fe0.87Co0.13)2As2: A comparison to 122 iron-based superconductors parent compounds EuFe2As2 and CaFe2As2,"57Fe and 151Eu Moessbauer spectra were obtained versus temperature for
Eu0.57Ca0.43Fe2As2 compound with 3d and 4f magnetic order and
Eu0.73Ca0.27(Fe0.87Co0.13)2As2 re-entrant superconductor, where the finite
resistivity reappears while approaching the ground state. They were compared
with previously obtained spectra for parent compounds EuFe2As2 and CaFe2As2. It
was found that substitution beyond the Fe-As layers does not lead to the
rotation (canting) of the Eu2+ magnetic moments and does not generate Eu3+
states. On the other hand, re-entrant superconductor exhibits rotation
(canting) of the Eu2+ moments on the c-axis of the unit cell leading to the
transferred hyperfine magnetic field on iron nuclei. Divalent europium orders
magnetically within the bulk of the re-entrant superconducting phase. The
re-entrant superconductor remains in the inhomogeneous state close to the
ground state with about 27 % of the volume being free of 3d magnetism, while
the remainder exhibits weak spin density wave. Those two regions slightly
differ by the electric field gradient and electron density on iron nuclei.",1710.08887v3
2017-11-01,Spectroscopic properties of a two-dimensional time-dependent Cepheid model II. Determination of stellar parameters and abundances,"Standard spectroscopic analyses of variable stars are based on hydrostatic
one-dimensional model atmospheres. This quasi-static approach has theoretically
not been validated. We aim at investigating the validity of the quasi-static
approximation for Cepheid variables. We focus on the spectroscopic
determination of the effective temperature $T_\mathrm{eff}$, surface gravity
$\log \,g$, microturbulent velocity $\xi_\mathrm{t}$, and a generic metal
abundance $\log\,A$ -- here taken as iron. We calculate a grid of 1D
hydrostatic plane-parallel models covering the ranges in effective temperature
and gravity encountered during the evolution of a two-dimensional
time-dependent envelope model of a Cepheid computed with the
radiation-hydrodynamics code CO5BOLD. We perform 1D spectral syntheses for
artificial iron lines in local thermodynamic equilibrium varying the
microturbulent velocity and abundance. We fit the resulting equivalent widths
to corresponding values obtained from our dynamical model. For the
four-parametric case, the stellar parameters are typically underestimated
exhibiting a bias in the iron abundance of $\approx-0.2\,\mbox{dex}$. To avoid
biases of this kind it is favourable to restrict the spectroscopic analysis to
photometric phases $\phi_\mathrm{ph}\approx0.3\ldots 0.65$ using additional
information to fix effective temperature and surface gravity. Hydrostatic 1D
model atmospheres can provide unbiased estimates of stellar parameters and
abundances of Cepheid variables for particular phases of their pulsations. We
identified convective inhomogeneities as the main driver behind potential
biases. For obtaining a complete view on the effects when determining stellar
parameters with 1D models, multi-dimensional Cepheid atmosphere models are
necessary for variables of longer period than investigated here.",1711.00236v2
2017-11-08,Chemical Study of the Metal-rich Globular Cluster NGC 5927,"Globular Clusters (GCs) are natural laboratories where stellar and chemical
evolution can be studied in detail. In addition, their chemical patterns and
kinematics can tell us wich Galactic structure (Disk, Bulge, Halo or
extragalactic) the cluster belongs to. NGC 5927 is one of most metal-rich GCs
in the Galaxy and its kinematics links it to the Thick Disk. We present
abundance analysis based on high resolution spectra of 7 giant stars. The data
were obtained using FLAMES/UVES spectrograph mounted on UT2 telescope of the
European Southern Observatory. The principal motivation of this work is to
perform a wide and detailed chemical abundance analysis of the cluster and look
for possible Multiple Populations (MPs). We determined stellar parameters and
measured 22 elements corresponding to light (Na, Al), alpha (O, Mg, Si, Ca,
Ti), iron-peak (Sc, V, Cr, Mn, Fe, Co, Ni, Cu, Zn) and heavy elements (Y, Zr,
Ba, Ce, Nd, Eu). We found a mean iron content of [Fe/H]=-0.47 $\pm$0.02 (error
on the mean). We confirm the existence of MPs in this GC with an O-Na
anti-correlation, and moderate spread in Al abundances. We estimate a mean
[$\alpha$/Fe]=0.25 $\pm$0.08. Iron-peak elements shows no significant spread.
The [Ba/Eu] ratios indicate a predominant contribution from SNeII for the
formation of the cluster.",1711.03176v1
2017-12-25,Discovery of 6.4 keV line and soft X-ray emissions from G323.7$-$1.0 with Suzaku,"In this paper, the Suzaku X-ray data of the Galactic Supernova Remnant (SNR)
candidate G323.7$-$1.0 are analyzed to search for X-ray emission.
Spatially-extended enhancements in the 6.4 keV line and in soft X-rays are
found inside or on the radio shell. The soft X-ray enhancement would be the
hottest part of the shell-like X-ray emission along the radio shell. The 6.4
keV line enhancement is detected at a significance level of $4.1 \sigma$. The
lower limit of the equivalent width (EW) is 1.2 keV. The energy centroid of the
6.4 keV line is $6.40 \pm 0.04$ keV, indicating that the iron is less ionized
than the Ne-like state. If the 6.4 keV line originates from ionizing
non-equilibrium thermal plasma, presence of iron-rich ejecta in a
low-ionization state is required, which is disfavored by the relatively old age
of the SNR. The 6.4 keV line enhancement would be due to K-shell ionization of
iron atoms in a dense interstellar medium by high-energy particles. Since there
is no irradiating X-ray source, the origin of the 6.4 keV line enhancement is
not likely the photoionization. The large EW can only be explained by K-shell
ionization due to cosmic-ray protons with an energy of $\sim 10$ MeV, which
might be generated by the shock acceleration in G323.7$-$1.0.",1712.09024v1
2018-02-06,Odd and even modes of neutron spin resonance in the bilayer iron-based superconductor CaKFe$_4$As$_4$,"We report an inelastic neutron scattering study on the spin resonance in the
bilayer iron-based superconductor CaKFe$_4$As$_4$. In contrast to its
quasi-two-dimensional electron structure, three strongly $L$-dependent modes of
spin resonance are found below $T_c=35$ K. The mode energies are below and
linearly scale with the total superconducting gaps summed on the nesting hole
and electron pockets, essentially in agreement with the results in cuprate and
heavy fermion superconductors. This observation supports the sign-reversed
Cooper pairing mechanism under multiple pairing channels and resolves the
long-standing puzzles concerning the broadening and dispersive spin resonance
peak in iron pnictides. More importantly, the triple resonant modes can be
classified into odd and even symmetries with respect to the distance of Fe-Fe
planes within the Fe-As bilayer unit. Thus, our results closely resemble those
in the bilayer cuprates with nondegenerate spin excitations, suggesting that
these two high-$T_c$ superconducting families share a common nature.",1802.01901v2
2018-03-02,Neutron spin resonance in the 112-type iron-based superconductor,"We use inelastic neutron scattering to study the low-energy spin excitations
of 112-type iron pnictide Ca$_{0.82}$La$_{0.18}$Fe$_{0.96}$Ni$_{0.04}$As$_{2}$
with bulk superconductivity below $T_c=22$ K. A two-dimensional spin resonance
mode is found around $E=$ 11 meV, where the resonance energy is almost
temperature independent and linearly scales with $T_c$ along with other
iron-based superconductors. Polarized neutron analysis reveals the resonance is
nearly isotropic in spin space without any $L$ modulations. Due to the unique
monoclinic structure with additional zigzag arsenic chains, the As $4p$
orbitals contribute to a three-dimensional hole pocket around $\Gamma$ point
and an extra electron pocket at $X$ point. Our results suggest that the energy
and momentum distribution of spin resonance does not directly response to the
$k_z$ dependence of fermiology, and the spin resonance intrinsically is a
spin-1 mode from singlet-triplet excitations of the Cooper pairs in the case of
weak spin-orbital coupling.",1803.00779v2
2018-04-12,Lateral manipulation with combined atomic force and scanning tunneling microscopy using CO-terminated tips,"CO-terminated tips currently provide the best spatial resolution obtainable
in atomic force microscopy. Due to their chemical inertness, they allow to
probe interactions dominated by Pauli repulsion. The small size and inertness
of the oxygen front atom yields unprecedented resolution of organic molecules,
metal clusters and surfaces. We study the capability of CO-terminated tips to
laterally manipulate single iron adatoms on the Cu(111) surface with combined
atomic force and scanning tunneling microscopy at 7\,K. Furthermore, we find
that even a slight asymmetry of the tip results in a distortion of the lateral
force field. In addition, the influence of the tilt of the CO tip on the
lateral force field is inverted compared to the use of a monoatomic metal tip
which we can attribute to the inverted dipole moment of a CO tip with respect
to a metal tip. Moreover, we demonstrate atom-by-atom assembly of iron clusters
with CO tips while using the high-resolution capability of the CO tips in
between to determine the arrangement of the individual iron atoms within the
cluster. Additionally, we were able to laterally manipulate single copper and
silicon adatoms without changing or losing the CO from the tip's apex.",1804.04382v3
2018-05-03,Uncertainties in s-process nucleosynthesis in low mass stars determined from Monte Carlo variations,"The main s-process taking place in low mass stars produces about half of the
elements heavier than iron. It is therefore very important to determine the
importance and impact of nuclear physics uncertainties on this process. We have
performed extensive nuclear reaction network calculations using individual and
temperature-dependent uncertainties for reactions involving elements heavier
than iron, within a Monte Carlo framework. Using this technique, we determined
the uncertainty in the main s-process abundance predictions due to nuclear
uncertainties link to weak interactions and neutron captures on elements
heavier than iron. We also identified the key nuclear reactions dominating
these uncertainties. We found that $\beta$-decay rate uncertainties affect only
a few nuclides near s-process branchings, whereas most of the uncertainty in
the final abundances is caused by uncertainties in neutron capture rates,
either directly producing or destroying the nuclide of interest. Combined total
nuclear uncertainties due to reactions on heavy elements are in general small
(less than 50%). Three key reactions, nevertheless, stand out because they
significantly affect the uncertainties of a large number of nuclides. These are
$^{56}$Fe(n,$\gamma$), $^{64}$Ni(n,$\gamma$), and $^{138}$Ba(n,$\gamma$). We
discuss the prospect of reducing uncertainties in the key reactions identified
in this study with future experiments.",1805.01250v1
2018-05-20,High-pressure effects on isotropic superconductivity in the iron-free layered pnictide superconductor BaPd2As2,"While the layered 122 iron arsenide superconductors are highly anisotropic,
unconventional, and exhibit several forms of electronic orders that coexist or
compete with superconductivity in different regions of their phase diagrams, we
find in the absence of iron in the structure that the superconducting
characteristics of the end member BaPd2As2 are surprisingly conventional. Here
we report on complementary measurements of specific heat, magnetic
susceptibility, resistivity measurements, Andreev spectroscopy, and synchrotron
high pressure x-ray diffraction measurements supplemented with theoretical
calculations for BaPd2As2. Its superconducting properties are completely
isotropic as demonstrated by the critical fields, which do not depend on the
direction of the applied field. Under the application of high pressure, Tc is
linearly suppressed, which is the typical behavior of classical phonon-mediated
superconductors with some additional effect of a pressure-induced decrease in
the electronic density of states and the electron-phonon coupling parameters.
Structural changes in the layered BaPd2As2 have been studied by means of
angle-dispersive diffraction in a diamond-anvil cell. At 12 GPa and 24.2 GPa we
observed pressure induced lattice distortions manifesting as the discontinuity
and, hence discontinuity in the Birch-Murnaghan equation of state. The bulk
modulus is B0=40(6) GPa below 12 GPa and B0=142(3) GPa below 27.2 GPa.",1805.07838v1
2018-05-24,Antiferromagnetically assisted electron-phonon coupling and spin-lattice interaction in Fe-based superconductors,"We present a theoretical ab-initio approach that allows us to explicitly
calculate the superconducting transition temperatures (Tc) of the iron-based
superconductors of LaFeAsO1-xFx, SmFeAsO1-xFx, NdFeAsO1-xFx, Ba1-xKxFe2As2,
FeSe and LiFeAs that fit perfectly with the experiments. We consider recent
evidence that electron-phonon coupling may have been underestimated previously,
and a prediction that antiferromagnetism can greatly enhance electron-phonon
coupling through localized iron d orbitals. We then include the contribution of
these localized orbitals in a McMillan formalism. In addition, we take into
account the spin-lattice interaction between the spin-polarized electrons at
the Fermi surface and the iron orbitals in combination with a modified exchange
Hamiltonian involving a ferrimagnetic coupling between Fe and As. With this
approach we can accurately calculate the Tc of FeSe (11 family), LiFeAs (111
family), LaFeAsO0.9F0.1 (1111 family) and BaFe2As2 (122 family) as a function
of pressure. In addition, we also obtain the correct doping dependence of Tc of
LaFeAsO0.9F0.1 (1111 family) and BaFe2As2 (122 family).",1805.09754v5
2018-05-25,Room Temperature Magnetic Order in Air-Stable Ultra-Thin Iron Oxide,"Certain two-dimensional (2D) materials exhibit intriguing properties such as
valley polarization, ferroelectricity, superconductivity and charge-density
waves. Many of these materials can be manually assembled into atomic-scale
multilayer devices under ambient conditions, owing to their exceptional
chemical stability. Efforts have been made to add a magnetic degree of freedom
to these 2D materials via defects, but only local magnetism has been achieved.
Only with the recent discoveries of 2D materials supporting intrinsic
ferromagnetism have stacked spintronic devices become realistic. Assembling 2D
multilayer devices with these ferromagnets under ambient conditions remains
challenging due to their sensitivity to environmental degradation, and magnetic
order at room temperature is rare in van der Waals materials. Here, we report
the growth of air-stable ultra-thin epsilon-phase iron oxide crystals that
exhibit magnetic order at room temperature. These crystals require no
passivation and can be prepared in large quantity by cost-effective chemical
vapor deposition (CVD). We find that the epsilon phase, which is energetically
unfavorable and does not form in bulk, can be easily made in 2D down to a seven
unit-cell thickness. Magneto-optical Kerr effect (MOKE) magnetometry of
individual crystals shows that even at this ultrathin limit the epsilon phase
exhibits robust magnetism with coercive fields of hundreds of mT. These
measurements highlight the advantages of ultrathin iron oxide as a promising
candidate towards air-stable 2D magnetism and integration into 2D spintronic
devices.",1805.10372v1
2018-06-21,A numerical study on the softening process of iron ore particles in the cohesive zone of an experimental blast furnace using a coupled CFD-DEM method,"Reduced iron-bearing materials start softening in the cohesive zone of a
blast furnace due to the high temperature and the weight of the burden above.
Softening process causes a reduction of void space between particles. As a
result, the pressure drop and gas flow change remarkably in this particular
zone. As a consequence, it has a significant influence on the performance of a
blast furnace and is needed to be fully characterized. For this reason, the gas
rheology along with the deformation of the particles and the heat transfer
between particle-particle and particle-gas should be adequately described. In
this paper, the eXtended Discrete Element Method (XDEM), as a CFD-DEM approach
coupled with the heat transfer, is applied to model complex gas- solid flow
during the softening process of pre-reduced iron ore pellets in an Experimental
Blast Furnace (EBF). The particle deformation, displacement, temperature, and
gas pressure drop and flow under conditions relevant to the EBF operations are
examined. Moreover, to accurately capture the high gas velocity inlet, a
dual-grid multi-scale approach is applied. The approach and findings are
helpful to understand the effect of the softening process on the pressure drop
and gas flow in the cohesive zone of the blast furnace.",1806.08114v1
2018-07-02,Time-Variability of equivalent width of 6.4 keV line from the Arches Complex: reflected X-rays or charged particles?,"Molecular gas in Arches cloud located near the Arches cluster is one of the
emitters of K-$\alpha$ line of neutral iron and X-ray continuum in the Galactic
center (GC). Similarly to the cloud Sgr B2, another well-known emitter of the
iron line in the GC, the Arches cloud demonstrates temporal decline of the
X-ray emission. The most natural origin of this emission is irradiation of
primary photons of an X-ray flare from a distant source, most likely Sgr A*.
However, recent observations of the Arches cloud discovered variations of
equivalent width of the 6.4 keV iron line, which indicated that the X-ray
emission from the cloud is a combination of two components with different
origin and different equivalent width, one of which is time-variable, while the
other is stationary during the period of observations. We considered two
different scenarios: a) this emission is formed by reflection from two clouds,
which are at some distance from each other, when they are irradiated by two
different flares; and b) the other scenario assumes a combination of X-ray
fluxes produced in the same cloud by reflection of primary photons and by
subrelativistic cosmic rays. We present restrictions for both model and
conditions at which these scenarios can be realized. Although none of the
models can be completely ruled out, we find that the X-ray reflection model
requires less assumption and therefore is the most viable.",1807.00526v1
2018-07-24,Orbital selectivity versus Pomeranchuk instability in the iron-chalcogenide superconductors: A two-loop renormalization group study,"We perform a two-loop renormalization group (RG) analysis of a 2D effective
multiband model, which is relevant for describing the low-energy properties of
some iron-chalcogenide superconducting materials. Crucial ingredients in this
analysis are the calculation of higher-order contributions in the RG scheme
that go beyond the widely-used parquet approximation and the consequent
inclusion of nontrivial self-energy effects of the model that yield an
anisotropic renormalization of the quasiparticle weight in the system. The
motivation of our work is the experimental discovery by Sprau et al. (2017)
that orbitally-selective renormalization of the quasiparticle weight in the
Hund's metal phase at moderate temperatures underpins the highly unusual gap in
the superconducting phase of the FeSe compound at lower temperatures. One
prediction we arrive here is that the underlying origin of nematicity in these
systems may indeed come from orbital-selectivity, instead of a Pomeranchuk
instability in the $d_{\pm}$ channel. This orbital selectivity is driven by the
presence of stripe-type antiferromagnetic fluctuations in the model. Therefore,
we argue that the present RG results may provide a scenario from a
weak-to-moderate coupling perspective, in which the role of orbital selectivity
to describe the physical properties of some iron-chalcogenide superconductors
is emphasized.",1807.09007v2
2018-08-09,Blocking of iron magnetic moments and Spin density wave in FeTi2S4 and Fe2TiS4,"Iron-titanium sulfides FeTi2S4 and Fe2TiS4 have been structurally and
magnetically characterized using powder X Ray Diffraction with Rietveld
refinement method and 57Fe M\""ossbauer spectroscopy at variable temperature.
Both sulfides have the same crystallographic phase, based on the monoclinic
Cr3S4 type structure and vary in atomic coordinates; FeTi2S4 retains the ideal
atomic positions proposed for the Cr3S4 phase, while in Fe2TiS4 the metal
displacements from ideal sites are noticeable. M\""ossbauer spectra reveal
different magnetic behaviors; in FeTi2S4 there is a transition from
paramagnetic to magnetic ordering at temperature Tc = 145 K, giving rise to
unusually low hyperfine magnetic field of 2.5 T (at 77 K) if compared with
values of iron magnetic moments reported previously, this behavior is explained
on the basis of blocking Fe localized magnetic moments by the Spin density wave
(SDW) originated from 3d Ti atoms. In Fe2TiS4 a transition from paramagnetic to
(SDW) arises at Tc = 290 K, the SDW is spread in both Fe and Ti metals through
[101] crystallographic plane and undergoes a transition of first order from
Incommensurate SDW (ISWD) to Commensurate SDW (CSDW) at TIC = 255 K. The atomic
positions in the unit cell are correlated to the magnetic behavior in both
sulfides.",1808.03362v1
2018-08-22,Coexistence of ferromagnetic and stripe-type antiferromagnetic spin fluctuations in YFe$_2$Ge$_2$,"We report neutron scattering measurements of single-crystalline YFe$_2$Ge$_2$
in the normal state, which has the same crystal structure to the 122 family of
iron pnictide superconductors. YFe$_2$Ge$_2$ does not exhibit long range
magnetic order, but exhibits strong spin fluctuations. Like the iron pnictides,
YFe$_2$Ge$_2$ displays anisotropic stripe-type antiferromagnetic spin
fluctuations at ($\pi$, $0$, $\pi$). More interesting, however, is the
observation of strong spin fluctuations at the in-plane ferromagnetic
wavevector ($0$, $0$, $\pi$). These ferromagnetic spin fluctuations are
isotropic in the ($H$, $K$) plane, whose intensity exceeds that of stripe spin
fluctuations. Both the ferromagnetic and stripe spin fluctuations remain
gapless down to the lowest measured energies. Our results naturally explain the
absence of magnetic order in YFe$_2$Ge$_2$ and also imply that the
ferromagnetic correlations may be a key ingredient for iron-based materials.",1808.07262v1
2018-08-26,Phase transition in CaFeAsH: bridging 1111 and 122 iron-based superconductors,"Iron-based superconductors can be categorized as two types of parent
compounds by considering the nature of their temperature-induced phase
transitions; namely, first order transitions for 122- and 11-type compounds and
second-order transitions for 1111-type compounds. This work examines the
structural and magnetic transitions (ST and MT) of CaFeAsH by specific heat,
X-ray diffraction, neutron diffraction, and electrical resistivity
measurements. Heat capacity measurements revealed a second-order phase
transition accompanies an apparent single peak at 96 K. However, a clear ST
from the tetragonal to orthorhombic phase and a MT from the paramagnetic to
antiferromagnetic phase were detected. The structural (Ts) and N\'eel
temperatures (TN) were respectively determined to be 95(2) and 96 K by X-ray
and neutron diffraction and resistivity measurements. This small temperature
difference, Ts - TN, was attributed to strong magnetic coupling in the
inter-layer direction owing to CaFeAsH having the shortest lattice constant c
among parent 1111-type iron arsenides. Considering that a first-order
transition takes place in 11- and 122-type compounds with a short inter-layer
distance, we conclude that the nature of the ST and MT in CaFeAsH is
intermediate in character, between the second-order transition for 1111-type
compounds and the first-order transition for other 11- and 122-type compounds.",1808.08564v1
2018-09-23,"Electronic structure and spin dynamics of ACo2As2 (A=Ba, Sr, Ca)","The electronic structures, charge and spin dynamics of the cobalt pnictide
compounds ACo2As2 (A=Ba, Sr, Ca) in the paramagnetic state are investigated by
using density functional theory combined with dynamical mean-field theory. In
contrast to their iron counterparts, these cobalt pnictide compounds have
three-dimensional electronic structures and strong ferromagnetic low-energy
spin excitations. The Co 3d eg orbitals dominate the electronic states around
the Fermi level and have stronger electronic correlation strength than the Co
3d t2g orbitals. The overall electronic correlation strength is much weaker
than that in the iron arsenides, however, the most strongly correlated Co 3d
x2-y2 orbital, especially in CaCo2As2, has electronic correlation strength
comparable to Fe 3d t2g orbitals in iron arsenides. ACo2As2 (A=Ba, Sr, Ca)
shows similar electronic structures where a conduction band of primarily Co 3d
x2-y2 orbital character is close to a Van Hove singularity around the
Brillouin-zone corner, which promotes ferromagnetic low-energy spin
excitations. Originated from its increased nearest-neighbor Co-Co distance and
significantly reduced As height from the Co plane, the strong electronic
correlation strength and close proximity to the Van Hove singularity of the Co
3d x2-y2 orbital in CaCo2As2 is responsible for its unique A-type
antiferromagnetic order observed in experiments. In comparison, despite
substantial ferromagnetic low-energy spin excitations, BaCo2As2 and SrCo2As2
remain paramagnetic down to very low temperature because the Co 3d x2-y2
orbital has weaker electronic correlation strength and is further away from the
Van Hove singularity.",1809.08550v1
2018-10-15,The Limited Contribution of Low- and High-Luminosity Gamma-Ray Bursts to Ultra-High Energy Cosmic Rays,"The acceleration site for ultra-high energy cosmic rays (UHECR) is still an
open question despite extended research. In this paper, we reconsider the
prompt phase of gamma-ray bursts (GRBs) as a possible candidate for this
acceleration and constrain the maximum proton energy in optically thin
synchrotron and photospheric models, using properties of the prompt photon
spectra. We find that neither of the models favour acceleration of protons to
$10^{20}$ eV in high-luminosity bursts. We repeat the calculations for
low-luminosity GRBs (llGRBs) considering both protons and completely stripped
iron and find that the highest obtainable energies are $< 10^{19}$ eV and $<
10^{20}$ eV for protons and iron respectively, regardless of the model. We
conclude therefore that for our fiducial parameters, GRBs, including
low-luminosity bursts, contribute little to none to the UHECR observed. We
further constrain the conditions necessary for an association between UHECR and
llGRBs and find that iron can be accelerated to $10^{20}$ eV in photospheric
models, given very efficiency acceleration and/or a small fractional energy
given to a small fraction of accelerated electrons. This will necessarily
result in high prompt optical fluxes, and the detection of such a signal could
therefore be an indication of successful UHECR acceleration at the source.",1810.06579v2
2018-10-24,Simulation of the electromagnetic wall response during Vertical Displacement Events (VDE) in ITER tokamak,"The key basis for tokamak plasma disruption modeling is to understand how
currents flow to the plasma facing surfaces during plasma disruption events. In
ITER tokamak, the occurrence of a limited number of major disruptions will
definitively damage the chamber with no possibility to restore the device. In
the current exchange plasma-wall-plasma, according to the Helmholtz
decomposition theorem, our surface current density in the conducting shell -
the unknown of our problem - being a vector field twice continuously
differentiable in 3D, has been splited into two components: an irrotational
(curl-free) vector field and a solenoidal (divergence-free) vector field.
Developing a weak formulation form and minimizing the correspondent energy
functionals in a Finite Element approach, we have obtained the space and time
distribution of the surface currents. We verified successfully our numerical
simulation with an analytical solution with pure homogeneous Neumann B.C. and
satisfying the necessary existence condition. By considering the iron core
presence in JET tokamak, we have split the magnetization currents - the
unknowns in some integral equations - into two components, the first producing
a magnetic field in the iron region only and the second producing a magnetic
field in the vacuum, obtaining thus a better evaluation of the influence of the
iron core on the plasma equilibrium. To reduce the influence of the
singularities appearing during the surface currents determination in multiply
connected domains (L-shaped domains) we have used a conformal transformation
method.",1810.10277v1
2018-11-07,Stabilizing spin systems via symmetrically tailored RKKY interactions,"The spin of a single atom adsorbed on a substrate is a promising building
block for future spintronics and quantum computation schemes. To process spin
information and also for increased magnetic stability, these building blocks
have to be coupled. For a single atom, a high symmetry of the environment is
known to lead to increased spin stability. However, little is known about the
role of the nature and symmetry of the magnetic couplings. Here, we study
arrays of atomic spins coupled via the ubiquitous Ruderman-Kittel-Kasuya-Yosida
(RKKY) interaction, focusing on its two anisotropic parts: the
Dzyaloshinskii-Moriya (DM) and the symmetric anisotropic exchange interactions.
First, we show that the high spin stability of an iron trimer can be remotely
detected by a nearby iron atom, and how the DM interaction can lead to its
destabilization. Second, we find that adding more nearby iron atoms almost
always leads to a destabilization of the trimer, due to a non-local effective
transverse anisotropy originating in the symmetric anisotropic exchange
interaction. This transverse anisotropy can be quenched only for highly
symmetric structures, for which the spin lifetime of the array is increased by
orders of magnitude.",1811.02807v1
2018-11-20,Topological Fermi-arc surface resonances in bcc iron,"The topological classification of matter has been extended to include
semimetallic phases characterized by the presence of topologically protected
band degeneracies. In Weyl semimetals, the foundational gapless topological
phase, chiral degeneracies are isolated near the Fermi level and give rise to
the Fermi-arc surface states. However, it is now recognized that chiral
degeneracies are ubiquitous in the band structures of systems with broken
spatial inversion ($\mathcal{P}$) or time-reversal ($\mathcal{T}$) symmetry.
This leads to a broadly defined notion of topological metals, which implies the
presence of disconnected Fermi surface sheets characterized by non-zero Chern
numbers inherited from the enclosed chiral degeneracies. Here, we address the
possibility of experimentally observing surface-related signatures of chiral
degeneracies in metals. As a representative system we choose bcc iron, a
well-studied archetypal ferromagnetic metal with two nontrivial electron
pockets. We find that the (110) surface presents arc-like resonances attached
to the topologically nontrivial electron pockets. These Fermi-arc resonances
are due to two different chiral degeneracies, a type-I elementary Weyl point
and a type-II composite (Chern numbers $\pm 2$) Weyl point, located at slightly
different energies close to the Fermi level. We further show that these surface
resonances can be controlled by changing the orientation of magnetization,
eventually being eliminated following a topological phase transition. Our study
thus shows that the intricate Fermi-arc features can be observed in materials
as simple as ferromagnetic iron, and are possibly very common in polar and
magnetic materials broadly speaking. Our study also provides methodological
guidelines to identifying Fermi-arc surface states and resonances, establishing
their topological origin and designing control protocols.",1811.08178v1
2018-12-07,Optimal Dynamic Auctions are Virtual Welfare Maximizers,"We are interested in the setting where a seller sells sequentially arriving
items, one per period, via a dynamic auction. At the beginning of each period,
each buyer draws a private valuation for the item to be sold in that period and
this valuation is independent across buyers and periods. The auction can be
dynamic in the sense that the auction at period $t$ can be conditional on the
bids in that period and all previous periods, subject to certain appropriately
defined incentive compatible and individually rational conditions. Perhaps not
surprisingly, the revenue optimal dynamic auctions are computationally hard to
find and existing literatures that aim to approximate the optimal auctions are
all based on solving complex dynamic programs. It remains largely open on the
structural interpretability of the optimal dynamic auctions.
  In this paper, we show that any optimal dynamic auction is a virtual welfare
maximizer subject to some monotone allocation constraints. In particular, the
explicit definition of the virtual value function above arises naturally from
the primal-dual analysis by relaxing the monotone constraints. We further
develop an ironing technique that gets rid of the monotone allocation
constraints. Quite different from Myerson's ironing approach, our technique is
more technically involved due to the interdependence of the virtual value
functions across buyers. We nevertheless show that ironing can be done
approximately and efficiently, which in turn leads to a Fully Polynomial Time
Approximation Scheme of the optimal dynamic auction.",1812.02993v1
2018-12-14,Multitude of iron lines including a Compton scattered component in OAO 1657--415 detected with Chandra,"We present a high resolution X-ray spectrum of the accreting X-ray pulsar,
OAO 1657--415 with HETG+ACIS-S onboard \emph{Chandra},revealing the presence of
a broad line component around $\sim$ 6.3 keV associated with the neutral iron
K$_\alpha$ line at 6.4 \rm{keV}. This is interpreted as Compton shoulder
arising from the Compton scattering of the 6.4 \rm{keV} fluorescence photons
making OAO 1657--415 the second accreting neutron star where such a feature is
detected. A Compton shoulder reveals the presence of dense matter surrounding
the X-ray source. We did not detect any periodicity in the lightcurve and
obtained an upper limit of $\sim$ 2\% for the pulse fraction during this
observation. This could be due to the smearing of the pulses when X-ray photons
are scattered from a large region around the neutron star. In addition to the
Fe K$_\alpha$, Fe $K_\beta$ and Ni $K_\alpha$ lines already reported for this
source, we also report for the first time, the presence of He-like and H-like
iron emission lines at 6.7 and 6.97 \rm{keV} in the first order HETG spectrum.
The detection of such ionized lines, indicative of a highly ionized surrounding
medium, is rare in X-ray binaries.",1812.06108v1
2018-12-20,Storing magnetic fields in pre-collapse cores of massive stars,"We argue that the radiative zone above the iron core in pre-collapse cores of
massive stars can store strong magnetic fields. To reach this conclusion we use
the stellar evolutionary code MESA to simulate the evolution of two stellar
models with initial masses of 15Mo and 25Mo, and reveal the entropy profile
above the iron core just before core collapse. Just above the iron core there
is a thin zone with convective shells. We assume that a dynamo in these
convective shells amplifies magnetic fields and forms magnetic flux loops. By
considering the buoyancy of magnetic flux loops we show that the steep entropy
rise in the radiative zone above the dynamo can prevent buoyancy of flux loops
with magnetic fields below about 10^{13}G. When this radiative zone collapses
on to the newly born neutron star the converging inflow further amplifies the
magnetic fields by a factor of about a hundred. After passing through the
stalled shock at about a hundred kilometres from the center, these strong
magnetic fields together with instabilities can facilitate the launching of
jets that explode the star in the frame of the jittering jets explosion
mechanism. Our study further supports the claim for the necessity to include
magnetic fields in simulating the explosion of CCSNe.",1812.08518v2
2019-01-31,Intertwined magnetic and nematic orders in semiconducting KFe$_{0.8}$Ag$_{1.2}$Te$_2$,"Superconductivity in the iron pnictides emerges from metallic parent
compounds exhibiting intertwined stripe-type magnetic order and nematic order,
with itinerant electrons suggested to be essential for both. Here we use X-ray
and neutron scattering to show that a similar intertwined state is realized in
semiconducting KFe$_{0.8}$Ag$_{1.2}$Te$_2$ (K$_5$Fe$_4$Ag$_6$Te$_{10}$) without
itinerant electrons. We find Fe atoms in KFe$_{0.8}$Ag$_{1.2}$Te$_2$ form
isolated $2\times2$ blocks, separated by nonmagnetic Ag atoms. Long-range
magnetic order sets in below $T_{\rm N}\approx35$ K, with magnetic moments
within the $2\times2$ Fe blocks ordering into the stripe-type configuration. A
nematic order accompanies the magnetic transition, manifest as a structural
distortion that breaks the fourfold rotational symmetry of the lattice. The
nematic orders in KFe$_{0.8}$Ag$_{1.2}$Te$_2$ and iron pnictide parent
compounds are similar in magnitude and how they relate to the magnetic order,
indicating a common origin. Since KFe$_{0.8}$Ag$_{1.2}$Te$_2$ is a
semiconductor without itinerant electrons, this indicates that local-moment
magnetic interactions are integral to its magnetic and nematic orders, and such
interactions may play a key role in iron-based superconductivity.",1901.11206v1
2019-02-18,"The antiferromagnetic and phonon-mediated model of the NaFeAs, LiFeAs and FeSe superconductors","Recently it has been suggested that the role of electron-phonon coupling in
the mechanism of iron-based superconductors may have been underestimated and
that the antiferromagnetism and the induced xy potential may even have a
dramatic amplification effect on electron-phonon coupling. To substantiate the
recently announced xy potential in the literature, we create a two-channel
model to separately superimpose the dynamics of the electron in the upper and
lower tetrahedral plane. The results of our two-channel model support the
literature data. While the scientists are still searching for a universal DFT
functional that can describe the pairing mechanism of all iron-based
superconductors, we are designing an empirical combination of DFT functional to
calculate the electron-phonon coupling and antiferromagetism of LiFeAs, NaFeAs
and FeSe. We use ARPES data to revise the electron-phonon scattering matrix in
superconducting state to ensure that all electrons involved in iron-based
superconductivity are included in the ab-inito calculation. We present an
ab-initio theoretical approach that takes into account this amplifying effect
of antiferromagnetism and the correction of the electron-phonon scattering
matrix together with the abnormal soft out-of-plane lattice vibration of the
layered structure, which allows us to calculate theoretical Tc values of
LiFeAs, NaFeAs and FeSe as a function of pressure that correspond reasonably
well to the experimental values.",1902.06463v4
2019-02-18,On the iron ionization balance of cool stars,"High-resolution spectroscopic studies of solar-type stars have revealed
higher iron abundances derived from singly ionized species compared to neutral,
violating the ionization equilibrium under the assumption of local
thermodynamic equilibrium. In this work, we investigate the overabundances of
FeII lines reported in our previous work for a sample of 451 solar-type HARPS
stars in the solar neighborhood. The spectroscopic surface gravities of this
sample which emerge from the ionization balance, appear underestimated for the
K-type stars. In order to understand this behavior, we search our FeII line
list for unresolved blends and outliers. First, we use the VALD to identify
possible unresolved blends around our lines and calculate which ones are strong
enough to cause overestimations in the equivalent width measurements. Second,
for our sample we use reference parameters (effective temperature and
metallicity) and the Gaia DR2 parallaxes to derive surface gravities
(trigonometric gravities) and calculate the FeI and FeII abundances from
different line lists. We exclude the FeII lines which produce overabundances
above 0.10 dex. The derived surface gravities from the clean line list are now
in agreement with the trigonometric. Moreover, the difference between FeI and
FeII abundance does not show now a correlation with the effective temperature.
Finally, we show that the ionization balance of Ti can provide better estimates
of surface gravities than iron. With this analysis, we provide a solution to
the ionization balance problem observed in the atmospheres of cool dwarfs.",1902.06769v1
2019-02-27,Intertwined spin-orbital coupled orders in the iron-based superconductors,"The underdoped phase diagram of the iron-based superconductors exemplifies
the complexity common to many correlated materials. Indeed, multiple ordered
states that break different symmetries but display comparable transition
temperatures are present. Here, we argue that such a complexity can be
understood within a simple unifying framework. This framework, built to respect
the symmetries of the non-symmorphic space group of the FeAs/Se layer, consists
of primary magnetically-ordered states and their vestigial phases that
intertwine spin and orbital degrees of freedom. All vestigial phases have
Ising-like and zero wave-vector order parameters, described in terms of
composite spin order and exotic orbital-order patterns such as spin-orbital
loop-currents, staggered atomic spin-orbit coupling, and emergent Rashba- and
Dresselhaus-type spin-orbit interactions. Moreover, they host unusual
phenomena, such as the electro-nematic effect, by which electric fields acts as
transverse fields to the nematic order parameter, and the ferro-N\'eel effect,
by which a uniform magnetic field induces N\'eel order. We discuss the
experimental implications of our findings to iron-based superconductors and
possible extensions to other correlated compounds with similar space groups.",1902.10831v2
2019-03-08,Local Superconductivity in Vanadium Iron Arsenide,"We investigate the chemical substitution of group 5 into BaFe2As2 (122) iron
arsenide, in the effort to understand why Fe-site hole doping of this compound
(e.g., using group 5 or 6) does not yield bulk superconductivity. We find an
increase in c-lattice parameter of the BaFe2As2 with the substitution of V, Nb,
or Ta; the reduction in c predicts the lack of bulk superconductivity [1] that
is confirmed here through transport and magnetization results. However, our
spectroscopy measurements find a coexistence of antiferromagnetic and local
superconducting nanoscale regions in V-122, observed for the first time in a
transition-metal hole-doped iron arsenide. In BaFe2As2, there is a complex
connection between local parameters such as composition and lattice strain,
average lattice details, and the emergence of bulk quantum states such as
superconductivity and magnetism. [1] L. M. N. Konzen, and A. S. Sefat, J.
Phys.: Condens. Matter 29 (2017), 083001.",1903.03660v3
2019-03-12,Zero Field Assembly of Long Magnetic Dipolar Chains in 2D Polymer Nanocomposite Films,"The existence of magnetic dipolar nanoparticle chains at zero field has been
predicted theoretically for decades, but these structures are rarely observed
experimentally. A prerequisite is a permanent magnetic moment on the particles
forming the chain. Here we report on the observation of magnetic dipolar chains
of spherical iron oxide nanoparticles with a diameter of
\SI{12.8}{\nano\meter}. The nanoparticles are embedded in an ultrathin polymer
film. Due to the high viscosity of the polymer matrix, the dominating
aggregation mechanism is driven by dipolar interactions. Smaller iron oxide
nanoparticles (\SI{9.4}{\nano\meter}) show no permanent magnetic moment and do
not form chains but compact aggregates. Mixed monolayers of different iron
oxide nanoparticles and polymer at the air-water interface are characterized by
Langmuir isotherms and in-situ X-ray reflectometry (XRR). The combination of
the particles with a polymer leads to a stable polymer nanocomposite film at
the air-water interface. XRR experiments show that nanoparticles are immersed
in a thin polymer matrix of \SI{3}{\nano\meter}. Using atomic force microscopy
(AFM) on Langmuir-Blodgett films, we measure the lateral distribution of
particles in the film. An analysis of single structures within transferred
films results in fractal dimensions that are in excellent agreement with 2D
simulations.",1903.04877v1
2019-04-09,Back to the Lithium Plateau with J0023+0307 with [Fe/H]<-6,"We present an analysis of the UVES high-resolution spectroscopic observations
at the 8.2m VLT of J0023+0307, a main-sequence extremely iron-poor dwarf star.
We are unable to detect iron lines in the spectrum but derive [Fe/H]<-6.1 from
the Ca II resonance lines assuming [Ca/Fe]>0.40. The chemical abundance pattern
of J0023+0307, with very low [Fe/Mg] and [Ca/Mg] abundance ratios, but
relatively high absolute Mg and Si abundances, suggests J0023+0307 is a second
generation star formed from a molecular cloud polluted by only one supernova in
which the fall-back mechanism played a role. We measure a carbon abundance of
A(C)=6.2 that places J0023+0307 on the low band in the A(C)-[Fe/H] diagram,
suggesting no contamination from a binary companion. This star is also unique
having a lithium abundance (A(Li)=2.02+-0.08) close to the level of the Lithium
Plateau, in contrast with lower Li determinations or upper limits in all other
extremely iron-poor stars. The upper envelope of the lithium abundances in
unevolved stars spanning more than three orders of magnitude in metallicity
(-6<[Fe/H]<-2.5) defines a nearly constant value. We argue that it is unlikely
that such uniformity is the result of depletion processes in stars from a
significantly higher initial Li abundance, but suggests instead a lower
primordial production, pointing to new physics such as decaying massive
particles, varying fundamental constants, or nuclear resonances, that could
have affected the primordial 7Li production.",1904.04892v1
2019-05-28,Strain-derivative of thermoelectric properties: a sensitive probe for nematicity,"The nematic instability of iron-based superconductors is an undebatable
ingredient of the physics of iron-based superconductors. Yet, its origin
remains enigmatic as it involves a fermiology with an intricate interplay of
lattice-, orbital- and spin- degrees of freedom. It is well known that
thermoelectric transport is an excellent probe for revealing even subtle
signatures of instabilities and pertinent fluctuations. In this paper, we
report a strong response of the thermoelectric transport properties of two
underdoped 1111 iron-based superconductors to a vanishingly small strain. By
introducing the strain-derivative of the Seebeck and the Nernst coefficients,
we provide a novel description of the nematic order parameter, proving the
existence of an anisotropic Peltier-tensor beside an anisotropic
conductivity-tensor. Our measurements reveal that the transport nematic
phenomenology is the result of the combined effect of both an anisotropic
scattering time and Fermi surface distortions, pointing out that in a realistic
description, abreast of the spin-fluctuations also the orbital character is a
fundamental ingredient. In addition, we show that nematic fluctuations
universally relax in a Curie-Weiss fashion above T_S in all the
elasto-transport measurements and we provide evidences that nematicity must be
band-selective.",1905.11660v2
2019-06-07,Identification of nutrient deficiency in bean plants by prompt chlorophyll fluorescence measurements and Artificial Neural Networks,"The deficiency of macro (N, P, S, Ca, Mg and K) and micro (Zn, Cu, B, Mo, Cl,
Mn and Fe) minerals has a major effect on plant development. The lack of some
nutrient minerals especially of nitrogen, potassium, calcium, phosphorus and
iron is a huge problem for agriculture and early warning and prevention of the
problem will be very useful for agro-industry. Methods currently used to
determine nutritional deficiency in plants are soil analysis, plant tissue
analysis, or combined methods. But these methods are slow and expensive. In
this study, a new method for determining nutrient deficiency in plants based on
the prompt fluorescence of chlorophyll a is proposed. In this paper bean plants
are grown on a complete nutrient solution (control) were compared with those
grown in a medium, which lacked one of these elements - N, P, K, Ca and Fe. In
this article the mineral deficiency in nutrient solution was evaluated by the
stress response of the plants estimated by leaves photosynthetic activity. The
photosynthetic activity was estimated by analysis of the chlorophyll
fluorescence using JIP-test approach that reflects functional activity of
Photosystems I and II and of electron transfer chain between them, as well as
the physiological state of the photosynthetic apparatus as whole. Next the
fluorescence transient recorded from plants grown in nutrient solution with
deficiency of N, P, K, Ca and Iron, as an input data in Artificial Neural
Network was used. This ANN was train to recognise deficiency of N, P, K, Ca and
Iron in bean plants. The results obtained were of high recognition accuracy.
The ANN of fluorescence transient was presented as a possible approach to
identify/predict the nutrient deficiency using the fast chlorophyll
fluorescence records.",1906.03312v1
2019-07-29,Imaging Nematic Transitions in Iron-Pnictide Superconductors with a Quantum Gas,"The SQCRAMscope is a recently realized Scanning Quantum CRyogenic Atom
Microscope that utilizes an atomic Bose-Einstein condensate to measure magnetic
fields emanating from solid-state samples. The quantum sensor does so with
unprecedented DC sensitivity at micron resolution from room-to-cryogenic
temperatures. An additional advantage of the SQCRAMscope is the preservation of
optical access to the sample: Magnetometry imaging of, e.g., electron transport
may be performed in concert with other imaging techniques. This multimodal
imaging capability can be brought to bear with great effect in the study of
nematicity in iron-pnictide high-temperature superconductors, where the
relationship between electronic and structural symmetry-breaking resulting in a
nematic phase is under debate. Here, we combine the SQCRAMscope with an in situ
microscope that measures optical birefringence near the surface. This enables
simultaneous and spatially resolved detection of both bulk and near-surface
manifestations of nematicity via transport and structural deformation channels,
respectively. By performing the first local measurement of emergent resistivity
anisotropy in iron pnictides, we observe sharp, nearly concurrent transport and
structural transitions. More broadly, these measurements demonstrate the
SQCRAMscope's ability to reveal important insights into the physics of complex
quantum materials.",1907.12601v2
2019-08-17,"Homogeneous Analysis of Hot Earths: Masses, Sizes, and Compositions","Terrestrial planets have been found orbiting Sun-like stars with extremely
short periods --- some as short as 4 hours. These ""ultra-short-period planets""
or ""hot Earths"" are so strongly irradiated that any initial H/He atmosphere has
probably been lost to photoevaporation. As such, the sample of hot Earths may
give us a glimpse at the rocky cores that are often enshrouded by thick H/He
envelopes on wider-orbiting planets. However, the mass and radius measurements
of hot Earths have been derived from a hodgepodge of different modeling
approaches, and include several cases of contradictory results. Here, we
perform a homogeneous analysis of the complete sample of 11 known hot Earths
with an insolation exceeding 650 times that of the Earth. We combine all
available data for each planet, incorporate parallax information from {\it
Gaia} to improve the stellar and planetary parameters, and use Gaussian Process
regression to account for correlated noise in the radial-velocity data. The
homogeneous analysis leads to a smaller dispersion in the apparent composition
of hot Earths, although there does still appear to be some intrinsic
dispersion. Most of the planets are consistent with an Earth-like composition
(35\% iron and 65\% rock), but two planets (K2-141b and K2-229b) show evidence
for a higher iron fraction, and one planet (55\,Cnc\,e) has either a very low
iron fraction or an envelope of low-density volatiles. All of the planets are
less massive than 8\,$M_\oplus$, despite the selection bias towards more
massive planets, suggesting that 8\,$M_\oplus$ is the critical mass for runaway
accretion.",1908.06299v2
2019-09-03,Effects of spin-orbit coupling on spin-fluctuation induced pairing in iron-based superconductors,"We perform a theoretical study of the leading pairing instabilities and the
associated superconducting gap functions within the spin-fluctuation mediated
pairing scenario in the presence of spin-orbit coupling (SOC). Focussing on
iron-based superconductors (FeSCs), our model Hamiltonian consists of a
realistic density functional theory (DFT)-derived ten-band hopping term,
spin-orbit coupling, and electron-electron interactions included via the
multi-orbital Hubbard-Hund Hamiltonian. We perform an extensive parameter sweep
and investigate different doping regimes including cases with only hole- or
only electron Fermi pockets. In addition, we explore two different
bandstructures: a rather generic band derived for LaFeAsO but known to
represent standard DFT-obtained bands for iron-based superconductors, and a
band specifically tailored for FeSe which exhibits a notably different Fermi
surface compared to the generic case. It is found that for the generic FeSCs
band, even rather large SOC has negligible effect on the resulting gap
structure; the $s_{+-}$ (pseudo-)spin singlet pairing remains strongly favored
and SOC does not lead to any SOC-characteristic gap oscillations along the
various Fermi surfaces. By contrast in the strongly hole-doped case featuring
only hole-pockets around the $\Gamma$-point, the leading solution is $d$-wave
pseudo-spin singlet, but with a notable SOC-driven tendency towards helical
pseudo-spin triplet pairing, which may even become the leading instability. In
the heavily electron doped situation, featuring only electron pockets centered
around the $M$-point, the leading superconducting instabilities are pseudo-spin
singlets with SOC favoring the $s$-wave case as compared to $d$-wave pairing,
which is the favored gap symmetry for vanishing SOC.",1909.01313v1
2019-10-08,Silicon and iron dust in gamma-ray burst host galaxy absorbers,"Depletion studies provide a way to understand the chemical composition of
interstellar dust grains. We here examine 23 gamma-ray bursts (GRB) optical
afterglow spectra (spanning 0.6<z<5.0) and compare their silicon and iron
dust-phase column densities with different extinction curve parameters to study
the composition of the interstellar dust grains in these high-redshift GRB host
galaxies. The majority of our sample (87%) show featureless extinction curves
and only vary in shape. We observe strong correlations (with >96% significance)
between the total-to-selective extinction, R_V, and the dust-phase column
densities of Si and Fe. Since a large fraction of interstellar iron is locked
in silicate grains, this indicates that high Si and Fe depletion leads to an
increase in the fraction of large silicate grains and vice versa. This suggests
that silicates play a vital role to induce the entire extinction at any
wavelength. On the other hand, the far-UV extinction is usually attributed to
the presence of small silicates. However, we find no trend between the far-UV
parameter of the extinction curve, c_4, and the abundance of Si and Fe in the
dust phase. We, therefore, propose that the far-UV extinction could be a
combined effect of small (probably nanoparticles) dust grains from various
species.",1910.03207v1
2019-10-18,Trapping and electrical characterization of single core/shell iron-based nanoparticles in self-aligned nanogaps,"We report on the fabrication and measurements of platinum-self-aligned
nanogap devices containing cubed iron (core)/iron oxide (shell) nanoparticles
(NPs) with two average different sizes (13 and 17 nm). The nanoparticles are
deposited by means of a cluster gun technique. Their trapping across the
nanogap is demonstrated by comparing the current vs voltage characteristics
(I-Vs) before and after the deposition. At low temperature, the I-Vs can be
well fitted to the Korotkov and Nazarov Coulomb blockade model, which captures
the coexistence of single-electron tunneling and tunnel barrier suppression
upon a bias voltage increase. The measurements thus show that Coulomb-blockaded
devices can be made with a nanoparticle cluster source, which extends the
existing possibilities to fabricate such devices to those in which it is very
challenging to reduce the usual NP agglomeration given by a solution method.",1910.08326v2
2020-02-17,The Chandra High Resolution X-ray Spectrum of Quiescent Emission from Sgr A*,"In quiescence, Sgr A* is surprisingly dim, shining 100,000 times less than
expected for its environment. This problem has motivated a host of theoretical
models to explain radiatively inefficient accretion flows (RIAFs). The Chandra
Galactic Center (GC) X-ray Visionary Program obtained approximately 3 Ms (one
month) of Chandra HETG data, offering the only opportunity to examine the
quiescent X-ray emission of Sgr A* with high resolution spectroscopy. Utilizing
custom background regions and filters for removing overlapping point sources,
this work provides the first ever look at stacked HETG spectra of Sgr A*. We
model the background datasets with a cubic spline and fit the unbinned Sgr A*
spectra with a simple parametric model of a power law plus Gaussian lines under
the effects of interstellar extinction. We detect a strong 6.7 keV iron
emission line in the HEG spectra and a 3.1 keV emission line in the MEG
spectra. In all cases, the line centroids and equivalent widths are consistent
with those measured from low-resolution CCD spectra. An examination of the
unbinned, stacked HEG+/-1 spectrum reveals fine structure in the iron line
complex. In addition to resolving the resonant and forbidden lines from He-like
iron, there are apparent emission features arising with higher statistical
significance at lower energy, potentially associated with FeXX-XXIV ions in a
~1 keV plasma arising near the Bondi radius of Sgr A*. With this work, we
release the cleaned and stacked Sgr A* and background HETG spectra to the
public as a special legacy dataset.",2002.07198v1
2020-03-03,Non-local correlations in Iron Pnictides and Chalcogenides,"Deviations of low-energy electronic structure of iron-based superconductors
from density functional theory predictions have been parametrized in terms of
band- and orbital-dependent mass renormalizations and energy shifts. The former
have typically been described in terms of a local self-energy within the
framework of dynamical mean field theory, while the latter appears to require
non-local effects due to interband scattering. By calculating the renormalized
bandstructure in both random phase approximation (RPA) and the two-particle
self-consistent approximation (TPSC), we show that correlations in pnictide
systems like LaFeAsO and LiFeAs can be described rather well by a non-local
self-energy. In particular, Fermi pocket shrinkage as seen in experiment occurs
due to repulsive interband finite-energy scattering. For the canonical iron
chalcogenide system FeSe in its bulk tetragonal phase, the situation is however
more complex since even including momentum-dependent band renormalizations
cannot explain experimental findings. We propose that the long-range Coulomb
interaction may play an important role in band-structure renormalization in
FeSe. We further compare our evaluations of non-local quasiparticle scattering
lifetime within RPA and TPSC with experimental data for LiFeAs.",2003.01638v2
2020-03-27,Distant sequence similarity between hepcidin and the novel coronavirus spike glycoprotein: a potential hint at the possibility of local iron dysregulation in COVID-19,"The spike glycoprotein of the SARS-CoV-2 virus, which causes COVID-19, has
attracted attention for its vaccine potential and binding capacity to host cell
surface receptors. Much of this research focus has centered on the ectodomain
of the spike protein. The ectodomain is anchored to a transmembrane region,
followed by a cytoplasmic tail. Here we report a distant sequence similarity
between the cysteine-rich cytoplasmic tail of the coronavirus spike protein and
the hepcidin protein that is found in humans and other vertebrates. Hepcidin is
thought to be the key regulator of iron metabolism in humans. An implication of
this preliminary observation is to suggest a potential route of investigation
in the coronavirus research field making use of an already-established
literature on the interplay of local and systemic iron regulation,
cytokine-mediated inflammatory processes, respiratory infections and the
hepcidin protein. The question of possible homology and an evolutionary
connection between the viral spike protein and hepcidin is not assessed in this
report, but some scenarios for its study are discussed.",2003.12191v3
2020-03-27,Boundary-obstructed topological high-T$_c$ superconductivity in iron pnictides,"Non-trivial topology and unconventional pairing are two central guiding
principles in the contemporary search for and analysis of superconducting
materials and heterostructure compounds. Previously, a topological
superconductor has been predominantly conceived to result from a topologically
non-trivial band subject to intrinsic or external superconducting proximity
effect. Here, we propose a new class of topological superconductors which are
uniquely induced by unconventional pairing. They exhibit a boundary-obstructed
higher-order topological character and, depending on their dimensionality,
feature unprecedently robust Majorana bound states or hinge modes protected by
chiral symmetry. We predict the 112-family of iron pnictides, such as
Ca$_{1-x}$La$_x$FeAs$_2$, to be a highly suited material candidate for our
proposal, which can be tested by edge spectroscopy. Because of the
boundary-obstruction, the topologically non-trivial feature of the 112
pnictides does not reveal itself for a bulk-only torus band analysis without
boundaries, and as such had evaded previous investigations. Our proposal not
only opens a new arena for highly stable Majorana modes in high-temperature
superconductors, but also provides the smoking gun evidence for extended s-wave
order in the iron pnictides.",2003.12204v2
2020-05-11,Accurate Treatment of Comptonization in X-ray Illuminated Accretion Disks,"A large fraction of accreting black hole and neutron stars systems present
clear evidence of the reprocessing of X-rays in the atmosphere of an
optically-thick accretion disk. The main hallmarks of X-ray reflection include
fluorescent K-shell emission lines from iron ($\sim 6.4-6.9$ keV), the
absorption iron K-edge ($\sim 7-9$ keV), and a broad featureless component
known as the Compton hump ($\sim 20-40$ keV). This Compton hump is produced as
the result of the scattering of high-energy photons ($E \gtrsim 10$ keV) of the
relatively colder electrons ($T_e \sim 10^5-10^7$ K) in the accretion disk, in
combination with photoelectric absorption from iron. The treatment of this
process in most current models of ionized X-ray reflection has been done using
an approximated Gaussian redistribution kernel. This approach works
sufficiently well up to $\sim100$ keV, but it becomes largely inaccurate at
higher energies and at relativistic temperatures ($T_e\sim10^9$ K). We present
new calculations of X-ray reflection using a modified version of our code
XILLVER, including an accurate solution for Compton scattering of the reflected
unpolarized photons in the disk atmosphere. This solution takes into account
quantum electrodynamic and relativistic effects allowing the correct treatment
of high photon energies and electron temperatures. We show new reflection
spectra computed with this model, and discuss the improvements achieved in the
reproducing the correct shape of the Compton hump, the discrepancies with
previous calculations, and the expected impact of these new models in the
interpretation of observational data.",2005.04852v1
2020-05-13,Neutron spin resonance in a quasi-two-dimensional iron-based superconductor,"Magnetically mediated Cooper pairing is generally regarded as a key to
establish the unified mechanism of unconventional superconductivity. One
crucial evidence is the neutron spin resonance arising in the superconducting
state, which is commonly interpreted as a spin-exciton from collective
particle-hole excitations confined below the superconducting pair-breaking gap
($2\Delta$). Here, on the basis of inelastic neutron scattering measurements on
a quasi-two-dimensional iron-based superconductor KCa$_2$Fe$_4$As$_4$F$_2$, we
have discovered a two-dimensional spin resonant mode with downward dispersions,
a behavior closely resembling the low branch of the hour-glass-type spin
resonance in cuprates. The resonant intensity is predominant by two broad
incommensurate peaks near $Q=$(0.5, 0.5) with a sharp energy peak at $E_R=16$
meV. The overall energy dispersion of the mode exceeds the measured maximum
total gap $\Delta_{\rm tot}=|\Delta_k|+|\Delta_{k+Q}|$. These experimental
results deeply challenge the conventional understanding of the resonance modes
as magnetic excitons regardless of underlining pairing symmetry schemes, and it
also points out that when the iron-based superconductivity becomes very
quasi-two-dimensional, the electronic behaviors are similar to those in
cuprates.",2005.06146v1
2020-05-19,Speciation of FeS and FeS$_2$ by means of X-ray Emission Spectroscopy using a compact full-cylinder von Hamos spectrometer,"We present Fe K$\beta$ X-ray emission (XES) and Fe K X-ray absorption spectra
(XAS) of Iron(II)sulfide (FeS) and Iron(II)disulfide (FeS$_2$). While XES and
XAS offer different discrimination capabilities for chemical speciation,
depending on the valence states of the compounds probed, XES allows for using
different excitation sources. The XES data was measured using polychromatic
X-ray radiation with a full-cylinder von Hamos spectrometer being characterized
by an energy window of up to 700 eV and a spectral resolving power of $E/
\Delta E = 800$. The large energy window at a single position of the
spectrometer components is made profit of to circumvent the instrumental
sensitivity of wavelength-dispersive spectrometers to sample positioning. This
results in a robust energy scale which is used to compare experimental data
with ab initio valence-to-core calculations, which are carried out using the
OCEAN package. To validate the reliability of the OCEAN package for the two
sample systems, near edge X-ray absorption fine structure measurements of the
Fe K absorption edge are compared to theory using the same input parameters as
in the case of the X-ray emission calculations. Based on the example of iron
sulfide compounds, the combination of XES experiments and OCEAN calculations
allows unravelling the electronic structure of different transition metal
sulfides and qualifying XES investigations for the speciation of different
compounds.",2005.09509v1
2020-05-19,"Hydrostatic and uniaxial pressure tuning of iron-based superconductors: Insights into superconductivity, magnetism, nematicity and collapsed tetragonal transitions","Iron-based superconductors are well-known for their intriguing phase
diagrams, which manifest a complex interplay of electronic, magnetic and
structural degrees of freedom. Among the phase transitions observed are
superconducting, magnetic, and several types of structural transitions,
including a tetragonal-to-orthorhombic and a collapsed-tetragonal transition.
In particular, the widely-observed tetragonal-to-orthorhombic transition is
believed to be a result of an electronic order that is coupled to the
crystalline lattice and is, thus, referred to as nematic transition. Nematicity
is therefore a prominent feature of these materials, which signals the
importance of the coupling of electronic and lattice properties.
Correspondingly, these systems are particularly susceptible to tuning via
pressure (hydrostatic, uniaxial, or some combination). We review efforts to
probe the phase diagrams of pressure-tuned iron-based superconductors, with a
strong focus on our own recent insights into the phase diagrams of several
members of this material class under hydrostatic pressure. These studies on
FeSe, Ba(Fe$_{1-x}$Co$_x$)$_2$As$_2$, Ca(Fe$_{1-x}$Co$_x$)$_2$As$_2$ and
CaK(Fe$_{1-x}$Ni$_x$)$_4$As$_4$ were, to a significant extent, made possible by
advances of what measurements can be adapted to the use under differing
pressure environments. We point out the potential impact of these tools for the
study of the wider class of strongly correlated electron systems.",2005.09791v1
2020-06-29,Nematic Fluctuations in an Orbital Selective Superconductor Fe$_{1+y}$Te$_{1-x}$Se$_{x}$,"We present a systematic study of the nematic fluctuations in the iron
chalcogenide superconductor Fe$_{1+y}$Te$_{1-x}$Se$_{x}$ ($0 \leq x \leq 0.53$)
using the elastoresistivity technique. Near $x = 0$, in proximity to the
double-stripe magnetic order of Fe$_{1+y}$Te, a diverging $B_{1g}$ nematic
susceptibility is observed. Upon increasing $x$, despite the absence of
magnetic order, the $B_{2g}$ nematic susceptibility increases and becomes
dominant, closely following the strength of the $(\pi, \pi)$ spin fluctuations.
Over a wide range of compositions ($0.17 \leq x \leq 0.53$), while the $B_{2g}$
nematic susceptibility follows a Curie temperature dependence (with zero Weiss
temperature) at low temperatures, it shows deviations from Curie-Weiss behavior
for temperatures higher than $50K$. This is the opposite of what is observed in
typical iron pnictides, where Curie-Weiss deviations are seen at low
temperatures. We attribute this unusual temperature dependence to a loss of
coherence of the $d_{xy}$ orbital, which is supported by our theoretical
calculations. Our results highlight the importance of orbital differentiation
on the nematic properties of iron-based materials.",2006.15887v1
2020-07-19,Anomalous spectral weight transfer in the nematic state of iron-selenide superconductor,"Nematic phase intertwines closely with high-Tc superconductivity in
iron-based superconductors. Its mechanism, which is closely related to the
pairing mechanism of superconductivity, still remains controversial.
Comprehensive characterization of how the electronic state reconstructs in the
nematic phase is thus crucial. However, most experiments focus only on the
reconstruction of band dispersions. Another important characteristic of
electronic state, the spectral weight, has not been studied in details so far.
Here, we studied the spectral weight transfer in the nematic phase of
FeSe$_{0.9}$S$_{0.1}$ using angle-resolved photoemission spectroscopy and
in-situ detwinning technique. There are two elliptical electron pockets
overlapping with each other orthogonally at the Brillouin zone corner. We found
that, upon cooling, one electron pocket loses spectral weight and fades away,
while the other electron pocket gains spectral weight and becomes pronounced.
Our results show that the symmetry breaking of electronic state is manifested
by not only the anisotropic band dispersion but also the band-selective
modulation of spectral weight. Our observation completes our understanding of
the nematic electronic state, and put strong constraints on the theoretical
models. It further provide crucial clues to understand the gap anisotropy and
orbital-selective pairing in iron-selenide superconductors.",2007.09565v1
2020-07-20,Vortex-line topology in iron-based superconductors with and without second-order topology,"The band topology of a superconductor is known to have profound impact on the
existence of Majorana zero modes in vortices. As iron-based superconductors
with band inversion and $s_{\pm}$-wave pairing can give rise to time-reversal
invariant second-order topological superconductivity, manifested by the
presence of helical Majorana hinge states in three dimensions, we are motivated
to investigate the interplay between the second-order topology and the vortex
lines in both weak- and strong-Zeeman-field regimes. In the weak-Zeeman-field
regime, we find that vortex lines far away from the hinges are topologically
nontrivial in the weakly doped regime, regardless of whether the second-order
topology is present or not. However, when the superconductor falls into the
second-order topological phase and a topological vortex line is moved close to
the helical Majorana hinge states, we find that their hybridization will
trivialize the vortex line and transfer robust Majorana zero modes to the
hinges. Furthermore, when the Zeeman field is large enough, we find that the
helical Majorana hinge states are changed into chiral Majorana hinge modes and
thus a chiral second-order topological superconducting phase is realized. In
this regime, the vortex lines are always topologically trivial, no matter how
far away they are from the chiral Majorana hinge modes. By incorporating a
realistic assumption of inhomogeneous superconductivity, our findings can
explain the recent experimental observation of the peculiar coexistence and
evolution of topologically nontrivial and trivial vortex lines in iron-based
superconductors.",2007.10326v4
2020-08-05,Black Dwarf Supernova in the Far Future,"In the far future long after star formation has ceased the universe will be
populated by sparse degenerate remnants, mostly white dwarfs, though their
ultimate fate is an open question. These white dwarfs will cool and freeze
solid into black dwarfs while pycnonuclear fusion will slowly process their
composition to iron-56. However, due to the declining electron fraction the
Chandrasekhar limit of these stars will be decreasing and will eventually be
below that of the most massive black dwarfs. As such, isolated dwarf stars with
masses greater than $\sim 1.2 M_\odot$ will collapse in the far future due to
the slow accumulation of iron-56 in their cores. If proton decay does not occur
then this is the ultimate fate of about $10^{21}$ stars, approximately one
percent of all stars in the observable universe. We present calculations of the
internal structure of black dwarfs with iron cores as a model for progenitors.
From pycnonuclear fusion rates we estimate their lifetime and thus delay time
to be $10^{1100}$ years. We speculate that high mass black dwarf supernovae
resemble accretion induced collapse of O/Ne/Mg white dwarfs while later low
mass transients will be similar to stripped-envelope core-collapse supernova,
and may be the last interesting astrophysical transients to occur prior to heat
death.",2008.02296v1
2020-08-18,Returning radiation in strong gravity around black holes: Reverberation from the accretion disc,"We study reflected X-ray emission that returns to the accretion disc in the
strong gravitational fields around black holes using General Relativistic ray
tracing and radiative transfer calculations. Reflected X-rays that are produced
when the inner regions of the disc are illuminated by the corona are subject to
strong gravitational light bending, causing up to 47 per cent of the reflected
emission to be returned to the disc around a rapidly spinning black hole,
depending upon the scale height of the corona. The iron K line is enhanced
relative to the continuum by 25 per cent, and the Compton hump by up to a
factor of three. Additional light travel time between primary and secondary
reflections increases the reverberation time lag measured in the iron K band by
49 per cent, while the soft X-ray lag is increased by 25 per cent and the
Compton hump response time is increased by 60 per cent. Measured samples of
X-ray reverberation lags are shown to be consistent with X-rays returning to
the accretion disc in strong gravity. Understanding the effects of returning
radiation is important in interpreting reverberation observations to probe
black holes. Reflected X-rays returning to the disc can be uniquely identified
by blueshifted returning iron K line photons that are Compton scattered from
the inner disc, producing excess, delayed emission in the 3.5-4.5keV energy
range that will be detectable with forthcoming X-ray observatories,
representing a unique test of General Relativity in the strong field limit.",2008.08083v1
2021-02-09,Reinforcing Iron Metal Matrix Composite by Multi-Wall Carbon Nanotube: A Combined Theoretical and Computational Approach,"Carbon nanotube (CNT) reinforced metal matrix composites have been the focus
of researchers due to their high load-bearing capacity. Among single and
multi-wall carbon nanotubes (MWCNT), the latter is preferred by manufacturers
and engineers for making composites due to their economic feasibility of
synthesizing. However, the effect of layer numbers along with other parameters
of the reinforcing MWCNT must be understood before its industrial application.
In this article, we developed a novel theoretical approach for predicting the
variation of strength and stiffness of MWCNT reinforced iron composites
(MWCNT-Fe) with the layer number of reinforcing MWCNT and validated the
prediction with a series of Molecular dynamics (MD) simulation. Our analysis
revealed that for every addition of two extra layers, the strength and
stiffness of the composite increase 9.8% and 7.2% respectively up to eight
layered MWCNT and then becomes saturated. We also employed MD simulations for
investigating the effect of grain boundary on the failure mechanism of CNT
reinforced iron composites in contrast to previous studies. Our investigations
revealed that instead of the matrix-fiber interface, the failure was initiated
from the grain boundary and merges with the interface. The results in this
study will not only help engineers and manufacturers choose optimal layered
MWCNT for synthesizing composite for a specific application but also provide
scientists a new method to model composites for predicting desired properties.",2102.05025v1
2021-04-07,Fundamental mechanism of the creation of chemical bimodality in the Milky Way disc in the cold accretion theory,"Chemical bimodality of the Milky Way (MW) disc stars constitutes one of the
most remarkable properties of MW. The cold accretion theory for the
cosmological gas accretion provides one viable explanation to this phenomenon.
In this scenario, the rapid cold-mode accretion in the early epoch creates the
first generation stars relatively rich in $\alpha$-elements(O,Mg,Si,S,Ca,etc)
and later cooling flow produces iron-rich second generation stars, creating the
bimodality in the [$\alpha$/Fe] ratio. We employ a cosmologically motivated
chemical evolution model for disc galaxies to elucidate the role played by type
Ia supernovae (SNIa), which serve as the major source of iron, in the creation
of the bimodality. To this end, we divide SNIa into two groups, those formed
from the 1st generation stars (the first SNIa) and those formed from the 2nd
generation stars (the second SNIa). The model with the first SNIa suppressed
during the {\it second} star formation stage produces stars having high
[$\alpha$/Fe] in the early phase of this stage, whereas the model which
prohibits the second SNIa produces high [$\alpha$/Fe] stars in the late phase.
Both models fail to create a well-defined bimodality. We thus conclude that the
cooperation of the first and the second SNIa plays a crucial role in creating
the bimodality by maintaining rich iron content in the interstellar gas
throughout the second star formation stage.",2104.02976v1
2021-05-10,"Quantum magnetism of iron-based ladders: Blocks, spirals, and spin flux","Motivated by increasing experimental evidence of exotic magnetism in
low-dimensional iron-based materials, we present a comprehensive theoretical
analysis of magnetic states of the multiorbital Hubbard ladder in the
orbital-selective Mott phase (OSMP). The model we used is relevant for
iron-based compounds of the AFe$_2$X$_3$ family (where A${}={}$Cs, Rb, Ba, K
are alkali metals and X${}={}$S, Se are chalcogenides). To reduce computational
effort, and obtain almost exact numerical results in the ladder geometry, we
utilize a low-energy description of the Hubbard model in the OSMP - the
generalized Kondo-Heisenberg Hamiltonian. Our main result is the doping vs
interaction magnetic phase diagram. We reproduce the experimental findings on
the AFe$_2$X$_3$ materials, especially the exotic block magnetism of
BaFe$_2$Se$_3$ (antiferromagnetically coupled $2\times 2$ ferromagnetic islands
of the $\uparrow\uparrow\downarrow\downarrow$ form). As in recent studies of
the chain geometry, we also unveil block magnetism beyond the $2 \times 2$
pattern (with block sizes varying as a function of the electron doping) and
also an interaction-induced frustrated block-spiral state (a spiral order of
rigidly rotating ferromagnetic islands). Moreover, we predict new phases beyond
the one-dimensional system: a robust regime of phase separation close to
half-filling, incommensurate antiferromagnetism for weak interaction, and a
quantum spin-flux phase of staggered plaquette spin currents at intermediate
doping. Finally, exploiting the bonding/antibonding band occupations, we
provide an intuitive physical picture giving insight into the structure of the
phase diagram.",2105.04391v2
2021-05-14,Spectral and timing properties of the black hole candidate X1755-338 observed in 1989-1995,"We report results of an analysis of the black hole (BH) candidate source
X1755-338 in 1989, 1990, and 1991 with Ginga, and in 1995 with ASCA. The
spectra were well represented by a model consisting of a soft thermal emission
from an accretion disk and a hard X-ray tail. The normalization of the
multi-color disk model, relating to the inner disk radius, was similar to each
other. The unabsorbed X-ray fluxes from the disk component in the 0.01-10 keV
band were estimated to be 1.3x10^{-9}, 3.0x10^{-9}, 9.8x10^{-10}, and
2.4x10^{-9} erg s^{-1} cm^{-2} in 1989, 1990, 1991, and 1995, respectively, and
are proportional to kT_{in}^4, where kT_{in} is a temperature at the inner disk
radius. Based on the standard accretion disk model for a non-rotating BH, our
results suggest either a small BH mass or a large inclination angle. Otherwise,
X1755-338 is a rotating BH. The hard X-ray intensity was found to be variable,
while the soft X-ray intensity was stable. Although the previous work showed
the existence of an iron line at 6.7 keV, no clear iron line feature was found
in all the spectra. We infer that most of the iron line flux reported in the
previous work was due to contamination of the Galactic diffuse X-ray emission.",2105.06628v1
2021-05-20,The Abundance of Lead in Four Metal-Poor Stars,"Cowan et al. (2021) review how roughly half the elements heavier than iron
found in the Sun are produced by rapid neutron capture and half by slow neutron
capture, the r- and s-processes. In the Sun, their relative contribution to
individual elemental abundances is well understood, except for the lightest and
heaviest elements beyond iron. Their contributions are especially uncertain for
the heaviest non-radioactive element, lead (Pb, Z=82). This is constrained by
deriving lead abundances in metal-poor stars. For in the most metal-poor halo
stars, strontium and heavier elements are found in the solar r-process
proportion; s-process elements appear only at metallicities above one-thirtieth
solar.
  In unevolved metal-poor stars of roughly solar heavy-element content, only
two UV Pb lines are detectable. Four such stars have high-resolution spectra of
the strongest line, Pb II at 2203.53A. Roederer et al. (2020) analyzed this
line in one star, deriving a lead-to-iron abundance ratio ten times solar. This
and its blue-shifted profile suggested strong s-process production.
  This work analyzes the UV spectra of all four stars. Calculations including a
predicted Fe I line blueward of the Pb II line, and assuming the lead abundance
scales with r-process abundances, match all four profiles extremely well. A
scaled s-process contribution might improve the match to the much lower lead
abundance found in the unevolved star analyzed previously, but its s-process
excess is modest. An Fe II line blends the other lead line, Pb I at 2833.05A,
which constrains the lead abundance only in the coolest star.",2105.09456v1
2021-07-07,Correlations of r-Process Elements in Very Metal-Poor Stars as Clues to their Nucleosynthesis Sites,"Various nucleosynthesis studies have pointed out that the r-process elements
in very metal-poor (VMP) halo stars might have different origins. By means of
familiar concepts from statistics (correlations, cluster analysis, rank tests
of elemental abundances), we look for causally correlated elemental abundance
patterns and attempt to link them to astrophysical events. Some of these events
produce the r-process elements jointly with iron, while others do not have any
significant iron contribution. In the early stage of our Galaxy, at least three
r-process nucleosynthesis sites have been active. The first two produce and
eject iron and the majority of the lighter r-process elements. We assign them
to two different types of core-collapse events, not identical to regular
core-collapse supernovae (CCSNe), which produce only light trans-Fe elements.
The third category is characterized by a strong r-process and responsible for
the major fraction of the heavy main r-process elements without a significant
co-production of Fe. It does not appear to be connected to CCSNe, in fact the
Fe found in the related r-process enriched stars must come from previously
occurring CCSNe. The existence of actinide boost stars indicates a further
division among strong r-process sites. We assign these two strong r-process
sites to neutron star mergers without fast black hole formation and to events
where the ejecta are dominated by black hole accretion disk outflows.
Indications from the lowest-metallicity stars hint at a connection to massive
single stars (collapsars) forming black holes in the early Galaxy.",2107.03486v1
2021-07-08,"Magnetic properties of 3d, 4d, and 5d transition-metal atomic monolayers in Fe/TM/Fe sandwiches: Systematic first-principles study","Previous studies have accurately determined the effect of transition metal
point defects on the properties of bcc iron. The magnetic properties of
transition metal monolayers on the iron surfaces have been studied equally
intensively. In this work, we investigated the magnetic properties of the 3d,
4d, and 5d transition-metal (TM) atomic monolayers in Fe/TM/Fe sandwiches using
the full-potential local-orbital (FPLO) scheme of density functional theory. We
prepared models of Fe/TM/Fe structures using the supercell method. We selected
the total thickness of our system so that the Fe atomic layers furthest from
the TM layer exhibit bulk iron-bcc properties. Along the direction
perpendicular to the TM layer, we observe oscillations of spin and charge
density. For Pt and W we obtained the largest values of perpendicular
magnetocrystalline anisotropy and for Lu and Ir the largest values of in-plane
magnetocrystalline anisotropy. All TM layers, except Co and Ni, reduce the
total spin magnetic moment in the generated models, which is in good agreement
with the Slater-Pauling curve. Density of states calculations showed that for
Ag, Pd, Ir, and Au monolayers, a distinct van Hove singularity associated with
TM/Fe interface can be observed at the Fermi level.",2107.03768v1
2021-07-09,Three-Dimensional Hydrodynamic Simulations of Convective Nuclear Burning In Massive Stars Near Iron Core Collapse,"Non-spherical structure in massive stars at the point of iron core collapse
can have a qualitative impact on the properties of the ensuing core-collapse
supernova explosions and the multi-messenger signals they produce. Strong
perturbations can aid successful explosions by strengthening turbulence in the
post-shock region. Here, we report on a set of $4\pi$ 3D hydrodynamic
simulations of O- and Si-shell burning in massive star models of varied initial
masses using MESA and the FLASH simulation framework. We evolve four separate
3D models for roughly the final ten minutes prior to, and including, iron core
collapse. We consider initial 1D MESA models with masses of 14-, 20-, and 25
$M_{\odot}$ to survey a range of O/Si shell density and compositional
configurations. We characterize the convective shells in our 3D models and
compare them to the corresponding 1D models. In general, we find that the
angle-average convective speeds in our 3D simulations near collapse are three
to four times larger than the convective speeds predicted by MESA at the same
epoch for our chosen mixing length parameter of $\alpha_{\rm{MLT}}=1.5$. In
three of our simulations, we observe significant power in the spherical
harmonic decomposition of the radial velocity field at harmonic indices of
$\ell=1-3$ near collapse. Our results suggest that large-scale modes are common
in massive stars near collapse and should be considered a key aspect of
pre-supernova progenitor models.",2107.04617v1
2021-08-10,Site-selective magnetic moment collapse in compressed Fe5O6,"Iron oxide is one of the most important components in Earth's mantle. Recent
discovery of the stable presence of Fe5O6 at Earth's mantle environment
stimulates significant interests in the understanding of this new category of
iron oxides. In this paper, we report the electronic structure and magnetic
properties of Fe5O6 calculated by the density functional theory plus dynamic
mean field theory (DFT+DMFT) approach. Our calculations indicate that Fe5O6 is
a conductor at the ambient pressure with dominant Fe-3d density of states at
the Fermi level. The magnetic moments of iron atoms at three non-equivalent
crystallographic sites in Fe5O6 collapse at significantly different rate under
pressure. Such site-selective collapse of magnetic moments originates from the
shifting of energy levels and the consequent charge transfer among the Fe-3d
orbits when Fe5O6 is being compressed. Our simulations suggest that there could
be high conductivity and volume contraction in Fe5O6 at high pressure, which
may induce anomalous features in seismic velocity, energy exchange, and mass
distribution at the deep interior of Earth.",2108.04473v1
2021-09-08,"A new set of chisels for Galactic archaeology: Sc, V and Zn as taggers of accreted globular clusters","Chemical tagging is a powerful tool to reveal the origin of stars and
globular clusters (GCs), especially when dynamics alone cannot provide robust
answers. So far, mostly $\alpha$- and neutron capture elements have been used
to distinguish stars born in the Milky Way (MW) from those born in external
environments such as that of dwarf galaxies. Here, instead, we use iron-peak
elements abundances to investigate the origin of a sample of metal-rich
globular clusters. By homogeneously analyzing high-resolution UVES spectra of
giant stars belonging to four metal-rich GCs (namely NGC 5927, NGC 6388, NGC
6441, NGC 6496), we find that while the $\alpha$-elements Si and Ca have
similar abundance ratios for all the four GCs, and Ti and neutron capture
elements (La, Ba and Eu) only show a marginal discrepancy, a stark difference
is found when considering the abundances of some iron-peak elements (Sc, V and
Zn). In particular, NGC 6388 and NGC 6441 have abundance ratios for these
iron-peak elements significantly lower (by ~ 0.5 dex) than those measured in
NGC 5927 and NGC 6496, which are clearly identified as born in-situ MW clusters
through an analysis of their orbital properties. These measurements indicate
that the environment in which these clusters formed is different, and provide
robust evidence supporting an accreted origin from the same progenitor for NGC
6388 and NGC 6441.",2109.03837v1
2021-09-22,Coupling between Antiferromagnetic and Spin Glass Orders in the Quasi-One-Dimensional Iron Telluride TaFe$_{1+x}$Te$_3$ ($x$=0.25),"Understanding the interplay among different magnetic exchange interactions
and its physical consequences, especially in the presence of itinerant
electrons and disorders, remains one of the central themes in condensed matter
physics. In this vein, the coupling between antiferromagnetic and spin glass
orders may lead to large exchange bias, a property of potential broad
technological applications. In this article, we report the coexistence of
antiferromagnetic order and spin glass behaviors in a quasi-one-dimensional
iron telluride TaFe$_{1+x}$Te$_3$ ($x$=0.25). Its antiferromagnetism is
believed to arise from the antiferromagnetic interchain coupling between the
ferromagnetically aligned FeTe chains along the $b$-axis, while the spin glassy
state stems from the disordered Fe interstitials. This dichotomic role of chain
and interstitial sublattices is responsible for the large exchange bias
observed at low temperatures, with the interstitial Fe acting as the
uncompensated moment and its neighboring Fe chain providing the source for its
pinning. This iron-based telluride may thereby represent a new paradigm to
study the large family of transition metal chalcogenides whose magnetic order
or even the dimensionality can be tuned to a large extent, forming a fertile
playground to manipulate or switch the spin degrees of freedom thereof.",2109.10740v1
2021-09-22,Intermediate spin state and the B1-B2 transition in ferropericlase at tera-Pascal pressures,"Ferropericlase (fp), (Mg$_{1-x}$Fe$_x$)O, the second most abundant mineral in
the Earth's lower mantle, is expected to be an essential component of
super-Earths' mantles. Here we present an ab initio investigation of the
structure and magnetic ground state of fp up to $\sim$ 3 TPa with iron
concentrations (x$_{Fe}$) varying from 0.03 to 0.12. Calculations were
performed using LDA+U$_{sc}$ and PBE exchange-correlation functionals to
elucidate the pressure range for which the Hubbard U (U$_{sc}$) is required.
Similar to the end-members FeO and MgO, fp also undergoes a B1 to B2 phase
transition that should be essential for modeling the structure and dynamics of
super-Earths' mantles. This structural transition involves a simultaneous
change in magnetic state from a low spin (LS) B1 phase with iron total spin S=0
to an intermediate spin (IS) B2 phase with S=1. This is a rare form of
pressure/strain-induced magnetism produced by local cation coordination
changes. Phonon calculations confirm the dynamical stability of the iron B2-IS
state. Free energy calculations are then carried out including vibrational
effects and electronic and magnetic entropy contributions. The phase diagram is
then obtained for low concentration fp using a quasi-ideal solid solution
model. For x$_{Fe}$ > 0.12 this approach is no longer valid. At ultra-high
pressures, there is an IS to LS spin state change in Fe in the B2 phase, but
the transition pressure depends sensitively on thermal electronic excitations
and on x$_{Fe}$.",2109.11008v2
2021-09-26,Superconducting gap and pseudogap in the surface states of the iron-based superconductor PrFeAsO$_{1-y}$ studied by angle-resolved photoemission spectroscopy,"In order to study the possible superconductivity at the polar surfaces of
1111-type iron-based superconductors, which is doped with a large amount of
holes in spite of the electron doping in bulk materials, we have performed
angle-resolved photoemission spectroscopy (ARPES) studies on superconducting
PrFeAsO$_{1-y}$~crystals. We have indeed observed the opening of a
superconducting gap on surface-derived hole pockets as well as on a
bulk-derived hole pocket. The superconducting gap is found to open on the
surface-derived hole pockets below the bulk $T_c$, which suggests that the
surface superconductivity is possibly induced by proximity effect from the
bulk. We have also observed the opening of a large pseudogap on the
surface-derived hole pockets, which is similar to the pseudogap in 122-type
bulk superconductors doped with a smaller amount of holes. This suggests that
the opening of a large pseudogap is a characteristic property of hole-doped
iron-based superconductors.",2109.12522v2
2021-09-28,Atomistic Graph Neural Networks for metals: Application to bcc iron,"The prediction of the atomistic structure and properties of crystals
including defects based on ab-initio accurate simulations is essential for
unraveling the nano-scale mechanisms that control the micromechanical and
macroscopic behaviour of metals. Density functional theory (DFT) can enable the
quantum-accurate prediction of some of these properties, however at high
computational costs and thus limited to systems of ~1,000 atoms. In order to
predict with quantum-accuracy the mechanical behaviour of nanoscale structures
involving from thousands to several millions of atoms, machine learning
interatomic potentials have been recently developed. Here, we explore the
performance of a new class of interatomic potentials based on Graph Neural
Networks (GNNs), a recent field of research in Deep Learning. Two
state-of-the-art GNN models are considered, SchNet and DimeNet, and trained on
an extensive DFT database of ferromagnetic bcc iron. We find that the DimeNet
GNN Fe potential including three-body terms can reproduce with DFT accuracy the
equation of state and the Bain path, as well as defected configurations
(vacancy and surfaces). To the best of our knowledge, this is the first
demonstration of the capability of GNN of reproducing the energetics of defects
in bcc iron. We provide an open-source implementation of DimeNet that can be
used to train other metallic systems for further exploration of the GNN
capabilities.",2109.14012v1
2021-09-30,Atomistic simulation of the FEBID-driven growth of iron-based nanostructures,"The growth of iron-containing nanostructures in the process of focused
electron beam-induced deposition (FEBID) of Fe(CO)$_5$ is studied by means of
atomistic irradiation-driven molecular dynamics (IDMD) simulations. The
geometrical characteristics (lateral size, height and volume), morphology and
metal content of the grown nanostructures are analyzed at different irradiation
and precursor replenishment conditions corresponding to the electron-limited
and precursor-limited regimes (ELR & PLR) of FEBID. A significant variation of
the deposit's morphology and elemental composition is observed with increasing
the electron current from 1 to 4 nA. At low beam current (1 nA) corresponding
to the ELR and a low degree of Fe(CO)$_5$ fragmentation, the nanogranular
structures are formed which consist of isolated iron clusters embedded into an
organic matrix. In this regime, metal clusters do not coalesce with increasing
electron fluence, resulting in relatively low metal content of the
nanostructures. A higher beam current of 4 nA corresponding to the PLR
facilitates the precursor fragmentation and the coalescence of metal clusters
into a dendrite-like structure with the size corresponding to the primary
electron beam. The IDMD simulations enable atomistic-level predictions on the
nanoscopic characterization of the initial phase of nanostructure growth in the
FEBID process. These predictions can be verified in high-resolution
transmission electron microscopy experiments.",2109.15191v2
2021-10-06,Novel Model of an Ultra-stripped Supernova Progenitor of a Double Neutron Star,"Recent discoveries of double neutron star (DNS) mergers and ultra-stripped
supernovae (SNe) raise the questions of their origin and connection. We present
the first 1D~model of a DNS progenitor system which is calculated
self-consistently until an ultra-stripped iron core collapse. We apply the
\texttt{MESA} code starting from a post-common envelope binary consisting of a
$1.35\;M_\odot$ NS and a $3.20\;M_\odot$ zero-age main-sequence helium star and
continue the modelling via Case~BB Roche-lobe overflow until the infall
velocity of the collapsing iron core exceeds $1000\;{\rm km\,s}^{-1}$. The
exploding star has a total mass of $\sim 1.90\;M_\odot$, consisting of a $\sim
0.29\;M_\odot$ He-rich envelope embedding a CO core of $\sim 1.61\;M_\odot$ and
an iron-rich core of $\sim 1.50\;M_\odot$. The resulting second-born NS has an
estimated mass of $\sim 1.44\;M_\odot$ and we discuss the fate of the post-SN
system, as well as the mild recycling of the first-born NS. Depending on the
initial conditions, this family of systems is anticipated to reproduce the DNS
mergers detected by the LIGO-network.",2110.02979v1
2021-10-11,"Dispersionless orbital excitations in (Li,Fe)OHFeSe superconductors","The superconducting critical temperature $T_{\mathrm{c}}$ of intercalated
iron-selenide superconductor (Li,Fe)OHFeSe (FeSe11111) can be increased to 42 K
from 8 K of bulk FeSe. It shows remarkably similar electronic properties as the
high-$T_{\mathrm{c}}$ monolayer FeSe and provides a bulk counterpart to
investigate the origin of enhanced superconductivity. Unraveling the nature of
excitations is crucial for understanding the pairing mechanism in
high-$T_{\mathrm{c}}$ iron selenides. Here we use resonant inelastic x-ray
scattering (RIXS) to investigate the excitations in FeSe11111. Our high-quality
data exhibit several Raman-like excitations, which are dispersionless and
isotropic in momentum transfer and robust against varying $T_{\mathrm{c}}$.
Using atomic multiplet calculations, we assign the low-energy $\sim 0.3$ and
0.7 eV Raman peaks as local $e_g-e_g$ and $e_g-t_{2g}$ orbital excitations. The
intensity of these two features decreases with increasing temperature,
suggesting a primary contribution of the orbital fluctuations. Our results
highlight the importance of orbital degree of freedom for high-$T_{\mathrm{c}}$
iron selenides.",2110.05361v2
2021-10-21,Competing Vortex Topologies in Iron-based Superconductors,"In this work, we establish a new theoretical paradigm for vortex Majorana
physics in the recently discovered topological iron-based superconductors
(tFeSCs). While tFeSCs are widely accepted as an exemplar of topological
insulators (TIs) with intrinsic $s$-wave superconductivity, our theory implies
that such common belief could be oversimplified. Our main finding is that the
normal-state bulk Dirac nodes, usually ignored in TI-based vortex Majorana
theories for tFeSCs, will play a key role of determining the vortex state
topology. In particular, the interplay between TI and Dirac nodal bands will
lead to multiple competing topological phases for a superconducting vortex line
in tFeSCs, including an unprecedented hybrid topological vortex state that
carries both Majorana bound states and a gapless dispersion. Remarkably, this
exotic hybrid vortex phase generally exists in the vortex phase diagram for our
minimal model for tFeSCs and is directly relevant to tFeSC candidates such as
LiFeAs.When the four-fold rotation symmetry is broken by vortex-line tilting or
curving, the hybrid vortex gets topologically trivialized and becomes
Majorana-free, which could explain the puzzle of ubiquitous trivial vortices
observed in LiFeAs. Origin of Majorana signal in other tFeSC candidates such as
FeTe$_x$Se$_{1-x}$ and CaKFe$_4$As$_4$ are also interpreted within our theory
framework. Our theory sheds new light on theoretically understanding and
experimentally engineering Majorana physics in high-temperature iron-based
systems.",2110.11357v2
2021-11-17,Exoplanetary Interiors,"The first mass-estimate of an exoplanet around a Sun-like star, 51 Peg b and
the first radius measurement of an exoplanet, HD209458b pointed to the
challenges of understanding the atmosphere, interior, and evolution of
exoplanets including the possibility of mass loss of planets on close-orbits
that are exposed to strong irradiation. These discoveries raised the question
of heating and inflation mechanisms, and of the nature of these objects in
terms of composition compared to the known planets in the Solar system. The
field of exoplanet interior modeling was born. Here, we outline and discuss
current big science questions: (i) What is the amount of heavy elements in a
planet and do all planets possess an iron-rock core? We suggest that a
promising and novel approach for exoplanets can be measuring their tidal
response in form of the Love numbers h2 and k2. (ii) How much and through what
mechanisms are the interiors of planets heated or delayed from cooling? Many
strongly irradiated gaseous planets require an additional heat source to
explain their large radii. (iii) What is the origin of the observed populations
in the radius-period diagram? Objects in and along the radius valley are
excellent targets to study planetary formation and evaporation. (iv) What does
the composition of rocky planets tell us about their formation? Planets more
iron-rich than Mercury are found, as well as planets that if rocky, are
depleted in iron with respect to Earth. We do not have yet a reliable formation
theory that would explain their existence.",2111.09357v1
2022-01-07,Correlation-Driven Electronic Reconstruction in FeTe$_{1-x}$Se$_x$,"Electronic correlation is of fundamental importance to high temperature
superconductivity. While the low energy electronic states in cuprates are
dominantly affected by correlation effects across the phase diagram,
observation of correlation-driven changes in fermiology amongst the iron-based
superconductors remains rare. Here we present experimental evidence for a
correlation-driven reconstruction of the Fermi surface tuned independently by
two orthogonal axes of temperature and Se/Te ratio in the iron chalcogenide
family FeTe$_{1-x}$Se$_x$. We demonstrate that this reconstruction is driven by
the de-hybridization of a strongly renormalized $d_{xy}$ orbital with the
remaining itinerant iron 3$d$ orbitals in the emergence of an orbital-selective
Mott phase. Our observations are further supported by our theoretical
calculations to be salient spectroscopic signatures of such a non-thermal
evolution from a strongly correlated metallic phase into an orbital-selective
Mott phase in $d_{xy}$ as Se concentration is reduced.",2201.02667v1
2022-02-24,Preferred Spin Excitations in the Bilayer Iron-Based Superconductor CaK(Fe$_{0.96}$Ni$_{0.04}$)$_4$As$_4$ with Spin-Vortex Crystal Order,"The spin-orbit coupling (SOC) is a key to understand the magnetically driven
superconductivity in iron-based superconductors, where both local and itinerant
electrons are present and the orbital angular momentum is not completely
quenched. Here, we report a neutron scattering study on the bilayer compound
CaK(Fe$_{0.96}$Ni$_{0.04}$)$_4$As$_4$ with superconductivity coexisting with a
non-collinear spin-vortex crystal magnetic order that preserves the tetragonal
symmetry of Fe-Fe plane. In the superconducting state, two spin resonance modes
with odd and even $L$ symmetries due to the bilayer coupling are found similar
to the undoped compound CaKFe$_4$As$_4$ but at lower energies. Polarization
analysis reveals that the odd mode is $c-$axis polarized, and the low-energy
spin anisotropy can persist to the paramagnetic phase at high temperature,
which closely resembles other systems with in-plane collinear and $c-$axis
biaxial magnetic orders. These results provide the missing piece of the puzzle
on the SOC effect in iron-pnictide superconductors, and also establish a common
picture of $c-$axis preferred magnetic excitations below $T_c$ regardless of
the details of magnetic pattern or lattice symmetry.",2202.11933v1
2022-04-05,ConfPred: A layered intergrowth structure prediction model based on confinement self-assembly in two-dimensional interlayer space,"We constructed a simple but effective model to predict the layered
intergrowth structures by combining the self-assembly phenomenon in confined
space and the sandwich configuration of layered materials. In this model, a
two-dimensional confined space is constructed by two known block layers, such
as the Fe$_2$As$_2$ block of iron-based superconductors. Then, the crystal
structure prediction is carried out only inside the confined space to search
for brand-new block layers. We realized this model on the basis of the USPEX9.4
code. In the test, the already existing iron-based superconductors can be
always successfully found, such as Ba$_2$Ti$_2$Fe$_2$As$_4$O,
Sr$_3$Sc$_2$Fe$_2$As$_2$O$_5$, Sr$_4$V$_2$Fe$_2$As$_2$O$_6$, and so on. The
comparison test suggests that our model has remarkable advantages in searching
for intergrowth structures. With this space confinement prediction model, a
structure prediction of layered intergrowth materials even with up to six
elements can be performed with an acceptable machine time consumption. So far,
we have done some multi-composition crystal structure predictions of iron-based
superconductor, and found several stable and metastable structures, such as
Ba$_2$Fe$_2$As$_3$, Eu$_2$Fe$_2$As$_3$, La$_2$O$_2$ClFeAs,
LiOMn$_2$As,Li$_4$OFe$_2$As$_2$.",2204.02355v1
2022-04-11,Polarimetry of M-type asteroids in the context of their surface composition,"Aims. We aim to investigate how polarimetric observations can improve our
understanding of the nature and diversity of M/X-type asteroids. Methods.
Polarimetric observations of the selected M/X-type asteroids were carried out
at the Tohoku 0.6-m telescope at Haleakala Observatory, Hawaii (simultaneously
in BVR filters), the 2-m telescope of the Bulgarian National Astronomical
Observatory in Rozhen (in R filter), and the 2.15-m telescope of the Complejo
Astron\'omico El Leoncito (CASLEO), Argentina (in V filter). We analysed the
polarimetric characteristics of M/X-type asteroids along with the available
data obtained by other techniques. Results. New polarimetric observations of 22
M/X-type asteroids combined with published observations provide a data set of
41 asteroids for which the depth of a negative polarisation branch and/or
inversion angle were determined. We found that the depth of the negative
polarisation branch tends to increase with decreasing steepness of the
near-infrared spectra. Asteroids with a deeper negative polarisation branch
tend to have a higher radar circular polarisation ratio. We show that, based on
the relationship of the depth of the negative polarisation branch and inversion
angle, two main sub-types can be distinguished among M-type asteroids. We
suggest that these groups may be related to different surface compositions
similar to (1) irons and stony-irons and (2) enstatite and iron-rich
carbonaceous chondrites.",2204.04929v1
2022-04-20,Long Term X-Ray Spectral Variation of the Wolf-Rayet Binary WR 102-1 in the Galactic bulge: evidence for wind distortion in the binary,"WR~102-1 was detected by Suzaku as a conspicuous point source in the 6.7 keV
intensity map of the central region of the Milky Way. The source was suggested
as a possible Wolf-Rayet binary based on its X-ray and infrared spectral
characteristics. The iron line emission is expected to originate in the
Wolf-Rayet star's dynamic stellar-wind when colliding the companion's mild
stellar wind. Here, we report the result of a long-term X-ray monitoring of
WR~102-1 since 1998 using archival data of ASCA, XMM-Newton, Chandra, Suzaku,
and Swift to reveal variations of the iron K-emission line and the
circumstellar absorption. Consequently, we have detected significant redshifts
of the iron K-emission line from the XMM-Newton observation in March 2003 and
the Suzaku observation in September 2006. Furthermore, when the red-shift was
observed, which suggests that the Wolf-Rayet star was in front of the companion
star, the circumstellar absorption values were smaller than other periods.
These results appear contrary to the expectation if the Wolf-Rayet's stellar
wind is spherically symmetric, but may be understood if the Wolf-Rayet star's
stellar wind is significantly distorted due to the rapid orbital motion near
the periastron.",2204.09349v1
2022-06-20,Prevalence of short-lived radioactive isotopes across exoplanetary systems inferred from polluted white dwarfs,"In the Solar System short-lived radioisotopes, such as 26Al, played a crucial
role during the formation planetary bodies by providing a significant
additional source of heat. Notably, this led to early and large-scale melting
and iron core formation in planetesimals and their loss of volatile elements,
such as hydrogen and carbon. In the context exoplanetary systems, therefore,
the prevalence of short-lived radioisotopes is key to interpreting the observed
bulk volatile budget and atmospheric diversity among low-mass exoplanets. White
dwarfs that have accreted planetary material provide a unique means to infer
the frequency of iron core formation in extrasolar planetesimals, and hence the
ubiquity of planetary systems forming with high short-lived radioisotope
abundances. Here, we devise a quantitative method to infer the fraction of
planetary systems enriched with shortlived radionuclides upon planetesimal
formation from white dwarf data. We argue that the current evidence from white
dwarfs point towards a significant fraction of exo-planetesimals having formed
an iron core. Although the data may be explained by the accretion of exo-moon
or Pluto-sized bodies that were able to differentiate due to gravitational
potential energy release, our results suggest that the most likely explanation
for the prevalence of differentiated material among polluted white dwarfs is
that the Solar System is not unusual in being enriched in 26Al. The models
presented here suggest a ubiquitous pathway for the enrichment of exoplanetary
systems by short-lived radioisotopes, disfavouring short-lived radioisotope
enrichment scenarios relying on rare chance encounters with single nearby
supernovae, Wolf-Rayet or AGB stars.",2206.09675v1
2022-06-30,Magnetic field measurements on the mini-ICAL detector using Hall probes,"The magnetised 51 kton Iron Calorimeter (ICAL) detector proposed to be built
at INO is designed with a focus on detecting 1-20 GeV muons. The magnetic field
will enable the measurement of the momentum of the $\mu^-$ and $\mu^+$
generated from the charge current interactions of $\nu_\mu$ and $\bar\nu_\mu$
separately within iron in the detector, thus permitting the determination of
the neutrino mass ordering/hierarchy, among other important goals of ICAL.
Hence it is important to determine the magnetic field as accurately as
possible. The mini-ICAL detector is an 85-ton prototype of ICAL, which is
operational at Madurai in South India. We describe here the first measurement
of the magnetic field in mini-ICAL using Hall sensor PCBs. A set-up developed
to calibrate the Hall probe sensors using an electromagnet. The readout system
has been designed using an Arduino Nano board for selection of channels of Hall
probes mounted on the PCB and to convert the analog voltage to a digital
output. The magnetic field has been measured in the small gaps (provided for
the purpose) between iron plates in the top layer of mini-ICAL as well as in
the air just outside the detector. A precision of better than 3% was obtained,
with a sensitivity down to about 0.03 kGauss when measuring the small fringe
fields outside the detector.",2206.15082v1
2022-07-01,Particle acceleration and radiation reaction in a strongly magnetized rotating dipole,"Abridged. Neutron stars are surrounded by ultra-relativistic particles
efficiently accelerated by ultra strong electromagnetic fields. However so far,
no numerical simulations were able to handle such extreme regimes of very high
Lorentz factors and magnetic field strengths. It is the purpose of this paper
to study particle acceleration and radiation reaction damping in a rotating
magnetic dipole with realistic field strengths typical of millisecond and young
pulsars as well as of magnetars. To this end, we implemented an exact
analytical particle pusher including radiation reaction in the reduced
Landau-Lifshitz approximation where the electromagnetic field is assumed
constant in time and uniform in space during one time step integration. The
position update is performed using a velocity Verlet method. We extensively
tested our algorithm against time independent background electromagnetic fields
like the electric drift in cross electric and magnetic fields and the magnetic
drift and mirror motion in a dipole. Eventually, we apply it to realistic
neutron star environments. We investigated particle acceleration and the impact
of radiation reaction for electrons, protons and iron nuclei plunged around
millisecond pulsars, young pulsars and magnetars, comparing it to situations
without radiation reaction. We found that the maximum Lorentz factor depends on
the particle species but only weakly on the neutron star type. Electrons reach
energies up to $\gamma_e \approx 10^8-10^9$ whereas protons energies up to
$\gamma_p \approx 10^5-10^6$ and iron up to $\gamma \approx 10^4-10^5$. While
protons and irons are not affected by radiation reaction, electrons are
drastically decelerated, reducing their maximum Lorentz factor by 2 orders of
magnitude. We also found that the radiation reaction limit trajectories fairly
agree with the reduced Landau-Lifshitz approximation in almost all cases.",2207.00624v1
2022-08-10,Dimensionality and Background Cancellation in Energy Selective X-Ray Imaging,"Purpose: The set of linear attenuation coefficients that belong to materials
in the human body is commonly assumed to be spanned by two basis functions in
the range of clinical x-ray energies, even though there is evidence that the
dimensionality of this set is greater than two. It has not yet been clear that
the use of a third basis function could be beneficial in absence of contrast
agents.
  Approach: In this work, the choice of the number of basis functions used in
the basis decomposition method is studied for the task of producing an image
where a third material is separated from a background of two other materials,
in a case where none of the materials have a K-edge in the range of considered
x-ray energies (20-140 keV). The case of separating iron from mixtures of liver
and adipose tissue is studied with a simulated phantom which incorporates
random and realistic tissue variability.
  Results: Inclusion of a third basis function improves the quantitative
estimate of iron concentration by several orders of magnitude in terms of mean
squared error in the resulting image.
  Conclusions: The inclusion of a third basis function in the basis
decomposition is essential for the studied imaging task and could have
potential application for quantitative estimation of iron concentration from
material decomposed images.",2208.05362v1
2022-08-11,Atomistic fracture in bcc iron revealed by active learning of Gaussian approximation potential,"The prediction of atomistic fracture mechanisms in body-centred cubic (bcc)
iron is essential for understanding its semi-brittle nature. Existing atomistic
simulations of the crack-tip deformation mechanisms under mode-I loading based
on classical interatomic potentials yield contradicting predictions. To enable
fracture prediction with quantum accuracy, we develop a Gaussian approximation
potential (GAP) using an active learning strategy by extending a density
functional theory (DFT) database of ferromagnetic bcc iron. We apply the active
learning algorithm and obtain a Fe GAP model with a maximum predicted error of
8 meV/atom over a broad range of stress intensity factors (SIFs) and for four
crack systems. The learning efficiency of the approach is analysed, and the
predicted critical SIFs are compared with Griffith and Rice theories. The
simulations reveal that cleavage along the original crack plane is the crack
tip mechanism for {100} and {110} crack planes at T=0K, thus settling a
long-standing dispute. Our work also highlights the need for a multiscale
approach to predicting fracture and intrinsic ductility, whereby finite
temperature, finite loading rate effects and pre-existing defects (e.g.
nanovoids, dislocations) should be taken explicitly into account.",2208.05912v2
2022-08-12,Thermal Evolution and magnetic history of rocky planets,"We present a thermal evolution model coupled with a Henyey solver to study
the circumstances under which a rocky planet could potentially host a dynamo in
its liquid iron core and/or magma ocean. We calculate the evolution of planet
thermal profiles by solving the energy balance equations for both the mantle
and the core. We use a modified mixing length theory to model the convective
heat flow in both the magma ocean and solid mantle. In addition, by including
the Henyey solver, we self-consistently account for adjustments in the interior
structure and heating (cooling) due to planet contraction (expansion). We
evaluate whether a dynamo can operate using the critical magnetic Reynolds
number. We run simulations to explore how planet mass ($M_{pl}$), core mass
fraction (CMF) and equilibrium temperature ($T_{eq}$) affect the evolution and
lifetime of possible dynamo sources. We find that the $T_{eq}$ determines the
solidification regime of the magma ocean, and only layers with melt fraction
greater than a critical value of 0.4 may contribute to the dynamo source region
in the magma ocean. We find that the mantle mass, determined by $M_{pl}$ and
CMF, controls the thermal isolating effect on the iron core. In addition, we
show that the liquid core last longer with increasing planet mass. For a core
thermal conductivity of 40$\ \mathrm{Wm^{-1}K^{-1}}$, the lifetime of the
dynamo in the iron core is limited by the lifetime of the liquid core for
1$M_{\oplus}$ planets, and by the lack of thermal convection for 3$M_{\oplus}$
planets.",2208.06523v1
2022-09-10,Discovery of a pair density wave state in a monolayer high-Tc iron-based superconductor,"The pair density wave (PDW) is an extraordinary superconducting state where
Cooper pairs carry nonzero momentum. It can emerge when the full condensation
of zero momentum Cooper pairs is frustrated. Evidence for the existence of
intrinsic PDW order in high-temperature (high-Tc) cuprate superconductors and
kagome superconductors has emerged recently. However, the PDW order in
iron-based high-Tc superconductors has not been observed experimentally. Here,
using scanning tunneling microscopy/spectroscopy, we report the discovery of
the PDW state in monolayer iron-based high-Tc Fe(Te,Se) films grown on
SrTiO3(001) substrates. The PDW state with a period of {\lambda}~3.6a_Fe (a_Fe
is the distance between neighboring Fe atoms) is observed at the domain walls
by the spatial electronic modulations of the local density of states,
superconducting gap, and the {\pi}-phase shift boundaries of the PDW around the
dislocations of the intertwined charge density wave order. The discovery of the
PDW state in the monolayer Fe(Te,Se) film provides a low-dimensional platform
to study the interplay between the correlated electronic states and
unconventional Cooper pairing in high-Tc superconductors.",2209.04592v2
2022-09-16,Spin fluctuations in the 112-type iron-based superconductor Ca$_{0.82}$La$_{0.18}$Fe$_{0.96}$Ni$_{0.04}$As$_{2}$,"We report time-of-flight inelastic neutron scattering (INS) investigations on
the spin fluctuation spectrum in the 112-type iron-based superconductor (FeSC)
Ca$_{0.82}$La$_{0.18}$Fe$_{0.96}$Ni$_{0.04}$As$_{2}$ (CaLa-112). In comparison
to the 122-type FeSCs with a centrosymmetric tetragonal lattice structure
(space group $I4/mmm$) at room temperature and an in-plane stripe-type
antiferromagnetic (AF) order at low temperature, the 112 system has a
noncentrosymmetric structure (space group $P2_{1}$) with additional zigzag
arsenic chains between Ca/La layers and a magnetic ground state with similar
wavevector $\mathbf{Q}_{\mathrm{AF}}$ but different orientations of ordered
moments in the parent compounds. Our INS study clearly reveals that the
in-plane dispersions and the bandwidth of spin excitations in the
superconducting CaLa-112 closely resemble to those in 122 systems. While the
total fluctuating moments $\langle m^2 \rangle\approx 4.6\pm0.2 \mu_B^2$/Fe are
larger than 122 system, the dynamic correlation lengths are similar
($\xi\approx 10$ \AA). These results suggest that superconductivity in iron
arsenides may have a common magnetic origin under similar magnetic exchange
couplings with a dual nature from local moments and itinerant electrons,
despite their different magnetic patterns and lattice symmetries.",2209.07726v1
2022-10-04,Strengthened proximity effect at grain boundaries to enhance inter-grain supercurrent in Ba1-xKxFe2As2 superconductors,"Iron-based superconductors have great potential for high-power applications
due to their prominent high-field properties. One of the central issues in
enhancing the critical current density of iron-based superconducting wires is
to reveal the roles and limitations of grain boundaries in supercurrent
transport. Here, we finely tuned the electronic properties of grain boundaries
by doping Ba1-xKxFe2As2 superconductors in a wide range (0.25<x<0.598). It is
found that the intra-grain Jcintra peaks near x~0.287, while the inter-grain
Jcinter has a maximum at about x~0.458. Remarkably, the grain boundary
transparency parameter defined as Jcinter/Jcintra rises monotonically with
doping. Through detailed microscopic analysis, we suggest that the FeAs
segregation phase commonly existing at grain boundaries and the adjacent grains
constitute superconductor-normal metal-superconductor (SNS) Josephson junctions
which play a key role in transporting supercurrent. A sandwich model based on
the proximity effect and the SNS junction is proposed to well interpret our
data. It is found that overdoping in superconducting grains largely strengthens
the proximity effect and consequently enhances the intergrain supercurrent. Our
results will shed new insights and inspirations for improving the application
parameters of iron-based superconductors by grain boundary engineering.",2210.01305v1
2022-10-18,In-plane electronic anisotropy revealed by interlayer resistivity measurements on the iron-based superconductor parent compound CaFeAsF,"Both cuprates and iron-based superconductors demonstrate nematicity, defined
as the spontaneous breaking of rotational symmetry in electron systems. The
nematic state can play a role in the high-transition-temperature
superconductivity of these compounds. However, the microscopic mechanism
responsible for the transport anisotropy in iron-based compounds remains
debatable. Here, we investigate the electronic anisotropy of CaFeAsF by
measuring its interlayer resistivity under magnetic fields with varying field
directions. Counterintuitively, the interlayer resistivity was larger in the
longitudinal configuration ($B \parallel I \parallel c$) than in the transverse
one ($B \perp I \parallel c$). The interlayer resistivity exhibited a so-called
coherence peak under in-plane fields and was highly anisotropic with respect to
the in-plane field direction. At $T$ = 4 K and $B$ = 14 T, the
magnetoresistance $\Delta\rho/\rho_0$ was seven times larger in the $B
\parallel b_o$ than in the $B \parallel a_o$ configuration. Our theoretical
calculations of the conductivity based on the first-principles electronic band
structure qualitatively reproduced the above observations but underestimated
the magnitudes of the observed features. The proposed methodology can be a
powerful tool for probing the nematic electronic state in various materials.",2210.09533v2
2022-10-19,X-ray spectroscopy of the accretion disk corona source 2S 0921-630 with Suzaku archival data,"2S 0921$-$630 is an eclipsing low-mass X-ray binary (LMXB) with an orbital
period of $\sim$ 9 days. Past X-ray observations have revealed that 2S
0921$-$630 has an extended accretion disk corona (ADC), from which most of the
X-rays from the system are emitted. We report the result of our Suzaku archival
data analysis of 2S 0921$-$630. The average X-ray spectrum is reproduced with a
blackbody emission ($kT_{\rm bb} \sim 0.3$ keV) Comptonized by optically-thick
gas (``Compton cloud''; optical depth $\tau \sim 21$) with a temperature of
$\sim 2$ keV, combined with thirteen emission lines. We find that most of the
emission lines correspond to highly ionized atoms: O, Ne, Mg, Si, S, Ar, and
Fe. A K$\alpha$ emission line and an absorption edge of semi-neutral iron (Fe I
-- XVII) are also detected. The semi-neutral iron K$\alpha$ line is
significantly broad with a width of $0.11 \pm 0.02$ keV in sigma, which
corresponds to the Doppler broadening by the Kepler motion at a radius of $\sim
10^9$ cm. We suggest that the observed semi-neutral iron line originates at the
inner part of the accretion disk in the immediate outside of the Compton cloud,
i.e., the Compton cloud may have a radius of $\sim 10^9$ cm.",2210.10792v1
2022-11-02,Fourier Disentangled Multimodal Prior Knowledge Fusion for Red Nucleus Segmentation in Brain MRI,"Early and accurate diagnosis of parkinsonian syndromes is critical to provide
appropriate care to patients and for inclusion in therapeutic trials. The red
nucleus is a structure of the midbrain that plays an important role in these
disorders. It can be visualized using iron-sensitive magnetic resonance imaging
(MRI) sequences. Different iron-sensitive contrasts can be produced with MRI.
Combining such multimodal data has the potential to improve segmentation of the
red nucleus. Current multimodal segmentation algorithms are computationally
consuming, cannot deal with missing modalities and need annotations for all
modalities. In this paper, we propose a new model that integrates prior
knowledge from different contrasts for red nucleus segmentation. The method
consists of three main stages. First, it disentangles the image into high-level
information representing the brain structure, and low-frequency information
representing the contrast. The high-frequency information is then fed into a
network to learn anatomical features, while the list of multimodal
low-frequency information is processed by another module. Finally, feature
fusion is performed to complete the segmentation task. The proposed method was
used with several iron-sensitive contrasts (iMag, QSM, R2*, SWI). Experiments
demonstrate that our proposed model substantially outperforms a baseline UNet
model when the training set size is very small.",2211.01353v1
2022-12-05,"Quasi two-dimensional nature of high-Tc superconductivity in iron-based (Li,Fe)OHFeSe","The intercalated iron selenide (Li,Fe)OHFeSe has a strongly layered structure
analogous to the quasi two-dimensional (2D) bismuth cuprate superconductors,
and exhibits both high-temperature (Tc) and topological superconductivity.
However, the issue of its superconductivity dimensionality has not yet been
fully investigated so far. Here we report that the quasi-2D superconductivity
features, including the high anisotropy {\gamma} = 151 and the associated
quasi-2D vortices, are also revealed for (Li,Fe)OHFeSe, based on systematic
experiments of the electrical transport and magnetization and model fittings.
Thus, we establish a new vortex phase diagram for (Li,Fe)OHFeSe, which
delineates an emergent quasi-2D vortex-liquid state, and a subsequent
vortex-solid dimensional crossover from a pancake-like to a three-dimensional
state with decreasing temperature and magnetic field. Furthermore, we find that
all the quasi-2D characteristics revealed here for the high-Tc iron selenide
superconductor are very similar to those reported for the high-Tc bismuth
cuprate superconductors.",2212.02022v1
2022-12-19,Exchange interactions in iron and nickel: DFT+DMFT study in paramagnetic phase,"We analyze possible ways to calculate magnetic exchange interactions within
the density functional theory plus dynamical mean-field theory (DFT+DMFT)
approach in the paramagnetic phase. Using the susceptibilities obtained within
the ladder DMFT approach together with the random phase approximation result
for the Heisenberg model, we obtain bilinear exchange interactions. We show
that the earlier obtained result of Stepanov et al. [Phys. Rev. Lett. 121,
037204 (2018); Phys. Rev. B 105, 155151 (2022)] corresponds to considering
individual magnetic moments in each orbital in the leading-order approximation
in the non-local correlations. We consider a more general approach and apply it
to evaluate the effective magnetic parameters of iron and nickel. We show that
the analysis, based on the inverse orbital-summed susceptibilities, yields
reasonable results for both, weak and strong magnets. For iron we find, in the
low-temperature limit, the exchange interaction $J_0\simeq 0.20$ eV, while for
nickel we obtain $J_0\simeq 1.2$ eV. The considered method also allows one to
describe the spin-wave dispersion at temperatures $T\sim T_C$, which is in
agreement with the experimental data.",2212.09267v2
2023-02-08,"Microstructure-dependent magnetic properties of iron silicon single, bi- and oligo-crystals measured with a miniaturised Single-Sheet-Tester","Electrical iron silicon steel is the most commonly used soft magnetic
material in electrical energy conversion and transmission, and its demand is
expected to increase with the need for electrification of the transportation
sector and the transition to renewable energy to combat climate change.
Although iron silicon steel has been used for more than 100 years, some
fundamental relationships between microstructure and magnetic performance
remain vague, especially with regard to the role of crystal defects such as
grain boundaries and dislocations that are induced during the final cutting
step of the process chain. In this paper we present first results of a new
approach to quantify the effects of orientation, grain boundaries and
deformation on the magnetic properties of single, bi- and oligo-crystals using
a miniaturised Single-Sheet-Tester. In this way, we were able to better resolve
the orientation-dependent polarisation curves at low field strengths, revealing
an additional intersection between the medium and hard axis. Furthermore, we
were able to distinguish the effects of different deformation structures - from
single dislocations to tangles to localised deformation and twins - on
different magnetic properties such as on coercivity, remanence and
susceptibility, and we found that our particular grain boundary strongly
reduces the remanence.",2302.03808v1
2023-02-08,Plant-wide byproduct gas distribution under uncertainty in iron and steel industry via quantile forecasting and robust optimization,"In the modern iron and steel industry, the efficient distribution of
byproduct gases faces significant challenges due to quantity- and
quality-related uncertainties of gases. This study presents an optimal approach
to gas distribution that addresses this issue by incorporating the energy flow
network and the uncertain surplus gases from the manufacturing system. The
uncertain optimization problem is formulated as a two-stage robust optimization
(TSRO) model, including ""here-and-now"" decisions aimed at minimizing the
start-stop cost of energy conversion units, as well as ""wait-and-see"" decisions
aimed at minimizing the operating cost of gasholders and the penalties
resulting from energy excess or shortage. To facilitate practical
implementation, we propose a ""first quantify, then optimize"" approach: (1)
quantifying the uncertainty of surplus gases via a conditional quantile
regression (CDQ)-based T-step time series model, and (2)finding the optimal
solution through a column-and-constraint generation algorithm. Furthermore, a
case study is conducted on an industrial energy system to validate the proposed
methodology. Computational results, using evaluation indicators, such as MAPE,
RMSE, PICP, and PINAW, confirm the effectiveness of the data-driven time series
model in accurately quantifying uncertainties in each period. Sensitivity
analysis demonstrates that the proposed TSRO model achieves a favorable balance
between robustness and flexibility by selecting the combination of ""budget and
quantile"" and the parameters of storage and conversion units. Consequently,
TSRO can efficiently find a robust gas distribution solution with the desired
level of conservativeness for integrated iron and steel plants.",2302.03946v2
2023-02-28,Spectroscopic studies of the superconducting gap in the 12442 family of iron-based compounds,"The iron-based compounds of the so-called 12442 family are very peculiar in
various respects. They originate from the intergrowth of 122 and 1111 building
blocks, display a large in-plane vs. out-of-plane anisotropy, possess double
layers of FeAs separated by insulating layers, and are generally very similar
to double-layer cuprates. Moreover, they are stoichiometric superconductors
because of an intrinsic hole doping. Establishing their superconducting
properties, and in particular the symmetry of the order parameter, is thus
particularly relevant in order to understand to what extent these compounds can
be considered as the iron-based counterpart of cuprates. In this work we review
the results of various techniques from the current literature and compare them
with ours, obtained in Rb-12442 by combining point-contact Andreev-reflection
spectroscopy and coplanar waveguide resonator measurements of the superfluid
density. It turns out that the compound possesses at least two gaps, one of
which is certainly nodal. The compatibility of this result with the
theoretically allowed gap structures, as well as with the other results in
literature, is discussed in detail.",2302.14767v2
2023-03-08,Proximity effect and inverse proximity effect in a topological-insulator/iron-based-superconductor heterostructure,"We theoretically study the proximity effect and the inverse proximity effect
in a topological insulator/iron-based superconductor heterostructure based on
the microscopic model. The superconducting order parameter is self-consistently
calculated. Its magnitude decreases when the coupling of these two systems
increases. The induced pairing order parameter exhibits negative and positive
values, while the negative pairing near the $\Gamma=(0,0)$ point is dominant.
This parameter has twofold symmetry and includes an $s$-wave component and a
$d$-wave component. The magnitude of the induced pairing order parameter has a
maximal value at the coupling strength $t_p=0.3\approx 0.06$ eV. The spectral
function and the local density of states are calculated and may be used to
probe the proximity effect. We also discuss the feedback of the topological
insulator to the iron-based superconductor layer. The normal-state Fermi
surface is distorted by the coupling, and additional Fermi pockets are induced.
An effective spin-orbit interaction term is induced. In the superconducting
state, the previous fourfold symmetry of the order parameter is broken, and a
$d$-wave component pairing term is also induced. Our main results can be well
understood by analyzing the Fermi surfaces of the original systems.",2303.04586v1
2023-03-16,Nucleosynthesis in neutrino-heated ejecta and neutrino-driven winds of core-collapse supernovae; neutrino-induced nucleosynthesis,"The innermost ejecta of core-collapse supernovae are considered to be the
sources of some iron-group and heavier nuclei. The ejecta are predominantly
driven by neutrino heating, principally due to neutrino capture on free
neutrons and protons. Such neutrino interaction plays a crucial role for
setting neutron richness in the ejecta. Recent hydrodynamics work with
sophisticated neutrino transport indicates that the ejecta are only mildly
neutron rich or even proton rich. In such conditions a wide variety of
trans-iron isotopes are synthesized, while the neutron richness is insufficient
for the production of r-process nuclei. In this capter, basic concepts of
nucleosynthesis in neutrino-heated ejecta and neutrino-driven winds of
core-collapse supernovae are presented along with latest studies.
Neutrino-heated ejecta indicate the early ejecta component within the first few
seocnds in which anisotropic convective activities of material above the
neutrinosphere become important for nucleosynthesis. Then, neutrino-driven
winds follow, which are approximately isotropic outflows emerging from the
surface of a proto-neutron star . According to such characteristics, studies of
nucleosynthesis here are based on recent multi-dimentional hydrodynamics
simulations and semi-alalytic wind solutions, respectively. These studies
suggest that trans-iron species up to the atomic mass number of 90, as well as
some rare isotopes such as 48Ca and 92Mo, are produced in the neutrino-heated
ejecta. Neutrino-driven winds are unlikely sources of r-process nuclei, but
rather promising sources of proton-rich isotopes up to the atomic number of
110.",2303.09442v1
2023-03-28,Iron-rich Metal-poor Stars and the Astrophysics of Thermonuclear Events Observationally Classified as Type Ia Supernovae. I. Establishing the Connection,"The progenitor systems and explosion mechanisms responsible for the
thermonuclear events observationally classified as Type Ia supernovae are
uncertain and difficult to uniquely constrain using traditional observations of
Type Ia supernova host galaxies, progenitors, light curves, and remnants. For
the subset of thermonuclear events that are prolific producers of iron, we use
published theoretical nucleosynthetic yields to identify a set of elemental
abundance ratios infrequently observed in metal-poor stars but shared across a
range of progenitor systems and explosion mechanisms: [Na,Mg,Co/Fe]<0. We label
stars with this abundance signature ``iron-rich metal-poor'' or IRMP stars. We
suggest that IRMP stars formed in environments dominated by thermonuclear
nucleosynthesis and consequently that their elemental abundances can be used to
constrain both the progenitor systems and explosion mechanisms responsible for
thermonuclear explosions. We identify three IRMP in the literature and
homogeneously infer their elemental abundances. We find that the elemental
abundances of BD+80 245, HE 0533--5340, and SMSS J034249.53--284216.0 are best
explained by the (double) detonations of sub-Chandrasekhar mass CO white
dwarfs. If our interpretation of IRMP stars is accurate, then they should be
very rare in globular clusters and more common in the Magellanic Clouds and
dwarf spheroidal galaxies than in the Milky Way's halo. We propose that future
studies of IRMP stars will quantify the relative occurrences of different
thermonuclear event progenitor systems and explosion mechanisms.",2303.16357v1
2023-04-11,Orbital Selective Mott Transition Effects and Non-Trivial Topology of Iron Chalcogenide,"The iron-based superconductor FeSe$_{1-x}$Te$_{x}$ (FST) has recently gained
significant attention as a host of two distinct physical phenomena: ($i$)
Majorana zero modes which can serve as potential topologically protected
qubits, and ($ii$) a realization of the orbital selective Mott transition
(OSMT). In this Letter, we connect these two phenomena and provide new insights
into the interplay between strong electronic correlations and non-trivial
topology in FST. Using linearized quasiparticle self-consistent GW plus
dynamical mean-field theory, we show that the topologically protected Dirac
surface state has substantial Fe($d_{xy}$) character. The proximity to the OSMT
plays a dual role, it facilitates the appearance of the topological surface
state by bringing the Dirac cone close to the chemical potential, but destroys
the Z$_{2}$ topological superconductivity when the system is too close to the
orbital selective Mott phase (OSMP). We derive a reduced effective Hamiltonian
that describes the topological band. Its parameters capture all the chemical
trends found in the first principles calculation. Our findings provide a
framework for further study of the interplay between strong electronic
correlations and non-trivial topology in other iron-based superconductors.",2304.05002v2
2023-04-12,Charge order driven by multiple-Q spin fluctuations in heavily electron-doped iron selenide superconductors,"Intertwined spin and charge orders have been widely studied in
high-temperature superconductors, since their fluctuations may facilitate
electron pairing; however, they are rarely identified in heavily electron-doped
iron selenides. Here, using scanning tunneling microscopy, we show that when
the superconductivity of (Li0.84Fe0.16OH)Fe1-xSe is suppressed by introducing
Fe-site defects, a short-ranged checkerboard charge order emerges, propagating
along the Fe-Fe directions with an approximately 2aFe period. It persists
throughout the whole phase space tuned by Fe-site defect density, from a
defect-pinned local pattern in optimally doped samples to an extended order in
samples with lower Tc or non-superconducting. Intriguingly, our simulations
indicate that the charge order is likely driven by multiple-Q spin density
waves originating from the spin fluctuations observed by inelastic neutron
scattering. Our study proves the presence of a competing order in heavily
electron-doped iron selenides, and demonstrates the potential of charge order
as a tool to detect spin fluctuations.",2304.05854v1
2023-04-22,A Multi-frequency Magnetic Particle Spectroscopy System for the Characterization of Magnetic Nanoparticles,"Magnetic particle spectroscopy (MPS) is one of the most versatile methods to
characterize the magnetic properties of magnetic nanoparticles (MNPs). The
excitation magnetic field is one of the most crucial factors that affects the
MPS signal of the MNPs. In this study, a multi-frequency MPS system is
developed to investigate the MPS signal of MNPs in different ac magnetic
fields. The MPS system consists of a multi-channel excitation module for the
generation of different-frequency ac magnetic fields and a detection module for
the measurement of the magnetic response of the MNPs. The MPS system allows to
generate ac magnetic fields with a frequency up to 32.6 kHz and amplitude up to
25 mT. The MPS signals of the MNPs in different ac magnetic fields are measured
to systematically evaluate the performance of the multi-frequency MPS system,
including the MNP spectra and its dynamic magnetization curve. In addition, the
signal-to-noise ratio (SNR) of the MPS system is quantitively assessed with
measured MPS signals of a given MNP sample and DI water. Furthermore, a series
of MNP samples with different iron concentrations are prepared and measured to
evaluate the limit-of-detection (LOD) in terms of iron concentration. The
influence of the excitation magnetic field, including frequency and amplitude,
is discussed based on the SNRs of the measured harmonics. Experimental results
show that the LOD is 2.3 ng in terms of iron.",2304.11290v1
2023-05-10,The spin measurement of MAXI J0637-430: a black hole candidate with high disk density,"The Galactic black hole candidate MAXI J0637-430 was first discovered by
$\textit{MAXI/GSC}$ on 2019 November 02. We study the spectral properties of
MAXI J0637-430 by using the archived $\textit{NuSTAR}$ data and
$\textit{Swift}$/XRT data. After fitting the eight spectra by using a disk
component and a powerlaw component model with absorption, we select the spectra
with relatively strong reflection components for detailed X-ray reflection
spectroscopy. Using the most state-of-art reflection model $\tt{relxillCp}$,
the spectral fitting measures a black hole spin $\textit{a}_{\rm{*}} > 0.72$
and the inclination angle of the accretion disk $i$ = $46.1_{-5.3}^{+4.0}$
degrees, at 90 per cent confidence level. In addition, the fitting results show
an extreme supersolar iron abundance. Combined with the fitting results of the
reflection model $\tt{reflionx\_hd}$, we consider that this unphysical iron
abundance may be caused by a very high density accretion disk ( $n_{\rm{e}} >
2.34 \times 10^{21}$ $\rm{cm}^{-3}$ ) or a strong Fe K$\alpha$ emission line.
The soft excess is found in the soft state spectral fitting results, which may
be an extra free-free heating effect caused by high density of the accretion
disk. Finally, we discuss the robustness of black hole spin obtained by X-ray
reflection spectroscopy. The result of relatively high spin is self-consistent
with broadened Fe K$\alpha$ line. Iron abundance and disk density have no
effect on the spin results.",2305.05914v1
2023-07-20,Stray magnetic field imaging of thin exfoliated iron halides flakes,"Magnetic van der Waals materials are often proposed for use in future
spintronic devices, aiming to leverage the combination of long-range magnetic
order and near-atomic thinness to produce energy-efficient components. One
class of material that has been discussed in this context are the iron halides
FeCl$_2$ and FeBr$_2$, which are A-type antiferromagnets with strong uniaxial
magnetocrystalline anisotropy. However, despite characterization of the bulk
materials, the possibility for sustaining the magnetic behaviors that would
underpin such applications in thin flakes has not been investigated. In this
work, we use nitrogen-vacancy (NV) center microscopy to quantitatively image
magnetism in individual exfoliated flakes of these iron halides, revealing the
absence of magnetic remanence, a weak induced magnetization under bias field
and variable behavior versus temperature. We show that our results are
consistent with the antiferromagnetic behavior of the bulk material with a soft
ferromagnetic uncompensated layer, indicating that extended ($>1~\mu$m)
ferromagnetic domains are not sustained even at low temperatures (down to 4 K).
Finally, we find that the magnetic order is strongly affected by the sample
preparation, with a surprising diamagnetic order observed in a thin, hydrated
sample.",2307.10561v1
2023-07-20,Tuning superconductivity and spin-vortex fluctuations in CaKFe$_4$As$_4$ through in-plane antisymmetric strains,"Lattice strains of appropriate symmetry have served as an excellent tool to
explore the interaction of superconductivity in the iron-based superconductors
with nematic and stripe spin-density wave (SSDW) order, which are both closely
tied to an orthorhombic distortion. In this work, we contribute to a broader
understanding of the coupling of strain to superconductivity and competing
normal-state orders by studying CaKFe$_4$As$_4$ under large, in-plane strains
of $B_{1g}$ and $B_{2g}$ symmetry. In contrast to the majority of iron-based
superconductors, pure CaKFe$_4$As$_4$ exhibits superconductivity with
relatively high transition temperature of $T_c\,\sim\,$35 K in proximity of a
non-collinear, tetragonal, hedgehog spin-vortex crystal (SVC) order. Through
experiments, we demonstrate an anisotropic in-plane strain response of $T_c$,
which is reminiscent of the behavior of other pnictides with nematicity.
However, our calculations suggest that in CaKFe$_4$As$_4$, this anisotropic
response correlates with the one of the SVC fluctuations, highlighting the
close interrelation of magnetism and high-$T_c$ superconductivity. By
suggesting moderate $B_{2g}$ strains as an effective parameter to change the
stability of SVC and SSDW, we outline a pathway to a unified phase diagram of
iron-based superconductivity.",2307.10604v1
2023-09-07,The impact of rare events on the chemical enrichment in dwarf galaxies,"In the environments where the abundance of heavy elements is low, rare events
are expected to impact the chemical enrichment. Dwarf galaxies have small
masses, low average metallicities and in general low star formation rates, and
thus investigating the chemical enrichment provides understanding on the impact
of each source of elements on the chemical abundance. Using a chemical
evolution model in which the rarity is introduced, we investigate the impact of
rare events on the chemical enrichment for Local Group dwarf galaxies. In the
model, the occurrence of individual sources of elements is estimated with the
star formation history derived by the colour-magnitude diagram. The abundance
ratios of trans-iron elements to iron predicted by the model show the
oscillation at the lowest metallicities because of the r-process events. In the
case of a galaxy of a lower mass, the oscillation caused by neutron star
mergers is also seen at higher metallicities, which suggests that the rarity
can be important in lower-mass systems. Regarding the source of the chemical
enrichment, we observe that the r-process sites seem to contribute more to the
production of trans-iron elements at low metallicities, but massive stars of
different rotating velocities also contribute to create part of the dispersion
of the abundance ratios through the s-process. Both observational and
theoretical data, including nucleosynthesis calculations and the chemical
abundance of metal-poor stars, are needed to obtain deeper insights into the
sources of the chemical enrichment at low metallicities.",2309.03795v1
2023-09-29,Fossil and present-day stromatolite ooids contain a meteoritic polymer of glycine and iron,"Hemoglycin, a space polymer of glycine and iron, has been identified in the
carbonaceous chondritic meteorites Allende, Acfer 086, Kaba, Sutters Mill and
Orgueil. Its core form has a mass of 1494Da and is basically an antiparallel
pair of polyglycine strands linked at each end by an iron atom. The polymer
forms two- and three- dimensional lattices with an inter-vertex distance of
4.9nm. Here the extraction technique for meteorites is applied to a 2.1Gya
fossil stromatolite to reveal the presence of hemoglycin by mass spectrometry.
Intact ooids from a recent (3,000Ya) stromatolite exhibited the same visible
hemoglycin fluorescence in response to x-rays as an intact crystal from the
Orgueil meteorite. X-ray analysis confirmed the existence in ooids of an
internal 3-dimensional lattice of 4.9nm inter-vertex spacing, matching the
spacing of lattices in meteoritic crystals. FTIR measurements of acid-treated
ooid and a Sutters Mill meteoritic crystal both show the presence, via the
splitting of the Amide I band, of an extended anti-parallel beta sheet
structure. It seems probable that the copious in-fall of carbonaceous
meteoritic material, from Archaean times onward, has left traces of hemoglycin
in sedimentary carbonates and potentially has influenced ooid formation.",2309.17195v2
2023-10-17,Dealing with broad-band X-ray spectra of faint AGN: a case study,"In this work we analyse 3 average-luminosity hard X-ray selected AGN: ESO
506-G27, IGR J19039+3344 and NGC 7465. They have simultaneous Swift/XRT and
NuSTAR data never published before and have been poorly studied at X-ray
energies. These sources make for interesting targets both from a methodological
and scientific point of view. Scientifically, they are of interest since they
are possibly heavily absorbed objects, belong to a peculiar class and are
variable both in flux and in spectral shape. Methodologically, because it is an
interesting exercise to understand how existing spectral models can be applied
to faint sources and how the use of NuSTAR data alone and then simultaneous
and/or average data impacts on the spectral parameters determination. In this
work we demonstrate that simultaneous data are not sufficient if their
statistical quality is poor. Moreover, we show that also the use of
time-averaged data when dealing with faint AGN does not always provide
confident results as for brighter AGN. Regardless of the poor data quality
employed in our analysis, we are able to provide insights into the spectral
characteristics of each source. We analyse in detail for the first time the
iron line complex of ESO 506-G27, finding not only the presence of the iron
K$\alpha$ and K$\beta$ lines, but also of the iron K edge around 7 keV in the
NuSTAR data. We also highlight changes in the absorption properties of IGR
J19039+3344 and confirm NGC 7465 to be an unabsorbed type 1 LINER.",2310.11319v1
2023-11-04,On the likely magnesium-iron silicate dusty tails of catastrophically evaporating rocky planets,"Catastrophically evaporating rocky planets provide a unique opportunity to
study the composition of small planets. The surface composition of these
planets can be constrained via modelling their comet-like tails of dust. In
this work, we present a new self-consistent model of the dusty tails: we
physically model the trajectory of the dust grains after they have left the
gaseous outflow, including an on-the-fly calculation of the dust cloud's
optical depth. We model two catastrophically evaporating planets: KIC 1255b and
K2-22b. For both planets, we find the dust is likely composed of magnesium-iron
silicates (olivine and pyroxene), consistent with an Earth-like composition. We
constrain the initial dust grain sizes to be $\sim$ 1.25-1.75 $\mu$m and the
average (dusty) planetary mass-loss rate to be $\sim$ 3$M_\oplus
\mathrm{Gyr^{-1}}$. Our model shows the origin of the leading tail of dust of
K2-22b is likely a combination of the geometry of the outflow and a low
radiation pressure force to stellar gravitational force ratio. We find the
optical depth of the dust cloud to be a factor of a few in the vicinity of the
planet. Our composition constraint supports the recently suggested idea that
the dusty outflows of these planets go through a greenhouse effect-nuclear
winter cycle, which gives origin to the observed transit depth time
variability. Magnesium-iron silicates have the necessary visible-to-infrared
opacity ratio to give origin to this cycle in the high mass-loss state.",2311.02477v2
2023-11-24,Layer-dependent superconductivity in iron-based superconductors,"The Hohenberg-Mermin-Wagner theorem states that a two-dimensional system
cannot spontaneously break a continuous symmetry at finite temperature. This is
supported by the observation of layer-dependent superconductivity in the
quasi-two-dimensional superconductor NbSe2, in which the superconducting
transition temperature (Tc) is reduced by about 60% in the monolayer limit.
However, for the extremely anisotropic copper-based high-Tc superconductor
Bi2Sr2CaCu2O8+{\delta} (Bi-2212), the Tc of the monolayer is almost identical
to that of its bulk counterpart. To clarify the effect of dimensionality on
superconductivity, here we successfully fabricate ultrathin flakes of
CsCa2Fe4As4F2, a highly anisotropic iron-based high-Tc superconductor, down to
monolayer. The monolayer flake exhibits the highest Tc of 24 K (after tuning to
the optimal doping by ionic liquid gating), which is about 20% lower than that
of the bulk crystal. We also fabricate ultrathin flakes of CaKFe4As4, another
iron-based superconductor with much smaller anisotropy. The Tc of the 3-layer
flake decreases by 46%, showing a more pronounced dimensional effect than that
of CsCa2Fe4As4F2. By carefully examining their anisotropy and the c-axis
coherence length, we reveal the general trend and empirical law of the
layer-dependent superconductivity in these quasi-two-dimensional
superconductors. From this, the Tc of a new monolayer superconductor can be
extrapolated.",2311.14559v1
2023-11-29,Magnetic field simulations and measurements on the mini-ICAL detector,"The ICAL (Iron Calorimeter) is a 51 kTon magnetized detector proposed by the
INO collaboration. It is designed to detect muons with energies in the 1-20 GeV
range. A magnetic field of about 1.5 T in the ICAL detector will be generated
by passing a DC current through suitable copper coils. This will enable it to
distinguish between muons and anti-muons that will be generated from the
interaction of atmospheric muon neutrinos and anti-neutrinos with iron. This
will help in resolving the open question of mass ordering in the neutrino
sector. Apart from charge identification, the magnetic field will be used to
reconstruct the muon momentum (direction and magnitude). Therefore it is
important to know the magnetic field in the detector as accurately as possible.
We present here an (indirect) measurement of the magnetic field in the 85 ton
prototype mini-ICAL detector working in Madurai, Tamil Nadu, for different coil
currents. A detailed 3-D finite element simulation was done for the mini-ICAL
geometry using Infolytica MagNet software and the magnetic field was computed
for different coil currents. This paper presents, for the first time, a
comparison of the magnetic field measured in the air gaps with the simulated
magnetic field, to validate the simulation using real time data. Using the
simulations the magnetic field inside the iron is estimated.",2311.17364v1
2023-11-30,Highly efficient and transferable interatomic potentials for α-iron and α-iron/hydrogen binary systems using deep neural networks,"Artificial neural network potentials (NNPs) have emerged as effective tools
for understanding atomic interactions at the atomic scale in various phenomena.
Recently, we developed highly transferable NNPs for {\alpha}-iron and
{\alpha}-iron/hydrogen binary systems (Physical Review Materials 5 (11),
113606, 2021). These potentials allowed us to investigate deformation and
fracture in {\alpha}-iron under the influence of hydrogen. However, the
computational cost of the NNP remains relatively high compared to empirical
potentials, limiting their applicability in addressing practical issues related
to hydrogen embrittlement. In this work, building upon our prior research on
iron-hydrogen NNP, we developed a new NNP that not only maintains the excellent
transferability but also significantly improves computational efficiency (more
than 40 times faster). We applied this new NNP to study the impact of hydrogen
on the cracking of iron and the deformation of polycrystalline iron. We
employed large-scale through-thickness {110}<110> crack models and large-scale
polycrystalline {\alpha}-iron models. The results clearly show that hydrogen
atoms segregated at crack tips promote brittle-cleavage failure followed by
crack growth. Additionally, hydrogen atoms at grain boundaries facilitate the
nucleation of intergranular nanovoids and subsequent intergranular fracture. We
anticipate that this high-efficiency NNP will serve as a valuable tool for
gaining atomic-scale insights into hydrogen embrittlement.",2311.18686v1
2023-12-08,Numerical determination of iron dust laminar flame speeds with the counterflow twin-flame technique,"Iron dust counter-flow flames have been studied with the low-Mach-number
combustion approximation. The model considers full coupling between the two
phases, including particle/droplet drag. The dispersed phase flow strain
relations are derived under the assumption of low Reynolds number conditions.
The importance of solving a particle flow strain model is demonstrated by
comparing three different models: a free unstrained flame, a counter-flow flame
where particle flow strain is assumed equal to gas flow strain and one case in
which the particle flow strain is solved. All three cases showed preferential
diffusion effects, due to the lack of diffusion of iron in the fuel mixture,
e.g. DFe,m = 0. The preferential diffusion effect causes a peak in the fuel
equivalence ratio in the preheat zone. At the burned side, the combined effect
of strain and preferential diffusion showed a decrease in fuel equivalence
ratio. Inertia effects, which are only included in the resolved particle flow
strain case, counteract this effect and result in an increase of the fuel
equivalence ratio at the burned side. A laminar flame speed analysis is
performed and a recommendation is given on how to experimentally determine the
flame speed in a counter-flow set-up.",2312.04994v1
2023-12-19,The distribution of impactor core material during large impacts on Earth-like planets,"Large impacts onto young rocky planets may transform their compositions,
creating highly reducing conditions at their surfaces and reintroducing highly
siderophile metals to their mantles. Key to these processes is the availability
of an impactor's chemically reduced core material (metallic iron). It is,
therefore, important to constrain how much of an impactor's core remains
accessible to a planet's mantle/surface, how much is sequestered to its core,
and how much escapes. Here, we present 3D simulations of such impact scenarios
using the shock physics code iSALE to determine the fate of impactor iron.
iSALE's inclusion of material strength is vital in capturing the behavior of
both solid and fluid components of the planet and thus characterizing iron
sequestration to the core. We find that the mass fractions of impactor core
material that accretes to the planet core ($f_{core}$) or escapes ($f_{esc}$)
can be readily parameterized as a function of a modified specific impact
energy, with $f_{core} > f_{esc}$ for a wide set of impacts. These results
differ from previous works that do not incorporate material strength. Our work
shows that large impacts can place substantial reducing impactor core material
in the mantles of young rocky planets. Impact-generated reducing atmospheres
may thus be common for such worlds. However, through escape and sequestration
to a planet's core, large fractions of an impactor's core can be geochemically
hidden from a planet's mantle. Consequently, geochemical estimates of late
bombardments of planets based on mantle siderophile element abundances may be
underestimates.",2312.12132v1
2023-12-30,Evidence of grain alignment by magnetically enhanced radiative torques from multi-wavelength dust polarization modeling of HL Tau,"Atacama Large Millimeter/Submillimeter Array (ALMA) has revolutionized the
field of dust polarization in protoplanetary disks across multiple wavelengths.
Previous observations and empirical modeling suggested multiple mechanisms of
dust polarization toward HL Tau, including grain alignment and dust scattering.
However, a detailed modeling of dust polarization based on grain alignment
physics is not yet available. Here, using our updated POLARIS code, we perform
numerical modeling of dust polarization arising from both grain alignment by
Magnetically Enhanced Radiative Torque (MRAT) mechanism and self-scattering to
reproduce the HL Tau polarization observed at three wavelengths 0.87, 1.3, and
3.1$\,$mm. Our modeling results show that the observed multi-wavelength
polarization could be reproduced only when large grains contain embedded iron
inclusions and those with slow internal relaxation must have wrong internal
alignment (i.e., the grain's major axis parallel to its angular momentum). The
abundance of iron embedded inside grains in the form of clusters is constrained
to be $\gtrsim 16$%, and the number of iron atoms per cluster is $N_{\rm cl}
\sim 2\times10^3$. Maximum grain sizes probed at wavelengths $\lambda$ = 0.87,
1.3, and 3.1$\,$mm are constrained at $\sim$ 60, 90, and 130$\,\mu$m,
respectively. Assuming a dust differential settling effect with grain sizes
from the constraint gives the value of maximum grain size at the disk mid-plane
to be millimeter-scaled.",2401.00220v1
2024-02-13,"A Search for Magnetized Quark Nuggets (MQNs), a Candidate for Dark Matter, Accumulating in Iron Ore","A search has been carried out for Magnetized Quark Nuggets (MQNs)
accumulating in iron ore over geologic time. MQNs, which are theoretically
consistent with the Standard Models of Physics and of Cosmology, have been
suggested as dark-matter candidates. Indirect evidence of MQNs has been
previously inferred from observations of magnetars and of non-meteorite impact
craters. It is shown in this paper that MQNs can accumulate in taconite (iron
ore) and be transferred into ferromagnetic rod-mill liners during processing of
the ore. When the liners are recycled to make fresh steel, they are heated to
higher than the Curie temperature so that their ferromagnetic properties are
destroyed. The MQNs would then be released and fall into the ferromagnetic
furnace bottom where they would be trapped. Three such furnace bottoms have
been magnetically scanned to search for the magnetic anomalies consistent with
trapped MQNs. The observed magnetic anomalies are equivalent to an accumulation
rate of ~1 kg of MQNs per 1.2 x $10^8$ kg of taconite ore processed. The
results are consistent with MQNs but there could be other, unknown
explanations. We propose an experiment and calculations to definitively test
the MQN hypothesis for dark matter.",2402.08163v1
2024-03-28,"Combine Influences of Nanoparticulate Hematite Thin Film Thickness, Roughness, and Weight on Its Photoelectrochemical Performance and Viscous/ Thermal Characteristics of Source Precursor","The objective of this work was to investigate the photoelectrochemical (PEC)
performance of nanoparticulate hematite thin film photoelectrodes prepared by a
soft-chemistry route. Two cost-effective thin film fabrication techniques were
employed to deposit the hematite film. First, the film was deposited on
conducting glass substrates by dip coating of the organic precursor containing
fatty acid derivatives of iron salts. Process parameters such as the
concentration of iron oleic acid derivative precursor solution, the thickness
of the organic film, before annealing and the number of deposited layers along
with their weight and roughness were studied. In the second approach, the
influence of the spin coating process on film formation and respective
photoelectrochemical (PEC) performance have been discussed. It was found that
the PEC performance of spin-coated samples was lower than that of dip coated
samples due to the effect of films rough and smooth characteristics. It is
found that the rough surface of the photoelectrode is a prerequisite to
achieving good photocurrent values. Here, three-layer samples with roughness
between 600nm to 800nm and bulk thickness up to 700nm provided photocurrent
densities of 0.6mA/cm2. In part 2 of the manuscript, we have elaborately
discussed the roughness and smooth behavior of thin films using X-ray
reflectometry technique. Followed by this, a detailed account of the viscous
and thermal properties of the fatty acid derivatives of iron precursor have
been discussed.",2403.19069v1
2024-03-28,Synthetic Oil Gels With Organoclays In The Formulation Of Magnetorheological Fluids,"Magnetorheological fluids (MRF) are smart composite materials that, under an
external magnetic field, show a reversible solid-liquid transition in less than
10 ms. This study aimed to evaluate which organoclays would jellify a synthetic
oil for the formulation of MRF. Three dispersant additives for carbonyl iron
powder were evaluated. Fifteen different gelling additives from four clay
families, bentonites, hectorites, montmorillonites, and mixed mineral
thixotropes (MMT), were dispersed in oil only, keeping the same concentration,
without iron particles. The gels were then tested through amplitude and
frequency sweeps in oscillatory rheometry to evaluate their viscoelastic
behavior. All the MRFs were prepared using carbonyl iron powder HS in oil gels
with the same organoclay. All three dispersant additives showed a thixotropic
recovery above 100% in the three-interval test. Regarding the dispersibility
after one year, the MRF formulations with octan-1-amine and lecithin were
reproved, as they reached normal force peaks of 19 and 24 N, while the work was
28 and 415 mJ, respectively. The best MRF was formulated with octan-1-ol, and
resulted in a normal force of 0.33 N and 3.4 mJ at 35 mm of vane penetration.
Therefore, we conclude that the MRF with octan-1-ol and montmorillonite #6
showed a better balance between thixotropy, MR effect, and, above all, good
redispersibility.",2403.19774v1
1998-06-25,Low-Metallicity Inhibition of Type Ia Supernovae and Galactic and Cosmic Chemical Evolution,"We introduce a metallicity dependence of Type Ia supernova (SN Ia) rate into
the Galactic and cosmic chemical evolution models. In our SN Ia progenitor
scenario, the accreting white dwarf (WD) blows a strong wind to reach the
Chandrasekhar mass limit. If the iron abundance of the progenitors is as low as
[Fe/H] < -1, then the wind is too weak for SNe Ia to occur. Our model
successfully reproduces the observed chemical evolution in the solar
neighborhood. We make the following predictions which can test this metallicity
effect: 1) SNe Ia are not found in the low-iron abundance environments such as
dwarf galaxies and the outskirts of spirals. 2) The cosmic SN Ia rate drops at
z \sim 1-2 due to the low-iron abundance, which can be observed with the Next
Generation Space Telescope. At z > 1-2, SNe Ia can be found only in the
environments where the timescale of metal enrichment is sufficiently short as
in starburst galaxies and ellipticals.
  The low-metallicity inhibition of SNe Ia can shed new light on the following
issues: 1) The limited metallicity range of the SN Ia progenitors would imply
that ``evolution effects'' are relatively small for the use of high redshift
SNe Ia to determine the cosmological parameters. 2) WDs of halo populations are
poor producers of SNe Ia, so that the WD contribution to the halo mass is not
constrained from the iron abundance in the halo. 3) The abundance patterns of
globular clusters and field stars in the Galactic halo lack of SN Ia signatures
in spite of their age difference of several Gyrs, which can be explained by the
low-metallicity inhibition of SNe Ia. 4) It could also explain why the SN Ia
contamination is not seen in the damped Ly\alpha systems for over a wide range
of redshift.",9806335v1
1999-02-08,Metallicity Gradients in the Intracluster Gas of Abell 496,"Analysis of spatially resolved ASCA spectra of the intracluster gas in Abell
496 confirms there are mild metal abundance enhancements near the center, as
previously found by White et al. (1994) in a joint analysis of Ginga LAC and
Einstein SSS spectra. Simultaneous analysis of spectra from all ASCA
instruments (SIS + GIS) shows that the iron abundance is 0.36 +- 0.03 solar
3-12' from the center of the cluster and rises ~50% to 0.53 +- 0.04 solar
within the central 2'. The F-test shows that this abundance gradient is
significant at the >99.99% level. Nickel and sulfur abundances are also
centrally enhanced. We use a variety of elemental abundance ratios to assess
the relative contribution of SN Ia and SN II to the metal enrichment of the
intracluster gas. We find spatial gradients in several abundance ratios,
indicating that the fraction of iron from SN Ia increases toward the cluster
center, with SN Ia accounting for ~50% of the iron mass 3-12' from the center
and ~70% within 2'. The increased proportion of SN Ia ejecta at the center is
such that the central iron abundance enhancement can be attributed wholly to SN
Ia; we find no significant gradient in SN II ejecta. These spatial gradients in
the proportion of SN Ia/II ejecta imply that the dominant metal enrichment
mechanism near the center is different than in the outer parts of the cluster.
We show that the central abundance enhancement is unlikely to be due to ram
pressure stripping of gas from cluster galaxies, or to secularly accumulated
stellar mass loss within the central cD. We suggest that the additional SN Ia
ejecta near the center is the vestige of a secondary SN Ia-driven wind from the
cD (following a more energetic protogalactic SN II-driven wind phase), which
was partially smothered in the cD due to its location at the cluster center.",9902112v2
1999-03-24,Further studies of 1E 1740.7-2942 with ASCA,"We report the ASCA results of the Great Annihilator 1E 1740.7-2942 obtained
with five pointing observations in a time span of 3.5 years. The X-ray spectrum
for each period is well fitted with a single power-law absorbed by a high
column of gas. The X-ray flux changes by a factor of 2 from period to period,
but the other spectral parameters show no significant change. The photon index
is flat with \Gamma = 0.9--1.3. The column densities of hydrogen N_H is $\sim$
1.0 x 10^{23} H cm^{-2} and that of iron N_{Fe} is $\sim$ 10^{19} Fe cm^{-2}.
These large column densities indicate that 1E 1740.7-2942 is near at the
Galactic Center. The column density ratio leads the iron abundance to be 2
times larger than the other elements in a unit of the solar ratio. The
equivalent width of the K\alpha-line from a neutral iron is less than 15 eV in
90% confidence. This indicates that the iron column density within several
parsecs from 1E 1740.7-2942 is less than 5 x 10^{17} Fe cm^{-2}. In addition,
the derived hydrogen column density is about 1/6 of that of giant molecular
clouds in the line of sight. All these facts support that 1E 1740.7-2942 is not
in a molecular cloud, but possibly in front of it; the X-rays are not powered
by accretion from a molecular cloud, but from a companion star like ordinary
X-ray binaries.",9903376v2
1999-05-20,Soft X-ray spectroscopy of Compton-thick Seyfert 2 galaxies with BeppoSAX,"We present a X-ray spectroscopic study of the bright Compton-thick Seyfert 2s
NGC1068 and the Circinus Galaxy, performed with BeppoSAX. Matt et al. (1997 and
1998) interpreted the spectrum above 4 keV as the superposition of Compton
reflection and warm plasma scattering of the nuclear radiation. When this
continuum is extrapolated downwards to 0.1 keV, further components arise. The
NGC1068 spectrum is rich in emission lines, mainly due to K-alpha transitions
of He-like elements from oxygen to iron, plus a K-alpha fluorescent line from
neutral iron. If the ionized lines originate in the warm scatterer, its thermal
and ionization structure must be complex. From the continuum and line
properties, we estimate a column density, of the warm scatterer less than a few
10^21 atoms/cm/cm. In the Circinus Galaxy, the absence of highly ionized iron
is consistent with a scattering medium with ionization parameter U<5 and
density about a few times 10^22 atoms/cm/cm. In both cases the neutral iron
line is most naturally explained as fluorescence in the medium responsible for
the Compton reflection continuum. In NGC1068 an optically thin plasma emission
with kT~500 eV and strongly sub-solar metallicity is required, while such a
component is only marginal in the Circinus Galaxy. We tentatively identify this
component as emission of diffuse hot gas in the nuclear starbursts. Possible
causes for the metal depletion are discussed.",9905261v1
2000-02-22,Non-LTE Effects in Berylium Abundances,"In this work we analyze the beryllium-iron chemical diagram from the point of
view of non-LTE effects. Be abundances were re-calculated by considering
non-LTE corrections in ionization equilibrium (logg) and Fe abundances
([Fe/H]). These corrections seem do not affect the linear relation between
Be-Fe for metal-poor stars already found in the literature for LTE derived
abundances.",0002408v1
2000-05-01,Reflected Iron Line From a Source Above a Kerr Black Hole Accretion Disc,"In this paper we present a fully relativistic approach to modelling both the
continuum emission and the reflected fluorescent iron line from a primary X-ray
source near a Kerr black hole. The X-ray source is located above an accretion
disc orbiting around the black hole. The source is assumed to be a static point
source located on an arbitrary position above the disc, on or off the axis of
rotation. We carry out Monte Carlo simulations in order to estimate the iron
line spectrum as well as its equivalent width. Because of the gravitational
lensing effect, an enhancement of the iron line is expected when the primary
source is located close to the central black hole. We find that for a source
located on the axis of rotation the enhancement is relatively modest. An
observer at inclination 30 degrees would measure an equivalent width of ~300eV
in the extreme case of a maximally rotating black hole and a source located at
height 1.5 gravitational radius from the centre. This corresponds to an
equivalent width enhancement factor of about 2 compared to the classical value
where no lensing effect comes into play. However, when allowing the source to
be located off the axis of rotation, much stronger enhancement can be obtained.
In the extreme case of a maximally rotating black hole and a source located
just above the approaching side of the disc, an observer at inclination 30d
egrees could measure an equivalent width as high as ~1.5 keV (i.e. ~10 times
the classical value). We also find that observers located at high inclination
angles observe a stronger line than observers at low inclination angles.",0005020v1
2000-05-30,BeppoSAX broad-band observations of low-redshift quasars: Spectral curvature and iron K_alpha lines,"We present results from BeppoSAX observations of 10 low redshift quasars. The
quasars are part of the Laor et al. (1997) sample of 23 optically selected PG
quasars with redshift <0.4 and low Galactic absorption along the line of sight.
Significant spectral curvature is detected for the 6 quasars with the highest
signal to noise ratio in their low energy spectra. The average curvature can be
parameterized as a flattening of the underlying power law by Delta_alpha ~ 0.5
above ~1 keV. We find that quasars with a steeper soft X-ray (0.1-2 keV)
spectrum tend to be steeper also at higher (2-10 keV) energies. The
distribution of the best fit 2-10 keV slopes is similar to that found for other
radio-quiet AGN and characterized by a large dispersion around the mean:
alpha_E ~ 1.0+/-0.3. Iron K_alpha lines are detected in 4 quasars. In the
narrow-line quasar PG 1115+407, the rest frame line energy (6.69+/-0.11 keV)
and equivalent width (580+/-280 eV) are consistent with those found in a few
low redshift narrow-line Seyfert 1 galaxies (NLSy1). This, together with the
similarity of the 0.1-10 keV X-ray continuum, suggests that this quasar is the
higher redshift and luminosity analog of a NLSy1. In the broad line quasar PG
0947+396, the rest-frame line energy suggests fluorescence from cold iron. The
line equivalent width (> 400 eV) is however about 2-3 times higher than that
usually found in Seyfert 1 galaxies. The high energy power-law slopes and the
iron line emission properties seem to be unrelated to the X-ray luminosity.",0005567v1
2000-10-20,Abundances and Evolution of Lithium in the Galactic Halo and Disk,"We have measured the Li abundance of 18 stars with -2 <~ [Fe/H] ~< -1 and
6000 K <~ Teff <~ 6400 K, a parameter range that was poorly represented in
previous studies. We examine the Galactic chemical evolution (GCE) of this
element, combining these data with previous samples of turnoff stars over the
full range of halo metallicities. We find that A(Li) increases from a level of
\~2.10 at [Fe/H] = -3.5, to ~2.40 at [Fe/H] = -1.0, where A(Li) = log_10
(n(Li)/n(H)) + 12.00.
  We compare the observations with several GCE calculations, including existing
one-zone models, and a new model developed in the framework of inhomogeneous
evolution of the Galactic halo. We show that Li evolved at a constant rate
relative to iron throughout the halo and old-disk epochs, but that during the
formation of young-disk stars, the production of Li relative to iron increased
significantly. These observations can be understood in the context of models in
which post-primordial Li evolution during the halo and old-disk epochs is
dominated by Galactic cosmic ray fusion and spallation reactions, with some
contribution from the $\nu$-process in supernovae. The onset of more efficient
Li production (relative to iron) in the young disk coincides with the
appearance of Li from novae and AGB stars. The major challenge facing the
models is to reconcile the mild evolution of Li during the halo and old-disk
phases with the more efficient production (relative to iron) at [Fe/H] > -0.5.
We speculate that cool-bottom processing (production) of Li in low-mass stars
may provide an important late-appearing source of Li, without attendant Fe
production, that might explain the Li production in the young disk.",0010411v1
2000-11-28,Presupernova Evolution with Improved Rates for Weak Interactions,"Recent shell-model calculations of weak-interaction rates for nuclei in the
mass range A = 45 - 65 have resulted in substantial revisions to the hitherto
standard set of Fuller, Fowler, & Newman (FFN). In particular, key
electron-capture rates, such as that for Co60 are much smaller. We consider
here the effects of these revised rates on the presupernova (post-oxygen
burning) evolution of massive stars in the mass range 11 to 40 M_sun. Moreover,
we include, for the first time in models by our group, the effects of modern
rates for beta-decay in addition to electron capture and positron emission.
Values for the central electron mole number at the time of iron core collapse
in the new models are typically larger, by delta Y_e = 0.005 to 0.015, than
those of Woosley & Weaver 1995, with a tendency for the more massive models to
display larger differences. About half of this change is a consequence of
including beta-decay; the other half, result of the smaller rates for electron
capture. Unlike what might be expected solely on basis of the larger Y_e's, the
new iron core masses are systematically smaller owing to a decrease in the
entropy in the outer iron core. The changes in iron core mass range from zero
to 0.1 M_sun. We also observe, as predicted by Aufderheide et al. (1994), a
tendency towards beta-equilibrium just prior to the collapse of the core, and
the subsequent loss of that equilibrium as core collapse proceeds. We discuss
the key weak reaction rates, both beta-decay and electron-capture, responsible
for the evolution of Y_e and make suggestions for future measurements.",0011507v1
2001-01-24,"Issues of LiBeB, Oxygen and Iron Evolution","We discuss the highlights of our recent research, specifically the refractory
vs. volatile interpretation of the rise of [O/Fe] with decreasing [Fe/H], and
the issue of primary vs. secondary evolution of Be.",0101432v1
2001-12-05,Caught in the Act; Chandra Observations of Microlensing of the Radio-Loud Quasar MG J0414+0534,"We present results from monitoring of the distant (z = 2.64), gravitationally
lensed quasar MG J0414+0534 with the Chandra X-ray Observatory. An Fe Ka line
at 6.49 +/- 0.09 keV (rest-frame) with an equivalent width of ~ 190eV
consistent with fluorescence from a cold medium is detected at the 99 percent
confidence level in the spectrum of the brightest image A. During the last two
observations of our monitoring program we detected a five-fold increase of the
equivalent width of a narrow Fe Ka line in the spectrum of image B but not in
the brighter image A whereas image C is too faint to resolve the line. The
continuum emission component of image B did not follow the sudden enhancement
of the iron line in the last two observations. We propose that the sudden
increase in the iron line strength from ~ 190eV to 900eV only in image B can be
explained with a caustic crossing due to microlensing that selectively enhances
a strip of the line emission region of the accretion disk. The non-enhancement
of the continuum emission in the spectrum of image B suggests that the
continuum emission region is concentrated closer to the center of the accretion
disk than the iron line emission region and the magnification caustic has not
reached close enough to the former region to amplify it. A model of a caustic
crossing event predicts discontinuities in the light-curve of the magnification
and provides an upper limit of ~ 5 x 10^(-4) pc on the outer radius of the Fe
Ka emission region. The non-detection of any relativistic or Doppler shifts of
the iron line in the spectrum of image B implies that the magnification caustic
for the last two observations was located at a radius greater than ~ 100
gravitational radii.",0112112v1
2001-12-07,Fe Kαemission from photoionized slabs: the impact of the iron abundance,"Iron K\alpha emission from photoionized and optically thick material is
observed in a variety of astrophysical environments including X-ray binaries,
active galactic nuclei, and possibly gamma-ray bursts. This paper presents
calculations showing how the equivalent width (EW) of the Fe K line depends on
the iron abundance of the illuminated gas and its ionization state -- two
variables subject to significant cosmic scatter. Reflection spectra from a
constant density slab which is illuminated with a power-law spectrum with
photon-index \Gamma are computed using the code of Ross & Fabian. When the Fe K
EW is measured from the reflection spectra alone, we find that it can reach
values greater than 6 keV if the Fe abundance is about 10 times solar and the
illuminated gas is neutral. EWs of about 1 keV are obtained when the gas is
ionized. In contrast, when the EW is measured from the incident+reflected
spectrum, the largest EWs are ~800 keV and are found when the gas is ionized.
When \Gamma is increased, the Fe K line generally weakens, but significant
emission can persist to larger ionization parameters. The iron abundance has
its greatest impact on the EW when it is less than 5 times solar. When the
abundance is further increased, the line strengthens only marginally.
Therefore, we conclude that Fe K lines with EWs much greater than 800 eV are
unlikely to be produced by gas with a supersolar Fe abundance. These results
should be useful in interpreting Fe K emission whenever it arises from
optically thick fluorescence.",0112179v1
2002-06-04,Resolving the Effects of Resonant X-ray Line Scattering in Cen X-3 with Chandra,"The massive X-ray binary Cen X-3 was observed over approximately one quarter
of the system's 2.08 day orbit, beginning before eclipse and ending slightly
after eclipse center with the Chandra X-ray Observatory using its High-Energy
Transmission Grating Spectrometer. The spectra show K shell emission lines from
hydrogen- and helium-like ions of magnesium, silicon, sulfur, and iron as well
as a K-alpha fluorescence emission feature from near-neutral iron. The
helium-like n=2->1 triplet of silicon is fully resolved and the analogous
triplet of iron is partially resolved. The helium-like triplet component flux
ratios outside of eclipse are consistent with emission from recombination and
subsequent cascades (recombination radiation) from a photoionized plasma. In
eclipse, however, the w (resonance) lines of silicon and iron are stronger than
that expected for recombination radiation, and are consistent with emission
from a collisionally ionized plasma. The triplet line flux ratios at both
phases can be explained more naturally, however, as emission from a
photoionized plasma if the effects of resonant line scattering are included in
addition to recombination radiation. We show that the emissivity due to
resonant scattering depends sensitively on the line optical depth and, in the
case of winds in X-ray binaries, this allows constraints on the wind velocity
even when Doppler shifts cannot be resolved.",0206065v2
2002-12-03,Fluorescent iron lines as a probe of astrophysical black hole systems,"(abridged) With most physicists and astrophysicists in agreement that black
holes do indeed exist, the focus of astrophysical black hole research has
shifted to the detailed properties of these systems. Nature has provided us
with an extremely useful probe of the region very close to an accreting black
hole - X-ray irradiation of relatively cold material in the vicinity of the
black hole can imprint characteristic features into the X-ray spectra of black
hole systems, most notably the Kalpha fluorescent line of iron. Detailed X-ray
spectroscopy of these features can be used to study Doppler and gravitational
redshifts, thereby providing key information on the location and kinematics of
the cold material. This is a powerful tool that allows us to probe within a few
gravitational radii, or less, of the event horizon. Here, we present a
comprehensive review of relativistic iron line studies for both accreting
stellar mass black holes (i.e., Galactic Black Hole Candidate systems; GBHCs),
and accreting supermassive black holes (i.e., active galactic nuclei; AGN).
After a pedagogical introduction to black hole astrophysics, we discuss studies
of relativistic iron lines in the AGN context and show how differences between
classes of AGN can be diagnosed using X-ray spectroscopy. Furthermore, through
a detailed discussion of one particular object (MCG--6-30-15), we illustrate
how the exotic physics of black hole spin are now open to observational study.
We proceed to discuss GBHCs, which turn out to possess rather more complicated
X-ray spectra, making robust conclusions more difficult to draw. However, even
in these cases, modern X-ray observatories are now providing convincing
evidence for relativistic effects. We conclude by discussing the science that
can be addressed by future X-ray observatories.",0212065v2
2003-04-01,XMM-Newton observations of Broad FeKalpha emission from a Seyfert 1.9 galaxy MCG-5-23-16,"XMM-Newton observations of the bright Seyfert 1.9 galaxy MCG-5-23-16 have
revealed a broad FeKalpha emission line which is nearly symmetric in contrast
to the broad and red-shifted asymmetric FeKalpha line sometimes observed from
Seyfert 1 galaxies. The FeKalpha line has two distinct components - a narrow
unresolved component with equivalent width of 40 eV and a broad component with
full width at half maximum of 40000 km/s and equivalent width of 120 eV. An
absorption feature at 7.1 keV has also been observed. The energies of the
emission and absorption features are consistent with those arising from neutral
iron. The broad component is consistent with an FeKalpha emission line expected
from a relativistic accretion disk around a Schwarzschild or a Kerr black hole.
Alternatively, most of the flux in the broad component could also be modeled as
reflection emission which mimics emission line like feature due to the presence
of iron K-shell edge at 7.1eV, however, the reflection fraction is much higher
than that inferred from the BeppoSax observations. The disk inclination angle
of about 47 deg, inferred from the disk-line fits, and the absorption column of
about 10^{22} cm^{-2}, inferred from the low-energy spectral curvature due to
photoelectric absorption, suggest that our line of sight passes through the
outer edge of a putative torus and are consistent with those expected for a
Seyfert 1.9 galaxy falling within the unification scheme. The strength of the
narrow iron Kalpha emission and the optical depth of the iron K absorption edge
suggest their origin in the putative torus with N_H about 10^{24} cm^{-2} in
the inner regions and N_H about 10^{22} cm^{-2} in the outer edges.",0304037v1
2003-12-01,On Sensitivity of Cherenkov Radiation to the Dynamics of High Energy Cosmic Ray Interactions,"A simulation study of the effects resulting from creation of quark--gluon
plasma in high energy collisions of cosmic iron nuclei with the air has been
carried out. The Cherenkov light emission has been found to reveal some
features of the dynamics of high energy hadronic interactions.",0312027v1
2003-12-11,"IZw1 observed with XMM-Newton: Low-energy spectral complexity, iron lines, and hard X-ray flares","We present a 20 ks XMM-Newton observation of the prototypical Narrow-Line
Seyfert 1 galaxy IZw1. The best-fit model to the data is a double blackbody
plus a dominant power-law, on which complex soft absorption (possibly a blended
edge or absorption lines) and/or OVII emission are superimposed, as well as
strong Fe Kalpha emission. The iron feature in the high-energy spectra appears
broad; however, on close examination of the EPIC pn data, there exists the
possibility that the broad emission feature can be attributed to a neutral Fe
Kalpha line in addition to a blend of He- and H-like Fe Kalpha lines. The light
curve shows a strong, hard X-ray flare concentrated in the 3-12 keV band. The
flare appears to induce spectral variability, showing spectral hardening to be
occuring as the flare intensifies. A detailed examination suggests that the
spectral variability is most likely due to an increase in the 3-12 keV flux
relative to the soft flux during the flare. A difference spectrum and complete
modelling of the flare and non-flare spectra show intrinsic changes only in the
normalisation of the continuum components and not in their shape parameters.
The timing results are consistent with the flare originating in the accretion
disc corona. The iron emission line(s) do not appear to respond to changes in
the continuum flux during the flare; the iron lines are stronger in equivalent
width during the low-flux (non-flare) states, and weaker during the flare.",0312298v1
2003-12-12,XMM-Newton view of the prototype narrow-line Seyfert 1 galaxy I Zw 1,"We present results based on an XMM-Newton observation of the prototype
narrow-line Seyfert 1 galaxy I Zw 1 performed in June 2002. The 0.6-12 keV
spectrum is well described by a steep power-law (Gamma\sim 2.3) and a weak soft
blackbody component (kT \sim 200 eV) below 2 kev. The soft X-ray excess
emission is featureless and contributes only about 10% to the total X-ray
emission in the $0.6-2\kev$ band. There are tentative evidences for an iron
iron Kalpha line and an iron K edge, both from high ionized He-like iron. The
0.6-12kev continuum of I Zw 1 can be explained in terms of a blackbody (kT \sim
40eV), thermal comptonization and its reflection off the surface of an ionized
accretion disk. We note that characterizing the soft excess copmonent `above a
power law continuum' may not be appropriate due to the low energy curvature of
a comptonized spectrum. X-ray emission from I Zw 1 was highly variabile during
the observation. I Zw 1 showed a large, symmetric X-ray flare during which the
X-ray luminosity increased by about 6e43 erg/s in an interval of 2800s only.
The X-ray spectral variability was unusual during the flare. In contrast to the
general observation of spectral steepening with flux from Seyfert galaxies,
there is a clear evidence for hardening of the 0.6-10kev spectrum of I Zw 1
with increasing flux. This hardening is due to a stronger and slightly flatter
power-law component at higher flux without any change in the soft X-ray excess
component. The large flare, the accompanying spectral flattening, and the
steady nature of the soft excess component may be due to an additional flatter
power-law component during the flare possibly arising as a result of ejection
of electron plasma and the SSC process.",0312342v1
2004-03-02,Abundance differences between components of wide binaries,"In this paper we present iron abundance analysis for 23 wide binaries with
main sequence components in the temperture range 4900-6300 K, taken from the
sample of the pairs currently included in the radial velocity planet search on
going at the TNG. The use of a line-by-line differential analysis technique
between the components of each pair allows to reach errors of about 0.02 dex in
the iron content difference. Most of the pairs have abundance differences lower
than 0.02 dex and there are no pairs with differences larger than 0.07 dex. The
four cases of differences larger than 0.02 dex may be spouriuos because of the
larger error bars affecting pairs with large temperature difference, cold stars
and rotating stars. The pair HD 219542, previously reported by us to have
different composition, results instead normal. For non-rotating stars warmer
than 5500 K, we are able to exclude in most cases the ingestion of more than 1
Earth Mass of iron (about 5 Earth masses of meteoritic material) during the
main sequence lifetime of the stars, placing more stringent limits (about 0.4
Earth masses of iron) in five cases of warm stars. This latter limit is similar
to the estimates of rocky material accreted by the Sun during its main sequence
lifetime. Combining the results of the present analysis with those for the
Hyades and Pleiades, we conclude that the hypothesis that pollution by
planetary material is the only responsible for the highest metallicity of the
stars with planets may be rejected at more than 99% level of confidence if the
incidence of planets in these samples is as high as 8% and similar to the field
stars included in current radial velocity surveys. However, the significance of
this result drops considerably if the incidence of planets around stars in
binary systems and clusters is less than a half than around normal field stars.",0403051v2
2004-03-04,S4N: A Spectroscopic Survey of Stars in the Solar Neighborhood,"[ABRIDGED] We report the results of a high-resolution spectroscopic survey of
all the stars more luminous than Mv = 6.5 mag within 14.5 pc from the Sun. We
derive stellar parameters and perform a preliminary abundance and kinematic
analysis of the F-G-K stars in the sample. The inferred metallicity ([Fe/H])
distribution is centered at about -0.1 dex, and shows a standard deviation of
0.2 dex.
  We identify a number of metal-rich K-type stars which appear to be very old,
confirming the claims for the existence of such stars in the solar
neighborhood. With atmospheric effective temperatures and gravities derived
independently of the spectra, we find that our classical LTE model-atmosphere
analysis of metal-rich (and mainly K-type) stars provides discrepant abundances
from neutral and ionized lines of several metals. Based on transitions of
majority species, we discuss abundances of 16 chemical elements.
  In agreement with earlier studies we find that the abundance ratios to iron
of Si, Sc, Ti, Co, and Zn become smaller as the iron abundance increases until
approaching the solar values, but the trends reverse for higher iron
abundances. At any given metallicity, stars with a `low' galactic rotational
velocity tend to have high abundances of Mg, Si, Ca, Sc, Ti, Co, Zn, and Eu,
but low abundances of Ba, Ce, and Nd. The Sun appears deficient by roughly 0.1
dex in O, Si, Ca, Sc, Ti, Y, Ce, Nd, and Eu, compared to its immediate
neighbors with similar iron abundances.",0403108v1
2004-05-18,Iron K-alpha Fluorescent Line Profiles from Spiral Accretion Flows in AGNs,"We present 6.4 keV iron K-alpha fluorescent line profiles predicted for a
relativistic black hole accretion disk in the presence of a spiral motion in
Kerr geometry, the work extended from an earlier literature motivated by recent
magnetohydrodynamic (MHD) simulations. The velocity field of the spiral motion,
superposed on the background Keplerian flow, results in a complicated redshift
distribution in the accretion disk. An X-ray source attributed to a localized
flaring region on the black hole symmetry axis illuminates the iron in the
disk. The emissivity form becomes very steep because of the light bending
effect from the primary X-ray source to the disk. The predicted line profile is
calculated for various spiral waves, and we found, regardless of the source
height, that: (i) a multiple-peak along with a classical double-peak structure
generally appears, (ii) such a multiple-peak can be categorized into two types,
sharp sub-peaks and periodic spiky peaks, (iii) a tightly-packed spiral wave
tends to produce more spiky multiple peaks, whereas (iv) a spiral wave with a
larger amplitude seems to generate more sharp sub-peaks, (v) the effect seems
to be less significant when the spiral wave is centrally concentrated, (vi) the
line shape may show a drastic change (forming a double-peak, triple-peak or
multiple-peak feature) as the spiral wave rotates with the disk. Our results
emphasize that around a rapidly-rotating black hole an extremely redshifted
iron line profile with a noticeable spike-like feature can be realized in the
presence of the spiral wave. Future X-ray observations, from {\it Astro-E2} for
example, will have sufficient spectral resolution for testing our spiral wave
model which exhibits unique spike-like features.",0405337v1
2004-08-23,"An extreme, blueshifted iron line profile in the Narrow Line Seyfert 1 PG 1402+261; an edge-on accretion disk or highly ionized absorption?","We report on a short XMM-Newton observation of the radio-quiet Narrow Line
Seyfert 1 PG 1402+261. The EPIC X-ray spectrum of PG 1402+261 shows a strong
excess of counts between 6-9 keV in the rest frame. This feature can be modeled
by an unusually strong (equivalent width 2 keV) and very broad (FWHM velocity
of 110000 km/s) iron K-shell emission line. The line centroid energy at 7.3 keV
appears blue-shifted with respect to the iron Kalpha emission band between
6.4-6.97 keV, while the blue-wing of the line extends to 9 keV in the quasar
rest frame. The line profile can be fitted by reflection from the inner
accretion disk, but an inclination angle of >60 deg is required to model the
extreme blue-wing of the line. Furthermore the extreme strength of the line
requires a geometry whereby the hard X-ray emission from PG 1402+261 above 2
keV is dominated by the pure-reflection component from the disk, while little
or none of the direct hard power-law is observed. Alternatively the spectrum
above 2 keV may instead be explained by an ionized absorber, if the column
density is sufficiently high (N_H > 3 x 10^23 cm^-2) and if the matter is
ionized enough to produce a deep (tau~1) iron K-shell absorption edge at 9 keV.
This absorber could originate in a large column density, high velocity outflow,
perhaps similar to those which appear to be observed in several other high
accretion rate AGN. Further observations, especially at higher spectral
resolution, are required to distinguish between the accretion disk reflection
or outflow scenarios.",0408403v1
2004-10-28,Composition of the Solar Interior: Information from Isotope Ratios,"Measurements are reviewed showing that the interior of the Sun, the inner
planets, and ordinary meteorites consist mostly of the same elements: Iron,
oxygen, nickel, silicon, magnesium, sulfur and calcium. These results do not
support the standard solar model.",0410717v1
2005-11-15,Kappa-Mechanism Excitation of Retrograde Mixed Modes in B-Type Stars,"The stability of retrograde mixed modes in rotating B-type stars is
investigated. It is found that these modes are susceptible to kappa-mechanism
excitation, due to the iron opacity bump at log T ~ 5.3. The findings are
discussed in the context of the pulsation of SPB and Be stars.",0511455v1
2006-08-08,XMM-Newton high-resolution spectroscopy reveals the chemical evolution of M 87,"We present here a study of chemical abundances in the giant elliptical galaxy
M 87 using high-resolution spectra obtained with the Reflection Grating
Spectrometers during two deep XMM-Newton observations. While we confirm the
two-temperature structure of the inter-stellar medium (ISM) in M 87, we also
show that a continuous temperature distribution describes the data equally
well. The high statistics allows us, for the first time, to determine
relatively accurate abundance values also for carbon and nitrogen. The
comparison of the abundance ratios of C, N, O and Fe in the ISM of M 87 with
those in the stellar population of our Galaxy shows that the relative
contribution of core-collapse supernovae to the enrichment of the ISM in M 87
is significantly less than in the Milky Way and indicates that the enrichment
of the ISM by iron through Type Ia supernovae and by carbon and nitrogen is
occurring in parallel. This suggests that the main source of carbon and
nitrogen in M 87 are the low- and intermediate-mass asymptotic giant branch
stars. From the oxygen to iron abundance ratio in the hot gas we estimate that
the relative number of core collapse and type Ia supernovae contributing to the
enrichment of the ISM in the core of M 87 is ~60% and ~40% respectively. The
spatial distributions of iron and oxygen are different. While the oxygen
abundance distribution is flat the iron abundance peaks in the core and has a
gradient throughout the ~4' wide field of view of the instrument, suggesting an
early enrichment by core-collapse supernovae and a continuous contribution of
type Ia supernovae.",0608177v1
2006-09-08,Iron and Nickel Line Diagnostics for the Galactic Center Diffuse Emission,"We have observed the diffuse X-ray emission from the Galactic center (GC)
using the X-ray Imaging Spectrometer (XIS) on Suzaku. The high-energy
resolution and the low-background orbit provide excellent spectra of the GC
diffuse X-rays (GCDX). The XIS found many emission lines in the GCDX near the
energy of K-shell transitions of iron and nickel. The most pronounced features
are FeI K alpha at 6.4 keV and K-shell absorption edge at 7.1 keV, which are
from neutral and/or low ionization states of iron, and the K-shell lines at 6.7
keV and 6.9 keV from He-like (FeXXV K alpha) and hydrogenic (FeXXVI Ly alpha)
ions of iron. In addition, K alpha lines from neutral or low ionization nickel
(NiI K alpha) and He-like nickel (NiXXVII K alpha), and FeI K beta, FeXXV K
beta, FeXXVI Ly beta, FeXXV K gamma and FeXXVI Ly gamma are detected for the
first time. The line center energies and widths of FeXXV K alpha and FeXXVI Ly
alpha favor a collisional excitation (CE) plasma for the origin of the GCDX.
The electron temperature determined from the line flux ratio of FeXXV K alpha /
FeXXV K beta is similar to the ionization temperature determined from that of
FeXXV K alpha /FeXXVI Ly alpha. Thus it would appear that the GCDX plasma is
close to ionization equilibrium. The 6.7 keV flux and temperature distribution
to the galactic longitude is smooth and monotonic,in contrast to the integrated
point source flux distribution. These facts support the hypothesis that the
GCDX is truly diffuse emission rather than the integration of the outputs of a
large number of unresolved point sources. In addition, our results demonstrate
that the chemical composition of Fe in the interstellar gas near the GC is
constrained to be about 3.5 times solar.",0609215v1
2006-10-16,Helium and Iron in X-ray galaxy clusters,"I discuss the role of the sedimentation of helium in galaxy cluster cores on
the observed X-ray properties and present a history of the metal accumulation
in the ICM, with new calculations with respect to my previous work following
the recent evidence of a bi-modal distribution of the delay time in Supernovae
Type Ia.",0610466v1
2006-10-17,Suzaku discovery of iron absorption lines in outburst spectra of the X-ray transient 4U 1630-472,"We present the results of six Suzaku observations of the recurrent black hole
transient 4U1630-472 during its decline from outburst from February 8 to March
23 in 2006. All observations show the typical high/soft state spectral shape in
the 2-50keV band, roughly described by an optically thick disk spectrum in the
soft energy band plus a weak power-law tail that becomes dominant only above
\~20keV. The disk temperature decreases from 1.4keV to 1.2keV as the flux
decreases by a factor 2, consistent with a constant radius as expected for
disk-dominated spectra. All the observations reveal significant absorption
lines from highly ionized (H-like and He-like) iron Ka at 7.0keV and 6.7keV.
The brightest datasets also show significant but weaker absorption structures
between 7.8keV and 8.2keV, which we identify as a blend of iron Kb and nickel
Ka absorption lines. The energies of these absorption lines suggest a blue
shift with an outflow velocity of ~1000km/s.. The H-like iron Ka equivalent
width remains approximately constant at ~30 eV over all the observations, while
that of the He-like Ka line increases from 7 eV to 20 eV. Thus the ionization
state of the material decreases, as expected from the decline in flux. We fit
the profiles with Voigt functions (curve of growth) to derive absorbing
columns, then use these together with detailed photo-ionization calculations to
derive physical parameters of the absorbing material. The data then constrain
the velocity dispersion of the absorber to 200-2000 km/s, and the size of the
plasma as ~1E10 cm assuming a source distance of 10 kpc.",0610496v1
2006-11-01,Magnetic flares in Active Galactic Nuclei: Modeling the iron Kalpha-line,"The X-ray spectra of Active Galactic Nuclei (AGN) are complex and vary
rapidly in time as seen in recent observations. Magnetic flares above the
accretion disk can account for the extreme variability of AGN. They also
explain the observed iron Kalpha fluorescence lines. We present radiative
transfer modeling of the X-ray reflection due to emission from magnetic flares
close to the marginally stable orbit. The hard X-ray primary radiation coming
from the flare source illuminates the accretion disk. A Compton
reflection/reprocessed component coming from the disk surface is computed for
different emission directions. We assume that the density structure remains
adjusted to the hydrostatic equilibrium without external illumination because
the flare duration is only a quarter-orbit. The model takes into account the
variations of the incident radiation across the hot spot underneath the flare
source. The integrated spectrum seen by a distant observer is computed for
flares at different orbital phases close to the marginally stable orbit of a
Schwarzschild black hole and of a maximally rotating Kerr black hole. The
calculations include relativistic and Doppler corrections of the spectra using
a ray tracing technique. We explore the practical possibilities to map out the
azimuthal irradiation pattern of the inner accretion disks and conclude that
the next generation of X-ray satellites should reveal this structure from iron
Kalpha line profiles and X-ray lightcurves.",0611020v1
2006-11-03,Suzaku Spectroscopy Study of Hard X-Ray Emission in the Arches Cluster,"We present the results of a Suzaku study of the Arches cluster. A high S/N
spectrum in the 3-12 keV band was obtained with the XIS. We found that the
spectrum consists of a thermal plasma, a hard power-law tail, and two Gaussian
lines. The plasma component (kT~2.2 keV) is established from the presence of
CaXIX and FeXXV K alpha lines as well as the absence of FeXXVI K alpha line.
The two Gaussian lines represent the K alpha and beta lines from iron at lower
ionization stages. Both the line centers and the intensity ratio of these two
lines are consistent with the neutral iron. The hard power-law tail (index~0.7)
was found to have no pronounced iron K edge feature. In comparison with the
published Chandra spectra, we conclude that the thermal component is from the
ensemble of point-like sources plus thermal diffuse emission concentrated at
the cluster center, while the Gaussian and the hard tail components are from
the non-thermal diffuse emission extended in a larger scale. In the
band-limited XIS images, the distribution of the 7.5-10.0 keV emission
resembles that of the 6.4 keV emission. This strongly suggests that the
power-law emission is related to the 6.4 and 7.1 keV lines in the underlying
physics. We discuss two ideas to explain both the hard continuum and the lines:
(1) X-ray photoionization that produces fluorescence lines and the Thomson
scattering continuum and (2) non-thermal electron impact ionization of iron
atoms and bremsstrahlung continuum. But whichever scenario is adopted, the
photon or particle flux from the Arches cluster is too low to account for the
observed line and continuum intensity.",0611104v1
2001-02-16,Finite-temperature magnetism of transition metals: an LDA+DMFT approach,"We present an ab initio quantum theory of the finite temperature magnetism of
iron and nickel. A recently developed technique which combines dynamical
mean-field theory with realistic electronic structure methods, successfully
describes the many-body features of the one electron spectra and the observed
magnetic moments below and above the Curie temperature.",0102297v1
2002-03-07,Segmented Band Mechanism for Itinerant Ferromagnetism,"We introduce a novel mechanism for itinerant ferromagnetism, which is based
on a simple two-band model, and using numerical and analytical methods, we show
that the Periodic Anderson Model (PAM) contains this mechanism. We propose that
the mechanism, which does not assume an intra-atomic Hund's coupling, is
present in both the iron group and some $f$ electron compounds.",0203172v1
2002-04-08,Determining the Saddle Point in Micromagnetic Models of Magnetization Switching,"A numerical model of single-domain nanoscale iron magnets fabricated using
scanning-microscope-assisted chemical vapor deposition is simulated using
finite-temperature micromagnetics. A Projective-dynamics method is used to
determine the magnetization at the saddle point as a function of temperature.
This magnetization is found to decrease linearly as the temperature is raised.",0204180v1
2002-09-06,Electric conductivity of lead iron niobate,"Results of d.c. electric conductivity and Seebeck coefficient measurements
for PFN, PFN+Li ceramic samples and PFN single crystals are presented. Marked
influence of doping with lithium on the value of electric conductivity, and on
the type of electric conductance has been found.",0209154v1
2002-09-12,Some physical properties of lead iron niobate,"The results of the X-ray, microscopic, magnetic, and dielectric measurements
performed for PFN single crystals and ceramic samples are presented. The
influence of the technological conditions on selected physical properties of
the materials examined is shown.",0209289v1
2004-09-10,Reversal Modes of Simulated Iron Nanopillars in an Obliquely Oriented Field,"Stochastic micromagnetic simulations are employed to study switching in
three-dimensional magnetic nanopillars exposed to highly misaligned fields. The
switching appears to proceed through two different decay modes, characterized
by very different average lifetimes and different average values of the
transverse magnetization components.",0409277v1
2006-09-29,Negative four-terminal resistance as a probe of crossed Andreev reflection,"We report on the experimental investigation of electronic transport in
superconductor-ferromagnet spin-valve structures. Our samples consist of two
ferromagnetic iron leads forming planar tunnel contacts to a superconducting
aluminum wire. At energies below the superconducting gap, we observe a negative
four-probe resistance that can be explained by crossed Andreev reflection.",0609766v1
2005-05-23,The Cyborg Astrobiologist: Scouting Red Beds for Uncommon Features with Geological Significance,"The `Cyborg Astrobiologist' (CA) has undergone a second geological field
trial, at a red sandstone site in northern Guadalajara, Spain, near Riba de
Santiuste. The Cyborg Astrobiologist is a wearable computer and video camera
system that has demonstrated a capability to find uncommon interest points in
geological imagery in real-time in the field. The first (of three) geological
structures that we studied was an outcrop of nearly homogeneous sandstone,
which exhibits oxidized-iron impurities in red and and an absence of these iron
impurities in white. The white areas in these ``red beds'' have turned white
because the iron has been removed by chemical reduction, perhaps by a
biological agent. The computer vision system found in one instance several
(iron-free) white spots to be uncommon and therefore interesting, as well as
several small and dark nodules. The second geological structure contained
white, textured mineral deposits on the surface of the sandstone, which were
found by the CA to be interesting. The third geological structure was a 50 cm
thick paleosol layer, with fossilized root structures of some plants, which
were found by the CA to be interesting. A quasi-blind comparison of the Cyborg
Astrobiologist's interest points for these images with the interest points
determined afterwards by a human geologist shows that the Cyborg Astrobiologist
concurred with the human geologist 68% of the time (true positive rate), with a
32% false positive rate and a 32% false negative rate.
  (abstract has been abridged).",0505058v1
1998-05-27,Signals of phase transition in atmospheric showers,"We discuss collective effects like percolation, quark gluon plasma, or string
fusion and their effect on the longitudinal development of high energy showers
in air. It is shown that iron-air showers could develop more slowly than
expected and produce the observed change in the slope of $X_max$ at the highest
energies.",9805475v1
2007-06-01,Unveiling the broad band X-ray continuum and iron line complex in Mkr 841,"Mkr 841 is a bright Seyfert 1 galaxy known to harbor a strong soft excess and
a variable K$\alpha$ iron line. It has been observed during 3 different periods
by XMM for a total cumulated exposure time of $\sim$108 ks. We present in this
paper a broad band spectral analysis of the complete EPIC-pn data sets. We were
able to test two different models for the soft excess, a relativistically
blurred photoionized reflection (\r model) and a relativistically smeared
ionized absorption (\a model). The continuum is modeled by a simple cut-off
power law and we also add a neutral reflection. These observations reveal the
extreme and puzzling spectral and temporal behaviors of the soft excess and
iron line. The 0.5-3 keV soft X-ray flux decreases by a factor 3 between 2001
and 2005 and the line shape appears to be a mixture of broad and narrow
components. We succeed in describing this complex broad-band 0.5-10 keV
spectral variability using either \r or \a to fit the soft excess. Both models
give statistically equivalent results even including simultaneous BeppoSAX data
up to 200 keV. Both models are consistent with the presence of remote
reflection characterized by a constant narrow component in the data. However
they differ in the presence of a broad line component present in \r but not
needed in \a. This study also reveals the sporadic presence of relativistically
redshifted narrow iron lines.",0706.0134v1
2007-10-04,Broad band X-ray spectroscopy of A0535+262 with SUZAKU,"The transient X-ray binary pulsar A0535+262 was observed with Suzaku on 2005
September 14 when the source was in the declining phase of the August-September
minor outburst. The ~103 s X-ray pulse profile was strongly energy dependent, a
double peaked profile at soft X-ray energy band (<3 keV) and a single peaked
smooth profile at hard X-rays. The width of the primary dip is found to be
increasing with energy. The broad-band energy spectrum of the pulsar is well
described with a Negative and Positive power-law with EXponential (NPEX)
continuum model along with a blackbody component for soft excess. A weak iron
K_alpha emission line with an equivalent width ~25 eV was detected in the
source spectrum. The blackbody component is found to be pulsating over the
pulse phase implying the accretion column and/or the inner edge of the
accretion disk may be the possible emission site of the soft excess in
A0535+262. The higher value of the column density is believed to be the cause
of the secondary dip at the soft X-ray energy band. The iron line equivalent
width is found to be constant (within errors) over the pulse phase. However, a
sinusoidal type of flux variation of iron emission line, in phase with the hard
X-ray flux suggests that the inner accretion disk is the possible emission
region of the iron fluorescence line.",0710.0961v1
2008-04-16,"Discovery of superstrong, fading, iron line emission and double-peaked Balmer lines of the galaxy SDSSJ0952+2143 - the light echo of a huge flare","We report the discovery of superstrong, fading, high-ionization iron line
emission in the galaxy SDSSJ095209.56+214313.3 (SDSSJ0952+2143 hereafter),
which must have been caused by an X-ray outburst of large amplitude.
SDSSJ0952+2143 is unique in its strong multiwavelength variability; such a
broadband emission-line and continuum response has not been observed before.
The strong iron line emission is accompanied by unusual Balmer line emission
with a broad base, narrow core and double-peaked narrow horns, and strong HeII
emission. These lines, while strong in the SDSS spectrum taken in 2005, have
faded away significantly in new spectra taken in December 2007. Comparison of
SDSS, 2MASS, GALEX and follow-up GROND photometry reveals variability in the
NUV, optical and NIR band. Taken together, these unusual observations can be
explained by a giant outburst in the EUV--X-ray band, detected even in the
optical and NIR. The intense and variable iron, Helium and Balmer lines
represent the ``light echo'' of the flare, as it traveled through circumnuclear
material. The outburst may have been caused by the tidal disruption of a star
by a supermassive black hole. Spectroscopic surveys such as SDSS are well
suited to detect emission-line light echoes of such rare flare events.
Reverberation-mapping of these light echoes can then be used as a new and
efficient probe of the physical conditions in the circumnuclear material in
non-active or active galaxies.",0804.2670v1
2008-05-26,Around the Pair Instability Valley - Massive SN Progenitors,"The discovery of the extremely luminous supernova SN 2006gy, possibly
interpreted as a pair instability supernova, renewed the interest in very
massive stars. We explore the evolution of these objects, which end their life
as pair instability supernovae or as core collapse supernovae with relatively
massive iron cores, up to about $3 M_\odot$.",0805.3874v1
2008-06-05,"Cu, Pu and Fe high Tc superconductors: all the same mechanism!","The new iron based high Tc superconductors with Tc up to 55 K have stirred
new interest in this field. It is consensus that the BCS mechanism is not able
to explain the high Tc's. In the following we propose that spin holes in
antiferromagnetic clusters combine to make nonmagnetic bipolarons, which can
condense and lead to superconductivity.",0806.0900v1
2008-06-22,The most massive core collapse supernova progenitors,"The discovery of the extremely luminous supernova SN 2006gy, possibly
interpreted as a pair instability supernova, renewed the interest in very
massive stars. We explore the evolution of these objects, which end their life
as pair instability supernovae or as core collapse supernovae with relatively
massive iron cores, up to about $3 M_\odot$.",0806.3544v2
2008-07-08,The influence of chemical composition on the properties of Cepheid stars. II-The iron content,"The Cepheid period-luminosity (PL) relation is unquestionably one of the most
powerful tools at our disposal for determining the extragalactic distance
scale. While significant progress has been made in the past few years towards
its understanding and characterization both on the observational and
theoretical sides, the debate on the influence that chemical composition may
have on the PL relation is still unsettled. With the aim to assess the
influence of the stellar iron content on the PL relation in the V and K bands,
we have related the V-band and the K-band residuals from the standard PL
relations of Freedman et al. (2001) and Persson et al. (2004), respectively, to
[Fe/H]. We used direct measurements of the iron abundances of 68 Galactic and
Magellanic Cepheids from FEROS and UVES high-resolution and high
signal-to-noise spectra. We find a mean iron abundance ([Fe/H]) about solar
(sigma = 0.10) for our Galactic sample (32 stars), -0.33 dex (sigma = 0.13) for
the Large Magellanic Cloud (LMC) sample (22 stars) and -0.75 dex (sigma = 0.08)
for the Small Magellanic Cloud (SMC) sample (14 stars). Our abundance
measurements of the Magellanic Cepheids double the number of stars studied up
to now at high resolution. The metallicity affects the V-band Cepheid PL
relation and metal-rich Cepheids appear to be systematically fainter than
metal-poor ones. These findings depend neither on the adopted distance scale
for Galactic Cepheids nor on the adopted LMC distance modulus. Current data do
not allow us to reach a firm conclusion concerning the metallicity dependence
of the K-band PL relation. The new Galactic distances indicate a small effect,
whereas the old ones support a marginal effect.",0807.1196v2
2008-09-21,The Suzaku Observations of SS Cygni in Quiescence and Outburst,"We present results from the Suzaku observations of the dwarf nova SS Cyg in
quiescence and outburst in 2005 November. Owing to high sensitivity of the HXD
PIN detector and high spectral resolution of the XIS, we have determined
parameters of the plasma with unprecedented precision. The maximum temperature
of the plasma in quiescence 20.4 +4.0-2.6 (stat.) +/- 3.0 (sys.) keV is
significantly higher than that in outburst 6.0 +0.2-1.3 keV. The elemental
abundances are close to the solar ones for the medium-Z elements (Si, S, Ar)
whereas they decline both in lighter and heavier elements. Those of oxygen and
iron are 0.46 and 0.37 solar, respectively. That of carbon is exceptionally
high and 2 solar at least. The solid angle of the reflector subtending over the
optically thin thermal plasma is Omega/2\pi = 1.7+/-0.2 (stat.) +/-0.1 (sys.)
in quiescence. A 6.4 keV iron Ka line is resolved into a narrow and broad
components. These facts indicate that both the white dwarf and the accretion
disk contribute to the continuum reflection and the 6.4 keV iron Ka line. We
consider the standard optically thin boundary layer as the most plausible
picture for the plasma configuration in quiescence. The solid angle of the
reflector in outburst Omega/2\pi = 0.9 +0.5-0.4 and a broad 6.4 keV iron line
indicates that the reflection in outburst originates from the accretion disk
and an equatorial accretion belt. From the energy width of the 6.4 keV line, we
consider the optically thin thermal plasma in outburst as being distributed on
the accretion disk like solar coronae.",0809.3559v2
2008-10-14,Probing the accretion disk and central engine structure of NGC4258 with Suzaku and XMM-Newton observations,"[abridged] We present an X-ray study of the low-luminosity active galactic
nucleus (AGN) in NGC4258 using data from Suzaku, XMM-Newton, and the Swift/BAT
survey. We find that signatures of X-ray reprocessing by cold gas are very weak
in the spectrum of this Seyfert-2 galaxy; a weak, narrow fluorescent-Kalpha
emission line of cold iron is robustly detected in both the Suzaku and
XMM-Newton spectra but at a level much below that of most other Seyfert-2
galaxies. We conclude that the circumnuclear environment of this AGN is very
""clean"" and lacks the Compton-thick obscuring torus of unified Seyfert schemes.
  From the narrowness of the iron line, together with evidence for line flux
variability between the Suzaku and XMM-Newton observations, we constrain the
line emitting region to be between $3\times 10^3r_g$ and $4\times 10^4r_g$ from
the black hole. We show that the observed properties of the iron line can be
explained if the line originates from the surface layers of a warped accretion
disk. In particular, we present explicit calculations of the expected iron line
from a disk warped by Lens-Thirring precession from a misaligned central black
hole. Finally, the Suzaku data reveal clear evidence for large amplitude
2-10keV variability on timescales of 50ksec as well as smaller amplitude flares
on timescales as short as 5-10ksec. If associated with accretion disk
processes, such rapid variability requires an origin in the innermost regions
of the disk ($r\approx 10r_g$ or less).",0810.2543v1
2008-11-24,Fe-based superconductors: unity or diversity?,"Does the high temperature superconductivity observed in the newly discovered
iron-pnictide materials represent another example of the same essential physics
responsible for superconductivity in the cuprates, or does it embody a new
mechanism?",0811.3973v1
2008-12-06,Piezonuclear Neutrons,"We report the results of neutron measurements carried out during the
application of ultrasounds to a solution containing only stable elements like
Iron and Chlorine, without any other radioactive source of any kind. These
measurements, carried out by CR39 detectors and a Boron TriFouride electronic
detector, evidenced the emission of neutron pulses. These pulses stand well
above the electronic noise and the background of the laboratory where the
measurements were carried out.",0812.1272v1
2009-03-01,Excitonic spin density wave state in iron pnictides,"We examine the appearance of a spin density wave in the FeAs parent compounds
due to an excitonic instability. Using a realistic four-band model, we show
that the magnetic state depends very sensitively upon the details of the band
structure. We demonstrate that an orthorhombic distortion of the crystal
enhances the stability of the antiferromagnetic order.",0903.0124v1
2009-03-25,Isotropic superconducting state and high critical currents in Fe1+yTe1-xSx single crystals,"We report single crystal growth and a study of superconducting properties in
Fe_{1+y}Te_{1-x}S_{x}. We demonstrate the smallest upper critical field
anisotropy, gamma=H_{c2}^{//c}/H_{c2}^{//a}, among all iron based
superconductors, the value of gamma reaches 1.05 at T=0.65T_{C} for
Fe_{1.09}Te_{0.89}S_{0.11}, while still maintaining large values of upper
critical field.",0903.4430v2
2009-10-21,"Correspondence on ""Electronic correlations in the iron pnictides""","I point out that the observed discrepancy between the measured and calculated
Drude weights in LaFePO may be caused not only by mass renormalization, but
also by a DFT inaccuracy in determining the relative positions of the hole and
electron band.",0910.4117v1
2009-10-28,Experimentally Realized Correlated Electron Materials: From Superconductors to Topological Insulators,"Recent discoveries, as well as open questions, in experimentally realized
correlated electron materials are reviewed. In particular, high temperature
superconductivity in the cuprates and in the recently discovered iron
pnictides, possible chiral p-wave superconductivity in strontium ruthenate, the
search for quantum spin liquid behavior in real materials, and new experimental
discoveries in topological insulators are discussed.",0910.5513v1
2009-12-09,Pairing mechanism in Fe pnictide superconductors,"By applying an exact unitary transformation to a two-band hamiltonian which
also includes the effects due to large pnictogen polarizabilities, we show that
an attractive spin-mediated Hubbard term appears in the $d_{xz}$, $d_{yz}$
nearest-neighbour channel. This pairing mechanism implies a singlet
superconducting order parameter in iron pnictides.",0912.1811v1
2009-12-18,"Nodes to the grindstone: viewpoint on ``Band- and momentum-dependent electron dynamics in superconducting Ba(Fe$_{1-x}$Co$_x$)$_2$As$_2$ as seen via electronic Raman scattering"" [arXiv:0910.0898]","Raman spectroscopy of a cobalt-doped iron-pnictide superconductor reveals the
complex electronic structure of the superconducting state in this material.
[Viewpoint on Phys. Rev. B 80, 180510 (2009), arXiv:0910.0898]",0912.3756v1
2010-03-19,New Baade-Wesselink distances and radii for four metal-rich Galactic Cepheids,"We provided accurate estimates of distances, radii and iron abundances for
four metal-rich Cepheids, namely V340 Ara, UZ Sct, AV Sgr and VY Sgr. The main
aim of this investigation is to constrain their pulsation properties and their
location across the Galactic inner disk. We adopted new accurate NIR (J,H,K)
light curves and new radial velocity measurements for the target Cepheids to
determinate their distances and radii using the Baade-Wesselink technique. In
particular, we adopted the most recent calibration of the IR surface brightness
relation and of the projection factor. Moreover, we also provided accurate
measurements of the iron abundance of the target Cepheids. Current distance
estimates agree within one sigma with similar distances based either on
empirical or on theoretical NIR Period-Luminosity relations. However, the
uncertainties of the Baade-Wesselink distances are on average a factor of 3-4
smaller when compared with errors affecting other distance determinations. Mean
Baade-Wesselink radii also agree at one sigma level with Cepheid radii based
either on empirical or on theoretical Period-Radius relations. Iron abundances
are, within one sigma, similar to the iron contents provided by Andrievsky and
collaborators, thus confirming the super metal-rich nature of the target
Cepheids. We also found that the luminosity amplitudes of classical Cepheids,
at odds with RR Lyrae stars, do not show a clear correlation with the
metal-content. This circumstantial evidence appears to be the consequence of
the Hertzsprung progression together with the dependence of the topology of the
instability strip on metallicity, evolutionary effects and binaries.",1003.3854v1
2010-05-17,Interatomic exchange coupling of BCC iron,"We performed first-principle calculations on the exchange interaction (EI)
between atoms in BCC-Fe strained volumetrically. Our results show that the
volume-dependence of the EI deviates considerably from the Bethe-Slater curve.
This behavior is discussed in terms of the on-site and/or inter-site direct
exchange interactions between electrons.",1005.2931v1
2010-06-16,Apparent high metallicity in 3-4 keV galaxy clusters: the inverse iron-bias in action in the case of the merging cluster Abell 2028,"Recent work based on a global measurement of the ICM properties find evidence
for an increase of the iron abundance in galaxy clusters with temperature
around 2-4 keV up to a value about 3 times larger than that typical of very hot
clusters. We have started a study of the metal distribution in these objects
from the sample of Baumgartner et al. (2005), aiming at resolving spatially the
metal content of the ICM. We report here on a 42ks XMM observation of the first
object of the sample, the cluster Abell 2028. The XMM observation reveals a
complex structure of the cluster over scale of 300 kpc, showing an interaction
between two sub-clusters in cometary-like configurations. At the leading edges
of the two substructures cold fronts have been detected. The core of the main
subcluster is likely hosting a cool corona. We show that a one-component fit
for this region returns a biased high metallicity. This inverse iron bias is
due to the behavior of the fitting code in shaping the Fe-L complex. In
presence of a multi-temperature structure of the ICM, the best-fit metallicity
is artificially higher when the projected spectrum is modeled with a single
temperature component and it is not related to the presence of both Fe-L and
Fe-K emission lines in the spectrum. After accounting for the bias, the overall
abundance of the cluster is consistent with the one typical of hotter, more
massive clusters. We caution the interpretation of high abundances inferred
when fitting a single thermal component to spectra derived from relatively
large apertures in 3-4 keV clusters, because the inverse iron bias can be
present. Most of the inferences trying to relate high abundances in 3-4 keV
clusters to fundamental physical processes will likely have to be revised.",1006.3255v2
2010-06-18,The Type Ia Supernova Rate in Redshift 0.5--0.9 Galaxy Clusters,"Supernova (SN) rates are potentially powerful diagnostics of metal enrichment
and SN physics, particularly in galaxy clusters with their deep,
metal-retaining potentials and relatively simple star-formation histories. We
have carried out a survey for supernovae (SNe) in galaxy clusters, at a
redshift range 0.5<z<0.9, using the Advanced Camera for Surveys (ACS) on the
Hubble Space Telescope. We reimaged a sample of 15 clusters that were
previously imaged by ACS, thus obtaining two to three epochs per cluster, in
which we discovered five likely cluster SNe, six possible cluster SNe Ia, two
hostless SN candidates, and several background and foreground events. Keck
spectra of the host galaxies were obtained to establish cluster membership. We
conducted detailed efficiency simulations, and measured the stellar
luminosities of the clusters using Subaru images. We derive a cluster SN rate
of 0.35 SNuB +0.17/-0.12 (statistical) \pm0.13 (classification) \pm0.01
(systematic) [where SNuB = SNe (100 yr 10^10 L_B_sun)^-1] and 0.112 SNuM
+0.055/-0.039 (statistical) \pm0.042 (classification) \pm0.005 (systematic)
[where SNuM = SNe (100 yr 10^10 M_sun)^-1]. As in previous measurements of
cluster SN rates, the uncertainties are dominated by small-number statistics.
The SN rate in this redshift bin is consistent with the SN rate in clusters at
lower redshifts (to within the uncertainties), and shows that there is, at
most, only a slight increase of cluster SN rate with increasing redshift. The
low and fairly constant SN Ia rate out to z~1 implies that the bulk of the iron
mass in clusters was already in place by z~1. The recently observed doubling of
iron abundances in the intracluster medium between z=1 and 0, if real, is
likely the result of redistribution of existing iron, rather than new
production of iron.",1006.3757v1
2010-07-09,"The broad-band X-ray spectrum of the Seyfert 1 galaxy, MCG+8-11-11","We present a long (100 ks) Suzaku observation of one of the X-ray brightest
AGN, MCG+8-11-11. These data were complemented with the 54-month Swift BAT
spectrum, allowing us to perform a broad-band fit in the 0.6-150 keV range. The
fits performed in the 0.6-10 keV band give consistent results with respect to a
previous XMM-Newton observation, i.e. the lack of a soft excess, warm
absorption along the line of sight, a large Compton reflection component (R~1)
and the absence of a relativistic component of the neutral iron K$\alpha$
emission line. However, when the PIN and Swift BAT data are included, the
reflection amount drops significantly (R~0.2-0.3), and a relativistic iron line
is required, the latter confirmed by a phenomenological analysis in a
restricted energy band (3-10 keV). When a self-consistent model is applied to
the whole broadband data, the observed reflection component appears to be all
associated to the relativistic component of the iron K$\alpha$ line. The
resulting scenario, though strongly model-dependent, requires that all the
reprocessing spectral components from Compton-thick material must be associated
to the accretion disc, and no evidence for the classical pc-scale torus is
found. The narrow core of the neutral iron K$\alpha$ line is therefore produced
in a Compton-thin material, like the BLR, similarly to what found in another
Seyfert galaxy, NGC7213, but with the notable difference that MCG+8-11-11
presents spectral signatures from an accretion disc. The very low accretion
rate of NGC7213 could explain the lack of relativistic signatures in its
spectrum, but the absence of the torus in both sources is more difficult to
explain, since their luminosities are comparable, and their accretion rates are
completely different.",1007.1638v1
2010-07-16,Magnetism and Charge Dynamics in Iron Pnictides,"In a wide variety of materials, such as copper oxides, heavy fermions,
organic salts, and the recently discovered iron pnictides, superconductivity is
found in close proximity to a magnetically ordered state. The character of the
proximate magnetic phase is thus believed to be crucial for understanding the
differences between the various families of unconventional superconductors and
the mechanism of superconductivity. Unlike the AFM order in cuprates, the
nature of the magnetism and of the underlying electronic state in the iron
pnictide superconductors is not well understood. Neither density functional
theory nor models based on atomic physics and superexchange, account for the
small size of the magnetic moment. Many low energy probes such as transport,
STM and ARPES measured strong anisotropy of the electronic states akin to the
nematic order in a liquid crystal, but there is no consensus on its physical
origin, and a three dimensional picture of electronic states and its relations
to the optical conductivity in the magnetic state is lacking. Using a first
principles approach, we obtained the experimentally observed magnetic moment,
optical conductivity, and the anisotropy of the electronic states. The theory
connects ARPES, which measures one particle electronic states, optical
spectroscopy, probing the particle hole excitations of the solid and neutron
scattering which measures the magnetic moment. We predict a manifestation of
the anisotropy in the optical conductivity, and we show that the magnetic phase
arises from the paramagnetic phase by a large gain of the Hund's rule coupling
energy and a smaller loss of kinetic energy, indicating that iron pnictides
represent a new class of compounds where the nature of magnetism is
intermediate between the spin density wave of almost independent particles, and
the antiferromagnetic state of local moments.",1007.2867v1
2010-10-29,The Stellar Abundances for Galactic Archaeology (SAGA) Database II - Implications for Mixing and Nucleosynthesis in Extremely Metal-Poor Stars and Chemical Enrichment of the Galaxy,"We discuss the characteristics of known extremely metal-poor (EMP) stars in
the Galaxy using the Stellar Abundances for Galactic Archaeology (SAGA)
database (Suda et al. 2008, PASJ, 60, 1159).The analyses of carbon-enhanced
stars in our sample suggest that the nucleosynthesis in AGB stars can
contribute to the carbon enrichment in a different way depending on whether the
metallicity is above or below [Fe/H] ~ -2.5, which is consistent with the
current models of stellar evolution at low metallicity. We find the transition
of the initial mass function at [Fe/H] ~ -2 in the viewpoint of the
distribution of carbon abundance and the frequency of carbon-enhanced stars.
For observed EMP stars, we confirmed that some, not all, of observed stars
might have undergone at least two types of extra mixing to change their surface
abundances. One is to deplete the lithium abundance during the early phase of
red giant branch. Another is to decrease the C/N ratio by one order of
magnitude during the red giant branch phase. Observed small scatters of
abundances for alpha-elements and iron-group elements suggest that the chemical
enrichment of our Galaxy takes place in a well-mixed interstellar medium. We
find that the abundance trends of alpha-elements are highly correlated with
each other, while the abundances of iron-group elements are subject to
different slopes relative to the iron abundance. This implies that the
supernova yields of alpha-elements are almost independent of mass and
metallicity, while those of iron-group elements have a metallicity dependence
or mass dependence with the variable initial mass function.The occurrence of
the hot bottom burning in the mass range of 5 <~ M / Msun <~ 6 is consistent
with the initial mass function of the Galaxy peaked at ~ 10 - 12 Msun to be
compatible with the statistics of carbon enhanced stars with and without
s-process element (truncated)",1010.6272v1
2011-01-18,Discovery of strong Iron Kα emitting Compton thick quasars at z=2.5 and 2.9,"We report the detection of the 6.4 keV Iron K{\alpha} emission line in two
infrared-luminous, massive, star-forming BzK galaxies at z = 2.578 and z = 2.90
in the CDF-S. The Chandra 4 Ms spectra of BzK4892 and BzK8608 show a reflection
dominated continuum with strong Iron lines, with rest-frame equivalent widths
EW-2.3 keV and 1.2 keV, respectively, demonstrating Compton thick obscuration
of the central AGN. For BzK8608 the line identification closely matches the
existing photometric redshift derived from the stellar emission. We use the
observed luminosities of the Iron K{\alpha} line, of the rest-frame mid-IR
continuum and of the UV rest-frame narrow emission lines to infer intrinsic
L(2-10 keV)>1e44 erg/s, about 1.0-2.5 dex larger than the observed ones, hence
confirming the presence of an absorber with N(H) > 1e24 cm-2. The two BzK
galaxies have stellar masses of 5e10 M\odot and, based on VLA 1.4 GHz and submm
870{\mu}m observations, they appear to host vigorous starburst activity with
SFR - 300-700 M\odot/yr that is also optically thick. We estimate that the AGN
might also conceivably account for an important fraction of the bolometric
far-IR emission of the galaxies. The implied volume density of Compton thick
(CT) AGN with L(2-10 keV)>1e44 erg/s is in agreement with predictions from
X-ray background synthesis models. These sources provide one of the first
clearcut observations of the long-sought phase of simultaneous, heavily
obscured quasar and star formation activity, predicted by models of massive
galaxy evolution at high redshifts.",1101.3478v1
2011-02-02,Gold slows down the growth of helium bubble in iron,"We predict by first-principles calculations that Au have strong affinity to
He in bcc Fe. The Au-Au bonding in the segregated Au layer at the He bubble
surface is stronger than Fe-Fe and Au-Fe interactions; therefore this layer
becomes an effective barrier to further He and slows down the bubble growth.",1102.0355v1
2011-03-07,Reversibly tuning the insulating and superconducting state in KxFe2-ySe2 crystals by post-annealing,"Since the discovery of superconductivity at 26 K in oxy-pnictide
LaFeAsO1-xFx, enormous interests have been stimulated in the field of condensed
matter physics and material sciences. Among the many kind of structures in the
iron pnictide superconductors, FeSe with the PbO structure has received special
attention since there is not poisonous pnictogen element in chemical
composition and its structure is the simplest one. However, the superconducting
transition temperature (Tc) in iron chalcogenide compounds is not enhanced as
high as other iron pnictide superconductors under ambient pressure until the
superconductivity at above 30 K in potassium intercalated iron selenide
KxFe2-ySe2 was discovered. The insulating and the superconducting state are
both observed in KxFe2-ySe2 with different stoichiometries and some groups have
tuned the system from insulating to superconducting state by varying the ratio
of starting materials[10, 11]. The recent data from neutron scattering suggest
that the superconductivity may be built upon an ordered state of Fe vacancies
as well as the antiferromagnetic state with a very strong ordered magnetic
moment 3.4 B. Here we show that the superconductivity can actually be tuned on
a single sample directly from an insulating state by post-annealing and fast
quenching. Upon waiting for some days at room temperatures, the
superconductivity will disappear and the resistivity exhibits an insulating
behavior again. The spatial distribution of the compositions of the as-grown
sample and the post-annealed-quenched one was analyzed by the Energy Dispersive
X-ray Spectrum (EDXS) and found to be very close to each other. Therefore it is
tempting to conclude that the superconductivity is achieved when the
Fe-vacancies are in a random (disordered) state. Once they arrange in an
ordered state by relaxation or slow cooling, the system turns out to be an
insulator.",1103.1347v1
2011-04-07,Insight Into the Formation of the Milky Way Through Cold Halo Substructure. II. The Elemental Abundances of ECHOS,"We determine the average metallicities of the elements of cold halo
substructure (ECHOS) that we previously identified in the inner halo of the
Milky Way within 17.5 kpc of the Sun. As a population, we find that stars
kinematically associated with ECHOS are chemically distinct from the background
kinematically smooth inner halo stellar population along the same Sloan
Extension for Galactic Understanding and Exploration (SEGUE) line of sight.
ECHOS are systematically more iron-rich, but less alpha-enhanced than the
kinematically-smooth component of the inner halo. ECHOS are also chemically
distinct from other Milky Way components: more iron-poor than typical
thick-disk stars and both more iron-poor and alpha-enhanced than typical
thin-disk stars. In addition, the radial velocity dispersion distribution of
ECHOS extends beyond sigma ~ 20 km s^-1. Globular clusters are unlikely ECHOS
progenitors, as ECHOS have large velocity dispersions and are found in a region
of the Galaxy in which iron-rich globular clusters are very rare. Likewise, the
chemical composition of stars in ECHOS do not match predictions for stars
formed in the Milky Way and subsequently scattered into the inner halo. Dwarf
spheroidal (dSph) galaxies are possible ECHOS progenitors, and if ECHOS are
formed through the tidal disruption of one or more dSph galaxies, the typical
ECHOS [Fe/H] ~ -1.0 and radial velocity dispersion sigma ~ 20 km s^-1 implies a
dSph with M_tot >~ 10^9 M_Sun. Our observations confirm the predictions of
theoretical models of Milky Way halo formation that suggest that prominent
substructures are likely to be metal-rich, and our result implies that the most
likely metallicity for a recently accreted star currently in the inner halo is
[Fe/H] ~ -1.0.",1104.1424v1
2011-05-10,Superconductivity in the Honeycomb-Lattice Pnictide SrPtAs,"We report superconductivity in the honeycomb-lattice pnictide SrPtAs with Tc
= 2.4 K. To our knowledge, SrPtAs is the first superconducting pnictide with a
honeycomb lattice structure. Our finding opens up new playground to develop
pnictide superconductors with honeycomb lattices, in addition to square
lattices known in iron-based superconductors.",1105.1848v1
2011-05-18,Specifics of impurity effects in ferropnictide superconductors,"Effects of impurities and disorder on quasiparticle spectrum in
superconducting iron pnictides are considered. Possibility for occurrence of
localized energy levels due to impurities within the superconducting gap and
the related modification of band structure and of superconducting order
parameter are discussed. The evolution of superconducting state with impurity
doping is traced.",1105.3608v1
2011-06-02,X-ray Spectroscopy of the High Mass X-ray Binary Pulsar Centaurus X-3 over its Binary Orbit,"We present a comprehensive spectral analysis of the high mass X-ray binary
(HMXB) pulsar Centaurus X-3 with the Suzaku observatory covering nearly one
orbital period. The light curve shows the presence of extended dips which are
rarely seen in HMXBs. These dips are seen up to as high as ~40 keV. The pulsar
spectra during the eclipse, out-of-eclipse, and dips are found to be well
described by a partial covering power-law model with high energy cut-off and
three Gaussian functions for 6.4 keV, 6.7 keV, and 6.97 keV iron emission
lines. The dips in the light curve can be explained by the presence of an
additional absorption component with high column density and covering fraction,
the values of which are not significant during the rest of the orbital phases.
The iron line parameters during the dips and eclipse are significantly
different compared to those during the rest of the observation. During the
dips, the iron line intensities are found to be lesser by a factor of 2--3 with
significant increase in the line equivalent widths. However, the continuum flux
at the corresponding orbital phase is estimated to be lesser by more than an
order of magnitude. Similarities in the changes in the iron line flux and
equivalent widths during the dips and eclipse segments suggests the dipping
activity in Cen X-3 is caused by obscuration of the neutron star by dense
matter, probably structures in the outer region of the accretion disk, as in
case of dipping low mass X-ray binaries.",1106.0370v1
2011-06-29,Phase Separation and Superconductivity in Fe1+xTe0.5Se0.5,"Fe1+xTe0.5Se0.5 is the archetypical iron-based superconductor. Here we show
that the superconducting state is controlled by the stacking of its anti-PbO
layers, such that homogeneous ordering hinders superconductivity and the
highest volume fractions are observed in phase separated structures as
evidenced by either a distribution of lattice parameters or microstrain.",1106.5955v1
2011-12-19,XMM-Newton observation of 4U 1820-30: Broad band spectrum and the contribution of the cold interstellar medium,"We present the analysis of the bright X-ray binary 4U 1820-30, based mainly
on XMM-Newton-RGS data, but using complementary data from XMM-Epic, Integral,
and Chandra-HETG, to investigate different aspects of the source. The broad
band continuum is well fitted by a classical combination of black body and
Comptonized emission. The continuum shape and the high flux of the source
(L/L_Edd\sim0.16) are consistent with a ""high state"" of the source. We do not
find significant evidence of iron emission at energies >=6.4 keV. The soft
X-ray spectrum contain a number of absorption features. Here we focus on the
cold-mildly ionized gas. The neutral gas column density is N_H\sim1.63x10^21
cm^-2. The detailed study of the oxygen and iron edge reveals that those
elements are depleted, defined here as the ratio between dust and the total ISM
cold phase, by a factor 0.20\pm0.02 and 0.87\pm0.14, respectively. Using the
available dust models, the best fit points to a major contribution of Mg-rich
silicates, with metallic iron inclusion. Although we find that a large fraction
of Fe is in dust form, the fit shows that Fe-rich silicates are disfavored. The
measured Mg:Fe ratio is 2.0\pm0.3. Interestingly, this modeling may point to a
well studied dust constituent (GEMS), sometimes proposed as a silicate
constituent in our Galaxy. Oxygen and iron are found to be slightly over- and
under-abundant, respectively (1.23 and 0.85 times the solar value) along this
line of sight. We also report the detection of two absorption lines,
tentatively identified as part of an outflow of mildly ionized gas
(\xi\sim-0.5) at a velocity of \sim1200 km/s.",1112.4349v1
2012-02-27,Testing the No-Hair Theorem with Observations in the Electromagnetic Spectrum. IV. Relativistically Broadened Iron Lines,"According to the no-hair theorem, astrophysical black holes are fully
characterized by their masses and spins and are described by the Kerr metric.
This theorem can be tested observationally by measuring (at least) three
different multipole moments of the spacetimes of black holes. In this paper, we
calculate the profiles of fluorescent iron lines emitted from the accretion
flows around black hole candidates within a framework that allows us to perform
the calculation as a function of its mass and spin as well as of a free
parameter that measures potential deviations from the Kerr metric. We show that
such deviations lead to line profiles that are significantly altered and may
exhibit a modified flux ratio of the two peaks in their characteristic
double-peaked shape. We also show that the disk inclination can be measured
independently of the spin and the deviation parameter at low to intermediate
inclination angles as in the case of Kerr black holes. We estimate the
precision that near-future X-ray missions such as Astro-H and ATHENA+ are
required to achieve in order to resolve deviations from the Kerr metric in iron
line profiles and show that constraints on such deviations will be strongest
for rapidly spinning black holes. More generally, we show that measuring the
line profile with a precision of ~5% at disk inclinations of 30 or 60 degrees
constraints the deviation parameter to order unity for values of the spin
a>0.5M.",1202.6069v2
2012-03-20,"Neutrino cooling rates due to $^{54,55,56}$Fe for presupernova evolution of massive stars","Accurate estimate of neutrino energy loss rates are needed for the study of
the late stages of the stellar evolution, in particular for cooling of neutron
stars and white dwarfs. Proton-neutron quasi-particle random phase
approximation (pn-QRPA) theory has recently being used for a microscopic
calculation of stellar weak interaction rates of iron isotopes with success.
Here I present the detailed calculation of neutrino and antineutrino cooling
rates due to key iron isotopes in stellar matter using the pn-QRPA theory. The
rates are calculated on a fine grid of temperature-density scale suitable for
core-collapse simulators. The calculated rates are compared against earlier
calculations. The neutrino cooling rates due to isotopes of iron are in overall
good agreement with the rates calculated using the large-scale shell model.
During the presupernova evolution of massive stars, from oxygen shell burning
till around end of convective core silicon burning phases, the calculated
neutrino cooling rates due to $^{54}$Fe are three to four times larger than the
corresponding shell model rates. The Brink's hypothesis used in previous
calculations can at times lead to erroneous results. The Brink's hypothesis
assumes that the Gamow-Teller strength distributions for all excited states are
the same. It is, however, shown by the present calculation that both the
centroid and total strength for excited states differ appreciably from the
ground state distribution. These changes in the strength distributions of
thermally populated excited states can alter the total weak interaction rates
rather significantly. The calculated antineutrino cooling rates, due to
positron capture and $\beta$-decay of iron isotopes, are orders of magnitude
smaller than the corresponding neutrino cooling rates and can safely be
neglected specially at low temperatures and high stellar densities.",1203.4344v1
2012-03-21,Ground and excited states Gamow-Teller strength distributions of iron isotopes and associated capture rates for core-collapse simulations,"This paper reports on the microscopic calculation of ground and excited
states Gamow-Teller (GT) strength distributions, both in the electron capture
and electron decay direction, for $^{54,55,56}$Fe. The associated electron and
positron capture rates for these isotopes of iron are also calculated in
stellar matter. These calculations were recently introduced and this paper is a
follow-up which discusses in detail the GT strength distributions and stellar
capture rates of key iron isotopes. The calculations are performed within the
framework of the proton-neutron quasiparticle random phase approximation
(pn-QRPA) theory. The pn-QRPA theory allows a microscopic
\textit{state-by-state} calculation of GT strength functions and stellar
capture rates which greatly increases the reliability of the results. For the
first time experimental deformation of nuclei are taken into account. In the
core of massive stars isotopes of iron, $^{54,55,56}$Fe, are considered to be
key players in decreasing the electron-to-baryon ratio ($Y_{e}$) mainly via
electron capture on these nuclide. The structure of the presupernova star is
altered both by the changes in $Y_{e}$ and the entropy of the core material.
Results are encouraging and are compared against measurements (where possible)
and other calculations. The calculated electron capture rates are in overall
good agreement with the shell model results. During the presupernova evolution
of massive stars, from oxygen shell burning stages till around end of
convective core silicon burning, the calculated electron capture rates on
$^{54}$Fe are around three times bigger than the corresponding shell model
rates. The calculated positron capture rates, however, are suppressed by two to
five orders of magnitude.",1203.4675v1
2012-03-22,Thermal and electrical conductivity of iron at Earth's core conditions,"The Earth acts as a gigantic heat engine driven by decay of radiogenic
isotopes and slow cooling, which gives rise to plate tectonics, volcanoes, and
mountain building. Another key product is the geomagnetic field, generated in
the liquid iron core by a dynamo running on heat released by cooling and
freezing to grow the solid inner core, and on chemical convection due to light
elements expelled from the liquid on freezing. The power supplied to the
geodynamo, measured by the heat-flux across the core-mantle boundary (CMB),
places constraints on Earth's evolution. Estimates of CMB heat-flux depend on
properties of iron mixtures under the extreme pressure and temperature
conditions in the core, most critically on the thermal and electrical
conductivities. These quantities remain poorly known because of inherent
difficulties in experimentation and theory. Here we use density functional
theory to compute these conductivities in liquid iron mixtures at core
conditions from first principles- the first directly computed values that do
not rely on estimates based on extrapolations. The mixtures of Fe, O, S, and Si
are taken from earlier work and fit the seismologically-determined core density
and inner-core boundary density jump. We find both conductivities to be 2-3
times higher than estimates in current use. The changes are so large that core
thermal histories and power requirements must be reassessed. New estimates of
adiabatic heat-flux give 15-16 TW at the CMB, higher than present estimates of
CMB heat-flux based on mantle convection; the top of the core must be thermally
stratified and any convection in the upper core driven by chemical convection
against the adverse thermal buoyancy or lateral variations in CMB heat flow.
Power for the geodynamo is greatly restricted and future models of mantle
evolution must incorporate a high CMB heat-flux and explain recent formation of
the inner core.",1203.4970v1
2012-03-22,Enhancement of superconducting transition temperature of FeSe by intercalation of a molecular spacer layer,"The recent discovery of high temperature superconductivity in a layered iron
arsenide has led to an intensive search to optimize the superconducting
properties of iron-based superconductors by changing the chemical composition
of the spacer layer that is inserted between adjacent anionic iron arsenide
layers. Until now, superconductivity has only been found in compounds with a
cationic spacer layer consisting of metal ions: Li+, Na+, K+, Ba2+ or a
PbO-type or perovskite-type oxide layer. Electronic doping is usually necessary
to control the fine balance between antiferromagnetism and superconductivity.
Superconductivity has also been reported in FeSe, which contains neutral layers
similar in structure to those found in the iron arsenides but without the
spacer layer. Here we demonstrate the synthesis of Lix(NH2)y(NH3)1-yFe2Se2 (x
~0.6 ; y ~ 0.2), with lithium ions, lithium amide and ammonia acting as the
spacer layer, which exhibits superconductivity at 43(1) K, higher than in any
FeSe-derived compound reported so far and four times higher at ambient pressure
than the transition temperature, Tc, of the parent Fe1.01Se. We have determined
the crystal structure using neutron powder diffraction and used magnetometry
and muon-spin rotation data to determine the superconducting properties. This
new synthetic route opens up the possibility of further exploitation of related
molecular intercalations in this and other systems in order to greatly optimize
the superconducting properties in this family.",1203.5046v2
2012-04-05,"""Cigar"" Fermi surface as a possible requisite for superconductivity in iron-based superconductors","Recently discovered A-Fe-Se (A - alkali metal) materials have questioned the
most popular theories of iron-based superconductors because of their unusual
electronic structure [1]. Controversial photoemission data taken in the
superconducting state [2-7] are in conflict with highly magnetic state seen by
neutron-, muSR-spectroscopies and transport/thermodynamic probes [8-10]. These
results lead to suggestions to consider all iron-based materials as originating
from Mott-insulators or semiconductors, thus once again raising the question of
close relation between the cuprates and Fe-based superconductors [e.g. 2]. Here
we study electronic and magnetic properties of Rb0.77Fe1.61Se2 (Tc = 32.6 K) in
normal and superconducting states by means of photoemission and muSR
spectroscopies as well as band structure calculations. We demonstrate that the
puzzling behavior of these novel materials is the result of separation into
metallic (~12%) and insulating (~ 88%) phases. Only the former becomes
superconducting and has a usual electronic structure of electron-doped
FeSe-slabs. Our results thus imply that the antiferromagnetic insulating phase
is just a byproduct of Rb-intercalation and its magnetic properties have hardly
any relation to the superconductivity. Instead, we find that also in this,
already third class of iron-based compounds, the key ingredient for
superconductivity is a certain proximity of a van Hove singularity to the Fermi
level. These findings set the direction for effective search of new
superconducting materials.",1204.1316v1
2012-06-03,Fe-C and Fe-H systems at pressures of the Earth's inner core,"The solid inner core of the Earth is predominantly composed of iron alloyed
with several percent Ni and some lighter elements, Si, S, O, H, and C being the
prime candidates. There have been a growing number of papers investigating C
and H as possible light elements in the core, but the results are
contradictory. Here, using ab initio simulations, we study the Fe-C and Fe-H
systems at inner core pressures (330-364 GPa). Using the evolutionary structure
prediction algorithm USPEX, we have determined the lowest-enthalpy structures
of possible carbides (FeC, Fe2C, Fe3C, Fe4C, FeC2, FeC3, FeC4 and Fe7C3) and
hydrides (Fe4H, Fe3H, Fe2H, FeH, FeH2, FeH3, FeH4) and have found that Fe2C
(Pnma) is the most stable iron carbide at pressures of the inner core, while
FeH, FeH3 and FeH4 are stable iron hydrides at these conditions. For Fe3C, the
cementite structure (Pnma) and the Cmcm structure recently found by random
sampling are less stable than the I-4 and C2/m structures found here. We found
that FeH3 and FeH4 adopt chemically interesting thermodynamically stable
structures, in both compounds containing trivalent iron. The density of the
inner core can be matched with a reasonable concentration of carbon, 11-15
mol.percent (2.6-3.7 wt.percent) at relevant pressures and temperatures. This
concentration matches that in CI carbonaceous chondrites and corresponds to the
average atomic mass in the range 49.3-51.0, in close agreement with inferences
from the Birch's law for the inner core. Similarly made estimates for the
maximum hydrogen content are unrealistically high, 17-22 mol.percent (0.4-0.5
wt.percent), which corresponds to the average atomic mass in the range
43.8-46.5. We conclude that carbon is a better candidate light alloying element
than hydrogen.",1206.0467v1
2012-06-28,High-spin low-spin transition,"Temperature dependent nuclear inelastic-scattering (NIS) of synchrotron
radiation was applied to investigate both spin states of the spin-crossover
complex [Fe(tpa)(NCS)(2)] (tpa = tris(2-pyridylmethyl)amine). A remarkable
increase of the iron-ligand bond stretching upon spin crossover has
unambiguously been identified by comparing the measured NIS spectra with
theoretical simulations based on density-functional calculations.",1206.6683v1
2012-08-03,The effect of frame dragging on the iron K alpha line in X-ray binaries,"The clear characteristic timescale picked out by the low frequency
quasi-periodic oscillations (QPOs) seen in many black hole and neutron star
binaries has the potential to provide a very powerful diagnostic of the inner
regions of the accretion flow. However, this potential cannot be realised
without a quantitative model for the QPO. We have recently shown that the same
truncated disc/hot inner flow geometry which is used to interpret the spectral
transitions can also directly produce the QPO from Lense-Thirring (vertical)
precession of the hot inner flow. This correctly predicts both the frequency
and spectrum of the QPO, and the tight correlation of these properties with the
total spectrum of the source via a changing truncation radius between the disc
and hot flow. This model predicts a unique iron line signature as a vertically
tilted flow illuminates different azimuths of the disc as it precesses. The
iron line arising from this rotating illumination is blue shifted when the flow
irradiates the approaching region of the spinning disc and red shifted when the
flow irradiates the receding region of the disc. This gives rise to a
characteristic rocking of the iron line on the QPO frequency which is a
necessary (and probably sufficient) test of a Lense-Thirring origin. This is
also an independent test of disc truncation models for the low/hard state, as
vertical precession cannot occur if there is a disc in the midplane.
  We show that it may be possible to observe this effect using archival data
from the Rossi X-ray timing explorer (RXTE) or XMM Newton. However, a clean
test requires a combination of moderate resolution and good statistics, such as
would be available from a long XMM-Newton observation or with data from the
proposed ESA mission LOFT.",1208.0728v1
2012-08-06,The UV/optical spectra of the Type Ia supernova SN 2010jn: a bright supernova with outer layers rich in iron-group elements,"Radiative transfer studies of Type Ia supernovae (SNe Ia) hold the promise of
constraining both the time-dependent density profile of the SN ejecta and its
stratification by element abundance which, in turn, may discriminate between
different explosion mechanisms and progenitor classes. Here we present a
detailed analysis of Hubble Space Telescope ultraviolet (UV) and ground-based
optical spectra and light curves of the SN Ia SN 2010jn (PTF10ygu). SN 2010jn
was discovered by the Palomar Transient Factory (PTF) 15 days before maximum
light, allowing us to secure a time-series of four UV spectra at epochs from
-11 to +5 days relative to B-band maximum. The photospheric UV spectra are
excellent diagnostics of the iron-group abundances in the outer layers of the
ejecta, particularly those at very early times. Using the method of 'Abundance
Tomography' we have derived iron-group abundances in SN 2010jn with a precision
better than in any previously studied SN Ia. Optimum fits to the data can be
obtained if burned material is present even at high velocities, including
significant mass fractions of iron-group elements. This is consistent with the
slow decline rate (or high 'stretch') of the light curve of SN 2010jn, and
consistent with the results of delayed-detonation models. Early-phase UV
spectra and detailed time-dependent series of further SNe Ia offer a promising
probe of the nature of the SN Ia mechanism.",1208.1267v3
2012-09-07,Phase relations in K_xFe_{2-y}Se_2 and the structure of superconducting K_xFe_2Se_2 via high-resolution synchrotron diffraction,"Superconductivity in iron selenides has experienced a rapid growth, but not
without major inconsistencies in the reported properties. For
alkali-intercalated iron selenides, even the structure of the superconducting
phase is a subject of debate, in part because the onset of superconductivity is
affected much more delicately by stoichiometry and preparation than in cuprate
or pnictide superconductors. If high-quality, pure, superconducting
intercalated iron selenides are ever to be made, the intertwined physics and
chemistry must be explained by systematic studies of how these materials form
and by and identifying the many coexisting phases. To that end, we prepared
pure K_2Fe_4Se_5 powder and superconductors in the K_xFe_{2-y}Se_2 system, and
examined differences in their structures by high-resolution synchrotron and
single-crystal x-ray diffraction. We found four distinct phases: semiconducting
K_2Fe_4Se_5, a metallic superconducting phase K_xFe_2Se_2 with x ranging from
0.38 to 0.58, an insulator KFe_{1.6}Se_2 with no vacancy ordering, and an
oxidized phase K_{0.51(5)}Fe_{0.70(2)}Se that forms the PbClF structure upon
exposure to moisture. We find that the vacancy-ordered phase K_2Fe_4Se_5 does
not become superconducting by doping, but the distinct iron-rich minority phase
K_xFe_2Se_2 precipitates from single crystals upon cooling from above the
vacancy ordering temperature. This coexistence of metallic and semiconducting
phases explains a broad maximum in resistivity around 100 K. Further studies to
understand the solubility of excess Fe in the K_xFe_{2-y}Se_2 structure will
shed light on the maximum fraction of superconducting K_xFe_2Se_2 that can be
obtained by solid state synthesis.",1209.1650v1
2012-10-10,Composition of Near-Earth Asteroid (4179) Toutatis,"Surface composition of near-Earth asteroid (4179) Toutatis is consistent with
an undifferentiated L-chondrite composition. This is inconsistent with early
observations that suggested high pyroxene iron content and a differentiated
body.",1210.2853v1
2012-11-14,Timing and Spectral Analysis of the Unusual X-Ray Transient XTE J0421+560/CI Camelopardalis,"We present a detailed X-ray study of the 2003 XMM-Newton observation of the
High Mass X-ray Binary XTE J0421+560/CI Cam. The continuum of the X-ray
spectrum is well described by a flat power law (Gamma=1.0+/-0.2) with a large
intrinsic absorbing column (N_H=(4.4+/-0.5)\times10^{23} cm^{-2}). We have
decomposed the broad iron line into 3 separate components:
Fe\textsc{i}-K$\alpha$, Fe\textsc{i}-K$\beta$ and Fe\textsc{xxiv-xxv}K$\alpha$.
It is unclear how both neutral and almost fully ionised iron can exist
simultaneously, however we suggest this could be evidence that the compact
object is embedded in the circumstellar material. This doesn't appear to be
consistent with the X-ray flux and spectrum of the source, which has remained
essentially unchanged since the initial outburst. The iron abundance implied by
the ratio of the neutral Fe-K$\alpha$ and Fe-K$\beta$ is compatible with solar.
We search for lags in the neutral Fe-K$\alpha$ with respect to the continuum
and find marginal evidence for a lag at ~10 ks. We interpret this as the light
crossing time of the torus which would suggest that the neutral iron is located
at a radius of 10 AU. This result depends on several assumptions including the
distance to the system, the inclination, the mass of system and the orbital
period none of which are known with any great certainty. Better constraints on
these system parameters and further observations of this system are required to
confirm this result. We discuss the nature of this system in light of our
results and place it in context with other binary B[e] stars.",1211.3400v1
2013-01-22,"First principles study of helium, carbon and nitrogen in austenite, dilute austenitic iron alloys and nickel","An extensive set of first-principles density functional theory calculations
have been performed to study the behaviour of He, C and N solutes in austenite,
dilute Fe-Cr-Ni austenitic alloys and Ni in order to investigate their
influence on the microstructural evolution of austenitic steel alloys under
irradiation.",1301.5317v1
2013-03-25,Broad iron line in the fast spinning neutron-star system 4U 1636-53,"We analysed the X-ray spectra of six observations, simultaneously taken with
XMM-Newton and Rossi X-ray Timing Explorer (RXTE), of the neutron star low-mass
X-ray binary 4U 1636-53. The observations cover several states of the source,
and therefore a large range of inferred mass accretion rate. These six
observations show a broad emission line in the spectrum at around 6.5 keV,
likely due to iron. We fitted this line with a set of phenomenological models
of a relativistically broadened line, plus a model that accounts for
relativistically smeared and ionised reflection from the accretion disc. The
latter model includes the incident emission from both the neutron-star surface
or boundary layer and the corona that is responsible for the high-energy
emission in these systems. From the fits with the reflection model we found
that in four out of the six observations the main contribution to the reflected
spectrum comes from the neutron-star surface or boundary layer, whereas in the
other two observations the main contribution to the reflected spectrum comes
from the corona. We found that the relative contribution of these two
components is not correlated to the state of the source. From the
phenomenological models we found that the iron line profile is better described
by a symmetric, albeit broad, profile. The width of the line cannot be
explained only by Compton broadening, and we therefore explored the case of
relativistic broadening. We further found that the direct emission from the
disc, boundary layer, and corona generally evolved in a manner consistent with
the standard accretion disc model, with the disc and boundary layer becoming
hotter and the disc moving inwards as the source changed from the hard in to
the soft state. The iron line, however, did not appear to follow the same
trend.",1303.6337v1
2013-04-03,Universal formula for the muon-induced neutron yield,"The experimental data on the yield of muon-induced neutrons for liquid
scintillator, iron and lead accumulated during 60 years of muon interaction
underground study have been analyzed. A universal formula connecting the yield
with muon energy loss in the matter and neutron production in hadronic and
electromagnetic showers is presented.",1304.0919v1
2013-06-20,Unexpected radial trend of the iron abundance in a sample of monometallic Galactic globular clusters,"We study the relationship between the iron abundance (IA) in red giant branch
(RGB) stars and their radial distribution (RD) in Galactic globular clusters
(GCs). We relied on publicly available archival data on IA in red giants (RGs)
of GCs. We built a sample of ten target GCs in which the number of these RGs
exceeded one hundred stars. In each GC of the sample, we compared the RDs of
two sub-samples of stars, more iron-rich (IR) and more iron-poor (IP) than the
clusters' mean values of [Fe/H]. Their RDs turned out to be different at
statistically significant confidence levels in NGC 104 (47 Tuc), NGC 1851, NGC
3201, and NGC 6752 in the sense that the IP RGs were more centrally
concentrated than their IR counterparts. In 47 Tuc, the difference is
significant at a higher confidence level within the PRAD of R = 8.0', where the
IA increases by Delta[Fe/H] ~ 0.03 dex toward the cluster outskirts. In the
latter three GCs, Delta[Fe/H] ~ 0.05 dex. Interestingly, the V magnitude of the
RGB bump and the horizontal branch was recently shown to fade outward in 47 Tuc
and was suggested to originate from a He abundance trend. The fading caused by
the IA trend is similar to that observed for the RGB bump. Although the
difference between the RDs of IP and IR RGs is statistically insignificant in
other GCs, NGC 288 is the only GC of the sample, in which IR RGB stars are
formally more centrally concentrated. Interestingly, three of the four GCs are
highly concentrated. (Abridged)",1306.4930v1
2013-07-29,Effect of surface hydrogen on the anomalous surface segregation behavior of Cr in Fe-rich Fe-Cr alloys,"The segregation behavior of Cr in dilute Fe-Cr alloys is known to be
anomalous since the main barrier for surface segregation of Cr in these alloys
arises not from the topmost surface layer but from the subsurface layer where
the solution energy of Cr is much more endothermic as compared to the topmost
surface layer. The Fe-Cr alloys are candidate structural materials for the new
generation of nuclear reactors. The surfaces of these alloys will be exposed to
hydrogen or its isotopes in these reactors, and although hydrogen is soluble
neither in Fe nor in Fe-Cr alloys, it is known that the adsorption energy of
hydrogen on the surface of iron is not only exothermic but relatively large.
This clearly raises the question of the effect of the hydrogen adsorbed on the
surface of iron on the segregation behavior of chromium towards the surface of
iron. In this paper we show, on the basis of our ab initio density functional
theory calculations, that the presence of hydrogen on the surface of iron leads
to a considerably reduced barrier for Cr segregation to both the topmost
surface layer and the subsurface layer, but the subsurface layer still controls
the barrier for surface segregation. This reduction in the barrier for surface
segregation is due to the nature of the Cr-H couple that acts in a complex and
synergistic manner. The presence of Cr enhances the exothermic nature of
hydrogen adsorption that in turn leads to a reduced barrier for surface
segregation. These results should be included in the multiscale modeling of
Fe-Cr alloys.",1307.7588v1
2013-09-23,The diagnostic potential of Fe lines applied to protostellar jets,"We investigate the diagnostic capabilities of the iron lines for tracing the
physical conditions of the shock-excited gas in jets driven by pre-main
sequence stars. We have analyzed the 300-2500 nm X-shooter spectra of two jets
driven by the pre-main sequence stars ESO-Halpha 574 and Par-Lup 3-4. Both
spectra are very rich in [FeII] lines over the whole spectral range; in
addition, lines from [FeIII] are detected in the ESO-H\alpha 574 spectrum. NLTE
codes along with codes for the ionization equilibrium are used to derive the
gas excitation conditions of electron temperature and density, and fractional
ionization. The iron gas-phase abundance is provided by comparing the iron
lines emissivity with that of [OI] 630 nm. The [FeII] lines indicate ESO-Halpha
574 jet is, on average, colder (T_e = 9000 K), less dense (n_e = 2 10^4 cm^-3)
and more ionized (x_e = 0.7) than the Par-Lup 3-4 jet (T_e = 13000 K, n_e = 6
10^4 cm^-3, x_e < 0.4), even if the existence of a higher density component
(n_e = 2 10^5 cm^-3) is probed by the [FeIII] and [FeII] ultra-violet lines.
Theoretical models suggest that the shock at work in ESO-Halpha 574 is faster
and likely more energetic than the Par-Lup 3-4 shock. This latter feature is
confirmed by the high percentage of gas-phase iron measured in ESO-Halpha 574
(50-60% of its solar abundance in comparison with less than 30% in Par-Lup
3-4), which testifies that the ESO-Halpha 574 shock is powerful enough to
partially destroy the dust present inside the jet. This work demonstrates that
a multiline Fe analysis can be effectively used to probe the excitation and
ionization conditions of the gas in a jet without any assumption on ionic
abundances. The main limitation on the diagnostics resides in the large
uncertainties of the atomic data, which, however, can be overcome through a
statistical approach involving many lines.",1309.5827v1
2014-07-03,The Composition of M-type asteroids II: Synthesis of spectroscopic and radar observations,"This work updates and expands on results of our long-term radar-driven
observational campaign of main-belt asteroids (MBAs) focused on Bus-DeMeo Xc-
and Xk-type objects (Tholen X and M class asteroids) using the Arecibo radar
and NASA Infrared Telescope Facilities (Ockert-Bell et al. 2008; 2010; Shepard
et al. 2008; 2010). Eighteen of our targets were near-simultaneously observed
with radar and those observations are described in Shepard et al. (2010). We
combine our near-infrared data with available visible wavelength data for a
more complete compositional analysis of our targets. Compositional evidence is
derived from our target asteroid spectra using two different methods, a \c{hi}2
search for spectral matches in the RELAB database and parametric comparisons
with meteorites. We present four new methods of parametric comparison,
including discriminant analysis. Discriminant analysis identifies meteorite
type with 85% accuracy. This paper synthesizes the results of these two analog
search algorithms and reconciles those results with analogs suggested from
radar data (Shepard et al. 2010). We have observed 29 asteroids, 18 in
conjunction with radar observations. For eighteen out of twenty-nine objects
observed (62%) our compositional predictions are consistent over two or more
methods applied. We find that for our Xc and Xk targets the best fit is an iron
meteorite for 34% of the samples. Enstatite Chondrites were best fits for 6 of
our targets (21%). Stony-iron meteorites were best fits for 2 of our targets
(7%). A discriminant analysis suggests that asteroids with no absorption band
can be compared to iron meteorites and asteroids with both a 0.9 and 1.9 {\mu}m
absorption band can be compared to stony-iron meteorites.",1407.0750v1
2014-08-05,Collective Mode at Lifshitz Transition in Iron-Pnictide Superconductors,"We obtain the exact low-energy spectrum of two mobile holes in a t-J model
for an isolated layer in an iron-pnictide superconductor. The minimum d xz and
d yz orbitals per iron atom are included, with no hybridization between the
two. After tuning the Hund coupling to a putative quantum critical point (QCP)
that separates a commensurate spin-density wave from a hidden-order
antiferromagnet at half filling, we find an s-wave hole-pair groundstate and a
d-wave hole-pair excited state. Near the QCP, both alternate in sign between
hole Fermi surface pockets at the Brillouin zone center and emergent electron
Fermi surface pockets at momenta that correspond to commensurate spin-density
waves (cSDW). The dependence of the energy splitting with increasing Hund
coupling yields evidence for a true QCP in the thermodynamic limit near the
putative one, at which the s-wave and d-wave Cooper pairs are degenerate. A
collective s-to-d-wave oscillation of the macroscopic superconductor that
couples to orthorhombic shear strain is also identified. Its resonant frequency
is predicted to collapse to zero at the QCP in the limit of low hole
concentration. This implies degeneracy of Cooper pairs with s, d and s+id
symmetry in the corresponding quantum critical state. We argue that the
critical state describes Cooper pairs in hole-doped iron superconductors at the
Lifshitz transition, where electron bands first rise above the Fermi level. We
thereby predict that the s-to-d-wave collective mode observed by Raman
spectroscopy in Ba1-xKxFe2As2 at optimal doping should also be observed at
higher doping near the Lifshitz transition.",1408.0864v4
2014-08-09,Structure determination and coexistence of superconductivity and antiferromagnetic order in (Li0.8Fe0.2)OHFeSe,"FeSe-derived superconductors show some unique behaviors relative to
iron-pnictide superconductors, which are very helpful to understand the
mechanism of superconductivity in high-Tc iron-based superconductors. The
low-energy electronic structure of the heavily electron-doped AxFe2Se2 (A=K,
Rb, Cs) demonstrates that interband scattering or Fermi surface nesting is not
a necessary ingredient for the unconventional superconductivity in iron-based
superconductors. The superconducting transition temperature (Tc) in the
one-unit-cell FeSe on SrTiO3 substrate can reach as high as ~65 K, largely
transcending the bulk Tc of all known iron-based superconductors. However, in
the case of AxFe2Se2, the inter-grown antiferromagnetic insulating phase makes
it difficult to study the underlying physics. Superconductors of alkali metal
ions and NH3 molecules or organic-molecules intercalated FeSe and single layer
or thin film FeSe on SrTiO3 substrate are extremely air-sensitive, which
prevents the further investigation of their physical properties. Therefore, it
is urgent to find a stable and accessible FeSe-derived superconductor for
physical property measurements so as to study the underlying mechanism of
superconductivity. Here, we report the air-stable superconductor
(Li0.8Fe0.2)OHFeSe with high temperature superconductivity at ~40 K synthesized
by a novel hydrothermal method. The crystal structure is unambiguously
determined by the combination of X-ray and neutron powder diffraction and
nuclear magnetic resonance. It is also found that an antiferromagnetic order
coexists with superconductivity in such new FeSe-derived superconductor. This
novel synthetic route opens a new avenue for exploring other superconductors in
the related systems. The combination of different structure characterization
techniques helps to complementarily determine and understand the details of the
complicated structures.",1408.2006v1
2014-12-22,Fe-based superconductors: seven years later,"Iron-based superconductors were discovered seven years ago, in 2008. This
short review summarizes what we learned about these materials over the last
seven years, what are open questions, and what new physics we expect to extract
from studies of this new class of high-temperature superconductors.",1412.7104v1
2015-01-07,Superoxide reductase from Desulfoarculus baarsii: reaction mechanism and role of glutamate 47 and lysine 48 in catalysis,"Superoxide reductase (SOR) is a small metalloenzyme that catalyzes reduction
of O(2)(*)(-) to H(2)O(2) and thus provides an antioxidant mechanism against
superoxide radicals. Its active site contains an unusual mononuclear ferrous
center, which is very efficient during electron transfer to O(2)(*)(-)
[Lombard, M., Fontecave, M., Touati, D., and Nivi{\`e}re, V. (2000) J. Biol.
Chem. 275, 115-121]. The reaction of the enzyme from Desulfoarculus baarsii
with superoxide was studied by pulse radiolysis methods. The first step is an
extremely fast bimolecular reaction of superoxide reductase with superoxide,
with a rate constant of (1.1 +/- 0.3) x 10(9) M(-1) s(-1). A first intermediate
is formed which is converted to a second one at a much slower rate constant of
500 +/- 50 s(-1). Decay of the second intermediate occurs with a rate constant
of 25 +/- 5 s(-1). These intermediates are suggested to be iron-superoxide and
iron-peroxide species. Furthermore, the role of glutamate 47 and lysine 48,
which are the closest charged residues to the vacant sixth iron coordination
site, has been investigated by site-directed mutagenesis. Mutation of glutamate
47 into alanine has no effect on the rates of the reaction. On the contrary,
mutation of lysine 48 into an isoleucine led to a 20-30-fold decrease of the
rate constant of the bimolecular reaction, suggesting that lysine 48 plays an
important role during guiding and binding of superoxide to the iron center II.
In addition, we report that expression of the lysine 48 sor mutant gene hardly
restored to a superoxide dismutase-deficient Escherichia coli mutant the
ability to grow under aerobic conditions.",1501.01442v1
2015-09-02,Energy and matter,"Our work is an approach between matter and energy. Using the famous equation
E = mc^2, Einstein and the Law of Universal Gravitation of Newton, we estimate
that a small amount matter converted into energy is needed to lift, using the
gravitational potential energy equation on the surface, a mountain of solid
iron or even Mount Everest.",1509.02892v1
2015-10-27,Constraining distance and inclination angle of V4641 Sgr using ${\it SWIFT}$ and ${\it NuSTAR}$ observations during low soft spectral state,"We present results from ${\it NuSTAR}$ and ${\it SWIFT}$/XRT joint spectral
analysis of V4641 Sgr during a disk dominated or soft state as well as a
powerlaw dominated or hard state. The soft state spectrum is well modeled by a
relativistically blurred disk emission, a powerlaw, a broad Iron line, two
narrow emission lines and two edges. The Markov Chain Monte Carlo simulation
technique and the relativistic effects seen in the disk and broad Iron line
allow us to self-consistently constrain the inner disk radius, disk inclination
angle and distance to the source at 2.43$^{+0.39}_{-0.17}$ R$_g$ (GM/c$^2$),
69.5$^{+12.8}_{-4.2}$ degrees and 10.8$^{+1.6}_{-2.5}$ kpc respectively. For
the hard state, the spectrum is a power-law with a weakly broad Iron line and
an edge. The distance estimate gives a measure of the Eddington fraction,
$L_{2.0 - 80.0 keV}/L_{Edd}$, to be $\sim$1.3 $\times$ 10$^{-2}$ and $\sim$1.9
$\times$ 10$^{-3}$ for the soft and hard states respectively. Unlike many other
typical black hole systems which are always in a hard state at such low
Eddington fraction, V4641 Sgr shows a soft, disk dominated state. The soft
state spectrum shows narrow emission lines at $\sim 6.95$ and $\sim 8.31$ keV
which can be identified as being due to emission from highly ionized Iron and
Nickel in an X$-$ray irradiated wind respectively. If not due to instrumental
effect or calibration error, this would be the first detection of a Ni
fluorescent line in a black hole X$-$ray binary.",1510.07837v1
2015-12-17,Disorder-promoted $C_4$-symmetric magnetic order in iron-based superconductors,"In most iron-based superconductors, the transition to the magnetically
ordered state is closely linked to a lowering of structural symmetry from
tetragonal ($C_{4}$) to orthorhombic ($C_{2}$). However, recently, a regime of
$C_{4}$-symmetric magnetic order has been reported in certain hole-doped
iron-based superconductors. This novel magnetic ground state can be understood
as a double-$\mathbf{Q}$ spin density wave characterized by two order
parameters $\mathbf{M}_{1}$ and $\mathbf{M}_{2}$ related to each of the two
$\mathbf{Q}$ vectors. Depending on the relative orientations of the order
parameters, either a noncollinear spin-vortex crystal or a nonuniform
charge-spin density wave could form. Experimentally, M\""ossbauer spectroscopy,
neutron scattering, and muon spin rotation established the latter as the
magnetic configuration of some of these optimally hole-doped iron-based
superconductors. Theoretically, low-energy itinerant models do support a
transition from single-$\mathbf{Q}$ to double-$\mathbf{Q}$ magnetic order, but
with nearly-degenerate spin-vortex crystal and charge-spin density wave states.
In fact, extensions of these low-energy models including additional electronic
interactions tip the balance in favor of the spin-vortex crystal, in apparent
contradiction with the recent experimental findings. In this paper, we revisit
the phase diagram of magnetic ground states of low-energy multi-band models in
the presence of weak disorder. We show that impurity scattering not only
promotes the transition from $C_{2}$ to $C_{4}$-magnetic order, but it also
favors the charge-spin density wave over the spin-vortex crystal phase.
Additionally, in the single-$\mathbf{Q}$ phase, our analysis of the nematic
coupling constant in the presence of disorder supports the experimental finding
that the splitting between the structural and stripe-magnetic transition is
enhanced by disorder.",1512.05747v1
2016-01-22,Revised Masses and Densities of the Planets around Kepler-10,"Determining which small exoplanets have stony-iron compositions is necessary
for quantifying the occurrence of such planets and for understanding the
physics of planet formation. Kepler-10 hosts the stony-iron world Kepler-10b
(K10b), and also contains what has been reported to be the largest solid
silicate-ice planet, Kepler-10c (K10c). Using 220 radial velocities (RVs),
including 72 precise RVs from Keck-HIRES of which 20 are new from 2014-2015,
and 17 quarters of Kepler photometry, we obtain the most complete picture of
the Kepler-10 system to date. We find that K10b (Rp=1.47 Re) has mass
3.72$\pm$0.42 Me and density 6.46$\pm$0.73 g/cc. Modeling the interior of K10b
as an iron core overlaid with a silicate mantle, we find that the iron core
constitutes 0.17$\pm$0.11 of the planet mass. For K10c (Rp=2.35 Re) we measure
Mp=13.98$\pm$1.79 Me and $\rho$=5.94$\pm$0.76 g/cc, significantly lower than
the mass computed in Dumusque et al. (2014, 17.2$\pm$1.9 Me). Internal
compositional modeling reveals that at least $10\%$ of the radius of Kepler-10c
is a volatile envelope composed of hydrogen-helium ($0.2\%$ of the mass, $16\%$
of the radius) or super-ionic water ($28\%$ of the mass, $29\%$ of the radius).
Analysis of only HIRES data yields a higher mass for K10b and a lower mass for
K10c than does analysis of the HARPS-N data alone, with the mass estimates for
K10c formally inconsistent by 3$\sigma$. Splitting the RVs from each instrument
leads to inconsistent measurements for the mass of planet c in each data set.
This suggests that time-correlated noise is present and that the uncertainties
in the planet masses (especially K10c) exceed our formal estimates. Transit
timing variations (TTVs) of K10c indicate the likely presence of a third planet
in the system, KOI-72.X. The TTVs and RVs are consistent with KOI-72.X having
an orbital period of 24, 71, or 101 days, and a mass from 1-7 Me.",1601.06168v1
2016-01-13,On electrical conductivity of melts of boron and its compounds under pressure,"The electrical conductivity of melts of boron and its carbide (B4C), nitride
(BN), and phosphide (BP) has been studied at pressures to 7.7 GPa and
temperatures to 3500 K. It has been shown that these melts are good conductors
with specific electrical conductivity values comparable with that of iron melt
at ambient pressure.",1601.06828v1
2016-03-04,FeS: Structure and Composition Relations to Superconductivity and Magnetism,"Structure and composition of iron chalcogenides have a delicate relationship
with magnetism and superconductivity. In this report we investigate the iron
sulfide layered tetragonal phase (t-FeS), and compare with three-dimensional
hexagonal phase (h-FeS). X-ray diffraction reveals the absence of structural
transitions for both t- and h-FeS below room temperature, and gives phase
compositions of Fe0.93(1)S and Fe0.84(1)S, respectively, for the samples
studied here. The a lattice parameter of bigger than 3.68 A is significant for
causing bulk superconductivity in iron sulfide, which is controlled by
composition and structural details such as iron stoichiometry and concentration
of vacancy. While h-FeS with a = 3.4436(1) A has magnetic ordering well above
room temperature, our t-FeS with a =3.6779(8)A shows filamentary
superconductivity below Tc = 4 K with less than 15% superconducting volume
fraction. Also for t-FeS, the magnetic susceptibility shows an anomaly at ~ 15
K, and neutron diffraction reveals a commensurate antiferromagnetic ordering
below TN = 116 K, with wave vector km= (0.25,0.25,0) and 0.46(2)uB/Fe. Although
two synthesis routes are used here to stabilize t vs h crystal structures
(hydrothermal vs solid-state methods), both FeS compounds order on two
length-scales of ~1000 nm sheets or blocks and ~ 20 nm smaller particles, shown
by neutron scattering. First principles calculations reveal a high sensitivity
to the structure for the electronic and magnetic properties in t-FeS,
predicting marginal antiferromagnetic instability for our compound (sulfur
height of zS ~0.252) with an ordering energy of ~11 meV/Fe, while h-FeS is
magnetically stable.",1603.01598v1
2016-04-21,Transition from sign-reversed to sign-preserved Cooper-pairing symmetry in sulfur-doped iron selenide superconductors,"An essential step toward elucidating the mechanism of superconductivity is to
determine the sign/phase of superconducting order parameter, as it is closely
related to the pairing interaction. In conventional superconductors, the
electron-phonon interaction induces attraction between electrons near the Fermi
energy and results in a sign-preserved s-wave pairing. For high-temperature
superconductors, including cuprates and iron-based superconductors, prevalent
weak coupling theories suggest that the electron pairing is mediated by spin
fluctuations which lead to repulsive interactions, and therefore that a
sign-reversed pairing with an s+-or d-wave symmetry is favored. Here, by using
magnetic neutron scattering, a phase sensitive probe of superconducting gap, we
report the observation of a transition from the sign-reversed to sign-preserved
Cooper-pairing symmetry with insignificant changes in Tc in the S-doped iron
selenide superconductors KxFe2-y(Se1-zSz)2. We show that a rather sharp
magnetic resonant mode well below the superconducting gap (2delta) in the
undoped sample (z = 0) is replaced by a broad hump structure above 2delta under
50% S doping. These results cannot be readily explained by simple spin
fluctuation-exchange pairing theories and, therefore, multiple pairing channels
are required to describe superconductivity in this system. Our findings may
also yield a simple explanation for the sometimes contradictory data on the
sign of the superconducting order parameter in iron-based materials.",1604.06222v1
2016-06-03,Quantum Transitions of Nematic Phases in a Spin-$1$ Bilinear-Biquadratic Model and Their Implications for FeSe,"Since its discovery, iron-based superconductivity has been known to develop
near an antiferromagnetic order, but this paradigm fails in the iron
chalcogenide FeSe, whose single-layer version holds the record for the highest
superconducting transition temperature in the iron-based superconductors. The
striking puzzle that FeSe displays nematic order (spontaneously broken lattice
rotational symmetry) while being non-magnetic, has led to several competing
proposals for its origin in terms of either the $3d$-electron's orbital degrees
of freedom or spin physics in the form of frustrated magnetism. Here we argue
that the phase diagram of FeSe under pressure could be qualitatively described
by a quantum spin model with highly frustrated interactions. We implement both
the site-factorized wave-function analysis and the large-scale density matrix
renormalization group (DMRG) in cylinders to study the spin-$1$
bilinear-biquadratic model on the square lattice, and identify quantum
transitions from the well-known $(\pi,0)$ antiferromagnetic state to an exotic
$(\pi,0)$ antiferroquadrupolar order, either directly or through a
$(\pi/2,\pi)$ antiferromagnetic state. These many phases, while distinct, are
all nematic. We also discuss our theoretical ground-state phase diagram for the
understanding of the experimental low-temperature phase diagram obtained by the
NMR [P. S. Wang {\it et al.}, Phys. Rev. Lett. 117, 237001 (2016)] and X-ray
scattering [K. Kothapalli {\it et al.}, Nature Communications 7, 12728 (2016)]
measurements in pressurized FeSe. Our results suggest that superconductivity in
a wide range of iron-based materials has a common origin in the
antiferromagnetic correlations of strongly correlated electrons.",1606.01235v4
2016-07-04,Low-energy microscopic models for iron-based superconductors: a review,"The development of sensible microscopic models is essential to elucidate the
normal-state and superconducting properties of the iron-based superconductors.
Because these materials are mostly metallic, a good starting point is an
effective low-energy model that captures the electronic states near the Fermi
level and their interactions. However, in contrast to cuprates, iron-based
high-$T_{c}$ compounds are multi-orbital systems with Hubbard and Hund
interactions, resulting in a rather involved 10-orbital lattice model. Here we
review different minimal models that have been proposed to unveil the universal
features of these systems. We first review minimal models defined solely in the
orbital basis, which focus on a particular subspace of orbitals, or solely in
the band basis, which rely only on the geometry of the Fermi surface. The
former, while providing important qualitative insight into the role of the
orbital degrees of freedom, do not distinguish between high-energy and
low-energy sectors and, for this reason, generally do not go beyond mean-field.
The latter allow one to go beyond mean-field and investigate the interplay
between superconducting and magnetic orders as well as Ising-nematic order.
However, they cannot capture orbital-dependent features like spontaneous
orbital order. We then review recent proposals for a minimal model that
operates in the band basis but fully incorporates the orbital composition and
symmetries of the low-energy excitations. We discuss the results of the
renormalization group study of such a model, particularly of the interplay
between superconductivity, magnetism, and spontaneous orbital order, and
compare theoretical predictions with experiments on iron pnictides and
chalcogenides. We also discuss the impact of the glide-plane symmetry on the
low-energy models, highlighting the key role played by the spin-orbit coupling.",1607.00865v2
2016-10-04,Optical signatures of low spin Fe3+: a new probe for the spin state of bridgmanite and post-perovskite,"Iron spin transition directly affects properties of lower mantle minerals and
can thus alter geophysical and geochemical characteristics of the deep Earth.
While the spin transition in ferropericlase has been vigorously established at
P ~ 60 GPa and 300 K, experimental evidence for spin transitions in other
rock-forming minerals, such as bridgmanite and post-perovskite, remains
controversial. Multiple valence, spin, and coordination states of iron in
bridgmanite and post-perovskite are difficult to resolve with conventional
spin-probing techniques. Optical spectroscopy, on the other hand, is sensitive
to high/low spin ferrous/ferric iron at different sites; thus, it can be a
powerful probe for spin transitions. Here we establish the optical signature of
low spin Fe3+O6, a plausible low spin unit in bridgmanite and post-perovskite,
by optical absorption experiments in diamond anvil cells. We show that the
optical absorption of Fe3+O6 in NAL (new aluminous phase) is very sensitive to
the iron spin state and represents a model behavior of bridgmanite and
post-perovskite in the deep lower mantle across a spin transition.
Specifically, an absorption band centered at ~ 19000 cm-1 is characteristic of
the 2T2g to 2T1g (2A2g) transition in low spin Fe3+ in NAL at 40 GPa. This new
spectroscopic information constrains the crystal field splitting energy of low
spin Fe3+ to ~ 22200 cm-1 which we also independently confirm by our
first-principles calculations. Together with available information on the
electronic structure of Fe3+O6-compounds, we constrain the spin-pairing energy
of Fe3+ in an octahedral field to ~ 20000-23000 cm-1. This implies that
octahedrally-coordinated Fe3+ in bridgmanite is low spin at P > ~ 40 GPa.",1610.01048v1
2016-12-22,The AMBRE project: Iron-peak elements in the solar neighbourhood,"The aim of this paper is to characterise the abundance patterns of five
iron-peak elements (Mn, Fe, Ni, Cu, and Zn) for which the stellar origin and
chemical evolution are still debated. We automatically derived iron peak (Mn,
Fe, Ni, Cu, and Zn) and alpha element (Mg) chemical abundances for 4666 stars.
We used the bimodal distribution of [Mg/Fe] to chemically classify sample stars
into different Galactic substructures: thin disc, metal-poor and high-alpha
metal rich, high-alpha and low-alpha metal-poor populations. High-alpha and
low-alpha metal-poor populations are fully distinct in Mg, Cu, and Zn. Thin
disc trends of [Ni/Fe] and [Cu/Fe] are very similar and show a small increase
at supersolar metallicities. Thin and thick disc trends of Ni and Cu are very
similar and indistinguishable. Mn looks different from Ni and Cu. [Mn/Fe]
trends of thin and thick discs actually have noticeable differences: the thin
disc is slightly Mn richer than the thick disc. [Zn/Fe] trends look very
similar to those of [alpha/Fe] trends. The dispersion of results in both discs
is low (approx 0.05 dex for [Mg, Mn, and Cu/Fe]) and is even much lower for
[Ni/Fe] (approx 0.035 dex). Zn is an alpha-like element and could be used to
separate thin and thick disc stars. [Mn/Mg] ratio could also be a very good
tool for tagging Galactic substructures. Some models can partially reproduce
the observed Mg, Zn, and, Cu behaviours. Models mostly fail to reproduce Mn and
Ni in all metallicity domains, however, models adopting yields normalised from
solar chemical properties reproduce Mn and Ni better, suggesting that there is
still a lack of realistic theoretical yields of some iron-peak elements. Very
low scatter (approx 0.05 dex) in thin and thick disc sequences could provide an
observational constrain for Galactic evolutionary models that study the
efficiency of stellar radial migration.",1612.07622v2
2017-01-31,Heterodiffusion coefficients in α-iron,"The diffusion of tungsten in {\alpha}-iron is important for the application
of ferritic-iron alloys to thermal power plants. These data, over a wide
temperature range across the Curie temperature, have been recently reported. We
show that these diffusion coefficients can be satisfactory reproduced in terms
of the bulk elastic and expansivity data by means of a thermodynamical model
that interconnects point defects parameters with bulk qualities.",1701.08993v1
2017-08-18,Diffuse X-Ray Sky in the Galactic Center,"The Galactic Diffuse X-ray Emission (GDXE) in the Milky Way Galaxy is
spatially and spectrally decomposed into the Galactic Center X-ray Emission
(GCXE), the Galactic Ridge X-ray Emission (GRXE) and the Galactic Bulge X-ray
Emission (GBXE). The X-ray spectra of the GDXE are characterized by the strong
K-shell lines of the highly ionized atoms, the brightest are the K-shell
transition (principal quantum number transition of $n=2\rightarrow1$) of
neutral iron (SXV-He$\alpha$), He-like iron (FeXXV-He$\alpha$) and He-like
sulfur (SXV-He$\alpha$) lines. Accordingly, the GDXE is composed of a
high-temperature plasma of $\sim$7 keV (HTP) and a low-temperature plasma of
$\sim$1 keV (LTP), which emit the FeXXV-He$\alpha$ and SXV-He$\alpha$ lines,
respectively. The FeI-K$\alpha$ line is emitted from nearly neutral irons, and
hence the third component of the GDXE is a Cool Gas (CG). The FeI-K$\alpha$
distribution in the GCXE region is clumpy (FeI-K$\alpha$ clump), associated
with giant molecular cloud (MC) complexes, Sagittarius A, B, C, D and E, in the
central molecular zone. The origin of the FeI-K$\alpha$ clumps is the
fluorescence and Thomson scattering from the MCs irradiated by past big flares
of the super massive black hole Sagittarius A$^*$. The scale heights and
equivalent widths of the FeI-K$\alpha$, FeXXV-He$\alpha$, and FeXXVI-Ly$\alpha$
($n=2\rightarrow1$ transition of H-like iron) lines are different among the
GCXE, GBXE and GRXE. Therefore the structure and origin are separately
examined. This paper overviews the research history and the present
understandings of the GDXE, in particular focus on the origin of the HTP and CG
in the GCXE.",1708.05501v1
2017-10-09,Pressure-induced spin pairing transition of Fe$^{3+}$ in oxygen octahedra,"High pressure can provoke spin transitions in transition metal-bearing
compounds. These transitions are of high interest not only for fundamental
physics and chemistry, but also may have important implications for
geochemistry and geophysics of the Earth and planetary interiors. Here we have
carried out a comparative study of the pressure-induced spin transition in
compounds with trivalent iron, octahedrally coordinated by oxygen.
High-pressure single-crystal M\""{o}ssbauer spectroscopy data for FeBO$_3$,
Fe$_2$O$_3$ and Fe$_3$(Fe$_{1.766(2)}$Si$_{0.234(2)}$)(SiO$_4$)$_3$ are
presented together with detailed analysis of hyperfine parameter behavior. We
argue that $\zeta$-Fe$_2$O$_3$ is an intermediate phase in the reconstructive
phase transition between $\iota$-Fe$_2$O$_3$ and $\theta$-Fe$_2$O$_3$ and
question the proposed perovskite-type structure for $\zeta$-Fe$_2$O$_3$.The
structural data show that the spin transition is closely related to the volume
of the iron octahedron. The transition starts when volumes reach 8.9-9.3
\AA$^3$, which corresponds to pressures of 45-60 GPa, depending on the
compound. Based on phenomenological arguments we conclude that the spin
transition can proceed only as a first-order phase transition in
magnetically-ordered compounds. An empirical rule for prediction of cooperative
behavior at the spin transition is proposed. The instability of iron octahedra,
together with strong interactions between them in the vicinity of the critical
volume, may trigger a phase transition in the metastable phase. We find that
the isomer shift of high spin iron ions depends linearly on the octahedron
volume with approximately the same coefficient, independent of the particular
compounds and/or oxidation state. For eight-fold coordinated Fe$^{2+}$ we
observe a significantly weaker nonlinear volume dependence.",1710.03192v1
2018-01-03,Reconciling Magma-Ocean Crystallization Models with the present-day Structure of the Earth's mantle,"Terrestrial planets are thought to experience episode(s) of large-scale
melting early in their history. Fractionation during magma-ocean freezing leads
to unstable stratification within the related cumulate layers due to
progressive iron enrichment upward, but the effects of incremental cumulate
overturns during MO crystallization remain to be explored. Here, we use
geodynamic models with a moving-boundary approach to study convection and
mixing within the growing cumulate layer, and thereafter within the fully
crystallized mantle. For fractional crystallization, cumulates are efficiently
stirred due to subsequent incremental overturns, except for strongly
iron-enriched late-stage cumulates, which persist as a stably stratified layer
at the base of the mantle for billions of years. Less extreme crystallization
scenarios can lead to somewhat more subtle stratification. In any case, the
long-term preservation of at least a thin layer of extremely enriched cumulates
with Fe#>0.4, as predicted by all our models, is inconsistent with seismic
constraints. Based on scaling relationships, however, we infer that final-stage
Fe-rich magma-ocean cumulates originally formed near the surface should have
overturned as small diapirs, and hence undergone melting and reaction with the
host rock during sinking. The resulting moderately iron-enriched
metasomatized/hybrid rock assemblages should have accumulated at the base of
the mantle, potentially fed an intermittent basal magma ocean, and be preserved
through the present-day. Such moderately iron-enriched rock assemblages can
reconcile the physical properties of the large low shear-wave velocity
provinces in the presentday lower mantle. Thus, we reveal Hadean melting and
rock-reaction processes by integrating magmaocean crystallization models with
the seismic-tomography snapshot.",1801.00991v1
2018-01-03,The formation of the heaviest elements,"The rapid neutron-capture process needed to build up many of the elements
heavier than iron seems to take place primarily in neutron-star mergers, not
supernova explosions.",1801.01190v1
2018-01-10,Lifshitz transitions induced by magnetic field,"The Fermi surface can be changed by different external conditions like, e.g.,
pressure or doping. It can lead to a change in the Fermi surface topology,
called as the Lifshitz transition. Here, we briefly describe the Lifshitz
transitions induced by the external magnetic field in a one-dimensional optical
lattice and iron-based superconductors. We also discuss physical consequences
emerging from these transitions.",1801.03556v1
2018-01-22,Alternative explanations for extreme supersolar iron abundances inferred from the energy spectrum of Cygnus X-1,"Here we study a 1-200 keV energy spectrum of the black hole binary Cygnus X-1
taken with NuSTAR and Suzaku. This is the first report of a NuSTAR observation
of Cyg X-1 in the intermediate state, and the observation was taken during the
part of the binary orbit where absorption due to the companion's stellar wind
is minimal. The spectrum includes a multi-temperature thermal disk component, a
cutoff power-law component, and relativistic and non-relativistic reflection
components. Our initial fits with publicly available constant density
reflection models (relxill and reflionx) lead to extremely high iron abundances
(>9.96 and 10.6(+1.6)(-0.9) times solar, respectively). Although supersolar
iron abundances have been reported previously for Cyg X-1, our measurements are
much higher and such variability is almost certainly unphysical. Using a new
version of reflionx that we modified to make the electron density a free
parameter, we obtain better fits to the spectrum even with solar iron
abundances. We report on how the higher density (n_e = (3.98(+0.12)(-0.25))E20
cm-3) impacts other parameters such as the inner radius and inclination of the
disk.",1801.07267v1
2018-09-25,Multiple topological states in iron-based superconductors,"Topological insulators and semimetals as well as unconventional iron-based
superconductors have attracted major recent attention in condensed matter
physics. Previously, however, little overlap has been identified between these
two vibrant fields, even though the principal combination of topological bands
and superconductivity promises exotic unprecedented avenues of superconducting
states and Majorana bound states (MBSs), the central building block for
topological quantum computation. Along with progressing laser-based
spin-resolved and angle-resolved photoemission spectroscopy (ARPES) towards
high energy and momentum resolution, we have resolved topological insulator
(TI) and topological Dirac semimetal (TDS) bands near the Fermi level
($E_{\text{F}}$) in the iron-based superconductors Li(Fe,Co)As and Fe(Te,Se),
respectively. The TI and TDS bands can be individually tuned to locate close to
$E_{\text{F}}$ by carrier doping, allowing to potentially access a plethora of
different superconducting topological states in the same material. Our results
reveal the generic coexistence of superconductivity and multiple topological
states in iron-based superconductors, rendering these materials a promising
platform for high-$T_{\text{c}}$ topological superconductivity.",1809.09977v1
2018-12-11,Variable stars in Terzan 5: additional evidence of multi-age and multi-iron stellar populations,"Terzan 5 is a complex stellar system in the Galactic bulge, harboring stellar
populations with very different iron content ({\Delta}[Fe/H] ~1 dex) and with
ages differing by several Gyrs. Here we present an investigation of its
variable stars. We report on the discovery and characterization of three RR
Lyrae stars. For these newly discovered RR Lyrae and for six Miras of known
periods we provide radial velocity and chemical abundances from spectra
acquired with X-SHOOTER at the VLT. We find that the three RR Lyrae and the
three short period Miras (P<300 d) have radial velocity consistent with being
Terzan 5 members. They have sub-solar iron abundances and enhanced
[{\alpha}/Fe], well matching the age and abundance patterns of the 12 Gyr
metal-poor stellar populations of Terzan 5. Only one, out of the three long
period (P>300 d) Miras analyzed in this study, has a radial velocity consistent
with being Terzan 5 member. Its super-solar iron abundance and solar-scaled
[{\alpha}/Fe] nicely match the chemical properties of the metal rich stellar
population of Terzan 5 and its derived mass nicely agrees with being several
Gyrs younger than the short period Miras. This young variable is an additional
proof of the surprising young sub-population discovered in Terzan 5.",1812.04325v1
2019-02-06,Iron oxide nanoparticles for magnetic hyperthermia,"Assemblies of magnetic nanoparticles show a great potential for application
in biomedicine, in particular, in magnetic hyperthermia. However, to achieve
desired therapeutic effect in magnetic hyperthermia the assembly of
nanoparticles should have a sufficiently high specific absorption rate in
alternating magnetic field of moderate amplitude and frequency.",1902.02220v1
2019-07-01,A new Majorana platform in an Fe-As bilayer superconductor,"Recently, iron-chalcogenide superconductors have emerged as a new and
promising platform for studying and manipulating Majorana zero mode (MZM). By
combining topological band structure and superconductivity in a multiband
material, they provide significant advantages such as higher superconducting
transition temperature (Tc) and isolated Majorana mode. However,
iron-chalcogenide superconductors, especially Fe(Te,Se), suffer from strong
inhomogeneity which may hamper their practical application. On the other hand,
some iron-pnictide (Fe-As) superconductors, such as LiFeAs, have been
demonstrated to have a similar topological band structure, yet no MZM has been
observed in its vortex cores, raising a question of universality of MZM
presence in iron-based superconductors. In this work, by using high-resolution
angle-resolved photoemission spectroscopy and scanning tunneling
microscopy/spectroscopy, we identify the first Fe-As superconductor CaKFe4As4
(Tc = 35 K) which has both the superconducting Dirac surface states and the
MZMs inside its vortex cores. The topological band inversion is largely due to
the down-shift of the pz band caused by the bilayer band folding in this
material. More strikingly, the energies and spatial line profiles of MZM and
multiple quantized Caroli-de Gennes-Matricon bound states observed inside the
topological vortex can be accurately reproduced by a simple theoretical model
derived from a surface Dirac cone, firmly establishing Majorana nature of the
zero mode.",1907.00904v1
2020-01-13,Spectroscopic Evidence of Bilayer Splitting and Interlayer Pairing in an Iron Based Superconductor,"In high temperature cuprate superconductors, the interlayer coupling between
the CuO$_2$ planes plays an important role in dictating superconductivity, as
indicated by the sensitive dependence of the critical temperature (T$_C$) on
the number of CuO$_2$ planes in one structural unit. In
Bi$_2$Sr$_2$CaCu$_2$O$_{8+\delta}$ superconductor with two CuO$_2$ planes in
one structural unit, the interaction between the two CuO$_2$ planes gives rise
to band splitting into two Fermi surface sheets (bilayer splitting) that have
distinct superconducting gap. The iron based superconductors are composed of
stacking of the FeAs/FeSe layers; whether the interlayer coupling can cause
similar band splitting and its effect on superconductivity remain unclear. Here
we report high resolution laser-based angle-resolved photoemission spectroscopy
(ARPES) measurements on a newly discovered iron based superconductor,
KCa$_2$Fe$_4$As$_4$F$_2$ (T$_C$=33.5\,K) which consists of stacking FeAs blocks
with two FeAs layers separated by insulating Ca$_2$F$_2$ blocks. Bilayer
splitting effect is observed for the first time that gives rise to totally five
hole-like Fermi surface sheets around the Brilliouin zone center. Band
structure calculations reproduce the observed bilayer splitting by identifying
interlayer interorbital interaction between the two FeAs layers within one FeAs
block. All the hole-like pockets around the zone center exhibit Fermi
surface-dependent and nodeless superconducting gap. The gap functions with
short-range antiferromagetic fluctuations are proposed and the gap symmetry can
be well understood when the interlayer pairing is considered. The particularly
strong interlayer pairing is observed for one of the bands. Our observations
provide key information on the interlayer coupling and interlayer pairing in
understanding superconductivity in iron based superconductors.",2001.04082v1
2020-04-14,"Trans-iron Ge, As, Se, and heavier elements in the dwarf metal-poor stars, HD~19445, HD~84937, HD~94028, HD~140283, and HD~160617","Spectra of unevolved metal-poor halo stars uniquely reflect the elemental
abundances incorporated during the earliest Galactic epoch. Their heavy-element
content is well understood as the products of neutron capture on iron-peak
elements. However, the lightest elements just past the iron peak, with atomic
number 30<Z<52, show striking abundance patterns open to several
interpretations. Understanding their nature may illuminate the diverse halo,
thick disk, or extragalactic origins of metal-poor stars. For five metal-poor
dwarfs, we analyzed high-resolution echelle UV spectra from the Hubble Space
Telescope Imaging Spectrograph, as well as archival optical echelle spectra.
The goal was to derive reliable halo dwarf abundances and uncertainties for six
trans-iron elements from UV spectra, and optical abundances for four additional
trans-Fe elements and two well-understood heavier elements. Our two independent
analyses showed that the largest source of discrepancy is UV continuum
placement. Once rectified, the internal results agree to 0.2 dex for
moderately-unblended, moderately strong lines. Our results similarly agree with
previous work, except where new data and unidentified Fe I lines are important.
We show that these heavily congregate blueward of 2000A and redward of 2600A.
Our exclusion of trans-Fe lines blended by such lines proved critical for
arsenic. A metallicity-dependent odd-even effect is uncovered among trans-Fe
elements: an odd-Z element abundance is depressed relative to those of adjacent
even-Z elements, especially at low metallicity. This is supported by previous
studies of Sr-Y-Zr, and also appears in some theoretical calculations. To date,
no calculations predict the high Mo/Ge ratio, independent of Mo/Fe, that we
find in all five stars.",2004.06359v1
2020-04-23,Neutral Iron Emission Lines From The Day-side Of KELT-9b -- The GAPS Programme With HARPS-N At TNG XX,"We present the first detection of atomic emission lines from the atmosphere
of an exoplanet. We detect neutral iron lines from the day-side of KELT-9b (Teq
$\sim$ 4, 000 K). We combined thousands of spectrally resolved lines observed
during one night with the HARPS-N spectrograph (R $\sim$ 115, 000), mounted at
the Telescopio Nazionale Galileo. We introduce a novel statistical approach to
extract the planetary parameters from the binary mask cross-correlation
analysis. We also adapt the concept of contribution function to the context of
high spectral resolution observations, to identify the location in the
planetary atmosphere where the detected emission originates. The average
planetary line profile intersected by a stellar G2 binary mask was found in
emission with a contrast of 84 $\pm$ 14 ppm relative to the planetary plus
stellar continuum (40 $\pm$ 5$\%$ relative to the planetary continuum only).
This result unambiguously indicates the presence of an atmospheric thermal
inversion. Finally, assuming a modelled temperature profile previously
published (Lothringer et al. 2018), we show that an iron abundance consistent
with a few times the stellar value explains the data well. In this scenario,
the iron emission originates at the $10^{-3}$-$10^{-5}$ bar level.",2004.11335v1
2020-04-26,Resolving the soft X-ray ultra fast outflow in PDS 456,"Past X-ray observations of the nearby luminous quasar PDS 456 (at $z=0.184$)
have revealed a wide angle accretion disk wind (Nardini et al. 2015), with an
outflow velocity of $\sim-0.25c$, as observed through observations of its
blue-shifted iron K-shell absorption line profile. Here we present three new
XMM-Newton observations of PDS 456; one in September 2018 where the quasar was
bright and featureless, and two in September 2019, 22 days apart, occurring
when the quasar was five times fainter and where strong blue-shifted lines from
the wind were present. During the second September 2019 observation, three
broad ($\sigma=3000$ km s$^{-1}$) absorption lines were resolved in the high
resolution RGS spectrum, which are identified with blue-shifted OVIII
Ly$\alpha$, NeIX He$\alpha$ and NeX Ly$\alpha$. The outflow velocity of this
soft X-ray absorber was found to be $v/c=-0.258\pm0.003$, fully consistent with
iron K absorber with $v/c=-0.261\pm0.007$. The ionization parameter and column
density of the soft X-ray component ($\log\xi=3.4$, $N_{\rm H}=2\times10^{21}$
cm$^{-2}$) outflow was lower by about two orders of magnitude, when compared to
the high ionization wind at iron K ($\log\xi=5$, $N_{\rm H}=7\times10^{23}$
cm$^{-2}$). Substantial variability was seen in the soft X-ray absorber between
the 2019 observations, declining from $N_{\rm H}=10^{23}$ cm$^{-2}$ to $N_{\rm
H}=10^{21}$ cm$^{-2}$ over 20 days, while the iron K component was remarkably
stable. We conclude that the soft X-ray wind may originate from an
inhomogeneous wind streamline passing across the line of sight and which due to
its lower ionization, is located further from the black hole, on parsec scales,
than the innermost disk wind.",2004.12439v1
2020-06-09,The lively accretion disk in NGC 2992. I. Transient iron K emission lines in the high flux state,"We report on one of the brightest flux levels of the Seyfert 2 galaxy NGC
2992 ever observed in X-rays, on May 2019. The source has been monitored every
few days from March 26, 2019 to December 14, 2019 by Swift-XRT, and
simultaneous XMM-Newton (250 ks) and NuSTAR (120 ks) observations were
triggered on May 6, 2019. The high count rate of the source (its 2-10 keV flux
ranged between 0.7 and $1.0\times10^{-10}$ erg cm$^{-2}$ s$^{-1}$) allows us to
perform a time-resolved spectroscopy, probing spatial scales of tens of
gravitational radii from the central black hole. By constructing a map of the
excess emission over the primary continuum, we find several emission structures
in the 5.0-7.2 keV energy band. From fitting the 50 EPIC pn spectral slices of
$\sim$5 ks duration, we interpret them as a constant narrow iron K$\alpha$ line
and three variable components in the iron K complex. When a self-consistent
model accounting for the accretion disk emission is considered (KYNrline), two
of these features (in the 5.0-5.8 keV and 6.8-7.2 keV bands) can be ascribed to
a flaring region of the accretion disk located at ${r_{in}}\simeq15$-40
r$_{g\rm }$ from the black hole. The third one (6.5-6.8 keV) is likely produced
at much larger radii ($r_{in}>50$ r$_{g\rm }$). The inner radius and the
azimuthal extension retrieved from the coadded spectra of the flaring states
are ${ r_{in}}=15\pm3$ r$_{g\rm }$ and $\phi=165^{\circ}-330^{\circ}$,
suggesting that the emitting region responsible for the broad iron K component
is a relatively compact annular sector within the disk. Our findings support a
physical scenario in which the accretion disk in NGC 2992 becomes more active
at high accretion rates ($L_{\rm bol}/L_{\rm Edd}\geq4\%$).",2006.05280v1
2020-08-14,New luminous blue variable candidates in the NGC 247 galaxy,"We search for LBV stars in galaxies outside the Local Group. Here we present
a study of two bright $H\alpha$ sources in the NGC 247 galaxy. Object
j004703.27-204708.4 ($M_V=-9.08 \pm 0.15^m$) shows the spectral lines typical
for well-studied LBV stars: broad and bright emission lines of hydrogen and
helium He I with P Cyg profiles, emission lines of iron Fe II, silicon Si II,
nitrogen N II and carbon C II, forbidden iron [Fe II] and nitrogen [N II]
lines. The variability of the object is $\Delta B = 0.74\pm0.09^m$ and $\Delta
V = 0.88\pm0.09^m$, which makes it reliable LBV candidate. The star
j004702.18-204739.93 ($M_V=-9.66 \pm 0.23^m$) shows many emission lines of iron
Fe II, forbidden iron lines [Fe II], bright hydrogen lines with broad wings,
and also forbidden lines of oxygen [O I] and calcium [Ca II] formed in the
circumstellar matter. The study of the light curve of this star also did not
reveal significant variations in brightness ($\Delta V = 0.29\pm0.09^m$). We
obtained estimates of interstellar absorption, the photosphere temperature, as
well as bolometric magnitudes $M_\text{bol}=-10.5^{+0.5}_{-0.4}$ and
$M_\text{bol}=-10.8^{+0.5}_{-0.6}$, which corresponds to bolometric
luminosities $\log(L_\text{bol}/L_{\odot})=6.11^{+0.20}_{-0.16}$ and
$6.24^{+0.20}_{-0.25}$ for j004703.27-204708.4 and j004702.18-204739.93
respectively. Thus, the object j004703.27-204708.4 remains a reliable LBV
candidate, while the object j004702.18-204739.93 can be classified as
B[e]-supergiant.",2008.06215v1
2020-09-11,An Extraordinary Response of Iron Emission to the Central Outburst in a Tidal Disruption Event Candidate,"Understanding the origin of \feii\ emission is important because it is
crucial to construct the main sequence of Active Galactic Nuclei (AGNs).
Despite several decades of observational and theoretical effort, the location
of the optical iron emitting region and the mechanism responsible for the
positive correlation between the \feii\ strength and the black hole accretion
rate remain open questions as yet. In this letter, we report the optical \feii\
response to the central outburst in PS1-10adi, a candidate tidal disruption
event (TDE) taking place in an AGN at $z = 0.203$ that has aroused extensive
attention. For the first time, we observe that the \feii\ response in the
rising phase of its central luminosity is significantly more prominent than
that in the decline phase, showing a hysteresis effect. We interpret this
hysteresis effect as a consequence of the gradual sublimation of the dust
grains situating at the inner surface of the torus into gas when the luminosity
of the central engine increases. It is the iron element released from the
sublimated dust that contributes evidently to the observed \feii\ emission.
This interpretation, together with the weak response of the \hb\ emission as we
observe, naturally explains the applicability of relative \feii\ strength as a
tracer of the Eddington ratio. In addition, optical iron emission of this
origin renders the \feii\ time lag a potential ""standard candle"" with
cosmological implications.",2009.05243v2
2020-12-01,Variability in NGC 3201 giant stars and its impact on their spectroscopic [Fe/H] determination,"We present the analysis of 34 light curves in $V$ and $I$ of 17 giant stars
in the globular cluster NGC 3201, to check if such stars are variable and if
their variability has some kind of impact on the iron abundance as obtained
from spectroscopic measurements. First, we computed the Generalized
Lomb-Scargle and Phase Dispersion Minimization periodograms on the sample to
check if the stars were variables. In this way, 7 stars of the sample were
found to be non-variable, 2 stars are considered as possible variables, and 8
stars were found to be variable, with periods ranging from $0.0881\pm0.0001$ to
$0.5418\pm0.0027$ days. According to the literature, the variables have
distinct values of $\text{[Fe I/H]}$: the 3 most metal-rich stars are in the
RGB stage, one has an $\text{[Fe I/H]}=-1.37$ dex, while the other two have
$\text{[Fe I/H]}=-1.31$ dex. The two most metal-poor variables have $\text{[Fe
I/H]}=-1.61$ dex and $\text{[Fe I/H]}=-1.62$ dex, and are AGB stars; the
remaining variables have $\text{[Fe I/H]}=-1.44$, $-1.48$, and $-1.50$ dex, the
first two being RGB while the last is AGB star. On the other hand, stars that
appear to be non-variables have $-1.56\leq\text{[Fe I/H]}\leq-1.40$. We
conclude that variability somehow affects the spectroscopic determination of
the iron content of giant stars in NGC 3201 increasing the iron spread of the
cluster. If variability is not taken into account, this spread could be wrongly
interpreted as due to an intrinsic iron spread affecting the stars of the
cluster.",2012.00520v1
2020-12-09,"First measurement using a nuclear emulsion detector of the $ν_μ$ charged-current cross section on iron around the 1$\,$GeV energy region","We have carried out $\nu_{\mu}$ charged-current interaction measurement on
iron using an emulsion detector exposed to the T2K neutrino beam in the J-PARC
neutrino facility. The data samples correspond to 4.0$\times$10$^{19}$ protons
on target, and the neutrino mean energy is 1.49$\,$GeV. The emulsion detector
is suitable for precision measurements of charged particles produced in
neutrino-iron interactions with a low momentum threshold thanks to thin-layered
structure and sub-$\mu$m spatial resolution. The charged particles are
successfully detected, and their multiplicities are measured using the emulsion
detector. The cross section was measured to be
$\sigma^{\mathrm{Fe}}_{\mathrm{CC}} = (1.28 \pm
0.11({\mathrm{stat.}})^{+0.12}_{-0.11}({\mathrm{syst.}})) \times 10^{-38} \,
{\mathrm{cm}}^{2}/{\mathrm{nucleon}}$. The cross section in a limited kinematic
phase space of induced muons, $\theta_{\mu} < 45^{\circ}$ and $p_{\mu} > 400 \,
{\rm MeV}/c$, on iron was $\sigma^{\mathrm{Fe}}_{\mathrm{CC \hspace{1mm} phase
\hspace{0.5mm} space}} = (0.84 \pm
0.07({\mathrm{stat.}})^{+0.07}_{-0.06}({\mathrm{syst.}})) \times 10^{-38} \,
{\mathrm{cm}}^{2}/{\mathrm{nucleon}}$. The cross-section results are consistent
with previous values obtained via different techniques using the same beamline,
and they are well reproduced by current neutrino interaction models. These
results demonstrate the capability of the detector towards the detailed
measurements of the neutrino-nucleus interactions around the 1$\,$GeV energy
region.",2012.05221v2
2021-01-03,Magnetic surface reconstruction in the van-der-Waals antiferromagnet Fe$_{1+x}$Te,"Fe$_{1+x}$Te is a two dimensional van der Waals antiferromagnet that becomes
superconducting on anion substitution on the Te site. The parent phase of
Fe$_{1+x}$Te is sensitive to the amount of interstitial iron situated between
the iron-tellurium layers displaying collinear magnetic order coexisting with
low temperature metallic resistivity for small concentrations of interstitial
iron $x$ and helical magnetic order for large values of $x$. While this phase
diagram has been established through scattering [see for example E. E.
Rodriguez $\textit{et al.}$ Phys. Rev. B ${\bf{84}}$, 064403 (2011) and S.
R\""ossler $\textit{et al.}$ Phys. Rev. B ${\bf{84}}$, 174506 (2011)], recent
scanning tunnelling microscopy measurements [C. Trainer $\textit{et al.}$ Sci.
Adv. ${\bf{5}}$, eaav3478 (2019)] have observed a different magnetic structure
for small interstitial iron concentrations $x$ with a significant canting of
the magnetic moments along the crystallographic $c$ axis of $\theta$=28 $\pm$
3$^{\circ}$. In this paper, we revisit the magnetic structure of Fe$_{1.09}$Te
using spherical neutron polarimetry and scanning tunnelling microscopy to
search for this canting in the bulk phase and compare surface and bulk
magnetism. The results show that the bulk magnetic structure of Fe$_{1.09}$Te
is consistent with collinear in-plane order ($\theta=0$ with an error of $\sim$
5$^{\circ}$). Comparison with scanning tunnelling microscopy on a series of
Fe$_{1+x}$Te samples reveals that the surface exhibits a magnetic surface
reconstruction with a canting angle of the spins of $\theta=29.8^{\circ}$. We
suggest that this is a consequence of structural relaxation of the surface
layer resulting in an out-of-plane magnetocrystalline anisotropy. The magnetism
in Fe$_{1+x}$Te displays different properties at the surface when the symmetry
constraints of the bulk are removed.",2101.00569v1
2021-03-04,"Crater shape as a possible record of the impact environment of metallic bodies: Effects of temperature, impact velocity and impactor density","Metallic bodies that were the cores of differentiated bodies are sources of
iron meteorites and are considered to have formed early in the terrestrial
planet region before migrating to the main asteroid belt. Surface temperatures
and mutual collision velocities differ between the terrestrial planet region
and the main asteroid belt. To investigate the dependence of crater shape on
temperature, velocity and impactor density, we conducted impact experiments on
room- and low-temperature iron meteorite and iron alloy targets (carbon steel
SS400 and iron-nickel alloy) with velocities of 0.8-7 km/s. The projectiles
were rock cylinders and metal spheres and cylinders. Oblique impact experiments
were also conducted using stainless steel projectiles and SS400 steel targets
which produced more prominent radial patterns downrange at room temperature
than at low temperature. Crater diameters and depths were measured and compiled
using non-dimensional parameter sets based on the $\pi$-group crater scaling
relations. Two-dimensional numerical simulations were conducted using iSALE-2D
code with the Johnson-Cook strength model. Both experimental and numerical
results showed that the crater depth and diameter decreased with decreasing
temperature, which strengthened the target, and with decreasing impact
velocity. The decreasing tendency was more prominent for depth than for
diameter, i.e., the depth/diameter ratio was smaller for the low temperature
and low velocity conditions. The depth/diameter ratios of craters formed by
rock projectiles were shallower than those of craters formed by metallic
projectiles. Our results imply that the frequency distribution of the
depth/diameter ratio for craters on the surface of metallic bodies may be used
as a probe of the past impact environment of metallic bodies.",2103.03128v2
2021-04-20,Stellar winds and metal enrichment from fast-rotating Population III stars,"Stellar winds from fast-rotating Population III (Pop III) stars have long
been suspected to make important contributions to early metal enrichment, as
features in the nucleosynthesis of such `spinstars' are consistent with the
chemical abundance patterns of some metal-poor stars in the local Universe.
Particularly, stellar winds rich in light elements can provide another pathway
towards explaining the carbon enhancement in carbon-enhanced metal-poor (CEMP)
stars. In this work, we focus on the feedback of Pop III stellar winds combined
with supernovae (SNe), and derive the resulting chemical signatures in the
enriched medium. We explore a large parameter space of Pop III star formation,
feedback, yields from winds and SNe with a semi-analytical model. The predicted
pattern of carbon and iron abundances of second-generation stars agrees well
with observations of CEMP-no stars ($[\rm Ba/Fe]<0$) at $[\rm Fe/H]\lesssim -3$
and $A(\mathrm{C})\lesssim 7$, under the optimistic assumption of significant
mass loss by winds from massive ($\gtrsim 25\ \rm M_{\odot}$) stars that
collapse into BHs without SNe. In this scenario, carbon-rich but iron-free
second-generation stars can form in systems dominated by enrichment from winds,
gaining trace amounts of iron by accretion from the interstellar medium, to
become the most iron-poor and carbon-enhanced stars seen in observations ($[\rm
Fe/H]\lesssim -4$, $[\rm C/Fe]\gtrsim 2$). We conclude that the observed
CEMP-no stars can be explained by both our winds + ISM accretion channel as
well as the well-studied faint SN scenario. Wind feedback from Pop~III
spinstars deserves more detailed modelling in early cosmic structure formation.",2104.10046v2
2021-05-06,The Iron Yield of Normal Type II Supernovae,"We present $^{56}$Ni mass estimates for 110 normal Type II supernovae (SNe
II), computed here from their luminosity in the radioactive tail. This sample
consists of SNe from the literature, with at least three photometric
measurements in a single optical band within 95-320 d since explosion. To
convert apparent magnitudes to bolometric ones, we compute bolometric
corrections (BCs) using 15 SNe in our sample having optical and near-IR
photometry, along with three sets of SN II atmosphere models to account for the
unobserved flux. We find that the $I$- and $i$-band are best suited to estimate
luminosities through the BC technique. The $^{56}$Ni mass distribution of our
SN sample has a minimum and maximum of 0.005 and 0.177 M$_{\odot}$,
respectively, and a selection-bias-corrected average of $0.037\pm0.005$
M$_{\odot}$. Using the latter value together with iron isotope ratios of two
sets of core-collapse (CC) nucleosynthesis models, we calculate a mean iron
yield of $0.040\pm0.005$ M$_{\odot}$ for normal SNe II. Combining this result
with recent mean $^{56}$Ni mass measurements for other CC SN subtypes, we
estimate a mean iron yield $<$0.068 M$_{\odot}$ for CC SNe, where the
contribution of normal SNe II is $>$36 per cent. We also find that the
empirical relation between $^{56}$Ni mass and steepness parameter ($S$) is
poorly suited to measure the $^{56}$Ni mass of normal SNe II. Instead, we
present a correlation between $^{56}$Ni mass, $S$, and absolute magnitude at 50
d since explosion. The latter allows to measure $^{56}$Ni masses of normal SNe
II with a precision around 30 per cent.",2105.03268v1
2021-06-24,Time-resolved diffraction and photoelectron spectroscopy investigation of the reactive molecular beam epitaxy of $\mathrm{Fe_3O_4}$ ultrathin films,"We present time-resolved high energy x-ray diffraction (tr-HEXRD),
time-resolved hard x-ray photoelectron spectroscopy (tr-HAXPES) and
time-resolved grazing incidence small angle x-ray scattering (tr-GISAXS) data
of the reactive molecular beam epitaxy (RMBE) of $\mathrm{Fe_3O_4}$ ultrathin
films on various substrates. Reciprocal space maps are recorded during the
deposition of $\mathrm{Fe_3O_4}$ on $\mathrm{SrTiO_3(001)}$, MgO(001) and
NiO/MgO(001) in order to observe the temporal evolution of Bragg reflections
sensitive to the octahedral and tetrahedral sublattices of the inverse spinel
structure of $\mathrm{Fe_3O_4}$. A time delay between the appearance of rock
salt and spinel-exclusive reflections reveals that first, the iron oxide film
grows with $\mathrm{Fe_{1-\delta}O}$ rock salt structure with exclusive
occupation of octahedral lattice sites. When this film is 1.1$\,$nm thick, the
further growth of the iron oxide film proceeds in the inverse spinel structure,
with both octahedral and tetrahedral lattice sites being occupied. In addition,
iron oxide on $\mathrm{SrTiO_3(001)}$ initially grows with none of these
structures. Here, the formation of the rock salt structure starts when the film
is 1.5$\,$nm thick. This is confirmed by tr-HAXPES data obtained during growth
of iron oxide on $\mathrm{SrTiO_3(001)}$, which demonstrate an excess of
$\mathrm{Fe^{2+}}$ cations in growing films thinner than 3.2$\,$nm. This rock
salt phase only appears during growth and vanishes after the supply of the Fe
molecular beam is stopped. Thus, it can be concluded the rock salt structure of
the interlayer is a property of the dynamic growth process. The tr-GISAXS data
link these structural results to an island growth mode of the first 2-3$\,$nm
on both MgO(001) and $\mathrm{SrTiO_3(001)}$ substrates.",2106.13192v1
2021-10-15,Type Ia Supernova Models: Asymmetric Remnants and Supernova Remnant G1.9+0.3,"The youngest Galactic supernova remnant G1.9+0.3, probably the result of a
Type Ia supernova, shows surprising anomalies in the distribution of its ejecta
in space and velocity. In particular, high-velocity shocked iron is seen in
several locations far from the remnant center, in some cases beyond prominent
silicon and sulfur emission. These asymmetries strongly suggest a highly
asymmetric explosion. We present high-resolution hydrodynamic simulations in
two and three dimensions of the evolution from ages of 100 seconds to hundreds
of years of two asymmetric Type Ia models, expanding into a uniform medium. At
the age of G1.9+0.3 (about 100 years), our 2D model shows almost no iron
shocked to become visible in X-rays. Only in a much higher-density environment
could significant iron be shocked, at which time the model's expansion speed is
completely inconsistent with the observations of G1.9+0.3. Our 3D model,
evolving the most asymmetric of a suite of Type Ia SN models from Seitenzahl et
al.~(2013), shows some features resembling G1.9+0.3. We characterize its
evolution with images of composition in three classes: C and O,
intermediate-mass elements (IMEs), and iron-group elements (IGEs). From ages of
13 to 1800 years, we follow the evolution of the highly asymmetric initial
remnant as the explosion asymmetries decrease in relative strength to be
replaced by asymmetries due to evolutionary hydrodynamic instabilities. At an
age of about 100 years, our 3D model has comparable shocked masses of C+O,
IMEs, and IGEs, with about 0.03 $M_\odot$ each. Evolutionary changes appear to
be rapid enough that continued monitoring with the Chandra X-ray Observatory
may show significant variations.",2110.08360v1
2021-10-28,Non-homogeneous exoplanets in metric-affine gravity,"The improved description of the planets' interior is provided. We examine the
modified gravity effects on the Earth-like planets composed of the iron core
and silicate mantle. We confirm that the mass-radius relations, as well as
density profiles, differ with respect to the commonly adopted Newtonian models.",2110.15139v2
2021-12-03,The 1966 International Congress of Mathematicians: A micro-memoir,"To an extent, the 1966 congress was a hole in the iron curtain. At least that
how a young Soviet mathematician saw it.",2112.04900v4
2022-03-21,Accurate Determination of the Electron Spin Polarization In Magnetized Iron and Nickel Foils for Møller Polarimetry,"The M{\o}ller polarimeter in Hall A at Jefferson Lab in Newport News, VA, has
provided reliable measurements of electron beam polarization for the past two
decades reaching the typically required $\pm$1\% level of absolute uncertainty.
However, the upcoming proposed experimental program including MOLLER and SoLID
have stringent requirements on beam polarimetry precision at the level of 0.4\%
\cite{MOLLER2014, SoLID2019}, requiring a systematic re-examination of all the
contributing uncertainties.
  M{\o}ller polarimetry uses the double polarized scattering asymmetry of a
polarized electron beam on a target with polarized atomic electrons. The target
is a ferromagnetic material magnetized to align the spins in a given direction.
In Hall A, the target is a pure iron foil aligned perpendicular to the beam and
magnetized out of plane parallel or antiparallel to the beam direction. The
acceptance of the detector is engineered to collect scattered electrons close
to 90$^{\circ}$ in the center of mass frame where the analyzing power is a
maximum (-7/9).
  One of the leading systematic errors comes from determination of the target
foil polarization. Polarization of a magnetically saturated target foil
requires knowledge of both the saturation magnetization and $g^\prime$, the
electron $g$-factor which includes components from both spin and orbital
angular momentum from which the spin fraction of magnetization is determined.
This paper utilizes the existing world data to provide a best estimate for
target polarization for both nickel and iron foils including uncertainties in
magnetization, high-field and temperature dependence, and fractional
contribution to magnetization from orbital effects. We determine the foil
electron spin polarization at 294~K to be 0.08020$\pm$0.00018 (@4~T applied
field) for iron and 0.018845$\pm0.000053$ (@2~T applied field) for nickel.",2203.11238v2
2022-04-19,Characterizing the Advective Hot Flows of Nova-Like Cataclysmic Variables in the X-rays: The case of BZ Cam and V592 Cas,"We present a joint spectral analysis of ROSAT PSPC, Swift XRT, and NuSTAR
FPMA/B data of the nova-like (NL) cataclysmic variables (CVs), BZ Cam and V592
Cas in the 0.1-78.0 keV band. Plasma models of collisional equilibrium fail to
model the 6.0-7.0 iron line complex and continuum with $\chi^2_\nu$ larger than
2.0. Our results show nonequilibrium ionization (NEI) conditions in the X-ray
plasma with temperatures of 8.2-9.4 keV and 10.0-12.9 keV for BZ Cam and V592
Cas, respectively. The centroids of He-like and H-like iron ionization lines
are not at their equilibrium values as expected from NEI conditions. We find
power law spectral components that reveal the existence of scattering and
Comptonization with a photon index of 1.50-1.87. We detect a P Cygni profile in
the H-like iron line of BZ Cam translating to outflows of 4500-8700 km s$^{-1}$
consistent with the fast winds in the optical and UV. This is the first time
such a fast collimated outflow is detected in the X-rays from an accreting CV.
An Iron K$\alpha$ line around 6.2-6.5 keV is found revealing the existence of
reflection effects in both sources. We study the broadband noise and find that
the optically thick disk truncates in BZ Cam and V592 Cas consistent with
transition to an advective hot flow structure. V592 Cas also exhibits a
quasi-periodic oscillation at 1.4$^{+2.6}_{-0.3}$ mHz. In general, we find that
the two NLs portray spectral and noise characteristics as expected from
advective hot accretion flows at low radiative efficiency.",2204.08842v1
2022-05-04,On Internal and External Alignment of Dust Grains in Protostellar Environments,"We study the physical processes inducing the alignment of the grain axis of
maximum inertia moment with the angular momentum (${\bf J}$, i.e., internal
alignment) and of ${\bf J}$ with the magnetic field (i.e., external alignment)
of very large grains (VLGs, of radius $a>10\mu$m) using the grain alignment
framework based on radiative torques (RATs) and mechanical torques (METs). We
derive analytical formulae for critical sizes of grain alignment, assuming that
grains are aligned at both low$-J$ and high$-J$ attractors by RATs (METs). For
protostellar cores, we find that super-Barnett relaxation can induce efficient
internal alignment for VLGs with large iron inclusions aligned at high$-J$
attractors by RATs (METs). In contrast, inelastic relaxation can be efficient
for VLGs made of any composition. For external alignment, we find that VLGs
with iron inclusions aligned at high$-J$ attractors can have magnetic alignment
by RATs ($B-$RAT) or METs ($B-$ MET), enabling dust polarization as a reliable
tracer of magnetic fields in such dense regions. Still, grains at low$-J$
attractors or grains without iron inclusions have alignment along the radiation
direction ($k-$RAT) or gas flow ($v-$MET). For protostellar disks, we find that
super-Barnett relaxation can be efficient for grains with large iron inclusions
in the outer disk thanks to spinup by METs, but inelastic relaxation is
inefficient. VLGs aligned at low-J attractors can have $k-$RAT ($v-$MET)
alignment, but grains aligned at high$-J$ attractors have likely $B-$RAT
($B-$MET) alignment. Grain alignment by METs appears to be more important than
RATs in protostellar disks.",2205.02334v2
2022-05-18,Internet Performance in the 2022 Conflict in Ukraine: An Asymmetric Analysis,"On 24 February 2022 Russia invaded Ukraine, starting one of the largest
military conflicts in Europe in recent years. In this paper we present
preliminary findings about the impact of the conflict on the Internet
performance in Ukraine and in Russia, introducing an ironically asymmetric
picture: the Internet performance in Ukraine has significantly degraded, while
the performance in Russia has improved.",2205.08912v1
2022-07-12,Investigating a predicted metallicity [Fe/H] variation in the Type II Globular Cluster NGC 362,"NGC 362 is a non-common Type II Galactic globular cluster, showing a complex
pseudo two-color diagram or 'chromosome map'. The clear separation of its
stellar populations in the color-magnitude diagram and the distribution of the
giant stars in the chromosome map strongly suggests that NGC 362 could host
stars with both cluster-nominal as well as enhanced heavy-element abundances,
and one of them could be iron. However, despite previous spectroscopic
observations of NGC 362, no such iron variation has been detected. Our main
goal is to confirm or disprove this result by searching for any internal
variation of [Fe/H] which would give us insight into the formation and
evolution of this interesting globular cluster. In this paper, we present the
abundance analysis for a sample of 11 red giant branch members based on
high-resolution and high S/N spectra obtained with the MIKE echelle
spectrograph mounted at the Magellan-Clay telescope. HST and GAIA photometry
and astrometry has been used to determine atmospheric parameters and
membership. We obtained T$_{\text{eff}}$, log(g) and v$_{\text{t}}$ for our
target stars and measured the mean iron content of the sample and its
dispersion with three different methods, which lead to
[Fe/H]$_1$=-1.10$\pm0.02$, [Fe/H]$_2$=-1.09$\pm0.01$ and
[Fe/H]$_3$=-1.10$\pm0.01$, while the internal dispersion turned out to be
$\sigma_{[\text{Fe/H}]_1}$=0.06$\pm0.01$,
$\sigma_{[\text{Fe/H}]_2}$=0.03$\pm0.01$ and
$\sigma_{[\text{Fe/H}]_3}$=0.05$\pm0.01$ respectively. The error analysis gives
an internal dispersion due to observational error of 0.05 dex. Comparing the
observed dispersion with the internal errors, we conclude that NGC 362 does not
show any trace of an internal iron spread.",2207.05693v1
2022-09-12,The Iron Yield of Core-collapse Supernovae,"We present a systematic analysis of 191 stripped-envelope supernovae (SE
SNe), aimed to compute their $^{56}$Ni masses from the luminosity in their
radioactive tails ($M_\mathrm{Ni}^\mathrm{tail}$) and/or in their maximum
light, and the mean $^{56}$Ni and iron yields of SE SNe and core-collapse SNe.
Our sample consists of SNe IIb, Ib, and Ic from the literature and from the
Zwicky Transient Facility Bright Transient Survey. To calculate luminosities
from optical photometry, we compute bolometric corrections using 49 SE SNe with
optical and near-IR photometry, and develop corrections to account for the
unobserved UV and IR flux. We find that the equation of Khatami & Kasen for
radioactive $^{56}$Ni-powered transients with a single free parameter does not
fit the observed peak time-luminosity relation of SE SNe. Instead, we find a
correlation between $M_\mathrm{Ni}^\mathrm{tail}$, peak time, peak luminosity,
and decline rate, which allows measuring individual $^{56}$Ni masses to a
precision of 14%. Applying this method to the whole sample, we find, for SNe
IIb, Ib, and Ic, mean $^{56}$Ni masses of $0.066\pm0.006$, $0.082\pm0.009$, and
$0.132\pm0.011\,\mathrm{M}_{\odot}$, respectively. After accounting for their
relative rates, for SE SNe as a whole we compute mean $^{56}$Ni and iron yields
of $0.090\pm0.005$ and $0.097\pm0.007\,\mathrm{M}_{\odot}$, respectively.
Combining these results with the recent Type II SN mean $^{56}$Ni mass derived
by Rodr\'iguez et al., core-collapse SNe, as a whole, have mean $^{56}$Ni and
iron yields of $0.055\pm0.006$ and $0.058\pm0.007\,\mathrm{M}_{\odot}$,
respectively. We also find that radioactive $^{56}$Ni-powered models typically
underestimate the peak luminosity of SE SNe by 60-70%, suggesting the presence
of an additional power source contributing to the luminosity at peak.",2209.05552v2
2023-02-08,A portable and high intensity 24 keV neutron source based on $^{124}$Sb-$^{9}$Be photoneutrons and an iron filter,"A portable monoenergetic 24 keV neutron source based on the $^{124}$Sb-$^9$Be
photoneutron reaction and an iron filter has been constructed and
characterized. The coincidence of the neutron energy from SbBe and the low
interaction cross-section with iron (mean free path up to 29 cm) makes pure
iron specially suited to shield against gamma rays from $^{124}$Sb decays while
letting through the neutrons. To increase the $^{124}$Sb activity and thus the
neutron flux, a $>$1 GBq $^{124}$Sb source was produced by irradiating a
natural Sb metal pellet with a high flux of thermal neutrons in a nuclear
reactor. The design of the source shielding structure makes for easy
transportation and deployment. A hydrogen gas proportional counter is used to
characterize the neutrons emitted by the source and a NaI detector is used for
gamma background characterization. At the exit opening of the neutron beam, the
characterization determined the neutron flux in the energy range 20-25 keV to
be 5.36$\pm$0.20 neutrons per cm$^2$ per second and the total gamma flux to be
213$\pm$6 gammas per cm$^2$ per second (numbers scaled to 1 GBq activity of the
$^{124}$Sb source). A liquid scintillator detector is demonstrated to be
sensitive to neutrons with incident kinetic energies from 8 to 17 keV, so it
can be paired with the source as a backing detector for neutron scattering
calibration experiments. This photoneutron source provides a good tool for
in-situ low energy nuclear recoil calibration for dark matter experiments and
coherent elastic neutrino-nucleus scattering experiments.",2302.03869v1
2023-04-17,A structural study of hcp and liquid iron under shock compression up to 275 GPa,"We combine nanosecond laser shock compression with \emph{in-situ} picosecond
X-ray diffraction to provide structural data on iron up to 275 GPa. We
constrain the extent of hcp-liquid coexistence, the onset of total melt, and
the structure within the liquid phase. Our results indicate that iron, under
shock compression, melts completely by 258(8) GPa. A coordination number
analysis indicates that iron is a simple liquid at these pressure-temperature
conditions. We also perform texture analysis between the ambient
body-centered-cubic (bcc) $\alpha$, and the hexagonal-closed-packed (hcp)
high-pressure $\epsilon-$phase. We rule out the Rong-Dunlop orientation
relationship (OR) between the $\alpha$ and $\epsilon-$phases. However, we
cannot distinguish between three other closely related ORs: Burger's,
Mao-Bassett-Takahashi, and Potter's OR. The solid-liquid coexistence region is
constrained from a melt onset pressure of 225(3) GPa from previously published
sound speed measurements and full melt (246.5(1.8)-258(8) GPa) from X-ray
diffraction measurements, with an associated maximum latent heat of melting of
623 J/g. This value is lower than recently reported theoretical estimates and
suggests that the contribution to the earth's geodynamo energy budget from heat
release due to freezing of the inner core is smaller than previously thought.
Melt pressures for these nanosecond shock experiments are consistent with gas
gun shock experiments that last for microseconds, indicating that the melt
transition occurs rapidly.",2304.07933v3
2023-05-08,First evidence of multi-iron sub-populations in the Bulge Fossil Fragment candidate Liller 1,"In the context of a project aimed at characterizing the properties of the
so-called Bulge Fossil Fragments (the fossil remnants of the bulge formation
epoch), here we present the first determination of the metallicity distribution
of Liller 1. For a sample of 64 individual member stars we used ESO- MUSE
spectra to measure the equivalent width of the CaII triplet and then derive the
iron abundance. To test the validity of the adopted calibration in the
metal-rich regime, the procedure was first applied to three reference bulge
globular clusters (NGC 6569, NGC 6440, and NGC 6528). In all the three cases,
we found single-component iron distributions, with abundance values fully in
agreement with those reported in the literature. The application of the same
methodology to Liller 1 yielded, instead, a clear bimodal iron distribution,
with a sub-solar component at $\text{[Fe/H]}= -0.48\,$dex ($\sigma = 0.22$) and
a super-solar component at $\text{[Fe/H]}= +0.26\,$dex ($\sigma = 0.17$). The
latter is found to be significantly more centrally concentrated than the
metal-poor population, as expected in a self-enrichment scenario and in
agreement with what found in another bulge system, Terzan 5. The obtained
metallicity distribution is astonishingly similar to that predicted by the
reconstructed star formation history of Liller 1, which is characterized by
three main bursts and a low, but constant, activity of star formation over the
entire lifetime. These findings provide further support to the possibility
that, similar to Terzan 5, also Liller 1 is a Bulge Fossil Fragment.",2305.04595v1
2023-05-13,mechanical properties of CaFe2As2 ab-initio study,"We report results on the ab-initio study of the mechanical, electronic and
structural properties of the iron Pnictide compound CaFe_2 As_2 at zero
pressure. Ground State energy computation was done within the Density
Functional Theory (DFT) using the Projector Augmented Wave (PAW) Pseudo
Potentials and the Plane Wave (PW) basis set. The Generalized Gradient
Approximation (GGA) facilitated the exchange-correlation.",2305.07949v1
2023-06-28,"Preliminary Tc calculations for iron-based superconductivity in NaFeAs, LiFeAs, FeSe and nanostructured FeSe/SrTiO3 Superconductors","Many theoretical models of iron-based superconductors have been proposed but
Tc calculations based on the models are usually missing. We have chosen two
models of iron-based superconductors in the literature and then compute the Tc
values accordingly: Recently two models have been announced which suggest that
superconducting electron concentration involved in the pairing mechanism of
iron-based superconductors may have been underestimated, and that the
antiferromagnetism and the induced xy potential may even have a dramatic
amplification effect on electron-phonon coupling. We use bulk FeSe, LiFeAs and
NaFeAs data to calculate the Tc based on these models and test if the combined
model can predict the superconducting transition temperature (Tc) of the
nanostructured FeSe monolayer well. To substantiate the recently announced xy
potential in the literature, we create a two-channel model to separately
superimpose the dynamics of the electron in the upper and lower tetrahedral
plane. The results of our two-channel model support the literature data. Our
computational model takes into account this amplifying effect of
antiferromagnetism and the correction of the electron-phonon scattering matrix
together with the abnormal soft out-of-plane lattice vibration of the layered
structure, which allows us to calculate theoretical Tc values of LiFeAs, NaFeAs
and FeSe as a function of pressure that correspond reasonably well to the
experimental values. More importantly, by taking into account the interfacial
effect between an FeSe monolayer and its SrTiO3 substrate as an additional gain
factor, our calculated Tc value is up to 91 K high, and provides evidence that
the strong Tc enhancement recently observed in such monolayers with Tc reaching
100 K may be contributed from the electrons within the ARPES range.",2306.15892v1
2023-10-14,Order-disorder phase transition and elastic-to-plastic vortex creep crossover in a triclinic iron pnictide superconductor (Ca0.85La0.15)10(Pt3As8)(Fe2As2)5,"Vortex matter in layered high-$T_c$ superconductors, including
iron-pnictides, undergo several thermodynamic phase transitions due to the
complex interplay of pinning energy, thermal energy and elastic energy.
Moreover, the presence of anisotropy makes their vortex physics even more
intriguing. Here, we report a detailed vortex dynamics study, using dc
magnetization measurements, in a triclinic iron-pnictide superconductor
(Ca$_{0.85}$La$_{0.15}$)$_{10}$(Pt$_3$As$_8$)(Fe$_2$As$_2$)$_5$, with a
superconducting transition temperature, T$_c$ $\sim$ 31 K. A second
magnetization peak (SMP) feature is observed for magnetic field perpendicular
($H$$\parallel$$c$) and parallel ($H$$\parallel$$ab$) to the crystal plane.
However, its fundamental origin is quite different in both directions. For
$H$$\parallel$$c$, the SMP can be well explained using an elastic-to-plastic
vortex creep crossover, using collective creep theory. In addition, a possible
rhombic-to-square vortex lattice phase transition is also observed for fields
in between the onset-field and peak-field related to the SMP. On the other
hand, for $H$$\parallel$$ab$, a clear signature of an order-disorder vortex
phase transition is observed in the isothermal $M$($H$) measurements at $T$
$\geq$ 6 K. The disordered phase exhibits the characteristics of entangled
pinned vortex-liquid. We construct a comprehensive vortex phase diagram by
displaying characteristic temperatures and magnetic fields for both crystal
geometries in this unique superconducting compound. Our study sheds light on
the intricate vortex dynamics and pinning in an iron-pnictide superconductor
with triclinic symmetry.",2310.09557v1
2024-03-05,Spatially resolving the AGB star V3 in the metal-poor globular cluster 47 Tuc with VLTI/GRAVITY,"Mass loss at the asymptotic giant branch (AGB) plays an important role not
only in the final fates of stars, but also in the chemical evolution of
galaxies. Nevertheless, the metallicity effects on AGB mass loss are not yet
fully understood. We present spatially resolved observations of an AGB star,
V3, in the metal-poor globular cluster 47 Tuc (NGC 104). The AGB star 47 Tuc V3
was observed using the GRAVITY instrument at ESO's Very Large Telescope
Interferometer (VLTI) at 2-2.45 micron with a projected baseline length of up
to 96 m. The object 47 Tuc V3 has been spatially resolved and stands as the
first to attempt to spatially resolve an individual star in a globular cluster.
The uniform-disk fit to the observed data results in an angular diameter of
~0.7 mas. Our modeling of the spectral energy distribution and near-infrared
interferometric GRAVITY data suggests that the observed data can be explained
by an optically thin dust shell with a 0.55 micron optical depth of 0.05-0.25,
consisting of metallic iron grains, likely together with effects of the
extended atmosphere of the central star. The dust temperature at the inner
shell boundary is 500-800 K (corresponding to 23-90 stellar radii),
significantly lower than observed in nearby oxygen-rich AGB stars. Radiation
pressure on small (< 0.05 micron) iron grains is not sufficient to drive
stellar winds. Therefore, iron grains may grow to larger sizes, even in the
metal-poor environment. Alternatively, it is possible that the observed iron
grain formation is a result of the mass outflow initiated by some other
mechanism(s). The sensitivity and angular resolution of VLTI provides a new
window onto spatially resolving individual stars in metal-poor globular
clusters. This allows us to improve subsequent studies of the metallicity
dependence of dust formation and mass loss.",2403.03287v2
2003-11-12,Heavy elements abundances in turn-off stars and early subgiants in NGC 6752,"High resolution spectra (R > 40 000) for 9 main sequence turn-off stars and 9
subgiants in the globular cluster NGC 6752 were acquired with UVES on the
VLT-Kueyen (UT2). These data have been used to determine the abundances of some
heavy elements (strontium, yttrium, barium and europium). This paper presents
for the first time accurate results for heavy elements in this globular
cluster. We did not find any systematic effect between the abundances found in
turn-off stars, subgiants, and giants. We obtain the following mean abundances
for these elements in our sample (turn-off stars and subgiants): [Sr/Fe] = 0.06
+/- 0.16, [Y/Fe] = -0.01 +/- 0.12, [Ba/Fe] = 0.18 +/- 0.11, and [Eu/Fe] = 0.41
+/- 0.09. The dispersion in the abundance ratios of the different elements is
low and can be totally explained by uncertainties in their derivation. These
ratios are in agreement with the values found in field halo stars with the same
metallicity. We did not observe any correlation between the [n-capture/Fe]
ratios and the star-to-star variations of the O and Na abundances. The [Ba/Eu]
and [Sr/Ba] ratios show clearly that this globular cluster has also been
uniformly enriched by r- and s-process synthesis.",0311278v1
2008-02-22,A comparison of the s- and r-process element evolution in local dwarf spheroidal galaxies and in the Milky Way,"We study the nucleosynthesis of several neutron capture elements (barium,
europium, lanthanum, and yttrium) in local group dwarf spheroidal (dSph)
galaxies and in the Milky Way by comparing the evolution of [Ba/Fe], [Eu/Fe],
[La/Fe], [Y/Fe], [Ba/Y], [Ba/Eu], [Y/Eu], and [La/Eu] observed in dSph galaxies
and in our Galaxy with predictions of detailed chemical evolution models. The
models for all dSph galaxies and for the Milky Way are able to reproduce
several observational features of these galaxies, such as a series of abundance
ratios and the stellar metallicities distributions. The Milky Way model adopts
the two-infall scenario, whereas the most important features of the models for
the dSph galaxies are the low star-formation rate and the occurrence of intense
galactic winds. We predict that the [s-r/Fe] ratios in dSphs are generally
different than the corresponding ratios in the Milky Way, at the same [Fe/H]
values. This is interpreted as a consequence of the time-delay model coupled
with different star formation histories. In particular, the star-formation is
less efficient in dSphs than in our Galaxy and it is influenced by strong
galactic winds. Our predictions are in very good agreement with the available
observational data. The time-delay model for the galactic chemical enrichment
coupled with different histories of star formation in different galaxies allow
us to succesfully interpret the observed differences in the abundance ratios of
s- and r- process elements, as well as of $\alpha$-elements in dSphs and in the
Milky Way. These differences strongly suggest that the main stellar populations
of these galaxies could not have had a common origin and, consequently, that
the progenitors of local dSphs might not be the same objects as the building
blocks of our Galaxy.",0802.3368v1
2008-08-29,Mass measurements in the vicinity of the rp-process and the nu p-process paths with JYFLTRAP and SHIPTRAP,"The masses of very neutron-deficient nuclides close to the astrophysical rp-
and nu p-process paths have been determined with the Penning trap facilities
JYFLTRAP at JYFL/Jyv\""askyl\""a and SHIPTRAP at GSI/Darmstadt. Isotopes from
yttrium (Z = 39) to palladium (Z = 46) have been produced in heavy-ion
fusion-evaporation reactions. In total 21 nuclides were studied and almost half
of the mass values were experimentally determined for the first time: 88Tc,
90-92Ru, 92-94Rh, and 94,95Pd. For the 95Pdm, (21/2^+) high-spin state, a first
direct mass determination was performed. Relative mass uncertainties of
typically $\delta m / m = 5 \times 10^{-8}$ were obtained. The impact of the
new mass values has been studied in nu p-process nucleosynthesis calculations.
The resulting reaction flow and the final abundances are compared to those
obtained with the data of the Atomic Mass Evaluation 2003.",0808.4065v1
2009-10-05,The Hamburg/ESO R-process Enhanced Star survey (HERES) IV. Detailed abundance analysis and age dating of the strongly r-process enhanced stars CS 29491-069 and HE 1219-0312,"We report on a detailed abundance analysis of two strongly r-process
enhanced, very metal-poor stars newly discovered in the HERES project, CS
29491-069 ([Fe/H]=-2.51, [r/Fe]=+1.1) and HE 1219-0312 ([Fe/H]=-2.96,
[r/Fe]=+1.5). The analysis is based on high-quality VLT/UVES spectra and MARCS
model atmospheres. We detect lines of 15 heavy elements in the spectrum of CS
29491-069, and 18 in HE 1219-0312; in both cases including the Th II 4019 {\AA}
line. The heavy-element abundance patterns of these two stars are mostly
well-matched to scaled solar residual abundances not formed by the s-process.
We also compare the observed pattern with recent high-entropy wind (HEW)
calculations, which assume core-collapse supernovae of massive stars as the
astrophysical environment for the r-process, and find good agreement for most
lanthanides. The abundance ratios of the lighter elements strontium, yttrium,
and zirconium, which are presumably not formed by the main r-process, are
reproduced well by the model. Radioactive dating for CS 29491-069 with the
observed thorium and rare-earth element abundance pairs results in an average
age of 9.5 Gyr, when based on solar r-process residuals, and 17.6 Gyr, when
using HEW model predictions. Chronometry seems to fail in the case of HE
1219-0312, resulting in a negative age due to its high thorium abundance. HE
1219-0312 could therefore exhibit an overabundance of the heaviest elements,
which is sometimes called an ""actinide boost"".",0910.0707v1
2009-11-23,A Two Micron All-Sky Survey View of the Sagittarius Dwarf Galaxy: VI. s-Process and Titanium Abundance Variations Along the Sagittarius Stream,"We present high-resolution spectroscopic measurements of the abundances of
titanium (Ti), yttrium (Y) and lanthanum (La) for M giant candidates of the
Sagittarius (Sgr) dwarf spheroidal (dSph) + tidal tail system pre-selected on
the basis of position and radial velocity. The majority of these stars show
peculiar abundance patterns compared to those of nominal Milky Way (MW) stars.
The overall [Ti/Fe], [Y/Fe], [La/Fe] and [La/Y] patterns with [Fe/H] of the Sgr
stream plus Sgr core do resemble those seen in the Large Magellanic Cloud (LMC)
and other dSphs, only shifted [Fe/H] by ~+0.4 from the LMC and by ~+1 dex from
the other dSphs; these relative shifts reflect the faster and/or more efficient
chemical evolution of Sgr compared to the other satellites, and show that Sgr
has had an enrichment history more like the LMC than the other dSphs. By
tracking the evolution of the abundance patterns along the Sgr stream we can
follow the time variation of the chemical make-up of dSph stars donated to the
MW halo by Sgr. This evolution demonstrates that while the bulk of the stars
currently in the Sgr dSph are quite unlike those of the MW halo, an increasing
number of stars farther along the Sgr stream have abundances like MW halo
stars, a trend that shows clearly how the MW halo could have been contributed
by present day satellite galaxies even if the present chemistry of those
satellites is now different from typical halo field stars. Finally, we analyze
the chemical abundances of a moving group of M giants among the Sgr leading arm
stars at the North Galactic Cap, but having radial velocities unlike the
infalling Sgr leading arm debris there. Through use of ""chemical
fingerprinting"", we conclude that these northern hemisphere M giants also are
Sgr stars, likely trailing arm debris overlapping the leading arm in the north.",0911.4364v1
2010-09-22,The Ubiquity of the Rapid Neutron-Capture Process,"To better characterize the abundance patterns produced by the r-process, we
have derived new abundances or upper limits for the heavy elements zinc (Zn),
yttrium (Y), lanthanum (La), europium (Eu), and lead (Pb). Our sample of 161
metal-poor stars includes new measurements from 88 high resolution and high
signal-to-noise spectra obtained with the Tull Spectrograph on the 2.7m Smith
Telescope at McDonald Observatory, and other abundances are adopted from the
literature. We use models of the s-process in AGB stars to characterize the
high Pb/Eu ratios produced in the s-process at low metallicity, and our new
observations then allow us to identify a sample of stars with no detectable
s-process material. In these stars, we find no significant increase in the
Pb/Eu ratios with increasing metallicity. This suggests that s-process material
was not widely dispersed until the overall Galactic metallicity grew
considerably, perhaps even as high as [Fe/H]=-1.4. We identify a dispersion of
at least 0.5 dex in [La/Eu] in metal-poor stars with [Eu/Fe]<+0.6 attributable
to the r-process, suggesting that there is no unique ""pure"" r-process elemental
ratio among pairs of rare earth elements. We confirm earlier detections of an
anti-correlation between Y/Eu and Eu/Fe bookended by stars strongly enriched in
the r-process (e.g., CS 22892-052) and those with deficiencies of the heavy
elements (e.g., HD 122563). We can reproduce the range of Y/Eu ratios using
simulations of high-entropy neutrino winds of core-collapse supernovae that
include charged-particle and neutron-capture components of r-process
nucleosynthesis. The heavy element abundance patterns in most metal-poor stars
do not resemble that of CS 22892-052, but the presence of heavy elements such
as Ba in nearly all metal-poor stars without s-process enrichment suggests that
the r-process is a common phenomenon.",1009.4496v1
2012-05-28,The Chemical composition of the post-AGB F-supergiant CRL 2688,"We present an analysis of a high resolution (R~50,000) optical spectrum of
the central region of the proto-planetary nebula CRL 2688. This object is
thought to have recently moved off the AGB, and display abundance patterns of
CNO and heavy elements that can provide us with important clues to understand
the nucleosynthesis, dredge-up and mixing experienced by the envelope of the
central star during its AGB stage of evolution. The analysis of the molecular
features, presumably originated from the circumstellar matter provides further
constraints on the chemistry and velocity of the expanding shell, expelled as a
consequence of the strong mass loss experienced by the central star. We confirm
that the central star shows a spectrum typical of an F-type supergiant with
Teff=7250 K, log g=0.5 and [Fe/H]=-0.3 dex. We find that the abundance pattern
of this object is characterized by enhancements of Carbon ([C/Fe]=0.6),
Nitrogen ([N/Fe]=1.0) and Na ([Na/Fe]=0.7), similar to other previously known
carbon-rich post-AGB stars. Yttrium is also enhanced while the [Ba/Y] ratio is
very low (-1.0), indicating that only the light s-process elements are
enhanced. The Zinc abundance is found to be normal, [Zn/Fe]=0.0, suggesting
that there is no depletion of refractory elements. The Halpha, Na I and K I
resonance lines show prominent emission components, whose helio-centric radial
velocities are offsetted by -41 km/s relative to the photospheric
metal-absorption lines. The molecular features of C_2 and CN also show emission
components, whose velocities are consistent with the emission components of the
Halpha, Na I, and K I lines. On the other hand, their absorption components are
more highly blue shifted than the corresponding emission components, which
suggests that the regions where the emission and absorption components arise
are expanding at different velocities.",1205.6101v4
2013-03-28,Non-monotonic residual entropy in diluted spin ice: a comparison between Monte Carlo simulations of diluted dipolar spin ice models and experimental results,"Spin ice materials, such as Dy2Ti2O7 and Ho2Ti2O7, have been the subject of
much interest for over the past fifteen years. Their low temperature strongly
correlated state can be mapped onto the proton disordered state of common water
ice and, consequently, spin ices display the same low temperature residual
Pauling entropy as water ice. Interestingly, it was found in a previous study
[X. Ke {\it et. al.} Phys. Rev. Lett. {\bf 99}, 137203 (2007)] that, upon
dilution of the magnetic rare-earth ions (Dy^{3+} and Ho^{3+}) by non-magnetic
Yttrium (Y^{3+}) ions, the residual entropy depends {\it non-monotonically} on
the concentration of Y^{3+} ions. In the present work, we report results from
Monte Carlo simulations of site-diluted microscopic dipolar spin ice models
(DSIM) that account quantitatively for the experimental specific heat
measurements, and thus also for the residual entropy, as a function of
dilution, for both Dy2Ti2O7 and Ho2Ti2O7. The main features of the dilution
physics displayed by the magnetic specific heat data are quantitatively
captured by the diluted DSIM up to, and including, 85% of the magnetic ions
diluted (x=1.7). The previously reported departures in the residual entropy
between Dy2Ti2O7 versus Ho2Ti2O7, as well as with a site-dilution variant of
Pauling's approximation, are thus rationalized through the site-diluted DSIM.
For 90% (x=1.8) and 95% (x=1.9) of the magnetic ions diluted, we find a
significant discrepancy between the experimental and Monte Carlo specific heat
results. We discuss some possible reasons for this disagreement.",1303.7240v1
2015-07-21,Testing and Performance of UFFO Burst Alert & Trigger Telescope,"The Ultra-Fast Flash Observatory pathfinder (UFFO-p) is a new space mission
dedicated to detect Gamma-Ray Bursts (GRBs) and rapidly follow their afterglows
in order to provide early optical/ultraviolet measurements. A GRB location is
determined in a few seconds by the UFFO Burst Alert & Trigger telescope (UBAT)
employing the coded mask imaging technique and the detector combination of
Yttrium Oxyorthosilicate (YSO) scintillating crystals and multi-anode
photomultiplier tubes. The results of the laboratory tests of UBAT's
functionality and performance are described in this article. The detector
setting, the pixel-to-pixel response to X-rays of different energies, the
imaging capability for <50 keV X-rays, the localization accuracy measurements,
and the combined test with the Block for X-ray and Gamma-Radiation Detection
(BDRG) scintillator detector to check the efficiency of UBAT are all described.
The UBAT instrument has been assembled and integrated with other equipment on
UFFO-p and should be launched on board the Lomonosov satellite in late-2015.",1507.05696v1
2016-11-16,Spectral hole lifetimes and spin population relaxation dynamics in neodymium-doped yttrium orthosilicate,"We present a detailed study of the lifetime of optical spectral holes due to
population storage in Zeeman sublevels of Nd$^{3+}$:Y$_2$SiO$_5$. The lifetime
is measured as a function of magnetic field strength and orientation,
temperature and Nd$^{3+}$ doping concentration. At the lowest temperature of 3
K we find a general trend where the lifetime is short at low field strengths,
then increases to a maximum lifetime at a few hundreds of mT, and then finally
decays rapidly for high field strengths. This behaviour can be modelled with a
relaxation rate dominated by Nd$^{3+}$-Nd$^{3+}$ cross relaxation at low fields
and spin lattice relaxation at high magnetic fields. The maximum lifetime
depends strongly on both the field strength and orientation, due to the
competition between these processes and their different angular dependencies.
The cross relaxation limits the maximum lifetime for concentrations as low as
30 ppm of Nd$^{3+}$ ions. By decreasing the concentration to less than 1 ppm we
could completely eliminate the cross relaxation, reaching a lifetime of 3.8 s
at 3~K. At higher temperatures the spectral hole lifetime is limited by the
magnetic-field independent Raman and Orbach processes. In addition we show that
the cross relaxation rate can be strongly reduced by creating spectrally large
holes of the order of the optical inhomogeneous broadening. Our results are
important for the development and design of new rare-earth-ion doped crystals
for quantum information processing and narrow-band spectral filtering for
biological tissue imaging.",1611.05444v1
2017-06-20,Abundance analysis of a CEMP-no star in the Carina dwarf spheroidal galaxy,"Carbon-enhanced metal-poor (CEMP) stars bear important imprints of the early
chemical enrichment of any stellar system. While these stars are known to exist
in copious amounts in the Milky Way halo, detailed chemical abundance data from
the faint dwarf spheroidal (dSph) satellites are still sparse, although the
relative fraction of these stars increases with decreasing metallicity. Here,
we report the abundance analysis of a metal-poor ([Fe/H]=$-2.5$ dex),
carbon-rich ([C/Fe]=1.4 dex) star, ALW-8, in the Carina dSph using
high-resolution spectroscopy obtained with the ESO/UVES instrument. Its
spectrum does not indicate any over-enhancements of neutron capture elements.
Thus classified as a CEMP-no star, this is the first detection of this kind of
star in Carina. Another of our sample stars, ALW-1, is shown to be a CEMP-$s$
star, but its immediate binarity prompted us to discard it from a detailed
analysis. The majority of the 18 chemical elements we measured are typical of
Carina's field star population and also agree with CEMP stars in other dSph
galaxies. Similar to the only known CEMP-no star in the Sculptor dSph and the
weak-$r$-process star HD 122563, the lack of any strong barium-enhancement is
accompanied by a moderate overabundance in yttrium, indicating a weak
$r$-process activity. The overall abundance pattern confirms that, also in
Carina, the formation site for CEMP-no stars has been affected by both faint
supernovae and by standard core collapse supernovae. Whichever process was
responsible for the heavy element production in ALW-8 must be a ubiquitous
source to pollute the CEMP-no stars, acting independently of the environment
such as in the Galactic halo or in dSphs.",1706.06599v1
2018-02-22,"Super-Solar Metallicity Stars in the Galactic Center Nuclear Star Cluster: Unusual Sc, V, and Y Abundances","We present adaptive-optics assisted near-infrared high-spectral resolution
observations of late-type giants in the nuclear star cluster of the Milky Way.
The metallicity and elemental abundance measurements of these stars offer us an
opportunity to understand the formation and evolution of the nuclear star
cluster. In addition, their proximity to the supermassive black hole ($\sim
0.5$ pc) offers a unique probe of the star formation and chemical enrichment in
this extreme environment. We observed two stars identified by medium
spectral-resolution observations as potentially having very high metallicities.
We use spectral-template fitting with the PHOENIX grid and Bayesian inference
to simultaneously constrain the overall metallicity, [M/H], alpha-element
abundance [$\alpha$/Fe], effective temperature, and surface gravity of these
stars. We find that one of the stars has very high metallicity ([M/H] $> 0.6$)
and the other is slightly above solar metallicity. Both Galactic center stars
have lines from scandium (Sc), vanadium (V), and yttrium (Y) that are much
stronger than allowed by the PHOENIX grid. We find, using the spectral
synthesis code Spectroscopy Made Easy, that [Sc/Fe] may be an order of
magnitude above solar. For comparison, we also observed an empirical calibrator
in NGC6791, the highest metallicity cluster known ([M/H] $\sim 0.4$). Most
lines are well matched between the calibrator and the Galactic center stars,
except for Sc, V, and Y, which confirms that their abundances must be
anomalously high in these stars. These unusual abundances, which may be a
unique signature of nuclear star clusters, offer an opportunity to test models
of chemical enrichment in this region.",1802.08270v2
2019-11-01,Which oxidation state of uranium and thorium as point defects in xenotime is favorable?,"Relativistic study of xenotime, YPO$_4$, containing atoms thorium and uranium
as point defects is performed in the framework of cluster model with using the
compound-tunable embedding potential (CTEP) method proposed by us recently. The
Y-(PO$_4$)$_6$-Y'$_{22}$-O'$_{104}$ cluster for xenotime is considered, in
which central part, [Y-(PO$_4$)$_6$]$^{-15}$, is the main cluster, whereas
outermost 22 atoms of yttrium and 104 atoms of oxygen are treated as its
environment and compose electron-free CTEP with the total charge of $+15$. The
P and O atoms of the orthophosphate groups nearest to the central Y atom are
treated at all-electron level. The central Y, its substitutes, Th and U,
together with environmental Y atoms are described within different versions of
the generalized relativistic pseudopotential method. Correctness of our cluster
and CTEP models, constructed in the paper, is justified by comparing the Y-O
and P-O bond lengths with corresponding periodic structure values of the \ypo4
crystal, both experimental and theoretical. Using this cluster model, chemical
properties of solitary point defects, X = U, Th, in xenotime are analyzed. It
has been shown that the oxidation state ${+3}$ is energetically more profitable
than ${+4}$ not only for thorium but for uranium as well ($\Delta E \approx 5$
eV) despite the notably higher ionic radius of U$^{+3}$ compared to Y$^{+3}$,
whereas ionic radii of U$^{+4}$ and Y$^{+3}$ are close. This leads to notable
local deformation of crystal geometry around the U$^{+3}$ impurity in xenotime
and contradicts to widespread opinion about favorite oxidation state of uranium
in such kind of minerals.",1911.00365v3
2020-07-17,"Crystalline and magnetic structures, magnetization, heat capacity and anisotropic magnetostriction effect in a yttrium-chromium oxide","We have studied a nearly stoichiometric insulating
Y$_{0.97(2)}$Cr$_{0.98(2)}$O$_{3.00(2)}$ single crystal by performing
measurements of magnetization, heat capacity, and neutron diffraction. Albeit
that the YCrO$_3$ compound behaviors like a soft ferromagnet with a coersive
force of $\sim$ 0.05 T, there exist strong antiferromagnetic (AFM) interactions
between Cr$^{3+}$ spins due to a strongly negative paramagnetic Curie-Weiss
temperature, i.e., -433.2(6) K. The coexistence of ferromagnetism and
antiferromagnetism may indicate a canted AFM structure. The AFM phase
transition occurs at $T_\textrm{N} =$ 141.5(1) K, which increases to
$T_\textrm{N}$(5T) = 144.5(1) K at 5 T. Within the accuracy of the present
neuron-diffraction studies, we determine a G-type AFM structure with a
propagation vector \textbf{k} = (1 1 0) and Cr$^{3+}$ spin directions along the
crystallographic \emph{c} axis of the orthorhombic structure with space group
\emph{Pnma} below $T_\textrm{N}$. At 12 K, the refined moment size is 2.45(6)
$\mu_\textrm{B}$, $\sim$ 82\% of the theoretical saturation value 3
$\mu_\textrm{B}$. The Cr$^{3+}$ spin interactions are probably two-dimensional
Ising like within the reciprocal (1 1 0) scattering plane. Below
$T_\textrm{N}$, the lattice configuration (\emph{a}, \emph{b}, \emph{c}, and
\emph{V}) deviates largely downward from the Gr$\ddot{\textrm{u}}$neisen law,
displaying an anisotropic magnetostriction effect and a magnetoelastic effect.
Especially, the sample contraction upon cooling is enhanced below the AFM
transition temperature. There is evidence to suggest that the actual
crystalline symmetry of YCrO$_3$ compound is probably lower than the currently
assumed one. Additionally, we compared the $t_{2\textrm{g}}$ YCrO$_3$ and the
$e_\textrm{g}$ La$_{7/8}$Sr$_{1/8}$MnO$_3$ single crystals for a further
understanding of the reason for the possible symmetry lowering.",2007.08985v2
2020-10-01,Yttrium-90 TOF-PET based EUD predicts response post liver radioembolizations using standard manufacturer reconstruction parameters,"Purpose: Explaining why 90Y TOF-PET based equivalent uniform dose (EUD) using
standard FDG reconstruction parameters has been shown to predict response.
  Methods: The hot rods insert of a Jaszczak deluxe phantom was partially
filled with a 2.65 GBq 90Y - 300ml DTPA water solution resulting in a 100 Gy
mean absorbed dose in the 6 sectors. A two bed 20min/position acquisition was
performed on a 550ps- and on a 320ps- TOF-PET/CT and reconstructed with
standard FDG reconstruction parameters, without and with additional filtering.
The whole procedure was repeated on both PET after adding a 300ml of water
(50Gy setup). The phantom was acquired again after decay by a factor 10 (5Gy
setup), but with 200min per bed position. For comparison the phantom was also
acquired with 18F activity corresponding to a clinical FDG whole body
acquisition.
  Results: The 100Gy-setup provided hot rod sectors image almost as good as in
18F phantom. However, despite acquisition time compensation the 5Gy-setup
provides much lower quality imaging. TOF-PET based sectors EUDs for the three
large rod sectors were in agreement with the actual EUDs computed with a
radiosensitivity 0.021Gy-1 well in the range observed in external beam
radiotherapy (EBRT), i.e. 0.01-0.04Gy-1. This agreement explains the
reunification of the dose-response relationships of the glass and resin spheres
in HCC using the TOF-PET based EUD. Additional filtering reduced the EUDs
agreement quality.
  Conclusions: Standard FDG reconstruction parameters are suitable in TOF-PET
post 90Y liver radioembolization for accurate tumor EUD computation. The
present results clearly rules out the use of low specific activity phantom
studies to optimize reconstruction parameters.",2010.00303v1
2021-04-13,Selectivity in yttrium manganese oxide synthesis via local chemical potentials in hyperdimensional phase space,"In sharp contrast to molecular synthesis, materials synthesis is generally
presumed to lack selectivity. The few known methods of designing selectivity in
solid-state reactions have limited scope, such as topotactic reactions or
strain stabilization. This contribution describes a general approach for
searching large chemical spaces to identify selective reactions. This novel
approach explains the ability of a nominally ""innocent"" Na$_2$CO$_3$ precursor
to enable the metathesis synthesis of single-phase Y$_2$Mn$_2$O$_7$ -- an
outcome that was previously only accomplished at extreme pressures and which
cannot be achieved with closely related precursors of Li$_2$CO$_3$ and
K$_2$CO$_3$. By calculating the required change in chemical potential across
all possible reactant-product interfaces in an expanded chemical space
including Y, Mn, O, alkali metals, and halogens, using thermodynamic parameters
obtained from density functional theory calculations, we identify reactions
that minimize the thermodynamic competition from intermediates. In this manner,
only the Na-based intermediates minimize the distance in the hyperdimensional
chemical potential space to Y$_2$Mn$_2$O$_7$, thus providing selective access
to a phase which was previously thought to be metastable. Experimental evidence
validating this mechanism for pathway-dependent selectivity is provided by
intermediates identified from in situ synchrotron-based crystallographic
analysis. This approach of calculating chemical potential distances in
hyperdimensional compositional spaces provides a general method for designing
selective solid-state syntheses that will be useful for gaining access to
metastable phases and for identifying reaction pathways that can reduce the
synthesis temperature, and cost, of technological materials.",2104.05986v3
2021-07-12,The systematic study on the stability and superconductivity of Y-Mg-H compounds under high pressure,"Motivated by recent discovery of yttrium-based high-temperature ternary
superconducting hydrides (e.g., CaYH$_{12}$, LaYH$_{12}$, and ScYH$_{6}$), we
have employed evolutionary algorithm and first-principles calculations to
comprehensively examine the structural stability and superconductivity of the
YMgH$_{x}$ system at high pressure. The hydrogen content $x$ and the pressure
are both important factors in the stability of these candidate structures. We
find that the stability of hydrogen-rich materials frequently necessitates
higher pressure. For instance, the pressures to stabilize $P4/mmm$-YMgH$_{8}$
and $Cmmm$-YMgH$_{12}$ are both more than 250 GPa. Hydrogen-less materials,
such as $I4_{1}/amd$-YMgH$_{2}$ and $P6_{3}/mmc$-YMgH$_{3}$, can be stable at
pressures as low as 100 GPa. In addition, we find a metastable structure for
YMgH$_{6}$ with the same space group as the $P4/mmm$-YMgH$_{8}$. A metastable
sodalite-like face-centered cubic (FCC) structure is also found in YMgH$_{12}$.
These four clathrate structures of $P4/mmm$-YMgH$_{6}$, $P4/mmm$-YMgH$_{8}$,
$Cmmm$-YMgH$_{12}$, and $Fd\bar{3}m$-YMgH$_{12}$ is made up of H14, H18, H24,
and H24 cages, respectively, in which the H-H pair exhibits weak covalent
bonding. According to phonon calculations, $P4/mmm$-YMgH$_{6}$ and
$P4/mmm$-YMgH$_{8}$ require a pressure of 300 GPa to maintain dynamic
stability, however $Cmmm$-YMgH$_{12}$ and $Fd\bar{3}m$-YMgH$_{12}$ can maintain
dynamic stability at pressures of 200 GPa and 250 GPa, respectively.
Electron-phonon coupling calculations indicate that they might be potential
high-temperature superconductors, with superconductivity intimately linked to
the H cage structure. The sodalite structure $Fd\bar{3}m$-YMgH$_{12}$ has a
$T_\mathrm{c}$ value of 190 K and a strong electron-phonon coupling constant of
2.18.",2107.05498v2
2021-10-27,Orbital and atmospheric parameters of two wide O-type subdwarf binaries: BD$-$11$^{\rm{o}}$162 and Feige 80,"There are 23 long-period binary systems discovered to date that contain a
B-type hot subdwarf(sdB) whose orbital parameters have been fully solved. They
evolve into O-type subdwarfs (sdO) once the helium burning transitions from the
core to the He shell. Their study will help constraint parameters on the
formation and evolution of these binaries and explain some of their puzzling
features. In this study, we aim to solve orbital and atmospheric parameters of
two long-period sdO binaries and, for the first time, investigate the chemical
composition of their main-sequence (MS) companions. HERMES high-resolution
spectra are used to obtain radial velocities and solve their orbits. The Grid
Search in Stellar Parameter code (GSSP) is used to derive the atmospheric
parameters and photospheric chemical abundances of the MS companions. Stellar
evolution models (MIST) are fitted to the companion atmospheric parameters to
derive masses. In the bimodal period-eccentricity diagram, the orbital
parameters indicate that Feige 80 matches the same correlation as the majority
of the systems. The analysis suggests that Feige 80 has a canonical subdwarf
mass and followed a standard formation channel. However, BD-11$^{\rm{o}}$162 is
an exceptional system with a lower mass. It also shows a carbon overabundance,
which could be caused by a higher progenitor mass. The yttrium depletion in
both MS companions could indicate the existence of a circumbinary disk in these
systems' pasts. Nevertheless, a chemical analysis of a larger sample is
necessary to draw strong conclusions.",2110.14339v1
2021-10-29,Sr-Doped Molecular Hydrogen: Synthesis and Properties of SrH$_{22}$,"Recently, several research groups announced reaching the point of
metallization of hydrogen above 400 GPa. Following the mainstream of extensive
investigations of compressed polyhydrides, in this work we demonstrate that
small (4 atom %) doping of molecular hydrogen by strontium leads to a dramatic
reduction in the metallization pressure to about 200 GPa. Studying the
high-pressure chemistry of the Sr-H system at 56-180 GPa, we observed the
formation of several previously unknown compounds: C2/m-Sr$_3$H$_{13}$,
pseudocubic SrH$_6$, SrH$_9$ with cubic F-43m Sr sublattice, and
pseudotetragonal P1-SrH$_{22}$, the metal hydride with the highest hydrogen
content discovered so far. Unlike Ca and Y, strontium forms molecular
semiconducting polyhydrides, whereas calcium and yttrium polyhydrides are
high-Tc superconductors with an atomic H sublattice. The latter phase,
SrH$_{22}$ or Sr$_{0.04}$H$_{0.96}$, may be considered as a convenient model of
the consistent bandgap closure and metallization of hydrogen. Using the
impedance measurements in diamond anvil cells at 300-440 K, we estimated the
direct bandgap of the Pm-3n-like compound P1-SrH$_6$ to be 0.44-0.51 eV at 150
GPa, and its metallization pressure to be 220 GPa. Together with the machine
learning interatomic potentials, the impedance spectroscopy allowed us to
estimate the diffusion coefficients of hydrogen D$_H$ = 1.0-2.8 E-10 m$^2$/s in
SrH$_6$ and 1.2-2.1 E-9 m$^2$/s in P1-SrH$_{22}$ at 500-600 K.",2110.15628v2
2021-12-04,Hole- and electron-injection driven phase transitions in transition metal dichalcogenides and beyond: A unified understanding,"The phase transitions among polymorphic two-dimensional (2D) transition metal
dichalcogenides (TMDs) have attracted increasing attention for their potential
in enabling distinct functionalities in the same material for making integrated
devices. Electron-injection to TMDs has been proved to be a feasible way to
drive structural phase transition from the semiconducting H-phase to the
semimetal dT-phase. In this contribution, based on density-functional theory
(DFT) calculations, firstly we demonstrate that hole-injection drives the
transition of the H-phase more efficiently to the metallic T-phase than to the
semimetallic dT-phase for group VI-B TMDs (MoS2, WS2, and MoSe2, etc.). The
origin can be attributed to the smaller work function of the T-phase than that
of the dT-phase. Our work function analysis can distinguish the T and dT phases
quantitatively while it is challenging for the commonly used crystal field
splitting analysis. In addition, our analysis provides a unified understanding
for both hole- and electron-injection induced phase transitions for 2D
materials beyond TMDs, such as the newly synthesized MoSi2N4 family. Moreover,
the hole-driven T-phase transition mechanism can explain the recent experiment
of WS2 phase transition by hole-doping with yttrium (Y) atoms. Using 1/3
Y-doped WS2 and MoSe2 as examples, we show that the Mo and W valency increases
to 5+. These above findings open up an avenue to obtain the metallic T-phase,
which expands the possible stable phases of 2D materials.",2112.02319v1
2022-05-30,Comparative characterization study of LYSO:Ce crystals for timing applications,"Cerium-doped Lutetium-Yttrium Oxyorthosilicate (LYSO:Ce)is one of the most
widely used Cerium-doped Lutetium based scintillation crystals. Initially
developed for medical detectors it rapidly became attractive for High Energy
Particle Physics (HEP) applications, especially in the frame of high luminosity
particle colliders. In this paper, a comprehensive and systematic study of
LYSO:Ce ($[Lu_{(1-x)}Y_x]_2SiO_5$:$Ce$) crystals is presented. It involves for
the first time a large number of crystal samples (180) of the same size from a
dozen of producers.The study consists of a comparative characterization of
LYSO:Ce crystal products available on the market by mechanical, optical and
scintillation measurements and aims specifically, to investigate key parameters
of timing applications for HEP.",2205.14890v2
2022-06-21,Is [Y/Mg] a Reliable Age Diagnostic for FGK Stars?,"Current spectroscopic surveys are producing large catalogs of chemical
abundances for stars of all types. The yttrium to magnesium ratio, [Y/Mg], has
emerged as a candidate age indicator for solar twins in the local stellar
neighborhood. However, it is unclear whether it is a viable age diagnostic for
more diverse stellar types, so we investigate [Y/Mg] as an age indicator for
the FGK-type planet host stars observed by $Kepler$. We find that the [Y/Mg]
""Clock"" is most precise for solar twins, with a [Y/Mg]/Age slope of $m$ =
$-$0.0370 $\pm$ 0.0071 dex/Gyr and $\sigma_{\mathrm{Age}}$ = 2.6 Gyr. We
attribute the lower precision compared to literature results to non-solar twins
contaminating our solar twin sample and recommend a 1.5 Gyr systematic
uncertainty for stellar ages derived with any [Y/Mg]-Age relation. We also
analyzed the [Y/Mg] Clock as a function of $T_{\mathrm{eff}}$, $\log g$, and
metallicity individually and find no strong trends, but compute statistically
significant [Y/Mg]-Age relations for subsamples defined by ranges in
$T_{\mathrm{eff}}$, $\log g$, and metallicity. Finally, we compare [Y/Mg] and
rotation ages and find statistically similar trends as for isochrone ages,
although we find that rotation ages perform better for GK dwarfs while
isochrones perform better for FG subgiants. We conclude that the [Y/Mg] Clock
is most precise for solar twins and analogs but is also a useful age diagnostic
for FGK stars.",2206.10624v2
2022-09-14,Spectroscopic r-Process Abundance Retrieval for Kilonovae I: The Inferred Abundance Pattern of Early Emission from GW170817,"Freshly-synthesized r-process elements in kilonovae ejecta imprint absorption
features on optical spectra, as observed in the GW170817 binary neutron star
merger. These spectral features encode insights into the physical conditions of
the r-process and the origins of the ejected material, but associating features
with particular elements and inferring the resultant abundance pattern is
computationally challenging. We introduce Spectroscopic r-Process Abundance
Retrieval for Kilonovae (SPARK), a modular framework to perform Bayesian
inference on kilonova spectra with the goals of inferring elemental abundance
patterns and identifying absorption features at early times. SPARK inputs an
atomic line list and abundance patterns from reaction network calculations into
the TARDIS radiative transfer code. It then performs fast Bayesian inference on
observed kilonova spectra by training a Gaussian process surrogate for the
approximate posteriors of kilonova ejecta parameters, via active learning. We
use the spectrum of GW170817 at 1.4 days to perform the first inference on a
kilonova spectrum, and recover a complete abundance pattern. Our inference
shows that this ejecta was generated by an r-process with either (1) high
electron fraction Y_e ~ 0.35 and high entropy s/k_B ~ 25, or, (2) a more
moderate Y_e ~ 0.30 and s/k_B ~ 14. These parameters are consistent with a
shocked, polar dynamical component, and a viscously-driven outflow from a
remnant accretion disk, respectively. We also recover previous identifications
of strontium absorption at ~8000 AA, and tentatively identify yttrium and/or
zirconium at < 4500 AA. Our approach will enable computationally-tractable
inference on the spectra of future kilonovae discovered through multi-messenger
observations.",2209.06951v2
2022-11-23,Evidence for centrosymmetry breaking and multiferroic properties in the A-site ordered quadruple perovskite YMn$_3$Mn$_4$O$_{12}$,"By means of single-crystal X-ray diffraction we have revealed the breaking of
centrosymmetry when lowering the temperature under T$_s$ = 200 K concomitantly
with the setting of a commensurate superstructure in the small A-site quadruple
perovskite YMn$_3$Mn$_4$O$_{12}$. This results is in agreement with all data
already reported for this compounds and solve the previous inconsistency about
the Yttrium position. The superstructure is characterized by the appearing of
satellite reflections in the single crystal pattern, consistent with an
I-centered pseudo-orthorhombic commensurate supercell with $a \approx
\sqrt{a_F} = 10.4352(7)$ \AA, $b \approx 2b_F = 14.6049(9)$ \AA, $c \approx
\sqrt{c_F} = 10.6961(7)$ \AA and $\beta = 90.110(3)^\circ$, where F stands for
the ""fundamental"" high-temperature cell ($a_F \approx c_F \approx 7.45$ \AA,
$b_F \approx 7.34$ \AA, and $\beta \approx 90^\circ$). The space-group was
unequivocally found to be Ia, which is non polar, thus allowing for a non-zero
polarization in the material. We then have investigated in detail the
pyrocurrent, transport, dielectric and the DC and AC magnetic properties of
polycrystalline sample of YMn$_3$Mn$_4$O$_{12}$ over a wide temperature range.
These measurements clearly highlight several critical temperatures in the
material and correlation between the different orders: i) the centrosymmetry is
broken at high temperature (T$_S$ = 200K), ii) then the long-range magnetic
order of B-sites occurs at T$_{N,B}$ = 108 K and at this same temperature the
compound enters in an insulating dielectric state. iii) Finally, a remnant
polarization is stabilized concomitantly with a magnetic anomaly at T* = 70 K.
We propose that YMn$_3$Mn$_4$O$_{12}$ is a peculiar magnetic ferroelectric in
which the polar state is driven by short-range magnetic order.",2211.13037v1
2023-04-24,Development of an eReaxFF Force Field for BZY20 Solid Oxide Electrocatalysis,"Electrocatalysis is a catalytic process where the rate of an electrochemical
reaction occurring at the electrode-electrolyte interface can be controlled by
varying the electrical potential. Electrocatalysis can be applied to generate
hydrogen which can be stored for future use in fuel cells for clean
electricity. The use of solid oxide in electrocatalysis specially in hydrogen
evolution reaction is promising. However, further improvements are essential in
order to meet the ever-increasing global energy demand. Improvement of the
performance of these high energy chemical systems is directly linked to the
understanding and improving the complex physical and chemical phenomena and
exchanges that take place at their different interfaces. To enable large length
and time scale atomistic simulations of solid oxide electrocatalysis for
hydrogen generation, we developed an eReaxFF force field for barium zirconate
doped with 20 mol% of yttrium (BZY20). All parameters for the eReaxFF were
optimized to reproduce quantum mechanical (QM) calculations on relevant
condensed phase and cluster systems describing oxygen vacancies, vacancy
migrations, water adsorption, water splitting and hydrogen generation on the
surfaces of the BZY20 solid oxide. Using the developed force field, we
performed zero-voltage molecular dynamics simulations to observe water
adsorption and the eventual hydrogen production. Based on our simulation
results, we conclude that this force field sets a stage for the introduction of
explicit electron concept in order to simulate electron conductivity, electron
leakage and non-zero-voltage effects on hydrogen generation. Overall, we
demonstrate how atomistic-scale simulations can enhance our understanding of
processes at interfaces in solid oxide materials.",2304.14256v1
2023-07-20,Decoding the compositions of four bright $r$-process-enhanced stars,"There has been a concerted effort in recent years to identify the
astrophysical sites of the $r$-process that can operate early in the Galaxy.
The discovery of many $r$-process-enhanced (RPE) stars (especially by the
$R$-process Alliance collaboration) has significantly accelerated this effort.
However, only limited data exist on the detailed elemental abundances covering
the primary neutron-capture peaks. Subtle differences in the structure of the
$r$-process pattern, such as the relative abundances of elements in the third
peak, in particular, are expected to constrain the $r$-process sites further.
Here, we present a detailed elemental-abundance analysis of four bright RPE
stars selected from the HESP-GOMPA survey. Observations were carried out with
the 10-m class telescope Gran Telescopio Canarias (GTC), Spain. The high
spectral signal-to-noise ratios obtained allow us to derive abundances for 20
neutron-capture elements, including the third $r$-process peak element osmium
(Os). We detect thorium (Th) in two stars, which we use to estimate their ages.
We discuss the metallicity evolution of Mg, Sr, Ba, Eu, Os, and Th in $r$-II
and $r$-I stars, based on a compilation of RPE stars from the literature. The
strontium (Sr) abundance trend with respect to europium (Eu) suggests the need
for an additional production site for Sr (similar to several earlier studies);
this requirement could be milder for yttrium (Y) and zirconium (Zr). We also
show that there could be some time delay between $r$-II and $r$-I star
formation, based on the Mg/Th abundance ratios.",2307.10762v1
2023-08-11,NEMA NU 2-2018 performance evaluation of a new generation digital 32-cm axial field-of-view Omni Legend PET-CT,"A NEMA performance evaluation was conducted on the new General Electric (GE)
digital Omni Legend PET-CT system with 32-cm extended field-of-view. This study
marks the introduction of the first-ever commercially available clinical
digital bismuth germanate technology. Testing was performed in accordance with
the NEMA NU2-2018 standard. A comparison was made with the performance of two
other commercial GE scanners with extended fields-of-view. A digital lutetium
yttrium orthosilicate system (Discovery MI - 6 ring) and a non-digital bismuth
germanate system (Discovery IQ). For the Omni assessment, the tangential,
radial, and axial spatial resolutions at 1 cm radial offset were measured as
3.76 mm, 3.73 mm, and 4.25 mm FWHM. The total system sensitivity to a line
source at the center was 44.36 cps/kBq. The peak NECR was 501 kcps at 17.8
kBq/mL. The scatter fraction at NECR peak was 35.48%, and the maximum
count-rate error at and below NEC peak was 5.5%. Sphere contrast recovery
coefficients were from 52% (10 mm) to 93% (37 mm). The system does not use time
of flight; thus, no assessment of timing resolution was made. The PET-CT
co-registration accuracy was 2.4 mm. The performance of the Omni Legend
surpassed that of the Discovery MI on all NEMA tests, except for assessments of
background variability (image noise). Time of flight is associated with
inherent improvements in signal-to-noise ratio. In lieu of time of flight
capabilities, the Omni provides software corrections in the form of a
pre-trained neural network (trained on non-ToF to ToF). With such corrections,
average performance is competitive when compared to ToF systems. Further
validation is required to optimize clinical imaging protocols and
hyperparameters associated with such software corrections and to examine the
effect of non-linear corrections with varying target size, particularly for
real world, clinical scans.",2308.06255v1
2023-08-23,Observational constraints on the origin of the elements. VII. NLTE analysis of Y II lines in spectra of cool stars and implications for Y as a Galactic chemical clock,"Yttrium (Y), a key s-process element, is commonly used in nucleosynthesis
studies and as a Galactic chemical clock when combined with magnesium (Mg). We
study the applicability of the previously assumed LTE line formation assumption
in Y abundance studies of main-sequence and red giant stars, and probe the
impact of NLTE effects on the [Y/Mg] ratio, a proposed stellar age indicator.
We derive stellar parameters, ages, and NLTE abundances of Fe, Mg, and Y for 48
solar analogue stars from high-resolution spectra acquired within the Gaia-ESO
survey. For Y, we present a new NLTE atomic model. We determine a solar NLTE
abundance of A(Y)$_{\rm NLTE}=2.12\pm0.04$ dex, $0.04$ dex higher than LTE.
NLTE effects on Y abundance are modest for optical Y II lines, which are
frequently used in Sun-like stars diagnostics. NLTE has a small impact on the
[Y/Mg] ratio in such stars. For metal-poor red giants, NLTE effects on Y II
lines are substantial, potentially exceeding $+0.5$ dex. For the
Gaia/4MOST/WEAVE benchmark star, HD 122563, we find the NLTE abundance ratio of
[Y/Fe]$_{\rm NLTE}=-0.55\pm0.04$ dex with consistent abundances obtained from
different Y II lines. NLTE has a differential effect on Y abundance diagnostics
in late-type stars. They notably affect Y II lines in red giants and very
metal-poor stars, which are typical Galactic enrichment tracers of
neutron-capture elements. For main-sequence stars, NLTE effects on optical
diagnostic Y II lines remain minimal across metallicities. This affirms the
[Y/Mg] ratio's reliability as a cosmochronometer for Sun-like stars.",2308.12092v1
2023-11-09,"Observational constraints on the origin of the elements. VIII. Constraining the Barium, Strontium and Yttrium chemical evolution in metal-poor stars","Recently Lian et al. (2023), thanks to Gaia-ESO data, studied the chemical
evolution of neutron-capture elements in the regime [Fe/H]>-1. We aim here to
complement this study down to [Fe/H]=-3, and focus on Ba, Y, Sr, and abundance
ratios of [Ba/Y] and [Sr/Y], which give comprehensive views on s-process
nucleosynthesis channels. We measured LTE and NLTE abundances of Ba, Y, and Sr
in 323 Galactic metal-poor stars using high-resolution optical spectra with
high S/N. We used the spectral fitting code TSFitPy, together with 1D model
atmospheres using previously determined LTE and NLTE atmospheric parameters.
The NLTE effects are on the order of -0.1 to ~0.2dex depending on the element.
T he ratio between heavy and light s-process elements [Ba/Y] varies weakly with
[Fe/H] even in the metal-poor regime, consistently with the behavior in the
metal-rich regime. The [Ba/Y] scatter at a given metallicity is larger than the
abundance measurement uncertainties. Homogeneous chemical evolution models with
different yields prescriptions are unable to accurately reproduce the [Ba/Y]
scatter at low-[Fe/H]. Adopting the stochastic chemical evolution model by
Cescutti & Chaippini (2014) allows to reproduce the observed scatter in the
abundance pattern of [Ba/Y] and [Ba/Sr]. With our observations, we rule out the
need for an arbitrary scaling of the r-process contribution as previously
suggested by the model authors. We have showed how important it is to properly
include NLTE effects when measuring chemical abundances, especially in the
metal-poor regime. This work shows that the choice of the Galactic chemical
evolution model (stochastic vs. 1-zone) is key when comparing models to
observations. The upcoming surveys such as 4MOST and WEAVE will deliver high
quality spectra of many thousands of metal-poor stars, and this work gives a
typical case study of what could be achieved with such surveys.",2311.05459v1
2024-02-26,Disorder-induced local strain distribution in Y-substituted TmVO4,"We report an investigation of the effect of substitution of Y for Tm in
$Tm_{1-x}Y_xVO4$ via low-temperature heat capacity measurements, with the
yttrium content $x$ varying from $0$ to $0.997$. Because the Tm ions support a
local quadrupolar (nematic) moment, they act as reporters of the local strain
state in the material, with the splitting of the ion's non-Kramers crystal
field groundstate proportional to the quadrature sum of the in-plane tetragonal
symmetry-breaking transverse and longitudinal strains experienced by each ion
individually. Analysis of the heat capacity therefore provides detailed
insights into the distribution of local strains that arise as a consequence of
the chemical substitution. These local strains suppress long-range quadrupole
order for $x>0.22$, and result in a broad Schottky-like feature for higher
concentrations. Heat capacity data are compared to expectations for a
distribution of uncorrelated (random) strains. For dilute Tm concentrations,
the heat capacity cannot be accounted for by randomly distributed strains,
demonstrating the presence of significant strain correlations between sites.
For intermediate Tm concentrations, these correlations must still exist, but
the data cannot be distinguished from that which would be obtained from a 2D
Gaussian distribution. The cross-over between these limits is discussed in
terms of the interplay of key length scales in the substituted material. The
central result of this work, that local strains arising from chemical
substitution are not uncorrelated, has implications for the range of validity
of theoretical models based on random effective fields that are used to
describe such chemically substituted materials, particularly when electronic
nematic correlations are present.",2402.17049v1
1999-06-03,Transition to Long Range Magnetic Order in the Highly Frustrated Insulating Pyrochlore Antiferromagnet Gd_2Ti_2O_7,"Experimental evidence from measurements of the a.c. and d.c. susceptibility,
and heat capacity data show that the pyrochlore structure oxide, Gd_2Ti_2O_7,
exhibits short range order that starts developing at 30K, as well as long range
magnetic order at $T\sim 1$K. The Curie-Weiss temperature, $\theta_{CW}$ =
-9.6K, is largely due to exchange interactions. Deviations from the Curie-Weiss
law occur below $\sim$10K while magnetic heat capacity contributions are found
at temperatures above 20K. A sharp maximum in the heat capacity at $T_c=0.97$K
signals a transition to a long range ordered state, with the magnetic specific
accounting for only $\sim$ 50% of the magnetic entropy. The heat capacity above
the phase transition can be modeled by assuming that a distribution of random
fields acts on the $^8S_{7/2}$ ground state for Gd$^{3+}$. There is no
frequency dependence to the a.c. susceptibility in either the short range or
long range ordered regimes, hence suggesting the absence of any spin-glassy
behavior. Mean field theoretical calculations show that no long range ordered
ground state exists for the conditions of nearest-neighbor antiferromagnetic
exchange and long range dipolar couplings. At the mean-field level, long range
order at various commensurate or incommensurate wave vectors is found only upon
inclusion of exchange interactions beyond nearest-neighbor exchange and dipolar
coupling. The properties of Gd$_2Ti_2O_7 are compared with other geometrically
frustrated antiferromagnets such as the Gd_3Ga_5O_{12} gadolinium gallium
garnet, RE_2Ti_2O_7 pyrochlores where RE = Tb, Ho and Tm, and Heisenberg-type
pyrochlore such as Y_2Mo_2O_7, Tb_2Mo_2O_7, and spinels such as ZnFe_2O_4",9906043v1
2015-05-09,Solutions of the Two Dimensional Hubbard Model: Benchmarks and Results from a Wide Range of Numerical Algorithms,"Numerical results for ground state and excited state properties (energies,
double occupancies, and Matsubara-axis self energies) of the single-orbital
Hubbard model on a two-dimensional square lattice are presented, in order to
provide an assessment of our ability to compute accurate results in the
thermodynamic limit. Many methods are employed, including auxiliary field
quantum Monte Carlo, bare and bold-line diagrammatic Monte Carlo, method of
dual fermions, density matrix embedding theory, density matrix renormalization
group, dynamical cluster approximation, diffusion Monte Carlo within a fixed
node approximation, unrestricted coupled cluster theory, and multi-reference
projected Hartree-Fock. Comparison of results obtained by different methods
allows for the identification of uncertainties and systematic errors. The
importance of extrapolation to converged thermodynamic limit values is
emphasized. Cases where agreement between different methods is obtained
establish benchmark results that may be useful in the validation of new
approaches and the improvement of existing methods.",1505.02290v2
2017-03-14,Spin-projected matrix product states (SP-MPS): a versatile tool for strongly correlated systems,"We present a new wavefunction ansatz that combines the strengths of spin
projection with the language of matrix product states (MPS) and matrix product
operators (MPO) as used in the density matrix renormalization group (DMRG).
Specifically, spin-projected matrix product states (SP-MPS) are constructed as
$|\Psi^{(N,S,M)}_{SP-MPS}\rangle=\mathcal{P}_S|\Psi_{MPS}^{(N,M)}\rangle$,
where $\mathcal{P}_S$ is the spin projector for total spin $S$ and
$|\Psi_{MPS}^{(N,M)}\rangle$ is an MPS wavefunction with a given particle
number $N$ and spin projection $M$. This new ansatz possesses several
attractive features: (1) It provides a much simpler route to achieve
spin-adaptation (i.e. to create eigenfunctions of $\hat{S}^2$) compared to
explicitly incorporating the non-Abelian SU(2) symmetry into the MPS. In
particular, since the underlying state in the SP-MPS uses only Abelian
symmetries, one does not need the singlet embedding scheme for non-singlet
states, as normally employed in spin-adapted DMRG, to achieve a single
consistent variationally optimized state. (2) Due to the use of
$|\Psi_{MPS}^{(N,M)}\rangle$ as its underlying state, the SP-MPS can be closely
connected to broken symmetry mean-field states. This allows to
straightforwardly generate the large number of broken symmetry guesses needed
to explore complex electronic landscapes in magnetic systems. Further, this
connection can be exploited in the future development of quantum embedding
theories for open-shell systems. (3) The sum of MPOs representation for the
Hamiltonian and spin projector $\mathcal{P}_S$ naturally leads to an
embarrassingly parallel algorithm for computing expectation values and
optimizing SP-MPS. (4) Optimizing SP-MPS belongs to the
variation-after-projection (VAP) class of spin projected theories.",1703.04789v3
2018-07-17,"Ce-doped Gd${}_{3}$Al${}_{2}$Ga${}_{3}$O${}_{12}$ scintillator for compact, effective and high time resolution detector of the fast neutrons","Gadolinium-aluminum-gallium garnet
Gd${}_{3}$Al${}_{2}$Ga${}_{3}$O${}_{12}$:Ce scintillator is demonstrated to be
an excellent scintillation material for detector of fast neutrons for the first
time. Moreover, its application allows to obtain different responses to
neutrons depending on their energy spectrum. This is achieved because the
material, firstly, has high content of Gd, which absorbs neutrons with
following emission of $\gamma$-quanta, and, secondly, detects this radiation
efficiently thanks to high stopping power, fast scintillation kinetics, high
scintillation light yield and good energy resolution. It was shown by
simulation that several characteristic regions could be distinguished in
$\gamma$-quanta pulse height spectra acquired with GAGG:Ce crystal under
neutron irradiation, with energies nearly 90 and 190, and 511 keV; all these
lines have different relative intensities depending on incident neutrons
kinetic energy. This was confirmed by followed measurements with Am-Be neutron
source. Scintillator shows coincidence time resolution better than 200ps
for$\gamma$-quanta of 511 keV energy, what makes it the material of choice to
separate neutrons by time-of-flight technique. Combining of detecting
properties creates prospects to construct compact and fast neutron detector,
capable of detection of each particle individually and registration of its
specific response. This possibility could bring benefits to neutron-based
examination techniques, e.g. utilizing time of flight methods and new
capabilities of accelerator based bright neutron sources.",1807.06390v1
2019-03-21,Quantitative magneto-optical imaging with ferrite garnets,"Magneto-optical imaging is a powerful technique for studying qualitative
features of magnetic flux distributions in superconductors and other magnetic
samples. However, magneto-optical imaging does not automatically return
two-dimensional maps with the actual values of the magnetic field, due to the
non-linear response functions of magneto-optical indicator films and in
practice also non-uniform illumination. A quantitative treatment is needed in
order to achieve such a calibration. After calibration, one can proceed to
deduce the corresponding two-dimensional maps of the current density
distribution from inversion of the Biot-Savart law. While there has been
published a large amount of work on quantitative magneto-optical imaging, the
material is scattered and notation differs significantly between different
authors. These notes originate from parts of the Ph. D. thesis of the author
and collect the most important materials into a unified and updated treatment.
Basic aspects of magnetic flux penetration in superconductors including the
Bean model are reviewed briefly in chapter 1. In chapter 2, the method of
magneto-optical imaging using the Faraday effect is introduced, together with
practical aspects of magneto-optical experiments at low temperatures and the
semi-qualitative technique of RGB addition for checking the reproducibility of
flux patterns. The physics of magneto-optical indicator films and calibration
of magneto-optical images into maps of magnetic field values are discussed in
chapter 3. Next, in chapter 4 the Biot-Savart law and fast Fourier
transformations are discussed before proceeding to inversion of magnetic field
maps into current density maps. Finally, magnetometry with Faraday
magneto-optical imaging is treated. MATLAB codes for several of the discussed
concepts can be found at https://github.com/atlejq/Magneto-optics",1903.09130v1
2019-07-21,A Compton polarimeter using scintillators read out with MPPCs through Citiroc ASIC,"In recent years, a number of purpose-built scintillator-based polarimeters
have studied bright astronomical sources for the first time in the hard X-ray
band (tens to hundreds of keV). The addition of polarimetry can help data
interpretation by resolving model-dependent degeneracies. The typical
instrument approach is that incident X-rays scatter off a plastic scintillator
into an adjacent scintillator cell. In all missions to date, the scintillators
are read out using traditional vacuum tube photo-multipliers (PMTs). The advent
of solid-state PMTs (""silicon PM"" or ""MPPC"") is attractive for space-based
instruments since the devices are compact, robust and require a low bias
voltage. We have characterised the plastic scintillator, EJ-248M, optically
coupled to a multi-pixel photon counter (MPPC) and read out with the Citiroc
ASIC. A light-yield of 1.6 photoelectrons/keV has been obtained, with a low
energy detection threshold of $\lesssim$5 keV at room temperature. We have also
constructed an MPPC-based polarimeter-demonstrator in order to investigate the
feasibility of such an approach for future instruments. Incident X-rays scatter
from a plastic-scintillator bar to surrounding cerium-doped GAGG (Gadolinium
Aluminium Gallium Garnet) scintillators yielding time-coincident signals in the
scintillators. We have determined the polarimetric response of this set-up
using both unpolarised and polarised $\sim$50 keV X-rays. We observe a clear
asymmetry in the GAGG counting rates for the polarised beam. The low-energy
detection threshold in the plastic scintillator can be further reduced using a
coincidence technique. The demonstrated polarimeter design shows promise as a
space-based Compton polarimeter and we discuss ways in which our polarimeter
can be adapted for such a mission.",1907.09030v1
2020-01-14,Ground-state phase diagram of the three-band Hubbard model from density matrix embedding theory,"We determine the ground-state phase diagram of the three-band Hubbard model
across a range of model parameters using density matrix embedding theory. We
study the atomic-scale nature of the antiferromagnetic (AFM) and
superconducting (SC) orders, explicitly including the oxygen degrees of
freedom. All parametrizations of the model display AFM and SC phases, but the
decay of AFM order with doping is too slow compared to the experimental phase
diagram, and further, coexistence of AFM and SC orders occurs in all parameter
sets. The local magnetic moment localizes entirely at the copper sites. The
magnetic phase diagram is particularly sensitive to $\Delta_{pd}$ and $t_{pp}$,
and existing estimates of the charge transfer gap $\Delta_{pd}$ appear too
large in so-called minimal model parametrizations. The electron-doped side of
the phase diagram is qualitatively distinct from hole-doped side and we find an
unusual two-peak structure in the SC in the full model parametrization.
Examining the SC order at the atomic scale, within the larger scale $d_{x^2 -
y^2}$-wave SC pairing order between Cu-Cu and O-O, we also observe a local
$p_{x (y)}$ [or $d_{xz (yz)}$]-symmetry modulation of the pair density on the
Cu-O bonds. Our work highlights some of the features that arise in a three-band
versus one-band picture, the role of the oxygen degrees of freedom in new kinds
of atomic-scale SC orders, and the necessity of re-evaluating current
parametrizations of the three-band Hubbard model.",2001.04951v4
2020-02-28,Recent developments in the PySCF program package,"PYSCF is a Python-based general-purpose electronic structure platform that
both supports first-principles simulations of molecules and solids, as well as
accelerates the development of new methodology and complex computational
workflows. The present paper explains the design and philosophy behind PYSCF
that enables it to meet these twin objectives. With several case studies, we
show how users can easily implement their own methods using PYSCF as a
development environment. We then summarize the capabilities of PYSCF for
molecular and solid-state simulations. Finally, we describe the growing
ecosystem of projects that use PYSCF across the domains of quantum chemistry,
materials science, machine learning and quantum information science.",2002.12531v2
2020-05-21,Emergent magnetic behaviour in the frustrated Yb$_3$Ga$_5$O$_{12}$ garnet,"We report neutron scattering, magnetic susceptibility and Monte Carlo
theoretical analysis to verify the short range nature of the magnetic structure
and spin-spin correlations in a Yb$_3$Ga$_5$O$_{12}$ single crystal. The
quantum spin state of Yb$^{3+}$ in Yb$_3$Ga$_5$O$_{12}$ is verified. The
quantum spins organise into a short ranged emergent director state for T $<$
0.4 K derived from anisotropy and near neighbour exchange. We derive the
magnitude of the near neighbour exchange interactions $0.6\; {\rm K} < J_1 <
0.7\; {\rm K}, J_2 = 0.12$~K and the magnitude of the dipolar exchange
interaction, $D$, in the range $0.18 < D < 0.21$ K. Certain aspects of the
broad experimental dataset can be modelled using a $J_1D$ model with
ferromagnetic near neighbour spin-spin correlations while other aspects of the
data can be accurately reproduced using a $J_1J_2D$ model with
antiferromagnetic near neighbour spin-spin correlation. As such, although we do
not quantify all the relevant exchange interactions we nevertheless provide a
strong basis for the understanding of the complex Hamiltonian required to fully
describe the magnetic state of Yb$_3$Ga$_5$O$_{12}$.",2005.10605v5
2020-08-06,The Ground State Electronic Energy of Benzene,"We report on the findings of a blind challenge devoted to determining the
frozen-core, full configuration interaction (FCI) ground state energy of the
benzene molecule in a standard correlation-consistent basis set of
double-$\zeta$ quality. As a broad international endeavour, our suite of wave
function-based correlation methods collectively represents a diverse view of
the high-accuracy repertoire offered by modern electronic structure theory. In
our assessment, the evaluated high-level methods are all found to qualitatively
agree on a final correlation energy, with most methods yielding an estimate of
the FCI value around $-863$ m$E_{\text{H}}$. However, we find the
root-mean-square deviation of the energies from the studied methods to be
considerable (1.3 m$E_{\text{H}}$), which in light of the acclaimed performance
of each of the methods for smaller molecular systems clearly displays the
challenges faced in extending reliable, near-exact correlation methods to
larger systems. While the discrepancies exposed by our study thus emphasize the
fact that the current state-of-the-art approaches leave room for improvement,
we still expect the present assessment to provide a valuable community resource
for benchmark and calibration purposes going forward.",2008.02678v2
2020-08-26,Waveguide integrated high performance magneto-optical isolators and circulators on silicon nitride platforms,"Optical isolators and circulators are indispensable for photonic integrated
circuits (PICs). Despite of significant progress in silicon-on-insulator (SOI)
platforms, integrated optical isolators and circulators have been rarely
reported on silicon nitride (SiN) platforms. In this paper, we report
monolithic integration of magneto-optical (MO) isolators on SiN platforms with
record high performances based on standard silicon photonics foundry process
and magneto-optical thin film deposition. We successfully grow high quality MO
garnet thin films on SiN with large Faraday rotation up to -5900 deg/cm. We
show a superior magneto-optical figure of merit (FoM) of MO/SiN waveguides
compared to that of MO/SOI in an optimized device design. We demonstrate TM/TE
mode broadband and narrow band optical isolators and circulators on SiN with
high isolation ratio, low cross talk and low insertion loss. In particular, we
observe 1 dB insertion loss and 28 dB isolation ratio in a SiN racetrack
resonator-based isolator at 1570.2 nm wavelength. The low thermo-optic
coefficient of SiN also ensures excellent temperature stability of the device.
Our work paves the way for integration of high performance nonreciprocal
photonic devices on SiN platforms.",2010.01969v1
2021-01-08,A summary on an investigation of GAGG:Ce afterglow emission in the context of future space applications within the HERMES nanosatellite mission,"GAGG:Ce (Cerium-doped Gadolinium Aluminium Gallium Garnet) is a promising new
scintillator crystal. A wide array of interesting features, such as high light
output, fast decay times, almost non-existent intrinsic background and
robustness, make GAGG:Ce an interesting candidate as a component of new
space-based gamma-ray detectors. As a consequence of its novelty, literature on
GAGG:Ce is still lacking on points crucial to its applicability in space
missions. In particular, GAGG:Ce is characterized by unusually high and
long-lasting delayed luminescence. This afterglow emission can be stimulated by
the interactions between the scintillator and the particles of the near-Earth
radiation environment. By contributing to the noise, it will impact the
detector performance to some degree. In this manuscript we summarize the
results of an irradiation campaign of GAGG:Ce crystals with protons, conducted
in the framework of the HERMES-TP/SP (High Energy Rapid Modular Ensemble of
Satellites - Technological and Scientific Pathfinder) mission. A GAGG:Ce sample
was irradiated with 70 MeV protons, at doses equivalent to those expected in
equatorial and sun-synchronous Low-Earth orbits over orbital periods spanning 6
months to 10 years, time lapses representative of satellite lifetimes. We
introduce a new model of GAGG:Ce afterglow emission able to fully capture our
observations. Results are applied to the HERMES-TP/SP scenario, aiming at an
upper-bound estimate of the detector performance degradation due to the
afterglow emission expected from the interaction between the scintillator and
the near-Earth radiation environment.",2101.03945v1
2022-03-29,"Doping effect and Li-ion conduction mechanism of ALi6XO6 (A = K or Rb, and X = pentavalent): A first-principles study","Recent theoretical and experimental evaluations demonstrated that KLi6TaO6 is
a good Li-ion conductor. In this study, the energetics and detailed mechanism
of Li-ion migration, relevant to the point defects of KLi6TaO6, were analyzed
by first-principles calculations. Defect formation energy analysis suggested
that it has limited chemical potential conditions for attaining Li-excess
conditions through doping (substituting tetravalent elements for Ta). The
formation of other native defects, such as Li vacancies, hinders the
stabilization of the dopant and compensates for the interstitial Li. When the
doping is successful, the interactions between the coexisting dopant and
interstitial Li can increase the migration energy barrier of the interstitial
Li. This phenomenon limits the factors responsible for achieving high Li-ion
conductivity in this material. Based on the results of the investigations on
KLi6TaO6, isostructural materials of the form ALi6XO6, with various
combinations of constituent elements A and X, were each screened on the basis
of high stability and low Li-ion migration energy. Twelve structures of the
form (A = K or Rb)Li6XO6 were suggested, of which X was pentavalent. They also
exhibited limited chemical potential conditions for achieving Li-excess
conditions through doping. Combinations of the suggested isostructural oxides
and dopants were identified to reduce the interactions between interstitial Li
and dopant. Some isostructural oxides were doped using Sn and were evaluated
using first-principles molecular dynamics; their Li-ion conductivities at room
temperature were found to be comparable with those of garnet-type Li-ion
conductors.",2203.15384v4
2022-08-10,CLARION2-TRINITY: a Compton-suppressed HPGe and GAGG:Ce-Si-Si array for absolute cross-section measurements with heavy ions,"The design and performance of a new Compton-suppressed HPGe and
charged-particle array, CLARION2-TRINITY, are described. The TRINITY
charged-particle array is comprised of 64 Cerium-doped Gadolinium Aluminium
Gallium Garnet (GAGG:Ce) crystals configured into five rings spanning 7-54
degrees, and two annular silicon detectors that can shadow or extend the
angular coverage to backward angles with minimal $\gamma$-ray attenuation.
GAGG:Ce is a non-hygroscopic, bright, and relatively fast scintillator with a
light distribution well matched to SiPMs. Count rates up to 40 kHz per crystal
are sustainable. Fundamental characteristics of GAGG:Ce are measured and
presented, including light- and heavy-ion particle identification (PID)
capability, pulse-height defects, radiation hardness, and emission spectra. The
CLARION2 array consists of up to 16 Compton-suppressed HPGe Clover detectors
($\approx4\%$ efficiency at 1 MeV) configured into four rings (eight HPGe
crystal rings) using a non-Archimedean geometry that suppresses back-to-back
coincident 511-keV gamma rays. The entire array is instrumented with 100- and
500-MHz (14 bit) waveform digitizers which enable triggerless operation,
pulse-shape discrimination, fast timing, and pileup correction. Finally, two
examples of experimental data taken during the commissioning of the
CLARION2-TRINITY system are given: a PID spectrum from $^{16}$O + $^{18}$O
fusion-evaporation, and PID and Doppler-corrected $\gamma$-ray spectra from
$^{48}$Ti + $^{12}$C Coulomb excitation.",2208.05449v1
2022-11-16,Interacting models for twisted bilayer graphene: a quantum chemistry approach,"The nature of correlated states in twisted bilayer graphene (TBG) at the
magic angle has received intense attention in recent years. We present a
numerical study of an interacting Bistritzer-MacDonald (IBM) model of TBG using
a suite of methods in quantum chemistry, including Hartree-Fock, coupled
cluster singles, doubles (CCSD), and perturbative triples (CCSD(T)), as well as
a quantum chemistry formulation of the density matrix renormalization group
method (DMRG). Our treatment of TBG is agnostic to gauge choices, and hence we
present a new gauge-invariant formulation to detect the spontaneous symmetry
breaking in interacting models. To benchmark our approach, we focus on a
simplified spinless, valleyless IBM model. At integer filling ($\nu=0$), all
numerical methods agree in terms of energy and $C_{2z} \mathcal{T}$ symmetry
breaking. Additionally, as part of our benchmarking, we explore the impact of
different schemes for removing ``double-counting'' in the IBM model. Our
results at integer filling suggest that cross-validation of different IBM
models may be needed for future studies of the TBG system. After benchmarking
our approach at integer filling, we perform the first systematic study of the
IBM model near integer filling (for $|\nu|< 0.2$). In this regime, we find that
the ground state can be in a metallic and $C_{2z} \mathcal{T}$ symmetry
breaking phase. The ground state appears to have low entropy, and therefore can
be relatively well approximated by a single Slater determinant. Furthermore, we
observe many low entropy states with energies very close to the ground state
energy in the near integer filling regime.",2211.09243v1
2023-03-15,Chiral phonons and phononic birefringence in ferromagnetic metal - bulk acoustic resonator hybrids,"Magnomechanical devices, in which magnetic excitations couple to mechanical
vibrations, have been discussed as efficient and broadband microwave signal
transducers in the classical and quantum limit. We experimentally investigate
the magnetoelastic coupling between the ferromagnetic resonance (FMR) modes in
a metallic Co$_{25}$Fe$_{75}$ thin film, featuring ultra-low magnetic damping
as well as sizable magnetostriction, and standing transverse elastic phonon
modes in sapphire, silicon and gadolinium gallium garnet by performing
broadband FMR spectroscopy at cryogenic temperatures. For all these substrate
materials, we observe an interaction between the resonant acoustic and magnetic
modes, which can be tailored by the propagation direction of the acoustic mode
with respect to the crystallographic axes. We identify these phonon modes as
transverse shear waves propagating with slightly different velocities with
relative magnitudes of $\Delta v/v\simeq10^{-5}$, i.e., all substrates show
phononic birefringence. Upon appropriately choosing the phononic mode, the
hybrid magnomechanical system enters the Purcell enhanced coupling regime.",2303.08429v1
1994-12-01,A Determination of the Thick Disk Chemical Abundance Distribution: Implications for Galaxy Evolution,"We present a determination of the thick disk iron abundance distribution
obtained from an in situ sample of F/G stars. These stars are faint, $15 \simlt
V \simlt 18$, selected on the basis of color, being a subset of the larger
survey of Gilmore and Wyse designed to determine the properties of the stellar
populations several kiloparsecs from the Sun. The fields studied in the present
paper probe the iron abundance distribution of the stellar populations of the
Galaxy at 500--3000pc above the plane, at the solar Galactocentric distance.",9411116v1
1995-05-23,Bimodal star formation in elliptical galaxies and the enrichment of the intra-cluster medium,"A detailed model of galactic evolution is proposed to explain both the iron
content of the Intra-Cluster Medium (ICM) and of the ellipticals pertaining to
the cluster. SNII are responsible for the production of Fe in the galaxies and
of its partial ejection in the surrounding medium. A high formation rate of
massive stars only ($m>3~{\rm M_{\sun}}$) at the very early stage of evolution
of ellipticals, reminiscent of starburst galaxies, is advocated. The high rate
of SNII explosions induces a powerful galactic wind, followed by a more
quiescent evolution where stars are formed, with a normal Initial Mass Function
(IMF), from the enriched gas remaining after the wind phase and from the gas
restored by the longest living stars produced during the early phase. Most of
the iron is produced by the high-mass stars created in the early burst phase.",9505107v2
1995-06-07,Good Abundances from Bad Spectra :II. Application and a New Stellar Color--Temperature Relation,"Stellar spectra derived from current multiple-object fiber-fed spectroscopic
radial-velocity surveys, of the type feasible with, among other examples,
AUTOFIB, 2dF, HYDRA, NESSIE, and the Sloan survey, differ significantly from
those traditionally used for determination of stellar abundances. The spectra
tend to be of moderate resolution (around $1\,${\AA}) and signal-to-noise ratio
(around 10-20 per resolution element), and cannot usually have reliable
continuum shapes determined over wavelength ranges in excess of a few tens of
Angstroms. Nonetheless, we have developed techniques to extract true iron
abundances and surface gravities from such spectra of G-type stars in the
4000--$5000\,${\AA} wavelength region. The theoretical basis and calibration
using synthetic spectra are described in detail in another paper. The practical
application of these techniques to observational data is given in the present
paper. We show that this method can provide true iron abundances, with an
uncertainty of less than $ 0.2$ dex over the range of metallicity found in the
Galactic thick and thin disks, from spectra obtained with fiber-fed
spectrographs.",9506044v1
1995-07-15,On broad iron K-alpha lines in Seyfert 1 galaxies,"The X-ray spectrum obtained by Tanaka et al from a long observation of the
active galaxy MCG$-6-30-15$ shows a broad iron K$\alpha$ line skewed to low
energies. The simplest interpretation of the shape of the line is that it is
due to doppler and gravitational redshifts from the inner parts of a disk about
a massive black hole. Similarly broad lines are evident in shorter observations
of several other active galaxies. In this paper we investigate other line
broadening and skewing mechanisms such as Comptonization in cold gas and
doppler shifts from outflows. We have also fitted complex spectral models to
the data of MCG$-6-30-15$ to see whether the broad skewed line can be mimicked
well by other absorption or emission features. No satisfactory mechanism or
spectral model is found, thus strengthening the relativistic disk line model.",9507061v1
1996-01-25,Non-LTE Treatment of Fe II in Astrophysical Plasmas,"We describe our implementation of an extremely detailed model atom of singly
ionized iron for NLTE computations in static and moving astrophysical plasmas.
Our model atom includes 617 levels, 13675 primary permitted transitions and up
to 1.2 million secondary transitions. Our approach guarantees that the total
iron opacity is included at the correct wavelength with reasonable memory and
CPU requirements. We find that the lines saturate the wavelength space, such
that special wavelength points inserted along the detailed profile functions
may be replaced with a statistical sampling method. We describe the results of
various test calculations for novae and supernovae.",9601148v1
1996-03-17,"Dormant dwarf spheroidal galaxies, deactivated by Type Ia supernovae","Some dwarf spheroidal galaxies have experienced many Gyrs long periods
without star formation. We show that Type Ia supernovae, formed from a first
generation of stars, can delay a second epoch of star formation by several
Gyrs, if the total gas mass in the dwarf spheroidals is smaller than $10^8
M_{\odot}$. The details depend on the assumed Type Ia supernova model and the
mass fraction of stars formed in the first population. This scenario requires
that dwarf spheroidals be confined by dark matter halos, as otherwise the
heated gas would have been lost due to tidal effects and galactic winds. If
Type Ia supernovae played an important role, heating the gas in dwarf
spheroidals, they should also have increased their iron abundance during the
epoch without star formation. The subsequent stellar generation should then
start with a higher [Fe/H] than that of the most iron-rich stars found in the
previous generation.",9603089v1
1996-05-19,Multiphase Chemical Evolution in Elliptical Galaxies,"The recent {\em ASCA} results show that the iron abundance of the X-ray gas
of elliptical galaxies is less than the solar abundance ($Z_{\sun}$). The
observed low iron abundance is inconsistent with the predictions of the
previous chemical evolution models. In order to solve this problem, we present
a simple model of chemical evolution for elliptical galaxies after the galactic
wind period under the assumption that the gases ejected from stars do not mix
with the circumferential gas. The ejected gas components evolve separately
according to their birth time and origin. We have investigated their evolution
qualitatively. The gas components originated from supernova remnant shells cool
and drop out of the hot gas faster than the other components because of their
high density and metal abundance. As a result, supernovae cannot heat the whole
gas of the elliptical galaxies effectively, in contrary to the previous
results. If the metal abundance of mass-loss gas is not uniform, the mass-loss
gas with higher abundance also easily drops out and the average abundance can
decrease. We believe that this is a hint of solving the low abundance problem.",9605115v1
1996-10-23,Magnetized Iron Atmospheres for Neutron Stars,"Using a Hartree-Fock formalism, we estimate energy levels and photon cross
sections for atomic iron in magnetic fields B ~ 10^13 G. Computing ionization
equilibrium and normal mode opacities with these data, we construct LTE neutron
star model atmospheres at 5.5 < Log(T_eff) < 6.5 and compute emergent spectra.
We examine the dependence of the emergent spectra on T_eff and B. We also show
the spectral variation with the angle between the magnetic field and the
atmosphere normal and describe the significant limb darkening in the X-ray
band. These results are compared with recent detailed computations of neutron
star H model atmospheres in high fields and with low field Fe and H model
atmospheres constructed from detailed opacities. The large spectral differences
for different surface compositions may be discernible with present X-ray data;
we also note improvements needed to allow comparison of Fe models with high
quality spectra.",9610177v2
1997-04-17,The profile and equivalent width of the X-ray iron emission-line from a disk around a Kerr black hole,"Recent X-ray observations have shown broad, skewed iron line emission from
Seyfert 1 galaxies which is explained by the emission being fluorescence on a
disk close to a black hole. During one interval, the line in MCG--6-30-15 was
so broad and redshifted that a Kerr black hole is implied. We are therefore
studying the effects of the Kerr metric on the line profile, and extending the
work by Laor and Kojima which dealt only with extreme values of the spin
parameter. Here we report that the spin parameter of the black hole in
MCG--6-30-15 is high (a/M>0.94), and invert the line profile to obtain the disk
emissivity profile, which approximates a power-law. Continuum radiation
returning to the disk because of the Kerr metric does not enhance the
equivalent width of the line seen above 3 keV by more than about 20 per cent if
the continuum source corotates with the disk.",9704177v1
1997-08-04,On the dependence of the iron K-line profiles with luminosity in Active Galactic Nuclei,"We present evidence for changes in the strength and profile of the iron
K-alpha line in Active Galactic Nuclei (AGN), based on X-ray observations with
ASCA. There is a clear decrease in the strength of the line with increasing
luminosity. This relation is is not due solely to radio power, as it persists
when only radio-quiet AGN are considered and therefore cannot be fully
explained by relativistic beaming. In addition to the change in strength, the
line profile also appears to be different in higher luminosity sources. We
discuss these results in terms of a model where the accretion disk becomes
ionized as a function of the accretion rate.",9708030v1
1997-12-15,BeppoSAX observations of Narrow-Line Seyfert 1 galaxies:I. Ton S 180,"We report on the first spectrum up to 10 keV of the bright narrow-line
Seyfert 1 galaxy Ton S 180, obtained with the imaging instruments onboard
BeppoSAX. This is the first observed source in a sample of a dozen narrow-line
Seyfert 1 galaxies in the BeppoSAX Core Program. We also present and discuss a
high quality optical spectrum taken at the 1.5 m telescope at La Silla two
months before the BeppoSAX observation. The X-ray spectrum shows a clear
hardening above about 2 keV, where a power law with Gamma = 2.3 plus an iron
line provide a good description of the data. This slope is significantly
steeper than the typical one for classical Seyfert 1's and quasars. The best
fit line energy is suggestive of highly ionized iron, which would support the
idea that the high accretion rate is (one of) the fundamental parameter(s)
characterizing the Narrow Line Seyfert 1 phenomenon.",9712182v1
1998-04-18,Lyman Alpha Fluorescent Excitation of FeII in Active Galactic Nuclei,"We have calculated FeII emission line strengths for Active Galactic Nuclei
Broad-Line Regions using precise radiative transfer and Iron Project atomic
data. We improve the treatment of all previously considered excitation
mechanisms for the FeII emission, continuum fluorescence, collisional
excitation, fluorescence by self-overlap among the iron lines, and fluorescent
excitation by Lyman-alpha. We demonstrate that Lyman-alpha fluorescence is of
fundamental importance in determining the strength of the FeII emission. In
addition to enhancing the ultraviolet and optical FeII flux, Lyman-alpha
fluorescence also results in significant near-infrared FeII emission in the
8500-9500 Angstrom wavelength range. New observations are suggested to probe
this effect in strong FeII emitting quasars.",9804183v1
1998-05-15,ASCA Observation of the polar RX J1802.1+1804,"We present X-ray data of RX J1802.1+1804 obtained by ASCA. Although it shows
a clear orbital intensity modulation with an amplitude of nearly 100% below 0.5
keV in ROSAT data, the ASCA light curves are nearly flat except for a possible
dip lasting about one-tenth of the orbital period. We discuss this within the
model assumption of a stream-eclipsing geometry as derived from the ROSAT
observations. The ASCA X-ray spectrum can be represented by a two temperature
optically thin thermal plasma emission model with temperatures of ~1keV and >7
keV, suggesting postshock cooling as observed in EX Hya. A remarkable feature
of the spectrum is the strong iron K_alpha emission line whose equivalent width
is ~4 keV. To account for this, an iron abundance of greater than at least 1.3
times Solar is required. A combined spectral analysis of the ROSAT PSPC and
ASCA data indicates that the N_H-corrected flux ratio of the soft blackbody
(0.1-2.4 keV) to the hard optically thin thermal plasma emission (2-10 keV) is
as large as ~10^4.",9805211v1
1998-10-05,New Insights into the Early Stage of the Galactic Chemical Evolution,"The supernova yields of several heavy elements including alpha-, iron-group,
and r-process elements are obtained as a function of the mass of their
progenitor main-sequence stars M_ms from the abundance patterns of extremely
metal-poor stars with a procedure recently proposed by Shigeyama and Tsujimoto
(1998). The ejected masses of alpha- and iron-group elements increase with
M_ms, whereas more Eu is ejected from supernovae with lower M_ms. For these
several heavy elements, it is shown that the average abundance ratios weighted
by the Salpeter initial mass function coincide with the ratios observed in
stars with -2<[Fe/H]<-1 within 0.1 dex. It follows that the correlations of
stellar abundance ratios with the metallicity are twofold. One is the abundance
ratios for [Fe/H] <-2.5 imprinted by the nucleosynthesis in individual
supernovae on the timescale 10^7yr and the other for [Fe/H]>-2 results from the
mixing of the products from a whole site of the nucleosynthesis, taking place
on the timescale longer than 10^9yr.",9810056v1
1998-11-13,Detection of Iron Emission Line from the Galaxy Cluster Including the Distant Radio Galaxy 3C220.1,"We detected an emission line feature at 4 keV in the X-ray spectrum of a sky
region including the distant radio galaxy 3C220.1(z=0.62) obtained with ASCA.
The line energy is 6.1 - 7.0 keV (90% confidence) in the rest frame of 3C220.1.
Within the present statistics, the observed spectra are consistent with two
different models; a non-thermal model consisting of a power-law continuum plus
a 6.4 keV iron emission line, and a Raymond-Smith thin-thermal emission model
of kT ~6 keV with a metal abundance of ~0.5 solar. However, the large (~500 eV)
equivalent width of the line indicates that a significant fraction of the X-ray
emission is likel y to arise from the hot intracluster gas which associates the
galaxy cluster including 3C220.1. The spectral parameters of the thermal
emission is consistent with the luminosity-temperature relation of nearby
clusters and the mass estimates from the giant luminous arc.",9811212v2
1999-01-07,Comparisons of various model fits to the Iron line profile in MCG-6-30-15,"The broad Iron line in MCG-6-30-15 is fitted to the Comptonization model
where line broadening occurs due to Compton down-scattering in a highly ionized
optically thick cloud. These results are compared to the disk line model where
the broadening is due to Gravitational/Doppler effects in the vicinity of a
black hole. We find that both models fit the data well and it is not possible
to differentiate between them by fitting only the ASCA data. The best fit
temperature and optical depth of the cloud are found to be kT = 0.54 keV and
$\tau = 4.0$ from the Comptonization model. This model further suggests that
while the temperature can be assumed to be constant, the optical depth varies
during the observation period. We emphasis an earlier conclusion that
simultaneous broad band data ($3 - 50$ keV) can rule out (or confirm) the
Comptonization model.",9901065v1
1999-03-12,On the nature of the X-ray source 1E 1024.0--5732/Wack 2134,"Two different models have been put forward to explain the origin of the X-ray
emission of the unusual X-ray source 1E 1024.0-5732/Wack 2134: a high-mass
X-ray binary system (HMXB) and a colliding wind binary (CWB). We present new
optical and X-ray data in an attempt to clarify the nature of this system. The
data seem to favour the colliding wind model since the optical spectra show
characteristics of both, a Wolf-Rayet and an O-type star, implying that these
two type of stars may be present in the system. The lack of coherent modulation
(pulsations) and the relatively soft and low luminosity X-ray emission seems to
exclude the presence of a neutron star as the body generating the X-ray
emission. We present the first X-ray energy spectrum of this source at energies
above 3 keV and discuss the implications of the spectral parameters obtained
from the model fitting. We comment on the fact that the iron lines in CWB are
centred at higher energies, ~ 6.6 keV, than those detected in supergiant HMXB,
where a value of 6.4 keV is found, implying that the degree of ionisation of
iron is higher in CWB.",9903197v1
1999-04-07,Variation of the broad X-ray iron line in MCG-6-30-15 during a flare,"We report results on the broad iron emission line of the Seyfert galaxy
MCG-6-30-15, obtained from the second long ASCA observation in 1997. The
time-averaged profile of the broad line is very similar to that seen with ASCA
in 1994, so confirming the detailed model fit then obtained. A bright flare is
seen in the light curve, during which the continuum was soft. At that time the
emission line peaks around 5 keV and most of its emission is shifted below 6
keV with no component detected at 6.4 keV (EW<60 eV). This can be interpreted
as the result of an extraordinarily large gravitational redshift due to a
dominant flare occurring very close to the black hole at a radius of <5m.",9904078v1
1999-04-27,Physical Parameters of Hot Horizontal-Branch Stars in NGC 6752: Deep Mixing and Radiative Levitation,"Atmospheric parameters (Teff, log g and log(He/H)) are derived for 42 hot
horizontal branch (HB) stars in the globular cluster NGC 6752. For 19 stars
MgII and FeII lines are detected indicating an iron enrichment by a factor 50
on average with respect to the cluster abundance whereas the magnesium
abundances are consistent with the cluster metallicity. This finding adds to
the growing evidence that radiative levitation plays a significant role in
determining the physical parameters of blue HB stars. Indeed, we find that iron
enrichment can explain part, but not all, of the problem of anomalously low
gravities along the blue HB. Thus the physical parameters of horizontal branch
stars hotter than about 11,500K in NGC 6752, as derived in this paper, are best
explained by a combination of helium mixing and radiative levitation effects.",9904377v1
1999-05-20,Metal Enrichment in the Early Galactic Halo,"An early history of metal enrichment in the Galactic halo is studied. We
investigate chemical inhomogeneity by using a stochastic chemical evolution
model. The model confronts with metallicity distribution function of long-lived
halo stars which is found to be a clue to obtain the best model prescriptions.
We find that the star formation in the halo virtually terminated by around 1
Gyr and that the halo has never been chemically homogeneous in its star
formation history. This conclusion does not depend whether mass loss from the
halo is taken into account or not. Observed ratios of alpha-elements with
respect to iron do not show scatters on a [alpha/Fe]-[Fe/H] plane, but this
does not imply that interstellar matter in the halo was homogeneous because a
chemical evolution path on this diagram is degenerate in the star formation
rate. On the other hand, apparent spread of [Sr/Fe] ratio among metal-poor halo
stars does not reflect an inhomogeneous metal enrichment, instead it is due to
a sharp increase in a production rate of strontium that is probably synthesised
in slightly less massive stars than progenitor of iron-producing SNII.",9905260v2
1999-06-11,Frequency resolved spectroscopy of Cyg X-1: fast variability of the Fe K_alpha line,"We studied the frequency resolved energy spectra of Cyg X--1 during the
standard low (hard) spectral state using the data of the Rossi X-Ray Timing
Explorer. We found that the relative amplitude of the reflection features --
the iron fluorescent line at ~6.5 keV and the smeared edge above ~7 keV --
decreases with the increasing frequency. In particular we found that the
equivalent width of the iron line decreases above ~1 Hz and drops twice at
frequency of ~10 Hz.
  An assumption that such behavior is solely due to a finite light crossing
time of the reflecting media, would imply the characteristic size of the
reflector ~5E8 cm, corresponding to ~150 Rg for a 10Msun black hole.
Alternatively lack of high frequency oscillations of the reflected component
may indicate that the short time scale, ~50-100 msec, variations of the primary
continuum appear in geometrically different, likely inner, part of the
accretion flow and give a rise to a significantly weaker, if any, reflected
emission than the longer time scale events.",9906198v1
1999-06-17,On the anomalous X-ray afterglows of GRB 970508 and GRB 970828,"Recently, BeppoSAX and ASCA have reported an unusual resurgence of soft X-ray
emission during the afterglows of GRB 970508 and GRB 970828, together with
marginal evidence for the existence of Fe-lines in both objects. We consider
the implications of the existence of a torus of iron-rich material surrounding
the sites of gamma ray bursts as would be expected in the SupraNova model; in
particular, we show that the fireball will quickly hit this torus, and bring it
to a temperature ~3x10^7 K. Bremsstrahlung emission from the heated up torus
will cause a resurgence of the soft X-ray emission with all expected
characteristics (flux level, duration and spectral hardening with time)
identical to those observed during the reburst. Also, thermal emission from the
torus will account for the observed iron line flux. These events are also
observable, for instance by new missions such as SWIFT, when beaming away from
our line sight makes us miss the main burst, as Fast (soft) X-ray Transients,
with durations ~10^3 s, and fluences ~10^-7-10^-4 erg cm^-2. This model
provides evidence in favor of the SupraNova model for Gamma Ray Bursts.",9906288v1
1999-08-17,Detection of Iron Emission Line from the Galaxy Cluster Including the Radio Galaxy 3C220.1 at z=0.62,"We have detected an emission line feature at 4 keV in the X-ray emission from
a sky region including the distant radio galaxy 3C220.1(z=0.62) obtained with
ASCA. The line energy is 6.1 - 7.0 keV (90% confidence) in the rest frame of
3C220.1. Within the present statistics, the observed spectra are consistent
with two different models: a non-thermal model consisting of a power-law
continuum plus a 6.4 keV iron emission line, and a Raymond-Smith thin-thermal
emission model of kT ~6 keV with a metal abundance of ~0.5 solar. However,
because of the large (~ 500 eV) equivalent width of the line, a significant
fraction of the X-ray emission is likely to arise from the hot intracluster gas
associated with the galaxy cluster that includes 3C220.1. The spectral
parameters of the thermal emission are consistent with the
luminosity-temperature relation of nearby clusters.",9908178v1
1999-12-07,On the inability of Comptonization to produce the broad X-ray iron lines observed in Seyfert nuclei,"It has recently been suggested that Compton downscattering may give rise to
the broad iron lines seen in the X-ray spectra of Seyfert 1 galaxies. This
challenges the standard model in which these lines originate from the innermost
regions of the black hole accretion disk with Doppler shifts and gravitational
redshifts giving rise to the broadened line profile. Here, we apply
observational constraints to the Compton downscattering model for MCG-6-30-15
and NGC3516, the two best cases to date of Seyfert galaxies with
relativistically broad lines. We show that the continuum source in MCG-6-30-15
required by the constrained model violates the black body limit. In the case of
NGC3516, only a very small region of parameter space is compatible with the
constraints. Hence, we conclude that the Comptonization model is not a viable
one for the broad line seen in these two objects. The accretion disk model
remains the best interpretation of these data.",9912120v2
1999-12-08,A two zone model for the broad Iron line emission in MCG-6-30-15,"We reanalyze the ASCA and BeppoSAX data of MCG-6-30-15, using a double zone
model for the Iron line profile. In this model, the X-ray source is located
around $\approx 10$ Schwarzschild radius and the regions interior and exterior
to the X-ray source produce the line emission. We find that this model fits the
data with similar reduced $\chi^2$ as the standard single zone model. The best
fit inclination angle of the source ($i \approx 10^o$) for the medium intensity
ASCA data set is compatible with that determined by earlier modeling of optical
lines. The observed variability of the line profile with intensity can be
explained as variations of the X-ray source size. That several AGN with broad
lines have the peak centroid near 6.4 keV can be explained within the framework
of this model under certain conditions.
  We also show that the simultaneous broad band observations of this source by
BeppoSAX rules out the Comptonization model which was an alternative to the
standard inner disk one. We thereby strengthen the case that the line
broadening occurs due to the strong gravitational influence of a Black Hole.",9912178v1
2000-01-26,Growth of a Vortex Mode during Gravitational Collapse Resulting in Type II Supernova,"We investigate stability of a gravitationally collapsing iron core against
non-spherical perturbation. The gravitationally collapsing iron core is
approximated by a similarity solution for dynamically collapsing polytropic gas
sphere. We find that the similarity solution is unstable against non-spherical
perturbations. The perturbation grows in proportion to $ (t - t_0) ^{-\sigma} $
while the the central density increases in proportion to $ (t - t_0) ^{-2} $.
The growth rate is $ \sigma = 1/3 + \ell (\gamma - 4/3) $, where $ \gamma $ and
$ \ell $ denote the polytropic index and the parameter $ \ell $ of the
spherical harmonics, $ Y_{\ell} ^m (\theta, \phi) $, respectively. The growing
perturbation is dominated by vortex motion. Thus it excites global convection
during the collapse and may contribute to material mixing in a type II
supernova.",0001447v1
2000-03-30,"Discovery of a new pulsating X-ray source with a 1549.1-s period, AX J183220-0840","A new pulsating X-ray source, AX J183220-0840, with a 1549.1-s period was
discovered at R.A.= 18h32m20s and Dec.=-8d40'30'' (J2000,
uncertainty=0.6degree) during an ASCA observation on the Galactic plane. The
source was observed two times, in 1997 and in 1999. A phase-averaged X-ray flux
of 1.1E-11 ergs cm-2 s-1 and pulsation period of 1549.1+/-0.4 s were
consistently obtained from these two observations. The X-ray spectrum was
represented by a flat absorbed power-law with a photon-index of =~0.8 and an
absorption column density of =~1.3E22 cm-2. Also, a signature of iron K-shell
line emission with a centroid of 6.7 keV and an equivalent width of
approximately 450 eV was detected. From the pulsation period and the iron-line
feature, AX J183220-0840 is likely to be a magnetic white dwarf binary with a
complexly absorbed thermal spectrum with a temperature of about 10 keV.",0003448v1
2000-05-30,BeppoSAX Observations of Bright Radio Galaxies,"BeppoSAX observations of Broad Line Radio Galaxies (BLRGs) have shown that
they have a considerable variety of spectral properties and important
differences with respect to their radio-quiet counter-part Seyfert 1s. In radio
galaxies the soft photons are often absorbed by cold material. In contrast, in
Seyfert 1s the soft photons are generally absorbed by warm gas. The iron lines,
always detected in Seyfert 1s, are not always present in BLRGs and generally
are weak. In addition, small iron line equivalent widths seem to correspond to
weak reflection components in radio galaxies.
  The emerging picture of BLRGs is complex. Probably several X-ray components,
jet, accretion flow and molecular torus, mixed in different way in different
objects, contribute to the production of their X-ray spectrum and determine the
observed variety. The weakness of the reprocessed features can be explained
either by a dilution of the Seyfert-like continuum from non-thermal (jet)
radiation or by an accretion gas that is hot and geometrically thick close to
the black hole and cold geometrically thin (i.e. able to reprocess the primary
X-ray radiation) at larger radii.",0005577v1
2000-06-01,Possible Evidence for a Truncated Thin Disk in Seyfert 1 Galaxy NGC4593,"We compile the multi-band spectral energy distribution (SED) of Seyfert 1
galaxy NGC4593, and investigate its optical-to-ultraviolet (OUV) continuum and
iron K\alpha line profile. No strong ``big blue bump'' is found in OUV band.
The iron K\alpha line profile is not as broad as expected from a disk which
extends down to the last stable orbit. Both of them can be modeled by a
truncated thin disk, and support the existence of a truncated thin disk in the
system. It is of much interest that NGC4593 may be a typical object with an
accretion rate \dot{m}=\dot{M}/M_{Edd} \sim 0.01-0.1 and harbors a two
component accretion flow: an outer thin disk and an inner hot flow--possibly
ADAF, analogous to the low and intermediate state of low mass X-ray binaries
(LMXB).",0006004v1
2000-06-14,A cloud model of active galactic nuclei: the iron K-alpha line diagnostics,"The origin and the profile of the iron K-alpha line from active galactic
nuclei is being studied. The model with a quasi-spherical distribution of
clouds around a compact galactic nucleus is explored in which the intrinsic
spectral feature around 6-7 keV is substantially affected by Comptonization of
primary X-rays. The predicted spectral profiles are influenced mainly by motion
of the clouds in strong gravitational field of the centre, and by orientation
of the source with respect to the observer. The case of the Seyfert galaxy
MCG-6-30-15 is examined in more detail and free parameters of the model are
determined. A robust result is obtained: acceptable fits to the observed
profile correspond to the spherical distribution of the clouds with strong
self-obscuration effects and with rather high value of ionization parameter.
This is a different situation from that considered in the model of a cold
illuminated disc. Nevertheless, geometrically flat (disc-type) configurations
are not rejected.",0006187v1
2000-07-26,New constraints from Haverah Park data on the photon and iron fluxes of UHE cosmic rays,"Using data from inclined events ($60^{\circ}<\theta<80^{\circ}$) recorded by
the Haverah Park shower detector, we show that above 10^19 eV less than 30% of
the primary cosmic rays can be photons or iron nuclei at the 95% confidence
level. Above 4 10^19 eV less than 55% of the cosmic rays can be photonic at the
same confidence level. These limits place important constraints on some models
of the origin of ultra high energy cosmic rays. Details of two new events above
10^20 eV are reported.",0007386v2
2000-08-09,Detection of a broad iron emission line and sub-millisecond quasiperiodic oscillations from the type I X-ray burster 4U1728-34 in a high state,"We report results from simultaneous RossiXTE and BeppoSAX observations of the
neutron-star x-ray binary and type I X-ray burster 4U1728-34. The source was
found in a high luminosity state, L_X near 0.1 L_Edd, and quasiperiodic
oscillations were detected at 1284 +/- 6 Hz, the highest frequency ever
observed from this source. The x-ray spectrum shows a broad, FWHM = 0.8 keV,
iron K-alpha fluorescence line. We discuss interpretations of the broad line
and the quasiperiodic oscillations and how future simultaneous spectral and
timing observations can be used to test these interpretations and, potentially,
to estimate the mass of the compact object.",0008141v1
2000-08-15,RXTE observations of the Seyfert galaxy NGC 5506: evidence for reflection from disk and torus,"We report on observations of the narrow line Seyfert galaxy NGC 5506 with the
Rossi X-ray TIming Explorer. The observations cover a time interval of ~1000
days during which the source showed strong flux and spectral variability. The
spectrum clearly shows iron fluorescence emission at 6.4 keV and significant
reflection features. Both the equivalent width of the iron line and the
relative strength of the reflected continuum are higher during low flux states.
The variability of the reflection features can be explained by the presence of
two reflected components: one that responds rapidly to flux changes of the
primary continuum and a second, slowly variable, component originating from a
distant reflector, e.g. a molecular torus.",0008219v1
2000-09-06,Evolution of the X-ray luminosity and metallicity of starburst blown superbubbles,"We calculate the time-dependent metal production expected from starbursts and
use them as boundary conditions in our 2D simulations of evolving superbubbles.
We assume that the produced metals (oxygen and iron) thoroughly mix with the
ejected stellar envelopes, and/or with the matter thermally evaporated from the
superbubble cold outer shell. The metal production process determines the
time-dependent metallicity in hot superbubble interiors, and leads to values of
Z greater or equal than solar, when oxygen is used as tracer, and under-solar
when the metallicity is measured with respect to iron. In either case, the
enhanced metallicity boosts the X-ray emissivity of superbubbles, bringing
theory and observations closer together.",0009092v1
2000-09-15,Iron Abundance Profiles of 12 Clusters of Galaxies Observed With BeppoSAX,"We have derived azimuthally-averaged radial iron abundance profiles of the
X-ray gas contained within 12 clusters of galaxies with redshift 0.03 < z < 0.2
observed with BeppoSAX. We find evidence for a negative metal abundance
gradient in most of the clusters, particularly significant in clusters that
possess cooling flows. The composite profile from the 12 clusters resembles
that of cluster simulations of Metzler & Evrard (1997). This abundance gradient
could be the result of the spatial distribution of gas-losing galaxies within
the cluster being more centrally condensed than the primordial hot gas. Both
inside and outside the core region, we find a higher abundance in cooling flow
clusters than in non-cooling flow clusters. Outside of the cooling region this
difference cannot be the result of more efficient sputtering of metals into the
gaseous phase in cooling flow clusters, but might be the result of the mixing
of low metallicity gas from the outer regions of the cluster during a merger.",0009237v1
2000-10-24,BeppoSAX observations of Narrow-Line Seyfert 1 galaxies: II. Ionized iron features in Arakelian 564,"The BeppoSAX observations of the bright Narrow-Line Seyfert 1 galaxy Ark 564
are presented along with a high quality optical spectrum taken at the 1.5m
telescope at La Silla. The 0.1-10 keV X-ray spectrum is characterized by a
strong soft component which is best described by blackbody-like emission with a
temperature of about 160 eV. At higher energies a steep (Gamma = 2.4) power-law
tail is present. There is evidence of an ionized reflector in the form of an
iron line and edge. We do not find significant evidence of soft X-ray features
if the spectrum is modelled with a two component continuum. The optical and
X-ray spectral properties support the hypothesis of a high accretion rate onto
a low mass black hole.",0010476v1
2000-10-31,Complex resonance absorption structure in the X-ray spectrum of IRAS13349+2438,"The luminous infrared-loud quasar IRAS 13349+2438 was observed with the
XMM-Newton Observatory as part of the Performance Verification program. The
spectrum obtained by the Reflection Grating Spectrometer (RGS) exhibits broad
(v ~ 1400 km/s FWHM) absorption lines from highly ionized elements including
hydrogen- and helium-like carbon, nitrogen, oxygen, and neon, and several iron
L-shell ions (Fe XVII - XX). Also shown in the spectrum is the first
astrophysical detection of a broad absorption feature around lambda = 16 - 17
Ang identified as an unresolved transition array (UTA) of 2p - 3d inner-shell
absorption by iron M-shell ions in a much cooler medium; a feature that might
be misidentified as an O VII edge when observed with moderate resolution
spectrometers. No absorption edges are clearly detected in the spectrum. We
demonstrate that the RGS spectrum of IRAS 13349+2438 exhibits absorption lines
from at least two distinct regions, one of which is tentatively associated with
the medium that produces the optical/UV reddening.",0010660v1
2000-11-17,Observation of X-ray lines from a Gamma-Ray Burst (GRB991216): Evidence of Moving Ejecta from the Progenitor,"We report on the discovery of two emission features observed in the X-ray
spectrum of the afterglow of the gamma-ray burst (GRB) of 16 Dec. 1999 by the
Chandra X-Ray Observatory. These features are identified with the Ly$_{\alpha}$
line and the narrow recombination continuum by hydrogenic ions of iron at a
redshift $z=1.00\pm0.02$, providing an unambiguous measurement of the distance
of a GRB. Line width and intensity imply that the progenitor of the GRB was a
massive star system that ejected, before the GRB event, $\approx 0.01 \Ms$ of
iron at a velocity $\approx 0.1 c$, probably by a supernova explosion.",0011337v1
2000-11-30,"Illuminated, and enlightened, by GRB 991216","We consider models for the generation of the emission line recently
discovered in the X-ray afterglow spectrum of several bursts, and especially of
GRB 991216 observed by Chandra. These observations suggest the presence of
0.1-1 solar masses of iron in the vicinity of the bursts. We show that there
are strong geometrical and kinematical constraints on the line emitting
material. We discuss several classes of models, favoring one where the line
photons are produced by reflection off the walls of a wide funnel of
semi-opening angle 45 degrees, excavated in a young (a few months old)
supernova remnant made of ~10 solar masses with radius 6x10^15 cm, and ~1 solar
mass of iron, providing strong support for the SupraNova model.",0011580v2
2000-12-27,Galactic chemical abundance evolution in the solar neighborhood up to the Iron peak,"We have developed a detailed standard chemical evolution model to study the
evolution of all the chemical elements up to the iron peak in the solar
vicinity. We consider that the Galaxy was formed through two episodes of
exponentially decreasing infall, out of extragalactic gas. In a first infall
episode, with a duration of $\sim$ 1 Gyr, the halo and the thick disk were
assembled out of primordial gas, while the thin disk formed in a second episode
of infall of slightly enriched extragalactic gas, with much longer timescale.
The model nicely reproduces the main observational constraints of the solar
neighborhood, and the calculated elemental abundances at the time of the solar
birth are in excellent agreement with the solar abundances. By the inclusion of
metallicity dependent yields for the whole range of stellar masses we follow
the evolution of 76 isotopes of all the chemical elements between hydrogen and
zinc. Those results are confronted with a large and recent body of
observational data, and we discuss in detail the implications for stellar
nucleosynthesis.",0012505v1
2001-05-10,VLT Observations of Turnoff stars in the Globular Cluster NGC 6397,"VLT-UVES high resolution spectra of seven turnoff stars in the metal-poor
globular cluster NGC 6397 have been obtained. Atmospheric parameters and
abundances of several elements (Li, Na, Mg, Ca, Sc, Ti, Cr, Fe, Ni, Zn and Ba)
were derived for program stars. The mean iron abundance is [Fe/H] = -2.02, with
no star-to-star variation. The mean abundances of the alpha-elements (Ca, Ti)
and of the iron-peak elements (Sc, Cr, Ni) are consistent with abundances
derived for field stars of similar metallicity. Magnesium is also almost solar,
consistent with the values found by Idiart & Th\'evenin (2000) when non-LTE
effects (NLTE hereafter) are taken into account. The sodium abundance derived
for five stars is essentially solar, but one object (A447) is clearly Na
deficient. These results are compatible with the expected abundance range
estimated from the stochastic evolutionary halo model by Argast et al. (2000)
when at the epoch of [Fe/H] $\sim$ -2 the interstellar medium is supposed to
become well-mixed.",0105166v1
2001-05-16,Chandra Observations of Diffuse X-Rays from the Sagittarius B2 Cloud,"We present the first Chandra results of the giant molecular cloud Sagittarius
B2 (Sgr B2), located about 100 pc away from the Galactic center. Diffuse X-rays
are clearly separated from one-and-a-half dozen resolved point sources. The
X-ray spectrum exhibits pronounced iron K-shell transition lines at 6.40 keV (K
alpha) and 7.06 keV (K beta), deep iron K-edge at 7.11 keV and large
photo-electric absorption at low energy. The absorption-corrected X-ray
luminosity is \sim 1 times 10^{35} erg s^{-1}, two orders of magnitude larger
than the integrated luminosity of all the resolved point sources. The diffuse
X-rays come mainly from the south-west half of the cloud with a concave-shape
pointing to the Galactic center direction. These results strongly support the
ASCA model that Sgr B2 is irradiated by an X-ray source at the Galactic center
side.",0105273v1
2001-07-13,High-Resolution X-Ray Spectroscopy of the Accretion Disk Corona Source 4U 1822-37,"We present a preliminary analysis of the X-ray spectrum of the accretion disk
corona source, 4U 1822-37, obtained with the High Energy Transmission Grating
Spectrometer onboard the Chandra X-ray Observatory. We detect discrete emission
lines from photoionized iron, silicon, magnesium, neon, and oxygen, as well as
a bright iron fluorescence line. Phase-resolved spectroscopy suggests that the
recombination emission comes from an X-ray illuminated bulge located at the
predicted point of impact between the disk and the accretion stream. The
fluorescence emission originates in an extended region on the disk that is
illuminated by light scattered from the corona.",0107247v1
2001-08-20,Iron K-alpha Emission from X-ray Reflection: Predictions for Gamma-Ray Burst Models,"Recent observations of several gamma-ray burst (GRB) afterglows have shown
evidence for a large amount of X-ray line emitting material, possibly arising
from ionized iron. A significant detection of an X-ray spectral feature, such
as that found in the Chandra observation of GRB 991216, may provide important
constraints on the immediate environment of the burst and hence on progenitor
models. The large Fe K-alpha equivalent widths inferred from the X-ray
observations favor models in which the line is produced when the primary X-ray
emission from the source strikes Thomson-thick material and Compton scatters
into our line of sight. We present such reflection spectra here, computed in a
fully self-consistent manner, and discuss the range of ionization parameters
that may be relevant to different models of GRBs. We argue that the presence of
a strong hydrogen-like K-alpha line is unlikely, because Fe-XXVI photons would
be trapped resonantly and removed from the line core by Compton scattering. In
contrast, a strong narrow emission line from He-like Fe-XXV is prominent in the
model spectra. We briefly discuss how these constraints may affect the line
energy determination in GRB 991216.",0108324v1
2001-09-30,Massive Star Evolution: Nucleosynthesis and Nuclear Reaction Rate Uncertainties,"We present a nucleosynthesis calculation of a 25 solar mass star of solar
composition that includes all relevant isotopes up to polonium. In particular,
all stable isotopes and necessary nuclear reaction rates are covered. We follow
the stellar evolution from hydrogen burning till iron core collapse and
simulate the explosion using a ``piston'' approach. We discuss the influence of
two key nuclear reaction rates, C12(a,g) and Ne22(a,n), on stellar evolution
and nucleosynthesis. The former significantly influences the resulting core
sizes (iron, silicon, oxygen) and the overall presupernova structure of the
star. It thus has significant consequences for the supernova explosion itself
and the compact remnant formed. The later rate considerably affects the
s-process in massive stars and we demonstrate the changes that different
currently suggested values for this rate cause.",0110015v1
2001-11-27,The X-ray Spectrum of Cyg X-2,"The spectra of disc accreting neutron stars generally show complex curvature,
and individual components from the disc, boundary layer and neutron star
surface cannot be uniquely identified. Here we show that much of the confusion
over the spectral form derives from inadequate approximations for
comptonization and for the iron line. There is an intrinsic low energy cutoff
in comptonised spectra at the seed photon energy. It is very important to model
this correctly in neutron star systems as these have expected seed photon
temperatures (from either the neutron star surface, inner disc or self-absorbed
cyclotron) of ~1 keV, clearly within the observed X-ray energy band. There is
also reflected continuum emission which must accompany the observed iron line,
which distorts the higher energy spectrum. We illustrate these points by a
reanalysis of the GINGA spectra of Cyg X-2 at all points along its Z track, and
show that the spectrum can be well fit by models in which the low energy
spectrum is dominated by the disc, while the higher energy spectrum is
dominated by comptonised emission from the boundary layer, together with its
reflected spectrum from a relativistically smeared, ionised disc.",0111497v1
2002-01-18,Detection of FeO towards SgrB2,"We have observed the J=5-4 ground state transition of FeO at a frequency of
153 GHz towards a selection of galactic sources.
  Towards the galactic center source SgrB2, we see weak absorption at
approximately the velocity of other features towards this source (62 km
s$^{-1}$ LSR).
  Towards other sources, the results were negative as they were also for
MgOH(3-2) and FeC(6-5). We tentatively conclude that the absorption seen toward
SgrB2 is due to FeO in the hot ($\sim $ 500 K) relatively low density absorbing
gas known to be present in this line of sight.
  This is the first (albeit tentative) detection of FeO or any iron--containing
molecule in the interstellar gas. Assuming the observed absorption to be due to
FeO, we estimate [FeO]/[SiO] to be of order or less than 0.002 and
[FeO]/[H$_{2}$] of order $3 10^{-11}$. This is compatible with our negative
results in other sources.
  Our results suggest that the iron liberated from grains in the shocks
associated with SgrB2 remains atomic and is not processed into molecular form.",0201311v1
2002-02-01,"Diffuse X-rays in the Galactic center region -- The zoo of iron line clumps, non-thermal filaments and hot plasmas --","This paper reports the diffuse X-ray features around the Galactic center
observed with Chandra. We confirm the ASCA and Ginga discoveries of the
large-scale thin-thermal plasma with strong lines in the Galactic center
region. In addition, many small clumps of emission lines from neutral (6.4 keV
line) to He-like (6.7 keV line) irons are discovered. The 6.4 keV line clumps
would be reflection nebulae, while those of the 6.7 keV line are likely SNRs.
We also find emission lines of intermediate energy between 6.5-6.7 keV, which
are attributable to young SNRs in non equilibrium ionization. Non-thermal
filaments or belts with X-ray spectra of no emission line are found, suggesting
the Fermi acceleration site in a rapidly expanding shell. All these suggest
that multiple-supernovae or extremely large explosion had occurred around the
Galactic center region in the recent past.",0202010v1
2002-03-12,Evidence for a relativistic iron line in GRS 1915+105,"We report on the discovery of a relativistic iron K\alpha fluorescent
emission line in the BeppoSAX spectrum of the microquasar GRS 1915+105, taken
on April 19, 1998, when the line was unusually intense. The feature is broad
and skewed, clearly indicating emission from the innermost regions of the
accretion disc. The inner emitting orbit is larger than the innermost stable
orbit, even in Schwarzschild metric: thus, a non-zero BH spin is not required
by these data.",0203185v1
2002-04-23,"Tables of the partition functions for iron, Fe I -- Fe X","We present extensive tables of the Atomic Partition Function for iron ions,
Fe I -- Fe X, and discuss details of the computational method. Partition
functions are given in wide range of temperatures, 10^3 K < T < 10^6 K, and
lowering of ionization energy (0.001 eV < LIE < 5.0 eV). Our APF take into
account all energy levels predicted by quantum mechanics, including
autoionization levels. The tables can be applied for the computations of model
stellar atmospheres and theoretical spectra over all existing spectral and
luminosity classes.",0204384v1
2002-04-30,Detection of Iron Emission in the z = 5.74 QSO SDSSp J104433.04-012502.2,"We obtained near-infrared spectroscopy of the z=5.74 QSO, SDSSp
J104433.04-012 502.2 with the Infrared Camera and Spectrograph of the Subaru
telescope. The redshift of 5.74 corresponds to a cosmological age of 1.0 Gyr
for the current Lambda-dominated cosmology. We found a similar strength of the
Fe II (3000-3500 A) emission lines in SDSSp J104433.04-012502.2 as in low
redshift QSOs. This is the highest redshift detection of iron. We subtracted a
power-law continuum from the spectrum and fitted model Fe II emission and
Balmer continuum. The rest equivalent width of Fe II (3000-3500 A) is ~30 A
which is similar to those of low redshift QSOs measured by the same manner. The
chemical enrichment models that assume the life time of the progenitor of SNe
Ia is longer than 1 Gyr predict that weaker Fe II emission than low red shift.
However, none of the observed high redshift (z > 3) QSOs show a systematic dec
rease of Fe II emission compared with low redshift QSOs. This may due to a
shorter lifetime of SNe Ia in QSO nuclei than in the solar neighborhood.
Another reason of strong Fe II emission at z=5.74 may be longer cosmological
age due to smaller Omega_M.",0204505v1
2002-05-15,Galaxy Evolution tool: Construction and Applications,"We present a dual-infall galactic chemical evolution model which uses a new
set of stellar yields calculated by Limongi et al (2001) to constrain the
amount of iron-peak elements ejected by massive stars. The age-metallicity
relation, G-dwarf distribution and evolution of abundance ratios are predicted
using Galaxy Evolution tool (GEtool), a software package currently being
developed to self-consistenly model the chemical and spectral evolution of disk
galaxies. A comparison with results obtained using the Woosley & Weaver (1995)
core-collapse supernova models suggests that the observed behaviour of key
abundance patterns cannot be reproduced if the iron yield of massive stars
increases with initial mass.",0205249v1
2002-05-24,The relativistic Iron K-alpha line from an accretion disc onto a static non-baryonic compact object,"This paper continues the study of the properties of an accretion disc
rotating around a non-baryonic (assumed super-massive) compact object. This
kind of objects, generically known as boson stars, were earlier proposed as a
possible alternative scenario to the existence of super-masive black holes in
the center of every galaxy. A dilute boson star has also been proposed as a
large part of the non-baryonic dark matter, flattening galactic rotational
velocities curves. In this contribution, we compute the profile of the emission
lines of Iron; its shape has been for long known as a useful diagnosis of the
space-time geometry. We compare with the case of a Schwarzschild black hole,
concluding that the differences are observationally distinguishable.",0205418v1
2002-06-04,Extreme X-ray Iron Lines in Active Galactic Nuclei,"We analyze X-ray spectra of heavily obscured (N_H > 10^{24} cm^{-2}) active
galaxies obtained with Chandra, concentrating on the iron K alpha fluorescence
line. We measure very large equivalent widths in most cases, up to 5 keV in the
most extreme example. The geometry of an obscuring torus of material near the
active galactic nucleus (AGN) determines the Fe emission, which we model as a
function of torus opening angle, viewing angle, and optical depth. The
starburst/AGN composite galaxies in this sample require small opening angles.
Starburst/AGN composite galaxies in general therefore present few direct lines
of sight to their central engines. These composite galaxies are common, and
their large covering fractions and heavy obscuration effectively hide their
intrinsically bright X-ray continua. While few distant obscured AGNs have been
identified, we propose to exploit their signature large Fe K alpha equivalent
widths to find more examples in X-ray surveys.",0206071v1
2002-07-29,"Cosmic Ray Diffusion from the Galactic Spiral Arms, Iron Meteorites, and a possible climatic connection?","We construct a Galactic cosmic ray (CR) diffusion model while considering
that CR sources reside predominantly in the Galactic spiral arms. We find that
the CR flux (CRF) reaching the solar system should periodically increase each
crossing of a Galactic spiral arm. We search for this signal in the CR exposure
age record of Iron meteorites and confirm this prediction. We then check the
hypothesis that climate, and in particular the temperature, is affected by the
CRF to the extent that glaciations can be induced or completely hindered by
possible climatic variations. We find that although the geological evidence for
the occurrence of IAEs in the past Eon is not unequivocal, it appears to have a
nontrivial correlation with the spiral arm crossings--agreeing in period and
phase. Thus, a better timing study of glaciations could either confirm this
result as an explanation to the occurrence of IAEs or refute a CRF climatic
connection.",0207637v1
2002-09-07,Iron Emission Lines from Extended X-ray Jets in SS 433: Reheating of Atomic Nuclei,"Powerful relativistic jets are among the most ubiquitous and energetic
observational consequences of accretion around supermassive black holes in
active galactic nuclei and neutron stars and stellar-mass black holes in x-ray
binary (XRB) systems. But despite more than three decades of study, the
structure and composition of these jets remain unknown. Here we present
spatially resolved x-ray spectroscopy of arc second-scale x-ray jets from the
XRB SS 433 analized with the Chandra advanced charge-coupled device imaging
spectrometer. These observations reveal evidence for a hot continuum and
Doppler-shifted iron emission lines from spatially resolved regions.
Apparently, in situ reheating of the baryonic component of the jets takes place
in a flow that moves with relativistic bulk velocity even more than 100 days
after launch from the binary core.",0209131v1
2002-12-01,Magnetic fields in AGNs and microquasars,"Observations of AGNs and microquasars by ASCA, RXTE, Chandra and XMM-Newton
indicate the existence of wide X-ray emission lines of heavy ionized elements
in their spectra. The emission can arise in the inner parts of accretion discs
where the effects of General Relativity (GR) must be counted, moreover such
effects can dominate. We describe a procedure to estimate an upper limit of the
magnetic fields in the regions where X-ray photons are emitted. We simulate
typical profiles of the iron $K_\alpha$ line in the presence of a magnetic
field and compare them with observational data. As an illustration we find $H <
10^{10} - 10^{11}$ Gs for Seyfert galaxy MCG--6--30--15. Using the perspective
facilities of measurement devices (e.g. Constellation-X mission) a better
resolution of the blue peak structure of iron $K_\alpha$ line will allow to
find the value of the magnetic fields if the latter are high enough.",0212008v2
2002-12-26,On the Galactic Disk Metallicity Distribution from Open Clusters I. New Catalogues and Abundance Gradient,"In this paper we have compiled two new open cluster catalogues. In the first
one, there are 119 objects with ages, distances and metallicities available,
while in the second one, 144 objects have both absolute proper motion and
radial velocity data, of which 45 clusters also with metallicity data
available. Taking advantages of the large number of objects included in our
sample, we present an iron radial gradient of about -0.063$\pm$0.008 dex/kpc
from the first sample. By dividing clusters into age groups, we show that iron
gradient was steeper in the past, which is consistent with the recent result
from Galactic planetary nebulae data, and also consistent with the inside-out
galactic disk formation scenarios. Based on the cluster sample, we also
discussed the metallicity distribution, cluster kinematics and space
distribution. A disk age-metallicity relation could be implied from those
properties, although we could not give conclusive result from the age
metallicity diagram based on the current sample. More observations are needed
for metal poor clusters.",0212542v1
2003-02-06,The history of the iron K-alpha line profile in the Piccinotti AGN ESO198-G24,"This paper presents ASCA (July 1997), XMM-Newton (December 2000) and BeppoSAX
(January 2001) observations of the Piccinotti Seyfert 1 galaxy ESO198-G24. The
BeppoSAX 0.1-200 keV spectrum exhibits reprocessing features, probably produced
by an X-ray illuminated, relativistic accretion disk subtending a solid angle
\~2 pi. During the XMM-Newton observation the fluorescent iron K-alpha line
profile (centroid energy E~6.4 keV) was broad and twice as bright as in the
BeppoSAX observation. An additional emission feature (E~5.7 keV), detected at
the 96.3% confidence level, may be part of a relativistic, double-peaked
profile. By contrast, in the earlier ASCA observation the line profile is
dominated by a remarkably narrow ""core"" (intrinsic width <50 eV). If this
component is produced by reflection off the inner surface of a molecular torus,
its large Equivalent Width (~300 eV) most likely represents the ""echo"" of a
previously brighter flux state, in agreement with the dynamical range covered
by the historical X-ray light curve in ESO198-G24.",0302117v1
2003-05-18,Spectroscopic Constraints on the Surface Magnetic Field of the Accreting Neutron Star EXO 0748-676,"Gravitationally redshifted absorption lines of Fe XXVI, Fe XXV, and O VIII
were inferred recently in the X-ray spectrum of the bursting neutron star EXO
0748-676. We place an upper limit on the stellar magnetic field based on the
iron lines. The oxygen absorption feature shows a multiple component profile
that is consistent with Zeeman splitting in a magnetic field of ~(1-2)x10^9
gauss, and for which the corresponding Zeeman components of the iron lines are
expected to be blended together. In other systems, a field strength >5x10^{10}
gauss could induce a blueshift of the line centroids that would counteract
gravitational redshift and complicate the derivation of constraints on the
equation of state of the neutron star.",0305311v1
2003-09-02,HST/STIS observations of sdBV stars: testing diffusion and pulsation theory,"We present the initial results of an abundance analysis of echelle UV spectra
of 5 hot subdwarf B (sdB) stars. These stars have been identified as core
helium burning objects on the extreme Horizontal Branch. Around 5% of sdBs show
short-period acoustic mode oscillations. Models predict that these oscillations
are due to an opacity bump caused by the ionisation of iron group elements. The
necessary metal abundance has to be maintained by diffusive equilibrium between
gravitational settling and radiative levitation. However, analyses of high
resolution optical spectra has revealed that we cannot discriminate between
pulsating and non-pulsating sdBs on the basis of the surface iron abundance. We
have therefore obtained HST/STIS observations of 3 pulsators and 2
non-pulsators in the near and far UV to measure the surface abundance of
elements that are unobservable from the ground. The overall aim of our study is
to test diffusion and pulsation calculations by searching for significant
differences between these surface abundances.",0309062v1
2003-09-17,Infrared emission towards 11 years after outburst: Properties of the circumstellar dust,"Detailed models are presented for the late epoch mid infrared (MIR) emission
from collisionally heated grains in the shocked circumstellar gas around SN
1987A. Thermal dust emission from a region of moderate density interior to the
thick inner ring seen with the Hubble Space Telescope (HST) is found to be a
natural explanation for the MIR spectral energy distribution measured by
ISOCAM. The MIR-spectrum can be reproduced by a mixture of silicate-iron or
silicate-graphite grains or by a composition of pure graphite grains. A
composition of pure iron grains on the other hand can be excluded and a pure
silicate composition does not seem to be very likely. The dust-to-gas ratio in
the interaction zone is ~0.01%, an order of magnitude lower than estimates for
dust abundances in the winds of red supergiant (RSG) stars in the LMC. This low
dust abundance can be accounted for by a combination of evaporation through the
UV-flash from the supernova outburst and subsequent sputtering in the shocked
gas. For this explanation to hold, dust in the pre-supernova circumstellar
medium (CSM) would have to have been predominantly composed of grains other
than graphite, with a maximum size smaller than ~0.1 microns.",0309473v1
2003-09-30,Axisymmetric MHD simulations of the collapsar model for gamma-ray bursts,"We present results from axisymmetric, time-dependent magnetohydrodynamic
(MHD) simulations of the collapsar model for gamma-ray bursts. We begin the
simulations after the 1.7 MSUN iron core of a 25 MSUN presupernova star has
collapsed and study the ensuing accretion of the 7 MSUN helium envelope onto
the central black hole formed by the collapsed iron core. We consider a
spherically symmetric progenitor model, but with spherical symmetry broken by
the introduction of a small, latitude-dependent angular momentum and a weak
radial magnetic field. Our MHD simulations include a realistic equation of
state, neutrino cooling, photodisintegration of helium, and resistive heating.
Our main conclusion is that, within the collapsar model, MHD effects alone are
able to launch, accelerate and sustain a strong polar outflow. We also find
that the outflow is Poynting flux-dominated, and note that this provides
favorable initial conditions for the subsequent production of a baryon-poor
fireball.",0310002v1
2003-10-08,"Determining the Metallicity of Cepheid Stars in the SMC, LMC and the Galaxy","The Cepheid Period-Luminosity relation is unquestionably one of the most
powerful tools at our disposal for determining the extragalactic distance
scale. While significant progress has been made in the past few years towards
its understanding and characterisation, both on the observational (e.g. the HST
Key Project) and theoretical (e.g. non-linear pulsation models, non-LTE
atmospheres etc.) sides, the debate on the influence that chemical composition
may have on the Period-Luminosity relation is still unsettled. Current
estimates lead to differences in the distance as large as 15%, effectively
limiting the accuracy of Cepheids as distance indicators.
  To further tackle this problem, we have obtained high resolution spectra of a
large sample of Cepheids in our Galaxy and the Magellanic Clouds. The superb
quality of the data allow us to probe the detailed effects of chemical
composition (alpha, iron-group, and heavy elements) over more than a factor of
ten in metallicity. Here, we present the first preliminary results of the
analysis of iron abundances in a sub-sample of Cepheids.",0310217v1
2003-10-15,Galactic metallicity distribution from open clusters,"We have compiled two new Galactic open cluster catalogues. The first one has
119 objects with age, distance and metallicity data, while the second one has
144 objects with both absolute proper motion and radial velocity data, of which
45 clusters also with metallicity data available. An iron radial gradient of
about $-0.063\pm$0.008 \dexkpc is obtained from our sample. By dividing
clusters into age groups, we show that iron gradient was steeper in the past. A
disk age-metallicity relation could very probably exist based on the current
sample.",0310395v1
2003-12-10,Is the soft excess in AGN real?,"We systematically analyse all publicly available XMM-Newton spectra of
radio-quiet PG quasars. The soft X-ray excess in these objects is well modelled
by an additional, cool, Compton scattering region. However, the remarkably
constant temperature derived for this component over the whole sample requires
a puzzling fine tuning of the parameters. Instead, we propose that the soft
excess is an artifact of strong, relativistically smeared, partially ionized
absorption. The strong jump in opacity at ~0.7 keV from OVII, OVIII and iron
can lead to an apparent soft excess below this energy, which is trivially
constant since it depends on atomic processes. This can have a dramatic effect
on the derived spectrum, which has implications for fitting the relativistic
smearing of the reflected iron line emission from the disc.",0312271v2
2003-12-18,New constraints on the mass composition of cosmic rays above 10^17 eV from Volcano Ranch measurements,"Linsley used the Volcano Ranch array to collect data on the lateral
distribution of showers produced by cosmic rays at energies above 10^17 eV.
Very precise measurements of the steepness of the lateral distribution function
were made on 366 events. The current availability of sophisticated hadronic
interaction models has prompted an interpretation of the measurements. In this
analysis we use the AIRES Monte Carlo code to generate showers, together with
GEANT4 to simulate the detector response to ground particles. The results show
that, with the assumption of a bi-modal proton and iron mix, iron is the
dominant component of cosmic rays between 5x10^17 and 10^19 eV, assuming that
hadronic interactions are well-described by QGSJET at this energy range.",0312463v1
2004-04-19,A broad iron K alpha line at z=1.146,"We report the discovery of a strong iron K alpha line in the hard X-ray
selected source CXOJ 123716.7+621733 in the Chandra Deep Field North survey at
z=1.146. The analysis is made possible by the very deep exposure ~2 Ms and low
background of the ACIS detector. The line profile seems to be inconsistent with
a narrow feature. The best fit solution is achieved with a broad line. Most of
the flux in the broad component originates at energies below 6.4 keV with a
shape similar to that expected from emission in the innermost regions of the
accretion disk.",0404364v1
2004-05-13,On the iron Kalpha complex in magnetic cataclysmic variables,"We present a compilation of spectra of the iron Kalpha region in magnetic
cataclysmic variables, using data from the Chandra-HETG. The H-like, He-like
and fluorescent components are clearly resolved, and there are hints of the
structure within each component. The different shape of the He-like component
in AM Her might be related to greater cyclotron cooling in this star. A
surprising absence of Doppler shifts in the H-like and He-like components
implies that the X-ray emission is predominantly from the denser,
lower-velocity base of the accretion columns. This absence will allow ASTRO-E2
to resolve the structure in each component, leading to temperature diagnostics.
  We do not confirm the report that the H-like and He-like components of AO Psc
are Compton broadened; however we do detect a Compton-downshifted shoulder to
the fluorescent line of GK Per. Further, a Doppler-shifted wing of this line
arises in the high-velocity, pre-shock flow.",0405254v1
2004-05-21,Atmospheric parameters and abundances of sdB stars,"We summarize recent results of quantitative spectral analyses using NLTE and
metal line-blanketed LTE model atmospheres. Temperatures and gravities derived
for hundreds of sdB stars are now available and allow us to investigate
systematic uncertainties of teff, log g scales and to test the theory of
stellar evolution and pulsations. Surface abundance patterns of about two dozen
sdB stars are surprisingly homogenous. In particular the iron abundance is
almost solar for most sdBs. We highlight one iron deficient and three super
metal-rich sdBs, a challenge to diffusion theory. SdB stars are slowly rotating
stars unless they are in close binary systems which is hard to understand if
the sdB stars were formed in merger events. The only exception is the pulsator
PG 1605+072 rotating at v sin i = 39km/s. Signatures of stellar winds from sdB
stars have possibly been found.",0405426v1
2004-07-22,Shot cutoff timescales in different spectral states of Cygnus X-1,"We investigate the shot cutoff timescale evolutions during different spectral
states in the black hole binary Cygnus X-1 with the recently proposed w
spectral analysis technique. For low energy shots, their cutoff timescale
decreases from the low state to intermediate state, and to high state
monotonically. However in the high energy range, where shots are believed to be
reprocessed in the hot corona, timescales are almost the same for different
spectral states. A linear correlation is found between the energy spectrum
photon index and the shot cutoff timescale at low energies. Both narrow and
broad iron Kalpha lines are distinguished from timing analysis, providing
dynamical evidence that broad and narrow iron lines originate respectively at
small and large radii of the accretion disk. Possible mechanisms for state
transitions and accretion flow geometry in accreting stellar mass black holes
are discussed.",0407470v1
2004-07-30,X-ray Lines in Gamma-ray Bursts and Cerenkov Line Mechanism,"X-ray emission and absorption features are of great importance in our
understanding the nature and environment of gamma-ray bursts (GRBs). So far,
iron emission lines have been detected in at least four GRB afterglows. In this
paper, the observational properties and physical constraints on materials
surrounding GRB sources are reviewed, and several classes of theoretical models
are also discussed. We will specially concentrate on the Cerenkov line
mechanism, in which the broad iron lines are expected, and a small mass of Fe
is required to produce the large line luminosity. In addition, our
interpretation can favor the recent jet unified model for different classes of
gamma-ray bursts with a standard energy reservoir.",0407626v1
2004-09-19,On the variability of the iron line in Mrk 841,"Petrucci et al. (2002; hereafter P02) have reported extraordinary behaviour
of the iron K alpha line in the type 1 AGN Mrk 841. At the XMM-Newton/EPIC
resolution, a narrow line was observed in a short observation, which then
apparently disappeared around 0.5 days later when another observation was
performed. The limits are such that the line cannot both be narrow, and
variable at this level, as the light-travel time places the material at a
radius where broadening by the black hole's gravitational field is inevitable.
Adding an additional observation taken before the P02 data, we present a
different interpretation of the apparent variability. The data support the
hypothesis that the line in fact varies in width, not only in flux. Rather than
showing no line, and despite the strong Compton reflection component, the final
observation exhibits broad emission at ~ 6.2-6.4 keV, with a width of ~0.8 keV,
typical of a relativistic accretion disc. We suggest that the apparently narrow
line in the early observations arises from local illumination by a flare
inducing an hotspot in the inner disc, which then becomes progressively
broadened as the disc rotates.",0409459v1
2004-10-28,Insight into AGB and post-AGB stellar evolution with FUSE,"FUSE spectroscopy has proved that extremely hot hydrogen-deficient post-AGB
stars (PG1159 stars) display matter on their surface that usually remains
hidden in the region between the H- and He-burning shells of the former AGB
star. Hence, the spectral analysis of PG1159 stars allows to study directly the
chemistry of this intershell region which is the outcome of complicated burning
and mixing processes during AGB evolution. Detailed abundance determinations
provide constraints for these processes which are still poorly understood. With
FUSE we have discovered high neon and fluorine overabundances. There is also a
significant iron deficiency, which may be caused by s-process neutron capture
transforming iron into heavier elements.",0410689v1
2004-11-10,"The Origin, Composition, and Energy Source for the Sun","Heterogeneous supernova debris formed the solar system. Cores of inner
planets formed in the central iron rich region. The Sun formed on the collapsed
supernova core. Lighter elements and the lighter isotopes of each element are
enriched at the solar surface. The most abundant nuclide in the Sun is Iron 56,
the decay product of doubly magic Nickel 56. Doubly magic Oxygen 16 is next
most abundant. The least abundant elements, Li, Be, and B, have loosely bound
nucleons. Abundance is linked with nuclear stability, except for an over
abundance of H from neutron emission and neutron decay near the core. The main
elements in the Sun, Fe, Ni, O, Si, S, Mg, and Ca, comprise 99 percent of
meteorites. Neutron emission from the SN core triggers a series of reactions
that produce solar luminosity, solar neutrinos, excess H, and an annual
outpouring of 2.7 E 43 Hydrogen atoms in the solar wind.",0411255v1
2004-11-15,Iron Abundance in Hydrogen-Rich Central Stars of Planetary Nebulae,"We report on an on-going analysis of high-resolution UV spectra of hot
hydrogen-rich central stars of planetary nebulae (CSPN), obtained with the
Hubble Space Telescope and FUSE. Since UV spectra of many CSPN are dominated by
Fe and Ni lines, we intend to use them as temperature indicators to check the
CSPN temperature scale we have derived earlier from CNO ionization balances.
Furthermore, the observed line strengths of heavy metals show large variations
between different objects suggesting a possible spread in abundances. We will
determine abundances of iron group elements by quantitative spectral analyses
with non-LTE model atmospheres.",0411404v1
2004-11-18,A Multiband Approach to AGN: Radioscopy & Radio Astronomy,"Only in the radio-loud population of active galactic nuclei (AGN) does the
production, collimation, and acceleration of powerful relativistic jets take
place. We introduce here a concept of combined VLBI- and X-ray spectroscopic
observations of sources with relativistic, broad iron lines. This approach has
enormous potential to yield deep insights into the accretion/jet-production
process in AGN. Better knowledge of the milliarcsecond-resolution radio
structure of the nuclear radio cores in so-called ``radio-quiet''
broad-iron-line Seyfert galaxies is essential for future combined radio/X-ray
studies of the different modes of radio-jet production in accreting black hole
systems.",0411534v1
2004-11-25,Influence of Primary Cosmic Radiation Mass Composition on the Estimation of Eas Energy,"At the Yakutsk EAS array E_em is determined by using measurements of EAS
Cherenkov light flux and charged particle flux. It is known from calculations
that these characteristics depend on a sort of primary particle and, therefore,
the estimation of E_em depends on a primary particle mass. In the work the
dependence of the E_em/E_0 ratio on the energy is given and experimental data
are compared with calculations by the QGSJET model. The calculations have been
carried out for the primary proton and iron nucleus. The average calculated
meaning of the value of E_em/E_0 ratio (between the proton and iron nucleus)
within experimental errors is in agreement with experimental data that doesnt
contradict to the mixed mass composition of primary cosmic radiation.",0411682v2
2004-12-03,Narrow Iron K$α$ Lines in Active Galactic Nuclei: Evolving Populations?,"We assemble a sample consisting of 66 active galactic nuclei (AGNs) from
literature and the {\em XMM-Newton} archive in order to investigate the origin
of the 6.4 keV narrow iron K$\alpha$ line (NIKAL). The X-ray Baldwin effect of
the NIKAL is confirmed in this sample. We find the equivalent width ($EW$) of
the NIKAL is more strongly inversely correlated with Eddington ratio ($\ce$)
than the 2-10 keV X-ray luminosity. Our sample favors the origin from the dusty
torus and the X-ray Baldwin effect is caused by the changing opening angle of
the dusty torus. The relation $EW-\ce$ can be derived from a toy model of the
dusty torus. If the unification scheme is valid in all AGNs, we can derive the
Baldwin effect from the fraction of type {\sc ii} AGNs to the total population
given by {\em Chandra} and {\em Hubble} deep surveys. Thus the evolution of
populations could be reflected by the NIKAL's Baldwin effect.",0412075v1
2005-01-10,West-Side Story (On the History of Density-Wave Spiral Theories in the 1960s),"This paper deals with the history of Density-Wave Spiral Theories in the
1960s. The motivation to write the paper was the publication of two papers on
the history of these theories (Pasha 2004a,b). Pasha's papers tell only a part
of the story that took place on the Western side of the Iron Curtain in the
1960s. But giving only a part of the full story is a distortion of historical
truth. Important work done on the Eastern side of the Iron Curtain is still
little known in the West. In this paper, I fill the gaps and correct
chronological inaccuracies in Pasha's story and mention facts that are still
unknown (or little known) to the astronomical community in the West. I also
give my recollection of the development of Density-Wave Spiral Theories in the
1960s.",0501170v1
2005-02-10,Plasma Diffuser Sorts Light Atoms to Solar Surface,"The Sun operates like a giant plasma diffuser that sorts lighter isotopes and
elements to the solar surface. Measurements indicate that the interior of the
Sun consists mostly of the same seven, even-numbered elements as ordinary
meteorites: Iron, oxygen, nickel, silicon, sulfur, magnesium, and calcium.
These ordinary elements compose clothing on the central neutron star that was
produced at the core of the supernova that exploded here 5 billion years ago.
Neutron emission generates most solar energy. Neutron-decay near the core
produces Hydrogen ions that are accelerated upward by deep-seated magnetic
fields. This is the carrier gas that maintains mass separation in the Sun. Like
smoke, Hydrogen is a by-product from the solar furnace that powers the Sun. As
smoke passes over catalytic converters in the flue of a high-efficiency
furnace, most Hydrogen is fused into Helium during its upward journey. H-fusion
makes less than 38 percent of solar energy. Each year 50 trillion tons of
Hydrogen reach the solar surface and are flung off in the solar wind, with
isotopes of other trace elements carefully sorted by mass. Hydrogen is smoke
from the solar furnace, rather than its primary fuel.",0502206v1
2005-03-28,A Compiled Catalogue of Spectroscopically Determined Elemental Abundances for Stars with Accurate Parallaxes. I.Magnesium,"We present a compiled catalogue of effective temperatures, surface gravities,
iron and magnesium abundances, distances, velocity components, and orbital
elements for stars in the solar neighborhood. The atmospheric parameters and
iron abundances are averages of published values derived from model synthetic
spectra for a total of about 2000 values in 80 publications. Our relative
magnesium abundances were found from 1412 values in 31 publications for 876
dwarfs and subgiants using a three-step iteration averaging procedure, with
weights assigned to each source of data as well as to each individual
determination and taking into account systematic deviations of each scale
relative to the reduced mean scale. The estimated assumed completeness for data
sources containing more than five stars, up to late December 2003, exceeds 90%.
For the vast majority of stars in the catalogue, the spatial velocity
components were derived from modern high-precision astrometric observations,
and their Galactic orbit elements were computed using a three-component model
of the Galaxy, consisting of a disk, a bulge, and a massive extended halo.",0503591v2
2005-04-06,On the periodic clustering of cosmic ray exposure ages of iron meteorites,"Two recent papers claimed to have found a periodic variation of the galactic
cosmic ray (CR) flux over the last 1-2 Gyr, using the CR exposure ages of iron
meteorites. This was attributed to higher CR flux during the passage of the
Earth through the spiral arms of the Milky Way, as suggested by models. The
derived period was 143+-10 Myrs. We perform a more detailed analysis of the CR
exposure ages on the same data set, using extensive simulation to estimate the
influence of different error sources on the significance of the periodicity
signal. We find no evidence for significant clustering of the CR exposure ages
at a 143 Myr period nor for any other period between 100 and 250 Myrs. Rather,
we find the data to be consistent with being drawn from a uniform distribution
of CR exposure ages. The different conclusion of the original studies is due to
their neglecting the influence of (i) data treatment on the statistics, (ii)
several error sources, and (iii) number statistics.",0504155v1
2005-05-27,Iron Needles in Supernova Remnants?,"It has been suggested by Dwek (2004) that iron needles could explain the
submillimetre emission from the Cas A supernova remnant (SNR) with only a very
small total mass. We investigate whether a similar model holds for the Kepler
supernova remnant, and find that its emission could indeed be explained by a
dust mass of less than 10^-2 M_sun dependent on the axial ratio (l/a) of the
needles - which we constrain to be less than 700. But the implied needle model
for Kepler is inconsistent with that suggested for Cas A since either the
needles would have to have a resistivity one or two orders of magnitude greater
than those in Cas A or the electron density in Kepler's shocked plasma must be
40 times greater than suggested by X-ray observations. An additional problem
with the needle model is that the implied thickness of the needles seems to be
implausibly small, if the emission properties are calculated under the usual
approximations.",0505557v2
2005-05-30,High-resolution spectroscopy of the old open cluster Collinder 261:abundances of Iron and other elements,"We present the analysis of high resolution spectra of six red giant stars in
the old open cluster Collinder 261. Reddening values for individual stars,
derived from the relation between colours and temperatures (deduced from our
fully spectroscopic analysis) are consistent with previous determinations based
on photometry. For this cluster we derive an iron abundance of [Fe/H] = -0.03
+/- 0.03. We also obtain the abundances of light metals (O, Na and Al),
alpha-elements (Mg, Si, Ca, Ti), elements of the Fe-group (Sc, Cr, Mn, Co, Ni)
and the neutron-capture element Ba. No intrinsic star-to-star scatter is
present in any of these elements within our sample. We compare our findings
with previous investigations on this cluster, discussing in detail differences
in analysis methods and results.",0505606v1
2005-06-29,Oxygen in Galactic Disk Stars: non-LTE abundances from the 777 nm O I triplet,"Oxygen abundances for a large sample of dwarf and giant stars kinematically
selected to be part of the Galactic thin and thick disks have been determined
from a non-LTE analysis of the O I triplet lines at 777 nm. The abundance
analysis was performed using the infrared flux method temperature scale,
trigonometric surface gravities, and accurate atomic data. Within this
framework, the ionization balance of iron lines could not be satisfied and so
we adopted the iron abundances from Fe II lines only given that they are
relatively less sensitive to changes in the atmospheric parameters. We show the
resulting [O/Fe] vs. [Fe/H] relationship and briefly discuss its implications.",0506744v1
2005-07-18,The X-ray spectra of accreting Kerr black holes,"The relativistic broad iron lines seen in the X-ray spectra of several active
galaxies and Galactic black hole systems are reviewed. Most such objects
require emission from within the innermost stable orbit of a non-rotating black
hole, suggesting that the black holes are rapidly spinning Kerr holes. We
discuss the soft excess, the broad iron line and the Compton hump
characteristic of reflection from partially ionized gas and show that they may
be a common ingredient in the X-ray spectra of many radiatively-efficient,
accreting black holes. Strong gravitational bending of the radiation close to a
Kerr black hole can explain the otherwise puzzling spectral variability seen in
some objects. The Narrow Line Seyfert 1 galaxies may be among the most extreme
objects yet seen.",0507409v1
2005-09-01,"XMM-Newton observation of the bright Seyfert 1 galaxy, MCG+8-11-11","We report on the XMM-Newton observation of the bright Seyfert 1 galaxy,
MCG+8-11-11. Data from the EPIC/p-n camera, the Reflection Gratings
Spectrometers (RGS) and the Optical Monitor (OM) have been analyzed. The p-n
spectrum is well fitted by a power law, a spectrally unresolved Fe Kalpha line,
a Compton reflection component (whose large value, when compared to the iron
line equivalent width, suggests iron underabundance), and absorption by warm
material. Absorption lines are apparent in the RGS spectra, but their
identification is uncertain and would require large matter velocities. The UV
fluxes measured by the OM are well above the extrapolation of the X-ray
spectrum, indicating the presence of a UV bump.",0509017v1
2005-10-05,Pixie Dust: The Silicate Features in the Diffuse Interstellar Medium,"We have analyzed the 9.7 and ``18'' micron interstellar silicate absorption
features along the line of sight toward four heavily extincted galactic WC-type
Wolf-Rayet (WR) stars. We construct two interstellar extinction curves from
1.25 to 25 micron using near-IR extinction measurements from the literature
along with the silicate profiles of WR 98a (representing the local ISM) and GCS
3 (representing the Galactic Center). We have investigated the mineralogy of
the interstellar silicates by comparing extinction profiles for amorphous
silicates with olivine and pyroxene stochiometry to the 9.7 and ``18'' micron
absorption features in the WR 98a spectrum. In this analysis, we have
considered solid and porous spheres and a continuous distribution of
ellipsoids. While it is not possible to simultaneously provide a perfect match
to both profiles, we find the best match requires a mixture of these two types
of compounds. We also consider iron oxides, aluminosilicates and silicate
carbide (SiC) as grain components. Iron oxides cannot be accommodated in the
observed spectrum, while the amount of Si in SiC is limited to <4%. Finally, we
discuss the cosmic elemental abundance constraints on the silicate mineralogy,
grain shape and porosity.",0510156v1
2006-01-04,ASCA Observations of OAO 1657-415 and its Dust-Scattered X-Ray Halo,"We report on two ASCA observations of the high-mass X-ray binary pulsar OAO
1657-415. A short observation near mid-eclipse caught the source in a
low-intensity state, with a weak continuum and iron emission dominated by the
6.4-keV fluorescent line. A later, longer observation found the source in a
high-intensity state and covered the uneclipsed through mid-eclipse phases. In
the high-intensity state, the non-eclipse spectrum has an absorbed continuum
component due to scattering by material near the pulsar and 80 per cent of the
fluorescent iron emission comes from less than 19 lt-sec away from the pulsar.
We find a dust-scattered X-ray halo whose intensity decays through the eclipse.
We use this halo to estimate the distance to the source as 7.1 +/- 1.3 kpc.",0601075v1
2006-03-21,"On the Unusual Depletions toward Sk 155, or What Are the Small Magellanic Cloud Dust Grains Made of?","The dust in the Small Magellanic Cloud (SMC), an ideal analog of primordial
galaxies at high redshifts, differs markedly from that in the Milky Way by
exhibiting a steeply rising far-ultraviolet extinction curve, an absence of the
2175 Angstrom extinction feature, and a local minimum at ~12 micron in its
infrared emission spectrum, suggesting the lack of ultrasmall carbonaceous
grains (i.e. polycyclic aromatic hydrocarbon molecules) which are ubiquitously
seen in the Milky Way. While current models for the SMC dust all rely heavily
on silicates, recent observations of the SMC sightline toward Sk 155 indicated
that Si and Mg are essentially undepleted and the depletions of Fe range from
mild to severe, suggesting that metallic grains and/or iron oxides, instead of
silicates, may dominate the SMC dust. However, in this Letter we apply the
Kramers-Kronig relation to demonstrate that neither metallic grains nor iron
oxides are capable of accounting for the observed extinction; silicates remain
as an important contributor to the extinction, consistent with current models
for the SMC dust.",0603573v1
2006-04-03,Detection of Highly Ionized Metal Absorption Lines in the Ultracompact X-ray Dipper 4U 1916-05,"We present the high-resolution Chandra X-ray Observatory persistent (non-dip)
spectrum of 4U 1916-05 which revealed narrow absorption lines from hydrogenic
neon, magnesium, silicon, and sulfur, in addition to the previous identified
hydrogenic and helium-like iron absorption lines. This makes 4U 1916-05 only
the second of the classical X-ray dipper systems to show narrow absorption
lines from elements other than iron. We propose two possible explanations for
the small measured line widths (>~ 500-2000 km s^{-1}), compared to the
expected Keplerian velocities (> 1000 km s^{-1}) of the accretion disk in this
50-min orbital period system, and lack of wavelength shifts (>~ 250 km s^{-1}).
First, the ionized absorber may be stationary. Alternatively, the line
properties may measure the relative size of the emission region. From this
hypothesis, we find that the emission region is constrained to be >~ 0.25 times
the radial extent of the absorber. Our results also imply that the ionized
absorber spans a range of ionization parameters.",0604046v1
2006-05-09,The chemical compositions of the extreme halo stars HE0107-5240 and HE1327-2326 inferred from 3D hydrodynamical model atmospheres,"We investigate the impact of realistic 3D hydrodynamical model stellar
atmospheres on the determination of elemental abundances in the carbon-rich,
hyper iron-poor stars HE0107-5240 and HE1327-2326. We derive the chemical
compositions of the two stars by means of a detailed 3D analysis of spectral
lines under the assumption of local thermodynamic equilibrium (LTE). The lower
temperatures of the line-forming regions of the hydrodynamical models cause
changes in the predicted spectral line strengths. In particular we find the 3D
abundances of C, N, and O to be lower by ~ -0.8 dex (or more) than estimated
from a 1D analysis. The 3D abundances of iron-peak elements are also decreased
but by smaller factors (~ -0.2 dex). We caution however that the neglected
non-LTE effects might actually be substantial for these metals. We finally
discuss possible implications for studies of early Galactic chemical evolution.",0605219v1
2006-05-25,"On the Iron content of NGC 1978 in the LMC: a metal rich, chemically homogeneous cluster","We present a detailed abundance analysis of giant stars in NGC 1978, a
massive, intermediate-age stellar cluster in the Large Magellanic Cloud,
characterized by a high ellipticity and suspected to have a metallicity spread.
We analyzed 11 giants, all cluster members, by using high resolution spectra
acquired with the UVES/FLAMES spectrograph at the ESO-Very Large Telescope. We
find an iron content of [Fe/H]=-0.38 dex with very low (0.07 dex) dispersion,
and a mean heliocentric radial velocity Vr=293.1 (with an error of 0.9 km/s)
and a velocity dispersion (3.1 km/s), thus excluding the presence of a
significant metallicity, as well as velocity, spread within the cluster.",0605646v1
2006-07-18,Dielectronic recombination of Fe^{13+}: benchmarking the M-shell,"We have carried-out a series of multi-configuration Breit-Pauli AUTOSTRUCTURE
calculations for the dielectronic recombination of Fe^{13+}. We present a
detailed comparison of the results with the high-energy resolution measurements
reported recently from the Heidelberg Test Storage Ring by Schmidt et al. Many
Rydberg series contribute significantly from this initial 3s^2 3p M-shell ion,
resulting in a complex recombination `spectrum'. While there is much close
agreement between theory and experiment, differences of typically 50% in the
summed resonance strengths over 0.1-10 eV result in the experimentally based
total Maxwellian recombination rate coefficient being a factor of 1.52-1.38
larger than theory over 10^4-10^5 K, which is a typical temperature range of
peak abundance for Fe^{13+} in a photoionized plasma. Nevertheless, this
theoretical recombination rate coefficient is an order of magnitude larger than
that used by modellers to-date. This may help explain the discrepancy between
the iron M-shell ionization balance predicted by photoionization modelling
codes such as ION and CLOUDY and that deduced from the iron M-shell
unresolved-transition-array absorption feature observed in the X-ray spectrum
of many active galactic nuclei. Similar data are required for Fe^{8+} through
Fe^{12+} to remove the question mark hanging over the atomic data though.",0607412v1
2006-07-20,RXTE Observations of 1A 1744-361: Correlated Spectral and Timing Behavior,"We analyze Rossi X-ray Timing Explorer (RXTE) Proportional Counter Array
(PCA) data of the transient low mass X-ray binary (LMXB) system 1A 1744-361. We
explore the X-ray intensity and spectral evolution of the source, perform
timing analysis, and find that 1A 1744-361 shows `atoll' behavior during the
outbursts. The color-color diagram indicates that this LMXB was observed in a
low intensity spectrally hard (low-hard) state and in a high intensity `banana'
state. The low-hard state shows a horizontal pattern in the color-color
diagram, and the previously reported `dipper QPO' appears only during this
state. We also perform energy spectral analyses, and report the first detection
of broad iron emission line and iron absorption edge from 1A 1744-361.",0607475v1
2006-07-21,Gravity-mode pulsations in subdwarf B stars: a critical test of stellar opacity,"The identification of non-radial g-mode oscillations as the cause of
variability in cool subdwarf B stars (PG1716 variables) has been frustrated by
a 5 000 K discrepancy between the observed and theoretical blue edge of the
instability domain (Fontaine et al. 2003). A major component in the solution to
this problem has been identified} by (a) using updated OP instead of OPAL
opacities and (b) considering an enhancement of nickel, in addition to that of
iron, in the driving zone. The reason for this success is that, in OP, the
``Fe-bump'' contributions from iron and nickel occur at higher temperatures
than in OPAL. As well as pointing to a solution of an important problem in
stellar pulsation theory, this result provides a critical test for stellar
opacities and the atomic physics used to compute them.",0607505v1
2006-08-23,Effect of turbulent diffusion on iron abundance profiles,"We compare the observed peaked iron abundance profiles for a small sample of
groups and clusters with the predictions of a simple model involving the metal
ejection from the brightest galaxy and the subsequent diffusion of metals by
stochastic gas motions. Extending the analysis of Rebusco et al. (2005) we
found that for 5 out of 8 objects in the sample an effective diffusion
coefficient of the order of $10^{29}$ cm$^{2}$ s$^{-1}$ is needed. For AWM4,
Centaurus and AWM7 the results are different suggesting substantial
intermittence in the process of metal spreading across the cluster. There is no
obvious dependence of the diffusion coefficient on the mass of the system.
  We also estimated the characteristic velocities and the spatial scales of the
gas motions needed to balance the cooling losses by the dissipation of the same
gas motions. A comparison of the derived spatial scales and the sizes of
observed radio bubbles inflated in the ICM by a central active galactic nucleus
(AGN) suggests that the AGN/ICM interaction makes an important (if not a
dominant) contribution to the gas motions in the cluster cores.",0608491v1
2006-10-19,An XMM-Newton survey of broad iron lines in AGN,"We report on the iron K-alpha line properties of a sample of Seyfert galaxies
observed with the XMM-Newton EPIC pn instrument. Using a systematic and uniform
analysis, we find that complexity at iron-K is extremely common in the XMM
spectra. Once appropriate soft X-ray absorption, narrow 6.4 keV emission and
associated Compton reflection are accounted for, ~75 of the sample show an
improvement when a further Gaussian component is introduced. The typical
properties of the broad emission are both qualitatively and quantitatively
consistent with previous results from ASCA. The complexity is in general very
well described by relativistic accretion disk models. In most cases the
characteristic emission radius is constrained to be within ~50 R_g, where
strong gravitational effects become important. We find in about 1/3 of the
sample the accretion disk interpretation is strongly favoured over competing
models. In a few objects no broad line is apparent. We find evidence for
emission within 6 R_g in only two cases, both of which exhibit highly complex
absorption. Evidence for black hole spin based on the X-ray spectra therefore
remains tentative.",0610585v1
2006-12-08,Solar Chemical Peculiarities?,"Several investigations of FGK stars in the solar neighborhood have suggested
that thin-disk stars with an iron abundance similar to the Sun appear to show
higher abundances of other elements, such as silicon, titanium, or nickel.
Offsets could arise if the samples contain stars with ages, mean galactocentric
distances, or kinematics, that differ on average from the solar values. They
could also arise due to systematic errors in the abundance determinations, if
the samples contain stars that are different from the Sun regarding their
atmospheric parameters. We re-examine this issue by studying a sample of 80
nearby stars with solar-like colors and luminosities. Among these solar
""analogs"", the objects with solar iron abundances exhibit solar abundances of
carbon, silicon, calcium, titanium and nickel.",0612200v1
2006-12-12,Relativistic inflow in the Seyfert 1 Mrk 335 revealed through X-ray absorption,"The analysis of hard X-ray features in XMM-Newton data of the bright Sy 1
galaxy Mrk 335 is reported here. The presence of a broad, ionised iron K alpha
emission line in the spectrum, first found by Gondoin et al.(2002), is
confirmed. The broad line can be modeled successfully by relativistic accretion
disc reflection models.
  Regardless of the underlying continuum we report, for the first time in this
source, the detection of a narrow absorption feature at the rest frame energy
of ~5.9 keV. If the feature is identified with a resonance absorption line of
iron in a highly ionised medium, the redshift of the line corresponds to an
inflow velocity of ~0.11-0.15 c. Preliminary results from a longer (100ks)
exposure are also presented.",0612315v1
2006-12-19,Heavy metals and lead isotopes in sdB stars,"We present a detailed abundance analysis of high-resolution ultraviolet
echelle spectra of five subdwarf B stars obtained with HST-STIS The goal of our
observations was to test the hypothesis that pulsations in sdBs are correlated
to the surface abundances of iron-group elements. We study two pulsators and
three non-pulsators and determined abundances for 25 elements including the
iron group and even heavier elements such as tin and lead using LTE spectrum
synthesis techniques. We find strong enrichments of heavy elements up to 2.9dex
with respect to solar which are probably caused by atomic diffusion processes.
No clear-cut correlation between pulsations and metal abundances becomes
apparent. Abundances for lead isotopes are derived from very high resolution
spectra using an UV line of triply ionised lead. As Pb terminates the s-process
sequence Pb isotopic abundance ratios yield important constraints. It is very
difficult to measure them in hot stars. For the first time we were able to
measure them in two subluminous B stars and conclude that the 207Pb/208Pb is
solar.",0612535v1
2006-12-19,Hard X-rays and Fluorescent Iron Emission from the Embedded Infrared Cluster in NGC 2071,"We present first results of XMM-Newton X-ray observations of the infrared
cluster lying near the NGC 2071 reflection nebula in the Orion B region. This
cluster is of interest because it is one of the closest regions known to harbor
embedded high-mass stars. We report the discovery of hard X-ray emission from
the dense central NGC 2071-IR subgroup which contains at least three high-mass
young stellar objects (NGC 2071 IRS-1, IRS-2, and IRS-3). A prominent X-ray
source is detected within 1 arcsecond of the infrared source IRS-1, which is
thought to drive a powerful bipolar molecular outflow. The X-ray spectrum of
this source is quite unusual compared to the optically thin plasma spectra
normally observed in young stellar objects (YSOs). The spectrum is
characterized by a hard broad-band continuum plus an exceptionally broad
emission line at approximately 6.4 keV from neutral or near-neutral iron. The
fluorescent Fe line likely originates in cold material near the embedded star
(i.e. a disk or envelope) that is irradiated by the hard heavily-absorbed X-ray
source.",0612563v1
2006-12-21,Rotating Collapse of Stellar Iron Cores in General Relativity,"We present results from the first 2+1 and 3+1 simulations of the collapse of
rotating stellar iron cores in general relativity employing a
finite-temperature equation of state and an approximate treatment of
deleptonization during collapse. We compare full 3+1 and conformally-flat
spacetime evolution methods and find that the conformally-flat treatment is
sufficiently accurate for the core-collapse supernova problem. We focus on the
gravitational wave (GW) emission from rotating collapse, core bounce, and early
postbounce phases. Our results indicate that the GW signature of these phases
is much more generic than previously estimated. In addition, we track the
growth of a nonaxisymmetric instability of dominant m = 1 character in two of
our models that leads to prolonged narrow-band GW emission at ~ 920-930 Hz over
several tens of milliseconds.",0612638v2
2007-02-13,A Common Explosion Mechanism for Type Ia Supernovae,"Type Ia supernovae, the thermonuclear explosions of white dwarf stars
composed of carbon and oxygen, were instrumental as distance indicators in
establishing the acceleration of the universe's expansion. However, the physics
of the explosion are debated. Here we report a systematic spectral analysis of
a large sample of well observed type Ia supernovae. Mapping the velocity
distribution of the main products of nuclear burning, we constrain theoretical
scenarios. We find that all supernovae have low-velocity cores of stable
iron-group elements. Outside this core, nickel-56 dominates the supernova
ejecta. The outer extent of the iron-group material depends on the amount of
nickel-56 and coincides with the inner extent of silicon, the principal product
of incomplete burning. The outer extent of the bulk of silicon is similar in
all SNe, having an expansion velocity of ~11000 km/s and corresponding to a
mass of slightly over one solar mass. This indicates that all the supernovae
considered here burned similar masses, and suggests that their progenitors had
the same mass. Synthetic light curve parameters and three-dimensional explosion
simulations support this interpretation. A single explosion scenario, possibly
a delayed detonation, may thus explain most type Ia supernovae.",0702351v1
1996-03-21,Density Matrix Functional Calculations for Matter in Strong Magnetic Fields: I. Atomic Properties,"We report on a numerical study of the density matrix functional introduced by
Lieb, Solovej and Yngvason for the investigation of heavy atoms in high
magnetic fields. This functional describes {\em exactly} the quantum mechanical
ground state of atoms and ions in the limit when the nuclear charge $Z$ and the
electron number $N$ tend to infinity with $N/Z$ fixed, and the magnetic field
$B$ tends to infinity in such a way that $B/Z^{4/3}\to\infty$. We have
calculated electronic density profiles and ground state energies for values of
the parameters that prevail on neutron star surfaces and compared them with
results obtained by other methods. For iron at $B=10^{12}$ G the ground state
energy differs by less than 2 \% from the Hartree-Fock value. We have also
studied the maximal negative ionization of heavy atoms in this model at various
field strengths. In contrast to Thomas-Fermi type theories atoms can bind
excess negative charge in the density matrix model. For iron at $B=10^{12}$ G
the maximal excess charge in this model corresponds to about one electron.",9603005v1
1995-10-25,First Principles LCGO Calculation of the Magneto-optical Properties of Nickel and Iron,"We report a first principles, self-consistent, all electron, linear
combination of Gaussian orbitals (LCGO) calculation of a comprehensive
collection of magneto-optical properties of nickel and iron based on density
functional theory. Among the many magneto-optical effects, we have studied the
equatorial Kerr effect for absorption in the optical as well as soft X-ray
region, where it is called X-ray magnetic linear dichroism (X-MLD). In the
optical region the effect is of the order of 2\% while in the X-ray region it
is of the order of 1\% for the incident angles considered. In addition, the
polar Kerr effect, X-ray magnetic circular dichroism (X-MCD) and total X-ray
absorption at the L$_{2,3}$ edges, soft X-ray Faraday effect at the L$_{2,3}$
edges have also been calculated. Our results are in good agreement with
experiments and other first principles methods that have been used to calculate
some of these properties.",9510148v1
1996-06-05,Multiple-Scattering Theory of X-Ray Magnetic Circular Dichroism: Implementation and Results for Iron K-edge,"An implementation of the multiple-scattering approach to x-ray magnetic
circular dichroism (XMCD) in K-edge x-ray absorption spectroscopy is presented.
The convergence problems due to the cluster size and the relativistic
corrections are solved using an expansion of the Dirac Green function for
complex energies up to the second order in 1/$c$. The Fermi energy is dealt
with via a complex plane integration. Numerical methods used to obtain the
semi-relativistic Green function in the whole complex plane are explained. We
present a calculation of the magnetic circular dichroism at the K-edge of
bcc-iron including the core hole effect. A good agreement is found at high
energy. The physical origins of the XMCD spectrum near the edge and far from
the edge are analyzed. The influence of the core hole, the possibility of a
multiple-scattering expansion and the relation of XMCD with the spin-polarized
density of states are discussed. A simple interpretation of XMCD at the K-edge
is presented in terms of a rigid-band model.",9606022v1
1998-08-10,LDA++ approach to electronic structure of magnets: correlation effects in iron,"A novel approach to investigation of correlation effects in the electronic
structure of magnetic crystals which takes into account a frequency dependence
of the self energy (so called ``LDA++ approach'') is developed. The fluctuation
exchange approximation is generalized to the spin-polarized multi-band case and
its local version is proposed. As an example, we calculate the electronic
quasiparticle spectrum of ferromagnetic iron. It is shown that the Fermi liquid
description of the bands near the Fermi level is reasonable, while the
quasiparticle states beyond approximately 1 eV range are strongly damped, in
agreement with photoemission data. The result of the spin-polarized
thermoemission experiment is explained satisfactory. The problem of satellite
structure is discussed.",9808094v1
1999-08-20,Density-functional-theory calculations of molecular nitrogen on ruthenium cluster,"Density-functional-theory calculations for the adsorption of molecular
nitrogen on ruthenium surface are reported. It is found that nitrogen molecule
is adsorbed while standing perpendicular to the triangular surface of
ruthenium. The doping by K atoms favours the adsorption of molecular nitrogen.
The calculation of the adsorption energy has also been performed on iron and
osmium clusters which shows that ruthenium adsorbs better than iron or osmium.
It is found that potential for atomic nitrogen is deeper and more stable than
that of molecular nitrogen and hence atomic nitrogen is important for
catalysis.",9908300v1
1999-08-27,Thermodynamics of hexagonal-close-packed iron under Earth's core conditions,"The free energy and other thermodynamic properties of hexagonal-close-packed
iron are calculated by direct {\em ab initio} methods over a wide range of
pressures and temperatures relevant to the Earth's core. The {\em ab initio}
calculations are based on density-functional theory in the generalised-gradient
approximation, and are performed using the projector augmented wave (PAW)
approach. Thermal excitation of electrons is fully included. The Helmholtz free
energy consists of three parts, associated with the rigid perfect lattice,
harmonic lattice vibrations, and anharmonic contributions, and the technical
problems of calculating these parts to high precision are investigated. The
harmonic part is obtained by computing the phonon frequencies over the entire
Brillouin zone, and by summation of the free-energy contributions associated
with the phonon modes. The anharmonic part is computed by the technique of
thermodynamic integration using carefully designed reference systems. Detailed
results are presented for the pressure, specific heat, bulk modulus, expansion
coefficient and Gr\""{u}neisen parameter, and comparisons are made with values
obtained from diamond-anvil-cell and shock experiments.",9908400v1
2000-01-05,Circularly polarized light emission in scanning tunneling microscopy of magnetic systems,"Light is produced when a scanning tunneling microscope is used to probe a
metal surface. Recent experiments on cobalt utilizing a tungsten tip found that
the light is circularly polarized; the sense of circular polarization depends
on the direction of the sample magnetization, and the degree of polarization is
of order 10 %. This raises the possibility of constructing a magnetic
microscope with very good spatial resolution. We present a theory of this
effect for iron and cobalt and find a degree of polarization of order 0.1 %.
This is in disagreement with the experiments on cobalt as well as previous
theoretical work which found order of magnitude agreement with the experimental
results. However, a recent experiment on iron showed 0.0 ${\pm}$2 %. We predict
that the use of a silver tip would increase the degree of circular polarization
for a range of photon energies.",0001044v1
2000-02-14,Thermodynamic stability of Fe/O solid solution at inner-core conditions,"We present a new technique which allows the fully {\em ab initio} calculation
of the chemical potential of a substitutional impurity in a high-temperature
crystal, including harmonic and anharmonic lattice vibrations. The technique
uses the combination of thermodynamic integration and reference models
developed recently for the {\em ab initio} calculation of the free energy of
liquids and anharmonic solids. We apply the technique to the case of the
substitutional oxygen impurity in h.c.p. iron under Earth's core conditions,
which earlier static {\em ab initio} calculations indicated to be
thermodynamically very unstable. Our results show that entropic effects arising
from the large vibrational amplitude of the oxygen impurity give a major
reduction of the oxygen chemical potential, so that oxygen dissolved in h.c.p.
iron may be stabilised at concentrations up a few mol % under core conditions.",0002208v1
2001-07-09,On the Magnetism of the Normal State in MgB2,"The experimentally observed ferromagnetism in MgB2 in the normal state is
attributed to micro phase separated inclusions of iron. This magnetic character
is also observed when the iron content of the samples is reduced below 20
micro-g/g, however in these samples the diamagnetism of MgB2 is apparent and is
measured. It is found experimentally that the diamagnetic susceptibility at
room temperature of B element, MgB2 and MgB4 is close to the ratio 1:2:4,
suggesting that the diamagnetism in these borides is confined to the boron
atoms. This observation supports a picture in which the two electrons of Mg are
donated to B in MgB2",0107169v3
2001-10-01,"Importance of Magnetism in Phase Stability, Equations of State, and Elasticity","The effects of magnetism on high pressure properties of transition metals and
transition metal compounds can be quite important. In the case of Fe, magnetism
is responsible for stability of the body-centered cubic (bcc) phase at ambient
conditions, and the large thermal expansivity in face-centered cubic (fcc)
iron, and also has large effects on the equation of state and elasticity of
hexagonal close-packed (hcp) iron. In transition metal oxides, local magnetic
moments are responsible for their insulating behavior. LDA+U results are
presented for CoO and FeO, and predictions are made for high pressure
metallization. The inclusion of a local Coulomb repulsion, U, greatly inhibits
the high-spin low-spin transitions found with conventional exchange-correlation
functionals (i.e. generalized gradient corrections, GGA). We discuss theory and
computations for the effects of magnetism on high pressure cohesive properties.",0110025v5
2001-11-14,Interlayer exchange coupling and giant magnetoresistance in Fe/V (001) superlattices,"Magnetization and magnetoresistivity studies of Fe/V (001) superlattices are
reported. The first giant magnetoresistance peak with respect to the vanadium
and iron layer thicknesses is investigated. The interlayer antiferromagnetic
coupling strength is found to show a peak at a vanadium layer thickness of
  13 atomic monolayers ($\approx$ 20 \AA) with a full width at half maximum of
about 2 monolayers. The antiferromagnetic coupling shows a maximum at an iron
layer thickness of about 6 monolayers ($\approx$ 9 \AA) for series of
superlattices with vanadium thicknesses around 13 monolayers. The magnitude of
the giant magnetoresistance shows a similar variation as the antiferromagnetic
coupling strength.",0111255v1
2002-05-13,Direct visualization of iron sheath shielding effect in MgB_2 superconducting wires,"Local magneto-optical imaging and global magnetization measurement techniques
were used in order to visualize shielding effects in the superconducting core
of MgB_2 wires sheathed by ferromagnetic iron (Fe). The magnetic shielding can
provide a Meissner-like state in the superconducting core in applied magnetic
fields up to ~1T. The maximum shielding fields are shown to correlate with the
saturation fields of magnetization in Fe-sheaths. The shielding has been found
to facilitate the appearance of an overcritical state, which is capable of
achieving a critical current density (J_c) in the core which is larger than J_c
in the same wire without the sheath by a factor of ~2. Other effects caused by
the magnetic interaction between the sheath and the superconducting core are
discussed.",0205253v2
2002-05-27,Superconductivity of epsilon-Fe: complete resistive transition,"Last year, iron was reported to become superconducting at temperatures below
2K and pressures between 15 and 30 GPa. The evidence presented was a weak
resistivity drop, suppressed by a magnetic field above 0.2 T, and a small
Meissner signal. However, a compelling demonstration, such as the occurrence of
zero resistance, was lacking. Here we report the measurement of a complete
resistive transition at 22.2 GPa with an onset slightly above 2 K in two very
pure samples of iron, of different origins. The superconductivity appears
unusually sensitive to disorder, developing only when the electronic mean free
path is above a threshold value, while the normal state resistivity is
characteristic of a nearly ferromagnetic metal.",0205557v1
2003-05-16,Avoiding quenching in superconducting rings,"A procedure for avoiding the quenching associated to a previously reported
method for inducing currents in superconducting rings [H. Gonzalez-Jorge et
al., Appl. Phys. Lett. 81, 4207 (2002)] is proposed. High persistent currents
are induced in two textured YBCO rings (1536 and 2870 A) using a modified
version of the original procedure that consist on a straightforward magnetic
circuit made up of an iron core and a permanent magnet. The insertion of an
iron core into the ring reduces the current to an exent sufficing to avoid
quenching as the critical temperature is overcame and preserving thus the
structures of the samples. Such a simple operation can be extended to other
situations involving quenching (e. g. the use of superconducting coils):",0305392v1
2003-06-17,"Electron Spectroscopy and Density-Functional Study of ""Ferric Wheel"" Molecules","The Li-centered ""ferric wheel"" molecules with six oxo-bridged iron atoms form
molecular crystals. We probed their electronic structure by X-ray photoelectron
(XPS) and soft X-ray emission spectroscopy (XES), having calculated in parallel
the electronic structure of a single ""ferric wheel"" molecule from
first-principles by tools of the density-functional theory, using,
specifically, the Siesta method. The Fe local moments were found to be 4 mu_B,
irrespective of their mutual orientation. Neighbouring atoms, primarily oxygen,
exhibit a noticeable magnetic polarization, yielding effective spin S=5/2 per
iron atom, that can get inverted as a ""rigid"" one in magnetic transitions.
Corresponding energy preferences can be mapped onto the Heisenberg model with
effective exchange parameter J of about -80 K.",0306430v1
2004-01-21,Ab initio investigation of structural and magnetic properties of Fe|ZnSe(001),"We investigate 1, 2, 3, and 4 monolayers of iron grown on the (001) surface
of ZnSe using spin density functional theory, plane-wave expansion, and
ultrasoft pseudopotentials. An ideal structure of the interface is plausible
due to the very small lattice mismatch between both materials. However, we
observe dramatic deviations from this idealized configuration. The most
distinctive variations arise in the case of a single monolayer. Here a
terminating Zn layer is buoying upwards. The thicker the Fe layer the weaker
are the relaxations in the iron region. Nevertheless, in the case of the
Se-terminated surface, the structure changes significantly inside the
semiconductor near the interface. The profiles of the electronic density and
the magnetization perpendicular to the surface are quite sensitive to the
change from the ideal to the real structure.",0401388v1
2004-03-09,Room temperature study of a strain-induced electronic superstructure on a magnetite (111) surface,"A magnetite (Fe3O4) single crystal (111) surface has been studied at various
oxygen-iron surface stoichiometries. The stoichiometry was modified by
controlling the in-situ sample anneal conditions. We have found the conditions
that lead to the formation of an oxygen-rich surface that forms a
quasi-hexagonal superstructure with a 42A periodicity. The superstructure is
highly regular and was observed by both LEED and STM. The superstructure
consists of three regions, two of which have identical atomic scale structures
with a periodicity of 2.8A, and a third having a periodicity that is about 10%
larger (3.1A). The subtle difference in the atomic periodicities between the
three areas results from the modulation of intrinsic strain developed along the
surface. The superstructure results from electronic effects rather than being a
mosaic of different iron oxide terminations. The onset of the superstructure is
sensitive to the surface stoichiometry. From our results we could estimate the
critical density of defects leading to the disappearance of the superstructure.
We have modelled the experimental results and calculated the electron density
using a DFT algorithm. The model clearly shows the development of strain along
the surface.",0403238v1
2004-03-18,Overcritical state in superconducting round wires sheathed by iron,"Magnetic measurements carried out on MgB_2 superconducting round wires have
shown that the critical current density J_c(B_a) in wires sheathed by iron can
be significantly higher than that in the same bare (unsheathed) wires over a
wide applied magnetic field B_a range. The magnetic behavior is, however,
strongly dependent on the magnetic history of the sheathed wires, as well as on
the wire orientation with respect to the direction of the applied field. The
behavior observed can be explained by magnetic interaction between the soft
magnetic sheath and superconducting core, which can result in a redistribution
of supercurrents in the flux filled superconductor. A phenomenological model
explaining the observed behavior is proposed.",0403454v1
2004-11-08,High-frequency electron paramagnetic resonance investigation of the Fe3+ impurity center in polycrystalline PbTiO3 in its ferroelectric phase,"The intrinsic iron(III) impurity center in polycrystalline lead titanate was
investigated by means of high-frequency electron paramagnetic resonance (EPR)
spectroscopy in order to determine the local-environment sensitive fine
structure parameter D. At a spectrometer frequency of 190 GHz, spectral
analysis of a powder sample was unambiguously possible. The observed mean value
D = +35.28 GHz can be rationalized if Fe3+ ions substitute for Ti4+ at the
B-site of the perovskite ABO3 lattice forming a directly coordinated iron -
oxygen vacancy defect associate. A consistent fit of the multi-frequency data
necessitated use of a distribution of D values with a variance of about 1 GHz.
This statistical distribution of values is probably related to more distant
defects and vacancies.",0411167v1
2004-12-23,Nanocrystallization and Amorphization Induced by Reactive Nitrogen Sputtering in Iron and Permalloy,"Thin films of iron and permalloy Ni80Fe20 were prepared using an Ar+N2
mixture with magnetron sputtering technique at ambient temperature. The
nitrogen partial pressure, during sputtering process was varied in the range of
0 to 100%, keeping the total gas flow at constant. At lower nitrogen pressures
RN2<33% both Fe and NiFe, first form a nanocrystalline structure and an
increase in nitrogen partail pressure results in formation of an amorphous
structure. At intermediate nitrogen partial pressures, nitrides of Fe and NiFe
were obtained while at even higher nitrogen partial pressures, nitrides
themselves became nanocrystalline or amorphous. The surface, structural and
magnetic properties of the deposited films were studied using x-ray reflection
and diffraction, transmission electron microscopy, polarized neutron
reflectivity and using a DC extraction magnetometer. The growth behavior for
amorphous film was found different as compared with poly or nanocrystalline
films. The soft-magnetic properties of FeN were improved on nanocrystallization
while those of NiFeN were degraded. A mechanism inducing nanocrystallization
and amorphization in Fe and NiFe due to reactive nitrogen sputtering is
discussed in the present article.",0412657v1
2005-01-25,Fermi Surface and Electron Correlation Effects of Ferromagnetic Iron,"The electronic band structure of bulk ferromagnetic iron is explored by
angle-resolved photoemission for electron correlation effects. Fermi surface
cross-sections as well as band maps are contrasted with density functional
calculations. The Fermi vectors and band parameters obtained from photoemission
and their prediction from band theory are analyzed in detail. Generally good
agreement is found for the Fermi surface. A bandwidth reduction for shallow
bands of ~ 30 % is observed. Additional strong quasiparticle renormalization
effects are found near the Fermi level, leading to a considerable mass
enhancement. The role of electronic correlation effects and the electronic
coupling to magnetic excitations is discussed in view of the experimental
results.",0501585v1
2005-01-28,Spin waves in paramagnetic BCC iron: spin dynamics simulations,"Large scale computer simulations are used to elucidate a longstanding
controversy regarding the existence, or otherwise, of spin waves in
paramagnetic BCC iron. Spin dynamics simulations of the dynamic structure
factor of a Heisenberg model of Fe with first principles interactions reveal
that well defined peaks persist far above Curie temperature T_c. At large wave
vectors these peaks can be ascribed to propagating spin waves, at small wave
vectors the peaks correspond to over-damped spin waves. Paradoxically, spin
wave excitations exist despite only limited magnetic short-range order at and
above T_c.",0501713v1
2005-03-11,Ambipolar Cu- and Fe-Phthalocyanine single-crystal field-effect transistors,"We report the observation of ambipolar transport in field-effect transistors
fabricated on single crystals of Copper- and Iron-Phthalocyanine, using gold as
a high work-function metal for the fabrication of source and drain electrodes.
In these devices, the room-temperature mobility of holes reaches 0.3 cm$^2$/Vs
in both materials. The highest mobility for electrons is observed for
Iron-Phthalocyanines and is approximately one order of magnitude lower. Our
measurements indicate that these values are limited by extrinsic contact
effects due to the transistor fabrication and suggest that considerably higher
values for the electron and hole mobility can be achieved in these materials.",0503282v1
2005-08-03,Comparative study of the catalytic growth of patterned carbon nanotube films,"Three different catalysts (Fe, Ni, Co nitrates dissolved in ethanol) were
patterned on a SiO2/Si substrate and multi-wall carbon nanotubes were grown by
catalytic decomposition of acetylene. We compare the growth of the carbon
nanostructures in the temperature range between 580C and 1000C. With our
experimental set-up the catalyst solutions of cobalt and nickel were found to
be less efficient than the one of iron. An optimal production of multi-wall
nanotubes was observed at temperatures between 650C and 720C with the iron
solution as catalyst. We found a tendency towards thicker structures with
higher temperatures. Finally, we suggest a mechanism for the growth of these
carbon structures.",0508112v2
2005-12-19,Lattice dynamics and thermodynamics of bcc iron at pressure: first-principles linear response study,"We compute the lattice-dynamical and thermal equation of state properties of
ferromagnetic bcc iron using the first principles linear response
linear-muffin-tin-orbital method in the generalized-gradient approximation. The
calculated phonon dispersion and phonon density of states, both at ambient and
high pressures, show good agreement with inelastic neutron scattering data. We
find the free energy as a function of volume and temperature, including both
electronic excitations and phonon contributions, and we have derived various
thermodynamic properties at high pressure and temperature. The thermal equation
of state at ambient temperature agrees well with diamond-anvil-cell
measurements. We have performed detailed investigations on the behavior of
various thermal equation of state parameters, such as the bulk modulus, the
thermal expansivity, the Anderson-Gruneisen parameter, the Gruneisen ratio, and
the heat capacity as function of temperature and pressure. A detailed
comparison has been made with available experimental measurements, as well as
results from similar theoretical studies on nonmagnetic bcc Tantalum.",0512469v1
2006-07-30,Molecular Dynamics Study of the Catalyst Particle Size Dependence on Carbon Nanotube Growth,"The molecular dynamics method, based on an empirical potential energy
surface, was used to study the effect of catalyst particle size on the growth
mechanism and structure of single-walled carbon nanotubes (SWNTs). The
temperature for nanotube nucleation (800-1100 K), which occurs on the surface
of the cluster, is similar to that used in catalyst chemical vapor deposition
experiments, and the growth mechanism, which is described within the
vapor-liquid-solid model, is the same for all cluster sizes studied here (iron
clusters containing between 10 and 200 atoms were simulated). Large catalyst
particles, that contain at least 20 iron atoms, nucleate SWNTs and have a far
better tubular structure than SWNTs nucleated from smaller clusters. In
addition, the SWNTs that grow from the larger clusters have diameters that are
similar to the cluster diameter, whereas the smaller clusters, which have
diameters less than 0.5 nm, nucleate nanotubes that are approximately 0.6-0.7
nm in diameter. This is in agreement with the experimental observations that
SWNT diameters are similar to the catalyst particle diameter, and that the
narrowest free-standing SWNT is 0.6-0.7 nm.",0607800v1
2006-08-29,ODMR Of Impurity Centers Embedded In Silicon Microcavities,"We present the findings of high efficient light absorption in self-assembled
quantum wells (SQW) embedded in silicon microcavities that exhibit a
distributed feedback identified by the FIR transmission spectra. The excitonic
normal-mode coupling (NMC) is found to result in high efficient bound exciton
photoluminescence in the range of the Rabi splitting. The bound excitons at the
iron-boron pair and the erbium-related centers inserted in SQW are shown to
cause giant exchange splitting of the center multiplets as a result of the
strong sp-d and sp-f mixing in the absence of the external magnetic field. The
NMC regime is observed to reveal this exchange splitting in the angular
dependencies of the transmission spectra measured in the range of the Rabi
splitting that are evidence of the ODMR of the trigonal iron-boron pairs and
trigonal erbium-related centers.",0608630v1
2006-08-29,Iron-Based Heavy Quasiparticles in SrFe$_{4}$Sb$_{12}$: An Infrared Spectroscopic Study,"Temperature-dependent infrared reflectivity spectra of SrFe$_{4}$Sb$_{12}$
has been measured. A renormalized Drude peak with a heavy effective mass and a
pronounced pseudogap of 10 meV develops in the optical conductivity spectra at
low temperatures. As the temperature decreases below 100 K, the effective mass
($m^{*}$) rapidly increases, and the scattering rate ($1/\tau$) is quenched.
The temperature dependence of $m^{*}$ and $1/\tau$ indicates that the
hybridization between the Fe 3d spins and the charge carriers plays an
important role in determining the physical properties of SrFe$_{4}$Sb$_{12}$ at
low temperatures. This result is the clear evidence of the iron-based heavy
quasiparticles.",0608637v1
2006-09-07,The Evolution of Magnetism in Iron from the Atom to the Bulk,"The evolution of the magnetic moment in iron clusters containing 20 to 400
atoms is investigated using first-principles numerical calculations based on
density-functional theory and real-space pseudopotentials. Three families of
clusters are studied, characterized by the arrangement of atoms: icosahedral,
body-centered cubic centered on an atom site, and body-centered cubic centered
on the bridge between two neighboring atoms. We find an overall decrease of
magnetic moment as the clusters grow in size towards the bulk limit. Clusters
with faceted surfaces are predicted to have magnetic moment lower than other
clusters with similar size. As a result, the magnetic moment is observed to
decrease as function of size in a non-monotonic manner, which explains
measurements performed at low temperatures.",0609154v1
2006-10-12,Effect of the Fe substitution in Ti-Ni shape memory alloys,"Shape memory Ti-Ni alloys attracted much attention in the recent years, since
they are shape memory, intelligent as well as functional materials. In the
present investigation Ti51Ni49 and Ti51Ni45Fe4 alloys were synthesized through
radio frequency (RF) induction melting. The alloy was characterized through
x-ray diffraction (XRD), scanning electron microscopy (SEM), Mossbauer
spectroscopy (MS) and positron annihilation techniques (PAT).The Fe
substitution stabilized the TiNi type cubic (a=2.998 A) phase. The surface
microstructure and presence of the oxide layer in Ti51Ni45Fe4 alloy have been
investigated by SEM. The Positron annihilation measurements indicated a similar
bulk electron density in both the as-cast and annealed (1000 0 C for 30 hrs)
alloys, typically like that of bulk Ti. Mossbauer spectroscopy studies of
as-cast and annealed iron substituted samples showed regions in the samples
where nuclear Zeeman splitting of Fe levels occurred and an oxide phase was
found to be present in as cast Ti51Ni45Fe4 alloy, while annealed sample
indicated the presence of bcc iron phase .",0610340v1
2006-10-23,"Theory of quasiparticle spectra for Fe, Co, and Ni: bulk and surface","The correlated electronic structure of iron, cobalt and nickel is
investigated within the dynamical mean-field theory formalism, using the newly
developed full-potential LMTO-based LDA+DMFT code. Detailed analysis of the
calculated electron self-energy, density of states and the spectral density are
presented for these metals. It has been found that all these elements show
strong correlation effects for majority spin electrons, such as strong damping
of quasiparticles and formation of a density of states satellite at about -7 eV
below the Fermi level. The LDA+DMFT data for fcc nickel and cobalt (111)
surfaces and bcc iron (001) surface is also presented. The electron self energy
is found to depend strongly on the number of nearest neighbors, and it
practically reaches the bulk value already in the second layer from the
surface. The dependence of correlation effects on the dimensionality of the
problem is also discussed.",0610621v1
2006-10-25,High quality Fe3-deltaO4/InAs hybrid structure for electrical spin injection,"Single Crystalline Fe3-deltaO4 (0<=delta<=0.33) films have been epitaxially
grown on InAs (001) substrates by molecular beam epitaxy using O2 as source of
active oxygen. Under optimum growth conditions in-situ real time reflection
high-energy electron diffraction patterns along with ex-situ atomic force
microscopy indicated the (001) Fe3-deltaO4 to be grown under step-flow-growth
mode with a characteristic surface reconstruction. X-ray photoelectron
spectroscopy demonstrate the possibility to obtain iron oxides with
compositions ranging from Fe3O4 to gamma-Fe2O3. Superconducting quantum
interference device magnetometer at 300K shows well behaved magnetic properties
giving therefore credibility to the promise of iron based oxides for spintronic
applications.",0610697v1
2004-02-14,Effects of a cosmological constant on the X-ray fluorescence spectra of black hole accretion disks,"We investigate the effects of cosmological constant on the characteristic
peaks in the iron line profile in the black hole accretion disk X-ray spectrum.
Our results show that for a fixed mass black hole, the peaks become less
pronounced and closer together with increasing cosmological constant. This
effect is mainly due to the slower rotational velocity of Keplerian orbits at
large radii in the Schwarzschild-de Sitter spacetime as compared to those for
the Schwarzschild spacetime. This change of the iron line profile is similar to
that obtained from increasing the outer radius of the accretion disk size or
reducing the emission intensity power law exponent in the accretion disk
emissivity models.",0402066v1
1997-06-26,KARMEN: Present Neutrino-Oscillation Limits and Perspectives after the Upgrade,"The neutrino experiment KARMEN is situated at the beam stop neutrino source
ISIS. It provides nu_mu's, nu_e's and nu_mu_bar's in equal intensities from the
pi+ mu+ decay at rest. The oscillation channels nu_mu->nu_e and
nu_mu_bar->nu_e_bar are investigated with a 56t liquid scintillation
calorimeter at a mean distance of 17.6m from the nu source. No evidence for
oscillations could be found with KARMEN, resulting in 90% CL exclusion limits
of sin(2th) < 8.5 10^-3 (nu_mu_bar->nu_e_bar) and sin(2th) < 4.0 10^-2
(nu_mu->nu_e) for Delta m^2 > 100eV^2. In 1996, the KARMEN neutrino experiment
has been upgraded by an additional veto system. Vetoing of cosmic muons passing
the 7000t massive iron shielding of the detector suppresses energetic neutrons
from deep inelastic scattering of muons as well as from mu-capture in iron. Up
to 1996, these neutrons penetrating into the detector represented the main
background for the nu_mu_bar->nu_e_bar oscillation search. With an expected
reduction of the background rate by a factor of 40 the experimental sensitivity
for nu_mu_bar->nu_e_bar will be significantly enhanced towards sin(2th) = 10^-3
for large Delta m^2.",9706023v1
1999-10-14,Search for nucleon decay into lepton + K0 final states using Soudan 2,"A search for nucleon decay into two-body final states containing K^0 mesons
has been conducted using the 963 metric ton Soudan 2 iron tracking calorimeter.
The topologies, ionizations, and kinematics of contained events recorded in a
5.52 kiloton-year total exposure (4.41 kton-year fiducial volume exposure) are
examined for compatibility with nucleon decays in an iron medium. For proton
decay into the fully visible final states \mu^+K^0_s and e^+K^0_s, zero and one
event candidates are observed respectively. The lifetime lower limits (\tau /B)
thus implied are 1.5 \times 10^{32} years and 1.2 \times 10^{32} years,
respectively. Lifetime lower limits are also reported for proton decay into
l^+K^0_l, and for neutron decay into \nu K^0_s.",9910026v2
2002-05-28,Search for Neutron-Antineutron Oscillations Using Multiprong Events in Soudan 2,"We have searched for neutron-antineutron oscillations using the 5.56 fiducial
kiloton-year exposure of the Soudan 2 iron tracking calorimeter. We require
candidate n-nbar occurrences to have .GE. 4 prongs (tracks and showers) and to
have kinematics compatible with nbar-N annihilation within a nucleus. We
observe five candidate events, with an estimated background from atmospheric
neutrino and cosmic ray induced events of 4.5 \pm 1.2 events. Previous
experiments with smaller exposures observed no candidates, with estimated
background rates similar to this experiment. We set a lifetime lower limit for
oscillation time in iron: T_A(Fe) > 7.2x10^{31} years. The corresponding lower
limit for oscillation of free neutrons is \tau_{n-nbar} > 1.3x10^8 seconds.",0205093v1
1999-09-28,Detection of Slow Magnetic Monopole,"Numerous and all unsuccessful attempts of experimental search for monopole in
cosmic rays and on accelerators in high energy particle collisions have been
done since the possibility of existence of a magnetic monopole has been
surveyed in 1931. Also the searches have been carried out in mica for monopole
tracks as well as for relict monopoles, entrapped by ferromagnetic inclusions
in iron-ores, moon rock and meteorites.
  A new method of search for supermassive cosmic and relict monopoles by
magnetically ordered film is considered. This approach resembles the
traditional method of nuclear emulsion chamber. Apparently the proposed method
is particularly attractive for detection of relict monopoles, released from
melting iron ore.",9909528v1
2005-05-03,Exploration prospects of a long baseline Beta Beam neutrino experiment with an iron calorimeter detector,"A high intensity source of a single neutrino flavour with known spectrum is
most desirable for precision measurements, the consensus direction for the
future. The beta beam is an especially suitable option for this. We discuss the
prospects of a very long baseline beta beam experiment with a magnetized iron
calorimeter detector. In particular, with the source at CERN and the detector
at the proposed India-based Neutrino Observatory (INO) the baseline is near the
`magic' value where the effect of the CP phase is small. We observe that this
experiment will be well suited to determine the sign of $m_3^2 - m_2^2$ and
will be capable of probing $\theta_{13}$ down to about 1$^\circ$.",0505015v2
2002-12-17,Destabilization of fronts in a class of bi-stable systems,"In this article, we consider a class of bi-stable reaction-diffusion
equations in two components on the real line. We assume that the system is
singularly perturbed, i.e. that the ratio of the diffusion coefficients is
(asymptotically) small. This class admits front solutions that are
asymptotically close to the (stable) front solution of the `trivial' scalar
bi-stable limit system $u_t = u_{xx} + u(1-u^2)$. However, in the system these
fronts can become unstable by varying parameters. This destabilization is
either caused by the essential spectrum associated to the linearized stability
problem, or by an eigenvalue that exists near the essential spectrum. We use
the Evans function to study the various bifurcation mechanisms and establish an
explicit connection between the character of the destabilization and the
possible appearance of saddle-node bifurcations of heteroclinic orbits in the
existence problem.",0212231v1
1994-02-03,Complete 0 hbar omega calculations of Gamow-Teller strengths for nuclei in the iron region,"Gamow-Teller strengths for selected nuclei in the iron region (A~56) have
been investigated via shell-model Monte Carlo calculations with realistic
interactions in the complete fp basis. Results for all cases show significant
quenching relative to single-particle estimates, in quantitative agreement with
(n,p) data. The J=1,T=0 residual interaction and the f_{7/2}-f_{5/2} spin-orbit
splitting are shown to play major roles in the quenching mechanism. Calculated
B(E2, 2^+_1 -> 0^+_1) values are in fair agreement with experiment using
effective charges of e_p=1.1e and e_n=0.1e.",9402006v1
2000-03-27,The role of $ν$-induced reactions on lead and iron in neutrino detectors,"We have calculated cross sections and branching ratios for neutrino induced
reactions on ^{208}Pb and ^{56}Fe for various supernova and
accelerator-relevant neutrino spectra. This was motivated by the facts that
lead and iron will be used on one hand as target materials in future neutrino
detectors, on the other hand have been and are still used as shielding
materials in accelerator-based experiments. In particular we study the
inclusive ^{56}$Fe(\nu_e,e^-)$^{56}Co and ^{208}$Pb(\nu_e,e^-)$^{208}Bi cross
sections and calculate the neutron energy spectra following the decay of the
daughter nuclei. These reactions give a potential background signal in the
KARMEN and LSND experiment and are discussed as a detection scheme for
supernova neutrinos in the proposed OMNIS and LAND detectors. We also study the
neutron-emission following the neutrino-induced neutral-current excitation of
^{56}Fe and ^{208}Pb.",0003060v2
2005-03-17,The Muon System of the Run II D0 Detector,"We describe the design, construction and performance of the upgraded DO muon
system for Run II of the Fermilab Tevatron collider. Significant improvements
have been made to the major subsystems of the DO muon detector: trigger
scintillation counters, tracking detectors, and electronics. The Run II central
muon detector has a new scintillation counter system inside the iron toroid and
an improved scintillation counter system outside the iron toroid. In the
forward region, new scintillation counter and tracking systems have been
installed. Extensive shielding has been added in the forward region. A large
fraction of the muon system electronics is also new.",0503151v1
2007-04-10,Compton thick AGN in the Suzaku era,"Suzaku observations of two hard X-ray (> 10 keV) selected nearby Seyfert 2
galaxies are presented. Both sources were clearly detected with the PIN Hard
X-ray Detector up to several tens of keV, allowing for a fairly good
characterization of the broad band X-ray continuum. Both sources are heavily
obscured, one of which (NGC 5728) being Compton thick, while at lower energies
the shape and intensity of the scattered/reflected continuum is very different.
Strong iron Kalpha lines are detected in both sources. There are also hints for
the presence of a broad relativistic iron line in NGC 4992.",0704.1253v1
2007-05-30,Two Modes of Magnetization Switching in a Simulated Iron Nanopillar in an Obliquely Oriented Field,"Finite-temperature micromagnetics simulations are employed to study the
magnetization-switching dynamics driven by a field applied at an angle to the
long axis of an iron nanopillar. A bi-modal distribution in the switching times
is observed, and evidence for two competing modes of magnetization-switching
dynamics is presented. For the conditions studied here, temperature $T = 20$ K
and the reversal field 3160 Oe at an angle of 75$^\circ$ to the long axis,
approximately 70% of the switches involve unstable decay (no free-energy
barrier) and 30% involve metastable decay (a free-energy barrier is crossed).
The latter are indistinguishable from switches which are constrained to start
at a metastable free-energy minimum. Competition between unstable and
metastable decay could greatly complicate applications involving magnetization
switches near the coercive field.",0705.4454v1
2007-06-27,Reconstructing WIMP properties with neutrino detectors,"If the dark matter of the Universe is constituted by weakly interacting
massive particles (WIMP), they would accumulate in the core of astrophysical
objects as the Sun and annihilate into particles of the Standard Model.
High-energy neutrinos would be produced in the annihilations, both directly and
via the subsequent decay of leptons, quarks and bosons. While Cherenkov
neutrino detectors/telescopes can only count the number of neutrinos above some
threshold energy, we study how, by exploiting their energy resolution, large
magnetized iron calorimeter and, possibly, liquid argon and totally active
scintillator detectors, planned for future long baseline neutrino experiments,
have the capability of reconstructing the neutrino spectrum and might provide
information on the dark matter properties. In particular, for a given value of
the WIMP mass, we show that a future iron calorimeter could break the
degeneracy between the WIMP-proton cross section and the annihilation branching
ratios, present for Cherenkov detectors, and constrain their values with good
accuracy.",0706.3909v2
2007-07-06,Muon Identification at ATLAS and CMS,"Muonic final states will provide clean signatures formany physics processes
at the LHC. The two LHC experiments ATLAS and CMS will be able to identify
muons with a high reconstruction efficiency above 96% and a high transverse
momentum resolution better than 2% for transverse momenta below 400 GeV/c and
about 10% at 1 TeV/c. The two experiments follow complentary concepts of muon
detection. ATLAS has an instrumented air-toroid mangetic system serving as a
stand-alone muon spectrometer. CMS relies on high bending power and momentum
resolution in the inner detector, and uses an iron yoke to increase its
magnetic field. The iron yoke is instrumented with chambers used for muon
identification. Therefore, muon momenta can only be reconstructed with high
precision by combining inner-detector information with the data from the muon
chambers.",0707.0905v1
2007-07-16,Zener double exchange from local valence fluctuations in magnetite,"Magnetite (Fe$_{3}$O$_{4}$) is a mixed valent system where electronic
conductivity occurs on the B-site (octahedral) iron sublattice of the spinel
structure. Below $T_{V}=122$ K, a metal-insulator transition occurs which is
argued to arise from the charge ordering of 2+ and 3+ iron valences on the
B-sites (Verwey transition). Inelastic neutron scattering measurements show
that optical spin waves propagating on the B-site sublattice ($\sim$80 meV) are
shifted upwards in energy above $T_{V}$ due to the occurrence of B-B
ferromagnetic double exchange in the mixed valent metallic phase. The double
exchange interaction affects only spin waves of $\Delta_{5}$ symmetry, not all
modes, indicating that valence fluctuations are slow and the double exchange is
constrained by electron correlations above $T_{V}$.",0707.2253v1
2007-07-16,Search for medium modification of the $ρ$ meson,"The photoproduction of vector mesons on various nuclei has been studied using
the CEBAF Large Acceptance Spectrometer (CLAS) at Jefferson Laboratory. The
vector mesons, $\rho$, $\omega$, and $\phi$, are observed via their decay to
$e^+e^-$, in order to reduce the effects of final state interactions in the
nucleus. Of particular interest are possible in-medium effects on the
properties of the $\rho$ meson. The $\rho$ spectral function is extracted from
the data on various nuclei, carbon, iron, and titanium, and compared to the
spectrum from liquid deuterium, which is relatively free of nuclear effects. We
observe no significant mass shift for the $\rho$ meson; however, there is some
widening of the resonance in titanium and iron, which is consistent with
expected collisional broadening.",0707.2324v3
2007-07-17,New homogeneous iron abundances of double-mode Cepheids from high-resolution echelle spectroscopy,"Aims: We define the relationship between the double-mode pulsation of
Cepheids and metallicity in a more accurate way, determine the empirical
metallicities of double-mode Cepheids from homogeneous, high-resolution
spectroscopic data, and study of the period-ratio -- metallicity dependence.
Methods: The high S/N echelle spectra obtained with the FEROS spectrograph were
analyzed using a self-developed IRAF script, and the iron abundances were
determined by comparing with synthetic spectra assuming LTE. Results: Accurate
[Fe/H] values of 17 galactic beat Cepheids were determined. All these stars
have solar or slightly subsolar metallicity. Their period ratio P1/P0 shows
strong correlation with their derived [Fe/H] values. The corresponding period
ratio -- metallicity relation has been evaluated.",0707.2530v1
2007-07-19,Nuclear Georeactor Generation of Earth's Geomagnetic Field,"The purpose of this communication is to suggest that the mechanism for
generating the geomagnetic field and the energy source for powering it are one
and the same, a nuclear georeactor at the center of the Earth. Toward this end,
I: i) Present evidence that the nuclear georeactor fission-product sub-shell is
fluid; ii)Suggest that the geomagnetic field is generated within the georeactor
sub-shell, rather than within Earth's iron-alloy fluid core; iii) Describe why
convection appears more feasible within the georeactor sub-shell than within
the iron-alloy core; iv) Disclose additional relative physical advantages for
georeactor sub-shell dynamo operation; and, v) Outline briefly the research
that should be conducted to advance the state of knowledge of
georeactor-geomagnetic field generation. The concept of geomagnetic field
production by the nuclear georeactor is presented specifically for the Earth.
The concepts and principles, however, are generally applicable to planetary
magnetic field production.",0707.2850v4
2007-08-07,Near Optimal Broadcast with Network Coding in Large Sensor Networks,"We study efficient broadcasting for wireless sensor networks, with network
coding. We address this issue for homogeneous sensor networks in the plane. Our
results are based on a simple principle (IREN/IRON), which sets the same rate
on most of the nodes (wireless links) of the network. With this rate selection,
we give a value of the maximum achievable broadcast rate of the source: our
central result is a proof of the value of the min-cut for such networks, viewed
as hypergraphs. Our metric for efficiency is the number of transmissions
necessary to transmit one packet from the source to every destination: we show
that IREN/IRON achieves near optimality for large networks; that is,
asymptotically, nearly every transmission brings new information from the
source to the receiver. As a consequence, network coding asymptotically
outperforms any scheme that does not use network coding.",0708.0975v1
2007-08-08,The Near-Infrared Broad Emission Line Region of Active Galactic Nuclei -- I. The Observations,"We present high quality (high signal-to-noise ratio and moderate spectral
resolution) near-infrared (near-IR) spectroscopic observations of 23 well-known
broad-emission line active galactic nuclei (AGN). Additionally, we obtained
simultaneous (within two months) optical spectroscopy of similar quality. The
near-IR broad emission line spectrum of AGN is dominated by permitted
transitions of hydrogen, helium, oxygen, and calcium, and by the rich spectrum
of singly-ionized iron. In this paper we present the spectra, line
identifications and measurements, and address briefly some of the important
issues regarding the physics of AGN broad emission line regions. In particular,
we investigate the excitation mechanism of neutral oxygen and confront for the
first time theoretical predictions of the near-IR iron emission spectrum with
observations.",0708.1083v1
2007-09-26,High-resolution saturation spectroscopy of singly-ionized iron with a pulsed uv laser,"We describe the design and realization of a scheme for uv laser spectroscopy
of singly-ionized iron (Fe II) with very high resolution. A buffer-gas cooled
laser ablation source is used to provide a plasma close to room temperature
with a high density of Fe II. We combine this with a scheme for pulsed-laser
saturation spectroscopy to yield sub-Doppler resolution. In a demonstration
experiment, we have examined an Fe II transition near 260 nm, attaining a
linewidth of about 250 MHz. The method is well-suited to measuring transition
frequencies and hyperfine structure. It could also be used to measure small
isotope shifts in isotope-enriched samples.",0709.4032v1
2007-10-01,nu-Process Nucleosynthesis in Population III Core-Collapse Supernovae,"We investigate the effects of neutrino-nucleus interactions (the nu-process)
on the production of iron-peak elements in Population III core-collapse
supernovae. The nu-process and the following proton and neutron capture
reactions produce odd-Z iron-peak elements in complete and incomplete Si
burning region. This reaction sequence enhances the abundances of Sc, Mn, and
Co in the supernova ejecta. The supernova explosion models of 15 M_sol and 25
M_sol stars with the nu-process well reproduce the averaged Mn/Fe ratio
observed in extremely metal-poor halo stars. In order to reproduce the observed
Mn/Fe ratio, the total neutrino energy in the supernovae should be 3 - 9 x
10^{53} ergs. Stronger neutrino irradiation and other production sites are
necessary to reproduce the observed Sc/Fe and Co/Fe ratios, although these
ratios increase by the nu-process.",0710.0251v1
2007-11-02,Chandra Observations of Early-type Galaxies,"We have performed uniform analysis of a sample of 54 nearby, early-type
galaxies observed with \emph{Chandra}. In this work we present the spectral
results for both the diffuse Interstellar Medium, ISM, and low-mass X-ray
binaries, LMXBs. We determine the metallicity of the hot ISM in the 22
brightest galaxies and find a narrow range of abundance ratios relative to
iron. The average iron metallicity of these bright galaxies is $0.96\pm0.33$
relative to solar. By assuming these enrichment patterns continue to fainter
galaxies, we are able to extend accurate ISM modeling down to the faintest
galaxies in the sample. The sample of galaxies span 4.5 orders of magnitude in
X-ray luminosity starting at $L_X=10^{38} erg \cdot s^{-1}$ and the average gas
temperature in the sample is $0.58\pm0.24 keV$. We present the X-ray properties
of these galaxies scaled to one effective radius as well as radial variations
of gas and stellar binary luminosities, and radial variations of gas
temperature, metallicity, mass, entropy and density.",0711.0395v1
2007-11-19,A Time-Variable X-Ray Echo: Indications of a Past Flare of the Galactic-Center Black Hole,"A time-variability study of the neutral iron line flux at 6.40keV in the Sgr
B2 region from data of Suzaku and Chandra is presented. The highly ionized iron
line at 6.68keV is due to Galactic Center Diffuse X-rays (GCDX), and is thus
time invariable. By comparing the 6.68keV and 6.40keV line fluxes, we found
that the 6.40keV flux from the SgrB2 complex region is time variable;
particularly the giant molecular cloud M0.66-0.02, known as ``Sgr B2 cloud'' is
highly variable. The variability of the 6.40keV line in intensity and spatial
distribution strongly supports the scenario that the molecular clouds in the
SgrB2 region are X-ray Reflection Nebulae irradiated by the Galactic Center
(GC) black hole Sgr A*.",0711.2853v1
2007-11-26,Cepheids as tracers of the metallicity gradient across the Galactic disk,"We present iron abundance measurements, based on high resolution
spectroscopy, and accurate distance determinations, based on near infrared
photometry, for 34 Galactic Cepheids. The new data are used to constrain the
Galactic iron abundance gradient in the outer disk, namely from 10 to 14 kpc.
We confirm the flattening of the gradient toward the outer disk. In this region
we also found an increase in the metallicity dispersion. Current data do not
support the occurrence of a jump in the metallicity gradient for Galactocentric
distances of the order of 10-12 kpc.",0711.3988v1
2007-12-03,Signatures of Granulation in the Spectra of K-Dwarfs,"Very high resolution (R>150,000) spectra of a small sample of nearby K-dwarfs
have been acquired to measure the line asymmetries and central wavelength
shifts caused by convective motions present in stellar photospheres. This
phenomenon of granulation is modeled by 3D hydrodynamical simulations but they
need to be confronted with accurate observations to test their realism before
they are used in stellar abundance studies. We find that the line profiles
computed with a 3D model agree reasonably well with the observations. The line
bisectors and central wavelength shifts on K-dwarf spectra have a maximum
amplitude of only about 200 m/s and we have been able to resolve these
granulation effects with a very careful observing strategy. By computing a
number of iron lines with 1D and 3D models (assuming local thermodynamic
equilibrium), we find that the impact of 3D-LTE effects on classical iron
abundance determinations is negligible.",0712.0387v1
2007-12-30,Specific heat evidence for two-gap superconductivity in ternary-iron silicide Lu$_{2}$Fe$_{3}$Si$_{5}$,"We report low-temperature specific heat studies on single-crystalline
ternary-iron silicide superconductor Lu$_{2}$Fe$_{3}$Si$_{5}$ with$T_c$ = 6.1 K
down to $\sim T_c/20$. We confirm a reduced normalized jump in specific heat at
$T_c$, and find that the specific heat divided by temperature $C/T$ shows
sudden drop at $\sim T_c/5$ and goes to zero with further decreasing
temperature. These results indicate the presence of two distinct
superconducting gaps in Lu$_{2}$Fe$_{3}$Si$_{5}$, similar to a typical two-gap
superconductor MgB$_{2}$. We also report Hall coefficients, band structure
calculation, and the anisotropy of upper critical fields for
Lu$_{2}$Fe$_{3}$Si$_{5}$, which support the anisotropic multiband nature and
reinforce the existence of two superconducting gaps in
Lu$_{2}$Fe$_{3}$Si$_{5}$.",0801.0111v1
2008-01-07,DC transferred arc thermal plasma assisted growth of nanoparticles with different crystalline phases,"The control of the crystalline phases of the nanoparticles grown in a
direct-current transferred-arc plasma-assisted reactor is reported. The
crystalline phases of the as synthesized nanoparticles are shown to critically
depend on the operating gas pressure. The paper reports about the change in the
crystalline phases of three distinct compounds namely aluminium oxide (Al2O3),
aluminium nitride (AlN) and iron oxide (FexOy). The major outcome of the
present work is that the phases having higher defect densities are more
probable to form at the sub-atmospheric operating pressure. The variations in
the crystalline structures are discussed on the basis of the equilibrium defect
density formed during the homogeneous nucleation. The as synthesized
nanoparticles were examined by X-ray diffraction analysis and transmission
electron microscopy. In addition, the confirmatory analysis for the crystalline
phases of the as synthesized iron oxides was carried out with the help of
Mossbauer spectroscopy.",0801.0945v1
2008-01-25,Ab initio study of spin-dependent transport in carbon nanotubes with iron and vanadium adatoms,"We present an ab initio study of spin dependent transport in armchair carbon
nanotubes with transition metal adsorbates, iron or vanadium. We neglect the
effect of tube curvature and model the nanotube by graphene with periodic
boundary conditions. A density functional theory based nonequilibrium Green's
function method is used to compute the electronic structure and zero-bias
conductance. The presence of the adsorbate causes a strong scattering of
electrons of one spin type only. The scattering is shown to be due to coupling
of the two armchair band states to the metal 3d orbitals with matching symmetry
causing Fano resonances appearing as dips in the transmission function. The
spin type (majority/minority) being scattered depends on the adsorbate and is
explained in terms of d-state filling. The results are qualitatively reproduced
using a simple tight-binding model, which is then used to investigate the
dependence of the transmission on the nanotube width. We find a decrease in the
width of the transmission dip as the tube-size increases.",0801.3997v1
2008-03-01,"Search For Iron, Nickel, and Fluorine in PG1159 Stars","A possible origin of the iron-deficiency in PG1159 stars could be neutron
captures on Fe nuclei. A nickel overabundance would corroborate this idea.
Consequently we are looking for nickel lines in PG1159 stars. Prime targets are
relatively cool objects, because Ni VI is the dominant ionisation stage and the
spectral lines of this ion are accessible with UV observations. We do not find
such lines in the coolest PG1159 star observed by FUSE (PG1707+427, Teff =
85,000 K) and conclude that the nickel abundance is not enhanced. Hence, the
Fe-deficiency in PG1159 stars remains unexplained. In addition, we present
results of a wind analysis of the hybrid-PG1159 star NGC 7094 and the
[WC]-PG1159 transition-type object Abell 78 in order to derive F abundances
from the F VI 1139.5 Angstrom line. In both cases, we find F overabundances, in
agreement with results of photospheric analyses of many PG1159 stars.
Surprisingly, we find indications for a very low O abundance in NGC 7094.",0803.0066v1
2008-03-09,"Upper critical field, Hall effect and magnetoresistance in the iron-based layered superconductor LaFeAsO_{0.9}F_{0.1-δ}","By using a two-step method, we successfully synthesized the iron based new
superconductor LaFeAsO_{0.9}F_{0.1-\delta}$. The resistive transition curves
under different magnetic fields were measured, leading to the determination of
the upper critical field Hc2(T) of this new superconductor. The value of Hc2 at
zero temperature is estimated to be about 50 Tesla roughly. In addition, the
Hall effect and magnetoresistance were measured in wide temperature region. A
negative Hall coefficient R_H has been found, implying a dominant conduction
mainly by electron-like charge carriers in this material. The charge carrier
density determined at 100 K is about 9.8E20cm^{-3}, which is close to the
cuprate superconductors. It is further found that the magnetoresistance does
not follow Kohler's law. Meanwhile, the different temperature dependence
behaviors of resistivity, Hall coefficient, and magnetoresistance have
anomalous properties at about 230 K, which may be induced by some exotic
scattering mechanism.",0803.1288v2
2008-03-24,Tracing the [FeII]/[NeII] ratio within star forming dwarf galaxies: a Spitzer IRS archival study,"Archival Spitzer observations of 41 starburst galaxies that span a wide range
in metallicity reveal for the first time a correlation between the
[FeII]/[NeII] 26.0/12.8 micron ratio and the electron gas density as traced by
the 18.7/33.4 micron [SIII] ratio, with the [FeII]/[NeII] ratio decreasing with
increasing gas density. We also find a strong correlation between the gas
density and the PAH peak to continuum strength. Using shock and photoionization
models, we see the driver of the observed [FeII]/[NeII] ratios is metallicity.
The majority of [FeII] emission in low metallicity galaxies may be
shock-derived, whilst at high metallicity, the [FeII] emission may be instead
dominated by contributions from HII and in particular from dense PDR regions.
However, the observed [FeII]/[NeII] ratios may instead be following a
metallicity-abundance relationship, with iron being less depleted onto grains
in low metallicity galaxies - a result that would have profound implications
for the use of iron emission lines as unambiguous tracers of shocks.",0803.3403v1
2008-04-05,Doubly degenerate orbital system in honeycomb lattice: implication of orbital state in layered iron oxide,"We study a doubly-degenerate orbital model on a honeycomb attice. This is a
model for orbital states in multiferroic layered iron oxides. The classical and
quantum models are analyzed by spin-wave approximation, Monte-Carlo simulation
and Lanczos method. A macroscopic number of degeneracy exists in the classical
ground state. In the classical model, a peak in the specific heat appears at a
temperature which is much lower than the mean-field ordering one. Below this
temperature, angle of orbital pseudo-spin is fixed, but conventional orbital
orders are not suggested. The degeneracy in the ground state is partially
lifted by thermal fluctuation. We suggest a role of zero-dimensional
fluctuation in hexagons on a low-temperature orbital structure. Lifting of the
degeneracy also occurs at zero temperature due to the quantum zero-point
fluctuation. We show that the ground-state wave function is well represented by
a linear combination of the states where a honeycomb lattice is covered by
nearest-neighboring pairs of orbitals with the minimum bond energy.",0804.0843v1
2008-04-08,Models of the iron K_alpha fluorescence line and the Compton shoulder in irradiated accretion disk spectra,"We present a full set of model atmosphere equations for the accretion disk
around a supermassive black hole irradiated by hard X-ray lamp of power-law
spectral distribution. Model equations allow for multiple Compton scattering of
radiation on free electrons, and for large relative photon-electron energy
exchange at the time of scattering. We present spectra in specific intensities
integrated over the disk surface. Theoretical outgoing intensity spectra show
soft X-ray excess below 1 keV, and distinct K_alpha and K_beta fluorescent
lines of iron. We demonstrate the existence of the Compton Shoulder and claim
that it can contribute to the asymmetry and equivalent widths of some observed
Fe K_alpha lines in AGN. Our models exhibit the effect of limb-brightening in
reflected X-rays.",0804.1232v1
2008-04-08,Nernst effect of the new iron-based superconductor LaO$_{1-x}$F$_{x}$FeAs,"We report the first Nernst effect measurement on the new iron-based
superconductor LaO$_{1-x}$F$_{x}$FeAs $(x=0.1)$. In the normal state, the
Nernst signal is negative and very small. Below $T_{c}$ a large positive peak
caused by vortex motion is observed. The flux flowing regime is quite large
compared to conventional type-II superconductors. However, a clear deviation of
the Nernst signal from normal state background and an anomalous depression of
off-diagonal thermoelectric current in the normal state between $T_{c}$ and 50
K are observed. We propose that this anomaly in the normal state Nernst effect
could correlate with the SDW fluctuations.",0804.1324v2
2008-04-13,Superconductivity at 55 K in iron-based F-doped layered quaternary compound Sm[O1-xFx]FeAs,"Here we report the superconductivity in the iron-based oxyarsenide
Sm[O1-xFx]FeAs, with the onset resistivity transition temperature at 55.0 K and
Meissner transition at 54.6 K. This compound has the same crystal structure as
LaOFeAs with shrunk crystal lattices, and becomes the superconductor with the
highest critical temperature among all materials besides copper oxides.",0804.2053v2
2008-04-16,Strong Correlations and Magnetic Frustration in the High Tc Iron Pnictides,"We consider the iron pnictides in terms of a proximity to a Mott insulator.
The superexchange interactions contain competing nearest-neighbor and
next-nearest-neighbor components. In the undoped parent compound, these
frustrated interactions lead to a two-sublattice collinear antiferromagnet
(each sublattice forming a Neel ordering), with a reduced magnitude for the
ordered moment. Electron or hole doping, together with the frustration effect,
suppresses the magnetic ordering and allows a superconducting state. The
exchange interactions favor a d-wave superconducting order parameter; in the
notation appropriate for the Fe square lattice, its orbital symmetry is
$d_{xy}$. A number of existing and future experiments are discussed in light of
the theoretical considerations.",0804.2480v2
2008-04-16,Ab initio approach of the hydrogen insertion effects on the magnetic properties of $ {\bf ScFe_2} $,"The electronic and magnetic structures of $ {\rm ScFe_2} $ and of its
dihydride $ {\rm ScFe_2H_2} $ are self-consistently calculated within the
density functional theory (DFT) using the all electron augmented spherical wave
(ASW) method with the local spin density approximation (LSDA) for treating
effects of exchange and correlation. The results of the enhancement of the
magnetization upon hydrogen insertion are assessed within an analysis of the
chemical bonding properties from which we suggest that both hydrogen bond with
iron and cell expansion effects play a role in the change of the magnitude of
magnetization. In agreement with average experimental findings for both the
intermetallic system and its dihydride, the calculated Fermi contact terms
$H_{FC}$ of the $^{57}$Fe M\""ossbauer spectroscopy for hyperfine field, at the
two iron sites, exhibit an original inversion for the order of magnitudes upon
hydriding.",0804.2537v1
2008-04-23,Superconductivity of powder-in-tube LaO0.9F0.1FeAs wires,"We demonstrate that Fe sheathed LaO0.9F0.1FeAs wires with Ti as a buffer
layer were successfully fabricated by the powder-in-tube (PIT) method.
Comparing to the common two-step vacuum quartz tube synthesis method, the PIT
method is more convenient and safe for synthesizing the novel iron-based
layered superconductors. Structural analysis by mean of x-ray diffraction shows
that the main phase of LaO0.9F0.1FeAs was obtained by this synthesis method.
The transition temperature of the LaO0.9F0.1FeAs wire is around 25 K. The
micrograph shows a homogeneous microstructure with a grain size of 1-3
micrometers. The results suggest that the PIT process is promising in preparing
high-quality iron-based layered superconductor wires.",0804.3738v2
2008-04-25,"Spin Fluctuations, Interband Coupling, and Unconventional Pairing in Iron-based Superconductors","Based on an effective two-band model and using the fluctuation-exchange
(FLEX) approach, we explore spin fluctuations and unconventional
superconducting pairing in Fe-based layer superconductors. It is elaborated
that one type of interband antiferromagnetic (AF) spin fluctuation stems from
the interband Coulomb repulsion, while the other type of intraband AF spin
fluctuation originates from the intraband Coulomb repulsion. Due to the
Fermi-surface topology, a spin-singlet extended s-wave superconducting state is
more favorable than the nodal $d_{XY}$-wave state if the interband AF spin
fluctuation is more significant than the intraband one, otherwise vice versa.
It is also revealed that the effective interband coupling plays an important
role in the intraband pairings, which is a distinct feature of the present
two-band system.",0804.4166v3
2008-04-28,Ising and Spin orders in Iron-based Superconductors,"Motivated by recent neutron scattering experiments, we study the ordering of
spins in the iron-based superconductors La(O_{1-x}F_x)FeAs, assuming them in
proximity to a Mott insulator in the phase diagram. The ground state of the
parent system with x = 0 is a spin density wave with ordering wave vector Q =
(0, \pi) or (\pi, 0). Upon raising the temperature, we find the system to
restore SU(2) symmetry, while an Ising symmetry remains broken, explaining the
experimentally observed lattice distortion to a monoclinic crystal structure.
Upon further temperature increase, the spins finally disorder at a second
transition. The phase transition driven by doping with charge carriers
similarly splits into an O(3) transition, and an Ising transition with z = 3 at
larger doping.",0804.4293v4
2008-05-07,Pairing symmetry and properties of iron-based high temperature superconductors,"Pairing symmetry is important to indentify the pairing mechanism. The
analysis becomes particularly timely and important for the newly discovered
iron-based multi-orbital superconductors. From group theory point of view we
classified all pairing matrices (in the orbital space) that carry irreducible
representations of the system. The quasiparticle gap falls into three
categories: full, nodal and gapless. The nodal-gap states show conventional
Volovik effect even for on-site pairing. The gapless states are odd in orbital
space, have a negative superfluid density and are therefore unstable. In
connection to experiments we proposed possible pairing states and implications
for the pairing mechanism.",0805.0923v3
2008-05-16,Iron-60 evidence for early injection and efficient mixing of stellar debris in the protosolar nebula,"Among extinct radioactivities present in meteorites, 60Fe (t1/2 = 1.49 Myr)
plays a key role as a high-resolution chronometer, a heat source in
planetesimals, and a fingerprint of the astrophysical setting of solar system
formation. A critical issue with 60Fe is that it could have been
heterogeneously distributed in the protoplanetary disk, calling into question
the efficiency of mixing in the solar nebula or the timing of 60Fe injection
relative to planetesimal formation. If this were the case, one would expect
meteorites that did not incorporate 60Fe (either because of late injection or
incomplete mixing) to show 60Ni deficits (from lack of 60Fe decay) and
collateral effects on other neutron-rich isotopes of Fe and Ni (coproduced with
60Fe in core-collapse supernovae and AGB-stars). Here, we show that measured
iron meteorites and chondrites have Fe and Ni isotopic compositions identical
to Earth. This demonstrates that 60Fe must have been injected into the
protosolar nebula and mixed to less than 10 % heterogeneity before formation of
planetary bodies.",0805.2607v1
2008-05-17,Unusual Pseudogap-like Features Observed in Iron Oxypnictide Superconductors,"We have performed a temperature-dependent angle-integrated laser
photoemission study of iron oxypnictide superconductors LaFeAsO:F and LaFePO:F
exhibiting critical transition temperatures (Tc's) of 26 K and 5 K,
respectively. We find that high-Tc LaFeAsO:F exhibits a temperature-dependent
pseudogap-like feature extending over ~0.1 eV about the Fermi level at 250 K,
whereas such a feature is absent in low-Tc LaFePO:F. We also find ~20-meV
pseudogap-like features and signatures of superconducting gaps both in
LaFeAsO:F and LaFePO:F. We discuss the possible origins of the unusual
pseudogap-like features through comparison with the high-Tc cuprates.",0805.2647v2
2008-05-20,Superconducting Gap and Pseudogap in Iron-Based Layered Superconductor La(O$_{1-x}$F$_x$)FeAs,"We report high-resolution photoemission spectroscopy of newly-discovered
iron-based layered superconductor La(O$_{0.93}$F$_{0.07}$)FeAs (Tc = 24 K). We
found that the superconducting gap shows a marked deviation from the isotropic
s-wave symmetry. The estimated gap size at 5 K is 3.6 meV in the s- or axial
p-wave case, while it is 4.1 meV in the polar p- or d-wave case. We also found
a pseudogap of 15-20 meV above Tc, which is gradually filled-in with increasing
temperature and closes at temperature far above Tc similarly to copper-oxide
high-temperature superconductors.",0805.3001v1
2008-05-23,Discoveries of 3 K-shell Lines of Iron and a Coherent Pulsation of 593-sec from SAX J1748.2-2808,"SAX J1748.2$-$2808 is a unique X-ray object with a flat spectrum and strong
emission lines at 6.4--7.0 keV. The Suzaku satellite resolved the emission
lines into 3 K-shell lines from neutral and highly ionized irons. A clear
coherent pulsation with a period of 593-sec was found from the Suzaku and
XMM-Newton archives. These facts favor that SAX J1748.2$-$2808 isan
intermediate polar, a subclass of magnetized white dwarf binary (cataclysmic
variable: CV). This paper reports on details of the findings and discusses the
origin of this source.",0805.3608v2
2008-05-28,Photonic Dipole Contours of Ferrofluid Hele-Shaw Cell,"This investigation describes and demonstrates a novel technique for the
visualization of magnetic fields. Two ferrofluid Hele-Shaw cells have been
constructed to facilitate the imaging of magnetic field lines. We deduce that
magnetically induced photonic band gap arrays similar to electrostatic liquid
crystal operation are responsible for the photographed images and seek to
mathematically prove the images are of dipole nature.
  A simple way of explaining this work is to think of the old magnetic iron
filling experiments; but now each iron filling is a molecule floating in a
liquid. Each molecule has the freedom to act as an independent lens that can be
aligned by an external magnetic field. Because each lens directs light, the
external field can be analyzed by following the light paths captured in the
photographs.",0805.4364v2
2008-05-30,Multiband effects on the conductivity for a multiband Hubbard model,"The newly discovered iron-based superconductors have attracted lots of
interests, and the corresponding theoretical studies suggest that the system
should have six bands. In this paper, we study the multiband effects on the
conductivity based on the exact solutions of one-dimensional two-band Hubbard
model. We find that the orbital degree of freedom might enhance the critical
value $U_c$ of on-site interaction of the transition from a metal to an
insulator. This observation is helpful to understand why undoped High-$T_c$
superconductors are usually insulators, while recently discovered iron-based
superconductors are metal. Our results imply that the orbital degree of freedom
in the latter cases might play an essential role.",0805.4669v1
2008-05-31,Doping-insensitive density-of-states suppression in polycrystalline iron-based superconductor SmO$_{1-x}$F$_{x}$FeAs,"We investigated the temperature dependence of the density-of-states in the
iron-based superconductor SmO_1-xF_xFeAs (x=0, 0.12, 0.15, 0.2) with high
resolution angle-integrated photoemission spectroscopy. The density-of-states
suppression is observed with decreasing temperature in all samples, revealing
two characteristic energy scales (10meV and 80meV). However, no obvious doping
dependence is observed. We argue that the 10meV suppression is due to an
anomalously doping-independent normal state pseudogap, which becomes the
superconducting gap once in the superconducting state; and alert the
possibility that the 80meV-scale suppression might be an artifact of the
polycrystalline samples.",0806.0078v1
2008-06-20,The Fermi surface of Ba(1-x)K(x)Fe2As2 and its evolution with doping,"We use angle-resolved photoemission spectroscopy (ARPES) to investigate the
electronic properties of the newly discovered iron-arsenic superconductor,
Ba(1-x)K(x)Fe2As2 and non-supercondcuting BaFe2As2. Our study indicates that
the Fermi surface of the undoped, parent compound BaFe$_2$As$_2$ consists of
hole pocket(s) at Gamma (0,0) and larger electron pocket(s) at X (1,0), in
general agreement with full-potential linearized plane wave (FLAPW)
calculations. Upon doping with potassium, the hole pocket expands and the
electron pocket becomes smaller with its bottom approaching the chemical
potential. Such an evolution of the Fermi surface is consistent with hole
doping within a rigid band shift model. Our results also indicate that FLAPW
calculation is a reasonable approach for modeling the electronic properties of
both undoped and K-doped iron arsenites.",0806.3453v1
2008-06-22,"Electronic structures of ternary iron arsenides AFe$_2$As$_2$ (A=Ba, Ca, or Sr)","We have studied the electronic and magnetic structures of the ternary iron
arsenides AFe$_2$As$_2$ (A = Ba, Ca, or Sr) using the first-principles density
functional theory. The ground states of these compounds are in a collinear
antiferromagnetic order, resulting from the interplay between the nearest and
the next-nearest neighbor superexchange antiferromagnetic interactions bridged
by As $4p$ orbitals. The correction from the spin-orbit interaction to the band
structure is small. The pressure can reduce dramatically the magnetic moment
and diminish the collinear antiferromagnetic order. Based on the calculations,
we propose that the low energy dynamics of these materials is described
effectively by a $t-J_H-J_1-J_2$-type model.",0806.3526v3
2008-06-27,75As NMR study of the ternary iron arsenide BaFe2As2,"We report 75As-NMR measurements of the ternary iron arsenide BaFe2As2.
75As-NMR spectra clearly revealed that magnetic transition occurs at around 131
K in our samples, which corresponds to the emergence of spin density wave.
Temperature dependence of the internal magnetic field suggests that the
transition is likely of the first order. The critical-slowing-down phenomenon
in the spin-lattice relaxation rate 1/T1 is not pronounced in this material.",0806.4514v3
2008-06-30,Quantum oscillations in the parent magnetic phase of an iron arsenide high temperature superconductor,"We report quantum oscillation measurements in SrFe2As2 - which is an
antiferromagnetic parent of the iron-arsenide family of superconductors - known
to become superconducting under doping and the application of pressure. The
magnetic field and temperature dependences of the oscillations between 20 and
55 T in the liquid helium temperature range suggest that the electronic
excitations are those of a Fermi liquid. We show that the observed Fermi
surface comprising small pockets is consistent with the formation of a
spin-density wave. Our measurements thus demonstrate that high Tc
superconductivity can occur on doping or pressurizing a conventional metallic
spin-density wave state.",0806.4726v2
2008-06-29,Structural and magnetic phase transitions in the ternary iron arsenides SrFe2As2 and EuFe2As2,"The structural and magnetic phase transitions of the ternary iron arsenides
SrFe2As2 and EuFe2As2 were studied by temperature-dependent x-ray powder
diffraction and 57-Fe Moessbauer spectroscopy. Both compounds crystallize in
the tetragonal ThCr2Si2-type structure at room temperature and exhibit
displacive structural transitions at 203 K (SrFe2As2) or 190 K (EuFe2As2) to
orthorhombic lattice symmetry in agreement with the group-subgroup relationship
between I4/mmm and Fmmm. 57-Fe Moessbauer spectroscopy experiments with SrFe2
As2 show full hyperfine field splitting below the phase transition temperature
(8.91(1) T at 4.2 K). Order parameters were extracted from detailed
measurements of the lattice parameters and fitted to a simple power law. We
find a relation between the critical exponents and the transition temperatures
for AFe2As2 compounds, which shows that the transition of BaFe2As2 is indeed
more continuous than the transition of SrFe2As2 but it remains second order
even in the latter case.",0806.4782v2
2008-06-30,LDA + Negative U Solves a Puzzle of too Large Calculated Magnetic Moment in Iron-based Superconductor LaFeAsO_{1-x}F_x,"A puzzle in the iron-based superconductor LaFeAsO_{1-x}F_x is that the
magnetic moment obtained by first-principle electronic structure calculations
is unexpectedly much larger than the experimentally observed one. For example,
the calculated value is ~ 2.0 \mu_B in the mother compound, while it is ~ 0.3
\mu_B in experiments. We find that the puzzle is solved within the framework
LDA + U by expanding the U value into a slightly negative range. We show U
dependence of the obtained magnetic moment in both the undoped x=0.0 and doped
x = 0.125. These results reveal that the magnetic moment is drastically reduced
when entering to the slightly negative range of U. Moreover, the negative U
well explains other measurement data, e.g., lattice constants and electronic
DOS at the Fermi level. We discuss possible origins of the negative U in these
compounds.",0806.4804v1
2008-07-21,Superconductivity at 34.7 K in the iron arsenide Eu0.7Na0.3Fe2As2,"EuFe2As2 is a member of the ternary iron arsenide family. Similar to BaFe2As2
and SrFe2As2, EuFe2As2 exhibits a clear anomaly in resistivity near 200 K. It
suggests that EuFe2As2 is another promising parent compound in which
superconductivity may be realized by appropriate doping. Here we report the
discovery of superconductivity in Eu0.7Na0.3Fe2As2 by partial substitution of
the europium site with sodium. ThCr2Si2 tetragonal structure, as expected for
EuFe2As2, is formed as the main phase for the composition Eu0.7Na0.3Fe2As2.
Resistivity measurement reveals a transition temperature as high as 34.7 K in
this compound, which is higher than the Tc of Eu0.5K0.5Fe2As2.",0807.3293v3
2008-08-05,"Local antiferromagnetic correlations in the iron pnictide superconductors LaFeAsO{1-x}F{x} and Ca(Fe,Co)2As2 as seen via normal-state susceptibility","We have studied the interplay of magnetism and superconductivity in
LaFeAsO$_{1-x}$F$_x$ and Ca(Fe$_{1-x}$Co$_x$)$_2$As$_2$. While
antiferromagnetic spin density wave formation is suppressed and
superconductivity evolves, all samples show a doping independent strong
increase of the normal state susceptibility upon heating which appears a
general feature of iron pnictides. The data provide evidence for robust local
antiferromagnetic correlations persisting even in the superconducting regime of
the phase diagram.",0808.0708v2
2008-08-07,Sheet Dependence on Superconducting Gap in Oxygen-Deficient Iron-based Oxypnictide Superconductors NdFeAs0.85,"Photoemission spectroscopy with low-energy tunable photons on
oxygen-deficient iron-based oxypnictide superconductors NdFeAsO0.85 (Tc=52K)
reveals a distinct photon-energy dependence of the electronic structure near
the Fermi level (EF). A clear shift of the leading-edge can be observed in the
superconducting states with 9.5 eV photons, while a clear Fermi cutoff with
little leading-edge shift can be observed with 6.0 eV photons. The results are
indicative of the superconducting gap opening not on the hole-like ones around
Gamma (0,0) point but on the electron-like sheets around M(pi,pi) point.",0808.1063v1
2008-08-08,Electronic states and pairing symmetry in the two-dimensional 16 band d-p model for iron-based superconductor,"The electronic states of the FeAs plane in iron-based superconductors are
investigated on the basis of the two-dimensional 16-band d-p model, where the
tight-binding parameters are determined so as to fit the band structure
obtained by the density functional calculation for LaFeAsO. The model includes
the Coulomb interaction on a Fe site: the intra- and inter-orbital direct terms
U and U', the exchange coupling J and the pair-transfer J'. Within the random
phase approximation (RPA), we discuss the pairing symmetry of possible
superconducting states including s-wave and d-wave pairing on the U'-J plane.",0808.1192v3
2008-08-10,Heavy anion solvation of polarity fluctuations in Pnictides,"Once again the condensed matter world has been surprised by the discovery of
yet another class of high temperature superconductors. The discovery of
iron-pnictide (FeAs) and chalcogenide (FeSe) based superconductors with a $T_c$
of up to 55 K is again evidence of how complex the many body problem really is,
or in another view how resourceful nature is. The first reactions would of
course be that these new materials must in some way be related to the
copper-oxide based superconductors for which a large number of theories exist
although a general consensus regarding the correct theory has not yet been
reached. Here we point out that the basic physical paradigm of the new iron
based superconductors is entirely different from the cuprates. Their
fundamental properties, structural and electronic, are dominated by the
exceptionally large pnictide polarizabilities.",0808.1390v1
2008-09-01,Competition between antiferromagnetic instability and frustrations in Fe-Se,"Using linear-response density-functional theory, we obtain the magnetic
interactions in the several iron pnictides. The ground state has been found to
be non-collinear in FeSe, with a large continuum of nearly degenerate states
lying very close to the magnetic ""striped"" structure. The presence of
non-collinearity also seems to be a generic feature of iron pnictides when the
Fe moment is small. At small R_{Fe-Se} the system is itinerant: strong
frustration give rise to excess of spin entropy, long ranged interactions
create incommensurate orderings and strong biquadratic (or ring) couplings
violate the applicability of Heisenberg model. There is a smooth transition to
more localized behavior as R_{Fe-Se} increases: stable magnetic orbital order
develops which favor long range AFM stripe ordering with strongly anisotropic
in-plane exchange couplings. The stabilization of the stripe magnetic order is
accompanied by the inversion of the exchange coupling.",0809.0283v2
2008-09-18,Magnetism and Superconductivity in the Two-Dimensional 16 Band d-p Model for Iron-Based Superconductors,"The electronic states of the Fe2As2 plane in iron-based superconductors are
investigated on the basis of the two-dimensional 16-band d-p model which
includes the Coulomb interaction on a Fe site: the intra- and inter-orbital
direct terms U and U', the Hund's coupling J and the pair-transfer J'. Using
the random phase approximation (RPA), we obtain the magnetic phase diagram
including the stripe and the incommensurate order on the U'-J plane. We also
solve the superconducting gap equation within the RPA and find that, for large
J, the most favorable pairing symmetry is extended s-wave whose order parameter
changes its sign between the hole pockets and the electron pockets, while it is
dxy-wave for small J.",0809.3189v5
2008-09-20,Effect of magnetic state on the $γ-α$ transition in iron: First-principle calculations of the Bain transformation path,"Energetics of the fcc ($\gamma$) - bcc ($\alpha$) lattice transformation by
the Bain tetragonal deformation is calculated for both magnetically ordered and
paramagnetic (disordered local moment) states of iron. The first-principle
computational results manifest a relevance of the magnetic order in a scenario
of the $\gamma$ - $\alpha$ transition and reveal a special role of the Curie
temperature of $\alpha$-Fe, $T_C$, where a character of the transformation is
changed. At a cooling down to the temperatures $T < T_C$ one can expect that
the transformation is developed as a lattice instability whereas for $T > T_C$
it follows a standard mechanism of creation and growth of an embryo of the new
phase. It explains a closeness of $T_C$ to the temperature of start of the
martensitic transformation, $M_s$.",0809.3515v1
2008-09-23,Universal linear-temperature dependence of static magnetic susceptibility in iron-pnictides,"A universal linear-temperature dependence of the uniform magnetic
susceptibility has been observed in the nonmagnetic normal state of
iron-pnictides. This non-Pauli and non-Curie-Weiss-like paramagnetic behavior
cannot be understood within a pure itinerant picture. We argue that it results
from the existence of a wide antiferromagnetic fluctuation window in which the
local spin-density-wave correlations exist but the global directional order has
not been established yet.",0809.3874v3
2008-09-24,"A Unified Theory for the Cuprates, Iron-Based and Similar Superconducting Systems: Application for Spin and Charge Excitations in the Hole-Doped Cuprates","A unified theory for the cuprates and the iron-based superconductors is
derived on the basis of common features in their electronic structures
including quasi-two-dimensionality, and the large-U nature of the electron
orbitals close to E_F (smaller-U hybridized orbitals reside at bonding and
antibonding states away from E_F). Consequently, low-energy excitations are
described in terms of auxiliary particles, representing combinations of
atomic-like electron configurations, rather than electron-like quasiparticles.
The introduction of a Lagrange Bose field is necessary to enable the treatments
of these auxiliary particles as bosons or fermions. The condensation of the
bosons results in static or dynamical inhomogeneities, and consequently in a
commensurate or an incommensurate resonance mode. The dynamics of the fermions
determines the charge transport, and their strong coupling to the
Lagrange-field bosons results in pairing and superconductivity. The calculated
resonance mode in hole-doped cuprates agrees with the experimental results, and
is shown to be correlated with the pairing gap on the Fermi arcs.",0809.4237v3
2008-10-02,Iron Emission Lines on the Galactic Ridge Observed with Suzaku,"In order to elucidate origin of the Galactic Ridge X-ray Emission, we
analyzed Suzaku data taken at various regions along the Galactic plane and
studied their Fe-K emission line features. Suzaku resolved the Fe line complex
into three narrow lines at ~6.4 keV,~6.7 keV and ~6.97 keV, which are K-lines
from neutral (or low-ionized), He-like, and H-like iron ions, respectively. The
6.7 keV line is clearly seen in all the observed regions and its longitudinal
distribution is consistent with that determined from previous observations. The
6.4 keV emission line was also found in various Galactic plane regions (b~0).
Differences in flux ratios of the 6.4 keV/6.7 keV and 6.97 keV/6.7 keV lines
between the Galactic plane and the Galactic center regions are studied and its
implication is discussed.",0810.0317v1
2008-10-03,"Small anisotropy, weak thermal fluctuations, and high field superconductivity in Co-doped iron pnictide Ba(Fe1-xCox)2As2","We performed high-field magnetotransport and magnetization measurements on a
single crystal of the 122-phase iron pnictide Ba(Fe1-xCox)2As2. Unlike the HTS
cuprates and 1111-phase oxypnictides, Ba(Fe1-xCox)2As2 showed practically no
broadening of the resistive transitions under magnetic fields up to 45 T. The
mass anisotropy gamma = Hc2ab/Hc2c deduced from the slopes of the upper
critical field dHc2ab/dT = 4.9T/K and dHc2c/dT = 2.5T/K decreases from ~2 near
Tc, to ~1.5 at lower temperatures. We observed the irreversibility field close
to Hc2, and a rather unusual symmetric volume pinning force curve Fp(H)
suggestive of strong pinning nano-structure.",0810.0699v2
2008-10-10,Pseudogap and Superconductivity in Iron-Based Layered Superconductor studied by Fluctuation-Exchange Approximation,"We investigate interplay between magnetic fluctuations and superconductivity
in the effective five-band Hubbard model for iron-oxypnictide superconductors
on the basis of the fluctuation-exchange approximation. As for the normal-state
properties, we find the pseudogap behavior in the NMR relaxation rate and the
spectral weight in the electron-doped region, while we cannot find such
behavior in the hole-doped region. The pseudogap behavior originates from the
band structure effect, that is, existence of high density of states just below
the Fermi level.
  Solving the superconducting Eliashberg equation, we find that the most
probable candidate for the pairing symmetry is the sign-changed s-wave
spin-singlet state. For small Hund's coupling J, the eigenvalue is not so
sensitive to carrier doping, and seems to be irrelevant with antiferromagnetic
(AF) spin fluctuation. We suggest that correlation between spin and
spin-quadrupole is important as the pairing mechanism as well as the AF
fluctuation.",0810.1828v2
2008-10-15,"Electronic Structure, Magnetism and Superconductivity of Layered Iron Compounds","The layered iron superconductors are discussed using electronic structure
calculations. The four families of compounds discovered so far, including
Fe(Se,Te) have closely related electronic structures. The Fermi surface
consists of disconnected hole and electron cylinders and additional hole
sections that depend on the specific material. This places the materials in
proximity to itinerant magnetism, both due to the high density of states and
due to nesting. Comparison of density functional results and experiment
provides strong evidence for itinerant spin fluctuations, which are discussed
in relation to superconductivity. It is proposed that the intermediate phase
between the structural transition and the SDW transition in the oxy-pnictides
is a nematic phase.",0810.2682v2
2008-10-15,Temperature dependence and resonance effects in Raman scattering of phonons in NdFeAsO$_{x}$F$_{1-x}$ single crystals,"We report plane-polarized Raman scattering spectra of iron oxypnictide
superconductor NdFeAsO$_{1-x}$F$_x$ single crystals with varying fluorine $x$
content. The spectra exhibit sharp and symmetrical phonon lines with a weak
dependence on fluorine doping $x$. The temperature dependence does not show any
phonon anomaly at the superconducting transition. The Fe related phonon
intensity shows a strong resonant enhancement below 2 eV. We associate the
resonant enhancement to the presence of an interband transition around 2 eV
observed in optical conductivity. Our results point to a rather weak coupling
between Raman-active phonons and electronic excitations in iron oxypnictides
superconductors.",0810.2735v1
2008-10-18,Elastic theory for the vortex-lattice melting in iron-based high-Tc superconductors,"The vortex-lattice melting transitions in two typical iron-based high-Tc
superconductor $Ba(Fe_{1-x}Co_{x})_{2}As_{2}$ (122-type)
and$Nd(O_{1-x}F_{x})FeAs$ (1111-type) for magnetic fields both parallel and
perpendicular to the anisotropy axis are studied within the elastic theory.
Using the parameters from experiments, the vortex-lattice melting lines in the
H-T diagram are located systematically by various groups of Lindemann numbers.
It is observed that the theoretical result for the vortex melting on
$Ba(Fe_{1-x}Co_{x})_{2}As_{2}$ for parallel fields agrees well the recent
experimental data. The future experimental results for the vortex melting can
be compared with the present theoretical prediction by tuning reasonable
Lindemann numbers.",0810.3292v2
2008-10-24,Interplay between magnetic properties and Fermi surface nesting in iron pnictides,"The wave-vector q and doping (x,y) dependences of the magnetic energy, iron
moment, and effective exchange interactions in LaFeAsO{1-x}F{x} and
Ba{1-2y}K{2y}Fe2As2 are studied by self-consistent LSDA calculations for
co-planar spin spirals. For the undoped compounds (x=0, y=0), the minimum of
the calculated total energy, E(q), is for q corresponding to stripe
antiferromagnetic order. Already at low levels of electron doping (x), this
minimum becomes flat in LaFeAsO{1-x}F{x} and for x>=5, it shifts to an
incommensurate q. In Ba{1-2y}K{2y}Fe2As2, stripe order remains stable for hole
doping up to y=0.3. These results are explained in terms of the band structure.
The magnetic interactions cannot be accurately described by a simple classical
Heisenberg model and the effective exchange interactions fitted to E(q) depend
strongly on doping. The doping dependence of the E(q) curves is compared with
that of the noninteracting magnetic susceptibility for which similar trends are
found.",0810.4469v2
2008-11-01,Synthesis and Microstructural Studies of Iron Oxypnictide LaO1-xFxFeAs Superconductors,"We report on the synthesis and structural/ microstructural studies of iron
based fluorine doped LaOFeAs superconductors. We have successfully synthesized
fluorine doped superconducting LaO1-xFxFeAs materials by choosing lower
temperature (1150^0C) and longer synthesis duration (60 hours) as compared to
the standard values of these employed in the pioneering first contribution
[Kamihara et al 2008 J Am Chem Soc 130 3296]. Decrease of lattice parameters as
determined by x-ray diffraction confirm the substitution of fluorine. The
superconducting transition temperature is 27.5 K which is observed at doping
level of x=0.2. This superconducting material LaO1-xFxFeAs exhibits interesting
microstructural characteristic. This relates to the existence of another
structural phase, besides the standard phase, having c parameters of ~12.67A.
This suggests existence of modulated structure, similar to the cuprates, in
these new oxypnictides. This phase may have new impacts on this new high-Tc
family.",0811.0094v1
2008-11-11,Unconventional superconductivity originating from disconnected Fermi surfaces in the iron-based compound,"The iron-based LaFeAsO$_{1-x}$F$_x$ recently discovered by Hosono's group is
a fresh theoretical challenge as a new class of high-temperature
superconductors. Here we describe the electronic structure of the material and
the mechanism of superconductivity. We start with constructing a tight-binding
model in terms of the maximally localized Wannier orbitals from a
first-principles electronic structure calculation, which has turned out to
involve all the five Fe 3d bands. This is used to calculate the spin and charge
susceptibilities with the random phase approximation. The spin susceptibility
has peaks around ${\Vec k} = (\pi, 0), (0, \pi)$ arising from a nesting across
disconnected Fermi surface pockets. We have then plugged the susceptibilities
into the linearised Eliashberg equation. For the doping concentration $x =
0.1$, we obtain an unconventional s-wave pairing, which is roughly an extended
s in that the gap changes sign between the Fermi pockets, but the gap function
is actually a 5$\times$5 matrix. Its experimental implications are also
discussed.",0811.1656v1
2008-11-17,Perturbation Theory of High-Tc Superconductivity in Iron Pnictides,"The high-transition-temperature (high-Tc) superconductivity discovered
recently in iron pnictides is analyzed within a perturbation theory.
Specifically, the probable pairing symmetry, the doping dependence of the
transition temperature and the pairing mechanism are studied by solving the
Eliashberg equation for multi-band (2- and 5-band) Hubbard models with
realistic electronic structures. The effective pairing interaction is expanded
perturbatively in the on-site Coulomb integrals up to third order. Our
perturbative weak-coupling approach shows that sufficiently large eigenvalues
of the Eliashberg equation are obtained to explain the actual high transition
temperatures by taking realistic on-site Coulomb integrals in the 5-band model.
Thus, unconventional (non-phonon-mediated) superconductivity is highly likely
to be realized. The superconducting order parameter does not change its sign on
the Fermi surfaces, but it does change between the electron and hole Fermi
surfaces. Consequently, the probable pairing symmetry is always ""a nodeless
extended s-wave symmetry (more specifically, an s_{+-}-wave symmetry)"" over the
whole parameter region that we investigated. It is suggested that the 2-band
model is insufficient to explain the high values of Tc.",0811.2462v2
2008-11-25,Spin-orbital frustrations and anomalous metallic state in iron-pnictide superconductors,"We develop an understanding of the anomalous metal state of the parent
compounds of recently discovered iron based superconductors starting from a
strong coupling viewpoint, including orbital degrees of freedom. On the basis
of an intermediate-spin (S=1) state for the Fe^{2+} ions, we derive a
Kugel-Khomskii spin-orbital Hamiltonian for the active t_{2g} orbitals. It
turns out to be a highly complex model with frustrated spin and orbital
interactions. We compute its classical phase diagrams and provide an
understanding for the stability of the various phases by investigating its
spin-only and orbital-only limits. The experimentally observed spin-stripe
state is found to be stable over a wide regime of physical parameters and can
be accompanied by three different types of orbital orders. Of these the
orbital-ferro and orbital-stripe orders are particularly interesting since they
break the in-plane lattice symmetry -- a robust feature of the undoped
compounds. We compute the magnetic excitation spectra for the effective spin
Hamiltonian, observing a strong reduction of the ordered moment, and point out
that the proposed orbital ordering pattern can be measured in resonant X-ray
diffraction.",0811.4104v1
2008-11-25,Coexistence of Itinerant Electrons and Local Moments in Iron-Based Superconductors,"In view of the recent experimental facts in the iron-pnictides, we make a
proposal that the itinerant electrons and local moments are simultaneously
present in such multiband materials. We study a minimal model composed of
coupled itinerant electrons and local moments to illustrate how a consistent
explanation of the experimental measurements can be obtained in the leading
order approximation. In this mean-field approach, the spin-density-wave (SDW)
order and superconducting pairing of the itinerant electrons are not directly
driven by the Fermi surface nesting, but are mainly induced by their coupling
to the local moments. The presence of the local moments as independent degrees
of freedom naturally provides strong pairing strength for superconductivity and
also explains the normal-state linear-temperature magnetic susceptibility above
the SDW transition temperature. We show that this simple model is supported by
various anomalous magnetic properties and isotope effect which are in
quantitative agreement with experiments.",0811.4111v4
2008-12-15,Collective modes and emergent SO(6) symmetry in the iron pnictides,"We show the existence of an emergent SO(6) symmetry in the low energy
description of the iron pnictides. This approximate symmetry provides a
unifying framework for the occurrence of spin density wave (SDW) and
superconductivity (SC) in these materials. We use this symmetry to make several
predictions for future experiments, including the topology of the phase diagram
and the presence of various resonant modes in neutron scattering experiments in
both the SC and SDW phases. We also predict the existence of a new ""Orbital
Density Wave"" state, which competes with both SDW and SC orders.",0812.2907v2
2008-12-16,Hard (State) Problems,"For microquasars, the one time when these systems exhibit steady and powerful
jets is when they are in the hard state. Thus, our understanding of this state
is key to learning about the disk/jet connection. Recent observational and
theoretical results have led to questions about whether we really understand
the physical properties of this state, and even our basic picture of this state
is uncertain. Here, I discuss some of the recent developments and possible
problems with our understanding of this state. Overall, it appears that the
strongest challenge to the standard truncated disk picture is the detection of
broad iron features in the X-ray spectra, and it seems that either there is a
problem with the truncated disk picture or there is a problem with the
relativistic reflection models used to explain the broad iron features.",0812.2980v1
2008-12-19,Evidence for nodal superconductivity in LaFePO,"In several iron-arsenide superconductors there is strong evidence for a fully
gapped superconducting state consistent with either a conventional s-wave
symmetry or an unusual $s_\pm$ state where there the gap changes sign between
the electron and hole Fermi surface sheets. Here we report measurements of the
penetration depth $\lambda(T)$ in very clean samples of the related
iron-phosphide superconductor, LaFePO, at temperatures down to $\sim$ 100 mK.
We find that $\lambda(T)$ varies almost perfectly linearly with $T$ strongly
suggesting the presence of gap nodes in this compound. Taken together with
other data, this suggests the gap function may not be generic to all pnictide
superconductors.",0812.3858v1
2008-12-22,The role of striction at magnetic and structural transitions in iron-pnictides,"We discuss the role of striction in the intertwined magnetic and structural
phase transitions in the underdoped iron-pnictides. The magneto-elastic
coupling to acoustic modes is then derived and estimated in framework of the
multiband spectrum for itinerant electrons with nesting features. We argue that
the 1-st order character of the magneto-elastic phase transition originates
from the lattice instabilities near the onset of spin-density wave order
introducing, thus, a shear acoustic mode as a new order parameter. Taking
non-harmonic termis in the lattice energy into account may explain the
splitting of the structural and magnetic transitions in some oxypnictides.
Fluctuations of the magnetic order parameter show up in the precursory
temperature dependence of the elastic moduli.",0812.4277v2
2008-12-30,Structure and magnetism in ultrathin iron oxides characterized by low energy electron microscopy,"We have grown epitaxial films a few atomic layers thick of iron oxides on
ruthenium. We characterize the growth by low energy electron microscopy. Using
selected area diffraction and intensity vs. voltage spectroscopy, we detect two
distinct phases which are assigned to wustite and magnetite. Spin polarized low
energy electron microscopy shows magnetic domain patterns in the magnetite
phase at room temperature.",0812.5049v2
2009-01-01,Multiple Bands - A Key to High - Temperature Superconductivity in Iron Arsenides?,"In the framework of four-band model of superconductivity in iron arsenides
proposed by Barzykin and Gor'kov we analyze the gap ratios on hole - like and
electron - like Fermi - surface cylinders. It is shown that experimentally
observed (ARPES) gap ratios can be obtained only within rather strict limits on
the values of pairing coupling constants. The difference of T_c values in 1111
and 122 systems is reasonably explained by the relative values of partial
densities of states. The multiple bands electronic structure of these systems
leads to a significant enhancement of effective pairing coupling constant
determining T_c, so that high enough T_c values can be achieved even for the
case of rather small intraband and interband pairing interactions.",0901.0164v1
2009-01-07,Band renormalization and Fermi surface reconstruction in iron-based superconductors,"Using the fluctuation exchange approximation and a three-orbital model, we
study the band renormalization, Fermi surface reconstruction and the
superconducting pairing symmetry in the newly-discovered iron-based
superconductors. We find that the inter-orbital spin fluctuations lead to the
strong anisotropic band renormalization and the renormalization is orbital
dependent. As a result, the topology of Fermi surface displays distinct
variation with doping from the electron type to the hole type, which is
consistent with the recent experiments. This shows that the Coulomb
interactions will have a strong effect on the band renormalization and the
topology of the electron Fermi pocket. In addition, the pairing state mediated
by the inter-orbital spin fluctuation is of an extended s-wave symmetry.",0901.0821v1
2009-01-22,Fermi surface in BaNi$_2$P$_2$,"We report measurements of the de Haas-van Alphen (dHvA) oscillation and a
band structure calculation for the pnictide superconductor BaNi$_2$P$_2$, which
is isostructural to BaFe$_2$As$_2$, the mother compound of the iron-pnictide
high-$T_c$ superconductor (Ba$_{1-x}$K$_x$)Fe$_2$As$_2$. Six dHvA-frequency
branches with frequencies up to $\sim$8 kT were observed, and they are in
excellent agreement with results of the band-structure calculation. The
determined Fermi surface is large, enclosing about one electron and hole per
formula unit, and three-dimensional. This is in contrast to the small
two-dimensional Fermi surface expected for the iron-pnictide high-$T_c$
superconductors. The mass enhancement is about two.",0901.3394v3
2009-01-26,Quantum Oscillation Studies of the Fermi Surface of LaFePO,"We review recent experimental measurements of the Fermi surface of the
iron-pnictide superconductor LaFePO using quantum oscillation techniques. These
studies show that the Fermi surface topology is close to that predicted by
first principles density functional theory calculations, consisting of
quasi-two-dimensional electron-like and hole-like sheets. The total volume of
the two hole sheets is almost equal to that of the two electron sheets, and the
hole and electron Fermi surface sheets are close to a nesting condition. No
evidence for the predicted three dimensional pocket arising from the Fe
$d_{z^2}$ band is found. Measurements of the effective mass suggest a
renormalisation of around two, close to the value for the overall band
renormalisation found in recent angle resolved photoemission measurements.",0901.3976v2
2009-02-03,Anharmonic softening of Raman active phonons in Iron-Pnictides; estimating the Fe isotope effect due to anharmonic expansion,"We present Raman measurements on the iron-pnictide superconductors
CeFeAsO_{1-x}F_{x} and NdFeAsO{1-x}F_{x}. Modeling the Fe-As plane in terms of
harmonic and a cubic anharmonic Fe-As interaction we calculate the temperature
dependence of the energy and lifetime of the Raman active Fe B_{1g} mode and
fit to the observed energy shift. The shifts and lifetimes are in good
agreement with those measured also in other Raman studies which demonstrate
that the phonon spectrum is well represented by phonon-phonon interactions
without any significant electronic contribution. We also estimate the
anharmonic expansion from Fe (56->54) isotope substitution to \Delta a=5.1
10^{-4}\AA and \Delta d_{Fe-As}= 2.510^{-4}\AA and the shift of harmonic zero
point fluctuations of bond lengths <\Delta x^2><=3 10^{-5}\AA^2, giving a total
relative average decrease of electronic hopping integrals of |\delta t|/t<= 2.0
10^{-4}. The results poses a serious challenge for any theory of
superconductivity in the pnictides that does not include electron-phonon
interactions to produce a sizable Fe-isotope effect.",0902.0505v2
2009-02-13,Dominant role of local-moment interactions in the magnetism in iron pnictides : comparative study of arsenides and antimonides from first-principles,"The magnetic properties of various iron pnictides are investigated using
first-principles pseudopotential calculations. We consider three different
families, LaFePnO, BaFe$_2$Pn$_2$, and LiFePn with Pn=As and Sb, and find that
the Fe local spin moment and the stability of the stripe-type antiferromagnetic
phase increases from As to Sb for all of the three families, with a partial gap
formed at the Fermi energy. In the meanwhile, the Fermi-surface nesting is
found to be enhanced from Pn=As to Sb for LaFePnO, but not for BaFe$_2$Pn$_2$
and LiFePn. These results indicate that it is not the Fermi surface nesting but
the local moment interaction that determines the stability of the magnetic
phase in these materials, and that the partial gap is an induced feature by a
specific magnetic order.",0902.2359v2
2009-02-16,The f-spin physics of rare-earth iron pnictides: influence of d-electron antiferromagnetic order on the heavy fermion phase diagram,"Some of the high Tc iron pnictides contain magnetic rare-earth elements,
raising the question of how the existence and tunability of a d-electron
antiferromagnetic order influences the heavy fermion behavior of the f-moments.
With CeOFeP and CeOFeAs in mind as prototypes, we derive an extended Anderson
lattice model appropriate for these quaternary systems. We show that the Kondo
screening of the f-moments are efficiently suppressed by the d-electron
ordering. We also argue that, inside the d-electron ordered state (as in
CeOFeAs), the f-moments provide a rare realization of a quantum frustrated
magnet with competing J1-J2-J3 interactions in an effective square lattice.
Implications for the heavy fermion physics in broader contexts are also
discussed.",0902.2423v2
2009-02-16,Point contact Andreev reflection spectroscopy of superconducting energy gaps in 122-type family of iron pnictides,"A brief overview of the superconducting energy gap studies on 122-type family
of iron pnictides is given. It seems that the situation in the hole-doped
Ba1-xKxFe2As2 is well resolved. Most of the measurements including the
presented here point-contact Andreev reflection spectra agree on existence of
multiple nodeless gaps in the excitation spectrum of this multiband system. The
gaps have basically two sizes - the small one with a strength up to the BCS
weak coupling limit and the large one with a very strong coupling with
2Delta/kTc ~ 6 - 8. In the electron doped Ba(Fe1-xCox)2As2 the most of the
experiments including our point contact measurements reveal in quite broadened
spectra only a single gap with a strong coupling strength. The high precision
ARPES measurements on this system identified two gaps but very close to each
other, both showing a strong coupling with 2Delta/kTc ~ 5 and 6, respectively.",0902.2667v1
2009-02-19,Quantum Entanglement in Nitrosyl Iron Complexes,"Recent magnetic susceptibility measurements for polycrystalline samples of
binuclear nitrosyl iron complexes [Fe_2(C_3H_3N_2S)_2(NO)_4] (I) and
[Fe_2(SC_3H_5N_2)_2(NO)_4] (II), suggest that quantum-mechanical entanglement
of the spin degrees of freedom exists in these compounds. Entanglement E exists
below the temperature T_E that we have estimated for complexes I and II to be
80-90 and 110-120 K, respectively. Using an expression of entanglement in terms
of magnetic susceptibility for a Heisenberg dimer, we find the temperature
dependence of the entanglement for complex II. Having arisen at the temperature
T_E, the entanglement increases monotonically with decreasing temperature and
reaches 90-95% in this complex at T=25 K, when the subordinate effects are
still small.",0902.3337v1
2009-02-19,Theory of Multiband Superconductivity in Iron Pnictides,"The precise nature of unconventional superconductivity in Iron Pnictides is
presently a hotly debated issue. Here, using insights from normal state
electronic structure and symmetry arguments, we show how an unconventional SC
emerges from the bad metal ""normal"" state. Short-ranged, multi-band spin- and
charge correlations generates nodeless SC in the active planar $d_{xz,yz}$
bands, and an inter-band proximity effect induces out-of-plane gap nodes in the
passive $d_{3z^{2}-r^{2}}$ band. While very good quantitative agreement with
various key observations in the SC state and reconciliation with NMR and
penetration depth data in the same picture are particularly attractive features
of our proposal, clinching evidence would be an experimental confirmation of
c-axis nodes in future work.",0902.3400v2
2009-02-27,Probing the pairing symmetry of the iron pnictides with electronic Raman scattering,"An important issue in the study of the iron-arsenic based superconductors is
the symmetry of the superconducting gap, a problem complicated by multiple gaps
on different Fermi surface sheets. Electronic Raman scattering is a flexible
bulk probe which allows one in principle to determine gap magnitudes and test
for gap nodes in different regions of the Brillouin zone by employing different
photon polarization states. Here we calculate the clean Raman intensity for
$A_{1g}$, $B_{1g}$ and $B_{2g}$ polarizations, and discuss the peak structures
and low-energy power laws which might be expected for several popular models of
the superconducting gap in these systems.",0902.4745v1
2009-02-28,Influence of Magnetism on Phonons in CaFe2As2 Via Inelastic X-ray Scattering,"In the iron pnictides, the strong sensitivity of the iron magnetic moment to
the arsenic position suggests a significant relationship between phonons and
magnetism. We measured the phonon dispersion of several branches in the high
temperature tetragonal phase of CaFe2As2 using inelastic x-ray scattering on
single-crystal samples. These measurements were compared to ab initio
calculations of the phonons. Spin polarized calculations imposing the
antiferromagnetic order present in the low temperature orthorhombic phase
dramatically improve agreement between theory and experiment. This is discussed
in terms of the strong antiferromagnetic correlations that are known to persist
in the tetragonal phase.",0903.0017v2
2009-03-04,"Resistivity Anisotropy of $AE$Fe$_2$As$_2$ ($AE$ =Ca, Sr, Ba): direct versus Montgomery technique measurements","The anisotropy of electrical resistivity was measured in parent compounds of
the iron-arsenic high temperature superconductors, AEFe2As2 with Alkali Earth
elements AE=Ca,Sr, Ba. Measurements were performed using both the Montgomery
technique and direct resistivity measurements on samples cut along principal
crystallographic directions. The anisotropy ratio \gamma_\rho=\rho_c/\rho_a is
well below 10 for all compounds in the whole temperature range studied (4 to
300 K), in notable contrast to previous reports. The anisotropy at room
temperature increases from about 2 in Ca, to about 4 in Sr and Ba. In all
compounds the resistivity ratio decreases on cooling through the
structural/antiferromagnetic transition temperature T_{SM}, with the change
mainly coming from stronger variation in \rho_a as compared with \rho_c. This
suggests that the transitions stronger affect the two-dimensional parts of the
Fermi surface. We compare our experimental observations with band structure
calculations, and find similar trend in the evolution of anisotropy with the
size of AE ion. Our results show that the electronic structure of the iron
pnictides has large contribution from three-dimensional areas of the Fermi
surface.",0903.0820v1
2009-03-09,Theory of Magnetic Fluctuations in Iron Pnictides,"Magnetic fluctuations in an unconventional superconductor (U-SC) can
distinguish between distinct proposals for the symmetry of the order parameter.
Motivated thereby, we undertake a study magnetic fluctuations in Iron
pnictides, tracking their evolution from the incoherent normal, pseudogapped
metal, to the U-SC state. Within our proposal of extended-s-plus s_{xy} inplane
gap with proximity-induced out-of-plane line nodes, (i) we describe the
evolution of the spin-lattice relaxation rate, from a non-Korringa form in the
normal state, to a power-law form in the U-SC in good agreement with
experiment, and (ii) we predict a sharp resonance in the U-SC state along
(\pi,\pi), but not along (\pi/2,0), along with modulated c-axis intensity in
inelastic neutron scattering work as a specific and testable manifestation of
our proposal.",0903.1568v1
2009-03-10,Quasiparticle Scattering Interference in Superconducting Iron-pnictides,"Using both two orbital and five orbital models, we investigate the
quasiparticle interference (QPI) patterns in the superconducting (SC) state of
iron-based superconductors. We compare the results for nonmagnetic and magnetic
impurities in sign-changed s-wave $\cos(k_x)\cdot\cos(k_y)$ and sign-unchanged
$|\cos(k_x)\cdot\cos(k_y)|$ SC states. While the patterns strongly depend on
the chosen band structures, the sensitivity of peaks around $(\pm\pi,0)$ and
$(0,\pm\pi)$ wavevectors on magnetic or non-magnetic impurity, and sign change
or sign unchanged SC orders is common in two models. Our results strongly
suggest that QPI may provide direct information of band structures and evidence
of the pairing symmetry in the SC states.",0903.1694v1
2009-03-11,Magnetic Properties of the Superconducting State of Iron-Based Superconductors,"We show that features of the dynamical spin susceptibility can unambiguously
distinguish between different pairing symmetries of the superconducting state
in iron-based superconductors. A magnetic resonance is a unique feature for the
extended $s_{x^2y^2}$-wave $\cos k_x\cos k_y$ pairing symmetry. It is present
in the pure superconducting (SC) state, but weakens in the mixed SC and
magnetically ordered state. We calculate the the RPA correction to the NMR spin
relaxation rate $1/T_1$ and the Knight shift in the above states and show a
good agreement with experimental results. Moreover, we argue that the energy
dispersion of the magnetic resonance along c axis observed in neutron
scattering experiments is also an indirect evidence supporting the $s_{x^2y^2}$
pairing symmetry.",0903.2025v1
2009-03-19,Superconductivity at 17 K in (Fe2P2)(Sr4Sc2O6): a new superconducting layered pnictide oxide with a thick perovskite oxide layer,"A new layered oxypnictide (Fe2P2)(Sr4Sc2O6) have been synthesized by
solid-state reaction. This material has an alternating layer stacking structure
of anti-fluorite Fe2P2 and perovskite-based Sr4Sc2O6 oxide layers. Space group
of the material is P4/nmm and lattice constants a and c are 4.016 A and 15.543
A, respectively. The interlayer Fe-Fe distance corresponding to the c-axis
length is the longest ever reported in the iron-based oxypnictide systems. In
both magnetization and resistivity measurements, the present compound exhibited
superconductivity below 17 K, which is much higher than that of LaFePO and the
highest in arsenic-free iron-based oxypnictide systems under ambient pressure.",0903.3314v3
2009-03-20,"Inverse Iron Isotope Effect on the transition temperature of the (Ba,K)Fe2As2 superconductor","We report that (Ba,K)Fe2As2 superconductor (a transition temperature, Tc = 38
K) shows inverse Iron isotope effect (-0.18) (the sample including the larger
atomic weight of Fe depicts higher Tc). Measurements of both temperature
dependent magnetization and resistivity reveal a clear inverse shift by
systematic studies on Tc using three types of Fe-isotopes (Fe-54, natural Fe
and Fe-57). This indicates the first evidence of the inverse isotope effect in
high-Tc superconductors. This atomic mass dependence on Tc implies the exotic
coupling mechanism.",0903.3515v3
2009-03-25,Orbital coupling and superconductivity in the iron pnictides,"We demonstrate that strong inter-orbital interaction is very efficient to
achieve superconductivity due to magnetic fluctuations in the iron pnictides.
Fermi surface states that are coupled by the antiferromagnetic wave vector are
often of different orbital nature, causing pair-hopping interactions between
distinct Fe-3d orbitals to become important. Performing a self-consistent FLEX
calculation below $T_{c}$ we determine the superconducting order parameter as
function of intra- and inter-orbital couplings. We find an $s^{\pm}$-pairing
state with $T_{c}\simeq80\mathrm{K}$ for realistic parameters.",0903.4473v2
2009-03-30,"New iron-based arsenide oxides (Fe2As2)(Sr4M2O6)(M = Sc, Cr)","We have discovered new layered oxyarsenides (Fe2As2)(Sr4M2O6) (M = Sc, Cr:
M-22426). These materials are isostructural with (Fe2P2)(Sr4Sc2O6), which was
found in our previous study. The new compounds are tetragonal with a space
group of P4/nmm and consist of the anti-fluorite type FeAs layer and
perovskite-type blocking layer. The lattice constants are a = 4.050 A, c =
15.809 A for M = Sc and a = 3.918 A, c = 15.683 A for M = Cr. These compounds
have long interlayer Fe-Fe distances corresponding to the c-axis length, the
15.8 A in Sc-22426 is the longest in the iron-based oxypnictide systems.
Chemical flexibility of the perovskite block in this system was probed by
chromium containing (Fe2As2)(Sr4Cr2O6). Different trends were found in bond
angle and bond length of the new oxypnictides compared to the reported systems,
such as REFePnO. Absence of superconductivity in these compounds is considered
to be due to insufficient carrier concentration as in the case of undoped
REFeAsO.",0903.5124v3
2009-03-31,Structure and Physical properties of New layered oxypnictides $Sr_4Sc_2O_6M_2As_2$ (M=Fe and Co),"We have successfully prepared the new layered oxypnictides
$Sr_4Sc_2O_6M_2As_2$ (M=Fe and Co). They adopt the tetragonal structure, being
the same as that of $Sr_4Sc_2O_6Fe_2P_2$. The lattice constants are a=0.4045 nm
and c= 0.5802 nm for M=Fe, and a=0.4045 nm and c=1.5695 nm for M=Co,
respectively. Their transport and magnetic properties have been systematically
studied. The temperature dependence of Hall coefficient and thermoelectric
powder for $Sr_4Sc_2O_6Fe_2As_2$ compound show complicated behavior, similar to
that of iron-based parent compounds LnOFeAs and $BaFe_2As_2$. It suggests that
the $Sr_4Sc_2O_6Fe_2As_2$ could be considered a new parent compound as
iron-based superconductors.",0903.5484v1
2009-03-31,Momentum dependence and nodes of the superconducting gap in iron-pnictides,"We discuss the structure of the superconducting gap in iron pnictides. In the
itinerant electron picture, gaps with or without nodes have the extended s-wave
(s+) symmetry and emerge within the same pairing mechanism, determined by the
interplay between intra-pocket repulsion and inter-band pair hopping. If the
pair hopping is stronger, the system develops an s+ gap without nodes. In the
opposite case the superconductivity is governed by of the momentum-dependent
part of the pair-hopping, and an s+ gap shows nodes on electron Fermi surfaces.
We argue that the gap without/with nodes emerges in systems with a
stronger/weaker tendency towards a spin-density-wave order.",0903.5547v1
2009-04-05,Superconductivity in Ir-doped LaFe1-xIrxAsO,"We report the realization of superconductivity by 5d element Ir doping in
LaFeAsO, a prototype parent compound of high-temperature iron based
superconductors. X-ray diffraction patterns indicate that the material has
formed the ZrCuSiAs-type structure with a space group P4/nmm. The systematic
evolution of the lattice constants demonstrated that the Fe ions were
successfully replaced by the Ir. Both electrical resistance and magnetization
measurements show superconductivity up to 11 K in LaFe1-xIrxAsO. The
superconducting transitions at different magnetic fields were also measured
yielding a slope of -dHc2/dT = 6.7 T / K near Tc, and the upper critical field
at zero K is found to be about 55 T. This is the first example of bulk
superconductivity induced by replacing the Fe sites with higher d-orbital
electrons in FeAs-1111 family, which should add more ingredients to the
underlying physics of the iron-based superconductors.",0904.0772v4
2009-04-06,Superconductivity in Ti-doped Iron-Arsenide Compound Sr4Cr0.8Ti1.2O6Fe2As2,"Superconductivity was achieved in Ti-doped iron-arsenide compound
Sr4Cr0.8Ti1.2O6Fe2As2 (abbreviated as Cr-FeAs-42622). The x-ray diffraction
measurement shows that this material has a layered structure with the space
group of \emph{P4/nmm}, and with the lattice constants a = b = 3.9003 A and c =
15.8376 A. Clear diamagnetic signals in ac susceptibility data and
zero-resistance in resistivity data were detected at about 6 K, confirming the
occurrence of bulk superconductivity. Meanwhile we observed a superconducting
transition in the resistive data with the onset transition temperature at 29.2
K, which may be induced by the nonuniform distribution of the Cr/Ti content in
the FeAs-42622 phase, or due to some other minority phase.",0904.0972v3
2009-04-20,Constraints on the absorption-dominated model for the X-ray spectrum of MCG-6-30-15,"Complexities in the X-ray spectrum of the nearby Seyfert 1.2 galaxy
MCG-6-30-15 are commonly interpreted in terms of a broad iron line and the
associated Compton reflection hump from the innermost relativistic regions of
an accretion disk around a rapidly spinning black hole. However, an alternative
model has recently been proposed in which these spectral features are caused
entirely by complex (ionized and partial-covering) absorption. By considering
the fluorescent emission that must accompany photoelectric absorption, we show
that the absorption-dominated model over-predicts the 6.4keV iron line flux
unless the marginally Compton-thick absorber responsible for the hard X-ray
hump satisfies very restrictive geometric constraints. In the absence of a
specific model that both obeys these geometrical constraints and is
physically-plausible, the relativistic-reflection model is favoured.",0904.3099v1
2009-04-24,"Synthesis, characterization and low temperature studies of iron chalcogenide superconductors","We have synthesized tetragonal iron selenide and telluride superconductors
through solid state reaction at 450deg.C and 550deg.C respectively. These
synthesis temperatures have been established by optimization. Electrical
resistivity and magnetic susceptibility measurements (4.2-300 K) confirm
superconductivity with Tc of around 8.5 K in all selenide samples of nominal
composition Fe1+deltaSe (delta=0.02-0.22). However, Scanning Electron
Microscopy/ Energy Dispersive Spectroscopy studies clearly indicate that the
actual stoichiometric ratio of Fe : Se for all the samples synthesized is
around 1:1. Also all the samples exhibit identical phase transition
temperatures from tetragonal to orthorhombic structure below ~ 100 K implying
identical phase composition. The partial substitution of Se by Te leads to an
enhancement of Tc to ~ 13 K. The non-superconducting telluride Fe1.09Te
exhibits a metal-insulator phase transition at ~ 82 K. Substitution studies of
this telluride system by S and Si have in addition been carried out to
investigate if chemical pressure induces superconductivity.",0904.3851v1
2009-04-26,Computational Physics and Reality: Looking for Some Overlap at the Blacksmith Shop,"The paper describes two general problems encountered in computational
assignments at the introductory level. First, novice students often treat
computer code as almost magic incantations, and like novices in many fields,
have trouble creating new algorithms or procedures to solve novel problems.
Second, the nature of computational studies often means that the results
generated are interpreted via theoretically devised quantities, which may not
meet a student's internal standards for proof when compared to an experimental
measurement.
  The paper then offers a lab/programming assignment, used in a calculus-based
physics course, which was devised to address these problems. In the assignment,
students created a computational model of the heat flow involved in heating an
iron rod in a blacksmith's forge. After creating the simulation, students
attended a blacksmithing seminar and had a chance to work with iron and take
data on its heating in a coke-fueled forge. On their return to campus, students
revised their computational models in light of their experimental data.",0904.3960v3
2009-04-28,Impurity effect as a probe for order parameter symmetry in iron-based superconductors,"The pointlike impurity scattering is studied for a superconductor with
different pairing symmetries based on a minimal two band model proposed by S.
Raghu $et$ $al.$ [Phys. Rev. B {\bf 77}, R220503 (2008)], and the
self-consistent Bogoliubov-de Gennes equations. Two intra-gap resonance peaks
are found at or near the nonmagnetic impurity site for a typical $s_{x^2y^2}$
symmetry and strong scattering potentials. Such intra-gap resonance peaks are
absent for the sign unchanged s-wave and $d_{x^2-y^2}$-wave order parameter.
Thus we propose that a non-magnetic impurity with strong scattering potentials
can be used to probe the pairing symmetry in iron-based superconductors.",0904.4273v8
2009-04-28,Low-temperature thermal conductivity of BaFe2As2: Parent compound of iron-arsenide superconductors,"We report low-temperature thermal conductivity down to 40 mK of the
antiferromagnet BaFe$_2$As$_{2}$, which is the parent compound of recently
discovered iron-based superconductors. In the investigated temperature range
below 4 K, the thermal conductivity $\kappa$ is well described by the
expression $\kappa$ = $aT$ + $bT^{2.22}$. We attribute the ``$aT$''-term to an
electronic contribution which is found to satisfy the Wiedemann-Franz law in
the $T$ $\to$ 0 K limit, and the remaining thermal conductivity, $\sim$
$T^{2.22}$, is attributed to phonon conductivity. A small influence on thermal
conductivity by magnetic fields up to 8 T is well accounted by the observed
magnetoresistance. The result is consistent with a fully gapped magnon
spectrum, inferred previously from inelastic neutron scattering measurements.",0904.4470v3
2009-05-04,Unusual Fermi surface nesting in parent compounds of iron arsenic high temperature superconductors revealed by Angle Resolved Photoemission Spectroscopy,"We use angle resolved photoemission spectroscopy (ARPES) to study the band
structure of BaFe2As2 and CaFe2As2, two of the parent compounds of the iron
arsenic high temperature superconductors. We find clear evidence for band back
folding and hybridization demonstrating that conduction electrons are strongly
affected by the emergence of magnetic order. Our high quality data revealed
that although the Fermi surface is strongly three-dimensional, it does indeed
have long parallel segments along the kz direction that can lead to the
emergence of magnetic order. More interestingly, we find very unusual
incommensurate nesting of the Fermi surface in the a-b plane that is present
only at low temperatures. We speculate that this is a signature of a failed
Charge Density Wave (CDW) state that was predicted by renormalization group
studies.",0905.0271v1
2009-05-12,Metal - Insulator transition in Fe1.01-xCuxSe,"Iron Selenide, Fe1.01Se, the layered parent compound of the recently
discovered superconducting arsenide family, has previously been shown to be non
magnetic and superconducting with a critical temperature of 8 K. Here we show
that copper can be substituted at the iron site in Fe1.01Se up to a solubility
limit of 20-30 %, after which a first order transition to the three-dimensional
CuFeSe2 structure type is observed. As little as 1.5 % percent copper is
sufficient to suppress the superconductivity, and 4 % drives the system through
a metal-insulator transition. A local magnetic moment is introduced, which
maximizes near 12% doping, where a spin-glass transition near 15 K is observed.",0905.1875v1
2009-05-22,Intergrain Josephson Currents in Multigap Superconductors: Microscopic Origin of Low Intergrain Critical Current and Its Recovery Potential in Iron-Pnictide Materials,"We microscopically examine the intergrain Josephson current in iron-pnictide
superconductors in order to solve the puzzle of why the intergrain current is
much lower than the intragrain one. The theory predicts that the intergrain
Josephson current is significantly reduced by the $\pm$s-wave symmetry when the
incoherent tunneling becomes predominant and the density of states and the gap
amplitude between two bands are identical. We find in such a situation that the
temperature dependence of the intergrain Josephson current shows an anomalously
flat curve over a wide temperature range. Finally, we suggest important points
for increasing the intergrain current.",0905.3592v3
2009-05-29,Bragg diffraction and the Iron crust of cold Neutron Stars,"If cooled-down neutron stars have a thin atomic crystalline-iron crust, they
must diffract X-rays of appropriate wavelength. If the diffracted beam is to be
visible from Earth, the illuminating source must be very intense and near the
reflecting star. An example is a binary system composed of two neutron stars in
close orbit, one of them inert, the other an X-ray pulsar (perhaps an
""anomalous"" X-ray pulsar or magnetar, not powered by gas absorption from the
companion or surrounding space, would be the cleanest example). The observable
to be searched for is a secondary peak added (quasi-) periodically to the main
X-ray pulse. The distinguishing feature of this secondary peak is that it
appears at wavelengths related by simple integer numbers, lambda, lambda/2,
lambda/3... lambda/n because of Bragg's diffraction law.",0905.4837v3
2009-06-10,Three-dimensional electronic structure of superconducting iron pnictides observed by angle-resolved photoemission spectroscopy,"We have performed an angle-resolved photoemission spectroscopy (ARPES) study
of the undoped and electron-doped iron pnictides BaFe2\_{-x}CoxAs2 (Ba122)
(x=0, 0.14) and studied the Fermi surfaces (FSs) and band dispersions near the
Fermi level. The FS sheets we observed are consistent with the shrinkage of the
hole-like pockets around the Brillouin Zone (BZ) center and the expansion of
the electron pockets around the BZ corner in the electron-doped compound as
compared to the undoped parent compound. Band dispersions and FSs around the BZ
center strongly depend on the photon energy, indicating the three-dimensional
(3D) electronic structure. This observation suggests that the
antiferromagnetism and superconductivity in the pnictides may have to be
considered including the orbital-dependent 3D electronic structure, where FS
nesting is not necessarily strong.",0906.1846v1
2009-06-19,High Resolution Optical Spectroscopy of a Newly Discovered Post-AGB Star with a Surprising Metallicity in the Globular Cluster M79,"An abundance analysis based on a high-resolution spectrum is presented for a
newly discovered post-AGB star in the globular cluster M79. The surprising
result is that the iron abundance of the star is apparently about 0.6 dex less
than that of the cluster's red giants as reported by published studies
including a recent high-resolution spectroscopic analysis by Carretta and
colleagues. Abundances relative to iron appear to be the same for the post-AGB
star and the red giants for the 15 common elements. It is suggested that the
explanation for the lower abundances of the post-AGB star may be that its
atmospheric structure differs from that of a classical atmosphere; the
temperature gradient may be flatter than predicted by a classical atmosphere.",0906.3706v2
2009-06-21,Multi-gap nodeless superconductivity in iron selenide FeSe$_x$: evident from quasiparticle heat transport,"The in-plane thermal conductivity $\kappa$ of the iron selenide
superconductor FeSe$_x$ ($T_c$ = 8.8 K) were measured down to 120 mK and up to
14.5 T ($\simeq 3/4 H_{c2}$). In zero field, the residual linear term
$\kappa_0/T$ at $ T \to 0$ is only about 16 $\mu$W K$^{-2}$ cm$^{-1}$, less
than 4% of its normal state value. Such a small $\kappa_0/T$ does not support
the existence of nodes in the superconducting gap. More importantly, the field
dependence of $\kappa_0/T$ in FeSe$_x$ is very similar to that in NbSe$_2$, a
typical multi-gap s-wave superconductor. We consider our data as strong
evidence for multi-gap nodeless superconductivity in FeSe$_x$. This kind of
superconducting gap structure may be generic for all Fe-based superconductors.",0906.3852v1
2009-06-24,Doping-dependent pairing symmetry in the Iron-Pnictides,"We use the functional renormalization group method to analyze the phase
diagram of a 4-band model for the iron-pnictides subject to band interactions
with certain A_{1g} momentum dependence. We determine the parameter regimes
where an extended s-wave pairing instability with and without nodes emerges. On
the electron-doped side, the parameter regime in which a nodal gap appears is
found to be much narrower than recently predicted in arXiv:0903.5547. On the
hole-doped side, the extended s-wave pairing never becomes nodal: above a
critical strength of the intra-band repulsion, the system favors an exotic
extended d-wave instability on the enlarged hole pockets at much lower T_c. At
half filling, we find that a strong momentum dependence of inter-band pair
hopping yields an extended s-wave instability instead of spin-density wave
(SDW) ordering. These results demonstrate that an interaction anisotropy around
the Fermi surfaces generally leads to a pronounced sensitivity of the pairing
state on the system parameters.",0906.4475v1
2009-06-25,Doping dependence of the lattice dynamics in Ba(Fe$_{1-x}$Co$_x$)$_2$As$_2$ studied by Raman spectroscopy,"We report Raman scattering spectra of iron-pnictide superconductor
Ba(Fe$_{1-x}$Co$_x$)$_2$As$_2$ single crystals with varying cobalt $x$ content.
Upon cooling through the tetragonal-to-orthorhombic transition, we observe a
large splitting of the E$_g$ in-plane phonon modes involving Fe and As
displacements. The splitting of the in-plane phonons at the transition is
strongly reduced upon doping and disappears for $x=0.06$ qualitatively
following the trend displayed by the Fe magnetic moment. The origin of the
splitting is discussed in terms of magnetic frustration inherent to
iron-pnictide systems and we argue that such enhanced splitting may be linked
to strong spin-phonon coupling.",0906.4569v1
2009-06-26,A consistent description of the iron dimer spectrum with a correlated single-determinant wave function,"We study the iron dimer by using an accurate ansatz for quantum chemical
calculations based on a simple variational wave function, defined by a single
geminal expanded in molecular orbitals and combined with a real space
correlation factor. By means of this approach we predict that, contrary to
previous expectations, the neutral ground state is $^7 \Delta$ while the ground
state of the anion is $^8 \Sigma_g^-$, hence explaining in a simple way a long
standing controversy in the interpretation of the experiments. Moreover, we
characterize consistently the states seen in the photoemission spectroscopy by
Leopold \emph{et al.}. It is shown that the non-dynamical correlations included
in the geminal expansion are relevant to correctly reproduce the energy
ordering of the low-lying spin states.",0906.4824v1
2009-07-01,The CTOF measurements and Monte Carlo analyses of neutron spectra for backward direction from iron target irradiated by protons with energies from 400 to 1200 MeV,"A calorimetric-time-of-flight (CTOF) technique was used for real-time,
high-precision measurement of neutron spectrum at the angle of 175 degrees from
the initial proton beam direction, which hits a face plane of a cylindrical
iron target of 20 cm in diameter and 25 cm thick. A comparison was performed
between the neutron spectra predicted by the MARS and the MCNPX code systems
and measured by experiments for 0.4-, 0.6-, 0.8-, 1.0-, and 1.2-GeV protons.",0907.0181v1
2009-07-06,Electrosteric enhanced stability of functional sub-10 nm cerium and iron oxide particles in cell culture medium,"Applications of nanoparticles in biology require that the nanoparticles
remain stable in solutions containing high concentrations of proteins and
salts, as well as in cell culture media. In this work, we developed simple
protocols for the coating of sub-10 nm nanoparticles and evaluated the
colloidal stability of dispersions in various environments. Ligands (citric
acid), oligomers (phosphonate-terminated poly(ethylene oxide)) and polymers
(poly(acrylic acid)) were used as nanometer-thick adlayers for cerium (CeO2)
and iron (gamma-Fe2O3) oxide nanoparticles. The organic functionalities were
adsorbed on the particle surfaces via physical (electrostatic) forces.
Stability assays at high ionic strength and in cell culture media were
performed by static and dynamic light scattering. Among the three coating
examined, we found that only poly(acrylic acid) fully preserved the dispersion
stability on the long term (> weeks). The improved stability was explained by
the multi-point attachments of the chains onto the particle surface, and by the
adlayer-mediated electrosteric interactions. These results suggest that
anionically charged polymers represent an effective alternative to conventional
coating agents.",0907.1008v1
2009-07-07,Tight binding model for iron pnictides,"We propose a five-band tight-binding model for the Fe-As layers of iron
pnictides with the hopping amplitudes calculated within the Slater-Koster
framework. The band structure found in DFT, including the orbital content of
the bands, is well reproduced using only four fitting parameters to determine
all the hopping amplitudes. The model allows to study the changes in the
electronic structure caused by a modification of the angle $\alpha$ formed by
the Fe-As bonds and the Fe-plane and recovers the phenomenology previously
discussed in the literature. We also find that changes in $\alpha$ modify the
shape and orbital content of the Fermi surface sheets.",0907.1259v2
2009-07-16,Spin-Phonon Coupling and Superconductivity in Fe Pnictides,"We propose a theory of strong spin-lattice and spin-phonon coupling in iron
pnictides and discuss its implications on superconductivity. Strong
magneto-volume effect in iron compounds has long been known as the Invar
effect. Fe pnictides also exhibit this effect, reflected in particular to the
atomic volume of Fe defined by the nearest neighbor atoms. Through the
phenomenological Landau theory, developed on the basis of the calculations by
the density functional theory (DFT) and the experimental results, we quantify
the strength of the spin-lattice interaction as it relates to the Stoner
criterion for the onset of magnetism. We suggest that the coupling between
electrons and phonons through the spin channel may be sufficiently strong to be
an important part of the superconductivity mechanism in Fe pnictides.",0907.2734v1
2009-07-22,Relativistic Broadening of Iron Emission Lines in a Sample of AGN,"We present a uniform X-ray spectral analysis of eight type-1 active galactic
nuclei (AGN) that have been previously observed with relativistically broadened
iron emission lines. Utilizing data from the XMM-Newton European Photon Imaging
Camera (EPIC-pn) we carefully model the spectral continuum, taking complex
intrinsic absorption and emission into account. We then proceed to model the
broad Fe K feature in each source with two different accretion disk emission
line codes, as well as a self-consistent, ionized accretion disk spectrum
convolved with relativistic smearing from the inner disk. Comparing the
results, we show that relativistic blurring of the disk emission is required to
explain the spectrum in most sources, even when one models the full reflection
spectrum from the photoionized disk.",0907.3850v1
2009-07-23,Large specific absorption rates in the magnetic hyperthermia properties of metallic iron nanocubes,"We report on the magnetic hyperthermia properties of chemically synthesized
ferromagnetic 11 and 16 nm Fe(0) nanoparticles of cubic shape displaying the
saturation magnetization of bulk iron. The specific absorption rate measured on
16 nm nanocubes is 1690+-160 W/g at 300 kHz and 66 mT. This corresponds to
specific losses-per-cycle of 5.6 mJ/g, largely exceeding the ones reported in
other systems. A way to quantify the degree of optimization of any system with
respect to hyperthermia applications is proposed. Applied here, this method
shows that our nanoparticles are not fully optimized, probably due to the
strong influence of magnetic interactions on their magnetic response. Once
protected from oxidation and further optimized, such nano-objects could
constitute efficient magnetic cores for biomedical applications requiring very
large heating power.",0907.4063v3
2009-07-23,Superconductivity in the Iron-Pnictide Parent Compound SrFe2As2,"The appearance of superconductivity at ambient pressures in the undoped iron
pnictide parent compound SrFe2As2 is studied experimentally using several
techniques and approaches to aid in understanding the nature of this phase. Low
temperature magnetization measurements of single crystals of SrFe2As2 reveal
diamagnetic screening due to the onset of superconductivity below 21 K, with
volume fraction estimates varying between 0 and 15 percent. The effects of heat
treatment and cold-working via severe mechanical deformation on the
superconducting phase found are studied, showing that superconductivity can be
suppressed via modest annealing and reinstated by cold-working.",0907.4141v1
2009-08-21,Magnetooptic enhancement and magnetic properties in Fe antidot films with hexagonal symmetry,"The magnetooptic and magnetic properties of hexagonal arrays of holes in
optically thin iron films are presented. We analyze their dependence on the
hole radius and compare the results to a continuous iron film of same
thickness. We observe a large enhancement of the magnetooptic Kerr rotation
with respect to that of the continuous film, at frequecies where surface
plasmons excitations are expected. Additional simulations are in very good
agreement with the experiment and thus confirm the effect of the surface
plasmons on the Kerr rotation. The altering of the magnetic properties by the
hole array is also visible in the hysteretic behavior of the sample where a
dramatic change is observed.",0908.3129v2
2009-09-02,"Origin of critical-temperature enhancement of an iron-based high-T_c superconductor, LaFeAsO_{1-x}F_{x} : NMR study under high pressure","Nuclear magnetic resonance (NMR) measurements of an iron (Fe)-based
superconductor LaFeAsO_{1-x}F_x (x = 0.08 and 0.14) were performed at ambient
pressure and under pressure. The relaxation rate 1/T_1 for the overdoped
samples (x = 0.14) shows T-linear behavior just above T_c, and pressure
application enhances 1/T_1T similar to the behavior of T_c. This implies that
1/T_1T = constant originates from the Korringa relation, and an increase in the
density of states at the Fermi energy D(E_F) leads to the enhancement of T_c.
In the underdoped samples (x = 0.08), 1/T_1T measured at ambient pressure also
shows T-independent behavior in a wide temperature range above T_c. However, it
shows Curie-Weiss-like T dependence at 3.0 GPa accompanied by a small increase
in T_c, suggesting that predominant antiferromagnetic fluctuation suppresses
development of superconductivity or remarkable enhancement of T_c. The
qualitatively different features between underdoped and overdoped samples are
systematically explained by a band calculation with hole and electron pockets.",0909.0318v2
2009-09-02,Computational study of boron nitride nanotube synthesis: how catalyst morphology stabilizes the boron nitride bond,"In an attempt to understand why catalytic methods for the growth of boron
nitride nanotubes work much worse than for their carbon counterparts, we use
first-principles calculations to study the energetics of elemental reactions
forming N2, B2 and BN molecules on an iron catalyst. We observe that in the
case of these small molecules, the catalytic activity is hindered by the
formation of B2 on the iron surface. We also observe that the local morphology
of a step edge present in our nanoparticle model stabilizes the boron nitride
molecule with respect to B2 due to the ability of the step edge to offer sites
with different coordination simultaneously for nitrogen and boron. Our results
emphasize the importance of atomic steps for a high yield chemical vapor
deposition growth of BN nanotubes and may outline new directions for improving
the efficiency of the method.",0909.0545v1
2009-09-07,On the Crustal Matter of Magnetars,"We have investigated some of the properties of dense sub-nuclear matter at
the crustal region (both the outer crust and the inner crust region) of a
magnetar. The relativistic version of Thomas-Fermi (TF) model is used in
presence of strong quantizing magnetic field for the outer crust matter. The
compressed matter in the outer crust, which is a crystal of metallic iron, is
replaced by a regular array of spherically symmetric Wigner-Seitz (WS) cells.
In the inner crust region, a mixture of iron and heavier neutron rich nuclei
along with electrons and free neutrons has been considered. Conventional
Harrison-Wheeler (HW) and Bethe-Baym-Pethick (BBP) equation of states are used
for the nuclear mass formula. A lot of significant changes in the
characteristic properties of dense crustal matter, both at the outer crust and
the inner crust, have been observed.",0909.1173v1
2009-09-08,Molecular dynamics study of hcp/fcc nucleation and growth in bcc iron driven by uniaxial strain,"Molecular dynamics simulations are performed to investigate the structural
phase transition in body-centered cubic (bcc) single crystal iron under high
strain rate loading. We study the nucleation and growth of the
hexagonal-close-packed (hcp) and face-centered-cubic (fcc) phases, and their
crystal orientation dependence. Results reveal that the transition pressures
are less dependent on the crystal orientations ($\mathtt{\sim}$14 GPa for
loading along [001], [011], and [111] directions). However, the pressure
interval of mixed phase for [011] loading is much shorter than loading along
other orientations. And the temperature increased amplitude for [001] loading
is evidently lower than other orientations. The hcp/fcc nucleation process is
presented by the topological medium-range-order analysis. For loading along
[001] direction, we find that the hcp structure occurs firstly and grows into
laminar morphology in the (011)$_{\text{bcc}}$ planes with a little fcc atoms
as intermediate structure. For loading along [011] and [111] directions, both
the hcp and fcc structures nucleation and growth along the
\{110\}$_{\text{bcc}}$ planes are observed, whose morphology is also discussed.",0909.1407v1
2009-09-16,Chalcogen-height dependent magnetic interactions and magnetic order switching in FeSe$_x$Te$_{1-x}$,"Magnetic properties of iron chalcogenide superconducting materials are
investigated using density functional calculations. We find the stability of
magnetic phases is very sensitive to the height of chalcogen species from the
Fe plane: while FeTe with optimized Te height has the double-stripe-type
$(\pi,0)$ magnetic ordering, the single-stripe-type $(\pi,\pi)$ ordering
becomes the ground state phase when Te height is lowered below a critical value
by, e.g., Se doping. This behavior is understood by opposite Te-height
dependences of the superexchange interaction and a longer-range magnetic
interaction mediated by itinerant electrons. We also demonstrate a linear
temperature dependence of the macroscopic magnetic susceptibility in the
single-stripe phase in contrast to a constant behavior in the double-stripe
phase. Our findings provide a comprehensive and unified view to understand the
magnetism in FeSe$_x$Te$_{1-x}$ and iron pnictide superconductors.",0909.2916v1
2009-09-16,"Superconductivity at 39 K in New Iron Pnictide Oxide (Fe2As2)(Sr4(Mg,Ti)2O6)","We have discovered a new iron pnictide oxide superconductor
(Fe2As2)(Sr4(Mg,Ti)2O6). This material is isostructual with (Fe2As2)(Sr4M2O6)
(M = Sc, Cr), which was found in our previous study. The structure of this
compound is tetragonal with a space group of P4/nmm and consists of the
anti-fluorite type FeAs and perovskite-type blocking layers. The lattice
constants are a = 3.935 A and c = 15.952 A for (Fe2As2)(Sr4MgTiO6). In both
magnetization and resistivity measurements, this compound exhibits
superconductivity below 10 K. Moreover, ratio of Mg and Ti in this compound can
be changed toward Ti-rich composition. (Fe2As2)(Sr4Mg1-xTi1+xO6) phase is
obtained at 0 < x as a main phase, and Tc and superconducting volume fraction
increase with increasing x. The highest Tc(onset) was confirmed at 39 K for x =
0.6 in resistivity measurement.",0909.2945v3
2009-09-21,Study of sdO models. Pulsation Analysis,"We have explored the possibility of driving pulsation modes in models of sdO
stars in which the effects of element diffusion, gravitational settling and
radiative levitation have been neglected so that the distribution of iron-peak
elements remains uniform throughout the evolution. The stability of these
models was determined using a non-adiabatic oscillations code. We analysed 27
sdO models from 16 different evolutionary sequences and discovered the first
ever sdO models capable of driving high-radial order g-modes. In one model, the
driving is by a classical kappa-mechanism due to the opacity bump from
iron-peak elements at temperature ~200,000 K. In a second model, the driving
result from the combined action of kappa-mechanisms operating in three distinct
regions of the star: (i) a carbon-oxygen partial ionization zone at temperature
~2 10^6 K, (ii) a deeper region at temperature ~2 10^7 K, which we attribute to
ionization of argon, and (iii) at the transition from radiative to conductive
opacity in the core of the star.",0909.3778v1
2009-10-01,First-Principles Study for the Anisotropy of Iron-based Superconductors toward Power and Device Applications,"Performing the first-principles calculations, we investigate the anisotropy
in the superconducting state of iron-based superconductors to gain an insight
into their potential applications. The anisotropy ratio $\gamma_\lambda$ of the
c-axis penetration depth to the ab-plane one is relatively small in BaFe2As2
and LiFeAs, i.e., $\gamma_\lambda \sim 3$, indicating that the transport
applications are promising in these superconductors. On the other hand, in
those having perovskite type blocking layers such as Sr2ScFePO3 we find a very
large value, $\gamma_\lambda \sim 200$, comparable to that in strongly
anisotropic high-Tc cuprate Bi2Sr2CaCu2O{8-\delta}. Thus, the intrinsic
Josephson junction stacks are expected to be formed along the c-axis, and novel
Josephson effects due to the multi-gap nature are also suggested in these
superconductors.",0910.0107v1
2009-10-12,Neutrino and Antineutrino Inclusive Charged-current Cross Section Measurements with the MINOS Near Detector,"The energy dependence of the neutrino-iron and antineutrino-iron inclusive
charged-current cross sections and their ratio have been measured using a
high-statistics sample with the MINOS Near Detector exposed to the NuMI beam
from the Main Injector at Fermilab. Neutrino and antineutrino fluxes were
determined using a low hadronic energy subsample of charged-current events. We
report measurements of neutrino-Fe (antineutrinoFe) cross section in the energy
range 3-50 GeV (5-50 GeV) with precision of 2-8% (3-9%) and their ratio which
is measured with precision 2-8%. The data set spans the region from low energy,
where accurate measurements are sparse, up to the high-energy scaling region
where the cross section is well understood.",0910.2201v2
2009-10-30,Antiphase magnetic boundaries in iron-based superconductors: A first-principle density-functional theory study,"Superconductivity arises in the layered iron-pnictide compounds when magnetic
long range order disappears. We use first principles density functional methods
to study magnetic arrangements that may compete with long range order near the
phase boundary. Specifically, we study the energetics and charge density
distribution (through calculation of the electric field gradients) for ordered
supercells with varying densities of antiphase magnetic boundaries. We quantify
the amount by which Fe atoms with low spin moments at the antiphase boundaries
have higher energies than Fe atoms with high spin moments away from the
antiphase boundaries. These disruptions in magnetic order should be useful in
accounting for experimental data such as electric field gradients and hyperfine
fields on both Fe and As atoms.",0911.0036v1
2009-11-01,Andreev bound states in iron pnictide superconductors,"Recently, Andreev bound states in iron pnictide have been proposed as an
experimental probe to detect the relative minus sign in the $s_\pm$-wave
pairing. While previous theoretical investigations demonstrated the feasibility
of the approach, the local density of states in the midgap regime is small,
making the detection hard in experiments. We revisit this important problem
from the Bogoliubov-de Gennes Hamiltonian on the square lattice with
appropriate boundary conditions. Significant spectral weights in the midgap
regime are spotted, leading to easy detection of the Andreev bound states in
experiments. Peaks in the momentum-resolved local density of states appear and
lead to enhanced quasiparticle interferences at specific momenta. We analyze
the locations of these magic spots and propose they can be verified in
experiments by the Fourier-transformed scanning tunneling spectroscopy.",0911.0175v1
2009-11-02,Spin-Density-Wave and Asymmetry of Coherence Peaks in iron-Pnictide Superconductors from a two-orbital model,"We study theoretically the coexistence of the spin-density-wave (SDW) and
superconductivity in electron-doped iron-pnictide superconductors based on the
two orbital model and Bogoliubov-de Gennes equations. The phase diagram is
mapped out and the evolution of the Fermi surface as the doping varies is
presented. The local density of states (LDOS) has also been calculated from low
to high doping. We show that the strength of the superconducting coherent peak
at the positive energy gets enhanced and the one at the negative energy is
suppressed by the SDW order in the underdoped region. Several features of our
results are in good agreement with the experiments.",0911.0385v3
2009-11-02,Non-stoichiometry and the magnetic structure of Sr2CrO3FeAs,"The iron arsenide Sr2CrO3FeAs with the tetragonal Sr2GaO3CuS-type structure
was synthesized and its crystal structure re-determined by neutron powder
diffraction. In contrast to previous X-ray crystallographic studies, a mixed
occupancy of chromium and iron was found within the FeAs4/4 layer (93+/-1% Fe :
7+/-1% Cr). We suggest that the partial Cr-doping at the Fe site is the reason
for the absence of a spin-density wave anomaly and superconductivity in this
compound. Additional experiments via neutron polarization analysis revealed
short-range spin correlations below ~100 K and long-range antiferromagnetic
ordering below T_N = 36 K with a magnetic propagation vector of q = (1/2, 1/2,
0). The Cr3+ ions form a collinear magnetic structure of the C-type in the
magnetic space group C_Pmma' (a' = a-b, b'=a+b, c'=c), where Cr3+-ions occupy
the 4g (0, 1/4, z) Wyckoff position. The magnetic moments are aligned along the
orthorhombic a'-axis. At 3.5 K, an ordered magnetic moment of 2.75+/-0.05 mu_B
for the Cr3+-sublattice was refined.",0911.0450v2
2009-11-09,Small-q Phonon Mediated Unconventional Superconductivity in the Iron Pnictides,"We report self-consistent calculations of the gap symmetry for the iron-based
high-temperature superconductors using realistic small-q phonon mediated
pairing potentials and four-band energy dispersions. When both electron and
hole Fermi surface pockets are present, we obtain the nodeless $s_\pm$ state
that was first encountered in a spin-fluctuations mechanism picture. Nodal gap
structures such as $d_{x^2-y^2}$ and $s_\pm+d_{x^2-y^2}$ and even a p-wave
triplet state, are accessible upon doping within our phononic mechanism. Our
results resolve the conflict between phase sensitive experiments reporting a
gap changing sign attributed previously only to a non-phononic mechanism and
isotope effect measurements proving the involvement of phonons in the pairing.",0911.1461v3
2009-11-10,"Fermi-liquid, non-Fermi-liquid, and Mott phases in iron pnictides and cuprates","The role of Coulomb correlations in the iron pnictide LaFeAsO is studied by
generalizing exact diagonalization dynamical mean field theory to five
orbitals. For rotationally invariant Hund's rule coupling a continuous
transition from a paramagnetic Fermi-liquid phase to a non-Fermi-liquid
metallic phase exhibiting frozen moments is found at moderate Coulomb energies.
For Ising-like exchange, this transition is first order and occurs at a lower
critical Coulomb energy. The correlation-induced scattering rate as a function
of doping relative to half-filling, i.e., delta = n/5-1, where n=6 for the
undoped material, is shown to be qualitatively similar to the one in the
two-dimensional single-band Hubbard model. In this scenario, the parent Mott
insulator of LaFeAsO is the half-filled n=5 limit, while the undoped n=6
material corresponds to the critical doping region delta_c ~ 0.2 in the
cuprates, on the verge between the Fermi-liquid phase of the overdoped region
and the non-Fermi-liquid pseudogap phase in the underdoped region.",0911.1940v2
2009-11-17,A re--analysis of the iron line in the XMM-Newton data from the low/hard state in GX339--4,"The detection of an extremely broad iron line in XMM-Newton MOS data from the
low/hard state of the black hole binary GX339-4 is the only piece of evidence
which unambiguously conflicts with the otherwise extremely successful truncated
disc interpretation of this state. However, it also conflicts with some aspect
of observational data for all other alternative geometries of the low/hard
state, including jet models, making it very difficult to understand. We
re-analyse these data and show that they are strongly affected by pileup even
with extensive centroid removal as the source is ~200x brighter than the
recommended maximum countrate. Instead, we extract the simultaneous PN timing
mode data which should not be affected by pileup. These show a line which is
significantly narrower than in the MOS data. Thus these data are easily
consistent with a truncated disc, and indeed, strongly support such an
interpretation.",0911.3243v2
2009-11-19,Magnetic impurity resonance states and symmetry of the superconducting order parameter in iron-based superconductors,"We investigate the effect of magnetic impurities on the local quasiparticle
density of states (LDOS) in iron-based superconductors. Employing the
two-orbital model where 3$d$ electron and hole conduction bands are hybridizing
with the localized $f$-orbital of the impurity spin, we investigate how various
symmetries of the superconducting gap and its nodal structure influence the
quasiparticle excitations and impurity bound states. We show that the bound
states behave qualitatively different for each symmetry. Most importantly we
find that the impurity-induced bound states can be used to identify the nodal
structure of the extended s-wave symmetry ($S^{\pm}$) that is actively
discussed in ferropnictides.",0911.3738v2
2009-11-20,HTSC-glue in doped copper oxides and iron pnictides: mobile CT-excitons within in-plane Ginzburg HTSC-sandwich,"It is demonstrated that high critical temperature of superconducting
transition in cuprates and new iron-based superconductors is reached because of
the Little-Ginzburg exciton mechanism of HTSC when Cooper pairing of mobile
charge carriers is mediated by excitons which characteristic energy is
essentially higher than Debye one for phonons. The effectiveness of such
mechanism in these doped compounds is provided due to a series of planar
Ginzburg HTSC-'sandwiches': 'insulator'-'metal'- 'insulator' (stripe structure)
naturally forming in conducting planes below the onset pseudogap temperature in
the normal state. The parameters of mobile, planar charge-transfer (CT)
excitons in outer 'insulating' plates of such in-plane HTSC-'sandwich' are
exactly within the optimal range predicted by Ginzburg about forty years ago.",0911.4089v1
2009-11-27,Superconductivity in iron telluride thin films under tensile stress,"By realizing in thin films a tensile stress state, superconductivity of 13 K
was introduced into FeTe, an non-superconducting parent compound of the iron
pnictides and chalcogenides, with transition temperature higher than that of
its superconducting isostructural counterpart FeSe. For these tensile stressed
films, the superconductivity is accompanied by the softening of the first-order
magnetic and structural phase transition; and also, the in-plane extension and
out-of-plane contraction are universal in all FeTe films independent of sign of
lattice mismatch, either positive or negative. Moreover, the correlations were
found exist between the transition temperatures and the tetrahedra bond angles
in these thin films.",0911.5282v1
2009-11-30,Stochastic statistical theory of nucleation and evolution of nano-sized precipitates in alloys with application to precipitation of copper in iron,"The consistent and computationally efficient stochastic statistical approach
(SSA) is suggested to study kinetics of nucleation and evolution of nano-sized
precipitates in alloys. An important parameter of the theory is the size of
locally equilibrated regions at the nucleation stage which is estimated using
the ""maximum thermodynamic gain"" principle suggested.
  For several realistic models of iron-copper alloys studied, the results of
the SSA-based simulations of precipitation kinetics agree well with the kinetic
Monte Carlo simulation results for all main characteristics of microstructure.
The approach developed is also used to study kinetics of nucleation and changes
in microstructural evolution under variations of temperature or concentration.",0911.5558v2
2009-12-02,Vortex as a probe - suggested measurement of the order parameter structure in iron-based superconductors,"Impurities, inevitably present in all samples, induce elastic transitions
between quasiparticle states on the contours of constant energy. These
transitions may be seen in Fourier transformed scanning tunneling spectroscopy
experiments, sorted by their momentum transfer. In a superconductor, anomalous
scattering in the pairing channel may be introduced by magnetic field. When a
magnetic field is applied, vortices act as additional sources of scattering.
These additional transition may enhance or suppress the impurity-induced
scattering. We find that the vortex contribution to the transitions is
sensitive to the momentum-space structure of the pairing function. In the
iron-based superconductors there are both electron and hole pockets at
different regions of the Brillouin zone. Scattering processes therefore
represent intrapocket or interpocket transitions, depending on the momentum
transfer in the process. In this work we show that while in a simple s-wave
superconductors all transitions are enhanced by vortex scattering, in an s+-
superconductor only intra-pocket transitions are affected. We suggest this
effect as a probe for the existence of the sign change of the order parameter.",0912.0527v2
2009-12-08,About chemical composition of the primary cosmic radiation at ultra-high energies,"The fluxes of electrons, positrons, gammas, Cherenkov photons and muons in
individual extensive air showers induced by the primary protons and helium,
oxygen and iron nuclei at the level of observation have been estimated with
help of the code CORSICA 6.616. The comparison show that the values of the
function Xi**2 per one degree of freedom changes from 1.1 for iron nuclei to
0.9 for primary protons. As this difference is small all readings of detectors
of the Vavilov-Cherenkov radiation have been used. At last, readings of
underground detectors of muons with energies above 1 GeV have been exploited to
make definite conclusion about chemical composition.",0912.1478v1
2009-12-08,Neutron diffraction study on phase transition and thermal expansion of SrFeAsF,"The magnetic ordering and crystal structure of iron pnictide SrFeAsF was
investigated by using neutron powder diffraction method. With decreasing
temperature, the tetragonal to orthorhombic phase transition is found at 180 K,
while the paramagnetic to antiferromagnetic phase transition set in at 133 K.
Similar to the parent compound of other iron pnictide system, the striped Fe
magnetism is confirmed in antiferromagnetic phase and the Fe moment of 0.58(6)
uB aligned along long a axis. The thermal expansion of orthorhombic phase of
SrFeAsF is also investigated. Based on the Grueneisen approximation and Debye
approximation for internal energy, the volume of SrFeAsF can be well fitted
with Debye temperature of 347(5) K. The experimental atomic displacement
parameters for different crystallographic sites in SrFeAsF are analyzed with
Debye model. The results suggested that the expansion of FeAs layers plays an
important role in determining the thermal expansion coefficient.",0912.1530v1
2009-12-09,"Superconductivity in New Iron Pnictide Oxide (Fe2As2)(Sr4(Mg,Ti)2O6)","We have discovered a new iron pnictide oxide superconductor
(Fe2As2)(Sr4(Mg,Ti)2O6). This material is isostructual with (Fe2As2)(Sr4M2O6)
(M = Sc, Cr, V), which were found in previous studies. The structure of this
compound is tetragonal with a space group of P4/nmm and consists of the
anti-fluorite type FeAs layer and perovskite-type block layer. The lattice
constants are a = 3.935 A and c = 15.952 A for (Fe2As2)(Sr4MgTiO6). Bulk
superconductivity with Tc(onset) of ~26 K was observed for a partially Co
substituted sample. Moreover, Co-free and Ti-rich samples exhibited higher
Tc(onset)'s above 35 K, which were further enhanced by applying high pressures
up to ~43 K.",0912.1840v1
2009-12-10,Phase diagram and Gap anisotropy in Iron-Pnictide Superconductors,"Using the fluctuation-exchange (FLEX) approximation we study an effective
five-band Hubbard model for iron-pnictide superconductors obtained from the
first-principles band structure. We preclude deformations of the Fermi surface
due to electronic correlations by introducing a static potential, which mimics
the effect of charge relaxation. Evaluating the Eliashberg equation for various
dopings and interaction parameters, we find that superconductivity can sustain
higher hole than electron doping. Analyzing the symmetry of the superconducting
order parameter we observe clear differences between the hole and electron
doped systems. We discuss the importance of the pnictogen height for
superconductivity. Finally, we dissect the pairing interaction into various
contributions, which allows us to clarify the relationship between the
superconducting transition temperature and the proximity to the
anti-ferromagnetic phase.",0912.1893v2
2009-12-10,Orbital Fluctuation Mediated Superconductivity in Iron Pnictides: Analysis of Five Orbital Hubbard-Holstein Model,"In iron pnictides, we find that the moderate electron-phonon interaction due
to the Fe-ion oscillation can induce the critical d-orbital fluctuations,
without being prohibited by the Coulomb interaction. These fluctuations give
rise to the strong pairing interaction for the s-wave superconducting (SC)
state without sign reversal ($s_{++}$-wave state), which is consistent with
experimentally observed robustness of superconductivity against impurities.
When the magnetic fluctuations due to Coulomb interaction are also strong, the
SC state shows a smooth crossover from the s-wave state with sign reversal
($s_\pm$-wave state) to the $s_{++}$-wave state as impurity concentration
increases.",0912.1975v2
2009-12-11,Superconductivity in a Two-Orbital Hubbard Model with Electron and Hole Fermi Pockets: Application in Iron Oxypnictide Superconductors,"We investigate the electronic states of a one-dimensional two-orbital Hubbard
model with band splitting by the exact diagonalization method. The Luttinger
liquid parameter $K_{\rho}$ is calculated to obtain superconducting (SC) phase
diagram as a function of on-site interactions: the intra- and inter-orbital
Coulomb $U$ and $U'$, the Hund coupling $J$, and the pair transfer $J'$. In
this model, electron and hole Fermi pockets are produced when the Fermi level
crosses both the upper and lower orbital bands. We find that the system shows
two types of SC phases, the SC \Roman{u'-large} for $U>U'$ and the SC
\Roman{u-large} for $U<U'$, in the wide parameter region including both weak
and strong correlation regimes. Pairing correlation functions indicate that the
most dominant pairing for the SC \Roman{u'-large} (SC \Roman{u-large}) is the
intersite (on-site) intraorbital spin-singlet with (without) sign reversal of
the order parameters between two Fermi pockets. The result of the SC
\Roman{u'-large} is consistent with the sign-reversing s-wave pairing that has
recently been proposed for iron oxypnictide superconductors.",0912.2173v1
2009-12-16,Strong electron correlations in the normal state of FeSe0.42Te0.58,"We investigate the normal state of the '11' iron-based superconductor
FeSe0.42Te0.58 by angle resolved photoemission. Our data reveal a highly
renormalized quasiparticle dispersion characteristic of a strongly correlated
metal. We find sheet dependent effective carrier masses between ~ 3 - 16 m_e
corresponding to a mass enhancement over band structure values of m*/m_band ~ 6
- 20. This is nearly an order of magnitude higher than the renormalization
reported previously for iron-arsenide superconductors of the '1111' and '122'
families but fully consistent with the bulk specific heat.",0912.3152v2
2009-12-17,Universal Decomposition of the Low-Frequency Conductivity Spectra of Iron-Pnictides Uncovering Fermi-Liquid Behavior,"Infrared reflectivity measurements on 122 iron-pnictides reveal the existence
of two electronic subsystems. The one gapped due to the spin-density-wave
transition in the parent materials, such as EuFe$_2$As$_{2}$, is responsible
for superconductivity in the doped compounds, like
Ba(Fe$_{0.92}$Co$_{0.08})_2$As$_{2}$ and Ba(Fe$_{0.95}$Ni$_{0.05})_2$As$_{2}$.
Analyzing the dc resistivity and scattering rate of this contribution, a hidden
$T^2$ dependence is found, indicating that superconductivity evolves out of a
Fermi-liquid state. The second subsystem gives rise to incoherent background,
present in all 122 compounds, which is basically temperature independent, but
affected by the superconducting transition.",0912.3334v2
2009-12-18,Coexistence between superconducting and spin density wave states in iron-based superconductors: Ginzburg-Landau analysis,"We consider the interplay between superconducting (SC) and commensurate
spin-density-wave (SDW) orders in iron-pnictides by analyzing a multiple order
Ginzburg-Landau free energy. We are particularly interested in whether the
doping-induced transition between the two states is first order, or the two
pure phases are separated by an intermediate phase with coexisting SC and SDW
orders. For perfect nesting, the two orders do not coexist, because SDW order,
which comes first, gaps the full Fermi surface leaving no space for SC to
develop. When nesting is not perfect due to either ellipticity of electron
bands or doping-induced difference in chemical potentials for holes and
electrons, SDW order still leaves modified Fermi surfaces for not too strong
SDW magnetism and the SC order may develop. We show that the two orders coexist
only when certain relations between ellipticity and doping are met. In
particular, in a compensated metal, ellipticity alone is not sufficient for
coexistence of the two orders.",0912.3556v1
2009-12-21,Possible origin of the reduced magnetic moment in iron pnictides: A dynamical mean field theory study,"We investigate the phase diagram of a two-band frustrated Hubbard model in
the framework of dynamical mean field theory. While a first-order phase
transition occurs from a paramagnetic (PM) metal to an antiferromagnetic (AF)
insulator when both bands are equally frustrated, an intermediate AF metallic
phase appears in each band at different $U_c$ values if only one of the two
bands is frustrated, resulting in continuous orbital-selective phase
transitions from PM metal to AF metal and AF metal to AF insulator. We argue
that such intermediate phases are possibly related to the puzzling AF metallic
state with small magnetization observed in undoped iron-pnictide
superconductors as well as to the pseudogap features observed in optical
experiments.",0912.4024v2
2010-01-07,Superconductivity without magnetism in LiFeAs,"The particular shape of the Fermi surface can give rise to a number of
collective quantum phenomena in solids, such as density wave orderings or even
superconductivity. In many new iron superconductors this shape, the 'nested'
Fermi surface, is indeed observed, but its role in the formation of
spin-density waves or superconductivity is not clear. We have studied the
electronic structure of the non-magnetic LiFeAs (Tc~18K) superconductor using
angle-resolved photoemission spectroscopy. We find a notable absence of the
Fermi surface nesting, strong renormalization of the conduction bands by a
factor of three, high density of states at the Fermi level caused by a Van Hove
singularity, and no evidence for either a static or fluctuating order except
superconductivity with in-plane isotropic energy gaps. Our observations set a
new hierarchy of the electronic properties necessary for the superconductivity
in iron pnictides and, possibly, in other materials.",1001.1147v1
2010-01-12,Magnetic form factor of SrFe$_2$As$_2$,"Neutron diffraction measurements have been carried out to investigate the
magnetic form factor of the parent SrFe2As2 system of the iron-based
superconductors. The general feature is that the form factor is approximately
isotropic in wave vector, indicating that multiple d-orbitals of the iron atoms
are occupied as expected based on band theory. Inversion of the diffraction
data suggests that there is some elongation of the spin density toward the As
atoms. We have also extended the diffraction measurements to investigate a
possible jump in the c-axis lattice parameter at the structural phase
transition, but find no detectable change within the experimental
uncertainties.",1001.1941v1
2010-01-22,X-ray spectroscopy of the hot has in the M31 bulge,"We present an X-ray spectroscopic study of the nuclear region of the M31
bulge, based on observations of the Xmm-Newton Reflection Grating
Spectrometers. The obtained high-resolution grating spectra clearly show
individual emission lines of highly-ionized iron and oxygen, which
unambiguously confirm the presence of diffuse hot gas in the bulge, as
indicated from previous X-ray CCD imaging studies. We model the spectra with
detailed Monte-Carlo simulations, which provide a robust spectroscopic estimate
of the hot gas temperature $\sim0.29$ keV and the O/Fe ratio $\sim0.3$ solar.
The results indicate that iron ejecta of type Ia supernovae are partly-mixed
with the hot gas. The observed spectra show an intensity excess at the OVII
triplet, which most likely represents emission from charge exchanges at the
interface between the hot gas and a known cool gas spiral in the same nuclear
region.",1001.4058v1
2010-01-30,Magnetic properties of iron pnictides from spin-spiral calculations,"The wave-vector (q) and doping dependences of the magnetic energy, iron
moment, and effective exchange interactions in LaFeAsO, BaFe2As2, and SrFe2As2\
are studied by self-consistent LSDA calculations for co-planar spin spirals.
For the undoped compounds, the calculated total energy, E(q), reaches its
minimum at q corresponding to stripe anti-ferromagnetic order. In LaFeAsO, this
minimum becomes flat already at low levels of electron-doping and shifts to an
incommensurate q at delta=0.2, where delta is the number of additional
electrons (delta>0) or holes (delta<0) per Fe. In BaFe2As2 and SrFe2As2, stripe
order remains stable for hole doping down to delta=-0.3. Under electron doping,
on the other hand, the E(q) minimum shifts to incommensurate q already at
delta=0.1.",1002.0061v1
2010-02-08,Theory of itinerant magnetic excitations in the SDW phase of iron-based superconductors,"We argue that salient experimental features of the magnetic excitations in
the SDW phase of iron-based superconductors can be understood within an
itinerant model. We identify a minimal itinerant model and use a multi-band RPA
treatment of the dynamical spin susceptibility. Weakly-damped spin-waves are
found near the ordering momentum and it is shown how they dissolve into the
particle-hole continuum. We show that ellipticity of the electron bands
accounts for the anisotropy of the spin waves along different crystallographic
directions and the gap at the momentum conjugated to the ordering one. We argue
that our theory agrees well with the neutron scattering data.",1002.1668v2
2010-02-09,Pressure-induced high-Tc superconducting phase in FeSe: correlation between anion height and Tc,"In this study, we performed high-pressure electrical resistivity measurements
of polycrystalline FeSe in the pressure range of 1-16.0 GPa at temperatures of
4-300 K. A precise evaluation of Tc from zero-resistivity temperatures revealed
that Tc shows a slightly distorted dome-shaped curve, with maximum Tc (30 K) at
6 GPa, which is lower than a previously reported Tc value (~37 K). With the
application of pressure, the temperature dependence of resistivity above Tc
changes dramatically to a linear dependence; a non-Fermi-liquid-like ""high-Tc""
phase appears above 3 GPa. We found a striking correlation between Tc and the
Se height: the lower the Se height, the more enhanced is Tc. Moreover, this
relation is broadly applicable to other iron pnictides, strongly indicating
that high-temperature superconductivity can appear only around the optimum
anion height (~1.38A). On the basis of these results, we suggest that the anion
height should be considered as a key determining factor of Tc of iron-based
superconductors containing various anions.",1002.1832v2
2010-02-09,Normal state charge dynamics of Fe1.06Te0.88S0.14 superconductor probed with infrared spectroscopy,"We have used optical spectroscopy to probe the normal state electrodynamic
response of Fe$_{1.06}$Te$_{0.88}$S$_{0.14}$, a member of the 11 family of
iron-based superconductors with T$_c$= 8 K. Measurements have been conducted
over a wide frequency range (50 - 50000 cm$^{-1}$) at selected temperatures
between 10 and 300 K. At low temperatures the material behaves as an
""incoherent metal"": a Drude-like peak is absent from the optical conductivity,
and all optical functions reveal that quasiparticles are not well defined down
to the lowest measured temperature. We introduce ""generalized spectral weight""
analysis and use it to track temperature induced redistribution of spectral
weight. Our results, combined with previous reports, indicate that the 11
family of iron-based superconductors might be different from other families.",1002.1948v1
2010-02-10,Half-metallic Antiferromagnet BaCrFeAs2,"First-principles calculations and a tight-binding analysis predict that the
iron-pnictide BaCrFeAs2 is a promising candidate for half-metallic material
with fully-compensated magnetization. The transition-metal ions Cr and Fe
prefer the three-dimensional intervening lattice, which yields the
antiferromagnetic order of spin orientations. Due to the difference between Cr
and Fe in the electronegativity, a band gap is opened at the Fermi level in the
spin channel in which Fe provides the majority carriers. The selective
hybridization between 3d orbitals of Cr and As:4p states due to the peculiar
lattice structure of the iron-pnictide is shown to be crucial for the novel
properties.",1002.2018v2
2010-02-16,"Orbital Ordering and Unfrustrated $(π,0)$ Magnetism from Degenerate Double Exchange in the Iron Pnictides","The magnetic excitations of the iron pnictides are explained within a
degenerate double-exchange model. The local-moment spins are coupled by
superexchanges $J_1$ and $J_2$ between nearest and next-nearest neighbors,
respectively, and interact with the itinerant electrons of the degenerate
$d_{xz}$ and $d_{yz}$ orbitals via a ferromagnetic Hund exchange. The latter
stabilizes $(\pi,0)$ stripe antiferromagnetism due to emergent ferro-orbital
order and the resulting kinetic energy gain by hopping preferably along the
ferromagnetic spin direction. Taking the quantum nature of the spins into
account, we calculate the magnetic excitation spectra in the presence of both,
super- and double-exchange. A dramatic increase of the spin-wave energies at
the competing N\'eel ordering wave vector is found, in agreement with recent
neutron scattering data. The spectra are fitted to a spin-only model with a
strong spatial anisotropy and additional longer ranged couplings along the
ferromagnetic chains. Over a realistic parameter range, the effective couplings
along the chains are negative corresponding to unfrustrated stripe
antiferromagnetism.",1002.3165v3
2010-02-17,"Nodes in the Gap Function of LaFePO, the Gap Function of the Fe(Se,Te) Systems, and the STM Signature of the s$_{\pm}$ Pairing","We reiterate, in more details, our previous proposal of using quasi-particle
interference to determine the pairing form factor in iron-based
superconductors. We also present our functional renormalization group(FRG)
results on LaFePO and Fe(Se,Te) superconductors. In particular we found that
the leading pairing channel in LaFePO is nodal s$_{\pm}$, with nodes on
electron Fermi surfaces. For Fe(Se,Te) system we found fully gapped s$_{\pm}$
pairing, with substantial gap anisotropy on electron Fermi surfaces, and large
gap is concentrated in regions with dominant $xy$ orbital character. We further
fit the form factor obtained by FRG to real space orbital basis pairing
picture, which shows more clearly the differences between different iron-based
superconductors.",1002.3358v2
2010-02-18,Nanocrystal Growth on Graphene with Various Degrees of Oxidation,"We show a general two-step method to grow hydroxide and oxide nanocrystals of
the iron family elements (Ni, Co, Fe) on graphene with two degrees of
oxidation. Drastically different nanocrystal growth behaviors were observed on
low-oxidation graphene sheets (GS) and highly oxidized graphite oxide (GO) in
hydrothermal reactions. Small particles pre-coated on GS with few
oxygen-containing surface groups diffused and recrystallized into
single-crystalline nickel hydroxide Ni(OH)2 hexagonal nanoplates or iron oxide
Fe2O3 nanorods with well defined morphologies. In contrast, particles
pre-coated on GO were pinned by the high-concentration oxygen groups and
defects on GO without recrystallization into well-defined shapes. Adjusting
reaction temperature can be combined to further control materials grown on
graphene. For materials with weak interactions with graphene, increasing the
reaction temperature can lead to diffusion and recrystallization of surface
species into larger crystals even on highly oxidized and defective GO. Our
results suggest an interesting new approach to controlling the morphology of
nanomaterials grown on graphene by tuning the surface chemistry of graphene as
substrates for crystal nucleation and growth.",1002.3435v1
2010-02-24,Doping dependence of spin fluctuations and electron correlations in iron pnictides,"Doping dependence of the spin fluctuations and the electron correlations in
the effective five-band Hubbard model for iron pnictides is investigated using
the fluctuation-exchange approximation. For a moderate hole doping, we find a
dominant low-energy spin excitation at Q=(\pi,0), which becomes critical at low
temperature. The low-energy spin excitations in the heavily hole-doped region
are characterized by weak Q dependence. The electron doping leads to an
appearance of a pseudogap in spin excitation spectrum. Correspondingly, the
NMR-1/T1 relaxation rate is strongly enhanced on the hole-doped side and
suppressed on the electron-doped side of the phase diagram. This behavior can
be to large extent understood by systematic changes of the Fermi-surface
topology.",1002.4471v2
2010-02-25,Electronic correlations and unusual superconducting response in the optical properties of the iron-chalcogenide FeTe0.55Se0.45,"The in-plane complex optical properties of the iron-chalcogenide
superconductor FeTe0.55Se0.45 have been determined above and below the critical
temperature Tc = 14 K. At room temperature the conductivity is described by a
weakly-interacting Fermi liquid; however, below 100 K the scattering rate
develops a frequency dependence in the terahertz region, signaling the
increasingly correlated nature of this material. We estimate the dc
conductivity just above Tc to be sigma_dc ~ 3500 Ohm-1cm-1 and the superfluid
density rho_s0 ~ 9 x 10^6 cm-2, which places this material close to the scaling
line rho_s0/8 ~ 8.1 sigma_dc Tc for a BCS dirty-limit superconductor. Below Tc
the optical conductivity reveals two gap features at Delta_1,2 ~ 2.5 and ~ 5.1
meV.",1002.4846v2
2010-02-28,"Iron Rings, Doctor Honoris Causa Raoul Bott, Carl Herz, and a Hidden Hand","The degree of Doctor of Sciences, honoris causa, was conferred on Raoul Bott
by McGill University in 1987. Much of the work to make this happen was done by
Carl Herz. Some of the author's personal recollections of both professors are
included, along with some context for the awarding of this degree and ample
historical tangents. Some cultural aspects occurring in the addresses are
elaborated on, primarily, the Canadian engineer's iron ring. This paper also
reprints both the convocation address of Raoul Bott and the presentation of
Carl Herz on that occasion.",1003.0152v1
2010-03-01,Minimum Radii of Super-Earths: Constraints from Giant Impacts,"The detailed interior structure models of super-Earth planets show that there
is degeneracy in the possible bulk compositions of a super-Earth at a given
mass and radius, determined via radial velocity and transit measurements,
respectively. In addition, the upper and lower envelopes in the mass--radius
relationship, corresponding to pure ice planets and pure iron planets,
respectively, are not astrophysically well motivated with regard to the
physical processes involved in planet formation. Here we apply the results of
numerical simulations of giant impacts to constrain the lower bound in the
mass--radius diagram that could arise from collisional mantle stripping of
differentiated rocky/iron planets. We provide a very conservative estimate for
the minimum radius boundary for the entire mass range of large terrestrial
planets. This envelope is a readily testable prediction for the population of
planets to be discovered by the Kepler mission.",1003.0451v1
2010-03-03,"Atomic data activities by the OP and IP consortia: past, present and new perspectives within the VAMDC","The Opacity Project (OP) and Iron Project (IP) are pioneering international
collaborations which have been computing, for more than 25 years, massive
atomic data sets for astrophysical applications. We review the data activities
that have been carried out, namely curation, analysis and preservation, and the
development of databases and computer tools for data dissemination and end-user
processing. New opportunities within the current data-intensive boom referred
to as e-science are described, in particular the Virtual Atomic and Molecular
Data Center (VAMDC) that has been recently launched to consolidate and promote
atomic and molecular database services. Key words: atomic data; Opacity
Project; Iron Project; laboratory astrophysics; databases; e-science; virtual
data centers.",1003.0843v1
2010-03-04,Zeeman Relaxation of Cold Atomic Iron and Nickel in Collisions with 3He,"We have measured the ratio of the diffusion cross-section to the angular
momentum reorientation cross-section in the colliding Fe-3He and Ni-3He
systems. Nickel (Ni) and iron (Fe) atoms are introduced via laser ablation into
a cryogenically cooled experimental cell containing cold (< 1 K) 3He buffer
gas. Elastic collisions rapidly cool the translational temperature of the
ablated atoms to the helium temperature. The cross-section ratio is extracted
by measuring the decays of the atomic Zeeman sublevels. For our experimental
conditions, thermal energy is comparable to the Zeeman splitting. As a result,
thermal excitations between Zeeman sublevels significantly impact the observed
decay. To determine the cross-section ratio accurately, we introduce a model of
Zeeman state dynamics that includes thermal excitations. We find the
cross-section ratio for Ni-3He = 5 x 10^3 and Fe-3He <= 3 x 10^3 at 0.75 K in a
0.8 T magnetic field. These measurements are interpreted in the context of
submerged shell suppression of spin relaxation as studied previously in
transition metals and rare earth atoms.",1003.1106v1
2010-03-08,Design and construction of a novel tribometer with on-line topography and wear measurement,"We present a novel experimental platform that links topographical and
material changes with the friction and wear behavior of oil-lubricated metal
surfaces. This concept combines state-of-the-art methods for the analysis of
the surface topography on the micro- and nano-scale with the online measurement
of wear. At the same time, it allows for frictional and lateral force
detection. Information on the topography of one of the two surfaces is gathered
in-situ with a 3D holography microscope at a maximum frequency of 15 fps and
higher resolution images are provided at defined time intervals by an atomic
force microscope (AFM). The wear measurement is conducted on-line by means of
radio nuclide technique (RNT). The quantitative measurement of the lateral and
frictional forces is conducted with a custom-built 3D force sensor. The
surfaces can be lubricated with an optically transparent oil or water. The
stability and precision of the setup have been tested in a model experiment.
The results show that the exact same position can be relocated and examined
after each load cycle. Wear and topography measurements were performed with a
radioactive labeled iron pin sliding against an iron plate.",1003.1638v1
2010-03-08,Orbital-transverse density-wave instabilities in iron-based superconductors,"Besides the conventional spin-density-wave (SDW) state, a new kind of
orbital-transverse density-wave (OTDW) state is shown to exist generally in
multi-orbital systems. We demonstrate that the orbital character of Fermi
surface nesting plays an important role in density responses. The relationship
between antiferromagnetism and structural phase transition in LaFeAsO (1111)
and BaFe$_2$As$_2$ (122) compounds of iron-based superconductors may be
understood in terms of the interplay between the SDW and OTDW with a
five-orbital Hamiltonian. We propose that the essential difference between 1111
and 122 compounds is crucially determined by the presence of the
two-dimensional $d_{xy}$-like Fermi surface around (0,0) being only in 1111
parent compounds.",1003.1660v2
2010-03-29,Topological and Transport Properties of Dirac Fermions in Antiferromagnetic Metallic Phase of Iron-Based Superconductors,"We investigate Dirac fermions in the antifferomagnetic metallic state of
iron-based superconduc- tors. Deriving an effective Hamiltonian for Dirac
fermions, we reveal that there exist two Dirac cones carrying the same
chirality, contrary to graphene, compensated by a Fermi surface with a
quadratic energy dispersion as a consequence of a non-trivial topological
property inherent in the band structure. We also find that the presence of the
Dirac fermions gives the difference of sign- change temperatures between the
Hall coefficient and the thermopower. This is consistent with available
experimental data.",1003.5469v3
2010-04-01,Ambegaokar-Baratoff relations of Josephson critical current in heterojunctions with multi-gap superconductors,"An extension of the Ambegaokar-Baratoff relation to a
superconductor-insulator-superconductor (SIS) Josephson junction with multiple
tunneling channels is derived. Appling the resultant relation to a SIS
Josephson junction formed by an iron-based (five-band) and a single-band
Bardeen-Cooper-Schrieffer (BCS) type superconductors, a theoretical bound of
the Josephson critical current ($I_{\rm c}$) multiplied by the resistance of
the junction ($R_{\rm n}$) is given. We reveal that such a bound is useful for
identifying the pairing symmetry of iron-pnictide superconductors. One finds
that if a measured value of $I_{\rm c}R_{\rm n}$ is smaller than the bound then
the symmetry is $\pm s$-wave, and otherwise $s$-wave without any sign changes.
In addition, we stress that temperature dependence of $I_{\rm c}R_{\rm n}$ is
sensitive to the difference of the gap functions from the BCS type gap formula
in the above heterojunction.",1004.0044v2
2010-04-09,Electrodynamics of electron doped iron-pnictide superconductors: Normal state properties,"The electrodynamic properties of Ba(Fe$_{0.92}$Co$_{0.08})_2$As$_{2}$ and
Ba(Fe$_{0.95}$Ni$_{0.05})_As$_{2}$ single crystals have been investigated by
reflectivity measurements in a wide frequency range. In the metallic state, the
optical conductivity consists of a broad incoherent background and a narrow
Drude-like component which determines the transport properties; only the latter
contribution strongly depends on the composition and temperature. This
subsystem reveals a $T^2$ behavior in the dc resistivity and scattering rate
disclosing a hidden Fermi-liquid behavior in the 122 iron-pnictide family. An
extended Drude analysis yields the frequency dependence of the effective mass
(with $m^*/m_b\approx 5$ in the static limit) and scattering rate that does not
disclose a simple power law. The spectral weight shifts to lower energies upon
cooling; a significant fraction is not recovered within the infrared range of
frequencies.",1004.1658v1
2010-04-19,Magnetic and Quasiparticle Excitation Spectra of an Itinerant $J_1-J_2$ Model for Iron Pnictide Superconductors,"We calculate the magnetic and quasiparticle excitation spectra of an
itinerant $J_1-J_2$ model for iron pnictides. In addition to an acoustic
spin-wave branch, the magnetic spectrum has a second, optical branch, resulting
from the coupled four-sublattice magnetic structure. The spin-wave velocity has
also a planar directional anisotropy, due to the collinear/striped
antiferromagnetism. Within the magnetically ordered phase, the quasiparticle
spectrum is composed of two Dirac cones, resulting from the folding of the
magnetic Brillouin zone. We discuss the relevance of our findings to the
understanding of both neutron scattering and photoemission spectroscopy results
for SrFe$_{2}$As$_{2}$.",1004.3187v2
2010-04-20,Leggett mode in a strong-coupling model of iron arsenide superconductors,"Using a two-orbital model of the superconducting phase of the pnictides, we
compute the spectrum of the Leggett mode -- a collective excitation of the
phase of the superconducting gap known to exist in multi-gap superconductors --
for different possible symmetries of the superconducting order parameter.
Specifically, we identify the small regions of parameter space where the
Leggett mode lies below the two-particle continuum, and hence should be visible
as a sharp resonance peak. We discuss the possible utility of the Leggett mode
in distinguishing different momentum dependencies of the superconducting gap.
We argue that the observation of a sharp Leggett mode would be consistent with
the presence of strong electron-electron correlations in iron-based
superconductors. We also emphasize the importance of the orbital character of
the Leggett mode, which can result in an experimental observation of the mode
in channels other than $A_{1g}$.",1004.3576v1
2010-04-22,Discovery of K-Shell Emission Lines of Neutral Atoms in the Galactic Center Region,"The K-shell emission line of neutral irons from the Galactic center (GC)
region is one of the key for the structure and activity of the GC. The origin
is still open question, but possibly due either to X-ray radiation or to
electron bombarding to neutral atoms. To address this issue, we analyzed the
Suzaku X-ray spectrum from the GC region of intense neutral iron line emission,
and report on the discovery of Kalpha lines of neutral argon, calcium, chrome,
and manganese atoms. The equivalent widths of these Kalpha lines indicate that
the metal abundances in the GC region should be ~1.6 and ~4 of solar value,
depending on the X-ray and the electron origins, respectively. On the other
hand, the metal abundances in the hot plasma in the GC region are found to be
~1-2 solar. These results favor that the origin of the neutral Kalpha lines are
due to X-ray irradiation.",1004.3891v1
2010-04-26,Orbital Order and Spontaneous Orthorhombicity in Iron Pnictides,"A growing list of experiments show orthorhombic electronic anisotropy in the
iron pnictides, in some cases at temperatures well above the spin density wave
transition. These experiments include neutron scattering, resistivity and
magnetoresistance measurements, and a variety of spectroscopies. We explore the
idea that these anisotropies stem from a common underlying cause: orbital order
manifest in an unequal occupation of $d_{xz}$ and $d_{yz}$ orbitals, arising
from the coupled spin-orbital degrees of freedom. We emphasize the distinction
between the total orbital occupation (the integrated density of states), where
the order parameter may be small, and the orbital polarization near the Fermi
level which can be more pronounced. We also discuss light-polarization studies
of angle-resolved photoemission, and demonstrate how x-ray absorption linear
dichroism may be used as a method to detect an orbital order parameter.",1004.4611v2
2010-04-29,Large $D-2$ Theory of Superconducting Fluctuations in a Magnetic Field and its Application to Iron-Pnictides,"A Ginzburg-Landau approach to fluctuations of a layered superconductor in a
magnetic field is used to show that the interlayer coupling can be incorporated
within an interacting self-consistent theory of a single layer, in the limit of
a large number of neighboring layers. The theory exhibits two phase transitions
-- a vortex liquid-to-solid transition is followed by a Bose-Einstein
condensation into the Abrikosov lattice -- illustrating the essential role of
interlayer coupling. Using this theory, explicit expressions for magnetization,
specific heat, and fluctuation conductivity are derived. We compare our results
with recent experimental data on the iron-pnictide superconductors.",1004.5277v3
2010-04-30,Quasiparticle interference in the spin-density wave phase of iron-based superconductors,"We propose an explanation for the electronic nematic state observed recently
in parent iron-based superconductors [T.-M. Chuang et al., Science 327, 181
(2010)]. We argue that the quasi-one-dimensional nanostructure identified in
the quasiparticle interference (QPI) is a consequence of the interplay of the
magnetic ($\pi$, 0) spin-density wave (SDW) order with the underlying
electronic structure. We show that the evolution of the QPI peaks largely
reflects quasiparticle scattering between electronic bands involved in the SDW
formation. Because of the ellipticity of the electron pocket and the fact that
only one of the electron pockets is involved in the SDW, the resulting QPI has
a pronounced one-dimensional structure. We further predict that the QPI crosses
over to two-dimensionality on an energy scale, set by the SDW gap, which we
estimate from neutron scattering data to be around 90 meV.",1004.5460v1
2010-04-30,Coherent interfacial bonding on the FeAs tetrahedron in Fe/Ba(Fe(1-x)Co(x))2As2 bilayers,"We demonstrate the growth of epitaxial Fe/Ba(Fe(1-x)Co(x))2As2 (Fe/Ba-122)
bilayers on MgO(001) and LSAT(001) single crystal substrates using Pulsed Laser
Deposition (PLD). By exploiting the metallic nature of the FeAs tetrahedron in
the Ba-122 crystal structure, we achieve a coherent interfacial bond between
bcc iron and Co-doped Ba-122. Tc values for both bilayers were close to that of
the PLD target. Direct observation of interfacial bonding between Fe and the
Ba-122 FeAs sublattice by atomic resolution transmission electron microscopy
implies that this bilayer architecture may work for other iron pnictide systems
and pave the way for the fabrication of superconducting/ferromagnetic
heterostructures.",1004.5557v1
2010-05-03,Strong Coupling Superconductivity in Iron-Chalcogenide FeTe$_{0.55}$Se$_{0.45}$,"The superconducting order parameter in the iron-chalcogenide superconductor
FeTe$_{0.55}$Se$_{0.45}$ ($T_\textrm{c}$ = 14.2 K) is investigated by
point-contact Andreev reflection spectroscopy. The energy gap magnitude (3.8
meV at 1.70 K) and temperature dependence as extracted from the Andreev
conductance spectra reveal strong-coupling superconductivity and is consistent
with $s$-wave order parameter symmetry. No clear evidence for multiple order
parameters or interference from multiple bands is observed. A conductance
enhancement persists above $T_\textrm{c}$ to $\sim 18-20$ K and possible
origins, including novel quasiparticle scattering due to strong
antiferromagnetic spin fluctuations, are discussed.",1005.0190v1
2010-05-04,High Pressure Synthesis of Indirectly electron-doped 122 Iron Superconductor Sr1-xLaxFe2As2 with a maximum Tc = 22 K,"Compounds of Sr1-xLaxFe2As2 were synthesized by solid state reaction at 1273
K, under pressures of 2 or 3 GPa. The Sr1-xLaxFe2As2 phase was dominant up to x
= 0.5, and superconductivity was observed at $x \ge 0.2$. A maximum critical
temperature Tc of 22 K, and a maximum shielding volume fraction of ~70 % were
obtained at x = 0.4. This is the first experimental demonstration of
electron-doped superconductivity in 122-type iron pnictides, where electrons
were doped through aliovalent substitution at the site of the alkaline earth
metal. The optimal Tc was slightly higher than that for the Co-doped (directly
electron-doped) samples (19 K), and much lower than that for the hole-doped
case (37 K). The bulk superconductivity range was narrower than that for the
Co-substituted case, and both ranges were much narrower than that for the
hole-doped case. These observations revealed that differences in the
electron-doping mode (direct or indirect) did not have a prominent effect on
the optimal Tc or superconductivity range, compared with differences in carrier
polarity.",1005.0528v2
2010-05-06,Electronic structure and possible pseudogap behavior in iron based superconductors,"Starting from the simplified analytic model of electronic spectrum of iron -
pnictogen (chalcogen) high - temperature superconductors close to the Fermi
level, we discuss the influence of antiferromagneting (AFM)scattering both for
stoichiometric case and the region of possible short - range order AFM
fluctuations in doped compounds. Qualitative picture of the evolution of
electronic spectrum and Fermi surfaces (FS) for different dopings is presented,
with the aim of comparison with existing and future ARPES experiments. Both
electron and hole dopings are considered and possible pseudogap behavior
connected with partial FS ""destruction"" is demonstrated, explaining some recent
experiments.",1005.0884v4
2010-05-12,Stripe antiferromagnetic correlations in LaFeAsO1-xFx probed by 75As NMR,"The anisotropy of the nuclear spin-lattice relaxation rate $1/T_{1}$ of
$^{75}$As was investigated in the iron-based superconductor
LaFeAs(O$_{1-x}$F$_{x}$) ($x = 0.07, 0.11$ and 0.14) as well as LaFeAsO. While
the temperature dependence of the normal-state $1/T_1T$ in the superconducting
(SC) $x = 0.07$ is different from that in the SC $x = 0.11$, their anisotropy
of $1/T_1$, $R \equiv (1/T_{1})_{H \parallel ab}/(1/T_{1})_{H \parallel c}$ in
the normal state is almost the same ($\simeq$ 1.5). The observed anisotropy is
ascribable to the presence of the local stripe correlations with $Q = (\pi, 0)$
or $(0, \pi)$. In contrast, $1/T_1$ is isotropic and $R$ is approximately 1 in
the overdoped $x = 0.14$ sample, where superconductivity is almost suppressed.
These results suggest that the presence of the local stripe correlations
originating from the nesting between hole and electron Fermi surfaces is linked
to high-$T_c$ superconductivity in iron pnictides.",1005.2013v2
2010-05-12,Striped-magnetic-order suppresses giant optical anisotropy and drives structural distortion in iron arsenide superconductors,"To examine the role of magnetism in superconductivity of iron-based
superconductors, we first present first-principles optical calculations on
three representative parent compounds: LaFeAsO, BaFe2As2 and LiFeAs. Both
nonmagnetic (NM) and spin-density wave (SDW) with striped antiferromagnetic
order are considered. Due to their layer structure, these compounds in NM
states show anomalously large optical anisotropy with a conductivity ratio
$\sigma_{zz}/\sigma{xx}$ as large as 313% in LaFeAsO and 530% in LiFeAs.
Interestingly the giant optical anisotropy is significantly suppressed by SDW.
On the other hand, the variable-cell-shape optimizations confirm that SDW does
drive an orthorhombic-distortion. The drive force is dependent on the local
magnetic moment on Fe sublattice, which is tuned by its bonding environment.
Based on these results, we discussed the delicate role of magnetism in
superconductivity.",1005.2121v2
2010-05-12,Charge doping-induced quasiparticle scattering in iron-pnictide superconductors as probed by vortex pinning,"Charge doping of iron-pnictide superconductors leads to collective pinning of
flux vortices, whereas isovalent doping does not. Moreover, flux pinning in the
charge-doped compounds is consistently described by the mean-free path
fluctuations introduced by the dopant atoms, allowing for the extraction of the
elastic quasiparticle scattering rate. The absence of scattering by dopant
atoms in isovalently doped BaFe$_{2}$(As$_{1-x}$P$_{x}$)$_{2}$ is consistent
with the observation of a linear temperature dependence of the low-temperature
penetration depth in this material.",1005.2129v2
2010-05-15,A Theoretical Study of the Equation of States for Crustal Matter of Strongly Magnetized Neutron Stars,"We have investigated some of the properties of dense sub-nuclear matter at
the crustal region (both the outer crust and the inner crust region) of a
magnetar. The relativistic version of Thomas-Fermi (TF) model is used in
presence of strong quantizing magnetic field for the outer crust matter. The
compressed matter in the outer crust, which is a crystal of metallic iron, is
replaced by a regular array of spherically symmetric Wigner-Seitz (WS) cells.
In the inner crust region, a mixture of iron and heavier neutron rich nuclei
along with electrons and free neutrons has been considered. Conventional
Harrison-Wheeler (HW) and Bethe-Baym-Pethick (BBP) equation of states are used
for the nuclear mass formula. A lot of significant changes in the
characteristic properties of dense crustal matter, both at the outer crust and
the inner crust, have been observed.",1005.2658v1
2010-05-24,Reduction in iron losses in Indirect Vector-Controlled IM Drive using FLC,"This paper describes the use of fuzzy logic controller for efficiency
optimization control of a drive while keeping good dynamic response. At
steady-state light-load condition, the fuzzy controller adaptively adjusts the
excitation current with respect to the torque current to give the minimum total
copper and iron loss. The measured input power such that, for a given load
torque and speed, the drive settles down to the minimum input power, i.e.,
operates at maximum efficiency. The low-frequency pulsating torque due to
decrementation of flux is compensated in a feed forward manner. If the load
torque or speed commands changes, the efficiency search algorithm is abandoned
and the rated flux is established to get the best dynamic response. The drive
system with the proposed efficiency optimization controller has been simulated
with lossy models of converter and machine, and its performance has been
thoroughly investigated.",1005.4265v1
2010-06-02,Local moments and symmetry breaking in metallic PrMnSbO,"We report a combined experimental and theoretical investigation of the
layered antimonide PrMnSbO which is isostructural to the parent phase of the
iron pnictide superconductors. We find linear resistivity near room temperature
and Fermi liquid-like T^{2} behaviour below 150 K. Neutron powder diffraction
shows that unfrustrated C-type Mn magnetic order develops below \sim 230 K,
followed by a spin-flop coupled to induced Pr order. At T \sim 35 K, we find a
tetragonal to orthorhombic (T-O) transition. First principles calculations show
that the large magnetic moments observed in this metallic compound are of local
origin. Our results are thus inconsistent with either the itinerant or
frustrated models proposed for symmetry breaking in the iron pnictides. We show
that PrMnSbO is instead a rare example of a metal where structural distortions
are driven by f-electron degrees of freedom.",1006.0341v1
2010-06-02,Robust accidental nodes and zeroes and critical quasiparticle scaling in iron-based multiband superconductors,"We study multigap superconductivity, with strong angular variations of one of
the gaps, as appropriate for certain iron-based high-temperature
superconductors. We solve the gap equations of this model and find that the
nodes or zeroes in the gap function present at Tc - although purely accidental
-- typically survive down to T=0. Based on this result, we investigate the line
of quantum transitions at which gap zeroes first appear. The peculiar
""zero-point"" critical scaling emanating from this line dominates quasiparticle
thermodynamics and transport properties over much of the phase diagram, and
supplants more familiar forms of scaling associated with accidental nodes.",1006.0447v3
2010-06-18,"A New Iron Pnictide Oxide (Fe2As2)(Ca5(Mg,Ti)4Oy) and a New Phase in Fe-As-Ca-Mg-Ti-O system","A new layered iron arsenide oxide (Fe2As2)(Ca5(Mg,Ti)4Oy) and its structural
derivative were found in the Fe-As-Ca-Mg-Ti-O system. The crystal structure of
(Fe2As2)(Ca5(Mg,Ti)4Oy) is identical to that of (Fe2As2)(Ca5(Sc,Ti)4Oy), which
was reported in our previous study. The lattice constants of this compound are
a = 3.86(4) A and c = 41.05(2) A. In addition, another phase with a thicker
blocking layer was found. The structure of the compound and its derivative was
tentatively assigned through STEM observation as (Fe2As2)(Ca8(Mg,Ti)6Oy) with
sextuple perovskite-type sheets divided by a rock salt layer. The interlayer
Fe-Fe distance of this compound is ~30 A. The compound and its derivative
exhibited bulk superconductivity, as found from magnetization and resistivity
measurements.",1006.3769v4
2010-06-18,Inelastic neutron scattering study on the resonance mode in an optimally doped superconductor LaFeAsO$_{0.92}$F$_{0.08}$,"An optimally doped iron-based superconductor LaFeAsO$_{0.92}$F$_{0.08}$ with
$T_c = 29$ K has been studied by inelastic powder neutron scattering. The
magnetic excitation at $Q=1.15$ \AA$^{-1}$ is enhanced below $T_c$, leading to
a peak at $E_{res}\sim13$ meV as the resonance mode, in addition to the
formation of a gap at low energy below the crossover energy $\Delta_{c}\sim10
meV$. The peak energy at $Q=1.15$ \AA$^{-1}$ corresponds to $5.2 k_B T_c$ in
good agreement with the other values of resonance mode observed in the various
iron-based superconductors, even in the high-$T_c$ cuprates. Although the
phonon density of states has a peak at the same energy as the resonance mode in
the present superconductor, the $Q$-dependence is consistent with the resonance
being of predominately magnetic origin.",1006.4640v1
2010-06-24,Electronic correlations in iron-pnictide superconductors and beyond; what can we learn from optics,"The Coulomb repulsion, impeding electrons' motion, has an important impact on
the charge dynamics. It mainly causes a reduction of the effective metallic
Drude weight (proportional to the so-called optical kinetic energy),
encountered in the optical conductivity, with respect to the expectation within
the nearly-free electron limit (defining the so-called band kinetic energy), as
evinced from band-structure theory. In principle, the ratio between the optical
and band kinetic energy allows defining the degree of electronic correlations.
Through spectral weight arguments based on the excitation spectrum, we provide
an experimental tool, free from any theoretical or band-structure based
assumptions, in order to estimate the degree of electronic correlations in
several systems. We first address the novel iron-pnictide superconductors,
which serve to set the stage for our approach. We then revisit a large variety
of materials, ranging from superconductors, to Kondo-like systems as well as
materials close to the Mott-insulating state. As comparison we also tackle
materials, where the electron-phonon coupling dominates. We establish a direct
relationship between the strength of interaction and the resulting reduction of
the optical kinetic energy of the itinerant charge carriers.",1006.4698v1
2010-06-27,The effect of disorder on electronic Raman scattering in the superconducting state of iron pnictides,"Electronic Raman scattering measures a polarization-dependent scattering
intensity which can provide information about the location of nodes in the
energy gap of an unconventional superconductor as well as its overall symmetry.
In this paper, we calculate the Raman intensity in the presence of disorder for
several models of the iron pnictide superconducting state. We include, for
completeness, $d$-wave and isotropic $s_\pm$ responses in addition to more
realistic extended $s_\pm$ superconducting gaps. The effect of disorder is
modeled using a self-consistent $T$-matrix approximation, and is studied in the
limits of isotropic and intraband-only scattering. We show how recent
experiments on Ba(Fe$_{1-x}$Co$_x$)$_2$As$_2$ may be consistent with ""node
lifting"" by intraband disorder.",1006.5245v1
2010-07-06,"Spin waves in the (0,pi) and (0,pi,pi) ordered SDW states of the t-t' Hubbard model: Application to doped iron pnictides","Spin waves in (0,pi) and (0,pi,pi) ordered spin-density-wave (SDW) states of
the t-t' Hubbard model are investigated at finite doping. In the presence of
small t', these composite ferro-antiferromagnetic (F-AF) states are found to be
strongly stabilized at finite hole doping due to enhanced carrier-induced
ferromagnetic spin couplings as in metallic ferromagnets. Anisotropic spin-wave
velocities, spin-wave energy scale of around 200meV, reduced magnetic moment,
and rapid suppression of magnetic order with electron doping x (corresponding
to F substitution of O atoms in La O_{1-x} F_x Fe As or Ni substitution of Fe
atoms in Ba Fe_{2-x} Ni_x As_2) obtained in this model are in agreement with
observed magnetic properties of doped iron pnictides.",1007.0812v1
2010-07-08,Optical properties of the iron-chalcogenide superconductor FeTe0.55Se0.45,"The complex optical properties of the iron-chalcogenide superconductor
FeTe0.55Se0.45 with Tc=14K have been examined over a wide frequency range for
light polarized in the Fe-Te(Se) planes above and below Tc. At room temperature
the optical response may be described by a weakly-interacting Fermi liquid;
however, just above Tc this picture breaks down and the scattering rate takes
on a linear frequency dependence. Below Tc there is evidence for two gap
features in the optical conductivity at Delta_1 ~ 2.5 meV and Delta_2 ~ 5.1
meV. Less than 20% of the free carriers collapse into the condensate for T <<
Tc, and this material is observed to fall on the universal scaling line for a
BCS dirty-limit superconductor in the weak-coupling limit.",1007.1447v2
2010-07-15,Absence of an appreciable iron isotope effect on the transition temperature of the optimally doped SmFeAsO_{1-y} superconductor,"We report the iron (Fe) isotope effect on the transition temperature (Tc) in
the oxygen-deficient SmFeAsO_{1-y}, a 50 K-class Fe-based superconductor. For
the optimally-doped samples with Tc = 54 K, change of the Fe average atomic
mass (MFe) causes a negligibly small shift in Tc, with the Fe isotope
coefficient (alphaFe) as small as -0.024 \pm 0.015. This result contrasts with
the finite, inverse isotope shift observed in optimally-doped (Ba,K)Fe2As2,
indicating that the contribution of the electron-phonon interaction markedly
differs between these two Fe-based high-Tc superconductors.",1007.2666v1
2010-07-16,Fermi surfaces and quasi-particle band dispersions of the iron pnictides superconductor KFe2As2 observed by angle-resolved photoemission spectroscopy,"We have performed an angle-resolved photoemission study of the iron pnictide
superconductor KFe2As2 with Tc 4 K. Most of the observed Fermi surfaces show
almost two-dimensional shapes, while one of the quasi-particle bands near the
Fermi level has a strong dispersion along the kz direction, consistent with the
result of a band-structure calculation. However, hole Fermi surfaces \alpha and
\zeta are smaller than those predicted by the calculation while other Fermi
surfaces are larger. These observations are consistent with the result of a de
Haas-van Alphen study and a theoretical prediction on inter-band scattering,
possibly indicating many body effects on the electronic structure.",1007.2698v2
2010-07-20,Conductivity anisotropy in the antiferromagnetic state of iron pnictides,"Recent experiments on iron pnictides have uncovered a large in-plane
resistivity anisotropy with a surprising result: the system conducts better in
the antiferromagnetic x direction than in the ferromagnetic y direction. We
address this problem by calculating the ratio of the Drude weight along the x
and y directions, Dx/Dy, for the mean-field Q=(\pi,0) magnetic phase diagram of
a five-band model for the undoped pnictides. We find that Dx/Dy ranges between
0.3 < D_x/D_y < 1.4 for different interaction parameters. Large values of
orbital ordering favor an anisotropy opposite to the one found experimentally.
On the other hand D_x/D_y is strongly dependent on the topology and morfology
of the reconstructed Fermi surface. Our results points against orbital ordering
as the origin of the observed conductivity anisotropy, which may be ascribed to
the anisotropy of the Fermi velocity.",1007.3483v2
2010-07-22,Stratification of the elements in the atmospheres of blue horizontal-branch stars,"Blue horizontal-branch (BHB) stars with $T_{\rm eff}$ approximately larger
than 11500 K show several observational anomalies. In globular clusters, they
exhibit low rotational velocities, abundance anomalies (as compared to cluster
abundances), photometric jumps and gaps and spectroscopic gravities lower than
predicted by canonical models. It is commonly believed that the low rotational
velocities of these stars permit atomic diffusion to be efficient in their
atmosphere thereby causing the observed anomalies. Recent detections of
vertical stratification of iron (and some other chemical elements) in several
BHB stars concur with this framework. In this paper, improved model atmospheres
that include the vertical stratification of the elements are applied to BHB
stars to verify if they can explain their observational anomalies. The results
from theoretical model atmospheres are consistent with the photometric jumps
and gaps observed for BHB stars in globular clusters. It is found that iron
stratification in the theoretical models and that obtained from observations
have similar tendancies. Our results also show that the spectroscopic gravities
obtained while using chemically homogeneous model atmospheres to fit
observations are underestimated. These results significantly strengthen the
belief that atomic diffusion is responsible for these BHB-star anomalies.",1007.4023v1
2010-08-08,MHD Simulations of Core Collapse Supernovae with Cosmos++,"We performed 2D, axisymmetric, MHD simulations with Cosmos++ in order to
examine the growth of the magnetorotational instability (MRI) in core--collapse
supernovae. We have initialized a non--rotating 15 solar mass progenitor,
infused with differential rotation and poloidal magnetic fields. The collapse
of the iron core is simulated with the Shen EOS, and the parametric Ye and
entropy evolution. The wavelength of the unstable mode in the post--collapse
environment is expected to be only ~ 200 m. In order to achieve the fine
spatial resolution requirement, we employed remapping technique after the iron
core has collapsed and bounced.
  The MRI unstable region appears near the equator and angular momentum and
entropy are transported outward. Higher resolution remap run display more
vigorous overturns and stronger transport of angular momentum and entropy. Our
results are in agreement with the earlier work by Akiyama et al. (2003) and
Obergaulinger et al. (2009).",1008.1422v1
2010-08-29,Quasiparticle interference in iron-based superconductors,"We systematically calculate quasiparticle interference (QPI) signatures for
the whole phase diagram of iron-based superconductors. Impurities inherent in
the sample together with ordered phases lead to distinct features in the QPI
images that are believed to be measured in spectroscopic imaging-scanning
tunneling microscopy (SI-STM). In the spin-density wave phase the rotational
symmetry of the electronic structure is broken, signatures of which are also
seen in the coexistence regime with both superconducting and magnetic order. In
the superconducting regime we show how the different scattering behavior for
magnetic and non-magnetic impurities allows to verify the $s^{+-}$ symmetry of
the order parameter. The effect of possible gap minima or nodes is discussed.",1008.4930v2
2010-09-01,"Uniaxial ""nematic-like"" electronic structure and Fermi surface of untwinned CaFe2As2","Obtaining the electronic structure of the newly discovered iron-based
superconductors is the key to understanding the mechanism of their
high-temperature superconductivity. We used angle-resolved photoemission
spectroscopy (ARPES) to make direct measurements of the electronic structure
and Fermi surface (FS) of the untwinned uniaxial state of CaFe2As2, the parent
compound of iron-based superconductors. We observed unequal dispersions and FS
geometries along the orthogonal Fe-Fe bond directions. More importantly,
unidirectional straight and flat FS segments are observed near the zone center,
which indicates the existence of a unidirectional nematic charge density wave
order, strengthening the case for a quantum electronic liquid crystalline
""nematic"" phase. Further, the doping dependence extrapolates to a possible
quantum critical point of the disappearance of this order in the heavily
overdoped regime of these materials.",1009.0271v1
2010-09-04,Electronic dispersion anomalies in the iron pnictide superconductor Ba_{1-x}K_xFe_2As_2,"The pairing mechanism in the iron-pnictide superconductors is still unknown.
However, similarities to the cuprate high-temperature superconductors suggest
that a similar mechanism may be at work. Recently, careful experimental studies
of the spin excitation spectrum revealed, like in the cuprates, a strong
temperature dependence in the normal state and a resonance feature in the
superconducting state. Motivated by these findings, we develop a model of
electrons interacting with a temperature dependent magnetic excitation spectrum
based on these experimental observations. We apply it to analyse angle resolved
photoemission and tunnelling spectra in Ba{1-x}KxFe2As2. We reproduce in
quantitative agreement with experiment a renormalisation of the quasiparticle
dispersion both in the normal and the superconducting state, and the dependence
of the quasiparticle linewidth on binding energy. We estimate the strength of
the coupling between electronic and spin excitations. Our findings support the
possibility of a pairing mechanism based dominantly on such a coupling.",1009.0849v1
2010-09-20,Hydrogen in $α$ iron: modification of elastic properties and solubility in strain fields,"The effect of interstitial hydrogen on the elastic properties of
$\alpha$-iron is investigated using \textit{ab initio} density functional
theory. We find that while the overall strength properties are reduced by H,
the effects are mainly due to the resulting local volume expansion. We use
these concentration-dependent elastic moduli to model the effects of
homogeneous strain fields on H solubility and make extrapolations to
H-solubility in the spatially-varying strain fields of realistic dislocations.
We find that H is strongly trapped by dislocations of both the edge and screw
variety, leading to a remarkable increase in the local H concentration near the
dislocation cores. The strain dependence of the solution energy leading to
accumulation of H near dislocation cores, as well as the reduction of elastic
moduli which our calculations predict, is consistent with numerous experimental
studies which indicate that the trapping of H near dislocations plays a
significant role in the embrittlement of iron and steels.",1009.3784v4
2010-09-30,Effects of iron doping on the topological insulator surfaces,"Topological insulators embody a newly discovered state of matter
characterized by conducting spin-momentum locked surface states that span the
bulk band gap. So far, most of the study on topological insulator surfaces has
been limited to understanding their properties without strong Coulomb
perturbation or breaking of time reversal symmetry. We have used deposited
iron, with a large positive ionization state and significant magnetic moment as
a strong probe to modify the surface electronic structure of the Bi2Se3 surface
at the gap energy scale. We observe that such perturbation leads to the
creation of multiple Dirac fermions consistent with Z2 or Mod(2) symmetry.
Taken collectively, these results are a helpful guide in manipulating
topological surfaces for probing fundamental physics or developing device
applications.",1009.6216v2
2010-10-05,Structural and magnetic characterization of self-assembled iron oxide nanoparticle arrays,"We report about a combined structural and magnetometric characterization of
self-assembled magnetic nanoparticle arrays. Monodisperse iron oxide
nanoparticles with a diameter of 20 nm were synthesized by thermal
decomposition. The nanoparticle suspension was spin-coated on Si substrates to
achieve self-organized arrays of particles and subsequently annealed at various
conditions. The samples were characterized by x-ray diffraction, bright and
dark field high resolution transmission electron microscopy (HRTEM). The
structural analysis is compared to the magnetic behavior investigated by
superconducting interference device (SQUID) magnetometry. We can identify
either multi-phase FeO/g-Fe2O3 or multi-phase FeO/Fe3O4 nanoparticles. The
FeO/g-Fe2O3 system shows a pronounced exchange bias effect which explains the
peculiar magnetization data obtained for this system.",1010.0938v1
2010-10-12,Turbulence and magnetic spots at the surface of hot massive stars,"Hot luminous stars show a variety of phenomena in their photospheres and in
their winds which still lack clear physical explanations at this time. Among
these phenomena are non-thermal line broadening, line profile variability
(LPVs), discrete absorption components (DACs), wind clumping and stochastically
excited pulsations. Cantiello et al. (2009) argued that a convection zone close
to the surface of hot, massive stars, could be responsible for some of these
phenomena. This convective zone is caused by a peak in the opacity due to iron
recombination and for this reason is referred as the ""iron convection zone""
(FeCZ). 3D MHD simulations are used to explore the possible effects of such
subsurface convection on the surface properties of hot, massive stars. We argue
that turbulence and localized magnetic spots at the surface are the likely
consequence of subsurface convection in early type stars.",1010.2498v1
2010-10-18,Possible three dimensional nodes in the $s{\pm}$ superconducting gap of BaFe$_2$(As$_{1-x}$P$_x$)$_2$,"We examine theoretically the superconducting state of
BaFe$_2$(As$_{1-x}$P$_x$)$_2$, an isovalent doping 122 iron pnictide
superconductor. We construct a three dimensional ten orbital model from first
principles band calculation, and investigate the superconducting gap within the
spin fluctuation mediated pairing mechanism. The gap is basically $s\pm$, where
the gap changes its sign between electron and hole Fermi surfaces, but three
dimensional nodal structures appear in the largely warped hole Fermi surface
having strong $Z^2/XZ/YZ$ orbital character. The present result, together with
our previous study on 1111 systems, explains the strong material dependence of
the superconducting gap in the iron pnictides.",1010.3542v2
2010-10-18,Observation of anisotropic diamagnetism above the superconducting transition in iron-pnictide Ba_(1-x)K_xFe2As2 single crystals due to thermodynamic fluctuations,"High resolution magnetization measurements performed in a high quality
Ba_(1-x)K_xFe2As2 single crystal allowed to determine the diamagnetism induced
above the superconducting transition by thermally activated Cooper pairs. These
data, obtained with magnetic fields applied along and transverse to the crystal
ab layers, demonstrate experimentally that the superconducting transition of
iron pnictides may be explained at a phenomenological level in terms of the
Gaussian Ginzburg-Landau approach for three-dimensional anisotropic
superconductors.",1010.3581v4
2010-10-22,A single-sided linear synchronous motor with a high temperature superconducting coil as the excitation system,"Thrust measurements were performed on a coil made of YBa2Cu3O7-d coated
conductor acting as the excitation system of a single-sided linear synchronous
motor. The superconducting coil was a single pancake in the shape of a
racetrack with 100 turns, the width and effective lengths were 42 mm and 84 mm,
respectively. The stator was made of conventional copper wire. At 77 K and a
gap of 10 mm, with an operating direct current of I_DC=30 A for the
superconducting coil and alternating current of I_AC=9 A for the stator coils,
thrust of 24 N was achieved. With addition of an iron core, thrust was
increased by 49%. With addition of an iron back plate, thrust was increased by
70%.",1010.4775v1
2010-10-25,Discovery Prospects for a Supernova Signature of Biogenic Origin,"Approximately 2.8 Myr before the present our planet was subjected to the
debris of a supernova explosion. The terrestrial proxy for this event was the
discovery of live atoms of 60Fe in a deep-sea ferromanganese crust. The
signature for this supernova event should also reside in magnetite Fe3O4
microfossils produced by magnetotactic bacteria extant at the time of the
Earth-supernova interaction, provided the bacteria preferentially uptake iron
from fine-grained iron oxides and ferric hydroxides. Using estimates for the
terrestrial supernova 60Fe flux, combined with our empirically derived
microfossil concentrations in a deep-sea drill core, we deduce a conservative
estimate of the ^{60}{Fe} fraction as 60Fe/Fe ~ 3.6 x 10^{-15}. This value sits
comfortably within the sensitivity limit of present accelerator mass
spectrometry capabilities. The implication is that a biogenic signature of this
cosmic event is detectable in the Earth's fossil record.",1010.5109v3
2010-10-28,Magnetism and Disorder Effects on muSR Measurements of the Magnetic Penetration Depth in Iron-Based Superconductors,"It is shown that attempts to accurately deduce the magnetic penetration depth
of overdoped BaFe_{1.82}Co_{0.18}As2 single crystals by transverse-field muon
spin rotation (TF-muSR) are thwarted by field-induced magnetic order and strong
vortex-lattice disorder. We explain how substantial deviations from the
magnetic field distribution of a nearly perfect vortex lattice by one or both
of these factors is also significant for other iron-based superconductors, and
this introduces considerable uncertainty in the values of the magnetic
penetration depth obtained by TF-muSR.",1010.6046v1
2010-11-03,Electrostatic fluctuations promote the dynamical transition in proteins,"Atomic displacements of hydrated proteins are dominated by phonon vibrations
at low temperatures and by dissipative large-amplitude motions at high
temperatures. A crossover between the two regimes is known as a dynamical
transition. Recent experiments indicate a connection between the dynamical
transition and the dielectric response of the hydrated protein. We analyze two
mechanisms of the coupling between the protein atomic motions and the
protein-water interface. The first mechanism considers viscoelastic changes in
the global shape of the protein plasticized by its coupling to the hydration
shell. The second mechanism involves modulations of the motions of partial
charges inside the protein by electrostatic fluctuations. The model is used to
analyze mean square displacements of iron of metmyoglobin reported by
Moessbauer spectroscopy. We show that high flexibility of heme iron at
physiological temperatures is dominated by electrostatic fluctuations. Two
onsets, one arising from the viscoelastic response and the second from
electrostatic fluctuations, are seen in the temperature dependence of the mean
square displacements when the corresponding relaxation times enter the
instrumental resolution window.",1011.1023v1
2010-11-06,Search for pressure induced superconductivity in CeFeAsO and CeFePO iron pnictides,"The CeFeAsO and CeFePO iron pnictide compounds were studied via electrical
transport measurements under high-pressure. In CeFeAsO polycrystals, the
magnetic phases involving the Fe and Ce ions coexist up to 15 GPa, with no
signs of pressure-induced superconductivity up to 50 GPa. For the CeFePO single
crystals, pressure stabilizes the Kondo screening of the Ce 4f-electron
magnetic moments.",1011.1593v2
2010-11-07,Spectrophotometric variability of the magnetic CP star 56 Arietis in spectral region from 1950 to 3200 A,"The spectrophotometric variability of the magnetic CP star 56 Arietis (56
Ari) in the ultraviolet spectral region from 1950 to 3200 A is investigated.
This study is based on the archival International Ultraviolet Explorer data
obtained at different phases of the rotational cycle. The brightness of 56 Ari
is not constant in the investigated wavelengths over the whole rotational
period. The monochromatic light curves continuously change their shape with
wavelength. This indicates that we do not observe a truly 'null wavelength
region' where the monochromatic light curve has a zero amplitude. Probably, an
uneven surface distribution of silicon and iron mainly influences the flux
redistribution from the far-UV to near-UV spectral regions, although additional
sources of opacity may be involved. The redistribution of the flux at phase
0.25 is connected with the nonuniform distribution of silicon on the stellar
surface of 56 Ari. On the other hand, the redistribution of the flux at phase
0.65 is quite complex, because there are additional blocking and redistribution
of the flux by iron lines in the near-UV spectral region.",1011.1659v1
2010-11-12,Antiferromagnetic ordering in the absence of a structural distortion in Ba(Fe{1-x}Mn{x})2As2,"Neutron and x-ray diffraction studies of Ba(Fe{1-x}Mn{x})2As2 for low doping
concentrations (x <= 0.176) reveal that at a critical concentration, 0.102 < x
< 0.118, the tetragonal-to-orthorhombic transition abruptly disappears whereas
magnetic ordering with a propagation vector of (1/2 1/2 1) persists. Among all
of the iron arsenides this observation is unique to Mn-doping, and unexpected
because all models for ""stripe-like"" antiferromagnetic order anticipate an
attendant orthorhombic distortion due to magnetoelastic effects. We discuss
these observations and their consequences in terms of previous studies of
Ba(Fe{1-x}TM{x})2As2 compounds (TM = Transition Metal), and models for magnetic
ordering in the iron arsenide compounds.",1011.2816v1
2010-11-14,Strong spin resonance on BaFe2(As0.65P0.35)2 with Tc = 30 K,"We performed inelastic neutron scattering on powder sample of the P-doped
iron-based superconductor BaFe2(As0.65P0.35)2 with Tc = 30K, whose
superconducting (SC) order parameter is expected to have line nodes. We have
observed spin resonance at Q $\sim$ 1.2{\AA}^{-1} and E=12 meV in the SC state.
The resonance enhancement, which can be a measure of the area of sign reversal
between the hole and electron Fermi surfaces (FSs), is comparable to those of
other iron-based superconductors without line nodes. This fact indicates that
the sign reversal between the FSs is still dominant in this system, and the
line nodes should create only limited area of sign-reversal on a single FS.
Hence the system can hold relatively high-Tc. Comparison with theoretical
calculation indicates horizontal line nodes may be a candidate to reproduce the
observation.",1011.3191v1
2010-11-26,Advantageous grain boundaries in iron pnictide superconductors,"High critical temperature superconductors have zero power consumption and
could be used to produce ideal electric power lines. The principal obstacle in
fabricating superconducting wires and tapes is grain boundaries-the
misalignment of crystalline orientations at grain boundaries, which is
unavoidable for polycrystals, largely deteriorates critical current density.
Here, we report that High critical temperature iron pnictide superconductors
have advantages over cuprates with respect to these grain boundary issues. The
transport properties through well-defined bicrystal grain boundary junctions
with various misorientation angles (thetaGB) were systematically investigated
for cobalt-doped BaFe2As2 (BaFe2As2:Co) epitaxial films fabricated on bicrystal
substrates. The critical current density through bicrystal grain boundary
(JcBGB) remained high (> 1 MA/cm2) and nearly constant up to a critical angle
thetac of ~9o, which is substantially larger than the thetac of ~5o for YBCO.
Even at thetaGB > thetac, the decay of JcBGB was much smaller than that of
YBCO.",1011.5721v2
2010-12-03,Origin of In-Plane Anisotropy in Optical Conductivity for Antiferromagnetic Metallic Phase of Iron Pnictides,"We examine the optical conductivity in antiferromagnetic (AFM) iron pnictides
by mean-field calculation in a five-band Hubbard model. The calculated spectra
are well consistent with the in-plane anisotropy observed in the measurements,
where the optical conductivity along the direction with the AFM alignment of
neighboring spins is larger than that along the ferromagnetic (FM) direction in
the low-energy region; however, that along the FM direction becomes larger in
the higher-energy region. The difference between the two directions is
explained by taking account of orbital characters in both occupied and
unoccupied states as well as of the nature of Dirac-type linear dispersions
near the Fermi level.",1012.0670v2
2010-12-13,Accretion and diffusion in the DAZ white dwarf GALEX J1931+0117,"We present an analysis of high-dispersion and high signal-to-noise ratio
spectra of the DAZ white dwarf GALEX J1931+0117. The spectra obtained with the
VLT-Kueyen/UV-Visual Echelle Spectrograph show several well-resolved Si II
spectral lines enabling a study of pressure effects on line profiles. We
observed large Stark shifts in silicon lines in agreement with laboratory
measurements. A model atmosphere analysis shows that the magnesium, silicon and
iron abundances exceed solar abundances, while the oxygen and calcium
abundances are below solar. Also, we compared the observed line profiles to
synthetic spectra computed with variable accretion rates and vertical abundance
distributions assuming diffusion steady-state. The inferred accretion rates
vary from dM/dt=2x10^6 for calcium to 2x10^9 g/s for oxygen and indicate that
the accretion flow is dominated by oxygen, silicon and iron while being
deficient in carbon, magnesium and calcium. The lack of radial velocity
variations between two measurement epochs suggests that GALEX J1931+0117 is
probably not in a close binary and that the source of the accreted material
resides in a debris disc.",1012.2644v1
2010-12-14,Electron and hole Dirac cone states in-pairs in Ba(FeAs)$_2$ confirmed by magnetoresistance,"The quantum transport of Dirac cone states in the iron pnictide Ba(FeAs)$_2$
with a d-\,multiband system is studied by using single crystal samples. The
transverse magnetoresistance develops linearly against magnetic field at low
temperatures. The transport phenomena are interpreted in terms of the 0$^{th}$
Landau level by applying the theory predicted by Abrikosov. The results of the
semiclassical analyses of a two carrier system under low magnetic field limit
show that both electron and hole reside as the high mobility states, being
indicative to the fact that both electron- and hole Dirac cone states should be
taken into account in pairs for having the real interpretation of low
temperature electronic states in iron pnictides, being in contrast to the
previous reports.",1012.3029v4
2010-12-15,Theory of two magnon Raman scattering in antiferromagnetic iron pnictides,"Although the parent iron-based pnictides and chalcogenides are itinerant
antiferromagnets, the use of local moment picture to understand their magnetic
properties is still widespread. We study magnetic Raman scattering from a local
moment perspective for various quantum spin models proposed for this new class
of superconductors. These models vary greatly in the level of magnetic
frustration and show a vastly different two-magnon Raman response. Light
scattering by two-magnon excitations thus provides a robust and independent
measure of the underlying spin interactions. In accord with other recent
experiments, our results indicate that the amount of magnetic frustration in
these systems may be small.",1012.3254v2
2010-12-21,Resistivity scaling in 1111 iron-pnictide superconductors,"We show that the zero field normal-state resistivity above Tc for various
levels of electron doping - both for LaO1-xFxFeAs (La-1111) and SmO1-xFxFeAs
(Sm-1111) members of the 1111-iron-pnictide superconductor family - can be
scaled in a broad temperature range from 20 to 300 K onto single curves for
underdoped La-1111 (x=0.05-0.075), for optimally and overdoped La-1111
(x=0.1-0.2) and for underdoped Sm-1111 (x=0.06-0.1) compounds. The scaling was
performed using the energy scale {\Delta}, the resistivity {\rho}_{\Delta} and
the residual resistivity {\rho}_0 as scaling parameters as well as by applying
a recently proposed model-independent scaling method (H. G. Luo, Y. H. Su, and
T. Xiang, Phys. Rev. B 77, 014529 (2008)). The scaling parameters have been
calculated and the compositional variation of {\Delta} has been determined. The
observed scaling behaviour for {\rho}(T) is interpreted as an indication of a
common mechanism which dominates the scattering of the charge carriers in
underdoped La-1111, in optimally and overdoped La-1111 and in underdoped
Sm-1111 compounds..",1012.4682v1
2010-12-23,Revised Phase Diagram for FeTe1-xSex system with less excess Fe atoms,"We observed bulk superconductivity in the FeTe1-xSex crystals with a low Se
concentration after the excess Fe atoms existing unavoidably in crystals
as-grown are partially removed by means of annealing in the air. A revised
magnetism and superconductivity phase diagram is obtained via resistivity and
magnetic susceptibility measurements for FeTe1-xSex system. It is found that
bulk superconductivity coexists with antiferromagnetic order in the crystals
with 0.05<x<0.20. The phase diagram is very similar to the case of the K-doping
or Co-doping BaFe2As2, as well as of SmFeAsO1-xFx iron-pnictide system, perhaps
indicating that all iron-based systems have a generic phase diagram, although
antiferromagnetic wave vector in the parent compounds of these systems is
remarkable different.",1012.5188v1
2010-12-26,"Electronic and magnetic structures of ternary iron selenides AFe$_2$Se$_2$ (A=K, Cs, or Tl)","By the first-principles electronic structure calculations, we find that the
ground state of ternary iron selenides AFe$_2$Se$_2$ (A=K, Cs, or Tl) is in a
bi-collinear antiferromagnetic order, in which the Fe local moments
($\sim2.8\mu_B$) align ferromagnetically along a diagonal direction and
antiferromagnetically along the other diagonal direction on the Fe-Fe square
lattice. This bi-collinear antiferromagnetic order results from the interplay
among the nearest, the next nearest, and the next next nearest neighbor
superexchange interactions, mediated by Se $4p$-orbitals.",1012.5536v1
2010-12-29,Absence of holelike Fermi surface in superconducting K0.8Fe1.7Se2 revealed by ARPES,"We have performed an angle-resolved photoemission spectroscopy study of the
new iron-based superconductor K0.8Fe1.7Se2 (Tc ~ 30 K). Clear band dispersion
is observed with the overall bandwidth renormalized by a factor of 2.5 compared
to our local density approximation calculations, indicating relatively strong
correlation effects. Only an electronlike band crosses the Fermi energy,
forming a nearly circular Fermi surface (FS) at M ({\pi}, 0). The holelike band
at {\Gamma} sinks ~ 90 meV below the Fermi energy, with an indirect band gap of
30 meV to the bottom of the electronlike band. The observed FS topology in this
superconductor favors ({\pi}, {\pi}) inter-FS scattering between the
electronlike FSs at the M points, in sharp contrast with other iron-based
superconductors which favor ({\pi}, 0) inter-FS scattering between holelike and
electronlike FSs.",1012.6017v1
2010-12-30,Possible Signs of Water and Differentiation in a Rocky Exoplanetary Body,"Spitzer observations reveal the presence of warm debris from a tidally
destroyed rocky and possibly icy planetary body orbiting the white dwarf GD 61.
Ultraviolet and optical spectroscopy of the metal-contaminated stellar
photosphere reveal traces of hydrogen, oxygen, magnesium, silicon, iron, and
calcium. The nominal ratios of these elements indicate an excess of oxygen
relative to that expected from rock-forming metal oxides, and thus it is
possible that water was accreted together with the terrestrial-like debris.
Iron is found to be deficient relative to magnesium and silicon, suggesting the
material may have originated as the outer layers of a differentiated parent
body, as is widely accepted for the Moon.",1101.0158v2
2011-01-03,Observation of a first order phase transition in fluid iron at pressures of 3 to 5 GPa,"Direct measurements of resistivity and caloric equation of state have been
performed for fluid iron at pressures of 2 to 12 GPa in a wide density range.
We found that the isochoric temperature coefficient of resistivity becomes
negative, and this is considered as an indication of the metal-to-nonmetal
transition, when density decreased by a factor of 3 to 4 compared to the normal
solid density. We detected also that isentropes plotted in the pressure -
specific volume plane have well-defined kinks localized on a convex curve with
a maximum at about 5 GPa. Such behavior of isentropes evidences about a first
order phase transition with a critical pressure one order of magnitude higher
than the predicted pressure of the liquid-vapor critical point. Arguments are
presented that the observed phase transition is most likely the liquid-vapor
transition rather than an extra first order transition in the fluid state. We
show that the gaseous nonmetallic phase represents dense plasma in the 1-2-th
state of ionization so that it is a plasma phase transition as well.",1101.0487v2
2011-01-03,Electronic Structure and Mott Localization in Iron Deficient TlFe$_{1.5}$Se$_2$ with Superstructures,"Electronic structure and magnetic properties for iron deficient
TlFe$_{2-x}$Se$_2$ compounds are studied by first-principles calculations. We
find that for the case of $x=0.5$ with a Fe-vacancy ordered orthorhombic
superstructure, the ground state exhibits a stripe-like antiferromagnetic
ordering and opens a sizable band gap if the short-ranged Coulomb interaction
of Fe-3d electrons is moderately strong, manifesting a possible Mott insulating
state. While increasing Fe-vacancies from the $x=0$ side, where the band
structure is similar to that of a heavily electron-doped FeSe system, the Mott
localization can be driven by kinetic energy reduction as evidenced by the band
narrowing effect. Implications of this scenario in the recent experiments on
TlFe$_{2-x}$Se$_2$ are discussed.",1101.0533v2
2011-01-03,Infrared spectrum and its implications for the electronic structure of the semiconducting iron selenide K$_{0.83}$Fe$_{1.53}$Se$_2$,"We report an infrared spectroscopy study on K$_{0.83}$Fe$_{1.53}$Se$_2$, a
semiconducting parent compound of the new iron-selenide system. The major
spectral features are found to be distinctly different from all other Fe-based
superconducting systems. Our measurement revealed two peculiar spectral
structures: a double peak structure between 4000-6000 cm$^{-1}$ and abundant
phonon modes much more than those expected for a 122 structure. We elaborate
that those features could be naturally explained from the blocked
antiferromagnetism due to the presence of Fe vacancy ordering as determined by
recent neutron diffraction experiments. The double peaks reflect the
coexistence of ferromagnetic and antiferromagnetic couplings between the
neighboring Fe sites.",1101.0572v3
2011-01-04,Electronic structure and magnetic properties of the graphene/Fe/Ni(111) intercalation-like system,"The electronic structure and magnetic properties of the graphene/Fe/Ni(111)
system were investigated via combination of the density functional theory
calculations and electron-spectroscopy methods. This system was prepared via
intercalation of thin Fe layer (1 ML) underneath graphene on Ni(111) and its
inert properties were verified by means of photoelectron spectroscopy.
Intercalation of iron in the space between graphene and Ni(111) changes
drastically the magnetic response from the graphene layer that is explained by
the formation of the highly spin-polarized $3d_{z^2}$ quantum-well state in the
thin iron layer.",1101.0771v1
2011-01-17,The upper critical field and its anisotropy in LiFeAs,"The upper critical field $\mu_0H_{c2}(T_c)$ of LiFeAs single crystals has
been determined by measuring the electrical resistivity using the facilities of
pulsed magnetic field at Los Alamos. We found that $\mu_0H_{c2}(T_c)$ of LiFeAs
shows a moderate anisotropy among the layered iron-based superconductors; its
anisotropic parameter $\gamma$ monotonically decreases with decreasing
temperature and approaches $\gamma\simeq 1.5$ as $T\rightarrow 0$. The upper
critical field reaches 15T ($H\parallel c$) and 24.2T ($H\parallel ab$) at
$T=$1.4K, which value is much smaller than other iron-based high $T_c$
superconductors. The temperature dependence of $\mu_0H_{c2}(T_c)$ can be
described by the Werthamer-Helfand-Hohenberg (WHH) method, showing orbitally
and (likely) spin-paramagnetically limited upper critical field for $H\parallel
c$ and $H\parallel ab$, respectively.",1101.3159v1
2011-01-19,77Se NMR Evidence of Strongly Coupled Superconductivity in K0.8Fe2-xSe2,"We report the 77Se NMR Knight shift and spin-lattice relaxation studies on
the superconducting state of the ternary iron selenide K0.8Fe2-xSe2 with Tc~30
K. Just below Tc, the Knight shift 77Kn shows an immediate drop, indicating a
singlet pairing. The spin-lattice relaxation rate 1/77T1 decreases rapidly in
the temperature range from TC to Tc/2, which can be fit with an isotropic gap
of \Delta~3.8\pm 0.5 k_BTc. The Hebel-Slichter coherence peak is not observed.
These data give bulk evidence for a strongly coupled superconductivity with
isotropic gaps in K0.8Fe2-xSe2, which is similar to other iron-based high
temperature superconductors. Below Tc/2, the spin-part of the Knight shift
levels off to a constant value (~0.09%), and the spin-lattice relaxation
follows a 1/T1 T^2 behavior, which are not well understood.",1101.3687v1
2011-02-01,Comprehensive study of the magnetic stars HD 5797 and HD 40711 with large chromium and iron overabundances,"We present the results of a comprehensive study of the chemically peculiar
stars HD 5797 and HD 40711. The stars have the same effective temperature, Teff
= 8900 K, and a similar chemical composition with large iron (+1.5 dex) and
chromium (+3 dex) overabundances compared to the Sun. The overabundance of
rare-earth elements typically reaches +3 dex. We have measured the magnetic
field of HD 5797. The longitudinal field component Be has been found to vary
sinusoidally between -100 and +1000 G with a period of 69 days. Our estimate of
the evolutionary status of the stars suggests that HD 5797 and HD 40711, old
objects with an age t \approx 5 \times 108 yr, are near the end of the core
hydrogen burning phase.",1102.0150v1
2011-02-02,Cation vacancy order in the K0.8+xFe1.6-ySe2 system: five-fold cell expansion accommodates 20% tetrahedral vacancies,"Ordering of the tetrahedral site vacancies in two crystals of refined
compositions K0.93(1)Fe1.52(1)Se2 and K0.862(3)Fe1.563(4)Se2 produces a
fivefold expansion of the parent ThCr2Si2 unit cell in the ab plane which can
accommodate 20% vacancies on a single site within the square FeSe layer. The
iron charge state is maintained close to +2 by coupling of the level of alkali
metal and iron vacancies, producing a potential doping mechanism which can
operate at both average and local structure levels.",1102.0488v3
2011-02-10,Impact of Valence States on Superconductivity of Oxygen Incorporated Iron Telluride and Iron Selenide Films,"We report on the local electronic structure of oxygen incorporated FeTe and
FeSe films and how this relates to superconductivity observed in these films.
In the case of FeTe, intially grown films are measured to be
non-superconducting, but become superconducting following oxygen incorporation.
In FeSe the opposite happens, initially grown films are measured to be
superconducting, but experience a quenching of superconductivity following
oxygen incorporation. Total Fluorescence Yield (TFY) X-ray absorption
experiments show that oxygen incorporation changes the initial Fe valence state
in both the initially grown FeTe and FeSe films to mainly Fe3+ in the oxygen
incorporated films. In contrast we observe that while Te moves to a mixed
Te0/Te4+ valence state, the Se always remains Se0. This work highlights how
different responses of the electronic structure by the respective chalcogenides
to oxidation could be related to the mechanisms which are inducing
superconductivity in FeTe and quenching superconductivity in FeSe.",1102.2155v1
2011-02-15,Magnetic and superconducting instabilities in a hybrid model of itinerant/localized electrons for iron pnictides,"We study a unified mechanism for spin-density-wave (SDW) and
superconductivity in a minimal model, in which itinerant electrons and local
moments coexist as previously proposed for the iron pnictides [EPL, 88, 17010
(2009)]. The phase diagram obtained at the mean field level is in qualitative
agreement with the experiment, which shows how the magnetic and superconducting
(SC) instabilities are driven by the critial coupling between the
itinerant/localized electrons. The spin and charge response functions at the
random phase approximation (RPA) level further characterize the dynamical
evolution of the system. In particular, the dynamic spin susceptibility
displays a Goldstone mode in the SDW phase, which evolves into a gapped
resonance-like mode in the superconducting phase. The latter persists all the
way into the normal state above Tc, where a strong scattering between the
itinerant electrons and local moments is restored, as an essential feature of
the model.",1102.3200v2
2011-02-17,Superconductivity tuned by the iron vacancy order in K$_{\bf x}$Fe$_{\bf 2-y}$Se$_2$,"Combining in-depth neutron diffraction and systematic bulk studies, we
discover that the $\sqrt{5}\times\sqrt{5}$ Fe vacancy order with its associated
block antiferromagnetic order is the ground state, with varying occupancy ratio
of the iron 16i and vacancy 4d sites, across the phase-diagram of K$_{\bf
x}$Fe$_{\bf 2-y}$Se$_2$. The orthorhombic order with one of the four Fe sites
vacant appears only at intermediate temperature as a competing phase. The
material experiences an insulator to metal crossover when the
$\sqrt{5}\times\sqrt{5}$ order has highly developed. Superconductivity occurs
in such a metallic phase.",1102.3674v2
2011-02-21,"Structural, electronic properties and Fermi surface of ThCr2Si2-type tetragonal KFe2S2, KFe2Se2, and KFe2Te2 phases as parent systems of new ternary iron-chalcogenide superconductors","First principles FLAPW-GGA method was used for the comparative study of the
structural and electronic properties of three related tetragonal ThCr2Si2-type
phases KFe2Ch2, where Ch are S, Se, and Te. The main trends in electronic
bands, densities of states and Fermi surfaces for AFe2Ch2 are analyzed in
relation to their structural parameters. We found that at the anion
replacements (S<->Se<->Te) any critical changes in electronic structure of
KFe2Ch2 phases are absent. On the other hand, our analysis of structural and
electronic parameters for hypothetical KFe2Te2 allows to assume that this
system may be proposed as perspective parent phase for search of new
iron-chalcogenide superconducting materials.",1102.4173v2
2011-02-27,Multiorbital Spin Susceptibility in a Magnetically Ordered State - Orbital versus Excitonic Spin Density Wave Scenario,"We present a general theory of multiorbital spin waves in magnetically
ordered metallic systems. Motivated by the itinerant magnetism of iron-based
superconductors, we compare the magnetic excitations for two different
scenarios: when the magnetic order either sets in on the on-site orbital level;
or when it appears as an electron-hole pairing between different bands of
electron and hole character. As an example we treat the two-orbital model for
iron-based superconductors. For small magnetic moments the spin excitations
look similar in both scenarios. Going to larger interactions and larger
magnetic moments, the difference between both scenarios becomes striking. While
in the excitonic scenario the spin waves form a closed structure over the
entire Brillouin zone and the particle-hole continuum is gapped, the spin
excitations in the orbital scenario can be treated as spin waves only in a
close vicinity to the ordering momenta. The origin of this is a gapless
electronic structure with Dirac cones which is a source of large damping. We
analyze our results in connection with recent neutron scattering measurements
and show that certain features of the orbital scenario with multiple order
parameters can be observed experimentally.",1102.5532v1
2011-03-01,57-Fe Mossbauer study of magnetic ordering in superconducting K_0.85Fe_1.83Se_2.09 single crystals,"The magnetic ordering of superconducting single crystals of
K_0.85Fe_1.83Se_2.09 has been studied between 10K and 550K using 57-Fe
Mossbauer spectroscopy. Despite being superconducting below T_sc ~30K, the iron
sublattice in K_0.85Fe_1.83Se_2.09 clearly exhibits magnetic order from well
below T_sc to its N\'eel temperature of T_N = 532 +/- 2K. The iron moments are
ordered perpendicular to the single crystal plates, i.e. parallel to the
crystal c-axis. The order collapses rapidly above 500K and the accompanying
growth of a paramagnetic component suggests that the magnetic transition may be
first order, which may explain the unusual temperature dependence reported in
recent neutron diffraction studies.",1103.0059v1
2011-03-01,Spin excitations in K$_{0.84}$Fe$_{1.99}$Se$_2$ superconductor as studied by Mössbauer spectroscopy,"M\""ossbauer spectroscopy was used to probe the site specific information of
the $K_{0.84}Fe_{1.99}Se_2$ superconductor. Possibility of coexistence of
superconductivity and magnetism is discussed. A spin excitation gap, $\Delta E
\approx$5\,meV, is observed by analyzing the temperature dependence of the
hyperfine magnetic field (HMF) at the iron site within the spin wave theory.
Using a simple model suggested in the literature, the temperature dependence of
the HMF is well reproduced, suggesting that, below room temperature, the
iron-selenide superconductors can be regarded as ferromagnetically coupled spin
blocks that interact with each other antiferromagnetically to form the observed
checkerboard-like magnetic structure.",1103.0098v5
2011-03-03,Determination of the pairing state in iron-based superconductors through neutron scattering,"We calculate the spin susceptibility in the s_{+-} and s_{++} superconducting
states of the iron pnictides using the effective five orbital model and
considering the quasiparticle damping. For the experimentally evaluated
magnitude of the quasiparticle damping and the superconducting gap, the results
at the wave vector ~ (pi,0) show that the s_{+-} state is more consistent with
the neutron scattering experiments, while for larger quasiparticle damping and
the superconducting gap, the s_{++} state can be more consistent. To
distinguish between two cases that reproduce the experiments at the wave vector
~ (pi,0), we propose to investigate experimentally the wave vector ~ (pi,pi).",1103.0586v2
2011-03-06,Hydrogen in layered iron arsenide: indirect electron doping to induce superconductivity,"Utilizing the high stability of calcium and rare earth hydrides, CaFeAsF1-xHx
(x = 0.0-1.0) and SmFeAsO1-xHx (x = 0.0-0.47) have been first synthesized using
high pressure to form hydrogen-substituted 1111 type iron-arsenide
superconductors. Neutron diffraction and density functional calculations have
demonstrated that the hydrogens are incorporated as H- ions occupying F- sites
in the blocking layer of CaFeAsF. The resulting CaFeAsF1-xHx is
non-superconducting, whereas SmFeAsO1-xHx is a superconductor, with an optimal
Tc = 55 K at x 0.2. It was found that up to 40% of the O2- ions can be replaced
by H- ions, with electrons being supplied into the FeAs-layer to maintain
neutrality (O2- = H-+ e-). When x exceeded 0.2, Tc was reduced corresponding to
an electron over-doped region.",1103.1177v3
2011-03-09,Phase diagram and a possible unified description of intercalated iron selenide superconductors,"We propose a theoretical description of the phase diagram and physical
properties in A2Fe4Se5-type (A=K, Tl) compounds based on a coexistent local
moment and itinerant electron picture. Using neutron scattering and ARPES
measurements to fix the general structure of the local moment and itinerant
Fermi pockets, we find a superconducting (SC) regime with s-wave pairing at the
M pockets and an incipient sign-change s-wave near the Gamma point, which is
adjacent to an insulating state at low doping and a charge-density-wave (CDW)
state at high doping. The uniform susceptibility and resistivity are found to
be consistent with the experiment. The main distinction with iron pnictide
superconductors is also discussed.",1103.1902v3
2011-03-15,Two-band model of Raman scattering on iron pnictide superconductors,"Based on a two-band model, we study the electronic Raman scattering intensity
in both normal and superconducting states of iron-pnictide superconductors. For
the normal state, due to the match or mismatch of the symmetries between band
hybridization and Raman vertex, it is predicted that overall $B_{1g}$ Raman
intensity should be much weaker than that of the $B_{2g}$ channel. Moreover, in
the non-resonant regime, there should exhibit a interband excitation peak at
frequency $\omega\simeq 7.3 t_1 (6.8t_1)$ in the $B_{1g}$ ($B_{2g}$) channel.
For the superconducting state, it is shown that $\beta$-band contributes most
to the $B_{2g}$ Raman intensity as a result of multiple effects of Raman
vertex, gap symmetry, and Fermi surface topology. Both extended $s$- and
$d_{xy}$-wave pairings in the unfolded BZ can give a good description to the
reported $B_{2g}$ Raman data [Muschler {\em et al.}, Phys. Rev. B. {\bf 80},
180510 (2009).], while $d_{x^2-y^2}$-wave pairing in the unfolded BZ seems to
be ruled out.",1103.3191v1
2011-03-16,Enhancement of the critical temperature in iron-pnictide superconductors by finite size effects,"Recent experiments have shown that, in agreement with previous theoretical
predictions, superconductivity in metallic nanostructures can be enhanced with
respect to the bulk limit. Motivated by these results we study finite size
effects (FSE) in an iron-pnictide superconductor. For realistic values of the
bulk critical temperature Tc ~ 20-50K, we find that, in the nanoscale region L
~ 10 nm, Tc(L) has a complicated oscillating pattern as a function of the
system size L. A substantial enhancement of Tc with respect to the bulk limit
is observed for different boundary conditions, geometries and two microscopic
models of superconductivity. Thermal fluctuations, which break long range
order, are still small in this region. Finally we show that the differential
conductance, an experimental observable, is also very sensitive to FSE.",1103.3290v1
2011-03-16,High impact of spin-nematic order on the lattice domains in thin films of iron-based superconductors,"The spin-nematic scenario proposed for the structural instability of
iron-based superconductors is studied theoretically within a Ginzburg-Landau
approach in epitaxial thin films. The transition temperature and the domains
that appear due the interface with the substrate are computed analytically by
following a variatonal procedure. It is predicted a cross-over thickness $l_*$
that separates the Kittel regime, in which the size of the domains goes as the
square root of the film thickness $l$, from a new ultrathin regime in which the
system tends to reach the single-domain state as $l \to 0$. The experimental
observation of this cross-over is therefore proposed as a direct probe of spin
nematiciy.",1103.3302v1
2011-04-12,"Synthesis, Structure and Magnetic Properties of New Layered Iron-Oxychalcogenide Na2Fe2OSe2","A new layered iron-oxychalcogenide Na2Fe2OSe2 has been synthesized and
structurally characterized by powder X-ray diffraction. The structure is formed
by alternate stacking of the newly discovered [Fe2OSe2] blocks and double
layers of Na. Conductivity study shows that Na2Fe2OSe2 is a semiconductor with
activation energy of 0.26 eV. Magnetic susceptibility and heat capacity
measurements reveal an antiferromagnetic phase transition occurs at TN=73 K. A
broad maximum of magnetic susceptibility and a slow decay of the specific heat
above TN, arises as a result of two-dimensional short-range spin correlation.",1104.2176v2
2011-04-21,Importance of electronic correlations for structural and magnetic properties of the iron pnictide superconductor LaFeAsO,"We present calculations of structural and magnetic properties of the
iron-pnictide superconductor LaFeAsO including electron-electron correlations.
For this purpose we apply a fully charge self-consistent combination of
Density-Functional Theory with the Dynamical Mean-Field theory, allowing for
the calculation of total energies. We find that the inclusion of correlation
effects gives a good agreement of the Arsenic z position with experimental data
even in the paramagnetic (high-temperature) phase. Going to low temperatures,
we study the formation of the ordered moment in the striped spin-density-wave
phase, yielding an ordered moment of about 0.60, again in good agreement with
experiments. This shows that the inclusion of correlation effects improves both
structural and magnetic properties of LaFeAsO at the same time.",1104.4361v2
2011-04-23,Orbital density wave induced by electron-lattice coupling in orthorhombic iron pnictides,"In this paper we explore the magnetic and orbital properties closely related
to a tetragonal-orthorhombic structural phase transition in iron pnictides
based on both two- and five-orbital Hubbard models. The electron-lattice
coupling, which interplays with electronic interaction, is self-consistently
treated. Our results reveal that the orbital polarization stabilizes the spin
density wave (SDW) order in both tetragonal and orthorhombic phases. However,
the ferro-orbital density wave (F-ODW) only occurs in the orthorhombic phase
rather than in the tetragonal one. Magnetic moments of Fe are small in the
intermediate Coulomb interaction region for the striped antiferromangnetic
phase in the realistic five orbital model. The anisotropic Fermi surface in the
SDW/ODW orthorhombic phase is well in agreement with the recent angle-resolved
photoemission spectroscopy experiments. These results suggest a scenario that
the magnetic phase transition is driven by the ODW order mainly arising from
the electron-lattice coupling.",1104.4575v1
2011-05-06,Physical State of the Deep Interior of the CoRoT-7b Exoplanet,"The present study takes the CoRoT-7b exoplanet as an analogue for massive
terrestrial planets to investigate conditions, under which intrinsic magnetic
fields could be sustained in liquid cores. We examine the effect of
depth-dependent transport parameters (e.g., activation volume of mantle rock)
on a planet's thermal structure and the related heat flux across the core
mantle boundary. For terrestrial planets more massive than the Earth, our
calculations suggest that a substantial part of the lowermost mantle is in a
sluggish convective regime, primarily due to pressure effects on viscosity.
Hence, we find substantially higher core temperatures than previously reported
from parameterized convection models. We also discuss the effect of melting
point depression in the presence of impurities (e.g., sulfur) in iron-rich
cores and compare corresponding melting relations to the calculated thermal
structure. Since impurity effects become less important at the elevated
pressure and temperature conditions prevalent in the deep interior of CoRoT-7b,
iron-rich cores are likely solid, implying that a self-sustained magnetic field
would be absent.",1105.1271v1
2011-05-19,Anisotropic in-plane resistivity in the nematic phase of the iron pnictides,"We show that the interference between scattering by impurities and by
critical spin fluctuations gives rise to anisotropic transport in the
Ising-nematic state of the iron pnictides. The effect is closely related to the
non-Fermi liquid behavior of the resistivity near an antiferromagnetic quantum
critical point. Our theory not only explains the observed sign of the
resistivity anisotropy $\Delta\rho$ in electron doped systems, but also
predicts a sign change of $\Delta\rho$ upon sufficient hole doping.
Furthermore, our model naturally addresses the changes in $\Delta\rho$ upon
sample annealing and alkaline-earth substitution.",1105.3906v2
2011-05-23,Orbitally and Magnetically Induced Anisotropy in Iron-based Superconductors,"Recent experimental developments in the iron pnictides have unambiguously
demonstrated the existence of in-plane electronic anisotropy in the absence of
the long-range magnetic order. Such anisotropy can arise from orbital ordering,
which is described by an energy splitting between the two otherwise degenerate
$d_{xz}$ and $d_{yz}$ orbitals. By including this phenomenological orbital
order into a five-orbital Hubbard model, we obtain the mean-field solutions
where the magnetic order is determined self-consistently. Despite sensitivity
of the resulting states to the input parameters, we find that a weak orbital
order that places the $d_{yz}$ orbital slightly higher in energy than the
$d_{xz}$ orbital, combined with intermediate on-site interactions, produces
band dispersions that are compatible with the photoemission results. In this
regime, the stripe antiferromagnetic order is further stabilized and the
resistivity displays the observed anisotropy. We also calculate the optical
conductivity and show that it agrees with the temperature evolution of the
anisotropy seen experimentally.",1105.4630v3
2011-05-24,Complete renormalization group calculation up to two-loop order of an effective two-band model for iron-based superconductors,"We perform a renormalization group (RG) study up to two-loop order of an
effective low-energy two-band model to describe some of the recently discovered
iron-based superconductors. Our starting point is the itinerant electronic
model proposed by Chubukov \emph{et al.} [Phys. Rev. B \textbf{78}, 134512
(2008)], which displays two small, almost nested Fermi pockets with one hole
pocket centered at $(0,0)$ and one electron pocket centered at $\mathbf{Q} =
(\pi,\pi)$ in the folded Brillouin zone. We then proceed to implement a
complete two-loop RG calculation for this model of four-point vertex
corrections, quasiparticle weight and several order-parameter susceptibilities
in order to evaluate the robustness of one-loop RG results available in the
literature with respect to including self-energy effects and higher-order
quantum fluctuations.",1105.4897v2
2011-05-29,Ab initio parametrised model of strain-dependent solubility of H in alpha-iron,"The calculated effects of interstitial hydrogen on the elastic properties of
alpha-iron from our earlier work are used to describe the H interactions with
homogeneous strain fields using ab initio methods. In particular we calculate
the H solublility in Fe subject to hydrostatic, uniaxial, and shear strain. For
comparison, these interactions are parametrised successfully using a simple
model with parameters entirely derived from ab initio methods. The results are
used to predict the solubility of H in spatially-varying elastic strain fields,
representative of realistic dislocations outside their core. We find a strong
directional dependence of the H-dislocation interaction, leading to strong
attraction of H by the axial strain components of edge dislocations and by
screw dislocations oriented along the critical < 111 > slip direction. We
further find a H concentration enhancement around dislocation cores, consistent
with experimental observations.",1105.5758v3
2011-06-08,Coexistence of Dirac-Cone States and Superconductivity in Iron Pnictide Ba(Fe$_{1-x}$Ru$_x$As)$_2$,"The Ru doping effect on the Dirac cone states is investigated in iron
pnictide superconductors Ba(Fe$_{1-x}$Ru$_x$As)$_2$ using the transverse
magnetoresistance (MR) measurements as a function of temperature. The linear
development of MR against magnetic field $B$ is observed for $x$ = 0 - 0.244 at
low temperatures below the antiferromagnetic transition. The $B$-linear MR is
interpreted in terms of the quantum limit of the Dirac cone states by using the
model proposed by Abrikosov. An intriguing evidence is shown that the Dirac
cone state persists on the electronic phase diagram where the
antiferromagnetism and the superconductivity coexist.",1106.1496v2
2011-06-08,Superconductivity in Iron Compounds,"Kamihara and coworkers' report of superconductivity at Tc = 26 K in
fluorine-doped LaFeAsO inspired a worldwide effort to understand the nature of
the superconductivity in this new class of compounds. These iron pnictide and
chalcogenide (FePn/Ch) superconductors have Fe electrons at the Fermi surface,
plus an unusual Fermiology that can change rapidly with doping, which lead to
normal and superconducting state properties very different from those in
standard electron-phonon coupled 'conventional' superconductors. Clearly
superconductivity and magnetism/magnetic fluctuations are intimately related in
the FePn/Ch - and even coexist in some. Open questions, including the
superconducting nodal structure in a number of compounds, abound and are often
dependent on improved sample quality for their solution. With Tc values up to
56 K, the six distinct Fe-containing superconducting structures exhibit complex
but often comparable behaviors. The search for correlations and explanations in
this fascinating field of research would benefit from an organization of the
large, seemingly disparate data set. This review attempts to provide an
overview, using numerous references, with a focus on the materials and their
superconductivity.",1106.1618v1
2011-06-13,"Comment on arXiv:1105.6233 entitled ""Neutron-Inelastic-Scattering Peak by Dissipationless Mechanism in the s++-wave State in Iron-based Superconductors"" by S. Onari and H. Kontani","Recently, Onari and Kontani submitted a paper [arXiv:1105.6233] which
criticizes our recent theoretical study [arXiv:1103.0586] on the neutron
scattering experiment as a probe for determining the superconducting gap in the
iron pnictides. In their paper, Onari and Kontani have developed a formalism in
which the imaginary part of the dynamical spin susceptibility
(Im$\chi_s(\Vec{q},\omega)$) in the superconducting state can be more
accurately calculated especially in the $\omega<2\Delta$ regime, where $\Delta$
is the superconducting gap. In section IIIC of their paper, they mention that
the conclusions of our paper are ""incorrect based on inaccurate numerical
calculation"". In the present Comment, we show that this in fact is not correct.",1106.2376v1
2011-06-13,Temperature dependent local structure of NdFeAsO1-xFx system using arsenic K-edge extended x-ray absorption fine structure,"Local structure of NdFeAsO$_{1-x}$F$_{x}$ ($x$=0.0, 0.05, 0.15 and 0.18) high
temperature iron pnictide superconductor system is studied using arsenic
$K$-edge extended x-ray absorption fine structure measurements as a function of
temperature. Fe-As bondlength shows only a weak temperature and F-substitution
dependence, consistent with the strong covalent nature of this bond. The
temperature dependence of the mean-square relative-displacements of the Fe-As
bondlength are well described by the correlated-Einstein model for all the
samples, but with different Einstein-temperatures for the superconducting and
non-superconducting samples. The results indicate distinct local Fe-As lattice
dynamics in the superconducting and non-superconducting iron-pnictide systems.",1106.2567v1
2011-06-14,Crossover between two different magnetization reversal modes in arrays of iron oxide nanotubes,"The magnetization reversal in ordered arrays of iron oxide nanotubes of 50 nm
outer diameter grown by atomic layer deposition is investigated theoretically
as a function of the tube wall thickness, $d_{w}$. In thin tubes ($d_{w}<13$
nm) the reversal of magnetization is achieved by the propagation of a vortex
domain boundary, while in thick tubes ($d_{w}>13$ nm) the reversal is driven by
the propagation of a transverse domain boundary. Magnetostatic interactions
between the tubes are responsible for a decrease of the coercive field in the
array. Our calculations are in agreement with recently reported experimental
results. We predict that the crossover between the vortex and transverse modes
of magnetization reversal is a general phenomenon on the length scale
considered.",1106.2833v1
2011-06-17,Influence of electronic correlations on orbital polarizations in the parent and doped iron pnictides,"Orbital polarization and electronic correlation are two essential aspects in
understanding the normal state and superconducting properties of multiorbital
FeAs-based superconductors. In this Letter, we present a systematical study on
the orbital polarization of iron pnictides from weak to strong Coulomb
correlations within the KRSB approach. The magnetic phase diagram of the
two-orbital model for LaFeAsO clearly shows that the striped antiferromagnetic
metallic phase with considerable orbital polarization exists over a wide doping
range. The reversal of the orbital polarization occurs in the intermediate
correlation regime.A small crystal field splitting enhances the orbital density
wave order.",1106.3487v1
2011-06-22,Extended Hubbard model of superconductivity driven by charge fluctuations in iron-pnictides,"We present a scenario for iron-pnictide superconductivity mediated by charge
fluctuations that are strongly enhanced by Fe-As intersite electronic
interactions. Deriving an eight-band extended Hubbard model including Fe 3$d$
and As 4$p$ orbitals for the LaOFeAs family, we show that charge fluctuations
induced by $p$-$d$ charge transfer and As orbital polarization interactions in
the Fe-pnictogen structure peak at wavevectors $(0, 0)$, and ($\pi$, 0) and
($\pi$, $\pi$) respectively. Intraorbital spin-singlet pairing attraction
develops at these wavevectors and the solution of the linearized gap equation
shows robust s-wave superconductivity with both $s_\pm$ and $s_{++}$ gap
functions.",1106.4552v2
2011-07-01,Spin Hall effect in iron-based superconductors: A Dirac-point effect,"We have theoretically explored the intrinsic spin Hall effect (SHE) in the
iron-based superconductor family with a variety of materials. The study is
motivated by an observation that, in addition to an appreciable spin-orbit
coupling in the Fe 3d states, a character of the band structure in which Dirac
cones appear below the Fermi energy may play a crucial role in producing a
large SHE. Our investigation does indeed predict a substantially large spin
Hall conductivity in the heavily hole-doped regime such as KFe$_2$As$_2$. The
magnitude of the SHE has turned out to be comparable with that for Pt despite a
relatively small spin-orbit coupling, which we identify to come from a huge
contribution from the gap opening induced by the spin-orbit coupling at the
Dirac point, which can become close to the Fermi energy for the heavy hole
doping.",1107.0122v2
2011-07-05,Isotropic superconducting gaps with enhanced pairing on electron Fermi surfaces in FeTe0.55Se0.45,"The momentum distribution of the energy gap opening at the Fermi level of
superconductors is a direct fingerprint of the pairing mechanism. While the
phase diagram of the iron-based superconductors promotes antiferromagnetic
fluctuations as a natural candidate for electron pairing, the precise origin of
the interaction is highly debated. We used angle-resolved photoemission
spectroscopy to reveal directly the momentum distribution of the
superconducting gap in FeTe1-xSex, which has the simplest structure of all
iron-based superconductors. We found isotropic superconducting gaps on all
Fermi surfaces whose sizes can be fitted by a single gap function derived from
a strong coupling approach, strongly suggesting local antiferromagnetic
exchange interactions as the pairing origin.",1107.0985v1
2011-07-08,Magnetic Resonant Mode in the Low-Energy Spin-Excitation Spectrum of Superconducting Rb2Fe4Se5 Single Crystals,"We have studied the low-energy spin-excitation spectrum of the
single-crystalline Rb2Fe4Se5 superconductor (Tc = 32 K) by means of inelastic
neutron scattering. In the superconducting state, we observe a magnetic
resonant mode centered at an energy of 14 meV and at the (0.5 0.25 0.5) wave
vector (unfolded Fe-sublattice notation), which differs from the ones
characterizing magnetic resonant modes in other iron-based superconductors. Our
finding suggests that the 245-iron-selenides are unconventional superconductors
with a sign-changing order parameter, in which bulk superconductivity coexists
with the sqrt(5) x sqrt(5) magnetic superstructure. The estimated ratios of the
resonance energy to Tc and the superconducting gap indicate moderate pairing
strength in this compound, similar to that in optimally doped 1111- and
122-pnictides.",1107.1703v2
2011-07-12,"An aluminum/calcium-rich, iron-poor, white dwarf star: evidence for an extrasolar planetary lithosphere?","The presence of elements heavier than helium in white dwarf atmospheres is
often a signpost for the existence of rocky objects that currently or
previously orbited these stars. We have measured the abundances of various
elements in the hydrogen-atmosphere white dwarfs G149-28 and NLTT 43806. In
comparison with other white dwarfs with atmospheres polluted by heavy elements,
NLTT 43806 is substantially enriched in aluminum but relatively poor in iron.
We compare the relative abundances of Al and eight other heavy elements seen in
NLTT 43806 with the elemental composition of bulk Earth, with simulated
extrasolar rocky planets, with solar system meteorites, with the atmospheric
compositions of other polluted white dwarfs, and with the outer layers of the
Moon and Earth. Best agreement is found with a model that involves accretion of
a mixture of terrestrial crust and upper mantle material onto NLTT 43806. The
implication is that NLTT 43806 is orbited by a differentiated rocky planet,
perhaps quite similar to Earth, that has suffered a collision that stripped
away some of its outer layers.",1107.2167v1
2011-07-12,Magnetic interactions in iron superconductors studied with a five-orbital model within the Hartree-Fock and Heisenberg approximations,"We have analyzed the magnetic interactions of a five orbital model for iron
superconductors treated both within Hartree-Fock and Heisenberg approximations.
We have found that the exchange constants depend non-trivially on the Fe-As-Fe
angle and on the charge and orbital filling. Within the localized picture,
columnar ordering is found for intermediate Hund's coupling J_H. At smaller
J_H, an unusual orbital reorganization stabilizes checkerboard ordering.
Ferromagnetism appears at large J_H. Ferromagnetic correlations are enhanced
with electron doping while large hole doping stabilizes checkerboard
antiferromagnetism, explaining the change in magnetic interactions upon
substitution of Fe by Co or Mn. For intermediate and large values of U,
Hartree-Fock shows similar results as strong coupling though with a double
stripe phase instead of ferromagnetism. Itinerancy enhances the stability of
the columnar ordering. Comparison of the two approaches reveals a metallic
region of the phase diagram where strong coupling physics is determinant.",1107.2279v2
2011-07-22,Nodeless vs nodal order parameters in LiFeAs and LiFeP superconductors,"High-precision measurements of magnetic penetration depth $\lambda$ in clean
single crystals of LiFeAs and LiFeP superconductors reveal contrasting
low-energy quasiparticle excitations. In LiFeAs the low-temperature
$\lambda(T)$ shows a flat dependence indicative of a fully gapped state, which
is consistent with previous studies. In contrast, LiFeP exhibits a $T$-linear
dependence of superfluid density $\propto \lambda^{-2}$, indicating a nodal
superconducting order parameter. A systematic comparison of quasiparticle
excitations in the 1111, 122, and 111 families of iron-pnictide superconductors
implies that the nodal state is induced when the pnictogen height from the iron
plane decreases below a threshold value of $\sim 1.33$\,\AA.",1107.4505v1
2011-07-29,Hyperfine Field and Hyperfine Anomalies of Copper Impurities in Iron,"A new value for the hyperfine magnetic field of copper impurities in iron is
obtained by combining resonance frequencies from experiments involving
{\beta}-NMR on oriented nuclei on 59-Cu, 69-Cu, and 71-Cu with magnetic moment
values from collinear laser spectroscopy measurements on these isotopes. The
resulting value, i.e., Bhf(CuFe) = -21.794(10) T, is in agreement with the
value adopted until now but is an order of magnitude more precise. It is
consistent with predictions from ab initio calculations. Comparing the
hyperfine field values obtained for the individual isotopes, the hyperfine
anomalies in Fe were determined to be 59{\Delta}69=0.15(9)% and
71{\Delta}69=0.07(11)%.",1107.5999v1
2011-07-29,Superconductivity at 38 K in Iron-Based Compound with Platinum-Arsenide Layers Ca10(Pt4As8)(Fe2-xPtxAs2)5,"We report superconductivity in novel iron-based compounds
Ca10(PtnAs8)(Fe2-xPtxAs2)5 with n = 3 and 4. Both compounds crystallize in
triclinic structures (space group P-1), in which Fe2As2 layers alternate with
PtnAs8 spacer layers. Superconductivity with a transition temperature of 38 K
is observed in the n = 4 compound with a Pt content of x ~ 0.36 in the Fe2As2
layers. The compound with n = 3 exhibits superconductivity at 13 K.",1108.0029v2
2011-08-02,Electronic structure and chemical bonding in novel tetragonal phase Ca10(Pt4As8)(Fe2As2)5 as a parent material for the new family of high-TC iron-pnictide superconductors,"By means of first-principles calculations, the electronic structure and
chemical bonding for the recently discovered tetragonal (s.g. P4/n; # 85)
superconducting (Tc ~ 25K) phase Ca10(Pt4As8)(Fe2As2)5 have been examined in
details, and the optimized structural parameters, electronic bands, densities
of states, and inter-atomic bonding picture were evaluated and analyzed in
comparison with related layered iron-based superconducting materials. We have
shown that (i) Ca10(Pt4As8)(Fe2As2)5 is metallic-like, and the electronic bands
in the window around the Fermi level are formed mainly by the Fe 3d states of
(Fe2As2)5 blocks; (ii) the (Pt4As8) blocks will behave as semi-metals with very
low densities of states at the Fermi level; (iii) the near-Fermi bands adopt a
""mixed"" character: simultaneously with quasi-flat bands, a series of
high-dispersive bands which intersect the Fermi level was found; (iv) the of
chemical bonding in Ca10(Pt4As8)(Fe2As2)5 is very complicated and includes an
anisotropic mixture of covalent, metallic, and ionic inter-atomic and
inter-block interactions.",1108.0495v2
2011-08-02,Fermi-Suface Evolution by Transition-metal Substitution in the Iron-based Superconductor LaFeAsO,"We study how Co- and Ni-substitution affect the electronic structure of the
iron-based superconductor, LaFeAsO. We perform {\it ab initio} supercell
calculations and unfold the first Brillouin zone (BZ) to calculate the spectral
function in the BZ for the normal cell. The charge density distribution in real
space shows that doped extra electrons are trapped around Co (Ni) atom. This
seems to mean that Co(Ni)-substitution does not work as carrier doping.
However, the present momentum-space analysis indicates that the Fermi-surface
volume indeed expands by substitutions, which can be well described by the
rigid-band shift. By taking into account this effective doping, we discuss
whether the sign-reversing s-wave ($s_{\pm}$-wave) scenario is compatible with
experiments.",1108.0585v2
2011-08-04,The broad iron Kalpha line of Cygnus X-1 as seen by XMM-Newton in the EPIC-pn modified timing mode,"We present the analysis of the broadened, flourescent iron Kalpha line in
simultaneous XMM-Newton and RXTE data from the black hole Cygnus X-1. The
XMM-Newton data were taken in a modified version of the timing mode of the
EPIC-pn camera. In this mode the lower energy threshold of the instrument is
increased to 2.8 keV to avoid telemetry drop outs due to the brightness of the
source, while at the same time preserving the signal-to-noise ratio in the Fe
Kalpha band. We find that the best-fit spectrum consists of the sum of an
exponentially cut off power-law and relativistically smeared, ionized
reflection. The shape of the broadened Fe Kalpha feature is due to strong
Compton broadening combined with relativistic broadening. Assuming a standard,
thin accretion disk, the black hole is close to rotating maximally.",1108.1157v1
2011-08-11,Effects of the vortices and impurities on the nuclear spin relaxation rate in iron-based superconductors,"The effects of magnetic vortices and nonmagnetic impurities on the low energy
quasiparticle excitations and the spin-lattice relaxation rate are examined in
the iron-based superconductors for the $s_{\pm}$-, $s$- and d-wave pairing
symmetries, respectively. The main effect of the vortices is to enhance the
quasiparticle excitations and the spin-lattice relaxation rate for all
symmetries, and leads to a $T^{3}$ dependence of the relaxation rate followed
by a nearly $T$-linearity at lower temperatures. This enhancement can only be
seen for the $s_{\pm}$- and d-wave symmetries in the presence of nonmagnetic
impurities. These results suggest that the $s_{\pm}$-wave and d-wave pairing
states behave similarly in response to the magnetic field and nonmagnetic
impurities, therefore it may be impossible to distinguish them on the basis of
the measurements of spin-lattice relaxation rates when a magnetic field and/or
impurity scatterings are present.",1108.2312v1
2011-08-10,The role of the coating and aggregation state in the interactions between iron oxide nanoparticles and 3T3 fibroblasts,"Recent nanotoxicity studies revealed that the physico-chemical
characteristics of engineered nanomaterials play an important role in the
interactions with living cells. Here, we report on the toxicity and uptake of
the iron oxide sub-10 nm nanoparticles by NIH/3T3 mouse fibroblasts. Coating
strategies include low-molecular weight ligands (citric acid) and polymers
(poly(acrylic acid), MW = 2000 g mol-1). We find that most particles were
biocompatible, as exposed cells remained 100% viable relative to controls. The
strong uptake shown by the citrate-coated particles is related to the
destabilization of the dispersions in the cell culture medium and their
sedimentation down to the cell membranes.",1108.2395v1
2011-08-25,Fabrication of magnetic clusters and rods using electrostatic co-assembly,"Using a novel protocol for mixing oppositely charged colloids and
macromolecules, magnetic clusters and rods are fabricated using 10 nm-iron
oxide nanoparticles and polymers. Here, we show that as the dispersions undergo
the so-called desalting transition, spherical clusters in the range 100 nm - 1
{\mu}m form spontaneously upon dialysis or dilution. With a magnetic field
applied during the dialysis, a one-dimensional growth of the aggregates is
initiated, resulting in the formation of 1 - 100 {\mu}m rods of average
diameter 200 nm. In this paper, we demonstrate that the nanostructured rods
have inherited the properties of the iron oxide particles, namely to be
superparamagnetic. We also discuss the dependence of the magnetic properties as
a function of the nanoparticle diameter.",1108.5023v1
2011-08-25,Magnetic Reconnection in Non-Equilibrium Ionization Plasma,"We have studied the effect of time-dependent ionization and recombination
processes on magnetic reconnection in the solar corona. Petschek-type steady
reconnection, in which model the magnetic energy is mainly converted at the
slow-mode shocks, was assumed. We carried out the time-dependent ionization
calculation in the magnetic reconnection structure. We only calculated the
transient ionization of iron; the other species were assumed to be in
ionization equilibrium. The intensity of line emissions at specific wavelengths
were also calculated for comparison with {\it Hinode} or other observations in
future. What we found is as follows: (1) iron is mostly in non-equilibrium
ionization in the reconnection region, (2) the intensity of line emission
estimated by the time-dependent ionization calculation is significantly
different from that with the ionization equilibrium assumption, (3) the effect
of time-dependent ionization is sensitive to the electron density in the case
that the electron density is less than $10^{10}$ cm$^{-3}$, (4) the effect of
thermal conduction lessens the time-dependent ionization effect, (5) the effect
of radiative cooling is negligibly small even if we take into account
time-dependent ionization.",1108.5026v1
2011-08-25,How the effects of resonant absorption on black hole reflection spectra can mimic high-velocity outflows,"Narrow absorption lines seen in the 2-10 keV spectra of active galaxies and
Galactic black holes are normally attributed to iron in high velocity outflows
or inflows. We consider the possibility that such features could arise
naturally in the accretion disc. Resonant absorption by highly ionised iron
(e.g. Fe XXVI and Fe XXV) in an optically-thin plasma that is located above the
disc and rotating with it could reproduce narrow features in the reflection
component of the spectrum as it emerges from the disc. Depending on the
inclination of the disc and the exact geometry of the hot plasma (e.g. does it
blanket the disc or a ring) apparently narrow absorption features could be
detected between 4-10 keV. Such an explanation requires no high velocity
outflow/inflow and is consistent with a reflection-based interpretation for
accreting black holes systems.",1108.5060v1
2011-09-01,Nodal superconducting gap structure in ferropnictide superconductor BaFe2(As0.7P0.3)2,"The superconducting gap is a pivotal character for a superconductor. While
the cuprates and conventional phonon-mediated superconductors are characterized
by distinct d-wave and s-wave pairing symmetry with nodal and nodeless gap
distribution respectively, the superconducting gap distributions in iron-based
superconductors are rather diversified. While nodeless gap distributions have
been directly observed in Ba1-xKxFe2As2, BaFe2-xCoxAs2, KxFe2-ySe2, and
FeTe1-xSex, the signatures of nodal superconducting gap have been reported in
LaOFeP, LiFeP, KFe2As2, BaFe2(As1-xPx)2, BaFe2-xRuxAs2 and FeSe. We here report
the angle resolved photoemission spectroscopy (ARPES) measurements on the
superconducting gap structure of BaFe2(As1-xPx)2 in the momentum space, and
particularly, the first direct observation of a circular line node on the
largest hole Fermi surface around the Z point at the Brillouin zone boundary.
Our data rules out the d-wave pairing origin of the nodal gap, and unify both
the nodaland nodeless gaps in iron pnictides under the s\pm pairing symmetry.",1109.0229v1
2011-09-02,A gamma-ray signature of energetic sources of cosmic-ray nuclei,"Astrophysical sources of nuclei are expected to produce a broad spectrum of
isotopes, many of which are unstable. An unstable nucleus can beta-decay
outside the source into a single-electron ion. Heavy one-electron ions, thus
formed, can be excited in their interactions with cosmic microwave background
photons, in which case they relax to the ground state with the emission of a
gamma ray. Repetitive cycles of excitation and gamma-ray emission can produce
an observable feature in the gamma-ray spectrum with a maximum around 8 GeV
(for iron). We find that the observed spectrum of Centaurus A is consistent
with a substantial flux of nuclei accelerated to 0.1 EeV. A characteristic
5--10 GeV (iron) shoulder in the gamma-ray spectra of various sources can help
identify astrophysical accelerators of nuclei or set upper limits on nuclear
acceleration.",1109.0565v3
2011-09-14,First-principles study of pressure-induced magnetic phase transitions in ternary iron selenide K$_{0.8}$Fe$_{1.6}$Se$_2$,"We have studied the pressure effect on electronic structures and magnetic
orders of ternary iron selenide K$_{0.8}$Fe$_{1.6}$Se$_2$ by the
first-principles electronic structure calculations. At low pressure, the
compound is in the blocked checkerboard antiferromagnetic (AFM) semiconducting
phase, as observed by the neutron scatting measurements. Applying pressure
induces two phase transitions, first from the blocked checkerboard AFM
semiconducting phase to a collinear AFM metallic phase around 12 GPa, and then
to a non-magnetic metallic phase around 25 GPa, respectively. Our results help
to clarify the recent experimental measurements under pressure.",1109.3049v1
2011-09-20,Dynamical Ionic Clusters with Flowing Electron Bubbles from Warm to Hot Dense Iron along the Hugoniot Curve,"The complex structures of warm and hot dense matter are essential to
understand the behaviors of materials in high energy density physics processes
and provide new features of matter constitutions. Here, along a new unified
first-principle determined Hugoniot curve of iron from normal condensed
condition up to 1 Gbar, the novel structures characterized by the ionic
clusters and separated ""electron bubbles"" are revolutionarily unraveled using
newly developed quantum Langevin molecular dynamics (QLMD). Subsistence of
complex clusters, with bonds formed by inner shell electrons of neighbor ions,
can persist in the time length of 50 femto-seconds dynamically with quantum
flowing bubbles, which are produced by the interplay of Fermi electron
degeneracy, the ionic coupling and the dynamical nature. With the inclusion of
those complicated features in QLMD, the present data could serve as a
first-principle benchmark in a wide range of temperatures and densities.",1109.4252v3
2011-09-20,Common origin of the two types of magnetic fluctuations in iron chalcogenides,"We use inelastic neutron scattering to study the low energy spin excitations
in moderately doped non-superconducting Fe$_{1.01}$Te$_{0.72}$Se$_{0.28}$. The
spin excitations in this system contain components near (0.5,0,0) and
(0.5,0.5,0) in a-b plane reciprocal lattice units using tetragonal unit cell
notation (a=b=3.772 \AA and c=6.061 \AA). At low energies the scattering is
centered around (0.5,0,0). With increasing energy, the spectral weight of low
energy spin excitations centered around (0.5,0,0) abruptly shifts around 3 meV
to the incommensurate spin excitations centered around (0.5,0.5,0). However
both types of spin fluctuations exhibit the identical temperature dependence.
These results indicate that the (0.5,0,0) type spin excitations and the
incommensurate excitations around the (0.5,0.5,0) position have a common origin
and both must be taken into account to understand the nature of magnetism and
superconducting pairing in the iron chalcogenides.",1109.4339v1
2011-09-22,Self-Diffusion of Iron in L10 FePd film - as revealed by reflectometric methods,"L10 (CuAu(I)-type) ordered FePd as well as FePt and CoPt, due to their high
magnetic anisotropy, are candidate materials for future ultra-high density
magnetic recording. Atomic diffusion governs the structural relaxation and
associated changes in the physical and magnetic properties in these alloys.
Such processes involve diffusion paths of a few angstroms. In developing modern
storage devices it is indispensable to understand these processes. Neutron
reflectometry (NR) and Synchrotron M\""ossbauer Reflectometry (SMR) are suitable
non destructive methods to study self-diffusion in a chemically homogenous
isotope multilayer with diffusion lengths of the order of a few angstroms. From
the diffusion parameters obtained from NR and SMR evaluation we determined
activation energies (Q) and preexponent factors (D0) for the distinct
environment in the FePd samples. We obtained the highest activation energy
(1.82\pm0.38 eV)and lowest preexponential factor((5.76\pm0.35)*10-14 m2/s) for
the ordered L10 as oppose to the iron rich regions were the activation energy
(1.48\pm0.26 \pmV) found to be lowest and the preexponential factor the highest
((1.01\pm0.61)*10-13 m2/s).",1109.4751v1
2011-09-23,Low-Energy Quasiparticles Probed by Heat Transport in the Iron Based Superconductor LaFePO,"We have measured the thermal conductivity of the iron pnictide superconductor
LaFePO down to temperatures as low as T=60mK and in magnetic fields up to 5 T.
The data shows a large residual contribution that is linear in temperature,
consistent with the presence of low energy electronic quasiparticles. We
interpret the magnitude of the linear term, as well as the field and
temperature dependence of thermal transport in several pairing scenarios. The
presence of an unusual supralinear temperature dependence of the electronic
thermal conductivity in zero magnetic field, and a high scattering rate with
minimal Tc suppression argues for a sign-changing nodal s+/- state.",1109.5092v1
2011-09-26,Vortex pinning : a probe for nanoscale disorder in iron-based superconductors,"The pinning of quantized flux lines, or vortices, in the mixed state is used
to quantify the effect of impurities in iron-based superconductors (IBS).
Disorder at two length scales is relevant in these materials. Strong flux
pinning resulting from nm-scale heterogeneity of the superconducting properties
leads to the very disordered vortex ensembles observed in the IBS, and to the
pronounced maximum in the critical current density jc at low magnetic fields.
Disorder at the atomic scale, most likely induced by the dopant atoms, leads to
""weak collective pinning"" and a magnetic field-independent contribution jcoll.
The latter allows one to estimate quasi-particle scattering rates.",1109.5479v1
2011-09-27,Impurity-induced quasiparticle interference in the parent compounds of iron-pnictide superconductors,"The impurity-induced quasiparticle interference(QPI) in the parent compounds
of iron-pnictide superconductors is investigated based on a phenomenological
two-orbital four-band model and T-matrix method. We find the QPI is sensitive
to the value of the magnetic order which may vary from one compound to another.
For small value of the magnetic order, the pattern of oscillation in the local
density of states (LDOS) induced by the QPI exhibits two-dimensional
characteristics, consistent with the standing wave state observed in the 1111
compound. For larger value of the magnetic order, the main feature of the
spatial modulation of the LDOS is the existence of one-dimensional stripe
structure which is in agreement with the nematic structure in the parent
compound of the 122 system. In both cases the system shows $C_2$ symmetry and
only in the larger magnetic order case, there exist in-gap bound states. The
corresponding QPI in $q$-space is also presented. The patterns of modulation in
the LDOS at nonzero energies are attributed to the interplay between the
underlying band structure and Fermi surfaces.",1109.5928v1
2011-09-29,Signatures of electronic correlations in iron silicide,"The intermetallic FeSi exhibits an unusual temperature dependence in its
electronic and magnetic degrees of freedom, epitomized by the crossover from a
low temperature non-magnetic semiconductor to a high temperature paramagnetic
metal with a Curie-Weiss like susceptibility. Many proposals for this
unconventional behavior have been advanced, yet a consensus remains elusive.
Using realistic many-body calculations, we here reproduce the signatures of the
metal-insulator crossover in various observables: the spectral function, the
optical conductivity, the spin susceptibility, and the Seebeck coefficient.
Validated by quantitative agreement with experiment, we then address the
underlying microscopic picture. We propose a new scenario in which FeSi is a
band-insulator at low temperatures and is metalized with increasing temperature
through correlation induced incoherence. We explain that the emergent
incoherence is linked to the unlocking of iron fluctuating moments which are
almost temperature independent at short time scales. Finally, we make explicit
suggestions for improving the thermoelectric performance of FeSi based systems.",1109.6561v2
2011-10-03,Phase transitions in spin-orbital models with spin-space anisotropies for iron-pnictides: A study through Monte Carlo simulations,"The common phase diagrams of superconducting iron pnictides show interesting
material specificities in the structural and magnetic phase transitions. In
some cases the two transitions are separate and second order, while in others
they appear to happen concomitantly as a single first order transition. We
explore these differences using Monte Carlo simulations of a two-dimensional
Hamiltonian with coupled Heisenberg-spin and Ising-orbital degrees of freedom.
In this spin-orbital model, the finite-temperature orbital-ordering transition
results in a tetragonal-to-orthorhombic symmetry reduction and is associated
with the structural transition in the iron-pnictide materials. With a zero or
very small spin space anisotropy, the magnetic transition separates from the
orbital one in temperature, and the orbital transition is found to be in the
Ising universality class. With increasing anisotropy, the two transitions
rapidly merge together and tend to become weakly first order. We also study the
case of a single-ion anisotropy and propose that the preferred spin-orientation
along the antiferromagnetic direction in these materials is driven by orbital
order.",1110.0434v2
2011-10-04,Two-orbital quantum spin model of magnetism in the iron pnictides,"We study a two-orbital spin model to describe (pi,0) stripe
antiferromagnetism in the iron pnictides. The ""double-spin"" model has an
on-site Hunds's coupling and inter-site interactions extending to second
neighbors (inter- and intra-orbital) on the square lattice. Using a variational
method based on a cluster decomposition, we optimize wave functions with up to
8 cluster sites (up to 2^16 variational parameters). We focus on the
anomalously small ordered moments in the stripe state of the pnictides. To
account for it, and large variations among different compounds, we show that
the second-neighbor cross-orbital exchange constant should be ferromagnetic,
which leads to ""partially hidden"" stripe order, with a moment that can be
varied over a large range by small changes in the coupling constants. In a
different parameter region, we confirm the existence of a canted state
previously found in spin-wave theory. We also identify several other phases of
the model.",1110.0761v2
2011-10-14,Interplay between spin density wave and superconductivity in '122' iron pnictides: 57Fe Mössbauer study,"Iron-based superconductors Ba0.7Rb0.3Fe2As2 and CaFe1.92Co0.08As2 of the
'122' family have been investigated by means of the 14.41-keV Moessbauer
transition in 57Fe versus temperature ranging from the room temperature till
4.2 K. A comparison is made with the previously investigated parent compounds
BaFe2As2 and CaFe2As2. It has been found that Moessbauer spectra of these
superconductors are composed of the magnetically split component due to
development of spin density wave (SDW) and non-magnetic component surviving
even at lowest temperatures. The latter component is responsible for
superconductivity. Hence, the superconductivity occurs in the part of the
sample despite the sample is single phase. This phenomenon is caused by the
slight variation of the dopant concentration across the sample (crystal).",1110.3170v1
2011-10-19,Synthesis of novel rare earth - iron oxide chalcogenides with the La2Fe2O3Se2 structure,"Our searches for new oxide chalcogenides of rare earths and Fe, Co, Ni, and
Zn resulted in preparation of two new compounds Ce2Fe2O3S2 and Pr2Fe2O3S2 which
are isostructural to La2Fe2O3Se2 and Sm2Ti2O3Sb2. Crystal structures of the new
compounds Ce2Fe2O3S2 and Pr2Fe2O3S2 were determined from powder X-ray
diffraction data. Magnetic measurements were performed for Ce2Fe2O3S2 and
revealed behavior very similar to that of isostructural oxide chalcogenides of
iron and pnictides of titanium. In particular, no superconductivity was
observed down to 4 K. Crystal chemical factors determining the stability of the
La2Fe2O3Se2 structure type are discussed.",1110.4234v1
2011-10-21,P-T phase diagram of iron arsenide superconductor NdFeAsO0.88F0.12,"NdFeAsO0.88F0.12 belongs to the recently discovered family of high-TC
iron-based superconductors. The influence of high pressure on transport
properties of this material has been studied. Contrary to La-based compounds,
we did not observe a maximum in TC under pressure. Under compression, TC drops
rapidly as a linear function of pressure with the slope k = -2.8 \pm 0.1 K /
GPa. The extrapolated value of TC at zero pressure is about TC (0) = 51.7 \pm
0.4 K. At pressures higher than ~18.4 GPa, the superconducting state disappears
at all measured temperatures. The resistance changes slope and shows a turn-up
behavior, which may be related to the Kondo effect or a weak localization of
two-dimensional carriers below ~45 K that is above TC and thus competing with
the superconducting phase. The behavior of the sample is completely reversible
at the decompression. On the bases of our experimental data, we propose a
tentative P-T phase diagram of NdFeAsO0.88F0.12.",1110.4909v1
2011-10-22,Strong field effects on emission line profiles: Kerr black holes and warped accretion disks,"If an accretion disk around a black hole is illuminated by hard X-rays from
non-thermal coronae, fluorescent iron lines will be emitted from the inner
region of the accretion disk. The emission line profiles will show a variety of
strong field effects, which may be used as a probe of the spin parameter of the
black hole and the structure of the accretion disk. In this paper we generalize
the previous relativistic line profile models by including both the black hole
spinning effects and the non-axisymmetries of warped accretion disks. Our
results show different features from the conventional calculations for either a
flat disk around a Kerr black hole or a warped disk around a Schwarzschild
black hole by presenting, at the same time, multiple peaks, rather long red
tails and time variations of line profiles with the precession of the disk. We
show disk images as seen by a distant observer, which are distorted by the
strong gravity. Although we are primarily concerned with the iron K-shell lines
in this paper, the calculation is general and is valid for any emission lines
produced from a warped accretion disk around a black hole.",1110.4997v1
2011-10-30,Microwave Surface Impedance Measurements of the Electronic State and Dissipation of Magnetic Vortices in Superconducting Iron-Based LiFeAs Single Crystals,"LiFeAs is one of the iron-based superconductors having multiple gaps with the
possible sign reversal. To clarify how those novel natures affect the energy
dissipation of magnetic vortices, we investigated the microwave surface
impedance of LiFeAs single crystals under finite magnetic fields. The flux-flow
resistivity enhanced rapidly at low magnetic fields, which is similar to the
case of MgB$_{2}$. This is probably the consequence of the multiple-gap nature
and the gap anisotropy. This suggest that the sign-reversal is not important
for the flux-flow even for multiple-gap superconductors. As for the electronic
state, the vortex core of LiFeAs turned out to be ""moderately clean"".
Furthermore, the mean free path inside the vortex core was much shorter than
that outside, and was close to the core radius. These results strongly suggest
a process specific to the core boundary is important for a scattering mechanism
inside the vortex core.",1110.6575v2
2011-10-31,Spin-dependent recombination in Czochralski silicon containing oxide precipitates,"Electrically detected magnetic resonance is used to identify recombination
centers in a set of Czochralski grown silicon samples processed to contain
strained oxide precipitates with a wide range of densities (~ 1e9 cm-3 to ~
7e10 cm-3). Measurements reveal that photo-excited charge carriers recombine
through Pb0 and Pb1 dangling bonds and comparison to precipitate-free material
indicates that these are present at both the sample surface and the oxide
precipitates. The electronic recombination rates vary approximately linearly
with precipitate density. Additional resonance lines arising from iron-boron
and interstitial iron are observed and discussed. Our observations are
inconsistent with bolometric heating and interpreted in terms of spin-dependent
recombination. Electrically detected magnetic resonance is thus a very powerful
and sensitive spectroscopic technique to selectively probe recombination
centers in modern photovoltaic device materials.",1110.6727v1
2011-10-31,One-sign order parameter in iron based superconductor,"The onset of superconductivity at the transition temperature is marked by the
onset of order, which is characterized by an energy gap. Most models of the
iron-based superconductors find a sign-changing (s\pm) order parameter [1-6],
with the physical implication that pairing is driven by spin fluctuations.
Recent work, however, has indicated that LiFeAs has a simple isotropic order
parameter [7-9] and spin fluctuations are not necessary [7,10], contrary to the
models [1-6]. The strength of the spin fluctuations has been controversial
[11,12], meaning that the mechanism of superconductivity cannot as yet be
determined. Here we report the momentum dependence of the superconducting
energy gap, where we find an anisotropy that rules out coupling through spin
fluctuations and the sign change. The results instead suggest that orbital
fluctuations assisted by phonons [13,14] are the best explanation for
superconductivity.",1110.6922v2
2011-11-17,Competition between commensurate and incommensurate magnetic ordering in Fe(1+y)Te,"The Fe1+y Te1-x Sex compounds belong to the family of iron-based high
temperature superconductors, in which superconductivity often appears upon
doping antiferromagnetic parent compounds. Unlike other Fe-based
superconductors (in which the antiferromagnetic order is at the Fermi surface
nesting wavevector [1/2,1/2,1]), the Fe1+y Te1-x Sex parent compound Fe1+y Te
orders at a different wavevector, [1/2, 0, 1/2]. Furthermore, the ordering
wavevector depends on y, the occupation of interstitial sites with excess iron;
the origin of this behavior is controversial. Using inelastic neutron
scattering on Fe1.08 Te, we find incommensurate magnetic fluctuations above the
Neel temperature, even though the ordered state is bicollinear and commensurate
with gapped spin waves. This behavior can be understood in terms of a
competition between commensurate and incommensurate order, which we explain as
a lock-in transition caused by the magnetic anisotropy.",1111.4236v2
2011-11-26,Electronic reconstruction through the structural and magnetic transitions in detwinned NaFeAs,"We use angle-resolved photoemission spectroscopy to study twinned and
detwinned iron pnictide compound NaFeAs. Distinct signatures of electronic
reconstruction are observed to occur at the structural (TS) and magnetic (TSDW)
transitions. At TS, C4 rotational symmetry is broken in the form of an
anisotropic shift of the orthogonal dxz and dyz bands. The magnitude of this
orbital anisotropy rapidly develops to near completion upon approaching TSDW,
at which temperature band folding occurs via the antiferromagnetic ordering
wave vector. Interestingly, the anisotropic band shift onsetting at TS develops
in such a way to enhance the nesting conditions in the C2 symmetric state,
hence is intimately correlated with the long range collinear AFM order.
Furthermore, the similar behaviors of the electronic reconstruction in NaFeAs
and Ba(Fe1-xCox)2As2 suggests that this rapid development of large orbital
anisotropy between TS and TSDW is likely a general feature of the electronic
nematic phase in the iron pnictides, and the associated orbital fluctuations
may play an important role in determining the ground state properties.",1111.6134v1
2011-11-29,Suzaku Observation of the Black Hole Candidate MAXI J1836-194 in a Hard/Intermediate Spectral State,"We report on a Suzaku observation of the newly discovered X-ray binary MAXI
J1836-194. The source is found to be in the hard/intermediate spectral state
and displays a clear and strong relativistically broadened iron emission line.
We fit the spectra with a variety of phenomenological, as well as physically
motivated disk reflection models, and find that the breadth and strength of the
iron line is always characteristic of emission within a few gravitational radii
around a black hole. This result is independent of the continuum used and
strongly points toward the central object in MAXI J1836-194 being a stellar
mass black hole rotating with a spin of $a=0.88\pm0.03$ (90% confidence). We
discuss this result in the context of spectral state definitions, physical
changes (or lack thereof) in the accretion disk and on the potential importance
of the accretion disk corona in state transitions.",1111.6665v3
2011-12-07,Reciprocal-space structure and dispersion of the magnetic resonant mode in the superconducting phase of Rb(x)Fe(2-y)Se2 single crystals,"Inelastic neutron scattering is employed to study the reciprocal-space
structure and dispersion of magnetic excitations in the normal and
superconducting states of single-crystalline Rb0.8Fe1.6Se2. We show that the
recently discovered magnetic resonant mode in this compound has a
quasi-two-dimensional character, similar to overdoped iron-pnictide
superconductors. Moreover, it has a rich in-plane structure that is dominated
by four elliptical peaks, symmetrically surrounding the Brillouin zone corner,
without sqrt(5) x sqrt(5) reconstruction. We also present evidence for the
dispersion of the resonance peak, as its position in momentum space depends on
energy. Comparison of our findings with the results of band structure
calculations provides strong support for the itinerant origin of the observed
signal. It can be traced back to the nesting of electron-like Fermi pockets in
the doped metallic phase of the sample in the absence of iron-vacancy ordering.",1112.1636v1
2011-12-19,Anomalous isotope effect in phonon-dressed iron-based superconductor,"The role of electron-phonon interactions in iron-based superconductor is
currently under debate with conflicting experimental reports on the isotope
effect. To address this important issue, we employ the renormalization-group
method to investigate the competition between electron-electron and
electron-phonon interactions in these materials. The renormalization-group
analysis shows that the ground state is a phonon-dressed unconventional
superconductor: the dominant electronic interactions account for pairing
mechanism while electron-phonon interactions are subdominant. Because of the
phonon dressing, the isotope effect of the critical temperature can be normal
or reversed, depending on whether the retarded intra- or inter-band
interactions are altered upon isotope substitutions. The connection between the
anomalous isotope effect and the unconventional pairing symmetry is discussed
at the end.",1112.4326v3
2011-12-20,Do Transition Metal Substitutions Dope Carriers in Iron Based Superconductors?,"We investigate the currently debated issue concerning whether transition
metal substitutions dope carriers in iron based superconductors. From
first-principles calculations of the configuration-averaged spectral function
of BaFe$_2$As$_2$ with disordered Co/Zn substitutions of Fe, important doping
effects are found beyond merely changing the carrier density. While the
chemical potential shifts suggest doping of a large amount of carriers, a
reduction of the coherent carrier density is found due to the loss of spectral
weight. Therefore, none of the change in the Fermi surface, density of states,
or charge distribution can be solely used for counting doped coherent carriers,
let alone presenting the full effects of the disordered substitutions. Our
study highlights the necessity of including disorder effects in the studies of
doped materials in general.",1112.4858v3
2011-12-30,"Structural, Magnetic and Electronic Properties of the Iron-Chalcogenide A$_x$Fe$_{2-y}$Se$_2$ (A=K, Cs, Rb, Tl and etc.) Superconductors","The latest discovery of a new iron-chalcogenide superconductor
A$_x$Fe$_{2-y}$Se$_2$(A=K, Cs, Rb, Tl and etc.) has attracted much attention
due to a number of its unique characteristics, such as the possible insulating
state of the parent compound, the existence of Fe-vacancy and its ordering, a
new form of magnetic structure and its interplay with superconductivity, and
the peculiar electronic structures that are distinct from other Fe-based
superconductors. In this paper, we present a brief review on the structural,
magnetic and electronic properties of this new superconductor, with an emphasis
on the electronic structure and superconducting gap. Issues and future
perspectives are discussed at the end of the paper.",1201.0085v1
2012-01-01,Effect of transition-metal substitution in iron-based superconductors,"We study theoretically the current debatable issue about the effect of
transition-metal (TM) substitution in iron-based superconductors through
treating all of the TM ions as randomly distributed impurities. The extra
electrons from TM elements are localized at the impurity sites. In the mean
time the chemical potential shifts upon substitution. The phase diagram is
mapped out and it seems that the TM elements can act as effective dopants. The
local density of states (LDOS) is calculated and the bottom becomes V-shaped as
the impurity concentration increases. The LDOS at the Fermi energy
$\rho(\omega=0)$ is finite and reaches the minimum at the optimal doping level.
Our results are in good agreement with the scanning tunneling microscopy
experiments.",1201.0363v2
2012-01-12,Q-scan-analysis of the neutron scattering in iron-based superconductors,"We propose a way to determine the pairing state of the iron pnictide
superconductors exploiting the momentum (Q) scan of the neutron scattering
data. We investigate the spin susceptibility in the s+- and s++ superconducting
states for various doping levels using the effective five-orbital model and
considering the quasiparticle damping. The peak position of the intensity
shifts from the position on the line Qx = pi to that on the line Qy = 0 as the
doping level is decreased from electron doping to hole doping. We find that the
Q-dependence of the ratio of the intensity in the superconducting state to that
in the normal state is qualitatively different between the s+- -wave and s++
-wave pairings. We propose to investigate experimentally this ratio in Q-space
to distinguish the two pairing states.",1201.2453v2
2012-01-16,"(PI,0) antiferromagnetic spin excitations in superconducting Rb0.82Fe1.68Se2","We use inelastic neutron scattering to show that superconducting (SC)
rubidium iron selenide Rb0.82Fe1.68Se2 exhibits antiferromagnetic (AF) spin
excitations near the in-plane wave vector Q = (PI, 0) identical to that for
iron arsenide superconductors. Moreover, we find that these excitations change
from incommensurate to commensurate with increasing energy, and occur at the
expense of spin waves associated with the coexisting sqrt(5)\timessqrt(5) block
AF phase. Since angle resolved photoemission experiments reveal no evidence for
hole-like Fermi surface at Gamma(0, 0), our results suggest that the Q = (PI,
0) excitations in SC Rb0.82Fe1.68Se2 come from localized moments and may have a
similar origin as the hourglass-like spin excitations in copper oxide
superconductors.",1201.3348v1
2012-01-20,Non-destructive imaging of an individual protein,"The mode of action of proteins is to a large extent given by their ability to
adopt different conformations. This is why imaging single biomolecules at
atomic resolution is one of the ultimate goals of biophysics and structural
biology. The existing protein database has emerged from X-ray crystallography,
NMR or cryo-TEM investigations. However, these tools all require averaging over
a large number of proteins and thus over different conformations. This of
course results in the loss of structural information. Likewise it has been
shown that even the emergent X-FEL technique will not get away without
averaging over a large quantity of molecules. Here we report the first
recordings of a protein at sub-nanometer resolution obtained from one
individual ferritin by means of low-energy electron holography. One single
protein could be imaged for an extended period of time without any sign of
radiation damage. Since ferritin exhibits an iron core, the holographic
reconstructions could also be cross-validated against TEM images of the very
same molecule by imaging the iron cluster inside the molecule while the protein
shell is decomposed.",1201.4300v1
2012-01-25,Pressure Effects on Magnetically-Driven Electronic Nematic States in Iron-Pnictides,"In a magnetically driven electronic nematic state, an externally applied
uniaxial strain rounds the nematic transition and increases the magnetic
transition temperature. We study both effects in a simple classical model of
the iron-pnictides expressed in terms of local SO(N) spins (with N = 3) which
we solve to leading order in 1=N. The magnetic transition temperature is shown
to increase linearly in response to an external strain while a sharp crossover,
which is a remnant of the nematic transition, can only be identified for
extremely small strain. We show that these results can reasonably account for
recent neutron experimental data in BaFe2As2 by C. Dhital et al [1].",1201.5174v1
2012-02-01,120-mm superconducting quadrupole for interaction regions of hadron colliders,"Magnetic and mechanical designs of a Nb3Sn quadrupole magnet with 120-mm
aperture suitable for interaction regions of hadron colliders are presented.
The magnet is based on a two-layer shell-type coil and a cold iron yoke.
Special spacers made of a low-Z material are implemented in the coil mid-planes
to reduce the level of radiation heat deposition and radiation dose in the
coil. The quadrupole mechanical structure is based on aluminum collars
supported by an iron yoke and a stainless steel skin. Magnet parameters
including maximum field gradient and field harmonics, Nb3Sn coil pre-stress and
protection at the operating temperatures of 4.5 and 1.9 K are reported. The
level and distribution of radiation heat deposition in the coil and other
magnet components are discussed.",1202.0293v1
2012-02-03,Gap opening and orbital modification of superconducting FeSe above the structural distortion,"We utilize steady-state and transient optical spectroscopies to examine the
responses of nonthermal quasiparticles with respect to orbital modifications in
normal-state iron-chalcogenide superconductors. The dynamics shows the
emergence of gap-like quasiparticles (associated to a ~36 meV energy gap) with
a coincident transfer of the optical spectral weight in the visible range, at
temperatures above the structural distortion. Our observations suggest that
opening of the high-temperature gap and the lattice symmetry breaking are
possibly driven by short-range orbital and/or charge orders, implicating a
close correlation between electronic nematicity and precursor order in
iron-based superconductors.",1202.0658v1
2012-02-08,Pairing Symmetry and Spin Excitations of Iron Selenide Superconductors,"We propose an effective single-band model for the newly discovered iron
selenide superconductors A$_x$Fe$_{2-y}$Se$_2$ (A=Tl,K,Rb,Cs). Based on this
minimum model and the random phase approximation, the $d_{x^2-y^2}$ pairing
symmetry is revealed theoretically, which may be understood in the framework of
Fermi surface topology. A common origin of superconductivity is elucidated for
this compound and other high-T$_c$ materials. The spin excitations at
$(\pi,\pi/2)$ in superconducting states are observed, in good agreement with
the neutron scattering experiments. The spin resonance is indicated to show up
only for the d-wave pairing, which provides an additional indication for the
d-wave pairing symmetry in this family of superconductors.",1202.1607v1
2012-02-16,Transport and magnetic properties of La-doped CaFe$_2$As$_2$,"We measured the transport properties and susceptibility of single crystals
Ca$_{1-x}$La$_x$Fe$_2$As$_2$(x=0, 0.05, 0.1, 0.15, 0.19 and 0.25). Large
in-plane resistivity anisotropy similar to that in Co-doped 122 iron-pnictides
is observed although no transition metals were introduced in the FeAs-plane.
The in-plane resistivity anisotropy gradually increases with La doping below
T$_{SDW}$, being different from the hole-doped 122 superconductors. The
susceptibilities of the samples show that La doping leads to suppression of SDW
and induces a Curie-Weiss-like behavior at low temperature, which is much
stronger than the other 122 iron-based superconductors.",1202.3589v1
2012-02-20,Sign-reversal of the in-plane resistivity anisotropy in hole-doped iron pnictides,"The in-plane anisotropy of the electrical resistivity across the coupled
orthorhombic and magnetic transitions of the iron pnictides has been
extensively studied in the parent and electron-doped compounds. All these
studies universally show that the resistivity $\rho_{a}$ across the long
orthorhombic axis $a_{O}$ - along which the spins couple antiferromagnetically
below the magnetic transition temperature - is smaller than the resistivity
$\rho_{b}$ of the short orthorhombic axis $b_{O}$, i. e. $\rho_{a}<\rho_{b}$.
Here we report that in the hole-doped compounds
Ba$_{1-x}$K$_{x}$Fe$_{2}$As$_{2}$, as the doping level increases, the
resistivity anisotropy initially becomes vanishingly small, and eventually
changes sign for sufficiently large doping, i. e. $\rho_{b}<\rho_{a}$. This
observation is in agreement with a recent theoretical prediction that considers
the anisotropic scattering of electrons by spin-fluctuations in the
orthorhombic/nematic state.",1202.4430v2
2012-03-05,Gap nodes induced by coexistence with antiferromagnetism in iron-based superconductors,"We investigate the pairing in iron pnictides in the coexistence phase, which
displays both superconducting and antiferromagnetic orders. By solving the
pairing problem on the Fermi surface reconstructed by long-range magnetic
order, we find that the pairing interaction necessarily becomes
angle-dependent, even if it was isotropic in the paramagnetic phase, which
results in an angular variation of the superconducting gap along the Fermi
surfaces. We find that the gap has no nodes for a small antiferromagnetic order
parameter M, but may develop accidental nodes for intermediate values of M,
when one pair of the reconstructed Fermi surface pockets disappear. For even
larger M, when the other pair of reconstructed Fermi pockets is gapped by
long-range magnetic order, superconductivity still exists, but the
quasiparticle spectrum becomes nodeless again. We also show that the
application of an external magnetic field facilitates the formation of nodes.
We argue that this mechanism for a nodeless-nodal-nodeless transition explains
recent thermal conductivity measurements of hole-doped Ba_{1-x}K_xFe_2As_2.
[J-Ph. Read et.al. arXiv:1105.2232].",1203.0991v1
2012-03-06,Nanoscale Metallic Iron for Environmental Remediation: Prospects and Limitations,"The amendment of the subsurface with nanoscale metallic iron particles
(nano-Fe0) has been discussed in the literature as an efficient in situ
technology for groundwater remediation. However, the introduction of this
technology was controversial and its efficiency has never been univocally
established. This unsatisfying situation has motivated this communication whose
objective was a comprehensive discussion of the intrinsic reactivity of
nano-Fe0 based on the contemporary knowledge on the mechanism of contaminant
removal by Fe0 and a mathematical model. It is showed that due to limitations
of the mass transfer of nano-Fe0 to contaminants, available concepts cannot
explain the success of nano-Fe0 injection for in situ groundwater remediation.
It is recommended to test the possibility of introducing nano-Fe0 to initiate
the formation of roll-fronts which propagation would induce the reductive
transformation of both dissolved and adsorbed contaminants. Within a
roll-front, FeII from nano-Fe0 is the reducing agent for contaminants. FeII is
recycled by biotic or abiotic FeIII reduction. While the roll-front concept
could explain the success of already implemented reaction zones, more research
is needed for a science-based recommendation of nano- Fe0 for subsurface
treatment by roll-fronts",1203.1128v1
2012-03-08,NMR Study in the Iron-Selenide Rb0.74Fe1.6Se2: Determination of the Superconducting Phase as Iron Vacancy-Free Rb0.3Fe2Se2,"77Se and 87Rb nuclear magnetic resonance (NMR) experiments on Rb0.74Fe1.6Se2
reveal clearly distinct spectra originating from a majority antiferromagnetic
(AF) and a minority metallic-superconducting (SC) phase. The very narrow NMR
line of the SC phase evidences the absence of Fe vacancies and any trace of AF
order. The Rb content of the SC phase is deduced from intensity measurements
identifying Rb0.3(1)Fe2Se2 as the actual composition of the SC fraction. The
resulting estimate of 0:15 electrons/Fe brings this class of superconductors
245 family closer to the other Fe-based superconductor families.",1203.1834v2
2012-03-08,Simulation of proton-induced and iron-induced extensive air showers at extreme energies,"The development of extensive air showers at extreme energies is studied using
a simulation model much simpler and cruder, but also more transparent and
flexible, than existing sophisticated codes. Evidence for its satisfactory
performance is presented. As an illustration, shower elongation rates are
evaluated in the $10^{18}$ to $10^{20}$ eV region and compared with recently
published data. Lateral distribution functions of both muons and
electrons/photons are also briefly discussed. Reliable results are obtained in
the comparison between proton-induced and iron-induced showers.",1203.1845v1
2012-03-13,Self-Consistent Vertex Correction Analysis for Iron-Based Superconductors: Mechanism of Coulomb-Interaction-Driven Orbital Fluctuations,"We study the mechanism of orbital/spin fluctuations due to multiorbital
Coulomb interaction in iron-based superconductors, going beyond the
random-phase-approximation. For this purpose, we develop a self-consistent
vertex correction (SC-VC) method, and find that multiple orbital fluctuations
in addition to spin fluctuations are mutually emphasized by the ""multimode
interference effect"" described by the VC. Then, both the antiferro-orbital and
ferro-orbital (=nematic) fluctuations simultaneously develop for $J/U \sim
0.1$, both of which contribute to the s-wave superconductivity. Especially, the
ferro-orbital fluctuations give the orthorhombic structure transition as well
as the softening of shear modulus $C_{66}$.",1203.2874v3
2012-03-16,Interstellar polarization and grain alignment: the role of iron and silicon,"We compiled the polarimetric data for a sample of lines of sight with known
abundances of Mg, Si, and Fe. We correlated the degree of interstellar
polarization $P$ and polarization efficiency (the ratio of $P$ to the colour
excess $E(B-V)$ or extinction $A_V$) with dust phase abundances. We detect an
anticorrelation between $P$ and the dust phase abundance of iron in non
silicate - containing grains $< [\rm Fe(rest)/H > ]_\rm d$, a correlation
between $P$ and the abundance of Si, and no correlation between $P/E(B-V)$ or
$P/A_V$ and dust phase abundances. These findings can be explained if mainly
the silicate grains aligned by the radiative mechanism are responsible for the
observed interstellar linear polarization.",1203.3677v1
2012-03-19,Photoionization Cross-Sections for the trans-iron element Se$^+$ from 18 eV to 31 eV,"Absolute photoionization cross-section calculations are presented for Se$^+$
using large-scale close-coupling calculations within the Breit-Pauli and
Dirac-Coulomb R-matrix approximations. The results from our theoretical work
are compared with recent measurements made at the Advanced Light Source (ALS)
radiation facility in Berkeley, California, USA. We report on results for the
photon energy range 18.0 eV -- 31.0 eV, which spans the ionization thresholds
of the $\rm ^4S^o_{3/2}$ ground state and the low-lying $\rm ^2D^o_{5/2,3/2}$
and $\rm ^2P^o_{3/2,1/2}$ metastable states. Metastable fractions are inferred
from our present work. Resonance energies and quantum defects of the prominent
Rydberg resonances series identified in the spectra are compared for the $\rm
4p \rightarrow nd$ transitions with the recent ALS experimental measurements
made on this complex trans-iron element.",1203.4102v1
2012-03-21,Non-Fermi-Liquid Transport Phenomena and Superconductivity Driven by Orbital Fluctuations in Iron Pnictides: Analysis by Fluctuation-Exchange Approximation,"We study the five-orbital Hubbard model including the charge quadrupole
interaction for iron pnictides. Using the fluctuation-exchange (FLEX)
approximation, orbital fluctuations evolve inversely proportional to the
temperature, and therefore the resistivity shows linear or convex T-dependence
for wide range of temperatures. We also analyze the Eliashberg gap equation,
and show that s-wave superconducting state without sign reversal (s++ -wave
state) emerges when the orbital fluctuations dominate over the spin
fluctuations. When both fluctuations are comparable, their competition gives
rise to a nodal s-wave state. The present study offers us a unified explanation
for both the normal and superconducting states.",1203.4639v2
2012-03-22,Universal pair-breaking in transition metal-substituted iron-pnictide superconductors,"The experimental transport scattering rate was determined for a wide range of
optimally doped transition metal-substituted FeAs-based compounds with the
ThCr2Si2 (122) crystal structure. The maximum transition temperature Tc for
several Ba-, Sr-, and Ca-based 122 systems follows a universal rate of
suppression with increasing scattering rate indicative of a common
pair-breaking mechanism. Extraction of standard pair-breaking parameters puts a
limit of \sim26 K on the maximum Tc for all transition metal-substituted 122
systems, in agreement with experimental observations, and sets a critical
scattering rate of 1.5x10^14 s^-1 for the suppression of the superconducting
phase. The observed critical scattering rate is much weaker than that expected
for a sign-changing order parameter, providing important constraints on the
nature of the superconducting gap in the 122 family of iron-based
superconductors.",1203.5114v3
2012-04-07,KFe_2Se_2 is the parent compound of K-doped iron selenide superconductors,"We elucidate the existing controversies in the newly discovered K-doped iron
selenide (KxFe2-ySe2-z) superconductors. The stoichiometric KFe2Se2 with
\surd2\times\surd2 charge ordering was identified as the parent compound of
KxFe2-ySe2-z superconductor using scanning tunneling microscopy and
spectroscopy. The superconductivity is induced in KFe2Se2 by either Se
vacancies or interacting with the anti-ferromagnetic K2Fe4Se5 compound. Totally
four phases were found to exist in KxFe2-ySe2-z: parent compound KFe2Se2,
superconducting KFe2Se2 with \surd2\times\surd5 charge ordering,
superconducting KFe2Se2-z with Se vacancies and insulating K2Fe4Se5 with
\surd5\times\surd5 Fe vacancy order. The phase separation takes place at the
mesoscopic scale under standard molecular beam epitaxy condition.",1204.1588v1
2012-04-08,Vie Physarale: Evaluation of Roman roads with slime mould,"Roman Empire is renowned for sharp logical design and outstanding building
quality of its road system. Many roads built by Romans are still use in
continental Europe and UK. The Roman roads were built for military
transportations with efficiency in mind, as straight as possible. Thus the
roads make an ideal test-bed for developing experimental laboratory techniques
for evaluating man-made transport systems using living creatures. We imitate
development of road networks in Iron Age Italy using slime mould Physarum
polycephalum. We represent ten Roman cities with oat flakes, inoculate the
slime mould in Roma, wait till slime mould spans all flakes-cities with its
network of protoplasmic tubes, and analyse structures of the protoplasmic
networks. We found that most Roman roads, apart of those linking Placentia to
Bononia and Genua to Florenzia are represented in development of Physarum
polycephalum. Transport networks developed by Romans and by slime mould show
strong affinity of planar proximity graphs, and particular minimum spanning
tree. Based on laboratory experiments we reconstructed a speculative sequence
of road development in Iron Age Italy.",1204.2260v1
2012-04-10,The symplectic-N t-J model and s$_\pm$ superconductors,"The possible discovery of $s_\pm$ superconducting gaps in the moderately
correlated iron-based superconductors has raised the question of how to
properly treat $s_\pm$ gaps in strongly correlated superconductors. Unlike the
d-wave cuprates, the Coulomb repulsion does not vanish by symmetry, and a
careful treatment is essential. Thus far, only the weak correlation approaches
have included this Coulomb pseudopotential, so here we introduce a symplectic N
treatment of the t-J model that incorporates the strong Coulomb repulsion
through the complete elimination of on-site pairing. Through a proper extension
of time-reversal symmetry to the large N limit, symplectic-N is the first
superconducting large N solution of the t-J model. For d-wave superconductors,
the previous uncontrolled mean field solutions are reproduced, while for
$s_\pm$ superconductors, the SU(2) constraint enforcing single occupancy acts
as a pair chemical potential adjusting the location of the gap nodes. This
adjustment can capture the wide variety of gaps proposed for the iron based
superconductors: line and point nodes, as well as two different, but related
full gaps on different Fermi surfaces.",1204.2302v2
2012-04-18,Electronic properties and magnetism of iron at the Earth's inner core conditions,"We employ state-of-the-art ab initio simulations within the dynamical
mean-field theory to study three likely phases of iron (hexogonal close-packed,
hcp, face centered cubic, fcc, and body centered cubic, bcc) at the Earth's
core conditions. We demonstrate that the correction to the electronic free
energy due to correlations can be significant for the relative stability of the
phases. The strongest effect is observed in bcc Fe, which shows a non-Fermi
liquid behaviour, and where a Curie-Weiss behaviour of the uniform
susceptbility hints at a local magnetic moment still existing at 5800 K and 300
GPa. We predict that all three structures have sufficiently high magnetic
susceptibility to stabilize the geodynamo.",1204.3954v2
2012-04-19,"Paramagnetic Phase of a Heavy-Fermion Compound, CeFePO, Probed by 57Fe Mössbauer Spectroscopy","57Fe M\""{o}ssbauer spectroscopy was applied to an iron-based layered compound
CeFePO. At temperatures from 9.4 to 293 K, no magnetic splitting was observed
in the M\""ossbauer spectra of CeFePO indicating a paramagnetic phase of the Fe
magnetic sublattice. All the spectra were fitted with a small quadrupole
splitting, and the Debye temperature of CeFePO was found to be \sim448 K. The
isomer shift at room temperature, 0.32 mm/s, was almost equal to those of
LnFeAsO (Ln = La, Ce, Sm). Comparing s-electron density using the isomer shifts
and unit cell volumes, it was found that the Fe of CeFePO has a similar valence
state to other layered iron-based quaternary oxypnictides except LaFePO.",1204.4266v1
2012-04-25,Susceptibility anisotropy in an iron arsenide superconductor revealed by x-ray diffraction in pulsed magnetic fields,"In addition to unconventional high-Tc superconductivity, the iron arsenides
exhibit strong magnetoelastic coupling and a notable electronic anisotropy
within the a-b plane. We relate these properties by studying underdoped
Ba(Fe{1-x}Co{x})2As2 by x-ray diffraction in pulsed magnetic fields up to 27.5
Tesla. We exploit magnetic detwinning effects to demonstrate anisotropy in the
in-plane susceptibility, which develops at the structural phase transition
despite the absence of magnetic order. The degree of detwinning increases
smoothly with decreasing temperature, and a single- domain condition is
realized over a range of field and temperature. At low temperatures we observe
an activated behavior, with a large hysteretic remnant effect. Detwinning was
not observed within the superconducting phase for accessible magnetic fields.",1204.5693v1
2012-05-08,X-Ray view of Misaligned AGNs,"The Fermi-LAT satellite has recently discovered a small group of radio
galaxies and steep spectrum radio sources: the misaligned AGNs (MAGNs) sample.
We present the X-ray analysis of all the sources of this sample (7 FRIs and 3
FRIIs) with a firm GeV association. This study supports the idea that FRIIs
host more efficient accretion mechanisms (m_dot >0.1) than FRIs (m_dot <0.003).
Furthermore, in objects with high accretion rates the Broad Line Regions appear
to be very active zones where, in addition to optical lines, the fluorescence
iron Kalpha feature at 6.4 keV is also produced. It seems that the FRII jets
propagate in an environment very rich in photons, explaining, at least at
zeroth order, why the External Compton is the preferred mechanism to produce
gamma-rays. In FRIs, where also the iron line is difficult to be detected, the
paucity of photons in the circumnuclear ambient seems to favor the Synchrotron
Self Compton process.",1205.1691v1
2012-05-08,Short-range symmetry breaking induced structural collapse and Tc enhancement in 122-type iron pnictide superconductors,"In this paper, we investigate analytically the experimental observations of
structural collapse and Tc enhancement in the rare earth-doped 122-type
iron-based pnictide superconductors [S. R. Saha et.al. Phys. Rev. B 85, 024525
(2012), arXiv:1105.4798 (2011); B. Lv et al. PNAS 108, 15705 (2011).]. Based on
the real-space effective c-axis lattice constant theory of superconductivity
[X. Q. Huang, arXiv:1001.5067], it is shown that the abrupt c-axis reduction of
the superconductors is due to the structural phase transition (an
ultra-short-range symmetry breaking) of the charge stripe lattice. The
existence of this phase transition corresponds to the change from the
full-doped superconducting planes to the half-doped superconducting planes in
the studied superconductors. It is estimated that this phase transition may
help to promote the superconducting transition temperature of the 122 family up
to as high as 80 K.",1205.1837v1
2012-05-11,Theory of Mixed-State Effect on Quasiparticle Interference in Iron-based Superconductors,"Based on a phenomenological model with $s_{\pm}$ or s-wave pairing symmetry,
the mixed-state effect on quasiparticle interference in iron-based
superconductors is investigated by solving large-scale Bogoliubov-de Gennes
equations based on the Chebyshev polynomial expansion. Taking into account the
presence of magnetic field, our result for the $s_{\pm}$ pairing is in
qualitative agreement with recent scanning tunneling microscopy experiment
while for the s-wave pairing, the result is in apparent contradiction with
experimental observations, thus excluding the s-wave pairing. Furthermore, we
treat the effect of vortices rigorously instead of approximating the vortices
as magnetic impurities, thus our results are robust and should be more capable
of explaining the experimental data.",1205.2418v1
2012-05-23,Breaking of four-fold lattice symmetry in a model for pnictide superconductors,"We investigate the interplay of onsite Coulomb repulsion and various
mechanisms breaking the fourfold lattice symmetry in a three-band model for the
iron planes of iron-based superconductors. Using cluster-perturbation theory
allows us to locally break the symmetry between the x- and y-directions without
imposing long-range magnetic order. Previously investigated anisotropic
magnetic couplings are compared to an orbital-ordering field and anisotropic
hoppings. We find that all three mechanisms for a broken rotational symmetry
lead to similar signatures once onsite interactions are strong enough to bring
the system close to a spin-density wave. The band distortions near the Fermi
level are independent of differences between the total densities found in xz
and yz orbitals.",1205.5102v1
2012-05-27,The Topological Relation Between Bulk Gap Nodes and Surface Bound States : Application to Iron-based Superconductors,"In the past few years materials with protected gapless surface (edge) states
have risen to the central stage of condensed matter physics. Almost all
discussions centered around topological insulators and superconductors, which
possess full quasiparticle gaps in the bulk. In this paper we argue systems
with topological stable bulk nodes offer another class of materials with robust
gapless surface states. Moreover the location of the bulk nodes determines the
Miller index of the surfaces that show (or not show) such states. Measuring the
spectroscopic signature of these zero modes allows a phase-sensitive
determination of the nodal structures of unconventional superconductors when
other phase-sensitive techniques are not applicable. We apply this idea to
gapless iron based superconductors and show how to distinguish accidental from
symmetry dictated nodes. We shall argue the same idea leads to a method for
detecting a class of the elusive spin liquids.",1205.5933v3
2012-05-30,New Phase Induced by Pressure in the Iron-Arsenide Superconductor K-Ba122,"The electrical resistivity rho of the iron-arsenide superconductor
Ba1-xKxFe2As2 was measured in applied pressures up to 2.6 GPa for four
underdoped samples, with x = 0.16, 0.18, 0.19 and 0.21. The antiferromagnetic
ordering temperature T_N, detected as a sharp anomaly in rho(T), decreases
linearly with pressure. At pressures above around 1.0 GPa, a second sharp
anomaly is detected at a lower temperature T_0, which rises with pressure. We
attribute this second anomaly to the onset of a phase that causes a
reconstruction of the Fermi surface. This new phase expands with increasing x
and it competes with superconductivity. We discuss the possibility that a
second spin-density wave orders at T_0, with a Q vector distinct from that of
the spin-density wave that sets in at T_N.",1205.6730v2
2012-05-30,The Submm and mm Excess of the SMC: Magnetic Dipole Emission from Magnetic Nanoparticles?,"The Small Magellanic Cloud (SMC) has surprisingly strong submm and
mm-wavelength emission that is inconsistent with standard dust models,
including those with emission from spinning dust. Here we show that the
emission from the SMC may be understood if the interstellar dust mixture
includes magnetic nanoparticles, emitting magnetic dipole radiation resulting
from thermal fluctuations in the magnetization. The magnetic grains can be
metallic iron, magnetite Fe3O4, or maghemite gamma-Fe2O3. The required mass of
iron is consistent with elemental abundance constraints. The magnetic dipole
emission is predicted to be polarized orthogonally to the normal electric
dipole radiation if the nanoparticles are inclusions in larger grains. We
speculate that other low-metallicity galaxies may also have a large fraction of
the interstellar Fe in magnetic materials.",1205.6810v1
2012-06-02,Effect of substitution and heat treatment route on polycrystalline FeSe0.5Te0.5 Superconductors,"The effect of atomic substitution of Te in iron based superconductors FeSe
(1:1 type), which exhibits the simplest crystal structure among the iron-based
superconductors, has been investigated in terms of structural, electronic
transport and magnetic properties. Polycrystalline samples with nominal Se:Te
in FeSe1-xTex samples for x=0.5350{\deg}C, 0.5700{\deg}C, 0.6700{\deg}C and
0.75700{\deg}C were synthesized by the solid-state reaction method. It has been
observed that the most superconducting properties seen in x=0.6700{\deg}C
samples as dc magnetic susceptibility, ac susceptibility and resistivity
measurements. Tc enhancement is well correlated with the Te substitution up to
75% and c lattice parameters monotonically increased with increasing Te
concentration.",1206.0401v2
2012-06-05,Fractional power-law behavior and its origin in iron-chalcogenide and ruthenate superconductors: Insights from first-principles calculations,"We perform realistic first-principles calculations of iron chalcogenides and
ruthenate based materials to identify experimental signatures of Hund's
coupling induced correlations in these systems. We find that FeTe and
K$_x$Fe$_{2-y}$Se$_2$ display unusual orbital dependent fractional powerlaw
behavior in their quasiparticle self energy and optical conductivity, a
phenomena first identified in SrRuO$_3$. Strong incoherence in the paramagnetic
state of these materials results in electronic states hidden to angle-resolved
photoemission spectroscopy which reemerge at low temperatures. We identify the
effective low energy Hamiltonian describing these systems and show that these
anomalies are not controlled by the proximity to a quantum critical point but
result from coexistence of fast quantum mechanical orbital fluctuations and
slow spin fluctuations.",1206.0801v3
2012-06-08,Studies of concentration and temperature dependencies of precipitation kinetics in iron-copper alloys using kinetic monte carlo and stochastic statistical simulations,"The earlier-developed ab initio model and the kinetic Monte Carlo method
(KMCM) are used to simulate precipitation in a number of iron-copper alloys
with different copper concentrations x and temperatures T. The same simulations
are also made using the improved version of the earlier-suggested stochastic
statistical method (SSM). The results obtained enable us to make a number of
general conclusions about the dependencies of the decomposition kinetics in
Fe-Cu alloys on x and T. We also show that the SSM describes the precipitation
kinetics in a fair agreement with the KMCM, and employing the SSM in
conjunction with the KMCM enables us to extend the KMC simulations to the
longer evolution times. The results of simulations seem to agree with available
experimental data for Fe-Cu alloys within statistical errors of simulations and
the scatter of experimental results. Comparison of results of simulations to
experiments for some multicomponent Fe-Cu-based alloys enables us to make
certain conclusions about the influence of alloying elements in these alloys on
the precipitation kinetics at different stages of evolution.",1206.1792v1
2012-06-12,Density functional theory calculations and vibrational spectroscopy on iron spin-crossover compounds,"Iron complexes with a suitable ligand field undergo spin-crossover (SCO),
which can be induced reversibly by temperature, pressure or even light.
Therefore, these compounds are highly interesting candidates for optical
information storage, for display devices and pressure sensors. The SCO
phenomenon can be conveniently studied by spectroscopic techniques like Raman
and infrared spectroscopy as well as nuclear inelastic scattering, a technique
which makes use of the M\""ossbauer effect. This review covers new developments
which have evolved during the last years like, e.g. picosecond infrared
spectroscopy and thin film studies but also gives an overviewon newtechniques
for the theoretical calculation of spin transition phenomena and vibrational
spectroscopic data of SCO complexes.",1206.2469v1
2012-06-13,Dynamics of Metal Centers Monitored by Nuclear Inelastic Scattering,"Nuclear inelastic scattering of synchrotron radiation has been used now since
10 years as a tool for vibrational spectroscopy. This method has turned out
especially useful in case of large molecules that contain a M\""ossbauer active
metal center. Recent applications to iron-sulfur proteins, to iron(II) spin
crossover complexes and to tin-DNA complexes are discussed. Special emphasis is
given to the combination of nuclear inelastic scattering and density functional
calculations.",1206.2760v1
2012-06-25,Structure and physical properties of new layered iron oxychalcogenide BaFe2OSe2,"We have successfully synthesized a new layered iron oxychalcogenide BaFe2OSe2
single crystal. This compound is built up of Ba and Fe-Se(O) layers
alternatively stacked along the c-axis. The Fe-Se(O) layers contain double
chains of edge-shared Fe-Se(O) tetrahedra that propagate along the b-axis and
are bridged by oxygen along the a-axis. Physical property measurements indicate
that BaFe2OSe2 is a semiconductor without the Curie-Weiss behavior up to 350 K.
There is a possible long range antiferromagnetic (AFM) transition at 240 K,
corresponding to the peak in specific heat measurement and two glassy
transitions at 115 K and 43 K. The magnetic entropy up to 300 K is much smaller
than the expected value for Fe2+ in tetrahedral crystal fields and Mosbauer
spectrum indicates that long range magnetic order is unlikely at 294 K. Both
results suggest that a short range magnetic correlations exist above the room
temperature.",1206.5788v1
2012-06-29,Synthesis of a new alkali metal-organic solvent intercalated iron selenide superconductor with Tc{\approx}45K,"We report on a new iron selenide superconductor with a TC onset of 45K and
the nominal composition Lix(C5H5N)yFe2-zSe2, synthesized via intercalation of
dissolved alkaline metal in anhydrous pyridine at room temperature. This
superconductor exhibits a broad transition, reaching zero resistance at 10K.
Magnetization measurements reveal a superconducting shielding fraction of
approximately 30%. Analogous phases intercalated with Na, K and Rb were also
synthesized and characterized. The superconducting transition temperature of
Lix(C5H5N)yFe2-zSe2 is clearly enhanced in comparison to the known
superconductors FeSe0.98 (Tc ~ 8K) and AxFe2-ySe2 (TC ~ 27-32K) and is in close
agreement with critical temperatures recently reported for Lix(NH3)yFe2-zSe2.
Post-annealing of intercalated material (Lix(C5H5N)yFe2-zSe2) at elevated
temperatures drastically enlarges the c-parameter of the unit cell (~44%) and
increases the amount of superconducting shielding fraction to nearly 100%. Our
findings indicate a new synthesis road leading to possibly even higher critical
temperatures in this class of materials by intercalation of organic compounds
between Fe-Se layers.",1206.7022v1
2012-07-09,Multifractal scaling of flux penetration in the Iron-based Superconductor Ba(Fe$_{0.93}$Co$_{0.07}$)$_{2}$As$_2$,"The penetration of magnetic flux fronts in the optimally-doped iron-based
superconductor Ba(Fe$_{1-x}$Co$_{x}$)$_{2}$As$_2$ ($x = 0.07 \pm 0.005$) is
studied by means of magneto-optical imaging and Bitter decoration. The
higher-order analysis of roughening and growth of the magnetic flux front
reveals anomalous scaling properties, indicative of non-Gaussian correlations
of the disorder potential. While higher-order spatial correlation functions
reveal multi-fractal behavior for the roughening, the usual Kardar-Parisi-Zhang
growth exponent is found. Both exponents are found to be independent of
temperature. The scaling behavior is manifestly different from that found for
other modes of flux penetration, such as that mediated by avalanches,
suggesting that multi-scaling is a powerful tool for the characterization of
roughened interfaces. We propose a scenario for vortex penetration based on
two-dimensional percolation and cluster aggregation for an inhomogeneously
disordered superconductor.",1207.2068v2
2012-07-10,Optical properties of the iron-pnictide analog BaMn2As2,"We have investigated the infrared and Raman optical properties of BaMn2As2 in
the ab-plane and along the c-axis. The most prominent features in the infrared
spectra are the Eu and A2u phonon modes which show clear TO-LO splitting from
the energy loss function analysis. All the phonon features we observed in
infrared and Raman spectra are consistent with the calculated values. Compared
to the iron-pnictide analog AFe2As2, this compound is much more two-dimensional
in its electronic properties. For E || c-axis, the overall infrared
reflectivity is insulating like. Within the ab-plane the material exhibits a
semiconducting behavior. An energy gap 2{\Delta}=48 meV can be clearly
identified below room temperature.",1207.2360v1
2012-07-10,NLTE line formation of Fe in late-type stars II: 1D spectroscopic stellar parameters,"We investigate departures from local thermodynamic equilibrium (NLTE) in the
line formation of neutral and singly ionised iron lines and their impact on
spectroscopic stellar parameters. The calculations are performed for an
extensive grid of 1D MARCS models of metal-rich and metal-poor late-type dwarfs
and giants. We find that iron abundances derived from FeI lines are
increasingly underestimated in hotter, lower surface-gravity, and more
metal-poor stars, in a simple and well-defined pattern, while LTE is usually a
realistic approximation for FeII lines. For the vast majority of dwarfs and
giants, the perturbed ionisation balance of FeI and FeII is the main relevant
NLTE effect to consider in the determination of spectroscopic parameters, while
for extremely metal-poor stars and hot giant stars significant impact is seen
also on the excitation balance and on the microturbulence determination from
FeI lines.",1207.2454v1
2012-07-12,Strong electronic correlations from Hund's coupling,"Strong electronic correlations are often associated with the proximity of a
Mott insulating state. In recent years however, it has become increasingly
clear that the Hund's rule coupling (intra-atomic exchange) is responsible for
strong correlations in multi-orbital metallic materials which are not close to
a Mott insulator. Hund's coupling has two effects: it influences the energetics
of the Mott gap and strongly suppresses the coherence scale for the formation
of a Fermi-liquid. A global picture has emerged recently, which emphasizes the
importance of the average occupancy of the shell as a control parameter. The
most dramatic effects occur away from half-filling or single occupancy. The
theoretical understanding and physical properties of these `Hund's metals' are
reviewed, together with the relevance of this concept to transition-metal
oxides of the 3d, and especially 4d series (such as ruthenates), as well as to
the iron-based superconductors (iron pnictides and chalcogenides).",1207.3033v2
2012-07-13,Investigation of the Superconducting Gap Structure in SrFe$_2$(As$_{0.7}$P$_{0.3}$)$_2$ by Magnetic Penetration Depth and Flux Flow Resistivity Analysis,"We measured the microwave surface impedances and obtained the superfluid
density and flux flow resistivity in single crystals of a phosphor-doped
iron-based superconductor SrFe$_2$(As$_{1-x}$P$_{x}$)$_2$ single crystals
($x=0.30$, $T_c=25 \mathrm{K}$). At low temperatures, the superfluid density,
$n_s (T)/n_s(0)$, obeys a power law, $n_s (T)/n_s (0)=1-C(T/T_c)^n$, with a
fractional exponent of $n=1.5$-1.6. The flux flow resistivity was significantly
enhanced at low magnetic fields. These features are consistent with the
presences of both a gap with line nodes and nodeless gaps with a deep minimum.
The remarkable difference observed in the superconducting gap structure between
SrFe$_2$(As$_{1-x}$P$_{x}$)$_2$ and BaFe$_2$(As$_{1-x}$P$_{x}$)$_2$ in our
experiments is important for clarifying the mechanism of iron-based
superconductivity.",1207.3155v1
2012-07-26,High pressure transport studies of the LiFeAs analogues CuFeTe2 and Fe2As,"We have synthesized two iron-pnictide/chalcogenide materials, CuFeTe2 and
Fe2As, which share crystallographic features with known iron-based
superconductors, and carried out high-pressure electrical resistivity
measurements on these materials to pressures in excess of 30 GPa. Both
compounds crystallize in the Cu2Sb-type crystal structure that is
characteristic of LiFeAs (with CuFeTe2 exhibiting a disordered variant). At
ambient pressure, CuFeTe2 is a semiconductor and has been suggested to exhibit
a spin-density-wave transition, while Fe2As is a metallic antiferromagnet. The
electrical resistivity of CuFeTe2, measured at 4 K, decreases by almost two
orders of magnitude between ambient pressure and 2.4 GPa. At 34 GPa, the
electrical resistivity decreases upon cooling the sample below 150 K,
suggesting the proximity of the compound to a metal-insulator transition.
Neither CuFeTe2 nor Fe2As superconduct above 1.1 K throughout the measured
pressure range.",1207.6272v1
2012-07-29,Oriented gap opening in the magnetically ordered state of Iron-pnicitides: an impact of intrinsic unit cell doubling on the $Fe$ square lattice by $As$ atoms,"We show that the complicated band reconstruction near Fermi surfaces in the
magnetically ordered state of iron-pnictides observed by angle-resolved
photoemission spectroscopies (ARPES) can be understood in a meanfield level if
the \emph{intrinsic unit cell doubling} due to As atoms is properly considered
as shown in the recently constructed S$_{4}$ microscopic effective model. The
(0,$\pi$) or ($\pi$,0) col-linear antiferromagnetic (C-AFM) order does not open
gaps between two points at Fermi surfaces linked by the ordered wave vector but
forces a band reconstruction involving four points in unfolded Brillouin zone
(BZ) and gives rise to small pockets or hot spots. The S$_4$ symmetry naturally
chooses a staggered orbital order over a ferro-orbital order to coexist with
the C-AFM order. These results strongly suggest that the kinematics based on
the S$_{4}$ symmetry captures the essential low energy physics of iron-based
superconductors.",1207.6798v1
2012-07-30,Surface adatom conductance filtering in scanning tunneling spectroscopy of Co-doped BaFe2As2 iron pnictide superconductors,"We establish in a combination of ab initio theory and experiments that the
tunneling process in scanning tunneling microscopy/spectroscopy on the A-122
iron pnictide superconductors - in this case BaFe$_{2-x}$Co$_x$As$_2$ - involve
a strong adatom filtering of the differential conductance from the near-EF Fe3d
states, which in turn originates from the top-most sub-surface Fe layer of the
crystal. The calculations show that the dominance of surface Ba-related
tunneling pathways leaves fingerprints found in the experimental differential
conductance data, including large particle-hole asymmetry and an
energy-dependent contrast inversion.",1207.7122v1
2012-08-06,Superconductivity in striped and multi-Fermi-surface Hubbard models: From the cuprates to the pnictides,"Single- and multi-band Hubbard models have been found to describe many of the
complex phenomena that are observed in the cuprate and iron-based
high-temperature superconductors. Simulations of these models therefore provide
an ideal framework to study and understand the superconducting properties of
these systems and the mechanisms responsible for them. Here we review recent
dynamic cluster quantum Monte Carlo simulations of these models, which provide
an unbiased view of the leading correlations in the system. In particular, we
discuss what these simulations tell us about superconductivity in the
homogeneous 2D single-orbital Hubbard model, and how charge stripes affect this
behavior. We then describe recent simulations of a bilayer Hubbard model, which
provides a simple model to study the type and nature of pairing in systems with
multiple Fermi surfaces such as the iron-based superconductors.",1208.1158v1
2012-08-09,Orbital differentiation and the role of orbital ordering in the magnetic state of Fe superconductors,"We analyze the metallic (pi,0) antiferromagnetic state of a five-orbital
model for iron superconductors. We find that with increasing interactions the
system does not evolve trivially from the pure itinerant to the pure localized
regime. Instead we find a region with a strong orbital differentiation between
xy and yz, which are half-filled gapped states at the Fermi level, and
itinerant zx, 3z^2-r^2 and x^2-y^2. We argue that orbital ordering between yz
and zx orbitals arises as a consequence of the interplay of the exchange energy
in the antiferromagnetic x direction and the kinetic energy gained by the
itinerant orbitals along the ferromagnetic y direction with an overall
dominance of the kinetic energy gain. We indicate that iron superconductors are
close to the boundary between the itinerant and the orbital differentiated
regimes and that it could be possible to cross this boundary with doping.",1208.1917v2
2012-08-10,Effective medium approximation and the complex optical properties of the inhomogeneous superconductor K_{0.8}Fe_{2-y}Se_2,"The in-plane optical properties of the inhomogeneous iron-chalcogenide
superconductor K_{0.8}Fe_{2-y}Se_2 with a critical temperature Tc = 31 K have
been modeled in the normal state using the Bruggeman effective medium
approximation for metallic inclusions in an insulating matrix. The volume
fraction for the inclusions is estimated to be ~ 10%; however, they appear to
be highly distorted, suggesting a filamentary network of conducting regions
joined through weak links. The value for the Drude plasma frequency in the
inclusions is much larger than the volume average, which when considered with
the reasonably low values for the scattering rate, suggests that the transport
in the grains is always metallic. Estimates for the dc conductivity and the
superfluid density in the grains places the inclusions on the universal scaling
line close to the other homogeneous iron-based superconductors.",1208.2240v2
2012-08-14,Nematicity from mixed S_{+-} + d_{x^2-y^2} states in iron-based superconductors,"We demonstrate that in iron-based superconductors, the extended S_{+-} SC
state coexists with the d_{x^2-y^2} state under generic conditions. The mixed
S_{+-} + d_{x^2-y^2} SC is a natural nematic state in which the tetragonal
symmetry C_4 is broken to C_2 explaining puzzling findings of nematic SC in
FeSe films [Science 332, 1410 (2011)]. Moreover, we report the possibility of a
first order transition at low-T from the nematic S_{+-} + d_{x^2-y^2} state to
the pure d_{x^2-y^2} state induced by the Zeeman magnetic field proposing an
original experimental strategy for identifying our mixed nematic state in FeSe
films. Extrapolating our findings, we argue that nematicity in non
superconducting states of underdoped and undoped pnictides may reflect mixed
S_{+-} + d_{x^2-y^2} Density Wave states.",1208.2881v3
2012-08-16,Suppression of superconductivity by Neel-type magnetic fluctuations in the iron pnictides,"Motivated by recent experimental detection of Neel-type ($(\pi,\pi)$)
magnetic fluctuations in some iron pnictides, we study the impact of competing
$(\pi,\pi)$ and $(\pi,0)$ spin fluctuations on the superconductivity of these
materials. We show that, counter-intuitively, even short-range, weak Neel
fluctuations strongly suppress the $s^{+-}$ state, with the main effect arising
from a repulsive contribution to the $s^{+-}$ pairing interaction, complemented
by low frequency inelastic scattering. Further increasing the strength of the
Neel fluctuations leads to a low-$T_{c}$ d-wave state, with a possible
intermediate $s+id$ phase. The results suggest that the absence of
superconductivity in a series of hole-doped pnictides is due to the combination
of short-range Neel fluctuations and pair-breaking impurity scattering, and
also that $T_{c}$ of optimally doped pnictides could be further increased if
residual $(\pi,\pi)$ fluctuations were reduced.",1208.3412v2
2012-08-18,On the dual role of the d-electrons in iron-pnictides,"In the stoichiometric Fe-pnictides the same d-electrons form the local
moments and participate in the metallic conductivity. In the manuscript the
emergence of the magnetic moments on the Fe-sites, their interaction with the
itinerant electrons are studied in the paramagnetic phase at the different
relations between the onsite Coulomb repulsion and the intraatomic Hund's
exchange. The energy of the local center that is due to its interaction with
the conduction electrons is calculated exactly. It is found that the spin
density wave transition is controlled by the RKKY interactions between the
centers rather than by the nesting mechanism. In the paramagnetic phase the
electrons scatter on the randomly oriented moments. The calculated inverse mean
free time provides the interpretation for few available experimental data on
the conductivity. The multi-band structure of the energy spectrum in iron
pnictides is taken into account.",1208.3740v2
2012-08-19,A Model of the Cellular Iron Homeostasis Network Using Semi-Formal Methods for Parameter Space Exploration,"This paper presents a novel framework for the modeling of biological
networks. It makes use of recent tools analyzing the robust satisfaction of
properties of (hybrid) dynamical systems. The main challenge of this approach
as applied to biological systems is to get access to the relevant parameter
sets despite gaps in the available knowledge. An initial estimate of useful
parameters was sought by formalizing the known behavior of the biological
network in the STL logic using the tool Breach. Then, once a set of parameter
values consistent with known biological properties was found, we tried to
locally expand it into the largest possible valid region. We applied this
methodology in an effort to model and better understand the complex network
regulating iron homeostasis in mammalian cells. This system plays an important
role in many biological functions, including erythropoiesis, resistance against
infections, and proliferation of cancer cells.",1208.3851v1
2012-08-24,Raman-Scattering Detection of Nearly Degenerate $s$-Wave and $d$-Wave Pairing Channels in Iron-Based Ba$_{0.6}$K$_{0.4}$Fe$_2$As$_2$ and Rb$_{0.8}$Fe$_{1.6}$Se$_2$ Superconductors,"We show that electronic Raman scattering affords a window into the essential
properties of the pairing potential $V_{\mathbf{k},\mathbf{k^{\prime}}}$ of
iron-based superconductors. In Ba$_{0.6}$K$_{0.4}$Fe$_2$As$_2$ we observe band
dependent energy gaps along with excitonic Bardasis-Schrieffer modes
characterizing, respectively, the dominant and subdominant pairing channel. The
$d_{x^2-y^2}$ symmetry of all excitons allows us to identify the subdominant
channel to originate from the interaction between the electron bands.
Consequently, the dominant channel driving superconductivity results from the
interaction between the electron and hole bands and has the full lattice
symmetry. The results in Rb$_{0.8}$Fe$_{1.6}$Se$_2$ along with earlier ones in
Ba(Fe$_{0.939}$Co$_{0.061}$)$_2$As$_2$ highlight the influence of the Fermi
surface topology on the pairing interactions.",1208.5006v2
2012-08-29,Quantum Oscillations in Iron Pnictide Superconductors,"Insight into the electronic structure of the pnictide family of
superconductors is obtained from quantum oscillation measurements. Here we
review experimental quantum oscillation data that reveal a transformation from
large quasi-two dimensional electron and hole cylinders in the paramagnetic
overdoped members of the pnictide family to significantly smaller
three-dimensional Fermi surface sections in the antiferromagnetic parent
members, via a potential quantum critical point at which an effective mass
enhancement is observed. Similarities with the Fermi surface evolution from the
overdoped to the underdoped normal state of the cuprate superconducting family
are discussed, along with the enhancement in antiferromagnetic correlations in
both these classes of materials, and the potential implications for
superconductivity.",1208.5862v1
2012-09-01,"Iron based superconductors: magnetism, superconductivity and electronic structure","Angle resolved photoemission spectroscopy (ARPES) reveals the features of the
electronic structure of quasi-two-dimensional crystals, which are crucial for
the formation of spin and charge ordering and determine the mechanisms of
electron-electron interaction, including the superconducting pairing. The newly
discovered iron based superconductors (FeSC) promise interesting physics that
stems, on one hand, from a coexistence of superconductivity and magnetism and,
on the other hand, from complex multi-band electronic structure. In this review
I want to give a simple introduction to the FeSC physics, and to advocate an
opinion that all the complexity of FeSC properties is encapsulated in their
electronic structure. For many compounds, this structure was determined in
numerous ARPES experiments and agrees reasonably well with the results of band
structure calculations. Nevertheless, the existing small differences may help
to understand the mechanisms of the magnetic ordering and superconducting
pairing in FeSC.",1209.0140v1
2012-09-03,Magnetism and its microscopic origin in iron-based high-temperature superconductors,"High-temperature superconductivity in the iron-based materials emerges from,
or sometimes coexists with, their metallic or insulating parent compound
states. This is surprising since these undoped states display dramatically
different antiferromagnetic (AF) spin arrangements and N$\rm \acute{e}$el
temperatures. Although there is general consensus that magnetic interactions
are important for superconductivity, much is still unknown concerning the
microscopic origin of the magnetic states. In this review, progress in this
area is summarized, focusing on recent experimental and theoretical results and
discussing their microscopic implications. It is concluded that the parent
compounds are in a state that is more complex than implied by a simple Fermi
surface nesting scenario, and a dual description including both itinerant and
localized degrees of freedom is needed to properly describe these fascinating
materials.",1209.0381v1
2012-09-06,The role of 245 phase in alkaline iron selenide superconductors revealed by high pressure studies,"Here we show that a pressure of about 8 GPa suppresses both the vacancy order
and the insulating phase, and a further increase of the pressure to about 18
GPa induces a second transition or crossover. No superconductivity has been
found in compressed insulating 245 phase. The metallic phase in the
intermediate pressure range has a distinct behavior in the transport property,
which is also observed in the superconducting sample. We interpret this
intermediate metal as an orbital selective Mott phase (OSMP). Our results
suggest that the OSMP provides the physical pathway connecting the insulating
and superconducting phases of these iron selenide materials.",1209.1340v2
2012-09-10,Anisotropic but nodeless superconducting gap in the presence of spin density wave in iron-pnictide superconductor NaFe1-xCoxAs,"The coexisting regime of spin density wave (SDW) and superconductivity in the
iron pnictides represents a novel ground state. We have performed high
resolution angle-resolved photoemission measurements on NaFe1-xCoxAs (x =
0.0175) in this regime and revealed its distinctive electronic structure, which
provides some microscopic understandings of its behavior. The SDW signature and
the superconducting gap are observed on the same bands, illustrating the
intrinsic nature of the coexistence. However, because the SDW and
superconductivity are manifested in different parts of the band structure,
their competition is non-exclusive. Particularly, we found that the gap
distribution is anisotropic and nodeless, in contrast to the isotropic
superconducting gap observed in an SDW-free NaFe1-xCoxAs (x=0.045), which puts
strong constraints on theory.",1209.1967v2
2012-09-14,Acoustic and optical phonon dynamics from femtosecond time-resolved optical spectroscopy of superconducting iron pnictide Ca(Fe_0.944Co_0.056)_2As_2,"We report temperature evolution of coherently excited acoustic and optical
phonon dynamics in superconducting iron pnictide single crystal
Ca(Fe_0.944Co_0.056)_2As_2 across the spin density wave transition at T_SDW ~
85 K and superconducting transition at T_SC ~20 K. Strain pulse propagation
model applied to the generation of the acoustic phonons yields the temperature
dependence of the optical constants, and longitudinal and transverse sound
velocities in the temperature range of 3.1 K to 300 K. The frequency and
dephasing times of the phonons show anomalous temperature dependence below T_SC
indicating a coupling of these low energy excitations with the Cooper-pair
quasiparticles. A maximum in the amplitude of the acoustic modes at T ~ 170 is
seen, attributed to spin fluctuations and strong spin-lattice coupling before
T_SDW.",1209.3174v2
2012-09-22,Dynamical Mean-Field Study of Local Pairing Interaction Mediated by Spin and Orbital Fluctuations in Iron Pnictide Superconductors,"We investigate the two-orbital Hubbard model, which reproduces the electron
and hole Fermi surfaces in the iron pnictide superconductors, in the presence
of the Jahn-Teller electron-phonon coupling by using the dynamical mean-field
theory. When the intra- and inter-orbital Coulomb interactions, $U$ and $U'$,
increase with $U=U'$, both the local spin and orbital susceptibilities,
$\chi_{s}$ and $\chi_{o}$, increase with $\chi_{s}=\chi_{o}$ because of the
spin-orbital symmetry. Due to the Hund's rule coupling $J$, $\chi_{s}$ is
enhanced and dominates over $\chi_{o}$ resulting in the repulsive local pairing
interaction $V_{\rm loc}>0$, while due to the electron-phonon coupling $g$,
$\chi_{o}$ is enhanced and dominates over $\chi_{s}$ resulting in the
attractive one $V_{\rm loc}<0$ which induces the intra-orbital s-wave pairing.
Remarkably, $V_{\rm loc}$ is weakly dependent on doping and can be attractive
for heavily electron-doped regime where the superconductivity is observed
without Fermi surface nesting.",1209.4954v2
2012-09-24,Magnetic phase separation and superfluid density measurements in alkali metal-organic solvent intercalated iron selenide superconductor Lix(C5H5N)yFe2-zSe2,"We report the low-temperature electronic and magnetic properties of the
alkali metal-organic solvent intercalated iron selenide superconductor
Lix(C5H5N)yFe2-zSe using muon-spin-spectroscopy measurements. The zero-field
\muSR results indicate that nearly half of the sample is magnetically ordered
and there is a spatial phase separation between the superconducting and the
magnetic fraction. The transverse-field \muSR results show that the temperature
dependence of the penetration depth \lambda(T) in the mixed state of
Lix(C5H5N)yFe2-zSe can be explained using a two-gap s+s-wave model with gap
values of 6.82(92) and 0.93(7) meV. This implies that the symmetry of the
superconducting gap in this system remains unaltered to the parent compound
FeSe even after the intercalation with the molecular spacer layer. We obtain
\lambda (0) = 485(21) nm at T = 0 K.",1209.5279v1
2012-09-24,Ba1-xNaxTi2Sb2O (0.0 <= x <= 0.33): A Layered Titanium-based Pnictide Oxide Superconductor,"A new layered Ti-based pnictide oxide superconductor, Ba1-xNaxTi2Sb2O (0.0 <=
x <= 0.33), is reported. X-ray studies reveal it crystallizes in the tetragonal
CeCr2Si2C structure. The undoped parent compound, BaTi2Sb2O (P4/mmm;
a=4.1196(1){\AA}; c=8.0951(2){\AA}), exhibits a CDW/SDW transition at 54K. Upon
chemical doping with Na, the CDW/SDW transition is systematically suppressed
and super-conductivity arises with the critical temperatures, Tc, increasing to
5.5 K. Bulk superconductivity is confirmed by resistivity, magnetic and heat
capacity measurements. Like the high-Tc cuprates and the iron pnictides,
superconductivity in BaTi2Sb2O arises from an ordered state. Similarities and
differences to the cuprate and iron pnictide supercon-ductors are discussed.",1209.5447v2
2012-09-27,Oxygen Reduction Activity of Carbon Nitride Supported on Carbon Nanotubes,"Fuel cells offer an alternative to burning fossil fuels, but use platinum as
a catalyst which is expensive and scarce. Cheap, alternative catalysts could
enable fuel cells to become serious contenders in the green energy sector. One
promising class of catalyst for electrochemical oxygen reduction is
iron-containing, nanostructured, nitrogen-doped carbon. The catalytic activity
of such N-doped carbons has improved vastly over the years bringing industrial
applications ever closer. Stoichiometric carbon nitride powder has only been
observed in recent years. It has nitrogen content up to 57% and as such is an
extremely interesting material to work with. The electrochemical activity of
carbon nitride has already been explored, confirming that iron is not a
necessary ingredient for 4-electron oxygen reduction. Here, we synthesize
carbon nitride on a carbon nanotube support and subject it to high temperature
treatment in an effort to increase the surface area and conductivity. The
results lend insight into the mechanism of oxygen reduction and show the
potential for carbon nanotube-supported carbon nitride to be used as a catalyst
to replace platinum in fuel cells.",1209.6112v1
2012-09-27,Temperature dependence of the paramagnetic spin excitations in BaFe$_2$As$_2$,"We use inelastic neutron scattering to study temperature dependence of the
paramagnetic spin excitations in iron pnictide BaFe$_2$As$_2$ throughout the
Brillouin zone. In contrast to a conventional local moment Heisenberg system,
where paramagnetic spin excitations are expected to have a Lorentzian function
centered at zero energy transfer, the high-energy ($\hbar\omega>100$ meV)
paramagnetic spin excitations in BaFe$_2$As$_2$ exhibit spin-wave-like features
up to at least 290 K ($T= 2.1T_N$). Furthermore, we find that the sizes of the
fluctuating magnetic moments $<m^2>\approx 3.6\ \mu^2_B$ per Fe are essentially
temperature independent from the AF ordered state at $0.05T_N$ to $2.1T_N$,
which differs considerably from the temperature dependent fluctuating moment
observed in the iron chalcogenide Fe$_{1.1}$Te [I. A. Zaliznyak {\it et al.},
Phys. Rev. Lett. {\bf 107}, 216403 (2011).]. These results suggest
unconventional magnetism and strong electron correlation effects in
BaFe$_2$As$_2$.",1209.6271v1
2012-10-01,The distinct in-plane resistivity anisotropy in the nematic states of detwinned NaFeAs and FeTe single crystals: evidences for Hund's rule metal,"The in-plane resistivity anisotropy has been studied with the Montgomery
method on two detwinned parent compounds of the iron-based superconductors,
NaFeAs and FeTe. For NaFeAs, the resistivity in the antiferromagnetic (AFM)
direction is smaller than that in the ferromagnetic (FM) direction, similar to
that observed in BaFe2As2 before. While for FeTe, the resistivity in the AFM
direction is larger than that in the FM direction. We show that these two
opposite resistivity anisotropy behaviors could be attributed to the strong
Hund's rule coupling effects: while the iron pnictides are in the itinerant
regime, where the Hund's rule coupling causes strong reconstruction and
nematicity of the electronic structure; the FeTe is in the localized regime,
where Hund's rule coupling makes hopping along the FM direction easier than
along the AFMdirection, similar to the colossal magnetoresistance observed in
some manganites.",1210.0397v1
2012-10-02,Magnetism of iron and nickel from rotationally invariant Hirsch-Fye quantum Monte Carlo calculations,"We present a rotationally invariant Hirsch-Fye quantum Monte Carlo algorithm
in which the spin rotational invariance of Hund's exchange is approximated by
averaging over all possible directions of the spin quantization axis. We employ
this technique to perform benchmark calculations for the two- and three-band
Hubbard models on the infinite-dimensional Bethe lattice. Our results agree
quantitatively well with those obtained using the continuous-time quantum Monte
Carlo method with rotationally invariant Coulomb interaction. The proposed
approach is employed to compute the electronic and magnetic properties of
paramagnetic $\alpha$ iron and nickel. The obtained Curie temperatures agree
well with experiment. Our results indicate that the magnetic transition
temperature is significantly overestimated by using the density-density type of
Coulomb interaction.",1210.0911v3
2012-10-09,Indirect evidence for strong coupling superconductivity in FeSe under pressure from first-principle calculations,"Whether the pairing mechanism for superconductivity in iron-based
superconductors is of itinerant or local character is a question still debated
on. In order to investigate the influence of Fermi surface nesting, we
calculate from first-principles the static susceptibility of FeSe under applied
pressures, both hydrostatic and non-hydrostatic. We show that the electronic
band structures are highly sensitive to the way pressure is applied and
confront our theoretical results with conclusions drawn from experiments. Given
that the critical temperature of FeSe is quite universal as function of
pressure, this is clear evidence that in FeSe the evolution of Fermi surface
nesting cannot account for the evolution of the critical temperature with
pressure. Hence we argue that the pairing in iron-chalcogenide compounds should
be of strong-coupling spin fluctuation origin.",1210.2593v1
2012-10-19,Non-collinear magnetic ordering in compressed FePd$_3$ ordered alloy: a first principles study,"By means of ab initio calculations based on the density functional theory we
investigated magnetic phase diagram of ordered FePd$_3$ alloy as a function of
external pressure.
  Considering several magnetic configurations we concluded that the system
under pressure has a tendency to non-collinear spin alignment. Analysis of the
Heisenberg exchange parameters $J_{ij}$ revealed strong dependence of iron-iron
magnetic couplings on polarization of Pd atoms. To take into account the latter
effect we built an extended Heisenberg model with higher order (biquadratic)
terms. Minimizing the energy of this Hamiltonian, fully parameterized using the
results of ab initio calculations, we found a candidate for a ground state of
compressed FePd$_3$, which can be seen as two interpenetrating ""triple-Q""
phases.",1210.5478v2
2012-11-08,Orbital Selectivity in Hund's metals: The Iron Chalcogenides,"We show that electron correlations lead to a bad metallic state in
chalcogenides FeSe and FeTe despite the intermediate value of the Hubbard
repulsion $U$ and Hund's rule coupling $J$. The evolution of the quasi particle
weight $Z$ as a function of the interaction terms reveals a clear crossover at
$U \simeq$ 2.5 eV. In the weak coupling limit $Z$ decreases for all correlated
$d$ orbitals as a function of $U$ and beyond the crossover coupling they become
weakly dependent on $U$ while strongly depend on $J$. A marked orbital
dependence of the $Z$'s emerges even if in general the orbital-selective Mott
transition only occurs for relatively large values of $U$. This two-stage
reduction of the quasi particle coherence due to the combined effect of Hubbard
$U$ and the Hund's $J$, suggests that the iron-based superconductors can be
referred to as Hund's correlated metals.",1211.2015v1
2012-11-12,Spectral effects simulation with two-dimensional magnetohydrodynamic models of the solar photosphere,"To study the structure of spatially unresolved features of the solar
photosphere, we calculated the Stokes profiles of seven photospheric iron lines
using two-dimensional nonstationary MHD models of solar granulation for various
amounts of magnetic flux (0, 10, 20, 30 mT). We investigate variations in the
absolute wavelength shifts and bisectors of the I profiles, as well as
variations in the zero-crossing wavelength shifts, amplitude and area asymmetry
of the V profiles as functions of magnetic field strength and time. The
center-to-limb variations of the Stokes profiles are analyzed. The iron
abundance is found to be 7.57, with the photosphere inhomogeneities taken into
account. Although most of the spectral effects simulated within the scope of
the two-dimensional MHD models are in satisfactory agreement with observational
data, these models cannot always give a quantitative agreement. The absolute
wavelength shifts of the Stokes profiles of Fe II lines calculated with the MHD
models are substantially smaller than the observed ones.",1211.2791v1
2012-11-19,"Electronic band structure and momentum dependence of the superconducting gap in (Ca, Na)Fe2As2 from angle-resolved photoemission spectroscopy","Electronic structure of newly synthesized single crystals of calcium iron
arsenide doped with sodium with Tc ranging from 33 to 14 K has been determined
by angle-resolved photoemission spectroscopy (ARPES). The measured band
dispersion is in general agreement with theoretical calculations, nonetheless
implies absence of Fermi surface nesting at antiferromagnetic vector. A clearly
developing below Tc strongly band-dependant superconducting gap has been
revealed for samples with various doping levels. BCS ratio for optimal doping,
$2\Delta/k_{\rm B}T_{\rm c}=5.5$, is substantially smaller than the numbers
reported for related compounds, implying a non-trivial relation between
electronic dispersion and superconducting gap in iron arsenides.",1211.4593v1
2012-11-20,Transport properties for liquid silicon-oxygen-iron mixtures at Earth's core conditions,"We report on the thermal and electrical conductivities of two liquid
silicon-oxygen-iron mixtures (Fe$_{0.82}$Si$_{0.10}$O$_{0.08}$ and
Fe$_{0.79}$Si$_{0.08}$O$_{0.13}$), representative of the composition of the
Earth's outer core at the relevant pressure-temperature conditions, obtained
from density functional theory calculations with the Kubo-Greenwood
formulation. We find thermal conductivities $k$ =100 (160) W m$^{-1}$ K$^{-1}$,
and electrical conductivities $\sigma = 1.1 (1.3) \times 10^6 \Omega^{-1}$
m$^{-1}$ at the top (bottom) of the outer core. These new values are between 2
and 3 times higher than previous estimates, and have profound implications for
our understanding of the Earth's thermal history and the functioning of the
Earth's magnetic field, including rapid cooling rate for the whole core or high
level of radiogenic elements in the core. We also show results for a number of
structural and dynamic properties of the mixtures, including the partial radial
distribution functions, mean square displacements, viscosities and speeds of
sound.",1211.4718v1
2012-11-26,The nature of high-energy radiation damage in iron: Modeling results,"Understanding and predicting a material's performance in response to
high-energy radiation damage, as well as designing future materials to be used
in intense radiation environments, requires the knowledge of the structure,
morphology and amount of radiation-induced structural change. We report the
results of molecular dynamics simulations of high-energy radiation damage in
iron in the range 0.2-0.5 MeV. We analyze and quantify the nature of collision
cascades both at the global and local scale. We find that the structure of
high-energy collision cascades becomes increasingly continuous as opposed to
showing sub-cascade branching reported previously. At the local length scale,
we find large defect clusters and novel small vacancy and interstitial
clusters. These features form the basis for physical models aimed at
understanding the effects of high energy radiation damage in structural
materials.",1211.6147v1
2012-11-30,Sensitivity of the r-process to nuclear masses,"The rapid neutron capture process (r-process) is thought to be responsible
for the creation of more than half of all elements beyond iron. The scientific
challenges to understanding the origin of the heavy elements beyond iron lie in
both the uncertainties associated with astrophysical conditions that are needed
to allow an r-process to occur and a vast lack of knowledge about the
properties of nuclei far from stability. There is great global competition to
access and measure the most exotic nuclei that existing facilities can reach,
while simultaneously building new, more powerful accelerators to make even more
exotic nuclei. This work is an attempt to determine the most crucial nuclear
masses to measure using an r-process simulation code and several mass models
(FRDM, Duflo-Zuker, and HFB-21). The most important nuclear masses to measure
are determined by the changes in the resulting r-process abundances. Nuclei
around the closed shells near N=50, 82, and 126 have the largest impact on
r-process abundances irrespective of the mass models used.",1211.7310v1
2012-11-30,Paramagnetic spin excitations in insulating Rb$_{0.8}$Fe$_{1.6}$Se$_2$,"We use neutron scattering to study temperature dependent spin excitations in
insulating antiferromagnetic (AF) Rb$_{0.8}$Fe$_{1.6}$Se$_2$. In the
low-temperature AF state, spin waves can be accurately described by a local
moment Heisenberg Hamiltonian. On warming to around the Neel temperature of
T_N=500$ K, low-energy (E<30meV) paramagnetic spin excitations form
Lorentzian-like quasielastic peaks centered at the AF wave vectors associated
with spin waves, while high-energy (E>50meV) spin excitations become heavily
damped. Upon further warming to above the structural distortion temperature of
T_s=524K, the entire paramagnetic excitations become overdamped. These results
suggest that AF Rb$_{0.8}$Fe$_{1.6}$Se$_2$ is not a copper-oxide-like Mott
insulator, and has less electron correlations compared with metallic iron
pnictides and iron chalcogenides.",1211.7328v1
2012-12-04,"Growth, Characterization, Vortex Pinning and Vortex Flow Properties of Single Crystals of Iron Chalcogenide Superconductor FeCr$_{0.02}$Se","We report the growth and characterization of single crystals of iron
chalcogenide superconductor FeCr$_{0.02}$Se. There is an enhancement of the
superconducting transition temperature (T$_{\rm c}$) as compared to the T$_{\rm
c}$ of the single crystals of the parent compound Fe$_{1+x}$Se by about 25%.
The superconducting parameters such as the critical fields, coherence length,
penetration depth and the Ginzburg-Landau parameter have been estimated for
these single crystals. Analysis of the critical current data suggests a
fluctuation in electronic mean free path induced ($\delta l$) pinning mechanism
in this material. Thermally activated transport across the superconducting
transition in the presence of external magnetic fields suggests a crossover
from a single vortex pinning regime at low fields to a collective flux creep
regime at higher magnetic fields. The nature of charge carriers in the normal
state estimated from the Hall effect and thermal transport measurements could
provide crucial information on the mechanism of superconductivity in Fe-based
materials.",1212.0814v2
2012-12-06,Quantum transport modeling of Fe/MgO/Fe magnetic tunnel junction with FeO$_{0.5}$ buffer layer: the effects of correlations,"We report \textit{ab initio} simulations of quantum transport properties of
Fe/MgO/Fe trilayer structures with FeO$_{0.5}$ buffer iron oxide layer, where
on-site Coulomb interaction is explicitly taken into account by local density
approximation + Hubbard \textit{U} approach. We show that on-site Coulomb
repulsion in the iron-oxygen layer can cause a dramatic drop of the tunnel
magnetoresistance of the system. We present an understanding of microscopic
details of this phenomenon, connecting it to localization of the Fermi
electrons of particular symmetry, which takes place in the buffer Fe-O layer,
when on-site Coulomb repulsion is introduced. We further study the possible
influence of the symmetry reduction in the buffer Fe-O layer on the transport
properties of the Fe/MgO/Fe interface.",1212.1374v1
2012-12-19,Optical conductivity and Raman scattering of iron superconductors,"We discuss how to analyze the optical conductivity and Raman spectra of
multi-orbital systems using the velocity and the Raman vertices in a similar
way Raman vertices were used to disentangle nodal and antinodal regions in
cuprates. We apply this method to iron superconductors in the magnetic and
non-magnetic states, studied at the mean field level. We find that the
anisotropy in the optical conductivity at low frequencies reflects the
difference between the magnetic gaps at the X and Y electron pockets. Both gaps
are sampled by Raman spectroscopy. We also show that the Drude weight
anisotropy in the magnetic state is sensitive to small changes in the lattice
structure.",1212.4765v2
2013-01-09,Power-law Temperature Dependent Hall Angle in the Normal State and its Correlation with Superconductivity in iron-pnictides,"We report Hall measurement of the normal state in K- and Co-doped
BaFe$_2$As$_2$, as well NaFe$_{1-x}$Co$_x$As. We found that a power-law
temperature dependence of Hall angle, cot$\theta_{\rm H}$$\propto$ $T^\beta$,
prevails in normal state with temperature range well above the structural,
spin-density-wave and superconducting transitions for the all samples with
various doping levels. The power $\beta$ is nearly 4 for the parent compounds
and the heavily underdoped samples, while around 3 for the superconducting
samples. The $\beta$ suddenly changes from 4 to 3 at a doping level that is
close to the emergence of superconductivity. It suggests that the $\beta$ of
$\sim 3$ is clearly tied to the superconductivity. Our data suggest that,
similar to cuprates, there exists a connection between the physics in the
normal state and superconductivity of iron-pnictides. These findings shed light
on the mechanism of high-temperature superconductivity.",1301.1734v1
2013-01-09,Interplay between lattice and spin states degree of freedom in the FeSe superconductor: dynamic spin state instabilities,"Polarized Raman-scattering spectra of superconducting, single-crystalline
FeSe evidence pronounced phonon anomalies with temperature reduction. A large
6.5% hardening of the B_1g(Fe) phonon mode is attributed to the suppression of
local fluctuations of the iron spin state with the gradual decrease of the iron
paramagnetic moment. The ab-initio lattice dynamic calculations support this
conclusion. The enhancement of the low-frequency spectral weight above the
structural phase transition temperature T_s and its change below T_s is
discussed in relation with the opening of an energy gap between low (S=0) and
higher spin states which prevents magnetic order in FeSe. The very narrow
phonon line widths compared to observations in FeTe suggests the absence of
intermediate spin states in the fluctuating spin state manifold in FeSe.",1301.1960v1
2013-01-14,Pressure-Induced Superconductivity and Its Scaling with Doping-Induced Superconductivity in the Iron Pnictide with Skutterudite Intermediary Layers,"The Ca10(PtnAs8)(Fe2As2)5 (n=3,4) compounds are a new type of iron pnictide
superconductors whose structures consist of stacking Ca-PtnAs8-Ca-Fe2As2 layers
in a unit cell. When n=3 (the 10-3-8 phase), the undoped compound is an
antiferromagnetic (AFM) semiconductor, while, when n=4 (the 10-4-8 phase), the
undoped compound is a superconductor with the transition temperature of 26K.
Here we report the results of high-pressure studies on the 10-3-8 compound
obtained through a combination of in-situ resistance, magnetic susceptibility,
and Hall coefficient measurements. We find that its AFM order can be suppressed
completely at 3.5 GPa and then superconducting state appears in the pressure
range of 3.5-7 GPa. The pressure dependence of superconducting transition
temperature displays a dome-like shape.",1301.2863v2
2013-01-16,High-Pressure Evolution of the Specific Heat of a Strongly Underdoped Ba(Fe0.963Co0.037)As2 Iron-Based Superconductor,"We report specific-heat experiments under the influence of high pressure on a
strongly underdoped Co-substituted BaFe2As2 single crystal. This allows us to
study the phase diagram of this iron pnictide superconductor with a bulk
thermodynamic method and pressure as a clean control parameter. The data show
large specific-heat anomalies at the superconducting transition temperature,
which proves the bulk nature of pressure-induced superconductivity. The
transitions in the specific heat are sharper than in resistivity, which
demonstrates the necessity of employing bulk thermodynamic methods to explore
the exact phase diagram of pressure-induced Fe-based superconductors. The Tc at
optimal pressure and the superconducting condensation energy are found to be
larger than in optimally Co-doped samples at ambient pressure, which we
attribute to a weak pair breaking effect of the Co ions.",1301.3579v3
2013-01-31,Electronic structure of vacancy-ordered iron-selenide K$_{0.5}$Fe$_{1.75}$Se$_2$,"The electronic structure of the vacancy-ordered K$_{0.5}$Fe$_{1.75}$Se$_2$
iron-selenide compound (278 phase) is studied using the first-principles
density functional method. The ground state of the 278 phase is stripe-like
antiferromagnetic, and its bare electron susceptibility shows a large peak
around $(\pi, \pi)$ in the folded Brillouin zone. Near Fermi level, the density
of states are dominated by the Fe-3d orbitals, and both electron-like and
hole-like Fermi surfaces appear in the Brillouin zone. Unfolded band structure
shows limited similarities to a hole doped 122 phase. With 0.1e electron
doping, the susceptibility peak is quickly suppressed and broadened; while the
two-dimensionality of the electron-like Fermi surfaces are greatly enhanced,
resulting in a better nesting behavior. Our study should be relevant to the
recently reported superconducting phase K$_{0.5+x}$Fe$_{1.75+y}$Se$_2$ with
both $x$ and $y$ very tiny.",1301.7655v3
2013-02-02,Carrier density dependence of the magnetic properties in iron-doped Bi2Se3 topological insulator,"The electronic and magnetic properties of iron-doped topological insulator
Bi1.84-xFe0.16CaxSe3 single crystals were studied. By co-doping Fe and Ca
atoms, ferromagnetic bulk states with different carrier density (from n-type to
p-type) were obtained. Effective magnetic moments for each Fe atom was
estimated as small as about 0.07$\mu$B. Magnetic and non-magnetic phases
separation was observed in all samples. Our results suggest that the bulk
ferromagnetism in Fe-doped Bi2Se3 is not intrinsic and regardless of carrier
density.",1302.0371v1
2013-02-07,Discovery of Fe K-alpha X-ray reverberation around the black holes in MCG-5-23-16 and NGC 7314,"Several X-ray observations have recently revealed the presence of
reverberation time delays between spectral components in AGN. Most of the
observed lags are between the power-law Comptonization component, seen
directly, and the soft excess produced by reflection in the vicinity of the
black hole. NGC 4151 was the first object to show these lags in the iron K
band. Here, we report the discovery of reverberation lags in the Fe K band in
two other sources: MCG-5-23-16 and NGC 7314. In both objects, the 6-7 keV band,
where the Fe K line peaks, lags the bands at lower and higher energies with a
time delay of ~ 1 kilo-seconds. These lags are unlikely to be due to the narrow
Fe K line. They are fully consistent with reverberation of the
relativistically-broadened iron K line. The measured lags, their time-scale and
spectral modeling, indicate that most of the radiation is emitted at ~ 5 and 24
gravitational radii for MCG-5-23-16 and NGC 7314 respectively.",1302.1761v2
2013-02-10,Nodal gap in iron-based superconductor CsFe$_2$As$_2$ probed by quasiparticle heat transport,"The thermal conductivity of iron-based superconductor CsFe$_2$As$_2$ single
crystal ($T_c =$ 1.81 K) was measured down to 50 mK. A significant residual
linear term $\kappa_0/T$ = 1.27 mW K$^{-2}$ cm$^{-1}$ is observed in zero
magnetic field, which is about 1/10 of the normal-state value in upper critical
field $H_{c2}$. In low magnetic field, $\kappa_0/T$ increases rapidly with
field. The overall field dependence of $\kappa_0/T$ for our CsFe$_2$As$_2$
(with residual resistivity $\rho_0$ = 1.80 $\mu\Omega$ cm) lies between the
dirty KFe$_2$As$_2$ (with $\rho_0$ = 3.32 $\mu\Omega$ cm) and the clean
KFe$_2$As$_2$ (with $\rho_0$ = 0.21 $\mu\Omega$ cm). These results strongly
suggest nodal superconducting gap in CsFe$_2$As$_2$, similar to its sister
compound KFe$_2$As$_2$.",1302.2300v2
2013-02-12,Anomalous Surface Segregation Profiles in Ferritic FeCr Stainless Steel,"The iron-chromium alloy and its derivatives are widely used for their
remarkable resistance to corrosion, which only occurs in a narrow concentration
range around 9 to 13 atomic percent chromium. Although known to be due to
chromium enrichment of a few atoms thick layer at the surfaces, the
understanding of its complex atomistic origin has been a remaining challenge.
We report an investigation of the thermodynamics of such surfaces at the atomic
scale by means of Monte Carlo simulations. We use a Hamiltonian which provides
a parameterization of previous ab initio results and successfully describes the
alloy's unusual thermodynamics. We report a strong enrichment in Cr of the
surfaces for low bulk concentrations, with a narrow optimum around 12 atomic
percent chromium, beyond which the surface composition decreases drastically.
This behavior is explained by a synergy between (i) the complex phase
separation in the bulk alloy, (ii) local phase transitions that tune the layers
closest to the surface to an iron-rich state and inhibit the bulk phase
separation in this region, and (iii) its compensation by a strong and
non-linear enrichment in Cr of the next few layers. Implications with respect
to the design of prospective nanomaterials are briefly discussed.",1302.2838v1
2013-02-19,High critical current density and low anisotropy in textured Sr1-xKxFe2As2 tapes for high field applications,"From the application point of view, large critical current densities Jc (H)
for superconducting wires are required, preferably for magnetic fields higher
than 5 T. Here we show that strong c-axis textured Sr1-xKxFe2As2 tapes with
nearly isotropic transport Jc were fabricated by an ex-situ powder-in-tube
(PIT) process. At 4.2 K, the Jc values show extremely weak magnetic field
dependence and reach high values of 1.7x10^4 A/cm^2 at 10 T and 1.4x10^4 A/cm^2
at 14 T, respectively, these values are by far the highest ever reported for
iron based wires and approach the Jc level desired for practical applications.
Transmission electron microscopy investigations revealed that amorphous oxide
layers at grain boundaries were significantly reduced by Sn addition which
resulted in greatly improved intergranular connectivity. Our results
demonstrated the strong potential of using iron based superconductors for high
field applications.",1302.4583v1
2013-02-19,Orbital Resonance Mode in Superconducting Iron Pnictides,"We show that the fluctuations associated with ferro orbital order in the
$d_{xz}$ and $d_{yz}$ orbitals can develop a sharp resonance mode in the
superconducting state with a nodeless gap on the Fermi surface. This orbital
resonance mode appears below the particle-hole continuum and is analogous to
the magnetic resonance mode found in various unconventional superconductors. If
the pairing symmetry is $s_{\pm}$, a dynamical coupling between the orbital
ordering and the d-wave subdominant pairing channels is present by symmetry.
Therefore the nature of the resonance mode depends on the relative strengths of
the fluctuations in these two channels, which could vary significantly for
different families of the iron based superconductors. The application of our
theory to a recent observation of a new $\delta$-function-like peak in the
B$_{1g}$ Raman spectrum of Ba$_{0.6}$K$_{0.4}$Fe$_2$As$_2$ is discussed.",1302.4749v2
2013-02-28,Superconducting Phases in Potassium-Intercalated Iron Selenides,"The ubiquitous coexistence of majority insulating 245 phases and minority
superconducting (SC) phases in AxFe2-ySe2 (A = K, Cs, Rb, Tl/Rb, Tl/K) formed
by high-temperature routes makes pure SC phases highly desirable for studying
the intrinsic properties of this SC family. Here we report that there are at
least two pure SC phases, KxFe2Se2(NH3)y (x ~ 0.3 and 0.6), determined mainly
by potassium concentration in the K-intercalated iron selenides formed via the
liquid ammonia route. K0.3Fe2Se2(NH3)0.47 corresponds to the 44 K phase with
lattice constant c = 15.56(1) angstroms and K0.6Fe2Se2(NH3)0.37 to the 30 K
phase with c = 14.84(1) angstroms. With higher potassium doping, the 44 K phase
can be converted into the 30 K phase. NH3 has little, if any, effect on
superconductivity. Thus, the conclusions should apply to both K0.3Fe2Se2 and
K0.6Fe2Se2 SC phases. K0.3Fe2Se2(NH3)0.47 and K0.6Fe2Se2(NH3)0.37 stand out
among known superconductors as their structures are stable only at particular
potassium doping levels, and hence the variation of Tc with doping is not
dome-like.",1302.7178v1
2013-03-11,Magnetic glassy phase in FeSeTe single crystals,"The evolution of the magnetic order in FeSeTe crystals as a function of Se
content was investigated by means of ac/dc magnetometry and muon-spin
spectroscopy. Experimental results and self-consistent DFT calculations both
indicate that muons are implanted in vacant iron-excess sites, where they probe
a local field mainly of dipolar origin, resulting from an antiferromagnetic
(AFM) bicollinear arrangement of iron spins. This long-range AFM phase
disorders progressively with increasing Se content. At the same time all the
tested samples manifest a marked glassy character that vanishes for high Se
contents. The presence of local electronic/compositional inhomogeneities most
likely favours the growth of clusters whose magnetic moment ""freezes"" at low
temperature. This glassy magnetic phase justifies both the coherent muon
precession seen at short times in the asymmetry data, as well as the glassy
behaviour evidenced by both dc and ac magnetometry.",1303.2585v1
2013-03-14,"Study of some steller iron group fusion materials for (n,p) reactions","The excitation functions for (n,p) reactions from reaction threshold to 24
MeV on some important iron (Fe) group target elements for astrophysical (n, p)
reactions such as Si, Ca, Sc, Ti, Cr, Fe, Co and Ni were calculated using
TALYS-1.0 nuclear model code. The new calculations on the excitation functions
Of 28Si(n,p)28Al, 29Si(n, p)29Al, 42Ca(n, p)42K, 45Sc(n, p)45Ca, 46Ti(n,p)46Sc,
52Cr(n, p)52V, 53Cr(n, p)53V, 54Fe(n,p)54Mn, 57Fe(n,p)57Mn, 59Co(n, p)59Fe,
58Ni(n, p)58Co and 60Ni(n, p)60Co reactions have been carried out up to 24 MeV
incident neutron energy. In these calculations, the pre-equilibrium and
equilibrium effects have been investigated. Statistical model calculations,
based on the Hauser-Feshbach formalism, have been carried out using the
TALYS-1.0 and were compared with existing experimental data as well as with
evaluated data files (Experimental Nuclear Reaction Data (EXFOR).According to
these calculations, we assume that these model calculations can be applied to
some heavy elements, ejected into interstellar medium by dramatic supernova
events.",1303.3581v1
2013-03-15,Superconductivity from orbital nematic fluctuations,"Recent experiments suggest that besides of antiferromagnetic fluctuations
nematic fluctuations may contribute to the occurrence of superconductivity in
iron pnictides. Motivated by this observation we study superconductivity from
nematic fluctuations in a minimal two-band model. The employed band parameters
are appropriate for iron pnictides and lead to four pockets for the Fermi line.
It is shown that low-energy, long-wavelength nematic fluctuations within the
pockets give rise to strong-coupling superconductivity whereas the large
momenta density fluctuations between pockets are rather irrelevant. The
obtained transition temperatures are similar to those typically found in the
pnictides and are rather robust against repulsive Coulomb interactions. The
superconducting and nematic states coexist in a large region of the phase
diagram.",1303.3806v2
2013-03-17,"Hidden $(π,0)$ instability as an itinerant origin of bicollinear antiferromagnetism in Fe$_{1+x}$Te","By calculating orbitally resolved Pauli susceptibilities within maximally
localized Wannier orbital basis transformed from first principles band
structures, we find that magnetism in Fe$_{1+x}$Te still has its itinerant
origin even without Fermi surface nesting, provided orbital modulation of
particle-hole excitations are considered. This leads to strong magnetic
instabilities at wave vector (0,$\pi$)/($\pi$,0) in d$_{xz}$/d$_{yz}$ orbitals
that are responsible for the bicollinear antiferromagnetic state as extra
electrons donated from excess Fe are considered. Magnetic exchange coupling
between excess Fe and in-plane Fe further stabilizes the bicollinear
antiferromagnetic order. Our results reveal that magnetism and
superconductivity in iron chalcogenides may have different orbital origin, as
Pauli susceptibilities of different orbitals evolve differently as a function
of concentration of excess Fe and height of the chalcogen atom measured from
the iron plane.",1303.4072v1
2013-03-18,Superconductivity From Repulsive Electronic Correlations on Alternant Cuprate and Iron-based Lattices,"A key question in the theory of high-temperature superconductivity is whether
Off-diagonal Long-Range Order (ODLRO) can be induced wholly or in large part by
repulsive electronic correlations. Electron pairs on Cuprate and the iron-based
pnictide and chalcogenide alternant lattices may interact with a strong
short-range Coulomb repulsion and much weaker longer range attractive tail.
Here we show that such interacting electrons can cooperate to produce a
superconducting state in which time-reversed electron pairs effectively avoid
the repulsive part but reside predominantly in the attractive region of the
potential. The alternant lattice structure is a key feature of such a
stabilization mechanism leading to the occurrence of high temperature
superconductivity with dx2 -y2 or sign alternating s-wave or s plus/minus
condensate symmetries.",1303.4235v1
2013-03-19,In-plane optical spectroscopy study on FeSe epitaxial thin film grown on SrTiO$_3$ substrate,"We perform in-plane optical spectroscopy measurement on (00l) FeSe thin-film
grown on SrTiO$_3$ substrate by pulsed laser deposition method. The study
indicates that the low frequency conductivity consists of two Drude components,
a broad one which takes up most of the spectral weight and a very narrow one
roughly below 100-150 \cm. The narrow Drude component locates at so low
frequencies that no such behavior was observed in iron pnictides. The overall
plasma frequency is found to be smaller than the FeAs based compounds,
suggesting a stronger correlation effect. Similar to iron pnictides, a
temperature-induced spectral weight transfer is observed for FeSe. However, the
relevant energy scale is lower. Additionally, different from a recent ARPES
measurement which revealed a spin density wave (SDW) order at low temperature
for FeSe thin films grown on SrTiO$_3$ substrate, no signature of the band
structure reconstruction arising from the formation of the SDW order is seen by
optical measurement in the thick FeSe films.",1303.4473v1
2013-03-19,Electronic Structure and Resonant X-ray Emission Spectra of Carbon Shells of Iron Nanoparticles,"The electronic structure of carbon shells of carbon encapsulated iron
nanoparticles carbon encapsulated Fe@C has been studied by X-ray resonant
emission and X-ray absorption spectroscopy. The recorded spectra have been
compared to the density functional calculations of the electronic structure of
graphene. It has been shown that an Fe@C carbon shell can be represented in the
form of several graphene layers with Stone-Wales defects. The dispersion of
energy bands of Fe@C has been examined using the measured C Ka resonant X-ray
emission spectra.",1303.4507v1
2013-03-20,Optical Properties of Iron Silicates in the Infrared to Millimeter as a Function of Temperatures and Wavelength,"The Optical Properties of Astronomical Silicates with Infrared Techniques
(OPASI-T) program utilizes multiple instruments to provide spectral data over a
wide range of temperature and wavelengths. Experimental methods include Vector
Network Analyzer (VNA) and Fourier Transform Spectroscopy (FTS) transmission,
and reflection/scattering measurements. From this data, we can determine the
optical parameters for the index of refraction, \textit{n}, and the absorption
coefficient, \textit{k}. The analysis of the laboratory transmittance data for
each sample type is based upon different mathematical models, which are applied
to each data set according to their degree of coherence. Presented here are
results from iron silicate dust grain analogs, in several sample preparations
and at temperatures ranging from 5--300 K, across the infrared and millimeter
portion of the spectrum (from 2.5--10,000 \mic\ or 4,000--1 \wvn).",1303.4950v1
2013-03-26,Measurements of the fluctuation-induced in-plane magnetoconductivity at high reduced temperatures and magnetic fields in the iron arsenide BaFe(2-x)NixAs2,"The superconducting fluctuations well inside the normal state of Fe-based
superconductors were studied through measurements of the in-plane
paraconductivity and magnetoconductivity in high quality BaFe(2-x)NixAs2
crystals with doping levels from the optimal (x=0.10) up to the highly
overdoped (x=0.20). These measurements, performed in magnetic fields up to 9 T
perpendicular to the ab (Fe) layers, allowed a reliable check of the
applicability to iron-based superconductors of Ginzburg-Landau approaches for
3D anisotropic compounds, even at high reduced temperatures and magnetic
fields. Our results also allowed us to gain valuable insights into the
dependence on the doping level of some central superconducting parameters
(coherence lengths and anisotropy factor).",1303.6565v1
2013-04-02,The effect of Hydrogen atom on the Screw Dislocation Mobility in BCC Iron: A First-Principles Study,"We investigate the effect of hydrogen on the mobility of a screw dislocation
in body-centered cubic (bcc) iron using first-principles calculations, and show
that an increase of screw dislocation velocity is expected for a limited
temperature range. The interaction energy between a screw dislocation and
hydrogen atoms is calculated for various hydrogen positions and dislocation
configurations with careful estimations of the finite size effects, and the
strongest binding energy of a hydrogen atom to the stable screw dislocation
configuration is estimated to be $256\pm32$ meV. These results are incorporated
into a line tension model of a curved dislocation line to elucidate the effect
of hydrogen on the dislocation migration process. Both the softening and
hardening effect of hydrogen, caused by the reduction of kink nucleation
enthalpy and kink trapping, respectively, are evaluated. A clear transition
between softening and hardening behavior at the lower critical temperature is
predicted, which is in qualitative agreement with the experimental observation.",1304.0602v3
2013-04-04,Surface parameters of ferritic iron-rich Fe-Cr alloy,"Using first-principles density functional theory in the implementation of the
exact muffin-tin orbitals method and the coherent potential approximation, we
studied the surface energy and the surface stress of the thermodynamically most
stable surface facet (100) of the homogeneous disordered body-centred cubic
iron-chromium system in the concentration interval up to 20 at.% Cr. For the
low-index surface facets of Fe and Cr, the surface energy of Cr is slightly
larger than the one of Fe, while the surface stress of Cr is considerably
smaller than the one of Fe. We find that Cr addition to Fe generally increases
the surface energy of the Fe-Cr alloy, however, an increase of the bulk amount
of Cr also increases the surface stress. As a result of this unexpected trend,
the (100) surface of Fe-Cr becomes more stable against reconstruction with
increasing Cr concentration. We show that the observed trends are of magnetic
origin. In addition to the homogeneous alloy case, we also investigated the
impact of surface segregation on both surface parameters.",1304.1278v2
2013-04-13,Intrinsic high-temperature superconductivity in ternary iron selenides,"We examine superconductivity in the mesoscopically mixed
antiferromagnetic(AF) and superconducting (SC) phases of ternary iron selenides
K$_{y}$Fe$_{2-x}$Se$_{2}$. It is shown that the interlayer hopping and AF order
are key factors to determine $T_{c}$ of the SC phase. In general, the hopping
will produce deformed Fermi surfaces (FS's) that tend to suppress
superconductivity. However, contrary to the common expectation, we find that
larger AF order actually results in larger SC order, which explains the
observed relatively high $T_{c}$ in these phases. Furthermore our results
indicate that by reducing the interlayer hopping appropriately, phase-separated
K$_{y}$Fe$_{2-x}$Se$_{2}$ may exhibit its intrinsic SC phase in the two
dimensional limit with a much higher $T_{c}$ ($\sim 65K$) than what has been
observed.",1304.3785v3
2013-04-16,Possible Nematic Order Driven by Magnetic Fluctuations in Iron Pnictides,"In this paper, instabilities of the isotropic metallic phase in iron
pnictides are investigated. The relevant quartic fermionic interaction terms in
the model are identified using phase space arguments. Using the functional
integral formalism, a Hubbard-Stratonovich transformation is used to decouple
these quartic terms. This procedure introduces several bosonic fields which
describe the low-energy collective modes of the system. By studying the
behavior of these collective modes, a possible instability is found in the
forward scattering channel of the isotropic phase driven by magnetic
fluctuations. Using mean field analysis, we obtain a static and homogeneous
ground state. This ground state is metallic, but the electron Fermi pockets are
distorted unequally at different pockets in momentum space. This results in a
desirable nematic ordering which breaks the lattice C4 symmetry but preserves
translational symmetry and may explain several experimental observations.",1304.4617v1
2013-04-19,Robust spin fluctuations and $s\pm$ pairing in the heavily electron doped iron-based superconductors,"We theoretically study the spin fluctuation and superconductivity in La1111
and Sm1111 iron-based superconductors for a wide range of electron doping. When
we take into account the band structure variation by electron doping, the hole
Fermi surface originating from the $d_{X^2-Y^2}$ orbital turns out to be robust
against electron doping, and this gives rise to large spin fluctuations and
consequently $s\pm$ pairing even in the heavily doped regime. The stable hole
Fermi surface is larger for Sm1111 than for La1111, which can be considered as
the origin of the apparent difference in the phase diagram.",1304.5303v2
2013-04-22,Magnetic anisotropic energy gap and low energy spin wave excitation in antiferromagnetic block phase of K2Fe4Se5,"Neutron scattering experiments were performed to investigate magnetic order
and magnetic excitations in ternary iron chalcogenide K2Fe4Se5. The formation
of a superlattice structure below 580 K together with the decoupling between
the Fe-vacancy order-disorder transition and the antiferromagnetic order
transition appears to be a common feature in the A2Fe4Se5 family. The study of
spin dynamics of K2Fe4Se5 reveals two distinct energy gaps at the magnetic
Brillouin zone center, which indicates the presence of magnetic anisotropy and
the decrease of local symmetry due to electronic and orbital anisotropy. The
low-energy spin wave excitations of K2Fe4Se5 can be properly described by
linear spin wave theory within a Heisenberg model. Compared to iron pnictides,
K2Fe4Se5 exhibits a more two-dimensional magnetism as characterized by large
differences not only between out-of-plane and in-plane spin wave velocities,
but also between out-of-plane and in-plane exchange interactions.",1304.5950v1
2013-05-13,Normal state spin dynamics in the iron-pnictide superconductors BaFe2(As1-xPx)2 and Ba(Fe1-xCox)2As2 probed with NMR measurements,"The NMR results in iron pnictides BaFe2(As1-xPx)2 and Ba(Fe1-xCox)2As2 are
analyzed based on the self-consistent renormalization (SCR) spin fluctuation
theory. The temperature dependence of the NMR relaxation rate (T_1)^{-1} as
well as the electrical resistivity is well reproduced by a SCR model where
two-dimensional antiferromagnetic (AF) spin fluctuations are dominant. The
successful description of the crossover feature from non-Fermi liquid to Fermi
liquid behavior strongly suggests that low-lying spin fluctuations in
BaFe2(As1-xPx)2 and Ba(Fe1-xCox)2As2 possess an itinerant AF nature, and that
chemical substitution in the two compounds tunes the distance of these systems
to an AF quantum critical point. The close relationship between spin
fluctuations and superconductivity is discussed compared with the other
unconventional superconductors, cuprate and heavy fermion superconductors. In
addition, it is suggested that magnetism and lattice instability in these
pnictides are strongly linked via orbital degrees of freedom.",1305.2656v1
2013-05-13,Simultaneous optimization of spin fluctuations and superconductivity under pressure in an iron-based superconductor,"We present a high-pressure NMR study of the overdoped iron pnictide
superconductor NaFe$_{0.94}$Co$_{0.06}$As. The low-energy antiferromagnetic
spin fluctuations in the normal state, manifest as the Curie-Weiss upturn in
the spin-lattice relaxation rate $1/^{75}T_1T$, first increase strongly with
pressure but fall again at $P > P_{\rm opt} =$ 2.2 GPa. Neither long-ranged
magnetic order nor a structural phase transition is encountered up to 2.5 GPa.
The superconducting transition temperature $T_c$ shows a pressure-dependence
identical to the spin fluctuations. Our observations demonstrate that magnetic
correlations and superconductivity are optimized simultaneously as a function
of the electronic structure, thereby supporting very strongly a magnetic origin
of superconductivity.",1305.2705v2
2013-05-14,Effect of electron-phonon interactions on orbital fluctuations in iron-based superconductors,"To investigate the possibility whether electron-phonon coupling can enhance
orbital fluctuations in iron-based superconductors, we develop an ab initio
method to construct the effective low-energy models including the
phonon-related terms. With the derived effective electron-phonon interactions
and phonon frequencies, we estimate the static part (\omega=0) of the
phonon-mediated effective on-site intra- or inter-orbital electron-electron
attractions as ~ -0.4 eV and exchange or pair-hopping terms as ~ -0.02 eV. We
analyze the model with the derived interactions together with the electronic
repulsions within the random phase approximation. We find that the enhancement
of the orbital fluctuations due to the electron-phonon interactions is small,
making the spin fluctuations dominant. As a result, the superconducting state
with the sign reversal in gap functions ($s_\pm$-wave) is realized.",1305.2995v2
2013-05-17,"Comparative Study of Electronic structure of New Superconductors (Sr,Ca)Pd2As2 and related compound BaPd2As2","This paper presents the comparative study of LDA calculated electronic
structure of new isostructural to iron based systems superconductors
(Sr,Ca)Pd2As2 with Tc about 1K and similar but structurally different system
BaPd2As2. Despite chemical formula looks similar to iron superconductors and
even main structural motif is the same - layers of Fe square lattices,
electronic structure of (Sr,Ca)Pd2As2 and BaPd2As2 differs from Fe(As,Se)-HTSC
completely. All these systems have essentially three dimensional Fermi surfaces
in contrast to Fe(As,Se) materials. The Fermi level is crossed by low intensive
tails of Pd-4d and As-4p states. However (Sr,Ca)Pd2As2 and BaPd2As2 materials
have rather well developed peaks of Pd-4d(x2-y2) band. Thus by doping of about
2 holes per unit cell one can increase density of states at the Fermi level by
a factor about 2.5. Since experimentally these compounds were found to be
simple BCS superconductors the hole doping may considerably increase Tc. LDA
calculated total densities of states at the Fermi level for stoichiometric
systems perfectly agree with experimental estimates signifying rather small
role of electronic correlations.",1305.3979v1
2013-05-20,Effect of magnetic criticality and Fermi-surface topology on the magnetic penetration depth,"We investigate the effect of anti-ferromagnetic (AF) quantum criticality on
the magnetic penetration depth $\lambda(T)$ in line-nodal superconductors,
including the cuprates, the iron pnictides, and the heavy-fermion
superconductors. The critical magnetic fluctuation renormalizes the current
vertex and drastically enhances zero-temperature penetration depth
$\lambda(0)$, which is more remarkable in the iron-pnictide case due to the
Fermi-surface topology. Additional temperature ($T$) dependence of the current
renormalization makes the expected $T$-linear behavior at low temperatures
approaching to $T^{1.5}$ asymptotically. These anomalous behaviors are well
consistent with experimental observations. We stress that $\lambda(T)$ is a
good probe to detect the AF quantum critical point in the superconducting
state.",1305.4427v1
2013-05-20,How many quantum phase transitions exist inside the superconducting dome of the iron pnictides?,"Recent experiments on two iron-pnictide families suggest the existence of a
single quantum phase transition (QPT) inside the superconducting dome despite
the fact that two separate transition lines - magnetic and nematic - cross the
superconducting dome at $T_{c}$. Here we argue that these two observations are
actually consistent. We show, using a microscopic model, that each order
coexists with superconductivity for a wide range of parameters, and both
transition lines continue into the superconducting dome below $T_{c}$. However,
at some $T_{\mathrm{merge}}<T_{c}$, the two transitions merge and continue down
to T=0 as a single simultaneous first-order nematic/magnetic transition. We
show that superconductivity has a profound effect on the character of this
first-order transition, rendering it weakly first-order and allowing strong
fluctuations to exist near the QPT.",1305.4670v2
2013-05-21,"Spin fluctuations away from (pi,0) in the superconducting phase of molecular-intercalated FeSe","Magnetic fluctuations in the molecular-intercalated FeSe superconductor
Li{x}(ND2){y}(ND3){1-y}Fe2Se2 (Tc = 43K) have been measured by inelastic
neutron scattering from a powder sample. The strongest magnetic scattering is
observed at a wave vector Q ~ 1.4 A^{-1}, which is not consistent with the
(pi,0) nesting wave vector that characterizes magnetic fluctuations in several
other iron-based superconductors, but is close to the (pi, pi/2) position found
for A{x}Fe{2-y}Se2 systems. At the energies probed (~ 5kB Tc), the magnetic
scattering increases in intensity with decreasing temperature below Tc,
consistent with the superconductivity-induced magnetic resonance found in other
iron-based superconductors.",1305.4898v1
2013-06-03,Scaling between magnetic and lattice fluctuations in iron-pnictide superconductors,"The phase diagram of the iron arsenides is dominated by a magnetic and a
structural phase transition, which need to be suppressed in order for
superconductivity to appear. The proximity between the two transition
temperature lines indicates correlation between these two phases, whose nature
remains unsettled. Here, we find a scaling relation between nuclear magnetic
resonance (NMR) and shear modulus data in the tetragonal phase of
electron-doped $\mathrm{Ba(Fe_{1-x}Co_{x})_{2}As_{2}}$ compounds. Because the
former probes the strength of magnetic fluctuations while the latter is
sensitive to orthorhombic fluctuations, our results provide strong evidence for
a magnetically-driven structural transition.",1306.0521v2
2013-06-17,Two-Fluid Description for Iron-Based Superconductors,"We present a two-fluid description for iron-based superconductors, which
contains an itinerant electron Fermi-liquid and a local moment spin-liquid,
coupled together via an effective Hund's rule interaction. We examine the
low-energy collective behavior of such a system. We find that an
electron-spinon composite mode emerges in the intermediate coupling regime,
which may account for the hump-dip behavior observed in the resent scanning
tunneling spectroscopy experiments. The superconductivity and spin-density-wave
phases are consistently described within the same framework. Possible
experimental test is also proposed.",1306.3740v3
2013-06-18,X-ray resonant photoexcitation: line widths and energies of Kα transitions in highly charged Fe ions,"Photoabsorption by and fluorescence of the K{\alpha} transitions in highly
charged iron ions are essential mechanisms for X-ray radiation transfer in
astrophysical environments. We study photoabsorption due to the main K{\alpha}
transitions in highly charged iron ions from heliumlike to fluorinelike (Fe
24+...17+) using monochromatic X-rays around 6.6 keV at the PETRA III
synchrotron photon source. Natural linewidths were determined with hitherto
unattained accuracy. The observed transitions are of particular interest for
the understanding of photoexcited plasmas found in X-ray binaries and active
galactic nuclei.",1306.4348v3
2013-06-20,A new way to measure supermassive black hole spin in accretion disc dominated Active Galaxies,"We show that disc continuum fitting can be used to constrain black hole spin
in a subclass of Narrow Line Seyfert 1 (NLS1) AGN as their low mass and high
mass accretion rate means that the disc peaks at energies just below the soft
X-ray bandpass. We apply the technique to the NLS1 PG1244+026, where the
optical/UV/X-ray spectrum is consistent with being dominated by a standard disc
component. This gives a best estimate for black hole spin which is low, with a
firm upper limit of $a_*<0.86$. This contrasts with the recent X-ray
determinations of (close to) maximal black hole spin in other NLS1 based on
relativistic smearing of the iron profile. While our data on PG1244+026 does
not have sufficient statistics at high energy to give a good measure of black
hole spin from the iron line profile, cosmological simulations predict that
black holes with similar masses have similar growth histories and so should
have similar spins. This suggests that there is a problem either in our
understanding of disc spectra, or/and X-ray reflection or/and the evolution of
black hole spin.",1306.4786v1
2013-06-28,"The role of orbital order in the stabilization of the $(π,0)$ ordered magnetic state in a minimal two-band model for iron pnictides","Spin wave excitations and stability of the ($\pi,0$) ordered magnetic state
are investigated in a minimal two-band itinerant-electron model for iron
pnictides. Presence of hopping anisotropy generates a strong ferro-orbital
order in the $d_{xz}$ and $d_{yz}$ Fe orbitals. The orbital order sign is as
observed in experiments. The induced ferro-orbital order strongly enhances the
spin wave energy scale and stabilizes the magnetic state by optimizing the
strength of the emergent AF and F spin couplings through optimal band fillings
in the two orbitals. The calculated spin-wave dispersion is in quantitative
agreement with neutron scattering measurements. Finite inter-orbital Hund's
coupling is shown to further enhance the spin wave energies state by coupling
the two magnetic sub-systems. A more realistic two-band model with less hopping
anisotropy is also considered which yields not only the circular hole pockets,
also correct ferro-orbital order and emergent F spin coupling.",1306.6727v2
2013-07-05,Orbital-Selective Mottness in Layered Iron Oxychalcogenides: The Case of Na_{2}Fe_{2}OSe_{2},"Using a combination of th local-density approximtion (LDA) and dynamicla
mean-field theory (DMFT) calculations, we explore the correlated electronic
structure of a member of the layered Iron oxychalcogenide Na_{2}Fe_{2}OSe_{2}.
We find that the parent compund is a multi-orbital Mott insulator.
Surprisingly, and somewhat reminiscent of the doped high-T_{c} cuprates,
carrier localization is found to persist upon weak hole doping because the
chemical potential lies in a gap structure wit almost vanishing
density-of-states (DOS). On the other hand, in remarkable contrast, electron
doping drives an orbital-selective metallic phase (OSMP) with co-existing
pseudogapped (Mott localized) and itinerant carriers. These remarkably
contrasting behaviors in a single system thus stem from drastic electronic
reconstruction caused by large-scale transfe of dynamical spectral
weightinvolving states with distinct orbital character at low energies, putting
the Fe oxychalcogenidesneatly into the increasingly visible tendency of Fe-baed
systems as ones in orbital-selective Mott phases. We detail the implications of
our analysis, and discuss the nature and symmetry of the superconductive states
that may arise upon proper doping or pressurizing Na_{2}Fe_{2}OSe_{2}.",1307.1693v1
2013-07-08,Weak magnetism and the Mott-state of vanadium in superconducting Sr2VO3FeAs,"We report neutron scattering data and DFT calculations of the stoichiometric
iron-arsenide superconductor Sr2VO3FeAs. Rietveld refinements of neutron powder
patterns confirm the ideal composition without oxygen deficiencies. Experiments
with polarized neutrons prove weak magnetic ordering in the V-sublattice of
Sr2VO3FeAs at ~ 45 K with a probable propagation vector q = (1/8,1/8,0). The
ordered moment of ~ 0.1 muB is too small to remove the V-3d bands from the
Fermi level by magnetic exchange splitting, and much smaller than predicted
from a recent LDA+U study. By using DFT calculations with a GGA+EECE functional
we recover the typical quasi-nested Fermi-surface even without magnetic moment.
From this we suggest that the V-atoms are in a Mott-state where the electronic
correlations are dominated by on-site Coulomb-repulsion which shifts the V-3d
states away from the Fermi energy. Our results are consistent with
photoemission data and clearly reveal that Sr2VO3FeAs is a typical
iron-arsenide superconductor with quasi-nested hole- and electron-like Fermi
surface sheets, and constitutes no new paradigm. We suggest that intrinsic
electron-doping through V3+/V4+ mixed valence is responsible for the absence of
SDW ordering.",1307.2138v1
2013-07-09,Lattice Instability and Competing Spin Structures in the Double Perovskite Insulator Sr2FeOsO6,"The semiconductor Sr2FeOsO6, depending on temperature, adopts two types of
spin structures that differ in the spin sequence of ferrimagnetic iron - osmium
layers along the tetragonal c-axis. Neutron powder diffraction experiments,
57Fe M\""ossbauer spectra, and density-functional theory calculations suggest
that this behavior arises because a lattice instability resulting in
alternating iron-osmium distances fine-tunes the balance of competing exchange
interactions. Thus, Sr2FeOsO6 is an example for a double perovskite, in which
the electronic phases are controlled by the interplay of spin, orbital, and
lattice degrees of freedom.",1307.2587v2
2013-07-11,Anomalous compressibility of ferropericlase throughout the iron spin crossover,"The thermoelastic properties of ferropericlase Mg1-xFexO (x = 0.1875)
throughout the iron high-to-low spin crossover have been investigated by first
principles at Earth's lower mantle conditions. This crossover has important
consequences for elasticity such as an anomalous bulk modulus (KS) reduction.
At room temperature the anomaly is somewhat sharp in pressure but broadens with
increasing temperature. Along a typical geotherm it occurs across most of the
lower mantle with a more significant KS reduction around 1400-1600 km depth.
This anomaly might also cause a reduction in the effective activation energy
for viscous creep and lead to a viscosity minimum in the mid-lower mantle, in
apparent agreement with results from inversion of data related with mantle
convection and postglacial rebound.",1307.3270v1
2013-07-12,Swift and RXTE observations of the black hole transient GX 339-4 in the hard state between outbursts,"We use simultaneous Swift and RXTE observations of the black hole binary GX
339-4 to measure the inner radius of its accretion disk in the hard state down
to 0.4% L_{Edd} via modeling of the thermal disk emission and the
relativistically broadened iron line. For the luminosity range covered in this
work, our results rule out a significantly truncated disk at 100-1000 R_g as
predicted by the advection-dominated accretion flow paradigm. The measurements
depend strongly on the assumed emission geometry, with most results providing
no clear picture of radius evolution. If the inclination is constrained to
roughly 20 degrees, however, the measurements based on the thermal disk
emission suggest a mildly receding disk at a luminosity of 0.4% L_{Edd}. The
iron abundance varies between roughly 1-2 solar abundances, with the i=20
degrees results indicating a negative correlation with luminosity, though this
is likely due to a change in disk illumination geometry.",1307.3503v1
2013-07-15,"The Roche limit for close-orbiting planets: Minimum density, composition constraints, and application to the 4.2-hour planet KOI 1843.03","The requirement that a planet must orbit outside of its Roche limit gives a
lower limit on the planet's mean density. The minimum density depends almost
entirely on the orbital period and is immune to systematic errors in the
stellar properties. We consider the implications of this density constraint for
the newly-identified class of small planets with periods shorter than half a
day. When the planet's radius is known accurately, this lower limit to the
density can be used to restrict the possible combinations of iron and rock
within the planet. Applied to KOI 1843.03, with a radius of 0.6 Earth radii and
the shortest known orbital period of 4.245 hr, the planet's mean density must
be greater than approximately 7 g/cm^3. By modeling the planetary interior
subject to this constraint, we find the composition of the planet must be
mostly iron, with at most a modest fraction of silicates (less than
approximately 30% by mass).",1307.4080v1
2013-07-18,Origin of electronic dimers in the spin-density wave phase of Fe-based superconductors,"We investigate the emergent impurity-induced states arising from point-like
scatterers in the spin-density wave phase of iron-based superconductors within
a microscopic five-band model. Independent of the details of the band-structure
and disorder potential, it is shown how stable magnetic (pi,pi) unidirectional
nematogens are formed locally by the impurities. Interestingly, these
nematogens exhibit a dimer structure in the electronic density, are directed
along the antiferromagnetic a-axis, and have typical lengths of order 10
lattice constants in excellent agreement with recent scanning tunnelling
experiments. These electronic dimers provide a natural explanation of the
dopant-induced transport anisotropy found e.g. in the 122 iron pnictides.",1307.4913v2
2013-07-26,Electron-phonon coupling in cuprate and iron-based superconductors revealed by Raman scattering,"Electron-phonon coupling (EPC) is one of the most common and fundamental
interactions in solids. It not only dominates many basic dynamic processes like
resistivity, thermal conductivity etc, but also provides the pairing glue in
conventional superconductors. But in high-temperature superconductors (HTSC),
it is still controversial whether or not EPC is in favor of paring. Despite the
controversies, many experiments have provided clear evidence for EPC in HTSC.
In this paper, we briefly review EPC in cuprate and iron-based superconducting
systems revealed by Raman scattering. We introduce how to extract the coupling
information through phonon lineshape. Then we discuss the strength of EPC in
different HTSC systems and possible factors affecting the strength. The
comparative study between Raman phonon theories and experiments allows us to
gain insight into some crucial electronic properties, especially
superconductivity. Finally we summarize and compare EPC in the two existing
HTSC systems, and discuss what role it may play in HTSC.",1307.6972v1
2013-07-26,Switching of intra-orbital spin excitations in electron-doped iron pnictide superconductors,"We investigate the doping dependence of the magnetic excitations in
two-superconducting-dome-system LaFeAsO1-xDx. Using inelastic neutron
scattering, spin fluctuations at different wavenumbers were observed under both
superconducting domes around x = 0.1 and 0.4, but vanished at x = 0.2
corresponding to the Tc valley. Theoretical calculations indicate that the
characteristic doping dependence of spin fluctuations is rationally explained
as a consequence of the switching of the two intra-orbital nestings within
Fe-3dYZ, ZX and 3dX2-Y2 by electron doping. The present results imply that the
multi-orbital nature plays an important role in the doping and / or material
dependence of the Tc of the iron pnictide superconductors.",1307.7016v2
2013-07-26,Coupling of the A_{1g} As-phonon to magnetism in iron pnictides,"Charge, spin and lattice degrees of freedom are strongly entangled in iron
superconductors. A neat consequence of this entanglement is the behavior of the
A_{1g} As-phonon resonance in the different polarization symmetries of Raman
spectroscopy when undergoing the magneto-structural transition. In this work we
show that the observed behavior could be a direct consequence of the coupling
of the phonons with the electronic excitations in the anisotropic magnetic
state. We discuss this scenario within a five orbital tight-binding model
coupled to phonons via the dependence of the Slater-Koster parameters on the As
position. We identify two qualitatively different channels of the
electron-phonon interaction: a geometrical one related to the Fe-As-Fe angle
and another one associated with the modification upon As displacement of the
Fe-As energy integrals pdsigma and pdpi. While both mechanisms result in a
finite B_{1g} response, the behavior of the phonon intensity in the A_{1g} and
B_{1g} Raman polarization geometries is qualitatively different when the
coupling is driven by the angle or by the energy integral dependence. We
discuss our results in view of the experimental reports.",1307.7065v1
2013-07-31,A view from inside iron-based superconductors,"Muon spin spectroscopy is one of the most powerful tools to investigate the
microscopic properties of superconductors. In this manuscript, an overview on
some of the main achievements obtained by this technique in the iron-based
superconductors (IBS) are presented. It is shown how the muons allow to probe
the whole phase diagram of IBS, from the magnetic to the superconducting phase,
and their sensitivity to unravel the modifications of the magnetic and the
superconducting order parameters, as the phase diagram is spanned either by
charge doping, by an external pressure or by introducing magnetic and
non-magnetic impurities. Moreover, it is highlighted that the muons are unique
probes for the study of the nanoscopic coexistence between magnetism and
superconductivity taking place at the crossover between the two ground-states.",1307.8283v1
2013-08-12,Constraining possible variations of the fine structure constant in strong gravitational fields with the K$α$ iron line,"In extensions of general relativity and in theories aiming at unifying
gravity with the forces of the Standard Model, the value of the ""fundamental
constants"" is often determined by the vacuum expectation value of new fields,
which may thus change in different backgrounds. Variations of fundamental
constants with respect to the values measured today in laboratories on Earth
are expected to be more evident on cosmological timescales and/or in strong
gravitational fields. In this paper, I show that the analysis of the K$\alpha$
iron line observed in the X-ray spectrum of black holes can potentially be used
to probe the fine structure constant $\alpha$ in gravitational potentials
relative to Earth of $\Delta \phi \approx 0.1$. At present, systematic effects
not fully under control prevent to get robust and stringent bounds on possible
variations of the value of $\alpha$ with this technique, but the fact that
current data can be fitted with models based on standard physics already rules
out variations of the fine structure constant larger than some percent.",1308.2470v2
2013-08-15,Evidence of Increased UV FeII Emission in Quasars in Candidate Overdense Regions,"We present evidence for a skewed distribution of UV FeII emission in quasars
within candidate overdense regions spanning spatial scales of ~ 50 Mpc at 1.11
< z < 1.67, compared to quasars in field environments at comparable redshifts.
The overdense regions have an excess of high equivalent width sources (W2400 >
42 \AA), and a dearth of low equivalent width sources. There are various
possible explanations for this effect, including dust, Ly\alpha fluorescence,
microturbulence, and iron abundance. We find that the most plausible of these
is enhanced iron abundance in the overdense regions, consistent with an
enhanced star formation rate in the overdense regions compared to the field.",1308.3514v1
2013-08-18,Impurity-induced sub-gap bound gap states in alkali doped iron chalcogenide superconductors,"Measurements of the local density of states near impurities can be useful for
identifying the superconducting gap structure in alkali doped iron chalcogenide
superconductors K_xFe_{2-y}Se_2. Here, we study the effects of nonmagnetic and
magnetic impurities within a nearest neighbor d-wave and next-nearest neighbor
s-wave superconducting state. For both repulsive and attractive nonmagnetic
impurities, it is shown that sub-gap bound states exist only for d-wave
superconductors with the positions of these bound states depending rather
sensitively on the electron doping level. Further, for such disorder Coulomb
interactions can lead to local impurity-induced magnetism in the case of d-wave
superconductivity. For magnetic impurities, both s-wave and d-wave
superconducting states support sub-gap bound states. The above results can be
explained by a simple analytic model that provides a semi-quantitative
understanding of the variation of the impurity bound states energies as a
function of impurity potential and chemical doping level.",1308.3887v1
2013-09-03,Producing a Set of Models for the Iron Homeostasis Network,"This paper presents a method for modeling biological systems which combines
formal techniques on intervals, numerical simulations and satisfaction of
Signal Temporal Logic (STL) formulas. The main modeling challenge addressed by
this approach is the large uncertainty in the values of the parameters due to
the experimental difficulties of getting accurate biological data. This method
considers intervals for each parameter and a formal description of the expected
behavior of the model. In a first step, it produces reduced intervals of
possible parameter values. Then by performing a systematic search in these
intervals, it defines sets of parameter values used in the next step. This
procedure aims at finding a sub-space where the model robustly behaves as
expected. We apply this method to the modeling of the cellular iron homeostasis
network in erythroid progenitors. The produced model describes explicitly the
regulation mechanism which acts at the translational level.",1309.0872v1
2013-09-05,Influence of the spreading resistance on the conductance spectrum of planar hybrid thin film SNS' junctions based on iron pnictides,"To investigate the superconducting properties of iron pnictides we prepared
planar hybrid SNS' junctions in thin film technology with a pnictide base
electrode, a gold barrier layer and a lead counter electrode. Our design allows
characterization of the electrodes and the junction independently in a 4-probe
method. We show how both electrodes influence the measured spectra due to their
spreading resistance. While the Pb electrode has a constant resistance above
its $T_c$, the contribution of the pnictide electrode is clearly
current-dependent and thus it needs a more advanced method to be corrected. We
present an empirical method, which is simple to apply and allows to deal with
the spreading resistance in our junctions to recalculate the actual conductance
and voltage of one junction at given temperature.",1309.1641v2
2013-09-10,Microlensing of Quasar UV Iron Emission,"We measure the differential microlensing of the UV Fe II and Fe III emission
line blends between 14 quasar image pairs in 13 gravitational lenses. We find
that the UV iron emission is strongly microlensed in 4 cases with amplitudes
comparable to that of the continuum. Statistically modeling the magnifications
we infer a typical size of r ~ 4*sqrt(M/Msun) light-days for the Fe line
emitting regions which is comparable to the size of the region generating the
UV continuum (3 ~ 7 light-days). This may indicate that a significant part of
the UV Fe II and Fe III emission originates in the quasar accretion disk.",1309.2603v2
2013-09-13,Adsorption geometry and electronic structure of iron phthalocyanine on Ag surfaces: A LEED and photoelectron momentum mapping study,"We present a comprehensive study of the adsorption behavior of iron
phthalocyanine on the low-index crystal faces of silver. By combining
measurements of the reciprocal space by means of photoelectron momentum mapping
and low energy electron diffraction, the real space adsorption geometries are
reconstructed. At monolayer coverage ordered superstructures exist on all
studied surfaces containing one molecule in the unit cell in case of Ag(100)
and Ag(111), and two molecules per unit cell for Ag(110). The azimuthal tilt
angle of the molecules against the high symmetry directions of the substrate is
derived from the photoelectron momentum maps. A comparative analysis of the
momentum patterns on the substrates with different symmetry indicates that both
constituents of the twofold degenerate FePc lowest unoccupied molecular orbital
are occupied by charge transfer from the substrate at the interface.",1309.3476v1
2013-09-18,"Magnetocrystalline anisotropy energy of Fe$(001)$, Fe$(110)$ slabs and nanoclusters: a detailed local analysis within a tight-binding model","We report tight-binding (TB) calculations of magnetocrystalline anisotropy
energy (MAE) of Iron slabs and nanoclusters with a particuler focus on local
analysis. After clarifying various concepts and formulations for the
determination of MAE, we apply our realistic TB model to the analysis of the
magnetic anisotropy of Fe$(001)$, Fe$(110)$ slabs and of two large Fe clusters
with $(001)$ and $(110)$ facets only: a truncated pyramid and a truncated
bipyramid containg 620 and 1096 atoms, respectively. It is shown that the MAE
of slabs originates mainly from outer layers, a small contribution from the
bulk gives rise, however, to an oscillatory behavior for large thicknesses.
Interestingly, the MAE of the nanoclusters considered is almost solely due to
$(001)$ facets and the base perimeter of the pyramid. We believe that this fact
could be used to efficiently control the anisotropy of Iron nanoparticles and
could also have consequences on their spin dynamics.",1309.4578v1
2013-09-20,Evidence for Orbital Order and its Relation to Superconductivity in FeSe0.4Te0.6,"The emergence of nematic electronic states accompanied by a structural phase
transition is a recurring theme in many correlated electron materials,
including the high-temperature copper oxide- and iron-based superconductors. We
provide evidence for nematic electronic states in the iron-chalcogenide
superconductor FeSe0.4Te0.6 from quasi-particle scattering detected in
spectroscopic maps. The symmetry-breaking states persist above Tc into the
normal state. We interpret the scattering patterns by comparison with
quasi-particle interference patterns obtained from a tight-binding model,
accounting for orbital ordering. The relation to superconductivity and the
influence on the coherence length are discussed.",1309.5210v3
2013-10-09,Impurity states and cooperative magnetic order in Fe-based superconductors,"We study impurity bound states and impurity-induced order in the
superconducting state of LiFeAs within a realistic five-band model based on the
band structure and impurity potentials obtained from density functional theory
(DFT). In agreement with recent experiments, we find that Co impurities are too
weak produce sub-gap bound states, whereas stronger impurities like Cu do. We
also obtain the bound state spectrum for magnetic impurities, such as Mn, and
show how spin-resolved tunnelling may determine the nature of the various
defect sites in iron pnictides, a prerequisite for using impurity bound states
as a probe of the ground state pairing symmetry. Lastly we show how impurities
pin both orbital and magnetic order, providing an explanation for a growing set
of experimental evidence for unusual magnetic phases in doped iron pnictides.",1310.2455v1
2013-10-09,Fe KαLine in Hard X-ray Emitting Symbiotic Stars,"The 6.4 keV iron emission line is typically created by irradiation of the
neutral (or low ionized) iron by a hard X-ray source. Whereas the 6.7 and 7.0
keV emission lines are mainly produced by photoionization and collisional
excitation in hot plasma, the 6.4 keV fluorescence line is typically a
signature of either reflection from an accretion disk or absorption. We have
surveyed the emission using a collection of Suzaku ob- servations of hard X-ray
emitting symbiotic stars to better understand the geometry of these systems. We
find that they do not seem to have a single geometry, and that while
absorption-induced fluorescence leads to some emission in three of the hard
X-ray emitting symbiotic stars (hSSs) in our study, CH Cyg, T CrB and RT Cru
there are strong hints that significant 6.4 keV emission arises in the
accretion disk irradiated by the hard X-rays from the boundary layer between
the accretion disk and hot white dwarf in one of our sources, SS73 17. The 6.7
and 7.0 keV lines, however, are largely produced by collisional excitation in
the vicinity of the compact white dwarf.",1310.2461v2
2013-10-17,Achievement of practical level critical current densities in PIT Ba1-xKxFe2As2/Ag tapes by conventional cold mechanical deformation,"We found that transport critical current density (Jc) of the Ba1-xKxFe2As2/Ag
tapes is significantly enhanced by the combination process of cold flat rolling
and uniaxial pressing. At 4.2 K, the Jc reaches a high value of 9.1x104 A/cm2
in 4 T, which is almost the practical level of 105 A/cm2. The Jc-H curve shows
extremely small magnetic field dependence and keeps a high value of 6.9x104
A/cm2 in 10 T. These are the highest values reported so far for iron based
superconducting wires. We also show our successful attempts of the fabrication
of multi-filamentary tapes. A high Jc value of 5.3x104 A/cm2 (4.2 K, 10 T) was
obtained in seven-filamentary tapes. The hardness and microstructure
investigations reveal that the superior Jc in uniaxial pressed tape samples is
due to the high core density, more textured grains and the change of microcrack
structure. These results indicate that iron based superconductors are promising
for high magnetic field applications.",1310.4623v1
2013-10-17,Double neutron spin resonances and gap anisotropy in underdoped superconducting NaFe0.985Co0.015As,"We use inelastic neutron scattering to show that superconductivity in
electron-underdoped NaFe0.985Co0.015As induces a dispersive sharp resonance
near Er1 = 3:25 meV and a broad dis- persionless mode at Er2 = 6 meV. However,
similar measurements on overdoped superconducting NaFe0:955Co0:045As find only
a single sharp resonance at Er = 7 meV. We connect these results with the
observations of angle-resolved photoemission spectroscopy that the
superconducting gaps in the electron Fermi pockets are anisotropic in the
underdoped material but become isotropic in the overdoped case. Our analysis
indicates that both the double neutron spin resonances and gap anisotropy
originate from the orbital dependence of the superconducting pairing in the
iron pnic- tides. Our discovery also shows the importance of the inelastic
neutron scattering in detecting the multiorbital superconducting gap structures
of iron pnictides.",1310.4817v1
2013-10-28,Local correlation effects on the s+-- and s++-wave superconductivities mediated by magnetic and orbital fluctuations in the 5-orbital Hubbard model for iron pnictides,"We investigate the electronic state and the superconductivity in the
5-orbital Hubbard model for iron pnictides by using the dynamical mean-field
theory in conjunction with the Eliashberg equation. The renormalization factor
exhibits significant orbital dependence resulting in the large change in the
band dispersion as observed in recent ARPES experiments. The critical
interactions towards the magnetic, orbital and superconducting instabilities
are suppressed as compared with those from the random phase approximation (RPA)
due to local correlation effects. Remarkably, the s++-pairing phase due to the
orbital fluctuation is largely expanded relative to the RPA result, while the
s+--pairing phase due to the magnetic fluctuation is reduced.",1310.7325v2
2013-11-06,"Discovery of New Layered Iron Arsenide Superconductor (Ca,Pr)FeAs2","A new iron-based superconductor (Ca,Pr)FeAs2 was discovered. Plate-like
crystals of the new phase were obtained and crystal structure was investigated
by single-crystal X-ray diffraction analysis. The structure was identified as
the monoclinic system with space group P21/m, and is composed of two Ca(Pr)
planes, anti-fluorite Fe2As2 layers, and As2 zigzag chain layers. Plate-like
crystals composed of the new phase showed superconductivity with Tc ~20 K in
both magnetization and resistivity measurements.",1311.1302v1
2013-11-06,Superconductivity in Ca1-xLaxFeAs2: A Novel 112-Type Iron Pnictide with Arsenic Zigzag Bonds,"We report superconductivity in the novel 112-type iron-based compound
Ca1-xLaxFeAs2. Single-crystal X-ray diffraction analysis revealed that the
compound crystallizes in a monoclinic structure (space group P21), in which
Fe2As2 layers alternate with Ca2As2 spacer layers such that monovalent arsenic
forms zigzag chains. Superconductivity with a transition temperature (Tc) of 34
K was observed for the x = 0.1 sample, while the x = 0.21 sample exhibited
trace superconductivity at 45 K. First-principles band calculations
demonstrated the presence of almost cylindrical Fermi surfaces, favorable for
the high Tc in La-doped CaFeAs2.",1311.1303v1
2013-11-06,Non-conventional superconducting fluctuations in Ba(Fe1-xRhx)2As2 iron-based superconductors,"We measured the static uniform spin susceptibility of
Ba(Fe$_{1-x}$Rh$_x$)$_2$As$_2$ iron-based superconductors, over a broad range
of doping ($0.041\leq x\leq 0.094$) and magnetic fields. At small fields ($H
\le$ 1 kOe) we observed, above the transition temperature $T_c$, the occurrence
of precursor diamagnetism, which is not ascribable to the Ginzburg-Landau
theory. On the contrary, our data fit a phase fluctuation model, which has been
used to interpret a similar phenomenology occurring in the high-$T_c$ cuprate
superconductors. On the other hand, in presence of strong fields the
unconventional fluctuating diamagnetism is suppressed, whereas 3D fluctuations
are found, in agreement with literature.",1311.1336v2
2013-11-27,Evolution of the Fermi surface topology in doped 122 iron pnictides,"Based on the minimum two-orbital model and the phase diagram recently
proposed by Tai et al.\ (Europhys. Lett. \textbf{103}, 67001(2013)) for both
electron- and hole-doped 122 iron-based superconducting compounds, we use the
Bogoliubov-de Gennes equations to perform a comprehensive investigation of the
evolution of the Fermi surface (FS) topology in the presence of the collinear
spin-density-wave (SDW) order as the doping is changed. In the parent compound,
the ground state is the SDW order, where the FS is not completely gapped, and
two types of Dirac cones, one electron-doped and the other hole-doped emerge in
the magnetic Brillouin zone. Our findings are qualitatively consistent with
recent angle-resolved photoemission spectroscopy and magneto-resistivity
measurements. We also examine the FS evolution of both electron- and hole-doped
cases and compare them with measurements, as well as with those obtained by
other model Hamiltonians.",1311.7047v1
2013-12-09,Memory function approach to in-plane anisotropic resistivity in the antiferromagnetic phase of iron arsenide superconductors,"We theoretically examine anisotropy of in-plane resistivity in the striped
antiferromagnetic phase of an iron arsenide superconductor by applying a memory
function approach to the ordered phase with isotropic nonmagnetic impurity. We
find that the anisotropy of the scattering rate is independent of carrier
density when the topology of the Fermi surface is changed after the
introduction of holes. On the other hand, the anisotropy of the Drude weight
monotonically decreases reflecting the distortion of the Dirac Fermi surface
and eventually leads to the reverse of anisotropy of resistivity, being
consistent with experiment. The origin of the anisotropy is thus attributed to
the interplay of impurity scattering and anisotropic electronic states.",1312.2322v3
2013-12-17,Superconducting pairing in the spin-density-wave phase of iron pnictides,"Some of the iron pnictides show coexisting superconductivity and
spin-density-wave order. We study the superconducting pairing instability in
the spin-density-wave phase. Assuming that the pairing interaction is due to
spin fluctuations, we calculate the effective pairing interactions in the
singlet and triplet channels by summing the bubble and ladder diagrams taking
the reconstructed band structure into account. The leading pairing
instabilities and the corresponding superconducting gap structures are then
obtained from the superconducting gap equation. We illustrate this approach for
a minimal two-band model of the pnictides. Analytical and numerical results
show that the existence of propagating magnons in the spin-density-wave phase
strongly enhances the pairing in both the singlet and the spin s_z=0 triplet
channel. Over a limited parameter range, a spin s_z=0 triplet p_x-wave state is
the dominant instability. It competes with various singlet states, which have
mostly s^\pm-type structures. We analyze the effect of various symmetry-allowed
interactions on the pairing in some detail.",1312.4720v2
2013-12-20,Impact of local-moment fluctuations on the magnetic degeneracy of iron arsenide superconductors,"We investigate the fate of the orthorhombic stripe-type magnetic state
(ordering vectors $\left(\pi,0\right)$/$\left(0,\pi\right)$), observed in most
iron-pnictide superconductors, in the presence of localized magnetic moments
that tend to form a Neel state (ordering vector $\left(\pi,\pi\right)$). We
show that before long-range Neel order sets in, the coupling between the
conduction electrons and the fluctuations of the local moments favors an
unusual magnetic state consisting of a coherent superposition of the
$\left(\pi,0\right)$ and $\left(0,\pi\right)$ orders that preserves tetragonal
symmetry. The magnetization of this state is non-uniform and induces a
simultaneous checkerboard charge order. We discuss signatures of this magnetic
configuration on the electronic spectrum and its impact on the superconducting
state, showing that its phase space for coexistence with the $s^{+-}$ state is
smaller than the stripe-type state. Our results shed light on recent
experimental observations on $\mathrm{Ba(Fe_{1-x}Mn_{x})_{2}As_{2}}$ compounds,
where the Neel-type local Mn moments interact with the Fe conduction electrons.",1312.6176v2
2013-12-24,Controlling Factors of Tc-Dome Structure in 1111-Type Iron Arsenide Superconductors,"We investigated the effects of phosphorus substitution on the shape of the
Tc(x) dome in 1111-type SmFeAs1-yPyO1-xHx (0 < x < 0.5). Hydride ion
substitution of oxide sites (O2- -> H-) exerts a chemical pressure effect,
i.e., a structural reduction of the Pn-Fe-Pn angle {\alpha} (Pn = P, As) and
also dopes electrons into the FePn layer to induce superconductivity. Isovalent
phosphorus substitution (P3- -> As3-) can induce only a chemical pressure
effect, i.e., an increase of {\alpha} for La-substitution of Sm-sites. As y
increases from 0.0 to 0.5, the single Tc dome gradually splits into two domes,
similar to those of LaFeAsO1-xHx with a Tc valley at x ~ 0.16. We found that
the Tc valley is located around (x, {\alpha}) ~ (0.16, 113{\deg}) for both
SmFeAs1-yPyO1-xHx and LaFeAsO1-xHx series, irrespective of changes in the Pn
anion and Ln cation species. This result suggests that suppression of Tc leads
to the emergence of a Tc valley when both the shape of FePn4 tetrahedra
represented by {\alpha} and electron doping level of x meet the above criterion
in 1111 type iron oxypnictide superconductors.",1312.6747v1
2014-01-01,Unfolding the electronic structure of Ca$_{10}$(Fe$_{1-x}$Pt$_x$As)$_{10}$(Pt$_n$As$_8$),"The platinum iron arsenides
Ca$_{10}$(Fe$_{1-x}$Pt$_x$As)$_{10}$(Pt$_n$As$_8$) are the first Fe based
superconductors with metallic spacer layers. Furthermore they display a large
variation in their critical temperatures depending on the amount of Pt in their
spacer layers: $(n=3,4)$. To gain more insight into the role of the spacer
layer the electronic structures of the iron arsenic platenides are represented
in the momentum space of the underlying Fe sublattice using a first principles
unfolding method. We find that Ca$_{10}$(FeAs)$_{10}$(Pt$_4$As$_8$), contrary
to Ca$_{10}$(FeAs)$_{10}$(Pt$_3$As$_8$), shows a net electron doping and a
non-negligible interlayer coupling. Both effects could account for the
difference in the critical temperatures.",1401.0298v2
2014-01-01,Analytic theory of Hund's metals: a renormalization group perspective,"We study the emergence of quasiparticles in Hund's metals with an
SU($M$)$\times$SU($N$)-symmetric Kondo impurity model carrying both spin and
orbital degrees of freedom. We show that the coupling of the impurity spin to
the conduction electrons can be \emph{ferromagnetic}, notably for hole-doped
iron pnictides. We derive the weak-coupling renormalization group (RG)
equations for arbitrary representations of SU($M$)$\times$SU($N$). A
ferromagnetic spin coupling results in a protracted RG flow, accounting for the
surprising particle-hole asymmetry that is observed in the iron-pnictide
systems. We establish the low coherence scale $T_{\rm K}$ which depends on the
filling through the impurity representation. We also discuss the temperature
dependence of the spin and orbital susceptibilities. Finally, we argue that
this mechanism explains the strong valence dependence of the coherence scale
observed in dilute transition-metal magnetic alloys.",1401.0331v3
2014-01-03,Effect of SDW fluctuations on the specific heat jump in iron pnictides at a superconducting transition,"Measurements of the specific heat jump at the onset of superconducting
transition in the iron-pnictide compounds revealed strong variation of its
magnitude as a function of doping that is peaked near the optimal doping. We
show that this behavior is direct manifestation of the coexistence between
spin-density-wave and superconducting orders and the peak originates from
thermal fluctuations of the spin-density-waves near the end point of the
coexistence phase -- a tetracritical point. Thermal fluctuations result in a
power-law dependence of the specific heat jump that is stronger than the
contribution of mass renormalization due to quantum fluctuations of
spin-density-waves in the vicinity of the putative critical point beneath the
superconducting dome.",1401.1118v1
2014-01-13,Simulation studies of hadron energy resolution as a function of iron plate thickness at INO-ICAL,"We report on a detailed simulation study of the hadron energy resolution as a
function of the thickness of the absorber plates for the proposed Iron
Calorimeter (ICAL) detector at the India-based Neutrino Observatory (INO). We
compare the hadron resolutions obtained with absorber thicknesses in the range
1.5--8 cm for neutrino interactions in the energy range 2--15 GeV, which is
relevant to hadron production in atmospheric neutrino interactions. We find
that at lower energies, the thickness dependence of energy resolution is
steeper than at higher energies, however there is a thickness-independent
contribution that dominates at the lower thicknesses discussed in this work. As
a result, the gain in hadron energy resolution with decreasing plate thickness
is marginal. We present the results in the form of fits to a function with
energy-dependent exponent.",1401.2779v2
2014-01-15,Strong Coupling of the Iron-Quadrupole and Anion-Dipole Polarizations in Ba(Fe$_{1-x}$Co$_x$)$_2$As$_2$,"We use a quantitative convergent beam electron diffraction (CBED) based
method to image the valence electron density distribution in
Ba(Fe$_{1-x}$Co$_x$)$_2$As$_2$. We show a remarkable increase in both the
charge quadrupole of the Fe cations and the charge dipole of the arsenic anions
upon Co doping from $x=0$ ($T_c=0$ K) to $x=0.1$ ($T_c=22.5$ K). Our data
suggest that an unexpected electronic correlation effect, namely strong
coupling of Fe orbital fluctuation and anion electronic polarization, is
present in iron-based superconductors.",1401.3706v1
2014-01-18,Quantum rate theory of the trapping of hydrogen and deuterium by a vacancy in iron,"We apply quantum rate theory to calculate the transition rates as hydrogen or
deuterium atoms escape from a vacancy trap in iron into a neighbouring
metastable site. We determine transition rates and corresponding activation
energies over a wide range of temperatures covering both the quantum and
classically dominated regimes. We find that quantum effects lead to an increase
of the transition rate activation energy and to very significant recrossing of
the transition state dividing surface. As a result of recrossing quantum
transition state theory overestimates the rate of proton transfer by more than
an order of magnitude and the rate of deuteron transfer by a factor of two.",1401.4530v1
2014-02-11,Weak spin interactions in Mott insulating La2O2Fe2OSe2,"Identifying and characterizing the parent phases of iron-based
superconductors is an important step towards understanding the mechanism for
their high temperature superconductivity. We present an investigation into the
magnetic interactions in the Mott insulator La2O2Fe2OSe2. This iron oxyselenide
adopts a 2-k magnetic structure with low levels of magnetic frustration. This
magnetic ground state is found to be dominated by next-nearest neighbor
interactions J2 and J2' and the magnetocrystalline anisotropy of the Fe2+ site,
leading to 2D-Ising-like spin S=2 fluctuations. In contrast to calculations,
the values are small and confine the spin excitations below ~ 25 meV. This is
further corroborated by sum rules of neutron scattering. This indicates that
superconductivity in related materials may derive from a weakly coupled and
unfrustrated magnetic structure.",1402.2684v1
2014-02-17,A High-Tc Mechanism of Iron Pnictide Superconductivity due to Cooperation of Ferro-orbital and Antiferromagnetic Fluctuations,"The electronic states and superconductivity in iron pnictides are studied on
the basis of the 16 band $d$-$p$ model which includes both the onsite Coulomb
interaction between Fe $d$ electrons and the intersite one between Fe $d$ and
pnictogen $p$ electrons. The model well accounts for experimentally observed
two fluctuations: the $d$-$d$ interaction-enhanced antiferromagnetic (AFM)
fluctuation and the $d$-$p$ interaction-enhanced ferro-orbital (FO) fluctuation
responsible for the $C_{66}$ elastic softening. The AFM fluctuation induces the
repulsive pairing interaction for $\bm{q}\sim \bm{Q}_{\rm AF}$ while the FO
does the attractive one for $\bm{q}\sim \bm{0}$ resulting in the $s_{\pm}$-wave
superconductivity where the two fluctuations cooperatively enhance the
superconducting transition temperature $T_{c}$ without any competition by
virtue of the $\bm{q}$-space segregation.",1402.3908v2
2014-02-19,Coexistence of localized and itinerant magnetism in newly discovered iron-selenide superconductor LiFeO2Fe2Se2,"The electronic structure and magnetism of LiFeO$_{2}$Fe$_{2}$Se$_{2}$ are
investigated using the first-principle calculations. The ground state is
N$\acute{e}$el antiferromagnetic (AFM) Mott insulating state for Fe1 with
localized magnetism in LiFeO$_{2}$ layer and striped AFM metallic state for Fe2
with itinerant magnetism in Fe$_{2}$Se$_{2}$ layer, accompanied with a weak
interlayer AFM coupling between Fe1 and Fe2 ions, resulting in a coexistence of
localized and itinerant magnetism. Moreover, the layered LiFeO$_{2}$ is found
to be more than an insulating block layer but responsible for enhanced AFM
correlation in Fe$_{2}$Se$_{2}$ layer through the interlayer magnetic coupling.
The interplay between the magnetisms of Fe1 and Fe2 introduces a control
mechanism for spin fluctuations associated with superconductivity in iron-based
superconductors.",1402.4711v1
2014-02-19,The effect of As-Chain layers in CaFeAs$_2$,"The new discovered iron-based superconductors have chain-like As layers.
These layers generate an additional 3-dimensional hole pocket and cone-like
electron pockets. The former is attributed to the Ca $d$ and As1 $p_z$ orbitals
and the latter are attributed to the anisotropic Dirac cone, contributed by As1
$p_x$ and $p_y$ orbitals. We find that large gaps on these pockets open in the
collinear antiferromagnetic ground state of CaFeAs$_2$, suggesting that the
chain-like As layers are strongly coupled to FeAs layers. Moreover due to the
low symmetry crystal induced by the As layers, the bands attributed to FeAs
layers in $k_y=\pi$ plane are two-fold degenerate but in $k_x=\pi$ plane are
lifted. This degeneracy is protected by a hidden symmetry
$\hat{\Upsilon}=\hat{T}\hat{R}_y$. Ignoring the electron cones, the materials
can be well described by a six-band model, including five Fe $d$ and As1 $p_z$
orbitals. We suggest that these new features may help us to identify the sign
change and pairing symmetry in iron based superconductors.",1402.4712v1
2014-02-19,"Electron-impact excitation of Fe$^{2+}$: a comparison of intermediate coupling frame transformation, Breit-Pauli and Dirac R-matrix calculations","Modeling the spectral emission of low-charge iron group ions enables the
diagnostic determination of the local physical conditions of many cool plasma
environments such as those found in H II regions, planetary nebulae, active
galactic nuclei etc. Electron-impact excitation drives the population of the
emitting levels and, hence, their emissivities. By carrying-out Breit-Pauli and
intermediate coupling frame transformation (ICFT) R-matrix calculations for the
electron-impact excitation of Fe$^{2+}$ which both use the exact same atomic
structure and the same close-coupling expansion, we demonstrate the validity of
the application of the powerful ICFT method to low-charge iron group ions. This
is in contradiction to the finding of Bautista et al. [Ap.J.Lett, 718, L189,
(2010)] who carried-out ICFT and Dirac R-matrix calculations for the same ion.
We discuss possible reasons.",1402.4743v1
2014-02-24,Spectrally-resolved femtosecond reflectivity relaxation dynamics in undoped SDW 122-structure iron based pnictides,"We systematically investigate temperature- and spectrally-dependent optical
reflectivity dynamics in AAs$_{2}$Fe$_{2}$, (A=Ba, Sr and Eu), iron-based
superconductors parent spin-density-wave (SDW) compounds. Two different
relaxation processes are identified. The behavior of the slower process, which
is strongly sensitive to the magneto-structural transition, is analyzed in the
framework of the relaxation-bottleneck model involving magnons. The results are
compared to recent time resolved angular photoemission results (TR-ARPES) and
possible alternative assignment of the slower relaxation to the
magneto-structural order parameter relaxation is discussed.",1402.5811v1
2014-02-25,Probing Lorentz and CPT Violation in a Magnetized Iron Detector using Atmospheric Neutrinos,"We study the sensitivity of the Iron Calorimeter (ICAL) at the India-Based
Neutrino Observatory (INO) to Lorentz and CPT violation in the neutrino sector.
Its ability to identify the charge of muons in addition to their direction and
energy makes ICAL a useful tool in putting constraints on these fundamental
symmetries. Using resolution, efficiencies, errors and uncertainties obtained
from ICAL detector simulations, we determine sensitivities to $\delta{b}_{31}$,
which parametizes the violations in the muon neutrino sector. We carry out
calculations for three generic cases representing mixing in the CPT violating
part of the hamiltonian, specifically, when the mixing is 1) small, 2) large,
3) the same as that in the PMNS matrix. We find that for both types of
hierarchy, ICAL at INO should be sensitive to $\delta{b}_{31}$ $\gtrsim$
$4\times10^{-23}$ GeV at 99% C.L. for 500 kt-yr exposure, unless the mixing in
the CPT violation sector is small.",1402.6265v1
2014-02-27,Power Law Like Correlation between Condensation Energy and Superconducting Transition Temperatures in Iron Pnictide/Chalcogenide Superconductors: Beyond the BCS Understanding,"Superconducting condensation energy $U_0^{int}$ has been determined by
integrating the electronic entropy in various iron pnictide/chalcogenide
superconducting systems. It is found that $U_0^{int}\propto T_c^n$ with $n$ = 3
to 4, which is in sharp contrast to the simple BCS prediction
$U_0^{BCS}=1/2N_F\Delta_s^2$ with $N_F$ the quasiparticle density of states at
the Fermi energy, $\Delta_s$ the superconducting gap. A similar correlation
holds if we compute the condensation energy through
$U_0^{cal}=3\gamma_n^{eff}\Delta_s^2/4\pi^2k_B^2$ with $\gamma_n^{eff}$ the
effective normal state electronic specific heat coefficient. This indicates a
general relationship $\gamma_n^{eff} \propto T_c^m$ with $m$ = 1 to 2, which is
not predicted by the BCS scheme. A picture based on quantum criticality is
proposed to explain this phenomenon.",1402.6762v1
2014-03-13,Enhancing magnetic stripe order in iron pnictides by RKKY exchange interactions,"Recent experimental studies have revealed several unexpected properties of
Mn-doped BaFe2As2. These include extension of the stripe-like magnetic (pi,0)
phase to high temperatures above a critical Mn concentration only, the presence
of diffusive and weakly temperature dependent magnetic (pi,pi) checkerboard
scattering, and an apparent absent structural distortion from tetragonal to
orthorhombic. Here, we study the effects of magnetic impurities both below and
above the N\'eel transition temperature within a real-space five-band model
appropriate to the iron pnictides. We show how these experimental findings can
be explained by a cooperative behavior of the magnetic impurities and the
conduction electrons mediating the Ruderman-Kittel-Kasuya-Yosida (RKKY)
interactions between them.",1403.3324v1
2014-03-21,Functional renormalization group study of an eight-band model for the iron arsenides,"We investigate the superconducting pairing instabilities of eight-band models
for the iron arsenides. Using a functional renormalization group treatment, we
determine how the critical energy scale for superconductivity depends on the
electronic band structure. Most importantly, if we vary the parameters from
values corresponding to LaFeAsO to SmFeAsO, the pairing scale is strongly
enhanced, in accordance with the experimental observation. We analyze the
reasons for this trend and compare the results of the eight-band approach to
those found using five-band models.",1403.5487v3
2014-03-24,Effect of weak disorder on the phase competition in iron pnictides,"We analyze the effect of weak disorder on the competition between
antiferromagnetic order and superconductivity in a model for iron-based
superconductors. Under the assumption of an approximate particle-hole symmetry
we show that conventional $s^{++}$ superconductivity cannot be realized in the
case of coexisting magnetic and superconductive orders, observed experimentally
at intermediate doping levels. This result holds for arbitrary impurity
concentrations, and, in particular, in the clean limit. The inclusion of
disorder further amplifies the phase competition between itinerant
antiferromagnetism and conventional superconductivity. In addition, we analyze
the effect of disorder on the characteristic length scales of the two order
parameters, and find that in a disordered sample the staggered moment
fluctuates on shorter scales than the superconductive order parameter.",1403.6103v2
2014-04-04,Superconducting states of a J1-J2-K model for iron pnictides,"We study the symmetry and strength of the superconducting pairing in a
two-orbital t-J1-J2-K model for iron pnictides using the salve boson mean-field
theory. We show that the nearest-neighbor biquadratic interaction -K (S_i *
S_j)^2 inflences the superconducting pairing phase diagram by promoting the
d_{x2-y2} B_{1g} and the s_{x^2+y^2} A_{1g} channels. The resulting phase
diagram consists of several competing pairing channels, including an isotropic
s_{\pm} A_{1g} channel, an anisotropic d_{x2-y2} B_{1g} channel, and two s+id
pairing channels. We have investigated the evolution of superconducting states
with electron doping, and find that with the biquadratic interaction various
pairing channels may dominate at different doping concentrations. We show that
this is crucial in understanding the doping evolution of superconducting gap
anisotropy observed in some angle resolved photoemission spectrum measurements.",1404.1307v1
2014-04-11,A new library of theoretical stellar spectra with scaled-solar and alpha-enhanced mixtures,"Theoretical stellar libraries have been increasingly used to overcome
limitations of empirical libraries, e.g. by exploring atmospheric parameter
spaces not well represented in the latter. This work presents a new theoretical
library which covers 3000 $\leq$ Teff $\leq$ 25000\,K, -0.5 $\leq$ log g $\leq$
5.5, and 12 chemical mixtures covering 0.0017 $\leq$ Z $\leq$ 0.049 at both
scaled-solar and $\alpha$-enhanced compositions. This library complements
previous ones by providing: (i) homogeneous computations of opacity
distribution functions, models atmospheres, statistical surface fluxes and high
resolution spectra; (ii) high resolution spectra with continua slopes corrected
by the effect of predicted lines, and; (iii) two families of $\alpha$-enhanced
mixtures for each scaled-solar iron abundance, to allow studies of the
$\alpha$-enhancement both at `fixed iron' and `fixed Z' cases. Comparisons to
observed spectra were performed and confirm that the synthetic spectra
reproduce well the observations, although there are wavelength regions which
should be still improved. The atmospheric parameter scale of the model library
was compared to one derived from a widely used empirical library, and no
systematic difference between the scales was found. This is particularly
reassuring for methods which use synthetic spectra for deriving atmospheric
parameters of stars in spectroscopic surveys.",1404.3243v1
2014-04-14,Magnetic correlations and pairing in the 1/5-depleted square lattice Hubbard model,"We study the single-orbital Hubbard model on the 1/5-depleted square lattice
geometry, which arises in such diverse systems as the spin-gap magnetic
insulator CaV4O9 and ordered-vacancy iron selenides, presenting new issues
regarding the origin of both magnetic ordering and superconductivity in these
materials. We find a rich phase diagram that includes a plaquette singlet
phase, a dimer singlet phase, a Neel and a block-spin antiferromagnetic phase,
and stripe phases. Quantum Monte Carlo simulations show that the dominant
pairing correlations at half filling change character from d-wave in the
plaquette phase to extended s-wave upon transition to the Neel phase. These
findings have intriguing connections to iron-based superconductors, and suggest
that some physics of multiorbital systems can be captured by a single-orbital
model at different dopings.",1404.3731v2
2014-04-25,Role of vibrational entropy in the stabilization of the high-temperature phases of iron,"The phonon dispersions of the bcc and fcc phases of pure iron ({\alpha}-Fe,
{\gamma}-Fe and {\delta}-Fe) at ambient pressure were investigated close to the
respective phase transition temperatures. In the open bcc structure the
transverse phonons along T1 [{\xi}{\xi}0] and T1 [{\xi}{\xi}2{\xi}] are of
particularly low energy. The eigenvectors of these phonons correspond to
displacements needed for the transformation to the fcc {\gamma}-phase.
Especially these phonons, but also all other phonons soften considerably with
increasing temperature. Comparing thermodynamic properties of the fcc and the
two bcc phases it is shown that the high temperature bcc phase is stabilized
predominantly by vibrational entropy, whereas for the stabilization of the fcc
phase electronic entropy provides an equal contribution.",1404.6459v1
2014-05-07,Topological surface states and Andreev bound states in superconducting iron pnictides,"The nontrivial topology of the electronic structure of iron pnictides can
lead to the appearance of surface states. We study such states in various strip
geometries with a focus on the superconducting phase. In the presence of
unconventional superconducting pairing with $s_\pm$-wave gap structure, the
topological states are quite robust and partly remain in the superconducting
gap. Furthermore, Andreev bound states appear, which coexist with the
topological states for small superconducting gaps and merge with them for
larger gap values. The bulk and surface dispersions are obtained from exact
diagonalization for two-orbital and five-orbital models in strip geometries.",1405.1632v2
2014-05-15,"High-pressure single-crystal neutron scattering study of magnetic and Fe vacancy orders in (Tl,Rb)2Fe4Se5 superconductor","The magnetic and iron vacancy orders in superconducting (Tl,Rb)2Fe4Se5
single-crystals are investigated by using a high-pressure neutron diffraction
technique. Similar to the temperature effect, the block antiferromagnetic order
gradually decreases upon increasing pressure while the Fe vacancy
superstructural order remains intact before its precipitous disappearance at
the critical pressure Pc = 8.3 GPa. Combined with previously determined Pc for
superconductivity, our phase diagram under pressure reveals the concurrence of
the block AFM order, the iron vacancy order and superconductivity for the 245
superconductor. A synthesis of current experimental data in a coherent physical
picture is attempted.",1405.4020v2
2014-05-19,Radiation from an emitter revolving around a magnetized non-rotating black hole,"One of the methods of study of black holes in astrophysics is based on
broadening of the spectrum of radiation of ionized Iron atoms. The line
K$\alpha$ associated with Iron emission at 6.4 keV is very narrow. If such an
ion is revolving around a black hole, this line is effectively broadened as a
result of the Doppler and gravitational redshift effects. The profile of the
broaden spectrum contains information about the gravitational field of the
black hole. In the presence of a regular magnetic field in the vicinity of a
black holes the characteristics of the motion of charged ions are modified. In
particular, their innermost stable circular orbits become closer to the
horizon. The purpose of this work is to study how this effect modifies the
spectrum broadening of lines emitted by such an ion. Our final goal is to
analyze whether the change of the spectrum profiles can give us information
about the magnetic field in the black hole vicinity.",1405.4899v1
2014-05-20,Resistive anisotropy due to spin-fluctuation scattering in the nematic phase of iron pnictides,"The large in-plane anisotropy of the resistivity is a hallmark of the nematic
state of the iron pnictides. Solving the Boltzmann transport equation, we show
that the prominent doping dependence as well as the large values of the
anisotropy can be well explained by momentum-dependent spin-fluctuation
scattering without assuming anisotropic impurity states. Due to the
forward-scattering corrections, the hot spots contribute to the resistive
anisotropy even in the case of strong spin fluctuations, which makes large
values of the anisotropy possible. The ellipticity of the electron pockets
plays an important role in explaining the dominance of positive values of the
anisotropy, i.e., larger resistivity in the direction with weaker spin
fluctuations, throughout the doping range.",1405.5084v3
2014-05-21,Theoretical approach to resonant inelastic x-ray scattering in iron-based superconductors at the energy scale of the superconducting gap,"We develop a phenomenological theory to predict the characteristic features
of the momentum-dependent scattering amplitude in resonant inelastic x-ray
scattering (RIXS) at the energy scale of the superconducting gap in iron-based
superconductors. Taking into account all relevant orbital states as well as
their specific content along the Fermi surface we evaluate the charge and spin
dynamical structure factors for the compounds LaOFeAs and LiFeAs, based on
tight-binding models which are fully consistent with recent angle-resolved
photoemission spectroscopy (ARPES) data. We find a characteristic intensity
redistribution between charge and spin dynamical structure factors which
discriminates between sign-reversing and sign-preserving quasiparticle
excitations. Consequently, our results show that RIXS spectra can distinguish
between $s_\pm$ and $s_{++}$ wave gap functions in the singlet pairing case. In
addition, we find that an analogous intensity redistribution at small momenta
can reveal the presence of a chiral $p$-wave triplet pairing.",1405.5556v2
2014-05-23,Collective modes in multiband superconductors: Raman scattering in iron selenides,"We study Raman scattering in the superconducting state of alkali-intercalated
iron selenide materials AxFe2-ySe2 (A=K,Rb,Cs) in which Fermi surface has only
electron pockets. Theory predicts that both s-wave and d-wave pairing channels
are attractive in this material, and the gap can have either s-wave or d-wave
symmetry, depending on the system parameters. ARPES data favor $s-$wave
superconductivity. We present the theory of Raman scattering in AxFe2-ySe2
assuming that the ground state has s-wave symmetry but $d-$ wave is a close
second. We argue that Raman profile in d-wave B2g channel displays two
collective modes. One is a particle-hole exciton, another is a
Bardasis-Schrieffer-type mode associated with superconducting fluctuations in
d-wave channel. At a finite damping, the two modes merge into one broad peak.
We present Raman data for AxFe2-ySe2 and compare them with theoretical Raman
profile.",1405.6246v1
2014-05-28,A Simulations Study of the Muon Response of the Iron Calorimeter Detector at the India-based Neutrino Observatory,"The magnetised Iron CALorimeter detector (ICAL), proposed to be built at the
India-based Neutrino Observatory (INO), is designed to study atmospheric
neutrino oscillations. The ICAL detector is optimized to measure the muon
momentum, its direction and charge. A GEANT4-based package has been developed
by the INO collaboration to simulate the ICAL geometry and propagation of
particles through the detector. The simulated muon tracks are reconstructed
using the Kalman Filter algorithm. Here we present the first study of the
response of the ICAL detector to muons using this simulations package to
determine the muon momentum and direction resolutions as well as their
reconstruction and charge identification efficiencies. For 1-20 GeV/c muons in
the central region of the detector, we obtain an average angle-dependent
momentum resolution of 9-14%, an angular resolution of about a degree,
reconstruction efficiency of about 80% and a correct charge identification of
about 98%.",1405.7243v1
2014-06-19,Magnetic form factor analysis on detwinned single crystal of BaFe$_2$As$_2$,"We have performed neutron diffraction measurement on a single crystal of
parent compound of iron-based superconductor, BaFe$_2$As$_2$ at 12~K. In order
to investigate in-plane anisotropy of magnetic form factor in the
antiferromagnetic phase, the detwinned single crystal is used in the
measurement. The magnetic structure factor and magnetic form factor are well
explained by the spin densities consisting of $3d_{yz}$ electrons with a
fraction of about 40~\% and the electrons in the other four $3d$ orbitals with
each fraction of about 15~\%. Such anisotropic magnetic form factor is
qualitatively consistent with the anisotropic magnetic behaviors observed in
the antiferromagnetic phase of the parent compound of iron-based
superconductor.",1406.4935v1
2014-06-20,Coexistence of Antiferromagnetism and Superconductivity in Iron-Based Superconductors,"We theoretically investigate the coexistence of antiferromagnetism and
superconductivity in the iron-based superconductors by using the mean-field
theory for two- and three-orbital models. We find that both the s_{+-}-wave and
s_{++}-wave superconductivity can coexist with antiferromagnetism in the two
models. On Dirac Fermi surfaces emerging in the antiferromagnetic phase, a
superconducting-gap function has a node for s_{++} wave but is nodeless for
s_{+-} wave. On the other hand, the gap function on non-Dirac Fermi surfaces is
either nodeless or accidentally nodal, depending on the parameters of pairing
interaction, which is independent of pairing symmetry.",1406.5339v2
2014-06-21,Fermi-surface topology of the iron pnictide LaFe$_2$P$_2$,"We report on a comprehensive de Haas--van Alphen (dHvA) study of the iron
pnictide LaFe$_2$P$_2$. Our extensive density-functional band-structure
calculations can well explain the measured angular-dependent dHvA frequencies.
As salient feature, we observe only one quasi-two-dimensional Fermi-surface
sheet, i.e., a hole-like Fermi-surface cylinder around $\Gamma$, essential for
$s_\pm$ pairing, is missing. In spite of considerable mass enhancements due to
many-body effects, LaFe$_2$P$_2$ shows no superconductivity. This is likely
caused by the absence of any nesting between electron and hole bands.",1406.5642v1
2014-06-26,High-Energy Damping by Particle-Hole Excitations in the Spin-Wave Spectrum of Iron-Based Superconductors,"Using a degenerate double-exchange model, we investigate the spin excitation
spectra of iron pnictides. The model consists of local spin moments on each Fe
site, as well as itinerant electrons from the degenerate $d_{xz}$ and $d_{yz}$
orbitals. The local moments interact with each other through antiferromagnetic
$J_{1}$-$J_{2}$ Heisenberg interactions, and they couple to the itinerant
electrons through a ferromagnetic Hund coupling. We employ the fermionic spinon
representation for the local moments and perform a generalized random-phase
approximation calculation on both spinons and itinerant electrons. We find that
in the $\left(\pi,0\right)$ magnetically-ordered state, the spin-wave
excitation at $\left(\pi,\pi\right)$ is pushed to a higher energy due to the
presence of itinerant electrons, which is consistent with a previous study
using the Holstein-Primakoff transformation. In the paramagnetic state, the
particle-hole continuum keeps the collective spin excitation near
$\left(\pi,\pi\right)$ at a higher energy even without any $C_{4}$ symmetry
breaking. The implications for recent high temperature neutron scattering
measurements will be discussed.",1406.6737v3
2014-07-02,Short-range cluster spin glass near optimal superconductivity in BaFe$_{2-x}$Ni$_{x}$As$_{2}$,"High-temperature superconductivity in iron pnictides occurs when electrons
are doped into their antiferromagnetic (AF) parent compounds. In addition to
inducing superconductivity, electron-doping also changes the static
commensurate AF order in the undoped parent compounds into short-range
incommensurate AF order near optimal superconductivity. Here we use neutron
scattering to demonstrate that the incommensurate AF order in
BaFe$_{2-x}$Ni$_{x}$As$_{2}$ is not a spin-density-wave arising from the
itinerant electrons in nested Fermi surfaces, but consistent with a cluster
spin glass in the matrix of the superconducting phase. Therefore, optimal
superconductivity in iron pnictides coexists and competes with a mesoscopically
separated cluster spin glass phase, much different from the homogeneous
coexisting AF and superconducting phases in the underdoped regime.",1407.0568v1
2014-07-07,Enhancement of Transition Temperature in FexSe0.5Te0.5 Film via Iron Vacancies,"The effects of iron deficiency in FexSe0.5Te0.5 thin films (0.8<x<1) on
superconductivity and electronic properties have been studied. A significant
enhancement of the superconducting transition temperature (TC) up to 21K was
observed in the most Fe deficient film (x=0.8). Based on the observed and
simulated structural variation results, there is a high possibility that Fe
vacancies can be formed in the FexSe0.5Te0.5 films. The enhancement of TC shows
a strong relationship with the lattice strain effect induced by Fe vacancies.
Importantly, the presence of Fe vacancies alters the charge carrier population
by introducing electron charge carriers, with the Fe deficient film showing
more metallic behavior than the defect-free film. Our study provides a means to
enhance the superconductivity and tune the charge carriers via Fe vacancy, with
no reliance on chemical doping.",1407.1575v1
2014-07-11,"Superconductivity by transition metal doping in Ca$_{10}$(Fe$_{1-x}$M$_x$As)$_{10}$(Pt$_3$As$_8$) (M = Co, Ni, Cu)","We report the successful substitution of cobalt, nickel, and copper for iron
in the 1038 phase parent compound Ca$_{10}$(FeAs)$_{10}$(Pt$_3$As$_8$) yielding
Ca$_{10}$(Fe$_{1-x}$Co$_x$As)$_{10}$(Pt$_3$As$_8$),
Ca$_{10}$(Fe$_{1-x}$Ni$_x$As)$_{10}$(Pt$_3$As$_8$), and
Ca$_{10}$(Fe$_{1-x}$Cu$_x$As)$_{10}$(Pt$_3$As$_8$), respectively.
Superconductivity is induced in Co and Ni doped compounds reaching critical
temperatures up to 15 K, similar to known Pt substituted
Ca$_{10}$(Fe$_{1-x}$Pt$_x$As)$_{10}$(Pt$_3$As$_8$), whereas no
superconductivity was detected in
Ca$_{10}$(Fe$_{1-x}$Cu$_x$As)$_{10}$(Pt$_3$As$_8$). The obtained Tc(x) phase
diagrams are very similar to those of other iron arsenide superconductors
indicating rather universal behavior despite the more complex structures of the
1038-type compounds, where the physics is primarily determined by the FeAs
layer.",1407.3100v1
2014-07-19,Magnetic states of iron-based superconducting compounds calculated by using GGA$+U$ method with negative \emph{U},"The magnetic moments per Fe atom in high-$T{_\textrm{c}}$ iron-based
superconducting compounds, BaFe$_{2}$As$_{2}$ and LaFeAsO obtained from the
first-principles calculation with local-spin-density approximation are much
larger than those obtained from experiments. To resolve the contradictory
results between theory and experiment we employed the so-called LDA$+ U$ (or
more exactly GGA$+ U$) technique with negative \emph{U} in the first-principles
calculation. The calculated values with negative \emph{U}, $- 0.09$ Ry and $-
0.10$ Ry for BaFe$_{2}$As$_{2}$ and LaFeAsO, respectively, are in excellent
agreement with the experimental ones. By comparing the differences in
\emph{d}-orbital occupation numbers and spin densities calculated by using a
simple GGA and GGA$+ U$ with negative $U$, the magnetic moments of the two
compounds are found to be similar to the case of low-spin state of metamagnetic
Fe$_{3}$Al alloy.",1407.5137v1
2014-08-04,In-gap Bound States Induced by Interstitial Fe Impurities in Iron-based Superconductors,"Based on a two-orbit four-band tight binding model, we investigate the
low-lying electronic states around the interstitial excess Fe ions in the
iron-based superconductors by using T-matrix approach. It is shown that the
local density of states at the interstitial Fe impurity (IFI) possesses a
strong resonance inside the gap, which seems to be insensitive to the doping
and the pairing symmetry in the Fe-Fe plane, while a single or two resonances
appear at the nearest neighboring (NN) Fe sites. The location and height of the
resonance peaks only depend on the hopping $t$ and the pairing parameter
$\Delta_I$ between the IFI and the NN Fe sites. These in-gap resonances are
originated in the Andreev's bound states due to the quasiparticle tunneling
through the IFI, leading to the change of the magnitude of the superconducting
order parameter. When both $t$ and $\Delta_I$ are small, this robust
zero-energy bound state near the IFI is consistent with recent scanning
tunneling microscopy observations.",1408.0567v1
2014-08-12,"Mechano-sysntesis and structural, magnetic and thermal characterization of $α$-Fe nanoparticles embedded in a Wüstite matrix","Magnetic materials for specific applications require an accurate control and
complete comprehension of their magnetic properties. In particular,
nanoparticles embedded in a polycrystalline matrix emerge as good candidates
for applications due to the possibility of tuning the magnetic properties
through interface interaction effects. Here, iron/w\""ustite composite is
prepared using high energy mechanical milling from iron powder and water. The
sample is analyzed by X-ray diffraction, dynamic laser light scattering,
M\""ossbauer spectroscopy, field cooling and zero field cooling curves,
magnetization curves, and magnetic hyperthermia. Based on the results, we
identify that the produced sample is like Fe nanoparticles embedded in a
w\""ustite matrix, with high stability in time, and shows noticeable features
such as exchange bias effect at low temperatures and promising temperatures
reached in a short time interval when considered magnetic hyperthermia, $\sim
46\,^\circ$C, becoming an interesting candidate for biological applications,
such as the one employed for cancer therapy.",1408.2703v1
2014-08-20,Hot pressing to enhance the transport Jc of Sr0.6K0.4Fe2As2 superconducting tapes,"High-performance Sr0.6K0.4Fe2As2 (Sr-122) tapes have been successfully
fabricated using hot pressing (HP) process. The effect of HP temperatures
(850-925 C) on the c-axis texture, resistivity, Vickers micro-hardness,
microstructure and critical current properties has been systematically studied.
Taking advantage of high degree of c-axis texture, well grain connectivity and
and large concentration of strong-pinning defects, we are able to obtain an
excellent Jc of 1.2x10^5 A/cm^2 at 4.2 K and 10 T for Sr-122 tapes. More
importantly, the field dependence of Jc turns out to be very weak, such that in
14 T the Jc remains ~1.0x10^5 A/cm^2. These Jc values are the highest ever
reported so far for iron-pnictide wires and tapes, achieving the level desired
for practical applications. Our results clearly strengthen the position of
iron-pnictide conductors as a competitor to the conventional and MgB2
superconductors for high field applications.",1408.4516v2
2014-08-29,"What You Should Know About Megaprojects, and Why: An Overview","This paper takes stock of megaproject management, an emerging and hugely
costly field of study. First, it answers the question of how large megaprojects
are by measuring them in the units mega, giga, and tera, concluding we are
presently entering a new ""tera era"" of trillion-dollar projects. Second, total
global megaproject spending is assessed, at USD 6-9 trillion annually, or 8
percent of total global GDP, which denotes the biggest investment boom in human
history. Third, four ""sublimes"" - political, technological, economic, and
aesthetic - are identified to explain the increased size and frequency of
megaprojects. Fourth, the ""iron law of megaprojects"" is laid out and
documented: Over budget, over time, over and over again. Moreover, the
""break-fix model"" of megaproject management is introduced as an explanation of
the iron law. Fifth, Albert O. Hirschman's theory of the Hiding Hand is
revisited and critiqued as unfounded and corrupting for megaproject thinking in
both the academy and policy. Sixth, it is shown how megaprojects are
systematically subject to ""survival of the unfittest,"" explaining why the worst
projects get built instead of the best. Finally, it is argued that the
conventional way of managing megaprojects has reached a ""tension point,"" where
tradition is challenged and reform is emerging.",1409.0003v1
2014-09-04,Anomalous High-Energy Electronic Interaction in Iron-Based Superconductor,"Strong electron interactions in solids increase effective mass, and shrink
the electronic bands [1]. One of the most unique and robust experimental facts
about iron-based superconductors [2-4] is the renormalization of the conduction
band by factor of 3 near the Fermi level [5-9]. Obviously related to
superconductivity, this unusual behaviour remains unexplained. Here, by
studying the momentum-resolved spectrum of the whole valence band in a
representative material, we show that this phenomenon originates from
electronic interaction on a much larger energy scale. We observe an abrupt
depletion of the spectral weight in the middle of the Fe $3d$ band, which is
accompanied by a drastic increase of the scattering rate. Remarkably, all
spectral anomalies including the low-energy renormalization can be explained by
coupling to excitations, strongly peaked at about 0.5 eV. Such high-energy
interaction distinguishes all unconventional superconductors from common
metals.",1409.1537v1
2014-09-05,The electronic structure of rare-earth iron silicide R2Fe3Si5 superconductors,"The electronic structures of R2Fe3Si5 (where R = Lu, Tm, Er, Tb, Yb)
intermetallics have been calculated from first principles in local-spin density
(LSDA) and LSDA + U approaches. The majority of rare-earth iron silicides,
except for the heavy-fermion Yb-based compound, exhibit almost equal values of
density of states at the Fermi level (EF) as well as very similar Fermi surface
topology. The electronic structure around EF in the 235-type Fe-based compounds
is completely dominated by the Fe 3d states. Thus the different superconducting
properties of some members of the R2Fe3Si5 family are rather related to a
presence of local magnetic moments of R-atoms than to electronic-structure
features at EF.",1409.1861v1
2014-09-10,$X_{max}^μ$ vs. $N^μ$ from Extensive Air Showers as estimator for the mass of primary UHECR's. Application for the Pierre Auger Observatory,"We study the possibility of primary mass estimation for Ultra High Energy
Cosmic Rays (UHECR's) using the $X_{max}^{\mu}$ (the height where the number of
muons produced on the core of Extensive Air Showers (EAS) is maximum) and the
number $N^{\mu}$ of muons detected on ground. We use the 2D distribution -
$X_{max}^{\mu}$ against $N^{\mu}$ in order to find its sensitivity to the mass
of the primary particle. For that, we construct a 2D Probability Function
$Prob(p,Fe \ | \ X_{max}^{\mu},N^{\mu})$ which estimates the probability that a
certain point from the plane $(X_{max}^{\mu}$, $N^{\mu})$ corresponds to a
shower induced by a proton, respectively an iron nucleus. To test the
procedure, we analyze a set of simulated EAS induced by protons and iron nuclei
at energies of $10^{19} eV$ and $20^{\circ}$ zenith angle with CORSIKA. Using
the Bayesian approach and taking into account the geometry of the infill
detectors from the Pierre Auger Observatory, we observe an improvement in the
accuracy of the primary mass reconstruction in comparison with the results
obtained using only the $X_{max}^{\mu}$ distributions.",1409.2972v1
2014-09-11,Challenges in the Theoretical Description of Nanoparticle Reactivity: Nano Zero-Valent Iron,"The reactivity of iron atoms, clusters and nanoparticles (nZVI) is of
increasing interest owing to their important practical applications, ranging
from the steel industry to water remediation technologies. Here, we provide an
overview of computational methods and models that can be applied to study nZVI
reactions and discuss their benefits and limitations. We also report current
progress in calculations through recent examples treating the reactivity of
nZVI particles. Finally, we consider the potential use of highly accurate
methods with favorable scaling (such as quantum Monte Carlo or random phase
approximation), which are currently considered too computationally expensive
but are expected to become more amenable in the future as computer power
increases.",1409.3529v1
2014-09-23,The effect of Cr impurity to superconductivity in electron-doped BaFe2-xNixAs2,"We use transport and magnetization measurements to study the effect of
Cr-doping to the phase diagram of the electron-doped superconducting
BaFe2-xNixAs2 iron pnictides. In principle, adding Cr to electron-doped
BaFe2-xNixAs2 should be equivalent to the effect of hole-doping. However, we
find that Cr doping suppresses superconductivity via impurity effect, while not
affecting the normal state resistivity above 100 K. We establish the phase
diagram of Cr-doped BaFe2-x-yNixCryAs2 iron pnictides, and demonstrate that
Cr-doping near optimal superconductivity restore the long-range
antiferromagnetic order suppressed by superconductivity.",1409.6402v1
2014-09-29,Fe I Oscillator Strengths for Transitions from High-lying Even-Parity Levels,"New radiative lifetimes, measured to $\pm$ 5 % accuracy, are reported for 31
even-parity levels of Fe I ranging from 45061 cm$^{-1}$ to 56842 cm$^{-1}$.
These lifetimes have been measured using single-step and two-step time-resolved
laser-induced fluorescence on a slow atomic beam of iron atoms. Branching
fractions have been attempted for all of these levels, and completed for 20
levels. This set of levels represents an extension of the collaborative work
reported in Ruffoni et al. (2014). The radiative lifetimes combined with the
branching fractions yields new oscillator strengths for 203 lines of Fe I.
Utilizing a 1D-LTE model of the solar photosphere, spectral syntheses for a
subset of these lines which are unblended in the solar spectrum yields a mean
iron abundance of <log[{\epsilon}(Fe)]> = 7.45 $\pm$ 0.06.",1409.8142v1
2014-09-30,Direct observation of spin-orbit coupling in iron-based superconductors,"Spin-orbit coupling (SOC) is a fundamental interaction in solids which can
induce a broad spectrum of unusual physical properties from topologically
non-trivial insulating states to unconventional pairing in superconductors. In
iron-based superconductors (IBS) its role has so far been considered
insignificant with the models based on spin- or orbital fluctuations pairing
being the most advanced in the field. Using angle-resolved photoemission
spectroscopy we directly observe a sizeable spin-orbit splitting in all main
families of IBS. We demonstrate that its impact on the low-energy electronic
structure and details of the Fermi surface topology is much stronger than that
of possible nematic ordering. Intriguingly, the largest pairing gap is always
supported exactly by SOC-induced Fermi surfaces.",1409.8669v2
2014-10-10,BaFe$_2$Se$_3$: a high $T_{\rm C}$ magnetic multiferroic with large ferrielectric polarization,"The iron-selenides are important because of their superconducting properties.
Here, an unexpected phenomenon is predicted to occur in an iron-selenide
compound with a quasi-one-dimensional ladder geometry: BaFe$_2$Se$_3$ should be
a magnetic ferrielectric system, driven by its magnetic block order via
exchange striction. A robust performance (high $T_{\rm C}$ and large
polarization) is expected. Different from most multiferroics, BaFe$_2$Se$_3$ is
ferrielectric, with a polarization that mostly cancels between ladders.
However, its strong magnetostriction still produces a net polarization that is
large ($\sim$$0.1$ $\mu$C/cm$^2$) as compared with most magnetic multiferroics.
Its fully ferroelectric state, with energy only slightly higher than the
ferrielectric, has a giant improper polarization $\sim$$2-3$ $\mu$C/cm$^2$.",1410.2682v1
2014-10-12,"Comment on ""Multiorbital Effects on the Transport and the Superconducting Fluctuations in LiFeAs""","In the commented work (PRL 109, 187005 (2012)), Rullier-Albenque et al.
present measurements of transverse magnetoresistivity above the transition
temperature Tc in clean LiFeAs. By analyzing their data, these authors conclude
that the conductivity induced by fluctuations follows a two-dimensional (2D)
behavior even close to Tc, in spite that for LiFeAs the transverse coherence
length ($\xi_c$(0)=1.6 nm) is larger than the Fe-layers spacing (s=0.636 nm),
which would rather suggest a three-dimensional (3D) behavior. This striking
proposal would have deep implications in the theoretical understanding of the
multiband structure of iron pnictides, but it also contrasts with the 3D
behavior observed near Tc in the same compound and in other iron pnictides with
even smaller $\xi_c$(0)/s ratios. Here we show that the proposal of Rullier et
al. could be just an artifact associated to an inadequate subtraction of the
normal-state contribution.",1410.3139v3
2014-10-13,Dusty tails of evaporating exoplanets. I. Constraints on the dust composition,"Recently, two exoplanet candidates have been discovered, KIC 12557548b and
KOI-2700b, whose transit profiles show evidence for a comet-like tail of dust
trailing the planet, thought to be fed by the evaporation of the planet's
surface. We aim to put constraints on the composition of the dust ejected by
these objects from the shape of their transit light curves. We derive a
semi-analytical expression for the attenuation of dust cross-section in the
tail, incorporating the sublimation of dust grains as well as their drift away
from the planet. This expression shows that the length of the tail is highly
sensitive to the sublimation properties of the dust material. We compute tail
lengths for several possible dust compositions, and compare these to
observational estimates of the tail lengths of KIC 12557548b and KOI-2700b,
inferred from their light curves. The observed tail lengths are consistent with
dust grains composed of corundum (Al2O3) or iron-rich silicate minerals (e.g.,
fayalite, Fe2SiO4). Pure iron and carbonaceous compositions are disfavoured. In
addition, we estimate dust mass loss rates of 1.7 +/- 0.5 M_earth/Gyr for KIC
12557548b, and > 0.007 M_earth/Gyr (1-sigma lower limit) for KOI-2700b.",1410.3494v1
2014-10-17,Coexistence of ferromagnetism and superconductivity in iron based pnictides: a time resolved magnetooptical study,"Ferromagnetism and superconductivity are antagonistic phenomena. Their
coexistence implies either a modulated ferromagnetic order parameter on a
lengthscale shorter than the superconducting coherence length or a weak
exchange coupling between the itinerant superconducting electrons and the
localized ordered spins. In some iron based pnictide superconductors the
coexistence of ferromagnetism and superconductivity has been clearly
demonstrated. The nature of the coexistence, however, remains elusive since no
clear understanding of the spin structure in the superconducting state has been
reached and the reports on the coupling strength are controversial. We show, by
a direct optical pump-probe experiment, that the coupling is weak, since the
transfer of the excess energy from the itinerant electrons to ordered localized
spins is much slower than the electron-phonon relaxation, implying the
coexistence without the short-lengthscale ferromagnetic order parameter
modulation. Remarkably, the polarization analysis of the coherently excited
spin wave response points towards a simple ferromagnetic ordering of spins with
two distinct types of ferromagnetic domains.",1410.4651v1
2014-10-21,Searching for high magnetization density in bulk Fe: the new metastable Fe$_6$ phase,"We report the discovery of a new allotrope of iron by first principles
calculations. This phase has $Pmn2_1$ symmetry, a six-atom unit cell (hence the
name Fe$_6$), and the highest magnetization density (M$_s$) among all known
crystalline phases of iron. Obtained from the structural optimizations of the
Fe$_3$C-cementite crystal upon carbon removal, $Pmn2_1$ Fe$_6$ is shown to
result from the stabilization of a ferromagnetic FCC phase, further strained
along the Bain path. Although metastable from 0 to 50 GPa, the new phase is
more stable, at low pressures, than the other well-known HCP and FCC allotropes
and smoothly transforms into the FCC phase under compression. If stabilized to
room temperature, e.g., by interstitial impurities, Fe$_{6}$ could become the
basis material for high M$_s$ rare-earth-free permanent magnets and high-impact
applications such as, light-weight electric engine rotors or high-density
recording media. The new phase could also be key to explain the enigmatic high
M$_s$ of Fe$_{16}$N$_2$, which is currently attracting an intense research
activity.",1410.5875v1
2014-10-23,On the origin of the electronic anisotropy in iron pnicitde superconductors,"We use polarization-resolved Raman spectroscopy to study the anisotropy of
the electronic characteristics of the iron-pnictide parent compounds
$A$Fe$_{2}$As$_{2}$ ($A$~=~Eu, Sr). We demonstrate that above the structural
phase transition at Ts the dynamical anisotropic properties of the 122
compounds are governed by the emergence of $xy$-symmetry critical collective
mode foretelling a condensation into a state with spontaneously broken
four-fold symmetry at a temperature $T^{*}$. However, the mode's critical
slowing down is intervened by a structural transition at Ts, about 80~K above
$T^{*}$, resulting in an anisotropic density wave state.",1410.6452v1
2014-10-23,Critical Quadrupole Fluctuations and Collective Modes in Iron Pnictide Superconductors,"The multiband nature of iron pnictides gives rise to a rich
temperature-doping phase diagram of competing orders and a plethora of
collective phenomena. At low dopings, the tetragonal-to-orthorhombic structural
transition is closely followed by a spin density wave transition both being in
close proximity to the superconducting phase. A key question is the nature of
high-$T_c$ superconductivity and its relation to orbital ordering and
magnetism. Here we study the NaFe$_{1-x}$Co$_{x}$As superconductor using
polarization-resolved Raman spectroscopy. The Raman susceptibility displays
critical enhancement of non-symmetric charge fluctuations across the entire
phase diagram which are precursors to a $d$-wave Pomeranchuk instability at
temperature $\theta(\mbox{x})$. The charge fluctuations are interpreted in
terms of quadrupole inter-orbital excitations in which the electron and hole
Fermi surfaces breathe in-phase. Below $T_c$, the critical fluctuations acquire
coherence and undergo a metamorphosis into a coherent ingap mode of
extraordinary strength.",1410.6456v2
2014-10-24,Strong Coupling Between Whispering Gallery Photons and Spin States of Iron Group Impurity Ions,"Interaction of Whispering Gallery Modes (WGM) with dilute spin ensembles in
solids is an interesting paradigm of Hybrid Quantum Systems potentially
beneficial for Quantum Signal Processing applications. In the present work, WGM
spectroscopy of Rare-Earth doped YSO crystal reveals the existence of Iron
Group Ion (IGI) co-dopings with concentration levels of order 100 ppb. The IGI
spin ensembles demonstrate large Zero Field Splittings at 14.7GHz, 18.4GHz and
25.4GHz, considerable anisotropy of the \textrm{g}-tensors, as well as two
inequivalent lattice sites. Strong coupling regimes between an ensemble of IGI
spins and WGM photons have been demonstrated at $18.4$ GHz and near zero field.
This approach together with useful optical properties of these ions opens a new
avenue for 'spins-in-solids' Quantum Electrodynamics.",1410.6578v4
2014-10-24,Investigation of the crystal and magnetic structures of the trigonal multiferroic iron-boracite Fe3B7O13(OH),"We have investigated the crystal and magnetic structures of the trigonal
iron-boracite Fe3B7O13X with X = OH by neutron diffraction. Neutron diffraction
enables us to locate the hydrogen atom of the hydroxyl group and determine the
magnetic ground state of this member of the multiferroic boracite family. No
evidence was found for a monoclinic distortion in the magnetic ordered state.
The magnetic symmetry allows for magnetoelectric and ferroelectric properties.
The N/'eel tempera- ture TN of 4.86(4) K confirms the general trends within the
boracites that TN decreases from X = I > Br > Cl > OH. Surprisingly while
Fe3B7O13OH exhibits the largest frustration with $|\theta/T_N| = 5.6$ within
the Fe3B7O13X series, no reduction of the magnetic moment is found using
neutron diffraction.",1410.6602v1
2014-11-06,Study of magnetic iron nitride thin films deposited by high power impulse magnetron sputtering,"In this work, we studied phase formation, structural and magnetic properties
of iron-nitride (Fe-N) thin films deposited using high power impulse magnetron
sputtering (HiPIMS) and direct current magnetron sputtering (dc-MS). The
nitrogen partial pressure during deposition was systematically varied both in
HiPIMS and dc-MS. Resulting Fe-N films were characterized for their
microstructure, magnetic properties and nitrogen concentration. We found that
HiPIMS deposited Fe-N films show a globular nanocrystalline microstructure and
improved soft magnetic properties. In addition, it was found that the nitrogen
reactivity impedes in HiPIMS as compared to dc-MS. Obtained results can be
understood in terms of distinct plasma properties of HiPIMS.",1411.1614v2
2014-11-12,Block magnetic excitations in the orbitally selective Mott insulator BaFe2Se3,"Iron pnictides and selenides display a variety of unusual magnetic phases
originating from the interplay between electronic, orbital, and lattice degrees
of freedom. Using powder inelastic neutron scattering on the two-leg ladder
BaFe2Se3, we fully characterize the static and dynamic spin correlations
associated with the Fe4 block state, an exotic magnetic ground state observed
in this low-dimensional magnet and in Rb0.89Fe1.58Se2. All the magnetic
excitations of the Fe4 block state predicted by an effective Heisenberg model
with localized spins are observed below 300 meV and quantitatively reproduced.
However, the data only account for 16 mub^2 per Fe2+, approximatively 2/3 of
the total spectral weight expected for localized S=2 moments. Our results
highlight how orbital degrees of freedom in iron-based magnets can conspire to
stabilize an exotic magnetic state.",1411.3337v2
2014-11-18,High critical current density in textured Ba-122/Ag tapes fabricated by scalable rolling process,"The industrial manufacturing of the long-length iron-pnictide wires and tapes
requires simple and low-cost technology. Although the transport critical
current density of the FeAs-122 tapes has already achieved the practical
application level, their fabrication procedures are relatively complicated or
required specialized instruments. Ag-sheathed Ba0.6K0.4Fe2As2 superconducting
tapes were fabricated by the scalable rolling process. At 4.2 K and 10 T, the
critical current density Jc has achieved 5.4x10^4 A/cm2. We ascribe the
excellent performance to the high purity and homogeneity of the superconducting
phase, high density and high c-axis texture of the superconducting core. Our
method provides a simple way to scale up the production of the long-length
iron-based superconducting tapes with high Jc.",1411.4720v2
2014-11-19,QSGW+DMFT: an electronic structure scheme for the iron pnictides and beyond,"While in strongly correlated materials one often focuses on local electronic
correlations, the influence of non-local exchange and correlation effects
beyond band-theory can be pertinent in systems with more extended orbitals.
Thus in many compounds an adequate theoretical description requires the joint
treatment of local and non-local self-energies. Here, I will argue that this is
the case for the iron pnictide and chalcogenide superconductors. As an approach
to tackle their electronic structure, I will detail the implementation of the
recently proposed scheme that combines the quasi-particle self-consistent GW
approach with dynamical mean-field theory: QSGW+DMFT. I will showcase the
possibilities of QSGW+DMFT with an application on BaFe2As2. Further, I will
discuss the empirical finding that in pnictides dynamical and non-local
correlation effects separate within the quasi-particle band-width.",1411.5180v1
2014-11-24,Superconductivity In K- And Na- Doped Bafe2as2: What Can We Learn From Heat Capacity And Pressure Dependence of Tc,"A brief overview of changes in the superconducting transition temperature
under pressure and evolution of specific heat capacity jump at Tc for two
related families of iron - based superconductors, Ba{1-x}KxFe2As2 (0.2 < x <
1.0) and Ba{1-x}NaxFe2As2 (0.2 < x < 0.9) will be given. For Ba{1-x}KxFe2As2
the specific heat capacity jump at Tc measured over the whole extent of the
superconducting dome shows clear deviation from the empirical, Delta Cp (Tc) ~
Tc^3, scaling (known as the BNC scaling) for x > 0.7. At the same
concentrations range apparent equivalence of effects of pressure and K-
substitution on Tc fails. These observations suggests a significant change of
the superconducting state for x > 0.7. In contrast, the data for the large
portion of Ba{1-x}NaxFe2As2 (0.2 < x < 0.9) series follow the BNC scaling.
However, the pressure dependence of Tc (measured up to ~ 12 kbar) have clear
non-linearities for Na concentration in 0.2 - 0.25 region, that may be
consistent with Tc crossing the phase boundaries of the emergent, narrow,
antiferromagnetic/tetragonal phase. Results will be discussed in context other
studies of these two and related families of iron-based superconductors.",1411.6485v1
2014-11-27,Short-Time Dynamics of Fe2/V13 Magnetic Superlattice Models,"Critical relaxation from a low-temperature fully ordered state of Fe2/V13
iron-vanadium magnetic superlattice models has been studied using the method of
short-time dynamics. Systems with three variants of the ratio R of inter- to
intralayer exchange coupling have been considered. Particles with N = 262144
spins have been simulated with periodic boundary conditions. Calculations have
been performed using the standard Metropolis algorithm of the Monte Carlo
method. The static critical exponents of magnetization and correlation radius,
as well as the dynamic critical exponent, have been calculated for three R
values. It is established that a small decrease in the exchange ratio (from R =
1.0 to 0.8) does not significantly influence the character of the short-time
dynamics in the models studied. A further significant decrease in this ratio
(to R = 0.01), for which a transition from three-dimensional to
quasi-twodimensional magnetism is possible, leads to significant changes in the
dynamic behavior of iron-vanadium magnetic superlattice models.",1411.7546v1
2014-12-02,Unabridged phase diagram for single-phased FeSexTe1-x thin films,"A complete phase diagram and its corresponding physical properties are
essential prerequisites to understand the underlying mechanism of iron based
superconductivity. For the structurally simplest 11 (FeSeTe) system, earlier
attempts using bulk samples have not been able to do so due to the fabrication
difficulties. Here, thin FeSexTe1-x films with the Se content covering the full
range were fabricated by using pulsed laser deposition method. Crystal
structure analysis shows that all films retain the tetragonal structure in room
temperature. Significantly, the highest superconducting transition temperature
(TC = 20 K) occurs in the newly discovered domain, 0.6 - 0.8. The single-phased
superconducting dome for the full Se doping range is the first of its kind in
iron chalcogenide superconductors. Our results present a new avenue to explore
novel physics as well as to optimize superconductors.",1412.0888v1
2014-12-02,Quantum Criticality in the 122 Iron Pnictide Superconductors Emerging from Orbital-Selective Mottness,"The twin issues of the nature of the normal state and competing order(s) in
the iron arsenides are central to understanding their unconventional, high-Tc
superconductivity. We use a combination of transport anisotropy measurements on
detwinned Sr(Fe(1-x)Co(x))2As2 single crystals and local density approximation
plus dynamical mean field theory (LDA + DMFT) calculations to revisit these
issues. The peculiar resistivity anisotropy and its evolution with x are
naturally interpreted in terms of an underlying orbital-selective Mott
transition (OSMT) that gaps out the dxz or dyz states. Further, we use a
Landau-Ginzburg approach using LDA + DMFT input to rationalize a wide range of
anomalies seen up to optimal doping, providing strong evidence for secondary
electronic nematic order. These findings suggest that strong dynamical
fluctuations linked to a marginal quantum-critical point associated with this
OSMT and a secondary electronic nematic order constitute an intrinsically
electronic pairing mechanism for superconductivity in Fe arsenides.",1412.1034v2
2014-12-04,Coexistence pressure for a martensitic transformation from theory and experiment: revisiting the bcc-hcp transition of iron under pressure,"The coexistence pressure of two phases is a well-defined point at fixed
temperature. In experiment, however, due to non-hydrostatic stresses and a
stress-dependent potential energy barrier, different measurements yield
different ranges of pressure with a hysteresis. Accounting for these effects,
we propose an inequality for comparison of the theoretical value to a plurality
of measured intervals. We revisit decades of pressure experiments on the bcc -
hcp transformations in iron, which are sensitive to non-hydrostatic conditions
and sample size. From electronic-structure calculations, we find a bcc - hcp
coexistence pressure of 8.4 GPa. We construct the equation of state for
competing phases under hydrostatic pressure, compare to experiments and other
calculations, and address the observed pressure hysteresis and range of onset
pressures of the nucleating phase.",1412.1849v2
2014-12-07,Suppression of superconductivity and structural phase transition against pressure in Ca$_{10}$(Ir$_{4}$As$_{8}$)(Fe$_{2-x}$Ir$_{x}$As$_{2}$)$_{5}$,"We measured the pressure dependence of in-plane resistivity $\rho_{ab}$ in
the recently-discovered iron-based superconductor
Ca$_{10}$(Ir$_{4}$As$_{8}$)(Fe$_{2-x}$Ir$_{x}$As$_{2}$)$_{5}$, which shows a
unique structural phase transition in the absence of magnetic ordering, with a
superconducting transition temperature $T_{\rm c}$ = 16 K and structural phase
transition temperature $T_{\rm s}$ $\simeq$ 100 K at ambient pressure. $T_{\rm
c}$ and $T_{\rm s}$ are suppressed on applying pressure and disappear at
approximately 0.5 GPa, suggesting a relationship between superconductivity and
structure. Ca$_{10}$(Ir$_{4}$As$_{8}$)(Fe$_{2-x}$Ir$_{x}$As$_{2}$)$_{5}$ is a
rather rare example in which the superconductivity appears only in a
low-temperature ordered phase. The fact that the change in the crystal
structure is directly linked with superconductivity suggests that the crystal
structure as well as magnetism are important factors governing
superconductivity in iron pnictides.",1412.2317v1
2014-12-09,Spin excitations in the nematic phase and the metallic stripe spin-density wave phase of iron pnictides,"We present a general study of the magnetic excitations within a weak-coupling
five-orbital model relevant to itinerant iron pnictides. As a function of
enhanced electronic correlations, the spin excitations in the symmetry broken
spin-density wave phase evolve from broad low-energy modes in the limit of weak
interactions to sharply dispersing spin wave prevailing to higher energies at
larger interaction strengths. We show how the resulting spin response at high
energies depends qualitatively on the magnitude of the interactions. We also
calculate the magnetic excitations in the nematic phase by including an orbital
splitting, and find a pronounced C_2 symmetric excitation spectrum right above
the transition to long-range magnetic order. Finally, we discuss the C_2 versus
C_4 symmetry of the spin excitations as a function of energy for both the
nematic and the spin-density wave phase.",1412.2912v1
2014-12-09,Optimization of a Non-arsenic Iron-based Superconductor for Wire Fabrication,"We report on the optimization of synthesis of iron-selenide (non-arsenic)
superconducting powders that are based on '122' composition, with optimal Tc =
38 K and Jc = 10^5 A/cm2 (4 K). We also report on the wire proof-of concept for
these materials, by producing ~ 40 ft of wire that produce Ic. The 122
selenides are more difficult to synthesize and have more complex crystal
structures compared to '11' selenides (FeSe and FeSe1-xTex), but they do offer
higher Tc and might provoke a natural extension for 11 work.",1412.3065v1
2015-01-07,Temperature dependence of iron local magnetic moment in phase-separated superconducting chalcogenide,"We have studied local magnetic moment and electronic phase separation in
superconducting K$_{x}$Fe$_{2-y}$Se$_2$ by x-ray emission and absorption
spectroscopy. Detailed temperature dependent measurements at the Fe K-edge have
revealed coexisting electronic phases and their correlation with the transport
properties. By cooling down, the local magnetic moment of Fe shows a sharp drop
across the superconducting transition temperature (T$_c$) and the coexisting
phases exchange spectral weights with the low spin state gaining intensity at
the expense of the higher spin state. After annealing the sample across the
iron-vacancy order temperature, the system does not recover the initial state
and the spectral weight anomaly at T$_c$ as well as superconductivity
disappear. The results clearly underline that the coexistence of the low spin
and high spin phases and the transitions between them provide unusual magnetic
fluctuations and have a fundamental role in the superconducting mechanism of
electronically inhomogeneous K$_{x}$Fe$_{2-y}$Se$_2$ system.",1501.01558v1
2015-01-09,First-principles theory of electron-spin fluctuation coupling and superconducting instabilities in iron selenide,"We present first-principles calculations of the coupling of quasiparticles to
spin fluctuations in iron selenide and discuss which types of superconducting
instabilities this coupling gives rise to. We find that strong
antiferromagnetic stripe-phase spin fluctuations lead to large coupling
constants for superconducting gaps with $s_\pm$-symmetry, but these coupling
constants are significantly reduced by other spin fluctuations with small wave
vectors. An accurate description of this competition and an inclusion of band
structure and Stoner parameter renormalization effects lead to a value of the
coupling constant for an $s_\pm$-symmetric gap which can produce a
superconducting transition temperature consistent with experimental
measurements.",1501.02200v1
2015-01-15,Strain effects in monolayer Iron-Chalcogenide superconductors,"The successful fabrication of one monolayer FeSe on SrTiO$_{3}$ represented a
real breakthrough in searching for high-T$_{c}$ Fe-based superconductors (Ref.
1). Motivated by this important discovery, we studied the effects of tensile
strain on one monolayer and bulk iron-chalcogenide superconductors (FeSe and
FeTe), showing that it produces important magnetic and electronic changes in
the systems. We found that the magnetic ground state of bulk and monolayer FeSe
is the block-checkerboard phase, which turns into the collinear stripe phase
under in plane tensile strain. FeTe, in both bulk and monolayer phases, shows
two magnetic transitions upon increasing the tensile strain: from bicollinear
in the ground state to block-checkerboard ending up to the collinear
antiferromagnetic phase which could bring it in the superconducting state.
Finally, the study of the mechanical properties of both FeSe and FeTe
monolayers reveals their enormous tensile strain limits and opens the
possibility to grow them on different substrates.",1501.03630v1
2015-01-16,"Spectroscopic Studies of Iron-based Superconductors, Multi-ferroic Oxides and Double-perovskite: Phonons, Electronic and Spin Excitations","Raman spectroscopy is a very powerful probe to study the nature of
quasi-particle excitations in condensed matter physics. The work presented in
this thesis is focused on two different families of novel materials, namely the
iron-based superconductors (FeBS), multiferroic oxides and double perovskite.
Although the properties of these two systems are quite different, some
comparison can still be drawn between them. For instance, in both of these
systems magnetism plays a crucial role and intricate coupling between phononic,
magnetic and orbital degrees of freedom is crucial to understand their
underlying physics responsible for their various exotic physical properties.
Understanding the microscopic origin of quasi-particle excitations, such as
phonons, magnons, orbitons, plasmons etc., and coupling between them in these
complex materials, has been an intense field of research because it is believed
that these excitations hold the key for explaining their rich physics. The
systems studied in the thesis include (A) FeBS - (i) FeSe0.82 (ii)
Ce1-zYzFeAsO1-xFx (z = 0, 0.4; x = 0.1, 0.2) (iii) Ca4Al2O5.7Fe2As2 (iv)
Ca(Fe1-xCox)2As2 (x = 0.03, 0.05). (B) Multiferroic oxides - (i) AlFeO3 (ii)
TbMnO3 and double perovskite (iii) La2NiMnO6.",1501.04055v1
2015-01-19,Superconductivity at 52 K in hydrogen-substituted LaFeAsO1-xHx under high pressure,"The 1111-type iron-based superconductor LnFeAsO1-xFx (Ln stands for
lanthanide) is the first material with a Tc above 50 K, other than cuprate
superconductors. Electron doping into LaFeAsO by H, rather than F, revealed a
double-dome-shaped Tc-x diagram, with a first dome (SC1, 0.05<x<0.20) and a
second dome (SC2, 0.2<x<0.5). Here, we report the Tc for the whole
hydrogen-doping range in LaFeAsO1-xHx under pressures of up to 19 GPa. Tc rises
to 52 K at 6 GPa for the Tc-valley composition between the two Tc domes. This
is the first instance of the Tc exceeding 50 K in La-1111-type iron-based
superconductors. On the other hand, the Tc of SmFeAsO1-xHx decreased
continually, keeping its single-dome structure up to 15 GPa. The present
findings strongly suggest that the main reason for realization of the Tc >50 K
observed in RE-1111 compounds (RE: Pr, Sm, and Gd) at ambient pressure is the
merging of SC1 and SC2.",1501.04544v1
2015-01-20,"Structural, electronic, and magnetic properties of tris(8-hydroxyquinoline)iron(III) molecules and its magnetic coupling with ferromagnetic surface: first-principles study","Using first-principles calculations, we have systematically investigated the
structural, electronic, and magnetic properties of facial (fac-) and meridional
(mer-) tris(8-hydroxyquinoline)iron(III) (Feq3) molecules and their interaction
with ferromagnetic substrate. Our calculation results show that for the
isolated Feq3, mer-Feq3 is more stable than the fac-Feq3; and both Feq3 isomers
have a high spin-state of 5 {\mu}B as the ground state when an on-site
Hubbard-U term is included to treat the highly localized Fe 3d electrons; while
the standard DFT calculations produce a low spin-state of 1 {\mu}B. These
magnetic behaviors can be understood by the octahedral ligand field splitting
theory. Furthermore, we found that fac-Feq3 has a stronger bonding to the Co
surface than mer-Feq3 and an anti-ferromagnetic coupling was discovered between
Fe and Co substrate, originating from the superexchange coupling between Fe and
Co mediated by the interface oxygen and nitrogen atoms. These findings suggest
that Feq3 molecular films may serve as a promising spin-filter material in
spintronic devices.",1501.04926v1
2015-01-23,Antiferroquadrupolar and Ising-Nematic Orders of a Frustrated Bilinear-Biquadratic Heisenberg Model and Implications for the Magnetism of FeSe,"Motivated by the properties of the iron chalcogenides, we study the phase
diagram of a generalized Heisenberg model with frustrated bilinear-biquadratic
interactions on a square lattice. We identify zero-temperature phases with
antiferroquadrupolar and Ising-nematic orders. The effects of quantum
fluctuations and interlayer couplings are analyzed. We propose the
Ising-nematic order as underlying the structural phase transition observed in
the normal state of FeSe, and discuss the role of the Goldstone modes of the
antiferroquadrupolar order for the dipolar magnetic fluctuations in this
system. Our results provide a considerably broadened perspective on the overall
magnetic phase diagram of the iron chalcogenides and pnictides, and are
amenable to tests by new experiments.",1501.05926v4
2015-01-26,A Large Sample of Am Candidates from LAMOST Data Release 1,"We present a sample of metallic-line star (Am) candidates from the Large sky
Area Multi-Object fiber Spectroscopic Telescope Data Release one (LAMOST DR1).
According to the characteristic of under-abundance of calcium and overabundance
of iron element of Am stars, we propose an empirical separation curve derived
from line indices of Ca II K-line and iron lines we choose for low resolution
spectra. 3537 Am candidates are ultimately selected from more than 30,000 stars
which are classified as A-type or early-F stars by both LAMOST pipeline and
visual inspection. Then we make some analysis on this sample and finally
provide a list of these Am candidates with 10 relevant parameters. Comparing
with other catalogues, Am candidates selected from LAMOST DR1 are much fainter
on the whole. Obviously, our list is an important complementary to already
known bright Am catalogues, and it offers valuable material for the research on
this type of chemically peculiar stars.",1501.06233v1
2015-01-28,Dynamics and stability of icosahedral Fe-Pt nanoparticles,"The structure, dynamics and stability of Fe-Pt nanoparticles have been
investigated using DFT-based techniques: total energy calculations and DFT
molecular dynamics. The investigated systems included multi-shell and
disordered nanoparticles of iron and platinum. The study is concerned with
icosahedral particles with magic number of atoms (55): iron-terminated
Fe$_{43}$Pt$_{12}$, platinum-terminated Fe$_{12}$Pt$_{43}$, and disordered
Fe$_{27}$Pt$_{28}$. Additionally, the Fe$_6$Pt$_7$ cluster has been
investigated to probe behaviour of extremely small Fe-Pt particles. Molecular
dynamics simulations have been performed for a few temperatures between
$T=150-1000$ K. The calculations revealed high structural instability of the
Fe-terminated nanoparticles and a strong stabilising effect of the
Pt-termination in the shell-type icosahedral particles. The platinum
termination prevented disordering of the particle even at $T=1000$ K indicating
very high melting temperatures of these Fe-Pt icosahedral structures. The
analysis of evolution of the radial distribution function has shown significant
tendency of Pt atoms to move to the outside layer of the particles -- even in
the platinum deficient cases.",1501.07143v2
2015-01-28,57Fe Mossbauer study of Lu2Fe3Si5 iron silicide superconductor,"With the advent of Fe-As based superconductivity it has become important to
study how superconductivity manifests itself in details of 57Fe Mossbauer
spectroscopy of conventional, Fe - bearing superconductors. To this end, the
iron-based superconductor Lu2Fe3Si5 has been studied by 57Fe Mossbauer
spectroscopy over the temperature range from 4.4 K to room temperature with
particular attention to the region close to the superconducting transition
temperature (Tc = 6.1 K). Consistent with the two crystallographic sites for Fe
in this structure, the observed spectra appear to have a pattern consisting of
two doublets over the whole temperature range. The value of Debye temperature
was estimated from temperature dependence of the isomer shift and the total
spectral area and compared with the specific heat capacity data. Neither
abnormal behavior of the hyperfine parameters at or near Tc, nor phonon
softening were observed.",1501.07254v2
2015-02-12,"Strong $(π,0)$ spin fluctuations in $β$-FeSe observed by neutron spectroscopy","We have performed powder inelastic neutron scattering measurements on the
unconventional superconductor $\beta$-FeSe ($T_{\rm c} \simeq 8\,\mathrm{K}$).
The spectra reveal highly dispersive paramagnetic fluctuations emerging from
the square-lattice wave vector $(\pi,0)$ extending beyond 80 meV in energy.
Measurements as a function of temperature at an energy of $\sim
13\,\mathrm{meV}$ did not show any variation from $T_{\rm c}$ to
$104\,\mathrm{K}$. The results show that FeSe is close to an instability
towards $(\pi,0)$ antiferromagnetism characteristic of the parent phases of the
high-$T_{\rm c}$ iron arsenide superconductors, and that the iron paramagnetic
moment is neither affected by the orthorhombic-to-tetragonal structural
transition at $T_{\rm s} \simeq 90\,\mathrm{K}$ nor does it undergo a change in
spin state over the temperature range studied.",1502.03838v2
2015-02-15,In situ observation of phase separation and hierarchical microstructure of KxFe2-ySe2 single crystals,"The nature of the phase separation in KxFe2-ySe2 single crystals is not well
understood. Here, temperature dependent SEM images provide compelling evidence
that phase separation corresponds to a nucleation and growth process rather
than a spinodal decomposition. The superconducting phase is the remnant of high
temperature phase after iron vacancy order-disorder transition. Three-dimension
(3D) spatial distribution of superconducting phase in the iron vacancy ordered
matrix was revealed by using focused ion beam scanning electron microscopy
(FIB-SEM). Our results clearly show that superconducting phase forms a
hierarchical structure. Understanding the formation of this hierarchical
structure not only can guide the synthesis of bulk superconductors in the
future, but also greatly enrich our knowledge about the interplay between phase
separation and solid-state phase transformations.",1502.04335v1
2015-02-16,Tuning electronic correlations in transition metal pnictides: chemistry beyond the valence count,"The effects of electron-electron correlations on the low-energy electronic
structure and their relationship with unconventional superconductivity are
central aspects in the research on the iron-based pnictide superconductors.
Here we use soft X-ray angle-resolved photoemission spectroscopy (SX-ARPES) to
study how electronic correlations evolve in different chemically substituted
iron pnictides. We find that correlations are intrinsically related to the
effective filling of the correlated orbitals, rather than to the filling
obtained by valence counting. Combined density functional theory (DFT) and
dynamical mean-field theory (DMFT) calculations capture these effects,
reproducing the experimentally observed trend in the correlation strength. The
occupation-driven trend in the electronic correlation reported in our work
supports the recently proposed connection between cuprate and pnictides phase
diagrams.",1502.04565v1
2015-02-20,Competing magnetic double-Q phases and superconductivity-induced re-entrance of C2 magnetic stripe order in iron pnictides,"We perform a microscopic theoretical study of the generic properties of
competing magnetic phases in iron pnictides. As a function of electron filling
and temperature, the magnetic stripe (single-Q) order forms a dome, but
competing non-collinear and non-uniform double-Q phases exist at the foot of
the dome in agreement with recent experiments. We compute and compare the
electronic properties of the different magnetic phases, investigate the role of
competing superconductivity, and show how disorder may stabilize double-Q
order. Superconductivity is shown to compete more strongly with double-Q
magnetic phases, which can lead to re-entrance of the C2 (single-Q) order in
agreement with recent thermal expansion measurements on K-doped Ba-122
crystals.",1502.05859v2
2015-02-20,Valence fluctuations in a lattice of magnetic molecules: application to iron(II) phtalocyanine molecules on Au(111),"We study theoretically a square lattice of the organometallic Kondo adsorbate
iron(II) phtalocyanine (FePc) deposited on top of Au(111), motivated by recent
scanning tunneling microscopy experiments. We describe the system by means of
an effective Hubbard-Anderson model, where each molecule has degenerate
effective $d-$orbitals with $xz$ and $yz$ symmetry, which we solve for
arbitrary occupation and arbitrary on-site repulsion $U$. To that end, we
introduce a generalized slave-boson mean-field approximation (SBMFA) which
correctly describes both the non-interacting limit (NIL) $U=0$ and the
strongly-interacting limit $U \rightarrow \infty$, where our formalism
reproduces the correct value of the Kondo temperature for an isolated FePc
molecule. Our results indicate that while the isolated molecule can be
described by an SU(4) Anderson model in the Kondo regime, the case of the
square lattice corresponds to the intermediate-valence regime, with a total
occupation of nearly 1.65 holes in the FePc molecular orbitals. Our results
have important implications for the physical interpretation of the experiment.",1502.05995v1
2015-02-23,Spin fluctuations in iron pnictides and chalcogenides: From antiferromagnetism to superconductivity,"The present article reviews recent experimental investigations of spin
dynamics in iron-based superconductors and their parent compounds by means of
inelastic neutron scattering. It mainly focuses on the most contemporary
developments in this field, pertaining to the observations of magnetic resonant
modes in new superconductors, spin anisotropy of low-energy magnetic
fluctuations that has now been observed in a wide range of chemical
compositions and doping levels, as well as their momentum-space anisotropy
incurred by the spin-nematic order. The implications of these new findings for
our understanding of the superconducting state, along with the remaining
unsettled challenges for neutron spectroscopy, are discussed.",1502.06570v1
2015-02-25,Robust $s_{\pm}$-wave superconductivity against multi-impurity in iron-based superconductors,"Effects of disorder on electron-doped iron pnictides are investigated
systematically based on self-consistent Bogoliubov-de Gennes equations.
Multiply impurities with same scattering potential (SP) are randomly
distributed in a square lattice. Probability distribution functions of
normalized order parameters for different impurity concentrations
$\delta_{imp}$, different electron doping concentrations $\delta$ are
investigated for given SPs. Samples are found to be very robust against weak
SP, in which order parameters do not have qualitative change even at very large
$\delta_{imp}$. While strong SP is able to easily break down the order
parameters. For moderate SP, variations of order parameters on and around
impurities strongly depend on $\delta$, however the distribution functions of
normalized order parameters have similar behavior as $\delta_{imp}$ increases.
Compared with superconducting (SC) order, the magnetic order is more sensitive
to multi-impurity effect. The spatial spin density wave pattern has already
been destroyed before the system loses its superconductivity. Dependence of SC
order on temperature is similar to that of impurity-free case, with the
critical temperature being remarkably suppressed for high $\delta_{imp}$.",1502.07305v1
2015-03-09,Magnetic Cluster Expansion model for random and ordered magnetic face-centered cubic Fe-Ni-Cr alloys,"A Magnetic Cluster Expansion (MCE) model for ternary face-centered cubic
Fe-Ni-Cr alloys has been developed using DFT data spanning binary and ternary
alloy configurations. Using this MCE model Hamiltonian, we perform Monte Carlo
simulations and explore magnetic structures of alloys over the entire range of
alloy compositions, considering both random and ordered alloy structures. In
random alloys, the removal of magnetic collinearity constraint reduces the
total magnetic moment but does not affect the predicted range of compositions
where the alloys adopt low temperature ferromagnetic configurations. During
alloying of ordered fcc Fe-Ni compounds with Cr, chromium atoms tend to replace
nickel rather than iron atoms. Replacement of Ni by Cr in alloys with high iron
content increases the Curie temperature of the alloys. This can be explained by
strong antiferromagnetic Fe-Cr coupling, similar to that found in bcc Fe-Cr
solutions, where the Curie temperature increase, predicted by simulations as a
function of Cr concentration, is confirmed by experimental observations.",1503.02481v1
2015-03-19,"Oxygen, α-element and iron abundance distributions in the inner part of the Galactic thin disc","We derived elemental abundances in 27 Cepheids, the great majority situated
within a zone of Galactocentric distances ranging from 5 to 7 kpc. One star of
our sample, SU Sct, has a Galactocentric distance of about 3 kpc, and thus
falls in a poorly investigated region of the inner thin disc. Our new results,
combined with data on abundances in the very central part of our Galaxy taken
from literature, show that iron, magnesium, silicon, sulfur, calcium and
titanium LTE abundance radial distributions, as well as NLTE distribution of
oxygen reveal a plateau-like structure or even positive abundance gradient in
the region extending from the Galactic center to about 5 kpc.",1503.05898v1
2015-03-27,Temperature and composition phase diagram in the iron-based ladder compounds Ba1-xCsxFe2Se3,"We investigated the iron-based ladder compounds (Ba,Cs)Fe$_2$Se$_3$. Their
parent compounds, BaFe$_2$Se$_3$ and CsFe$_2$Se$_3$, have different space
groups, formal valences of Fe and magnetic structures. Electrical resistivity,
specific heat, magnetic susceptibility, X-ray diffraction and powder neutron
diffraction measurements were conducted to obtain temperature and composition
phase diagram of this system. Block magnetism observed in BaFe$_2$Se$_3$ is
drastically suppressed with Cs doping. In contrast, stripe magnetism observed
in CsFe$_2$Se$_3$ is not so fragile against Ba doping. New type of magnetic
structure appears in intermediate compositions, which is similar to stripe
magnetism of CsFe$_2$Se$_3$, but inter-ladder spin configuration is different.
Intermediate compounds show insulating behavior, nevertheless finite $T$-linear
contribution in specific heat was obtained at low temperatures.",1503.08129v1
2015-04-09,Low-field microwave absorption and magnetoresistance in iron nanostructures grown by electrodeposition on n-type lightly-doped silicon substrates,"In this study we investigate magnetic properties, surface morphology and
crystal structure in iron nanoclusters electrodeposited on lightly-doped (100)
n-type silicon substrates. Our goal is to investigate the spin injection and
detection in the Fe/Si lateral structures. The samples obtained under electric
percolation were characterized by magnetoresistive and magnetic resonance
measurements with cycling the sweeping applied field in order to understand the
spin dynamics in the as-produced samples. The observed hysteresis in the
magnetic resonance spectra, plus the presence of a broad peak in the
non-saturated regime confirming the low field microwave absorption (LFMA), were
correlated to the peaks and slopes found in the magnetoresistance curves. The
results suggest long range spin injection and detection in low resistive
silicon and the magnetic resonance technique is herein introduced as a
promising tool for analysis of electric contactless magnetoresistive samples.",1504.02508v1
2015-04-14,Strong similarities between the local electronic structure of insulating iron pnictide and lightly doped cuprate,"One of the major puzzles regarding unconventional superconductivity is how
some of the most interesting superconductors are related to an insulating phase
that lies in close proximity. Here we report scanning tunneling microscopy
studies of the local electronic structure of Cu doped NaFeAs across the
superconductor to insulator transition. We find that in the highly insulating
regime the electronic spectrum develops an energy gap with diminishing density
of state at the Fermi level. The overall lineshape and strong spatial
variations of the spectra are strikingly similar to that of lightly doped
cuprates close to the parent Mott insulator. We propose that the suppression of
itinerant electron state and strong impurity potential induced by Cu dopants
lead to this insulating iron pnictide.",1504.03515v1
2015-04-14,Pressure Induced Enhancement of Superconductivity in LaRu2P2,"To explore new superconductors beyond the copper-based and iron-based systems
is very important. The Ru element locates just below the Fe in the periodic
table and behaves like the Fe in many ways. One of the common thread to induce
high temperature superconductivity is to introduce moderate correlation into
the system. In this paper, we report the significant enhancement of
superconducting transition temperature from 3.84K to 5.77K by using a pressure
only of 1.74 GPa in LaRu2P2 which has an iso-structure of the iron-based 122
superconductors. The ab-initio calculation shows that the superconductivity in
LaRu2P2 at ambient pressure can be explained by the McMillan's theory with
strong electron-phonon coupling. However, it is difficult to interpret the
significant enhancement of Tc versus pressure within this picture. Detailed
analysis of the pressure induced evolution of resistivity and upper critical
field Hc2(T) reveals that the increases of Tc with pressure may be accompanied
by the involvement of extra electronic correlation effect. This suggests that
the Ru-based system has some commonality as the Fe-based superconductors.",1504.03652v1
2015-04-14,Vestigial chiral and charge orders from bidirectional spin-density waves: Application to the iron-based superconductors,"Recent experiments in optimally hole-doped iron arsenides have revealed a
novel magnetically ordered ground state that preserves tetragonal symmetry,
consistent with either a charge-spin density wave (CSDW), which displays a
non-uniform magnetization, or a spin-vortex crystal (SVC), which displays a
non-collinear magnetization. Here we show that, similarly to the partial
melting of the usual stripe antiferromagnet into a nematic phase, either of
these phases can also melt in two stages. As a result, intermediate
paramagnetic phases with vestigial order appears: a checkerboard charge
density-wave for the CSDW ground state, characterized by an Ising-like order
parameter, and a remarkable spin-vorticity density-wave for the SVC ground
state -- a triplet d-density wave characterized by a vector chiral order
parameter. We propose experimentally detectable signatures of these phases,
show that their fluctuations can enhance the superconducting transition
temperature, and discuss their relevance to other correlated materials.",1504.03656v3
2015-04-20,Raman scattering as a probe of nematic correlations,"We use the symmetry constrained low energy effective Hamiltonian of iron
based superconductors to study the Raman scattering in the normal state of
underdoped iron-based superconductors. The incoming and scattered Raman photons
couple directly to orbital fluctuations and indirectly to the spin
fluctuations. We computed both couplings within the same low energy model. The
symmetry constrained Hamiltonian yields the coupling between the orbital and
spin fluctuations of only the same symmetry type. Attraction in B2g symmetry
channel was assumed for the system to develop the subleading instability
towards the discrete in-plane rotational symmetry breaking, referred to as
Ising nematic transition. We find that upon approaching this instability, the
Raman spectral function develops a quasi-elastic peak as a function of energy
transferred by photons to the crystal. We attribute this low-energy B2g
scattering to the critical slow-down associated with the build up of nematic
correlations.",1504.05054v2
2015-04-23,The origin of anomalous diffusion in iron mononitride thin films,"We have studied the origin of a counter intuitive diffusion behavior of Fe
and N atoms in a iron mononitride (FeN) thin film. It was observed that
in-spite of a larger atomic size, Fe tend to diffuse more rapidly than smaller
N atoms. This only happens in the N-rich region of Fe-N phase diagram, in the
N-poor regions, N diffusion coefficient is orders of magnitude larger than Fe.
Detailed self-diffusion measurements performed in FeN thin films reveal that
the diffusion mechanism of Fe and N is different - Fe atoms diffuse through a
complex process, which in addition to a volume diffusion, pre-dominantly
controlled by a fast grain boundary diffusion. On the other hand N atoms
diffuse through a classical volume-type diffusion process. Observed results
have been explained in terms of stronger Fe-N (than Fe-Fe) bonds generally
predicted theoretically for mononitride compositions of transition metals.",1504.06047v1
2015-04-28,Emergent loop-nodal s$_\pm$-wave superconductivity in CeCu$_2$Si$_2$: similarities to the iron-based superconductors,"Heavy-fermion superconductors are prime candidates for novel electron-pairing
states due to the spin-orbital coupled degrees of freedom and electron
correlations. Superconductivity in CeCu$_2$Si$_2$ discovered in 1979, which is
a prototype of unconventional (non-BCS) superconductors in strongly correlated
electron systems, still remains unsolved. Here we provide the first report of
superconductivity based on the advanced first-principles theoretical approach.
We find that the promising candidate is an $s_\pm$-wave state with loop-shaped
nodes on the Fermi surface, different from the widely expected line-nodal
$d$-wave state. The dominant pairing glue is magnetic but high-rank octupolar
fluctuations. This system shares the importance of multi-orbital degrees of
freedom with the iron-based superconductors. Our findings reveal not only the
long-standing puzzle in this material, but also urge us to reconsider the
pairing states and mechanisms in all heavy-fermion superconductors.",1504.07312v1
2015-05-09,Exploration of new superconductors and functional materials and fabrication of superconducting tapes and wires of iron pnictides,"This paper reviews the highlights of a 4-years-long research project
supported by the Japanese Government to explore new superconducting materials
and relevant functional materials. The project found several tens of new
superconductors by examining ~1000 materials, each of which was chosen by
Japanese team member experts with a background in solid state chemistry. This
review summarizes the major achievements of the project in newly found
superconducting materials, and the wire and tape fabrication of iron-based
superconductors. It is a unique feature of this review to incorporate a list of
~700 unsuccessful materials examined for superconductivity in the project. In
addition, described are new functional materials and functionalities discovered
during the project.",1505.02240v1
2015-05-19,Electronic structure of NaFeAs superconductor: LDA+DMFT calculations compared with ARPES experiment,"We present the results of extended theoretical LDA+DMFT calculations for a
new iron-pnictide high temperature superconductor NaFeAs compared with the
recent high quality angle-resolved photoemission (ARPES) experiments on this
system [1]. The universal manifestation of correlation effects in
iron-pnictides is narrowing of conducting bands near the Fermi level. Our
calculations demonstrate that for NaFeAs the effective mass is renormalized on
average by a factor of the order of 3, in good agreement with ARPES data. This
is essentially due to correlation effects on Fe-3d orbitals only and no
additional interactions with with any kind of Boson modes, as suggested in [1],
are necessary to describe the experiment. Also we show that ARPES data taken at
about 160 eV beam energy most probably corresponds to $k_z=\pi$ Brillouin zone
boundary, while ARPES data measured at about 80 eV beam energy rather
represents $k_z=0$. Contributions of different Fe-3d orbitals into spectral
function map are also discussed.",1505.04963v1
2015-05-20,Effect of Al doping on phase formation and thermal stability of iron nitride thin films,"In the present work, we systematically studied the effect of Al doping on the
phase formation of iron nitride (Fe-N) thin films. Fe-N thin films with
different concentration of Al (Al=0, 2, 3, 6, and 12 at.%) were deposited using
dc magnetron sputtering by varying the nitrogen partial pressure between 0 to
100%. The structural and magnetic properties of the films were studied using
X-ray diffraction and polarized neutron reflectivity. It was observed that at
the lowest doping level (2 at.% of Al), nitrogen rich non-magnetic Fe-N phase
gets formed at a lower nitrogen partial pressure as compared to the un-doped
sample. Interestingly, we observed that as Al doping is increased beyond 3at.%,
nitrogen rich non-magnetic Fe-N phase appears at higher nitrogen partial
pressure as compared to un-doped sample. The thermal stability of films were
also investigated. Un-doped Fe-N films deposited at 10% nitrogen partial
pressure possess poor thermal stability. Doping of Al at 2at.% improves it
marginally, whereas, for 3, 6 and 12at.% Al doping, it shows significant
improvement. The obtained results have been explained in terms of
thermodynamics of Fe-N and Al-N.",1505.05371v1
2015-05-21,Abundances in the atmosphere of the metal-rich planet-host star HD 77338,"Abundances of Fe, Si, Ni, Ti, Na, Mg, Cu, Zn, Mn, Cr and Ca in the atmosphere
of the K-dwarf HD 77338 are determined and discussed. HD 77338 hosts a hot
Uranus-like planet and is currently the most metal-rich single star to host any
planet. Determination of abundances was carried out in the framework of a
self-consistent approach developed by Pavlenko et al. (2012). Abundances were
computed iteratively by the program ABEL8, and the process converged after 4
iterations. We find that most elements follow the iron abundance, however some
of the iron peak elements are found to be over-abundant in this star.",1505.05843v1
2015-06-02,Coexistence of antiferromagnetic and ferromagnetic spin correlations in SrCo2As2 revealed by 59Co and 75As NMR,"In nonsuperconducting, metallic paramagnetic SrCo2As2, inelastic neutron
scattering measurements have revealed strong stripe-type $\chi$(q) = ($\pi$,0)
antiferromagnetic (AFM) spin correlations. Here, using nuclear magnetic
resonance (NMR) measurements on 59Co and 75As nuclei, we demonstrate that
stronger ferromagnetic (FM) spin correlations coexist in SrCo2As2. Our NMR data
are consistent with density functional theory (DFT) calculations which show
enhancements at both q = ($\pi$,0) and the in-plane FM q = 0 wavevectors in
static magnetic susceptibility $\chi$(q). We suggest that the strong FM
fluctuations prevent superconductivity in SrCo2As2, despite the presence of
stripe-type AFM fluctuations. Furthermore, since DFT calculations have
consistently revealed similar enhancements of the $\chi$(q) at both q =
($\pi$,0) and q = 0 in the iron-based superconductors and parent compounds, our
observation of FM correlations in SrCo2As2 calls for detailed studies of FM
correlations in the iron-based superconductors.",1506.00994v2
2015-06-03,Magneto-structural transformations via a solid-state nudged elastic band method: Application to iron under pressure,"We extend the solid-state nudged elastic band method to handle a
non-conserved order parameter - in particular, magnetization, that couples to
volume and leads to many observed effects in magnetic systems. We apply this
formalism to the well-studied magneto-volume collapse during the
pressure-induced transformation in iron - from ferromagnetic body-centered
cubic (bcc) austenite to hexagonal close-packed (hcp) martensite. We find a
bcc-hcp equilibrium coexistence pressure of 8.4 GPa, with the transition-state
enthalpy of 156 meV/Fe at this pressure. A discontinuity in magnetization and
coherent stress occurs at the transition state, which has a form of a cusp on
the potential-energy surface (yet all the atomic and cell degrees of freedom
are continuous); the calculated pressure jump of 25 GPa is related to the
observed 25 GPa spread in measured coexistence pressures arising from
martensitic and coherency stresses in samples. Our results agree with
experiments, but necessarily differ from those arising from drag and restricted
parametrization methods having improperly constrained or uncontrolled degrees
of freedom.",1506.01403v1
2015-06-15,Tuning orbital-selective correlation effects in superconducting Rb$_{0.75}$Fe$_{1.6}$Se$_{2-z}$S$_z$,"We report on terahertz time-domain spectroscopy on superconducting and
metallic iron chalcogenides Rb$_{0.75}$Fe$_{1.6}$Se$_{2-z}$S$_z$. The
superconducting transition is reduced from $T_c=$ 32 K ($z=0$) to 22 K
($z=1.0$), and finally suppressed ($z=1.4$) by isoelectronic substitution of Se
with S. Dielectric constant and optical conductivity exhibit a
metal-to-insulator transition associated with an orbital-selective Mott phase.
This orbital-selective Mott transition appears at higher temperature $T_{met}$
with increasing sulfur content, identifying sulfur substitution as an efficient
parameter to tune orbital-dependent correlation effects in iron-chalcogenide
superconductors. The reduced correlations of the $d_{xy}$ charge carriers can
account for the suppression of the superconductivity and the pseudogap-like
feature between $T_c$ and $T_{met}$ that was observed for $z=0$.",1506.04614v3
2015-06-15,The effects of Coulomb interactions on the superconducting gaps in iron-based superconductors,"Recent angle-resolved photoemission spectroscopy measurements of Co-doped
LiFeAs report a large and robust superconducting gap on the $\Gamma$-centered
hole band that lies 8 meV below the Fermi level. We show that, unlike a
conventional superconductor described by BCS theory, a multiband system with
strong interband Coulomb interactions can explain these observations. We model
LiFeAs with a five-band model in which the shallow hole band is coupled with
the other bands by only Coulomb interactions. Using Eliashberg theory, we find
reasonable interaction parameters that reproduce the $T_c$ and all five gaps of
LiFeAs. The energy independence of the Coulomb interactions then ensures the
robustness of the gap induced on the shallow band. Furthermore, due to the
repulsive nature of the Coulomb interactions, the gap changes sign between the
shallow band and the other hole pockets, corresponding to an unconventional
$s_{\pm}$ gap symmetry. Unlike other families of iron-based superconductors,
the gap symmetry of LiFeAs has not been ascertained experimentally. The
experimental implications of this sign-changing state are discussed.",1506.04762v3
2015-06-29,First-principle study of antimony doping effects on the iron-based superconductor CaFe(Sb$_{x}$As$_{1-x}$)$_{2}$,"We study antimony doping effects in the iron-based superconductor
CaFe(Sb$_{x}$As$_{1-x}$)$_{2}$ by using the first-principle calculation. The
calculations reveal that the substitution of the doped antimony atom into As of
the chainlike As layers is more stable than that in FeAs layers. This
prediction can be checked by experiments. Our results suggest that doping
homologous elements into the chainlike As layers existing only in novel 112
system is responsible for rising up the critical temperature. We discuss
antimony doping effects on the electronic structure. It is found that the
calculated band structures with and without the antimony doping are similar to
each other within our framework.",1506.08515v1
2015-07-07,Anisotropy of iron-platinum-arsenide Ca10(PtnAs8)(Fe2-xPtxAs2)5 single crystals,"The upper critical field Hc2 anisotropy of Ca10(PtnAs8)(Fe2-xPtxAs2)5 (n = 3,
4) single crystals with long FeAs interlayer distance (d) was studied by
angular dependent resistivity measurements. A scaling of the angular dependent
resistivity was realized for both single crystals using the anisotropic
Ginzburg-Landau (AGL) approach with an appropriate anisotropy parameter
{\gamma}. The AGL scaling parameter {\gamma} increases with decreasing
temperature and reaches a value of about 10 at 0.8Tc for both single crystals.
These values are much larger than those of other iron-based superconductors
(FeSCs). Remarkably, the values of {\gamma}2 show an almost linear increase
with the FeAs/FeSe interlayer distance d for FeSCs. Compared to cuprates, FeSCs
are less anisotropic, indicating that two dimensionality of the
superconductivity is intrinsically weak.",1507.01987v1
2015-07-10,Proper motions in Terzan 5: membership of the multi-iron sub-populations and first constrain to the orbit,"By exploiting two sets of high-resolution images obtained with HST ACS/WFC
over a baseline of ~10 years we have measured relative proper motions of
~70,000 stars in the stellar system Terzan 5. The results confirm the
membership of the three sub-populations with different iron abudances
discovered in the system. The orbit of the system has been derived from a first
estimate of its absolute proper motion, obtained by using bulge stars as
reference. The results of the integration of this orbit within an axisymmetric
Galactic model exclude any external accretion origin for this cluster. Terzan 5
is known to have chemistry similar to the Galactic bulge; our findings support
a kinematic link between the cluster and the bulge, further strengthening the
possibility that Terzan 5 is the fossil remnant of one of the pristine clumps
that originated the bulge.",1507.03020v1
2015-07-16,Magnetic penetration depth in disordered iron-based superconductors,"We study the effect of disorder on the London penetration depth in iron-based
superconductors. The theory is based on a two-band model with
quasi-two-dimensional Fermi surfaces, which allows for the coexistence region
in the phase diagram between magnetic and superconducting states in the
presence of intraband and interband scattering. Within the quasiclassical
approximation we derive and solve Eilenberger's equations, which include a weak
external magnetic field, and provide analytical expressions for the penetration
depth in the various limiting cases. A complete numerical analysis of the
doping and temperature dependence of the London penetration depth reveals the
crucial effect of disorder scattering, which is especially pronounced in the
coexistence phase. The experimental implications of our results are discussed.",1507.04762v1
2015-07-17,Testing the Kerr Paradigm with X-ray Observations,"Astrophysical black hole candidates are thought to be the Kerr black holes of
general relativity, but the actual nature of these objects has still to be
confirmed. The continuum-fitting and the iron line methods are currently the
only available techniques to probe the spacetime geometry around these bodies
and test the Kerr black hole paradigm. The continuum-fitting method is a robust
approach, but the shape of the disk's thermal spectrum is in general too simple
to measure the spin and to constrain possible deviations from the Kerr solution
at the same time. The iron line analysis is potentially a powerful technique,
but at the moment we do not have high quality data and a robust astrophysical
model.",1507.05036v1
2015-07-20,Minimum X-ray source size for a lamp-post corona in light-bending models for AGN,"The lamppost model is often used to describe the X-ray source geometry in
AGN, where an infinitesimal point source is located on the black hole spin
axis. This is especially invoked for Narrow Line Seyfert 1 (NLS1) galaxies,
where an extremely broad iron line seen in episodes of low X-ray flux can both
be explained by extremely strong relativistic effects as the source approaches
the black hole horizon. The most extreme spectrum seen from the NLS1 1H0707-495
requires that the source is less than 1Rg above the event horizon in this
geometry. However, the source must also be large enough to intercept sufficient
seed photons from the disk to make the hard X-ray Compton continuum which
produces the observed iron line/reflected spectrum. We use a fully relativistic
ray tracing code to show that this implies that the source must be
substantially larger than 1Rg in 1H0707-495 if the disk is the source of seed
photons. Hence the source cannot fit as close as 1Rg to the horizon, so the
observed spectrum and variability are not formed purely by effects of strong
gravity but probably also by changes in corona and inner accretion flow
geometry.",1507.05564v1
2015-07-28,"Deep X-ray spectroscopy and imaging of the Seyfert 2 galaxy, ESO 138-G001","We present a spectral and imaging analysis of the XMM-Newton and Chandra
observations of the Seyfert 2 galaxy ESO138-G001, with the aim of
characterizing the circumnuclear material responsible for the soft (0.3-2.0
keV) and hard (5-10 keV) X-ray emission. We confirm that the source is absorbed
by Compton-thick gas. However, if a self-consistent model of reprocessing from
cold toroidal material is used (MYTorus), a possible scenario requires the
absorber to be inhomogenous, its column density along the line of sight being
larger than the average column density integrated over all lines- of-sight
through the torus. The iron emission line may be produced by moderately ionised
iron (FeXII-FeXIII), as suggested by the shifted centroid energy and the low
K{\beta}/K{\alpha} flux ratio. The soft X-ray emission is dominated by emission
features, whose main excitation mechanism appears to be photoionisation, as
confirmed by line diagnostics and the use of self-consistent models (CLOUDY).",1507.07708v1
2015-07-31,"Emergent Kondo scaling in iron-based superconductors AFe2As2 (A = K, Rb, Cs)","Unconventional superconductivity from heavy fermion (HF) is always observed
in f-electron systems, in which Kondo physics between localized f-electrons and
itinerant electrons plays an essential role. Whether HF superconductivity could
be achieved in other systems without f electrons, especially for d-electron
systems, is still elusive. Here, we experimentally study the origin of
d-electron HF behavior in iron-based superconductors (FeSCs) AFe2As2 (A = K,
Rb, Cs). Nuclear magnetic resonance on 75As reveals a universal
coherent-incoherent crossover with a characteristic temperature T*. Below T*, a
so-called 'Knight shift anomaly' is first observed in FeSCs, which exhibits a
scaling behavior similar to f-electron HF materials. Furthermore, the scaling
rule also regulates the manifestation of magnetic fluctuation. These results
undoubtedly support an emergent Kondo scenario for the d-electron HF behavior,
which suggests the AFe2As2 (A = K, Rb, Cs) as the first material realization of
d-electron HF superconductors.",1507.08732v2
2015-08-04,Toward precision mass measurements of neutron-rich nuclei relevant to $r$-process nucleosynthesis,"The open question of where, when, and how the heavy elements beyond iron
enrich our Universe has triggered a new era in nuclear physics studies.\ Of all
the relevant nuclear physics inputs, the mass of very neutron-rich nuclides is
a key quantity for revealing the origin of heavy elements beyond iron.\
Although the precise determination of this property is a great challenge,
enormous progress has been made in recent decades, and it has contributed
significantly to both nuclear structure and astrophysical nucleosynthesis
studies.\ In this review, we first survey our present knowledge of the nuclear
mass surface, emphasizing the importance of nuclear mass precision in
$r$-process calculations.\ We then discuss recent progress in various methods
of nuclear mass measurement with a few selected examples.\ For each method, we
focus on recent breakthroughs and discuss possible ways of improving the
weighing of $r$-process nuclides.",1508.00695v1
2015-08-17,Engineering the magnetic anisotropy of atomic-scale nanostructure under electric field,"Atomic-scale magnetic nanostructures are promising candidates for future
information processing devices. Utilizing external electric field to manipulate
their magnetic properties is an especially thrilling project. Here, by careful
identifying different contributions of each atomic orbital to the magnetic
anisotropy energy (MAE) of the ferromagnetic metal films, we argue that it is
possible to engineer both the MAE and the magnetic response to the electric
field of atomic-scale magnetic nanostructures. Taking the iron monolayer as a
matrix, we propose several interesting iron nanostructures with dramatically
different magnetic properties. Such nanostructures could exhibit strong
magnetoelectric effect. Our work may open a new avenue to the artificial design
of electrically controlled magnetic devices.",1508.03917v1
2015-08-24,A template method for measuring the iron spectrum in cosmic rays with Cherenkov telescopes,"The energy-dependent abundance of elements in cosmic rays plays an important
role in understanding their acceleration and propagation. Most current results
are obtained either from direct measurements by balloon- or satellite-borne
detectors, or from indirect measurements by air shower detector arrays on the
Earth's surface. Imaging Atmospheric Cherenkov Telescopes (IACTs), used
primarily for $\gamma$-ray astronomy, can also be used for cosmic-ray physics.
They are able to measure Cherenkov light emitted both by heavy nuclei and by
secondary particles produced in air showers, and are thus sensitive to the
charge and energy of cosmic ray particles with energies of tens to hundreds of
TeV. A template-based method, which can be used to reconstruct the charge and
energy of primary particles simultaneously from images taken by IACTs, will be
introduced. Heavy nuclei, such as iron, can be separated from lighter cosmic
rays with this method, and thus the abundance and spectrum of these nuclei can
be measured in the range of tens to hundreds of TeV.",1508.05823v1
2015-09-07,Valence fluctuations and empty-state resonance for Fe adatom on a surface,"We report on the formation of the high-energy empty-state resonance in the
electronic spectrum of the iron adatom on the Pt(111) surface. By using the
combination of the first-principles methods and the finite-temperature exact
diagonalization approach, we show that the resonance is the result of the
valence fluctuations between atomic configurations of the impurity. Our
theoretical finding is fully confirmed by the results of the scanning tunneling
microscopy measurements [M.F. Crommie et al., Phys. Rev. B 48, 2851 (1993)]. In
contrast to the previous theoretical results obtained by using local spin
density approximation, the paramagnetic state of the impurity in the experiment
is naturally reproduced within our approach. This opens a new way for
interpretation of STM data collected earlier for metallic surface nanosystems
with iron impurities.",1509.02109v2
2015-09-29,"The far-ultraviolet spectra of ""cool"" PG1159 stars","We present a comprehensive study of Far Ultraviolet Spectroscopic Explorer
(FUSE) spectra (912-1190 A) of two members of the PG1159 spectral class, which
consists of hydrogen-deficient (pre-) white dwarfs with effective temperatures
in the range Teff = 75,000-200,000 K. As two representatives of the cooler
objects, we have selected PG1707+427 (Teff = 85,000 K) and PG1424+535 (Teff =
110,000 K), complementing a previous study of the hotter prototype PG1159-035
(Teff = 140,000 K). The helium-dominated atmospheres are strongly enriched in
carbon and oxygen, therefore, their spectra are dominated by lines from C
III-IV and O III-VI, many of which were never observed before in hot stars. In
addition, lines of many other metals (N, F, Ne, Si, P, S, Ar, Fe) are
detectable, demonstrating that observations in this spectral region are most
rewarding when compared to the near-ultraviolet and optical wavelength bands.
We perform abundance analyses of these species and derive upper limits for
several undetected light and heavy metals including iron-group and trans-iron
elements. The results are compared to predictions of stellar evolution models
for neutron-capture nucleosynthesis and good agreement is found.",1509.08927v1
2015-10-02,"Electronic structure and magnetic properties of FeTe, BiFeO$_3$, SrFe$_{12}$O$_{19}$ and SrCoTiFe$_{10}$O$_{19}$ compounds","The electronic energy structures and magnetic properties of iron-based
compounds with group VI elements (FeTe, BiFeO$_3$, SrFe$_{12}$O$_{19}$ and
SrCoTiFe$_{10}$O$_{19}$) are studied using the density functional theory (DFT)
methods. Manifestations of different types of chemical bonds in magnetism of
these compounds are studied theoretically. Calculations of electronic
structures of these systems were performed using the generalized gradient
approximation (GGA) for description of the exchange and correlation effects
within DFT. For SrFe$_{12}$O$_{19}$ and SrCoTiFe$_{10}$O$_{19}$ hexaferrites
the GGA+$U$ method was also employed to deal with strongly correlated
3$d$-electrons. The calculations have revealed distinctive features of
electronic structure of the investigated iron-based compounds with strongly
correlated 3$d$-electrons, which can be responsible for their peculiar
structural and magnetic properties.",1510.00513v1
2015-10-05,Spin-Driven Nematic Instability of the Multi-Orbital Hubbard Model: Application to Iron-Based Superconductors,"Nematic order resulting from the partial melting of density-waves has been
proposed as the mechanism to explain nematicity in iron-based superconductors.
An outstanding question, however, is whether the microscopic electronic model
for these systems -- the multi-orbital Hubbard model -- displays such an
ordered state as its leading instability. In contrast to usual electronic
instabilities, such as magnetic and charge order, this fluctuation-driven
phenomenon cannot be captured by the standard RPA method. Here, by including
fluctuations beyond RPA in the multi-orbital Hubbard model, we derive its
nematic susceptibility and contrast it with its ferro-orbital order
susceptibility, showing that its leading instability is the spin-driven nematic
phase. Our results also demonstrate the primary role played by the $d_{xy}$
orbital in driving the nematic transition, and reveal that high-energy magnetic
fluctuations are essential to stabilize nematic order in the absence of
magnetic order.",1510.01389v2
2015-10-08,"Orbital order, spin waves, and doping effects in the $(π,0)$ SDW state --- comparative study of the three band models for iron pnictides","Aimed at identifying the role of microscopic Hamiltonian parameters on spin
wave excitations, orbital order, and magnetic moments in the $(\pi,0)$ SDW
state, two different three band models for iron pnictides are compared --- one
at two-third filling ($n=4$) and another at half filling $(n=3)$ --- both of
which yield qualitatively correct Fermi surface structure in the paramagnetic
state. Spin wave analysis of the model at $n=4$ shows instability of the SDW
state, which is attributed to weakly developed magnetic moments and weak
magnetic couplings due to overfilling, as inferred from the observed
stabilization of the SDW state and enhancement of magnetic excitation energies
upon hole doping. In contrast, the model at $n=3$ (half filling) yields a
gapped SDW state with well developed magnetic moments and the calculated spin
wave excitations are in excellent agreement with INS experiments. The sign of
the orbital order ($n_{xz} - n_{yz} \approx +0.2$) is also in agreement with
experiments. Both the zone boundary spin wave energies in the F and AF
directions as well as the orbital order are shown to peak near half filling,
highlighting the correlation between orbital order and SDW state stabilization.",1510.02276v1
2015-10-23,Charge doping versus impurity scattering in chemically substituted iron-pnictides,"To reveal the relative importance of charge doping and defect scattering in
substitutionally modified 122 iron pnictides, we perform a systematic first
principles study on selected bands at the Fermi level. Disorder effects are
induced by various substitutions using an orbital based coherent potential
approximation (CPA). Pronounced level shifts of individual bands suggest that
transition metal substitutions introduce mobile charge carriers into the
system. However, important deviations from such a rigid band scenario as well
as spectral broadenings due to impurity scattering correlate with the band
character. Finally a $T$-matrix analysis exhibits a larger intraband than
interband scattering consistent with an $s^{+-}$ pairing state. Comparing
different substitutions reveals an increase of pair-breaking along the
transition metal series.",1510.06941v1
2015-10-29,Robust Majorana signature detection with a coupled quantum dot-nanomechanical resonator in all-optical domain,"Motivated by a recent experiment [Nadj-Perge et al., Science 346, 602 (2014)]
providing evidence for Majorana zero modes in iron chains on the
superconducting Pb surface, in the present work, we theoretically propose an
all-optical scheme to detect Majorana fermions, which is very different from
the current tunneling measurement based on electrical means. The optical
detection proposal consists of a quantum dot embedded in a nanomechanical
resonator with optical pump-probe technology. With the optical means, the
signal in the coherent optical spectrum presents a distinct signature for the
existence of Majorana fermions in the end of iron chains. Further, the
vibration of the nanomechanical resonator behaving as a phonon cavity will
enhance the exciton resonance spectrum, which makes the Majorana fermions more
sensitive to be detectable. This optical scheme affords a potential supplement
for detection of Majorana fermions and supports to use Majorana fermions in Fe
chains as qubits for potential applications in quantum computing devices.",1510.08679v1
2015-11-03,Doping-Enhanced Antiferromagnetism in Ca1-xLaxFeAs2,"In iron pnictides, high temperature superconductivity emerges after
suppressing antiferromagnetism by doping. Here we show that antiferromagnetism
in Ca$_{1-x}$La$_x$FeAs$_2$ is robust against and even enhanced by doping.
Using $^{75}$As-nuclear magnetic resonance and nuclear quadrupole resonance
techniques, we find that an antiferromagnetic order occurs below the N\'eel
temperature $T_{\rm N}$ = 62 K at a high doping concentration ($x$ = 0.15)
where superconductivity sets in at the transition temperature $T_{\rm c}$ = 35
K. Unexpectedly, $T_{\rm N}$ is enhanced with increasing doping, rising up to
$T_{\rm N}$ = 70 K at $x$ = 0.24. The obtained phase diagram of this new system
enriches the physics of iron-based high-$T_{\rm c}$ superconductors.",1511.00760v1
2015-11-03,The role of spin-orbit interaction in the ultrafast demagnetization of small iron clusters,"The ultra-fast demagnetization of small iron clusters initiated by an intense
optical excitation is studied with time-dependent spin density functional
theory (TDSDFT). In particular we investigate the effect of the spin-orbit
interaction on the onset of the demagnetization process. It is found that the
initial rate of coherent spin loss is proportional to the square of the atomic
spin-orbit coupling constant, $\lambda$. A simplified quantum spin model
comprising spin-orbit interaction and a local time-dependent magnetic field is
found to be the minimal model able to reproduce our {\it ab initio} results.
The model predicts the $\lambda^2$ dependence of the onset rate of
demagnetization when it is solved either numerically or analytically in the
linear response limit. Our findings are supported by additional TDSDFT
simulations of clusters made of Co and Ni.",1511.00864v1
2015-11-09,Energy dependence of the spin excitation anisotropy in uniaxial-strained BaFe1.9Ni0.1As2,"We use inelastic neutron scattering to study the temperature and energy
dependence of the spin excitation anisotropy in uniaxial-strained
electron-doped iron pnictide BaFe$_{1.9}$Ni$_{0.1}$As$_2$ near optimal
superconductivity ($T_c=20$ K). Our work has been motivated by the observation
of in-plane resistivity anisotropy in the paramagnetic tetragonal phase of
electron-underdoped iron pnictides under uniaxial pressure, which has been
attributed to a spin-driven Ising-nematic state or orbital ordering. Here we
show that the spin excitation anisotropy, a signature of the spin-driven
Ising-nematic phase, exists for energies below $\sim$60 meV in
uniaxial-strained BaFe$_{1.9}$Ni$_{0.1}$As$_2$. Since this energy scale is
considerably larger than the energy splitting of the $d_{xz}$ and $d_{yz}$
bands of uniaxial-strained Ba(Fe$_{1-x}$Co$_x$)$_2$As$_2$ near optimal
superconductivity, spin Ising-nematic correlations is likely the driving force
for the resistivity anisotropy and associated electronic nematic correlations.",1511.02759v1
2015-12-07,Origin of the DC and AC conductivity anisotropy in iron-based superconductors: scattering rate versus spectral weight effects,"To shed light on the mechanism responsible for the in-plane resistivity
anisotropy in the nematic phase of the iron-based superconductors, we
investigate the impact of spin fluctuations on the anisotropic AC conductivity.
On the one hand, the scattering of electrons off magnetic fluctuations causes
an anisotropic scattering rate. On the other hand, the accompanying Fermi
velocity renormalization contributes to both the plasma frequency and the
scattering rate in antagonistic ways, giving rise to anisotropies in these
quantities that exactly cancel each other in the DC limit. As a result, the
effective scattering rate changes its sign as function of temperature, but the
DC conductivity retains the same sign, in agreement with recent experiments.",1512.02259v2
2015-12-08,Multi-orbital quantum antiferromagnetism in iron pnictides --- effective spin couplings and quantum corrections to sublattice magnetization,"Towards understanding the multi-orbital quantum antiferromagnetism in iron
pnictides, effective spin couplings and spin fluctuation induced quantum
corrections to sublattice magnetization are obtained in the $(\pi,0)$ AF state
of a realistic three band interacting electron model involving $xz$, $yz$, and
$xy$ Fe 3d orbitals. The $xy$ orbital is found to be mainly responsible for the
generation of strong ferromagnetic spin coupling in the $b$ direction, which is
critically important to fully account for the spin wave dispersion as measured
in inelastic neutron scattering experiments. The ferromagnetic spin coupling is
strongly suppressed as the $xy$ band approaches half filling, and is ascribed
to particle-hole exchange in the partially filled $xy$ band. The strongest AF
spin coupling in the $a$ direction is found to be in the orbital off diagonal
sector involving the $xz$ and $xy$ orbitals. First order quantum corrections to
sublattice magnetization are evaluated for the three orbitals, and yield a
significant $37\%$ average reduction from the Hartree-Fock value.",1512.02398v1
2015-12-15,Elastic coupling and spin-driven nematicity in iron-based superconductors,"Spin-driven nematic order that has been proposed for iron-based
superconductors is generated by pronounced fluctuations of a striped density
wave state. On the other hand it is a well known fact that nematic order
parameter couples bilinearly to the strain, which supresses the fluctuations of
the nematic order parameter itself and lowers the upper critical dimension,
yielding mean-field behaviour of the nematic degrees of freedom for $d>2$. This
is consistent with the measured Currie-Weiss behaviour of the nematic
susceptibility. Here we reconcile this apparent contradiction between
pronounced magnetic fluctuations and mean-field behaviour of the nematic
degrees of freedom. We show, by developing a $\varphi^4$ theory for the nematic
degrees of freedom, that the coupling to elastic strain does not suppress the
fluctuations that cause the nematic order in the first place (magnetic
fluctuations), yet it does transform the Ising-nematic transition into a
mean-field transition. In addition, we demonstrate that the mean field behavior
occurs in the entire temperature regime where a softening of the shear modulus
is observed.",1512.04861v1
2015-12-28,Hole-$s_{\pm}$ State Induced by Coexisting Ferro- and Aniferromagnetic and Aniferro-orbital Fluctuations in the Iron Pnictides,"The multi-orbital Hubbard model is investigated in order to clarify the
electron correlation effects and the superconductivity in the iron-based
superconductor. The renormalization effects on the self-energy and the
two-particle irreducible vertex function are calculated on the basis of the
dynamical mean field theory. We find that the vertex function exhibits a strong
renormalization with the significant orbital dependence as compared with the
renormalization factor, when the antiferromagnetic and the antiferro-orbital
fluctuations are comparably enhanced due to the electron and the hole Fermi
surfaces nesting effects. The orbital-dependent vertex function together with
the $q\sim0$ nesting between the two-hole Fermi surfaces results in the
inter-orbital ferromagnetic fluctuation gradually enhanced which is expected to
be observed in LiFeAs. We show that the hole-$s_{\pm}$-wave superconductivity
with the sign change of the two-hole Fermi surfaces is realized by the enhanced
ferromagnetic fluctuation accompanied by the antiferromagnetic fluctuation and
the antiferro-orbital fluctuation.",1512.08327v1
2016-01-08,Detecting the orbital character of the spin fluctuation in the Iron-based superconductors with the resonant inelastic X-ray scattering spectroscopy,"The orbital distribution of the spin fluctuation in the iron-based
superconductors(IBSs) is the key information needed to understand the
magnetism, superconductivity and electronic nematicity in these multi-orbital
systems. In this work, we propose that the resonant inelastic X-ray
scattering(RIXS) technique can be used to probe selectively the spin
fluctuation on different Fe $3d$ orbitals. In particular, the spin fluctuation
on the three $t_{2g}$ orbitals, namely, the $3d_{xz}$, $3d_{yz}$ and the
$3d_{xy}$ orbital, can be selectively probed in the $\sigma\rightarrow\pi'$
scattering geometry by aligning the direction of the outgoing photon in the
$y$, $x$ and $z$ direction. Such orbital-resolved information on the spin
fluctuation is invaluable for the study of the orbital-selective physics in the
IBSs and can greatly advance our understanding on the relation between orbital
ordering and spin nematicity in the IBSs and the orbital-selective pairing
mechanism in these multi-orbital systems.",1601.01809v3
2016-01-12,The B/C and sub-Iron/Iron Cosmic ray ratios - further evidence in favor of the spiral arm diffusion model,"The Boron to Carbon (B/C) and sub-Fe/Fe ratios provides an important clue on
Cosmic Ray (CR) propagation within the Galaxy. These ratios estimate the
grammage that the CR traverse as they propagate from their sources to Earth.
Attempts to explain these ratios within the standard CR propagation models
require ad hoc modifications and even with those these models necessitate
inconsistent grammages to explain both ratios. As an alternative, physically
motivated model, we have proposed that CR originate preferably within the
galactic spiral arms. CR propagation from dynamic spiral arms has important
imprints on various secondary to primary ratios, such as the B/C ratio and the
positron fraction. We use our spiral arm diffusion model with the spallation
network extended up to Nickel to calculate the sub-Fe/Fe ratio. We show that
without any additional parameters the spiral arm model consistently explains
both ratios with the same grammage, providing further evidence in favor of this
model.",1601.03072v2
2016-01-13,Relationship between Pairing Symmetries and Interaction Parameters in Iron-Based Superconductors from Functional Renormalization Group Calculations,"Pairing symmetries of iron-based superconductors are investigated
systematically in a five-orbital model within the different regions of
interaction parameters by functional renormalization group(FRG). Even for a
fixed Fermi surface with both hole and electron pockets, it is found that
depending on interaction parameters, a variety of pairing symmetries, including
two types of $d$-wave and two types of $s$-wave pairing symmetries, can emerge.
Only the $d_{x^2-y^2}$ and the $s\pm$ waves are robustly supported by the
nearest-neighbor(NN) intra-orbital $J_1$ and the next-nearest-neighbor(NNN)
intra-orbital $J_2$ antiferromagnetic(AFM) exchange couplings respectively.
This study suggests that the accurate initial input of interaction parameters
are essential to make FRG an useful method to determine the leading channel of
superconducting instability.",1601.03228v2
2016-01-14,Coupled multiple-mode theory for $s_{\pm}$ pairing mechanism in iron based superconductors,"We investigate the interplay between the magnetic and the superconducting
degrees of freedom in unconventional multi-band superconductors such as iron
pnictides. For this purpose a dynamical mode-mode coupling theory is developed
based on the coupled Bethe-Salpeter equations. In order to investigate the
region of the phase diagram not too far from the tetracritical point where the
magnetic spin density wave, (SDW) and superconducting (SC) transition
temperatures coincide, we also construct a Ginzburg - Landau functional
including both SC and SDW fluctuations in a critical region above the
transition temperatures. The fluctuation corrections tend to suppress the
magnetic transition, but in the superconducting channel the intraband and
interband contribution of the fluctuations nearly compensate each other.",1601.03552v2
2016-01-21,Effect of nonsymmorphic space group on correlation functions in iron-based superconductors,"The orbital basis is natural when one needs to calculate the effect of local
interactions or to unravel the role of orbital physics in the response to
external probes. In systems with nonsymmorphic point groups, such as the
iron-based superconductors, we show that symmetries that emerge in observable
response functions at certain wave vectors are absent from generalized
susceptibilities calculated with tight-binding Hamiltonians in the orbital
basis. Such symmetries are recovered only when the generalized susceptibilities
are embeded back to the continuum using appropriate matrix elements between
basis states. This is illustrated with the case of LiFeAs and is further
clarified using a minimal tight-binding Hamiltonian with non-symmorphic space
group.",1601.05813v3
2016-02-02,Fast synthesis of Fe1.1Se1-xTex superconductors in a self-heating and furnace-free way,"A fast and furnace-free method of combustion synthesis is employed for the
first time to synthesize iron-based superconductors. Using this method,
Fe1.1Se1-xTex (0<=x<=1) samples can be prepared from self-sustained reactions
of element powders in only tens of seconds. The obtained Fe1.1Se1-xTex samples
show clear zero resistivity and corresponding magnetic susceptibility drop at
around 10-14 K. The Fe1.1Se0.33Te0.67 sample shows the highest onset Tc of
about 14 K, and its upper critical field is estimated to be approximately 54 T.
Compared with conventional solid state reaction for preparing polycrystalline
FeSe samples, combustion synthesis exhibits much-reduced time and energy
consumption, but offers comparable superconducting properties. It is expected
that the combustion synthesis method is available for preparing plenty of
iron-based superconductors, and in this direction further related work is in
progress.",1602.00880v1
2016-02-04,A quantum protective mechanism in photosynthesis,"Since the emergence of oxygenic photosynthesis, living systems have developed
protective mechanisms against reactive oxygen species. During charge separation
in photosynthetic reaction centres, triplet states can react with molecular
oxygen generating destructive singlet oxygen. The triplet product yield in
bacteria is observed to be reduced by weak magnetic fields. Reaction centres
from plants' photosystem II share many features with bacterial reaction
centres, including a high-spin iron whose function has remained obscure. To
explain observations that the magnetic field effect is reduced by the iron, we
propose that its fast-relaxing spin plays a protective role in photosynthesis
by generating an effective magnetic field. We consider a simple model of the
system, derive an analytical expression for the effective magnetic field and
analyse the resulting triplet yield reduction. The protective mechanism is
robust for realistic parameter ranges, constituting a clear example of a
quantum effect playing a macroscopic role vital for life.",1602.01689v1
2016-02-12,Nucleosynthesis in the first massive stars,"The nucleosynthesis in the first massive stars may be constrained by
observing the surface composition of long-lived very iron-poor stars born
around 10 billion years ago from material enriched by their ejecta. Many
interesting clues on physical processes having occurred in the first stars can
be obtained just based on nuclear aspects. Two facts are particularly clear, 1)
in these first massive stars, mixing must have occurred between the H-burning
and the He-burning zone during their nuclear lifetimes; 2) only the outer
layers of these massive stars have enriched the material from which the very
iron-poor stars, observed today in the halo, have formed. These two basic
requirements can be obtained by rotating stellar models at very low
metallicity. In the present paper, we discuss the arguments supporting this
view and illustrates the sensitivity of the results concerning the [Mg/Al]
ratio on the rate of the reaction Na(23)(p,\gamma)Mg(24).",1602.04122v1
2016-02-15,Electrical Switching of Magnetization in Films of alpha-Iron with Naturally Hydroxidized Surface,"Control of the magnetization vector in ferromagnetic films and
heterostructures by using electric tools instead of external magnetic fields
can lead to low-power memory devices. We observe the robust changes in
magnetization states of a thin (about 30 nm) film of alpha-Fe covered by the
naturally formed layer ( about 6 nm in thickness) of iron ohyhydroxides (FeOOH)
under discharging a capacitor through the film. Strikingly, the magnetization
vector is switchable by the discharge even with no any biasing field at room
temperatures. In this electrically induced magnetization switching (EIMS) we
reveal the key role of the FeOOH layer. We demonstrate experimental evidences
that not the discharge current itself but the electric field (of the order of
10 kV/m) generated by this current is responsible for EIMS. The results
reported here provide a plausible explanation of the observed phenomenon in
terms of electric-field-induced weak ferromagnetism in the FeOOH layer and its
coupling with the underlying alpha-Fe.",1602.04590v1
2016-03-01,"Nuclear medium effects in $F_{2A}^{EM}(x,Q^2)$ and $F_{2A}^{Weak}(x,Q^2)$ structure functions","Recent phenomenological analysis of experimental data on DIS processes
induced by charged leptons and neutrinos/antineutrinos beams on nuclear targets
by CTEQ collaboration has confirmed the observation of CCFR and NuTeV
collaborations, that weak structure function $F_{2A}^{Weak} (x,Q^2)$ is
different from electromagnetic structure function $F_{2A}^{EM} (x,Q^2)$ in a
nucleus like iron, specially in the region of low $x$ and $Q^2$. In view of
this observation we have made a study of nuclear medium effects on
$F_{2A}^{Weak} (x,Q^2)$ and $F_{2A}^{EM} (x,Q^2)$ for a wide range of $x$ and
$Q^2$ using a microscopic nuclear model. We have considered Fermi motion,
binding energy, nucleon correlations, mesonic contributions from pion and rho
mesons and shadowing effects to incorporate nuclear medium effects.
  The calculations are performed in a local density approximation using a
relativistic nucleon spectral function which includes nucleon correlations. The
numerical results in the case of iron nucleus are compared with the
experimental data.",1603.00164v2
2016-03-07,A new insight into neutrino energy loss by electron capture of iron group nuclei in magnetars surface,"Based on the relativistic mean-field effective interactions theory, and Lai
dong model \citep{b37, b38, b39}, we discuss the influences of superstrong
magnetic fields (SMFs) on electron Fermi energy, nuclear blinding energy, and
single-particle level structure in magnetars surface. By using the method of
Shell-Model Monte Carlo (SMMC), and the Random Phase Approximation (RPA)
theory, we detailed analyze the neutrino energy loss rates(NELRs) by electron
capture (EC) for iron group nuclei in SMFs.",1603.01898v2
2016-03-08,Quasiparticle scattering interference in iron pnictides: A probe of the origin of nematicity,"In this paper, we investigate the quasiparticle scattering interference(QPI)
in the nematic phase of iron pnictides, based on the magnetic and orbital
scenarios of nematicity, respectively. In the spin density wave(SDW) state, the
QPI pattern exhibits a dimer structure in the energy region of the SDW gap,
with its orientation along the ferromagnetic direction of the SDW order. When
the energy is increased to be near the Fermi level, it exhibits two sets of
dimers along the same direction. The dimer structure of the QPI patterns
persists with the decrease of the SDW correlation length in the magnetic driven
nematic phase, although it tends to merge together for the scattering patterns
with energies close to the Fermi level. While in the orbital scenario, the QPI
patterns exhibit a dimer structure in a wide energy region. It undergoes a
{\pi}/2 rotation with the increasing of energy, which is associated with the
inequivalent energies of the two Dirac nodes induced by the orbital order.
These distinct features may be used to probe or distinguish two kinds of
scenarios of the nemeticity.",1603.02517v2
2016-03-09,Antiferroquadrupolar order and rotational symmetry breaking in a generalized bilinear-biquadratic model on a square lattice,"The magnetic and nematic properties of the iron chalcogenides have recently
been the subject of intense interest. Motivated by the proposed
antiferroquadrupolar and Ising-nematic orders for the bulk FeSe, we study the
phase diagram of an $S=1$ generalized bilinear-biquadratic model with
multi-neighbor interactions. We find a large parameter regime for a ($\pi$,0)
antiferroquadrupolar phase, showing how quantum fluctuations stabilize it by
lifting an infinite degeneracy of certain semiclassical states. Evidence for
this C$_4$-symmetry-breaking quadrupolar phase is also provided by an unbiased
density matrix renormalization group analysis. We discuss the implications of
our results for FeSe and related iron-based superconductors.",1603.03027v5
2016-03-14,Strong cooperative coupling of pressure-induced magnetic order and nematicity in FeSe,"A hallmark of the iron-based superconductors is the strong coupling between
magnetic, structural and electronic degrees of freedom. However, a universal
picture of the normal state properties of these compounds has been confounded
by recent investigations of FeSe where the nematic (structural) and magnetic
transitions appear to be decoupled. Here, using synchrotron-based high-energy
x-ray diffraction and time-domain Moessbauer spectroscopy, we show that
nematicity and magnetism in FeSe under applied pressure are indeed strongly
coupled. Distinct structural and magnetic transitions are observed for
pressures, 1.0 GPa <= p <= 1.7 GPa, which merge into a single first-order phase
line for p >= 1.7 GPa, reminiscent of what has been observed, both
experimentally and theoretically, for the evolution of these transitions in the
prototypical doped system, Ba(Fe[1-x]Co[x])2As2. Our results support a
spin-driven mechanism for nematic order in FeSe and provide an important step
towards a universal description of the normal state properties of the
iron-based superconductors.",1603.04135v1
2016-03-22,Thermal Conductivity of the Iron-Based Superconductor FeSe : Nodeless Gap with Strong Two-Band Character,"The thermal conductivity of the iron-based superconductor FeSe was measured
at temperatures down to 50 mK in magnetic fields up to 17 T. In zero magnetic
field, the electronic residual linear term in the T = 0 limit, \kappa_0/T, is
vanishingly small. Application of a magnetic field H causes no increase in
\kappa_0/T initially. Those two observations show that there are no zero-energy
quasiparticles that carry heat and therefore no nodes in the superconducting
gap of FeSe. The full field dependence of \kappa_0/T has the classic shape of a
two-band superconductor, such as MgB2: it rises exponentially at very low
field, with a characteristic field H* << Hc2, and then more slowly up to the
upper critical field Hc2. This shows that the superconducting gap is very small
on one of the pockets in the Fermi surface of FeSe.",1603.06917v1
2016-04-01,Nematic quantum critical point without magnetism in FeSe1-xSx superconductors,"The importance of antiferromagnetic fluctuations are widely acknowledged in
most unconventional superconductors. In addition, cuprates and iron pnictides
often exhibit unidirectional (nematic) electronic correlations, including
stripe and orbital orders, whose fluctuations may also play a key role for
electron pairing. However, these nematic correlations are intertwined with
antiferromagnetic or charge orders, preventing us to identify the essential
role of nematic fluctuations. This calls for new materials having only
nematicity without competing or coexisting orders. Here we report systematic
elastoresistance measurements in FeSe$_{1-x}$S$_{x}$ superconductors, which,
unlike other iron-based families, exhibit an electronic nematic order without
accompanying antiferromagnetic order. We find that the nematic transition
temperature decreases with sulphur content $x$, whereas the nematic
fluctuations are strongly enhanced. Near $x\approx0.17$, the nematic
susceptibility diverges towards absolute zero, revealing a nematic quantum
critical point. This highlights FeSe$_{1-x}$S$_{x}$ as a unique nonmagnetic
system suitable for studying the impact of nematicity on superconductivity.",1604.00184v2
2016-04-05,Effects of single- and multi-substituted Zn ions in doped-122 type iron-based superconductors,"Recent experiments on Zn-substituted 122-type iron-based superconductors
(FeSCs) at electron- and hole- doped region provide us with a testing ground
for understanding the effect of Zn impurities in these systems. Our
first-principle calculations of the electronic structure reveal that the Zn 3d
orbitals are far below the Fermi level and chemically inactive, while the Zn
4s-orbital is partially occupied and its wave function overlapping with those
3d-orbitals of neighboring Fe-ions. This suggests that the impurity effect is
originating in the Zn 4s-orbital, not its 3d-orbitals. Employing a
phenomenological two-orbital lattice model for 122-FeSCs and the
self-consistent Bogoliubov-de Gennes equations, we study how the Zn-impurities
suppress the superconductivity in electron- and hole- doped compounds. Our
obtained results qualitatively agree with the experimental measurements.",1604.01323v1
2016-04-06,Effect of strain and temperature on the threshold displacement energy in body-centered cubic iron,"The threshold displacement energy (TDE) is the minimum amount of kinetic
energy required to displace an atom from its lattice site. The magnitude of the
TDE displays significant variance as a function of the crystallographic
direction, system temperature and applied strain, among a variety of other
factors. It is critically important to determine an accurate value of the TDE
in order to calculate the total number of displacements due to a given
irradiation condition, and thus to understand the materials response to
irradiation. In this study, molecular dynamics simulations have been performed
to calculate the threshold displacement energy in body-centered cubic iron as a
function of strain and temperature. With applied strain, a decrease of the TDE
of up to approximately 14 eV was observed. A temperature increase from 300 K to
500 K can result in an increase of the TDE of up to approximately 9 eV.",1604.01791v1
2016-04-08,Tribochemistry of graphene on iron and its possible role in lubrication of steel,"Recent tribological experiments revealed that graphene is able to lubricate
macroscale steel-on-steel sliding contacts very effectively both in dry and
humid conditions. This effect has been attributed to a mechanical action of
graphene related to its load-carrying capacity. Here we provide further insight
into the functionality of graphene as lubricant by analysing its tribochemical
action. By means of first principles calculations we show that graphene binds
strongly to native iron surfaces highly reducing their surface energy. Thanks
to a passivating effect, the metal surfaces coated by graphene become almost
inert and present very low adhesion and shear strength when mated in a sliding
contact. We generalize the result by establishing a connection between the
tribological and the electronic properties of interfaces, which is relevant to
understand the fundamental nature of frictional forces.",1604.02306v2
2016-04-10,Quasi-periodic oscillations as a tool for testing the Kerr metric: A comparison with gravitational waves and iron line,"QPOs are a common feature in the X-ray power density spectrum of black hole
binaries and a potentially powerful tool to probe the spacetime geometry around
these objects. Here we discuss their constraining power to test the Kerr black
hole hypothesis within the relativistic precession model. We compare our
results with the constraints that can be obtained from gravitational waves and
iron line. We find that QPOs may provide very precise measurements, but they
are strongly affected by parameter degeneracy, and it is difficult to test the
Kerr metric with this approach in the absence of independent observations to
constrain the mass or the spin.",1604.02643v2
2016-04-11,Interatomic Fe-H potential for irradiation and embrittlement simulations,"The behavior of hydrogen in iron and iron alloys is of interest in many
fields of physics and materials science. To enable large-scale molecular
dynamics simulations of systems with Fe-H interactions, we develop, based on
density-functional theory calculations, an interatomic Fe-H potential in the
Tersoff-Brenner formalism. The obtained analytical potential is suitable for
simulations of H in bulk Fe as well as for modeling small FeH molecules, and it
can be directly combined with our previously constructed potential for the
stainless steel Fe-Cr-C system. This will allow simulations of, e.g.,
hydrocarbon molecule chemistry on steel surfaces. In the current work, we apply
the potential to simulating hydrogen-induced embrittlement in monocrystalline
bulk Fe and in an Fe bicrystal with a grain boundary. In both cases, hydrogen
is found to soften the material.",1604.02829v1
2016-04-11,Anomalous carrier density independent superconductivity in iron pnictides,"Dome-shape superconductivity phase diagram can commonly be observed in
cuprate and iron-based systems via tuning parameters such as charge carrier
doping, pressure, bond angle, and etc. We report doping electrons from
transition-metal elements (TM = Co, Ni) substitution can induce high-Tc
superconductivity around 35 K in Ca0.94La0.06Fe2As2, which emerges abruptly
before the total suppression of the innate
spin-density-wave/anti-ferromagnetism (SDW/AFM) state. Unexpectedly, the onset
critical temperature for the high-Tc superconductivity stays constant for a
wide range of TM doping. Possible extrinsic factors like phase separation,
chemical inhomogeneity, and charge carrier cancelation effect are all excluded.
This anomalous charge carrier density independent SC is very similar to the
interface superconductivity in La2-xSrxCuO4-La2CuO4 bilayer system. The further
verified two-dimensional (2D) nature of superconductivity by the Tinkham's
angular-dependent critical field model as well as by the angle-resolved
magneto-resistance measurements jointly supports the idea of interfacial effect
induced high-Tc superconductivity.",1604.02839v1
2016-04-18,Observation of two distinct superconducting domes under pressure in tetragonal FeS,"As the simplest iron-based superconductor, FeSe forms a tetragonal structure
with transition temperature Tc ~ 8 K. With assistance of pressure, or other
techniques, Tc can be greatly enhanced, even to above liquid nitrogen
temperature. The newly discovered superconducting tetragonal FeS (Tc ~ 4.5 K),
a sulfide counterpart of FeSe, promotes us on its high pressure investigation.
The transport and structure evolution of FeS with pressure have been studied. A
rapid suppression of Tc and vanishing of superconductivity at 4.0 GPa are
observed, followed by a second superconducting dome with a 30% enhancement in
maximum Tc. An onsite tetragonal to hexagonal phase transition occurs around
7.0 GPa, followed by a broad pressure range of phase coexistence. The residual
deformed tetragonal phase is considered as the source of second superconducting
dome. The observation of two superconducting domes in iron-based
superconductors poses great challenges for understanding their pairing
mechanism.",1604.05254v2
2016-04-22,Temperature-induced band selective localization and coherent-incoherent crossover in single-layer FeSe/Nb:BaTiO3 /KTaO3,"Iron chalcogenide superconductors are multi-band systems with strong electron
correlations. Here we use angle-resolved photoemission spectroscopy to study
band dependent correlation effects in single-layer FeSe/Nb:BaTiO3/KTaO3, a new
iron chalcogenide superconductor with non-degenerate electron pockets and
interface-enhanced superconductivity. The non-degeneracy of the electron bands
helps to resolve the temperature dependent evolution of different bands. With
increasing temperature, the single layer FeSe undergoes a band-selective
localization, in which the coherent spectral weight of one electron band is
completely depleted while that of the other one remains finite. In addition,
the spectral weight of the incoherent background is enhanced with increasing
temperature, indicating a coherent-incoherent crossover. Signatures of
polaronic behavior are observed, suggesting electron-boson interactions. These
phenomena help to construct a more complete picture of electron correlations in
the FeSe family.",1604.06526v1
2016-05-12,The production of proton-rich isotopes beyond iron: The $γ$ process in stars,"Beyond iron, a small fraction of the total abundances in the Solar System is
made of proton-rich isotopes, the p nuclei. The clear understanding of their
production is a fundamental challenge for nuclear astrophysics. The p nuclei
constrain the nucleosynthesis in core-collapse and thermonuclear supernovae.
The $\gamma$ process is the most established scenario for the production of the
p nuclei, which are produced via different photodisintegration paths starting
on heavier nuclei. A large effort from nuclear physics is needed to access the
relevant nuclear reaction rates far from the valley of stability. This review
describes the production of the heavy proton-rich isotopes by the $\gamma$
process in stars, and explores the state of the art of experimental nuclear
physics to provide nuclear data for stellar nucleosynthesis.",1605.03690v1
2016-06-08,Large enhancement in high-energy photoionization of Fe XVII and missing continuum plasma opacity,"Aimed at solving the outstanding problem of solar opacity, and radiation
transport plasma models in general, we report substantial photoabsorption in
the high-energy regime due to atomic core photo-excitations not heretofore
considered. In extensive R-Matrix calculations of unprecedented complexity for
an important iron ion Fe xvii (Fe$^{16+}$), with a wave function expansion of
99 Fe xviii (Fe$^{17+}$) LS core states from $n \leq 4$ complexes (equivalent
to 218 fine structure levels), we find: i) up to orders of magnitude
enhancement in background photoionization cross sections, in addition to
strongly peaked photo-excitation-of-core resonances not considered in current
opacity models, and ii) demonstrate convergence with respect to successive core
excitations. The resulting increase in the monochromatic continuum, and 35% in
the Rosseland Mean Opacity, are compared with the ""higher-than-predicted"" iron
opacity measured at the Sandia Z-pinch fusion device at solar interior
conditions.",1606.02731v1
2016-06-09,Effect of nematic ordering on electronic structure of FeSe,"Electronically driven nematic order is often considered as an essential
ingredient of high-temperature superconductivity. Its elusive nature in
iron-based supercon- ductors resulted in a controversy not only as regards its
origin but also as to the degree of its influence on the electronic structure
even in the simplest representative material FeSe. Here we utilized
angle-resolved photoemission spectroscopy and density functional theory
calculations to study the influence of the nematic order on the electronic
structure of FeSe and determine its exact energy and momentum scales. Our
results strongly suggest that the nematicity in FeSe is electronically driven,
we resolve the recent controversy and provide the necessary quantitative
experimental basis for a successful theory of superconductivity in iron-based
materials which takes into account both, spin-orbit interaction and electronic
nematicity.",1606.03022v1
2016-06-15,Signature of the Leggett mode in the A1g Raman response: from MgB2 to iron-based superconductors,"The Raman response in a superconductor is a powerful probe to investigate the
symmetry of the superconducting gap. Here we show that in a multiband
superconductor it also offers the unique opportunity to establish if the
driving pairing interaction has an intraband or interband character. In the
model with one hole and one electron band the full gauge-invariant Raman
response, obtained by accounting for the fluctuations of both the density and
superconducting phase degrees of freedom, is always dominated by the Leggett
mode, regardless its nature. However, while in the case of intra-band dominated
pairing the Josephson-like phase fluctuations of the two condensates identify a
well-defined peak, as observed in MgB$_2$, for dominant interband pairing the
Leggett resonance is pushed at twice the largest gap, resembling apparently a
pair-breaking peak. The latter case is in very good agreement with experimental
data in iron-based superconductors, suggesting that an interband pairing
mechanism should be at play in these systems. These results have also
interesting implications for the non-linear optical response probed by means of
intense THz fields.",1606.04784v2
2016-06-20,Nodeless multiband superconductivity in stoichiometric single crystalline CaKFe$_4$As$_4$,"Measurements of the London penetration depth and tunneling conductance in
single crystals of the recently discovered stoicheometric, iron - based
superconductor, CaKFe$_4$As$_4$ (CaK1144) show nodeless, two effective gap
superconductivity with a larger gap of about 6-9 meV and a smaller gap of about
1-4 meV. Having a critical temperature, $T_{c,onset}\approx$35.8 K, this
material behaves similar to slightly overdoped Ba$_{1-x}$K$_x$)Fe$_2$As$_2$
(e.g. $x=$0.54, $T_c \approx$ 34 K)---a known multigap $s_{\pm}$
superconductor. We conclude that the superconducting behavior of stoichiometric
CaK1144 demonstrates that two-gap $s_{\pm}$ superconductivity is an essential
property of high temperature superconductivity in iron - based superconductors,
independent of the degree of substitutional disorder.",1606.06245v1
2016-06-28,Resonant inelastic x-ray scattering study of entangled spin-orbital excitations in superconducting PrFeAsO0.7,"Low-energy electron excitation spectra were measured on a single crystal of a
typical iron-based superconductor PrFeAsO$_{0.7}$ using resonant inelastic
X-ray scattering (RIXS) at the Fe-$L_3$ edge. Characteristic RIXS features are
clearly observed around 0.5, 1-1.5 and 2-3 eV energy losses. These excitations
are analyzed microscopically with theoretical calculations using a 22-orbital
model derived from first-principles electronic structure calculation. Based on
the agreement with the experiment, the RIXS features are assigned to Fe-$d$
orbital excitations which, at low energies, are accompanied by spin flipping
and dominated by Fe $d_{yz}$ and $d_{xz}$ orbital characters. Furthermore, our
calculations suggest dispersive momentum dependence of the RIXS excitations
below 0.5 eV, and predict remarkable splitting and merging of the lower-energy
excitations in momentum space. Those excitations, which were not observed in
the present experiment, highlight the potential of RIXS with an improved energy
resolution to unravel new details of the electronic structure of the iron-based
superconductors.",1606.08917v2
2016-07-01,"Oxygen, $α$-element and iron abundance distributions in the inner part of the Galactic thin disc. II","We have derived the abundances of 36 chemical elements in one Cepheid star,
ASAS 181024--2049.6, located R$_{\rm G}= 2.53$ kpc from the Galactic center.
This star falls within a region of the inner thin disc poorly sampled in
Cepheids. Our spectral analysis shows that iron, magnesium, silicon, calcium
and titanium LTE abundances in that star support the presence of a plateau-like
abundance distribution in the thin disc within 5 kpc of the Galactic center, as
previously suggested by \cite{Maret15}. If confirmed, the flattening of the
abundance gradient within that region could be the result of a decrease in the
star formation rate due to dynamic effects, possibly from the central Galactic
bar.",1607.00129v1
2016-07-01,Evolution of superconducting gap anisotropy in hole-doped 122 iron pnictides,"Motivated by recent experimental findings, we investigate the evolution of
the superconducting gap anisotropy in 122 iron pnictides as a function of hole
doping. Employing both a functional and a weak coupling renormalization group
approach (FRG and WRG), we analyse the Fermi surface instabilities of an
effective 122 model band structure at different hole dopings x, and derive the
gap anisotropy from the leading superconducting instability. In the transition
regime from collinear magnetism to s_{\pm}-wave, where strong correlations are
present, we employ FRG to identify a non- monotonous change of the gap
anisotropy in qualitative agreement with new experimental findings. From the
WRG, which is asymptotically exact in the weak coupling limit, we find an
s_{\pm}-wave to d-wave transition as a function of hole doping, complementing
previous findings from FRG [Thomale et al., Phys. Rev. Lett. 107, 117001
(2011)]. The gap anisotropy of the s_{\pm}-wave monotonously increases towards
the transition to d-wave as a function of x.",1607.00412v1
2016-07-03,First-Principles Momentum Dependent Local Ansatz Approach to the Ground-State Properties of Iron-Group Transition Metals,"The ground-state properties of iron-group transition metals from Sc to Cu
have been investigated on the basis of the first-principles momentum dependent
local ansatz (MLA) theory. Correlation energy gain is found to show large
values for Mn and Fe: 0.090 Ry (Mn) and 0.094 Ry (Fe). The Hund-rule coupling
energies are found to be 3000 K (Fe), 1400 K (Co), and 300 K (Ni). It is
sugested that these values can resolve the inconsistency in magnetic energy
between the density functional theory and the first-principles dynamical
coherent potential approximation theory at finite temperatures. Charge
fluctuations are shown to be suppressed by the intra-orbital correlations and
inter-orbital charge-charge correlations, so that they show nearly constant
values from V to Fe: 1.57 (V and Cr), 1.52 (Mn), and 1.44 (Fe), which are
roughly twice as large as those obtained by the $d$ band model. The amplitudes
of local moments are enhanced by the intra-orbital and inter-orbital spin-spin
correlations and show large values for Mn and Fe: 2.87 (Mn) and 2.58 (Fe).
These values are in good agreement with the experimental values estimated from
the effective Bohr magneton number and the inner core photoemission data.",1607.00632v1
2016-07-07,Orbital-selective Mott phase of Cu-substituted iron-based Superconductors,"We study the phase transition in Cu-substituted iron-based superconductors
with a new developed real-space Green's function method. We find that Cu
substitution has strong effect on the orbital-selective Mott transition
introduced by the Hund's rule coupling. The redistribution of the orbital
occupancy which is caused by the increase of the Hund's rule coupling, gives
rise to the Mott-Hubbard metal-insulator transition in the half-filled $d_{xy}$
orbital. We also find that more and more electronic states appear inside that
Mott gap of the $d_{xy}$ orbital with the increase of Cu substitution, and the
in-gap states around the Fermi level are strongly localized at some specific
lattice sites. Further, a distinctive phase diagram, obtained for the
Cu-substituted Fe-based superconductors, displays an orbital-selective
insulating phase, as a result of the cooperative effect of the Hund's rule
coupling and the impurity-induced disorder.",1607.01900v1
2016-07-11,Impact of Iron-site defects on Superconductivity in LiFeAs,"In conventional s-wave superconductors, only magnetic impurities exhibit
impurity bound states, whereas for an s+- order parameter they can occur for
both magnetic and non-magnetic impurities. Impurity bound states in
superconductors can thus provide important insight into the order parameter.
Here, we present a combined experimental and theoretical study of native and
engineered iron-site defects in LiFeAs. Detailed comparison of tunneling
spectra measured on impurities with spin fluctuation theory reveals a
continuous evolution from negligible impurity bound state features for weaker
scattering potential to clearly detectable states for somewhat stronger
scattering potentials. All bound states for these intermediate strength
potentials are pinned at or close to the gap edge of the smaller gap, a
phenomenon that we explain and ascribe to multi-orbital physics.",1607.03192v1
2016-07-14,Room temperature polarization in the ferrimagnetic Ga2-xFexO3 ceramics,"The effect of the Fe-Ga ratio on the magnetic and electric properties of the
multiferroic Ga2-xFexO3 compound has been studied in order to determine the
composition range exhibiting magnetic and electric orders coexistence and their
critical temperatures. A magnetoelectric phase diagram, showing the evolution
of both the Neel magnetic ordering temperature and the electric ordering
temperature, versus the iron content has been established for x values between
0.9 and 1.4. While the ferrimagnetic Neel temperature increases with the iron
content, the electric ordering temperature shows an opposite trend. The
electric polarization has been found to exist far above room temperature for
the x value of 1.1 composition which shows the highest observed electric
ordering temperature of approx. 580K. The compounds with x values of 1.3 and
1.4 are ferrimagnetic-electric relaxors with both properties coexisting at room
temperature.",1607.04312v1
2016-07-18,Unified Spin Model for Magnetic Excitations in Iron Chalcogenides,"Recent inelastic neutron scattering (INS) measurements on FeSe and
Fe(Te$_{1-x}$Se$_x$), have sparked intense debate over the nature of the ground
state in these materials. Here we propose an effective bilinear-biquadratic
spin model which is shown to consistently describe the evolution of low-energy
spin excitations in FeSe, both under applied pressure and upon Se/Te
substitution. The phase diagram, studied using a combination of variational
mean-field, flavor-wave calculations, and density-matrix renormalization group
(DMRG), exhibits a sequence of transitions between the columnar antiferromagnet
common to the iron pnictides, the non-magnetic ferroquadrupolar phase
attributed to FeSe, and the double-stripe antiferromagnetic order known to
exist in Fe$_{1+y}$Te. The calculated spin structure factor in these phases
mimics closely that observed with INS in the Fe(Te$_{1-x}$Se$_x$), series. In
addition to the experimentally established phases, the possibility of
incommensurate magnetic order is also predicted.",1607.05295v3
2016-07-28,Modeling many-body physics with Slave-Spin Mean-Field: Mott and Hund's physics in Fe-superconductors,"Slave-spin mean-field theory, a light and accurate technique to model
electronic correlations in Fermi-liquid phases of multi-orbital materials, is
pedagogically exposed in this chapter, with a focus on its recent successful
application to the physics of Iron-based superconductors. Beside introducing
electronic correlations and recalling the Fermi-liquid phenomenology, the
manuscript accompanies the step-by-step explanation of the slave-spin technique
with a set of useful complements providing analytical insight into Mott and
Hund's physics, which are at the heart of the physics of strongly correlated
materials. Some original research material is also exposed, such as the
Hund-induced shrinking of the Hubbard bands flanking the gap of the half-filled
Mott insulator, and the low-energy description of the ""orbital-decoupling""
mechanism.",1607.08468v1
2016-07-31,Spin resonance peak in Fe-based superconductors with unequal gaps,"We study the spin resonance in superconducting state of iron-based materials
within multiband models with two unequal gaps, $\Delta_L$ and $\Delta_S$, on
different Fermi surface pockets. We show that due to the indirect nature of the
gap entering the spin susceptibility at the nesting wave vector $\mathbf{Q}$
the total gap $\tilde\Delta$ in the bare susceptibility is determined by the
sum of gaps on two different Fermi surface sheets connected by $\mathbf{Q}$.
For the Fermi surface geometry characteristic to the most of iron pnictides and
chalcogenides, the indirect gap is either $\tilde\Delta = \Delta_L + \Delta_S$
or $\tilde\Delta = 2\Delta_L$. In the $s_{++}$ state, spin excitations below
$\tilde\Delta$ are absent unless additional scattering mechanisms are assumed.
The spin resonance appears in the $s_\pm$ superconducting state at frequency
$\omega_R \leq \tilde\Delta$. Comparison with available inelastic neutron
scattering data confirms that what is seen is the true spin resonance and not a
peak inherent to the $s_{++}$ state.",1608.00245v2
2016-08-22,Nano-scale Inhomogeneous Superconductivity in Fe(Te1-xSex) Probed by Nanostructure-transport,"Among iron based superconductors, the layered iron chalcogenide Fe(Te1-xSex)
is structurally the simplest and has attracted considerable attentions. It has
been speculated from bulk studies that nanoscale inhomogeneous
superconductivity may inherently exist in this system. However, this has not
been directly observed from nanoscale transport measurements. In this work,
through simple micromechanical exfoliation and high precision low-energy ion
milling thinning, we prepared Fe(Te0.5Se0.5) nano-flake with various thickness
and systematically studied the correlation between the thickness and
superconducting phase transition. Our result revealed a systematic evolution of
superconducting transition with thickness. When the thickness of Fe(Te0.5Se0.5)
flake is reduced down to 12nm, i.e. the characteristic length of Te/Se
fluctuation, the superconducting current path and the metallicity of normal
state in Fe(Te0.5Se0.5) atomic sheets is suppressed. This observation provides
the first direct transport evidence for the nano-scale inhomogeneous nature of
superconductivity in Fe(Te1-xSex).",1608.06332v1
2016-08-29,Impurity effects on spin dynamics in magnetic and superconducting iron pnictides and chalcogenides,"In this paper we summarize the effects of magnetic and nonmagnetic impurities
on the spin dynamics in Febased superconductors and their parent compounds. The
effects of chemical substitution, vacancies, and disorder on the suppression or
stabilization of superconductivity and spin-density-wave phases are reviewed in
the context of recent neutron-spectroscopy measurements of spin excitations. We
also present new results on the structure of magnetic fluctuations in BaFe2As2
single crystals doped with Mn local moments and discuss them in relationship to
the previously reported (pi, pi) branch of checkerboard magnetic excitations.",1608.08123v4
2016-09-05,Cationic Effect on Pressure driven Spin-State Transition and cooperativity in Hybrid Perosvkites,"Hybrid or metal organic framework (MOF) perovskites of general composition,
ABX$_3$, are known to show interesting properties which can lead to variety of
technological applications. Our first principles study shows they are also
potential candidates for exhibiting cooperative spin-state transitions upon
application of external stimuli. We demonstrate this by considering two
specific Fe-based MOF perovskites, namely Dimethylammonium Iron Formate,
[CH$_{3}$NH$_{2}$CH$_{3}$][Fe(HCOO)$_3$] and Hydroxylammonium Iron Formate,
[NH$_{3}$OH][Fe(HCOO)$_3$]. Both the compounds are found to undergo high-spin
(S=2) to low-spin (S=0) transition at Fe(II) site upon application of moderate
strength of hydrostatic pressure, along with large hysteresis. This spin-state
transition is signaled by the changes in electronic, magnetic and optical
properties. We find both the transition pressure and the width of the
hysteresis to be strongly dependent of the choice of A-site cation,
Dimethylammonium or Hydroxylammonium, implying tuning of spin-switching
properties achievable by chemical variation of the amine cation in the
structure. Our finding opens up novel functionalities in this family of
materials of recent interest, which can have important usage in sensors and
memory devices.",1609.01020v1
2016-09-08,Block antiferromagnetism and possible ferroelectricity in KFe$_2$Se$_2$,"Superconductors and multiferroics are two of the hottest branches in
condensed matter physics. The connections between those two fields are
fundamentally meaningful to unify the physical rules of correlated electrons.
Recently, BaFe$_2$Se$_3$, was predicted to be multiferroic [Phys. Rev. Lett.
113, 187204 (2014)] due to its unique one-dimensional block-type
antiferromagnetism. Here, another iron-selenide KFe$_2$Se$_2$, a parent state
of iron-based superconductor, is predicted to be multiferroic. Its
two-dimensional block-type antiferromagnetism can generate a moderate electric
dipole for each Fe-Se layer via the Fe-Se-Fe exchange striction. Different
stacking configurations of these magnetic blocks give closely proximate
energies and thus the ground state of KFe$_2$Se$_2$ may be switchable between
antiferroelectric and ferroelectric phases.",1609.02614v2
2016-09-15,Highly siderophile elements were stripped from Earth's mantle by iron sulfide segregation,"Highly siderophile elements (HSEs) are strongly depleted in the bulk silicate
Earth (BSE) but are present in near-chondritic relative abundances. The
conventional explanation is that the HSEs were stripped from the mantle by the
segregation of metal during core formation but were added back in
near-chondritic proportions by late accretion, after core formation had ceased.
Here we show that metal-silicate equilibration and segregation during Earth's
core formation actually increased HSE mantle concentrations because HSE
partition coefficients are relatively low at the high pressures of core
formation within Earth. The pervasive exsolution and segregation of iron
sulfide liquid from silicate liquid (the ""Hadean matte"") stripped magma oceans
of HSEs during cooling and crystallization, before late accretion, and resulted
in slightly suprachondritic palladium/iridium and ruthenium/iridium ratios.",1609.04751v1
2016-09-16,A new Measurement of Thermal Conductivity of Iron at high pressures and temperatures,"Thermal conductivity of the most abundant element in the planetary core, Iron
(Fe) is measured up to Earth's outer core pressure $\sim 120$ GPa. The
measurements are carried out using the laser heated diamond anvil cell
facility, where the absorbed power by Fe metal foil is calculated using
thermodynamical equation. The thermal conductivity of $\gamma-Fe$ linearly
increases up to a maximum experimental pressure 40 GPa. Thermal conductivity of
$\epsilon-Fe$ measured by us shows a saturated value $\sim$ 52 ($\pm$ 5)
$Wm^{-1}K^{-1}$ in the pressure range 77 - 120 GPa. At different pressures
temperature dependence of thermal conductivity show a sharp drop during
melting, which indicates the formation of liquid layer resulting in a thermal
buffer to the heat conduction.",1609.05088v2
2016-09-26,Topology optimized permanent magnet systems,"Topology optimization of permanent magnet systems consisting of permanent
magnets, high permeability iron and air is presented. An implementation of
topology optimization for magnetostatics is discussed and three examples are
considered. First, the Halbach cylinder is topology optimized with iron and an
increase of 15% in magnetic efficiency is shown, albeit with an increase of 3.8
pp. in field inhomogeneity - a value compared to the inhomogeneity in a 16
segmented Halbach cylinder. Following this a topology optimized structure to
concentrate a homogeneous field is shown to increase the magnitude of the field
by 111% for the chosen dimensions. Finally, a permanent magnet with alternating
high and low field regions is considered. Here a $\Lambda_\mathrm{cool}$ figure
of merit of 0.472 is reached, which is an increase of 100% compared to a
previous optimized design.",1609.08113v2
2016-09-29,Prediction of superconducting iron-bismuth intermetallic compounds at high pressure,"The synthesis of materials in high-pressure experiments has recently
attracted increasing attention, especially since the discovery of record
breaking superconducting temperatures in the sulfur-hydrogen and other
hydrogen-rich systems. Commonly, the initial precursor in a high pressure
experiment contains constituent elements that are known to form compounds at
ambient conditions, however the discovery of high-pressure phases in systems
immiscible under ambient conditions poses an additional materials design
challenge. We performed an extensive multi component $ab\,initio$ structural
search in the immiscible Fe--Bi system at high pressure and report on the
surprising discovery of two stable compounds at pressures above $\approx36$
GPa, FeBi$_2$ and FeBi$_3$. According to our predictions, FeBi$_2$ is a metal
at the border of magnetism with a conventional electron-phonon mediated
superconducting transition temperature of $T_{\rm c}=1.3$ K at 40 GPa. In
analogy to other iron-based materials, FeBi$_2$ is possibly a non-conventional
superconductor with a real $T_{\rm c}$ significantly exceeding the values
obtained within Bardeen-Cooper-Schrieffer (BCS) theory.",1609.09536v1
2016-10-26,Influence of the iron spin crossover in ferropericlase on the lower mantle geotherm,"The iron spin crossover in ferropericlase introduces anomalies in its
thermodynamics and thermoelastic properties. Here we investigate how these
anomalies can affect the lower mantle geotherm. The effect is examined in
mantle aggregates consisting of mixtures of bridgmanite, ferropericlase, and
CaSiO$_3$ perovskite, with different Mg/Si ratios varying from harzburgitic to
perovskitic (Mg/Si$\sim$1.5 to 0.8). We find that the anomalies introduced by
the spin crossover increase the isentropic gradient and thus the geotherm
proportionally to the amount of ferropericlase. The geotherms can be as much as
$\sim$ 200K hotter than the conventional adiabatic geotherm at deep lower
mantle conditions. Aggregate elastic moduli and seismic velocities are also
sensitive to the spin crossover and the geotherm, which impacts analyses of
lower mantle velocities and composition.",1610.08412v2
2016-10-27,Constraining the Kerr parameters via X-ray reflection spectroscopy,"In a recent paper [Ghasemi-Nodehi & Bambi, EPJC 76 (2016) 290], we have
proposed a new parametrization for testing the Kerr nature of astrophysical
black hole candidates. In the present work, we study the possibility of
constraining the ""Kerr parameters"" of our proposal using X-ray reflection
spectroscopy, the so-called iron line method. We simulate observations with the
LAD instrument on board of the future eXTP mission assuming an exposure time of
200~ks. We fit the simulated data to see if the Kerr parameters can be
constrained. If we have the correct astrophysical model, 200~ks observations
with LAD/eXTP can constrain all the Kerr parameters with the exception of
$b_{11}$, whose impact on the iron line profile is extremely weak and its
measurement looks very challenging.",1610.08791v2
2016-10-29,Searching for New Spin-Dependent Interactions with SmCo$_5$ Spin Sources and a SERF Comagnetometer,"We propose a novel method to search for possible new macro-scale spin- and/or
velocity-dependent forces (SVDFs) based on specially designed SmCo$_5$ spin
sources and a spin exchange relaxation-free (SERF) comagnetometer. A simulation
shows that, by covering a SmCo$_5$ permanent magnet with a layer of pure iron,
a high net spin density source of about $1\times 10^{22}$/cm$^3$ could be
obtained. Taking advantages of the high spin density of this iron-shielded
SmCo$_5$ and the high sensitivity of the SERF, the proposed method could set up
new limits of greater than 10 orders of magnitude more sensitive than those
from previous experiments or proposals in exploring SVDFs in force ranges
larger than 1 cm.",1610.09483v1
2016-10-29,Strong correlations and the search for high-Tc superconductivity in chromium pnictides and chalcogenides,"Undoped iron superconductors accommodate $n=6$ electrons in five d-orbitals.
Experimental and theoretical evidence shows that the strength of correlations
increases with hole-doping, as the electronic filling approaches half-filling
with $n=5$ electrons. This evidence delineates a scenario in which the parent
compound of iron superconductors is the half-filled system, in analogy to
cuprate superconductors. In cuprates the superconductivity can be induced upon
electron or hole doping. In this work we propose to search for high-Tc
superconductivity and strong correlations in chromium pnictides and
chalcogenides with $n<5$ electrons. By means of ab-initio, slave spin and
multi-orbital RPA calculations we analyse the strength of the correlations and
the superconducting and magnetic instabilities in these systems with main focus
on LaCrAsO. We find that electron-doped LaCrAsO is a strongly correlated system
with competing magnetic interactions, being $(\pi,\pi)$ antiferromagnetism and
nodal d-wave pairing the most plausible magnetic and superconducting
instabilities, respectively.",1610.09560v1
2016-11-01,Shear softening of Earth's inner core indicated by its high Poisson's ratio and elastic anisotropy,"Earth's inner core exhibits an unusually high Poisson's ratio and noticeable
elastic anisotropy. The mechanisms responsible for these features are critical
for understanding the evolution of the Earth but remain unclear. This study
indicates that once the correct formula for the shear modulus is used, shear
softening can simultaneously explain the high Poisson's ratio and strong
anisotropy of the inner core. Body-centred-cubic (bcc) iron shows shear
instability at the pressures found in the inner-core and can be dynamically
stabilized by temperature and light elements. It is very likely that some
combinations of light elements stabilize the bcc iron alloy under inner-core
conditions. Such a bcc phase would exhibit significant shear softening and
match the geophysical constraints of the inner core. Identifying which light
elements and what concentrations of these elements stabilize the bcc phase will
provide critical information on the light elements of the inner core.",1611.00244v1
2016-11-02,Surface effects on ferromagnetic resonance in magnetic nanocubes,"We study the effect of surface anisotropy on the spectrum of spin-wave
excitations in a magnetic nanocluster and compute the corresponding absorbed
power. For this, we develop a general numerical method based on the (undamped)
Landau-Lifshitz equation, either linearized around the equilibrium state
leading to an eigenvalue problem or solved using a symplectic technique. For
box-shaped clusters, the numerical results are favorably compared to those of
the finite-size linear spin-wave theory. Our numerical method allows us to
disentangle the contributions of the core and surface spins to the spectral
weight and absorbed power. In regard to the recent developments in synthesis
and characterization of assemblies of well defined nano-elements, we study the
effects of free boundaries and surface anisotropy on the spin-wave spectrum in
iron nanocubes and give orders of magnitude of the expected spin-wave
resonances. For an 8 nm iron nanocube, we show that the absorbed power spectrum
should exhibit a low-energy peak around 10 GHz, typical of the uniform mode,
followed by other low-energy features that couple to the uniform mode but with
a stronger contribution from the surface. There are also high-frequency
exchange-mode peaks around 60 GHz.",1611.00614v1
2016-11-08,Orbital selective pairing and gap structures of iron-based superconductors,"We discuss the influence on spin-fluctuation pairing theory of orbital
selective strong correlation effects in Fe-based superconductors, particularly
Fe chalcogenide systems. We propose that a key ingredient for an improved
itinerant pairing theory is orbital selectivity, i.e., incorporating the
reduced coherence of quasiparticles occupying specific orbital states. This
modifies the usual spin-fluctuation via suppression of pair scattering
processes involving those less coherent states and results in orbital selective
Cooper pairing of electrons in the remaining states. We show that this paradigm
yields remarkably good agreement with the experimentally observed anisotropic
gap structures in both bulk and monolayer FeSe, as well as LiFeAs, indicating
that orbital selective Cooper pairing plays a key role in the more strongly
correlated iron-based superconductors.",1611.02643v2
2016-11-09,A possible new family of unconventional high temperature superconductors,"We suggest a new family of Co/Ni-based materials that may host unconventional
high temperature superconductivity (high-T$_c$). These materials carry layered
square lattices with each layer being formed by vertex-shared transition metal
tetrahedra cation-anion complexes. The electronic physics in these materials is
determined by the two dimensional layer and is fully attributed to the three
near degenerated $t_{2g}$ d-orbitals close to a $d^7$ filling configuration in
the d-shell of Co/Ni atoms . The electronic structure meets the necessary
criteria for unconventional high T$_c$ materials proposed recently by us to
unify the two known high-T$_c$ families, cuprates and iron-based
superconductors. We predict that they host superconducting states with a d-wave
pairing symmetry with T$_c$ potentially higher than those of iron-based
superconductors. These materials, if realized, can be a fertile new ground to
study strongly correlated electronic physics and provide decisive evidence for
superconducting pairing mechanism.",1611.02835v1
2016-11-21,Discovery of a novel 112-type iron-pnictide and La-doping induced superconductivity in Eu1-xLaxFeAs2 (x = 0 ~ 0.15),"We report the discovery and characterization of a novel 112-type iron
pnictide EuFeAs2, with La-doping induced superconductivity in a series of
Eu1-xLaxFeAs2. The polycrystalline samples were synthesized through solid state
reaction method only within a very narrow temperature window around 1073 K.
Small single crystals were also grown from a flux method with the size about
100 um. The crystal structure was identified by single crystal X-ray
diffraction analysis as a monoclinic structure with space group of P21/m. From
resistivity and magnetic susceptibility measurements, we found that the parent
compound EuFeAs2 shows a Fe2+ related antiferromagnetic/structural phase
transition near 110 K and a Eu2+ related antiferromagnetic phase transition
near 40 K. La doping suppressed the both phase transitions and induced
superconducting transition with a Tc ~ 11 K for Eu0.85La0.15FeAs2.",1611.06821v1
2016-12-15,Magnetic excitations in the normal and nematic phases of iron pnictides,"In this paper, we study theoretically the behaviors of the magnetic
excitations(MEs) in the normal and nematic phases of iron pnictides. The normal
state MEs exhibit commensurability to diamond and to square-like structure
transition with the increase of energy. This structure transition persists in
the spin and orbital scenarios of nematic phases, although the MEs show
anisotropic behaviors due to the C4 symmetry breaking induced by the nematic
orders. The MEs exhibit distinct energy evolution behaviors between the spin
and orbital scenarios of nematicity. For the spinnematic scenario, the
anisotropy of the MEs persists up to the high energy region. In contrast, for
the orbital-nematic scenario, it reduces dramatically in the low energy region
and is negligible in the high energy region. These distinct behaviors of the
MEs are attributed to the different origins between the spin and orbital
scenarios of nematic orders.",1612.04961v1
2016-12-19,Ultra metal-poor stars: Spectroscopic determination of stellar atmospheric parameters using iron Non-LTE line abundances,"We present new ultra-metal-poor (UMP) stars parameters with [Fe/H]<-4.0 based
on line-by-line non-local thermodynamic equilibrium (NLTE) abundances using an
up-to-date iron model atom with a new recipe for non-elastic hydrogen collision
rates. We study the departures from LTE in their atmospheric parameter and show
that they can grow up to ~1.0 dex in [Fe/H], 150K in Teff and 0.5 dex in log g
toward the lowest metallicities. Accurate NLTE atmospheric stellar parameters,
in particular [Fe/H] being signifcantly higher, are the first step to
eventually providing full NLTE abundance patterns that can be compared with
Population III supernova nucleosynthesis yields to derive properties of the
first stars. Overall, this maximizes the potential of these likely
second-generation stars to investigate the early universe and how the chemical
elements were formed.",1612.06309v2
2016-12-22,Tunable Finite-Sized Chains to Control Magnetic Relaxation,"The magnetic dynamics of low-dimensional iron ion chains have been studied
with regards to the tunable finite-sized chain length using iron phthalocyanine
thin films. The deposition temperature varies the diffusion length during thin
film growth by limiting the average crystal size in the range from 40 to 110
nm. Using a method common for single chain magnets, the magnetic relaxation
time for each chain length is determined from temporal remanence data and fit
to a stretched exponential form in the temperature range below 5 K, the onset
for magnetic hysteresis. A temperature-independent master curve is generated by
scaling the remanence by its relaxation time to fit the energy barrier for spin
reversal, and the single spin relaxation time. The energy barrier of 95 K is
found to be independent of the chain length. In contrast, the single spin
relaxation time increases with longer chains from under 1 ps to 800 ps. We show
that thin films provide the nano-architecture to control magnetic relaxation
and a testbed to study finite-size effects in low-dimensional magnetic systems.",1612.07397v1
2017-01-03,Magnetite nano-islands on silicon-carbide with graphene,"X-ray magnetic circular dichroism (XMCD) measurements of iron nano-islands
grown on graphene and covered with a Au film for passivation reveal that the
oxidation through defects in the Au film spontaneously leads to the formation
of magnetite nano-particles (i.e, $Fe_3$$O_4$). The Fe nano-islands (20 and 75
monolayers; MLs) are grown on epitaxial graphene formed by thermally annealing
6H-SiC(0001) and subsequently covered, in the growth chamber, with nominal 20
layers of Au. Our X-ray absorption spectroscopy and XMCD measurements at
applied magnetic fields show that the thin film (20 ML) is totally converted to
magnetite whereas the thicker film (75 ML) exhibits properties of magnetite but
also those of pure metallic iron. Temperature dependence of the XMCD signal (of
both samples) shows a clear transition at $T_{\rm V}\approx 120$ K consistent
with the Verwey transition of bulk magnetite. These results have implications
on the synthesis of magnetite nano-crystals and also on their regular
arrangements on functional substrates such as graphene.",1701.00861v1
2017-01-10,"Ru-doping on iron based pnictides: the ""unfolded"" dominant role of structural effects for superconductivity","We present an ab-initio study of Ru substitution in two different compounds,
BaFe2As2 and LaFeAsO, pure and F-doped. Despite the many similarities among
them, Ru substitution has very different effects on these compounds. By means
of an unfolding technique, which allows us to trace back the electronic states
into the primitive cell of the pure compounds, we are able to disentangle the
effects brought by the local structural deformations and by the impurity
potential to the states at the Fermi level. Our results are compared with
available experiments and show: i) satisfying agreement of the calculated
electronic properties with experiments, confirming the presence of a magnetic
order on a short range scale; ii) Fermi surfaces strongly dependent on the
internal structural parameters, more than on the impurity potential. These
results enter a widely discussed field in the literature and provide a better
understanding of the role of Ru in iron pnictides: although isovalent to Fe,
the Ru-Fe substitution leads to changes in the band structure at the Fermi
level mainly related to local structural modifications.",1701.02498v1
2017-01-18,Ion beam test results of the Plastic Scintillator Detector of DAMPE,"The DArk Matter Particle Explorer (DAMPE) is one of the four satellites
within Strategic Pioneer Research Program in Space Science of the Chinese
Academy of Science (CAS). DAMPE can detect electrons, photons and ions in a
wide energy range (5 GeV to 10 TeV) and ions up to iron (100GeV to 100 TeV).
Plastic Scintillator Detector (PSD) is one of the four payloads in DAMPE,
providing e/{\gamma} separation and charge identification up to Iron. An ion
beam test was carried out for the Qualification Model of PSD in CERN with
40GeV/u Argon primary beams. The Birk's saturation and charge resolution of PSD
were investigated.",1701.04947v2
2017-01-20,Plasma Effects On Atomic Data For The K-Vacancy States Of Highly Charged Iron Ions,"The main goal of the present work is to estimate the effects of plasma
environment on the atomic parameters associated with the K-vacancy states in
highly charged iron ions within the astrophysical context of accretion disks
around black holes. In order to do this, multiconfiguration Dirac-Fock
computations have been carried out by considering a time averaged
Debye-H\""uckel potential for both the electron-nucleus and electron-electron
interactions. In the present paper, a first sample of results related to the
ionization potentials, the K-thresholds, the transition energies and the
radiative emission rates is reported for the ions Fe 23+ and Fe 24+ .",1701.05757v1
2017-02-01,Nanoscratching of iron: a novel approach to characterize dislocation microstructures,"A new approach for characterizing the dislocation microstructure obtained
from atomistic simulations is introduced, which relies on converting properties
of discrete lines to continuous data. This data is represented by a number of
density and density-like field variables containing detailed information about
properties of the dislocation microstructure. Applying this methodology to
atomistic simulations of nanoscratching in iron reveals a pronounced ""length
scale effect"": With increasing scratching length the number of dislocations
increases but the density of geometrically necessary dislocations remains
constant resulting in decreasing shear stress. During scratching dislocations
are mostly generated at the scratch front. The nucleation rate versus
scratching length has an approximately antisymmetric shape with respect to the
scratch front leading to an almost constant curvature.",1702.00457v3
2017-02-02,Two-temperature equations of state for d-band metals irradiated by femtosecond laser pulses,"The cold curves for energy and pressure of Copper, Iron, and Tantalum were
obtained using methods of the density functional theory. We consider
hydrostatic and uniaxial deformations in the range from double compression of
the initial volume per atom to double stretching. The presence of allotropic
transformation from $\alpha$ - phase of Iron to the hexaferrum with the growth
of pressure is observed. In the case of hydrostatic deformations we also have
obtained analogous cold curves, but with non-zero electronic temperatures in
the range up to 5 eV. The similar volume and electronic temperature ranges have
been considered recently. The behavior of electronic internal energy, pressure,
and density of states was investigated in the volume and temperature ranges
called above. The maximum hydrostatic strains and the types of lattice
instabilities were theoretically predicted for the considered metals. The
influence of high electronic temperature on the electronic heat conductivity
and electric resistivity has been provided for d-band metals by the approach
based on the solution of Boltzmann kinetic equation in $\tau$-approximation.
This data is compared with the results of quantum molecular dynamics for Gold.",1702.00825v3
2017-02-05,First-Principles Momentum Dependent Local Ansatz Approach to the Momentum Distribution Function in Iron-Group Transition Metals,"The momentum distribution function (MDF) bands of iron-group transition
metals from Sc to Cu have been investigated on the basis of the
first-principles momentum dependent local ansatz wavefunction method. It is
found that the MDF for $d$ electrons show a strong momentum dependence and a
large deviation from the Fermi-Dirac distribution function along high-symmetry
lines of the first Brillouin zone, while the $sp$ electrons behave as
independent electrons. In particular, the deviation in bcc Fe (fcc Ni) is shown
to be enhanced by the narrow $e_{g}$ ($t_{2g}$) bands with flat dispersion in
the vicinity of the Fermi level. Mass enhancement factors (MEF) calculated from
the jump on the Fermi surface are also shown to be momentum dependent. Large
mass enhancements of Mn and Fe are found to be caused by spin fluctuations due
to $d$ electrons, while that for Ni is mainly caused by charge fluctuations.
Calculated MEF are consistent with electronic specific heat data as well as the
recent angle resolved photoemission spectroscopy data.",1702.01370v1
2017-02-07,Pure iron grains are rare in the universe,"The abundant forms in which the major elements in the universe exist have
been determined from numerous astronomical observations and meteoritic
analyses. Iron (Fe) is an exception, in that only depletion of gaseous Fe has
been detected in the interstellar medium, suggesting that Fe is condensed into
a solid, possibly the astronomically invisible metal. To determine the primary
form of Fe, we replicated the formation of Fe grains in gaseous ejecta of
evolved stars by means of microgravity experiments. We found that the sticking
probability for formation of Fe grains is extremely small; only several atoms
will stick per hundred thousand collisions, so that homogeneous nucleation of
metallic Fe grains is highly ineffective, even in the Fe-rich ejecta of Type Ia
supernovae. This implies that most Fe is locked up as grains of Fe compounds or
as impurities accreted onto other grains in the interstellar medium.",1702.01921v1
2017-02-07,Anomalous temperature evolution of the electronic structure of FeSe,"We present ARPES data taken from the structurally simplest representative of
iron-based superconductors, FeSe, in a wide temperature range. Apart from the
variations related to the nematic transition, we detect very pronounced shifts
of the dispersions on the scale of hundreds of kelvins. Remarkably, upon
warming the sample up, the band structure has a tendency to relax to the one
predicted by conventional band structure calculations, right opposite to what
is intuitively expected. Our findings shed light on the origin of the dominant
interaction shaping the electronic states responsible for high-temperature
superconductivity in iron-based materials.",1702.02088v1
2017-02-13,"Coexistence of localized and itinerant magnetism in intercalated iron-selenide (Li,Fe)OHFeSe","The electronic structure and magnetism of a new magnetic intercalation
compound (Li0.8Fe0.2)OHFeSe are investigated theoretically. The electronic
structure calculations predict that the Fe in the (Li,Fe)OH intercalated layer
is in +2 valence state, i.e. there is electron doping to the FeSe layer,
resulting in the shrinking of the Fermi surface (FS) pocket around Gamma and a
strong suppression of dynamical spin susceptibility at M in comparison with the
bulk FeSe compound. The ground state of the FeSe layer is a striped
antiferromagnetic (SAFM) metal, while the (Li,Fe)OH layer displays a very weak
localized magnetism, with an interlayer ferromagnetic (FM) coupling between the
FeSe and intercalated (Li,Fe)OH layers. Moreover, the (Li,Fe)OH is more than a
block layer; it is responsible for enhancing the antiferromagnetic (AFM)
correlation in the FeSe layer through interlayer magnetic coupling. We propose
that the magnetic spacer layer introduces a tuning mechanism for spin
fluctuations associated with superconductivity in iron-based superconductors.",1702.03845v1
2017-02-16,Thermal and structural properties of iron at high pressure by molecular dynamics,"We investigate the basic thermal, mechanical and structural properties of
body centred cubic iron ($\alpha$-Fe) at several temperatures and positive
loading by means of Molecular Dynamics simulations in conjunction with the
embedded-atom method potential and its modified counterpart one. Computations
of its thermal properties like average energy and density of atoms, transport
sound velocities at finite temperatures and pressures are detailed studied as
well. Moreover, there are suggestions to obtain hexagonal close- packed
structure ($\varepsilon$-phase) of this metal under positive loading. To
demonstrate that, one can increase sufficiently the pressure of simulated
system at several temperature's ranges; these structural changes depend only on
potential type used. The ensuring structures are studied via the pair radial
distribution functions (PRDF) and precise common- neighbour analysis method
(CNA) as well.",1702.04909v1
2017-02-20,Evolution of magnetism in cerium doped LaCo2P2 crystals: a magnetic phase diagram,"ThCr2Si2-type phosphide ACo2P2 (A=Rare earth elements) has the same structure
as iron arsenides, but their magnetic behaviors are quite distinct. In this
paper, we for the first time grew a series of La1-xCexCo2P2 single crystals
(x=0.0 to1.0), and made structural and magnetic characterizations. This allows
us to carry out a careful investigation on the evolution of magnetism with
cerium content and build a magnetic phase diagram. We found that the
introduction of cerium induces a rapid decrease of c-axis and a change from
ferromagnetic (FM) to antiferromagnetic (AFM) states. By employing
first-principles band-structure calculations, we identify the formation of P-P
bonding with the shortening of c-axis, which effectively drives an increase of
AFM interaction and eventually leads to AFM ordering in the high doping region.
The present study may shed light on the interplay between the structural
collapsing and electronic/magnetic properties in 122 iron pnictides.",1702.05965v1
2017-03-20,Spin-wave excitations in the SDW state of doped iron pnictides,"We investigate the spin-wave excitations in the spin-density wave state of
doped iron pnictides within a five-orbital model. We find that the excitations
along ($\pi, 0$)$\rightarrow$($\pi, \pi$) are very sensitive to the doping
whereas they do not exhibit a similar sensitivity along ($0, 0$) $\rightarrow$
($\pi, 0$). Secondly, anisotropy in the excitations around ($\pi, 0$) with an
elliptical shape grows on moving towards the hole-doped region for low energy,
whereas it decreases for the high-energy excitations on the contrary. Thirdly,
spin-wave spectral weight shifts towards the low-energy region on moving away
from zero doping. We find these features to be in qualitative agreement with
the inelastic neutron-scattering measurements for the doped pnictides.",1703.06601v1
2017-03-20,Iron K$α$ line of Kerr black holes with Proca hair,"We continue our study on the capabilities of present and future X-ray
missions to test the nature of astrophysical black hole candidates via X-ray
reflection spectroscopy and distinguish Kerr black holes from other solutions
of 4-dimensional Einstein's gravity in the presence of a matter field. Here we
investigate the case of Kerr black holes with Proca hair [1]. The analysis of a
sample of these configurations suggests that even extremely hairy black holes
can mimic the iron line profile of the standard Kerr black holes, and, at least
for the configurations of our study, we find that current X-ray missions cannot
distinguish these objects from Kerr black holes. This contrasts with our
previous findings for the case of Kerr black holes with scalar (rather than
Proca) hair [2], even though such comparison may be biased by the limited
sample. Future X-ray missions can detect the presence of Proca hair, but a
theoretical knowledge of the expected intensity profile (currently missing) can
be crucial to obtain strong constraints.",1703.06836v2
2017-03-20,Imaging the Real Space Structure of the Spin Fluctuations in an Iron-based superconductor,"Spin fluctuations are a leading candidate for the pairing mechanism in high
temperature superconductors, supported by the common appearance of a distinct
resonance in the spin susceptibility across the cuprates, iron-based
superconductors and many heavy fermion materials. The information we have about
the spin resonance comes almost exclusively from neutron scattering. Here we
demonstrate that by using low-temperature scanning tunnelling microscopy and
spectroscopy we can characterize the spin resonance in real space. We show that
inelastic tunnelling leads to the characteristic dip-hump feature seen in
tunnelling spectra in high temperature superconductors and that this feature
arises from excitations of the spin fluctuations. Spatial mapping of this
feature near defects allows us to probe non-local properties of the spin
susceptibility and to image its real space structure.",1703.07002v2
2017-04-05,Coexistence of magnetism and superconductivity in separate layers of the iron-based superconductor Li_{1-x}Fe_{x}(OH)Fe_{1-y}Se,"The magnetic properties attributed to the hydroxide layer of
Li1-xFex(OH)Fe1-ySe have been elucidated by the study of superconducting and
nonsuperconducting members of this family. Both ac magnetometry and muon spin
relaxation measurements of nonsuperconductors find a magnetic state existing
below approximately 10 K which exhibits slow relaxation of magnetization. This
magnetic state is accompanied by a low-temperature heat capacity anomaly
present in both superconducting and nonsuperconducting variants suggesting that
the magnetism persists into the superconducting state. The estimated value of
magnetic moment present within the hydroxide layer supports a picture of a
glassy magnetic state, probably comprising clusters of iron ions of varying
cluster sizes distributed within the lithium hydroxide layer.",1704.01492v1
2017-04-16,Highly anisotropic quasiparticle interference patterns in the spin-density wave state of the iron pnictides,"We investigate the impurity scattering induced quasiparticle interference in
the ($\pi, 0$) spin-density wave phase of the iron pnictides. We use a five
orbital tight binding model and our mean field theory in the clean limit
captures key features of the Fermi surface observed in angle-resolved
photoemission. We use a t-matrix formalism to incorporate the effect of doping
induced impurities on this state. The impurities lead to a spatial modulation
of the local density of states about the impurity site, with a periodicity of
$\sim 8a_{{\rm Fe}-{\rm Fe}}$ along the antiferromagnetic direction. The
associated momentum space quasiparticle interference pattern is anisotropic,
with major peaks located at $\sim (\pm \pi/4,0)$, consistent with spectroscopic
imaging scanning tunneling microscopy. We trace the origin of this pattern to
an elliptical contour of constant energy around momentum (0,0), with major axis
oriented along the (0,1) direction, in the mean field electronic structure.",1704.04783v1
2017-04-26,Magnetic Force Microscopy Characterization of Superparamagnetic Iron Oxide Nanoparticles (SPIONs),"Superparamagnetic iron oxide nanoparticles (SPIONs), due to their
controllable sizes, relatively long in vivo half-life and limited
agglomeration, are ideal for biomedical applications such as magnetic labeling,
hyperthermia cancer treatment, targeted drug delivery and for magnetic
resonance imaging (MRI) as contrast enhancement agents. In order to understand
how SPIONs interact with cells and cellular membranes it would be of interest
to characterize individual SPIONs at the nanoscale in physiologically relevant
conditions without labeling them. We demonstrate that Magnetic Force Microscopy
(MFM) can be used to image SPIONs in air as well as in liquid. The magnetic
properties of bare and SiO2 coated SPIONs are compared using MFM. We report
that surface modification using (3-mercaptopropyl)-trimethoxysilane
significantly improves adsorption and distribution of SPIONs on gold surfaces.
To obtain proof of principle that SPIONS can be imaged with MFM inside the cell
we imaged SPIONs buried in thin polymer films (polystyrene (PS) and poly
methyl-methacrylate (PMMA)). This opens the possibility of visualizing SPIONs
inside the cell without any labeling or modifications and present MFM as a
potential magnetic analogue for fluorescence microscopy. The results of these
studies may have a valuable impact for characterization and further development
of biomedical applications of SPIONs and other magnetic nanoparticles.",1704.08316v1
2017-04-27,The utility of a Bayesian analysis of complex models and the study of archeological ${}^{14}$C data,"The paper presents a critical introduction to the complex statistical models
used in ${}^{14}$C dating. The emphasis is on the estimation of the transit
time between a sequence of archeological layers. Although a frequentist
estimation of the parameters is relatively simple, confidence intervals
constructions are not standard as the models are not regular. I argue that that
the Bayesian paradigm is a natural approach to these models. It is simple, and
gives immediate solutions to credible sets, with natural interpretation and
simple construction. Indeed it is the standard tool of ${}^{14}$C analysis.
However and necessarily, the Bayesian approach is based on technical
assumptions that may dominate the scientific conclusion in a hard to predict
way. I exemplify the discussion in two ways. Firstly, I simulate toy models.
Secondly, I analyze a particular data set from the Iron Age period in Tel
Rehov. These data are important to the debate on the absolute time of the Iron
Age I/IIA transition in the Levant, and in particular to the feasibility of the
Bible story about the United Monarchy of David and Solomon. Our conclusion is
that the data in question cannot resolve this debate.",1704.08479v1
2017-05-15,Momentum-dependent susceptibilities and magnetic exchange in bcc iron from supercell DMFT calculations,"We analyze the momentum- and temperature dependences of the magnetic
susceptibilities and magnetic exchange interaction in paramagnetic bcc iron by
a combination of density functional theory and dynamical mean-field theory
(DFT+DMFT). By considering a general derivation of the orbital-resolved
effective model for spin degrees of freedom for Hund's metals, we relate
momentum-dependent susceptibilities in the paramagnetic phase to the magnetic
exchange. We then calculate non-uniform orbital-resolved susceptibilities at
high-symmetry wave vectors by constructing appropriate supercells in the DMFT
approach. Extracting the irreducible parts of susceptibilities with respect to
Hund's exchange interaction, we determine the corresponding orbital-resolved
exchange interactions, which are then interpolated to the whole Brillouin zone.
Using the spherical model we estimate the temperature dependence of the
resulting exchange between local moments.",1705.05296v2
2017-05-15,"Orbital superconductivity, defects and pinned nematic fluctuations in the doped iron chalcogenide FeSe$_{0.45}$Te$_{0.55}$","We demonstrate that the differential conductance, $dI/dV$, measured via
spectroscopic imaging scanning tunneling microscopy in the doped iron
chalcogenide FeSe$_{0.45}$Te$_{0.55}$, possesses a series of characteristic
features that allow one to extract the orbital structure of the superconducting
gaps. This yields nearly isotropic superconducting gaps on the two hole-like
Fermi surfaces, and a strongly anisotropic gap on the electron-like Fermi
surface. Moreover, we show that the pinning of nematic fluctuations by defects
can give rise to a dumbbell-like spatial structure of the induced impurity
bound states, and explains the related $C_2$-symmetry in the Fourier
transformed differential conductance.",1705.05384v1
2017-05-16,A large moment antiferromagnetic order in overdoped high-Tc superconductor 154SmFeAsO1-xDx,"In iron-based superconductors, high critical temperature (Tc)
superconductivity over 50 K has only been accomplished in electron-doped
hREFeAsO (hRE = heavy rare earth (RE) element). While hREFeAsO has the highest
bulk Tc (58 K), progress in understanding its physical properties has been
relatively slow due to difficulties in achieving high concentration
electron-doping and carrying out neutron-experiments. Here, we present a
systematic neutron powder diffraction (NPD) study of 154SmFeAsO1-xDx, and the
discovery of a new long-range antiferromagnetic ordering with x >= 0.56 (AFM2)
accompanying a structural transition from tetragonal to orthorhombic.
Surprisingly, the Fe magnetic moment in AFM2 reaches a magnitude of 2.73
muB/Fe, which is the largest in all non-doped iron pnictides and chalcogenides.
Theoretical calculations suggest that the AFM2 phase originates in kinetic
frustration of the Fe-3dxy orbital, in which the nearest neighbor hopping
parameter becomes zero. The unique phase diagram, i. e., highest-Tc
superconducting phase is adjacent to the strongly correlated phase in
electron-overdoped regime, yields important clues to the unconventional origins
of superconductivity.",1705.05504v1
2017-05-02,"Nesting-induced Local Electronic Patterns around a Single As (Te, Se) Vacancy in Iron-based Superconductors","The local electronic states around a single As (Te, Se) vacancy are
investigated in order to shed light on the role of ligands in a series of
iron-based superconductors. Such a vacancy can produce a local hopping
correction ranging from $-0.22$ eV to 0.12 eV and always induce two in-gap
resonance peaks in the local density of states (LDOS) at the fixed symmetrical
bias voltages, which are rather robust and irrelevant to the phase of
superconducting order parameter. The LDOS images near the defect predominantly
possess $0^o$ and $45^o$ stripes. These energy-dependent charge modulations
created by quasiparticle interference are originated in the nesting effect
between the inner (outer) hole Fermi surface around $\Gamma$ point and the
inner (outer) electron Fermi surface around $M$ point.",1705.06570v1
2017-06-06,"A uniform metallicity in the outskirts of massive, nearby galaxy clusters","Suzaku measurements of a homogeneous metal distribution of $Z\sim0.3$ Solar
in the outskirts of the nearby Perseus cluster suggest that chemical elements
were deposited and mixed into the intergalactic medium before clusters formed,
likely over 10 billion years ago. A key prediction of this early enrichment
scenario is that the intracluster medium in all massive clusters should be
uniformly enriched to a similar level. Here, we confirm this prediction by
determining the iron abundances in the outskirts ($r>0.25r_{200}$) of a sample
of ten other nearby galaxy clusters observed with Suzaku for which robust
measurements based on the Fe-K lines can be made. Across our sample the iron
abundances are consistent with a constant value, $Z_{\rm Fe}=0.316\pm0.012$
Solar ($\chi^2=28.85$ for 25 degrees of freedom). This is remarkably similar to
the measurements for the Perseus cluster of $Z_{\rm Fe}=0.314\pm0.012$ Solar,
using the Solar abundance scale of Asplund et al. (2009).",1706.01567v2
2017-06-06,Comparison of the Structure Function F2 as Measured by Charged Lepton and Neutrino Scattering from Iron Targets,"A comparison study of world data for the structure function F2 for Iron, as
measured by both charged lepton and neutrino scattering experiments, is
presented. Consistency of results for both charged lepton and neutrino
scattering is observed for the full global data set in the valence regime.
Consistency is also observed at low x for the various neutrino data sets, as
well as for the charged lepton data sets, independently. However, data from the
two probes exhibit differences on the order of 15% in the
shadowing/anti-shadowing transition region where the Bjorken scaling variable x
is < 0.15. This observation is indicative that neutrino probes of nucleon
structure might be sensitive to different nuclear effects than charged lepton
probes. Details and results of the data comparison are here presented.",1706.02002v1
2017-06-08,Characterization of physicochemical and colloidal properties of hydrogel chitosan-coated iron-oxide nanoparticles for cancer therapy,"Superparamagnetic iron oxide nanoparticles have recently been investigated
for their potential to kill cancer cells with promising results, owing to their
ability to be targeted and heated by magnetic fields. In this study, novel
hydrogel, chitosan Fe3O4 magnetic nanoparticles were synthesized to induce
magnetic hyperthermia, and targeted delivering of chemotherapeutics in the
cancer microenvironment. The characteristic properties of synthesized bare and
CS-MNPs were analyzed by various analytical methods: X-ray diffraction, Fourier
transformed infrared spectroscopy, Scanning electron microscopy and
Thermo-gravimetric analysis/differential thermal analysis. Magnetic
nanoparticles were successfully synthesized using the co-precipitation method.
This synthesis technique resulted in nanoparticles with an average particle
size of 16 nm. The pure obtained nanoparticles were then successfully
encapsulated with 4-nm-thick chitosan coating. The formation of chitosan on the
surface of nanoparticles was confirmed by physicochemical analyses. Heating
experiments at safe magnetic field (f = 100 kHz, H =10-20 kA m-1) revealed that
the maximum achieved temperature of water stable chitosan-coated nanoparticles
(50 mg ml-1) is fully in agreement with cancer therapy and biomedical
applications.",1706.02590v1
2017-06-19,Competing Ferromagnetic and Anti-Ferromagnetic interactions in Iron Nitride $ζ$-Fe$_2$N,"The paper discusses the magnetic state of zeta phase of iron nitride viz.
$\zeta$-Fe$_2$N on the basis of spin polarized first principles electronic
structure calculations together with a review of already published data.
Results of our first principles study suggest that the ground state of
$\zeta$-Fe$_2$N is ferromagnetic (FM) with a magnetic moment of 1.528
$\mu_\text{B}$ on the Fe site. The FM ground state is lower than the
anti-ferromagnetic (AFM) state by 8.44 meV and non-magnetic(NM) state by 191
meV per formula unit. These results are important in view of reports which
claim that $\zeta$-Fe$_2$N undergoes an AFM transition below 10K and others
which do not observe any magnetic transition up to 4.2K. We argue that the
experimental results of AFM transition below 10K are inconclusive and we
propose the presence of competing FM and AFM superexchange interactions between
Fe sites mediated by nitrogen atoms, which are consistent with
Goodenough-Kanamori-Anderson rules. We find that the anti-ferromagnetically
coupled Fe sites are outnumbered by ferromagnetically coupled Fe sites leading
to a stable FM ground state. A Stoner analysis of the results also supports our
claim of a FM ground state.",1706.05879v1
2017-06-20,Spatially resolved Fe K spectroscopy of NGC 4945,"We present the imaging and spectroscopic analysis of the combined Chandra
ACIS-S observations of the Compton-thick Seyfert 2 galaxy NGC 4945. We
performed a spatially-resolved spectroscopy of the circumnuclear environment of
the source, picturing the innermost 200 parsecs around the highly absorbed
nucleus. The additional 200 ks ACIS-S data with respect to the previous
campaign allowed us to map with even greater detail the central structure of
this source and to discover an enhanced iron emission in the innermost nuclear
region, with respect to the associated Compton reflection continuum. We
revealed that the Equivalent Width of the iron K$\alpha$ line is spatially
variable (ranging from 0.5 to 3 keV), on scales of tens of parsecs, likely due
to the ionization state and orientation effects of the reprocessing material,
with respect to the central X-ray illuminating source. A clump of highly
ionized Fe XXV He-$\alpha$ is also detected, 40 parsecs east to the nucleus.
When observations taken years apart are considered, the central unresolved
reflected emission is found to remain constant.",1706.06362v1
2017-06-25,Local stability and global instability in iron-opaque disks,"The thermal stability of accretion disk and the possibility to see a
limit-cycle behaviour strongly depends on the ability of the disk plasma to
cool down. Various processes connected with radiation-matter interaction
appearing in hot accretion disk plasma contribute to opacity. For the case of
geometrically thin and optically thick accretion disk, we can estimate the
influence of several different components of function \kappa, given by the
Roseland mean. In the case of high temperatures, the electron Thomson
scattering is dominant. At lower temperatures atomic processes become
important. The slope d log \kappa/d log T can have locally stabilizing or
destabilizing effect on the disk. Although the local MHD simulation postulate
the stabilizing influence of the atomic processes, only the global
time-dependent model can reveal the global disk stability range estimation.
This is due to global diffusive nature of that processes. In this paper, using
previously tested GLADIS code with modified prescription of the viscous
dissipation, we examine the stabilizing effect of the Iron Opacity Bump.",1706.08180v1
2017-06-30,Achieving DFT accuracy with a machine-learning interatomic potential: thermomechanics and defects in bcc ferromagnetic iron,"We show that the Gaussian Approximation Potential machine learning framework
can describe complex magnetic potential energy surfaces, taking ferromagnetic
iron as a paradigmatic challenging case. The training database includes total
energies, forces, and stresses obtained from density-functional theory in the
generalized-gradient approximation, and comprises approximately 150,000 local
atomic environments, ranging from pristine and defected bulk configurations to
surfaces and generalized stacking faults with different crystallographic
orientations. We find the structural, vibrational and thermodynamic properties
of the GAP model to be in excellent agreement with those obtained directly from
first-principles electronic-structure calculations. There is good
transferability to quantities, such as Peierls energy barriers, which are
determined to a large extent by atomic configurations that were not part of the
training set. We observe the benefit and the need of using highly converged
electronic-structure calculations to sample a target potential energy surface.
The end result is a systematically improvable potential that can achieve the
same accuracy of density-functional theory calculations, but at a fraction of
the computational cost.",1706.10229v1
2017-07-13,Towards the ab initio based theory of the phase transformations in iron and steel,"Despite of the appearance of numerous new materials, the iron based alloys
and steels continue to play an essential role in modern technology. The
properties of a steel are determined by its structural state (ferrite,
cementite, pearlite, bainite, martensite, and their combination) that is formed
under thermal treatment as a result of the shear lattice reconstruction ""gamma""
(fcc) -> ""alpha"" (bcc) and carbon diffusion redistribution. We present a review
on a recent progress in the development of a quantitative theory of the phase
transformations and microstructure formation in steel that is based on an ab
initio parameterization of the Ginzburg-Landau free energy functional. The
results of computer modeling describe the regular change of transformation
scenario under cooling from ferritic (nucleation and diffusion-controlled
growth of the ""alpha"" phase to martensitic (the shear lattice instability
""gamma"" -> ""alpha""). It has been shown that the increase in short-range
magnetic order with decreasing the temperature plays a key role in the change
of transformation scenarios. Phase-field modeling in the framework of a
discussed approach demonstrates the typical transformation patterns.",1707.04287v1
2017-07-26,Evidence of Spontaneous Vortex Ground State in An Iron-Based Ferromagnetic Superconductor,"Spontaneous vortex phase (SVP) is an exotic quantum matter in which quantized
superconducting vortices form in the absence of external magnetic field.
Although being predicted theoretically nearly 40 years ago, its rigorous
experimental verification still appears to be lacking. Here we present
low-field magnetic measurements on single crystals of the iron-based
ferromagnetic superconductor Eu(Fe$_{0.91}$Rh$_{0.09}$)$_{2}$As$_{2}$ which
undergoes a superconducting transition at $T_\mathrm{sc}$ = 19.6 K followed by
a magnetic transition at $T_\mathrm{m}$ = 16.8 K. We observe a characteristic
first-order transition from a Meissner state within
$T_\mathrm{m}<T<T_\mathrm{sc}$ to an SVP below $T_\mathrm{m}$, under a magnetic
field approaching zero. Additional isothermal magnetization and ac
magnetization measurements at $T\ll T_\mathrm{sc}$ confirm that the system is
intrinsically in a spontaneous-vortex ground state. The unambiguous
demonstration of SVP in the title material lays a solid foundation for future
imaging and spectroscopic studies on this intriguing quantum matter.",1707.08420v1
2017-07-27,Impact of Disorder on the Superconducting Phase Diagram in BaFe$_2$(As$_{1-x}$P$_x$)$_2$,"In many classes of unconventional superconductors, the question of whether
the superconductivity is enhanced by the quantum-critical fluctuations on the
verge of an ordered phase remains elusive. One of the most direct ways of
addressing this issue is to investigate how the superconducting dome traces a
shift of the ordered phase. Here, we study how the phase diagram of the
iron-based superconductor BaFe$_2$(As$_{1-x}$P$_x$)$_2$ changes with disorder
via electron irradiation, which keeps the carrier concentrations intact. With
increasing disorder, we find that the magneto-structural transition is
suppressed, indicating that the critical concentration is shifted to the lower
side. Although the superconducting transition temperature $T_c$ is depressed at
high concentrations ($x\gtrsim$0.28), it shows an initial increase at lower
$x$. This implies that the superconducting dome tracks the shift of the
antiferromagnetic phase, supporting the view of the crucial role played by
quantum-critical fluctuations in enhancing superconductivity in this iron-based
high-$T_c$ family.",1707.08670v1
2017-08-03,Spin Resonance in the New-Structure-Type Iron-Based Superconductor CaKFe4As4,"The dynamical spin susceptibility in the new-structure-type iron-based
superconductor CaKFe$_4$As$_4$ was investigated by using a combination of
inelastic neutron scattering (INS) measurements and random phase approximation
(RPA) calculations. Powder INS measurements show that the spin resonance at
$Q_\text{res}=1.17(1)$~$\text{\AA}^{-1}$, corresponding to the $(\pi,\pi)$
nesting wave vector in tetragonal notation, evolves below $T_\text{c}$. The
characteristic energy of the spin resonance $E_\text{res}=12.5$~meV is smaller
than twice the size of the superconducting gap ($2\Delta$). The broad energy
feature of the dynamical susceptibility of the spin resonance can be explained
by the RPA calculations, in which the different superconducting gaps on
different Fermi surfaces are taken into account. Our INS and PRA studies
demonstrate that the superconducting pairing nature in CaKFe$_4$As$_4$ is the
$s_\pm$ symmetry.",1708.01006v2
2017-08-09,Bubble Magnetometry of Nanoparticle Heterogeneity and Interaction,"Bubbles have a rich history as transducers in particle-physics experiments.
In a solid-state analogue, we use bubble domains in nanomagnetic films to
measure magnetic nanoparticles. This technique can determine the magnetic
orientation of a single nanoparticle in a fraction of a second, and generate a
full hysteresis loop in a few seconds, which is much faster than any other
reported technique. We achieve this unprecedented speed by tuning the
nanomagnetic properties of the films, including the Dzyaloshinskii-Moriya
interaction, in the first application of topological protection from the
skyrmion state to a nanoparticle sensor. We demonstrate the technique on
iron/nickel nanorods and iron oxide nanoparticles, which delineate a wide range
of properties and applications. Bubble magnetometry enables the first
measurement with high throughput for statistical analysis of the magnetic
hysteresis of dispersed nanoparticles, and the first direct measurement of a
transition from superparamagnetic behavior as single nanoparticles to
collective behavior in nanoscale agglomerates. These results demonstrate a
breakthrough capability for measuring the heterogeneity and interaction of
magnetic nanoparticles.",1708.02706v2
2017-08-11,Critical divergence of the symmetric ($A_{1g}$) nonlinear elastoresistance near the nematic transition in an iron-based superconductor,"We report the observation of a nonlinear elastoresistivity response for the
prototypical underdoped iron pnictide Ba(Fe$_{0.975}$Co$_{0.025}$)$_2$As$_2$.
Our measurements reveal a large quadratic term in the isotropic ($A_{1g}$)
electronic response that was produced by a purely shear ($B_{2g}$) strain. The
divergence of this quantity upon cooling towards the structural phase
transition reflects the temperature dependence of the nematic susceptibility.
This observation shows that nematic fluctuations play a significant role in
determining even the isotropic properties of this family of compounds.",1708.03682v1
2017-08-21,Solar Line Asymmetries: Modelling the Effect of Granulation on the Solar Spectrum,"A parametric model of granulation employing a small number of parameters was
developed. Synthetic spectra calculated using this model closely match observed
spectra and, in particular, reproduce the asymmetries observed in spectral
lines. Both the microturbulent motions and the large-scale flow velocity
decrease exponentially with a scale height of 368 km as the height within the
photosphere increases. The model agrees with observations of the solar
granulation (from which it was derived).
  The horizontal motions associated with granulation were found and used to
calculate spectra emergent away from disk centre. These calculated spectra were
compared to observed spectra, with the agreement supporting the accuracy of the
granular model.
  Also in the course of this work, the Brueckner-O'Mara damping theory was
found to predict damping constants accurately. The photospheric abundances of a
number of elements were determined. The abundance obtained for iron agrees with
the meteoric iron abundance. Astrophysical f-values for some lines were also
determined.",1708.06408v1
2017-08-27,Electronic and spin dynamics in the insulating iron pnictide NaFe$_{0.5}$Cu$_{0.5}$As,"NaFe$_{0.5}$Cu$_{0.5}$As represents a rare exception in the metallic iron
pnictide family, in which a small insulating gap is opened. Based on
first-principles study, we provide a comprehensive theoretical characterization
of this insulating compound. The Fe$^{3+} $spin degree of freedom is quantified
as a quasi-1D $S=\frac{5}{2}$ Heisenberg model. The itinerant As hole state is
downfolded to a $p_{xy}$-orbital hopping model on a square lattice. A unique
orbital-dependent Hund's coupling between the spin and the hole is revealed.
Several important material properties are analyzed, including (a) factors
affecting the small $p-d$ charge-transfer gap; (b) role of the extra interchain
Fe; and (c) the quasi-1D spin excitation in the Fe chains. The experimental
manifestations of these properties are discussed.",1708.08065v1
2017-09-09,Nature of the electromagnetic force between classical magnetic dipoles,"The Lorentz force law of classical electrodynamics states that the force F
exerted by the magnetic induction B on a particle of charge q moving with
velocity V is given by F=qVxB. Since this force is orthogonal to the direction
of motion, the magnetic field is said to be incapable of performing mechanical
work. Yet there is no denying that a permanent magnet can readily perform
mechanical work by pushing/pulling on another permanent magnet -- or by
attracting pieces of magnetizable material such as scrap iron or iron filings.
We explain this apparent contradiction by examining the magnetic Lorentz force
acting on an Amperian current loop, which is the model for a magnetic dipole.
We then extend the discussion by analyzing the Einstein-Laub model of magnetic
dipoles in the presence of external magnetic fields.",1709.02921v1
2017-09-10,High pressure growth and electron transport properties of superconducting SmFeAsO1-xHx single crystals,"We report the single crystal growth and characterization of the highest Tc
iron-based superconductor SmFeAsO1-xHx. Some sub-millimeter-sized crystals were
grown using the mixture flux of Na3As + 3NaH + As at 3.0 GPa and 1473 K. The
chemical composition analyses confirmed 10% substitution of hydrogen for the
oxygen site (x = 0.10), however, the structural analyses suggested that the
obtained crystal forms a multi-domain structure. By using the FIB technique we
fabricated the single domain SmFeAsO0.9H0.10 crystal with the Tc of 42 K, and
revealed the metallic conduction in in-plane (rhoab), while semiconducting in
the out-of-plane (rhoc). From the in-plane Hall coefficient measurements, we
confirmed that the dominant carrier of SmFeAsO0.9H0.10 crystal is an electron,
and the hydride ion occupied at the site of the oxygen ion effectively supplies
a carrier electron per iron following the equation: O2- = H- + e-.",1709.03049v1
2017-09-08,Ultrafast carbon monoxide photolysis and heme spin-crossover in myoglobin via nonadiabatic quantum dynamics,"Light absorption of myoglobin triggers diatomic ligand photolysis and spin
crossover transition of iron(II) that initiate protein conformational change.
The photolysis and spin crossover reactions happen concurrently on a
femtosecond timescale. The microscopic origin of these reactions remains
controversial. Here, we apply quantum wavepacket dynamics to elucidate the
ultrafast photochemical mechanism for a heme--carbon monoxide (heme--CO)
complex. We observe coherent oscillations of the Fe-CO bond distance with a
period of 42 fs and an amplitude of $\sim$1 \AA{}. These nuclear motions induce
pronounced geometric reorganization, which makes the CO dissociation
irreversible. The reaction is initially dominated by symmetry breaking
vibrations inducing an electron transfer from porphyrin to iron. Subsequently,
the wavepacket relaxes to the triplet manifold in $\sim$75 fs and to the
quintet manifold in $\sim$430 fs. Our results highlight the central role of
nuclear vibrations at the origin of the ultrafast photodynamics of
organometallic complexes.",1709.03402v4
2017-09-26,Frustrated spin order and stripe fluctuations in FeSe,"The charge and spin dynamics of the structurally simplest iron-based
superconductor, FeSe, may hold the key to understanding the physics of high
temperature superconductors in general. Unlike the iron pnictides, FeSe lacks
long range magnetic order in spite of a similar structural transition around
90\,K. Here, we report results of Raman scattering experiments as a function of
temperature and polarization and simulations based on exact diagonalization of
a frustrated spin model. Both experiment and theory find a persistent low
energy peak close to 500cm$^{-1}$ in $B_{1g}$ symmetry, which softens slightly
around 100\,K, that we assign to spin excitations. By comparing with results
from neutron scattering, this study provides evidence for nearly frustrated
stripe order in FeSe.",1709.08998v3
2017-10-18,Quantum Phase transition under pressure in a heavily hydrogen-doped iron-based superconductor LaFeAsO,"Hydrogen (H)-doped LaFeAsO is a prototypical iron-based superconductor.
However, its phase diagram extends beyond the standard framework, where a
superconducting (SC) phase follows an antiferromagnetic (AF) phase upon carrier
doping; instead, the SC phase is sandwiched between two AF phases appearing in
lightly and heavily H-doped regimes. We performed nuclear magnetic resonance
(NMR) measurements under pressure, focusing on the second AF phase in the
heavily H-doped regime. The second AF phase is strongly suppressed when a
pressure of 3.0 GPa is applied, and apparently shifts to a highly H-doped
regime, thereby a ""bare"" quantum critical point (QCP) emerges. A quantum
critical regime emerges in a paramagnetic state near the QCP, however, the
influence of the AF critical fluctuations to the SC phase is limited in the
narrow doping regime near the QCP. The optimal SC condition ($T_c \sim$ 48 K)
is unaffected by AF fluctuations.",1710.06640v1
2017-10-25,Determination of the Superconducting Order Parameter from Defect Bound State Quasiparticle Interference,"The superconducting order parameter is directly related to the pairing
interaction, with the amplitude determined by the interaction strength, while
the phase reflects the spatial structure of the interaction. However, given the
large variety of materials and their rich physical properties within the
iron-based high-Tc superconductors, the structure of the order parameter
remains controversial in many cases. Here, we introduce Defect Bound State
Quasi Particle Interference (DBS-QPI) as a new method to determine the
superconducting order parameter. Using a low-temperature scanning tunneling
microscope, we image in-gap bound states in the stoichiometric iron-based
superconductor LiFeAs and show that the bound states induced by defect
scattering are formed from Bogoliubov quasiparticles that have significant
spatial extent. Quasiparticle interference from these bound states has unique
signatures from which one can determine the phase of the order parameter as
well as the nature of the defect, i.e. whether it is better described as a
magnetic vs a nonmagnetic scatterer. DBS-QPI provides an easy but general
method to characterize the pairing symmetry of superconducting condensates.",1710.09089v1
2017-10-30,X-ray reflection from the inner disk of the AGN Ton S180,"We analyse a long archival XMM-Newton observation of the narrow-line Seyfert
1 galaxy Ton S180, using the latest reflection models to explore the high
quality X-ray spectrum. We find that the iron line is relatively narrow and
sharp, and the soft excess is extremely smooth. We cannot find an acceptable
reflection model that describes both components, and conclude that the soft
excess cannot be produced by relativistic reflection. Fitting the 3-10 keV band
with relativistic reflection to model the iron line strongly prefers low spin
values (< 0.4), with the exact value depending on the model and not well
constrained. We then model the broad- band spectrum with a two-component
Comptonization continuum plus relativistic reflection. This gives a much better
fit than a pure reflection model, which again prefers a low spin value. The
photon index of the reflection component is intermediate between the two
Comptoniza- tion components, suggesting that both illuminate the disk a similar
amount and therefore both contribute to the reflection.",1710.11166v1
2017-11-08,Effect of density of states peculiarities on Hund's metal behavior,"We investigate a possibility of Hund's metal behavior in the Hubbard model
with asymmetric density of states having peak(s). Specifically, we consider the
degenerate two-band model and compare its results to the five-band model with
realistic density of states of iron and nickel, showing that the obtained
results are more general, provided that the hybridization between states of
different symmetry is sufficiently small. We find that quasiparticle damping
and the formation of local magnetic moments due to Hund's exchange interaction
are enhanced by both, the density of states asymmetry, which yields stronger
correlated electron or hole excitations, and the larger density of states at
the Fermi level, increasing the number of virtual electron-hole excitations.
For realistic densities of states these two factors are often interrelated
because the Fermi level is attracted towards peaks of the density of states. We
discuss the implication of the obtained results to various substances and
compounds, such as transition metals, iron pnictides, and cuprates.",1711.02991v3
2017-11-15,Phase-sensitive evidence for the sign-reversal s+- symmetry of the order parameter in an iron-pnictide superconductor using Nb/Ba1-xNaxFe2As2 Josephson junctions,"Josephson current between two superconductors provides a phase sensitive tool
for probing their pairing symmetries. Here we fabricate and study
experimentally high-quality Josephson junctions between a conventional s-wave
superconductor Nb and a multi-band iron-pnictide Ba$_{1-x}$Na$_x$Fe$_2$As$_2$.
Junctions exhibit a large enough critical current density to preclude the
d-wave symmetry of the order parameter in the pnictide. However, the $I_cR_n$
product is very small $\simeq 3~\mu$V, which is not consistent with the
sign-preserving $s_{++}$ symmetry either. We argue that the small $I_cR_n$
value along with its unusual temperature dependence provide evidence for the
$s_{\pm}$ symmetry of the order parameter in Ba$_{1-x}$Na$_x$Fe$_2$As$_2$. We
conclude that it is the phase sensitivity of our junctions that leads to an
almost complete (bellow a sub-percent) cancellation of opposite supercurrents
from the sign-reversal $s_{\pm}$ bands in the pnictide.",1711.05718v2
2017-11-17,"Nematicity, magnetism and superconductivity in FeSe","Iron-based superconductors are well known for their complex interplay between
structure, magnetism and superconductivity. FeSe offers a particularly
fascinating example. This material has been intensely discussed because of its
extended nematic phase, whose relationship with magnetism is not obvious.
Superconductivity in FeSe is highly tunable, with the superconducting
transition temperature, $T_\mathrm{c}$, ranging from 8 K in bulk single
crystals at ambient pressure to almost 40 K under pressure or in intercalated
systems, and to even higher temperatures in thin films. In this topical review,
we present an overview of nematicity, magnetism and superconductivity, and
discuss the interplay of these phases in FeSe. We focus on bulk FeSe and the
effects of physical pressure and chemical substitutions as tuning parameters.
The experimental results are discussed in the context of the well-studied
iron-pnictide superconductors and interpretations from theoretical approaches
are presented.",1711.06473v1
2017-11-28,Doping evolution of the anisotropic upper critical fields in iron-based superconductor Ba$_{1-x}$K$_x$Fe$_2$As$_2$,"In-plane resistivity measurements as a function of temperature and magnetic
field up to 35~T with precise orientation within the crystallographic
$ac-$plane were used to study the upper critical field, $H_{c2}$, of the
hole-doped iron-based superconductor Ba$_{1-x}$K$_x$Fe$_2$As$_2$. Compositions
of the samples studied were spanning from underdoped $x=$0.17 ($T_c$=12~K) and
$x$=0.22 ($T_c$=20~K), both in the coexistence range of stripe magnetism and
superconductivity, though optimal doping $x$=0.39 ($T_c$=38.4~K), $x$=0.47
($T_c$=37.2~K), to overdoped $x$=0.65 ($T_c$=22~K), $x$=0.83 ($T_c$=10~K). We
find notable doping asymmetry of the shapes of the anisotropic $H_{c2}(T)$
suggesting important role of paramagnetic limiting effects in $H \parallel a$
configuration in overdoped compositions and multi-band effects in underdoped
compositions.",1711.10094v1
2017-11-30,"Iron superhydrides FeH5 and FeH6: stability, electronic properties and superconductivity","Recently a big number of works devoted to search for new hydrides with record
high-temperature superconductivity and at the same time the successful
synthesis of potential high-TC superconducting FeH5 was reported. We present a
systematic search for stable compounds in the Fe-H system using
variable-composition version of the evolutionary algorithm USPEX. All known
(FeH, FeH3, FeH5) and several new Fe3H5, Fe3H13 and FeH6 iron hydrides were
found to be stable, resulting in a very complex phase diagram with rich
structural relationships between phases. We calculate electronic properties of
two potentially high-TC FeH5 and FeH6 phases in the pressure range from 150 to
300 GPa. Indeed, hydrogen-rich FeH5 and FeH6 phases were found to be
superconducting within Bardeen-Cooper-Schrieffer theory, with TC values of up
to 46 K.",1711.11352v3
2017-12-12,Substitution- and Strain-induced Magnetic Phase Transition in Iron Carbide,"Cementite-type carbides are of interest for magnetocaloric applications owing
to their temperature- or pressure-induced magnetic phase transition. Here,
using first-principles calculations, we investigate the magnetism and the
magnetic phase transition in iron carbide (Fe3C) with the substitution of Cr
atoms at Fe sites with the strain effect. The presence of Cr atoms is found to
give rise to a second-order magnetic phase transition from a ferromagnetic
phase for Fe3C to a nonmagnetic phase in chromium carbide (Cr3C).While the
ternary Fe2CrC and Cr2FeC compounds prefer the ferrimagnetic ground state, the
magnitudes of both the Fe and Cr spin moments, which are antiparallel in
orientation, decrease as x increases in Fe3-xCrxC (x = 0, 1, 2, and 3).
Furthermore, the fixed spin-moment calculations indicate that the magnetization
of Fe3-xCrxC compounds can be delicately altered via the strain effect and that
the magnetic-nonmagnetic phase transition occurs at an early stage of Cr
substitution, x = 2.",1712.04128v1
2017-12-12,In situ annealing effects on the iron-based ladder material BaFe_2S_3: A route to improve the crystal quality,"We have grown single crystals of the iron-based ladder material BaFe_2S_3,
which is superconductive under high pressure, adopting different conditions. By
comparing the behaviors of these samples, it is found that the in situ
annealing process can affect the crystal structure and the electrical
transport, enhance the antiferromagnetic transition temperature, and reduce the
extrinsic ferromagnetic component of the system. An in-depth analysis indicates
that the crystal quality is improved by the in situ annealing in terms of
reducing both the Fe deficiency and the Fe impurity in the samples. The
improvement of the sample quality will facilitate the investigations on the
intrinsic properties of this material.",1712.04241v1
2017-12-25,"Magnon and Phonon Dispersion, Lifetime and Thermal Conductivity of Iron from Spin-Lattice Dynamics Simulations","In recent years, the fundamental physics of spin-thermal (i.e.,
magnon-phonon) interaction has attracted significant experimental and
theoretical interests given its potential paradigm-shifting impacts in areas
like spin-thermoelectrics, spin-caloritronics and spintronics. Modelling
studies of the transport of magnons and phonons in magnetic crystals are very
rare. In this paper, we use spin-lattice dynamics (SLD) simulations to model
ferromagnetic crystalline iron, where the spin and lattice systems are coupled
through the atomic position-dependent exchange function, and thus the
interaction between magnon and phonon is naturally considered. We then present
a method combining SLD simulations with spectral energy analysis to calculate
the magnon and phonon harmonic (e.g., dispersion, specific heat, group
velocity) and anharmonic (e.g., scattering rate) properties, based on which
their thermal conductivity values are calculated. This work represents an
example of using SLD simulations to understand the transport properties
involving coupled magnon and phonon dynamics.",1712.09002v1
2017-12-31,"Magnetic and Structural Properties of the Iron Oxychalcogenides La$_{2}$O$_{2}$Fe$_{2}$O$M_{2}$ ($M$= S, Se)","We present the results of structural and magnetic phase comparisons of the
iron oxychalcogenides La$_{2}$O$_{2}$Fe$_{2}$O$M$$_{2}$ ($M$ = S, Se). Elastic
neutron scattering reveals that $M$ = S and Se have similar nuclear structures
at room and low temperatures. We find that both materials obtain
antiferromagnetic ordering at a Neel temperature $T_{N}$ 90.1 $\pm$ 0.16 K and
107.2 $\pm$ 0.06 K for $M$= Se and S, respectively. The magnetic arrangements
of $M$ = S, Se are obtained through Rietveld refinement. We find the order
parameter exponent $\beta$ to be 0.129 $\pm$ 0.006 for $M$ = Se and 0.133 $\pm$
0.007 for $M$ = S. Each of these values is near the Ising symmetry value of
1/8. This suggests that although lattice and electronic structural
modifications result from chalcogen exchange, the nature of the magnetic
interactions is similar in these materials.",1801.00342v2
2018-01-03,Structures and magnetic properties of iron silicide from adaptive genetic algorithm and first-principles calculations,"We performed a systematic search for low-energy structures of binary iron
silicide over a wide range of compositions using the crystal structure
prediction method based on adaptive genetic algorithm. 36 structures with
formation energies within 50 meV/atom (11 of them are within 20 meV) above the
convex hull formed by experimentally known stable structures are predicted.
Magnetic properties of these low-energy structures are investigated. Some of
these structures can be promising candidates for rare-earth-free permanent
magnet.",1801.01004v1
2018-01-15,Testing exterior spacetime of the neutron star via X-ray reflection spectroscopy,"The exterior geometry of a neutron star can be approximated by relativistic
multipole moments of a parametrized metric using Ernst potential formalism.
This spacetime can be tested with electromagnetic wave observation of
astrophysical black holes. In the present paper, I simulate X-ray reflection
spectra of a thin accretion disk with future X-ray missions. The purpose of
this work is to understand whether X-ray reflection spectroscopy can
distinguish the neutron star from the Kerr solution of General Relativity. I
found that for the higher value of spin and multipole moment parameters, there
are small differences in the shape of neutron star iron lines. It is hard to
distinguish neutron star iron lines from Kerr ones due to the small deviations.
Also, electromagnetic wave observation of slow rotating neutron stars is
marginally consistent with Kerr black holes of general relativity.",1801.04657v2
2018-01-19,Spectral analysis of the He-enriched sdO-star HD 127493,"The bright sdO star HD 127493 is known to be of mixed H/He composition and
excellent archival spectra covering both optical and ultraviolet ranges are
available. UV spectra play a key role as they give access to many chemical
species that do not show spectral lines in the optical, such as iron and
nickel. This encouraged the quantitative spectral analysis of this prototypical
mixed H/He composition sdO star. We determined atmospheric parameters for HD
127493 in addition to the abundance of C, N, O, Si, S, Fe, and Ni in the
atmosphere using non-LTE model atmospheres calculated with TLUSTY/SYNSPEC. A
comparison between the parallax distance measured by Hipparcos and the derived
spectroscopic distance indicate that the derived atmospheric parameters are
realistic. From our metal abundance analysis, we find a strong CNO signature
and enrichment in iron and nickel.",1801.06350v1
2018-01-31,Detection of bosonic mode as a signature of magnetic excitation in one unit cell FeSe on SrTiO3,"We report an in situ scanning tunneling spectroscopy study of one-unit-cell
(1-UC) FeSe film on SrTiO3(001) (STO) substrate. In quasiparticle density of
states, bosonic excitation mode characterized by the ""dip-hump"" structure is
detected outside the larger superconducting gap with energy comparable with
phonon and spin resonance modes in heavily electron-doped iron selenides.
Statistically, the excitation mode, which is intimately correlated with
superconductivity, shows an anticorrelation with pairing strength and yields an
energy scale upper-bounded by twice the superconducting gap coinciding with the
characteristics of magnetic resonance in cuprates and iron-based
superconductors. The local response of tunneling spectra to magnetically
different Se defects all exhibits the induced in-gap quasiparticle bound
states, indicating an unconventional sign-reversing pairing. These results
support the magnetic nature of the excitation mode and possibly reveal a
signature of electron-magnetic-excitation coupling in high-temperature
superconductivity of 1-UC FeSe/STO.",1801.10363v2
2018-02-08,Direct observation of spin excitation anisotropy in the paramagnetic orthorhombic state of BaFe$_{2-x}$Ni$_x$As$_2$,"We use transport and inelastic neutron scattering measurements to investigate
single crystals of iron pnictide BaFe$_{2-x}$Ni$_{x}$As$_{2}$ ($x=0,0.03$),
which exhibit a tetragonal-to-orthorhombic structural transition at $T_s$ and
stripe antiferromagnetic order at $T_N$ ($T_s\geq T_N$).
  Using a tunable uniaxial pressure device, we detwin the crystals and study
their transport and spin excitation properties at antiferromagnetic wave vector
$S_1(1,0)$ and its 90$^\circ$ rotated wave vector $S_2(0,1)$ under different
pressure conditions. We find that uniaxial pressure necessary to detwin and
maintain single domain orthorhombic antiferromagnetic phase of
BaFe$_{2-x}$Ni$_{x}$As$_{2}$ induces resistivity and spin excitation anisotropy
at temperatures above zero pressure $T_s$. In uniaxial pressure-free detwinned
sample, spin excitation anisotropy between $S_1(1,0)$ and $S_2(0,1)$ first
appear in the paramagnetic orthorhombic phase below $T_s$. These results are
consistent with predictions of spin nematic theory, suggesting the absence of
structural or nematic phase transition above $T_s$ in iron pnictides.",1802.02713v1
2018-02-20,Magnetic exchange and susceptibilities in fcc iron: A supercell dynamical mean-field theory study,"We study the momentum- and temperature dependencies of magnetic
susceptibilities and magnetic exchange in paramagnetic fcc iron by a
combination of density functional theory and supercell dynamical mean-field
theory (DFT+DMFT). We find that in agreement with experimental results the
antiferromagnetic correlations with the wave vector close to $(0,0,2\pi)$
dominate at low temperatures (as was also obtained previously theoretically),
while the antiferromagnetic and ferromagnetic correlations closely compete at
the temperatures $T\sim 1000$ K, where $\gamma$-iron exists in nature. Inverse
staggered susceptibility has linear temperature dependence at low temperatures,
with negative Weiss temperature $\theta_{\rm stagg} \approx -340$ K; the
inverse local susceptibility is also linear at not too low temperatures,
showing well formed local moments. Analysis of magnetic exchange shows that the
dominant contribution comes from first two coordination spheres. In agreement
with the analysis of the susceptibility, the nearest-neighbor exchange is found
to be antiferromagnetic at low temperatures, while at temperature of the
$\alpha$-$\gamma$ structural phase transition its absolute value becomes small,
and the system appears on the boundary between the regimes with strongest
antiferro- and ferromagnetic correlations.",1802.07061v2
2018-03-01,Hydrogen embrittlement controlled by reaction of dislocation with grain boundary in alpha-iron,"Hydrogen atoms absorbed by metals in the hydrogen-containing environments can
lead to the premature fracture of the metal components used in load-bearing
conditions. Since metals used in practice are mostly polycrystalline, grain
boundaries (GBs) can play an important role in hydrogen embrittlement of
metals. Here we show that the reaction of GB with lattice dislocations is a key
component in hydrogen embrittlement mechanism for polycrystalline metals. We
use atomistic modeling methods to investigate the mechanical response of GBs in
alpha-iron with various hydrogen concentrations. Analysis indicates that
dislocations impingement and emission on the GB cause the GB to locally
transform into an activated state with a more disordered atomistic structure,
and introduce a local stress concentration. The activation of the GB segregated
with hydrogen atoms can greatly facilitate decohesion of the GB. We show that
the hydrogen embrittlement model proposed here can give better explanation of
many experimental observations.",1803.00287v2
2018-03-06,Combined Molecular and Spin Dynamics Simulation of BCC Iron with Vacancy Defects,"Utilizing an atomistic computational model which handles both translational
and spin degrees of freedom, combined molecular and spin dynamics simulations
have been performed to investigate the effect of vacancy defects on spin wave
excitations in ferromagnetic iron. Fourier transforms of space and
time-displaced correlation functions yield the dynamic structure factor,
providing characteristic frequencies and lifetimes of the spin wave modes.
Comparison of the system with a 5% vacancy concentration with pure lattice data
shows a decrease in frequency as well as a decrease in lifetime for all
transverse spin wave excitations observed. Additionally, a rugged spin wave
line shape for low-q spin waves indicates the presence of multiple localized
excitations near defect sites resulting in reduced excitation lifetimes due to
increased magnon-magnon scattering. We observe further evidence of increased
magnon-magnon scattering as the peaks in the longitudinal spin wave spectrum
become less distinct.",1803.02468v1
2018-03-07,Antiphase Fermi-surface modulations accompanying displacement excitation in a parent compound of iron-based superconductors,"We investigate the transient electronic structure of BaFe2As2, a parent
compound of iron-based superconductors, by time- and angle-resolved
photoemission spectroscopy. In order to probe the entire Brillouin zone, we
utilize extreme ultraviolet photons and observe photoemission intensity
oscillation with the frequency of the A1g phonon which is antiphase between the
zone-centered hole Fermi surfaces (FSs) and zone-cornered electron FSs. We
attribute the antiphase behavior to the warping in one of the zone-centered
hole FSs accompanying the displacement of the pnictogen height, and find that
this displacement is the same direction as that induced by substitution of P
for As, where superconductivity is induced by a structural modification without
carrier doping in this system.",1803.02599v1
2018-03-07,New Experimental Limits on Exotic Spin-Spin-Velocity-Dependent Interactions By Using SmCo$_5$ Spin Sources,"We report the latest results of searching for possible new macro-scale
spin-spin-velocity-dependent forces (SSVDFs) based on specially designed
iron-shielded SmCo$_5$ (ISSC) spin sources and a spin exchange relaxation free
(SERF) co-magnetometer. The ISSCs have high net electron spin densities of
about $1.7\times 10^{21}$ cm$^{-3}$, which mean high detecting sensitivity; and
low magnetic field leakage of about $\sim$mG level due to iron shielding, which
means low detecting noise. With help from the ISSCs, the high sensitivity SERF
co-magnetometer, and the similarity analysis method, new constraints on SSVDFs
with forms of $V_{6+7}$, $V_8$, $V_{15}$, and $V_{16}$ have been obtained,
which represent the tightest limits in force range of 5 cm -- 1 km to the best
of our knowledge.",1803.02813v2
2018-03-15,Nodal-to-nodeless superconducting order parameter in LaFeAs$_{1-x}$P$_x$O synthesized under high pressure,"Similar to chemical doping, pressure produces and stabilizes new phases of
known materials, whose properties may differ greatly from those of their
standard counterparts. Here, by considering a series of LaFeAs$_{1-x}$P$_x$O
iron-pnictides synthesized under high-pressure high-temperature conditions, we
investigate the simultaneous effects of pressure and isoelectronic doping in
the 1111 family. Results of numerous macro- and microscopic technique
measurements, unambiguously show a radically different phase diagram for the
pressure-grown materials, characterized by the lack of magnetic order and the
persistence of superconductivity across the whole $0.3 \leq x \leq 0.7$ doping
range. This unexpected scenario is accompanied by a branching in the electronic
properties across $x = 0.5$, involving both the normal and superconducting
phases. Most notably, the superconducting order parameter evolves from nodal
(for $x < 0.5$) to nodeless (for $x \geq 0.5$), in clear contrast to other 1111
and 122 iron-based materials grown under ambient-pressure conditions.",1803.05733v1
2018-03-22,On the performance of interatomic potential models of iron: comparison of the phase diagrams,"In order to study the performance of interatomic potentials and their
reliability at higher pressures, the phase diagram of four different
embedded-atom type potential models of iron is compared. The calculations were
done by the nested sampling technique in the pressure range 0.1 GPa-100 GPa.
The low pressure stable structure is found to be the body- centred cubic in all
cases, but the higher pressure phases show a great variation, being
face-centred cubic, hexagonal close-packed and - at very low temperatures -
different body-centred tetragonal phases are observed as well. The melting line
is overestimated considerably for three of the models, but for the one where
liquid properties had been taken into account during the potential fitting
process, the agreement with experimental results is good, even at very high
pressures.",1803.08400v1
2018-03-27,Oxygen and zinc abundances in 417 Galactic bulge red giants,"Oxygen and zinc in the Galactic bulge are key elements for the understanding
of the bulge chemical evolution. Oxygen-to-iron abundance ratios provide a most
robust indicator of the star formation rate and chemical evolution of the
bulge. Zinc is enhanced in metal-poor stars, behaving as an $\alpha$-element,
and its production may require nucleosynthesis in hypernovae. Most of the
neutral gas at high redshift is in damped Lyman-alpha systems (DLAs), where Zn
is also observed to behave as an alpha-element. The aim of this work is the
derivation of the alpha-element oxygen, together with nitrogen, and the
iron-peak element zinc abundances in 417 bulge giants, from moderate resolution
(R~22,000) FLAMES-GIRAFFE spectra. For stars in common with a set of UVES
spectra with higher resolution (R~45,000), the data are intercompared. The
results are compared with literature data and chemodynamical models.",1803.09942v1
2018-04-10,The Dark Side of the Sun A Plea for a Next-Generation Opacity Calculation,"Is the Sun likely to have a more opaque interior than previously thought? The
solar oxygen (or abundance) problem can be solved with higher interior
opacities, reconciling abundance analyses based on 3D convective atmospheres
with the helioseismic structure of the solar interior. This has been known for
more than a decade, but last year we learned that the absorption by just iron
may contribute 7\% more to the solar opacity at the bottom of the convection
zone than predicted by any opacity calculation so far, and by OP05 in
particular. I find that artificial changes to the absorption (calibrated
against the iron experiment) by other elements in a solar mixture give an
opacity increase of a shape and magnitude that can restore agreement between
modern abundance analysis and helioseismology. This suggests that improved
opacity calculations will solve the solar oxygen problem.",1804.03746v1
2018-04-16,Ultrafast destruction and recovery of the spin density wave order in iron based pnictides: a multi-pulse optical study,"We report on systematic excitation-density dependent all-optical femtosecond
time resolved study of the spin-density wave state in iron-based
superconductors. The destruction and recovery dynamics are measured by means of
the standard and a multi-pulse pump-probe technique. The experimental data are
analyzed and interpreted in the framework of an extended three temperature
model. The analysis suggests that the optical-phonons energy-relaxation plays
an important role in the recovery of almost exclusively electronically driven
spin density wave order.",1804.05769v1
2018-04-25,Magnon thermal Hall effect in kagome antiferromagnets with Dzyaloshinskii-Moriya interactions,"We theoretically study magnetic and topological properties of
antiferromagnetic kagome spin systems in the presence of both in- and
out-of-plane Dzyaloshinskii-Moriya interactions. In materials such as the iron
jarosites, the in-plane interactions stabilize a canted noncollinear ""umbrella""
magnetic configuration with finite scalar spin chirality. We derive expressions
for the canting angle, and use the resulting order as a starting point for a
spin-wave analysis. We find topological magnon bands, characterized by non-zero
Chern numbers. We calculate the magnon thermal Hall conductivity, and propose
the iron jarosites as a promising candidate system for observing the magnon
thermal Hall effect in a noncollinear spin configuration. We also show that the
thermal conductivity can be tuned by varying an applied magnetic field, or the
in-plane Dzyaloshinskii-Moriya strength. In contrast with previous studies of
topological magnon bands, the effect is found to be large even in the limit of
small canting.",1804.09783v2
2018-04-26,TRAPPIST-1e Has a Large Iron Core,"The TRAPPIST-1 system provides an exquisite laboratory for understanding
exoplanetary atmospheres and interiors. Their mutual gravitational interactions
leads to transit timing variations, from which Grimm et al. (2018) recently
measured the planetary masses with precisions ranging from 5% to 12%. Using
these masses and the <5% radius measurements on each planet, we apply the
method described in Suissa et al. (2018) to infer the minimum and maximum CRF
(core radius fraction) of each planet. Further, we modify the maximum limit to
account for the fact that a light volatile envelope is excluded for planets b
through f. Only planet e is found to have a significant probability of having a
non-zero minimum CRF, with a 0.7% false-alarm probability it has no core. Our
method further allows us to measure the CRF of planet e to be greater than (49
+/- 7)% but less than (72 +/- 2)%, which is compatible with that of the Earth.
TRAPPIST-1e therefore possess a large iron core similar to the Earth, in
addition to being Earth-sized and located in the temperature zone.",1804.10618v1
2018-05-07,Nebular spectroscopy of SN 2014J: Detection of stable nickel in near infrared spectra,"We present near infrared (NIR) spectroscopy of the nearby supernova 2014J
obtained $\sim$450 d after explosion. We detect the [Ni II] 1.939 $\mu$m line
in the spectra indicating the presence of stable $^{58}$Ni in the ejecta. The
stable nickel is not centrally concentrated but rather distributed as the iron.
The spectra are dominated by forbidden [Fe II] and [Co II] lines. We use lines,
in the NIR spectra, arising from the same upper energy levels to place
constraints on the extinction from host galaxy dust. We find that that our data
are in agreement with the high $A_V$ and low $R_V$ found in earlier studies
from data near maximum light. Using a $^{56}$Ni mass prior from near maximum
light $\gamma$-ray observations, we find $\sim$0.05 M$_\odot$ of stable nickel
to be present in the ejecta. We find that the iron group features are
redshifted from the host galaxy rest frame by $\sim$600 km s$^{-1}$.",1805.02420v1
2018-05-17,Exploring the spectral variability of the Seyfert 1.5 galaxy Markarian 530 with Suzaku,"A 2012 Suzaku observation of the Seyfert 1.5 galaxy Markarian 530 was
analysed and found to exhibit two distinct modes of variability, which were
found to be independent from one another. Firstly, the spectrum undergoes a
smooth transition from a soft to a hard spectrum. Secondly, the spectrum
displays more rapid variability seemingly confined to a very narrow energy band
(~ 1-3 keV). Three physical models (blurred reflection, partial covering, and
soft Comptonisation) were explored to characterise the average spectrum of the
observation as well as the spectral state change. All three models were found
to fit the average spectrum and the spectral changes equally well. The more
rapid variability appears as two cycles of a sinusoidal function, but we cannot
attribute this to periodic variability. The Fe K-alpha band exhibits a narrow
6.4 keV emission line consistent with an origin from the distant torus. In
addition, features blueward of the neutral iron line are consistent with
emission from He-like and H-like iron that could be originating from the highly
ionised layer of the torus, but a broad Gaussian profile at ~ 6.7 keV also fits
the spectrum well.",1805.06742v1
2018-05-24,Quasi-one Dimensional Nanostructures as Sign of Nematicity in Iron Pnictides and Chalcogenides,"Impurity scattering is found to lead to quasi-one dimensional nanoscale
modulation of the local density of states in the iron pnictides and
chalcogenides. This `quasiparticle interference' feature is remarkably similar
across a wide variety of pnictide and chalcogenide phases, suggesting a common
origin. We show that a unified understanding of the experiments can be obtained
by simply invoking a four-fold symmetry breaking $d_{xz}-d_{yz}$ orbital
splitting, of a magnitude already suggested by the experiments. This can
explain the one-dimensional characteristics in the local density of states
observed in the orthorhombic nematic, tetragonal paramagnetic, as well as the
spin-density wave and superconducting states in these materials.",1805.09582v2
2018-05-28,Friction and friction heat of micronscale iron,"The paper investigates friction and friction heat of the micronscale iron
under influences of velocity of the slider and temperature of the substrate by
using smoothed particle hydrodynamics simulations. In the velocity range of 10
- 100 m/s, change of friction coefficient via velocity well complies with
exponent or hyperbolic tangent form and friction coefficient begins to approach
a stable value of 0.3 at around a velocity of 50 m/s after a rapidly increasing
situation. Friction coefficient steady maintains over the temperature range of
200 - 400 K at each velocity of 10, 50 or 100 m/s. Friction heat is detailed
analyzed via sliding time. Change of temperature of the system via sliding time
well complies with sigmoidal functions, an exception of that of the particle
layer directly causing friction. The layer causing friction has the highest
steady temperature and its temperature rise is the largest one. The temperature
rise is found to be dependent on increment of the initial temperatures of the
substrate and the slider while the incnt does not efect on configration of the
slid time - temperature curve",1805.10781v1
2018-05-29,Trends in pressure-induced layer-selective half-collapsed tetragonal phases in the iron-based superconductor family $Ae{}A$Fe$_4$As$_4$,"By performing pressure simulations within density functional theory for the
family of iron-based superconductors $Ae{}A$Fe$_4$As$_4$ with $Ae$ = Ca, Sr, Ba
and $A$ = K, Rb, Cs we predict in these systems the appearance of two
consecutive half-collapsed tetragonal transitions at pressures $P_{c_1}$ and
$P_{c_2}$, which have a different character in terms of their effect on the
electronic structure. We find that, similarly to previous studies for
CaKFe$_4$As$_4$, spin-vortex magnetic fluctuations on the Fe sublattice play a
key role for an accurate structure prediction in these materials at zero
pressure. We identify clear trends of critical pressures and discuss the
relevance of the collapsed phases in connection to magnetism and
superconductivity. Finally, the intriguing cases of EuRbFe$_4$As$_4$ and
EuCsFe$_4$As$_4$, where Eu magnetism coexists with superconductivity, are
discussed as well in the context of half-collapsed phases.",1805.11409v1
2018-06-01,Two-stage three-channel Kondo physics for an FePc molecule on the Au(111) surface,"We study an impurity Anderson model to describe an iron phthalocyanine (FePc)
molecule on Au(111), motivated by previous results of scanning tunneling
spectroscopy (STS) and theoretical studies. The model hybridizes a spin doublet
consisting in one hole at the $3d_{z^2}$ orbital of iron and two degenerate
doublets corresponding to one hole either in the $3d_{xz}$ or in the $3d_{yz}$
orbital (called $\pi$ orbitals) with two degenerate Hund-rule triplets with one
hole in the $3d_{z}$ orbital and another one in a $\pi$ orbital. We solve the
model using a slave-boson mean-field approximation (SBMFA). For reasonable
parameters we can describe very well the observed STS spectrum between sample
bias -60 mV to 20 mV. For these parameters the Kondo stage takes place in two
stages, with different energy scales $T_K^z > T_K^\pi$ corresponding to the
Kondo temperatures related with the hopping of the $z^2$ and $\pi$ orbitals
respectively. There is a strong interference between the different channels and
the Kondo temperatures, particularly the lowest one is strongly reduced
compared with the value in the absence of the competing channel.",1806.00402v1
2018-06-04,Pressure tuned superconductivity and normal state behavior in Ba(Fe$_{0.943}$Co$_{0.057}$)$_2$As$_2$ near the antiferromagnetic boundary,"Superconductivity in iron pnictides is unconventional and pairing may be
mediated by magnetic fluctuations in the Fe-sublattice. Pressure is a clean
method to explore superconductivity in iron based superconductors by tuning the
ground state continuously without introducing disorder. Here we present a
systematic high pressure transport study in Ba(Fe$_{1-x}$Co$_{x}$)$_2$As$_2$
single crystals with $x=$ 0.057, which is near the antiferromagnetic
instability. Resistivity $\rho=\rho_0+AT^{n}$ was studied under applied
pressure up to 7.90 GPa. The parameter $n$ approaches a minimum value of
$n\approx 1$ at a critical pressure $P_c =$ 3.65 GPa. Near $P_c$, the
superconducting transition temperature $T_c$ reaches a maximum value of 25.8 K.
In addition, the superconducting diamagnetism at 2 K shows a sudden change
around the same critical pressure. These results may be associated with a
possible quantum critical point hidden inside the superconducting dome, near
optimum $T_c$.",1806.01432v1
2018-06-06,Effect of electron correlations on spin excitation bandwidth in Ba$_{0.75}$K$_{0.25}$Fe$_{2}$As$_{2}$ as seen via time-of-flight inelastic neutron scattering,"We use inelastic neutron scattering (INS) to investigate the effect of
electron correlations on spin dynamics in the iron-based superconductor
Ba$_{0.75}$K$_{0.25}$Fe$_{2}$As$_{2}$. Our INS data show a spin-wave-like
dispersive feature, with a zone boundary energy of 200 meV. A first principles
analysis of dynamical spin susceptibility, incorporating the mass
renormalization factor of 3, as determined by angle-resolved photoemission
spectroscopy, provides a reasonable description of the observed spin
excitations. This analysis shows that electron correlations in the Fe-3$d$
bands yield enhanced effective electron masses, and consequently, induce
substantial narrowing of the spin excitation bandwidth. Our results highlight
the importance of electron correlations in an itinerant description of the spin
excitations in iron-based superconductors.",1806.02097v1
2018-06-23,The driving mechanism of the d-wave orbital order in the iron-based superconductors,"We study the driving mechanism and the form of the orbital order in the
electronic nematic phase of the iron-based superconductors(IBSs) within the
random phase approximation of a 5-band model. We find the magnetic correlation
energy of the system can be significantly improved when an orbital order of the
d-wave form is spontaneously generated. On the other hand, the magnetic
correlation energy increases as one introduce either an on-site or an extended
s-wave orbital order. More specifically, we find that the on-site orbital order
is disfavored by the Hund's rule coupling and the extended s-wave orbital order
is disfavored by the stripy magnetic correlation pattern in the IBSs.",1806.08907v1
2018-07-05,Probing Charge Transfer Dynamics in a Single Iron Tetraphenylporphyrin Dyad Adsorbed on an Insulating Surface,"Although the dynamics of charge transfer (CT) processes can be probed with
ultimate lifetime resolution, the helplessness to control CT at the nanoscale
constitutes one of the most important road-blocks to revealing some of its deep
fundamental aspects. In this work, we present an investigation of CT dynamics
in a single iron tetraphenylporphyrin (Fe-TPP) donor/acceptor dyad adsorbed on
a CaF2/Si(100) insulating surface. The tip of a scanning tunneling microscope
(STM) is used to create local ionic states in one fragment of the dyad. The CT
process is monitored by imaging subsequent changes in the neighbor acceptor
molecule and its efficiency is mapped revealing the influence of the initial
excited state in the donor molecule. In validation of the experiments,
simulations based on density functional theory show that holes have a higher
donor-acceptor CT rate compared to electrons and highlight a noticeable initial
state dependence on the CT process. We leverage the unprecedented spatial
resolution achieved in our experiments to show that the CT process in the dyad
is governed via molecule-molecule coherent tunneling with negligible
surface-mediated character.",1807.01876v1
2018-07-28,Stability and magnetism of FeN high-pressure phases,"Experimentally discovered compounds in the iron-nitrogen system belong to the
low concentration part of the Fe-N phase diagram. In our paper, which is based
on ab initio calculations we have studied formation and stability of
high-pressure iron mono-nitride phases, and particularly the new magnetic phase
with a NiAs-type structure. We have investigated the role of dynamic,
thermodynamic and electronic properties, such as electronic correlations and
pressure-induced phase stabilisation. We demonstrate that the new hexagonal FeN
phase is stable for a wide range of external pressure and it can be formed as a
metastable phase at zero pressure. We show that it has relativity small Curie
temperature and it may possess a non-collinear magnetism.",1807.10874v2
2018-08-01,Disruption of a planet spiralling into its host star,"The processes leading deformation and destruction of planets spiraling into
the convective envelope of their host stars are described. The planet is
compressed by the ram pressure, and deformed into a flattened shape for which a
quantitative model is developed. Compression increases the planet's density
contrast with the envelope and its gravitational binding energy. This increases
the survivability especially of gas planets. An estimate is given for the depth
of disruption by ram pressure, and for the subsequent fragmentation of the
remnants. We show how the debris of rocky or iron planets, instead of mixing
through the convection zone, sinks below the base of the convection zone. The
time scale of the entire sequence of events is of the order of a few orbital
times of the planet. If spiral-in of (partly) icy, rocky or iron planets has
happened to the pre-main sequence Sun, it could account for the higher opacity
below the base of the convection zone as inferred from helioseismology.",1808.00467v1
2018-08-17,Cepheid Abundances: Multiphase Results and Spatial Gradients,"Parameters and abundances have been derived for 435 Cepheids based on an
analysis of 1127 spectra. Results from five or more phases are available for 52
of the program stars. The latter set of stars span periods between 1.5 and 68
days. The parameters and abundances show excellent consistency across phase.
For iron, the average range in the determined abundance is 0.11 from these 52
stars. For 163 stars with more than one phase available the average range is
0.07. The variation in effective temperature tracks well with phase, as does
the total broadening velocity. The gravity and microturbulent velocity follow
phase, but with less variation and regularity.
  Abundance gradients have been derived using GAIA DR2 parallax data (GAIA
Collaboration et al. 2016, 2018), as well as Bayesian distance estimates based
upon GAIA DR2 from Bailer-Jones et al. (2018). The abundance gradient derived
for iron is d[Fe/H]/dR = -0.05 dex/kpc, similar to gradients derived in
previous studies.",1808.05863v1
2018-09-03,On the relationship between metallicity distributions of globular clusters and of circumgalactic gas,"The abundance of alpha elements and iron in stars of globular clusters shows
the composition of the gaseous medium, in which they have been formed. In the
present paper, we discuss a possibility to consider dense clouds of
circumgalactic gas (partial Lyman limit systems and Lyman limit systems)
observed in the 100 - 130 kpc neighbourhood of galaxies at redshifts of
0.1<z<1.1 as being the residual parts of clouds, in which globular clusters
have been formed. Conclusions have been drawn based on statistical analysis of
the abundance of magnesium and iron in globular clusters and in circumgalactic
clouds and on the spatial location of objects of both types.",1809.00621v2
2018-09-05,"Widespread orthorhombic fluctuations in the (Sr,Na)Fe$_2$As$_2$ family of superconductors","We report comprehensive pair distribution function measurements of the
hole-doped iron-based superconductor system Sr$_{1-x}$Na$_{x}$Fe$_2$As$_2$.
Structural refinements performed as a function of temperature and length scale
reveal orthorhombic distortions of the instantaneous local structure across a
large region of the phase diagram possessing average tetragonal symmetry,
indicative of fluctuating nematicity. These nematic fluctuations are present up
to high doping levels ($x \gtrsim 0.48$, near optimal superconductivity) and
high temperatures (above room temperature for $x = 0$, decreasing to 150 K for
$x = 0.48$), with a typical length scale of 1-3 nm. This work highlights the
ubiquity of nematic fluctuations in a representative iron-based superconductor
and provides important details about the evolution of these fluctuations across
the phase diagram.",1809.01764v2
2018-09-21,Crystal Structures and Properties of Iron Hydrides at High Pressure,"Evolutionary algorithms and the particle swarm optimization method have been
used to predict stable and metastable high hydrides of iron between 150-300 GPa
that have not been discussed in previous studies. Cmca FeH5, Pmma FeH6 and P2/c
FeH6 contain hydrogenic lattices that result from slight distortions of the
previously predicted I4/mmm FeH5 and Cmmm FeH6 structures. Density functional
theory calculations show that neither the I4/mmm nor the Cmca symmetry FeH5
phases are superconducting. A P1 symmetry FeH7 phase, which is found to be
dynamically stable at 200 and 300 GPa, adds another member to the set of
predicted nonmetallic transition metal hydrides under pressure. Two metastable
phases of FeH$_8$ are found, and the preferred structure at 300 GPa contains a
unique 1-dimensional hydrogenic lattice.",1809.08323v1
2018-09-24,Simulation of muon-induced neutral particle background for a shallow depth Iron Calorimeter detector,"The Iron Calorimeter (ICAL) detector at the India based Neutrino Observatory
(INO) is planned to be set up in an underground cavern with a rock overburden
of more than 1 km. This overburden reduces the cosmic muon flux by a factor of
10$^{6}$ with respect to that at sea level. In this paper, we examine the
possibility of a 100 m shallow depth ICAL (SICAL) detector. The cosmic muons
would have to be detected in a veto detector surrounding ICAL with an
efficiency of 99.99 % in order to have the same level of muon background
leaking undetected through the veto detector as at the 1 km depth underground
site. However, an additional background arises from interactions of cosmic
muons with the rock. Since the neutral particles produced in such interactions
can pass through the veto detector without any interaction, they can possibly
mimic neutrino events in ICAL. In this paper, the results of a GEANT4 based
simulation study to estimate the background signals due to muon induced
interactions with the rock for SICAL are presented.",1809.08834v2
2018-09-27,An investigation of the interrelationship between pressure and correlation in LaFeAsO under pressure,"Here, we investigated the interrelationship between pressure and correlation
in the LaFeAsO compound by the density functional theory method combined with
the dynamical mean field theory (DFT+DMFT) method. The spectral function and
the occupation number (ON) of Fe-3d orbitals at different pressures were
extracted from the calculations, and the importance of the role of correlation
in superconductivity in iron-based compounds was indicated. The measured ON of
Fe-3d orbitals demonstrated charge transfer between them and also the crucial
role of the Fe-3dxy (xy) orbital in superconductivity in these materials. A
switching behavior between high and low TC through decreasing the correlation
was observed in our calculations, originating from the orbital switching. This
shows the significant role of the orbital degrees of freedom in iron-based
superconductors.",1809.10661v1
2018-10-01,Composition dependence of bulk superconductivity in YFe2Ge2,"In the layered iron-based superconductor YFe2Ge2, a high Sommerfeld ratio of
~100 mJ/molK^2 and a T^(3/2) temperature dependence of the electrical
resistivity at low temperature T indicate strong electronic correlations and
point towards an unconventional pairing state. We have investigated the role of
composition and annealing conditions in optimizing the growth of high-quality
YFe2Ge2. Our findings confirm that bulk superconductivity is observed in
samples with disorder scattering rates less than 2 k_B T_c/hbar. Fe deficiency
on the Fe site is identified as the dominant source of disorder, which can be
minimised by precipitating from a slightly iron-rich melt, following by
annealing.",1810.00947v1
2018-10-06,Impact of Angular Deviation from Coincidence Site Lattice Grain Boundaries on Hydrogen Segregation and Diffusion in Alpha-iron,"Coincidence Site Lattice (CSL) grain boundaries (GBs) are believed to be
low-energy, resistant to intergranular fracture, as well as to hydrogen
embrittlement. Nevertheless, the behavior of CSL-GBs are generally confused
with their angular deviations. In the current study, the effect of angular
deviation from the perfect sigma3 (111) [1-10] GBs in Alpha-iron on the
hydrogen diffusion and the susceptibility of the GB to hydrogen embrittlement
is investigated through molecular static and dynamics simulations. By utilizing
Rice-Wang model it is shown that the ideal GB shows the highest resistance to
decohesion below the hydrogen saturation limit. Finally, the hydrogen
diffusivity along the ideal GB is observed to be the highest.",1810.02988v1
2018-10-10,Superconductivity-induced nematicity,"The role of nematic order for the mechanism of high-temperature
superconductivity is highly debated. In most iron-based superconductors (IBS)
the tetragonal symmetry is broken already in the normal state, resulting in
orthorhombic lattice distortions, static stripe magnetic order, or both.
Superconductivity then emerges, at least at weak doping, already from the state
with broken $C_4$ rotational symmetry. One of the few stoichiometric IBS,
lithium iron arsenide, superconducts below 18 K and does not display either
structural or magnetic transition in the normal state. Here we demonstrate,
using angle-resolved photoemission, that even superconducting state in LiFeAs
is also a nematic one. We observe spontaneous breaking of the rotational
symmetry in the gap amplitude on all Fermi surfaces, as well as unidirectional
distortion of the Fermi pockets. Remarkably, these deformations disappear above
superconducting $T_c$. Our results demonstrate the realization of a novel
phenomenon of superconductivity-induced nematicity in IBS, emphasizing the
intimate relation between them. We suggest a theoretical explanation based on
the emergence of a secondary instability inside the superconducting state,
which leads to the nematic order and s-d mixing in the gap function.",1810.04446v1
2018-10-15,Evidence of nodal gap structure in the basal plane of the FeSe superconductor,"Identifying the symmetry of the wave function describing the Cooper pairs is
pivotal in understanding the origin of high-temperature superconductivity in
iron-based superconductors. Despite nearly a decade of intense investigation,
the answer to this question remains elusive. Here we use the muon spin
rotation/relaxation (muSR) technique to investigate the underlying symmetry of
the pairing state of the FeSe superconductor, the basic building block of all
iron-chalcogenide superconductors. Contrary to earlier muSR studies on powders
and crystals, we show that while the superconducting gap is most probably
anisotropic but nodeless along the crystallographic c-axis, it is nodal in the
ab-plane, as indicated by the linear increase of the superfluid density at low
temperature. We further show that the superconducting properties of FeSe
display a less pronounced anisotropy than expected.",1810.06269v1
2018-11-13,Nanoscale ordered Layered-Segregation of Cobalt and Iron in the Perovskite SmFe0.5Co0.5O3,"The possibility to segregate cobalt and iron in a single perovskite, at a
nanoscale in the form of layers has been investigated, using sol gel technic
synthesis. Quite remarkably, it is shown that such a nanoscale ordering, which
can only be detected by a combined HAADF-STEM and EELS study, has a significant
impact upon the magnetic properties of this SmFe0.5Co0.5O3 oxide. This suggests
that careful nanoscale characterization of oxides will be necessary in the
future before proceeding to a viable interpretation of their physical
properties, at least in the field of magnetism.",1811.05221v1
2018-11-23,Melting and phase change for laser-shocked iron,"Using the LCLS facility at the SLAC National Accelerator Laboratory, we have
observed X-ray scattering from iron compressed with laser driven shocks to
Earth-core like pressures above 400GPa. The data shows shots where melting is
incomplete and we observe hexagonal close packed (hcp) crystal structure at
shock compressed densities up to 14.0 gcm-3 but no evidence of a
double-hexagonal close packed (dhcp) crystal. The observation of a crystalline
structure at these densities, where shock heating is expected to be in excess
of the equilibrium melt temperature, may indicate superheating of the solid.
These results are important for equation of state modelling at high strain
rates relevant for impact scenarios and laser-driven shock wave experiments.",1811.09467v1
2018-11-25,Identification of two-dimensional $FeO_2$ termination of hematite $α-Fe_2O_3(0001)$ surface,"Iron oxides are among the most abundant compounds on Earth and have
consequently been studied and used extensively in industrial processes. Despite
these efforts, concrete understanding of some of their surface phase structures
has remained elusive, in particular the oxidized ${\alpha}-Fe_2O_3(0001)$
hematite surface. We detail an optimized recipe to produce this phase over the
entire hematite surface and study the geometrical parameters and composition of
its complex structure by means of atomically resolved microscopy, electron
diffraction and surface-sensitive spectroscopies. We conclude that the oxidized
${\alpha}-Fe_2O_3(0001)$ surface is terminated by a two-dimensional iron oxide
with structure, lattice parameters, and orientation different from the bulk
substrate. Using total-energy density functional theory for simulation of a
large-scale atomic model, we identify the structure of the surface layer as
antiferromagnetic, conductive $1T-FeO_2$ attached on half-metal terminated
bulk. The model succeeds in reproducing the characteristic modulations observed
in the atomically resolved images and electron diffraction patterns.",1811.09996v1
2018-11-29,Chemical evolution of the metal poor Globular Cluster NGC 6809,"We present the abundances analysis for a sample of 11 red giant branch stars
in the metal-poor globular cluster NGC 6809 based on high-resolution spectra.
Our main goals are to characterize its chemical composition and analyze this
cluster's behavior associated with the Multiple Population (MPs) phenomenon. In
our work we obtained the stellar parameters and chemical abundances of 24
elements (O, Na, Mg, Al, Si, Ca, Ti, V, Cr, Mn, Fe, Co, Sc, Ni, Cu, Zn, Y, Zr,
Ba, La, Ce, Eu, Nd and Dy). We found a radial velocity of 174.7 $\pm$ 3.2 km
$s^{-1}$ and a mean iron content of [Fe/H]=-2.01 $\pm$ 0.02 in good agreement
with other studies. Moreover, we found a large spread in the abundances of the
light elements O, Na and Al confirming the presence of a Na-O anti-correlation
a Na-Al correlation. The Mg-Al anti-correlation is also present in our cluster.
The $\alpha$ and iron-peak elements show good agreement with the halo field
star trend. The heavy elements are dominated by the r-process.",1811.12457v1
2018-11-30,Magnetic and mechanical effects of Mn substitutions in AlFe2B2,"The mechanical and magnetic properties of the newly discovered MAB-phase
class of materials based upon AlFe2B2 were investigated. The samples were
synthesised from stoichiometric amounts of all constituent elements. X-ray
diffraction shows that the main phase is orthorhombic with an elongated b-axis,
similar to AlFe2B2. The low hardness and visual inspection of the samples after
deformation indicate that these compounds are deformed via a delamination
process. When substituting iron in AlFe2B2 with manganese, the magnetism in the
system goes from being ferro- to antiferromagnetic via a disordered
ferrimagnetic phase exhibited by AlFeMnB2. Density functional theory
calculations indicate a weakening of the magnetic interactions among the
transitions metal ions as iron is substituted by manganese in AlFe2B2. The
Mn-Mn exchange interactions in AlMn2 B2 are found to be very small.",1811.12720v1
2018-12-24,Magnetic measurements on micron-size samples under high pressure using designed NV centers,"Pressure is a unique tool to tune the interplay between structural,
electronic and magnetic interactions. It leads to remarkable properties of
materials such as recent temperature records in superconductivity. Advanced
magnetic measurements under very high pressure in the Diamond Anvil Cell (DAC)
use synchrotron approaches but these are lacking a formal link to the
macroscopic magnetic properties. We report an alternative method consisting in
optical magnetometry based on nitrogen-vacancy (NV) centers created at the
surface of a diamond anvil. We illustrate the method by two measurements
realized at room and low temperature respectively: the pressure evolution of
the magnetization of an iron bead up to 30 GPa showing the iron ferromagnetic
collapse and the detection of the superconducting transition of MgB2 at 7 GPa.",1812.09894v1
2019-01-04,Experimental and Numerical Investigation of the Fracture Behavior of Particle Reinforced Alkali Activated Slag Mortars,"This paper presents fracture response of alkali-activated slag (AAS) mortars
with up to 30% (by volume) of slag being replaced by waste iron powder which
contains a significant fraction of elongated particles. The elongated iron
particles act as micro-reinforcement and improve the crack resistance of AAS
mortars by increasing the area of fracture process zone (FPZ). Increased area
of FPZ signifies increased energy-dissipation which is reflected in the form of
significant increase in the crack growth resistance as determined from
R-curves. Fracture response of notched AAS mortar beams under three-point
bending is simulated using extended finite element method (XFEM) to develop a
tool for direct determination of fracture characteristics such as crack
extension and fracture toughness in particulate-reinforced AAS mortars.
Fracture response simulated using the XFEM based framework correlates well with
experimental observations. The comprehensive fracture studies reported here
provide an economical and sustainable means towards improving the ductility of
AAS systems which are generally more brittle than their conventional ordinary
portland cement counterparts.",1901.01025v1
2019-01-07,Thermoelectric signature of the nematic phase in iron-based superconductor,"Studies of the copper-based superconductors demonstrate how their phase
diagram becomes more complex as experimental probes improve, able to
distinguish among subtly different electronic phases. One of those phases,
nematicity, has become the matter of great interest also in the iron-based
superconductors, where it is detected deep in the tetragonal state. Here we
present the evolution of the in-plane Nernst effect anisotropy in the strain
detwinned Ca(Fe1-xCox)2As2 single crystals, whose behaviour can be explained
within the approach developed to describe the nematic order parameter in liquid
crystals [1,2]. Furthermore, the employed method turns out to be universally
applicable to data from other superconductors: Ba(Fe1-xCox)2As2 [3] as well as
YBa2Cu3Oy [4]. We conclude the observed broken rotational symmetry of the
electronic system is a consequence of the emerging thermodynamic electronic
nematic order at a temperature much higher than onset of the magnetic and
structural transitions.",1901.01788v2
2019-01-09,Crystal structures and the sign reversal Hall resistivity in iron-based superconductors Lix(C3H10N2)0.32FeSe (0.15<x<0.4),"We report the crystal structure, superconductivity and normal state
properties of two iron-based materials, Li0.15(C3H10N2)0.32FeSe(P-4) and
Lix(C3H10N2)0.32FeSe(P4/nmm, 0.25<x<0.4) with superconducting transition
temperature from 40~46K. The determined crystal structures revealed a coupling
between Li concentration and the oritation of 1,2-Diaminopropane molecules
within the hyper expanded FeSe layers. Further fitting on resistivity in terms
of the Lawence-Doniach model suggests the two superconductors belong to the
quasi-two dimonsional system. With increasing temperature, a differences in
crystal structures and doping levels. First principle calculations revealed the
increase in FeSe layer diatance will restruct the Fermi surface and generate a
new hole pocket around Gamma point in the Brillouin Zone. Our findings support
that the increase in two dimensionalities will leads to a temperature induced
Lifshitz transition in electron doped FeSe superconductors.",1901.02580v1
2019-01-11,Carbon and oxygen in metal-poor halo stars,"Carbon and oxygen are key tracers of the Galactic chemical evolution; in
particular, a reported upturn in [C/O] towards decreasing [O/H] in metal-poor
halo stars could be a signature of nucleosynthesis by massive Population III
stars. We reanalyse carbon, oxygen, and iron abundances in thirty-nine
metal-poor turn-off stars. For the first time, we take into account
three-dimensional (3D) hydrodynamic effects together with departures from local
thermodynamic equilibrium (LTE) when determining both the stellar parameters
and the elemental abundances, by deriving effective temperatures from 3D
non-LTE H$\beta$ profiles, surface gravities from Gaia parallaxes, iron
abundances from 3D LTE Feii equivalent widths, and carbon and oxygen abundances
from 3D non-LTE Ci and Oi equivalent widths. We find that [C/Fe] stays flat
with [Fe/H], whereas [O/Fe] increases linearly up to $0.75$ dex with decreasing
[Fe/H] down to $-3.0$ dex. As such [C/O] monotonically decreases towards
decreasing [O/H], in contrast to previous findings, mainly by virtue of less
severe non-LTE effects for Oi at low [Fe/H] with our improved calculations.",1901.03592v2
2019-01-11,Discovery of stars surrounded by iron dust in the LMC,"We consider a small sample of oxygen-rich, asymptotic giant branch stars in
the Large Magellanic Cloud, observed by the Spitzer Space Telescope, exhibiting
a peculiar spectral energy distribution, which can be hardly explained by the
common assumption that dust around AGB stars is primarily composed of silicate
grains. We suggest that this uncommon class of objects are the progeny of a
metal-poor generation of stars, with metallicity $Z \sim 1-2\times 10^{-3}$,
formed $\sim 100$ Myr ago. The main dust component in the circumstellar
envelope is solid iron. In these stars the poor formation of silicates is set
by the strong nucleosynthesis experienced at the base of the envelope, which
provokes a scarcity of magnesium atoms and water molecules, required to the
silicate formation. The importance of the present results to interpret the data
from the incoming James Webb Space Telescope is also discussed.",1901.03621v1
2019-01-11,Crystalline symmetry protected helical Majorana modes in the iron pnictides,"We propose that propagating one-dimensional Majorana fermions will develop in
the vortex cores of certain iron-based superconductors, most notably
Li(Fe$_{1-x}$Co$_x$)As. A key ingredient of this proposal are the 3D Dirac
cones recently observed in ARPES experiments [P. Zhang et al., Nat. Phys.
$\textbf{15}$, 41 (2019)]. Using an effective Hamiltonian around the $\Gamma-Z$
line we demonstrate the development of gapless one-dimensional helical Majorana
modes, protected by $C_4$ symmetry. A topological index is derived which links
the helical Majorana modes to the presence of monopoles in the Berry curvature
of the normal state. We present various experimental consequences of this
theory and discuss its possible connections with cosmic strings.",1901.03692v3
2019-01-24,Nuclear spallation in active galaxies,"A number of works point to the presence of narrow emission features at
unusual energies in the X-ray spectra of active galactic nuclei (AGN) or to
potentially low iron abundances as possible evidence for the spallation of
iron. With the imminence of high-resolution calorimeter spectroscopy, the
potential to test spallation models in astrophysical sources will soon be
possible. Previously determined nuclear spallation reactions of Fe are
recalculated making use of improved total inelastic and partial reaction cross
sections that result in different absolute and relative abundances of the main
spallation elements Mn, Cr, V, and Ti. The effects of ionisation and dynamics
near the black hole are examined in simulated spectra with CCD and calorimeter
(i.e. Hitomi) resolution. With high-resolution, differences in relative
abundances and ionisation should be detectable if spallation is originating at
large distances from the black hole (e.g. torus or disc wind) where blurring is
not significant. If spallation were occurring in the inner accretion disc, it
would likely be undetected as blurring effects would cause significant blending
of spectral features.",1901.08383v1
2019-01-25,Self-assembly of a binary mixture of iron oxide nanoparticles in Langmuir film: X-ray scattering study,"In present study we exploited Langmuir technique to produce self-assembled
arrays composed of monodisperse iron oxide nanoparticles 10 nm and 20 nm in
diameter and of their binary mixture. A combination of in-situ X-ray
reflectometry and Grazing-incident small-Angle X-ray scattering was used to
obtain in-plane and out-of-plane structure of the arrays directly on the water
surface. Surface pressure isotherms and X-ray reflectometry analysis showed
that monodisperse 10 nm nanoparticles form a highly ordered monolayer, while 20
nm particles pack in three-dimensional clusters with a short-range
(nearest-neighbor) correlations between the particles. In a binary mixture of
10 nm and 20 nm nanoparticles composed in proportion 3:1 the self-assembly
process results in a structure where the monolayer of 10 nm particles is
perturbed by the larger particles. Non-trivial mixing causes an enlargement of
interparticle distance but keeps the symmetry of two-dimensional lattice of
smaller nanoparticles. Estimation of the acting interactions and micromagnetic
simulation suggest the optimal formation for monodisperse and binary ensembles.",1901.08822v1
2019-01-28,X-ray scattering characterization of iron oxide nanoparticles Langmuir film on water surface and on a solid substrate,"In the present study we compare a structure of a Langmuir film assembled from
magnetic iron oxide nanoparticles on water surface and a structure of the same
film after its transfer to a solid substrate by the Langmuir-Schaefer method.
In contrast to most of related studies, where different techniques are used to
characterize the films before and after the deposition, we use the same
combination of X-ray reflectometry and Grazing Incidence Small-Angle X-ray
scattering. In both cases -- on a liquid and on a solid substrate -- the film
was identified as a well-ordered monolayer of the nanoparticles laterally
organized in a two-dimensional hexagonal lattice. However parameters of the
lattice were found to be slightly different depending on the type of the
substrate. It is also demonstrated that Langmuir-Schaefer technique is the
right way for deposition of such kind of the particles on a solid substrate.",1901.09636v1
2019-02-13,Anisotropic thermal transport in magnetic intercalates Fe$_{x}$TiS$_2$,"We present a study of the of thermal transport in thin single crystals of
iron-intercalated titanium disulphide, Fe$_{x}$TiS$_2$ for $0\leq x \leq 0.20$.
We determine the distribution of intercalants using high-resolution
crystallographic and magnetic measurements, confirming the insertion of Fe
without long-range ordering. We find that iron intercalation perturbs the
lattice very little, and suppresses the tendency of TiS$_2$ to self-intercalate
with excess Ti. We observe trends in the thermal conductivity that are
compatible with our ab initio calculations of thermal transport in perfectly
stoichiometric TiS$_2$.",1902.04975v1
2019-02-19,Electronic structure of Ni-doped EuRbFe$_4$As$_4$: Unique crystal field splitting and multiband RKKY interactions,"The relationship between magnetism and superconductivity has been one of the
most discussed topics in iron-based superconductors. Using the first-principles
calculations, we have studied the electronic structure of 1144-type iron-based
superconductor EuRbFe$_4$As$_4$. We find the crystal field splitting of
EuRbFe$_4$As$_4$ is unique, such that the $d_{z^2}$ orbitals are closer to the
Fermi level $\epsilon_F$ than the $d_{xy}$ orbitals. The RKKY interaction
strength is estimated to be approximately 0.12 meV in prestine
EuRbFe$_4$As$_4$. Upon Ni-doping on the Fe site, the RKKY interaction strength
is barely changed upon Ni doping due to the highly anisotropic FSs and
multiband effect, despite of the drastically reduced $d_{zx(y)}$ DOS at
$\epsilon_F$. Finally, in both pristine and doped compounds, the RKKY
interaction is primarily mediated through bands due to Fe-$d_{z^2}$
orbitals.Our calculations suggest the RKKY interaction mediated by $d_{z^2}$
orbital is probably responsible for the magnetism in EuRbFe$_4$As$_4$ and
doesn't change upon Ni-doping.",1902.06867v1
2019-03-01,Topological Ultranodal pair states in iron-based superconductors,"Bogoliubov Fermi surfaces are contours of zero-energy excitations that are
protected in the superconducting state. Here we show that multiband
superconductors with dominant spin singlet, intraband pairing of spin-1/2
electrons can undergo a transition to a state with Bogoliubov Fermi surfaces if
spin-orbit coupling, interband pairing and time reversal symmetry breaking are
also present. These latter effects may be small, but drive the transition to
the topological state for appropriate nodal structure of the intra-band pair.
Such a state should display nonzero zero-bias density of states and
corresponding residual Sommerfeld coefficient as for a disordered nodal
superconductor, but occurring even in the pure case. We present a model
appropriate for iron-based superconductors where the topological transition
associated with creation of a Bogoliubov Fermi surface can be studied. The
model gives results that strongly resemble experiments on FeSe$_{1-x}$S$_x$
across the nematic transition, where this ultranodal behavior may already have
been observed.",1903.00481v2
2019-03-04,57Fe enrichment in mice for \b{eta}-thalassaemia studies via Mossbauer spectroscopy of blood samples,"In this work, wild-type and heterozygous \b{eta}-thalassaemic mice were
enriched with 57Fe through gastrointestinal absorption to characterize in more
details the iron complexes appeared in the measured Mossbauer spectra. The 57Fe
enrichment method was validated and Mossbauer spectra were obtained at 80K from
blood samples from wild-type and \b{eta}-thalassaemic mice at 1, 3, 6, and 9
months of age. As expected, the haemoglobin levels of the thalassaemic mice
were lower than from normal mice indicating anaemia. Furthermore, significant
amounts of ferritin-like iron were observed in the thalassaemic mice samples,
which decreased with mouse age, reflecting the pattern of reticulocyte count
reduction reported in the literature.",1903.01245v2
2019-03-20,Lifted electron pocket and reversed orbital occupancy imbalance in FeSe,"The FeSe nematic phase has been the focus of recent research on iron based
superconductors (IBSs) due to its unique properties. A number of electronic
structure studies were performed to find the origin of the phase. However, such
attempts came out with conflicting results and caused additional controversies.
Here, we report results from angle resolved photoemission and X-ray absorption
spectroscopy studies on FeSe with detwinning by a piezo stack. We have fully
resolved band dispersions with orbital characters near the Brillouin zone
corner which reveals absence of a Fermi pocket at the Y point in the 1Fe
Brillouin zone. In addition, the occupation imbalance between dxz and dyz
orbitals is found to be opposite to that of iron pnictides, which is consistent
with the identified band characters. These results settle down controversial
issues in the FeSe nematic phase and shed light on the origin of nematic phases
in IBSs.",1903.08360v1
2019-03-20,Discovery of polarizations from ground state absorption lines: tracer of sub-Gauss magnetic field on 89Her,"We report the identification of the polarization of ground state absorption
lines from post-AGB 89~Hercules. Two ground state neutral iron lines are found
to have counterintuitive high-amplitude polarizations and an unchanged
polarization direction through the orbital period, as opposed to the pattern of
polarizations of absorption lines from excited states, which are synchronized
with the orbital phase owing to optical pumping. This can be explained with
magnetic realignment on the ground state. The 3D mean magnetic field is thereby
unveiled from the degree and direction of the polarizations of the two iron
lines. The field strength is also constrained to be $\lesssim 100\,{\rm mG}$.
Our result has thus improved the accuracy by orders of magnitude compared to
the previous $10\,{\rm G}$ upper limit set by non-detection of the Zeeman
effect.",1903.08675v2
2019-04-12,Quantitative characterization of short-range orthorhombic fluctuations in FeSe through pair distribution function analysis,"Neutron and x-ray total scattering measurements have been performed on powder
samples of the iron chalcogenide superconductor FeSe. Using pair distribution
function (PDF) analysis of the total scattering data to investigate short-range
atomic correlations, we establish the existence of an instantaneous, local
orthorhombic structural distortion attributable to nematic fluctuations that
persists well into the high-temperature tetragonal phase, at least up to 300 K
and likely to significantly higher temperatures. This short-range orthorhombic
distortion is correlated over a length scale of about 1 nm at 300 K and grows
to several nm as the temperature is lowered toward the long-range structural
transition temperature. In the low-temperature nematic state, the local
instantaneous structure exhibits an enhanced orthorhombic distortion relative
to the average structure with a typical relaxation length of 3 nm. The
quantitative characterization of these orthorhombic fluctuations sheds light on
nematicity in this canonical iron-based superconductor.",1904.06440v2
2019-05-14,Hidden robust presence of a hole Fermi surface in a heavily electron doped iron based superconductor LaFe$_2$As$_2$,"We investigate the electronic structure of a recently discovered, heavily
electron-doped iron based superconductor LaFe$_2$As$_2$. Although first
principles calculation shows apparent absence of hole Fermi surfaces around the
$\Gamma$ point, we reveal, by hypothetically removing the La $d$ orbital
contribution, that a hole Fermi surface around the $\Gamma$ point is
essentially present. In the collapsed phase of LaFe$_2$As$_2$, which is
non-superconducting, the hole Fermi surface is found to be absent, and the
difference from the uncollapsed superconducting phase can be naturally
understood within the spin-fluctuation mediated pairing scenario.",1905.05488v2
2019-05-14,Revealing the complex nature of bonding in binary high-pressure compound FeO$_2$,"Extreme pressures and temperatures are known to drastically affect the
chemistry of iron oxides resulting in numerous compounds forming homologous
series $n$FeO$\cdot m$Fe$_2$O$_3$ and the appearance of FeO$_2$. Here, based on
the results of \emph{in situ} single-crystal X-ray diffraction, M\""ossbauer
spectroscopy, X-ray absorption spectroscopy, and DFT+dynamical mean-field
theory calculations we demonstrate that iron in high pressure cubic FeO$_2$ and
isostructural FeO$_2$H$_{0.5}$ is ferric (Fe$^{3+}$), and oxygen has a formal
valence less than two. Reduction of oxygen valence from 2, common for oxides,
down to 1.5 can be explained by a formation of a localized hole at oxygen
sites.",1905.05497v2
2019-05-16,Pressure-induced quantum critical point in a heavily hydrogen-doped iron-based superconductor LaFeAsO,"An iron-based superconductor LaFeAsO$_{1-x}$H$_x$ (0 $\leq x \leq$ 0.6)
undergoes two antiferromagnetic (AF) phases upon H doping. We investigated the
second AF phase ($x$=0.6) using NMR techniques under pressure. At pressures up
to 2 GPa, the ground state is a spin-density-wave state with a large gap;
however, the gap closes at 4.0 GPa, suggesting a pressure-induced quantum
critical point. Interestingly, the gapped excitation coexists with gapless
magnetic fluctuations at pressures between 2 and 4 GPa. This coexistence is
attributable to the lift up of the $d_{xy}$ orbital to the Fermi level, a
Lifshitz transition under pressure.",1905.06606v1
2019-05-16,Thickness-dependent electron momentum relaxation times in thin iron films,"Terahertz time-domain conductivity measurements in 2 to 100 nm thick iron
films resolve the femtosecond time delay between applied electric fields and
resulting currents. This response time decreases for thinner metal films. The
macroscopic response time depends on the mean and the variance of the
distribution of microscopic momentum relaxation times of the conducting
electrons. Comparing the recorded response times with DC-conductivities
demonstrates increasing variance of the microscopic relaxation times with
increasing film thickness. At least two electron species contribute to
conduction in bulk with substantially differing relaxation times. The different
electron species are affected differently by the confinement because they have
different mean free paths.",1905.06739v1
2019-06-11,Iron Embedded Magnetic Nanodiamonds for in vivo MRI Contrast Enhancement,"Although nanodiamonds have long being considered as a potential tool for
biomedical research, the practical in vivo application of nanodiamonds remains
relatively unexplored. In this paper, we present the first application of in
vivo MRI contrast enhancement using only iron embedded magnetic nanodiamonds.
MR image enhancement was clearly demonstrated in the rendering of T2-weighted
images of mice obtained using an unmodified commercial MRI scanner. The
excellent contrast obtained using these nanodiamonds opens the door to the
non-invasive in vivo tracking of NDs and image enhancement. In the future, one
can apply these magnetic nanodiamonds together with surface modifications to
facilitate drug delivery, targeted therapy, localized thermal treatment, and
diagnostic imaging.",1906.04414v1
2019-06-12,Many-body effects in porphyrin-like transition metal complexes embedded in graphene,"We introduce a new computational method to study porphyrin-like transition
metal complexes, bridging density functional theory and exact many-body
techniques, such as the density matrix renormalization group (DMRG). We first
derive a multi-orbital Anderson impurity Hamiltonian starting from first
principles considerations that qualitatively reproduce GGA+U results when
ignoring inter-orbital Coulomb repulsion $U'$ and Hund exchange $J$. An exact
canonical transformation is used to reduce the dimensionality of the problem
and make it amenable to DMRG calculations, including all many-body terms (both
intra, and inter-orbital), which are treated in a numerically exact way. We
apply this technique to FeN$_4$ centers in graphene and show that the inclusion
of these terms has dramatic effects: as the iron orbitals become single
occupied due to the Coulomb repulsion, the inter-orbital interaction further
reduces the occupation yielding a non-monotonic behavior of the magnetic moment
as a function of the interactions, with maximum polarization only in a small
window at intermediate values of the parameters. Furthermore, $U'$ changes the
relative position of the peaks in the density of states, particularly on the
iron $d_{z^2}$ orbital, which is expected to greatly affect the binding of
ligands.",1906.05236v1
2019-06-07,The influence of hydrogen core force shielding on dislocation junctions in iron,"The influence of hydrogen on dislocation junctions was analysed by
incorporating a hydrogen dependent core force into nodal based discrete
dislocation dynamics. Hydrogen reduces the core energy of dislocations, which
reduces the magnitude of the dislocation core force. We refer to this as
hydrogen core force shielding, as it is analogous to hydrogen elastic shielding
but occurs at much lower hydrogen concentrations. The dislocation core energy
change due to hydrogen was calibrated at the atomic scale accounting for the
nonlinear inter-atomic interactions at the dislocation core, giving the model a
sound physical basis. Hydrogen was found to strengthen binary junctions and
promote the nucleation of dislocations from triple junctions. Simulations of
microcantilever bend tests with hydrogen core force shielding showed an
increase in the junction density and subsequent hardening. These simulations
were performed at a small hydrogen concentration realistic for bcc iron.",1906.05344v2
2019-06-25,"First-principles study of the structural, electronic, magnetic and ferroelectric properties of a charge ordered Iron(II)- Iron(III) formate framework","Density functional theory calculations have been performed for the
structural, electronic, magnetic and ferroelectric properties of a
mixed-valence Fe(II)-Fe(III) formate framework [NH$_2$(CH$_3$)$_2$][Fe$^{\rm
III}$Fe$^{\rm II}$(HCOO)$_6$] (DMAFeFe). Recent experiments report a
spontaneous electric polarization and our calculations are in agreement with
the reported experimental value. Furthermore, we shed light into the
microscopic mechanism leading to the observed value and as well how to possibly
enhanced the polarization. The interplay between charge ordering, dipolar
ordering of DMA$^+$ cations and the induced structural distortions suggest new
interesting directions to explore in these complex multifunctional hybrid
perovskites.",1906.10512v1
2019-06-26,Nanoscale Interlayer Defects in Iron Arsenides,"Using a local real-space microscopy probe, we discover evidence of nanoscale
interlayer defects along the c-crystallographic direction in BaFe2As2 (122)
based iron-arsenide superconductors. We find ordered 122 atomic arrangements
within the ab-plane, and within regions of ~10 to 20 nm size perpendicular to
this plane. While the FeAs substructure is very rigid, Ba ions are relatively
weakly bound and can be displaced from the 122, forming stacking faults
resulting in the physical separation of the 122 between adjacent ordered
domains. The evidence for interlayer defects between the FeAs superconducting
planes gives perspective on the minimal connection between interlayer chemical
disorder and high-temperature superconductivity. In particular, the Cooper
pairs may be finding a way around such localized interlayer defects through a
percolative path of the ordered layered 122 lattice that may not affect Tc.",1906.11090v2
2019-06-27,Contribution of type Ia supernovae to the chemical enrichment of the ultra-faint dwarf galaxy Bootes I,"For three stars in the ultra-faint dwarf (UFD) galaxy Bootes I we have
determined the atmospheric parameters, performed a new reduction of
high-resolution spectra from the Subaru archive, and derived the abundances of
eight chemical elements without using the LTE assumption. As a result, among
the galaxies of its class Bootes I now has the largest sample of stars (11)
with a homogeneous set of atmospheric parameters and chemical abundances, and
this makes it the most promising for studying the chemical evolution of UFD
galaxies. We show that in the range -3<[Fe/H]<-2 for each of the three
$\alpha$--process elements, magnesium, calcium, and titanium, a transition from
their overabundance relative to iron with [$\alpha$/Fe]$\approx$0.3 to the
solar [$\alpha$/Fe] ratio occurs. This most likely suggests the commenced
production of iron in type Ia supernovae. The behaviour of the carbon, sodium,
nickel, and barium abundances does not differ from that in more massive
galaxies, our Galaxy and classical dwarf spheroidal galaxies.",1906.11540v1
2019-07-01,Bulk superconductivity and role of fluctuations in the iron-based superconductor FeSe at high pressures,"The iron-based superconductor FeSe offers a unique possibility to study the
interplay of superconductivity with purely nematic as well magnetic-nematic
order by pressure (p) tuning. By measuring specific heat under p up to 2.36GPa,
we study the multiple phases in FeSe using a thermodynamic probe. We conclude
that superconductivity is bulk across the entire p range and competes with
magnetism. Our analysis suggests that superconducting and magnetic fluctuations
exist over a wide temperature range above the respective bulk transition
temperatures, whenever magnetism is present. These observations highlight
similarities between FeSe and underdoped cuprate superconductors where
fluctuations play a crucial role.",1907.01015v2
2019-07-17,Novel Receiver for Superparamagnetic Iron Oxide Nanoparticles in a Molecular Communication Setting,"Superparamagnetic iron oxide nanoparticles (SPIONs) have recently been
introduced as information carriers in a testbed for molecular communication
(MC) in duct flow. Here, a new receiver for this testbed is presented, based on
the concept of a bridge circuit. The capability for a reliable transmission
using the testbed and detection of the proposed receiver was evaluated by
sending a text message and a 80 bit random sequence at a bit rate of 1/s, which
resulted in a bit error rate of 0 %. Furthermore, the sensitivity of the device
was assessed by a dilution series, which gave a limit for the detectability of
peaks between 0.1 to 0.5 mg/mL. Compared to the commercial susceptometer that
was previously used as receiver, the new detector provides an increased
sampling rate of 100 samples/s and flexibility in the dimensions of the
propagation channel. Furthermore, it allows to implement both single-ended and
differential signaling in SPION-bases MC testbeds.",1907.07805v1
2019-07-22,Plaquette instability competing with bicollinear ground state in detwinned FeTe,"We use inelastic neutron scattering to show that long-range spin waves
arising from the static bicollinear antiferromagnetic (AF) order in FeTe, which
have twofold rotational symmetry in a fully detwinned crystal, rapidly dissolve
above $E\approx 26$ meV into ridges of scattering with fourfold rotational
symmetry and a nearly isotropic magnetic fluctuation spectrum. With increasing
temperature above $T_N\approx 68$ K, the twofold spin waves change into broad
regions of scattering with fourfold symmetry. Since the scattering patterns
from plaquette magnetic order generated within a bilinear biquadratic
Hamiltonian have fourfold rotational symmetry consistent with the high-energy,
spin-isotropic spin waves of FeTe, we conclude that the bicollinear AF state in
FeTe is quasidegenerate with plaquette magnetic order, providing evidence for
the strongly frustrated nature of the local moments in iron chalcogenide family
of iron-based superconductors.",1907.09420v1
2019-07-29,Growth of nematic susceptibility in the field-induced normal state of an iron-based superconductor revealed by elastoresistivity measurements in a 65 T pulsed magnet,"In the iron-based superconductors, both nematic and magnetic fluctuations are
expected to enhance superconductivity and may originate from a quantum critical
point hidden beneath the superconducting dome. The behavior of the
non-superconducting state can be an important piece of the puzzle, motivating
in this paper the use of high magnetic fields to suppress superconductivity and
measure the nematic susceptibility of the normal state at low temperatures. We
describe experimental advances which make it possible to measure a resistive
gauge factor (which is a proxy for the nematic susceptibility) in the
field-induced normal state in a 65 T pulsed magnet, and report measurements of
the gauge factor of a micromachined single crystal of
Ba(Fe$_{0.926}$Co$_{0.074}$)$_2$As$_2$ at temperatures down to 1.2 K. The
nematic susceptibility increases monotonically in the field-induced normal
state as the temperature decreases, consistent with the presence of a quantum
critical point nearby in composition.",1907.12191v1
2019-08-02,The superconductivity mechanism in Nd-1111 iron-based superconductor doped by calcium,"We described the effect of nonmagnetic impurity on the superconductivity
behavior of the NdFeAsO0.8F0.2 iron-based superconductor. The resistivity
measurement showed that the superconductivity suppressed upon increasing the
low amounts of calcium impurity (x<0.05). Also, the Tc decreased with the
increase in the residual resistivity. Such behavior was qualitatively described
by the Abrikosov-Gorkov theory and confirmed that these impurities act as
scattering centers. For our samples, the exchange constant between the calcium
and the conduction electron spins was estimated Jexc=|8| meV. Moreover, we
presented the phase diagram of our synthesized samples for the various calcium
dopings and found that according to increase of the calcium impurities and
temperature decreasing of the spin-density wave (TSDW), Fe ions arranged stripe
antiferromagnetically at lower temperatures and also the superconducting
transition temperature (TC) declined. Based on our results and in agreement
with the available theories as explained in the text, since the S++ state has
not an effect on the impurity doped samples, and the S+- state that is
attributed to the spin fluctuations mechanism causes the superconducting
suppression for low amounts of calcium. So, it confirms the role of the
spinfluctuations as a dominant pairing mechanism in our synthesized samples.",1908.00675v1
2019-08-07,Tunability of Room Temperature Ferromagnetism in Spintronic Semiconductors through Non-magnetic Atoms,"The implementation and control of room temperature ferromagnetism (RTFM) by
adding magnetic atoms to a semiconductor's lattice has been one of the most
important problems in solid state state physics in the last decade. Herein we
report for the first time, to our knowledge, on the mechanism that allows RTFM
to be tuned by the inclusion of \emph{non-magnetic} aluminum in nickel ferrite.
This material, NiFe$_{2-x}$Al$_x$O$_4$ (x=0, 0.5, 1.5), has already shown much
promise for magnetic semiconductor technologies, and we are able to add to its
versatility technological viability with our results. The site occupancies and
valencies of Fe atoms (Fe$^{3+}$ T$_d$, Fe$^{2+}$ O$_h$, and Fe$^{3+}$ O$_h$)
can be methodically controlled by including aluminum. Using the fact that
aluminum strongly prefers a 3+ octahedral environment, we can selectively fill
iron sites with aluminum atoms, and hence specifically tune the magnetic
contributions for each of the iron sites, and therefore the bulk material as
well. Interestingly, the influence of the aluminum is weak on the electronic
structure (supplemental material), allowing one to retain the desirable
electronic properties while achieving desirable magnetic properties.",1908.02610v1
2019-08-07,Momentum Dependence of the Nematic Order Parameter in Iron-Based Superconductors,"The momentum dependence of the nematic order parameter is an important
ingredient in the microscopic description of iron-based high-temperature
superconductors. While recent reports on FeSe indicate that the nematic order
parameter changes sign between electron and hole bands, detailed knowledge is
still missing for other compounds. Combining angle-resolved photoemission
spectroscopy (ARPES) with uniaxial strain tuning, we measure the nematic band
splitting in both FeSe and BaFe$_2$As$_2$ without interference from either
twinning or magnetic order. We find that the nematic order parameter exhibits
the same momentum dependence in both compounds with a sign change between the
Brillouin center and the corner. This suggests that the same microscopic
mechanism drives the nematic order in spite of the very different phase
diagrams.",1908.02790v1
2019-08-12,BaTh$_2$Fe$_4$As$_4$(N$_{0.7}$O$_{0.3}$)$_2$: An Iron-Based Superconductor Stabilized by Inter-Block-Layer Charge Transfer,"Recently, An electron-doped 12442-type iron-based superconductor
BaTh$_2$Fe$_4$As$_4$(N$_{0.7}$O$_{0.3}$)$_2$ has been successfully synthesized
with high-temperature solid-state reactions on basis of a structural design.
The inter-block-layer charge transfer between the constituent units of
""BaFe$_2$As$_2$"" and ""ThFeAsN$_{0.7}$O$_{0.3}$"" was found to be essential to
stabilize the target compound. Dominant electron-type conduction and bulk
superconducting transition at ~22 K were demonstrated.",1908.03992v1
2019-08-28,Synergy between Hund-driven correlations and boson-mediated Superconductivity,"Multiorbital systems such as the iron-based superconductors provide a new
avenue to attack the longstanding problem of superconductivity in strongly
correlated systems. In this work we study the superconductivity driven by a
generic bosonic mechanism in a multiorbital model including the full dynamical
electronic correlations induced by the Hubbard U and the Hund's coupling. We
show that superconductivity survives much more in a Hund's metal than in an
ordinary correlated metal with the same degree of correlation. The crucial role
of the redistribution of spectral weight in the Hund's metal reflects also in
the enhancement of the orbital-selective character of the superconducting gaps,
in agreement with experiments in iron-based superconductors.",1908.10901v2
2019-08-28,Impact of anharmonicity on sound wave velocities at extreme conditions,"Theoretical calculations of sound-wave velocities of materials at extreme
conditions are of great importance to various fields, in particular geophysics.
For example, the seismic data on sound-wave propagation through the solid
iron-rich Earth's inner core have been the main source for elucidating its
properties and building models. As the laboratory experiments at very high
temperatures and pressures are non-trivial, ab initio predictions are
invaluable. The latter, however, tend to disagree with experiment. We notice
that many attempts to calculate sound-wave velocities of matter at extreme
conditions in the framework of quantum-mechanics based methods have not been
taking into account the effect of anharmonic atomic vibrations. We show how
anharmonic effects can be incorporated into ab initio calculations and
demonstrate that in particular they might be non-negligible for iron in Earth's
core. Therefore, we open an avenue to reconcile experiment and ab initio
theory.",1908.10927v1
2019-09-04,Unconventional Multi-gap Superconductivity and Antiferromagnetic Spin Fluctuations in New Iron-arsenide LaFe2As2 in Heavily Electron-doped Regime,"We report 75As-NMR/NQR results on new iron-arsenide compounds
(La0.5-xNa0.5+x)Fe2As2. The parent compound x=0 exhibits a stripe-type
antiferromagnetic (AFM) order below T_N=130 K. The measurement of nuclear spin
relaxation rate at hole-doped x=+0.3 and heavily electron-doped x=-0.5 revealed
that the normal-state properties are dominated by AFM spin fluctuations
(AFMSFs), which are more significant at x=+0.3 than at x=-0.5. Their
superconducting (SC) phases are characterized by unconventional multi-gap SC
state, where the smaller SC gaps are particularly weaken in common. The
experimental results indicate the close relationship between the AFMSFs and the
SC from the hole-doped state to heavily electron-doped state, which shed light
on a unique SC phase emerged in the heavily electron-doped regime being
formally equivalent to non-SC compound Ba(Fe0.5Co0.5)Fe2As2.",1909.01569v2
2019-08-28,Artificial Neural Networks and Adaptive Neuro-fuzzy Models for Prediction of Remaining Useful Life,"The U.S. water distribution system contains thousands of miles of pipes
constructed from different materials, and of various sizes, and age. These
pipes suffer from physical, environmental, structural and operational stresses,
causing deterioration which eventually leads to their failure. Pipe
deterioration results in increased break rates, reduced hydraulic capacity, and
detrimental impacts on water quality. Therefore, it is crucial to use accurate
models to forecast deterioration rates along with estimating the remaining
useful life of the pipes to implement essential interference plans in order to
prevent catastrophic failures. This paper discusses a computational model that
forecasts the RUL of water pipes by applying Artificial Neural Networks (ANNs)
as well as Adaptive Neural Fuzzy Inference System (ANFIS). These models are
trained and tested acquired field data to identify the significant parameters
that impact the prediction of RUL. It is concluded that, on average, with
approximately 10\% of wall thickness loss in existing cast iron, ductile iron,
asbestos-cement, and steel water pipes, the reduction of the remaining useful
life is approximately 50%",1909.02115v1
2019-09-13,A Neural Approach to Irony Generation,"Ironies can not only express stronger emotions but also show a sense of
humor. With the development of social media, ironies are widely used in public.
Although many prior research studies have been conducted in irony detection,
few studies focus on irony generation. The main challenges for irony generation
are the lack of large-scale irony dataset and difficulties in modeling the
ironic pattern. In this work, we first systematically define irony generation
based on style transfer task. To address the lack of data, we make use of
twitter and build a large-scale dataset. We also design a combination of
rewards for reinforcement learning to control the generation of ironic
sentences. Experimental results demonstrate the effectiveness of our model in
terms of irony accuracy, sentiment preservation, and content preservation.",1909.06200v2
2019-09-18,Observation of a C-type short range antiferromagnetic order in expanded FeS,"We report neutron diffraction studies of FeS single crystals obtained from
Rb$_x$Fe$_{2-y}$S$_2$ single crystals via a hydrothermal method. While no
$\sqrt {5}\times \sqrt {5}$ iron vacancy order or block antiferromagnetic order
typical of Rb$_x$Fe$_{2-y}$S$_2$ is found in our samples, we observe $C$-type
short range antiferromagnetic order with moments pointed along the $c$-axis
hosted by a new phase of FeS with an expanded inter-layer spacing. The N\'{e}el
temperature for this magnetic order is determined to be 165 K. Our finding of a
variant FeS structure hosting this $C$-type antiferromagnetic order
demonstrates that the known FeS phase synthesized in this method is in the
vicinity of a magnetically ordered ground state, providing insights into
understanding a variety of phenomena observed in FeS and the related
FeSe$_{1-x}$S$_x$ iron chalcogenide system.",1909.08325v1
2019-10-08,The Triplet Resonating Valence Bond State and Superconductivity in Hund's Metals,"A central idea in strongly correlated systems is that doping a Mott insulator
leads to a superconductor by transforming the resonating valence bonds (RVBs)
into spin-singlet Cooper pairs. Here, we argue that a spin-triplet RVB (tRVB)
state, driven by spatially, or orbitally anisotropic ferromagnetic interactions
can provide the parent state for triplet superconductivity. We apply this idea
to the iron-based superconductors, arguing that strong onsite Hund's
interactions develop intra-atomic tRVBs between the t$_{2g}$ orbitals. On
doping, the presence of two iron atoms per unit cell allows these inter-orbital
triplets to coherently delocalize onto the Fermi surface, forming a fully
gapped triplet superconductor. This mechanism gives rise to a unique staggered
structure of onsite pair correlations, detectable as an alternating $\pi$ phase
shift in a scanning tunnelling Josephson microscope.",1910.03168v2
2019-10-08,"AFeSe2 (A=Tl, K, Rb, or Cs): Iron-based superconducting analog of the cuprates","It has long been a challenging task to find compounds with similar crystal
and electronic structures as cuprate superconductors with low dimensionality
and strong antiferromagnetic fluctuations. The parent compounds of cuprate
superconductors are Mott insulators with strong in-plane antiferromagnetic
exchange interactions between Cu moments. Here we show, based on
first-principles density functional calculations, that AFeSe2 (A=Tl, K, Rb, or
Cs) exhibit many of the physical properties common to the cuprate parent
compounds: (1) the FeSe2 layer in AFeSe2 is similar in crystalline and
electronic structures to the CuO2 plane in cuprates, although Se atoms are not
coplanar to the square Fe-lattice; (2) they are antiferromagnetic insulators,
but with relatively small charge excitation gaps; (3) their ground states are
Neel antiferromagnetic ordered, similar as in cuprates; and (4) the
antiferromagnetic exchange interactions between Fe moments are larger than in
other iron-based superconducting materials, but comparable to those in
cuprates. Like cuprates, these compounds may become high-Tc superconductors
upon doping of charge carriers either by chemical substitution or intercalation
or by liquid or solid gating.",1910.03545v2
2019-10-22,An expression for the eddy field in a circular vacuum chamber for HEPS booster dipole,"The analytical expression of the magnetic field distribution within the
aperture of a circular vacuum chamber due to the induced eddy is derived. Two
cases are discussed, one is the absence of iron, the other is that the vacuum
chamber is between the iron poles, that implies the use of the image current
methods. The current angular distribution in the vacuum chamber can be
calculated from the ramping rate of the exposed field, then the contour
integration is applied to the circular current to obtain the field
distribution. The formula can be used to estimate the undesired fields from a
circular beam box when it is exposed to a ramping field.",1910.09781v1
2019-10-22,Ultrafast Quasiparticle Dynamics and Electron-Phonon Coupling in (Li0.84Fe0.16)OHFe0.98Se,"Distinctive superconducting behaviors between bulk and monolayer FeSe make it
challenging to obtain a unified picture of all FeSe-based superconductors. We
investigate the ultrafast quasiparticle (QP) dynamics of an intercalated
superconductor (Li1-xFex)OHFe1-ySe, which is a bulk crystal but shares a
similar electronic structure with single-layer FeSe on SrTiO3. We obtain the
electron-phonon coupling (EPC) constant {\lambda}A1g (0.22 +/- 0.04), which
well bridges that of bulk FeSe crystal and single-layer FeSe on SrTiO3.
Moreover, we find that such a positive correlation between {\lambda}A1g and
superconducting Tc holds among all known FeSe-based superconductors, even in
line with reported FeAs-based superconductors. Our observation indicates
possible universal role of EPC in the superconductivity of all known categories
of iron-based superconductors, which is a critical step towards achieving a
unified superconducting mechanism for all iron-based superconductors.",1910.09859v1
2019-11-13,An investigation of the Brumadinho Dam Break with HEC RAS simulation,"The Brumadinho dam disaster occurred on the 25 January, 2019 when Dam I, an
upstream tailings dam at the Corrego do Feijao iron ore mine, 9 kilometres (5.6
mi) east of Brumadinho, Minas Gerais, Brazil, suffered a catastrophic failure.
Over 248 people died and over 2.88 billion worth of property were lost or
damaged due to the subsequent mud flow and flooding. This is merely 4 years
after the previous Mariana dam break affecting over 1 million people downstream
due to iron ore mining waste flowing downstream into river basin. To prevent a
similar tragedy from reoccurring, it's useful to examine the cause of the
Brumadinho dam break and compare observations with model simulations. HEC RAS,
developed by US Army Corps of Engineers, is used to model the mud flow from the
Brumadinho dam break based on the NASA SRTM elevation dataset over Brazil. The
extent of the mud flow from the HEC RAS simulation matches the actual flooding
due to the dam break. This simulation technique can later be used for future
dam collapse predictions.",1911.05219v1
2019-11-18,ONETEP + TOSCAM: uniting dynamical mean field theory and linear-scaling density functional theory,"We introduce the unification of dynamical mean field theory (DMFT) and
linear-scaling density functional theory (DFT), as recently implemented in
ONETEP, a linear-scaling DFT package, and TOSCAM, a DMFT toolbox. This code can
account for strongly correlated electronic behavior while simultaneously
including the effects of the environment, making it ideally suited for studying
complex and heterogeneous systems containing transition metals and lanthanides,
such as metalloproteins. We systematically introduce the necessary formalism,
which must account for the non-orthogonal basis set used by ONETEP. In order to
demonstrate the capabilities of this code, we apply it to carbon
monoxide-ligated iron porphyrin and explore the distinctly quantum-mechanical
character of the iron $3d$ electrons during the process of photodissociation.",1911.07752v2
2019-11-21,First discovery of trans-iron elements in a DAO-type white dwarf (BD$-22{^\circ}3467$),"We have identified 484 lines of the trans-iron elements (TIEs) Zn, Ga, Ge,
Se, Br, Kr, Sr, Zr, Mo, In, Te, I, Xe, and Ba, for the first time in the
ultraviolet spectrum of a DAO-type WD, namely BD$-22{^\circ}3467$, surrounded
by the ionized nebula Abell 35. Our TIE abundance determination shows extremely
high overabundances of up to five dex -- a similar effect is already known from
hot, H-deficient (DO-type) white dwarfs. In contrast to these where a
pulse-driven convection zone has enriched the photosphere with TIEs during a
final thermal pulse and radiative levitation has established the extreme TIE
overabundances, {here the extreme TIE overabundances are exclusively driven by
radiative levitation on the initial stellar metallicity. The very low mass
($0.533^{+0.040}_{-0.025}\,M_\odot$) of BD$-22{^\circ}3467$ implies that a
third dredge-up with enrichment of s-process elements in the photosphere did
not occur in the AGB precursor.",1911.09573v1
2019-11-25,Local metallicity distribution function derived from Galactic large-scale radial iron pattern modelling,"We develop an approach for fitting the results of modeling of wriggling
radial large scale iron pattern along the Galactic disk, derived over young
(high massive) Cepheids, with the metallicity distribution, obtained using low
mass long living dwarf stars in the close solar vicinity. For this, at the step
of computing of the theoretical abundance distribution over low mass stars in
the solar vicinity we propose to redefine the initial mass function so as the
resulting theoretical stellar distribution over masses would be close to the
distribution in the observed sample. By means of the above algorithm and
subsequent corrections of the theoretical metallicity distribution function,
described in literature, we have achieved fairly well agreement of the
theoretical and observed metallicity distribution functions for low mass stars
in the local solar vicinity.",1911.10842v1
2019-12-09,Pulsation in faint blue stars,"Following the discovery of blue large-amplitude pulsators (BLAPs) by the OGLE
survey, additional hot, high-amplitude pulsating stars have been discovered by
the Zwicky Transient Facility. It has been proposed that all of these objects
are low-mass pre-white dwarfs and that their pulsations are driven by the
opacity of iron-group elements. With this expanded population of pulsating
objects, it was decided to compute a sequence of post-common-envelope stellar
models using the MESA stellar evolution code and to examine the pulsation
properties of low-mass pre-white dwarfs using non-adiabatic analysis with the
GYRE stellar oscillation code. By including the effects of atomic diffusion and
radiative levitation, it is shown that a large region of instability exists
from effective temperatures of 30,000 K up to temperatures of at least 50,000 K
and at a wide range of surface gravities. This encompasses both groups of
pulsator observed so far, and confirms that the driving mechanism is through
iron group element opacity. We make some conservative estimates about the range
of periods, masses, temperatures and gravities in which further such pulsators
might be observed.",1912.04129v1
2019-12-18,"Giant enhancement of critical current density at high field in superconducting (Li,Fe)OHFeSe films by Mn doping","Critical current density (Jc) is one of the major limiting factors for high
field applications of iron-based superconductors. Here, we report that Mn-ions
are successfully incorporated into nontoxic superconducting (Li,Fe)OHFeSe
films. Remarkably, the Jc is significantly enhanced from 0.03 to 0.32 MA/cm^2
under 33 T, and the vortex pinning force density monotonically increases up to
106 GN/m^3, which is the highest record so far among all iron-based
superconductors. Our results demonstrate that Mn incorporation is an effective
method to optimize the performance of (Li,Fe)OHFeSe films, offering a promising
candidate for high-field applications.",1912.08414v1
2019-12-19,The influence of hydrogen on plasticity in pure iron-theory and experiment,"Tensile stress relaxation is combined with transmission electron microscopy
to reveal dramatic changes in dislocation structure and sub structure in pure
alpha iron as a result of the effects of dissolved hydrogen. We find that
hydrogen charged specimens after plastic deformation display a very
characteristic pattern of trailing dipoles and prismatic loops which are absent
in uncharged pure metal. We explain these observations by use of a new self
consistent kinetic Monte Carlo model, which in fact was initially used to
predict the now observed microstructure. The results of this combined theory
and experimental study is to shed light on the fundamental mechanism of
hydrogen enhanced localised plasticity.",1912.09313v1
2019-12-22,Effects of momentum-dependent quasiparticle renormalization on the gap structure of iron-based superconductors,"We discuss the influence of momentum-dependent correlations on the
superconducting gap structure in iron-based superconductors. Within the weak
coupling approach including self-energy effects at the one-loop
spin-fluctuation level, we construct a dimensionless pairing strength
functional which includes the effects of quasiparticle renormalization. The
stationary solution of this equation determines the gap function at $T_c$. The
resulting equations represent the simplest generalization of spin fluctuation
pairing theory to include the effects of an anisotropic quasiparticle weight.
We obtain good agreement with experimentally observed anisotropic gap
structures in LiFeAs, indicating that the inclusion of quasiparticle
renormalization effects in the existing weak-coupling theories can account for
the observed anomalies in the gap structure of Fe-based superconductors.",1912.10453v3
2019-12-23,Measuring transferability issues in machine-learning force fields: The example of Gold-Iron interactions with linearized potentials,"Machine-learning force fields have been increasingly employed in order to
extend the possibility of current first-principles calculations. However, the
transferability of the obtained potential can not always be guaranteed in
situations that are outside the original database. To study such limitation, we
examined the very difficult case of the interactions in gold-iron
nanoparticles. For the machine-learning potential, we employed a linearized
formulation that is parameterized using a penalizing regression scheme which
allows us to control the complexity of the obtained potential. We showed that
while having a more complex potential allows for a better agreement with the
training database, it can also lead to overfitting issues and a lower accuracy
in untrained systems.",1912.10761v3
2020-01-08,Nucleosynthesis in early rotating massive stars and chemical composition of CEMP stars,"The first massive stars triggered the onset of chemical evolution by
releasing the first metals (elements heavier than helium) in the Universe. The
nature of these stars and how the early chemical enrichment took place is still
largely unknown. Rotational-induced mixing in the stellar interior can impact
the nucleosynthesis during the stellar life of massive stars and lead to
stellar ejecta having various chemical compositions. We present low and
zero-metallicity 20, 25 and 40 $M_{\odot}$ stellar models with various initial
rotation rates and assumptions for the nuclear reactions rates. With increasing
initial rotation, the yields of light (from $\sim$ C to Al) and trans-iron
elements are boosted. The trans-iron elements (especially elements heavier than
Ba) are significantly affected by the nuclear reaction uncertainties. The
chemical composition of the observed CEMP (carbon-enhanced metal-poor) stars
CS29528-028 and HE0336+0113 are consistent with the chemical composition of the
material ejected by a fast rotating 40~$M_{\odot}$ model.",2001.02341v1
2020-01-17,Dissociated dislocation-mediated carbon transport and diffusion in austenitic iron,"Dislocation-solute interaction plays fundamental roles in mechanical
properties of alloys. Here, we disclose the essential features of
dislocation-carbon interaction in austenitic Fe at the atomistic scale. We show
that passage of a Shockley partial dislocation in face-centered cubic iron is
able to move carbon atoms on the slip plane forward by one Burgers vector,
revealing a novel dissociated dislocation-mediated transport mechanism. This
mechanism is induced by shear, which is distinct from the normal thermally
activated diffusion process. Furthermore, we show that there exists a fast
diffusion channel with significantly reduced diffusion energy barrier in the
partial dislocation core, which is highly localized and directional. These
inherent geometrical features are crucial for understanding the dependence of
the diffusivity of dislocation pipe diffusion on the character of dislocations;
most importantly, they can result in unbalanced pinning effect on the leading
and trailing partials in a mixed dislocation, consequently facilitating
stacking fault formation and deformation twinning. This explains the
controversial effects of carbon on deformation twinning observed in various
alloys. Our findings pave the road to tune mechanical properties of materials
by manipulating dislocation-interstitial interaction.",2001.06196v1
2020-01-23,Testing general relativity with the stellar-mass black hole in LMC X-1 using the continuum-fitting method,"The iron line and the continuum-fitting methods are currently the two leading
techniques for measuring black hole spins with electromagnetic radiation. They
can be naturally extended for probing the spacetime geometry around black holes
and testing general relativity in the strong field regime. In the past couple
of years, there has been significant work to use the iron line method to test
the nature of black holes. In this Letter, we use the continuum-fitting method
and we show its capability of constraining the spacetime geometry around black
holes by analyzing 17 RXTE data of the X-ray binary LMC X-1.",2001.08391v2
2020-01-24,Passivation mechanisms and pre-oxidation effects on model surfaces of FeCrNi austenitic stainless steel,"Passivation mechanisms were investigated on (100)-oriented Fe-18Cr-13Ni
surfaces with direct transfer between surface preparation and analysis by X-ray
photoelectron spectroscopy and scanning tunneling microscopy and
electrochemical characterization. Starting from oxide-free surfaces,
pre-oxidation at saturation under ultra-low pressure (ULP) oxygen markedly
promotes the oxide film Cr(III) enrichment and hinders/delays subsequent iron
oxidation in water-containing environment. Exposure to sulfuric acid at open
circuit potential causes preferential dissolution of oxidized iron species.
Anodic passivation forces oxide film re-growth, Cr(III) dehydroxylation and
further enrichment. ULP pre-oxidation promotes Cr(III) hydroxide formation at
open circuit potential, compactness of the nanogranular oxide film and
corrosion protection.",2001.09025v1
2020-02-04,Magnetically controlled vector based on E coli Nissle 1917,"In this paper, it is first discovered that EcN has natural magnetically
controlled properties, that is, E coli Nissle 1917 cells move in a gradient
magnetic field of permanent magnets without artificial magnetic labeling. It is
also shown in the paper that the cultivation of EcN in a medium enriched with
iron chelates and under the influence of an external magnetic field increases
several times the magnetophoretic mobility of E coli Nissle 1917 cells compared
to cultivation under standard conditions. Thus, the speed of movement of E coli
Nissle 1917 cells in a gradient magnetic field of laboratory magnets is
achieved of the order of several mm/s. It has also been shown for the first
time that the cultivation of E coli Nissle 1917 biomass is accelerated by
cultivation in an external magnetic field, while the change in the
concentration of iron chelates in the medium has no effect on the cultivation
dynamics of the E coli Nissle 1917 culture.",2002.01958v1
2020-02-10,Structural and magneto-transport studies of iron intercalated Bi2Se3 single crystals,"A detailed investigation on the structural and magneto-transport properties
of iron intercalated Bi2Se3 single crystals have been presented. The x-ray
diffraction and Raman studies confirm the intercalation of Fe in the van der
Waals gaps between the layers. The electrical resistivity of the compounds
decreases upon intercalation, and Hall resistivity shows the enhancement of the
charge carriers upon intercalation. The magnetoresistance shows the
non-saturating linear behavior at higher magnetic field and low temperature.
Intercalation of Fe increases the onset of the linear magnetoresistance
behavior, indicating the reduction in quantum effects. The Kohler scaling
employed on the magnetoresistance data indicates single scattering process for
all these compounds in the measured temperature range of 3- 300 K.",2002.03609v2
2020-02-24,"Local Structure of Mott Insulating Iron Oxychalcogenides La$_{2}$O$_{2}$Fe$_{2}$O$M$$_{2}$ ($M$ = S, Se)","We describe the local structural properties of the iron oxychalcogenides,
La$_2$O$_2$Fe$_2$O$M_2$ ($M$ = S, Se), by using pair distribution function
(PDF) analysis applied to total scattering data. Our results of neutron powder
diffraction show that $M$ = S and Se possess similar nuclear structure at low
and room temperatures. The local crystal structures were studied by
investigating deviations in atomic positions and the extent of the formation of
orthorhombicity. Analysis of the total scattering data suggests that buckling
of the Fe$_2$O plane occurs below 100 K. The buckling may occur concomitantly
with a change in octahedral height. Furthermore, within a typical range of 1-2
nm, we observed short-range orthorhombic-like structure suggestive of nematic
fluctuations in both of these materials.",2002.10305v2
2020-03-06,Adsorption property of fatty acid on iron surface with $Σ$3(111) grain boundary,"Reducing the coefficient of boundary friction on steel surfaces is one of key
technologies to improve the efficiency of machines such as automotive engines.
It has been shown that the boundary friction on nanostructured steel surfaces
in the sliding test using hydrocarbon lubricant molecules is smaller than the
friction of normal steel surfaces. The main difference between the
nanostructured and a normal surfaces is the density of grain boundaries and
other surface defects. The surface defect can attract lubricant molecules and
enhance lubricating film formation on metal surfaces. This can be one of the
mechanisms that induce the friction reduction on the nanosructured steel
surface. In this work, using first principles calculations, the adsorbability
of a lubricant molecule, a fatty acid, on a defected iron surfaces has been
studied. Adsorbability of the Fe(110) surface with symmetrical tilt
{\Sigma}3(111) grain boundary was compared to that of the clean Fe(110)
surface. As a result, we found that the molecule is adsorbed on sites close to
the grain boundary more strongly (0.77 eV in average) than on the Fe surface
without grain boundary.",2003.03061v1
2020-03-12,Band Engineering of Dirac cones in Iron Chalcogenides,"By band engineering the iron chalcogenide Fe(Se,Te) via ab-initio
calculations, we search for topological surface states and realizations of
Majorana bound states. Proposed topological states are expected to occur for
non-stoichiometric compositions on a surface Dirac cone where issues like
disorder scattering and charge transfer between relevant electronic states have
to be addressed. However, this surface Dirac cone is well above the
Fermi-level. Our goal is to theoretically design a substituted crystal in which
the surface Dirac cone is shifted towards the Fermi-level by modifying the bulk
material without disturbing the surface. Going beyond conventional density
functional theory (DFT), we apply the coherent potential approximation
(BEB-CPA) in a mixed basis pseudo-potential framework to scan the
substitutional phase-space of co-substitutions on the Se-sites. We have
identified iodine as a promising candidate for intrinsic doping. Our specific
proposal is that FeSe$_{0.325}$I$_{0.175}$Te$_{0.5}$ is a very likely candidate
to exhibit a Dirac cone right at the Fermi energy without inducing strong
disorder scattering.",2003.05732v2
2020-03-24,Momentum dependent $d_{xz/yz}$ band splitting in LaFeAsO,"We performed angle-resolved photoemission spectroscopy (ARPES) studies of the
electronic structure of the nematic phase in LaFeAsO. Degeneracy breaking
between the dxz and dyz hole bands near the {\Gamma} and M point is observed in
the nematic phase. Different temperature dependent band splitting behaviors are
observed at the {\Gamma} and M points. The energy of the band splitting near
the M point decreases as the temperature decreases while it has little
temperature dependence near the {\Gamma} point. The nematic nature of the band
shift near the M point is confirmed through a detwin experiment using a piezo
device. Since a momentum dependent splitting behavior has been observed in
other iron based superconductors, our observation confirms that the behavior is
a universal one among iron based superconductors.",2003.10618v1
2020-03-26,Quasiclassical theory of $C_4$-symmetric magnetic order in disordered multiband metals,"Recent experimental studies performed in the normal state of iron-based
superconductors have discovered the existence of the $C_4$-symmetric
(tetragonal) itinerant magnetic state. This state can be described as a spin
density wave with two distinct magnetic vectors ${\vec Q}_1$ and ${\vec Q}_2$.
Given an itinerant nature of magnetism in iron-pnictides, we develop a
quasiclassical theory of tetragonal magnetic order in disordered three-band
metal with anisotropic band structure. Within our model we find that the
$C_4$-symmetric magnetism competes with the $C_2$-symmetric state with a single
${\vec Q}$ magnetic structure vector. Our main results is that disorder
promotes tetragonal magnetic state which is in agreement with earlier
theoretical studies.",2003.12124v1
2020-03-30,Electronic correlation effects and local magnetic moments in L1$_0$ phase of FeNi,"We study the electronic and magnetic properties of L1$_0$ phase of FeNi, a
perspective rare-earth-free permanent magnet, by using a combination of density
functional and dynamical mean-field theory. Although L1$_0$ FeNi has a slightly
tetragonally distorted fcc lattice, we find that magnetic properties of its
constituent Fe atoms resemble those in pure bcc Fe. In particular, our results
indicate the presence of well-localized magnetic moments on Fe sites, which are
formed due to Hund's exchange. At the same time, magnetism of Ni sites is much
more itinerant. Similarly to pure bcc Fe, the self-energy of Fe $3d$ states is
found to show the non-Fermi-liquid behavior. This can be explained by
peculiarities of density of Fe $3d$ states, which has pronounced peaks near the
Fermi level. Our study of local spin correlation function and momentum
dependence of particle-hole bubble suggests that the magnetic exchange in this
substance is expected to be of RKKY-type, with iron states providing
local-moment contribution, and the states corresponding to nickel sites
(including virtual hopping to iron sites) providing itinerant contribution.",2003.13347v2
2020-03-03,Novel Meta-Heuristic Model for Discrimination between Iron Deficiency Anemia and B-Thalassemia with CBC Indices Based on Dynamic Harmony Search,"In recent decades, attention has been directed at anemia classification for
various medical purposes, such as thalassemia screening and predicting iron
deficiency anemia (IDA). In this study, a new method has been successfully
tested for discrimination between IDA and \b{eta}-thalassemia trait
(\b{eta}-TT). The method is based on a Dynamic Harmony Search (DHS). Complete
blood count (CBC), a fast and inexpensive laboratory test, is used as the input
of the system. Other models, such as a genetic programming method called
structured representation on genetic algorithm in non-linear function fitting
(STROGANOFF), an artificial neural network (ANN), an adaptive neuro-fuzzy
inference system (ANFIS), a support vector machine (SVM), k-nearest neighbor
(KNN), and certain traditional methods, are compared with the proposed method.",2004.00480v1
2020-04-03,Spin-Excitations Anisotropy in the Bilayer Iron-Based Superconductor CaKFe$_4$As$_4$,"We use polarized inelastic neutron scattering to study the spin-excitations
anisotropy in the bilayer iron-based superconductor CaKFe$_4$As$_4$ ($T_c$ = 35
K). In the superconducting state, both odd and even $L-$modulations of spin
resonance have been observed in our previous unpolarized neutron scattering
experiments (T. Xie {\it et al.} Phys. Rev. Lett. {\bf 120}, 267003 (2018)).
Here we find that the high-energy even mode ($\sim 18$ meV) is isotropic in
spin space, but the low-energy odd modes consist of a $c-$axis polarized mode
around 9 meV along with another partially overlapped in-plane mode around 12
meV. We argue that such spin anisotropy is induced by the spin-orbit coupling
in the spin-vortex-type fluctuations of this unique compound. The spin
anisotropy is strongly affected by the superconductivity, where it is weak
below 6 meV in the normal state and then transferred to higher energy and
further enhanced in the odd mode of spin resonance below $T_c$.",2004.01405v1
2020-04-13,"Topological magnetic line defects in Fe(Te,Se) high-temperature superconductors","Magnetic impurity chains on top of conventional superconductors are promising
platforms to realize Majorana modes. Iron-based high-temperature
superconductors are known in the vicinity of magnetic states due to the strong
Hund's coupling in iron atoms. Here we propose that the line defects with
missing Te/Se anions in Fe(Se,Te) superconductors provide the realization of
intrinsic antiferromagnetic(AFM) chains with Rashba spin-orbit coupling.
Against conventional wisdom, Majorana zero modes (MZMs) can be robustly
generated at these AFM chain ends. These results can consistently explain the
recent experimental observation of zero-energy end states in line defects of
monolayer Fe(Te,Se)/SrTiO$_3$ by scanning tunneling microscopy (STM)
measurements. Our research not only demonstrates an unprecedented interplay
among native line defect, emergent magnetism and topological superconductivity
but also explores a high-temperature platform for Majorana fermions.",2004.05848v1
2020-04-27,Permanent Magnet Penning Trap,"The Penning trap has been investigated as the basis of a small nuclear fusion
reactor using a superconducting solenoid magnet. To extend this investigation,
we designed, constructed, and evaluated a permanent magnet Penning trap. The
device consists of a solenoid formed from an annular array of neodymium bar
magnets between two iron pole pieces designed to give a uniform magnetic field
in the central volume of the device. Critical to achieving the uniform
solenoidal field is an iron equatorial ring supported within the annular array
of magnets. A nonmagnetic titanium Penning trap with hyperbolic surfaces
designed to produce a spherical potential well was mounted inside the permanent
magnet assembly. The trap was fitted with a nonmagnetic hairpin filament
electron source and demonstrated to produce electron trapping at the
theoretically predicted magnetic fields and trap potentials. Trap potentials
achievable were limited by electrical breakdown within the trap operating in
constant potential mode. Efforts were made to extend the trap potentials using
pulsed anode voltages, but nuclear fusion in a Penning trap has not yet been
demonstrated. The design and construction of the permanent magnet solenoid and
nonmagnetic trap are presented here as potentially useful also in other
studies.",2004.13103v1
2020-05-13,Importance of Fermi surface and magnetic interactions for the superconducting dome in electron doped FeSe intercalates,"The van-der-Waals gap of iron chalcogenide superconductors can be
intercalated with a variety of inorganic and organic compounds that modify the
electron doping level of the iron layers. In Lix(C3N2H10)0.37FeSe, a dome in
the superconducting transition temperature Tc has been reported to occur in the
doping range of x=0.06 to x=0.68. We use a combination of density functional
theory and spin fluctuation theory to capture the evolution of superconducting
transition temperatures theoretically. We clearly demonstrate how the changing
electronic structure supports an increasing superconducting Tc. The suppression
of Tc at high doping levels can, however, only be understood by analyzing the
magnetic tendencies, which evolve from stripe-type at low doping to bicollinear
at high doping.",2005.06215v1
2020-06-07,Kinetics of segregation formation in elastic field of edge dislocation in bcc iron,"We study the kinetics of the redistribution of impurity atoms in the elastic
fields of dislocations by computer simulation methods. A work consists of
several stages. The first is the simulation of a dislocation core structure
with a Burgers vector along [100] direction by using the modified molecular
static method. The second is obtaining the coefficients that determine the
influence of the components of the strain tensor on the diagonal elements of
the matrix of diffusion coefficients and in the equations for fluxes of carbon
atoms in bcc iron. The third stage is associated with modeling the diffusion
characteristics of carbon atoms by the method of molecular dynamics in a
crystal without defects. The fourth and final stage uses the data about atomic
structure that we obtained at first stage, as well as the characteristics
calculated in the second and third, is a simulation of the formation of
segregations of interstitial atoms, which is based on solving diffusion
equations that take into account the elastic deformations created by the
dislocation. The complex of developed models is used to analyze the kinetics of
segregation formation. 3D graphs illustrate the distribution of interstitial
atoms in the vicinity of a dislocation for different times at certain
temperatures.",2006.04036v1
2020-06-10,Quantum-Critical Spin-Density Waves in Iron-Selenide High-Tc Superconductors,"Hidden spin-density waves (hSDW) with Neel ordering vector (pi,pi) have been
proposed recently as parent groundstates to electron-doped iron-selenide
superconductors. Doping such groundstates can result in visible electron-type
Fermi surface pockets and faint hole-type Fermi surface pockets at the corner
of the folded Brillouin zone. A Cooper pair instability that alternates in sign
between the electron-type and the hole-type Fermi surfaces has recently been
predicted. The previous is due to the interaction of electrons and holes with
hidden spin fluctuations connected with hSDW order that is near a
quantum-critical point. Quantum criticality is tuned in by increasing the
strength of Hund's Rule from the hSDW state. We find that the exchange of
hidden spin fluctuations by electrons/holes in the critical hSDW state results
in asymptotic freedom. In particular, the strength of spin-flip interactions
becomes weaker and weaker on length scales that are shorter and shorter
compared to the range of hSDW order. We then argue that string states that
connect well-separated particle/hole excitations in the hSDW are robust. This
suggests a picture where the hole degrees of freedom mentioned previously are
confined.",2006.05680v1
2020-06-11,Low thermal conductivity of iron-silicon alloys at Earth core conditions with implications for the geodynamo,"Earth core is composed of iron (Fe) alloyed with light elements, e.g.,
silicon (Si). Its thermal conductivity critically affects Earth thermal
structure, evolution, and dynamics, as it controls the magnitude of thermal and
compositional sources required to sustain a geodynamo over Earth history. Here
we directly measured thermal conductivities of solid Fe and Fe-Si alloys up to
144 GPa and 3300 K. 15 at% Si alloyed in Fe substantially reduces its
conductivity by about 2 folds at 132 GPa and 3000 K. An outer core with 15 at%
Si would have a conductivity of about 20 W m-1 K-1, lower than pure Fe at
similar pressure-temperature conditions. This suggests a lower minimum heat
flow, around 3 TW, across the core-mantle boundary than previously expected,
and thus less thermal energy needed to operate the geodynamo. Our results
provide key constraints on inner core age that could be older than two
billion-years.",2006.06271v2
2020-06-11,Double single-channel Kondo coupling in graphene with Fe molecules,"We study the interaction between graphene and a single-molecule-magnet,
[Fe4(L)2(dpm)6]. Focusing on the closest Iron ion in a hollow position with
respect to the graphene sheet, we derive a channel selective tunneling
Hamiltonian, that couples different d orbitals of the Iron atom to precise
independent combinations of sublattice and valley degrees of freedom of the
electrons in graphene. When looking at the spin-spin interaction between the
molecule and the graphene electrons, close to the Dirac point the channel
selectivity results in a channel decoupling of the Kondo interaction, with two
almost independent Kondo systems weakly interacting among themselves. The
formation of magnetic moments and the development of a full Kondo effect
depends on the charge state of the graphene layer.",2006.06723v1
2020-06-24,Iron line reverberation mapping in Ghasemi-Nodehi-Bambi background,"The reverberation associated with the iron line is the time lag between
direct photons from the corona and the photons reflected from the disk. The
resulting line spectrum is called the 2D transfer function. The shape of the 2D
transfer function is determined by the geometry of spacetime and the properties
of BH. In a paper (Ghasemi-Nodehi and Bambi in EPJC 76:290, 2016), the authors
have proposed a parametrization. This parametrization is aimed to test the Kerr
nature of astrophysical black hole candidates. In this paper, I provide a
reverberation mapping of the Ghasemi-Nodehi-Bambi metric in order to constrain
the parameter of spacetime. All parameters can be constrained with the
exception of b11. The parameter b4 is harder to constrain too.",2006.13640v1
2020-07-13,Effect of interactions and non-uniform magnetic states on the magnetization reversal of iron nanowire arrays,"Ordered ferromagnetic nanowire arrays are widely studied due to the diversity
of possible applications. However, there is still no complete understanding of
the relation between the array's parameters and its magnetic behavior. The
effect of vortex states on the magnetization reversal of large-diameter
nanowires is of particular interest. Here, we compare analytical and
micromagnetic models with experimental results for three arrays of iron
nanowires with diameters of 33, 52 and 70 nm in order to find the balance
between the number of approximations and resources used for the calculations.
The influence of the vortex states and the effect of interwire interactions on
the remagnetization curves is discussed. It has been found that 7 nanowires
treated by a mean field model are able to reproduce well the reversal behaviour
of the whole array in the case of large diameter nanowires. Vortex states tend
to decrease the influence of the structural inhomogeneities on reversal process
and thus lead to the increased predictability of the system.",2007.06499v1
2020-07-19,Isostructural spin-density-wave and superconducting gap anisotropies in iron-arsenide superconductors,"When passing through a phase transition, electronic system saves energy by
opening energy gaps at the Fermi level. Delineating the energy gap anisotropy
provides insights into the origin of the interactions that drive the phase
transition. Here, we report the angle-resolved photoemission spectroscopy
(ARPES) study on the detailed gap anisotropies in both the tetragonal magnetic
and superconducting phases in Sr$_{1-x}$Na$_x$Fe$_2$As$_2$. First, we found
that the spin-density-wave (SDW) gap is strongly anisotropic in the tetragonal
magnetic phase. The gap magnitude correlates with the orbital character of
Fermi surface closely. Second, we found that the SDW gap anisotropy is
isostructural to the superconducting gap anisotropy regarding to the angular
dependence, gap minima locations, and relative gap magnitudes. Our results
indicate that the superconducting pairing interaction and magnetic interaction
share the same origin. The intra-orbital scattering plays an important role in
constructing these interactions resulting in the orbital-selective magnetism
and superconductivity in iron-based superconductors.",2007.09572v1
2020-07-15,Structure and Properties of Thermoresponsive Diblock Copolymers Embedded with Metal Oxide Nanoparticles,"Nanostructured polymer-metal oxide composites are a current research area of
great importance due to its highlight applications in sensors, optics,
catalysts and drug delivery. Particularly the use of thermoresponsive polymers
gives more flexibilities and possibilities in the design and construction of
polymer templates. In the present investigation, the structure and magnetic
properties of hybrid metal oxide/DBC films composed of two kinds of
polystyrene-block-poly (N-isopropylacrylamide)(PS-b-PNIPAM) diblock copolymers
(DBCs) with PS and PNIPAM as the major polymer domains respectively, and iron
oxide were investigated. The thermoresponsive PNIPAM has a lower critical
solution temperature (LCST) in aqueous solution at 32{\deg}C, which enables the
controllable volume ratio of PS and PNIPAM in the structure of PS-b-PNIPAM
diblock copolymers (DBCs). Thus, a temperature and humidity controlling cell
was designed and built for precisely tuning the block structure of PS-b-PNIPAM
DBCs, which was investigated by in-situ small-angle X-ray scattering (SAXS) and
grazing-incidence small-angle X-ray scattering (GISAXS) measurements. The
superparamagnetic behavior of the heat-treated hybrid iron oxide/PS-b-PNIPAM
DBC films was investigated using a superconducting quantum interference device
(SQUID) magnetometer.",2007.10111v1
2020-08-09,The Iron Line Profile from Warped Black Hole Accretion Disks,"The profile of the fluorescent iron line from black hole accretion disks is a
powerful diagnostic of black hole properties, such as spin and inclination. The
state-of-the-art, however, considers an accretion disk whose angular momentum
is aligned with that of the black hole; this is a very constraining assumption
which is unlikely to apply to many or even most astrophysical systems. Here, we
present the first simulation of the reflection spectrum from warped accretion
disks using a realistic model of the reflected emission based on the xillver
code. We present the effects that the radial location of the warp and the tilt
angle have on the line profile, and highlight that the results are highly
dependent on the azimuth position of the observer relative to the tilt angle.
We fit these profiles in XSpec with the standard relxill lamppost model to
quantify the effect that neglecting the disk warps has on the inferred black
hole spins and inclinations. We show that fits with two-component relxill can
be used to derive more accurate spin and inclination estimates.",2008.03829v2
2020-08-13,Detection of a possible multiphase ultra-fast outflow in IRAS 13349+2438 with NuSTAR and XMM-Newton,"We present joint NuSTAR and XMM-Newton observations of the bright, variable
quasar IRAS 13349+2438. This combined dataset shows two clear iron absorption
lines at 8 and 9 keV, which are most likely associated with two layers of
mildly relativistic blueshifted absorption, with velocities of 0.14c and 0.27c.
We also find strong evidence for a series of Ly$\alpha$ absorption lines at
intermediate energies in a stacked XMM-Newton EPIC-pn spectrum, at the same
blueshift as the lower velocity iron feature. This is consistent with a
scenario where an outflowing wind is radially stratified, so faster, higher
ionization material is observed closer to the black hole, and cooler, slower
material is seen from streamlines at larger radii.",2008.05965v1
2020-08-18,Thickness-dependent electron momentum relaxation times in iron films,"Terahertz time-domain conductivity measurements in 2 to 100 nm thick iron
films resolve the femtosecond time delay between applied electric fields and
resulting currents. This current response time decreases from 29 fs for
thickest films to 7 fs for the thinnest films. The macroscopic response time is
not strictly proportional to the conductivity. This excludes the existence of a
single relaxation time universal for all conduction electrons. We must assume a
distribution of microscopic momentum relaxation times. The macroscopic response
time depends on average and variation of this distribution; the observed
deviation between response time and conductivity scaling corresponds to the
scaling of the variation. The variation of microscopic relaxation times depends
on film thickness because electrons with different relaxation times are
affected differently by the confinement since they have different mean free
paths.",2008.07852v1
2020-09-14,BaCuS2: a superconductor with moderate electron-electron correlation,"We show that the layered-structure BaCuS$_2$ is a moderately correlated
electron system in which the electronic structure of the CuS layer bears a
resemblance to those in both cuprates and iron-based superconductors.
Theoretical calculations reveal that the in-plane $d$-$p$ $\sigma^*$-bonding
bands are isolated near the Fermi level. As the energy separation between the
$d$ and $p$ orbitals are much smaller than those in cuprates and iron-based
superconductors, BaCuS$_2$ is expected to be moderately correlated. We suggest
that this material is an ideal system to study the competitive/collaborative
nature between two distinct superconducting pairing mechanisms, namely the
conventional BCS electron-phonon interaction and the electron-electron
correlation, which may be helpful to establish the elusive mechanism of
unconventional high-temperature superconductivity.",2009.06230v1
2020-09-29,On the possibility of through passage of asteroid bodies across the Earth's atmosphere,"We have studied the conditions of through passage of asteroids with diameters
200, 100 and 50 m, consisting of three types of materials -- iron, stone and
water ice across the Earth's atmosphere with the minimum trajectory altitude
10--15 km. The conditions of this passage with subsequent exit into outer space
with the preservation of a substantial fraction of the initial mass have been
found. The results obtained support our idea explaining one of the
long-standing problems of astronomy -- the Tunguska phenomenon which has not
received reasonable and comprehensive interpretations to date. We argue that
Tunguska event was caused by an iron asteroid body, which passed through the
Earth's atmosphere and continued to the near-solar orbit.",2009.14234v1
2020-10-02,Effect of the surface shape of a large space body on its fragmentation in a planetary atmosphere,"Employing the finite element and computational fluid dynamics methods, we
have determined the conditions for the fragmentation of space bodies or
preservation of their integrity when they penetrate into the Earth's
atmosphere. The origin of forces contributing to the fragmentation of space
iron bodies during the passage through the dense layers of the planetary
atmosphere has been studied. It was shown that the irregular shape of the
surface can produce transverse aerodynamic forces capable of causing
deformation stress in the body exceeding the tensile strength threshold of
iron.",2010.01095v1
2020-10-09,"Pressure-induced magnetism in iron-based superconductors $A$Fe$_2$As$_2$ ($A=$ K, Cs, Rb)","The magnetic properties of iron-based superconductors $A$Fe$_2$As$_2$ ($A=$K,
Cs, and Rb), which are characterized by the V-shaped dependence of the critical
temperature ($T_{\rm c}$) on pressure ($P$) were studied by means of the muon
spin rotation/relaxation technique. In all three systems studied the magnetism
was found to appear for pressures slightly below the critical one ($P_{\rm
c}$), i.e. at pressure where $T_{\rm c}(P)$ changes the slope. Rather than
competing, magnetism and superconductivity in $A$Fe$_2$As$_2$ are coexisting at
$P\gtrsim P_{\rm c}$ pressure region. Our results support the scenario of a
transition from one pairing state to another, with different symmetries on
either side of $P_{\rm c}$.",2010.04448v1
2020-11-24,Short-range nematic fluctuations in Sr1-xNaxFe2As2 superconductors,"Interactions between nematic fluctuations, magnetic order and
superconductivity are central to the physics of iron-based superconductors.
Here we report on in-plane transverse acoustic phonons in hole-doped
Sr$_{1-x}$Na$_x$Fe$_2$As$_2$ measured via inelastic X-ray scattering, and
extract both the nematic susceptibility and the nematic correlation length. By
a self-contained method of analysis, for the underdoped ($x=0.36$) sample,
which harbors a magnetically-ordered tetragonal phase, we find it hosts a short
nematic correlation length $\xi$ ~ 10 $\AA$ and a large nematic susceptibility
$\chi_{\rm nem}$. The optimal-doped ($x=0.55$) sample exhibits weaker phonon
softening effects, indicative of both reduced $\xi$ and $\chi_{\rm nem}$. Our
results suggest short-range nematic fluctuations may favor superconductivity,
placing emphasis on the nematic correlation length for understanding the
iron-based superconductors.",2011.12444v1
2020-12-07,Magnetic anisotropy from linear defect structures in correlated electron systems,"Correlated electron systems, particularly iron-based superconductors, are
extremely sensitive to strain, which inevitably occurs in the crystal growth
process. Built-in strain of this type has been proposed as a possible
explanation for experiments where nematic order has been observed at high
temperatures corresponding to the nominally tetragonal phase of iron-based
superconductors. Strain is assumed to produce linear defect structures, e.g.
dislocations, which are quite similar to O vacancy chainlets in the underdoped
cuprate superconductor YBCO. Here we investigate a simple microscopic model of
dislocations in the presence of electronic correlations, which create defect
states that can drive magnetic anisotropy of this kind, if spin orbit
interaction is present. We estimate the contribution of these dislocations to
magnetic anisotropy as detected by current torque magnetometry experiments in
both cuprates and Fe-based systems.",2012.03824v2
2020-12-08,Mean field theory and Monte Carlo simulation of Phase transitions and Magnetic Properties of a tridimensional Fe7S8 Compound,"The structural, electronic and magnetic properties of Fe7S8 material have
been studied within the framework of the ab-initio calculations, the mean field
approximation (MFA) and Monte Carlo simulation (MCS). Our study shows that two
forms of the iron atoms, Fe2+ with spin S=2, and Fe3+ with spin {\sigma}=5/2
are the most probable configurations. A mixed Ising model with ferromagnetic
spin coupling between Fe2+ and Fe3+ ions and between Fe3+ and Fe3+ ions, and
with antiferromagnetic spin coupling between Fe2+ ions of adjacent layers has
been used to study the magnetic properties of this compound. We demonstrated
that the magnetic phase transition can be either of the first or of the second
order, depending on the value of the exchange interaction and crystal field.
The presence of vacancies in every second iron layer leads to incomplete
cancellation of magnetic moments, hence to the emergence of the ferrimagnetism.
Anomalies in the magnetization behavior have been found and compared with the
experimental results.",2012.04306v1
2020-12-13,Under an Iron Sky: On the Entropy at the Start of the Universe,"Curiously, our Universe was born in a low entropy state, with abundant free
energy to power stars and life. The form that this free energy takes is usually
thought to be gravitational: the Universe is almost perfectly smooth, and so
can produce sources of energy as matter collapses under gravity. It has
recently been argued that a more important source of low-entropy energy is
nuclear: the Universe expands too fast to remain in nuclear statistical
equilibrium (NSE), effectively shutting off nucleosynthesis in the first few
minutes, providing leftover hydrogen as fuel for stars. Here, we fill in the
astrophysical details of this scenario, and seek the conditions under which a
Universe will emerge from early nucleosynthesis as almost-purely iron. In so
doing, we identify a hitherto-overlooked character in the story of the origin
of the second law: matter-antimatter asymmetry.",2012.06975v2
2020-12-24,Intrinsic Time-reversal-invariant Topological Superconductivity in Thin Films of Iron-based Superconductors,"We establish quasi-two-dimensional thin films of iron-based superconductors
(FeSCs) as a new high-temperature platform for hosting intrinsic
time-reversal-invariant helical topological superconductivity (TSC). Based on
the combination of Dirac surface state and bulk extended $s$-wave pairing, our
theory should be directly applicable to a large class of experimentally
established FeSCs, opening a new TSC paradigm. In particular, an applied
electric field serves as a ""topological switch"" for helical Majorana edge modes
in FeSC thin films, allowing for an experimentally feasible design of
gate-controlled helical Majorana circuits. Applying an in-plane magnetic field
drives the helical TSC phase into a higher-order TSC carrying corner-localized
Majorana zero modes. Our proposal should enable the experimental realization of
helical Majorana fermions.",2012.13411v2
2021-01-14,Thermal response of the iron-based Ba122 superconductor to in situ and ex situ processes,"The thermal properties are one of the key parameters to control phase purity
and microstructure of polycrystalline materials. The melting point of the
iron-based BaFe2As2 superconductor (Ba122), which foresees high-field
applications, remains controversial. In this work,
thermogravimetry-differential scanning calorimetry measurements (TG-DSC) of
undoped and Co-doped Ba122 were carried out. Mixtures of elemental metals and
pre-reacted Ba122 powders were prepared to investigate the thermal responses
during in situ and ex situ synthesis routes, respectively. In addition, the
phases and microstructures of the quenched samples were evaluated to elucidate
the observed exothermic/endothermic peaks. Our results suggest that the melting
point of Ba122 is ~1300{\deg}C.",2101.05502v1
2021-01-19,Role of interface morphology on the martensitic transformation in pure Fe,"Using classical molecular dynamics simulations, we study austenite to ferrite
phase transformation in iron, focusing on the role of interface morphology. We
compare two different morphologies; a \textit{flat} interface in which the two
phases are joined according to Nishiyama-Wasserman orientation relationship vs.
a \textit{ledged} one, having steps similar to the vicinal surface. We identify
the atomic displacements along a misfit dislocation network at the interface
leading to the phase transformation. In case of \textit{ledged} interface,
stacking faults are nucleated at the steps, which hinder the interface motion,
leading to a lower mobility of the inter-phase boundary, than that of flat
interface. Interestingly, we also find the temperature dependence of the
interface mobility to show opposite trends in case of \textit{flat} vs.
\textit{ledged} boundary. We believe that our study is going to present a
unified and comprehensive view of martensitic transformation in iron with
different interface morphology, which is lacking at present, as \textit{flat}
and \textit{ledged} interfaces are treated separately in the existing
literature.",2101.07468v1
2021-02-19,Superconducting FeSe monolayer with milli-electron volt Fermi energy,"Iron selenide (FeSe) is an iron-based superconductor which shows unique
properties, including strongly anisotropic superconducting gap, paramagnetism
in undoped compound and extremely small Fermi pocket size. In this work, we
demonstrate that the sizes of electron and hole pockets in FeSe monolayer
become much smaller than those in bulk. The Fermi energy is in the order of a
few meV and can be fine-tuned by the thickness of graphene layers underneath.
Despite the low carrier density, the FeSe monolayers grown on trilayer or
multi-layer graphene are superconducting. The superconducting gap size is
sensitive to the Fermi energy of the hole band. Remarkably, the FeSe monolayer
provides the opportunity to study the physics in the crossover regime where the
Fermi energy and superconducting gap are comparable to each other.",2102.09792v1
2021-02-19,Revealing the intrinsic superconducting gap anisotropy in surface-neutralized BaFe$_2$(As$_{0.7}$P$_{0.3}$)$_2$,"Alkaline-earth iron arsenide (122) is one of the most studied families of
iron-based superconductors, especially for angle-resolved photoemission
spectroscopy. While extensive photoemission results have been obtained, the
surface complexity of 122 caused by its charge-non-neutral surface is rarely
considered. Here, we show that the surface of 122 can be neutralized by
potassium deposition. In potassium-coated BaFe$_2$(As$_{0.7}$P$_{0.3}$)$_2$,
the surface-induced spectral broadening is strongly suppressed, and hence the
coherent spectra that reflect the intrinsic bulk electronic state recover. This
enables the measuring of superconducting gap with unpreceded precision. The
result shows the existence of two pairing channels. While the gap anisotropy on
the outer hole/electron pockets can be well fitted using an s$_\pm$ gap
function, the gap anisotropy on the inner hole/electron shows a clear
deviation. Our results provide quantitative constraints for refining
theoretical models and also demonstrate an experimental method for revealing
the intrinsic electronic properties of 122 in future studies.",2102.09919v1
2021-02-22,Influence of the Fermi surface geometry on a Josephson effect between an iron-pnictide and conventional superconductors,"We study Josephson junctions between a multi-band iron-pnictide
Ba1-xNaxFe2As2 and conventional s-wave superconductors Nb and Cu/Nb bilayer. We
observe that junctions with a Cu interlayer exhibit much larger IcRn, despite a
weaker proximity-induced superconductivity. This counterintuitive result is
attributed to the difference in Fermi surface geometries of Nb and Cu, which
leads to a selective one-band tunneling from Cu and a non-selective multi-band
tunnelng from Nb. The latter leads to a mutual cancellation of supercurrents
due to the sign-reversal s+- symmetry of the order parameter in the pnictide.
Our results indicate that Fermi surface geometries play a crucial role for
pnictide-based junctions. This provides a new tool for phase sensitive studies
and paves a way to a conscious engineering of such junctions.",2102.10972v1
2021-02-24,Intermediate mass and heavy Galactic cosmic-ray nuclei: the case of new AMS-02 measurements,"The recent measurement of the spectra of intermediate mass nuclei and iron
nuclei carried out with the AMS-02 experiment provided us with the most
complete set of data on cosmic ray fluxes to date, and allowed us to test the
standard model for the transport of these particles through the Galaxy to the
finest details. We show that the parameters derived from lighter primary and
secondary elements in the cosmic radiation also lead to a good description of
the data on heavier nuclei, with no need to invoke different injection spectra
for such nuclei, provided the whole chain of fragmentation is properly
accounted for. The only exception to this finding is represented by iron
nuclei, which show a very unusual trend at rigidity $\lesssim 100$ GV. This
trend reflects in a Fe/O ratio that is at odds with the results of the standard
model of cosmic ray transport, and is in contradiction with data collected by
HEAO, ACE-CRIS and Voyager at lower energy. We speculate on possible origins of
such findings.",2102.12576v2
2021-03-06,Autonomous detection of molecular configurations in microscopic images based on deep convolutional neural network,"In an effort to explore high-throughput processing of microscopic image data,
a method based on deep convolutional neural network is proposed. The
state-of-the-art computer vision algorithm, Faster R-CNN, was trained for the
detection of iron (II) phthalocyanines on Se-terminated Au(111) platform
resolved by scanning probe microscopy. The construction of the feature pyramid
enables the multi-scale molecule detection in images of different scales from
10 nm to 50 nm. After the detection, the orientation of each molecule is
measured by a following program. Based on the statistical distribution of the
orientation angles, the preferred adsorption configurations of iron (II)
phthalocyanine on the platform are revealed. This method yields high accuracy
and recall with F1 score close to 1 after optimization of hyperparameters and
training. It is expected to be a feasible solution in the scenarios where
autonomous and high-throughput processing of microscopic image data is needed.",2103.04213v1
2021-03-11,Stimuli-responsive assembly of iron oxide nanoparticles into magnetic flexible filaments,"The combination of multiple functionalities in a single material is an
appealing strategy for the de-velopment of smart materials with unique
features. In this work, we present the preparation of thermoresponsive magnetic
nanoparticles and their one-dimensional assembly into transient
micro-filaments. The material is based on 9.4 nm iron oxide nanoparticles
grafted with poly(N-n-propylacrylamide) via multiphosphonic acid anchoring
sites. The hybrid nanoparticles present a low critical solution temperature
(LCST) transition between 21 {\deg}C and 28 {\deg}C, depending on the pH and
the ionic strength. When heated above the LCST in defined conditions, the
nanoparticles ag-gregate and respond to an external magnetic field. An
intrinsic characteristic of the thermorespon-sive particles is an asymmetric
transition between cooling and heating cycles, that was favorably exploited to
build one-dimensional permanent microstructures, such as magnetic
microfilaments and cilia. In summary, we present the development of a
nanoplatform responsive to multiple stimu-li, including temperature, magnetic
field, pH and ionic strength and its transformation into magneti-cally active
microfilaments that could find potential applications in remotely controlled
devices.",2103.06837v1
2021-03-24,Proximity Effect of Epitaxial Iron Phthalocyanine Molecules on High-Quality Graphene Devices,"Depositing magnetic insulators on graphene has been a promising route to
introduce magnetism via exchange proximity interaction in graphene for future
spintronics applications. Molecule-based magnets may offer unique opportunities
because of their synthesis versatility. Here, we investigated the magnetic
proximity effect of epitaxial iron phthalocyanine (FePc) molecules on
high-quality monolayer and bilayer graphene devices on hexagonal boron nitride
substrate by probing the local and non-local transport. Although the FePc
molecules introduce large hole doping effects combined with mobility
degradation, the magnetic proximity gives rise to a canted antiferromagnetic
state under a magnetic field in the monolayer graphene. On bilayer graphene and
FePc heterostructure devices, the non-local transport reveals a pronounced
Zeeman spin-Hall effect. Further analysis of the scattering mechanism in the
bilayer shows a dominated long-range scattering. Our findings in
graphene/organic magnetic insulator heterostructure provide a new insight for
the use of molecule-based magnets in two-dimensional spintronic devices.",2103.12974v1
2021-03-29,Fluorescence intensity correlation imaging with high resolution and elemental contrast using intense x-ray pulses,"We theoretically investigate the fluorescence intensity correlation (FIC) of
Ar clusters and Mo-doped iron oxide nanoparticles subjected to intense,
femtosecond and sub-femtosecond XFEL pulses for high-resolution and elemental
contrast imaging. We present the FIC of {\Ka} and {\Kah} emission in Ar
clusters and discuss the impact of sample damage on retrieving high-resolution
structural information and compare the obtained structural information with
those from the coherent difractive imaging (CDI) approach. We found that, while
sub-femtosecond pulses will substantially benefit the CDI approach,
few-femtosecond pulses may be sufficient for achieving high-resolution
information with FIC. Furthermore, we show that the fluorescence intensity
correlation computed from the fluorescence of Mo atoms in Mo-doped iron oxide
nanoparticles can be used to image dopant distributions.",2103.15872v1
2021-03-31,Slip band interactions and GND latent hardening in a galling resistant stainless steel,"Slip activation, slip band interactions, and GND densities in iron-base,
galling resistant alloy Nitronic 60 have been characterised at the grain length
scale using small-scale mechanical testing with high resolution digital image
correlation and high-angular resolution electron backscatter diffraction. By
correlating the two measurement techniques, new insight into slip band
interactions, the generation of lattice curvature and the corresponding
accumulation of geometrically necessary dislocations (GNDs) is provided.
Multiple discrete slip bands are typically active within single grains,
resulting in significant slip band interactions. Crossing slip bands were found
to generate accumulations of GNDs. Regions where slip bands block other slip
bands were associated with the highest GND densities, in excess of three time
the densities of crossing slip bands. Representative crystal plasticity
modelling investigations have demonstrated that discrete slip blocking events
are responsible for locally elevated GND density. This behaviour is
rationalised in terms of lattice curvature associated with the differing levels
of constraint provided by the crossing or blocking-type behaviours. Ferrite
grains are also found to contribute to the generation of GNDs. Together, these
two effects provide significant work hardening mechanisms, likely to be key to
the development of future iron-base hard facing alloys.",2103.16864v1
2021-01-21,Time-Dependent Density Functional Theory Applied to Average Atom Opacity,"We focus on studying the opacity of iron, chromium, and nickel plasmas at
conditions relevant to experiments carried out at Sandia National Laboratories
[J. E. Bailey et al., Nature 517, 56 (2015)]. We calculate the photo-absorption
cross-sections and subsequent opacity for plasmas using linear response
time-dependent density functional theory (TD-DFT). Our results indicate that
the physics of channel mixing accounted for in linear response TD-DFT leads to
an increase in the opacity in the bound-free quasi-continuum, where the Sandia
experiments indicate that models under-predict iron opacity. However, the
increase seen in our calculations is only in the range of 5-10%. Further, we do
not see any change in this trend for chromium and nickel. This behavior
indicates that channel mixing effects do not explain the trends in opacity
observed in the Sandia experiments.",2104.00551v1
2021-04-15,Unconventional iron-magnesium compounds at terapascal pressures,"Being a lithophile element at ambient pressure, magnesium is long believed to
be immiscible with iron. A recent study by Gao et al. [1] showed that pressure
turns magnesium into a siderophile element and can produce unconventional Fe-Mg
compounds. Here, we extend the investigation to exoplanetary pressure
conditions using an adaptive genetic algorithm-based variable-composition
structural prediction approach. We identify several Fe-Mg phases up to 3 TPa.
Our cluster alignment analysis reveals that most of the predicted Fe-Mg
compounds prefer a BCC packing motif at terapascal pressures. This study
provides a more comprehensive structure database to support future
investigations of the high-pressure structural behavior of Fe-Mg and ternary,
quaternary, etc. compounds involving these elements.",2104.07700v1
2021-04-19,Infrared phonon spectroscopy on the Cairo pentagonal antiferromagnet Bi2Fe4O9: a study through the pressure induced structural transition,"Magnetic and crystallographic transitions in the Cairo pentagonal magnet
Bi2Fe4O9 are investigated by means of infrared synchrotron-based spectroscopy
as a function of temperature (20 - 300 K) and pressure (0 - 15.5 GPa). One of
the phonon modes is shown to exhibit an anomalous softening as a function of
temperature in the antiferromagnetic phase below 240 K, highlighting
spin-lattice coupling. Moreover, under applied pressure at 40 K, an even larger
softening is observed through the pressure induced structural transition.
Lattice dynamical calculations reveal that this mode is indeed very peculiar as
it involves a minimal bending of the strongest superexchange path in the
pentagonal planes, as well as a decrease of the distances between second
neighbor irons. The latter confirms the hypothesis made by Friedrich et al.,1
about an increase in the oxygen coordination of irons being at the origin of
the pressure-induced structural transition. As a consequence, one expects a new
magnetic superexchange path that may alter the magnetic structure under
pressure.",2104.09384v1
2021-04-21,The effect of core formation on surface composition and planetary habitability,"The melt productivity of a differentiated planet's mantle is primarily
controlled by its iron content, which is itself approximated by the planet's
core mass fraction (CMF). Here we show that estimates of an exo-planet's CMF
allows robust predictions of the thickness, composition and mineralogy of the
derivative crust. These predicted crustal compositions allow constraints to be
placed on volatile cycling between surface and the deep planetary interior,
with implications for the evolution of habitable planetary surfaces. Planets
with large, terrestrial-like, CMFs ($\geq$0.32) will exhibit thin crusts that
are inefficient at transporting surface water and other volatiles into the
underlying mantle. By contrast, rocky planets with smaller CMFs ($\leq$0.24)
and higher, Mars-like, mantle iron contents will develop thick crusts capable
of stabilizing hydrous minerals, which can effectively sequester volatiles into
planetary interiors and act to remove surface water over timescales relevant to
evolution. The extent of core formation has profound consequences for the
subsequent planetary surface environment and may provide additional constraints
in the hunt for habitable, Earth-like exo-planets.",2104.10612v1
2021-04-22,Hund's metal crossover and superconductivity in the 111 family of iron-based superconductors,"We study LiFeP, LiFeAs and NaFeAs in their paramagnetic metallic phase
including dynamical electronic correlations within a density functional theory
+ slave-spin mean-field framework. The three compounds are found to lie next to
the crossover between a normal and a Hund's metal, where a region of enhanced
electronic compressibility that may boost superconductivity is systematically
present in this type of systems. We find that LiFeP lies in the normal metallic
regime, LiFeAs at the crossover, and NaFeAs is in the Hund's metal regime,
which possibly explains the different experimental trends for the pressure- and
doping-dependence of superconductivity in these compounds. Our picture captures
the orbitally-resolved mass renormalizations measured in these materials, while
an analysis of the Sommerfeld specific-heat coefficient highlights some
limitations of currently used implementations of density-functional theory for
the correct prediction of the details of band structures in the iron-based
superconductors.",2104.11018v1
2021-05-03,A Bayesian Method for Estimating Uncertainty in Excavated Material,"This paper proposes a method to probabilistically quantify the moments (mean
and variance) of excavated material during excavation by aggregating the prior
moments of the grade blocks around the given bucket dig location. By modelling
the moments as random probability density functions (pdf) at sampled locations,
a formulation of the sums of Gaussian based uncertainty estimation is presented
that jointly estimates the location pdfs, as well as the prior values for
uncertainty coming from ore body knowledge (obk) sub block models. The moments
calculated at each random location is a single Gaussian and they are the
components of Gaussian mixture distribution. The overall uncertainty of the
excavated material at the given bucket location is represented by the Gaussian
Mixture Model (GMM) and therefore moment matching method is proposed to
estimate the moments of the reduced GMM. The method was tested in a region at a
Pilbara iron ore deposit situated in the Brockman Iron Formation of the
Hamersley Province, Western Australia, and suggests a frame work to quantify
the uncertainty in the excavated material that hasn't been studied anywhere in
the literature yet.",2105.00600v1
2021-05-19,Thermal conductivity of iron and nickel during melting: Implication to Planetary liquid outer core,"We report the measurements of the thermal conductivity ($\kappa$) of iron
(Fe) and nickel (Ni) at high pressures and high temperatures. $\kappa$ values
are estimated from the temperature measurements across the sample surface in a
laser heated diamond anvil cell (LHDAC) and using the COMSOL software.
Near-isothermal $\kappa$'s are observed to increase with pressure in both the
metals due to the increase of density of the pressed metals. In both metals
$\kappa$'s are observed to follow a sharp fall during melting at different
pressure points and are consistence with the other multi-anvil measurements.
Constant values of $\kappa$ in these metals during melting at different
pressures reveal the loss of long range order, which creates independent
movement of atomic metals. The melting temperature measured in these metals
from the sudden drop of $\kappa$-values are in a good agreement with the other
melting measurements in LHDAC. The results obtained in this study is expected
to provide an insight to the studies on the planets Mercury and Mars and their
interior.",2105.08962v1
2021-05-19,Origin of insulating ferromagnetism in iron oxychalcogenide Ce$_2$O$_2$FeSe$_2$,"An insulating ferromagnetic (FM) phase exists in the quasi-one-dimensional
iron chalcogenide Ce$_2$O$_2$FeSe$_2$ but its origin is unknown. To understand
the FM mechanism, here a systematic investigation of this material is provided,
analyzing the competition between ferromagnetic and antiferromagnetic
tendencies and the interplay of hoppings, Coulomb interactions, Hund's
coupling, and crystal-field splittings. Our intuitive analysis based on
second-order perturbation theory shows that large entanglements between
doubly-occupied and half-filled orbitals play a key role in stabilizing the FM
order in Ce$_2$O$_2$FeSe$_2$. In addition, via many-body computational
techniques applied to a multi-orbital Hubbard model, the phase diagram confirms
the proposed FM mechanism, in agreement with experiments.",2105.09239v2
2021-05-24,Unveiling non-Abelian statistics of vortex Majorana bound states in iron-based superconductors using fermionic modes,"Motivated by the recent experiments that reported the discovery of vortex
Majorana bound states (vMBSs) in iron-based superconductors, we establish a
portable scheme to unveil the non-Abelian statistics of vMBSs using normal
fermionic modes. The unique non-Abelian statistics of vMBSs is characterized by
the charge flip signal of the fermions that can be easily read out through the
charge sensing measurement. In particular, the charge flip signal will be
significantly suppressed for strong hybridized vMBSs or trivial vortex modes,
which efficiently identifies genuine vMBSs. To eliminate the error induced by
the unnecessary dynamical evolution of the fermionic modes, we further propose
a correction strategy by continually reversing the energy of the fermions,
reminiscent of the quantum Zeno effect. Finally, we establish a feasible
protocol to perform non-Abelian braiding operations on vMBSs.",2105.11199v1
2021-05-24,Redox hysteresis of super-Earth exoplanets from magma ocean circulation,"Internal redox reactions may irreversibly alter the mantle composition and
volatile inventory of terrestrial and super-Earth exoplanets and affect the
prospects for atmospheric observations. The global efficacy of these
mechanisms, however, hinges on the transfer of reduced iron from the molten
silicate mantle to the metal core. Scaling analysis indicates that turbulent
diffusion in the internal magma oceans of sub-Neptunes can kinetically entrain
liquid iron droplets and quench core formation. This suggests that the chemical
equilibration between core, mantle, and atmosphere may be energetically limited
by convective overturn in the magma flow. Hence, molten super-Earths possibly
retain a compositional memory of their accretion path. Redox control by magma
ocean circulation is positively correlated with planetary heat flow, internal
gravity, and planet size. The presence and speciation of remanent atmospheres,
surface mineralogy, and core mass fraction of atmosphere-stripped exoplanets
may thus constrain magma ocean dynamics.",2105.11208v1
2021-05-27,"Iron phthalocyanine on Au(111) is a ""non-Landau"" Fermi liquid","The paradigm of Landau's Fermi liquid theory has been challenged with the
finding of a strongly interacting Fermi liquid that cannot be adiabatically
connected to a non-interacting system. A spin-1 two-channel Kondo impurity with
anisotropy D has a quantum phase transition between two topologically different
Fermi liquids with a peak (dip) in the Fermi level for D < Dc (D > Dc).
Extending this theory to general multi-orbital problems with finite magnetic
field, we reinterpret in a unified and consistent fashion several experimental
studies of iron phthalocyanine molecules on Au(111) that were previously
described in disconnected and conflicting ways. The differential conductance
shows a zero-bias dip that widens when the molecule is lifted from the surface
(reducing the Kondo couplings) and is transformed continuously into a peak
under an applied magnetic field. We reproduce all features and propose an
experiment to induce the topological transition.",2105.13248v2
2021-06-04,Finite element stress analysis of a combined stacker-reclaimer machine: A design audit report,"Design audit or design verification is an important step in engineering of
heavy mobile materials handling equipment. Usually, the costumers employ third
parties for audition of contractors engineering. Here a part of design audit of
a combined stacker-reclaimer machine is reported. This equipment is designed
and constructed by a local supplier in Iran for the iron ore pelletizing plants
at GOHARZAMIN Iron Ore Company. The structure plays an important role in mobile
material handling machines such as Stackers and Reclaimers and its failure and
damage may cause considerable financial and human life losses. In this report
the undercarriage of stacker-reclaimer machine including gantry and traveling
system are numerically analyzed. The Finite Element Method is used for stress
prediction under the critical operating loads according to the design
standards. The critical areas of the undercarriage are identified and it is
observed that, the maximum stress is in the safe range.",2106.02291v1
2021-06-16,Random iron-nickel alloys: From first principles to dynamic spin fluctuation theory,"We provide a systematic analysis of finite-temperature magnetic properties of
random alloys Fe$_x$Ni$_{1-x}$ with the face-centered-cubic structure over a
broad concentration range $x$. By means of the spin-polarized relativistic
Korringa-Kohn-Rostoker method we calculate the electronic structure of
disordered iron-nickel alloys and discuss how a composition change affects
magnetic moments of Fe and Ni and the density of states. We investigate how the
Curie temperature depends on Fe concentration using conventional approaches,
such as mean-field approximation or Monte Carlo simulations, and dynamic
spin-fluctuation theory. Being devised to account for spin fluctuations
explicitly, the latter method shows the best fit to experimental results.",2106.08765v2
2021-06-22,Quantum-confined charge transfer that enhances magnetic anisotropy in lanthanum M-type hexaferrites,"Iron-based hexaferrites are critical-element-free permanent magnet components
of magnetic devices. Of particular interest is electron-doped M-type
hexaferrite i.e., LaFe$_{12}$O$_{19}$ (LaM) in which extra electrons introduced
by lanthanum substitution of barium/strontium play a key role in uplifting the
magnetocrystalline anisotropy. We investigate the electronic structure of
lanthanum hexaferrite using a \textit{localized} density functional theory
which reproduces semiconducting behavior and identifies the origin of the very
large magnetocrystalline anisotropy. Localized charge transfer from lanthanum
to the iron at the crystal's $2a$ site produces a narrow $3d_{z^2}$ valence
band strongly locking the magnetization along the $c$ axis. The calculated
uniaxial magnetic anisotropy energies from fully self-consistent calculations
are nearly double the single-shot values, and agree well with available
experiments. The chemical similarity of lanthanum to other rare earths suggests
that LaM can host for other rare earths possessing non-trivial $4f$ electronic
states for, \textit{e.g.,} microwave-optical quantum transduction.",2106.11947v1
2021-07-02,Breakdown of the Hund's Rule in CuFeAs,"The ground-state properties of CuFeAs were investigated by applying density
functional theory calculations within generalized gradient approximation (GGA)
and GGA+U. We find that the bicollinear antiferromagnetic state with
antiparallel orbital magnetic moments on each iron which violates the Hund's
rule is favored by the on-site Coulomb interaction, which is further stabilized
by Cu vacancy. The magnetic ground state can be used to understand weak
antiferromagnetism in CuFeAs observed experimentally. We argue that breakdown
of the Hund's rule may be the possible origin for reduced magnetism in iron
pnictides, rather than magnetic fluctuations induced by electronic
correlations.",2107.01014v1
2021-07-06,The role of orbital nesting in the superconductivity of Iron-based Superconductors,"We analyze the magnetic excitations and the spin-mediated superconductivity
in iron-based superconductors within a low-energy model that operates in the
band basis but fully incorporates the orbital character of the spin
excitations. We show how the orbital selectivity, encoded in our low-energy
description, simplifies substantially the analysis and allows for analytical
treatments, while retaining all the main features of both spin-excitations and
gap functions computed using multiorbital models. Importantly, our analysis
unveils the orbital matching between the hole and electron pockets as the key
parameter to determine the momentum-dependence and the hierarchy of the
superconducting gaps, instead of the Fermi surface matching as in the common
nesting scenario.",2107.02825v2
2021-07-14,"Phase-manipulation-induced Majorana Mode and Braiding Realization in Iron-based Superconductor Fe(Te,Se)","Recent experiment reported the evidence of dispersing one-dimensional
Majorana mode trapped by the crystalline domain walls in
FeSe$_{0.45}$Te$_{0.55}$. Here, we perform the first-principles calculations to
show that iron atoms in the domain wall spontaneously form the ferromagnetic
order in line with orientation of the wall. The ferromagnetism can impose a
$\pi$ phase difference between the domain-wall-separated surface
superconducting regimes under the appropriate width and magnetization of the
wall. Accordingly, the topological surface superconducting state of
FeSe$_{0.45}$Te$_{0.55}$ can give rise to one-dimensional Majorana modes
trapped by the wall. More interestingly, we further propose a surface junction
in the form of FeSe$_{0.45}$Te$_{0.55}$/ferromagnet/FeSe$_{0.45}$Te$_{0.55}$,
which can be adopted to create and fuse the Majorana zero modes through
controlling the width or magnetization of the interior ferromagnetic barrier.
The braiding and readout of Majorana zero modes can be realized by the designed
device. Such surface junction has the potential application in the
superconducting topological quantum computation.",2107.06558v3
2021-07-15,Multipolar nematic state of nonmagnetic FeSe based on the DFT+$U$,"Clarifying the origin of nematic state in FeSe is one of urgent problems in
the field of iron-based superconductivity. Motivated by the discovery of a
nematic solution in the density-functional theory implemented by on-site
Coulomb interaction (DFT+$U$) [npj Quantum Mater. \textbf{5}, 50 (2020)], we
reexamine the $U$ dependence of electronic states in the nonmagnetic normal
state of FeSe and perform full multipolar analyses for the nematic state. We
find that with increasing $U$ the normal state experiences a topological change
in the Fermi surfaces before the emergence of a nematic ground state. The
resulting nematic ground state is a multipolar state having both
antiferrohexadecapoles in the $E$ representation and ferromultipoles in the
$B_2$ representation on each Fe site. Cooperative coupling between the $E$ and
the $B_2$ multipoles in the local coordinate with the $D_{2d}$ point group will
play an important role in the formation of the $d_{xz},~d_{yz}$
orbital-splitting nematic state not only in FeSe, but also in other iron
pnictides.",2107.07244v3
2021-07-16,Discovery and implications of hidden atomic-scale structure in a metallic meteorite,"Iron and its alloys have made modern civilisation possible, with metallic
meteorites providing one of the human's earliest sources of usable iron as well
as providing a window into our solar system's billion-year history. Here
highest-resolution tools reveal the existence of a previously hidden FeNi
nanophase within the extremely slowly cooled metallic meteorite NWA 6259. This
new nanophase exists alongside Ni-poor and Ni-rich nanoprecipitates within a
matrix of tetrataenite, the uniaxial, chemically ordered form of FeNi. The
ferromagnetic nature of the nanoprecipitates combined with the
antiferromagnetic character of the FeNi nanophases give rise to a complex
magnetic state that evolves dramatically with temperature. These observations
extend and possibly alter our understanding of celestial metallurgy, provide
new knowledge concerning the archetypal Fe-Ni phase diagram and supply new
information for the development of new types of sustainable, technologically
critical high-energy magnets.",2107.07909v1
2021-07-24,Controllable Majorana vortex states in iron-based superconducting nanowires,"There has been experimental evidence for the Majorana zero modes (MZMs) in
solid state systems, which are building blocks for potential topological
quantum computing. It is important to design devices, in which MZMs are easy to
manipulate and possess a broad topological non-trivial parameter space for
fusion and braiding. Here, we propose that the Majorana vortex states in
iron-based superconducting nanowires fulfill these desirable conditions. This
system has a radius-induced topological phase transition, giving a lower limit
to the radius of the nanowire. In the topological phase, there is only one pair
of MZMs in the nanowire over a wide range of radius, chemical potential, and
external magnetic field. The wavefunction of the MZM has a sizable distribution
at the side edge of the nanowire. This property enables one to control the
interaction of the MZMs in neighboring vortex nanowires, and paves the way for
Majorana fusion and braiding.",2107.11562v1
2021-08-07,Strong Momentum-Dependent Electron-Magnon Renormalization of a Surface Resonance on Iron,"The coupling of fermionic quasiparticles to magnons is essential for a wide
range of processes, from ultrafast magnetization dynamics in ferromagnets to
Cooper pairing in superconductors. Although magnon energies are generally much
larger than phonon energies, up to now their electronic band renormalization
effect in ferromagnetic metals suggests a significantly weaker quasiparticle
interaction. Here, using spin- and angle-resolved photoemission, we show an
extraordinarily strong renormalization leading to replica-band formation of an
iron surface resonance at ~200 meV. Its strong magnetic linear dichroism
unveils the magnetic nature and momentum dependence of the energy
renormalization. By determining the frequency- and momentum-dependent
self-energy due to generic electron-boson interaction to compute the resultant
electron spectral function, we show that the surface-state replica formation is
consistent with strong coupling to an optical spin wave in a Fe thin film.",2108.03421v1
2021-08-13,Discovery of mesoscopic nematicity wave in iron-based superconductors,"Nematicity is ubiquitous in electronic phases of high transition temperature
superconductors, particularly in iron-based superconductors (IBSCs). Order
parameter that characterizes the nematic phase has been investigated in
momentum space, but its real-space arrangement remains largely unclear. We use
linear dichroism (LD) in low-temperature laser-photoemission electron
microscope to map out the nematic order parameter of nonmagentic FeSe and
antiferromagnetic BaFe2(As0.87P0.13)2. In contrast to the structural domains
that have atomic-scale domain walls, the LD patterns in both materials show
peculiar sinusoidal waves of electronic nematicity with mesoscopic wavelength.
The analysis reveals that the nematic order has an extremely long coherence
length, more than 1000 times longer than the unit cell. Our direct
visualization of electronic spatial variation uncovers a new fundamental aspect
of quantum liquid crystalline states of correlated electrons in IBSCs.",2108.06122v3
2021-08-17,Importance of the many-body effects for structural properties of the novel iron oxide: Fe$_2$O,"The importance of many-body effects on electronic and magnetic properties and
stability of different structural phases was studied in novel iron oxide -
Fe$_2$O. It was found that while Hubbard repulsion hardly affects the
electronic spectrum of this material ($m^*/m \sim 1.2$), but it strongly
changes its phase diagram shifting critical pressures of structural transitions
to much lower values. Moreover, one of the previously obtained in the density
functional theory (DFT) structures (P$\bar 3$m1) becomes energetically unstable
if many-body effects are taken into consideration. It is shown that this is an
account of magnetic moment fluctuations in the DFT+DMFT approach, which
strongly contributes to modification of the phase diagram of Fe$_2$O.",2108.07645v1
2021-08-26,Magnetic design study of coil-dominated superconducting quadrupole magnets based on racetrack coils,"Several coil structures have been used in accelerator superconducting
quadrupole magnets, and cos2{\theta} quadrupole magnets are the most mature in
theoretical research and engineering applications. However, the cos2{\theta}
quadrupole magnet has a complicated coil structure, especially at the end of
the coil, which makes it difficult to apply strain-sensitive high-temperature
superconductors. Racetrack quadrupole magnets are friendly to high-temperature
superconductors. Field strength of iron-dominated racetrack magnets is limited
by the magnetic saturation of the iron poles. Therefore, coil-dominated
racetrack quadrupole magnets with simple geometry have become the focus of our
research. In this paper, analytical expressions of the magnetic field harmonics
related to racetrack quadrupole coil parameters are obtained. These expressions
are used to find the solution of coil geometry parameters with field harmonics
on the order of 10-4. Then, examples are given to build ideal quadrupole model
and verify the theoretical formulas. Next, the design and optimization of
example racetrack quadrupole magnets are completed in ROXIE. Finally, the
advantages and disadvantages of the racetrack coils and the cos2{\theta} coils
are compared and discussed.",2108.11643v1
2021-09-13,Pseudospin-Triplet Pairing in Iron-Chalcogenide Superconductors,"We study superconductivity of electron systems with both spin and
pseudospin-1/2 degrees of freedom. By solving linearized gap equations, we
derive a weak coupling criterion for the even-parity spin-singlet
pseudospin-triplet pairing. It can generally mix with the on-site s-wave
pairing since both of them belong to the same symmetry representation
($A_{1g}$) and their mixture could naturally give rise to anisotropic
intra-band pairing gap functions with or without nodes. This may directly
explain why some of the iron-chalcogenide superconductors are fully gapped
(e.g. FeSe thin film) and some have nodes (e.g. LaFePO and LiFeP). We also find
that the anisotropy of gap functions can be enhanced when the principal
rotation symmetry is spontaneously broken in the normal state such as
nematicity, and the energetic stabilization of pseudospin-triplet pairings
indicates the coexistence of nematicity and superconductivity. This could be
potentially applied to bulk FeSe, where gap anisotropy has been experimentally
observed.",2109.06039v4
2021-09-15,Exploring DFT$+U$ parameter space with a Bayesian calibration assisted by Markov chain Monte Carlo sampling,"Density-functional theory is widely used to predict the physical properties
of materials. However, it usually fails for strongly correlated materials. A
popular solution is to use the Hubbard corrections to treat strongly correlated
electronic states. Unfortunately, the exact values of the Hubbard $U$ and $J$
parameters are initially unknown, and they can vary from one material to
another. In this semi-empirical study, we explore the $U$ and $J$ parameter
space of a group of iron-based compounds to simultaneously improve the
prediction of physical properties (volume, magnetic moment, and bandgap). We
used a Bayesian calibration assisted by Markov chain Monte Carlo sampling for
three different exchange-correlation functionals (LDA, PBE, and PBEsol). We
found that LDA requires the largest $U$ correction. PBE has the smallest
standard deviation and its $U$ and $J$ parameters are the most transferable to
other iron-based compounds. Lastly, PBE predicts lattice parameters reasonably
well without the Hubbard correction.",2109.07617v1
2021-09-16,"Zero-energy Andreev bound states in iron-based superconductor Fe(Te,Se)","Majorana bound states have been predicted to exist in vortices of topological
superconductors (SC). A realization of the Fu-Kane model, based on a
three-dimensional topological insulator brought into proximity to an $s$-wave
SC, in iron-based SC Fe(Te,Se) has attracted strong interest after pronounced
zero-energy bias peaks were observed in several experiments. Here, we show
that, by taking into account inhomogeneities of the chemical potential or the
presence of potential impurities on the surface of Fe(Te,Se), the emergence of
these zero-energy bias peaks can be explained by trivial Andreev bound states
(ABSs) whose energies are close to zero. Our numerical simulations reveal that
the ABSs behave similarly to Majorana bound states. ABSs are localized only on
the, say, top surface and cannot be distinguished from their topological
counterparts in transport experiments performed with STM tips. Thus, such ABSs
deserve a careful investigation of their own.",2109.08200v1
2021-09-29,High-performance Ba1-xKxFe2As2 superconducting joints for persistent current operation,"Superconducting joints are one of the key technologies to make Ba1-xKxFe2As2
(Ba-122) superconducting wires or tapes for high-field applications. Herein,
superconducting joints were fabricated by a simple cold-pressing method, and
the joint resistance of the iron-based superconducting joint was estimated for
the first time. The superconducting properties, microstructures, and elements
distribution in the joint regions were investigated. At 4.2 K and 10 T, a
transport critical current Ic of 105 A for the joint was obtained, and the
critical current ratio (CCR= Ic-joint/Ic-tape) of the joint was 94.6%. On the
other hand, the joint show very low joint resistance of 2.7x10^-13 ohm in
self-field at 4.2 K. Among iron-based superconductors (IBS), this work is the
first to successfully realize a superconducting joint with such high CCR and
low joint resistance. This work shows great potential to apply Ba-122 in a
range of practical applications, where superconducting joints are essential.",2109.14300v1
2021-10-06,A New Weakly Supervised Learning Approach for Real-time Iron Ore Feed Load Estimation,"Iron ore feed load control is one of the most critical settings in a mineral
grinding process, directly impacting the quality of final products. The setting
of the feed load is mainly determined by the characteristics of the ore
pellets. However, the characterisation of ore is challenging to acquire in many
production environments, leading to poor feed load settings and inefficient
production processes. This paper presents our work using deep learning models
for direct ore feed load estimation from ore pellet images. To address the
challenges caused by the large size of a full ore pellets image and the
shortage of accurately annotated data, we treat the whole modelling process as
a weakly supervised learning problem. A two-stage model training algorithm and
two neural network architectures are proposed. The experiment results show
competitive model performance, and the trained models can be used for real-time
feed load estimation for grind process optimisation.",2110.04063v1
2021-10-13,Oxygen adsorption induced superconductivity in ultrathin FeTe film on SrTiO3(001),"The phenomenon of oxygen incorporation induced superconductivity in iron
telluride (Fe1+yTe, with antiferromagnetic (AFM) orders) is intriguing and
quite different from the case of FeSe. Until now, the microscopic origin of the
induced superconductivity and the role of oxygen are far from clear. Here, by
combining in-situ scanning tunneling microscopy/spectroscopy (STM/STS) and
x-ray photoemission spectroscopy (XPS) on oxygenated FeTe, we found physically
adsorbed O2 molecules crystallized into c(2/3x2) structure as an oxygen
overlayer at low temperature, which was vital for superconductivity. The O2
overlayer were not epitaxial on the FeTe lattice, which implied weak O2-FeTe
interaction but strong molecular interactions. Energy shift observed in the STS
and XPS measurements indicated hole doping effect from the O2 overlayer to the
FeTe layer, leading to a superconducting gap of 4.5 meV opened across the Fermi
level. Our direct microscopic probe clarified the role of oxygen on FeTe and
emphasized the importance of charge transfer effect to induce superconductivity
in iron-chalcogenide thin films.",2110.06417v1
2021-10-20,High-entropy ejecta plumes in Cassiopeia A from neutrino-driven convection,"Recent multi-dimensional simulations suggest that high-entropy buoyant plumes
help massive stars to explode. Outwardly protruding iron-rich fingers in the
galactic supernova remnant Cassiopeia A are uniquely suggestive of this
picture. Detecting signatures of specific elements synthesized in the
high-entropy nuclear burning regime (i.e., $\alpha$-rich freeze out) would be
among the strongest substantiating evidence. Here we report the discovery of
such elements, stable Ti and Cr, at a confidence level greater than 5$\sigma$
in the shocked high-velocity iron-rich ejecta of Cassiopeia A. We found the
observed Ti/Fe and Cr/Fe mass ratios require $\alpha$-rich freeze out,
providing the first observational demonstration for the existence of
high-entropy ejecta plumes that boosted the shock wave at explosion. The metal
composition of the plumes agrees well with predictions for strongly
neutrino-processed proton-rich ejecta. These results support the operation of
the convective supernova engine via neutrino heating in the supernova that
produced Cassiopeia A.",2110.10384v1
2021-10-26,Tunable discontinuous shear thickening in capillary flow of MR suspensions,"Very concentrated suspensions of iron particles in water or ethylene glycol
can be obtained thanks to the use of superplasticizer molecules used in cement
industry. At high volume fractions, these suspensions show a discontinuous
shear thickening which was thoroughly characterized in rotational geometries.
We will show that the jamming transition is also present in a capillary flow,
and that it manifests through the formation of a non-consolidated porous medium
at the constriction between the barrel and the capillary. In suspension of iron
particles, the dynamics of formation of this porous medium, and so the
pressure, can be controlled by a low magnetic field and is reversible for a
constant volume flow rate, opening potential new applications in the domain of
dampers and force control devices.",2110.13759v1
2021-12-04,"Quantitative relationship between structural orthorhombicity, shear modulus and heat capacity anomaly of the nematic transition in iron-based superconductors","Electronic nematicity in iron pnictide materials has been extensively studied
by various experimental techniques, yet its heat capacity anomaly at the phase
transition has not been examined quantitatively. In this work we review the
thermodynamic description of nematicity in $Ba(Fe_{1-x}Co_{x})_{2}As_{2}$ using
the Landau free energy, which defines the behavior of three thermodynamic
quantities: the structural orthorhombicity that develops below the nematic
transition, the softening shear modulus above the transition, and the
discontinuous heat capacity at the transition. We derive a quantitative
relationship between these three quantities, which is found to hold for a range
of dopings. This result shows that the nematic transition is exceedingly well
described by a mean-field model in the underdoped regime of the phase diagram.",2112.02239v2
2021-12-23,The Three-Dimensional Collapse of a Rapidly Rotating 16 $M_{\odot}$ Star,"We report on the three-dimensional (3D) hydrodynamic evolution to iron
core-collapse of a rapidly rotating 16 $M_{\odot}$ star. For the first time, we
follow the 3D evolution of the angular momentum (AM) distribution in the iron
core and convective shell burning regions for the final 10 minutes up to and
including gravitational instability and core-collapse. In 3D, we find that
convective regions show efficient AM transport that leads to an AM profile that
differs in shape and magnitude from $\texttt{MESA}$ within a few shell
convective turnover timescales. For different progenitor models, such as those
with tightly coupled Si/O convective shells, efficient AM transport in 3D
simulations could lead to a significantly different AM distribution in the
stellar interior affecting estimates of the natal neutron star or black hole
spin. Our results suggest that 3D AM transport in convective and rotating shell
burning regions are critical components in models of massive stars and could
qualitatively alter the explosion outcome and inferred compact remnant
properties.",2112.12800v1
2021-12-28,Cluster structure of superconducting phase and the nature of peaks in the doping dependences of the London penetration depth in iron pnictides,"The mechanism of formation of dome-like phase diagrams and the features of
magnetic field penetration in iron pnictides with hetero- and isovalent doping
are considered within the framework of the previously proposed model, which
assumes the local character of doping and the cluster structure of resulted
superconducting phase. It is shown that the proposed model, despite its
simplicity and neglect of the features of the electronic structure, makes it
possible not only to accurately calculate the positions of superconducting
domes on the phase diagrams of specific HTSC compounds, but also to explain the
nature and position of sharp peaks in the London penetration depth depending on
the doping level.",2112.14167v2
2022-01-18,The Wrought Iron Beauty of Poncelet Loci,"We've built a web-based tool for the real-time interaction with loci of
Poncelet triangle families. Our initial goals were to facilitate exploratory
detection of geometric properties of such families. During frequent walks in my
neighborhood, it appeared to me Poncelet loci shared a palette of motifs with
those found in wrought iron gates at the entrance of many a residential
building. As a result, I started to look at Poncelet loci aesthetically, a kind
of generative art. Features were gradually added to the tool with the sole
purpose of beautifying the output. Hundreds of interesting loci were
subsequently collected into an online ""gallery"", with some further enhanced by
a graphic designer. We will tour some of these byproducts here. An interesting
question is if Poncelet loci could serve as the basis for future metalwork
and/or architectural designs.",2201.06960v1
2022-01-18,In-situ alignment of anisotropic hard magnets of 3D printed magnets,"Within this work, we demonstrate in-situ easy-axis alignment of
single-crystal magnetic particles inside a polymer matrix using fused filament
fabrication. Two different magnetic materials are investigated: (i) Strontium
hexaferrite inside a PA6 matrix, fill grade: 49 vol% and (ii) Samarium iron
nitride inside a PA12 matrix, fill grade: 44 vol%. In the presence of the
external alignment field, the strontium hexaferrite particles inside the PA6
matrix can be well aligned with a ratio of remanent magnetization to saturation
magnetization of 0.7. No significant alignment for samarium iron nitride could
be achieved. The results show the feasibility to fabricate magnets with
arbitrary and locally defined easy axis using fused filament fabrication since
the permanent magnets used for the alignment (or alternatively an
electromagnet) can be mounted on a rotatable platform.",2201.07111v1
2022-01-19,Nodal multigap superconductivity in the anisotropic iron-based compound RbCa2Fe4As4F2,"The 12442 compounds are a recently discovered family of iron-based
superconductors, that share several features with the cuprates due to their
strongly anisotropic structure, but are so far poorly understood. Here, we
report on the gap structure and anisotropy of RbCa2(Fe1-xNix)4As4F2 single
crystals, investigated by a combination of directional point-contact
Andreev-reflection spectroscopy and coplanar waveguide resonator measurements.
Two gaps were identified, with clear signatures of d-wave-like nodal structures
which persist upon Ni doping, well described by a two-band d-d state with
symmetry-imposed nodes. A large London penetration depth anisotropy was
revealed, weakly dependent on temperature and fully compatible with the d-d
model.",2201.07593v1
2022-01-24,Hund's coupling and electronic anisotropy in the spin-density wave state of iron pnictides,"In the multiband systems, Hund's coupling ($J$) plays a significant role in
the spin and charge excitations. We study the dependence of electronic
anisotropy on $J$ in terms of Drude-weight along different directions as well
as the orbital order in the four-fold symmetry broken spin-density wave state
of iron pnictides. A robust behavior of the Drude-weight anisotropy within a
small window around $J \sim 0.25U$ with $U$ as intraorbital Coulomb interaction
is described in terms of orbital-weight distribution along the reconstructed
Fermi surfaces. We also find that the ferro-orbital order increases with $J$ in
the widely accepted regime for the latter, which is explained as a consequence
of rising exchange field with an increase in magnetization.",2201.09808v1
2022-01-24,Low-energy physics for an iron phthalocyanine molecule on Au(111),"The system of an iron phthalocyanine molecule on the Au(111) surface, has
been studied recently due to its peculiar properties. In particular, several
surprising results of scanning tunneling spectroscopy changing the position of
the molecule and applying magnetic field can be explained by the {\it
non-Landau} Fermi liquid state of a 2-channel spin-1 Kondo model with
anisotropy. The localized orbitals near the Fermi level are three, one of
symmetry $z^2$ and two (nearly) degenerate $\pi$ orbitals of symmetry $xz$ and
$yz$. Previous studies using the numerical renormalization group neglected one
of these orbitals to render the problem tractable. Here we investigate, using a
slave-boson mean-field approximation, if the splitting $S$ between $\pi$
orbitals caused by spin-orbit coupling (SOC) justifies this approximation. We
obtain an abrupt transition from a 3-band regime to a 2-band one at a value of
$S$ which is about 1/3 of the atomic SOC for Fe, justifying the 2-band model
for the system.",2201.10010v2
2022-01-25,Multiscale machine-learning interatomic potentials for ferromagnetic and liquid iron,"We develop and compare four interatomic potentials for iron: a simple
machine-learned embedded atom method (EAM) potential, a potential with
machine-learned two- and three-body-dependent terms, a potential with
machine-learned EAM and three-body terms, and a Gaussian approximation
potential with the SOAP descriptor. All potentials are trained to the same
diverse database of body-centered cubic and liquid structures computed with
density functional theory. The four presented potentials represent different
levels of complexity and span three orders of magnitude in computational cost.
The first three potentials are tabulated and evaluated efficiently using cubic
spline interpolations, while the fourth one is implemented without additional
optimization. We compare and discuss the advantages of each implementation,
transferability and applicability in terms of the balance between required
accuracy versus computational cost.",2201.10237v1
2022-01-31,Mathematical analysis of a thermodynamically consistent reduced model for iron corrosion,"We are interested in a reduced model for corrosion of iron, in which ferric
cations and electrons evolve in a fixed oxide layer subject to a
self-consistent electrostatic potential. Reactions at the boundaries are
modeled thanks to Butler-Volmer formulas, whereas the boundary conditions on
the electrostatic potential model capacitors located at the interfaces between
the materials. Our model takes inspiration in existing papers, to which we
bring slight modifications in order to make it consistent with thermodynamics
and its second principle. Building on a free energy estimate, we establish the
global in time existence of a solution to the problem without any restriction
on the physical parameters, in opposition to previous works. The proof further
relies on uniform estimates on the chemical potentials that are obtained thanks
to Moser iterations. Numerical illustrations are finally provided to highlight
the similarities and the differences between our new model and the one
previously studied in the literature.",2201.13193v1
2022-05-10,A Machine-Learned Spin-Lattice Potential for Dynamic Simulations of Defective Magnetic Iron,"A machine-learned spin-lattice interatomic potential (MSLP) for magnetic iron
is developed and applied to mesoscopic scale defects. It is achieved by
augmenting a spin-lattice Hamiltonian with a neural network term trained to
descriptors representing a mix of local atomic configuration and magnetic
environments. It reproduces the cohesive energy of BCC and FCC phases with
various magnetic states. It predicts the formation energy and complex magnetic
structure of point defects in quantitative agreement with density functional
theory (DFT) including the reversal and quenching of magnetic moments near the
core of defects. The Curie temperature is calculated through spin-lattice
dynamics showing good computational stability at high temperature. The
potential is applied to study magnetic fluctuations near sizable dislocation
loops. The MSLP transcends current treatments using DFT and molecular dynamics,
and surpasses other spin-lattice potentials that only treat near-perfect
crystal cases.",2205.04732v1
2022-05-26,Elastoresistivity of heavily hole doped 122 iron pnictides superconductors,"Nematicity in the heavily hole-doped iron pnictide superconductors remains
controversial. Sizeable nematic fluctuations and even nematic orders far from a
magnetic instability were declared in RbFe$_2$As$_2$ and its sister compounds.
Here we report a systematic elastoresistance study of series of isovalent- and
electron-doped KFe$_2$As$_2$ crystals. We found divergent elastoresistance upon
cooling for all the crystals along their [110] direction. The amplitude of
elastoresistivity diverges if K is substituted with larger ions or if the
system is driven towards a Lifshitz transition. However, we conclude none of
them necessarily indicates an independent nematic critical point. Instead, the
increased nematicity can be associated with another electronic criticality. In
particular, we propose a mechanism how elastoresistivity is enhanced at a
Lifshitz transition.",2205.13663v1
2022-07-10,Semimetallic spin-density wave state in iron pnictides,"We examine the existence of semimetallic spin-density wave states in iron
pnictides. In the experimentally observed metallic spin-density wave state, the
symmetry-protected Dirac cones are located away from the Fermi surface giving
rise to tiny pockets and there are also additional Fermi pockets such as one
around $\Gamma$. We find that the location of a pair of Dirac points with
respect to the Fermi surface exhibits significant sensitivity to the orbital
splitting between the $d_{xz}$ and $d_{yz}$ orbitals. Besides, in the presence
of orbital splitting, the Fermi pockets not associated with the Dirac cones,
can be suppressed so that a semimetallic spin-density wave state can be
realized. We explain these finding in terms of difference in the slopes and
orbital contents of the bands which form the Dirac cone, and obtain the
necessary conditions dependent on these two and other parameters for the
coexisting Dirac semimetallic and spin-density wave states. Additionally, the
topologically protected edge states are studied in the ribbon geometry when the
same are oriented either along $x$ or $y$ axes.",2207.04365v1
2022-07-22,Orbital and magnetic ordering in single-layer FePS3: A DFT+U study,"Among the numerous 2D system that can be prepared via exfoliation, iron
phosphorus trisulfide (FePS3) attracts a lot of attention recently due to its
broad-range photoresponse, its unusual Ising-type magnetic order and possible
applications in spintronic nano-devices. Despite various experimental and
theoretical-computational reports, there are still uncertainties in identifying
its magnetic ground state. In this paper, we investigate the structural and
magnetic properties of single-layer FePS3 by using Density Functional Theory.
Our findings show that orbital ordering leads to a variation in distance
between pairs of iron atoms by 0.14 Angstrom. These lattice distortions, albeit
small, trigger different (ferromagnetic and antiferromagnetic) exchange
couplings so that the ground state consists of ferromagnetically aligned zigzag
chains along the long Fe-Fe bonds which couple antiferromagnetically along the
shorter Fe-Fe bonds. Within the DFT+U framework, we parameterize a spin
Hamiltonian including Heisenberg, single-ion anisotropy, Dzyaloshinskii-Moriya
and biquadratic interactions. Using U=2.22eV gives a consistent description of
both the electronic band gap and the Neel temperature in 2D FePS3.",2207.11283v2
2022-07-25,Anomalous Shiba states in topological iron-based superconductors,"We demonstrate the formation of robust zero energy modes close to magnetic
impurities in the iron-based superconductor FeSe$_{1-x}$Te$_x$. We find that
the Zeeman field generated by the impurity favors a spin-triplet inter-orbital
pairing as opposed to the spin-singlet intra-orbital pairing prevalent in the
bulk. The preferred spin-triplet pairing preserves time-reversal symmetry and
is topological, as robust, topologically-protected zero modes emerge at the
boundary between regions with different pairing states. Moreover, the zero
modes form Kramers doublets that are insensitive to the direction of the spin
polarization or to the separation between impurities. We argue that our
theoretical results are consistent with recent experimental measurements on
FeSe$_{1-x}$Te$_x$.",2207.12425v2
2022-08-16,Core-shell enhanced single particle model for lithium iron phosphate batteries: model formulation and analysis of numerical solutions,"In this paper, a core-shell enhanced single particle model for iron-phosphate
battery cells is formulated, implemented, and verified. Starting from the
description of the positive and negative electrodes charge and mass transport
dynamics, the positive electrode intercalation and deintercalation phenomena
and associated phase transitions are described with the core-shell modeling
paradigm. Assuming two phases are formed in the positive electrode, one rich
and one poor in lithium, a core-shrinking problem is formulated and the phase
transition is modeled through a shell phase that covers the core one. A careful
discretization of the coupled partial differential equations is proposed and
used to convert the model into a system of ordinary differential equations. To
ensure robust and accurate numerical solutions of the governing equations, a
sensitivity analysis of numerical solutions is performed and the best setting,
in terms of solver tolerances, solid phase concentration discretization points,
and input current sampling time, is determined in a newly developed
probabilistic framework. Finally, unknown model parameters are identified at
different C-rate scenarios and the model is verified against experimental data.",2208.07485v1
2022-08-26,Pure nematic state in iron-based superconductor,"Lattice and electronic states of thin FeSe films on LaAlO$_3$ substrates are
investigated in the vicinity of the nematic phase transition. No evidence of
structural phase transition is found by x-ray diffraction below $T^\ast \sim
90$ K, while results obtained from resistivity measurement and angle-resolved
photoemission spectroscopy clearly show the appearance of a nematic state.
These results indicate formation of a pure nematic state in the iron-based
superconductor and provide conclusive evidence that the nematic state
originates from the electronic degrees of freedom. This pure nematicity in the
thin film implies difference in the electron-lattice interaction from bulk FeSe
crystals. FeSe films provide valuable playgrounds for observing the pure
response of ""bare"" electron systems free from the electron-lattice interaction,
and should make important contribution to investigate nematicity and its
relationship with superconductivity.",2208.12384v4
2022-08-27,Magnetic bond-order potential for iron-cobalt alloys,"For large-scale atomistic simulations of magnetic materials, the interplay of
atomic and magnetic degrees of freedom needs to be described with high
computational efficiency. Here we present an analytic bond-order potential
(BOP) for iron-cobalt, an interatomic potential based on a coarse-grained
description of the electronic structure. We fitted BOP parameters to magnetic
and non-magnetic density-functional theory (DFT) calculations of Fe, Co, and
Fe-Co bulk phases. Our BOP captures the electronic structure of magnetic and
non-magnetic Fe-Co phases. It provides accurate predictions of structural
stability, elastic constants, phonons, point and planar defects, and structural
transformations. It also reproduces the DFT-predicted sequence of stable
ordered phases peculiar to Fe-Co and the stabilization of B2 against disordered
phases by magnetism. Our Fe-Co BOP is suitable for atomistic simulations with
thousands and millions of atoms.",2208.12973v2
2022-08-31,The giants that were born swiftly -- Implications of the top-heavy stellar initial mass function on the birth conditions of globular clusters,"Recent results suggest that the initial mass function (IMF) of globular
clusters (GCs) is metallicity and density dependent. Here it is studied how
this variation affects the initial masses and the numbers of core collapse
supernovae (CCSNe) required to reproduce the observed iron spreads in GCs. The
IMFs of all of the investigated GCs were top-heavy implying larger initial
masses compared to previous results computed assuming an invariant canonical
IMF. This leads to more CCSNe being required to explain the observed iron
abundance spreads. The results imply that the more massive GCs formed at
smaller Galactocentric radii, possibly suggesting in-situ formation of the
population II halo. The time until star formation (SF) ended within a proto-GC
is computed to be 3.5 - 4 Myr, being slightly shorter than the 4 Myr obtained
using the canonical IMF. Therefore, the impact of the IMF on the time for which
SF lasts is small.",2209.00045v1
2022-09-05,Increased muon field at surface and substrate interface of palladium thin films,"We performed depth-dependent low-energy muon spin spectroscopy ($\mu$SR)
studies on three palladium 100 nm thin films, both undoped and doped with 170
ppm of iron. Muons implanted in the surface and substrate interface region
probe an increased local magnetic field compared to the inner part of the
sample. The field increase extends over a few nanometers, it is
temperature-independent (in the range of 3.7 - 100 K), stronger for the
iron-doped samples and accompanied by an increase in local field inhomogeneity.
We consider various potential origins for this magnetic surface state, such as
adsorbents and supressed d-states. Our conclusion is that orbital moments
induced at the surface / interface by localized spins and charges are the most
likely explanation, potentially accompanied by magnetic moments due to crystal
irregularities.",2209.02002v1
2022-09-17,Onset Temperatures for Superconducting Fluctuations in Te-annealed FeTe$_{1-x}$Se$_x$ Single Crystals: Evidence for the BCS-BEC Crossover,"Recently, the superconductors' community has witnessed an unsettled debate
regarding whether iron-based superconductors, in particular FeSe and
FeSe$_{1-x}$S$_x$, are in the Bardeen-Cooper-Shrieffer (BCS) - Bose-Einstein
condensation (BEC) crossover regime. Nonetheless, one particular system,
FeTe$_{1-x}$Se$_x$, has been less investigated in this regard owing to the
screening of its intrinsic superconducting properties by the inevitable iron
excess. Herein, the onset temperatures for superconducting fluctuations
($T_{scf}$) are investigated by measuring the magnetoresistance (MR) of
Te-annealed, high-quality FeTe$_{1-x}$Se$_x$ ($x$ = 0.1, 0.2, 0.3, and 0.4)
single crystals. The results reveal very high $T_{scf}$ values for these
crystals. Particularly for $x$ = 0.4, $T_{scf}$ reaches approximately 40 K,
which is 2.7 times larger than $T_c$. This indicates that the superconductivity
of the FeTe$_{1-x}$Se$_x$ system is well within the BCS-BEC crossover regime.",2209.08238v1
2022-09-19,"Anisotropic gap structure and sign reversal symmetry in monolayer Fe(Se,Te)","The iron-based superconductors are an ideal platform to reveal the enigma of
the unconventional superconductivity and potential topological
superconductivity. Among them, the monolayer Fe(Se,Te)/SrTiO3(001), which is
proposed to be topological nontrivial, shows interface-enhanced
high-temperature superconductivity in the two dimensional limit. However, the
experimental studies on the superconducting pairing mechanism of monolayer
Fe(Se,Te) films are still limited. Here, by measuring quasiparticle
interference in monolayer Fe(Se,Te)/SrTiO3(001), we report the observation of
the anisotropic structure of the large superconducting gap and the sign change
of the superconducting gap on different electron pockets. The results are well
consistent with the 'bonding-antibonding' s+- wave pairing symmetry driven by
spin fluctuations in conjunction with spin-orbit coupling. Our work is of basic
significance not only for a unified superconducting formalism in the iron-based
superconductors, but also for understanding of topological superconductivity in
high-temperature superconductors.",2209.08683v2
2022-10-03,"Energetics, electronic states, and magnetism of iron phthalocyanine on pristine and defected graphene layers","Transition metal phthalocyanines (TMPc's) are under intense scrutiny in the
field of spintronics, as they may be promising storage devices. The simplicity
and cheapness of such molecules increase their commercial potential. There is
an active study of how the magnetic moment of the metal centre of such
molecules can be changed. Here, we particularly consider the iron
phthalocyanine molecule (FePc) on a graphene layer as a substrate. We study how
graphene defects (the Stone-Wales defect, B-doping, N-doping, S-doping, and
combined B (N, S)-doped Stone-Wales defects) change the FePc electronic
structure. We present ab initio study of the systems, which is done using
several approaches: based on periodic plane wave density functional theory
(DFT), a linear combination of atomic orbitals (LCAO) DFT with a cluster
representation of graphene, and multiconfigurational methods with the pyrene
molecule presented as a miniaturised graphene cluster. The treatment of the
FePc/Graphene hybrid system using multiconfigurational methods was done for the
first time. It was found that the hybrid systems with B- and N- dopings have
quasi-degenerate ground states and it is necessary to go beyond the
approximation of one Slater determinant.",2210.01025v1
2022-10-19,Competing ferromagnetic superconducting states in europium-based iron pnictides,"In europium-based iron pnictides superconducting Fe-planes can be influenced
by a Zeeman field originated from the neighboring Eu-planes. The field tends to
induce spin-density waves with a ferromagnetic average which coexists with the
superconducting order by forming complementary patterns of the superconducting
and magnetic order parameters in a Fulde-Ferrell-Larkin-Ovchinnikov phase and a
two-dimensional textured-superconducting phase. The hard gap around the Fermi
energy disappears in these fragile inhomogeneous superconducting states, which
features, instead, V-shaped spin-resolved local density of states. The
inhomogeneous states are also competing with either a homogeneous
superconducting or a homogeneous ferromagnetic state, manifesting the
intertwining influences of the magnetic orders in Fe and Eu planes, the
spin-density wave band structure, and the superconducting pairing order.",2210.10312v1
2022-11-14,Rapid Formation of Exoplanetesimals Revealed by White Dwarfs,"The timing of formation for the first planetesimals determines the mode of
planetary accretion and their geophysical and compositional evolution.
Astronomical observations of circumstellar discs and Solar System geochronology
provide evidence for planetesimal formation during molecular cloud collapse,
much earlier than previously estimated. Here, we present distinct observational
evidence from white dwarf planetary systems for planetesimal formation
occurring during the first few hundred thousand years after cloud collapse in
exoplanetary systems. A significant fraction of white dwarfs have accreted
planetary material rich in iron core or mantle material. In order for the
exo-asteroids accreted by white dwarfs to form iron cores, substantial heating
is required. By simulating planetesimal evolution and collisional evolution we
show that the most likely heat source is short-lived radioactive nuclides such
as Al-2 (half life of approximately 0.7 Myr). Core-rich materials in the
atmospheres of white dwarfs, therefore, provide independent evidence for rapid
planetesimal formation, concurrent with star formation.",2211.07244v1
2022-12-06,Transient gap generation in BaFe$_2$As$_2$ driven by coherent lattice vibrations,"The electronic structure and the magnetic properties of iron-based
superconductors are highly sensitive to the pnictogen height. Coherent
excitation of the $A_{1g}$ phonon by femtosecond laser directly modulates the
pnictogen height, which has been used to control the physical properties of
iron-based superconductors. Previous studies show that the driven $A_{1g}$
phonon resulted in a transient increase of the pnictogen height in
BaFe$_2$As$_2$, favoring an enhanced Fe magnetic moment. Here, we use
time-resolved broadband terahertz spectroscopy to investigate the dynamics of
BaFe$_2$As$_2$ in the $A_{1g}$ phonon driven state. Below the spin-density wave
(SDW) transition temperature, we observe a transient gap generation at early
time delays. A similar transient feature is observed in the normal state up to
room temperature.",2212.03337v1
2022-12-28,ISAI: Investigating Solar Axion by Iron-57,"The existence of the axion is a unique solution for the strong CP problem,
and the axion is one of the most promising candidates of the dark matter.
Investigating Solar Axion by Iron-57 (ISAI) is being prepared as a complemented
table-top experiment to confirm the solar axion scenario. Probing an X-ray
emission from the nuclear transitions associated with the axion-nucleon
coupling is a leading approach. ISAI searches for the monochromatic 14.4 keV
X-ray from the first excited state of 57Fe using a state-of-the-art pixelized
silicon detector, dubbed XRPIX, under an extremely low-background environment.
We highlight scientific objectives, experimental design and the latest status
of ISAI.",2212.13708v1
2023-02-27,Predicting elastic and plastic properties of small iron polycrystals by machine learning,"Deformation of crystalline materials is an interesting example of complex
system behaviour. Small samples typically exhibit a stochastic-like, irregular
response to externally applied stresses, manifested as significant
sample-to-sample variation in their mechanical properties. In this work we
study the predictability of the sample-dependent shear moduli and yield
stresses of a large set of small cube-shaped iron polycrystals generated by
Voronoi tesselation, by combining molecular dynamics simulations and machine
learning. Training a convolutional neural network to infer the mapping between
the initial polycrystalline structure of the samples and features of the
ensuing stress-strain curves reveals that the shear modulus can be predicted
better than the yield stress. We discuss our results in the context of the
sensitivity of the system's response to small perturbations of its initial
state.",2302.13745v3
2023-04-13,Aromatic molecules as sustainable lubricants explored by ab initio simulations,"In the pursuit of sustainable lubricant materials, the conversion of common
organic molecules into graphitic material has been recently shown to
effectively reduce friction of metallic interfaces. Aromatic molecules are
perfect candidates due to their inertness and possibility to form carbon-based
tribofilms. Among many promising possibilities, we selected a group of common
aromatic compounds and we investigated their capability to reduce the adhesion
of iron interface. Ab initio molecular dynamic simulations of the sliding
interface show that hypericin, a component of St. John's wort, effectively
separates the mating iron surfaces better than graphene. This phenomenon is due
to the size of the molecule, the reactivity of the moieties at its edges and
the possibility to stack several of these structures that can easily slide on
top of each other. The decomposition of the lateral groups of hypericin
observed in the dynamic simulations suggests that the clustering of several
molecules is possible, offering innovative paths to lubricate sliding contacts
with compounds not typically employed in tribology.",2304.06501v2
2023-04-17,Ultrafast Relaxation Dynamics of Spin-Density Wave Order in BaFe$_2$As$_2$ under High Pressures,"BaFe$_2$As$_2$ is the parent compound for a family of iron-based
high-temperature superconductors as well as a prototypical example of the
spin-density wave (SDW) system. In this study, we perform an optical pump-probe
study of this compound to systematically investigate the SDW order across the
pressure-temperature phase diagram. The suppression of the SDW order by
pressure manifests itself by the increase of relaxation time together with the
decrease of the pump-probe signal and the pump energy necessary for complete
vaporization of the SDW condensate. We have found that the pressure-driven
suppression of the SDW order at low temperature occurs gradually in contrast to
the thermally-induced SDW transition. Our results suggest that the
pressure-driven quantum phase transition in BaFe$_2$As$_2$ (and probably other
iron pnictides) is continuous and it is caused by the gradual worsening of the
Fermi-surface nesting conditions.",2304.08080v1
2023-04-18,Electron correlation effects in paramagnetic cobalt,"We study the influence of Coulomb correlations on spectral and magnetic
properties of fcc cobalt using a combination of density functional theory and
dynamical mean-field theory. The computed uniform and local magnetic
susceptibilities obey the Curie-Weiss law, which, as we demonstrate, occurs due
to the partial formation of local magnetic moments. We find that the lifetime
of these moments in cobalt is significantly less than in bcc iron, suggesting a
more itinerant magnetism in cobalt. In contrast to the bcc iron, the obtained
electronic self-energies exhibit a quasiparticle shape with the quasiparticle
mass enhancement factor ${m^*/m}\sim$1.8, corresponding to moderately
correlated metal. Finally, our calculations reveal that the static magnetic
susceptibility of cobalt is dominated by ferromagnetic correlations, as
evidenced by its momentum dependence.",2304.08980v1
2023-04-27,Influence of oxygen on electronic correlation and transport in iron in the outer Earth's core,"Knowing the transport properties of iron under realistic conditions present
in the Earth's core is essential for the geophysical modeling of Earth's
magnetic field generation. Besides by extreme pressures and temperatures,
transport may be influenced importantly also by the presence of light elements.
Using a combination of molecular dynamics, density functional theory, and
dynamical mean-field theory methods we investigate how oxygen impurities
influence the electronic correlations and transport in the liquid outer Earth's
core. We consider a case with an oxygen content of ~10 atomic%, a value that is
believed to be close to the composition of the core. We find that the
electronic correlations are enhanced but their effect on conductivities is
moderate (compared to pure Fe, electrical conductivity drops by 10% and thermal
conductivity by 18%). The effect of electron-electron scattering alone, whereas
not large, is comparable to effects of the compositional disorder. We reveal
the mechanism behind the larger suppression of the thermal conductivity and
associated reduction of the Lorenz ratio and discuss its geophysical
significance.",2304.13962v1
2023-05-08,Uniaxial-Strain Tuning of the Intertwined Orders in BaFe$_2$(As$_{1-x}$P$_{x}$)$_2$,"An experimental determination of electronic phase diagrams of high-transition
temperature (high-$T_c$) superconductors forms the basis for a microscopic
understanding of unconventional superconductivity. For most high-$T_c$
superconductors, the electronic phase diagrams are established through partial
chemical substitution, which also induces lattice disorder. Here we show that
symmetry-specific uniaxial strain can be used to study electronic phases in
iron-based superconductors, composed of two-dimensional nearly square iron
lattice planed separated by other elements. By applying tunable uniaxial strain
along different high symmetry directions and carrying out transport
measurements, we establish strain-tuning dependent electronic nematicity,
antiferromagnetic (AF) order, and superconductivity of
BaFe$_2$(As$_{1-x}$P$_{x}$)$_2$ superconductor. We find that uniaxial strain
along the nearest Fe-Fe direction can dramatically tune the AF order and
superconductivity, producing an electronic phase diagram clearly different from
the chemical substitution-induced one. Our results thus establish strain tuning
as a way to study the intertwined orders in correlated electron materials
without using chemical substitution.",2305.04424v1
2023-06-19,Kinetics of hydrogen and vacancy diffusion in iron: A Kinetic Activation Relaxation technique (k-ART) study,"We investigate hydrogen (H) and mono and divacancy-hydrogen complexes (VH$_x$
and V$_2$H$_x$) diffusion in body-centered-cubic (BCC) iron using the kinetic
Activation-Relaxation Technique (k-ART), an off-lattice kinetic Monte Carlo
approach with on-the-fly event catalog building, to explore diffusion barriers
and associated mechanisms for these defects. K-ART uncovers complex diffusion
pathways for the bound complexes, with important barrier variations that depend
on the geometrical relations between the position of the inserting Fe atom and
that of the bound H. Since H is small and brings little lattice deformation
around itself, these bound complexes are compact and H is fully unbound at the
second neighbour site already. As more H are added, however, vacancies deform
and affect the lattice over longer distances, contributing to increasing the
VH$_x$ complex diffusion barrier and its impact on its local environment. We
find, moreover, that the importance of this trapping decreases when going from
mono to divacancy complexes, although diffusion barriers for these complexes
increase with the number of trapped H.",2306.11176v1
2023-06-30,Orbital-selective correlations for topology in FeSe$_{x}$Te$_{1-x}$,"Strong correlations lead to emergent excitations at low energies. When
combined with symmetry constraints, they may produce topological electronic
states near the Fermi energy. Within this general framework, here we address
the topological features in iron-based superconductors. We examine the effects
of orbital-selective correlations on the band inversion in the iron
chalcogenide FeSe$_{x}$Te$_{1-x}$ near its doping of optimal superconductivity,
within a multiorbital model and using a $U(1)$ slave spin theory. The orbital
selectivity of the quasiparticle spectral weight, along with its counterpart of
the energy level renormalization, leads to a band inversion and Dirac node
formation pinned to the immediate vicinity of the Fermi energy. Our work
demonstrates both the naturalness and robustness of the topological properties
in FeSe$_{x}$Te$_{1-x}$, and uncovers a new setting in which strong
correlations and space-group symmetry cooperate in generating strongly
correlated electronic topology.",2306.17739v1
2023-07-02,"Thermochemical Stability of Low-Iron, Manganese-Enriched Olivine in Astrophysical Environments","Low-iron, manganese-enriched (LIME) olivine grains are found in cometary
samples returned by the Stardust mission to comet 81P/Wild 2. Similar grains
are found in primitive meteoritic clasts and unequilibrated meteorite matrix.
LIME olivine is thermodynamically stable in a vapor of solar composition at
high temperature at total pressures of a millibar to a microbar, but enrichment
of solar composition vapor in a dust of chondritic composition causes the
FeO/MnO ratio of olivine to increase. The compositions of LIME olivines in
primitive materials indicate oxygen fugacities close to that of a very reducing
vapor of solar composition. The compositional zoning of LIME olivines in
amoeboid olivine aggregates is consistent with equilibration with nebular vapor
in the stability field of olivine, without reequilibration at lower
temperatures. A similar history is likely for LIME olivines found in comet
samples and in interplanetary dust particles. LIME olivine is not likely to
persist in nebular conditions in which silicate liquids are stable.",2307.00652v1
2023-08-10,Absence of superconductivity in electron-doped chromium pnictides ThCrAsN$_{1-x}$O$_x$,"Theoretical studies predicted possible superconductivity in electron-doped
chromium pnictides isostructural to their iron counterparts. Here, we report
the synthesis and characterization of a new ZrCuSiAs-type Cr-based compound
ThCrAsN, as well as its oxygen-doped variants. All samples of
ThCrAsN$_{1-x}$O$_x$ show metallic conduction, but no superconductivity is
observed above 30 mK even though the oxygen substitution reaches 75\%. The
magnetic structure of ThCrAsN is determined to be G-type antiferromagnetic by
magnetization measurements and first-principles calculations jointly. The
calculations also indicate that the in-plane Cr--Cr direct interaction of
ThCrAsN is robust against the heavy electron doping. The calculated density of
states of the orbital occupations of Cr for ThCrAs(N,O) is strongly
spin-polarized. Our results suggest the similarities between chromium pnictides
and iron-based superconductors shouldn't be overestimated.",2308.05267v1
2023-08-16,Phase separation and phase transitions in undoped and Rh3+ doped iron pnictide CaFe2As2: a Raman scattering study,"Iron-pnictides Ca(Fe1-xRhx)2As2 (x = 0, 0.035, and 0.19) were studied across
the tetragonal-orthorhombic and uncollapsed to collapsed tetragonal phase
transitions using Raman spectroscopy. The effect of the phase separation was
observed in the high-temperature phase for the first time. Two phases with the
low-spin and high-spin states of the Fe2+ ions coexist in the undoped (x = 0)
and doped (x = 0.035) samples at ambient conditions. These two phases are
present on a larger length scale and they are not limited to the local
distortions. Both phases in the undoped sample successfully undergo
tetra-to-ortho phase transitions approximately at the same temperature T0 = 160
K. In doped samples, a cascade of phase transitions is observed at temperatures
T* = 100 K and Tc = 72 K with cooling for the first time. A complex type of the
re-entrant magnetic structure is realized in the x = 0.035 sample at
temperatures below Tc, which is distinct from the usual orthorhombic twofold
one. The overdoped sample (x = 0.19) also shows phase separation at
temperatures 7 - 295 K in Raman spectra similar to these of the remnant phase.",2308.08633v1
2023-08-23,Oxygen-Terminated (1x1) Reconstruction of Reduced Magnetite Fe$_3$O$_4$(111),"The (111) facet of magnetite (Fe$_3$O$_4$) has been studied extensively by
experimental and theoretical methods, but controversy remains regarding the
structure of its low-energy surface terminations. Using density functional
theory (DFT) computations, we demonstrate three reconstructions that are more
favorable than the accepted Fe$_{\rm oct2}$ termination in reducing conditions.
All three structures change the coordination of iron in the kagome Fe$_{\rm
oct1}$ layer to tetrahedral. With atomically-resolved microscopy techniques, we
show that the termination that coexists with the Fe$_{\rm tet1}$ termination
consists of tetrahedral iron capped by three-fold coordinated oxygen atoms.
This structure explains the inert nature of the reduced patches.",2308.12023v1
2023-08-25,Causally Sound Priors for Binary Experiments,"We introduce the BREASE framework for the Bayesian analysis of randomized
controlled trials with a binary treatment and a binary outcome. Approaching the
problem from a causal inference perspective, we propose parameterizing the
likelihood in terms of the baseline risk, efficacy, and adverse side effects of
the treatment, along with a flexible, yet intuitive and tractable jointly
independent beta prior distribution on these parameters, which we show to be a
generalization of the Dirichlet prior for the joint distribution of potential
outcomes. Our approach has a number of desirable characteristics when compared
to current mainstream alternatives: (i) it naturally induces prior dependence
between expected outcomes in the treatment and control groups; (ii) as the
baseline risk, efficacy and risk of adverse side effects are quantities
commonly present in the clinicians' vocabulary, the hyperparameters of the
prior are directly interpretable, thus facilitating the elicitation of prior
knowledge and sensitivity analysis; and (iii) we provide analytical formulae
for the marginal likelihood, Bayes factor, and other posterior quantities, as
well as exact posterior sampling via simulation, in cases where traditional
MCMC fails. Empirical examples demonstrate the utility of our methods for
estimation, hypothesis testing, and sensitivity analysis of treatment effects.",2308.13713v2
2023-08-30,Mechanism of cathodic protection of iron and steel in porous media,"Cathodic protection (CP) was introduced two centuries ago and since has found
widespread application in protecting structures such as pipelines, offshore
installations, and bridges from corrosion. Despite its extensive use, the
fundamental working mechanism of CP remains debated, particularly for metals in
porous media such as soil. Here, we offer resolution to the long-standing
debate by employing in-situ and ex-situ characterisation techniques coupled
with electrochemical measurements to characterise the spatio-temporal changes
occurring at the steel-electrolyte interface. We show that upon CP, the
interfacial electrolyte undergoes alkalinisation and deoxygenation, and that
depending on polarisation conditions, an iron oxide film can simultaneously
form on the steel surface. We further demonstrate that these changes in
interfacial electrolyte chemistry and steel surface state result in altered
anodic and cathodic reactions and their kinetics. We propose a mechanism of CP
that integrates the long debated theories, based on both concentration and
activation polarisation, complimentarily. Implications of this coherent
scientific understanding for enhancing corrosion protection technologies and
the safe, economic, and environmental-friendly operation of critical
steel-based infrastructures are discussed.",2308.15953v1
2023-09-08,Interband scattering- and nematicity-induced quantum oscillation frequency in FeSe,"Understanding the nematic phase observed in the iron-chalcogenide materials
is crucial for describing their superconducting pairing. Experiments on
FeSe$_{1-x}$S$_x$ showed that one of the slow Shubnikov--de Haas quantum
oscillation frequencies disappears when tuning the material out of the nematic
phase via chemical substitution or pressure, which has been interpreted as a
Lifshitz transition [Coldea et al., npj Quant Mater 4, 2 (2019), Reiss et al.,
Nat. Phys. 16, 89-94 (2020)]. Here, we present a generic, alternative scenario
for a nematicity-induced sharp quantum oscillation frequency which disappears
in the tetragonal phase and is not connected to an underlying Fermi surface
pocket. We show that different microscopic interband scattering mechanisms -
for example, orbital-selective scattering - in conjunction with nematic order
can give rise to this quantum oscillation frequency beyond the standard Onsager
relation. We discuss implications for iron-chalcogenides and the interpretation
of quantum oscillations in other correlated materials.",2309.04237v1
2023-09-21,Spectral study of neutron star low mass X-ray binary source 1A 1744-361,"We present X-ray observations of the recent outburst of 2022 from the neutron
star low mass X-ray binary (LMXB) source 1A 1744-361. Spectral properties of
the source have been analyzed using joint NuSTAR and NICER observations. During
our observations, the source happens to be in the banana state (soft state) of
the hardness intensity diagram (HID). In addition to a power-law with a high
energy cutoff, the spectrum is found to exhibit broad iron $K_{\alpha}$
emission along with distinct absorption features. A prominent absorption
feature observed at 6.92 keV may be interpreted as $K_{\alpha}$ absorption line
from hydrogen-like iron. The absorption feature observed at 7.98 keV may be
interpreted as a blend of Fe XXV and Ni XXVII transitions. We have summarized
the evidence of variability of the spectral features observed in the X-ray
continuum by time-resolved spectroscopy.",2309.11817v1
2023-09-21,"Interface of Equation-of-State, Atomic Data and Opacities in the Solar Problem","Convergence of the Rosseland Mean Opacity (RMO) is investigated with respect
to the equation-of-state (EOS) and the number of atomic levels of iron ions
prevalent at the solar radiative/convection boundary. The ""chemical picture""
Mihalas-Hummer-D\""{a}ppen MHD-EOS, and its variant QMHD-EOS, are studied at two
representative temperature-density sets at the base of the convection zone
(BCZ) and the Sandia Z experiment: $(2 \times 10^6K, \ 10^{23}/cc)$ and $(2.11
\times 10^6K, \ 3.16 \times 10^{22}/cc)$, respectively. It is found that
whereas the new atomic datasets from accurate R-matrix calculations for
opacities (RMOP) are vastly overcomplete, involving hundreds to over a thousand
levels of each of the three Fe ions considered -- FeXVII, FeXVIII and FeXIX --
the EOS constrains contributions to RMOs by relatively fewer levels. The RMOP
iron opacity spectrum is quite different from the Opacity Project distorted
wave model and shows considerably more plasma broadening effects. This work
points to possible improvements needed in the EOS for opacities in
high-energy-density (HED) plasma sources.",2309.12073v1
2023-09-26,Polymer amide as a source of the cosmic 6.2 micron emission and absorption,"Cosmic infrared emission and absorption spectra often carry a well-defined
and invariant 6.2 micron band that has been proposed to emanate from very small
dust grains that may carry polyaromatic hydrocarbons. Hemoglycin, a
well-defined polymer of glycine that also contains iron, has been found in
meteorites of the primordial CV3 class and therefore originated in the solar
protoplanetary disc. In approximate calculations, the principal amide I
infrared absorption band of hemoglycin is at 6.04 microns. Hemoglycin, an
antiparallel beta sheet structure with two 11-mer glycine chains, has an exact
structural analog in antiparallel poly-L-lysine beta sheets which in the
laboratory have an absorption peak at 6.21 microns. This wavelength
coincidence, the demonstrated propensity of hemoglycin 4.9nm rods to form
accreting lattice structures, and its proven existence in the solar
protoplanetary disc strongly suggest that the cosmic 6.2 micron emission and
absorption could be from small grains that are hemoglycin lattices or
shell-like vesicles carrying internal organic molecules of various types.
Calculated hemoglycin ultraviolet absorptions associated with iron in the
molecule match the observed ultraviolet extinction feature at nominal 2175
Angstroms.",2309.14914v1
2023-10-10,Improved iron-tolerance in recycled aluminum alloys via direct strip casting process,"Recycled aluminum alloys are pivotal for sustainable manufacturing, offering
strength, durability, and environmental advantages. However, the presence of
iron (Fe) impurities poses a major challenge, undermining their properties and
recyclability. Conventional manufacturing processes result in coarse Fe-rich
intermetallic compounds that limit the tolerance of Fe content and negatively
influence performance of advanced aluminum alloys. To address this, rapid
solidification techniques like direct strip casting have been explored. In this
work, a detailed study of the strip cast microstructure was conducted by
scanning electron microscopy, electron backscattered diffraction and atom probe
tomography. Our results reveal that alloys produced by DSC exhibit
significantly refined microstructures and are free from coarse Fe-rich
intermetallics, thereby retaining the majority of Fe in solid solution. These
findings indicate that strip casting significantly enhances Fe-tolerance in
aluminum alloys, making it an attractive process for future aluminum recycling,
with implications for sustainable high-performance applications.",2310.06327v1
2023-10-16,Spectral Properties of GX~339--4 in the Intermediate State Using AstroSat Observation,"We present the results obtained from the spectral studies of black hole X-ray
binary GX~339--4 using \astrosat~ observations during its 2021 outburst.
\astrosat~ observed the source in the intermediate state for $\sim600$ ks. The
combined spectra of SXT and LAXPC in the $0.7-25$ keV energy range are studied
with phenomenological and physical models. The spectral study reveals a
receding disc and a contracting corona during the observation period. The
outflow rate is found to be increased though the accretion rates did not vary
during the observation period. The X-ray flux decreases as the disc recedes and
the spectrum becomes hard. At the same time, the Comptonized flux decreases
with increasing fraction of thermal emission. This could be plausible that
episodic jet ejection modified the corona and reduced Comptonized flux. An iron
emission line at 6.4 keV is observed in the spectra of all the orbits of
observation. We find that the equivalent width of the iron emission line
correlates with the photon index, indicating a decrease in the reflection
strength as the spectrum becomes hard. We observe that the disc flux does not
follow $F_{\rm DBB}-T^{4}$ relation.",2310.10444v1
2023-10-16,Quantum hardware calculations of the activation and dissociation of nitrogen on iron clusters and surfaces,"Catalytic processes are vital in the chemical industry, with
nitrogen-to-ammonia conversion being a major industrial process. Designing
catalysts relies on computational chemistry methods like Density Functional
Theory (DFT), which have limitations in accuracy, especially for complex
materials. Quantum computing advancements offer promise for precise ab-initio
methods. We introduce a hybrid quantum-classical workflow to model chemical
reactions on surfaces, demonstrated on nitrogen activation and dissociation on
small Fe clusters and an iron surface. We decoupled key electronic structures
using CASSCF, translated them into qubits, and estimated energies with quantum
and classical simulations, showing potential for quantum computing in catalysis
research as technology scales up.",2310.10478v1
2023-10-31,The Larmor frequency shift of a white matter magnetic microstructure model with multiple sources,"Magnetic susceptibility imaging may provide valuable information about
chemical composition and microstructural organization of tissue. However, its
estimation from the MRI signal phase is particularly difficult as it is
sensitive to magnetic tissue properties ranging from the molecular to
macroscopic scale. The MRI Larmor frequency shift measured in white matter (WM)
tissue depends on the myelinated axons and other magnetizable sources such as
iron-filled ferritin. We have previously derived the Larmor frequency shift
arising from a dense media of cylinders with scalar susceptibility and
arbitrary orientation dispersion. Here we extend our model to include
microscopic WM susceptibility anisotropy as well as spherical inclusions with
scalar susceptibility to represent subcellular structures, biologically stored
iron etc. We validate our analytical results with computer simulations and
investigate the feasibility of estimating susceptibility using simple iterative
linear least squares without regularization or preconditioning. This is done in
a digital brain phantom synthesized from diffusion MRI (dMRI) measurements of
an ex vivo mouse brain at ultra-high field.",2311.00086v3
2023-11-19,Diverse features of dust particles and their aggregates inferred from experimental nanoparticles,"Nanometre- to micrometre-sized solid dust particles play a vital role in star
and planet formations. Despite of their importance, however, our understanding
of physical and chemical properties of dust particles is still provisional. We
have conducted a condensation experiment of the vapour generated from a solid
starting material having nearly cosmic proportions in elements. A laser flash
heating and subsequent cooling has produced a diverse type of nanoparticles
simultaneously. Here we introduce four types of nanoparticles as potential dust
particles in space: amorphous silicate nanoparticles (type S); core/mantle
nanoparticles with iron or hydrogenised-iron core and amorphous silicate mantle
(type IS); silicon oxycarbide nanoparticles and hydrogenised silicon oxycarbide
nanoparticles (type SiOC); and carbon nanoparticles (type C), all produced in a
single heating-cooling event. Type IS and SiOC nanoparticles are new for
potential astrophysical dust. The nanoparticles are aggregated to a wide
variety of structures, from compact, fluffy, and networked. A simultaneous
formation of nanoparticles, which are diverse in chemistry, shape, and
structure, prompts a re-evaluation of astrophysical dust particles",2311.11213v1
2023-12-14,Confinement of electron holes via the peroxo group formation in the negative charge-transfer materials on the example of SrFeO3: plane-wave density functional theory predictions,"The present work puts forward a concept that the thermostable O1s XPS peaks
with energy of about 531 eV in negative charge-transfer SrFeO_{3-\delta}
perovskite are determined by the peroxo-like oxygen species. The peroxo group
forms via coupling two oxygen anions coordinated to iron cations with
d^5\bar-under{L} (\bar-under{L}-oxygen electron hole) configuration. By means
of plane-wave DFT+U approach there have been shown that the peroxo group
represents a metastable state in the absence of oxygen vacancies nearby. The
O-O bonding confines two electron holes freezing the 3+ oxidation state for two
iron cations bridged by peroxide. Increasing the peroxo group numbers makes the
ferrite a semiconductor with charge-transfer gap of about 0.6 eV.",2312.08665v1
2023-12-18,Quantum criticality in quasi-binary compounds of iron-based superconductors,"In this work, we present the studies of structural phase transitions in
Fe(Se,Te) crystals in the range of about 30% selenium substitution by
tellurium. We found a significant change in the properties of the ordered state
of these compositions compared to the case of pure FeSe. The resistivity at low
temperatures for the studied Fe(Se,Te) is proportional to the square of the
temperature while for pure FeSe below the structural transition it depends
almost linearly on temperature. The NMR data show a noticeable line broadening
below the structural transition and an anomaly in the temperature dependence of
the relaxation rate in the tellurium-substituted compounds, which was not
observed in the pure FeSe. This reveals in quasi-binary compounds of iron-based
superconductors a region of quantum criticality similar to that which exists
when the nematicity of FeSe is suppressed under pressure and which precedes the
emergence of high-temperature superconductivity in FeSe under hydrostatic
pressure.",2312.10901v1
2024-01-05,Comparison of Two Detector Magnetic Systems for the Future Circular Hadron-Hadron Collider,"The conceptual design study of a Future Circular hadron-hadron Collider
(FCC-hh) to be con-structed at CERN with a center-of-mass energy of the order
of 100 TeV requires superconducting magnetic systems with a central magnetic
flux density of an order of 4 T for the experimental detectors. The developed
concept of the FCC-hh detector involves the use of an iron-free magnetic system
consisting of three superconducting solenoids. A superconducting magnet with a
minimal steel yoke is proposed as an alternative to the baseline iron-free
design. In this study, both magnetic system options for the FCC-hh detector are
modeled with the same electrical parameters using Cobham$'$s program TOSCA. All
the main characteristics of both designs are compared and discussed.",2401.02835v1
2024-01-08,"Harvesting nucleating structures in nanoparticle crystallization: The example of gold, silver and iron","The thermodynamics and kinetics of crystallization of nanoparticles, as
opposed to bulk phases, may be influenced by surface and size effects. We
investigate the importance of such factors in the crystallization process of
gold, silver, and iron nanodroplets using numerical simulations in the form of
molecular dynamics combined with path sampling. This modeling strategy is
targeted at obtaining representative ensembles of structures located at the
transition state of the crystallization process. A structural analysis of the
transition state ensembles reveals that both the average size and location of
the critical nucleation cluster are influenced by surface and nanoscale size
effets. Furthermore, we also show that transition state structures in smaller
nanodroplets exhibit a more ordered liquid phase, and differentiating between a
well-ordered critical cluster and its surrounding disordered liquid phase
becomes less evident. All in all, these findings demonstrate that
crystallization mechanisms in nanoparticles go beyond the assumptions of
classical nucleation theory.",2401.03969v1
2024-01-16,"Influence of temperature, doping, and amorphization on the electronic structure and magnetic damping of iron","Hybrid magnonic quantum systems have drawn increased attention in recent
years for coherent quantum information processing, but too large magnetic
damping is a persistent concern when metallic magnets are used. Their intrinsic
damping is largely determined by electron-magnon scattering induced by
spin-orbit interactions. In the low scattering limit, damping is dominated by
intra-band electronic transitions, which has been theoretically shown to be
proportional to the electronic density of states at the Fermi level. In this
work, we focus on body-centered-cubic iron as a paradigmatic ferromagnetic
material. We comprehensively study its electronic structure using
first-principles density functional theory simulations and account for finite
lattice temperature, boron (B) doping, and structure amorphization. Our results
indicate that temperature induced atomic disorder and amorphous atomic
geometries only have a minor influence. Instead, boron doping noticeably
decreases the density of states near the Fermi level with an optimal doping
level of 6.25%. In addition, we show that this reduction varies significantly
for different atomic geometries and report that the highest reduction
correlates with a large magnetization of the material. This may suggest
materials growth under external magnetic fields as a route to explore in
experiment.",2401.08076v1
2024-01-23,Understanding atom probe's analytical performance for iron oxides using correlation histograms and ab initio calculations,"Field evaporation from ionic or covalently bonded materials often leads to
the emission of molecular ions. The metastability of these molecular ions,
particularly under the influence of the intense electrostatic field (1010
Vm-1), makes them prone to dissociation with or without an exchange of energy
amongst them. These processes can affect the analytical performance of atom
probe tomography (APT). For instance, neutral species formed through
dissociation may not be detected at all or with a time of flight no longer
related to their mass, causing their loss from the analysis. Here, we evaluated
the changes in the measured composition of FeO, Fe2O3 and Fe3O4 across a wide
range of analysis conditions. Possible dissociation reactions are predicted by
density-functional theory (DFT) calculations considering the spin states of the
molecules. The energetically favoured reactions are traced on to the multi-hit
ion correlation histograms, to confirm their existence within experiments,
using an automated Python-based routine. The detected reactions are carefully
analysed to reflect upon the influence of these neutrals from dissociation
reactions on the performance of APT for analysing iron oxides.",2401.12784v1
2024-01-29,HEQuant: Marrying Homomorphic Encryption and Quantization for Communication-Efficient Private Inference,"Secure two-party computation with homomorphic encryption (HE) protects data
privacy with a formal security guarantee but suffers from high communication
overhead. While previous works, e.g., Cheetah, Iron, etc, have proposed
efficient HE-based protocols for different neural network (NN) operations, they
still assume high precision, e.g., fixed point 37 bit, for the NN operations
and ignore NNs' native robustness against quantization error. In this paper, we
propose HEQuant, which features low-precision-quantization-aware optimization
for the HE-based protocols. We observe the benefit of a naive combination of
quantization and HE quickly saturates as bit precision goes down. Hence, to
further improve communication efficiency, we propose a series of optimizations,
including an intra-coefficient packing algorithm and a quantization-aware
tiling algorithm, to simultaneously reduce the number and precision of the
transferred data. Compared with prior-art HE-based protocols, e.g., CrypTFlow2,
Cheetah, Iron, etc, HEQuant achieves $3.5\sim 23.4\times$ communication
reduction and $3.0\sim 9.3\times$ latency reduction. Meanwhile, when compared
with prior-art network optimization frameworks, e.g., SENet, SNL, etc, HEQuant
also achieves $3.1\sim 3.6\times$ communication reduction.",2401.15970v2
2024-01-30,A New Database of Giant Impacts over a Wide Range of Masses and with Material Strength: A First Analysis of Outcomes,"In the late stage of terrestrial planet formation, planets are predicted to
undergo pairwise collisions known as giant impacts. Here we present a
high-resolution database of giant impacts for differentiated colliding bodies
of iron-silicate composition, with target masses ranging from 10^-4 M_Earth up
to super-Earths (5 M_Earth). We vary impactor-to-target mass ratio, core-mantle
(iron-silicate) fraction, impact velocity, and impact angle. Strength in the
form of friction is included in all simulations. We find that due to strength,
collisions with bodies smaller than about 2*10^-3 M_Earth can result in
irregular shapes, compound core structures, and captured binaries. We observe
that the characteristic escaping velocity of smaller remnants (debris) is
approximately half of the impact velocity, significantly faster than currently
assumed in N-body simulations of planet formation. Incorporating these results
in N-body planet formation studies would provide more realistic debris-debris
and debris-planet interactions.",2401.17356v1
2024-02-09,Copper phosphate micro-flowers coated with indocyanine green and iron oxide nanoparticles for in vivo localization optoacoustic tomography and magnetic actuation,"Efficient drug delivery is a major challenge in modern medicine and
pharmaceutical research. Micrometer-scale robots have recently been proposed as
a promising venue to amplify precision of drug administration. Remotely
controlled microrobots sufficiently small to navigate through microvascular
networks can reach any part of the human body, yet real-time tracking is
crucial for providing precise guidance and verifying successful arrival at the
target. In vivo deep-tissue monitoring of individual microrobots is currently
hampered by the lack of sensitivity and/or spatio-temporal resolution of
commonly used clinical imaging modalities. We synthesized biocompatible and
biodegradable copper phosphate micro-flowers loaded with indocyanine green and
iron oxide nanoparticles to enable in vivo individual detection with
localization optoacoustic tomography. We demonstrate magnetic actuation and
optoacoustic tracking of these decorated micro-flowers at a per-particle level.
Functional super-resolution imaging achieved via tracking intravenously
injected particles provides a means of identifying microvascular targets and
quantifying blood flow, while the versatile carrying capacity can be further
exploited for transporting multiple types of drug formulations.",2402.06749v1
2024-03-24,Rigorous ESR spectroscopy of $Fe^{3+}$ impurity ion with oxygen vacancy in ferroelectric $SrTiO_3$ crystal at 20 mK,"Impurity $Fe^{3+}$ ion electron spin resonance (ESR) spectroscopy using
multiple dielectric modes in a $SrTiO_3$ dielectric resonator has been
performed with a tuneable DC magnetic field of up to $1.6~T$. The
$Ti^{4+}(d^0)$ ion is substituted by $Fe^{3+}$ ion forming $FeO_6$ octahedral
complex with an iron-oxygen-vacancy $(Fe^{3+}-V_O)$. In such a metal-ligand
complex, a giant g-factor of $g_{\scriptscriptstyle\parallel F} = 5.51$ was
observed in the ferroelectric phase at $20~mK$. The the change of $Fe^{3+}$ ion
center-symmetry in the $FeO_6$ complex as a soft-mode characteristics of
ferroelectric phase transition and the influences of iron-oxygen-vacancy
$(Fe^{3+}-V_O)$, interactively sensitive to asymmetry in the octahedral
rotational parameter $\Phi$ in $SrTi0_3$.",2403.16299v1
2024-03-29,Synthesis and Characterization of Superparamagnetic Iron Oxide Nanoparticles: A Series of Laboratory Experiments,"The following laboratory procedure provides students with a hands-on
experience in nanomaterials chemistry and characterization. This three-day
protocol is easy to follow for undergraduates with basic chemistry or materials
science backgrounds and is suitable for inclusion in upper division courses in
inorganic chemistry or materials science. Students use air-free chemistry
procedures to synthesize and separate iron oxide magnetic nanoparticles and
subsequently modify the nanoparticle surface using a chemical stripping agent.
The morphology and chemical composition of the nanoparticles are characterized
using electron microscopy and dynamic light scattering measurements.
Additionally, magnetic characterization of the particles is performed using an
open-source (3D-printed), inexpensive magnetophotometer. Possible modifications
to the synthesis procedure including the incorporation of dopants to modify the
magnetic response and alternative characterization techniques are discussed.
The three-day synthesis, purification, and characterization laboratory will
prepare students with crucial skills for advanced technology industries such as
semiconductor manufacturing, nanomedicine, and green chemistry.",2403.19970v1
2024-04-10,Microbial iron reduction under oxic conditions: implications for subsurface biogeochemistry,"Iron (Fe) reduction is one of Earth's most ancient microbial metabolisms, but
after atmosphere-ocean oxygenation, this anaerobic process was relegated to
niche anoxic environments below the water and soil surface. However, new
technologies to monitor redox processes at the microscale relevant to microbial
cells have recently revealed that the oxygen (O2) concentrations controlling
the distribution of aerobic and anaerobic metabolisms are more heterogeneous
than previously believed. To explore how O2 levels regulate microbial Fe
reduction, we cultivated a facultative Fe-reducing bacterium using a
cutting-edge microfluidic reactor integrated with transparent planar O2
sensors. Contrary to expectations, microbial growth induced Fe(III)-oxide
(ferrihydrite) reduction under fully oxygenated conditions without forming
O2-depleted microsites. Batch incubations highlighted the importance of the
process at a larger scale, fundamentally changing our understanding of Fe
cycling from the conceptualization of metal and nutrient mobility in the
subsurface to our interpretation of Fe mineralogy in the rock record.",2404.07137v1
2021-06-15,Measurement of the Iron Spectrum in Cosmic Rays from 10 GeV$/n$ to 2.0 TeV$/n$ with the Calorimetric Electron Telescope on the International Space Station,"The Calorimetric Electron Telescope (CALET), in operation on the
International Space Station since 2015, collected a large sample of cosmic-ray
iron over a wide energy interval. In this Letter a measurement of the iron
spectrum is presented in the range of kinetic energy per nucleon from 10
GeV$/n$ to 2.0 TeV$/n$ allowing the inclusion of iron in the list of elements
studied with unprecedented precision by space-borne instruments. The
measurement is based on observations carried out from January 2016 to May 2020.
The CALET instrument can identify individual nuclear species via a measurement
of their electric charge with a dynamic range extending far beyond iron (up to
atomic number $Z$ = 40). The energy is measured by a homogeneous calorimeter
with a total equivalent thickness of 1.2 proton interaction lengths preceded by
a thin (3 radiation lengths) imaging section providing tracking and energy
sampling. The analysis of the data and the detailed assessment of systematic
uncertainties are described and results are compared with the findings of
previous experiments. The observed differential spectrum is consistent within
the errors with previous experiments. In the region from 50 GeV$/n$ to 2
TeV$/n$ our present data are compatible with a single power law with spectral
index -2.60 $\pm$ 0.03.",2106.08036v1
2023-04-13,Probing magnetic ordering in air stable iron-rich van der Waals minerals,"In the rapidly expanding field of two-dimensional materials, magnetic
monolayers show great promise for the future applications in nanoelectronics,
data storage, and sensing. The research in intrinsically magnetic
two-dimensional materials mainly focuses on synthetic iodide and telluride
based compounds, which inherently suffer from the lack of ambient stability. So
far, naturally occurring layered magnetic materials have been vastly
overlooked. These minerals offer a unique opportunity to explore air-stable
complex layered systems with high concentration of local moment bearing ions.
We demonstrate magnetic ordering in iron-rich two-dimensional phyllosilicates,
focusing on mineral species of minnesotaite, annite, and biotite. These are
naturally occurring van der Waals magnetic materials which integrate local
moment baring ions of iron via magnesium/aluminium substitution in their
octahedral sites. Due to self-inherent capping by silicate/aluminate
tetrahedral groups, ultra-thin layers are air-stable. Chemical
characterization, quantitative elemental analysis, and iron oxidation states
were determined via Raman spectroscopy, wavelength disperse X-ray spectroscopy,
X-ray absorption spectroscopy, and X-ray photoelectron spectroscopy.
Superconducting quantum interference device magnetometry measurements were
performed to examine the magnetic ordering. These layered materials exhibit
paramagnetic or superparamagnetic characteristics at room temperature. At low
temperature ferrimagnetic or antiferromagnetic ordering occurs, with the
critical ordering temperature of 38.7 K for minnesotaite, 36.1 K for annite,
and 4.9 K for biotite. In-field magnetic force microscopy on iron bearing
phyllosilicates confirmed the paramagnetic response at room temperature,
present down to monolayers.",2304.06533v1
2023-11-08,A human brain atlas of chi-separation for normative iron and myelin distributions,"Iron and myelin are primary susceptibility sources in the human brain. These
substances are essential for healthy brain, and their abnormalities are often
related to various neurological disorders. Recently, an advanced susceptibility
mapping technique, which is referred to as chi-separation, has been proposed,
successfully disentangling paramagnetic iron from diamagnetic myelin. This
method opened a potential for generating high resolution iron and myelin maps
in the brain. Utilizing this technique, this study constructs a normative
chi-separation atlas from 106 healthy human brains. The resulting atlas
provides detailed anatomical structures associated with the distributions of
iron and myelin, clearly delineating subcortical nuclei, thalamic nuclei, and
white matter fiber bundles. Additionally, susceptibility values in a number of
regions of interest are reported along with age-dependent changes. This atlas
may have direct applications such as localization of subcortical structures for
deep brain stimulation or high-intensity focused ultrasound and also serve as a
valuable resource for future research.",2311.04468v3
1997-12-18,ASCA detection of the FeK edge in the spectrum of the Seyfert 2 galaxy IRAS 04575-7537: a sign of a complex absorber,"ASCA X-ray spectral analysis of the Seyfert 2 galaxy IRAS 04575-7537 is
presented. The main result is the presence of a significant iron edge at a rest
energy of 7.13^+0.21_-0.16 keV. The spectrum is flat (Gamma = 1.5) with a
substantial absorption Nh = 10^22 cm^-2 and does not require any reflection
component. There is also evidence of a narrow Fe Kalpha emission line, whose
rest energy (E = 6.35^+0.08_ -0.03 keV) and equivalent width (EW = 130+-50 eV)
suggest that the line originates from thick and cold matter. The intensity of
the line and, in particular, the depth of the iron edge are too strong to be
explained by simple transmission through the measured absorption column
density. This strongly suggests that a model more complex than a single
absorbed power law is needed. We propose an absorption model that we call
""leaky-total absorber"" which can explain the spectrum flatness, the iron
emission line and the edge absorption feature and has also the advantage of
having a straightforward physical interpretation in the framework of Unified
models. In this model a thick absorber (Nh = 10^23 cm^-2), possibly associated
with broad line region (BLR) clouds, partially (36 %) covers the source
continuum with Gamma fixed to 1.9 as observed in Sey 1 galaxies. The escaping
radiation is then absorbed by a column density Nh = 10^22 cm^-2, which can be
attributed to the torus, seen through its rim.",9712250v1
1999-07-13,A Consistency Test of Spectroscopic Gravities for Late-Type Stars,"Chemical analyses of late-type stars are usually carried out following the
classical recipe: LTE line formation and homogeneous, plane-parallel,
flux-constant, and LTE model atmospheres. We review different results in the
literature that have suggested significant inconsistencies in the spectroscopic
analyses, pointing out the difficulties in deriving independent estimates of
the stellar fundamental parameters and hence,detecting systematic errors.
  The trigonometric parallaxes measured by the HIPPARCOS mission provide
accurate appraisals of the stellar surface gravity for nearby stars, which are
used here to check the gravities obtained from the photospheric iron ionization
balance. We find an approximate agreement for stars in the metallicity range -1
<= [Fe/H] <= 0, but the comparison shows that the differences between the
spectroscopic and trigonometric gravities decrease towards lower metallicities
for more metal-deficient dwarfs (-2.5 <= [Fe/H] <= -1.0), which casts a shadow
upon the abundance analyses for extreme metal-poor stars that make use of the
ionization equilibrium to constrain the gravity. The comparison with the
strong-line gravities derived by Edvardsson (1988) and Fuhrmann (1998a)
confirms that this method provides systematically larger gravities than the
ionization balance. The strong-line gravities get closer to the physical ones
for the stars analyzed by Fuhrmann, but they are even further away than the
iron ionization gravities for the stars of lower gravities in Edvardsson's
sample. The confrontation of the deviations of the iron ionization gravities in
metal-poor stars reported here with departures from the excitation balance
found in the literature, show that they are likely to be induced by the same
physical mechanism(s).",9907155v1
2000-01-07,The variability of the Seyfert galaxy NGC 2992: the case for a revived AGN,"We report the transition to an active state of the nucleus in the Seyfert 1.9
galaxy NGC 2992, discovered by means of new hard X-ray data. While the 2-10 keV
flux declined by a factor of ~ 20 from 1978 to 1994, two recent BeppoSAX
observations in 1997 and in 1998 caught the nuclear emission raising back to
the same level of activity observed in 1978.
  In both BeppoSAX observations the X-ray spectrum of the source is well
represented by a power law with spectral index Gamma ~ 1.7, absorbed by a
column density of N_H ~ 10^{22} cm^{-2} and characterized by a prominent iron
K\alpha line. While in the second BeppoSAX data set the line properties appear
to be consistent with those expected from accretion disc models, in the first
BeppoSAX data set the iron feature is rather peculiar. The broadening is not
significant and the line energy is E_{K\alpha}=6.62 +/- 0.07 keV, indicating
emission from highly ionized iron. The line has too high equivalent width (~
700 eV) to be produced by a hot scattering medium. By comparing these data with
data previously in the literature, we interpret the spectral and flux changes
in terms of different phases of rebuilding an accretion disc. The timescale for
the disc rebuilding is estimated to range between 1 and 5 years.
  The X-ray data are complemented with optical and near-infrared followup
spectra taken 1.5 months after the discovery of the X-ray burst. The spectra
are characterized by prominent broad emission lines. There is also evidence for
hot dust emission in the H and K bands that, however, is probably still in the
process of increasing.",0001107v1
2000-08-31,Variable Iron K-alpha Lines in Seyfert 1 Galaxies,"We find that variability of the iron K-alpha line is common in Seyfert 1
galaxies. Using data from the ASCA archive for objects that have been observed
more than once during the mission, we study the time-averaged spectra from
individual observations, thereby probing variability on timescales that range
from days to years. Since the statistics of the data do not warrant searches
for line variability in terms of a complex physical model, we use a a simple
Gaussian to model the gross shape of the line, and then use the centroid
energy, intensity and equivalent width as robust indicators of changes in the
line profile. We find that ~70% of Seyfert 1s (ten out of fifteen) show
variability in at least one of these parameters: the centroid energy,
intensity, and equivalent width vary in six, four, and eight sources
respectively. Due to the low S/N, limited sampling and time averaging, we
consider these results to represent lower limits to the rate of incidence of
variability. In most cases changes in the line do not appear to track changes
in the continuum. In particular, we find no evidence for variability of the
line intensity in NGC 4151, suggesting an origin in a region larger than the
putative accretion disk, where most of the iron line has been thought to
originate. Mkn 279 is investigated on short timescales. The time-averaged
effective line energy is 6.5 keV in the galaxy rest frame. As the continuum
flux increases by 20% in a few hours, the Fe K line responds with the effective
line energy increasing by 0.22 keV (~10,500 km s^-1). Problems with the ASCA
and Rosat calibration that affect simultaneous spectral fits are discussed in
an appendix.",0008522v1
2000-09-13,First Stellar Abundances in NGC 6822 from VLT-UVES and Keck-HIRES Spectroscopy,"We have obtained the first high resolution spectra of individual stars in the
dwarf irregular galaxy, NGC 6822. The spectra of the two A-type supergiants
were obtained at the VLT and Keck Observatories, using UVES and HIRES,
respectively. A detailed model atmospheres analysis has been used to determine
their atmospheric parameters and elemental abundances. The mean iron abundance
from these two stars is $<$[Fe/H]$>=-$0.49 $\pm$0.22 ({\it $\pm$0.21}, with Cr
yielding a similar underabundance, $<$[Cr/H]$>=-$0.50 $\pm$0.20 ({\it
$\pm$0.16}). This confirms that NGC 6822 has a metallicity that is slightly
higher than that of the SMC, and is the first determination of the present-day
iron-group abundances in NGC 6822. The mean stellar oxygen abundance,
12+log(O/H)=8.36 $\pm$0.19 ({\it $\pm$0.21}),is in good agreement with the
nebular oxygen results. Oxygen has the same underabundance as iron,
$<$[O/Fe]$>$=+0.02 $\pm$0.20 ({\it $\pm$0.21}). This O/Fe ratio is very similar
to that seen in the Magellanic Clouds, which supports the picture that chemical
evolution occurs more slowly in these lower mass galaxies, although the O/Fe
ratio is also consistent with that observed in comparatively metal-poor stars
in the Galactic disk. Combining all of the available abundance observations for
NGC 6822 shows that there is no trend in abundance with galactocentric
distance. However, a subset of the highest quality data are consistent with a
radial abundance gradient.",0009213v1
2000-10-17,Estimation of relativistic accretion disk parameters from iron line emission,"The observed iron K-alpha fluorescence lines in Seyfert-1 galaxies provide
strong evidence for an accretion disk near a supermassive black hole as a
source of the emission. Here we present an analysis of the geometrical and
kinematic properties of the disk based on the extreme frequency shifts of a
line profile as determined by measurable flux in both the red and blue wings.
The edges of the line are insensitive to the distribution of the X-ray flux
over the disk, and hence provide a robust alternative to profile fitting of
disk parameters. Our approach yields new, strong bounds on the inclination
angle of the disk and the location of the emitting region. We apply our method
to interpret observational data from MCG-6-30-15 and find that the commonly
assumed inclination 30 deg for the accretion disk in MCG-6-30-15 is
inconsistent with the position of the blue edge of the line at a 3 sigma level.
A thick turbulent disk model or the presence of highly ionized iron may
reconcile the bounds on inclination from the line edges with the full line
profile fits based on simple, geometrically thin disk models. The bounds on the
innermost radius of disk emission indicate that the black hole in MCG-6-30-15
is rotating faster than 30 % of theoretical maximum. When applied to data from
NGC 4151, our method gives bounds on the inclination angle of the X-ray
emitting inner disk of 50\pm 10 deg, consistent with the presence of an
ionization cone grazing the disk as proposed by Pedlar et al. (1993). The
frequency extrema analysis also provides limits to the innermost disk radius in
another Seyfert-1 galaxy, NGC 3516.",0010318v1
2001-03-07,Chandra observtaion of A2256 - a cluster at the early stage of merging,"We present here \chandra observations of the rich cluster of galaxies A2256.
In addition to the known cool subcluster, a new structure was resolved 2$'$
east of the peak of the main cluster. Its position is roughtly at the center of
a low-brightness radio halo. Spectral analysis shows that the ""shoulder"" has
high iron abundance ($\sim$ 1). We suggest that this structure is either
another merging component or an internal structure of the main cluster. The
X-ray redshifts of several regions were measured. The results agree with the
optical ones and suggest that the main cluster, the subcluster and the
""shoulder"" are physically associated and interacting. The subcluster has low
temperature ($\sim$ 4.5 keV) and high iron abundance ($\sim$ 0.6) in the
central 150 kpc. The \chandra image shows a relatively sharp brightness
gradient at the south of the subcluster peak running south-south-east (SSE). A
temperature jump was found across the edge, with higher temperature ahead of
the edge in the low density region. This phenomenon is qualitatively similar to
the ""cold fronts"" found in A2142 and A3667. If the ""shoulder"" is ignored, the
temperature map resembles those simulations at the early stage of merging while
the subcluster approached the main cluster from somewhere west. This fact and
the observed edge, in combination with the clear iron abundance contrast
between the center of the subcluster ($\sim$ 0.6) and the main cluster ($\sim$
0.2), all imply that the ongoing merger is still at the early stage. At least
three member galaxies, including a radio head-tail galaxy, were found to have
corresponding X-ray emission.",0103103v2
2001-03-15,Nucleosynthesis of Zinc and Iron-Peak Elements in Pop III Type II Supernovae : Comparison with abundances of Very Metal-Poor Halo Stars,"We calculate nucleosynthesis in core-collapse explosions of massive Pop III
stars, and compare the results with abundances of metal-poor halo stars to
constrain the parameters of Pop III supernovae. We focus on iron-peak elements
and, in particular, we try to reproduce the large [Zn/Fe] observed in extremely
metal-poor stars. The interesting trends of the observed ratios [Zn, Co, Mn,
Cr, V/Fe] can be related to the variation of the relative mass of the complete
and incomplete Si-burning regions in supernova ejecta. We find that [Zn/Fe] is
larger for deeper mass-cuts, smaller neutron excess, and larger explosion
energies. The large [Zn/Fe] and [O/Fe] observed in the very metal-poor halo
stars suggest deep mixing of complete Si-burning material and a significant
amount of fall-back in Type II supernovae. Furthermore, large explosion
energies (E_51 >~ 2 for M ~ 13 Msun and E_51 >~ 20 for M >~ 20 Msun) are
required to reproduce [Zn/Fe] ~ 0.5. The observed trends of the abundance
ratios among the iron-peak elements are better explained with this high energy
(``Hypernova'') models rather than the simple ``deep'' mass-cut effect, because
the overabundance of Ni can be avoided in the hypernova models. We also present
the yields of pair-instability supernova explosions of M = 130 - 300 Msun
stars, and discuss that the abundance features of very metal-poor stars cannot
be explained by pair-instability supernovae.",0103241v4
2001-04-10,Partially Absorbed Comptonization Spectrum from the Nearly Edge-on Source X 1822-371,"We report the results of a spectral analysis over the range 0.1-200 keV
performed on the dipping source X 1822-371 observed by BeppoSAX. We find the
best fit to the continuum using a partially covered Comptonization model, due
to scattering off soft seed photons by electrons at a temperature of ~4.8 keV,
without the presence of any soft blackbody emission. The equivalent hydrogen
column obtained for the absorbed component is ~4.5 10^{22} cm^{-2}, an order of
magnitude larger than the Galactic absorption for this source, and the covering
fraction is ~71%. Because the inclination angle of X 1822-371 to the line of
sight is ~85^\circ, this model gives a reasonable scenario for the source: the
Comptonized spectrum could come from an extended accretion disk corona (ADC),
probably the only region that can be directly observed due to the high
inclination. The excess of matter producing the partial covering could be close
to the equatorial plane of the system, above the outer disk, occulting the
emission from the inner disk and the inner part of the ADC. An iron emission
line is also present at ~6.5 keV with an equivalent width of ~150 eV. We argue
that this strong iron line cannot be explained as reflection of the Comptonized
spectrum by the accretion disk. It is probably produced in the ADC. An emission
line at ~1.9 keV (with an equivalent width of ~54 eV) and an absorption edge at
\~8.7 keV (with an optical depth of ~0.1) are also required to fit this
spectrum. These features are probably produced by highly ionized iron (Fe XXIV)
present in the outer part of the ADC, where the plasma density is
\~10^{11}-10^{12} cm^{-3} and ionized plasma is present.",0104171v2
2001-09-21,A Chandra HETG Observation of the Quasar H 1821+643 and Its Surrounding Cluster,"We present the high-resolution X-ray spectrum of the low-redshift quasar H
1821+643 and its surrounding hot cluster observed with the Chandra High Energy
Transmission Grating Spectrometer (HETGS). An iron emission line attributed to
the quasar at ~6.43 keV (rest frame) is clearly resolved, with an equivalent
width of ~100 eV. Although we cannot rule out contributions to the line from a
putative torus, the diskline model provides an acceptable fit to this iron
line. We also detect a weak emission feature at ~6.9 keV (rest frame). We
suggest that both lines could originate in an accretion disk comprised of a
highly ionized optically thin atmosphere sitting atop a mostly neutral disk. We
search for absorption features from a warm/hot component of the intergalactic
medium along the ~1.5Gpc/h line of sight to the quasar. No absorption features
are detected at or above the 3 sigma level while a total of six OVI intervening
absorption systems have been detected with HST and FUSE. Based on the lack of
OVII and OVIII absorption lines and by assuming collisionally ionization, we
constrain the gas temperature of a typical OVI absorber to 10^5 < T < 10^6 K,
which is consistent with the results from hydrodynamic simulations of the
intergalactic medium. The zeroth order image reveals the extended emission from
the surrounding cluster. We have been able to separate the moderate CCD X-ray
spectrum of the surrounding cluster from the central quasar and find that this
is a hot cluster with a temperature of ~10 keV and a metal abundance of ~0.3
Zo. We also independently obtain the redshift of the cluster, which is
consistent with the optical results. We estimate that the cluster makes
negligible contributions to the 6.9 keV iron K line flux.",0109389v1
2003-02-21,The iron $K_α$-line diagnostics of a rotational black hole metric,"The original idea to show the spacetime geometry using few geodesics was
developed by Johnson and Ruffini (1974). We used this idea to interpret the
observational data for rotating BH's. We developed the imitation approach to
simulate a propagation of radiation near BH's. An important problem for this
approach is the diagnostics of a black hole metric using X-ray observational
data of the iron $K_\alpha$-line.
  Observations of Seyfert galaxies in X-ray region reveal the broad emissiion
lines in their spectra, which can arise in inner parts of accretion disks,
where the effects of General Relativity (GR) must be counted. A spectrum of a
solitary emission line (the $K_\alpha$-line of iron, for example) of a hot spot
in Kerr accretion disk is simulated, depending on the radial coordinate $r$ and
the angular momentum $a=J/M$ of a black hole, under the assumption of an
equatorial circular motion of a hot spot. Using results of numerical
simulations it is shown that the characteristic two-peak line profile with the
sharp edges arises at a large distance, (about $r \approx (3-10)r_g$). The
inner regions emit the line, which is observed with one maximum and extremely
broad red wing. High accuracy future spectral observations, being carried out,
could detect the angular momentum $a$ of the black hole. We analyzed the
different parameters of problems on the observable shape of this line and
discussed some possible kinds of these shapes. The total number of geodesics is
about $10^9$ (to simulate possible shapes of the $K_\alpha$-line), so the
number is great enough, especially in comparison with few geodesics in the
original paper by Johnson and Ruffini (1974).",0302454v1
2003-09-22,The Effects of Binary Evolution on the Dynamics of Core Collapse and Neutron-Star Kicks,"We systematically examine how the presence in a binary affects the final core
structure of a massive star and its consequences for the subsequent supernova
explosion. Interactions with a companion star may change the final rate of
rotation, the size of the helium core, the strength of carbon burning and the
final iron core mass. Stars with initial masses larger than \sim 11\Ms that
experiece core collapse will generally have smaller iron cores at the time of
the explosion if they lost their envelopes due to a previous binary
interaction. Stars below \sim 11\Ms, on the other hand, can end up with larger
helium and metal cores if they have a close companion, since the second
dredge-up phase which reduces the helium core mass dramatically in single stars
does not occur once the hydrogen envelope is lost. We find that the initially
more massive stars in binary systems with masses in the range 8 - 11\Ms are
likely to undergo an electron-capture supernova, while single stars in the same
mass range would end as ONeMg white dwarfs. We suggest that the core collapse
in an electron-capture supernova (and possibly in the case of relatively small
iron cores) leads to a prompt explosion rather than a delayed neutrino-driven
explosion and that this naturally produces neutron stars with low-velocity
kicks. This leads to a dichotomous distribution of neutron star kicks, as
inferred previously, where neutron stars in relatively close binaries attain
low kick velocities. We illustrate the consequences of such a dichotomous kick
scenario using binary population synthesis simulations and discuss its
implications. This scenario has also important consequences for the minimum
initial mass of a massive star that becomes a neutron star. (Abbreviated.)",0309588v2
2003-09-25,Close and distant reprocessing media in Mkn509 studied with BeppoSAX,"We present the broad band analysis of two BeppoSAX observations of the Sy 1
Mkn509. In 2000 the source was in a typical flux state,
F{2-10keV}=2.7x10^{-11}erg cm^{-2} s^{-1}, while in 1998 it was found in a high
flux state, F{2-10keV}=5.7x10^{-11} erg cm^{-2} s^{-1}. A comparison between
the two states shows a energy-dependent flux variation. A soft excess, a narrow
iron line and a Compton reflection hump above 10 keV, are clearly apparent in
the residuals after fitting the spectra with a simple power law. We tested two
alternative models. In the first the iron line and the high energy bump are
well reproduced by reprocessing in a cold and Compton thick material. The
intensity of the iron line (also consistent with a Chandra measurement) as well
as the normalization of the reflection hump are consistent with a constant in
the two epochs: this, combined with the fact that the line is narrow as
observed by Chandra, suggests a common origin from distant and optically thick
matter. This model further requires a component to model the soft excess: the
empirical choice of two black bodies accounts well for the excess in both
observations, their combined strength was a factor about three higher in the
high than in the low flux state defined above. However the relative
contribution of the soft excess is higher in the low flux state. In the second
model we attempted to reproduce all spectral features, except for the narrow
cold line, with reflection from an ionized disc. This model is successful only
in the high flux state,but it fails in the low flux state, when the soft excess
is only partially accounted for. In either models, the slope of the power law
is larger in the high than in the low flux state, in agreement with a behaviour
known to be shared by several objects of the same type.",0309699v1
2003-10-20,Chandra X-ray Observations of NGC 4258: Iron Absorption Lines from the Nucleus,"We report sub-arcsecond resolution X-ray imaging spectroscopy of the low
luminosity active galactic nucleus of NGC 4258 and its immediate surroundings
with the Chandra X-ray Observatory. NGC 4258 was observed four times, with the
first two observations separated by one month, followed over a year later by
two consecutive observations. The spectrum of the nucleus is well described by
a heavily absorbed, hard X-ray power law of variable luminosity, plus a
constant, thermal soft X-ray component. We do not detect an iron K alpha
emission line with the upper limit to the equivalent width of a narrow, neutral
iron line ranging between 94 and 887 eV (90% confidence) for the different
observations. During the second observation on 2000-04-17, two narrow
absorption features are seen with >99.5% confidence at ~6.4 keV and ~6.9 keV,
which we identify as resonant absorption lines of Fe XVIII - Fe XIX K alpha and
Fe XXVI K alpha, respectively. In addition, the 6.9 keV absorption line is
probably variable on a timescale of ~6000 sec. The absorption lines are
analyzed through a curve of growth analysis, which allows the relationship
between ionic column and kinematic temperature or velocity dispersion to be
obtained for the observed equivalent widths. We discuss the properties of the
absorbing gas for both photo and collisionally ionized models. Given that the
maser disk is viewed at an inclination i = 82 degrees, the gas responsible for
the 6.9 keV absorption line may be in an inner disk, a disk-wind boundary layer
or be thermal gas entrained at the base of the jet. The gas which gives rise to
the photoelectric absorption may be the same as that which causes the 6.4 keV
Fe K alpha absorption provided that the gas has a bulk velocity dispersion of a
few thousand km/s. (Abstract abridged).",0310553v1
2004-07-22,XMM-Newton observation of the Seyfert 1.8 ESO 113-G010: discovery of a highly redshifted iron line at 5.4 keV,"We present a spectral analysis of the Seyfert 1.8 ESO 113-G010 observed with
XMM-Newton for 4 ks. The spectrum shows a soft excess below 0.7 keV and more
interestingly a narrow emission Gaussian line at 5.4 keV (in its rest-frame),
most probably originating from a redshifted iron Kalpha line. No significant
line at or above 6.4 keV is found contrary to other objects showing redshifted
lines, ruling out a strong blue-wing to the line profile. The line is detected
at 99% confidence, from performing Monte Carlo simulations which fully account
for the range of energies where a narrow iron line is likely to occur. The
energy of the line could indicate emission from relativistic (0.17 - 0.23 c)
ejected matter moving away from the observer, as proposed for Mrk 766 by Turner
et al. (2004). Alternatively, the emission from a narrow annulus at the surface
of the accretion disk is unlikely due to the very small inclination angle (i.e.
less than 10 deg) required to explain the narrow, redshifted line in this
intermediate Seyfert galaxy. However emission from a small, localized hot-spot
on the disk, occurring within a fraction of a complete disk orbit, could also
explain the redshifted line. This scenario would be directly testable in a
longer observation, as one would see significant variations in the energy and
intensity of the line within an orbital timescale.",0407472v2
2004-08-12,The Li Overabundance of J37: Diffusion or Accretion?,"In September 2002 the discovery of a super Li-rich F-dwarf (J37) in NGC 6633,
an iron poor analogue of the better studied Hyades and Praecepe open clusters,
was announced. This unique star was thought to be the smoking gun for the
action of diffusion, models of which predict a narrow ""Li-peak"" at
approximately the correct temperature. However, with more detailed studies into
J37s abundance pattern this star provides firm evidence for the accretion of
planetesimals or other material from the circumstellar environment of new born
stars.
  Thanks to the specific predictions made about the behaviour of Be abundances,
(the most striking of which being no Be in super-Li-rich dwarfs subject to
diffusion) the opposing diffusion/accretion predictions can be tested.
  Initial modelling of the Be line indicates that J37 is as Be rich as it is Li
rich; log N(Be) = 2.25 +/- 0.25, and so is broadly consistent with an
accretion-fuelled enhancement. However, that both Li and Be are enhanced by
much more than the iron-peak elements (as determined in previous studies)
suggests that diffusion also plays a role in increasing the abundances of Li
and Be specifically.
  Furthermore, a new data set from the UVES/UT2 combination has allowed the
elemental abundance of Iron to be measured, and the set of preliminary stellar
parameters determined; Teff ~ 7340 K, log g ~ 4.1, microturbulence ~ 4.3 km/s,
[Fe/H] ~ 0.50. This again provides distinct evidence for the effects of
accretion in J37 and requires a new synthesis of the Be doublet.",0408223v1
2004-09-29,Chemical Abundances for Seven Giant Stars in M68 (NGC 4590) : A Globular Cluster with Abnormal Silicon and Titanium Abundances,"We present a detailed chemical abundance study of seven giant stars in M68
including six red giants and one post-AGB star. We find significant differences
in the gravities determined using photometry and those obtained from ionization
balance, which suggests that non-LTE effects are important for these
low-gravity, metal-poor stars. We adopt an iron abundance using photometric
gravities and Fe II lines to minimize those effects, finding [Fe/H] = -2.16 +/-
0.02. For element-to-iron ratios,we rely on neutral lines vs. Fe I and ionized
lines vs. FeII (except for [O/Fe]) to also minimize non-LTE effects.
  We find variations in the abundances of sodium among the program stars.
However, there is no correlation (or anti-correlation) with the oxygen
abundances. Further, the post-AGB star has a normal (low) abundance of sodium.
Both of these facts add further support to the idea that the variations seen
among some light elements within individual globular clusters arises from
primordial variations, and not from deep mixing.
  M68, like M15, shows elevated abundances of silicon compared to other
globular clusters and comparable metallicity field stars. But M68 deviates even
more in showing a relative underabundance of titanium. We speculate that in
M68, titanium is behaving like an iron-peak element rather than its more
commonly observed adherence to enhancements seen in the ""alpha"" elements such
as magnesium, silicon, and calcium. We interpret this result as implying that
the chemical enrichment seen in M68 may have arisen from contributions from
supernovae with somewhat more massive progenitors than contribute normally to
abundances seen in other globular clusters.",0409706v1
2005-04-14,Three-dimensional modeling of Type Ia supernovae - The power of late time spectra,"Late time synthetic spectra of Type Ia supernovae, based on three-dimensional
deflagration models, are presented. We mainly focus on one
model,""c3_3d_256_10s"", for which the hydrodynamics (Roepke 2005) and
nucleosynthesis (Travaglio et al. 2004) was calculated up to the homologous
phase of the explosion. Other models with different ignition conditions and
different resolution are also briefly discussed. The synthetic spectra are
compared to observed late time spectra. We find that while the model spectra
after 300 to 500 days show a good agreement with the observed Fe II-III
features, they also show too strong O I and C I lines compared to the observed
late time spectra. The oxygen and carbon emission originates from the
low-velocity unburned material in the central regions of these models. To get
agreement between the models and observations we find that only a small mass of
unburned material may be left in the center after the explosion. This may be a
problem for pure deflagration models, although improved initial conditions, as
well as higher resolution decrease the discrepancy. The relative intensity from
the different ionization stages of iron is sensitive to the density of the
emitting iron-rich material. We find that clumping, with the presence of low
density regions, is needed to reproduce the observed iron emission, especially
in the range between 4000 and 6000 AA. Both temperature and ionization depend
sensitively on density, abundances and radioactive content. This work therefore
illustrates the importance of including the inhomogeneous nature of realistic
three-dimensional explosion models. We briefly discuss the implications of the
spectral modeling for the nature of the explosion.",0504317v1
2006-02-25,Probing Multiple Sight Lines through the SN 1006 Remnant by UV Absorption Spectroscopy,"Absorption-line spectroscopy is an effective probe for cold ejecta within an
SNR, provided that suitable background UV sources can be identified. For the SN
1006 remnant we have identified four such sources, in addition to the
much-studied Schweitzer-Middleditch (SM) star. We have used STIS on HST to
obtain UV spectra of all four sources, to study ""core samples"" of the SN 1006
interior. The line of sight closest to the center of the SNR shell, passing
only 2.0 arcmin away, is to a V = 19.5 QSO at z = 1.026. Its spectrum shows
broad Fe II absorption lines, asymmetric with red wings broader than blue. The
similarity of these profiles to those seen in the SM star, which is 2.8 arcmin
from the center in the opposite direction, confirms the existence of a bulge on
the far side of SN 1006. The Fe II equivalent widths in the QSO spectrum are ~
50% greater than in the SM star, suggesting that somewhat more iron may be
present within SN 1006 than studies of the SM star alone have indicated, but
this is still far short of what most SNIa models require. The absorption
spectrum against a brighter z = 0.337 QSO seen at 57% of the shell radius shows
broad silicon absorption lines but no iron other than narrow, probably
interstellar lines. The cold iron expanding in this direction must be confined
within v <~ 5200 km/s, also consistent with a high-velocity bulge on the far
side only. The broad silicon lines indicate that the silicon layer has expanded
beyond this point, and that it has probably been heated by a reverse shock.
Finally, the spectra of two ~ A0V stars near the southern shell rim show no
broad or unusually strong absorption lines, suggesting that the low-ionization
ejecta are confined within 83% of the shell radius, at least at the azimuths of
these background sources.",0602555v1
2006-05-15,Accretion processes in AGN: The X-ray View,"We discuss constraints on the physics of the inner accretion disk, as well as
the properties of the black hole itself, that can be derived by a detailed
examination of the relativistically broadened spectral features (especially the
fluorescent iron line) in the Seyfert galaxy MCG-6-30-15. To begin with, we
show that spectral models which purport to eliminate the broad iron line in
MCG-6-30-15 by invoking a moderately high ionization absorber are ruled out by
recent high-resolution spectra from the Chandra High Energy Transmission
Gratings. We then discuss the comparison of XMM-Newton data with accretion disk
models. The ""standard'' black hole disk model of Novikov, Page and Thorne
supplemented by the so-called local corona assumption fails to produce
sufficient broadening; this indicates that the real accretion disk in
MCG-6-30-15 has significantly more centrally concentrated pattern of X-ray
irradiation that predicted by this model. We discuss two possible resolutions.
Firstly, the inner disk may be energized from torques imposed by magnetic
connections between the disk-proper and either the plunging region or the
rotating event horizon itself. Secondly, X-ray emission from a high-latitude
source (such as would be the case of the X-ray source is actually the base of a
jet) would be gravitationally focused onto the central portions of the disk. We
discuss how spectral variability may be used to examine these possibilities and
highlight the still outstanding mystery concerning the anti-correlation between
the iron line equivalent width and relative normalization of the Compton
reflection hump. We end with a few words about the exciting future of these
studies in the future era of Constellation-X and LISA.",0605368v1
2006-11-09,Medium resolution spectroscopy in Omega Centauri: abundances of 400 subgiant and turn-off region,"Medium resolution spectra of more than 400 subgiant and turn-off region stars
in Omega Centauri were analysed. The observations were performed at the
VLT/Paranal with FORS2/MXU. In order to determine the metallicities of the
sample stars, we defined a set of line indices (mostly iron) adjusted to the
resolution of our spectra. The indices as determined for Omega Centauri were
then compared to line indices from stars in the chemically homogeneous globular
cluster M55, in addition to standard stars and synthetic spectra. The
uncertainties in the derived metallicities are of the order of 0.2 dex. Our
study confirms the large variations in iron abundances found on the giant
branch in earlier studies (-2.2 <[Fe/H]< -0.7 dex). In addition, we studied the
alpha-element and CN/CH abundances. Stars of different metallicity groups not
only show distinct ages, but also different behaviours in their relative
abundances. The alpha abundances increase smoothly with increasing metallicity
resulting in a flat [alpha/Fe] ratio over the whole observed metallicity range.
The combined CN+CH abundance increases smoothly with increasing iron abundance.
The most metal-rich stars are CN-enriched. In a CN vs. CH plot, though, the
individual abundances divide into CN- and CH-rich branches. The large abundance
variations observed in our sample of (unevolved) subgiant branch stars most
probably have their origin in the pre-enriched material rather than in internal
mixing effects. Together with the age spread of the different sub-populations,
our findings favour the formation of Omega Centauri within a more massive
progenitor.",0611286v1
2006-12-28,Probing the Disk-jet Connection of the Radio Galaxy 3C120 Observed with Suzaku,"Broad line radio galaxies (BLRGs) are a rare type of radio-loud AGN, in which
the broad optical permitted emission lines have been detected in addition to
the extended jet emission. Here we report on deep (40ksec x4) observations of
the bright BLRG 3C~120 using Suzaku. The observations were spaced a week apart,
and sample a range of continuum fluxes. An excellent broadband spectrum was
obtained over two decades of frequency (0.6 to 50 keV) within each 40 ksec
exposure. We clearly resolved the iron K emission line complex, finding that it
consists of a narrow K_a core (sigma ~ 110 eV or an EW of 60 eV), a 6.9 keV
line, and an underlying broad iron line. Our confirmation of the broad line
contrasts with the XMM-Newton observation in 2003, where the broad line was not
required. The most natural interpretation of the broad line is iron K line
emission from a face-on accretion disk which is truncated at ~10 r_g. Above 10
keV, a relatively weak Compton hump was detected (reflection fraction of R ~
0.6), superposed on the primary X-ray continuum of Gamma ~ 1.75. Thanks to the
good photon statistics and low background of the Suzaku data, we clearly
confirm the spectral evolution of 3C120, whereby the variability amplitude
decreases with increasing energy. More strikingly, we discovered that the
variability is caused by a steep power-law component of Gamma ~2.7, possibly
related to the non-thermal jet emission. We discuss our findings in the context
of similarities and differences between radio-loud/quiet objects.",0612754v1
2007-02-16,Accretion of chemically fractionated material on a wide binary with a blue straggler,"The components of the wide binary HIP64030=HD 113984 show a large (about 0.25
dex) iron content difference (Desidera et al.~2006 A&A 454, 581). The positions
of the components on the color magnitude diagram suggest that the primary is a
blue straggler. We studied the abundance difference of several elements besides
iron, and we searched for stellar and substellar companions around the
components to unveil the origin of the observed iron difference. A line-by-line
differential abundance analysis for several elements was performed, while
suitable spectral synthesis was performed for C, N, and Li. High precision
radial velocities obtained with the iodine cell were combined with available
literature data. The analysis of additional elements shows that the abundance
difference for the elements studied increases with increasing condensation
temperature, suggesting that accretion of chemically fractionated material
might have occurred in the system. Alteration of C and N likely due to CNO
processing is also observed. We also show that the primary is a spectroscopic
binary with a period of 445 days and moderate eccentricity. The minimum mass of
the companion is 0.17 Msun. Two scenarios were explored to explain the observed
abundance pattern. In the first, all abundance anomalies arise on the blue
straggler. If this is the case, the dust-gas separation may have been occurred
in a circumbinary disk around the blue straggler and its expected white dwarf
companion, as observed in several RV Tauri and post AGB binaries. In the second
scenario, accretion of dust-rich material occurred on the secondary. This would
also explain the anomalous carbon isotopic ratio of the secondary. Such a
scenario requires that a substantial amount of mass lost by the central binary
has been accreted by the wide component.",0702439v1
2007-07-17,Wide-band spectroscopy of the Compton thick Seyfert 2 galaxy Mrk 3 with Suzaku,"We obtained a wide-band spectrum of the Compton-thick Seyfert 2 galaxy Mrk 3
with Suzaku. The observed spectrum was clearly resolved into weak, soft
power-law emission, a heavily absorbed power-law component, cold reflection,
and many emission lines. The heavily absorbed component, absorbed by gas with a
column density of 1.1x10^24 cm^-2, has an intrinsic 2--10 keV luminosity of
~1.6x10^43 erg s^-1, and is considered to be direct emission from the Mrk 3
nucleus. The reflection component was interpreted as reflection of the direct
light off cold, thick material; the reflection fraction $R$ was 1.36+/-0.20.
The cold material is inferred to be located > 1 pc from the central black hole
of Mrk 3 due to the low ionization parameter of iron (xi < 1 erg cm s^-1) and
the narrow iron line width (s < 22 eV). A Compton shoulder to the iron line was
detected, but the intensity of the shoulder component was less than that
expected from spherically distributed Compton-thick material. The weak, soft
power-law emission is considered to be scattered light by ionized gas. The
existence of many highly-ionized lines from O, Ne, Mg, Si, S, and Fe in the
observed spectrum indicates that the ionized gas has a broad ionized structure,
with xi=10--1000. The scattering fraction with respect to the direct light was
estimated to be 0.9+/-0.2%, which indicates that the column density of the
scattering region is about 3.6x10^22 cm^-2. This high-quality spectrum obtained
by Suzaku can be considered a template for studies of Seyfert 2 galaxies.",0707.2425v1
2007-07-19,Relativistic Iron K Emission and absorption in the Seyfert 1.9 galaxy MCG-5-23-16,"We present the results of the simultaneous deep XMM and Chandra observations
of the bright Seyfert 1.9 galaxy MCG-5-23-16, which is thought to have one of
the best known examples of a relativistically broadened iron K-alpha line. The
time averaged spectral analysis shows that the iron K-shell complex is best
modeled with an unresolved narrow emission component (FWHM < 5000 km/s, EW ~ 60
eV) plus a broad component. This latter component has FWHM ~ 44000 km/s and EW
~ 50 eV. Its profile is well described by an emission line originating from an
accretion disk viewed with an inclination angle ~ 40^\circ and with the
emission arising from within a few tens of gravitational radii of the central
black hole. The time-resolved spectral analysis of the XMM EPIC-pn spectrum
shows that both the narrow and broad components of the Fe K emission line
appear to be constant in time within the errors. We detected a narrow sporadic
absorption line at 7.7 keV which appears to be variable on a time-scale of 20
ksec. If associated with Fe XXVI Ly-alpha this absorption is indicative of a
possibly variable, high ionization, high velocity outflow. The variability of
this absorption feature appears to rule out a local (z=0) origin. The analysis
of the XMM RGS spectrum reveals that the soft X-ray emission of MCG-5-23-16 is
likely dominated by several emission lines superimposed on an unabsorbed
scattered power-law continuum. The lack of strong Fe L shell emission together
with the detection of a strong forbidden line in the O VII triplet is
consistent with a scenario where the soft X-ray emission lines are produced in
a plasma photoionized by the nuclear emission.",0707.2950v1
2007-07-26,Different Methods of Forming Cold Fronts in Non-Merging Clusters,"Sharp edges in X-ray surface brightness with continuous gas pressure called
cold fronts have been often found in relaxed galaxy clusters such as Abell 496.
Models that explain cold fronts as surviving cores of head-on subcluster
mergers do not work well for these clusters and competing models involving gas
sloshing have been recently proposed. Here, we test some concrete predictions
of these models in a combined analysis of density, temperature, metal
abundances and abundance ratios in a deep Chandra exposure of Abell 496. We
confirm that the chemical discontinuities found in this cluster are not
consistent with a core merger remnant scenario. However, we find chemical
gradients across a spiral ""arm"" discovered at 73 kpc north of the cluster
center and coincident with the sharp edge of the main cold front in the
cluster. Despite the overall SN Ia iron mass fraction dominance found within
the cooling radius of this cluster, the metal enrichment along the arm,
determined from silicon and iron abundances, is consistent with a lower SN Ia
iron mass fraction (51% +- 14%) than that measured in the surrounding regions
(85% +- 14%). The ""arm"" is also significantly colder than the surroundings by
0.5-1.6 keV. The arm extends from a boxy colder region surrounding the center
of the cluster, where two other cold fronts are found. This cold arm is a
prediction of current high resolution numerical simulations as a result of an
off-center encounter with a less massive pure dark matter halo and we suggest
that the cold fronts in A496 provide the first clear corroboration of such
model, where the closest encounter happened ~ 0.5 Gyr ago. We also argue for a
possible candidate dark matter halo responsible for the cold fronts in the
outskirts of A496.",0707.4001v1
2007-08-25,Modeling the chemical evolution of Omega Centauri using three-dimensional hydrodynamical simulations,"We present a hydrodynamical and chemical model for the globular cluster Omega
Cen, under the assumption that it is the remnant of an ancient dwarf spheroidal
galaxy (dSph), the bulk of which was disrupted and accreted by our Galaxy ~10
Gyr ago. We highlight the very different roles played by Type II and Type Ia
supernovae (SNe) in the chemical enrichment of the inner regions of the
putative parent dSph. While the SNe II pollute the interstellar medium rather
uniformly, the SNe Ia ejecta may remain confined inside dense pockets of gas as
long as succesive SNe II explosions spread them out. Stars forming in such
pockets have lower alpha-to-iron ratios than the stars forming elsewhere. Owing
to the inhomogeneous pollution by SNe Ia, the metal distribution of the stars
in the central region differs substantially from that of the main population of
the dwarf galaxy, and resembles that observed in Omega Cen. This inhomogeneous
mixing is also responsible for a radial segregation of iron-rich stars with
depleted [alpha/Fe] ratios, as observed in some dSphs. Assuming a star
formation history of ~1.5 Gyr, our model succeeds in reproducing both the iron
and calcium distributions observed in Omega Cen and the main features observed
in the empirical alpha/Fe versus Fe/H plane. Finally, our model reproduces the
overall spread of the color-magnitude diagram, but fails in reproducing the
morphology of the SGB-a and the double morphology of the main sequence.
However, the inhomogeneous pollution reduces (but does not eliminate) the need
for a significantly enhanced helium abundance to explain the anomalous position
of the blue main sequence. Further models taking into account the dynamical
interaction of the parent dwarf galaxy with the Milky Way and the effect of AGB
pollution will be required.",0708.3445v1
2007-09-10,Iron lines from transient and persisting hot spots on AGN accretion disks,"[abridged] We model the X-ray reprocessing from a strong co-rotating flare
above an accretion disk in active galactic nuclei. We explore the horizontal
structure and evolution of the underlying hot spot. To obtain the spectral
evolution seen by a distant observer, we apply a general relativity ray-tracing
technique. We concentrate on the energy band around the iron K-line, where the
relativistic effects are most pronounced. Persistent flares lasting for a
significant fraction of the orbital time scale and short, transient flares are
considered. In our time-resolved analysis, the spectra recorded by a distant
observer depend on the position of the flare/spot with respect to the central
black hole. If the flare duration significantly exceeds the light travel time
across the spot, then the spot horizontal stratification is unimportant. On the
other hand, if the flare duration is comparable to the light travel time across
the spot radius, the lightcurves exhibit a typical asymmetry in their time
profiles. The sequence of dynamical spectra proceeds from more strongly to less
strongly ionized re-emission. At all locations within the spot the spectral
intensity increases towards edge-on emission angles, revealing the limb
brightening effect. Future X-ray observatories with significantly larger
effective collecting areas will enable to spectroscopically map out the
azimuthal irradiation structure of the accretion disk and to localize
persistent flares. If the hot spot is not located too close to the marginally
stable orbit of the black hole, it will be possible to probe the reflecting
medium via the sub-structure of the iron K-line. Indications for transient
flares will only be obtained from analyzing the observed lightcurves on the
gravitational time scale of the accreting supermassive black hole.",0709.1356v1
2007-10-31,The Proto-neutron Star Phase of the Collapsar Model and the Route to Long-soft Gamma-ray Bursts and Hypernovae,"Recent stellar evolutionary calculations of low-metallicity massive
fast-rotating main-sequence stars yield iron cores at collapse endowed with
high angular momentum. It is thought that high angular momentum and black hole
formation are critical ingredients of the collapsar model of long-soft
gamma-ray bursts (GRBs). Here, we present 2D multi-group,
flux-limited-diffusion MHD simulations of the collapse, bounce, and immediate
post-bounce phases of a 35-Msun collapsar-candidate model of Woosley & Heger.
We find that, provided the magneto-rotational instability (MRI) operates in the
differentially-rotating surface layers of the millisecond-period neutron star,
a magnetically-driven explosion ensues during the proto-neutron star phase, in
the form of a baryon-loaded non-relativistic jet, and that a black hole,
central to the collapsar model, does not form. Paradoxically, and although much
uncertainty surrounds stellar mass loss, angular momentum transport, magnetic
fields, and the MRI, current models of chemically homogeneous evolution at low
metallicity yield massive stars with iron cores that may have too much angular
momentum to avoid a magnetically-driven, hypernova-like, explosion in the
immediate post-bounce phase. We surmise that fast rotation in the iron core may
inhibit, rather than enable, collapsar formation, which requires a large
angular momentum not in the core but above it. Variations in the angular
momentum distribution of massive stars at core collapse might explain both the
diversity of Type Ic supernovae/hypernovae and their possible association with
a GRB. A corollary might be that, rather than the progenitor mass, the angular
momentum distribution, through its effect on magnetic field amplification,
distinguishes these outcomes.",0710.5789v2
2008-02-14,Complexity on Small Scales III: Iron and alpha Element Abundances in the Carina Dwarf Spheroidal Galaxy,"We have obtained high-resolution spectroscopy of ten red giants in the Carina
dwarf spheroidal (dSph) with UVES at the ESO/VLT. Here we present the
abundances of O,Na,Mg,Si,Ca,Ti and Fe. By comparing the iron abundances [Fe/H]
with calcium triplet (CaT) metallicities we show that the empirical CaT
technique yields good agreement with the high-resolution data for [Fe/H]>-2
dex, but tends to deviate at lower metallicities. We identify two metal poor
stars with iron abundances of -2.72 and -2.50 dex. These stars are found to
have enhanced [alpha/Fe] ratios similar to those of stars in the Milky Way
halo. However, the bulk of the Carina red giants are depleted in the [alpha/Fe]
abundance ratios with respect to the Galactic halo at a given metallicity. One
of our targets, with a [Fe/H] of -1.5 dex, is considerably depleted in almost
all of the alpha-elements by ~0.5 dex compared to the solar values. Such a low
[alpha/Fe] can be produced by stochastical fluctuations in terms of an
incomplete mixing of single Type Ia and II SNe events into the ISM. Our derived
element ratios are consistent with the episodic and extended SF in Carina known
from its color-magnitude diagram. We find a considerable star-to-star scatter
in the abundance ratios. This suggests that Carina's SF history varies with
position within the galaxy, with incomplete mixing. Alternatively, the SF rate
is so low that the high-mass stellar IMF is sparsely populated, as
statistically expected in low-mass star clusters, leading to real scatter in
the resultant mass-integrated yields. Both ideas are consistent with slow
stochastic SF in dissolving associations, so that one may not speak of a single
SF history at a detailed level (Abridged).",0802.2104v1
2008-03-04,A large population of recently-quenched red-sequence dwarf galaxies in the outskirts of the Coma Cluster,"We analyse the stellar populations of 75 red-sequence dwarf galaxies in the
Coma cluster, based on high signal-to-noise spectroscopy from the 6.5m MMT. The
sample covers a luminosity range 3-4 magnitudes below M*, in the cluster core
and in a field centred 1 deg to the south-west. We find a strong dependence of
the absorption line strengths with location in the cluster. Galaxies further
from the cluster centre have stronger Balmer lines than inner-field galaxies of
the same luminosity. The magnesium lines are weaker at large radius, while the
iron lines are not correlated with radius. Converting the line strengths into
estimates of stellar age, metallicity and abundance ratios, we find the
gradients are driven by variations in age (>6 sigma significance) and in the
iron abundance Fe/H (~2.7 sigma significance). The light element (Mg, C, N, Ca)
abundances are almost independent of radius. At radius of 0.4-1.3 degree
(~0.3-1.0x the virial radius), dwarf galaxies have ages ~3.8 Gyr on average,
compared to ~6 Gyr near the cluster centre. The outer dwarfs are also ~50% more
iron-enriched, at given luminosity. Our results confirm earlier indications
that the ages of red-sequence galaxies depend on location within clusters, and
in Coma in particular. The exceptionally strong trends found here suggest that
dwarf galaxies are especially susceptible to environmental ""quenching"", and/or
that the south-west part of Coma is a particularly clear example of recent
quenching in an infalling subcluster.",0803.0327v1
2008-09-01,Abundance profiles in cooling-core clusters: a fossil record of past AGN-driven convection?,"Central peaks in the iron abundance of intracluster plasma are a common
feature of cooling-core galaxy clusters. These abundance peaks have a much
broader profile than the stars of the central brightest cluster galaxy (BCG),
which produce the excess iron, indicating that metal-enriched plasma is
transported out of the BCG by some process such as turbulent diffusion. At the
same time, cooling-core clusters are likely heated by central active galactic
nuclei (AGNs) by means of jets, cosmic-ray bubbles, and convection. The recent
AGN-driven convection model of Chandran&Rasera predicts the turbulent velocity
profile in a steady-state cluster in which radiative cooling is balanced by
heating from a combination of AGN-driven convection and thermal conduction. We
use the velocity profiles as input into an advection/diffusion model for the
transport of metals in the intracluster medium, taking the iron to be injected
by the BCG. We compare the results of our model to XMM and Chandra observations
of eight clusters. Assuming a constant turbulence level over a cluster's
lifetime, the turbulent velocities in the model can explain the observed
abundance profiles in only five of the eight clusters. However, we go on to
develop an analytic fit of the turbulent velocity profile as a function of the
AGN power. We then deduce for each cluster the average AGN power (during the
past 10 Gyr) required to match the abundance profiles. The required average
values are between 10^43 and 2.10^44 erg/s, while the present AGN powers span a
much larger range from 6.10^41 (Virgo) to 2.10^44 erg/s (Hydra A). Our results
suggest that AGN-driven convection can account for the observed abundance
profiles if the AGN power varies over a cluster's lifetime between Virgo-like
and Hydra-A-like values, with average values in the above-quoted range.",0809.0238v1
2008-11-04,"Influence of the rare-earth element on the effects of the structural and magnetic phase transitions in CeFeAsO, PrFeAsO, and NdFeAsO","We present results of transport and magnetic properties and heat capacity
measurements on polycrystalline CeFeAsO, PrFeAsO, and NdFeAsO. These materials
undergo structural phase transitions, spin density wave-like magnetic ordering
of small moments on iron, and antiferromagnetic ordering of rare earth moments.
The temperature dependence of the electrical resistivity, Seebeck coefficient,
thermal conductivity, Hall coefficient, and magnetoresistance are reported. The
magnetic behavior of the materials have been investigated using Mossbauer
spectroscopy and magnetization measurements. Transport and magnetic properties
are affected strongly by the structural and magnetic transitions, suggesting
significant changes in the band structure and/or carrier mobilities occur, and
phonon-phonon scattering is reduced upon transformation to the low temperature
structure. Results are compared to recent reports for LaFeAsO, and systematic
variations in properties as the identity of Ln is changed are observed and
discussed. As Ln progresses across the rare-earth series from La to Nd, an
increase in the hole contributions to Seebeck coefficient, and increases in
magnetoresistance and the Hall coefficient are observed in the low temperature
phase. Analysis of hyperfine fields at the iron nuclei determined from
Mossbauer spectra indicates that the moment on Fe in the orthorhombic phase is
nearly independent of the identity of Ln, in apparent contrast to reports of
powder neutron diffraction refinements.",0811.0589v3
2009-01-29,A Galaxy Merger Scenario for the NGC 1550 Galaxy from Metal Distributions in the X-ray Emitting Plasma,"The elliptical galaxy NGC 1550 at a redshift of $z=0.01239$, identified with
an extended X-ray source RX J0419+0225, was observed with {\it XMM-Newton} for
31 ks. From the X-ray data and archival near infra-red data of Two Micron All
Sky survay, we derive the profiles of components constituting the NGC 1550
system; the gas mass, total mass, metal mass, and galaxy luminosity. The metals
(oxygen, silicon, and iron) are extended to $\sim 200$ kpc from the center,
wherein $\sim$ 70% of the $K$-band luminosity is carried by NGC 1550 itself. As
first revealed with {\it ASCA}, the data reconfirms the presence of a dark
halo, of which the mass ($1.6 \times 10^{13} M_{\odot}$) is typical of a galaxy
group rather than of a single galaxy. Within 210 kpc, the $K$-band
mass-to-light ratio reaches $75 M_{\odot}/L_{\odot}$, which is comparable to
those of clusters of galaxies. The iron-mass-to-light ratio profile (silicon-
and oxygen mass-to-light ratio profiles as well) exhibits about two orders of
magnitude decrease toward the center. Further studies comparing mass densities
of metals with those of the other cluster components reveal that the iron (as
well as silicon) in the ICM traces very well the total gravitating mass,
whereas the stellar component is significantly more concentrated to within
several tens kpc of the NGC 1550 nucleus. Thus, in the central region, the
amount of metals is significantly depleted for the luminous galaxy light. Among
a few possible explanations of this effect, the most likely scenario is that
galaxies in this system were initially much more extended than today, and
gradually fell to the center and merged into NGC 1550.",0901.4626v1
2009-02-02,Type-Ia Supernova-driven Galactic Bulge Wind,"Stellar feedback in galactic bulges plays an essential role in shaping the
evolution of galaxies. To quantify this role and facilitate comparisons with
X-ray observations, we conduct 3D hydrodynamical simulations with the adaptive
mesh refinement code, FLASH, to investigate the physical properties of hot gas
inside a galactic bulge, similar to that of our Galaxy or M31. We assume that
the dynamical and thermal properties of the hot gas are dominated by mechanical
energy input from SNe, primarily Type Ia, and mass injection from evolved stars
as well as iron enrichment from SNe. We study the bulge-wide outflow as well as
the SN heating on scales down to ~4 pc. An embedding scheme that is devised to
plant individual SNR seeds, allows to examine, for the first time, the effect
of sporadic SNe on the density, temperature, and iron ejecta distribution of
the hot gas as well as the resultant X-ray morphology and spectrum. We find
that the SNe produce a bulge wind with highly filamentary density structures
and patchy ejecta. Compared with a 1D spherical wind model, the non-uniformity
of simulated gas density, temperature, and metallicity substantially alters the
spectral shape and increases the diffuse X-ray luminosity. The differential
emission measure as a function of temperature of the simulated gas exhibits a
log-normal distribution, with a peak value much lower than that of the
corresponding 1D model. The bulk of the X-ray emission comes from the
relatively low temperature and low abundance gas shells associated with SN
blastwaves. SN ejecta are not well mixed with the ambient medium, at least in
the bulge region. These results, at least partly, account for the apparent lack
of evidence for iron enrichment in the soft X-ray-emitting gas in galactic
bulges and intermediate-mass elliptical galaxies.[...]",0902.0386v1
2009-02-10,A Study of the Accuracy of Mass-Radius Relationships for Silicate-Rich and Ice-Rich Planets up to 100 Earth Masses,"A mass-radius relationship is proposed for solid planets and solid cores
ranging from 1 to 100 Earth-mass planets. It relies on the assumption that
solid spheres are composed of iron and silicates, around which a variable
amount of water is added. The M-R law has been set up assuming that the
planetary composition is similar to the averaged composition for silicates and
iron obtained from the major elements ratio of 94 stars hosting exoplanets.
Except on Earth for which a tremendous amount of data is available, the
composition of silicate mantles and metallic cores cannot be constrained.
Similarly, thermal profiles are poorly known. In this work, the effect of
compositional parameters and thermal profiles on radii estimates is quantified.
It will be demonstrated that uncertainties related to composition and
temperature are of second order compared to the effect of the water amount. The
Super-Earths family includes four classes of planets: iron-rich, silicate-rich,
water-rich, or with a thick atmosphere. For a given mass, the planetary radius
increases significantly from the ironrich to the atmospheric-rich planet. Even
if some overlaps are likely, M-R measurements could be accurate enough to
ascertain the discovery of an earth-like planet .The present work describes how
the amount of water can be assessed from M-R measurements. Such an estimate
depends on several assumptions including i) the accuracy of the internal
structure model and ii) the accuracy of mass and radius measurements. It is
shown that if the mass and the radius are perfectly known, the standard
deviation on the amount of water is about 4.5 %. This value increases rapidly
with the radius uncertainty but does not strongly depend on the mass
uncertainty.",0902.1640v1
2009-02-20,"Frustrated Magnetic Interactions, Giant Magneto-Elastic Coupling, and Magnetic Phonons in Iron-Pnictides","We present a detailed first principles study of Fe-pnictides with particular
emphasis on competing magnetic interactions, structural phase transition, giant
magneto-elastic coupling and its effect on phonons. The exchange interactions
$J_{i,j}(R)$ are calculated up to $\approx 12 $\AA $. We find that $J_{i,j}(R)$
has an oscillatory character with an envelop decaying as $1/R^3$ along the
stripe-direction while it is very short range along the diagonal direction and
antiferromagnetic. A brief discussion of the neutron scattering determination
of these exchange constants from a single crystal sample with orthorhombic
twinning is given. The lattice parameter dependence of the exchange constants,
$dJ_{i,j}/da$ are calculated for a simple spin-Peierls like model to explain
the fine details of the tetragonal-orthorhombic phase transition. We then
discuss giant magneto-elastic effects in these systems. We show that when the
Fe-spin is turned off the optimized c-values are shorter than experimetnal
values by 1.4 \AA $ $ for CaFe$_2$As$_2$, by 0.4 \AA $ $ for BaFe$_2$As$_2$,
and by 0.13 \AA $ $ for LaOFeAs. Finally, we show that Fe-spin is also required
to obtain the right phonon energies, in particular As c-polarized and Fe-Fe
in-plane modes. Since treating iron as magnetic ion always gives much better
results than non-magnetic ones and since there is no large c-axis reduction
during the normal to superconducting phase transition, the iron magnetic moment
should be present in Fe-pnictides at all times. We discuss the implications of
our results on the mechanism of superconductivity in these fascinating
Fe-pnictide systems.",0902.3462v1
2009-03-20,Spectral Analysis of the Accretion Flow in NGC 1052 with Suzaku,"We present an analysis of the 101 ks, 2007 Suzaku spectrum of the LINER
galaxy NGC 1052. The 0.5-10 keV continuum is well-modeled by a power-law
modified by Galactic and intrinsic absorption, and it exhibits a soft, thermal
emission component below 1 keV. Both a narrow core and a broader component of
Fe K emission centered at 6.4 keV are robustly detected. While the narrow line
is consistent with an origin in material distant from the black hole, the broad
line is best fit empirically by a model that describes fluorescent emission
from the inner accretion disk around a rapidly rotating black hole. We find no
evidence in this observation for Comptonized reflection of the hard X-ray
source by the disk above 10 keV, however, which casts doubt on the hypothesis
that the broad iron line originates in the inner regions of a standard
accretion disk. We explore other possible scenarios for producing this spectral
feature and conclude that the high equivalent width (EW ~ 185 keV) and
full-width-half-maximum velocity of the broad iron line (v ~ 0.37c) necessitate
an origin within d ~ 8 gravitational radii of the hard X-ray source. Based on
the confirmed presence of a strong radio jet in this galaxy nucleus, the broad
iron line may be produced in dense plasma near the base of the jet, implying
that emission mechanisms in the centralmost portions of active galactic nuclei
are more complex than previously thought.",0903.3583v1
2009-04-06,New insight into the physics of iron pnictides from optical and penetration depth data,"We report theoretical values for the unscreened plasma frequencies Omega_p of
several Fe pnictides obtained from DFT based calculations within the LDA and
compare them with experimental plasma frequencies obtained from reflectivity
data. The sizable renormalization observed for all considered compounds points
to the presence of many-body effects beyond the LDA. From the large empirical
background dielectric constant of about 12-15, we estimate a large arsenic
polarizability of about 9.5 +- 1.2 Angstroem^3 where the details depend on the
polarizabilities of the remaining ions taken from the literature. This large
polarizability can significantly reduce the value of the Coulomb repulsion U_d
about 4 eV on iron known from iron oxides to a level of 2 eV or below. In
general, this result points to rather strong polaronic effects as suggested by
G.A. Sawatzky et al., in Refs. arXiv:0808.1390 and arXiv:0811.0214 (Berciu et
al.). Possible consequences for the conditions of a formation of bipolarons are
discussed, too. From the extrapolated muon spin rotation penetration depth data
at T= 0 and the experimental Omega_p we estimate the total coupling constant
lambda_tot for the el-boson interaction within the Eliashberg-theory adopting a
single band approximation. For LaFeAsO_0.9F_0.1 a weak to intermediately strong
coupling regime and a quasi-clean limit behaviour are found. For a pronounced
multiband case we obtain a constraint for various intraband coupling constants
which in principle allows for a sizable strong coupling in bands with either
slow electrons or holes.",0904.0827v1
2009-04-07,Search for associations containing young stars (SACY):II. Chemical abundances of stars in 11 young Associations in the Solar neighborhood,"The recently discovered coeval, moving groups of young stellar objects in the
solar neighborhood represent invaluable laboratories to study recent star
formation and to search for high metallicity stars which can be included in
future exo-planet surveys. In this study we derived through an uniform and
homogeneous method stellar atmospheric parameters and abundances for iron,
silicium and nickel in 63 Post T-Tauri Stars from 11 nearby young associations.
We further compare the results with two different pre-main sequence (PMS) and
main sequence (MS) star populations. The stellar atmospheric parameters and the
abundances presented here were derived using the equivalent width of individual
lines in the stellar spectra through the excitation/ionization equilibrium of
iron. Moreover, we compared the observed Balmer lines with synthetic profiles
calculated for model atmospheres with a different line formation code. We found
that the synthetic profiles agree reasonably well with the observed profiles,
although the Balmer lines of many stars are substantially filled-in, probably
by chromospheric emission. Solar metallicity is found to be a common trend on
all the nearby young associations studied. The low abundance dispersion within
each association strengthens the idea that the origin of these nearby young
associations is related to the nearby Star Forming regions (SFR). Abundances of
elements other than iron are consistent with previous results on Main Sequence
stars in the solar neighborhood. The chemical characterization of the members
of the newly found nearby young associations, performed in this study and
intended to proceed in subsequent works, is essential for understanding and
testing the context of local star formation and the evolutionary history of the
galaxy.",0904.1221v1
2009-06-17,On the metallicity gradient of the Galactic disk,"Aims: The iron abundance gradient in the Galactic stellar disk provides
fundamental constraints on the chemical evolution of this important Galaxy
component. However the spread around the mean slope is, at fixed Galactocentric
distance, larger than estimated uncertainties. Methods: To provide quantitative
constraints on these trends we adopted iron abundances for 265 classical
Cepheids (more than 50% of the currently known sample) based either on
high-resolution spectra or on photometric metallicity indices. Homogeneous
distances were estimated using near-infrared Period-Luminosity relations. The
sample covers the four disk quadrants and their Galactocentric distances range
from ~5 to ~17 kpc. Results: A linear regression over the entire sample
provides an iron gradient of -0.051+/-0.004 dex/kpc. The above slope agrees
quite well, within the errors, with previous estimates based either on Cepheids
or on open clusters covering similar Galactocentric distances. However, once we
split the sample in inner (Rg < 8 kpc) and outer disk Cepheids we found that
the slope (-0.130+/-0.015 dex/kpc) in the former region is ~3 times steeper
than the slope in the latter one (-0.042+/-0.004 dex/kpc). We found that in the
outer disk the radial distribution of metal-poor (MP, [Fe/H]<-0.02 dex) and
metal-rich (MR) Cepheids across the four disk quadrants does not show a clear
trend when moving from the innermost to the external disk regions. We also
found that the relative fractions of MP and MR Cepheids in the 1st and in the
3rd quadrant differ at 8 sigma (MP) and 15 sigma (MR) level.",0906.3140v1
2009-10-09,Critical change in the Fermi surface of iron arsenic superconductors at the onset of superconductivity,"The phase diagram of a correlated material is the result of a complex
interplay between several degrees of freedom, providing a map of the material's
behavior. One can understand (and ultimately control) the material's ground
state by associating features and regions of the phase diagram, with specific
physical events or underlying quantum mechanical properties. The phase diagram
of the newly discovered iron arsenic high temperature superconductors is
particularly rich and interesting. In the AE(Fe1-xTx)2As2 class (AE being Ca,
Sr, Ba, T being transition metals), the simultaneous structural/magnetic phase
transition that occurs at elevated temperature in the undoped material, splits
and is suppressed by carrier doping, the suppression being complete around
optimal doping. A dome of superconductivity exists with apparent equal ease in
the orthorhombic / antiferromagnetic (AFM) state as well as in the tetragonal
state with no long range magnetic order. The question then is what determines
the critical doping at which superconductivity emerges, if the AFM order is
fully suppressed only at higher doping values. Here we report evidence from
angle resolved photoemission spectroscopy (ARPES) that critical changes in the
Fermi surface (FS) occur at the doping level that marks the onset of
superconductivity. The presence of the AFM order leads to a reconstruction of
the electronic structure, most significantly the appearance of the small hole
pockets at the Fermi level. These hole pockets vanish, i. e. undergo a Lifshitz
transition, at the onset of superconductivity. Superconductivity and magnetism
are competing states in the iron arsenic superconductors. In the presence of
the hole pockets superconductivity is fully suppressed, while in their absence
the two states can coexist.",0910.1799v2
2009-11-06,"Accurate Fundamental Parameters or A, F, and G-type Supergiants in the Solar Neighbourhood","The following parameters are determined for 63 Galactic supergiants in the
solar neighbourhood: effective temperature Teff, surface gravity log g, iron
abundance log e(Fe), microturbulent parameter Vt, mass M/Msun, age t and
distance d. A significant improvement in the accuracy of the determination of
log g and, all parameters dependent on it, is obtained through application of
van Leeuwens (2007) re-reduction of the Hipparcos parallaxes. The typical error
in the log g values is now +-0.06 dex for supergiants with distances d < 300 pc
and +-0.12 dex for supergiants with d between 300 and 700 pc; the mean error in
Teff for these stars is +-120 K. For supergiants with d > 700 pc parallaxes are
uncertain or unmeasurable, so typical errors in their log g values are 0.2-0.3
dex.
  A new Teff scale for A5-G5 stars of luminosity classes Ib-II is presented.
Spectral subtypes and luminosity classes of several stars are corrected.
Combining the Teff and log g with evolutionary tracks, stellar masses and ages
are determined; a majority of the sample has masses between 4 Msun and 15 Msun
and, hence, their progenitors were early to middle B-type main sequence stars.
  Using Fe ii lines, which are insensitive to departures from LTE, the
microturbulent parameter Vt and the iron abundance log e(Fe) are determined
from high-resolution spectra. The parameter Vt is correlated with gravity: Vt
increases with decreasing log g. The mean iron abundance for the 48 supergiants
with distances d < 700 pc is log e(Fe)=7.48+-0.09, a value close to the solar
value of 7.45+-0.05, and thus the local supergiants and the Sun have the same
metallicity.",0911.1335v2
2009-12-09,Empirically Derived Integrated Stellar Yields of Fe-Peak Elements,"We present here the initial results of a new study of massive star yields of
Fe-peak elements. We have compiled from the literature a database of carefully
determined solar neighborhood stellar abundances of seven iron-peak elements,
Ti, V, Cr, Mn, Fe, Co, and Ni and then plotted [X/Fe] versus [Fe/H] to study
the trends as functions of metallicity. Chemical evolution models were then
employed to force a fit to the observed trends by adjusting the input massive
star metallicity-sensitive yields of Kobayashi et al. Our results suggest that
yields of Ti, V, and Co are generally larger as well as anticorrelated with
metallicity, in contrast to the Kobayashi et al. predictions. We also find the
yields of Cr and Mn to be generally smaller and directly correlated with
metallicity compared to the theoretical results. Our results for Ni are
consistent with theory, although our model suggests that all Ni yields should
be scaled up slightly. The outcome of this exercise is the computation of a set
of integrated yields, i.e., stellar yields weighted by a slightly flattened
time-independent Salpeter initial mass function and integrated over stellar
mass, for each of the above elements at several metallicity points spanned by
the broad range of observations. These results are designed to be used as
empirical constraints on future iron-peak yield predictions by stellar
evolution modelers. Special attention is paid to the interesting behavior of
[Cr/Co] with metallicity -- these two elements have opposite slopes -- as well
as the indirect correlation of [Ti/Fe] with [Fe/H]. These particular trends, as
well as those exhibited by the inferred integrated yields of all iron-peak
elements with metallicity, are discussed in terms of both supernova
nucleosynthesis and atomic physics.",0912.1816v1
2010-01-03,Suzaku Monitoring of the Iron K Emission Line in the Type 1 AGN NGC 5548,"We present 7 sequential weekly observations of NGC 5548 conducted in 2007
with the \textit{Suzaku} X-ray Imaging Spectrometer (XIS) in the 0.2-12 keV
band and Hard X-ray Detector (HXD) in 10-600 keV band. The iron K$\alpha$ line
is well detected in all seven observations and K$\beta$ line is also detected
in four observations. In this paper, we investigate the origin of the Fe K
lines using both the width of the line and the reverberation mapping method.
  With the co-added XIS and HXD spectra, we identify Fe K$\alpha$ and K$\beta$
line at 6.396$_{-0.007}^{+0.009}$ keV and 7.08$_{-0.05}^{+0.05}$ keV,
respectively. The width of line obtained from the co-added spectra is
38$_{-18}^{+16}$ eV ($\textrm{FWHM}=4200_{-2000}^{+1800}$ km/s) which
corresponds to a radius of 20$_{-10}^{+50}$ light days, for the virial
production of $1.220\times10^7$ M$_{\odot}$ in NCG 5548.
  To quantitatively investigate the origin of the narrow Fe line by the
reverberation mapping method, we compare the observed light curves of Fe
K$\alpha$ line with the predicted ones, which are obtained by convolving the
continuum light curve with the transfer functions in a thin shell and an
inclined disk. The best-fit result is given by the disk case with $i=30^\circ$
which is better than a fit to a constant flux of the Fe K line at the 92.7%
level (F-test). We find that the emitting radius obtained from the light curve
is 25-37 light days, which is consistent with the radius derived from the Fe K
line width. Combining the results of the line width and variation, the most
likely site for the origin of the narrow iron lines is 20-40 light days away
from the central engine, though other possibilities are not completely ruled
out. (abridged)",1001.0356v1
2010-01-07,Supernova 2007bi as a pair-instability explosion,"Stars with initial masses 10 M_{solar} < M_{initial} < 100 M_{solar} fuse
progressively heavier elements in their centres, up to inert iron. The core
then gravitationally collapses to a neutron star or a black hole, leading to an
explosion -- an iron-core-collapse supernova (SN). In contrast, extremely
massive stars (M_{initial} > 140 M_{solar}), if such exist, have oxygen cores
which exceed M_{core} = 50 M_{solar}. There, high temperatures are reached at
relatively low densities. Conversion of energetic, pressure-supporting photons
into electron-positron pairs occurs prior to oxygen ignition, and leads to a
violent contraction that triggers a catastrophic nuclear explosion. Tremendous
energies (>~ 10^{52} erg) are released, completely unbinding the star in a
pair-instability SN (PISN), with no compact remnant. Transitional objects with
100 M_{solar} < M_{initial} < 140 M_{solar}, which end up as iron-core-collapse
supernovae following violent mass ejections, perhaps due to short instances of
the pair instability, may have been identified. However, genuine PISNe, perhaps
common in the early Universe, have not been observed to date. Here, we present
our discovery of SN 2007bi, a luminous, slowly evolving supernova located
within a dwarf galaxy (~1% the size of the Milky Way). We measure the exploding
core mass to be likely ~100 M_{solar}, in which case theory unambiguously
predicts a PISN outcome. We show that >3 M_{solar} of radioactive 56Ni were
synthesized, and that our observations are well fit by PISN models. A PISN
explosion in the local Universe indicates that nearby dwarf galaxies probably
host extremely massive stars, above the apparent Galactic limit, perhaps
resulting from star formation processes similar to those that created the first
stars in the Universe.",1001.1156v1
2010-03-29,Ferromagnetism in defect-ridden oxides and related materials,"The existence of high-temperature ferromagnetism in thin films and
nanoparticles of oxides containing small quantities of magnetic dopants remains
controversial. Some regard these materials as dilute magnetic semiconductors,
while others think they are ferromagnetic only because the magnetic dopants
form secondary ferromagnetic impurity phases such as cobalt metal or magnetite.
There are also reports in d0 systems and other defective oxides that contain no
magnetic ions. Here, we investigate TiO2 (rutile) containing 1 - 5% of iron
cations and find that the room-temperature ferromagnetism of films prepared by
pulsed-laser deposition is not due to magnetic ordering of the iron. The films
are neither dilute magnetic semiconductors nor hosts to an iron-based
ferromagnetic impurity phase. A new model is developed for defect-related
ferromagnetism which involves a spin-split defect band populated by charge
transfer from a proximate charge reservoir in the present case a mixture Fe2+
and Fe3+ ions in the oxide lattice. The phase diagram for the model shows how
inhomogeneous Stoner ferromagnetism depends on the total number of electrons
Ntot, the Stoner exchange integral I and the defect bandwidth W; the band
occupancy is governed by the d-d Coulomb interaction U. There are regions of
ferromagnetic metal, half-metal and insulator as well as nonmagnetic metal and
insulator. A characteristic feature of the high-temperature Stoner magnetism is
an an anhysteretic magnetization curve which is practically temperature
independent below room temperature. This is related to a wandering
ferromagnetic axis which is determined by local dipole fields. The
magnetization is limited by the defect concentration, not by the 3d doping.
Only 1-2 % of the volume of the films is magnetically ordered.",1003.5558v1
2010-04-26,Chemical Abundances for the Outer Halo Cluster Pal 4 from Co-added High-Resolution Spectroscopy,"Context: Chemical element abundances for distant Galactic globular clusters
(GCs) hold important clues to the origin of the Milky Way halo and its
substructures. Aims: We study the chemical composition of red giant stars in
Pal 4 - one of the most remote GCs in the Milky Way - and compare our abundance
measurements to those for both low surface brightness dwarf galaxies, and GCs
in the inner and the outer halo. Methods: By co-adding high-resolution, low-S/N
Keck/HIRES spectra of 19 stars along the red giant branch, we estimate chemical
abundance ratios of 20 alpha-, iron peak-, and neutron-capture elements. Our
method gives total uncertainties on most element-to-iron ratios of typically
0.2 dex. Results: We measure [Fe/H] = -1.41 +- 0.04 (statistical) +- 0.17
(systematic) and an alpha-enhancement of [alpha/Fe] = +0.38 +- 0.11 dex, which
is consistent with the canonical value of +0.4 dex found for Galactic halo
field stars and most halo GCs at this metallicity. Although Pal 4 has higher
enhancements in the heavier elements with respect to the halo, the majority of
the element ratios are, within the measurement errors, consistent with those
for local halo field stars. We find, however, evidence for a lower [Mg/Ca]
ratio than in other halo clusters. Conclusions: Based on the available
evidence, we conclude that the material from which Pal 4 and the Galactic halo
formed experienced similar enrichment processes, despite the apparently younger
age of this cluster. Within the limitations of our methodology we find no
significant indication of an iron spread, as is typical of genuine GCs of the
Milky Way. However, abundance ratios for individual stars in Pal 4 and other
distant satellites are urgently needed to understand the relationship, if any,
between remote GCs and other halo substructures (i.e., luminous and ultra-faint
dwarf spheroidal galaxies).",1004.4625v1
2010-06-05,Variations in the X-ray eclipse transitions of Cen X-3,"We report here an investigation of the X-ray eclipse transitions of the high
mass X-ray binary pulsar Cen X-3 in different intensity states. Long term light
curve of Cen X-3 obtained with RXTE-ASM spanning for more than 5000 days shows
strong aperiodic flux variations with low and high states. We have investigated
the eclipse transitions of Cen X-3 in different intensity states with data
obtained from pointed observations with the more sensitive instruments on board
ASCA, BeppoSAX, XMM-Newton, Chandra and RXTE. We found a very clear trend of
sharp eclipse transitions in the high state and longer transitions in the low
state. This is a confirmation of this feature first observed with the RXTE-ASM
but now with much better clarity. From the light curves obtained from several
missions, it is seen that the eclipse egress in the low state starts earlier by
an orbital phase of 0.02 indicating that the observed X-rays originate from a
much larger region. We have also performed spectral analysis of the
post-eclipse part of each observations. From BeppoSAX observations, the
out-of-eclipse X-ray fluxes is found to differ by a factor of ~ 26 during the
high and low intensity states while the eclipse count rates differ by a factor
of only ~ 4.7. This indicates that in the low state, there is an additional
scattering medium which scatters some of the source photons towards the
observer even when the neutron star is completely eclipsed. We could also
resolve the three iron line components using XMM-Newton observation in the low
state. By comparing the iron line equivalent width during the high and low
states, it is seen that the width of iron line is relatively large during the
low state which supports the fact that significant reprocessing and scattering
of X-rays takes place in the low state.",1006.1035v1
2010-06-17,The supernova delay time distribution in galaxy clusters and implications for Type-Ia progenitors and metal enrichment,"Knowledge of the supernova (SN) delay time distribution (DTD) - the SN rate
versus time that would follow a hypothetical brief burst of star formation -
can shed light on SN progenitors and physics. We compile recent measurements of
the Type-Ia SN (SN Ia) rate in galaxy clusters at redshifts z=0-1.45. Together
with the observed iron-to-stellar mass ratio in clusters, which constrains the
time-integrated number of SN Ia events in clusters, we recover the DTD of SNe
Ia in cluster environments. The DTD peaks at the shortest time-delay interval
we probe, 0<t<2.2 Gyr, with a low tail out to delays of ~10 Gyr, and is
remarkably consistent with several recent DTD reconstructions based on
different methods, in different environments. We test DTD models from the
literature, requiring that they simultaneously reproduce the observed cluster
SN rates and the observed iron-to-stellar mass ratios. A power-law DTD of the
form t^{-1.2+/-0.3}, extending to a Hubble time, can satisfy both constraints.
Shallower power laws, such as t^{-1/2} cannot, assuming a single DTD, and a
single star-formation burst (either brief or extended) at high z. This implies
50-85% of SNe Ia explode within 1 Gyr of star formation. DTDs from
double-degenerate (DD) models, which generically have ~t^{-1} shapes over a
wide range of timescales, match the data, but only if their predictions are
scaled up by factors of 5-10. Single degenerate (SD) DTDs always give poor fits
to the data, due to a lack of delayed SNe and overall low numbers of SNe. The
observations also permit a combination of two SN Ia populations - prompt (e.g.
SD) SNe Ia that explode within a few Gyr of star formation, and produce about
60% of the iron mass in clusters, and a DD population that contributes the
events seen at z<1.4. Our results support the existence of a DD progenitor
channel for SNe Ia, if the overall predicted numbers can be suitably increased.",1006.3576v3
2010-08-01,Chemical Enrichment in the Faintest Galaxies: the Carbon and Iron Abundance Spreads in the Boötes I Dwarf Spheroidal Galaxy and the Segue 1 System,"We present an AAOmega spectroscopic study of red giant stars in Bootes I,
which is an ultra-faint dwarf galaxy, and Segue 1, suggested to be either an
extremely low-luminosity dwarf galaxy or a star cluster. Our focus is
quantifying the mean abundance and abundance dispersion in iron and carbon, and
searching for distant radial-velocity members, in these systems.
  The primary conclusion of our investigation is that the spread of carbon
abundance in both Bootes I and Segue 1 is large. For Bootes I, 4 of our 16
velocity members have [C/H] < ~-3.1, while 2 have [C/H] > ~-2.3, suggesting a
range of Delta[C/H] ~ 0.8. For Segue 1 there exists a range Delta[C/H] ~ 1.0,
including our discovery of a star with [Fe/H] = -3.5 and [C/Fe] = +2.3, which
is a radial velocity member at a distance of 4 half-light radii from the system
center. The accompanying ranges in iron abundance are Delta[Fe/H] ~ 1.6 for
both Bootes I and Segue 1. For [Fe/H] < -3.0, the Galaxy's dwarf galaxy
satellites exhibit a dependence of [C/Fe] on [Fe/H] which is very similar to
that observed in its halo populations. We find [C/Fe] ~ 0.3 for stars in the
dwarf systems that we believe are the counterpart of the Spite et al. (2005)
``unmixed'' giants of the Galactic halo and for which they report [C/Fe] ~ 0.2,
and which presumably represents the natal relative abundance of carbon for
material with [Fe/H] = -3.0 to -4.0.
  We confirm the correlation between luminosity and both mean metallicity and
abundance dispersion in the Galaxy's dwarf satellites, which extends to at
least as faint as Mv = -5. The very low mean metallicity of Segue 1, and the
high carbon dispersion in Bootes I, consistent with inhomogeneous chemical
evolution in near zero-abundance gas, suggest these ultra-faint systems could
be surviving examples of the very first bound systems.",1008.0137v1
2010-11-29,New Atomic Data for Trans-Iron Elements and Their Application to Abundance Determinations in Planetary Nebulae,"[Abridged] Investigations of neutron(n)-capture element nucleosynthesis and
chemical evolution have largely been based on stellar spectroscopy. However,
the recent detection of these elements in several planetary nebulae (PNe)
indicates that nebular spectroscopy is a promising new tool for such studies.
In PNe, n-capture element abundance determinations reveal details of s-process
nucleosynthesis and convective mixing in evolved low-mass stars, as well as the
chemical evolution of elements that cannot be detected in stellar spectra. Only
one or two ions of a given trans-iron element can typically be detected in
individual nebulae. Elemental abundance determinations thus require corrections
for the abundances of unobserved ions. Such corrections rely on the
availability of atomic data for processes that control the ionization
equilibrium of nebulae. Until recently, these data were unknown for virtually
all n-capture element ions. For the first five ions of Se, Kr, and Xe -- the
three most widely detected n-capture elements in PNe -- we are calculating
photoionization cross sections and radiative and dielectronic recombination
rate coefficients using the multi-configuration Breit-Pauli atomic structure
code AUTOSTRUCTURE. Charge transfer rate coefficients are being determined with
a multichannel Landau-Zener code. To calibrate these calculations, we have
measured absolute photoionization cross sections of Se and Xe ions at the
Advanced Light Source synchrotron radiation facility. These atomic data can be
incorporated into photoionization codes, which we will use to derive ionization
corrections (hence abundances) for Se, Kr, and Xe in ionized nebulae. These
results are critical for honing nebular spectroscopy into a more effective tool
for investigating the production and chemical evolution of trans-iron elements
in the Universe.",1011.6311v1
2011-03-31,The metal contents of two groups of galaxies,"The hot gas in clusters and groups of galaxies is continuously being enriched
with metals from supernovae and stars. It is well established that the
enrichment of the gas with elements from oxygen to iron is mainly caused by
supernova explosions. The origins of nitrogen and carbon are still being
debated. Possible candidates include massive, metal-rich stars, early
generations of massive stars, intermediate or low mass stars and Asymptotic
Giant Branch (AGB) stars. In this paper we accurately determine the metal
abundances of the gas in the groups of galaxies NGC 5044 and NGC 5813, and
discuss the nature of the objects that create these metals.
  We mainly focus on carbon and nitrogen. We use spatially-resolved
high-resolution X-ray spectroscopy from XMM-Newton. For the spectral fitting,
multi-temperature hot gas models are used. The abundance ratios of carbon over
oxygen and nitrogen over oxygen that we find are high compared to the ratios in
the stars in the disk of our Galaxy. The oxygen and nitrogen abundances we
derive are similar to what was found in earlier work on other giant ellipticals
in comparable environments. We show that the iron abundances in both our
sources have a gradient along the cross-dispersion direction of the Reflection
Grating Spectrometer (RGS). We conclude that it is unlikely that the creation
of nitrogen and carbon takes place in massive stars, which end their lives as
core-collapse supernovae, enriching the medium with oxygen because oxygen
should then also be enhanced. Therefore we favour low-and intermediate mass
stars as sources of these elements. The abundances in the hot gas can best be
explained by a 30-40% contribution of type Ia supernovae based on the measured
oxygen and iron abundances and under the assumption of a Salpeter Initial Mass
Function (IMF).",1104.0001v1
2011-04-11,Self-consistent spin-wave theory for a frustrated Heisenberg model with biquadratic exchange in the columnar phase and its application to iron pnictides,"Recent neutron scattering studies revealed the three dimensional character of
the magnetism in the iron pnictides and a strong anisotropy between the
exchange perpendicular and parallel to the spin stripes. We extend studies of
the J1-J2-Jc Heisenberg model with S = 1 using self-consistent spin-wave
theory. A discussion of two scenarios for the instability of the columnar phase
is provided. The relevance of a biquadratic exchange term between in-plane
nearest neighbors is discussed. We introduce mean-field decouplings for
biquadratic terms using the Dyson-Maleev and the Schwinger boson
representation. Remarkably their respective mean-field theories do not lead to
the same results, even at zero temperature. They are gauged in the N'eel phase
in comparison to exact diagonalization and series expansion. The J1-J2-Jc model
is analyzed under the influence of the biquadratic exchange Jbq and a detailed
description of the staggered magnetization and of the magnetic excitations is
given. The biquadratic exchange increases the renormalization of the in-plane
exchange constants which enhances the anisotropy between the exchange parallel
and perpendicular to the spin stripes. Applying the model to iron pnictides, it
is possible to reproduce the spin-wave dispersion for CaFe2As2 in the direction
perpendicular to the spin stripes and perpendicular to the planes.
Discrepancies remain in the direction parallel to the spin stripes which can be
resolved by passing from S = 1 to S = 2. In addition, results for the dynamical
structure factor within the self-consistent spin-wave theory are provided.",1104.1954v2
2011-04-22,K-shell Emission of Neutral Iron Line from Sgr B2 Excited by Subrelativistic Protons,"We investigated the emission of K$\alpha$ iron line from the massive
molecular clouds in the Galactic center (GC). We assume that at present the
total flux of this emission consists of time variable component generated by
primary X-ray photons ejected by Sagittarius A$^\ast$ (Sgr A$^\ast$) in the
past and a relatively weak quasi-stationary component excited by impact of
protons which were generated by star accretion onto the central black hole. The
level of background emission was estimated from a rise of the 6.4 keV line
intensity in the direction of several molecular clouds, that we interpreted as
a stage when the X-ray front ejected by Sgr A$^\ast$ entered into these clouds.
The 6.4 keV emission before this intensity jump we interpreted as emission
generated by subrelativistic cosmic rays there. The cross-section of K$\alpha$
vacancies produced by protons differs from that of electrons or X-rays.
Therefore, we expect that this processes can be distinguished from the analysis
of the equivalent width of the iron line and time variations of the width can
be predicted. The line intensity from the clouds depends on their distance from
Sgr A$^\ast$ and the coefficient of spacial diffusion near the Galactic center.
We expect that in a few years the line intensity for the cloud G\,0.11$-$0.11
which is relatively close to Sgr A$^\ast$ will decreases to the level
$\lesssim$ 10% from its present value. For the cloud Sagittarius B2 (Sgr B2)
the situation is more intricate. If the diffusion coefficient $D\gtrsim
10^{27}$ cm$^2$ s$^{-1}$ then the expected stationary flux should be about 10%
of its level in 2000. In the opposite case the line intensity from Sgr B2
should drop down to zero because the protons do not reach the cloud.",1104.4484v1
2011-07-05,A giant planet in the triple system HD132563,"As part of our radial velocity planet-search survey performed with SARG at
TNG, we monitored the components of HD 132563 for ten years. It is a binary
system formed by two rather similar solar type stars with a projected
separation of 4.1 arcsec, which corresponds to 400 AU at the distance of 96 pc.
The two components are moderately metal-poor and the age of the system is about
5 Gyr. We detected RV variations of HD 132563B with period of 1544 days and
semi-amplitude of 26 m/s. From the star characteristics and line profile
measurements, we infer their Keplerian origin. Therefore HD 132563B turns out
to host a planet with a projected mass msini=1.49 MJup at 2.6 AU with a
moderately eccentric orbit (e=0.22). The planet around HD 132563B is one of the
few that are known in triple stellar systems, as we found that the primary HD
132563A is itself a spectroscopic binary with a period longer than 15 years and
an eccentricity higher than 0.65. The spectroscopic component was not detected
in adaptive-optics images taken with AdOpt@TNG, since it expected at a
projected separation that was smaller than 0.2 arcsec at the time of our
observations. A small excess in K band difference between the components with
respect to the difference in V band is compatible with a companion of about
0.55 Msun. A preliminary statistical analysis of the occurrence of planets in
triple systems indicate a similar frequency of planets around the isolated
component in a triple system, components of wide binaries and single stars.
There is no significant iron abundance difference between the components. The
lack of stars in binary systems and open clusters showing strong enhancements
of iron abundance, comparable to the typical metallicity difference between
stars with and without giant planets, agrees with the idea that accretion of
planetary material producing iron abundance anomalies larger than 0.1 dex is
rare.",1107.0918v1
2011-11-21,Iron and alpha-element Production in the First One Billion Years after the Big Bang,"We present measurements of carbon, oxygen, silicon, and iron in quasar
absorption systems existing when the universe was roughly one billion years
old. We measure column densities in nine low-ionization systems at 4.7 < z <
6.3 using Keck, Magellan, and VLT optical and near-infrared spectra with
moderate to high resolution. The column density ratios among C II, O I, Si II,
and Fe II are nearly identical to sub-DLAs and metal-poor ([M/H] < -1) DLAs at
lower redshifts, with no significant evolution over 2 < z < 6. The estimated
intrinsic scatter in the ratio of any two elements is also small, with a
typical r.m.s. deviation of <0.1 dex. These facts suggest that dust depletion
and ionization effects are minimal in our z > 4.7 systems, as in the
lower-redshift DLAs, and that the column density ratios are close to the
intrinsic relative element abundances. The abundances in our z > 4.7 systems
are therefore likely to represent the typical integrated yields from stellar
populations within the first gigayear of cosmic history. Due to the time limit
imposed by the age of the universe at these redshifts, our measurements thus
place direct constraints on the metal production of massive stars, including
iron yields of prompt supernovae. The lack of redshift evolution further
suggests that the metal inventories of most metal-poor absorption systems at z
> 2 are also dominated by massive stars, with minimal contributions from
delayed Type Ia supernovae or AGB winds. The relative abundances in our systems
broadly agree with those in very metal-poor, non-carbon-enhanced Galactic halo
stars. This is consistent with the picture in which present-day metal-poor
stars were potentially formed as early as one billion years after the Big Bang.",1111.4843v1
2012-01-04,Synthesis and physical properties of the new potassium iron selenide superconductor K0.80Fe1.76Se2,"In this article we review our studies of the K0.80Fe1.76Se2 superconductor,
with an attempt to elucidate the crystal growth details and basic physical
properties over a wide range of temperatures and applied magnetic field,
including anisotropic magnetic and electrical transport properties,
thermodynamic, London penetration depth, magneto-optical imaging and Mossbauer
measurements. We find that: (i) Single crystals of similar stoichiometry can be
grown both by furnace-cooled and decanted methods; (ii) Single crystalline
K0.80Fe1.76Se2 shows moderate anisotropy in both magnetic susceptibility and
electrical resistivity and a small modulation of stoichiometry of the crystal,
which gives rise to broadened transitions; (iii) The upper critical field,
Hc2(T) is ~ 55 T at 2 K for H||c, manifesting a temperature dependent
anisotropy that peaks near 3.6 at 27 K and drops to 2.5 by 18 K; (iv) Mossbauer
measurements reveal that the iron sublattice in K0.80Fe1.76Se2 clearly exhibits
magnetic order, probably of the first order, from well below Tc to its Neel
temperature of Tn = 532 +/- 2 K. It is very important to note that, although,
at first glance there is an apparent dilemma posed by these data: high Tc
superconductivity in a near insulating, large ordered moment material, analysis
indicates that the sample may well consist of two phases with the minority
superconducting phase (that does not exhibit magnetic order) being finely
distributed, but connected with in an antiferromagnetic, poorly conducting,
matrix, essentially making a superconducting aerogel.",1201.0953v2
2012-02-13,A Variable Partial Covering Model for the Seyfert 1 Galaxy MCG-6-30-15,"We propose a simple spectral model for the Seyfert 1 Galaxy MCG-6-30-15 that
can explain most of the 1 - 40 keV spectral variation by change of the partial
covering fraction, similar to the one proposed by Miller et al. (2008). Our
spectral model is composed of three continuum components; (1) a direct
power-law component, (2) a heavily absorbed power-law component by mildly
ionized intervening matter, and (3) a cold disk reflection component far from
the black hole with moderate solid-angle ({\Omega}/2{\pi} \approx 0.3)
accompanying a narrow fluorescent iron line. The first two components are
affected by the surrounding highly ionized thin absorber with N_H \approx
10^{23.4}cm-2 and log {\xi} \approx 3.4. The heavy absorber in the second
component is fragmented into many clouds, each of which is composed of radial
zones with different ionization states and column densities, the main body (N_H
\approx 10^24.2cm-2, log {\xi} \approx 1.6), the envelope (N_H \approx
10^22.1cm-2, log {\xi} \approx 1.9) and presumably a completely opaque core.
These parameters of the ionized absorbers, as well as the intrinsic spectral
shape of the X-ray source, are unchanged at all. The central X-ray source is
moderately extended, and its luminosity is not significantly variable. The
observed flux and spectral variations are mostly explained by variation of the
geometrical partial covering fraction of the central source from 0 (uncovered)
to \sim0.63 by the intervening ionized clouds in the line of sight. The ionized
iron K-edge of the heavily absorbed component explains most of the seemingly
broad line-like feature, a well-known spectral characteristic of MCG-6-30-15.
The direct component and the absorbed component anti-correlate, cancelling
their variations each other, so that the fractional spectral variation becomes
the minimum at the iron energy band; another observational characteristic of
MCG-6-30-15 is thus explained.",1202.2797v3
2012-02-23,The Similarity of Broad Iron Lines in X-ray Binaries and Active Galactic Nuclei,"We have compared the 2001 XMM-Newton spectra of the stellar mass black hole
binary XTE J1650-500 and the active galaxy MGC-6-30-15, focusing on the broad,
excess emission features at ~4--7 keV displayed by both sources. Such features
are frequently observed in both low mass X-ray binaries and active galactic
nuclei. For the former case it is generally accepted that the excess arises due
to iron emission, but there is some controversy over whether their width is
partially enhanced by instrumental processes, and hence also over the intrinsic
broadening mechanism. Meanwhile, in the latter case, the origin of this feature
is still subject to debate; physically motivated reflection and absorption
interpretations are both able to reproduce the observed spectra. In this work
we make use of the contemporaneous BeppoSAX data to demonstrate that the
breadth of the excess observed in XTE J1650-500 is astrophysical rather than
instrumental, and proceed to highlight the similarity of the excesses present
in this source and MGC-6-30-15. Both optically thick accretion discs and
optically thin coronae, which in combination naturally give rise to
relativistically-broadened iron lines when the disc extends close to the black
hole, are commonly observed in both class of object. The simplest solution is
that the broad emission features present arise from a common process, which we
argue must be reflection from the inner regions of an accretion disc around a
rapidly rotating black hole; for XTE J1650-500 we find spin constraints of 0.84
< a* < 0.98 at the 90 per cent confidence level. Other interpretations proposed
for AGN add potentially unnecessary complexities to the theoretical framework
of accretion in strong gravity.",1202.5193v1
2012-03-02,Testing the effects of opacity and the chemical mixture on the excitation of pulsations in B stars of the Magellanic Clouds,"The B-type pulsators known as \beta Cephei and Slowly Pulsating B (SPB) stars
present pulsations driven by the \kappa mechanism, which operates thanks to an
opacity bump due to the iron group elements. In low-metallicity environments
such as the Magellanic Clouds, \beta Cep and SPB pulsations are not expected.
Nevertheless, recent observations show evidence for the presence of B-type
pulsator candidates in both galaxies. We seek an explanation for the excitation
of \beta Cep and SPB modes in those galaxies by examining basic input physics
in stellar modelling: i) the specific metal mixture of B-type stars in the
Magellanic Clouds; ii) the role of a potential underestimation of stellar
opacities. We first derive the present-day chemical mixtures of B-type stars in
the Magellanic Clouds. Then, we compute stellar models for that metal mixture
and perform a non-adiabatic analysis of these models. In a second approach, we
simulate parametric enhancements of stellar opacities due to different iron
group elements. We then study their effects in models of B stars and their
stability. We find that adopting a representative chemical mixture of B stars
in the Small Magellanic Cloud cannot explain the presence of B-type pulsators
there. An increase of the opacity in the region of the iron-group bump could
drive B-type pulsations, but only if this increase occurs at the temperature
corresponding to the maximum contribution of Ni to this opacity bump. We
recommend an accurate computation of Ni opacity to understand B-type pulsators
in the Small Magellanic Cloud, as well as the frequency domain observed in some
Galactic hybrid \beta Cep-SPB stars.",1203.0527v1
2012-03-19,Hot Gas in Galaxy Groups: Recent Observations,"Galaxy groups are the least massive systems where the bulk of baryons begin
to be accounted for. Not simply the scaled-down versions of rich clusters
following self-similar relations, galaxy groups are ideal systems to study
baryon physics, which is important for both cluster cosmology and galaxy
formation. We review the recent observational results on the hot gas in galaxy
groups. The first part of the paper is on the scaling relations, including
X-ray luminosity, entropy, gas fraction, baryon fraction and metal abundance.
Compared to clusters, groups have a lower fraction of hot gas around the center
(e.g., r < r_2500), but may have a comparable gas fraction at large radii
(e.g., r_2500 < r < r_500). Better constraints on the group gas and baryon
fractions require sample studies with different selection functions and deep
observations at r > r_500 regions. The hot gas in groups is also iron poor at
large radii (0.3 r_500 - 0.7 r_500). The iron content of the hot gas within the
central regions (r < 0.3 r_500) correlates with the group mass, in contrast to
the trend of the stellar mass fraction. It remains to be seen where the missing
iron in low-mass groups is. In the second part, we discuss several aspects of
X-ray cool cores in galaxy groups, including their difference from cluster cool
cores, radio AGN heating in groups and the cold gas in group cool cores.
Because of the vulnerability of the group cool cores to radio AGN heating and
the weak heat conduction in groups, group cool cores are important systems to
test the AGN feedback models and the multiphase cool core models. At the end of
the paper, some outstanding questions are listed.",1203.4228v1
2012-03-28,Dependence of the structural and physical properties of Tl1-yFe2-z(Se1-xSx)2 with isovalent substitution of Se by S: decrease of TNeel with S content,"The effect of selenium substitution by sulfur or tellurium in the
Tl1-yFe2-zSe2 antiferromagnet was studied by x-ray and electron diffraction,
magnetization and transport measurements. Tl0.8Fe1.5(Se1-xXx)2 (nominal
composition) solid solutions were synthesized in the full x range (0<x<1) for
X=S and up to x=0.5 for X=Te, using the sealed tube technique. No
superconductivity was found down to 4.2K in the case of sulfur despite the fact
that the optimal crystallographic parameters, determined by Rietveld
refinements, are reached in the series (i.e. the Fe-(Se,S) interplane height
and (Se,S)-Fe-(Se,S) angle for which the critical superconducting transition
T$_{c}$ is usually maximal in pnictides). Quasi full Tl site (y=0.05) compared
to significant alkaline deficiency (y=0.2-0.3) in analogous A1-yFe2-zSe2 (A =
K, Rb, Cs), and the resulting differences in iron valency, density of states
and doping, are suggested to explain this absence of superconductivity.
Compounds substituted with tellurium, at least up to x=0.25, show
superconducting transitions but probably due to tetragonal Fe(Se,Te) impurity
phase. Transmission electron microscopy confirmed the existence of ordered iron
vacancies network in the samples from the
Tl$_{0.8}$Fe$_{1.5}$(Se$_{1-x}$S$_{x}$)$_{2}$ series in the form of the
tetragonal $\sqrt{5}$ a $\times \sqrt{5}$ a $\times$ c superstructure
(\textit{I4/m}) (mixed with the orthorhombic $\sqrt{2}$ a $\times 2\sqrt{2}$ a
$\times$ c form (\textit{Ibam}) if the iron vacancies level is increased). The
N\'{e}el temperature (T$_{N}$) indicating the onset of antiferromagnetism order
in the $\sqrt{5}$ a $\times \sqrt{5}$ a $\times$ c supercell decreases from
450K in the selenide (x=0) to 330K in the sulfide (x=1). We finally demonstrate
a direct linear relationship between $T_{N\acute{e}el}$ and the Fe-(Se,S) bond
length (or Fe-(Se,S) height).",1203.6181v2
2012-05-21,Very High Resolution Solar X-ray Imaging Using Diffractive Optics,"This paper describes the development of X-ray diffractive optics for imaging
solar flares with better than 0.1 arcsec angular resolution. X-ray images with
this resolution of the \geq10 MK plasma in solar active regions and solar
flares would allow the cross-sectional area of magnetic loops to be resolved
and the coronal flare energy release region itself to be probed. The objective
of this work is to obtain X-ray images in the iron-line complex at 6.7 keV
observed during solar flares with an angular resolution as fine as 0.1 arcsec -
over an order of magnitude finer than is now possible. This line emission is
from highly ionized iron atoms, primarily Fe xxv, in the hottest flare plasma
at temperatures in excess of \approx10 MK. It provides information on the flare
morphology, the iron abundance, and the distribution of the hot plasma.
Studying how this plasma is heated to such high temperatures in such short
times during solar flares is of critical importance in understanding these
powerful transient events, one of the major objectives of solar physics. We
describe the design, fabrication, and testing of phase zone plate X-ray lenses
with focal lengths of \approx100 m at these energies that would be capable of
achieving these objectives. We show how such lenses could be included on a
two-spacecraft formation-flying mission with the lenses on the spacecraft
closest to the Sun and an X-ray imaging array on the second spacecraft in the
focal plane \approx100 m away. High resolution X-ray images could be obtained
when the two spacecraft are aligned with the region of interest on the Sun.
Requirements and constraints for the control of the two spacecraft are
discussed together with the overall feasibility of such a formation-flying
mission.",1205.4762v1
2012-07-04,Nematic and meta-nematic transitions in the iron pnictides,"Strongly interacting electrons can exhibit novel collective phases, among
which the electronic nematic phases are perhaps the most surprising as they
spontaneously break rotational symmetry of the underlying crystal lattice. The
electron nematicity has been recently observed in the iron-pnictide and cuprate
high-temperature superconductors. Whether such a tendency of electrons to
self-organise unidirectionally has a common feature in these superconductors
is, however, a highly controversial issue. In the cuprates, the nematicity has
been suggested as a possible source of the pseudogap phase, whilst in the
iron-pnictides, it has been commonly associated with the
tetragonal-to-orthorhombic structural phase transition at $T_s$. Here, we
provide the first thermodynamic evidence in BaFe2(As1-xPx)2 that the nematicity
develops well above the structural transition and persists to the nonmagnetic
superconducting regime, resulting in a new phase diagram strikingly similar to
the pseudogap phase diagram in the cuprates. Our highly sensitive magnetic
anisotropy measurements using microcantilever torque-magnetometry under
in-plane field rotation reveal pronounced two-fold oscillations, which break
the tetragonal symmetry. Combined with complementary high-resolution
synchrotron X-ray and resistivity measurements, our results consistently
identify two distinct temperatures - one at $T^{\ast}$, signifying a true
nematic transition, and the other at $T_s (< T^{\ast})$, which we show to be
not a true phase transition, but rather what we refer to as a ""meta-nematic
transition"", in analogy to the well-known metamagnetic transition in the theory
of magnetism. Our observation of the extended nematic phase above the
superconducting dome establishes that the nematicity has primarily an
electronic origin, inherent in the normal state of high-temperature
superconductors.",1207.1045v1
2012-08-24,Failed-Detonation Supernovae: Sub-Luminous Low-Velocity Ia Supernovae and Their Kicked Remnant White Dwarfs with Iron-Rich Cores,"Type Ia supernovae (SNe Ia) originate from the thermonuclear explosions of
carbon-oxygen (C-O) white dwarfs (WDs). The single-degenerate scenario is a
well-explored model of SNe Ia where unstable thermonuclear burning initiates in
an accreting, Chandrasekhar-mass WD and forms an advancing flame. By several
proposed physical processes the rising, burning material triggers a detonation,
which subsequently consumes and unbinds the WD. However, if a detonation is not
triggered and the deflagration is too weak to unbind the star, a completely
different scenario unfolds. We explore the failure of the
Gravitationally-Confined Detonation (GCD) mechanism of SNe Ia, and demonstrate
through 2D and 3D simulations the properties of failed-detonation SNe. We show
that failed-detonation SNe expel a few 0.1 solar masses of burned and
partially-burned material and that a fraction of the material falls back onto
the WD, polluting the remnant WD with intermediate-mass and iron-group
elements, that likely segregate to the core forming an WD whose core is iron
rich. The remaining material is asymmetrically ejected at velocities comparable
to the escape velocity from the WD, and in response, the WD is kicked to
velocities of a few hundred km/s. These kicks may unbind the binary and eject a
runaway/hyper-velocity WD. Although the energy and ejected mass of the
failed-detonation SN are a fraction of typical thermonuclear SNe, they are
likely to appear as sub-luminous low-velocity SNe Ia. Such failed detonations
might therefore explain or are related to the observed branch of peculiar SNe
Ia, such as the family of low-velocity sub-luminous SNe (SN 2002cx/SN
2008ha-like SNe).",1208.5069v2
2012-11-26,Local Structure and Hyperfine Interactions of 57Fe in NaFeAs Studied by Mossbauer Spectroscopy,"Detailed 57Fe Mossbauer spectroscopy measurements on superconducting NaFeAs
powder samples have been performed in the temperature range 13 K < T < 300 K.
The 57Fe spectra recorded in the paramagnetic range (T > TN ~ 46 K) were
discussed supposing that most of the Fe2+ ions are located in distorted (FeAs4)
tetrahedral of NaFeAs phase, while additional minor (< 10%) component of the
spectra corresponds to impurity or intergrowth NaFe2As2 phase with a nominal
composition near ""NaFe2As2"". Our results reveal that the structural transition
(TS ~ 55K) has a weak effect on the electronic structure of iron ions, while at
T < TN the spectra show a continuous distribution of hyperfine fields HFe .
Shape of these spectra was analyzed in term of two models: (i) an
incommensurate spin density wave modulation of iron magnetic structure, (ii) a
formation of a microdomain structure or phase separation. It was shown that the
hyperfine parameters obtained using these two methods have very similar values
over the whole temperature range. The analysis of the temperature dependence
HFe(T) with the Bean-Rodbell model leads to ksi = 1.16 +/- 0.05, suggesting
that the magnetic phase transition is first-order in nature. A sharp evolution
of the VZZ(T) and etha(T) parameters of the full Hamiltonian of hyperfine
interactions near T ~ (TN, TS), were interpreted as a manifestation of the
anisotropic electron redistribution between the dxz, dyz- and dxy-orbitals of
the iron ions.",1211.5967v3
2012-12-02,Tunable interplay between 3d and 4f electrons in Co-doped iron pnictides,"We study the interplay of 3d and 4f electrons in the iron pnictides
CeFe$_{1-x}$Co$_x$AsO and GdFe$_{1-y}$Co$_y$AsO, which correspond to two very
different cases of $4f$-magnetic moment. Both CeFeAsO and GdFeAsO undergo a
spin-density-wave (SDW) transition associated with Fe 3d electrons at high
temperatures, which is rapidly suppressed by Fe/Co substitution.
Superconductivity appears in a narrow doping range: $0.05 < x < 0.2$ for
CeFe$_{1-x}$Co$_x$AsO and $0.05 < y < 0.25$ for GdFe$_{1-y}$Co$_y$AsO, showing
a maximum transition temperature $T_\textup{sc}$ of about 13.5 K for Ce and 19
K for Gd. In both compounds, the $4f$-electrons form an antiferromagnetic (AFM)
order at low temperatures over the entire doping range and Co 3d electrons are
ferromagnetically ordered on the Co-rich side; the Curie temperature reaches
$T_\textup{C}^\textup{Co} \approx$ 75 K at $x = 1$ and $y = 1$. In the
Ce-compounds, the N\'{e}el temperature $T_\textup{N}^\textup{Ce}$ increases
upon suppressing the SDW transition of Fe and then remains nearly unchanged
with further increasing Co concentration up to $x \simeq 0.8$
($T_\textup{N}^\textup{Ce}\approx$ 4 K). Furthermore, evidence of Co-induced
polarization on Ce-moments is observed on the Co-rich side. In the
Gd-compounds, the two magnetic species of Gd and Co are coupled
antiferromagnetically to give rise to ferrimagnetic behavior in the magnetic
susceptibility on the Co-rich side. For $0.7 \leq y < 1.0$, the system
undergoes a possible magnetic reorientation below the N\'{e}el temperature of
Gd ($T_\textup{N}^\textup{Gd}$). Our results suggest that the effects of both
electron hybridizations and magnetic exchange coupling between the 3d-4f
electrons give rise to a rich phase diagram in the rare-earth iron pnictides.",1212.0221v2
2013-01-15,Pulse phase and precession phase resolved spectroscopy of Her X-1: studying a representative Main-On with RXTE,"We performed a detailed pulse phase resolved spectroscopy of the accreting
binary X-ray pulsar Her X-1 in the energy range 3.5-75 keV and have established
pulse phase profiles for all spectral parameters. For the centroid of the
cyclotron line, the photon index and the flux of the 6.4 keV iron line, we have
studied the variation as a function of 35 d phase. We analyzed RXTE
observations of the Main-On of November 2002. Four different time intervals of
about 1 d duration were selected to provide a good coverage of a complete
Main-On. The intervals are centered at 35 d phase 0.03, 0.10, 0.15, and 0.20,
respectively. All spectral parameters show a strong modulation with pulse
phase. While the centroid energy of the cyclotron line follows roughly the
shape of the pulse profile, both the photon index and the iron line intensity
exhibit distinct minima around the peak of the X-ray pulse. With respect to
variations of the observed profiles with 35 d phase, we find that there is a
clear evolution of the shape of the pulse profiles (flux versus pulse phase), a
moderate increase of the maximum cyclotron line energy (found around pulse
phase 0.7), but no significant evolution of the shape of the pulse phase
profiles of the cyclotron line energy, the spectral power law index or the iron
line intensity. The variation of spectral parameters as a function of the pulse
phase provides important information about the system: 1. the disappearance of
the Fe line flux near the highest continuum flux may be an indication of a
hollow cone geometry of the accretion structure; ii. the apparent
non-dependence of the cyclotron line energy profiles on 35 d phase provides a
new possibility to test the model of free precession of the neutron star,
proposed to be responsible for the systematic variations in the pulse profiles.",1301.3378v1
2013-01-24,The wind of the M-type AGB star RT Virginis probed by VLTI/MIDI,"We study the circumstellar environment of the M-type AGB star RT Vir using
mid-infrared high spatial resolution observations from the ESO-VLTI focal
instrument MIDI. The aim of this study is to provide observational constraints
on theoretical prediction that the winds of M-type AGB objects can be driven by
photon scattering on iron-free silicate grains located in the close environment
(about 2 to 3 stellar radii) of the star. We interpreted
spectro-interferometric data, first using wavelength-dependent geometric
models. We then used a self-consistent dynamic model atmosphere containing a
time-dependent description of grain growth for pure forsterite dust particles
to reproduce the photometric, spectrometric, and interferometric measurements
of RT Vir. Since the hydrodynamic computation needs stellar parameters as
input, a considerable effort was first made to determine these parameters. MIDI
differential phases reveal the presence of an asymmetry in the stellar
vicinity. Results from the geometrical modeling give us clues to the presence
of aluminum and silicate dust in the close circumstellar environment (< ~5
stellar radii). Comparison between spectro-interferometric data and a
self-consistent dust-driven wind model reveals that silicate dust has to be
present in the region between 2 to 3 stellar radii to reproduce the 59 and 63 m
baseline visibility measurements around 9.8 micron. This gives additional
observational evidence in favor of winds driven by photon scattering on
iron-free silicate grains located in the close vicinity of an M-type star.
However, other sources of opacity are clearly missing to reproduce the 10-13
micron visibility measurements for all baselines. This study is a first attempt
to understand the wind mechanism of M-type AGB stars by comparing photometric,
spectrometric, and interferometric measurements with state-of-the-art,
self-consistent dust-driven wind models. The agreement of the dynamic model
atmosphere with interferometric measurements in the 8-10 micron spectral region
gives additional observational evidence that the winds of M-type stars can be
driven by photon scattering on iron-free silicate grains. Finally, a larger
statistical study and progress in advanced self-consistent 3D modeling are
still required to solve the remaining problems.",1301.5872v1
2013-03-15,The 69 micron forsterite band in spectra of protoplanetary disks - Results from the Herschel DIGIT programme,"Context: We have analysed Herschel-PACS spectra of 32 circumstellar disks
around Herbig Ae/Be and T-Tauri stars obtained within the Herschel key
programme DIGIT. In this paper we focus on the 69mu emission band of the
crystalline silicate forsterite.
  Aims: This work provides an overview of the 69mu forsterite bands in the
DIGIT sample. We aim to derive the temperature and composition of the
forsterite grains. With this information, constraints can be placed on the
spatial distribution of the forsterite in the disk and its formation history.
  Methods: Position and shape of the 69mu band are used to derive the
temperature and composition of the dust by comparison to laboratory spectra of
that band. We combine our data with existing Spitzer IRS spectra to compare the
presence and strength of the 69mu band to the forsterite bands at shorter
wavelengths.
  Results: A total of 32 sources have been observed, 8 of them show a 69mu
emission band that can be attributed to forsterite. With the exception of the
T-Tauri star AS205, all of the detections are for disks associated with Herbig
Ae/Be stars. Most of the forsterite grains that give rise to the 69mu bands are
warm (~100-200 K) and iron-poor (less than ~2% iron). Only AB-Aur requires
approximately 3-4% of iron.
  Conclusions: Our findings support the hypothesis that the forsterite grains
form through an equilibrium condensation process at high temperatures. The
connection between the strength of the 69 and 33mu bands shows that at least
part of the emission in these bands originates from the same dust grains.
Further, any model that explains the PACS and the Spitzer IRS observations must
take the effects of a wavelength dependent optical depth into account. We find
indications of a correlation of the detection rate of the 69mu band with the
spectral type of the host stars. However, our sample is too small to obtain a
definitive result.",1303.3744v1
2013-04-30,Superconductivity induced by hydrogen anion substitution in 1111-type iron arsenides,"Hydrogen is the simplest bipolar element and its valence state can be
controlled from +1 to -1. We synthesized the 1111-type CaFeAsH and LnFeAsO1-xHx
(Ln = lanthanide) with the ZrCuSiAs type structure by a high-pressure synthesis
method. The position and valence state of the substituted H were determined by
neutron diffraction and density functional theory calculations. The close
similarity in the structural and electrical properties of CaFeAsH and CaFeAsF
indicated the formation of the hydride ion (H-), which is isovalent with the
fluoride ion (F-), in the 1111-type iron arsenides. When some of the O2- ions
in LnFeAsO are replaced by H-, superconductivity is induced by electron doping
to the FeAs-layer to maintain charge neutrality. Since the substitution limit
of hydrogen in LnFeAsO (x~0.5) is much higher than that of fluorine (x~0.2),
the hydrogen substitution technique provides an effective pathway for
high-density electron-doping, making it possible to draw the complete
electronic phase diagram of LnFeAsO. The x-T diagrams of LnFeAsO1-xHx (Ln = La,
Ce, Sm, Gd) have a wide superconducting (SC) region spanning the range x = 0.04
to 0.4, which is far from the parent antiferromagnetic region near x = 0.0. For
Ln=La, another SC dome region was found in the range x = ~ 0.2 to ~0.5 with a
maximum Tc = 36 K, in addition to a conventional SC dome located at x ~0.08
with maximum Tc = 29 K. Density functional theory calculations performed for
LaFeAsO1-xHx indicated that the newly observed Tc is correlated with the
appearance of degeneration of the Fe 3d bands (dxy, dyz and dzx), which is
caused not only by regularization of the tetrahedral shape of FeAs4 due to
chemical pressure effects but also by selective band occupation with doped
electrons. In this article, we review the recent progress of superconductivity
in iron (oxy)arsenides and related compounds induced by hydrogen substitution.",1304.7900v1
2013-05-23,On magnetic inhibition of photospheric macro-turbulence generated in the iron-bump opacity zone of O-stars,"Massive, hot OB-stars show clear evidence of strong macroscopic broadening
(in addition to rotation) in their photospheric spectral lines. This paper
examines the occurrence of such ""macro-turbulence"" in slowly rotating O-stars
with strong, organised surface magnetic fields. Focusing on the CIV 5811A line,
we find evidence for significant macro-turbulent broadening in all stars except
NGC1624-2, which also has (by far) the strongest magnetic field. Instead, the
very sharp CIV lines in NGC1624-2 are dominated by magnetic Zeeman broadening,
from which we estimate a dipolar field of approximately 20 kG. By contrast,
magnetic broadening is negligible in the other stars (due to their weaker field
strengths, on order 1 kG), and their CIV profiles are typically very broad and
similar to corresponding lines observed in non-magnetic O-stars. Quantifying
this by an isotropic, Gaussian macro-turbulence, we derive vmac = 2.2 (+-
0.9/2.2) km/s for NGC1624-2, and vmac = 20-65 km/s for the rest of the magnetic
sample. We use these observational results to test the hypothesis that the
field can stabilise the atmosphere and suppress the generation of
macro-turbulence down to stellar layers where the magnetic pressure PB and the
gas pressure Pg are comparable. Using a simple grey atmosphere to estimate the
temperature T0 at which PB = Pg, we find that T0 > Teff for all investigated
magnetic stars, but that T0 reaches the ~160000 K layers associated with the
iron opacity-bump in hot stars only for NGC1624-2. This is consistent with the
view that the responsible physical mechanism for photospheric O-star
macro-turbulence may be stellar gravity-mode oscillations excited by
sub-surface convection zones, and suggests that a sufficiently strong magnetic
field can suppress such iron-bump generated convection and associated
pulsational excitation.",1305.5549v1
2013-06-14,Dynamic Transcript Profiling of Candida Albicans Infection in Zebrafish: a Pathogen-Host Interaction Study,"Candida albicans is responsible for a number of life-threatening infections
and causes considerable morbidity and mortality in immunocompromised patients.
Previous studies of C. albicans pathogenesis have suggested several steps must
occur before virulent infection, including early adhesion, invasion, and late
tissue damage. However, the mechanism that triggers C. albicans transformation
from yeast to hyphae form during infection has yet to be fully elucidated. This
study used a systems biology approach to investigate C. albicans infection in
zebrafish. The surviving fish were sampled at different post-infection time
points to obtain time-lapsed, genome-wide transcriptomic data from both
organisms, which were accompanied with in sync histological analyses. Principal
component analysis (PCA) was used to analyze the dynamic gene expression
profiles of significant variations in both C. albicans and zebrafish. The
results categorized C. albicans infection into three progressing phases:
adhesion, invasion, and damage. Such findings were highly supported by the
corresponding histological analysis. Furthermore, the dynamic interspecies
transcript profiling revealed that C. albicans activated its filamentous
formation during invasion and the iron scavenging functions during the damage
phases, whereas zebrafish ceased its iron homeostasis function following
massive hemorrhage during the later stages of infection. This was followed by
massive hemorrhaging toward the end stage of infection. Most of the immune
related genes were expressed as the infection progressed from invasion to the
damage phase. Such global, inter-species evidence of virulence-immune and iron
competition dynamics during C. albicans infection could be crucial in
understanding control fungal pathogenesis.",1306.3312v1
2013-10-09,Electron doping evolution of the magnetic excitations in BaFe2-xNixAs2,"We use inelastic neutron scattering (INS) spectroscopy to study the magnetic
excitations spectra throughout the Brioullion zone in electron-doped iron
pnictide superconductors BaFe$_{2-x}$Ni$_{x}$As$_{2}$ with $x=0.096,0.15,0.18$.
While the $x=0.096$ sample is near optimal superconductivity with $T_c=20$ K
and has coexisting static incommensurate magnetic order, the $x=0.15,0.18$
samples are electron-overdoped with reduced $T_c$ of 14 K and 8 K,
respectively, and have no static antiferromagnetic (AF) order. In previous INS
work on undoped ($x=0$) and electron optimally doped ($x=0.1$) samples, the
effect of electron-doping was found to modify spin waves in the parent compound
BaFe$_2$As$_2$ below $\sim$100 meV and induce a neutron spin resonance at the
commensurate AF ordering wave vector that couples with superconductivity. While
the new data collected on the $x=0.096$ sample confirms the overall features of
the earlier work, our careful temperature dependent study of the resonance
reveals that the resonance suddenly changes its $Q$-width below $T_c$ similar
to that of the optimally hole-doped iron pnictides
Ba$_{0.67}$K$_{0.33}$Fe$_2$As$_2$. In addition, we establish the dispersion of
the resonance and find it to change from commensurate to transversely
incommensurate with increasing energy. Upon further electron-doping to
overdoped iron pnictides with $x=0.15$ and 0.18, the resonance becomes weaker
and transversely incommensurate at all energies, while spin excitations above
$\sim$100 meV are still not much affected. Our absolute spin excitation
intensity measurements throughout the Brillouin zone for $x=0.096,0.15,0.18$
confirm the notion that the low-energy spin excitation coupling with itinerant
electron is important for superconductivity in these materials, even though the
high-energy spin excitations are weakly doping dependent.",1310.2333v1
2013-10-11,The return to the hard state of GX 339-4 as seen by Suzaku,"The microquasar GX 339-4 was observed by Suzaku five times, spaced by a few
days, during its transition back to the hard state at the end of its 2010-2011
outburst. The 2-10 keV source flux decreases by a factor ~10 between the
beginning and the end of the monitoring. Simultaneous radio and OIR
observations highlighted the re-ignition of the radio emission just before the
beginning of the campaign, the maximum radio emission being reached between the
two first Suzaku pointings, while the IR peaked a few weeks latter. A
fluorescent iron line is always significantly detected. Fits with a gaussian or
Laor profiles give statistically equivalent results. In the case of a Laor
profile, fits of the five data sets simultaneously agree with a disk
inclination angle of ~20 degrees. The disk inner radius is <10-30 R_g in the
first two observations but almost unconstrained in the last three. A soft X-ray
excess is also present in these two first observations. Fits with a multicolor
disk component give disk inner radii in agreement with those obtained with the
iron line fits. The use of a physically more realistic model, including a
blurred reflection component and a comptonization continuum, give some hints of
the increase of the disk inner radius but the significances are always weak.
Interestingly, the addition of warm absorption significantly improves the fit
of OBS1 while it is not needed in the other observations. The radio-jet
re-ignition occurring between OBS1 and OBS2, these absorption features may
indicate the natural evolution from a disk wind and a jet. The comparison with
a long 2008 Suzaku observation of GX 339-4 in a persistent faint hard state
where a narrow iron line clearly indicates a disk recession, is discussed.",1310.3039v2
2013-10-30,On the Origin of the 6.4 keV Line in the Galactic Center Region,"We analyse the 6.4 keV iron line component produced in the Galactic Center
(GC) region by cosmic rays in dense molecular clouds (MCs) and in the diffuse
molecular gas. We showed that this component, in principle, can be seen in
several years in the direction of the cloud Srg B2. If this emission is
produced by low energy CRs which ionize the interstellar molecular gas the
intensity of the line is quite small, < 1%. However, we cannot exclude that
local sources of CRs or X-ray photons nearby the cloud may provide much higher
intensity of the line from there. Production of the line emission from
molecular clouds depends strongly on processes of CR penetration into them. We
show that turbulent motions of neutral gas may generate strong magnetic
fluctuations in the clouds which prevent free penetration of CRs into the
clouds from outside. We provide a special analysis of the line production by
high energy electrons. We concluded that these electrons hardly provide the
diffuse 6.4 keV line emission from the GC because their density is depleted by
ionization losses. We do not exclude that local sources of electrons may
provide an excesses of the 6.4 keV line emission in some molecular clouds and
even reproduce a relatively short time variations of the iron line emission.
However, we doubt whether a single electron source provides the simultaneous
short time variability of the iron line emission from clouds which are distant
from each other on hundred pc as observed for the GC clouds. An alternative
speculation is that local electron sources could also provide the necessary
effect of the line variations in different clouds that are seen simultaneously
by chance that seems, however, very unlikely.",1310.8177v1
2013-11-04,On the role of AGN feedback on the thermal and chemodynamical properties of the hot intra-cluster medium,"We present an analysis of the properties of the ICM in an extended set of
cosmological hydrodynamical simulations of galaxy clusters and groups performed
with the TreePM+SPH GADGET-3 code. Besides a set of non-radiative simulations,
we carried out two sets of simulations including radiative cooling, star
formation, metal enrichment and feedback from supernovae, one of which also
accounts for the effect of feedback from AGN resulting from gas accretion onto
super-massive black holes. These simulations are analysed with the aim of
studying the relative role played by SN and AGN feedback on the general
properties of the diffuse hot baryons in galaxy clusters and groups: scaling
relations, temperature, entropy and pressure radial profiles, and ICM chemical
enrichment. We find that simulations including AGN feedback produce scaling
relations that are in good agreement with X-ray observations at all mass
scales. However, our simulations are not able to account for the observed
diversity between CC and NCC clusters: unlike for observations, we find that
temperature and entropy profiles of relaxed and unrelaxed clusters are quite
similar and resemble more the observed behaviour of NCC clusters. As for the
pattern of metal enrichment, we find that an enhanced level of iron abundance
is produced by AGN feedback with respect to the case of purely SN feedback. As
a result, while simulations including AGN produce values of iron abundance in
groups in agreement with observations, they over-enrich the ICM in massive
clusters. The efficiency of AGN feedback in displacing enriched gas from halos
into the inter-galactic medium at high redshift also creates a widespread
enrichment in the outskirts of clusters and produces profiles of iron abundance
whose slope is in better agreement with observations.",1311.0818v1
2013-11-07,GIANO-TNG spectroscopy of red supergiants in the young star cluster RSGC2,"The inner disk of the Galaxy has a number of young star clusters dominated by
red supergiants that are heavily obscured by dust extinction and observable
only at infrared wavelengths. These clusters are important tracers of the
recent star formation and chemical enrichment history in the inner Galaxy.
During the technical commissioning and as a first science verification of the
GIANO spectrograph at the Telescopio Nazionale Galileo, we secured
high-resolution (R~50,000) near-infrared spectra of three red supergiants in
the young Scutum cluster RSGC2. Taking advantage of the full YJHK spectral
coverage of GIANO in a single exposure, we were able to identify several tens
of atomic and molecular lines suitable for chemical abundance determinations.
By means of spectral synthesis and line equivalent width measurements, we
obtained abundances of Fe and other iron-peak elements such as V, Cr, Ni, of
alpha (O, Mg, Si, Ca and Ti) and other light elements (C, N, Na, Al, K, Sc),
and of some s-process elements (Y, Sr). We found iron abundances between half
and one third solar and solar-scaled [X/Fe] abundance patterns of iron-peak,
alpha and most of the light elements, consistent with a thin-disk chemistry. We
found a depletion of [C/Fe] and enhancement of [N/Fe], consistent with CN
burning, and low 12C/13C abundance ratios (between 9 and 11), requiring
extra-mixing processes in the stellar interiors during the post-main sequence
evolution. Finally, we found a slight [Sr/Fe] enhancement and a slight [Y/Fe]
depletion (by a factor of <=2), with respect to solar.",1311.1639v1
2013-12-20,Nematic order in iron superconductors - who is in the driver's seat?,"Although the existence of nematic order in iron-based superconductors is now
a well-established experimental fact, its origin remains controversial. Nematic
order breaks the discrete lattice rotational symmetry by making the $x$ and $y$
directions in the Fe plane non-equivalent. This can happen because of (i) a
tetragonal to orthorhombic structural transition, (ii) a spontaneous breaking
of an orbital symmetry, or (iii) a spontaneous development of an Ising-type
spin-nematic order - a magnetic state that breaks rotational symmetry but
preserves time-reversal symmetry. The Landau theory of phase transitions
dictates that the development of one of these orders should immediately induce
the other two, making the origin of nematicity a physics realization of a
""chicken and egg problem"". The three scenarios are, however, quite different
from a microscopic perspective. While in the structural scenario lattice
vibrations (phonons) play the dominant role, in the other two scenarios
electronic correlations are responsible for the nematic order. In this review,
we argue that experimental and theoretical evidence strongly points to the
electronic rather than phononic mechanism, placing the nematic order in the
class of correlation-driven electronic instabilities, like superconductivity
and density-wave transitions. We discuss different microscopic models for
nematicity in the iron pnictides, and link nematicity to other ordered states
of the global phase diagram of these materials -- magnetism and
superconductivity. In the magnetic model nematic order pre-empts stripe-type
magnetic order, and the same interaction which favors nematicity also gives
rise to an unconventional $s^{+-}$ superconductivity. In the charge/orbital
model magnetism appears as a secondary effect of ferro-orbital order, and the
interaction which favors nematicity gives rise to a conventional $s^{++}$
superconductivity.",1312.6085v1
2014-03-24,On the fine structure of the Cepheid metallicity gradient in the Galactic thin disk,"We present homogeneous and accurate iron abundances for 42 Galactic Cepheids
based on high-spectral resolution (R~38,000) high signal-to-noise ratio
(SNR>100) optical spectra collected with UVES at VLT (128 spectra). The above
abundances were complemented with high-quality iron abundances provided either
by our group (86) or available in the literature. We paid attention in deriving
a common metallicity scale and ended up with a sample of 450 Cepheids. We also
estimated for the entire sample accurate individual distances by using
homogeneous near-infrared photometry and the reddening free Period-Wesenheit
relations. The new metallicity gradient is linear over a broad range of
Galactocentric distances (Rg~5-19 kpc) and agrees quite well with similar
estimates available in the literature (-0.060+/-0.002 dex/kpc). We also uncover
evidence which suggests that the residuals of the metallicity gradient are
tightly correlated with candidate Cepheid Groups (CGs). The candidate CGs have
been identified as spatial overdensities of Cepheids located across the thin
disk. They account for a significant fraction of the residual fluctuations, and
in turn for the large intrinsic dispersion of the metallicity gradient. We
performed a detailed comparison with metallicity gradients based on different
tracers: OB stars and open clusters. We found very similar metallicity
gradients for ages younger than 3 Gyrs, while for older ages we found a
shallower slope and an increase in the intrinsic spread. The above findings
rely on homogeneous age, metallicity and distance scales. Finally we found, by
using a large sample of Galactic and Magellanic Cepheids for which are
available accurate iron abundances, that the dependence of the luminosity
amplitude on metallicity is vanishing.",1403.6128v1
2014-07-03,The Detection of Earth-mass Planets around Active Stars: The Mass of Kepler-78b,"Kepler-78b is a transiting Earth-mass planet in an 8.5 hr orbit discovered by
the Kepler Space Mission. We performed an analysis of the published radial
velocity measurements for Kepler-78 in order to derive a refined measurement
for the planet mass. Kepler-78 is an active star and radial velocity variations
due to activity were removed using a Floating Chunk Offset (FCO) method where
an orbital solution was made to the data by allowing the velocity offsets of
individual nights to vary. We show that if we had no a priori knowledge of the
transit period the FCO method used as a periodogram would still have detected
Kepler-78b in the radial velocity data. It can thus be effective at finding
unknown short-period signals in the presence of significant activity noise.
Using the FCO method while keeping the ephemeris and orbital phase fixed to the
photometric values and using only data from nights where 6-10 measurements were
taken results in a K-amplitude of 1.34 +/- 0.25 m/s. a planet mass of 1.31 +/-
0.24 M_Earth, and a planet density of rho = 4.5 (-2.0/+2.2) g/cm^3. Allowing
the orbital phase to be a free parameter reproduces the transit phase to within
the uncertainty. The corresponding density implies that Kepler-78b may have a
structure that is deficient in iron and is thus more like the Moon. Although
the various approaches that were used to filter out the activity of Kepler 78
produce consistent radial velocity amplitudes to within the errors, these are
still too large to constrain the structure of this planet. The uncertainty in
the mass for Kepler-78b is large enough to encompass models with structures
ranging from Mercury-like (iron enriched) to Moon-like (iron deficient). A more
accurate K-amplitude as well as a better determination of the planet radius are
needed to distinguish between these models.",1407.0853v1
2014-08-06,Theory of the evolution of magnetic order in Fe$_{1+y}$Te compounds with increasing interstitial iron,"We examine the influence of the excess of interstitial Fe on the magnetic
properties of Fe$_{1+y}$Te compounds. Because in iron chalcogenides the
correlations are stronger than in the iron arsenides, we assume in our model
that some of the Fe orbitals give rise to localized magnetic moments. These
moments interact with each other via exchange interactions as well as
phonon-mediated biquadratic interactions that favor a collinear double-stripe
state, corresponding to the ordering vectors $\left(\pm\pi/2,\pm\pi/2\right)$.
The remaining Fe orbitals are assumed to be itinerant, giving rise to the
first-principle derived Fermi surface displaying nesting features at momenta
$\left(\pi,0\right)/\left(0,\pi\right)$. Increasing the amount of itinerant
electrons due to excess Fe, $y$, leads to changes in the Fermi surface and to
the suppression of its nesting properties. As a result, due to the Hund's
coupling between the itinerant and localized moments, increasing $y$ leads to
modifications in the local moments' exchange interactions via the multi-orbital
generalization of the long-range Ruderman-Kittel-Kasuya-Yosida (RKKY)
interaction. By numerically computing the RKKY corrections and minimizing the
resulting effective exchange Hamiltonian, we find, in general, that the excess
electrons introduced in the system change the classical magnetic ground state
from a double-stripe state to an incommensurate spiral, consistent with the
experimental observations. We show that these results can be understood as a
result of the suppression of magnetic spectral weight of the itinerant
electrons at momenta $\left(\pi,0\right)/\left(0,\pi\right)$, combined with the
transfer of broad magnetic spectral weight from large to small momenta,
promoted by the introduction of excess Fe.",1408.1418v2
2014-11-28,Superconducting properties and pseudogap from preformed Cooper pairs in the triclinic (CaFe$_{1-x}$Pt$_x$As)$_{10}$Pt$_3$As$_8$,"Using a combination of muon-spin relaxation ($\mu$SR), inelastic neutron
scattering (INS) and nuclear magnetic resonance (NMR), we investigated the
novel iron-based superconductor with a triclinic crystal structure
(CaFe$_{1-x}$Pt$_x$As)$_{10}$Pt$_3$As$_8$ (T$_{\rm c}$ = 13 K), containing
platinum-arsenide intermediary layers. The temperature dependence of the
superfluid density obtained from the $\mu$SR relaxation-rate measurements
indicates the presence of two superconducting gaps,
$\Delta_\text{1}\gg\Delta_\text{2}$. According to our INS measurements,
commensurate spin fluctuations are centered at the ($\pi$, 0) wave vector, like
in most other iron arsenides. Their intensity remains unchanged across
T$_\text{c}$, indicating the absence of a spin resonance typical for many
Fe-based superconductors. Instead, we observed a peak in the spin-excitation
spectrum around $\hslash\omega_0=\,$7 meV at the same wave vector, which
persists above T$_{\rm c}$ and is characterized by the ratio
$\hslash\omega_0/k_\text{B}T_\text{c}\approx\,$6.2, which is significantly
higher than typical values for the magnetic resonant modes in iron pnictides
(~4.3). The temperature dependence of magnetic intensity at 7 meV revealed an
anomaly around T* = 45 K related to the disappearance of this new mode. A
suppression of the spin-lattice relaxation rate, $1/T_1T$, observed by NMR
immediately below T* without any notable subsequent anomaly at T$_{\rm c}$,
indicates that T* could mark the onset of a pseudogap in
(CaFe$_{1-x}$Pt$_x$As)$_{10}$Pt$_3$As$_8$, which is likely associated with the
emergence of preformed Cooper pairs.",1411.7858v1
2014-12-30,An XSPEC model to explore spectral features from black-hole sources - II. The relativistic iron line in the lamp-post geometry,"In X-ray spectra of several active galactic nuclei and Galactic black hole
binaries a broad relativistically smeared iron line is observed. This feature
arises by fluorescence when the accretion disc is illuminated by hot corona
above it. Due to central location of the corona the illumination and thus also
the line emission decrease with radius. It was reported in the literature that
this decrease is very steep in some of the sources, suggesting a highly compact
corona.
  We revisit the lamp-post setup in which the corona is positioned on the axis
above the rotating black hole and investigate to what extent the steep
emissivity can be explained by this scenario. We show the contributions of the
relativistic effects to the disc illumination by the primary source - energy
shift, light bending and aberration. The lamp-post radial illumination pattern
is compared to the widely used radial broken power-law emissivity profile. We
find that very steep emissivities require the primary illuminating source to be
positioned very near the black hole horizon and/or the spectral power-law index
of the primary emission to be very high. The broken power-law approximation of
the illumination can be safely used when the primary source is located at
larger heights. However, for low heights the lamp-post illumination
considerably differs from this approximation.
  We also show the variations of the iron line local flux over the disc due to
the flux dependence on incident and emission angles. The former depends mainly
on the height of the primary source while the latter depends on the inclination
angle of the observer. Thus the strength of the line varies substantially
across the disc. This effect may contribute to the observed steeper emissivity.",1412.8627v1
2015-03-14,"Deep SDSS optical spectroscopy of distant halo stars II. Iron, calcium, and magnesium abundances","We analyze a sample of 3,944 low-resolution (R ~ 2000) optical spectra from
the Sloan Digital Sky Survey (SDSS), focusing on stars with effective
temperatures 5800 < Teff < 6300 K, and distances from the Milky Way plane in
excess of 5 kpc, and determine their abundances of Fe, Ca, and Mg. We followed
the same methodology as in the previous paper in this series, deriving
atmospheric parameters by chi2 minimization, but this time we obtained the
abundances of individual elements by fitting their associated spectral lines.
Distances were calculated from absolute magnitudes obtained by a statistical
comparison of our stellar parameters with stellar-evolution models. The
observations reveal a decrease in the abundances of iron, calcium, and
magnesium at large distances from the Galactic center. The median abundances
for the halo stars analyzed are fairly constant up to a Galactocentric distance
r ~ 20 kpc, rapidly decrease between r ~ 20 and r ~ 40 kpc, and flatten out to
significantly lower values at larger distances, consistent with previous
studies. In addition, we examine the [Ca/Fe] and [Mg/Fe] as a function of Fe/H
and Galactocentric distance. Our results show that the most distant parts of
the halo show a steeper variation of the [Ca/Fe] and [Mg/Fe] with iron. We
found that at the range -1.6 < [Fe/H] < -0.4 [Ca/Fe] decreases with distance,
in agreement with earlier results based on local stars. However, the opposite
trend is apparent for [Mg/Fe]. Our conclusion that the outer regions of the
halo are more metal-poor than the inner regions, based on in situ observations
of distant stars, agrees with recent results based on inferences from the
kinematics of more local stars, and with predictions of recent galaxy formation
simulations for galaxies similar to the Milky Way.",1503.04362v1
2015-05-29,NuSTAR and Suzaku observations of the hard state in Cygnus X-1: locating the inner accretion disk,"We present simultaneous Nuclear Spectroscopic Telescope Array (NuSTAR ) and
Suzaku observations of the X-ray binary Cygnus X-1 in the hard state. This is
the first time this state has been observed in Cyg X-1 with NuSTAR, which
enables us to study the reflection and broad-band spectra in unprecedented
detail. We confirm that the iron line cannot be fit with a combination of
narrow lines and absorption features, and instead requires a relativistically
blurred profile in combination with a narrow line and absorption from the
companion wind. We use the reflection models of Garcia et al. (2014) to
simultaneously measure the black hole spin, disk inner radius, and coronal
height in a self-consistent manner. Detailed fits to the iron line profile
indicate a high level of relativistic blurring, indicative of reflection from
the inner accretion disk. We find a high spin, a small inner disk radius, and a
low source height, and rule out truncation to greater than three gravitational
radii at the 3{\sigma} confidence level. In addition, we find that the line
profile has not changed greatly in the switch from soft to hard states, and
that the differences are consistent with changes in the underlying reflection
spectrum rather than the relativistic blurring. We find that the blurring
parameters are consistent when fitting either just the iron line or the entire
broad-band spectrum, which is well modelled with a Comptonized continuum plus
reflection model.",1506.00007v1
2015-06-03,The complex accretion geometry of GX 339-4 as seen by NuSTAR and Swift,"We present spectral analysis of five NuSTAR and Swift observations of GX
339-4 taken during a failed outburst in summer 2013. These observations cover
Eddington luminosity fractions in the range ~0.9-6%. Throughout this outburst,
GX 339-4 stayed in the hard state, and all five observations show similar X-ray
spectra with a hard power-law with a photon index near 1.6 and significant
contribution from reflection. Using simple reflection models we find
unrealistically high iron abundances. Allowing for different photon indices for
the continuum incident on the reflector relative to the underlying observed
continuum results in a statistically better fit and reduced iron abundances.
With a photon index around 1.3, the input power-law on the reflector is
significantly harder than that which is directly observed. We study the
influence of different emissivity profiles and geometries and consistently find
an improvement when using separate photon indices. The inferred inner accretion
disk radius is strongly model dependent, but we do not find evidence for a
truncation radius larger than 100 r_g in any model. The data do not allow
independent spin constraints but the results are consistent with the literature
(i.e., a>0). Our best-fit models indicate an inclination angle in the range
40-60 degrees, consistent with limits on the orbital inclination but higher
than reported in the literature using standard reflection models. The iron line
around 6.4 keV is clearly broadened, and we detect a superimposed narrow core
as well. This core originates from a fluorescence region outside the influence
of the strong gravity of the black hole and we discuss possible geometries.",1506.01381v1
2015-06-05,NuSTAR and Swift observations of the black hole candidate XTE J1908+094 during its 2013 outburst,"The black hole candidate XTE J1908+094 went into outburst for the first time
since 2003 in October 2013. We report on an observation with the Nuclear
Spectroscopic Telescope Array (NuSTAR) and monitoring observations with Swift
during the outburst. NuSTAR caught the source in the soft state: the spectra
show a broad relativistic iron line, and the light curves reveal a ~40 ks flare
with the count rate peaking about 40% above the non-flare level and with
significant spectral variation. A model combining a multi-temperature thermal
component, a power-law, and a reflection component with an iron line provides a
good description of the NuSTAR spectrum. Although relativistic broadening of
the iron line is observed, it is not possible to constrain the black hole spin
with these data. The variability of the power-law component, which can also be
modeled as a Comptonization component, is responsible for the flux and spectral
change during the flare, suggesting that changes in the corona (or possibly
continued jet activity) are the likely cause of the flare.",1506.02001v2
2015-07-28,Probing M subdwarf metallicity with an esdK5+esdM5.5 binary,"We present a spectral analysis of the binary G 224-58 AB that consists of the
coolest M extreme subdwarf (esdM5.5) and a brighter primary (esdK5). This
binary may serve as a benchmark for metallicity measurement calibrations and as
a test-bed for atmospheric and evolutionary models for esdM objects.
  We determine abundances primarily using high resolution optical spectra of
the primary. Other parameters were determined from the fits of synthetic
spectra computed with these abundances to the observed spectra from 0.4 to 2.5
microns for both components.
  We determine \Tef =4625 $\pm$ 100 K, \logg = 4.5 $\pm$ 0.5 for the A
component and \Tef = 3200 $\pm$ 100 K, \logg = 5.0 $\pm$ 0.5, for the B
component. We obtained abundances of [Mg/H]=$-$1.51$\pm$0.08,
[Ca/H]=$-$1.39$\pm$0.03, [Ti/H]=$-$1.37$\pm$0.03 for alpha group elements and
[CrH]=$-$1.88$\pm$0.07, [Mn/H]=$-$1.96$\pm$0.06, [Fe/H]=$-$1.92$\pm$0.02,
[Ni/H]=$-$1.81$\pm$0.05 and [Ba/H]W=$-$1.87$\pm$0.11 for iron group elements
from fits to the spectral lines observed in the optical and infrared spectral
regions of the primary. We find consistent abundances with fits to the
secondary albeit at lower signal-to-noise.
  Abundances of elements in \ga and \gb atmospheres cannot be described by one
metallicity parameter. The offset of $\sim$ 0.4 dex between the abundances
derived from alpha element and iron group elements corresponds with our
expectation for metal-deficient stars. We thus clarify that some indices used
to date to measure metallicities for establishing esdM stars based on CaH, MgH
and TiO band system strength ratios in the optical and H$_2$O in the infrared
relate to abundances of alpha-element group rather than to iron peak elements.
For metal deficient M dwarfs with [Fe/H] < -1.0, this provides a ready
explanation for apparently inconsistent ""metallicities"" derived using different
methods.",1507.07740v1
2015-10-16,The Transient Accereting X-Ray Pulsar XTE J1946+274: Stability of the X-Ray Properties at Low Flux and Updated Orbital Solution,"We present a timing and spectral analysis of the X-ray pulsar XTE J1946+274
observed with Suzaku during an outburst decline in 2010 October and compare
with previous results. XTE J1946+274 is a transient X-ray binary consisting of
a Be-type star and a neutron star with a 15.75 s pulse period in a 172 d orbit
with 2-3 outbursts per orbit during phases of activity. We improve the orbital
solution using data from multiple instruments. The X-ray spectrum can be
described by an absorbed Fermi-Dirac cutoff power law model along with a narrow
Fe K line at 6.4 keV and a weak Cyclotron Resonance Scattering Feature (CRSF)
at ~35 keV. The Suzaku data are consistent with the previously observed
continuum flux versus iron line flux correlation expected from fluorescence
emission along the line of sight. However, the observed iron line flux is
slightly higher, indicating the possibility of a higher iron abundance or the
presence of non-uniform material. We argue that the source most likely has only
been observed in the subcritical (non-radiation dominated) state since its
pulse profile is stable over all observed luminosities and the energy of the
CRSF is approximately the same at the highest (~$5 \times 10^{37} $erg
s$^{-1}$) and lowest (~$5 \times 10^{36} $erg s$^{-1}$) observed 3-60 keV
luminosities.",1510.05032v1
2015-11-02,Electron correlation effects and scattering rates in Fe$_{1+y}$Te$_{1-x}$Se$_x$ superconductor,"Using angle-resolved photoemission spectroscopy we have studied the
low-energy electronic structure and the Fermi surface topology of
Fe$_{1+y}$Te$_{1-x}$Se$_x$ superconductors. Similar to the known iron pnictides
we observe hole pockets at the center and electron pockets at the corner of the
Brillouin zone (BZ). However, on a finer level, the electronic structure around
the $\Gamma$- and $Z$-points in $k$-space is substantially different from other
iron pnictides, in that we observe two hole pockets at the $\Gamma$-point, and
more interestingly only one hole pocket is seen at the $Z$-point, whereas in
$1111$-, $111$-, and $122$-type compounds, three hole pockets could be readily
found at the zone center. Another major difference noted in the
Fe$_{1+y}$Te$_{1-x}$Se$_x$ superconductors is that the top of innermost
hole-like band moves away from the Fermi level to higher binding energy on
going from $\Gamma$ to $Z$, quite opposite to the iron pnictides. The
polarization dependence of the observed features was used to aid the
attribution of the orbital character of the observed bands. Photon energy
dependent measurements suggest a weak $k_z$ dispersion for the outer hole
pocket and a moderate $k_z$ dispersion for the inner hole pocket. By evaluating
the momentum and energy dependent spectral widths, the single-particle
self-energy was extracted and interestingly this shows a pronounced non-Fermi
liquid behaviour for these compounds. The experimental observations are
discussed in context of electronic band structure calculations and models for
the self-energy such as the spin-fermion model and the marginal-Fermi liquid.",1511.00424v1
2015-12-03,Strong anisotropy in nearly ideal-tetrahedral superconducting FeS single crystals,"We report the novel preparation of single crystals of tetragonal iron
sulfide, FeS, which exhibits a nearly ideal tetrahedral geometry with S--Fe--S
bond angles of 110.2(2) $^\circ$ and 108.1(2) $^\circ$. Grown via hydrothermal
de-intercalation of K${_x}$Fe${_{2-y}}$S${_2}$ crystals under basic and
reducing conditions, the silver, plate-like crystals of FeS remain stable up to
200 $^\circ$C under air and 250 $^\circ$C under inert conditions, even though
the mineral ""mackinawite"" (FeS) is known to be metastable. FeS single crystals
exhibit a superconducting state below $T_c=4$ K as determined by electrical
resistivity, magnetic susceptibility, and heat capacity measurements,
confirming the presence of a bulk superconducting state. Normal state
measurements yield an electronic specific heat of 5~mJ/mol-K$^2$, and
paramagnetic, metallic behavior with a low residual resistivity of
250~$\mu\Omega\cdot$cm. Magnetoresistance measurements performed as a function
of magnetic field angle tilted toward both transverse and longitudinal
orientations with respect to the applied current reveal remarkable
two-dimensional behavior. This is paralleled in the superconducting state,
which exhibits the largest known upper critical field $H_{c2}$ anisotropy of
all iron-based superconductors, with $H_{c2}^{||ab}(0) /
H_{c2}^{||c}(0)=$(2.75~T)/(0.275~T)=10. Comparisons to theoretical models for
2D and anisotropic-3D superconductors, however, suggest that FeS is the latter
case with a large effective mass anisotropy. We place FeS in context to other
closely related iron-based superconductors and discuss the role of structural
parameters such as anion height on superconductivity.",1512.01245v3
2016-01-26,Low-energy Population III supernovae and the origin of extremely metal-poor stars,"Some ancient, dim, metal-poor stars may have formed in the ashes of the first
supernovae (SNe). If their chemical abundances can be reconciled with the
elemental yields of specific Population III (Pop III) explosions, they could
reveal the properties of primordial stars. But multidimensional simulations of
such explosions are required to predict their yields because dynamical
instabilities can dredge material up from deep in the ejecta that would
otherwise be predicted to fall back on to the central remnant and be lost in
one-dimensional (1D) models. We have performed two-dimensional (2D) numerical
simulations of two low-energy Pop III SNe, a 12.4 Msun explosion and a 60 Msun
explosion, and find that they produce elemental yields that are a good fit to
those measured in the most iron-poor star discovered to date, SMSS
J031300.36-670839.3 (J031300). Fallback on to the compact remnant in these weak
explosions accounts for the lack of measurable iron in J031300 and its low
iron-group abundances in general. Our 2D explosions produce higher abundances
of heavy elements (atomic number Z > 20) than their 1D counterparts due to
dredge-up by fluid instabilities. Since almost no Ni is ejected by these weak
SNe, their low luminosities will prevent their detection in the near-infrared
with the James Webb Space Telescope and future 30-m telescopes on the ground.
The only evidence that they ever occurred will be in the fossil abundance
record.",1601.06896v3
2016-02-29,"Andreev spectroscopy of iron-based superconductors: temperature dependence of the order parameters and scaling of the $Δ_{L,S}$ with $T_C$","We studied iron-based superconductors of various families with critical
temperatures covering almost all range $T_C = 9 - 53$ K. In natural arrays of
contacts formed in these materials we observed intrinsic multiple Andreev
reflections effect (IMARE). By using IMARE spectroscopy, we detected the
two-gap superconductivity, determined the value of the large and the small
superconducting gaps, and the corresponding BCS-ratios. The temperature
dependencies of the large and the small gaps $\Delta_{L,S}(T)$ are similar for
various families of the Fe-based superconductors and could be well-fitted in
the framework of the two-band model by Moskalenko and Suhl. We concluded on the
extended s-wave symmetry of the $\Delta_L$ order parameter (20-30 % anisotropy
in k-space) and on the absence of nodes for $\Delta_S$. The BCS-ratio
$2\Delta_L/k_BT_C \approx 5.2$ is nearly constant within the whole range of
$T_C$ (this means that coupling rate is unchanged), reflecting the 20 %
reduction of the $T_C^{local}$ in relation to the eigen $T_C^L$, and the large
gap roughly corresponds to the energy of magnetic resonance $2\Delta_L \approx
E_{res}$. This result requires a special theoretical consideration. Our
estimation of the relative coupling constants and eigen parameters of each
condensate (in a hypothetical case of a zero interband interaction)
$2\Delta_L/k_BT_C^L = 4.2 - 4.8$ and $2\Delta_S/k_BT_C^S = 3.5 - 4.5$ leads to
indirect conclusion that namely a strong electron-phonon interaction in each
condensate described in the framework of the Eliashberg theory plays the key
role in the superconductivity of iron-based oxypnictides. With it, the two
condensates interact weakly with each other. The observed scaling of
$\Delta_{L,S}$ with $T_C$, as was discussed above, is caused mainly by changing
of the density of states $N_{L,S}$ in the bands, whereas Ln-O spacers act as
charge reservoirs.",1602.09114v2
2016-03-01,X-ray-binary spectra in the lamp post model,"[Abridged] Context. The high-energy radiation from black-hole binaries may be
due to the reprocessing of a lamp located on the black hole axis, emitting
X-rays. The observed spectrum is made of 3 components: the direct spectrum; the
thermal bump; and the reflected spectrum made of the Compton hump and the
iron-line complex.
  Aims. We aim at computing accurately the complete reprocessed spectrum
(thermal bump + reflected) of black-hole binaries over the entire X-ray band.
We also determine the strength of the direct component. Our choice of
parameters is adapted to a source showing an important thermal component.
  Methods. We compute in full GR the illumination of a thin disk by a lamp
along the rotation axis. We use the ATM21 radiative transfer code to compute
the spectrum emitted along the disk. We ray trace this local spectrum to
determine the reprocessed spectrum as observed at infinity. We discuss the
dependence of the local and ray-traced spectra on the emission angle and spin.
  Results. We show the importance of the angle dependence of the total disk
specific intensity spectrum emitted by the illuminated atmosphere when the
thermal disk emission if fully taken into account. High spin implies high
temperature in the inner regions, so the emitted thermal disk spectrum covers
the iron-line complex. As a result we locally observe absorption lines produced
in the hot disk atmosphere. Absorption lines are narrow and disappear after ray
tracing the local spectrum.
  Conclusions. Our results mainly highlight the importance of considering the
angle dependence of the local spectrum when computing reprocessed spectra, as
was already found in a recent study. The main new result of our work is to show
the importance of computing the thermal bump of the spectrum, as this feature
can change considerably the observed iron-line complex.",1603.00185v2
2016-09-15,Self-consistent mapping: Effect of local environment on formation of magnetic moment in alpha-FeSi2,"We suggest here the method of the mapping of DFT calculations on the
multiorbital model in a following way: the parameters of the formulated
multiorbital model should be determined from the requirement that the
self-consistent charge and spin densities found from the ab initio and model
calculations have to be as close to each other as possible. The analysis of the
model allows for detailed understanding of the role played by different
parameters of the model in the physics of interest. As an example of the
approach we present the study of the effect of silicon atoms substitution by
the iron atoms and vice versa on the magnetic properties in the iron silicide
alpha-FeSi2. The DFT+GGA calculations are mapped to the model with intraatomic
Coulomb and exchange interactions, hoppings to nearest and next nearest atoms
and exchange of the delocalized electrons between iron atoms; the magnetic
moments on atoms and charge densities of the material are found
self-consistently within the Hartree-Fock approximation. We find that while the
stoichiometric alpha-FeSi2 is nonmagnetic, the substitutions generate different
magnetic structures. For example, the substitution of three Si atoms by the Fe
atoms results in the ferrimagnetic structure whereas the substitution of four
Si atoms by Fe atoms gives rise to either the nonmagnetic or the ferromagnetic
state depending on the type of local enviroment of the substitutional Fe atoms.
Besides, contrary to the commonly accepted statement that the destruction of
the magnetic moment is controlled only by the number of Fe-Si nearest
neighbors, we find that actually it is controlled by the Fe-Fe
next-nearest-neighbors. This finding led us to the counterintuitive conclusion:
an increase of Si concentration in Fe1-xSi2+x ordered alloys may lead to a
ferromagnetism. This conclusion is confirmed by the calculation within
GGA-to-DFT.",1609.04624v1
2016-09-26,Phase Transition of Iron-based Single Crystals at Extreme Strain Rates under Dynamic Loadings,"Phase transition of iron, as a prototype of martensite phase transition under
dynamic loadings, exhibits huge diverges in its TP among experiments with
different pressure medium and loading rates, even in the same initial samples.
Great achievements are made in understanding strain or stress dependence of the
TP under dynamic loadings. However, present understandings on the strain rate
dependence of the TP are far from clear, even a virgin for extreme high strain
rates. In this work, large scale NEMD simulations are conducted to study the
effects of strain rates on the phase transition of iron-based single crystals.
Our results show that the phase transition is preceded by lattice instabilities
under ramp compressions, but present theory, represented by modified Born
criteria, cannot correctly predict observed onsets of the instability. Through
considering both strain and strain gradient disturbances, new instability
criteria are proposed, which could be generally applied for studying
instabilities under either static or dynamic loadings. For the ramp with a
strain rate smaller than about 1010s-1, the observed onset of instabilities is
indeed equal to the one predicted by the new instability criteria under small
gradient disturbances. The observed onsets deviates from the predicted one at
lager strain rates because of finite strain gradient effect. Interestingly, the
strain rate dependence of the TP also exhibits an obvious change at the same
strain rate, i.e., 1010 s-1. When 1010 s-1, a certain power law is obeyed, but
it is not applicable at larger strain rates. This strain rate effect on the TP
is well interpreted with nucleation time and the finite strain gradient effect.
According to these basic understandings, the roles of strain rates on
nucleation and growth of the phase transition are studied.",1609.07829v2
2017-01-24,Nucleosynthesis in the Innermost Ejecta of Neutrino-Drive Supernova Explosions in Two Dimensions,"We examine the nucleosynthesis in the innermost, neutrino-processed ejecta (a
few $10^{-3}\,M_\odot$) of self-consistent, two-dimensional explosion models of
core-collapse supernovae for six progenitor stars with different initial
masses. Three models have initial masses near the low-mass end of the supernova
range, $8.8\,M_\odot$ (e8.8; electron-capture supernova), $9.6\,M_\odot$
(z9.6), and $8.1\,M_\odot$ (u8.1), with initial metallicities of 1, 0, and
$10^{-4}$ times the solar metallicity, respectively. The other three are
solar-metallicity models with initial masses of $11.2\,M_\odot$ (s11),
$15\,M_\odot$ (s15), and $27\,M_\odot$ (s27). The low-mass models e8.8, z9.6,
and u8.1 exhibit high production factors (nucleosynthetic abundances relative
to the solar ones) of 100--200 for light trans-iron elements from Zn to Zr.
This is associated with appreciable ejection of neutron-rich matter in these
models. Remarkably, the nucleosynthetic outcomes for progenitors e8.8 and z9.6
are almost identical, including interesting productions of $^{48}$Ca and
$^{60}$Fe, irrespective of their quite different (O-Ne-Mg and Fe) cores prior
to collapse. In the more massive models s11, s15, and s27, several proton-rich
isotopes of light trans-iron elements, including the $p$-isotope $^{92}$Mo (for
s27) are made, up to production factors of $\sim$30. Both electron-capture and
core-collapse supernovae near the low-mass end can therefore be dominant
contributors to the Galactic inventory of light trans-iron elements from Zn to
Zr and probably $^{48}$Ca and live $^{60}$Fe. The innermost ejecta of more
massive supernovae may have only sub-dominant contributions to the chemical
enrichment of the Galaxy except for $^{92}$Mo.",1701.06786v2
2017-04-04,"Competing spin density wave, collinear, and helical magnetism in Fe1+xTe","The Fe1+xTe phase diagram consists of two distinct magnetic structures with
collinear order present at low interstitial iron concentrations and a helical
phase at large values of x with these phases separated by a Lifshitz point. We
use unpolarized single crystal diffraction to confirm the helical phase for
large interstitial iron concentrations and polarized single crystal diffraction
to demonstrate the collinear order for the iron deficient side of the Fe1+xTe
phase diagram. Polarized neutron inelastic scattering show that the
fluctuations associated with this collinear order are predominately transverse
at low energy transfers, consistent with a localized magnetic moment picture.
We then apply neutron inelastic scattering and polarization analysis to
investigate the dynamics and structure near the boundary between collinear and
helical order in the Fe1+xTe phase diagram. We first show that the phase
separating collinear and helical order is characterized by a spin-density wave
with a single propagation wave vector of (~ 0.45, 0, 0.5). We do not observe
harmonics or the presence of a charge density wave. The magnetic fluctuations
associated with this wavevector are different from the collinear phase being
strongly longitudinal in nature and correlated anisotropically in the (H,K)
plane. The excitations preserve the C4 symmetry of the lattice, but display
different widths in momentum along the two tetragonal directions at low energy
transfers. While the low energy excitations and minimal magnetic phase diagram
can be understood in terms of localized interactions, we suggest that the
presence of density wave phase implies the importance of electronic and orbital
properties.",1704.01111v1
2017-05-07,The peculiar Na-O anticorrelation of the bulge globular cluster NGC 6440,"Context. Galactic Globular Clusters (GCs) are essential tools to understand
the earliest epoch of the Milky Way, since they are among the oldest objects in
the Universe and can be used to trace its formation and evolution. Current
studies using high resolution spectroscopy for many stars in each of a large
sample of GCs allow us to develop a detailed observational picture about their
formation and their relation with the Galaxy. However, it is necessary to
complete this picture by including GCs that belong to all major Galactic
components, including the Bulge. Aims. Our aim is to perform a detailed
chemical analyses of the bulge GC NGC 6440 in order to determine if this object
has Multiple Populations (MPs) and investigate its relation with the Bulge of
the Milky Way and with the other Galactic GCs, especially those associated with
the Bulge, which are largely poorly studied. Methods. We determined the stellar
parameters and the chemical abundances of light elements (Na, Al), iron-peak
elements (Fe, Sc, Mn, Co, Ni), $\alpha$-elements (O, Mg, Si, Ca, Ti) and heavy
elements (Ba, Eu) in seven red giant members of NGC 6440 using high resolution
spectroscopy from FLAMES@UVES. Results. We found a mean iron content of
[Fe/H]=-0.50$\pm$0.03 dex in agreement with other studies. We found no internal
iron spread. On the other hand, Na and Al show a significant intrinsic spread,
but the cluster has no significant O-Na anticorrelation nor exhibits a Mg-Al
anticorrelation. The $\alpha$-elements show good agreement with the Bulge field
star trend, although they are at the high alpha end and are also higher than
those of other GCs of comparable metallicity. The heavy elements are dominated
by the r-process, indicating a strong contribution by SNeII. The chemical
analysis suggests an origin similar to that of the Bulge field stars.",1705.02684v1
2017-05-10,Direct Measurement of Nuclear Dependence of Charged Current Quasielastic-like Neutrino Interactions using MINERvA,"Charged-current $\nu_{\mu}$ interactions on carbon, iron, and lead with a
final state hadronic system of one or more protons with zero mesons are used to
investigate the influence of the nuclear environment on quasielastic-like
interactions. The transfered four-momentum squared to the target nucleus,
$Q^2$, is reconstructed based on the kinematics of the leading proton, and
differential cross sections versus $Q^2$ and the cross-section ratios of iron,
lead and carbon to scintillator are measured for the first time in a single
experiment. The measurements show a dependence on atomic number. While the
quasielastic-like scattering on carbon is compatible with predictions, the
trends exhibited by scattering on iron and lead favor a prediction with
intranuclear rescattering of hadrons accounted for by a conventional particle
cascade treatment. These measurements help discriminate between different
models of both initial state nucleons and final state interactions used in the
neutrino oscillation experiments.",1705.03791v1
2017-05-30,Chemical Complexity in the Eu-enhanced Monometallic Globular Cluster NGC 5986,"NGC 5986 is a poorly studied but relatively massive Galactic globular cluster
that shares several physical and morphological characteristics with
""iron-complex"" clusters known to exhibit significant metallicity and heavy
element dispersions. In order to determine if NGC 5986 joins the iron-complex
cluster class, we investigated the chemical composition of 25 red giant branch
and asymptotic giant branch cluster stars using high resolution spectra
obtained with the Magellan-M2FS instrument. Cluster membership was verified
using a combination of radial velocity and [Fe/H] measurements, and we found
the cluster to have a mean heliocentric radial velocity of +99.76 km s^-1
(sigma = 7.44 km s^-1). We derived a mean metallicity of [Fe/H] = -1.54 dex
(sigma = 0.08 dex), but the cluster's small dispersion in [Fe/H] and low
[La/Eu] abundance preclude it from being an iron-complex cluster. NGC 5986 has
<[Eu/Fe]> = +0.76 dex (sigma = 0.08 dex), which is among the highest ratios
detected in a Galactic cluster. NGC 5986 exhibits classical globular cluster
characteristics, such as uniformly enhanced [alpha/Fe] ratios, a small
dispersion in Fe-peak abundances, and (anti-)correlated light element
variations. Similar to NGC 2808, we find evidence that NGC 5986 may host at
least 4-5 populations with distinct light element compositions, and the
presence of a clear Mg-Al anti-correlation along with an Al-Si correlation
suggests that the cluster gas experienced processing at temperatures >65-70 MK.
However, the current data do not support burning temperatures exceeding ~100
MK. We find some evidence that the first and second generation stars in NGC
5986 may be fully spatially mixed, which could indicate that the cluster has
lost a significant fraction of its original mass. [abridged]",1705.10840v1
2017-07-11,First results from the IllustrisTNG simulations: A tale of two elements -- chemical evolution of magnesium and europium,"The distribution of elements in galaxies provides a wealth of information
about their production sites and their subsequent mixing into the interstellar
medium. Here we investigate the distribution of elements within stars in the
IllustrisTNG simulations. In particular, we analyze the abundance ratios of
magnesium and europium in Milky Way-like galaxies from the TNG100 simulation
(stellar masses ${\log} (M_\star / {\rm M}_\odot) \sim 9.7 - 11.2$). As
abundances of magnesium and europium for individual stars in the Milky Way are
observed across a variety of spatial locations and metallicities, comparison
with the stellar abundances in our more than $850$ Milky Way-like galaxies
provides stringent constraints on our chemical evolutionary methods. To this
end we use the magnesium to iron ratio as a proxy for the effects of our SNII
and SNIa metal return prescription, and a means to compare our simulated
abundances to a wide variety of galactic observations. The europium to iron
ratio tracks the rare ejecta from neutron star -- neutron star mergers, the
assumed primary site of europium production in our models, which in turn is a
sensitive probe of the effects of metal diffusion within the gas in our
simulations. We find that europium abundances in Milky Way-like galaxies show
no correlation with assembly history, present day galactic properties, and
average galactic stellar population age. In general, we reproduce the europium
to iron spread at low metallicities observed in the Milky Way, with the level
of enhancement being sensitive to gas properties during redshifts $z \approx
2-4$. We show that while the overall normalization of [Eu/Fe] is susceptible to
resolution and post-processing assumptions, the relatively large spread of
[Eu/Fe] at low [Fe/H] when compared to that at high [Fe/H] is very robust.",1707.03401v2
2017-08-20,"Large anomalous Nernst and spin Nernst effects in noncollinear antiferromagnets Mn$_3X$ ($X$ = Sn, Ge, Ga)","Noncollinear antiferromagnets have recently been attracting considerable
interest partly due to recent surprising discoveries of the anomalous Hall
effect (AHE) in them and partly because they have promising applications in
antiferromagnetic spintronics. Here we study the anomalous Nernst effect (ANE),
a phenomenon having the same origin as the AHE, and also the spin Nernst effect
(SNE) as well as AHE and the spin Hall effect (SHE) in noncollinear
antiferromagnetic Mn$_3X$ ($X$ = Sn, Ge, Ga) within the Berry phase formalism
based on {\it ab initio} relativistic band structure calculations. For
comparison, we also calculate the anomalous Nernst conductivity (ANC) and
anomalous Hall conductivity (AHC) of ferromagnetic iron as well as the spin
Nernst conductivity (SNC) of platinum metal. Remarkably, the calculated ANC at
room temperature (300 K) for all three alloys is huge, being up to 5 times
larger than that of iron. Moreover, the calculated SNC for Mn$_3$Sn and
Mn$_3$Ga is also large, being as large as that of platinum. This suggests that
these anitferromagnets would be useful materials for thermoelectronic devices
and spin caloritronic devices. The calculated ANC of Mn$_3$Sn and iron are in
reasonably good agreement with the very recent experiments. The calculated SNC
of platinum also agrees with the very recent experiments in both sign and
magnitude. The calculated thermoelectric and thermomagnetic properties are
analyzed in terms of the band structures as well as the energy-dependent AHC,
ANC, SNC and spin Hall conductivity via the Mott relations.",1708.05933v3
2017-09-15,Investigating the interstellar dust through the Fe K-edge,"The chemical and physical properties of interstellar dust in the densest
regions of the Galaxy are still not well understood. X-rays provide a powerful
probe since they can penetrate gas and dust over a wide range of column
densities (up to $10^{24}\ \rm{cm}^{-2}$). The interaction (scattering and
absorption) with the medium imprints spectral signatures that reflect the
individual atoms which constitute the gas, molecule, or solid. In this work we
investigate the ability of high resolution X-ray spectroscopy to probe the
properties of cosmic grains containing iron. Although iron is heavily depleted
into interstellar dust, the nature of the Fe-bearing grains is still largely
uncertain. In our analysis we use iron K-edge synchrotron data of minerals
likely present in the ISM dust taken at the European Synchrotron Radiation
Facility. We explore the prospects of determining the chemical composition and
the size of astrophysical dust in the Galactic centre and in molecular clouds
with future X-ray missions. The energy resolution and the effective area of the
present X-ray telescopes are not sufficient to detect and study the Fe K-edge,
even for bright X-ray sources. From the analysis of the extinction cross
sections of our dust models implemented in the spectral fitting program SPEX,
the Fe K-edge is promising for investigating both the chemistry and the size
distribution of the interstellar dust. We find that the chemical composition
regulates the X-ray absorption fine structures in the post edge region, whereas
the scattering feature in the pre-edge is sensitive to the mean grain size.
Finally, we note that the Fe K-edge is insensitive to other dust properties,
such as the porosity and the geometry of the dust.",1709.05359v1
2017-10-11,Fermi surface with Dirac fermions in CaFeAsF determined via quantum oscillation measurements,"Despite the fact that 1111-type iron arsenides hold the record transition
temperature of iron-based superconductors, their electronic structures have not
been studied much because of the lack of high-quality single crystals. In this
study, we completely determine the Fermi surface in the antiferromagnetic state
of CaFeAsF, a 1111 iron-arsenide parent compound, by performing quantum
oscillation measurements and band-structure calculations. The determined Fermi
surface consists of a symmetry-related pair of Dirac electron cylinders and a
normal hole cylinder. From analyses of quantum-oscillation phases, we
demonstrate that the electron cylinders carry a nontrivial Berry phase $\pi$.
The carrier density is of the order of 10$^{-3}$ per Fe. This unusual metallic
state with the extremely small carrier density is a consequence of the
previously discussed topological feature of the band structure which prevents
the antiferromagnetic gap from being a full gap. We also report a nearly
linear-in-$B$ magnetoresistance and an anomalous resistivity increase above
about 30 T for $B \parallel c$, the latter of which is likely related to the
quantum limit of the electron orbit. Intriguingly, the electrical resistivity
exhibits a nonmetallic temperature dependence in the paramagnetic tetragonal
phase ($T >$ 118 K), which may suggest an incoherent state. Our study provides
a detailed knowledge of the Fermi surface in the antiferromagnetic state of
1111 parent compounds and moreover opens up a new possibility to explore
Dirac-fermion physics in those compounds.",1710.03938v3
2017-10-26,X-ray reflection from cold white dwarfs in magnetic cataclysmic variables,"We model X-ray reflection from white dwarfs (WD) in magnetic cataclysmic
variables (mCVs) with a Monte Carlo simulation. A point source with a power-law
spectrum or a realistic post-shock accretion column (PSAC) source irradiates a
cool and spherical WD. The PSAC source emits thermal spectra of various
temperatures stratified along the column according to the PSAC model. In the
point source simulation, we confirm (1) a source harder and nearer to the WD
enhances the reflection, (2) higher iron abundance enhances the equivalent
widths (EWs) of fluorescent iron K${\alpha}_{1,2}$ lines and their Compton
shoulder, and increases cut-off energy of a Compton hump, and (3) significant
reflection appears from an area that is more than 90 deg apart from the
position right under the point X-ray source because of the WD curvature. The
PSAC simulation reveals that (1) a more massive WD basically enhances the
intensities of the fluorescent iron K${\alpha}_{1,2}$ lines and the Compton
hump, except for some specific accretion rate, because the more massive WD
makes the hotter PSAC from which higher energy X-rays are preferentially
emitted, (2) a larger specific accretion rate monotonically enhances the
reflection because it makes the hotter and shorter PSAC, and (3) the intrinsic
thermal component hardens by occultation of the cool base of the PSAC by the
WD. We quantitatively evaluate influences of the parameters on the EWs and the
Compton hump with both types of sources. We also calculate X-ray modulation
profiles brought about by the WD spin. They depend on angles of the spin axis
from the line of sight and from the PSAC, and whether the two PSACs can be
seen. The reflection spectral model and the modulation model involve the
fluorescent lines and the Compton hump and can directly be compared to the data
which allow us to evaluate these geometrical parameters with unprecedented
accuracy.",1710.09931v1
2017-12-19,Magnetic phase diagram of the iron pnictides in the presence of spin-orbit coupling: Frustration between $C_2$ and $C_4$ magnetic phases,"We investigate the impact of spin anisotropic interactions, promoted by
spin-orbit coupling, on the magnetic phase diagram of the iron-based
superconductors. Three distinct magnetic phases with Bragg peaks at $(\pi,0)$
and $(0,\pi)$ are possible in these systems: one $C_2$ (i.e. orthorhombic)
symmetric stripe magnetic phase and two $C_4$ (i.e. tetragonal) symmetric
magnetic phases. While the spin anisotropic interactions allow the magnetic
moments to point in any direction in the $C_2$ phase, they restrict the
possible moment orientations in the $C_4$ phases. As a result, an interesting
scenario arises in which the spin anisotropic interactions favor a $C_2$ phase,
but the other spin isotropic interactions favor a $C_4$ phase. We study this
frustration via both mean-field and renormalization-group approaches. We find
that, to lift this frustration, a rich magnetic landscape emerges well below
the magnetic transition temperature, with novel $C_2$, $C_4$, and mixed
$C_2$-$C_4$ phases. Near the putative magnetic quantum critical point, spin
anisotropies promote a stable Gaussian fixed point in the renormalization-group
flow, which is absent in the spin isotropic case, and is associated with a
near-degeneracy between $C_2$ and $C_4$ phases. We argue that this frustration
is the reason why most $C_4$ phases in the iron pnictides only appear inside
the $C_2$ phase, and discuss additional manifestations of this frustration in
the phase diagrams of these materials.",1712.07192v4
2018-01-03,Sequential structural and antiferromagnetic transitions in BaFe$_2$Se$_3$ under pressure,"The discovery of superconductivity in the two-leg ladder compound
BaFe$_2$S$_3$ has established the 123-type iron chalcogenides as a novel and
interesting subgroup of the iron-based superconductors family. However, in this
123 series, BaFe$_2$Se$_3$ is an exceptional member, with a magnetic order and
crystalline structure different from all others. Recently, an exciting
experiment reported the emergence of superconductivity in BaFe$_2$Se$_3$ at
high pressure [J.-J. Ying, et al., Phys. Rev. B 95, 241109 (R) (2017)]. In this
publication, we report a first principles study of BaFe$_2$Se$_3$. Our analysis
unveils a variety of qualitative differences between BaFe$_2$S$_3$ and
BaFe$_2$Se$_3$, including in the latter an unexpected chain of transitions with
increasing pressure. First, by gradually reducing the tilting angle of iron
ladders, the crystalline structure smoothly transforms from Pnma to Cmcm at ~6
GPa. Second, the system becomes metallic at 10.4 GPa. Third, its unique ambient
pressure Block antiferromagnetic ground state is replaced by the more common CX
antiferromagnetic order at ~12 GPa, the same magnetic state of the 123-S
ladder. This transition is found at a pressure very similar to the experimental
superconducting transition. Finally, all magnetic moments vanish at 30 GPa.
This reported theoretical diagram of the complete phase evolution is important
because of the technical challenges to capture many physical properties in
high-pressure experiments. The information obtained in our calculations suggest
different characteristics for superconductivity in BaFe$_2$Se$_3$ and
BaFe$_2$S$_3$: in 123-S pairing occurs when magnetic moments vanish, while in
123-Se the transition region from Block- to CX-type magnetism appears to
catalyze superconductivity. Finally, an additional superconducting dome above
~30 GPa is expected to occur.",1801.00877v1
2018-02-12,"Superconducting transition temperatures in the electronic and magnetic phase diagrams of Sr2VFeAsO3-delta, a superconductor","We elucidate the magnetic phases and superconducting transition temperatures
(Tc) in Sr2VFeAsO3-delta (21113V), an iron-based superconductor with a
thick-blocking layer fabricated from a perovskite-related transition metal
oxide. At low temperatures (T < 37.1 K), 21113V exhibited a superconducting
phase in the range 0.031 =< delta =< 0.145 and an antiferromagnetic (AFM) iron
sublattice in the range 0.267 =< delta =< 0.664. Mixed-valent vanadium
exhibited a dominant AFM phase in 0.031 =< delta =< 0.088, and a partial
ferrimagnetic (Ferri.) phase in the range 0.124 =< delta =< 0.664. The Ferri.
phase was the most dominant at a delta value of 0.267, showing an AFM phase of
Fe at T < 20 K. Increasing the spontaneous magnetic moments reduced the
magnetic shielding volume fraction due to the superconducting phase. This
result was attributed to the magnetic phase of vanadium, which dominates the
superconductivity of Fe in 21113V. The Tc-delta curve showed two maxima. The
smaller and larger of Tc maxima occurred at delta = 0.073 and delta = 0.145,
respectively; the latter resides on the phase boundary between AFM and the
partial Ferri. phases of vanadium. 21113V is a useful platform for verifing new
mechanisms of Tc enhancement in iron-based superconductors.",1802.03907v2
2018-07-20,Measurement of the Iron Spectrum in Cosmic Rays by VERITAS,"We present a new measurement of the energy spectrum of iron nuclei in cosmic
rays from 20 to 500 TeV. The measurement makes use of a template-based analysis
method, which, for the first time, is applied to the energy reconstruction of
iron-induced air showers recorded by the VERITAS array of imaging atmospheric
Cherenkov telescopes. The event selection makes use of the direct Cherenkov
light which is emitted by charged particles before the first interaction, as
well as other parameters related to the shape of the recorded air shower
images. The measured spectrum is well described by a power law
$\frac{\mathrm{d} F}{\mathrm{d} E}=f_0\cdot
\left(\frac{E}{E_0}\right)^{-\gamma}$ over the full energy range, with $\gamma
= 2.82 \pm 0.30 \mathrm{(stat.)} ^{+0.24}_{-0.27} \mathrm{(syst.)}$ and $f_0 =
\left( 4.82 \pm 0.98 \mathrm{(stat.)}^{+2.12}_{-2.70} \mathrm{(syst.)}
\right)\cdot 10^{-7}$m$^{-2}$s$^{-1}$sr$^{-1}$TeV$^{-1}$ at $E_0=50$TeV, with
no indication of a cutoff or spectral break. The measured differential flux is
compatible with previous results, with improved statistical uncertainty at the
highest energies.",1807.08010v1
2018-07-23,The Quantum Field Of A Magnet Shown By A Nanomagnetic Ferrolens,"It has been more than two hundred years since the first iron filings
experiment, showing us the 2D macroscopic magnetic imprint of the field of a
permanent magnet. However, latest developments in modern nanomagnetic passive
direct observation devices reveal in real-time and color a more intriguing 3D
dynamic and detailed image of the field of a magnet, with surprising new
findings, that can change our perspective for dipole magnetism forever and lead
to new research. This research is a continuation of our previous work (DOI:
10.1016/j.jmmm.2017.12.023). The magnetostatic fields were under our scope and
examined with the aid of the ferrolens. We are presenting experimental and
photographical evidence, demonstrating the true complex 3D Euclidian geometry
of the quantum field of permanent magnets that have never been seen before and
the classic iron filings experiment, apart of its 2D limitations, fails to
depict. An analysis of why and what these iron filings inherent limitations
are, giving us an incomplete and also in some degree misguiding image of the
magnetic field of a magnet is carried out, whereas, as we prove the ferrolens
is free of these limitations and its far more advanced visualization
capabilities is allowing it to show the quantum image with depth of field
information, of the dipole field of a permanent magnet. For the first time the
domain wall (i.e. Bloch or Neel wall) region of the field of a magnet is
clearly made visible by the ferrolens along with what phenomenon is actually
taking place there, leading to the inescapable conclusion, novel observation
and experimental evidence that the field of any dipole magnet actually consists
of two distinct and separate toroidal shaped 3D magnetic bubbles, each located
at either side of the dipole around the exact spatial regions where the two
poles of the magnet reside.",1807.08751v1
2018-10-05,(16) Psyche: A mesosiderite-like asteroid?,"Asteroid (16) Psyche is the target of the NASA Psyche mission. It is
considered one of the few main-belt bodies that could be an exposed
proto-planetary metallic core and that would thus be related to iron
meteorites. Such an association is however challenged by both its near- and
mid-infrared spectral properties and the reported estimates of its density.
Here, we aim to refine the density of (16) Psyche to set further constraints on
its bulk composition and determine its potential meteoritic analog.
  We observed (16) Psyche with ESO VLT/SPHERE/ZIMPOL as part of our large
program (ID 199.C-0074). We used the high angular resolution of these
observations to refine Psyche's three-dimensional (3D) shape model and
subsequently its density when combined with the most recent mass estimates. In
addition, we searched for potential companions around the asteroid. We derived
a bulk density of 3.99\,$\pm$\,0.26\,g$\cdot$cm$^{-3}$ for Psyche. While such
density is incompatible at the 3-sigma level with any iron meteorites
($\sim$7.8\,g$\cdot$cm$^{-3}$), it appears fully consistent with that of
stony-iron meteorites such as mesosiderites (density
$\sim$4.25\,$\cdot$cm$^{-3}$). In addition, we found no satellite in our images
and set an upper limit on the diameter of any non-detected satellite of
1460\,$\pm$\,200}\,m at 150\,km from Psyche (0.2\%\,$\times$\,R$_{Hill}$, the
Hill radius) and 800\,$\pm$\,200\,m at 2,000\,km (3\%\,$\times$\,$R_{Hill}$).
  Considering that the visible and near-infrared spectral properties of
mesosiderites are similar to those of Psyche, there is merit to a
long-published initial hypothesis that Psyche could be a plausible candidate
parent body for mesosiderites.",1810.02771v1
2018-11-26,Confirming the presence of second population stars and the iron discrepancy along the AGB of the globular cluster NGC 6752,"Asymptotic giant branch (AGB) stars in the globular cluster NGC6752 have been
found to exhibit some chemical peculiarities with respect to the red giant
branch (RGB) stars. A discrepancy between [FeI/H] and [FeII/H] (not observed in
RGB stars) has been detected adopting spectroscopic temperatures. Moreover, a
possible lack of second-population stars along the AGB was claimed. The use of
photometric temperatures based on (V-K) colors was proposed to erase this iron
discrepancy. Also, ad hoc scenarios have been proposed to explain the absence
of second-population AGB stars. Here we analyzed a sample of 19 AGB and 14 RGB
stars of NGC6752 observed with the spectrographs UVES. The two temperature
scales agree very well for the RGB stars while for the AGB stars there is a
systematic offset of ~100 K. We found that even if the photometric temperatures
alleviate the iron discrepancy with respect to the spectroscopic ones, a
systematic difference between [FeI/H] and [FeII/H] is still found among the AGB
stars. An unexpected result is that the photometric temperatures do not satisfy
the excitation equilibrium in the AGB stars. This suggests that standard 1D-LTE
model atmospheres are unable to properly describe the thermal structure of AGB
stars, at variance with the RGB stars. The use of photometric temperatures
confirms the previous detection of second-population AGB stars in this cluster,
with the presence of clear correlations/anticorrelations among the light
element abundances. This firmly demonstrates that both first and
second-population stars evolve along the AGB of NGC6752.",1811.10626v1
2019-03-06,Lattice Disorder Effect on Magnetic Ordering of Iron Arsenides,"This study investigates the changes of magnetic ordering temperature via
nano- and mesoscale structural features in an iron arsenide. Although magnetic
ground states in quantum materials can be theoretically predicted from known
crystal structures and chemical compositions, the ordering temperature is
harder to pinpoint due to such local lattice variations. In this work we find
surprisingly that a locally disordered material can exhibit a significantly
larger Neel temperature (TN) than an ordered material of precisely the same
chemical stoichiometry. Here, a EuFe2As2 crystal, which is a 122 parent of iron
arsenide superconductors, is found through synthesis to have ordering below TN
= 195 K (for the disordered crystal) or TN = 175 K (for the ordered crystal).
In the higher TN crystals, there are shorter planar Fe-Fe bonds [2.7692(2) A
vs. 2.7745(3) A], a randomized in-plane defect structure, and diffuse
scattering along the [00L] crystallographic direction that manifests as a
rather broad specific heat peak. For the lower TN crystals, the a-lattice
parameter is larger and the in-plane microscopic structure shows defect
ordering along the antiphase boundaries, giving a larger TN and a higher
superconducting temperature (Tc) upon the application of pressure. First
principles calculations find a strong interaction between c-axis strain and
interlayer magnetic coupling, but little impact of planar strain on the
magnetic order. Neutron single-crystal diffraction shows that the
low-temperature magnetic phase transition due to localized Eu moments is not
lattice or disorder sensitive, unlike the higher-temperature Fe sublattice
ordering. This study demonstrates a higher magnetic ordering point arising from
local disorder in 122.",1903.02545v2
2019-05-24,How much of the Solar System should we leave as Wilderness?,"""How much of the Solar System should we reserve as wilderness, off-limits to
human development?"" We argue that, as a matter of policy, development should be
limited to one eighth, with the remainder set aside. We argue that adopting a
""1/8 principle"" is far less restrictive, overall, than it might seem. One
eighth of the iron in the asteroid belt is more than a million times greater
than all of the Earth's estimated iron reserves and may suffice for centuries.
A limit of some sort is needed because of the problems associated with
exponential growth. Humans are poor at estimating the pace of such growth, so
the limitations of a resource are hard to recognize before the final three
doubling times which take utilization successively from 1/8 to 1/4 to 1/2, and
then to the point of exhaustion. Population growth and climate change are
instances of unchecked exponential growth. Each places strains upon ouru
available resources. Each is a problem we would like to control but attempts to
do so at this comparatively late stage have not been encouraging. Our limited
ability to see ahead suggests that we should set ourselves a 'tripwire' that
gives us at least 3 doubling times as leeway, i.e. when 1/8 of Solar System
resources are close to being exploited. At a 3.5 percent growth rate for the
space economy, comparable to that of the iron use from the beginning of the
Industrial Revolution until now, the 1/8 point would be reached after 400
years. At that point the 20 year doubling time of a 3.5 percent growth rate
means that only 60 years would remain to transition the economic system to new
""steady state"" conditions. The rationale for adopting the 1/8 principle now is
that it may be far easier to implement in principle restrictions at an early
stage, rather than later, when vested and competing interests have come into
existence.",1905.13681v1
2019-07-26,Stabilization of $\varepsilon$-Fe$_2$O$_3$ epitaxial layer on MgO(111)/GaN via an intermediate $γ$-Fe$_2$O$_3$-phase,"In the present study we have demonstrated epitaxial stabilization of the
metastable magnetically-hard $\varepsilon$-Fe$_2$O$_3$ phase on top of a thin
MgO(111) buffer layer grown onto the GaN (0001) surface. The primary purpose to
introduce a 4\,nm-thick buffer layer of MgO in between Fe$_2$O$_3$ and GaN was
to stop thermal migration of Ga into the iron oxide layer. Though such
migration and successive formation of the orthorhombic GaFeO$_3$ was supposed
earlier to be a potential trigger of the nucleation of the isostructural
$\varepsilon$-Fe$_2$O$_3$, the present work demonstrates that the growth of
single crystalline uniform films of epsilon ferrite by pulsed laser deposition
is possible even on the MgO capped GaN. The structural properties of the 60\,nm
thick Fe$_2$O$_3$ layer on MgO / GaN were probed by electron and x-ray
diffraction, both suggesting that the growth of $\varepsilon$-Fe$_2$O$_3$ is
preceded by formation of a thin layer of $\gamma$-Fe$_2$O$_3$. The presence of
the magnetically hard epsilon ferrite was independently confirmed by
temperature dependent magnetometry measurements. The depth-resolved x-ray and
polarized neutron reflectometry reveal that the 10\,nm iron oxide layer at the
interface has a lower density and a higher magnetization than the main volume
of the $\varepsilon$-Fe$_2$O$_3$ film. The density and magnetic moment depth
profiles derived from fitting the reflectometry data are in a good agreement
with the presence of the magnetically degraded $\gamma$-Fe$_2$O$_3$ transition
layer between MgO and $\varepsilon$-Fe$_2$O$_3$. The natural occurrence of the
interface between magnetoelectric $\varepsilon$- and spin caloritronic
$\gamma$- iron oxide phases can enable further opportunities to design novel
all-oxide-on-semiconductor devices.",1907.11611v2
2019-08-06,On the use of field RR Lyrae as Galactic probes: I. The Oosterhoff dichotomy based on fundamental variables,"We collected a large data set of field RR Lyrae stars (RRLs) by using
catalogues already available in the literature and Gaia DR2. We estimated the
iron abundances for a sub-sample of 2,382 fundamental RRLs ($\Delta$S method:
CaIIK, H$\beta$, H$\gamma$ and H$\delta$ lines) for which are publicly
available medium-resolution SDSS-SEGUE spectra. We also included similar
estimates available in the literature ending up with the largest and most
homogeneous spectroscopic data set ever collected for RRLs (2,903). The
metallicity scale was validated by using iron abundances based on high
resolution spectra for a fundamental field RRL (V~Ind), for which we collected
X-shooter spectra covering the entire pulsation cycle. The peak
([Fe/H]=-1.59$\pm$0.01) and the standard deviation ($\sigma$=0.43 dex) of the
metallicity distribution agree quite well with similar estimates available in
the literature. The current measurements disclose a well defined metal-rich
tail approaching Solar iron abundance. The spectroscopic sample plotted in the
Bailey diagram (period vs luminosity amplitude) shows a steady variation when
moving from the metal-poor ([Fe/H]=-3.0/-2.5) to the metal-rich
([Fe/H]=-0.5/0.0) regime. The smooth transition in the peak of the period
distribution as a function of the metallicity strongly indicates that the
long-standing problem of the Oosterhoff dichotomy among Galactic globulars is
the consequence of the lack of metal-intermediate clusters hosting RRLs. We
also found that the luminosity amplitude, in contrast with period, does not
show a solid correlation with metallicity. This suggests that
period-amplitude-metallicity relations should be cautiously treated.",1908.02064v2
2019-08-27,"Carbon, oxygen, and iron abundances in disk and halo stars. Implications of 3D non-LTE spectral line formation","The abundances of carbon, oxygen, and iron in late-type stars are important
parameters in exoplanetary and stellar physics, as well as key tracers of
stellar populations and Galactic chemical evolution. We carried out
three-dimensional (3D) non-LTE radiative transfer calculations for CI and OI,
and 3D LTE radiative transfer calculations for FeII, across the STAGGER-grid of
3D hydrodynamic model atmospheres. The absolute 3D non-LTE versus 1D LTE
abundance corrections can be as severe as $-0.3$ dex for CI lines in
low-metallicity F dwarfs, and $-0.6$ dex for OI lines in high-metallicity F
dwarfs. The 3D LTE versus 1D LTE abundance corrections for FeII lines are less
severe, typically less than $+0.15$ dex. We used the corrections in a
re-analysis of carbon, oxygen, and iron in $187$ F and G dwarfs in the Galactic
disk and halo. Applying the differential 3D non-LTE corrections to 1D LTE
abundances visibly reduces the scatter in the abundance plots. The thick disk
and high-$\alpha$ halo population rise in carbon and oxygen with decreasing
metallicity, and reach a maximum of [C/Fe]$\approx0.2$ and a plateau of
[O/Fe]$\approx0.6$ at [Fe/H]$\approx-1.0$. The low-$\alpha$ halo population is
qualitatively similar, albeit offset towards lower metallicities and with
larger scatter. Nevertheless, these populations overlap in the [C/O] versus
[O/H] plane, decreasing to a plateau of [C/O]$\approx-0.6$ below
[O/H]$\approx-1.0$. In the thin-disk, stars having confirmed planet detections
tend to have higher values of C/O at given [O/H]; this potential signature of
planet formation is only apparent after applying the abundance corrections to
the 1D LTE results. Our grids of line-by-line abundance corrections are
publicly available and can be readily used to improve the accuracy of
spectroscopic analyses of late-type stars.",1908.10319v2
2020-01-03,The chemical composition of the accretion disk and donor star in Ultra Compact X-ray Binaries: A comprehensive X-ray analysis,"We have analyzed the X-ray spectra of all known Ultra Compact X-ray Binaries
(UCXBs), with the purpose of constraining the chemical composition of their
accretion disk and donor star. Our investigation was focused on the presence
(or absence) of the Fe K${\alpha}$ emission line, which was used as the probe
of chemical composition of the disk, based on previously established
theoretical predictions for the reflection of X-ray radiation off the surface
of C/O-rich or He-rich accretion disks in UCXBs. We have contrasted the results
of our spectral analysis to the history of type I X-ray bursts from these
systems, which can also indicate donor star composition. We found that UCXBs
with prominent and persistent iron K${\alpha}$ emission also featured repeat
bursting activity. On the other hand, the UCXBs for which no iron line was
detected, appear to have few or no type I X-ray bursts detected over more than
a decade of monitoring. Based on Monte Carlo simulations, demonstrating a
strong correlation between the Fe K${\alpha}$ line strength and the abundance
of C and O in the accretion disk material and given the expected correlation
between the H/He abundance and the recurrence rate of type I X-ray bursts, we
propose that there is a considerable likelihood that UCXBs with persistent iron
emission have He-rich donors, while those that do not, likely have C/O or
O/Ne/Mg-rich donors. Our results strongly advocate for the development of more
sophisticated simulations of X-ray reflection from hydrogen-poor accretion
disks.",2001.00716v2
2020-01-20,The extreme CNO-enhanced composition of the primitive iron-poor dwarf star J0815+4729,"We present an analysis of high-resolution Keck/HIRES spectroscopic
observations of J0815+4729, an extremely carbon-enhanced, iron-poor dwarf star.
These high-quality data allow us to derive a metallicity of
[Fe/H]$=-5.49{\pm}0.14$ from the three strongest \ion{Fe}{1} lines and to
measure a high [Ca/Fe]~$=0.75{\pm}0.14$. The large carbon abundance of
A(C)~$=7.43{\pm}0.17$ (or [C/Fe]~$\sim 4.49{\pm}0.11$) places this star in the
upper boundary of the low-carbon band in the A(C)-[Fe/H] diagram, suggesting no
contamination from a binary AGB companion. We detect the oxygen triplet at
777nm for the first time in an ultra-metal poor star, indicating a large
oxygen-to-iron abundance ratio of [O/Fe]~$=4.03{\pm}0.12$
(A(O)~$=7.23{\pm}0.14$), significantly higher than the previously most
metal-poor dwarf J2209-0028 with an oxygen triplet detection with
[O/Fe]~$\sim2.2$~dex at [Fe/H]~$\sim -3.9$. Nitrogen is also dramatically
enhanced with (A(N)~$=6.75{\pm}0.08$) and an abundance ratio [N/Fe]~$\sim
4.41{\pm}0.08$. We also detect Ca, Na and Mg, while provide upper limits for
eight other elements. The abundance pattern of J0815+4729 resembles that of
HE~1327-2326, indicating that both are second-generation stars contaminated by
a $\sim 21-27$~\msun~single, zero-metallicity low-energy supernova with very
little mixing and substantial fallback. The absence of lithium implies an
upper-limit abundance A(Li)~$<1.3$~dex, about 0.7~dex below the detected Li
abundance in J0023+0307 which has a similar metallicity, exacerbating the
cosmological lithium problem.",2001.07257v2
2020-01-21,Observation of magnetic adatom-induced Majorana vortex and its hybridization with field-induced Majorana vortex in an iron-based superconductor,"Braiding Majorana zero modes is essential for fault-tolerant topological
quantum computing. Iron-based superconductors with nontrivial band topology
have recently emerged as a surprisingly promising platform for creating
distinct Majorana zero modes in magnetic vortices in a single material and at
relatively high temperatures. The magnetic field-induced Abrikosov vortex
lattice makes it difficult to braid a set of Majorana zero modes or to study
the coupling of a Majorana doublet due to overlapping wave functions. Here we
report the observation of the proposed quantum anomalous vortex with integer
quantized vortex core states and the Majorana zero mode induced by magnetic Fe
adatoms deposited on the surface. We observe its hybridization with a nearby
field-induced Majorana vortex in iron-based superconductor FeTe0.55Se0.45. We
also observe vortex-free Yu-Shiba-Rusinov bound states at the Fe adatoms with a
weaker coupling to the substrate, and discover a reversible transition between
Yu-Shiba-Rusinov states and Majorana zero mode by manipulating the exchange
coupling strength. The dual origin of the Majorana zero modes, from magnetic
adatoms and external magnetic field, provides a new single-material platform
for studying their interactions and braiding in superconductors bearing
topological band structures.",2001.07376v2
2020-06-05,Chandra View of the LINER-type Nucleus in the Radio-Loud Galaxy CGCG 292-057: Ionized Iron Line and Jet-ISM Interactions,"We present an analysis of the new, deep (94\,ksec) {\it Chandra} ACIS-S
observation of radio-loud active galaxy CGCG\,292$-$057, characterized by a
LINER-type nucleus and a complex radio structure that indicates intermittent
jet activity. On the scale of the host galaxy bulge, we detected excess X-ray
emission with a spectrum best fit by a thermal plasma model with a temperature
of $\sim 0.8$\,keV. We argue that this excess emission results from compression
and heating of the hot diffuse fraction of the interstellar medium displaced by
the expanding inner, $\sim 20$\, kpc-scale lobes observed in this restarted
radio galaxy. The nuclear X-ray spectrum of the target clearly displays an
ionized iron line at $\sim 6.7$\,keV, and is best fitted with a
phenomenological model consisting of a power-law (photon index $\simeq 1.8$)
continuum absorbed by a relatively large amount of cold matter (hydrogen column
density $\simeq 0.7 \times 10^{23}$\,cm$^{-2}$), and partly scattered (fraction
$\sim 3\%$) by ionized gas, giving rise to a soft excess component and
K$\alpha$ line from iron ions. We demonstrate that the observed X-ray spectrum,
particularly the equivalent width of Fe\,\texttt{XXV} K$\alpha$ (of order
$0.3$\,keV) can in principle, be explained in a scenario involving a
Compton-thin gas located at the scale of the broad-lined region in this source
and photoionized by nuclear illumination. We compare the general spectral
properties of the CGCG\,292$-$057 nucleus, with those of other nearby LINERs
studied in X-rays.",2006.03717v2
2020-06-29,No Redshift Evolution in the Broad Line Region Metallicity up to z=7.54: Deep NIR Spectroscopy of ULAS J1342+0928,"We present deep (9 hours) Gemini-N/GNIRS near-infrared spectroscopic
observations of ULAS J1342+0928, a luminous quasar at z=7.54. Various broad
emission lines were detected, as well as the underlying continuum and iron
forests over the rest-frame wavelength 970-2930A. There is a clear trend that
higher-ionization emission lines show larger blueshifts with CIV1549 exhibiting
5510^{+240}_{-110} km s-1 blueshift with respect to the systematic redshift
from the far-infrared [CII] 158um emission line. Those high ionization lines
have wide profiles with FWHM more than 10000 km s-1. A modest blueshift of
340^{+110}_{-80} km s-1 is also seen in MgII, the lowest ionization line
identified in the spectrum. The updated MgII-based black hole mass of
M_BH=9.1_{-1.3}^{+1.4} x 10^8 M_sun and the Eddington ratio of
L_bol/L_Edd=1.1_{-0.2}^{+0.2} confirm that ULAS J1342+0928 is powered by a
massive and actively accreting black hole. There is no significant difference
in the emission line ratios such as SiIV/CIV and AlIII/CIV when compared to
lower-redshift quasars in a similar luminosity range, which suggests early
metal pollution of the broad-line-region clouds. This trend also holds for the
FeII/MgII line ratio, known as a cosmic clock that traces the iron enrichment
in the early universe. Different iron templates and continuum fitting ranges
were used to explore how the FeII/MgII measurement changes as a function of
spectral modeling. Quasars at even higher redshift or at fainter luminosity
range (L_bol<10^46 erg s-1) are needed to probe the sites of early metal
enrichment and a corresponding change in the FeII/MgII ratio.",2006.16268v1
2020-08-05,Orbital-selective spin waves in detwinned NaFeAs,"The existence of orbital-dependent electronic correlations has been
recognized as an essential ingredient to describe the physics of iron-based
superconductors. NaFeAs, a parent compound of iron based superconductors,
exhibits a tetragonal-to-orthorhombic lattice distortion below $T_s\approx 60$
K, forming an electronic nematic phase with two 90$^\circ$ rotated (twinned)
domains, and orders antiferromagnetically below $T_N\approx 42$ K. We use
inelastic neutron scattering to study spin waves in uniaxial pressure-detwinned
NaFeAs. By comparing the data with combined density functional theory and
dynamical mean-field theory calculations, we conclude that spin waves up to an
energy scale of $E_\text{crossover} \approx 100$ meV are dominated by
$d_{yz}$-$d_{yz}$ intra-orbital scattering processes, which have the two-fold
($C_2$) rotational symmetry of the underlying lattice. On the other hand, the
spin wave excitations above $E_\text{crossover}$, which have approximately
fourfold ($C_4$) rotational symmetry, arise from the $d_{xy}$-$d_{xy}$
intra-orbital scattering that controls the overall magnetic bandwidth in this
material. In addition, we find that the low-energy ($E\approx 6$ meV) spin
excitations change from approximate $C_4$ to $C_2$ rotational symmetry below a
temperature $T^\ast$ ($>T_s$), while spin excitations at energies above
$E_\text{crossover}$ have approximate $C_4$ rotational symmetry and are weakly
temperature dependent. These results are consistent with angle resolved
photoemission spectroscopy measurements, where the presence of an uniaxial
strain necessary to detwin NaFeAs also raises the onset temperature $T^\ast$ of
observable orbital-dependent band splitting to above $T_s$, thus supporting the
notion of orbital selective spin waves in the nematic phase of iron-based
superconductors.",2008.02314v1
2020-10-26,Simulation of hydrogen permeation through pure iron for trapping and surface phenomena characterisation,"There is a need for numerical models capable of predicting local accumulation
of hydrogen near stress concentrators and crack tips to prevent and mitigate
hydrogen assisted fracture in steels. The experimental characterisation of
trapping parameters in metals, which is required for an accurate simulation of
hydrogen transport, is usually performed through the electropermeation test. In
order to study grain size influence and grain boundary trapping during
permeation, two modelling approaches are explored; a 1D Finite Element model
including trap density and binding energy as input parameters and a
polycrystalline model based on the assignment of a lower diffusivity and
solubility to the grain boundaries. Samples of pure iron after two different
heat treatments - 950C for 40 minutes and 1100C for 5 minutes - are tested
applying three consecutive rising permeation steps and three decaying steps.
Experimental results show that the finer grain microstructure promotes a
diffusion delay due to grain boundary trapping. The usual methodology for the
determination of trap densities and binding energies is revisited in which the
limiting diluted and saturated cases are considered. To this purpose, apparent
diffusivities are fitted including also the influence of boundary conditions
and comparing results provided by the constant concentration with the constant
flux assumption. Grain boundaries are characterised for pure iron with a
binding energy between 37.8 and 39.9 kJ/mol and a low trap density but it is
numerically demonstrated that saturated or diluted assumptions are not always
verified, and a univocal determination of trapping parameters requires a
broader range of charging conditions for permeation. The relationship between
surface parameters, i.e. charging current, recombination current and surface
concentrations, is also studied.",2010.13567v1
2020-11-11,Non-stoichiometric amorphous magnesium-iron silicates in circumstellar dust shells. Dust growth in outflows from supergiants,"We investigate the dust growth in oxygen-rich stellar outflows for a set of
nine well-observed massive supergiants with optically thin dust shells. Models
of the infrared emission from their circumstellar dust shells are compared to
their observed infrared spectra so as to derive the essential parameters that
govern dust formation in the extended envelope of these stars. The results
obtained from the comparative study are also compared with the predictions of a
model for silicate dust condensation solely based on laboratory data and basic
stellar properties. The infrared emission in the wavelength range between 6 and
25 mu can be reproduced rather well by a mixture of non-stoichiometric
iron-bearing silicates, alumina, and metallic iron dust particles for all nine
objects. The observed spectra obtained from three objects, mu Cep, RW Cyg, and
RS Per, can be reproduced by a stationary and (essentially) spherically
symmetric outflow which enables a direct comparison with predictions from a
theoretical dust growth model. The temperature at the onset of massive silicate
dust growth is of the order of 920 K and the corresponding outflow velocity of
the order of the sound velocity for these objects. The condensation temperature
suggests that the silicate dust grows on the corundum dust grains that are
formed well in the interior of the silicate dust shell at a much higher
temperature. Our results propose that regarding the two major problems of dust
formation in stellar outflows: (i) formation of seed nuclei; (ii) their growth
to macroscopic dust grains, we are gradually coming close to a quantitative
understanding of the second item.",2011.05903v1
2020-11-17,On the Probability that a Rocky Planet's Composition Reflects its Host Star,"The bulk density of a planet, as measured by mass and radius, is a result of
planet structure and composition. Relative proportions of iron core, rocky
mantle, and gaseous envelopes are degenerate for a given density. This
degeneracy is reduced for rocky planets without significant gaseous envelopes
when the structure is assumed to be a differentiated iron core and rocky
mantle, in which the core mass fraction (CMF) is a first-order description of a
planet's bulk composition. A rocky planet's CMF may be derived both from bulk
density and by assuming the planet reflects the host star's major rock-building
elemental abundances (Fe, Mg, and Si). Contrasting CMF measures, therefore,
shed light on the outcome diversity of planet formation from processes
including mantle stripping, out-gassing, and/or late-stage volatile delivery.
We present a statistically rigorous analysis of the consistency of these two
CMF measures accounting for observational uncertainties of planet mass and
radius and host-star chemical abundances. We find that these two measures are
unlikely to be resolvable as statistically different unless the bulk density
CMF is at least 40% greater than or 50% less than the CMF as inferred from the
host star. Applied to 11 probable rocky exoplanets, Kepler-107c has a CMF as
inferred from bulk density that is significantly greater than the inferred CMF
from its host star (2$\sigma$) and is therefore likely an iron-enriched
super-Mercury. K2-229b, previously described as a super-Mercury, however, does
not meet the threshold for a super-Mercury at a 1- or 2- $\sigma$ level.",2011.08893v4
2021-01-22,Spin dynamics in NaFeAs and NaFe$_{0.53}$Cu$_{0.47}$As probed by resonant inelastic X-ray scattering,"The parent compounds of iron-based superconductors are magnetically-ordered
bad metals, with superconductivity appearing near a putative magnetic quantum
critical point. The presence of both Hubbard repulsion and Hund's coupling
leads to rich physics in these multiorbital systems, and motivated descriptions
of magnetism in terms of itinerant electrons or localized spins. The
NaFe$_{1-x}$Cu$_x$As series consists of magnetically-ordered bad metal ($x=0$),
superconducting ($x\approx0.02$) and magnetically-ordered
semiconducing/insulating ($x\approx0.5$) phases, providing a platform to
investigate the connection between superconductivity, magnetism and electronic
correlations. Here we use X-ray absorption spectroscopy and resonant inelastic
X-ray scattering to study the valence state of Fe and spin dynamics in two
NaFe$_{1-x}$Cu$_x$As compounds ($x=0$ and 0.47). We find that magnetism in both
compounds arises from Fe$^{2+}$ atoms, and exhibits underdamped dispersive spin
waves in their respective ordered states. The dispersion of spin excitations in
NaFe$_{0.53}$Cu$_{0.47}$As is consistent with being quasi-one-dimensional.
Compared to NaFeAs, the band top of spin waves in NaFe$_{0.53}$Cu$_{0.47}$As is
slightly softened with significantly more spectral weight of the spin
excitations. Our results indicate the spin dynamics in
NaFe$_{0.53}$Cu$_{0.47}$As arise from localized magnetic moments and suggest
the iron-based superconductors are proximate to a correlated insulating state
with localized iron moments.",2101.08948v1
2021-02-17,Single particle tunneling spectroscopy and superconducting gaps in layered iron based superconductor KCa$_{2}$Fe$_{4}$As$_{4}$F$_{2}$,"We perform scanning tunneling microscopy/spectroscopy study on the layered
iron based superconductor KCa$_2$Fe$_4$As$_4$F$_2$ with a critical temperature
of about 33.5 K. Two types of terminated surfaces are generally observed after
cleaving the samples in vacuum. On one commonly obtained surface, we observe a
full gap feature with energy gap values close to 4.6 meV. This type of spectrum
shows a clean and uniform full gap in space, which indicates the absence of gap
nodes in this superconductor. Quasiparticle interference patterns have also
been measured, which show no scattering patterns between the hole and tiny
electron pockets, but rather an intra-band scattering pattern is observed
possibly due to the hole-like $\alpha$ pocket. The Fermi energy of this band is
only about $24\pm6$ meV as derived from the energy dispersion result.
Meanwhile, impurity induced bound-state peaks can be observed at about $\pm2.2$
meV on some spectra, and the peak value seems to be independent to magnetic
field. On the second type of surface which is rarely obtained, the fully gapped
feature can still be observed on the tunneling spectra, although multiple gaps
are obtained either from a single spectrum or separate ones, and the gap values
determined from coherence peaks locate mainly in the range from 4 to 8 meV. Our
results clearly indicate multiple and nodeless superconducting gap nature in
this layered superconductor KCa$_2$Fe$_4$As$_4$F$_2$, and the superfluid is
mainly contributed by the hole-like Fermi surfaces near $\Gamma$ point. This
would inspire further consideration on the effect of the shallow and incipient
bands near M point, and help to understand the pairing mechanism in this highly
layered iron-based superconductor.",2102.08785v1
2021-03-11,"Intertwined charge, spin, and pairing orders in doped iron ladders","Motivated by recent experimental progress on iron-based ladder compounds, we
study the doped two-orbital Hubbard model for the two-leg ladder BaFe$_2$S$_3$.
The model is constructed by using {\it ab initio} hopping parameters and the
ground state properties are investigated using the density matrix
renormalization group method. We show that the $(\pi,0)$ magnetic ordering at
half-filling, with ferromagnetic rungs and antiferromagnetic legs, becomes
incommensurate upon hole doping. Moreover, depending on the strength of the
Hubbard $U$ coupling, other magnetic patterns, such as $(0,\pi)$, are also
stabilized. We found that the binding energy for two holes becomes negative for
intermediate Hubbard interaction strength, indicating hole pairing. Due to the
crystal-field split among orbitals, the holes primarily reside in one orbital,
with the other one remaining half-filled. This resembles orbital selective Mott
states. The formation of tight hole pairs continues with increasing hole
density, as long as the magnetic order remains antiferromagnetic in one
direction. The study of pair-pair correlations indicates the dominance of the
intra-orbital spin-singlet channel, as opposed to other pairing channels.
Although in a range of hole doping pairing correlations decay slowly, our
results can also be interpreted as corresponding to a charge-density-wave made
of pairs, a precursor of eventual superconductivity after interladder couplings
are included. Such scenario of intertwined orders has been extensively
discussed before in the cuprates, and our results suggest a similar physics
could exist in ladder iron-based superconductors. Finally, we also show that a
robust Hund's coupling is needed for pairing to occur.",2103.06407v2
2021-03-11,Enhancement of Superconductivity Linked with Linear-in-Temperature/Field Resistivity in Ion-Gated FeSe Films,"Iron selenide (FeSe) - the structurally simplest iron-based superconductor,
has attracted tremendous interest in the past years. While the transition
temperature (Tc) of bulk FeSe is $\sim$ 8 K, it can be significantly enhanced
to 40 - 50 K by various ways of electron doping. However, the underlying
physics for such great enhancement of Tc and so the Cooper pairing mechanism
still remain puzzles. Here, we report a systematic study of the
superconducting- and normal-state properties of FeSe films via ionic liquid
gating. With fine tuning, Tc evolves continuously from below 10 K to above 40
K; in situ two-coil mutual inductance measurements unambiguously confirm the
gating is a uniform bulk effect. Close to Tc, the normal-state resistivity
shows a linear dependence on temperature and the linearity extends to lower
temperatures with the superconductivity suppressed by high magnetic fields. At
high fields, the normal-state magnetoresistance exhibits a linear-in-field
dependence and obeys a simple scaling relation between applied field and
temperature. Consistent behaviors are observed for different-Tc states
throughout the gating process, suggesting the pairing mechanism very likely
remains the same from low- to high-Tc state. Importantly, the coefficient of
the linear-in-temperature resistivity is positively correlated with Tc,
similarly to the observations in cuprates, Bechgaard salts and iron pnictide
superconductors. Our study points to a short-range antiferromagnetic exchange
interaction mediated pairing mechanism in FeSe.",2103.06512v2
2021-06-08,"Atomic iron and nickel in the coma of C/1996 B2 (Hyakutake): production rates, emission mechanisms, and possible parents","Two papers recently reported the detection of gaseous nickel and iron in the
comae of over 20 comets from observations collected over two decades, including
interstellar comet 2I/Borisov. To evaluate the state of the laboratory data in
support of these identifications, we re-analyzed archived spectra of comet
C/1996 B2 (Hyakutake), one of the nearest and brightest comets of the last
century, using a combined experimental and computational approach. We developed
a new, many-level fluorescence model that indicates that the fluorescence
emission of Fe I and Ni I vary greatly with heliocentric velocity. Combining
this model with laboratory spectra of an Fe-Ni plasma, we identified 22 lines
of Fe I and 14 lines of Ni I in the spectrum of Hyakutake. Using Haser models,
we estimate the nickel and iron production rates as Q(Ni) = 2.6 - 4.1 x 10^22
s^-1 and Q(Fe) = 0.4 - 2.8 x 10^23 s^-1. From derived column densities, the
Ni/Fe abundance ratio log10[Ni/Fe] = -0.15 +/- 0.07 deviates significantly from
solar abundance ratios, and it is consistent with the ratios observed in solar
system comets. Possible production and emission mechanisms are analyzed in
context of existing laboratory measurements. Based on the observed spatial
distributions, excellent fluorescence model agreement, and Ni/Fe ratio, our
findings support an origin consisting of a short-lived unknown parent followed
by fluorescence emission. Our models suggest that the strong heliocentric
velocity dependence of the fluorescence efficiencies can provide a meaningful
test of the physical process responsible for the Fe I and Ni I emission.",2106.04701v2
2021-09-01,No umbrella needed: Confronting the hypothesis of iron rain on WASP-76b with post-processed general circulation models,"High-resolution spectra are unique indicators of three-dimensional processes
in exoplanetary atmospheres. For instance, in 2020, Ehrenreich et al. reported
transmission spectra from the ESPRESSO spectrograph yielding an anomalously
large Doppler blueshift from the ultra-hot Jupiter WASP-76b. Interpretations of
these observations invoke toy model depictions of gas-phase iron condensation
in lower-temperature regions of the planet's atmosphere. In this work, we
forward model the atmosphere of WASP-76b with double-gray general circulation
models (GCMs) and ray-striking radiative transfer to diagnose the planet's
high-resolution transmission spectrum. We confirm that a physical mechanism
driving strong east-west asymmetries across the terminator must exist to
reproduce large Doppler blueshifts in WASP-76b's transmission spectrum. We
identify low atmospheric drag and a deep radiative-convective boundary as
necessary components of our GCM to produce this asymmetry (the latter is
consistent with existing Spitzer phase curves). However, we cannot reproduce
either the magnitude or the time-dependence of the WASP-76b Doppler signature
with gas-phase iron condensation alone. Instead, we find that high-altitude,
optically thick clouds composed of $\rm Al_2O_3$, Fe, or $\rm Mg_2SiO_4$
provide reasonable fits to the Ehrenreich et al. observations -- with marginal
contributions from condensation. This fit is further improved by allowing a
small orbital eccentricity ($e \approx 0.017$), consistent with prior WASP-76b
orbital constraints. We additionally validate our forward-modeled spectra by
reproducing lines of nearly all species detected in WASP-76b by Tabernero et
al. 2021. Our procedure's success in diagnosing phase-resolved Doppler shifts
demonstrates the benefits of physical, self-consistent, three-dimensional
simulations in modeling high-resolution spectra of exoplanet atmospheres.",2109.00163v2
2021-10-21,Heat Capacity of oxide scale in the range from 0 C to 1300 C: Generalized estimates with account for movability of phase transitions,"The known data on the heat capacity of magnetite (Fe3O4), hematite (Fe2O3)
and iron (Fe) at different temperatures are approximated by formulas containing
phase transition temperatures as varying parameters. This allows to take into
account the effect of phase transition shifts, for example, due to impurities,
lattice defects, grain sizes or high cooling rates. For this purpose, the
entire target temperature range from 0 C to 1300 C is divided by phase
transition temperatures into separate intervals. The conjugation of the
approximating functions between the intervals at the magnetic transition point
is performed without a gap, and at the point of polymorphic transformation
(alpha Fe - gamma Fe) with a finite gap of heat capacity values. For wustite
Fe1-xO which does not experience phase transformations, the temperature
dependence of the heat capacity is approximated by a single smooth function. In
combination with previously obtained formulas for the density of iron oxides
and iron the proposed approximations allow us to estimate the specific mass
heat capacity of oxide scale depending of its structural composition and
temperature. By model calculations it is shown that at temperatures of 200 C
and 900 C specific mass heat capacity of oxide scale practically does not
depend on the percentage of its individual components and is approximately 750
and 850 J/(kg K) respectively. At a temperature of about 575 C, on contrary,
actually possible variations in the composition of oxide scale can lead to a
change in its specific heat capacity from 850 to 1150 J/(kg K). The obtained
dependencies are recommended for use in mathematical modeling of production and
processing of steel products in the presence of oxide scale on their surface",2110.11101v1
2021-11-20,Gaia-ESO Survey: Detailed elemental abundances in red giants of the peculiar globular cluster NGC 1851,"Context. NGC 1851 is one of several globular clusters for which multiple
stellar populations of the subgiant branch have been clearly identified and a
difference in metallicity detected. A crucial piece of information on the
formation history of this cluster can be provided by the sum of A(C+N+O)
abundances. However, these values have lacked a general consensus thus far. The
separation of the subgiant branch can be based on age and/or A(C+N+O) abundance
differences. Aims. Our main aim was to determine carbon, nitrogen, and oxygen
abundances for evolved giants in the globular cluster NGC1851 in order to check
whether or not the double populations of stars are coeval. Methods.
High-resolution spectra, observed with the FLAMES-UVES spectrograph on the ESO
VLT telescope, were analysed using a differential model atmosphere method.
Results. We provide abundances of up to 29 chemical elements for a sample of 45
giants in NGC 1851. The investigated stars can be separated into two
populations with a difference of 0.07 dex in the mean metallicity, 0.3 dex in
the mean C/N, and 0.35 dex in the mean s-process dominated element-to-iron
abundance ratios [s/Fe]. No significant difference was determined in the mean
values of A(C+N+O) as well as in abundance to iron ratios of carbon, alpha- and
iron-peak-elements, and of europium. Conclusions. As the averaged A(C+N+O)
values between the two populations do not differ, additional evidence is given
that NGC 1851 is composed of two clusters, the metal-rich cluster being by
about 0.6 Gyr older than the metal-poor one. A global overview of NGC 1851
properties and the detailed abundances of chemical elements favour its
formation in a dwarf spheroidal galaxy that was accreted by the Milky Way.",2111.10684v1
2021-12-12,Top-heavy stellar mass distribution in galactic nuclei inferred from the universally high abundance ratio of [Fe/Mg],"Recent observations of active galactic nuclei (AGNs) have shown a high
Fe~II/Mg~II line-flux ratio in their broad-line regions, nearly independent of
redshift up to $z \gtrsim 6$. The high flux ratio requires rapid production of
iron in galactic nuclei to reach an abundance ratio of ${\rm [Fe/Mg]} \gtrsim
0.2$ as high as those observed in matured galaxies in the local universe. We
propose a possible explanation of rapid iron enrichment in AGNs by massive star
formation that follows a top-heavy initial mass function (IMF) with a power-law
index of $\Gamma$ larger than the canonical value of $\Gamma=-2.35$ for a
Salpeter IMF. Taking into account metal production channels from different
types of SNe, we find that the high value of ${\rm [Fe/Mg]} \gtrsim 0.2$
requires the IMF to be characterized with $\Gamma \gtrsim -1$ ($\Gamma \gtrsim
0$) and a high-mass cutoff at $M_{\rm max} \simeq 100$--$150~{\rm M_\odot}$
$(M_{\rm max} \gtrsim 250~{\rm M_\odot})$. Given the conditions, core-collapse
SNe with $M_\ast \gtrsim 70~{\rm M_\odot}$ and pair-instability SNe give a
major contribution for iron enrichment. Such top-heavy stellar IMFs would be a
natural consequence from mass growth of stars formed in dense AGN disks under
Bondi-like gas accretion that is regulated by feedback at $M_\ast \gtrsim
10~{\rm M_\odot}$. The massive stellar population formed in AGN disks also
leave stellar-mass black hole remnants, whose mergers associated with
gravitational-wave emission account for at most 10 \% of the merger rate
inferred from LIGO/Virgo observations to simultaneously explain the high ${\rm
[Fe/Mg]}$ ratio with metal ejection.",2112.06151v1
2022-03-16,"Measurements of protons and charged pions emitted from $ν_μ$ charged-current interactions on iron at a mean neutrino energy of 1.49$\,$GeV using a nuclear emulsion detector","This study conducted an analysis of muons, protons, and charged pions emitted
from $\nu_{\mu}$ charged-current interactions on iron using a nuclear emulsion
detector. The emulsion detector with a 65$\,$kg iron target was exposed to a
neutrino beam corresponding to 4.0$\times$10$^{19}$ protons on target with a
mean neutrino energy of 1.49$\,$GeV. The measurements were performed at a
momentum threshold of 200 (50)$\,$MeV/$c$ for protons (pions), which are the
lowest momentum thresholds attempted up to now. The measured quantities are the
multiplicities, emission angles, and momenta of the muons, protons, and charged
pions. In addition to these inclusive measurements, exclusive measurements such
as the muon-proton emission-angle correlations of specific channels and the
opening angle between the protons of CC0$\pi$2$p$ events were performed. The
data were compared to Monte Carlo (MC) predictions and some significant
differences were observed. The results of the study demonstrate the capability
of detailed measurements of neutrino-nucleus interactions using a nuclear
emulsion detector to improve neutrino interaction models.",2203.08367v3
2022-07-06,Atomic diffusion and turbulent mixing in solar-like stars: Impact on the fundamental properties of FG-type stars,"Chemical composition is an important factor that affects stellar evolution.
The element abundance on the stellar surface evolves along the lifetime of the
star because of transport processes, including atomic diffusion. However,
models of stars with masses higher than about 1.2Msun predict unrealistic
variations at the stellar surface. This indicates the need for competing
transport processes that are mostly computationally expensive for large grids
of stellar models. The purpose of this study is to implement turbulent mixing
in stellar models and assess the possibility of reproducing the effect of
radiative accelerations with turbulent mixing for elements like iron in order
to make the computation of large grids possible. We computed stellar models
with MESA and assessed the effects of atomic diffusion (with radiative
acceleration) in the presence of turbulent mixing. We parametrised the effect
of radiative accelerations on iron with a turbulent diffusion coefficient.
Finally, we tested this parametrisation by modelling two F-type stars of the
Kepler Legacy sample. We found that, for iron, a parametrisation of turbulent
mixing that simulates the effect of radiative acceleration is possible. This
leads to an increase in the efficiency of the turbulent mixing to counteract
the effect of gravitational settling. This approximation does not affect
significantly the surface abundances of the other elements we studied, except
for oxygen and calcium. We demonstrate that this parametrisation has a
negligible impact on the accuracy of the seismic properties inferred with these
models. Moreover, turbulent mixing makes the computation of realistic F-type
star models including the effect atomic diffusion possible. This leads to
differences of about 10% in the inferred ages compared to results obtained with
models that neglect these processes.",2207.02779v1
2022-07-28,Symmetry protected 1D chains in mixed-valence iron oxides,"During the last decade of high-pressure research a whole new series of iron
oxides was discovered, like Fe$_4$O$_5$, Fe$_5$O$_6$, Fe$_7$O$_9$ etc.,
featuring closely related structures with arrays of one-dimensional (1D) chains
of trigonal prisms embedded between slabs of octahedra. Here, we develop a
unified approach to the series based on a specific crystallographic generation
mechanism which predicts the structures of these oxides and naturally
classifies them in terms of the slab cycle. When including magnetic
interactions, we show that the 1D chains have a symmetry protection against
magnetic perturbations from the iron ions in the slabs, and that the slab size
determines the type of magnetic order, which is either ferromagnetic or
antiferromagnetic. Dynamical mean-field theory calculations reveal the
orbitally selective Mott state of the Fe ions and tendency of conductivity to
low-dimensional behavior with particular enhancement along the 1D chains.
Across the series, the decoupling of the chains increases, and so with the
inherent charge ordering of the slabs, these structures have the potential to
allow experimental realization of the model system of coupled 1D wires. We
point out the possibility to stabilize these compounds in the thin-film form
that, together with a wide range of possible ionic substitutions and fact that
these compounds are recoverable at ambient pressure, makes them a very
promising platform to engineer physical systems with interesting
magnetotransport phenomena, as corroborated by the recent discovery of quantum
Hall effect in ZrTe$_5$.",2207.14111v1
2022-08-01,"Sustainable steel through hydrogen plasma reduction of iron ore: process, kinetics, microstructure, chemistry","Fe- and steelmaking is the largest single industrial CO2 emitter, accounting
for 6.5% of all CO2 emissions on the planet. This fact challenges the current
technologies to achieve carbon-lean steel production and to align with the
requirement of a drastic reduction of 80% in all CO2 emissions by around 2050.
Thus, alternative reduction technologies have to be implemented for extracting
iron from its ores. The H-based direct reduction has been explored as a
sustainable route to mitigate CO2 emissions, where the reduction kinetics of
the intermediate oxide product FexO wustite into Fe is the rate-limiting step
of the process. The total reaction has an endothermic net energy balance.
Reduction based on a H plasma may offer an attractive alternative. Here, we
present a study about the reduction of hematite using H plasma. The evolution
of both, chemical composition and phase transformations was investigated in
several intermediate states. We found that hematite reduction kinetics depends
on the balance between the initial input mass and the arc power. For an
optimized input mass-arc power ratio, complete reduction was obtained within 15
min of exposure to the H plasma. The wustite reduction is also the
rate-limiting step towards complete reduction. Nonetheless, the reduction
reaction is exothermic, and its rates are comparable with those found in
H-based direct reduction. Chemical and microstructure analysis revealed that
the gangue elements partition to the remaining oxide regions, probed by energy
dispersive spectroscopy and atom probe tomography. Si-enrichment was observed
in the interdendritic fayalite domains, at the wustite/Fe hetero-interfaces and
in the primarily solidified oxide particles inside the Fe. With proceeding
reduction, however, such elements are gradually removed from the samples so
that the final iron product is nearly free of gangue-related impurities.",2208.00661v1
2022-09-27,3D non-LTE iron abundances in FG-type dwarfs,"Spectroscopic measurements of iron abundances are prone to systematic
modelling errors. We present 3D non-LTE calculations across 32 STAGGER-grid
models with effective temperatures from 5000 K to 6500 K, surface gravities of
4.0 dex and 4.5 dex, and metallicities from $-$3 dex to 0 dex, and study the
effects on 171 Fe I and 12 Fe II optical lines. In warm metal-poor stars, the
3D non-LTE abundances are up to 0.5 dex larger than 1D LTE abundances inferred
from Fe I lines of intermediate excitation potential. In contrast, the 3D
non-LTE abundances can be 0.2 dex smaller in cool metal-poor stars when using
Fe I lines of low excitation potential. The corresponding abundance differences
between 3D non-LTE and 1D non-LTE are generally less severe but can still reach
$\pm$0.2 dex. For Fe II lines the 3D abundances range from up to 0.15 dex
larger, to 0.10 dex smaller, than 1D abundances, with negligible departures
from 3D LTE except for the warmest stars at the lowest metallicities. The
results were used to correct 1D LTE abundances of the Sun and Procyon (HD
61421), and of the metal-poor stars HD 84937 and HD 140283, using an
interpolation routine based on neural networks. The 3D non-LTE models achieve
an improved ionisation balance in all four stars. In the two metal-poor stars,
they remove excitation imbalances that amount to 250 K to 300 K errors in
effective temperature. For Procyon, the 3D non-LTE models suggest [Fe/H] = 0.11
$\pm$ 0.03, which is significantly larger than literature values based on
simpler models. We make the 3D non-LTE interpolation routine for FG-type dwarfs
publicly available, in addition to 1D non-LTE departure coefficients for
standard MARCS models of FGKM-type dwarfs and giants. These tools, together
with an extended 3D LTE grid for Fe II from 2019, can help improve the accuracy
of stellar parameter and iron abundance determinations for late-type stars.",2209.13449v3
2022-10-24,High-precision abundances of first population stars in NGC 2808: confirmation of a metallicity spread,"Photometric investigations have revealed that Galactic globular clusters
exhibit internal metallicity variations amongst the so-called first-population
stars, until now considered to have a homogeneous initial chemical composition.
This is not fully supported by the sparse spectroscopic evidence, which so far
gives conflicting results. Here, we present a high-resolution re-analysis of
five stars in the Galactic globular cluster NGC 2808 taken from the literature.
Target stars are bright red giants with nearly identical atmospheric parameters
belonging to the first population according to their identification in the
chromosome map of the cluster, and we have measured precise differential
abundances for Fe, Si, Ca, Ti, and Ni to the ~0.03 dex level.
  Thanks to the very small uncertainties associated to the differential
atmospheric parameters and abundance measurements, we find that target stars
span a range of iron abundance equal to 0.25 +/- 0.06 dex. The individual
elemental abundances are highly correlated with the position of the star along
the extended sequence described by first population objects in the cluster
chromosome map: bluer stars have a lower iron content. This agrees with
inferences from the photometric analysis.
  The differential abundances for all other elements also show statistically
significant ranges that point to intrinsic abundance spreads. The Si, Ca, Ti,
and Ni variations are highly correlated with iron variations and the total
abundance spreads for all elements are consistent within the error bars. This
suggests a scenario in which short-lived massive stars exploding as supernovae
contributed to the self-enrichment of the gas in the natal cloud while star
formation was still ongoing.",2210.13369v1
2023-01-07,Changes in the distribution of circum-binary material around the HMXB GX 301-2 during a rapid spin-up episode of the neutron star,"Some accretion powered X-ray pulsars with supergiant companion stars undergo
occasional rapid spin-up episodes that last for weeks to a few months. We
explore the changes in the accretion environment of the pulsar GX 301-2 during
its latest 80 days long spin-up episode in 2019 when the spin frequency of the
pulsar increased by ~2% over two orbits of the binary. By performing
time-resolved spectroscopy with the MAXI/GSC spectra of the source, we
estimated the equivalent hydrogen column density and equivalent width of the
iron fluorescence line during the spin-up episode, and compared them with the
long-term average values estimated by orbital-phase resolved spectroscopy. The
measured absorption column density during the spin-up episode is about twice
that of an average orbit, while the equivalent width of the iron line is less
than half of an average orbit. Though the spin-up episode started immediately
after a pre-periastron flare and lasted for the two consecutive orbits of the
binary, the associated enhancement in luminosity started a few days after the
pre-periastron flare and lasted only during the first orbit, and some
enhancement was seen again during the pre-periastron passage of the second
orbit. The absorption column density and iron line equivalent width vary
throughout the spin-up episode and are distinct from an average orbit. These
observations indicate a significant change in the accretion and reprocessing
environment in GX 301-2 during the spin-up episode and may hold important clues
for the phenomenon in this source and several other sources with supergiant
companions.",2301.02815v1
2023-03-09,Saline bolus for negative contrast perfusion imaging in magnetic particle imaging,"Objective. Magnetic Particle Imaging (MPI) is capable of high temporal
resolution measurements of the spatial distribution of magnetic nanoparticles
and therefore well suited for perfusion imaging, which is an important tool in
medical diagnosis. Perfusion imaging in MPI usually requires a fresh bolus of
tracer material to capture the key signal dynamics. Here, we propose a method
to decouple the imaging sequence from the injection of additional tracer
material, without further increasing the administered iron dose in the body
with each image. Approach. A bolus of physiological saline solution without any
particles (negative contrast) diminishes the steady-state concentration of a
long-circulating tracer during passage. This depression in the measured
concentration contributes to the required contrast dynamics. The presence of a
long-circulating tracer is therefore a prerequisite to obtain the negative
contrast. As a quantitative tracer based imaging method, the signal is linear
in the tracer concentration for any location that contains nanoparticles and
zero in the surrounding tissue which does not provide any intrinsic signal.
After tracer injection, the concentration over time (positive contrast) can be
utilized to calculate dynamic diagnostic parameters like perfusion parameters
in vessels and organs. Every acquired perfusion image thus requires a new bolus
of tracer with a sufficiently large iron dose to be visible above the
background. Main results. Perfusion parameters are calculated based on the time
response of the proposed negative bolus and compared to a positive bolus.
Results from phantom experiments show that normalized signals from positive and
negative boli are concurrent and deviations of calculated perfusion maps are
low. Significance. Our method opens up the possibility to increase the total
monitoring time, while minimizing the iron dose per acquired image.",2303.05439v2
2023-03-19,In-situ visualization of local distortions in the high-$T_c$ molecule-intercalated $Li_x(C_5H_5N)_yFe_{2-z}Se_2$ superconductor,"A time-resolved synchrotron X-ray total scattering study sheds light on the
evolution of the different structural length scales involved during the
intercalation of the layered iron-selenide host by organic molecular donors,
aiming at the formation of the expanded lattice $Li_x(C_5H_5N)_yFe_{2-z}Se_2$
hybrid superconductor. The intercalates are found to crystallize in the
tetragonal $ThCr_2Si_2$-type structure at the average level, however, with an
enhanced interlayer iron-selenide spacing (d= 16.2 \r{A}) that accommodates the
heterocyclic molecular spacers. Quantitative atomic pair distribution function
(PDF) analysis at variable times, suggests distorted $FeSe_4$ tetrahedral local
environments that appear swollen with respect to those in the parent
$\beta$-FeSe. Simultaneously acquired, in-situ synchrotron X-ray powder
diffraction data disclose that secondary phases ($\alpha$-Fe and $Li_2Se$),
grow significantly when higher Li-concentration is used in the solvothermal
reaction or when the solution is aged. These observations are in line with the
strongly reducing character of the intercalation medium's solvated electrons
that mediate the defect chemistry of the expanded lattice superconductor. In
the latter, intralayer correlated local distortions indicate electron donating
aspects that reflect in somewhat enlarged Fe-Se bonds. They also reveal a
degree of relief of chemical pressure associated with a large distance between
Fe and Se sheets ('taller' anion height) and a stretched Fe-Fe square planar
topology. The elongation of the latter, derived from the in-situ PDF study,
speaks for a plausible increase in the Fe-site vacancy concentration. The
evolution of the local structural parameters suggests an optimum reaction
window where kinetically stabilized phases resemble the distortions of the
edge-sharing Fe-Se tetrahedra, required for high-$T_c$ in expanded lattice
iron-chalcogenides.",2303.10698v1
2023-05-12,Impact of errors in the magnetic field measurement on the precision determination of neutrino oscillation parameters at the proposed ICAL detector at INO,"The magnetised iron calorimeter (ICAL) detector proposed at the India-based
Neutrino Observatory will be a 51 kton detector made up of 151 layers of 56 mm
thick soft iron with 40 mm air gap in between where the RPCs, the active
detectors, will be placed. The main goal of ICAL is to make precision
measurements of the neutrino oscillation parameters using the atmospheric
neutrinos as source. The charged current interactions of the atmospheric muon
neutrinos and anti-neutrinos in the detector produce charged muons. The
magnetic field, with a maximum value of $\sim$ 1.5 T in the central region of
ICAL, is a critical component since it will be used to distinguish the charges
and determine the momentum and direction of these muons. It is difficult to
measure the magnetic field inside the iron. The existing methods can only
estimate the internal field and hence will be prone to error. This paper
presents the first simulations study of the effect of errors in the measurement
of the magnetic field in ICAL on its physics potential, especially the neutrino
mass ordering and precision measurement of oscillation parameters in the 2--3
sector. The study is a GEANT4-based analysis, using measurements of the
magnetic field at the prototype ICAL detector. We find that there is only a
small effect on the determination of the mass ordering. While local
fluctuations in the magnetic field measurement are well-tolerated, calibration
errors must remain well within 5\% to retain good precision determination of
the parameters $\sin^2\theta_{23}$ and $\Delta m^2_{32}$.",2305.07291v2
2023-06-16,Tailoring defects and nanocrystal transformation for optimal heating power in bimagnetic $Co_yFe_{1-y}O@Co_xFe_{3-x}O_4$ particles,"The effects of cobalt incorporation in spherical heterostructured iron oxide
nanocrystals (NCs) of sub-critical size have been explored by colloidal
chemistry methods. Synchrotron X-ray total scattering methods suggest that
cobalt (Co) substitution in rock salt iron oxide NCs tends to remedy its vacant
iron sites, offering a higher degree of resistance to oxidative conversion.
Self-passivation still creates a spinel-like shell, but with higher volume
fraction of the rock salt Co-containing phase in the core. The higher divalent
metal stoichiometry in the rock salt phase, with increasing Co content, results
in a population of unoccupied tetrahedral metal sites in the spinel part,
likely through oxidative shell creation, involving an ordered defect-clustering
mechanism, directly correlated to the core stabilization. To shed light on the
effects of Co-substitution and atomic-scale defects (vacant sites), Monte Carlo
simulations suggest that designed NCs, with desirable, enhanced magnetic
properties (cf. exchange bias and coercivity), are developed with
magnetocrystalline anisotropy raised at relatively low content of Co ions in
the lattice. Growth of optimally performing candidates combines also a strongly
exchange-coupled system, secured through a high volumetric ratio rock salt
phase, interfaced by a not so defective spinel shell. In view of these
requirements, Specific Absorption Rate (SAR) calculations demonstrate that the
sufficiently protected from oxidation rock salt core and preserved over time
heterostructure, play a key role in magnetically-mediated heating efficacies,
for potential use of such NCs in magnetic hyperthermia applications.",2306.09684v1
2023-06-22,Studying the mass sensitivity of air-shower observables using simulated cosmic rays,"Using CORSIKA simulations, we investigate the mass sensitivity of cosmic-ray
air-shower observables for sites at the South Pole and Malarg\""ue, Argentina,
the respective locations of the IceCube Neutrino Observatory and the Pierre
Auger Observatory. Exact knowledge of observables from air-shower simulations
was used to study the event-by-event mass separation between proton, helium,
oxygen, and iron primary cosmic rays with a Fisher linear discriminant
analysis. Dependencies on the observation site as well as the energy and zenith
angle of the primary particle were studied in the ranges from
$10^{16.0}-10^{18.5}\,$eV and $0^\circ$ to $60^\circ$: they are mostly weak and
do not change the qualitative results. Promising proton-iron mass separation is
achieved using combined knowledge of all studied observables, also when typical
reconstruction uncertainties are accounted for. However, even with exact
measurements, event-by-event separation of intermediate-mass nuclei is
challenging and better methods than the Fisher discriminant and/or the
inclusion of additional observables will be needed. As an individual
observable, high-energy muons ($> 500\,$GeV) provide the best event-by-event
mass discrimination, but the combination of muons of any energy and
$X_{\text{max}}$ provides already a high event-by-event separation between
proton-iron primaries at both sites. We also confirm that the asymmetry and
width parameters of the air-shower longitudinal profile, $R$ and $L$, are mass
sensitive. Only $R$ seems to be suitable for event-by-event mass separation,
but $L$ can potentially be used to statistically determine the proton-helium
ratio. Overall, our results motivate the coincident measurement of several
air-shower observables, including at least $X_{\text{max}}$ and the sizes of
the muonic and electromagnetic shower components, for the next generation of
air-shower experiments.",2306.13246v2
2023-07-19,"Efficiency, Accuracy, and Transferability of Machine Learning Potentials: Application to Dislocations and Cracks in Iron","Machine learning interatomic potentials (ML-IAPs) enable quantum-accurate,
classical molecular dynamics simulations of large systems, beyond reach of
density functional theory (DFT). Yet, their efficiency and ability to predict
systems larger than DFT supercells are not fully explored, posing a question
regarding transferability to large-scale simulations with defects (e.g.
dislocations, cracks). Here, we apply a three-step validation approach to
body-centered-cubic iron. First, accuracy and efficiency are assessed by
optimizing ML-IAPs based on four state-of-the-art ML packages. The Pareto front
of computational speed versus testing root-mean-square-error (RMSE) is
computed. Second, benchmark properties relevant to plasticity and fracture are
evaluated. Their average relative error Q with respect to DFT is found to
correlate with RMSE. Third, transferability of ML-IAPs to dislocations and
cracks is investigated by using per-atom model uncertainty quantification. The
core structures and Peierls barriers of screw, M111 and three edge dislocations
are compared with DFT. Traction-separation curve and critical stress intensity
factor (K_Ic) are also predicted. Cleavage on the pre-existing crack plane is
found to be the zero-temperature atomistic fracture mechanism of pure
body-centered-cubic iron under mode-I loading, independent of ML package and
training database. Quantitative predictions of dislocation glide paths and KIc
can be sensitive to database, ML package, cutoff radius, and are limited by DFT
accuracy. Our results highlight the importance of validating ML-IAPs by using
indicators beyond RMSE. Moreover, significant computational speed-ups can be
achieved by using the most efficient ML-IAP package, yet the assessment of the
accuracy and transferability should be performed with care.",2307.10072v2
2023-11-12,Star Formation in Self-gravitating Disks in Active Galactic Nuclei. III. Efficient Production of Iron and Infrared Spectral Energy Distributions,"Strong iron lines are a common feature of the optical spectra of active
galactic nuclei (AGNs) and quasars from $z\sim 6-7$ to the local Universe, and
[Fe/Mg] ratios do not show cosmic evolution. During active episodes, accretion
disks surrounding supermassive black holes (SMBHs) inevitably form stars in the
self-gravitating part and these stars accrete with high accretion rates. In
this paper, we investigate the population evolution of accretion-modified stars
(AMSs) to produce irons and magnesium in AGNs. The AMSs as a new type of stars
are allowed to have any metallicity but without significant loss from stellar
winds since the winds are choked by the dense medium of the disks and return to
the core stars. Mass functions of the AMS population show a pile-up or cutoff
pile-up shape in top-heavy or top-dominant forms if the stellar winds are
strong, consistent with the narrow range of supernovae (SN) explosions driven
by the known pair-instability. This provides an efficient way to produce
metals. Meanwhile, SN explosions support an inflated disk as a dusty torus.
Furthermore, the evolving top-heavy initial mass functions (IMFs) lead to
bright luminosity in infrared bands in dusty regions. This contributes a new
component in infrared bands which is independent of the emissions from the
central part of accretion disks, appearing as a long-term trending of the NIR
continuum compared to optical variations. Moreover, the model can be further
tested through reverberation mapping of emission lines, including LIGO/LISA
detections of gravitational waves and signatures from spatially resolved
observations of GRAVITY+/VLTI.",2311.06782v1
2024-01-18,The 2022 Outburst of IGR J17091-3624: Connecting the exotic GRS 1915+105 to standard black hole X-ray binaries,"While the standard X-ray variability of black hole X-ray binaries (BHXBs) is
stochastic and noisy, there are two known BHXBs that exhibit exotic
`heartbeat'-like variability in their light curves: GRS 1915+105 and IGR
J17091-3624. In 2022, IGR J17091-3624 went into outburst for the first time in
the NICER/NuSTAR era. These exquisite data allow us to simultaneously track the
exotic variability and the corresponding spectral features with unprecedented
detail. We find that as in typical BHXBs, the outburst began in the hard state,
then the intermediate state, but then transitioned to an exotic soft state
where we identify two types of heartbeat-like variability (Class V and a new
Class X). The flux-energy spectra show a broad iron emission line due to
relativistic reflection when there is no exotic variability, and absorption
features from highly ionized iron when the source exhibits exotic variability.
Whether absorption lines from highly ionized iron are detected in IGR
J17091-3624 is not determined by the spectral state alone, but rather is
determined by the presence of exotic variability; in a soft spectral state,
absorption lines are only detected along with exotic variability. Our finding
indicates that IGR J17091-3624 can be seen as a bridge between the most
peculiar BHXB GRS 1915+105 and `normal' BHXBs because it alternates between the
conventional and exotic behavior of BHXBs. We discuss the physical nature of
the absorbing material and exotic variability in light of this new legacy
dataset.",2401.10192v1
2024-03-15,Asteroid reflectance spectra from Gaia DR3: Near-UV in primitive asteroids,"In the context of charge-coupled devices (CCDs), the ultraviolet (UV) region
has mostly remained unexplored after the 1990s. Gaia DR3 offers the community a
unique opportunity to explore tens of thousands of asteroids in the near-UV as
a proxy of the UV absorption. This absorption has been proposed in previous
works as a diagnostic of hydration, organics, and space weathering. Aims. In
this work, we aim to explore the potential of the NUV as a diagnostic region
for primitive asteroids using Gaia DR3. We used a corrective factor over the
blue part of Gaia spectra to erase the solar analog selection effect. We
identified an artificial relation between the band noise and slope and applied
a signal-to-noise ratio (S/N) threshold for Gaia bands. Meeting the quality
standards, we employed a Markov chain Monte Carlo (MCMC) algorithm to compute
the albedo threshold, maximizing primitive asteroid inclusion. Utilizing one-
and two-dimensional (1D and 2D) projections, along with
dimensionality-reduction methods (such as PCA and UMAP), we identified
primitive asteroid populations. We uncovered: (a) the first observational
evidence linking UV absorption to the 0.7 {\mu}m band, tied to hydrated
iron-rich phyllosilicates; and (b) a 2D space revealing a split in C-type
asteroids based on spectral features, including UV absorption. The computed
average depth (3.5 +- 1.0 %) and center (0.70 +- 0.03 {\mu}m) of the 0.7 {\mu}m
absorption band for primitive asteroids observed with Gaia is in agreement with
the literature values. In this paper, we shed light on the importance of the UV
absorption feature to discriminate among different mineralogies (i.e.,
iron-rich phyllosilicates vs. iron-poor) or to identify taxonomies that are
conflated in the visible (i.e., F-types vs. B-types). We have shown that this
is a promising region for diagnostic studies of the composition of primitive
asteroids.",2403.10321v1
1993-01-29,A Possible Forest of Emission Lines from Proto-galaxies,"The possibility of detecting proto-galaxies in the UV band is pointed out,
assuming that galaxy formation occured at z $\sim 5-6$. It is shown that the
diffuse gas in collapsing galaxy sized objects with temperatures $\sim
10^{6\pm0.5}$ K, and with a modest amount of metallicity, should copiously
produce emission lines from highly ionized Iron atoms. The expected luminosity
from models of galaxy formation is compared with the sensitivity of HST.",9301012v1
1995-10-23,X-ray spectra from convective photospheres of neutron stars,"We present first results of modeling convective photospheres of neutron
stars. We show that in photospheres composed of the light elements convection
arises only at relatively low effective temperatures (< 3-5*10^4 K), whereas in
the case of iron compositon it arises at < 3*10^ K. Convection changes the
depth dependence of the photosphere temperature and the shapes of the emergent
spectra. Thus, it should be taken into account for the proper interpretation of
EUV/soft-X-ray observations of the thermal radiation from neutron stars.",9510116v2
1997-01-22,Two-phase pair corona model for AGN: physical modelling and diagnostics,"The predictions of the two-phase accretion disc-corona models for active
galactic nuclei are compared with observations. We discuss the possibility to
use X-ray spectral slopes, equivalent widths of the iron line, and the observed
flux-spectral index correlation as diagnostics of the X/gamma-ray source
compactness and geometry as well as of the cold disc temperature. As an example
of the application of the modelling tools, we use XSPEC to fit the broad-band
data of Seyfert 1 galaxy, IC4329A, with a theoretical spectrum from a
hemisphere-corona.",9701168v1
1997-03-04,RXTE Observation of the Seyfert 2 Galaxy NGC4507,"Preliminary results of the RXTE observation of the Seyfert 2 Galaxy NGC4507
are presented. The observed broadband [4-100 keV] spectrum is intrinsically
hard (Gamma = 1.2); an iron line is detected with a relatively high equivalent
width (EW = 400 eV). The remaining calibration uncertanties are briefly
discussed, as well as the scientific implications of our results.",9703019v1
1997-05-12,The most Distant [OIII]-emitting Quasar PKS 1937-101 at redshift 3.8,"We report the discovery of a high-z quasar with unambiguous [OIII]5007
emission; PKS 1937-101 at redshift 3.8. This quasar, however, shows little
evidence for rest-frame ultraviolet and optical FeII emission. It is thus shown
that PKS 1937-101 does not belong to a class of super iron-rich high-z quasars
reported by Elston, Thompson, & Hill (1994). The epoch of major star formation
in the host galaxy is discussed briefly.",9705075v1
1997-08-08,A depression before a bump in the highest energy cosmic ray spectrum,"We re-examine the interaction of ultra high energy nuclei with the microwave
background radiation. We find that the giant dipole resonance leaves a new
signature in the differential energy spectrum of iron sources located around 3
Mpc: A depression before the bump which is followed by the expected cutoff.",9708082v2
1997-10-07,Fe I line shifts in the optical spectrum of the Sun,"New improvements in the measurement of both the optical solar spectrum and
laboratory wavelengths for lines of neutral iron are combined to extract
central wavelength shifts for 1446 lines observed in the Sun. This provides the
largest available database of accurate solar wavelengths useful as a reference
for comparison with other solar-type stars. It is shown how the velocity shifts
correlate with line strength, approaching a constant value, close to zero, for
lines with equivalent widths larger than 200 mA.",9710066v1
1998-05-15,The double-lined spectroscopic binary alpha Andromedae: orbital elements and elemental abundances,"We performed a spectroscopic study of the SB2 Mercury-Manganese star alpha
And. Our measurements of the secondary's radial velocities result in improved
orbital elements. The secondary shows abundances typical of the metallic-line
stars: a Ca deficiency, small overabundances of the iron-peak elements, and 1.0
dex overabundances of Sr and Ba.",9805205v1
1998-05-27,Strong gravity and X-ray spectroscopy,"This paper reviews the effects of general relativity in an X-ray spectrum
reflected from a cold matter accreting onto a black hole. The spectrum consists
of the iron K$\alpha$ line and the Compton reflection. We sketch the overall
picture of radiative processes in the central parts of the accretion flow with
relation to the relativistic effects derived from the discrete features in the
X-ray spectrum. We discuss implications for detection of relativistic effects
and computational tools of spectral analysis.",9805328v1
1999-05-25,"First results on characterization of Cerenkov images through combined use of Hillas, fractal and wavelet parameters","Based on Monte Carlo simulations using the CORSIKA code, it is shown that
Cerenkov images produced by ultrahigh energy $\gamma$-rays and cosmic ray
nuclei (proton, Neon and Iron) are fractal in nature. The resulting
multifractal and wavelet moments when employed in association with the
conventional Hillas parameters as inputs to a properly-trained artificial
neural network are found to provide more efficient primary characterization
scheme than the one based on the use of Hillas or fractal parameters alone.",9905312v1
1999-11-24,Discovery of molecular hydrogen in a high-velocity cloud of the Galactic halo,"We report the discovery of molecular hydrogen absorption in a Galactic
high-velocity cloud (HVC) in the direction of the Large Magellanic Cloud. For
the same HVC we derive an iron abundance which is half of the solar value.
Thus, all evidence points to a Galactic origin for high-velocity cloud complex
in front of the LMC.",9911455v1
1999-11-30,"Prompt Iron Enrichment, Two r-Process Components, and Abundances in Very Metal-Poor Stars","We present a model to explain the wide range of abundances for heavy
r-process elements (mass number A > 130) at low [Fe/H]. This model requires
rapid star formation and/or an initial population of supermassive stars in the
earliest condensed clots of matter to provide a prompt or initial Fe inventory.
Subsequent Fe and r-process enrichment was provided by two types of supernovae:
one producing heavy r-elements with no Fe on a rather short timescale and the
other producing light r-elements (A < or = 130) with Fe on a much longer
timescale.",9911526v1
2000-03-29,A Comparative Study of the Depth of Maximum of Simulated Air Shower Longitudinal Profiles,"A comparative study of simulated air shower longitudinal profiles is
presented. An appropriate thinning level for the calculations is first
determined empirically. High statistics results are then provided, over a wide
energy range, (10^14.0 to 10^20.5 eV), for proton & iron primaries, using four
combinations of the MOCCA & CORSIKA program frameworks, and the SIBYLL & QGSJET
high energy hadronic interaction models. These results are compared to existing
experimental data. The way in which the first interaction controls Xmax is
investigated, as is the distribution of Xmax.",0003442v2
2000-04-20,X-rays from Radio-Galaxies: BeppoSAX Observations,"We briefly review BeppoSAX observations of X-ray bright radio-galaxies. Their
X-ray spectra are quite varied, and perhaps surprisingly, any similarity
between radio-loud AGN and Seyfert galaxies is the exception rather than the
rule. When detected, reprocessing features (iron line and reflection) are
generally weak, suggesting two possible scenarios: either: (1) non-thermal
(jet?) radiation dilutes the X-ray emission from the disk in radio-loud
objects, or (2) the solid angle subtended by the X-ray reprocessing material is
smaller in radio-loud than in radio-quiet AGN due to different characteristics
of the accretion disk itself.",0004291v1
2000-05-08,Properties of Warm absorbers in Narrow-Line Seyfert 1 galaxies,"We present a study of the X-ray properties of several NLS1 galaxies, focusing
on their warm absorbers. In the first part, we discuss properties of dusty and
dust-free warm absorbers in NLS1s, and study their potential contribution to
high-ionization optical iron lines. In the second part, we summarize our work
on the exceptional spectral variability of the NLS1 galaxy RX J0134.3-4258
(from Gamma about -4.4 in the ROSAT all-sky survey observation, to about -2.2
in our subsequent pointed observation).",0005172v1
2000-06-05,"A pot of gold at the end of the cosmic ""raynbow""?","We critically review the common belief that ultrahigh energy cosmic rays are
protons or atomic nuclei with masses not exceeding that of iron. We find that
heavier nuclei are indeed possible, and discuss possible sources and
acceleration mechanisms for such primaries. We also show detailed simulations
of extensive air showers produced by ``superheavy'' nuclei, and discuss
prospects for their detection in future experiments.",0006071v1
2000-06-19,Abundances and Kinematics of Field Halo and Disk Stars I: Observational Data and Abundance Analysis,"We describe observations and abundance analysis of a high-resolution,
high-S/N survey of 168 stars, most of which are metal-poor dwarfs. We follow a
self-consistent LTE analysis technique to determine the stellar parameters and
abundances, and estimate the effects of random and systematic uncertainties on
the resulting abundances. Element-to-iron ratios are derived for key alpha,
odd, Fe-peak, r- and s-process elements. Effects of Non-LTE on the analysis of
Fe I lines are shown to be very small on the average. Spectroscopically
determined surface gravities are derived that are generally close to those
obtained from Hipparcos parallaxes.",0006260v1
2000-09-18,Age-metallicity relation and Chemical evolution of the LMC from UVES spectra of Globular Cluster giants,"We report on the first high-resolution spectroscopy of 10 giants in LMC
Globular Clusters in a wide age range, obtained with the newly commissioned
spectrograph UVES at VLT UT2. These observations are used to derive oxygen and
iron content of these clusters, and the abundances are then used to cast a more
precise view, not only on the age-metallicity relation in the LMC, but also on
the chemical evolution of this dwarf irregular galaxy.",0009273v1
2000-09-20,The BeppoSAX observation of Mrk 766,"The Narrow Line Seyfert 1 galaxy Mrk 766 has been observed by BeppoSAX on May
1997. The source was fairly variable, both in flux and spectrum, during the
observation. The variability is the largest around 2 keV, possibly due to
variations in the warm absorber properties. An oxygen line is clearly detected,
at least in the first part of the observation. An edge around 7.5 keV, coupled
with the lack of any detectable iron line, suggests either reprocessing of the
primary X-rays by a mildly ionized disc or absorption by a further, thicker and
more ionized material.",0009322v1
2000-11-24,Lithium-Beryllium-Boron and Oxygen in the early Galaxy,"Oxygen is a much better evolutionary index than iron to follow the history of
Lithium-Beryllium-Boron (LiBeB) since it is the main producer of these light
elements at least in the early Galaxy. The O-Fe relation is crucial to the
determination of the exact physical process responsible for the LiBeB
production. Calculated nucleosynthetic yields of massive stars, estimates of
the energy cost of Be production, and above all recent observations reported in
this meeting seem to favor a mechanism in which fast nuclei enriched into He, C
and O arising from supernovae are accelerated in superbubbles and fragment on H
and He in the interstellar medium.",0011449v1
2001-02-27,Variable line profiles due to non-axisymmetric patterns in an accretion disc around a rotating black hole,"We have explored spectral line profiles due to spiral patterns in accretion
discs around black holes. A parametrization was employed for the shape and
emissivity of spiral waves, which can be produced by non-axisymmetric
perturbations affecting the disc density and ionization structure. The effects
of the light-travel time, energy shift, and gravitational focusing near to a
rotating black hole were taken into account. A high-resolution ray-tracing code
was used to follow the time variations of the synthetic line profile. A variety
of expected spectral features were examined and the scheme applied to a broad
iron line observed in MCG-6-30-15.",0102460v1
2001-03-21,An iterative technique for solving equations of statistical equilibrium,"Superlevel partitioning is combined with a simple relaxation procedure to
construct an iterative technique for solving equations of statistical
equilibrium. In treating an $N$-level model atom, the technique avoids the
$N^{3}$ scaling in computer time for direct solutions with standard linear
equation routines and also does not fail at large $N$ due to the accumulation
of round-off errors. In consequence, the technique allows detailed model atoms
with $N \ga 10^{3}$, such as those required for iron peak elements, to be
incorporated into diagnostic codes for analysing astronomical spectra. Tests
are reported for a 394-level Fe II ion and a 1266-level Ni I--IV atom.",0103338v1
2001-03-27,X-rays and accretion discs as probes of the strong gravity of black holes,"The observations and interpretation of broad iron lines in the X-ray spectra
of Seyfert 1 galaxies are reviewed. The line profiles observed from
MCG--6-30-15 and NGC 3516 show extended red wings to the line explained by
large gravitational redshifts. The results are consistent with the emission
expected from an X-ray irradiated flat accretion disc orbiting very close to a
black hole. Results from XMM-Newton and Chandra are presented and the
possibility of broad oxygen lines discussed.",0103438v1
2001-06-13,Non-pulsing emission from X-ray pulsars,"Results of GRANAT/ART-P observations of three X-ray pulsars in non-pulsing
states are presented: 1) a statistically significant non-pulsing flux with a
simple power-law spectrum was detected during the ``off''- state of Her X-1; 2)
a significant (13 $\sigma$) non-pulsing flux with a strong iron emission line
at energies ~ 6.7-6.9 keV was detected during the eclipse ingress of Cen X-3;
3) a weak non-pulsing flux was detected during the X-ray eclipse of Vela X-1,
which probably resulted from scattering of the pulsar emission in the stellar
wind of an optical star.",0106237v1
2001-11-04,Polarization of X-ray emission from the Sgr B2 cloud,"The Sgr B2 giant molecular cloud is claimed to be an ""X-ray reflection
nebula"" - the reprocessing site of a powerful flare of the Sgr A* source,
occurred few hundred years ago. The shape of the X-ray spectrum and the
strength of the iron fluorescent line support this hypothesis. We argue that
the most clean test of the origin of X-rays from Sgr B2 would be a detection of
polarized emission from this source.",0111065v1
2001-12-17,Probing the Central Engine of the Narrow-Line Seyfert 1 Galaxies,"The central engine of the the Narrow Line Seyfert 1 galaxies is being probed.
We use the ASCA and RXTE data to model the X-ray primary continuum as well as
the reflected component and iron $K\alpha$ line. Since these are strongly
coupled, we obtain independent measurements of the disc ionization level and
the orientation dependent reflection amplitude. Using the available Optical/UV
data we also estimate the black hole masses and the $L/L_{Edd}$ ratios, which
are probably related to Boroson & Green eigenvector~1.",0112388v1
2002-06-01,On the Progenitors of Collapsars,"We study the evolution of stars that may be the progenitors of common
(long-soft) GRBs. Bare rotating helium stars, presumed to have lost their
envelopes due to winds or companions, are followed from central helium ignition
to iron core collapse. Including realistic estimates of angular momentum
transport (Heger, Langer, & Woosley 2000) by non-magnetic processes and mass
loss, one is still able to create a collapsed object at the end with sufficient
angular momentum to form a centrifugally supported disk, i.e., to drive a
collapsar engine. However, inclusion of current estimates of magnetic torques
(Spruit 2002) results in too little angular momentum for collapsars.",0206005v1
2002-07-05,"Cosmic ray drift, the second knee and galactic anisotropies","We show that the second knee in the cosmic ray spectrum (i.e. the steepening
occurring at $E\simeq 4\times 10^{17}$ eV) could be related to drift effects
affecting the heaviest nuclear component, the iron group nuclei, in a scenario
in which the knee at $3\times 10^{15}$ eV indicates the onset of drift effects
in the lighter proton component. We also study the anisotropies resulting from
diffusion and drift currents in the Galaxy, showing their potential relevance
to account for the AGASA observations at $E\sim 10^{18}$ eV, before the
extragalactic component becomes dominant.",0207143v1
2002-07-19,Carbon Isotopic Abundances in the Red Giants of Omega Centauri (NGC5139),"Carbon-12 and carbon-13 abundances are measured in eleven red-giant members
of the globular cluster Omega Centauri via observations of first-overtone CO
bands near 2.3 microns. The mean value for the entire sample is <12C/13C>= 4.3
+/-0.4, with nine giants equal, within the errors, to the equilibrium ration of
12C/13C= 3.5. No correlation is found within Omega Cen between 12C/13C and the
abundance of iron. The relation between 12C/13C and other abundance ratios,
such as [O/Fe], {Na/Fe], or [Al/Fe] are also discussed.",0207434v1
2002-07-20,Antimatter in the Universe,"Different scenarios of baryogenesis are briefly reviewed from the point of
view of possibility of generation of cosmologically interesting amount of
antimatter. It is argued that creation of antimatter is possible and natural in
many models. In some models not only anti-helium may be produced but also a
heavier anti-elements and future observations of the latter would be critical
for discovery or establishing stronger upper limits on existence of antimatter.
Incidentally a recent observation of iron-rich quasar may present a support to
one special model of antimatter creation.",0207441v1
2002-11-12,Line Profiles from Different Accretion Engine Geometries,"Line profiles represent an important probe of the geometry and dynamics of
the central accretion engines in AGN. Although a flat disk illuminated from
above can explain the relativistic Fe K alpha line profile in some cases,
current data, plausible disk physics, and future comparison to the iron and
other AGN lines invite some consideration of other geometries. General features
of line profiles calculated fom concave discs, warped discs, thick clumpy
(inflow/outflow) discs, and disks with spiral structure, are briefly
summarized.",0211236v1
2002-11-26,Spectral properties of the X-ray binary pulsar LMC X-4 during different intensity states,"We present spectral variations of the binary X-ray pulsar LMC X-4 observed
with the RXTE/PCA during different phases of its 30.5 day long third period.
Only out of eclipse data were used for this study. The 3-25 keV spectrum,
modeled with high energy cut-off power-law and iron line emission is found to
show strong dependence on the intensity state. Correlations between the Fe line
emission flux and different parameters of the continuum are presented here.",0211558v1
2003-08-29,Iron Line Diagnostics for the GRS 1915+105 Black Hole,"The properties of the broad Fe line detected in two BeppoSAX observations of
the microquasar GRS 1915+105 are summarized.",0308539v1
2003-12-09,The ionization equilibrium of iron in H II regions,"We study the ionization equilibrium of Fe using photoionization models that
incorporate improved values for the ionization and recombination cross-sections
and the charge-exchange rates for the Fe ions. The previously available
photoionization models predict concentrations of Fe3+ which are a factor of 3-8
higher than the values inferred from emission lines of [Fe III] and [Fe IV].
Our new models reduce these discrepancies to factors of 2-5. We discuss the
possible reasons behind the remaining discrepancies and present an updated
ionization correction factor for obtaining the Fe abundance from the Fe++
abundance.",0312246v1
2004-01-16,Modeling AGN spectra with PHOENIX: a self-consistent approach,"We find that spectra of certain Iron Low Ionization Broad Absorption Line
(FeLOBAL) QSOs, which are characterized by low--ionization emission and blue
shifted absorption lines, can be well matched with the spectral synthesis code
SYNOW. SYNOW is a resonance scattering code and assumes that line emission
comes from a single line forming region. This interpretation is novel as
traditionally line emission and absorption in BALQSOs are thought to come from
two different regions. We extend this analysis by using the detailed PHOENIX
code to model the spectra. We present a SYNOW fit and a preliminary model
result from PHOENIX.",0401346v1
2004-08-12,Chemical analysis of 24 dusty (pre-)main-sequence stars,"We have analysed the chemical photospheric composition of 24 Herbig Ae/Be and
Vega-type stars in search for the lambda Bootis phenomenon. We present the
results of the elemental abundances of the sample stars. Some of the stars were
never before studied spectroscopically at optical wavelengths. We have
determined the projected rotational velocities of our sample stars.
Furthermore, we discuss stars that depict a (selective) depletion pattern in
detail. HD 4881 and HD 139614 seem to display an overall deficiency. AB Aur and
possibly HD 126367 have subsolar values for the iron abundance, but are almost
solar in silicon. HD 100546 is the only clear lambda Bootis star in our sample.",0408221v1
2004-09-10,The L to T Dwarf Transition,"While the precise mechanism responsible for the L to T dwarf transition
remains unclear, it is clearly caused by changing cloud characteristics. Here
we briefly review data relevant to understanding the nature of the transition
and argue that changing atmospheric dynamics produce the transition by opening
holes through the global iron and silicate cloud decks. Other possibilities,
such as a sudden vertical collapse in these cloud decks are also considered.
Any acceptable model of the L to T transition must ultimately connect changing
cloud properties to the underlying atmospheric dynamics.",0409267v1
2004-10-27,An Iron-Rich Sun and Its Source of Energy,"Mass-fractionation enriches light elements and the lighter isotopes of each
element at the solar surface, making a photosphere that is 91 percent H and 9
percent He. The solar interior consists mostly of elements that comprise 99
percent of ordinary meteorites (Fe, O, Ni, Si, S, Mg and Ca) elements made in
the deep interior of a supernova. Solar energy arises from a series of nuclear
reactions triggered by neutron-emission from the collapsed supernova core on
which the Sun formed. Solar mass-fractionation, solar neutrinos, and the annual
solar-wind outpouring of 3 E43 H atoms from the solar surface are by-products
of solar luminosity.",0410646v1
2004-11-04,"Filamentary jets as a cosmic-ray ""Zevatron""","Strong, anisotropic turbulence reflecting magnetized filaments is considered,
to model the diffusive acceleration of particles by shock waves in active
galactic nucleus jets. We address that at knot A of the nearby M87 jet, the
shock involving the filamentary turbulence can accelerate an iron nucleus to
zetta-eV (ZeV; 10^{21} eV) ranges. A smaller value of the particle diffusion
coefficient is found to be essential to achieve a ZeV cosmic-ray accelerator, a
""Zevatron.""",0411101v3
2005-01-23,Supernova Rates in Galaxy Clusters,"Measurements of SN rates in different environments and redshifts can shed
light on the nature of SN-Ia progenitors, star formation history, and chemical
enrichment history. I summarize some recent work by our group in this area, and
discuss the implications. The current evidence favors production of most of the
iron in the ICM (and perhaps everywhere) by core-collapse SNe, rather than
SNe-Ia. These SNe may have been produced by the first, top-heavy-IMF,
generation of stars that reionized the Universe. Improved rate measurements can
sharpen the picture, and I describe our recent efforts in this direction.",0501492v1
2005-02-24,The polarized electron target as a new solar-neutrino detector,"In this paper, we analyze the scattering of solar neutrinos on the polarized
electron target, and predict how the effect of parity violation in weak
interactions may help to distinguish neutrino signal from detector background.
We indicate that the knowledge of the Sun motion across the sky is sufficient
to predict the day/night asymmetry in the $(\nu_ee^-)$ scattering on the
polarized electron target. To make this detection feasible, the polarized
electron target for solar neutrinos needs to be build from magnetic materials,
e.g. from ferromagnetic iron foils, paramagnetic scintillator crystals or
scintillating ferrofluids.",0502522v1
2005-04-12,ASCA and XMM-Newton Observations of A2029,"The X-ray data of A2029 obtained with XMM-Newton show no evidence of an
embedded AGN in the central region of this cluster, which was suggested from
the analysis of restored ASCA image data, although some hot spots are seen
within or around the central cD galaxy. The absence of AGN at the cluster
center is consistentent with the result of Chandra observations. Radial
profiles of the iron abundance and the 2D (surface) temperature obtained from
the XMM-Newton data are in good agreement with the Chandra data as a whole.",0504268v1
2005-07-12,Disentangling the composite continuum of symbiotic binaries I. S-type systems,"We describe a method of disentangling the composite,0.12-5 microns continuum
of symbiotic binaries.The observed SED is determined by the IUE/HST archival
spectra and flux-points corresponding to the optical UBVRI and infrared JHKLM
photometric measurements. The modeled SED is given by superposition of fluxes
from the cool giant, hot stellar source and nebula including the effect of the
Rayleigh scattering process and considering influence of the iron curtain
absorptions.We applied this method to 21 S-type symbiotic stars during
quiescence, activity and eclipses.",0507272v1
2005-09-08,"HE1327-2326, an unevolved star with [Fe/H]<-5.0. I. A Comprehensive Abundance Analysis","We present the elemental abundances of HE1327-2326, the most iron-deficient
star known, determined from a comprehensive analysis of spectra obtained with
the Subaru Telescope High Dispersion Spectrograph.",0509206v1
2005-12-05,Nonideal strongly magnetized plasmas of neutron stars and their electromagnetic radiation,"We study the equation of state, polarization and radiation properties for
nonideal, strongly magnetized plasmas which compose outer envelopes of magnetic
neutron stars. Detailed calculations are performed for partially ionized
hydrogen atmospheres and for condensed hydrogen or iron surfaces of these
stars. This is a companion paper to astro-ph/0511803",0512088v1
2005-12-27,"Observations of H-alpha, iron, and oxygen lines in B, Be, and shell stars","We have carried out a spectroscopic survey of several B, Be, and shell stars
in optical and near-infrared regions. Line profiles of the H-alpha line and of
selected Fe II and O I lines are presented.",0512619v1
2006-05-06,"Abundances of s-process elements in planetary nebulae: Br, Kr & Xe","We identify emission lines of post-iron peak elements in very high
signal-to-noise spectra of a sample of planetary nebulae. Analysis of lines
from ions of Kr and Xe reveals enhancements in most of the PNe, in agreement
with the theories of s-process in AGB star. Surprisingly, we did not detect
lines from Br even though s-process calculations indicate that it should be
produced with Kr at detectable levels.",0605181v1
2006-10-01,HST and FUSE Spectroscopy of the DAO-type Central Star LS V+4621,"The DAO-type white dwarf LS V+4621 is the hydrogen-rich central star of the
possible planetary nebula Sh 2-216. We have taken high-resolution, high-S/N
ultraviolet spectra with STIS aboard the HST and FUSE in order to constrain its
photospheric parameters. A detailed spectral analysis by means of
state-of-the-art NLTE model-atmosphere techniques is presented which includes
the determination the individual abundances of iron-group elements.",0610019v1
2006-10-07,General Relativity effects and line emission,"General Relativity effects (gravitational redshift, light bending, ...)
strongly modify the characteristics of the lines emitted close to the Black
Hole in Active Galactic Nuclei and Galactic Black Hole systems. These effects
are reviewed and illustrated, with particular emphasis on line emission from
the accretion disc. Methods, based on the iron line, to measure the two
astrophysically relevant parameters of a Black Hole, the mass and spin, are
briefly discussed.",0610224v1
2006-11-16,A Sr-Rich Star on the Main Sequence of Omega Centauri,"Abundance ratios relative to iron for carbon, nitrogen, strontium and barium
are presented for a metal-rich main sequence star ([Fe/H]=--0.74) in the
globular cluster omega Centauri. This star, designated 2015448, shows depleted
carbon and solar nitrogen, but more interestingly, shows an enhanced abundance
ratio of strontium [Sr/Fe] ~ 1.6 dex, while the barium abundance ratio is
[Ba/Fe]<0.6 dex. At this metallicity one usually sees strontium and barium
abundance ratios that are roughly equal. Possible formation scenarios of this
peculiar object are considered.",0611509v1
2006-11-29,Spectropolarimetric diagnostics of thermonuclear supernova explosions,"Even at extragalactic distances, the shape of supernova ejecta can be
effectively diagnosed by spectropolarimetry. We present here results for 17
Type Ia supernovae that allow a statistical study of the correlation among the
geometric structures and other observable parameters of Type Ia supernovae.
These observations suggest that their ejecta typically consist of a smooth,
central iron rich core and an outer layer with chemical asymmetries. The degree
of this peripheral asphericity is correlated with the light-curve decline rate
of Type Ia supernovae. These observations lend strong support to
delayed-detonation models of Type Ia supernovae.",0611902v1
2007-03-20,Limits on iron-dominated fallback disk in SN 1987A,"The non-detection of a point source in SN1987A imposes an upper limit for the
optical luminosity of L=2L_sun. This limits the size of a possible fallback
disk around the stellar remnant. Assuming a steady-state thin disk with
blackbody emission requires a disk smaller than 100,000 km if the accretion
rate is at 30% of the Eddington rate (Graves et al. 2005). We have performed
detailed non-LTE radiation transfer calculations to model the disk spectrum
more realistically. It turns out that the observational limit on the disk
extension becomes even tighter, namely 70,000 km.",0703520v1
1995-07-07,Nonlinear magneto-optical Kerr spectra of thin ferromagnetic iron films calculated with ab initio theory,"Using a spin-polarized full-potential linear muffin-tin orbital method we
present calculations of the nonlinear magneto-optical Kerr effect for thin bcc
Fe films within a slab geometry. Film layer dependent contributions to the Kerr
spectrum are determined. Thus, we calculate the magneto-optical Kerr spectra
for the linear and nonlinear case. Our results show clearly that the Kerr
spectra of thin films are characteristicly different from those at surfaces of
bulk materials. In the case of linear Kerr spectra of Au/Fe(bcc)/Au(001) films
our theoretical results are in good agreement with observed frequency- and
thickness-dependent spectra.",9507018v1
1997-03-04,Magnetic and thermodynamic properties of Sr_{2}LaFe_{3}O_{9},"Using a Dirac-Heisenberg Hamiltonian with biquadratic exchange interactions,
we study the effect of iron disproportionation on the magnetic ordering, and
describe the first-order magnetic transition occurring in the perovskite
Sr_{2}LaFe_{3}O_{9}. Upon fitting the experimental data, we give an estimate of
the exchange integrals for the antiferromagntic and ferromagnetic interactions,
in agreement with previous works on kindered compounds. Spin-wave theory yields
a magnon spectrum with a gapless antiferromagnetic mode together with two
gapped ferromagnetic ones.",9703044v1
1998-05-07,The first principles calculation of transport coefficients,"We demonstrate the practical feasibility of calculating transport
coefficients such as the viscosity of liquids completely from first principles
using the Green-Kubo relations. Results presented for liquid aluminum are shown
to have a statistical error of only ca. 5%. The importance of such calculations
is illustrated by results for a liquid iron-sulfur alloy under Earth's core
conditions, which indicate that the viscosity of the liquid outer core is not
substantially higher than that of typical liquid metals under ambient
conditions.",9805082v1
1999-04-29,First- principle calculations of magnetic interactions in correlated systems,"We present a novel approach to calculate the effective exchange interaction
parameters based on the realistic electronic structure of correlated magnetic
crystals in local approach with the frequency dependent self energy. The analog
of ``local force theorem'' in the density functional theory is proven for
highly correlated systems. The expressions for effective exchange parameters,
Dzialoshinskii- Moriya interaction, and magnetic anisotropy are derived. The
first-principle calculations of magnetic excitation spectrum for ferromagnetic
iron, with the local correlation effects from the numerically exact QMC-scheme
is presented.",9904428v1
1999-08-24,Tunable Charge Density Wave Transport in a Current-Effect Transistor,"The collective charge density wave (CDW) conduction is modulated by a
transverse single-particle current in a transistor-like device. Nonequilibrium
conditions in this geometry lead to an exponential reduction of the depinning
threshold, allowing the CDWs to slide for much lower bias fields. The results
are in excellent agreement with a recently proposed dynamical model in which
''wrinkles'' in the CDW wavefronts are ''ironed'' by the transverse current.
The experiment might have important implications for other driven periodic
media, such as moving vortex lattices or ''striped phases'' in high-Tc
superconductors.",9908339v1
1999-08-26,Magnons in real materials from density-functional theory,"We present an implementation of the adiabatic spin-wave dynamics of Niu and
Kleinman. This technique allows to decouple the spin and charge excitations of
a many-electron system using a generalization of the adiabatic approximation.
The only input for the spin-wave equations of motion are the energies and Berry
curvatures of many-electron states describing frozen spin spirals. The latter
are computed using a newly developed technique based on constrained
density-functional theory, within the local spin density approximation and the
pseudo-potential plane-wave method. Calculations for iron show an excellent
agreement with experiments.",9908386v1
2000-11-29,Giant Magnetoresistance at the Interface of Iron Thin Films,"Ag/Fe/Ag and Cr/Fe/Cr trilayers with a single $25 nm$ thick ferromagnetic
layer exhibit giant magnetoresistance (GMR) type behavior. The resistance
decreases for parallel and transversal magnetic field alignements with a
Langevin-type magnetic field dependence up to B=12 T. The phenomenon is
explained by a granular interface structure. Results on Fe/Ag multilayers are
also interpreted in terms of a granular interface magnetoresistance.",0011491v1
2002-05-30,Spin-dependent properties of a two-dimensional electron gas with ferromagnetic gates,"A theoretical prediction of the spin-dependent electron self-energy and
in-plane transport of a two-dimensional electron gas in proximity with a
ferromagnetic gate is presented. The application of the predicted
spin-dependent properties is illustrated by the proposal of a device
configuration with two neighboring ferromagnetic gates which produces a
magnetoresistance effect on the channel current generated by nonmagnetic source
and drain contacts. Specific results are shown for a silicon inversion layer
with iron gates. The gate leakage current is found to be beneficial to the spin
effects.",0205651v2
2002-07-10,Different routes to charge disproportionation in perovskites-type Fe oxides,"Iron perovskites CaFeO_3 and La_{0.33}Sr_{0.67}FeO_3 show charge
disproportionation, resulting in charge-ordered states with Fe^{3+}:Fe^{5+}
=1:1 and =2:1, respectively. We have made photoemission and unrestricted
Hartree-Fock band-structure calculation of CaFeO_3 and compared it with
La_{0.33}Sr_{0.67}FeO_3. With decreasing temperature, a gradual decrease of the
spectral weight near the Fermi level occurred in CaFeO_3 as in
La_{0.33}Sr_{0.67}FeO_3 although lattice distortion occurs only in CaFeO_3.
Hartree-Fock calculations have indicated that both the breathing and tilting
distortions are necessary to induce the charge disproportionation in CaFeO_3,
while no lattice distortion is necessary for the charge disproportionation in
La_{0.33}Sr_{0.67}FeO_3.",0207250v1
2002-07-26,Ballistic versus diffusive magnetoresistance of a magnetic point contact,"The quasiclassical theory of a nanosize point contacts (PC) between two
ferromagnets is developed. The maximum available magnetoresistance values in PC
are calculated for ballistic versus diffusive transport through the area of a
contact. In the ballistic regime the magnetoresistance in excess of few
hundreds percents is obtained for the iron-group ferromagnets. The necessary
conditions for realization of so large magnetoresistance in PC, and the
experimental results by Garcia et al are discussed",0207648v1
2002-11-01,Exploring dynamical magnetism with time-dependent density-functional theory: from spin fluctuations to Gilbert damping,"We use time-dependent spin-density-functional theory to study dynamical
magnetic phenomena. First, we recall that the local-spin-density approximation
(LSDA) fails to account correctly for magnetic fluctuations in the paramagnetic
state of iron and other itinerant ferromagnets. Next, we construct a
gradient-dependent density functional that does not suffer from this problem of
the LSDA. This functional is then used to derive, for the first time, the
phenomenological Gilbert equation of micromagnetics directly from
time-dependent density-functional theory. Limitations and extensions of Gilbert
damping are discussed on this basis, and some comparisons with phenomenological
theories and experiments are made.",0211021v1
2003-05-06,Probing the shape of atoms in real space,"The structure of single atoms in real space is investigated by scanning
tunneling microscopy. Very high resolution is possible by a dramatic reduction
of the tip-sample distance. The instabilities which are normally encountered
when using small tip-sample distances are avoided by oscillating the tip of the
scanning tunneling microscope vertically with respect to the sample. The
surface atoms of Si(111)-(7 x 7) with their well-known electronic configuration
are used to image individual samarium, cobalt, iron and silicon atoms. The
resulting images resemble the charge density corresponding to 4f, 3d and 3p
atomic orbitals.",0305103v1
2003-06-21,The Effect of Disorder on a Quantum Phase Transition,"The conductivity and magnetization of Fe1-xCoxS2 were measured to investigate
quantum critical behavior in disordered itinerant magnets. Small x (<0.001) is
required to convert insulating iron pyrite into a metal, followed by a
paramagnetic-to-ferromagnetic metal transition at x = 0.032+/-0.004. Singular
contributions are discovered that are distinct from those at either
metal-insulator or magnetic transitions. Our data reveal that disorder and low
carrier density associated with proximity to a metal-insulator transition
fundamentally modifies the critical behavior of the magnetic transition.",0306541v1
2003-09-09,Finite-Temperature Micromagnetics of Hysterisis for Misaligned Single Iron Nanopillars,"We present micromagnetic results for the hysterisis of a single magnetic
nanopillar which is misaligned with respect to the applied magnetic field. We
provide results for both a one dimensional stack of magnetic rotors and of full
micromagnetic simulations. The results are compared to the Stoner-Wohlfarth
model.",0309237v1
2004-01-12,Generalized Friedel sum rule and anomalies of the mobility due to the resonant scattering of electrons by donor impurities in semiconductors,"On the basis of Friedel approach the theoretical description of the effects
of resonance scattering of conduction electrons by donor impurities in
semiconductors with allowance for the stabilization of electron concentration
in coinciding the Fermi energy with the resonance level energy has been
developed. It has been shown that such a stabilization gives rise to the
appearance of maximum in concentration dependence and to its related anomalies
of temperature dependences of electron mobility. The advantage of the
application of the approach based on the proposed theory to the interpretation
of experimental data on mercury selenide with iron impurities is discussed.
PACS: 72.20.Dp; 72.20.Fr Keywords: semiconductors, impurities in
semiconductors, electron states, electron transport",0401174v1
2004-02-13,Intersite elastic coupling and invar effect,"The invar phenomenon (very small thermal expansion in some iron alloys or
compounds) is usually explained by the thermally-induced transitions between
different spin states of Fe, having different atomic volumes. We consider these
processes taking into account elastic interaction between Fe atoms in different
spin states. Inclusion of these interactions explains why thermal expansion may
be close to zero in a broad temperature interval and thus gives rise to the
invar effect.",0402374v1
2004-04-08,Projective Dynamics in Realistic Models of Nanomagnets,"The free-energy extrema governing the magnetization-reversal process for a
model of an iron nanopillar are investigated using the projective dynamics
method. Since the time evolution of the model is computationally intensive, one
could question whether sufficient statistics can be generated, with current
resources, to evaluate the position of the metastable configuration.
Justification for the fine-grained discretization of the model that we use here
is given, and it is shown that tractable results can be obtained for this
system on realistic time scales.",0404198v1
2004-10-06,Spin and Valence-Fluctuation Mediated Superconductivity in Pressurized Fe and CeCu2(Si/Ge)2,"We review the evidence supporting valence-fluctuation mediated
superconductivity in CeCu2Si2 and CeCu2Ge2, where Tc reaches 2.4 K at high
pressure. In these systems the valence and magnetic critical points, at p_V and
p_c respectively, are well separated. Characteristic signatures associated with
both phenomena are distinct. In contrast, the valence and spin fluctuation
regions appear much closer in most Ce based compounds. Concerning d-transition
metals, superconductivity in pure iron emerges in the pressure window 15-30 GPa
with the onset of Tc up to almost 3 K. All relevant observations point to
unconventional superconductivity, likely mediated by ferromagnetic spin
fluctuations.",0410143v1
2005-01-17,"Jahn-Teller stabilization of a ""polar"" metal oxide surface: Fe3O4(001)","Using ab initio thermodynamics we compile a phase diagram for the surface of
Fe3O4(001) as a function of temperature and oxygen pressures. A hitherto
ignored polar termination with octahedral iron and oxygen forming a wave-like
structure along the [110]-direction is identified as the lowest energy
configuration over a broad range of oxygen gas-phase conditions. This novel
geometry is confirmed in a x-ray diffraction analysis. The stabilization of the
Fe3O4(001)-surface goes together with dramatic changes in the electronic and
magnetic properties, e.g., a halfmetal-to-metal transition.",0501402v1
2005-07-06,Inverse Magnetoresistance of Molecular Junctions,"We present calculations of spin-dependent electron transport through single
organic molecules bridging pairs of iron nanocontacts. We predict the
magnetoresistance of these systems to switch from positive to negative with
increasing applied bias for both conducting and insulating molecules. This
novel inverse magnetoresistance phenomenon is robust, does not depend on the
presence of impurities, and is unique to molecular and atomic nanoscale
magnetic junctions. Its physical origin is identified and its relevance to
experiment and to potential technological applications is discussed.",0507126v2
2005-09-09,Correlated hybridization in transition metal complexes,"We apply local orbital basis density functional theory (using SIESTA) coupled
with a mapping to the Anderson impurity model to estimate the Coulomb assisted
or correlated hybridization between transition metal d-orbitals and ligand
sp-orbitals for a number of molecular complexes. We find remarkably high values
which can have several physical implications including: (i) renormalization of
effective single band or multiband Hubbard model parameters for the cuprates
and, potentially, elemental iron, and (ii) spin polarizing molecular
transistors.",0509259v4
2005-09-12,Linear scaling Krylov subspace method for large scale {\it ab initio} electronic structure calculations of metals,"An efficient and robust linear scaling method is presented for large scale
{\it ab initio} electronic structure calculations of a wide variety of
materials including metals. The detailed short range and the effective long
range contributions to the electronic structure are taken into account by
solving an embedded cluster defined in a Krylov subspace, which provides rapid
convergence for not only insulators but also metals.
  As an illustration of the method, we present a large scale calculation based
on density functional theory for a palladium cluster with a single iron
impurity.",0509291v1
2005-12-19,Experimental Evidence for Crossed Andreev Reflection,"We report on electronic transport properties of mesoscopic
superconductor-ferromagnet spin-valve structures. Two ferromagnetic iron leads
form planar tunnel contacts to a superconducting aluminum wire, where the
distance of the two contacts is of the order of the coherence length of the
aluminum. We observe a negative non-local resistance which can be explained by
crossed Andreev reflection, a process where an electron incident from one of
the leads gets reflected as a hole into the other, thereby creating a pair of
spatially separated, entangled particles.",0512445v1
2005-12-19,Spin injection into a short DNA chain,"Quantun spin transport through a short DNA chain connected to ferromagnetic
electrodes has been investigated by the transfer matrix method. We describe the
system by a tight-binding model where the parameters are extracted from the
experimental data and realistic metal energy bands. For ferromagnetic iron
electrodes, the magnetoresistance of a 30-basepair Poly(G)-Poly(C) DNA is found
to be lower than 10% at a bias of < 4 V, but can rach up to 20% at a bias of 5
V. In the presence of the spin-flip mechanism, the magnetoresistance is
significantly enhanced when the spin-flip coupling is weak but as the coupling
becomes stronger the decreasing magnetoresistance develops an oscillatory
behavior.",0512473v1
2005-12-22,Point defect concentrations in metastable Fe-C alloys,"Point defect species and concentrations in metastable Fe-C alloys are
determined using density functional theory and a constrained free-energy
functional. Carbon interstitials dominate unless iron vacancies are in
significant excess, whereas excess carbon causes greatly enhances vacancy
concentration. Our predictions are amenable to experimental verification; they
provide a baseline for rationalizing complex microstructures known in hardened
and tempered steels, and by extension other technological materials created by
or subjected to extreme environments.",0512598v2
2005-12-31,Physical nature of fcc-bcc martensitic transformation in iron based alloys,"The summary of the models offered by the author revealing features of the
physical mechanisms controlling processes of martensite crystal formation is
resulted. The rapid growth of a cooling martensite crystal is considered as a
self-organized process controlled by the quasi-longitudinal lattice
displacement waves (DW). It is shown, that processes of the heterogeneous
nucleation and wave growth have the genetic connection in case of spontaneous
fcc-bcc martensitic transformation. The exposition of strain martensite
formation is considered in the context of a cryston model.",0601002v1
2006-02-03,Low Ghz loss in sputtered epitaxial Fe,"We show that sputtered, pure epitaxial iron films can have high-frequency
loss as low as, or lower than, any known metallic ferromagnetic
heterostructure. Minimum 34 Ghz ferromagnetic resonance (FMR) linewidths of 41
Oe are demonstrated, some ~ 5-10 % lower than the previous minimum reported for
molecular beam epitaxially (MBE) deposited Fe. Intrinsic and extrinsic damping
have been separated over 0-40 Ghz, giving a lower bound for intrinsic LL(G)
relaxation rates of lambda or G = 85 MHz (alpha = 0.0027) and extrinsic 50 Mhz.
Swept frequency measurements indicate the potential for integrated frequency
domain devices with Q>100 at 30-40 Ghz.",0602094v1
2006-06-01,Structure peculiarities of cementite and their influence on the magnetic characteristics,"The iron carbide $Fe_3C$ is studied by the first-principle density functional
theory. It is shown that the crystal structure with the carbon disposition in a
prismatic environment has the lowest total energy and the highest energy of
magnetic anisotropy as compared to the structure with carbon in an octahedron
environment. This fact explains the behavior of the coercive force upon
annealing of the plastically deformed samples. The appearance of carbon atoms
in the octahedron environment can be revealed by Mossbauer experiment.",0606024v1
2007-02-06,Comment on Resonant X-ray diffraction studies on the charge ordering in magnetite,"In a recent letter, E. Nazarenko et al [Phys. Rev. Lett. 97, 056403 (2006)
and cond-mat/0606596] have investigated the low temperature phase of magnetite
by means of resonant X-ray scattering. The paper puts forward the quantitative
determination of an effective charge ordering (CO) of 0.24 electron among the
octahedral iron atoms in the insulating phase. The comment puts in evidence
that the analysis performed by Nazarenko et al is wrong and that some of their
conclusions are unsupported .",0702135v2
2001-02-23,The fate of classical tensor inhomogeneities in pre-big-bang string cosmology,"In pre-big-bang string cosmology one uses a phase of dilaton-driven inflation
to stretch an initial (microscopic) spatial patch to the (much larger) size of
the big-bang fireball. We show that the dilaton-driven inflationary phase does
not naturally iron out the initial classical tensor inhomogeneities unless the
initial value of the string coupling is smaller than 10^(-35).",0102102v1
1995-08-02,Search for Magnetic Monopoles Trapped in Matter,"There have been many searches for magnetic monopoles in flight, but few for
monopoles in matter. We have searched for magnetic monopoles in meteorites,
schists, ferromanganese nodules, iron ores and other materials. The detector
was a superconducting induction coil connected to a SQUID (Superconducting
Quantum Interference Device) with a room temperature bore 15 cm in diameter. We
tested a total of more than 331 kg of material including 112 kg of meteorites.
We found no monopole and conclude the overall monopole/nucleon ratio in the
samples is $<1.2 \times 10^{-29}$ with a 90\% confidence level.",9508003v1
1998-12-11,The OPERA Experiment,"OPERA(Oscillation Project with Emulsion-tRacking Apparatus) is a new detector
concept, iron(lead)-emulsion for a long-baseline neutrino oscillation
experiment. This experiment would perform an appearance search for nu_mu-nu_tau
oscillation in the parameter region indicated by the atmospheric neutrino
anomaly. OPERA can run at the Gran Sasso Laboratory in the proposed NGS
(Neutrino to Gran Sasso) Beam from CERN.",9812015v3
1999-03-22,Study of the Hadron Shower Profiles with the Tile Hadron Calorimeter,"The lateral and longitudinal profiles of the hadronic showers detected by
iron-scintillator tile hadron calorimeter with longitudinal tile configuration
have been investigated. The results are based on 100 GeV pion beam data. Due to
the beam scan provided many different beam impact locations with cells it is
succeeded to obtain detailed picture of transverse shower behavior. The
underlying radial energy densities for four depths and for overall calorimeter
have been reconstructed. The three-dimensional hadronic shower parametrisation
have been suggested.",9903052v1
1999-08-20,Precision Calibration of the NuTeV Calorimeter,"NuTeV is a neutrino-nucleon deep-inelastic scattering experiment at Fermilab.
The detector consists of an iron-scintillator sampling calorimeter interspersed
with drift chambers, followed by a muon toroidal spectrometer. We present
determinations of response and resolution functions of the NuTeV calorimeter
for electrons, hadrons, and muons over an energy range of 4.8 to 190 GeV. The
absolute hadronic energy scale is determined to an accuracy of 0.43%. We
compare our measurements to predictions from calorimeter theory and GEANT3
simulations.",9908056v1
1999-12-23,Recent atmospheric neutrino results from Soudan 2,"An updated measurement of the atmospheric nu_mu/nu_e ratio-of-ratios,
0.68+-0.11+-0.06, has been obtained using a 4.6-kty exposure of the Soudan-2
iron tracking calorimeter. The L/E distributions have been analyzed for effects
of nu_mu -> nu_x oscillations, and an allowed region in the Delta m^2 vs. sin^2
2 theta plane has been determined.",9912060v1
2001-09-18,"Nuclear transparency from quasielastic A(e,e'p) reactions uo to Q^2=8.1 (GeV/c)^2","The quasielastic (e,e$^\prime$p) reaction was studied on targets of
deuterium, carbon, and iron up to a value of momentum transfer $Q^2$ of 8.1
(GeV/c)$^2$. A nuclear transparency was determined by comparing the data to
calculations in the Plane-Wave Impulse Approximation. The dependence of the
nuclear transparency on $Q^2$ and the mass number $A$ was investigated in a
search for the onset of the Color Transparency phenomenon. We find no evidence
for the onset of Color Transparency within our range of $Q^2$. A fit to the
world's nuclear transparency data reflects the energy dependence of the free
proton-nucleon cross section.",0109027v1
2002-01-10,A method for detecting $ν_τ$ appearance in the spectra of quasielastic CC events,"A method for detecting the transition \omutau in long-baseline accelerator
experiments, that consists in comparing the far-to-near ratios of the spectra
of quasielastic CC events generated by high- and low-energy beams of muon
neutrinos, is proposed. The test may be accessible to big water Cherenkov
detectors and iron--scintillator calorimeters, and is limited by statistics
rather than systematics.",0201019v1
2003-07-02,NuTeV Cross Section and Structure Function Measurements,"The NuTeV experiment has obtained a unique high statistics sample of neutrino
and antineutrino interactions using its high-energy sign-selected beam.
Charged-current neutrino and anti-neutrino differential cross sections are
extracted. Neutrino-Iron structure functions, F_2(x,Q^2) and xF_3(x,Q^2), are
determined by fitting the y-dependence of the differential cross sections.
NuTeV has precise understanding of its hadron and muon energy scales, which
improves the systematic precision of this measurement.",0307005v2
2005-07-02,The MINOS Detectors,"The Main Injector Neutrino Oscillation Search (MINOS) experiment's primary
goal is the precision measurement of the neutrino oscillation parameters in the
atmospheric neutrino sector. This long-baseline experiment uses Fermilab's NuMI
beam, measured with a Near Detector at Fermilab, and again 735 km later using a
Far Detector in the Soudan Mine Underground Lab in northern Minnesota. The
detectors are magnetized iron/scintillator calorimeters. The Far Detector has
been operational for cosmic ray and atmospheric neutrino data from July of
2003, the Near Detector from September 2004, and the NuMI beam started in early
2005. This poster presents details of the two detectors.",0507018v1
2005-07-09,NuTeV Structure Function Measurement,"The NuTeV experiment obtained high statistics samples of neutrino and
anti-neutrino charged current events during the 1996-1997 Fermilab fixed target
run. The experiment combines sign-selected neutrino and anti-neutrino beams and
the upgraded CCFR iron-scintillator neutrino detector. A precision continuous
calibration beam was used to determine the muon and hadron energy scales to a
precision of 0.7% and 0.43% respectively. The structure functions F_2(x,Q^2)
and xF_3(x,Q^2) obtained by fitting the y-dependence of the sum and the
difference of the neutrino and anti-neutrino differential cross sections are
presented.",0507040v1
1996-07-10,QCD analysis of the CCFR data for $xF_3$ and Higher--Twist Contribution,"The QCD analysis of the $xF_3$ structure function measured in deep-inelastic
scattering of neutrinos and antineutrinos on an iron target at the Fermilab
Tevatron is done in 1--, 2-- and 3--loop order of QCD. The x dependence of the
higher--twist contribution is evaluated. The experimental value of
higher--twist corrections to the Gross--Llewellyn Smith sum rule is discussed.",9607275v2
1997-12-06,Atmospheric neutrino interactions in Soudan-2,"A new measurement of the atmospheric numu/nue ratio-of-ratios, 0.61 +- 0.15
+- 0.05, has been obtained using a 3.2-kty exposure of the Soudan-2 underground
detector. This measurement, based upon neutrino reactions in an iron tracking
calorimeter of honeycomb-lattice geometry, is in agreement with the anomalously
low value reported by the underground water detectors.",9712281v1
1998-08-24,Limits on Pauli principle violation by nucleons,"We consider nuclei produced in core collapse supernovae and subjected to a
high neutron flux. We show that an accelerator mass spectrometry experiment
that searched for traces of anomalous iron isotopes could set limits on the
order of $10^{-20}-10^{-25}$ on (or perhaps discover) Pauli principle violation
by neutrons. A similar search for anomalous Co isotopes could set limits in the
range $10^{-13}-10^{-18}$ on Pauli principle violation by protons. We show that
existing data on Oxygen can be used to set a limit of about $10^{-17}$ in one
proposed model of such violation.",9808397v1
1999-11-12,Muon's Behaviors under Bremsstrahlung with both the LPM effect and the Ter-Mikaelian effect and Direct Pair Production with the LPM effect,"Differential and integral cross sections of the muon are calculated in the
materials: water, standard rock, iron and lead with and without the LPM effect.
The corresponding cross sections are also calculated with dielectric supression
effect (Ter-Mikaelian effect), in addition to the LPM effect. To demonstrate
the importance of the LPM effect in the bremsstrahlung process, depth intensity
relation of muon, energy spectrum, range distribution and survival probability
are calculated taking into account bremsstrahlung spectrum.",9911330v1
2000-09-13,Nuclear effects and higher twists in F3 structure function,"We analyze the CCFR collaboration iron target data on the xF3 structure
function making particular emphasis on the extraction of the higher twist
contributions from data. Corrections for nuclear effects are applied in order
to extract data on the structure function of the isoscalar nucleon. Our
analysis confirms the observation made earlier, that the higher twist terms
depend strongly on the level to which QCD perturbation theory analysis is
applied. We discuss the impact of nuclear effects on the higher twist term as
well as on the QCD scale parameter Lambda_{\bar{MS}} extracted from the fit to
data.",0009150v1
2000-12-06,Can We Observe the Quark Gluon Plasma in Cosmic Ray Showers ?,"The possibility of detection of some features of high energy particle
interactions with detectors placed at medium depths underground through studies
on high energy muons is investigated. These muons carry information about the
early interactions occurring during the development of the hadron cascade near
the top of the atmosphere. They might reveal the effects resulting from
creation of quark gluon plasma in interactions of ultra high energy cosmic ray
iron nuclei with air nuclei.",0012068v3
2001-12-14,Differential Distributions for NLO Analyses of Charged Current Neutrino-Production of Charm,"Experimental analyses of charged current deep inelastic charm production --
as observed through dimuon events in neutrino-iron scattering -- measure the
strangeness component of the nucleon sea. A complete analysis requires a Monte
Carlo simulation to account for experimental detector acceptance effects;
therefore, a fully differential theoretical calculation is necessary to provide
complete kinematic information. We investigate the theoretical issues involved
in calculating these differential distributions at Next-Leading-Order (NLO).
Numerical results are presented for typical fixed target kinematics. We present
a corresponding FORTRAN code suitable for experimental NLO analysis.",0112191v1
2003-09-09,Re/Os constraint on the time-variability of the fine-structure constant,"We argue that the accuracy by which the isochron parameters of the decay
$^{187}{\rm Re}\to ^{187}{\rm Os}$ are determined by dating iron meteorites may
not directly constrain the possible time-dependence of the decay rate and hence
of the fine-structure constant $\alpha$. From this point of view, some of the
attempts to analyze the Oklo constraint and the results of the QSO absorption
lines are re-examined.",0309087v2
2003-10-01,NUFACT'03: The Fate of the Clones,"We present a Neutrino-Factory-based setup with three detectors of different
kind in principle capable to solve the eightfold-degeneracy in the simultaneous
measurement of $\theta_{13}$ and $\delta$, for $\theta_{13} \geq 1^\circ
(\sin^2 (2 \theta_{13}) \geq 10^{-3})$. Our setup includes a Superbeam-driven
water Cherenkov (the Superbeam conceived as the first stage of the Neutrino
Factory); two muon-storage-ring-driven detectors (namely, a large magnetized
iron calorimeter and an emulsion cloud chamber) to take advantage of both the
so-called ""golden"" ($\nu_e \to \nu_\mu$) and ""silver"" ($\nu_e \to \nu_\tau$)
channels.",0310014v1
2004-08-23,Possible Explanations for the NuTeV Weinberg Angle Measurement,"The NuTeV collaboration has made an independent determination of the Weinberg
angle by measuring charged and neutral-current cross sections from neutrino and
antineutrino DIS on iron. Their value differs by 3 standard deviations from
that obtained from measurements at the Z pole. We review this experiment and
assess various possible explanations for this result, both within the Standard
Model (""old physics"") and outside the Standard Model (""new physics"").",0408243v2
2005-09-22,Moments of nuclear and nucleon structure functions at low Q^2 and the momentum sum rule,"New nuclear structure function data from Jefferson Lab covering the higher x
and lower Q^2 regime make it possible to extract the higher order F_2 moments
for iron and deuterium at low four-momentum transfer squared Q^2. These moments
allow for an experimental investigation of the nuclear momentum sum rule and a
direct comparison of the non-singlet nucleon moment with Lattice QCD results.",0509241v2
2005-12-09,New solutions for the color-flavor locked strangelets,"Recent publications rule out the negatively charged beta equilibrium
strangelets in ordinary phase, and the color-flavor locked (CFL) strangelets
are reported to be also positively charged. This letter presents new solutions
to the system equations where CFL strangelets are slightly negatively charged.
If the ratio of the square-root bag constant to the gap parameter is smaller
than 170 MeV, the CFL strangelets are more stable than iron and the normal
unpaired strangelets. For the same parameters, however, the positively charged
CFL strangelets are more stable.",0512112v1
2006-10-04,Can we learn something more on oscillations from atmospheric neutrinos?,"We show that for long-baseline experiments using a Mt water Cerenkov detector
atmospheric neutrino data provide a powerful method to resolve parameter
degeneracies. In particular, the combination of long-baseline and atmospheric
data increases significantly the sensitivity to the neutrino mass hierarchy and
the octant of $\theta_{23}$. Furthermore, we discuss the possibility to use
$\mu$-like atmospheric neutrino data from a big magnetized iron calorimeter to
determine the neutrino mass hierarchy.",0610053v1
1999-12-23,On the discovery of doubly-magic $^{48}$Ni,"The paper reports on the first observation of doubly-magic Nickel-48 in an
experimental at the SISSI/LISE3 facility of GANIL. Four Nickel-48 isotopes were
identified. In addition, roughly 100 Nickel-49, 50 Iron-45, and 290 Chromium-42
isotopes were observed. This opens the possibility to search for two-proton
emission from these nuclei.",9912012v1
2006-09-06,Dynamics Of Hadronization From Nuclear Semi Inclusive Deep Inelastic Scattering,"The CLAS experiment E02-104, part of the EG2 run at Jefferson Lab, was
performed to study the hadronization process using semi inclusive deep
inelastic scattering off nuclei. Electron beam energy of 5 GeV and the CLAS
large acceptance detector were used to study charged pion production. The high
luminosity available at Jefferson Lab and the CLAS large acceptance are key
factors for such measurements allowing high statistics and therefore
multidimensional analyses of the data. Both the multiplicity ratio and the
transverse momentum broadening for carbon, iron and lead relative to deuterium
are measured. Preliminary results for positive pions are discussed.",0609005v1
1997-03-17,Fermionic Molecular Dynamics: Multifragmentation in heavy-ion collisions and in excited nuclei,"Within Fermionic Molecular Dynamics we investigate fragmentation of a
compound system which was created in a heavy-ion collision at a beam energy in
the Fermi energy domain and the decay of excited iron nuclei. We show that in
FMD many-body correlations play an important role in the formation of
fragments.",9703035v1
1997-07-17,Total and Parity-Projected Level Densities of Iron-Region Nuclei in the Auxiliary Fields Monte Carlo Shell Model,"We use the auxiliary-fields Monte Carlo method for the shell model in the
complete $(pf+0g_{9/2})$-shell to calculate level densities. We introduce
parity projection techniques which enable us to calculate the parity dependence
of the level density. Results are presented for $^{56}$Fe, where the calculated
total level density is found to be in remarkable agreement with the
experimental level density. The parity-projected densities are well described
by a backshifted Bethe formula, but with significant dependence of the
single-particle level-density and backshift parameters on parity. We compare
our exact results with those of the thermal Hartree-Fock approximation.",9707027v1
2000-09-05,Signature of a Pairing Transition in the Heat Capacity of Finite Nuclei,"The heat capacity of iron isotopes is calculated within the interacting shell
model using the complete $(pf+0g_{9/2})$-shell. We identify a signature of the
pairing transition in the heat capacity that is correlated with the suppression
of the number of spin-zero neutron pairs as the temperature increases. Our
results are obtained by a novel method that significantly reduces the
statistical errors in the heat capacity calculated by the shell model Monte
Carlo approach. The Monte Carlo results are compared with finite-temperature
Fermi gas and BCS calculations.",0009006v1
2000-12-08,Effect of nuclear structure on Type Ia supernova nucleosynthesis,"The relationship among nuclear structure, the weak processes in nuclei, and
astrophysics becomes quite apparent in supernova explosion and nucleosynthesis
studies. In this brief article, I report on progress made in the last few years
on calculating electron capture and beta-decay rates in iron-group nuclei. I
also report on applications of these rates to Type-Ia nucleosynthesis studies.",0012027v1
2002-01-10,Neutral-current neutrino reactions in the supernova environment,"We study the neutral-current neutrino scattering for four nuclei in the iron
region. We evaluate the cross sections for the relevant temperatures during the
supernova core collapse and derive Gamow-Teller distributions from large-scale
shell-model calculations. We show that the thermal population of the excited
states significantly enhances the cross sections at low neutrino energies.
Calculations of the outgoing neutrino spectra indicate the prospect of neutrino
upscattering at finite temperatures. Both results are particularly notable in
even-even nuclei.",0201025v1
2003-03-06,Gamow-Teller strength distributions in Fe and Ni stable isotopes,"We study Gamow-Teller strength distributions in some selected nuclei of
particular Astrophysical interest within the iron mass region. The theoretical
framework is based on a proton-neutron Quasiparticle Random Phase Approximation
built on a deformed selfconsistent mean field basis obtained from two-body
density-dependent Skyrme forces. We compare our results to available
experimental information obtained from (n,p) and (p,n) charge exchange
reactions.",0303015v1
2006-07-27,Spin projection in the shell model Monte Carlo method and the spin distribution of nuclear level densities,"We introduce spin projection methods in the shell model Monte Carlo approach
and apply them to calculate the spin distribution of level densities for
iron-region nuclei using the complete $(pf+g_{9/2})$-shell. We compare the
calculated distributions with the spin-cutoff model and extract an
energy-dependent moment of inertia. For even-even nuclei and at low excitation
energies, we observe a significant suppression of the moment of inertia and
odd-even staggering in the spin dependence of level densities.",0607062v1
2000-03-22,RF-induced evaporative cooling and BEC in a high magnetic field,"We present the design of our iron-core electromagnet for BEC, and how to
solve the specific experimental problems raised by this technique. After
presenting the experimental set-up, we address the interruption of runaway
evaporative cooling when the Zeeman effect is not linear. We present the ways
to circumvent this problem, use of multiple RF frequencies, sympathetic cooling
and show some applications of these high magnetic fields (cavity coupling, high
confinement).",0003050v1
2007-02-13,LHCb Level-0 Trigger Detectors,"The calorimeter and muon systems are essential components to provide a
trigger for the LHCb experiment. The calorimeter system comprises a
scintillating pad detector and pre-shower, followed by electromagnetic and
hadronic calorimeters. The calorimeter system allows photons, electrons and
hadrons to be identified, and their energy to be measured. The muon system
consists of five measuring stations equipped with Multi-Wire Proportional
Chambers (MWPCs) and triple-Gas Electron Multiplier (GEM) detectors, separated
by iron filters. It allows the muons identification and transverse momentum
measurement. The status of the two systems and their expected performance is
presented.",0702103v1
2006-03-21,Quantum description of spin tunneling in magnetic molecules: a new view,"Starting from a phenomenological Hamiltonian originally written in terms of
angular momentum operators we derive a new quantum angle-based Hamiltonian that
allows for a discussion on the quantum spin tunneling. The study of the
applicability of the present approach, carried out in calculations with a
soluble quasi-spin model, shows that we are allowed to use our method in the
description of physical systems such as the Mn12-acetate molecule, as well as
the octanuclear iron cluster, Fe8, in a reliable way. With the present
description the interpretation of the spin tunneling is seen to be direct, the
spectra and energy barriers of those systems are obtained, and it is shown that
they agree with the experimental ones.",0603183v1
2007-02-06,Spin tunneling in magnetic molecules: Quantitative estimates for Fe8 clusters,"Spin tunneling in the particular case of the magnetic molecular cluster
octanuclear iron(III), Fe8, is treated by an effective Hamiltonian that allows
for an angle-based description of the process. The presence of an external
magnetic field along the easy axis is also taken into account in this
description. Analytic expressions for the energy levels and barriers are
obtained from a harmonic approximation of the potential function which give
results in good agreement with the experimental results. The energy splittings
due to spin tunneling is treated in an adapted WKB approach and it is shown
that the present description can give results to a reliable degree of accuracy.",0702051v1
2007-04-19,Iron Line Profiles from Relativistic Thick Accretion Disk,"We present a new code for calculating the Fe Kalpha line profiles from
relativistic accretion disks with finite thickness around a rotating black
hole. The thin Keplerian accretion disk must become thicker and sub-Keplerian
with increasing accretion rates. We here embark on, for the first time, a fully
relativistic computation which is aimed at gaining an insight into the effects
of geometrical thickness and the sub-Keplerian orbital velocity on the line
profiles. This code is also well-suited to produce accretion disk images.",0704.2460v1
2007-04-20,Neutrino beams as a probe of the nuclear isospin and spin-isospin excitations,"We explore the possibility of performing nuclear structure studies using low
energy neutrino beams. In particular, low energy beta-beams and conventional
sources (muon decay-at-rest) are considered. We present results on the total
charged-current as well as flux-averaged cross sections associated to electron
(anti)-neutrino scattering on oxygen, iron, molybdenum and lead, as typical
examples. It is shown that by using neutrinos from low energy beta-beams,
information on forbidden states, in particular the spin-dipole, could be
extracted.",0704.2724v2
2007-05-14,On the Enhanced Reverse Beta Processes in Graphene-Iron Composite Nanostructures at High Temperatures in Strong Magnetic Field,"Strong dense many-spin interactions have been proposed to organize novel
orbital dynamics (the Little Effect) for novel chemical and catalytic
phenomena. The recent determinations of the relativistic and quantum Hall
effects of carriers in graphene under strong magnetic confinement have
substantiated the Little Effect. Moreover such nonclassical phenomena under the
stronger magnetic confinement of ferro-nanocatalysts are here shown to organize
reverse beta processes and possibly pycnonuclear reactions under high
temperature and high-pressure conditions. Such processes have implications for
reverse beta reactions and nuclear reactions within the interior of the earth
and new technologies for carbon nanotube-ferrometal and nanographene-ferrometal
composites.",0705.1909v1
2007-06-22,A cool R Coronae Borealis star Z UMi,"The high resolution spectra of a R CrB type star Z UMi are analysed. The
atmospheric parameters of Z UMi are estimated: Teff=5250+/-250K and log
g=0.5+/-0.3. This places Z UMi among the coolest R CrB stars. The hydrogen
deficiency of Z UMi is confirmed. The abundances of other elements resemble
those found for the minority group of R CrB stars. We note very low iron
abundance, [Fe/H]=-1.85, and an excess of lithium, [Li/Fe]=+1.9.",0706.3271v1
2007-06-27,Molecular dynamics simulations of the dipolar-induced formation of magnetic nanochains and nanorings,"Iron, cobalt and nickel nanoparticles, grown in the gas phase, are known to
arrange in chains and bracelet-like rings due to the long-range dipolar
interaction between the ferromagnetic (or super-paramagnetic) particles. We
investigate the dynamics and thermodynamics of such magnetic dipolar
nanoparticles for low densities using molecular dynamics simulations and
analyze the influence of temperature and external magnetic fields on two- and
three-dimensional systems. The obtained phase diagrams can be understood by
using simple energetic arguments.",0706.3920v1
2007-07-23,Magic Baseline Beta Beam,"We study the physics reach of an experiment where neutrinos produced in a
beta-beam facility at CERN are observed in a large magnetized iron calorimeter
(ICAL) at the India-based Neutrino Observatory (INO). The CERN-INO distance is
close to the so-called ""magic"" baseline which helps evade some of the parameter
degeneracies and allows for a better measurement of the neutrino mass hierarchy
and $\theta_{13}$.",0707.3367v1
2007-08-09,The Rest-Frame UV Spectrum of Elliptical Galaxies at High Redshift,"Beyond redshift ~1.4 the only spectral feature that allows one to get the
redshift of passively evolving galaxies (PEG) with optical spectrographs is a
characteristic structure due to a set of iron and magnesium lines lines at
2600-2850 Angstrom in the rest frame. The same feature permits also to estimate
the time elapsed since the cessation of star formation. Current efforts at
observing high redshift PEGs at the VLT and SUBARU telescopes are briefly
reviewed.",0708.1240v1
2007-09-03,Galactic neutrino background from cosmic ray interaction with the ISM content,"We use a diffusive model for the propagation of Galactic cosmic rays to
estimate the charged pion production in interactions with protons of the
interstellar medium. Cosmic ray nuclei from proton to iron are considered and
the corresponding contribution to the neutrino secondary flux produced as a
result of spallation is also estimated.",0709.0278v2
2007-09-06,Structural peculiarities of plastically-deformed cementite and their influence on magnetic characteristics and Mossbauer parameters,"Cementite Fe3C is studied with first-principles calculations. Two possible
positions of carbon atoms in the iron sublattice are considered: with prismatic
or octahedral environment. Mossbauer spectra (MS) with parameters calculated
for both modifications are simulated above and below the Curie temperature. A
possibility to detect the change in carbon position upon annealing from MS is
discussed. It is shown that this is hardly possible using a standard approach
to treatment of MS, but it can be seen in more subtle details of the MS below
the Curie temperature, such as widths and positions of separate lines.",0709.0789v1
2007-11-28,Nuclear effects in F_3 structure function of nucleon,"We study nuclear effects in the $F^A_3(x)$ structure function in the deep
inelastic neutrino reactions on iron by using a relativistic framework to
describe the nucleon spectral functions in the nucleus.
  The results for the ratio $R(x,Q^2)=\frac{F^A_3(x,Q^2)}{AF^N_3(x, Q^2)}$ and
the Gross-Llewellyn Smith(GLS) integral $G(x,Q^2)=\int_x^1 dx F^A_3(x,Q^2)$ in
nuclei are discussed and compared with the recent results available in
literature from theoretical and phenomenological analyses of experimental data.",0711.4443v2
2007-12-05,Investigating Possible Neutrino Decay in Long Baseline Experiment Using ICAL as Far end Detector,"We investigate the effects of possible decay of neutrinos from a neutrino
factory in a long baseline experiment. We consider the neutrinos from a factory
at CERN and the detector to be the 50 kTon iron calorimeter (ICAL) detector
proposed for India-based Neutrino Observatory (INO). We found considerable
depletion of muon yield at INO for certain value of decay parameters.",0712.0697v2
2007-12-20,On the Simbol-X capability of detecting red/blue-shifted emission and absorption Fe K lines,"The detection of red/blue-shifted iron lines in the spectra of astronomical
X-ray sources is of great importance, as it allows to trace the environment
around compact objects, like black holes in AGNs. We report on extensive
simulations to test the Simbol-X capability of detecting such spectral
features, focusing on the low energy detector (0.5-30 keV).",0712.3427v1
2008-01-16,Light-induced scattering and energy transfer between orthogonally-polarized waves,"We present a detailed experimental investigation on polarization-isotropic
and polarization-anisotropic holographic scattering in lithium niobate crystal
doped with iron when recording parasitic gratings with an ordinary polarized
pump beam. The kinetics of both types of scattering during the whole process of
recording is studied. Holographic scattering is presented as a simple technique
to monitor the energy transfer between beams of different polarization.
Moreover, the spectral and the angular dependence of the transmitted intensity
of the crystal during the reconstruction of the auto-generated parasitic
gratings are measured.",0801.2489v1
2008-01-30,Long-range magnetic order and spin-lattice coupling in the delafossite CuFeO2,"The electronic and magnetic properties of the delafossite CuFeO2 are
investigated by means of electronic structure calculations. They are performed
using density functional theory in the generalized gradient approximation as
well as the new full-potential augmented spherical wave method. The
calculations reveal three different spin states at the iron sites. Taking into
account the correct crystal structure, we find long-range antiferromagnetic
ordering in agreement with experiment. Contrasting previous work, our
calculations show that non-local exchange interactions lead to a semiconducting
ground state.",0801.4787v1
2008-01-31,The Impact of Transit Observations on Planetary Physics,"We highlight the importance of transit observations on understanding the
physics of planetary atmospheres and interiors. Transmission spectra and
emission spectra allow us to characterize this exotic atmospheres, which
possess TiO, VO, H2O, CO, Na, and K, as principal absorbers. We calculate
mass-radius relations for water-rock-iron and gas giant planets and examine
these relations in light of current and future transit observations. A brief
review is given of mechanisms that could lead to the large radii observed for
some transiting planets.",0801.4943v1
2008-02-06,The Suppression and Recovery of the Ferroelectric Phase in Multiferroic $MnWO_4$,"We report the discovery of a complete suppression of ferroelectricity in
$MnWO_4$ by 10 % iron substitution and its restoration in external magnetic
fields. The spontaneous polarization in $Mn_{0.9}Fe_{0.1}WO_4$ arises below 12
K in external fields above 4 T. The magnetic/ferroelectric phase diagram is
constructed from the anomalies of the dielectric constant, polarization,
magnetization, and heat capacity. The observations are qualitatively described
by a mean field model with competing interactions and strong anisotropy. We
propose that the magnetic field induces a non-collinear inversion symmetry
breaking magnetic structure in $Mn_{0.9}Fe_{0.1}WO_4$.",0802.0839v1
2008-03-31,Hole superconductivity in Arsenic-Iron compounds,"Superconductivity above 25K, and possibly above 40K, has recently been
discovered in $LaO_{1-x}F_xFeAs$ and related compounds. We propose that this is
another example of the mechanism of hole superconductivity at play. This
requires the existence of hole carriers at the Fermi energy, which appears to
contradict current observations. We propose that two-band conduction is taking
place in these materials, that the negative ion $As^{-3}$ plays a key role, and
that superconductivity is non-phononic and driven by pairing and undressing of
heavily dressed hole carriers to lower their kinetic energy. We make several
predictions of future observations based on our theory.",0804.0002v1
2008-04-03,Understanding the Unique Structural and Electronic Properties of SrFeO2,"We report a first-principles study of SrFeO$_2$, an infinite-layer oxide with
Fe atoms in a perfect square-planar coordination down to essentially 0 K. Our
results reveal this striking behavior relies on the double occupation of the
3$d_{z^2}$ orbitals of high-spin Fe$^{2+}$. Such an electronic state results
from the hybridization of iron's 3$d_{z^2}$ and 4$s$ orbitals, which enables a
large reduction of the intra-atomic exchange splitting of the $z^2$ electrons.
The generality of the phenomenon is discussed.",0804.0495v1
2008-04-21,Unusual magnetic behavior in ferrite hollow nanospheres,"We report unusual magnetic behavior in iron oxide hollow nanospheres of 9.3
$nm$ in diameter. The large fraction of atoms existing at the inner and outer
surfaces gives rise to a high magnetic disorder. The overall magnetic behavior
can be explained considering the coexistence of a soft superparamagnetic phase
and a hard phase corresponding to the highly frustrated cluster-glass like
phase at the surface regions.",0804.3292v1
2008-04-24,Graphene-protected iron layer on Ni(111),"Here we report the photoemission studies of intercalation process of Fe
underneath graphene layer on Ni(111). The process of intercalation was
monitored via XPS of corresponding core levels and UPS of the graphene-derived
$\pi$ states in the valence band. \textit{fcc}-Fe films with thickness of 2-5
monolayers at the interface between graphene and Ni(111) form epitaxial
magnetic layer passivated from the reactive environment, like for example
oxygen gas.",0804.3942v1
2008-04-24,19-F NMR Investigation of Iron-pnictide Superconductor LaFeAsO(0.89)F(0.11),"We report 19-F NMR investigation of the new high temperature superconductor
LaFeAsO(0.89)F(0.11) (Tc ~ 28K). We demonstrate that low frequency spin
fluctuations exhibit pseudo gap behavior above Tc. We also deduce the London
penetration depth lambda from NMR line broadening below Tc.",0804.4026v3
2008-04-25,"Structural, magnetic and electronic properties of quaternary oxybismuthides LaOMBi (where M = Sc, Ti ... Ni, Cu) - possible parent phases for new superconducting materials","The extensive ab initio total energy calculations using the VASP-PAW method
with the generalized gradient approximation (GGA) for the exchange-correlation
potential are applied to systematic investigation of structural, electronic and
magnetic properties in quaternary oxybismuthides LaOMBi (where M = Sc, Ti...Ni,
Cu). The energy spectrum features similar to lanthanum-iron oxyarsenide LaOFeAs
and non-magnetic ground state are indicative of superconductivity possible in
lanthanum-nickel oxybismuthide LaONiBi.",0804.4064v1
2008-05-23,Normal State Correlated Electronic Structure of Iron Pnictides,"We describe the correlated electronic structure of a prototype Fe-pnictide
superconductor, $SmO_{1-x}F_{x}FeAs$, using LDA+DMFT. Strong, multi-orbital
electronic correlations generate a low-energy pseudogap in the undistorted
phase, giving a bad, incoherent metal in qualitative agreement with
observations. Very good semi-quantitative agreement with the experimental
spectral functions is seen, and interpreted, within a correlated, multi-orbital
picture. Our results show that Fe-pnictides should be understood as low-carrier
density, incoherent metals, in resemblance to the underdoped cuprate
superconductors.",0805.3636v1
2008-05-26,Observation of magnetic field lines in the vicinity of a superconductor with the naked eye,"Meissner effect and pinning effect are clearly observed with the naked eye. A
GdBaCuO high-temperature superconductor (HTS) disk fabricated by Nippon Steel
Corporation, a 100mm cubic NdFeB sintered magnet, and iron wires coated by
colored are used. When the HTS is put in the magnetic field of the magnet, it
can be observed by the wires that the magnetic field lines are excluded from
the superconductor (Meissner effect) as well as are pinned in the
superconductor (pinning effect).",0805.3990v4
2008-06-05,Low temperature synthesis and pressure induced insulator-metal transition of the newly found NdFeAsO0.75,"As low as 900 oC, iron-based layered quaternary compound NdFeAsO0.75 was
synthesized through solid state reaction method. XRD measurements illustrate
almost pure phase of tetragonal phase NdFeAsO was formed. The synthesis
temperature in our experiment is the lowest among all the reported methods
without the help of any mineralizer. After further treatment under high
pressure of 6 GPa at temperature of 1300 oC for 2 hours, the electrical
transport property of NdFeAsO0.75 was transformed from insulator-like to metal-
like behavior.",0806.0976v1
2008-06-11,On superconducting and magnetic properties of iron-oxypnictides,"Pairing symmetry in oxypnictides, a new family of multiband high-Tc
superconductors, is partially imposed by the positions of multiple Fermi
pockets, which itself can give rise to new order parameters, such as s+,-
states or the state of dx^2-y^2 symmetry. Other pairing states may appear on
small pockets for long range interactions, but they are expected to be
sensitive to defects. We identify the competing antiferromagnetic order with
the triplet exciton transition in the semi- metallic background and discuss
whether its coexistence with superconductivity explains the doping dependence
of Tc.",0806.1933v2
2008-06-14,Pressure-induced superconductivity in PrOxFeAs,"Superconductivity with Tc of 45 K was realized in the tetragonal
ZrCuSiAs-type PrOxFeAs (x=0.75) under heat treatment of 1300 oC and pressure of
6 GPa for 2 hours. Although the sample prepared at 900 oC in vaccum possessed
the same phase as that treated in pressure, the electrical transport
measurement showed the similar behavior with its parent ReOFeAs (Re: rare-earth
metal). This pressure-induced superconductivity could give us a hint to
understand the origins of the newly-found iron based superconductors.",0806.2379v1
2008-06-17,Improved parameters of the hydrogen-deficient binary star KSPer,"Using the high resolution spectral observations obtained with the Nasmyth
Echelle Spectrograph NES of the 6m telescope we analysed the optical spectrum
of the hydrogen-deficient binary star KSPer. The atmospheric parameters derived
are: effective temperature Teff=9500+/-300 K, surface gravity log g=2.0+/-0.5,
and microturbulent velocity Vt=9.5+/-0.5km/s. The hydrogen deficiency is
H/He=3x10^{-5}, iron abundance is reduced by 0.8dex; nitrogen abundance is very
high [N/Fe]=1.4, but carbon and oxygen abundances are low. The star luminosity
is log L/Lo=3.3. A complex absorption and emission structure of the NaI D
doublet was revealed. We suggest that the emission component forms in the
circumbinary gaseous envelope.",0806.2709v1
2008-06-19,Real Space Coulomb Interaction: A Pairing Glue for FeAs Superconductors,"In this paper we present a real space pairing glue for the iron-based layered
superconductors. It is shown that two static electrons embedded symmetrically
into two adjacent Fe plaquettes of the superconductor can be bounded due to the
Coulombic interaction. The pairing mechanism favors the existence of the
pseudogap in the underdoped FeAs superconductors. A criterion is introduced to
distinguish whether or not the pseudogap can open in a material.",0806.3125v2
2008-06-25,"Mossbauer Spectroscopy Determination of iron foreign phases in the Superconducting Systems; RAsFeO1-x, RAsFeO1-xFx and Sr1-xKxFe2As2","The recently discovered superconducting - spin density wave materials,
containing Fe and As, have raised huge interest. However most materials
prepared to date, suffer from a varying degree of content of foreign Fe-As
phases, Fe2As, FeAs2 and FeAs, which can lead to wrong conclusions concerning
the properties of these materials. We show here that Mossbauer Spectroscopy is
able to determine quite easily the relative content of the foreign phases. This
procedure is demonstrated by a study of seven samples of superconducting or
spin density wave materials, prepared in three different laboratories.",0806.4078v1
2008-06-26,Some improvements of the ART method for finding transition pathways on potential energy surfaces,"The Activation-Relaxation Technique nouveau (ARTn) is an eigenvector
following method for systematic search of saddle points and transition pathways
on a given potential energy surface. We propose a variation of this method
aiming at improving the efficiency of the local convergence close to the saddle
point. We prove the convergence and robustness of this new algorithm. The
efficiency of the method is tested in the case of point defects in body
centered cubic iron.",0806.4354v1
2008-07-14,Superconductivity in SrFe_(2-x)Co_xAs_2: Internal Doping of the Iron Arsenide Layers,"In the electron doped compounds SrFe_(2-x)Co_xAs_2 superconductivity with T_c
up to 20 K is observed for 0.2 < x < 0.4. Results of structure determination,
magnetic susceptibility, electrical resistivity, and specific heat are
reported. The observation of bulk superconductivity in all thermodynamic
properties -- despite strong disorder in the Fe-As layer -- favors an itinerant
picture in contrast to the cuprates and renders a p- or d-wave scenario
unlikely. DFT calculations find that the substitution of Fe by Co (x > 0.3)
leads to the suppression of the magnetic ordering present in SrFe_2As_2 due to
a rigid down-shift of the Fe-3d_(x^2-y^2) related band edge in the density of
states.",0807.2223v1
2008-07-14,Structure and superconductivity of LiFeAs,"The lithium ions in Lithium iron arsenide phases with compositions close to
LiFeAs have been located using powder neutron diffraction. These phases exhibit
superconductivity at temperatures at least as high as 16 K demonstrating that
superconductivity in compounds with [FeAs]- anti-PbO-type anionic layers occurs
in compounds with at least three different structure types and occurs for a
wide range of As-Fe-As bond angles.",0807.2228v2
2008-07-31,Superconductivity in nickel-based compound GdONiBi and hole doped Gd0.9Sr0.1ONiBi,"We successfully synthesized the nickel-based compound GdONiBi with
superconducting transition temperature about 4.5 K. By partially substituting
the element Gd with Sr to introduce holes into the material, we got new
superconductor Gd0.9Sr0.1ONiBi with critical temperature about 4.7 K. The
normal state resistivity in nickel-based samples shows a metallic behavior. The
magnetoresistance measurements show a different behavior compared to those in
iron-based compounds which indicates that the mechanism in the two kinds of
superconductors maybe different.",0807.5045v1
2008-08-04,Superconductivity in Co-doped SmFeAsO,"Here we report the synthesis and basic characterization of SmFe1-xCoxAsO
(x=0.10, 0.15). The parent compound SmFeAsO itself is not superconducting but
shows an antiferromagnetic order near 150 K, which must be suppressed by doping
before superconductivity emerges. With Co-doping in the FeAs planes,
antiferromagnetic order is destroyed and superconductivity occurs at 15 K.
Similar to LaFe1-xCoxAsO, the SmFe1-xCoxAsO system appears to tolerate
considerable disorder in the FeAs planes. This result is important, which
indicates difference between cuprare superconductors and the iron-based
arsenide ones.",0808.0197v2
2008-08-13,Superconductivity in layered iron Selenide induced by cobalt- and sodium-doping,"Superconductivity with zero resistance transition temperature (Tc) up to 8.4
K and 8.3 K can be obtained by doping cobalt and sodium in alfa-FeSe with the
nominal composition of Fe0.92Co0.08Se and Na0.1FeSe, respectively. The
electrical resistivity and AC magnetic susceptibility of the prepared samples,
measured with physical property measurement system (PPMS), unambiguously
consistent with each other to indicate that the samples are superconductive.
The respective doping mechanisms for cobalt and sodium into the parent
alfa-FeSe are the Fe-site substitution and the interlayer insertion. It is the
first time that alfa-FeSe can be induced to be a superconductor with Na+
intercalated into the interlayers.",0808.1784v1
2008-08-14,"Heteroepitaxial growth and optoelectronic properties of layered iron oxyarsenide, LaFeAsO","Epitaxial thin films of LaFeAsO were fabricated on MgO (001) and
mixed-perovskite (La, Sr)(Al, Ta)O3 (001) single-crystal substrates by pulsed
laser deposition using a Nd:YAG second harmonic source and a 10 at.% F-doped
LaFeAsO disk target. Temperature dependences of the electrical resistivities
showed no superconducting transition in the temperature range of 2-300 K, and
were similar to those of undoped polycrystalline bulk samples. The
transmittance spectrum exhibited a clear peak at ~0.2 eV, which is explained by
ab-initio calculations.",0808.1956v2
2008-08-28,Electric excitation of spin resonance in antiferromagnetic conductors,"Antiferromagnetism couples electron spin to its orbital motion, thus allowing
excitation of electron-spin transitions by an ac electric rather than magnetic
field - with absorption, exceeding that of common electron spin resonance at
least by four orders of magnitude. In addition to potential applications in
spin electronics, this phenomenon may be used as a spectroscopy to study
antiferromagnetic materials of interest - from chromium to borocarbides,
cuprates, iron pnictides, and organic and heavy fermion conductors.",0808.3946v2
2008-08-30,A new family of iron pnictides: BaFeAs2 and BaFeSb2,"We investigate the structural, electronic, and magnetic properties of the
hypothetical compound BaFePn2 (Pn = As and Sb), which is isostructural to the
parent compound of the high temperature superconductor LaFeAsO1-xFx. Using
density functional theory, we show that the Fermi surface, electronic structure
and the spin density wave instability of BaFePn2 are very similar to the Fe
based superconductors. Additionally, there are very dispersive metallic bands
of a spacer Pn layer, which are almost decoupled from FePn layer. Our results
show that experimental study of BaFePn2 can test the role of charge and
polarization fluctuation, importance of two dimensionality in mechanism of
superconductivity.",0809.0041v2
2008-09-03,Imaging the antiparallel magnetic alignment of adjacent Fe and MnAs thin films,"The magnetic coupling between iron and alpha - MnAs in the epitaxial system
Fe/MnAs/GaAs(001) has been studied at the sub-micron scale, using element
selective x-ray photoemission electron microscopy. At room temperature, MnAs
layers display ridges and grooves, alternating alpha (magnetic) and beta
(non-magnetic) phases. The self-organised microstructure of MnAs and the stray
fields that it generates govern the local alignment between the Fe and alpha -
MnAs magnetization directions, which is mostly antiparallel with a marked
dependence upon the magnetic domain size.",0809.0620v1
2008-09-08,Pressure Study of Superconducting Oxypnictide LaFePO,"Electrical resistivity and magnetic susceptibility measurements under high
pressure were performed on an iron-based superconductor LaFePO. A steep
increase in superconducting transition temperature (Tc) of LaFePO with dTc/dP >
4 K/GPa to a maximum of 8.8 K for P = 0.8 GPa was observed. These results are
similar to isocrystalline LaFeAsO1-xFx system reported previously. X-ray
diffraction measurements were also performed under high pressure up to 10 GPa,
where linear compressibility ka and kc are presented.",0809.1239v1
2008-09-10,Structural and electronic response upon hole-doping of rare-earth iron oxyarsenides Nd1-xSrxFeAsO (0 < x < 0.2),"Hole-doping of NdFeAsO via partial replacement of Nd3+ by Sr2+ is a
successful route to obtain superconducting phases (Tc = 13.5 K for a Sr2+
content of 20%); however, the structural and electronic response with doping is
different from and non-symmetric to that in the electron-doped side of the
phase diagram.",0809.1755v1
2008-09-17,Phonon Density of States in Nd(O$_{1-x}$F$_{x}$)FeAs,"We report measurements of the phonon density-of-states in iron oxypnictide
superconductors by inelastic x-ray scattering. A good agreement with ab-initio
calculations that do not take into account strong electronic correlations is
found, and an unpredicted softening of phonon branches under F doping of these
compounds is observed. Raman scattering experiments lead us to conclude that
this softening is not related to zone center phonons, and consequently imply an
important softening of the relevant phonon branches at finite momentum transfer
Q.",0809.2898v1
2008-10-08,Pressure-induced superconductivity in Iron pnictide compound SrFe2As2,"Electrical resistivity under high pressure have been measured on nominally
pure SrFe2As2 up to 14 GPa. The resistivity drop appeared with increasing
pressure, and we clearly observed zero resistivity. The maximum of
superconducting transition temperature (Tc) is 38 K. The value is corresponding
to the one of optimally doping AFe2As2 (A=Sr, Ba) system with K+ ions at the
A2+ site.",0810.1377v1
2008-10-17,Magnetic Phase Diagram of FeAs based superconductors,"The recently discovered high-temperature superconductivity in doped
quaternary iron oxypnictides correlates experimentally with a magnetic
instability. We have used first-principles calculations to determine a magnetic
phase diagram of ReO$_{1-\delta}$FeAs (Re=La--Dy) as a function of the doping
$\delta$, of the FeAs in-plane lattice constant $a$, and of the distance
between the Fe and As planes, that is qualitatively consistent with recent
experimental findings on the doping, internal (chemical) and external pressure
dependence. The existence of a tricritical point (TCP) in the phase diagram
suggests new ways of enhancing $T_c$.",0810.3246v1
2008-10-18,Density Functional Study of Excess Fe in Fe$_{1+x}$Te: Magnetism and Doping,"The electronic and magnetic properties of the excess Fe in iron telluride
Fe$_{(1+x)}$Te are investigated by density functional calculations. We find
that the excess Fe occurs with valence near Fe$^{+}$, and therefore provides
electron doping with approximately one carrier per Fe, and furthermore that the
excess Fe is strongly magnetic. Thus it will provide local moments that
interact with the plane Fe magnetism, and these are expected to persist in
phases where the magnetism of the planes is destroyed for example by pressure
or doping. These results are discussed in the context of superconductivity.",0810.3274v1
2008-10-29,FeTe as a candidate material for new iron-based superconductor,"Tetragonal FeSe is a superconductor with a transition temperature Tc of 8 K
and shows a huge enhancement of Tc with applying pressure. Tetragonal FeTe has
a structure very analogous to superconducting FeSe, but does not show
superconducting transition. We investigated the pressure effect of resistivity
on FeTe. The resistivity at room temperature decreased with increasing
pressure. An anomaly in resistivity around 80 K shifted towards a lower
temperature with increasing pressure.",0810.5191v1
2008-11-08,Theory of Magnetic Order in $ Fe_{1+y}Te_{1-x}Se_x$,"We develop a local spin model to explain the rich magnetic structures in the
iron-based superconductors $Fe_{1+y}Te_{1-x}Se_x$. We show that our model
exhibits both commensurate antiferromagnetic and incommensurate magnetic order
along the crystal a-axis. The transition from the commensurate to the
incommensurate phase is induced when the concentration of excess $Fe$ atoms is
larger than a critical value. Experimentally measurable spin-wave features are
calculated, and the mean-field phase diagram of the model is obtained. Our
model also suggests the existence of a large quantum critical region due to
strong spin frustration upon increasing $Se$ concentration.",0811.1294v1
2008-11-26,Spin-Valve Effect of the Spin Accumulation Resistance in a Double Ferromagnet - Superconductor Junction,"We have measured the transport properties of Ferromagnet - Superconductor
nanostructures, where two superconducting aluminum (Al) electrodes are
connected through two ferromagnetic iron (Fe) ellipsoids in parallel. We find
that, below the superconducting critical temperature of Al, the resistance
depends on the relative alignment of the ferromagnets' magnetization. This
spin-valve effect is analyzed in terms of spin accumulation in the
superconducting electrode submitted to inverse proximity effect.",0811.4252v2
2008-11-28,Crystalline multilayers of the confined Yukawa system,"The phase diagram of Yukawa particles confined between two parallel hard
walls is calculated at zero-temperature beyond the bilayer regime by
lattice-sum-minimization. Tuning the screening, a rich phase behavior is found
in the regime bounded by stable two-triangular layers and 3-square layers. In
this regime, alternating prism phases with square and triangular basis,
structures derived from a hcp bulk lattice, and a structure with two outer
layers and two inner staggered rectangular layers, reminiscent of a Belgian
waffle iron, are stable. These structures are verifiable in experiments on
charged colloidal suspensions and dusty plasma sheets.",0811.4763v2
2008-12-03,Relationship between the magnetic hyperfine field and the magnetic moment,"Based on experimental data it is shown, for some chosen alloys and compounds
of iron, that there is no one unique relationship between the 57Fe-site
magnetic hyperfine field, Bhf, and the magnetic moment per Fe atom, m. Instead,
the Bhf-m plot consists of several branches, each of them being characteristic
of a given alloy or compound. Consequently, the effective proportionality
constant (hyperfine coupling constant) depends on the alloy system or compound,
and for a given alloy system or compound it depends on the composition or even
on the lattice site. Consequently, the scaling of Bhf into the underlying m
cannot be done a priopri.",0812.0671v1
2008-12-05,In-gap bound states and tunneling conductance of multiband superconductors through a normal/superconductor/superconductor junction,"The tunneling conductance between a metal and a multiband s-wave
superconductor with a thin layer of single-band s-wave superconductor
sandwiched in between is examined in this paper. We show that an in-gap peak in
conductance curve is found as a result of the formation of in-gap bound state
between the single-band and multiband superconductor junctions if the phases of
the superconducting order parameters of the multiband superconductor are
frustrated. The implication of this result in determining the gap symmetry of
the iron-based superconductors is discussed.",0812.1068v2
2008-12-12,Physics Potential of Future Atmospheric Neutrino Searches,"The potential of future high statistics atmospheric neutrino experiments is
considered, having in mind currently discussed huge detectors of various
technologies (water Cerekov, magnetized iron, liquid Argon). I focus on the
possibility to use atmospheric data to determine the octant of $\theta_{23}$
and the neutrino mass hierarchy. The sensitivity to the $\theta_{23}$-octant of
atmospheric neutrinos is competitive (or even superior) to long-baseline
experiments. I discuss the ideal properties of a fictitious atmospheric
neutrino detector to determine the neutrino mass hierarchy.",0812.2392v1
2008-12-12,Interplay between magnetism and superconductivity in Fe-pnictides,"We consider phase transitions and potential co-existence of spin-density-wave
(SDW) magnetic order and extended s-wave ($s^+$) superconducting order within a
two-band itinerant model of iron pnictides, in which SDW magnetism and $s^+$
superconductivity are competing orders. We show that depending on parameters,
the transition between these two states is either first order, or involves an
intermediate phase in which the two orders co-exist. We demonstrate that such
co-existence is possible when SDW order is incommensurate.",0812.2469v1
2008-12-22,The calculation of the effective interaction parameter in LDA+U method by linear response approach for Fe(OH)2,"In this paper we have investigated the electronic properties of Fe(OH)2
hydroxide by using the LSDA+U as well as the generalized gradient
approximation. Our calculations for the iron-hydroxide show that the LSDA
results are greatly at variance with experimental findings. On the other hand
we have shown that LSDA+U is capable of opening a gap at the Fermi level
resulting in insulating ground state in agreement with experimental
observations.",0812.4116v1
2008-12-30,Maxwell Tension Supports the Water Bridge,"A cylindrical flexible cable made up of pure fluid water can be
experimentally spanned across a spatial gap with cable endpoints fixed to the
top edges of two glass beakers. The cable has been called a water bridge in
close analogy to iron cables employed to build ordinary span bridges. A
necessary condition for the construction of a water bridge is that a large
electric field exists parallel to and located within the water cable.
Presently, there is no accepted detailed theory which quantitatively explains
the forces which hold up the bridge. Our purpose is to present such theory
based on the Maxwell pressure tensor induced by the electric field albeit
within the condensed matter dielectric fluid cable.",0812.4845v1
2009-01-11,A Possible Theoretical Model For Studying Superconductivity In Fe-based Systems,"A theoretical approach with a microscopic model is proposed for the observed
""high temperature superconductivity"" in the Iron-based compounds. The above
scheme takes into account two important aspects viz. (i) superconducting
transition close to magnetic ordering and (ii) the layered structure. From the
calculation of the superconducting transition temperature, it is shown that in
the Fe-based superconductors the magnetic mechanism for superconductivity,
operating through the effective attractive Coulomb interaction within the
framework of the Fermi Liquid theory, is highly plausible.",0901.1438v1
2009-02-09,Dislocation Core Energies and Core Fields from First Principles,"Ab initio calculations in bcc iron show that a <111> screw dislocation
induces a short-range dilatation field in addition to the Volterra elastic
field. This core field is modeled in anisotropic elastic theory using force
dipoles. The elastic modeling thus better reproduces the atom displacements
observed in ab initio calculations. Including this core field in the
computation of the elastic energy allows deriving a core energy which converges
faster with the cell size, thus leading to a result which does not depend on
the geometry of the dislocation array used for the simulation.",0902.1451v1
2009-02-21,"Unconventional Pairing in Doped Band Insulators on a Honeycomb Lattice : the Role of the Disconnected Fermi Surface and a Possible Application to Superconducting $β$-MNCl (M=Hf,Zr)","We investigate the possibility of realizing unconventional superconductivity
in doped band insulators on the square lattice and the honeycomb lattice, where
the latter is found to be a good candidate due to the disconnectivity of the
Fermi surface. We propose applying the theory to the superconductivity in doped
layered nitride $\beta$-$M$NCl ($M=$Hf, Zr). Finally, we compare two groups of
superconductors with disconnected Fermi surface, $\beta$-$M$NCl and the iron
pnictides, which have high $T_c$ despite some faults against superconductivity
are present.",0902.3695v1
2009-03-02,Fermi surface shrinking and interband coupling in iron-based pnictides,"Recent measurements of Fermi surface with de Haas-van Alphen oscillations in
LaFePO showed a shrinking of the Fermi pockets with respect to first-principle
LDA calculations, suggesting an energy shift of the hole and electrons bands
with respect to LDA. We show that these shifts are a natural consequence of the
strong particle-hole asymmetry of electronic bands in pnictides, and that they
provide an indirect experimental evidence of a dominant interband scattering in
these systems.",0903.0315v2
2009-03-08,Predictions of highest Transition-temperature for electron-phonon superconductors,"Using the Eliashberg strong coupling theory with vertex correction, we
calculate maps of transition temperatures (T$_{c}$) of electron-phonon
superconductors in full parameter space. The maximums of transition
temperatures for superconductors are predicted based on the maps and the
criterion of instability of superconductivity. The strong vertex correction and
high transition temperature are tightly correlated in superconductors. We
predict that the maximum of T$_{c}$ of new iron-based superconductors will be
close to 90(K).",0903.1395v1
2009-03-18,Piezonuclear neutrons from fracturing of inert solids,"Neutron emission measurements by means of helium-3 neutron detectors were
performed on solid test specimens during crushing failure. The materials used
were marble and granite, selected in that they present a different behaviour in
compression failure (i.e., a different brittleness index) and a different iron
content. All the test specimens were of the same size and shape. Neutron
emissions from the granite test specimens were found to be of about one order
of magnitude higher than the natural background level at the time of failure.",0903.3104v1
2009-03-26,SCES '08 - concluding remarks,"This year's SCES has proved exciting in the array of unconventional phenomena
discovered both in novel systems, and by the renewed investigation of age-old
systems, arguably in the vicinity of QCPs. From heavy fermion systems, to
cuprate superconductors, and in a new twist iron pnictide superconductors -
some questions remain: just how similar or different are correlated phenomena
in these systems? Further, how ubiquitous are ultra-strongly correlated effects
such as the fractional quantum Hall effect (QHE), and can cold atom systems
mimic such correlated phases? We shall discuss some of these issues here.",0903.4548v1
2009-04-05,Destruction of graphene by metal adatoms,"The formation energies for mono- and bivacancies in graphene in the presence
of adatoms of various metals and small metallic clusters have been calculated.
It is shown that transition metal impurities, such as iron, nickel and,
especially, cobalt reduce dramatically the vacancy formation energies whereas
gold impurities have almost no effect on characteristics of the vacancies. This
results highlight that special measures are required in order to protect
graphene from damage by transition metal leads.",0904.0807v2
2009-04-30,Preparation and superconductivity of iron selenide thin films,"FeSex (x = 0.80, 0.84, 0.88, 0.92) thin films were prepared on SrTiO3(001)
(STO), (La,Sr)(Al,Ta)O3(001) (LSAT), and LaAlO3(001) (LAO) substrates by pulsed
laser deposition method. All thin films show single-phase and c-axis oriented
epitaxial growth, and are superconducting. Among them, the FeSe0.88 thin films
show Tc, onset of 11.8 K and Tc, 0 of 3.4 K. The upper critical magnetic field
is estimated to be 14.0 T.",0904.4731v1
2009-05-02,Quantum fluctuation and geometrical frustration effects on electric polarization,"We examine theoretically a possibility of ferroelectricity caused by
electronic charge order without inversion symmetry, motivated by layered iron
oxides. Quantum electronic models in a paired-triangular lattice are analyzed
by utilizing the variational Monte Carlo simulation. Our calculation
demonstrates that combined effects of electron transfer between the layers,
corresponding to quantum fluctuation between the potential minima, and
geometrical frustration promote appearance of an electric polarization. Present
results are in contrast to the conventional manner of quantum fluctuation in
ferroelectricity.",0905.0182v1
2009-05-04,Berry Phase Coupling and the Cuprate Neutron Scattering Resonance,"We examine the influence of coupling between particle-hole and
particle-particle spin fluctuations on the inelastic neutron scattering
resonance (INSR) in cuprate superconductors in both weak and strong interaction
limits. For weak-interactions in the particle-hole channel, we find that the
interchannel coupling can eliminate the resonance. For strong interactions
which drive the system close to a $\bm{Q}=(\pi,\pi)$ magnetic instablity, the
resonance frequency always approaches zero but its value is influenced by the
interchannel coupling. We comment on constraints imposed on cuprate physics by
the INSR phenomenology, and a comparison between the cuprates and the
newly-discovered iron pnictide superconductors is discussed.",0905.0464v1
2009-05-12,Magnetic vortex as a ground state for sub-micron antiferromagnetic particles,"For submicron particles shaped as any axisymmetric body and made with
standard canted antiferromagnet like hematite or iron borate, the ground state
may comprise of a magnetic vortex with topologically non-trivial distribution
of the sublattice magnetization $\vec{l}$ and planar coreless vortex-like
structure for the net magnetization $\vec{M}$. For antiferromagnetic particles
in the vortex state, in addition to low-frequency modes, there are high
frequency modes with frequencies over the range of hundreds gigahertz,
including a mode localized in the region of the radius 30-40 nm near a vortex
core.",0905.1966v2
2009-05-24,Magnetic impurities in the two-band $s_\pm$-wave superconductors,"We investigate the effects of magnetic impurities in a superconducting state
with $s_\pm$ pairing symmetry. Within a two-band model, we find that the
intra-band magnetic scattering serves as a pair breaker while the inter-band
magnetic scattering preserves pairing and hardly affects transition temperature
in the Born limit. We also show that the same physics can persist beyond the
weak scattering region. Our results coincide with recent experimental
measurements in iron-based superconductors and thus provides an indirect
evidence of the possible $s_\pm$ pairing symmetry in these materials.",0905.3883v2
2009-05-25,Electron Spin Resonance investigation of undoped and Li-doped CdWO_4 scintillator crystals,"Electron spin resonance (ESR) spectra of Fe3+ and Mn2+ ions have been studied
in the nominally pure and 0.05% Li-doped single crystals of CdWO4. The
zero-field splitting parameters are determined with a high precision for both
of the impurities. The result suggest that the Li-doping leads to the increase
of the ionic charge of iron from 3+ to 4+ and of manganese, from 1+ to 2+.",0905.4011v1
2009-06-02,Enhancement of Critical Current Densities in Co-Doped BaFe$_{2}$As$_{2}$ with Columnar Defects Introduced by Heavy-Ion Irradiation,"We report the first realization of columnar defects in Co-doped
BaFe$_{2}$As$_{2}$ single crystals by heavy-iron irradiation. The columnar
defects are confirmed by transmission electron microscopy and their density is
about 40 % of the irradiation dose. Magneto-optical imaging and bulk
magnetization measurements reveal that the critical current density is strongly
enhanced in the irradiated region. We also find that vortex creep rates are
strongly suppressed by the columnar defects. We compare the effect of heavy-ion
irradiation into Co-doped BaFe$_{2}$As$_{2}$ and cuprate superconductors.",0906.0444v1
2009-06-14,The Radial Dependence of Temperature and Iron Abundance: Galaxy Clusters from z=0.14 to z=0.89,"Using archival Chandra and XMM-Newton data on 35 galaxy clusters, we measured
average temperature and metallicity profiles for clusters based separated by
temperature, cooling time, and redshift. Our results show no evidence for
significant changes in the metallicity or temperature profiles with redshift
once these selection effects are taken into account.",0906.2564v1
2009-06-22,Kondo resonance narrowing in d- and f-electron systems,"By developing a simple scaling theory for the effect of Hund's interactions
on the Kondo effect, we show how an exponential narrowing of the Kondo
resonance develops in magnetic ions with large Hund's interaction. Our theory
predicts an exponential reduction of the Kondo temperature with spin S of the
Hund's coupled moment, a little-known effect first observed in d-electron
alloys in the 1960's, and more recently encountered in numerical calculations
on multi-band Hubbard models with Hund's interactions. We discuss the
consequences of Kondo resonance narrowing for the Mott transition in d-band
materials, particularly iron pnictides, and the narrow ESR linewidth recently
observed in ferromagnetically correlated f-electron materials.",0906.4107v1
2009-06-29,Elastic energy of a straight dislocation and contribution from core tractions,"We derive an expression of the core traction contribution to the dislocation
elastic energy within linear anisotropic elasticity theory using the sextic
formalism. With this contribution, the elastic energy is a state variable
consistent with the work of the Peach-Koehler forces. This contribution needs
also to be considered when extracting from atomic simulations core energies.
The core energies thus obtained are real intrinsic dislocation properties: they
do not depend on the presence and position of other defects. This is
illustrated by calculating core energies of edge dislocation in bcc iron, where
we show that dislocations gliding in {110} planes are more stable than those
gliding in {112} planes.",0906.5332v1
2009-07-15,Perfect and partial hedging for swing game options in discrete time,"The paper introduces and studies hedging for game (Israeli) style extension
of swing options considered as multiple exercise derivatives. Assuming that the
underlying security can be traded without restrictions we derive a formula for
valuation of multiple exercise options via classical hedging arguments.
Introducing the notion of the shortfall risk for such options we study also
partial hedging which leads to minimization of this risk.",0907.2541v1
2009-08-06,Track fitting by Kalman Filter method for a prototype cosmic ray muon detector,"We have developed a track fitting procedure based on Kalman Filter technique
for an Iron Calorimeter (ICAL) prototype detector when the detector is flushed
with single muon tracks. The relevant track parameters i.e., momentum,
direction and charge are reconstructed and analyzed. This paper discusses the
design of the prototype detector, its geometry simulation by Geant4, and the
detector response with the cosmic ray muons. Finally we show the resolution of
reconstructed momenta and also the charge identification efficiency of $\mu^+$
and $\mu^-$ events in the magnetized ICAL.",0908.0851v1
2009-08-11,Large single crystal growth of BaFe1.87Co0.13As2 using a nucleation pole,"Co-doped iron arsenic single crystal of BaFe1.87Co0.13As2 with dimension up
to 20 x 10 x 2 mm3 were grown by a nucleation pole: an alumina stick served as
nucleation center during growth. The high quality of crystalline was
illustrated by the measurements of neutron rocking curve and X-ray diffraction
pattern. A very sharp superconducting transition temperature Tc~25 K was
revealed by both resistivity and susceptibility measurements. A nearly 100%
shielding fraction and bulk nature of the superconductivity for the single
crystal were confirmed using magnetic susceptibility data.",0908.1486v2
2009-09-07,Evidence of Strong Electron Correlations in Gamma-Iron,"Single-particle excitation spectra of gamma-Fe in the paramagnetic state have
been investigated by means of the first-principles dynamical coherent potential
approximation theory which has recently been developed. It is found that the
central peak in the density of states consisting of the t2g bands is destroyed
by electron correlations, and the Mott-Hubbard type correlated bands appear.
The results indicate that the gamma-Fe can behave as correlated electrons at
high temperatures.",0909.1122v1
2009-09-07,The theory of photorefractive resonance for localized beams in two-carrier photorefractive systems,"This paper extends the existing theory of two carrier photorefractivity
resonance, which is generally applied to Iron doped Indium Phosphide (InP:Fe),
to the case of low non-harmonic illumination. The space charge field profile is
computed, and the variations of its amplitude, width and position are
determined as functions of the background intensity. The effect of
photorefractive resonance on these quantities is evidenced, contributing to the
understanding of published experimental results in InP:Fe.",0909.1217v1
2009-09-16,Intrinsic ferromagnetic impurity phases in SmFeAsO1-xFx detected by muSR,"We report about muSR measurements on SmFeAsO1-xFx which helped us to identify
the signature of diluted ferromagnetic inclusions, ubiquitous in the iron
pnictides. These impurities are characterized by a Curie temperature close to
room temperature and they seem responsible for a non negligible magnetic
relaxation of the implanted muons, that should not be confused with intrinsic
pnictide properties.",0909.3004v1
2009-10-06,"Superconductivity Near a Quantum Critical Point in Ba(Fe,Co)2As2","We will examine the possible link between spin fluctuations and the
superconducting mechanism in the iron-based high temperature superconductor
Ba(Fe,Co)2As2 based on NMR and high pressure transport measurements.",0910.1071v2
2009-10-08,Resonant inelastic x-ray scattering in single-crystal superconducting PrFeAsO0.7,"Resonant inelastic x-ray scattering (RIXS) spectra at the Fe K-edge were
measured for a single crystal of the iron oxypnictide superconductor PrFeAsO0.7
(Tc=42 K). They disclose a weak, broad feature centered around 4.5 eV energy
loss, which is slightly resonantly enhanced when the incident energy is tuned
in the vicinity of the 4p white line. We tentatively ascribe it to the
charge-transfer excitation between As 4p and Fe 3d.",0910.1423v1
2009-10-08,The Puzzling Frequencies of CEMP and NEMP Stars,"We present the results of binary population simulations of carbon- and
nitrogen-enhanced metal-poor (CEMP and NEMP) stars. We show that the observed
paucity of very nitrogen-rich stars puts strong constraints on possible
modifications of the initial mass function at low metallicity.",0910.1489v1
2009-10-19,Fe-peak element abundances in disk and halo stars,"At present none of Galactic chemical evolution (GCE) models provides a
self-consistent description of observed trends for all iron-peak elements with
metallicity simultaneously. The question is whether the discrepancy is due to
deficiencies of GCE models, such as stellar yields, or due to erroneous
spectroscopically-determined abundances of these elements in metal-poor stars.
The present work aims at a critical reevaluation of the abundance trends for
several odd and even-Z Fe-peak elements, which are important for understanding
explosive nucleosynthesis in supernovae.",0910.3689v1
2009-10-20,$α$-FeSe as an orbital-selective incoherent metal: An LDA+DMFT study,"$\alpha$-FeSe, a prototype iron-chalcogenide superconductor, shows clear
signatures of a strange incoherent normal state. Motivated thereby, we use
LDA+DMFT to show how strong multi-band correlations generate a low-energy
pseudogap in the normal state, giving an incoherent metal in very good
semi-quantitative agreement with observations. We interpret our results in
terms of $\alpha$-FeSe being close to Mottness. A wide range of anomalous
responses in the ""normal"" state are consistently explained, lending strong
support for this view. Implications for superconductivity arising from such an
anomalous state are touched upon.",0910.3828v1
2009-10-21,Surface-angle dependence of the tunneling spectroscopy in iron-based superconductors: sign-reversing s-wave scenarios,"We discuss the surface Andreev bound states in Fe-based superconductors with
the use of an effective five-band model and investigate the surface-angle
dependence of the tunneling spectroscopy by a quasiclassical approach for an
isotropic and an anisotropic /pm s-wave gap superconductivity. We show that
information on the normal state is important for the Andreev bound state and
its peak positions do not depend on the gap amplitude anisotropy.",0910.4040v1
2009-12-02,Evolution of two-gap behavior of the superconductor FeSe_1-x,"The superfluid density, \rho_s, of the iron chalcogenide superconductor,
FeSe_1-x, was studied as a function of pressure by means of muon-spin rotation.
The zero-temperature value of \rho_s increases with increasing transition
temperature T_c (increasing pressure) following the tendency observed for
various Fe-based and cuprate superconductors. The analysis of \rho_s(T) within
the two-gap scheme reveals that the effect on both, T_c and \rho_s(0), is
entirely determined by the band(s) where the large superconducting gap
develops, while the band(s) with the small gap become practically unaffected.",0912.0471v1
2009-12-10,Capillary force-induced structural instability in liquid infiltrated elastic circular tubes,"The capillary-induced structural instability of an elastic circular tube
partially filled by a liquid is studied by combining theoretical analysis and
molecular dynamics simulations. The analysis shows that, associated with the
instability, there is a well-defined length scale (elasto-capillary length),
which exhibits a scaling relationship with the characteristic length of the
tube, regardless of the interaction details. We validate this scaling
relationship for a carbon nanotube partially filled by liquid iron. The
capillary-induced structural transformation could have potential applications
for nano-devices.",0912.1894v1
2009-12-22,Superconductivity Induced in Iron Telluride Films by Low Temperature Oxygen Incorporation,"We report superconductivity induced in films of the non-superconducting,
antiferromagnetic parent material FeTe by low temperature oxygen incorporation
in a reversible manner. X-ray absorption shows that oxygen doping changes the
nominal Fe valence state from 2+ in the non-superconducting state to mainly 3+
in the superconducting state. Thus superconductivity in O doped FeTe occurs in
a quite different charge and strain state than the more common
FeTe$_{1-x}$Se$_x$. This work also suggests a convenient path for conducting
doping experiments in-situ with many measurement techniques.",0912.4539v2
2010-01-07,Genesis of coexisting itinerant and localized electrons in Iron Pnictides,"We show how the general features of the electronic structure of the Fe-based
high-Tc superconductors are a natural setting for a selective localization of
the conduction electrons to arise. Slave-spin and Dynamical mean-field
calculations support this picture and allow for a comparison of the magnetic
properties with experiments.",1001.1098v1
2010-01-07,Calculated Cleavage Behavior and Surface States of LaOFeAs,"The layered structure of the iron based superconductors gives rise to a more
or less pronounced two-dimensionality of their electronic structure, most
pronounced in LaOFeAs. A consequence are distinct surface states to be expected
to influence any surface sensitive experimental probe. In this work a detailed
density functional analysis of the cleavage behavior and the surface electronic
structure of LaOFeAs is presented. The surface states are obtained to form
two-dimensional bands with their own Fermi surfaces markedly different from the
bulk electronic structure.",1001.1127v1
2010-01-19,"Superconductivity at 33 K in ""111"" single crystals at ambient pressure","We have successfully grown single crystalline NaFeAs with cobalt or phosphor
doping. Bulk superconductivity occurs in NaFe$_{0.95}$Co$_{0.05}$As at 19 K
while much higher transition temperature is observed in
NaFeAs$_{0.8}$P$_{0.2}$, in which the Tc of 33 K is even higher than the
highest value realized by applying pressure in NaFeAs and all other
isoelectronic element substituted samples. We discuss these behaviours by
comparison with 122 and 1111 systems. We hope that our findings will help
improve our understanding of iron-based superconductivity.",1001.3311v2
2010-02-05,High resolution Compton scattering as a Probe of the Fermi surface in the Iron-based superconductor $LaO_{1-x}F_xFeAs$,"We have carried out first principles all-electron calculations of the
(001)-projected 2D electron momentum density and the directional Compton
profiles along the [100], [001] and [110] directions in the Fe-based
superconductor LaOFeAs within the framework of the local density approximation.
We identify Fermi surface features in the 2D electron momentum density and the
directional Compton profiles, and discuss issues related to the observation of
these features via Compton scattering experiments.",1002.1072v1
2010-02-10,The heavily polluted atmosphere of the DAZ white dwarf GALEX J193156.8+011745,"We report on the discovery of a new heavily polluted white dwarf. The DAZ
white dwarf GALEX J193156.8+011745 was identified in a joint GALEX/GSC survey
of ultraviolet-excess objects. Optical spectra obtained at ESO NTT show strong
absorption lines of magnesium and silicon and a detailed abundance analysis
based on VLT-Kueyen UVES spectra reveal super-solar abundances of silicon and
magnesium, and near-solar abundances of oxygen, calcium, and iron. The overall
abundance pattern bears the signature of ongoing accretion onto the white dwarf
atmosphere. The infrared spectral energy distribution shows an excess in the H
and K bands likely associated with the accretion source.",1002.2069v1
2010-02-12,Iron isotope effect on the superconducting transition temperature and the crystal structure of FeSe_1-x,"The Fe isotope effect (Fe-IE) on the transition temperature T_c and the
crystal structure was studied in the Fe chalcogenide superconductor FeSe_1-x by
means of magnetization and neutron powder diffraction (NPD). The substitution
of natural Fe (containing \simeq 92% of ^{56}Fe) by its lighter ^{54}Fe isotope
leads to a shift of T_c of 0.22(5)K corresponding to an Fe-IE exponent of
\alpha_Fe=0.81(15). Simultaneously, a small structural change with isotope
substitution is observed by NDP which may contribute to the total Fe isotope
shift of T_c.",1002.2510v2
2010-02-26,"Comment on ""Nonmagnetic Impurity Resonances as a Signature of Sign-Reversal Pairing in Fe-As-Based Superconductors""","In a recent Letter [PRL 103, 186402 (2009)], the energy band structure of
Fe-As-based superconductors is fitted with a tight-binding model with two Fe
ions per unit cell and two degenerate xz and yz orbitals per Fe ion. The author
claims that the proposed model, which differs markedly from a model previously
used by other authors for the same two orbitals in the same compounds,
possesses the symmetry required to describe the Fe-As planes in iron-pnictide
superconductors. In this comment we argue that this is not the case.",1002.4939v1
2010-03-03,Temperature - pressure phase diagram of the superconducting iron pnictide LiFeP,"Electrical-resistivity and magnetic-susceptibility measurements under
hydrostatic pressure up to p = 2.75 GPa have been performed on superconducting
LiFeP. A broad superconducting (SC) region exists in the temperature - pressure
(T-p) phase diagram. No indications for a spin-density-wave transition have
been found, but an enhanced resistivity coefficient at low pressures hints at
the presence of magnetic fluctuations. Our results show that the
superconducting state in LiFeP is more robust than in the isostructural and
isoelectronic LiFeAs. We suggest that this finding is related to the nearly
regular [FeP_4] tetrahedron in LiFeP.",1003.0785v1
2010-03-05,Theoretical evidence for strong correlations and incoherent metallic state in FeSe,"The role of electronic Coulomb correlations in iron-based superconductors is
an important open question. We provide theoretical evidence for strong
correlation effects in the FeSe compound, based on dynamical mean field
calculations. A lower Hubbard band is found in the spectral properties.
Moreover, together with significant orbital-dependent mass enhancements, we
find that the normal state is a bad metal over an extended temperature range,
implying a non-Fermi liquid. Predictions for angle-resolved photoemission
spectroscopy are made.",1003.1286v2
2010-03-09,Implementation of the SU(2) Hamiltonian Symmetry for the DMRG Algorithm,"In the Density Matrix Renormalization Group (DMRG) algorithm, Hamiltonian
symmetries play an important role. Using symmetries, the matrix representation
of the Hamiltonian can be blocked. Diagonalizing each matrix block is more
efficient than diagonalizing the original matrix. This paper explains how the
the DMRG++ code has been extended to handle the non-local SU(2) symmetry in a
model independent way. Improvements in CPU times compared to runs with only
local symmetries are discussed for the one-orbital Hubbard model, and for a
two-orbital Hubbard model for iron-based superconductors. The computational
bottleneck of the algorithm and the use of shared memory parallelization are
also addressed.",1003.1919v1
2010-03-19,Non-equilibrium current and noise in inelastic tunneling through a magnetic atom,"In a recent experiment, Hirjibehedin {\it et al.} [Science {\bf 317}, 1199
(2007)] performed inelastic tunneling spectroscopy of a single iron atom
absorbed on a nonmagnetic substrate. The observed steps in the differential
conductance marked the spin excitation energies. In this Letter, we explain
observed nonmonotonicities in the differential conductance by a nonequilibrium
population of the atom spin states. Furthermore, we predict super-Poissonian
current noise due to this nonequilibrium situation. By introducing an
anisotropic relaxation channel we are also able to explain the remarkable
absence of nonequilibrium features at certain conductance steps.",1003.3794v2
2010-04-05,Magnetic vortex as a ground state for micron-scale antiferromagnetic samples,"Here we consider micron-sized samples with any axisymmetric body shape and
made with a canted antiferromagnet, like hematite or iron borate. We find that
its ground state can be a magnetic vortex with a topologically non-trivial
distribution of the sublattice magnetization $\vec{l}$ and planar coreless
vortex-like structure for the net magnetization $\vec{M}$. For
antiferromagnetic samples in the vortex state, in addition to low-frequency
modes, we find high-frequency modes with frequencies over the range of hundreds
of gigahertz, including a mode localized in a region of radius $\sim$ 30--40 nm
near the vortex core.",1004.0606v1
2010-05-11,"Comment on ""Nematic Electronic Structure in the ""Parent"" State of the Iron-Based Superconductor Ca(Fe1-xCox)2As2""","Chuang et al (Reports, 8th of January 2010, p. 181)1 report quasiparticle
interference (QPI) imaging that shows pronounced C2 asymmetry. They interpreted
this result as indication of an electronic nematic phase with an electron band
dispersive only along the b-axis of this orthorhombic material. We argue that
this asymmetry is consistent with the underlying long range magnetic order and
that LDA electronic structure provides a better description of the QPI images
than the 1D band structure conjectured by Chuang et al.",1005.1761v1
2010-06-09,Interaction of iron clusters (Fe_n; n <= 6) with a divacancy in graphene,"In this work, we have studied the chemical and magnetic interactions of Fe_n;
n <= 6, clusters with a divacancy site in a graphene sheet by ab-initio density
functional calculations. Our results show significant chemical interactions
between the cluster and graphene. As a result, a complex distribution of
magnetic moments appear on the distorted Fe clusters in presence of graphene
and results in a lower average magnetic moments compared to the free clusters.
The presence of cluster also prevents the formation of 5-8-5 ringed structure
known to exhibit in a graphene sheet having a divacancy defect. The clusters
induce electronic states primarily of d-character near the Fermi level.",1006.1910v1
2010-06-24,Magnetic Properties of Ab initio Model for Iron-Based Superconductors LaFeAsO,"By using variational Monte Carlo method, we examine an effective low-energy
model for LaFeAsO derived from an ab initio downfolding scheme. We show that
quantum and many-body fluctuations near a quantum critical point largely reduce
the antiferromagnetic (AF) ordered moment and the model not only quantitatively
reproduces the small ordered moment in LaFeAsO, but also explains the diverse
dependence on LaFePO, BaFe2As2 and FeTe. We also find that LaFeAsO is under
large orbital fluctuations, sandwiched by the AF Mott insulator and weakly
correlated metals. The orbital fluctuations and Dirac-cone dispersion hold keys
for the diverse magnetic properties.",1006.4812v1
2010-07-09,UHECRs from magnetic reconnection in relativistic jets,"Ultra-high energy cosmic rays (UHECRs) may be produced in active galactic
nuclei (AGN) or gamma-ray burst (GRB) jets. I argue that magnetic reconnection
in jets can accelerate UHECRs rather independently of physical processes in the
magnetic dissipation region. First order Fermi acceleration can efficiently
take place in the region where the unreconnected (upstream) magnetized fluid
converges into the reconnection layer. I find that protons can reach energies
up to E~10^{20} eV in GRB and powerful AGN jets while iron nuclei can reach
similar energies in AGN jets of more moderate luminosity.",1007.1522v2
2010-07-20,First-principles studies on electrical resistivity of iron under pressure,"We investigate the temperature and pressure dependences of the electrical
resistivity for bcc and hcp Fe using the low-order variational approximation
and theoretical transport spectral functions calculated from first principles
linear response linear-muffin-tin-orbital method in the generalized-gradient
approximation. The calculated values are in close agreement with available
experimental data, and show strong increase with temperature and decrease with
pressure. We also discuss the behavior of the electrical resistivity for the
bcc -> hcp phase transition.",1007.3423v1
2010-07-26,Ab initio Low-Dimensional Physics Opened Up by Dimensional Downfolding: Application to LaFeAsO,"An ab initio downfolding method is formulated to construct low-dimensional
models for correlated electrons. In addition to the band downfolding by
constrained random phase approximation formulated for 3D models, screening away
from the target layer (chain) is further involved. Eliminating the off-target
degrees of freedom, namely, dimensional downfolding yields ab initio
low-dimensional models. The method is applied to derive a 2D model for a
layered superconductor LaFeAsO, where the interlayer screening crucially makes
the effective interaction short ranged and reduces the onsite Coulomb
interactions by 10-20 \% from the 3D model for the 5 iron-3d orbitals.",1007.4429v1
2010-08-07,Superconductivity in SrFe2As2 with Pt Doping,"We have synthesized polycrystalline samples of Pt-substituted SrFe2As2 and
measured the temperature dependence of magnetization and electrical
resistivity. We have observed the superconducting transition at Tc = 17 K with
the maximum shielding volume fraction at x = 0.125 in Sr(Fe1-xPtx)2As2. It is
found that the maximum Tc depends on the substituted element, so it is
important to substitute various elements to explore new iron-based
superconductors with higher Tc.",1008.1297v1
2010-08-16,Quasiparticle interference of C2-symmetric surface states in LaOFeAs parent compound,"We present scanning tunneling microscopy studies of the LaOFeAs parent
compound of iron pnictide superconductors. Topographic imaging reveals two
types of atomically flat surfaces, corresponding to the exposed LaO layer and
FeAs layer respectively. On one type of surface, we observe strong standing
wave patterns induced by quasiparticle interference of two-dimensional surface
states. The distribution of scattering wavevectors exhibits pronounced two-fold
symmetry, consistent with the nematic electronic structure found in the
Ca(Fe1-xCox)2As2 parent state.",1008.2642v1
2010-08-23,Vortex states in hole-doped iron-pnictide superconductors,"Based on a phenomenological model with competing spin-density-wave (SDW) and
extended $s-$wave superconductivity, the vortex states in
Ba$_{1-x}$K$_{x}$Fe$_{2}$As$_{2}$ are investigated by solving Bogoliubov-de
Gennes equations. Our result for the optimally doped compound without induced
SDW is in qualitative agreement with recent scanning tunneling microscopy
experiment. We also propose that the main effect of the SDW on the vortex
states is to reduce the intensity of the in-gap peak in the local density of
states and transfer the spectral weight to form additional peaks outside the
gap.",1008.3885v1
2010-08-31,Proximity of Iron Pnictide Superconductors to a Quantum Tricritical Point,"We determine the nature of the magnetic quantum critical point in the doped
LaFeAsO using a set of constrained density functional calculations that provide
ab initio coefficients for a Landau order parameter analysis. The system turns
out to be remarkably close to a quantum tricritical point, where the nature of
the phase transition changes from first to second order. We compare with the
effective field theory and discuss the experimental consequences.",1009.0009v1
2010-09-16,Consistency of neutrino DIS and the present parton distribution functions,"We study the nuclear effects in the neutrino\anti-neutrino-nucleon deep
inelastic scattering (DIS) by comparing the NuTeV, CDHSW, and CHORUS
cross-sections from Iron and Lead targets to the predictions derived from the
latest parton distribution functions (PDFs). The nuclear modifications found
seem to display agreement with those in charged lepton DIS. Our study thus
lends support to the consistency of employing neutrino data in global fits of
PDFs.",1009.3143v1
2010-09-26,Spin dependent electron-phonon interaction in SmFeAsO by low-temperature Raman spectroscopy,"The interplay between spin dynamics and lattice vibration has been suggested
as an important part of the puzzle of high-temperature superconductivity. Here
we report the strong interaction between spin fluctuation and phonon in
SmFeAsO, a parent compound of the iron arsenide family of superconductors,
revealed by low-temperature Raman spectroscopy. Anomalous zone-boundary-phonon
Raman scattering from spin superstructure was observed at temperatures below
the antiferromagnetic ordering point, which offers compelling evidence on spin
dependent electron-phonon coupling in pnictides.",1009.5050v2
2010-10-06,The Relation Between Charged Particles and Muons With Threshold Energy 1 GeV in Extensive Air Showers Registered at the Yakutsk EAS Array,"Characteristics of the muon component in EAS are analyzed together with their
fluctuations. The aim of this analysis -- a comparison of experimental data
with computational results obtained within frameworks of various hadron
interaction models for protons and iron nuclei and an estimation of cosmic ray
mass composition in the ultra-high energy region.",1010.1182v1
2010-10-19,Coexistence of Superconductivity and Charge Density Wave in SrPt2As2,"SrPt2As2 is a novel arsenide superconductor, which crystallizes in the
CaBe2Ge2-type structure as a different polymorphic form of the ThCr2Si2-type
structure. SrPt2As2 exhibits a charge-density-wave (CDW) ordering at about 470
K and enters into a superconducting state at Tc = 5.2 K. The coexistence of
superconductivity and CDW refers to Peierls instability with a moderately
strong electron-phonon interaction. Thus SrPt2As2 can be viewed as a
nonmagnetic analog of iron-based superconductors, such as doped BaFe2As2, in
which superconductivity emerges in close proximity to spin-density-wave
ordering.",1010.3950v2
2010-11-03,The role of correlations in the high-pressure phase of FeSe,"We present a systematic study of the high-pressure FeSe phase performed by
means of the first-principle electronic structure calculations. Basing on
available experimental information about the unit cell geometry we calculate
the band structure and characterize the related properties during their
pressure driven evolution. The electronic structure including the hybrid
functional B3LYP or the Hubbard parameter U for the iron d states lead to the
correct semiconducting ground state for the hexagonal stoichiometric FeSe
within the broad pressure range (up to 30 GPa).",1011.0848v1
2010-11-11,"Half-metallic Antiferromagnet Sheets in Sr4M2O6CrFeAs2 (M=Sc, Cr) and Their Bulk Form","We reveal by first-principles calculations that in iron pnictides
Sr4M2O6CrFeAs2 (M=Sc, Cr) the two-dimensional CrFeAs2 layers exhibit a robust
band structure of half-metallic antiferromagnet (HMAFM). Due to the thick
blocking layer, the interlayer coupling is vanishingly small and thus the
conductive channels in individual layers may take the alternative spin
direction randomly. We show that, since the spin magnetizations of Fe and Cr
are different in a ferromagnetic state, applying a strong magnetic field and
ramping it down gradually can align the spin direction of conductive channel of
all HMAFM layers, which restores the bulk HMAFM.",1011.2576v2
2010-11-21,Magnetoelectric studies on polycrystalline FeVO4,"We report the magnetic, dielectric and ferroelectric properties of
polycrystalline iron vanadate(FeVO4), which has been recently found to exhibit
multiferroicity in low temperature with noncollinear magnetic orderings. The
influence of external magnetic field up to 9T on these properties is
systematically investigated. Besides the suppressing effect on the original
ferroelectric transition, the strong magnetic field seems to induce a secondary
ferroelectric transition at a slight lower temperature. And the corresponding
magnetization measurement reveals a field-induced metamagnetic transition at
low temperatures. Our results will help to clarify the complex magnetic
structure and microscopic mechanism of multiferroicity in FeVO4.",1011.4677v2
2010-11-30,Enhanced superconducting properties in FeCr$_x$Se,"We report an enhancement of superconducting transition temperature ($T_{\rm
c}$) when Chromium (Cr) is substituted in excess at the Iron (Fe) site
(FeCr$_x$Se, $x=$0.01, 0.02 and 0.03). There is a corresponding increase in the
superconducting volume fraction with $T_{\rm c}$ attaining a value of 11.2 K on
2 $%$ Cr substitution when compared to a $T_{\rm c}$ of 8.5 K for the
conventional tetragonal Fe-excess sample Fe$_{1+x}$Se. The results point to the
role of chemical pressure (introduced via ionic size variation at the Fe site
upon Cr substitution in excess) on superconducting properties.",1011.6519v1
2010-12-13,Abundance analysis of DAZ white dwarfs,"We present an abundance analysis of a sample of 33 hydrogen-rich (DA) white
dwarfs. We have used archival high-resolution spectra to measure abundances of
calcium, magnesium and iron in a set of 30 objects. In addition, we present
preliminary calcium abundances in three new white dwarfs based on
low-dispersion spectra. We investigate some abundance ratios (Mg/Ca, Fe/Ca)
that may help uncover the composition of the accretion source.",1012.2639v1
2010-12-14,Superconductivity in the iron selenide KxFe2Se2 (0 <= x <= 1),"We report the superconductivity at above 30 K in a new FeSe-layer compound
K0.8Fe2Se2 (nominal composition) achieved by metal K intercalating in between
FeSe layers. It is isostructural to BaFe2As2 and possesses the highest Tc for
FeSe-layer materials so far under ambient pressure. Hall effect indicates the
carriers are dominated by electron in this superconductor. We confirm that the
observed superconductivity at above 30 K is due to this new FeSe-based 122
phase. Our results demonstrate that FeSe-layer materials are really remarkable
superconductors via structure and carrier modulation.",1012.2924v1
2011-01-05,Variety of c-axis collective excitations in layered multigap superconductors,"We present a dynamical theory for the phase differences along a stacked
direction of intrinsic Josephson junctions (IJJ's) in layered multigap
superconductors, motivated by the discovery of highly-anisotropic iron-based
superconductors with thick perovskite-type blocking layers. The dynamical
equations describing AC and DC intrinsic Josephson effects peculiar to multigap
IJJ's are derived, and collective Leggett mode excitations in addition to the
Josephson plasma established in single-gap IJJ's are predicted. The dispersion
relations of their collective modes are explicitly displayed, and the
remarkable peculiarity of the Leggett mode is demonstrated.",1101.0886v2
2011-01-17,Upper critical field of the 122-type iron pnictide superconductors,"The upper critical fields ($H_{c2}$) of the single crystals
$\rm(Sr,Na)Fe_2As_2$ and $\rm Ba_{0.55}K_{0.45}Fe_2As_2$ were determined by
means of measuring the electrical resistivity, $ \rho_{xx}(\mu_0H)$, using the
facilities of pulsed magnetic field at Los Alamos. In general, these compounds
possess a very large upper critical field ($H_{c2}(0)$) with a weak anisotropic
effect. The detailed curvature of $H_{c2}(T_c)$ may depend on the magnetic
field orientation and the sample compositions. We argue that such a difference
mainly results from the multi-band effect, which might be modified via doping.",1101.3150v1
2011-01-20,Ab initio Random Structure Searching,"It is essential to know the arrangement of the atoms in a material in order
to compute and understand its properties. Searching for stable structures of
materials using first-principles electronic structure methods, such as density
functional theory (DFT), is a rapidly growing field. Here we describe our
simple, elegant and powerful approach to searching for structures with DFT
which we call ab initio random structure searching (AIRSS). Applications to
discovering structures of solids, point defects, surfaces, and clusters are
reviewed. New results for iron clusters on graphene, silicon clusters,
polymeric nitrogen, hydrogen-rich lithium hydrides, and boron are presented.",1101.3987v1
2011-02-04,Anisotropy in transport and magnetic properties of K0.64Fe1.44Se2,"We report a study of anisotropy in transport and magnetic properties of
K0.64Fe1.44Se2.00 single crystals. The anisotropy in resistivity is up to one
order of magnitude between 1.8 K and 300 K. Magnetic susceptibility exhibits
weak temperature dependence in the normal state with decrease in temperature
with no significant anomalies. The lower critical fields Hc1 of
K0.64Fe1.44Se2.00 are only about 3 Oe and the anisotropy of Hc1,c/Hc1,ab is
about 1. The critical currents for H||ab and H||c are about 10-10^3 A/cm2,
smaller than in iron pnictides and in FeTe_{1-x}Se_{x} and nearly isotropic.",1102.1010v3
2011-02-05,Simulations of decomposition kinetics of Fe-Cr solid solutions during thermal aging,"The decomposition of Fe-Cr solid solutions during thermal aging is modeled by
Atomistic Kinetic Monte Carlo (AKMC) simulations, using a rigid lattice
approximation with composition dependant pair interactions that can reproduce
the change of sign of the mixing energy with the alloy composition. The
interactions are fitted on ab initio mixing energies and on the experimental
phase diagram, as well as on the migration barriers in iron and chromium rich
phases. Simulated kinetics is compared with 3D atom probe and neutron
scattering experiments.",1102.1091v1
2011-02-08,Coupling of replicate order-parameters in incommensurate multiferroics,"The specific properties of incommensurate multiferroic phases resulting from
the coupling of order-parameter replicates are worked out using the
illustrative example of iron vanadate. The dephasing between the
order-parameter copies induces an additional broken symmetry phase
corresponding to the lowest symmetry of the system and varies critically at the
transition to the multiferroic phase. It reflects the temperature dependence of
the angle between paired spins in the antiferromagnetic spiral structure.
Expressing the transition order-parameters in terms of spin-density waves
allows showing that isotropic exchange interactions contribute to the
stabilization of the ferroelectric phase.",1102.1575v1
2011-02-10,Thermoelectric studies of KxFe2-ySe2: weakly correlated superconductor,"We report thermal transport measurement of KxFe2-ySe2 superconducting single
crystal. Significant peak anomaly in thermal conductivity is observed at nearly
TC/2 indicating a large phonon mean-free-path in the superconducting state. The
zero-temperature extrapolated thermoelectric power is smaller than the value in
typical strongly correlated superconductors, implying large normalized Fermi
temperature. In contrast to other iron superconductors, thermoelectric power in
our sample does not exhibit significant anomalies. These findings indicate that
KxFe2-ySe2 is a weakly or intermediately correlated superconductor without
significant Fermi surface nesting.",1102.2217v2
2011-02-17,Superconductivity on the verge of Mott localization in ternary iron sulfide,"We report the results of electrical and magnetic properties on two new
compounds, K0.8Fe1.7S2 and K0.8Fe1.7SeS, both having similar structures to
newly discovered superconducting K0.8Fe1.7Se2. K0.8Fe1.7S2 exhibits a
semiconductor-like electrical property and undergoes an anti-ferromagnetic
transition at about 260 K. Upon replacing half of S with Se, K0.8Fe1.7SSe
becomes a superconductor at 25 K, implying the superconductivity evolves from a
Mott AFM state in Fe-Se based superconductors.",1102.3505v1
2011-02-17,Quenching of superconductivity by Co doping in K0.8Fe2Se2,"We synthesized a series of K0.8Fe2-xCoxSe2 samples with nominal compositions
0\leq x\leq 0.035 and investigated their physical properties. The results show
that the superconductivity in K0.8Fe2-xCoxSe2 is quenched down to 5 K by 0.5
at. % Co doping, the fastest quenching rate ever-reported. The role played here
by Co is in contrast with the one in FeAs based superconductors where Co
usually induces superconductivity from parent compounds. Such a rapid quenching
favors a localized 3d model against the itinerant one for iron pnictide
superconductors.",1102.3506v1
2011-03-29,Spin waves in the block checkerboard antiferromagnetic phase,"Motivated by the discovery of new family 122 iron-based superconductors, we
present the theoretical results on the ground state phase diagram, spin wave
and dynamic structure factor of the extended $J_{1}-J_{2}$ Heisenberg model. In
the reasonable physical parameter region of $K_{2}Fe_{4}Se_{5}$, we fi{}nd the
block checkerboard antiferromagnetic order phase is stable. There are two
acoustic branches and six optical branches spin wave in the block checkerboard
antiferromagnetic phase, which has analytic expression in the high symmetry
points. To compare the further neutron scattering experiments, we discuss the
saddlepoint structure in the magnetic excitation spectrum and calculate the
predicted inelastic neutron scattering pattern based on linear spin wave
theory.",1103.5521v1
2011-04-08,Materials and mechanisms of hole superconductivity,"The theory of hole superconductivity proposes that there is a single
mechanism of superconductivity that applies to all superconducting materials.
This paper discusses several material families where superconductivity occurs
and how they can be understood within this theory. Materials discussed include
the elements, transition metal alloys, high $T_c$ cuprates both hole-doped and
electron-doped, $MgB_2$, iron pnictides, doped semiconductors, and elements
under high pressure.",1104.1624v2
2011-05-02,Impeding effect of cerium on the growth of helium bubble in iron,"Our first-principles density functional theory calculations suggest that the
rare earth element, Ce, has a stronger attraction (-1.31eV) to He than He-He
(-1.18eV) in bcc Fe. Consequently, the mobile He atoms could be pinned to Ce,
and hence a reduced merging of He clusters. Moreover, we find that the
segregated Ce layer at the He bubble surface presents an energy barrier of 0.33
eV to the upcoming He atom and thus slows down the bubble growth.",1105.0458v1
2011-05-09,Status Update for the MINER$ν$A Experiment,"MINER$\nu$A (Main INjEctoR $\nu$-A) is a few-GeV neutrino cross section
experiment that began taking data in the FNAL NuMI beam-line in the fall of
2009. MINER$\nu$A employs a fine-grained detector capable of complete kinematic
characterization of neutrino interactions. The detector consists of an
approximately 6.5 ton active target region composed of plastic scintillator
with additional carbon, iron, and lead targets upstream of the active region.
The experiment will provide important inputs for neutrino oscillation searches
and a pure weak probe of nuclear structure. Here we offer a set of initial
kinematic distributions of interest and provide a general status update.",1105.1698v1
2011-06-16,Evidence of defect-induced ferromagnetism in ZnFe$_{2}$O$_{4}$ thin films,"X-ray absorption near-edge and grazing incidence X-ray fluorescence
spectroscopy are employed to investigate the electronic structure of
ZnFe$_{2}$O$_{4}$ thin films. The spectroscopy techniques are used to determine
the non-equilibrium cation site occupancy as a function of depth and oxygen
pressure during deposition and its effects on the magnetic properties. It is
found that low deposition pressures below 10$^{-3}$ mbar cause iron
superoccupation of tetrahedral sites without Zn$^{2+}$ inversion, resulting in
an ordered magnetic phase with high room temperature magnetic moment.",1106.3128v1
2011-06-27,Charge redistribution at the antiferromagnetic phase transition in SrFeAsF compound,"The relationship between spin, electron, and crystal structure has been one
of the foremost issues in understanding the superconducting mechanism since the
discovery of iron-based high temperature superconductors. Here, we report
M\""ossbauer and first-principles calculations studies of the parent compound
SrFeAsF with the largest temperature gap ($\sim$50\,K) between the structural
and antiferromagnetic (AFM) transitions. Our results reveal that the structural
transition has little effect on the electronic structure of the compound
SrFeAsF while the development of the AFM order induces a redistribution of the
charges near the Fermi level.",1106.5370v2
2011-07-18,Recent Measurements of Neutrino-Nucleus Quasi-Elastic Scattering,"We present recent measurements of neutrino charged current quasi-elastic (CC
QE) scattering, nu_mu + p -> mu- + n. Measurements of CC QE on carbon near 1
GeV by MiniBooNE and SciBooNE, as well as measurements on iron at 3 GeV by
MINOS, disagree with current interaction models, while measurements at higher
energies on carbon by NOMAD show excellent agreement with those same models.",1107.3400v1
2011-07-26,Nuclear structure in strong magnetic fields: nuclei in the crust of a magnetar,"Covariant density functional theory is used to study the effect of strong
magnetic fields, up to the limit predicted for neutron stars (for magnetars $B
\approx10^{18}$G), on nuclear structure. All new terms in the equation of
motion resulting from time reversal symmetry breaking by the magnetic field and
the induced currents, as well as axial deformation, are taken into account in a
self-consistent fashion. For nuclei in the iron region of the nuclear chart it
is found that fields in the order of magnitude of $10^{17}$G significantly
affect bulk properties like masses and radii.",1107.5243v1
2011-07-29,Neutrino nucleus reactions at high energies within the GiBUU model,"The GiBUU model, which implements all reaction channels relevant at medium
neutrino energy, is used to investigate the neutrino and antineutrino
scattering on iron. Results for integrated cross sections are compared with
NOMAD and MINOS data. It is shown, that final state interaction can noticeably
change the spectra of the outgoing hadrons. Predictions for the Miner$\nu$a
experiment are made for pion spectra, averaged over NuMI neutrino and
antineutrino fluxes.",1107.5944v1
2011-08-04,Storage-ring ionization and recombination experiments with multiply charged ions relevant to astrophysical and fusion plasmas,"Past and ongoing research activities at the Heidelberg heavy-ion storage-ring
TSR are reviewed which aim at providing accurate absolute rate coefficients and
cross sections of atomic collision processes for applications in astrophysics
and magnetically confined fusion. In particular, dielectronic recombination and
electron impact ionization of iron ions are discussed as well as dielectronic
recombination of tungsten ions.",1108.1073v1
2011-08-09,Magnetic resonance from the interplay of frustration and superconductivity,"Motivated by the iron-based superconductors, we develop a self-consistent
electronic theory for the itinerant spin excitations in the regime of
coexistence of the antiferromagnetic stripe order with wavevector ${\bf Q}_{1}
= (\pi,0)$ and $s^{+-}$ superconductivity. The onset of superconductivity leads
to the appearance of a {\em magnetic} resonance near the wavevector ${\bf
Q}_{2} = (0,\pi)$ where magnetic order is absent. This resonance is isotropic
in spin space, unlike the excitations near ${\bf Q}_{1}$ where the magnetic
Goldstone mode resides. We discuss several features which can be observed
experimentally.",1108.2046v1
2011-08-17,The hyperfine properties of a hydrogenated Fe/V superlattice,": We study the effect of hydrogen on the electronic, magnetic and hyperfine
structures of an iron-vanadium superlattice consisting of three Fe monolayers
and nine V monolayers. The contact charge density ({\rho}), the contact
hyperfine field (Bhf) and the electronic field gradient (EFG) at the Fe sites
for different H locations and H fillings are calculated using the first
principle full-potential linear-augmented-plane-wave (FP-LAPW) method . It is
found that sizeable changes in the hyperfine properties are obtained only when
H is in the interface region.",1108.3388v1
2011-08-22,Pressure effects on strained FeSe0.5Te0.5 thin films,"The pressure effect on the resistivity and superconducting Tc of prestrained
thin films of the iron chalcogenide superconductor FeSe0.5Te0.5 is studied.
Films with different anion heights above the Fe layer showing different values
of ambient pressure Tc's are compressed up to a pressure of 1.7 GPa. All films
exhibit a significant increase of Tc with pressure. The results cannot solely
be explained by a pressure-induced decrease of the anion height but other
parameters have to be considered to explain the data for all films.",1108.4399v1
2011-08-23,Superconductivity and local non-centrosymmetricity in crystal lattices,"Symmetry of the crystal lattice can be a determining factor for the structure
of Cooper pairs in unconventional superconductors. In this study we extend the
discussion of superconductivity in non-centrosymmetric materials to the case
when inversion symmetry is missing locally, but is present on a global level.
Concretely, we investigate the staggered non-centrosymmetricity within a
regular sublattice structure, in some analogy to the discussion of
superconductivity in antiferromagnetic systems. Three crystal structures are
analyzed in detail as illustrative examples for the extended classification of
Cooper-pairing channels. One of the cases may be relevant for the class of
iron-pnictide superconductors.",1108.4694v1
2011-09-01,High-energy pseudogap in degenerate Hubbard model induced via Hund coupling,"Hund coupling in the degenerate five-band Hubbard model near n=6 occupancy is
shown to give rise to a significant depletion of spectral weight above the
Fermi level. Calculations within dynamical mean field theory combined with
exact diagonalization reveal that this pseudogap is associated with a
collective mode in the self-energy caused by spin fluctuations. The pseudogap
is remarkably stable over a wide range of Coulomb and exchange energies, but
disappears for weak Hund coupling. The implications of this phenomenon for
optical spectra of iron pnictides are discussed.",1109.0162v1
2011-09-05,Gutzwiller theory of band magnetism in LaOFeAs,"We use the Gutzwiller variational theory to calculate the ground-state phase
diagram and quasi-particle bands of LaOFeAs. The Fe3d--As4p Wannier-orbital
basis obtained from density-functional theory defines the band part of our
eight-band Hubbard model. The full atomic interaction between the electrons in
the iron orbitals is parameterized by the Hubbard interaction U and an average
Hund's-rule interaction J. We reproduce the experimentally observed small
ordered magnetic moment over a large region of (U,J) parameter space. The
magnetically ordered phase is a stripe spin-density wave of quasi-particles.",1109.0929v1
2011-09-09,Theoretical Investigation of the Magnetic Order in FeAs,"The magnetic structure of the iron monoarsenide FeAs is studied using
first-principles calculations. We consider the collinear and non-collinear
(spin-spiral wave) magnetic ordering and magnetic anisotropy. It is
analitically shown that a magnetic triaxial anisotropy results in a sum of two
spin-spiral waves with opposite directions of wave vectors and different spin
amplitudes, so that the magnetic moments in two perpendicular directions do not
equal each other.",1109.1924v1
2011-09-12,Spin-transfer mechanism for magnon-drag thermopower,"We point out a relation between the dissipative spin-transfer-torque
parameter $\beta$ and the contribution of magnon drag to the thermoelectric
power in conducting ferromagnets. Using this result we estimate $\beta$ in iron
at low temperatures, where magnon drag is believed to be the dominant
contribution to the thermopower. Our results may be used to determine $\beta$
from magnon-drag-thermopower experiments, or, conversely, to infer the strength
of magnon drag via experiments on spin transfer.",1109.2414v1
2011-09-13,Instability of vortex-antivortex interface in optimally-doped Ba(Fe_{1-x}Co_{x})_{2}As_{2},"We explore the flux front patterns during virgin penetration and after
remagnetization in the iron-based superconductor Ba(Fe_{1-x}Co_{x})_{2}As_{2}.
After remagnetization we observe an instability characterized by turbulent
dynamics at the vortex-antivortex boundary. Associated with the turbulent flux
boundary a band of excess current density is observed. The turbulence is
contrasted with the instability observed in the cuprate superconductors. Our
results suggest turbulent instability at the vortex-antivortex interface may be
a common feature in all remagnetized type-II superconductors.",1109.2703v1
2011-09-22,The interaction of Fe thin layers between MgO(100)-MgO and MgO(100)-Ag surfaces,"The atomic interaction and magnetic properties of ultrathin Fe films grown on
cleaved and polished MgO(100) surfaces were studied by conversion electron
M\""{o}ssbauer spectroscopy (CEMS) in broad temperature range. Fe with different
layer thickness was deposited on MgO substrates. The layers were formed on
polished and cleaved substrate surfaces at RT. The analysis of the spectra
showed no Fe-O$^{2-}$ interaction in MgO/Fe interface. Iron layers showed
different magnetic anisotropy depending on their thickness.",1109.4811v1
2011-09-22,Ironsilicide formation by high temperature codeposition of Fe-2Si with different thicknesses on Si (111),"Fe and 2Si were co-deposited on Si (111) surface at 853 K. The formation of
silicides was investigated by Mossbauer spectroscopy and electron microscopy.
Depending on the thickness of the deposited films different phases were formed.
At low thickness, stable $\epsilon$-FeSi (B20) and metastable
[CsCl]-Fe$_{1-x}$Si (B2) phases were observed. In the latter case, because of
the presence of Fe vacancies in the lattice the local symmetry around the iron
components was lower than cubic. At larger (12 nm) deposited thickness, stable
$\beta$-FeSi$_2$ has been formed.",1109.4825v1
2011-09-22,Predicting dislocation climb: Classical modeling versus atomistic simulations,"The classical modeling of dislocation climb based on a continuous description
of vacancy diffusion is compared to recent atomistic simulations of dislocation
climb in body-centered cubic iron under vacancy supersaturation [Phys. Rev.
Lett. 105 095501 (2010)]. A quantitative agreement is obtained, showing the
ability of the classical approach to describe dislocation climb. The analytical
model is then used to extrapolate dislocation climb velocities to lower
dislocation densities, in the range corresponding to experiments. This allows
testing of the validity of the pure climb creep model proposed by Kabir et al.
[Phys. Rev. Lett. 105 095501 (2010)].",1109.4905v1
2011-09-30,Stellar Parameters and Chemical Abundances of G Giants,"We present basic stellar parameters of 99 late-type G giants based on high
resolution spectra obtained by the High Dispersion Spectrograph attached to
Subaru Telescope. These stars are targets of a Doppler survey program searching
for extra-solar planets among evolved stars, with a metallicity of
-0.8<[Fe/H]<+0.2. We also derived their abundances of 15 chemical elements,
including four $\alpha$-elements (Mg, Si, Ca, Ti), three odd-Z light elements
(Al, K, Sc), four iron peak elements (V, Cr, Fe, Ni), and four neutron-capture
elements (Y, Ba, La, Eu). Kinematic properties reveal that most of the program
stars belong to the thin disk.",1109.6742v1
2011-10-04,Neutrino nucleus reactions within the GiBUU model,"The GiBUU model, which implements all reaction channels relevant at medium
neutrino energy, is used to investigate the neutrino and antineutrino
scattering on iron. Results for integrated cross sections are compared with
NOMAD and MINOS data. It is shown, that final state interaction can noticeably
change the spectra of the outgoing hadrons. Predictions for the Miner$\nu$a
experiment are made for pion spectra, averaged over NuMI neutrino and
antineutrino fluxes.",1110.0674v1
2011-11-01,Electronic band structure of ferro-pnictide superconductors from ARPES experiment,"ARPES experiments on iron based superconductors show that the differences
between the measured and calculated electronic band structures look
insignificant but can be crucial for understanding of the mechanism of high
temperature superconductivity. Here we focus on those differences for 111 and
122 compounds and discuss the observed correlation of the experimental band
structure with the superconductivity.",1111.0288v1
2011-11-02,Electrochemical synthesis of iron-based superconductor FeSe films,"The superconducting FeSe films were successfully fabricated using the
electrochemical synthesis. The composition ratio of Fe and Se can be controlled
by the electric potential and pH value. We found that the FeSe films deposited
at the electric potential -1.75 V and pH 2.3 show the superconducting
transition at 3.5 K. The establishment of this electrochemical synthesis
technique will provide many advantages for application.",1111.0611v1
2011-11-18,Stripes and Superconductivity in Cuprates,"Holes doped into the CuO2 planes of cuprate parent compounds frustrate the
antiferromagnetic order. The development of spin and charge stripes provides a
compromise between the competing magnetic and kinetic energies. Static stripe
order has been observed only in certain particular compounds, but there are
signatures which suggest that dynamic stripe correlations are common in the
cuprates. Though stripe order is bad for superconducting phase coherence,
stripes are compatible with strong pairing. Ironically, magnetic-field-induced
stripe order appears to enhance the stability of superconducting order within
the planes.",1111.4268v1
2012-01-13,Observation of multiple superconducting gaps in Fe1+yTe1-xSex via a nano-scale approach to point-contact spectroscopy,"We report a distinct experimental approach to point-contact Andreev
reflection spectroscopy with diagnostic capability via a unique design of
nano-scale normal metal/superconductor devices with excellent thermo-mechanical
stability, and have employed this method to unveil the existence of two
superconducting energy gaps in iron chalcogenide Fe1+yTe1-xSex which is crucial
for understanding its pairing mechanism. This work opens up new opportunities
to study gap structures in superconductors and elemental excitations in solids.",1201.2881v2
2012-01-16,Odd-particle systems in the shell model Monte Carlo: circumventing a sign problem,"We introduce a novel method within the shell model Monte Carlo approach to
calculate the ground-state energy of a finite-size system with an odd number of
particles by using the asymptotic behavior of the imaginary-time
single-particle Green's functions. The method circumvents the sign problem that
originates from the projection on an odd number of particles and has hampered
direct application of the shell model Monte Carlo method to odd-particle
systems. We apply this method to calculate pairing gaps of nuclei in the iron
region. Our results are in good agreement with experimental pairing gaps.",1201.3341v1
2012-02-08,Role of spin-orbit coupling on the electronic structure and properties of SrPtAs,"The effect of spin-orbit coupling on the electronic structure of the layered
iron-free pnictide superconductor, SrPtAs, has been studied using the full
potential linearized augmented plane wave method. The anisotropy in Fermi
velocity, conductivity and plasma frequency stemming from the layered structure
are found to be enhanced by spin-orbit coupling. The relationship between
spin-orbit interaction and the lack of two-dimensional inversion in the PtAs
layers is analyzed within a tight-binding Hamiltonian based on the
first-principles calculations. Finally, the band structure suggests that
electron doping could increase $T_c$.",1202.1604v1
2012-02-16,Comparison of EPOS and QGSJET-II in EAS Simulation using CORSIKA,"In this work we compare the predictions of two representative hadronic
interaction models, EPOS 1.99, and QGSJET II-03 with several extensive air
showers (EAS) parameters for proton and iron primaries in the energy range
$10^{17}$ - $10^{19} eV$ using CORSIKA-6990. The EAS parameters depth of shower
maximum, shower size, size of muon shower, muon number distribution, electron
number distribution,size of hadron shower, hadron energy sum, electron muon
correlations, and, hadron energy spectra are studied in this paper.",1202.3661v4
2012-02-28,Finite Elements Magnetic Analysis of the CLIC MDI Region,"Considering the current CLIC SiD detector design and the machine parameter
L*, the final focus quadrupole QD0 will be placed inside the experiment itself.
This configuration is very challenging from an integration point of view. Among
several other aspects, the iron-dominated QD0 will need an active magnetic
shielding to avoid undesired interactions with the magnetic field generated by
the main solenoid of the detector. This shielding will be provided by a
superconducting anti-solenoid, and this paper aims to describe the method used
to design such device, the results obtained and the issues still to be solved.",1202.6334v1
2012-03-01,Magnetic and transport properties of iron-platinum arsenide Ca10(Pt4-δAs8)(Fe2-xPtxAs2)5 single crystal,"We report superconducting properties of single crystalline
Ca10(Pt4-{\delta}As8)(Fe2-xPtxAs2)5 by X-ray diffraction, magnetization,
resistivity, and magneto-optical imaging measurements. The magnetization
measurements reveal fish-tail hysteresis loop and relatively high critical
current density Jc ~ 0.8\times105 A/cm2 at low temperatures. The exponential
temperature dependence of Jc, which arises from nonlinear effective flux-creep
activation energy, has been observed. Upper critical field determined by
resistive transition shows a relatively large anisotropy. The magneto-optical
images reveal homogenous current flow within the crystal.",1203.0099v1
2012-03-05,Breakdown of Chemical Scaling for Pt-Doped CaFe2As2,"We report a breakdown of the scaling of the antiferromagnetic transition
temperature T_N on chemical doping for Pt-doped CaFe2As2. The substitution of
Pt is ineffective in the reduction of antiferromagnetic ordering as well as in
inducing superconductivity in Ca(Fe1-xPtx)2As2. The Pt-doped CaFe2As2 that does
not exhibit superconductivity will, however, provide us an ideal opportunity to
elucidate the role of chemical doping in the occurrence of superconductivity in
iron-based materials.",1203.0822v1
2012-03-07,Structural distortion as prerequisite for superconductivity in LiFeAs,"The nonadiabatic Heisenberg model predicts a structural distortion in LiFeAs
below a temperature higher than (or at least equal to) the superconducting
transition temperature. Within this group-theoretical model, the reduction of
the symmetry caused by the distortion is a prerequisite for the superconducting
state in this compound and can be realized by a mere displacement of the iron
atoms from their positions in the space group P4/nmm.",1203.1543v1
2012-03-29,Field-Induced Magnetostructural Transitions in Antiferromagnetic Fe1+yTe1-xSx,"The transport and structural properties of Fe1+yTe1-xSx (x=0, 0.05, and 0.10)
crystals were studied in pulsed magnetic fields up to 65 T. The application of
high magnetic fields results in positive magnetoresistance effect with
prominent hystereses in the antiferromagnetic state. Polarizing microscope
images obtained at high magnetic fields showed simultaneous occurrence of
structural transitions. These results indicate that magnetoelastic coupling is
the origin of the bicollinear magnetic order in iron chalcogenides.",1203.6482v1
2012-04-12,Effective doping and suppression of Fermi surface reconstruction via Fe vacancy disorder in KxFe2-ySe2,"We investigate the effect of disordered vacancies on the normal-state
electronic structure of the newly discovered alkali-intercalated iron selenide
superconductors. To this end we use a recently developed Wannier function based
method to calculate from first principles the configuration-averaged spectral
function <A(k,w)> of K0.8Fe1.6Se2 with disordered Fe and K vacancies. We find
that the disorder can suppress the expected Fermi surface reconstruction
without completely destroying the Fermi surface. More interestingly, the
disorder effect raises the chemical potential significantly, giving enlarged
electron pockets almost identical to highly doped KFe2Se2, without adding
carriers to the system.",1204.2849v1
2012-05-04,Thermodynamic evidence for pressure-induced bulk superconductivity in the Fe-As pnictide superconductor CaFe2As2,"We report specific-heat and resistivity experiments performed in parallel in
a Bridgman-type of pressure cell in order to investigate the nature of
pressure-induced superconductivity in the iron pnictide compound CaFe2As2. The
presence of a pronounced specific-heat anomaly at Tc reveals a bulk nature of
the superconducting state. The thermodynamic transition temperature differs
dramatically from the onset of the resistive transition. Our data indicates
that superconductivity occurs in the vicinity of a crystallographic phase
transition. We discuss the discrepancy between the two methods as caused by
strain-induced superconducting precursors formed above the bulk thermodynamic
transition due to the vicinity of the structural instability.",1205.0874v1
2012-06-04,Microscopic origin of the linear temperature increase of the magnetic susceptibility of BaFe$_{2}$As$_{2}$,"Employing a combination of \emph{ab initio} band structure theory and
dynamical mean-field theory we explain the experimentally observed linear
temperature increase of the magnetic susceptibility of the iron pnictide
material BaFe$_{2}$As$_{2}$. The microscopic origin of this anomalous behaviour
is traced to a sharp peak in the spectral function located approximately 100
meV below the Fermi level. This peak is due to the weak dispersion of
two-dimensional bands associated with the layered crystal structure of
pnictides.",1206.0569v2
2012-06-06,Modulations of the local pairing interaction near magnetic impurities in d-wave superconductors,"The spin-fluctuation based pairing mechanism has proven successful in
explaining the pairing symmetries due to Fermi surface nesting of both cuprates
and iron-based materials. In this work, we study signatures of a
spin-fluctuation mediated pairing at the local scale. Specifically, we focus on
magnetic impurities and calculate both the local antiferromagnetism and the
resulting modulated pairing interaction. The latter gives rise to distinct
local enhancements of the superconducting gap in the immediate vicinity of the
impurities. Our results show that Coulomb-driven pairing naturally leads to
unusual superconducting gap modulations near disorder potentials.",1206.1129v1
2012-06-14,DFT Calculations as a Tool to Analyse Quadrupole Splittings of Spin Crossover Fe(II) complexes,"Density functional methods have been applied to calculate the quadrupole
splitting of a series of iron(II) spin crossover complexes. Experimental and
calculated values are in reasonable agreement. In one case spin-orbit coupling
is necessary to explain the very small quadrupole splitting value of 0.77 mm/s
at 293 K for a high-spin isomer.",1206.3036v1
2012-06-18,Interpretation of Mössbauer spectra in the energy and time domain with neural networks,"An artificial neural network for extracting reasonable and fast estimates of
hyperfine parameters from M\""ossbauer spectra in the energy or time domain is
outlined. First promising results for determining the asymmetry of the electric
field gradient at the nucleus of a diamagnetic iron center as derived with
different types of neural networks are reported.",1206.3892v1
2012-06-20,Fermi surface topology of LaFePO and LiFeP,"We perform charge self-consistent LDA+DMFT (density functional theory
combined with dynamical mean field theory) calculations to study correlation
effects on the Fermi surfaces of the iron pnictide superconductors LaFePO and
LiFeP. We find a distinctive change in the topology of the Fermi surface in
both compounds where a hole pocket with Fe dz^2 orbital character changes its
geometry from a closed shape in LDA to an open shape upon inclusion of
correlations.",1206.4551v3
2012-06-22,Evolution of the neutron resonances in AFe2Se2,"Recent experiments on the alkali-intercalated iron selenides have raised
questions about the symmetry of the superconducting phase. Random phase
approximation calculations of the leading pairing eigenstate for a tight-
binding 5-orbital Hubbard-Hund model of AFe2Se2 find that a d-wave (B1g) state
evolves into an extended s{\pm} (A1g) state as the system is hole-doped.
However, over a range of doping these two states are nearly degenerate. Here,
we calculate the imaginary part of the magnetic spin susceptibility
\chi""(q,{\omega}) for these gaps and discuss how the evolution of neutron
scattering resonances can distinguish between them.",1206.5235v1
2012-06-27,"Electronic, magnetic properties and correlation effects in the layered quaternary iron oxyselenide Na2Fe2Se2O from first principles","By means of the first-principle calculations, we have investigated
electronic, magnetic properties and correlation effects for the newly
discovered layered oxyselenide Na2Fe2Se2O. Our results reveal that the electron
correlations in the Fe 3d bands promote a transition of Na2Fe2Se2O from
magnetic metallic or half-metallic states to the antiferromagnetic
Mott-insulating state. In addition, the bonding picture in Na2Fe2Se2O is
described as an anisotropic mixture of ionic and covalent contributions.",1206.6182v1
2012-06-30,Anticollinear magnetic order induced by impurities in the frustrated Heisenberg model of pnictides,"We present Monte Carlo simulations for a classical antiferromagnetic
Heisenberg model with both nearest ($J_1$) and next-nearest ($J_2$) exchange
couplings on the square lattice in the presence of non-magnetic impurities. We
show that the order-by-disorder entropy selection, associated with the
Ising-like phase transition that appears for $J_2/J_1>1/2$ in the pure spin
model, is quenched at low temperature due to the presence of non-magnetic
impurities. Evidences that a new competing order is stabilized around the
impurities, and in turn induces a re-entrance phase transition are reported.
Implications for local magnetic measurement of the parent compound of iron
pnictides are briefly discussed.",1207.0095v1
2012-07-13,Theoretical study of the hyperfine field at Cu impurities diluted in an iron host,"Magnetic hyperfine field at Cu isotopes as impurities in Fe were recently
measured at low temperature. A model to explain these experimental results is
proposed. The diluted Cu impurities in the ferromagnetic Fe host are described
by an extension of the Daniel-Friedel model, including the next neighbor
perturbation. In order to account for the available experimental data in Cu
isotopes with atomic masses $A$ = 59, 67, 69 and 71 as impurity, we needed to
incorporate the Cu anomaly volume in the effective charge to be screened and in
the self-consistent procedures.",1207.3327v1
2012-08-09,E906/SeaQuest MARS15 Simulation,"A series of MARS15 simulations were done to verify and guide the design of
steel and concrete shielding, around the first E906-SeaQuest spectrometer
magnet, and the target area immediately upstream of it. The result of the last
round of simulations is summarized here. This magnet is a solid iron dipole
magnet and serves as a beam dump, as well as a muon analysis magnet.
  The E906-SeaQuest spectrometer is designed to measure high energy muons
produced in the forward direction by interactions of the FNAL 120-GeV Main
Injector proton beam, with a variety of targets.",1208.1998v1
2012-08-17,Majorana Zero Modes in Semiconductor Nanowires in Contact with Higher-$T_c$ Superconductors,"We analyze the prospects for stabilizing Majorana zero modes in semiconductor
nanowires that are proximity-coupled to higher-temperature superconductors. We
begin with the case of iron pnictides which, though they are s-wave
superconductors, are believed to have superconducting gaps that change sign. We
then consider the case of cuprate superconudctors. We show that a nanowire on a
step-like surface, especially in an orthorhombic material such as YBCO, can
support Majorana zero modes at an elevated temperature.",1208.3701v2
2012-09-16,Stabilization of STEP electrolyses in lithium-free molten carbonates,"This communication reports on effective electrolyses in lithium-free molten
carbonates. Processes that utilize solar thermal energy to drive efficient
electrolyses are termed Solar Thermal Electrochemical Processes (STEP).
Lithium-free molten carbonates, such as a sodium-potassium carbonate eutectic
using an iridium anode, or a calcium-sodium-potassium carbonate eutectic using
a nickel anode, can provide an effective medium for STEP electrolyses. Such
electrolyses are useful in STEP carbon capture, and the production of staples
including STEP fuel, iron, and cement.",1209.3512v1
2012-09-17,Size and polydispersity effect on the magnetization of densely packed magnetic nanoparticles,"The magnetic properties of densely packed magnetic nanoparticles (MNP)
assemblies are investigated from Monte Carlo simulations. The case of iron
oxide nanoparticles is considered as a typical example of MNP. The main focus
is put on particle size and size polydispersity influences on the magnetization
curve. The particles are modeled as uniformly magnetized spheres isolated one
from each other by a non magnetic layer representing the organic coating. A
comparison with recent experimental results on $\gamma-$Fe$_2$O$_3$ powder
samples differing by their size is given.",1209.3566v1
2012-10-01,Disc atmospheres and winds in X-ray binaries,"We review the current status of studies of disc atmospheres and winds in low
mass X-ray binaries. We discuss the possible wind launching mechanisms and
compare the predictions of the models with the existent observations. We
conclude that a combination of thermal and radiative pressure (the latter being
relevant at high luminosities) can explain the current observations of
atmospheres and winds in both neutron star and black hole binaries. Moreover,
these winds and atmospheres could contribute significantly to the broad iron
emission line observed in these systems.",1210.0318v1
2012-10-09,Thermopower as sensitive probe of electronic nematicity in iron pnictides,"We study the in-plane anisotropy of the thermoelectric power and electrical
resistivity on detwinned single crystals of isovalent substituted
EuFe$_{2}$(As$_{1-x}$P$_{x}$)$_2$. Compared to the resistivity anisotropy the
thermopower anisotropy is more pronounced and clearly visible already at
temperatures much above the structural and magnetic phase transitions. Most
remarkably, the thermopower anisotropy changes sign below the structural
transition. This is associated with the interplay of two contributions due to
anisotropic scattering and orbital polarization, which dominate at high- and
low-temperatures, respectively.",1210.2634v2
2012-10-22,Holographic model of the S^{+/-} multiband superconductor,"We construct the holographic model of an $S^\pm$ multiband superconductor.
This system is a candidate to explain the anomalous features of the iron-based
superconductors (e.g. LaFeAsO, BFe2As2, and other pnictides and arsenides). We
study the framework, which allows formation of the sign-interchanging order
parameter. We also calculate the electric AC conductivity and study its
features, related to the interband interaction.",1210.6074v3
2012-12-13,On the existence of solutions for a drift-diffusion system arising in corrosion modelling,"In this paper, we consider a drift-diffusion system describing the corrosion
of an iron based alloy in a nuclear waste repository. In comparison with the
classical drift-diffusion system arising in the modeling of semiconductor
devices, the originality of the corrosion model lies in the boundary conditions
which are of Robin type and induce an additional coupling between the
equations. We prove the existence of a weak solution by passing to the limit on
a sequence of approximate solutions given by a semi-discretization in time.",1212.3279v1
2012-12-23,Excited nuclei in neutron star crusts,"The paper considers the chains of successive electron capture reactions by
nuclei of the iron group which take place in the crystal structures of neutron
star envelopes. It is shown that as a result of such reactions the daughter
nuclei in excited states accumulate within certain layers of neutron star
crusts. The phonon model of interactions is proposed between the excited nuclei
in the crystalline structure, as well as formation of highly excited nuclear
states which emit neutrons and higher energy photons.",1212.5767v1
2012-12-23,Acausality of Massive Gravity,"We show, by analyzing its characteristics, that the ghost-free, 5 degree of
freedom, Wess--Zumino massive gravity model admits superluminal shock wave
solutions and thus is acausal. Ironically, this pathology arises from the very
constraint that removes the (sixth) Boulware-Deser ghost mode.",1212.5835v3
2013-01-08,Normal and superconducting properties of LiFeAs explained in the framework of four-band Eliashberg Theory,"In this paper we propose a model to reproduce superconductive and normal
properties of the iron pnictide LiFeAs in the framework of the four-band spm
wave Eliashberg theory. A confirmation of the multiband nature of the system
rises from the experimental measurements of the superconductive gaps and
resistivity as function of temperature. We found that the most plausible
mechanism is the antiferromagnetic spin fluctuation and the estimated values of
the total antiferromagnetic spin fluctuation coupling constant in the
superconductive and normal state are lambda{tot}=2.00 and lambda{tot,tr}=0.77.",1301.1542v1
2013-01-24,Pressure effects in hollow and solid iron oxide nanoparticles,"We report a study on the pressure response of the anisotropy energy of hollow
and solid maghemite nanoparticles. The differences between the maghemite
samples are understood in terms of size, magnetic anisotropy and shape of the
particles. In particular, the differences between hollow and solid samples are
due to the different shape of the nanoparticles and by comparing both pressure
responses it is possible to conclude that the shell has a larger pressure
response when compared to the core.",1301.5708v1
2013-04-10,"Normal state bottleneck and nematic fluctuations from femtosecond quasi-particle relaxation dynamics in Sm(Fe,Co)AsO","We investigate temperature and fluence dependent dynamics of the photoexcited
quasi-particle relaxation and low-energy electronic structure in electron-doped
1111-structure Sm(Fe_{0.93}Co_{0.07})AsO single crystal. We find that the
behavior is qualitatively identical to the 122-structure Ba(Fe,Co)_{2}As_{2}
including the presence of a normal state pseudogap and a marked 2-fold symmetry
breaking in the tetragonal phase that we relate to the electronic nematicity.
The 2-fold symmetry breaking appears to be a general feature of the electron
doped iron pnictides.",1304.2866v1
2013-04-26,Ferroelectricity from iron valence ordering in rare earth ferrites?,"The possibility of multiferroicity arising from charge ordering in LuFe2O4
and structurally related rare earth ferrites is reviewed. Recent experimental
work on macroscopic indications of ferroelectricity and microscopic
determination of coupled spin and charge order indicates that this scenario
does not hold. Understanding the origin of the experimentally observed charge
and spin order will require further theoretical work. Other aspects of recent
research in these materials, such as geometrical frustration effects, possible
electric-field-induced transitions, or orbital order are also briefly treated.",1304.7255v1
2013-07-04,"Molten Air -- A new, highest energy class of rechargeable batteries","This study introduces the principles of a new class of batteries,
rechargeable molten air batteries, and several battery chemistry examples are
demonstrated. The new battery class uses a molten electrolyte, are quasi
reversible, and have amongst the highest intrinsic battery electric energy
storage capacities. Three examples of the new batteries are demonstrated. These
are the iron, carbon and VB2 molten air batteries with respective intrinsic
volumetric energy capacities of 10,000, 19,000 and 27,000 Wh per liter.",1307.1305v1
2013-07-16,On the He burning phases of the Carina dSph,"We performed a detailed comparison between predicted He burning phases and
multiband photometry of the Carina dwarf spheroidal galaxy. We found a good
agreement with the predictions computed assuming an {\alpha}-enhanced chemical
mixture, indicating a mean metallicity [Fe/H] ~ -1.8 with a raw observed
peak-to-peak spread in iron abundance of 0.4\pm0.2 dex.",1307.4324v1
2013-08-05,Sub-Piconewton Force Detection using Micron-Size Wire Deflections,"The mechanical properties of nanostructured wires obtained by co-assembly of
iron oxide particles are studied. The intrinsic magnetic properties of the
wires are used to induce and quantify the bending of the one-dimensional
objects. From the relationship between the deflection and the magnitude of the
magnetic field, the elastic rigidity and Young modulus of the wires are
determined. Young moduli in the megapascal range are obtained and are
consistent with sub-piconewton force detection.",1308.0893v1
2013-08-13,Strain effects on electronic structure of the iron selenide superconductor,"The influence of various strains on crystal and electronic structures of
superconducting FeSe has been studied ab initio. We consider changes in the
Fermi surface nesting with a vector Q=(0.5,0.5)*(2\pi /a) as crucial for rising
superconductivity (SC) mediated by spin-fluctuations (SF). Our results indicate
that the c-axis strained FeSe exhibits the most imperfect nesting, which
enhances SF and, hence, also SC. In turn, the ab-plane compressive strain
slightly weakens this} nesting while the tensile strain destroys it completely.
These findings are consistent with reported earlier experimental dependencies
of superconducting transition temperatures on strain in FeSe thin films.",1308.2933v1
2013-08-26,Modélisation micromagnétique du comportement magnéto-mécanique,"A magneto-mechanical static modeling of ferromagnetic particle based on
minimization of an energy function is presented. This modeling is made of a
conjugate gradient method coupled with finite element method for the mechanical
problem resolution. Some illustrations on iron single crystal are given in 2D
framework.",1308.5494v1
2013-08-26,Sulfur annealing effect for superconductivity in iron chalcogenide compounds,"We discovered a novel annealing method for Fe-chalcogenide superconductors.
It was found that sulfur annealing deintercalated excess Fe via formation of
FeS2. Due to its specifics, sulfur annealing is applicable when preparing
Fe-chalcogenide-based wires or cables.",1308.5642v1
2013-08-28,26Al in the Early Solar System: Not so Unusual After All,"Recently acquired evidence shows that extrasolar asteroids exhibit over a
factor of 100 variation in the iron to aluminum abundance ratio. This large
range likely is a consequence of igneous differentiation that resulted from
heating produced by radioactive decay of 26Al with an abundance comparable to
that in the solar system's protoplanetary disk at birth. If so, the
conventional view that our solar system began with an unusually high amount of
26Al should be discarded.",1308.6325v2
2013-09-11,Investigating of longitudinal development parameters through air shower simulation by different hadronic models,"In this work the simulation of the Extensive Air Showers was performed by
investigating the longitudinal development parameters (N and Xmax) by using a
system for air shower simulation which is called AIRES version 2.6.0 at the
energy range (10^14-10^19 eV) for different primary particles like (gamma,
electron, positron, proton and iron nuclei) and different zenith angles. The
comparison of simulated longitudinal profile was fulfilled for different
hadronic models (SIBYLL, QGSJET99 and SIBYLL S16).",1309.2934v1
2013-10-11,Impurity bound states and disorder-induced orbital and magnetic order in the s+- state of Fe-based superconductors,"We study the presence of impurity bound states within a five-band Hubbard
model relevant to iron-based superconductors. In agreement with earlier
studies, we find that in the absence of Coulomb correlations there exists a
range of repulsive impurity potentials where in-gap states are generated. In
the presence of weak correlations, these states are generally pushed to the
edges of the gap, whereas for larger correlations the onsite impurity potential
induces a local magnetic region which reintroduces the low-energy bound states
into the gap.",1310.3022v1
2013-10-14,From quantum mechanics to the physical metallurgy of steels,"In the last decade there has been a breakthrough in the construction of
theories leading to models for the simulation of atomic scale processes in
steel. In this paper the theory is described and developed and used to
demonstrate calculations of the diffusivity and trapping of hydrogen in iron
and the structures of carbon vacancy complexes in steel.",1310.3778v3
2013-11-13,A DFT+Nonhomogeneous DMFT approach for Finite Systems,"For reliable and efficient inclusion of electron-electron correlation effects
in nanosystems we propose a combined density-functional-theory/nonhomogeneous
dynamical-mean-field-theory (DFT + DMFT) approach which employs an approximate
Iterative Perturbative Theory (IPT) impurity solver. The validity of the method
is demonstrated by successful examination of the size-dependent magnetic
properties of iron nanoparticles containing 11-100 atoms. We show that the DFT+
DMFT solution is in very good agreement with experimental data, in particular
it does not lead to the overestimation of magnetization that is found with the
DFT and DFT+U techniques. More importantly, we demonstrate that DFT+DMFT
approach can be used for accurate and realistic description of nanosystems
containing about hundred atoms.",1311.3147v1
2014-01-10,"A density functional theory study of FeAs comparing LDA+U, GGA+U and hybrid functionals","We use density functional theory within the local density approximation
(LDA), LDA+U, generalized gradient approximation (GGA), GGA+U, and
hybrid-functional methods to calculate the properties of iron monoarsenide.
FeAs, which forms in the MnP structure, is of current interest for potential
spintronic applications as well as being the parent compound for the
newly-identified pnictide superconductors. We compare the calculated
structural, magnetic and electronic properties obtained using the different
functionals to each other and to experiment, and investigate the origin of a
recently-reported magnetic spiral. Our results indicate the appropriateness or
otherwise of the various functionals for describing FeAs and the related
Fe-pnictide superconductors.",1401.2277v1
2014-03-19,Spin-orbit coupling effects on spin-dependent inelastic electronic lifetimes in ferromagnets,"For the 3d ferromagnets iron, cobalt and nickel we compute the spin-dependent
inelastic electronic lifetimes due to carrier-carrier Coulomb interaction
including spin-orbit coupling. We find that the spin-dependent
density-of-states at the Fermi energy does not, in general, determine the spin
dependence of the lifetimes because of the effective spin-flip transitions
allowed by the spin mixing. The majority and minority electron lifetimes
computed including spin-orbit coupling for these three 3-d ferromagnets do not
differ by more than a factor of 2, and agree with experimental results.",1403.4728v1
2014-03-19,Topological Phases in the Single-Layer FeSe,"A distinct electronic structure was observed in the single-layer FeSe which
shows surprising high temperature superconductivity over 65k. Here we
demonstrate that the electronic structure can be explained by the strain effect
due to substrates. More importantly, we find that this electronic structure can
be tuned into robust topological phases from a topologically trivial metallic
phase by the spin-orbital interaction and couplings to substrates. The
topological phase is robust against any perturbations that preserve the
time-reversal symmetry. Our studies suggest that topological phases and
topologically related properties such as Majorana Fermions can be realized in
iron-based high T$_{c}$ superconductors.",1403.4740v1
2014-05-23,New observations of chemically peculiar stars with ESPaDOnS,"We present the first results of the estimation of gravity and effective
temperature for some poorly studied chemically peculiar stars that were
recently observed with the spectropolarimeter ESPaDOnS at CFHT. We have
analyzed the spectra of HD71030, HD95608 and HD116235 to determine their radial
velocity, Vsin(i) and the average abundance of several chemical species. We
have also analyzed our results to verify for possible vertical abundance
stratification of iron and chromium in these stars.",1405.6203v1
2014-06-12,A Simple Apparatus for the Direct Measurement of Magnetic Forces and Magnetic Properties of Materials,"In this paper, we describe a simple apparatus consisting of a scale, capable
of a one milligram resolution, and a commonly obtainable magnet to measure
magnetic forces. This simple apparatus is capable of measuring magnetic
properties of materials in either a research or an instructional laboratory. We
illustrate the capability of this apparatus by the measurement of the force of
iron samples exerted on the magnet, the force of a paramagnetic sample, that by
a current carrying wire, and the force of a high temperature superconductor.",1406.3341v3
2014-06-15,Magnetotransport studies of FeSe under hydrostatic pressure,"The discoveries of iron-based superconductors with relatively high transition
temperature are under intense experimental and theoretical investigation. Here
we present magnetotransport measurements on FeSe superconductor under
hydrostatic pressure. We show that in Fe-deficient tetragonal FeSe binary
compound, the onset of superconducting transition is almost doubled under
1.98GPa pressure and the estimated upper critical field of 26.7Tesla is
increased to 47.5Tesla.",1406.3795v2
2014-06-29,Specific Heat of Ca0.33Na0.67Fe2As2,"The specific heat of single crystal hole-doped Ca0.33Na0.67Fe2As2,
Tc(onset)=33.7 K, was measured from 0.4 to 40 K. The discontinuity in the
specific heat at Tc, deltaC, divided by Tc is 105 +- 5 mJ/molK2, consistent
with values found previously for hole-doped Ba0.6K0.4Fe2As2 and somewhat above
the general trend for deltaC/Tc vs Tc for the iron based superconductors
established by Bud'ko, Ni and Canfield. The usefulness of measured valued of
deltaC/Tc as an important metric for the quality of samples is discussed.",1406.7519v1
2014-06-30,Primary Beam Steering Due to Field Leakage from Superconducting SHMS Magnets,"Simulations of the magnetic fields from the Super High Momentum Spectrometer
in Hall C at Thomas Jefferson National Accelerator Facility show significant
field leakage into the region of the primary beam line between the target and
the beam dump. Without mitigation, these remnant fields will steer the
unscattered beam enough to limit beam operations at small scattering angles.
Presented here are magnetic field simulations of the spectrometer magnets and a
solution using optimal placement of a minimal amount of shielding iron around
the beam line.",1406.7856v2
2014-07-13,Investigation on mass composition of UHE cosmic rays using CRPropa 2.0,"In this paper, we used the Monte Carlo code CRPropa version 2.0 to simulate
the propagation of UHE cosmic rays. In the simulation, uniform cosmic ray
sources with spectral indices of {\alpha} = 1.4, {\alpha} = 2 and Emax = 1021
eV for pure iron composition at the source position are assumed. We obtained
the logarithmic average mass of cosmic rays as a function of energy and
compared it with the experimental values in the ankle, and we demonstrated how
the mass composition changes before and after the ankle.",1407.3468v1
2014-07-18,Superconductivity in FeTe{1-x}S_x induced by electrochemical reaction using ionic liquid solution,"Superconductivity in FeTe0.8S0.2 is successfully induced by an
electrochemical reaction using an ionic liquid solution. A clear correlation
between the Fe concentration in the solution and the manifestation of
superconductivity was confirmed, suggesting that superconductivity was induced
by the deintercalation of excess iron.",1407.4932v1
2014-07-22,Femtosecond intrapulse evolution of the magneto-optic Kerr effect in magnetoplasmonic crystals,"In magnetoplasmonics, it is possible to tailor the magneto-optical properties
of nanostructures by exciting surface plasmon polaritons (SPPs). Thus far,
magnetoplasmonic effects have been considered static. Here, we describe
ultrafast manifestations of magnetoplasmonics by observing the non-trivial
evolution of the transverse magneto-optic Kerr effect within 45-fs pulses
reflected from an iron-based magnetoplasmonic crystal. The effect occurs for
resonant SPP excitations, displays opposite time derivative signs for different
slopes of the resonance, and is explained with the magnetization-dependent
dispersion relation of SPPs.",1407.5845v1
2014-07-28,Minimal model of point contact Andreev reflection spectroscopy of multiband superconductors,"We formulate a minimal model of point contact Andreev reflection spectroscopy
of a normal- metal/multiband superconductor interface. The theory generalizes
the Blonder-Tinkham-Klapwijk (BTK) formulation to a multiband superconductor
and it is based on the quantum waveguides theory. The proposed approach allows
an analytic evaluation of the Andreev and normal reflection coefficients and
thus is suitable for a data fitting of point contact experiments. The obtained
differential conductance curves present distinctive features similar to the
ones measured in the experiments on multiband systems, like the iron-based
pnictides and the MgB2.",1407.7397v1
2014-06-18,Artificial_Micrometeorites,"An iron ball, a beryllium sphere and a tungsten tube segment with diameter
twenty microns, are electrically charged while proton beam irradiating. These
bodies are accelerated by the running pulse field in a spiral waveguide up to
velocity: thirty kilometers per second. The accelerator, generating
micrometeorites is placed at satellites on the Earth orbit. This article
considers processes of penetration of micrometeorites into the Earth
atmosphere. It is shown that micrometeorites evaporate at the height of one
hundred kilometers-one hundred fifty kilometers from the surface of the Earth.
A micrometeorite which is a segment of the beryllium tube equipped with a
graphite cone in the head part is the very meteorite to reach the Earth surface
without being broken.",1407.8542v1
2014-08-10,Growth of (NaxKy)FezSe2 crystals by chlorides flux at low temperatures,"(NaxKy)FezSe2 crystals are prepared by Na, Fe, and Se as starting materials
in NaCl/KCl flux at low temperatures~720 {\deg}C. It is found that K is more
preferred than Na to enter in between FeSe layers and forms the phase.
Thus-obtained crystals contain more superconducting phase in volume fraction
and exhibit new features in transport property. Our results provide a promising
new synthetic route for preparing quality crystals of iron selenide
superconductors.",1408.2181v1
2014-09-16,X-ray Filament with a Strong 6.7 keV Line in the Galactic Center Region,"An elongated X-ray source with a strong K-shell line from He-like iron (Fe
XXVI) is found at (RA, Dec)_{J2000.0}=(17h44m00s.0, -29D13'40''.9) in the
Galactic center region. The position coincides with the X-ray thread,
G359.55+0.16, which is aligned with the radio non-thermal filament. The X-ray
spectrum is well fitted with an absorbed thin thermal plasma (apec) model. The
best-fit temperature, metal abundance, and column density are 4.1^{+2.7}_{-1.8}
keV, 0.58^{+0.41}_{-0.32} solar, and 6.1^{+2.5}_{-1.3}x10^{22} cm^{-2},
respectively. These values are similar to those of the largely extended
Galactic center X-ray emission.",1409.4520v1
2014-09-22,Local magnetization nucleated by non-magnetic impurities in Fe-based superconductors,"We study impurity-induced magnetic order within a five-band Hubbard model
relevant to the normal paramagnetic phase of iron-based superconductors. The
existence of the local magnetic order is explained in terms of an
impurity-enhancement of states near the Fermi level, and we map out the
resulting phase diagram of the existence of magnetization as a function of
impurity strength and Coulomb correlations. In particular, the presence of
impurity-induced magnetism in only a certain range of potential scattering
strengths can be understood from the specific behavior of the impurity resonant
state.",1409.6068v1
2014-10-06,Analysis of point contact spectra of kfe2as2 in the thermal regime,"The point-contact spectra of the iron-based compound KFe2As2 were analyzed
according to the thermal regime theory. We have obtained the values of the
residual resistivity, the Lorentz number, and the electron mean free path in
the contacts. It was shown that the most point-contact spectra can be described
by this theory. The reasons for this behavior are discussed.",1410.1322v1
2014-10-21,Concentrator of elastic waves,"This article is dedicated to an opportunity of concentrating elastic waves in
the iron and water cones on the square of the cone vertex of the order of one
square centimeter. The square of the base of the cone is equal to one square
meter, its height one meter. The calculations assume that the cone hexogen
network lying in the cone basis explodes during the time of one microsecond and
causes an explosive wave converging to the vertex of the cone. It is shown that
this explosive wave can accelerate the body having a mass of three grams to
speed five kilometers per second.",1410.5537v1
2014-11-08,Ab-initio theory of Iron based superconductors,"We report the first-principles study of superconducting critical temperature
and superconducting properties of Fe-based superconductors taking into account
on the same footing phonon, charge and spin-fluctuation mediated Cooper
pairing. We show that in FeSe this leads to a modulated s$\pm$ gap symmetry,
and that the antiferromagnetic paramagnons are the leading mechanism for
superconductivity in FeSe, overcoming the strong repulsive effect of both
phonons and charge pairing.",1411.2121v1
2014-11-16,Replica-exchange Wang-Landau sampling: Pushing the limits of Monte Carlo simulations in materials sciences,"We describe the study of thermodynamics of materials using replica-exchange
Wang-Landau (REWL) sampling, a generic framework for massively parallel
implementations of the Wang-Landau Monte Carlo method. To evaluate the
performance and scalability of the method, we investigate the magnetic phase
transition in body-centered cubic (bcc) iron using the classical Heisenberg
model parametrized with first principles calculations. We demonstrate that our
framework leads to a significant speedup without compromising the accuracy and
precision and facilitates the study of much larger systems than is possible
with its serial counterpart.",1411.4212v1
2015-01-28,Magnetic Design of Superconducting Magnets,"In this paper we discuss the main principles of magnetic design for
superconducting magnets (dipoles and quadrupoles) for particle accelerators. We
give approximated equations that govern the relation between the
field/gradient, the current density, the type of superconductor (Nb-Ti or
Nb3Sn), the thickness of the coil, and the fraction of stabilizer. We also
state the main principle controlling the field quality optimization, and
discuss the role of iron. A few examples are given to show the application of
the equations and their validity limits.",1501.07149v1
2015-01-31,Calculation of the specific heat of optimally K-doped BaFe$_2$As$_2$,"The calculated specific heat of optimally K-doped BaFe$_2$As$_2$ in density
functional theory is about five times smaller than that found in the
experiment. We report that by adjusting the potential on the iron atom to be
slightly more repulsive for electrons improves the calculated heat capacity as
well as the structural, magnetic, and electronic properties of
Ba$_{0.6}$K$_{0.4}$Fe$_2$As$_2$. Applying the same correction to the
antiferromagnetic state, we find that the electron-phonon coupling is strongly
enhanced.",1502.00055v2
2015-04-20,Orbital-lattice coupling and orbital ordering instability in iron pnictides,"Orbital-ordering instability arising due to the intrapocket nesting is
investigated for the tight-binding models of pnictides in the presence of
orbital-lattice coupling. The incommensurate instabilities with small momentum,
which may play an important role in the nematic-ordering transition, vary from
model to model besides being more favorable in comparison to the spin-density
wave instability in the absence of good interpocket nesting. We also examine
the doping dependence of such instabilities. The electron-phonon coupling
parameter required to induce them are compared with the first-principle
calculations.",1504.04915v1
2015-05-12,Unified picture for the colossal thermopower compound FeSb$_2$,"We identify the driving mechanism of the gigantic Seebeck coefficient in
FeSb$_2$ as the phonon-drag effect associated with an in-gap density of states
that we demonstrate to derive from excess iron. We accurately model electronic
and thermoelectric transport coefficients and explain the so far ill-understood
correlation of maxima and inflection points in different response functions.
Our scenario has far-reaching consequences for attempts to harvest the
spectacular powerfactor of FeSb$_2$.",1505.02946v1
2015-05-26,Violation of the Wiedemann-Franz law as an evidence of the pseudogap in the iron-based superconductor Ba(Fe1-xCox)2As2,"Longitudinal and transverse transport coefficients of the Ba(Fe1-xCox)2As2
single crystals with x = 0, 0.045, 0.06 and 0.244 were measured in the
temperature range 1.4 - 300 K and in magnetic fields up to 12.5 T. The
resulting data were used to determine the temperature dependence of the Hall
Lorenz number (Lxy) and its evolution with doping. Lxy is defined by the
electronic contributions to the thermal and electrical conductivities and it is
found to differ from its canonical behavior. This shows the emergence of a
pseudogap in samples at intermediate doping.",1505.06993v1
2015-06-09,Convergence of a Finite Volume Scheme for a Corrosion Model,"In this paper, we study the numerical approximation of a system of partial
dif-ferential equations describing the corrosion of an iron based alloy in a
nuclear waste repository. In particular, we are interested in the convergence
of a numerical scheme consisting in an implicit Euler scheme in time and a
Scharfetter-Gummel finite volume scheme in space.",1506.02996v1
2015-06-12,Predicting Unconventional High Temperature Superconductors in Trigonal Bipyramidal Coordinations,"Cuprates and iron-based superconductors are two classes of unconventional
high Tc superconductors based on 3d transition elements. Recently, two
principles, correspondence principle and magnetic selective pairing rule, have
been emerged to unify their high Tc superconducting mechanisms. These
principles strongly regulate electronic structures that can host high Tc
superconductivity. Guided by these principles, here we propose high Tc
superconducting candidates that are formed by cation-anion trigonal bipyramidal
complexes with a d^7 filling configuration on the cation ions. Their
superconducting states are expected to be dominated by the d+id pairing
symmetry.",1506.03904v2
2015-08-06,Time-reversal symmetry breaking state in dirty three-band superconductor,"I study the effects of disorder on the superconductivity of a three-band
model with repulsive interband pairing. Such a model can support several
possible superconducting order parameters, including a complex time-reversal
symmetry breaking (TRSB) state. Impurity scattering suppresses the critical
temperature of all these states, but the complex state survives, and remains a
part of the phase diagram of the model even in the presence of moderate amount
of disorder. This means that the TRSB states could be experimentally accessible
in multiband materials like iron pnictides and chalcogenides.",1508.01517v1
2015-09-14,A Practioner's Guide to Evaluating Entity Resolution Results,"Entity resolution (ER) is the task of identifying records belonging to the
same entity (e.g. individual, group) across one or multiple databases.
Ironically, it has multiple names: deduplication and record linkage, among
others. In this paper we survey metrics used to evaluate ER results in order to
iteratively improve performance and guarantee sufficient quality prior to
deployment. Some of these metrics are borrowed from multi-class classification
and clustering domains, though some key differences exist differentiating
entity resolution from general clustering. Menestrina et al. empirically showed
rankings from these metrics often conflict with each other, thus our primary
motivation for studying them. This paper provides practitioners the basic
knowledge to begin evaluating their entity resolution results.",1509.04238v1
2015-09-15,Lambda Boo Abundance Patterns: Accretion from Orbiting Sources,"The abundance anomalies in lambda Boo stars are popularly explained by
element-specific mass inflows at rates that are much greater than
empirically-inferred bounds for interstellar accretion. Therefore, a lambda Boo
star's thin outer envelope must derive from a companion star, planet, analogs
to Kuiper Belt Objects or a circumstellar disk. Because radiation pressure on
gas-phase ions might selectively allow the accretion of carbon, nitrogen, and
oxygen and inhibit the inflow of elements such as iron, the source of the
acquired matter need not contain dust. We propose that at least some lambda Boo
stars accrete from the winds of hot Jupiters.",1509.04672v2
2015-09-20,Antimatter in the Direct-Action Theory of Fields,"One of Feynman's greatest contributions to physics was the interpretation of
negative energies as antimatter in quantum field theory. A key component of
this interpretation is the Feynman propagator, which seeks to describe the
behavior of antimatter at the virtual particle level. Ironically, it turns out
that one can dispense with the Feynman propagator in a direct-action theory of
fields, while still retaining the interpretation of negative energy solutions
as antiparticles.",1509.06040v1
2015-10-07,Electromagnetically controlled multiferroic thermal diode,"We propose an electromagnetically tunable thermal diode based on a two phase
multiferroics composite. Analytical and full numerical calculations for
prototypical heterojunction composed of Iron on Barium titanate in the
tetragonal phase demonstrate a strong heat rectification effect that can be
controlled externally by a moderate electric field. This finding is of an
importance for thermally based information processing and sensing and can also
be integrated in (spin)electronic circuits for heat management and recycling.",1510.02058v1
2015-10-29,New intercalation superconductor Lix(C6H16N2)yFe2-zSe2 with a very large interlayer-spacing and Tc = 38 K,"A new iron-based superconductor, Lix(C6H16N2)yFe2-zSe2, with Tc = 38 K has
successfully been synthesized via the intercalation of lithium and
hexamethylenediamine into FeSe. The superconducting transition has been
confirmed not only by magnetic susceptibility measurements but also by
electrical resistivity ones. The interlayer spacing, namely, the dicstance
between neighboring Fe layers, d, is 16.225(5) $\mathring{\text{A}}$, which is
the largest among those of FeSe-based intercalation compounds. It has been
found that the dependence of Tc on d in FeSe-based intercalation
superconductors appears domic.",1510.08625v1
2015-10-29,First-principles study of FeSe epitaxial films on SrTiO3,"The discovery of high temperature superconductivity in FeSe films on SrTiO3
substrate has inspired great experimental and theoretical interests.
First-principles density functional theory calculations, which have played an
important role in the study of bulk iron-based superconductors, also
participate in the investigation of interfacial superconductivity. In this
article, we review the calculation results on the electronic and magnetic
structures of FeSe epitaxial films, emphasizing on the interplay between
different degrees of freedom, such as charge, spin, and lattice vibrations.
Furthermore, the comparison between FeSe monolayer and bilayer films on SrTiO3
is discussed.",1510.08630v1
2015-11-10,Slow in-plane magnetoresistance oscillations in multiband quasi-two-dimensional metals,"Slow oscillations (SlO) of magnetoresistance is a convenient tool to measure
electronic structure parameters in quasi-two-dimensional metals. We study the
possibility to apply this method to multi-band conductors, e.g. to iron-based
high-temperature superconducting materials. We show that SlO can be used to
measure the interlayer transfer integral in multi-band conductors similar to
single-band metals. In addition, the SlO allow to measure and compare the
effective masses or the electron scattering rates in various bands.",1511.03178v1
2015-11-16,Mixture model of pottery distributions from Lake Chad Basin archaeological sites reveals ancient segregation patterns,"We present a new statistical approach to analyzing an extremely common
archaeological data type -- potsherds -- that infers the structure of cultural
relationships across a set of excavations. This method, applied to data from a
set of complex, culturally heterogeneous sites around the Mandara mountains in
the Lake Chad Basin, articulates currently understood cultural succession into
the Iron Age. We show how the approach can be integrated with radiocarbon dates
to provide detailed portraits of cultural dynamics and deposition patterns
within single excavations that, in this context, indicate historical
ethnolinguistic segregation patterns. We conclude with a discussion of the many
possible model extensions using other archaeological data types.",1511.05185v1
2015-12-17,Point defect absorption by grain boundaries in $α$-iron by atomic density function modeling,"Using the atomic density function theory (ADFT), we examine the point defect
absorption at [110] symmetrical tilt grain boundaries in body-centered cubic
iron. It is found that the sink strength strongly depends on misorientation
angle. We also show that the ADFT is able to reproduce reasonably well the
elastic properties and the point defect formation volume in $\alpha$-iron.",1512.05492v1
2016-01-14,Giant domain wall response of highly twinned ferroelastic materials,"Many ferroelastic crystals display at sufficiently low measurement
frequencies a huge elastic softening below Tc which is caused by domain wall
motion. Materials range from perovskites to iron based superconductors and
shape memory materials. We present a model - based on Landau-Ginzburg theory
including long range elastic interaction between needle shaped ferroelastic
domains - to describe the observed superelastic softening. The theory predicts
that the domain wall contribution to the elastic susceptibility is different
for improper and proper ferroelastic materials. A test of the theory against
experimental data on SrTiO3, KMnF3, LaAlO3, La1-xNdxP5O14 and NH4HC2O4.1/2H2O
yields excellent agreement.",1601.03590v1
2016-01-25,Influence of Lifshitz transitions and correlation effects on the scattering rates of the charge carriers in iron-based superconductors,"Minimum model calculations on the co-action of hole vanishing Lifshitz
transitions and correlation effects in ferropnictides are presented. The
calculations predict non-Fermi-liquid behaviour and huge mass enhancements of
the charge carriers at the Fermi level. The findings are compared with recent
ARPES experiments and with measurements of transport and thermal properties of
ferropnictides. The results from the calculation can be also applied to other
unconventional superconductors and question the traditional view of quantum
critical points.",1601.06516v1
2016-02-01,A Short Note on Improved Logic Circuits in a Hexagonal Minesweeper,"This paper aims to present an advanced version of PP-hardness proof of
Minesweeper by Bondt. The advancement includes improved Minesweeper
configurations for 'logic circuits' in a hexagonal Minesweeper. To do so, I
demonstrate logical uncertainty in Minesweeper, which ironically allows a
possibility to make some Boolean operators.
  The fact that existing hexagonal logic circuits did not clearly distinguish
the true and false signal needs an improved form of a hexagonal wire. I
introduce new forms of logic circuits such as NOT, AND, OR gates, a curve and a
splitter of wires. Moreover, these new logic circuits complement Bondt's proof
for PP-hardness of Minesweeper by giving a new figure.",1602.00398v1
2016-03-10,First-Principles Momentum-Dependent Local Ansatz Wavefunction and Momentum Distribution Function Bands of Iron,"We have developed a first-principles local ansatz wavefunction approach with
momentum-dependent variational parameters on the basis of the tight-binding
LDA+U Hamiltonian. The theory goes beyond the first-principles Gutzwiller
approach and quantitatively describes correlated electron systems. Using the
theory, we find that the momentum distribution function (MDF) bands of
paramagnetic bcc Fe along high-symmetry lines show a large deviation from the
Fermi-Dirac function for the $d$ electrons with $e_{g}$ symmetry and yield the
momentum-dependent mass enhancement factors. The calculated average mass
enhancement $m^{\ast}/m = 1.65$ is consistent with low-temperature specific
heat data as well as recent angle-resolved photoemission spectroscopy (ARPES)
data.",1603.03118v1
2016-03-19,Magnetic behaviour of dirty multiband superconductors near the upper critical field,"Magnetic properties of dirty multiband superconductors near the upper
critical field are studied. The parameter $\kappa_2$ characterizing
magnetization slope is shown to have a significant temperature variation which
is quite sensitive to the pairing interactions and relative strengths of
intraband impurity scattering. In contrast to single-band superconductors the
increase of $\kappa_2$ at low temperatures can be arbitrary large determined by
the ratio of minimal and maximal diffusion coefficients in different bands.
Temperature dependencies of $\kappa_2(T)$ in two-band MgB$_2$ and iron-based
superconductors are shown to be much more sensitive to the multiband effects
than the upper critical field $H_{c2}(T)$.",1603.06054v1
2016-03-23,Large Magnetoresistance at Room Temperature in Ferromagnet/Topological Insulator Contacts,"We report magnetoresistance for current flow through iron/topological
insulator (Fe/TI) and Fe/evaporated-oxide/TI contacts when a magnetic field is
used to initially orient the magnetic alignment of the incorporated
ferromagnetic Fe bar, at temperatures ranging from 100 K to room temperature.
This magnetoresistance is associated with the relative orientation of the Fe
bar magnetization and spin-polarization of electrons moving on the surface of
the TI with helical spin-momentum locking. The magnitude of the observed
magnetoresistance is relatively large compared to that observed in prior work.",1603.07283v1
2016-04-11,Doubling of the critical temperature of FeSe observed in point contacts,"Rise in superconducting critical temperature Tc more than two times
(exceeding 20 K) is discov- ered in point-contacts created between
iron-chalcogenide FeSe single crystal and Cu. The possible reasons of such Tc
increase in point-contacts are discussed. The most probable cause for this may
be the interfacial carriers doping and/or interfacial enhanced electron-phonon
interaction.",1604.02921v2
2016-04-04,The Fine Structure Constant and Habitable Planets,"We use the existence of habitable planets to impose anthropic requirements on
the fine structure constant, $\alpha$. To this effect, we present two
considerations that restrict its value to be very near the one observed. The
first, that the end product of stellar fusion is iron and not one of its
neighboring elements, restricts $\alpha^{-1}$ to be $145\pm 50$. The second,
that radiogenic heat in the Earth's interior remains adequately productive for
billions of years, restricts it to be $145\pm9$. A connection with the grand
unified theory window is discussed, effectively providing a route to probe
ultra-high energy physics with upcoming advances in planetary science.",1604.03151v1
2016-04-15,Electron magnetic resonance in magnetic nanoparticles: dependence on the particle size and applicability of the modified giant spin model,"Superparamagnetic nanoparticles containing hundreds and thousands of coupled
electron spins are on the boundary between classical and quantum behavior, and
demonstrate features which are typical for paramagnetic spins and absent in
macroscopic ferromagnetic systems. In order to better understand the evolution
of magnetization dynamics from quantum to classical behavior with the increase
in the system size, we study the electron magnetic resonance signal in
suspensions of iron oxide nanoparticles as the function of the particle size.
The experimental data are compared with numerical simulations based on the
giant spin approach.",1604.04594v2
2016-04-21,Non-equilibrium magnetic fields in ab initio spin dynamics,"Starting from the continuity equation for the magnetization in time-dependent
spin-density functional theory, we derive an expression for the effective
time-dependent magnetic fields driving the out-of-equilibrium spin dynamics in
magnetic systems. We evaluate these, so called, kinetic magnetic fields in the
ultrafast demagnetization response to optical pulse excitations of
ferromagnetic iron-based materials, namely Fe$_6$ cluster and bulk bcc Fe. We
identify spatial ""hot spots"" where the demagnetization is particularly enhanced
as a result of the increased kinetic torque.",1604.06262v2
2016-05-02,Study of glass properties as electrode for RPC,"Operation and performance of the Resistive Plate Chambers (RPCs) mostly
depend on the quality and characteristics of the electrode materials. The
India-based Neutrino Observatory collaboration has chosen glass RPCs as the
active detector elements for its Iron Calorimeter detector and is going to
deploy RPCs in an unprecedented scale. Therefore, it is imperative that we
study the electrode material aspects in detail. We report here, systematic
characterization studies on the glasses from two manufacturers. RPC detectors
were built using these glasses and performances of the same were compared with
their material properties.",1605.01044v1
2016-05-07,Effect of glass thickness variations on the performance of RPC detectors,"The India-based Neutrino Observatory (INO) is planning to build a magnetized
iron calorimeter detector (ICAL) in which Resistive Plate Chambers (RPCs) will
be the active detector elements. A study of the performance of RPCs, made using
electrodes of various thicknesses, is pivotal in optimizing the design
parameters of the ICAL RPCs. We fabricated RPCs with glasses of various
thicknesses and studied their performance in the same environmental conditions.
A study of detector efficiency, noise rate, time resolution and charge
distribution is presented in this paper.",1605.02189v2
2016-06-11,Hydrodynamics of Domain Walls in Multiferroics: Impact on Memory Devices,"We show that switching in ferroelectric lead germanate and lead iron
tantalate zirconate titanate (PZTFT) does not resemble the equilibrium domain
structure evolution of the Landau-Lifshitz-Kittel model but is instead highly
nonequilibrium and similar, respectively, to the Richtmyer-Meshkov instability
in liquids and the Helfrich-Hursault sliding instability in liquid crystals.
The resulting nano-domain structures in PZTFT are circular or parabolic and
involving folding bifurcations. These may have an undesirable impact on
ferroelectric thin-film memoriesthat are also ferroelastic.",1606.03586v1
2016-06-12,Validity of the Local Approximation in Iron- Pnictides and Chalcogenides,"We introduce a cluster DMFT (Dynamical Mean Field Theory) approach to study
the normal state of the iron pnictides and chalcogenides. In the regime of
moderate mass renormalizations, the self-energy is very local, justifying the
success of single site DMFT for these materials and for other Hunds metals. We
solve the corresponding impurity model with CTQMC (Continuous Time Quantum
Monte-Carlo) and find that the minus sign problem is not severe in regimes of
moderate mass renormalization.",1606.03660v1
2016-06-16,Three-dimensional Critical Dirac semimetal in KMgBi,"We predicted that AMgBi (A=K,Rb Cs), which have the same lattice structures
as the 111 family of iron-based superconductors (Na/LiFeAs), are
symmetry-protected Dirac semimetals located near the boundary of type-I and
type-II Dirac semimetal phases. Doping Rb or Cs into KMgBi can drive the
transition between the two phases. The materials can also be turned into Weyl
semimetals and topological insulators by explicitly or spontaneously breaking
time-reversal symmetry and C$_4$ lattice symmetry respectively.",1606.05042v2
2016-06-23,"Understanding doping, vacancy, lattice stability and superconductivity in KxFe2-ySe2","Metal-intercalated iron selenides are a class of superconductors that have
received much attention but are less understood in comparison with their
FeAs-based counterparts. Here, the controversial issues such as Fe vacancy, the
real phase responsible for superconductivity, and lattice stability have been
addressed based on first-principles calculations. New insights into the
distinct features in terms of carrier doping have been revealed.",1606.07217v1
2016-08-03,Compressive deformation of Fe nanopillar : Modalities of dislocation dynamics,"Unlike the tensile mode, compressive deformation of a bcc metallic
nanostructure is mediated by the glide of screw dislocation. Although the bcc
screw dislocations are well known to possess unusual attributes, it is still
unclear how these unique effects manifest in a nanoscale solid. In the present
study, atomistic simulations render a close look at the dislocation activities
underlying the compressive deformation of bcc iron nanopillars. It is found
that instead of performing simple glide motion, the line defects exhibit a host
of complex features. In this regard, the temperature is observed to have a
pronounced effect on the dislocation mechanisms and consequently, on the
overall plastic response of the material. Additionally, statistical features of
the load-strain data have been explored.",1608.01166v1
2016-08-07,Spin-orbit coupling in Fe-based superconductors,"We study the spin resonance peak in recently discovered iron-based
superconductors. The resonance peak observed in inelastic neutron scattering
experiments agrees well with predicted results for the extended $s$-wave
($s_\pm$) gap symmetry. Recent neutron scattering measurements show that there
is a disparity between longitudinal and transverse components of the dynamical
spin susceptibility. Such breaking of the spin-rotational invariance in the
spin-liquid phase can occur due to spin-orbit coupling. We study the role of
the spin-orbit interaction in the multiorbital model for Fe-pnictides and show
how it affects the spin resonance feature.",1608.02230v1
2016-08-09,Theory Perspective: SCES 2016,"New discoveries and developments in almost every area of correlated electron
physics were presented at SCES 2016. Here, I provide a personal perspective on
some of these developments, highlighting some new ideas in computational
physics, discussing the ""hidden order"" challenges of cuprate and heavy electron
superconductors, the mysterious bulk excitations of the topological Kondo
insulator SmB$_{6}$ and new progress in research on quantum spin ice, iron
based superconductors and quantum criticality.",1608.02925v3
2016-08-15,Design and Measurement of Dipole Magnets for CSNS 1.6GeV RCS,"The Rapid Cycling Synchrotron (RCS) in Chinese Spallation Neutron Source
(CSNS) accelerates proton beam from 80Mev to 1.6GeV at a repetition rate of
25Hz. All dipole magnets of RCS are operated at AC with biased DC. Aiming at
the properties of these dipole magnets, we take some methods to improve
magnetic field quality in the good region and reduce eddy currents in the iron
core . In this paper, we would present the process of the magnet design and
temperature rise calculation. At the same time, the field measurement results
and temperature test of the prototype magnet are also described and discussed.",1608.04199v1
2016-08-25,Two-dimensional Superconductors with Atomic-scale Thicknesses,"Recent progress in two-dimensional superconductors with atomic-scale
thicknesses is reviewed mainly from the experimental point of view. The
superconducting systems treated here involve a variety of materials and forms:
elemental-metal ultrathin films and atomic layers on semiconductor surfaces;
interfaces and superlattices of heterostructures made of cuprates, perovskite
oxides, and rare-earth metal heavy-fermion compounds; interfaces of
electric-double-layer transistors; graphene and atomic sheets of
transition-metal dichalcogenide; iron selenide and organic conductors on oxide
and metal surfaces, respectively. Unique phenomena arising from the ultimate
two-dimensionality of the system and the physics behind them are discussed.",1608.06997v1
2016-09-18,Lattice dynamics of KNi2Se2,"We report the first principle calculations of the lattice dynamics of
KNi$_{2}$Se$_2$ together with the Raman scattering study.\ We have observed
three out of four Raman active modes predicted by the factor group analysis.
Calculated phonon frequencies are in good agreement with experimental
findings.\ Contrary to its iron counterpart (K$_x$Fe$_{2-y}$Se$_2$),
K$_{0.95}$Ni$_{1.86}$Se$_2$ does not show vacancy ordering.",1609.05547v1
2016-10-08,Causal-order superposition as an enabler of free will,"It is often argued that bottom-up causation under a physicalist, reductionist
worldview precludes free will in the libertarian sense. On the one hand, the
paradigm of classical mechanics makes determinism inescapable, while on the
other, the leading models that allow a role for quantum effects are
noncommittal regarding how conscious agents are supposed to translate
indeterminacy into self-formed choice. Recent developments, however, not only
imply that self-formed decisions are possible, but actually suggest how they
might come about. The cornerstone appears to be causality superposition rather
than quantum-state entanglement, as is usually assumed, and the natural arena
for applying these developments is (perhaps ironically) a framework that was
built without any consideration for quantum effects.",1610.02395v1
2016-12-12,Classification of exoplanets according to density,"Considering probability distribution as a function of the average density
$\bar{\rho}$ computed for 424 extrasolar planets we identify three log-normal
Gaussian population components. The two most populous components at
$\bar{\rho}\simeq0.7$ g/cc and $\bar{\rho}\simeq7$ g/cc are the ice/gas giants
and iron/rock super-Earths, respectively. A third component at
$\bar{\rho}\simeq30$ g/cc is consistent with brown dwarfs, i.e., electron
degeneracy supported objects. We note presence of several extreme density
planetary objects.",1612.03556v1
2016-12-21,MPS and ACS with an atomic magnetometer,"We show that a single atomic magnetometer in a magnetically unshielded
environment can be used to perform magnetic particle spectroscopy (MPS) and AC
susceptometry (ACS) on liquid-suspended magnetic nanoparticles. We demonstrate
methods allowing a simultaneous recording of M(H) and dM/dH(H) dependences of
samples containing down to 1 $\mu$g of iron. Our results pave the way towards
an atomic magnetometer based MPI scanner.",1612.07094v1
2016-12-21,Grain boundary relaxation and reconstruction: effect on local magnetic moment,"We present a detailed numerical study on structure and local magnetic
properties of $\langle 100 \rangle$ symmetric tilt grain boundaries in
bcc-iron. Particular attention is paid to connection between type of grain
boundary relaxation and local magnetic properties. Results from first
principles calculation showed that grain boundary reconstruction leads to
non-uniform distribution of local magnetic moments in grain boundary plane.
This is in contrast with the result obtained in grain boundary plane, where
simple relaxation is observed. Well optimized atomic configurations in the
vicinity of the interface were achieved by simulated annealing optimization
technique improved by combination with genetic algorithm.",1612.07181v1
2017-01-10,The giant effect of magnetic ordering on a sound velocity in a sigma-Fe55Cr45 alloy,"We studied atomic dynamics of sigma-Fe(100-x)Cr(x) (x=45 and 49.5) alloys
using nuclear inelastic scattering of synchrotron radiation. For the
sigma-Fe55Cr45 alloy, the derived reduced iron-partial density of phonon states
reveal a huge difference in the low-energy region between magnetic and
paramagnetic states. The latter implies a ca.36% increase of the sound velocity
in the magnetic phase, which testifies to a magnetically-induced hardening of
the lattice.",1701.02467v1
2017-02-01,Structural characterization of magnetoferritin,"The physicochemical characterization of the magnetoferritin biomacromolecule
in terms of morphology, structural and magnetic properties shows that iron
oxides can be efficiently loaded into apoferritin molecules, preserving their
native biocompatible structure and affecting the morphology of the protein
shell.",1702.00138v1
2017-02-09,Site-Selective Antimony Doping in Arsenic Zigzag Chains of 112-type Ca1-xLaxFeAs2,"Single crystal X-ray diffraction studies were performed for the Sb-doped
112-type iron-based superconductor Ca1-xLaxFeAs2 with the superconducting
transition temperature Tc of 47 K. Doped Sb preferably substituted not for
As(1) in the FeAs layers but for As(2) in the layers of As zigzag chains.
Structural reasons for Tc enhancement by Sb doping were discussed.",1702.02672v1
2017-02-14,Hidden radical reactivity of the [FeO]2+ group of the (hydro)oxide species in the H-abstraction from methane: a DFT and CASPT2 study,"Reactivity of the [FeO]2+ group in the abstraction of hydrogen from methane
is determined by metastable oxyl state FeIII-O* causing the negative spin
polarization of the methyl moiety as was shown by quantum-chemical means with
the use of model iron hydroxide species FeO(OH)2, Fe2O(OH)5, and Fe4O5(OH)3 as
an example.",1702.04092v1
2017-04-19,Remote Document Encryption - encrypting data for e-passport holders,"We show how any party can encrypt data for an e-passport holder such that
only with physical possession of the e-passport decryption is possible. The
same is possible for electronic identity cards and driver licenses. We also
indicate possible applications. Dutch passports allow for 160 bit security,
theoretically giving sufficient security beyond the year 2079, exceeding
current good practice of 128 bit security. We also introduce the notion of RDE
Extraction PIN which effectively provides the same security as a regular PIN.
Our results ironically suggest that carrying a passport when traveling abroad
might violate export or import laws on strong cryptography.",1704.05647v3
2017-05-02,Computation of the unifying thread in high temperature superconductors from first principles quantum Monte Carlo,"It has long been a challenge to describe the origin of unconventional
superconductivity. The two known examples with high Tc, based on iron and
copper, have very different electronic structures, while other materials with
similar electronic structure may not show superconductivity at all. In this
paper, the authors show that by using high accuracy diffusion Monte Carlo
calculations, the unconventional superconductors of both high Tc types form a
cluster at intermediate spin-charge coupling. The spin-charge coupling may
serve as a normal state marker for unconventional superconductivity, and
provides evidence that unconventional superconductivity is due to interaction
of charge with local spins in materials.",1705.01008v1
2017-06-09,Ultrasound attenuation in $s^\pm$-wave two-band superconductors,"The two-band $s^{\pm}$-wave state is currently considered to be the most
promising candidate for newly discovered iron-based high-$T_c$ superconductors.
In this work we study theoretically the ultrasound attenuation in
$s^{\pm}$-wave two-band superconductors. The impurity effect is calculated
within the $\mathcal{T}$-matrix approximation. In particular, our theory
predict that, when the sizes of two order parameter are comparable, a
Hebel-Slichter peak may show up in the ultrasound attenuation versus
temperature curves. Our calculations also confirmed the presence of the
resonant impurity scattering at low temperature, observed previously by other
authors in the calculation of the NMR relaxation rate $1/T_{1}$.",1706.02963v1
2017-07-29,Thermodynamics of the SmCo5 compound doped with Fe and Ni: an ab initio study,"SmCo5 permanent magnets exhibit enormous uniaxial magnetocrystalline
anisotropy energy and have a high Curie temperature. However, a low energy
product presents a significant drawback in the performance of SmCo5 permanent
magnets. In order to increase the energy product in SmCo5, we propose
substituting fixed amount of cobalt with iron in a new magnet, SmFe3CoNi, where
inclusion of nickel metal makes this magnet thermodynamically stable. We
further discuss some basic theoretical magnetic properties of the SmCo5
compound.",1707.09447v1
2017-08-29,Prediction of a new efficient permanent magnet SmCoNiFe3,"We propose a new efficient permanent magnet, SmCoNiFe3, that is a
breakthrough development of the well-known SmCo5 prototype. More modern
neodymium magnets of the Nd-Fe-B type have an advantage over SmCo5 because of
their greater maximum energy products due to their iron-rich stoichiometry. Our
new magnet, however, removes most of this disadvantage of SmCo5 while
preserving its superior high-temperature efficiency over the neodymium magnets.",1708.08957v1
2017-09-08,Enhanced superconducting-fluctuation effects on thermodynamic properties in BCS-BEC-crossover regime,"Effects of superconducting fluctuation (SCF) on thermodynamic properties of
electron systems in the so-called BCS-BEC-crossover regime are studied. As the
attractive interaction between electrons becomes stronger upon approaching the
BCS-BEC-crossover regime, importance of the mode coupling between SCF
drastically increases. The enhanced mode coupling leads to lowering of both the
zero-field superconducting critical temperature and the depairing field
$B_\text{c2} (T)$. Consequently, SCF-induced contributions to the specific heat
and the diamagnetic susceptibility can seemingly exceed the corresponding
values in the Gaussian approximation. We discuss relevance of the present
results to the anomalous SCF-induced diamagnetic response observed in the iron
selenide (FeSe).",1709.02553v1
2017-10-26,"SDSS J090152.05+624342.6: A New ""Overlapping-Trough"" FeLoBAL Quasar At Z$\sim2$","We here report an identification of SDSS J090152.04+624342.6 as a new
""overlapping-trough"" iron low-ionization broad absorption line quasar at
redshift of $z\sim2.1$. No strong variation of the broad absorption lines can
be revealed through the two spectra taken by the Sloan Digital Sky Survey with
a time interval of $\sim6$yr. Further optical and infrared spectroscopic study
on this object is suggested.",1710.09527v1
2017-11-03,"Supernova β^- decay of nuclides 53Fe, 54Fe, 55Fe, and 56Fe in strongly screened plasma","The electron screening strong effect on the electron energy and threshold
energy of the beta decay reaction. in this paper, we study the $\beta^-$ decay
rates of some iron isotopes. The electron screening beta decay rates increase
by about two orders of magnitude. The strong screening beta decay rates due to
Q-value correction are by more than one order of magnitude higher than those of
without Q-value correction.",1711.01955v3
2017-11-29,The Memory Function Formalism: A Review,"An introduction to the Zwanzig-Mori-G\""{o}tze-W\""{o}lfle memory function
formalism (or generalized Drude formalism) is presented. This formalism is used
extensively in analyzing the experimentally obtained optical conductivity of
strongly correlated systems like cuprates and Iron based superconductors etc.
For a broader perspective both the generalised Langevin equation approach and
the projection operator approach for the memory function formalism are given.
The G\""{o}tze-W\""{o}lfle perturbative expansion of memory function is presented
and its application to the computation of the dynamical conductivity of metals
is also reviewd. This review of the formalism contains all the mathematical
details for pedagogical purposes.",1711.10758v1
2017-11-30,A note on the contribution of multi-photon processes to radiative opacity,"Recently, Bailey et al. performed iron opacity measurements on the Z machine
at Sandia National Laboratory in conditions close to the ones of the base of
the convective zone of the Sun. Such experiments have raised questions about
the physical models commonly used in opacity codes. To understand the
discrepancy between experiment and theory, More et al. investigated the role of
two-photon processes. In the present work we show, by a simple estimate and
using hydrogenic formulas, that due to the intensity of the backlight radiation
seen by the sample, such processes are likely to play an important role only
for highly excited states.",1711.11295v1
2017-12-10,Visible evidence to magnetism of graphene oxide,"Graphene oxide continues to amaze scientific community for multiple
potentials in a broad span of applications such as catalysts, adsorbents,
oxidants, etc., determined by constant unveiling of its fantastic natures. Of
them, magnetism is not ultimately identified and directly observed by naked
eyes. Herein, we report graphene oxide directionally migrated and deposited
together simply under external magnetic field from common Nd-Fe-B magnet,
whereas the ferromagnetism of graphene oxide did not exhibit that strong as
iron. Therefore, we illustrated this interesting pathway to keep close to such
2D carbon materials and potentially promoted magnetic-oriented applications.",1712.03570v4
2017-12-22,Novel Method for Background Phase Removal on MRI Proton Resonance Frequency Measurements,"MR images have a magnitude and a phase, but in almost all clinical
applications only the magnitude images are used, because the phase images have
a smooth but strong background signal that masks useful information. The phase
contains information such as the temperature during thermal ablation, and the
iron content of brain tissue. We describe a novel method to suppress the
background that is based on higher order edge detection and sparse image
representation.",1712.08651v1
2018-02-23,Electronic entropy in Green's-function calculations at finite temperatures,"We revise critically existing approaches to evaluation of thermodynamic
potentials within the Green's function calculations at finite electronic
temperatures. We focus on the entropy and show that usual technical problems
related to the multivalued nature of the complex logarithm can be overcome.
This results in a simple expression for the electronic entropy, which does not
require any contour integration in the complex energy plane. Properties of the
developed formalism are discussed and its illustrating applications to selected
model systems and to bcc iron with disordered local magnetic moments are
presented as well.",1802.08495v1
2018-03-01,High Temperature Electronic Structure with KKR,"Modeling high temperature (10's or 100's of eV), dense plasmas is challenging
due to the multitude of non-negligible physical effects including significant
partial ionization and multi-site effects. These effects cause the breakdown or
intractability of common methods and approximations used at low temperatures,
such as pseudopotentials or plane wave basis sets. Here we explore the KKR
Green's function method at these high temperature conditions. The method is
all-electron, does not rely on pseudopotentials, and uses a spherical harmonic
basis set, and so avoids the aforementioned limitations. It is found to be
accurate for solid density aluminum and iron plasmas compared when compared to
a plane wave method at low temperature, while being able to access high
temperatures.",1803.00596v1
2018-03-18,Effect of gap anisotropy on the spin resonance peak in the superconducting state of iron-based materials,"Spin resonance in the superconducting state of Fe-based materials within the
multiorbital model with unequal anisotropic gaps on different Fermi surface
sheets is studied. On the basis of the model gap function and the one
calculated within the spin fluctuation theory of pairing, I show that the
resonance peak shifts to higher frequencies with increasing the zero-amplitude
gap magnitude. On the contrary, with increasing the gap anisotropy, it shifts
to lower frequencies and lose some intensity.",1803.06736v2
2018-05-03,Binarizer at SemEval-2018 Task 3: Parsing dependency and deep learning for irony detection,"In this paper, we describe the system submitted for the SemEval 2018 Task 3
(Irony detection in English tweets) Subtask A by the team Binarizer. Irony
detection is a key task for many natural language processing works. Our method
treats ironical tweets to consist of smaller parts containing different
emotions. We break down tweets into separate phrases using a dependency parser.
We then embed those phrases using an LSTM-based neural network model which is
pre-trained to predict emoticons for tweets. Finally, we train a
fully-connected network to achieve classification.",1805.01112v1
2018-05-15,Nuclear EMC effect through $\barΛ/Λ$ production in semi-inclusive deep-inelastic scattering processes,"We calculate $\Lambda$ and $\bar{\Lambda}$ hadron production cross sections
in charged lepton semi-inclusive deep-inelastic scattering off nuclear target
($A$, using iron $\mathrm{Fe}$ as an example) and deuteron ($D$) target. The
results show that the ratio
$(\bar{\Lambda}^{A}/\Lambda^{A})/(\bar{\Lambda}^{D}/\Lambda^{D})$ is sensitive
to the sea quark content of the nucleus. We adopt three different models to
take the nuclear EMC effect into account. The ratio
$(\bar{\Lambda}^{A}/\Lambda^{A})/(\bar{\Lambda}^{D}/\Lambda^{D})$ is predicted
to be different by these different models.",1805.05544v1
2018-05-16,Lattice distortions and/or intercalation as ways to induce magnetism in a-FeSi2: a theoretical study,"The possibilities to induce magnetism in the non-magnetic bulk alpha-FeSi2 by
means of lattice distortions or intercalation with metal or non-metal ions of
light elements is investigated theoretically by combined ab initio and model
methods. We find that the distortions indeed can induce the formation of
magnetic moment on iron atoms in certain local environments; however, the
required strength of the distortions often is too large to be achieved in
experiments. For this reason we suggest using ""chemical pressure"" that is,
intercalating the alpha-FeSi2 films by light elements. We find that some of
such variants have promising characteristic.",1805.06189v1
2018-05-25,Pairing Mechanism in Hunds Metal Superconductors and the Universality of the Superconducting Gap to Critical Temperature Ratio,"We analyze a simple model containing the physical ingredients of a Hund's
metal, the local spin fluctuations with power-law correlators,
$(\Omega_0/|\Omega|)^\gamma$, with $\gamma$ greater than one, interacting with
electronic quasiparticles. While the critical temperature and the gap change
significantly with varying parameters, the $2\Delta_{max}/k_BT_c$ remains close
to twice the BCS value in agreement with experimental observations in the
iron-based superconductors (FeSC).",1805.10280v2
2018-05-30,Charged and Neutral Current Pion Production in Neutrino-Nucleus Scattering,"In this article, we present the charged and neutral current coherent pion
production in the neutrino-nucleus interaction in the resonance region using
the formalism based on the partially conserved axial current (PCAC) theorem
which relates the neutrino-nucleus cross section to the pion-nucleus elastic
cross section. The pion nucleus elastic cross section is calculated using the
Glauber model approach. We calculate the integrated cross sections for
neutrino-carbon, neutrino-iron and neutrino-oxygen scattering. The results of
integrated cross-section calculations are compared with the measured data",1805.11836v1
2018-06-08,The Role of Opacities in Stellar Pulsation,"We examine the role of opacities in stellar pulsation with reference to
Cepheids and RR Lyraes, and examine the effect of augmented opacities on the
theoretical pulsation light curves in key temperature ranges. The temperature
ranges are provided by recent experimental and theoretical work that have
suggested that the iron opacities have been considerably underestimated. For
Cepheids, we find that the augmented opacities have noticeable effects in
certain period ranges (around $\log P \approx 1$) even though there is a
degeneracy with mixing length. We also find significant effects in theoretical
models of B-star pulsators.",1806.02996v1
2018-08-01,Long range dynamical coupling between magnetic adatoms mediated by a 2D topological insulator,"We study the spin excitation spectra and the dynamical exchange coupling
between iron adatoms on a Bi bilayer nanoribbon. We show that the topological
character of the edge states is preserved in the presence of the magnetic
adatoms. Nevertheless, they couple significantly to the edge spin currents, as
witnessed by the large and long-ranged dynamical coupling we obtain in our
calcula- tions. The large effective magnetocrystalline anisotropy of the
magnetic adatoms combined with the transport properties of the topologically
protected edge states make this system a strong candidate for implementation of
spintronics devices and quantum information and/or computation protocols.",1808.00347v1
2018-08-07,"Origin of superconductivity in Ni-doped SrFe_2As_2 , an Insight from DMFT","I describe the issues of the competing orders in normal state of a parent and
Ni-doped iron pnictide superconductor, SrF e 2 As 2 , using LMTO band structure
calculation plus multi orbital dynamical mean-field theory. Strong, electronic
correlations along with minimal antiferromagnetic instability create a
partially gapped Fermi surface, in qualitative agreement with earlier
experiments. A good semiquantitative similarity in both normal and ordered
state with the earlier experimental transport data is observed along with
suppression of magnetic ordering and explained within a correlated, mul-
tiorbital viewpoint. These results suggest that soft electronic fluctuation
mediate superconductivity in broad class of parent and underdoped 122 pnictides
with suppression of magnetic ordering.",1808.02298v1
2019-11-12,Classification of materials with phonon angular momentum and microscopic origin of angular momentum,"We group materials into five symmetry classes and determine in which of these
classes phonons carry angular momentum in the Brillouin zone, away from a
high-symmetry point, line, or plane. In some materials phonons acquire angular
momentum via the forces induced by relative displacements of atoms out of their
equilibrium positions. However, for other materials, such as ferromagnetic
iron, phonon angular momentum arises from the forces induced by relative
velocities of atoms. These effects are driven by the spin-orbit interaction.",1911.05064v3
2020-01-27,Influence of Iron Losses on Switching Dynamics of an Electromagnet from Experiment and Simulation,"The switching behaviour of electromagnets is determined by the inertia of the
armature, the stiffness of the return spring and the magnetostatic forces
between armature and yoke. For highly dynamic systems, hysteresis and eddy
current losses have a slowing effect. In this paper we consider the
experimentally observed behaviour of a switching magnet and compare it with
simulation results including hysteresis and eddy current losses.",2001.09638v1
2020-05-21,Cluster Dynamics Modeling of Niobium and Titanium Carbide Precipitates,"Kinetics of niobium and titanium carbide precipitates in iron has been
simulated with cluster dynamics. The simulations, carried out in austenite and
ferrite for niobium carbides, respectively in austenite for titanium carbide,
were analyzed for dependency on temperature, solute concentration, and initial
cluster distribution. The results are presented for different temperatures and
solute concentrations and compared to available experimental data. They show
little impact of initial cluster distribution beyond a certain relaxation time
and that highly dilute alloys with only monomers present a significantly
different behavior than less dilute alloys or alloys with different initial
cluster distribution.",2005.10574v2
2020-07-12,Reconstruction of 3D Image of Nanorice Particle from Randomly Oriented Single-Shot Experimental Diffraction Patterns Using Angular Correlation Method,"We reconstructed intensities in Fourier space and electron densities in the
real space for an azimuthally symmetric object Nanorice particle (Iron Oxide
nanoparticle) exposed in the ultrashort, bright and coherent x-ray free
electron laser (XFEL) pulses with random unknown orientations through the
method of angular correlations among intensities appeared in ninety eight 2D
diffraction patterns collected at Linac Coherent Light Source (LCLS).",2007.06030v1
2021-06-17,Effects of Covid-19 Pandemic on Chinese Commodity Futures Markets,"In this study, empirical moments and the cointegration for all the liquid
commodity futures traded in the Chinese futures markets are analyzed for the
periods before and after Covid-19, which is important for trading strategies
such as pairs trading. The results show that the positive change in the average
returns of the products such as soybean, corn, corn starch, and iron ore
futures are significantly stronger than other products in the post Covid-19
era, whereas the volatility increased most for silver, petroleum asphalt and
egg futures after the pandemic started. The number of cointegrated pairs are
reduced after the pandemic indicating the differentiation in returns due to the
structural changes caused in the demand and supply conditions across
commodities.",2106.09250v1
2021-06-28,Strap-on magnets: a framework for rapid prototyping of magnets and beam lines,"We describe a framework to assemble permanent-magnet cubes in 3D-printed
frames to construct dipole, quadrupole, and solenoid magnets, whose field, in
the absence of iron, can be calculated analytically in three spatial
dimensions. Rotating closely spaced dipoles and quadrupoles in opposite
directions allows us to adjust the integrated strength of a multipole.
Contributions of unwanted harmonics are calculated and found to be moderate. We
then combine multiple magnets to construct beam-line modules: chicane, triplet
cell, and solenoid focusing system.",2106.14676v1
2021-07-08,Warm Magnets,"Warm magnets are magnets that function in normal ambient temperature
conditions. These types are mostly using a soft steel yoke for field
amplification and either Copper or Aluminium coils or permanent magnets to
generate the field. Magnets powered with such normal-conducting coils are often
also called classical, iron dominated or resistive magnets. Since decades these
types of magnets are the workhorse for most linear and circular accelerators
and beam transfer lines.",2107.03965v1
2021-11-08,Thermogravimetric study of the non-stoichiometric wüstite FeOx. Pseudo phases w i and w' i . New T-P-X equilibrium phase diagram,"A statistical numerical analysis of thermogravimetric measurements
(temperature, mass variation, oxygen pressure) leads to a new equilibrium phase
diagram T-P-X of the iron monoxide or w\""ustite FeOx. Three varieties or pseudo
phases W1, W2, W3 are revealed above 911 {\textdegree}C, three others W'1, W'2,
W'3 below. This diagram displays their subfields, and shows 25 invariant points
between stable phases and 8 possible invariant points between metastable
phases. A thermodynamic approach is pointed out, which makes possible to
characterize the point defects and their clusters as components of the crystal
lattice.",2111.04346v1
2017-04-19,Remote Document Encryption - encrypting data for e-passport holders,"We show how any party can encrypt data for an e-passport holder such that
only with physical possession of the e-passport decryption is possible. The
same is possible for electronic identity cards and driver licenses. We also
indicate possible applications. Dutch passports allow for 160 bit security,
theoretically giving sufficient security beyond the year 2079, exceeding
current good practice of 128 bit security. We also introduce the notion of RDE
Extraction PIN which effectively provides the same security as a regular PIN.
Our results ironically suggest that carrying a passport when traveling abroad
might violate export or import laws on strong cryptography.",1704.05647v3
2017-05-02,Computation of the unifying thread in high temperature superconductors from first principles quantum Monte Carlo,"It has long been a challenge to describe the origin of unconventional
superconductivity. The two known examples with high Tc, based on iron and
copper, have very different electronic structures, while other materials with
similar electronic structure may not show superconductivity at all. In this
paper, the authors show that by using high accuracy diffusion Monte Carlo
calculations, the unconventional superconductors of both high Tc types form a
cluster at intermediate spin-charge coupling. The spin-charge coupling may
serve as a normal state marker for unconventional superconductivity, and
provides evidence that unconventional superconductivity is due to interaction
of charge with local spins in materials.",1705.01008v1
2017-06-09,Ultrasound attenuation in $s^\pm$-wave two-band superconductors,"The two-band $s^{\pm}$-wave state is currently considered to be the most
promising candidate for newly discovered iron-based high-$T_c$ superconductors.
In this work we study theoretically the ultrasound attenuation in
$s^{\pm}$-wave two-band superconductors. The impurity effect is calculated
within the $\mathcal{T}$-matrix approximation. In particular, our theory
predict that, when the sizes of two order parameter are comparable, a
Hebel-Slichter peak may show up in the ultrasound attenuation versus
temperature curves. Our calculations also confirmed the presence of the
resonant impurity scattering at low temperature, observed previously by other
authors in the calculation of the NMR relaxation rate $1/T_{1}$.",1706.02963v1
2018-02-23,Electronic entropy in Green's-function calculations at finite temperatures,"We revise critically existing approaches to evaluation of thermodynamic
potentials within the Green's function calculations at finite electronic
temperatures. We focus on the entropy and show that usual technical problems
related to the multivalued nature of the complex logarithm can be overcome.
This results in a simple expression for the electronic entropy, which does not
require any contour integration in the complex energy plane. Properties of the
developed formalism are discussed and its illustrating applications to selected
model systems and to bcc iron with disordered local magnetic moments are
presented as well.",1802.08495v1
2018-08-01,Long range dynamical coupling between magnetic adatoms mediated by a 2D topological insulator,"We study the spin excitation spectra and the dynamical exchange coupling
between iron adatoms on a Bi bilayer nanoribbon. We show that the topological
character of the edge states is preserved in the presence of the magnetic
adatoms. Nevertheless, they couple significantly to the edge spin currents, as
witnessed by the large and long-ranged dynamical coupling we obtain in our
calcula- tions. The large effective magnetocrystalline anisotropy of the
magnetic adatoms combined with the transport properties of the topologically
protected edge states make this system a strong candidate for implementation of
spintronics devices and quantum information and/or computation protocols.",1808.00347v1
2018-08-07,"Origin of superconductivity in Ni-doped SrFe_2As_2 , an Insight from DMFT","I describe the issues of the competing orders in normal state of a parent and
Ni-doped iron pnictide superconductor, SrF e 2 As 2 , using LMTO band structure
calculation plus multi orbital dynamical mean-field theory. Strong, electronic
correlations along with minimal antiferromagnetic instability create a
partially gapped Fermi surface, in qualitative agreement with earlier
experiments. A good semiquantitative similarity in both normal and ordered
state with the earlier experimental transport data is observed along with
suppression of magnetic ordering and explained within a correlated, mul-
tiorbital viewpoint. These results suggest that soft electronic fluctuation
mediate superconductivity in broad class of parent and underdoped 122 pnictides
with suppression of magnetic ordering.",1808.02298v1
2018-08-19,Size-dependent phase morphologies in LiFePO4 battery particles,"Lithium iron phosphate (LiFePO$_4$) is the prototypical two-phase battery
material, whose complex patterns of lithium ion intercalation provide a testing
ground for theories of electrochemical thermodynamics. Using a depth-averaged
(a-b plane) phase-field model of coherent phase separation driven by Faradaic
reactions, we reconcile conflicting experimental observations of diamond-like
phase patterns in micron-sized platelets and surface-controlled patterns in
nanoparticles. Elastic analysis predicts this morphological transition for
particles whose a-axis dimension exceeds the bulk elastic stripe period. We
also simulate a rich variety of non-equilibrium patterns, influenced by
size-dependent spinodal points and electro-autocatalytic control of
thermodynamic stability.",1808.06164v1
2018-08-20,Production of Metal-free Diamond Nanoparticles,"In this paper, the controlled production of high quality metal-free diamond
nanoparticles is demonstrated. Milling with tempered steel is shown to leave
behind iron oxide contamination which is difficult to remove. Milling with SiN
alleviates this issue but generates more non diamond carbon. Thus the choice of
milling materials is critically determined by the acceptable contaminants in
the ultimate application. The removal of metal impurities, present in all
commercially available nanoparticles, will open new possibilities towards the
production of customised diamond nanoparticles, covering the most demanding
quantum applications.",1808.06425v1
2018-10-14,Plasma opacity calculations using the Starrett and Saumon average-atom model with ion correlations,"We present the opacities of iron, aluminum, and bromine plasmas calculated
using the Starrett and Saumon average-atom model allowing for ion correlations.
We show that the use of earlier average-atom ion-correlation model of Rozsnyai,
as has recently been done in the solar opacity calculations, overestimates the
effect of ion correlations on plasma opacities. The reason for this
overestimation is discussed.",1810.06027v1
2019-01-03,A magnetic tight-binding model : surface properties of transition metals and cobalt nanoparticules,"The magnetic and surface properties of some transition metals have been
investigated through the tight-binding approximation including Coulomb
correlations. These surface properties are derived from a charge neutrality
rule restricted to the d-band leading to a charge distribution including sp
surface states in agreement with a Linear Muffin-Tin Orbital (LMTO)
calculation. This new approach describes the local magnetism, surface energies
and work functions without recourse to the total energy. Our investigation
focuses on fcc cobalt, bcc iron, fcc nickel and fcc platinum surfaces with an
exploration of fcc cobalt nanoparticles.",1901.00841v4
2019-01-28,X-ray diffraction analysis to support phase identification in FeSe and Fe$_7$Se$_8$ epitaxial thin films,"X-ray diffraction (XRD) data and analysis for epitaxial iron selenide thin
films grown by pulsed laser deposition (PLD) are presented. The films contain
${\beta}$-FeSe and Fe$_7$Se$_8$ phases in a double epitaxy configuration with
the ${\beta}$-FeSe phase (001) oriented on the (001) MgO growth substrate.
Fe$_7$Se$_8$ simultaneously takes on two different epitaxial orientations in
certain growth conditions, exhibiting both (101)- and (001)- orientations. Each
of these orientations are verified with the presented XRD data. Additionally,
XRD data used to determine the PLD target composition as well as mosaic
structure of the ${\beta}$-FeSe phase are shown.",1901.09794v1
2019-07-17,Role of interactions in the energy of the spin resonance peak in Fe-based superconductors,"We consider the spin response within the five-orbital model for iron-based
superconductors and study two cases: equal and unequal gaps in different bands.
In the first case, the spin resonance peak in the superconducting state appears
below the characteristic energy scale determined by the gap magnitude,
$2\Delta_L$. In the second case, the energy scale corresponds to the sum of
smaller and larger gap magnitudes, $\Delta_L + \Delta_S$. Increasing the values
of the Hubbard interaction and the Hund's exchange, we observe a shift of the
spin resonance energy to lower frequencies.",1907.08133v1
2019-10-07,Thermodynamic dislocation theory for polycrystals under tension/compression,"Starting from the assumption that all possible orientations of grains are
equally probable, we prove that the geometric factor of thermodynamic
dislocation theory for polycrystals subjected to axially symmetric tension or
compression must be equal to 2. We then use large-scale least-square analysis
to identify the physics based parameters of this theory and show that the
simulated stress-strain curves for OFHC copper, ARMCO iron and 4340 steel agree
well with the experiments of Johnson and Cook.",1910.02642v2
2019-10-25,Portable system for the prediction of anemia based on the ocular conjunctiva using Artificial Intelligence,"Anemia is a major health burden worldwide. Examining the hemoglobin level of
blood is an important way to achieve the diagnosis of anemia, but it requires
blood drawing and a blood test. In this work we propose a non-invasive, fast,
and cost-effective screening test for iron-deficiency anemia in Peruvian young
children. Our initial results show promising evidence for detecting
conjunctival pallor anemia and Artificial Intelligence techniques with photos
taken with a popular smartphone.",1910.12399v1
2020-03-04,Classical Nova Carinae 2018: Discovery of circumbinary iron and oxygen,"We present time-lapse spectroscopy of a classical nova explosion commencing 9
days after discovery. These data reveal the appearance of a transient feature
in Fe II and [O I]. We explore different models for this feature and conclude
that it is best explained by a circumbinary disc shock-heated following the
classical nova event. Circumbinary discs may play an important role in novae in
accounting for the absorption systems known as THEA, the transfer of angular
momentum, and the possible triggering of the nova event itself.",2003.02008v1
2020-08-21,Multipole Orders in a Chain Ferrate Na2FeSe,"Fundamental block and staggered orders of magnetic Fe multipoles in Na2FeSe2
are classified by their symmetry and magnetoelectric properties. Our structure
model incorporates ferromagnetic or antiferromagnetic coupling between chains.
The ferrate salt is valued in studies of highly correlated electrons as the
only iron selenide known to possess chain-like structural units hosting ferrous
cations. Axial and polar (Dirac) multipoles are compulsory in the electronic
structure since Fe ions exhibit enantiomorphic symmetry in the parent
K2ZnO2-type compound. Calculated Bragg diffraction patterns for neutrons and
x-rays reveal specific contributions from both multipole types.",2008.09374v1
2020-09-07,Anomalous In-plane Magnetic Anisotropy in Strain-mediated Converse Magnetoelectric Coupling,"Magnetic axis rotation (MAR) in ferromagnetic (FM) layers is crucial for
strain-mediated converse magnetoelectric coupling. Employing the density
functional theory (DFT), we computationally study the magnetic anisotropy of
selected deformed FM materials such as body-centered iron. The results show
that the short axis is more energy-favorable at high in-plane strain difference
than previously predicted phenomenologically. This anomalous trend and the
complex energy behaviors at different strain conditions explain why
spin-lattice dynamics (SLD) simulation does not produce in-plane MAR and imply
couplings between different energy terms together with high order coefficient
contributions.",2009.03045v2
2020-10-27,Thermodynamic approach to electric quadrupole moments,"Higher-rank electric/magnetic multipole moments are attracting attention
these days as candidate order parameters for exotic material phases. However,
quantum-mechanical formulation of those multipole moments is still an ongoing
issue. In this paper, we propose a thermodynamic definition of electric
quadrupole moments as a measure of symmetry breaking, following previous
studies of orbital magnetic dipole moments and magnetic quadrupole moments. The
obtained formulas are illustrated with a model of orbital-ordered nematic
phases of iron-based superconductors.",2010.13999v1
2020-11-18,Spin superfluidity in noncollinear antiferromagnets,"We explore the spin superfluid transport in exchange interaction dominated
three-sublattice antiferromagnets. The system in the long-wavelength regime is
described by an $SO(3)$ invariant field theory. Additional corrections from
Dzyaloshinskii-Moriya interactions or anisotropies can break the symmetry;
however, the system still approximately holds a $U(1)$-rotation symmetry. Thus,
the power-law spatial decay signature of spin superfluidity is identified in a
nonlocal-measurement setup where the spin injection is described by the
generalized spin-mixing conductance. We suggest iron jarosites as promising
material candidates for realizing our proposal.",2011.09102v2
2020-12-22,Unusual Scaling of Kondo Spin Relaxation,"The relation between the Kondo spin relaxation rate $ {\tau_{sK}}^{-1} $ and
the Kondo momentum relaxation rate $ {\tau_{eK}}^{-1} $ is explored by using
nonlocal spin valves with submicron copper channels that contain dilute iron
impurities. A linear relation between $ {\tau_{sK}}^{-1} $ and $
{\tau_{eK}}^{-1} $ is established under varying temperatures. However, under
varying impurity concentrations, ${\tau_{sK}}^{-1}$ remains nearly constant
despite variation of $ {\tau_{eK}}^{-1} $ by a factor of 10. This surprising
relation can be understood by considering spin relaxation through overlapping
Kondo screening clouds and supports the physical existence of the elusive Kondo
clouds.",2012.11781v1
2020-12-23,Magnetic Moment Tensor Potentials for collinear spin-polarized materials reproduce different magnetic states of bcc Fe,"We present the magnetic Moment Tensor Potentials (mMTPs), a class of
machine-learning interatomic potentials, accurately reproducing both
vibrational and magnetic degrees of freedom as provided, e.g., from
first-principles calculations. The accuracy is achieved by a two-step
minimization scheme that coarse-grains the atomic and the spin space. The
performance of the mMTPs is demonstrated for the prototype magnetic system bcc
iron, with applications to phonon calculations for different magnetic states,
and molecular dynamics simulations with fluctuating magnetic moments.",2012.12763v2
2021-03-08,All-order relativistic computations for atoms and molecules using an explicitly correlated Gaussian basis,"A variational solution procedure is reported for the many-particle no-pair
Dirac-Coulomb-Breit Hamiltonian aiming at a parts-per-billion (ppb) convergence
of the atomic and molecular energies, described within the fixed nuclei
approximation. The procedure is tested for nuclear charge numbers from $Z=1$
(hydrogen) to $28$ (iron). Already for the lowest $Z$ values, a significant
difference is observed from leading-order Foldy-Woythusen perturbation theory,
but the observed deviations are smaller than the estimated self-energy and
vacuum polarization corrections.",2103.04923v1
2021-03-14,Nuclear effects in neutrino-nucleus DIS and probe for short range correlation,"We investigate charged-current neutrino-nucleus deep inelastic scattering
with particular interests in relationship of short range correlation (SRC) and
EMC effect. The structure functions $F^A_2(x,Q^2)$, $x F^A_3(x,Q^2)$ and ratios
of differential cross sections are presented where the nuclei $A$ are chosen to
be carbon, iron and lead. We propose a kind of universal modification functions
which would provide a nontrivial test of SRC universality on the platform of
neutrino-nucleus scattering and improve our understanding of nucleon structure
substantially.",2103.07873v1
2021-04-05,Two-magnon Raman scattering in antiferromagnetic phases of frustrated spin models on the honeycomb lattice,"We calculate the two-magnon Raman scattering spectra in antiferromagnetic
phases of several frustrated spin models defined on the honeycomb lattice.
These include the N\'{e}el antiferromagnetic phase of a $J_1$-$J_2$-$J_3$ model
and the stripe phase of the Heisenberg-Kitaev model. We show that both the
magnetic frustration and the anisotropy of interactions may significantly
affect the Raman spectra. We further discuss the implications of our results to
the magnetic excitations of the iron-based compound BaFe$_2$Se$_2$O and show
how the magnetic interactions can be extracted from fit to the Raman spectrum.",2104.01903v1
2021-04-08,Ferromagnetism in a Semiconductor with Mobile Carriers via Low-Level Nonmagnetic Doping,"We show that doped cubic iron pyrite, which is a diamagnetic semiconductor,
becomes ferromagnetic when $p$-type doped. We furthermore find that this
material can exhibit high spin polarization both for tunneling and transport
devices. These results are based on first principles electronic structure and
transport calculations. This illustrates the use of $p$-type doping without
magnetic impurities as a strategy for obtaining ferromagnetic semiconducting
behavior, with implications for spintronic applications that require both
magnetic ordering and good mobility. This is a combination that has been
difficult to achieve by doping semiconductors with magnetic impurities. We show
that phosphorus and arsenic may be effective dopants for achieving this
behavior.",2104.03877v1
2021-09-30,Pairing enhanced by local orbital fluctuations in a model for monolayer FeSe,"The pairing mechanism in different classes of correlated materials, including
iron based superconductors, is still under debate. For FeSe monolayers, uniform
nematic fluctuations have been shown in a lattice Monte Carlo study to play a
potentially important role. Here, using dynamical mean field theory
calculations for the same model system, we obtain a similar phase diagram and
provide an alternative interpretation of the superconductivity in terms of
local orbital fluctuations and phase rigidity. Our study clarifies the relation
between the superconducting order parameter, superfluid stiffness and orbital
fluctuations, and provides a link between the spin/orbital freezing theory of
unconventional superconductivity and theoretical works considering the role of
nematic fluctuations.",2109.15312v1
2021-12-16,Investigating the Longitudinal Development of EAS with Ultra High Energies,"The simulation of the extensive air showers was performed by investigating
the longitudinal development parameters (N and Xmax) by using AIRES system
version 19.04.0. The simulation was performed at the energy range (10^18-10^20
eV) for different primary particles (such as primary proton and iron nuclei)
and different zenith angles. The longitudinal development curves of EAS are
fitted using Gaussian function that gave a new parameters for different primary
particles and different zenith angles at the energy range (10^18-10^20 eV).",2201.00401v1
2022-01-13,The FACET Project: Forward Aperture CMS ExTension to search for new Long-Lived Particles,"FACET is a proposed new subsysem for CMS to search for portals such as dark
photons, dark higgs, heavy neutral leptons and axion-like particles in the very
forward direction at the High Luminosity LHC. Such particles can penetrate up
to 50 m of iron and then decay inside a 14 m$^3$ vacuum pipe made by enlarging
an 18 m long section of the LHC pipe to a radius of 50 cm.",2201.05224v1
2022-01-28,Theory of spin-excitation anisotropy in the nematic phase of FeSe obtained from RIXS measurements,"Recent resonant inelastic x-ray scattering (RIXS) experiments have detected a
significant high-energy spin-excitation anisotropy in the nematic phase of the
enigmatic iron-based superconductor FeSe, whose origin remains controversial.
We apply an itinerant model previously used to describe the spin-excitation
anisotropy as measured by neutron scattering measurements, with magnetic
fluctuations included within the RPA approximation. The calculated RIXS cross
section exhibits overall agreement with the RIXS data, including the high
energy spin-excitation anisotropy.",2201.12008v2
2022-04-28,Spin-glass-like behaviour in SmFeAsO0.8F0.2,"The iron-based oxypnictide superconductor SmFeAsO0.8F0.2 was synthesized
under high-pressure and investigated by measuring dc magnetic susceptibility.
The zero-field cooled (ZFC) magnetic susceptibility confirmed the bulk
superconductivity of the sample with a critical temperature of Tc = 50 K and a
significant jump in the magnetization at 4.3 K, usually attributed to the
antiferromagnetic ordering of Sm3+ ions in this system. Since the occurrence of
the jump depends on the cooling history, our data strongly suggest a
spin-glass-like behaviour.",2204.13473v2
2022-05-16,Feedback of non-local $d_{xy}$ nematicity on the magnetic anisotropy in FeSe,"We analyze theoretically the magnetic anisotropy in the nematic phase of FeSe
by computing the spin and the orbital susceptibilities from the microscopic
multiorbital model. In particular, we take into account both the $xz/yz$ and
the recently proposed non-local $xy$ nematic ordering and show that the latter
one could play a crucial role in reproducing the experimentally-measured
temperature dependence of the magnetic anisotropy. This provides a direct
fingerprint of the different nematic scenarios on the magnetic properties of
FeSe.",2205.07718v1
2022-08-05,Exploring the bouncing cosmological models in symmetric teleparallel gravity,"In this study, cosmological models with perfect fluid and a gravitational
framework f(Q) will be examined. In this modified theory of gravity, the
gravitational force has the form f(Q), where Q stands for the non-metricity
scalar. I create two bouncing cosmological models, one in which the Lagrangian
f(Q) is assumed to have a linear dependence on Q and the other in which it has
a polynomial functional form. It has been discovered that the parameters of the
individual models largely determine how they will behave. The resulting models'
equation of state (EoS) parameter captures the universe's ironic behavior. It
should be highlighted that the built-in cosmological models go against the
energy requirements. The models' kinematical and physical characteristics are
discussed.",2208.03171v1
2022-10-01,"India Based Neutrino Observatory, Physics Reach and Status Report","The India-based Neutrino Observatory (INO) is a proposed underground facility
located in India that will primarily house the magnetised Iron CALorimeter
(ICAL) detector to study atmospheric neutrinos produced by interactions of
cosmic rays with Earth's atmosphere. The physics goal is to to make precision
measurements of the neutrino mixing and oscillation parameters through such a
study. We present here the results from detailed simulations studies, as well
as a status report on the project. In particular, we highlight the sensitivity
of ICAL to the open issue of the neutrino mass ordering, which can be
determined {\it independent of the CP phase} at ICAL.",2210.00206v2
2022-10-31,Superconducting Magnet System Concept with a Mechanical Energy Transfer in the Magnetic Field,"There is an interest to design superconducting magnet systems working in a
persistent current mode. These systems continuously generate magnetic field
with disconnected power source working like permanent magnet devices. In this
paper proposed a magnet system concept based on the direct mechanical energy
transfer in the magnetic field. Short circuited superconducting coils do not
have current leads and power source. To pump the mechanical energy in the
superconducting coil used a magnetizer which magnetically coupled with the
coil. The mechanical removing the magnetizer from the magnet induces a
persistent current in the superconducting coil which generates the magnetic
field. Iron dominated magnet system concept was investigated using OPERA3d code
which confirmed a visibility of proposed approach.",2211.00102v1
2022-10-31,HTS Dipole Magnet with a Mechanical Energy Transfer in the Magnetic Field,"There were designed and successfully tested at Fermilab several high
temperature superconducting (HTS) model magnets for particle accelerators. Some
of them worked in a persistent current mode continuously generating magnetic
field in the iron dominated magnet gap. In the paper was investigated a novel
HT dipole magnet concept with a mechanical energy transfer in the magnetic
field. To pump the energy in the superconducting HTS dipole magnet used a
detachable magnetizer. The HTS dipole magnet was build and successfully tested
at a liquid nitrogen temperature. Discussed the magnet design, test results,
the proposed approach limits, and efficiency.",2211.00105v1
2022-11-02,A brief perspective of high temperature superconductivity in the cuprates: Strong correlations combined with superexchange match experiment,"High temperature superconductivity encompasses the cuprates, nickelates, iron
pnictides, and LaH$_x$ compounds. The first three groups of compounds involve
in the pairing electrons, which are strongly to moderately correlated, whereas
in the last class of systems specific phonon excitations. In this overview we
concentrate first on the (semi)quantitative theory of high T$_{C}$
superconductivity in the cuprates based on our original vibrational approach
beyond the renormalized mean field theory. The model we explore mainly is
$t$-$J$-$U$ model containing both the superexchange (kinetic energy) combined
with strong interelectronic correlations. Selected equilibrium and
dynamic-excitation properties are analyzed briefly. General questions regarding
the pseudogap and two--dimensional character of those systems are raised.",2211.01024v1
2022-12-01,Numerical simulation of non-central collisions of spherical magnets,"We present a computational model of non-central collisions of two spherical
neodymium-iron-boron magnets, suggested as a demonstration of angular momentum
conservation. Our program uses an attractive dipole-dipole force and a
repulsive contact force to solve the Newtonian equations of motion for the
magnets. We confirm the conservation of angular momentum and study the changes
in energy throughout the interaction. Using the exact expression for the
dipole-dipole force, including non-central terms, we correctly model the final
rotational frequencies, which is not possible with a simple power-law
approximation.",2212.00876v1
2022-12-19,Equivalence of Active and Passive Gravitational Mass Tested with Lunar Laser Ranging,"LLR measures the distance between observatories on Earth and retro-reflectors
on Moon since 1969. In this paper, we study the possible violation of the
equality of passive and active gravitational mass ($m_{a}/m_{p}$), for
Aluminium (Al) and Iron (Fe), using LLR data. Our new limit of
$3.9\cdot10^{-14}$ is about 100 times better than that of Bartlett and Van
Buren [1986] reflecting the benefit of the many years of LLR data.",2212.09407v1
2022-12-27,Tuning quantum paramagnetism and d-wave superconductivity in single-layer iron chalcogenides by chemical pressure,"By substituting S into single-layer FeSe/SrTiO3, chemical pressure is applied
to tune its paramagnetic state that is modeled as an incoherent superposition
of spin-spiral states. The resulting electronic bands resemble an ordered
checkerboard antiferromagnetic structure, consistent with angle-resolved
photoemission spectroscopy measurements. Scanning tunneling spectroscopy
reveals a gap evolving from U-shaped for FeSe to V-shaped for FeS with
decreasing size, attributed to a d-wave superconducting state for which nodes
emerge once the gap size is smaller than the effective spin-orbit coupling.",2212.13603v2
2023-02-03,An Equilibrated Error Estimator for the 2D/1D MSFEM T-Formulation of the Eddy Current Problem,"The 2D/1D multiscale finite element method (MSFEM) is an efficient way to
simulate rotating machines in which each iron sheet is exposed to the same
field. It allows the reduction of the three dimensional sheet to a two
dimensional cross-section by resolving the dependence along the thickness of
the sheet with a polynomial expansion. This work presents an equilibrated error
estimator based on flux equilibration and the theorem of Prager and Synge for
the T-formulation of the eddy current problem in a 2D/1D MSFEM setting. The
estimator is shown to give both a good approximation of the total error and to
allow for adaptive mesh refinement by correctly estimating the local error
distribution.",2302.01601v1
2023-03-09,Full-waveform tomography reveals iron spin crossover in Earth lower mantle,"Joint interpretation of bulk and shear wave speeds constrains the chemistry
of the deep mantle. At all depths, the diversity of wave speeds cannot be
explained by an isochemical mantle. Between 1000 and 2500 km depth,
hypothetical mantle models containing an electronic spin crossover in (Mg,Fe)O
provide a significantly better fit to the wave-speed distributions, as well as
more realistic temperatures and silica contents, than models without a spin
crossover. Below 2500 km, wave speed distributions are explained by enrichment
in silica towards the core-mantle-boundary. This silica enrichment may
represent the fractionated remains of an ancient basal magma ocean.",2303.05476v1
2023-05-07,Surface supercurrent diode effect,"We propose a new type of supercurrent diode effect on the surface of a
superconductor with surface states under in-plane magnetic fields. Surface
supercurrent diode effect can lead to a perfect supercurrent diode in a
considerably wide range of fields. For comparison, the conventional
supercurrent diode effect due to the spin-orbit coupling in a two-dimensional
superconductor cannot be perfect in usual cases. Candidates such as the (001)
surface of iron-based superconductors BaFe$_{2-x}$Co$_x$As$_2$ are discussed.
Calculations are performed under the Ginzburg-Landau formalism.",2305.04219v2
2023-05-12,DFT+U Type Strong Correlation Functional Derived from Multiconfigurational Wavefunction Theory,"We present a DFT+U-type functional for strong correlation, derived from
multiconfigurational wavefunction theory. The reference system experiences
electron-electron interactions only in DFT+U-type atomic states, yielding a
block-localized configuration interaction Hamiltonian which depends on the
atomic state occupancies and the promotion energies of doubly excited
determinants. Simple approximations for the promotion energies recover the
flat-plane condition and provide beyond-zero-sum accuracy for iron
spin-crossover complexes.",2305.07736v2
2023-05-15,Easily Computed Marginal Likelihoods from Posterior Simulation Using the THAMES Estimator,"We propose an easily computed estimator of marginal likelihoods from
posterior simulation output, via reciprocal importance sampling, combining
earlier proposals of DiCiccio et al (1997) and Robert and Wraith (2009). This
involves only the unnormalized posterior densities from the sampled parameter
values, and does not involve additional simulations beyond the main posterior
simulation, or additional complicated calculations. It is unbiased for the
reciprocal of the marginal likelihood, consistent, has finite variance, and is
asymptotically normal. It involves one user-specified control parameter, and we
derive an optimal way of specifying this. We illustrate it with several
numerical examples.",2305.08952v1
2023-08-01,Overview of superconductivity in field-cooled magnetic materials,"Considerable experimental skills have been accumulated in the preparation of
field-cooled (FC) magnetic materials. This stimulates the search for FC
magnetic materials that are superconductors.
  The article overviews the recent proposed mechanism of superconductivity in
field-cooled magnetic materials.
  It is based on previously published results for magnon-induced
superconductivity in field-cooled spin-1/2 antiferromagnets $[PRB96,214409]$
(arXiv:1712.02983), Sequence of superconducting states in field cooled
$FeCr_2S_4$ $[JPCM33,495604]$
  (arXiv:2111.02765) and Partial order induced superconductivity in $Fe^{2+}$
iron. $[EPL126,47001]$ (arXiv:1902.02290).",2308.00470v1
2023-10-31,Generating site saturation mutagenesis libraries and transferring them to broad host range plasmids using type IIS restriction enzymes,"Protein engineering is an established method for tailoring enzymatic
reactivity. A commonly used method is directed evolution, where the mutagenesis
and natural selection process is mimicked and accelerated in the laboratory.
Here, we describe a reliable method for generating saturation mutagenesis
libraries by golden gate cloning in a broad host range plasmid containing the
pBBR1 replicon. The applicability is demonstrated by generating a mutant
library of the iron nitrogenase gene cluster (anfHDGK) of Rhodobacter
capsulatus, which is subsequently screened for the improved formation of
molecular hydrogen.",2311.00138v1
2023-11-21,"Comment on ""Ironing, sweeping, and multidimensional screening''","In their study of price discrimination for a monopolist selling heterogeneous
products to consumers having private information about their own
multidimensional types, Rochet and Chon\'e (1998) discovered a new form of
screening in which consumers with intermediate types are bunched together into
isochoice groups of various dimensions incentivized to purchase the same
product. They analyzed a particular example involving customer types
distributed uniformly over the unit square. For this example, we prove that
their proposed solution is not selfconsistent, and we indicate how consistency
can be restored.",2311.13012v2
2024-01-04,Multiband Quantum Materials,"Quantum materials are defined by the emergence of new properties resulting
from collective quantum effects and by holding promise for their quantum
applications. Novel superconductors, from high-Tc cuprates and iron-based
superconductors to twisted monolayers, exhibit a higher level of emergent
complexity, with a multiband electronic structure playing a pivotal role in
their comprehension and potential applications. Here, we provide a brief
overview of key multiband effects in these superconductors and topological
semimetals, offering guidelines for the theory-assisted development of new
quantum materials and devices.",2401.02237v1
2024-01-07,Mid-infrared evidence for iron-rich dust in the multi-ringed inner disk of HD 144432,"Context. Rocky planets form by the concentration of solid particles in the
inner few au regions of planet-forming disks. Their chemical composition
reflects the materials in the disk available in the solid phase at the time the
planets were forming. Aims. We aim to constrain the structure and dust
composition of the inner disk of the young star HD 144432, using an extensive
set of infrared interferometric data taken by the Very Large Telescope
Interferometer (VLTI), combining PIONIER, GRAVITY, and MATISSE observations.
Methods. We introduced a new physical disk model, TGMdust, to image the
interferometric data, and to fit the disk structure and dust composition. We
also performed equilibrium condensation calculations with GGchem. Results. Our
best-fit model has three disk zones with ring-like structures at 0.15, 1.3, and
4.1 au. Assuming that the dark regions in the disk at ~0.9 au and at ~3 au are
gaps opened by planets, we estimate the masses of the putative gap-opening
planets to be around a Jupiter mass. We find evidence for an optically thin
emission ($\tau<0.4$) from the inner two disk zones ($r<4$ au) at $\lambda>3\
\mu$m. Our silicate compositional fits confirm radial mineralogy gradients. To
identify the dust component responsible for the infrared continuum emission, we
explore two cases for the dust composition, one with a silicate+iron mixture
and the other with a silicate+carbon one. We find that the iron-rich model
provides a better fit to the spectral energy distribution. Conclusions. We
propose that in the warm inner regions ($r<5$ au) of typical planet-forming
disks, most if not all carbon is in the gas phase, while iron and iron sulfide
grains are major constituents of the solid mixture along with forsterite and
enstatite. Our analysis demonstrates the need for detailed studies of the dust
in inner disks with new mid-infrared instruments such as MATISSE and JWST/MIRI.",2401.03437v1
2024-01-16,The effect of iron layer thickness on the interlayer exchange coupling in Fe/MgO (001) superlattices,"We describe the effect of the Fe layer thickness on the antiferromagnetic
interlayer exchange coupling in [Fe/MgO]$_N$ superlattices. An increase in
coupling strength with increasing Fe layer thickness is observed, which
highlights the need of including the extension of both the layers when
discussing the interlayer exchange coupling in superlattices.",2401.08336v1
2023-11-10,Automatic extraction and 3D reconstruction of split wire from point cloud data based on improved DPC algorithm,"In order to solve the problem of point cloud data splitting improved by DPC
algorithm, a research on automatic separation and 3D reconstruction of point
cloud data split lines is proposed. First, the relative coordinates of each
point in the cloud point are calculated. Second, it is planned to develop a
relative ensemble-based DPC swarm algorithm for analyzing the number of
separation lines to determine all parts in the cloud content. Finally, fit each
separator using the least squares method. iron. The cloud point of the
resulting split subconductors has a clear demarcation line, and the distance
between adjacent split subconductors is 0.45 m, divided by the four vertices of
the square.",2401.08587v1
2024-02-20,Electron-phonon coupling in ferromagnetic Fe-Co alloys from first principles,"We calculate from first principles the electron-phonon coupling strength in
ferromagnetic iron-cobalt Fe$_{1-x}$Co$_x$ alloys for compositions ranging from
$x=0$ to $x=0.75$. We find strong, spin-dependent variation of the
electron-phonon coupling strength with alloy composition. The minimum of the
electron-phonon interaction is found near the composition $x=0.25$. We analyze
the variation of the electron-phonon interaction with composition, as a
function of electron spin, density of states, electron-phonon matrix elements,
and phonon frequencies. Our results are in good qualitative agreement with
magnetization dynamics experiments.",2402.12650v1
2024-02-20,Enhancement of the critical current by surface irregularities in Fe-based superconductors,"The critical current $I_c$ of single crystals of the iron pnictide
superconductor BaFe$_2$(As$_{1-x}$P$_x$)$_2$, has been studied through
measurements of magnetic hysteresis cycles. We show that the introduction of
surface irregularities in the $\mu$m scale significantly increase $I_c$,
primarily near the irreversibility magnetic field $H_{irr}$, where the surface
currents are the main contribution to $I_c$. Such an increase is consistent
with a theoretical estimate for the maximum non-dissipative current that a
rough surface can sustain, based on Mathieu-Simon continuum theory for the
vortex state.",2402.12933v1
2024-03-28,X-ray reflectometric studies of nanoparticulate hematite films to decouple the rough and smooth behaviors of it and crystallographic and morphological properties concerning fatty acid chain length,"In this study, the use of X-Ray reflectometry technique signifies the types
of rough and smooth surfaces of hematite film prepared from different fatty
acid derivatives of the iron salt. Followed by this, the film morphology and
crystallographic properties concerning different fatty acid chain length have
been discussed.",2403.19065v1
1995-06-14,ASCA PV observations of the Seyfert 1 galaxy MCG-6-30-15 : rapid variability of the warm absorber,"We present a detailed re-analysis of the two {\it ASCA} Performance
Verification observations of the nearby Seyfert 1 galaxy MCG-6-30-15.
Confirming the results of Fabian et al. (1994), we find definite evidence for
the {\sc O\,vii} and {\sc O\,viii} K-shell absorption edges of the warm
absorber and a doubling of the warm absorber column density within the 3 weeks
separating the two observations. No intra-day {\it flux-correlated} variability
of the warm absorber is found. However, we report the discovery of an `event'
in which the warm absorber parameters temporarily change for
\sim10\,000\thinspace s before returning to their original values. Possible
interpretations are discussed but a contradiction remains: the constancy of the
ionization state of the warm absorber argues that it lies at large distances
from the central source whereas the short term change in column density argues
for small distances. Fluorescent iron emission is examined. As found by Fabian
et al. (1994), the iron line is broad and strong (equivalent width
\sim300\thinspace eV). The line profile is also suggestive of it being skewed.
Such a line would be expected from a relativistic accretion disk. We also find
very rapid primary X-ray variability. Assuming relativistic beaming to be
unimportant, the derived efficiency is comparable to the maximum obtainable
from accretion onto a Schwarzschild black hole. Correlated variability outside
of the energy range of {\it ASCA} might exceed this maximum, thus requiring
efficient accretion onto a Kerr hole.",9506086v1
1996-03-18,The X-Ray Spectral Variability of Mrk 766,"Analysis results from ASCA and ROSAT observations of the narrow-line Seyfert
1 galaxy Mrk 766 are reported. In the ASCA observation we observed rapid
variability with a doubling time scale of 1000 seconds. A spectral variability
event was observed in which the spectrum softened and hardened above and below
~1 keV, respectively, as the flux increased. The spectra could be modeled with
5 components: a power law, warm absorber, iron K(alpha) line and soft excess
component flux. The spectral variability resulted from a highly significant
change in the intrinsic photon law index from Gamma ~1.6 to ~2.0, an increase
in the warm absorber ionization, and a marginally significant decrease in the
soft component normalization. A ~100 eV equivalent width narrow iron K(alpha)
line was detected in the high state spectrum. Spectral hardening during flux
increases was observed in three ROSAT observations.
  The change in intrinsic photon index and disappearance of the soft excess
component in the ASCA spectra can be explained as a transition from a first
order pair reprocessed spectrum to a pair cascade brought about by a sudden
increase in the injected electron Lorentz factor. The change in the ionization
of the warm absorber, though model dependent, could correspond to the increase
in flux at the oxygen edges resulting from the spectral index change. The ROSAT
spectral variability can be interpreted by variable intensity hard power law
and a relatively nonvarying soft component, possibly primary disk emission.
These results are compared with those reported from other narrow-line Seyfert 1
galaxies.",9603091v1
1996-04-23,The Luminosity-Metallicity Relation for Bulges of Spiral Galaxies,"Optical integrated spectra of bulges have been obtained for 28 spiral
galaxies. By applying an appropriate aperture size for each galaxy, the
unavoidable contamination of disk starlight has been carefully minimized and
set to $\sim$ 1/7 of the total stellar light. The sample covers a wide range in
bulge luminosity and morphology. The Mg$_2$ index shows a tight correlation
with the bulge intrinsic luminosity, similar - and extended at fainter
magnitudes - to the relationship known for ellipticals. Other features such as
CaIIK, CN, G-band, and TiO show similar trend with the bulge luminosity. On the
contrary, the Fe5270 and Fe5335 iron lines show a constant equivalent width -
within some dispersion - for all bulges. A simple application of a stellar
population synthesis model suggests that magnesium should be most enhanced with
respect to iron in the brightest bulges. Concerning the structural parameters,
bulges do occupy the same region in the fundamental plane as ellipticals. In
conclusion, the present study favors the idea that the bulk of stars in bulges
have formed with only moderate or negligible influence of the disk material,
likely by very similar processes as those driving the formation of elliptical
galaxies.",9604132v1
1996-06-17,The variable iron K emission line in MCG-6-30-15,"We report on the variability of the iron K emission line in the Seyfert 1
galaxy MCG--6-30-15 during a four-day ASCA observation. The line consists of a
narrow core at an energy of about 6.4 keV, and a broad red wing extending to
below 5 keV, which are interpreted as line emission arising from the inner
parts of an accretion disk. The narrow core correlates well with the continuum
flux whereas the broad wing weakly anti-correlates. When the source is
brightest, the line is dominated by the narrow core, whilst during a deep
minimum, the narrow core is very weak and a huge red tail appears. However, at
other times when the continuum shows rather rapid changes, the broad wing is
more variable than the narrow core, and shows evidence for correlated changes
contrary to its long time scale behaviour. The peculiar line profile during the
deep minimum spectrum suggests that the line emitting region is very close to a
central spinning (Kerr) black hole where enormous gravitational effects
operate.",9606103v1
1996-08-03,New beryllium observations in low-metallicity stars,"We present observations of the Be II 313.0 nm resonance doublet in 14 halo
and old disk stars with metallicities ranging from [Fe/H]=-0.4 to about -3.0
obtained with the CASPEC spectrograph of the ESO 3.6m telescope at a FWHM about
8.6 km/s resolution. Abundances are derived by means of the synthetic spectra
technique employing Kurucz (1993) atmospheric models, with enhanced
alpha-elements and no overshooting. The derived abundances together with those
available in literature show that for -2.7 < [Fe/H] < -0.8 Be correlates
linearly with iron [Be] proportional to 1.07(+/- 0.08)[Fe/H], giving strength
to previous results. However, a steeper correlation is still possible at
metallicities lower than [Fe/H]<-1.4 with [Be] proportional to 1.6(+/-
0.44)[Fe/H]. When iron is replaced with oxygen, Be is found tracking closely
oxygen up to solar values, without signs of breaking in correspondence of the
onset of the Galactic disk. No evidence of intrinsic dispersion is found, ought
to the large errors involved in the Be abundance determinations, but for three
stars (HD 106516, HD 3795, HD 211998) a significant upper limit in the Be
abundance can be placed at about 1 dex below the mean trend of the Be-Fe
relation. For such stars non conventional mixing is required to explain Be
depletion. Be observations can be used to discriminate strongly Li-depleted
stars. These are the stars which show less Li than that expected by high energy
cosmic rays production as deduced from Be observations. The available Be
observations imply that some of the stars which contribute to the scatter in
the Li-Fe diagramme are Li-depleted stars.",9608011v1
1996-09-15,Multiwavelength observations of isolated neutron stars as a tool to probe the properties of their surfaces,"We show that an analysis of multiwavelength observations of isolated neutron
stars based on neutron star atmosphere models can be used not only to evaluate
the neutron star effective temperature, but also to determine chemical
composition of its surface. To demonstrate how this new method can be applied
to a specific object, we chose the old isolated neutron star candidate
RXJ1856.5-3754, whose soft X-ray radiation has been studied recently by Walter
et al. (1996). We fitted the soft X-ray spectrum of this object with neutron
star atmosphere models of different chemical compositions and used these fits
to calculate the source spectrum over a broad wavelength range. We showed, in
particular, that the optical/UV flux expected from this object depends
drastically on the composition of its surface. In particular, the neutron star
covered with hydrogen would be 5-6 magnitudes brighter than the neutron star
with an iron surface. The object should also be observable with $EUVE$; the EUV
flux is expected to be almost twice higher for the iron surface than for the
hydrogen one. Thus, multiwavelength observations of this object would enable
one to examine, for the first time, chemical composition of the neutron star
surface. The method proposed can be applied to other nearby isolated neutron
stars.",9609097v2
1996-10-16,An X-ray spectral study of 24 type-1 AGN,"I present a study of the X-ray spectral properties of a sample containing 24
type-1 active galactic nuclei using the medium spectral resolution of ``ASCA''.
The sample consists of 20 radio-quiet objects and 4 radio-loud objects. A
simple power-law continuum absorbed by Galactic material provides a very poor
description of the spectra of most objects. Deviations from the power-law form
are interpreted in terms of X-ray reprocessing/absorption processes. In
particular, at least half of the objects show K-shell absorption edges of warm
oxygen (O vii and O viii) characteristic of optically-thin, photoionized
material along the line-of-sight to the central engine, the so-called warm
absorber. It is found that objects with significant optical reddening display
deep O vii edges. Coupled with other evidence, this suggests the existence of
dusty warm plasma. A radiatively driven outflow originating from the molecular
torus is probably the source of this plasma. Rapid variability of the warm
absorber also points to there being another component closer to the central
source and probably situated within the broad line region.
  Spectral features at energies characteristic of cold fluorescent iron
K$\alpha$ emission are common. Radio-quiet objects have iron emission well
described as originating from either the inner regions of an accretion disk or,
in a small number of cases, from the molecular torus. Two of the radio-loud
objects (3C~120 and 3C~382) have a much broader feature which presents problems
for the relativistic disk model. The presence of radio-jets may be important in
forming this spectral feature.",9610127v1
1996-12-10,An Investigation of Neutrino-Driven Convection and the Core Collapse Supernova Mechanism Using Multigroup Neutrino Transport,"We investigate neutrino-driven convection in core collapse supernovae and its
ramifications for the explosion mechanism. We begin with an ``optimistic'' 15
solar mass precollapse model, which is representative of the class of stars
with compact iron cores. This model is evolved through core collapse and bounce
in one dimension using multigroup (neutrino-energy--dependent) flux-limited
diffusion (MGFLD) neutrino transport and Lagrangian hydrodynamics, providing
realistic initial conditions for the postbounce convection and evolution. Our
two-dimensional simulation begins at 106 ms after bounce at a time when there
is a well-developed gain region, and proceeds for 400 ms. We couple
two-dimensional (PPM) hydrodynamics to one-dimensional MGFLD neutrino
transport. At 225 ms after bounce we see large-scale convection behind the
shock, characterized by high-entropy, mushroom-like, expanding upflows and
dense, low-entropy, finger-like downflows. The upflows reach the shock and
distort it from sphericity. The radial convection velocities become supersonic
just below the shock, reaching magnitudes in excess of 10^9 cm/sec. Eventually,
however, the shock recedes to smaller radii, and at about 500 ms after bounce
there is no evidence in our simulation of an explosion or of a developing
explosion. Failure in our ``optimistic'' 15 solar mass Newtonian model leads us
to conclude that it is unlikely, at least in our approximation, that
neutrino-driven convection will lead to explosions for more massive stars with
fatter iron cores or in cases in which general relativity is included.",9612107v1
1997-01-08,A new chemo-evolutionary population synthesis model for early-type galaxies. II: Observations and Results,"We present here the results of applying a new chemo-evolutionary stellar
population model developed by ourselves in a previous paper (Vazdekis et al.
1996) to new high quality observational data of the nuclear regions of two
representative elliptical galaxies and the bulge of the Sombrero galaxy. Here
we fit in detail about 20 absorption lines and 6 optical and near-infrared
colors following two approaches: fitting a single-age single-metallicity model
and fitting our full chemical evolutionary model. We find that all of the iron
lines are weaker than the best fitting models predict, indicating that the
iron-abundance is anomalous and deficient. We also find that the Ca_I index at
4227 A is much lower than predicted by the models. We can obtain good fits for
all the other lines and observed colors with models of old and metal-rich
stellar populations, and can show that the observed radial gradients are due to
metallicity decreasing outward. We find that good fits are obtained both with
fully evolutionary models and with single-age single-metallicity models. This
is due to the fact that in the evolutionary model more than 80% of stars form
with in 1.5 Gyr after the formation of the galaxies. The fact that slightly
better fits are obtained with evolutionary models indicates these galaxies
contain a small spread in metallicity.",9701036v1
1997-02-24,A New Approach to Determine the Initial Mass Function in the Solar Neighborhood,"Oxygen to iron abundance ratios of metal-poor stars provide information on
nucleosynthesis yields from massive stars which end in Type II supernova
explosions. Using a standard model of chemical evolution of the Galaxy we have
reproduced the solar neighborhood abundance data and estimated the oxygen and
iron yields of genuine SN II origin. The estimated yields are compared with the
theoretical yields to derive the relation between the lower and upper mass
limits in each generation of stars and the IMF slope. Independently of this
relation, we furthermore derive the relation between the lower mass limit and
the IMF slope from the stellar mass to light ratio in the solar neighborhood.
These independent relations unambiguously determine the upper mass limit of
$m_u=50 \pm 10 M_sun$ and the IMF slope index of 1.3 - 1.6 above 1 M_sun. This
upper mass limit corresponds to the mass beyond which stars end as black holes
without ejecting processed matter into the interstellar medium. We also find
that the IMF slope index below 0.5 M_sun cannot be much shallower than 0.8.",9702205v2
1997-07-15,Rotating Astrophysical Systems and a Gauge Theory Approach to Gravity,"We discuss three applications of a gauge theory of gravity to rotating
astrophysical systems. The theory employs gauge fields in a flat Minkowski
background spacetime to describe gravitational interactions. The iron
fluorescence line observed in AGN is discussed, assuming that the line
originates from matter in an accretion disk around a Kerr (rotating) black
hole. Gauge-theory gravity, expressed in the language of Geometric Algebra,
allows very efficient numerical calculation of photon paths. From these paths
we are able to infer the line shape of the iron line. Comparison with
observational data allows us to constrain the black hole parameters, and, for
the first time, infer an emissivity profile for the accretion disk. The
topological constraints imposed by gauge-theory gravity are exploited to
investigate the nature of the Kerr singularity. This reveals a simple physical
picture of a ring of matter moving at the speed of light which surrounds a
sheet of pure isotropic tension. Implications for the end-points of collapse
processes are discussed. Finally we consider rigidly-rotating cosmic strings.
It is shown that a solution in the literature has an unphysical stress-energy
tensor on the axis. Well defined solutions are presented for an ideal
two-dimensional fluid. The exterior vacuum solution admits closed timelike
curves and exerts a confining force.",9707165v1
1997-10-28,Chemical abundances in the young galaxy at z=2.309 towards PHL 957,"We present high-resolution UES spectra of the quasar PHL 957 obtained for
studying the foreground Damped Ly-alpha galaxy at z=2.309. Measurements of
absorption lines lead to accurate abundance determinations of Fe, S and N which
complement measurements of Zn, Cr and Ni already available for this system. We
find [Fe/H]= -2.0 (+/-0.1), [S/H]= -1.54 (+/-0.06) and [N/H]=-2.76 (+/-0.07).
The ratio [Fe/Zn]=-0.44 provides evidence that about 74% of iron and about 28%
of zinc are locked into dust grains with a dust-to-gas ratio of about 3% of the
Galactic one. The total iron content in both gas and dust in the DLA system is
[Fe/H]=-1.4. This confirms a rather low metallicity in the galaxy, which is in
the early stages of its chemical evolution. The detection of SII allows us to
measure the SII/ZnII ratio, which is a unique diagnostic tool for tracing back
its chemical history, since it is not affected by the presence of dust.
Surprisingly, the resulting relative abundance is [S/Zn]=0.0 (+/-0.1), at
variance with the overabundance found in the Galactic halo stars with similar
metallicity. We emphasize that the [S/Zn] ratio is solar in all the three DLA
absorbers with extant data. Upper limits are also found for Mn, Mg, O and P
and, once the dust depletion is accounted for, we obtain [Mg/Fe]_{c} <+0.2,
[O/Fe]_{c}< 0.4, [Mn/Fe]_{c}<+0.0 and [P/Fe]_{c}<-0.7. The [alpha/Fe] values do
not support a Galactic halo-like abundances implying that the chemical
evolution of this young galaxy is not reproducing our own Galaxy's evolution.",9710314v1
1997-12-02,Detecting Compton Reflection and a Broad Iron Line in MCG-5-23-16 with the Rossi X-ray Timing Explorer,"We report the detection with the Rossi X-ray Timing Explorer of a Compton
reflection signature in the Seyfert galaxy MCG-5-23-16. RXTE also resolves the
Fe K-alpha fluorescence line with FWHM ~48,000 km s^{-1}. This measurement
provides the first independent confirmation of ASCA detections in Seyfert
galaxies of broad Fe K-alpha lines that are thought to be the signature of
emission from the inner regions of an accretion disk orbiting a black hole.
Under the assumption that reflection arises from an isotropic source located
above a neutral accretion disk, and using a theoretical model that accounts for
the dependence of the reflected spectrum on inclination angle, we derive a 90%
confidence range for the disk inclination of i = 50 to 81 degrees. The large
inclination is consistent with that expected from the unified model for
MCG-5-23-16 based on its Seyfert 1.9 classification. If we assume that the
high-energy cutoff in the incident spectrum lies at energies larger than a few
hundred keV, then the equivalent width of the Fe K-alpha line is much larger
than predicted for the amount of reflection. This implies either an enhanced
iron abundance, a covering factor of reflecting material > 0.5, or a cutoff in
the incident spectrum at energies between ~60 and ~200 keV.",9712035v2
1997-12-03,Resonance Averaged Photoionization Cross Sections for Astrophysical Models,"We present ground state photoionization cross sections of atoms and ions
averaged over resonance structures for photoionization modeling of
astrophysical sources. The detailed cross sections calculated in the
close-coupling approximation using the R-matrix method, with resonances
delineated at thousands of energies, are taken from the Opacity Project
database TOPbase and the Iron Project, including new data for the low
ionization stages of iron Fe I--V. The resonance-averaged cross sections are
obtained by convolving the detailed cross sections with a Gaussian distribution
over the autoionizing resonances. This procedure is expected to minimize errors
in the derived ionization rates that could result from small uncertainties in
computed positions of resonances, while preserving the overall resonant
contribution to the cross sections in the important near threshold regions. The
detailed photoionization cross sections at low photon energies are complemented
by new relativistic distorted-wave calculations for Z<= 12, and from
central-field calculations for Z>12 at high energies, including inner-shell
ionization. The effective cross sections are then represented by a small number
of points that can be readily interpolated linearly for practical applications;
a Fortran subroutine and data are available. The present numerically averaged
cross sections are compared with analytic fits that do not accurately represent
the effective cross sections in regions dominated by resonances.",9712037v1
1997-12-25,Broadening of the Iron emission line in MCG-6-30-15 by Comptonization,"We show that the Iron K emission line from MCG-6-30-15 could be broadened due
to Comptonization by a surrounding highly ionized cloud with radius $\sim
10^{14}$ cms. We calculate the temperature of the cloud to be $\sim0.21\kev$,
provided a reasonable estimate of the UV flux is made. The X-ray/$\gamma$-ray
emission observed from the source is compatible with this model. Such a cloud
should be highly ionized and strong absorption edges are not expected from the
source (Fabian et al 1995).
  For a $\onlyten{6}\msol$ black hole the size of the could corresponds to
about 300 Schwarzschild radius. The intrinsic line could then be emitted far
from the black hole and gravitational red-shift and Doppler effects would be
negligible. If the black hole mass is much larger than $\onlyten{6}\msol$,
gravitational/Doppler red-shifts would also contribute significantly to the
broadening.
  We argue that the broad red wing observed in the source does not by itself
imply emission from regions close ($R < 5 r_s$) to the black hole. However,
Comptonization cannot produce a double peak. The presence of such a feature is
a clear sign of inner disk emission influenced by gravitational and Doppler
effects, perhaps broadened by the Comptonization. We note that simultaneous
broad band (2-100 keV) study of this source can also reveal (or rule out) the
presence of such a Comptonizing cloud.",9712327v1
1998-02-11,The 6.4 keV Fluorescent Iron Line from Cluster Cooling Flows,"For the inner region of the cooling flow (e.g. within the radius of
$\sim$50--100 kpc) the Thomson optical depth of the hot gas in a massive
cooling flow can be as large as $\sim 0.01$. Assuming that the cooling time in
the inner region is few times shorter than the life time of the cluster, the
Thomson depth of the accumulated cold gas can be higher accordingly (if most of
the gas remains in the form of clouds). The illumination of the cold clouds by
the X-ray emission of the hot gas should lead to the appearance of a 6.4 keV
iron fluorescent line, with an equivalent width proportional to $\tau_T$. The
equivalent width only weakly depends on the detailed properties of the clouds,
e.g. on the column density of individual clouds, as long as the column density
is less than few $10^{23} cm^{-2}$. Another effect also associated exclusively
with the cold gas is a flux in the Compton shoulder of bright X-ray emission
lines. It also scales linearly with the Thomson optical depth of the cold gas.
With the new generation of X-ray telescopes, combining large effective area and
high spectral resolution, the mass of the cold gas in cooling flows (and it's
distribution) can be measured.",9802130v1
1998-04-23,The broad-band X-ray spectrum of Mrk 3,"We have used non-simultaneous Ginga, ASCA and ROSAT observations to
investigate the complex X-ray spectrum of the Seyfert 2 galaxy Mrk 3. We find
that the composite spectrum can be well described in terms of a heavily cut-off
hard X-ray continuum, iron K_alpha emission and a soft X-ray excess, with
spectral variability confined to changes in the continuum normalisation and the
flux in the iron line. Previous studies have suggested that the power-law
continuum in Mrk 3 is unusually hard. We obtain a canonical value for the
energy index of the continuum (i.e. alpha approx 0.7) when a warm absorber
(responsible for an absorption edge observed near 8 keV) is included in the
spectral model. Alternatively, the inclusion of a reflection component yields a
comparable power-law index. The soft-excess flux cannot be modelled solely in
terms of pure electron scattering of the underlying power-law continuum.
However, a better fit to the spectral data is obtained if we include the
effects of both emission and absorption in a partially photoionized scattering
medium. In particular the spectral feature prominent at $\sim 0.9$ keV could
represent O VIII recombination radiation produced in a hot photoionized medium.
We discuss our results in the context of other recent studies of the soft X-ray
spectra of Seyfert 2 galaxies.",9804247v1
1998-05-05,Chemical composition and fundamental parameters of roAp stars,"Element abundances of three roAp stars, HD 166473, HD 203932, and HD 217522,
were determined using Kurucz model atmospheres with metal abundances scaled to
solar ones and the results were compared with data from the literature
concerning three further roAp stars, normal B and A stars and two lambda Bootis
stars. Up to 38 elements could be identified and therefore, this work
represents the most complete chemical investigation hitherto published, which
can be summarized as follows:
  - all investigated roAp stars have a similar abundance pattern,
  - the overabundances of rare earth and other heavy elements are comparable to
cool non-pulsating Ap-stars,
  - iron belongs to the most deficient and cobalt to the most enhanced elements
in the group of the iron peak elements, and
  - the light elements carbon, nitrogen, and oxygen are less abundant than in
atmospheres with abundances scaled to the Sun.
  Beside an unexpected possible relation between effective temperature and
metallicity of roAp stars, no outstanding differences from non-pulsating Ap
stars could be detected. This statement, however, suffers from the lack of
comparably detailed investigations of the latter.",9805037v1
1998-07-01,Magnetic Dipole Microwave Emission from Dust Grains,"Thermal fluctuations in the magnetization of interstellar grains will produce
magnetic dipole emission at frequencies below ~100 GHz. We show how to
calculate absorption and emission from small particles composed of magnetic
materials. The Kramers-Kronig relations for a dusty medium are generalized to
include the possibility of magnetic grains. The frequency-dependent magnetic
permeability is discussed for candidate grain materials, including iron and
magnetite.
  We calculate emission spectra for various interstellar grain candidates.
While paramagnetic grains or magnetite grains cannot account for the observed
""anomalous"" emission from dust in the 14-90 GHz range, stronger magnetic dipole
emission will result if a fraction of the grain material is ferromagnetic, as
could be the case given the high Fe content of interstellar dust. The observed
emission from dust near 90 GHz implies that not more than 5% of interstellar Fe
is in the form of metallic iron grains or inclusions (e.g., in ""GEMS"").
However, we show that if most interstellar Fe is in a moderately ferromagnetic
material, it could contribute a substantial fraction of the observed 14-90 GHz
emission, perhaps comparable to the contribution from spinning ultrasmall dust
grains. The two emission mechanisms can be distinguished by measuring the
emission from dark clouds. The expected polarization of magnetic dipole
emission is discussed",9807009v1
1998-08-03,Cloud model of the mean quasar spectrum,"We assume a distribution of clouds optically thick for electron scattering
(OTCM) which are moderately optically thin for absorption and we consider them
as a model of the mean quasar spectrum of Laor et al. (1997). We show that the
model is particularly sensitive to the value of the ionization parameter $\xi$
and that for $\xi \sim 500$ the model well reproduces the optical/UV/X-ray mean
quasar spectrum, in agreement with the estimates of the ionization parameter
based on the energy of the iron $K_{\alpha}$ line. We cannot definitively
reject synchrotron emission as a source of primary radiation but we favor the
model in which the hard X-ray emission is produced by Compton scattering of
soft photons in a central hot medium surrounded by cool clouds. In such a model
clouds are located typically at the distance of $\sim 12 R_{Schw}$, with the
covering factor about 0.88 and the radius of hot plasma is $\sim 9 R_{Schw}$.
The model explains optical/UV emission as predominantly due to the dark sides
of the clouds and the soft X-ray emission as due to the reflection by the
irradiated sides of the clouds. Therefore, atomic features are expected in
these bands although they are hardly present in the observational data. The
kinematical effects connected with the cloud motion affect those features but
do not remove them. The level of the primary emission required to model the
mean quasar spectrum is too low to reproduce the equivalent width of the iron
K$_{\alpha}$ line correctly but more detailed computations may resolve this
problem.",9808014v1
1998-08-10,The Enrichment History of Hot Gas in Poor Galaxy Groups,"We have analyzed the ASCA SIS and GIS data for seventeen groups and
determined the average temperature and abundance of the hot x-ray emitting gas.
For groups with gas temperatures less than 1.5 keV we find that the abundance
is correlated with the gas temperature and luminosity. We have also determined
the abundance of the alpha-elements and iron independently for those groups
with sufficient counts. We find that for the cool groups (i.e. kT <1.5 keV) the
ratio of alpha-elements to iron is ~1, about half that seen in clusters.
Spectral fits with the S, Si and Fe abundances allowed to vary separately
suggest the S/Fe ratio is similar to that seen in clusters while the Si/Fe
ratio in groups is half the value determined for richer systems. The mass of
metals per unit blue luminosity drops rapidly in groups as the temperature
drops. There are two possible explanations for this decrease. One is that the
star formation in groups is very different from that in rich clusters. The
other explanation is that groups lose much of their enriched material via winds
during the early evolution of ellipticals. If the latter is true, we find that
poor groups will have contributed significantly (roughly 1/3 of the metals) to
the enrichment of the intergalactic medium.",9808085v1
1998-08-27,Iron Opacity and the Pulsar of Supernova 1987A,"Neutron stars formed in Type II supernovae are likely to be initially
obscured by late-time fallback. Although much of the late-time fallback is
quickly accreted via neutrino cooling, some material remains on the neutron
star, forming an atmosphere which slowly accretes through photon emission. In
this paper, we derive structure equations of the fallback atmosphere and
present results of one-dimensional simulations of that fallback. The atmosphere
remaining after neutrino cooling becomes unimportant (less than the Compton
Eddington limit) is only a fraction of the total mass accreted (10^-8 of the
accreted mass or 10^-9 solar masses.) Recombined iron dominates the opacity in
the outer regions leading to an opacity 1000-10,000 times higher than that of
electron scattering alone. The resultant photon emission of the remnant
atmosphere is limited to 1/1000th the Compton Eddington Luminosity. The
late-time evolution of this system leads to the formation of a photon-driven
wind from the accretion of the inner portion of the atmosphere, leaving, for
most cases, a bare neutron star on timescales shorter than a year. The
degenerate remnant of 1987a may not be a black hole. Instead, the fallback
material may have already accreted or blown off in the accretion-driven wind.
If the neutron star has either a low magnetic field or a low rotational spin
frequency, we would not expect to see the neutron star remnant of 1987a.",9808309v1
1998-10-28,Reprocessing and Variable Cold Absorption in the Broad-Line Radio Galaxy 3C390.3,"A BeppoSAX observation of the BLRG 3C390.3 is reported. For the first time,
both the 6.4 keV iron line and a strong reflection hump, produced by the
illumination of the primary X-ray emission on cold matter, are detected in this
source. The 0.1-100 keV continuum is modeled by an absorbed power law (\Gamma~
1.8) reflected at high energies by material with a fairly large covering factor
(\Omega/2\pi~1). The iron line is intrinsically narrow ($\sigma=73(+207,-73)
eV) and has an equivalent width of ~140$ eV. We discuss the results in the
context of current models for AGNs and suggest that the primary X-ray power law
continuum is probably produced by a hot inner flow, while the reprocessed
radiation comes from an outer cold thin disk, and/or from a thick torus at even
larger radii. Further observations with BeppoSAX could distinguish between the
latter two cases. Beamed radiation associated to the radio jet is unlikely to
contribute significantly to the X-ray emission. Finally, an historical study of
the column density NH, also reported here, shows that the absorption along the
line of sight changes in time. The NH time variability, which is not correlated
with that of the primary continuum, seems to imply variations of the geometry
of the absorber rather than variations in the ionization state of the gas.",9810450v1
1998-11-16,A Comparison of Metal Enrichment Histories in Rich Clusters and Individual Luminous Elliptical Galaxies,"Hot, X-ray emitting gaseous halos around massive elliptical galaxies are a
result of both stellar mass loss and inflow toward the overdensity from which
giant ellipticals and their associated galaxy groups formed. The metal
abundance in this gas contains important information about early star formation
and past supernova activity. We find that Type II supernovae based on a
Salpeter IMF, plus a small number of additional Type Ia supernovae, can explain
the the density, temperature and abundance profiles currently observed in
gaseous halos around massive ellipticals. Within the central, optically bright
regions of luminous ellipticals, approximately half of the interstellar iron is
produced by Type Ia supernovae and half by mass lost from evolving stars which
were originally enriched by Type II supernovae. However, iron and silicon
abundances in the intracluster gas within rich clusters suggest enrichment by a
larger number of supernovae per unit optical light than we require for massive
ellipticals, either more Type Ia or more Type II from a flatter IMF. Since the
enrichment histories of massive ellipticals and rich clusters are fundamentally
different, E and SO galaxies may not be the only sources of metal enrichment in
rich cluster gas.",9811258v1
1999-01-09,Constraining the Role of SN Ia and SN II in Galaxy Groups by Spatially Resolved Analysis of ROSAT and ASCA Observations,"We present the results of modelling the distribution of gas properties in the
galaxy groups HCG51, HCG62 and NGC5044, and in the poor cluster AWM7, using
both ASCA SIS and ROSAT data. The spectral quality of the ASCA data allows the
radial distribution in the abundances of several elements to be resolved. In
all systems apart from HCG51, we see both central cooling flows, and a general
decline in metal abundances with radius. The ratio of iron to alpha-element
abundances varies significantly, and in comparison with theoretical supernova
yields, indicates a significant contribution to the metal abundance of the
intergalactic medium (IGM) from type Ia supernovae. This is seen both within
the groups, and also throughout much of the cluster AWM7. The total energy
input into the IGM from supernovae can be calculated from our results, and is
typically 20-40 per cent of the thermal energy of the gas, mostly from SNe II.
Our results support the idea that the SN II ejecta have been more widely
distributed in the IGM, probably due to the action of galaxy winds, and the
lower iron mass to light ratio in groups suggests that some of this enriched
gas has been lost altogether from the shallower potential wells of the smaller
systems.",9901100v1
1999-01-16,Concave Accretion Discs and X-ray Reprocessing,"Spectra of Seyfert Is are commonly modelled as emission from an X-ray
illuminated flat accretion disc orbiting a central black hole. This provides
both a reprocessed and direct component of the X-ray emission as required by
observations of individual objects and possibly a fraction of the cosmological
X-ray background. There is some observational motivation to at least consider
the role that an effectively concave disc surface might play: (1) a reprocessed
fraction $\gsim 1/2$ in some Seyferts and possibly in the X-ray background, and
(2) the commonality of a sharp iron line peak for Seyferts at 6.4KeV despite a
dependence of peak location on inclination angle for flat disc models. Here it
is shown that a concave disc may not only provide a larger total fraction of
reprocessed photons, but can also reprocess a much larger fraction of photons
in its outer regions when compared to a flat disc. This reduces the sensitivity
of the 6.4KeV peak location to the inner disc inclination angle because the
outer regions are less affected by Doppler and gravitational effects. If the
X-ray source is isotropic, the reprocessed fraction is directly determined by
the concavity. If the X-ray source is anisotropic, the location of iron line
peak can still be determined by concavity but the total reflected fraction need
not be as large as for the isotropic emitter case. The geometric calculations
herein are applicable to general accretion disc systems illuminated from the
center.",9901216v2
1999-03-30,The complex 0.1-200 keV spectrum of the Seyfert 1 Galaxy NGC4593,"We report on the first observation of the Seyfert 1 galaxy NGC4593 in the
0.1-200 keV band, performed with the BeppoSAX observatory. Its spectral
components are for the first time simultaneously measured: a power-law with
photon spectral index ~1.9; the Compton-reflection of the primary power-law; a
moderately broad (>60 eV) K-alpha fluorescent line from neutral iron; and an
absorption edge, whose threshold energy is consistent with K-shell
photoionization from OVII. The amount of reflection and the iron line
properties are consistent with both being produced in a plane-parallel, X-ray
illuminated relativistic accretion disc surrounding the nuclear black hole,
seen at an inclination of 30 degrees. Any cutoff of the intrinsic continuum is
constrained to lay above 150 keV. The claim for a strongly variable soft excess
is dismissed by our data and by a reanalysis of archival ASCA and ROSAT data.",9903449v1
1999-06-23,Iron line signatures in X-ray afterglows of GRB by BeppoSAX,"We report the possible detection (99.3% of statistical significance) of
redshifted Fe iron line emission in the X-ray afterglow of Gamma-ray burst
GRB970508 observed by BeppoSAX. Its energy is consistent with the redshift of
the putative host galaxy determined from optical spectroscopy. In contrast to
the fairly clean environment expected in the merging of two neutron stars, the
observed line properties would imply that the site of the burst is embedded in
a large mass of material ($>0.5 \Ms$), consistent with pre-explosion ejecta of
a very massive star. This material could be related with the outburst observed
in the afterglow 1 day after the GRB and with the spectral variations measured
during this phase. We did not find evidence of Fe line in two other GRB with
known redshift (GB971214 and GB980613), but we note that the upper limits are
of the same order of the intensity measured in GB97508 and that none of these
afterglows shows rebursting activity.",9906363v1
1999-07-09,Simultaneous EUVE/ASCA/RXTE Observations of NGC 5548,"We present simultaneous observations by EUVE, ASCA, and RXTE of the type~1
Seyfert galaxy NGC 5548. These data indicate that variations in the EUV
emission (at $\sim 0.2 $keV) appear to lead similar modulations in higher
energy ($\ga 1 $keV) X-rays by $\sim$10--30 ks. This is contrary to popular
models which attribute the correlated variability of the EUV, UV and optical
emission in type~1 Seyferts to reprocessing of higher energy radiation. This
behavior instead suggests that the variability of the optical through EUV
emission is an important driver for the variability of the harder X-rays which
are likely produced by thermal Comptonization. We also investigate the spectral
characteristics of the fluorescent iron K$\alpha$ line and Compton reflection
emission. In contrast to prior measurements of these spectral features, we find
that the iron K$\alpha$ line has a relatively small equivalent width
($W_{K\alpha} \sim 100 $eV) and that the reflection component is consistent
with a covering factor which is significantly less than unity ($\Omega/2\pi
\sim 0.4$--0.5). Notably, although the 2--10 keV X-ray flux varies by $\sim \pm
25$% and the derived reflection fraction appears to be constant throughout our
observations, the flux in the Fe~K$\alpha$ line is also constant. This behavior
is difficult to reconcile in the context of standard Compton reflection models.",9907114v1
1999-07-14,The properties of the relativistic iron K-line in NGC 3516,"We present an analysis of the relativistic iron K-alpha line in the Seyfert 1
galaxy NGC 3516, based on a continuous, five-day ASCA observation. The broad
profile which has been found in several other AGN is confirmed in NGC 3516 with
unprecedented signal-to-noise ratio. Disk-line models with either a Kerr or
Schwarzschild metric fit the integrated profile, but both require emission very
strongly concentrated in the inner disk. We find tentative evidence for the
line signatures of Ni K-alpha and/or Fe K-beta. The continuum flux varied by
\~50 per cent during the observation and time-resolved analysis shows that the
line also changes. The line core seems to follow the continuum, but the blue
wing is unrelated and shows a greater amplitude (factor ~2) of variability. The
red wing is formally consistent with a constant but appears to be correlated
with the blue wing. We interpret this as evidence for independent variability
of the broadest parts of the line. There also appears to be an absorption
feature in the profile, consistent with resonance scattering in infalling
material. This variable feature may be the signature of material being accreted
by the central black hole.",9907193v1
1999-09-01,Evidence for Doppler-Shifted Iron Emission Lines in Black Hole Candidate 4U 1630-47,"We report the first detection of a pair of correlated emission lines in the
X-ray spectrum of black hole candidate 4U 1630-47 during its 1996 outburst,
based on RXTE observations of the source. At the peak plateau of the outburst,
the emission lines are detected, centered mostly at $\sim$5.7 keV and $\sim$7.7
keV, respectively, while the line energies exhibit random variability $\sim$5%.
Interestingly, the lines move in a concerted manner to keep their separation
roughly constant. The lines also vary greatly in strength, but with the
lower-energy line always much stronger than the higher-energy one. The measured
equivalent width ranges from $\sim$50 eV to $\sim$270 eV for the former, and
from insignificant detection to $\sim$140 eV for the latter; the two are
reasonably correlated.
  The correlation between the lines implies a causal connection --- perhaps
they share a common origin. Both lines may arise from a single $K_{\alpha}$
line of highly ionized iron that is Doppler-shifted either in a Keplerian
accretion disk or in a bi-polar outflow or even both. In both scenarios, a
change in the line energy might simply reflect a change in the ionization state
of line-emitting matter. We discuss the implication of the results and also
raise some questions about such interpretations.",9909023v1
1999-11-10,Nucleosynthesis and Clump Formation in a Core Collapse Supernova,"High-resolution two-dimensional simulations were performed for the first five
minutes of the evolution of a core collapse supernova explosion in a 15 solar
mass blue supergiant progenitor. The computations start shortly after bounce
and include neutrino-matter interactions by using a light-bulb approximation
for the neutrinos, and a treatment of the nucleosynthesis due to explosive
silicon and oxygen burning. We find that newly formed iron-group elements are
distributed throughout the inner half of the helium core by Rayleigh-Taylor
instabilities at the Ni+Si/O and C+O/He interfaces, seeded by convective
overturn during the early stages of the explosion. Fast moving nickel mushrooms
with velocities up to about 4000 km/s are observed. This offers a natural
explanation for the mixing required in light curve and spectral synthesis
studies of Type Ib explosions. A continuation of the calculations to later
times, however, indicates that the iron velocities observed in SN 1987 A cannot
be reproduced because of a strong deceleration of the clumps in the dense shell
left behind by the shock at the He/H interface.",9911183v2
1999-12-07,BeppoSAX uncovers a type-2 QSO in the hyperluminous infrared galaxy IRAS 09104+4109,"We studied with BeppoSAX the infrared luminous galaxy IRAS 09104+4109 over a
very wide X-ray band from 0.1 to 80 keV. Our observations indicate the
dominance of a thermal component at energies below 8 keV, which we attribute to
the free-free emission from the intracluster (IC) plasma surrounding the
source. Above 10 keV we find evidence for the existence of flux in excess with
respect to the free-free IC plasma emission. This, together with the marginal
detection of a neutral iron line at $\sim 6.4$ keV, gives a strong indication
for the presence of an AGN deeply buried within the source. This component is
best modelled by a strongly absorbed (N_H > 5 10^{24} cm^{-2}) power-law plus
unabsorbed reflection spectrum (0.15<R<0.3), which is also responsible for the
cold iron line. The unabsorbed broad-band (2-100 keV) X-ray emission of this
AGN is 2.5 10$^{46} erg/s, well within the range of quasar luminosities. Our
results indicate that IRAS 09104+4109 is indeed the prototype of a rare class
of sources, the luminous type-2 QSOs. The association of this source with a
huge cooling-flow of $\sim 1000 M_\odot$ in the cluster, as indicated by the
X-ray data, might suggest that such condition of extremely fast mass
accumulation could favour the survival of a thick obscuring envelope, which
would otherwise be quickly destroyed by the very luminous central source.",9912127v1
1999-12-25,Global Relationships among Physical Properties of Galaxy Cluster Cores,"Using X-ray data, we investigate interrelations between gas density rho_0,
virial density rho_vir, core radius R, temperature T, entropy S_gas, and metal
abundance Z in the core region of clusters of galaxies. First, we confirm that
fundamental relations among rho_0, R, and T found by Fujita and Takahara are
reproduced by another data catalogue. Second, we find that, when clusters have
two components in their surface brightness distribution, the inner components
also satisfy the same fundamental relations on the assumption that the average
temperature of the inner component is the same as that of the outer component.
These results strengthen our interpretation that clusters form a two parameter
family in terms of mass and rho_vir; larger rho_vir corresponds to earlier
formation epoch. We argue that the inner components represent distinct dark
matter components which collapsed ahead of the outer components. Third, we also
find a tight relation between S_gas and rho_vir both for the outer and inner
components; S_gas is smaller for larger rho_vir but is larger than that
produced through gravitational collapse alone for larger rho_vir. Although
radiative cooling affects the thermal evolution, the tight relationship
discovered suggests the existence of stable heating sources or stable energy
transmission mechanisms. Finally, we find that the iron abundance at the
centers of clusters is correlated with rho_vir for the inner components. This
implies that iron produced by Type Ia supernovae has more accumulated for
clusters formed earlier. We briefly discuss the implications of these findings.",9912515v1
2000-01-15,Helium Emission in the Type Ic SN 1999cq,"We present the first unambiguous detection of helium emission lines in
spectra of Type Ic supernovae (SNe Ic). The presence of He I lines, with full
width at half maximum ~ 2000 km/s, and the distinct absence of any other
intermediate-width emission (e.g., Halpha), implies that the ejecta of SN Ic
1999cq are interacting with dense circumstellar material composed of almost
pure helium. This strengthens the argument that the progenitors of SNe Ic are
core-collapse events in stars that have lost both their hydrogen and helium
envelopes, either through a dense wind or mass-transfer to a companion. In this
way, SN 1999cq is similar to supernovae such as SN 1987K and SN 1993J that
helped firmly establish a physical connection between Type Ib and Type II
supernovae. The light curve of SN 1999cq is very fast, with an extremely rapid
rise followed by a quick decline. SN 1999cq is also found to exhibit a high
level of emission at blue wavelengths (< 5500 A), likely resulting from either
an unusually large amount of iron and iron-group element emission or
uncharacteristically low reddening compared with other SNe Ic.",0001270v1
2000-01-18,WWhat Heavy Elements in Clusters of Galaxies Tell About Clusters and Galaxies,"Clusters of galaxies allow a direct estimate of the metallicity and metal
production yield on the largest scale so far. The ratio of the total iron mass
in the ICM to the total optical luminosity of the cluster (the iron
mass-to-light-ratio) is the same for all clusters which ICM is hotter than
$\sim 2$ keV, and the elemental proportions (i.e. the [$\alpha$/Fe] ratio)
appear to be solar. The simplest interpretation of these evidences is that both
the IMF as well the relative contributions of SN types are universal. Currently
available abundances in cooler clusters and groups are much more uncertain,
possibly due to insufficiently accurate atomic physics data for multi-electron
ions, or to the ICM being multi-phase, or to a combination thereof. This
uncertainty automatically extends to the reality of radial abundance gradients
so far reported in cool clusters. It is emphasized that most metals reside in
the ICM rather than in galaxies, which demonstrates that energetic winds
operated early in the evolution of massive galaxies, the likely producers of
most metals now in the ICM. The ICM metallicity is also used to set a
semiempirical constraint of $\sim 0.1$ keV per particle to the ICM {\it
preheating} due to supernova driven galactic winds. A lower limit of the
universe global metallicity at $z=3$ is also mentioned.",0001312v1
2000-02-01,The relativistic iron line profile in the Seyfert 1 Galaxy IC4329a,"We present simultaneous ASCA and RXTE data on the bright Seyfert 1 galaxy
IC4329a. The iron line is significantly broadened, but not to the extent
expected from an accretion disk which extends down to the last stable orbit
around a black hole. We marginally detect a narrow line component, presumably
from the molecular torus, but even including this gives a line profile from the
accretion disk which is significantly narrower that that seen in MCG-6-30-15,
and is much more like that seen from the low/hard state galactic black hole
candidates. This is consistent with the inner disk being truncated before the
last stable orbit, forming a hot flow at small radii as in the ADAF models.
However, we cannot rule out the presence of an inner disk which does not
contribute to the reflected spectrum, either because of extreme ionisation
suppressing the characteristic atomic features of the reflected spectrum or
because the X-ray source is intrinsically anisotropic, so it does not
illuminate the inner disk.
  The source was monitored by RXTE every 2 days for 2 months, and these
snapshot spectra show that there is intrinsic spectral variability. The data
are good enough to disentangle the power law from the reflected continuum and
we see that the power law softens as the source brightens. The lack of a
corresponding increase in the observed reflected spectrum implies that either
the changes in disk inner radial extent/ionisation structure are small, or that
the variability is actually driven by changes in the seed photons which are
decoupled from the hard X-ray mechanism.",0002023v1
2000-02-02,Stellar Iron Abundances at the Galactic Center,"We present measurements of [Fe/H] for six M supergiant stars and three giant
stars within 0.5 pc of the Galactic Center (GC) and one M supergiant star
within 30 pc of the GC. The results are based on high-resolution (lambda /
Delta lambda =40,000) K-band spectra, taken with CSHELL at the NASA Infrared
Telescope Facility.We determine the iron abundance by detailed abundance
analysis,performed with the spectral synthesis program MOOG.The mean [Fe/H] of
the GC stars is determined to be near solar,[Fe/H] = +0.12 $\pm$ 0.22. Our
analysis is a differential analysis, as we have observed and applied the same
analysis technique to eleven cool, luminous stars in the solar neighborhood
with similar temperatures and luminosities as the GC stars. The mean [Fe/H] of
the solar neighborhood comparison stars, [Fe/H] = +0.03 $\pm$ 0.16, is similar
to that of the GC stars. The width of the GC [Fe/H] distribution is found to be
narrower than the width of the [Fe/H] distribution of Baade's Window in the
bulge but consistent with the width of the [Fe/H] distribution of giant and
supergiant stars in the solar neighborhood.",0002062v1
2000-02-23,ISO spectroscopy of circumstellar dust in the Herbig Ae systems AB Aur and HD 163296,"Using both the Short- and Long-wavelength Spectrometers on board the Infrared
Space Observatory (ISO), we have obtained infrared spectra of the Herbig Ae
systems AB Aur and HD 163296. In addition, we obtained ground-based N band
images of HD 163296. Our results can be summarized as follows: (1) The main
dust components in AB Aur are amorphous silicates, iron oxide and PAHs; (2) The
circumstellar dust in HD 163296 consists of amorphous silicates, iron oxide,
water ice and a small fraction of crystalline silicates; (3) The infrared
fluxes of HD 163296 are dominated by solid state features; (4) The colour
temperature of the underlying continuum is much cooler in HD 163296 than in AB
Aur, pointing to the existence of a population of very large (mm sized) dust
grains in HD 163296; (5) The composition and degree of crystallization of
circumstellar dust are poorly correlated with the age of the central star. The
processes of crystallization and grain growth are also not necessarily coupled.
This means that either the evolution of circumstellar dust in protoplanetary
disks happens very rapidly (within a few Myr), or that this evolution is
governed by factors other than stellar mass and age.",0002440v1
2000-06-05,Iron K line Variability in the Low-Luminosity AGN NGC 4579,"We present results of new ASCA observations of the low-luminosity AGN (LLAGN)
NGC 4579 obtained on 1998 December 18 and 28, and we report on detection of
variability of an iron K emission line. The X-ray luminosities in the 2--10 keV
band for the two observations are nearly identical (LX $\approx$
2$\times10^{41}$ ergs/s), but they are $\sim$35% larger than that measured in
1995 July by Terashima et al. An Fe K emission line is detected at
$6.39\pm0.09$ keV (source rest frame) which is lower than the line energy
$6.73^{+0.13}_{-0.12}$ keV in the 1995 observation. If we fit the Fe lines with
a blend of two Gaussians centered at 6.39 keV and 6.73 keV, the intensity of
the 6.7 keV line decreases, while the intensity of the 6.4 keV line increases,
within an interval of 3.5 yr. This variability rules out thermal plasmas in the
host galaxy as the origin of the ionized Fe line in this LLAGN. The detection
and variability of the 6.4 keV line indicates that cold matter subtends a large
solid angle viewed from the nucleus and that it is located within $\sim1$ pc
from the nucleus. It could be identified with an optically thick standard
accretion disk. If this is the case, a standard accretion disk is present at
the Eddington ratio of $L_{\rm Bol}/L_{\rm Eddington} \sim 2\times10^{-3}$. A
broad disk-line profile is not clearly seen and the structure of the innermost
part of accretion disk remains unclear.",0006055v1
2000-06-30,Chemical abundances in seven red giants of NGC 2360 and NGC 2447,"Chemical abundances of about fifteen elements from oxygen to europium are
measured in seven red giants of the two open clusters NGC 2360 and NGC 2447.
The effective temperatures of the giants are determined spectroscopically by
taking advantage of their known masses (~2 Mo in NGC 2360 and ~3 Mo in NGC
2447) and bolometric magnitudes.
  The average iron abundances we obtain for the two clusters are [Fe/H]=0.07
for NGC 2360 and [Fe/H]=0.03 for NGC 2447.
  Evolutionary stellar model calculations are performed in the mass range 1-4
Mo in order to analyze the surface Na and O abundances predicted after the
first dredge-up. The sodium abundance shows a well defined correlation with
stellar mass in the 2-3 Mo range. The agreement between our Na abundance
determinations in NGC 2360 and our model predictions at 2 Mo is very good. In
contrast, the overabundance in one of the three stars in NGC 2447 exceeds that
predicted at 3 Mo by ~0.08 dex, which is significant compared to the
observational error bars. The effects of core overshooting, convection
prescription, metallicity and nuclear reaction rates on the Na surface
predictions of our models are investigated.
  An oxygen deficiency relative to iron by 0.2 dex is measured in our stars, in
disagreement with our model predictions. Assuming that the Sun is 0.1-0.3 dex
enriched in oxygen relative to neighbor stars could explain the discrepancy.",0006442v1
2000-07-24,Iron K line emission in AGN: observations,"Iron K-alpha lines are key diagnostics of the central regions of AGN. Their
profiles indicate that they are formed deep in the potential well of the
central black hole, where extreme broadening and red shift occur. The profiles
are most easily reproducible in an accretion disk: the lack of significant
emission blue-ward of the rest energy is difficult produce in other geometries.
In one source an apparent (and perhaps variable) absorption feature in the red
wing of the line may represent rare evidence for inflow onto the black hole.
Sample analysis has defined the mean properties, showing a strong concentration
of the emission in the central regions and face-on accretion disks, at least in
Seyfert 1 galaxies. Surprising results have been obtained from examination of
the line variability. Strong profile changes may be accounted for by changes in
the illumination pattern of the central, relativistic part of the disk. In at
least the case of MCG-6-30-15, there is evidence for emission from within 6
R_g, possibly indicating a spinning black hole. Developing an understanding of
these complex changes has the potential to reveal the geometry and kinematics
of the inner few gravitational radii around extragalactic black holes.",0007356v1
2000-08-01,Atomic data from the Iron Project XLV. Relativistic transition probabilities for carbon-like Ar XIII and Fe XXI using Breit-Pauli R-matrix method,"The Breit-Pauli R-matrix method developed under the Iron Project has been
used to obtain extensive sets of oscillator strengths and transition
probabilities for dipole allowed and intercombination fine structure
transitions in carbon like ions, Ar XIII and Fe XXI. The complete set consists
of 1274 fine structure bound energy levels and 198,259 oscillator strengths for
Ar XIII, and 1611 bound levels and 300,079 oscillator strengths for Fe XXI.
These correspond to levels of total angular momenta of 0 <= J <= 7 of even and
odd parities formed from total spin of 2S+1=5,3,1, and orbital angular momenta
0 <= L <= 9 with n <= 10, 0 <= l <= 9 for each ion. The relativistic effects
are included in the Breit-Pauli approximation. The close coupling wavefunction
expansion for each ion is represented by the lowest 15 fine structure levels of
target configuations, 2s2.2p, 2s.2p2 and 2p3. The energy levels are identified
spectroscopically using a newly developed identification procedure. The
procedure also makes a correspondence between the fine strucure energy levels
and LS terms. This provides the check for completeness of the calculated
levels. Comparison is made of the present energies and the f-values with the
available observed and theoretical values. Present transition probabilitis
agree very well with the relativistic atomic structure calculations of Mendoza
et al. for the intercombination transitions, 2s.2p3(5So)2 -
2s2.2p2(3P){1,2},(1D)2. This further indicates that the importance of the
neglected Breit interaction decreases with ion charge and constrains the
uncertainty in the present calculations to within 15% even for the weak
transitions.",0008032v1
2000-09-17,Reprocessed emission line profiles from dense clouds in geometrically thick accretion engines,"The central engines of active galactic nuclei (AGN) contain cold, dense
material as well as hot X-ray emitting gas. The standard paradigm for the
engine geometry is a cold thin disc sandwiched between hot X-ray coronae.
Strong support for this geometry in Seyferts comes from the study of
fluorescent iron line profiles, although the evidence is not ubiquitously air
tight. The thin disc model of line profiles in AGN and in X-ray binaries should
be bench marked against other plausible possibilities. One proposed alternative
is an engine consisting of dense clouds embedded in an optically thin,
geometrically thick X-ray emitting engine. This model is further motivated by
studies of geometrically thick engines such as advection dominated accretion
flows (ADAFs). Here we compute the reprocessed iron line profiles from dense
clouds embedded in geometrically thick, optically thin X-ray emitting discs
near a Schwarzchild black hole. We consider a range of cloud distributions and
disc solutions, including ADAFs, pure radial infall, and bipolar outflows. We
find that such models can reproduce line profiles similar to those from
geometrically thin, optically thick discs and might help alleviate some of the
problems encountered from the latter.",0009263v2
2000-09-20,"ASCA Observations of the Twin Supernova Remnants in the Large Magellanic Cloud, DEM L316","We report results from an ASCA X-ray study of DEM L316, an emission nebula in
the Large Magellanic Cloud (LMC) consisting of two closely-spaced supernova
remnants (SNRs). The SIS image shows separate X-ray sources located at the
positions of the two radio- and optically-emitting SNR shells, 0547$-$69.7A and
0547$-$69.7B (hereafter, shell A and B). The individual X-ray spectrum of each
shell is well described by optically-thin thermal emission, although the
characteristics of the emission differ in important details between them. Shell
A exhibits strong iron L emission, which we attribute to the presence of
iron-rich ejecta leading to the suggestion that this SNR originates from a Type
Ia SN, an explosion of a moderate mass progenitor. Shell B, on the other hand,
has a chemical composition similar to that of the interstellar medium of the
LMC and so its X-ray emission is dominated by swept-up matter. The different
spectral features strongly disfavor the hypothesis that the two shells are due
to one supernova explosion into an interconnected bubble. We could not obtain
the evidence which positively supports the collision between two SNRs.",0009318v1
2000-09-20,Matter in Strong Magnetic Fields,"The properties of matter are significantly modified by strong magnetic
fields, $B>>2.35\times 10^9$ Gauss ($1 G =10^{-4} Tesla$), as are typically
found on the surfaces of neutron stars. In such strong magnetic fields, the
Coulomb force on an electron acts as a small perturbation compared to the
magnetic force. The strong field condition can also be mimicked in laboratory
semiconductors. Because of the strong magnetic confinement of electrons
perpendicular to the field, atoms attain a much greater binding energy compared
to the zero-field case, and various other bound states become possible,
including molecular chains and three-dimensional condensed matter. This article
reviews the electronic structure of atoms, molecules and bulk matter, as well
as the thermodynamic properties of dense plasma, in strong magnetic fields,
$10^9G << B < 10^{16}G$. The focus is on the basic physical pictures and
approximate scaling relations, although various theoretical approaches and
numerical results are also discussed. For the neutron star surface composed of
light elements such as hydrogen or helium, the outermost layer constitutes a
nondegenerate, partially ionized Coulomb plasma if $B<<10^{14}G$, and may be in
the form of a condensed liquid if the magnetic field is stronger (and
temperature $<10^6$ K). For the iron surface, the outermost layer of the
neutron star can be in a gaseous or a condensed phase depending on the cohesive
property of the iron condensate.",0009333v2
2000-10-13,Evidence for Rapid Iron K_alpha Line Flux Variability in MCG--6-30-15,"This paper employs direct spectral fitting of individual orbital data in
order to measure rapid X-ray iron K_alpha line and continuum spectral slope
variations in Seyfert 1 galaxies with unprecedented temporal resolution.
Application of this technique to a long RXTE observation of MCG--6-30-15
indicates that the line flux does vary on short (~1d) timescales, but that
these variations are not correlated with changes in the continuum flux or
slope. These rapid variations indicate that the line does indeed originate
close to the black hole, confirming predictions based on its very broad
profile. However, the lack of a correlation with the continuum presents
problems for models in which the line variations are driven by those in the
continuum, modified only by light-travel time effects. Instead, it may be that
the line responds according to a physical process with a different time scale,
such as ionization instabilities in the disk, or perhaps that the geometry and
physical picture is more complex than implied by the simplest disk-corona
models.
  These data also indicate that the slope of the underlying power-law continuum
(Gamma) shows strong variability and is tightly correlated with the continuum
flux in the sense that the spectrum steepens as the source brightens. All of
these results have been checked with extensive simulations, which also
indicated that a spurious correlation between Gamma and Compton reflection
fraction (R) will result if these quantities are measured from the same
spectra. This casts serious doubts on previous claims of such a Gamma-R
correlation.",0010274v1
2000-10-18,The first XMM-Newton spectrum of a high redshift quasar - PKS 0537-286,"We present XMM-Newton observations of the high redshift z=3.104, radio-loud
quasar PKS 0537-286. The EPIC CCD cameras provide the highest signal-to-noise
spectrum of a high-z quasar to date. The EPIC observations show that PKS
0537-286 is extremely X-ray luminous (Lx=2x10^47 erg/s), with an unusually hard
X-ray spectrum (Gamma=1.27+/-0.02). The flat power-law emission extends over
the whole observed energy range; there is no evidence of intrinsic absorption,
which has been claimed in PKS 0537-286 and other high z quasars.
  However, there is evidence for weak Compton reflection. A redshifted iron K
line, observed at 1.5 keV - corresponding to 6.15 keV in the quasar rest frame
- is detected at 95% confidence. If confirmed, this is the most distant iron K
line known. The line equivalent width is small (33eV), consistent with the
`X-ray Baldwin effect' observed in other luminous quasars. The reflected
continuum is also weak (R=0.25). We find the overall spectral energy
distribution of PKS 0537-286 is dominated by the X-ray emission, which,
together with the flat power-law and weak reflection features, suggests that
the X-radiation from PKS 0537-286 is dominated by inverse Compton emission
associated with a face-on relativistic jet.",0010367v1
2000-12-14,Discovery of a Transient Absorption Edge in the X-ray Spectrum of GRB 990705,"We report the discovery of a transient equivalent hydrogen column density
with an absorption edge at ~3.8 kiloelectron volts in the spectrum of the
prompt x-ray emission of gamma-ray burst (GRB) 990705. This feature can be
satisfactorily modeled with a photoelectric absorption by a medium located at a
redshift of ~0.86 and with an iron abundance of ~75 times the solar one. The
transient behavior is attributed to the strong ionization produced in the
circumburst medium by the GRB photons. The high iron abundance points to the
existence of a burst environment enriched by a supernova along the line of
sight. The supernova explosion is estimated to have occurred about 10 years
before the burst. Our results agree with models in which GRBs originate from
the collapse of very massive stars and are preceded by a supernova event",0012318v1
2001-01-12,Accretion and emission processes in AGN,"The UV-X continuum, the X-ray spectral features, and the variability in these
bands provide powerful tools for studying the innermost regions of AGNs from
which we gain an insight into the accretion process. In this chapter the
discussion focusses on luminous AGN, i.e. Seyfert galaxies and quasars. The
standard accretion disk model (a stationary geometrically thin disk) is
described, and vertically averaged solutions for the radial structure are
given. The emission of the standard disk is discussed using different
approximations, and it is compared to the observations. This leads to the
conclusion that more complex models are required, such as the irradiated disk
and the disk-corona models. The advantage of this last model is that it
explains the overall UV-X spectral distribution. In the framework of these disk
models, the profile, intensity, and variability properties of the X-ray iron
line can be explained by reprocessing at the surface of the cold disk very
close to the black hole (the ""relativistic disk model""). An alternative
possibility is discussed, where the UV-X continuum is produced by a
quasi-spherical distribution of dense clouds surrounded by (or embedded in) a
hot medium. In such a model the iron line profile could be due to
Comptonization instead of relativistic effects.",0101203v2
2001-03-06,A Simple Model for r-Process Scatter and Halo Evolution,"Recent observations of heavy elements produced by rapid neutron capture
(r-process) in the halo have shown a striking and unexpected behavior: within a
single star, the relative abundances of r-process elements heavier than Eu are
the same as the same as those of solar system matter, while across stars with
similar metallicity Fe/H, the r/Fe ratio varies over two orders of magnitude.
In this paper we present a simple analytic model which describes a star's
abundances in terms of its ``ancestry,'' i.e., the number of nucleosynthesis
events (e.g., supernova explosions) which contributed to the star's
composition. This model leads to a very simple analytic expression for the
abundance scatter versus Fe/H, which is in good agreement with the data and
with more sophisticated numerical models. We investigate two classes of
scenarios for r-process nucleosynthesis, one in which r-process synthesis
events occur in only \sim 4% of supernovae but iron synthesis is ubiquitous,
and one in which iron nucleosynthesis occurs in only about 9% of supernovae.
(the Wasserburg- Qian model). We find that the predictions in these scenarios
are similar for [Fe/H] \ga -2.5, but that these models can be readily
distinguished observationally by measuring the dispersion in r/Fe at [Fe/H] \la
-3.",0103083v1
2001-03-26,Weak Reprocessed Features in the Broad Line Radio Galaxy 3C382,"We present a detailed X-ray study of the Broad Line Radio Galaxy 3C382,
observed with the BeppoSAX satellite in a very bright state. The continuum
emission is well modeled with a power law that steepens at high energies, with
an e-folding energy of about 120 keV. At soft energies a clear excess of
emission is detected, which can not be explained solely by the extended thermal
halo seen in a ROSAT HRI image. A second, more intense soft X-ray component,
possibly related to an accretion disk, is required by the data. Both a
reflection component (R=0.3) and an iron line (EW \sim 50) are detected, at
levels much weaker than in Seyfert galaxies, suggesting a common origin.
Combining our measurements with results from the literature we find that the
iron line has remained approximately constant over 9 years while the continuum
varied by a factor of 5. Thus the fluorescent gas does not respond promptly to
the variations of the X-ray primary source, suggesting that the reprocessing
site is located away, likely at parsec distances. While the continuum shape
indicates that X-rays derive from a thermal Comptonization process, the
weakness of other spectral features implies that either the upper layers of the
optically thick accretion disk are completely ionized or the corona above the
disk is outflowing with mildly relativistic velocity.",0103413v1
2001-03-29,Abundances in Stars from the Red Giant Branch Tip to the Near Main Sequence in M71: II. Iron Abundance,"We present [Ffe/H] abundance results that involve a sample of stars with a
wide range in luminosity from luminous giants to stars near the turnoff in a
globular cluster. Our sample of 25 stars in M71 includes 10 giant stars more
luminous than the RHB, 3 horizontal branch stars, 9 giant stars less luminous
than the RHB, and 3 stars near the turnoff. We analyzed both Fe I and Fe II
lines in high dispersion spectra observed with HIRES at the W. M. Keck
Observatory. We find that the [Fe/H] abundances from both Fe I and Fe II lines
agree with each other and with earlier determinations. Also the [Fe/H] obtained
from Fe I and Fe II lines is constant within the rather small uncertainties for
this group of stars over the full range in Teff and luminosity, suggesting that
NLTE effects are negligible in our iron abundance determination. In this
globular cluster, there is no difference among the mean [Fe/H] of giant stars
located at or above the RHB, RHB stars, giant stars located below the RHB and
stars near the turnoff.",0103494v2
2001-04-04,X-Ray Probing of the Central Regions of Clusters of Galaxies,"Results of ASCA X-ray study of central regions of medium-richness clusters of
galaxies are summarized, emphasizing differences between cD and non-cD
clusters. The intra-cluster medium (ICM) is likely to consist of two (hot and
cool) phases within $\sim 100$ kpc of a cD galaxy, where the ICM metallicity is
also enhanced. In contrast, the ICM in non-cD clusters appears to be isothermal
with little metallicity gradient right to the center. The gravitational
potential exhibits a hierarchical nesting around cD galaxies, while a total
mass-density profile with a central cusp is indicated for a non-cD cluster
Abell~1060. The iron-mass-to-light ratio of the ICM decreases toward the center
in both types of clusters, although it is radially constant in peripheral
regions. The silicon-to-iron abundance ratio in the ICM increases with the
cluster richness, but remains close to the solar ratio around cD galaxies.
These overall results are interpreted without appealing to the popular
cooling-flow hypothesis. Instead, an emphasis is put on the halo-in-halo
structure formed around cD galaxies.",0104079v1
2001-06-01,"X-Ray Spectroscopy of II Pegasi: Coronal Temperature Structure, Abundances, and Variability","We have obtained high resolution X-ray spectra of the coronally active
binary, II Pegasi (HD 224085), covering the wavelength range of 1.5-25
Angstroms. For the first half of our 44 ksec observation, the source was in a
quiescent state with constant X-ray flux, after which it flared, reaching twice
the quiescent flux in 12 ksec, then decreasing. We analyze the emission-line
spectrum and continuum during quiescent and flaring states. The differential
emission measure derived from lines fluxes shows a hot corona with a continuous
distribution in temperature. During the non-flare state, the distribution peaks
near log T = 7.2, and when flaring, near 7.6. High-temperature lines are
enhanced slightly during the flare, but most of the change occurs in the
continuum. Coronal abundance anomalies are apparent, with iron very deficient
relative to oxygen and significantly weaker than expected from photospheric
measurements, while neon is enhanced relative to oxygen. We find no evidence of
appreciable resonant scattering optical depth in line ratios of iron and
oxygen. The flare light curve is consistent with Solar two-ribbon flare models,
but with a very long reconnection time-constant of about 65 ks. We infer loop
lengths of about 0.05 stellar radii, to about 0.25 in the flare, if the flare
emission originated from a single, low-density loop.",0106007v1
2001-06-28,On a possible GRB-supernova time sequence,"The data from the Chandra satellite on the iron emission lines in the
afterglow of GRB 991216 are used to give further support for the EMBH theory,
which links the origin of the energy of GRBs to the extractable energy of
electromagnetic black holes (EMBHs), leading to an interpretation of the
GRB-supernova correlation. Following the relative space-time transformation
(RSTT) paradigm and the interpretation of the burst structure (IBS) paradigm,
we introduce a paradigm for the correlation between GRBs and supernovae. The
following sequence of events is shown as kinematically possible and consistent
with the available data: a) the GRB-progenitor star $P_1$ first collapses to an
EMBH, b) the proper GRB (P-GRB) and the peak of the afterglow (E-APE) propagate
in interstellar space until the impact on a supernova-progenitor star $P_2$ at
a distance $\le 2.69\times 10^{17}$ cm, and they induce the supernova
explosion, c) the accelerated baryonic matter (ABM) pulse, originating the
afterglow, reaches the supernova remnants 18.5 hours after the supernova
explosion and gives rise to the iron emission lines. Some considerations on the
dynamical implementation of the paradigm are presented. The concept of induced
supernova explosion introduced here specifically for the GRB-supernova
correlation may have more general application in relativistic astrophysics.",0106534v1
2001-07-09,BeppoSAX observations of Mrk 841 and Mrk335,"We present and discuss BeppoSAX observations of Mrk841 and Mrk335, two
Seyfert 1 galaxies in which previous observations have established the presence
of soft excesses. We confirm the soft excess in both sources, even if for
Mrk~841 a warm absorber provides a fit almost as good as the one with a true
excess. As far as the hard X-ray continuum is concerned, a Comptonization model
provides a fit as good as a power law and a physically sound solution for
Mrk841. For Mrk335, the Comptonization model gives a result which is somewhat
better on statistical ground, but rather problematic on physical ground. The
most interesting results regard the reprocessing components. For Mrk841 we find
a very large reflection continuum but an almost normal iron line equivalent
width even if, within the errors, a solution in which both components are a
factor ~2 larger than expected for an accretion disc is still marginally
acceptable. If this is the case, an anisotropy of the primary emission seems
the best explanation. On the contrary, in Mrk335 we find a very large iron line
EW but a reflection component not accordingly large. In this case, the best
solution seems to be in terms of reflection from an ionized disc.",0107151v1
2001-07-20,On the GRB progenitors: possible consequences for supernovae connection with gamma-ray bursts,"Unique data on $BVRI$ light curves of the optical transient (OT) of GRB
970508 obtained with the 6-m telescope have been interpreted in the framework
of the idea of a straightforward link between supernovae (SNe) and long
duration gamma-ray bursts (GRBs). The effect must be maximum in the $I_{c}$
band as for OT GRB 970228. The peak absolute ($M_{B}$) magnitude of the
suggested SN must be around -19.5 for the OT of GRB 970508. So, in addition to
the characteristic ""shoulders"" on the light curves of the OTs of GRB 970228,
GRB 980326, 990712, 991208, more evidence of the link between GRBs and Type
Ib/c SNe (or core-collapse SNe) was found, which could be an argument in favor
of the idea of massive stars as progenitors of long duration GRBs. If all or
the main part of long duration GRBs are associated with the SNe, GRB host
galaxies (for ground-based observations, at least) must be dimmer than the peak
magnitude of a SN. If some GRB/SN relation really exists, and if all or at
least the main part of long duration GRBs are associated with SNe, then as a
consequence we have a very strong $\gamma$-ray beaming with a solid angle of up
to $\Omega_{beam} \sim (10^{-5} - 10^{-6})\cdot 4\pi$. Besides, the
observations of K$_{\alpha}$ lines of iron in the X-ray afterglow spectra of
GRBs (970508, 970828, 991216, 000214) and the observation of redshifted
absorption feature of neutral iron (7.1 keV) simultaneously with GRB 990705 are
also evidence in favor of massive stars -- progenitors of GRBs.",0107399v1
2001-07-25,The X-ray emission of the Intermediate Polar V709 Cas,"We present RXTE and BeppoSAX observations of the Intermediate Polar V709 Cas
acquired in 1997 and 1998 respectively. The X-ray emission from 0.1 to 30keV is
dominated by the strong pulsation at the rotational period of the white dwarf
(312.8s) with no sign of orbital or sideband periodicity, thus confirming
previous ROSAT results. However, we detect changes in the power spectra between
the two epochs. While the second harmonic of the spin period is present during
both observations, the first harmonic is absent in 1997. An increase in the
amplitude of the spin pulsation is found between 1997 and 1998 together with a
decrease in the X-ray flux. The average X-ray spectrum from 0.1 to 100keV is
well described by an isothermal plasma at ~27keV plus complex absorption and an
iron K(alpha) fluorescent line, due to reflection from the white dwarf surface.
The rotational pulsation is compatible with complex absorption dominating the
low energy range, while the high energy spin modulation can be attributed to
tall shocks above the accreting poles. The RXTE spectrum in 1997 also shows the
presence of an absorption edge from ionized iron likely located in the
pre-shock accretion flow. The variations along the spin period of the partial
covering absorber and of reflection are compatible with the classical accretion
curtain scenario. The variations in the spin pulse characteristics and X-ray
flux indicate that V709 Cas experiences changes in the mass accretion rate on
timescales from months to years.",0107480v1
2001-08-15,Boron Abundances in Main Sequence B-type Stars: A Test of Rotational Depletion during Main Sequence Evolution,"Boron abundances have been derived for seven main sequence B-type stars from
HST STIS spectra around the B III 2066 A line. In two stars, boron appears to
be undepleted with respect to the presumed initial abundance. In one star,
boron is detectable but it is clearly depleted. In the other four stars, boron
is undetectable implying depletions of 1 to 2 dex. Three of these four stars
are nitrogen enriched, but the fourth shows no enrichment of nitrogen. Only
rotationally induced mixing predicts that boron depletions are unaccompanied by
nitrogen enrichments. The inferred rate of boron depletion from our
observations is in good agreement with these predictions. Other boron-depleted
nitrogen-normal stars are identified from the literature. Also, several
boron-depleted nitrogen-rich stars are identified, and while all fall on the
boron-nitrogen trend predicted by rotationally-induced mixing, a majority have
nitrogen enrichments that are not uniquely explained by rotation.
  The spectra have also been used to determine iron-group (Cr, Mn, Fe, and Ni)
abundances. The seven B-type stars have near solar iron-group abundances, as
expected for young stars in the solar neighborhood. We have also analysed the
halo B-type star, PG0832+676. We find [Fe/H] = -0.88 +/- 0.10, and the absence
of the B III line gives the upper limit [B/H]<2.5. These and other published
abundances are used to infer the star's evolutionary status as a post-AGB star.",0108263v1
2001-09-20,"An XMM-Newton observation of the extreme Narrow Line Seyfert 1 Galaxy, Mrk 359","We present XMM-Newton observations of Mrk 359, the first Narrow Line Seyfert
1 galaxy discovered. Even among NLS1s, Mrk 359 is an extreme case with
extraordinarily narrow optical emission lines. The XMM-Newton data show that
Mrk 359 has a significant soft X-ray excess which displays only weak absorption
and emission features. The (2-10) keV continuum, including reflection, is
flatter than the typical NLS1, with Gamma approximately 1.84. A strong emission
line of equivalent width approximately 200 eV is also observed, centred near
6.4 keV. We fit this emission with two line components of approximately equal
strength: a broad iron-line from an accretion disc and a narrow, unresolved
core. The unresolved line core has an equivalent width of approximately 120 eV
and is consistent with fluorescence from neutral iron in distant reprocessing
gas, possibly in the form of a `molecular torus'. Comparison of the narrow-line
strengths in Mrk 359 and other low-moderate luminosity Seyfert 1 galaxies with
those in QSOs suggests that the solid angle subtended by the distant
reprocessing gas decreases with increasing AGN luminosity.",0109346v1
2001-11-21,Detection of an Iron Emission Feature from the Lensed BAL QSO H1413+117 at z=2.56,"We present the X-ray energy spectrum of the lensed BAL QSO H1413+117 (the
Cloverleaf) at z=2.56 observed with the Chandra X-ray observatory. We detected
293 photons in a 40 ks Advanced CCD Imaging Spectrometer (ACIS-S) observation.
The X-ray image consists of four lensed image components, thus the photons are
from the lensed QSO itself. The overall spectrum can be described with a
power-law function heavily absorbed by neutral matter at a redshift consistent
with the QSO redshift. This supports the idea that intrinsic absorption is
significant for BAL QSOs. The spectral fit significantly (99% confidence)
improves when we include an emission line. The centroid energy and intrinsic
width (Gaussian \sigma) of the line are 6.21 \pm 0.16 keV and 220
^{+270}_{-130} eV (90% errors), respectively, in the QSO rest frame, assuming
the absorbed power-law as the continuum. The equivalent width of the line in
the QSO rest frame is 960 ^{+1400}_{-480} eV. We suggest that the large
equivalent width, the centroid energy, and the line broadness can be explained
by iron K emission arising from X-ray reprocessing in the BAL flow, assuming it
has a conical thin-sheet structure.",0111410v1
2001-11-30,Deep inside the core of Abell 1795: the Chandra view,"We present X-ray spatial and spectral analysis of the Chandra data from the
central 400 kpc (H0 = 50 km/s/Mpc) of the cluster of galaxies Abell 1795. The
plasma temperature rises outwards by a factor of 3, whereas the iron abundance
decreases by a factor of 4. The spatial distribution of Oxygen, Neon, Sulphur,
Silicon and Iron shows that supernovae Type Ia dominate the metal enrichment
process of the cluster plasma within the inner 150 kpc. Resolving both the gas
density and temperature in 9 radial bins, we recover the gravitational mass
density profile and show that it flattens within 100 kpc as rho_DM \propto
r^{-0.6} with a power law index flatter than -1 at >3 sigma level. The observed
motion of the central galaxy and the presence of excesses and deficits along
the North-South direction in the brightness distribution indicate that the
central cluster region is not relaxed. In the absence of any non-gravitational
heating source, the data from the inner ~200 kpc indicate the presence of a
cooling flow with an integrated mass deposition rate of about 100 Msun/yr. Over
the same cluster region, the observed rate of 74 Msun/yr is consistent with the
recent XMM Reflection Grating Spectrometer limit of 150 Msun/yr.",0111586v1
2001-12-01,"Production of neutrons, neutrinos and gamma-rays by a very fast pulsar in the Galactic Center region","We consider the possibility that the excess of cosmic rays near $\sim
10^{18}$ eV, reported by the AGASA and SUGAR groups from the direction of the
Galactic Center, is caused by a young, very fast pulsar in the high density
medium. The pulsar accelerates iron nuclei to energies $\sim 10^{20}$ eV, as
postulated by the Galactic models for the origin of the highest energy cosmic
rays. The iron nuclei, after about 1 yr since pulsar formation, leave the
supernova envelope without energy losses and diffuse through the dense central
region of the Galaxy. Some of them collide with the background matter creating
neutrons (from desintegration of Fe), neutrinos and gamma-rays (in inelastic
collisions). Wse suggest that neutrons produced at a specific time after the
pulsar formation are responsible for the observed excess of cosmic rays at
$\sim 10^{18}$ eV. From normalization of the calculated neutron flux to the one
observed in the cosmic ray excess, we predict the neutrino and gamma-ray
fluxes. It has been found that the 1 km$^2$ neutrino detector of the IceCube
type should detect from a few up to several events per year from the Galactic
Center, depending on the parameters of the considered model. Also future
systems of Cherenkov telescopes (CANGAROO III, HESS, VERITAS) should be able to
observe 1 - 10 TeV $\gamma$-rays from the Galactic Center if the pulsar was
created inside a huge molecular cloud about $3-10\times 10^3$ yrs ago.",0112008v1
2001-12-02,Asymmetric Supernovae from Magneto-Centrifugal Jets,"Strong toroidal magnetic fields generated in stellar collapse can generate
magneto-centrifugal jets in analogy to those found in simulations of black hole
accretion and explain why all core collapse supernovae are found to be
substantially asymmetric and predominantly bi-polar. We describe two phases:
the initial LeBlanc-Wilson jet and a subsequent protopulsar or toroidal jet
that propagates at about the core escape velocity. The jets will produce bow
shocks that tend to expel matter, including iron and silicon, into equatorial
tori, accounting for observations of the element distribution in Cas A. A
magnetic ``switch'' mechanism may apply in instances of low density and large
magnetic field with subsequent increase in the speed and collimation of the
toroidal jet, depositing relatively little momentum. The result could be enough
infall to form a black hole with a third, highly relativistic jet that could
catch up to the protopulsar jet after it has emerged from the star. The
interaction of these two jets could generate internal shocks and explain the
presence of iron lines in the afterglow. Recent estimates that typical
gamma-ray burst energy is about 3x10^50 erg imply either a very low efficiency
for conversion of rotation into jets, or a rather rapid turnoff of the jet
process even though the black hole still rotates rapidly. Magnetars and
``hypernovae'' might arise in an intermediate parameter regime of energetic
jets that yield larger magnetic fields and provide more energy than the routine
case, but that are not so tightly collimated that they yield failed supernova.
(slightly abridged)",0112020v1
2002-03-04,X-ray Sources and Star Formation Activity in the Sgr B2 Cloud Observed with Chandra,"We report the X-ray population study in the giant molecular cloud Sagittarius
B2 (SgrB2). More than a dozen of X-ray cloud members (and candidates) are
discovered with Chandra. Two bright X-ray sources are located near Sgr B2 Main,
the most copious complex of the ultra compact HII sources. The X-ray spectra
are fitted with a thin thermal plasma model of 5-10 keV temperature. The
intrinsic luminosity after correcting the absorption of 5 x 10^23 H/cm^2 is
about 10^33 erg/s. Although these two X-ray sources are attributable to young
stellar objects (YSOs) in the same HII complex, they are in sharp contrast; one
at the center of the HII complex exhibits strong K-shell transition lines of
iron, while the other near the east has only weak lines. The other HII
complexes, SgrB2 North and South, also show hard and highly absorbed X-ray
emissions due possibly to the star formation activity. The composite X-ray
spectrum of the other cloud member X-ray sources is fitted with a thin thermal
plasma of about 10-keV temperature with the hydrogen column density (N_H) of
1.3 x 10^23 H/cm^2, and the individual X-ray luminosity of a few times of
10^31-32$ erg/s. These are likely to be a single or cluster of YSO(s), but
neither radio nor infrared counterpart is found. An alternative scenario of
isolated white dwarfs powered by the Bondi-Hoyle accretion from the dense cloud
gas is also discussed. The X-ray spectra exhibit an additional 6.4-keV line of
neutral or low-ionization irons, which indicates that the environment gas is
concentrated near at the sources.",0203035v1
2002-04-08,X-Ray Resonance Opacity of Oxygen and Iron in AGN MCG--6-30-15,"Theoretical differential oscillator strengths related to monochromatic
opacity due to K- and L-shell absorption from oxygen and iron ions are directly
compared with the Chandra and Xmm-Newton spectra of Seyfert~1 galaxy
MCG--6-30-15. We compute the highly resolved continuum with resonances due to O
I - VI and Fe XVI. It is found that the KLn (n --> infty) resonance series
limits in O VI, and the lowest LMM resonance in Fe XVI, lie at the prominent
17.5 A break in the observed spectra. We also calculate and identify, for the
first time, the observed gap in spectral flux at 22-23 A in the Chandra spectra
due to K --> L resonant absorption features from all O-ions O I - VI,
potentially leading to abundance determination of several or all ionization
stages; similar signature gaps may be predicted due to other elements. The
precise atomic parameters are computed in the relativistic close coupling
approximation using the Breit-Pauli R-matrix method. The new X-ray opacities
might possibly distinguish between models of a dusty warm absorber, and/or
gravitational redshift and broadening due to a massive black hole in
MCG--6-30-15.",0204116v2
2002-05-02,History of Milky Way Dwarf Spheroidal Galaxies Imprinted on Abundance Patterns of Neutron-Capture Elements,"Stellar abundance pattern of neutron-capture elements such as barium is used
as a powerful tool to infer how star formation proceeded in dwarf spheroidal
(dSph) galaxies. It is found that the abundance correlation of barium with iron
in stars belonging to dSph galaxies orbiting the Milky Way, i.e., Draco,
Sextans, and Ursa Minor have a feature similar to the barium-iron correlation
in Galactic metal-poor stars. The common feature of these two correlations can
be realized by our inhomogeneous chemical evolution model based on the
supernova-driven star formation scenario if dSph stars formed from gas with a
velocity dispersion of ~26 km/s. This velocity dispersion together with the
stellar luminosities strongly suggest that dark matter dominated dSph galaxies.
The tidal force of the Milky Way links this velocity dispersion with the
currently observed value <10 km/s by stripping the dark matter in dSph
galaxies. As a result, the total mass of each dSph galaxy is found to have been
originally ~25 times larger than at present. Our inhomogeneous chemical
evolution model succeeds in reproducing the stellar [Fe/H] distribution
function observed in Sextans. In this model, supernovae immediately after the
end of the star formation epoch can expel the remaining gas over the
gravitational potential of the dSph galaxy.",0205013v1
2002-06-06,Predicted FeII Emission-Line Strengths from Active Galactic Nuclei,"We present theoretical FeII emission line strengths for physical conditions
typical of Active Galactic Nuclei with Broad-Line Regions. The FeII line
strengths were computed with a precise treatment of radiative transfer using
extensive and accurate atomic data from the Iron Project. Excitation mechanisms
for the FeII emission included continuum fluorescence, collisional excitation,
self-fluorescence amoung the FeII transitions, and fluorescent excitation by
Lyman-alpha and Lyman-beta. A large FeII atomic model consisting of 827 fine
structure levels (including states to E ~ 15 eV) was used to predict fluxes for
approximately 23,000 FeII transitions, covering most of the UV, optical, and IR
wavelengths of astrophysical interest. Spectral synthesis for wavelengths from
1600 Angstroms to 1.2 microns is presented. Applications of present theoretical
templates to the analysis of observations are described. In particular, we
discuss recent observations of near-IR FeII lines in the 8500 Angstrom -- 1
micron region which are predicted by the Lyman-alpha fluorescence mechanism. We
also compare our UV spectral synthesis with an empirical iron template for the
prototypical, narrow-line Seyfert galaxy I Zw 1. The theoretical FeII template
presented in this work should also applicable to a variety of objects with FeII
spectra formed under similar excitation conditions, such as supernovae and
symbiotic stars.",0206096v1
2002-07-10,The Iron Project and Non-LTE stellar modeling,"Latest developments in theoretical computations since the international
Opacity Project (OP), under the new the Iron Project (IP) and extensions, are
described for applications to a variety of objects such as stellar atmospheres,
nebulae, and active galactic nuclei. The primary atomic processes are: electron
impact excitation (EIE), photoionization, electron-ion recombination, and
bound-bound transitions, all considered using the accurate and powerful
R-matrix method including relativistic effects. As an extension of the OP and
the IP, a self-consistent and unified theoretical treatment of photoionization
and recombination has been developed. Both the radiative and the dielectronic
recombination (RR and DR) processes are considered in a unified manner.
Photoionization and recombination cross sections are computed with identical
wavefunction expansions, thus ensuring self-consistency in an ab initio manner.
The new unified results differ from the sum of previous results for RR and DR
by up to a factor of 4 for the important but complex atomic systems such as Fe
I - V. The fundamental differences are due to quantum mechanical intereference
and coupling effects neglected in simpler approximations that unphysically
treat RR and DR separately, which can not be independently measured or
observed. I will also describe the electronic, web-interactive, database,
TIPTOPBASE, to archive the OP/IP data in a readily accessible manner.
TIPTOPBASE would also include electron-ion recombination data and new fine
structure transition probabilities. Efficient codes developed by M.J. Seaton to
calculate `customized' mixture opacities and radiative accelerations
('levitation') in stars will also be available.",0207223v1
2002-08-06,The Magnetorotational Instability in Core Collapse Supernova Explosions,"We investigate the action of the magnetorotational instability (MRI) in the
context of iron-core collapse. Exponential growth of the field on the rotation
time scale by the MRI will dominate the linear growth process of field line
""wrapping"" with the same characteristic time. We examine a variety of initial
rotation states, with solid body rotation or a gradient in rotational velocity,
that correspond to models in the literature. A relatively modest value of the
initial rotation, a period of ~ 10 s, will give a very rapidly rotating PNS and
hence strong differential rotation with respect to the infalling matter. We
assume conservation of angular momentum on spherical shells. Results are
discussed for two examples of saturation fields, a fiducial field that
corresponds to Alfven velocity = rotational velocity and a field that
corresponds to the maximum growing mode of the MRI. Modest initial rotation
velocities of the iron core result in sub-Keplerian rotation and a
sub-equipartition magnetic field that nevertheless produce substantial MHD
luminosity and hoop stresses: saturation fields of order 10^{15} - 10^{16} G
develop within 300 msec after bounce with an associated MHD luminosity of about
10^{52} erg/s. Bi-polar flows driven by this MHD power can affect or even cause
the explosions associated with core-collapse supernovae.",0208128v2
2002-09-12,Integrated Spectroscopy of Bulge Globular Clusters and Fields I. The Data Base and Comparison of Individual Lick Indices in Clusters and Bulge,"We present a comprehensive spectroscopic study of the integrated light of
metal-rich Galactic globular clusters and the stellar population in the
Galactic bulge. We measure line indices which are defined by the Lick standard
system and compare index strengths of the clusters and Galactic bulge. Both
metal-rich globular clusters and the bulge are similar in most of the indices,
except for the CN index. We find a significant enhancement in the CN/<Fe> index
ratio in metal-rich globular clusters compared with the Galactic bulge. The
mean iron index <Fe> of the two metal-rich globular clusters NGC 6528 and NGC
6553 is comparable with the mean iron index of the bulge. Index ratios such as
Mgb/<Fe>, Mg2/<Fe>, Ca4227/<Fe>, and TiO/<Fe>, are comparable in both stellar
population indicating similar enhancements in individual elements which are
traced by the indices. From the globular cluster data we fully empirically
calibrate several metallicity-sensitive indices as a function of [Fe/H] and
find tightest correlations for the Mg2 index and the composite [MgFe] index. We
find that all indices show a similar behavior with galactocentric radius,
except for the Balmer series, which show a large scatter at all radii. However,
the scatter is entirely consistent with the cluster-to-cluster variations in
the horizontal branch morphology.",0209238v1
2002-09-12,"The Spiral Structure of the Milky Way, Cosmic Rays, and Ice Age Epochs on Earth","The short term variability of the Galactic cosmic ray flux (CRF) reaching
Earth has been previously associated with variations in the global low altitude
cloud cover. This CRF variability arises from changes in the solar wind
strength. However, cosmic ray variability also arises intrinsically from
variable activity of and motion through the Milky Way. Thus, if indeed the CRF
climate connection is real, the increased CRF witnessed while crossing the
spiral arms could be responsible for a larger global cloud cover and a reduced
temperature, thereby facilitating the occurrences of ice ages. This picture has
been recently shown to be supported by various data (Shaviv, 2001). In
particular, the variable CRF recorded in Iron meteorites appears to vary
synchronously with the appearance ice ages.
  Here we expand upon the original treatment with a more thorough analysis and
more supporting evidence. In particular, we discuss the cosmic ray diffusion
model which considers the motion of the Galactic spiral arms. We also elaborate
on the structure and dynamics of the Milky Way's spiral arms. In particular, we
bring forth new argumentation using HI observations which imply that the
galactic spiral arm pattern speed appears to be that which fits the glaciation
period and the cosmic-ray flux record extracted from Iron meteorites. In
addition, we show that apparent peaks in the star formation rate history, as
deduced by several authors, coincides with particularly icy epochs, while the
long period of 1 to 2 Gyr before present, during which no glaciations are known
to have occurred, coincides with a significant paucity in the past star
formation rate.",0209252v1
2002-11-07,Gamma-Ray Bursts in Pulsar Wind Bubbles: Putting the Pieces Together,"We present the main observational features expected for GRBs that occur
inside pulsar wind bubbles (PWBs). This is the most natural outcome of
supranova model where initially a supernova explosion takes place, leaving a
supra-massive NS, which loses its rotational energy over a time t_sd and
collapses to a BH, triggering a GRB explosion. We find that the time delay t_sd
between the supernova and GRB events is the most important parameter that
determines the behavior of the system. We consider the afterglow, prompt GRB
and direct emission from the PWB. The observational signatures for different
t_sd are described and joined together into one coherent framework. Constraints
on the model are derived for a spherical PWB, from the lack of detection of the
PWB emission and afterglow observations. For very low values of t_sd<1 hr the
supranova model reduces to the collapsar model; 0.4<t_sd/1yr<1 is required to
produce the iron lines seen in some X-ray afterglows. However, we find that for
a spherical PWB, this implies no detectable radio afterglow, a small jet break
time and non-relativistic transition time, in disagreement with observations
for some of these GRBs. These discrepancies with the observations may be
reconciled by resorting to a non-spherical geometry. We find that light element
lines, recently detected in a few X-ray afterglows, are expected to dominate
over iron lines for small t_sd, while for large t_sd the situation is reversed.
Finally, we predict that external Compton scattering of the PWB photons by the
afterglow relativistic electrons, should lead to high energy emission during
the early afterglow that may explain the GeV photons detected by EGRET in some
GRBs, and should be detectable by future missions (GLAST).",0211136v1
2002-11-20,Magnetic Field in Supernovae,"A relatively modest value of the initial rotation of the iron core, a period
of ~ 6-31 s, will give a very rapidly rotating protoneutron star and hence
strong differential rotation with respect to the infalling matter. Under these
conditions, a seed field is expected to be amplified by the MRI and to grow
exponentially. Exponential growth of the field on the time scale Omega^{-1} by
the magnetorotational instability (MRI) will dominate the linear growth process
of field line ""wrapping"" with the same characteristic time. The shear is
strongest at the boundary of the newly formed protoneutron star. Modest initial
rotation velocities of the iron core result in sub-Keplerian rotation and a
sub-equipartition magnetic field that nevertheless produce substantial MHD
luminosity and hoop stresses: saturation fields of order 10^{15} - 10^{16} G
develop ~ 300 msec after bounce with an associated MHD luminosity of ~ 10^{49}
- 10^{53} erg s^{-1}. Bi-polar flows driven by this MHD power can affect or
even cause the explosions associated with core-collapse supernovae. If the
initial rotation is too slow, then there will not be enough rotational energy
to power the supernova despite the high luminosities. The MRI should be active
and may qualitatively alter the flow if a black hole forms directly or after a
fall-back delay.",0211458v1
2002-12-27,Iron is not Depleted in High-Ionization Nuclear Emission-Line Regions of Active Galactic Nuclei,"In order to examine whether or not high-ionization nuclear emission-line
regions (HINERs) in narrow-line regions of active galactic nuclei are dusty, we
focus on two high-ionization forbidden emission lines, [Fe VII]6087 and [Ne
V]3426. We perform photoionization model calculations to investigate possible
dependences of the flux ratio of [Fe VII]6087/[Ne V]3426 on various gas
properties, in order to investigate how useful this flux ratio to explore the
dust abundances in HINERs. Based on our photoionization model calculations, we
show that the observed range of the flux ratio of [Fe VII]6087/[Ne V]3426 is
consistent with the dust-free models while that is hard to be explained by the
dusty models. This suggests that iron is not depleted at HINERs, which implies
that the HINERs are not dusty. This results is consistent with the idea that
the HINERs are located closer than the dust-sublimation radius (i.e., inner
radius of dusty tori) and thus can be hidden by dusty tori when seen from a
edge-on view toward the tori, which has been also suggested by the AGN-type
dependence of the visibility of high-ionization emission lines.",0212546v1
2003-02-26,Atomic data from the Iron Project. LIII. Relativistic allowed and forbidden transition probabilities for Fe XVII,"An extensive set of fine structure levels and corresponding transition
probabilities for allowed and forbidden transitions in Fe XVII is presented. A
total of 490 bound energy levels of Fe XVII of total angular momenta 0 <= J <=
7 of even and odd parities with 2 <= n <= 10, 0 <= l <= 8, 0 <= L <= 8, and
singlet and triplet multiplicities, are obtained. They translate to over 2.6 x
10^4 allowed (E1) transitions that are of dipole and intercombination type, and
about 3000 forbidden transitions that include electric quadrupole (E2),
magnetic dipole (M1), electric octopole (E3), and magnetic quadrupole (M2) type
representing the most detailed calculations to date for the ion. Oscillator
strengths f, line strengths S, and coefficients A of spontaneous emission for
the E1 type transitions are obtained in the relativistic Breit-Pauli R-matrix
approximation. A valus for the forbidden transitions are obtained from atomic
structure calculations using codes SUPERSTRUCTURE and GRASP. The energy levels
are identified in spectroscopic notation with the help of a newly developed
level identification algorithm. Nearly all 52 spectroscopically observed levels
have been identified, their binding energies agreeing within 1% with our
calculation. Computed transition probabilities are compared with other
calculations and measurement. The effect of 2-body magnetic terms and other
interactions is discussed. Present data set enhances by more than an order of
magnitude the heretofore available data for the transition probabilities of Fe
XVII.",0302561v1
2003-04-08,BeppoSAX average spectra of Seyfert galaxies,"We have studied the average 3-200 keV spectra of Seyfert galaxies of type 1
and 2, using data obtained with BeppoSAX. The average Seyfert 1 spectrum is
well-fitted by a power law continuum with photon spectral index Gamma~1.9, a
Compton reflection component R~0.6-1 (depending on the inclination angle
between the line of sight and the reflecting material) and a high-energy cutoff
at around 200 keV; there is also an iron line at 6.4 keV characterized by an
equivalent width of 120 eV. Seyfert 2's on the other hand show stronger neutral
absorption (NH=3-4 x 10^{22} atoms cm-2) as expected but are also characterized
by an X-ray power law which is substantially harder (Gamma~1.75) and with a
cut-off at lower energies (E_c~130 keV); the iron line parameters are instead
substantially similar to those measured in type 1 objects. There are only two
possible solutions to this problem: to assume more reflection in Seyfert 2
galaxies than observed in Seyfert 1 or more complex absorption than estimated
in the first instance. The first possibility is ruled out by the Seyfert 2 to
Seyfert 1 ratio while the second provides an average Seyfert 2 intrinsic
spectrum very similar to that of the Seyfert 1. The extra absorber is likely an
artifact due to summing spectra with different amounts of absorption, althought
we cannot exclude its presence in at least some individual sources. Our result
argues strongly for a very similar central engine in both type of galaxies as
expected under the unified theory.",0304133v1
2003-04-26,Hot HB stars in globular clusters - Physical parameters and consequences for theory. VI. The second parameter pair M 3 and M 13,"We present the results of spectroscopic analyses of hot horizontal branch
(HB) stars in M 13 and M 3, which form a famous ``second parameter'' pair. From
the spectra and Stroemgren photometry we derived -- for the first time in M 13
-- atmospheric parameters (effective temperature and surface gravity). For
stars with Stroemgren temperatures between 10,000 and 12,000 K we found
excellent agreement between the atmospheric parameters derived from Stroemgren
photometry and those derived from Balmer line profile fits. However, for cooler
stars there is a disagreement in the parameters derived by the two methods, for
which we have no satisfactory explanation. Stars hotter than 12,000 K show
evidence for helium depletion and iron enrichment, both in M 3 and M 13.
Accounting for the iron enrichment substantially improves the agreement with
canonical evolutionary models, although the derived gravities and masses are
still somewhat too low. This remaining discrepancy may be an indication that
scaled-solar metal-rich model atmospheres do not adequately represent the
highly non-solar abundance ratios found in blue HB stars affected by diffusion.
We discuss the effects of an enhancement in the envelope helium abundance on
the atmospheric parameters of the blue HB stars, as might be caused by deep
mixing on the red giant branch or primordial pollution from an earlier
generation of intermediate mass asymptotic giant branch stars.",0304475v1
2003-05-24,A New Population of Old Stars,"We report the results of a coherent study of three chemically anomalous
metal-poor ([Fe/H] ~ -2) stars. These objects exhibit unusually low abundances
of Mg, Si, Ca (alpha-elements) and Sr, Y, and Ba (neutron-capture elements).
Our analyses confirm and expand upon earlier reports of atypical abundances in
BD+80~245, G4-36, and CS22966-043. We also find that the latter two stars
exhibit enhanced abundances of Cr, Mn, Ni, and Zn (iron-peak elements), along
with what appears to be large abundances of Ga, with respect to the abundance
of iron. Comparing the chemical abundances of these stars to supernova model
yields, we derive supernovae ratios of Type Ia versus Type II events in the
range of 0.6 <= (N_Ia/N_II) <= 1.3. Whereas, for the Sun, we derive supernovae
ratios in good agreement with those found in the literature: 0.18 +/- 0.01 <
(N_Ia/N_II)_sun < 0.25 +/- 0.06. Given the relatively low metallicity and high
(N_Ia/N_II) ratios of the low-alpha stars studied here, these objects may have
witnessed, or been born from material produced in the yields of the earliest
supernova Type Ia events.",0305479v1
2003-06-26,An intense and broad FeKalpha line observed in the X-ray luminous quasar Q0056-363 with XMM-Newton,"We present an XMM-Newton observation of the radio-quiet quasar Q0056-363
(z=0.162). This is the first time that this quasar is observed in the hard
X-ray range (above 2 keV). We find that Q0056-363 is a powerful X-ray quasar,
with a 0.3-12 keV unabsorbed luminosity of about 1.2 x 10^45 erg s-1 with the
largest part (~67%) emitted below 2 keV. The spectrum reveals a large
featureless soft X-ray excess below 2 keV and a strong broad FeKalpha line at
6.4 keV (in the quasar frame). The FeK alpha line is due to low to moderate
ionization states of iron (i.e., < Fe XVII), with an equivalent width of about
250 eV and a velocity width of about 25,000 km s-1. Q0056-363 is presently the
most luminous AGN known to exhibit such a broad and intense FeKalpha line
profile from near neutral iron. The line can be fitted with a relativistic
profile from an accretion disc around either a Schwarzschild (non-rotating) or
a Kerr (rotating) black hole. A combination of two thermal Comptonization
components and a disc reflection model is favored to explain both the continuum
over the energy range 0.3-12 keV and the FeK alpha line. A patchy corona
covering a large part of the inner disc surface is needed in order to be
compatible with the accretion rate inferred from the spectral energy
distribution of Q0056-363, unless the mass of the black hole is much higher
than about 5 x 10^8 M_odot.",0306550v1
2003-08-05,The hard X-ray view of the low-luminosity blazar in the radio galaxy NGC6251,"We present results from a BeppoSAX (July 2001) observation of the FRI radio
galaxy NGC6251, together with a re-analysis of archival ASCA (October 1994) and
Chandra (September 2000) data. The weak detection above 10 keV and the lack of
iron fluorescent K-alpha emission lines in the BeppoSAX spectrum rule out that
the bulk of the X-ray emission is due to an obscured Seyfert nucleus. The study
of the multiwavelength spectral energy distribution suggests instead that
X-rays probably originate as inverse-Compton of synchrotron seed photons in a
relativistic jet, indicating that NGC6251 hosts a low radio luminosity [L(5
GHz) ~10^40 erg/s] blazar. The BeppoSAX spectrum is flatter than in the earlier
ASCA observation. This might be due to the emergence of a different spectral
component during phases of lower X-ray flux. In this context, we discuss some
possible explanations for the intense and mildly-ionized fluorescent iron line
measured by ASCA.",0308076v3
2003-08-11,The XMM/BeppoSAX observation of Mkn 841,"Mkn 841 has been observed simultaneously by XMM and BeppoSAX in January 2001.
Due to operational contingency, the 30ks XMM observation was split into two
parts, separated by about 15 hours. We first report the presence of a narrow
iron line which appears to be rapidly variable between the two pointings,
requiring a non-standard interpretation. We then focus on the analysis of the
broad band (0.3-200 keV) continuum using the XMM/EPIC, RGS and SAX/PDS data.
The Mkn 841 spectrum is well fitted by a comptonization model in a geometry
more photon-fed than a simple slab geometry above a passive disk. It presents a
relatively large reflection (R>2) which does not agree with an apparently weak
iron line. It also show the presence of a strong soft excess wellfitted by a
comptonized spectrum in a cool plasma, suggesting the presence of a
multi-temperature corona.",0308176v1
2003-09-15,The X-ray spectra of the flaring and quiescent states of AT Microscopii observed by XMM-Newton,"The X-ray spectrum of the late-type M-dwarf binary AT Mic (dM4.5e+dM4.5e) is
observed in the wavelength range 1 - 40 Angstrom by means of rgs and epic-mos
on board XMM-Newton. During the exposure a flare occured. We have performed a
3-temperature fit and a DEM-modeling to the flaring and quiescent part of the
spectrum. We report the coronal temperature distribution, emission measures,
and abundances of the flaring and quiescent state of this bright X-ray source.
The temperature range stretches from about 1 to 60 MK. The total volume
emission measure in this temperature interval is ~12.2*10^51 cm^-3 for the
quiescent state and ~19.5*10^51 cm^-3 for the flare state. This difference is
due to the contribution of the hot temperature component. The high-resolution
spectrum of AT Mic, obtained by rgs, is dominated by the H- and He-like
transitions of C, N, O, and Ne and by Fe XVII lines, produced by the plasma
with temperatures from 1 to 10 MK. The epic-mos spectrum below 10 Angstrom
shows H- and He-like Ne, Si and the iron K-shell transitions. They are produced
by the hot component (30 MK). The iron K-shell is more prominent in the flare
state. The abundance pattern in the quiescent state of AT Mic shows the
depletion of low-FIP elements relative to high-FIP elements, indicating the
presence of an I(nverse)FIP effect in this active star. In the flare state,
however, some flattening of this IFIP effect is present.",0309383v1
2003-09-16,Timing and spectral studies of LMC X-4 in high and low states with Beppo-SAX: Detection of pulsations in the soft spectral component,"We report here detailed timing and spectral analysis of two Beppo-SAX
observations of the binary X-ray pulsar LMC X-4 carried out during the low and
high states of its 30.5 days long super-orbital period. Timing analysis clearly
shows 13.5 s X-ray pulsations in the high state of the super-orbital period
which allows us to measure the mid-eclipse time during this observation.
Combining this with two other mid-eclipse times derived earlier with the ASCA,
we derived a new estimate of the orbital period derivative. Pulse-phase
averaged spectroscopy in the high and low states shows that the energy spectrum
in the 0.1 - 10 keV band comprises of a hard power-law, a soft excess, and a
strong iron emission line. The continuum flux is found to decrease by a factor
of ~ 60 in the low state while the decrease in the iron line flux is only by a
factor of ~ 12, suggesting a different site for the production of the line
emission. In the low state, we have not found any significant increase in the
absorption column density. The X-ray emission is found to come from a very
large region, comparable to the size of the companion star. Pulse phase
resolved spectroscopy in the high state shows a pulsating nature of the soft
spectral component with some phase offset compared to the hard X-rays, as is
known in some other binary X-ray pulsars.",0309431v1
2003-09-19,The photospheric abundances of active binaries II. Atmospheric parameters and abundance patterns for 6 single-lined RS CVn systems,"Photospheric parameters and abundances are presented for a sample of
single-lined chromospherically active binaries from a differential LTE analysis
of high-resolution spectra. Abundances have been derived for 13 chemical
species, including several key elements such as Li, Mg, and Ca. Two methods
have been used. The effective temperatures, surface gravities and
microturbulent velocities were first derived from a fully self-consistent
analysis of the spectra, whereby the temperature is determined from the
excitation equilibrium of the Fe I lines. The second approach relies on
temperatures derived from the (B-V) colour index. These two methods give
broadly consistent results for the stars in our sample, suggesting that the
neutral iron lines are formed under conditions close to LTE. We discuss the
reliability in the context of chromospherically active stars of various colour
indices used as temperature indicators, and conclude that the (V-R) and (V-I)
colours are likely to be significantly affected by activity processes.
Irrespective of the method used, our results indicate that the X-ray active
binaries studied are not as metal poor as previously claimed, but are at most
mildly iron-depleted relative to the Sun (-0.41<[Fe/H]<+0.11). A significant
overabundance of several chemical species is observed (e.g., the
alpha-synthezised elements). These abundance patterns are discussed in relation
to stellar activity.",0309535v1
2003-10-09,BeppoSAX observations of Seyfert 1s in the Piccinotti sample I: poorly studied sources,"In this work we present the first of two papers devoted to the study of the
X-ray spectral characteristics of Seyfert 1 galaxies in the Piccinotti sample.
In particular we analyse here the BeppoSAX broad band (0.1-100 keV) data of 4
objects which, despite their X-ray brightness, have been historically poorly
studied due to their late identification with an AGN; these are H0111-149
(MKN1152), H0235-525 (ESO198-G24), H0557-385 (IRAS F05563-3820) and H1846-786
(IRAS F18389-7834). We have assumed for all the sources a baseline model which
includes a power law with an exponential cut-off plus a reflection component
and an iron K_alpha line; we have also searched for the presence of intrinsic
absorption and/or a soft excess component. Our analysis indicates the presence
of complex absorption in two objects (H0557-385 and H0111-149) best described
by a combination of two uniform absorbers, one cold and one warm. Only in one
source, H0557-385, a soft excess component has been measured. The primary
continuum is best described by a canonical power law (Gamma=1.7-2) with a high
energy cut-off in the range 40-130 keV. A cold reflection component is likely
present in all sources with values ranging from less than 0.6 to higher than 2.
In 3 out of 4 objects we find a cold iron line having equivalent width typical
of Seyfert 1s (100-200 eV).",0310248v1
2003-10-22,A Method for energy estimation and mass composition determination of primary cosmic rays at Chacaltaya observation level based on atmospheric Cerenkov light technique,"A new method for energy and mass composition estimation of primary cosmic ray
radiation based on atmospheric Cerenkov light flux in extensive air showers
(EAS) analysis is proposed. The Cerenkov light flux in EAS initiated by primary
protons and iron nuclei is simulated with CORSIKA 5.62 code for Chacaltaya
observation level (536 g/cm2) in the energy range 10 TeV - 10 PeV. An adequate
model, approximation of lateral distribution of Cerenkov light in showers is
obtained. Using the proposed model and solution of overdetermined system of
nonlinear equations based on Gauss Newton method with autoregularization, two
different array detector arrangements are compared. The detector response for
the detector sets is simulated. The accuracies in energy and shower axis
determination are studied and the corresponding selection criteria are
proposed. An approximation with nonlinear fit is obtained and the energy
dependence of the proposed model function parameters is studied. The
approximation of model parameters as function of the primary energy is carried
out. This permits, taking into account the properties of the proposed method
and model, to distinguish proton primaries from iron primaries. The detector
response for the detector sets is simulated and the accuracies in energy
determination are calculated. Moreover the accuracies in shower axis
determination are studied and criteria in shower axis position estimation are
proposed.",0310651v2
2003-11-20,"A long, hard look at MCG-6-30-15 with XMM-Newton II: detailed EPIC analysis and modelling","The bright Seyfert 1 galaxy MCG-6-30-15 has provided some of the best
evidence to date for the existence of supermassive black holes in active
galactic nuclei. Observations with ASCA revealed an X-ray iron line profile
shaped by strong Doppler and gravitational effects. In this paper the shape of
the iron line, its variability characteristics and the robustness of this
spectral interpretation are examined using the long XMM-Newton observation
taken in 2001. A variety of spectral models, both including and excluding the
effects of strong gravity, are compared to the data in a uniform fashion. The
results strongly favour models in which the spectrum is shaped by emission from
a relativistic accretion disc. It is far more difficult to explain the 3-10 keV
spectrum using models dominated by absorption (either by warm or partially
covering cold matter), emission line blends, curved continua or additional
continuum components. These provide a substantially worse fit to the data and
fail to explain other observations (such as the simultaneous BeppoSAX
spectrum). This reaffirms the veracity of the relativistic `disc line'
interpretation. The short term variability in the shape of the energy spectrum
is investigated and explained in terms of a two-component emission model. Using
a combination of spectral variability analyses the spectrum is successfully
decomposed into a variable power-law component (PLC) and a reflection dominated
component (RDC). The former is highly variable while the latter is
approximately constant throughout the observation, leading to the well-known
spectral variability patterns. (Abridged)",0311473v1
2004-01-09,Theoretical FeI/II/III Emission-Line Strengths from Active Galactic Nuclei with Broad-Line Regions,"We present theoretical iron emission line strengths for physical conditions
typical of Active Galactic Nuclei with Broad-Line Regions. The non-local
thermodynamic equilibrium (NLTE) models include a new and extensive treatment
of radiative transfer in the FeIII ion, complementing the FeII emission line
strengths predicted in our earlier works. We also briefly present preliminary
results for the FeI emission from AGN using a reduced atom model. We can
satisfactorily reproduce the empirical UV FeIII emission line template of
Vestergaard & Wilkes (2001) for the prototypical narrow-line Seyfert 1 galaxy I
Zw 1, both in terms of the general FeIII flux distribution and the relative
strength of the FeIII and FeII emission. However, a number of detailed features
are still not matched; the most prominent example is the strongest single FeIII
feature observed in the I Zw 1 spectrum, UV47: it is predicted to be strong
only in models suppressing Fe-H charge exchange reactions. We examine the role
of variations in cloud turbulent velocity and iron abundance and carry out
Monte Carlo simulations to demonstrate the effect of uncertainties in atomic
data on the computed spectra.",0401168v1
2004-01-20,Nitrogen abundances in Planet-harbouring stars,"We present a detailed spectroscopic analysis of nitrogen abundances in 91
solar-type stars, 66 with and 25 without known planetary mass companions. All
comparison sample stars and 28 planet hosts were analysed by spectral synthesis
of the near-UV NH band at 3360 \AA observed at high resolution with the
VLT/UVES,while the near-IR NI 7468 \AA was measured in 31 objects. These two
abundance indicators are in good agreement. We found that nitrogen abundance
scales with that of iron in the metallicity range -0.6 <[Fe/H]< +0.4 with the
slope 1.08 \pm 0.05. Our results show that the bulk of nitrogen production at
high metallicities was coupled with iron. We found that the nitrogen abundance
distribution in stars with exoplanets is the high [Fe/H] extension of the curve
traced by the comparison sample of stars with no known planets. A comparison of
our nitrogen abundances with those available in the literature shows a good
agreement.",0401396v1
2004-02-09,The Toroidal Iron Atmosphere of a Protoneutron Star: Numerical Solution,"A numerical method presented by Imshennik et al. (2002) is used to solve the
two dimensional axisymmetric hydrodynamic problem on the formation of a
toroidal atmosphere during the collapse of an iron stellar core and outer
stellar layers. An evolutionary model from Boyes et al. (1999) with a total
mass of $25M_{\odot}$ is used as the initial data for the distribution of
thermodynamic quantities in the outer shells of a high-mass star. We analyze in
detail the results of three calculations in which the difference mesh and the
location of the inner boundary of the computational region are varied. In the
initial data, we roughly specify an angular velocity distribution that is
actually justified by the final result - the formation of a hydrostatic
equilibrium toroidal atmosphere with reasonable total mass, $M^{tot} = (0.117
\div 0.122)M_{\odot}$, and total angular momentum, $J^{tot} = (0.445 \div
0.472) x 10^{50} erg \cdot s$, for the two main calculations. We compare the
numerical solution with our previous analytical solution in the form of
toroidal atmospheres (Imshennik and Manukovskii 2000). This comparison
indicates that they are identical if we take into account the more general and
complex equation of state with a nonzero temperature and self-gravitation
effects in the atmosphere. Our numerical calculations, first, prove the
stability of toroidal atmospheres on characteristic hydrodynamic time scales
and, second, show the possibility of sporadic fragmentation of these
atmospheres even after a hydrodynamic equilibrium is established. The
calculations were carried out under the assumption of equatorial symmetry of
the problem and up to relatively long time scales $(\approx 10s)$.",0402191v1
2004-02-10,Discovery of Soft Spectral Component and Transient 22.7s Quasi Periodic Oscillations of SAX J2103.5+4545,"XMM-Newton observed SAX J2103.5+4545 on January 6, 2003, while RXTE was
monitoring the source. Using RXTE-PCA dataset between December 3, 2002 and
January 29, 2003, the spin period and average spin-up rate during the
XMM-Newton observations were found to be $354.7940\pm0.0008$ s and
$(7.4\pm0.9)\times10^{-13}$Hz s$^{-1}$ respectively. In the power spectrum of
the 0.9-11 keV EPIC-PN lightcurve, we found quasi periodic oscillations around
0.044 Hz (22.7 s) with an rms fractional amplitude $\sim $6.6 %. We interpreted
this QPO feature as the Keplerian motion of inhomogenuities through the inner
disk. In the X-ray spectrum, in addition to the power law component with high
energy cutoff and $\sim6.4$ keV fluorescent iron emission line (Baykal et al.,
2002), we discovered a soft component consistent with a blackbody emission with
${\rm{kT}}\sim1.9$keV. The pulse phase spectroscopy of the source revealed that
the blackbody flux peaked at the peak of the pulse with an emission radius
$\sim 0.3$ km, suggesting the polar cap on the neutron star surface as the
source of blackbody emission. The flux of the iron emission line at $\sim 6.42$
keV was shown to peak at the off-pulse phase, supporting the idea that this
feature arises from fluorescent emission of the circumstellar material around
the neutron star rather than the hot region in the vicinity of the neutron star
polar cap.",0402221v2
2004-02-13,The high energy X-ray tail of Eta Car revealed by BeppoSAX,"We report on the June 2000 long (100 ks) BeppoSAX exposure that has unveiled
above 10 keV a new very high energy component of the X-ray spectrum of Eta Car
extending to at least 50 keV. We find that the 2-150 keV spectrum is best
reproduced by a thermal + non-thermal model. The thermal component dominates
the 2-10 keV spectral range with kT_h=5.5 +/- 0.3 keV and log NH_h=22.68 +/-
0.01. The spectrum displays a prominent iron emission line centred at 6.70 keV.
Its equivalent width of 0.94 keV, if produced by the thermal source, gives a
slightly sub-solar iron abundance ([Fe/H]=-0.15 +/- 0.02).
  The high energy tail above 10 keV is best fitted by a power law with a photon
index of 2.42 +/- 0.04. The integrated 13-150 keV luminosity of ~12 L-sun is
comparable to that of the 2-10 keV thermal component. The present result can be
explained, in the Eta Car binary star scenario, by Comptonisation of low
frequency radiation by high energy electrons, probably generated in the
colliding wind shock front, or in instabilities in the wind of the S Dor
primary star. It is possible that the high energy tail had largely weakened
near the minimum of the 5.53 yr cycle. With respect to the thermal component,
it probably has a longer recovering time like that of the highest excitation
optical emission lines. Both features can be associated with the large
absorption measured by BeppoSAX at phase 0.05.",0402329v1
2004-03-03,XMM-Newton Observations of NGC 507: Super-solar Metal Abundances in the Hot ISM,"We present the results of the X-ray XMM-Newton observations of NGC 507, a
dominant elliptical galaxy in a small group of galaxies, and report
'super-solar' metal abundances of both Fe and a-elements in the hot ISM of this
galaxy. We find Z_Fe = 2-3 times solar inside the D25 ellipse of NGC 507. This
is the highest Z_Fe reported so far for the hot halo of an elliptical galaxy;
this high Iron abundance is fully consistent with the predictions of stellar
evolution models, which include the yield of both type II and Ia supernovae.
The spatially resolved, high quality XMM spectra provide enough statistics to
formally require at least three emission components: two soft thermal
components indicating a range of temperatures in the hot ISM, plus a harder
component, consistent with the integrated output of low mass X-ray binaries
(LMXBs). The abundance of a-elements (most accurately determined by Si) is also
found to be super-solar. The a-elements to Fe abundance ratio is close to the
solar ratio, suggesting that ~70% of the Iron mass in the hot ISM was
originated from SNe Type Ia. The a-element to Fe abundance ratio remains
constant out to at least 100 kpc, indicating that SNe Type II and Ia ejecta are
well mixed in a scale much larger than the extent of the stellar body.",0403105v2
2004-03-10,Far-UV Spectroscopic Analyses of Four Central Stars of Planetary Nebulae,"We analyze the Far-UV/UV spectra of four central stars of planetary nebulae
with strong wind features -- NGC 2371, Abell 78, IC 4776 and NGC 1535, and
derive their photospheric and wind parameters by modeling high-resolution FUSE
(Far-Ultraviolet Spectroscopic Explorer) data in the Far-UV and HST-STIS and
IUE data in the UV with spherical non-LTE line-blanketed model atmospheres.
Abell 78 is a hydrogen-deficient transitional [WR]-PG 1159 object, and we find
NGC 2371 to be in the same stage, both migrating from the constant-luminosity
phase to the white dwarf cooling sequence with Teff ~= 120 kK, Mdot ~= 5x10^-8
Msun/yr. NGC 1535 is a ``hydrogen-rich'' O(H) CSPN, and the exact nature of IC
4776 is ambiguous, although it appears to be helium burning. Both objects lie
on the constant-luminosity branch of post-AGB evolution and have Teff ~= 65 kK,
Mdot ~= 1x10^-8 Msun/yr. Thus, both the H-rich and H-deficient channels of PN
evolution are represented in our sample. We also investigate the effects of
including higher ionization stages of iron (up to FeX) in the model atmosphere
calculations of these hot objects (usually neglected in previous analyses), and
find iron to be a useful diagnostic of the stellar parameters in some cases.
The Far-UV spectra of all four objects show evidence of hot (T ~ 300 K)
molecular hydrogen in their circumstellar environments.",0403262v1
2004-04-15,"Iron abundances from high-resolution spectroscopy of the open clusters NGC 2506, NGC 6134, and IC 4651","This is the first of a series of papers devoted to derive the metallicity of
old open clusters in order to study the time evolution of the chemical
abundance gradient in the Galactic disk. We present detailed iron abundances
from high resolution (R~40000) spectra of several red clump and bright giant
stars in the open clusters IC 4651, NGC 2506 and NGC 6134. We observed 4 stars
of NGC 2506, 3 stars of NGC 6134, and 5 stars of IC 4651 with the FEROS
spectrograph at the ESO 1.5 m telescope; moreover, 3 other stars of NGC 6134
were observed with the UVES spectrograph on Kueyen (VLT UT2). After excluding
the cool giants near the red giant branch tip (one in IC 4651 and one in NGC
2506), we found overall [Fe/H] values of -0.20 +/- 0.01, rms = 0.02 dex (2
stars) for NGC 2506, +0.15 +/- 0.03, rms = 0.07 dex (6 stars) for NGC 6134, and
+0.11 +/- 0.01, rms = 0.01 dex (4 stars) for IC 4651. The metal abundances
derived from line analysis for each star were extensively checked using
spectrum synthesis of about 30 to 40 Fe I lines and 6 Fe II lines. Our
spectroscopic temperatures provide reddening values in good agreement with
literature data for these clusters, strengthening the reliability of the
adopted temperature and metallicity scale. Also, gravities from the Fe
equilibrium of ionization agree quite well with expectations based on cluster
distance moduli and evolutionary masses.",0404298v1
2004-05-19,Where Did The Moon Come From?,"The current standard theory of the origin of the Moon is that the Earth was
hit by a giant impactor the size of Mars causing ejection of iron poor impactor
mantle debris that coalesced to form the Moon. But where did this Mars-sized
impactor come from? Isotopic evidence suggests that it came from 1AU radius in
the solar nebula and computer simulations are consistent with it approaching
Earth on a zero-energy parabolic trajectory. But how could such a large object
form in the disk of planetesimals at 1AU without colliding with the Earth
early-on before having a chance to grow large or before its or the Earth's iron
core had formed? We propose that the giant impactor could have formed in a
stable orbit among debris at the Earth's Lagrange point $L_4$ (or $L_5$). We
show such a configuration is stable, even for a Mars-sized impactor. It could
grow gradually by accretion at $L_4$ (or $L_5$), but eventually gravitational
interactions with other growing planetesimals could kick it out into a chaotic
creeping orbit which we show would likely cause it to hit the Earth on a
zero-energy parabolic trajectory. This paper argues that this scenario is
possible and should be further studied.",0405372v2
2004-05-27,High resolution X-ray spectra of quasars,"Past X-ray observations by ASCA suggest that warm absorbers (O VII and O VIII
edges) are apparently rare in high luminosity AGNs (quasars) while they are
more common in low luminosity AGNs (Seyferts). However, this could be a
selection effect if high luminosity AGNs have mostly narrow absorption lines
(with no strong bound free edges), which escaped detection by the low
resolution of ASCA. To check this hypothesis we are studying the
high-resolution X-ray spectra of quasars from grating spectrometers on board
Chandra and XMM-Newton in search for absorption lines. In this contribution we
present spectra of three quasars. The spectra show narrow (several hundred
km/s) absorption and emission X-ray lines from H-like and He-like ions of O,
Ne, Mg, and other abundant elements. We also detect absorption from iron
L-shell lines and iron M-shell unresolved transition array. We present the
analysis of MR2251-178 where we find that at least two, and probably three,
distinct warm absorbers are needed to explain the high resolution spectrum of
this object. We re-analyze the high-resolution X-ray spectrum of PG1211+143 and
suggest that an outflow velocity of about 3000 km/s provides an adequate
explanation to these data. We also present preliminary results form the
Chandra/HETGS observation of the quasar 4C74.26.",0405563v1
2004-06-11,Intracluster Stars and the Chemical Enrichment of the Intracluster Medium,"We explore the contribution of intracluster stars (ICS) to the chemical
enrichment history of the intracluster medium (ICM). In contrast to scenarios
in which all the metals originate in cluster galaxies and are then transported
into the ICM, intracluster stars enrich the ICM in situ, thereby contributing
100% of their supernovae ejecta directly into the ICM. Modeling the ICS as an
ancient, single burst stellar population with a normal initial mass function,
we generate ICM iron abundances in the range of the observed values of several
tenths solar. Large observational and theoretical uncertainties preclude us
from concluding that the intracluster stars are the primary contributor of
metals to the ICM in general. However, for the two clusters in our sample, and
one from the literature, for which all of the required observational
constraints exist, we are able to reproduce between half and all of the ICM
iron. Due to the ubiquity of intracluster stars in clusters and their direct
connection with the ICM, we conclude that all models of the chemical enrichment
history and energy budget of the ICM should account for the impact of the ICS.",0406291v2
2004-07-19,The Origin of Fe II Emission in AGN,"We used a very large set of models of broad emission line (BEL) clouds in AGN
to investigate the formation of the observed Fe II emission lines. We show that
photoionized BEL clouds cannot produce both the observed shape and observed
equivalent width of the 2200-2800A Fe II UV bump unless there is considerable
velocity structure corresponding to a microturbulent velocity parameter v_turb
> 100 km/s for the LOC models used here. This could be either microturbulence
in gas that is confined by some phenomenon such as MHD waves, or a velocity
shear such as in the various models of winds flowing off the surfaces of
accretion disks. The alternative way that we can find to simultaneously match
both the observed shape and equivalent width of the Fe II UV bump is for the Fe
II emission to be the result of collisional excitation in a warm, dense gas.
Such gas would emit very few lines other than Fe II. However, since the
collisionally excited gas would constitute yet another component in an already
complicated picture of the BELR, we prefer the model involving turbulence. In
either model, the strength of Fe II emission relative to the emission lines of
other ions such as Mg II depends as much on other parameters (either v_turb or
the surface area of the collisionally excited gas) as it does on the iron
abundance. Therefore, the measurement of the iron abundance from the FeII
emission in quasars becomes a more difficult problem.",0407404v1
2004-07-29,A Study of the Composition of Ultra High Energy Cosmic Rays Using the High Resolution Fly's Eye,"The composition of Ultra High Energy Cosmic Rays (UHECR) is measured with the
High Resolution Fly's Eye cosmic ray observatory (HiRes) data using the Xmax
technique. Data were collected in stereo between 1999 November and 2001
September. The data are reconstructed with well-determined geometry.
Measurements of the atmospheric transmission are incorporated in the
reconstruction. The detector resolution is found to be 30 g cm^-2 in Xmax and
13% in Energy. The Xmax elongation rate between 10^18.0 eV and 10^19.4 eV is
measured to be 54.5 +/- 6.5 (stat) +/- 4.5 (sys) g cm^-2 per decade. This is
compared to predictions using the QGSJet01 and SIBYLL 2.1 hadronic interaction
models for both protons and iron nuclei. CORSIKA-generated Extensive Air
Showers (EAS) are incorporated directly into a detailed detector Monte Carlo
program. The elongation rate and the Xmax distribution widths are consistent
with a constant or slowly changing and predominantly light composition. A
simple model containing only protons and iron nuclei is compared to QGSJet and
SIBYLL. The best agreement between the model and the data is at 80% protons for
QGSJet and 60% protons for SIBYLL.",0407622v3
2004-08-27,The metal enrichment of the intracluster medium in hierarchical galaxy formation models,"We investigate the metal enrichment of the intracluster medium (ICM) in the
framework of hierarchical models of galaxy formation. We calculate the
formation and evolution of galaxies and clusters using a semi-analytical model
which includes the effects of flows of gas and metals both into and out of
galaxies. For the first time in a semi-analytical model, we calculate the
production of both alpha and iron-peak elements based on theoretical models for
the lifetimes and ejecta of type Ia and type II supernovae (SNe Ia and SNe II).
It is essential to include the long lifetimes of the SNIa progenitors in order
to correctly model the evolution of the iron-peak elements. We find that if all
stars form with an IMF similar to that found in the solar neighbourhood, then
the metallicities of O, Mg, Si and Fe in the ICM are predicted to be 2-3 times
lower than observed values. In contrast, a model (also favoured on other
grounds) in which stars formed in bursts triggered by galaxy mergers have a
top-heavy IMF reproduces the observed ICM abundances of O, Mg, Si and Fe. The
same model predicts ratios of ICM mass to total stellar luminosity in clusters
which agree well with observations. According to our model, the bulk of the
metals in clusters are produced by L* and brighter galaxies. [abridged]",0408529v2
2004-09-02,Orbital Phase Spectroscopy of GX 301--2 with RXTE-PCA,"We have investigated the orbital phase dependence of the X-ray spectrum of
the High Mass X-ray Binary pulsar GX 301--2. Here we present the results from a
spectral analysis of two sets of observations of GX 301--2 with the Rossi X-ray
Timing Explorer (RXTE). Of particular interest are the variations of the
absorption column density and the iron line flux along with other parameters of
the spectral model with the orbital phase. We found that the X-ray spectrum can
almost always be fitted with a partial covering absorption model. We have
detected enhanced absorption near the periastron. However, the column density
variation with orbital phase is not smooth, as is expected in a smooth stellar
wind model. We discuss the results of the column density variation in the light
of the two proposed models for GX 301-2, an equatorial disk emanating from the
companion star Wray 977 and a gas stream following the neutron star. We also
found that the iron K_alpha and K_beta line fluxes have peaks near the
periastron and are well correlated with the continuum hard X-ray flux. The line
equivalent width shows an interesting pattern with the column density,
reasonably constant for low values of the column density and increasing rapidly
beyond a certain value.",0409056v1
2004-09-17,Presupernova Evolution of Differentially Rotating Massive Stars Including Magnetic Fields,"As a massive star evolves through multiple stages of nuclear burning on its
way to becoming a supernova, a complex, differentially rotating structure is
set up. Angular momentum is transported by a variety of classic instabilities,
and also by magnetic torques from fields generated by the differential
rotation. We present the first stellar evolution calculations to follow the
evolution of rotating massive stars including, at least approximately, all
these effects, magnetic and non-magnetic, from the zero-age main sequence until
the onset of iron-core collapse. The evolution and action of the magnetic
fields is as described by Spruit 2002 and a range of uncertain parameters is
explored. In general, we find that magnetic torques decrease the final rotation
rate of the collapsing iron core by about a factor of 30 to 50 when compared
with the non-magnetic counterparts. Angular momentum in that part of the
presupernova star destined to become a neutron star is an increasing function
of main sequence mass. That is, pulsars derived from more massive stars will
rotate faster and rotation will play a more dominant role in the star's
explosion. The final angular momentum of the core is determined - to within a
factor of two - by the time the star ignites carbon burning. For the lighter
stars studied, around 15 solar masses, we predict pulsar periods at birth near
15 ms, though a factor of two range is easily tolerated by the uncertainties.
Several mechanisms for additional braking in a young neutron star, especially
by fall back, are also explored.",0409422v1
2004-11-12,An XMM-Newton Observation of the Seyfert 2 Galaxy NGC 6300. I. The Nucleus,"We present results from a half-day observation by XMM-Newton of the nucleus
of the nearby Seyfert 2 galaxy NGC 6300. The X-ray spectrum of the nucleus
consists of a heavily absorbed hard component dominating the 3--10 keV band and
a soft component seen in the 0.2--2 keV band. In the hard band, the spectrum is
well fitted by a power-law model with photon index of 1.83+/-0.08 attenuated by
a Compton-thin absorber (N_H \simeq 2.2 x 10^{23} cm^{-2}). A narrow iron line
is detected at 6.43_{-0.02}^{+0.01} keV with an equivalent width of ~150 eV;
the line velocity width is marginally resolved to be \sigma~60eV. The soft
emission can be modeled as a power-law and may be emission scattered by
surrounding plasma. Rapid and high-amplitude variability is observed in the
hard X-ray band, whereas both the iron line and the soft emission show no
significant variability. It is suggested that the nucleus has experienced an
overall long-term trend of decreasing hard X-ray intensity on a timescale of
years. We discuss the origins of the spectral components.",0411328v1
2004-11-18,An XMM-Newton view of the cluster of galaxies Abell 85,"We have observed the cluster of galaxies Abell 85 with XMM-Newton. These data
have allowed us to confirm in a previous paper the existence of the extended 4
Mpc filament detected by the ROSAT PSPC in the neighbourhood of this cluster,
and to determine an X-ray temperature of about about 2 keV. We now present a
thorough analysis of the properties of the X-ray gas in the cluster itself,
including temperature and metallicity maps for the entire cluster. These
results show that Abell 85 had intense merging activity in the past and is not
fully relaxed, even in the central region. We have also determined the
individual abundances for some iron-group metals and alpha-elements in various
regions; the ratios of these metallicities to the iron abundance show that both
supernova types Ia and II must be involved in the intra-cluster gas enrichment.
Spectral analysis of the central region suggests a different redshift of the
X-ray emitting gas compared to the mean cluster velocity derived from galaxy
member redshifts. We discuss the implications of the difference between the cD
galaxy redshift, the mean galaxy redshift and the hot gas redshift, as well as
the possibility of several groups being accreted on to Abell 85. Finally, we
obtain the dynamical mass profile and baryon fraction taking into account the
new determined temperature profile. The dynamical mass in Abell 85 has a steep
density profile, similar to the ones found in N-body simulations.",0411527v1
2004-11-22,The iron $K_α$-line as a tool for an evaluation of black hole parameters,"Recent X-ray observations of microquasars and Seyfert galaxies reveal broad
emission lines in their spectra, which can arise in the innermost parts of
accretion disks. Simulations indicate that at low inclination angle the line is
measured by a distant observer as characteristic two-peak profile. However, at
high inclination angles ($> 85^0$) two additional peaks arise. This phenomenon
was discovered by Matt et al. (1993) using the Schwarzschild black hole metric
to analyze such effect. They assumed that the effect is applicable to a Kerr
metric far beyond the range of parameters that they exploited. We check and
confirm their hypothesis about such a structure of the spectral line shape for
the Kerr metric case. We use no astrophysical assumptions about the physical
structure of the emission region except the assumption that the region should
be narrow enough.
  Positions and heights of these extra peaks drastically depend on both the
radial coordinate of the emitting region (annuli) and the inclination angle. It
was found that these extra peaks arise due to gravitational lens effect in the
strong gravitational field, namely they are formed by photons with some number
of revolutions around black hole. This conclusion is based only on relativistic
calculations without any assumption about physical parameters of the accretion
disc like X-ray surface emissivity etc.
  We discuss how analysis of the iron spectral line shapes could give an
information about an upper limit of magnetic field near black hole horizon.",0411611v1
2004-12-03,How do Uncertainties in the Surface Chemical Abundances of the Sun Affect the Predicted Solar Neutrino Fluxes?,"We show that uncertainties in the values of the surface heavy element
abundances of the Sun are the largest source of the theoretical uncertainty in
calculating the p-p, pep, 8B, 13N, 15O, and 17F solar neutrino fluxes. We
evaluate for the first time the sensitivity (partial derivative) of each solar
neutrino flux with respect to the surface abundance of each element. We then
calculate the uncertainties in each neutrino flux using `conservative
(preferred)' and `optimistic' estimates for the uncertainties in the element
abundances. The total conservative (optimistic) composition uncertainty in the
predicted 8B neutrino flux is 11.6% (5.0%) when sensitivities to individual
element abundances are used. The traditional method that lumps all abundances
into a single quantity (total heavy element to hydrogen ratio, Z/X) yields a
larger uncertainty, 20%. The uncertainties in the carbon, oxygen, neon,
silicon, sulphur, and iron abundances all make significant contributions to the
uncertainties in calculating solar neutrino fluxes; the uncertainties of
different elements are most important for different neutrino fluxes. The
uncertainty in the iron abundance is the largest source of the estimated
composition uncertainties of the important 7Be and 8B solar neutrinos. Carbon
is the largest contributor to the uncertainty in the calculation of the p-p,
13N, and 15O neutrino fluxes. However, for all neutrino fluxes, several
elements contribute comparable amounts to the total composition uncertainty.",0412096v2
2004-12-09,Unusual X-ray transients in the Galactic Centre,"We report the discovery in the Galactic Centre region of two hard X-ray
sources, designated as XMM J174457-2850.3 and XMM J174544-2913.0, which
exhibited flux variations in the 2--10 keV band in excess of a factor of 100 in
observations spanning roughly a year. In both cases the observed hydrogen
column density is consistent with a location near to the Galactic Centre,
implying peak X-ray luminosities of ~5 x 10^34 erg/s. These objects may
represent a new population of transient source with very different properties
to the much more luminous Galactic Centre transients associated with neutron
star and black-hole binary systems. Spectral analysis shows that XMM
J174457-2850.3 has relatively weak iron-line emission set against a very hard
continuum. XMM J174544-2913.0, on the other hand, has an extremely strong
K-line from helium-like iron with an equivalent width of ~2.4keV. The nature of
the latter source is of particular interest. Does it represent an entirely new
class of object or does it correspond to a known class of source in a very
extreme configuration?",0412236v1
2005-01-26,The XMM-Newton view of PG quasars: II. Properties of the Fe K-alpha line,"The properties of the fluorescence Fe K-alpha emission lines of a sample of
38 quasars (QSOs) observed with XMM-Newton are studied. These objects are
included in the optically selected sample from the Palomar-Green (PG) Bright
Quasar Survey with an X-ray luminosity 1.3E43<L(2-10 keV)<5.1E45 ergs/s and
z<1.72. For each object in the sample, we investigated the presence of both
narrow and broad iron lines in detail. A total of 20 out of the 38 QSOs show
evidence of an Fe K-alpha emission line with a narrow profile. The majority of
the lines are consistent with an origin in low ionization material, which is
likely to be located in the outer parts of the accretion disk, the molecular
torus, and/or the Broad Line Region. The average properties of the narrow Fe
K-alpha emission line observed in the sample are similar to those of Seyfert
type galaxies as inferred from recent XMM-Newton and Chandra studies. A broad
line has been significantly detected in only three objects. Furthermore, we
studied the relationship between the equivalent width (EW) of the iron line and
the hard band X-ray luminosity for radio quiet quasars. The analysis indicates
that no clear correlation between the strength of the line and the hard X-ray
luminosity is present, and our results do not show compelling evidence for an
anticorrelation between these two quantities, i.e. the so-called X-ray Baldwin
effect.",0501587v1
2005-02-13,Neural Networks as a Composition Diagnostic for Ultra-high Energy Cosmic Rays,"We analyze here the possibility of studying mass composition in the Auger
data sample using neural networks as a diagnostic tool. Extensive air showers
were simulated using the AIRES code, for the two hadronic interaction models in
current use: QGSJet and Sibyll. Both, photon and hadron primaries were
simulated and used to generate events. The output parameters from the ground
array were simulated for the typical instrumental and environmental conditions
at the Malarg\""ue Auger site using the code SAMPLE. Besides photons, hydrogen,
helium, carbon, oxygen, magnesium, silicon, calcium and iron nuclei were also
simulated. We show that Principal Components Analysis alone is enough to
separate individual photon from hadron events, but the same technique cannot be
applied to the classification of hadronic events. The latter requires the use
of a more robust diagnostic. We show that neural networks are potentially
powerful enough to discriminate proton from iron events almost on an
event-by-event basis. However, in the case of a more realistic multi-component
mixture of primary nuclei, only a statistical estimate of the average mass can
be reliably obtained. Although hybrid events are not explicitly simulated, we
show that, whenever hybrid information in the form of $X_{max}$ is introduced
in the training procedure of the neural networks, a considerable improvement
can be achieved in mass discrimination analysis.",0502255v1
2005-03-01,Nucleosynthetic signatures of the first stars,"The chemically most primitive stars provide constraints on the nature of the
first stellar objects that formed in the Universe; elements other than
hydrogen, helium and traces of lithium within these objects were generated by
nucleosynthesis in the very first stars. The relative abundances of elements in
the surviving primitive stars reflect the masses of the first stars, because
the pathways of nucleosynthesis are quite sensitive to stellar masses. Several
models have been suggested to explain the origin of the abundance pattern of
the giant star HE 0107-5240, which hitherto exhibited the highest deficiency of
heavy elements known. Here we report the discovery of HE 1327-2326, a subgiant
or main-sequence star with an iron abundance about a factor of two lower than
that of HE 0107-5240. Both stars show extreme overabundances of carbon and
nitrogen with respect to iron, suggesting a similar origin of the abundance
patterns. The unexpectedly low Li and high Sr abundances of HE 1327-2326,
however, challenge existing theoretical understanding: none predicts the high
Sr abundance or provides a Li depletion mechanism consistent with data
available for the most metal-poor stars.",0503021v2
2005-04-14,Iron abundances derived from RR Lyrae light curves and low-dispersion spectroscopy,"With the aid of the All Sky Automated Survey (ASAS) database on the Galactic
field, we compare the iron abundances of fundamental mode RR Lyrae stars
derived from the Fourier parameters with those obtained from low-dispersion
spectroscopy. We show from a set of 79 stars, distinct from the original
calibrating sample of the Fourier method and selected without quality control,
that almost all discrepant estimates are the results of some defects or
peculiarities either in the photometry or in the spectroscopy. Omitting objects
deviating by more than 0.4dex, the remaining subsample of 64 stars yields
Fourier abundances that fit the spectroscopic ones with a standard deviation of
0.20dex. Other, more stringent selection criteria and different Fourier
decompositions lead to smaller subsamples and concomitant better agreement,
down to 0.16dex standard deviation. Except perhaps for two variables among the
163 stars, comprised of the ASAS variables and those of the original
calibrating set of the Fourier method, all discrepant values can be accounted
for by observational noise and insufficient data coverage. We suggest that the
agreement can be further improved when new, more accurate spectroscopic data
become available for a test with the best photometric data. As a by-product of
this analysis, we also compute revised periods and select Blazhko variables.",0504327v1
2005-04-21,Sulphur abundances in Terzan 7,"We present here the first measurements of sulphur abundances in extragalactic
stars. We make use of high resolution spectra, obtained with UVES at the ESO
8.2 m Kueyen telescope, of three giants of the Globular Cluster Terzan 7, which
belongs to the Sagittarius dwarf galaxy. We measure the sulphur abundances
using the lines of S I multiplet 1. The S/Fe ratios for all three stars are
nearly solar, thus considerably lower than what is found in Galactic stars of
comparable iron content ([Fe/H] ~ -0.50). This finding is in keeping with the
abundances of other alpha-chain elements in this cluster and in Sagittarius and
other dSphs in general. These low alpha-chain elements to iron ratios suggest
that Sagittarius and its Globular Clusters have experienced a low or bursting
star-formation rate. Our sulphur abundances imply <\log (S/O)> = -1.61 which is
comparable to what is found in many H II regions of similar oxygen content, and
is slightly lower than the solar value (log (S/O)sun = -1.51). These are also
the first measurements of sulphur abundances in a Globular Cluster, thus a
direct comparison of Terzan 7 and Galactic Globular Clusters is not possible
yet. However our analysis suggests that the lines of S I multiplet 1 should be
measurable for other Globular Clusters at least down to a metallicity ~ -1.5.",0504463v1
2005-08-02,Charge Exchange Spectra of Hydrogenic and He-like Iron,"We present H-like Fe XXVI and He-like Fe XXV charge-exchange spectra
resulting from collisions of highly charged iron with N2 gas at an energy of 10
eV/amu in an electron beam ion trap. Although individual high-n emission lines
are not resolved in our measurements, we observe that the most likely level for
Fe25+ --> Fe24+ electron capture is n~9, in line with expectations, while the
most likely value for Fe26+ --> Fe25+ charge exchange is significantly higher.
In the Fe XXV spectrum, the K-alpha emission feature dominates, whether
produced via charge exchange or collisional excitation. The K-alpha centroid is
lower in energy for the former case than the latter (6666 versus 6685 eV,
respectively), as expected because of the strong enhancement of emission from
the forbidden and intercombination lines, relative to the resonance line, in
charge-exchange spectra. In contrast, the Fe XXVI high-n Lyman lines have a
summed intensity greater than that of Ly-alpha, and are substantially stronger
than predicted from theoretical calculations of charge exchange with atomic H.
We conclude that the angular momentum distribution resulting from electron
capture using a multi-electron target gas is significantly different from that
obtained with H, resulting in the observed high-n enhancement. A discussion is
presented of the relevance of our results to studies of diffuse Fe emission in
the Galactic Center and Galactic Ridge, particularly with ASTRO-E2/Suzaku.",0508078v1
2005-08-05,The Radiative Transport of Dust in Primordial Galaxies and Second-Generation Star Formation,"We investigate the radiative transport of dust in primordial galaxies in the
presence of the UV radiation field from the first metal-free stars. We find
that dust created in the first supernova (SN) explosions can be driven through
the interior of the SN remnant to accumulate in the SN shells, where
second-generation stars may form from compressed cooling gas. This scenario
requires metal-free stars to form continuously over timescales of up to 10 Myr,
consistent with recent estimates. Silicate and graphite grains, as well as
iron-bearing magnetites, are transported to the shells for reasonable parameter
assumptions, but their relative yields from primordial SNe is an important
factor in the resulting abundance ratios. We compare the results of segregated
grain transport with the current nucleosynthetic data on extremely metal-poor
Galactic halo stars. Fossil signatures of this process may already have been
detected in those iron-poor stars with enhanced carbon and silicate elements
such as magnesium, silicon and oxygen. We discuss the implications of our
results for the transition from first- to second-generation star formation in
primordial galaxies, and the role played by the radiative transport of dust in
this process.",0508163v2
2005-08-24,XMM-Newton spectroscopy of high-redshift QSOs,"XMM-Newton observations of 29 high redshift (z>2) quasars, including seven
radio-quiet, 16 radio-loud and six Broad Absorption Line (BAL) objects, are
presented; due to the high redshifts, the rest-frame energy bands extend up to
\~30-70 keV. Over 2-10 keV, the quasars can be well fitted in each case by a
simple power-law, with no strong evidence for iron emission lines. The lack of
iron lines is in agreement both with dilution by the radio jet emission (for
the radio-loud quasars) and the X-ray Baldwin effect. No Compton reflection
humps at higher energies (i.e., above 10 keV in the rest frame) are detected
either. Over the broad-band (0.3-10 keV), approximately half (nine out of 16)
of the radio-loud quasars are intrinsically absorbed, with the values of N_H
generally being 1-2 x 10^22 cm^-2 in the rest frames of the objects. None of
the seven radio-quiet objects shows excess absorption, while four of the six
BAL quasars are absorbed. The radio-loud quasars have flatter continuum slopes
than their radio-quiet counterparts (Gamma_RL ~ 1.55; Gamma_RQ ~ 1.98 over 2-10
keV), while, after modelling the absorption, the underlying photon index for
the six BAL quasars is formally consistent with the non-BAL radio-quiet
objects.",0508524v1
2005-09-22,"The new record holder for the most iron-poor star: HE 1327-2326, a dwarf or subgiant with [Fe/H]=-5.4","We describe the discovery of HE 1327-2326, a dwarf or subgiant with
[Fe/H]}=-5.4. The star was found in a sample of bright metal-poor stars
selected from the Hamburg/ESO survey. Its abundance pattern is characterized by
very high C and N abundances. The detection of Sr which is overabundant by a
factor of 10 as compared to iron and the Sun, suggests that neutron-capture
elements had already been produced in the very early Galaxy. A puzzling Li
depletion is observed in this unevolved star which contradicts the value of the
primordial Li derived from WMAP and other Li studies. Possible scenarios for
the origin of the abundance pattern (Pop. II or Pop. III) are presented as well
as an outlook on future observations.",0509658v1
2005-10-05,IGR J16393-4643: a new heavily-obscured X-ray pulsar,"An analysis of the high-energy emission from IGR J16393-4643 (=AX
J1639.0-4642) is presented using data from INTEGRAL and XMM-Newton. The source
is persistent in the 20-40 keV band at an average flux of 5.1x10^-11
ergs/cm2/s, with variations in intensity by at least an order of magnitude. A
pulse period of 912.0+/-0.1 s was discovered in the ISGRI and EPIC light
curves. The source spectrum is a strongly-absorbed (nH=(2.5+/-0.2)x10^23
atoms/cm2) power law that features a high-energy cutoff above 10 keV. Two iron
emission lines at 6.4 and 7.1 keV, an iron absorption edge >7.1 keV, and a soft
excess emission of 7x10^-15 ergs/cm2/s between 0.5-2 keV, are detected in the
EPIC spectrum. The shape of the spectrum does not change with the pulse. Its
persistence, pulsation, and spectrum place IGR J16393-4643 among the class of
heavily-absorbed HMXBs. The improved position from EPIC is R.A.
(J2000)=16:39:05.4 and Dec.=-46:42:12 (4"" uncertainty) which is compatible with
that of 2MASS J16390535-4642137.",0510112v2
2006-02-03,On the origin of the Fe K-alpha line cores in Active Galactic Nuclei,"X-ray observations with Chandra and XMM-Newton have shown that there are
relatively narrow cores to the iron K-alpha emission lines in active galactic
nuclei (AGN). Plausible origins for this core emission include the outer
regions of an accretion disk, a pc-scale molecular torus, and the optical
broad-line region (BLR). Using data from the literature it is shown that no
correlation exists between the Fe K-alpha core width and the BLR (specifically
H-beta) line width. This shows that in general the iron K-alpha core emission
does not arise from the BLR. There is a similar lack of correlation between the
width of the Fe K-alpha core and black hole mass. The average K-alpha width is
about a factor of two lower than the H-beta width. It therefore seems likely
that in many cases the narrow core arises in the torus. There is a very wide
range of observed Fe K-alpha core widths, however, and this argues for multiple
origins. The simplest explanation for the observed line profiles in AGN is that
they are due to a mixing of very narrow emission from the inner edge of the
torus, and broadened emission from the accretion disk, in varying proportions
from object-to-object.",0602081v1
2006-02-04,Comprehensive Analysis of RXTE Data from Cyg X-1: Spectral Index-Quasi-Periodic Oscillation Frequency-Luminosity Correlations,"We present timing and spectral analysis of ~ 2.2 Ms of RXTE archival data
from Cyg X-1. Using a generic Comptonization model we reveal that the spectrum
of Cyg X-1 consists of three components: a thermal seed photon spectrum, a
Comptonized part of the seed photon spectrum and the iron line. We find a
strong correlation between the 0.1-20 Hz frequencies of quasiperiodic
oscillations (QPOs) and the spectral index. Presence of two spectral phases
(states) are clearly seen in the data when the spectral indices saturate at low
and high values of QPO frequencies. This saturation effect was discovered
earlier in a number of black hole candidate (BHC) sources and now we strongly
confirm this phenomenon in Cyg X-1. In the soft state this index-QPO frequency
correlation shows a saturation of the photon index Gamma ~ 2.1 at high values
of the low frequency \nu_{L}. The saturation level of Gamma~ 2.1 is the lowest
value found yet in BHCs. The bolometric luminosity does not show clear
correlation with the index. We also show that Fe K_{\alpha} emission line
strength (equivalent width, EW) correlates with the QPO frequency. The EW
increases from 200 eV in the low/hard state to 1.5 keV in the high/soft state.
The observational correlations revealed compel us to propose a scenario for the
spectral transition and iron line formation which occur in BHC sources. We also
present the spectral state (power-law index) evolution for eight years of Cyg
X-1 observations by RXTE.",0602091v1
2006-02-27,Primordial Stellar Feedback and the Origin of Hyper Metal-Poor Stars,"The apparent absence of stars in the Milky Way halo with -5 ~< [Fe/H] ~< -4
suggests that the gas out of which the halo stars were born experienced a
period of low or delayed star formation after the local universe was lit up by
the first, metal-free generation of stars (Pop III). Negative feedback owed to
the Pop III stars could initially have prevented the pre-Galactic halo from
cooling, which thereby delayed the collapse and inhibited further star
formation. During this period, however, the nucleosynthesis products of the
first supernovae (SNe) had time to mix with the halo gas. As a result, the
initially primordial gas was already weakly enriched in heavy elements, in
particular iron, at the time of formation of the Galactic halo. The very high,
observed C/Fe ratios in the two recently discovered hyper metal-poor stars
([Fe/H]<-5) HE 0107-5240 and HE 1327-2326 as well as the diversity of C/Fe
ratios in the population of extremely metal-poor stars ([Fe/H]<-3) are then
naturally explained by a combination of pre-enrichment by Pop III stars and
local enrichment by subsequent generations of massive, rotating stars, for
which the most massive ones end their lives as black hole-forming SNe, only
ejecting their outer (carbon-rich) layers. The possible existence of
populations of mega metal-poor/iron-free stars ([Fe/H]<-6) is also discussed.",0602597v1
2006-04-03,Analysis of 26 Barium Stars I. Abundances,"We present a detailed analysis of 26 barium stars, including dwarf barium
stars, providing their atmospheric parameters (Teff, log g, [Fe/H], vt) and
elemental abundances. We aim at deriving gravities and luminosity classes of
the sample stars, in particular to confirm the existence of dwarf barium stars.
Accurate abundances of chemical elements were derived. Abundance ratios between
nucleosynthetic processes, by using Eu and Ba as representatives of the r- and
s-processes are presented. High-resolution spectra with the FEROS spectrograph
at the ESO-1.5m Telescope, and photometric data with Fotrap at the Zeiss
telescope at the LNA were obtained. The atmospheric parameters were derived in
an iterative way, with temperatures obtained from colour-temperature
calibrations. The abundances were derived using spectrum synthesis for Li, Na,
Al, alpha-, iron peak, s- and r-elements atomic lines, and C and N molecular
lines. Atmospheric parameters in the range 4300 < Teff < 6500, -1.2 < [Fe/H] <
0.0 and 1.4 < log g < 4.6 were derived, confirming that our sample contains
giants, subgiants and dwarfs. The abundance results obtained for Li, Al, Na,
alpha- and iron peak elements for the sample stars show that they are
compatible with the values found in the literature for normal disk stars in the
same range of metallicities. Enhancements of C, N and heavy elements relative
to Fe, that characterise barium stars, were derived and showed that [X/Ba] vs.
[Ba/H] and [X/Ba] vs. [Fe/H] present different behaviour as compared to [X/Eu]
vs. [Eu/H] and [X/Eu] vs. [Fe/H], reflecting the different nucleosynthetic
sites for the s- and r-processes.",0604036v1
2006-04-13,Extinction and metal column density of HI regions up to redshift z~2,"We used the photometric database of the Sloan Digital Sky Survey (SDSS) to
estimate the reddening of 13 SDSS quasars selected on the basis of the presence
of zinc absorption lines in an intervening Damped Ly alpha (DLA) system. In 5
of these quasars the reddening is detected at ~2 sigma confidence level in two
independent color indices of the SDSS ugriz photometric system. A detailed
analysis of the data supports an origin of the reddening in the intervening
absorbers. We used these rare measurements of extinction in DLA systems to
probe the relation between extinction and metal column density in the interval
of absorption redshift 0.7 </~ z </~ 2.0. We find that the mean extinction in
the V band per atom of iron in the dust is remarkably similar to that found in
interstellar clouds of the Milky Way. This result lends support to previous
estimates of the dust obscuration effect in DLA systems based on a Milky Way
extinction/metal column density relation. We propose a simple mechanism, based
on dust grain destruction/accretion properties, which may explain the
approximate constancy of the extinction per atom of iron in the dust.",0604296v1
2006-05-01,Broad band X-ray spectrum of KS 1947+300 with BeppoSAX,"We present results obtained from three BeppoSAX observations of the
accretion-powered transient X-ray pulsar KS 1947+300 carried out during the
declining phase of its 2000 November -- 2001 June outburst. A detailed spectral
study of KS 1947+300 across a wide X-ray band (0.1--100.0 keV) is attempted for
the first time here. Timing analysis of the data clearly shows a 18.7 s
pulsation in the X-ray light curves in the above energy band. The pulse profile
of KS 1947+300 is characterized by a broad peak with sharp rise followed by a
narrow dip. The dip in the pulse profile shows a very strong energy dependence.
Broad-band pulse-phase-averaged spectroscopy obtained with three of the
BeppoSAX instruments shows that the energy spectrum in the 0.1--100 keV energy
band has three components, a Comptonized component, a ~0.6 keV blackbody
component, and a narrow and weak iron emission line at 6.7 keV with a low
column density of material in the line of sight. We place an upper limit on the
equivalent width of the iron K_\alpha line at 6.4 keV of ~13 eV (for a width of
100 eV). Assuming a spherical blackbody emitting region and the distance of the
source to be 10 kpc, the radius of the emitting region is found to be in the
range of 14--22 km, which rules out the inner accretion disk as the soft X-ray
emitting region.",0605024v1
2006-06-06,Detailed XMM-Newton Observation of the Cluster of Galaxies Abell 1060,"We present results from the XMM-Newton observation of the non-cooling flow
cluster A1060. Large effective area of XMM-Newton enables us to investigate the
nature of this cluster in unprecedented detail. From the observed surface
brightness distribution, we have found that the gravitational mass distribution
is well described by the NFW profile but with a central density slope of ~1.5.
We have undoubtedly detected a radial temperature decrease of as large as ~30%
from the center to the outer region (r ~13'), which seems much larger than that
expected from the temperature profile averaged over nearby clusters. We have
established that the temperature of the region ~7' southeast of the center is
higher than the azimuthally averaged temperature of the same radius by ~20%.
Since the pressure of this region already reaches equilibrium with the
environment, the temperature structure can be interpreted as having been
produced between 4*10^7 yr (the sound-crossing time) and 3*10^8 yr (the thermal
conduction time) ago. We have found that the high-metallicity blob located at
\~1.'5 northeast of NGC 3311 is more extended and its iron mass of 1.9*10^7
M_solar is larger by an order of magnitude than estimated from our Chandra
observation. The amount of iron can still be considered as being injected
solely from the elliptical galaxy NGC3311.",0606115v1
2006-07-13,RHESSI Observations of the Solar Flare Iron-line Feature at 6.7 keV,"Analysis of RHESSI 3--10 keV spectra for 27 solar flares is reported. This
energy range includes thermal free--free and free--bound continuum and two line
features, at 6.7keV and 8keV, principally due to highly ionized iron (Fe). We
used the continuum and the flux in the so-called Fe-line feature at 6.7keV to
derive the electron temperature T_e, the emission measure, and the Fe-line
equivalent width as functions of time in each flare. The Fe/H abundance ratio
in each flare is derived from the Fe-line equivalent width as a function of
T_e. To minimize instrumental problems with high count rates and effects
associated with multi-temperature and nonthermal spectral components, spectra
are presented mostly during the flare decay phase, when the emission measure
and temperature were smoothly varying. We found flare Fe/H abundance ratios
that are consistent with the coronal abundance of Fe (i.e. 4 times the
photospheric abundance) to within 20% for at least 17 of the 27 flares; for 7
flares, the Fe/H abundance ratio is possibly higher by up to a factor of 2. We
find evidence that the Fe XXV ion fractions are less than the theoretically
predicted values by up to 60% at T_e=25 MK appear to be displaced from the most
recent theoretical values by between 1 and 3 MK.",0607309v1
2006-07-17,Chemical Evolution of the Galactic Bulge as Derived from High-Resolution Infrared Spectroscopy of K and M Red Giants,"We present chemical abundances in K and M red-giant members of the Galactic
bulge derived from high-resolution infrared spectra obtained with the Phoenix
spectrograph on Gemini-South. The elements studied are carbon, nitrogen,
oxygen, sodium, titanium, and iron. The evolution of C and N abundances in the
studied red-giants show that their oxygen abundances represent the original
values with which the stars were born. Oxygen is a superior element for probing
the timescale of bulge chemical enrichment via [O/Fe] versus [Fe/H]. The
[O/Fe]-[Fe/H] relation in the bulge does not follow the disk relation, with
[O/Fe] values falling above those of the disk. Titanium also behaves similarly
to oxygen with respect to iron. Based on these elevated values of [O/Fe] and
[Ti/Fe] extending to large Fe abundances, it is suggested that the bulge
underwent a more rapid chemical enrichment than the halo. In addition, there
are declines in both [O/Fe] and [Ti/Fe] in those bulge targets with the largest
Fe abundances, signifying another source affecting chemical evolution: perhaps
Supernovae of Type Ia. Sodium abundances increase dramatically in the bulge
with increasing metallicity, possibly reflecting the metallicity dependant
yields from supernovae of Type II, although Na contamination from H-burning in
intermediate mass stars cannot be ruled out.",0607393v1
2006-08-24,"Fall-back crust around a quark-nova compact remnant I: The degenerate shell case with applications to SGRs, AXPs and XDINs","We explore the formation and evolution of debris ejected around quark stars
in the Quark Nova scenario, and the application to Soft Gamma-ray Repeaters
(SGRs) and Anomolous X-ray Pulsars (AXPs). If an isolated neutron star explodes
as a Quark Nova, an Iron-rich shell of degenerate matter forms out of the
fall-back (crust) material. Our model can account for many of the observed
features of SGRs and AXPs such as: (i) the two types of bursts (giant and
regular); (ii) the spin-up and spin-down episodes during and following the
bursts with associated persistant increases in $\dot{P}$; (iii) the energetics
of the boxing day burst, SGR1806$+$20; (iv) the presence of an Iron line as
observed in SGR1900$+$14; (v) the correlation between the far-Infrared and the
X-ray fluxes during the bursting episode and the quiescent phase; (vi) the hard
X-ray component observed in SGRs during the giant bursts, and (vii) the
discrepancy between the ages of SGRs/AXPs and their supernova remnants. We also
find a natural evolutionary relationship between SGRs and AXPs in our model
which predicts that only the youngest SGRs/AXPs are most likely to exhibit
strong bursting. Many features of X-ray Dim Isolated Neutron stars (XDINs) are
also accounted for in our model such as, (i) the two-component blackbody
spectra; (ii) the absorption lines around 300 eV; and (iii) the excess optical
emission.",0608536v4
2006-09-18,The Sun is a plasma diffuser that sorts atoms by mass,"The Sun is a magnetic plasma diffuser that selectively moves light elements
like H and He and the lighter isotopes of each element to its surface. The Sun
formed on the collapsed core of a supernova. It consists mostly of iron,
oxygen, nickel, silicon and sulfur made near the SN core, like the rocky
planets and ordinary meteorites. H ions, generated by emission and decay of
neutrons at the core, are accelerated upward by deep magnetic fields, thus
acting as a carrier gas that maintains mass separation in the Sun. Neutron
emission from the central neutron star triggers a series of reactions that
generate solar luminosity, solar neutrinos, solar mass-fractionation, and an
outpouring of the neutron decay product, H, in the solar wind. Mass
fractionation appears to have operated in the parent star as well, and likely
occurs in other stars.",0609509v3
2006-09-19,Suzaku observations of the hard X-ray variability of MCG-6-30-15: the effects of strong gravity around a Kerr black hole,"Suzaku has, for the first time, enabled the hard X-ray variability of the
Seyfert 1 galaxy MCG-6-30-15 to be measured. The variability in the 14-45 keV
band, which is dominated by a strong reflection hump, is quenched relative to
that at a few keV. This directly demonstrates that the whole reflection
spectrum is much less variable than the power-law continuum. The broadband
spectral variability can be decomposed into two components - a highly variable
power-law and constant reflection - as previously inferred from other
observations in the 2-10 keV band. The strong reflection and high iron
abundance give rise to a strong broad iron line, which requires the inner disc
radius to be at about 2 gravitational radii. Our results are consistent with
the predictions of the light bending model which invokes the very strong
gravitational effects expected very close to a rapidly spinning black hole.",0609521v1
2006-09-26,Models for the X-ray spectra and variability of luminous accreting black holes,"The X-ray spectra of luminous Seyfert 1 galaxies often appear to be
reflection dominated. In a number of Narrow Line Seyfert 1 (NLS1) galaxies and
galactic black holes in the very high state, the variability of the continuum
and of the iron line are decoupled, the reflected component being often much
less variable than the continuum. These properties have been interpreted as
effects of gravitational light bending. In this framework, we present detailed
Monte-Carlo simulations of the reflection continuum in the Kerr metric. These
calculations confirm that the spectra and variability behaviour of these
sources can be reproduced by the light bending model. As an alternative to the
light bending model, we show that similar observational properties are expected
from radiation pressure dominated discs subject to violent clumping
instabilities and, as a result, have a highly inhomogeneous two-phase
structure. In this model, most of the observed spectral and variability
features originate from the complex geometrical structure of the inner regions
of near-Eddington accretion flows and are therefore a signature of accretion
physics rather than general relativity.",0609703v1
2006-09-29,3D Collapse of Rotating Stellar Iron Cores in General Relativity including Deleptonization and a Nuclear Equation of State,"We present results from the first 2D and 3D simulations of the collapse of
rotating stellar iron cores in general relativity employing a
finite-temperature equation of state and an approximate treatment of
deleptonization during collapse. We compare fully nonlinear and conformally
flat spacetime evolution methods and find that the conformally flat treatment
is sufficiently accurate for the core-collapse supernova problem. We focus on
the gravitational wave (GW) emission from rotating collapse, core bounce, and
early postbounce phases. Our results indicate that the GW signature of these
phases is much more generic than previously estimated. In addition, we track
the growth of a nonaxisymmetric instability of dominant m = 1 character in one
of our models that leads to prolonged narrow-band GW emission at ~930 Hz over
several tens of milliseconds.",0609819v2
2006-10-02,Suzaku Observation of Diffuse X-ray Emission from the Carina Nebula,"We studied extended X-ray emission from the Carina Nebula taken with the
Suzaku CCD camera XIS on 2005 Aug. 29. The X-ray morphology, plasma temperature
and absorption to the plasma are consistent with the earlier Einstein results.
The Suzaku spectra newly revealed emission lines from various species including
oxygen, but not from nitrogen. This result restricts the N/O ratio
significantly low, compared with evolved massive stellar winds, suggesting that
the diffuse emission is originated in an old supernova remnant or a super shell
produced by multiple supernova remnants. The X-ray spectra from the north and
south of Eta Carinae showed distinct differences between 0.3-2 keV. The south
spectrum shows strong L-shell lines of iron ions and K-shell lines of silicon
ions, while the north spectrum shows them weak in intensity. This means that
silicon and iron abundances are a factor of 2-4 higher in the south region than
in the north region. The abundance variation may be produced by an SNR ejecta,
or relate to the dust formation around the star forming core.",0610024v1
2006-11-30,Mass loss and yield uncertainty in low-mass asymptotic giant branch stars,"We investigate the uncertainty in surface abundances and yields of asymptotic
giant branch (AGB) stars. We apply three different mass loss laws to a 1.5
solar mass star of metallicity Z=0.008 at the beginning of the thermally
pulsing asymptotic giant branch (TP-AGB) phase. Efficient third dredge-up is
found even at very low envelope mass, contrary to previous simulations with
other evolution codes. We find that the yield of carbon is uncertain by about
15% and for most other light elements the yield is uncertain at the level of
20-80%. For iron group elements the uncertainty varies from around 30% for the
more abundant species to over a factor of two for the less abundant radioactive
species, like iron-60. The post-AGB surface abundances for this mass and
metallicity are much more uncertain due to the dilution of dredged-up material
in differing envelope masses in the later stages of the models. Our results are
compared to known planetary nebula (PN) and post-AGB abundances. We find that
the models are mostly consistent with observations but we are unable to
reproduce observations of some of the isotopes.",0612005v1
2006-12-12,Abundances and chemical stratification in the atmosphere of the HgMn star HD 175640,"We present the results of a study of the photospheric abundances of the HgMn
star HD 175640, conducted using archival ESO-UVES spectra. A large number of
unblended (titanium, chromium, manganese and iron) lines were studied to search
for the presence of chemical stratification in the atmosphere of this star. The
selected lines are located in the visible region of the spectrum, longward of
the Balmer jump, in orders with S/N $\geq$ 300. We derived the abundance of
each element by calculating independently the abundance associated each line.
We then characterized the depth of formation of each line, and examined the
dependence of abundance on optical depth. Titanium, chromium, manganese and
iron show no variation of their abundance with optical depth. These four
elements do not appear to be strongly stratified in the atmosphere of HD
175640. This indicates that if stratification occurs, it must be in atmospheric
layers which are not diagnosed by the spectral lines studied, or that it is too
weak to detect using these data. We also report evidence that HD 175640 is an
SB1, and furthermore report anomalous shifts of some strong Fe {\sc II} lines,
the origin of which is unclear.",0612323v1
2007-01-17,Detailed chemical composition of Galactic Cepheids. A determination of the Galactic abundance gradient in the 8-12 kpc region,"The recent introduction of high resolution/large spectral range spectrographs
provided the opportunity to investigate in detail the chemical composition of
classical Cepheids. This paper is focussed on new abundance determinations for
iron and 6 light metals (O, Na, Mg, Al, Si, Ca) in 30 Galactic Cepheids. We
also give a new estimate of the Galactic radial abundance gradient.
  The stellar effective temperatures have been determined using the method of
line depth ratios, while the surface gravity and the microturbulent velocity
v$_{t}$ by imposing the ionization balance between Fe I and Fe II and the help
of the curves of growth. Abundances were calculated with classical LTE
atmosphere models.
  Abundances are obtained with RMS accuracies of the order of 0.05-0.10 dex for
Fe, and 0.05-0.20 dex for the other elements. Cepheids in our sample have
solar-like abundances and current measurements agree quite-well with previous
determinations. We computed ``single zone'' Galactic radial abundance gradients
for the 8-12 kpc region and found a slope for iron of -0.061 dex kpc$^{-1}$.",0701499v2
2001-07-13,Iron under Earth's core conditions: Liquid-state thermodynamics and high-pressure melting curve,"{\em Ab initio} techniques based on density functional theory in the
projector-augmented-wave implementation are used to calculate the free energy
and a range of other thermodynamic properties of liquid iron at high pressures
and temperatures relevant to the Earth's core. The {\em ab initio} free energy
is obtained by using thermodynamic integration to calculate the change of free
energy on going from a simple reference system to the {\em ab initio} system,
with thermal averages computed by {\em ab initio} molecular dynamics
simulation. The reference system consists of the inverse-power pair-potential
model used in previous work. The liquid-state free energy is combined with the
free energy of hexagonal close packed Fe calculated earlier using identical
{\em ab initio} techniques to obtain the melting curve and volume and entropy
of melting. Comparisons of the calculated melting properties with experimental
measurement and with other recent {\em ab initio} predictions are presented.
Experiment-theory comparisons are also presented for the pressures at which the
solid and liquid Hugoniot curves cross the melting line, and the sound speed
and Gr\""{u}neisen parameter along the Hugoniot. Additional comparisons are made
with a commonly used equation of state for high-pressure/high-temperature Fe
based on experimental data.",0107307v1
2002-11-14,Ferromagnetism of a graphite nodule from the Canyon Diablo meteorite,"There have recently been various reports of weak ferromagnetism in graphite
(1,2) and synthetic carbon materials (3) such as rhombohedral C60 (4), as well
as a theoretical prediction of a ferromagnetic instability in graphene sheets
(5). With very small ferromagnetic signals, it is difficult to be certain that
the origin is intrinsic, rather than due to minute concentrations of iron-rich
impurities. Here we take a different experimental approach to study
ferromagnetism in graphitic materials, by making use of meteoritic graphite,
which is strongly ferromagnetic at room temperature. We examined ten samples of
extraterrestrial graphite from a nodule in the Canyon Diablo meteorite.
Graphite is the major phase in every sample but there are minor amounts of
magnetite, kamacite, akaganeite, and other phases. By analysing the phase
composition of a series of samples, we find that these iron-rich minerals can
only account for about two-thirds of the observed magnetization. The remainder
is somehow associated with graphite, corresponding to an average magnetization
of 23 Am2kg-1, or 0.05 Bohr magnetons per carbon atom. The magnetic ordering
temperature is near 570 K. We suggest that the ferromagnetism is a magnetic
proximity effect induced at the interface with magnetite or kamacite
inclusions.",0211275v1
2003-05-29,"Iron valence in double-perovskite (Ba,Sr,Ca)2FeMoO6: Isovalent substitution effect","In the Fe-Mo based B-site ordered double-perovskite, A2FeMoO6.0, with iron in
the mixed-valence II/III state, the valence value of Fe is not precisely fixed
at 2.5 but may be fine-tuned by means of applying chemical pressure at the
A-cation site. This is shown through a systematic 57Fe Mossbauer spectroscopy
study using a series of A2FeMoO6.0 [A = (Ba,Sr) or (Sr,Ca)] samples with high
degree of Fe/Mo order, the same stoichiometric oxygen content and also almost
the same grain size. The isomer shift values and other hyperfine parameters
obtained from the Mossbauer spectra confirm that Fe remains in the
mixed-valence state within the whole range of A constituents. However, upon
increasing the average cation size at the A site the precise valence of Fe is
found to decrease such that within the A = (Ba,Sr) regime the valence of Fe is
closer to II, while within the A = (Sr,Ca) regime it is closer to the actual
mixed-valence II/III state. As the valence of Fe approaches II, the difference
in charges between Fe and Mo increases, and parallel with this the degree of
Fe/Mo order increases. Additionally, for the less-ordered samples an increased
tendency of clustering of the anti-site Fe atoms is deduced from the Mossbauer
data.",0305679v1
2005-10-21,Carbon diffusion in alpha-iron: Evidence for quantum mechanical tunneling,"Recent experimental data on the diffusion coefficient of carbon in alpha-iron
below liquid nitrogen temperature (LNT) question the classical approach to the
observed temperature dependence. As the temperature is lowered below LNT, the
diffusion constant tends to a nearly temperature-independent value rather than
continuing its activated trend. The low temperature branch is apparently
characteristic of a quantum mechanical process dominated by tunneling in ground
state. Concommitantly, we apply an occurrence probability approach to
describing the overall temperature dependence as a single continuous rate.
Within the adiabatic approximation the electronic eigenvalue depending
parametrically on the nuclear coordinates is taken to be the potential energy
to control the motion of the nuclei. The resulting rate involves all
horizontal-tunneling energy-conserving elastic transitions at the quantized
energy levels of the migrating atom. A small though not negligible slope of in
the temperature dependence as the temperature is raised below 100 K is dealt
with by complementing for the rate of a parallel one-phonon inelastic tunneling
process in excess to the basic elastic-tunneling rate. Our combined approach
agrees well with the experimental data. In particular, the frequency of the
coupled vibration is obtained virtually identical to the carbon vibrational
frequency from inelastic neutron-scattering data. The migrational barrier is
also found to be within the limits expected for alpha-iron.",0510589v1
2006-12-11,Chemical ordering and composition fluctuations at the (001) surface of the Fe-Ni Invar alloy,"We report on a study of (001) oriented fcc Fe-Ni alloy surfaces which
combines first-principles calculations and low-temperature STM experiments.
Density functional theory calculations show that Fe-Ni alloy surfaces are
buckled with the Fe atoms slightly shifted outwards and the Ni atoms inwards.
This is consistent with the observation that the atoms in the surface layer can
be chemically distinguished in the STM image: brighter spots (corrugation
maxima with increased apparent height) indicate iron atoms, darker ones nickel
atoms. This chemical contrast reveals a c2x2 chemical order (50% Fe) with
frequent Fe-rich defects on Invar alloy surface. The calculations also indicate
that subsurface composition fluctuations may additionally modulate the apparent
height of the surface atoms. The STM images show that this effect is pronounced
compared to the surfaces of other disordered alloys, which suggests that some
chemical order and corresponding concentration fluctuations exist also in the
subsurface layers of Invar alloy. In addition, detailed electronic structure
calculations allow us to identify the nature of a distinct peak below the Fermi
level observed in the tunneling spectra. This peak corresponds to a surface
resonance band which is particularly pronounced in iron-rich surface regions
and provides a second type of chemical contrast with less spatial resolution
but one that is essentially independent of the subsurface composition.",0612262v1
2007-03-21,"Optical spectra, crystal-field parameters, and magnetic susceptibility of the new multiferroic NdFe3(BO3)4","We report high-resolution optical absorption spectra for NdFe3(BO3)4 trigonal
single crystal which is known to exhibit a giant magnetoelectric effect below
the temperature of magnetic ordering TN = 33 K. The analysis of the
temperature-dependent polarized spectra reveals the energies and, in some
cases, symmetries and exchange splittings of Nd3+ 84 Kramers doublets. We
perform crystal-field calculations starting from the exchange-charge model,
obtain a set of six real crystal-field parameters, and calculate wave functions
and magnetic g-factors. In particular, the values g(perpendicular) = 2.385,
g(parallel) = 1.376 were found for the Nd3+ ground-state doublet. We obtain
Bloc=7.88 T and |JFN|= 0.48 K for the values of the local effective magnetic
field at liquid helium temperatures at the Nd3+ site and the Nd - Fe exchange
integral, respectively, using the experimentally measured Nd3+ ground-state
splitting of 8.8 cm-1. To check reliability of our set of crystal field
parameters we model the magnetic susceptibility data from literature. A dimer
containing two nearest-neighbor iron ions in the spiral chain is considered to
partly account for quasi-one-dimensional properties of iron borates, and then
the mean-field approximation is used. The results of calculations with the
exchange parameters for Fe3+ ions Jnn = -6.25 K (intra-chain interactions) and
Jnnn = -1.92 K (inter-chain interactions) obtained from fitting agree well with
the experimental data.",0703549v1
2007-04-03,Diffuse X-ray Emission from the Carina Nebula Observed with Suzaku,"A number of giant HII regions are associated with soft diffuse X-ray
emission. Among these, the Carina nebula possesses the brightest soft diffuse
emission. The required plasma temperature and thermal energy can be produced by
collisions or termination of fast winds from main-sequence or embedded young O
stars, but the extended emission is often observed from regions apart from
massive stellar clusters. The origin of the X-ray emission is unknown.
  The XIS CCD camera onboard Suzaku has the best spectral resolution for
extended soft sources so far, and is therefore capable of measuring key
emission lines in the soft band. Suzaku observed the core and the eastern side
of the Carina nebula (Car-D1) in 2005 Aug and 2006 June, respectively. Spectra
of the south part of the core and Car-D1 similarly showed strong L-shell lines
of iron ions and K-shell lines of silicon ions, while in the north of the core
these lines were much weaker. Fitting the spectra with an absorbed thin-thermal
plasma model showed kT~0.2, 0.6 keV and NH~1-2e21 cm-2 with a factor of 2-3
abundance variation in oxygen, magnesium, silicon and iron. The plasma might
originate from an old supernova, or a super shell of multiple supernovae.",0704.0346v1
2007-04-12,Possible X-ray diagnostic for jet/disk dominance in Type 1 AGN,"Using Rossi X-ray Timing Explorer Seyfert 1 and 1.2 data spanning 9 years, we
study correlations between X-ray spectral features. The sample consists of 350
time-resolved spectra from 12 Seyfert 1 and 1.2 galaxies. Each spectrum is
fitted to a model with an intrinsic powerlaw X-ray spectrum produced close to
the central black hole that is reprocessed and absorbed by material around the
black hole. To test the robustness of our results, we performed Monte Carlo
simulations of the spectral sample. We find a complex relationship between the
iron line equivalent width (EW) and the underlying power law index (Gamma). The
data reveal a correlation between Gamma and EW which turns over at Gamma <~ 2,
but finds a weak anti-correlation for steeper photon indices. We propose that
this relationship is driven by dilution of a disk spectrum (which includes the
narrow iron line) by a beamed jet component and, hence, could be used as a
diagnostic of jet-dominance. In addition, our sample shows a strong correlation
between the reflection fraction (R) and Gamma, but we find that it is likely
the result of modeling degeneracies. We also see the X-ray Baldwin effect (an
anti-correlation between the 2-10 keV X-ray luminosity and EW) for the sample
as a whole, but not for the individual galaxies and galaxy types.",0704.1587v1
2007-05-12,Iron line profiles and self-shadowing from relativistic thick accretion discs,"We present Fe Kalpha line profiles from and images of relativistic discs with
finite thickness around a rotating black hole using a novel code. The line is
thought to be produced by iron fluorescence of a relatively cold X-ray
illuminated material in the innermost parts of the accretion disc and provides
an excellent diagnostic of accretion flows in the vicinity of black holes.
Previous studies have concentrated on the case of a thin, Keplerian accretion
disc. This disc must become thicker and sub-Keplerian with increasing accretion
rates. These can affect the line profiles and in turn can influence the
estimation of the accretion disc and black hole parameters from the observed
line profiles. We here embark on, for the first time, a fully relativistic
computation which offers key insights into the effects of geometrical thickness
and the sub-Keplerian orbital velocity on the line profiles. We include all
relativistic effects such as frame-dragging, Doppler boost, time dilation,
gravitational redshift and light bending. We find that the separation and the
relative height between the blue and red peaks of the line profile diminish as
the thickness of the disc increases. This code is also well-suited to produce
accretion disc images. We calculate the redshift and flux images of the
accretion disc and find that the observed image of the disc strongly depends on
the inclination angle. The self-shadowing effect appears remarkable for a high
inclination angle, and leads to the black hole shadow being completely hidden
by the disc itself.",0705.1796v2
2007-06-08,Evolution of interstellar dust and stardust in the solar neighbourhood,"The abundance evolution of interstellar dust species originating from stellar
sources and from condensation in molecular clouds in the local interstellar
medium of the Milky Way is studied and the input of dust material to the Solar
System is determined. A one-zone chemical evolution model of the Milky Way for
the elemental composition of the disk combined with an evolution model for its
interstellar dust component similar to that of Dwek (1998) is developed. The
dust model considers dust-mass return from AGB stars as calculated from
synthetic AGB models combined with models for dust condensation in stellar
outflows. Supernova dust formation is included in a simple parameterized form
which is gauged by observed abundances of presolar dust grains with supernova
origin. For dust growth in the ISM a simple method is developed for coupling
this with disk and dust evolution models. The time evolution of the abundance
of the following dust species is followed in the model: silicate, carbon,
silicon carbide, and iron dust from AGB stars and from SNe as well as silicate,
carbon, and iron dust grown in molecular clouds. It is shown that the
interstellar dust population is dominated by dust accreted in molecular clouds;
most of the dust material entering the Solar System at its formation does not
show isotopic abundance anomalies of the refractory elements, i.e.,
inconspicuous isotopic abundances do not point to a Solar System origin of dust
grains. The observed abundance ratios of presolar dust grains formed in SN
ejecta and in AGB star outflows requires that for the ejecta from SNe the
fraction of refractory elements condensed into dust is 0.15 for carbon dust and
is quite small ($\sim10^{-4}$) for other dust species.",0706.1155v1
2007-08-06,On the relativistic iron line and soft excess in the Seyfert 1 galaxy Markarian 335,"We report on a 133 ks XMM-Newton observation of the Seyfert 1 galaxy
Markarian 335. The 0.4-12 keV spectrum contains an underlying power law
continuum, a soft excess below 2 keV, and a double-peaked iron emission feature
in the 6-7 keV range. We investigate the possibility that the double-peaked
emission might represent the characteristic signature of the accretion disc.
Detailed investigations show that a moderately broad, accretion disc line is
most likely present, but that the peaks may be owing to narrower components
from more distant material. The peaks at 6.4 and 7 keV can be identified,
respectively, with the molecular torus in active galactic nucleus unification
schemes, and very highly ionized, optically thin gas filling the torus. The
X-ray variability spectra on both long (~100 ks) and short (~1 ks) timescales
disfavour the recent suggestion that the soft excess is an artifact of
variable, moderately ionized absorption.",0708.0751v1
2007-08-28,The Symbiotic System SS73 17 Seen with Suzaku,"We observed with Suzaku the symbiotic star SS73 17, motivated by the
discovery by the INTEGRAL satellite and the Swift BAT survey that it emits hard
X-rays. Our observations showed a highly-absorbed X-ray spectrum with NH >
10^23 cm-2, equivalent to A_V > 26, although the source has B magnitude 11.3
and is also bright in UV. The source also shows strong, narrow iron lines
including fluorescent Fe K as well as Fe xxv and Fe xxvi. The X-ray spectrum
can be fit with a thermal model including an absorption component that
partially covers the source. Most of the equivalent width of the iron
fluorescent line in this model can be explained as a combination of
reprocessing in a dense absorber plus reflection off a white dwarf surface, but
it is likely that the continuum is partially seen in reflection as well. Unlike
other symbiotic systems that show hard X-ray emission (CH Cyg, RT Cru, T CrB,
GX1+4), SS73 17 is not known to have shown nova-like optical variability, X-ray
flashes, or pulsations, and has always shown faint soft X-ray emission. As a
result, although it is likely a white dwarf, the nature of the compact object
in SS73 17 is still uncertain. SS73 17 is probably an extreme example of the
recently discovered and relatively small class of hard X-ray emitting symbiotic
systems.",0708.3833v1
2007-10-03,Abundance Patterns in Stars in the Bulge and Galactic Center,"We discuss oxygen and iron abundance patterns in K and M red-giant members of
the Galactic bulge and in the young and massive M-type stars inhabiting the
very center of the Milky Way. The abundance results from the different bulge
studies in the literature, both in the optical and the infrared, indicate that
the [O/Fe]-[Fe/H] relation in the bulge does not follow the disk relation, with
[O/Fe] values falling above those of the disk. Based on these elevated values
of [O/Fe] extending to large Fe abundances, it is suggested that the bulge
underwent a rapid chemical enrichment with perhaps a top-heavy initial mass
function. The Galactic Center stars reveal a nearly uniform and slightly
elevated (relative to solar) iron abundance for a studied sample which is
composed of 10 red giants and supergiants. Perhaps of more significance is the
fact that the young Galactic Center M-type stars show abundance patterns that
are reminiscent of those observed for the bulge population and contain enhanced
abundance ratios of alpha-elements relative to either the Sun or Milky Way disk
at near-solar metallicities.",0710.0866v1
2007-10-24,About Compiled Catalogue of Spectroscopically Determined $α$-Elements Abundances for Stars with Accurate Parallaxes,"We present a new version of the compiled catalogue of nearby stars for which
was published the spectoscopically determined effective temperatures, surface
gravities, and abundances of iron, magnesium, calcium, silicon, and titanium.
Distances, velocity components, galactic orbital elements, and ages was
calculated for all stars. The atmospheric parameters and iron abundances were
found from 4700 values in 136 publications, while relative abundances of
alpha-elements were found from 2800 values in 81 publications for ~2000 dwarfs
and giants using a three-step iteration averaging procedure, with weights
assigned to each source of data as well as to each individual determination and
taking into account systematic deviations of each scale relative to the reduced
mean scale. The estimated assumed completeness for data sources containing more
than five stars, up to late April 2007, exceeds 90%. For the vast majority of
stars in the catalogue, the spatial-velocity components were derived from
modern high-precision astrometric observations, and their Galactic orbit
elements were computed using a three-component model of the Galaxy, consisting
of a disk, a bulge, and a massive extended halo. Ages was determined for dwarfs
and subgiants using Yale isochrones~2004. For this purpose the original codes
was developed, based on interpolation with the 3D-spline functions of
theoretical isochrones, and with subsequent interpolation in metallicity and
abundances of \alpha-elements.",0710.4531v1
2007-10-25,Spectral analysis of LMC X-2 with XMM/Newton: unveiling the emission process in the extragalactic Z-source,"We present the results of the analysis of an archival observation of LMC X-2
performed with XMM/Newton. The spectra taken by high-precision instruments have
never been analyzed before. We find an X-ray position for the source that is
inconsistent with the one obtained by ROSAT, but in agreement with the Einstein
position and that of the optical counterpart. The correlated spectral and
timing behaviour of the source suggests that the source is probably in the
normal branch of its X-ray color-color diagram. The spectrum of the source can
be fitted with a blackbody with a temperature 1.5 keV plus a disk blackbody at
0.8 keV. Photoelectric absorption from neutral matter has an equivalent
hydrogen column of 4 x 10^{20} cm^{-2}. An emission line, which we identify as
the O VIII Lyman alpha line, is detected, while no feature due to iron is
detected in the spectrum. We argue that the emission of this source can be
straightforwardly interpreted as a sum of the emission from a boundary layer
between the NS and the disc and a blackbody component coming from the disc
itself. Other canonical models that are used to fit Z-sources do not give a
satisfactory fit to the data. The detection of the O VIII emission line (and
the lack of detection of lines in the iron region) can be due to the fact that
the source lies in the Large Magellanic Cloud.",0710.4934v1
2007-10-30,On variability and spectral distortion of the fluorescent iron lines from black-hole accretion discs,"We investigate properties of iron fluorescent line arising as a result of
illumination of a black hole accretion disc by an X-ray source located above
the disc surface. We study in details the light-bending model of variability of
the line, extending previous work on the subject.
  We indicate bending of photon trajectories to the equatorial plane, which is
a distinct property of the Kerr metric, as the most feasible effect underlying
reduced variability of the line observed in several objects. A model involving
an X-ray source with a varying radial distance, located within a few central
gravitational radii around a rapidly rotating black hole, close to the disc
surface, may explain both the elongated red wing of the line profile and the
complex variability pattern observed in MCG--6-30-15 by XMM-Newton.
  We point out also that illumination by radiation which returns to the disc
(following the previous reflection) contributes significantly to formation of
the line profile in some cases. As a result of this effect, the line profile
always has a pronounced blue peak (which is not observed in the deep minimum
state in MCG--6-30-15), unless the reflecting material is absent within the
innermost 2--3 gravitational radii.",0710.5578v2
2007-12-01,"Linear arrays of non homogeneous Cu sites in the CuO2 plane, a new scenario for pairing mechanisms in a currugated-iron-like plane","Experimental results obtained by using x-ray absorption spectroscopy show
that the configurations of Cu sites in the CuO2 plane of Bi 2:2:1:2 high Tc
superconductors are not homogeneous. Different Cu sites are characterized by
short 0.23 nm and long 0.245 nm Cu-O(apical) distances. The linear arrays of
different Cu sites forming domains with a corrugated-iron like shape is
proposed to be a key characteristic of superconducting domains in the CuO2
plane. The wavelength of the modulation is close to the superconducting
coherence length. The ordering of the distorted Cu sites is suggested to be
evidence for ordering of polarons driven by the pseudo Jahn Teller electron
lattice interaction. The Cu L3 XAS experiments on Bi 2:2:1:2 system indicate
that the electronic states added by doping, 4% have the a1 symmetry (i.e. with
Cu 3d(3z2-r2), the combination of O (planar) 2px,y orbital with a1 symmetry
L(a1), and O(apical) 2pz orbital character) and 15% have the b1 symmetry
(3d(x2-y2) and the combination of O (planar) 2p(x,y) orbital with b1 symmetry
L(b1)). This new scenario supports the pairing mechanisms for high Tc
superconductivity in the presence of two components: 1) the more delocalized
component with b1 symmetry and 2) the more localized component, with partially
a1 symmetry associated with different parts of the Fermi surface.",0712.0065v1
2007-12-18,Neutrino oscillation signatures of oxygen-neon-magnesium supernovae,"We discuss the flavor conversion of neutrinos from core collapse supernovae
that have oxygen-neon-magnesium (ONeMg) cores. Using the numerically calculated
evolution of the star up to 650 ms post bounce, we find that, for the normal
mass hierarchy, the electron neutrino flux in a detector shows signatures of
two typical features of an ONeMg-core supernova: a sharp step in the density
profile at the base of the He shell and a faster shock wave propagation
compared to iron core supernovae. Before the shock hits the density step (t ~
150 ms), the survival probability of electron neutrinos is about 0.68, in
contrast to values of 0.32 or less for an iron core supernova. The passage of
the shock through the step and its subsequent propagation cause a decrease of
the survival probability and a decrease of the amplitude of oscillations in the
Earth, reflecting the transition to a more adiabatic propagation inside the
star. These changes affect the lower energy neutrinos first; they are faster
and more sizable for larger theta_13. They are unique of ONeMg-core supernovae,
and give the possibility to test the speed of the shock wave. The time
modulation of the Earth effect and its negative sign at the neutronization peak
are the most robust signatures in a detector.",0712.3000v3
2008-01-31,Cosmic ray velocity and electric charge measurements with the AMS/RICH detector: prototype results,"The Alpha Magnetic Spectrometer (AMS) to be installed on the International
Space Station (ISS) will measure charged cosmic ray spectra of elements up to
iron, in the rigidity range from 1 GV to 1 TV, for at least three years. AMS is
a large angular spectrometer composed of different subdetectors, including a
proximity focusing Ring Imaging CHerenkov (RICH) detector. This will be
equipped with a mixed radiator made of aerogel and sodium fluoride (NaF), a
lateral conical mirror and a detection plane made of 680 photomultipliers
coupled to light guides. The RICH detector allows measurements of particle's
electric charge up to iron, and particle's velocity. Two possible methods for
reconstructing the Cherenkov angle and the electric charge with the RICH will
be discussed.
  A RICH prototype consisting of a detection matrix with 96 photomultipliers, a
segment of a conical mirror and samples of the radiator materials was built and
its performance was evaluated using ion beam data. Results from the last test
beam performed with ion fragments resulting from the collision of a 158
GeV/c/nucleon primary beam of indium ions (CERN SPS) on a lead target are
reported. The large amount of collected data allowed to test and characterize
different aerogel samples and the NaF radiator. In addition, the reflectivity
of the mirror was evaluated. The data analysis confirms the design goals.",0801.4952v1
2008-01-31,Cosmological black hole spin evolution by mergers and accretion,"Using recent results from numerical relativity simulations of black hole
mergers, we revisit previous studies of cosmological black hole spin evolution.
We show that mergers are very unlikely to yield large spins, unless alignment
of the spins of the merging holes with the orbital angular momentum is very
efficient. We analyze the spin evolution in three specific scenarios: (1) spin
evolves only through mergers, (2) spin evolves through mergers and prolonged
accretion episodes, (3) spin evolves through mergers and short-lived (chaotic)
accretion episodes. We study how different diagnostics can distinguish between
these evolutionary scenarios, assessing the discriminating power of
gravitational-wave measurements and X-ray spectroscopy. Gravitational radiation
can produce three different types of spin measurements, yielding respectively
the spins of the two black holes in a binary inspiral prior to merger, the spin
of the merger remnant (as encoded in the ringdown waves), and the spin of
``single'' black holes during the extreme mass-ratio inspiral (EMRI) of compact
objects. The latter spin population is also accessible to iron-line
measurements. We compute and compare the spin distributions relevant for these
different observations. If iron-line measurements and gravitational-wave
observations of EMRIs only yield dimensionless spins j=J/M^2>0.9, then
prolonged accretion should be responsible for spin-up, and chaotic accretion
scenarios would be very unlikely. If only a fraction of the whole population of
low-redshift black holes spins rapidly, spin-alignment during binary mergers
(rather than prolonged accretion) could be responsible for spin-ups.",0802.0025v2
2008-02-07,On the Dynamical Origin of the ICM Metallicity Evolution,"We present a study on the origin of the metallicity evolution of the
intra-cluster medium (ICM) by applying a semi-analytic model of galaxy
formation to N-body/SPH (smoothed particle hydrodynamic) non-radiative
numerical simulations of clusters of galaxies. The semi-analytic model includes
gas cooling, star formation, supernovae feedback and metal enrichment, and is
linked to the diffuse gas of the underlying simulations so that the chemical
properties of gas particles are dynamically and consistently generated from
stars in the galaxies. This hybrid model let us have information on the spatial
distribution of metals in the ICM. The results obtained for a set of clusters
with virial masses of ~1.5*10^15 h^{-1} M_sun contribute to the theoretical
interpretation of recent observational X-ray data, which indicate a decrease of
the average iron content of the intra-cluster gas with increasing redshift. We
find that this evolution arises mainly as a result of a progressive increase of
the iron abundance within ~0.15 R_vir. The clusters have been considerably
enriched by z~1 with very low contribution from recent star formation. Low
entropy gas that has been enriched at high redshift sinks to the cluster centre
contributing to the evolution of the metallicity profiles.",0802.0975v1
2008-02-15,Evolution of the metal content of the intra-cluster medium with hydrodynamical simulations,"We present a comparison between simulation results and X-ray observational
data on the evolution of the metallicity of the intra-cluster medium (ICM). The
simulations of galaxy clusters were performed with the Tree-SPH Gadget2 code
that includes a detailed model of chemical evolution, by assuming three
different shapes for the stellar initial mass function (IMF), namely the
Salpeter (1955), Kroupa (2001) and Arimoto-Yoshii (1987) IMF. Our simulations
predict significant radial gradients of the Iron abundance, which extend over
the whole cluster virialized region. At larger radii, we do not detect any
flattening of the metallicity profiles. As for the evolution of the ICM metal
(Iron) abundance out to z=1, we find that it is determined by the combined
action of (i) the sinking of already enriched gas, (ii) the ongoing metal
production in galaxies and (iii) the locking of ICM metals in newborn stars. As
a result, rather than suppressing the metallicity evolution, stopping star
formation at z=1 has the effect of producing an even too fast evolution of the
emission-weighted ICM metallicity with too high values at low redshift.
Finally, we compare simulations with the observed rate of type-Ia supernovae
per unit B-band luminosity (SnU_B). We find that our simulated clusters do not
reproduce the decreasing trend of SnU_B at low redshift, unless star formation
is truncated at z=1.",0802.2224v1
2008-02-25,NLTE Model of NGC 6543's Central Star and its Relation with the Surrounding Planetary Nebula,"We analyze the chemical composition of the central star of the planetary
nebula NGC 6543 based upon a detailed NLTE model of its stellar wind. The
logarithmic abundances by number are H=12.00, He=11.00, C=9.03, N=8.36, O=9.02,
Si=8.19, P=5.53, S=7.57 and Fe=7.24. Compared with the solar abundances, most
of the elements have solar composition with respect to hydrogen except C which
is overabundant by 0.28 dex and Fe which is depleted by $\sim 0.2$ dex.
Contrary to most previous work, we find that the star is not H-poor and has a
normal He composition. These abundances are compared with those found in the
diffuse X-ray plasma and the nebular gas. Compared to the plasma emitting in
diffuse X-rays, the stellar wind is much less depleted in iron. Since the iron
depletions in the nebular gas and X-ray plasma are similar, we conclude that
the plasma emitting diffuse X-rays is derived from the nebular gas rather than
the stellar wind. Excellent agreement is obtained between the abundances in the
stellar wind and the nebular recombination line abundances for He, C, and O
relative to H. On the other hand, the derived stellar N abundance is smaller
than the nebular N abundance derived from recombination lines and agrees with
the abundance found from collisionally-excited lines. The mean temperature
variation determined by five different methods indicates that the difference in
the nebular abundances between the recombination lines and collisionally
excited lines can be explained as due to the temperature variations in a
chemically homogeneous medium.",0802.3692v1
2008-03-04,The Chemical Evolution of Dwarf Spheroidal Galaxies: Dissecting the Inner Regions and their Stellar Populations,"Using 3-dimensional hydrodynamical simulations of isolated dwarf spheroidal
galaxies (dSphs), we undertake an analysis of the chemical properties of their
inner regions, identifying the respective roles played by Type Ia (SNe Ia) and
Type II (SNe II) supernovae. The effect of inhomogeneous pollution from SNe Ia
is shown to be prominent within two core radii, with the stars forming therein
amounting to ~20% of the total. These stars are relatively iron-rich and
alpha-element-depleted compared to the stars forming in the rest of the galaxy.
At odds with the projected stellar velocity dispersion radial profile, the
actual 3-dimensional one shows a depression in the central region, where the
most metal-rich (ie. [Fe/H]-rich) stars are partly segregated. This naturally
results in two different stellar populations, with an anti-correlation between
[Fe/H] and velocity dispersion, in the same sense as that observed in the
Sculptor and Fornax dSphs. Because the most iron-rich stars in our model are
also the most alpha-depleted, a natural prediction and test of our model is
that the same radial segregation effects should exist between [alpha/Fe] and
velocity dispersion.",0803.0385v1
2008-03-20,Tracing the [FeII]/[NeII] ratio and its relationship with other ISM indicators within star forming dwarf galaxies: a Spitzer IRS archival study,"Archival Spitzer observations of 41 starburst galaxies that span a wide range
in metallicity reveal for the first time a correlation between the
[FeII]/[NeII] 26.0/12.8 micron ratio and the electron gas density as traced by
the 18.7/33.4 micron [SIII] ratio, with the [FeII]/[NeII] ratio decreasing with
increasing gas density. The correlations of the [FeII]/[NeII] ratio, the PAH
peak to continuum strength & metallicity found in an earlier paper were
confirmed for a larger sample. We also find a strong correlation between the
gas density and the PAH peak to continuum strength. Using shock and
photoionization models, we see the driver of the observed [FeII]/[NeII] ratios
is metallicity. The majority of [FeII] emission in low metallicity galaxies may
be shock-derived, whilst at high metallicity, the [FeII] emission may be
instead dominated by contributions from HII and in particular from dense PDR
regions. However, the observed [FeII]/[NeII] ratios may instead be following a
metallicity-abundance relationship, with iron being less depleted onto grains
in low metallicity galaxies - a result that would have profound implications
for the use of iron emission lines as unambiguous tracers of shocks.",0803.3000v1
2008-03-31,A Generic Two-band Model for Unconventional Superconductivity and Spin-Density-Wave Order in Electron and Hole Doped Iron-Based Superconductors,"Based on experimental data on the newly synthesized iron-based
superconductors and the relevant band structure calculations, we propose a
minimal two-band BCS-type Hamiltonian with the interband Hubbard interaction
included. We illustrate that this two-band model is able to capture the
essential features of unconventional superconductivity and spin density wave
(SDW) ordering in this family of materials. It is found that bound
electron-hole pairs can be condensed to reveal the SDW ordering for zero and
very small doping, while the superconducting ordering emerges at small finite
doping, whose pairing symmetry is qualitatively analyzed to be of nodal d-wave.
The derived analytical formulas not only give out a nearly symmetric phase
diagram for electron and hole doping, but also is likely able to account for
existing main experimental results. Moreover, we also derive two important
relations for a general two-band model and elaborate how to apply them to
determine the band width ratio and the effective interband coupling strength
from experimental data.",0803.4346v3
2008-04-04,Magnetic Order versus superconductivity in the Iron-based layered La(O1-xFx)FeAs systems,"In high-transition temperature (high-Tc) copper oxides, it is generally
believed that antiferromagnetism plays a fundamental role in the
superconducting mechanism because superconductivity occurs when mobile
electrons or holes are doped into the antiferromagnetic parent compounds. The
recent discovery of superconductivity in the rare-earth (R) iron-based oxide
systems [RO1-xFxFeAs] has generated enormous interest because these materials
are the first noncopper oxide superconductors with Tc exceeding 50 K. The
parent (nonsuperconducting) LaOFeAs material is metallic but shows anomalies
near 150 K in both resistivity and dc magnetic susceptibility. While optical
conductivity and theoretical calculations suggest that LaOFeAs exhibits a
spin-density-wave (SDW) instability that is suppressed with doping electrons to
form superconductivity, there has been no direct evidence of the SDW order.
Here we use neutron scattering to demonstrate that LaOFeAs undergoes an abrupt
structural distortion below ~150 K, changing the symmetry from tetragonal
(space group P4/nmm) to monoclinic (space group P112/n) at low temperatures,
and then followed with the development of long range SDW-type antiferromagnetic
order at ~134 K with a small moment but simple magnetic structure. Doping the
system with flourine suppresses both the magnetic order and structural
distortion in favor of superconductivity. Therefore, much like high-Tc copper
oxides, the superconducting regime in these Fe-based materials occurs in close
proximity to a long-range ordered antiferromagnetic ground state. Since the
discovery of long",0804.0795v1
2008-04-14,The candidate filament close to the 3C295 galaxy cluster: optical and X-ray spectroscopy,"We present a detailed analysis of the overdensity of X-ray sources colse to
the 3C 295 galaxy cluster (z=0.46) to assess whether it is associated with a
filament of the large-scale structure of the Universe. We obtained optical
spectra of the optical counterparts of eleven sources associated with the
filament, finding that one is at z=0.474. This is a type 1 AGN at 1.5 arcmin
from the cluster center. We found three more sources with a redshift in the
range 0.37 - 0.53. We extracted the stacked X-ray spectrum of 47 X-ray sources
belonging to the putative filament. We found a significant narrow (at the
resolution of the Chandra ACIS-I) line at E ~ 4.4 keV, the energy of the iron
Kalpha line at the redshift of the cluster. The detection of this line is
confirmed at a confidence level of better than 3sigma and its energy is
constrained to be in the range 6.2--6.47 (at a 90% confidence level), excluding
an identification with the 6.7 helium-like iron line from the hot cluster ICM
at better than 4 sigma. We conclude that the detection of the redshifted line
is a strong indication that at least several of the excess sources lie at z ~
0.46 and that AGNs are efficient tracers of the ``filament'' connected with the
central cluster of galaxies.",0804.2143v1
2008-04-23,Specific heat of the iron-based high-$T_c$ superconductor SmO$_{1-x}$F$_x$FeAs,"The specific heat $C(T)$ of new iron-based high-$T_c$ superconductor
SmO$_{1-x}$F$_x$FeAs ($0 \leq x \leq 0.2$) was systematically studied. For
undoped $x$ = 0 sample, a specific heat jump was observed at 130 K. This is
attributed to the structural or spin-density-wave (SDW) transition, which also
manifests on resistivity as a rapid drop. However, this jump disappears with
slight F doping in $x$ = 0.05 sample, although the resistivity drop still
exists. The specific heat $C/T$ shows clear anomaly near $T_c$ for $x$ = 0.15
and 0.20 superconducting samples. Such anomaly has been absent in
LaO$_{1-x}$F$_x$FeAs. For the parent compound SmOFeAs, $C(T)$ shows a sharp
peak at 4.6 K, and with electron doping in $x$ = 0.15 sample, this peak shifts
to 3.7 K. It is interpreted that such a sharp peak results from the
antiferromagnetic ordering of Sm$^{3+}$ ions in this system, which mimics the
electron-doped high-$T_c$ cuprate Sm$_{2-x}$Ce$_x$CuO$_{4-\delta}$.",0804.3642v3
2008-05-08,On the peculiar properties of the narrow-line quasar PG 1543+489,"We present the analysis of four XMM-Newton observations of the narrow-line
quasar PG 1543+489 at z=0.400 carried out over a rest-frame time-scale of about
three years. The X-ray spectrum is characterized by a broad, relativistic iron
K_alpha emission line and a steep photon index, which can be both explained by
a ionized reflection model, where the source of X-ray photons is presumably
very close to the black hole. If this were the case, strong light-bending
effects are expected, and actually they provide the most plausible explanation
for the large equivalent width (EW=3.1+/-0.8 keV in the source rest frame) of
the iron line. Although the light-bending model provides a good description of
the X-ray data of PG 1543+489, it is not possible to rule out an absorption
model, where obscuring matter partially covers the X-ray source. However, the
apparent lack of variations in the properties of the absorber over the
time-scale probed by our observations may indicate that this model is less
likely.",0805.1227v1
2008-05-19,A Brief Comment on the Low-Temperature Structure of LaOFeAs,"In a recent paper [arXiv:0804.3569], Takatoshi Nomura {\it et al.} reported a
structural phase transition near 150 K in LaOFeAs and used space group ""Cmma""
to describe their X-ray diffraction data. However, they did not discuss how
their proposed structure compares with the early neutron study by Cruz {\it et
al.}[arXiv:0804.0795] where the low temperature structure of LaOFeAs was
described by space group ""P112/n"". This caused some confusion, suggesting that
there may be some disagreement on the low temperature structure of LaOFeAs as
evidenced by several inquiries that we received. Here we show that the proposed
structures from x-ray and neutron diffraction are basically identical. The P2/c
(i.e., P112/n) cell becomes the primitive cell of the Cmma cell when the
z-coordinate of the oxygen and iron are assumed to be exactly 0 and 0.5 (these
numbers were reported to be -0.0057 and 0.5006 in neutron study). Our
first-principles total-energy calculations suggest that the oxygen and iron
atoms prefer to lie on the z=0 and 1/2 plane, respectively, supporting Cmma
symmetry. However it is more convenient to describe the structural distortion
in the primitive P2/c cell which makes it easier to see the connection between
the high (i.e., P4/nmm) and low temperature structures.",0805.2888v1
2008-06-05,Raman spectra in iron-based quaternary CeO$_{1-x}$F$_x$FeAs and LaO$_{1-x}$F$_x$FeAs,"Raman spectra have been measured on iron-based quaternary
CeO$_{1-x}$F$_x$FeAs and LaO$_{1-x}$F$_x$FeAs with varying fluorine doping at
room temperatures. A group analysis has been made to clarify the optical modes.
Based on the first principle calculations, the observed phonon modes can be
assigned accordingly. In LaO$_{1-x}$F$_x$FeAs, the E$_g$ and A$_{1g}$ modes
related to the vibrations of La, are suppressed with increasing F doping.
However F doping only has a small effect on the E$_g$ and A$_{1g}$ modes of Fe
and As. The Raman modes of La and As are absent in rare-earth substituted
CeO$_{1-x}$F$_x$FeAs, and the E$_g$ mode of oxygen, corresponding to the
in-plane vibration of oxygen, moves to around 450 cm$^{-1}$ and shows a very
sharp peak. Electronic scattering background is low and electron-phonon
coupling is not evident for the observed phonon modes. Three features are found
above 500 cm$^{-1}$, which may be associated with multi-phonon process.
Nevertheless it is also possible that they are related to magnetic fluctuations
or interband transitions of d orbitals considering their energies.",0806.0885v1
2008-06-19,"75As NQR/NMR Studies on Oxygen-deficient Iron-based Oxypnictide Superconductors LaFeAsO_{1-y} (y=0,0.25,0.4) and NdFeAsO_{0.6}","We report 75As-NQR/NMR studies on the oxygen-deficient iron(Fe)-based
oxypnictide superconductors LaFeAsO_{0.6} (T_c=28 K) along with the results on
LaFeAsO, LaFeAsO_{0.75}(T_c=20 K) and NdFeAsO_{0.6}(T_c=53 K). Nuclear
spin-lattice relaxation rate 1/T_1 of 75As NQR at zero field on LaFeAsO_{0.6}
has revealed a T^3 dependence below T_c upon cooling without the coherence peak
just below T_c, evidencing the unconventional superconducting state with the
line-node gap. We have found an intimate relationship between the nuclear
quadrupole frequencyof 75As and T_c for four samples used in this study. It
implies microscopically that the local configuration of Fe and As atoms is
significantly related to the T_c of the Fe-oxypnictide superconductors, namely,
the T_c can be enhanced up to 50 K when the local configuration of Fe and As
atoms is optimal, in which the band structure may be also optimized through the
variation of hybridization between As 4p orbitals and Fe 3d orbitals.",0806.3238v2
2008-07-03,XMM-Newton X-ray spectra of the SNR 0509-67.5: data and models,"We report on X-ray observations of the supernova remnant 0509-67.5 in the
Large Magellanic Cloud with XMM-Newton X-ray observatory. We use the imaging
spectroscopy (EPIC) and Reflective Grating Spectrometer (RGS) data to
investigate properties of the remnant and its environment. The X-ray spectra
were analyzed with SPEX software package. In addition to this we performed a
numerical hydrodynamic simulation of the remnant. The EPIC data show prominent
Fe K line emission, but the deduced overall amount of iron in the shocked
ejecta is low. The data also show that the remnant has an asymmetric ejecta
structure: the bright southwest region of the remnant shows an overabundance of
metals. The analysis of the RGS spectrum shows that the remnant has a high
lines velocity broadening of ~5000 km/s. We found a hydrodynamical model for
the remnant with basic hydrodynamical and spectral parameters similar to the
observed ones. The data analysis show that the reverse shock just recently
reached iron layers of the ejecta. The brightness enhancement in the southwest
region could be a sign of an asymmetric explosion or it could be the result of
a density enhancement of the interstellar medium. We constructed numerical
models which are in good agreement with the observations, with circumstellar
density of 3e-25 g/cm^3, age of ~400 years, velocities of ~5000 km/s and an
electron to ion temperature ratio of 0.01.",0807.0579v1
2008-07-07,Local moment versus Kondo behavior of the 4f-electrons in rare-earth iron oxypnictides,"We consider the role played by the 4f states in the rare-earth oxyarsenides
REOFeAs (RE=Ce,Pr,Nd) and the oxyphosphate CeOFeP, using a first-principles
technique that combines the local density approximation and dynamical
mean-field theory (LDA+DMFT). In the Pr and Nd compounds, the 4f states are
located well below and above the Fermi level E_F, and essentially do not
interact with the iron 3d bands located near E_F, resulting in local moment
behavior. In the Ce compounds, our results reveal a qualitatively different
picture, with the 3d-4f hybridization being sufficiently strong to give rise to
an observable Kondo screening of the local 4f moment. Our LDA+DMFT electronic
structure calculations allow us to estimate the Kondo temperature T_K for both
CeOFeP and CeOFeAs. For the phosphate, the order of magnitude of our estimate
is consistent with the experimental observation of T_K around 10 K. At ambient
pressure, T_K is found to be negligibly small for CeOFeAs. Under applied
hydrostatic pressure, we predict an exponential increase of T_K which reaches
values comparable to the superconducting T_c around 40 K at pressures above 10
GPa. We conjecture that the competition between the Kondo effect and
superconductivity may be at the origin of the monotonous decrease of T_c
observed in CeOFeAs under pressure. We argue that the quantitative aspects of
this competition are inconsistent with a weak-coupling BCS description of the
superconductivity in the oxyarsenides.",0807.1037v2
2008-07-08,Fe and N self-diffusion in amorphous FeN: A SIMS and neutron reflectivity study,"Simultaneous measurement of self-diffusion of iron and nitrogen in amorphous
iron nitride (Fe86N14) using secondary ion mass spectroscopy (SIMS) technique
has been done. In addition neutron reflectivity (NR) technique was employed to
study the Fe diffusion in the same compound. The broadening of a tracer layer
of 57Fe8615N14 sandwiched between Fe86N14 layers was observed after isothermal
vacuum annealing of the films at different temperatures in SIMS measurements.
And a decay of the Bragg peak intensity after isothermal annealing was observed
in [Fe86N14/57Fe86N14]10 multilayers in NR. Strong structural relaxation of
diffusion coefficient was observed below the crystallization temperature of the
amorphous phase in both measurements. It was observed from the SIMS
measurements that Fe diffusion was about 2 orders of magnitude smaller compared
to nitrogen at a given temperature. The NR measurements reveal that the
mechanism of Fe self-diffusion is very similar to that in metal-metal type
metallic glasses. The structural relaxation time for Fe and N diffusion was
found comparable indicating that the obtained relaxation time essentially
pertain to the structural relaxation of the amorphous phase.",0807.1302v1
2008-07-08,Superconductivity induced by cobalt doping in iron-based oxyarsenides,"Chemical doping has recently become a very important strategy to induce
superconductivity especially in complex compounds. Distinguished examples
include Ba-doped La$_2$CuO$_4$ (the first high temperature superconductor),
K-doped BaBiO$_3$, K-doped C$_{60}$ and Na$_{x}$CoO$_{2}\cdot y$H$_{2}$O. The
most recent example is F-doped LaFeAsO, which leads to a new class of high
temperature superconductors. One notes that all the above dopants are
non-magnetic, because magnetic atoms generally break superconducting Cooper
pairs. In addition, the doping site was out of the (super)conducting structural
unit (layer or framework). Here we report that superconductivity was realized
by doping magnetic element cobalt into the (super)conducting-active
Fe$_2$As$_2$ layers in LaFe$_{1-x}$Co$_{x}$AsO. At surprisingly small Co-doping
level of $x$=0.025, the antiferromagnetic spin-density-wave transition in the
parent compound is completely suppressed, and superconductivity with $T_c\sim $
10 K emerges. With increasing Co content, $T_c$ shows a maximum of 13 K at
$x\sim 0.075$, and then drops to below 2 K at $x$=0.15. This result suggests
essential differences between previous cuprate superconductor and the present
iron-based arsenide one.",0807.1304v2
2008-07-24,Resonant Spin Excitation in the High Temperature Superconductor Ba0.6K0.4Fe2As2,"The recent observations of superconductivity at temperatures up to 55K in
compounds containing layers of iron arsenide have revealed a new class of high
temperature superconductors that show striking similarities to the more
familiar cuprates. In both series of compounds, the onset of superconductivity
is associated with the suppression of magnetic order by doping holes and/or
electrons into the band leading to theories in which magnetic fluctuations are
either responsible for or strongly coupled to the superconducting order
parameter. In the cuprates, theories of magnetic pairing have been invoked to
explain the observation of a resonant magnetic excitation that scales in energy
with the superconducting energy gap and is suppressed above the superconducting
transition temperature, Tc. Such resonant excitations have been shown by
inelastic neutron scattering to be a universal feature of the cuprate
superconductors, and have even been observed in heavy fermion superconductors
with much lower transition temperatures. In this paper, we show neutron
scattering evidence of a resonant excitation in Ba0.6K0.4Fe2As2, which is a
superconductor below 38K, at the momentum transfer associated with magnetic
order in the undoped compound, BaFe2As2, and at an energy transfer that is
consistent with scaling in other strongly correlated electron superconductors.
As in the cuprates, the peak disappears at Tc providing the first experimental
confirmation of a strong coupling of the magnetic fluctuation spectrum to the
superconducting order parameter in the new iron arsenide superconductors.",0807.3932v1
2008-07-25,Element-Specific Phonon Density of States of Iron in LaFeAsO_{1-x}F_{x} and La_{1-x}Ca_{x}FePO,"We have measured element-specific Fe-phonon densities of states (Fe-PDOS) of
LaFeAsO_{1-x}F_{x} (x = 0, 0.11) and La_{1-x}Ca_{x}FePO (x = 0.13) by using
nuclear resonant inelastic scattering of synchrotron radiation. The Fe-PDOS of
superconductor LaFeAsO_{0.89}F_{0.11} (Tc = 26 K) and that of
non-superconductor LaFeAsO have similar structures to both below Tc (15 K) and
above Tc (298 K) and, therefore, fluorine doping does not have notable effect
on the Fe-PDOS. As for the superconductor La_{0.87}Ca_{0.13}FePO (Tc = 5.4K),
the entire structure of Fe-PDOS resembles with that of LaFeAsO_{1-x}F_{x}, but
the energy of the highest peak is higher than that of LaFeAsO_{1-x}F_{x}. These
peaks are attributed to vibrational modes between Fe and pnicogen (As and P)
and the temperature-dependent energy shifts are observed for
LaFeAsO_{1-x}F_{x}. Observed Fe-PDOS of LaFeAsO_{1-x}F_{x} agrees well with an
previously calculated Fe-PDOS spectrum with a first-principles calculation and
shows the structural resemblance with an calculated Eliashberg function
#alpha^2F(x) giving small electron-phonon coupling. Therefore, our results
indicate that phonons are not the main contributors to the Tc superconductivity
of LaFeAsO_{1-x}F_{x}. From the experimental viewpoint, comparison of our
observed Fe-PDOS and an experimentally obtained bosonic glue spectrum will be
an important clue as to whether phonons are the main contributors to
superconductivity in iron-pnictide superconductors.",0807.3968v1
2008-07-29,Experimental Consequences of the S-wave $\cos(k_x) \cdot \cos(k_y)$ Superconductivity in the Iron-Pnictides,"The experimental consequences of different order parameters in iron-based
superconductors are theoretically analyzed. We consider both nodeless and nodal
order parameters, with an emphasis on the $\cos(k_x)\cdot \cos(k_y)$ nodeless
order parameter recently derived by two of us. We analyze the effect of this
order parameter on the spectral function, density of states, tunneling
differential conductance, penetration depth, and the NMR spin relaxation time.
This extended s-wave symmetry has line-zeroes in between the electron and hole
pockets, but they do not intersect the two Fermi surfaces for moderate doping,
and the superconductor is fully gapped. However, this suggests several
quantitative tests: the exponential decay of the penetration depth weakens and
the density of states reveals a smaller gap upon electron or hole doping.
Moreover, the $\cos(k_x) \cdot \cos(k_y)$ superconducting gap is largest on the
smallest (hole) Fermi surface. For the $1/T_1$ NMR spin relaxation rate, the
inter-band contribution is consistent with the current experimental results,
including a (non-universal) $T^{3}$ behavior and the absence of a coherence
peak. However, the intra-band contribution is considerably larger than the
inter-band contributions and still exhibits a small enhancement in the NMR spin
relaxation rate right below $T_c$ in the clean limit.",0807.4572v2
2008-08-06,Temperature and Spatial Dependence of the Superconducting and Pseudogap of NdFeAsO0.86F0.14,"The discovery of superconductivity with a critical temperature exceeding 55 K
in the iron-oxypnictides and related compounds has quite suddenly given the
community a new set of materials - breaking the tyranny of copper. This new
class of materials raises fundamental questions related to the origin of the
electron pairing in the superconducting state and to the similarity to
superconductivity in the cuprates. Here, we report spatially resolved
measurements using scanning tunneling microscopy/spectroscopy (STM/STS) of the
newly discovered iron-based layered superconductor NdFeAsO0.86F0.14 (Tc = 48 K)
as a function of temperature. The tunneling spectra at 17 K show a suppression
of spectral intensity within +/- 10 meV, indicative of the opening of the
superconducting gap (SG). Below Tc, the sample exhibits two characteristic gaps
- a large one (18 meV) and a small one (9 meV) - existing in different spatial
locations. Both gaps are closed above Tc at the bulk Tc, but only the small gap
can be fitted with a superconducting gap function. This gap displays a BCS -
like order parameter. Above Tc, at the same location where the small gap was
observed, a pseudogap (PG) opens abruptly at a temperature just above Tc and
closes at 120 K. In contrast to the cuprates, the SG and PG have competing
order parameters.",0808.0895v1
2008-08-18,"(pi,pi)-electronic order in iron arsenide superconductors","The distribution of valence electrons in metals usually follows the symmetry
of an ionic lattice. Modulations of this distribution often occur when those
electrons are not stable with respect to a new electronic order, such as spin
or charge density waves. Electron density waves have been observed in many
families of superconductors[1-3], and are often considered to be essential for
superconductivity to exist[4]. Recent measurements[5-9] seem to show that the
properties of the iron pnictides[10, 11] are in good agreement with band
structure calculations that do not include additional ordering, implying no
relation between density waves and superconductivity in those materials[12-15].
Here we report that the electronic structure of Ba1-xKxFe2As2 is in sharp
disagreement with those band structure calculations[12-15], instead revealing a
reconstruction characterized by a (pi,pi) wave vector. This electronic order
coexists with superconductivity and persists up to room temperature.",0808.2454v3
2008-09-01,Atomic diffusion and mixing in old stars II. Observations of stars in the globular cluster NGC 6397 with VLT/FLAMES-GIRAFFE,"Evolutionary trends in the surface abundances of heavier elements have
recently been identified in the globular cluster NGC 6397 ([Fe/H]=-2),
indicating the operation of atomic diffusion in these stars. Such trends
constitute important constraints for the extent to which diffusion modifies the
internal structure and surface abundances of solar-type, metal-poor stars. We
perform an independent check of the reality and size of abundance variations
within this metal-poor globular cluster. Observational data covering a large
stellar sample, located between the cluster turn-off point and the base of the
red giant branch, are homogeneously analysed. The spectroscopic data were
obtained with the medium-high resolution spectrograph FLAMES/GIRAFFE on
VLT-UT2. We derive independent effective-temperature scales from profile
fitting of Balmer lines and by applying colour-temperature calibrations to
Str\""omgren uvby and broad-band BVI photometry. An automated spectral analysis
code is used together with a grid of MARCS model atmospheres to derive stellar
surface abundances of Mg, Ca, Ti, and Fe. We identify systematically higher
iron abundances for more evolved stars. The turn-off point stars are found to
have 0.13dex lower surface abundances of iron compared to the coolest, most
evolved stars in our sample. There is a strong indication of a similar trend in
magnesium, whereas calcium and titanium abundances are more homogeneous. Within
reasonable error limits, the obtained abundance trends are in agreement with
the predictions of stellar structure models including diffusive processes
(sedimentation, levitation), if additional turbulent mixing below the outer
convection zone is included.",0809.0317v1
2008-10-02,The Delicate Electronic and Magnetic Structure of the LaOFePn System (Pn = pnictogen),"The occurrence of high temperature superconductivity, and the competition
with magnetism, in stoichiometric and doped LaOFeAs and isostructural
iron-oxypnictides is raising many fundamental questions about the electronic
structure and magnetic interactions in this class of materials. There are now
sufficient experimental data that it may be possible to identify the important
issues whose resolution will lead to the understanding of this system. In this
paper we address a number of the important issues. One important characteristic
is the Fe-As distance (or more abstractly the pnictogen (Pn) height $z$(Pn));
we present results for the effect of $z$(Pn) on the electronic structure,
energetics, and Fe magnetic moment. We also study LaOFeAs under pressure, and
investigate the effects of both electron and hole doping within the virtual
crystal approximation. The electric field gradients for all atoms in the
LaOFeAs compound are presented (undoped and doped) and compared with available
data. The observed $(\pi,\pi,\pi)$ magnetic order is studied and compared with
the computationally simpler $(\pi,\pi,0)$ order which is probably a very good
model in most respects. We investigate the crucial role of the pnictogen atom
in this class, and predict the structures and properties of the N and Sb
counterparts that have not yet been reported experimentally. At a certain
volume a gap opens at the Fermi level in LaOFeN, separating bonding from
antibonding bands and suggesting directions for a better simple understanding
of the seemingly intricate electronic structure of this system. Finally, we
address briefly on the possible effects of post-lanthanum rare earths, which
have been observed to enhance the superconducting critical temperature
substantially.",0810.0376v1
2008-10-09,Mottness underpins the anomalous optical response of Iron Pnictides,"The recent discovery of high-temperature superconductivity (HTSC) in doped
Iron pnictides is the latest example of unanticipated behavior exhibited by
$d$- and $f$-band materials. The symmetry of the SC gap, along with the
mechanism of its emergence from the ``normal'' state is a central issue in this
context. Here, motivated by a host of experimental signatures suggesting strong
correlations in the Fe-pnictides, we undertake a detailed study of their normal
state. Focussing on symmetry-unbroken phases, we use the correlated band
structure method, LDA+DMFT, to study the one-particle responses of both ${\rm
LaO_{1-x}FeAsF_{x}}$ and ${\rm SmO_{1-x}FeAsF_{x}}$ in detail. Basing ourselves
on excellent quantitative agreement between LDA+DMFT and key experiments
probing the one-particle responses, we extend our study, undertaking the first
detailed study of their normal state electrodynamic response. In particular, we
propose that near-total normal state incoherence, resulting from strong, {\it
local} correlations in the Fe $d$-shell in Fe-pnictides, underpins the
incoherent normal state transport found in these materials, and discuss the
specific electronic mechanisms leading to such behavior. We also discuss the
implications of our work for the multi-band nature of the SC by studying the
pairing ``glue'' function, which we find to be an overdamped, electronic
continuum. Similarities and differences between cuprates and Fe-pnictides are
also touched upon. Our study supports the view that SC in Fe-pnictides arises
from a bad metallic, incoherent ``normal'' state that is proximate to a Mott
insulator.",0810.1607v1
2008-10-15,Coulomb repulsion and correlation strength in LaFeAsO from Density Functional and Dynamical Mean-Field Theories,"LDA+DMFT (Local Density Approximation combined with Dynamical Mean-Field
Theory) computation scheme has been used to calculate spectral properties of
LaFeAsO -- the parent compound for new high-T$_c$ iron oxypnictides. Coulomb
repulsion $U$ and Hund's exchange $J$ parameters for iron 3d electrons were
calculated using \textit {first principles} constrained density functional
theory scheme in Wannier functions formalism. Resulting values strongly depend
on the number of states taken into account in calculations: when full set of
O-$2p$, As-$4p$, and Fe-3d orbitals with corresponding bands are included,
computation results in $U=3\div$4 eV and J=0.8 eV. In contrast to that when the
basis set is restricted to Fe-3d orbitals and bands only, computation gives
much smaller parameter values $F^0$=0.8 eV, $J$=0.5 eV. However, DMFT
calculations with both parameter sets and corresponding to them choice of basis
functions result in weakly correlated electronic structure that is in agreement
with experimental X-ray and photoemission spectra.",0810.2629v1
2008-10-19,Electronic Structure of New AFFeAs Prototype of Iron Arsenide Superconductors,"This work is provoked by recent discovery of new class prototype systems
AFFeAs (A=Sr,Ca) of novel layered ironpnictide High-Tc superconductors
(Tc=36K). Here we report ab initio LDA results for electronic structure of the
AFFeAs systems. We provide detailed comparison between electronic properties of
both new systems and reference LaOFeAs (La111) compound. In the vicinity of the
Fermi level all three systems have essentially the same band dispersions.
However for iron fluoride systems F(2p) states were found to be separated in
energy from As(4p) ones in contrast to La111, where O(2p) states strongly
overlaps with As(4p). Thus it should be more plausible to include only Fe(3d)
and As(4p) orbitals into a realistic noninteracting model than for La111.
Moreover Sr substitution with smaller ionic radius Ca in AFFeAs materials leads
to a lattice contruction and stronger Fe(3d)-As(4p) hybridization resulting in
smaller value of the density of states at the Fermi level in the case of Ca
compound. So to some extend Ca system reminds RE111 with later Rare Earths.
However Fermi surface of new fluorides is found to be nearly perfect
two-dimensional. Also we do not expect strong dependence of superconducting
properties with respect to different types of A substitutes.",0810.3377v1
2008-10-28,Mixing in Zero and Solar Metallicity Supernovae,"Two-dimensional simulations of mixing and fall back in non-rotating massive
stars have been carried out using realistic initial models for the presupernova
star and assuming standard spherically symmetric explosions of 1.2*10^51ergs.
Stars of 15 and 25 solar masses with both primordial and solar composition were
modeled. The zero metallicity supernova progenitors were compact blue stars and
the amount of Rayleigh-Taylor induced mixing in them was greatly reduced
compared with what was seen in the red supergiants with solar metallicity. The
compact zero-metal stars also experienced more fallback than their solar
metallicity counterparts. As a result, the ejected nucleosynthesis from the two
populations was very different. For the simple explosion model assumed, low
metallicity stars ejected ejected too little iron and intermediate mass
elements even to explain the abundance patterns in the most iron-poor stars
found to date, suggesting that some important ingredient is missing. Rotation
is likely to alter these conclusions by producing a greater fraction of red
supergiants among Population III stars. The velocities of the heavy elements in
all models considered - both red and blue supergiants - were less than observed
in SN 1987A, suggesting that at least occasionally, asymmetric aspects of the
explosion mechanism and fallback play a major role in mixing.",0810.5142v1
2008-11-10,The intrinsic electronic phase diagram of iron-oxypnictide superconductors,"We present the first comprehensive derivation of the intrinsic electronic
phase diagram of the iron-oxypnictide superconductors in the normal state based
on the analysis of the electrical resistivity $\rho$ of both
LaFeAsO$_{1-x}$F$_x$ and SmFeAsO$_{1-x}$F$_x$ for a wide range of doping. Our
data give clear-cut evidence for unusual normal state properties in these new
materials. In particular, the emergence of superconductivity at low doping
levels is accompanied by distinct anomalous transport behavior in $\rho$ of the
normal state which is reminiscent of the spin density wave (SDW) signature in
the parent material. At higher doping levels $\rho$ of LaFeAsO$_{1-x}$F$_x$
shows a clear transition from this pseudogap-like behavior to Fermi liquid-like
behavior, mimicking the phase diagram of the cuprates. Moreover, our data
reveal a correlation between the strength of the anomalous features and the
stability of the superconducting phase. The pseudogap-like features become
stronger in SmFeAsO$_{1-x}$F$_x$ where superconductivity is enhanced and vanish
when superconductivity is reduced in the doping region with Fermi liquid-like
behavior.",0811.1601v3
2008-11-13,Electronic phase separation in the slightly underdoped iron pnictide superconductor Ba(1-x)K(x)Fe(2)As(2),"Here we present a combined study of the slightly underdoped novel pnictide
superconductor Ba(1-x)K(x)Fe(2)As(2) by means of X-ray powder diffraction,
neutron scattering, muon spin rotation (muSR), and magnetic force microscopy
(MFM). Commensurate static magnetic order sets in below Tm ~ 70 K as inferred
from the emergence of the magnetic (1 0 -3) reflection in the neutron
scattering data and from the observation of damped oscillations in the
zero-field-muSR asymmetry. Transverse-field muSR below Tc shows a coexistence
of magnetically ordered and non-magnetic states, which is also confirmed by MFM
imaging. We explain such coexistence by electronic phase separation into
antiferromagnetic and superconducting/normal state regions on a lateral scale
of several tens of nanometers. Our findings indicate that such mesoscopic phase
separation can be considered an intrinsic property of some iron pnictide
superconductors.",0811.2224v1
2008-11-13,"On the importance of satellite lines to the He-like K ALPHA complex and the G ratio for calcium, iron, and nickel","New, more detailed calculations of the emission spectra of the He-like K
ALPHA complex of calcium, iron and nickel have been carried out using data from
both distorted-wave and R-matrix calculations. The value of the GD ratio (an
extended definition of the G ratio that accounts for the effect of resolved and
unresolved satellite lines) is significantly enhanced at temperatures below the
temperature of He-like maximum abundance. Furthermore it is shown that
satellite lines are important contributors to the GD ratio such that GD/G>1 at
temperatures well above the temperature of maximum abundance. These new
calculations demonstrate, with an improved treatment of the KLn (n>=3)
satellite lines, that K ALPHA satellite lines need to be included in models of
He like spectra even at relatively high temperatures. The excellent agreement
between spectra and line ratios calculated from R-matrix and distorted-wave
data also confirms the validity of models based on distorted-wave data for
highly charged systems, provided the effect of resonances are taken into
account as independent processes.",0811.2240v1
2009-01-15,"Discovery of a broad iron line in the black-hole candidate Swift J1753.5-0127, and the disk emission in the low/hard state revisited","We analyzed simultaneous archival XMM-Newton and RXTE observations of the
X-ray binary and black hole candidate Swift J1753.5-0127. In a previous
analysis of the same data a soft thermal component was found in the X-ray
spectrum, and the presence of an accretion disk extending close to the
innermost stable circular orbit was proposed. This is in contrast with the
standard picture in which the accretion disk is truncated at large radii in the
low/hard state. We tested a number of spectral models and we found that several
of them fit the observed spectra without the need of a soft disk-like
component. This result implies that the classical paradigm of a truncated
accretion disk in the low/hard state can not be ruled out by these data. We
further discovered a broad iron emission line between 6 and 7 keV in these
data. From fits to the line profile we found an inner disk radius that ranges
between ~6-16 gravitational radii, which can be in fact much larger, up to ~250
gravitational radii, depending on the model used to fit the continuum and the
line. We discuss the implications of these results in the context of a fully or
partially truncated accretion disk.",0901.2255v1
2009-01-17,Electrostatic co-assembly of iron oxide nanoparticles and polymers : towards the generation of highly persistent superparamagnetic nanorods,"A paradigm proposed recently by Boal et al. (A.K. Boal et al., Nature 404,
746-748, 2000) deals with the possibility to use inorganic nanoparticles as
building blocks for the design and fabrication of colloidal and supracolloidal
assemblies. It is anticipated that these constructs could be made of different
shapes, patterns and functionalities and could constitute the components of
future nanodevices including sensors, actuators or nanocircuits. Here we report
a protocol that allowed us to fabricate such nanoparticle aggregates. The
building blocks of the constructs were anionically coated iron oxide
nanocrytals (superparamagnetic, size 7 nm) and cationic-neutral block
copolymers. We have shown that the electrostatic interactions between charged
species can be controlled by tuning the ionic strength of the dispersion. Under
appropriate conditions, the control of electrostatics resulted in the
elaboration of spherical or elongated aggregates at the micrometer length
scale. The elongated aggregates were found to be rod-like, with diameters of a
few hundred nanometers and lengths between 1 and 50 micrometers. In addition to
their remarkable stiffness, the nanostructured rods were found to reorient
along with an externally applied magnetic field, in agreement with the laws of
superparamagnetism.",0901.2667v1
2009-01-18,"Iron pnictides: Single crystal growth and effect of doping on structural, transport and magnetic properties","We demonstrate the preparation of large, free standing iron pnictide single
crystals with a size up to 20 x 10 x 1 mm3 using solvents in zirconia crucibles
under argon atmosphere. Transport and magnetic properties are investigated to
study the effect of potassium doping on the structural and superconducting
property of the compounds. The spin density wave (SDW) anomaly at Ts ~138 K in
BaFe2As2 single crystals from self-flux shifts to Ts ~85 K due to Sn solvent
growth. We show direct evidence for an incorporation of Sn on the Fe site. The
electrical resistivity data show a sharp superconducting transition temperature
Tc~38.5 K for the single crystal of Ba0.68K0.32Fe2As2. A nearly 100% shielding
fraction and bulk nature of the superconductivity for the single crystal were
confirmed by magnetic susceptibility data. A sharp transition Tc~25 K occurred
for the single crystal of Sr0.85K0.15Fe2As2. There is direct evidence for a
coexistence of the SDW and superconductivity in the low doping regime of
Sr1-xKxFe2As2 single crystals. Structural implications of the doping effects as
well as the coexistence of the two order parameters are discussed.",0901.2728v3
2009-02-01,Neutron Studies of the Iron-based Family of High TC Magnetic Superconductors,"We review neutron scattering investigations of the crystal structures,
magnetic structures, and spin dynamics of the iron-based RFe(As,P)O (R=La, Ce,
Pr, Nd), (Ba,Sr,Ca)Fe2As2, and Fe1+x(Te-Se) systems. On cooling from room
temperature all the undoped materials exhibit universal behavior, where a
tetragonal-to-orthorhombic/monoclinic structural transition occurs, below which
the systems become antiferromagnets. For the first two classes of materials the
magnetic structure within the a-b plane consists of chains of parallel Fe spins
that are coupled antiferromagnetically in the orthogonal direction, with an
ordered moment typically less than one Bohr magneton. Hence these are itinerant
electron magnets, with a spin structure that is consistent with Fermi-surface
nesting and a very energetic spin wave bandwidth ~0.2 eV. With doping, the
structural and magnetic transitions are suppressed in favor of
superconductivity. Magnetic correlations are observed in the superconducting
regime, with a magnetic resonance that follows the superconducting order
parameter just like the cuprates. The rare-earth moments order
antiferromagnetically at low T like conventional magnetic-superconductors.
Pressure in CaFe2As2 transforms the system from a magnetically ordered
orthorhombic material to a collapsed non-magnetic tetragonal system. Tetragonal
Fe1+xTe transforms to a low T monoclinic structure at small x that changes to
orthorhombic at larger x, which is accompanied by a crossover from commensurate
to incommensurate magnetic order. Se doping suppresses the magnetic order.",0902.0091v2
2009-02-02,Doping dependent Irreversible Magnetic Properties of Ba(Fe1-xCox)2As2 Single Crystals,"We discuss the irreversible magnetic properties of self-flux grown
Ba(Fe1-xCox)2As2 single crystals for a wide range of concentrations covering
the whole phase diagram from the underdoped to the overdoped regime, x=0.038,
0.047, 0.058, 0.071, 0.074, 0.10, 0.106 and 0.118. Samples were characterized
by a magneto-optical method and show excellent spatial uniformity of the
superconducting state. The overall behavior closely follows classical Bean
model of the critical state. The field-dependent magnetization exhibits second
peak at a temperature and doping - dependent magnetic field, Hp. The evolution
of this fishtail feature with doping is discussed. Magnetic relaxation is
time-logarithmic and unusually fast. Similar to cuprates, there is an apparent
crossover from collective elastic to plastic flux creep above Hp. At high
fields, the field dependence of the relaxation rate becomes doping independent.
We discuss our results in the framework of the weak collective pinning and show
that vortex physics in iron-based pnictide crystals is much closer to high-Tc
cuprates than to conventional s-wave (including MgB2) superconductors.",0902.0201v1
2009-02-11,Non-exponential London penetration depth in Ba$_{1-}$K$_{x}$Fe$_{2}$As$_{2}$ single crystals,"We have studied the in- and out-of-plane magnetic penetration depths in the
hole- doped iron based superconductor Ba$_{1-x}$K$_{x}$Fe$_{2}$As$_{2}$
($T_{c}\approx$ 30K). The study was performed on single crystals grown from
different fluxes and we find that the results are nearly the same. The in-plane
London penetration depth $\lambda_{ab}$ does not show exponential saturation at
low temperature, as would be expected from a fully gapped superconductor.
Instead, $\lambda_{ab}(T)$ shows a power-law behavior, $\lambda\propto T^{n}$
($n\approx 2$), down to $T\approx 0.02 T_{c}$, similar to the electron doped
Ba(Fe$_{1-x}$Co$_{x}$)$_{2}$As$_{2}$. The penetration depth anisotropy
$\gamma_{\lambda}=\lambda_{c}(T)/\lambda_{ab}(T)$ increases upon cooling,
opposite to the trend observed in the anisotropy of the upper critical field,
$\gamma_{\xi}=H_{c2}^{\perp c}(0)/H_{c2}^{\parallel c}(0)$. These are universal
characteristics of both the electron and hole doped 122 systems, suggesting
unconventional superconductivity. The behavior of the in-plane superfluid
density $\rho_{ab}(T)$ is discussed in light of existing theoretical models
proposed for the iron pnictides superconductors.",0902.1804v1
2009-02-16,Electronic Structure of the BaFe$_2$As$_2$ Family of Iron Pnictides,"We use high resolution angle-resolved photoemission spectroscopy to study the
band structure and Fermi surface topology of the BaFe$_2$As$_2$ iron pnictides.
We observe two electron bands and two hole bands near the X-point, $(\pi,\pi)$
of the Brillouin zone, in the paramagnetic state for different doping levels,
including electron-doped Ba(Co$_{0.06}$Fe$_{0.94}$)$_2$As$_2$, undoped
BaFe$_2$As$_2$, and hole-doped Ba$_{0.6}$K$_{0.4}$Fe$_2$As$_2$. Among these
four bands, only the electron bands cross the Fermi level, forming two electron
pockets around X, while the hole bands approach but never reach the Fermi
level. We show that the band structure of the BaFe$_2$As$_2$ family matches
reasonably well with the prediction of LDA calculations after a
momentum-dependent shift and renormalization. Our finding resolves a number of
inconsistencies regarding the electronic structure of pnictides.",0902.2628v1
2009-03-11,Sub-surface convection zones in hot massive stars and their observable consequences,"We study the convection zones in the outer envelope of hot massive stars
which are caused by opacity peaks associated with iron and helium ionization.
We determine the occurrence and properties of these convection zones as
function of the stellar parameters. We then confront our results with
observations of OB stars. A stellar evolution code is used to compute a grid of
massive star models at different metallicities. In these models, the mixing
length theory is used to characterize the envelope convection zones. We find
the iron convection zone (FeCZ) to be more prominent for lower surface gravity,
higher luminosity and higher initial metallicity. It is absent for luminosities
below about $10^{3.2}\Lsun$, $10^{3.9}\Lsun$, and $10^{4.2}$\Lsun$ for the
Galaxy, LMC and SMC, respectively. We map the strength of the FeCZ on the
Hertzsprung-Russell diagram for three metallicities, and compare this with the
occurrence of observational phenomena in O stars: microturbulence, non-radial
pulsations, wind clumping, and line profile variability. The confirmation of
all three trends for the FeCZ as function of stellar parameters by empirical
microturbulent velocities argues for a physical connection between
sub-photospheric convective motions and small scale stochastic velocities in
the photosphere of O- and B-type stars. We further suggest that clumping in the
inner parts of the winds of OB stars could be caused by the same mechanism, and
that magnetic fields produced in the FeCZ could appear at the surface of OB
stars as diagnosed by discrete absorption components in ultraviolet absorption
lines.",0903.2049v1
2009-03-17,Solar System formation,"In this review, three major changes in our understanding of the early history
of the Solar System are presented.
  1) Early differentiation: A few recent results support the idea that
protoplanet formation and differentiation occurred partly simultaneously than
CAI formation. First, some iron meteorites, eucrites, and angrites older than
the chondrules or even than the CAI have been found. Second, iron meteorites
could be debris of early disrupted differentiated planetesimals, scattered from
the terrestrial planet region to the Main Belt. Finally, chondrules contain
fragments of planetesimal material.
  2) Earth and Moon: An equilibration mechanism explains the identical Oxygen
isotopic composition of the Earth and the Moon. In addition, it has been shown
that the Earth and the Moon mantles have the same 182^W anomaly, in contrast to
what was believed before. Consequently, the Moon forming impact should have
occurred after the extinction of the 182Hf radioactivity, about 60 Myr after
Solar System formation. This new datation is in agreement with new N-body
numerical simulations of the last phase of terrestrial planets formation, in
which giant impacts occur during about 100 Myr.
  3) Giant planets and Nice model: The migration of the giant planets in the
protoplanetary disc can be prevented if the planets are in resonance, close to
each other. In the ``Nice model'', the 4 outer planets of the Solar System were
in a compact configuration after the dissipation of gaseous disc. A few hundred
million years later, a global instability drives the planets on their present
orbits, producing the Late Heavy Bombardment. In this frame, a lot of
characteristics of our Solar System can be explained.",0903.3008v1
2009-03-19,Classification of quantum phases for the star-lattice antiferromagnet via a projective symmetry group analysis,"We study possible quantum ground states of the Heisenberg antiferromagnet on
the star lattice, which may be realized in the recently discovered polymeric
Iron Acetate,
Fe$_3$($\mu_3$-O)($\mu$-OAc)$_6$(H$_2$O)$_3$[Fe$_3$($\mu_3$-O)($\mu$-OAc)$_{7.5}$]$_2\cdot$
7H$_2$O. Even though the Fe$^{\rm III}$ moment in this material carries
spin-5/2 and the system eventually orders magnetically at low temperatures, the
magnetic ordering temperature is much lower than the estimated Curie-Weiss
temperature, revealing the frustrated nature of the spin interactions.
Anticipating that a lower spin analog of this material may be synthesized in
future, we investigate the effect of quantum fluctuations on the star-lattice
antiferromagnet using a large-$N$ Sp($N$) mean field theory and a projective
symmetry group analysis for possible bosonic quantum spin liquid phases. It is
found that there exist only two distinct gapped $Z_2$ spin liquid phases with
bosonic spinons for non-vanishing nearest-neighbor valence-bond-amplitudes. In
particular, the spin liquid phase which has a lower energy in the
nearest-neighbor exchange model can be stabilized for relatively higher spin
magnitudes. Hence it is perhaps a better candidate for the realization of
quantum spin liquid state. We also determine the magnetic ordering patterns
resulting from the condensation of the bosonic spinons in the two different
spin liquid phases. We expect these magnetic ordering patterns would directly
be relevant for the low temperature ordered phase of the Iron Acetate. The
phase diagram containing all of these phases and various dimerized states are
obtained for the nearest-neighbor exchange model and its implications are
discussed.",0903.3408v1
2009-04-28,Doping dependence of Normal-state Property in the Iron-based Oxypnictide Superconductors LaFeAsO1-y probed by 57Fe-NMR and 75As-NMR/NQR,"We report systematic 57Fe-NMR and 75As-NMR/NQR studies on an underdoped
sample (T_c=20 K), an optimally doped sample (T_c=28 K), and an overdoped
sample (T_c=22 K) of oxygen-deficient iron (Fe)-based oxypnictide
superconductor LaFeAsO_{1-y}$. A microscopic phase separation between
superconducting domains and magnetic domains is shown to take place in the
underdoped sample, indicating a local inhomogeneity in association with the
density distribution of oxygen deficiencies. As a result, 1/T_1T in the normal
state of the superconducting domain decreases significantly upon cooling at
both the Fe and As sites regardless of the electron-doping level in
LaFeAsO_{1-y}. On the basis of this result, we claim that $1/T_1T$ is not
always enhanced by antiferromagnetic fluctuations close to an antiferromagnetic
phase in the underdoped superconducting sample. This contrasts with the
behavior in hole-doped Ba_{0.6}K_{0.4}Fe2As2(T_c= 38 K), which exhibits a
significant increase in $1/T_1T$ upon cooling. We remark that the crucial
difference between the normal-state properties of LaFeAsO_{1-y} and
Ba_{0.6}K_{0.4}Fe2As2 originates from the fact that the relevant Fermi surface
topologies are differently modified depending on whether electrons or holes are
doped into the FeAs layers.",0904.4301v2
2009-05-01,Vortex core states in a minimal two-band model for iron-based superconductors,"The pairing symmetry is one of the major issues in the study of iron-based
superconductors. We adopt a minimal two-band tight-binding model with various
channels of pairing interaction, and derive a set of two-band Bogoliubov-de
Gennes (BdG) equations. The BdG equations are implemented in real space and
then solved self-consistently via exact diagonalization. In the uniform case,
we find that the $d_{x^2-y^2}$-wave pairing state is most favorable for a
nearest-neighbor pairing interaction while the $s_{x^2y^2}$-wave pairing state
is most favorable for a next-nearest-neighbor pairing interaction. The is
consistent with that reported by Seo {\em et al.} [Phys. Rev. Lett. {\bf 101},
206404 (2008)]. We then proceed to study the local electronic structure around
a magnetic vortex core for both $d_{x^2-y^2}$-wave and $s_{x^2y^2}$-wave
pairing symmetry in the mixed state. It is found from the local density of
states (LDOS) spectra and its spatial variation that the resonance core states
near the Fermi energy for the $d_{x^2-y^2}$-wave pairing symmetry are bound
while those for the $s_{x^2y^2}$-wave pairing symmetry can evolve from the
localized states into extended ones with varying electron filling factor.
Furthermore, by including an effective exchange interaction, the emergent
antiferromagnetic spin-density-wave (SDW) order can suppress the resonance core
states, which provides one possible avenue to understand the absence of
resonance peak as revealed by recent scanning tunneling microscopy experiment
(STM) by Yin {\em et al.} [Phys. Rev. Lett. {\bf 102}, 097002 (2009)].",0905.0014v2
2009-05-06,Impurity-induced bound states in iron-based superconductors with s-wave cos(kx)cos(ky) pairing symmetry,"Using both the self-consistent Bogoliubov-de Gennes formulation and
non-self-consistent T-matrix approach, we perform a comprehensive investigation
of the in-gap bound states induced by a localized single impurity in iron-based
superconductors. We focus on studying signatures associated with the
unconventional sign-changed s-wave pairing symmetry. For a non-magnetic
impurity, we find that there are two in-gap bounds, symmetric with respect to
zero energy, only in the sign changed s-wave pairing state, not in the
sign-unchanged s-wave state, due to the existence of non-trivial Andreev bound
states caused by the sign change. For a magnetic impurity, we find that due to
the breakdown of the local time-reversal symmetry, there exist only bound state
solutions (with orbital degeneracy) carrying one of the electron-spin
polarizations around the impurity. As increasing the scattering strength, the
system undergoes a quantum phase transition (level crossing) from a
spin-unpolarized ground state to a spin-polarized one. While the results for
the magnetic impurity are qualitatively similar in both the sign-changed and
sign-unchanged s-wave superconducting states, the bound states in the first
case are more robust and there is no $\pi$ phase shift of the SC gap near the
impurity in the strong scattering regime.",0905.0734v2
2009-05-20,A new look on the nature of high-spin to low-spin transition in Fe2O3,"Iron sesquioxide (Fe2O3) displays pressure and temperature induced spin and
structural transitions. Our calculations show that, density functional theory
(DFT), in the generalized gradient approximation (GGA) scheme, is capable of
capturing both the transitions. The ambient pressure corundum type phase
(hematite or alpha-Fe2O3), having R_3c symmetry, gets distorted by the
application of pressure and transforms to a distorted corundum type or
Rh2O3(II) phase with Pbcn symmetry, in agreement with recent experiments. GGA +
U calculations show the same trend but shift the transition pressures to higher
values. Experimentally, the onset of the structural transition begins in the
vicinity of the spin transition pressure and whether the system undergoes spin
transition in the corundum type (HP1) or in the Rh2O3(II) type (HP2) phase, is
still a controversial issue. With a relatively simple, but general, octahedral
structural parameter, Voct (the octahedral volume around iron ions), we show
that in order to acquire a low spin (LS) state from a high spin (HS) one, the
system does not necessarily need to change the crystal structure. Rather, the
spin transition is a phenomenon that concerns the cation octahedra and the spin
state of the system depends mainly on the value of Voct, which is governed by
two distinct equations of state, separated by a well defined volume gap, for
the HS and LS states respectively. Analysis of the results on the basis of
octahedral volume allows to sum up and bridge the gap between two experimental
results and thus provides a better description of the system in the region of
interest.",0905.3414v1
2009-06-01,"A Compton-thick Wind in the High Luminosity Quasar, PDS 456","PDS 456 is a nearby (z=0.184), luminous (L_bol ~10^47 erg/s) type I quasar. A
deep 190 ks Suzaku observation in February 2007 revealed the complex, broad
band X-ray spectrum of PDS 456. The Suzaku spectrum exhibits highly
statistically significant absorption features near 9 keV in the quasar
rest--frame. We show that the most plausible origin of the absorption is from
blue-shifted resonance (1s-2p) transitions of hydrogen-like iron (at 6.97 keV
in the rest frame). This indicates that a highly ionized outflow may be present
moving at near relativistic velocities (~0.25c). A possible hard X-ray excess
is detected above 15 keV with HXD (at 99.8% confidence), which may arise from
high column density gas (Nh>10^24cm^-2) partially covering the X-ray emission,
or through strong Compton reflection. Here we propose that the iron K-shell
absorption in PDS 456 is associated with a thick, possibly clumpy outflow,
covering about 20% of $4\pi$ steradian solid angle. The outflow is likely
launched from the inner accretion disk, within 15-100 gravitational radii of
the black hole. The kinetic power of the outflow may be similar to the
bolometric luminosity of PDS 456. Such a powerful wind could have a significant
effect on the co-evolution of the host galaxy and its supermassive black hole,
through feedback.",0906.0312v1
2009-06-17,The Kondo effect in ferromagnetic atomic contacts,"Iron, cobalt and nickel are archetypal ferromagnetic metals. In bulk,
electronic conduction in these materials takes place mainly through the $s$ and
$p$ electrons, whereas the magnetic moments are mostly in the narrow
$d$-electron bands, where they tend to align. This general picture may change
at the nanoscale because electrons at the surfaces of materials experience
interactions that differ from those in the bulk. Here we show direct evidence
for such changes: electronic transport in atomic-scale contacts of pure
ferromagnets (iron, cobalt and nickel), despite their strong bulk
ferromagnetism, unexpectedly reveal Kondo physics, that is, the screening of
local magnetic moments by the conduction electrons below a characteristic
temperature. The Kondo effect creates a sharp resonance at the Fermi energy,
affecting the electrical properties of the system;this appears as a Fano-Kondo
resonance in the conductance characteristics as observed in other artificial
nanostructures. The study of hundreds of contacts shows material-dependent
lognormal distributions of the resonance width that arise naturally from Kondo
theory. These resonances broaden and disappear with increasing temperature,
also as in standard Kondo systems. Our observations, supported by calculations,
imply that coordination changes can significantly modify magnetism at the
nanoscale. Therefore, in addition to standard micromagnetic physics, strong
electronic correlations along with atomic-scale geometry need to be considered
when investigating the magnetic properties of magnetic nanostructures.",0906.3135v1
2009-07-07,Doping dependence of heat transport in the iron-arsenide superconductor Ba(Fe$_{1-x}$Co$_x$)$_2$As$_2$: from isotropic to strongly $k$-dependent gap structure,"The temperature and magnetic field dependence of the in-plane thermal
conductivity $\kappa$ of the iron-arsenide superconductor
Ba(Fe$_{1-x}$Co$_x$)$_2$As$_2$ was measured down to $T \simeq 50$ mK and up to
$H = 15$ T as a function of Co concentration $x$ in the range 0.048 $ \leq x
\leq $ 0.114. In zero magnetic field, a negligible residual linear term in
$\kappa/T$ as $T \to 0$ at all $x$ shows that there are no zero-energy
quasiparticles and hence the superconducting gap has no nodes in the $ab$-plane
anywhere in the phase diagram. However, the field dependence of $\kappa$
reveals a systematic evolution of the superconducting gap with doping $x$, from
large everywhere on the Fermi surface in the underdoped regime, as evidenced by
a flat $\kappa (H)$ at $T \to 0$, to strongly $k$-dependent in the overdoped
regime, where a small magnetic field can induce a large residual linear term,
indicative of a deep minimum in the gap magnitude somewhere on the Fermi
surface. This shows that the superconducting gap structure has a strongly
$k$-dependent amplitude around the Fermi surface only outside the
antiferromagnetic/orthorhombic phase.",0907.1276v2
2009-09-09,Modeling the light curve of the transient SCP06F6,"We consider simple models based on core collapse or pair-formation supernovae
to account for the light curve of the transient SCP06F6. A radioactive decay
diffusion model provides estimates of the mass of the required radioactive
nickel and the ejecta as functions of the unknown redshift. An opacity change
such as by dust formation or a recombination front may account for the rapid
decline from maximum. We particularly investigate two specific redshifts:
$z=0.143$, for which Gaensicke et al. (2008) have proposed that the
unidentified broad absorption features in the spectrum of SCP06F6 are C$_{2}$
Swan bands, and $z=0.57$ based on a crude agreement with the Ca H&K and UV
iron-peak absorption features that are characteristic of supernovae of various
types. The ejected masses and kinetic energies are smaller for a more tightly
constrained model invoking envelope recombination. We also discuss the
possibilities of circumstellar matter (CSM) shell diffusion and shock
interaction models. In general, optically-thick CSM diffusion models can fit
the data with the underlying energy coming from an energetic buried supernova.
Models in which the CSM is of lower density so that the shock energy is both
rapidly thermalized and radiated tend not to be self-consistent. We suggest
that a model of SCP06F6 worth futher exploration is one in which the redshift
is $\sim$ 0.57, the spectral features are Ca and iron peak elements, and the
light curve is powered by the diffusive release of a substantial amount of
energy from nickel decay or from an energetic supernova buried in the ejecta of
an LBV-like event.",0909.1798v2
2009-09-10,New identified (3H)4d - (3H)4f transitions of Fe II from UVES spectra of HR 6000 and 46 Aql,"The analysis of the high-resolution UVES spectra of the CP stars HR 6000 and
46 Aql revealed the presence of an impressive number of unidentified lines, in
particular in the 5000 - 5400 A region. Because numerous 4d-4f transitions of
FeII lie in this spectral range, and because both stars are iron overabundant,
we investigated whether the unidentified lines can be due to FeII. ATLAS12
model atmospheres with parameters [13450K, 4.3] and [12560K, 3.8] were computed
for the individual abundances of HR 6000 and 46 Aql, respectively, in order to
use the stars as spectroscopic sources to identify FeII lines and to determine
FeII gf-values. After having identified several unknown lines in the stellar
spectra as due to (3H)4d - (3H)4f transitions of FeII, we derived stellar log
gf's for them by comparing observed and computed profiles. The energies of the
upper levels were assigned on the basis of both laboratory iron spectra and
predicted energy levels. We fixed 21 new levels of FeII with energies between
122910.9 cm^-1 and 123441.1 cm^-1. They allowed us to add 1700 new lines to the
Fe II line list in the range 810 - 15011 A.",0909.1936v1
2009-09-11,Direct Evidence for Outflow of Metal-enriched Gas Along the Radio Jets of Hydra A,"Using deep Chandra observations of the Hydra A galaxy cluster, we examine the
metallicity structure near the central galaxy and along its powerful radio
source. We show that the metallicity of the intracluster medium is enhanced by
up to 0.2 dex along the radio jets and lobes compared to the metallicity of the
undisturbed gas. The enhancements extend from a radius of 20 kpc from the
central galaxy to a distance of ~ 120 kpc. We estimate the total iron mass that
has been transported out of the central galaxy to be between 2 x 10^7 M_sun and
7 x 10^7 M_sun which represents 10% - 20% of the iron mass within the central
galaxy. The energy required to lift this gas is roughly 1% to 5% of the total
energetic output of the AGN. Evidently, Hydra A's powerful radio source is able
to redistribute metal-enriched, low entropy gas throughout the core of the
galaxy cluster. The short re-enrichment time scale < 10^9 yr implies that the
metals lost from the central galaxy will be quickly replenished.",0909.2252v2
2009-09-22,Chemistry of atmospheres formed during accretion of the Earth and other terrestrial planets,"We used chemical equilibrium and chemical kinetic calculations to model
chemistry of the volatiles released by heating different types of carbonaceous,
ordinary and enstatite chondritic material as a function of temperature and
pressure. Our results predict the composition of atmospheres formed by
outgassing during accretion of the Earth and other terrestrial planets.
Outgassing of CI and CM carbonaceous chondritic material produces H2O-rich
(steam) atmospheres in agreement with the results of impact experiments.
However, outgassing of other types of chondritic material produces atmospheres
dominated by other gases. Outgassing of ordinary (H, L, LL) and high iron
enstatite (EH) chondritic material yields H2-rich atmospheres with CO and H2O
being the second and third most abundant gases. Outgassing of low iron
enstatite (EL) chondritic material gives a CO-rich atmosphere with H2, CO2, and
H2O being the next most abundant gases. Outgassing of CV carbonaceous
chondritic material gives a CO2-rich atmosphere with H2O being the second most
abundant gas. Our results predict that the atmospheres formed during accretion
of the Earth and Mars were probably H2-rich unless the accreted material was
dominantly CI and CM carbonaceous chondritic material. We also predict
significant amounts of S, P, Cl, F, Na, and K in accretionary atmospheres at
high temperatures (1500-2500 K). Finally, our results may be useful for
interpreting spectroscopic observations of accreting extrasolar terrestrial
planets.",0909.4050v1
2009-10-12,"CCD time-series photometry of the globular cluster NGC 5053: RR Lyrae, Blue Stragglers and SX Phoenicis stars revisited","We report the results of CCD $V$, $r$ and $I$ time-series photometry of the
globular cluster NGC 5053. New times of maximum light are given for the eight
known RR Lyrae stars in the field of our images and their periods are revised.
Their $V$ light curves were Fourier decomposed to estimate their physical
parameters. A discussion on the accuracy of the Fourier-based iron abundances,
temperatures, masses and radii is given. New periods are found for the 5 known
SX Phe stars and a critical discussion of their secular period changes is
offered. The mean iron abundance for the RR Lyrae stars is found to be [Fe/H]
$\sim -1.97 \pm 0.16$ and lower values are not supported by the present
analysis. The absolute magnitude calibrations of the RR Lyrae stars yield an
average true distance modulus of $16.12 \pm 0.04$ or a distance of $16.7 \pm
0.3$ kpc. Comparison of the observational CMD with theoretical isochrones
indicates an age of $12.5 \pm 2.0$ Gyrs for the cluster. A careful
identification of all reported Blue Stragglers (BS) and their $V,I$ magnitudes
leads to the conclusion that BS12, BS22, BS23 and BS24 are not BS. On the other
hand, three new BS are reported. Variability was found in seven BS, very likely
of the SX Phe type in five of them, and in one red giant star. The new SX Phe
stars follow established $PL$ relationships and indicate a distance in
agreement with the distance from the RR Lyrae stars.",0910.2068v1
2009-10-21,Fe I/Fe II ionization equilibrium in cool stars: NLTE versus LTE,"Non-local thermodynamic equilibrium (NLTE) line formation for neutral and
singly-ionized iron is considered through a range of stellar parameters
characteristic of cool stars. A comprehensive model atom for Fe I and Fe II is
presented. Our NLTE calculations support the earlier conclusions that the
statistical equilibrium (SE) of Fe I shows an underpopulation of Fe I terms.
However, the inclusion of the predicted high-excitation levels of Fe I in our
model atom leads to a substantial decrease in the departures from LTE. As a
test and first application of the Fe I/II model atom, iron abundances are
determined for the Sun and four selected stars with well determined stellar
parameters and high-quality observed spectra. Within the error bars, lines of
Fe I and Fe II give consistent abundances for the Sun and two metal-poor stars
when inelastic collisions with hydrogen atoms are taken into account in the SE
calculations. For the close-to-solar metallicity stars Procyon and $\beta$ Vir,
the difference (Fe II - Fe I) is about 0.1 dex independent of the line
formation model, either NLTE or LTE. We evaluate the influence of departures
from LTE on Fe abundance and surface gravity determination for cool stars.",0910.3997v1
2009-10-22,Point-contact spectroscopic studies on normal and superconducting AFe_2As_2-type iron-pnictide single crystals,"Point-contact Andreev reflection spectroscopy (PCARS) is applied to
investigate the gap structure in iron pnictide single crystal superconductors
of the AFe_2As_2 (A=Ba, Sr) family (""Fe-122""). The observed point-contact
junction conductance curves, G(V), can be divided into two categories: one
where Andreev reflection is present for both (Ba_{0.6}K_{0.4})Fe_2As_2 and
Ba(Fe_{0.9}Co_{0.1})_2As_2, and the other with a V^{2/3} background conductance
universally observed extending even up to 100 meV for Sr_{0.6}Na_{0.4}Fe_2As_2
and Sr(Fe_{0.9}Co_{0.1})_2As_2. The latter is also observed in point-contact
junctions on the nonsuperconducting parent compound BaFe_2As_2. Mesoscopic
phase-separated coexistence of magnetic and superconducting orders is
considered to explain distinct behaviors in the superconducting samples. For
Ba_{0.6}K_{0.4}Fe_2As_2, double peaks due to Andreev reflection with
strongly-sloping background are frequently observed for point-contacts on
freshly-cleaved c-axis surfaces. If normalized by a background baseline and
analyzed by the Blonder-Tinkham-Klapwijk model, the data show a gap size
~3.0-4.0 meV with 2\Delta_0/k_BT_c ~ 2.0-2.6, consistent with the smaller gap
size reported in the LnFeAsO family (""Fe-1111""). For the
Ba(Fe_{0.9}Co_{0.1})_2As_2, G(V) curves typically display a zero-bias
conductance peak.",0910.4230v2
2009-11-01,Non-equilibrium ionization states in galaxy clusters,"X-ray imaging observatories have revealed hydrodynamic structures with linear
scales ~ 10 kpc in clusters of galaxies, such as shock waves in the 1E0657-56
and A520 galaxy clusters and the hot plasma bubble in the MKW 3s cluster. The
future X-ray observatory IXO will resolve for the first time the metal
distribution in galaxy clusters at the these scales. Heating of plasmas by
shocks and AGN activities can result in non-equilibrium ionization states of
metal ions. We study the effect of the non-equilibrium ionization at linear
scales <50 kpc in galaxy clusters. A condition for non-equilibrium ionization
is derived by comparing the ionization time-scale with the age of hydrodynamic
structures. Modeling of non-equilibrium ionization when the plasma temperature
suddenly change is performed. An analysis of relaxation processes of the FeXXV
and FeXXVI ions by means of eigenvectors of the transition matrix is given. We
conclude that the non-equilibrium ionization of iron can occur in galaxy
clusters if the baryonic overdensity delta is smaller than 11.0/tau, where
tau<<1 is the ratio of the hydrodynamic structure age to the Hubble time. Our
modeling indicates that the emissivity in the helium-like emission lines of
iron increases as a result of deviation from the ionization equilibrium. A slow
process of helium-like ionic fraction relaxation was analyzed. A new way to
determine a shock velocity is proposed.",0911.0119v1
2009-11-17,Limits on spin determination from disc spectral fitting in GX 339-4,"We attempt to constrain the black hole spin in GX 339-4 from spectral fitting
of disc dominated data using RXTE spectra from the three most recent outbursts.
We use the best current models for the disc emission, including full radiative
transfer through the photosphere rather than assuming that the intrinsic
emission from each radius has a (colour temperature corrected) blackbody
spectrum. The results strongly depend on the poorly known binary system
parameters, but we find a strict upper limit of a<0.9 for any distance greater
than 6 kpc, assuming that the orbital inclination is the same as that of the
inner disc. By contrast, the higher spin of 0.935 +/- 0.01 (statistical)
+/-0.01 (systematic) claimed from fitting the iron line profile in this object
requires that the inner disc is misaligned by over 20 degrees from the orbital
inclination. While some of these datasets are distorted by instrumental pileup,
the same spin/inclination constraints are derived from data which are not piled
up, so there is a real conflict between the two techniques to measure spin. We
argue that the disc spectral fits are more likely to be robust hence that there
are still issues to be understood in the iron line profile.",0911.3281v2
2009-12-05,Abundance Ratios in Stars vs. Hot Gas in Elliptical Galaxies: the Chemical Evolution Modeller Point of View,"I will present predictions from chemical evolution model aimed at a
self-consistent study of both optical (i.e. stellar) and X-ray (i.e.gas)
properties of present-day elliptical galaxies. Detailed cooling and heating
processes in the interstellar medium (ISM) are taken into and allow a reliable
modelling of the SN-driven galactic wind. SNe Ia activity, in fact, may power a
galactic wind lasting for a considerable amount of the galactic lifetime, even
in the case for which the efficiency of energy transfer into the ISM per SN Ia
event is less than unity. The model simultaneously reproduces the
mass-metallicity, the colour-magnitude, the L_X - L_B and the L_X - T
relations, as well as the observed trend of the [Mg/Fe] ratio as a function of
sigma, by adopting the prescriptions of Pipino & Matteucci (2004) for the gas
infall and star formation timescales. The ""iron discrepancy"", namely the too
high predicted iron abundance in X-ray haloes of ellipticals compared to
observations, can be solved by taking into account the existence of dust. I
will make predictions on several abundance ratios in the ISM and compare them
with the most recent observations.",0912.0971v1
2009-12-11,Similarities between structural distortions under pressure and chemical doping in superconducting BaFe2As2,"The discovery of a new family of high Tc materials, the iron arsenides
(FeAs), has led to a resurgence of interest in superconductivity. Several
important traits of these materials are now apparent, for example, layers of
iron tetrahedrally coordinated by arsenic are crucial structural ingredients.
It is also now well established that the parent non-superconducting phases are
itinerant magnets, and that superconductivity can be induced by either chemical
substitution or application of pressure, in sharp contrast to the cuprate
family of materials. The structure and properties of chemically substituted
samples are known to be intimately linked, however, remarkably little is known
about this relationship when high pressure is used to induce superconductivity
in undoped compounds. Here we show that the key structural features in
BaFe2As2, namely suppression of the tetragonal to orthorhombic phase transition
and reduction in the As-Fe-As bond angle and Fe-Fe distance, show the same
behavior under pressure as found in chemically substituted samples. Using
experimentally derived structural data, we show that the electronic structure
evolves similarly in both cases. These results suggest that modification of the
Fermi surface by structural distortions is more important than charge doping
for inducing superconductivity in BaFe2As2.",0912.2376v1
2009-12-17,XMM-Newton Observations of X-ray Pulsar Cen X-3,"We present the results of our study of X-ray pulsar Cen X-3 using XMM-Newton
observations. The light curve and the spectrum for this observations were built
and Fe triplet within 6.5-7 keV region was detected. The geometric model of
relativistic accretion disk for iron emission lines Fe I K alpha, Fe XXV and Fe
XXVI in 6.4-7.0 keV region was applied. The values of disc inclination, inner
and outer radii of the disc and mass of the central compact object (neutron
star) were obtained. Intensity variations of these lines during orbital motion
were also detected. The largest variation was detected for Fe I K alpha line,
that agrees with the results of other authors. These results conform the model
in which Fe I K alpha line forms in hot plasma of accretion disc and highly
ionized iron lines form in outer regions of binary system. Probably the most
interesting feature of Cen X-3 spectrum is Fe XXV triplet which was found by
Iaria et al. (2005) from Chandra data analysis. We did not find this triplet in
our analysis of XMM-Newton data and explain its absence by the insufficient
energy resolution of XMM-Newton instruments.",0912.3354v2
2009-12-22,XMM-Newton long-look observation of the narrow line Seyfert 1 galaxy PKS0558-504; I: Spectral analysis,"We present results from the spectral analysis of a long XMM-Newton
observation of the radio-loud NLS1 galaxy PKS0558-504. The source is highly
variable, on all sampled time scales. We did not observe any absorption
features in either the soft or hard X-ray band. We found weak evidence for the
presence of an iron line at ~6.8 keV, which is indicative of emission from
highly ionized iron. The 2-10 keV band spectrum is well fitted by a simple
power law model, whose slope steepens with increasing flux, similar to what is
observed in other Seyferts as well. The soft excess is variable both in flux
and shape, and it can be well described by a low-temperature Comptonisation
model, whose slope flattens with increasing flux. The soft excess flux
variations are moderately correlated with the hard band variations, and we
found weak evidence that they are leading them by ~20 ksec. Our results rule
out a jet origin for the bulk of the X-ray emission in this object. The
observed hard band spectral variations suggest intrinsic continuum slope
variations, caused by changes in the ""heating/cooling"" ratio of the hot corona.
The low-temperature Comptonising medium, responsible for the soft excess
emission, could be a hot layer in the inner disc of the source, which appears
due to the fact that the source is accreting at a super-Eddington rate. The
soft excess flux and spectral variations could be caused by random variations
of the accretion rate.",0912.4416v1
2009-12-28,Warm absorber and truncated accretion disc in IRAS 05078+1626,"X-ray observations of unabsorbed active galactic nuclei provide an
opportunity to explore the innermost regions of supermassive black hole
accretion discs. Our goal in this paper is to investigate the central
environment of a Seyfert 1.5 galaxy IRAS 05078+1626. We studied the
time-averaged spectrum obtained with the EPIC and RGS instruments. A power-law
continuum (photon index ~ 1.75) dominates the 2-10 keV energy range. A narrow
iron K alpha spectral line is clearly seen, presumably originating in a distant
torus, but no broad relativistic component was detected. However, the power law
and the iron K alpha line alone do not provide a satisfactory fit in the soft
X-ray band whose spectrum can be explained by the combination of three
components: a) a cold photoelectric absorber with column density ~ 10^(21)
cm^(-2). This gas could be located either in outer parts of the accretion disc,
at the rim of the torus or farther out in the host galaxy; b) a warm absorber
with high ionization parameter (log(xi) ~ 2.2) and column density ~ 10^(24)
cm^(-2); c) an ionized reflection where the reflecting gas could be either in
the inner wall of a warm absorber cone or in an ionized accretion disc. The
first X-ray spectroscopic measurement of IRAS05078+1626 unveils some of the
standard ingredients in Seyfert galaxies, such as a power-law primary
continuum, modified by reflection from the accretion disc and by the effect of
complex, multi-phase obscuration. However, data constrains the accretion disc,
if present, not to extend closer than to 60 gravitational radii from the black
hole.",0912.5165v2
2010-01-15,XMM-Newton unveils the complex iron K alpha region of Mrk 279,"We present the results of a ~160 ks-long XMM-Newton observation of the
Seyfert 1 galaxy Mrk 279. The spectrum shows evidence of both broad and narrow
emission features. The Fe K alpha line may be equally well explained by a
single broad Gaussian (FWHM~10,000 km/s) or by two components: an unresolved
core plus a very broad profile (FWHM~14,000 km/s). For the first time we
quantified, via the ""locally optimally emitting cloud"" model, the contribution
of the broad line region (BLR) to the absolute luminosity of the broad
component of the Fe K alpha at 6.4 keV. We find that the contribution of the
BLR is only ~3%. In the two-line component scenario, we also evaluated the
contribution of the highly ionized gas component, which produces the FeXXVI
line in the iron K region. This contribution to the narrow core of the Fe K
alpha line is marginal <0.1%. Most of the luminosity of the unresolved,
component of Fe K alpha may come from the obscuring torus, while the very-broad
associated component may come from the accretion disk. However, models of
reflection by cold gas are difficult to test because of the limited energy
band. The FeXXVI line at 6.9 keV is consistent to be produced in a high column
density (N_H~10^23 cm^{-2}), extremely ionized (log\xi~5.5-7) gas. This gas may
be a highly ionized outer layer of the torus.",1001.2712v1
2010-01-19,High-Resolution Spectroscopy of Extremely Metal-Poor Stars in the Least Evolved Galaxies: Leo IV,"We present high-resolution Magellan/MIKE spectroscopy of the brightest star
in the ultra-faint dwarf galaxy Leo IV. We measure an iron abundance of [Fe/H]
= -3.2, adding to the rapidly growing sample of extremely metal-poor stars
being identified in Milky Way satellite galaxies. The star is enhanced in the
alpha elements Mg, Ca, and Ti by ~0.3 dex, very similar to the typical Milky
Way halo abundance pattern. All of the light and iron-peak elements follow the
trends established by extremely metal-poor halo stars, but the neutron-capture
elements Ba and Sr are significantly underabundant. These results are quite
similar to those found for stars in the ultra-faint dwarfs Ursa Major II, Coma
Berenices, Bootes I, and Hercules, suggesting that the chemical evolution of
the lowest luminosity galaxies may be universal. The abundance pattern we
observe is consistent with predictions for nucleosynthesis from a Population
III supernova explosion. The extremely low metallicity of this star also
supports the idea that a significant fraction (>10%) of the stars in the
faintest dwarfs have metallicities below [Fe/H] = -3.0.",1001.3137v2
2010-02-16,Electron-doping evolution of the low-energy spin excitations in the iron arsenide BaFe$_{2-x}$Ni$_{x}$As$_{2}$ superconductors,"We use elastic and inelastic neutron scattering to systematically investigate
the evolution of the low-energy spin excitations of the iron arsenide
superconductor BaFe2-xNixAs2 as a function of nickel doping x. In the undoped
state, BaFe2As2 exhibits a tetragonal-to-orthorhombic structural phase
transition and simultaneously develops a collinear antiferromagnetic (AF) order
below TN = 143 K. Upon electron-doping of x = 0.075 to induce bulk
superconductivity with Tc = 12.3 K, the AF ordering temperature reduces to TN =
58 K.We show that the appearance of bulk superconductivity in
BaFe1.925Ni0.075As2 coincides with a dispersive neutron spin resonance in the
spin excitation spectra, and a reduction in the static ordered moment. For
optimally doped BaFe1.9Ni0.1As2 (Tc = 20 K) and overdoped BaFe1.85Ni0.15As2 (Tc
= 15 K) superconductors, the static AF long-range order is completely
suppressed and the spin excitation spectra are dominated by a resonance and
spin-gap at lower energies. We determine the electron-doping dependence of the
neutron spin resonance and spin gap energies, and demonstrate that the
three-dimensional nature of the resonance survives into the overdoped regime.
If spin excitations are important for superconductivity, these results would
suggest that the three-dimensional character of the electronic superconducting
gaps are prevalent throughout the phase diagram, and may be critical for
superconductivity in these materials.",1002.3133v2
2010-04-07,Iron oxide doped boron nitride nanotubes: structural and magnetic properties,"A first-principles formalism is employed to investigate the interaction of
iron oxide (FeO) with a boron nitride (BN) nanotube. The stable structure of
the FeO-nanotube has Fe atoms binding N atoms, with bond length of roughly
$\sim$2.1 \AA, and binding between O and B atoms, with bond length of 1.55 \AA.
In case of small FeO concentrations, the total magnetic moment is
(4$\mu_{Bohr}$) times the number of Fe atoms in the unit cell and it is
energetically favorable to FeO units to aggregate rather than randomly bind to
the tube. As a larger FeO concentration case, we study a BN nanotube fully
covered by a single layer of FeO. We found that such a structure has square FeO
lattice with Fe-O bond length of 2.11 \AA, similar to that of FeO bulk, and
total magnetic moment of 3.94$\mu_{Bohr}$ per Fe atom. Consistently with
experimental results, the FeO covered nanotube is a semi-half-metal which can
become a half-metal if a small change in the Fermi level is induced. Such a
structure may be important in the spintronics context.",1004.1151v2
2010-04-20,Terzan 5: an alternative interpretation for the split horizontal branch,"We consider the horizontal branch (HB) of the Globular Cluster Terzan 5,
recently shown to be split into two parts, the fainter one (delta M_K ~ 0.3mag)
having a lower metallicity than the more luminous. Both features show that it
contains at least two stellar populations. The separation in magnitude has been
ascribed to an age difference of ~6 Gyr and interpreted as the result of an
atypical evolutionary history for this cluster. We show that the observed HB
morphology is also consistent with a model in which the bright HB is composed
of second generation stars that are metal enriched and with a helium mass
fraction larger (by delta Y ~ 0.07) than that of first generation stars
populating the fainter part of the HB. Terzan 5 would therefore be anomalous,
compared to most ""normal"" clusters hosting multiple populations, only because
its second generation is strongly contaminated by supernova ejecta; the
previously proposed prolonged period of star formation, however, is not
required. The iron enrichment of the bright HB can be ascribed either to
contamination from Type Ia supernova ejecta of the low-iron, helium rich,
ejecta of the massive asympotic giant branch stars of the cluster, or to its
mixing with gas, accreting on the cluster from the environment, that has been
subject to fast metal enrichment due to its proximity with the galactic bulge.
The model here proposed requires only a small age difference, of ~100Myr.",1004.3426v1
2010-04-26,A strong and broad iron line in the XMM-Newton spectrum of the new X-ray transient and black-hole candidate XTE J1652-453,"We observed the new X-ray transient and black-hole candidate XTE J1652-453
simultaneously with XMM-Newton and the Rossi X-ray Timing Explorer (RXTE). The
observation was done during the decay of the 2009 outburst, when XTE J1652-453
was in the hard-intermediate state. The spectrum shows a strong and broad iron
emission line with an equivalent width of ~ 450 eV. The profile is consistent
with that of a line being produced by reflection off the accretion disk,
broadened by relativistic effects close to the black hole. The best-fitting
inner radius of the accretion disk is ~ 4 gravitational radii. Assuming that
the accretion disk is truncated at the radius of the innermost stable circular
orbit, the black hole in XTE J1652-453 has a spin parameter of ~ 0.5. The power
spectrum of the RXTE observation has an additional variability component above
50 Hz, which is typical for the hard-intermediate state. No coherent
quasi-periodic oscillations at low frequency are apparent in the power
spectrum, which may imply that we view the system at a rather low inclination
angle.",1004.4442v2
2010-04-28,Are C-rich ultra iron poor stars also He-rich?,"(abridged) The three most iron poor stars presently known ([Fe/H] equal to
-5.96, -5.4 and -4.75) are carbon-rich, they are called C-Rich Ultra-Metal Poor
Stars (CRUMPS). The origin of their peculiar surface abundances is not
understood. We propose a synthetic view of the different models so far proposed
to explain the peculiar abundances observed at the surface of the CRUMP stars.
We deduce some expected trends based on nucleosynthetic arguments and look for
signatures allowing to discriminate among models. We discuss the conditions for
having CRUMP stars which are He-rich, i.e. with a mass fraction of helium
greater than 0.30 and up to 0.60. We discuss the chemical composition of stars
made of interstellar medium mixed with wind material of very metal poor massive
stars, with wind plus supernova ejecta and with material extracted from the
envelope of early AGB stars. Rotating and non-rotating models are considered.
CRUMP stars formed from wind material of massive stars mixed with small amounts
of pristine interstellar medium are He-rich (helium mass fraction between 0.30
and 0.60), Li-depleted and present low $^{12}$C/$^{13}$C ratios (inferior to 10
in number). Such He-rich stars, if discovered, would confirm that the most
metal poor CRUMPs formed from essentially pure wind/envelope material. They
would provide the most direct way to probe the nucleosynthetic outputs of the
first generations of stars. We show that rotation is a key ingredient to
explain the abundance patterns of CRUMPS stars.",1004.5024v1
2010-05-08,Non-Resonant X-ray Magnetic Scattering on Rare-Earth Iron Borates RFe$_3$(BO$_3$)$_4$,"Hard x-ray scattering (HXS) experiments with a photon energy of 100keV were
performed as a function of temperature and applied magnetic field on selected
compounds of the RFe$_3$(BO$_3$)$_4$ family. The results show the presence of
several unexpected diffraction features, in particular non-resonant magnetic
reflections in the magnetically ordered phase, and structural reflections that
violate the diffraction conditions for the low temperature phase $P3_121$ of
the rare-earth iron borates. The temperature and field dependence of the
magnetic superlattice reflections corroborate the magnetic structures of the
borate compounds obtained by neutron diffraction. The detailed analysis of the
intensity and scattering cross section of the magnetic reflection reveals
details of the magnetic structure of these materials such as the spin domain
structure of NdFe$_3$(BO$_3$)$_4$ and GdFe$_3$(BO$_3$)$_4$. Furthermore we find
that the correlation length of the magnetic domains is around 100 \AA{} for all
the compounds and that the Fe moments are rotated $53^\circ\pm3^\circ$ off from
the hexagonal basal plane in GdFe$_3$(BO$_3$)$_4$",1005.1333v2
2010-05-13,Vacancy ordering and electronic structure of gamma-Fe2O3 (maghemite): a theoretical investigation,"The crystal structure of the iron oxide gamma-Fe2O3 is usually reported in
either the cubic system (space group P4332) with partial Fe vacancy disorder or
in the tetragonal system (space group P41212) with full site ordering and
c/a\approx 3. Using a supercell of the cubic structure, we obtain the spectrum
of energies of all the ordered configurations which contribute to the partially
disordered P4332 cubic structure. Our results show that the configuration with
space group P41212 is indeed much more stable than the others, and that this
stability arises from a favourable electrostatic contribution, as this
configuration exhibits the maximum possible homogeneity in the distribution of
iron cations and vacancies. Maghemite is therefore expected to be fully ordered
in equilibrium, and deviations from this behaviour should be associated with
metastable growth, extended anti-site defects and surface effects in the case
of small nanoparticles. The confirmation of the ordered tetragonal structure
allows us to investigate the electronic structure of the material using density
functional theory (DFT) calculations. The inclusion of a Hubbard (DFT+U)
correction allows the calculation of a band gap in good agreement with
experiment. The value of the gap is dependent on the electron spin, which is
the basis for the spin-filtering properties of maghemite.",1005.2370v1
2010-05-13,Competing order and nature of the pairing state in the iron pnictides,"We show that the competition between magnetism and superconductivity can be
used to determine the pairing state in the iron arsenides. To this end we
demonstrate that the itinerant antiferromagnetic phase (AFM) and the
unconventional $s^{+-}$ sign-changing superconducting state (SC) are near the
borderline of microscopic coexistence and macroscopic phase separation,
explaining the experimentally observed competition of both ordered states. In
contrast, conventional $s^{++}$ pairing is not able to coexist with magnetism.
Expanding the microscopic free energy of the system with competing orders
around the multicritical point, we find that static magnetism plays the role of
an intrinsic interband Josephson coupling, making the phase diagram sensitive
to the symmetry of the Cooper pair wavefunction. We relate this result to the
quasiparticle excitation spectrum and to the emergent SO$(5)$ symmetry of
systems with particle-hole symmetry. Our results rely on the assumption that
the same electrons that form the ordered moment contribute to the
superconducting condensate and that the system is close to particle-hole
symmetry. We also compare the suppression of SC in different regions of the
FeAs phase diagram, showing that while in the underdoped side it is due to the
competition with AFM, in the overdoped side it is related to the disappearance
of pockets from the Fermi surface.",1005.2437v3
2010-05-18,Spectral variability of the peculiar A-type supergiant 3Pup,"Optical spectra of the peculiar supergiant 3Pup taken in 1997-2008 are used
to analyze the spectral peculiarities and velocity field in its atmosphere. The
profiles of strong FeII lines and of the lines of other iron-group ions have a
specific shape: the wings are raised by emissions, whereas the core is
sharpened by a depression. The latter feature becomes more pronounced with the
increasing line strength, and the increasing wavelength. Line profiles are
variable: the magnitude and sign of the absorption asymmetry, and the
blue-to-red emission intensity ratios vary from one spectrum to another. The
temporal Vr variations are minimal for the forbidden emissions and sharp shell
cores of the absorption features of FeII(42), and other strong lines of
iron-group ions. The average velocity for the above lines can be adopted as the
systemic velocity: Vsys=28.5+/-0.5km/s. The weakest photospheric absorptions
and photospheric MgII, SiII absorptions exhibit well-defined day-to-day
velocity variations of up to 7km/s. Quantitative spectral classification yields
the spectral type of A2.7+/-0.3 Ib. The equivalent widths and profiles of
Hdelta and Hgamma, and the equivalent width of the OI7774A triplet yield an
absolute magnitude estimate of Mv=-5.5+/-0.3mag, implying the heliocentric
distance of 0.7kpc.",1005.3098v1
2010-05-18,A New Limit on the Distances of Nuclei UHECRs Sources,"Recent evidence from the Pierre Auger Observatory suggests a transition, at 5
EeV-10EeV in the composition of Ultra High Energy Cosmic Rays (UHECRs), from
protons to heavier nuclei such as iron. I consider here the implications of the
heavier composition on the sources of UHECRs. The smaller magnetic rigidity
implies that nuclei UHECRs are: (i) More easily accelerated (ii) Local, as they
can diffuse only a few Mpc from their sources before disintegrating (iii)
Isotropic, because large deflections in the extra galactic and the galactic
magnetic fields erase the directional information. Uncertainties in the
strength and structure of the the extra galactic magnetic field (EGMF) makes it
difficult to estimate the overall effects. However, with typical reasonable
parameters of a few nG and a coherence distance of a Mpc the distance a nuclei
UHECR above the GZK energy traverses before photodisintegrating is only a few
Mpc. In spite of the significantly weaker limits on the luminosity, Cen A is
the only currently active potential source of nuclei UHECRs within this
distance. The large deflections erases the directional anisotropy expected from
a single source. If indeed the composition of above-GZK-UHECRs is iron and if
the EGMF is not too small then Cen A is the dominant source of observed nuclei
UHECRs above the GZK limit.",1005.3311v1
2010-05-19,Thermodynamic Limits on Magnetodynamos in Rocky Exoplanets,"To ascertain whether magnetic dynamos operate in rocky exoplanets more
massive or hotter than the Earth, we developed a parametric model of a
differentiated rocky planet and its thermal evolution. Our model reproduces the
established properties of Earth's interior and magnetic field at the present
time. When applied to Venus, assuming that planet lacks plate tectonics and has
a dehydrated mantle with an elevated viscosity, the model shows that the dynamo
shuts down or never operated. Our model predicts that at a fixed planet mass,
dynamo history is sensitive to core size, but not to the initial inventory of
long-lived, heat-producing radionuclides. It predicts that rocky planets larger
than 2.5 Earth masses will not develop inner cores because the
temperature-pressure slope of the iron solidus becomes flatter than that of the
core adiabat. Instead, iron ""snow"" will condense near or at the top of these
cores, and the net transfer of latent heat upwards will suppress convection and
a dynamo. More massive planets can have anemic dynamos due to core cooling, but
only if they have mobile lids (plate tectonics). The lifetime of these dynamos
is shorter with increasing planet mass but longer with higher surface
temperature. Massive Venus-like planets with stagnant lids and more viscous
mantles will lack dynamos altogether. We identify two alternative sources of
magnetic fields on rocky planets: eddy currents induced in the hot or molten
upper layers of planets on very short period orbits, and dynamos in the ionic
conducting layers of ""ocean"" planets with ~10% mass in an upper mantle of water
(ice).",1005.3523v1
2010-05-21,Observation of Lattice and Andreev Bound States of Vortices in Ba0.6K0.4Fe2As2 Single Crystals with Scanning Tunneling Microscopy/Spectroscopy,"For a type-II superconductor, when the applied magnetic field is higher than
the lower critical value Hc1, the magnetic flux will penetrate into the
superconductor and form quantized vortices, which usually are arranged in an
Abrikosov lattice. For the newly discovered iron pnictide superconductors,
previous measurements have shown that, in electron-doped BaFe2As2, the vortices
form a highly disordered structure. In addition, the density of states (DOS)
within the vortex cores1 do not exhibit the Andreev bound states in
conventional superconductors. In this Letter, we report the observation of a
triangular vortex lattice and the Andreev bound states in hole-doped BaFe2As2
by using a low temperature scanning tunneling microscope (STM). Detailed study
of the vortex cores reveals that the spectrum of the Andreev bound states
inside the vortex core exhibits a distinct spatial evolution: at the center of
the vortex core, it appears as a single peak at 0.5 mV below the Fermi-energy;
away from the core center, it gradually evolves into two sub-peaks and they
eventually fade out. The drastic differences between the vortex cores of the
electron-doped and hole-doped counterparts are illusive to the pairing
mechanism of the iron pnictide superconductors.",1005.4038v1
2010-05-25,The pairing state in KFe2As2 studied by measurements of the magnetic vortex lattice,"Understanding the mechanism and symmetry of electron pairing in iron-based
superconductors represents an important challenge in condensed matter physics
[1-3]. The observation of magnetic flux lines - ""vortices"" - in a
superconductor can contribute to this issue, because the spatial variation of
magnetic field reflects the pairing. Unlike many other iron pnictides, our
KFe2As2 crystals have very weak vortex pinning, allowing
small-angle-neutron-scattering (SANS) observations of the intrinsic vortex
lattice (VL). We observe nearly isotropic hexagonal packing of vortices,
without VL-symmetry transitions up to high fields along the fourfold c-axis of
the crystals, indicating rather small anisotropy of the superconducting
properties around this axis. This rules out gap nodes parallel to the c-axis,
and thus d-wave and also anisotropic s-wave pairing [2, 3]. The strong
temperature-dependence of the intensity down to T<<Tc indicates either widely
different full gaps on different Fermi surface sheets, or nodal lines
perpendicular to the axis.",1005.4468v2
2010-06-11,Scaling of normal-state transport properties of 1111 iron-pnictide superconductors,"We show that the zero field normal-state resistivity above Tc for various
levels of electron doping-both for underdoped, optimally, and overdoped
LaO1-xFxFeAs, i.e. (x=0.05-0.075 and 0.1-0.2) and underdoped SmO1-xFxFeAs
(x=0.06- 0.1) members of the 1111-iron-pnictide superconductor family-can be
scaled in a broad temperature range from 20 to 300 K onto a single universal
curve. The scaling was performed using the energy scale Delta, the resistivity
rho(Delta) and the residual resistivity rho0 as scaling parameters as well as
applying a recently proposed model-independent scaling method (H. G. Luo, Y. H.
Su, and T. Xiang, Phys. Rev. B 77, 014529 (2008)). The scaling parameters have
been calculated and the compositional variation of Delta has been determined.
The existence of a universal metallic rho(T) curve is interpreted as an
indication of a single mechanism which dominates the scattering of the charge
carriers in LaO1-xFxFeAs (x= 0.05 to 0.075 and 0.1 to 0.2) and SmO1-xFxFeAs (x
= 0.06 to 0.1) .",1006.2350v2
2010-07-12,Magnetic order in orbital models of the iron pnictides,"We examine the appearance of the experimentally-observed stripe
spin-density-wave magnetic order in five different orbital models of the iron
pnictide parent compounds. A restricted mean-field ansatz is used to determine
the magnetic phase diagram of each model. Using the random phase approximation,
we then check this phase diagram by evaluating the static spin susceptibility
in the paramagnetic state close to the mean-field phase boundaries. The momenta
for which the susceptibility is peaked indicate in an unbiased way the actual
ordering vector of the nearby mean-field state. The dominant orbitally resolved
contributions to the spin susceptibility are also examined to determine the
origin of the magnetic instability. We find that the observed stripe magnetic
order is possible in four of the models, but it is extremely sensitive to the
degree of the nesting between the electron and hole Fermi pockets. In the more
realistic five-orbital models, this order competes with a strong-coupling
incommensurate state which appears to be controlled by details of the
electronic structure below the Fermi energy. We conclude by discussing the
implications of our work for the origin of the magnetic order in the pnictides.",1007.1949v2
2010-07-15,Spectroscopic survey of M--type asteroids,"M-type asteroids, as defined in the Tholen taxonomy (Tholen, 1984), are
medium albedo bodies supposed to have a metallic composition and to be the
progenitors both of differentiated iron-nickel meteorites and enstatite
chondrites. We carried out a spectroscopic survey in the visible and near
infrared wavelength range (0.4-2.5 micron) of 30 asteroids chosen from the
population of asteroids initially classified as Tholen M -types, aiming to
investigate their surface composition. The data were obtained during several
observing runs during the years 2004-2007 at the TNG, NTT, and IRTF telescopes.
We computed the spectral slopes in several wavelength ranges for each observed
asteroid, and we searched for diagnostic spectral features. We confirm a large
variety of spectral behaviors for these objects as their spectra are extended
into the near-infrared, including the identification of weak absorption bands,
mainly of the 0.9 micron band tentatively attributed to orthopyroxene, and of
the 0.43 micron band that may be associated to chlorites and Mg-rich
serpentines or pyroxene minerals such us pigeonite or augite. A comparison with
previously published data indicates that the surfaces of several asteroids
belonging to the M-class may vary significantly. We attempt to constrain the
asteroid surface compositions of our sample by looking for meteorite spectral
analogues in the RELAB database and by modelling with geographical mixtures of
selected meteorites/minerals. We confirm that iron meteorites, pallasites, and
enstatite chondrites are the best matches to most objects in our sample, as
suggested for M-type asteroids. The presence of subtle absorption features on
several asteroids confirms that not all objects defined by the Tholen M-class
have a pure metallic composition.",1007.2582v1
2010-07-16,High-Resolution X-ray Spectroscopy of the Interstellar Medium,"The interstellar medium (ISM) has a multiphase structure characterized by
gas, dust and molecules. The gas can be found in different charge states:
neutral, low-ionized (warm) and high-ionized (hot). It is possible to probe the
multiphase ISM through the observation of its absorption lines and edges in the
X-ray spectra of background sources. We present a high-quality RGS spectrum of
the low-mass X-ray binary GS 1826-238 with an unprecedent detailed treatment of
the absorption features due to the dust and both the neutral and ionized gas of
the ISM. We constrain the column density ratios within the different phases of
the ISM and measure the abundances of elements such as O, Ne, Fe and Mg. We
found significant deviations from the proto-Solar abundances: oxygen is
over-abundant by a factor 1.23 +/- 0.05, neon 1.75 +/- 0.11, iron 1.37 +/- 0.17
and magnesium 2.45 +/- 0.35. The abundances are consistent with the measured
metallicity gradient in our Galaxy: the ISM appears to be metal-rich in the
inner regions. The spectrum also shows the presence of warm/hot ionized gas.
The gas column has a total ionization degree less than 10%. We also show that
dust plays an important role as expected from the position of GS 1826-238: most
iron appears to be bound in dust grains, while 10-40% of oxygen consists of a
mixture of dust and molecules.",1007.2796v1
2010-07-16,Crystal Symmetry and Magnetic Order in Iron Pnictides: a Tight Binding Wannier Function Analysis,"To perform a local orbital analysis of electronic and magnetic interactions,
we construct the Wannier functions (WFs) of the Fe $3d$ orbitals in the parent
compound of the recently discovered iron pnictide superconductors, LaFeAsO, and
a comparison material LaFePO. Comparing the WFs for the stripe
antiferromagnetic order with those for no magnetic order, the difference is a
significant spreading (``{\it de}localization'') of specifically the $d_{xy}$
and $d_{xz}$ (but not $d_{yz}$) WFs, where parallel Fe spins lie along the $x$
direction. The WF basis gives a tight-binding representation of the first
principles, density functional based Fe-derived bands. Comparing hopping
parameters, it is found that changes due to stripe antiferromagnetism, even if
it is weak, enables more isotropic hopping involving spin-majority electrons in
the Fe $3d_{xz}$ (but not the $3d_{yz}$) orbital. This change,
counterintuitively, actually reinforces electronic anisotropy. Further insight
is gained by comparing the WFs of LaFeAsO and LaFePO, identifying how the
difference in WFs is related to the difference in hopping integrals and showing
how the pnictide atom is influential in forming the stripe antiferromagnetism.
Kinetic energy considerations suggest that orbital fluctuation, in addition to
spin fluctuation, may contribute to the decrease in observed ordered moment
compared to the calculated values.",1007.2878v1
2010-07-21,Pseudogap of Superconducting correlation origin in iron-pnictide superconductor Ba0.6+δK0.4-δFe2As2,"Pseudogap (PG), a phenomenon of opening of gap like features above
superconducting (SC) transition temperature (Tc), has been universally observed
in the high-Tc cuprates (HTC) (1,2), some heavy fermion superconductors (3),
and iron pnictides (4-7). Here, we report the observation of PG behavior in
optical conductivity in an underdoped Ba0.6+{\delta}K0.4-{\delta}Fe2As2
(Tconset =36 K) single crystal far above Tc, up to 100 K (~ 3Tc). Unique scale
separation in Ba0.6+{\delta}K0.4-{\delta}Fe2As2 compound - magnetic and SC
correlation energy scales being widely separated - enabled us to establish that
the PG structures observed in the range of 50 cm-1 - 150 cm-1 in optical
conductivity is caused by the SC correlation and the magnetic correlation
origin is ruled out. Theoretical calculations, based on the preformed Cooper
pair model (8), provided an excellent description to the temperature evolution
of the optical conductivity data from below to above Tc.",1007.3617v1
2010-07-29,Dissimilarities between the electronic structure of chemically doped and chemically pressurized iron pnictides from an angle-resolved photoemission spectroscopy study,"We have studied the electronic structure of EuFe2As2-xPx using high
resolution angle-resolved photoemission spectroscopy. Upon substituting As with
the isovalent P, which leads to a chemical pressure and to superconductivity,
we observe a non-rigid-band like change of the electronic structure along the
center of the Brillouin zone (BZ): an orbital and kz dependent increase or
decrease in the size of the hole pockets near the Gamma - Z line. On the other
hand, the diameter of the Fermi surface cylinders at the BZ corner forming
electron pockets, hardly changes. This is in stark contrast to p and n-type
doped iron pnictides where, on the basis of ARPES experiments, a more
rigid-band like behavior has been proposed. These findings indicate that there
are different ways in which the nesting conditions can be reduced causing the
destabilization of the antiferromagnetic order and the appearance of the
superconducting dome.",1007.5205v1
2010-07-29,Spectral analysis for the iron-based superconductors: Anisotropic spin fluctuations and fully gapped s^{\pm}-wave superconductivity,"Spin fluctuations are considered to be one of the candidates that drive a
sign-reversed s^{\pm} superconducting state in the iron pnictides. In the
magnetic scenario, whether the spin fluctuation spectrum exhibits certain
unique fine structures is an interesting aspect for theoretical study in order
to understand experimental observations. We investigate the detailed momentum
dependence of the short-range spin fluctuations using a 2-orbital model in the
self-consistent fluctuation exchange approximation and find that a common
feature of those fluctuations that are capable of inducing a fully gapped
s^{\pm} state is the momentum anisotropy with lengthened span along the
direction transverse to the antiferromagnetic momentum transfer. Performing a
qualitative analysis based on the orbital character and the deviation from
perfect nesting of the electronic structure for the 2-orbital and a more
complete 5-orbital model, we gain the insight that this type of anisotropic
spin fluctuations favor superconductivity due to their enhancement of
intra-orbital, but inter-band, pair scattering processes. The momentum
anisotropy leads to elliptically shaped magnetic responses which have been
observed in inelastic neutron scattering measurements. Meanwhile, our detailed
study on the magnetic and the electronic spectrum shows that the dispersion of
the magnetic resonance mode in the nearly isotropic s^{\pm} superconducting
state exhibits anisotropic propagating behavior in an upward pattern and the
coupling of the resonance mode to fermions leads to a dip feature in the
spectral function.",1007.5321v3
2010-09-22,3D MHD simulations of subsurface convection in OB stars,"During their main sequence evolution, massive stars can develop convective
regions very close to their surface. These regions are caused by an opacity
peak associated with iron ionization. Cantiello et al. (2009) found a possible
connection between the presence of sub-photospheric convective motions and
small scale stochastic velocities in the photosphere of early-type stars. This
supports a physical mechanism where microturbulence is caused by waves that are
triggered by subsurface convection zones. They further suggest that clumping in
the inner parts of the winds of OB stars could be related to subsurface
convection, and that the convective layers may also be responsible for
stochastic excitation of non-radial pulsations. Furthermore, magnetic fields
produced in the iron convection zone could appear at the surface of such
massive stars. Therefore subsurface convection could be responsible for the
occurrence of observable phenomena such as line profile variability and
discrete absorption components. These phenomena have been observed for decades,
but still evade a clear theoretical explanation. Here we present preliminary
results from 3D MHD simulations of such subsurface convection.",1009.4462v1
2010-10-05,"Renormalization group flow, competing phases, and the structure of superconducting gap in multi-band models of Iron based superconductors","We perform an analytical renormalization group (RG) study to address the role
of Coulomb repulsion, the competition between extended s-wave superconducting
order (s+-) and the spin-density wave (SDW) order and the angular dependence of
the superconducting gap in multi-pocket models of Iron based superconductors.
Previous analytic RG studies considered a toy model of one hole and one
electron pocket. We consider more realistic models of two electron pockets and
either two or three hole pockets, and also incorporate the angular dependence
of interaction. We neglect for simplicity one of the two hole pockets centered
at k=0, which is less nested with electron pockets, i.e., consider 3-pocket and
4-pocket models. In a toy 2-pocket model, SDW order always wins over s+- order
at perfect nesting, and s+- order only appears at a finite doping, and only if
RG flow extends long enough to overcome intra-pocket Coulomb repulsion. For
multi-pocket models, we find two new effects. First, there always exists an
attractive component of the interaction in s+- channel, such that the system
necessary becomes a superconductor once it overcomes the competition from the
SDW state. Second, in 3-pocket case (but not in 4-pocket case), there are
situations when s+- order wins over SDW order even for perfect nesting,
suggesting that SDW order is not a necessary pre-condition for the s+- order.
Our results are in good agreement with recent numerical functional RG studies
by Thomale et al. [arXiv:1002.3599]",1010.0984v3
2010-10-08,"Parity-odd multipoles, magnetic charges and chirality in haematite (alfa-Fe2O3)","Collinear and canted magnetic motifs in haematite were investigated by
Kokubun et al. (2008) using x-ray Bragg diffraction magnified at the iron
K-edge, and analyses of observations led to various potentially interesting
conclusions. We demonstrate that the reported analyses for both non-resonant
and resonant magnetic diffraction at low energies near the absorption K-edge
are not appropriate. In its place, we apply a radically different formulation,
thoroughly tried and tested, that incorporates all magnetic contributions to
resonant x-ray diffraction allowed by the established chemical and magnetic
structures. Essential to a correct formulation of diffraction by a magnetic
crystal with resonant ions at sites that are not centres of inversion symmetry
are parity-odd atomic multipoles, time-even (polar) and time-odd
(magneto-electric), that arise from enhancement by the electric-dipole (E1) -
electric-quadrupole (E2) event. Analyses of azimuthal-angle scans on two
space-group forbidden reflections, hexagonal (0, 0, 3)h and (0, 0, 9)h,
collected by Kokubun et al. above and below the Morin temperature (TM = 250K),
allow us to obtain good estimates of contributing polar and magneto-electric
multipoles, including the iron anapole. We show, beyond reasonable doubt, that
available data are inconsistent with parity-even events only (E1-E1 and E2-
E2). For future experiments, we show that chiral states of haematite couple to
circular polarization and differentiate E1-E2 and E2-E2 events, while the
collinear motif supports magnetic charges.",1010.1686v3
2010-11-02,Electron transport and anisotropy of the upper critical magnetic field in a Ba0.68K0.32Fe2As2 single crystals,"Early work on the iron-arsenide compounds supported the view, that a reduced
dimensionality might be a necessary prerequisite for high-Tc superconductivity.
Later, however, it was found that the zero-temperature upper critical magnetic
field, Hc2(0), for the 122 iron pnictides is in fact rather isotropic. Here, we
report measurements of the temperature dependence of the electrical
resistivity, \Gamma(T), in Ba0.5K0.5Fe2As2 and Ba0.68K0.32Fe2As2 single
crystals in zero magnetic field and for Ba0.68K0.32Fe2As2 as well in static and
pulsed magnetic fields up to 60 T. We find that the resistivity of both
compounds in zero field is well described by an exponential term due to
inter-sheet umklapp electron-phonon scattering between light electrons around
the M point to heavy hole sheets at the \Gamma point in reciprocal space. From
our data, we construct an H-T phase diagram for the inter-plane (H || c) and
in-plane (H || ab) directions for Ba0.68K0.32Fe2As2. Contrary to published data
for underdoped 122 FeAs compounds, we find that Hc2(T) is in fact anisotropic
in optimally doped samples down to low temperatures. The anisotropy parameter,
{\gamma} = Habc2/Hcc2, is about 2.2 at Tc. For both field orientations we find
a concave curvature of the Hc2 lines with decreasing anisotropy and saturation
towards lower temperature. Taking into account Pauli spin paramagnetism we
perfectly can describe Hc2(T) and its anisotropy.",1011.0698v1
2011-01-18,Microturbulent velocity from stellar spectra: a comparison between different approaches (Research Note),"Context --- The classical method to infer microturbulent velocity in stellar
spectra requires that the abundances of the iron lines are not correlated with
the observed equivalent widths. An alternative method, requiring the use of the
expected line strength, is often used to by-pass the risk of spurious slopes
due to the correlation between the errors in abundance and equivalent width.
Aims --- To compare the two methods and identify pros and cons and
applicability to the typical practical cases. Methods --- I performed a test
with a grid of synthetic spectra, including instrumental broadening and
Poissonian noise. For all these spectra, microturbulent velocity has been
derived by using the two approaches and compared with the original value with
which the synthetic spectra have been generated. Results --- The two methods
provide similar results for spectra with SNR$ > 70, while for lower SNR both
approaches underestimate the true microturbulent velocity, depending of the SNR
and the possible selection of the lines based on the equivalent width errors.
Basically, the values inferred by using the observed equivalent widths better
agree with those of the synthetic spectra. In fact, the method based on the
expected line strength is not totally free from a bias that can heavily affect
the determination of microturbulent velocity. Finally, I recommend to use the
classical approach (based on the observed equivalent widths) to infer this
parameter. In cases of full spectroscopical determination of all the
atmospherical parameters, the difference between the two approaches is reduced,
leading to an absolute difference in the derived iron abundances of less than
0.1 dex.",1101.3426v1
2011-01-24,Distinct Fermi Surface Topology and Nodeless Superconducting Gap in (Tl0.58Rb0.42)Fe1.72Se2 Superconductor,"High resolution angle-resolved photoemission measurements have been carried
out to study the electronic structure and superconducting gap of the
(Tl$_{0.58}$Rb$_{0.42}$)Fe$_{1.72}$Se$_2$ superconductor with a T$_c$=32 K. The
Fermi surface topology consists of two electron-like Fermi surface sheets
around $\Gamma$ point which is distinct from that in all other iron-based
compounds reported so far. The Fermi surface around the M point shows a nearly
isotropic superconducting gap of $\sim$12 meV. The large Fermi surface near the
$\Gamma$ point also shows a nearly isotropic superconducting gap of $\sim$15
meV while no superconducting gap opening is clearly observed for the inner tiny
Fermi surface. Our observed new Fermi surface topology and its associated
superconducting gap will provide key insights and constraints in understanding
superconductivity mechanism in the iron-based superconductors.",1101.4556v1
2011-02-10,An effective quantum parameter for strongly correlated metallic ferromagnets,"The correlated motion of electrons in multi-orbital metallic ferromagnets is
investigated in terms of a realistic Hubbard model with {\cal N}-fold orbital
degeneracy and arbitrary intra- and inter-orbital Coulomb interactions U and J
using a Goldstone-mode-preserving non-perturbative scheme. An effective quantum
parameter '\hbar'=\frac{U^2+({\cal N}-1)J^2}{(U+({\cal N}-1)J)^2} is obtained
which determines, in analogy with 1/S for quantum spin systems and 1/N for the
N-orbital Hubbard model, the strength of correlation-induced quantum
corrections to magnetic excitations. The rapid suppression of this quantum
parameter with Hund's coupling J, especially for large {\cal N}, provides
fundamental insight into the phenomenon of strong stabilization of metallic
ferromagnetism by orbital degeneracy and Hund's coupling. This approach is
illustrated for the case of ferromagnetic iron and the half metallic Heusler
alloy Co_2 Mn Si. For realistic values for iron, the calculated spin stiffness
and Curie temperature values obtained are in quantitative agreement with
measurements. Significantly, the contribution of long wavelength modes is shown
to yield a nearly ~25% reduction in the calculated Curie temperature. Finally,
an outline is presented for extending the approach to generic multi-band
metallic ferromagnets including realistic band-structure features of
non-degenerate orbitals and inter-orbital hopping as obtained from LDA
calculations.",1102.2115v1
2011-03-05,Physics and measurements of magnetic materials,"Magnetic materials, both hard and soft, are used extensively in several
components of particle accelerators. Magnetically soft iron-nickel alloys are
used as shields for the vacuum chambers of accelerator injection and extraction
septa; Fe-based material is widely employed for cores of accelerator and
experiment magnets; soft spinel ferrites are used in collimators to damp
trapped modes; innovative materials such as amorphous or nanocrystalline core
materials are envisaged in transformers for high-frequency polyphase resonant
convertors for application to the International Linear Collider (ILC). In the
field of fusion, for induction cores of the linac of heavy-ion inertial fusion
energy accelerators, based on induction accelerators requiring some 107 kg of
magnetic materials, nanocrystalline materials would show the best performance
in terms of core losses for magnetization rates as high as 105 T/s to 107 T/s.
After a review of the magnetic properties of materials and the different types
of magnetic behaviour, this paper deals with metallurgical aspects of
magnetism. The influence of the metallurgy and metalworking processes of
materials on their microstructure and magnetic properties is studied for
different categories of soft magnetic materials relevant for accelerator
technology. Their metallurgy is extensively treated. Innovative materials such
as iron powder core materials, amorphous and nanocrystalline materials are also
studied. A section considers the measurement, both destructive and
non-destructive, of magnetic properties. Finally, a section discusses magnetic
lag effects.",1103.1069v1
2011-03-22,Dipolar Interactions between Iron-Oxide Nanoparticles in Frozen Ferrofluids and Ferronematics,"We present a detailed study of the magnetic behavior of iron-oxide
(gamma-Fe2O3 and Fe3O4) nanoparticles constituents of ferrofluids (FF's) with
average particle sizes <d> = 2.5 and 10 nm. The particles were dispersed in the
frozen liquid carrier (pure FF) and in a frozen lyotropic liquid crystalline
matrix in the nematic phase or ferronematic (FN) (ferrolyomesophase). Both FF
and FN phases displayed superparamagnetic (SPM) behaviour at room temperature,
with blocking temperatures T_B ~ 10 and 100 K for <d> = 2.5 and 10 nm,
respectively. Dynamic ac susceptibility measurements showed a thermally
activated N\'eel-Brown dependence of the blocking temperature with applied
frequency. Our results show that dipolar interactions are small, but
non-negligible, as compared to the single-particle energy barriers from
magnetic anisotropy. From the fit of ac susceptibility we calculated the
effective magnetic anisotropy constant K_{eff} for 2.5 nm maghemite particles.
Although interparticle interactions present in highly diluted samples do not
appreciably modify the dynamic magnetic behavior of isolated particles, the
calculated magnetic anisotropy were abut one order of magnitude larger that the
bulk materials, suggesting the existence of large surface anisotropy. Using the
thermally activated model to fit the dynamic data yielded effective energy
barriers Ea = 3.5x10^{-21} J. From these data, we obtained K_{eff} = 422 kJ/m^3
for the single-particle effective magnetic anisotropy.",1103.4403v1
2011-04-04,X-ray Spectroscopy of MXB 1728-34 with XMM-Newton,"We have analysed an XMM-Newton observation of the low mass X-ray binary and
atoll source MXB 1728-34. The source was in a low luminosity state during the
XMM-Newton observation, corresponding to a bolometric X-ray luminosity of
5*10E36 d^2 erg/s, where d is the distance in units of 5.1 kpc. The 1-11 keV
X-ray spectrum of the source, obtained combining data from all the five
instruments on-board XMM-Newton, is well fitted by a Comptonized continuum.
Evident residuals are present at 6-7 keV which are ascribed to the presence of
a broad iron emission line. This feature can be equally well fitted by a
relativistically smeared line or by a self-consistent, relativistically
smeared, reflection model. Under the hypothesis that the iron line is produced
by reflection from the inner accretion disk, we can infer important information
on the physical parameters of the system, such as the inner disk radius, Rin =
25-100 km, and the inclination of the system, 44{\deg} < i < 60{\deg}.",1104.0566v1
2011-04-22,Non-LTE line formation for Fe I and Fe II in the atmospheres of A-F type stars,"Non-local thermodynamical equilibrium (non-LTE) line formation for neutral
and singly-ionized iron is considered through a range of spectral types when
the effective temperature varies from 6500 K up to 8500 K, the gravity from log
g = 4 down to log g = 3, and the metallicity is solar one. The non-LTE
calculations were performed with a comprehensive model atom for iron which was
treated in our earlier paper (Mashonkina et al. 2011, A&A, 528, A87). The
departures from LTE lead to systematically depleted total absorption in the Fe
I lines and positive abundance corrections, in qualitative agreement with the
Rentzsch-Holm (1996, A&A, 312, 966) study. However, our predicted magnitude of
the non-LTE effects is significantly smaller compared to the previous results
due to the use of rather complete model atom of Fe I. The non-LTE abundance
corrections do not exceed 0.1 dex for the dwarf models and 0.20 dex for the
giant ones. Non-LTE leads to strengthening the Fe II lines, however, the effect
is small, such that the abundance correction is at the level of -0.01 to -0.03
dex over the whole range of stellar parameters being considered. No firm
conclusion can be drawn with respect to whether or not the Fe I/Fe II
ionization equilibrium is fulfilled in the atmosphere of the Sun and Procyon
due to uncertainty in available gf-values for visible lines of Fe I and Fe II.",1104.4403v1
2011-05-11,Doping-induced vertical line nodes in the superconducting gap of the iron arsenide K-Ba122 from directional thermal conductivity,"The thermal conductivity k of the iron-arsenide superconductor K-Ba122 was
measured down to 50 mK in a magnetic field up to 15 T, for a heat current
parallel and perpendicular to the tetragonal c axis. In the range from optimal
doping (x ~ 0.4) down to x = 0.16, there is no residual linear term in k(T) at
T = 0, showing that there are no nodes in the superconducting gap anywhere on
the Fermi surface. Upon crossing below x = 0.16, a large residual linear term
suddenly appears, signaling the onset of nodes in the superconducting gap, most
likely vertical line nodes running along the c axis. We discuss two scenarios:
1) accidental nodes in an s-wave gap, resulting from a strong modulation of the
gap around the Fermi surface, in which minima deepen rapidly with underdoping;
2) a phase transition from a nodeless s-wave state to a d-wave state, in which
nodes are imposed by symmetry.",1105.2232v2
2011-05-21,"Specific Heat Discontinuity, deltaC, at Tc in BaFe2(As0.7P0.3)2 - Consistent with Unconventional Superconductivity","We report the specific heat discontinuity, deltaC/Tc, at Tc = 28.2 K of a
collage of single crystals of BaFe2(As0.7P0.3)2 and compare the measured value
of 38.5 mJ/molK**2 with other iron pnictide and iron chalcogenide (FePn/Ch)
superconductors. This value agrees well with the trend established by Bud'ko,
Ni and Canfield who found that deltaC/Tc ~ a*Tc**2 for 14 examples of doped
Ba1-xKxFe2As2 and BaFe2-xTMxAs2, where the transition metal TM=Co and Ni. We
extend their analysis to include all the FePn/Ch superconductors for which
deltaC/Tc is currently known and find deltaC/Tc ~ a*Tc**1.9 and a=0.083
mJ/molK**4. A comparison with the elemental superconductors with Tc>1 K and
with A-15 superconductors shows that, contrary to the FePn/Ch superconductors,
electron-phonon-coupled conventional superconductors exhibit a significantly
different dependence of deltaC on Tc, namely deltaC/Tc ~ Tc**0.9. However
deltaC/gamma*Tc appears to be comparable in all three classes (FePn/Ch,
elemental and A-15) of superconductors with, e. g., deltaC/gamma*Tc=2.4 for
BaFe2(As0.7P0.3)2. A discussion of the possible implications of these
phenomenological comparisons for the unconventional superconductivity believed
to exist in the FePn/Ch is given.",1105.4289v1
2011-06-03,Iron-based n-type electron-induced ferromagnetic semiconductor,"Carrier-induced ferromagnetic semiconductors (FMSs) have been intensively
studied for decades as they have novel functionalities that cannot be achieved
with conventional metallic materials. These include the ability to control
magnetism by electrical gating or light irradiation, while fully inheriting the
advantages of semiconductor materials such as band engineering. Prototype FMSs
such as (In,Mn)As or (Ga,Mn)As, however, are always p-type, making it difficult
to be used in real spin devices. This is because manganese (Mn) atoms in those
materials work as local magnetic moments and acceptors that provide holes for
carrier-mediated ferromagnetism. Here we show that by introducing iron (Fe)
into InAs, it is possible to fabricate a new FMS with the ability to control
ferromagnetism by both Fe and independent carrier doping. Despite the general
belief that the tetrahedral Fe-As bonding is antiferromagnetic, we demonstrate
that (In,Fe)As doped with electrons behaves as an n-type electron-induced FMS,
a missing piece of semiconductor spintronics for decades. This achievement
opens the way to realise novel spin-devices such as spin light-emitting diodes
or spin field-effect transistors, as well as helps understand the mechanism of
carrier-mediated ferromagnetism in FMSs.",1106.0561v3
2011-06-06,Correlation of conductivity and angle integrated valence band photoemission characteristics in single crystal iron perovskites for 300 K < T < 800 K: Comparison of surface and bulk sensitive methods,"A single crystal monolith of La0.9Sr0.1FeO3 and thin pulsed laser deposited
film of La0.8Sr0.2Fe0.8Ni0.2O3 were subject to angle integrated valence band
photoemission spectroscopy in ultra high vacuum and conductivity experiments in
ambient air at temperatures from 300 K to 800 K. Except for several sputtering
and annealing cycles, the specimen were not prepared in-situ.. Peculiar changes
in the temperature dependent, bulk representative conductivity profile as a
result of reversible phase transitions, and irreversible chemical changes are
semi-quantitatively reflected by the intensity variation in the more surface
representative valence band spectra near the Fermi energy. X-ray photoelectron
diffraction images reflect the symmetry as expected from bulk iron perovskites.
The correlation of spectral details in the valence band photoemission spectra
(VB PES) and details of the conductivity during temperature variation suggest
that valuable information on electronic structure and transport properties of
complex materials may be obtained without in-situ preparation.",1106.1034v1
2011-06-15,No X-Ray Excess from the HESS J1741-302 Region except a New Intermediate Polar Candidate,"With the Suzaku satellite, we observed an unidentified TeV gamma-ray source
HESS J1741$-$302 and its surroundings. No diffuse or point-like X-ray sources
are detected from the bright southern emission peak of HESS J1741$-$302. From
its neighborhood, we found a new intermediate polar candidate at the position
of $(\alpha, \delta)_{\rm J2000.0} = (\timeform{17h40m35.6s},
\timeform{-30D14m16s})$, which is designated as Suzaku J174035.6$-$301416. The
spectrum of Suzaku J174035.6$-$301416 exhibits emission lines at the energy of
6.4, 6.7 and 7.0 keV, which can be assigned as the K$\alpha$ lines from
neutral, He-like and H-like iron, respectively. A coherent pulsation is found
at a period of 432.1 $\pm$ 0.1 s. The pulse profile is quasi-sinusoidal in the
hard X-ray band (4$-$8 keV), but is more complicated in the soft X-ray band
(1$-$3 keV). The moderate period of pulsation, the energy flux, and the
presence of the iron K$\alpha$ lines indicate that Suzaku J174035.6$-$301416 is
likely an intermediate polar, a subclass of magnetized white dwarf binaries
(cataclysmic variables).
  Based on these discoveries, we give some implications on the origin of GCDX
and brief comments on HESS J1741$-$302 and PSR B1737$-$30.",1106.2861v1
2011-06-15,Electronic identification of the actual parental phase of KxFe2-ySe2 superconductor and its intrinsic mesoscopic phase separation,"While the parent compounds of the cuprate high temperature superconductors
(high-Tc's) are Mott insulators, the iron-pnictide high-Tc's are in the
vicinity of a metallic spin density wave (SDW) state, which highlights the
difference between these two families. However, insulating parent compounds
were identified for the newly discovered KxFe2-ySe2. This raises an intriguing
question as to whether the iron-based high-Tc's could be viewed as doped Mott
insulators like the cuprates. Here we report angle-resolved photoemission
spectroscopy (ARPES) evidence of two insulating and one semiconducting phases
of KxFe2-ySe2, and the mesoscopic phase separation between the
superconducting/semiconducting phase and the insulating phases. The insulating
phases are characterized by the depletion of electronic states over a 0.5 eV
window below the chemical potential, giving a compelling evidence for the
presence of Mott-like physics. The charging effects and the absence of band
folding in the superconducting/semiconducting phase further prove that the
static magnetic and vacancy orders are not related to the superconductivity.
Instead, the electronic structure of the superconducting phase is much closer
to the semiconducting phase, indicating the superconductivity is likely
developed by doping the semiconducting phase rather than the insulating phases.",1106.3026v1
2011-06-19,Iron Based Superconductors: Pnictides versus Chalcogenides,"We present a brief review of the present day situation with studies of
high-temperature superconductivity in iron pnictides and chalcogenides. Recent
discovery of superconductivity with T_c > 30 K in A_xFe_{2-x/2}Se_2
(A=K,Cs,Tl,...) represents the major new step in the development of new
concepts in the physics of Fe - based high-temperature superconductors. We
compare LDA and ARPES data on the band structure and Fermi surfaces of novel
superconductors and those of the previously studied FeAs superconductors,
especially isostructural 122 - superconductors like BaFe_2As_2. It appears that
electronic structure of new superconductors is rather different from that of
FeAs 122 - systems. In particular, no nesting properties of electron and hole -
like Fermi surfaces is observed, casting doubts on most popular theoretical
schemes of Cooper pairing for these systems. The discovery of Fe vacancies
ordering and antiferromagnetic (AFM) ordering at pretty high temperatures (T_N>
500 K), much exceeding superconducting T_c makes these systems unique
antiferromagnetic superconductors with highest T_N observed up to now. We
discuss the role of both vacancies and AFM ordering in transformations of band
structure and Fermi surfaces, as well as their importance for
superconductivity. In particular, we show that system remains metallic with
unfolded Fermi surfaces quite similar to that in paramagnetic state.
Superconducting transition temperature T_c of new superconductors is discussed
within the general picture of superconductivity in multiple band systems. It is
demonstrated that both in FeAs - superconductors and in new FeSe - systems the
value of T_c correlates with the value of the total density of states (DOS) at
the Fermi level.",1106.3707v1
2011-06-24,Unprecedented anisotropic metallic state in BaFe2As2 revealed by optical spectroscopy,"An ordered phase showing remarkable electronic anisotropy in proximity to the
superconducting phase is now a hot issue in the field of
high-transition-temperature superconductivity. As in the case of copper oxides,
superconductivity in iron arsenides competes or coexists with such an ordered
phase. Undoped and underdoped iron arsenides have a magnetostructural ordered
phase exhibiting stripe-like antiferromagnetic spin order accompanied by an
orthorhombic lattice distortion; both the spin order and lattice distortion
break the tetragonal symmetry of crystals of these compounds. In this ordered
state, anisotropy of in-plane electrical resistivity is anomalous and difficult
to attribute simply to the spin order and/or the lattice distortion. Here, we
present the anisotropic optical spectra measured on detwinned BaFe2As2 crystals
with light polarization parallel to the Fe planes. Pronounced anisotropy is
observed in the spectra, persisting up to an unexpectedly high photon energy of
about 2 eV. Such anisotropy arises from an anisotropic energy gap opening below
and slightly above the onset of the order. Detailed analysis of the optical
spectra reveals an unprecedented electronic state in the ordered phase.",1106.4967v1
2011-06-27,Silicon and Oxygen Abundances in Planet-Host Stars,"The positive correlation between planet detection rate and host star iron
abundance lends strong support to the core accretion theory of planet
formation. However, iron is not the most significant mass contributor to the
cores of giant planets. Since giant planet cores are thought to grow from
silicate grains with icy mantles, the likelihood of gas giant formation should
depend heavily on the oxygen and silicon abundance of the planet formation
environment. Here we compare the silicon and oxygen abundances of a set of 76
planet hosts and a control sample of 80 metal-rich stars without any known
giant planets. Our new, independent analysis was conducted using high
resolution, high signal-to-noise data obtained at McDonald Observatory. Because
we do not wish to simply reproduce the known planet-metallicity correlation, we
have devised a statistical method for matching the underlying [Fe/H]
distributions of our two sets of stars. We find a 99% probability that planet
detection rate depends on the silicon abundance of the host star, over and
above the observed planet-metallicity correlation. We do not detect any such
correlation for oxygen. Our results would thus seem to suggest that grain
nucleation, rather than subsequent icy mantle growth, is the important limiting
factor in forming giant planets via core accretion. Based on our results and
interpretation, we predict that planet detection should correlate with host
star abundance for refractory elements responsible for grain nucleation and
that no such trends should exist for the most abundant volatile elements
responsible for icy mantle growth.",1106.5509v1
2011-06-28,Pressure-induced isostructural phase transition and correlation of FeAs coordination with the superconducting properties of 111-type Na1-xFeAs,"The effect of pressure on the crystalline structure and superconducting
transition temperature (Tc) of the 111-type Na1-xFeAs system using in situ high
pressure synchrotron x-ray powder diffraction and diamond anvil cell techniques
is studied. A pressure-induced tetragonal to tetragonal isostructural phase
transition was found. The systematic evolution of the FeAs4 tetrahedron as a
function of pressure based on Rietveld refinements on the powder x-ray
diffraction patterns was obtained. The non-monotonic Tc(P) behavior of
Na1-xFeAs is found to correlate with the anomalies of the distance between the
anion (As) and the iron layer as well as the bond angle between As-Fe-As for
the two tetragonal phases. This behavior provides the key structural
information in understanding the origin of the pressure dependence of Tc for
111-type iron pnictide superconductors. A pressure-induced structural phase
transition is also observed at 20 GPa.",1106.5640v1
2011-06-30,Suzaku Observation of the Intermediate Polar V1223 Sagittarii,"We report on the Suzaku observation of the intermediate polar V1223
Sagittarii. Using a multi-temperature plasma emission model with its reflection
from a cold matter, we obtained the shock temperature to be 37.9^{+5.1}_{-4.6}
keV. This constrains the mass and the radius of the white dwarf (WD) in the
ranges 0.82^{+0.05}_{-0.06} solar masses and (6.9+/-0.4)x10^8 cm, respectively,
with the aid of a WD mass-radius relation. The solid angle of the reflector
viewed from the post-shock plasma was measured to be Omega/2pi = 0.91+/-0.26. A
fluorescent iron Kalpha emission line is detected, whose central energy is
discovered to be modulated with the WD rotation for the first time in
magnetic-CVs. Detailed spectral analysis indicates that the line comprises of a
stable 6.4 keV component and a red-shifted component, the latter of which
appears only around the rotational intensity-minimum phase. The equivalent
width (EW) of the former stable component ~80 eV together with the measured
Omega indicates the major reflector is the WD surface, and the shock height is
not more than 7% of the WD radius. Comparing this limitation to the height
predicted by the Aizu model (1973), we estimated the fractional area onto which
the accretion occurs to be < 7x10^{-3}$ of the WD radius, which is the most
severe constraint in non-eclipsing IPs. The red-shifted iron line component, on
the other hand, can be interpreted as emanating from the pre-shock accretion
flow via fluorescence. Its EW (28^{+44}_{-13} eV) and the central energy
(6.30_{-0.05}^{+0.07} keV) at the intensity-minimum phase are consistent with
this interpretation.",1106.6111v1
2011-08-09,Magnetic spots on hot massive stars,"Hot luminous stars show a variety of phenomena in their photospheres and
winds which still lack clear physical explanation. Among these phenomena are
photospheric turbulence, line profile variability (LPV), non-thermal emission,
non-radial pulsations, discrete absorption components (DACs) and wind clumping.
Cantiello et al. (2009) argued that a convection zone close to the stellar
surface could be responsible for some of these phenomena. This convective zone
is caused by a peak in the opacity associated with iron-group elements and is
referred to as the ""iron convection zone"" (FeCZ). Assuming dynamo action
producing magnetic fields at equipartition in the FeCZ, we investigate the
occurrence of subsurface magnetism in OB stars. Then we study the surface
emergence of these magnetic fields and discuss possible observational
signatures of magnetic spots. Simple estimates are made using the subsurface
properties of massive stars, as calculated in 1D stellar evolution models. We
find that magnetic fields of sufficient amplitude to affect the wind could
emerge at the surface via magnetic buoyancy. While at this stage it is
difficult to predict the geometry of these features, we show that magnetic
spots of size comparable to the local pressure scale height can manifest
themselves as hot, bright spots. Localized magnetic fields could be widespread
in those early type stars that have subsurface convection. This type of surface
magnetism could be responsible for photometric variability and play a role in
X-ray emission and wind clumping.",1108.2030v1
2011-08-23,Fine-Grid Calculations for Stellar Electron and Positron Capture Rates on Fe-Isotopes,"The acquisition of precise and reliable nuclear data is a prerequisite to
success for stellar evolution and nucleosynthesis studies. Core-collapse
simulators find it challenging to generate an explosion from the collapse of
the core of massive stars. It is believed that a better understanding of the
microphysics of core-collapse can lead to successful results. The weak
interaction processes are able to trigger the collapse and control the
lepton-to-baryon ratio ($Y_{e}$) of the core material. It is suggested that the
temporal variation of $Y_{e}$ within the core of a massive star has a pivotal
role to play in the stellar evolution and a fine-tuning of this parameter at
various stages of presupernova evolution is the key to generate an explosion.
During the presupernova evolution of massive stars, isotopes of iron, mainly
$^{54,55,56}$Fe, are considered to be key players in controlling $Y_{e}$ ratio
via electron capture on these nuclide. Recently an improved microscopic
calculation of weak interaction mediated rates for iron isotopes was introduced
using the proton-neutron quasiparticle random phase approximation (pn-QRPA)
theory. The pn-QRPA theory allows a microscopic \textit{state-by-state}
calculation of stellar capture rates which greatly increases the reliability of
calculated rates. The results were suggestive of some fine-tuning of the
$Y_{e}$ ratio during various phases of stellar evolution. Here we present for
the first time the fine-grid calculation of the electron and positron capture
rates on $^{54,55,56}$Fe. Core-collapse simulators may find this calculation
suitable for interpolation purposes and for necessary incorporation in the
stellar evolution codes.",1108.4569v1
2011-10-09,"Preemptive nematic order, pseudogap, and orbital order in the iron pnictides","Starting from a microscopic itinerant model, we derive and analyze the
effective low-energy model for collective magnetic excitations in the iron
pnictides. We show that the stripe magnetic order is generally preempted by an
Ising-nematic order which breaks $C_{4}$ lattice symmetry but preserves O(3)
spin-rotational symmetry. This leads to a rich phase diagram as function of
doping, pressure, and elastic moduli, displaying split magnetic and nematic
tri-critical points. The nematic transition may instantly bring the system to
the verge of a magnetic transition, or it may occur first, being followed by a
magnetic transition at a lower temperature. In the latter case, the preemptive
nematic transition is accompanied by either a jump or a rapid increase of the
magnetic correlation length, triggering a pseudogap behavior associated with
magnetic precursors. Furthermore, due to the distinct orbital character of each
Fermi pocket, the nematic transition also induces orbital order. We compare our
results to various experiments, showing that they correctly address the changes
in the character of the magneto-structural transition across the phase diagrams
of different compounds, as well as the relationship between the orthorhombic
and magnetic order parameters.",1110.1893v2
2011-11-08,Two Populations of X-ray Pulsars Produced by Two Types of Supernovae,"Two types of supernova are thought to produce the overwhelming majority of
neutron stars in the Universe. The first type, iron-core collapse supernovae,
occurs when a high-mass star develops a degenerate iron core that exceeds the
Chandrasekhar limit. The second type, electron-capture supernovae, is
associated with the collapse of a lower-mass oxygen-neon-magnesium core as it
loses pressure support owing to the sudden capture of electrons by neon and/or
magnesium nuclei. It has hitherto been impossible to identify the two distinct
families of neutron stars produced in these formation channels. Here we report
that a large, well-known class of neutron-star-hosting X-ray pulsars is
actually composed of two distinct sub-populations with different characteristic
spin periods, orbital periods and orbital eccentricities. This class, the
Be/X-ray binaries, contains neutron stars that accrete material from a more
massive companion star. The two sub-populations are most probably associated
with the two distinct types of neutron-star-forming supernovae, with
electron-capture supernovae preferentially producing system with short spin
period, short orbital periods and low eccentricity. Intriguingly, the split
between the two sub-populations is clearest in the distribution of the
logarithm of spin period, a result that had not been predicted and which still
remains to be explained.",1111.2051v1
2011-11-22,Microstructural magnetic phases in superconducting FeTe0.65Se0.35,"In this paper, we address a number of outstanding issues concerning the
nature and the role of magnetic inhomogenities in the iron chalcogenide system
FeTe1-xSex and their correlation with superconductivity in this system. We
report morphology of superconducting single crystals of FeTe0.65Se0.35 studied
with transmission electron microscopy, high angle annular dark field scanning
transmission electron microscopy and their magnetic and superconducting
properties characterized with magnetization, specific heat and magnetic
resonance spectroscopy. Our data demonstrate a presence of nanometre scale
hexagonal regions coexisting with tetragonal host lattice, a chemical disorder
demonstrating non homogeneous distribution of host atoms in the crystal
lattice, as well as hundreds-of-nanometres-long iron-deficient bands. From
magnetic data and ferromagnetic resonance temperature dependence, we attribute
magnetic phases in Fe-Te-Se to Fe3O4 inclusions and to hexagonal symmetry
nanometre scale regions with structure of Fe7Se8 type. Our results suggest that
nonhomogeneous distribution of host atoms might be an intrinsic feature of
superconducting Fe-Te-Se chalcogenides and we find a surprising correlation
indicating that faster grown crystal of inferior crystallographic properties is
a better superconductor.",1111.5176v2
2011-11-27,Evolution of structural properties of iron oxide nano particles during temperature treatment from 250°C - 900°C: X-ray diffraction and Fe K-shell pre-edge X-ray absorption study,"Iron oxide nano particles with nominal Fe2O3 stoichiometry were synthesized
by a wet, soft chemical method with the heat treatment temperatures from
250{\deg}C to 900{\deg}C in air. The variation in the structural properties of
the nano particles with the heat treatment temperature was studied by X-ray
diffraction and Fe K shell X-ray absorption study. X-ray diffractograms show
that at lower annealing temperatures nano particle comprises both maghemite and
hematite phases. With increasing temperature, the remainder of the maghemite
phase transformed completely to hematite. Profile analysis of the leading Bragg
reflections reveals that the average crystallite size increases from 50 nm to
150 nm with increasing temperature. The mean primary particle size decreased
from 105 nm to 90 nm with increasing heat treatment temperature. The X-ray
diffraction results are paralleled by systematic changes in the pre-edge
structure of the Fe K-edge X-ray absorption spectra, in particular by a gradual
decrease of the t2g/eg peak height ratio of the two leading pre-edge
resonances, confirming oxidation of the Fe from Fe2+ towards Fe3+. Transmission
electron microscopy (TEM) on the samples treated at temperatures as high as
900{\deg}C showed particles with prismatic morphology along with the formation
of stacking fault like defects. High resolution TEM with selected area electron
diffraction (SAED) of samples heat treated above 350{\deg}C showed that the
nano particles have well developed lattice fringes corresponding to that of
(110) plane of hematite.",1111.6204v1
2011-11-29,"A J-band detection of the donor star in the dwarf nova OY Carinae, and an optical detection of its `iron curtain'","Purely photometric models can be used to determine the binary parameters of
eclipsing cataclysmic variables with a high degree of precision. However, the
photometric method relies on a number of assumptions, and to date there have
been very few independent checks of this method in the literature. We present
time-resolved spectroscopy of the P=90.9 min eclipsing cataclysmic variable OY
Carinae obtained with X-shooter on the VLT, in which we detect the donor star
from K I lines in the J-band. We measure the radial velocity amplitude of the
donor star K2 = 470.0 +/- 2.7 km/s, consistent with predictions based upon the
photometric method (470 +/- 7 km/s). Additionally, the spectra obtained in the
UVB arm of X-shooter show a series of Fe I and Fe II lines with a phase and
velocity consistent with an origin in the accretion disc. This is the first
unambiguous detection at optical wavelengths of the `iron curtain' of disc
material which has been previously reported to veil the white dwarf in this
system. The velocities of these lines do not track the white dwarf, reflecting
a distortion of the outer disc that we see also in Doppler images. This is
evidence for considerable radial motion in the outer disk, at up to 90 km/s
towards and away from the white dwarf.",1111.6775v1
2011-12-08,Influence of high permeability disks in an axisymmetric model of the Cadarache dynamo experiment,"Numerical simulations of the kinematic induction equation are performed on a
model configuration of the Cadarache von-K\'arm\'an-Sodium dynamo experiment.
The effect of a localized axisymmetric distribution of relative permeability
{\mu} that represents soft iron material within the conducting fluid flow is
investigated. The critical magnetic Reynolds number Rm^c for dynamo action of
the first non-axisymmetric mode roughly scales like
Rm^c({\mu})-Rm^c({\mu}->infinity) ~ {\mu}^(-1/2) i.e. the threshold decreases
as {\mu} increases. This scaling law suggests a skin effect mechanism in the
soft iron disks. More important with regard to the Cadarache dynamo experiment,
we observe a purely toroidal axisymmetric mode localized in the high
permeability disks which becomes dominant for large {\mu}. In this limit, the
toroidal mode is close to the onset of dynamo action with a (negative)
growth-rate that is rather independent of the magnetic Reynolds number. We
qualitatively explain this effect by paramagnetic pumping at the fluid/disk
interface and propose a simplified model that quantitatively reproduces
numerical results. The crucial role of the high permeability disks for the mode
selection in the Cadarache dynamo experiment cannot be inferred from
computations using idealized pseudo-vacuum boundary conditions (H x n = 0).",1112.1780v2
2011-12-20,Spin Dynamics of a J1-J2-K Model for the Paramagnetic Phase of Iron Pnictides,"We study the finite-temperature spin dynamics of the paramagnetic phase of
iron pnictides within an antiferromagnetic J_1-J_2 Heisenberg model on a square
lattice with a biquadratic coupling $-K (S_i \cdot S_j)^2$ between the
nearest-neighbor spins. Our focus is on the paramagnetic phase in the parameter
regime of this J_1-J_2-K model where the ground state is a (\pi,0) collinear
antiferromagnet. We treat the biquadratic interaction via a
Hubbard-Stratonovich decomposition, and study the resulting effective
quadratic-coupling model using both modified spin wave and Schwinger boson
mean-field theories; the results for the spin dynamics derived from the two
methods are very similar. We show that the spectral weight of dynamical
structure factor S(q,\omega) is peaked at ellipses in the momentum space at low
excitation energies. With increasing energy, the elliptic features expand
towards the zone boundary, and gradually split into two parts, forming a
pattern around (\pi,\pi). Finally, the spectral weight is anisotropic, being
larger along the major axis of the ellipse than along its minor axis. These
characteristics of the dynamical structure factor are consistent with the
recent measurements of the inelastic neutron scattering spectra on BaFe_2As_2
and SrFe_2As_2.",1112.4785v3
2012-01-16,Universal heat conduction in the iron-arsenide superconductor KFe2As2 : Evidence of a d-wave state,"The thermal conductivity of the iron-arsenide superconductor KFe2As2 was
measured down to 50 mK for a heat current parallel and perpendicular to the
tetragonal c-axis. A residual linear term (RLT) at T=0 is observed for both
current directions, confirming the presence of nodes in the superconducting
gap. Our value of the RLT in the plane is equal to that reported by Dong et al.
[Phys. Rev. Lett. 104, 087005 (2010)] for a sample whose residual resistivity
was ten times larger. This independence of the RLT on impurity scattering is
the signature of universal heat transport, a property of superconducting states
with symmetry-imposed line nodes. This argues against an s-wave state with
accidental nodes. It favors instead a d-wave state, an assignment consistent
with five additional properties: the magnitude of the critical scattering rate
for suppressing Tc to zero; the magnitude of the RLT, and its dependence on
current direction and on magnetic field; the temperature dependence of the
thermal conductivity.",1201.3376v3
2012-01-26,Very fast photometric and X-ray observations of the intermediate polar V2069 Cygni (RX J2123.7+4217),"We present fast timing photometric observations of the intermediate polar
V2069 Cygni (RX J2123.7+4217) using the Optical Timing Analyzer (OPTIMA) at the
1.3 m telescope of Skinakas Observatory. The optical (450-950 nm) light curve
of V2069 Cygni was measured with sub-second resolution for the first time
during July 2009 and revealed a double-peaked pulsation with a period of 743.38
+0.25. A similar double-peaked modulation was found in the simultaneous Swift
satellite observations. We suggest that this period represents the spin of the
white dwarf accretor. Moreover, we present the results from a detailed analysis
of the XMM-Newton observation that also shows a double-peaked modulation,
however shifted in phase, with 742.35 +0.23 s period. The X-ray spectra
obtained from the XMM-Newton EPIC (European Photon Imaging Camera) instruments
were modelled by a plasma emission and a soft black body component with a
partial covering photo-electric absorption model with covering fraction of
0.65. An additional Gaussian emission line at 6.385 keV with an equivalent
width of 243 eV is required to account for fluorescent emission from neutral
iron. The iron fluorescence (~6.4 keV) and FeXXVI lines (~6.95 keV) are clearly
resolved in the EPIC spectra. In the Porb-Pspin diagram of IPs, V2069 Cyg shows
a low spin to orbit ratio of ~0.0276 in comparison with ~0.1 for other
intermediate polars.",1201.5629v1
2012-02-14,Nernst effect of iron pnictide and cuprate superconductors: signatures of spin density wave and stripe order,"The Nernst effect has recently proven a sensitive probe for detecting unusual
normal state properties of unconventional superconductors. In particular, it
may sensitively detect Fermi surface reconstructions which are connected to a
charge or spin density wave (SDW) ordered state, and even fluctuating forms of
such a state. Here we summarize recent results for the Nernst effect of the
iron pnictide superconductor $\rm LaO_{1-x}F_xFeAs$, whose ground state evolves
upon doping from an itinerant SDW to a superconducting state, and the cuprate
superconductor $\rm La_{1.8-x}Eu_{0.2}Sr_xCuO_4$ which exhibits static stripe
order as a ground state competing with the superconductivity. In $\rm
LaO_{1-x}F_xFeAs$, the SDW order leads to a huge Nernst response, which allows
to detect even fluctuating SDW precursors at superconducting doping levels
where long range SDW order is suppressed. This is in contrast to the impact of
stripe order on the normal state Nernst effect in $\rm
La_{1.8-x}Eu_{0.2}Sr_xCuO_4$. Here, though signatures of the stripe order are
detectable in the temperature dependence of the Nernst coefficient, its overall
temperature dependence is very similar to that of $\rm La_{2-x}Sr_xCuO_4$,
where stripe order is absent. The anomalies which are induced by the stripe
order are very subtle and the enhancement of the Nernst response due to static
stripe order in $\rm La_{1.8-x}Eu_{0.2}Sr_xCuO_4$ as compared to that of the
pseudogap phase in $\rm La_{2-x}Sr_xCuO_4$, if any, is very small.",1202.2959v1
2012-04-04,A New Disintegrative Capture Theory for the Origin of the Moon,"The object that resulted in the creation of the Moon started in the same
orbital path as Earth around the Sun, but at Earth's L4. This proto-Moon (PM)
was 4 times less massive than the usual Giant Impact (GI) object ""Theia"" and
was captured into Earth orbit. It had a 32% Iron-Nickel-Sulfur core supporting
a dynamo, which explains magnetized lunar rocks. Following capture, it was torn
apart by tidal forces and its core of iron plastered itself, with some of its
rock mantle, on the surface of Earth at a very flat angle (producing the ""Late
Veneer""). After tidal stripping, the remaining PM rock was driven away from
Earth to about 3.8 times Earth's radius and formed into what is now the Moon.
The GI theory has several troubles: The violent collision melts the entire
Earth, contrary to geological evidence. The Moon itself also has to condense
out of the vapor cloud generated in the collision, but there is evidence that
the Moon was not condensed out of vapor. In the new theory, the Moon as we know
it may be only 3.8 - 3.9 billion years old, not 4.56 as usually assumed. That
is the age of the PM. The minerals in the Moon would be about as old as the
Earth, but would have been re-arranged in the capture and temporary
disintegration process. If the Moon is as young as suggested, its origin would
coincide with the beginning of life on Earth, which is unexplained in the GI
theory. The manuscript asks, ""Was the Moon Turned Inside-Out"" and the answer is
""Essentially, Yes.""",1204.0980v2
2012-05-02,Negative thermal expansion and antiferromagnetism in the actinide oxypnictide NpFeAsO,"A neptunium analogue of the LaFeAsO tetragonal layered compound has been
synthesized and characterized by a variety of experimental techniques. The
occurrence of long-range magnetic order below a critical temperature T_N = 57 K
is suggested by anomalies in the temperature-dependent magnetic susceptibility,
electrical resistivity, Hall coefficient, and specific heat curves. Below T_N,
powder neutron diffraction measurements reveal an antiferromagnetic structure
of the Np sublattice, with an ordered magnetic moment of 1.70(0.07) \mu_B
aligned along the crystallographic c-axis. No magnetic order has been observed
on the Fe sublattice, setting an upper limit of about 0.3 \mu_B for the ordered
magnetic moment on the iron. High resolution x-ray powder diffraction
measurements exclude the occurrence of lattice transformations down to 5 K, in
sharp contrast to the observation of a tetragonal-to-orthorhombic distortion in
the rare-earth analogues, which has been associated with the stabilization of a
spin density wave on the iron sublattice. Instead, a significant expansion of
the NpFeAsO lattice parameters is observed with decreasing temperature below
T_N, corresponding to a relative volume change of about 0.2% and to an invar
behavior between 5 and 20 K. First-principle electronic structure calculations
based on the local-spin density plus Coulomb interaction and the local density
plus Hubbard-I approximations provide results in good agreement with the
experimental findings.",1205.0438v1
2012-05-14,The Central Engine Structure of 3C120: Evidence for a Retrograde Black Hole or a Refilling Accretion Disk,"The broad-line radio galaxy 3C120 is a powerful source of both X-ray and
radio emission including superluminal jet outflows. We report on our reanalysis
of 160 ks of Suzaku data taken in 2006, previously examined by Kataoka et al.
(2007). Spectral fits to the XIS and HXD/PIN data over a range of 0.7-45 keV
reveal a well-defined iron K line complex with a narrow Ka core and
relativistically broadened features consistent with emission from the inner
regions of the accretion disk. Furthermore, the inner region of the disk
appears to be truncated with an inner radius of r_in = 11.7^{+3.5}_{-5.2} r_g.
If we assume that fluorescent iron line features terminate at the inner-most
stable circular orbit (ISCO), we measure a black hole spin of a < -0.1 at a 90%
confidence level. A rapidly spinning prograde black hole (a > 0.8) can be ruled
out at the 99% confidence level. Alternatively, the disk may be truncated well
outside of the ISCO of a rapid prograde hole. The most compelling scenario is
the possibility that the inner regions of the disk were destroyed/ejected by
catastrophic instabilities just prior to the time these observations were made.",1205.3175v1
2012-05-21,Impact of the 2 Fe unit cell on the electronic structure measured by ARPES in iron pnictides,"In all iron pnictides, the positions of the ligand alternatively above and
below the Fe plane create 2 inequivalent Fe sites. This results in 10 Fe 3d
bands in the electronic structure. However, they do not all have the same
status for an ARPES experiment. There are interference effects between the 2 Fe
that modulate strongly the intensity of the bands and that can even switch
their parity. We give a simple description of these effects, notably showing
that ARPES polarization selection rules in these systems cannot be applied by
reference to a single Fe ion. We show that ARPES data for the electron pockets
in Ba(Fe0.92Co0.08)2As2 are in excellent agreement with this model. We observe
both the total suppression of some bands and the parity switching of some other
bands. Once these effects are properly taken into account, the structure of the
electron pockets, as measured by ARPES, becomes very clear and simple. By
combining ARPES measurements in different experimental configurations, we
clearly isolate each band forming one of the electron pockets. We identify a
deep electron band along one ellipse axis with the dxy orbital and a shallow
electron band along the perpendicular axis with the dxz/dyz orbitals, in good
agreement with band structure calculations. We show that the electron pockets
are warped as a function of kz as expected theoretically, but that they are
much smaller than predicted by the calculation.",1205.4513v1
2012-05-27,Neutron-Diffraction Measurements of an Antiferromagnetic Semiconducting Phase in the Vicinity of the High-Temperature Superconducting State of K$_x$Fe$_{2-y}$Se$_2$,"The recently discovered K-Fe-Se high temperature superconductor has caused
heated debate regarding the nature of its parent compound. Transport,
angle-resolved photoemission spectroscopy, and STM measurements have suggested
that its parent compound could be insulating, semiconducting or even metallic
[M. H. Fang, H.-D. Wang, C.-H. Dong, Z.-J. Li, C.-M. Feng, J. Chen, and H. Q.
Yuan, Europhys. Lett. 94, 27009 (2011); F. Chen et al. Phys. Rev. X 1, 021020
(2011); and W. Li et al.,Phys. Rev. Lett. 109, 057003 (2012)]. Because the
magnetic ground states associated with these different phases have not yet been
identified and the relationship between magnetism and superconductivity is not
fully understood, the real parent compound of this system remains elusive.
Here, we report neutron-diffraction experiments that reveal a semiconducting
antiferromagnetic (AFM) phase with rhombus iron vacancy order. The magnetic
order of the semiconducting phase is the same as the stripe AFM order of the
iron pnictide parent compounds. Moreover, while the root5*root5 block AFM phase
coexists with superconductivity, the stripe AFM order is suppressed by it. This
leads us to conjecture that the new semiconducting magnetic ordered phase is
the true parent phase of this superconductor.",1205.5992v2
2012-05-30,"The silicate model and carbon rich model of CoRoT-7b, Kepler-9d and Kepler-10b","Possible bulk compositions of the super-Earth exoplanets, CoRoT-7b,
Kepler-9d, and Kepler-10b are investigated by applying a commonly used silicate
and a non-standard carbon model. Their internal structures are deduced using
the suitable equation of state of the materials. The degeneracy problems of
their compositions can be partly overcome, based on the fact that all three
planets are extremely close to their host stars. By analyzing the numerical
results, we conclude: 1) The iron core of CoRoT-7b is not more than 27% of its
total mass within 1 $\sigma$ mass-radius error bars, so an Earth-like
composition is less likely, but its carbon rich model can be compatible with an
Earth-like core/mantle mass fraction; 2) Kepler-10b is more likely with a
Mercury-like composition, its old age implies that its high iron content may be
a result of strong solar wind or giant impact; 3) the transiting-only
super-Earth Kepler-9d is also discussed. Combining its possible composition
with the formation theory, we can place some constraints on its mass and bulk
composition.",1205.6554v2
2012-06-18,Impact of Dynamic Orbital Correlations on Magnetic Excitations in the Normal State of Iron-Based Superconductors,"We show here that orbital degrees of freedom produce a distinct signature in
the magnetic excitation spectrum of iron-based superconductors above the
magnetic ordering temperature. Because $d_{xz}$ and $d_{yz}$ orbitals are
strongly connected with the Fermi surface topology, the nature of magnetic
excitations can be modified significantly due to the presence of either static
or fluctuating orbital correlations. Within a five-orbital itinerant model, we
show that static orbital order generally leads to an enhancement of
commensurate magnetic excitations even when the original Fermi surface lacks
nesting at $(\pi,0)$ or $(0,\pi)$. When long-range orbital order is absent,
Gaussian fluctuations beyond the standard random-phase approximation (RPA)
capture the effects of fluctuating orbital correlations on the magnetic
excitations. We find that commensurate magnetic excitations can also be
enhanced if the orbital correlations are strong. Our results offer a natural
explanation for the incommensurate-to-commensurate transformation observed in a
recent neutron scattering measurement (Z. Xu, et. al., arXiv:1201.4404), and we
propose that this unusual transformation is an important signature to
distinguish orbital from spin physics in the normal state of the pnictides.
Implications for the magnetic and superconducting states are discussed.",1206.4095v2
2012-06-29,Laser spectroscopy of finite size and covering effects in magnetite nanoparticles,"The experiments on the impact of the size of magnetite clusters on various
magnetic properties (magnetic moment, Curie temperature, blocking temperature
etc.) have been carried out. The methods of magnetic separation, centrifuging
of water suspensions of biocompatible iron oxide nanoparticles (NPs) allow
producing fractions with diameter of nanoparticles in the range of 4{\div}22
nm. The size of NPs are controlled by the methods of dynamic light scattering
(DLS), transmission electron microscopy (TEM) and atomic force microscopy
(AFM). For the first time the DLS method is applied in real time to control the
size during the process of the separation of the NPs in aqueous suspensions.
The changes of the size of NPs cause a shift in the Curie temperature and in
the changes in the specific magnetic properties of the iron NPs. The
experimental data is interpreted on the basis of Monte Carlo simulations for
the classical Heisenberg model with different bulk and surface magnetic
moments. It is demonstrated experimentally and by theoretical modeling that
magnetic properties of magnetite NPs are determined not only by their sizes,
but also by the their surface spin states, while both growing and falling
dependences of the magnetic moment (per Fe3O4 formula unit) being possible,
depending on the number of magnetic atoms in the nanoparticle. Both NPs clean
and covered with a bioresorbable layer clusters have been investigated.",1206.6985v5
2012-07-03,Two-dome structure in electron-doped iron arsenide superconductors,"Iron arsenide superconductors based on the material LaFeAsO1-xFx are
characterized by a two-dimensional Fermi surface (FS) consisting of hole and
electron pockets yielding structural and antiferromagnetic transitions at x =
0. Electron doping by substituting O2- with F- suppresses these transitions and
gives rise to superconductivity with a maximum Tc = 26 K at x = 0.1. However,
the over-doped region cannot be accessed due to the poor solubility of F- above
x = 0.2. Here we overcome this problem by doping LaFeAsO with hydrogen. We
report the phase diagram of LaFeAsO1-xHx (x < 0.53) and, in addition to the
conventional superconducting dome seen in LaFeAsO1-xFx, we find a second dome
in the range 0.21 < x < 0.53, with a maximum Tc of 36 K at x = 0.3. Density
functional theory calculations reveal that the three Fe 3d bands (xy, yz, zx)
become degenerate at x = 0.36, whereas the FS nesting is weakened monotonically
with x. These results imply that the band degeneracy has an important role to
induce high Tc.",1207.0583v2
2012-07-13,The nature of the multi-wavelength emission of 3C 111,"We attempt to determine the nature of the high energy emission of the radio
galaxy 3C 111, by distinguishing between the effects of the thermal and
non-thermal processes. We study the X-ray spectrum of 3C 111 between 0.4 keV
and 200 keV, and its spectral energy distribution, using data from the Suzaku
satellite combined with INTEGRAL, Swift/BAT data, and Fermi/LAT data. We then
model the overall spectral energy distribution including radio and infrared
data. The combined Suzaku, Swift and INTEGRAL data are represented by an
absorbed exponentially cut-off power-law with reflection from neutral material
with a photon index Gamma = 1.68+-0.03, a high-energy cut-off Ecut = 227+143-67
keV, a reflection component with R = 0.7+-0.3 and a Gaussian component to
account for the iron emission-line at 6.4 keV with an equivalent width of EW =
85+-11 eV. The X-ray spectrum appears dominated by thermal, Seyfert-like
processes, but there are also indications of non-thermal processes. The radio
to gamma-ray spectral energy distribution can be fit with a single-zone
synchrotron-self Compton model, with no need for an additional thermal
component. We suggest a hybrid scenario to explain the broad-band emission,
including a thermal component (iron line, reflection) that dominates in the
X-ray regime and a non-thermal one to explain the spectral energy distribution.",1207.3308v2
2012-07-16,Searching for Massive Outflows in Holmberg IX X-1 and NGC 1313 X-1: The Iron K Band,"We have analysed all the good quality XMM-Newton data publicly available for
the bright ULXs Holmberg IX X-1 and NGC 1313 X-1, with the aim of searching for
discrete emission or absorption features in the Fe K band that could provide
observational evidence for the massive outflows predicted if these sources are
accreting at substantially super-Eddington rates. We do not find statistically
compelling evidence for any atomic lines, and the limits that are obtained have
interesting consequences. Any features in the immediate Fe K energy band (6-7
keV) must have equivalent widths weaker than ~30 eV for Holmberg IX X-1, and
weaker than ~50 eV for NGC 1313 X-1 (at 99 per cent confidence). In comparison
to the sub-Eddington outflows observed in GRS 1915+105, which imprint iron
absorption features with equivalent widths of ~30 eV, the limits obtained here
appear quite stringent, particularly when Holmberg IX X-1 and NGC 1313 X-1 must
be expelling at least 5-10 times as much material if they host black holes of
similar masses. The difficulty in reconciling these observational limits with
the presence of strong line-of-sight outflows suggests that either these
sources are not launching such outflows, or that they must be directed away
from our viewing angle.",1207.3839v1
2012-08-01,Coronae above accretion disks around black holes: The effect of Compton cooling,"The geometry of the accretion flow around stellar mass and supermassive black
holes depends on the accretion rate. Broad iron emission lines originating from
the irradiation of cool matter can indicate that there is an inner disk below a
hot coronal flow.These emission lines have been detected in X-ray binaries.
Observations with the Chandra X-ray Observatory, XMM Newton and Suzaku have
confirmed the presence of these emission lines also in a large fraction of
Seyfert-1 active galactic nuclei (AGN). We investigate the accretion flow
geometry for which broad iron emission lines can arise in hard and soft
spectral state. We study an ADAF-type coronal flow, where the ions are
viscously heated and electrons receive their heat only by collisions from the
ions and are Compton cooled by photons from an underlying cool disk. For a
strong mass flow in the disk and the resulting strong Compton cooling only a
very weak coronal flow is possible. This limitation allows the formation of
ADAF-type coronae above weak inner disks in the hard state, but almost rules
them out in the soft state. The observed hard X-ray luminosity in the soft
state, of up to 10% or more of the total flux, indicates that there is a
heating process that directly accelerates the electrons. This might point to
the action of magnetic flares of disk magnetic fields reaching into the corona.
Such flares have also been proposed by observations of the spectra of X-ray
black hole binaries without a thermal cut-off around 200 keV.",1208.0265v1
2012-08-18,Gap-dependent quasiparticle dynamics and coherent acoustic phonons in parent iron pnictide CaFe2As2 across the spin density wave phase transition,"We report ultrafast quasiparticle (QP) dynamics and coherent acoustic phonons
in undoped CaFe_2As_2 iron pnictide single crystals exhibiting spin-density
wave (SDW) and concurrent structural phase transition at temperature TSDW ~ 165
K using femtosecond time-resolved pump-probe spectroscopy. The contributions in
transient differential reflectivity arising from exponentially decaying QP
relaxation and oscillatory coherent acoustic phonon mode show large variations
in the vicinity of T_SDW. From the temperature-dependence of the QP
recombination dynamics in the SDW phase, we evaluate a BCS-like temperature
dependent charge gap with its zero-temperature value of ~(1.6+/-0.2)k_BT_SDW,
whereas, much above T_SDW, an electron-phonon coupling constant of ~0.13 has
been estimated from the linear temperature-dependence of the QP relaxation
time. The long-wavelength coherent acoustic phonons with typical time-period of
~100 ps have been analyzed in the light of propagating strain pulse model
providing important results for the optical constants, sounds velocity and the
elastic modulus of the crystal in the whole temperature range of 3 K to 300 K.",1208.3742v2
2012-08-29,Interpreting the near-infrared spectra of the 'golden standard' Type Ia supernova 2005cf,"We present nine near-infrared (NIR) spectra of supernova (SN) 2005cf at
epochs from -10 d to +42 d with respect to B-band maximum, complementing the
existing excellent data sets available for this prototypical Type Ia SN at
other wavelengths. The spectra show a time evolution and spectral features
characteristic of normal Type Ia SNe, as illustrated by a comparison with SNe
1999ee, 2002bo and 2003du. The broad-band spectral energy distribution (SED) of
SN 2005cf is studied in combined ultraviolet (UV), optical and NIR spectra at
five epochs between ~ 8 d before and ~ 10 d after maximum light. We also
present synthetic spectra of the hydrodynamic explosion model W7, which
reproduce the key properties of SN 2005cf not only at UV-optical as previously
reported, but also at NIR wavelengths. From the radiative-transfer calculations
we infer that fluorescence is the driving mechanism that shapes the SED of SNe
Ia. In particular, the NIR part of the spectrum is almost devoid of absorption
features, and instead dominated by fluorescent emission of both iron-group
material and intermediate-mass elements at pre-maximum epochs, and pure
iron-group material after maximum light. A single P-Cygni feature of Mg II at
early epochs and a series of relatively unblended Co II lines at late phases
allow us to constrain the regions of the ejecta in which the respective
elements are abundant.",1208.5949v1
2012-09-03,The Black Hole Spin and Soft X-ray Excess of the Luminous Seyfert Galaxy Fairall 9,"We present an analysis of all XMM-Newton and Suzaku X-ray spectra of the
nearby luminous Seyfert galaxy Fairall 9. Confirming previous analyses, we find
robust evidence for a broad iron line associated with X-ray reflection from the
innermost accretion disk. By fitting a spectral model that includes a
relativistically ionized reflection component, we examine the constraints on
the inclination of the inner accretion disk and the black hole spin, and the
complications introduced by the presence of a photoionized emission line
system. Employing multi-epoch fitting, we attempt to obtain robust and
concordant measures of the accretion disk parameters. We also clearly see a
soft X-ray excess in Fairall 9. During certain epochs, the soft excess can be
described with same disk reflection component that produces the iron line.
However, there are epochs where an additional soft component is required. This
can be attributed to either an additional highly-ionized, strongly blurred disk
reflection component, or a new X-ray continuum component.",1209.0468v1
2012-09-04,The enrichment history of the intracluster medium: a Bayesian approach,"This work measures the evolution of the iron content in galaxy clusters by a
rigorous analysis of the data of 130 clusters at 0.1<z<1.3. This task is made
difficult by a) the low signal-to-noise ratio of abundance measurements and the
upper limits, b) possible selection effects, c) boundaries in the parameter
space, d) non-Gaussian errors, e) the intrinsic variety of the objects studied,
and f) abundance systematics. We introduce a Bayesian model to address all
these issues at the same time, thus allowing cross-talk (covariance). On
simulated data, the Bayesian fit recovers the input enrichment history, unlike
in standard analysis. After accounting for a possible dependence on X-ray
temperature, for metal abundance systematics, and for the intrinsic variety of
studied objects, we found that the present-day metal content is not reached
either at high or at low redshifts, but gradually over time: iron abundance
increases by a factor 1.5 in the 7 Gyr sampled by the data. Therefore, feedback
in metal abundance does not end at high redshift. Evolution is established with
a moderate amount of evidence, 19 to 1 odds against faster or slower metal
enrichment histories. We quantify, for the first time, the intrinsic spread in
metal abundance, 18+/-3 %, after correcting for the effect of evolution, X-ray
temperature, and metal abundance systematics. Finally, we also present an
analytic approximation of the X-ray temperature and metal abundance likelihood
functions, which are useful for other regression fitting involving these
parameters. The data for the 130 clusters and code used for the stochastic
computation are provided with the paper.",1209.0565v1
2012-10-04,Manipulation and detection of spin state of Iron-Porphyrin by dedicated chemisorption on magnetic substrates,"One of the key factors behind the rapid evolution of molecular spintronics is
the efficient realization of spin manipulation of organic molecules with a
magnetic center. The spin state of such molecules may depend crucially on the
interaction with the substrate on which they are adsorbed. In this letter, we
demonstrate, using ab initio density functional calculations, that the
stabilization of a high spin state of an iron porphyrin (FeP) molecule can be
achieved via a dedicated chemisorption on magnetic substrates of different
species and orientations. It is shown that the strong covalent interaction with
the substrate increases Fe-N bond lengths in FeP and hence a switching to a
high spin state (S=2) from a low spin state (S=1) is achieved. A ferromagnetic
exchange interaction is established through a direct exchange between Fe and
substrate magnetic atoms as well as through an indirect exchange via the N
atoms in FeP. The mechanism of exchange interaction is further analyzed by
considering structural models constructed from ab initio calculations. Finally,
we illustrate the possibility of detecting a change in the molecular spin state
by x-ray magnetic circular dichroism, Raman spectroscopy and spin-polarized
scanning tunneling microscopy.",1210.1376v1
2012-12-07,Poly(acrylic acid)-coated iron oxide nanoparticles : quantitative evaluation of the coating properties and applications for the removal of a pollutant dye,"In this work, 6 to 12 nm iron oxide nanoparticles were synthesized and coated
with poly(acrylic acid) chains of molecular weight 2100 g/mol. Based on a
quantitative evaluation of the dispersions, the bare and coated particles were
thoroughly characterized. The number densities of polymers adsorbed at the
particle surface and of available chargeable groups were found to be 1.9 +/-
0.3 nm-2 and 26 +/- 4 nm-2, respectively. Occurring via a multi-site binding
mechanism, the electrostatic coupling leads to a solid and resilient anchoring
of the chains. To assess the efficacy of the particles for pollutant
remediation, the adsorption isotherm of methylene blue molecules, a model of
pollutant, was determined. The excellent agreement between the predicted and
measured amounts of adsorbed dyes suggests that most carboxylates participate
to the complexation and adsorption mechanisms. An adsorption of 830 mg/g was
obtained. This quantity compares well with the highest values available for
this dye.",1212.1580v1
2012-12-07,Magneto-optic Faraday effect in maghemite nanoparticles/silica matrix nanocomposites prepared by the Sol-Gel method,"Bulk monolithic samples of {\gamma}-Fe2O3/SiO2 composites with different iron
oxide/silica ratios have been prepared by the sol-gel technique. Iron oxide
nanoparticles are obtained in-situ during heat treatment of samples and silica
matrix consolidation. Preparation method was previously optimized to minimize
the percentage of antiferromagnetic {\alpha}-Fe2O3 and parallelepipeds of
roughly 2x5x12 mm3, with good mechanical stability, are obtained. RT
magnetization curves show a non-hysteretic behavior. Thus, magnetization
measurements have been well fitted to an expression that combines the Langevin
equation with an additional linear term, indicating that some of the
nanoparticles are still superparamagnetic as confirmed by X-ray diffraction and
electron microscopy measurements. Zero field cooled /field cooled experiments
show curves with slightly different shapes, depending on the size and shape
distribution of nanoparticles for a given composition. Magneto-optical Faraday
effect measurements show that the Faraday rotation is proportional to
magnetization of the samples, as expected. As a demonstration of their sensing
possibilities, the relative intensity of polarized light, measured at 5{\deg}
from the extinction angle, was plotted versus applied magnetic field.",1212.1690v1
2012-12-13,"Dopant Clustering, Electronic Inhomogeneity, and Vortex Pinning in Iron-Based Superconductors","We use scanning tunneling microscopy to map the surface structure, nanoscale
electronic inhomogeneity, and vitreous vortex phase in the hole-doped
superconductor Sr$_{0.75}$K$_{0.25}$Fe$_2$As$_2$ with $T_c$=32 K. We find the
low-$T$ cleaved surface is dominated by a half-Sr/K termination with $1\times
2$ ordering and ubiquitous superconducting gap, while patches of gapless,
unreconstructed As termination appear rarely. The superconducting gap varies by
$\sigma/\bar{\Delta}$=16% on a $\sim$3 nm length scale, with average
$2\bar{\Delta}/k_B T_c=3.6$ in the weak coupling limit. The vortex core size
provides a measure of the superconducting coherence length $\xi$=2.3 nm. We
quantify the vortex lattice correlation length at 9 T in comparison to several
iron-based superconductors. The comparison leads us to suggest the importance
of dopant size mismatch as a cause of dopant clustering, electronic
inhomogeneity, and strong vortex pinning.",1212.3240v3
2013-01-07,Persistent high-energy spin excitations in iron pnictide superconductors,"Motivated by the premise that superconductivity in iron-based superconductors
is unconventional and mediated by spin fluctuations, an intense research effort
has been focused on characterizing the spin excitation spectrum in the
magnetically ordered parent phases of the Fe-pnictides2,3 and - chalcogenides4.
For these undoped materials it is well-established that the spin excitation
spectrum consists of a sharp, highly dispersive magnon spanning an energy range
of up to 200 meV (ref. 3). The fate of these high-energy magnetic modes upon
sizable doping is hitherto unresolved. Using resonant inelastic x-ray
scattering we show that optimally doped superconducting Ba0.6K0.4Fe2As2 retains
well defined, dispersive high-energy modes of magnetic origin. These paramagnon
modes are softer than, though as intense as, the magnon of undoped
antiferromagnetic BaFe2As2. The persistence of spin excitations well into the
superconducting phase suggests that, if spin fluctuations are responsible for
superconducting pairing, they originate from a distinctly correlated
spin-state. This connects Fe-pnictide superconductors to the high-Tc cuprates,
for which in spite of fundamental differences in the electronic structure,
similar paramagnon modes are present5.",1301.1289v1
2013-02-21,The Mid-Infrared and Optical Decay of SN 2011fe,"We measure the decay rate of the mid-IR luminosity from type Ia supernova
2011fe between six months and one year after explosion using Spitzer/IRAC
observations. The fading in the 3.6 micron channel is 1.48+/-0.02 mag/100d,
which is similar to that seen in blue optical bands. The supernova brightness
fades at 0.78+/-0.02 mag/100d in the 4.5 micron channel which is close to that
observed in the near-IR. We argue that the difference is a result of doubly
ionized iron-peak elements dominating the bluer IRAC band while singly ionized
species are controlling the longer wavelength channel. To test this, we use
Large Binocular Telescope spectra taken during the same phases to show that
doubly ionized emission lines do fade more slowly than their singly ionized
cousins. We also find that [Co III] emission fades at more than twice the
radioactive decay rate due to the combination of decreasing excitation in the
nebula, recombination and cobalt decaying to iron. The nebular emission
velocities of [Fe III] and [Co III] lines show a smaller blue-shift than
emission from singly ionized atoms. The Si II velocity gradient near maximum
light combined with our nebular velocity measurements suggest SN 2011fe was a
typical member of the `low velocity gradient' class of type Ia. Analyzing IRAC
photometry from other supernovae we find that mid-IR color of type Ia events is
correlated with the early light curve width and can be used as an indicator of
the radioactive nickel yield.",1302.5421v1
2013-02-24,The X-ray Spectrum Of The Black Hole Candidate Swift J1753.5-0127,"We present a spectral analysis of the black hole candidate and X-ray
transient source Swift J1753.5 0127 making use of simultaneous observations of
XMM-Newton and Rossi X-ray Timing Explorer (RXTE) in 2006, when the source was
in outburst. The aim of this paper is to test whether a thermal component due
to the accretion disc is present in the X-ray spectrum. We fit the data with a
range of spectral models, and we find that for all of these models the fits to
the X-ray energy spectra significantly require the addition of the disc
black-body component. We also find a broad iron emission line at around 6.5
keV, most likely due to iron in the accretion disc. Our results confirm the
existence of a cool inner disc extending near or close to the innermost
circular orbit (ISCO).We further discovered broad emission lines of NVII and
OVIII at ~ 0.52 keV and 0.65 keV, respectively in the RGS spectrum of Swift
J1753.5-0127.",1302.5882v2
2013-03-04,Soft lags in neutron star kHz Quasi Periodic Oscillations: evidence for reverberation?,"High frequency soft reverberation lags have now been detected from stellar
mass and super massive black holes. Their interpretation involves reflection of
a hard source of photons onto an accretion disk, producing a delayed reflected
emission, with a time lag consistent with the light travel time between the
irradiating source and the disk. Independently of the location of the clock,
the kHz Quasi-Periodic Oscillation (QPO) emission is thought to arise from the
neutron star boundary layer. Here, we search for the signature of reverberation
of the kHz QPO emission, by measuring the soft lags and the lag energy spectrum
of the lower kHz QPOs from 4U1608-52. Soft lags, ranging from ~15 to ~40
microseconds, between the 3-8 keV and 8-30 keV modulated emissions are detected
between 565 and 890 Hz. The soft lags are not constant with frequency and show
a smooth decrease between 680 Hz and 890 Hz. The broad band X-ray spectrum is
modeled as the sum of a disk and a thermal comptonized component, plus a broad
iron line, expected from reflection. The spectral parameters follow a smooth
relationship with the QPO frequency, in particular the fitted inner disk radius
decreases steadily with frequency. Both the bump around the iron line in the
lag energy spectrum, and the consistency between the lag changes and the
inferred changes of the inner disk radius, from either spectral fitting or the
QPO frequency, suggest that the soft lags may indeed involve reverberation of
the hard pulsating QPO source on the disk.",1303.0750v2
2013-03-07,Abundances of neutron-capture elements in stars of the galactic disk substructures,"The aim of this work is to present and discuss the observations of the iron
peak (Fe, Ni) and neutron-capture element (Y, Zr, Ba, La, Ce, Nd, Sm, and Eu)
abundances for 276 FGK dwarfs, located in the galactic disk with metallicity -1
< [Fe/H] < +0.3. Atmospheric parameters and chemical composition of the studied
stars were determined from an high resolution, high signal-to-noise echelle
spectra obtained with the echelle spectrograph ELODIE at the Observatoire de
Haute-Provence (France). Effective temperatures were estimated by the line
depth ratio method and from the H_{\alpha} line-wing fitting. Surface gravities
(log g) were determined by parallaxes and the ionization balance of iron.
Abundance determinations were carried out using the LTE approach, taking the
hyperfine structure for Eu into account, and the abundance of Ba was computed
under the NLTE approximation. We are able to assign most of the stars in our
sample to the substructures of the Galaxy thick disk, thin disk, or Hercules
stream according to their kinematics. The classification of 27 stars is
uncertain. For most of the stars in the sample, the abundances of
neutron-capture elements have not been measured earlier. For all of them, we
provide the chemical composition and discuss the contribution from different
nucleosynthesis processes.",1303.1730v1
2013-03-28,New Diluted Ferromagnetic Semiconductor isostructural to 122 type iron pnictide superconductor with TC up to 180 K,"Diluted magnetic semiconductors (DMS) have received much attention due to its
potential applications to spintronics devices. A prototypical system (Ga,Mn)As
has been widely studied since 1990s. The simultaneous spin and charge doping
via hetero-valence (Ga3+,Mn2+) substitution, however, resulted in severely
limited solubility without availability of bulk specimens. Previously we
synthesized a new diluted ferromagnetic semiconductor of bulk Li(Zn,Mn)As with
Tc up to 50K, where isovalent (Zn,Mn) spin doping was separated from charge
control via Li concentrations. Here we report the synthesis of a new diluted
ferromagnetic semiconductor (Ba1-xKx)(Zn1-yMny)2As2, isostructural to iron 122
system, where holes are doped via (Ba2+, K1+), while spins via (Zn2+,Mn2+)
substitutions. Bulk samples with x=0.1-0.3 and y=0.05-0.15 exhibit
ferromagnetic order with TC up to 180K, comparable to that of record high Tc
for Ga(MnAs), significantly enhanced than Li(Zn,Mn)As. Moreover the
(Ba,K)(Zn,Mn)2As2 shares the same 122 crystal structure with semiconducting
BaZn2As2, antiferromagnetic BaMn2As2, and superconducting (Ba,K)Fe2As2, which
makes them promising to the development of multilayer functional devices.",1303.7157v1
2013-03-29,Seeing the orbital ordering in Iron-based superconductors with magnetic anisotropy,"The orbital fluctuation of the conduction electrons in the Iron-based
superconductors is found to contribute significantly to the magnetic response
of the system. With the use of a realistic five-band model and group
theoretical analysis, we have determined the orbital magnetic susceptibility in
such a multi-orbital system. At $n=6.1$, the in-plane orbital magnetic
susceptibility is predicted to be about 10$\mu_{\mathrm{B}}^{2}/\mathrm{eV}$,
which is more than 2/3 of the observed total susceptibility around 200 K in 122
systems(of about 14$\mu_{\mathrm{B}}^{2}/\mathrm{eV}$ or
$4.5\times10^{-4}\mathrm{erg}/\mathrm{G}^{2}\mathrm{mol}_{\mathrm{AS}}$\cite{Klingeler}).
We find the in-plane orbital magnetic response is sensitive to the breaking of
the tetragonal symmetry in the orbital space. In particular, when the observed
band splitting(between the $3d_{xz}$ and the $3d_{yz}$-dominated band) is used
to estimate the strength of the symmetry breaking perturbation\cite{Shen}, a
4.5% modulation in the in-plane orbital magnetic susceptibility can be
produced, making the latter a useful probe of the orbital ordering in such a
multi-orbital system. As a by product, the theory also explains the large
anisotropy between the in-plane and the out-of-plane magnetic response observed
universally in susceptibility and NMR measurements.",1303.7302v2
2013-04-01,Carbon and Oxygen Abundances in the Hot Jupiter Exoplanet Host Star XO-2N and its Binary Companion,"With the aim of connecting the compositions of stars and planets, we present
the abundances of carbon and oxygen, as well as iron and nickel, for the
transiting exoplanet host star XO-2N and its wide-separation binary companion
XO-2S. Stellar parameters are derived from high-resolution,
high-signal-to-noise spectra, and the two stars are found to be similar in
their Teff, log g, iron ([Fe/H]), nickel ([Ni/H]) abundances. Their carbon
([C/H]) and oxygen ([O/H]) abundances also overlap within errors, although
XO-2N may be slightly more C-rich and O-rich than XO-2S. The C/O ratios of both
stars (~0.60+/-0.20) may also be somewhat larger than solar (C/O~0.50). The
XO-2 system has a transiting hot Jupiter orbiting one binary component but not
the other, allowing us to probe the potential effects planet formation might
have on the host star composition. Additionally, with multiple observations of
its atmosphere the transiting exoplanet XO-2b lends itself to compositional
analysis, which can be compared to the natal chemical environment established
by our binary star elemental abundances. This work sets the stage for
determining how similar/different exoplanet and host star compositions are, and
the implications for planet formation, by discussing the C/O ratio measurements
in the unique environment of a visual binary system with one star hosting a
transiting hot Jupiter.",1304.0395v1
2013-04-03,"Molybdenum, Ruthenium, and the Heavy r-process Elements in Moderately Metal-Poor Main-Sequence Turnoff Stars","The ratios of elemental abundances observed in metal-poor stars of the
Galactic halo provide a unique present-day record of the nucleosynthesis
products of its earliest stars. While the heaviest elements were synthesized by
the r- and s-processes, dominant production mechanisms of light trans-ironic
elements were obscure until recently. This work investigates further our 2011
conclusion that the low-entropy regime of a high-entropy wind (HEW) produced
molybdenum and ruthenium in two moderately metal-poor turnoff stars that showed
extreme overabundances of those elements with respect to iron. Only a few, rare
nucleosynthesis events may have been involved.
  Here we determine abundances for Mo, Ru, and other trans-Fe elements for 28
similar stars by matching spectral calculations to well-exposed near-UV Keck
HIRES spectra obtained for beryllium abundances. In each of the 26 turnoff
stars with Mo or Ru line detections and no evidence for s-process production
(therefore old), we find Mo and Ru to be three to six times overabundant. In
contrast, the maximum overabundance is reduced to factors of three and two for
the neighboring elements zirconium and palladium. Since the overproduction
peaks sharply at Mo and Ru, a low-entropy HEW is confirmed as its origin.
  The overabundance level of the heavy r-process elements varies significantly,
from none to a factor of four, but is uncorrelated with Mo and Ru
overabundances. Despite their moderate metallicity, stars in this group trace
the products of different nucleosynthetic events: possibly very few events,
possibly events whose output depended on environment, metallicity, or time.",1304.1050v1
2013-04-04,Learning from Nature to Improve the Heat Generation of Iron-Oxide Nanoparticles for Magnetic Hyperthermia Applications,"The performance of magnetic nanoparticles is intimately entwined with their
structure, mean size and magnetic anisotropy. Besides, ensembles offer a unique
way of engineering the magnetic response by modifying the strength of the
dipolar interactions between particles. Here we report on an experimental and
theoretical analysis of magnetic hyperthermia, a rapidly developing technique
in medical research and oncology. Experimentally, we demonstrate that
single-domain cubic iron oxide particles resembling bacterial magnetosomes have
superior magnetic heating efficiency compared to spherical particles of similar
sizes. Monte Carlo simulations at the atomic level corroborate the larger
anisotropy of the cubic particles in comparison with the spherical ones, thus
evidencing the beneficial role of surface anisotropy in the improved heating
power. Moreover we establish a quantitative link between the particle
assembling, the interactions and the heating properties. This knowledge opens
new perspectives for improved hyperthermia, an alternative to conventional
cancer therapies.",1304.1298v1
2013-04-18,Hadron energy response of the Iron Calorimeter detector at the India-based Neutrino Observatory,"The results of a Monte Carlo simulation study of the hadron energy response
for the magnetized Iron CALorimeter detector, ICAL, proposed to be located at
the India-based Neutrino Observatory (INO) is presented. Using a GEANT4
modeling of the detector ICAL, interactions of atmospheric neutrinos with
target nuclei are simulated. The detector response to hadrons propagating
through it is investigated using the hadron hit multiplicity in the active
detector elements. The detector response to charged pions of fixed energy is
studied first, followed by the average response to the hadrons produced in
atmospheric neutrino interactions using events simulated with the NUANCE event
generator. The shape of the hit distribution is observed to fit the Vavilov
distribution, which reduces to a Gaussian at high energies. In terms of the
parameters of this distribution, we present the hadron energy resolution as a
function of hadron energy, and the calibration of hadron energy as a function
of the hit multiplicity. The energy resolution for hadrons is found to be in
the range 85% (for 1GeV) -- 36% (for 15 GeV).",1304.5115v2
2013-04-19,Understanding the re-entrant superconducting phase diagram of an iron-pnictide Ca$_4$Al$_2$O$_6$Fe$_2$(As$_{1-x}$P$_x$)$_2$,"Recently, a very rich phase diagram has been obtained for an iron-based
superconductor Ca4Al2O6Fe2(As1-xPx)2. It has been revealed that nodeless (x=0)
and nodal (x = 1) superconductivity are separated by an antiferromagnetic
phase. Here we study the origin of this peculiar phase diagram using a five
orbital model constructed from first principles band calculation, and applying
the fluctuation exchange approximation assuming spin fluctuation mediated
pairing. Based on the calculation results, we propose a scenario where the
frustration in momentum space degrades superconductivity in the intermediate x
regime, while antiferromangetism takes place due to a very good nesting. In
order to see whether the present theoretical scenario is consistent with the
actual nature of the competition between superconductivity and
antiferromagnetism, we also perform hydrostatic pressure experiment for
Ca4Al2O6Fe2(As1-xPx)2. In the intermediate x regime where antiferromagnetism
occurs at ambient pressure, applying hydrostatic pressure smears out the
antiferromagnetic transition, but superconductivity does not take place. This
supports our scenario that superconductivity is suppressed by the momentum
space frustration in the intermediate x regime, apart from the presence of the
antiferromangnetism.",1304.5360v1
2013-04-24,Deriving precise parameters for cool solar-type stars. Optimizing the iron line list,"Temperature, surface gravity, and metallicitity are basic stellar atmospheric
parameters necessary to characterize a star. We aim to improve the description
of the spectroscopic temperatures especially for the cooler stars where the
differences with the Infrared Flux Method are higher, as presented in previous
work. Our spectroscopic analysis is based on the iron excitation and ionization
balance, assuming Kurucz model atmospheres in LTE. The abundance analysis is
determined using the code MOOG. We optimize the line list using a cool star
with high resolution and high signal-to-noise spectrum, as a reference in order
to check for weak, isolated lines. We test the quality of the new line list by
re-deriving stellar parameters for 451 stars with high resolution and
signal-to-noise HARPS spectra, that were analyzed in a previous work with a
larger line list. The comparison in temperatures between this work and the
latest IRFM shows that the differences for the cooler stars are significantly
smaller and more homogeneously distributed than in previous studies for stars
with temperatures below 5000 K. We use the new line list to re-derive
parameters for some of the cooler stars that host planets. Finally, we present
the impact of the new temperatures on the [Cr I/Cr II] and [Ti I/Ti II]
abundance ratios that previously showed systematic trends with temperature.",1304.6639v1
2013-04-28,Point Contact Spectroscopy of Fe Pnictides & Chalcogenides In The Normal State,"We review the current status of point contact spectroscopy on the iron based
superconductors, focusing on their normal state. Point contact spectroscopy is
generally used to study superconductors via Andreev reflection, but in recent
years it has also proved to be a useful bulk probe of strongly correlated
electron systems. Point contact spectroscopy picks up a conductance enhancement
in the normal state, above the structural phase transition, of certain iron
based compounds. These include Co doped $\rm{BaFe_2As_2}$, $\rm{SrFe_2As_2}$,
$\rm{Fe_{1+y}Te}$ and F doped $\rm{SmFeAsO}$ and $\rm{LaFeAsO}$. Two materials
which do not show this conductance enhancement are $\rm{CaFe_2As_2}$ and K
doped $\rm{BaFe_2As_2}$. This conductance enhancement is thought to be tied to
orbital fluctuations. Orbital fluctuations in the normal state of these
compounds increases the single particle density of states at the Fermi level,
indicating that PCS is sensitive to this excess density of states. The
enhancement is only observed at those temperatures and dopings where an
in-plane resisitve anisotropy in the detwinned compounds is known to occur.
Thus point contact spectroscopy provides strong indications of electronic
nematicity in such materials. We also present diagnostics on how to judge if a
junction is impacted by joule heating or not. We conclude with the outstanding
challenges in the field and the new experiments that need to be carried out.",1304.7426v1
2013-05-08,A fully quantum mechanical calculation of the diffusivity of hydrogen in iron using the tight binding approximation and path integral theory,"We present calculations of free energy barriers and diffusivities as
functions of temperature for the diffusion of hydrogen in bcc-Fe. This is a
fully quantum mechanical approach since the total energy landscape is computed
using a new self consistent, transferable tight binding model for interstitial
impurities in magnetic iron. Also the hydrogen nucleus is treated quantum
mechanically and we compare here two approaches in the literature both based in
the Feynman path integral formulation of statistical mechanics. We find that
the quantum transition state theory which admits greater freedom for the proton
to explore phase space gives result in better agreement with experiment than
the alternative which is based on fixed centroid calculations of the free
energy barrier. We also find results in better agreement compared to recent
centroid molecular dynamics (CMD) calculations of the diffusivity which
employed a classical interatomic potential rather than our quantum mechanical
tight binding theory. In particular we find first that quantum effects persist
to higher temperatures than previously thought, and conversely that the low
temperature diffusivity is smaller than predicted in CMD calculations and
larger than predicted by classical transition state theory. This will have
impact on future modeling and simulation of hydrogen trapping and diffusion.",1305.1772v1
2013-05-10,Carbon Deflagration in Type Ia Supernova: I. Centrally Ignited Models,"A leading model for Type Ia supernovae (SNe Ia) begins with a white dwarf
near the Chandrasekhar mass that ignites a degenerate thermonuclear runaway
close to its center and explodes. In a series of papers, we shall explore the
consequences of ignition at several locations within such dwarfs. Here we
assume central ignition, which has been explored before, however, the problem
is worth revisiting, if only to validate those previous studies and to further
elucidate the relevant physics for future work. A perturbed sphere of hot iron
ash with a radius of ~100 km is initialized at the middle of the star. The
subsequent explosion is followed in several simulations using a thickened flame
model in which the flame speed is either fixed --- within the range expected
from turbulent combustion --- or based on the local turbulent intensity. Global
results, including the explosion energy and bulk nucleosynthesis (e.g. 56Ni of
0.48--0.56 $\Msun$) turn out to be insensitive to this speed. In all completed
runs, the energy released by the nuclear burning is adequate to unbind the
star, but not enough to give the energy and brightness of typical SNe Ia. As
found previously, the chemical stratification observed in typical events is not
reproduced. These models produce a large amount of unburned carbon and oxygen
in central low velocity regions, which is inconsistent with spectroscopic
observations, and the intermediate mass elements and iron group elements are
strongly mixed during the explosion.",1305.2433v1
2013-05-16,Effect of doping on the magnetostructural ordered phase of iron arsenides: A comparative study of the resistivity anisotropy in the doped BaFe$_2$As$_2$ with doping into three different sites,"In order to unravel a role of doping in the iron-based superconductors, we
investigated the in-plane resistivity for BaFe$_2$As$_2$ doped at either of the
three different lattice sites, Ba(Fe$_{1-x}$Co$_x$)$_2$As$_2$,
BaFe$_2$(As$_{1-x}$P$_x$)$_2$, and Ba$_{1-x}$K$_x$Fe$_2$As$_2$, focusing on the
doping effect in the low-temperature antiferromagnetic/orthorhombic (AFO)
phase. A major role of doping in the high-temperature paramagnetic/tetragonal
(PT) phase is known to change the Fermi surface by supplying charge carriers or
by exerting chemical pressure. In the AFO phase, we found a clear correlation
between the magnitude of residual resistivity and resistivity anisotropy. This
indicates that the resistivity anisotropy originates from the anisotropic
impurity scattering from dopant atoms. The magnitude of residual resistivity is
also found to be a parameter controlling the suppression rate of AFO ordering
temperature $T_s$. Therefore, the dominant role of doping in the AFO phase is
to introduce disorder to the system, distinct from that in the PT phase.",1305.3744v1
2013-05-31,Supernova Ejecta in the Youngest Galactic Supernova Remnant G1.9+0.3,"G1.9+0.3 is the youngest known Galactic supernova remnant (SNR), with an
estimated supernova (SN) explosion date of about 1900, and most likely located
near the Galactic Center. Only the outermost ejecta layers with free-expansion
velocities larger than about 18,000 km/s have been shocked so far in this
dynamically young, likely Type Ia SNR. A long (980 ks) Chandra observation in
2011 allowed spatially-resolved spectroscopy of heavy-element ejecta. We
denoised Chandra data with the spatio-spectral method of Krishnamurthy et al.,
and used a wavelet-based technique to spatially localize thermal emission
produced by intermediate-mass elements (IMEs: Si and S) and iron. The spatial
distribution of both IMEs and Fe is extremely asymmetric, with the strongest
ejecta emission in the northern rim. Fe Kalpha emission is particularly
prominent there, and fits with thermal models indicate strongly oversolar Fe
abundances. In a localized, outlying region in the northern rim, IMEs are less
abundant than Fe, indicating that undiluted Fe-group elements (including 56Ni)
with velocities larger than 18,000 km/s were ejected by this SN. But in the
inner west rim, we find Si- and S-rich ejecta without any traces of Fe, so
high-velocity products of O-burning were also ejected. G1.9+0.3 appears similar
to energetic Type Ia SNe such as SN 2010jn where iron-group elements at such
high free-expansion velocities have been recently detected. The pronounced
asymmetry in the ejecta distribution and abundance inhomogeneities are best
explained by a strongly asymmetric SN explosion, similar to those produced in
some recent 3D delayed-detonation Type Ia models.",1305.7399v1
2013-05-31,"Space Velocities of Southern Globular Clusters VII. NGC 6397, NGC 6626 (M 28) and NGC 6656 (M 22)","We have measured the absolute proper motions of globular clusters NGC 6397,
NGC 6626 (M 22) and NGC 6656 (M 28) as part of our ongoing Southern
Proper-Motion Program. The reference system is the ICRS via Hipparcos stars for
these three low galactic latitude clusters. Formal errors range between ~0.3
and 0.7 mas/yr. Notable is the result for NGC 6397 which differs by 2.5 mas/yr
from two HST determinations, while agreeing with previous ground-based ones. We
determine orbits for all three clusters in an axisymmetric and barred model of
the Galaxy and discuss these in the context of globular-cluster formation. M 22
is a well-known cluster with an iron abundance spread; such clusters are now
believed to have formed in massive parent systems that can retain ejecta of
core-collapsed SNe. We find that the five currently-accepted globular clusters
with iron/calcium abundance spread show orbits unrelated to each other, thus
suggesting at least five independent, massive progenitors that have contributed
to the build-up of the Milky-Way halo.",1305.7431v1
2013-06-26,Are there missing bond paths in Trimethylenemethane-Iron-tri-carbonyl [(CO)3Fe-(C4H6)] complex?,"In a recent paper [J. Organomet. Chem. (2013) doi: 10.1016 /j.jorganchem.
2013.03.047] analyzing the bonding mode of Trimethylenemethane (TMM) with some
metal carbonyls, Mousavi and Frenking have declared the absence of bond paths,
the so-called missed bond paths, between metal atoms and terminal carbon atoms
in several complexes. In this communication, it is first demonstrated that the
presupposition of the equivalence of a bond path and a chemical bond within the
context of the quantum theory of atoms in molecules (QTAIM) is superficial and
basically flawed which is not only against with the recent strict declaration
on the contrary [R.F.W. Bader, J. Phys. Chem. A 113 (2009) 10396], but also in
odd with the foundations of the QTAIM. Then, it is demonstrated that the
so-called missed bond paths indeed appear in molecular graphs of some
non-equilibrium geometries that are energetically quite accessible at room
temperatures. To emphasize on the importance of this observation the term
passionate neighbors is coined referring to the atomic basins that do not share
an inter-atomic surface at the equilibrium geometry but are neighbors, share an
inter-atomic surface, at non-equilibrium geometries accessible by nuclear
vibrations. Using the delocalization index as well as other evidence from
previous literature it is demonstrated that the QTAIM analysis is indeed
compatible with the presence of chemical bonds between iron metal and terminal
carbons in (CO)3Fe-TMM complex. Finally, some general discussions are done to
unravel the delicate relationship between the QTAIM proposed concepts, e.g.
bond paths and molecular graphs, and some orthodox concepts of chemistry, e.g.
chemical bonds and chemical structures, emphasizing that there is no one-to-one
relationship between these two categorizes.",1306.6350v2
2013-07-01,SWEET-Cat: A catalogue of parameters for Stars With ExoplanETs I. New atmospheric parameters and masses for 48 stars with planets,"Due to the importance that the star-planet relation has to our understanding
of the planet formation process, the precise determination of stellar
parameters for the ever increasing number of discovered extra-solar planets is
of great relevance. Furthermore, precise stellar parameters are needed to fully
characterize the planet properties. It is thus important to continue the
efforts to determine, in the most uniform way possible, the parameters for
stars with planets as new discoveries are announced. In this paper we present
new precise atmospheric parameters for a sample of 48 stars with planets. We
then take the opportunity to present a new catalogue of stellar parameters for
FGK and M stars with planets detected by radial velocity, transit, and
astrometry programs. Stellar atmospheric parameters and masses for the 48 stars
were derived assuming LTE and using high resolution and high signal-to-noise
spectra. The methodology used is based on the measurement of equivalent widths
for a list of iron lines and making use of iron ionization and excitation
equilibrium principles. For the catalog, and whenever possible, we used
parameters derived in previous works published by our team, using well defined
methodologies for the derivation of stellar atmospheric parameters. This set of
parameters amounts to over 65% of all planet host stars known, including more
than 90% of all stars with planets discovered through radial velocity surveys.
For the remaining targets, stellar parameters were collected from the
literature.",1307.0354v1
2013-07-17,The role of the Gamma-Eddington ratio relation on the X-ray Baldwin effect in Active Galactic Nuclei,"The X-ray Baldwin effect is the inverse correlation between the equivalent
width (EW) of the narrow component of the iron Kalpha line and the X-ray
luminosity of active galactic nuclei (AGN). A similar trend has also been
observed between Fe Kalpha EW and the Eddington ratio (lambda_Edd). Using
Chandra/HEG results of Shu et al. (2010) and bolometric corrections we study
the relation between EW and the lambda_Edd, and find that log EW =
(-0.13+/-0.03)log(lambda_Edd) + 1.47. We explore the role of the known positive
correlation between the photon index of the primary X-ray continuum (Gamma) and
lambda_Edd on the X-ray Baldwin effect. We simulate the iron Kalpha line
emitted by populations of unabsorbed AGN considering 3 different geometries of
the reflecting material: toroidal, spherical-toroidal and slab. We find that
the Gamma-lambda_Edd correlation cannot account for the whole X-ray Baldwin
effect, unless a strong dependence of Gamma on lambda_Edd, such as the one
recently found by Risaliti et al. (2009) and Jin et al. (2012), is assumed. No
clear correlation is found between EW and Gamma. We conclude that a good
understanding of the slope of the Gamma-lambda_Edd relation is critical to
assess whether the trend plays a leading or rather a marginal role in the X-ray
Baldwin effect.",1307.4507v2
2013-07-23,Variable X-ray reflection from 1H~0419--577,"We present detailed broadband X-ray spectral variability of a Seyfert 1
galaxy 1H~0419--577 based on an archival \suzaku{} observation in July 2007, a
new \suzaku{} observation performed in January 2010 and the two latest \xmm{}
observations from May 2010. All the observations show soft X-ray excess
emission below $2\kev$ and both \suzaku{} observations show a hard X-ray excess
emission above $10\kev$ when compared to a power-law. We have tested three
physical models -- a complex partial covering absorption model, a blurred
reflection model and an intrinsic disk Comptonization model. Among these three
models, the blurred reflection model provided statistically the best-fit to all
the four observations. Irrespective of the models used, the soft X-ray excess
emission requires contribution from a thermal component similar to that
expected from an accretion disk. The partial covering absorption model results
in a nonphysical high temperature ($kT_{in} \sim 100\ev$) for an accretion disk
and is also statistically the worst fit among the three models. 1H~0419--577
showed remarkable X-ray spectral variability. The soft X-ray excess and the
power-law both became weaker in January 2010 as well as in May 2010. A
moderately broad iron line, detected in July 2007, is absent in the January
2010 observation. Correlated variability of the soft X-ray excess and the iron
$K\alpha$ line strongly suggest reflection origin for both the components.
However, such spectral variability cannot be explained by the light bending
model alone and requires changes in the accretion disk/corona geometry possibly
arising from changes in the accretion rate.",1307.6223v1
2013-08-15,Structural and optical investigations of the iron-chalcogenide superconductor Fe$_{1.03}$Se$_{0.5}$Te$_{0.5}$ under high pressure,"Iron-chalcogenide superconductor Fe$_{1.03}$Se$_{0.5}$Te$_{0.5}$ has been
investigated under high pressure using synchrotron based x-ray diffraction and
mid-infrared reflectance measurements at room temperature. Pressure dependence
of the superconducting transition temperature (T$_c$) of the same sample has
been determined by temperature-dependent resistance measurements up to 10 GPa.
Although the high pressure orthorhombic phase ($\textit{Pbnm}$) starts emerging
at 4 GPa, structural transition becomes clearly observable above 10 GPa. A
strong correlation is observed between the Fe(Se,Te)$_{4}$ tetrahedral
deformation in the tetragonal phase ($\textit{P4/nmm}$) and the sharp rise of
T$_c$ up to $\sim$4 GPa, above which T$_c$ is found to be almost pressure
independent at least up to 10 GPa. A subtle structural modification of the
tetragonal phase is noticed above 10 GPa, suggesting a structural transition
with possible Fe$^{2+}$ spin-state transition. The evolution with pressure of
the optical conductivity shows that the Drude term increases systematically
with pressure up to 5.4 GPa, indicating the evolution of the tetragonal phase
towards a conventional metallic state. At further higher pressures the Drude
term reduces drastically implying a poor metallic character of the high
pressure orthorhombic phase. Our results suggest that occurrence of large onset
T$_c$ above 4 GPa is due to a systematic increase of high pressure orthorhombic
phase fraction.",1308.3367v1
2013-08-26,Constraints on the source of ultra-high energy cosmic rays using anisotropy vs chemical composition,"The joint analysis of anisotropy signals and chemical composition of
ultra-high energy cosmic rays offers strong potential for shedding light on the
sources of these particles. Following up on an earlier idea, this paper studies
the anisotropies produced by protons of energy >E/Z, assuming that anisotropies
at energy >E have been produced by nuclei of charge Z, which share the same
magnetic rigidity. We calculate the number of secondary protons produced
through photodisintegration of the primary heavy nuclei. Making the extreme
assumption that the source does not inject any proton, we find that the
source(s) responsible for anisotropies such as reported by the Pierre Auger
Observatory should lie closer than ~20-30, 80-100 and 180-200 Mpc if the
anisotropy signal is mainly composed of oxygen, silicon and iron nuclei
respectively. A violation of this constraint would otherwise result in the
secondary protons forming a more significant anisotropy signal at lower
energies. Even if the source were located closer than this distance, it would
require an extraordinary metallicity >120, 1600, 1100 times solar metallicity
in the acceleration zone of the source, for oxygen, silicon and iron
respectively, to ensure that the concomitantly injected protons not to produce
a more significant low energy anisotropy. This offers interesting prospects for
constraining the nature and the source of ultra-high energy cosmic rays with
the increase in statistics expected from next generation detectors.",1308.5699v2
2013-09-06,Probing the origin of the iron K_alpha line around stellar and supermassive black holes using X-ray polarimetry,"Asymmetric, broad iron lines are a common feature in the X-ray spectra of
both X-ray binaries (XRBs) and type-1 Active Galactic Nuclei (AGN). It was
suggested that the distortion of the Fe K_alpha emission results from Doppler
and relativistic effects affecting the radiative transfer close to the strong
gravitational well of the central compact object: a stellar mass black hole
(BH) or neutron star (NS) in the case of XRBs, or a super massive black hole
(SMBH) in the case of AGN. However, alternative approaches based on
reprocessing and transmission of radiation through surrounding media also
attempt to explain the line broadening. So far, spectroscopic and timing
analyzes have not yet convinced the whole community to discriminate between the
two scenarios. Here we study to which extent X-ray polarimetric measurements of
black hole X-ray binaries (BHXRBs) and type-1 AGN could help to identify the
possible origin of the line distortion. To do so, we report on recent
simulations obtained for the two BH flavors and show that the proposed
scenarios are found to behave differently in polarization degree and
polarization angle. A relativistic origin for the distortion is found to be
more probable in the context of BHXRBs, supporting the idea that the same
mechanism should lead the way also for AGN. We show that the discriminating
polarization signal could have been detectable by several X-ray polarimetry
missions proposed in the past.",1309.1684v1
2013-09-08,On Iron Monoxide Nanoparticles as a Carrier of the Mysterious 21 Micrometer Emission Feature in Post-Asymptotic Giant Branch Stars,"A prominent, mysterious emission feature peaking at ~20.1 micrometer ---
historically known as the ``21 micrometer' feature --- is seen in over two
dozen Galactic and Magellanic Cloud carbon-rich post-asymptotic giant branch
(post-AGB) stars. The nature of its carrier remains unknown since the first
detection of the 21 micrometer feature in 1989. Over a dozen materials have
been suggested as possible carrier candidates. However, none of them has been
accepted: they either require too much material (compared to what is available
in the circumstellar shells around these post-AGB stars), or exhibit additional
emission features which are not seen in these 21 micrometer sources.
  Recently, iron monoxide (FeO) nanoparticles seem to be a promising carrier
candidate as Fe is an abundant element and FeO emits exclusively at ~21
micrometer. In this work, using the proto-typical protoplanetary nebula HD
56126 as a test case, we examine FeO nanoparticles as a carrier for the 21
micrometer feature by modeling their infrared emission, with FeO being
stochastically heated by single stellar photons. We find that FeO emits too
broad a 21 micrometer feature to explain the observed one and the Fe abundance
required to be locked up in FeO exceeds what is available in HD 56126. We
therefore conclude that FeO nanoparticles are unlikely responsible for the 21
micrometer feature.",1309.1995v1
2013-09-09,Xenon Reacts with Iron at the Conditions of the Earth's Core,"Studies of the Earth's atmosphere have shown that more than 90% of xenon (Xe)
is depleted compared with its abundance in chondritic meteorites. This
long-standing missing Xe paradox has become the subject of considerable
interest and several models for a Xe reservoir have been proposed. Whether the
missing Xe is hiding in the Earth's core has remained a long unanswered
question. The key to address this issue lies in the reactivity of Xe with iron
(Fe, the main constituent of the Earth's core), which has been denied by
earlier studies. Here we report on the first evidence of the chemical reaction
of Xe and Fe at the conditions of the Earth's core, predicted through
first-principles calculations and unbiased structure searching techniques. We
find that Xe and Fe form a stable, inter-metallic compound of XeFe3, adopting a
Cu3Au-type face-centered cubic structure above 183 GPa and at 4470 K. As the
result of a Xe -> Fe charge transfer, Xe loses its chemical inertness by
opening up the filled 5p electron shell and functioning as a 5p-like element,
whilst Fe is unusually negatively charged, acting as an oxidant rather than a
reductant as usual. Our work establishes that the Earth's core is a natural
reservoir for Xe storage, and possibly provides the key to unlocking the
missing Xe paradox.",1309.2169v4
2013-09-24,"Mineralogy, reflectance spectra, and physical properties of the Chelyabinsk LL5 chondrite, insight into shock induced changes in asteroid regoliths","The mineralogy and physical properties of Chelyabinsk meteorites (fall,
February 15, 2013) are presented. Three types of meteorite material are
present, described as the light-colored, dark-colored, and impact-melt
lithologies. All are of LL5 composition with the impact-melt lithology being
close to whole-rock melt and the dark-colored lithology being shock-darkened
due to partial melting of iron metal and sulfides. This enables us to study the
effect of increasing shock on material with identical composition and origin.
Based on the magnetic susceptibility, the Chelyabinsk meteorites are richer in
metallic iron as compared to other LL chondrites. The measured bulk and grain
densities and the porosity closely resemble other LL chondrites. Shock
darkening does not have a significant effect on the material physical
properties, but causes a decrease of reflectance and decrease in silicate
absorption bands in the reflectance spectra. This is similar to the space
weathering effects observed on asteroids. However, compared to space weathered
materials, there is a negligible to minor slope change observed in impact-melt
and shock-darkened meteorite spectra. Thus, it is possible that some dark
asteroids with invisible silicate absorption bands may be composed of
relatively fresh shock-darkened chondritic material.",1309.6081v6
2013-10-14,"Field-induced nematic-like magnetic transition in an iron pnictide superconductor, Ca$_{10}$(Pt$_{3}$As$_{8}$)((Fe$_{1-x}$Pt$_{x}$)$_{2}$As$_{2}$)$_{5}$","We report a high magnetic field study up to 55 T of the nearly optimally
doped iron-pnictide superconductor Ca$_{10}$(Pt$_{3}$As$_{8}$)
((Fe$_{1-x}$Pt$_{x}$)$_{2}$As$_{2}$)$_{5}$ (x=0.078(6)) with a Tc 10 K using
magnetic torque, tunnel diode oscillator technique and transport measurements.
We determine the superconducting phase diagram, revealing an anisotropy of the
irreversibility field up to a factor of 10 near Tc and signatures of multiband
superconductivity. Unexpectedly, we find a spin-flop like anomaly in magnetic
torque at 22 T, when the magnetic field is applied perpendicular to the ab
planes, which becomes significantly more pronounced as the temperature is
lowered to 0.33 K. As our superconducting sample lies well outside the
antiferromagnetic region of the phase diagram, the observed field-induced
transition in torque indicates a spin-flop transition not of long-range ordered
moments, but of nematic-like antiferromagnetic fluctuations.",1310.3728v1
2013-10-14,High Pressure Effects on the Superconductivity in Rare-Earth Doped CaFe2As2,"High-pressure superconductivity in a rare-earth doped Ca0.86Pr0.14Fe2As2
single crystalline sample has been studied up to 12 GPa and temperatures down
to 11 K using designer diamond anvil cell under a quasi-hydrostatic pressure
medium. The electrical resistance measurements were complemented by high
pressure and low temperature x-ray diffraction studies at a synchrotron source.
The electrical resistance measurements show an intriguing observation of
superconductivity under pressure, with Tc as high as ~51 K at 1.9 GPa,
presenting the highest Tc reported in the intermetallic class of 1-2-2
iron-based superconductors. The resistive transition observed suggests a
possible existence of two superconducting phases at low pressures of 0.5 GPa:
one phase starting at Tc1 ~48 K, and the other starting at Tc2~16 K. The two
superconducting transitions show distinct variations with increasing pressure.
High pressure low temperature structural studies indicate that the
superconducting phase is a collapsed tetragonal ThCr2Si2-type (122) crystal
structure. Our high pressure studies indicate that high Tc state attributed to
non-bulk superconductivity in rare-earth doped 1-2-2 iron-based superconductors
is stable under compression over a broad pressure range.",1310.3842v2
2013-10-17,Coexistence of orbital degeneracy lifting and superconductivity in iron-based superconductors,"In contrast to conventional superconducting (SC) materials, superconductivity
in high-temperature superconductors (HTCs) usually emerges in the presence of
other fluctuating orders with similar or higher energy scales, thus instigating
debates over their relevance for the SC pairing mechanism. In iron-based
superconductors (IBSCs), local orbital fluctuations have been proposed to be
directly responsible for the structural phase transition and closely related to
the observed giant magnetic anisotropy and electronic nematicity. However,
whether superconductivity can emerge from, or even coexist with orbital
fluctuations, remains unclear. Here we report the angle-resolved photoemission
spectroscopy (ARPES) observation of the lifting of symmetry-protected band
degeneracy, and consequently the breakdown of local tetragonal symmetry in the
SC state of Li(Fe1-xCox)As. Supported by theoretical simulations, we analyse
the doping and temperature dependences of this band-splitting and demonstrate
an intimate connection between ferro-orbital correlations and
superconductivity.",1310.4601v3
2013-10-28,Metal-insulator transition and superconductivity in the two-orbital Hubbard-Holstein model for iron-based superconductors,"We investigate a two-orbital model for iron-based superconductors to
elucidate the effect of interplay between electron correlation and Jahn-Teller
electron-phonon coupling by using the dynamical mean-field theory combined with
the exact diagonalization method. When the intra- and inter-orbital Coulomb
interactions, $U$ and $U'$, increase with $U=U'$, both the local spin and
orbital susceptibilities, $\chi_{s}$ and $\chi_{o}$, increase with
$\chi_{s}=\chi_{o}$ in the absence of the Hund's rule coupling $J$ and the
electron-phonon coupling $g$. In the presence of $J$ and $g$, there are
distinct two regimes: for $J \stackrel{>}{_\sim} 2g^2/\omega_0$ with the phonon
frequency $\omega_0$, $\chi_{s}$ is enhanced relative to $\chi_{o}$ and shows a
divergence at $J=J_c$ above which the system becomes Mott insulator, while for
$J \stackrel{<}{_\sim} 2g^2/\omega_0$, $\chi_{o}$ is enhanced relative to
$\chi_{s}$ and shows a divergence at $g=g_c$ above which the system becomes
bipolaronic insulator. In the former regime, the superconductivity is mediated
by antiferromagnetic fluctuations enhanced due to Fermi-surface nesting and is
found to be largely dependent on carrier doping. On the other hand, in the
latter regime, the superconductivity is mediated by ferro-orbital fluctuations
and is observed for wide doping region including heavily doped case without the
Fermi-surface nesting.",1310.7327v3
2013-10-29,A uniform metal distribution in the intergalactic medium of the Perseus cluster of galaxies,"Most of the metals (elements heavier than helium) ever produced by stars in
the member galaxies of galaxy clusters currently reside within the hot, X-ray
emitting intra-cluster gas. Observations of X-ray line emission from this
intergalactic medium have suggested a relatively small cluster-to-cluster
scatter outside of the cluster centers and enrichment with iron out to large
radii, leading to the idea that the metal enrichment occurred early in the
history of the Universe. Models with early enrichment predict a uniform metal
distribution at large radii in clusters, while late-time enrichment, favored by
some previous studies, is expected to introduce significant spatial variations
of the metallicity. To discriminate clearly between these competing models, it
is essential to test for potential inhomogeneities by measuring the abundances
out to large radii along multiple directions in clusters, which has not
hitherto been done. Here we report a remarkably uniform measured iron
abundance, as a function of radius and azimuth, that is statistically
consistent with a constant value of 0.306+/-0.012 Solar out to the edge of the
nearby Perseus Cluster. This homogeneous distribution requires that most of the
metal enrichment of the intergalactic medium occurred before the cluster
formed, likely over 10 billion years ago, during the period of maximal star
formation and black hole activity.",1310.7948v1
2013-10-30,Close relationship between superconductivity and the bosonic mode in Ba0.6K0.4Fe2As2 and Na(Fe0.975Co0.025)As,"Since the discovery of high temperature superconductivity in the iron
pnictides and chalcogenides in early 2008, a central issue has been the
microscopic origin of the superconducting pairing. Although previous
experiments suggest that the pairing may be induced by exchanging the
antiferromagnetic spin fluctuations and the superconducting order parameter has
opposite signs in the electron and hole pockets as predicted by the S+- pairing
model, it remains unclear whether there is a bosonic mode from the tunneling
spectrum which has a close and universal relationship with superconductivity as
well as the spin excitation. In this paper, based on the measurements of
scanning tunneling spectroscopy, we show the clear evidence of a bosonic mode
with the energy identical to that of the neutron spin resonance in two
completely different systems Ba0.6K0.4Fe2As2 and Na(Fe0.975Co0.025)As with
different superconducting transition temperatures. In both samples, the
superconducting coherence peaks and the mode feature vanish simultaneously
inside the vortex core or above Tc, indicating a close relationship between
superconductivity and the bosonic mode. Our data also demonstrate a universal
ratio between the mode energy and superconducting transition temperature, that
is [mode energy]/kBTc ~ 4.3, which underlines the unconventional mechanism of
superconductivity in the iron pnictide superconductors.",1310.8160v1
2013-11-04,Variability of the High Velocity Outflow in the Quasar PDS 456,"We present a comparison of two Suzaku X-ray observations of the nearby
(z=0.184), luminous ($L_{bol} \sim 10^{47}$ erg s$^{-1}$) type I quasar,
PDS456. A new 125ks Suzaku observation in 2011 caught the quasar during a
period of low X-ray flux and with a hard X-ray spectrum, in contrast to a
previous 190ks Suzaku observation in 2007 when the quasar appeared brighter and
had a steep ($\Gamma>2$) X-ray spectrum. The 2011 X-ray spectrum contains a
pronounced trough near 9\,keV in the quasar rest frame, which can be modeled
with blue-shifted iron K-shell absorption, most likely from the He and H-like
transitions of iron. The absorption trough is observed at a similar rest-frame
energy as in the earlier 2007 observation, which appears to confirm the
existence of a persistent high velocity wind in PDS 456, at an outflow velocity
of $0.25-0.30$c. The spectral variability between 2007 and 2011 can be
accounted for by variations in a partial covering absorber, increasing in
covering fraction from the brighter 2007 observation to the hard and faint 2011
observation. Overall the low flux 2011 observation can be explained if PDS 456
is observed at relatively low inclination angles through a Compton thick wind,
originating from the accretion disk, which significantly attenuates the X-ray
flux from the quasar.",1311.0734v1
2013-11-19,Suzaku View of the Neutron Star in the Dipping Source 4U 1822$-$37,"The dipping X-ray source 4U 1822$-$37 was observed by Suzaku on 2006 Octrober
20 for a net exposure of 37 ks. The source was detected with the XIS at a 1-10
keV flux of 5.5$\times10^{-10}$ erg cm$^{-2}$ s$^{-1}$, and with the HXD
(HXD-PIN) at a 10-50 keV flux of 8.9$\times10^{-10}$ erg cm$^{-2}$ s$^{-1}$.
With HXD-PIN, the pulsation was detected at a barycentric period of 0.592437 s,
and its change rate was reconfirmed as $-2.43\times$10$^{-12}$ s s$^{-1}$. The
1-50 keV spectra of 4U 1822-37 were found to be very similar to those of Her
X-1 in the slopes, cutoff and iron lines. Three iron lines (Fe K$\alpha$, Fe
XXV, and Fe XXVI) were detected, on top of a 1-50 keV continuum that is
described by an NPEX model plus a soft blackbody. In addition, a cyclotron
resonance scattering feature was detected significantly ($>99\%$ confidence),
at an energy of 33$\pm$2 keV with a depth of 0.4$^{+0.6}_{-0.3}$. Therefore,
the neutron star in this source is concluded to have a strong magnetic field of
2.8$\times10^{12}$ G. Further assuming that the source has a relatively high
intrinsic luminosity of several times 10$^{37}$ erg s$^{-1}$, its spectral and
timing properties are consistently explained.",1311.4618v1
2013-11-19,Metal distributions out to 0.5 r180 in the intracluster medium of four galaxy groups observed with Suzaku,"We studied the distributions of metal abundances and metal-mass-to-light
ratios in the intracluster medium (ICM) of four galaxy groups, MKW 4, HCG 62,
the NGC 1550 group, and the NGC 5044 group, out to 0.5 r180 observed with
Suzaku. The Fe abundance decreases with radius, and about 0.2-0.4 solar beyond
0.1 r180. At a given radius in units of r180, the Fe abundance in the ICM of
the four galaxy groups were consistent or smaller than those of clusters of
galaxies. The Mg/Fe and Si/Fe ratios in the ICM are nearly constant at the
solar ratio out to 0.5 r180. We also studied systematic uncertainties in the
derived metal abundances comparing the results from two versions of atomic data
for astrophysicists (ATOMDB) and single- and two temperature model fits. Since
the metals have been synthesized in galaxies, we collected K-band luminosities
of galaxies from Two Micron All Sky Survey catalogue (2MASS) and calculated the
integrated iron-mass-to-light-ratios (IMLR), or the ratios of the iron mass in
the ICM to light from stars in galaxies. The groups with smaller gas mass to
light ratios have smaller IMLR values and the IMLR inversely correlated with
the entropy excess. Based on these abundance features, we discussed the past
history of metal enrichment process in groups of galaxies.",1311.4636v1
2013-11-23,"Fermi Surface and Band Structure of (Ca,La)FeAs2 Superconductor from Angle-Resolved Photoemission Spectroscopy","The (Ca,R)FeAs2 (R=La,Pr and etc.) superconductors with a signature of
superconductivity transition above 40 K possess a new kind of block layers that
consist of zig-zag As chains. In this paper, we report the electronic structure
of the new (Ca,La)FeAs2 superconductor investigated by both band structure
calculations and high resolution angle-resolved photoemission spectroscopy
measurements. Band structure calculations indicate that there are four
hole-like bands around the zone center $\Gamma$(0,0) and two electron-like
bands near the zone corner M(pi,pi) in CaFeAs2. In our angle-resolved
photoemission measurements on (Ca0.9La0.1})FeAs2, we have observed three
hole-like bands around the Gamma point and one electron-like Fermi surface near
the M(pi,pi) point. These results provide important information to compare and
contrast with the electronic structure of other iron-based compounds in
understanding the superconductivity mechanism in the iron-based
superconductors.",1311.6042v1
2013-12-10,Interfacial mode coupling as the origin of the enhancement of Tc in FeSe films on SrTiO3,"Single unit cell films of iron selenide (1UC FeSe) grown on SrTiO3 (STO)
substrates have recently shown superconducting energy gaps opening at
temperatures close to the boiling point of liquid nitrogen (77 K), a record for
iron-based superconductors. Towards understanding why Cooper pairs form at such
high temperatures, a primary question to address is the role, if any, of the
STO substrate. Here, we report high resolution angle resolved photoemission
spectroscopy (ARPES) results which reveal an unexpected and unique
characteristic of the 1UC FeSe/STO system: shake-off bands suggesting the
presence of bosonic modes, most likely oxygen optical phonons in STO, which
couple to the FeSe electrons with only small momentum transfer. Such coupling
has the unusual benefit of helping superconductivity in most channels,
including those mediated by spin fluctuations. Our calculations suggest such
coupling is responsible for raising the superconducting gap opening temperature
in 1UC FeSe/STO. This discovery suggests a pathway to engineer high temperature
superconductors.",1312.2633v6
2013-12-17,Defect ordering and defect-domain wall interactions in PbTiO$_3$: A first-principles study,"The properties of ferroelectric materials, such as lead zirconate titanate
(PZT), are heavily influenced by the interaction of defects with domain walls.
These defects are either intrinsic, or are induced by the addition of dopants.
We study here PbTiO$_3$ (the end member of a key family of solid solutions) in
the presence of acceptor (Fe) and donor (Nb) dopants, and the interactions of
the different defects and defect associates with the domain walls. For the case
iron acceptors, the calculations point to the formation of defect associates
involving an iron substitutional defect and a charged oxygen vacancy
(Fe$^{'}_{Ti}$-V$^{^{\textbf{..}}}_O$). This associate exhibits a strong
tendency to align in the direction of the bulk polarization; in fact, ordering
of defects is also observed in pure PbTiO$_3$ in the form of lead-oxygen
divacancies. Conversely, calculations on donor-doped PbTiO$_3$ do not indicate
the formation of polar defect complexes involving donor substitutions. Last, it
is observed that both isolated defects in donor-doped materials and defect
associates in acceptor-doped materials are more stable at 180$^o$ domain walls.
However, polar defect complexes lead to asymmetric potentials at domain walls
due to the interaction of the defect polarization with the bulk polarization.
The relative pinning characteristics of different defects are then compared, to
develop an understanding of defect-domain wall interactions in both doped and
pure PbTiO$_3$. These results may also help understanding hardening and
softening mechanisms in PZT.",1312.4701v1
2014-02-17,Near-substrate composition depth profile of direct current-plated and pulse-plated Fe-Ni alloys,"Composition depth profiles of d.c.-plated and pulseplated Fe-Ni alloys have
been investigated with the reverse depth profile analysis method. When d.c.
plating is applied, the mole fraction of iron near the substrate is higher than
during steadystate deposition since iron is preferentially deposited beside
nickel and the achievement of the steadystate deposition condition takes time.
The steadystate composition was achieved typically after depositing a
90-nm-thick alloy layer. In the pulseplating mode, samples with nearly uniform
composition could be obtained at a duty cycle of 0.2 or smaller, and a
continuous change in the composition profile could be seen as a function of the
duty cycle above this value. A constant sample composition was achieved with
pulseplating in a wide peak current density interval. The composition depth
profile was also measured for a wide range of Fe2+ concentration. The different
characteristics of the composition depth profile as a function of the
deposition mode can be explained mostly in terms of mass transport effects. The
elucidation of the results is fully in accord with the kinetic models of
anomalous codeposition and with the assumption of the superposition of a
stationary and a pulsating diffusion layer. The results achieved help to
identify the conditions for the deposition of ultrathin magnetic samples with
uniform composition along the growth direction.",1402.3943v1
2014-02-20,Ultrafast observation of critical nematic fluctuations and giant magnetoelastic coupling in iron pnictides,"Many of the iron pnictides have strongly anisotropic normal-state
characteristics, important for the exotic magnetic and superconducting behavior
these materials exhibit. Yet, the origin of the observed anisotropy is unclear.
Electronically driven nematicity has been suggested, but distinguishing this as
an independent degree of freedom from magnetic and structural orders is
difficult, as these couple together to break the same tetragonal symmetry. Here
we use time-resolved polarimetry to reveal critical nematic fluctuations in
unstrained Ba(Fe_(1-x)Co_x)_2As_2. The femtosecond anisotropic response, which
arises from the two-fold in-plane anisotropy of the complex refractive index,
displays a characteristic two-step recovery absent in the isotropic response.
The fast recovery appears only in the magnetically ordered state, whereas the
slow one persists in the paramagnetic phase with a critical divergence
approaching the structural transition temperature. The dynamics also reveal a
gigantic magnetoelastic coupling that far exceeds electron-spin and
electron-phonon couplings, opposite to conventional magnetic metals.",1402.4890v1
2014-02-21,The form and the origin of the orbital ordering in the electronic nematic phase of the Iron-based superconductors,"We investigated the form of the orbital ordering in the electronic nematic
phase of the Iron-based superconductors by applying a group theoretical
analysis on a realistic five-band model. We find the orbital order can be
either of the inter-orbital s-wave form or the intra-orbital d-wave form. From
the comparison with existing ARPES measurements of band splitting, we find the
orbital ordering in the 122 system is dominated by an intra-orbital d-wave
component, while that in the 111 system is dominated by an inter-orbital s-wave
component. We find both forms of orbital order are strongly entangled with the
nematicity in the spin correlation of the system. The condensation energy of
the magnetic ordered phase is found to be significantly improved(by more than
20 percents) when the degeneracy between the $(\pi,0)$ and $(0,\pi)$ ordering
pattern is lifted by the orbital order. We argue there should be large
difference in both the scattering rate and the size of the possible pseudogap
on the electron pocket around the $\mathrm{X}=(\pi,0)$ and $\mathrm{Y}=(0,\pi)$
point in the electronic nematic phase. We propose this as a possible origin for
the observed nematicity in resistivity measurements.",1402.5209v1
2014-02-24,Towards a novel laser-driven method of exotic nuclei extraction-acceleration for fundamental physics and technology,"The measurement of properties of exotic nuclei, essential for fundamental
nuclear physics, now confronts a formidable challenge for contemporary
radiofrequency accelerator technology. A promising option can be found in the
combination of state-of-the-art high-intensity short pulse laser system and
nuclear measurement techniques. We propose a novel Laser-driven Exotic Nuclei
extraction-acceleration method (LENex): a femtosecond petawatt laser,
irradiating a target bombarded by an external ion beam, extracts from the
target and accelerates to few GeV highly-charged nuclear reaction products.
Here a proof-of-principle experiment of LENex is presented: a few
hundred-terawatt laser focused onto an aluminum foil, with a small amount of
iron simulating nuclear reaction products, extracts almost fully stripped iron
nuclei and accelerate them up to 0.9 GeV. Our experiments and numerical
simulations show that short-lived, heavy exotic nuclei, with a much larger
charge-to-mass ratio than in conventional technology, can be obtained in the
form of an energetic, low-emittance, high-current beam.",1402.5729v1
2014-03-01,Sudden reversal in the pressure dependence of Tc in the iron-based superconductor CsFe2As2: A possible link between inelastic scattering and pairing symmetry,"We report a sudden reversal in the pressure dependence of Tc in the
iron-based superconductor CsFe2As2, similar to that discovered recently in
KFe2As2 [Tafti et al., Nat. Phys. 9, 349 (2013)]. As in KFe2As2, we observe no
change in the Hall coefficient at the zero temperature limit, again ruling out
a Lifshitz transition across the critical pressure Pc. We interpret the Tc
reversal in the two materials as a phase transition from one pairing state to
another, tuned by pressure, and investigate what parameters control this
transition. Comparing samples of different residual resistivity, we find that a
6-fold increase in impurity scattering does not shift Pc. From a study of X-ray
diffraction on KFe2As2 under pressure, we report the pressure dependence of
lattice constants and As-Fe-As bond angle. The pressure dependence of these
lattice parameters suggests that Pc should be significantly higher in CsFe2As2
than in KFe2As2, but we find on the contrary that Pc is lower in CsFe2As2.
Resistivity measurements under pressure reveal a change of regime across Pc,
suggesting a possible link between inelastic scattering and pairing symmetry.",1403.0110v3
2014-03-05,"Observation of a Robust Zero-energy Bound State in Iron-based Superconductor Fe(Te,Se)","A robust zero-energy bound state (ZBS) in a superconductor, such as a
Majorana or Andreev bound state, is often a consequence of non-trivial
topological or symmetry related properties, and can provide indispensable
information about the superconducting state. Here we use scanning tunneling
microscopy/spectroscopy to demonstrate, on the atomic scale, that an isotropic
ZBS emerges at the randomly distributed interstitial excess Fe sites in the
superconducting Fe(Te,Se). This ZBS is localized with a short decay length of ~
10 {\AA}, and surprisingly robust against a magnetic field up to 8 Tesla, as
well as perturbations by neighboring impurities. We find no natural explanation
for the observation of such a robust zero-energy bound state, indicating a
novel mechanism of impurities or an exotic pairing symmetry of the iron-based
superconductivity.",1403.1027v1
2014-03-10,A lithium-ion battery based on a graphene nanoflakes ink anode and a lithium iron phosphate cathode,"Li-ion rechargeable batteries have enabled the wireless revolution
transforming global communication. Future challenges, however, demands
distributed energy supply at a level that is not feasible with the current
energy-storage technology. New materials, capable of providing higher energy
density are needed. Here we report a new class of lithium-ion batteries based
on a graphene ink anode and a lithium iron phosphate cathode. By carefully
balancing the cell composition and suppressing the initial irreversible
capacity of the anode, we demonstrate an optimal battery performance in terms
of specific capacity, i.e. 165 mAhg-1, estimated energy density of about 190
Whkg-1 and life, with a stable operation for over 80 charge-discharge cycles.
We link these unique properties to the graphene nanoflake anode displaying
crystalline order and high uptake of lithium at the edges, as well as to its
structural and morphological optimization in relation to the overall battery
composition. Our approach, compatible with any printing technologies, is cheap
and scalable and opens up new opportunities for the development of
high-capacity Li-ion batteries.",1403.2161v1
2014-03-26,Realization of practical level current densities in Sr0.6K0.4Fe2As2 tape conductors for high-field applications,"122 type pnictide superconductors are of particular interest for high-field
applications because of their large upper critical fields Hc2 (> 100 T), low
Hc2 anisotropy r (< 2), and high thin-film critical current densities Jc (> 1
MA/cm2 at 4.2 K). Successful magnet applications require fabrication of
polycrystalline superconducting wires that exhibit large in-field Jc, which is
limited by poor grain coupling and weak-link behavior at grain boundaries. Here
we report our recent achievement in the developing Sr0.6K0.4Fe2As2 tapes with
transport Jc up to 0.1 MA/cm2 at 10 T and 4.2 K. This value is by far the
highest ever recorded for iron based superconducting wires and has surpassed
the threshold for practical application for the first time. The synergy effects
of enhanced grain connectivity, alleviation of the weak-link behavior at grain
boundaries, and the strong intrinsic pinning characteristics led to the
superior Jc performance exhibited in our samples. This advanced Jc result opens
up the possibility for iron-pnictide superconducting wires to win the race in
high-field magnet applications.",1403.6704v2
2014-04-15,Orbital phase resolved spectroscopy of GX 301-2 with MAXI,"GX 301-2, a bright HMXB with an orbital period of 41.5 days, exhibits stable
periodic orbital intensity modulations with a strong pre-periastron X-ray
flare. Several models have been proposed to explain the accretion at different
orbital phases, invoking accretion via stellar wind, equatorial disk, and
accretion stream from the companion star. We present results from exhaustive
orbital phase resolved spectroscopic measurements of GX 301-2 using data from
the Gas Slit Camera onboard MAXI. Using spectroscopic analysis of the MAXI data
with unprecendented orbital coverage for many orbits continuously, we have
found a strong orbital dependence of the absorption column density and
equivalent width of the iron emission line. A very large equivalent width of
the iron line along with a small value of the column density in the orbital
phase range 0.10-0.30 after the periastron passage indicates presence of high
density absorbing matter behind the neutron star in these orbital phase range.
A low energy excess is also found in the spectrum at orbital phases around the
pre-periastron X-ray flare. The orbital dependence of these parameters are then
used to examine the various models about mode of accretion onto the neutron
star in GX 301-2.",1404.3902v1
2014-05-01,The elemental composition of the Sun II. The iron group elements Sc to Ni,"We redetermine the abundances of all iron group nuclei in the Sun, based on
neutral and singly-ionised lines of Sc, Ti, V, Mn, Fe, Co and Ni in the solar
spectrum. We employ a realistic 3D hydrodynamic model solar atmosphere,
corrections for departures from local thermodynamic equilibrium (NLTE),
stringent line selection procedures and high quality observational data. We
have scoured the literature for the best quality oscillator strengths,
hyperfine constants and isotopic separations available for our chosen lines. We
find $\log \epsilon_\mathrm{Sc}=3.16\pm0.04$, $\log
\epsilon_\mathrm{Ti}=4.93\pm0.04$, $\log \epsilon_\mathrm{V}=3.89\pm0.08$,
$\log \epsilon_\mathrm{Cr}=5.62\pm0.04$, $\log
\epsilon_\mathrm{Mn}=5.42\pm0.04$, $\log \epsilon_\mathrm{Fe}=7.47\pm0.04$,
$\log \epsilon_\mathrm{Co}=4.93\pm0.05$ and $\log
\epsilon_\mathrm{Ni}=6.20\pm0.04$. Our uncertainties factor in both statistical
and systematic errors (the latter estimated for possible errors in the model
atmospheres and NLTE line formation). The new abundances are generally in good
agreement with the CI meteoritic abundances but with some notable exceptions.
This analysis constitutes both a full exposition and a slight update of the
preliminary results we presented in Asplund, Grevesse, Sauval & Scott
(arXiv:0909.0948), including full line lists and details of all input data we
employed.",1405.0287v2
2014-05-13,Intra-unit-cell nematic charge order in the titanium-oxypnictide family of superconductors,"Understanding the role played by broken symmetry states such as charge, spin,
and orbital orders in the mechanism of emergent properties such as
high-temperature superconductivity (HTSC) is a major current topic in materials
research. That the order may be within one unit cell, such as nematic, was only
recently considered theoretically, but its observation in the iron-pnictide and
doped cuprate superconductors places it at the forefront of current research.
Here we show that the recently discovered BaTi$_2$Sb$_2$O superconductor and
its ""parent"" compound BaTi$_2$As$_2$O form a symmetry-breaking nematic ground
state that can be naturally explained as an intra-unit-cell charge order with
$d$-wave symmetry, pointing to the ubiquity of the phenomenon. These findings,
together with the key structural features in these materials being intermediate
between the cuprate and iron-pnictide HTSC materials, render the titanium
oxypnictides an important new material system to understand the nature of
nematic order and its relationship to superconductivity.",1405.3236v2
2014-05-30,Evolution of quasiparticle states with and without a Zn-impurity in doped 122 iron pnictides,"Based on a minimal two-orbital model [Tai {\it et al.}, Europhys. Lett.
\textbf{103}, 67001 (2013)], which captures the canonical electron-hole-doping
phase diagram of the iron-pnictide BaFe$_{2}$As$_{2}$, we study the evolution
of quasiparticle states as a function of doping using the Bogoliubov-de Gennes
equations with and without a single impurity. Analyzing the density of states
of uniformly doped samples, we are able to identify the origin of the two
superconducting gaps observed in optimally hole- or electron-doped systems. The
local density of states (LDOS) is then examined near a single impurity in
samples without antiferromagnetic order. The qualitative features of our
results near the single impurity are consistent with a work based on a
five-orbital model[K. Toshikaze {\it et al.}, J. Phys. Soc. Jpn. \textbf{79},
083704 (2010)]. This further supports the validity of our two-orbital model in
dealing with LDOS in the single-impurity problem. Finally, we investigate the
evolution of the LDOS with doping near a single impurity in the unitary or
strong scattering limit, such as Zn replacing Fe. The positions of the ingap
resonance peaks exhibited in our LDOS may indirectly reflect the evolution of
the Fermi surface topology according to the phase diagram. Our prediction of
ingap states and the evolution of the LDOS near a strong scattering single
impurity can be validated by experiments probing the local quasiparticle
spectrum.",1406.0027v1
2014-06-02,Superconductivity in titanium-based pnictide oxide compounds,"Superconductivity in a novel class of layered materials, Ti-based pnictide
oxides, was recently discovered. These compounds have attracted interest since
they combine features of copper oxide and iron pnictide superconductors. Here
the transition metal (titanium) forms two-dimensional Ti$_2$O layers (anti
structure to the CuO$_2$ planes), capped by pnictogen ions (similar to
Fe$_2$As$_2$ layers). The pnictide oxide compounds show a spin or charge
density wave phase which coexists with superconductivity in some members of the
family. Unlike the cuprates, but similar to iron pnictides, the parent
compounds of pnictide oxides are metals with specific nesting properties of the
Fermi surface which leads to the density wave instability. The nature of the
superconductivity, coexisting with the density wave order, and the possible
competition or mutual interaction between both states is one of the central
questions of recent studies. This short review summarizes the current knowledge
from an experimental as well as theoretical point of view and discusses some of
the open questions and possible future developments.",1406.0442v1
2014-06-02,The Distribution of Alpha Elements in Andromeda Dwarf Galaxies,"We present alpha to iron abundance ratios for 226 individual red giant branch
stars in nine dwarf galaxies of the Andromeda (M 31) satellite system. The
abundances are measured from the combined signal of Mg, Si, Ca, and Ti lines in
Keck/DEIMOS medium-resolution spectra. This constitutes the first large sample
of alpha abundance ratios measured in the M 31 satellite system. The dwarf
galaxies in our sample exhibit a variety of alpha abundance ratios, with the
average values in each galaxy ranging from approximately solar ([alpha/Fe] ~
+0.0) to alpha-enhanced ([alpha/Fe] ~ +0.5). These variations do not show a
correlation with internal kinematics, environment, or stellar density. We
confirm radial gradients in the iron abundance of two galaxies out of the five
with sufficient data (NGC 185 and And II). There is only tentative evidence for
an alpha abundance radial gradient in NGC 185. We homogeneously compare our
results to the Milky Way classical dwarf spheroidals, finding evidence for
wider variation in average alpha abundance. In the absence of chemical
abundances for the M 31 stellar halo, we compare to the Milky Way stellar halo.
A stellar halo comprised of disrupted M31 satellites is too metal-rich and
inconsistent with the Milky Way halo alpha abundance distribution even if
considering only satellites with predominantly old stellar populations. The M
31 satellite population provides a second system in which to study chemical
abundances of dwarf galaxies and reveals a wider variety of abundance patterns
than the Milky Way.",1406.0510v1
2014-07-11,Band-edge BCS-BEC crossover in a two-band superconductor: physical properties and detection parameters,"Superconductivity in iron-based, magnesium diborides, and other novel
superconducting materials has a strong multi-band and multi-gap character.
Recent experiments support the possibillity for a BCS-BEC crossover induced by
strong-coupling and proximity of the chemical potential to the band edge of one
of the bands. Here we study the simplest theoretical model which accounts for
the BCS-BEC crossover in a two-band superconductor, considering tunable
interactions and tunable energy separations between the bands. Mean-field
results for condensate fraction, correlation length, and superconducting gap
are reported in typical crossover diagrams to locate the boundaries of the BCS,
crossover, and BEC regimes. When the superconducting gap is of the order of the
local chemical potential, superconductivity is in the crossover regime of the
BCS-BEC crossover and the Fermi surface of the small band is smeared by the gap
opening. In this situation, small and large Cooper pairs coexist in the total
condensate, which is the optimal condition for high-Tc superconductivity. The
ratio between the gap and the Fermi energy in a given band results to be the
best detection parameter for experiments to locate the system in the BCS-BEC
crossover. Using available experimental data, our analysis shows that
iron-based superconductors have the partial condensate of the small Fermi
surface in the crossover regime of the BCS-BEC crossover, supporting the recent
ARPES findings.",1407.3109v1
2014-07-25,Spectroscopic parameters for solar-type stars with moderate/high rotation. New parameters for 10 planet-hosts,"Planetary studies demand precise and accurate stellar parameters as input to
infer the planetary properties. Different methods often provide different
results that could lead to biases in the planetary parameters. In this work, we
present a refinement of the spectral synthesis technique designed to treat
better more rapidly rotating FGK stars. This method is used to derive precise
stellar parameters, namely effective temperature, surface gravity,
metallicitity and rotational velocity. This procedure is tested for samples of
low and moderate/fast rotating FGK stars. The spectroscopic analysis is based
on the spectral synthesis package Spectroscopy Made Easy (SME), assuming Kurucz
model atmospheres in LTE. The line list where the synthesis is conducted, is
comprised of iron lines and the atomic data are derived after solar
calibration. The comparison of our stellar parameters shows good agreement with
literature values, both for low and for higher rotating stars. In addition, our
results are on the same scale with the parameters derived from the iron
ionization and excitation method presented in our previous works. We present
new atmospheric parameters for 10 transiting planet-hosts as an update to the
SWEET-Cat catalogue. We also re-analyse their transit light curves to derive
new updated planetary properties.",1407.6765v1
2014-08-14,Iron based superconductors: A brief overview,"Fe-based superconductors were discovered in 2008. This discovery with T$_c$
values up to 56 K, generated a new belief in the field of superconductivity.
Till its discovery, high temperature superconductivity in cuprates, created a
prejudice that Cu-oxides are essential building blocks for a high temperature
superconducting material. These Fe based superconductors do not contain Cu-O
planes (some of the materials are even O free). It will be argued in this
review, that these iron pnictide and chalcogenide (FePn/Ch) superconductors
have Fe electrons at the Fermi surface together with an unusual Fermiology that
can change rapidly with doping. This may lead to very different normal and
superconducting state properties compared to those in standard electron-phonon
coupled {\it conventional} superconductors. There are a large number of
evidences showing that superconductivity, magnetism, orbital fluctuations are
intimately related and coexist in these materials although the mechanism of
superconductivity in these compounds is still unknown. The electronic specific
heat, $\frac{2\Delta}{k_B T_c}$ ratio, phase diagrams, isotope effect, crystal
structures and there correlation to T$_c$ from various available experimental
data are main inputs of this review to show the above.",1408.3244v1
2014-08-21,The changing X-ray time lag in MCG-6-30-15,"MCG-6-30-15 is one of the most observed Narrow Line Seyfert 1 galaxies in the
X-ray band. In this paper we examine the X-ray time lags in this source using a
total of 600 ks in observations (440 ks exposure) taken with the XMM-Newton
telescope (300 ks in 2001 and 300 ks in 2013). Both the old and new
observations show the usual hard lag that increases with energy, however, the
hard lag turns over to a soft lag at frequencies below ~1e-4 Hz. The highest
frequencies (~1e-3 Hz) in this source show a clear soft lag, as previously
presented for the first 300 ks observation, but no clear iron K lag is detected
in either the old or new observation. The soft lag is more significant in the
old observation than the new. The observations are consistent with a
reverberation interpretation, where the soft, reflected emission is delayed
with respect to the hard powerlaw component. These spectral timing results
suggest that two distinct variability mechanisms are important in this source:
intrinsic coronal variations (which lead to correlated variability in the
reprocessed emission), and geometrical changes in the corona. Variability due
to geometrical changes does not result in correlated variability in the
reflection, and therefore inhibits the clear detection of an iron K lag.",1408.5051v1
2014-09-01,Chemical Evolution on the Scale of Clusters of Galaxies: A Conundrum?,"The metal content of clusters of galaxies and its relation to their stellar
content is revisited making use of a cluster sample for which all four basic
parameters are homogeneously measured within consistent radii, namely
core-excised mass-weighted metallicity plus total, stellar and ICM masses. For
clusters of total mass $M_{500} >$ $\sim 10^{14}$ $M_{\odot}$ nice agreement is
found between their iron content and what expected from empirical supernova
yields. For the same clusters, there also appears to be at least as much iron
in the intracluster medium (ICM) as there is still locked into stars (i.e., the
ICM/stars metal share is about unity). However, for more massive clusters the
stellar mass fraction appears to drop substantially without being accompanied
by a drop in the ICM metallicity, thus generating a major tension with the
nucleosynthesis expectation and inflating the metal share to extremely high
values (up to $\sim 6$). Various possible solutions of this conundrum are
discussed, but are all considered either astrophysically implausible, or
lacking an independent observational support. For this reason we still
entertain the possibility that even some of the best cluster data may be
faulty, though we are not able to identify any obvious bias. Finally, based on
the stellar mass-metallicity relation for local galaxies we estimate the
contribution of galaxies to the ICM enrichment as a function of their mass,
concluding that even the most massive galaxies must have lost a major fraction
of the metals they have produced.",1409.0307v1
2014-09-05,Ceci n'est pas a globular cluster: the metallicity distribution of the stellar system Terzan 5,"We present new determinations of the iron abundance for 220 stars belonging
to the stellar system Terzan 5 in the Galactic bulge. The spectra have been
acquired with FLAMES at the Very Large Telescope of the European Southern
Observatory and DEIMOS at the Keck II Telescope. This is by far the largest
spectroscopic sample of stars ever observed in this stellar system. From this
dataset, a subsample of targets with spectra unaffected by TiO bands was
extracted and statistically decontaminated from field stars. Once combined with
34 additional stars previously published by our group, a total sample of 135
member stars covering the entire radial extent of the system has been used to
determine the metallicity distribution function of Terzan 5. The iron
distribution clearly shows three peaks: a super-solar component at
[Fe/H]$\simeq0.25$ dex, accounting for 29% of the sample, a dominant sub-solar
population at [Fe/H]$\simeq-0.30$ dex, corresponding to 62% of the total, and a
minor (6%) metal-poor component at [Fe/H]$\simeq-0.8$ dex. Such a broad,
multi-modal metallicity distribution demonstrates that Terzan 5 is not a
genuine globular cluster but the remnant of a much more complex stellar system.",1409.1682v1
2014-09-15,Do cluster properties affect the quenching rate?,"The quenching rate is known to depend on galaxy stellar mass and environment,
however, possible dependences on the hosting halo properties, such as mass,
richness, and dynamical status, are still debated. The determination of these
dependences is hampered by systematics, induced by noisy estimates of cluster
mass or by the lack of control on galaxy stellar mass, which may mask existing
trends or introduce fake trends. We studied a sample of local clusters (20 with
0.02<z<0.1 and log(M200/Msun)>14), selected independent of the galaxy
properties under study, having homogeneous optical photometry and X-ray
estimated properties. Using those top quality measurements of cluster mass,
hence of cluster scale, richness, iron abundance, and cooling time/presence of
a cool-core, we study the simultaneous dependence of quenching on these cluster
properties on galaxy stellar mass M and normalised cluster-centric distance
r/r200. We found that the quenching rate can be completely described by two
variables only, galaxy stellar mass and normalised cluster-centric distance,
and is independent of halo properties (mass, richness, iron abundance, presence
of a cool-core, and central cooling time). These halo properties change, in
most cases, by less than 3% the probability that a galaxy is quenched, once the
mass-size (M200-r200) scaling relation is accounted for through cluster-centric
distance normalisation.",1409.4416v1
2014-09-23,Structural and Magnetic Phase Diagram of CrAs and its Relationship with Pressure-induced Superconductivity,"Most unconventional superconductors, including cuprates and iron-based
superconductors, are derived from chemical doping or application of pressure on
their collinearly magnetic-ordered parent compounds[1-5]. The recently
discovered pressure-induced superconductor CrAs, as a rare example of a
non-collinear helimagnetic superconductor, has therefore generated great
interest in understanding microscopic magnetic properties and their interplay
with superconductivity [6-8]. Unlike cuprates and iron based superconductors
where the magnetic moment direction barely changes upon doping, here we show
that CrAs exhibits a spin reorientation from the ab plane to the ac plane,
along with an abrupt drop of the magnetic propagation vector at a critical
pressure (Pc~0.6 GPa). This magnetic phase transition coincides with the
emergence of bulk superconductivity, indicating a direct connection between
magnetism and superconductivity. With further increasing pressure, the magnetic
order completely disappears near the optimal Tc regime (P~0.94 GPa). Moreover,
the Cr magnetic moments between nearest neighbors tend to be aligned
antiparallel with increasing pressure toward the optimal superconductivity
regime. Our findings suggest that the non-collinear helimagnetic order is
strongly coupled to structural and electronic degrees of freedom, and that
antiferromagnetic correlations associated with the low magnetic vector phase
are crucial for superconductivity.",1409.6615v3
2014-09-29,Disk emission and absorption lines in LMXB. Note on the physical conditions of an absorbing material,"We show that the continuum X-ray spectrum of 4U 1630-472 with iron absorption
lines can be satisfactorily modeled by the spectrum from an accretion disk
atmosphere. We performed full radiative transfer calculations using our code
ATM21 to model the emission from an accretion disk surface that is seen at
different viewing angles. Computed models are then fitted to the
high-resolution X-ray spectra of 4U 1630-472 obtained by {\it Suzaku}
satellite. Absorption lines of highly ionized iron originating in a hot
accretion-disk atmospheres are important part of the observed line profile, and
can be an alternative or complementary explanation to the wind model usually
favored for this type of sources. Next, assuming that absorption lines
originate from the wind illuminated by X-ray central source in LMXBs, we can
put constrains on the wind location only if we know the volume density number
of the absorbing material. There are a few derivations of the distance to the
wind in X-ray binaries. We show here, that the density number and the wind
location agree with the density of an upper disk atmosphere at optical depth of
two-thirds, at the same distance from the black hole. This comparison is done
assuming optically thick, geometrically thin standard accretion disk model.
Nevertheless, it shows that the wind physical conditions are the same as in
thermalized disk gas, and we only have to figure out how the wind is blowing?",1409.8052v1
2014-11-03,Discovery of a ~2 hr high frequency X-ray QPO and iron K alpha reverberation in the active galaxy MS 2254.9-3712,"We report the discovery of a $\sim 1.5 \times 10^{-4}$ Hz ($\sim 2$ hr) X-ray
quasi-periodic oscillation (QPO) in the active galaxy MS 2254.9-3712, using a
$\sim 70$ ks XMM-Newton observation. The QPO is significantly detected ($\sim
3.3 \sigma$) in the $1.2 - 5.0$ keV band only, connecting its origin with the
primary X-ray power-law continuum. We detect a highly coherent soft lag between
the $0.3 - 0.7$ keV and $1.2 - 5.0$ keV energy bands at the QPO frequency and
at a frequency band in a 3:2 ratio, strongly suggesting the presence of a QPO
harmonic. An iron K$\alpha$ reverberation lag is found at the harmonic
frequency, indicating the reflecting material subtends some angle to the
primary continuum, which is modulated by the QPO mechanism. Frequency resolved
spectroscopy reveals the QPO and harmonic to have a hard energy dependence.
These properties of the QPO variability, together with the current black hole
mass estimate, $M_{\rm bh} \sim 4 \times 10^{6} M_{\rm sun}$, are consistent
with the QPO originating from the same process as the high frequency QPO
phenomenon observed in black hole X-ray binaries. Principle component analysis
reveals the spectral variability in MS 2254.9-3712 is similar to that of the
active galaxy RE J1034+396, a source which also displays an X-ray QPO. This
suggests a distinct spectral variability pattern for accreting black holes when
in a state where QPOs are present.",1411.0684v2
2014-11-06,Ising-nematic order in the bilinear-biquadratic model for the iron pnictides,"Motivated by the recent inelastic neutron scattering (INS) measurements in
the iron pnictides which show a strong anisotropy of spin excitations in
directions perpendicular and parallel to the ordering wave-vector even above
the magnetic transition temperature $T_N$, we study the frustrated Heisenberg
model with a biquadratic spin-spin exchange interaction. Using the Dyson-Maleev
(DM) representation, which proves appropriate for all temperature regimes, we
find that the spin-spin dynamical structure factors are in excellent agreement
with experiment, exhibiting breaking of the $C_4$ symmetry even into the
paramagnetic region $T_N<T<T_{\sigma}$ which we refer to as the Ising-nematic
phase. In addition to the Heisenberg spin interaction, we include the
biquadratic coupling $K (\mathbf{S}_i\cdot \mathbf{S}_j)^2$ and study its
effect on the dynamical temperature range $T_{\sigma}-T_N$ of the Ising-nematic
phase. We find that this range reduces dramatically when even small values of
the interlayer exchange $J_c$ and biquadratic coupling $K$ are included. To
supplement our analysis, we benchmark the results obtained using the DM method
against those from different non-linear spin-wave theories, including the
recently developed generalized spin-wave theory (GSWT), and find good
qualitative agreement among the different theoretical approaches as well as
experiment for both the spin-wave dispersions and the dynamical structure
factors.",1411.1462v2
2014-11-07,Phase-resolved spectroscopy of low frequency quasi-periodic oscillations in GRS 1915+105,"X-ray radiation from black hole binary (BHB) systems regularly displays
quasi-periodic oscillations (QPOs). In principle, a number of suggested
physical mechanisms can reproduce their power spectral properties, thus more
powerful diagnostics which preserve phase are required to discern between
different models. In this paper, we first find for two Rossi X-ray Timing
Explorer (RXTE) observations of the BHB GRS 1915+105 that the QPO has a well
defined average waveform. That is, the phase difference and amplitude ratios
between the first two harmonics vary tightly around a well defined mean. This
enables us to reconstruct QPO waveforms in each energy channel, in order to
constrain QPO phase-resolved spectra. We fit these phase resolved spectra
across 16 phases with a model including Comptonisation and reflection (Gaussian
and smeared edge components) to find strong spectral pivoting and a modulation
in the iron line equivalent width. The latter indicates the observed reflection
fraction is changing throughout the QPO cycle. This points to a geometric QPO
origin, although we note that the data presented here do not entirely rule out
an alternative interpretation of variable disc ionisation state. We also see
tentative hints of modulations in the iron line centroid and width which,
although not statistically significant, could result from a non-azimuthally
symmetric QPO mechanism.",1411.1967v1
2014-11-19,The Seyfert 2 galaxy NGC 2110: hard X-ray emission observed by NuSTAR and variability of the iron K$α$ line,"We present NuSTAR observations of the bright Seyfert 2 galaxy NGC 2110
obtained in 2012, when the source was at the highest flux level ever observed,
and in 2013, when the source was at a more typical flux level. We include
archival observations from other X-ray satellites, namely XMM-Newton, Suzaku,
BeppoSAX, Chandra and Swift. Simultaneous NuSTAR and Swift broad band spectra
(in the 3-80 keV range) indicate a cutoff energy $E_{\rm c}>210$ keV, with no
detectable contribution from Compton reflection. NGC 2110 is one of the very
few sources where no evidence for distant Compton thick scattering is found
and, by using temporal information collected over more than a decade, we
investigate variations of the iron K$\alpha$ line on time scales of years. The
Fe K$\alpha$ line is likely the sum of two components: one constant
(originating from distant Compton-thick material) and the other one variable
and linearly correlated with the source flux (possibly arising from
Compton-thin material much closer to the black hole).",1411.5151v1
2014-11-20,The Role of the Magnetorotational Instability in Massive Stars,"The magnetorotational instability (MRI) is key physics in accretion disks and
is widely considered to play some role in massive-star core collapse. Models of
rotating massive stars naturally develop very strong shear at composition
boundaries, a necessary condition for MRI instability, and the MRI is subject
to triply-diffusive destabilizing effects in radiative regions. We have used
the MESA stellar evolution code to compute magnetic effects due to the
Spruit-Taylor mechanism and the MRI, separately and together, in a sample of
massive star models. We find that the MRI can be active in the later stages of
massive star evolution, leading to mixing effects that are not captured in
models that neglect the MRI. The MRI and related magneto-rotational effects can
move models of given ZAMS mass across ""boundaries"" from degenerate CO cores to
degenerate O/Ne/Mg cores and from degenerate O/Ne/Mg cores to iron cores, thus
affecting the final evolution and the physics of core collapse. The MRI acting
alone can slow the rotation of the inner core in general agreement with the
observed ""initial"" rotation rates of pulsars. The MRI analysis suggests that
localized fields ~10^{12} G may exist at the boundary of the iron core. With
both the ST and MRI mechanisms active in the 20 solar mass model, we find that
the helium shell mixes entirely out into the envelope. Enhanced mixing could
yield a population of yellow or even blue supergiant supernova progenitors that
would not be standard SN IIP.",1411.5714v1
2014-12-05,A NuSTAR observation of the fast symbiotic nova V745 Sco in outburst,"The fast recurrent nova V745 Sco was observed in the 3-79 keV X-rays band
with NuSTAR 10 days after the optical discovery. The measured X-ray emission is
consistent with a collisionally ionized optically thin plasma at temperature of
about 2.7 keV. A prominent iron line observed at 6.7 keV does not require
enhanced iron in the ejecta. We attribute the X-ray flux to shocked
circumstellar material. No X-ray emission was observed at energies above 20
keV, and the flux in the 3-20 keV range was about 1.6 $\times$ 10$^{-11}$ erg
cm$^{-2}$ s$^{-1}$. The emission measure indicates an average electron density
of order of 10$^7$ cm$^{-3}$.
  The X-ray flux in the 0.3-10 keV band almost simultaneously measured with
Swift was about 40 times larger, mainly due to the luminous central supersoft
source emitting at energy below 1 keV. The fact that the NuSTAR spectrum cannot
be fitted with a power law, and the lack of hard X-ray emission, allow us to
rule out Comptonized gamma rays, and to place an upper limit of the order of
10$^{-11}$ erg cm$^{-2}$ s$^{-1}$ on the gamma-ray flux of the nova on the
tenth day of the outburst.",1412.2088v2
2014-12-09,The final fate of stars that ignite neon and oxygen off-center: electron capture or iron core-collapse supernova?,"In the ONeMg cores of $8.8-9.5~{\rm M}_\odot$ stars, neon and oxygen burning
is ignited off-center. Whether the neon-oxygen flame propagates to the center
is critical to determine whether these stars undergo Fe core collapse or
electron capture induced ONeMg core collapse. We present more details of stars
that ignite neon and oxygen burning off-center. The neon flame is established
in a similar manner to the carbon flame of super-AGB stars, albeit with a
narrower flame width. The criteria for establishing a flame are able to be met
if the strict Schwarzschild criterion for convective instability is adopted.
Mixing across the interface of the convective shell disrupts the conditions for
the propagation of the burning front and instead the shell burns as a series of
inward-moving flashes. While this may not directly affect whether the burning
will reach the center (as in super-AGB stars), the core is allowed to contract
between each shell flash. Reduction of the electron fraction in the shell
reduces the Chandrasekhar mass and the center reaches the threshold density for
the URCA process to activate and steer the remaining evolution of the core.
This highlights the importance of a more accurate treatment of mixing in the
stellar interior for yet another important question in stellar astrophysics -
determining the properties of stellar evolution and supernova progenitors at
the boundary between electron capture supernova and iron core-collapse
supernova.",1412.2878v2
2014-12-15,"Synthesis, Structural, and Transport Properties of Cr-doped BaTi_2As_2O","The interplay between unconventional superconductivity and the ordering of
charge/spin density wave is one of the most vital issues in both condensed
matter physics and material science. The Ti-based compound BaTi_2As_2O, which
can be seen as the parent phase of superconducting BaTi_2Sb_2O, has a layered
structure with a space group P4/mmm, similar to that of cuprate and iron-based
superconductors. This material exhibits a charge density wave (CDW) ordering
transition revealed by an anomaly at around 200 K in transport measurements.
Here, we report the synthesis and systematical study of the physical properties
in Cr-doped BaTi_{2-x}Cr_xAs_2O (x = 0 - 0.154), and demonstrate that the
transition temperature of the CDW ordering is suppressed gradually by the doped
Cr element. The magnetization measurements confirm the evolution of the CDW
ordering transition. These observed behaviors are similar to that observed in
iron-based superconductors, but no superconductivity emerges down to 2 K. In
addition, the first-principles calculations are also carried out for
well-understanding the nature of experimental observations.",1412.4469v1
2014-12-16,Characterization of 3 mm Glass Electrodes and Development of RPC Detectors for $INO-ICAL$ Experiment,"India-based Neutrino Observatory (INO) is a multi-institutional facility,
planned to be built up in South India. The INO facility will host a 51 kton
magnetized Iron CALorimeter (ICAL) detector to study atmospheric muon
neutrinos. Iron plates have been chosen as the target material whereas
Resistive Plate Chambers (RPCs) have been chosen as the active detector element
for the ICAL experiment. Due to the large number of RPCs needed ($\sim$ 28,000
of $2~m \times 2~m$ in size) for ICAL experiment and for the long lifetime of
the experiment, it is necessary to perform a detailed $R\&D$ such that each and
every parameter of the detector performance can be optimized to improve the
physics output. In this paper, we report on the detailed material and
electrical properties studies for various types of glass electrodes available
locally. We also report on the performance studies carried out on the RPCs made
with these electrodes as well as the effect of gas composition and
environmental temperature on the detector performance. We also lay emphasis on
the usage of materials for RPC electrodes and the suitable enviormental
conditions applicable for operating the RPC detector for optimal physics output
at INO-ICAL experiment.",1412.4998v1
2014-12-16,Thermally Induced Chemistry of Meteoritic Complex Organic Molecules: A New Heat-Diffusion Model for the Atmospheric Entry of Meteorites,"Research over the past four decades has shown a rich variety of complex
organic molecular content in some meteorites. This current study is an attempt
to gain a better insight into the thermal conditions experienced by these
molecules inside meteorites during atmospheric entry. In particular, we wish to
understand possible chemical processes that can occur during entry and that
might have had an effect on complex organic or prebiotic species that were
delivered in this way to the early Earth. A simulation was written in Fortran
to model heating by the shock generated during entry and the subsequent thermal
diffusion inside the body of a meteorite. Experimental data was used for the
thermal parameters of several types of meteorites, including iron-nickel and
several classes of chondrites. A Sutton-Graves model of stagnation-point
heating was used to calculate peak surface temperatures and an explicit
difference formula was used to generate thermal diffusion profiles for both
chondrites and iron-nickel type meteorites. Results from the simulation show
pyrolytic temperature penetration to a depth of ca. 0.5 to 1 cm.
Non-dissociative warming of meteorite interiors penetrates further to ca. 4 cm.
These results support the findings that extraterrestrial delivery is a viable
option for prebiotic molecular ""seeding"" of a planet.",1412.5134v3
2014-12-19,"Universal V-shaped temperature-pressure phase diagram in the iron-based superconductors KFe2As2, RbFe2As2, and CsFe2As2","We report a sudden reversal in the pressure dependence of Tc in the
iron-based superconductor RbFe2As2, at a critical pressure Pc = 11 kbar.
Combined with our prior results on KFe2As2 and CsFe2As2, we find a universal
V-shaped phase diagram for Tc vs P in these fully hole-doped 122 materials,
when measured relative to the critical point (Pc, Tc). From measurements of the
upper critical field Hc2(T) under pressure in KFe2As2 and RbFe2As2, we observe
the same two-fold jump in (1/Tc)(-dHc2/dT) across Pc, compelling evidence for a
sudden change in the structure of the superconducting gap. We argue that this
change is due to a transition from one pairing state to another, with different
symmetries on either side of Pc. We discuss a possible link between scattering
and pairing, and a scenario where a d-wave state favored by high-Q scattering
at low pressure changes to a state with s+- symmetry favored by low-Q
scattering at high pressure.",1412.6196v2
2014-12-19,Resonant inelastic x-ray scattering study of electronic excitations in insulating K$_{0.83}$Fe$_{1.53}$Se$_2$,"We report an Fe $K$-edge resonant inelastic X-ray scattering (RIXS) study of
K$_{0.83}$Fe$_{1.53}$Se$_2$. This material is an insulator, unlike many parent
compounds of iron-based superconductors. We found a sharp excitation around 1
eV, which is resonantly enhanced when the incident photon energy is tuned near
the pre-edge region of the absorption spectrum. The spectral weight and line
shape of this excitation exhibit clear momentum dependence. In addition, we
observe momentum-independent broad interband transitions at higher excitation
energy of 3-7 eV. Calculations based on a 70 band $dp$ orbital model, using a
moderate $U_{\rm eff}\approx 2.5$ eV, indicate that the $\sim$1 eV feature
originates from the correlated Fe 3$d$ electrons, with a dominant $d_{xz}$ and
$d_{yz}$ orbital character. We find that a moderate $U_{\rm eff}$ yields a
satisfying agreement with the experimental spectra, suggesting that the
electron correlations in the insulating and metallic iron based superconductors
are comparable.",1412.6429v2
2014-12-22,Inverse magneto-refraction as a mechanism for laser modification of spin-spin exchange parameters and subsequent terahertz emission from iron oxides,"Ultrafast non-thermal manipulation of magnetization by light relies on either
indirect coupling of the electric field component of the light with spins via
spin-orbit interaction or direct coupling between the magnetic field component
and spins. Here we propose a novel scenario for coupling between the electric
field of light and spins via optical modification of the exchange interaction,
one of the strongest quantum effects, the strength of which can reach 1000
Tesla. We demonstrate that this isotropic opto-magnetic effect, which can be
called the inverse magneto-refraction, is allowed in a material of any
symmetry. Its existence is corroborated by the experimental observation of THz
emission by magnetic-dipole active spin resonances optically excited in a broad
class of iron oxides with a canted spin configuration. From its strength we
estimate that a sub-picosecond laser pulse with a moderate fluence of ~ 1
mJ/cm^2 acts as a pulsed effective magnetic field of 0.01 Tesla, arising from
the optically perturbed balance between the exchange parameters. Our findings
are supported by a low-energy theory for the microscopic magnetic interactions
between non-equilibrium electrons subjected to an optical field which suggests
a possibility to modify the exchange interactions by light over 1 %.",1412.7094v1
2014-12-24,Tests of the nuclear equation of state and superfluid and superconducting gaps using the Cassiopeia A neutron star,"The observed rapid cooling of the Cassiopeia A neutron star can be
interpreted as being caused by neutron and proton transitions from normal to
superfluid and superconducting states in the stellar core. Here we present two
new Chandra ACIS-S Graded observations of this neutron star and measurements of
the neutron star mass M and radius R found from consistent fitting of both the
X-ray spectra and cooling behavior. This comparison is only possible for
individual nuclear equations of state. We test phenomenological superfluid and
superconducting gap models which mimic many of the known theoretical models
against the cooling behavior. Our best-fit solution to the Cassiopeia A data is
one in which the (M,R) = (1.44 Msun,12.6 km) neutron star is built with the
BSk21 equation of state, strong proton superconductor and moderate neutron
triplet superfluid gap models, and a pure iron envelope or a thin carbon layer
on top of an iron envelope, although there are still large observational and
theoretical uncertainties.",1412.7759v2
2015-01-07,Detoxification of superoxide without production of H2O2: antioxidant activity of superoxide reductase complexed with ferrocyanide,"The superoxide radical O(2)(-.) is a toxic by-product of oxygen metabolism.
Two O(2)(-.) detoxifying enzymes have been described so far, superoxide
dismutase and superoxide reductase (SOR), both forming H2O2 as a reaction
product. Recently, the SOR active site, a ferrous iron in a [Fe(2+) (N-His)(4)
(S-Cys)] pentacoordination, was shown to have the ability to form a complex
with the organometallic compound ferrocyanide. Here, we have investigated in
detail the reactivity of the SOR-ferrocyanide complex with O(2)(-.) by pulse
and gamma-ray radiolysis, infrared, and UV-visible spectroscopies. The complex
reacts very efficiently with O(2)(-.). However, the presence of the
ferrocyanide adduct markedly modifies the reaction mechanism of SOR, with the
formation of transient intermediates different from those observed for SOR
alone. A one-electron redox chemistry appears to be carried out by the
ferrocyanide moiety of the complex, whereas the SOR iron site remains in the
reduced state. Surprisingly, the toxic H2O2 species is no longer the reaction
product. Accordingly, in vivo experiments showed that formation of the
SOR-ferrocyanide complex increased the antioxidant capabilities of SOR
expressed in an Escherichia coli sodA sodB recA mutant strain. Altogether,
these data describe an unprecedented O(2)(-.) detoxification activity,
catalyzed by the SOR-ferrocyanide complex, which does not conduct to the
production of the toxic H2O2 species.",1501.01439v1
2015-01-12,X-ray Probes of Black Hole Accretion Disks for Testing the No-Hair Theorem,"The spins of a number of supermassive and stellar-mass black holes have been
measured based on detections of thermal continuum emission and relativistically
broadened iron lines in their x-ray spectra. Likewise, quasiperiodic
variability has been observed in several sources. Such measurements commonly
make the assumption that black holes are described by the Kerr metric, which
according to the no-hair theorem characterizes black holes uniquely in terms of
their masses and spins. This fundamental property of black holes can be tested
observationally by measuring potential deviations from the Kerr metric
introduced by a parametrically deformed Kerr-like spacetime. Thermal spectra,
iron lines, and variability have already been studied extensively in several
such metrics, which usually depend on only one particular type of deviation or
contain unphysical regions outside of the compact object. In this paper, I
study these x-ray probes in the background of a new Kerr-like metric which
depends on four independent deviation functions and is free of pathological
regions outside of the event horizon. I show that the observed signals depend
significantly on primarily two types of deviations and that the strong
correlation between the spin and the deviation parameters found previously in
other Kerr-like metrics is partially broken for rapidly spinning black holes.
This suggests that high-spin sources are the best candidates for tests of the
no-hair theorem with x-rays and I obtain first constraints on such deviations
from the stellar-mass black hole Cygnus X-1.",1501.02815v1
2015-01-22,Mathematical analysis of the $PO_4$-$DOP$-$Fe$ marine ecosystem model driven by 3-D ocean transport,"Marine ecosystem models are developed to understand and simulate the
biogeochemical processes involved in marine ecosystems. Parekh, Follows and
Boyle introduced the $PO_4$-$DOP$-$Fe$ model of the coupled phosphorus and iron
cycles in 2005. Especially the part describing the phosphorus cycle
($PO_4$-$DOP$ model) is often applied in the context of parameter
identification. The mathematical analysis presented in this study is concerned
with the existence of solutions and the reconstruction of parameters from given
data. Both are important questions in the numerical model's assessment and
validation not answered so far. In this study, we obtain transient, stationary
and periodic solutions (steady annual cycles) of the $PO_4$-$DOP$-$Fe$ model
equations after a slight change in the equation modeling iron. This result
confirms the validity of the solutions computed numerically. Furthermore, we
present a calculation showing that four of the $PO_4$-$DOP$ model's parameters
are possibly dependent, i.e. different parameter values might be associated
with the same model output. Thereby, we identify a relevant source of
uncertainty in parameter identification. On the basis of the results, possible
ways to overcome this deficit can be proposed. In addition, the stated
mathematical conditions for solvability are universal and thus applicable to
the analysis of other ecosystem models as well.",1501.05428v1
2015-01-26,Origin of the non-monotonic variance of Tc in the 1111 iron based superconductors with isovalent doping,"Motivated by recent experimental investigations of the isovalent doping
iron-based superconductors LaFe(AsxP1-x)O1-yFy and NdFe(AsxP1-x)O1-yFy we
theoretically study the correlation between the local lattice structure, the
Fermi surface, the spin fluctuation-mediated superconductivity, and the
composition ratio. In the phosphides, the dXZ and dYZ orbitals barely hybridize
around the Gamma point to give rise to two intersecting ellipse shape Fermi
surfaces. As the arsenic content increases and the Fe-As-Fe bond angle is
reduced, the hybridization increases, so that the two bands are mixed to result
in concentric inner and outer Fermi surfaces, and the orbital character
gradually changes to dxz and dyz, where x-y axes are rotated by 45 degrees from
X-Y. This makes the orbital matching between the electron and hole Fermi
surfaces better and enhances the spin fluctuation within the dxz/yz orbitals.
On the other hand, the hybridization splits the two bands, resulting in a more
dispersive inner band. Hence, there is a trade-off between the density of
states and the orbital matching, thereby locally maximizing the dxz/yz spin
fluctuation and superconductivity in the intermediate regime of As/P ratio. The
consistency with the experiment strongly indicate the importance of the spin
fluctuation played in this series of superconductors.",1501.06303v1
2015-03-03,Tunable room-temperature ferromagnet using an iron-oxide and graphene oxide nanocomposite,"Magnetic materials have found wide application ranging from electronics and
memories to medicine. Essential to these advances is the control of the
magnetic order. To date, most room-temperature applications have a fixed
magnetic moment whose orientation is manipulated for functionality. Here we
demonstrate an iron-oxide and graphene oxide nanocomposite based device that
acts as a tunable ferromagnet at room temperature. Not only can we tune its
transition temperature in a wide range of temperatures around room temperature,
but the magnetization can also be tuned from zero to 0.011 A.m$^2$/kg through
an initialization process with two readily accessible knobs (magnetic field and
electric current), after which the system retains its magnetic properties
semi-permanently until the next initialization process. We construct a
theoretical model to illustrate that this tunability originates from an
indirect exchange interaction mediated by spin-imbalanced electrons inside the
nanocomposite.",1503.00960v1
2015-03-03,Dark Matter Balls Help Supernovae to Explode,"As a solution to the well-known problem that the shock wave potentially
responsible for the explosion of a supernova actually tends to stall, we
propose a new energy source arising from our model for dark matter. Our earlier
model proposed that dark matter should consist of cm-large white dwarf-like
objects kept together by a skin separating two different sorts of vacua. These
dark matter balls or pearls will collect in the middle of any star throughout
its lifetime. At some stage during the development of a supernova the balls
will begin to take in neutrons and then other surrounding material. By passing
into a ball nucleons fall through a potential of order 10 MeV, causing a severe
production of heat - of order 10 foe for a solar mass of material eaten by the
balls. The temperature in the iron core will thereby be raised, splitting up
the iron into smaller nuclei. This provides a mechanism for reviving the shock
wave when it arrives and making the supernova explosion really occur. The onset
of the heating due to the dark matter balls would at first stop the collapse of
the supernova progenitor. This opens up the possibility of there being {\em
two} collapses giving two neutrino outbursts, as apparently seen in the
supernova SN1987A - one in Mont Blanc, and one 4 hours 43 minutes later in both
IMB and Kamiokande.",1503.01089v2
2015-03-05,Distinctive momentum dependence of the band reconstruction in the nematic state of FeSe thin film,"Nematic state, where the system is translationally invariant but breaks the
rotational symmetry, has drawn great attentions recently due to experimental
observations of such a state in both cuprates and iron-based superconductors.
The mechanism of nematicity that is likely tied to the pairing mechanism of
high-Tc, however, still remains controversial. Here, we studied the electronic
structure of multilayer FeSe film by angle-resolved photoemission spectroscopy
(ARPES). We found that the FeSe film enters the nematic state around 125 K,
while the electronic signature of long range magnetic order has not been
observed down to 20K indicating the non-magnetic origin of the nematicity. The
band reconstruction in the nematic state is characterized by the splitting of
the dxz and dyz bands. More intriguingly, such energy splitting is strong
momentum dependent with the largest band splitting of ~80meV at the zone
corner. The simple on-site ferro-orbital ordering is insufficient to reproduce
the nontrivial momentum dependence of the band reconstruction. Instead, our
results suggest that the nearest-neighbor hopping of dxz and dyz is highly
anisotropic in the nematic state, the origin of which holds the key in
understanding the nematicity in iron-based superconductors.",1503.01556v1
2015-03-09,Determination of the spectroscopic stellar parameters for 257 field giant stars,"The study of stellar parameters of planet-hosting stars, such as metallicity
and chemical abundances, help us to understand the theory of planet formation
and stellar evolution. Here, we present a catalogue of accurate stellar
atmospheric parameters and iron abundances for a sample of 257 K and G field
evolved stars that are being surveyed for planets using precise
radial--velocity measurements as part of the CORALIE programme to search for
planets around giants. The analysis was done using a set of high--resolution
and high--signal-to-noise Ultraviolet and Visible Echelle Spectrograph spectra.
The stellar parameters were derived using Fe I and II ionization and excitation
equilibrium methods. To take into account possible effects related to the
choice of the lines on the derived parameters, we used three different iron
line-list sets in our analysis, and the results differ among themselves by a
small factor for most of stars. {For those stars with previous literature
parameter estimates, we found very good agreement with our own values.} In the
present catalogue we are providing new precise spectroscopic measurements of
effective temperature, surface gravity, microturbulence, and metallicity for
190 stars for which it has not been found or published in previous articles.",1503.02556v1
2015-03-10,Detailed Abundances of 15 Stars in the Metal-Poor Globular Cluster NGC 4833,"We have observed 15 red giant stars in the relatively massive, metal-poor
globular cluster NGC 4833 using the Magellan Inamori Kyocera Echelle
spectrograph at Magellan. We calculate stellar parameters for each star and
perform a standard abundance analysis to derive abundances of 43 species of 39
elements, including 20 elements heavier than the iron group. We derive <[Fe/H]>
= -2.25 +/- 0.02 from Fe I lines and <[Fe/H> = -2.19 +/- 0.013 from Fe II
lines. We confirm earlier results that found no internal metallicity spread in
NGC 4833, and there are no significant star-to-star abundance dispersions among
any elements in the iron group (19 <= Z <= 30). We recover the usual abundance
variations among the light elements C, N, O, Na, Mg, Al, and possibly Si. The
heavy-element distribution reflects enrichment by r-process nucleosynthesis
([Eu/Fe] = +0.36 +/- 0.03), as found in many other metal-poor globular
clusters. We investigate small star-to-star variations found among the
neutron-capture elements, and we conclude that these are probably not real
variations. Upper limits on the Th abundance, log epsilon (Th/Eu) < -0.47 +/-
0.09, indicate that NGC 4833, like other globular clusters where Th has been
studied, did not experience a so-called ""actinide boost.""",1503.03079v2
2015-03-11,Molecular Beam Epitaxy Growth of Superconducting LiFeAs Film on SrTiO3(001) Substrate,"The stoichiometric ""111"" iron-based superconductor, LiFeAs, has attacted
great research interest in recent years. For the first time, we have
successfully grown LiFeAs thin film by molecular beam epitaxy (MBE) on
SrTiO3(001) substrate, and studied the interfacial growth behavior by
reflection high energy electron diffraction (RHEED) and low-temperature
scanning tunneling microscope (LT-STM). The effects of substrate temperature
and Li/Fe flux ratio were investigated. Uniform LiFeAs film as thin as 3
quintuple-layer (QL) is formed. Superconducting gap appears in LiFeAs films
thicker than 4 QL at 4.7 K. When the film is thicker than 13 QL, the
superconducting gap determined by the distance between coherence peaks is about
7 meV, close to the value of bulk material. The ex situ transport measurement
of thick LiFeAs film shows a sharp superconducting transition around 16 K. The
upper critical field, Hc2(0)=13.0 T, is estimated from the temperature
dependent magnetoresistance. The precise thickness and quality control of
LiFeAs film paves the road of growing similar ultrathin iron arsenide films.",1503.03216v1
2015-03-11,Simulations Study of Muon Response in the Peripheral Regions of the Iron Calorimeter Detector at the India-based Neutrino Observatory,"The magnetized Iron CALorimeter detector (ICAL) which is proposed to be built
in the India-based Neutrino Observatory (INO) laboratory, aims to study
atmospheric neutrino oscillations primarily through charged current
interactions of muon neutrinos and anti-neutrinos with the detector. The
response of muons and charge identification efficiency, angle and energy
resolution as a function of muon momentum and direction are studied from
GEANT4-based simulations in the peripheral regions of the detector. This
completes the characterisation of ICAL with respect to muons over the entire
detector and has implications for the sensitivity of ICAL to the oscillation
parameters and mass hierarchy compared to the studies where only the
resolutions and efficiencies of the central region of ICAL were assumed for the
entire detector.
  Selection criteria for track reconstruction in the peripheral region of the
detector were determined from the detector response. On applying these, for the
1--20 GeV energy region of interest for mass hierarchy studies, an average
angle-dependent momentum resolution of 15--24%, reconstruction efficiency of
about 60--70% and a correct charge identification of about 97% of the
reconstructed muons were obtained. In addition, muon response at higher
energies upto 50 GeV was studied as relevant for understanding the response to
so-called rock muons and cosmic ray muons. An angular resolution of better than
a degree for muon energies greater than 4 GeV was obtained in the peripheral
regions, which is the same as that in the central region.",1503.03369v1
2015-03-16,Spectral properties of the soft excess pulsar RX J0059.2-7138 during its 2013 outburst,"We report on an X-ray observation of the Be X-ray Binary Pulsar RX
J0059.2-7138, performed by XMM-Newton in March 2014. The 19 ks long observation
was carried out about three months after the discovery of the latest outburst
from this Small Magellanic Cloud transient, when the source luminosity was Lx ~
10$^{38}$ erg/s. A spin period of P=2.762383(5) s was derived, corresponding to
an average spin-up of $\dot{P}_{\mathrm{spin}} = -(1.27\pm0.01)\times10^{-12}$
s $s^{-1}$ from the only previous period measurement, obtained more than 20
years earlier. The time-averaged continuum spectrum (0.2-12 keV) consisted of a
hard power-law (photon index ~0.44) with an exponential cut-off at a
phase-dependent energy (20-50 keV) plus a significant soft excess below about
0.5 keV. In addition, several features were observed in the spectrum: an
emission line at 6.6 keV from highly ionized iron, a broad feature at 0.9-1 keV
likely due to a blend of Fe L-shell lines, and narrow emission and absorption
lines consistent with transitions in highly ionized oxygen, nitrogen and iron
visible in the high resolution RGS data (0.4-2.1 keV). Given the different
ionization stages of the narrow line components, indicative of photoionization
from the luminous X-ray pulsar, we argue that the soft excess in RX
J0059.2-7138 is produced by reprocessing of the pulsar emission in the inner
regions of the accretion disc.",1503.04574v1
2015-03-20,Relative Abundance Measurements in Plumes and Interplumes,"We present measurements of relative elemental abundances in plumes and
interplumes. Plumes are bright, narrow structures in coronal holes that extend
along open magnetic field lines far out into the corona. Previous work has
found that in some coronal structures the abundances of elements with a low
first ionization potential (FIP) < 10 eV are enhanced relative to their
photospheric abundances. This coronal-to-photospheric abundance ratio, commonly
called the FIP bias, is typically 1 for element with a high-FIP (> 10 eV). We
have used EIS spectroscopic observations made on 2007 March 13 and 14 over an
~24 hour period to characterize abundance variations in plumes and interplumes.
To assess their elemental composition, we have used a differential emission
measure (DEM) analysis, which accounts for the thermal structure of the
observed plasma. We have used lines from ions of iron, silicon, and sulfur.
From these we have estimated the ratio of the iron and silicon FIP bias
relative to that for sulfur. From the results, we have created FIP-bias-ratio
maps. We find that the FIP-bias ratio is sometimes higher in plumes than in
interplumes and that this enhancement can be time dependent. These results may
help to identify whether plumes or interplumes contribute to the fast solar
wind observed in situ and may also provides constraints on the formation and
heating mechanisms of plumes.",1503.06044v1
2015-04-01,The Case for a Hot Archean Climate and its Implications to the History of the Biosphere,"The case for a much warmer climate on the early Earth than now is presented.
The oxygen isotope record in sedimentary chert and the compelling case for a
near constant isotopic oxygen composition of seawater over geologic time
support thermophilic surface temperatures prevailing in the Archean, with some
support for hot conditions lasting until about 1.5 billion years ago, aside
from lower temperatures including glacial episodes at 2.1-2.4 Ga and possibly
an earlier one at 2.9 Ga. Other evidence includes the following: 1) Melting
temperatures of proteins resurrected from sequences inferred from robust
molecular phylogenies give paleotemperatures at emergence consistent with a
very warm early climate. 2) High atmospheric pCO2 levels in the Archean are
consistent with high climatic temperatures near the triple point of primary
iron minerals in banded iron formations, the formation of Mn-bicarbonate
clusters leading to oxygenic photosynthesis and generally higher weathering
intensities on land. These higher weathering intensities would not have
occurred if seafloor weathering dominated the carbon sink, pulling down the
temperature, hence this empirical evidence supports a hot climate and high
carbon dioxide levels. 3) The inferred viscosity of seawater at 2.7 Ga is
consistent with a hot Archean climate. 5) A cold Archean is hard to explain
taking into account the higher outgassing rates of carbon dioxide,
significantly smaller land areas and weaker biotic enhancement of weathering
than present in the context of the long-term carbon cycle, taking into account
the fainter Archean sun in climate modeling. This evidence points to an
important conclusion regarding biological evolution, namely to the critical
role of a temperature constraint holding back the emergence of major organismal
groups, starting with phototrophs, culminating with metazoans in the latest
Precambrian.",1504.00401v1
2015-05-05,Direct evidence for the emergence of a pressure induced nodal superconducting gap in the iron-based superconductor Ba_0.65Rb_0.35Fe_2As_2,"Identifying the superconducting (SC) gap structure of the iron-based
high-temperature superconductors (Fe-HTS's) remains a key issue for the
understanding of superconductivity in these materials. In contrast to other
unconventional superconductors, in the Fe-HTS's both $d$-wave and extended
s-wave pairing symmetries are close in energy, with the latter believed to be
generally favored over the former. Probing the proximity between these very
different SC states and identifying experimental parameters that can tune them,
are of central interest. Here we report high-pressure muon spin rotation
experiments on the temperature-dependent magnetic penetration depth (lambda) in
the optimally doped Fe-HTS Ba_0.65Rb_0.35Fe_2As_2. At ambient pressure this
material is known to be a nodeless s-wave superconductor. Upon pressure a
strong decrease of (lambda) is observed, while the SC transition temperature
remains nearly constant. More importantly, the low-temperature behavior of
(1/lambda^{2}) changes from exponential saturation at zero pressure to a
power-law with increasing pressure, providing unambiguous evidence that
hydrostatic pressure promotes nodal SC gaps. Comparison to microscopic models
favors a d-wave over a nodal s^{+-}-wave pairing as the origin of the nodes.
Our results provide a new route of understanding the complex topology of the SC
gap in Fe-HTS's.",1505.01223v1
2015-05-08,Magnetic spin moment reduction in photoexcited ferromagnets through exchange interaction quenching: Beyond the rigid band approximation,"The exchange interaction among electrons is one of the most fundamental
quantum mechanical interactions in nature and underlies any magnetic phenomena
from ferromagnetic ordering to magnetic storage. The current technology is
built upon a thermal or magnetic field, but a frontier is emerging to directly
control magnetism using ultrashort laser pulses. However, little is known about
the fate of the exchange interaction. Here we report unambiguously that
photoexcitation is capable of quenching the exchange interaction in all three
$3d$ ferromagnetic metals. The entire process starts with a small number of
photoexcited electrons which build up a new and self-destructive potential that
collapses the system into a new state with a reduced exchange splitting. The
spin moment reduction follows a Bloch-like law as $M_z(\Delta
E)=M_z(0)(1-{\Delta E}/{\Delta E_0})^{\frac{1}{\beta}}$, where $\Delta E$ is
the absorbed photon energy and $\beta$ is a scaling exponent. A good agreement
is found between the experimental and our theoretical results. Our findings may
have a broader implication for dynamic electron correlation effects in
laser-excited iron-based superconductors, iron borate, rare-earth
orthoferrites, hematites and rare-earth transition metal alloys.",1505.01904v1
2015-05-23,"Common Electronic Origin of Superconductivity in (Li,Fe)OHFeSe Bulk Superconductor and Single-Layer FeSe/SrTiO3 Films","The mechanism of high temperature superconductivity in the iron-based
superconductors remains an outstanding issue in condensed matter physics. The
electronic structure, in particular the Fermi surface topology, is considered
to play an essential role in dictating the superconductivity. Recent revelation
of distinct electronic structure and possible high temperature
superconductivity with a transition temperature Tc above 65 K in the
single-layer FeSe films grown on the SrTiO3 substrate provides key information
on the roles of Fermi surface topology and interface in inducing or enhancing
superconductivity. Here we report high resolution angle-resolved photoemission
measurement on the electronic structure and superconducting gap of a novel
FeSe-based superconductor, (Li0.84Fe0.16)OHFe0.98Se, with a Tc at 41 K. We find
that this single-phase bulk superconductor shows remarkably similar electronic
behaviors to that of the superconducting single-layer FeSe/SrTiO3 film in terms
of Fermi surface topology, band structure and nearly isotropic superconducting
gap without nodes. These observations provide significant insights in
understanding high temperature superconductivity in the single-layer
FeSe/SrTiO3 film in particular, and the mechanism of superconductivity in the
iron-based superconductors in general.",1505.06361v1
2015-05-29,Impact of oxygen doping and oxidation state of iron on the electronic and magnetic properties of BaFeO$_{3-δ},"We studied structural, electronic and magnetic properties of a cubic
perovskite BaFeO$_{3-\delta}$ ($0 \le \delta \le 0.5$) within the density
functional theory using a generalized gradient approximation and a GGA+U
method. According to our calculations, BaFeO$_3$ in its stoichiometric cubic
structure should be half-metallic and strongly ferromagnetic, with extremely
high Curie temperature ($T_C$) of 700 - 900 K. However, a such estimate of
$T_C$ disagrees with all available experiments, which report that $T_C$ of the
BaFeO$_3$ and undoped BaFeO$_{3-\delta}$ films varies between 111 K and 235 K
or, alternatively, that no ferromagnetic order was detected there. Fitting the
calculated x-ray magnetic circular dichroism spectra to the experimental
features seen for BaFeO$_3$, we concluded that the presence of oxygen vacancies
in our model enables a good agreement. Thus, the relatively low $T_C$ measured
in BaFeO$_3$ can be explained by oxygen vacancies intrinsically presented in
the material. Since iron species near the O vacancy change their oxidation
state from $4+$ to $3+$, the interaction between Fe$^{4+}$ and Fe$^{3+}$, which
is antiferromagnetic, weakens the effective magnetic interaction in the system,
which is predominantly ferromagnetic. With increasing $\delta$ in
BaFeO$_{3-\delta}$, its $T_C$ decreases down to the critical value when the
magnetic order becomes antiferromagnetic. Our calculations of the electronic
structure of BaFeO$_{3-\delta}$ illustrate how the ferromagnetism originates
and also how one can keep this cubic perovskite robustly ferromagnetic far
above the room temperature.",1505.07942v1
2015-06-04,Weak and strong electronic correlations in Fe superconductors,"In this chapter the strength of electronic correlations in the normal phase
of Fe-superconductors is discussed. It will be shown that the agreement between
a wealth of experiments and DFT+DMFT or similar approaches supports a scenario
in which strongly-correlated and weakly-correlated electrons coexist in the
conduction bands of these materials. I will then reverse-engineer the realistic
calculations and justify this scenario in terms of simpler behaviors easily
interpreted through model results. All pieces come together to show that Hund's
coupling, besides being responsible for the electronic correlations even in
absence of a strong Coulomb repulsion is also the origin of a subtle emergent
behavior: orbital decoupling. Indeed Hund's exchange decouples the charge
excitations in the different Iron orbitals involved in the conduction bands
thus causing an independent tuning of the degree of electronic correlation in
each one of them. The latter becomes sensitive almost only to the offset of the
orbital population from half-filling, where a Mott insulating state is
invariably realized at these interaction strengths. Depending on the difference
in orbital population a different 'Mottness' affects each orbital, and thus
reflects in the conduction bands and in the Fermi surfaces depending on the
orbital content.",1506.01678v1
2015-06-15,Simultaneous spectral and reverberation modelling of relativistic reflection in Mrk 335,"We present an X-ray spectral and timing model to investigate the broad and
variable iron line seen in the high flux state of Mrk 335. The model consists
of a variable X-ray source positioned along the rotation axis of the black hole
that illuminates the accretion disc producing a back-scattered, ionized
reflection spectrum. We compute time lags including full dilution effects and
perform simultaneous fitting of the 2-10 keV spectrum and the
frequency-dependent time lags of 2.5-4 vs. 4-6.5 keV bands. The best-fitting
parameters are consistent with a black hole mass of approximately 1.3 x 10^7
M_sun, disc inclination of 45 degrees and the photon index of the direct
continuum of 2.4. The iron abundance is 0.5 and the ionization parameter is
10^3 erg cm / s at the innermost part of the disc and decreases further out.
The X-ray source height is very small, approximately 2 r_g. Furthermore, we fit
the Fe L lags simultaneously with the 0.3-10 keV spectrum. The key parameters
are comparable to those previously obtained. We also report the differences
below 2 keV using the xillver and reflionx models which could affect the
interpretation of the soft excess. While simultaneously fitting spectroscopic
and timing data can break the degeneracy between the source height and the
black hole mass, we find that the measurements of the source height and the
central mass significantly depend on the ionization state of the disc and are
possibly model-dependent.",1506.04524v1
2015-07-07,The NuSTAR X-ray spectrum of the low-luminosity AGN in NGC 7213,"We present an analysis of the 3-79 keV NuSTAR spectrum of the low-luminosity
active galactic nucleus NGC 7213. In agreement with past observations, we find
a lower limit to the high-energy cut-off of Ec > 140 keV, no evidence for a
Compton-reflected continuum, and the presence of an iron Kalpha complex,
possibly produced in the broad-line region. From the application of the MYTorus
model, we find that the line-emitting material is consistent with the absence
of a significant Compton reflection if arising from a Compton-thin torus of gas
with a column density of 5.0(+2.0,-1.6) cm^-2. We report variability of the
equivalent width of the iron lines on the time-scale of years using archival
observations from XMM-Newton, Chandra and Suzaku. This analysis suggests a
possible contribution from dusty gas. A fit with a Comptonization model
indicates the presence of a hot corona with a temperature kTe > 40 keV and an
optical depth tau < 1, assuming a spherical geometry.",1507.01775v1
2015-07-09,The phase diagrams of iron-based superconductors: theory and experiments,"Phase diagrams play a primary role in the understanding of materials
properties. For iron-based superconductors (Fe-SC), the correct definition of
their phase diagrams is crucial because of the close interplay between their
crystallo-chemical and magnetic properties, on one side, and the possible
coexistence of magnetism and superconductivity, on the other. The two most
difficult issues for understanding the Fe-SC phase diagrams are: 1) the origin
of the structural transformation taking place during cooling and its
relationship with magnetism; 2) the correct description of the region where a
crossover between the magnetic and superconducting electronic ground states
takes place. Hence a proper and accurate definition of the structural, magnetic
and electronic phase boundaries provides an extremely powerful tool for
material scientists. For this reason, an exact definition of the thermodynamic
phase fields characterizing the different structural and physical properties
involved is needed, although it is not easy to obtain in many cases. Moreover,
physical properties can often be strongly dependent on the occurrence of
micro-structural and other local-scale features (lattice micro-strain, chemical
fluctuations, domain walls, grain boundaries, defects), which, as a rule, are
not described in a structural phase diagram. In this review, we critically
summarize the results for the most studied 11-, 122- and 1111-type compound
systems, providing a correlation between experimental evidence and theory.",1507.02406v1
2015-07-09,Stability of Two-Dimensional Iron-Carbides Suspended across Graphene Pores: First-principles Particle Swarm Optimization,"Inspired by recent experimental realizations of two-dimensional (2D) metals
and alloys, we theoretically investigate the stability and electronic
properties of monolayer (ML) Fe-C compounds and pure Fe. According to our and
others theoretical results, the experiment [Science 343, 1228 (2014)] proposed
ML pure Fe square-lattices embedded in graphene (Gr) pores are energetically
unstable compared to that of the Fe triangular-lattices in Gr. To solve the
above contradiction, we search for the stable structures of ML Fe-C with
various Fe to C ratios (as a generalization of ML Fe in Gr) using ab initio
particle swarm optimization technique. A Fe1C1 square-lattice embedded in Gr is
found. We propose and demonstrate that the square-lattices observed in the
experiment were iron-carbides (Fe-C) but not pure Fe from the square-lattice
shape, Fe-Fe lattice constant and energetic considerations. Note that the
coexistence of C with Fe cannot be excluded from the experiment. More
importantly, we find a lowest energy and dynamically stable structure, ML Fe2C2
with Fe atoms form distorted square lattices. High spin polarization around the
Fermi level is predicted for different 2D Fe-C structures due to significant
orbital hybridization between C and Fe.",1507.02418v2
2015-07-09,Chemical Abundances in the PN Wray16-423 in the Sagittarius Dwarf Spheroidal Galaxy: Constraining the Dust Composition,"We performed a detailed analysis of elemental abundances, dust features, and
polycyclic aromatic hydrocarbons (PAHs) in the C-rich planetary nebula (PN)
Wray16-423 in the Sagittarius dwarf spheroidal galaxy, based on a unique
dataset taken from the Subaru/HDS, MPG/ESO FEROS, HST/WFPC2, and Spitzer/IRS.
We performed the first measurements of Kr, Fe, and recombination O abundance in
this PN. The extremely small [Fe/H] implies that most Fe atoms are in the solid
phase, considering into account the abundance of [Ar/H]. The Spitzer/IRS
spectrum displays broad 16-24 um and 30 um features, as well as PAH bands at
6-9 um and 10-14 um. The unidentified broad 16-24 um feature may not be related
to iron sulfide (FeS), amorphous silicate, or PAHs. Using the spectral energy
distribution model, we derived the luminosity and effective temperature of the
central star, and the gas and dust masses. The observed elemental abundances
and derived gas mass are in good agreement with asymptotic giant branch
nucleosynthesis models for an initial mass of 1.90 Msun and a metallicity of
Z=0.004. We infer that respectively about 80 %, 50 %, and 90 % of the Mg, S,
and Fe atoms are in the solid phase. We also assessed the maximum possible
magnesium sulfide (MgS) and iron-rich sulfide (Fe50S) masses and tested whether
these species can produce the band flux of the observed 30 um feature.
Depending on what fraction of the sulfur is in sulfide molecules such as CS, we
conclude that MgS and Fe50S could be possible carriers of the 30 um feature in
this PN.",1507.02667v1
2015-08-07,Correlation-enhanced odd-parity inter-orbital singlet pairing in the iron-pnictide superconductor LiFeAs,"The rich variety of iron-based superconductors and their complex electronic
structure lead to a wide range of possibilities for gap symmetry and pairing
components. Here we solve in the 2-Fe Brillouin zone the full
frequency-dependent linearized Eliashberg equations for LiFeAs with
spin-fluctuation mediated pairing interactions. The magnetic excitations are
calculated with the random phase approximation on a correlated electronic
structure obtained with density functional theory and dynamical mean field
theory. Correlations induce long-lived local moments with orbital-dependent
dynamics. The interaction between electrons through Hund's coupling promotes
inter-orbital magnetic susceptibility. As a consequence, the leading pairing
channel, conventional $s^{+-}$, acquires sizeable inter-orbital
$d_{xy}-d_{xz(yz)}$ singlet pairing with odd parity under glide-plane symmetry.
These components reduce the superconducting gap magnitude induced by the
intra-orbital components of the gap function at the electron pockets
intersection where the Fe-d $t_{2g}$ orbitals strongly mix. This in turn makes
the results consistent with available experiments on the angular dependence of
the gaps observed on the different Fermi surfaces.",1508.01789v4
2015-08-21,Computational searches for iron oxides at high pressures,"We have used density-functional-theory methods and the ab initio random
structure searching (AIRSS) approach to predict stable structures and
stoichiometries of mixtures of iron and oxygen at high pressures. Searching was
performed for 12 different stoichiometries at pressures of 100, 350 and 500
GPa, which involved relaxing more than 32,000 structures. We find that
Fe$_2$O$_3$ and FeO$_2$ are the only phases stable to decomposition at 100 GPa,
while at 350 and 500 GPa several stoichiometries are found to be stable or very
nearly stable. We report a new structure of Fe$_2$O$_3$ with $P2_12_12_1$
symmetry which is found to be more stable than the known Rh$_2$O$_3$(II) phase
at pressures above $\sim$233 GPa. We also report two new structures of FeO,
with $Pnma$ and $R\bar{3}m$ symmetries, which are found to be stable within the
ranges 195-285 GPa and 285-500 GPa, respectively, and two new structures of
Fe$_3$O$_4$ with $Pca2_1$ and $P2_1/c$ symmetries, which are found to be stable
within the ranges 100-340 GPa and 340-500 GPa, respectively. Finally, we report
two new structures of Fe$_4$O$_5$ with $P4_2/n$ and $P\bar{3}m1$ symmetries,
which are found to be stable within the ranges 100-231 GPa and 231-500 GPa,
respectively. Our new structures of Fe$_3$O$_4$ and Fe$_4$O$_5$ are found to
have lower enthalpies than their known structures within their respective
stable pressure ranges.",1508.05247v1
2015-09-03,The Gaia-ESO Survey: chemical signatures of rocky accretion in a young solar-type star,"It is well known that newly formed planetary systems undergo processes of
orbital reconfiguration and planetary migration. As a result, planets or
protoplanetary objects may accrete onto the central star, being fused and mixed
into its external layers. If the accreted mass is sufficiently high and the
star has a sufficiently thin convective envelope, such events may result in a
modification of the chemical composition of the stellar photosphere in an
observable way, enhancing it with elements that were abundant in the accreted
mass. The recent Gaia-ESO Survey observations of the 10-20 Myr old Gamma
Velorum cluster have enabled identifying a star that is significantly enriched
in iron with respect to other cluster members. In this Letter we further
investigate the abundance pattern of this star, showing that its abundance
anomaly is not limited to iron, but is also present in the refractory elements,
whose overabundances are correlated with the condensation temperature. This
finding strongly supports the hypothesis of a recent accretion of rocky
material.",1509.00933v2
2015-09-05,Two-Dimensional Oxide Topological Insulator With Iron-Pnictide Superconductor LiFeAs Structure,"By using first-principles calculations, we propose that ZrSiO can be looked
as a three-dimensional (3D) oxide weak topological insulator (TI) and its
single layer is a long-sought-after 2D oxide TI with a band gap up to 30 meV.
Calculated phonon spectrum of the single layer ZrSiO indicates it is
dynamically stable and the experimental achievements in growing oxides with
atomic precision ensure that it can be readily synthesized. This will lead to
novel devices based on TIs, the so called ""topotronic"" devices, operating under
room-temperature and stable when exposed in the air. Thus, a new field of
""topotronics"" will arise. Another intriguing thing is this oxide 2D TI has the
similar crystal structure as the well-known iron-pnictide superconductor
LiFeAs. This brings great promise in realizing the combination of
superconductor and TI, paving the way to various extraordinary quantum
phenomena, such as topological superconductor and Majorana modes. We further
find that there are many other isostructural compounds hosting the similar
electronic structure and forming a $WHM$-family with $W$ being Zr, Hf or La,
$H$ being group IV or group V element, and $M$ being group VI one.",1509.01686v2
2015-09-11,New opacity measurement principle for LMJ-PETAL laser facility,"Stellar seismology reveals some interior properties of thousands of
solar-type stars but the solar seismic sound speed stays puzzling since a
decade as it disagrees with the Standard Solar Model (SSM) prediction. One of
the explanations of this disagreement may be found in the treatment of the
transport of radiation from the solar core to the surface. As the same
framework is used for other stars, it is important to check precisely the
reliability of the interacting cross sections of photons with each species in
order to ensure the energy transport for temperature T > 2 - 10$^6$ K and
density $\rho$ > 0.2 g/cm$^3$. In this paper, we propose a new technique to
reach the domain of temperature and density found in the solar radiative
interior. This technique called the Double Ablation Front (DAF) is based on a
high conversion of the laser energy into X-rays thanks to moderated Z material
irradiated by laser intensity between 1.5 $\times$ 10$^{15}$ W/cm$^2$ and 4
$\times$ 10$^{15}$ W/cm$^2$. This high conversion creates, in addition to the
electronic front a second ablation front in the moderated Z material. Between
the two fronts there is a plateau of density and temperature that we exploit to
heat a sample of iron or of oxide. The first simulations realized with the
hydrodynamic code CHIC show that this technique allows to reach conditions
equivalent to half the radiative zone of the Sun with high stability both in
time and space. We examine the possibility to measure both iron and oxygen
absorption spectra.",1509.03563v1
2015-09-17,Local Radiation Hydrodynamic Simulations of Massive Star Envelopes at the Iron Opacity Peak,"We perform three dimensional radiation hydrodynamic simulations of the
structure and dynamics of radiation dominated envelopes of massive stars at the
location of the iron opacity peak. One dimensional hydrostatic calculations
predict an unstable density inversion at this location, whereas our simulations
reveal a complex interplay of convective and radiative transport whose behavior
depends on the ratio of the photon diffusion time to the dynamical time. The
latter is set by the ratio of the optical depth per pressure scale height,
$\tau_0$, to $\tau_c=c/c_g$, where $c_g \approx$ 50 km/s is the isothermal
sound speed in the gas alone. When $\tau_0 \gg \tau_c$, convection reduces the
radiation acceleration and removes the density inversion. The turbulent energy
transport in the simulations agrees with mixing length theory and provides its
first numerical calibration in the radiation dominated regime. When $\tau_0 \ll
\tau_c$, convection becomes inefficient and the turbulent energy transport is
negligible. The turbulent velocities exceed $c_g$, driving shocks and large
density fluctuations that allow photons to preferentially diffuse out through
low-density regions. However, the effective radiation acceleration is still
larger than the gravitational acceleration so that the time average density
profile contains a modest density inversion. In addition, the simulated
envelope undergoes large-scale oscillations with periods of a few hours. The
turbulent velocity field may affect the broadening of spectral lines and
therefore stellar rotation measurements in massive stars, while the time
variable outer atmosphere could lead to variations in their mass loss and
stellar radius.",1509.05417v1
2015-09-18,Origin of the spectral upturn in the cosmic-ray C/Fe and O/Fe ratios,"The observed spectrum of Galactic cosmic rays has several exciting features
such as the rise in the positron fraction above ~10 GeV of energy and the
spectral hardening of protons and helium at ~300 GeV/nucleon of energy. The
ATIC-2 experiment has recently reported an unexpected spectral upturn in the
elemental ratios involving iron, such as the C/Fe or O/Fe ratios, at energy
above 50 GeV per nucleon. It is recognized that the observed positron excess
can be explained by pion production processes during diffusive shock
acceleration of cosmic-ray hadrons in nearby sources. Recently, it was
suggested that a scenario with nearby source dominating the GeV-TeV spectrum
may be connected with the change of slope observed in protons and nuclei, which
would be interpreted as a flux transition between the local component and the
large-scale distribution of Galactic sources. Here I show that, under a
two-component scenario with nearby source, the shape of the spectral transition
is expected to be slightly different for heavy nuclei, such as iron, because
their propagation range is spatially limited by inelastic collisions with the
interstellar matter. This enables a prediction for the primary/primary ratios
between light and heavy nuclei. From this effect, a spectral upturn is
predicted in the C/Fe and O/Fe ratios in good accordance with the ATIC-2 data.",1509.05774v1
2015-09-23,Anisotropic hyperfine interactions in FeP studied by 57Fe Mossbauer spectroscopy and 31P NMR,"We report results of 57Fe Mossbauer and 31P NMR studies of a phosphide FeP
powder sample performed in a wide temperature range including the point (TN ~
120 K) of magnetic phase transitions. The 57Fe Mossbauer spectra at low
temperatures T < TN consist of very diffuse Zeeman pattern with line
broadenings and sizeable spectral asymmetry. It was shown that the change of
the observed spectral shape is consistent with the transition into the space
modulated helicoidal magnetic structure. Analysis of the experimental spectra
was carried out assuming the anisotropy of the magnetic hyperfine field Hhf at
the 57Fe nuclei when the Fe3+ magnetic moment rotates with respect to the
principal axis of the electric field gradient (EFG) tensor. The obtained large
temperature independent anharmonicity parameter m ~ 0.96 of the helicoidal spin
structure results from easy-axis anisotropy in the plane of the iron spin
rotation. It was assumed that the very low maximal value of Hhf(11K) ~ 36 kOe
and its high anisotropy delta_Hanis(11K) ~ 30 kOe can be attributed to the
stabilization of iron cations in the low-spin state (SFe = 1/2). The 31P NMR
measurements demonstrate an extremely broad linewidth reflecting the spatial
distribution of the transferred internal magnetic fields of the Fe3+ ions onto
P sites in the magnetically ordered state.",1509.06953v2
2015-09-23,The 1999aa-like Type Ia Supernova iPTF14bdn in the Ultraviolet and Optical,"We present ultraviolet (UV) and optical photometry and spectra of the
1999aa-like supernova (SN) iPTF14bdn. The UV data were observed using the Swift
Ultraviolet/Optical Telescope (UVOT) and constitute the first UV spectral
series of a 1999aa-like SN. From the photometry we measure $\Delta m_{15}({\it
B})\,=\,0.84 \pm0.05$ mag and blue UV colors at epochs earlier than $-5$ days.
The spectra show that the early-time blue colors are the result of less
absorption between $2800 - 3200 \,\AA~$ than is present in normal SNe Ia. Using
model spectra fits of the data at $-10 $ and $+10 $ days, we identify the
origin of this spectral feature to be a temperature effect in which doubly
ionized iron group elements create an opacity 'window'. We determine that the
detection of high temperatures and large quantities of iron group elements at
early epochs imply the mixing of a high Ni mass into the outer layers of the SN
ejecta. We also identify the source of the I-band secondary maximum in
iPTF14bdn to be the decay of Fe III to Fe II, as is seen in normal SNe Ia.",1509.07129v1
2015-11-11,Discovery of Extremely Broad Balmer Absorption Lines in SDSS J152350.42+391405.2,"We present the discovery of Balmer line absorption from H$\alpha$ to
H$\gamma$ in an iron low-ionization broad absorption line (FeLoBAL) quasar SDSS
J152350.42+391405.2 (hereafter J1523), by the quasi-simultaneous optical and
near-infrared spectroscopy. The Balmer line absorption is at $z_{absor}$ =
0.6039 +/-0.0021 and blueshifted by v=10,353 km/s with respect to the Balmer
emission lines. All Balmer BALs have uniform absorption profile with the widths
of $\Delta$ v ~12,000 km/s. We also found the absorption trough in He 1*
$\lambda$10830 with the same velocity and width in the H-band TripleSpec
spectrum of J1523. This object is only the tenth active galactic nucleus known
to exhibit non-stellar Balmer absorption, and also the case with the highest
velocity and broadest Balmer absorption lines which have ever been found. A
CLOUDY analysis shows that the absorbers require an gas density of $log_{10} n_
e (cm^{-3})=9$ and an ionization parameter of $log_{10} U=-1.0$. They locate at
a distance of ~0.2 pc from the central ionizing source which is slightly
farther than that of BELRs. Furthermore, J1523 is one of the brightest
Balmer-BAL quasar ever reported, with unique iron absorption variations, making
it as the most promising candidate for follow up high-resolution spectroscopy,
multi-band observations, and long-term monitoring.",1511.03422v1
2015-12-17,The Fe/Ni ratio in ionized nebulae: clues on dust depletion patterns,"We perform a homogeneous analysis of the Fe/Ni abundance ratio in eight
Galactic planetary nebulae (PNe) and three Galactic H II regions that include
the Orion nebula, where we study four nebular zones and one shocked region. We
use [Fe ii], [Fe iii], and [Ni iii] lines, and ionization correction factors
(ICFs) that account for the unobserved ions. We derive an ICF for nickel from
an extensive grid of photoionization models. We compare our results with those
derived by other authors for 16 neutral clouds in the solar neighbourhood with
available Fe/Ni ratios in the literature. We find an excellent agreement
between the ionized nebulae and the diffuse clouds, with both types of regions
showing a clear correlation between the Fe/Ni ratios and the iron and nickel
depletion factors. The trend shows that the objects with a relatively low
depletion have near solar Fe/Ni ratios whereas at higher depletions the Fe/Ni
ratio increases with the depletion. Our results confirm that, compared to iron
atoms, nickel ones are more efficiently stuck to the dust grains in ambients
where dust formation or growth have been more efficient.",1512.05664v1
2015-12-18,Expansion of the tetragonal magnetic phase with pressure in the iron-arsenide superconductor Ba{1-x}KxFe2As2,"In the temperature-concentration phase diagram of most iron-based
superconductors, antiferromagnetic order is gradually suppressed to zero at a
critical point, and a dome of superconductivity forms around that point. The
nature of the magnetic phase and its fluctuations is of fundamental importance
for elucidating the pairing mechanism. In Ba{1-x}KxFe2As2 and Ba{1-x}NaxFe2As2,
it has recently become clear that the usual stripe-like magnetic phase, of
orthorhombic symmetry, gives way to a second magnetic phase, of tetragonal
symmetry, near the critical point, between x = 0.24 and x = 0.28. Here we
report measurements of the electrical resistivity of Ba{1-x}KxFe2As2 under
applied hydrostatic pressures up to 2.75 GPa, for x = 0.22, 0.24 and 0.28. We
track the onset of the tetragonal magnetic phase using the sharp anomaly it
produces in the resistivity. In the temperature-concentration phase diagram of
Ba{1-x}KxFe2As2, we find that pressure greatly expands the tetragonal magnetic
phase, while the stripe-like phase shrinks. This raises the interesting
possibility that the fluctuations of the former phase might be involved in the
pairing mechanism responsible for the superconductivity.",1512.05912v1
2015-12-22,Dome-shaped magnetic order competing with high-temperature superconductivity at high pressures in FeSe,"The coexistence and competition between superconductivity and electronic
orders, such as spin or charge density waves, have been a central issue in high
transition-temperature (${T_{\rm c}}$) superconductors. Unlike other iron-based
superconductors, FeSe exhibits nematic ordering without magnetism whose
relationship with its superconductivity remains unclear. More importantly, a
pressure-induced fourfold increase of ${T_{\rm c}}$ has been reported, which
poses a profound mystery. Here we report high-pressure magnetotransport
measurements in FeSe up to $\sim9$ GPa, which uncover a hidden magnetic dome
superseding the nematic order. Above ${\sim6}$ GPa the sudden enhancement of
superconductivity (${T_{\rm c}\le38.3}$ K) accompanies a suppression of
magnetic order, demonstrating their competing nature with very similar energy
scales. Above the magnetic dome we find anomalous transport properties
suggesting a possible pseudogap formation, whereas linear-in-temperature
resistivity is observed above the high-${T_{\rm c}}$ phase. The obtained phase
diagram highlights unique features among iron-based superconductors, but bears
some resemblance to that of high-${T_{\rm c}}$ cuprates.",1512.06951v1
2015-12-27,Two types of superconducting domes in unconventional superconductors,"Uncovering the origin of unconventional superconductivity is often plagued by
the overwhelming material diversity with varying normal and superconducting
(SC) properties. In this article, we deliver a comprehensive study of the SC
properties and phase diagrams using multiple tunings (such as disorder,
pressure or magnetic field in addition to doping and vice versa) across several
families of unconventional superconductors, including the copper-oxides,
heavy-fermions, organics and the recently discovered iron-pnictides,
iron-chalcogenides, and oxybismuthides. We discover that all these families
often possess two types of SC domes, with lower and higher superconducting
transition temperatures Tc, both unconventional but with distinct SC and normal
states properties. The lower Tc dome arises with or without a quantum critical
point (QCP), and not always associated with a non-Fermi liquid (NFL)
background. On the contrary, the higher-Tc dome clearly stems from a NFL or
strange metal phase, without an apparent intervening phase transition or a QCP.
The two domes appear either fully separated in the phase diagram, or merged
into one, or arise independently owing to their respective normal state
characteristics. Our findings suggest that a QCP-related mechanism is an
unlikely scenario for the NFL phase in these materials, and thereby narrows the
possibility towards short-range fluctuations of various degrees of freedom in
the momentum and frequency space. We also find that NFL physics may be a
generic route to higher-Tc superconductivity.",1512.08186v2
2016-01-04,An Intermediate Type Ia Supernova Between Normal And Super-Chandrasekhar,"In this paper, we report observations of a peculiar Type Ia supernova
iPTF13asv (a.k.a., SN2013cv) from the onset of the explosion to months after
its peak. The early-phase spectra of iPTF13asv show absence of iron absorption,
indicating that synthesized iron elements are confined to low-velocity regions
of the ejecta, which, in turn, implies a stratified ejecta structure along the
line of sight. Our analysis of iPTF13asv's light curves and spectra shows that
it is an intermediate case between normal and super-Chandrasekhar events. On
the one hand, its light curve shape (B-band $\Delta m_{15}=1.03\pm0.01$) and
overall spectral features resemble those of normal Type Ia supernovae. On the
other hand, similar to super-Chandrasekhar events, it shows large peak optical
and UV luminosity ($M_B=-19.84\,\rm{mag}$, $M_{uvm2}=-15.5\,\rm{mag}$) a
relatively low but almost constant \ion{Si}{2} velocities of about
$10,000\,\rm{km}\,\rm{s}^{-1}$, and persistent carbon absorption in the
spectra. We estimate a $^{56}$Ni mass of $0.81^{+0.10}_{-0.18}M_\odot$ and a
total ejecta mass of $1.59^{+0.45}_{-0.12}M_\odot$. The large ejecta mass of
iPTF13asv and its stratified ejecta structure together seemingly favor a
double-degenerate origin.",1601.00686v2
2016-01-21,The temperature and chronology of heavy-element synthesis in low-mass stars,"Roughly half of the heavy elements (atomic mass greater than that of iron)
are believed to be synthesized in the late evolutionary stages of stars with
masses between 0.8 and 8 solar masses. Deep inside the star, nuclei (mainly
iron) capture neutrons and progressively build up (through the
slow-neutron-capture process, or s-process) heavier elements that are
subsequently brought to the stellar surface by convection. Two neutron sources,
activated at distinct temperatures, have been proposed: 13C and 22Ne, each
releasing one neutron per alpha-particle (4He) captured. To explain the
measured stellar abundances, stellar evolution models invoking the 13C neutron
source (which operates at temperatures of about one hundred million kelvin) are
favoured. Isotopic ratios in primitive meteorites, however, reflecting
nucleosynthesis in the previous generations of stars that contributed material
to the Solar System, point to higher temperatures (more than three hundred
million kelvin), requiring at least a late activation of 22Ne. Here we report a
determination of the s-process temperature directly in evolved low-mass giant
stars, using zirconium and niobium abundances, independently of stellar
evolution models. The derived temperature supports 13C as the s-process neutron
source. The radioactive pair 93Zr-93Nb used to estimate the s-process
temperature also provides, together with the pair 99Tc-99Ru, chronometric
information on the time elapsed since the start of the s-process, which we
determine to be one million to three million years.",1601.05640v1
2016-01-21,Detailed magnetic and structural analysis mapping a robust magnetic C4 dome in Sr1-xNaxFe2As2,"The recently discovered $C_4$ tetragonal magnetic phase in hole-doped members
of the iron-based superconductors provides new insights into the origin of
unconventional superconductivity. Previously observed in
Ba$_{1-x}A_x$Fe$_2$As$_2$ (with $A =$ K, Na), the $C_4$ magnetic phase exists
within the well studied $C_2$ spin-density wave (SDW) dome, arising just before
the complete suppression of antiferromagnetic (AFM) order but after the onset
of superconductivity. Here, we present detailed x-ray and neutron diffraction
studies of Sr$_{1-x}$Na$_x$Fe$_2$As$_2$ ($0.10 \leq\ x \leq\ 0.60$) to
determine their structural evolution and the extent of the $C_4$ phase.
Spanning $\Delta x\sim 0.14$ in composition, the $C_4$ phase is found to extend
over a larger range of compositions, and to exhibit a significantly higher
transition temperature, $T_r \sim 65$K, than in either of the other systems in
which it has been observed. The onset of this phase is seen near a composition
($x \sim 0.30$) where the bonding angles of the Fe$_2$As$_2$ layers approach
the perfect $109.46^\circ$ tetrahedral angle. We discuss the possible role of
this return to a higher symmetry environment for the magnetic iron site in
triggering the magnetic reorientation and the coupled re-entrance to the
tetragonal structure. Finally, we present a new phase diagram, complete with
the $C_4$ phase, and use its observation in a third hole-doped 122 system to
suggest the universality of this phase.",1601.05693v1
2016-02-11,Doping evolution of the superconducting gap structure in the underdoped iron arsenide Ba1-xKxFe2As2 revealed by thermal conductivity,"The thermal conductivity kappa of the iron-arsenide superconductor
Ba1-xKxFe2As2 was measured for heat currents parallel and perpendicular to the
tetragonal c axis at temperatures down to 50 mK and in magnetic fields up to 15
T. Measurements were performed on samples with compositions ranging from
optimal doping (x = 0.34; Tc = 39 K) down to dopings deep into the region where
antiferromagnetic order coexists with superconductivity (x = 0.16; Tc = 7 K).
In zero field, there is no residual linear term in kappa(T) as T goes to 0 at
any doping, whether for in-plane or inter-plane transport. This shows that
there are no nodes in the superconducting gap. However, as x decreases into the
range of coexistence with antiferromagnetism, the residual linear term grows
more and more rapidly with applied magnetic field. This shows that the
superconducting energy gap develops minima at certain locations on the Fermi
surface and these minima deepen with decreasing x. We propose that the minima
in the gap structure arise when the Fermi surface of Ba1-xKxFe2As2 is
reconstructed by the antiferromagnetic order.",1602.03914v1
2016-03-03,"Fe dopant in ZnO: 2+ vs 3+ valency and ion-carrier s,p-d exchange interaction","Dopants of transition metal ions in II-VI semiconductors exhibit native 2+
valency. Despite this, 3+ or mixed 3+/2+ valency of iron ions in ZnO was
reported previously. Several contradictory mechanisms have been put forward for
explanation of this fact so far. Here, we analyze Fe valency in ZnO by
complementary theoretical and experimental studies. Our calculations within the
generalized gradient approximation (GGA+U) indicate that the Fe ion is a
relatively shallow donor. Its stable charge state is Fe2+ in ideal ZnO,
however, the high energy of the (+/0) transition level enhances the
compensation of Fe2+ to Fe3+ by non-intentional acceptors in real samples.
Using several experimental methods like electron paramagnetic resonance,
magnetometry, conductivity, excitonic magnetic circular dichroism and
magneto-photoluminescence we confirm the 3+ valency of the iron ions in
polycrystalline (Zn,Fe)O films with the Fe content attaining 0.2%.We find a
predicted increase of n-type conductivity upon the Fe doping with the Fe donor
ionization energy of 0.25 +/- 0.02 eV consistent with the results of
theoretical considerations. Moreover, our magnetooptical measurements confirm
the calculated non-vanishing s,p-d exchange interaction between band carriers
and localized magnetic moments of the Fe3+ ions in the ZnO, being so far an
unsettled issue.",1603.01123v2
2016-03-05,Development and characterization of single gap glass RPC,"India-based Neutrino Observatory (INO) facility is going to have a 50 kton
magnetized Iron CALorimeter (ICAL) detector for precision measurements of
neutrino oscillations using atmospheric neutrinos. The proposed ICAL detector
will be a stack of magnetized iron plates (acting as target material)
interleaved with glass Resistive Plate Chambers (RPCs) as the active detector
elements. An RPC is a gaseous detector made up of two parallel electrode plates
having high bulk resistivity like that of float glass and bakelite. For the
ICAL detector, glass is preferred over bakelite as it does not need any kind of
surface treatment to achieve better surface uniformity and also the cost of
associated electronics is reduced. Under the detector R&D efforts for the
proposed glass RPC detector, a few glass RPCs of 1m X 1m dimension are
fabricated procuring glass of ~ 2 mm thickness from one of the Indian glass
manufacturers (Asahi). In the present paper, we report the characterization of
RPC based on leakage current study, muon detection efficiency and noise rate
studies with varying gas compositions.",1603.01719v5
2016-03-09,Suppression of spin-exciton state in hole overdoped iron-based superconductors,"The mechanism of Cooper pair formation in iron-based superconductors remains
a controversial topic. The main question is whether spin or orbital
fluctuations are responsible for the pairing mechanism. To solve this problem,
a crucial clue can be obtained by examining the remarkable enhancement of
magnetic neutron scattering signals appearing in a superconducting phase. The
enhancement is called spin resonance for a spin fluctuation model, in which
their energy is restricted below twice the superconducting gap value (2Ds),
whereas larger energies are possible in other models such as an orbital
fluctuation model. Here we report the doping dependence of low-energy magnetic
excitation spectra in Ba1-xKxFe2As2 for 0.5<x<0.84 studied by inelastic neutron
scattering. We find that the behavior of the spin resonance dramatically
changes from optimum to overdoped regions. Strong resonance peaks are observed
clearly below 2Ds in the optimum doping region, while they are absent in the
overdoped region. Instead, there is a transfer of spectral weight from energies
below 2Ds to higher energies, peaking at values of 3Ds for x = 0.84. These
results suggest a reduced impact of magnetism on Cooper pair formation in the
overdoped region.",1603.02762v1
2016-03-17,The origin of the $α$-enhancement of massive galaxies,"We study the origin of the stellar $\alpha$-element-to-iron abundance ratio,
$[\alpha/\mathrm{Fe}]_{\ast}$, of present-day central galaxies, using
cosmological, hydrodynamical simulations from the Evolution and Assembly of
GaLaxies and their Environments (EAGLE) project. For galaxies with stellar
masses of $M_{\ast} > 10^{10.5}$ M$_{\odot}$, $[\alpha/\mathrm{Fe}]_{\ast}$
increases with increasing galaxy stellar mass and age. These trends are in good
agreement with observations of early-type galaxies, and are consistent with a
`downsizing' galaxy formation scenario: more massive galaxies have formed the
bulk of their stars earlier and more rapidly, hence from an interstellar medium
that was mostly $\alpha$-enriched by massive stars. In the absence of feedback
from active galactic nuclei (AGN), however, $[\alpha/\mathrm{Fe}]_{\ast}$ in
$M_{\ast} > 10^{10.5}$ M$_{\odot}$ galaxies is roughly constant with stellar
mass and decreases with mean stellar age, extending the trends found for
lower-mass galaxies in both simulations with and without AGN. We conclude that
AGN feedback can account for the $\alpha$-enhancement of massive galaxies, as
it suppresses their star formation, quenching more massive galaxies at earlier
times, thereby preventing the iron from longer-lived intermediate-mass stars
(supernova Type Ia) from being incorporated into younger stars.",1603.05653v3
2016-04-07,The super-super exchange mechanism in iron-based antiperovskite chalco-halides,"By using the first-principles electronic structure calculations, we have
systematically studied the magnetism in three recently synthesized iron-based
antiperovskite chalco-halides: Ba$_3$(FeS$_4$)Cl, Ba$_3$(FeS$_4$)Br, and
Ba$_3$(FeSe$_4$)Br. These compounds consist of edge-sharing Ba$Q_6$ ($Q$=Cl or
Br) octahedra intercalated with isolated Fe$X_4$ ($X$=S or Se) tetrahedra. We
find that even though the shortest distances between the nearest-neighboring Fe
atoms in these three compounds already exceed 6 \AA, much larger than the bond
length of a chemical bonding, they all remarkably show antiferromagnetic (AFM)
coupling along $b$ axis with very weak spin-spin correlation along $a$ axis.
Our study shows that the mechanism underlying this novel AFM coupling is such a
new type of exchange interaction between the nearest-neighboring Fe-based
super-moments mediated by Ba cations, which we call the super-super exchange
interaction, in which each magnetic Fe atom partially polarizes its four
nearest-neighboring $X$ atoms to form a super-moment through $p$-$d$ orbital
hybridization and the $X$ atoms in neighboring Fe$X_4$ tetrahedra along $b$
axis antiferromagnetically couple with each others through the intermediate Ba
cations. Different from the conventional superexchange, here it is cations
rather than anions that mediate two neighboring super-moments. According to the
calculated strength of the AFM coupling, we predict that among these compounds
the highest AFM phase transition temperature $T_N$ may reach 110 K in
Ba$_3$(FeSe$_4$)Br, in comparison with the observed $T_N$s of 84 K in
Ba$_3$(FeS$_4$)Br and 95 K in Ba$_3$(FeS$_4$)Cl.",1604.02044v1
2016-04-08,Detection of H2O and evidence for TiO/VO in an ultra hot exoplanet atmosphere,"We present a primary transit observation for the ultra hot (Teq~2400K) gas
giant expolanet WASP-121b, made using the Hubble Space Telescope Wide Field
Camera 3 in spectroscopic mode across the 1.12-1.64 micron wavelength range.
The 1.4 micron water absorption band is detected at high confidence (5.4 sigma)
in the planetary atmosphere. We also reanalyze ground-based photometric
lightcurves taken in the B, r', and z' filters. Significantly deeper transits
are measured in these optical bandpasses relative to the near-infrared
wavelengths. We conclude that scattering by high-altitude haze alone is
unlikely to account for this difference, and instead interpret it as evidence
for titanium oxide and vanadium oxide absorption. Enhanced opacity is also
inferred across the 1.12-1.3 micron wavelength range, possibly due to iron
hydride absorption. If confirmed, WASP-121b will be the first exoplanet with
titanium oxide, vanadium oxide, and iron hydride detected in transmission. The
latter are important species in M/L dwarfs, and their presence is likely to
have a significant effect on the overall physics and chemistry of the
atmosphere, including the production of a strong thermal inversion.",1604.02310v1
2016-04-12,A Statistical Study of the Average Iron Charge Distributions inside Magnetic Clouds for Solar Cycle 23,"Magnetic clouds (MCs) are the interplanetary counterpart of coronal magnetic
flux ropes. They can provide valuable information to reveal the flux rope
characteristics at their eruption stage in the corona, which are unable to be
explored in situ at present. In this paper, we make a comprehensive survey of
the average iron charge state (<Q>Fe) distributions inside 96 MCs for solar
cycle 23 using ACE (Advanced Composition Explorer) data. As the <Q>Fe in the
solar wind are typically around 9+ to 11+, the Fe charge state is defined as
high when the <Q>Fe is larger than 12+, which implies the existence of a
considerable amount of Fe ions with high charge states (e.g., \geq 16+). The
statistical results show that the <Q>Fe distributions of 92 (~ 96%) MCs can be
classified into four groups with different characteristics. In group A (11
MCs), the <Q>Fe shows a bimodal distribution with both peaks higher than 12+.
Group B (4 MCs) presents a unimodal distribution of <Q>Fe with its peak higher
than 12+. In groups C (29 MCs) and D (48 MCs), the <Q>Fe remains higher and
lower than 12+ throughout ACE passage through the MC, respectively. Possible
explanations to these distributions are discussed.",1604.03205v1
2016-04-14,Study of Glass and Bakelite properties as electrodes in RPCs,"India-based Neutrino Observatory (INO) collaboration is planning to build a
magnetized Iron-CALorimeter detector (ICAL) for the study of atmospheric
neutrinos. ICAL detector will be a stack of 151 layers of magnetized iron
plates interleaved with Resistive Plate Chambers (RPCs) as active detector
elements with a total mass of 50 kton. Resistive Plate Chambers are gaseous
detectors made up of two parallel electrodes of high bulk resistivity like
float glass and bakelite. These detectors are extensively used in several high
energy physics experiments since 1980s because of high count rate, excellent
time as well as spatial resolutions, simple to fabricate and operate. Due to
detector aging issue, it is necessary to characterize electrode material so as
to select appropriate electrode material before fabricating the detector. In
the present studies, we measured bulk resistivity and surface current of glass
as well as bakelite. Bulk resistivity of bakelite is ~ 100 times less than that
of glass and surface current of bakelite is higher than that of glass. Also
glass does not need any kind of surface treatment to achieve better surface
uniformity. Therefore, glass electrodes are preferred over bakelite electrodes
in most of the cases. Locally manufactured Asahi glass of ~2 mm thickness and
bakelite sheets were tested during the studies as reported in this paper before
the various stages of detector fabrication.",1604.04130v2
2016-04-25,Equilibrium and Sudden Events in Chemical Evolution,"We present new analytic solutions for one-zone (fully mixed) chemical
evolution models and explore their implications. In contrast to existing
analytic models, we incorporate a realistic delay time distribution for Type Ia
supernovae (SNIa) and can therefore track the separate evolution of
$\alpha$-elements produced by core collapse supernovae (CCSNe) and iron peak
elements synthesized in both CCSNe and SNIa. In generic cases, $\alpha$ and
iron abundances evolve to an equilibrium at which element production is
balanced by metal consumption and gas dilution, instead of continuing to
increase over time. The equilibrium absolute abundances depend principally on
supernova yields and the outflow mass loading parameter $\eta$, while the
equilibrium abundance ratio [$\alpha$/Fe] depends mainly on yields and
secondarily on star formation history. A stellar population can be metal-poor
either because it has not yet evolved to equilibrium or because high outflow
efficiency makes the equilibrium abundance itself low. Systems with ongoing gas
accretion develop metallicity distribution functions (MDFs) that are sharply
peaked, while ""gas starved"" systems with rapidly declining star formation have
broadly peaked MDFs. A burst of star formation that consumes a significant
fraction of a system's available gas can temporarily boost [$\alpha$/Fe] by
0.1-0.3 dex, a possible origin for rare, $\alpha$-enhanced stars with
intermediate age or high metallicity. Other sudden transitions in system
properties can produce surprising behavior, including backward evolution of a
stellar population from high metallicity to low metallicity. An Appendix
provides a user's guide for calculating enrichment histories, [$\alpha$/Fe]
tracks, and MDFs for a wide variety of scenarios, including flexible forms of
star formation history.",1604.07435v1
2016-05-01,Development of a method for measuring blood coagulation using superparamagnetic iron oxide nanoparticles and an alternating magnetic field,"We developed a method for measuring blood coagulation using superparamagnetic
iron oxide nanoparticles (SPIONs) and an alternating magnetic field (AMF). The
3rd and 5th harmonic signals from SPIONs mixed with blood induced by AMF were
detected using a gradiometer coil. Blood coagulation was induced artificially
by adding CaCl2 solution to whole blood of sheep at various temperatures and
hematocrits. We calculated the coagulation rate (k) and normalized signal
intensity at infinite time (Sinf) by fitting the time course of the normalized
3rd harmonic signal to S(t)=(1-Sinf)exp(-kt)+Sinf. The k values increased
significantly with increasing temperature and decreased significantly with
increasing hematocrit. The Sinf values decreased significantly with increasing
temperature and tended to increase with increasing hematocrit. Blood
anticoagulation was induced by adding heparin to the whole blood sampled from
mice. There were significant differences in both the 3rd and 5th harmonic
signals between groups with and without heparin at 25 min or more after adding
heparin. We also calculated the 3rd and 5th harmonic signals for viscosities
ranging from 0.001 to 1 kg/m/s, with an assumption that the magnetization and
particle size distribution of SPIONs obey the Langevin theory of paramagnetism
and log-normal distribution, respectively. The 3rd and 5th harmonic signals
increased slowly with increasing viscosity and had peaks at approximately 0.015
and 0.025 kg/m/s, respectively. After these peaks, they decreased monotonically
with increasing viscosity. These results confirm the rationale of our method.
In conclusion, our method will be useful for measuring blood coagulation and
anticoagulation and for studying their processes.",1605.00255v2
2016-06-02,Orbital selective spin excitations and their impact on superconductivity of LiFe1-xCoxAs,"We use neutron scattering to study spin excitations in single crystals of
LiFe$_{0.88}$Co$_{0.12}$As, which is located near the boundary of the
superconducting phase of LiFe$_{1-x}$Co$_{x}$As and exhibits non-Fermi-liquid
behavior indicative of a quantum critical point. By comparing spin excitations
of LiFe$_{0.88}$Co$_{0.12}$As with a combined density functional theory (DFT)
and dynamical mean field theory (DMFT) calculation, we conclude that
wave-vector correlated low energy spin excitations are mostly from the $d_{xy}$
orbitals, while high-energy spin excitations arise from the $d_{yz}$ and
$d_{xz}$ orbitals. Unlike most iron pnictides, the strong orbital selective
spin excitations in LiFeAs family cannot be described by anisotropic Heisenberg
Hamiltonian. While the evolution of low-energy spin excitations of
LiFe$_{1-x}$Co$_x$As are consistent with electron-hole Fermi surface nesting
condition for the $d_{xy}$ orbital, the reduced superconductivity in
LiFe$_{0.88}$Co$_{0.12}$As suggests that Fermi surface nesting conditions for
the $d_{yz}$ and $d_{xz}$ orbitals are also important for superconductivity in
iron pnictides.",1606.00727v1
2016-06-03,Swift J174540.7-290015: a new accreting binary in the Galactic Center,"We report on the identification of the new Galactic Center (GC) transient
Swift J174540.7-290015 as a likely low mass X-ray binary (LMXB) located at only
16 arcsec from Sgr A*. This transient was detected on 2016 February 6th during
the Swift GC monitoring, and it showed long-term spectral variations compatible
with a hard to soft state transition. We observed the field with XMM-Newton on
February 26th for 35 ks, detecting the source in the soft state, characterised
by a low level of variability and a soft X-ray thermal spectrum with a high
energy tail (detected by INTEGRAL up to ~50 keV), typical of either accreting
neutron stars or black holes. We observed: i) a high column density of neutral
absorbing material, suggesting that Swift J174540.7-290015 is located near or
beyond the GC and; ii) a sub-Solar Iron abundance, therefore we argue that Iron
is depleted into dust grains. The lack of detection of FeK absorption lines,
eclipses or dipping suggests that the accretion disc is observed at a low
inclination angle. Radio (VLA) observations did not detect any radio
counterpart to Swift J174540.7-290015. No evidence for X-ray or radio
periodicity is found. The location of the transient was observed also in the
near-IR with GROND at MPG/ESO La Silla 2.2m telescope and VLT/NaCo pre- and
post-outburst. Within the Chandra error region we find multiple objects that
display no significant variations.",1606.01138v1
2016-06-17,Time dependence of Fe/O ratio within a 3D Solar Energetic Particle propagation model including drift,"Context. The intensity profiles of iron and oxygen in Solar Energetic
Particle (SEP) events often display differences that result in a decreasing
Fe/O ratio over time. The physical mechanisms behind this behaviour are not
fully understood, but these observational signatures provide important tests of
physical modelling efforts. Aims. In this paper we study the propagation of
iron and oxygen SEP ions using a 3D model of propagation which includes the
effect of guiding centre drift in a Parker spiral magnetic field. We derive
time intensity profiles for a variety of observer locations and study the
temporal evolution of the Fe/O ratio. Methods. We use a 3D full orbit test
particle model which includes scattering. The configuration of the
interplanetary magnetic field is a unipolar Parker spiral. Particles are
released instantaneously from a compact region at 2 solar radii and allowed to
propagate in 3D. Results. Both Fe and O experience significant transport across
the magnetic field due to gradient and curvature drifts. We find that Fe ions
drift more than O ions due to their larger mass-to-charge ratio, so that an
observer that is not magnetically well connected to the source region will
observe Fe arriving before O, for particles within the same range in energy per
nucleon. As a result, for the majority of observer locations, the Fe/O ratio
displays a decrease in time. Conclusions. We conclude that propagation effects
associated with drifts produce a decay over time of the Fe/O ratio,
qualitatively reproducing that observed in SEP event profiles.",1606.05612v2
2016-07-05,Heavy Electron doping-induced antiferromagnetic phase as the parent for iron-oxypnictide superconductor LaFeAsO1-xHx,"We perform transport measurements and band structure calculations of
electron-doped LaFeAsO1-xHx over a wide range of x from 0.01 to 0.66. The T^2
and sqrt(T) dependency of the resistivity are observed at x ~ 0.17 and 0.41,
respectively. The sign change of RH without opening of the spin-density-wave
gap for 0.45 < x < 0.58 and T < TN as well as the calculated non-nested Fermi
surface at x = 0.5 indicate the more localized nature of the AF2 as compared to
spin density wave phase at non-doped sample. Considering the results from band
calculations and the finite size of Hund' s rule coupling, the change of the
normal conducting state with x is reasonably explained by a strong depression
of the coherent scale owing to the increased effective Coulomb repulsion in the
narrow anti-bonding 3dxy band that approaches the half-filled regime. The
following transition from the paramagnet to AF2 is understood as the quenching
or ordering of the less-screened spins with a large entropy at low temperature.
These results suggest that the normal conducting properties over a wide doping
range for the LaFeAsO1-xHx are strongly influenced by the local spins in the
incoherent region. Thus, we conclude that the parent phase in LaFeAsO1-xHx is
not the spin-density wave but the AF2, which may be primarily responsible for
the singular superconducting properties of the 1111 type compared with other
iron pnictides.",1607.01238v1
2016-07-05,Superconductivity-enhanced Nematicity and '$s+d$' Gap Symmetry in Fe(Se$_{1-x}$S$_x$),"Superconducting iron chalcogenide FeSe has the simplest crystal structure
among all the Fe-based superconductors. Unlike other iron pnictides, FeSe
exhibits no long range magnetic order accompanying the
tetragonal-to-orthorhombic structural distortion, which raises the fundamental
question about the role of magnetism and its associated spin fluctuations in
mediating both nematicity and superconductivity. The extreme sensitivity of
FeSe to external pressure suggests that chemical pressure, induced by
substitution of Se by the smaller ion S, could also a be good tuning parameter
to further study the coupling between superconductivity and nematicity and to
obtain information on both the Fermi-surface changes and the symmetry of the
superconducting state. Here we study the thermodynamic properties of
Fe(Se$_{1-x}$S$_{x}$) for 3 compositions, $x=0$, 0.08 and 0.15, using
heat-capacity and thermal-expansion measurements. With increasing S content we
observe a significant reduction of the tetragonal-to-orthorhombic transition
temperature T$_{s}$. However, this suppression of T$_{s}$ is counterintuitively
accompanied by an enhancement of the orthorhombic distortion $\delta$ below
T$_c$, which clearly indicates that superconductivity favors the nematic state.
In parallel, the superconducting transition temperature T$_{c}$ is sizeably
enhanced, whereas the increase of the Sommerfeld coefficient $\gamma_{n}$ is
quite moderate. In the T$\to$ 0 limit, an unusually large residual density of
states is found for $x>0$ indicative of significant substitution-induced
disorder. We discuss these observations in the context of $s+d$
superconducting-state symmetry.",1607.01288v2
2016-07-07,Deciphering chemical order/disorder and material properties at the single-atom level,"Correlating 3D arrangements of atoms and defects with material properties and
functionality forms the core of several scientific disciplines. Here, we
determined the 3D coordinates of 6,569 iron and 16,627 platinum atoms in a
model iron-platinum nanoparticle system to correlate 3D atomic arrangements and
chemical order/disorder with material properties at the single-atom level. We
identified rich structural variety and chemical order/disorder including 3D
atomic composition, grain boundaries, anti-phase boundaries, anti-site point
defects and swap defects. We show for the first time that experimentally
measured 3D atomic coordinates and chemical species with 22 pm precision can be
used as direct input for first-principles calculations of material properties
such as atomic magnetic moments and local magnetocrystalline anisotropy. This
work not only opens the door to determining 3D atomic arrangements and chemical
order/disorder of a wide range of nanostructured materials with high precision,
but also will transform our understanding of structure-property relationships
at the most fundamental level.",1607.02051v1
2016-07-09,Theoretical modelling of the AGN iron-line vs continuum time-lags in the lamp-post geometry,"Context: Theoretical modelling of time-lags between variations in the Fe
K$\alpha$ emission and the X-ray continuum might shed light on the physics and
geometry of the X-ray emitting region in active galaxies (AGN) and X-ray
binaries. We here present the results from a systematic analysis of time-lags
between variations in two energy bands ($5-7$ vs $2-4\,\mathrm{keV}$) for seven
X-ray bright and variable AGN.
  Aims: We estimate time-lags as accurately as possible and fit them with
theoretical models in the context of the lamp-post geometry. We also constrain
the geometry of the X-ray emitting region in AGN.
  Methods: We used all available archival \textit{XMM-Newton} data for the
sources in our sample and extracted light curves in the $5-7$ and
$2-4\,\mathrm{keV}$ energy bands. We used these light curves and applied a
thoroughly tested (through extensive numerical simulations) recipe to estimate
time-lags that have minimal bias, approximately follow a Gaussian distribution,
and have known errors. Using traditional $\chi^2$ minimisation techniques, we
then fitted the observed time-lags with two different models: a
phenomenological model where the time-lags have a power-law dependence on
frequency, and a physical model, using the reverberation time-lags expected in
the lamp-post geometry. The latter were computed assuming a point-like primary
X-ray source above a black hole surrounded by a neutral and prograde accretion
disc with solar iron abundance. We took all relativistic effects into account
for various X-ray source heights, inclination angles, and black hole spin
values.",1607.02625v2
2016-07-09,On the reality of broad iron L lines from the narrow line Seyfert 1 galaxies 1H0707-495 and IRAS 13224-3809,"We performed time resolved spectroscopy of 1H0707-495 and IRAS 13224-3809
using long XMM-Newton observations. These are strongly variable narrow line
Seyfert 1 galaxies and show broad features around 1 keV that has been
interpreted as relativistically broad Fe L$\alpha$ lines. Such features are not
clearly observed in other AGN despite sometimes having high iron abundance
required by the best fitted blurred reflection models. Given the importance of
these lines, we explore the possibility if rapid variability of spectral
parameters may introduce broad bumps/dips artificially in the time averaged
spectrum, which may then be mistaken as broadened lines. We tested this
hypothesis by performing time resolved spectroscopy using long (> 100 ks)
XMM-Newton observations and by dividing it into segments with typical exposure
of few ks. We extracted spectra from each such segment and modelled using a two
component phenomenological model consisting of a power law to represent hard
component and a black body to represent the soft emission. As expected both the
sources showed variations in the spectral parameters. Using these variation
trends, we simulated model spectra for each segment and then co-added to get a
combined simulated spectrum. In the simulated spectra, we found no broad
features below 1 keV and in particular no deviation near 0.9 keV as seen in the
real average spectra. This implies that the broad Fe L? line that is seen in
the spectra of these sources is not an artifact of the variation of spectral
components and hence providing evidence that the line is indeed genuine.",1607.02635v1
2016-07-11,"Magnetotransport of multiple-band nearly-antiferromagnetic metals due to ""hot-spot"" scattering","Multiple-band electronic structure and proximity to antiferromagnetic (AF)
instability are the key properties of iron-based superconductors. We explore
the influence of scattering by the AF spin fluctuations on transport of
multiple-band metals above the magnetic transition. A salient feature of
scattering on the AF fluctuations is that it is strongly enhanced at the Fermi
surface locations where the nesting is perfect (""hot spots"" or ""hot lines""). We
review derivation of the collision integral for the Boltzmann equation due to
AF-fluctuations scattering. In the paramagnetic state, the enhanced scattering
rate near the hot lines leads to anomalous behavior of electronic transport in
magnetic field. We explore this behavior by analytically solving Boltzmann
transport equation with approximate transition rates. This approach accounts
for return scattering events and is more accurate than the relaxation-time
approximation. The magnetic-field dependences are characterized by two very
different field scales, the lower scale is set by the hot-spot width and the
higher scale is set by the total scattering amplitude. A conventional
magnetotransport behavior is limited to magnetic fields below the lower scale.
In the wide range in between these two scales the longitudinal conductivity has
linear dependence on the magnetic field and the Hall conductivity has quadratic
dependence. The linear dependence of the diagonal component reflects growth of
the Fermi-surface area affected by hot spots proportional to the magnetic
field. We discuss applicability of this theoretical framework for describing of
anomalous magnetotransport properties in different iron pnictides and selenides
in the paramagnetic state.",1607.03194v2
2016-07-19,Sensitivity of the Fe K-alpha Compton shoulder to the geometry and variability of the X-ray illumination of cosmic objects,"In an X-ray reflection spectrum, a tail-like spectral feature generated via
Compton down-scattering, known as a Compton shoulder (CS), appears at the
low-energy side of the iron K$\alpha$ line. Despite its great diagnostic
potential, its use as a spectral probe of the reflector has been seriously
limited due to observational difficulties and modelling complexities. We
revisit the basic nature of the CS by systematic investigation into its
dependence on spatial and temporal parameters. The calculations are performed
by Monte-Carlo simulations for sphere and slab geometries. The dependence is
obtained in a two-dimensional space of column density and metal abundance,
demonstrating that the CS solves parameter degeneration between them which was
seen in conventional spectral analysis using photoelectric absorption and
fluorescence lines. Unlike the iron line, the CS does not suffer from any
observational dependence on the spectral hardness. The CS profile is highly
dependent on the inclination angle of the slab geometry unless the slab is
Compton-thick, and the time evolution of the CS is shown to be useful to
constrain temporal information on the source if the intrinsic radiation is
variable. We also discuss how atomic binding of the scattering electrons in
cold matter blurs the CS profile, finding that the effect is practically
similar to thermal broadening in a plasma with a moderate temperature of
$\sim$5 eV. Spectral diagnostics using the CS is demonstrated with grating data
of X-ray binary GX 301$-$2, and will be available in future with
high-resolution spectra of active galactic nuclei obtained by
microcalorimeters.",1607.05385v1
2016-07-19,Highly mobile carriers in orthorhombic phases of iron-based superconductors FeSe${}_{1-x}$S${}_{x}$,"The field and temperature dependencies of the longitudinal and Hall
resistivity have been measured for FeSe${}_{1-x}$S${}_{x}$ (x=0.04, 0.09 and
0.19) single crystals. The sample FeSe${}_{0.81}$S${}_{0.19}$ does not show a
transition to an orthorhombic phase and exhibits at low temperatures the
transport properties quite different from those of orthorhombic samples. The
behavior of FeSe${}_{0.81}$S${}_{0.19}$ is well described by the simple two
band model with comparable values of hole and electron mobility. In particular,
at low temperatures the transverse resistance shows a linear field dependence,
the magnetoresistance follow a quadratic field dependence and obeys to Kohler's
rule. In contrast, Kohler's rule is strongly violated for samples having an
orthorhombic low temperature structure. However, the transport properties of
the orthorhombic samples can be satisfactory described by the three band model
with the pair of almost equivalent to the tetragonal sample hole and electron
bands, supplemented with the highly mobile electron band which has two order
smaller carrier number. Therefore, the peculiarity of the low temperature
transport properties of the orthorhombic Fe(SeS) samples, as probably of many
other orthorhombic iron superconductors, is due to the presence of a small
number of highly mobile carriers which originate from the local regions of the
Fermi surface, presumably, nearby the Van Hove singularity points.",1607.05669v2
2016-08-02,Correlation of Fe-based Superconductivity and Electron-Phonon Coupling in an FeAs/Oxide Heterostructure,"Interfacial phonons between iron-based superconductors (FeSCs) and perovskite
substrates have received considerable attention due to the possibility of
enhancing preexisting superconductivity. Using scanning tunneling spectroscopy,
we studied the correlation between superconductivity and e-ph interaction with
interfacial-phonons in an iron-based superconductor Sr$_2$VO$_3$FeAs ($T_c
\approx$ 33 K) made of alternating FeSC and oxide layers. The quasiparticle
interference measurement over regions with systematically different average
superconducting gaps due to the e-ph coupling locally modulated by O vacancies
in VO$_2$ layer, and supporting self-consistent momentum-dependent Eliashberg
calculations provide a unique real-space evidence of the forward-scattering
interfacial phonon contribution to the total superconducting pairing.",1608.00886v4
2016-08-03,Structure of spin excitations in heavily electron-doped Li0.8Fe0.2ODFeSe superconductors,"Heavily electron-doped iron-selenide (HEDIS) high-transition-temperature
(high-$T_{\rm{c}}$) superconductors, which have no hole Fermi pockets, but have
a notably high $T_{\rm{c}}$, have challenged the prevailing $s$$_\pm$ pairing
scenario originally proposed for iron pnictides containing both electron and
hole pockets. The microscopic mechanism underlying the enhanced
superconductivity in HEDIS remains unclear. Here, we used neutron scattering to
study the spin excitations of the HEDIS material Li$_{0.8}$Fe$_{0.2}$ODFeSe
($T_{\rm{c}}$ = 41 K). Our data revealed nearly ring-shaped magnetic resonant
excitations surrounding ($\pi$, $\pi$) at $\sim$ 21 meV. As the energy
increased, the spin excitations assumed a diamond shape, and they dispersed
outward until the energy reached $\sim$ 60 meV and then inward at higher
energies. The observed energy-dependent momentum structure and twisted
dispersion of spin excitations near ($\pi$, $\pi$) are analogous to those of
hole-doped cuprates in several aspects, thus implying that such spin
excitations are essential for the remarkably high $T_{\rm{c}}$ in these
materials.",1608.01204v2
2016-08-04,Isotopic enrichment of forming planetary systems from supernova pollution,"Heating by short-lived radioisotopes (SLRs) such as aluminum-26 and iron-60
fundamentally shaped the thermal history and interior structure of Solar System
planetesimals during the early stages of planetary formation. The subsequent
thermo-mechanical evolution, such as internal differentiation or rapid volatile
degassing, yields important implications for the final structure, composition
and evolution of terrestrial planets. SLR-driven heating in the Solar System is
sensitive to the absolute abundance and homogeneity of SLRs within the
protoplanetary disk present during the condensation of the first solids. In
order to explain the diverse compositions found for extrasolar planets, it is
important to understand the distribution of SLRs in active planet formation
regions (star clusters) during their first few Myr of evolution. By
constraining the range of possible effects, we show how the imprint of SLRs can
be extrapolated to exoplanetary systems and derive statistical predictions for
the distribution of aluminum-26 and iron-60 based on N-body simulations of
typical to large clusters (1000-10000 stars) with a range of initial
conditions. We quantify the pollution of protoplanetary disks by supernova
ejecta and show that the likelihood of enrichment levels similar to or higher
than the Solar System can vary considerably, depending on the cluster
morphology. Furthermore, many enriched systems show an excess in radiogenic
heating compared to Solar System levels, which implies that the formation and
evolution of planetesimals could vary significantly depending on the birth
environment of their host stars.",1608.01435v1
2016-08-29,Universal Lower Limit on Vortex Creep in Superconductors,"Superconductors are excellent testbeds for studying vortices, topological
excitations that also appear in superfluids, liquid crystals, and Bose-Einstein
condensates. Vortex motion can be disruptive; it can cause phase transitions,
glitches in pulsars, and losses in superconducting microwave circuits, and it
limits the current carrying capacity of superconductors. Understanding vortex
dynamics is therefore of fundamental and technological importance, and the
competition between the effects of thermal energy and energy barriers defined
by material disorder is not completely understood. In particular, early
measurements of thermally-activated vortex motion (creep) in iron-based
superconductors unveiled fast rates (S) comparable to measurements of YBa2Cu3O7
(YBCO). This was puzzling because S is thought to somehow positively correlate
with the Ginzburg number (Gi), and Gi is orders of magnitude lower in most
iron-based superconductors than in YBCO. Here, we report very slow creep in
BaFe2(As0.67P0.33)2 films, and propose that there is a universal minimum
realizable (where Tc is the superconducting transition temperature) that has
been achieved in our films, few other materials, and violated by none. This
limitation provides new clues on how to design materials with slow creep and
helps elucidate open questions regarding the interplay between system-specific
length scales and vortex dynamics.",1608.08092v2
2016-09-01,Influence of interstitial Fe to the phase diagram of Fe$_{1+y}$Te$_{1-x}$Se$_x$ single crystals,"Superconductivity (SC) with the suppression of long-range antiferromagnetic
(AFM) order is observed in the parent compounds of both iron-based and cuprate
superconductors. The AFM wave vectors are bicollinear ($\pi$, 0) in the parent
compound FeTe different from the collinear AFM order ($\pi$, $\pi$) in most
iron pnictides. Study of the phase diagram of Fe$_{1+y}$Te$_{1-x}$Se$_x$ is the
most direct way to investigate the competition between bicollinear AFM and SC.
However, presence of interstitial Fe affects both magnetism and SC of
Fe$_{1+y}$Te$_{1-x}$Se$_x$, which hinders the establishment of the real phase
diagram. Here, we report the comparison of doping-temperature ($x$-$T$) phase
diagrams for Fe$_{1+y}$Te$_{1-x}$Se$_x$ (0 $\leq$ $x$ $\leq$ 0.43) single
crystals before and after removing interstitial Fe. Without interstitial Fe,
the AFM state survives only for $x$ $<$ 0.05, and bulk SC emerges from $x$ =
0.05, and does not coexist with the AFM state. The previously reported spin
glass state, and the coexistence of AFM and SC may be originated from the
effect of the interstitial Fe. The phase diagram of Fe$_{1+y}$Te$_{1-x}$Se$_x$
is found to be similar to the case of the ""1111"" system such as
LaFeAsO$_{1-x}$F$_x$, and is different from that of the ""122"" system.",1609.00105v1
2016-09-07,Efficiency of Planetesimal Ablation in Giant Planetary Envelopes,"Observations of exoplanetary spectra are leading to unprecedented constraints
on their atmospheric elemental abundances, particularly O/H, C/H, and C/O
ratios. Recent studies suggest that elemental ratios could provide important
constraints on formation and migration mechanisms of giant exoplanets. A
fundamental assumption in such studies is that the chemical composition of the
planetary envelope represents the sum-total of compositions of the accreted gas
and solids during the formation history of the planet. We investigate the
efficiency with which accreted planetesimals ablate in a giant planetary
envelope thereby contributing to its composition rather than sinking to the
core. From considerations of aerodynamic drag causing `frictional ablation' and
the envelope temperature structure causing `thermal ablation', we compute mass
ablations for impacting planetesimals of radii 30 m to 1 km for different
compositions (ice to iron) and a wide range of velocities and impact angles,
assuming spherical symmetry. Icy impactors are fully ablated in the outer
envelope for a wide range of parameters. Even for Fe impactors substantial
ablation occurs in the envelope for a wide range of sizes and velocities. For
example, iron impactors of sizes below ~0.5 km and velocities above ~30 km/s
are found to ablate by ~60-80% within the outer envelope at pressures below
10^3 bar due to frictional ablation alone. For deeper pressures (~10^7 bar),
substantial ablation happens over a wider range of parameters. Therefore, our
exploratory study suggests that atmospheric abundances of volatile elements in
giant planets reflect their accretion history during formation.",1609.02143v1
2016-09-18,Spintronics Detection of Interfacial Magnetic Switching in a Paramagnetic Tris(8-hydroxyquinoline)iron(III) Thin Film,"Organic semiconductors find increasing importance in spin transport devices
due to the modulation and control of their properties through chemical
synthetic versatility. The organic materials are used as interlayers between
two ferromagnet (FM) electrodes in organic spin valves (OSV), as well as for
magnetic spin manipulation of metal-organic complexes at the molecular level.
In the latter, specifically, the substrate-induced magnetic switching in a
paramagnetic molecule has been evoked extensively, but studied by delicate
surface spectroscopies. Here we present evidence of the substantial magnetic
switching in a nanosized thin film of the paramagnetic molecule,
tris(8-hydroxyquinoline)iron(III) (Feq3) deposited on a FM substrate, using the
magnetoresistance response of electrical spin-injection in an OSV structure,
and the inverse-spin-Hall effect induced by state-of-art pulsed microwave
spin-pumping. We show that interfacial spin control at the molecular level may
lead to a macroscopic organic spin transport device, thus, bridging the gap
between organic spintronics and molecular spintronics.",1609.05421v1
2016-10-04,Tomographic reflection modelling of quasi-periodic oscillations in the black hole binary H 1743-322,"Accreting stellar mass black holes (BHs) routinely exhibit Type-C
quasi-periodic oscillations (QPOs). These are often interpreted as
Lense-Thirring precession of the inner accretion flow, a relativistic effect
whereby the spin of the BH distorts the surrounding space-time, inducing nodal
precession. The best evidence for the precession model is the recent discovery,
using a long joint XMM-Newton and NuSTAR observation of H 1743-322, that the
centroid energy of the iron fluorescence line changes systematically with QPO
phase. This was interpreted as the inner flow illuminating different azimuths
of the accretion disc as it precesses, giving rise to a blue/red shifted iron
line when the approaching/receding disc material is illuminated. Here, we
develop a physical model for this interpretation, including a self-consistent
reflection continuum, and fit this to the same H 1743-322 data. We use an
analytic function to parameterise the asymmetric illumination pattern on the
disc surface that would result from inner flow precession, and find that the
data are well described if two bright patches rotate about the disc surface.
This model is preferred to alternatives considering an oscillating disc
ionisation parameter, disc inner radius and radial emissivity profile. We find
that the reflection fraction varies with QPO phase (3.5 sigma), adding to the
now formidable body of evidence that Type-C QPOs are a geometric effect. This
is the first example of tomographic QPO modelling, initiating a powerful new
technique that utilizes QPOs in order to map the dynamics of accreting material
close to the BH.",1610.00948v1
2016-09-29,Thin layered drawing media probed by THz time-domain spectroscopy,"Dry and wet drawing materials were investigated by THz time-domain
spectroscopy in transmission mode. Carbon-based and iron-gall inks have been
studied, some prepared following ancient recipes and others using current
synthetic materials; a commercial ink was studied as well. We measured the THz
signals on thin film of liquid inks deposited on polyethylene pellicles,
comparing the results with the thick pellets of dried inks blended with
polyethylene powder. This study required the implementation of a new
experimental method and data analysis procedure able to provide a reliable
extraction of the material transmission parameters from a structured sample
composed of thin layers, down to thickness of few tens of micrometers. THz
measurements on thin ink layers enabled the determination of both the
absorption and the refractive index in an absolute scale in the 0.1 - 3 THz
range, as well as the layer thickness. THz spectroscopic features of a paper
sheet dyed by one of the iron-gall inks were also investigated. Our results
showed that THz time-domain spectroscopy enables to discriminate the various
inks on different supports, including the application on paper, together with a
proper determination of the absorption coefficients and indices of refraction.",1610.01025v1
2016-10-31,Chromium analogues of Iron-based superconductors,"We theoretically investigate the $d^4$ (Cr$^{2+}$) compound BaCr$_2$As$_2$
and show that, despite non-negligible differences in the electronic structure,
its many-body physics mirrors that of BaFe$_2$As$_2$, which has instead a $d^6$
(Fe$^{2+}$) configuration. This reflects a symmetry of the electron correlation
effects around the half-filled $d^5$ Mott insulating state. The experimentally
known metallic antiferromagnetic phase is correctly modeled by dynamical
mean-field theory, and for realistic values of the interaction it shows a
moderate mass enhancement of order $\sim$2. This value decreases if the ordered
moment grows as a result of a stronger interaction. The antiferromagnetic phase
diagram for this $d^4$ shows similarities with that calculated for the $d^6$
systems. Correspondingly, in the paramagnetic phase the influence of the
half-filled Mott insulator shows up as a crossover from a weakly correlated to
an orbitally differentiated ""Hund's metal"" phase which reflects an analogous
phenomenon in $d^6$ iron compounds including a strong enhancement of the
compressibility in a zone just inside the frontier between the normal and the
Hund's metal. The experimental evidence and our theoretical description place
BaCr$_2$As$_2$ at interaction strength slightly below the crossover which
implies that negative pressures and/or electron doping (e.g. Cr $\rightarrow$
Mn,Fe or Ba $\rightarrow$ Sc,Y,La) might strongly enhance the compressibility,
thereby possibly inducing a pairing instability in this non-superconducting
compound.",1610.10054v1
2016-11-17,Deformation behaviour of body centered cubic iron nanopillars containing coherent twin boundaries,"Molecular dynamics simulations were performed to understand the role of twin
boundaries on deformation behaviour of body-centred cubic (BCC) iron (Fe)
nanopillars. The twin boundaries varying from one to five providing twin
boundary spacing in the range 8.5 - 2.8 nm were introduced perpendicular to the
loading direction. The simulation results indicated that the twin boundaries in
BCC Fe play a contrasting role during deformation under tensile and compressive
loadings. During tensile deformation, a large reduction in yield stress was
observed in twinned nanopillars compared to perfect nanopillar. However, the
yield stress exhibited only marginal variation with respect to twin boundary
spacing. On the contrary, a decrease in yield stress with increase in twin
boundary spacing was obtained during compressive deformation. This contrasting
behaviour originates from difference in operating mechanisms during yielding
and subsequent plastic deformation. It has been observed that the deformation
under tensile loading was dominated mainly by twin growth mechanism, due to
which the twin boundaries offers a negligible resistance to slip of twinning
partials. This is reflected in the negligible variation of yield stress as a
function of twin boundary spacing. On the other hand, the deformation was
dominated by nucleation and slip of full dislocations under compressive
loading. The twin boundaries offer a strong repulsive force on full
dislocations resulting in the yield stress dependence on twin boundary spacing.
Further, it has been observed that the curved twin boundary can acts as a
source for full dislocation. The occurrence of twin-twin interaction during
tensile deformation and dislocation-twin interaction during compressive
deformation were presented and discussed.",1611.05575v1
2016-12-16,Pressure-Induced Metallization in Iron-Based Ladder Compounds Ba$_{1-x}$Cs$_x$Fe$_2$Se$_3$,"Electrical resistivity measurements have been performed on the iron-based
ladder compounds Ba$_{1-x}$Cs$_x$Fe$_2$Se$_3$ ($x$ = 0, 0.25, 0.65, and 1)
under high pressure. A cubic anvil press was used up to 8.0 GPa, whereas
further higher pressure was applied using a diamond anvil cell up to 30.0 GPa.
Metallic behavior of the electrical conductivity was confirmed in the $x$ =
0.25 and 0.65 samples for pressures greater than 11.3 and 14.4 GPa,
respectively, with the low-temperature $\log T$ upturn being consistent with
weak localization of 2D electrons due to random potential. At pressures higher
than 23.8 GPa, three-dimensional Fermi-liquid-like behavior was observed in the
latter sample. No metallic conductivity was observed in the parent compounds
BaFe$_2$Se$_3$ ($x $ = 0) up to 30.0 GPa and CsFe$_2$Se$_3$ ($x$ = 1) up to
17.0 GPa. The present results indicate that the origins of the insulating
ground states in the parent and intermediate compounds are intrinsically
different; the former is a Mott insulator, whereas the latter is an Anderson
insulator owing to the random substitution of Cs for Ba.",1612.05394v1
2016-12-29,Molecular nucleation theory of dust formation in core-collapse supernovae applied to SN 1987A,"We model dust formation in the core collapse supernova explosion SN 1987A by
treating the gas-phase formation of dust grain nuclei as a chemical process. To
compute the synthesis of fourteen species of grains we integrate a
non-equilibrium network of nucleating and related chemical reactions and follow
the growth of the nuclei into grains via accretion and coagulation. The effects
of the radioactive cobalt, titanium, and sodium on the thermodynamics and
chemistry of the ejecta are taken into account. The grain temperature, which we
allow to differ from the gas temperature, affects the surface-tension-corrected
evaporation rate. We also account for He$^+$, Ne$^+$, Ar$^+$, and O weathering.
We combine our dust synthesis model with a crude prescription for anisotropic
radioactive nickel dredge-up into the core ejecta, the so-called `nickel
bubbles', to compute the total dust mass and molecular-species-specific grain
size distribution. The total mass varies between $0.41\,M_\odot$ and
$0.73\,M_\odot$, depending on the bubble shell density contrast. In the
decreasing order of abundance, the grain species produced are: magnesia,
silicon, forsterite, iron sulfide, carbon, silicon dioxide, alumina, and iron.
The combined grain size distribution is a power law $dN/da\propto a^{-4.39}$.
Early ejecta compaction by expanding radioactive nickel bubbles strongly
enhances dust synthesis. This underscores the need for improved understanding
of hydrodynamic transport and mixing over the entire pre-homologous expansion.",1612.09013v2
2017-01-11,Antiferromagnetic structure and electronic properties of BaCr2As2 and BaCrFeAs2,"The chromium arsenides BaCr2As2 and BaCrFeAs2 with ThCr2Si2 type structure
(space group I4/mmm; also adopted by '122' iron arsenide superconductors) have
been suggested as mother compounds for possible new superconductors. DFT-based
calculations of the electronic structure evidence metallic antiferromagnetic
ground states for both compounds. By powder neutron diffraction we confirm for
BaCr2As2 a robust ordering in the antiferromagnetic G-type structure at T_N =
580 K with mu_Cr = 1.9 mu_B at T = 2K. Anomalies in the lattice parameters
point to magneto-structural coupling effects. In BaCrFeAs2 the Cr and Fe atoms
randomly occupy the transition-metal site and G-type order is found below 265 K
with mu_Cr/Fe = 1.1 mu_B. 57Fe Moessbauer spectroscopy demonstrates that only a
small ordered moment is associated with the Fe atoms, in agreement with
electronic structure calculations with mu_Fe ~ 0. The temperature dependence of
the hyperfine field does not follow that of the total moments. Both compounds
are metallic but show large enhancements of the linear specific heat
coefficient gamma with respect to the band structure values. The metallic state
and the electrical transport in BaCrFeAs2 is dominated by the atomic disorder
of Cr and Fe and partial magnetic disorder of Fe. Our results indicate that
Neel-type order is unfavorable for the Fe moments and thus it is destabilized
with increasing iron content.",1701.03127v1
2017-01-16,Comprehensive Timing and X-ray Spectral Analysis of GX 1+4,"We present analysis of RXTE--PCA observations of GX 1+4 between March 3, 2001
and January 31, 2003 together with the CGRO--BATSE X-ray flux and frequency
derivative time series between 1991 and 1999. From the timing analysis of
RXTE-PCA observations, we are able to phase connect pulse arrival times of the
source within two different time intervals and obtain corresponding timing
solutions. Using these pulse arrival times, we contribute to long term pulse
frequency history of the source. We look for episodic correlations and
anti-correlations between torque and X-ray luminosity using CGRO--BATSE X-ray
flux and frequency derivative time series and find that correlation state of GX
1+4 seems to change on $\sim$ 100-200 days long intervals. We estimate torque
noise of the source and observe flickering noise ($f^{-1}$). We achieve to
measure the longest observed timescale for a noise process among accretion
powered X-ray pulsars by extending the noise estimate for a time scale ranging
from 31 days to 44 years. Spectral analysis of individual RXTE-PCA observations
indicates a significant correlation between iron line flux and unabsorbed X-ray
flux. Pulse phase resolved spectra of the source indicate a broadening of iron
line complex at the bin corresponding to the pulse minimum.",1701.04328v2
2017-01-17,Phase diagram and neutron spin resonance of superconducting NaFe$_{1-x}$Cu$_x$As,"We use transport and neutron scattering to study the electronic phase diagram
and spin excitations of NaFe$_{1-x}$Cu$_x$As single crystals. Similar to Co-
and Ni-doped NaFeAs, a bulk superconducting phase appears near $x\approx2\%$
with the suppression of stripe-type magnetic order in NaFeAs. Upon further
increasing Cu concentration the system becomes insulating, culminating in an
antiferromagnetically ordered insulating phase near $x\approx 50\%$. Using
transport measurements, we demonstrate that the resistivity in
NaFe$_{1-x}$Cu$_x$As exhibits non-Fermi-liquid behavior near $x\approx1.8\%$.
Our inelastic neutron scattering experiments reveal a single neutron spin
resonance mode exhibiting weak dispersion along $c$-axis in
NaFe$_{0.98}$Cu$_{0.02}$As. The resonance is high in energy relative to the
superconducting transition temperature $T_{\rm c}$ but weak in intensity,
likely resulting from impurity effects. These results are similar to other iron
pnictides superconductors despite the superconducting phase in
NaFe$_{1-x}$Cu$_x$As is continuously connected to an antiferromagnetically
ordered insulating phase near $x\approx 50\%$ with significant electronic
correlations. Therefore, electron correlations is an important ingredient of
superconductivity in NaFe$_{1-x}$Cu$_x$As and other iron pnictides.",1701.04874v1
2017-01-20,"Tuning sizes, morphologies, and magnetic properties of mono- vs. multi-core iron oxide nanoparticles through control of added water in the polyol synthesis","The polyol route is a versatile and up-scalable method to produce large
batches of iron oxide nanoparticles with well-defined structure and magnetic
properties. Controlling parameters such as temperature and duration of
reaction, heating profile, nature of polyol solvent or of organometallic
precursors were reported in previous studies of literature, but none of them
described yet the crucial role of water in the forced hydrolysis pathway, whose
presence is mandatory for nanoparticle production. This communication
investigates the influence of the water amount and temperature at which it is
injected in the reflux system for either pure polyol or mixture with a
poly(hydroxy) amine. Distinct morphologies of nanoparticles were thereby
obtained, from ultra-ultra-small smooth spheres down to 4 nm in diameter to
large ones up to 37 nm in diameter. Nanoflowers were also synthesized, which
are well-defined multi-core assemblies with narrow grain size dispersity. A
diverse and large library of samples was obtained by playing on the nature of
solvents and amount of water traces while keeping all the other parameters
fixed. The varied morphologies lead to magnetic nanoparticles well-fitting to
required applications among magnetic hyperthermia and MRI contrast agent, or
both.",1701.05858v3
2017-01-28,Deep Recurrent Neural Network for Protein Function Prediction from Sequence,"As high-throughput biological sequencing becomes faster and cheaper, the need
to extract useful information from sequencing becomes ever more paramount,
often limited by low-throughput experimental characterizations. For proteins,
accurate prediction of their functions directly from their primary amino-acid
sequences has been a long standing challenge. Here, machine learning using
artificial recurrent neural networks (RNN) was applied towards classification
of protein function directly from primary sequence without sequence alignment,
heuristic scoring or feature engineering. The RNN models containing
long-short-term-memory (LSTM) units trained on public, annotated datasets from
UniProt achieved high performance for in-class prediction of four important
protein functions tested, particularly compared to other machine learning
algorithms using sequence-derived protein features. RNN models were used also
for out-of-class predictions of phylogenetically distinct protein families with
similar functions, including proteins of the CRISPR-associated nuclease,
ferritin-like iron storage and cytochrome P450 families. Applying the trained
RNN models on the partially unannotated UniRef100 database predicted not only
candidates validated by existing annotations but also currently unannotated
sequences. Some RNN predictions for the ferritin-like iron sequestering
function were experimentally validated, even though their sequences differ
significantly from known, characterized proteins and from each other and cannot
be easily predicted using popular bioinformatics methods. As sequencing and
experimental characterization data increases rapidly, the machine-learning
approach based on RNN could be useful for discovery and prediction of
homologues for a wide range of protein functions.",1701.08318v1
2017-02-28,Neutrino Emission from Supernovae,"Supernovae are the most powerful cosmic sources of MeV neutrinos. These
elementary particles play a crucial role when the evolution of a massive star
is terminated by the collapse of its core to a neutron star or a black hole and
the star explodes as supernova. The release of electron neutrinos, which are
abundantly produced by electron captures, accelerates the catastrophic infall
and causes a gradual neutronization of the stellar plasma by converting protons
to neutrons as dominant constituents of neutron star matter. The emission of
neutrinos and antineutrinos of all flavors carries away the gravitational
binding energy of the compact remnant and drives its evolution from the hot
initial to the cold final state. The absorption of electron neutrinos and
antineutrinos in the surroundings of the newly formed neutron star can power
the supernova explosion and determines the conditions in the innermost
supernova ejecta, making them an interesting site for the nucleosynthesis of
iron-group elements and trans-iron nuclei. In this Chapter the basic neutrino
physics in supernova cores and nascent neutron stars will be discussed. This
includes the most relevant neutrino production, absorption, and scattering
processes, elementary aspects of neutrino transport in dense environments, the
characteristic neutrino emission phases with their typical signal features, and
the perspectives connected to a measurement of the neutrino signal from a
future galactic supernova.",1702.08713v1
2017-03-24,Role of the orbital degree of freedom in iron-based superconductors,"Almost a decade has passed since the serendipitous discovery of the
iron-based high temperature superconductors (FeSCs) in 2008. The question of
how much similarity the FeSCs have with the copper oxide high temperature
superconductors emerged since the initial discovery of long-range
antiferromagnetism in the FeSCs in proximity to superconductivity. Despite the
great resemblance in their phase diagrams, there exist important disparities
between FeSCs and cuprates that need to be considered in order to paint a full
picture of these two families of high temperature superconductors. One of the
key differences lies in the multi-orbital multi-band nature of FeSCs, in
contrast to the effective single-band model for cuprates. Due to the complexity
of multi-orbital band structures, the orbital degree of freedom is often
neglected in formulating the theoretical models for FeSCs. On the experimental
side, systematic studies of the orbital related phenomena in FeSCs have been
largely lacking. In this review, we summarize angle-resolved photoemission
spectroscopy (ARPES) measurements across various FeSC families in literature,
focusing on the systematic trend of orbital dependent electron correlations and
the role of different Fe 3d orbitals in driving the nematic transition, the
spin-density-wave transition, and implications for superconductivity.",1703.08622v2
2017-07-04,Blocking metal accretion onto population III stars by stellar wind,"Low-mass population III (PopIII) stars of $\lesssim 0.8 M_{\odot}$ could
survive up until the present. Non-detection of low-mass PopIII stars in our
Galaxy has already put a stringent constraint on the initial mass function
(IMF) of PopIII stars, suggesting that PopIII stars have a top-heavy IMF. On
the other hand, some claims that the lack of such stars stems from metal
enrichment of their surface by accretion of heavy elements from interstellar
medium (ISM). We investigate effects of the stellar wind on the metal accretion
onto low-mass PopIII stars because accretion of the local ISM onto the Sun is
prevented by the solar wind even for neutrals. The stellar wind and radiation
of low-mass PopIII stars are modeled based on knowledge of nearby low-mass
stellar systems including our Sun. We find that low-mass PopIII stars traveling
across the Galaxy forms the stellar magnetosphere in most of their life. Once
the magnetosphere is formed, most of neutral interstellar particles are
photoionized before reaching to the stellar surface and are blown away by the
wind. Especially, the accretion abundance of iron will be reduced by a factor
of $< 10^{-12}$ compared with Bondi-Hoyle-Lyttleton accretion. The metal
accretion can enhance iron abundance [Fe/H] only up to $\sim -14$. This
demonstrates that low-mass PopIII stars remain pristine and will be found as
metal free stars and that further searches for them are valuable to constrain
the IMF of PopIII stars.",1707.00989v1
2017-07-05,Interactions between Coherent Twin Boundaries and Phase Transition of Iron under Dynamic Loading and Unloading,"Under high pressures, phase transition, as well as deformation twins, are
constantly reported in many BCC metals, whose interactions are of fundamental
importance to understand strengthen mechanism of these metals under extreme
conditions. However, the interactions between twins and phase transition in BCC
metals are remain largely unexplored. In this work, interactions between
coherent twin boundaries and $\alpha \to \epsilon$ phase transition of iron are
investigated using both non- equilibrium molecular dynamics simulations and
nudge elastic band method. Mechanisms of both twin-assisted phase transition
and reverse phase transition are studied and orientation relationships between
BCC and HCP phase are found to be <11-1>BCC || <-12-10>HCP and <1-10>BCC ||
<0001>HCP for both cases. The twin boundary corresponds to after the phase
transition. It is amazing that the reverse transition seems to be able to
""memory"" and recover the initial BCC twins. The memory would partly loss when
plastic slips take place in the HCP phase before the reverse transition. In the
recovered initial BCC twins, three major twin spacing are observed, which are
well explained in terms of energy barriers of the transition from HCP phase to
BCC twin. Besides, variant selection rule of the twin assisted phase transition
is also discussed. The results of present work could be expected to give some
clues for producing ultra-fine grain structure in materials exhibiting
martensitic phase transition.",1707.01276v1
2017-07-06,Phonon Spectra in the Parent Superconducting Iron-tuned Telluride Fe$_{1+x}$Te from Inelastic Neutron Scattering and Ab Initio Calculations,"We report inelastic neutron scattering measurements of phonon spectra in the
parent superconductor iron-tuned chalcogenide Fe$_{1+x}$Te, for two different x
contents (x $\leq$ 0.11), using neutron time-of-flight technique. Thermal
neutron spectroscopy allowed to collect the low-temperature Stokes spectra over
an extended Q-range, at 2, 40 and 120K - hence covering both the magnetic
monoclinic and the paramagnetic tetragonal phases. Whereas cold-neutrons
allowed to measure high-resolution anti-Stokes spectra at 140, 220 and 300K,
thus covering the tetragonal phase. Our results evidence a spin-phonon coupling
behaviour towards the observed noticeable temperature-dependent change of the
Stokes spectra across the transition temperatures. On the other hand, the
anti-Stokes spectra reveal a pronounced hardening of the low-energy, acoustic
region, of the phonon spectrum, upon heating, indicating a strong anharmonicity
and a subtle dependence of phonons on structural evolution within the
tetragonal phase. Experimental results are accompanied by ab initio
calculations of phonon spectra of the tetragonal stoichiometric phase for a
comparison with the high-resolution anti-Stokes spectra. Calculations included
different density functional methods. Spin polarization and van der Waals
interaction, were either considered or neglected, individually or
concomitantly, in order to study their respective effect on lattice dynamics
description. Our results suggest that including van der Waals interaction has
only a slight effect on phonon dynamics, however, phonon spectra are better
described when spin polarization is included, in a cooperative way with van der
Waals interactions.",1707.01970v2
2017-07-17,Coupling of structure to magnetic and superconducting orders in quasi-one-dimensional $\text{K}_2\text{Cr}_3\text{As}_3$,"Quasi-one-dimensional $A_2\text{Cr}_3\text{As}_3$ (with $A = \text{K, Cs,
Rb}$) is an intriguing new family of superconductors which exhibit many similar
features to the cuprate and iron-based unconventional superconductor families.
Yet in contrast to these systems, no charge or magnetic ordering has been
observed which could provide the electronic correlations presumed necessary for
an unconventional superconducting pairing mechanism - an absence which defies
predictions of first principles models. We report the results of neutron
scattering experiments on polycrystalline $\text{K}_2\text{Cr}_3\text{As}_3$
$(T_c \sim 7\text{K})$ which probed the low temperature dynamics near $T_c$ .
Neutron diffraction data evidence a strong response of the nuclear lattice to
the onset of superconductivity while inelastic scattering reveals a highly
dispersive column of intensity at the commensurate wavevector $q =
(00\frac{1}{2})$ which loses intensity beneath $T_c$ - indicative of
short-range magnetic fluctuations. Using linear spin-wave theory we model the
observed scattering and suggest a possible structure to the short-range
magnetic order. These observations suggest that
$\text{K}_2\text{Cr}_3\text{As}_3$ is in close proximity to a magnetic
instability and that the incipient magnetic order both couples strongly to the
lattice and competes with superconductivity - in direct analogy with the
iron-based superconductors.",1707.05286v1
2017-07-20,Nuclear absorption and emission in the AGN merger NGC 6240: the hard X-ray view,"We present the analysis of four NuSTAR observations of the luminous infrared
galaxy merger NGC 6240, hosting a close pair of highly obscured active galactic
nuclei (AGN). Over a period of about two years, the source exhibits hard X-ray
variability of the order of 20 per cent, peaking around 20 keV. When the two
AGN are resolved with Chandra, column densities in the range $N_\textrm{H} \sim
1-2 \times 10^{24}$ cm$^{-2}$ are estimated for both of them. The exact values
are hard to determine, as they appear to depend on aspects that are sometimes
overlooked in Compton-thick objects, such as the covering factor of the
absorber, iron abundance, and the contamination in the Fe-K band from
foreground hot-gas emission. Nearly spherical covering and slightly subsolar
iron abundance are preferred in this case. While the southern nucleus is
suggested to be intrinsically more powerful, as also implied by the mid-IR and
2-10 keV brightness ratios, solutions involving a similar X-ray luminosity of
the two AGN cannot be ruled out. The observed variability is rather limited
compared to the one revealed by the Swift/BAT light curve, and it can be fully
explained by changes in the continuum flux from the two AGN, without requiring
significant column density variations. NGC 6240 is hereby confirmed to
represent a unique opportunity to investigate the X-ray (and broad-band)
properties of massive galaxy mergers, which were much more frequent in the
early Universe.",1707.07613v1
2017-08-18,Superconductivity across Lifshitz transition and anomalous insulating state in surface K-dosed (Li0.8Fe0.2OH)FeSe,"In the iron-based superconductors, understanding the relation between
superconductivity and electronic structure upon doping is crucial for exploring
the pairing mechanism. Recently it was found that in iron selenide (FeSe),
enhanced superconductivity (Tc over 40K) can be achieved via electron doping,
with the Fermi surface only comprising M-centered electron pockets. Here by
utilizing surface potassium dosing, scanning tunneling microscopy/spectroscopy
(STM/STS) and angle-resolved photoemission spectroscopy (ARPES), we studied the
electronic structure and superconductivity of (Li0.8Fe0.2OH)FeSe in the deep
electron-doped regime. We find that a {\Gamma}-centered electron band, which
originally lies above the Fermi level (EF), can be continuously tuned to cross
EF and contribute a new electron pocket at {\Gamma}. When this Lifshitz
transition occurs, the superconductivity in the M-centered electron pocket is
slightly suppressed; while a possible superconducting gap with small size (up
to ~5 meV) and a dome-like doping dependence is observed on the new {\Gamma}
electron pocket. Upon further K dosing, the system eventually evolves into an
insulating state. Our findings provide new clues to understand
superconductivity versus Fermi surface topology and the correlation effect in
FeSe-based superconductors.",1708.05635v1
2017-09-01,"Two-dimensional Massless Dirac Fermions in Antiferromagnetic AFe2As2 (A = Ba, Sr)","We report infrared studies of AFe$_{2}$As$_{2}$ (A = Ba, Sr), two
representative parent compounds of iron-arsenide superconductors, at magnetic
fields (B) up to 17.5 T. Optical transitions between Landau levels (LLs) were
observed in the antiferromagnetic states of these two parent compounds. Our
observation of a $\sqrt{B}$ dependence of the LL transition energies, the
zero-energy intercepts at B = 0 T under the linear extrapolations of the
transition energies and the energy ratio ($\sim$ 2.4) between the observed LL
transitions, combined with the linear band dispersions in two-dimensional (2D)
momentum space obtained by theoretical calculations, demonstrates the existence
of massless Dirac fermions in antiferromagnetic BaFe$_{2}$As$_{2}$. More
importantly, the observed dominance of the zeroth-LL-related absorption
features and the calculated bands with extremely weak dispersions along the
momentum direction $k_{z}$ indicate that massless Dirac fermions in
BaFe$_{2}$As$_{2}$ are 2D. Furthermore, we find that the total substitution of
the barium atoms in BaFe$_{2}$As$_{2}$ by strontium atoms not only maintains 2D
massless Dirac fermions in this system, but also enhances their Fermi velocity,
which supports that the Dirac points in iron-arsenide parent compounds are
topologically protected.",1709.00203v1
2017-09-08,Machine learning modeling of superconducting critical temperature,"Superconductivity has been the focus of enormous research effort since its
discovery more than a century ago. Yet, some features of this unique phenomenon
remain poorly understood; prime among these is the connection between
superconductivity and chemical/structural properties of materials. To bridge
the gap, several machine learning schemes are developed herein to model the
critical temperatures ($T_{\mathrm{c}}$) of the 12,000+ known superconductors
available via the SuperCon database. Materials are first divided into two
classes based on their $T_{\mathrm{c}}$ values, above and below 10 K, and a
classification model predicting this label is trained. The model uses
coarse-grained features based only on the chemical compositions. It shows
strong predictive power, with out-of-sample accuracy of about 92%. Separate
regression models are developed to predict the values of $T_{\mathrm{c}}$ for
cuprate, iron-based, and ""low-$T_{\mathrm{c}}$"" compounds. These models also
demonstrate good performance, with learned predictors offering potential
insights into the mechanisms behind superconductivity in different families of
materials. To improve the accuracy and interpretability of these models, new
features are incorporated using materials data from the AFLOW Online
Repositories. Finally, the classification and regression models are combined
into a single integrated pipeline and employed to search the entire Inorganic
Crystallographic Structure Database (ICSD) for potential new superconductors.
We identify more than 30 non-cuprate and non-iron-based oxides as candidate
materials.",1709.02727v2
2017-09-15,"Angular dependence of vortex instability in a layered superconductor: the case study of Fe(Se,Te) material","Anisotropy effects on flux pinning and flux flow are strongly effective in
cuprate as well as iron-based superconductors due to their intrinsically
layered crystallographic structure. However $\textrm{Fe(Se,Te)}$ thin films
grown on $\textrm{CaF}_2$ substrate result less anisotropic with respect to all
the other iron based superconductors. We present the first study on the angular
dependence of the flux flow instability, which occurs in the flux flow regime
as a current driven transition to the normal state at the instability point
($I^*$,$V^*$) in the current-voltage characteristics. The voltage jumps are
systematically investigated as a function of the temperature, the external
magnetic field, and the angle between the field and the $\textrm{Fe(Se,Te)}$
film. The scaling procedure based on the anisotropic Ginzburg-Landau approach
is successfully applied to the observed angular dependence of the critical
voltage $V^*$. Anyway, we find out that $\textrm{Fe(Se,Te)}$ represents the
case study of a layered material characterized by a weak anisotropy of its
static superconducting properties, but with an increased anisotropy in its
vortex dynamics due to the predominant perpendicular component of the external
applied magnetic field. Indeed, $I^*$ shows less sensitivity to angle
variations, thus being promising for high field applications.",1709.05089v3
2017-10-04,Surface abundance and the hunt for stratification in chemically peculiar hot subdwarfs: PG 0909+276 and UVO 0512-08,"Edelmann (2003) identified two chemically peculiar hot subdwarfs, PG 0909+276
and UVO 0512-08, as having very high overabundances of iron-group elements. We
obtained high-resolution ultraviolet spectroscopy in order to measure
abundances of species not observable in the optical, and to seek evidence for
chemical stratification in the photosphere. Abundances were measured in three
wavelength regions; the optical 3900\AA-6900\AA\ range was re-analysed to
confirm consistency with Edelmann. Ultraviolet spectra were obtained with the
Space Telescope Imaging Spectrograph (STIS) on the Hubble Space Telescope
(HST), covering the far-UV (1140\AA-1740\AA) and the near-UV (1740\AA-2500\AA).
We computed a grid of theoretical LTE spectra to find basic parameters
(effective temperatures, surface gravity, surface hydrogen and helium
fractions). We measured abundances using a spectral-synthesis approach in each
wavelength range. We confirm that several iron-group metals are highly
enriched, including cobalt, copper and zinc, relative to typical sdB stars. We
detect gallium, germanium, tin, and lead, similar to analysis of ultraviolet
spectra of some other sdB stars. Our results confirm that PG 0909+276 and UVO
0512-08 exhibit peculiarities which make them distinct from both the normal
H-rich sdB and intermediate He-rich sdB stars. The process which leads to this
particular composition has still to be identified.",1710.01663v1
2017-10-18,Using MRI Cell Tracking to Monitor Immune Cell Recruitment in Response to a Peptide-Based Cancer Vaccine,"Purpose: MRI cell tracking can be used to monitor immune cells involved in
the immunotherapy response, providing insight into the mechanism of action,
temporal progression of tumour growth and individual potency of therapies. To
evaluate whether MRI could be used to track immune cell populations in response
to immunotherapy, CD8+ cytotoxic T cells (CTLs), CD4+CD25+FoxP3+ regulatory T
cells (Tregs) and myeloid derived suppressor cells (MDSCs) were labelled with
superparamagnetic iron oxide (SPIO) particles.
  Methods: SPIO-labelled cells were injected into mice (one cell type/mouse)
implanted with an HPV-based cervical cancer model. Half of these mice were also
vaccinated with DepoVaxTM, a lipid-based vaccine platform that was developed to
enhance the potency of peptide-based vaccines.
  Results: MRI visualization of CTLs, Tregs and MDSCs was apparent 24 hours
post-injection, with hypointensities due to iron labelled cells clearing
approximately 72 hours post-injection. Vaccination resulted in increased
recruitment of CTLs and decreased recruitment of MDSCs and Tregs to the tumour.
We also found that MDSC and Treg recruitment was positively correlated with
final tumour volume.
  Conclusion: This type of analysis can be used to non-invasively study changes
in immune cell recruitment in individual mice over time, potentially allowing
improved application and combination of immunotherapies.",1710.06817v1
2017-11-02,Constraining planet structure and composition from stellar chemistry: trends in different stellar populations,"The chemical composition of stars that have orbiting planets provides
important clues about the frequency, architecture, and composition of exoplanet
systems. We explore the possibility that stars from different galactic
populations that have different intrinsic abundance ratios may produce planets
with a different overall composition. We compiled abundances for Fe, O, C, Mg,
and Si in a large sample of solar neighbourhood stars that belong to different
galactic populations. We then used a simple stoichiometric model to predict the
expected iron-to-silicate mass fraction and water mass fraction of the planet
building blocks, as well as the summed mass percentage of all heavy elements in
the disc. Assuming that overall the chemical composition of the planet building
blocks will be reflected in the composition of the formed planets, we show that
according to our model, discs around stars from different galactic populations,
as well as around stars from different regions in the Galaxy, are expected to
form rocky planets with significantly different iron-to-silicate mass
fractions. The available water mass fraction also changes significantly from
one galactic population to another. The results may be used to set constraints
for models of planet formation and chemical composition. Furthermore, the
results may have impact on our understanding of the frequency of planets in the
Galaxy, as well as on the existence of conditions for habitability.",1711.00777v1
2017-11-08,"Matrix-assisted fabrication and exotic charge mobility of (Li,Fe)OHFeSe superconductor films","Superconducting (Li1-xFex)OHFe1-ySe films are attractive for both the basic
research and practical application. However, the conventional vapor deposition
techniques are not applicable in synthesizing the films of such a complex
system. So no intrinsic charge transport measurements on the films are
available so far to reveal the nature of charge carriers, which is fundamental
to understanding the iron-based superconductivity mechanism. Herein we report a
soft chemical film technique (matrix-assisted hydrothermal epitaxial growth),
by which we have succeeded in growing a series of (Li1-xFex)OHFe1-ySe films
covering the whole superconducting regime, with the superconducting transition
temperature (Tc) from 4 K up to 42 K. This film technique opens up a new way
for fabricating other complex functional materials as well. Furthermore, our
systematic transport investigation on the film samples indicates that both the
electron and hole carriers contribute to the charge transport, with the
scattering rates deviating from the Fermi liquid. We find that the
superconductivity occurs upon the electron and hole mobility becoming
divergent. And in the high Tc samples, the electron carriers are found much
more mobile than the holes, a feature distinct from the low Tc samples. Hence,
our transport results provide key insights into the underlying physics for
iron-based high-Tc superconductivity.",1711.02920v1
2017-11-17,Nematic superconducting state in iron pnictide superconductors,"Nematic order often breaks the tetragonal symmetry of iron-based
superconductors. It arises from regular structural transition or electronic
instability in the normal phase. Here, we report the observation of a nematic
superconducting state, by measuring the angular dependence of the in-plane and
out-of-plane magnetoresistivity of Ba0.5K0.5Fe2As2 single crystals. We find
large twofold oscillations in the vicinity of the superconducting transition,
when the direction of applied magnetic field is rotated within the basal plane.
To avoid the influences from sample geometry or current flow direction, the
sample was designed as Corbino-shape for in-plane and mesa-shape for
out-of-plane measurements. Theoretical analysis shows that the nematic
superconductivity arises from the weak mixture of the quasi-degenerate s-wave
and d-wave components of the superconducting condensate, most probably induced
by a weak anisotropy of stresses inherent to single crystals.",1711.06383v1
2017-11-17,"Frustrated magnetism in tetragonal CoSe, analogue to superconducting FeSe","Recently synthesized metastable tetragonal CoSe, isostructural to the FeSe
superconductor, offers a new avenue for investigating systems in close
proximity to the iron-based superconductors. We present magnetic and transport
property measurements on powders and single crystals of CoSe. High field
magnetic susceptibility measurements indicate a suppression of the previously
reported 10 K ferromagnetic transition with the magnetic susceptibility
exhibiting time-dependence below the proposed transition. Dynamic scaling
analysis of the time-dependence yields a critical relaxation time of $\tau^{*}
= 0.064 \pm 0.008 $ s which in turn yields an activation energy of $E_{a}^{*}$
= 14.84 $\pm$ 0.59 K and an ideal glass temperature $T_{0}^{*}$ = 8.91 $\pm$
0.09 K from Vogel-Fulcher analysis. No transition is observed in resistivity
and specific heat measurements, but both measurements indicate that CoSe is
metallic. These results are interpreted on the basis of CoSe exhibiting
frustrated magnetic ordering arising from competing magnetic interactions.
Arrott analysis of single crystal magnetic susceptibility has indicated that
the magnetic moments lie in the $ab$-plane so frustration may arise from
intralayer magnetic fluctuations as well as interlayer coupling. The results
have implications for understanding the superconductivity in the iron
chalcogenide systems as well as utilizing CoSe as a host for chemical and
physical manipulation to tune and explore emergent phenomena within an
expanding new class of transition metal chalcogenides.",1711.06725v2
2017-11-21,The X-ray footprint of the CircumNuclear Disk,"We studied the central regions of the Galactic Centre to determine if the
CircumNuclear Disk (CND) acts as an absorber or a barrier for the central
X-rays diffuse emission. After reprocessing 4.6Ms of Chandra observations, we
were able to detect, for the first time, a depression in the X-ray luminosity
of the diffuse emission whose size and location correspond to those of the CND.
We extracted the X-ray spectra for various regions inside the CND footprint as
well as for the region where the footprint is observed and for a region located
outside the footprint. We simultaneously fitted these spectra as an optically
thin plasma whose absorption by the interstellar medium and by the local plasma
were fitted independently using the MCMC method. The hydrogen column density of
the ISM is 7.5x10^22 cm^-2. The X-ray diffuse emission inside the CND footprint
is formed by a 2T plasma of 1 and 4keV with slightly super-solar abundances
except for the iron and carbon which are sub-solar. The plasma from the CND, in
turn, is better described by a 1T model with abundances and local hydrogen
column density which are very different to those of the innermost regions. The
large iron abundance in this region confirms that the CND is dominated by the
shock-heated ejecta of the Sgr A East supernova remnant. We deduced that the
CND rather acts as a barrier for the Galactic Centre plasma and that the plasma
located outside the CND may correspond to the collimated outflow possibly
created by Sgr A* or the interaction between the wind of massive stars and the
mini-spiral material.",1711.07841v1
2017-11-28,SFXTs versus classical SgXBs: Does the difference lie in the companion wind?,"We present a comparative study of stellar winds in classical supergiant high
mass X-ray binaries (SgXBs) and supergiant fast X-ray transients (SFXTs) based
on the analysis of publicly available out-of-eclipse observations performed
with Suzaku and XMM-Newton. Our data-set includes 55 observations of classical
SgXBs and 21 observations of SFXTs. We found that classical SgXBs are
characterized by a systematically higher absorption and luminosity compared to
the SFXTs, confirming the results of previous works in the literature.
Additionally, we show that the equivalent width of the fluorescence K{\alpha}
iron line in the classical SgXBs is significantly larger than that of the SFXTs
(outside X-ray eclipses). Based on our current understanding of the physics of
accretion in these systems, we conclude that the most likely explanation of
these differences is to be ascribed to the presence of mechanisms inhibiting
accretion for most of the time in the SFXTs and leading to a much less
efficient photoionization of the stellar wind compared to classical SgXBs.We do
not find evidence for the previously reported anti-correlation between the
equivalent width of the fluorescence iron line and the luminosity of SgXBs.",1711.10510v3
2017-12-04,Chemical fingerprints of hot Jupiter planet formation,"The current paradigm to explain the presence of Jupiters with small orbital
periods (P $<$ 10 days; hot Jupiters) that involves their formation beyond the
snow line following inward migration, has been challenged by recent works that
explored the possibility of in situ formation. We aim to test whether stars
harbouring hot Jupiters and stars with more distant gas-giant planets show any
chemical peculiarity that could be related to different formation processes.
Our results show that stars with hot Jupiters have higher metallicities than
stars with cool distant gas-giant planets in the metallicity range +0.00/+0.20
dex. The data also shows a tendency of stars with cool Jupiters to show larger
abundances of $\alpha$ elements. No abundance differences between stars with
cool and hot Jupiters are found when considering iron peak, volatile elements
or the C/O, and Mg/Si ratios. The corresponding $p$-values from the statistical
tests comparing the cumulative distributions of cool and hot planet hosts are
0.20, $<$ 0.01, 0.81, and 0.16 for metallicity, $\alpha$, iron-peak, and
volatile elements, respectively. We confirm previous works suggesting that more
distant planets show higher planetary masses as well as larger eccentricities.
We note differences in age and spectral type between the hot and cool planet
hosts samples that might affect the abundance comparison. The differences in
the distribution of planetary mass, period, eccentricity, and stellar host
metallicity suggest a different formation mechanism for hot and cool Jupiters.
The slightly larger $\alpha$ abundances found in stars harbouring cool Jupiters
might compensate their lower metallicities allowing the formation of gas-giant
planets.",1712.01035v2
2017-12-04,Protonation induced high-Tc phases in iron-based superconductors evidenced by NMR and magnetization measurements,"Chemical substitution during growth is a well-established method to
manipulate electronic states of quantum materials, and leads to rich spectra of
phase diagrams in cuprate and iron-based superconductors. Here we report a
novel and generic strategy to achieve nonvolatile electron doping in series of
(i.e. 11 and 122 structures) Fe-based superconductors by ionic liquid gating
induced protonation at room temperature. Accumulation of protons in bulk
compounds induces superconductivity in the parent compounds, and enhances the
Tc largely in some superconducting ones. Furthermore, the existence of proton
in the lattice enables the first proton nuclear magnetic resonance (NMR) study
to probe directly superconductivity. Using FeS as a model system, our NMR study
reveals an emergent high-Tc phase with no coherence peak which is hard to
measure by NMR with other isotopes. This novel electric-field-induced proton
evolution opens up an avenue for manipulation of competing electronic states
(e.g. Mott insulators), and may provide an innovative way for a broad
perspective of NMR measurements with greatly enhanced detecting resolution.",1712.01191v4
2017-12-06,Constraining the final fates of massive stars by oxygen and iron enrichment history in the Galaxy,"Recent observational studies of core-collapse supernovae suggest only stars
with zero-age main sequence masses smaller than $16$-$18\ M_\odot$ explode when
they are red supergiants, producing type IIP supernovae. This may imply that
more massive stars produce other types of supernovae or they simply collapse to
black holes without giving rise to bright supernovae. This failed supernova
hypothesis can lead to significantly inefficient oxygen production because
oxygen abundantly produced in inner layers of massive stars with zero-age main
sequence masses around $20$-$30\ M_\odot$ might not be ejected into the
surrounding interstellar space. We first assume an unspecified population of
oxygen injection events related to massive stars and obtain a model-independent
constraint on how much oxygen should be released in a single event and how
frequently such events should happen. We further carry out one-box galactic
chemical enrichment calculations with different mass ranges of massive stars
exploding as core-collapse supernovae. Our results suggest that the model
assuming that all massive stars with $9$-$100\ M_\odot$ explode as
core-collapse supernovae is still most appropriate in explaining the solar
abundances of oxygen and iron and their enrichment history in the Galaxy. The
oxygen mass in the Galaxy is not explained when assuming that only massive
stars with zero-age main sequence masses in the range of 9-17 $M_\odot$,
contribute to the galactic oxygen enrichment. This finding implies that a good
fraction of stars more massive than $17M_\odot$ should eject their oxygen
layers in either supernova explosions or some other mass loss processes.",1712.02013v1
2017-12-06,Interaction of the accretion flows in corona and disk near the black hole in AGN,"Accretion flows toward black holes can be of a quite different nature,
described as an optically thick cool gas flow in a disk for high accretion
rates or as a hot coronal optically thin gas flow for low accretion rates,
possibly affected by outflowing gas. The detection of broad iron emission lines
in active galactic nuclei (AGN) indicates the coexistence of corona and disk.
The appearance and relative strength of such flows essentially depends on their
interaction. Liu et al. suggested that condensation of gas from the corona to
the disk allows to understand accretion flows of comparable strength of
emission. Matter inflow due to gravitational capture of gas is important for
the condensation process. We discuss observational features predicted by the
model. Data from simultaneous observations of AGN with {\it {Swift's}} X-ray
and UV-optical telescopes are compared with the theoretical predictions. The
frequent detection of broad iron K$\alpha$ emission lines and the dependence of
the emitted spectra on the Eddington ratio, described by the values of the
photon index $\Gamma$ and the two-point spectral index $\alpha_{\rm{ox}}$ are
in approximate agreement with the predictions of the condensation model; the
latter, however, with a large scatter. The model further yields a coronal
emission concentrated in a narrow inner region as is also deduced from the
analysis of emissivity profiles. The accretion flows in bright AGN could be
described by the accretion of stellar wind or interstellar medium and its
condensation into a thin disk.",1712.02031v1
2017-12-24,Search For Gravitational Redshifted Absorption Lines In LMXB Serpens X-1,"The equation of state for ultra-dense matter can be tested from observations
of the ratio of mass to radius of neutron stars. This could be measured
precisely from the redshift of a narrow line produced on the surface. X-rays
bursts have been intensively searched for such features, but so far without
detection. Here instead we search for redshifted lines in the persistent
emission, where the accretion flow dominates over the surface emission. We
discuss the requirements for narrow lines to be produced, and show that narrow
absorption lines from highly ionized iron can potentially be observable in
accreting low mass X-ray binaries (low B field) which have either low spin or
low inclination so that Doppler broadening is small. This selects Serpens X-1
as the only potential candidate persistent LMXB due to its low inclination.
Including surface models in the broad band accretion flow model predicts that
the absorption line from He-like iron at 6.7 keV should be redshifted to $\sim$
5.1 - 5.7 keV (10 - 15 km for $1.4\mathrm{M_\odot}$) and have an equivalent
width of 0.8 - 8.0 eV for surface temperatures of 7 - 10 $\times$ 10$^6$ K. We
use the high resolution Chandra grating data to give a firm upper limit of 2 -
3 eV for an absorption line at $\sim 5$ keV. We discuss possible reasons for
this lack of detection (the surface temperature and the geometry of the
boundary layer etc.). Future instruments with better sensitivity are required
in order to explore the existence of such features.",1712.08918v1
2018-01-09,"Diverse fluctuations and anisotropic Gr{\"" u}neisen parameter behavior in iron-based superconductor Ba(Fe$_{1-x}$Co$_x$)$_2$As$_2$ and their correlation with superconductivity","In this study, the temperature dependence of elastic constants $C_{11}$,
$C_{33}$, $C_{\rm E} = (C_{11}-C_{12})/2$, $C_{66}$ and $C_{44}$ of the
iron-based superconductor Ba(Fe$_{1-x}$Co$_{x}$)$_{2}$As$_{2}$ (0 $\leqq x
\leqq$ 0.245) have been measured. This system shows a large elastic softening
in $C_{66}$ towards low temperatures. In addition to $C_{66}$, which originates
from orthorhombic structural fluctuation, the samples near the optimal
concentration show remarkable structural fluctuation in $C_{11}$ and $C_{33}$
elastic modes, which correspond to $\Gamma_{1}$ (C4) symmetry. It suggests the
existence of diverse fluctuations in this system. Gr{\"" u}neisen parameters
were analyzed under some assumptions for structural and magnetic transition
temperatures. Results showed that the Gr{\"" u}neisen parameters for the
inter-plane strain are remarkably enhanced toward the QCP, while those for the
in-plane stress tend to turn down near the QCP. Gr{\"" u}neisen parameters for
the superconducting transition are anisotropic and shows remarkable
Co-concentration dependence, suggesting that the in-plane isotropic compression
and inter-layer elongation enhance the superconductivity. The correlation of
Gr{\"" u}neisen parameters between $T_{\rm S}$, $T_{\rm N}$ and $T_{\rm sc}$
shows $c$-axis elongation and its relevant role in the emergence of
superconductivity in this system.",1801.02791v1
2018-01-13,Advanced first-principles theory of superconductivity including both lattice vibrations and spin fluctuations: The case of FeB$_4$,"We present an advanced method to study spin fluctuations in superconductors
quantitatively, and entirely from first principles. This method can be
generally applied to materials where electron-phonon coupling and spin
fluctuations coexist. We employ it here to examine the recently synthesized
superconductor iron tetraboride (FeB$_4$) with experimental $T_{\mathrm{c}}\sim
2.4$ K [H. Gou \textit{et al.}, Phys. Rev. Lett. \textbf{111}, 157002 (2013)].
We prove that FeB$_4$ is particularly prone to ferromagnetic spin fluctuations
due to the presence of iron, resulting in a large Stoner interaction strength,
$I=1.5$ eV, as calculated from first principles. The other important factor is
its Fermi surface that consists of three separate sheets, among which two
nested ellipsoids. The resulting susceptibility has a ferromagnetic peak around
$\textbf{q}=0$, from which we calculated the repulsive interaction between
Cooper pair electrons using the random phase approximation. Subsequently, we
combined the electron-phonon interaction calculated from first principles with
the spin fluctuation interaction in fully anisotropic Eliashberg theory
calculations. We show that the resulting superconducting gap spectrum is
conventional, yet very strongly depleted due to coupling to the spin
fluctuations. The critical temperature decreases from $T_{\mathrm{c}}= 41$ K,
if they are not taken into account, to $T_{\mathrm{c}}= 1.7$ K, in good
agreement with the experimental value.",1801.04421v1
2018-01-15,Unconventional Charge Density Wave Order in the Pnictide Superconductor Ba(Ni$_{1-x}$Co$_x$)$_2$As$_2$,"Ba(Ni$_{1-x}$Co$_x$)$_2$As$_2$ is a structural homologue of the pnictide high
temperature superconductor, Ba(Fe$_{1-x}$Co$_x$)$_2$As$_2$, in which the Fe
atoms are replaced by Ni. Superconductivity is highly suppressed in this
system, reaching a maximum $T_c$ = 2.3 K, compared to 24 K in its iron-based
cousin, and the origin of this $T_c$ suppression is not known. Using x-ray
scattering, we show that Ba(Ni$_{1-x}$Co$_x$)$_2$As$_2$ exhibits a
unidirectional charge density wave (CDW) at its triclinic phase transition. The
CDW is incommensurate, exhibits a sizable lattice distortion, and is
accompanied by the appearance of $\alpha$ Fermi surface pockets in
photoemission [B. Zhou et al., Phys. Rev. B 83, 035110 (2011)], suggesting it
forms by an unconventional mechanism. Co doping suppresses the CDW, paralleling
the behavior of antiferromagnetism in iron-based superconductors. Our study
demonstrates that pnictide superconductors can exhibit competing CDW order,
which may be the origin of $T_c$ suppression in this system.",1801.04874v2
2018-01-26,Models for the Unusual Supernova iPTF14hls,"Supernova iPTF14hls maintained a bright, variable luminosity for more than
600 days, while lines of hydrogen and iron in its spectrum had different
speeds, but showed little evolution. Here several varieties of models are
explored for iPTF14hls-like events. They are based upon circumstellar medium
(CSM) interaction in an ordinary supernova, pulsational pair-instability
supernovae (PPISN), and magnetar formation. Each is able to explain the
enduring emission and brightness of iPTF14hls, but has shortcomings when
confronted with other observed characteristics. The PPISN model can, in some
cases, produce a presupernova transient like the one observed at the site of
iPTF14hls in 1954. It also offers a clear path to providing the necessary half
solar mass of material at $\sim 5 \times 10^{16}$ cm for CSM interaction to
work, and can give an irregular light curve without invoking additional
assumptions. It explains the 4000 km s$^{-1}$ seen in the iron lines, but
without additional energy input, strains to explain the nearly constant 8000 km
s$^{-1}$ velocity seen in H$_{\alpha}$. Magnetar models can also explain many
of the observed features, but give a smooth light curve and may require an
evolving magnetic field strength. Their dynamics may be difficult to reconcile
with the observation of slow-moving hydrogen at late times. The various models
predict different spectral characteristics and a remnant that, today, could be
a black hole, magnetar, or even a star. Further observations and calculations
of radiation transport will narrow the range of possibilities.",1801.08666v1
2018-03-01,Hydrogen Diffusion and Trapping in α-Iron: The Role of Quantum and Anharmonic Fluctuations,"We investigate the thermodynamics and kinetics of a hydrogen interstitial in
magnetic {\alpha}-iron, taking account of the quantum fluctuations of the
proton as well as the anharmonicities of lattice vibrations and hydrogen
hopping. We show that the diffusivity of hydrogen in the lattice of BCC iron
deviates strongly from an Arrhenius behavior at and below room temperature. We
compare a quantum transition state theory to explicit ring polymer molecular
dynamics in the calculation of diffusivity and we find that the role of phonons
is to inhibit, not to enhance, diffusivity at intermediate temperatures in
constrast to the usual polaron picture of hopping. We then address the trapping
of hydrogen by a vacancy as a prototype lattice defect. By a sequence of steps
in a thought experiment, each involving a thermodynamic integration, we are
able to separate out the binding free energy of a proton to a defect into
harmonic and anharmonic, and classical and quantum contributions. We find that
about 30% of a typical binding free energy of hydrogen to a lattice defect in
iron is accounted for by finite temperature effects and about half of these
arise from quantum proton fluctuations. This has huge implications for the
comparison between thermal desorption and permeation experiments and standard
electronic structure theory. The implications are even greater for the
interpretation of muon spin resonance experiments.",1803.00600v1
2018-03-02,"Topological Dirac semimetal phase in the iron-based superconductor Fe(Te,Se)","Topological Dirac semimetals (TDSs) exhibit bulk Dirac cones protected by
time reversal and crystal symmetry, as well as surface states originating from
non-trivial topology. While there is a manifold possible onset of
superconducting order in such systems, few observations of intrinsic
superconductivity have so far been reported for TDSs. We observe evidence for a
TDS phase in FeTe$_{1-x}$Se$_x$ ($x$ = 0.45), one of the high transition
temperature ($T_c$) iron-based superconductors. In angle-resolved photoelectron
spectroscopy (ARPES) and transport experiments, we find spin-polarized states
overlapping with the bulk states on the (001) surface, and linear
magnetoresistance (MR) starting from 6 T. Combined, this strongly suggests the
existence of a TDS phase, which is confirmed by theoretical calculations. In
total, the topological electronic states in Fe(Te,Se) provide a promising high
$T_c$ platform to realize multiple topological superconducting phases.",1803.00845v1
2018-03-20,"Further insight on the hypervelocity white dwarf, LP 40-365 (GD 492): a nearby emissary from a single-degenerate Type Ia supernova","The recently discovered hypervelocity white dwarf LP 40-65 (aka GD 492) has
been suggested as the outcome of the failed disruption of a white dwarf in a
sub-luminous Type Ia supernova (SN Ia). We present new observations confirming
GD 492 as a single star with unique spectral features. Our spectroscopic
analysis suggests that a helium-dominated atmosphere, with ~ 33 percent neon
and 2 percent oxygen by mass, can reproduce most of the observed properties of
this highly unusual star. Although our atmospheric model contrasts with the
previous analysis in terms of dominant atmospheric species, we confirm that the
atmosphere of GD 492 is strongly hydrogen deficient, log(H/He) < -5, and
displays traces of eleven other alpha- and iron-group elements (with sulfur,
chromium, manganese, and titanium as new detections), indicating nuclear
processing of carbon and silicon. We measure a manganese-to-iron ratio seven
times larger than Solar. While the observed abundances of GD 492 do not fully
match any predicted nuclear yields of a partially-burned supernova remnant, the
manganese excess strongly favors a link with a single-degenerate SN Ia event
over alternative scenarios.",1803.07564v1
2018-04-07,Bare and Polymer Coated Iron Oxide Superparamagnetic Nanoparticles for Effective Removal of U (VI) from Acidic and Neutral Aqueous Medium,"Superparamagnetic {\gamma}-Fe2O3 nanoparticles (5 nm diameter) were
synthesized in water. The bare particles exhibit good colloidal stability at ~
pH 2 because of the strong electrostatic repulsion with a surface charge of +25
mV. The polyacrylic acid (PAA)-coated particles exhibit remarkable colloidal
stability at ~ pH 7 with abundant free carboxyl groups as reactive sites for
subsequent functionalization. In this work, we used zeta potential analysis,
transmission electron microscopy, small angle X-ray scattering, and Inductively
coupled plasma mass spectrometry to investigate the adsorption behavior of U
(VI) on bare and coated colloidal superparamagnetic nanoparticles at pH 2 and
pH 7. At pH 2, uranyl ion (UO22+) absorbed on the surface of the bare particles
with decreasing particle surface charge. This induced particle agglomeration.
At pH 7, uranyl ion (UO22+) hydrolyzed and formed plate-like particles of
uranium hydroxide that were ~ 50 nm in diameter. The PAA-coated iron oxide
nanoparticles absorbed on the surface of these U (VI) hydroxide plates to form
large aggregates that precipitate to the bottom of the dispersion. At both pH 2
and pH 7, the resulting U (VI)/nanoparticle complex can be easily collected and
extracted from the aqueous environment via an external magnetic field. The
results show that both bare and polymer-coated superparamagnetic {\gamma}-Fe2O3
nanoparticles are potential absorbents for removing U (VI) from water.",1804.02522v1
2018-04-10,Absence of superconductivity in iron polyhydrides at high pressures,"Recently, C. M. P\'epin \textit{et al.} [Science \textbf{357}, 382 (2017)]
reported the formation of several new iron polyhydrides FeH$_x$ at pressures in
the megabar range, and spotted FeH$_5$, which forms above 130 GPa, as a
potential high-\tc \ superconductor, because of an alleged layer of dense
metallic hydrogen. Shortly after, two studies by A.~Majumdar \textit{et al.}
[Phys. Rev. B \textbf{96}, 201107 (2017)] and A.~G.~Kvashnin \textit{et al.}
[J. Phys. Chem. C \textbf{122}, 4731 (2018)] based on {\em ab initio}
Migdal-Eliashberg theory seemed to independently confirm such a conjecture. We
conversely find, on the same theoretical-numerical basis, that neither FeH$_5$
nor its precursor, FeH$_3$, shows any conventional superconductivity and
explain why this is the case. We also show that superconductivity may be
attained by transition-metal polyhydrides in the FeH$_3$ structure type by
adding more electrons to partially fill one of the Fe--H hybrid bands (as,
e.g., in NiH$_3$). Critical temperatures, however, will remain low because the
$d$--metal bonding, and not the metallic hydrogen, dominates the behavior of
electrons and phonons involved in the superconducting pairing in these
compounds.",1804.03572v2
2018-04-13,A Long Serendipitous XMM-Newton Observation of the Intermediate Polar XY Ari,"XY Ari is one of the few known eclipsing intermediate polars. We present
results from a detailed analysis of an unpublished archival observation using
XMM-Newton EPIC pn and MOS data in a quiescent state of XY Ari. The X-ray
orbital modulation and spin pulse variations were investigated for energy
dependent modulations in different energy bands. The broad orbital modulation
observed with various observations was confirmed with XMM-Newton at hard X-ray
(>1.6 keV). The EPIC light curves folded at the spin phases show a double peak
profile as expected from two pole accretion. The pulse profile is found to be
energy dependent. Hardness ratio variations and energy modulation depth during
spin modulation can be explained by photoelectric absorption. The
simultaneously fitted EPIC spectra with CEVMKL model yield maximum plasma
temperature of $28^{+3.1}_{-2.9}$ keV with an iron abundance
$\mathrm{Fe}/\mathrm{Fe}_\odot=0.37^{+0.06}_{-0.05}$. We find two intrinsic
partial covering absorption columns of $6.2^{+1.0}_{-0.9} \times 10^{22}$ and
$105.3^{+35.4}_{-30.4} \times 10^{22} \,\mathrm{cm^{-2}}$ with covering
fractions of $0.53^{+0.05}_{-0.04}$, $0.41^{+0.14}_{-0.13}$ respectively. In
addition, a Gaussian emission line at $6.43^{+0.01}_{-0.02}$ keV with an
equivalent width of $51^{+12}_{-10}$ eV is required to account for fluorescent
emission from neutral iron. The X-ray luminosity of the source is $4.2 \times
10^{32} \,\mathrm{erg \,s^{-1}}$ in the 0.2-10.0 keV energy band.",1804.04825v1
2018-04-23,Spectral and Timing Properties of Atoll Source 4U 1705-44 : LAXPC/AstroSat Results,"In this paper, we present the first results of spectral and timing properties
of the atoll source 4U 1705-44 using $\sim$ 100 ks data obtained with Large
Area X-ray Proportional Counter (LAXPC) onboard {\it AstroSat}. The source was
in the high-soft state during our observations and traced out a {\it banana
track} in the Hardness Intensity Diagram (HID). We study {\bf the} evolution of
the Power Density Spectra (PDS) and the energy spectra along the HID. PDS show
presence of a broad Lorentzian feature (Peaked Noise or PN) centered at $1-13$
Hz and a very low frequency noise (VLFN). The energy spectra can be described
by sum of a thermal Comptonized component, a power-law and a broad iron line.
The hard tail seen in the energy spectra is variable and contribute $4-30$\% of
the total flux. The iron line seen in this source is broad (FWHM $\sim$ 2 keV)
and strong (EW $\sim$ $369-512$ eV). Only relativistic smearing in the
accretion disc can not explain the origin of this feature and requires other
mechanism such as broadening by Comptonization process in the external part of
the `Comptonized Corona'. A subtle and systematic evolution of the spectral
parameters (optical depth, electron temperature etc.) is seen as the source
moves along the HID. We study the correlation between frequency of the PN and
the spectral parameters. PN frequency seems to be correlated with the strength
of the corona. We discuss the implication of the results in the paper.",1804.08371v1
2018-05-10,A Tale of Two Metals: contrasting criticalities in the pnictides and hole-doped cuprates,"The iron-based high temperature superconductors share a number of
similarities with their copper-based counterparts, such as reduced
dimensionality, proximity to states of competing order, and a critical role for
3d electron orbitals. Their respective temperature-doping phase diagrams also
contain certain commonalities that have led to claims that the metallic and
superconducting properties of both families are governed by their proximity to
a quantum critical point (QCP) located inside the superconducting dome. In this
review, we critically examine these claims and highlight significant
differences in the bulk physical properties of both systems. While there is now
a large body of evidence supporting the presence of a (magnetic) QCP in the
iron pnictides, the situation in the cuprates is much less apparent, at least
for the end point of the pseudogap phase. We argue that the opening of the
normal state pseudogap in cuprates, so often tied to a putative QCP, arises
from a momentum-dependent breakdown of quasiparticle coherence that sets in at
much higher doping levels but which is driven by the proximity to the Mott
insulating state at half filling. Finally, we present a new scenario for the
cuprates in which this loss of quasiparticle integrity and its evolution with
momentum, temperature and doping plays a key role in shaping the resultant
phase diagram.",1805.03866v1
2018-05-10,Stabilization of $s$-wave superconductivity through arsenic $p$-orbital hybridization in electron-doped BaFe$_2$As$_2$,"Using random-phase approximation spin-fluctuation theory, we study the
influence of the hybridization between iron $d$-orbitals and pnictide
$p$-orbitals on the superconducting pairing state in iron-based
superconductors. The calculations are performed for a 16-orbital Hubbard-Hund
tight-binding model of BaFe$_2$As$_2$ that includes the As-$p$ orbital degrees
of freedom in addition to the Fe-$d$ orbitals and compared to calculations for
a 10-orbital Fe-$d$ only model. In both models we find a leading $s^\pm$
pairing state and a subleading $d_ {x^2-y^2}$-wave state in the parent
compound. Upon doping, we find that the $s^\pm$ state remains the leading state
in the 16-orbital model up to a doping level of 0.475 electrons per unit cell,
at which the hole Fermi surface pockets at the zone center start to disappear.
This is in contrast to the 10-orbital model, where the $d$-wave state becomes
the leading state at a doping of less than 0.2 electrons. This improved
stability of $s^\pm$ pairing is found to arise from a decrease of $d_{xy}$
orbital weight on the electron pockets due to hybridization with the As-$p$
orbitals and the resulting reduction of near $(\pi,\pi)$ spin-fluctuation
scattering which favors the competing $d$-wave state. These results show that
the orbital dependent hybridization of Fermi surface Bloch states with the
usually neglected $p$-orbital states is an important ingredient in an improved
itinerant pairing theory.",1805.04181v2
2018-05-30,Tracking the Iron K$α$ line and the Ultra Fast Outflow in NGC 2992 at different accretion states,"The Seyfert 2 galaxy NGC 2992 has been monitored eight times by XMM-Newton in
2010 and then observed again in 2013, while in 2015 it was simultaneously
targeted by Swift and NuSTAR. XMM-Newton always caught the source in a faint
state (2-10 keV fluxes ranging from 0.3 to 1.6$\times10^{-11}$ erg cm$^{-2}$
s$^{-1}$) but NuSTAR showed an increase in the 2-10 keV flux up to
6$\times10^{-11}$ erg cm$^{-2}$ s$^{-1}$. We find possible evidence of an Ultra
Fast Outflow with velocity $v_1=0.21\pm0.01c$ (detected at about 99% confidence
level) in such a flux state. The UFO in NGC 2992 is consistent with being
ejected at a few tens of gravitational radii only at accretion rates greater
than 2% of the Eddington luminosity. The analysis of the low flux 2010/2013 XMM
data allowed us to determine that the Iron K$\alpha$ emission line complex in
this object is likely the sum of three distinct components: a constant, narrow
one due to reflection from cold, distant material (likely the molecular torus);
a narrow, but variable one which is more intense in brighter observations and a
broad relativistic one emitted in the innermost regions of the accretion disk,
which has been detected only in the 2003 XMM observation.",1805.12149v1
2018-06-04,Towards a systematically improvable many-body description of antiferromagnetic iron oxide,"We report variational and fixed-node diffusion quantum Monte Carlo (QMC)
calculations of anti-ferromagnetic iron oxide (FeO) in the ground state B1
crystal structure. The goal of this study was a systematic investigation of the
sensitivity of several ground state properties to a variety of QMC wave
function generation techniques including advanced wave functions such as
multi-determinant expansions and backflow transformations. We found that the
predicted lattice distortion was largely controlled by the choice of single
particle orbitals used to construct the wave function, rather than by
subsequent wave function optimization techniques within QMC. However, the
absolute magnetic moment was remarkably insensitive to the method of wave
function construction. QMC estimates of total spin density indicate that in
addition to strong electronic correlation of the Fe $3d$ states, charge
transfer may be an important but challenging piece of physics to accurately
capture within existing QMC methods. Finally, we highlight the need for
advanced and systematically improvable many-body wave functions suitable for
accurately describing challenging real systems.",1806.01383v2
2018-09-04,Anomalous peak effect in iron-based superconductors Ba$_{1-x}$K$_x$Fe$_2$As$_2$ ($x \approx$ 0.69 and 0.76) for magnetic-field directions close to the $ab$ plane and its possible relation to the spin paramagnetic effect,"We report magnetic torque measurements on iron-pnictide superconductors
Ba$_{1-x}$K$_x$Fe$_2$As$_2$ ($x \approx$ 0.69 and 0.76) up to an applied field
of $B_a$ = 45 T. The peak effect is observed in torque-vs-field curves below
the irreversibility field. It is enhanced and becomes asymmetric as the field
is tilted from the $c$ axis. For field directions close to the $ab$ plane,
increasing- and decreasing-field curves peak at markedly different fields, and
exhibit a sharp jump, suggestive of a first-order phase transition, on the
high- and the low-field side of the peak, respectively. Complicated history
dependence of the torque is observed in the peak-effect region. We construct
and discuss the temperature ($T$)--applied-magnetic-field ($B_a$) phase
diagram. Since the upper critical field for the $ab$-plane direction is
comparable to the Pauli limit, we also consider possible influence of the spin
paramagnetic effect on the anomalous peak effect.",1809.00762v3
2018-09-07,Electron-magnon scattering in elementary ferromagnets from first principles: lifetime broadening and band anomalies,"We study the electron-magnon scattering in bulk Fe, Co, and Ni within the
framework of many-body perturbation theory implemented in the full-potential
linearized augmented-plane-wave method. To this end, a $\mathbf{k}$-dependent
self-energy ($GT$ self-energy) describing the scattering of electrons and
magnons is constructed from the solution of a Bethe-Salpeter equation for the
two-particle (electron-hole) Green function, in which single-particle Stoner
and collective spin-wave excitations (magnons) are treated on the same footing.
Partial self-consistency is achieved by the alignment of the chemical
potentials. The resulting renormalized electronic band structures exhibit
strong spin-dependent lifetime effects close to the Fermi energy, which are
strongest in Fe. The renormalization can give rise to a loss of quasiparticle
character close to the Fermi energy, which we attribute to electron scattering
with spatially extended spin waves. This scattering is also responsible for
dispersion anomalies in conduction bands of iron and for the formation of
satellite bands in nickel. Furthermore, we find a band anomaly at a binding
energy of 1.5~eV in iron, which results from a coupling of the quasihole with
single-particle excitations that form a peak in the Stoner continuum. This band
anomaly was recently observed in photoemission experiments. On the theory side,
we show that the contribution of the Goldstone mode to the $GT$ self-energy is
expected to (nearly) vanish in the long-wavelength limit. We also present an
in-depth discussion about the possible violation of causality when an
incomplete subset of self-energy diagrams is chosen.",1809.02395v2
2018-09-21,Electronic Spin transition in FeO$_{2}$: evidence for Fe(II) with peroxide O$_{2}^{2-}$,"The discovery of FeO$_{2}$ containing more oxygen than hematite
(Fe$_{2}$O$_{3}$) that was previously believed to be the most oxygen rich iron
compounds, has important implications on the study of the deep lower mantle
compositions. Compared to other iron compounds, there are limited reports on
FeO$_{2}$ making studies of its physical properties of great interest in
fundamental condensed matter physics and geoscience. Even the oxidation state
of Fe in FeO$_{2}$ is the subject of debate in theoretical works and there have
not been reports from experimental electronic and magnetic properties
measurements. Here, we report the pressure-induced spin state transition from
synchrotron experiments and our computational results explain the underlying
mechanism. Using density functional theory and dynamical mean field theory, we
calculated spin states of Fe with volume and Hubbard interaction $U$ change,
which clearly demonstrate that Fe in FeO$_{2}$ consists of Fe(II) and peroxide
O$_{2}^{2-}$. Our study suggests that localized nature of both Fe 3$d$ orbitals
and O$_{2}$ molecular orbitals should be correctly treated for unveiling the
structural and electronic properties of FeO$_{2}$.",1809.07969v1
2018-09-24,The Variable Relativistic Outflow of IRAS 13224-3809,"The discovery of an ultrafast outflow has been reported in the z=0.0658
narrow line Seyfert galaxy IRAS 13224-3809 (Parker et al. 2017a). The ultrafast
outflow was first inferred through the detection of highly blueshifted
absorption lines (Parker et al. 2017a) and then confirmed with a principal
component analysis (PCA) (Parker et al. 2017b). Two of the reported properties
of this outflow differed from those typically detected in other AGN with
ultrafast outflows. First, the outflow velocity was found not to vary with
v=0.236c +/- 0.006c. Second, the equivalent width of the highly blueshifted
absorption line was reported to be anti-correlated with the 3-10 keV flux of
this source. We present a re-analysis of the XMM-Newton observations of IRAS
13224-3809 considering the influence of background. We also undertook a
different analysis approach in combining the spectra and investigated the
change of the properties of the outflow as a function of 3-10 keV flux and
time. We confirm the presence of an ultrafast outflow in IRAS 13224-3809,
however, we find that the background spectra used in the Parker et al. analyses
dominate the source spectra for energies near the blueshifted iron lines. By
reducing the source extraction regions to improve the signal-to-noise ratio we
discover larger than previously reported outflow velocities and find that the
outflow velocity varies from ~0.2c to ~0.3c and increases with 3-10~keV flux.
The previously reported anti-correlation between equivalent width of the iron
line and 3-10 keV flux disappears when the background spectra are reduced by
optimizing the source extraction regions.",1809.09138v1
2018-11-06,Energy scale of nematic ordering in the parent iron-based superconductor:BaFe2As2,"Nematicity plays an important role in the physics of iron-based
superconductors (IBS). Its microscopic origin and in particular its importance
for the mechanism of high-temperature superconductivity itself are highly
debated. A crucial knowledge in this regard is the degree to which the nematic
order influences the electronic structure of these materials. Earlier
angle-resolved photoemission spectroscopy (ARPES) studies found that the effect
is dramatic in three families of IBS including 11, 111 and 122 compounds:
energy splitting reaches 70 meV and Fermi surface becomes noticeably distorted.
More recent experiments, however, reported significantly lower energy scale in
11 and 111 families, thus questioning the degree and universality of the impact
of nematicity on the electronic structure of IBS. Here we revisit the
electronic structure of undoped parent BaFe2As2 (122 family). Our systematic
ARPES study including the detailed temperature and photon energy dependencies
points to the significantly smaller energy scale also in this family of
materials, thus establishing the universal scale of this phenomenon in IBS. Our
results form a necessary quantitative basis for theories of high-temperature
superconductivity focused on the nematicity.",1811.02430v2
2018-11-14,Giant anisotropy in superconducting single crystals of CsCa$_2$Fe$_4$As$_4$F$_2$,"CsCa$_2$Fe$_4$As$_4$F$_2$ is a newly discovered iron-based superconductor
with $T_\mathrm{c}\sim$ 30 K containing double Fe$_2$As$_2$ layers that are
separated by insulating Ca$_2$F$_2$ spacer layers. Here we report the transport
and magnetization measurements on CsCa$_2$Fe$_4$As$_4$F$_2$ single crystals
grown for the first time using the self flux of CsAs. We observed a huge
resistivity anisotropy $\rho_c(T)/\rho_{ab}(T)$, which increases with
decreasing temperature, from 750 at 300 K to 3150 at 32 K. The $\rho_c(T)$ data
exhibit a non-metallic behavior above $\sim$140 K, suggesting an incoherent
electronic state at high temperatures due to the dimension crossover. The
superconducting onset transition temperature in $\rho_{ab}$ is 0.7 K higher
than that in $\rho_c$, suggesting two-dimensional (2D) superconducting
fluctuations. The lower and upper critical fields also show an exceptional
anisotropy among iron-based superconductors. The $H_{c1}^\bot(T)$ data are well
fitted using the model with two $s$-wave-like superconducting gaps,
$\Delta_1(0)=6.75$ meV and $\Delta_2(0)=2.32$ meV. The inter-plane coherence
length $\xi_c(0)$ is $3.6$ \AA, remarkably smaller than the distance between
conducting layers (8.6 \AA), consolidating the 2D nature in the title material.",1811.05706v1
2018-12-04,Adsorption and dissociation of iron phthalocyanine on H/Si(111): Impact of van-der-Waals interactions and perspectives for subsurface doping,"The adsorption of iron phthalocyanine (FePc) on the passivated H/Si(111)
surface is explored from first principles. We find that the organic molecule is
predominantly physisorbed with a distance to the surface of $2.6 \pm 0.1$
Angstrom, but also exhibits sizable resonance with the underlying substrate.
This establishes the present system as interesting mixed
covalent-van-der-Waals-bound test case, which we use to compare the impact of
different approaches to van-der-Waals interactions. (Spin-polarized) scanning
tunneling microscopy (SP STM) images are simulated, selectively accessing
different molecular orbitals via the applied bias voltage in the spirit of
scanning tunneling spectroscopy. Comparison with experimental STM images
reveals very good agreement. We find a significant magnetic contrast exceeding
$\pm 1$ Angstrom in the SP STM images for $-2$ and $+1.5$ V. Binding energies
of different (transition metal) atoms in the center of the Pc ring are
presented, which particularly show that Fe is strongly bound in the molecule
(about $9.6$ eV). Finally, we discuss different reactions for subsurface doping
by room-temperature FePc deposition and point out two feasible reactions.",1812.01639v3
2018-12-06,Artificially Engineered Nanostrain in Iron Chalcogenide Superconductor Thin Film for Enhancing Supercurrent,"Although nanoscale deformation, such as nanostrain in iron chalcogenide
(FeSexTe1-x, FST) thin films, has attracted attention owing to the enhancement
of general superconducting properties, including critical current density (Jc)
and critical transition temperature, its formation has proven to be an
extremely challenging and complex process thus far. Herein, we successfully
fabricated an epitaxial FST thin film with uniformly distributed nanostrain by
injection of a trace amount of CeO2 inside FST matrix using sequential pulsed
laser deposition. Using transmission electron microscopy and geometrical phase
analysis, we verified that a trace amount of CeO2 injection forms nanoscale
fine defects with a nanostrained region, which has a tensile strain (ezz ~
0.02) along the c-axis of the FST matrix. The nanostrained FST thin film
achieves a remarkable Jc of 3.5 MA/cm2 for a self-field at 6 K and a highly
enhanced Jc under the entire magnetic field with respect to a pristine FST thin
film.",1812.02380v3
2018-12-13,Emergent XY electronic nematicity in iron-based superconductors,"Electronic nematicity, a correlated state that spontaneously breaks
rotational symmetry, is observed in several layered quantum materials. In
contrast to their liquid-crystal counterparts, the nematic director cannot
usually point in an arbitrary direction (XY nematics), but is locked by the
crystal to discrete directions (Ising nematics),resulting in strongly
anisotropic fluctuations above the transition. Here, we report on the
observation of nearly isotropic XY-nematic fluctuations, via elastoresistance
measurements, in hole-doped Ba$_{1-x}$Rb$_{x}$Fe$_{2}$As$_{2}$ iron-based
superconductors. While for $x=0$ the nematic director points along the in-plane
diagonals of the tetragonal lattice, for $x=1$ it points along the horizontal
and vertical axes. Remarkably, for intermediate doping, the susceptibilities of
these two symmetry-irreducible nematic channels display comparable Curie-Weiss
behavior, thus revealing a nearly XY-nematic state. This opens a new route to
assess this elusive electronic quantum liquid-crystalline state, which is a
candidate to host unique phenomena not present in the Ising-nematic case.",1812.05267v2
2018-12-13,Visualizing the Nonlinear Coupling between Strain and Electronic Nematicity in the Iron Pnictides by Elasto-Scanning Tunneling Spectroscopy,"Mechanical strain is a powerful technique for tuning electronic structure and
interactions in quantum materials. In a system with tetragonal symmetry, a
tunable uniaxial in-plane strain can be used to probe nematic correlations in
the same way that a tunable magnetic field is used to probe magnetic
correlations. Here, we present a new spectroscopic scanned probe technique that
provides atomic-resolution insight into the effect of anisotropic strain on the
electronic structure. We use this technique to study nematic fluctuations and
nematic order across the phase diagram of a prototypical iron-based
superconductor. By extracting quantitatively the electronic anisotropy as
function of applied strain, we show that while true long range nematic order is
established at the tetragonal to orthorhombic structural transition
temperature, sizable nematic fluctuations persist to high temperatures and also
to the overdoped end of the superconducting dome. Remarkably, we find that
uniaxial strain in the pnictides significantly enhances the amplitude of the
nematic fluctuations, indicating a strong nonlinear coupling between structure
and electronic nematicity.",1812.05287v1
2018-12-20,The long-term evolution and appearance of Type Iax postgenitor stars,"Type Iax supernovae may arise from failed explosions of white dwarfs that
leave behind a bound remnant (i.e., a ""postgenitor"" star) that could be
identified in wide field surveys. To understand their observational signatures,
we simulate these white dwarf (WD) postgenitors from shortly after explosion
until they move back down the WD cooling track, and we consider several
possible WD masses and explosion energies. To predict the peculiar surface
abundances of the WD postgenitors, our models take into account gravitational
settling and radiative levitation. We find that radiative levitation is
significant at temperatures above a mass-dependent critical temperature,
typically in the range Teff ~ 50-100 * 10^3 K, significantly increasing surface
abundances of iron-group elements. Due to enhanced iron group opacity compared
to normal WDs, the postgenitor peak luminosity and cooling timescale depend
sensitively on mass, with more massive WDs becoming brighter but cooling much
faster. We discuss our results in light of recently discovered hypervelocity
white dwarfs with peculiar surface compositions, finding that our low-mass
postgenitor models match many of their observational characteristics. Finally,
we explore the effects of thermohaline diffusion, tentatively finding that it
strongly suppresses abundance enhancements created by radiative levitation, but
more realistic modeling is required to reach a firm conclusion.",1812.08793v2
2019-02-14,Photoionization Emission Models for the Cyg X-3 X-ray Spectrum,"We present model fits to the X-ray line spectrum of the well known High Mass
X-ray binary Cyg X-3. The primary observational dataset is a spectrum taken
with the $Chandra$ X-ray Observatory High Energy Transmission Grating (HETG) in
2006, though we compare it to all the other observations of this source taken
so far by this instrument. We show that the density must be $\geq 10^{12}$
cm$^{-3}$ in the region responsible for most of the emission. We discuss the
influence of the dust scattering halo on the broad band spectrum and we argue
that dust scattering and extinction is not the most likely origin for the
narrow featureseen near the Si K edge. We identify the features of a wind in
the profiles of the strong resonance lines and we show that the wind is more
apparent in the lines from the lighter elements. We argue that this wind is
most likely associated with the companion star. We show that the intensities of
most lines can be fitted, crudely, by a single component photoionized model.
However, the iron K lines do not fit with this model. We show that the iron K
line variability as a function of orbital phase is different from the lower
energy lines, which indicates that the lines arise in physically distinct
regions. We discuss the interpretation of these results in the context of what
is known about the system and similar sys",1902.05589v3
2019-02-28,Quantum phase transition inside the superconducting dome of Ba(Fe$_{1-x}$Co$_x$)$_2$As$_2$ probed by optical magneto-sensing using NV-centers in diamond,"While unusual normal state properties, such as non-Fermi liquid behavior of
the resistivity, are commonly associated with strong quantum fluctuations,
evidence for its presence inside the superconducting dome are much scarcer. In
this paper, we use sensitive and minimally invasive optical magnetometry based
on NV-centers in diamond to probe the doping evolution of the $T=0$ penetration
depth in the electron-doped iron-based superconductor
Ba(Fe$_{1-x}$Co$_x$)$_2$As$_2$. A non-monotonic evolution with a pronounced
peak in the vicinity of the putative magnetic QPT is found. This behavior is
reminiscent to that previously seen in isovalently-substituted
BaFe$_2$(As$_{1-x}$P$_x$)$_2$ compounds, despite the notable differences
between these two systems. Whereas the latter is a very clean system that
displays nodal superconductivity and a single simultaneous first-order
nematic-magnetic transition above, and even somewhat below, $T_c$, the former
is a significantly dirtier system with fully gapped superconductivity and split
second-order nematic and magnetic transition above $T_c$. Thus our observation
that such distinct systems display remarkably similar penetration depth peaks,
combined with the theoretical result that a QPT alone does not ensure the
existence of a peak, unveils a puzzling and seemingly universal manifestation
of quantum fluctuations in the iron pnictides.",1903.00053v2
2019-03-01,Observations of the Ultraviolet-Bright Star Barnard 29 in the Globular Cluster M13 (NGC 6205),"We have analyzed FUSE, COS, GHRS, and Keck HIRES spectra of the UV-bright
star Barnard 29 in M13 (NGC 6205). By comparing the photospheric abundances
derived from multiple ionization states of C, N, O, Si, and S, we infer an
effective temperature T_eff = 21,400 +/- 400 K. Balmer-line fits yield a
surface gravity log g = 3.10 +/- 0.03. We derive photospheric abundances of He,
C, N, O, Mg, Al, Si, P, S, Cl, Ar, Ti, Cr, Fe, Ni, and Ge. Barnard 29 exhibits
an abundance pattern typical of the first-generation stars in M13, enhanced in
oxygen and depleted in aluminum. An underabundance of C and an overabundance of
N suggest that the star experienced nonconvective mixing on the RGB. We see no
evidence of significant chemical evolution since the star left the RGB; in
particular, it did not undergo third dredge-up. Previous workers found that the
star's FUV spectra yield an iron abundance about 0.5 dex lower than its optical
spectrum, but the iron abundances derived from all of our spectra are
consistent with the cluster value. We attribute this difference to our use of
model atmospheres without microturbulence, which is ruled out by careful fits
to optical absorption features. We derive a mass M_*/M_sun = 0.45 - 0.55 and
luminosity log (L_*/L_sun) = 3.26 - 3.35. Comparison with stellar-evolution
models suggests that Barnard 29 evolved from a ZAHB star of mass M_*/M_sun
between 0.50 and 0.55, near the boundary between the extreme and blue
horizontal branches.",1903.00350v1
2019-03-04,Structural and magnetic properties in sputtered iron oxide epitaxial thin films -- Magnetite Fe$_3$O$_4$ and epsilon ferrite e-Fe$_2$O$_3$,"Epitaxial thin film fabrication of iron oxides including magnetite Fe3O4 and
epsilon-ferrite epsilon-Fe2O3 with the potential for advancing electromagnetic
devices has been investigated, which led to the first ever epsilon-ferrite
epitaxial layer being synthesized in the conventional sputtering process.
Concerning Fe3O4 (100) / MgO (100) films, a cube-on-cube epitaxial relationship
and sharp rocking curves with FWHM of 50 - 350 arcsec were confirmed regardless
of the small amount of Ge additions. Sputtering Ar gas pressure PAr heavily
influenced their magnetic and transport properties. High PAr = 15 mTorr caused
a high magnetization of 6.52 kG for the Ge added sample and the clear Verwey
transition at 122 K for the non Ge addition case. Conversion electron Mossbauer
spectroscopy (CEMS) measurements revealed that low PAr < 10 mTorr causes Fe/O
off-stoichiometry on the oxidizing side for the non Ge addition case and the
reductive side for the Ge addition case, respectively. Regarding the
epsilon-Fe2O3 (001) / SrTiO3(111) epilayer synthesis, bilayer microstructure
composed of an approximately 5nm thick initially grown epsilon-Fe2O3 (001)
epilayer and subsequently grown e-Fe2O3 (001) epilayer was confirmed from
cross-sectional TEM observations. The coexistence of magnetically hard and soft
phases was confirmed from the magnetization measurements. As a possible
application of the single nm thick epsilon-Fe2O3 layer, 4-resistive-state
multiferroic tunnel junction (MFTJ) is considered.",1903.01022v1
2019-03-11,The Nematic Energy Scale and the Missing Electron Pocket in FeSe,"Superconductivity emerges in proximity to a nematic phase in most iron-based
superconductors. It is therefore important to understand the impact of
nematicity on the electronic structure. Orbital assignment and tracking across
the nematic phase transition prove to be challenging due to the multiband
nature of iron-based superconductors and twinning effects. Here, we report a
detailed study of the electronic structure of fully detwinned FeSe across the
nematic phase transition using angle-resolved photoemission spectroscopy. We
clearly observe a nematicity-driven band reconstruction involving dxz, dyz, and
dxy orbitals. The nematic energy scale between dxz and dyz bands reaches a
maximum of 50 meV at the Brillouin zone corner. We are also able to track the
dxz electron pocket across the nematic transition and explain its absence in
the nematic state. Our comprehensive data of the electronic structure provide
an accurate basis for theoretical models of the superconducting pairing in
FeSe.",1903.04557v2
2019-03-14,3D visualizations of nano-scale phase separation and ultrafast dynamic correlation between phases in (Na0.32K0.68)0.95Fe1.75Se2,"Phase separation of metallic and antiferromagnetic (AFM) insulating phases in
alkaline iron selenides (AxFe2-ySe2) continues to attract intense interest
because the relationship between two peculiar features probably is a key to
clarifying the pairing mechanism of AxFe2-ySe2 superconductors. Here we report
that the 3D visualizations of nano-scale phase separation in
(Na0.32K0.68)0.95Fe1.75Se2 single crystals are revealed by hybrid
focused-ion-beam scanning electron microscopy and the superconducting paths are
fully percolative in 3D. Moreover, the phase-related ultrafast dynamics in
(Na0.32K0.68)0.95Fe1.75Se2 is studied by dual-color pump-probe spectroscopy.
The anomalous changes in the electron and acoustic phonon components of
transient reflectivity change ({\Delta}R/R) identify two characteristic
temperatures T*~100 K (the onset temperature of coupling between nano-metallic
and AFM phases) and TH~230 K (the onset temperature of
metallic-interface-phase). An energy-transfer channel between the nano-metallic
and AFM phases is inferred. This proposed channel provides a new insight into
the pairing mechanism of alkaline iron selenide superconductors.",1903.05797v1
2019-03-15,Band-selective clean- and dirty-limit superconductivity with nodeless gaps in the bilayer iron-based superconductor CsCa$_2$Fe$_4$As$_4$F$_2$,"The optical properties of the new iron-based superconductor
CsCa$_2$Fe$_4$As$_4$F$_2$ with $T_c \sim 29$~K have been determined. In the
normal state a good description of the low-frequency response is obtained with
a superposition of two Drude components of which one has a very low scattering
rate (narrow Drude-peak) and the other a rather large one (broad Drude-peak).
Well below $T_c \sim 29$~K, a pronounced gap feature is observed which involves
a complete suppression of the optical conductivity below $\sim$ 110~cm$^{-1}$
and thus is characteristic of a nodeless superconducting state. The optical
response of the broad Drude-component can be described with a dirty-limit
Mattis-Bardeen-type response with a single isotropic gap of $2\Delta \simeq
14$~meV. To the contrary, the response of the narrow Drude-component is in the
ultra-clean-limit and its entire spectral weight is transferred to the
zero-frequency $\delta(\omega)$ function that accounts for the loss-free
response of the condensate. These observations provide clear evidence for a
band-selective coexistence of clean- and dirty-limit superconductivity with
nodeless gaps in CsCa$_2$Fe$_4$As$_4$F$_2$.",1903.06466v1
2019-05-07,Single-parameter scaling in the magnetoresistance of optimally doped La$_{2-x}$Sr$_{x}$CuO$_4$,"We show that the recent magnetoresistance data on thin-film
La$_{2-x}$Sr$_{x}$CuO$_4$ (LSCO) in strong magnetic fields ($B$) obeys a
single-parameter scaling of the form MR$(B,T)=f(\mu_H(T)B)$, where
$\mu_H^{-1}(T)\sim T^{\alpha}$ ($1\le\alpha\le2$), from $T=180$K until
$T\sim20$K, at which point the single-parameter scaling breaks down. The
functional form of the MR is distinct from the simple quadratic-to-linear
quadrature combination of temperature and magnetic field found in the optimally
doped iron superconductor BaFe${}_2$(As${}_{1-x}$P${}_x$)${}_2$. Further,
low-temperature departure of the MR in LSCO from its high-temperature scaling
law leads us to conclude that the MR curve collapse is not the result of
quantum critical scaling. We examine the classical effective medium theory
(EMT) previously used to obtain the quadrature resistivity dependence on field
and temperature for metals with a $T$-linear zero-field resistivity. It appears
that this scaling form results only for a binary, random distribution of
metallic components. More generally, we find a low-temperature, high-field
region where the resistivity is simultaneously $T$ and $B$ linear when multiple
metallic components are present. Our findings indicate that if mesoscopic
disorder is relevant to the magnetoresistance in strange metal materials, the
binary-distribution model which seems to be relevant to the iron pnictides is
distinct from the more broad-continuous distributions relevant to the cuprates.
Using the latter, we examine the applicability of classical effective medium
theory to the MR in LSCO and compare calculated MR curves with the experimental
data.",1905.02737v1
2019-05-13,"Kinetics of phase separation, border of miscibility gap in Fe-Cr and limit of Cr solubility in iron at 832 K","Kinetics of phase decomposition accompanied by precipitation of sigma-phase
in a Fe73.7Cr26.3 alloy isothermally annealed at 832 K was studied by means of
M\""ossbauer spectroscopy. Two stage decomposition process has been revealed by
three different quantities viz. the average hyperfine field, <H>, the
short-range parameter, alpha1, and the probability of atomic configuration with
no Cr atoms within the first two coordination shells around the probe Fe atoms,
P(0,0). The first stage, that has terminated after ca.300 h of annealing, has
been associated with the decomposition into Fe-rich phase in which the
concentration of Cr, determined as 20.9 at.%, can be interpreted as the border
of the metastable miscibility gap at 832 K. The second stage can be regarded as
a continuation of the phase decomposition process combined with a precipitation
of sigma. The three relevant parameters for this stage have also
saturation-like behavior vs. annealing time and the saturation can be
interpreted as termination of the two processes. The concentration of Cr in the
Fe-rich phase has been determined as 19.8 at.% and this value can be regarded
as the limit of Cr solubility in iron at 832 K. Both stages of the kinetics
were found to be in line with the Johnson-Mehl-Avrami-Kolgomorov equation
yielding values of the rate constant and the Avrami exponent. The activation
energy of the second-stage process was determined to be by ca.12 kJ/mol higher.",1905.05156v1
2019-05-24,The empirical aspects of Eliashberg formalism for the superconducting mechanism in Iron-based superconductors,"We have investigated experimentally how properties of NdFeAsO0.8F0.2
superconductor affected due to the substitution of the Ca2+/Nd3+ doping. Based
on the XRD data refinement, various structural parameters such as lattice
parameters, bond angles, bond length, and etc. were studied. We have determined
the upper limit of the calcium solubility in the NdFeAsO0.8F0.2 phase and it is
restricted to x=0.05. Also, we have found that the lattice parameters and the
cell volume decreased by increasing the calcium content. According to the XRD
data analysis, we have argued that these reductions are due to the variations
in the bond lengths and the bond angles of (O/F)-Nd-(O/F) and As-Fe-As i.e.
alpha, beta upon increasing the calcium dopant. So, we have expected that the
superconducting transition temperature (TC) will be sensitive to the calcium
doping values. Experimentally, the TC of our samples was reduced from 53 K (for
x = 0) to 48 K (for x = 0.01) and 27 K (for x=0.025) and disappeared for our
other sample. Then we have studied the dependence of TC and bond angles, bond
length, the pnictogen height, and the lattice parameter to examine the
available theories from an empirical point of view. The consistency of our
experimental results and the theoretical reports based on the spin- and the
orbital-fluctuation theories shows that these models play an important role in
the pairing mechanism of the iron-based superconductors.",1905.11378v1
2019-05-28,Photo-induced Superconducting State with Long-lived Disproportionate Band Filling in FeSe,"Photo-excitation is a very powerful way to instantaneously drive a material
into a novel quantum state without any fabrication, and variable ultrafast
techniques have been developed to observe how electron-, lattice-, and
spin-degrees of freedom change. One of the most spectacular phenomena is
photo-induced superconductivity, and it has been suggested in cuprates that the
transition temperature Tc can be enhanced from original Tc with significant
lattice modulations. Here we show another photo-induced high-Tc superconducting
state in the iron-based superconductor FeSe with semi-metallic hole and
electron bands. The transient electronic state in the entire Brillouin zone is
directly observed by the time- and angle-resolved photoemission spectroscopy
using extreme ultraviolet pulses obtained from high harmonic generation. Our
results of dynamical behaviors on timescales from 50 fs to 800 ps consistently
support the favorable superconducting state after photo-excitation well above
Tc. This finding demonstrates that multiband iron-based superconductors emerge
as an alternative candidate for photo-induced superconductors.",1905.12138v1
2019-05-29,Photoinduced nematic state in FeSe$_{0.4}$Te$_{0.6}$,"FeSe$_{x}$Te$_{1-x}$ compounds present a complex phase diagram, ranging from
the nematicity of FeSe to the $(\pi, \pi)$ magnetism of FeTe. We focus on
FeSe$_{0.4}$Te$_{0.6}$, where the nematic ordering is absent at equilibrium. We
use a time-resolved approach based on femtosecond light pulses to study the
dynamics following photoexcitation in this system. The use of
polarization-dependent time- and angle-resolved photoelectron spectroscopy
allows us to reveal a photoinduced nematic metastable state, whose
stabilization cannot be interpreted in terms of an effective photodoping. We
argue that the 1.55 eV photon-energy-pump-pulse perturbs the $C_4$ symmetry of
the system triggering the realization of the nematic state. The possibility to
induce nematicity using an ultra-short pulse sheds a new light on the driving
force behind the nematic symmetry breaking in iron-based superconductors. Our
results weaken the idea that a low-energy coupling with fluctuations is a
necessary condition to stabilize the nematic order and ascribe the origin of
the nematic order in iron-based superconductors to a clear tendency of those
systems towards orbital differentiation due to strong electronic correlations
induced by the Hund's coupling.",1905.12448v1
2019-05-30,Quantum dynamics of hydrogen in iron-based superconductor LaFeAsO0.9D0.1 measured with inelastic neutron spectroscopy,"Inelastic neutron scattering was performed for an iron-based superconductor
LaFeAsO0.9D0.1, where most of D (deuterium) replaces oxygen, while a tiny
amount goes into interstitial sites. By first-principle calculation, we
characterize the interstitial sites for D (and for H slightly mixed) with four
equivalent potential minima. Below the superconducting transition temperature
Tc = 26 K,new excitations emerge in the range 5-15 meV, while they are absent
in the reference system LaFeAsO0.9F0.1. The strong excitations at 14.5 meV and
11.1 meV broaden rapidly around 15 K and 20 K, respectively, where each energy
becomes comparable to twice of the superconducting gap. The strong excitations
are ascribed to a quantum rattling, or a band motion of hydrogen, which arises
only if the number of potential minima is larger than two.",1905.12826v2
2019-05-30,Changes in long-term properties of the Danube river level and flow induced by damming,"In this paper we assessed changes in scaling properties of the river Danube
level and flow data, associated with building of Djerdap/Iron Gates
hydrological power plants positioned on the border of Romania and Serbia. We
used detrended fluctuation analysis (DFA), wavelet transform spectral analysis
(WTS) and wavelet-based modulus maxima method (WTMM) to investigate time series
of river levels and river flows recorded at hydrological stations in the
vicinity of dams and in the area of up to 480 km upstream from dams, and time
series of simulated NOAA-CIRES 20th Century Global Reanalysis precipitation
records for the Djerdap/Iron Gates region. By comparing river dynamics during
the periods before and after construction of dams, we were able to register
changes in scaling that are different for recordings from upstream and from
downstream (from dams) areas. We found that damming caused appearance of
human-made or enhancement of natural cycles in the small time scales region,
which largely influenced the change in temporal scaling in downstream recording
stations. We additionally found disappearance or decline in the amplitude of
large-time-scale cycles as a result of damming, that changed the dynamics of
upstream data. The most prominent finding of our paper is a demonstration of a
complete or partial loss of annual cycles in the upstream stations' data that
we found to extend as far as 220 km from dams. We discussed probable sources of
such found changes in scaling, aiming to provide explanations that could be of
use in future environmental assessments.",1905.13144v2
2019-08-06,FeOOH instability at the lower mantle conditions,"Goethite, {\alpha}-FeOOH, is a major component among oxidized iron species,
called rust, which formed as a product of metabolism of anoxygenic prokaryotes
(1, 2) inhabiting the Earth from about 3.8 billion years (Gy) ago until the
Great Oxidation Event (GOE) of about 2.5 Gy ago. The rust was buried on the
ocean floor (1, 2) and had to submerge into the Earth mantle with subducting
slabs due to the plate tectonics started about 2.8 Gy ago (3). The fate and the
geological role of the rust at the lower mantle high-pressure and
high-temperature(HPHT) conditions is unknown. We studied the behavior of
goethite up to 82(2) GPa and 2300(100) K using in situ synchrotron
single-crystal X-ray diffraction. At these conditions, corresponding to the
coldest slabs at the depth of about 1000 km, {\alpha}-FeOOH decomposes to
various iron oxides (Fe2O3, Fe5O7, Fe7O10, Fe6.32O9) and an oxygen-rich fluid.
Our results suggest that recycling of the rust in the Earth mantle could
contribute to oxygen release to the atmosphere and explain the sporadic
increase of the oxygen level before the GOE linked to the formation of Large
Igneous Provinces(4).",1908.02114v1
2019-08-16,Itinerant ferromagnetism and intrinsic anomalous Hall effect in amorphous iron-germanium,"The amorphous iron-germanium system ($a$-Fe$_x$Ge$_{1-x}$) lacks long-range
structural order and hence lacks a meaningful Brillouin zone. The magnetization
of \aFeGe is well explained by the Stoner model for Fe concentrations $x$ above
the onset of magnetic order around $x=0.4$, indicating that the local order of
the amorphous structure preserves the spin-split density of states of the
Fe-$3d$ states sufficiently to polarize the electronic structure despite
$\mathbf{k}$ being a bad quantum number. Measurements reveal an enhanced
anomalous Hall resistivity $\rho_{xy}^{\mathrm{AH}}$ relative to crystalline
FeGe; this $\rho_{xy}^{\mathrm{AH}}$ is compared to density functional theory
calculations of the anomalous Hall conductivity to resolve its underlying
mechanisms. The intrinsic mechanism, typically understood as the Berry
curvature integrated over occupied $\mathbf{k}$-states but shown here to be
equivalent to the density of curvature integrated over occupied energies in
aperiodic materials, dominates the anomalous Hall conductivity of
$a$-Fe$_x$Ge$_{1-x}$ ($0.38 \leq x \leq 0.61$). The density of curvature is the
sum of spin-orbit correlations of local orbital states and can hence be
calculated with no reference to $\mathbf{k}$-space. This result and the
accompanying Stoner-like model for the intrinsic anomalous Hall conductivity
establish a unified understanding of the underlying physics of the anomalous
Hall effect in both crystalline and disordered systems.",1908.06055v3
2019-08-21,Stellar population astrophysics (SPA) with the TNG. GIANO-B spectroscopy of red supergiants in Alicante 7 and Alicante 10,"The Scutum complex in the inner disk of the Galaxy hosts a number of young
clusters and associations of red supergiant stars that are heavily obscured by
dust extinction. These stars are important tracers of the recent star formation
and chemical enrichment history in the inner Galaxy. Within the SPA Large
Programme at the TNG, we secured GIANO-B high-resolution (R=50,000) YJHK
spectra of 11 red supergiants toward the Alicante 7 and Alicante 10
associations near the RSGC3 cluster. Taking advantage of the full YJHK spectral
coverage of GIANO in a single exposure, we were able to measure several
hundreds of atomic and molecular lines that are suitable for chemical abundance
determinations. We also measured a prominent diffuse interstellar band at
lambda=1317.8 nm (vacuum). This provides an independent reddening estimate. The
radial velocities, Gaia proper motions, and extinction of seven red supergiants
in Alicante 7 and three in Alicante 10 are consistent with them being members
of the associations. One star toward Alicante 10 has kinematics and low
extinction that are inconsistent with a membership. By means of spectral
synthesis and line equivalent width measurements, we obtained chemical
abundances for iron-peak, CNO, alpha, other light, and a few neutron-capture
elements. We found average slightly subsolar iron abundances and solar-scaled
[X/Fe] abundance patterns for most of the elements, consistent with a thin-disk
chemistry. We found depletion of [C/Fe], enhancement of [N/Fe], and relatively
low 12C/13C<15, which is consistent with CN cycled material and possibly some
additional mixing in their atmospheres.",1908.07779v1
2019-08-28,Neutrino halo effect on collective neutrino oscillation in iron core-collapse supernova model of a 9.6 $M_{\odot}$ star,"We extend the multi-angle computational framework and investigate the time
evolution of the neutrino halo on collective neutrino oscillation in the core
collapse of an iron core progenitor. We find that in the case of the $9.6\, \rm
M_\odot$ progenitor adopted in this work, there are windows of time when the
effects of neutrino halo and collective neutrino oscillation are not
simultaneously large. Inside the shock, the impact of the inward-scattered halo
neutrino cannot in general be neglected compared to the outward-propagating
neutrino flux. However, during early epochs, collective neutrino oscillation is
effectively shut down by multi-angle matter suppression. During the
intermediate epoch, collective neutrino oscillation is not suppressed, but its
onset radius is beyond the still relatively small explosion shock front where
the halo is prominent. We also find in the case of the $9.6\, \rm M_\odot$
progenitor the halo neutrinos induce a delay in the onset of collective
neutrino oscillations. This causes novel flavor conversions which sharpen
collective neutrino oscillation spectral features. We predict that the
inclusion of neutrino halo effects makes neutrino signals that are more clearly
distinct from thermal emission that when halo neutrinos are omitted.",1908.10594v2
2019-09-04,Multi-epoch X-ray spectral analysis of the narrow-line Seyfert 1 galaxy Mrk 478,"A multi-epoch X-ray spectral and variability analysis is conducted for the
narrow-line Seyfert 1 (NLS1) active galactic nucleus (AGN) Mrk 478. All
available X-ray data from XMM-Newton and Suzaku satellites, spanning from 2001
to 2017, are modelled with a variety of physical models including partial
covering, soft-Comptonisation, and blurred reflection, to explain the observed
spectral shape and variability over the 16 years. All models are a similar
statistical fit to the data sets, though the analysis of the variability
between data sets favours the blurred reflection model. In particular, the
variability can be attributed to changes in flux of the primary coronal
emission. Different reflection models fit the data equally well, but differ in
interpretation. The use of reflionx predicts a low disc ionisation and power
law dominated spectrum, while relxill predicts a highly ionised and blurred
reflection dominated spectrum. A power law dominated spectrum might be more
consistent with the normal X-ray-to-UV spectral shape (aox). Both blurred
reflection models suggest a rapidly spinning black hole seen at a low
inclination angle, and both require a sub-solar (~0.5) abundance of iron. All
physical models require a narrow emission feature at 6.7 keV likely
attributable to Fe xxv emission, while no evidence for a narrow 6.4 keV line
from neutral iron is detected.",1909.01897v1
2019-09-16,Ferrovolcanism on metal worlds and the origin of pallasites,"As differentiated planetesimals cool, their cores can solidify from the
outside-in, as evidenced by paleomagnetic measurements and cooling rate
estimates of iron meteorites. The details of outside-in solidification and fate
of residual core melt are poorly understood. For a core primarily composed of
Fe and Ni alloyed with lighter constituent elements, like sulfur, such inward
core growth would likely be achieved by growth of solid FeNi dendrites. Growth
of FeNi dendrites results in interconnected pockets of residual melt that
become progressively enriched in sulfur up to a eutectic composition of 31 wt
percent sulfur as FeNi continues to solidify. Here we show that regions of
residual sulfur-enriched FeNi melt in the core attain sufficient excess
pressures to propagate via dikes into the mantle. Thus, core material will
intrude into the overlying rocky mantle or possibly even erupt onto the
plantesimals surface. We refer to these processes collectively as
ferrovolcanism. Our calculation show that ferrovolcanic surface eruptions are
more likely on bodies with mantles less than 50 km thick. We show that
intrusive ferromagmatism can produce pallasites, an enigmatic class of
meteorites composed of olivine crystals entrained in a matrix of FeNi metal.
Ferrovolcanic eruptions may explain the observations that Psyche has a bulk
density inconsistent with iron metorites yet shows evidence of a metallic
surface composition.",1909.07451v1
2019-09-24,Strongly correlated superconductor with polytypic 3D Dirac points,"Topological superconductors should be able to provide essential ingredients
for quantum computing, but are very challenging to realize. Spin-orbit
interaction in iron-based superconductors opens the energy gap between the
$p$-states of pnictogen and $d$-states of iron very close to the Fermi level,
and such $p$-states have been recently experimentally detected. Density
functional theory predicts existence of topological surface states within this
gap in FeTe$_{1-x}$Se$_x$ making it an attractive candidate material. Here we
use synchrotron-based angle-resolved photoemission spectroscopy and band
structure calculations to demonstrate that FeTe$_{1-x}$Se$_x$ (x=0.45) is a
superconducting 3D Dirac semimetal hosting type-I and type-II Dirac points and
that its electronic structure remains topologically trivial. We show that the
inverted band gap in FeTe$_{1-x}$Se$_x$ can possibly be realized by further
increase of Te content, but strong correlations reduce it to a sub-meV size,
making the experimental detection of this gap and corresponding topological
surface states very challenging, not to mention exact matching with the Fermi
level. On the other hand, the $p-d$ and $d-d$ interactions are responsible for
the formation of extremely flat band at the Fermi level pointing to its
intimate relation with the mechanism of high-T$_c$ superconductivity in IBS.",1909.10806v2
2019-11-08,Oxygen Reduction Reaction and X-ray Photoelectron Spectroscopy of Sputtered Fe-N-C Films,"Electrocatalysts for the oxygen reduction reaction (ORR) based on complexes
of iron and nitrogen in a carbon matrix (Fe-N-C) are a promising alternative to
platinum group metal (PGM) based catalysts in polymer electrolyte membrane
(PEM) fuel cells. Further improvements of Fe-N-C catalysts would benefit from
model thin film studies of activity and stability of catalytic sites, but
synthesis of Fe-N-C model thin films is challenging. Here we report on
synthesis and characterization of Fe-N-C thin films produced by co-sputtering
iron and carbon in a reactive nitrogen atmosphere onto removable glassy carbon
rotating disk electrode (RDE) tips. Scanning electron microscopy (SEM)
measurements indicate that the Fe-N-C films deposited at high temperature are
smoother than the films annealed at high temperature. ORR activity measured on
the thin Fe-N-C films is greater for both high-temperature samples than for the
room-temperature sample. From the analysis of X-ray photoelectron spectroscopy
(XPS) data, exposure of the films to high temperatures results in increased
graphitization of the carbon with the Fe-N-C films, and increased relative
amount of graphitic and hydrogenated nitrogen species. Overall the results of
this study demonstrate the feasibility of a thin film model system approach for
studying active sites in PGM-free catalysts.",1911.03368v1
2019-11-14,The Chemical Evolution of Iron-Peak Elements with Hypernovae,"We calculate the mean evolution of the iron-peak abundance ratios
[(Cr,Mn,Co,Zn)/Fe] in the Galaxy, using modern supernova and hypernova chemical
yields and a Galactic Chemical Evolution code that assumes homogeneous chemical
evolution. We investigate a range of hypernova occurrence rates and are able to
produce a chemical composition that is a reasonable fit to the observed values
in metal-poor stars. This requires a hypernova occurence rate that is large
(50%) in the early Universe, decreasing throughout evolution to a value that is
within present day observational constraints (>~ 1%). A large hypernova
occurence rate is beneficial to matching the high [Zn/Fe] observed in the most
metal-poor stars, although including hypernovae with progenitor mass >= 60
solar masses is detrimental to matching the observed [(Mn,Co)/Fe] evolution at
low [Fe/H]. A significant contribution from HNe seems to be critical for
producing supersolar [(Co,Zn)/Fe] at low metallicity, though more work will
need to be done in order to match the most extreme values. We also emphasise
the need to update models for the enrichment sources at higher metallicity, as
the satisfactory recovery of the solar values of [(Cr,Mn,Co,Zn)/Fe] still
presents a challenge.",1911.05901v2
2019-11-21,Weakness of Correlation Effect Manifestation in BaNi$_2$As$_2$: ARPES and LDA+DMFT study,"The electronic spectral function of BaNi$_2$As$_2$ is investigated using both
the angle-resolved photoemission spectroscopy (ARPES) and a combined
computational scheme of local density approximation together with dynamical
mean-field theory (LDA+DMFT). In contrast to well studied isostructural iron
arsenide high temperature superconductors, the BaNi$_2$As$_2$ demonstrate weak
correlation effects although Ni-3d elections have even lager on-site
interaction than Fe-3d ones. LDA+DMFT effective mass enhancement for bands
crossing the Fermi level is found to be only about $1.2$ which agrees well with
ARPES data. This reduction of the correlation manifestation with respect to
iron pnictides comes from the increase of 3d-orbital filling, when going from
Fe to Ni. The electron correlations cause remarkable reconstruction of the bare
BaNi$_2$As$_2$ LDA band structure below $-0.8$ eV due to self-energy effect. A
simplified toy model to understand weakness of correlation effects in
BaNi$_2$As$_2$ and to describe the LDA+DMFT self-energy shape is discussed. For
more realistic comparison of LDA+DMFT spectral function maps with ARPES data we
take into account several experimental features: the photoemission
cross-section, the experimental energy and angular resolutions and the
photo-hole lifetime effects. Thus presented here LDA+DMFT calculations with
experimental features included provide nearly qualitative agreement with ARPES
data and assure the observation of a dramatic apparent decrease of the
correlation strength compared to the Fe compounds.",1911.09300v2
2020-01-03,Disappearance of the Fe K$α$ emission line in Ultra Compact X-ray Binaries 4U 1543-624 and Swift J1756.9-2508,"We investigate the long-term variability of the K$\alpha$ line of iron in the
spectra of two Ultra Compact X-ray Sources (UCXBs) with C/O-rich donors. We
revisit archival observations by five different X-ray telescopes, over a
~twenty year period. Adopting physically motivated models for the spectral
continuum, we probe the long-term evolution of the source emission in a
self-consistent manner enabling physical interpretation of potential
variability in the primary X-ray emission continuum and/or any emission lines
from reflection off the accretion disk. We find that the spectral shape and
flux of the source emission (for both objects) has remained almost constant
throughout all the observations, displaying only minor variability in some
spectral parameters and the source flux (largest variation is a ~25% drop in
the flux of Swift J1756.9-2508). We note a striking variability of the Fe
K$\alpha$ line which fluctuates from a notable equivalent width of ~66-100 eV
in 4U 1543-624 and ~170 eV in Swift J1756.9-2508, to non-detections with upper
limits of 2-8 eV. We argue that the disappearance of the iron line is due to
the screening of the Fe K$\alpha$ line by the overabundant oxygen in the
C/O-rich UCXBs. This effect is cancelled when oxygen becomes fully ionized in
the inner disk region, resulting in the variability of the Fe K$\alpha$ line in
an otherwise unaltered spectral shape. This finding supports earlier
predictions on the consequences of H-poor, C/O-rich accretion disk on
reflection induced fluorescent lines in the spectra of UCXBs.",2001.00713v2
2020-01-06,Are Faint Supernovae Responsible for Carbon-Enhanced Metal-Poor Stars?,"Mixing and fallback models in faint supernova models are supposed to
reproduce the abundance patterns of observed carbon-enhanced metal-poor (CEMP)
stars in the Galactic halo. A fine tuning of the model parameters for
individual stars is required to reproduce the observed ratios of carbon to
iron. We focus on extremely metal-poor stars formed out of the ejecta from the
mixing and fallback models using a chemical evolution model. Our chemical
evolution models take into account the contribution of individual stars to
chemical enrichment in host halos together with their evolution in the context
of the hierarchical clustering. Parametrized models of mixing and fallback
models for Pop. III faint supernovae are implemented in the chemical evolution
models with merger trees to reproduce the observed CEMP stars. A variety of
choices for model parameters on star formation and metal-pollution by faint
supernovae is unable to reproduce the observed stars with [Fe/H] < -4 and [C/H]
> -2, which are the majority of CEMP stars among the lowest metallicity stars.
Only possible solution is to form stars from small ejecta mass, which produces
an inconsistent metallicity distribution function. We conclude that not all the
CEMP stars are explicable by the mixing and fallback models. We also tested the
contribution of binary mass transfers from AGB stars that are also supposed to
reproduce the abundances of known CEMP stars. This model reasonably reproduces
the distribution of carbon and iron abundances simultaneously only if we assume
that long-period binaries are favored at [Fe/H] < -3.5.",2001.01420v1
2020-02-09,A detailed study on the reflection component for the Black Hole Candidate MAXI J1836-194,"We present a detailed spectral analysis of the black hole candidate MAXI
J1836-194. The source was caught in the intermediate state during its 2011
outburst by Suzaku and RXTE. We jointly fit the X-ray data from these two
missions using the relxill model to study the reflection component, and a steep
inner emissivity profile indicating a compact corona as the primary source is
required in order to achieve a good fit. In addition, a reflection model with a
lamp-post configuration (relxilllp), which is normally invoked to explain the
steep emissivity profile, gives a worse fit and is excluded at 99% confidence
level compared to relxill. We also explore the effect of the ionization
gradient on the emissivity profile by fitting the data with two relativistic
reflection components, and it is found that the inner emissivity flattens.
These results may indicate that the ionization state of the disc is not
constant. All the models above require a supersolar iron abundance higher than
4.5. However, we find that the high-density version of reflionx can describe
the same spectra even with solar iron abundance well. A moderate rotating black
hole (a* = 0.84-0.94) is consistently obtained by our models, which is in
agreement with previously reported values.",2002.03315v1
2020-02-11,AstroSat/LAXPC view of GX 17+2: Spectral Evolution along the Z-track,"In this paper, we present the first results obtained using $\sim$ 50 ks
observations of the bright low-mass X-ray binary (LMXB) GX 17+2 with Large Area
X-ray Proportional Counter (LAXPC) onboard {\it AstroSat}. The source traced
out a complete Z-track in the hardness intensity diagram (HID). The spectra at
different sections of the Z-diagram are well described by either a combination
of a thermal Comptonization component, a power-law and a relativistic iron line
or a model consisting of a thermal disk component, a single temperature
blackbody, a power-law and a relativistic iron line. Fitting the spectra with
both phenomenological models suggests that the power-law component is strong in
the horizontal branch (HB), becomes weaker as the source moves down the normal
branch (NB) and then again becomes stronger as the sources moves up the flaring
branch (FB). However, we find that the strength of the power-law component is
model dependent, although the trend in the variation of the power-law strength
along the Z-track is similar. A simple model composed by a Comptonized emission
and power-law component, convolved with the ionized reflection, also describes
the spectra very well.
  A normal branch oscillation (NBO) with a centroid frequency 7.42$\pm$0.23 Hz,
quality factor (Q) $\sim$ 4.88, rms 1.41$\pm$0.29\% and significance
5.1$\sigma$ is detected at the middle of the NB. The parameters of the
Comptonized emission show a systematic evolution along the Z-diagram. The
optical depth of the corona increases as the source moves up along the FB,
suggesting possible trigger of an outflow or dumping of the disc material in to
the corona by radiation pressure.",2002.04489v1
2020-02-18,The Solar wind prevents re-accretion of debris after Mercury's giant impact,"The planet Mercury possesses an anomalously large iron core, and a
correspondingly high bulk density. Numerous hypotheses have been proposed in
order to explain such a large iron content. A long-standing idea holds that
Mercury once possessed a larger silicate mantle which was removed by a giant
impact early in the the Solar system's history. A central problem with this
idea has been that material ejected from Mercury is typically re-accreted onto
the planet after a short (~Myr) timescale. Here, we show that the primordial
Solar wind would have provided sufficient drag upon ejected debris to remove
them from Mercury-crossing trajectories before re-impacting the planet's
surface. Specifically, the young Sun likely possessed a stronger wind, fast
rotation and strong magnetic field. Depending upon the time of the giant
impact, the ram pressure associated with this wind would push particles outward
into the Solar system, or inward toward the Sun, on sub-Myr timescales,
depending upon the size of ejected debris. Accordingly, the giant impact
hypothesis remains a viable pathway toward the removal of planetary mantles,
both on Mercury and extrasolar planets, particularly those close to young stars
with strong winds.",2002.07847v2
2020-02-20,Chemical Diversity of Super-Earths As a Consequence of Formation,"Recent observations of rocky super-Earths have revealed an apparent wider
distribution of Fe/Mg ratios, or core to mantle ratios, than the planets in our
Solar System. This study aims to understand how much of the chemical diversity
in the super-Earth population can arise from giant impacts during planetary
formation. Planet formation simulations have only recently begun to treat
collisions more realistically in an attempt to replicate the planets in our
Solar System. We investigate planet formation more generally by simulating the
formation of rocky super-Earths with varying initial conditions using a version
of SyMBA, a gravitational N-body code, that incorporates realistic collisions.
We track the maximum plausible change in composition after each impact. The
final planets span a range of Fe/Mg ratios similar to the Solar System planets,
but do not completely match the distribution in super-Earth data. We only form
a few planets with minor iron-depletion, suggesting other mechanisms are at
work. The most iron-rich planets have a lower Fe/Mg ratio than Mercury, and are
less enriched than planets such as Kepler-100b. This indicates that further
work on our understanding of planet formation and further improvement of
precision of mass and radius measurements are required to explain planets at
the extremes of this Fe/Mg distribution.",2002.09042v1
2020-04-17,Thermodynamic signatures of an antiferromagnetic quantum critical point inside a superconducting dome,"Recent experiments in unconventional superconductors, and in particular
iron-based materials, have reported evidence of an antiferromagnetic quantum
critical point (AFM-QCP) emerging inside the superconducting dome of the phase
diagram. Fluctuations associated with such an AFM-QCP are expected to promote
unusual temperature dependencies of thermodynamic quantities. Here, we compute
the $T$ dependence of the specific heat $C(T)$ deep inside a fully gapped
$s^{+-}$ superconducting state as the AFM-QCP is approached. We find that, at
the AFM-QCP, the specific heat $C(T)$ vanishes quadratically with temperature,
as opposed to the typical exponential suppression seen in fully-gapped BCS
superconductors. This robust result is due to a non-analytic contribution to
the free-energy arising from the general form of the bosonic (AFM) propagator
in the SC state. Away from the AFM-QCP, as temperature is lowered, $C(T)$ shows
a crossover from a $T^2$ behavior to an exponential behavior, with the
crossover temperature scale set by the value of the superconducting gap and the
distance to the QCP. We argue that these features in the specific heat can be
used to unambiguously determine the existence of AFM-QCPs inside the
superconducting domes of iron-based and other fully gapped unconventional
superconductors.",2004.08300v3
2020-04-22,Crystal structures of Fe-gluconate,"Fe-gluconate, Fe(C_6H_11O_7_2xH_2O is a well-known material widely used for
iron supplementation. On the other hand, it is used in food industry as a
coloring agent, in cosmetic industry for skin and nail conditioning and
metallurgy. Despite of wide range of applications its physical properties were
not studied extensively. In this study, Fe-gluconate with three different
amount of water viz. x=2 (fully hydrated, 0 < x < 2 (intermediate) and x=0
(dry) was investigated by means of X-ray diffraction (XRD) and M\""ossbauer
spectroscopic (MS) methods. The former in the temperature range of 20-300 K,
and the latter at 295 K. Based on the XRD measurements crystallographic
structures were determined: monoclinic (space group I2) for the hydrated sample
and triclinic (space group P1) for the dry sample. The partially hydrated
sample was two-phased. Unit cells parameters for both structures show strong,
very complex and non-monotonic temperature dependences. M\""ossbauer
spectroscopic measurements gave evidence that iron in all samples exist in form
of Fe(II) and Fe(III) ions. The amount of the latter equals to ca.30% in the
hydrated sample and to ca.20% in the dry one.",2004.10535v3
2020-04-24,Magnetism driven by strong electronic correlation in the heavily carrier-doped iron oxypnictide LaFeAsO$_{0.49}$H$_{0.51}$,"The magnetism of the second antiferromagnetic phase (AF2) arising in the
iron-based LaFeAsO$_{1-x}$H$_{x}$ superconductor for $x\gtrsim0.4$ was
investigated by muon spin rotation measurements under hydrostatic pressure up
to 2.6 GPa. The N\'eel temperature ($T_{\rm N}$) obtained for a sample with
$x=0.51$ exhibits considerably greater sensitivity to pressure than that in the
pristine antiferromagnetic phase (AF1, $x\lesssim0.06$). Moreover, while the
AF1 phase is always accompanied by the structural transition (from tetragonal
to orthorhombic) at a temperature ($T_{\rm s}$) which is slightly higher than
$T_{\rm N}$, the AF2 phase prevails at higher pressures above $\sim$1.5 GPa
where the structural transition is suppressed ($T_{\rm s}=0$). These features
indicate that the microscopic origin of the AF2 phase is distinct from that of
AF1, suggesting that electronic correlation plays important role in the former
phase. We argue that the orbital-selective Mott transition is a plausible
scenario to account for the observed pressure dependence of $T_{\rm N}$ and
$T_{\rm s}$ in the AF2 phase.",2004.11547v2
2020-05-16,Vacancy-driven non-cubic local structure and magnetic anisotropy tailoring in Fe$_x$O-Fe$_{3-δ}$O$_4$ nanocrystals,"In contrast to bulk materials, nanoscale crystal growth is critically
influenced by size- and shape-dependent properties. However, it is challenging
to decipher how stoichiometry, in the realm of mixed-valence elements, can act
to control physical properties, especially when complex bonding is implicated
by short and long-range ordering of structural defects. Here, solution-grown
iron-oxide nanocrystals (NCs) of the pilot wustite system are found to convert
into iron-deficient rock-salt and ferro-spinel sub-domains, but attain a
surprising tetragonally distorted local structure. Cationic vacancies within
chemically uniform NCs are portrayed as the parameter to tweak the underlying
properties. These lattice imperfections are shown to produce local
exchange-anisotropy fields that reinforce the nanoparticles magnetization and
overcome the influence of finite-size effects. The concept of atomic-scale
defect control in subcritical size NCs, aspires to become a pathway to
tailor-made properties with improved performance for hyperthermia heating over
defect-free NCs.",2005.07947v1
2020-05-28,Rocklines as Cradles for Refractory Solids in the Protosolar Nebula,"In our solar system, terrestrial planets and meteoritical matter exhibit
various bulk compositions. To understand this variety of compositions,
formation mechanisms of meteorites are usually investigated via a thermodynamic
approach that neglect the processes of transport throughout the protosolar
nebula. Here, we investigate the role played by rocklines
(condensation/sublimation lines of refractory materials) in the innermost
regions of the protosolar nebula to compute the composition of particles
migrating inward the disk as a function of time. To do so, we utilize a
one-dimensional accretion disk model with a prescription for dust and vapor
transport, sublimation and recondensation of refractory materials (ferrosilite,
enstatite, fayalite, forsterite, iron sulfide, metal iron and nickel). We find
that the diversity of the bulk composition of cosmic spherules, chondrules and
chondrites can be explained by their formation close to rocklines, suggesting
that solid matter is concentrated in the vicinity of these
sublimation/condensation fronts. Although our model relies a lot on the number
of considered species and the availability of thermodynamic data governing
state changes, it suggests that rocklines played a major role in the formation
of small and large bodies in the innermost regions of the protosolar nebula.
Our model gives insights on the mechanisms that might have contributed to the
formation of Mercury's large core.",2005.14116v3
2020-06-12,SDSS J124043.01+671034.68: The partially burned remnant of a low-mass white dwarf that underwent thermonuclear ignition?,"The white dwarf SDSS J124043.01+671034.68 (SDSS J1240+6710) was previously
found to have an oxygen-dominated atmosphere with significant traces of neon,
magnesium, and silicon. A possible origin via a violent late thermal pulse or
binary interactions have been suggested to explain this very unusual
photospheric composition. We report the additional detection of carbon, sodium,
and aluminium in far-ultraviolet and optical follow-up spectroscopy. No
iron-group elements are detected, with tight upper limits on iron, cobalt and
nickel, suggesting that the star underwent partial oxygen burning, but failed
to ignite silicon burning. Modelling the spectral energy distribution and
adopting the distance based on the Gaia parallax, we infer a low white dwarf
mass, M(wd)=0.41+/-0.05Msun. The large space velocity of SDSS J1240+6710,
computed from the Gaia proper motion and its radial velocity, is compatible
with a Galactic rest-frame velocity of ~250km/s in the opposite direction with
respect to the Galactic rotation, strongly supporting a binary origin of this
star. We discuss the properties of SDSS J1240+6710 in the context of the
recently identified survivors of thermonuclear supernovae, the D6 and LP 40-365
stars, and conclude that it is unlikely related to either of those two groups.
We tentatively suggest that SDSS J1240+6710 is the partially burned remnant of
a low-mass white dwarf that underwent a thermonuclear event.",2006.07381v1
2020-06-15,Opacity Driven Convection and Variability in Accretion Disks around Supermassive Black Holes,"We study the structure of accretion disks around supermassive black holes in
the radial range $30\sim 100$ gravitational radii, using a three dimensional
radiation magneto-hydrodynamic simulation. For typical conditions in this
region of Active Galactic Nuclei (AGN), the Rosseland mean opacity is expected
to be larger than the electron scattering value. We show that the iron opacity
bump causes the disk to be convective unstable. Turbulence generated by
convection puffs up the disk due to additional turbulent pressure support and
enhances the local angular momentum transport. This also results in strong
fluctuations in surface density and heating of the disk. The opacity drops with
increasing temperature and convection is suppressed. The disk cools down and
the whole process repeats again. This causes strong oscillations of the disk
scale height and luminosity variations by more than a factor of $\approx 3-6$
over a few years' timescale. Since the iron opacity bump will move to different
locations of the disk for black holes with different masses and accretion
rates, we suggest that this is a physical mechanism that can explain the
variability of AGN with a wide range of amplitudes over a time scale of years
to decades.",2006.08657v1
2020-07-05,Size and temperature dependent magnetization of iron nanoclusters,"The magnetic behavior of bcc iron nanoclusters, with diameters between 2 and
8 nm, is investigated by means of spin dynamics (SD) simulations coupled to
molecular dynamics (MD-SD), using a distance-dependent exchange interaction.
Finite-size effects in the total magnetization as well as the influence of the
free surface and the surface/core proportion of the nanoclusters are analyzed
in detail for a wide temperature range, going beyond the cluster and bulk Curie
temperatures. Comparison is made with experimental data and with theoretical
models based on the mean-field Ising model adapted to small clusters, and
taking into account the influence of low coordinated spins at free surfaces.
Our results for the temperature dependence of the average magnetization per
atom M(T), including the thermalization of the transnational lattice degrees of
freedom, are in very good agreement with available experimental measurements on
small Fe nanoclusters. In contrast, significant discrepancies with experiment
are observed if the translational degrees of freedom are artificially frozen.
The finite-size effects on M(T) are found to be particularly important near the
cluster Curie temperature. Simulated magnetization above the Curie temperature
scales with cluster size as predicted by models assuming short-range magnetic
ordering (SRMO). Analytical approximations to the magnetization as a function
of temperature and size are proposed.",2007.02230v2
2020-07-06,On the Remarkable Superconductivity of FeSe and its Close Cousins,"Emergent electronic phenomena in iron-based superconductors have been at the
forefront of condensed matter physics for more than a decade. Much has been
learned about the origin and intertwined roles of ordered phases, including
nematicity, magnetism, and superconductivity, in this fascinating class of
materials. In recent years, focus has been centered on the peculiar and highly
unusual properties of FeSe and its close cousins. This family of materials has
attracted considerable attention due to the discovery of unexpected
superconducting gap structures, a wide range of superconducting critical
temperatures, and evidence for nontrivial band topology, including associated
spin-helical surface states and vortex-induced Majorana bound states. Here, we
review superconductivity in iron chalcogenide superconductors, including bulk
FeSe, doped bulk FeSe, FeTe$_{1-x}$Se$_x$, intercalated FeSe materials, and
monolayer FeSe and FeTe$_{1-x}$Se$_x$ on SrTiO$_3$. We focus on the
superconducting properties, including a survey of the relevant experimental
studies, and a discussion of the different proposed theoretical pairing
scenarios. In the last part of the paper, we review the growing recent evidence
for nontrivial topological effects in FeSe-related materials, focusing again on
interesting implications for superconductivity.",2007.02966v2
2020-07-11,Site preference of Fe atoms in the olivine (Fe$_x$Mg$_{2-x}$)SiO$_4$ and its surface,"Olivine is involved in many natural reactions and industrial reactions as a
catalyst. The catalytic ability is highly possible rely on the Fe$^{2+}$ in
olivine. We use density functional theory calculation and thermodynamics to
investigate the site preference of Fe atom in olivine which composition from
iron-rich to iron-poor and its surfaces. The Fe$^{2+}$ always shows its high
spin (quintet) state which has larger ion radius than Mg$^{2+}$ in olivine
crystal and surfaces. The Fe$^{2+}$ inside the surface slab prefers the smaller
M1 site than M2 site by enlarging the metal-oxygen octahedra when occupied the
metal site as in the bulk system. Energy contribution of entropies accumulation
caused temperature raise stops this preference at the temperature where a
cation order-disorder distribution energy crossover happen in olivine. Surface
exposed site provide Fe$^{2+}$ large space due its unsaturated nature. This
lead a higher level of preference of Fe$^{2+}$ to the surface site than any
metal site inside the crystal no matter M1 or M2 site is exposed. This indicate
the Fe$^{2+}$ in the bulk system can diffuse to a metal site exposed on the
surface driven by the energy difference. Many reactions can use the on surface
Fe$^{2+}$ as a catalyst because of the active chemical behavior of Fe.
Meanwhile this energetics preference should be considered in the future model
to explain the natural observed zoning olivine have a high Fe edge and low Fe
center. These microscopic understanding can be essential to many olivine
related geochemical and astrochemical reactions.",2007.05851v3
2020-07-19,A geometric approach to separate the effects of magnetic susceptibility and chemical shift/exchange in a phantom with isotropic magnetic susceptibility,"Purpose: To separate the effects of magnetic susceptibility and chemical
shift/exchange in a phantom with isotropic magnetic susceptibility. To generate
a chemical shift/exchange-corrected quantitative susceptibility mapping (QSM)
result.
  Theory and Methods: Magnetic susceptibility and chemical shift/exchange are
the properties of a material. Both are known to induce the resonance frequency
shift in MRI. In current QSM, the susceptibility is reconstructed from the
frequency shift, ignoring the contribution of the chemical shift/exchange. In
this work, a simple geometric approach, which averages the frequency shift maps
from three orthogonal B0 directions to generate a chemical shift/exchange map,
is developed using the fact that the average nullifies the (isotropic)
susceptibility effects. The resulting chemical shift/exchange map is subtracted
from the total frequency shift, producing a frequency shift map solely from
susceptibility. Finally, this frequency shift map is reconstructed to a
susceptibility map using a QSM algorithm. The proposed method is validated in
numerical simulations and applied to phantom experiments with olive oil, bovine
serum albumin, ferritin, and iron oxide solutions.
  Results: Both simulations and experiments confirm that the method
successfully separates the contributions of the susceptibility and chemical
shift/exchange, reporting the susceptibility and chemical shift/exchange of
olive oil (susceptibility: 0.62 ppm, chemical shift: -3.60 ppm), bovine serum
albumin (susceptibility: -0.059 ppm, chemical shift: 0.008 ppm), ferritin
(susceptibility: 0.125 ppm, chemical shift: -0.005 ppm), and iron oxide
(susceptibility: 0.30 ppm, chemical shift: -0.039 ppm) solutions.
  Conclusion: The proposed method successfully separates the susceptibility and
chemical shift/exchange in phantoms with isotropic magnetic susceptibility.",2007.09614v1
2020-07-21,Interplay of itinerant magnetism and reentrant spin-glass behavior in Fe$_{x}$Cr$_{1-x}$,"When suppressing the itinerant antiferromagnetism in chromium by doping with
the isostructual itinerant ferromagnet iron, a dome of spin-glass behavior
emerges around a putative quantum critical point at an iron concentration $x
\approx 0.15$. Here, we report a comprehensive investigation of polycrystalline
samples of Fe$_{x}$Cr$_{1-x}$ in the range $0.05 \leq x \leq 0.30$ using x-ray
powder diffraction, magnetization, ac susceptibility, and neutron
depolarization measurements, complemented by specific heat and electrical
resistivity data for $x = 0.15$. Besides antiferromagnetic ($x < 0.15$) and
ferromagnetic regimes ($0.15 \leq x$), we identify a dome of reentrant
spin-glass behavior at low temperatures for $0.10 \leq x \leq 0.25$ that is
preceded by a precursor phenomenon. Neutron depolarization indicates an
increase of the size of ferromagnetic clusters with increasing $x$ and the
Mydosh parameter $\phi$, inferred from the ac susceptibility, implies a
crossover from cluster-glass to superparamagnetic behavior. Taken together,
these findings consistently identify Fe$_{x}$Cr$_{1-x}$ as an
itinerant-electron system that permits to study the evolution of spin-glass
behavior of gradually varying character in unchanged crystalline environment.",2007.10644v1
2021-02-03,Stellar astrophysics in the near UV with VLT-CUBES,"Alongside future observations with the new European Extremely Large Telescope
(ELT), optimised instruments on the 8-10m generation of telescopes will still
be competitive at 'ground UV' wavelengths (3000-4000 A). The near UV provides a
wealth of unique information on the nucleosynthesis of iron-peak elements,
molecules, and neutron-capture elements. In the context of development of the
near-UV CUBES spectrograph for ESO's Very Large Telescope (VLT), we are
investigating the impact of spectral resolution on the ability to estimate
chemical abundances for beryllium and more than 30 iron-peak and heavy
elements. From work ahead of the Phase A conceptual design of CUBES, here we
present a comparison of the elements observable at the notional resolving power
of CUBES (R~20,000) to those with VLT-UVES (R~40,000). For most of the
considered lines signal-to-noise is a more critical factor than resolution. We
summarise the elements accessible with CUBES, several of which (e.g. Be, Ge,
Hf) are now the focus of quantitative simulations as part of the ongoing Phase
A study.",2102.02205v1
2021-02-07,Crystal structure and properties of iron-based spin-chain compound Ba9Fe3Se15,"We report the synthesis of a new quasi one-dimensional (1D) iron selenide.
Ba9Fe3Se15 was synthesized at high temperature and high pressure of 5.5 GPa and
systematically studied via structural, magnetic and transport measurements at
ambient and at high-pressures. Ba9Fe3Se15 crystallizes in a monoclinic
structure and consists of face-sharing FeSe6 octahedral chains along the c
axis. At ambient pressure it exhibits an insulating behavior with a band gap
~460 meV and undergoes a ferrimagnet-like phase transition at 14 K. Under high
pressure, a complete metallization occurs at ~29 GPa, which is accompanied by a
spin state crossover from high spin (HS) state to low spin (LS) state. The LS
appears for pressures P >36 GPa.",2102.03708v1
2021-02-07,The phonon mechanism explanation of the superconductivity dichotomy between FeSe and FeS monolayers on STO and other substrates,"It was observed recently (K. Shigekawa et al, PNAS 116, 2470 (2019)) that
while monolayer iron chalcigenide FeSe on SrTiO3 (STO) substrate has a very
high critical temperature, its chemical and structural ""twin"" material FeS=STO
has a very low Tc if any. To explain this the substrate interfacial phonon
model of superconductivity in iron chalcogenides is further developed. The main
glue is the oxygen ion (60mev) vibrations longitudinal optical (LO) mode. The
mode propagates mainly in the TiO2 layer adjacent to the monolayer (and
genrally present also in similar highly polarized ionic crystals like BaTiO3;
rutile, anatase). It has stronger electron - phonon coupling to electron gas in
FeSe than a well known (100mev) harder LO mode. It is shown that while (taking
into account screened Coulomb repulsion efects) the critical temperature of
FeSe on STO and TiO2 is above 65K, it becomes less than 5K for FeS due to two
factors suppressing the electron - phonon coupling. The efective mass in the
later is twice smaller and in addition the distance between the electron gas in
FeSe to the vibrating substrate oxygen atoms is 15% smaller than in FeS
reducinng the central peak in electron-phonon interaction. The theory is
extended to other ionic insulating substrates.",2102.03854v1
2021-02-09,Testing a Prototype 1U CubeSat on a Stratospheric Balloon Flight,"High-altitude balloon experiments are becoming very popular among
universities and research institutes as they can be used for testing
instruments eventually intended for space, and for simple astronomical
observations of Solar System objects like the Moon, comets, and asteroids,
difficult to observe from the ground due to atmosphere. Further, they are one
of the best platforms for atmospheric studies. In this experiment, we build a
simple 1U CubeSat and, by flying it on a high-altitude balloon to an altitude
of about 30 km, where the total payload weighted 4.9 kg and examine how some
parameters, such as magnetic field, humidity, temperature or pressure, vary as
a function of altitude. We also calibrate the magnetometer to remove the hard
iron and soft iron errors. Such experiments and studies through a stratospheric
balloon flights can also be used to study the performance of easily available
commercial sensors in extreme conditions as well. We present the results of the
first flight, which helped us study the functionality of the various sensors
and electronics at low temperatures reaching about -40 degrees Celsius. Further
the motion of the payload has been tracked throughout this flight. This
experiment took place on 8 March 2020 from the CREST campus of the Indian
Institute of Astrophysics, Bangalore. Using the results from this flight, we
identify and rectify the errors to obtain better results from the subsequent
flights.",2102.04847v1
2021-02-21,"Meteoritic Proteins with Glycine, Iron and Lithium","We report that polymer amide [1] with a protein backbone of mainly glycine
units and iron is present in the CV3 meteorites Acfer 086, Allende and KABA.
The evidence for this is from particles of these meteorites after Folch
extraction being analyzed by MALDI mass spectrometry and from the 3D physical
structures that form in the various Folch solvent phases. The two physical
forms we observe are branching rods and entrapping spheres on the 100micron
scale. Two potential molecular structures of polymer amide are presented in
this report. One we term hemolithin of mass 2320Da, contains glycine,
hydroxy-glycine, Fe, O and Li. The other, we term hemoglycin of mass 1494Da is
of glycine, hydroxy-glycine, Fe and O. Hemoglycin is connected covalently in
triplets by silicon to form a triskelion. Analysis of the complete spectrum of
isotopes associated with each molecular fragment shows very high 2H enhancement
above terrestrial averaging 25,700 parts per thousand (sigma = 3,500, n=15),
confirming extra-terrestrial origin and hence the existence of these molecules
within the asteroid parent body of the CV3 meteorite class. The hemoglycin
triskelia join via silicon bonds into an extended lattice, as seen in mass
spectrometry of lattice fragments at m/z 4641 and above [2]. The identification
of hemolithin and hemoglycin required careful methodology at room temperature
with the minimum of steps up to mass spectrometry analysis ensuring that only
the laser step fragmented the molecules. The 3D structures were imaged through
permanently closed Folch extraction V-vials at a magnification of 10.",2102.10700v1
2021-02-22,"Estimating SARS-CoV-2 Infections from Deaths, Confirmed Cases, Tests, and Random Surveys","There are many sources of data giving information about the number of
SARS-CoV-2 infections in the population, but all have major drawbacks,
including biases and delayed reporting. For example, the number of confirmed
cases largely underestimates the number of infections, deaths lag infections
substantially, while test positivity rates tend to greatly overestimate
prevalence. Representative random prevalence surveys, the only putatively
unbiased source, are sparse in time and space, and the results come with a big
delay. Reliable estimates of population prevalence are necessary for
understanding the spread of the virus and the effects of mitigation strategies.
We develop a simple Bayesian framework to estimate viral prevalence by
combining the main available data sources. It is based on a discrete-time SIR
model with time-varying reproductive parameter. Our model includes likelihood
components that incorporate data of deaths due to the virus, confirmed cases,
and the number of tests administered on each day. We anchor our inference with
data from random sample testing surveys in Indiana and Ohio. We use the results
from these two states to calibrate the model on positive test counts and
proceed to estimate the infection fatality rate and the number of new
infections on each day in each state in the USA. We estimate the extent to
which reported COVID cases have underestimated true infection counts, which was
large, especially in the first months of the pandemic. We explore the
implications of our results for progress towards herd immunity.",2102.10741v1
2021-06-03,Ultrafast demagnetization of iron induced by optical vs terahertz pulses,"We study ultrafast magnetization quenching of ferromagnetic iron following
excitation by an optical vs a terahertz pump pulse. While the optical pump
(photon energy of 3.1 eV) induces a strongly nonthermal electron distribution,
terahertz excitation (~4 meV) results in a quasi-thermal perturbation of the
electron population. The pump-induced spin and electron dynamics are
interrogated by the magneto-optic Kerr effect (MOKE). A deconvolution procedure
allows us to push the time resolution down to 130 fs, even though the driving
terahertz pulse is more than 0.5 ps long. Remarkably, the MOKE signals exhibit
an almost identical time evolution for both optical and terahertz pump pulses,
despite the three orders of magnitude different number of excited electrons. We
are able to quantitatively explain our results using a model based on
quasi-elastic spin-flip scattering. It shows that in the small-perturbation
limit, the rate of demagnetization of a metallic ferromagnet is proportional to
the excess energy of the electrons, independent of the precise shape of their
distribution. Our results reveal that the dynamics of ultrafast demagnetization
and of the closely related terahertz spin transport do not depend on the pump
photon energy.",2106.01967v1
2021-06-14,Spin-pure Stochastic-CASSCF via GUGA-FCIQMC applied to Iron Sulfur Clusters,"In this work we demonstrate how to compute the one- and two-body reduced
density matrices within the spin-adapted full configuration interaction quantum
Monte Carlo (FCIQMC) method, which is based on the graphical unitary group
approach (GUGA). This allows us to use GUGA-FCIQMC as a spin-pure configuration
interaction (CI) eigensolver within the complete active space self-consistent
field (CASSCF) procedure, and hence to stochastically treat active spaces far
larger than conventional CI solvers whilst variationally relaxing orbitals for
specific spin-pure states. We apply the method to investigate the spin-ladder
in iron-sulfur dimer and tetramer model systems. We demonstrate the importance
of the orbital relaxation by comparing the Heisenberg model magnetic coupling
parameters from the CASSCF procedure to those from a CI-only procedure based on
restricted open-shell Hartree-Fock orbitals. We show that orbital relaxation
differentially stabilizes the lower spin states, thus enlarging the coupling
parameters with respect to the values predicted by ignoring orbital relaxation
effects. Moreover, we find that while CI eigenvalues are well fit by a simple
bilinear Heisenberg Hamiltonian, the CASSCF eigenvalues exhibits deviations
that necessitate the inclusion of biquadratic terms in the model Hamiltonian.",2106.07775v1
2021-06-22,A two-stage robust optimization approach for oxygen flexible distribution under uncertainty in iron and steel plants,"Oxygen optimal distribution is one of the most important energy management
problems in the modern iron and steel industry. Normally, the supply of the
energy generation system is determined by the energy demand of manufacturing
processes. However, the balance between supply and demand fluctuates frequently
due to the uncertainty arising in manufacturing processes. In this paper, we
developed an oxygen optimal distribution model considering uncertain demands
and proposed a two-stage robust optimization (TSRO) with a budget-based
uncertainty set that protects the initial distribution decisions with low
conservatism. The main goal of the TSRO model is to make wait-and-see decisions
maximizing production profits and make here-and-now decisions minimizing
operational stability and surplus/shortage penalty. To represent the
uncertainty set of energy demands, we developed a Gaussian process (GP)-based
time series model to forecast the energy demands of continuous processes and a
capacity-constrained scheduling model to generate multi-scenario energy demands
of discrete processes. We carried out extensive computational studies on TSRO
and its components using well-synthetic instances from historical data. The
results of model validation and analysis are promising and demonstrate our
approach is adapted to solve industrial cases under uncertainty.",2106.11635v1
2021-06-23,Correlation Between Spin and Orbital Dynamics During Laser-Induced Femtosecond Demagnetization,"Spin and orbital angular momenta are two intrinsic properties of an electron
and are responsible for the physics of a solid. How the spin and orbital evolve
with respect to each other on several hundred femtoseconds is largely unknown,
but it is at the center of laser-induced ultrafast demagnetization. In this
paper, we introduce a concept of the spin-orbital correlation diagram, where
spin angular momentum is plotted against orbital angular momentum, much like
the position-velocity phase diagram in classical mechanics. We use four sets of
highly accurate time-resolved x-ray magnetic circular dichroism (TR-XMCD) data
to construct four correlation diagrams for iron and cobalt. To our surprise, a
pattern emerges. The trace on the correlation diagram for iron is an arc, and
at the end of demagnetization, it has a pronounced cusp. The correlation
diagram for cobalt is different and appears more linear, but with kinks. We
carry out first-principles calculations with two different methods:
time-dependent density functional theory (TDDFT) and time-dependent Liouville
density functional theory (TDLDFT). These two methods agree that the
experimental findings for both Fe and Co are not due t experimental errors. It
is the spin-orbit coupling that correlates the spin dynamics to the orbital
dynamics.Microscopically, Fe and Co have different orbital occupations, which
leads to distinctive correlation diagrams. We believe that this correlation
diagram presents a useful tool to better understand spin and orbital dynamics
on an ultrafast time scale. A brief discussion on the magnetic anisotropy
energy is also provided.",2106.12679v1
2021-07-09,Rapid interrogation of special nuclear materials by combining scattering and transmission nuclear resonance fluorescence spectroscopy,"The smuggling of special nuclear materials (SNMs) across national borders is
becoming a serious threat to nuclear nonproliferation. This paper presents a
feasibility study on the rapid interrogation of concealed SNMs by combining
scattering and transmission nuclear resonance fluorescence (sNRF and tNRF)
spectroscopy. In sNRF spectroscopy, SNMs such as $^{235, 238}$U are excited by
a wide-band photon beam of appropriate energy and exhibit unique NRF
signatures. Monte Carlo simulations show that one-dimensional scans can realize
isotopic identification of concealed $^{235, 238}$U when the detector array
used for interrogation has sufficiently high energy resolution. The simulated
isotopic ratio $^{235}U/^{238}U$ is in good agreement with the theoretical
value when the SNMs are enclosed in relatively thin iron. This interrogation is
followed by tNRF spectroscopy using a narrow-band photon beam with the goal of
obtaining tomographic images of the concealed SNMs. The reconstructed image
clearly reveals the position of the isotope $^{235}$U inside an iron rod. It is
shown that the interrogation time of sNRF and tNRF spectroscopy is one order of
magnitude lower than that when only tNRF spectroscopy is used and results in a
missed-detection rate of 10$^{-3}$. The proposed method can also be applied for
isotopic imaging of other SNMs such as $^{239, 240}$Pu and $^{237}$Np.",2107.04379v1
2021-11-01,Spectrum evolution and chirping of laser-induced spin wave packets in thin iron films,"We present the experimental study of ultrafast optical excitation of
magnetostatic surface spin wave (MSSW) packets and their spectral properties in
thin films of pure iron. As the packets leave the excitation area and propagate
in space, their spectra evolve non-trivially. Particularly, low or high
frequency components are suppressed at the border of the excitation area
depending on the orientation of the external magnetic field with respect to the
magnetocrystolline anisotropy axes of the film. The effect is ascribed to the
ultrafast local heating of the film. Further, the time resolution of the
implemented all-optical technique allows us to extract the chirp of the MSSW
packet in the time domain via wavelet analysis. The chirp is a result of the
group velocity dispersion of the MSSW and, thus, is controlled by the film
magnetic parameters, magnetization and anisotropy, and external field
orientation. The demonstrated tunable modulation of MSSW wave packets with
femtosecond laser pulses may find application in future magnonic-photonic
hybrid devices for wave-based data processing.",2111.00983v2
2021-11-08,"Microstructure, grain boundary evolution and anisotropic Fe segregation in (0001) textured Ti thin films","The structure and chemistry of grain boundaries (GBs) are crucial in
determining polycrystalline materials' properties. Faceting and solute
segregation to minimize the GB energy is a commonly observed phenomenon. In
this paper, a deposition process to obtain pure tilt GBs in titanium (Ti) thin
films is presented. By increasing the power density, a transition from
polycrystalline film growth to a maze bicrystalline Ti film on SrTiO$_3$ (001)
substrate is triggered. All the GBs in the bicrystalline thin film are
characterized to be $\Sigma$13 [0001] coincident site lattice (CSL) boundaries.
The GB planes are seen to distinctly facet into symmetric {$\bar{7}520$} and
asymmetric {$10\bar{1}0$} // {$11\bar{2}0$} segments of 20-50~nm length.
Additionally, EDS reveals preferential segregation of iron (Fe) in every
alternate symmetric {$\bar{7}520$} segment. Both the faceting and the
segregation are explained by a difference in the CSL density between the facet
planes. Furthermore, in the GB plane containing Fe segregation, atom probe
tomography is used to experimentally determine the GB excess solute to be
1.25~atoms/nm$^{2}$. In summary, the study reveals for the first time a
methodology to obtain bicrystalline Ti thin films with strong faceting and
anisotropy in iron (Fe) segregation behaviour within the same family of planes.",2111.04606v1
2021-11-08,The MOBH35 metal-organic barrier heights reconsidered: performance of local-orbital coupled cluster approaches in different static correlation regimes,"We have revisited the MOBH35 (Metal-Organic Barrier Heights, 35 reactions)
benchmark [Iron, M. A.; Janes, T. J. Phys. Chem. A 2019, 123 (17), 3761-3781;
ibid. 2019, 123, 6379-6380] for realistic organometallic catalytic reactions,
using both canonical CCSD(T) and localized orbital approximations to it. For
low levels of static correlation, all of DLPNO-CCSD(T), PNO-LCCSD(T), and
LNO-CCSD(T) perform well; for moderately strong levels of static correlation,
DLPNO-CCSD(T) and (T1) may break down catastrophically, and PNO-LCCSD(T) is
vulnerable as well. In contrast, LNO-CCSD(T) converges smoothly to the
canonical CCSD(T) answer with increasingly tight convergence settings. The only
two reactions for which our revised MOBH35 reference values differ
substantially from the original ones are reaction 9 and to a lesser extent 8,
both involving iron. For the purpose of evaluating DFT methods for MOBH35, it
would be best to excise reaction 9 entirely as its severe level of static
correlation is just too demanding a test. The magnitude of the difference
between DLPNO-CCSD(T) and DLPNO-CCSD(T1) is a reasonably good predictor for
errors in DLPNO-CCSD(T1) compared to canonical CCSD(T); [...]",2111.04777v3
2021-11-24,Metallicity of the globular cluster NGC 6388 from high resolution spectra of more than 160 giant stars,"NGC 6388 is one of the most massive Galactic globular clusters (GC) and it is
an old, metal-rich, Galactic bulge cluster. By exploiting previous
spectroscopic observations we were able to bypass the uncertainties in
membership related to the strong field stars contamination. We present the
abundance analysis of 12 new giant stars with UVES spectra and 150 giants with
GIRAFFE spectra acquired at the ESO-VLT. We derived radial velocities,
atmospheric parameters and iron abundances for all stars. When combined to
previous data, we obtain a grand total of 185 stars homogeneously analysed in
NGC 6388 from high-resolution spectroscopy. The average radial velocity of the
185 stars is 81.2+/-0.7, rms = 9.4 km/s. We obtain an average metallicity
[Fe/H]=-0.480 dex, rms = 0.045 dex (35 stars) and [Fe/H]=-0.488 dex, rms =
0.040 dex (150 stars) from the UVES and GIRAFFE samples, respectively.
Comparing these values to internal errors in abundance, we exclude the presence
of a significant intrinsic metallicity spread within the cluster. Since about a
third of giants in NGC 6388 is claimed to belong to the ""anomalous red giants""
in the HST pseudo-colour map defining the so-called type-II GCs, we conclude
that either enhanced metallicity is not a necessary requisite to explain this
classification (as also suggested by the null iron spread for NGC 362) or NGC
6388 is not a type-II globular cluster.",2111.12721v1
2022-06-30,SRG/eROSITA discovery of a radio faint X-ray candidate supernova remnant SRGe J003602.3+605421=G121.1-1.9,"We report the discovery of a candidate X-ray supernova remnant SRGe
J003602.3+605421=G121.1-1.9 in the course of \textit{SRG}/eROSITA all-sky
survey. The object is located at (l,b)=(121.1$^\circ$,-1.9$^\circ$), is
$\approx36$ arcmin in angular size and has a nearly circular shape. Clear
variations in spectral shape of the X-ray emission across the object are
detected, with the emission from the inner (within 9') and outer (9'-18') parts
dominated by iron and oxygen/neon lines, respectively. The non-equilibrium
plasma emission model is capable of describing the spectrum of the outer part
with the initial gas temperature 0.1 keV, final temperature 0.5 keV and the
ionization age $\sim 2\times10^{10}$ cm$^{-3}$ s. The observed spectrum of the
inner region is more complicated (plausibly due to the contribution of the
outer shell) and requires substantial overabundance of iron for all models we
have tried. The derived X-ray absorption equals to $(4-6)\times10^{21}$
cm$^{-2}$, locating the object at the distance beyond 1.5 kpc, and implying its
age $\sim(5-30)\times1000$ yrs. No bright radio, infrared, H$_\alpha$ or
gamma-ray counterpart of this object have been found in the publicly-available
archival data. A model invoking a canonical $10^{51}$ erg explosion (either SN
Ia or core collapse) in the hot and tenuous medium in the outer region of the
Galaxy $\sim$9 kpc away might explain the bulk of the observed features. This
scenario can be tested with future deep X-ray and radio observations.",2207.00064v2
2022-07-20,Dislocation Majorana Bound States in Iron-based Superconductors,"We show that lattice dislocations of topological iron-based superconductors
such as FeTe$_{1-x}$Se$_x$ will intrinsically trap non-Abelian Majorana
quasiparticles, in the absence of any external magnetic field. Our theory is
motivated by the recent experimental observations of normal-state topology and
surface magnetism that coexist with superconductivity in FeTe$_{1-x}$Se$_x$,
the combination of which naturally evokes an emergent second-order topological
superconductivity in a two-dimensional subsystem spanned by screw or edge
dislocations. This exemplifies a new embedded higher-order topological phase in
class D, where Majorana zero modes appear around the ""corners"" of a
low-dimensional embedded subsystem, instead of those of the full crystal. A
nested domain wall theory is developed to understand the origin of these defect
Majorana zero modes. When the surface magnetism is absent, we further find that
$s_{\pm}$ pairing symmetry itself is capable of inducing a different type of
class-DIII embedded higher-order topology with defect-bound Majorana Kramers
pairs. We also provide detailed discussions on the real-world material
candidates for our proposals, including FeTe$_{1-x}$Se$_x$, LiFeAs,
$\beta$-PdBi$_2$, and heterostructures of bismuth, etc. Our work establishes
lattice defects as a new venue to achieve high-temperature topological quantum
information processing.",2207.10113v2
2017-04-18,"Structure, magnetic susceptibility and specific heat of the spin-orbital-liquid candidate FeSc2S4 : Influence of fe off-stoichiometry","We report structural, susceptibility and specific heat studies of
stoichiometric and off-stoichiometric poly- and single crystals of the A-site
spinel compound FeSc2S4. In stoichiometric samples no long-range magnetic order
is found down to 1.8 K. The magnetic susceptibility of these samples is field
independent in the temperature range 10 - 400 K and does not show irreversible
effects at low temperatures. In contrast, the magnetic susceptibility of
samples with iron excess shows substantial field dependence at high
temperatures and manifests a pronounced magnetic irreversibility at low
temperatures with a difference between ZFC and FC susceptibilities and a
maximum at 10 K reminiscent of a magnetic transition. Single crystal x-ray
diffraction of the stoichiometric samples revealed a single phase spinel
structure without site inversion. In single crystalline samples with Fe excess
besides the main spinel phase a second ordered single-crystal phase was
detected with the diffraction pattern of a vacancy-ordered superstructure of
iron sulfide, close to the 5C polytype Fe9S10. Specific heat studies reveal a
broad anomaly, which evolves below 20 K in both stoichiometric and
off-stoichiometric crystals. We show that the low-temperature specific heat can
be well described by considering the low-lying spin-orbital electronic levels
of Fe2+ ions. Our results demonstrate significant influence of excess Fe ions
on intrinsic magnetic behavior of FeSc2S4 and provide support for the
spin-orbital liquid scenario proposed in earlier studies for the stoichiometric
compound.",1704.05275v1
2017-04-20,Experimental Demonstration of the Sign Reversal of the Order Parameter in (Li1-xFex)OHFe1-yZnySe,"Iron pnictides are the only known family of unconventional high-temperature
superconductors besides cuprates. Until recently, it was widely accepted that
superconductivity is spin-fluctuation driven and intimately related to their
fermiology, specifically, hole and electron pockets separated by the same wave
vector that characterizes the dominant spin fluctuations, and supporting order
parameters (OP) of opposite signs. This picture was questioned after the
discovery of a new family, based on the FeSe layers, either intercalated or in
the monolayer form. The critical temperatures there reach ~40 K, the same as in
optimally doped bulk FeSe - despite the fact that intercalation removes the
hole pockets from the Fermi level and, seemingly, undermines the basis for the
spin-fluctuation theory and the idea of a sign-changing OP. In this paper,
using the recently proposed phase-sensitive quasiparticle interference
technique, we show that in LiOH intercalated FeSe compound the OP does change
sign, albeit within the electronic pockets, and not between the hole and
electron ones. This result unifies the pairing mechanism of iron based
superconductors with or without the hole Fermi pockets and supports the
conclusion that spin fluctuations play the key role in electron pairing.",1704.06141v1
2017-04-25,Role of multiorbital effects in the magnetic phase diagram of iron-pnictides,"We elucidate the pivotal role of the bandstructure's orbital content in
deciding the type of commensurate magnetic order stabilized within the
itinerant scenario of iron-pnictides. Recent experimental findings in the
tetragonal magnetic phase attest to the existence of the so-called charge and
spin ordered density wave over the spin-vortex crystal phase, the latter of
which tends to be favored in simplified band models of itinerant magnetism.
Here we show that employing a multiorbital itinerant Landau approach based on
realistic bandstructures can account for the experimentally observed magnetic
phase, and thus shed light on the importance of the orbital content in deciding
the magnetic order. In addition, we remark that the presence of a hole pocket
centered at the Brillouin zone's ${\rm M}$-point favors a magnetic stripe
rather than a tetragonal magnetic phase. For inferring the symmetry properties
of the different magnetic phases, we formulate our theory in terms of magnetic
order parameters transforming according to irreducible representations of the
ensuing D$_{\rm 4h}$ point group. The latter method not only provides
transparent understanding of the symmetry breaking schemes but also reveals
that the leading instabilities always belong to the $\{A_{1g},B_{1g}\}$ subset
of irreducible representations, independent of their C$_2$ or C$_4$ nature.",1704.07862v2
2017-05-18,Effects of the Functional Group on the Lithium Ions Across the Port of Carbon Nanotube,"The mean axial velocity of lithium irons across the entrance of carbon
nanotube VLi is an important factor for the charge-discharge performances of
rechargeable Lithium battery. The molecular dynamics simulation method is
adopted to evaluate the factors and their effects on VLi which include the
diameter of carbon nanotube, functional group type on the port and the number
of a given type of functional group. The statistical analysis of the
calculation results shows that: In the selected carbon nanotubes of four
different diameters, VLi will gradually rise with the increase of CNT diameter
due to lithium irons migration resistance decreasing; as the port of CNT is
successively modified to hydrogen (-H), hydroxyl (-OH), amino (-NH2) and
carboxyl (-COOH), the corresponding migration resistance of lithium ions is
enhanced resulting in the dropping of VLi; in comparison to the effect strength
of four types of functional groups on VLi, -COOH shows strongest, -NH2 and -OH
perform relatively weaker, and the effect difference between -NH2 and -OH is
very small, -H displays weakest; When the number of a given non-hydrogen
functional group on the port sequentially increases, it also shows a trend that
lithium ion migration resistance gradually increases which makes VLi decreases
in turn. The more influential the functional group, the greater the impact of
functional group number changes on VLi. The results of this paper have some
significance on the precise production of lithium-ion battery electrode
materials, enhancing the overall battery cycle efficiency and charging speed.",1705.06650v1
2017-05-27,High transport current superconductivity in powder-in-tube Ba0.6K0.4Fe2As2 tapes at 27 tesla,"The high upper critical field and low anisotropy of iron-based
superconductors make them being particularly attractive for high-field
applications. However, the current carrying capability needs to be enhanced by
overcoming the weak-link effect between misaligned grains inside wire and tape
conductors. Here we demonstrate a high transport critical current density (Jc)
reaching 1.5x10^5 A/cm^2 (Ic = 437 A) at 4.2 K and 10 T in Ba0.6K0.4Fe2As2
(Ba-122) tapes prepared by a combination of conventional powder-in-tube method
and optimized hot-press technique. The transport Jc measured at 4.2 K under
high magnetic fields of 27 T is still on the level of 5.5x10^4 A/cm^2, which is
much higher than those of low-temperature superconductors. This is the first
report of hot-pressed Ba-122 superconducting tapes and these Jc values are by
far the highest ever reported for iron-based superconducting wires and tapes.
These high-performance tapes exhibit high degree of c-axis texture of Ba-122
grains and low anisotropy of transport Jc, showing great potential for
construction of high-field superconducting magnets.",1705.09788v1
2017-05-29,Critical Slowing Down of Quadrupole and Hexadecapole Orderings in Iron Pnictide Superconductor,"Ultrasonic measurements have been carried out to investigate the critical
dynamics of structural and superconducting transitions due to degenerate
orbital bands in iron pnictide compounds with the formula
Ba(Fe$_{1-x}$Co$_x$)$_2$As$_2$. The attenuation coefficient
$\alpha_{\mathrm{L}[110]}$ of the longitudinal ultrasonic wave for
$(C_{11}+C_{12}+2C_{66})/2$ for $x = 0.036$ reveals the critical slowing down
of the relaxation time around the structural transition at $T_\mathrm{s} = 65$
K, which is caused by ferro-type ordering of the quadrupole $O_{x'^2-y'^2}$
coupled to the strain $\varepsilon_{xy}$. The attenuation coefficient
$\alpha_{66}$ of the transverse ultrasonic wave for $C_{66}$ for $x = 0.071$
also exhibits the critical slowing down around the superconducting transition
at $T_\mathrm{SC} = 23$ K, which is caused by ferro-type ordering of the
hexadecapole $H_z^\alpha \bigl( \boldsymbol{r}_i, \boldsymbol{r}_j \bigr) =
O_{x'y'}\bigl( \boldsymbol{r}_i \bigr) O_{x'^2 - y'^2}\bigl( \boldsymbol{r}_j
\bigr)
  + O_{x'^2 - y'^2}\bigl( \boldsymbol{r}_i \bigr) O_{x'y'}\bigl(
\boldsymbol{r}_j \bigr)$ of the bound two-electron state coupled to the
rotation $\omega_{xy}$. It is proposed that the hexadecapole ordering
associated with the superconductivity brings about spontaneous rotation of the
macroscopic superconducting state with respect to the host tetragonal lattice.",1705.10057v1
2017-05-31,Terahertz spin currents and inverse spin Hall effect in thin-film heterostructures containing complex magnetic compounds,"Terahertz emission spectroscopy of ultrathin multilayers of magnetic and
heavy metals has recently attracted much interest. This method not only
provides fundamental insights into photoinduced spin transport and spin-orbit
interaction at highest frequencies but has also paved the way to applications
such as efficient and ultrabroadband emitters of terahertz electromagnetic
radiation. So far, predominantly standard ferromagnetic materials have been
exploited. Here, by introducing a suitable figure of merit, we systematically
compare the strength of terahertz emission from X/Pt bilayers with X being a
complex ferro-, ferri- and antiferromagnetic metal, that is, dysprosium cobalt
(DyCo$_5$), gadolinium iron (Gd$_{24}$Fe$_{76}$), Magnetite (Fe$_3$O$_4$) and
iron rhodium (FeRh). We find that the performance in terms of spin-current
generation not only depends on the spin polarization of the magnet's conduction
electrons but also on the specific interface conditions, thereby suggesting
terahertz emission spectroscopy to be a highly surface-sensitive technique. In
general, our results are relevant for all applications that rely on the optical
generation of ultrafast spin currents in spintronic metallic multilayers.",1705.11069v2
2017-06-02,Quenching current by flux-flow instability in iron-chalcogenides thin films,"The stability against quench is one of the main issue to be pursued in a
superconducting material which should be able to perform at very high levels of
current densities. Here we focus on the connection between the critical current
$I_c$ and the quenching current $I^*$ associated to the so-called flux-flow
instability phenomenon, which sets in as an abrupt transition from the flux
flow state to the normal state. To this purpose, we analyze several
current-voltage characteristics of three types of iron-based thin films,
acquired at different temperature and applied magnetic field values. For these
samples, we discuss the impact of a possible coexistence of intrinsic
electronic mechanisms and extrinsic thermal effects on the quenching current
dependence upon the applied magnetic field. The differences between the
quenching current and the critical current are reported also in the case of
predominant intrinsic mechanisms. Carrying out a comparison with
high-temperature cuprate superconductors, we suggest which material can be the
best trade-off between maximum operating temperature, higher upper critical
field and stability under high current bias.",1706.00772v1
2017-06-19,Evidence for Majorana bound state in an iron-based superconductor,"The search for Majorana bound state (MBS) has recently emerged as one of the
most active research areas in condensed matter physics, fueled by the prospect
of using its non-Abelian statistics for robust quantum computation. A highly
sought-after platform for MBS is two-dimensional topological superconductors,
where MBS is predicted to exist as a zero-energy mode in the core of a vortex.
A clear observation of MBS, however, is often hindered by the presence of
additional low-lying bound states inside the vortex core. By using scanning
tunneling microscope on the newly discovered superconducting Dirac surface
state of iron-based superconductor FeTe1-xSex (x = 0.45, superconducting
transition temperature Tc = 14.5 K), we clearly observe a sharp and non-split
zero-bias peak inside a vortex core. Systematic studies of its evolution under
different magnetic fields, temperatures, and tunneling barriers strongly
suggest that this is the case of tunneling to a nearly pure MBS, separated from
non-topological bound states which is moved away from the zero energy due to
the high ratio between the superconducting gap and the Fermi energy in this
material. This observation offers a new, robust platform for realizing and
manipulating MBSs at a relatively high temperature.",1706.06074v3
2017-06-25,Frustration-driven C4 symmetric orders in a hetero-structured iron-based superconductor,"A subtle balance between competing interactions in strongly correlated
systems can be easily tipped by additional interfacial interactions in a
heterostructure. This often induces exotic phases with unprecedented
properties, as recently exemplified by high-Tc superconductivity in FeSe
monolayer on the nonmagnetic SrTiO3. When the proximity-coupled layer is
magnetically active, even richer phase diagrams are expected in iron-based
superconductors (FeSCs), which however has not been explored due to the lack of
a proper material system. One promising candidate is Sr2VO3FeAs, a
naturally-assembled heterostructure of a FeSC and a Mott-insulating vanadium
oxide. Here, using high-quality single crystals and high-accuracy 75As and 51V
nuclear magnetic resonance (NMR) measurements, we show that a novel electronic
phase is emerging in the FeAs layer below T0 ~ 155 K without either static
magnetism or a crystal symmetry change, which has never been observed in other
FeSCs. We find that frustration of the otherwise dominant Fe stripe and V Neel
fluctuations via interfacial coupling induces a charge/orbital order with
C4-symmetry in the FeAs layers, while suppressing the Neel antiferromagnetism
in the SrVO3 layers. These findings demonstrate that the magnetic proximity
coupling is effective to stabilize a hidden order in FeSCs and, more generally,
in strongly correlated heterostructures.",1706.08157v1
2017-06-27,Magnetic fluctuations and superconducting properties of CaKFe4As4 studied by 75As NMR,"We report $^{75}$As nuclear magnetic resonance (NMR) studies on a new
iron-based superconductor CaKFe$_4$As$_4$ with $T_{\rm c}$ = 35 K. $^{75}$As
NMR spectra show two distinct lines corresponding to the As(1) and As(2) sites
close to the K and Ca layers, respectively, revealing that K and Ca layers are
well ordered without site inversions. We found that nuclear quadrupole
frequencies $\nu_{\rm Q}$ of the As(1) and As(2) sites show an opposite
temperature ($T$) dependence. Nearly $T$ independent behavior of the Knight
shifts $K$ are observed in the normal state, and a sudden decrease in $K$ in
the superconducting (SC) state clearly evidences spin-singlet Cooper pairs.
$^{75}$As spin-lattice relaxation rates 1/$T_1$ show a power law $T$ dependence
with different exponents for the two As sites. The isotropic antiferromagnetic
spin fluctuations characterized by the wavevector ${\bf q}$ = ($\pi$, 0) or (0,
$\pi$) in the single-iron Brillouin zone notation are revealed by 1/$T_1T$ and
$K$ measurements. Such magnetic fluctuations are necessary to explain the
observed temperature dependence of the $^{75}$As quadrupole frequencies, as
evidenced by our first-principles calculations. In the SC state, 1/$T_1$ shows
a rapid decrease below $T_{\rm c}$ without a Hebel-Slichter peak and decreases
exponentially at low $T$, consistent with an $s^{\pm}$ nodeless two-gap
superconductor.",1706.09075v2
2018-02-05,Discrete superconducting phases in FeSe-derived superconductors,"A general feature of unconventional superconductors is the existence of a
superconducting dome in the phase diagram as a function of carrier
concentration. For the simplest iron-based superconductor FeSe (with transition
temperature Tc ~ 8 K), its Tc can be greatly enhanced by doping electrons via
many routes, even up to 65 K in monolayer FeSe/SiTiO3. However, a clear phase
diagram with carrier concentration for FeSe-derived superconductors is still
lacking. Here, we report the observation of a series of discrete
superconducting phases in FeSe thin flakes by continuously tuning carrier
concentration through the intercalation of Li and Na ions with a solid ionic
gating technique. Such discrete superconducting phases are robust against the
substitution of Se by 20% S, but are vulnerable to the substitution of Fe by 2%
Cu, highlighting the importance of the iron site being intact. A complete
superconducting phase diagram for FeSe-derivatives is given, which is distinct
from other unconventional superconductors.",1802.01484v1
2018-02-06,Imaging Orbital-selective Quasiparticles in the Hund's Metal State of FeSe,"Strong electronic correlations, emerging from the parent Mott insulator
phase, are key to copper-based high temperature superconductivity (HTS). By
contrast, the parent phase of iron-based HTS is never a correlated insulator.
But this distinction may be deceptive because Fe has five active d-orbitals
while Cu has only one. In theory, such orbital multiplicity can generate a
Hund's Metal state, in which alignment of the Fe spins suppresses inter-orbital
fluctuations producing orbitally selective strong correlations. The spectral
weights $Z_m$ of quasiparticles associated with different Fe orbitals m should
then be radically different. Here we use quasiparticle scattering interference
resolved by orbital content to explore these predictions in FeSe. Signatures of
strong, orbitally selective differences of quasiparticle $Z_m$ appear on all
detectable bands over a wide energy range. Further, the quasiparticle
interference amplitudes reveal that $Z_{xy}<Z_{xz}<<Z_{yz}$, consistent with
earlier orbital-selective Cooper pairing studies. Thus, orbital-selective
strong correlations dominate the parent state of iron-based HTS in FeSe.",1802.02266v2
2018-02-20,Monte-Carlo simulations of the detailed iron absorption line profiles from thermal winds in X-ray binaries,"Blue shifted absorption lines from highly ionised iron are seen in some high
inclination X-ray binary systems, indicating the presence of an equatorial disc
wind. This launch mechanism is under debate, but thermal driving should be
ubiquitous. X-ray irradiation from the central source heats disc surface,
forming a wind from the outer disc where the local escape velocity is lower
than the sound speed. The mass loss rate from each part of the disc is
determined by the luminosity and spectral shape of the central source. We use
these together with an assumed density and velocity structure of the wind to
predict the column density and ionisation state, then combine this with a Monte
Carlo radiation transfer to predict the detailed shape of the absorption (and
emission) line profiles. We test this on the persistent wind seen in the bright
neutron star binary GX 13+1, with luminosity L/LEdd ~ 0.5. We approximately
include the effect of radiation pressure because of high luminosity, and
compute line features. We compare these to the highest resolution data, the
Chandra third order grating spectra, which we show here for the first time.
This is the first physical model for the wind in this system, and it succeeds
in reproducing many of the features seen in the data, showing that the wind in
GX13+1 is most likely a thermal-radiation driven wind. This approach, combined
with better streamline structures derived from full radiation hydrodynamic
simulations, will allow future calorimeter data to explore the detail wind
structure.",1802.07019v1
2018-07-04,Doping effects of Cr on the physical properties of BaFe$_{1.9-x}$Ni$_{0.1}$Cr$_{x}$As$_{2}$,"We present a systematic study on the heavily Cr doped iron pnictides
BaFe$_{1.9-x}$Ni$_{0.1}$Cr$_{x}$As$_{2}$ by using elastic neutron scattering,
high-resolution synchrotron X-ray diffraction (XRD), resistivity and Hall
transport measurements. When the Cr concentration increases from $x=$ 0 to 0.8,
neutron diffraction experiments suggest that the collinear antiferromagnetism
persists in the whole doping range, where the N\'{e}el temperature $T_N$
coincides with the tetragonal-to-orthorhombic structural transition temperature
$T_s$, and both of them keeps around 35 K. The magnetic ordered moment, on the
other hand, increases within increasing $x$ until $x=$ 0.5, and then decreases
with further increasing $x$. Detailed refinement of the powder XRD patterns
reveals that the Cr substitutions actually stretch the FeAs$_4$ tetrahedron
along the $c-$axis and lift the arsenic height away Fe-Fe plane. Transport
results indicate that the charge carriers become more localized upon Cr doping,
then changes from electron-type to hole-type around $x=$ 0.5. Our results
suggest that the ordered moment and the ordered temperature of static magnetism
in iron pnictides can be decoupled and tuned separately by chemical doping.",1807.01612v1
2018-07-17,Chemical Compositions of Field and Globular Cluster RR Lyrae Stars: I. NGC 3201,"We present a detailed spectroscopic analysis of horizontal branch stars in
the globular cluster NGC 3201. We collected optical (4580-5330 A), high
resolution (~34,000), high signal-to-noise ratio (~200) spectra for eleven RR
Lyrae stars and one red horizontal branch star with the multifiber spectrograph
M2FS at the 6.5m Magellan telescope at the Las Campanas Observatory. From
measured equivalent widths we derived atmospheric parameters and abundance
ratios for {\alpha} (Mg, Ca, Ti), iron peak (Sc, Cr, Ni, Zn) and s-process (Y)
elements. We found that NGC 3201 is a homogeneous, mono-metallic ([Fe/H]=-1.47
+- 0.04), {\alpha}-enhanced ([{\alpha}/Fe]=0.37 +- 0.04) cluster. The relative
abundances of the iron peak and s-process elements were found to be consistent
with solar values. In comparison with other large stellar samples, NGC 3201 RR
Lyraes have similar chemical enrichment histories as do those of other old
(t>10 Gyr) Halo components (globular clusters, red giants, blue and red
horizontal branch stars, RR Lyraes). We also provided a new average radial
velocity estimate for NGC 3201 by using a template velocity curve to overcome
the limit of single epoch measurements of variable stars: Vrad=494 +- 2 km
s-1({\sigma}=8 km s-1).",1807.06681v1
2018-07-27,Relativistic reflection from accretion disks in the population of Active Galactic Nuclei at z=0.5-4,"We report the detection of relativistically broadened iron K alpha emission
in the X-ray spectra of AGN detected in the 4Ms CDF-S. Using the Bayesian X-ray
analysis (BXA) package, we fit 199 hard band (2-7 keV) selected sources in the
redshift range z=0.5--4 with three models: (i) an absorbed power-law, (ii) the
first model plus a narrow reflection component, and (iii) the second model with
an additional relativistic broadened reflection. The Bayesian evidence for the
full sample of sources selects the model with the additional broad component as
being 10^5 times more probable to describe the data better than the second
model. For the two brightest sources in our sample, CID 190 (z=0.734) and CID
104 (z=0.543), BXA reveals the relativistic signatures in the individual
spectra. We estimate the fraction of sources containing a broad component to be
54^{+35}_{-37}% (107/199 sources). Considering that the low signal-to-noise
ratio of some spectra prevents the detection of the broad iron K alpha line, we
infer an intrinsic fraction with broad emission of around two thirds. The
detection of relativistic signatures in the X-ray spectra of these sources
suggests that they are powered by a radiatively efficient accretion disk.
Preliminary evidence is found that the spin of the black hole is high, with a
maximally spinning Kerr BH model (a=1) providing a significantly better fit
than a Schwarzschild model (a=0). Our analysis demonstrate the potential of
X-ray spectroscopy to measure this key parameter in typical SMBH systems at the
peak of BH growth.",1807.10677v1
2018-08-10,"Majority carrier type inversion in FeSe family and ""doped semimetal"" scheme in iron-based superconductors","The field and temperature dependencies of the longitudinal and Hall
resistivity have been studied for high-quality FeSe${}_{1-x}$S${}_{x}$ (x up to
0.14) single crystals. Quasiclassical analysis of the obtained data indicates a
strong variation of the electron and hole concentrations under the studied
isovalent substitution and proximity of FeSe to the point of the majority
carrier-type inversion. On this basis, we propose a `doped semimetal' scheme
for the superconducting phase diagram of the FeSe family, which can be applied
to other iron-based superconductors. In this scheme, the two local maxima of
the superconducting temperature can be associated with the Van Hove
singularities of a simplified semi-metallic electronic structure. The
multicarrier analysis of the experimental data also reveals the presence of a
tiny and highly mobile electron band for all the samples studied. Sulfur
substitution in the studied range leads to a decrease in the number of mobile
electrons by more than ten times, from about 3\% to about 0.2\%. This behavior
may indicate a successive change of the Fermi level position relative to
singular points of the electronic structure which is consistent with the `doped
semimetal' scheme. The scattering time for mobile carriers does not depend on
impurities, which allows us to consider this group as a possible source of
unusual acoustic properties of FeSe.",1808.03551v2
2018-08-11,Physical conditions for the r-process I. radioactive energy sources of kilonovae,"Radioactive energies from unstable nuclei made in the ejecta of neutron star
mergers play principal roles in powering kilonovae. In previous studies
power-law-type heating rates (e.g., ~ t^-1.3) have frequently been used, which
may be inadequate if the ejecta are dominated by nuclei other than the A ~ 130
region. We consider, therefore, two reference abundance distributions that
match the r-process residuals to the solar abundances for A >= 69 (light
trans-iron plus r-process elements) and A >= 90 (r-process elements).
Nucleosynthetic abundances are obtained by using free-expansion models with
three parameters: expansion velocity, entropy, and electron fraction.
Radioactive energies are calculated as an ensemble of weighted free-expansion
models that reproduce the reference abundance patterns. The results are
compared with the bolometric luminosity (> a few days since merger) of the
kilonova associated with GW170817. We find that the former case (fitted for A
>= 69) with an ejecta mass 0.06 M_sun reproduces the light curve remarkably
well including its steepening at > 7 days, in which the mass of r-process
elements is ~ 0.01 M_sun. Two beta-decay chains are identified: 66Ni -> 66Cu ->
66Zn and 72Zn -> 72Ga -> 72Ge with similar halflives of parent isotopes (~ 2
days), which leads to an exponential-like evolution of heating rates during
1-15 days. The light curve at late times (> 40 days) is consistent with
additional contributions from the spontaneous fission of 254Cf and a few Fm
isotopes. If this is the case, the event GW170817 is best explained by the
production of both light trans-iron and r-process elements that originate from
dynamical ejecta and subsequent disk outflows from the neutron star merger.",1808.03763v2
2018-08-15,c-axis pressure induced antiferromagnetic order in optimally P-doped BaFe2(As0.70P0.30)2 superconductor,"Superconductivity in BaFe2(As1-xPx)2 iron pnictides emerges when its in-plane
two-dimensional (2D) orthorhombic lattice distortion associated with nematic
phase at Ts and three-dimensional (3D) collinear antiferromagnetic (AF) order
at TN (Ts = TN) are gradually suppressed with increasing x, reaching optimal
superconductivity around x = 0.30 with Tc $\approx$ 30 K. Here we show that a
moderate uniaxial pressure along the c-axis in BaFe2(As0.70P0.30)2
spontaneously induces a 3D collinear AF order with TN = Ts > 30 K, while only
slightly suppresses Tc. Although a ~ 400 MPa pressure compresses the c-axis
lattice while expanding the in-plane lattice and increasing the
nearest-neighbor Fe-Fe distance, it barely changes the average iron-pnictogen
height in BaFe2(As0.70P0.30)2. Therefore, the pressure- induced AF order must
arise from a strong in-plane magnetoelastic coupling, suggesting that the 2D
nematic phase is a competing state with superconductivity.",1808.05153v1
2018-08-16,Relativistic Tidal Disruption and Nuclear Ignition of White Dwarf Stars by Intermediate Mass Black Holes,"We present results from general relativistic calculations of the tidal
disruption of white dwarf stars from near encounters with intermediate mass
black holes. We follow the evolution of 0.2 and $0.6 M_\odot$ stars on
parabolic trajectories that approach $10^3$ - $10^4 M_\odot$ black holes as
close as a few Schwarzschild radii at periapsis, paying particular attention to
the effect tidal disruption has on thermonuclear reactions and the synthesis of
intermediate to heavy ion elements. These encounters create diverse
thermonuclear environments characteristic of Type I supernovae and capable of
producing both intermediate and heavy mass elements in arbitrary ratios,
depending on the strength (or proximity) of the interaction. Nuclear ignition
is triggered in all of our calculations, even at weak tidal strengths $\beta
\sim 2.6$ and large periapsis radius $R_P \sim 28$ Schwarzschild radii. A
strong inverse correlation exists between the mass ratio of calcium to iron
group elements and tidal strength, with $\beta \lesssim 5$ producing
predominately calcium-rich debris. At these moderate to weak interactions,
nucleosynthesis is not especially efficient, limiting the total mass and
outflows of calcium group elements to $< 15$\% of available nuclear fuel. Iron
group elements however continue to be produced in greater quantity and ratio
with increasing tidal strength, peaking at $\sim 60$\% mass conversion
efficiency in our closest encounter cases. These events generate short bursts
of gravitational waves with characteristic frequencies 0.1-0.7 Hz and strain
amplitudes $0.5\times10^{-22}$ - $3.5\times10^{-22}$ at 10 Mpc source distance.",1808.05664v1
2018-08-18,"Ultra-high critical current densities, the vortex phase diagram and the effect of granularity of the stoichiometric high-Tc superconductor, CaKFe$_4$As$_4$","We present a comprehensive study of the critical current densities and the
superconducting vortex phase diagram in the stoichiometric superconductor
CaKFe$_4$As$_4$ which has a critical temperature of 35 K. We performed detailed
magnetization measurements both of high quality single crystals for different
orientations in an applied magnetic field up to 16 T and for a powder sample.
We find an extremely large critical current density, Jc, up to 10$^8$ A/cm2 for
single crystals when H||(ab) at 5 K, which remains robust in fields up to 16 T,
being the largest of any other iron-based superconductor. The critical current
density is reduced by a factor 10 in single crystals when H||c at 5 K and
significantly suppressed by the presence of grain boundaries in the powder
sample. We also observe the presence of the fishtail effect in the magnetic
hysteresis loops of single crystals when H||c. The flux pinning force density
and the pinning parameters suggest that the large critical current could be
linked to the existence of point core and surface pinning. Based on the vortex
phase diagram and the large critical current densities, CaKFe$_4$As$_4$ is now
established as a potential iron-based superconductor candidate for practical
applications.",1808.06072v1
2018-08-19,Local Electronic Structure of Interstitial Hydrogen in Iron Disulfide,"The electronic structure of interstitial hydrogen in a compound semiconductor
FeS$_2$ (naturally $n$-type) is inferred from a muon study. An implanted muon
(Mu, a pseudo-hydrogen) forms electronically different defect centers discerned
by the hyperfine parameter ($\omega_{\rm hf}$). A body of evidence indicates
that one muon is situated at the center of an iron-cornered tetrahedron with
nearly isotropic $\omega_{\rm hf}$ (Mu$_{\rm p}$), and that the other exists as
a diamagnetic state (Mu$_{\rm d}$, $\omega_{\rm hf}\simeq 0$). Their response
to thermal agitation indicates that the Mu$_{\rm d}$ center accompanies a
shallow level (donor or acceptor) understood by effective mass model while the
electronic structure of Mu$_{\rm p}$ center is more isolated from host than
Mu$_{\rm d}$ to form a deeper donor level. These observations suggest that
interstitial hydrogen also serves as an electronically active impurity in
FeS$_2$. Based on earlier reports on the hydrogen diffusion in FeS$_2$,
possibility of fast diffusion for Mu$_{\rm p}$ leading to formation of a
complex defect state (Mu$^*_{\rm d}$, $T\le 100$ K) or to motional narrowing
state (Mu$^*_{\rm p}$, $T\ge 150$ K) is also discussed.",1808.06153v1
2018-08-23,"Correlation between non-Fermi-liquid behavior and superconductivity in (Ca, La)(Fe,Co)As2 iron arsenides: A high-pressure study","Non-Fermi-liquid (NFL) phenomena associated with correlation effects have
been widely observed in the phase diagrams of unconventional superconducting
families. Exploration of the correlation between the normal state NFL,
regardless of its microscopic origins, and the superconductivity has been
argued as a key to unveiling the mystery of the high-Tc pairing mechanism. Here
we systematically investigate the pressure-dependent in-plane resistivity and
Hall coefficient (RH ) of a high-quality 112-type Fe-based superconductor
Ca1-xLaxFe1-yCoyAs2 (x = 0.2,y = 0.02). With increasing pressure, the
normal-state resistivity of the studied sample exhibits a pronounced crossover
from non-Fermi-liquid to Fermi-liquid behaviors. Accompanied with this
crossover, Tc is gradually suppressed. In parallel, the extremum in the Hall
coefficient RH (T ) curve, possibly due to anisotropic scattering induced by
spin fluctuations, is also gradually suppressed. The symbiosis of NFL and
superconductivity implies that these two phenomena are intimately related.
Further study on the pressure-dependent upper critical field reveals that the
two-band effects are also gradually weakened with increasing pressure and
reduced to the one-band Werthamer-Helfand-Hohenberg limit in the low-Tc regime.
Overall, our paper supports the picture that NFL, multigap, and extreme RH (T )
are all of the same magnetic origin, i.e., the spin fluctuations in the 112
iron arsenide superconductors.",1808.07609v1
2018-08-26,Intertwined Spin and Orbital Density Waves in MnP Uncovered by Resonant Soft X-ray Scattering,"Unconventional superconductors are often characterized by numerous competing
and even intertwined orders in their phase diagrams. In particular, the
electronic nematic phases, which spontaneously break rotational symmetry and
often simultaneously involve spin, charge and/or orbital orders, appear
conspicuously in both the cuprate and iron-based superconductors. The
fluctuations associated with these phases may provide the exotic pairing glue
that underlies their high-temperature superconductivity. Helimagnet MnP, the
first Mn-based superconductor under pressure, lacks high rotational symmetry.
However our resonant soft X-ray scattering (RSXS) experiment discovers novel
helical orbital density wave (ODW) orders in this three-dimensional,
low-symmetry system, and reveals intertwined ordering phenomena in
unprecedented detail. In particular, a ODW forms with half the period of the
spin order and fully develops slightly above the spin ordering temperature,
their domains develop simultaneously, yet the spin order domains are larger
than those of the ODW, and they cooperatively produce another ODW with 1/3 the
period of the spin order. These observations provide a comprehensive picture of
the intricate interplay between spin and orbital orders in correlated
materials, and they suggest that nematic-like physics ubiquitously exists
beyond two-dimensional and high-symmetry systems, and the superconducting
mechanism of MnP is likely analogous to those of cuprate and iron-based
superconductors.",1808.08562v1
2018-10-18,Human-sized Magnetic Particle Imaging for Brain Applications,"Determining the brain perfusion is an important task for the diagnosis and
treatment of vascular diseases such as occlusions and intracerebral
haemorrhage. Even after successful diagnosis and treatment, there is a high
risk of restenosis or rebleeding such that patients need intense and frequent
attention in the days after treatment. Within this work, we will present a
diagnostic tomographic imager that allows access to brain perfusion information
quantitatively in short intervals. The imager is the first functional magnetic
particle imaging device for brain imaging on a human-scale. It is highly
sensitive and allows the detection of an iron concentration of 14.7 ng /ml (263
pmol\ml), which is the lowest iron concentration imaged by MPI so far. The
imager is self-shielded and can be used in unshielded environments such as
intensive care units. In combination with the low technical requirements this
opens up a whole variety of possible medical applications and would allow
monitoring possibilities on the stroke and intensive care units.",1810.07987v1
2019-01-08,Observation of half-integer level shift of vortex bound states in an iron-based superconductor,"Vortices in topological superconductors host Majorana zero modes (MZMs),
which are proposed to be building blocks of fault-tolerant topological quantum
computers. Recently, a new single-material platform for realizing MZM has been
discovered in iron-based superconductors, without involving hybrid
semiconductor-superconductor structures. Here we report on a detailed scanning
tunneling spectroscopy study of a FeTe0.55Se0.45 single crystal, revealing two
distinct classes of vortices present in this system which differ by a
half-integer level shift in the energy spectra of the vortex bound states. This
level shift is directly tied with the presence or absence of zero-bias peak and
also alters the ratios of higher energy levels from integer to
half-odd-integer. Our model calculations fully reproduce the spectra of these
two types of vortex bound states, suggesting the presence of topological and
conventional superconducting regions that coexist within the same crystal. Our
findings provide strong evidence for the topological nature of
superconductivity in FeTe0.55Se0.45 and establish it as an excellent platform
for further studies on MZMs.",1901.02293v1
2019-01-19,Study of the X-ray properties of the neutron-star binary 4U 1728$-$34 from the soft to hard state,"We studied five XMM-Newton observations of the neutron-star binary 4U
1728$-$34 covering the hard, intermediate and soft spectral states. By jointly
fitting the spectra with several reflection models, we obtained an inclination
angle of 25$-$53$\deg$ and an iron abundance up to 10 times the solar. From the
fits with reflection models, we found that the fluxes of the reflection and the
Comptonised components vary inconsistently; since the latter is assumed to be
the illuminating source, this result possibly indicates the contribution of the
neutron star surface/boundary layer to the disc reflection. As the source
evolved from the relatively soft to the intermediate state, the disc inner
radius decreased, opposite to the prediction of the standard accretion disc
model. We also explore the possible reasons why the supersolar iron abundance
is required by the data and found that this high value is probably caused by
the absence of the hard photons in the XMM-Newton data.",1901.06473v1
2019-01-28,Super-Eddington accretion onto the Galactic ultraluminous X-ray pulsar Swift J0243.6+6124,"We report on the spectral behavior of the first Galactic ultraluminous X-ray
pulsar Swift J0243.6+6124 with NuSTAR observations during its 2017-2018
outburst. At sub-Eddington levels, the source spectrum is characterized by
three emission components, respectively from the accretion column, the hot
spot, and a broad iron line emission region. When the source is above the
Eddington limit, the hot spot temperature increases and the spectrum features
two more blackbody components. One blackbody component has a radius of 10-20 km
and is likely originated from the top of the accretion column. The other one
saturates at a blackbody luminosity of (1 - 2)*10^38 erg/s, coincident with the
Eddington limit of a neutron star. This is well consistent with the scenario
that super-Eddington accretion onto compact objects will power optically-thick
outflows and indicates an accretion rate 60-80 times the critical value. This
suggests that super-Eddington accretion onto magnetized systems can also power
massive winds. At super-Eddington levels, the iron line becomes more
significant and blueshifted, and is argued to be associated with the ultrafast
wind in the central funnel or jets. This source, if located in external
galaxies, will appear like other ultraluminous pulsars.",1901.09485v1
2019-04-01,A Chandra and ALMA Study of X-ray-irradiated Gas in the Central ~100 pc of the Circinus Galaxy,"We report a study of X-ray-irradiated gas in the central ~100 pc of the
Circinus galaxy, hosting a Compton-thick active galactic nucleus (AGN), at
10-pc resolution using Chandra and ALMA. Based on ~200 ksec Chandra/ACIS-S
data, we created an image of the Fe Kalpha line at 6.4 keV, tracing
X-ray-irradiated dense gas. The ALMA data in Bands 6 (~270 GHz) and 7 (~350
GHz) cover five molecular lines: CO(J=3--2), HCN(J=3--2), HCN(J=4--3),
HCO^+(J=3--2), and HCO^+(J=4--3). The detailed spatial distribution of dense
molecular gas was revealed, and compared to the iron line image. The molecular
gas emission appeared faint in regions with bright iron emission. Motivated by
this, we quantitatively discuss the possibility that the molecular gas is
efficiently dissociated by AGN X-ray irradiation (i.e., creating an
X-ray-dominated region). Based on a non-local thermodynamic equilibrium model,
we constrained the molecular gas densities and found that they are as low as
interpreted by X-ray dissociation. Furthermore, judging from inactive star
formation (SF) reported in the literature, we suggest that the X-ray emission
has potential to suppress SF, particularly in the proximity of the AGN.",1904.01144v1
2019-04-12,Nearly quantized conductance plateau of vortex zero mode in an iron-based superconductor,"Majorana zero-modes (MZMs) are spatially-localized zero-energy fractional
quasiparticles with non-Abelian braiding statistics that hold a great promise
for topological quantum computing. Due to its particle-antiparticle
equivalence, an MZM exhibits robust resonant Andreev reflection and 2e2/h
quantized conductance at low temperature. By utilizing variable-tunnel-coupled
scanning tunneling spectroscopy, we study tunneling conductance of vortex bound
states on FeTe0.55Se0.45 superconductors. We report observations of conductance
plateaus as a function of tunnel coupling for zero-energy vortex bound states
with values close to or even reaching the 2e2/h quantum conductance. In
contrast, no such plateau behaviors were observed on either finite energy
Caroli-de Genne-Matricon bound states or in the continuum of electronic states
outside the superconducting gap. This unique behavior of the zero-mode
conductance reaching a plateau strongly supports the existence of MZMs in this
iron-based superconductor, which serves as a promising single-material platform
for Majorana braiding at a relatively high temperature.",1904.06124v2
2019-04-14,Impact of the first order antiferromagnetic phase transition on the paramagnetic spin excitations and nematic phase of SrFe$_2$As$_2$,"Understanding the nature of the electronic nematic phase in iron pnictide
superconductors is important for elucidating its impact on high-temperature
superconductivity. Here we use transport and inelastic neutron scattering to
study spin excitations and in-plane resistivity anisotropy in uniaxial pressure
detwinned BaFe$_2$As$_2$ and SrFe$_2$As$_2$, the parent compounds of iron
pnictide superconductors. While BaFe$_2$As$_2$ exhibits weakly first order
tetragonal-to-orthorhombic structural and antiferromagnetic (AF) phase
transitions below $T_s > T_N\approx 138$ K, SrFe$_2$As$_2$ has strongly coupled
first order structural and AF transitions below $T_s= T_N\approx 210$ K. We
find that the direct signatures of the nematic phase persist to lower
temperatures above the phase transition in the case of SrFe$_2$As$_2$ compared
to BaFe$_2$As$_2$. Our findings support the conclusion that the strongly
first-order nature of the magnetic transition in SrFe$_2$As$_2$ weakens the
nematic phase and resistivity anisotropy in the system.",1904.06743v1
2019-06-13,"The influence of antiferromagnetism, soft out-of plane phonons and heavy electrons on the superconducting pairing mechanism of Ba1-xKxFe2As2","Based on ab-initio calculated parameters, we apply a theoretical model on the
iron-based BaFe2As2 superconductor that takes into account dramatic
enhancements of the electron-phonon coupling of soft transverse phonons in the
FeAs layers and antiferromagnetism. Our model is able to reproduce the Tc
values of BaFe2As2 found under pressure in experiments. To calculate the Tc of
the K-doped Ba1-xKxFe2As2 system as a function of the K content, we
additionally consider the experimentally observed effective mass enhancements
and Kondo temperatures in the strongly over-doped region (0.8 < x < 1), which
decouple the antiferromagnetism and electron-phonon scattering. The highest
theoretical Tc at the optimal doping concentration is reproduced after
optimization of antiferromagnetic fluctuations and electron-phonon coupling.
Our model is also able to reproduce the dip-like structure in Tc in the region
where a re-entrant tetragonal phase of C4 symmetry is found (0.24 < x < 0.28)
and indicates the weakening effect of local exchange correlation energy as
responsible for Tc reduction. Our model thus demonstrates that the high
transition temperatures and the exact doping and pressure dependence of this
iron-based superconductor can be explained within an extended electron-phonon
coupling model in which the structural, magnetic and electronic degrees of
freedom are strongly intertwined.",1906.05789v1
2019-06-24,Melting of vortex lattice in magnetic superconductor $\mathrm{Rb}\mathrm{Eu}\mathrm{Fe}_{4}\mathrm{As}_{4}$,"The iron-based superconductors are characterized by strong fluctuations due
to high transition temperatures and small coherence lengths. We investigate
fluctuation behavior in the magnetic iron-pnictide superconductor
$\mathrm{Rb}\mathrm{Eu}\mathrm{Fe}_{4}\mathrm{As}_{4}$ by calorimetry and
transport. We find that the broadening of the specific-heat transition in
magnetic fields is very well described by the lowest-Landau-level scaling. We
report calorimetric and transport observations for vortex-lattice melting,
which is seen as a sharp drop of the resistivity and a step of the specific
heat at the magnetic-field-dependent temperature. The melting line in the
temperature/magnetic-field plane lies noticeably below the upper-critical-field
line and its location is in quantitative agreement with theoretical predictions
without fitting parameters. Finally, we compare the melting behavior of
$\mathrm{Rb}\mathrm{Eu}\mathrm{Fe}_{4}\mathrm{As}_{4}$ with other
superconducting materials showing that thermal fluctuations of vortices are not
as prevalent as in the high-temperature superconducting cuprates, yet they
still noticeably influence the properties of the vortex matter.",1906.10236v2
2019-06-26,Near 100% CO Selectivity in Nanoscaled Iron-Based Oxygen Carriers for Chemical Looping Methane Partial Oxidation,"Chemical looping methane partial oxidation provides an energy and cost
effective route for methane utilization. However, there is considerable CO2
co-production in state-of-the-art chemical looping systems, rendering a
decreased productivity in value-added fuels or chemicals. In this work, we show
that the co-production of CO2 can be dramatically suppressed in methane partial
oxidation reactions using iron oxide nanoparticles, with a size of 2~8 nm, as
the oxygen carrier. To stabilize these nanoparticles at high temperatures, they
are embedded in an ordered, gas-permeable mesoporous silica matrix. We
experimentally obtained near 100% CO selectivity in a cyclic redox system at
750{\deg}C to 935{\deg}C, which is a significantly lower temperature range than
in conventional oxygen carrier systems. Density functional theory calculations
elucidate the origins for such selectivity and reveal that CH4 adsorption
energies decrease with increasing nanoparticle size. These calculations also
show that low-coordinated lattice oxygen atoms on the surface of nanoparticles
significantly promote Fe-O bond cleavage and CO formation. We envision that
embedded nanostructured oxygen carriers have the potential to serve as a
general materials platform for achieving 100% selectivity in redox reactions at
high temperatures.",1906.11160v1
2019-07-15,Stellar atmospheric parameters for 754 spectra from the X-shooter Spectral Library,"The X-shooter Spectral Library (XSL) is an empirical stellar library at
medium spectral resolution covering the wavelength range from 3000 \AA to 24
800 \AA. This library aims to provide a benchmark for stellar population
studies. In this work, we present a uniform set of stellar atmospheric
parameters, effective temperatures, surface gravities, and iron abundances for
754 spectra of 616 XSL stars. We used the full-spectrum fitting package ULySS
with the empirical MILES library as reference to fit the ultraviolet-blue (UVB)
and visible (VIS) spectra. We tested the internal consistency and we compared
our results with compilations from the literature. The stars cover a range of
effective temperature 2900 < Teff < 38 000 K, surface gravity 0 < log g < 5.7,
and iron abundance -2.5 < [Fe/H] < +1.0, with a couple of stars extending down
to [Fe/H] = -3.9. The precisions of the measurements for the G- and K-type
stars are 0.9%, 0.14, and 0.06 in Teff, log g, and [Fe/H], respectively. For
the cool giants with log g < 1, the precisions are 2.1%, 0.21, and 0.22, and
for the other cool stars these values are 1%, 0.14, and 0.10. For the hotter
stars (Teff > 6500 K), these values are 2.6%, 0.20, and 0.10 for the three
parameters.",1907.06391v1
2019-07-15,"Neutron powder diffraction study on the non-superconducting phases of ThFeAsN$_{1-x}$O$_x$ ($x=0.15, 0.6$) iron pnictide","We use neutron powder diffraction to study on the non-superconducting phases
of ThFeAsN$_{1-x}$O$_x$ with $x=0.15, 0.6$. In our previous results on the
superconducting phase ThFeAsN with $T_c=$ 30 K, no magnetic transition is
observed by cooling down to 6 K, and possible oxygen occupancy at the nitrogen
site is shown in the refinement(H. C. Mao \emph{et al.}, EPL, 117, 57005
(2017)). Here, in the oxygen doped system ThFeAsN$_{1-x}$O$_x$, two
superconducting region ($0\leqslant x \leqslant 0.1$ and $0.25\leqslant x
\leqslant 0.55$) have been identified by transport experiments (B. Z. Li
\emph{et al.}, J. Phys.: Condens. Matter 30, 255602 (2018)). However, within
the resolution of our neutron powder diffraction experiment, neither the
intermediate doping $x=0.15$ nor the heavily overdoped compound $x= 0.6$ shows
any magnetic order from 300 K to 4 K. Therefore, while it shares the common
phenomenon of two superconducting domes as most of 1111-type iron-based
superconductors, the magnetically ordered parent compound may not exist in this
nitride family.",1907.06531v1
2019-07-17,Detailed spectroscopic and photometric study of three detached eclipsing binaries,"Detached eclipsing binaries are remarkable systems to provide accurate
fundamental stellar parameters. The fundamental stellar parameters and the
metallicity values of stellar systems are needed to deeply understand the
stellar evolution and formation. In this study, we focus on the detailed
spectroscopic and photometric studies of three detached eclipsing binary
systems, V372\,And, V2080\,Cyg, and CF\,Lyn to obtain their accurate stellar,
atmospheric parameters,and chemical compositions. An analysis of light and
radial velocity curves was carried out to derive the orbital and stellar
parameters. The disentangled spectra of component stars were obtained for the
spectroscopic analysis. Final \teff, \logg, $\xi$, \vsini\, parameters and the
element abundances of component stars were derived by using the spectrum
synthesis method. The fundamental stellar parameters were determined with a
high certainty for V372\,And, V2080\,Cyg ($\sim$$1-2$\%) and with an accuracy
for CF\,Lyn ($\sim$$2-6$\%). The evolutionary status of the systems was
examined and their ages were obtained. It was found that the component stars of
V2080\,Cyg have similar iron abundance which is slightly lower than solar iron
abundance. Additionally, we showed that the primary component of CF\,Lyn
exhibits a non-spherical shape with its 80\% Roche lobe filling factor. It
could be estimated that CF\,Lyn will start its first Roche overflow in the next
0.02\,Gyr.",1907.07560v1
2019-07-29,Near-linear Scaling in DMRG-based Tailored Coupled Clusters: An Implementation of DLPNO-TCCSD and DLPNO-TCCSD(T),"We present a new implementation of DMRG-based tailored coupled clusters
method (TCCSD), which employs the domain-based local pair natural orbital
approach (DLPNO-TCCSD). Compared to the previous LPNO version of the method,
the new implementation is more accurate, offers more favorable scaling and
provides more consistent behavior across the variety of systems. On top of the
singles and doubles, we include the perturbative triples correction (T), which
is able to retrieve even more dynamic correlation. The methods were tested on
three systems: tetramethyleneethane, oxo-Mn(Salen) and Iron(II)-porphyrin
model. The first two were revisited to assess the performance with respect to
LPNO-TCCSD. For oxo-Mn(Salen), we retrieved between 99.8-99.9% of the total
canonical correlation energy which is the improvement of 0.2% over the LPNO
version in less than 63% of the total LPNO runtime. Similar results were
obtained for Iron(II)-porphyrin. When the perturbative triples correction was
employed, irrespective of the active space size or system, the obtained energy
differences between two spin states were within the chemical accuracy of 1
kcal/mol using the default DLPNO settings.",1907.13466v3
2019-10-02,Nuclear Ignition of White Dwarf Stars by Relativistic Encounters with Rotating Intermediate Mass Black Holes,"We present results from general relativistic calculations of nuclear ignition
in white dwarf stars triggered by near encounters with rotating intermediate
mass black holes with different spin and alignment parameters. These encounters
create thermonuclear environments characteristic of Type Ia supernovae capable
of producing both calcium and iron group elements in arbitrary ratios,
depending primarily on the proximity of the interaction which acts as a strong
moderator of nucleosynthesis. We explore the effects of black hole spin and
spin-orbital alignment on burn product synthesis to determine whether they
might also be capable of moderating reactive flows. When normalized to
equivalent impact penetration, accounting for frame dragging corrections, the
influence of spin is weak, no more than 25% as measured by nuclear energy
release and mass of burn products, even for near maximally rotating black
holes. Stars on prograde trajectories approach closer to the black hole and
produce significantly more unbound debris and iron group elements than is
possible by encounters with nonrotating black holes or by retrograde orbits, at
more than 50% mass conversion efficiency. The debris contains several
radioisotopes, most notably Ni56, made in amounts that produce sub-luminous
(but still observable) light curves compared to branch-normal SNe Ia.",1910.01054v1
2019-10-16,Controlling Ferromagnetic Ground States and Solitons in Thin Films and Nanowires built from Iron Phthalocyanine Chains,"Iron phthalocyanine (FePc) is a molecular semiconductor whose building blocks
are one-dimensional ferromagnetic chains. We show that its optical and magnetic
properties are controlled by the growth strategy, obtaining extremely high
coercivities of over 1 T and modulating the exchange constant between 15 and 29
K through tuning the crystal phase by switching from organic molecular beam
deposition, producing continuous thin films of nanocrystals with controlled
orientations, to organic vapour phase deposition, producing ultralong
nanowires. Magnetisation measurements are analysed using a suite of concepts
and simply stated formulas with broad applicability to all one-dimensional
ferromagnetic chains. They show that FePc is best described by a Heisenberg
model with a preference for the moments to lie in the molecular planes, where
the chain Hamiltonian is very similar to that for the classic inorganic magnet
CsNiF3, but with ferromagnetic rather than antiferromagnetic interchain
interactions. The data at large magnetic fields are well-described by the
soliton picture, where the dominant (and topologically non-trivial) degrees of
freedom are moving one-dimensional magnetic domain walls, which was successful
for CsNiF3, and at low temperatures and fields by the super-Curie-Weiss law of
1/(T^2+theta^2) characteristic of nearly one-dimensional xy and Heisenberg
ferromagnets. The ability to control the molecular orientation and
ferromagnetism of FePc systems, and produce them on flexible substrates as thin
films or nanowires, taken together with excellent transistor characteristics
reported previously for nanowires of copper and cobalt analogues, makes them
potentially useful for magneto-optical and spintronic devices.",1910.07229v1
2019-10-18,An ionised accretion disc wind in Hercules X-1,"Hercules X-1 is one of the best studied highly magnetised neutron star X-ray
binaries with a wealth of archival data. We present the discovery of an ionised
wind in its X-ray spectrum when the source is in the high state. The wind
detection is statistically significant in most of the XMM-Newton observations,
with velocities ranging from 200 to 1000 km/s. Observed features in the iron K
band can be explained by both wind absorption or by a forest of iron emission
lines. However, we also detect nitrogen, oxygen and neon absorption lines at
the same systematic velocity in the high-resolution RGS grating spectra. The
wind must be launched from the accretion disc, and could be the progenitor of
the UV absorption features observed at comparable velocities, but the latter
likely originate at significantly larger distances from the compact object. We
find strong correlations between the ionisation level of the outflowing
material and the ionising luminosity as well as the super-orbital phase. If the
luminosity is driving the correlation, the wind could be launched by a
combination of Compton heating and radiation pressure. If instead the
super-orbital phase is the driver for the variations, the observations are
likely scanning the wind at different heights above the warped accretion disc.
If this is the case, we can estimate the wind mass outflow rate, corrected for
the limited launching solid angle, to be roughly 70% of the mass accretion
rate.",1910.08337v2
2019-10-20,"PUSHing core-collapse supernovae to explosions in spherical symmetry IV: Explodability, remnant properties and nucleosynthesis yields of low metallicity stars","In this fourth paper of the series, we use the parametrized, spherically
symmetric explosion method PUSH to perform a systematic study of two sets of
non-rotating stellar progenitor models. Our study includes pre-explosion models
with metallicities Z=0 and Z=Z$_{\odot}\times 10^{-4}$ and covers a progenitor
mass range from 11 up to 75 M$_\odot$. We present and discuss the explosion
properties of all models and predict remnant (neutron star or black hole) mass
distributions within this approach. We also perform systematic nucleosynthesis
studies and predict detailed isotopic yields as function of the progenitor mass
and metallicity. We present a comparison of our nucleosynthesis results with
observationally derived $^{56}$Ni ejecta from normal core-collapse supernovae
and with iron-group abundances for metal-poor star HD~84937. Overall, our
results for explosion energies, remnant mass distribution, $^{56}$Ni mass, and
iron group yields are consistent with observations of normal CCSNe. We find
that stellar progenitors at low and zero metallicity are more prone to BH
formation than those at solar metallicity, which allows for the formation of
BHs in the mass range observed by LIGO/VIRGO.",1910.08958v2
2019-12-08,The vertical Na-O relation in the bulge globular cluster NGC 6553,"In this article, we present a detailed chemical analysis of seven red giant
members of NGC 6553 using high-resolution spectroscopy from VLT FLAMES. We
obtained the stellar parameters (Teff, Log(g), vt, [Fe/H]) of these stars from
the spectra, and we measured the chemical abundance for 20 elements, including
light elements, iron-peak elements, alpha-elements and neutron-capture
elements. The metallicities in our sample stars are consistent with a
homogeneous distribution. We found a mean of [Fe/H]=-0.14+/-0.07 dex, in
agreement with other studies. Using the alpha-elements Mg, Si, Ca and Ti we
obtain the mean of [alpha/Fe]=0.11+/-0.05. We found a vertical relation between
Na and O, characterized by a significant spread in Na and an almost
non-existent spread in O. In fact, Na and Al are the only two light elements
with a large intrinsic spread, which demonstrates the presence of Multiple
Populations (MPs). An intrinsic spread in Mg is not detected in this study. The
alpha, iron-peak and neutron capture elements show good agreement with the
trend of the bulge field stars, indicating similar origin and evolution, in
concordance with our previous studies for two other bulge GCs (NGC 6440 and NGC
6528).",1912.03742v2
2019-12-10,Magnetic properties of thin epitaxial Pd$_{1-x}$Fe$_x$ alloy films,"In the paper we present the results of extensive studies of palladium-rich
Pd1-xFex alloy films epitaxially grown on MgO single-crystal substrate. In a
composition range of x = 0.01-0.07 these materials are soft ferromagnets, the
saturation magnetization and magnetic anisotropy of which can be tuned by its
composition. Vibrating sample magnetometry was used to study temperature
dependences of spontaneous magnetic moment and to establish the temperature of
magnetic ordering (Curie temperature). Ferromagnetic resonance (FMR)
measurements at low temperatures in the in-plane and out-of-plane geometries
revealed the four-fold in-plane magnetic anisotropy with the easy directions
along the <110> axes of the substrate. The modelling of the angular dependence
of the field for resonance allowed to extract the cubic and tetragonal
contributions to the magnetic anisotropy of the films and establish their
dependence on the concentration of iron in the alloy. Experimental data are
discussed in the framework of existing theories of dilute magnetic alloys.
Using the anisotropy constants established from FMR, the magnetic hysteresis
loops are reproduced utilizing the Stoner-Wohlfarth model thus indicating the
predominant coherent magnetic moment rotation at low temperatures. The obtained
results compile a database of magnetic properties of a palladium-iron alloy
considered as a material for superconducting spintronics.",1912.04852v1
2019-12-16,High-Temperature Quantum Anomalous Hall Insulators in Lithium-Decorated Iron-Based Superconductor Materials,"Quantum anomalous Hall (QAH) insulator is the key material to study emergent
topological quantum effects, but its ultralow working temperature limits
experiments. Here, by first-principles calculations, we find a family of stable
two-dimensional (2D) structures generated by lithium decoration of layered
iron-based superconductor materials FeX (X = S, Se, Te), and predict
room-temperature ferromagnetic semiconductors together with large-gap
high-Chern-number QAH insulators in the 2D materials. The extremely robust
ferromagnetic order is induced by the electron injection from Li to Fe and
stabilized by strong ferromagnetic kinetic exchange in the 2D Fe layer. While
in the absence of spin-orbit coupling (SOC), the ferromagnetism polarizes the
system into a half Dirac semimetal state protected by mirror symmetry, the SOC
effect results in a spontaneous breaking of mirror symmetry and introduces a
Dirac mass term, which creates QAH states with sizable gaps (several tens of
meV) and multiple chiral edge modes. We also find a 3D QAH insulator phase
featured by macroscopic number of chiral conduction channels in bulk
LiOH-LiFeX. The findings open new opportunities to realize novel QAH physics
and applications at high temperatures.",1912.07461v4
2020-03-06,Ab initio theory of graphene-iron(II) phthalocyanine hybrid systems as scalable molecular spintronics,"Graphene - transition metal phthalocyanine (G-MPc) hybrid systems constitute
promising platforms for densely-packed single-molecule magnets (SMMs). Here, we
selected iron(II) phthalocyanine (FePc) and investigated its interaction with
pristine and defective graphene layers employing density functional theory. Our
calculations indicate that thorough proper dehydrogenation of the benzol rings
in the FePc molecule its adsorption to graphene is thermodynamically favorable.
In general, the presence of anchoring sites on the graphene layer, i.e. point
defects, additionally facilitates the adsorption of FePc, allowing one to
achieve high density of SMMs per unit area. Using the combination of group
theory, ligand field splitting, and the calculated PBE0 Kohn-Sham eigenvalue
spectrum, we resolved the electronic structure and predicted the spin states of
both, the isolated FePc and G-FePc hybrid systems. Regardless of adsorption
site and the number of removed hydrogen atoms from the benzol rings of FePc,
the magnetic moment of the SMM remains unchanged with respect to free FePc.
These results should mediate a successful synthesis of densely-packed G-MPc
systems and may open up new avenue in designing scalable graphene - SMMs
systems for spintronics applications.",2003.03189v1
2020-03-22,A statistical study of the plasma and composition distribution inside magnetic clouds: 1998-2011,"A comprehensive analysis of plasma and composition characteristics inside
magnetic clouds (MCs) observed by the Advanced Composition Explorer (ACE)
spacecraft from 1998 February to 2011 August is presented. The results show
that MCs have specific interior structures, and MCs of different speeds show
differences in composition and structure. Compared with the slow MCs, fast MCs
have enhanced mean charge states of iron, oxygen, silicon, magnesium,
$\mathrm{O^{7+}/O^{6+}}$, $\mathrm{C^{6+}/C^{5+}}$, $\mathrm{C^{6+}/C^{4+}}$
and $\mathrm{Fe^{\geq16+}/Fe_{total}}$ values. For ionic species in fast MCs, a
higher atomic number represents a greater enhancement of mean charge state than
slow MCs. We also find that both the fast and slow MCs display bimodal
structure distribution in the mean iron charge state ($\mathrm{\langle Q\rangle
Fe}$), which suggests that the existence of flux rope prior to the eruption is
common. Furthermore, the $\mathrm{\langle Q\rangle Fe} $,
$\mathrm{Fe^{\geq16+}/Fe_{total}}$, and $\mathrm{O^{7+}/O^{6+}}$ ratio
distribution inside fast MCs have the feature that the posterior peak is higher
than the anterior one. This result agrees with the ""standard model"" for
CME/flares, by which magnetic reconnection occurs beneath the flux rope,
thereby ionizing the ions of the posterior part of flux rope sufficiently by
high-energy electron collisions or by direct heating in the reconnection
region.",2003.09965v1
2020-08-03,When superconductivity does not fear magnetism: Insight into electronic structure of RbEuFe$_{4}$As$_{4}$,"In the novel stoichiometric iron-based material RbEuFe$_{4}$As$_{4}$
superconductivity coexists with a peculiar long-range magnetic order of Eu 4f
states. Using angle-resolved photoemission spectroscopy, we reveal a complex
three dimensional electronic structure and compare it with density functional
theory calculations. Multiple superconducting gaps were measured on various
sheets of the Fermi surface. High resolution resonant photoemission
spectroscopy reveals magnetic order of the Eu 4f states deep into the
superconducting phase. Both the absolute values and the anisotropy of the
superconducting gaps are remarkably similar to the sibling compound without Eu,
indicating that Eu magnetism does not affect the pairing of electrons. A
complete decoupling between Fe- and Eu-derived states was established from
their evolution with temperature, thus unambiguously demonstrating that
superconducting and a long range magnetic orders exist independently from each
other. The established electronic structure of RbEuFe$_{4}$As$_{4}$ opens
opportunities for the future studies of the highly unorthodox electron pairing
and phase competition in this family of iron-based superconductors with doping.",2008.00736v1
2020-08-10,On The Development of Multidimensional Progenitor Models For Core-collapse Supernovae,"Multidimensional hydrodynamic simulations of shell convection in massive
stars suggest the development of aspherical perturbations that may be amplified
during iron core-collapse. These perturbations have a crucial and qualitative
impact on the delayed neutrino-driven core-collapse supernova explosion
mechanism by increasing the total stress behind the stalled shock. In this
paper, we investigate the properties of a 15 \msun model evolved in 1-,2-, and
3-dimensions (3D) for the final $\sim$424 seconds before gravitational
instability and iron core-collapse using MESA and the FLASH simulation
framework. We find that just before collapse, our initially perturbed fully 3D
model reaches angle-averaged convective velocity magnitudes of $\approx$
240-260 km s$^{-1}$ in the Si- and O-shell regions with a Mach number $\approx$
0.06. We find the bulk of the power in the O-shell resides at large scales,
characterized by spherical harmonic orders ($\ell$) of 2-4, while the Si-shell
shows broad spectra on smaller scales of $\ell\approx30-40$. Both convective
regions show an increase in power at $\ell=5$ near collapse. We show that the
1D \texttt{MESA} model agrees with the convective velocity profile and speeds
of the Si-shell when compared to our highest resolution 3D model. However, in
the O-shell region, we find that \texttt{MESA} predicts speeds approximately
\emph{four} times slower than all of our 3D models suggest. All eight of the
multi-dimensional stellar models considered in this work are publicly
available.",2008.04266v1
2020-08-31,Creep deformation of WC hardmetals with iron-based binders,"Iron is a candidate to replace cobalt in WC hardmetals, due to its lower cost
and toxicity. A WC-FeCr hardmetal was compression tested at 900-1200 {\deg}C.
Particular attention is paid to the steady-state creep rates and
stress-exponents (n) during isostress treatments. Three regimes of stress
dependence are observed. Two of these were previously reported for WC-Co: power
law creep (n~3) at medium stresses; and grain boundary sliding (n~1) at higher
stresses, generally >100MPa. A previously unreported low stress (<10MPa) regime
with an exponent of n~2 is also observed. By combining electron microscopy with
X-ray diffraction texture measurements, the low stress regime is attributed to
viscous flow of the binder, which is accommodated by diffusional creep in the
WC skeleton. The mechanism may be applicable to other hardmetals. Compared to
analogous WC-Co materials, WC-FeCr shows improved creep resistance below 1000
{\deg}C, which can be explained by its lower self-diffusivity, and a lower
solubility for WC than Co. However, at temperatures corresponding to liquid
eutectic formation (~1140 {\deg}C), its creep resistance becomes inferior.
These results indicate FeCr may be a suitable replacement for Co provided the
eutectic temperature is not exceeded.",2008.13565v1
2020-09-02,Multimodal assessment of nigrosomal degeneration in Parkinson's disease,"Background: Approximately forty percent of all dopaminergic neurons in SNpc
are located in five dense neuronal clusters, named nigrosomes. T2- or
T2*-weighted images are used to delineate the largest nigrosome, named
nigrosome-1. In these images, nigrosome-1 is a hyperintense region in the
caudal and dorsal portion of the T2- or T2*-weighted substantia nigra. In PD,
nigrosome-1 experiences iron accumulation, which leads to a reduction in
T2-weighted hyperintensity. Here, we examine neuromelanin-depletion and iron
deposition in regions of interest (ROIs) derived from quantitative-voxel based
morphometry (qVBM) on neuromelanin-sensitive images and compare the ROIs with
nigrosome-1 identified in T2*-weighted images.
  Methods: Neuromelanin-sensitive and multi-echo gradient echo imaging data
were obtained. R2* was calculated from multi-echo gradient echo imaging data.
qVBM analysis was performed on neuromelanin-sensitive images and restricted to
SNpc. Mean neuromelanin-sensitive contrast and R2* was measured from the
resulting qVBM clusters. Nigrosome-1 was segmented in T2*-weighted images of
control subjects and its location was compared to the spatial location of the
qVBM clusters.
  Results: Two bilateral clusters emerged from the qVBM analysis. These
clusters showed reduced neuromelanin-sensitive contrast and increased mean R2*
in PD as compared to controls. Cluster-1 from the qVBM analysis was in a
similar spatial location as nigrosome-1, as seen in T2*-weighted images.
  Conclusion: qVBM cluster-1 shows reduced neuromelanin-sensitive contrast and
is in a similar spatial position as nigrosome-1. This region likely corresponds
to nigrosome-1 while the second cluster may correspond to nigrosome-2.",2009.01378v1
2020-09-09,Accretion disk's magnetic field controlled the composition of the terrestrial planets,"Chondrites, the building blocks of the terrestrial planets, have mass and
atomic proportions of oxygen, iron, magnesium, and silicon totaling $\geq$90\%
and variable Mg/Si ($\sim$25\%), Fe/Si (factor of $\geq$2), and Fe/O (factor of
$\geq$3). The Earth and terrestrial planets (Mercury, Venus, and Mars) are
differentiated into three layers: a metallic core, a silicate shell (mantle and
crust), and a volatile envelope of gases, ices, and, for the Earth, liquid
water. Each layer has different dominant elements (e.g., increasing Fe content
with depth and increasing oxygen content to the surface). What remains an
unknown is to what degree did physical processes during nebular disk accretion
versus those during post-nebular disk accretion (e.g., impact erosion)
influence these final bulk compositions. Here we predict terrestrial planet
compositions and show that their core mass fractions and uncompressed densities
correlate with their heliocentric distance, and follow a simple model of the
magnetic field strength in the protoplanetary disk. Our model assesses the
distribution of iron in terms of increasing oxidation state, aerodynamics, and
a decreasing magnetic field strength outward from the Sun, leading to
decreasing core size of the terrestrial planets with radial distance. This
distribution would enhance habitability in our solar system, and would be
equally applicable to exo-planetary systems.",2009.04311v1
2020-09-11,Electronic nematic states tuned by isoelectronic substitution in bulk FeSe1-xSx,"Isoelectronic substitution is an ideal tuning parameter to alter electronic
states and correlations in iron-based superconductors. As this substitution
takes place outside the conducting Fe planes, the electronic behaviour is less
affected by the impurity scattering experimentally and relevant key electronic
parameters can be accessed. In this short review, I present the experimental
progress made in understanding the electronic behaviour of the nematic
electronic superconductors, FeSe1-xSx. A direct signature of the nematic
electronic state is in-plane anisotropic distortion of the Fermi surface
triggered by orbital ordering effects and electronic interactions that result
in multi-band shifts detected by ARPES. Upon sulphur substitution, the
electronic correlations and the Fermi velocities decrease in the tetragonal
phase. Quantum oscillations are observed for the whole series in ultra-high
magnetic fields and show a complex spectra due to the presence of many small
orbits. Effective masses associated to the largest orbit display non-divergent
behaviour at the nematic end point (x~0.175(5)), as opposed to critical
spin-fluctuations in other iron pnictides. Magnetotransport behaviour has a
strong deviation from the Fermi liquid behaviour and linear T resistivity is
detected at low temperatures inside the nematic phase, where scattering from
low energy spin-fluctuations are likely to be present. The superconductivity is
not enhanced in FeSe1-xSx and there are no divergent electronic correlations at
the nematic end point. These manifestations indicate a strong coupling with the
lattice in FeSe1-xSx and a pairing mechanism likely promoted by spin
fluctuations.",2009.05523v1
2020-09-21,The Impact of Outflows driven by Active Galactic Nuclei on Metals in and around Galaxies,"Metals in the hot gaseous halos of galaxies encode the history of star
formation as well as the feedback processes that eject metals from the
galaxies. X-ray observations suggest that massive galaxies have extended
distributions of metals in their gas halos. We present predictions for the
metal properties of massive galaxies and their gaseous halos from recent high
resolution zoom-in simulations that include mechanical and radiation driven
feedback from Active Galactic Nuclei (AGN). In these simulations, AGN launch
high-velocity outflows, mimicking observed broad absorption line winds. By
comparing two sets of simulations with and without AGN feedback, we show that
our prescription for AGN feedback is capable of driving winds and enriching
halo gas `inside-out' by spreading centrally enriched metals to the outskirts
of galaxies, into the halo and beyond. The metal (iron) profiles of halos
simulated with AGN feedback have a flatter slope than those without AGN
feedback, consistent with recent X-ray observations. The predicted gas iron
abundance of group scale galaxies simulated with AGN feedback is $Z_{\rm Fe} =
0.23$ $Z_{\rm Fe,\odot}$ at $0.5 r_{500}$, which is 2.5 times higher than that
in simulations without AGN feedback. In these simulations, AGN winds are also
important for the metal enrichment of the intergalactic medium, as the vast
majority of metals ejected from the galaxy by AGN-driven winds end up beyond
the halo virial radius.",2009.10184v1
2020-09-24,Large magnetoresistance in the iron-free pnictide superconductor LaRu$_2$P$_2$,"The magnetoresistance of iron pnictide superconductors is often dominated by
electron-electron correlations and deviates from the H$^2$ or saturating
behaviors expected for uncorrelated metals. Contrary to similar Fe-based
pnictide systems, the superconductor LaRu$_2$P$_2$ (T$_c$ = 4 K) shows no
enhancement of electron-electron correlations. Here we report a non-saturating
magnetoresistance deviating from the H$^2$ or saturating behaviors in
LaRu$_2$P$_2$. We have grown and characterized high quality single crystals of
LaRu$_2$P$_2$ and measured a magnetoresistance following H$^{1.3}$ up to 22 T.
We discuss our result by comparing the bandstructure of LaRu$_2$P$_2$ with Fe
based pnictide superconductors. The different orbital structures of Fe and Ru
leads to a 3D Fermi surface with negligible bandwidth renormalization in
LaRu$_2$P$_2$, that contains a large open sheet over the whole Brillouin zone.
We show that the large magnetoresistance in LaRu$_2$P$_2$ is unrelated to the
one obtained in materials with strong electron-electron correlations and that
it is compatible instead with conduction due to open orbits on the rather
complex Fermi surface structure of LaRu$_2$P$_2$.",2009.11585v1
2020-09-28,"Intrusion of MeV-TeV Cosmic-Rays into Molecular Clouds Studied by Ionization, the Neutral Iron Line, and Gamma-Rays","Low-energy (~MeV) cosmic rays (CRs) ionize molecular clouds and create the
neutral iron line (Fe I K\alpha) at 6.4 keV. On the other hand, high-energy (>~
GeV) CRs interact with the dense cloud gas and produce gamma rays. Based on a
one-dimensional model, we study the spatial correlation among ionization rates
of gas, 6.4 keV line fluxes, and gamma-ray emissions from a molecular cloud
illuminated by CRs accelerated at an adjacent supernova remnant. We find that
the spatial distributions of these three observables depend on how CRs intrude
the cloud and on the internal structure of the cloud. If the intrusion is
represented by slow diffusion, the 6.4 keV line should be detected around the
cloud edge where ionization rates are high. On the other hand, if CRs freely
stream in the cloud, the 6.4 keV line should be observed where gamma rays are
emitted. In the former, the cooling time of the CRs responsible for the 6.4 keV
line is shorter than their cloud crossing time, and it is opposite in the
latter. Although we compare the results with observations, we cannot conclude
whether the diffusion or the free-streaming is dominantly realized. Our
predictions can be checked in more detail with future X-ray missions such as
XRISM and Athena and by observations of ionization rates that cover wider
fields.",2009.13524v3
2020-10-02,Singular magnetic anisotropy in the nematic phase of FeSe,"FeSe is arguably the simplest, yet the most enigmatic, iron-based
superconductor. Its nematic but non-magnetic ground state is unprecedented in
this class of materials and stands out as a current puzzle. Here, our NMR
measurements in the nematic state of mechanically detwinned FeSe reveal that
both the Knight shift and the spin-lattice relaxation rate 1/T_1 possess an
in-plane anisotropy opposite to that of the iron pnictides LaFeAsO and
BaFe2As2. Using a microscopic electron model that includes spin-orbit coupling,
our calculations show that an opposite quasiparticle weight ratio between the
d_xz and d_yz orbitals leads to an opposite anisotropy of the orbital magnetic
susceptibility, which explains our Knight shift results. We attribute this
property to a different nature of nematic order in the two compounds,
predominantly bond-type in FeSe and onsite ferro-orbital in pnictides. The T_1
anisotropy is found to be inconsistent with existing neutron scattering data in
FeSe, showing that the spin fluctuation spectrum reveals surprises at low
energy, possibly from fluctuations that do not break C_4 symmetry. Therefore,
our results reveal that important information is hidden in these anisotropies
and they place stringent constraints on the low-energy spin correlations as
well as on the nature of nematicity in FeSe.",2010.01020v1
2020-10-05,Magnetic Iron Nanocubes Effectively Capture Epithelial and Mesenchymal Cancer Cells,"Current methods for capturing circulating tumor cells (CTCs) are based on the
overexpression of cytokeratin (CK) or epithelial cell-adhesion molecule (EpCAM)
on cancer cells. However, during the process of metastasis, tumor cells undergo
epithelial to mesenchymal transition (EMT) that can lead to the loss of
CK/EpCAM expression. Therefore, it is vital to develop a capturing technique
independent of CK/EpCAM expression on the cancer cell. To develop this
technique, it is important to identify common secondary oncogenic markers
overexpressed on tumor cells before and after EMT. We analyzed the biomarker
expression levels in tumor cells, before and after EMT, and found two common
proteins human epidermal growth factor receptor 2 (Her2) and epidermal growth
factor receptor (EGFR) whose levels remained unaffected. So, we synthesized
immunomagnetic iron nanocubes covalently conjugated with antibodies of Her2 or
EGFR to capture cancer cells irrespective of the EMT status. The nanocubes
showed high specificity (6 to 9 fold) in isolating the cancer cells of interest
from a mixture of cells spiked in serum. We characterized the captured cells
for identifying their EMT status. Thus, we believe the results presented here
would help in the development of novel strategies for capturing both primary
and metastatic cancer cells from patients blood to develop an effective
treatment plan.",2010.02129v1
2020-10-14,An extremely metal-deficient globular cluster in the Andromeda Galaxy,"Globular clusters (GCs) are dense, gravitationally bound systems of thousands
to millions of stars. They are preferentially associated with the oldest
components of galaxies, and measurements of their composition can therefore
provide insight into the build-up of the chemical elements in galaxies in the
early Universe. We report a massive GC in the Andromeda Galaxy (M31) that is
extremely depleted in heavy elements. Its iron abundance is about 800 times
lower than that of the Sun, and about three times lower than in the most
iron-poor GCs previously known. It is also strongly depleted in magnesium.
These measurements challenge the notion of a metallicity floor for GCs and
theoretical expectations that massive GCs could not have formed at such low
metallicities.",2010.07395v1
2020-11-20,Photoionization Models for High Density Gas,"Relativistically broadened and redshifted 6.4 -- 6.9 keV iron K lines are
observed from many accretion powered objects, including X-ray binaries and
active galactic nuclei (AGN). Existence of gas close to the central engine
implies large radiation intensities and correspondingly large gas densities if
the gas is to remain partially ionized. Simple estimates indicate that high gas
densities are needed to allow survival of iron against ionization. These are
high enough that rates for many atomic processes are affected by mechanisms
related to interactions with nearby ions and electrons. Radiation intensities
are high enough that stimulated processes can be important. Most models
currently in use for interpreting relativistic lines use atomic rate
coefficients designed for use at low densities and neglect stimulated
processes. In our work so far we have presented atomic structure calculations
with the goal of providing physically appropriate models at densities
consistent with line-emitting gas near compact objects. In this paper we apply
these rates to photoionization calculations, and produce ionization balance
curves and X-ray emissivities and opacities which are appropriate for high
densities and high radiation intensities. The final step in our program will be
presented in a subsequent paper: Model atmosphere calculations which
incorporate these rates into synthetic spectra.",2011.10603v2
2020-12-18,Observation of d-wave Pomeranchuk nematic order in floating monolayer FeSe on FeSe/STO,"As a foundation of condensed matter physics, the normal states of most metals
are successfully described by Landau Fermi liquid theory with quasi-particles
and their Fermi surfaces (FSs). The FSs sometimes become deformed or gapped at
low temperatures owing to quasi-particle interactions, known as FS
instabilities. A notable example of a FS deformation that breaks only the
rotation symmetry, namely Pomeranchuk instability, is the d-wave FS distortion,
which is also proposed as one possible origin of electron nematicity in
iron-based superconductors. However, no clear evidence has been made for its
existence, mostly owing to the mixture of multiple orders. Here we report an
unequivocally observation of the Pomeranchuk nematic order in floating
monolayer (ML) FeSe on 1 ML-FeSe/SrTiO3 substrate. By using angle-resolve
photoemission spectroscopy, we find remarkably that the dxz and dyz bands are
degenerate at the Brillouin zone center (Gamma point), while their splitting is
even larger at zone corner (M point), in stark contrast to that in bulk FeSe.
Our detailed analysis show that the momentum-dependent nematic order in
floating monolayer FeSe is coming from the d-wave Pomeranchuk instability at M
point, shedding light on the origin of the ubiquitous nematicity in iron-based
superconductors. Our results establish the single-layer high-Tc superconductors
as an excellent material platform for investigating emergent quantum physics
under complex intertwinement.",2012.10136v1
2020-12-19,Majorana bound states in vortex lattices on iron-based superconductors,"Majorana quasi-particles may arise as zero-energy bound states in vortices on
the surface of a topological insulator that is proximitized by a conventional
superconductor. Such a system finds its natural realization in the iron-based
superconductor FeTe$_{0.55}$Se$_{0.45}$ that combines bulk $s$-wave pairing
with spin helical Dirac surface states, and which thus comprises the
ingredients for Majorana modes in absence of an additional proximitizing
superconductor. In this work, we investigate the emergence of Majorana vortex
modes and lattices in such materials depending on parameters like the magnetic
field strength and vortex lattice disorder. A simple 2D square lattice model
here allows us to capture the basic physics of the underlying materials system.
To address the problem of disordered vortex lattice, which occurs in real
systems, we adopt the technique of the singular gauge transformation which we
modify such that it can be used in a system with periodic boundary conditions.
This approach allows us to go to larger vortex lattices than otherwise
accessible, and is successful in replicating several experimental observations
of Majorana vortex bound states in the FeTe$_{0.55}$Se$_{0.45}$ platform.
Finally it can be related to a simple disordered Majorana lattice model that
should be useful for further investigations on the role of interactions, and
towards topological quantum computation.",2012.10588v2
2020-12-29,Supernova neutrino detection through neutron emission by nuclei,"Neutrinos from core collapse supernovae can excite nuclei of some detector
materials beyond their neutron emission thresholds. Detection of these neutrons
can give valuable information about the supernova explosion mechanism and
possibly also throw light on neutrino properties. In this article, we give a
brief review of the basic physics of neutrino induced neutron emission and
describe the results of some recent calculations of supernova neutrino induced
neutrons for some specific target detector materials due to charged current
(CC) interactions of the electron flavored neutrinos and antineutrinos as well
as due to neutral current (NC) interactions of neutrinos and antineutrinos of
all flavors with the detector nuclei. We highlight the fact that a detector
material such as lead with a relatively large neutron excess produces neutrons
dominantly through the CC interaction of the $\nu_e$s, whereas a material such
as iron with small neutron excess produces neutrons dominantly through the
combined NC interaction of all the six neutrino and antineutrino species. This
raises the interesting possibility of probing the fraction of mu- and tau
flavored neutrinos (which interact only through NC interaction) in the
supernova neutrino flux by means of simultaneous detection of a supernova in a
lead and an iron detector, for example.",2012.14888v1
2021-01-07,"An injectable, self-healing and MMP-inhibiting hyaluronic acid gel via iron coordination","Regulating the activity of matrix metalloproteinases (MMPs) is a potential
strategy for osteoarthritis (OA) therapy, although delivering this effect in a
spatially and temporally localised fashion remains a challenge. Here, we report
an injectable and self-healing hydrogel enabling factor-free MMP regulation and
biomechanical competence in situ. The hydrogel is realised within one minute
upon room temperature coordination between hyaluronic acid (HA) and a
cell-friendly iron-glutathione complex in aqueous environment. The resultant
gel displayed up to 300% in shear strain and tolerance towards ATDC 5
chondrocytes, in line with the elasticity and biocompatibility requirements for
connective tissue application. Significantly enhanced inhibition of MMP-13
activity was achieved after 12 hours in vitro, compared with a commercial HA
injection (OSTENIL PLUS). Noteworthy, 24-hour incubation of a clinical synovial
fluid sample collected from a late-stage OA patient with the reported hydrogel
was still shown to downregulate synovial fluid MMP activity (100.0 +/- 17.6 %
--> 81.0 +/- 7.5 %), with at least comparable extent to the case of the OSTENIL
PLUS-treated SF group (100.0 +/- 17.6 % --> 92.3 +/- 27.3 %). These results
therefore open up new possibilities in the use of HA as both
mechanically-competent hydrogel as well as a mediator of MMP regulation for OA
therapy.",2101.02414v1
2021-01-26,"Superconductivity at 40 K in lithiation-processed [(Fe,Al)(OH)2][FeSe]1.2 with a layered structure","Exploration of new superconductors has always been one of the research
directions in condensed matter physics. We report here a new layered
heterostructure of [(Fe,Al)(OH)2][FeSe]1.2, which is synthesized by the
hydrothermal ion-exchange technique. The structure is suggested by a
combination of X-ray powder diffraction and the electron diffraction (ED).
[(Fe,Al)(OH)2][FeSe]1.2 is composed of the alternating stacking of tetragonal
FeSe layer and hexagonal (Fe,Al)(OH)2 layer. In [(Fe,Al)(OH)2][FeSe]1.2, there
exists mismatch between the FeSe sub-layer and (Fe,Al)(OH)2 sub-layer, and the
lattice of the layered heterostructure is quasi-commensurate. The
as-synthesized [(Fe,Al)(OH)2][FeSe]1.2 is non-superconducting due to the Fe
vacancies in the FeSe layer. The superconductivity with a Tc of 40 K can be
achieved after a lithiation process, which is due to the elimination of the Fe
vacancies in the FeSe layer. The Tc is nearly the same as that of (Li,Fe)OHFeSe
although the structure of [(Fe,Al)(OH)2][FeSe]1.2 is quite different from that
of (Li,Fe)OHFeSe. The new layered heterostructure of [(Fe,Al)(OH)2][FeSe]1.2
contains an iron selenium tetragonal lattice interleaved with a hexagonal metal
hydroxide lattice. These results indicate that the superconductivity is very
robust for FeSe-based superconductors. It opens a path for exploring
super-conductivity in iron-base superconductors.",2101.10641v1
2021-04-08,The EOS/Resolution Conspiracy: Convergence in Proto-Planetary Collision Simulations,"We investigate how the choice of equation of state (EOS) and resolution
conspire to affect the outcomes of giant impact (GI) simulations. We focus on
the simple case of equal mass collisions of two Earth-like $0.5\,M_\oplus$
proto-planets showing that the choice of EOS has a profound impact on the
outcome of such collisions as well as on the numerical convergence with
resolution. In simulations where the Tillotson EOS is used, impacts generate an
excess amount of vapour due to the lack of a thermodynamically consistent
treatment of phase transitions and mixtures. In oblique collisions this
enhances the artificial angular momentum (AM) transport from the planet to the
circum-planetary disc reducing the planet's rotation period over time. Even at
a resolution of $1.3 \times 10^6$ particles the result is not converged. In
head-on collisions the lack of a proper treatment of the solid/liquid-vapour
phase transition allows the bound material to expand to very low densities
which in turn results in very slow numerical convergence of the critical
specific impact energy for catastrophic disruption $Q_{RD}^*$ with increasing
resolution as reported in prior work. The simulations where ANEOS is used for
oblique impacts are already converged at a modest resolution of $10^5$
particles, while head-on collisions converge when they evidence the post-shock
formation of a dense iron-rich ring, which promotes gravitational
re-accumulation of material. Once sufficient resolution is reached to resolve
the liquid-vapour phase transition of iron in the ANEOS case, and this ring is
resolved, the value of $Q_{RD}^*$ has then converged.",2104.03559v2
2021-04-22,Chemical composition of stars with massive planets,"Stellar parameters of 25 planet-hosting stars and abundances of Li, C, O, Na,
Mg, Al, S, Si, Ca, Sc, Ti, V, Cr, Mn, Fe, Ni, Zn, Y, Zr, Ba, Ce, Pr, Nd, Sm and
Eu, were studied based on homogeneous high resolution spectra and uniform
techniques. The iron abundance [Fe/H] and key elements (Li, C, O, Mg, Si)
indicative of the planet formation, as well as the dependencies of [El/Fe] on
$T_{cond}$, were analyzed. The iron abundances determined in our sample stars
with detected massive planets range within -0.3<[Fe/H]<0.4. The behaviour of
[C/Fe], [O/Fe], [Mg/Fe] and [Si/Fe] relative to [Fe/H] is consistent with the
Galactic Chemical Evolution trends. The mean values of C/O and [C/O] are <C/O>=
0.48 +/-0.07 and <[C/O]>=-0.07 +/-0.07, which are slightly lower than solar
ones. The Mg/Si ratios range from 0.83 to 0.95 for four stars in our sample and
from 1.0 to 1.86 for the remaining 21 stars. Various slopes of [El/Fe] vs.
Tcond were found. The dependencies of the planetary mass on metallicity, the
lithium abundance, the C/O and Mg/Si ratios, and also on the [El/Fe]-Tcond
slopes were considered.",2104.10894v1
2021-05-02,High-energy magnetic excitations from heavy quasiparticles in CeCu$_2$Si$_2$,"Magnetic fluctuations is the leading candidate for pairing in cuprate,
iron-based and heavy fermion superconductors. This view is challenged by the
recent discovery of nodeless superconductivity in CeCu$_2$Si$_2$, and calls for
a detailed understanding of the corresponding magnetic fluctuations. Here, we
mapped out the magnetic excitations in \ys{superconducting (S-type)}
CeCu$_2$Si$_2$ using inelastic neutron scattering, finding a strongly
asymmetric dispersion for $E\lesssim1.5$~meV, which at higher energies evolve
into broad columnar magnetic excitations that extend to $E\gtrsim 5$ meV. While
low-energy magnetic excitations exhibit marked three-dimensional
characteristics, the high-energy magnetic excitations in CeCu$_2$Si$_2$ are
almost two-dimensional, reminiscent of paramagnons found in cuprate and
iron-based superconductors. By comparing our experimental findings with
calculations in the random-phase approximation,we find that the magnetic
excitations in CeCu$_2$Si$_2$ arise from quasiparticles associated with its
heavy electron band, which are also responsible for superconductivity. Our
results provide a basis for understanding magnetism and superconductivity in
CeCu$_2$Si$_2$, and demonstrate the utility of neutron scattering in probing
band renormalization in heavy fermion metals.",2105.00387v1
2021-05-19,An examination of local strain fields evolution in ductile cast iron through micromechanical simulations based on 3D imaging,"Microscopic digital volume correlation (DVC) and finite element
precoalescence strain evaluations are compared for two nodular cast iron
specimens. Displacement fields from \textit{in-situ} 3D synchrotron
laminography images are obtained by DVC. Subsequently the microstructure is
explicitely meshed from the images considering nodules as voids. Boundary
conditions are applied from the DVC measurement. Image segmentation-related
uncertainties are taken into account and observed to be negligible with respect
to the differences between strain levels. Macroscopic as well as local strain
levels in coalescing ligaments between voids nucleated at large graphite
nodules are compared. Macroscopic strain levels are consistently predicted. A
very good agreement is observed for one of the specimens, while the strain
levels for the second specimen presents some discrepancies. Limitations of the
modeling and numerical framework are discussed in light of these differences. A
discussion of the use of strain as coalescence indicator is initiated.",2105.09859v3
2021-05-24,The Surface of (16) Psyche from Thermal Emission and Polarization Mapping,"The asteroid (16) Psyche is the largest of the M-type asteroids, which have
been hypothesized to be the cores of disrupted planetesimals and the parent
bodies of the iron meteorites. While recent evidence has collected against a
pure metal composition for Psyche, its spectrum and radar properties remain
anomalous. We observed (16) Psyche in thermal emission with the Atacama Large
(sub-)Millimeter Array (ALMA) at a resolution of 30 km over 2/3 of its
rotation. The diurnal temperature variations are at the $\sim$10 K level over
most of the surface and are best fit by a smooth surface with a thermal inertia
of 280$\pm$100 J m$^{-2}$ K$^{-1}$ s$^{-1/2}$. We measure a millimeter
emissivity of 0.61$\pm$0.02, which we interpret via a model that treats the
surface as a porous mixture of silicates and metals, where the latter may take
the form of iron sulfides/oxides or alternatively as conducting metallic
inclusions. The emissivity indicates a metal content of no less than 20\% and
potentially much higher, but the polarized emission that should be present for
a surface with $\geq$20\% metal content is almost completely absent. This
requires a highly scattering surface, which may be due to the presence of
reflective metallic inclusions. If such is the case, a consequence is that
metal-rich asteroids may produce less polarized emission than metal-poor
asteroids, exactly the opposite prediction from standard theory, arising from
the dominance of scattering over the bulk material properties.",2105.11372v1
2021-08-03,Spectroscopy and structural investigation of iron phosphorus trisulfide -- FePS$_3$,"Lamellar structures of transition metal phosphorus trisulfides possess strong
intralayer bonding, albeit adjacent layers are held by weak van der Waals
interactions. Those compounds received enormous interest due to their unique
combination of optical and long-range magnetic properties. Among them, iron
phosphorus trisulfide (FePS$_3$) gathered special attention for being a
semiconductor with an absorption edge in the near-infrared, as well as showing
an Ising-like anti-ferromagnetism. We report a successful growth of centimeter
size bulk FePS$_3$ crystals with a chemical yield above 70%, whose
crystallographic structure and composition were carefully identified by
advanced electron microscopy methodologies, including atomic resolution
elemental mapping, along with photoelectron spectroscopy. The knowledge on the
optical activity of FePS$_3$ is extended utilizing temperature-dependent
absorption and photoacoustic spectroscopies, while measurements were
corroborated with density-functional theory calculations. Temperature-dependent
experiments showed a small and monotonic band-edge energy shift down to 115 K
and exposed the interconnected importance of electron-phonon coupling. Most of
all, the correlation between the optical behavior and the magnetic phase
transition is revealed, which shows the practical utilization of
temperature-dependent optical absorption to investigate magnetic interactions.",2108.01742v3
2021-08-08,V488 Per revisited: no strong mid-infrared emission features and no evidence for stellar/sub-stellar companions,"We present characterization of the planetary system architecture for V488
Per, the dustiest main sequence star known with a fractional infrared
luminosity of ~16%. Far-infrared imaging photometry confirms the existence of
an outer planetary system dust population with blackbody-fit temperature of
~130 K. Mid-infrared spectroscopy probing the previously-identified ~800 K
inner planetary system dust population does not detect any obvious solid-state
emission features, suggesting either large grain sizes that mute such emission
and/or grain compositions dominated by species like amorphous carbon and
metallic iron which do not produce such features. In the latter case, the
presence of significant quantities of iron-rich material could be indicative of
the active formation of a Mercury-like planet around V488 Per. In any event,
the absence of solid-state emission features is very unusual among main
sequence stars with copious amounts of warm orbiting dust particles; we know of
no other such star whose mid-infrared spectrum lacks such features. Combined
radial velocity monitoring and adaptive optics imaging find no evidence for
stellar/sub-stellar companions within several hundred AU of V488 Per.",2108.03700v1
2021-08-20,Orbital-dependent modulation of the superconducting gap in uniaxially strained Ba$_{0.6}$K$_{0.4}$Fe$_2$As$_2$,"Pairing symmetry which characterizes the superconducting pairing mechanism is
normally determined by measuring the superconducting gap structure
($|\Delta_k|$). Here, we report the measurement of a strain-induced gap
modulation ($\partial|\Delta_k|$) in uniaxially strained
Ba$_{0.6}$K$_{0.4}$Fe$_2$As$_2$ utilizing angle-resolved photoemission
spectroscopy and $in$-$situ$ strain-tuning. We found that the uniaxial strain
drives Ba$_{0.6}$K$_{0.4}$Fe$_2$As$_2$ into a nematic superconducting state
which breaks the four-fold rotational symmetry of the superconducting pairing.
The superconducting gap increases on the $d_{yz}$ electron and hole pockets
while it decreases on the $d_{xz}$ counterparts. Such orbital selectivity
indicates that orbital-selective pairing exists intrinsically in non-nematic
iron-based superconductors. The $d_{xz}$ and $d_{yz}$ pairing channels are
balanced originally in the pristine superconducting state, but become
imbalanced under uniaxial strain. Our results highlight the important role of
intra-orbital scattering in mediating the superconducting pairing in iron-based
superconductors. It also highlights the measurement of $\partial|\Delta_k|$ as
an effective way to characterize the superconducting pairing from a
perturbation perspective.",2108.08986v1
2021-08-25,Synthesis of a High-Capacity α-Fe2O3@C Conversion Anode and a High-Voltage LiNi0.5Mn1.5O4 Spinel Cathode and Their Combination in a Li-Ion Battery,"A Li-conversion alpha-Fe2O3@C nanocomposite anode and a high-voltage
LiNi0.5Mn1.5O4 cathode are synthesized in parallel, characterized, and combined
in a Li-ion battery. alpha-Fe2O3@C is prepared via annealing of maghemite iron
oxide and sucrose under an argon atmosphere and subsequent oxidation in air.
The nanocomposite exhibits a satisfactory electrochemical response in a lithium
half-cell, delivering almost 900 mA h g-1, as well as a significantly longer
cycle life and higher rate capability compared to the bare iron oxide
precursor. The LiNi0.5Mn1.5O4 cathode, achieved using a modified
co-precipitation approach, reveals a well-defined spinel structure without
impurities, a sub-micrometrical morphology, and a reversible capacity of ca.
120 mA h g-1 in a lithium half-cell with an operating voltage of 4.8 V. Hence,
a lithium-ion battery is assembled by coupling the alpha-Fe2O3@C anode with the
LiNi0.5Mn1.5O4 cathode. This cell operates at about 3.2 V, delivering a stable
capacity of 110 mA h g-1 (referred to the cathode mass) with a Coulombic
efficiency exceeding 97%. Therefore, this cell is suggested as a promising
energy storage system with expected low economic and environmental impacts.",2108.11314v1
2021-08-25,Magnetic properties of BiFeO$_3$-BaTiO$_3$ ceramics in the morphotropic phase boundary: a role of crystal structure and structural parameters,"A correlation between the crystal structure and magnetic properties of system
(1-x)BiFeO$_3$-(x)BaTiO$_3$ with compounds across the morphotropic phase
boundary was studied using X-ray and neutron diffraction, magnetometry, and
Mossbauer spectroscopy measurements. Increase in the dopants content leads to
the structural transition from the rhombohedral phase to the cubic phase via a
formation of the two-phase region (0.2 < x < 0.33), wherein the magnetic
structure changes from the modulated G-type antiferromagnetic to the collinear
antiferromagnetic via a stabilization of the non-collinear antiferromagnetic
phase with non-zero remanent magnetization. The value of magnetic moment
calculated per iron ion based on the Mossbauer and neutron diffraction data
decreases from m = 4.4 mB for the compound with x=0.25 to m=3.2 mB for the
compound with x=0.35 testifying a dominance of 3+ oxidation state of the iron
ions. Increase in the amount of the cubic phase leads to a reduction in the
remanent magnetization from 0.02 emu.g for the compounds with the dominant
rhombohedral phase (x < 0.27) down to about 0.001 emu/g for the compounds with
dominant cubic structure (x >= 0.27). Rapid decrease in the remanent
magnetization observed in the compounds across the phase coexistence region
points at no direct correlation between the type of structural distortion and
non-zero remanent magnetization, while the oxygen octahedra tilting is the key
factor determining the presence of non-zero remanent magnetization.",2108.11447v1
2021-08-30,Thermodynamic Signatures of Diagonal Nematicity in RbFe$_2$As$_2$ Superconductor,"Electronic nematic states with broken rotational symmetry often emerge in
correlated materials. In most iron-based superconductors, the nematic
anisotropy is oriented in the Fe-Fe direction of the iron square lattice.
Recently, a novel type of nematicity along the diagonal Fe-As direction has
been suggested in heavily hole-doped $A$Fe$_2$As$_2$ ($A=$ Rb or Cs). However,
the transport studies focusing on the fluctuations of such nematicity have
provided controversial results regarding the presence of diagonal nematic
order. Here we report high-resolution heat capacity measurements under in-plane
field rotation in RbFe$_2$As$_2$. While the temperature dependence of specific
heat shows no discernible anomaly associated with the nematic transition, the
field-angle dependence of specific heat near the superconducting transition (at
$\sim 2.8$ K) reveals clear two-fold oscillations within the plane, providing
thermodynamic evidence for the diagonal nematicity. Moreover, we find that
M\""ossbauer spectroscopy sensitively probes the nematic transition at $\sim 50$
K with no evidence of static magnetism. These results imply that the diagonal
nematicity in RbFe$_2$As$_2$ has a unique mechanism involving charge degrees of
freedom, having unusual thermodynamic properties of the transition.",2108.13081v1
2021-09-03,A stellar census in globular clusters with MUSE. A new perspective on the multiple main sequences of $ω$ Centauri,"$\omega$ Cen is a rare example of a globular cluster where the iron abundance
of the stars spans more than one order of magnitude. Many spectroscopic
investigations of its red-giant- and sub-giant- branches have revealed multiple
peaks in the iron abundance distribution. The metallicity distribution of
main-sequence (MS) stars is not well characterized yet, due to the faintness of
the stars and lack of data. So far, almost all studies of MS stars are based on
photometric measurements. Our goal is to investigate the metallicity
distribution of a statistically significant sample of MS stars in $\omega$ Cen.
In particular, we aim at revisiting the metallicity difference between the red
and blue MS of the cluster. We used MUSE spectra obtained for the central
region of $\omega$ Cen to derive metallicities for $\approx$4200 MS stars. We
find that blue MS stars are on average $\approx$0.1 dex more metal-rich than
their red counterparts. On the basis of this new estimate, we find that the two
sequences can be fit on the Hubble Space Telescope color-magnitude diagram with
two isochrones having the same global metallicity and age but a higher helium
abundance for the blue MS, that is $\Delta Y \lesssim$ 0.1. Furthermore, we
determine the average metallicity of the five main populations along $\omega$
Cen MS and these estimates are consistent with expectations from previous
photometric studies.",2109.01540v2
2021-09-09,Collisional mixing between inner and outer solar system planetesimals inferred from the Nedagolla iron meteorite,"The ungrouped iron meteorite Nedagolla is the first meteorite with bulk Mo,
Ru, and Ni isotopic compositions that are intermediate between those of the
non-carbonaceous (NC) and carbonaceous (CC) meteorite reservoirs. The Hf-W
chronology of Nedagolla indicates that this mixed NC-CC isotopic composition
was established relatively late, more than 7 million years after Solar System
formation. The mixed NC-CC isotopic composition is consistent with the chemical
composition of Nedagolla, which combines signatures of metal segregation under
more oxidizing conditions (relative depletions in Mo and W), characteristic for
CC bodies, and more reducing conditions (high Si and Cr contents),
characteristic for some NC bodies, in a single sample. These data combined
suggest that Nedagolla formed as the result of collisional mixing of NC and CC
core material, which partially re-equilibrated with silicate mantle material
that predominantly derives from the NC body. These mixing processes might have
occurred during a hit-and-run collision between two differentiated bodies,
which also provides a possible pathway for Nedagolla's extreme volatile element
depletion. As such, Nedagolla provides the first isotopic evidence for early
collisional mixing of NC and CC bodies that is expected as a result of
Jupiter's growth.",2109.04224v1
2021-09-11,NuSTAR monitoring of MAXI J1348-630: evidence of high density disc reflection,"We present the broadband spectral analysis of all the six hard, intermediate
and soft state NuSTAR observations of the recently discovered transient black
hole X-ray binary MAXI J1348-630 during its first outburst in 2019. We first
model the data with a combination of a multi-colour disc and a relativistic
blurred reflection, and, whenever needed, a distant reflection. We find that
this simple model scheme is inadequate in explaining the spectra, resulting in
a very high iron abundance. We, therefore, explore the possibility of
reflection from a high-density disc. We use two different sets of models to
describe the high-density disc reflection: relxill-based reflection models, and
reflionx-based ones. The reflionx-based high-density disc reflection models
bring down the iron abundance to around the solar value, while the density is
found to be $10^{20.3-21.4} \rm cm^{-3}$. We also find evidence of a
high-velocity outflow in the form of $\sim$7.3 keV absorption lines. The
consistency between the best-fit parameters for different epochs and the
statistical significance of the corresponding model indicates the existence of
high-density disc reflection in MAXI J1348-630.",2109.05380v1
2021-09-14,Ultrafast Optical Spectroscopy Evidence of Pseudogap and Electron-Phonon Coupling in an Iron-Based Superconductor KCa$_2$Fe$_4$As$_4$F$_2$,"We use ultrafast optical spectroscopy to study the nonequilibrium
quasiparticle relaxation dynamics of the iron-based superconductor
KCa$_2$Fe$_4$As$_4$F$_2$ with $T_c=33.5$ K. Our results reveal a possible
pseudogap ($\Delta_{PG}$ = 2.4 $\pm$ 0.1 meV) below $T^*\approx 50$ K but prior
to the opening of a superconducting gap ($\Delta_{SC}$(0) $\approx$ 4.3 $\pm$
0.1 meV). Measurements under high pump fluence real two distinct, coherent
phonon oscillations with 1.95 and 5.51 THz frequencies, respectively. The
high-frequency $A_{1g}$(2) mode corresponds to the $c-$axis polarized
vibrations of FeAs planes with a nominal electron-phonon coupling constant
$\lambda_{A_{1g}(2)}$ = 0.194 $\pm$ 0.02. Our findings suggest that the
pseudogap is likely a precursor of superconductivity, and the electron-phonon
coupling may play an essential role in the superconducting pairing in
KCa$_2$Fe$_4$As$_4$F$_2$.",2109.06460v2
2021-09-27,The Three-Dimensional Electronic Structure of LiFeAs: Strong-coupling Superconductivity and Topology in the Iron Pnictides,"Amongst the iron-based superconductors, LiFeAs is unrivalled in the
simplicity of its crystal structure and phase diagram. However, our
understanding of this canonical compound suffers from conflict between mutually
incompatible descriptions of the material's electronic structure, as derived
from contradictory interpretations of the photoemission record. Here, we
explore the challenge of interpretation in such experiments. By combining
comprehensive photon energy- and polarization- dependent angle-resolved
photoemission spectroscopy (ARPES) measurements with numerical simulations, we
establish the providence of several contradictions in the present understanding
of this and related materials. We identify a confluence of surface-related
issues which have precluded unambiguous identification of both the number and
dimensionality of the Fermi surface sheets. Ultimately, we arrive at a scenario
which supports indications of topologically non-trivial states, while also
being incompatible with superconductivity as a spin-fluctuation driven Fermi
surface instability.",2109.13276v1
2021-10-12,Vortex dynamics and second magnetization peak in the iron-pnictide superconductor Ca$_{0.82}$La$_{0.18}$Fe$_{0.96}$Ni$_{0.04}$As$_2$,"We report the studies of detailed magnetic relaxation and isothermal
magnetization measurements in the vortex state of the 112-type iron-pnictide
Ca$_{0.82}$La$_{0.18}$Fe$_{0.96}$Ni$_{0.04}$As$_2$ superconductor with $T_c$
$\sim$ 22 K. In the isothermal $M(H)$, a well defined second magnetization peak
(SMP) feature is observed in the entire temperature range below $T_c$ for
measurements with $H$ $\parallel$ $c$-axis. However, for $H$ $\parallel$
$ab$-planes, the SMP feature is suppressed at low temperatures, which might be
due to 2D Josephson vortices forming at low temperatures and high magnetic
fields in such an anisotropic system. A rigorous analysis considering the
magnetic relaxation data for $H$ $\parallel$ $c$-axis suggests an elastic to
plastic pinning crossover across $H_p$, which also seems accompanied with a
possible phase transition in vortex lattice near $H_p$. Moreover, point
disorder and surface defects are likely to be the dominant sources of pinning,
which contribute to the $\delta l$-type of pinning in the sample. A high $J_c$,
in access of 10$^5$ A/cm$^2$ observed could potentially make this material
technologically important.",2110.05677v1
2021-10-19,Generalized estimates for the density of oxide scale in the range from 0 C to 1300 C,"Oxide scale formed on the surface of steel products during high-teperature
processes is studied as a composite material, the main solid components of
which, in general, are wustite, magnetite, hematite and metallic iron. To
estimate the density of each of these components in the temperature range from
0 C to 1300 C, formulas are proposed that are consistent with the empirical
functions of the coefficient of linear thermal expansion, which the authors
obtained earlier by generaizing data from open sources. The Curie and
polymorphic transformation temperatures are included in these generalized
formulas as variable parameters, which allows one to take into account the
movability of phase transitions due to impurities, crystal lattice defects,
particle sizes, cooling rate, and other factors. When specifying the particular
values of critical temperatures, the other parameters of the formulas are
recalculated automatically. In a particular form, the proposed formulas
correspond to the basic values of critical temperatures. According to the
calculation examples given, the true (not including pores) density of oxide
scale can be about 5200 to 5600 kg/m3, depending on the temperature and
percentage of components, whereby a local density minimum may be observed in
the region of 570 C due to eutectoid decomposition of wustite into magnetite
and iron. The proposed methods are recommended for use in mathematical
simulation of processing of steel products in the presence of oxide scale on
its surface.",2110.09791v1
2021-10-26,Stochastic Low Frequency Variability in 3-Dimensional Radiation Hydrodynamical Models of Massive Star Envelopes,"Increasing main sequence stellar luminosity with stellar mass leads to the
eventual dominance of radiation pressure in stellar envelope hydrostatic
balance. As the luminosity approaches the Eddington limit, additional
instabilities (beyond conventional convection) can occur. These instabilities
readily manifest in the outer envelopes of OB stars, where the opacity increase
associated with iron yields density and gas pressure inversions in 1D models.
Additionally, recent photometric surveys (e.g. TESS) have detected excess
broadband low frequency variability in power spectra of OB star lightcurves,
called stochastic low frequency variability (SLFV). This motivates our novel 3D
Athena++ radiation hydrodynamical (RHD) simulations of two 35$\,$M$_\odot$ star
envelopes (the outer $\approx$15$\%$ of the stellar radial extent), one on the
zero-age main sequence and the other in the middle of the main sequence. Both
models exhibit turbulent motion far above and below the conventional iron
opacity peak convection zone (FeCZ), obliterating any ``quiet"" part of the
near-surface region and leading to velocities at the photosphere of
10-100$\,$km$\,$s$^{-1}$, directly agreeing with spectroscopic data. Surface
turbulence also produces SLFV in model lightcurves with amplitudes and
power-law slopes that are strikingly similar to those of observed stars. The
characteristic frequencies associated with SLFV in our models are comparable to
the thermal time in the FeCZ ($\approx$3-7$\,$days$^{-1}$). These simulations,
which have no free parameters, are directly validated by observations and,
though more models are needed, we remain optimistic that 3D RHD models of main
sequence O star envelopes exhibit SLFV originating from the FeCZ.",2110.13944v1
2021-12-01,Orbital-Selective High-Temperature Cooper Pairing Developed in the Two-Dimensional Limit,"The orbital multiplicity in multiband superconductors yields orbital
differentiation in normal-state properties, and can lead to orbital-selective
spin-fluctuation Cooper pairing. This phenomenon has become increasingly
pivotal in clarifying the pairing 'enigma' particularly for multiband
high-temperature superconductors. In one-unit-cell (1-UC) FeSe/SrTiO3, the
thinnest and highest-Tc member of iron-based superconductors, the standard
electron-hole Fermi pocket nesting scenario is apparently not applicable since
the Gamma-centered hole pockets are absent, so the actual pairing mechanism is
the subject of intense debate. Here, by measuring high-resolution Bogoliubov
quasiparticle interference, we report observations of highly anisotropic
magnetic Cooper pairing in 1-UC FeSe. From a theoretical point of view, it is
important to incorporate effects of electronic correlations within a
spin-fluctuation pairing calculation, where the dxy orbital becomes
coherence-suppressed. The resulting pairing gap is compatible with the
experimental findings, which suggests that high-Tc Cooper pairing with orbital
selectivity applies to 1-UC FeSe. Our findings imply the general existence of
orbital selectivity in iron-based superconductors and the universal importance
of electron correlations in high-Tc superconductors.",2112.00383v1
2021-12-05,Optical singly-ionized iron emission in radio-quiet and relativistically jetted active galactic nuclei,"The issue of the difference between optical and UV properties of radio-quiet
and radio-loud (relativistically ""jetted"") active galactic nuclei (AGN) is a
long standing one, related to the fundamental question of why a minority of
powerful AGN possess strong radio emission due to relativistic ejections. This
paper examines a particular aspect: the singly-ionized iron emission in the
spectral range 4400 -- 5600 A, where the prominent HI H$\beta$ and [OIII] 4959,
5007 lines are also observed. We present a detailed comparison of the relative
intensity of Fe II multiplets in the spectral types of the quasar main sequence
where most jetted sources are found, and afterwards discuss radio-loud
narrow-line Seyfert 1 (NLSy1) nuclei with $\gamma$-ray detection and with
prominent Fe II emission. An Fe II template based on I Zw 1 provides an
accurate representation of the optical Fe II emission for RQ and, with some
caveats, also for RL sources. CLOUDY photoionization simulations indicate that
the observed spectral energy distribution can account for the modest Fe II
emission observed in composite radio-loud spectra. However, spectral energy
differences alone cannot account for the stronger Fe II emission observed in
radio-quiet sources, for similar physical parameters. As for RL NLSy1s, they do
not seem to behave like other RL sources, likely because of their different
physical properties that could be ultimately associated with a higher Eddington
ratio.",2112.02632v1
2021-12-10,Random-strain-induced correlations in materials with intertwined nematic and magnetic orders,"Electronic nematicity is rarely observed as an isolated instability of a
correlated electron system. Instead, in iron pnictides and in certain cuprates
and heavy-fermion materials, nematicity is intertwined with an underlying
spin-stripe or charge-stripe state. As a result, random strain, ubiquitous in
any real crystal, creates both random-field disorder for the nematic degrees of
freedom and random-bond disorder for the spin or charge ones. Here, we put
forward an Ashkin-Teller model with random Baxter fields to capture the dual
role of random strain in nematic systems for which nematicity is a composite
order arising from a stripe state. Using Monte Carlo to simulate this
$\textit{random Baxter-field model}$, we find not only the expected break-up of
the system into nematic domains, but also the emergence of nontrivial
disorder-promoted magnetic correlations. Such correlations enhance and tie up
the fluctuations associated with the two degenerate magnetic stripe states from
which nematicity arises, leaving characteristic signatures in the spatial
profile of the magnetic domains, in the configurational space of the spin
variables, and in the magnetic noise spectrum. We discuss possible experimental
manifestations of these effects in iron-pnictide superconductors. Our work
establishes the random Baxter-field model as a more complete alternative to the
random-field Ising model to describe complex electronic nematic phenomena in
the presence of disorder.",2112.05769v1
2021-12-15,A Suzaku sample of unabsorbed narrow-line and broad-line Seyfert 1 galaxies: II. Iron emission and absorption,"A sample of 22 narrow-line Seyfert 1 (NLS1) and 47 broad-line Seyfert 1
(BLS1) galaxies observed with Suzaku is used to examine the Fe K band
properties of each group. Three different models are used to examine the
presence of: narrow neutral Fe Ka line at 6.4 keV and ionised Fe xxv and Fe
xxvi emission lines (model A); a broad emission feature at around 6 - 7 keV
(model B); and an absorption edge at 7.1 keV (model C). In all three models,
the neutral Fe Ka line is weaker (lower luminosity and equivalent width) in
NLS1s than in BLS1s. Model (B) also finds a more significant broad component
(larger equivalent width) in NLS1s than in BLS1s. The feature does not appear
to be an artefact of steeper spectra in NLS1s, but rather an intrinsic property
of these sources. From model (C), the optical depth of the absorption edge
appears comparable between the two samples. When comparing the absorption with
the emission line properties, NLS1s seem to exhibit a lower ratio of
emission-to-absorption of iron than BLS1s, and than expected based on the
fluorescence yield. The observed differences may arise from different torus
geometries (e.g. larger opening angle in NLS1s), and/or additional sources of
Fe K emission and absorption in NLS1s beyond pure fluorescence (e.g.
originating in the disc and broad line region).",2112.08127v1
2021-12-15,Stellar population astrophysics (SPA) with the TNG -- The chemical content of the red supergiant population in the Perseus complex,"Context. The Perseus complex in the outer disk of the Galaxy hosts a number
of clusters and associations of young stars. Gaia is providing a detailed
characterization of their kinematic structure and evolutionary properties.
Aims. Within the SPA Large Programme at the TNG, we secured HARPS-N and GIANO-B
high-resolution optical and near-infrared (NIR) spectra of the young red
supergiant (RSG) stars in the Perseus complex, in order to obtain accurate
radial velocities, stellar parameters and detailed chemical abundances.
Methods. We used spectral synthesis to best-fit hundreds of atomic and
molecular lines in the spectra of the observed 27 RSGs. We obtained accurate
estimates of the stellar temperature, gravity, micro and macro turbulence
velocities and chemical abundances for 25 different elements. We also measured
the $^{12}$C/$^{13}$C abundance ratio. Results. Our combined optical and NIR
chemical study provides homogeneous half-solar iron with a small dispersion,
about solar-scaled abundance ratios for the iron-peak, alpha and other light
elements and a small enhancement of Na, K and neutron-capture elements,
consistent with the thin disk chemistry traced by older stellar populations at
a similar Galactocentric distance of about 10 kpc. We inferred enhancement of
N, depletion of C and of the $^{12}$C/$^{13}$C isotopic abundance ratio,
consistent with mixing processes in the stellar interiors during the RSG
evolution.",2112.08402v1
2021-12-28,Simulations of globular clusters within their parent galaxies: Metallicity spreads and anomalous precursor populations,"Recent observations of globular clusters (GCs) suggest that elemental
abundance variations may exist between first-generation (1G) stars. We propose
that metal abundance ('metallicity') spreads within GC forming giant molecular
clouds (GMCs) can influence the iron abundances of future cluster members. To
investigate this, we use original hydrodynamical simulations to model GMC
formation in a high redshift dwarf galaxy. Our simulations self-consistently
model physical processes such as stellar feedback, dust formation and
destruction, and molecular gas formation on dust grains, making them well
suited to the study of GMC formation. We conclude that iron abundance
variations in GMCs are due to the merging of gas clumps and self-enrichment
processes. The metallicity dispersions of GC forming clumps is ~0.1 dex,
reflecting a growing number of studies that claim a non-zero dispersion within
GCs. The galactic gas fraction is a key parameter for the formation of clumps
and the metallicity 'floor' observed for both Galactic and extragalactic GCs
are associated with the parent galaxy's capacity to form massive GMCs. Finally,
we argue that GMCs have the potential to trap surrounding metal-poor galactic
disc stars, which we interpret as a precursor population (0G). These low
metallicity stars are representative of the [Fe/H] value of the host dwarf and
thus the chemistry of this 0G may be a fossilized record of the parent galaxy.
These results depend on the initial metallicity and radial gradient of the
galaxy, the threshold gas density for star formation, and the star formation
prescription.",2112.13971v1
2022-01-04,Reconstruction of Air-Shower Parameters Through the Lateral Distribution Function of Ultra-High Energy Particles,"In this study, the necessity of the simulation study for exploring the
interactions of ultra-high energy particles cosmic rays was examined. Different
hadronic interaction models such as (SIBYLL, QGSJET, and EPOS) were simulated
by using air showers simulation AIRES system (version 19.04.00). Also, the
charged particle density of Extensive Air Showers (EAS) was calculated by
estimating the lateral distribution function (LDF). Moreover, the LDF
simulation of the two primary particles (proton and iron nuclei) was performed,
taking into account their primary energies effect and the zenith angle of
charged particles that produced in the EAS, within the energy range
(10^17-10^19) eV. At extremely high energies (10^17, 10^18, and 10^19) eV, new
parameters as a function of the primary energy were obtained by fitting the
lateral distribution curves of EAS using Sigmoidal function (Logistic model).
Comparison of the results showed a good agreement between the values obtained
from the parameterized LDF using Sigmoidal function with experimental results
by AGASA EAS observatory for the primaries proton as well iron nuclei, with the
production of (electron positron) pair and the charged muons secondary
particles at high energy about 10^19 eV and (theta = 0 degree).",2201.01368v1
2022-02-01,"Optical Properties of C$-$rich ($^{12}$C, SiC and FeC) Dust Layered Structure of Massive Stars","The composition and structure of interstellar dust are important and complex
for the study of the evolution of stars and the \textbf{interstellar medium}
(ISM). However, there is a lack of corresponding experimental data and model
theories. By theoretical calculations based on ab-initio method, we have
predicted and geometry optimized the structures of Carbon-rich (C-rich) dusts,
carbon ($^{12}$C), iron carbide (FeC), silicon carbide (SiC), even silicon
($^{28}$Si), iron ($^{56}$Fe), and investigated the optical absorption
coefficients and emission coefficients of these materials in 0D
(zero$-$dimensional), 1D, and 2D nanostructures. Comparing the \textbf{nebular
spectra} of the supernovae (SN) with the coefficient of dust, we find that the
optical absorption coefficient of the 2D $^{12}$C, $^{28}$Si, $^{56}$Fe, SiC
and FeC structure corresponds to the absorption peak displayed in the infrared
band (5$-$8) $\mu$$m$ of the spectrum at 7554 days after the SN1987A explosion.
And it also corresponds to the spectrum of 535 days after the explosion of
SN2018bsz, when the wavelength in the range of (0.2$-$0.8) and (3$-$10)
$\mu$$m$. Nevertheless, 2D SiC and FeC corresponds to the spectrum of 844 days
after the explosion of SN2010jl, when the wavelength is within (0.08$-$10)
$\mu$$m$. Therefore, FeC and SiC may be the second type of dust in SN1987A
corresponding to infrared band (5$-$8) $\mu$$m$ of dust and may be in the
ejecta of SN2010jl and SN2018bsz.",2202.00260v1
2022-01-30,Ultrahigh-Pressure Magnesium Hydrosilicates as Reservoirs of Water in Early Earth,"The origin of water on the Earth is a long-standing mystery, requiring a
comprehensive search for hydrous compounds, stable at conditions of the deep
Earth and made of Earth-abundant elements. Previous studies usually focused on
the current range of pressure-temperature conditions in the Earth's mantle and
ignored a possible difference in the past, such as the stage of the core-mantle
separation. Here, using ab initio evolutionary structure prediction, we find
that only two magnesium hydrosilicate phases are stable at megabar pressures,
$\alpha$-Mg$_2$SiO$_5$H$_2$ and $\beta$-Mg$_2$SiO$_5$H$_2$, stable at 262-338
GPa and >338 GPa,respectively (all these pressures now lie within the Earth's
iron core). Both are superionic conductors with quasi-one-dimensional proton
diffusion at relevant conditions. In the first 30 million years of Earth's
history, before the Earth's core was formed, these must have existed in the
Earth, hosting much of Earth's water. As dense iron alloys segregated to form
the Earth's core, Mg$_2$SiO$_5$H$_2$ phases decomposed and released water.
Thus, now-extinct Mg$_2$SiO$_5$H$_2$ phases have likely contributed in a major
way to the evolution of our planet.",2202.00752v1
2022-03-30,The Chemical Composition of Extreme-Velocity Stars,"Little is known about the origin of the fastest stars in the Galaxy. Our
understanding of the Milky Way and surrounding dwarf galaxies chemical
evolution history allows us to use the chemical composition of a star to
investigate its origin, and say whether a star was formed in-situ or was
accreted. However, the fastest stars, the hypervelocity stars, are young and
massive and their chemical composition has not yet been analyzed. Though it is
difficult to analyze the chemical composition of a massive young star, we are
well versed in the analysis of late-type stars. We have used high-resolution
ARCES/3.5m Apache Point Observatory, MIKE/Magellan spectra to study the
chemical details of 15 late-type hypervelocity stars candidates. With Gaia EDR3
astrometry and spectroscopically determined radial velocities we found total
velocities with a range of $274$ - $520$ km s$^{-1}$ and mean value of $381$ km
s$^{-1}$. Therefore, our sample stars are not fast enough to be classified as
Hypervelocity stars, and are what is known as extreme-velocity stars. Our
sample has a wide iron abundance range of $-2.5 \le \mathrm{[Fe/H]} \le -0.9$.
Their chemistry indicate that at least 50\% of them are accreted extragalactic
stars, with iron-peak elements consistent with prior sub-Chandrasekhar mass
type Ia supernova enrichment. Without indication of binary companions, their
chemical abundances and orbital parameters are indicative that they are the
accelerated tidal debris of disrupted dwarf galaxies.",2203.16364v1
2022-04-08,Estimation of Nitrogen-to-Iron Abundance Ratios From Low-Resolution Spectra,"We present a method to determine nitrogen abundance ratios with respect to
iron ([N/Fe]) from molecular CN-band features observed in low-resolution ($R
\sim$ 2000) stellar spectra obtained by the Sloan Digital Sky Survey (SDSS) and
the Large Sky Area Multi-Object Fiber Spectroscopic Telescope (LAMOST). Various
tests are carried out to check the systematic and random errors of our
technique, and the impact of signal-to-noise (S/N) ratios of stellar spectra on
the determined [N/Fe]. We find that the uncertainty of our derived [N/Fe] is
less than 0.3 dex for S/N ratios larger than 10 in the ranges $T_{eff}$ =
[4000, 6000] K, log g = [0.0, 3.5], [Fe/H] = [--3.0, 0.0], [C/Fe] = [--1.0,
+4.5], and [N/Fe] = [--1.0, +4.5], the parameter space that we are interested
in to identify N-enhanced stars in the Galactic halo. A star-by-star comparison
with a sample of stars with [N/Fe] estimates available from the Apache Point
Observatory Galactic Evolution Experiment (APOGEE) also suggests a similar
level of uncertainty in our measured [N/Fe], after removing its systematic
error. Based on these results, we conclude that our method is able to reproduce
[N/Fe] from low-resolution spectroscopic data, with an uncertainty sufficiently
small to discover N-rich stars that presumably originated from disrupted
Galactic globular clusters.",2204.03933v1
2022-04-08,Possible Implications of Relatively High Levels of Initial $^{60}$Fe in Iron Meteorites for the Non-Carbonaceous -- Carbonaceous Meteorite Dichotomy and Solar Nebula Formation,"Cook et al. (2021) found that iron meteorites have an initial abundance ratio
of the short-lived isotope $^{60}$Fe to the stable isotope $^{56}$Fe of
$^{60}$Fe/$^{56}$Fe $\sim$ $(6.4 \pm 2.0) \times 10^{-7}$. This appears to
require the injection of live $^{60}$Fe from a Type II supernova (SN II) into
the presolar molecular cloud core, as the observed ratio is over a factor of
ten times higher than would be expected to be found in the ambient interstellar
medium (ISM) as a result of galactic chemical evolution. The supernova
triggering and injection scenario offers a ready explanation for an elevated
initial $^{60}$Fe level, and in addition provides a physical mechanism for
explaining the non-carbonaceous -- carbonaceous (NC-CC) dichotomy of
meteorites. The NC-CC scenario hypothesizes the solar nebula first accreted
material that was enriched in supernova-derived nuclides, and then later
accreted material depleted in supernova-derived nuclides. While the NC-CC
dichotomy refers to stable nuclides, not short-lived isotopes like $^{60}$Fe,
the SN II triggering hypothesis provides an explanation for the otherwise
unexplained change in nuclides being accreted by the solar nebula. Three
dimensional hydrodynamical models of SN II shock-triggered collapse show that
after triggering collapse of the presolar cloud core, the shock front sweeps
away the local ISM while accelerating the resulting protostar/disk to a speed
of several km/s, sufficient for the protostar/disk system to encounter within
$\sim$ 1 Myr the more distant regions of a giant molecular cloud complex that
might be expected to have a depleted inventory of supernova-derived nuclides.",2204.04134v1
2022-04-21,Ferrous Metal Matrix Composites Status Scope and Challenges,"The present paper is an effort to culminate the status, scopes and challenges
in the development of ferrous metal matrix composites (FMMCs). The FMMCs are
old but less in use than the non-ferrous metal matrix composites (NFMMCs), as
far as literature and actual applications are concerned. Therefore, this
stimulates the exploration of the reasons behind the scarcity of literature and
field applications of the FMMCs, which must be investigated scientifically. The
powder metallurgy route is the most used process for fabricating iron and steel
based FMMCs by reinforcing particulates. At the same time, the in-situ method
has been used for the fabrication and cast iron-based FMMCs. The main
characteristics being considered during the designing and fabrication of FMMCs
are wear resistance and improved specific mechanical properties. To fabricate
cheaper and eco-friendly FMMCs, traditionally used costly reinforcements such
as SiC, WC, TiC, SiO2, TiO2, TiB2 are required to be replaced by inexpensive
industrial wastes like red-mud, fly-ashes and grinding swarf. The data
extracted from the web of science exhibited that the FMMCs have been researched
less than the NFMMCs. The increasing number of research papers on FMMCs
indicates a bright future. FMMCs are going to be a favourite topic among
researchers and manufacturers. Higher strengths, wear resistance, dimensional
stability at elevated temperatures, and, most importantly, the lower cost will
put forward the FMMCs as a stiff competitor of NFMMCs. In developing and mass
production of FMMCs for field applications, challenges like oxidation and
higher weight still require special research efforts.",2204.09999v2
2022-04-21,Detection of CO emission lines in the dayside atmospheres of WASP-33b and WASP-189b with GIANO,"Ultra-hot Jupiters (UHJs) are expected to possess temperature inversion
layers in their dayside atmospheres. Recent thermal emission observations have
discovered several atomic and molecular species along with temperature
inversions in UHJs. We observed the thermal emission spectra of two UHJs
(WASP-33b and WASP-189b) with the GIANO-B high-resolution near-infrared
spectrograph. Using the cross-correlation technique, we detected carbon
monoxide (CO) in the dayside atmospheres of both planets. The detected CO lines
are in emission, which agrees with previous discoveries of iron emission lines
and temperature inversions in the two planets. This is the first detection of
CO lines in emission with high-resolution spectroscopy. Further retrieval work
combining the CO lines with other spectral features will enable a comprehensive
understanding of the atmospheric properties such as temperature structures and
C/O ratios. The detected CO and iron emission lines of WASP-189b have
redshifted radial velocities of several km/s, which likely originate from a
dayside to nightside wind in its atmosphere. Such a redshifted velocity has not
been detected for the emission lines of WASP-33b, suggesting that the
atmospheric circulation patterns of the two UHJs may be different.",2204.10158v1
2022-05-17,A Disc Reflection Model for Ultra-Soft Narrow-Line Seyfert 1 Galaxies,"We present a detailed analysis of the XMM-Newton observations of five
narrow-line Seyfert 1 galaxies (NLS1s). They all show very soft continuum
emission in the X-ray band with a photon index of $\Gamma\gtrsim 2.5$.
Therefore, they are referred to as `ultra-soft' NLS1s in this paper. By
modeling their optical/UV-X-ray spectral energy distribution (SED) with a
reflection-based model, we find indications that the disc surface in these
ultra-soft NLS1s is in a higher ionisation state than other typical Seyfert 1
AGN. Our best-fit SED models suggest that these five ultra-soft NLS1s have an
Eddington ratio of $\lambda_{\rm Edd}=1-20$ assuming available black hole mass
measurements. In addition, our models infer that a significant fraction of the
disc energy in these ultra-soft NLS1s is radiated away in the form of
non-thermal emission instead of the thermal emission from the disc. Due to
their extreme properties, X-ray observations of these sources in the iron band
are particularly challenging. Future observations, e.g. from Athena, will
enable us to have a clearer view of the spectral shape in the iron band and
thus distinguish the reflection model from other interpretations of their
broadband spectra.",2205.08236v1
2022-05-28,Spectral Evidence for Unidirectional Charge Density Wave in Detwinned BaNi$_2$As$_2$,"The emergence of unconventional superconductivity in proximity to intertwined
electronic orders is especially relevant in the case of iron-based
superconductors. Such order consists of an electronic nematic order and a spin
density wave in these systems. BaNi$_2$As$_2$, like its well-known iron-based
analog BaFe$_2$As$_2$, also hosts a symmetry-breaking structural transition
that is coupled to a unidirectional charge density wave (CDW), providing a
novel platform to study intertwined orders. Here, through a systematic
angle-resolved photoemission spectroscopy study combined with a detwinning
$B_1g$ uniaxial strain, we identify distinct spectral evidence of band
evolution due to the structural transition as well as CDW-induced band folding.
In contrast to the nematicity and spin density wave in BaFe$_2$As$_2$, the
structural and CDW order parameters in BaNi$_2$As$_2$ are observed to be
strongly coupled and do not separate in the presence of uniaxial strain. Our
measurements point to a likely lattice origin of the CDW in BaNi$_2$As$_2$.",2205.14339v1
2022-06-02,Lithium detection in red supergiant stars of the Perseus complex,"We present the first systematic study of lithium abundance in a chemically
homogeneous sample of 27 red supergiants (RSGs) in the young Perseus complex.
For these stars, accurate stellar parameters and detailed chemical abundances
of iron and iron peak, CNO, alpha, light and neutron-capture elements have been
already obtained by means of high resolution optical and near-infrared
spectroscopy. The observed RSGs have half-solar metallicity, 10-30 Myr age,
bolometric luminosities in the 10$^4$-10$^5$ L$_{\odot}$ range and likely mass
progenitors in the 9-14 M$_{\odot}$ range. We detected the optical Li I doublet
in eight out of the 27 observed K and M type RSGs, finding relatively low
A(Li)$<$1.0 dex abundances, while for the remaining 19 RSGs upper limits of
A(Li)$<$-0.2 dex have been set. Warmer and less luminous (i.e. likely less
massive) as well as less mixed (i.e. with lower [C/N] and $^{12}$C/$^{13}$C
depletion) RSGs with Li detection show somewhat higher Li abundances. In order
to explain Li detection in $\sim$30\% of the observed RSGs, we speculate that
some stochasticity and a scenario where Li was not completely destroyed in the
convective atmospheres and/or a secondary production took place during the
post-Main Sequence evolution, should be at work.",2206.01218v1
2022-06-15,"Hyperfine fields at $^{66}$Ga, $^{67,69}$Ge implanted into iron and gadolinium hosts at 6 K, and applications to g-factor measurements","Isomers in $^{66}$Ga, $^{67}$Ge, and $^{69}$Ge were recoil-implanted into
ferromagnetic hosts of iron and gadolinium at $\approx 6$~K, and the hyperfine
magnetic fields were determined by Time Differential Perturbed Angular
Distribution (TDPAD) measurements. The hyperfine field strengths at $\approx
6$~K are compared to the results of previous higher-temperature measurements
and the amplitudes of the $R(t)$ functions are compared to empirical
expectations. The results show that gadolinium can be a suitable host for
high-precision in-beam $g$-factor measurements. The results of new $g$-factor
measurements for isomers in $^{66}$Ga and $^{67}$Ge are $g(^{66}$Ga$,7^{-}) =
+0.126(4)$, supporting a $[\pi_{f5/2} \otimes \nu g_{9/2}]_{7^-}$ configuration
assignment, and $g(^{67}$Ge$,\frac{9}{2}^{+})=-0.1932(22)$, derived from a new
measurement of the ratio $g(^{67}\mathrm{Ge})/g(^{69}\mathrm{Ge}) = 0.869(9)$.
These values are in agreement with previous results. The $R(t)$ amplitudes
indicate that the nuclear alignment produced in the isomeric states was
significantly lower than the empirically expected $\sigma/I \approx 0.35$.",2206.07294v1
2022-06-23,Size-dependent Failure Behavior of Lithium-Iron Phosphate Battery under Mechanical Abuse,"Under mechanical abuse conditions, the failure of lithium-ion batteries
occurs in various stages characterized by different force, temperature and
voltage response which require it's in-situ measurements for analysis. Firstly,
four sizes of commercially available lithium-iron phosphate batteries (LFPB)
viz. 18650, 22650, 26650, and 32650 are subjected to quasi static lateral,
longitudinal compression, and nail penetration tests. The failure,
characterized by the voltage drop and temperature rise, at the onset of the
first internal short-circuit (ISC), is identified by Aurdino-based voltage
sensor module and temperature measurement module, respectively. The battery
failure load and peak temperature at the onset of ISC are found to rely on the
battery size strongly. The failure is observed to be delayed for small-sized
18650 batteries during lateral compression, unlike longitudinal compression and
nail penetration test. At the onset of the short circuit, the temperature rise
above the ambient value is different for different LFPBs. It is found to be
maximum (64.4 degree C ) for LFPB 32650 under longitudinal compression and
minimum (29.5 degree C) under lateral compression tests amongst the considered
geometries. Further, LFPB 26650 exhibited a balanced thermal behavior during
the considered abused condition. Such data can be sensed timely for effective
thermal management and improved safety of lithium-ion batteries.",2206.11732v2
2022-08-03,Light-induced dynamics of liquid-crystalline droplets on the surface of iron-doped lithium niobate crystals,"We investigated the effect of a photovoltaic field generated on the surface
of iron-doped lithium niobate crystals on droplets of a ferroelectric nematic
liquid crystalline and a standard nematic liquid crystalline material deposited
on this surface. When such assembly is illuminated with a laser beam, a wide
range of dynamic phenomena are initiated. Droplets located outside the laser
spot are dragged in the direction of the illuminated area, while droplets
located inside the illuminated region tend to bridge each other and rearrange
into tendril-like structures. In the ferroelectric nematic phase (NF) these
processes take place via the formation of conical spikes evolving into jet
streams, similar to the behavior of droplets of conventional dielectric liquids
exposed to overcritical electric fields. However, in contrast to conventional
liquids, the jet streams of the NF phase exhibit profound branching. In the
nematic phase (N) of both the ferroelectric nematic and the standard nematic
material, dynamic processes occur via smooth-edged continuous features typical
for conventional liquids subjected to under-critical fields. The difference in
dynamic behavior is attributed to the large increase of dielectric permittivity
in the ferroelectric nematic phase with respect to the dielectric permittivity
of the nematic phase.",2208.02318v1
2022-09-07,Transport evidence for the surface state and spin-phonon interaction in FeTe$_{0.5}$Se$_{0.5}$,"The iron chalcogenides have been proved to be intrinsic topological
superconductors to implement quantum computation because of their unique
electronic structures. The topologically nontrivial surface states of
FeTe$_{0.5}$Se$_{0.5}$ have been predicted by several calculations and then
confirmed by high-resolution photoemission and scanning tunneling experiments.
However, so far, the shreds of the electrical transport evidence for
topological surface states are still in absence. By carrying out electrical
transport experiments, we observe a topological transition with a nonlinear
Hall conductivity and simultaneous linear magnetoresistance near the
superconducting transition temperature. Furthermore, we observe a sign reversal
of the Hall coefficient accompanied by a concurrently softening of the
${A}_{1g}$ phonon mode at about 40 K, indicating a nematic transition. The
synchronized phonon softening with nematicity manifests an enhanced fluctuation
state through spin-phonon interaction. Our results solidly corroborate the
topological surface states of FeTe$_{0.5}$Se$_{0.5}$ and provide an
understanding of the mechanism of the superconductivity in iron chalcogenides.",2209.03267v2
2022-09-14,Structural peculiarities of $\varepsilon$-Fe$_2$O$_3$ / GaN epitaxial layers unveiled by high-resolution transmission electron microscopy and neutron reflectometry,"The present paper is dedicated to the structural study of crystallographic
peculiarities appearing in epitaxial films of metastable epsilon iron oxide
($\varepsilon$-Fe$_2$O$_3$) grown by pulsed laser deposition onto a
semiconductor GaN (0001) substrate. The columnar structure of the nanoscale
$\varepsilon$-Fe$_2$O$_3$ films has been for the first time investigated using
high resolution electron microscopy (HRTEM) direct space technique complemented
by reciprocal space methods of high-energy electron diffraction and
color-enhanced HRTEM image Fourier filtering. The study of
$\varepsilon$-Fe$_2$O$_3$ / GaN interface formation has been further expanded
by carrying out a depth resolved analysis of density and chemical composition
by neutron reflectometry and energy-dispersive X-ray spectroscopy. The obtained
results shed light onto the properties and the origin of the enigmatic
few-nanometer thick low density transition layer residing at the
$\varepsilon$-Fe$_2$O$_3$ / GaN interface. A detailed knowledge of the
properties of this layer is believed to be highly important for the development
of $\varepsilon$-Fe$_2$O$_3$ / GaN heterostructures that can potentially become
part of the iron-oxide based ferroic-on-semiconductor devices with room
temperature magneto-electric coupling.",2209.06460v1
2022-09-15,Spin-charge coupling and decoupling in perovskite-type iron oxides (Sr$_{1-x}$Ba$_x$)$_{2/3}$La$_{1/3}$FeO$_3$,"The perovskite-type iron oxide Sr$_{2/3}$La$_{1/3}$FeO$_3$ is known to show
characteristic spin-charge ordering (SCO), where sixfold collinear spin
ordering and threefold charge ordering are coupled with each other. Here, we
report the discovery of a spin-charge decoupling and an antiferromagnetic (AFM)
state competing with the SCO phase in perovskites
(Sr$_{1-x}$Ba$_x$)$_{2/3}$La$_{1/3}$FeO$_3$. By comprehensive measurements
including neutron diffraction, M$\""{o}$ssbauer spectroscopy, and x-ray
absorption spectroscopy, we found that the isovalent Ba$^{2+}$ substitution
systematically reduces the critical temperature of the SCO phase and
additionally yields the spin-charge decoupling in $x$ > 0.75. Whereas the
ground state remains in the SCO phase in the whole $x$ region, an unexpected
G-type AFM phase with incoherent charge ordering or charge fluctuation appears
as the high-temperature phase in the range of $x$ > 0.75. Reflecting the
competing nature between them, the G-type AFM phase partially exists as a
metastable state in the SCO phase at low temperatures. We discuss the origin of
the spin-charge decoupling and the emergence of the G-type AFM phase with
charge fluctuation in terms of the bandwidth reduction by the Ba substitution.",2209.07310v1
2022-09-18,Revisit the Circumnuclear X-ray Emission of NGC 2992 in a Historically Low State,"The inner-most region of the Seyfert galaxy NGC 2992 has long been suspected
to be the location of intense AGN-host galaxy interaction, but photon pile-up
in previous high-resolution observations hampered the study of soft X-ray
excess and the interaction near its nucleus. We present an X-ray imaging
spectroscopic analysis of the circumnuclear
($1^{\prime\prime}$--$3^{\prime\prime}$) region of NGC 2992 using the
zeroth-order image of a 135 ks grating observation obtained with Chandra, which
captured the nucleus in a historically low flux state. Extended soft X-ray
emission is detected in the circumnuclear region with observed luminosity
$L_{\rm X} \sim 7 \times 10^{39}\rm\ erg\ s^{-1}$. The majority of previously
puzzling detection of soft excess could be associated with the outflow,
indicated by the morphological correspondences between soft X-ray emission and
figure-eight-shaped radio bubbles. An anomalous narrow emission line with the
centroid energy $\sim4.97$ keV is found. If attributed to redshifted highly
ionized iron emission (e.g., Fe xxv), the required outflow velocity is
$\sim0.23\,c$. An alternative explanation is that this line emission could be
produced by the nuclear spallation of iron. We also find asymmetric extended Fe
K$\alpha$ emission along the galactic disk, which could originate from
reflection by cold gas on $\sim 200$ pc scale.",2209.08534v1
2022-09-18,Efficient photocatalytic nitrogen fixation from air under sunlight via iron-doped WO$_3$,"Photocatalytic nitrogen fixation from air directly under sunlight can
contribute significantly to carbon neutralization. It is an ideal pathway to
replace the industrial Haber Bosch process in future. A Fe-doped layered WO$_3$
photocatalyst containing oxygen vacancies was developed which can fix nitrogen
from air directly under sunlight at atmospheric pressure. The iron doping
enhances the transport efficiency of photogenerated electrons. The
photocatalytic efficiency is around 4 times higher than that of pure WO$_3$.
The optimum nitrogen fixation conditions were examined by orthogonal
experiments and its nitrogen fixation performance could reach up to 477 $\mu
\text{g} \cdot \text{g}_{\text{cat}}^{-1} \cdot \text{h}^{-1}$ under sunlight.
In addition, the process of nitrogen fixation was detected by situ infrared,
which confirmed the reliability of nitrogen fixation. Also, modelling on the
interactions between light and the photocatalyst was carried out to study the
distribution of surface charge and validate the light absorption of the
photocatalyst. This work provides a simple and cheap strategy for
photocatalytic nitrogen fixation from air under mild conditions.",2209.08547v1
2022-09-30,Charge Transport in Ba$_{1-x}$Rb$_{x}$Fe$_{2}$As$_{2}$ Single Crystals,"Recent studies in heavily hole-doped iron-based superconductor RbFe$_2$As$_2$
have suggested the emergence of novel electronic nematicity directed along the
Fe-As direction, 45$^\circ$ rotated from the usual nematicity ubiquitously
found in BaFe$_2$As$_2$ and related materials. This motivates us to study the
physical properties of Ba$_{1-x}$Rb$_{x}$Fe$_{2}$As$_{2}$, details of which
remain largely unexplored. Here we report on the normal-state charge transport
in Ba$_{1-x}$Rb$_{x}$Fe$_{2}$As$_{2}$ superconductors by using high-quality
single crystals in the range of Rb concentration $0.14\le x \le 1.00$. From the
systematic measurements of the temperature dependence of electrical resistivity
$\rho(T)$, we find a signature of a deviation from the Fermi liquid behavior
around the optimal composition, which does not seem related to the
antiferromagnetic quantum criticality but has a potential link to hidden
nematic quantum criticality. In addition, electron correlations derived from
the coefficient of $T^2$ resistivity show a marked increase with Rb content
near the heavily hole-doped end, consistent with the putative Mott physics near
the $3d^5$ electron configuration in iron-based superconductors.",2209.15526v1
2022-10-20,"Kinetics of transformation, border of metastable miscibility gap in Fe-Cr alloy and limit of Cr solubility in iron at 858 K","The study was aimed at determination of the position of the Fe-rich border of
the metastable miscibility gap (MMG) and of the solubility limit of Cr in iron
at 858 K. Towards this end a Fe73.7Cr26.3 alloy was isothermally annealed at
858 K in vacuum up to 8144 hours and M\""ossbauer spectra were recorded at room
temperature after every step of the annealing. Three spectral parameters viz.
the average hyperfine field, <B>, the average isomer shift, <IS>, and the
probability of the atomic configuration with no Cr atoms in the two-shell
vicinity of the probe Fe atoms, P(0,0), gave evidence that the transformation
process takes place in two stages. All three parameters could have been well
described in terms of the Johnson-Mehl-Avrami-Kolmogorov equation, yielding
kinetics parameters. The first stage, associated with the phase decomposition,
proceeded much faster than the second stage, associated with the alpha-to-sigma
phase transformation. The most reliable estimation of the position of the MMG
and that of the value of the Cr solubility limit was obtained from the
annealing time dependence of <B>, namely 24.5 at.% Cr for the former and 20.3
at.% Cr for the latter. A comparison of these figures with the recent phase
diagrams pertinent to Fe-Cr system was done.",2210.11550v1
2022-11-04,Unusual Abundances from Planetary System Material Polluting the White Dwarf G238-44,"Ultraviolet and optical spectra of the hydrogen-dominated atmosphere white
dwarf star G238-44 obtained with FUSE, Keck/HIRES, HST/COS, and HST/STIS reveal
ten elements heavier than helium: C, N, O, Mg, Al, Si, P, S, Ca, and Fe.
G238-44 is only the third white dwarf with nitrogen detected in its atmosphere
from polluting planetary system material. Keck/HIRES data taken on eleven
nights over 24 years show no evidence for variation in the equivalent width of
measured absorption lines, suggesting stable and continuous accretion from a
circumstellar reservoir. From measured abundances and limits on other elements
we find an anomalous abundance pattern and evidence for the presence of
metallic iron. If the pollution is from a single parent body, then it would
have no known counterpart within the solar system. If we allow for two distinct
parent bodies, then we can reproduce the observed abundances with a mix of
iron-rich Mercury-like material and an analog of an icy Kuiper Belt object with
a respective mass ratio of 1.7:1. Such compositionally disparate objects would
provide chemical evidence for both rocky and icy bodies in an exoplanetary
system and would be indicative of a planetary system so strongly perturbed that
G238-44 is able to capture both asteroid- and Kuiper Belt-analog bodies
near-simultaneously within its $<$100 Myr cooling age.",2211.02673v1
2022-11-09,Asynchronous accretion can mimic diverse white dwarf pollutants I: core and mantle fragments,"Polluted white dwarfs serve as astrophysical mass spectrometers - their
photospheric abundances are used to infer the composition of planetary objects
that accrete onto them. We show that due to asymmetries in the accretion
process, the composition of the material falling onto a star may vary with time
during the accretion of a single planetary body. Consequently, the
instantaneous photospheric abundances of white dwarfs do not necessarily
reflect the bulk composition of their pollutants, especially when their
diffusion timescales are short. In particular, we predict that when an asteroid
with an iron core tidally disrupts around a white dwarf, a larger share of its
mantle is ejected, and that the core/mantle fraction of the accreting material
varies with time during the event. Crucially, this implies that the core
fraction of differentiated pollutants cannot be determined for white dwarfs
with short diffusion timescales, which sample only brief episodes of longer
accretion processes. The observed population of polluted white dwarfs backs up
the proposed theory. More white dwarfs have accreted material with high Fe/Ca
than low Fe/Ca relative to stellar abundance ratios, indicating the ejection of
mantle material. Additionally, we find tentative evidence that the accretion
rate of iron decreases more rapidly than that of magnesium or calcium, hinting
at variability of the accreted composition. Further corroboration of the
proposed theory will come from the up-coming analysis of large samples of young
white dwarfs.",2211.05114v1
2022-11-21,Discontinuous Shear Thickening (DST) transition with spherical iron particles coated by adsorbed brush polymer,"In this work we explore the rheology of very concentrated (0.55<$\Phi$<0.67)
suspensions of carbonyl iron (CI) particles coated by a small polymer. A strong
DST is observed in a large range of volume fraction presenting some
specificities relatively to other systems. In particular, in a given range of
volume fraction, the DST transition appears suddenly without being preceded by
shear thickening. The presence of a frictional network of particles is
confirmed by a simultaneous measurement of the electric resistance of the
suspension and of the rheological curve. Using the Wyart-Cates model we show
that, increasing the volume fraction, the fraction of frictional contacts grows
more and more quickly with the stress that disagrees with the prediction of
computer simulations. The same kind of behavior is observed in the presence of
a magnetic field with, in addition, a very strong increase of the viscosity
with the magnetic field before the transition. We interpret this behavior by
the interpenetration of the polymer layer under the effect of the shear
stress-and of the magnetic stress-followed by the expulsion of the polymer out
of the surfaces. Besides we point that, above the DST transition, we do not
observe a jamming in the range of volume fraction whereas it is predicted by
the W-C model. Based on the fact that in the absence of shear flow, the polymer
should come back to the surface and destroy the frictional contacts we can
predict an asymptotic non-zero shear rate and reproduce the experimental
behavior.",2211.11807v1
2022-12-03,Electron correlation in the Iron(II) Porphyrin by NOF approximations,"The relative stability of the singlet, triplet, and quintet spin states of
Iron(II) porphyrin (FeP) represents a challenging problem for electronic
structure methods. While it is currently accepted that the ground state is a
triplet, multiconfigurational wavefunction-based methods predict a quintet, and
density functional approximations vary between triplet and quintet states,
leading to a prediction that highly depends on the features of the method
employed. The recently proposed Global Natural Orbital Functional (GNOF) aims
to provide a balanced treatment between static and dynamic correlation, and
together with the previous Piris Natural Orbital Functionals (PNOFs), allowed
us to explore the importance of each type of correlation in the stability order
of the states of FeP with a method that conserves the spin of the system. It is
noteworthy that GNOF correlates all electrons in all available orbitals for a
given basis set; in the case of the FeP with a double zeta basis set as used in
this work; this means that GNOF can properly correlate 186 electrons in 465
orbitals, significantly increasing the sizes of systems amenable to
multiconfigurational treatment. Results show that PNOF5, PNOF7s and PNOF7
predict the quintet to have a lower energy than the triplet state; however, the
addition of dynamic correlation via second-order Moller-Plesset corrections
(NOF-MP2) turns the triplet state to be lower than the quintet state, a
prediction also reproduced by GNOF that incorporates much more dynamic
correlation than its predecessors.",2212.01640v1
2022-12-13,Collapse of Metallicity and High-$T_c$ Superconductivity in the High-Pressure phase of FeSe$_{0.89}$S$_{0.11}$,"We investigate the high-pressure phase of the iron-based superconductor
FeSe$_{0.89}$S$_{0.11}$ using transport and tunnel diode oscillator studies. We
construct detailed pressure-temperature phase diagrams that indicate that
outside of the nematic phase, the superconducting critical temperature reaches
a minimum before it is quickly enhanced towards 40 K above 4 GPa. The
resistivity data reveal signatures of a fan-like structure of non-Fermi liquid
behaviour which could indicate the existence of a putative quantum critical
point buried underneath the superconducting dome around 4.3 GPa. Further
increasing the pressure, the zero-field electrical resistivity develops a
non-metallic temperature dependence and the superconducting transition broadens
significantly. Eventually, the system fails to reach a fully zero-resistance
state despite a continuous finite superconducting transition temperature, and
any remaining resistance at low temperatures becomes strongly
current-dependent. Our results suggest that the high-pressure, high-$T_c$ phase
of iron chalcogenides is very fragile and sensitive to uniaxial effects of the
pressure medium, cell design and sample thickness which can trigger a
first-order transition. These high-pressure regions could be understood
assuming a real-space phase separation caused by concomitant electronic and
structural instabilities.",2212.06824v1
2022-12-21,Post-Synthetic Treatment of Nickel-Iron Layered Double Hydroxides for the Optimum Catalysis of the Oxygen Evolution Reaction,"Nickel-iron layered double hydroxide (NiFe LDH) platelets with high
morphological regularity and sub-micrometre lateral dimensions were synthesized
using a homogeneous precipitation technique for highly efficient catalysis of
the oxygen evolution reaction (OER). Considering edge sites are the point of
activity, efforts were made to control platelet size within the synthesized
dispersions. The goal is to controllably isolate and characterize size-reduced
NiFe LDH particles. Synthetic approaches for size control of NiFe LDH platelets
have not been transferable based on published work with other LDH materials and
for that reason, we instead use post-synthetic treatment techniques to improve
edge-site density. In the end, size reduced NiFe LDH/single-wall carbon
nanotube (SWCNT) composites allowed to further reduce the OER overpotential to
237 plus/minus 7 mV ( L = 0.16 plus/minus 0.01 micrometres, 20 wt% SWCNT),
which is one of the best values reported to date. This approach as well
improved the long term activity of the catalyst in operating conditions.",2212.11378v1
2023-01-03,"Extracting optical parameters of Cu-Mn-Fe spinel oxide nanoparticles for optimizing air-stable, high-efficiency solar selective coatings","High-temperature Cu-Mn-Fe spinel-oxide nanoparticle solar selective absorber
coatings are investigated experimentally and theoretically. A reliable, general
approach to evaluate absorption coefficient spectra from the optical
measurements of the nanoparticle-pigmented coatings is developed based on
solving the inverse problem using four-flux-radiative method. The derived
absorption properties of NP materials can be directly applied to predict the
solar absorptance, optimize the nanoparticle-pigmented coatings, and analyze
the thermal degradation, which agree well with the experimental results. The
analysis reveals that the Cu-Mn-Fe spinel oxides are fundamentally indirect
bandgap ranging from 1.7 to 2.1 eV, while iron-free CuMn2O4 is a direct bandgap
material with Eg=1.84 eV. With the same coating thickness and nanoparticle
load, the solar absorptance ranks in the order of Mn2O3 < MnFe2O4 < CuFe2O4 <
CuFeMnO4 < CuMn2O4. The optimized spray-coated iron-free CuMn2O4 NP-pigmented
coating demonstrates a high solar absorptance of 97%, a low emittance of 55%, a
high optical-to-thermal energy conversion efficiency of ~93.5 % under 1000x
solar concentration at 750 degrees C, and long-term endurance upon thermal
cycling between 750{\deg}C and room temperature in air. The optical parameter
analysis approach can be easily extended to other material systems to
facilitate the searching and optimizing high-temperature pigmented-solar
selective coatings.",2301.01194v1
2023-01-07,Orthogonal magnetic structures of Fe4O5:representation analysis and DFT calculations,"The magnetic and electronic structures of Fe4O5 have been investigated at
ambient and high pressures via a combination of representation analysis,
density functional theory (DFT+U) calculations, and M\""ossbauer spectroscopy. A
few spin configurations corresponding to the different irreducible
representations have been considered. The total-energy calculations reveal that
the magnetic ground state of Fe4O5 corresponds to an orthogonal spin order.
Depending on the magnetic propagation vector k two spin ordered phases with
minimal energy differences are realized. The lowest energy magnetic phase is
related to k = (0, 0, 0) and is characterized by the ferromagnetic ordering of
the iron magnetic moments at prismatic sites along the b axis and
antiferromagnetic ordering of iron moments at octahedral sites along the c
axis. For the k = (1/2, 0, 0) phase, the moments in the prisms are
antiferromagnetically ordered along the b axis and the moments in the octahedra
are still antiferromagnetically ordered along the c axis. Under high pressure,
the Fe4O5 exhibits magnetic transitions with corresponding electronic
transitions of the metal-insulator type. At a critical pressure PC ~ 60 GPa the
Fe ions at the octahedral sites undergo a high-spin to low-spin state crossover
with a decrease in the unit-cell volume of ~ 4%, while the Fe ions at the
prismatic sites remain in the high-spin state up to 130 GPa. This
site-dependent magnetic collapse is experimentally observed in the
transformation of M\""ossbauer spectra measured at room temperature and high
pressures.",2301.02824v1
2023-02-03,An empirical relation to estimate host galaxy stellar light from AGN spectra,"Measurement of black hole mass for low-$z$ ($z\leq 0.8$) Active Galactic
Nuclei (AGNs) is difficult due to the strong contribution from host galaxy
stellar light necessitating detailed spectral decomposition to estimate the AGN
luminosity. Here, we present an empirical relation to estimate host galaxy
stellar luminosity from the optical spectra of AGNs at $z\leq 0.8$. The
spectral data were selected from the fourteenth data release of the Sloan
Digital Sky Survey (SDSS-DR14) quasar catalog having a signal-to-noise ratio at
5100 \AA (SNR$_{5100}$) $>$10 containing 11415 quasars. The median total
luminosity (log ($L_\text{total}$/[erg s$^{-1}$])), stellar luminosity (log
($L_\text{star}$/[erg s$^{-1}$])), and AGN continuum luminosity (log
($L_\text{cont}$/[erg s$^{-1}$])) in our sample are 44.52, 44.06, and 44.30,
respectively. We fit the AGN power-law continuum, host galaxy, and iron blend
contribution, simultaneously over the entire available spectrum. We found the
host galaxy fraction to anti-correlate with continuum luminosity and can be
well-represented by a polynomial function, which can be used to correct the
stellar light contribution from AGN spectra. We also found anti-correlation
between host galaxy fraction and iron strength, Eddington ratio, and redshift.
The empirical relation gives comparable results of host-fraction with the image
decomposition method.",2302.01948v2
2023-02-13,Evolution of phase morphology in dispersed clay systems under the microwave irradiation,"The results of a study of the effect of microvolume emission (power 700 W,
frequency 2.45 GHz) on the structural changes in natural clay particles are
presented. The influence of the irradiation time (10 and 20 minutes) and the
environment in the microwave chamber (atmospheric air and air saturated with
water vapor) on the structural changes occurring in the particles was traced.
During the first 10 minutes, capillary water is completely removed and
agglomeration is carried out by attaching single dispersed particles (diffusion
limited aggregation model). At the second stage (10-20 minutes), already formed
agglomerates (cluster-cluster aggregation model) are growing. A complex of
independent optical-physical methods was used to analyze weak structural
changes. It includes X-ray phase analysis, colorimetry and wavelet analysis.
This approach has made it possible to increase the information content and
reliability of measurements, quantitatively characterize the structural
responses in disperse clay systems. In the air, the removal of capillary water
is accompanied by agglomerations of particles and polymorphic transformations
of oxides: montmorillonite is completely decomposed, amorphous phases
crystallize. The composition of the environment in the microwave chamber
affects the type of phase transformations in iron compounds: iron-alumina is
formed in air, magnetite appear in the water vapor medium. The studies carried
out using the developed set of experimental methods indicate the possibility of
regulating the processes of structure formation in disperse clay systems by
optimizing the regimes of exposure to microwave radiation.",2302.06330v1
2023-03-01,A Search for Chemical Anomalies of Seven A-types Stars,"We present a chemical abundance analysis of seven A-type stars with no
detailed chemical abundance measurements in the literature. High-resolution
spectra of the targets HD 2924, HD 4321, HD 26553, HD 125658, HD 137928, HD
154713, and HD 159834 were obtained using the Coude Echelle Spectrograph at the
TUBITAK National Observatory. We determined the atmospheric abundances of the
samples and measured the elemental abundances of C, N, O, Na, Mg, Al, Si, S, K,
Ca, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Sr, Y, Zr, Ba, La, Ce, Nd, Sm, Eu,
and Gd. The masses of the stars were estimated based on their evolutionary
tracks, and their ages were calculated using isochrones. We also calculated the
radii of the stars. The abundance patterns of HD 4321, HD 125658, and HD 154713
were found to be in agreement with those of classical Am stars, with
underabundant Ca and Sc, overabundant heavier elements, and moderate
overabundance of iron-peak elements. We found that HD 137928 and HD 159834 have
similar abundance characteristics to marginal Am-type stars. The elemental
distributions of HD 2924 and HD 26553 are consistent with the pattern of normal
A-type stars. The iron, nickel, and zinc abundances of HD 125658 and HD 137928
are significantly higher than other Am stars. These values suggest that they
are among the most metal-rich Am stars",2303.00584v1
2023-05-29,Intertwined charge and pair density orders in a monolayer high-Tc iron-based superconductor,"Symmetry-breaking electronic phase in unconventional high-temperature
(high-Tc) superconductors is a fascinating issue in condensed-matter physics,
among which the most attractive phases are charge density wave (CDW) phase with
four unit-cell periodicity in cuprates and nematic phase breaking the C4
rotational symmetry in iron-based superconductors (FeSCs). Recently, pair
density wave (PDW), an exotic superconducting phase with non-zero momentum
Cooper pairs, has been observed in high-Tc cuprates and the monolayer FeSC.
However, the interplay between the CDW, PDW and nematic phase remains to be
explored. Here, using scanning tunneling microscopy/spectroscopy, we detected
commensurate CDW and CDW-induced PDW orders with the same period of lambda =
4aFe (aFe is the distance between neighboring Fe atoms) in a monolayer high-Tc
Fe(Te,Se) film grown on SrTiO3(001) substrate. Further analyses demonstrate the
observed CDW is a smectic order, which breaks both translation and C4
rotational symmetry. Moreover, the smecticity of the CDW order is strongest
near the superconducting gap but weakens near defects and in an applied
magnetic field, indicating the interplay between the smectic CDW and PDW
orders. Our works provide a new platform to study the intertwined orders and
their interactions in high-Tc superconductors.",2305.17991v1
2023-06-22,Type Ia Supernova Nucleosynthesis: Metallicity-Dependent Yields,"Type Ia supernova explosions (SNIa) are fundamental sources of elements for
the chemical evolution of galaxies. They efficiently produce intermediate-mass
(with Z between 11 and 20) and iron group elements - for example, about 70% of
the solar iron is expected to be made by SNIa. In this work, we calculate
complete abundance yields for 39 models of SNIa explosions, based on three
progenitors - a 1.4M deflagration detonation model, a 1.0 double detonation
model and a 0.8 M double detonation model - and 13 metallicities, with 22Ne
mass fractions of 0, 1x10-7, 1x10-6, 1x10-5, 1x10-4, 1x10-3, 2x10-3, 5x10-3,
1x10-2, 1.4x10-2, 5x10-2, and 0.1 respectively. Nucleosynthesis calculations
are done using the NuGrid suite of codes, using a consistent nuclear reaction
network between the models. Complete tables with yields and production factors
are provided online at Zenodo: Yields. We discuss the main properties of our
yields in the light of the present understanding of SNIa nucleosynthesis,
depending on different progenitor mass and composition. Finally, we compare our
results with a number of relevant models from the literature.",2306.12885v1
2023-06-27,Permanent magnet systems to study the interaction between magnetic nanoparticles and cells in microslide channels,"We optimized designs of permanent magnet systems to study the effect of
magnetic nanoparticles on cell cultures in microslide channels. This produced
two designs, one of which is based on a large cylindrical magnet that applies a
uniform force density of 6 MN/m$^3$ on soft magnetic iron-oxide spherical
nanoparticles at a field strength of over 300 mT. We achieved a force
uniformity of better than 14% over the channel area leading to a concentration
variation that was below our measurement resolution. The second design was
aimed at maximizing the force by using a Halbach array. We indeed increased the
force by more than one order of magnitude at force density values over 400
MN/m$^3$, but at the cost of uniformity. However, the latter system can be used
to trap magnetic nanoparticles efficiently and to create concentration
gradients. We demonstrated both designs by analyzing the effect of magnetic
forces on the cell viability of human hepatoma HepG2 cells in the presence of
bare Fe$_2$O$_3$ and cross-linked dextran iron-oxide cluster-type particles
(MicroMod). Python scripts for magnetic force calculations and particle
trajectory modeling as well as source files for 3D prints have been made
available so these designs can be easily adapted and optimized for other
geometries.",2306.15459v2
2023-07-10,Design and processing as ultrathin films of a sublimable Iron(II) spin crossover material exhibiting efficient and fast light-induced spin transition,"Materials based on spin crossover (SCO) molecules have centred the attention
in Molecular Magnetism for more than forty years as they provide unique
examples of multifunctional and stimuli-responsive materials, which can be then
integrated into electronic devices to exploit their molecular bistability. This
process often requires the preparation of thermally stable SCO molecules that
can sublime and remain intact in contact with surfaces. However, the number of
robust sublimable SCO molecules is still very scarce. Here we report a novel
example of this kind. It is based on a neutral iron (II) coordination complex
formulated as [FeII(neoim)2], where neoimH is the ionogenic ligand
2-(1H-imidazol-2-yl)-9-methyl-1,10-phenanthroline. In the first part a
comprehensive study, which covers the synthesis and magneto-structural
characterization of the [FeII(neoim)2] complex as a bulk microcrystalline
material, is reported. Then, in the second part we investigate the suitability
of this material to form thin films through high vacuum (HV) sublimation.
Finally, the retainment of all present SCO capabilities in the bulk when the
material is processed is thoroughly studied by means of X-ray absorption
spectroscopy. In particular, a very efficient and fast light-induced spin
transition (LIESST effect) has been observed, even for ultrathin films of 15
nm.",2307.04591v1
2023-07-17,Controlling the Temperature of the Spin-Reorientation Transition In HoFe1-xMnxO3 Orthoferrite Single Crystals,"HoFe1-xMnxO3 (0 < x < 1) single crystals have been grown by the optical
floating zone technique. A structural transition from the orthorhombic to
hexagonal modification has been established in the crystals in the
concentration range of 0.7-0.8, which has been confirmed by the X-ray
diffraction data. For a series of the rhombic crystals, the room-temperature
Mossbauer study and magnetic measurements in the temperature range of 4.2-1000
K have been carried out. It has been observed that, with an increase in the
manganese content in the samples, the temperature of the spin-reorientation
transition increases significantly: from 60 K in the HoFeO3 compound to room
temperature in HoFe0.6Mn0.4O3. The magnetic measurements have shown that, upon
substitution of manganese for iron, the magnetic orientational type transition
changes from a second-order transition (AxFyGz -> CxGyFz) to first-order one
(AxFyGz -> GxCyAz) with a weak ferromagnetic moment only in the b direction
(for Pnma notation). The growth of the spin-reorientation transition
temperature has been attributed to the change in the value of the indirect
exchange in the iron subsystem under the action of manganese, which has been
found when studying the Mossbauer effect in the HoFe1-xMnxO3 (x < 0.4)
compound.",2307.08236v1
2023-07-19,Origin of Life Molecules in the Atmosphere After Big Impacts on the Early Earth,"The origin of life on Earth would benefit from a prebiotic atmosphere that
produced nitriles, like HCN, which enable ribonucleotide synthesis. However,
geochemical evidence suggests that Hadean air was relatively oxidizing with
negligible photochemical production of prebiotic molecules. These paradoxes are
resolved by iron-rich asteroid impacts that transiently reduced the entire
atmosphere, allowing nitriles to form in subsequent photochemistry. Here, we
investigate impact-generated reducing atmospheres using new time-dependent,
coupled atmospheric chemistry and climate models, which account for gas-phase
reactions and surface-catalysis. The resulting H$_2$-, CH$_4$- and NH$_3$-rich
atmospheres persist for millions of years, until hydrogen escapes to space. HCN
and HCCCN production and rainout to the surface can reach $10^9$ molecules
cm$^{-2}$ s$^{-1}$ in hazy atmospheres with a mole ratio of $\mathrm{CH_4} /
\mathrm{CO_2} > 0.1$. Smaller $\mathrm{CH_4} / \mathrm{CO_2}$ ratios produce
HCN rainout rates $< 10^5$ molecules cm$^{-2}$ s$^{-1}$, and negligible HCCCN.
The minimum impactor mass that creates atmospheric $\mathrm{CH_4} /
\mathrm{CO_2} > 0.1$ is $4 \times 10^{20}$ to $5 \times 10^{21}$ kg (570 to
1330 km diameter), depending on how efficiently iron reacts with a steam
atmosphere, the extent of atmospheric equilibration with an impact-induced melt
pond, and the surface area of nickel that catalyzes CH$_4$ production.
Alternatively, if steam permeates and deeply oxidizes crust, impactors $\sim
10^{20}$ kg could be effective. Atmospheres with copious nitriles have $> 360$
K surface temperatures, perhaps posing a challenge for RNA longevity, although
cloud albedo can produce cooler climates. Regardless, post-impact cyanide can
be stockpiled and used in prebiotic schemes after hydrogen has escaped to
space.",2307.09761v1
2023-07-28,"Structural phase transition, $s_{\pm}$-wave pairing and magnetic stripe order in the bilayered nickelate superconductor La$_3$Ni$_2$O$_7$ under pressure","Motivated by the recently discovered high-$T_c$ superconductor
La$_3$Ni$_2$O$_7$, we comprehensively study this system using density
functional theory and random phase approximation calculations. At low
pressures, the Amam phase is stable, containing the Y$^{2-}$ mode distortion
from the Fmmm phase, while the Fmmm phase is unstable. Because of small
differences in enthalpy and a considerable Y$^{2-}$ mode amplitude, the two
phases may coexist in the range between 10.6 and 14 GPa, beyond which the Fmmm
phase dominates. In addition, the magnetic stripe-type spin order with
wavevector ($\pi$, 0) was stable at the intermediate region. Pairing is induced
in the $s_{\pm}$-wave channel due to partial nesting between the {\bf M}=$(\pi,
\pi)$ centered pockets and portions of the Fermi surface centered at the {\bf
X}=$(\pi, 0)$ and {\bf Y}=$(0, \pi)$ points. This resembles results for
iron-based superconductors but has a fundamental difference with iron pnictides
and selenides. Moreover, our present efforts also suggest that
La$_3$Ni$_2$O$_7$ is qualitatively different from infinite-layer nickelates and
cuprate superconductors.",2307.15276v4
2023-08-01,The current state of disk wind observations in BHLMXBs through X-ray absorption lines in the iron band,"The presence of blueshifted absorption lines in the X-ray spectra of Black
Hole Low Mass X-ray Binaries is the telltale of massive outflows called winds.
These signatures are found almost exclusively in soft states of high-inclined
systems, hinting at equatorial ejections originating from the accretion disk
and deeply intertwined with the evolution of the outburst patterns displayed by
these systems. In the wake of the launch of the new generation of X-ray
spectrometers, studies of wind signatures remain mostly restricted to single
sources and outbursts, with some of the recent detections departing from the
commonly expected behaviors. We thus give an update to the current state of
iron band absorption lines detections, through the analysis of all publicly
available XMM-$Newton$-PN and $Chandra$-HETG exposures of known Black Hole
Low-Mass X-ray Binary candidates. Our results agree with previous studies, with
wind detections exclusively found in dipping, high-inclined sources, and almost
exclusively in bright ($L_{X}>0.01L_{Edd}$) soft ($HR<0.8$) states, with
blueshift values generally restricted to few 100 km s$^{-1}$. The line
parameters indicate similar properties between objects and outbursts of single
sources, and despite more than 20 years of data, very few sources have the HID
sampling necessary to properly study the evolution of the wind during single
outbursts. We provide an online tool with details of the wind signatures and
outburst evolution data for all sources in the sample.",2308.00691v1
2023-08-07,Energy-resolved pulse profiles of accreting pulsars: Diagnostic tools for spectral features,"We introduce a method for extracting spectral information from
energy-resolved light curves folded at the neutron star spin period (known as
pulse profiles) in accreting X-ray binaries. Spectra of these sources are
sometimes characterized by features superimposed on a smooth continuum, such as
iron emission lines and cyclotron resonant scattering features. We address here
the question on how to derive quantitative constraints on such features from
energy-dependent changes in the pulse profiles. We developed a robust method
for determining in each energy-selected bin the value of the pulsed fraction
using the fast Fourier transform opportunely truncated at the number of
harmonics needed to satisfactorily describe the actual profile. We determined
the uncertainty on this value by sampling through Monte Carlo simulations a
total of 1000 faked profiles. We rebinned the energy-resolved pulse profiles to
have a constant minimum signal-to-noise ratio throughout the whole energy band.
Finally we characterize the dependence of the energy-resolved pulsed fraction
using a phenomenological polynomial model and search for features corresponding
to spectral signatures of iron emission or cyclotron lines using Gaussian line
profiles. We apply our method to a representative sample of NuSTAR observations
of well-known accreting X-ray pulsars. We show that, with this method, it is
possible to characterize the pulsed fraction spectra, and to constrain the
position and widths of such features with a precision comparable with the
spectral results. We also explore how harmonic decomposition, correlation, and
lag spectra might be used as additional probes for detection and
characterization of such features.",2308.03395v1
2023-08-08,Designing optoelectronic properties by on-surface synthesis: formation and electronic structure of an iron-terpyridine macromolecular complex,"Supramolecular chemistry protocols applied on surfaces offer compelling
avenues for atomic scale control over organic-inorganic interface structures.
In this approach, adsorbate-surface interactions and two-dimensional
confinement can lead to morphologies and properties that differ dramatically
from those achieved via conventional synthetic approaches. Here, we describe
the bottom-up, on-surface synthesis of one-dimensional coordination
nanostructures based on an iron (Fe)-terpyridine (tpy) interaction borrowed
from functional metal-organic complexes used in photovoltaic and catalytic
applications. Thermally activated diffusion of sequentially deposited ligands
and metal atoms, and intra-ligand conformational changes, lead to Fe-tpy
coordination and formation of these nanochains. Low-temperature Scanning
Tunneling Microscopy and Density Functional Theory were used to elucidate the
atomic-scale morphology of the system, providing evidence of a linear tri-Fe
linkage between facing, coplanar tpy groups. Scanning Tunneling Spectroscopy
reveals highest occupied orbitals with dominant contributions from states
located at the Fe node, and ligand states that mostly contribute to the lowest
unoccupied orbitals. This electronic structure yields potential for hosting
photo-induced metal-to-ligand charge transfer in the visible/near-infrared. The
formation of this unusual tpy/tri-Fe/tpy coordination motif has not been
observed for wet chemistry synthesis methods, and is mediated by the bottom-up
on-surface approach used here.",2308.04105v1
2023-09-05,Magnetic and structural properties of the iron silicide superconductor LaFeSiH,"The magnetic and structural properties of the recently discovered
pnictogen/chalcogen-free superconductor LaFeSiH ($T_c\simeq10$~K) have been
investigated by $^{57}$Fe synchrotron M{\""o}ssbauer source (SMS) spectroscopy,
x-ray and neutron powder diffraction and $^{29}$Si nuclear magnetic resonance
spectroscopy (NMR). No sign of long range magnetic order or local moments has
been detected in any of the measurements and LaFeSiH remains tetragonal down to
2 K. The activated temperature dependence of both the NMR Knight shift and the
relaxation rate $1/T_1$ is analogous to that observed in strongly overdoped
Fe-based superconductors. These results, together with the
temperature-independent NMR linewidth, show that LaFeSiH is an homogeneous
metal, far from any magnetic or nematic instability, and with similar Fermi
surface properties as strongly overdoped iron pnictides. This raises the
prospect of enhancing the $T_c$ of LaFeSiH by reducing its carrier
concentration through appropriate chemical substitutions. Additional SMS
spectroscopy measurements under hydrostatic pressure up to 18.8~GPa found no
measurable hyperfine field.",2309.02241v1
2023-09-15,Superconductivity and vortex structure on Bi$_{2}$Te$_{3}$/FeTe$_{0.55}$Se$_{0.45}$ heterostructures with different thickness of Bi$_{2}$Te$_{3}$ films,"Using scanning tunnel microscopy (STM), we investigate the superconductivity
and vortex properties in topological insulator Bi$_{2}$Te$_{3}$ thin films
grown on the iron-based superconductor FeTe$_{0.55}$Se$_{0.45}$. The
proximity-induced superconductivity weakens in the Bi$_{2}$Te$_{3}$ film when
the thickness of the film increases. Unlike the elongated shape of vortex cores
observed in the Bi$_{2}$Te$_{3}$ film with 2-quintuple-layer (QL) thickness,
the isolated vortex cores exhibit a star shape with six rays in the 1-QL film,
and the rays are along the crystalline axes of the film. This is consistent
with the sixfold rotational symmetry of the film lattice, and the
proximity-induced superconductivity is still topologically trivial in the 1-QL
film. At a high magnetic field, when the direction between the two nearest
neighbored vortices deviates from that of any crystalline axes, two cores
connect each other by a pair of adjacent rays, forming a new type of electronic
structure of vortex cores. On the 3-QL film, the vortex cores elongate along
one of the crystalline axes of the Bi$_{2}$Te$_{3}$ film, similar to the
results obtained on 2-QL films. The elongated vortex cores indicate a twofold
symmetry of the superconducting gap induced by topological superconductivity
with odd parity. This observation confirms possible topological
superconductivity in heterostructures with a thickness of more than 2 QLs. Our
results provide rich information for the vortex cores and vortex-bound states
on the heterostructures consisting of the topological insulator and the
iron-based superconductor.",2309.08246v1
2023-09-22,Wavelet spectral timing: X-ray reverberation from a dynamic black hole corona hidden beneath ultrafast outflows,"Spectral timing analyses based upon wavelet transforms provide a new means to
study the variability of the X-ray emission from accreting systems, including
AGN, stellar mass black holes and neutron stars, and can be used to trace the
time variability of X-ray reverberation from the inner accretion disc. The
previously-missing iron K reverberation time lags in the AGN IRAS 13224-3809
and MCG-6-30-15 are detected and found to be transitory in nature.
Reverberation can be hidden during periods in which variability in the iron K
band becomes dominated by ultrafast outflows (UFO). Following the time
evolution of the reverberation lag between the corona and inner accretion disc,
we may observe the short-timescale increase in scale height of the corona as it
is accelerated away from the accretion disc during bright X-ray flares in the
AGN I Zw 1. Measuring the variation of the reverberation lag that corresponds
to the continuous, stochastic variations of the X-ray luminosity sheds new
light on the disc-corona connection around accreting black holes. Hysteresis is
observed between the X-ray count rate and the scale height of the corona, and a
time lag of 10~40ks is observed between the rise in luminosity and the increase
in reverberation lag. This correlation and lag are consistent with viscous
propagation through the inner accretion disc, leading first to an increase in
the flux of seed photons that are Comptonised by the corona, before mass
accretion rate fluctuations reach the inner disc and are able to modulate the
structure of the corona.",2309.13107v2
2023-10-13,Polarized microwave emission from space particles in the upper atmosphere of the Earth,"Tons of space particles enter the Earth atmosphere every year, being detected
when they produce fireballs, meteor showers, or when they impact the Earth
surface. Particle detection in the showers could also be attempted from space
using satellites in low Earth orbit. Measuring the polarization would provide
extra crucial information on the dominant alignment mechanisms and the
properties of the meteor families. In this article, we evaluate the expected
signal to aid in the design of space probes for this purpose. We have used the
RADMC-3D code to simulate the polarized microwave emission of aligned dust
particles with different compositions: silicates, carbonates and irons. We have
assumed a constant spatial particle density distribution of 0.22 cm$^{-3}$,
based on particle density measurements carried during meteor showers. Four
different grain size distributions with power indices ranging from $-3.5$ to
$-2.0$ and dust particles with radius ranging from 0.01 $\mathrm{\mu}$m to 1 cm
have been considered for the simulations. Silicates and carbonates align their
minor axis with the direction of the solar radiation field; during the flight
time into the Earth atmosphere, iron grains get oriented with the Earth's
magnetic field depending on their size. Alignment direction is reflected in the
$Q$-Stokes parameter and in the polarization variation along the orbit.
Polarization depends on the composition and on the size distribution of the
particles. The simulations show that some specific particle populations might
be detectable even with a small probe equipped with high sensitivity,
photon-counting microwave detectors operating in low Earth orbit.",2310.08941v1
2023-10-17,Towards atomistic understanding of Iron phosphate glass: a first-principles based DFT modeling and study of its physical properties,"Iron phosphate glasses (IPG) have been proposed as futuristic glass material
for nuclear waste immobilization, anode material for lithium batteries and also
as bioactive glass. In the last decade, there have been attempts to propose
atomistic models of IPG to explain their properties from atomistic viewpoint
and to predict their behavior in radioactive environment. In this paper, we
seek to produce small scale models of IPG that can be handled within the scheme
of Density Functional Theory (DFT) to study the electronic structure of this
material. The starting models generated using Monte Carlo (MC) method [S. Singh
and S. Chandra, Comp. Mat. Sci., 202, 110943, (2022)] were subsequently
annealed (at 1000 K) using ab-initio molecular dynamics (AIMD). This removes
coordination defects present in the MC models. The equilibrated structure at
this temperature was then force-relaxed using conjugate-gradient (CG)
optimization. This hybrid approach (MC + AIMD + 0K DFT-CG optimization)
produced good atomistic models of IPG which can reproduce experimentally
observed electronic band-gap, vibrational density of states (VDOS), magnetic
moment of Fe, the elastic constants as well as optical and dielectric
properties. Computationally expensive melt-quench simulation can be avoided
using present approach allowing the use of DFT for accurate calculations of
properties of complex glass like IPG.",2310.11135v1
2023-10-25,Post-main sequence thermal evolution of planetesimals,"White dwarfs that have accreted planetary materials provide a powerful tool
to probe the interiors and formation of exoplanets. In particular, the high
Fe/Si ratio of some white dwarf pollutants suggests that they are fragments of
bodies that were heated enough to undergo large-scale melting and iron core
formation. In the solar system, this phenomenon is associated with bodies that
formed early and so had short-lived radionuclides to power their melting,
and/or grew large. However, if the planetary bodies accreted by white dwarfs
formed during the (pre)-main sequence lifetime of the host star, they will have
potentially been exposed to a second era of heating during the star's giant
branches. This work aims to quantify the effect of stellar irradiation during
the giant branches on planetary bodies by coupling stellar evolution to thermal
and orbital evolution of planetesimals. We find that large-scale melting,
sufficient to form an iron core, can be induced by stellar irradiation, but
only in close-in small bodies: planetesimals with radii $\lesssim$ 30 km
originally within $\sim$ 2 AU orbiting a 1$-$3$\,M_{\odot}$ host star with
solar metallicity. Most of the observed white dwarf pollutants are too massive
to be explained by the accretion of these small planetesimals that are melted
during the giant branches. Therefore, we conclude that those white dwarfs that
have accreted large masses of materials with enhanced or reduced Fe/Si remain
an indicator of planetesimal's differentiation shortly after formation,
potentially linked to radiogenic heating.",2310.17057v1
2023-10-26,Honing cross-correlation tools for inference on ultra-high-energy cosmic-ray composition,"The chemical composition of the highest-energy cosmic rays, namely the atomic
number $Z$ of rays with energies $E\gg1~\text{EeV}$, remains to date largely
unknown. Some information on the composition can be inferred from the
deflections that charged ultra-high-energy cosmic rays experience while they
traverse intervening magnetic fields. Indeed, such deflections distort and
suppress the original anisotropy in the cosmic rays arrival directions; thus, a
measure of the anisotropy is also a measurement of the deflections, which in
turn informs us on the chemical composition. In this work, we show that, by
quantifying ultra-high-energy cosmic ray anisotropies through the angular,
harmonic cross-correlation between cosmic rays and galaxies, we are able to
exclude iron fractions $f_{\rm Fe}\leq{\cal O}(10\%)$ on a fiducial hydrogen
map at $2\sigma$ level, and even smaller fractions in the reverse case of
hydrogen on an iron map, going below $f_{\rm H}\lesssim10\%$ when we mask the
Galactic Centre up to latitudes of $40\,\text{deg}$. This is an improvement of
a factor of a few compared to our previous method, and is mostly ascribable to
a new test statistics which is sensitive to each harmonic multipole
individually. Our method can be applied to real data as an independent test of
the recent claim that current cosmic-ray data can not be reproduced by any
existing model of the Galactic magnetic field, as well as an additional handle
to compare any realistic, competing, data-driven composition models.",2310.17699v2
2023-10-31,Chemical evolution models: the role of type Ia supernovae in the $α$-elements over Iron relative abundances and their variations in time and space,"The role of type Ia supernovae, mainly the Delay Time Distributions (DTDs)
determined by the binary systems, and the yields of elements created by
different explosion mechanisms, are studied by using the {\sc MulChem} chemical
evolution model, applied to our Galaxy. We explored 15 DTDs, and 12 tables of
elemental yields produced by different SN Ia explosion mechanisms, doing a
total of 180 models. Chemical abundances for $\alpha$-elements (O, Mg, Si, S,
Ca) and Fe derived from these models, are compared with recent observational
data of $\alpha$-elements over Iron relative abundances, [X/Fe]. These data
have been compiled and binned in 13 datasets. By using a $\chi^2$-technique, no
model is able to fit simultaneously these datasets. A model computed with the
13 individual best models is good enough to reproduce them. Thus, a power law
with a logarithmic slope $\sim -1.1$ and a delay in the range $\Delta \tau=40
--350$ Myr is a possible DTD, but a combination of several channels is more
probable. Results of this average model for other disc regions show a high
dispersion, as observed, which might be explained by the stellar migration. The
dispersion might also come from a combination of DTDs or of explosion channels.
The stellar migration joined to a combination of scenarios for SNIa is the
probable cause of the observed dispersion.",2311.00076v1
2023-11-01,Annealing effects on the magnetic and magnetotransport properties of iron oxide nanoparticles self-assemblies,"In magnetic tunnel junctions based on iron oxide nanoparticles the disorder
and the oxidation state of the surface spin as well as the nanoparticles
functionalization play a crucial role in the magnetotransport properties. In
this work, we report a systematic study of the effects of vacuum annealing on
the structural, magnetic and transport properties of self-assembled ~10 nm
Fe3O4 nanoparticles. The high temperature treatment (from 573 to 873 K)
decomposes the organic coating into amorphous carbon, reducing the electrical
resistivity of the assemblies by 4 orders of magnitude. At the same time, the
3Fe2+/(Fe3++Fe2+) ratio is reduced from 1.11 to 0.13 when the annealing
temperature of the sample increases from 573 to 873 K, indicating an important
surface oxidation. Although the 2 nm physical gap remains unchanged with the
thermal treatment, a monotonous decrease of tunnel barrier width was obtained
from the electron transport measurements when the annealing temperature
increases, indicating an increment in the number of defects and hot-spots in
the gap between the nanoparticles. This is reflected in the reduction of the
spin dependent tunneling, which reduces the interparticle magnetoresistance.
This work shows new insights about influence of the nanoparticle interfacial
composition, as well their the spatial arrangement, on the tunnel transport of
self-assemblies, and evidence the importance of optimizing the nanostructure
fabrication for increasing the tunneling current without degrading the spin
polarized current.",2311.00700v1
2023-11-10,Enhancement of optical absorption in multiferroic (1-x)PZT-xPFN thin films: Experiments and first-principles analysis,"Multiferroic compounds have gained research attention in the field of
ferroelectric photovoltaics due to the presence of transition-metal d states
from magnetic ions, which tend to reduce the bandgap value. In this work,
0.5Pb(Zr0.52Ti0.48)O3 - 0.5Pb(Fe0.5Nb0.5)O3 PZTFN0.5 thin films were
synthesized using a sol-gel route to investigate the effect of iron doping on
optical and multiferroic properties. For comparative analysis, the end-member
compositions, Pb(Zr0.52Ti0.48)O3 (PZT) and Pb(Fe0.5Nb0.5)O3 (PFN), were also
synthesized under identical conditions. Our results revealed that the presence
of Fe ions, besides inducing multiferroic behavior, effectively enhances the
optical absorption of the material in the visible light region. Optical
transitions at 3.0 eV (2.4 eV) and 2.7 eV (2.2 eV) for the direct (indirect)
bandgap were determined for PZTFN0.5 and PFN, respectively, indicating that the
absorption edges of the iron-containing films result more promising than PZT
(Eg 3.6eV) for photovoltaic applications. Both PZTFN0.5 and PFN thin films
exhibit multiferroic behavior at room temperature, with different electric and
magnetic properties. While PZTFN0.5 presents saturated hysteresis loops with
remanent polarization values around 10 uC/cm2 and magnetization of 1.6 emu/cm2,
PFN displays significantly larger remanence (31 emu/cm2) but poorer
ferroelectric properties due to the presence of leakage. Microscopic insights
into the structural and electronic properties of the PZTFN0.5 solid solution
were provided from first-principles calculations.",2311.05855v1
2023-11-14,Superconductivity with $T_c$ up to 30.7 K in air-annealed CaFeAsF,"Exploring new unconventional superconductors is of great value for both
fundamental research and practical applications. It is a long-term challenge to
develop and study more hole-doped superconductors in 1111 system of iron-based
superconductors. However, fifteen years after the discovery of iron-based
superconductors, it has become increasingly difficult to discover new members
in this system by conventional means. Here we report the discovery of
superconductivity with the critical transition temperature up to 30.7 K in the
parent compound CaFeAsF by an annealing treatment in air atmosphere. The
superconducting behaviors are verified in both the single-crystalline and
polycrystalline samples by the resistance and magnetization measurements. The
analysis by combining the depth-resolved time-of-flight secondary ion mass
spectrometry (TOF-SIMS) and X-ray photoelectron spectroscopy (XPS) measurements
show that the introduction of oxygen elements and the consequent changing in Fe
valence by the annealing treatment may lead to the hole-type doping, which is
the origin for the occurrence of superconductivity. Our results provide a new
route to induce hole-doped superconductivity in Fe-based superconductors.",2311.07943v1
2023-12-14,X-ray Reflection from the Plunging Region of Black Hole Accretion Disks,"Accretion around black holes is very often characterized by distinctive X-ray
reflection features (mostly, iron inner-shell transitions), which arise due to
the primary radiation being reprocessed by a dense and relatively colder
medium, such as an accretion disk. Most reflection modeling assume that
emission stops at the inner-most stable circular orbit (ISCO), and that for
smaller radii - in the plunging region - the density drops and the accretion
flow is far too ionized for efficient line production. We investigate the
spectral features of the reflection in the plunging regions of optically-thick
and geometrically-thin accretion disks around black holes. We show that for
cases in which the density profile is considered constant (as expected in
highly magnetized flows), or in cases in which the disk density is high enough
such that the ionization still allows line formation within the ISCO, there is
a significant modification of the observed reflected spectrum. Consistent with
previous studies, we found that the impact of the radiation reprocessed in the
plunging region is stronger the lower the black hole spin, when the plunging
region subtends a larger area. Likewise, as for the case of standard reflection
modeling, the relativistic broadening of the iron line is more pronounced at
low inclination, whereas the blueshift and relativistic beaming effect is
dominant at high inclination. We also tested the effects of various
prescriptions of the stress at the ISCO radius on the reflection spectrum, and
found that several of these cases appear to show line profiles distinct enough
to be distinguishable with reasonably good quality observational data.",2312.09210v1
2024-01-05,Joint analysis of the iron emission in the optical and near-infrared spectrum of I Zw 1,"Constraining the physical conditions of the ionized media in the vicinity of
an active supermassive black hole (SMBH) is crucial to understanding how these
complex systems operate. Metal emission lines such as iron (Fe) are useful
probes to trace the gaseous media's abundance, activity, and evolution in these
accreting systems. Among these, the FeII emission has been the focus of many
prior studies to investigate the energetics, kinematics, and composition of the
broad-emission line region (BELR) from where these emission lines are produced.
In this work, we present the first simultaneous FeII modeling in the optical
and near-infrared (NIR) regions. We use CLOUDY photoionization code to simulate
both spectral regions in the wavelength interval 4000-12000 Angstroms. We
compare our model predictions with the observed line flux ratios for IZw1 - a
prototypical strong FeII-emitting active galactic nuclei (AGN). This allows
putting constraints on the BLR cloud density and metal content that is optimal
for the production of the FeII emission, which can be extended to IZw1-like
sources, by examining a broad parameter space. We demonstrate the salient and
distinct features of the FeII pseudo-continuum in the optical and NIR, giving
special attention to the effect of micro-turbulence on the intensity of the
FeII emission.",2401.02936v1
2024-01-16,Bias-Compensated State of Charge and State of Health Joint Estimation for Lithium Iron Phosphate Batteries,"Accurate estimation of the state of charge (SOC) and state of health (SOH) is
crucial for the safe and reliable operation of batteries. Voltage measurement
bias highly affects state estimation accuracy, especially in Lithium Iron
Phosphate (LFP) batteries, which are susceptible due to their flat open-circuit
voltage (OCV) curves. This work introduces a bias-compensated algorithm to
reliably estimate the SOC and SOH of LFP batteries under the influence of
voltage measurement bias. Specifically, SOC and SOH are estimated using the
Dual Extended Kalman Filter (DEKF) in the high-slope SOC range, where voltage
measurement bias effects are weak. Besides, the voltage measurement biases
estimated in the low-slope SOC regions are compensated in the following joint
estimation of SOC and SOH to enhance the state estimation accuracy further.
Experimental results indicate that the proposed algorithm significantly
outperforms the traditional method, which does not consider biases under
different temperatures and aging conditions. Additionally, the bias-compensated
algorithm can achieve low estimation errors of below 1.5% for SOC and 2% for
SOH, even with a 30mV voltage measurement bias. Finally, even if the voltage
measurement biases change in operation, the proposed algorithm can remain
robust and keep the estimated errors of states around 2%.",2401.08136v2
2024-01-19,Reflecting on naked singularities: iron line fitting as a probe of the cosmic censorship conjecture,"We demonstrate that the X-ray iron line fitting technique can be leveraged as
a powerful probe of the cosmic censorship conjecture. We do this by extending
existing emission line models to arbitrary spin parameters of the Kerr metric,
no longer restricted to black hole metrics with $|a_\bullet |< 1$. We show that
the emission lines from naked singularity metrics ($|a_\bullet| > 1$) show
significant differences to their black hole counterparts, even for those
metrics with identical locations of the innermost stable circular orbit, i.e.,
emission line fitting does not suffer from the degeneracy which affects
continuum fitting approaches. These differences are entirely attributable to
the disappearance of the event horizon for $|a_\bullet| > 1$. We highlight some
novel emission line features of naked singularity metrics, such as ``inverted''
emission lines (with sharp red wings and extended blue wings) and ``triple
lines''. The lack of detection of any of these novel features provides support
of the cosmic censorship conjecture. We publicly release {\tt XSPEC} packages
{\tt skline} and {\tt skconv} which can now be used to probe the cosmic
censorship conjecture in Galactic X-ray binaries and Active Galactic Nuclei.
The inclusion of super-extremal spacetimes can be alternatively posed as a way
of stress-testing conventional models of accretion.",2401.10565v1
2024-01-25,Nucleosynthesis in magnetorotational supernovae: impact of the magnetic field configuration,"The production of heavy elements is one of the main by-products of the
explosive end of massive stars. A long sought goal is finding differentiated
patterns in the nucleosynthesis yields, which could permit identifying a number
of properties of the explosive core. Among them, the traces of the magnetic
field topology are particularly important for \emph{extreme} supernova
explosions, most likely hosted by magnetorotational effects. We investigate the
nucleosynthesis of five state-of-the-art magnetohydrodynamic models with fast
rotation that have been previously calculated in full 3D and that involve an
accurate neutrino transport (M1). One of the models does not contain any
magnetic field and synthesizes elements around the iron group, in agreement
with other CC-SNe models in literature. All other models host a strong magnetic
field of the same intensity, but with different topology. For the first time,
we investigate the nucleosynthesis of MR-SNe models with a quadrupolar magnetic
field and a 90 degree tilted dipole. We obtain a large variety of ejecta
compositions reaching from iron nuclei to nuclei up to the third r-process
peak. We assess the robustness of our results by considering the impact of
different nuclear physics uncertainties such as different nuclear masses,
$\beta^{-}$-decays and $\beta^{-}$-delayed neutron emission probabilities,
neutrino reactions, fission, and a feedback of nuclear energy on the
temperature. We find that the qualitative results do not change with different
nuclear physics input. The properties of the explosion dynamics and the
magnetic field configuration are the dominant factors determining the ejecta
composition.",2401.14402v1
2024-02-15,A variable ionized disk wind in MAXI J1803-298 revealed by NICER,"We present the results from the NICER observation data of MAXI J1803-298
across the entire 2021 outburst. In the intermediate and soft state, we detect
significant absorption lines at $\sim 7.0$ keV and $\sim 6.7$ keV, arising from
the X-ray disk wind outflowing with a velocity of hundreds of km per second
along our line of sight. The fitting results from photoionized model suggest
that the wind is driven by thermal pressure and the mass-loss rate is low. We
find a clear transition for iron from predominantly H-like to predominantly
He-like during the intermediate-to-soft state transition. Our results indicate
this transition for iron is caused by the evolution of the illuminating
spectrum and the slow change of the geometric properties of the disk wind
together. The coexistence of disk wind and QPOs features in intermediate state
is also reported. Our study makes MAXI J1803-298 the first source in which a
transition from optical wind to X-ray wind is detected, offering new insights
into the evolution of disk winds across an entire outburst and long-term
coupling of accretion disks and mass outflows around accreting black holes.",2402.10315v1
2024-03-04,Interplay between alloying and tramp element effects on temper embrittlement in bcc iron: DFT and thermodynamic insights,"The details of the temper embrittlement mechanism in steels caused by
impurities are unknown. Especially from an atomistic point of view, there are
still open questions regarding their interactions with alloying elements such
as Ni, Cr, and Mo. Therefore, we used density functional theory to investigate
the segregation and co-segregation behavior and the resulting influence on the
cohesion of three representative tilt grain boundaries in iron. The results are
implemented in a multi-site and multi-component kinetic and thermodynamic model
for grain boundary segregation, to gain insights into the temporal and final
grain boundary coverage. Our results show that the segregation tendency of As,
Sb, and Sn is stronger than that of the alloying elements and significantly
mitigates the grain boundary cohesion. Depending on the GB type, interactions
between Sb and Sn vary from negligible to strongly attractive, which increases
the likelihood of co-segregation. The cohesion-weakening effect is further
amplified when elements such as Sb, Sn, and As co-segregate, compared to their
individual segregation. In contrast, the co-segregation of Ni and Cr does not
significantly increase the enrichment of impurities at grain boundaries, and
their impact on cohesion is found to be negligible. The ability of Mo to
mitigate reversible temper embrittlement is primarily attributed to its
cohesion-enhancing effect and its capability to repel tramp elements from GBs,
rather than scavenging them within the bulk, as suggested by previous
literature.",2403.02186v1
2024-03-10,Conventional Superconductivity in the Doped Kagome Superconductor Cs(V0.86Ta0.14)3Sb5 from Vortex Lattice Studies,"A hallmark of unconventional superconductors is their complex electronic
phase diagrams where ""intertwined orders"" of charge-spin-lattice degrees of
freedom compete and coexist as in copper oxides and iron pnictides. While the
electronic phase diagram of kagome lattice superconductor such as CsV3Sb5 also
exhibits complex behavior involving coexisting and competing charge density
wave order and superconductivity, much is unclear about the microscopic origin
of superconductivity. Here, we study the vortex lattice (VL) in superconducting
state of Cs(V0.86Ta0.14)3Sb5, where the Ta-doping suppresses charge order and
enhances superconductivity. Using small-angle neutron scattering, a strictly
bulk probe, we show that the VL exhibits a strikingly conventional behavior.
This includes a triangular VL with a period consistent with 2e-pairing, a field
dependent scattering intensity that follows a London model, and a temperature
dependence consistent with a uniform superconducting gap expected for s-wave
pairing. These results suggest that optimal bulk superconductivity in
Cs(V1-xTax)3Sb5 arises from a conventional Bardeen-Cooper-Schrieffer
electron-lattice coupling, different from spin fluctuation mediated
unconventional copper and iron based superconductors.",2403.06046v1
2024-03-14,An FFT based approach to account for elastic interactions in OkMC: Application to dislocation loops in iron,"Object kinetic Montecarlo (OkMC) is a fundamental tool for modeling defect
evolution in volumes and times far beyond atomistic models. The elastic
interaction between defects is classically considered using a dipolar
approximation but this approach is limited to simple cases and can be
inaccurate for large and close interacting defects. In this work a novel
framework is proposed to include ""exact"" elastic interactions between defects
in OkMC valid for any type of defect and anisotropic media. In this method, the
elastic interaction energy of a defect is computed by volume integration of its
elastic strain multiplied by the stress created by all the other defects, being
both fields obtained numerically using a FFT solver. The resulting interaction
energies reproduce analytical elastic solutions and show the limited accuracy
of dipole approaches for close and large defects.
  The OkMC framework proposed is used to simulate the evolution in space and
time of self-interstitial atoms and dislocation loops in iron. It is found that
including the anisotropy has a quantitative effect in the evolution of all the
type of defects studied. Regarding dislocation loops, it is observed that using
the ""exact"" interaction energy result in higher interactions than using the
dipole approximation for close loops.",2403.09158v1
2024-03-18,Primary Defect Production in Doped Iron Grain Boundaries during Low Energy Collision Cascades,"This study explores the intricate interactions between grain boundaries (GBs)
and irradiation-induced defects in nanocrystalline iron, highlighting the role
of dopants like copper. Utilizing molecular dynamics simulations, the research
delineates how GB properties, such as GB energy and defect formation energies,
influence the formation and evolution of defects in low energy collision
cascades. It reveals that GBs not only augment defect production but also show
a marked preference for interstitials over vacancies, a behavior significantly
modulated by the cascade's proximity to the GB. The presence of dopants is
shown to alter GB properties, affecting both the rate and type of defect
production, thereby underscoring the complex interplay between GB
characteristics, dopant elements, and defect dynamics. Moreover, the
investigation uncovers that the structural characteristics of GBs play a
crucial role in cascade evolution and defect generation, with certain GB
configurations undergoing reconfiguration in response to cascades. For
instance, the reconfiguration of one pure Fe twist GB suggests that GB geometry
can significantly influence defect generation mechanisms. These findings point
to the potential of GB engineering in developing materials with enhanced
radiation tolerance, advocating for a nuanced approach to material design. By
tailoring GB properties and selectively introducing dopant elements, materials
can be optimized to exhibit superior resistance to radiation-induced damage,
offering insights for applications in nuclear reactors and other
radiation-prone environments.",2403.12257v1
2022-04-02,Direct Measurement of the Nickel Spectrum in Cosmic Rays in the Energy Range from 8.8 GeV/n to 240 GeV/n with CALET on the International Space Station,"The relative abundance of cosmic ray nickel nuclei with respect to iron is by
far larger than for all other trans-iron elements, therefore it provides a
favorable opportunity for a low background measurement of its spectrum. Since
nickel, as well as iron, is one of the most stable nuclei, the nickel energy
spectrum and its relative abundance with respect to iron provide important
information to estimate the abundances at the cosmic ray source and to model
the Galactic propagation of heavy nuclei. However, only a few direct
measurements of cosmic-ray nickel at energy larger than $ \sim$ 3 GeV/n are
available at present in the literature and they are affected by strong
limitations in both energy reach and statistics. In this paper we present a
measurement of the differential energy spectrum of nickel in the energy range
from 8.8 to 240 GeV/n, carried out with unprecedented precision by the
Calorimetric Electron Telescope (CALET) in operation on the International Space
Station since 2015. The CALET instrument can identify individual nuclear
species via a measurement of their electric charge with a dynamic range
extending far beyond iron (up to atomic number $ Z $ = 40). The particle's
energy is measured by a homogeneous calorimeter (1.2 proton interaction
lengths, 27 radiation lengths) preceded by a thin imaging section (3 radiation
lengths) providing tracking and energy sampling. This paper follows our
previous measurement of the iron spectrum [O. Adriani et al., Phys. Rev. Lett.
126, 241101 (2021).], and it extends our investigation on the energy dependence
of the spectral index of heavy elements. It reports the analysis of nickel data
collected from November 2015 to May 2021 and a detailed assessment of the
systematic uncertainties. In the region from 20 to 240 GeV$ /n $ our present
data are compatible within the errors with a single power law with spectral
index $ -2.51 \pm 0.07 $.",2204.00845v1
2020-12-03,On the Use of Field RR Lyrae as Galactic Probes. II. A new $Δ$S calibration to estimate their metallicity,"We performed the largest and most homogeneous spectroscopic survey of field
RR Lyraes (RRLs). We secured $\approx$6,300 high resolution (HR, R$\sim$35,000)
spectra for 143 RRLs (111 fundamental, RRab; 32 first overtone, RRc). The
atmospheric parameters were estimated by using the traditional approach and the
iron abundances were measured by using an LTE line analysis. The resulting iron
distribution shows a well defined metal-rich tail approaching solar iron
abundance. This suggests that field RRLs experienced a complex chemical
enrichment in the early halo formation. We used these data to develop a new
calibration of the $\Delta$S method. This diagnostic, based on the equivalent
widths of CaII K and three Balmer (H$_{\delta,\gamma,\beta}$) lines, traces the
metallicity of RRLs. For the first time the new empirical calibration: i)
includes spectra collected over the entire pulsation cycle; ii) includes RRc
variables; iii) relies on spectroscopic calibrators covering more than three
dex in iron abundance; iv) provides independent calibrations based on
one/two/three Balmer lines. The new calibrations were applied to both
SEGUE-SDSS and degraded HR spectra totalling 6,451 low resolution (LR,
R$\sim$2,000) spectra for 5,001 RRLs (3,439 RRab, 1,562 RRc). This resulted in
an iron distribution with a median of -1.55$\pm$0.01 and $\sigma$=0.51 dex, in
good agreement with literature values. We also found that RRc are 0.10 dex more
metal-poor than RRab variables, and have a distribution with a smoother
metal-poor tail. This finding supports theoretical prescriptions suggesting a
steady decrease in the RRc number when moving from metal-poor to metal-rich
stellar environments.",2012.02284v1
2014-08-28,The Gaia-ESO Survey: the chemical structure of the Galactic discs from the first internal data release,"Most high-resolution spectroscopic studies of the Galactic discs were mostly
confined to objects in the solar vicinity. Here we aim at enlarging the volume
in which individual chemical abundances are used to characterise both discs,
using the first internal data release of the Gaia-ESO survey. We derive and
discuss the abundances of eight elements (Mg, Al, Si, Ca, Ti, Fe, Cr, Ni, and
Y). The trends of these elemental abundances with iron are very similar to
those in the solar neighbourhood. We find a natural division between alpha-rich
and alpha-poor stars, best seen in the bimodality of the [Mg/M] distributions
in bins of metallicity, which we attribute to thick- and thin-disc sequences,
respectively. With the possible exception of Al, the observed dispersion around
the trends is well described by the expected errors, leaving little room for
astrophysical dispersion. Using previously derived distances from Recio-Blanco
et al. (2014b), we further find that the thick-disc is more extended vertically
and is more centrally concentrated towards the inner Galaxy than the thin-disc,
which indicates a shorter scale-length. We derive the radial and vertical
gradients in metallicity, iron, four alpha-element abundances, and Al for the
two populations, taking into account the identified correlation between R_GC
and |Z|. Radial metallicity gradient is found in the thin disc. The positive
radial individual [alpha/M] gradients found are at variance from the gradients
observed in the RAVE survey. The thin disc also hosts a negative vertical
metallicity gradient, accompanied by positive individual [alpha/M] and [Al/M]
gradients. The thick-disc, presents no radial metallicity gradient, a shallower
vertical metallicity gradient than the thin-disc, an alpha-elements-to-iron
radial gradient in the opposite sense than that of the thin disc, and positive
vertical individual [alpha/M] and [Al/M] gradients.",1408.6687v1
2015-09-17,The XMM deep survey in the CDF-S. IX. An X-ray outflow in a luminous obscured quasar at z~1.6,"In active galactic nuclei (AGN)-galaxy co-evolution models, AGN winds and
outflows are often invoked to explain why super-massive black holes and
galaxies stop growing efficiently at a certain phase of their lives. They are
commonly referred to as the leading actors of feedback processes. Evidence of
ultra-fast (v>0.05c) outflows in the innermost regions of AGN has been
collected in the past decade by sensitive X-ray observations for sizable
samples of AGN, mostly at low redshift. Here we present ultra-deep XMM-Newton
and Chandra spectral data of an obscured (Nh~2x10^{23} cm^-2), intrinsically
luminous (L2-10keV~4x10^{44} erg/s) quasar (named PID352) at z~1.6 (derived
from the X-ray spectral analysis) in the Chandra Deep Field-South. The source
is characterized by an iron emission and absorption line complex at observed
energies of E~2-3 keV. While the emission line is interpreted as being due to
neutral iron (consistent with the presence of cold absorption), the absorption
feature is due to highly ionized iron transitions (FeXXV, FeXXVI) with an
outflowing velocity of 0.14^{+0.02}_{-0.06}c, as derived from photoionization
models. The mass outflow rate - ~2 Msun/yr - is similar to the source accretion
rate, and the derived mechanical energy rate is ~9.5x10^{44} erg/s,
corresponding to 9% of the source bolometric luminosity. PID352 represents one
of the few cases where indications of X-ray outflowing gas have been observed
at high redshift thus far. This wind is powerful enough to provide feedback on
the host galaxy.",1509.05413v1
2016-12-08,The distribution of radioactive $^{44}$Ti in Cassiopeia A,"The distribution of elements produced in the inner-most layers of a supernova
explosion is a key diagnostic for studying the collapse of massive stars. Here
we present the results of a 2.4 Ms \textit{NuSTAR} observing campaign aimed at
studying the supernova remnant Cassiopeia A (Cas A). We perform
spatially-resolved spectroscopic analyses of the $^{44}$Ti ejecta which we use
to determine the Doppler shift and thus the three-dimensional (3D) velocities
of the $^{44}$Ti ejecta. We find an initial $^{44}$Ti mass of 1.54 $\pm$ 0.21
$\times 10^{-4}$ M$_{\odot}$ which has a present day average momentum direction
of 340$^{\circ}$ $\pm$ 15$^{\circ}$ projected on to the plane of the sky
(measured clockwise from Celestial North) and tilted by 58$^{\circ}$ $\pm$
20$^{\circ}$ into the plane of the sky away from the observer, roughly opposite
to the inferred direction of motion of the central compact object. We find some
$^{44}$Ti ejecta that are clearly interior to the reverse shock and some that
are clearly exterior to the reverse shock. Where we observe $^{44}$Ti ejecta
exterior to the reverse shock we also see shock-heated iron; however, there are
regions where we see iron but do not observe $^{44}$Ti. This suggests that the
local conditions of the supernova shock during explosive nucleosynthesis varied
enough to suppress the production of $^{44}$Ti in some regions by at least a
factor of two, even in regions that are assumed to be the result of processes
like $\alpha$-rich freezeout that should produce both iron and titanium.",1612.02774v1
2020-06-06,EMPRESS. II. Highly Fe-Enriched Metal-poor Galaxies with $\sim 1.0$ (Fe/O)$_\odot$ and $0.02$ (O/H)$_\odot$ : Possible Traces of Super Massive ($>300 M_{\odot}$) Stars in Early Galaxies,"We present element abundance ratios and ionizing radiation of local young
low-mass (~$10^{6}$ M_sun) extremely metal poor galaxies (EMPGs) with a 2%
solar oxygen abundance (O/H)_sun and a high specific star-formation rate
(sSFR~300 Gyr$^{-1}$), and other (extremely) metal poor galaxies, which are
compiled from Extremely Metal-Poor Representatives Explored by the Subaru
Survey (EMPRESS) and the literature. Weak emission lines such as [FeIII]4658
and HeII4686 are detected in very deep optical spectra of the EMPGs taken with
8m-class telescopes including Keck and Subaru (Kojima et al. 2019, Izotov et
al. 2018), enabling us to derive element abundance ratios with photoionization
models. We find that neon- and argon-to-oxygen ratios are comparable to those
of known local dwarf galaxies, and that the nitrogen-to-oxygen abundance ratios
(N/O) are lower than 20% (N/O)_sun consistent with the low oxygen abundance.
However, the iron-to-oxygen abundance ratios (Fe/O) of the EMPGs are generally
high; the EMPGs with the 2%-solar oxygen abundance show high Fe/O ratios of
~90-140% (Fe/O)_sun, which are unlikely explained by suggested scenarios of
Type Ia supernova iron productions, iron's dust depletion, and metal-poor gas
inflow onto previously metal-riched galaxies with solar abundances. Moreover,
these EMPGs have very high HeII4686/H$\beta$ ratios of ~1/40, which are not
reproduced by existing models of high-mass X-ray binaries whose progenitor
stellar masses are less than 120 M_sun. Comparing stellar-nucleosynthesis and
photoionization models with a comprehensive sample of EMPGs identified by this
and previous EMPG studies, we propose that both the high Fe/O ratios and the
high HeII4686/H$\beta$ ratios are explained by the past existence of super
massive ($>$300 M_sun) stars, which may evolve into intermediate-mass black
holes ($\gtrsim$100 M_sun).",2006.03831v2
2021-07-02,On the use of field RR Lyrae as Galactic probes: IV. New insights into and around the Oosterhoff dichotomy,"We discuss the largest and most homogeneous spectroscopic dataset of field RR
Lyrae variables (RRLs) available to date. We estimated abundances using both
high-resolution and low-resolution ({\Delta S} method) spectra for fundamental
(RRab) and first overtone (RRc) RRLs. The iron abundances for 7,941 RRLs were
supplemented with similar literature estimates available, ending up with 9,015
RRLs (6,150 RRab, 2,865 RRc). The metallicity distribution shows a mean value
of <[Fe/H]> = -1.51\pm0.01, and {\sigma}(standard deviation)= 0.41 dex with a
long metal-poor tail approaching [Fe/H] = -3 and a sharp metal-rich tail
approaching solar iron abundance. The RRab variables are more metal-rich
(<[Fe/H]>ab = -1.48\pm0.01, {\sigma} = 0.41 dex) than RRc variables (<[Fe/H]>c
= -1.58\pm0.01, {\sigma} = 0.40 dex). The relative fraction of RRab variables
in the Bailey diagram (visual amplitude vs period) located along the
short-period (more metal-rich) and the long-period (more metal-poor) sequences
are 80% and 20\%, while RRc variables display an opposite trend, namely 30\%
and 70\%. We found that the pulsation period of both RRab and RRc variables
steadily decreases when moving from the metal-poor to the metal-rich regime.
The visual amplitude shows the same trend, but RRc amplitudes are almost two
times more sensitive than RRab amplitudes to metallicity. We also investigated
the dependence of the population ratio (Nc/Ntot) of field RRLs on the
metallicity and we found that the distribution is more complex than in globular
clusters. The population ratio steadily increases from ~0.25 to ~0.36 in the
metal-poor regime, it decreases from ~0.36 to ~0.18 for -1.8 < [Fe/H] < -0.9
and it increases to a value of ~0.3 approaching solar iron abundance.",2107.00919v1
2018-02-13,Disentangling superconducting and magnetic orders in NaFe_1-xNi_xAs using muon spin rotation,"Muon spin rotation and relaxation studies have been performed on a ""111""
family of iron-based superconductors NaFe_1-xNi_xAs. Static magnetic order was
characterized by obtaining the temperature and doping dependences of the local
ordered magnetic moment size and the volume fraction of the magnetically
ordered regions. For x = 0 and 0.4 %, a transition to a nearly-homogeneous long
range magnetically ordered state is observed, while for higher x than 0.4 %
magnetic order becomes more disordered and is completely suppressed for x = 1.5
%. The magnetic volume fraction continuously decreases with increasing x. The
combination of magnetic and superconducting volumes implies that a
spatially-overlapping coexistence of magnetism and superconductivity spans a
large region of the T-x phase diagram for NaFe_1-xNi_xAs . A strong reduction
of both the ordered moment size and the volume fraction is observed below the
superconducting T_C for x = 0.6, 1.0, and 1.3 %, in contrast to other iron
pnictides in which one of these two parameters exhibits a reduction below TC,
but not both. The suppression of magnetic order is further enhanced with
increased Ni doping, leading to a reentrant non-magnetic state below T_C for x
= 1.3 %. The reentrant behavior indicates an interplay between
antiferromagnetism and superconductivity involving competition for the same
electrons. These observations are consistent with the sign-changing s-wave
superconducting state, which is expected to appear on the verge of microscopic
coexistence and phase separation with magnetism. We also present a universal
linear relationship between the local ordered moment size and the
antiferromagnetic ordering temperature TN across a variety of iron-based
superconductors. We argue that this linear relationship is consistent with an
itinerant-electron approach, in which Fermi surface nesting drives
antiferromagnetic ordering.",1802.04458v1
2022-06-24,The origin and evolution of the normal Type Ia SN 2018aoz with infant-phase reddening and excess emission,"SN~2018aoz is a Type Ia SN with a $B$-band plateau and excess emission in the
infant-phase light curves $\lesssim$ 1 day after first light, evidencing an
over-density of surface iron-peak elements as shown in our previous study.
Here, we advance the constraints on the nature and origin of SN~2018aoz based
on its evolution until the nebular phase. Near-peak spectroscopic features show
the SN is intermediate between two subtypes of normal Type Ia: Core-Normal and
Broad-Line. The excess emission could have contributions from the radioactive
decay of surface iron-peak elements as well as ejecta interaction with either
the binary companion or a small torus of circumstellar material. Nebular-phase
limits on H$\alpha$ and He~I favour a white dwarf companion, consistent with
the small companion size constrained by the low early SN luminosity, while the
absence of [O~I] and He~I disfavours a violent merger of the progenitor. Of the
two main explosion mechanisms proposed to explain the distribution of surface
iron-peak elements in SN~2018aoz, the asymmetric Chandrasekhar-mass explosion
is less consistent with the progenitor constraints and the observed blueshifts
of nebular-phase [Fe~II] and [Ni~II]. The helium-shell double-detonation
explosion is compatible with the observed lack of C spectral features, but
current 1-D models are incompatible with the infant-phase excess emission,
$B_{\rm max}-V_{\rm max}$ color, and absence of nebular-phase [Ca~II]. Although
the explosion processes of SN~2018aoz still need to be more precisely
understood, the same processes could produce a significant fraction of Type Ia
SNe that appear normal after $\sim$ 1 day.",2206.12437v1
2022-10-31,A JWST Near- and Mid-Infrared Nebular Spectrum of the Type Ia Supernova 2021aefx,"We present JWST near- and mid-infrared spectroscopic observations of the
nearby normal Type Ia supernova SN 2021aefx in the nebular phase at $+255$ days
past maximum light. Our Near Infrared Spectrograph (NIRSpec) and Mid Infrared
Instrument (MIRI) observations, combined with ground-based optical data from
the South African Large Telescope (SALT), constitute the first complete optical
$+$ NIR $+$ MIR nebular SN Ia spectrum covering 0.3$-$14 $\mu$m. This spectrum
unveils the previously unobserved 2.5$-$5 $\mu$m region, revealing strong
nebular iron and stable nickel emission, indicative of high-density burning
that can constrain the progenitor mass. The data show a significant improvement
in sensitivity and resolution compared to previous Spitzer MIR data. We
identify numerous NIR and MIR nebular emission lines from iron-group elements
and as well as lines from the intermediate-mass element argon. The argon lines
extend to higher velocities than the iron-group elements, suggesting stratified
ejecta that are a hallmark of delayed-detonation or double-detonation SN Ia
models. We present fits to simple geometric line profiles to features beyond
1.2 $\mu$m and find that most lines are consistent with Gaussian or spherical
emission distributions, while the [Ar III] 8.99 $\mu$m line has a distinctively
flat-topped profile indicating a thick spherical shell of emission. Using our
line profile fits, we investigate the emissivity structure of SN 2021aefx and
measure kinematic properties. Continued observations of SN 2021aefx and other
SNe Ia with JWST will be transformative to the study of SN Ia composition,
ionization structure, density, and temperature, and will provide important
constraints on SN Ia progenitor and explosion models.",2211.00038v2
1995-10-11,Is the X-ray spectrum of the Seyfert 2 galaxy NGC5252 intrinsically flat?,"The first X-ray observation of the Seyfert 2 galaxy NGC5252 is reported. ASCA
collected $\sim 4000$ photons/detector enough to perform an accurate spectral
analysis of this source. The luminosity of NGC5252 is L$_{\rm X}$(0.7-10 keV)
$\simeq 2.6 \times 10^{43}$ erg s$^{-1}$, typical of a Seyfert 1 galaxy. A
simple description of the spectrum with a single power law is ruled out by the
SIS data which shows a strong soft excess at E $\lsimeq$ 1.2 keV. The spectrum
is best fitted by models assuming either partial covering of the central source
or scattering of the X-ray continuum. The best-fit partial covering model
results in a flat ($\Gamma \simeq 1.45 \pm 0.2$) power law continuum emitted by
a source almost completely covered (at $\sim$ 94-97\%) by neutral matter
($N_{\rm H} \simeq (4.3 \pm 0.6) \times 10^{22}$ cm$^{-2}$). The detected iron
line is remarkably weaker (EW $\sim 90 \pm 60$ eV) than normally found from
Seyfert 2 galaxies. In an effort to interpret the observed flat spectrum with
an intrinsically steep power law as predicted by unified models, we also
included in the models neutral reflection, ionized absorption (warm absorber),
and non-uniform cold absorption (dual-absorber). We find that the observed flat
continum {\bf and} weakness of the iron line poses a problem for neutral
reflection models, whatever the assumed geometry is. The use of an ionized
absorber (scattering + warm-absorber model) instead of a neutral absorber seems
not justified with the present data. The ``dual-absorber'' model, representing
nonuniform (density) absorption along the line of sight, may provide an
alternative explanation for the flatness of the spectrum, with no constraints
on the Fe K emission line. Another plausible interpretation of the present data
is that the X-ray spectrum of NGC5252 is truly intrinsically flat. Its strong",9510064v1
1996-04-10,The Hubble constant from $^{56}$Co-powered Nebular Candles,"Type Ia supernovae (SNe Ia), produced by the thermonuclear explosion of white
dwarf (WD) stars, are used here to derive extragalactic distances and an
estimate of the Hubble constant from their emission signatures at late phases
({\it Nebular SNe Ia Method}, NSM). The method, first developed in
Ruiz--Lapuente \& Lucy (1992), makes use here of an improved modeling of the
forbidden line emission at late phases. Hydrodynamic models of the explosion of
WDs of different masses, both sub--Chandrasekhar and Chandrasekhar, provide the
basis for comparison with the observations. It is shown that it is possible to
probe the overall density structure of the ejecta and the mass of the exploding
WD by the effect that the electron density profile has in shaping the forbidden
line emission of the iron ions, and that a robust diagnostic of the mass of the
exploding WD can be obtained. Cosmic distance scale can thus be related to
basic diagnostics of excitation of iron lines. Once the most adequate model is
selected, comparison of the predicted line emission at these phases with the
observed spectra gives an internal estimate of both the reddening and the
distance to the SNe Ia. The results presented here favor denser models than
those corresponding to sub--Chandrasekhar explosions. From a sample of seven
SNe Ia in Leo, Virgo, Fornax and beyond, a value of the Hubble constant $H_{0}
= 68 \ \pm 6\ (stat) \pm 7\ (syst)\ km\ s^{-1}\ Mpc^{-1}$ is derived. The depth
of the Virgo cluster is found to be large, ranging from 13 to 23 Mpc at least.
If NGC 4526 traces well the core of the Virgo Cluster, then the latter is
located at $16\pm 2 \ Mpc$. The galaxy NGC 3267 in Leo appears to be located at
9.8 $\pm$ 1.5 Mpc.",9604044v1
1996-06-27,ASCA observations of Seyfert 1 galaxies: II. Relativistic Iron K-alpha emission,"We present evidence for widespread relativistic effects in the central
regions of active galactic nuclei. In a sample of 18 Seyfert 1 galaxies
observed by \asca, 14 show an iron K$\alpha$ line which is is resolved, with
mean width $\sigma_{\rm K\alpha}=0.43\pm 0.12$~keV for a gaussian profile (Full
Width at Half Maximum, FWHM$\sim 50,000$~km s$^{-1}$). However, many of the
line profiles are asymmetric. A strong red wing is indicative of gravitational
redshifts close to a central black hole and accretion disk models provide an
excellent description of the data. The peak energy of the line is 6.4~keV,
indicating that it arises by fluorescence in near-neutral material. Our fits
imply a low inclination for the disk in these Seyfert 1 galaxies, with a mean
of 30\deg, consistent with orientation-dependent unification schemes.
Differences in the line profiles from source-to-source imply slight variations
in geometry, which cannot be accounted for solely by inclination. In most
cases, we require that the line emission arises from a range of radii. Although
a small contribution to the emission from a region other than the disk is not
ruled out, it is not generally required and has little effect on our
conclusions regarding the disk line. Our data are fit equally well with
rotating (Kerr) and non-rotating (Schwarzschild) black hole models. We find a
mean spectral index in the 3-10 keV range of $<\Gamma_{3-10}>=1.91\pm 0.07$
after accounting for the effects of reflection. Such observations probe the
innermost regions of AGN, and arguably provide the best evidence yet obtained
for the existence of super-massive black holes in the centers of active
galaxies.",9606169v2
1998-04-27,A Strange Star Model for Pulsars,"It is suggested in this paper that the `bare' strange star might be not bare,
and there could be a magnetosphere around it. As a strange star might be an
intensely magnetized rotator, the induced unipolar electric field would be
large enough to construct a magnetosphere around the strange matter core.
  This kind of magnetosphere is very similar to that of the rotating magnetized
neutron stars discussed by many authors. A magnetosphere will be established
very soon through pair production by gamma-B or two photon processes after a
strange star was born in a supernova explosion. It is emphasized that the fact
that the strange star surface can not supply charged particles does not stop
the formation of a space charge separated magnetosphere around the bare strange
star. An accretion crust is quite difficult to come into being around an
isolated strange star. Therefore the observed radio signals of an
rotation-powered pulsar may come from a bare strange stars rather than a
neutron stars or a strange star with an accretion crust. The idea, that the
radio pulsars are the strange stars without crusts, is supported by some
observations. The fact, that the iron emission lines have been observed in many
X-ray pulsars but never been reported in X-ray emission of radio pulsars, is
difficult to be understood if the radio pulsars are the neutron stars or
strange star with crust where the surface binding energy of iron ions is too
low to avoid a ion free-flow from the surface.",9804278v1
1998-10-07,Stellar Metallicities and SNIa Rates in the Early-type Galaxy NGC5846 from ROSAT and ASCA Observations,"In this paper we analyze the diffuse X-ray coronae surrounding the elliptical
galaxy NGC5846, combining measurements from two observatories, ROSAT and ASCA.
We map the gas temperature distribution and find a central cool region within
an approximately isothermal gas halo extending to a radius of about 50 kpc, and
evidence for a temperature decrease at larger radii. With a radially falling
temperature profile, the total mass converges to 9.6+/-1.0 10^12 Msun at ~230
kpc radius. Using the spectroscopic measurements, we also derive radial
distributions for the heavy elements silicon and iron and find that the
abundances of both decrease with galaxy radius. The mass ratio of Si to Fe lies
between the theoretical predictions for element production in SN Ia and SN II,
suggesting an important role for SN Ia, as well as SN II, for gas enrichment in
ellipticals. Using the SN Ia yield of Si, we set an upper limit of 0.012 SNU
for the SN Ia rate at radii >50 kpc, which is independent of possible
uncertainties in the iron L-shell modeling. We compare our observations with
the theoretical predictions for the chemical evolution of ellipticals, taken
from Matteucci & Gibson (1995). We conclude that the metal content in stars, if
explained by the star formation duration, requires a significant decline in the
duration of star formation with galaxy radius, ranging from ~1 Gyr at the
center to ~0.01 Gyr at 100 kpc radius. Alternatively, the decline in
metallicity with galaxy radius may be caused by a similar drop with radius in
the efficiency of star formation. Based on the Si and Fe measurements presented
in this paper, we conclude that the latter scenario is preferred, unless a
dependence of the SN Ia rate on stellar metallicity is invoked. (Abridged).",9810107v1
1999-02-25,"Chemical Evolution on the Scale of Clusters of Galaxies, and Beyond","Clusters of galaxies allow a direct estimate of the metallicity and metal
production yield on the largest scale so far. The ratio of the total iron mass
in the ICM to the total optical luminosity of the cluster (the iron
mass-to-light-ratio) is the same for all clusters which ICM is hotter than
$\sim 2$ keV, and the elemental proportions (i.e. the [$\alpha$/Fe] ratio)
appear to be solar. From these evidences it is argued that both the IMF as well
the relative contributions of SN types are likely to be universal. Constraints
on the past SN activity in galaxy clusters are then derived, and support is
given to the notion that the average SNIa rate was much higher in the past,
i.e. at least 10 times more than currently observed in local ellopticals. It is
also argued that cluster metallicity ($\sim 1/3$ solar) should be taken as
representative of the low-z universe as a whole. There is now compelling
evidence that the bulk of stars in cluster as well as in field ellipticals and
bulges formed at high redshifts ($z\gsim 3$). Since such stars account for at
least $\sim 30%$ of the baryons now locked into stars, it is argued that at
least 30% of stars and metals formed before $z\simeq 3$. As a consequence, the
metallicity of the universe at z=3 is predicted to be $\sim 1/10$ solar. This
requires the cosmic star formation rate to run at least flat from $z\sim 1$ to
$\sim 5$, which appears to agree with the most recent derect determinations of
the star formation rate in Lyman-break galaxies.",9902361v2
1999-04-12,Presupernova Evolution of Rotating Massive Stars I: Numerical Method and Evolution of the Internal Stellar Structure,"The evolution of rotating stars with zero-age main sequence (ZAMS) masses in
the range 8 to 25 M_sun is followed through all stages of stable evolution. The
initial angular momentum is chosen such that the star's equatorial rotational
velocity on the ZAMS ranges from zero to ~ 70 % of break-up. Redistribution of
angular momentum and chemical species are then followed as a consequence of
rotationally induced circulation and instablities. The effects of the
centrifugal force on the stellar structure are included. Uncertain mixing
efficiencies are gauged by observations. We find, as noted in previous work,
that rotation increases the helium core masses and enriches the stellar
envelopes with products of hydrogen burning. We determine, for the first time,
the angular momentum distribution in typical presupernova stars along with
their detailed chemical structure. Angular momentum loss due to (non-magnetic)
stellar winds and the redistribution of angular momentum during core hydrogen
burning are of crucial importance for the specific angular momentum of the
core. Neglecting magnetic fields, we find angular momentum transport from the
core to the envelope to be unimportant after core helium burning. We obtain
specific angular momenta for the iron core and overlaying material of
1E16...1E17 erg s. These values are insensitive to the initial angular
momentum. They are small enough to avoid triaxial deformations of the iron core
before it collapses, but could lead to neutron stars which rotate close to
break-up. They are also in the range required for the collapsar model of
gamma-ray bursts. The apparent discrepancy with the measured rotation rates of
young pulsars is discussed.",9904132v2
1999-07-12,"The Steep Spectrum Quasar PG1404+226 with ASCA, HST and ROSAT","(abridged) We present and discuss our observations of the NL quasar
PG1404+226 with ASCA and HST, and a re-analysis of our earlier observations
with ROSAT. The soft X-ray spectrum is very steep and displays an absorption
feature (edge or line at ~1.1 keV). We have applied a variety of models to the
ASCA and ROSAT spectra without finding a completely satisfactory fit, and the
identification of the edge remains uncertain. A satisfactory fit of the ASCA
spectrum assuming that the edge is produced by highly ionized iron (using the
code absori in XSPEC) is obtained with an overabundance of iron by a factor >
25 compared to solar, a suggestion supported by the extremely high equivalent
width of the Fe K_alpha line at 6.4 keV. A warm absorber model fitting the
absorption feature with NeVII-NeX edges and assuming a peculiar oxygen/neon
abundance ratio is consistent with the ROSAT data but not the ASCA data.
Finally, it is also possible that the observed edge is caused by a OVIII or
OVII edge or line, blueshifted by z_abs=0.2 to 0.5 depending on the specific
identification, as has been suggested previously for 2 other NL quasars, but
there are no other features in the UV and X-ray spectra in support of this
suggestion. Two systems of UV absorption lines, one nearly at rest in the
source frame, the other blueshifted by ~1900 km/s are identified in the HST/FOS
spectra.
  Photoionization models indicate that the UV absorption and the ~1 keV
absorption are probably caused by absorbers with different physical conditions.
PG1404+226 is one more case of AGN where both UV and X-ray absorption features
are detected, thereby increasing further the significance of the previously
noted statistical association of the two types of absorbers.",9907150v1
1999-10-11,ASCA and ROSAT observations of nearby cluster cooling flows,"We present a detailed analysis of the X-ray properties of the cooling flows
in a sample of nearby, X-ray bright clusters of galaxies using high-quality
ASCA spectra and ROSAT X-ray images. We demonstrate the need for multiphase
models to consistently explain the spectral and imaging X-ray data for the
clusters. The mass deposition rates of the cooling flows, independently
determined from the ASCA spectra and ROSAT images, exhibit reasonable
agreement. We confirm the presence of intrinsic X-ray absorption in the
clusters using a variety of spectral models. We also report detections of
extended $100\mu$m infrared emission, spatially coincident with the cooling
flows, in several of the systems studied. The observed infrared fluxes and flux
limits are in good agreement with the predicted values due to reprocessed X-ray
emission from the cooling flows. We present precise measurements of the
abundances of iron, magnesium, silicon and sulphur in the central regions of
the Virgo and Centaurus clusters. Our results firmly favour models in which a
high mass fraction (70-80 per cent) of the iron in the X-ray gas in these
regions is due to Type Ia supernovae. Finally, we present a series of methods
which may be used to measure the ages of cooling flows from the X-ray data. The
results for the present sample of clusters indicate ages of between 2.5 and 7
Gyr. If the ages of cooling flows are primarily set by subcluster merger
events, then our results suggest that in the largest clusters, mergers with
subclusters with masses of approximately 30 per cent of the final cluster mass
are likely to disrupt cooling flows.",9910188v2
1999-11-03,Hard X-ray Emission From Low Mass X-ray Binaries,"We report on Rossi X-ray Timing Explorer observations of four type I X-ray
bursters; namely 1E1724-3045, GS1826-238, SLX1735-269 and KS1731-260. The first
three were in a low state (LS) whereas KS1731-260 was in a high state. The LS
sources have very similar power spectra, displaying high frequency noise up to
\~200 Hz. For KS1731-260, its power spectrum is dominated by noise at
frequencies below 20 Hz. In addition a quasi-periodic oscillation at 1200 Hz is
detected. The 1-200 keV LS spectra are all consistent with resulting from
thermal Comptonization with an electron temperature (kTe) around 25-30 keV. For
KS1731-260, the spectrum is also dominated by Comptonization, but with kTe
around 3 keV and no significant hard X-ray emission. With the exception of
GS1826-238, there is an underlying soft component. For all sources, we have
detected an iron line at 6.4 keV. A reflection component is present in the
spectra of GS1826-238 and SLX1735-269. We suggest a model in which the region
of main energy release, where hard X-rays are produced would be an optically
thin boundary layer merged with an Advection Dominated Accretion Flow (ADAF).
The soft component observed probably represents the unscattered emission from
the accretion disk of variable inner radius. When the accretion rate increases,
the inner disk radius shrinks, the strength of the reflected component and
associated iron line increase, and the Comptonization region cools off in
response to an increased cooling flux from the accretion disk and from the
reprocessed/reflected component. Finally, in the light of these observations,
we discuss extensively the various criteria recently proposed to distinguish
between non-quiescent accreting black holes and neutron stars.",9911042v1
2000-02-10,Atomic data from the Iron Project.XLIII. Transition probabilities for Fe V,"An extensive set of dipole-allowed, intercombination, and forbidden
transition probabilities for Fe V is presented. The Breit-Pauli R-matrix (BPRM)
method is used to calculate 1.46 x 10^6 oscillator strengths for the allowed
and intercombination E1 transitions among 3,865 fine-structure levels dominated
by configuration complexes with n <= 10 and l <= 9. These data are complemented
by an atomic structure configuration interaction (CI) calculation using the
SUPERSTRUCTURE program for 362 relativistic quadrupole (E2) and magnetic dipole
(M1) transitions among 65 low-lying levels dominated by the 3d^4 and 3d^ 4s
configurations. Procedures have been developed for the identification of the
large number of fine-structure levels and transitions obtained through the BPRM
calculations. The target ion Fe VI is represented by an eigenfunction expansion
of 19 fine-structure levels of 3d^3 and a set of correlation configurations. Fe
V bound levels are obtained with angular and spin symmetries SL\pi and J\pi of
the (e + Fe VI) system such that 2S+1 = 5,3,1, L <= 10, J <= 8 of even and odd
parities. The completeness of the calculated dataset is verified in terms of
all possible bound levels belonging to relevant LS terms and transitions in
correspondence with the LS terms. The fine-structure averaged relativistic
values are compared with previous Opacity Project LS coupling data and other
works. The 362 forbidden transition probabilities considerably extend the
available data for the E2 and M1 transtions, and are in good agreement with
those computed by Garstang for the 3d^4 transitions.",0002230v1
2000-03-03,J-Band Infrared Spectroscopy of a Sample of Brown Dwarfs Using Nirspec on Keck II,"Near-infrared spectroscopic observations of a sample of very cool, low-mass
objects are presented with higher spectral resolution than in any previous
studies. Six of the objects are L-dwarfs, ranging in spectral class from L2 to
L8/9, and the seventh is a methane or T-dwarf. These new observations were
obtained during commissioning of NIRSPEC, the first high-resolution
near-infrared cryogenic spectrograph for the Keck II 10-meter telescope on
Mauna Kea, Hawaii. Spectra with a resolving power of R=2500 from 1.135 to 1.360
microns (approximately J-band) are presented for each source. At this
resolution, a rich spectral structure is revealed, much of which is due to
blending of unresolved molecular transitions. Strong lines due to neutral
potassium (K I), and bands due to iron hydride (FeH) and steam (H2O) change
significantly throughout the L sequence. Iron hydride disappears between L5 and
L8, the steam bands deepen and the K I lines gradually become weaker but wider
due to pressure broadening. An unidentified feature occurs at 1.22 microns
which has a temperature dependence like FeH but has no counterpart in the
available FeH opacity data. Because these objects are 3-6 magnitudes brighter
in the near-infrared compared to the I-band, spectral classification is
efficient. One of the objects studied (2MASSW J1523+3014) is the coolest
L-dwarf discovered so far by the 2-Micron All-Sky Survey (2MASS), but its
spectrum is still significantly different from the methane-dominated objects
such as Gl229B or SDSS 1624+0029.",0003035v1
2000-03-06,X-ray Spectra of a large sample of Quasars with ASCA,"The results from an X-ray spectral analysis of a large sample of quasars,
observed with ASCA, are presented. Data reduction leaves 62 quasars, 35
radio-loud and 27 radio-quiet, suitable for spectral analysis. Differences are
found between the radio-quiet quasars (RQQs) and the radio-loud quasars (RLQs),
in agreement with previous studies. A correlation between Gamma and optical
H-beta was also found for the radio-quiet quasars in this sample, whereby the
steepest X-ray spectra tend to be found in those objects with narrow H-beta
widths. The correlation is significant at >99% confidence, confirming the
well-known trend between Gamma and H-beta FWHM in Seyfert 1s (Brandt et al.
1997), but at higher luminosities. Other spectral complexities are observed
from this sample. A soft X-ray excess, with blackbody temperatures in the range
100 - 300 eV, is seen in many low z radio-quiet quasars. In most cases the
temperatures are probably too hot to originate directly from the disk. Iron K
line emission features are also found in the RQQs; but often from partially
ionised material. Indeed in the highest luminosity RQQs there is neither
evidence for iron line emission nor the reflection component expected from disk
models. These observations can be explained by an increase in the quasar
accretion rate with luminosity, leading to an increase in the ionisation state
of the surface layers of the disk. The occurrence of ionised or `warm'
absorbers is rare in this sample, with only 5 detections. However excess
neutral X-ray absorption is found towards several of the high z, predominantly
radio-loud, quasars. Although found to increase with quasar redshift, this
`intrinsic' absorption may be associated with radio-loud AGN.",0003080v1
2000-03-17,ASCA Observation of the New Transient X-ray Pulsar XTE J0111.2-7317 in the Small Magellanic Cloud,"The new transient X-ray pulsar XTE J0111.2-7317 was observed with Advanced
Satellite for Cosmology and Astrophysics (ASCA) on 1998 November 18, a few days
after its discovery with the Proportional Counter Array onboard the Rossi X-ray
Timing Explorer. The source was detected at a flux level of 3.6x10^-10 erg
cm^-2 s^-1 in the 0.7--10.0 keV band, which corresponds to the X-ray luminosity
of 1.8x10^38 erg s^-1, if a distance of 65 kpc for this pulsar in the Small
Magellanic Cloud is assumed. Nearly sinusoidal pulsations with a period of
30.9497 +/- 0.0004 s were unambiguously detected during the ASCA observation.
The pulsed fraction is low and slightly energy dependent with average value of
\~27%. The energy spectrum shows a large soft excess below ~2 keV when fitted
to a simple power-law type model. The soft excess is eliminated if the spectrum
is fitted to an ``inversely broken power-law'' model, in which photon indices
below and above a break energy of 1.5 keV are 2.3 and 0.8, respectively. The
soft excess can also be described by a blackbody or a thermal bremsstrahlung
when the spectrum above ~2 keV is modeled by a power-law. In these models,
however, the thermal soft component requires a very large emission zone, and
hence it is difficult to explain the observed pulsations at energies below 2
keV. A bright state of the source enables us to identify a weak iron line
feature at 6.4 keV with an equivalent width of 50 +/- 14 eV. Pulse phase
resolved spectroscopy revealed a slight hardening of the spectrum and marginal
indication of an increase in the iron line strength during the pulse maximum.",0003251v1
2000-05-31,Accretion disk models and their X-ray reflection signatures. I. Local spectra,"X-ray illumination of accretion disks is an invaluable diagnostic of the
structure of these disks because of the associated iron K$\alpha$ emission.
Here we point out that the resulting reflected spectra depend very sensitively
on the geometry of the X-ray source, and that this fact can be efficiently used
to test these models observationally. In particular, we discuss three different
accretion disk geometries: the ``lamppost model'', accretion disks with
magnetic flares, and the model with a full corona overlying a cold thin disk.
We show that in the case of the lamppost model, unless the X-ray luminosity of
the central source is larger than that of the cold disk by a factor of 10 or
more, a significant fraction of iron in the ionized skin of the disk is in the
hydrogen and helium-like ions. Because these ions have large fluorescence
yields, the resulting reflected spectra look strongly ionized, with Equivalent
Width (EW) of the line {\em increasing} with X-ray luminosity $L_x$ up to the
maximum of $\sim 500$ eV. This situation contrasts to the magnetic flare model,
where the large X-ray flux near flares completely ionizes the skin of the disk
and thus the resulting spectra appear to be that from a neutral material. The
line EW in this model {\em anti-correlates} with X-ray luminosity, and becomes
arbitrarily small when $L_x$ is a good fraction of the Eddington luminosity.
Finally, in the full corona case, due to the additional pressure and weight of
the corona, the gas pressure (and its density) below the corona is always large
enough to make the gas very cool and effectively neutral. No highly ionized
skin forms in such a model. If the corona is Thomson thin, then EW of the line
does not depend on the accretion disk or corona luminosities for the full
corona model.",0005597v1
2000-06-23,The Origin of the X-ray and Ultraviolet Emission in NGC 7469,"We present a spectral analysis of a 30d, near-continuous observation of the
Seyfert 1 galaxy NGC 7469 with RXTE. Daily integrations show strong spectral
changes during the observation. Ourmain result is that we find the X-ray
spectral index to be correlated with the UV flux. Furthermore, the broad-band
X-ray photon flux is also correlated with the UV continuum. These correlations
point towards a model in which the X-rays originate via thermal Comptonization
of UV seed photons. Furthermore, the UV is also correlated with the
extrapolation of the X-ray power law into the soft X-ray/EUV region. Our data
analysis therefore re-opens the possibility the the UV photons and their
variability arise from reprocessing, as long as the primary source of heating
is photo-electric absorption in the reprocessor, rather than Compton
downscattering, A coherent picture of the X-ray/UV variability can therefore be
constructed whereby absorption and reprocessing of EUV/soft X-rays in a
standard accretion disk produce a variable seed photon distribution which are
in turn up-scattered into the X-ray band. We also find a significant
correlation between the 2-10 keV flux and the 6.4 keV iron K-line suggesting
that at least some portion of the line originates within ~1 lt day of the X-ray
continuum source. Neither the power law photon index nor the Compton reflection
component are correlated with the 2-10 keV flux. The latter is not correlated
with the iron K line flux either. We do find an apparent correlation between
the X-ray spectral index and the strength of the Compton reflection component.
In an Appendix we show, however, that this can be produced by a combination of
statistical and systematic errors. We conclude the apparent variations in the
Compton reflection component may be an artifact of these effects.",0006339v1
2000-09-12,The Composite Broad Band Spectrum of Cir X-1 at the Periastron: a Peculiar Z-source,"We report on the spectral analysis of the peculiar source Cir X-1 observed by
the BeppoSAX satellite when the X-ray source was near the periastron. A flare
lasting $\sim 6 \times 10^3$ s is present at the beginning of the observation.
The luminosity during the persistent emission is $1 \times 10^{38}$ erg
s$^{-1}$, while during the flare is $2 \times 10^{38}$ erg s$^{-1}$. We
produced broad band (0.1-100 keV) energy spectra during the flare and the
persistent emission. At low energies the continuum is well fitted by a model
consisting of Comptonization of soft photons, with a temperature of $\sim 0.4$
keV, by electrons at a temperature of $\sim 1$ keV. Out of the flare a
power-law component, with photon index $\sim 3$, is dominant at energies higher
than 10 keV. This component contributes to $\sim 4%$ of the total luminosity.
During the flare its addition is not statistically significant. An absorption
edge at $\sim 8.4$ keV, with optical depth $\sim 1$, corresponding to the
K-edge of Fe XXIII-XXV, and an iron emission line at 6.7 keV are also present.
The iron line energy is in agreement with the ionization level of the
absorption edge. The hydrogen column deduced from the absorption edge is $\sim
10^{24}$ cm$^{-2}$, two order of magnitude larger than the absorption measured
in this source. We calculated the radius of the region originating the
comptonized seed photons, $R_W \sim 150$ km.
  We propose a scenario where $R_W$ is the inner disk radius, a highly ionized
torus surrounds the accretion disk and a magnetosphere is large up to $R_W$.
The absorption edge and the emission line could originate in the photoionized
torus, while the comptonized component originates in an inner region of the
disk.",0009183v1
2000-10-26,A High Resolution Method for Measuring Cosmic Ray Composition beyond 10 TeV,"The accurate determination of the elemental composition of cosmic rays at
high energies is expected to provide crucial clues on the origin of these
particles. Previous direct measurements of composition have been limited by
experiment collecting power, resulting in marginal statistics above $10^{14}$
eV, precisely the region where the ``knee'' of the cosmic-ray energy spectrum
is starting to develop. In contrast, indirect measurements using extensive air
showers can produce sufficient statistics in this region but generate elemental
measurements which have relatively large uncertainties. Here we discuss a
technique which has become possible through the use of modern ground-based
Cerenkov imaging detectors. We combine a measurement of the Cerenkov light
produced by the incoming cosmic-ray nucleus in the upper atmosphere with an
estimate of the total nucleus energy produced by the extensive air shower
initiated when the particle interacts deeper in the atmosphere. The emission
regions prior to and after the first hadronic interaction can be separated by
an imaging Cerenkov system with sufficient angular and temporal resolution.
Monte Carlo simulations indicate an expected charge resolution of $\Delta Z/Z
<5%$ for incident iron nuclei in the region of the ``knee'' of the cosmic-ray
energy spectrum. This technique also has the intriguing possibility to
unambiguously discover nuclei heavier than iron at energies above 10$^{14}$ eV.
The identification and rejection of background produced by charged particles in
ground based gamma-ray telescopes is also discussed.",0010554v2
2000-11-29,Variable X-ray Absorption in the Seyfert 2 Galaxy Mrk 348,"We present RXTE monitoring observations of the Seyfert 2 galaxy Mrk 348
spanning a 6 month period. The time-averaged spectrum in the 3-20 keV band
shows many features characteristic of a Compton-thin Seyfert 2 galaxy, namely a
hard underlying power-law continuum (photon index = 1.8) with heavy soft X-ray
absorption (N_h ~ 10^23 cm^-2) plus measureable iron line emission (equivalent
width ~ 100 eV) and, at high energy, evidence for a reflection component (R <
1). During the first half of the monitoring period the X-ray continuum flux
from Mrk 348 remained relatively steady. However this was followed by a
significant brightening of the source (by roughly a factor of 4) with the
fastest change corresponding to a doubling of its X-ray flux on a timescale of
about 20 days. The flux increase was accompanied by a marked softening of X-ray
spectrum most likely attributable to a factor 3 decline in the intrinsic
line-of-sight column density. In contrast the iron line and the reflection
components showed no evidence of variability. These observations suggest a
scenario in which the central X-ray source is surrounded by a patchy
distribution of absorbing material located within about a light-week of the
nucleus of Mrk 348. The random movement of individual clouds within the
absorbing screen, across our line of sight, produces substantial temporal
variations in the measured column density on timescales of weeks to months and
gives rise to the observed X-ray spectral variability. However, as viewed from
the nucleus the global coverage and typical thickness of the cloud layer
remains relatively constant.",0011542v1
2001-01-22,Spectral Evolution of the Continuum and Disc Line in Dipping in GRO J1655-40,"The discovery is reported of emission features in the X-ray spectrum of GRO
J1655-40 obtained using Rossi-XTE on 1997, Feb 26. The features have been
fitted firstly by two Gaussian lines, which in four spectra have average
energies of 5.85+/-0.08 keV and 7.32+/-0.13 keV, strongly suggestive that these
are the red- and blueshifted wings of an iron disc line from material with
velocity ~0.33 c. The blue wing is apparently less bright than expected for a
disc line subject to Doppler boosting, however, known absorption in the
spectrum of GRO J1655-40 at energies between ~7 and 8 keV can reduce the
apparent brightness of the blue wing. The spectra have also been fitted well
using the full relativistic disc line model of Laor, plus an absorption line.
This gives a restframe energy between 6.4 and 6.8 keV indicating that the line
is from highly ionized iron K_alpha. The Laor model also shows that the line
originates at radii extending from ~10 Schwarzschild radii (r_S) outwards. The
line is direct evidence for the black hole nature of the compact object. The
continuum is well described by dominant disc blackbody emission plus
Comptonized emission. During dipping, spectral evolution is well modelled by
allowing progressive covering of the disc blackbody and simple absorption of
the Comptonized emission showing that the thermal emission is more extended.
Acceptable fits are only obtained by including the disc line in the covering
term, indicating that it originates in the same inner disc region as the
thermal continuum. Dip ingress times and durations are used to provide the
radius of the disc blackbody emitter as 170-370 r_S, and the radius of the
absorber.",0101388v1
2001-05-18,The CHANDRA HETGS X-ray Grating Spectrum of Eta Car,"Eta Car may be the most massive and luminous star in the Galaxy and is
suspected to be a massive, colliding wind binary system. The CHANDRA X-ray
observatory has obtained a calibrated, high-resolution X-ray spectrum of the
star uncontaminated by the nearby extended soft X-ray emisssion. Our 89 ksec
CHANDRA observation with the High Energy Transmission Grating Spectrometer
(HETGS) shows that the hot gas near the star is non-isothermal. The temperature
distribution may represent the emission on either side of the colliding wind
bow shock, effectively ``resolving'' the shock. If so, the pre-shock wind
velocities are ~ 700 and ~ 1800 km/s in our analysis, and these velocities may
be interpreted as the terminal velocities of the winds from Eta Car and from
the hidden companion star. The forbidden-to-intercombination (f/i) line ratios
for the He-like ions of S, Si and Fe are large, indicating that the line
forming region lies far from the stellar photosphere. The iron fluorescent line
at 1.93 Angstrom, first detected by ASCA, is clearly resolved from the thermal
iron line in the CHANDRA grating spectrum. The Fe fluorescent line is weaker in
our CHANDRA observation than in any of the ASCA spectra. The CHANDRA
observation also provides an uninterrupted high-time resolution lightcurve of
the stellar X-ray emission from Eta Car and suggests that there was no
significant, coherent variability during the CHANDRA observation. The Eta Car
CHANDRA grating spectrum is unlike recently published X-ray grating spectra of
single massive stars in significant ways and is generally consistent with
colliding wind emission in a massive binary.",0105335v2
2001-06-29,Secondary antiprotons and propagation of cosmic rays in the Galaxy and heliosphere,"High-energy collisions of cosmic-ray nuclei with interstellar gas are
believed to be the mechanism producing the majority of cosmic ray antiprotons.
Due to the kinematics of the process they are created with a nonzero momentum;
the characteristic spectral shape with a maximum at ~2 GeV and a sharp decrease
towards lower energies makes antiprotons a unique probe of models for particle
propagation in the Galaxy and modulation in the heliosphere. On the other hand,
accurate calculation of the secondary antiproton flux provides a ``background''
for searches for exotic signals from the annihilation of supersymmetric
particles and primordial black hole evaporation. Recently new data with large
statistics on both low and high energy antiproton fluxes have become available
which allow such tests to be performed. We use our propagation code GALPROP to
calculate interstellar cosmic-ray propagation for a variety of models. We show
that there is no simple model capable of accurately describing the whole
variety of data: boron/carbon and sub-iron/iron ratios, spectra of protons,
helium, antiprotons, positrons, electrons, and diffuse gamma rays. We find that
only a model with a break in the diffusion coefficient plus convection can
reproduce measurements of cosmic-ray species, and the reproduction of primaries
(p, He) can be further improved by introducing a break in the primary injection
spectra. For our best-fit model we make predictions of proton and antiproton
fluxes near the Earth for different modulation levels and magnetic polarity
using a steady-state drift model of propagation in the heliosphere.",0106567v2
2001-07-17,The Unique Type Ia Supernova 2000cx in NGC 524,"We present extensive photometric and spectroscopic observations of the Type
Ia supernova (SN Ia) 2000cx in the S0 galaxy NGC 524, which reveal it to be
peculiar. Photometrically, SN 2000cx is different from all known SNe Ia, and
its light curves cannot be fit well by the fitting techniques currently
available. There is an apparent asymmetry in the $B$-band peak, in which the
premaximum brightening is relatively fast (similar to that of the normal SN
1994D), but the postmaximum decline is relatively slow (similar to that of the
overluminous SN 1991T). The color evolution of SN 2000cx is also peculiar: the
$(B - V)_0$ color has a unique plateau phase and the $(V - R)_0$ and $(V -
I)_0$ colors are very blue.
  Although the premaximum spectra of SN 2000cx are similar to those of SN
1991T-like objects (with weak Si II lines), its overall spectral evolution is
quite different. The Si II lines that emerged near maximum $B$-band brightness
stay strong in SN 2000cx until about three weeks past maximum. The change in
the excitation stages of iron-peak elements is slow. Both the iron-peak and the
intermediate-mass elements are found to be moving at very high expansion
velocities in the ejecta of SN 2000cx.
  We discuss theoretical models for SN 2000cx. SN 2000cx may be an overluminous
object like SN 1991T, but with a larger yield of $^{56}$Ni and a higher kinetic
energy in the ejecta. We also briefly discuss the implications of our
observations for the luminosity vs. light-curve width relation.",0107318v1
2001-09-03,The BeppoSAX 0.1 - 100 keV Spectrum of the X-ray Pulsar 4U 1538-52,"We report the results of temporal and spectral analysis performed on the
X-ray pulsar 4U 1538-52 observed by BeppoSAX. We obtained a new estimate of the
spin period of the neutron star P=528.24 \pm 0.01 s (corrected for the orbital
motion of the X-ray source): the source is still in the spin-up state, as since
1988. The pulse profile is double peaked, although significant variations of
the relative intensity of the peaks with energy are present. The broad band
(0.12-100 keV) out-of-eclipse spectrum is well described by an absorbed power
law modified by a high energy cutoff at \sim 16 keV (e-folding energy \sim 10
keV) plus an iron emission line at \sim 6.4 keV. A cyclotron line at \sim 21
keV is present. The width of the line is consistent with thermal Doppler
broadening at the temperature of the exponential cutoff. We searched for the
presence of the second harmonic, previously reported for this source. We found
no evidence of lines at \sim 42 keV, although an absorption feature at 51 keV
seems to be present (at 99% confidence level). A soft excess, modelled by a
blackbody with a temperature of \sim 0.08 keV could be present, probably
emitted by the matter at the magnetosphere. We also performed a spectral
analysis during the X-ray eclipse. The spectral evolution during the eclipse
can be well described by a progressive covering of the primary Comptonization
spectrum that is scattered into the line of sight. During the deep eclipse this
spectrum also softens, suggesting that the dust-scattered component becomes
important. An alternative, more complex model, with an emission iron line and
scattered components (as the one that has been used to fit the eclipse of
Centaurus X-3), also gives a good fit of the deep-eclipse data.",0109031v1
2001-10-08,The Population of Weak MgII Absorbers. II The Properties of Single-Cloud Systems,"We present an investigation of MgII absorbers characterized as single-cloud
weak systems at z~1. We measured column densities and Doppler parameters for
MgII and FeII in 15 systems found in HIRES/Keck spectra at 6.6 km/s. Using
these quantities and CIV, Lyman alpha and Lyman limit absorption observed with
FOS/HST (resolution ~230 km/s) we applied photoionization models to each system
to constrain metallicities, densities, ionization conditions, and sizes.
  We find that: (1) Single-cloud weak systems are optically thin in neutral
hydrogen and may have their origins in a population of objects distinct from
the optically thick strong MgII absorbers, which are associated with bright
galaxies. (2) Weak systems account for somewhere between 25% to 100% of the z <
1 Lyman alpha forest clouds in the range 15.8<log N(HI)<16.8 cm^-2. (3) At
least seven of 15 systems have two or more ionization phases of gas (multiphase
medium). (4) We identify a subset of weak MgII absorber that we term
``iron-rich''. These clouds are not alpha-group enhanced and are constrained to
have sizes of ~10 pc. At that size, to produce the observed redshift path
density, they would need to outnumber L* galaxies by approximately six orders
of magnitude.
  We discuss these results and the implications that the iron-rich systems
require enrichment from Type Ia supernovae. Further, we address how star
clusters or supernova remnants in dwarf galaxies might give rise to absorbers
with the inferred properties. This would imply far larger numbers of such
objects than are presently known, even locally. We compare the weak systems to
the weak kinematic subsystems in strong MgII absorbers and to Galactic high
velocity clouds. (abridged)",0110191v1
2001-10-29,Kinetic equilibrium of iron in the atmospheres of cool dwarf stars II. Weak Fe I lines in the solar spectrum,"NLTE line formation calculations of FeI in the solar atmosphere are extended
to include weak optical lines. Previously established atomic models are used to
discriminate between different ways of treating collisional interaction
processes. To derive a common solar FeI abundance from both strong and weak
lines, fine-tuning of the microturbulence velocity parameter and the van-der-
Waals damping constants is required. The solar FeI abundances based on all
available f-values are dominated by the large scatter already found for the
stronger lines. In particular the bulk of the data from the work of May et al.
and O'Brian et al. is not adequate for accurate abundance work. Based on
f-values measured by the Hannover and Oxford groups alone, the FeI LTE
abundances are eps(FeI,Sun)=7.57 for the empirical and eps(FeI,Sun) = 7.48 ...
7.51 for the line-blanketed solar model. The solar Fe ionization equilibrium
obtained for different atomic and atmospheric models rules out NLTE atomic
models with a low efficiency of hydrogen collisions. At variance with Paper I,
it is now in better agreement with laboratory FeII f-values for all types of
line-blanketed models. Our final model assumptions consistent with a single
unique solar Fe abundance eps(Fe,Sun) = 7.48 ... 7.51 calculated from NLTE line
formation are (a) a line-blanketed solar model atmosphere, (b) an iron model
atom with hydrogen collision rates 0.5 < S_H < 5 times the standard value to
compensate for the large photoionization cross-sections, (c) a microturbulence
velocity xi = 1.0 kms, (d) van-der-Waals damping parameters decreased by
Delta(log C6) = -0.10...-0.15 as compared to Anstee & O'Mara's calculations,
depending on S_H, (e) FeII f-values as published by Schnabel et al., and (f)
FeI f-values published by the Hannover and Oxford groups.",0110605v1
2002-02-04,The structure and radiation spectra of illuminated accretion discs in AGN. I. Moderate illumination,"We present detailed computations of the vertical structure of an accretion
disc illuminated by hard X-ray radiation with the code {\sc titan-noar}
suitable for Compton thick media. The energy generated via accretion is
dissipated partially in the cold disc as well as in the X-ray source. We study
the differences between the case where the X-ray source is in the form of a
lamp post above the accretion disc and the case of a heavy corona. We consider
radiative heating via Comptonization together with heating via photo-absorption
on numerous heavy elements as carbon, oxygen, silicon, iron. The transfer in
lines is precisely calculated. A better description of the heating/cooling
through the inclusion of line transfer, a correct description of the
temperature in the deeper layers, a correct description of the entire disc
vertical structure, as well as the study of the possible coronal pressure
effect, constitute an improvement in comparison to previous works. We show that
exact calculations of hydrostatic equilibrium and determination of the disc
thickness has a crucial impact on the optical depth of the hot illuminated
zone. We assume a moderate illumination where the viscous flux equals the X-ray
radiation flux. A highly ionized skin is created in the lamp post model, with
the outgoing spectrum containing many emission lines and ionization edges in
emission or absorption in the soft X-ray domain, as well as an iron line at
$\sim 7 $ keV consisting of a blend of low ionization line from the deepest
layers and hydrogen and helium like resonance line from the upper layers, and
almost no absorption edge, contrary to the case of a slab of constant density.A
full heavy corona completely suppresses the highly ionized zone on the top of
the accretion disc and in such case the spectrum is featureless.",0202069v2
2002-02-21,The BeppoSAX view of bright Compton-thin Seyfert 2 galaxies,"We present the analysis of 31 observations of 20 bright Compton thin Seyfert
2s, in the 0.1-200 keV band, performed with the BeppoSAX satellite. The sample
consists of all Seyfert 2s in the BeppoSAX public archive, with a 2-10 keV flux
higher than 5x10^(-12) erg/cm^2/s. The good statistics available and the broad
energy band permit a detailed study of the main continuum components of these
sources, i.e. the primary power-law, the reflected component, the soft emission
and the high-energy cut-off. The main results of our analysis are: (1) the
3-200 keV intrinsic power-law has a mean photon index Gamma=1.79+-0.01, with a
dispersion of sigma=0.23. (2) The high-energy exponential cut-off at E~100-300
keV is not an ubiquitous property of Seyfert galaxies: in ~30% of the objects
the continuum power-law does not drop up to energies of 300 keV or more. (3) A
reflected component is present in almost all the sources (17 out of 21). The
small variations of this component with respect to the intrinsic continuum, in
objects with multiple observations, suggests that the reflector is not the
accretion disk, but must be located much farther from the nucleus. (4) The
range of ratios between the reflected and intrinsic components suggests that
the circumnuclear medium is not homogeneous, and a significant fraction of the
solid angle is covered by a gas thicker than that along the line of sight. (5)
The iron Kalpha line is present is all but one the sources. The equivalent
width is in the typical range of Seyfert 1s (EW=100-300 eV) in sources with low
absorption (N_H < 3x10^23 cm^(-2)), and increases in more absorbed objects, as
expected according to unified models. (6) The energy resolution of BeppoSAX is
in general too low to measure the iron line width. However, in 6 cases we
measured a significant line broadening.",0202392v1
2002-03-05,The Reddest Quasars II. A gravitationally-lensed FeLoBAL quasar,"We report the discovery of a z=2.65 low-ionization iron broad absorption line
quasar, FIRST J100424.9+122922, which is gravitationally-lensed by a galaxy at
z~0.95. The object was discovered as part of a program to find very red quasars
by matching the FIRST radio survey with the 2-MASS near-infrared survey.
J100424.9+122922 is the second lensed system to be found in this program,
suggesting that many gravitational lenses are probably missed from conventional
optical quasar surveys. We have made a simple lens model and a rough estimate
of the reddening in the immediate environment of the quasar which suggests that
the quasar is intrinsically very luminous and is accreting at close to the
Eddington limit of its ~10^9 M_sun black hole. The lensing galaxy has a small
amount of dust which is responsible for some excess reddening observed in the
fainter image of the quasar, but is otherwise a fairly typical massive
elliptical galaxy. We model the selection effects working against the detection
of red quasars in both lensed and unlensed samples. We show that these
selection effects are very effective at removing even lightly-reddened high
redshift quasars from magnitude-limited samples, whether they are lensed or
not. This suggests that the red quasar population in general could be very
large, and in particular the class of iron broad absorption line quasars of
which J100424.9+122922 is a member may be much larger than their rarity in
magnitude-limited samples would suggest.",0203065v1
2002-04-03,Characterising the complex absorber in NGC 4151,"We present a detailed analysis of the complex absorption apparent in the 2-6
keV X-ray spectrum of the bright nearby Seyfert galaxy NGC 4151. We first
utilize the large bandpass and medium spectral resolution afforded by BeppoSAX
data to construct a 1-100 keV spectral template, which assumes the absorption
arises in both warm (i.e. partially photoionized) and cold gas present in the
line of sight to the active nucleus of the source. Application of this spectral
model to an ASCA ""long-look"" observation of NGC 4151 reveals a partial
correlation between the underlying continuum flux and the ionization state of
the warm absorber. Such a correlation is an intrinsic property of a warm
absorber and argues strongly in favour of this interpretation for the complex
absorbing column over alternative partial covering models. The inferred
relatively low density for the warm gas, implies an equilibration timescale for
the dominant ions of the same order or longer than the timescale of the
continuum variability. It follows that the warm component will invariably be
observed in a non-equilibrium ionization state.
  We also find that (i) the reported hardening of the spectrum of NGC 4151 as
the continuum level falls may be simply due to the presence of an underlying
(hard and relatively constant) Compton-reflection component and (ii) the iron
Ka line has a relatively narrow Gaussian profile and a line flux that remains
constant over both short (days) and long (months to years) timescales - a
relativistically broadened iron Ka feature was not required in our modelling.",0204057v2
2002-06-20,"Membership, metallicity and lithium abundances for solar-type stars in NGC 6633","We present spectroscopic observations of candidate F, G and K type stars in
NGC 6633, an open cluster with a similar age to the Hyades. We identify 10 new
cluster members including one short period binary system. Combining this survey
with that of Jeffries (1997), we identify a total of 30 solar-type members. We
have used the F and early G stars to spectroscopically estimate
[Fe/H]=-0.096+/-0.081 for NGC 6633 and with more precision that NGC 6633 has
(0.074+/-0.041) dex less iron than the Pleiades and (0.206+/-0.040) dex less
iron than the Hyades. Lithium abundances have been estimated for the NGC 6633
members and compared with consistently determined Li abundances in other
clusters. Several mid F stars in NGC 6633 show strong Li depletion at
approximately the same effective temperature that this phenomenon is seen in
the Hyades. At cooler temperatures the Li abundance patterns in several open
clusters with similar ages (NGC 6633, Hyades, Praesepe and Coma Berenices) are
remarkably similar, despite their differing [Fe/H]. There is however evidence
that the late G and K stars of NGC 6633 have depleted less Li than their Hyades
counterparts. This qualitatively agrees with models for pre-main sequence Li
depletion that feature only convective mixing, but these models cannot
simultaneously explain why these stars have in turn depleted Li by more than 1
dex compared with their ZAMS counterparts in the Pleiades. Two explanations are
put forward. The first is that elemental abundance ratios, particularly [O/Fe],
may have non-solar values in NGC 6633 and would have to be higher than in
either the Hyades or Pleiades. The second is that additional non-convective
mixing, driven by angular momentum loss, causes additional photospheric Li
depletion during the first few hundred Myr of main sequence evolution.",0206367v1
2002-08-08,BeppoSAX observations of the EXS 1737.9-2952 region II: Analysis of sources,"(Abridged) Spectral and time variability analysis of the region of the hard
X-ray transient EXS 1737.9-2952 near the Galactic Centre (GC), using data from
the Narrow Field Instruments of BeppoSAX is reported. The main results are the
MECS spectra of the 10 identified sources. Fluxes obtained with spectral fits
are 1.7-4.8E-12 erg / cm2 s. The absorption is in the range N_H=0.5-6.7E22 /
cm2, indicating that the sources are at least at the distance of the GC, and
thus have L_x > 2-5E34 erg/s (2-10 keV). A powerlaw with photon index 1.1-1.8
generally gives a fair fit, but a strong iron line (at 6-7 keV) is evident for
5 sources and exists at lower confidence in the others. The fits indicate
differences in line position in the range 6.1-7.0 keV suggesting that the
ionisation state and/or emission mechanism may not be the same in all sources.
The time-binned data indicates that two sources are variable on a time scale of
hours at confidence > 99.99%, and one at 99.67%. These sources could be
low-mass X-ray binaries. The other sources are most probably X-ray binaries or
SNRs. A MECS spectrum from a subfield including 8 of the new sources and a
major contribution of diffuse emission yielded a fairly good fit to a power-law
spectrum with photon index 1.3 and a strong iron line at 6.8 keV. Another field
with only residual emission and no point sources yielded spectral parameters
close to the diffuse emission near GC observed by other investigators, except
for the high interstellar absorption. The PDS spectrum of the same region is
more difficult to interpret due to lack of spatial resolution and a larger FOV
that contains the bright hard X-ray source 1E1740.7-2942. The source for the
hard X-ray transient EXS 17137.9-2952 cannot be identified from the present
observations.",0208179v1
2002-08-22,Chemical Abundances in Twelve Red Giants of the Large Magellanic Cloud from High-Resolution Infrared Spectroscopy,"High-resolution infrared spectra (R=50,000) have been obtained for twelve
red-giant members of the LMC with the Gemini South 8.3-meter telescope plus
Phoenix spectrometer. Quantitative chemical abundances of carbon-12, carbon-13,
nitrogen-14, and oxygen-16 were derived from molecular lines of CO, CN, and OH,
while sodium, scandium, titanium, and iron abundances were derived from neutral
atomic lines. The LMC giants have masses from about 1 to 4 solar masses and
span a metallicity range from [Fe/H]= -1.1 to -0.3. The program red giants all
show evidence of first dredge-up mixing, with low 12C/13C ratios, and low 12C
correlated with high 14N abundances. Comparisons of the oxygen-to-iron ratios
in the LMC and the Galaxy indicate that the trend of [O/Fe] versus [Fe/H] in
the LMC falls about 0.2 dex below the Galactic trend. Such an offset can be
modeled as due to an overall lower rate of supernovae per unit mass in the LMC
relative to the Galaxy, as well as a slightly lower ratio of supernovae of type
II to supernovae of type Ia.",0208417v1
2002-10-10,Abundances in Stars from the Red Giant Branch Tip to Near the Main Sequence Turn Off in M5,"We present the iron abundance and abundance ratios for 18 elements with
respect to Fe in a sample of stars with a wide range in luminosity from
luminous giants to stars near the turnoff in the globular cluster M5. The
analyzed spectra, obtained with HIRES at the Keck Observatory, are of high
dispersion (R=35,000). We find that the neutron capture, the iron peak and the
alpha-element abundance ratios show no trend with Teff, and low scatter around
the mean between the top of the RGB and near the main sequence turnoff To
within the precision of the measurements (~0.1 dex), gravitationally induced
heavy element diffusion does not appear to be present among the stars near the
main sequence turnoff studied here. Our work and other recent studies suggest
that heavy element diffusion is inhibited in the surface layers of metal poor
stars. Differences in the Na abundance from star to star which extend to the
main sequence turnoff are detected in our sample in M5. The anti-correlation
between O and Na abundances, observed in other metal poor globular clusters, is
not detected in our sample, but it may be hidden among stars with only upper
limits for their O abundances. Overall the abundance ratios of M5 appear very
similar to those of M71, with the possible exception of the neutron capture
element Ba, where we argue that the apparent difference may be due to
difficulties in the analysis. As in M71, the alpha-elements Mg, Ca, Si and Ti
are overabundant relative to Fe. The results of our abundance analysis of 25
stars in M5 provide further evidence of abundance variations among specific
light elements at unexpectedly low luminosities, which cannot be explained by
our current understanding of stellar evolution.",0210245v1
2003-02-24,XMM-NEWTON High Resolution Spectroscopy of NGC 5548,"We analyze a 137 ks exposure X-ray spectrum of the Seyfert 1 galaxy NGC 5548
obtained with the XMM-Newton Reflection Grating Spectrometer. Due to the long
exposure time, the spectrum is of higher statistical quality than the previous
observations of this AGN. Therefore, we detect for the first time in NGC 5548
inner-shell transitions from O III to O VI ions, and the Unresolved Transition
Array of M-shell iron. The warm absorber found from this X-ray observation
spans three orders of magnitude in ionization parameter. We detect O III, which
is as lowly ionized as the warm absorber detected in the UV band, to Fe XXIV.
For O VI the column density determined from our X-ray data is an order of
magnitude larger than the column density measured in previous UV observations.
We conclude that there is substantially more low ionized material than
previously deduced from UV observations. However, only a few percent of the
warm absorber detected in the X-rays is lowly ionized. A 99.9 % significant
increase in the derived absorbing column density with higher ionization states
is observed. The outflow velocities determined from the X-ray absorption lines
are consistent with those deduced from the UV lines, evidence, together with
the detection of O VI, that the X-ray and UV warm absorber are different
manifestations of the same phenomenon. From a simple mass conservation
argument, we indicate that our data set is consistent with an outflow with
small opening angle formed due to instabilities in the accretion disk. Possible
due to uncertainties in the radiative transport mechanism, an apparent deviant
iron to oxygen abundance is detected. No strong relativistically broadened
emission lines of O VIII, N VII and C VI were detected.",0302493v1
2003-03-03,XMM-Newton and Chandra Observations of the Galaxy Group NGC 5044. II. Metal Abundances and Supernova Fraction,"Using new XMM and Chandra observations we present an analysis of the metal
abundances of the hot gas within a radius of 100 kpc of the bright nearby
galaxy group NGC 5044. Motivated by the inconsistent abundance and temperature
determinations obtained by different observers for X-ray groups, we provide a
detailed investigation of the systematic errors on the derived abundances
considering the effects of the temperature distribution, calibration, plasma
codes, bandwidth, Galactic Nh, and background rate. The iron abundance (Fe)
drops from Fe ~1 solar within R ~50 kpc to Fe ~0.4 solar near R=100 kpc. This
radial decline in Fe is highly significant: Fe=1.09 +/- 0.04 solar (stat) +/-
0.05 solar + 0.18 solar (sys) within R=48 kpc (5') compared to Fe=0.44 +/- 0.02
solar (stat) +/- 0.10 solar + 0.13 solar (sys) over R=48-96 kpc (5'-10'). The
data rule out with high confidence a very sub-solar value for Fe within R=48
kpc confirming that previous claims of very sub-solar central Fe values in NGC
5044 were primarily the result of the Fe Bias: i.e., the incorrect assumption
of spatially isothermal and single-phase gas when in fact temperature
variations exist. Within R=48 kpc we obtain Si/Fe = 0.83 +/- 0.02 (stat) +/-
0.02 + 0.07 (sys) and S/Fe = 0.54 +/- 0.02 (stat) +/- 0.01 + 0.01 (sys) in
solar units. These ratios are consistent with their values at larger radii and
imply that SNIa have contributed ~80% of the iron mass within a 100 kpc radius
of NGC 5044. This SNIa fraction is similar to the Sun and suggests an IMF
similar to that of the Milky Way. At the very center (R ~2 kpc) the XMM and
Chandra CCDs and the XMM RGS show that the Fe drops to ~50% of its value at
immediately larger radius analogously to that seen in some galaxy clusters.
(Abridged)",0303054v2
2003-04-01,Near-IR Properties of Galaxy Clusters: Luminosity as a Binding Mass Predictor and the State of Cluster Baryons,"We explore the near-infrared properties of galaxies within 27 galaxy clusters
using data from the Two Micron All Sky Survey (2MASS). For a subsample of 13
clusters with available X-ray imaging data, we examine both the properties of
the galaxies and the intracluster medium. We show that the K-band luminosity is
correlated with cluster mass, providing a binding mass estimate accurate to
45%. The mass to light ratio in our ensemble increases by a factor of ~2 over
the cluster mass range (10^{14}-10^{15}M_sun). We examine the total baryon
fraction, showing that it is an increasing function of cluster mass. Using the
mass to light ratio of massive clusters, we find that Omega_M=0.19+/-0.03;
using the total baryon fraction we find that Omega_M=0.28+/-0.03, in good
agreement with recent cosmic microwave background anisotropy constraints.
Differences between these two estimates suggest that the K-band mass to light
ratio in massive clusters may be lower than that in the universe by as much as
\~30%.
  We examine the stellar mass fraction, the ICM mass to stellar mass ratio and
the cluster iron mass fraction. The stellar mass fraction decreases by a factor
of 1.8 from low to high mass clusters, and the ICM to stellar mass ratio
increases from 5.9 to 10.4 over the same mass range. Together, these
measurements suggest a decrease of star formation efficiency with increasing
cluster mass and provide constraints on models of the thermodynamic history of
the intracluster medium. The cluster iron mass to total mass ratio is constant
and high, suggesting that some efficient, and uniform enrichment process may
have taken place before the bulk of stars in cluster galaxies formed.",0304033v2
2003-04-09,Peculiar Broad Absorption Line Quasars found in DPOSS,"With the recent release of large (i.e., > hundred million objects),
well-calibrated photometric surveys, such as DPOSS, 2MASS, and SDSS,
spectroscopic identification of important targets is no longer a simple issue.
In order to enhance the returns from a spectroscopic survey, candidate sources
are often preferentially selected to be of interest, such as brown dwarfs or
high redshift quasars. This approach, while useful for targeted projects, risks
missing new or unusual species. We have, as a result, taken the alternative
path of spectroscopically identifying interesting sources with the sole
criterion being that they are in low density areas of the g - r and r - i
color-space defined by the DPOSS survey. In this paper, we present three
peculiar broad absorption line quasars that were discovered during this
spectroscopic survey, demonstrating the efficacy of this approach. PSS
J0052+2405 is an Iron LoBAL quasar at a redshift z = 2.4512 with very broad
absorption from many species. PSS J0141+3334 is a reddened LoBAL quasar at z =
3.005 with no obvious emission lines. PSS J1537+1227 is a Iron LoBAL at a
redshift of z = 1.212 with strong narrow Mgii and Feii emission. Follow-up high
resolution spectroscopy of these three quasars promises to improve our
understanding of BAL quasars. The sensitivity of particular parameter spaces,
in this case a two-color space, to the redshift of these three sources is
dramatic, raising questions about traditional techniques of defining quasar
populations for statistical analysis.",0304166v1
2003-04-11,The Contribution of Particle Impact to the Production of Fe K Emission from Accreting Black Holes,"The iron K line is perhaps the most important spectral diagnostic available
in the study of accreting black holes. The line is thought to result from the
reprocessing of external X-rays by the surface of the accretion disk. However,
as is observed in the solar corona, illumination by energetic particles may
also produce line emission. In principle, such a process may be uncorrelated
with the observed X-rays and could explain some of the unexpected variability
behavior of the Fe line. This paper compares predictions of iron K flux
generated by impacting electrons and protons to that from photoionization.
Non-thermal power-laws of electrons are considered as well as thermal
distributions of electrons and virialized protons. The electrons are thought to
originate in a magnetically dominated accretion disk corona, while the protons
are considered in the context of a two phase (hot/cold) accretion scenario. In
each case, the Fe K flux from particle impact is found to be < 1% of that
produced by photoionization by a hard X-ray power-law (normalized to the same
energy flux as the particles). Thus, the electrons or protons must strike the
disk with 100--10,000 times more energy flux than radiation for particle impact
to be a significant producer of Fe K flux. This situation is difficult to
reconcile with the observations of hard X-ray spectra, or the proposed particle
acceleration mechanisms in the accretion disk corona. Truncated accretion flows
must be externally illuminated by hard X-rays in order to produce the Fe line,
as proton impact is very inefficient in generating line emission. In contrast
to the Sun, our conclusion is that, with the possible exception for localized
regions around magnetic footpoints, particle impact will not be an important
contributor to the X-ray emission in accreting black holes.",0304218v1
2003-04-14,BeppoSAX Observations of Centaurus A: the Hard Continuum and the Iron Line Feature,"The radio galaxy Centaurus A was observed by the BeppoSAX satellite five
times from 1997 to 2000. From July 6 1999 to August 17 1999, the source was
also simultaneously pointed by COMPTEL on-board of the satellite CGRO.
Centaurus A has a complex spectrum with multiple extended components and a
strongly absorbed (N_H\sim 10^{23}$ cm${-2}) nucleus well fitted by a power law
(\Gamma \sim 1.8) which bends at high energies. When the BeppoSAX and COMPTEL
observations are combined together, an exponential cutoff with e-folding energy
\sim 1000 keV gives an adequate description of the spectral steepening. A
complex feature in emission at 6-7 keV is resolved into two Fe components, one
narrow cold line and an ionized line centred at 6.8 keV. Significant variations
have been observed in the iron feature, with the less prominent ionized line
seemingly being the only one responsible for them: its variations do not appear
to correlate with the strength of the continuum. The high energy cutoff and the
Fe feature suggest the presence of an accretion flow in the Centaurus A
nucleus. However the absence of a significant reflection, the narrowness of the
cold line as well as the lack of correlation between the continuum and 6.8 keV
line variations disfavour a standard cold/ionized thin disk (at least in the
inner regions). A more plausible configuration might be a hot thick optically
thin accretion flow surrounded by material with different opacities.
  Finally, we note that high energy break observed by BeppoSAX and COMPTEL
could be also reasonably explained by Inverse Compton radiation from a jet. If
this is the case, a structured jet with outer slow layers surrounding a beamed
inner region is necessary to explain the strong Fe feature observed by
BeppoSAX.",0304244v1
2003-06-13,Abundances in the Neutral Interstellar Medium of I Zw 18 from FUSE Observations,"We report on new FUSE far-UV spectroscopy of the most metal-poor blue compact
dwarf galaxy I Zw 18. The new data represent an improvement over previous FUSE
spectra by a factor of 1.7 in the signal-to-noise. Together with a larger
spectral coverage (917-1188 angstroms), this allows us to characterize
absorption lines in the interstellar medium with unprecedented accuracy. The
kinematics averaged over the large sampled region shows no clear evidence of
gas inflows or outflows. The H I absorption is interstellar with a column
density of 2.2 (+0.6,-0.5} * 10^21 cm^(-2). A conservative 3 sigma upper limit
of 5.25 * 10^(14) cm^(-2) is derived for the column density of diffuse H_2.
  From a simultaneous fitting of metal absorption lines in the interstellar
medium, we infer the following abundances: [Fe/H] = -1.76 +/- 0.12, [O/H] =
-2.06 +/- 0.28, [Si/H] = -2.09 +/- 0.12, [Ar/H] = -2.27 +/- 0.13, and [N/H] =
-2.88 +/- 0.11. This is in general several times lower than in the H II
regions. The only exception is iron, whose abundance is the same. The abundance
pattern of the interstellar medium suggests ancient star-formation activity
with an age of at least a Gyr that enriched the H I phase. Around 470 SNe Ia
are required to produce the iron content. A more recent episode that started 10
to several 100 Myr ago is responsible for the additional enrichment of
alpha-elements and nitrogen in the H II regions.",0306290v1
2003-06-17,Kinetic equilibrium of iron in the atmospheres of cool stars III. The ionization equilibrium of selected reference stars,"Non-LTE line formation calculations of Fe I are performed for a small number
of reference stars to investigate and quantify the efficiency of neutral
hydrogen collisions. Using the atomic model that was described in previous
publications, the final discrimination with respect to hydrogen collisions is
based on the condition that the surface gravities as determined by the Fe I/Fe
II ionization equilibria are in agreement with their astrometric counterparts
obtained from HIPPARCOS parallaxes. Depending on the choice of the hydrogen
collision scaling factor S_H, we find deviations from LTE in Fe I ranging from
0.00 (S_H = infinity) to 0.46 dex (S_H = 0 for HD140283) in the logarithmic
abundances while Fe II follows LTE.
  With the exception of Procyon, for which a mild temperature correction is
needed to fulfil the ionization balance, excellent consistency is obtained for
the metal-poor reference stars if Balmer profile temperatures are combined with
S_H = 3. The correct choice of collisional damping parameters (""van-der-Waals""
constants) is found to be generally more important for these little evolved
metal-poor stars than considering departures from LTE. For the Sun the
calibrated value for S_H leads to average Fe I non-LTE corrections of 0.02 dex
and a mean abundance from Fe I lines of log epsilon(Fe) = 7.49 \pm 0.08.
  We confront the deduced stellar parameters with comparable spectroscopic
analyses by other authors which also rely on the iron ionization equilibrium as
a gravity indicator. On the basis of the HIPPARCOS astrometry our results are
shown to be an order of magnitude more precise than published data sets, both
in terms of offset and star-to-star scatter.",0306337v1
2003-08-01,Variations in the Abundance Pattern of Extremely Metal-poor Stars and Nucleosynthesis in Population III Supernovae,"We calculate nucleosynthesis in Population (Pop) III supernovae (SNe) and
compare the yields with various abundance patterns of extremely metal-poor
(EMP) stars. We assume that the observed EMP stars are the second generation
stars, which have the metal-abundance patterns of Pop III SNe. Previous
theoretical yields of Pop III SNe cannot explain the trends in the abundance
ratios among iron-peak elements (Mn, Co, Ni, Zn)/Fe as well as the large C/Fe
ratio observed in certain EMP stars with [Fe/H] <~ -2.5. In the present paper,
we show that if we introduce higher explosion energies and mixing-fallback in
the core-collapse SN models of M ~ 20 - 130 Msun, the above abundance features
of both typical and C-rich EMP stars can be much better explained. We suggest
that the abundance patterns of the [Fe/H] ~ -2.5 stars correspond to supernova
yields with normal explosion energies, while those of the carbon un-enhanced
([C/Fe] < 1) stars with [Fe/H] =~ -4 ~ - 3 correspond to high-energy supernova
yields. The abundance patterns of the C-rich ([C/Fe]>~ 2) and low [Fe/H] (=~ -5
\~ -3.5) stars can be explained with the yields of faint SNe that eject little
56Ni as observed in SN1997D. In the supernova-induced star formation model, we
can qualitatively explain why the EMP stars formed by the faint or energetic
supernovae have lower [Fe/H] than the EMP stars formed by normal supernovae. We
also examine how the abundance ratios among iron-peak elements depend on the
electron mole fraction Ye, and conclude that a large explosion energy is still
needed to realize the large Co/Fe and Zn/Fe ratios observed in typical EMP
stars with [Fe/H] <~ -3.5.",0308029v3
2003-11-24,Sulphur and zinc abundances in Galactic stars and damped Lyman-alpha systems,"High resolution spectra of 34 halo population dwarf and subgiant stars have
been obtained with VLT/UVES and used to derive sulphur abundances from the
8694.0, 8694.6 A and 9212.9, 9237.5 A SI lines. In addition, iron abundances
have been determined from 19 FeII lines and zinc abundances from the 4722.2,
4810.5 ZnI lines. The abundances are based on a classical 1D, LTE model
atmosphere analysis, but effects of 3D hydrodynamical modelling on the [S/Fe],
[Zn/Fe] and [S/Zn] ratios are shown to be small. We find that most halo stars
with metallicities in the range -3.2 < [Fe/H] < -0.8 have a near-constant
[S/Fe] = +0.3; a least square fit to [S/Fe] vs. {Fe/H] shows a slope of only
-0.04 +/- 0.01. Among halo stars with -1.2 < [Fe/H] < -0.8 the majority have
[S/Fe] ~ +0.3, but two stars (previously shown to have low [alpha/Fe] ratios)
have [S/Fe] ~ 0. For disk stars with [Fe/H] > -1, [S/Fe] decreases with
increasing [Fe/H]. Hence, sulphur behaves like other typical alpha-capture
elements, Mg, Si and Ca. Zinc, on the other hand, traces iron over three orders
of magnitude in [Fe/H], although there is some evidence for a small systematic
Zn overabundance ([Zn/Fe] ~ +0.1) among metal-poor disk stars and for halo
stars with [Fe/H] < -2.0. Recent measurements of S and Zn in ten damped
Ly-alpha systems (DLAs) with redshifts between 1.9 and 3.4 and zinc abundances
in the range -2.1 < [Zn/H] < -0.15 show an offset relative to the [S/Zn] -
[Zn/H] relation in Galactic stars. Possible reasons for this offset are
discussed, including low and intermittent star formation rates in DLAs.",0311529v1
2004-01-21,First Stellar Abundances in the Dwarf Irregular Galaxy Sextans A,"We present the abundance analyses of three isolated A-type supergiant stars
in the dwarf irregular galaxy Sextans A from high-resolution spectra the UVES
spectrograph at the VLT. Detailed model atmosphere analyses have been used to
determine the stellar atmospheric parameters and the elemental abundances of
the stars. The mean iron group abundance was determined from these three stars
to be [(FeII,CrII)/H]=-0.99+/-0.04+/-0.06. This is the first determination of
the present-day iron group abundances in Sextans A. These three stars now
represent the most metal-poor massive stars for which detailed abundance
analyses have been carried out. The mean stellar alpha element abundance was
determined from the alpha element magnesium as
[alpha(MgI)/H]=-1.09+/-0.02+/-0.19. This is in excellent agreement with the
nebular alpha element abundances as determined from oxygen in the H II regions.
These results are consistent from star-to-star with no significant spatial
variations over a length of 0.8 kpc in Sextans A. This supports the nebular
abundance studies of dwarf irregular galaxies, where homogeneous oxygen
abundances are found throughout, and argues against in situ enrichment. The
alpha/Fe abundance ratio is [alpha(MgI)/FeII,CrII]=-0.11+/-0.02+/-0.10, which
is consistent with the solar ratio. This is consistent with the results from
A-supergiant analyses in other Local Group dwarf irregular galaxies but in
stark contrast with the high [alpha/Fe] results from metal-poor stars in the
Galaxy, and is most clearly seen from these three stars in Sextans A because of
their lower metallicities. The low [alpha/Fe] ratios are consistent with the
slow chemical evolution expected for dwarf galaxies from analyses of their
stellar populations.",0401411v1
2004-03-15,Raising the Dead: Clues to Type Ia Supernova Physics from the Remnant 0509-67.5,"We present Chandra X-ray observations of the young supernova remnant (SNR)
0509-67.5 in the Large Magellanic Cloud (LMC), believed to be the product of a
Type Ia supernova (SN Ia). The remnant is very round in shape, with a distinct
clumpy shell-like structure. Our Chandra data reveal the remnant to be rich in
silicon, sulfur, and iron. The yields of our fits to the global spectrum
confirm that 0509-67.5 is the remnant of an SN Ia and show a clear preference
for delayed detonation explosion models for SNe Ia. We study the spectrum of
the single brightest isolated knot in the remnant and find that it is enhanced
in iron by a factor of roughly two relative to the global remnant abundances.
This feature, along with similar knots seen in Tycho's SNR, argues for the
presence of modest small-scale composition inhomogeneities in SNe Ia. The
presence of both Si and Fe, with abundance ratios that vary from knot to knot,
indicates that these came from the transition region between the Si- and
Fe-rich zones in the exploded star, possibly as a result of energy input to the
ejecta at late times due to the radioactive decay of 56Ni and 56Co. Two cases
for the continuum emission from the global spectrum were modeled: one where the
continuum is dominated by hydrogen thermal bremsstrahlung radiation; another
where the continuum arises from non-thermal synchrotron radiation. The former
case requires a relatively large value for the ambient density (~1 cm^-3).
Another estimate of the ambient density comes from using the shell structure of
the remnant in the context of dynamical models. This requires a much lower
value for the density (<0.05 cm^-3) which is more consistent with other
evidence known about 0509-67.5. We therefore conclude that the bulk of the
continuum emission from 0509-67.5 has a non-thermal origin.",0403343v2
2004-04-20,XMM-Newton EPIC observations of 21 low-redshift PG quasars,"We present an X-ray spectral analysis of 21 low redshift quasars observed
with XMM-Newton EPIC. All the sources are Palomar Green quasars with redshifts
between 0.05 and 0.4 and have low Galactic absorption along the line-of-sight.
A large majority of quasars in the sample (19/21) exhibit a significant soft
excess below ~1-1.5keV, whilst two objects (PG1114+445 and IZw1) show a deficit
of soft X-ray flux due to the presence of a strong warm absorber. At least half
of the objects appear to harbor a warm absorber, as found previously in Seyfert
1 galaxies. We find significant detections of FeKalpha emission lines in at
least twelve objects, whilst there is evidence for some broadening of the line
profile, compared to the EPIC-pn resolution, in five of these quasars.
  The determination of the nature of this broadening (e.g., Keplerian motion, a
blend of lines, relativistic effects) is not possible with the present data and
requires either higher S/N or higher resolution spectra. In seven objects the
line is located between 6.7-7keV, corresponding to highly ionized iron, whereas
in the other five objects the line energy is consistent with 6.4 keV, i.e.
corresponding to near neutral iron. The ionized lines tend to be found in the
quasars with the steepest X-ray spectra. We also find a correlation between the
continuum power law index and the optical Hbeta width, in both the soft and
hard X-ray bands, whereby the steepest X-ray spectra are found in objects with
narrow Hbeta widths, which confirms previous ROSAT and ASCA results. The soft
and hard band X-ray photon indices are also strongly correlated, i.e. the
steepest soft X-ray spectra correspond the steepest hard X-ray spectra.",0404385v1
2004-08-23,"Detectability of GRB Iron Lines by Swift, Chandra and XMM","The rapid acquisition of positions by the upcoming Swift satellite will allow
the monitoring for X-ray lines in GRB afterglows at much earlier epochs than
was previously feasible. We calculate the possible significance levels of iron
line detections as a function of source redshift and observing time after the
trigger, for the Swift XRT, Chandra ACIS and XMM Epic detectors. For bursts
with standard luminosities, decay rates and equivalent widths of 1 keV assumed
constant starting at early source-frame epochs, Swift may be able to detect
lines up to z~1.5 with a significance of better than 3 sigma for times up to
10^4 s. The same lines would be detectable with better than 4 sigma
significance at z up to 6 by Chandra, and up to 8 by XMM, for times of up to
10^5 s. For similar bursts with a variable equivalent width peaking at 1 keV
between 0.5 and 1 days in the source frame, Swift achieves the same
significance level for z~1 at t~1 day, while Chandra reaches the previous
detection significances around t~ 1-2 days for z~ 2-4, i.e. the line is
detectable near the peak equivalent width times, and undetectable at earlier or
later times. For afterglows in the upper range of initial X-ray luminosites
afterglows, which may also be typical of pop. III bursts, similar significance
levels are obtained out to substantially higher redshifts. A distinction
between broad and narrow lines to better than 3 sigma is possible with Chandra
and XMM out to z~2 and ~6.5, respectively, while Swift can do so up to z~1, for
standard burst parameters. A distinction between different energy centroid
lines of 6.4 keV vs. 6.7 KeV (or 6.7 keV vs. Cobalt 7.2 keV) is possible up to
z~0.6, 1.2, and 2 (z~ 1, 5, 7.5), with Swift,Chandra, and XMM respectively.",0408414v3
2005-02-16,The FUSE Spectrum of the Planetary Nebula SwSt 1: Evidence for Inhomogeneities in the Gas and Dust,"[Abridged] We present Far Ultraviolet Spectroscopic Explorer (FUSE)
observations of the young, compact planetary nebula (PN) SwSt 1 along the line
of sight to its central star HD 167362. We detect circumstellar absorption
lines from several species against the continuum of the central star. The
physical parameters of the nebula derived from the FUSE data differ
significantly from those found from emission lines. We derive an electron
density n_e = 8800^{+4800}_{-2400} cm^{-3} from the column density ratio of the
excited S III fine structure levels, which is at least a factor of 3 lower than
all prior estimates. The gaseous iron abundance derived from the UV lines is
quite high ([Fe/S] = -0.35+/-0.12), which implies that iron is not
significantly depleted into dust. In contrast, optical and near-infrared
emission lines indicate that Fe is more strongly depleted: [Fe/H] =
-1.64+/-0.24 and [Fe/S] = -1.15+/-0.33. We do not detect nebular H_2
absorption, to a limit N(H_2) < 7\times10^14 cm^{-2}, at least four orders of
magnitude lower than the column density estimated from infrared H_2 emission
lines. Taken together, the lack of H_2 absorption, low n_e, and high gaseous Fe
abundance derived from the FUSE spectrum provide strong evidence that dense
structures (which can shield molecules and dust from the destructive effects of
energetic stellar photons) are not present along the line of sight to the
central star. On the other hand, there is substantial evidence for dust,
molecular material, and dense gas elsewhere in SwSt 1. Therefore, we conclude
that the nebula must have an inhomogeneous structure.",0502321v1
2005-08-18,Spectroscopic abundance analysis of dwarfs in young open cluster IC 4665,"We report a detailed spectroscopic abundance analysis for a sample of 18 F-K
dwarfs of the young open cluster IC 4665. Stellar parameters and element
abundances of Li, O, Mg, Si, Ca, Ti, Cr, Fe and Ni have been derived using the
spectroscopic synthesis tool SME (Spectroscopy Made Easy). Within the
measurement uncertainties the iron abundance is uniform with a standard
deviation of 0.04 dex. No correlation is found between the iron abundance and
the mass of the stellar convective zone, and between the Li abundance and the
Fe abundance. In other words, our results do not reveal any signature of
accretion and therefore do not support the scenario that stars with planets
(SWPs) acquire their on the average higher metallicity compared to field stars
via accretion of metal-rich planetary material. Instead the higher metallicity
of SWPs may simply reflect the fact that planet formation is more efficient in
high metallicity environs. However, since that many details of the planet
system formation processes remain poorly understood, further studies are needed
for a final settlement of the problem of the high metallicity of SWPs.
  The standard deviation of [Fe/H] deduced from our observations, taken as an
upper limit on the metallicity dispersion amongst the IC 4665 member stars, has
been used to constrain proto-planetary disk evolution, terrestrial and giant
planets formation and evolution processes. Our results do not support the
possibility that the migration of gas giants and the circularization of
terrestrial planets' orbits are regulated by their interaction with a residual
population of planetesimals and dust particles.",0508387v1
2005-12-20,Elemental Abundance Survey of The Galactic Thick Disk,"[Abridged abstract] We have performed an abundance analysis for 176 F- and G-
dwarfs of the Galactic thick disk component. Using accurate radial velocities
combined with $Hipparcos$ astrometry, kinematics (U, V, and W) and Galactic
orbital parameters were computed. We estimate the probability for a star to
belong to the thin disk, the thick disk or the halo.
  Abundances of C, O, Na, Mg, Al, Si, Ca, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu,
Zn, Y, Ba, Ce, Nd, and Eu have been obtained. The abundances for thick disk
stars are compared with those for thin disk members from Reddy et al. (2003).
The ratios of $\alpha$-elements (O, Mg, Si, Ca and Ti) to iron for thick disk
disk stars show a clear enhancement compared to thin disk members in the range
$-0.3 <$ [Fe/H] $ < -1.2$. There are also other elements -- Al, Sc, V, Co, and
possibly Zn -- which show enhanced ratios to iron in the thick disk relative to
the thin disk. The abundances of Na, Cr, Mn, Ni, and Cu (relative to Fe) are
very similar for thin and thick disk stars. The dispersion in abundance ratios
[X/Fe] at given [Fe/H] for thick disk stars is consistent with the expected
scatter due to measurement errors, suggesting a lack of `cosmic' scatter. The
observed compositions of the thin and thick disks seem to be consistent with
models of galaxy formation by hierarchical clustering in a $\Lambda$CDM
universe. In particular, the distinct abundance patterns observed in the thin
and thick disks, and the chemical homogeneity of the thick disk at different
galactocentric distances favor a scenario in which the majority of thick-disk
stars were formed {\it in situ}, from gas rich merging blocks.",0512505v1
2006-01-20,The Hamburg/ESO R-process Enhanced Star survey (HERES) III. HE 0338-3945 and the formation of the r+s stars,"We have derived abundances of 33 elements and upper limits for 6 additional
elements for the metal-poor ([Fe/H] = -2.42) turn-off star HE 0338-3945 from
high-quality VLT-UVES spectra. The star is heavily enriched, by about a factor
of 100 relative to iron and the Sun, in the heavy s-elements (Ba, La, ..). It
is also heavily enriched in Eu, which is generally considered an r-element, and
in other similar elements. It is less enriched, by about a factor of 10, in the
lighter s-elements (Sr, Y and Zr). C is also strongly enhanced and, to a
somewhat lesser degree, N and O. These abundance estimates are subject to
severe uncertainties due to NLTE and thermal inhomogeneities which are not
taken into detailed consideration. However, an interesting result, which is
most probably robust in spite of these uncertainties, emerges: the abundances
derived for this star are very similar to those of other stars with an overall
enhancement of all elements beyond the iron peak.
  We have defined criteria for this class of stars, r+s stars, and discuss nine
different scenarios to explain their origin. None of these explanations is
found to be entirely convincing. The most plausible hypotheses involve a binary
system in which the primary component goes through its giant branch and
asymptotic giant branch phases and produces CNO and s-elements which are dumped
onto the observed star. Whether the r-element Eu is produced by supernovae
before the star was formed (perhaps triggering the formation of a low-mass
binary), by a companion as it explodes as a supernova (possibly triggered by
mass transfer), or whether it is possibly produced in a high-neutron-density
version of the s-process is still unclear. Several suggestions are made on how
to clarify this situation.",0601476v1
2006-02-27,Chemical evolution in Sersic 159-03 observed with XMM-Newton,"Using a new long X-ray observation of the cluster of galaxies Sersic 159-03
with XMM-Newton, we derive radial temperature and abundance profiles using
single- and multi-temperature models. The fits to the EPIC and RGS spectra
prefer multi-temperature models especially in the core. The radial profiles of
oxygen and iron measured with EPIC/RGS and the line profiles in RGS suggest
that there is a dip in the O/Fe ratio in the centre of the cluster compared to
its immediate surroundings. A possible explanation for the large scale
metallicity distribution is that SNIa and SNII products are released in the ICM
through ram-pressure stripping of in-falling galaxies. This causes a peaked
metallicity distribution. In addition, SNIa in the central cD galaxy enrich
mainly the centre of the cluster with iron. This excess of SNIa products is
consistent with the low O/Fe ratio we detect in the centre of the cluster. We
fit the abundances we obtain with yields from SNIa, SNII and Population-III
stars to derive the clusters chemical evolution. We find that the measured
abundance pattern does not require a Population-III star contribution. The
relative contribution of the number of SNIa with respect to the total number of
SNe which enrich the ICM is about 25-50%. Furthermore, we discuss the possible
presence of a non-thermal component in the EPIC spectra. A potential source of
this non-thermal emission can be inverse-Compton scattering between Cosmic
Microwave Background (CMB) photons and relativistic electrons, which are
accelerated in bow shocks associated with ram-pressure stripping of in-falling
galaxies.",0602582v1
2006-03-10,Metal Enrichment of the ICM: a 3-D Picture of Chemical and Dynamical Properties,"We develop a model for the metal enrichment of the intracluster medium (ICM)
that combines a cosmological non-radiative hydrodynamical N-Body/SPH simulation
of a cluster of galaxies, and a semi-analytic model of galaxy formation. The
novel feature of our hybrid model is that the chemical properties of the
diffuse gas in the underlying simulation are dynamically and consistently
generated from stars in the galaxies. We follow the production of several
chemical elements, provided by low- and intermediate-mass stars, core collapse
and type Ia supernovae. We analyse the spatial distribution of metals in the
ICM, investigate the way in which the chemical enrichment proceeds, and use
iron emissivity as a tracer of gas motions. Fe and O radial abundance profiles
are enhanced in the inner 100 h^-1 kpc in the last Gyr because of the
convergence of enriched gas clumps to the cluster centre. Our results support a
scenario in which part of the central intracluster gas comes from gas clumps
that, in the redshift range of z~0.2 to ~0.5, have been enriched to solar
values and are at large distances from the cluster centre (from ~1 to ~6 h^-1
Mpc) moving at very high velocities (from ~1300 to ~2500 km s^-1). The
turbulent gas motions within the cluster, originated in the inhomogeneous gas
infall during the cluster assembly, are manifested in emission-weighted
velocity maps as gradients that can be as large as ~1000 km s^-1 over distances
of a few hundred kpc. Gradients of this magnitude are also seen in velocity
distributions along sightlines through the cluster centre. Doppler shifting and
broadening suffered by the Fe K 6.7 keV emission line along such sightlines
could be used to probe these gas large-scale motions when they are produced
within an area characterised by high iron line emissivity.",0603270v1
2006-04-05,Abundance analysis of 5 early-type stars in the young open cluster IC2391,"It is unclear whether chemically peculiar stars of the upper main sequence
represent a class completely distinct from normal A-type stars, or whether
there exists a continuous transition from the normal to the most peculiar late
F- to early B-type stars. A systematic abundance analysis of open cluster
early-type stars would help to relate the observed differences of the chemical
abundances of the photospheres to other stellar characteristics, without being
concerned by possible different original chemical composition. Furthermore, if
a continuous transition region from the very peculiar to the so called normal
A-F stars exists, it should be possible to detect objects with mild
peculiarities. As a first step of a larger project, an abundance analysis of 5
F-A type stars in the young cluster IC2391 was performed using high resolution
spectra obtained with the UVES instrument of the ESO VLT. Our targets seem to
follow a general abundance pattern: close to solar abundance of the light
elements and iron peak elements, heavy elements are slightly overabundant with
respect to the sun, similar to what was found in previous studies of normal
field A-type stars of the galactic plane. We detected a weakly chemically
peculiar star, HD74044. Its element pattern contains characteristics of CP1 as
well as CP2 stars, enhanced abundances of iron peak elements and also higher
abundances of Sc, Y, Ba and Ce. We did not detect a magnetic field in this star
(detection limit was 2kG). We also studied the star SHJM2, proposed as a
pre-main sequence object in previous works. Using spectroscopy we found a high
surface gravity, which suggests that the star is very close to the ZAMS.",0604100v1
2006-06-20,"Diffuse, Non-Thermal X-ray Emission from the Galactic Star Cluster Westerlund 1","We present the diffuse X-ray emission identified in Chandra observations of
the young, massive Galactic star cluster Westerlund 1. After removing
point-like X-ray sources down to a completeness limit of 2e31 erg/s, we
identify 3e34 erg/s (2--8 keV) of diffuse emission. The spatial distribution of
the emission can be described as a slightly-elliptical Lorentzian core with a
half-width half-maximum along the major axis of 25+/-1"", similar to the
distribution of point sources in the cluster, plus a 5' halo of extended
emission. The spectrum of the diffuse emission is dominated by a hard continuum
component that can be described as a kT>3 keV thermal plasma that has a low
iron abundance (<0.3 solar), or as non-thermal emission that could be stellar
light that is inverse-Compton scattered by MeV electrons. Only 5% of the flux
is produced by a kT=0.7 keV plasma. The low luminosity of the thermal emission
and the lack of a 6.7 keV iron line suggests that <40,000 unresolved stars with
masses between 0.3 and 2 Msun are present in the cluster. Moreover, the flux in
the diffuse emission is a factor of two lower than would be expected from a
supersonically-expanding cluster wind, and there is no evidence for thermal
remnants produced by supernovae. Less than 1e-5 of the mechanical luminosity of
the cluster is dissipated as 2--8 keV X-rays, leaving a large amount of energy
that either is radiated at other wavelengths, is dissipated beyond the bounds
of our image, or escapes into the intergalactic medium.",0606492v1
2006-08-06,"The magnetic Bp star 36 Lyncis, II. A spectroscopic analysis of its co-rotating disk","We report on the physical properties of the disk-like structure of B8 IIIp
star 36 Lyncis from line syntheses of phase-resolved, high resolution spectra
obtained from the IUE archives and from newly obtained ground-based H$\alpha$
spectra. This disk is highly inclined to the rotational axis and betrays its
existence every half rotation cycle as one of two opposing sectors pass in
front of the star. Although the disk absorption spectrum is at least ten times
too weak to be visible in optical iron lines during these occultations, its
properties can be readily examined in a large number of UV ""iron curtain"" lines
because of their higher opacities. The analysis of the variations of the UV
resonance lines brings out some interesting details about the radiative
properties of the disks: (1) they are optically thick in the C IV and Si IV
doublets, (2) the range of excitation of the UV resonance lines is larger at
the primary occultation ($\phi$ = 0.00) than at the secondary one, and (3) the
{\bf relative strengths of the absorption peaks} for the two occultations
varies substantially from line to line. We have modeled the absorptions of the
UV C IV resonance and H$\alpha$ absorptions by means of a simulated disk with
opaque and translucent components. Our simulations suggest that a gap separates
the star and the inner edge of the disk. The disk extends radially out to
$\geq$10 R$_{*}$. The disk scale height perpendicular to the plane is
$\approx$1R$_{*}$. However, the sector causing the primary occultation is about
four times thicker than the opposite sector. The C IV scattering region extends
to a larger height than the H$\alpha$ region does, probably because it results
from shock heating far from the cooler disk plane.",0608134v1
2006-09-14,Evidence for relativistic features in the X-ray spectrum of Mrk 335,"We present an analysis of hard X-ray features in the spectrum of the bright
Sy 1 galaxy Mrk 335 observed by the XMM-Newton satellite. Our analysis confi
rms the presence of a broad, ionised iron Kalpha emission line in the spectrum,
first found by Gondoin et al. The broad line can be modeled successfully by
relativistic accretion disc reflection models. This interpretation is unusually
robust in the case of Mrk 335 because of the lack of any ionised (`` warm'')
absorber and the absence a clear narrow core to the line. Partial covering by
neutral gas cannot, however, be ruled out statistically as the origin of the
broad residuals. Regardless of the underlyin g continuum we report, for the
first time in this source, the detection of a narrow absorption feature at the
rest frame energy of ~5.9 keV. If the feature is identified with a resonance
absorption line of iron in a highly ionised medium, the redshift of the line
corresponds to an inflow velocity of ~0.11 -0.15 c. We present a simple model
for the inflow, accounting approximate ly for relativistic and radiation
pressure effects, and use Monte Carlo methods to compute synthetic spectra for
qualitative comparison with the data. This mode ling shows that the absorption
feature can plausibly be reproduced by infalling gas providing that the feature
is identified with Fe xxvi. We require the inflowing gas to extend over a
limited range of radii at a few tens of rg to match the observed feature. The
mass accretion rate in the flow correspond s to 60% of the Eddington limit, in
remarkable agreement with the observed rate . The narrowness of the absorption
line tends to argue against a purely gravitational origin for the redshift of
the line, but given the current data quality we stress that such an
interpretation cannot be ruled out.",0609414v1
2006-09-20,Type Ia Supernova Light Curves,"The diversity of Type Ia supernova (SN Ia) photometry is explored using a
grid of 130 one-dimensional models. It is shown that the observable properties
of SNe Ia resulting from Chandrasekhar-mass explosions are chiefly determined
by their final composition and some measure of ``mixing'' in the explosion. A
grid of final compositions is explored including essentially all combinations
of 56Ni, stable ``iron'', and intermediate mass elements that result in an
unbound white dwarf. Light curves (and in some cases spectra) are calculated
for each model using two different approaches to the radiation transport
problem. Within the resulting templates are models that provide good
photometric matches to essentially the entire range of observed SNe Ia. On the
whole, the grid of models spans a wide range in B-band peak magnitudes and
decline rates, and does not obey a Phillips relation. In particular, models
with the same mass of 56Ni show large variations in their light curve decline
rates. We identify the physical parameters responsible for this dispersion, and
consider physically motivated ``cuts'' of the models that agree better with the
Phillips relation. For example, models that produce a constant total mass of
burned material of 1.1 +/- Msun do give a crude Phillips relation, albeit with
much scatter. The scatter is further reduced if one restricts that set to
models that make 0.1 to 0.3 Msun of stable iron and nickel isotopes, and then
mix the ejecta strongly between the center and 0.8 Msun. We conclude that the
supernovae that occur most frequently in nature are highly constrained by the
Phillips relation and that a large part of the currently observed scatter in
the relation is likely a consequence of the intrinsic diversity of these
objects.",0609562v1
2006-10-09,First stars VII. Lithium in extremely metal poor dwarfs,"Aims. This study aims to determine the level and constancy of the Spite
plateau as definitively as possible from homogeneous high-quality VLT-UVES
spectra of 19 of the most metal-poor dwarf stars known. Methods. Our
high-resolution (R ~ 43000), high S/N spectra are analysed with OSMARCS 1D LTE
model atmospheres and turbospectrum synthetic spectra to determine effective
temperatures, surface gravities, and metallicities, as well as Li abundances
for our stars. Results. Eliminating a cool subgiant and a spectroscopic binary,
we find 8 stars to have -3.5 < [Fe/H] < -3.0 and 9 stars with -3.0 < [Fe/H] <
-2.5. Our best value for the mean level of the plateau is A(Li) =2.10 +- 0.09.
The scatter around the mean is entirely explained by our estimate of the
observational error and does not allow for any intrinsic scatter in the Li
abundances. In addition, we conclude that a systematic error of the order of
200 K in any of the current temperature scales remains possible. The iron
excitation equilibria in our stars support our adopted temperature scale, which
is based on a fit to wings of the Halpha line, and disfavour hotter scales,
which would lead to a higher Li abundance, but fail to achieve excitation
equilibrium for iron. Conclusions. We confirm the previously noted discrepancy
between the Li abundance measured in extremely metal-poor turnoff stars and the
primordial Li abundance predicted by standard Big-Bang nucleosynthesis models
adopting the baryonic density inferred from WMAP. We discuss recent work
explaining the discrepancy in terms of diffusion and find that uncertain
temperature scales remain a major question. (abridged)",0610245v2
2006-10-10,"A longer XMM-Newton look at I Zwicky 1: Variability of the X-ray continuum, absorption, and iron Kalpha line","We present the second XMM-Newton observation (85 ks) of the narrow-line
Seyfert 1 galaxy (NLS1) I Zw 1 and describe its mean spectral and timing
characteristics. On average, I Zw 1 is ~35 per cent dimmer in 2005 than in the
shorter (20 ks) 2002 observation. Between the two epochs the intrinsic
absorption column density diminished, but there were also subtle changes in the
continuum shape. Considering the blurred ionised reflection model, the
long-term changes can be associated with a varying contribution of the power
law component relative to the total spectrum. Examination of normalised light
curves indicates that the high-energy variations are quite structured and that
there are delays, but only in some parts of the light curve. Interestingly, a
hard X-ray lag first appears during the most-distinct structure in the mean
light curve, a flux dip ~25 ks into the observation. The previously discovered
broad, ionised Fe Ka line shows significant variations over the course of the
2005 observation. The amplitude of the variations is 25-45 per cent and they
are unlikely due to changes in the Fe ka-producing region, but perhaps arise
from orbital motion around the black hole or obscuration in the broad iron
line-emitting region. The 2002 data are re-examined for variability of the Fe
Ka line at that epoch. There is evidence of energy and flux variations that are
associated with a hard X-ray flare that occurred during that observation.",0610283v2
2006-10-13,Revealing the High Energy Emission from the Obscured Seyfert Galaxy MCG -5-23-16 with Suzaku,"We report on a 100 ks Suzaku observation of the bright, nearby (z=0.008486)
Seyfert 1.9 galaxy MCG -5-23-16. The broad-band (0.4-100 keV) X-ray spectrum
allows us to determine the nature of the high energy emission with little
ambiguity. The X-ray continuum consists of a cutoff power-law of photon index
$\Gamma=1.9$, absorbed through Compton-thin matter of column density $N_{\rm
H}=1.6\times10^{22}$ cm$^{-2}$. A soft excess is observed below 1 keV and is
likely a combination of emission from scattered continuum photons and distant
photoionized gas. The iron K line profile is complex, showing narrow neutral
iron K$\alpha$ and K$\beta$ emission, as well as a broad line which can be
modeled by a moderately inclined accretion disk. The line profile shows either
the disk is truncated at a few tens of gravitational radii, or the disk
emissivity profile is relatively flat. A strong Compton reflection component is
detected above 10 keV, which is best modeled by a combination of reflection off
distant matter and the accretion disk. The reflection component does not appear
to vary. The overall picture is that this Seyfert 1.9 galaxy is viewed at
moderate (50 degrees) inclination through Compton-thin matter at the edge of a
Compton-thick torus covering $2\pi$ steradians, consistent with unified models.",0610434v1
2006-11-15,The broad band spectrum and variability of NGC 4151 observed by BeppoSAX,"We present an analysis of all SAX observations of NGC 4151. This source was
observed 5 times from 1996 to 2001 with durations ranging from a day to four
days. The intrinsic continuum, is absorbed at low energies by a complex system:
a cold patchy absorber plus a warm uniform screen photoionized by the central
continuum. We find that this dual absorber is the main driver of the observed
variability, up to a factor of eight, at 3 keV. In particular the covering
fraction of the cold absorber changes on time scales of the order of a day,
supporting its association with the Broad Line Region. The column density of
the warm gas varies on a longer time scale (months to year). Some of the small
amplitude spectral variability above 10 keV can be explained with an intrinsic
variation (\Delta\Gamma~0.2).The flux below 1 keV remains constant confirming
an extended origin. Its spectrum is reproduced by a combination of a thermal
component and a power law with the same slope as the intrinsic continuum but
with an intensity a few per cent. A Compton reflection component is
significantly detected in 1996 (averaged value of \Omega/2\pi ~0.4), with
intensity decreasing on time scale of year, and it desappears in 2000 and 2001.
The long time scale of variations argues for an association with an optically
thick torus at a distance of few light years. An iron line was detected in all
spectra. Its energy is consistent with fluorescence by cold iron. We find that
the line is variable. Its behaviour is reproduced by a variable component
proportional to the level of the reflection flux plus a constant component. The
flux of the latter is consistent with the extended line emission observed by
Chandra. We conclude that the first component is likely arising from the torus
and the second is produced in the extended Narrow Line Region.",0611470v1
2006-12-18,An XMM-Newton view of the X-ray flat radio-quiet quasar PG 1416-129,"(abridged) The radio-quiet quasar PG1416-129 (z=0.129) exhibits atypical
optical and X-ray properties. Between 1990 and 2000, in response to its optical
continuum decrease, the ``classical'' broad component of Hbeta almost
completely disappeared, with a factor of 10 decrease in the line flux. In the
X-ray band, this object was observed by Ginga in 1988 to have the hardest
quasar photon index, with Gamma=1.1+/-0.1. We present an XMM/EPIC observation
of PG1416-129 performed in July 2004. We analyze the time-averaged pn spectrum
of this quasar, as well as perform time-resolved spectroscopy. We find that
during the present XMM observation, PG1416-129 still has a rather hard photon
index, both in the soft and hard energy ranges, compared to radio-quiet quasars
but compatible with the photon index value found for radio-loud quasars. This
object also shows long-term luminosity variability over 16 years by a factor of
three with a variation of photon index from ~1.2 to ~1.8. In the soft energy
band (0.2-2keV), we found a very weak soft X-ray excess compared to other RQ
quasars. The whole time averaged spectrum is fit very well either by X-ray
ionized reflection from the accretion disk surface, by a warm absorber-emitter
plus power-law, or by a smeared absorption/emission from a relativistic
outflow. While no constant narrow FeK line at 6.4keV is observed, we find the
possible presence of two non-simultaneous transient iron lines: a redshifted
narrow iron line at about 5.5keV (96.4% confidence level according to
multi-trial Monte-Carlo simulations) at the beginning of this observation and
the appearance of a line at 6.3-6.4keV (99.1% c.l.) at the end of the
observation. These variable lines could be generated by discrete hot-spots on
the accretion disk surface.",0612485v1
2006-12-21,Planetary Radii across Five Orders of Magnitude in Mass and Stellar Insolation: Application to Transits,"To aid in the physical interpretation of planetary radii constrained through
observations of transiting planets, or eventually direct detections, we compute
model radii of pure hydrogen-helium, water, rock, and iron planets, along with
various mixtures. Masses ranging from 0.01 Earth masses to 10 Jupiter masses at
orbital distances of 0.02 to 10 AU are considered. For hydrogen-helium rich
planets, our models are the first to couple planetary evolution to stellar
irradiation over a wide range of orbital separations (0.02 to 10 AU) through a
non-gray radiative-convective equilibrium atmosphere model. Stellar irradiation
retards the contraction of giant planets, but its effect is not a simple
function of the irradiation level: a planet at 1 AU contracts as slowly as a
planet at 0.1 AU. For hydrogen-helium planets, we consider cores up to 90% of
the total planet mass, comparable to those of Uranus and Neptune. If ""hot
Neptunes"" have maintained their original masses and are not remnants of more
massive planets, radii of 0.30-0.45 times Jupiter's radius are expected. Water
planets are ~40-50% larger than rocky planets, independent of mass. Finally, we
provide tables of planetary radii at various ages and compositions, and for
ice-rock-iron planets we fit our results to analytic functions, which will
allow for quick composition estimates, given masses and radii, or mass
estimates, given only planetary radii. These results will assist in the
interpretation of observations for both the current transiting planet surveys
as well as upcoming space missions, including CoRoT and Kepler.",0612671v4
2007-01-05,A High-Abundance Arc in the Compact Group of Galaxies HCG 62: An AGN- or Merger-Induced Metal Outflow?,"We present a Chandra study of the metal distribution in the X-ray bright
compact group of galaxies HCG 62. We find that the diffuse X-ray emission is
peaked at the core of the central galaxy NGC 4778, and is dominated by the
contribution of the hot gas. The diffuse emission is roughly symmetric within
\simeq0.25^{\prime}, which is straddled by double-sided X-ray cavities aligned
in the northeast-southwest direction. By mapping the emission hardness ratio
distributions and by performing the 2-dimensional spectral analysis, we
identify a remarkable high-abundance arc region at about 2^{\prime}
(33.6h_{70}^{-1} kpc) from the X-ray peak that spans over a vast region from
south to northwest, a part of which roughly coinciding with the outer edge of
the southwest X-ray cavity. The measured average abundance in this arc is
higher than that in its neighboring regions by a factor of about 2, and the
abundance ratios therein are nicely consistent with the dominance of the SN Ia
yields. We estimate that the mass of iron contained in the arc is >3\times
10^{6}h_{70}^{-2.5} solar mass, which accounts for >3% of the iron synthesized
in the galaxy. The high-abundance arc could have been formed by the AGN
activities. However, it is also possible that the arc was formed in a recent
merger as is implied by the recent optical kinematic study (Spavone et al.
2006), which implies that mergers may be as important as AGN activities in
metal redistributions in early-type galaxies and their associated groups or
clusters.",0701119v1
2007-03-16,Coronal Abundances in Orion Nebula Cluster Stars,"Following the Chandra Orion Ultradeep Project (COUP) observation, we have
studied the chemical composition of the hot plasma in a sample of 146 X-ray
bright pre-main sequence stars in the Orion Nebula Cluster. We report
measurements of individual element abundances for a subsample of 86
slightly-absorbed and bright X-ray sources, using low resolution X-ray spectra
obtained from the Chandra ACIS instrument. The X-ray emission originates from a
plasma with temperatures and elemental abundances very similar to those of
active coronae in older stars. A clear pattern of abundances vs. First
Ionization Potential (FIP) is evident if solar photospheric abundances are
assumed as reference. The results are validated by extensive simulations. The
observed abundance distributions are compatible with a single pattern of
abundances for all stars, although a weak dependence on flare loop size may be
present. The abundance of calcium is the only one which appears to vary
substantially between stars, but this quantity is affected by relatively large
uncertainties. The ensemble properties of the X-ray bright COUP sources confirm
that the iron in the emitting plasma is underabundant with respect to both the
solar composition and to the average stellar photospheric values. Comparison of
the present plasma abundances with those of the stellar photospheres and those
of the gaseous component of the nebula, indicates a good agreement for all the
other elements with available measurements, and in particular for the high-FIP
elements (Ne, Ar, O, and S) and for the low-FIP element Si. We conclude that
there is evidence of a significant chemical fractionation effect only for iron,
which appears to be depleted by a factor 1.5--3 with respect to the stellar
composition.",0703439v1
2002-03-15,Distribution of carbon atoms in iron-carbon fcc phase: an experimental and theoretical study,"This paper presents an experimental and theoretical study of the distribution
of carbon atoms in the octahedral interstitial sites of the face-centered cubic
(fcc) phase of the iron-carbon system. The experimental part of the work
consists of Mossbauer measurements in Fe-C alloys with up to about 12 atomic
percent C, which are interpreted in terms of two alternative models for the
distribution of C atoms in the interstitial sites. The theoretical part
combines an analysis of the chemical potential of C based on the quasichemical
approximation to the statistical mechanics of interstitial solutions, with
three-dimensional Monte Carlo simulations. The latter were performed by
assuming a gas like mixture of C atoms and vacancies (Va) in the octahedral
interstitial sites. The number of C-C, C-Va and Va-Va pairs calculated using
Monte Carlo simulations are compared with those given by the quasichemical
model. Furthermore, the relative fraction of the various Fe environments were
calculated and compared with those extracted from the Mossbauer spectra. The
simulations reproduce remarkably well the relative fractions obtained assuming
the Fe(8)C(1-y) model for Mossbauer spectra, which includes some blocking of
the nearest neighbour interstitial sites by a C atom. With the new experimental
and theoretical information obtained in the present study, a critical
discussion is reported of the extent to which such blocking effect is accounted
for in current thermodynamic models of the Fe-C fcc phase.
  Abstract PACS Codes: 2.70.Uu, 76.",0203327v1
1998-09-16,Slow Magnetic Monopole: Interaction with Matter and New Possibility of Their Detection,"The possibility of existence of a magnetic monopole has been surveyed by P.
Dirac even in 1931, and then from the point of view of the modern theory by
A.M. Polyakov and G.~ 'tHooft in 1974. Numerous and unsuccessful attempts of
experimental search for monopole in cosmic rays and on accelerators in high
energy particle collisions have been done. Also the searches have been carried
out in mica for monopole tracks as well as for relict monopoles, entrapped by
ferromagnetic inclusions in iron-ores, moon rock and meteorites. These
entrapped monopoles, when released, would have the lowest velocities
$\beta<10^{-6}$ and do not yield ionization at all, and are hard to detect.
Therefore it is necessary to examine thoroughly the mechanisms of slow heavy
monopole interaction with matter and their scale of energy loss.
  We discuss here the interaction of a massive slow magnetic monopole with
magnetically ordered matter, with conductors, superconductors and with
condensed matter in general. Our results indicate that the energy loss of a
slow supermassive monopole reach $10^{8} eV/cm$ and more if we take into
consideration the Cherenkov radiation of magnons or phonons and conductivity of
the media. A new method of search for cosmic and relict monopoles by
magnetically ordered film is considered too. This approach resembles the
traditional method of nuclear emulsion chamber. Apparently the proposed method
is particularly attractive for detection of relict monopoles, released from
melting iron ore.",9809420v3
2004-06-08,"Three-Neutrino Oscillations of Atmospheric Neutrinos, theta13, Neutrino Mass Hierarchy and Iron Magnetized Detectors","We derive predictions for the Nadir angle (theta_n) dependence of the ratio
Nmu-/Nmu+ of the rates of the mu- and mu+ multi-GeV events, and for the mu- -
mu+ event rate asymmetry, A_{mu-mu+}=[Nmu- - Nmu+]/[Nmu- + Nmu+], in
iron-magnetized calorimeter detectors (MINOS, INO) in the case of 3-neutrino
oscillations of the atmospheric nu_mu and antinu_mu, driven by one neutrino
mass squared difference, |Delta m^2_{31}| >> Delta m^2_{21}. The asymmetry
A_{mu- mu+} (the ratio Nmu-/Nmu+) is shown to be particularly sensitive to the
Earth matter effects in the atmospheric neutrino oscillations, and thus to the
values of sin^2(theta13) and sin^2(theta23), theta13 and theta23 being the
neutrino mixing angles limited by the CHOOZ and Palo Verde experiments and that
responsible for the dominant atmospheric nu_mu -> nu_tau (antinu_mu ->
antinu_tau) oscillations. It is also very sensitive to the type of neutrino
mass spectrum which can be with normal (Delta m^2_{31}>0) or with inverted
(Delta m^2_{31} < 0) hierarchy. We find that for sin^2(theta23)>0.50, sin^2(2
theta13)>0.06 and Delta m^2_{31}=(2-3) 10^{-3} eV^2, the Earth matter effects
produce a relative difference between the integrated asymmetries barA_{mu- mu+}
and barA^{2nu}_{mu- mu+}$ in the mantle (cos(theta_n)=0.30-0.84) and core
(cos(theta_n)=0.84-1.0) bins, which is bigger in absolute value than ~15%, can
reach the values of (30-35)%, and thus can be sufficiently large to be
observable. The sign of the indicated asymmetry difference is anticorrelated
with the sign of Delta m^2_{31}. An observation of the Earth matter effects in
the Nadir angle distribution of the asymmetry A_{mu- mu+} (ratio Nmu-/Nmu+)
would clearly indicate that sin^2(2 theta13)>0.06 and sin^2(theta23)>0.50, and
would lead to the determination of the sign of Delta m^2_{31}.",0406096v1
2007-05-16,Viscous Torque and Dissipation in the Inner Region of a Thin Accretion Disk: Implications for Measuring Black Hole Spin,"We consider a simple Newtonian model of a steady accretion disk around a
black hole. The model is based on height-integrated hydrodynamic equations,
alpha-viscosity, and a pseudo-Newtonian potential that results in an innermost
stable circular orbit (ISCO) that closely approximates the one predicted by GR.
We find that the hydrodynamic models exhibit increasing deviations from the
standard disk model of Shakura & Sunyaev as disk thickness H/R or the value of
alpha increases. The latter is an analytical model in which the viscous torque
is assumed to vanish at the ISCO. We consider the implications of the results
for attempts to estimate black hole spin by using the standard disk model to
fit continuum spectra of black hole accretion disks. We find that the error in
the spin estimate is quite modest so long as H/R < 0.1 and alpha < 0.2. At
worst the error in the estimated value of the spin parameter is 0.1 for a
non-spinning black hole; the error is much less for a rapidly spinning hole. We
also consider the density and disk thickness contrast between the gas in the
disk and that inside the ISCO. The contrast needs to be large if black hole
spin is to be successfully estimated by fitting the relativistically-broadened
X-ray line profile of fluorescent iron emission from reflection off an
accretion disk. In our hydrodynamic models, the contrast in density and
thickness is low when H/R>0.1, sugesting that the iron line technique may be
most reliable in extemely thin disks. We caution that these results have been
obtained with a viscous hydrodynamic model and need to be confirmed with MHD
simulations of radiatively cooled thin disks.",0705.2244v3
2007-06-08,The Merger in Abell 576: A Line of Sight Bullet Cluster?,"Using a combination of Chandra and XMM observations, we confirmed the
presence of a significant velocity gradient along the NE/E-W/SW direction in
the intracluster gas of the cluster Abell 576. The results are consistent with
a previous ASCA SIS analysis of this cluster. The error weighted average over
ACIS-S3, EPIC MOS 1 & 2 spectrometers for the maximum velocity difference is
>3.3E03 km/s at the 90% confidence level, similar to the velocity limits
estimated indirectly for the ""bullet"" cluster (1E0657-56). The probability that
the velocity gradient is generated by standard random gain fluctuations with
Chandra and XMM is <0.1%. The regions of maximum velocity gradient are in CCD
zones that have the lowest temporal gain variations. It is unlikely that the
velocity gradient is due to Hubble distance differences between projected
clusters (probability<~0.01%). We mapped the distribution of elemental
abundance ratios across the cluster and detected a strong chemical
discontinuity using the abundance ratio of silicon to iron, equivalent to a
variation from 100% SN Ia iron mass fraction in the West-Northwest regions to
32% in the Eastern region. The ""center"" of the cluster is located at the
chemical discontinuity boundary, which is inconsistent with the radially
symmetric chemical gradient found in some regular clusters, but consistent with
a cluster merging scenario. We predict that the velocity gradient as measured
will produce a variation of the CMB temperature towards the East of the core of
the cluster that will be detectable by current and near-future bolometers. The
measured velocity gradient opens for the possibility that this cluster is
passing through a near line-of-sight merger stage where the cores have recently
crossed.",0706.1073v1
2007-06-07,An X-ray Spectral Analysis of the Central Regions of NGC 4593,"We present a detailed analysis of XMM-Newton EPIC-pn data for the Seyfert-1
galaxy NGC 4593. We discuss the X-ray spectral properties of this source as
well as its variations with time. The 0.5-10 keV spectrum shows significant
complexity beyond a simple power-law form, with clear evidence existing for a
""soft excess"" as well as absorption by highly ionized plasma (a warm absorber)
within the central engine of this active galactic nucleus. We show that the
soft excess is best described as originating from thermal Comptonization by
plasma that is appreciably cooler than the primary X-ray emitting plasma; we
find that the form of the soft excess cannot be reproduced adequately by
reflection from an ionized accretion disk. The only measurable deviation from
the power-law continuum in the hard spectrum comes from the presence of cold
and ionized fluorescent iron-K emission lines at 6.4 and 6.97 keV,
respectively. While constraints on the ionized iron line are weak, the cold
line is found to be narrow at CCD-resolution with a flux that does not track
the temporal changes in the underlying continuum, implying an origin in the
outer radii of the accretion disk or the putative molecular torus of Seyfert
unification schemes. The X-ray continuum itself varies on all accessible time
scales. We detect a ~230-second time-lag between soft and hard EPIC-pn bands
that, if interpreted as scattering timescales within a Comptonizing disk
corona, can be used to constrain the physical size of the primary X-ray source
to a characteristic length scale of ~2 gravitational radii. Taken together, the
small implied coronal size and the large implied iron line emitting region
indicate a departure from the current picture of a ""typical"" AGN geometry.",0706.1083v1
2007-06-15,High-resolution FUSE and HST ultraviolet spectroscopy of the white dwarf central star of Sh 2-216,"LS V +4621 is the DAO-type central star of the planetary nebula Sh 2-216. We
perform a comprehensive spectral analysis of high-resolution, high-S/N
ultraviolet observations obtained with FUSE and STIS aboard the HST as well as
the optical spectrum of LS V +4621 by means of state-of-the-art NLTE
model-atmosphere techniques in order to compare its photospheric properties to
theoretical predictions from stellar evolution theory as well as from diffusion
calculations.
  From the N IV - NV, O IV - O VI, Si IV - Si V, and Fe V - Fe VII ionization
equilibria, we determined an effective temperature of 95 +/- 2 kK with high
precision. The surface gravity is log g = 6.9 +/- 0.2. An unexplained
discrepancy appears between the spectroscopic distance d = 224 +46/-58 pc and
the parallax distance d = 129 +6/-5 pc of LS V +4621. For the first time, we
have identified Mg IV and Ar VI absorption lines in the spectrum of a
hydrogen-rich central star and determined the Mg and Ar abundances as well as
the individual abundances of iron-group elements (Cr, Mn, Fe, Co, and Ni). With
the realistic treatment of metal opacities up to the iron group in the
model-atmosphere calculations, the so-called Balmer-line problem (found in
models that neglect metal-line blanketing) vanishes.
  Spectral analysis by means of NLTE model atmospheres has presently arrived at
a high level of sophistication, which is now hampered largely by the lack of
reliable atomic data and accurate line-broadening tables. Strong efforts should
be made to improve upon this situation.",0706.2256v1
2007-08-09,Suzaku wide-band X-ray Spectroscopy of the Seyfert 2 AGN in NGC 4945,"Suzaku observed a nearby Seyfert 2 galaxy NGC4945, which hosts one of the
brightest active galactic nuclei above 20 keV. Combining data from the X-ray
CCD camera (XIS) and the Hard X-ray Detector (HXD), the AGN intrinsic nuclear
emission and its reprocessed signals were observed simultaneously. The
intrinsic emission is highly obscured with an absorbing column of $\sim 5
\times 10^{24}$ cm$^{-2}$, and was detectable only above $\sim 10$ keV. The
spectrum below 10 keV is dominated by reflection continuum and emission lines
from neutral/ionized material. Along with a neutral iron K$\alpha$ line, a
neutral iron K$\beta$ and a neutral nickel K$\alpha$ line were detected for the
first time from this source. The neutral lines and the cold reflection
continuum are consistent with both originating in the same location. The
Compton down-scattered shoulder in the neutral Fe-K$\alpha$ line is $\sim 10%$
in flux of the narrow core, which confirms that the line originates from
reflection rather than transmission. The weakness of the Compton shoulder also
indicates that the reflector is probably seen nearly edge-on. Flux of the
intrinsic emission varied by a factor of $\sim 2$ within $\sim 20$ ks, which
requires the obscuring material to be geometrically thin. Broadband spectral
modeling showed that the solid angle of the neutral reflector is less than a
few $\times 10^{-2} \times 2\pi$. All this evidence regarding the reprocessed
signals suggests that a disk-like absorber/reflector is viewed from a near
edge-on angle.",0708.1201v1
2007-09-05,Atomic Diffusion and Mixing in Old Stars I. VLT/FLAMES-UVES Observations of Stars in NGC 6397,"We present a homogeneous photometric and spectroscopic analysis of 18 stars
along the evolutionary sequence of the metal-poor globular cluster NGC 6397
([Fe/H] = -2), from the main-sequence turnoff point to red giants below the
bump. The spectroscopic stellar parameters, in particular stellar-parameter
differences between groups of stars, are in good agreement with broad-band and
Stroemgren photometry calibrated on the infrared-flux method. The spectroscopic
abundance analysis reveals, for the first time, systematic trends of iron
abundance with evolutionary stage. Iron is found to be 31% less abundant in the
turnoff-point stars than in the red giants. An abundance difference in lithium
is seen between the turnoff-point and warm subgiant stars. The impact of
potential systematic errors on these abundance trends (stellar parameters, the
hydrostatic and LTE approximations) is quantitatively evaluated and found not
to alter our conclusions significantly. Trends for various elements (Li, Mg,
Ca, Ti and Fe) are compared with stellar-structure models including the effects
of atomic diffusion and radiative acceleration. Such models are found to
describe the observed element-specific trends well, if extra (turbulent) mixing
just below the convection zone is introduced. It is concluded that atomic
diffusion and turbulent mixing are largely responsible for the sub-primordial
stellar lithium abundances of warm halo stars. Other consequences of atomic
diffusion in old metal-poor stars are also discussed.",0709.0639v1
2007-12-20,Comparing Suzaku and XMM-Newton Observations of the Soft X-ray Background: Evidence for Solar Wind Charge Exchange Emission,"We present an analysis of a pair of Suzaku spectra of the soft X-ray
background (SXRB), obtained from pointings on and off a nearby shadowing
filament in the southern Galactic hemisphere. Because of the different Galactic
column densities in the two pointing directions, the observed emission from the
Galactic halo has a different shape in the two spectra. We make use of this
difference when modeling the spectra to separate the absorbed halo emission
from the unabsorbed foreground emission from the Local Bubble (LB). The
temperatures and emission measures we obtain are significantly different from
those determined from an earlier analysis of XMM-Newton spectra from the same
pointing directions. We attribute this difference to the presence of previously
unrecognized solar wind charge exchange (SWCX) contamination in the XMM-Newton
spectra, possibly due to a localized enhancement in the solar wind moving
across the line of sight. Contemporaneous solar wind data from ACE show nothing
unusual during the course of the XMM-Newton observations. Our results therefore
suggest that simply examining contemporaneous solar wind data might be
inadequate for determining if a spectrum of the SXRB is contaminated by SWCX
emission. If our Suzaku spectra are not badly contaminated by SWCX emission,
our best-fitting LB model gives a temperature of log T = 5.98 +0.03/-0.04 and a
pressure of p/k = 13,100-16,100 cm^-3 K. These values are lower than those
obtained from other recent observations of the LB, suggesting the LB may not be
isothermal and may not be in pressure equilibrium. Our halo modeling,
meanwhile, suggests that neon may be enhanced relative to oxygen and iron,
possibly because oxygen and iron are partly in dust.",0712.3538v1
2008-01-08,GMASS Ultradeep Spectroscopy of Galaxies at redshift z~2. I. The stellar metallicity,"Context: Galaxy metallicities have been measured to redshift z~2 by gas-phase
oxygen abundances of the interstellar medium using the R23 and N2 methods.
Galaxy stellar metallicities provide crucial data for chemical evolution models
but have not been assessed reliably much outside the local Universe. Aims: We
determine the iron-abundance, stellar metallicity of star-forming galaxies
(SFGs) at redshift z~2, observed as part of the Galaxy Mass Assembly ultra-deep
Spectroscopic Survey (GMASS). Methods: We compute the equivalent width of a
rest-frame mid-ultraviolet, photospheric absorption-line index, the 1978 index
found to vary monotonically with stellar metallicity by Rix and collaborators.
We normalise and combine 75 SFG spectra from the GMASS survey to produce a
spectrum corresponding to a total integration time 1652.5 hours (and a
signal-to-noise ratio ~100 for our 1.5 angstrom binning) of FORS2 spectroscopic
observations at the Very Large Telescope. Results: We measure an
iron-abundance, stellar metallicity of log (Z/Zsolar) = -0.574+/-0.159 for our
spectrum representative of a galaxy of stellar mass 9.4 x 10^9 Msolar assuming
a Chabrier IMF. We find that the R04 model SFG spectrum for log (Z/Zsolar) =
-0.699 solar metallicity provides the best description of our GMASS coadded
spectrum. For similar galaxy stellar mass, our stellar metallicity is ~0.25 dex
lower than the oxygen-abundance, gas-phase metallicity quantified by Erb and
collaborators for UV-selected star-forming galaxies at z=2. Conclusions: We
conclude that we are witnessing the establishment of a light-element
overabundance in galaxies as they are being formed at redshift z~2. Our
measurements are reminiscent of the alpha-element enhancement seen in
low-redshift, galactic bulges and early-type galaxies. (Abridged)",0801.1193v1
2008-03-10,X-ray absorption in distant type II QSOs,"We present the results of the X-ray spectral analysis of an
XMM-Newton-selected type II QSO sample with z>0.5 and 0.5-10 keV flux of 0.3-33
x 10^{-14} erg/s/cm^2. The distribution of absorbing column densities in type
II QSOs is investigated and the dependence of absorption on X-ray luminosity
and redshift is studied.
  We inspected 51 spectroscopically classified type II QSO candidates from the
XMM-Newton Marano field survey, the XMM-Newton-2dF wide angle survey (XWAS),
and the AXIS survey to set-up a well-defined sample with secure optical type II
identifications. Fourteen type II QSOs were classified and an X-ray spectral
analysis performed. Since most of our sources have only ~40 X-ray counts
(PN-detector), we carefully studied the fit results of the simulated X-ray
spectra as a function of fit statistic and binning method. We determined that
fitting the spectra with the Cash-statistic and a binning of minimum one count
per bin recovers the input values of the simulated X-ray spectra best. Above
100 PN counts, the free fits of the spectrum's slope and absorbing hydrogen
column density are reliable.
  We find only moderate absorption (N_H=(2-10) x 10^22 cm^-2) and no obvious
trends with redshift and intrinsic X-ray luminosity. In a few cases a
Compton-thick absorber cannot be excluded. Two type II objects with no X-ray
absorption were discovered. We find no evidence for an intrinsic separation
between type II AGN and high X-ray luminosity type II QSO in terms of
absorption. The stacked X-ray spectrum of our 14 type II QSOs shows no iron
K-alpha line. In contrast, the stack of the 8 type II AGN reveals a very
prominent iron K-alpha line at an energy of ~ 6.6 keV and an EW ~ 2 keV.",0803.1440v1
2008-04-06,V2051 Oph after superoutburst: out-of-plane material and the superhump light source,"We performed a detailed spectroscopic analysis of the dwarf nova V2051 Oph at
the end of its 1999 superoutburst. We studied and interpreted the simultaneous
behaviour of various emission lines.
  We obtained high-resolution echelle spectroscopic data at ESO's NTT with
EMMI, covering the spectral range of 4000--7500 Angstrom. The analysis was
performed using standard IRAF tools. The indirect imaging technique of Doppler
tomography was applied, in order to map the accretion disc and distinguish
between the different emission sources.
  The spectra are characterised by strong Balmer emission, together with lines
of HeI and the iron triplet FeII 42. All lines are double-peaked, but the
blue-to-red peak strength and central absorption depth vary. The primary's
velocity was found to be 84.9 km/sec. The spectrograms of the emission lines
reveal the prograde rotation of a disc-like emitting region and, for the Balmer
and HeI lines, an enhancement of the red-wing during eclipse indicates a bright
spot origin. The modulation of the double-peak separation shows a highly
asymmetric disc with non-uniform emissivity. This is confirmed by the Doppler
maps, which apart from the disc and bright spot emission also indicate an
additional region of enhanced emission in the 4th quadrant (+Vx, -Vy), which we
associate with the superhump light source. Given the behaviour of the iron
triplet and its distinct differences from the rest of the lines, we attribute
its existence to an extended gas region above the disc. Its origin can be
explained through the fluorescence mechanism.",0804.0898v1
2008-08-18,On the nature of unabsorbed Seyfert 2 galaxies,"We present an analysis of six 12 um selected Seyfert 2 galaxies that have
been reported to be unabsorbed in the X-ray. By comparing the luminosities of
these galaxies in the mid-IR (12um), optical ([O III]) and hard X-ray (2-10
keV), we show that they are all under-luminous in the 2-10 keV X-ray band. Four
of the objects exhibit X-ray spectra indicative of a hard excess, consistent
with a heavily obscured X-ray component and hence a hidden nucleus. In these
objects the softer X-rays may be dominated by a strong soft scattered continuum
or contamination from the host galaxy, which is responsible for the unabsorbed
X-ray spectra observed, and accounts for the anomalously low 2-10 keV X-ray
luminosity. We confirm this assertion in NGC4501 with a Chandra observation,
which shows hard X-ray emission coincident with the nucleus, consistent with
heavy absorption, and a number of contaminating softer sources which account
for the bulk of the softer emission. We point out that such 'Compton thick'
sources need not necessarily present iron Ka emission of high EW. An example in
our sample is IRASF01475-0740, which we know must host an obscured AGN as it
hosts a HBLR seen in scattered light (Tran 2003). The X-ray spectrum is
nonetheless relatively unobscured and the iron Ka line only moderate in
strength. These observations can be reconciled if the hidden nuclear emission
is dominated by transmitted, rather than reflected X-rays, which can then be
weak compared to the soft scattered light or galactic emission. Despite these
considerations, we conclude that NGC3147 & 3660 may intrinsically lack a BLR,
confirming the recent results of Bianchi et al. (2008) for NGC3147. Neither
X-ray spectrum shows signs of hidden hard emission and both sources exhibit
X-ray variability leading us to believe we are viewing the nucleus directly.",0808.2385v1
2008-09-12,Absorption features in the spectra of X-ray bursting neutron stars,"The discovery of photospheric absorption lines in XMM-Newton spectra of the
X-ray bursting neutron star in EXO0748-676 by Cottam and collaborators allows
us to constrain the neutron star mass-radius ratio from the measured
gravitational redshift. A radius of R=9-12km for a plausible mass range of
M=1.4-1.8Msun was derived by these authors. It has been claimed that the
absorption features stem from gravitationally redshifted (z=0.35) n=2-3 lines
of H- and He-like iron. We investigate this identification and search for
alternatives. We compute LTE and non-LTE neutron-star model atmospheres and
detailed synthetic spectra for a wide range of effective temperatures
(effective temperatures of 1 - 20MK) and different chemical compositions.
  We are unable to confirm the identification of the absorption features in the
X-ray spectrum of EXO0748-676 as n=2-3 lines of H- and He-like iron (Fe XXVI
and Fe XXV). These are subordinate lines that are predicted by our models to be
too weak at any effective temperature. It is more likely that the strongest
feature is from the n=2-3 resonance transition in Fe XXIV with a redshift of
z=0.24. Adopting this value yields a larger neutron star radius, namely
R=12-15km for the mass range M=1.4-1.8Msun, favoring a stiff equation-of-state
and excluding mass-radius relations based on exotic matter. Combined with an
estimate of the stellar radius R>12.5km from the work of Oezel and
collaborators, the z=0.24 value provides a minimum neutron-star mass of
M>1.48Msun, instead of M>1.9Msun, when assuming z=0.35.",0809.2170v2
2008-10-02,Detection of blueshifted emission and absorption and a relativistic Iron line in the X-ray spectrum of ESO 323-G077,"We report on the X-ray observation of the Seyfert 1 ESO323-G077 performed
with XMM-Newton. The spectra show a complex spectrum with conspicuous
absorption and emission features. The continuum emission can be modelled with a
power law with an index of 1.99+/-0.02 in the whole XMM-Newton energy band,
marginally consistent with typical values of Type-I objects. An absorption
component with an uncommonly high equivalent Hydrogen column,
n_H=5.82(+0.12/-0.11)x10^22 cm-2, is affecting the soft part of the spectrum.
Additionally, two warm absorption components are also present. The lower
ionised one has an ionisation parameter of Log(U)=2.14(+0.06/-0.07) and an
outflowing velocity of v=3200(+600/-200) km/s. Two absorption lines located at
~6.7 and ~7.0 keV can be modelled with the highly ionised absorber. The
ionisation parameter and outflowing velocity of the gas measured are
Log(U)=3.26(+0.19/-0.15) and v=1700(+600/-400) km/s, respectively. Four
emission lines were also detected in the soft energy band. The most likely
explanation for these emission lines is that they are associated with an
outflowing gas with a velocity of ~2000 km/s. The data suggest that the same
gas which is causing the absorption could also being responsible of these
emission features. Finally, the spectrum shows the presence of a relativistic
iron emission line likely originated in the accretion disc of a Kerr BH with an
inclination of ~25 deg. We propose a model to explain the observed X-ray
properties which invokes the presence of a two-phase outflow with cone-like
structure and a velocity of the order of 2,000-4,000 km/s. The inner layer of
the cone would be less ionised, or even neutral, than the outer layer. The
inclination angle would be lower than the opening angle of the outflowing cone.",0810.0513v1
2008-12-04,The evolution of the Galactic metallicity gradient from high-resolution spectroscopy of open clusters,"Open clusters offer a unique possibility to study the time evolution of the
radial metallicity gradients of several elements in our Galaxy, because they
span large intervals in age and Galactocentric distance, and both quantities
can be more accurately derived than for field stars. We re-address the issue of
the Galactic metallicity gradient and its time evolution by comparing the
empirical gradients traced by a sample of 45 open clusters with a chemical
evolution model of the Galaxy. At variance with previous similar studies, we
have collected from the literature only abundances derived from
high--resolution spectra. The clusters have distances $7 < RGC<22$ kpc and ages
from $\sim 30$ Myr to 11 Gyr. We also consider the $\alpha$-elements Si, Ca,
Ti, and the iron-peak elements Cr and Ni. The data for iron-peak and
$\alpha$-elements indicate a steep metallicity gradient for R_GC<12$ kpc and a
plateau at larger radii. The time evolution of the metallicity distribution is
characterized by a uniform increase of the metallicity at all radii, preserving
the shape of the gradient, with marginal evidence for a flattening of the
gradient with time in the radial range 7-12 kpc. Our model is able to reproduce
the main features of the metallicity gradient and its evolution with an infall
law exponentially decreasing with radius and with a collapse time scale of the
order of 8 Gyr at the solar radius. This results in a rapid collapse in the
inner regions, i.e. $R_{\rm GC}\lesssim 12$ kpc (that we associate with an
early phase of disk formation from the collapse of the halo) and in a slow
inflow of material per unit area in the outer regions at a constant rate with
time.",0812.0854v1
2009-01-29,"Novel Superconducting Characteristics and Unusual Normal-State Properties in Iron-based Pnictide Superconductors: 57Fe-NMR and 75As-NQR/NMR studies in REFeAsO_1-y (RE=La,Pr,Nd) and Ba0.6K0.4Fe2As2","We discuss the novel superconducting characteristics and unusual normal-state
properties of iron (Fe)-based pnictide superconductors REFeAsO$_{1-y}$
(RE=La,Pr,Nd) and Ba$_{0.6}$K$_{0.4}$Fe$_2$As$_2$($T_{c}=$ 38 K) by means of
$^{57}$Fe-NMR and $^{75}$As-NQR/NMR. In the superconducting state of
LaFeAsO$_{0.7}$ ($T_{c}=$ 28 K), the spin component of the $^{57}$Fe-Knight
shift decreases to almost zero at low temperatures, which provide firm evidence
of the superconducting state formed by spin-singlet Cooper pairing. The nuclear
spin-lattice relaxation rates $(1/T_{1})$ in LaFeAsO$_{0.7}$ and
Ba$_{0.6}$K$_{0.4}$Fe$_2$As$_2$ exhibit a $T^{3}$-like dependence without a
coherence peak just below $T_{c}$, indicating that an unconventional
superconducting state is commonly realized in these Fe-based pnictide
compounds. All these events below $T_c$ are consistently argued in terms of an
extended s$_{\pm}$-wave pairing with a sign reversal of the order parameter
among Fermi surfaces. In the normal state, $1/T_1T$ decreases remarkably upon
cooling for both the Fe and As sites of LaFeAsO$_{0.7}$. In contrast, it
gradually increases upon cooling in Ba$_{0.6}$K$_{0.4}$Fe$_2$As$_2$. Despite
the similarity between the superconducting properties of these compounds, a
crucial difference was observed in their normal-state properties depending on
whether electrons or holes are doped into the FeAs layers. These results may
provide some hint to address a possible mechanism of Fe-based pnictide
superconductors.",0901.4607v2
2009-02-06,Effective area calibration of the Reflection Grating Spectrometers of XMM-Newton. I. X-ray spectroscopy of the Crab nebula,"The Crab nebula and pulsar have been widely used as a calibration source for
X-ray instruments. The in-flight effective area calibration of the Reflection
Grating Spectrometers (RGS) of XMM-Newton depend upon the availability of
reliable calibration sources. We investigate how the absolute effective area
calibration of RGS can be obtained using Crab as a standard candle. We have
analysed RGS observations of the Crab using different instrument configurations
and spatial offsets, and made use of previous determinations of the continuum
spectrum of the nebula plus pulsar. Due to the high spectral resolution of the
RGS, we resolve the main absorption edges and detect the strong 1s-2p
absorption lines of neutral oxygen. We get an excellent fit to the Crab
spectrum using this fixed continuum and the absorption spectrum determined by
RGS. We get accurate column densities for the neutral atoms of H, N, O, Ne, Mg,
and Fe, as well as a clear detection of Fe II and firm upper limits for other
ions. Our data are in good agreement with earlier optical and UV spectroscopic
measurements of some of these ions. We find solar abundances for N and O, while
Ne is overabundant by a factor of 1.7 and Fe is underabundant by a factor of
0.8. We confirm that there is less dust in the line of sight compared to the
prediction based on the absorption column. Our spectra suggest a more prominent
role of ferric iron in the dust compared to ferrous iron. Our high-resolution
observations confirm that Crab can be used as an X-ray calibration source. RGS
spectra have determined the absorption spectrum towards Crab with unprecedented
detail.",0902.1094v1
2009-04-09,"Interplay of Rare Earth and Iron magnetism in RFeAsO with R = La, Ce, Pr, and Sm: A muon spin relaxation study and symmetry analysis","We report zero field muon spin relaxation (muSR) measurements on RFeAsO with
R = La, Ce, Pr, and Sm. We study the interaction of the FeAs and R (rare earth)
electronic systems in the non superconducting magnetically ordered parent
compounds of RFeAsO{1-x}Fx superconductors via a detailed comparison of the
local hyperfine fields at the muon site with available Moessbauer spectroscopy
and neutron scattering data. These studies provide microscopic evidence of long
range commensurate magnetic Fe order with the Fe moments not varying by more
than 15 % within the series RFeAsO with R = La, Ce, Pr, and Sm. At low
temperatures, long range R magnetic order is also observed. Different combined
Fe and R magnetic structures are proposed for all compounds using the muon site
in the crystal structure obtained by electronic potential calculations. Our
data point to a strong effect of R order on the iron subsystem in the case of
different symmetry of Fe and R order parameters resulting in a Fe spin
reorientation in the R ordered phase in PrFeAsO. Our symmetry analysis proves
the absence of collinear Fe--R Heisenberg interactions in RFeAsO. A strong
Fe--Ce coupling due to non--Heisenberg anisotropic exchange is found in CeFeAsO
which results in a large staggered Ce magnetization induced by the magnetically
ordered Fe sublattice far above T_N{Ce}. Finally, we argue that the magnetic
R--Fe interaction is probably not crucial for the observed enhanced
superconductivity in RFeAsO{1-x}Fx with a magnetic R ion.",0904.1563v3
2009-04-17,Pnictogen height as a possible switch between high-T_c nodeless and low-T_c nodal pairings in the iron based superconductors,"We study the effect of the lattice structure on the spin-fluctuation mediated
superconductivity in the iron pnictides adopting the five-band models of
several virtual lattice structures of LaFeAsO as well as actual materials such
as NdFeAsO and LaFePO obtained from the maximally-localized Wannier orbitals.
Random phase approximation is applied to the models to solve the Eliashberg
equation. This reveals that the gap function and the strength of the
superconducting instability are determined by the cooperation or competition
among multiple spin fluctuation modes arising from several nestings among
disconnected pieces of the Fermi surface, which is affected by the lattice
structure. Specifically, the appearance of the Fermi surface $\gamma$ around
$(\pi,\pi)$ in the unfolded Brillouin zone is sensitive to the pnictogen height
$h_{\rm Pn}$ measured from the Fe plane, where $h_{\rm Pn}$ is shown to act as
a switch between high-$T_c$ nodeless and low-$T_c$ nodal pairings. We also find
that reduction of the lattice constants generally suppresses superconductivity.
We can then combine these to obtain a generic superconducting phase diagram
against the pnictogen height and lattice constant. This suggests that NdFeAsO
is expected to exhibit a fully-gapped, sign-reversing s-wave superconductivity
with a higher $T_c$ than in LaFeAsO, while a nodal pairing with a low $T_c$ is
expected for LaFePO, which is consistent with experiments.",0904.2612v2
2009-05-27,The detection of Broad Iron K and L line emission in the Narrow-Line Seyfert 1 Galaxy 1H0707-495 using XMM-Newton,"Since the discovery of the first broad iron-K line in 1995 from the Seyfert
Galaxy MCG--6-30-15, broad iron-K lines have been found in several other
Seyfert galaxies, from accreting stellar mass black holes and even from
accreting neutron stars. The iron-K line is prominent in the reflection
spectrum created by the hard X-ray continuum irradiating dense accreting
matter. Relativistic distortion of the line makes it sensitive to the strong
gravity and spin of the black hole. The accompanying iron-L line emission
should be detectable when the iron abundance is high. Here we report the first
discovery of both iron-K and L emission, using XMM-Newton observations of the
Narrow-Line Seyfert 1 Galaxy 1H0707-495. The bright Fe-L emission has enabled
us, for the first time, to detect a reverberation lag of 30 s between the
direct X-ray continuum and its reflection from matter falling into the hole.
The observed reverberation timescale is comparable to the light-crossing time
of the innermost radii around a supermassive black hole. The combination of
spectral and timing data on 1H0707-495 provides strong evidence that we are
witnessing emission from matter within a gravitational radius, or a fraction of
a light-minute, from the event horizon of a rapidly-spinning, massive black
hole.",0905.4383v1
2009-06-19,Dynamical Mean-Field Theory within an Augmented Plane-Wave Framework: Assessing Electronic Correlations in the Iron Pnictide LaFeAsO,"We present an approach that combines the local density approximation (LDA)
and the dynamical mean-field theory (DMFT) in the framework of the
full-potential linear augmented plane waves (FLAPW) method. Wannier-like
functions for the correlated shell are constructed by projecting local orbitals
onto a set of Bloch eigenstates located within a certain energy window. The
screened Coulomb interaction and Hund's coupling are calculated from a
first-principle constrained RPA scheme. We apply this LDA+DMFT implementation,
in conjunction with continuous-time quantum Monte-Carlo, to study the
electronic correlations in LaFeAsO. Our findings support the physical picture
of a metal with intermediate correlations. The average value of the mass
renormalization of the Fe 3d bands is about 1.6, in reasonable agreement with
the picture inferred from photoemission experiments. The discrepancies between
different LDA+DMFT calculations (all technically correct) which have been
reported in the literature are shown to have two causes: i) the specific value
of the interaction parameters used in these calculations and ii) the degree of
localization of the Wannier orbitals chosen to represent the Fe 3d states, to
which many-body terms are applied. The latter is a fundamental issue in the
application of many-body calculations, such as DMFT, in a realistic setting. We
provide strong evidence that the DMFT approximation is more accurate and more
straightforward to implement when well-localized orbitals are constructed from
a large energy window encompassing Fe-3d, As-4p and O-2p, and point out several
difficulties associated with the use of extended Wannier functions associated
with the low-energy iron bands. Some of these issues have important physical
consequences, regarding in particular the sensitivity to the Hund's coupling.",0906.3735v2
2009-07-17,Composition and fate of short-period super-Earths: The case of CoRoT-7b,"The discovery of CoRoT-7b, a planet of radius 1.68 +/- 0.09 R_E, mass 4.8 +/-
0.8 M_E and orbital period of 0.854 days demonstrates that small planets can
orbit extremely close to their star. We use knowledge of hot Jupiters, mass
loss estimates and models for the interior structure and evolution of planets
to understand its composition, structure and evolution. The inferred mass and
radius of CoRoT-7b are consistent with a rocky planet that would be depleted in
iron relative to Earth. However, a one sigma increase in mass (5.6 M_E) and
decrease in size (1.59 R_E) are compatible with an Earth-like composition (33%
iron, 67% silicates). Alternatively, it is possible that CoRoT-7b contains a
significant amount of volatiles. An equally good fit to the data is found for a
vapor envelope equal to 3% (and up to 10%) by mass above an Earth-like nucleus.
Because of its intense irradiation and small size, the planet cannot possess an
envelope of H and He of more than 1/10,000 of its total mass. We show that the
mass loss is significant (~ 10^11 g/s) and independent of planetary
composition. This is because the hydrodynamical escape rate is independent of
the atmosphere's mean molecular mass, and owing to the intense irradiation,
even a bare rocky planet would possess an equilibrium vapor atmosphere thick
enough to capture stellar UV photons. This escape rate rules out the
possibility of a H-He envelope as it would escape in only ~1 Ma. A water vapor
atmosphere would escape in ~ 1 Ga, and thus it is a plausible scenario. The
origin of CoRoT-7b cannot be inferred from present observations: It may have
formed rocky; or be the remnant of a Uranus-like ice giant, or a gas giant with
a small core that was stripped of its gaseous envelope.",0907.3067v2
2009-08-17,Role of emission angular directionality in spin determination of accreting black holes with broad iron line,"Spin of an accreting black hole can be determined by spectroscopy of the
emission and absorption features produced in the inner regions of an accretion
disc. We discuss the method employing the relativistic line profiles of iron in
the X-ray domain, where the emergent spectrum is blurred by general
relativistic effects. Precision of spectra fitting procedure could be
compromised by inappropriate account of the angular distribution of the disc
emission. Often a unique profile is assumed, invariable over the entire range
of radii in the disc and energy in the spectral band. We study how sensitive
the spin determination is to the assumptions about the intrinsic angular
distribution of the emitted photons. We find that the uncertainty of the
directional emission distribution translates to 20% uncertainty in
determination of the marginally stable orbit. By assuming a rotating black hole
in the centre of an accretion disc, we perform radiation transfer computations
of an X-ray irradiated disc atmosphere to determine the directionality of
outgoing X-rays in the 2-10 keV energy band. We implemented the simulation
results as a new extension to the KY software package for X-ray spectra fitting
of relativistic accretion disc models. Although the parameter space is rather
complex, leading to a rich variety of possible outcomes, we find that on
average the isotropic directionality reproduces our model data to the best
precision. Our results also suggest that an improper usage of limb darkening
can partly mimic a steeper profile of radial emissivity. We demonstrate these
results on the case of XMM-Newton observation of the Seyfert galaxy
MCG-6-30-15, for which we construct confidence levels of chi squared
statistics, and on the simulated data for the future X-ray IXO mission.",0908.2387v4
2009-09-03,Simulating the effect of AGN feedback on the metal enrichment of galaxy clusters,"We present a study of the effect of AGN feedback on metal enrichment and
thermal properties of the intracluster medium (ICM) in hydrodynamical
simulations. The cosmological simulations are performed for a set of clusters
using a version of the TreePM-SPH Gadget code that follows chemo-dynamical
evolution by accounting for metal enrichment by different stellar populations.
Besides runs not including any efficient form of energy feedback, we carry out
simulations including: (i) kinetic feedback in the form of galactic winds
triggered by supernova explosions; (ii) AGN feedback from gas accretion onto
super-massive black holes (BHs); (iii) AGN feedback in which a 'radio mode' is
included. We find that AGN feedback is able to quench star formation in the
brightest cluster galaxies at z<4 and provides correct temperature profiles in
the central regions of galaxy groups. However, its effect is not sufficient to
create cool cores in massive clusters. AGN feedback creates a widespread
enrichment in the outskirts of clusters, thanks to its efficiency in displacing
enriched gas from galactic halos to the inter-galactic medium at relatively
high redshift. Iron abundance profiles are in better agreement with
observations, with a more pristine enrichment of the ICM around and beyond the
cluster virial regions. From the pattern of the relative abundances of Silicon
and Iron, we conclude that a significant fraction of ICM enrichment in
simulations is contributed by a diffuse population of intra-cluster stars. Our
simulations also predict that profiles of Z_Si/Z_Fe abundance ratio do not
increase at least out to 0.5 R_vir. Our results clearly show that different
sources of energy feedback leave distinct imprints in the enrichment pattern of
the ICM, that are more evident when looking at cluster external regions.",0909.0664v1
2009-12-31,Production of the p-Process Nuclei in the Carbon-Deflagration Model for Type Ia Supernovae,"We calculate nucleosynthesis of proton-rich isotopes in the
carbon-deflagration model for Type Ia supernovae (SNe Ia). The seed abundances
are obtained by calculating the s-process nucleosynthesis that is expected to
occur in the repeating helium shell flashes on the carbon-oxygen (CO) white
dwarf (WD) during mass accretion from a binary companion. When the deflagration
wave passes through the outer layer of the CO WD, p-nuclei are produced by
photodisintegration reactions on s-nuclei in a region with the peak temperature
ranging from 1.9 to 3.6 x10^9 K. We confirm the sensitivity of the p-process on
the initial distribution of s-nuclei. We show that the initial C/O ratio in the
WD does not much affect the yield of p-nuclei. On the other hand, the abundance
of 22Ne left after the s-processing has a large influence on the p-process via
22Ne(alpha,n) reaction. We find that about 50% of p-nuclides are co-produced
when normalized to their solar abundances in all adopted cases of seed
distribution. Mo and Ru, which are largely underproduced in Type II supernovae
(SNe II), are produced more than in SNe II although they are underproduced with
respect to the yield levels of other p-nuclides. The ratios between p-nuclei
and iron in the ejecta are larger than the solar ratios by a factor of 1.2. We
also compare the yields of oxygen, iron, and p-nuclides in SNe Ia and SNe II
and suggest that SNe Ia could make a larger contribution than SNe II to the
solar system content of p-nuclei.",1001.0145v3
2010-01-19,"Analyzing the prices of the most expensive sheet iron all over the world: Modeling, prediction and regime change","The private car license plates issued in Shanghai are bestowed the title of
""the most expensive sheet iron all over the world"", more expensive than gold. A
citizen has to bid in an monthly auction to obtain a license plate for his new
private car. We perform statistical analysis to investigate the influence of
the minimal price $P_{\min}$ of the bidding winners, the quota $N_{\rm{quota}}$
of private car license plates, the number $N_{\rm{bidder}}$ of bidders, as well
as two external shocks including the legality debate of the auction in 2004 and
the auction regime reform in January 2008 on the average price $P_{\rm{mean}}$
of all bidding winners. It is found that the legality debate of the auction had
marginal transient impact on the average price in a short time period. In
contrast, the change of the auction rules has significant permanent influence
on the average price, which reduces the price by about 3020 yuan Renminbi. It
means that the average price exhibits nonlinear behaviors with a regime change.
The evolution of the average price is independent of the number
$N_{\rm{bidder}}$ of bidders in both regimes. In the early regime before
January 2008, the average price $P_{\rm{mean}}$ was influenced only by the
minimal price $P_{\min}$ in the preceding month with a positive correlation. In
the current regime since January 2008, the average price is positively
correlated with the minimal price and the quota in the preceding month and
negatively correlated with the quota in the same month. We test the predictive
power of the two models using 2-year and 3-year moving windows and find that
the latter outperforms the former. It seems that the auction market becomes
more efficient after the auction reform since the prediction error increases.",1001.3176v1
2010-02-12,Abundances and physical parameters for stars in the open clusters NGC 5822 and IC 4756,"Classical chemical analyses may be affected by systematic errors that would
cause observed abundance differences between dwarfs and giants. For some
elements, however, the abundance difference could be real. We address the issue
by observing 2 solar--type dwarfs in NGC 5822 and 3 in IC 4756, and comparing
their composition with that of 3 giants in either of the aforementioned
clusters. We determine iron abundance and stellar parameters of the dwarf
stars, and the abundances of calcium, sodium, nickel, titanium, aluminium,
chromium, silicon and oxygen for both the giants and dwarfs. We acquired UVES
high-resolution, of high signal--to--noise ratio (S/N) spectra. The width of
the cross correlation profiles was used to measure rotation velocities. For
abundance determinations, the standard equivalent width analysis was performed
differentially with respect to the Sun. For lithium and oxygen, we derived
abundances by comparing synthetic spectra with observed line features. We find
an iron abundance for dwarf stars equal to solar to within the margins of error
for IC 4756, and slightly above for NGC 5822 ([Fe/H]= 0.01 and 0.05 dex
respectively). The 3 stars in NG 4756 have lithium abundances between Log N(Li)
2.6 and 2.8 dex, the two stars in NGC 5822 have Log N(Li) ~ 2.8 and 2.5,
respectively. For sodium, silicon, and titanium, we show that abundances of
giants are significantly higher than those of the dwarfs of the same cluster
(about 0.15, 0.15, and 0.35 dex).",1002.2547v3
2010-03-18,"High magnetic field scales and critical currents in SmFeAs(O,F) crystals: promising for applications","Superconducting technology provides most sensitive field detectors, promising
implementations of qubits and high field magnets for medical imaging and for
most powerful particle accelerators. Thus, with the discovery of new
superconducting materials, such as the iron pnictides, exploring their
potential for applications is one of the foremost tasks. Even if the critical
temperature Tc is high, intrinsic electronic properties might render
applications rather difficult, particularly if extreme electronic anisotropy
prevents effective pinning of vortices and thus severely limits the critical
current density, a problem well known for cuprates. While many questions
concerning microscopic electronic properties of the iron pnictides have been
successfully addressed and estimates point to a very high upper critical field,
their application potential is less clarified. Thus we focus here on the
critical currents, their anisotropy and the onset of electrical dissipation in
high magnetic fields up to 65 T. Our detailed study of the transport properties
of optimally doped SmFeAs(O,F) single crystals reveals a promising combination
of high (>2 x 10^6 A/cm^2) and nearly isotropic critical current densities
along all crystal directions. This favorable intragrain current transport in
SmFeAs(O,F), which shows the highest Tc of 54 K at ambient pressure, is a
crucial requirement for possible applications. Essential in these experiments
are 4-probe measurements on Focused Ion Beam (FIB) cut single crystals with
sub-\mu\m^2 cross-section, with current along and perpendicular to the
crystallographic c-axis and very good signal-to-noise ratio (SNR) in pulsed
magnetic fields. The pinning forces have been characterized by scaling the
magnetically measured ""peak effect"".",1003.3612v2
2010-03-24,"Abundances of C, N, Sr and Ba on the red giant branch of omega Centauri","Abundances relative to iron for carbon, nitrogen, strontium and barium are
presented for 33 stars on the red giant branch of the globular cluster omega
Centauri. They are based on intermediate-resolution spectroscopic data covering
the blue spectral region analyzed using spectrum synthesis techniques. The data
reveal the existence of a broad range in the abundances of these elements, and
a comparison with similar data for main sequence stars enables insight into the
evolutionary history of the cluster. The majority of the red giant branch stars
were found to be depleted in carbon, i.e. [C/Fe]<0, while [N/Fe] for the same
stars shows a range of ~1 dex, from [N/Fe]~0.7 to 1.7 dex. The
strontium-to-iron abundance ratios varied from solar to mildly enhanced
(0.0<=[Sr/Fe]<=0.8), with [Ba/Fe] generally equal to or greater than [Sr/Fe].
The carbon and nitrogen abundance ratios for the one known CH star in the
sample, ROA 279, are [C/Fe]=0.6 and [N/Fe]=0.5 dex. Evidence for evolutionary
mixing on the red giant branch is found from the fact that the relative carbon
abundances on the main sequence are generally higher than those on the red
giant branch. However, comparison of the red giant branch and main sequence
samples shows that the upper level of nitrogen enhancement is similar in both
sets at [N/Fe]~2.0dex. This is most likely the result of primordial rather than
evolutionary mixing processes. One red giant branch star, ROA 276, was found to
have Sr and Ba abundance ratios. High resolution spectra of ROA 276 were
obtained with the Magellan Telescope/MIKE spectrograph combination to confirm
this result, revealing that ROA 276 is indeed an unusual star. For this star
calculations of the depletion effect strongly suggest that the observed Sr
enhancement in ROA 276 is of primordial origin, rather than originating from a
surface accretion event.",1003.4661v2
2010-04-12,A self-consistent approach to the hard and soft states of 4U 1705-44,"We analyzed two XMM-Newton observations of the bright atoll source 4U
1705-44, which can be considered a prototype of the class of the persistent NS
LMXBs showing both hard and soft states. The first observation was performed
when the source was in a hard low flux state, the second during a soft,
high-flux state. Both the spectra show broad iron emission lines. We fit the
spectra using a two-component model, together with a reflection model
specifically suited to the case of a neutron star, where the incident spectrum
has a blackbody shape. In the soft state, the reflection model, convolved with
a relativistic smearing component, consistently describes the broad features
present in the spectrum, and we find a clear relation between the temperature
of the incident flux and the temperature of the harder X-ray component that we
interpret as the boundary layer emission. In this state we find converging
evidence that the boundary layer outer radius is ~ 2 times the neutron star
radius. In the low flux state, we observe a change in the continuum shape of
the spectrum with respect to the soft state. Still, the broad local emission
features can be associated with a disk reflecting matter, but in a lower
ionization state, and possibly produced in an accretion disk truncated at
greater distance. Our analysis provides strong evidence that the reflection
component in soft states of LMXBs comes from to hard X-ray thermal irradiation,
which we identify with the boundary layer emission, also present in the
continuum model. In the hard state, the broad iron line if also produced by
reflection, and the continuum disk emission can be self-consistently accounted
if the disk is truncated at a greater distance than the soft state.",1004.1963v2
2010-04-13,Analysis of optical Fe II emission in a sample of AGN spectra,"We present a study of optical Fe II emission in 302 AGNs selected from the
SDSS. We group the strongest Fe II multiplets into three groups according to
the lower term of the transition (b $^4$F, a $^6$S and a $^4$G terms). These
correspond approximately to the blue, central, and red part respectively of the
""iron shelf"" around Hb. We calculate an Fe II template which takes into account
transitions into these three terms and an additional group of lines, based on a
reconstruction of the spectrum of I Zw 1. This Fe II template gives a more
precise fit of the Fe II lines in broad-line AGNs than other templates. We
extract Fe II, Ha, Hb, [O III] and [N II] emission parameters and investigate
correlations between them. We find that Fe II lines probably originate in an
Intermediate Line Region. We notice that the blue, red, and central parts of
the iron shelf have different relative intensities in different objects. Their
ratios depend on continuum luminosity, FWHM Hb, the velocity shift of Fe II,
and the Ha/Hb flux ratio. We examine the dependence of the well-known
anti-correlation between the equivalent widths of Fe II and [O III] on
continuum luminosity. We find that there is a Baldwin effect for [O III] but an
inverse Baldwin effect for the Fe II emission. The [O III]/Fe II ratio thus
decreases with L\lambda5100. Since the ratio is a major component of the
Boroson and Green eigenvector 1, this implies a connection between the Baldwin
effect and eigenvector 1, and could be connected with AGN evolution. We find
that spectra are different for Hb FWHMs greater and less than ~3000 km/s, and
that there are different correlation coefficients between the parameters.",1004.2212v2
2010-04-20,Convective shifts of iron lines in the spectrum of the solar photosphere,"The influence of the convective structure of the solar photosphere on the
shifts of spectral lines of iron was studied. Line profiles in the visible and
infrared spectrum were synthesized with the use of 2-D time-dependent
hydrodynamic solar model atmospheres. The dependence of line shifts on
excitation potential, wavelength, and line strength was analyzed, along with
the depression contribution functions. The line shifts were found to depend on
the location of the line formation region in convective cells and the
difference between the line depression contributions from granules and
intergranular lanes. In visible spectrum the weak and moderate lines are formed
deep in the photosphere. Their effective line formation region is located in
the central parts of granules, which make the major contribution to the
absorption of spatially unresolved lines. The cores of strong lines are formed
in upper photospheric layers where is formed reversed granulation due to
convection reversal and physical conditions change drastically there. As a
consequence the depression contributions in the strong line from intergranular
lanes with downflows substantially increase. This accounts for smaller blue
shifts of strong lines. In infrared spectrum the observed decrease in the blue
line shifts is explained by the fact that their effective line formation
regions lie higher in the photosphere and extend much further into the reversed
granulation region due to the line opacity rise with the increase of line
wavelength. Additionally the effective line formation depths of the synthesized
visible and infrared Fe I lines and their dependence on line parameters is
discussed.",1004.3438v1
2010-04-21,Nodes in the gap structure of the iron-arsenide superconductor Ba(Fe_{1-x}Co_x)_2As_2 from c-axis heat transport measurements,"The thermal conductivity k of the iron-arsenide superconductor
Ba(Fe_{1-x}Co_x)_2As_2 was measured down to 50 mK for a heat current parallel
(k_c) and perpendicular (k_a) to the tetragonal c axis, for seven Co
concentrations from underdoped to overdoped regions of the phase diagram (0.038
< x < 0.127). A residual linear term k_c0/T is observed in the T = 0 limit when
the current is along the c axis, revealing the presence of nodes in the gap.
Because the nodes appear as x moves away from the concentration of maximal T_c,
they must be accidental, not imposed by symmetry, and are therefore compatible
with an s_{+/-} state, for example. The fact that the in-plane residual linear
term k_a0/T is negligible at all x implies that the nodes are located in
regions of the Fermi surface that contribute strongly to c-axis conduction and
very little to in-plane conduction. Application of a moderate magnetic field
(e.g. H_c2/4) excites quasiparticles that conduct heat along the a axis just as
well as the nodal quasiparticles conduct along the c axis. This shows that the
gap must be very small (but non-zero) in regions of the Fermi surface which
contribute significantly to in-plane conduction. These findings can be
understood in terms of a strong k dependence of the gap Delta(k) which produces
nodes on a Fermi surface sheet with pronounced c-axis dispersion and deep
minima on the remaining, quasi-two-dimensional sheets.",1004.3804v1
2010-05-20,"Co-evolution of atmospheres, life, and climate","After Earth's origin, our host star, the Sun, was shining 20 to 25 percent
less brightly than today. Without greenhouse-like conditions to warm the
atmosphere, our early planet would have been an ice ball and life may never
have evolved. But life did evolve, which indicates that greenhouse gases must
have been present on early Earth to warm the planet. Evidence from the geologic
record indicates an abundance of the greenhouse gas CO2. CH4 was probably
present as well, and in this regard methanogenic bacteria, which belong to a
diverse group of anaerobic procaryotes that ferment CO 2 plus H2 to CH4, may
have contributed to modification of the early atmosphere. Molecular oxygen was
not present, as is indicated by the study of rocks from that era, which contain
iron carbonate rather than iron oxide. Multicellular organisms originated as
cells within colonies that became increasingly specialized. The development of
photosynthesis allowed the Sun's energy to be harvested directly by life forms.
The resultant oxygen accumulated in the atmosphere and formed the ozone layer
in the upper atmosphere. Aided by the absorption of harmful UV radiation in the
ozone layer, life colonized Earth's surface. Our own planet is a very good
example of how life forms modified the atmosphere over the planets' life time.
We show that these facts have to be taken into account when we discover and
characterize atmospheres of Earth-like exoplanets. If life has originated and
evolved on a planet, then it should be expected that a strong co-evolution
occurred between life and the atmosphere, the result of which is the planets'
climate.",1005.3589v1
2010-06-04,Spitzer spectral line mapping of the HH211 outflow,"Aims: We employ archival Spitzer slit-scan observations of the HH211 outflow
in order to investigate its warm gas content, assess the jet mass flux in the
form of H2 and probe for the existence of an embedded atomic jet. Methods:
Detected molecular and atomic lines are interpreted by means of emission line
diagnostics and an existing grid of molecular shock models. The physical
properties of the warm gas are compared against other molecular jet tracers and
to the results of a similar study towards the L1448-C outflow. Results: We have
detected and mapped the v=0-0 S(0) - S(7) H2 lines and fine-structure lines of
S, Fe+, and Si+. H2 is detected down to 5"" from the source and is characterized
by a ""cool"" T~300K and a ""warm"" T~1000 K component, with an extinction Av ~ 8
mag. The amount of cool H2 towards the jet agrees with that estimated from CO
assuming fully molecular gas. The warm component is well fitted by C-type
shocks with a low beam filling factor ~ 0.01-0.04 and a mass-flux similar to
the cool H2. The fine-structure line emission arises from dense gas with
ionization fraction ~0.5 - 5 x 10e-3, suggestive of dissociative shocks. Line
ratios to sulfur indicate that iron and silicon are depleted compared to solar
abundances by a factor ~10-50. Conclusions: Spitzer spectral mapping
observations reveal for the first time a cool H$_2$ component towards the CO
jet of HH211 consistent with the CO material being fully molecular and warm at
~ 300 K. The maps also reveal for the first time the existence of an embedded
atomic jet in the HH211 outflow that can be traced down to the central source
position. Its significant iron and silicon depletion excludes an origin from
within the dust sublimation zone around the protostar. The momentum-flux seems
insufficient to entrain the CO jet, although current uncertainties on jet speed
and shock conditions are too large for a definite conclusion.",1006.0821v1
2010-06-07,"Evidence for a Truncated Accretion Disc in the Low Luminosity Seyfert Galaxy, NGC 7213?","We present the broad-band 0.6-150 keV Suzaku and Swift BAT spectra of the low
luminosity Seyfert galaxy, NGC 7213. The time-averaged continuum emission is
well fitted by a single powerlaw of photon index Gamma = 1.75 and from
consideration of the Fermi flux limit we constrain the high energy cutoff to be
350 keV < E < 25 MeV. Line emission from both near-neutral iron K_alpha at 6.39
keV and highly ionised iron, from Fe_(xxv) and Fe_(xxvi), is strongly detected
in the Suzaku spectrum, further confirming the results of previous observations
with Chandra and XMM-Newton. We find the centroid energies for the Fe_(xxv) and
Fe_(xxvi) emission to be 6.60 keV and 6.95 keV respectively, with the latter
appearing to be resolved in the Suzaku spectrum. We show that the Fe_(xxv) and
Fe_(xxvi) emission can result from a highly photo-ionised plasma of column
density N_(H) ~ 3 x 10^(23) cm^(-2). A Compton reflection component, e.g.,
originating from an optically-thick accretion disc or a Compton-thick torus,
appears either very weak or absent in this AGN, subtending < 1 sr to the X-ray
source, consistent with previous findings. Indeed the absence of either neutral
or ionised Compton reflection coupled with the lack of any relativistic Fe K
signatures in the spectrum suggests that an inner, optically-thick accretion
disc is absent in this source. Instead, the accretion disc could be truncated
with the inner regions perhaps replaced by a Compton-thin Radiatively
Inefficient Accretion Flow. Thus, the Fe_(xxv) and Fe_(xxvi) emission could
both originate in ionised material perhaps at the transition region between the
hot, inner flow and the cold, truncated accretion disc on the order of 10^(3) -
10^(4) gravitational radii from the black hole. The origin for the unresolved
neutral Fe K_alpha emission is then likely to be further out, perhaps
originating in the optical BLR or a Compton-thin pc-scale torus.",1006.1318v1
2010-06-10,Fe II Emission in AGN: The Role of Total and Gas-Phase Iron Abundance,"Active galactic nuclei (AGN) have Fe II emission from the broad line region
(BLR) that differs greatly in strength from object to object. We examine the
role of the total and gas-phase iron abundance in determining Fe II strength.
Using AGN spectra from the Sloan Digital Sky Survey (SDSS) in the redshift
range of 0.2 < z < 0.35, we measure the Fe/Ne abundance of the narrow line
region (NLR) using the [Fe VII]/[Ne V] line intensity ratio. We find no
significant difference in the abundance of Fe relative to Ne in the NLR as a
function of Fe II/Hbeta. However, the N II/S II ratio increases a by a factor
of 2 with increasing Fe II strength. This indicates a trend in N/S abundance
ratio, and by implication in the overall metallicity of the NLR gas, with
increasing Fe II strength. We propose that the wide range of Fe II strength in
AGN largely results from the selective depletion of Fe into grains in the low
ionization portion of the BLR. Photoionization models show that the strength of
the optical Fe II lines varies almost linearly with gas-phase Fe abundance,
while the ultraviolet Fe II strength varies more weakly. Interstellar depletion
of Fe can be as large as two orders of magnitude, sufficient to explain the
wide range of optical Fe II strength in AGN. This picture is consistent with
the similarity of the BLR radius to the dust sublimation radius and with
indications of Fe II emitting gas flowing inwards from the dusty torus.",1006.2043v2
2010-07-22,Neutron-rich chromium isotope anomalies in supernova nanoparticles,"Neutron-rich isotopes with masses near that of iron are produced in type Ia
and II supernovae. Traces of such nucleosynthesis are found in primitive
meteorites in the form of variations in the isotopic abundance of 54Cr, the
most neutron-rich stable isotope of chromium. The hosts of these isotopic
anomalies must be presolar grains that condensed in the outflows of supernovae,
offering the opportunity to study the nucleosynthesis of iron-peak nuclei in
ways that complement spectroscopic observations and can inform models of
stellar evolution. However, despite almost two decades of extensive search, the
carrier of 54Cr anomalies is still unknown, presumably because it is
fine-grained and is chemically labile. Here we identify in the primitive
meteorite Orgueil the carrier of 54Cr-anomalies as nanoparticles, most likely
spinels that show large enrichments in 54Cr relative to solar composition
(54Cr/52Cr ratio >3.6xsolar). Such large enrichments in 54Cr can only be
produced in supernovae. The mineralogy of the grains supports condensation in
the O/Ne-O/C zones of a type II supernova, although a type Ia origin cannot be
excluded. We suggest that planetary materials incorporated different amounts of
these nanoparticles, possibly due to late injection by a nearby supernova that
also delivered 26Al and 60Fe to the solar system. This idea explains why the
relative abundance of 54Cr and other neutron-rich isotopes vary between planets
and meteorites. We anticipate that future isotopic studies of the grains
identified here will shed new light on the birth of the solar system and the
conditions insupernovae.",1007.4016v1
2010-07-29,The Mouse that Roared: A Superflare from the dMe Flare Star EV Lac detected by Swift and Konus-Wind,"We report on a large stellar flare from the nearby dMe flare star EV Lac
observed by the Swift and Konus-Wind satellites and the Liverpool Telescope. It
is the first large stellar flare from a dMe flare star to result in a Swift
trigger based on its hard X-ray intensity. Its peak f_X from 0.3--100 keV of
5.3x10^-8 erg/cm2/s is nearly 7000 times larger than the star's quiescent
coronal flux, and the change in magnitude in the white filter is >4.7. This
flare also caused a transient increase in EV Lac's bolometric luminosity
(L_bol) during the early stages of the flare, with a peak estimated L_X/L_bol
~3.1. We apply flare loop hydrodynamic modeling to the plasma parameter
temporal changes to derive a loop semi-length of l/Rstar =0.37 +/-0.07. The
soft X-ray spectrum of the flare reveals evidence of iron Kalpha emission at
6.4 keV. We model the Kalpha emission as fluorescence from the hot flare source
irradiating the photospheric iron, and derive loop heights of h/Rstar=0.1,
consistent within factors of a few with the heights inferred from hydrodynamic
modeling. The Kalpha emission feature shows variability on time scales of ~200
s which is difficult to interpret using the pure fluorescence hypothesis. We
examine Kalpha emission produced by collisional ionization from accelerated
particles, and find parameter values for the spectrum of accelerated particles
which can accommodate the increased amount of Kalpha flux and the lack of
observed nonthermal emission in the 20-50 keV spectral region.",1007.5300v1
2010-08-18,Optical properties of the iron-arsenic superconductor BaFe1.85Co0.15As2,"The transport and complex optical properties of the electron-doped
iron-arsenic superconductor BaFe1.85Co0.15As2 with Tc = 25 K have been examined
in the Fe-As planes above and below Tc. A Bloch-Gruneisen analysis of the
resistivity yields a weak electron-phonon coupling constant lambda_ph ~ 0.2.
The low-frequency optical response in the normal state appears to be dominated
by the electron pocket and may be described by a weakly-interacting Fermi
liquid with a Drude plasma frequency of omega_p,D ~ 7840 cm-1 (~ 0.972 eV) and
scattering rate 1/tau_D ~ 125 cm-1 (~ 15 meV) just above Tc. The
frequency-dependent scattering rate 1/tau(omega) has kinks at ~ 12 and 55 meV
that appear to be related to bosonic excitations. Below Tc the majority of the
superconducting plasma frequency originates from the electron pocket and is
estimated to be omega_p,S ~ 5200 cm-1 (lambda0 ~ 3000 Angstroms) for T << Tc,
indicating that less than half the free carriers in the normal state have
collapsed into the condensate, suggesting that this material is not in the
clean limit. Supporting this finding is the observation that this material
falls close to the universal scaling line for a BCS dirty-limit superconductor
in the weak-coupling limit. There are two energy scales for the
superconductivity in the optical conductivity and photo-induced reflectivity at
Delta1 ~ 3.1 +/- 0.2 meV and Delta2 ~ 7.4 +/- 0.3 meV. This corresponds to
either the gaping of the electron and hole pockets, respectively, or an
anisotropic s-wave gap on the electron pocket; both views are consistent with
the s+/- model.",1008.3098v2
2010-08-18,Cold fronts and multi-temperature structures in the core of Abell 2052,"The physics of the coolest phases in the hot Intra-Cluster Medium (ICM) of
clusters of galaxies is yet to be fully unveiled. X-ray cavities blown by the
central Active Galactic Nucleus (AGN) contain enough energy to heat the
surrounding gas and stop cooling, but locally blobs or filaments of gas appear
to be able to cool to low temperatures of 10^4 K. In X-rays, however, gas with
temperatures lower than 0.5 keV is not observed. Using a deep XMM-Newton
observation of the cluster of galaxies Abell 2052, we derive 2D maps of the
temperature, entropy, and iron abundance in the core region. About 130 kpc
South-West of the central galaxy, we discover a discontinuity in the surface
brightness of the hot gas which is consistent with a cold front. Interestingly,
the iron abundance jumps from ~0.75 to ~0.5 across the front. In a smaller
region to the North-West of the central galaxy we find a relatively high
contribution of cool 0.5 keV gas, but no X-ray emitting gas is detected below
that temperature. However, the region appears to be associated with much cooler
H-alpha filaments in the optical waveband. The elliptical shape of the cold
front in the SW of the cluster suggests that the front is caused by sloshing of
the hot gas in the clusters gravitational potential. This effect is probably an
important mechanism to transport metals from the core region to the outer parts
of the cluster. The smooth temperature profile across the sharp jump in the
metalicity indicates the presence of heat conduction and the lack of mixing
across the discontinuity. The cool blob of gas NW of the central galaxy was
probably pushed away from the core and squeezed by the adjacent bubble, where
it can cool efficiently and relatively undisturbed by the AGN. Shock induced
mixing between the two phases may cause the 0.5 keV gas to cool non-radiatively
and explain our non-detection of gas below 0.5 keV.",1008.3109v2
2010-08-18,"Open clusters towards the Galactic center: chemistry and dynamics. A VLT spectroscopic study of NGC6192, NGC6404, NGC6583","In the framework of the study of the Galactic metallicity gradient and its
time evolution, we present new high-resolution spectroscopic observations
obtained with FLAMES and the fiber link to UVES at VLT of three open clusters
(OCs) located within $\sim$7~kpc from the Galactic Center (GC): NGC~6192,
NGC~6404, NGC~6583. We also present new orbit determination for all OCs with
Galactocentric distances (R$_{\rm{GC}}) \leq$8~kpc and metallicity from
high-resolution spectroscopy. We aim to investigate the slope of the inner disk
metallicity gradient as traced by OCs and at discussing its implication on the
chemical evolution of our Galaxy. We have derived memberships of a group of
evolved stars for each clusters, obtaining a sample of 4, 4, and 2 member stars
in NGC~6192, NGC~6404, and NGC~6583, respectively. Using standard LTE analysis
we derived stellar parameters and abundance ratios for the iron-peak elements
Fe, Ni, Cr, and for the $\alpha$-elements Al, Mg, Si, Ti, Ca. We calculated the
orbits of the OCs currently located within 8~kpc from the GC, and discuss their
implication on the present-time radial location. {The average metallicities of
the three clusters are all oversolar: [Fe/H]= $+0.12\pm0.04$ (NGC~6192),
$+0.11\pm0.04$ (NGC 6404), $+0.37\pm0.03$ (NGC 6583). They are in qualitative
agreement with their Galactocentric distances, being all internal OCs, and thus
expected to be metal richer than the solar neighborhood. The abundance ratios
of the other elements over iron [X/Fe] are consistent with solar values. The
clusters we have analysed, together with other OC and Cepheid data, confirm a
steep gradient in the inner disk, a signature of an evolutionary rate different
than in the outer disk.",1008.3158v1
2010-10-01,Absorption Features in Spectra of Magnetized Neutron Stars,"The X-ray spectra of some magnetized isolated neutron stars (NSs) show
absorption features with equivalent widths (EWs) of 50 - 200 eV, whose nature
is not yet well known. To explain the prominent absorption features in the soft
X-ray spectra of the highly magnetized (B ~ 10^{14} G) X-ray dim isolated NSs
(XDINSs), we theoretically investigate different NS local surface models,
including naked condensed iron surfaces and partially ionized hydrogen model
atmospheres, with semi-infinite and thin atmospheres above the condensed
surface. We also developed a code for computing light curves and integral
emergent spectra of magnetized neutron stars with various temperature and
magnetic field distributions over the NS surface. We compare the general
properties of the computed and observed light curves and integral spectra for
XDINS RBS\,1223 and conclude that the observations can be explained by a thin
hydrogen atmosphere above the condensed iron surface, while the presence of a
strong toroidal magnetic field component on the XDINS surface is unlikely. We
suggest that the harmonically spaced absorption features in the soft X-ray
spectrum of the central compact object (CCO) 1E 1207.4-5209 (hereafter 1E 1207)
correspond to peaks in the energy dependence of the free-free opacity in a
quantizing magnetic field, known as quantum oscillations. To explore observable
properties of these quantum oscillations, we calculate models of hydrogen NS
atmospheres with B ~ 10^{10} - 10^{11} G (i.e., electron cyclotron energy
E_{c,e} ~ 0.1 - 1 keV) and T_eff = 1 - 3 MK. Such conditions are thought to be
typical for 1E 1207. We show that observable features at the electron cyclotron
harmonics with EWs \approx 100 - 200 eV can arise due to these quantum
oscillations.",1010.0125v1
2010-10-21,The RAVE Survey: Rich in Very Metal-Poor Stars,"Very metal-poor stars are of obvious importance for many problems in chemical
evolution, star formation, and galaxy evolution. Finding complete samples of
such stars which are also bright enough to allow high-precision individual
analyses is of considerable interest. We demonstrate here that stars with iron
abundances [Fe/H] < -2 dex, and down to below -4 dex, can be efficiently
identified within the Radial Velocity Experiment (RAVE) survey of bright stars,
without requiring additional confirmatory observations. We determine a
calibration of the equivalent width of the Calcium triplet lines measured from
the RAVE spectra onto true [Fe/H], using high spectral resolution data for a
subset of the stars. These RAVE iron abundances are accurate enough to obviate
the need for confirmatory higher-resolution spectroscopy. Our initial study has
identified 631 stars with [Fe/H] <= -2, from a RAVE database containing
approximately 200,000 stars. This RAVE-based sample is complete for stars with
[Fe/H] < -2.5, allowing statistical sample analysis. We identify three stars
with [Fe/H] <= -4. Of these, one was already known to be `ultra metal-poor',
one is a known carbon-enhanced metal-poor star, but we obtain [Fe/H]= -4.0,
rather than the published [Fe/H]=-3.3, and derive [C/Fe] = +0.9, and [N/Fe] =
+3.2, and the third is at the limit of our S/N. RAVE observations are on-going
and should prove to be a rich source of bright, easily studied, very metal-poor
stars.",1010.4491v1
2010-10-30,Symmetry breaking orbital anisotropy on detwinned Ba(Fe1-xCox)2As2 above the spin density wave transition,"Nematicity, defined as broken rotational symmetry, has recently been observed
in competing phases proximate to the superconducting phase in the cuprate high
temperature superconductors. Similarly, the new iron-based high temperature
superconductors exhibit a tetragonal to orthorhombic structural transition
(i.e. a broken C4 symmetry) that either precedes or is coincident with a
collinear spin density wave (SDW) transition in undoped parent compounds, and
superconductivity arises when both transitions are suppressed via doping.
Evidence for strong in-plane anisotropy in the SDW state in this family of
compounds has been reported by neutron scattering, scanning tunneling
microscopy, and transport measurements. Here we present an angle resolved
photoemission spectroscopy study of detwinned single crystals of a
representative family of electron-doped iron-arsenide superconductors,
Ba(Fe1-xCox)2As2 in the underdoped region. The crystals were detwinned via
application of in-plane uniaxial stress, enabling measurements of single domain
electronic structure in the orthorhombic state. At low temperatures, our
results clearly demonstrate an in-plane electronic anisotropy characterized by
a large energy splitting of two orthogonal bands with dominant dxz and dyz
character, which is consistent with anisotropy observed by other probes. For
compositions x>0, for which the structural transition (TS) precedes the
magnetic transition (TSDW), an anisotropic splitting is observed to develop
above TSDW, indicating that it is specifically associated with TS. For
unstressed crystals, the band splitting is observed close to TS, whereas for
stressed crystals the splitting is observed to considerably higher
temperatures, revealing the presence of a surprisingly large in-plane nematic
susceptibility in the electronic structure.",1011.0050v2
2010-11-07,On the multi-orbital band structure and itinerant magnetism of iron-based superconductors,"This paper explains the multi-orbital band structures and itinerant magnetism
of the iron-pnictide and chalcogenides. We first describe the generic band
structure of an isolated FeAs layer. Use of its Abelian glide-mirror group
allows us to reduce the primitive cell to one FeAs unit. From
density-functional theory, we generate the set of eight Fe $d$ and As $p$
localized Wannier functions for LaOFeAs and their tight-binding (TB)
Hamiltonian, $h(k)$. We discuss the topology of the bands, i.e. allowed and
avoided crossings, the origin of the d6 pseudogap, as well as the role of the
As $p$ orbitals and the elongation of the FeAs$_{4}$ tetrahedron. We then
couple the layers, mainly via interlayer hopping between As $p_{z}$ orbitals,
and give the formalism for simple and body-centered tetragonal stackings. This
allows us to explain the material-specific 3D band structures. Due to the high
symmetry, several level inversions take place as functions of $k_{z}$ or
pressure, resulting in linear band dispersions (Dirac cones). The underlying
symmetry elements are, however, easily broken, so that the Dirac points are not
protected, nor pinned to the Fermi level. From the paramagnetic TB Hamiltonian,
we form the band structures for spin spirals with wavevector $q$ by coupling
$h(k)$ and $h (k+q)$. The band structure for stripe order is studied as a
function of the exchange potential, $\Delta$, using Stoner theory. Gapping of
the Fermi surface (FS) for small $\Delta $ requires matching of FS dimensions
(nesting) and $d$-orbital characters. The origin of the propeller-shaped FS is
explained. Finally, we express the magnetic energy as the sum over
band-structure energies, which enables us to understand to what extent the
magnetic energies might be described by a Heisenberg Hamiltonian, and the
interplay between the magnetic moment and the elongation of the FeAs4
tetrahedron.",1011.1658v3
2010-12-02,Tracing the evolution of NGC6397 through the chemical composition of its stellar populations,"With the aim to constrain multiple populations in the metal-poor globular
cluster NGC6397, we analyse and discuss the chemical compositions of a large
number of elements in 21 red giant branch stars. High-resolution spectra were
obtained with the FLAMES/UVES spectrograph on VLT. We have determined non-LTE
abundances of Na and LTE abundances for the remaining 21 elements, including O,
Mg, Al, alpha, iron-peak, and neutron-capture elements, many of which have not
previously been analysed for this cluster. We have also considered the
influence of possible He enrichment in the analysis of stellar spectra. We find
that the Na abundances of evolved, as well as unevolved, stars show a distinct
bimodality, which suggests the presence of two stellar populations; one
primordial stellar generation with composition similar to field stars, and a
second generation that is enriched in material processed through
hydrogen-burning (enriched in Na and Al and depleted in O and Mg). The cluster
is dominated (75%) by the second generation. The red giant branch show a
similar bimodal distribution in the Stroemgren colour index c_y=c_1-(b-y),
implying a large difference also in N abundance. The two populations have the
same composition of all analysed elements heavier than Al, within the
measurement uncertainty of the analysis, with the possible exception of [Y/Fe].
Using two stars with close to identical stellar parameters, one from each
generation, we estimate the difference in He content, Delta Y=0.01+-0.06, given
the assumption that the mass fraction of iron is the same for the stars.
Finally, we show that winds from fast rotating massive stars of the first
generation can be held responsible for the abundance patterns observed in
NGC6397 second generation long-lived stars and estimate that the initial mass
of the cluster were at least ten times higher than its present-day value.",1012.0477v2
2011-01-24,A non-LTE study of neutral and singly-ionized iron line spectra in 1D models of the Sun and selected late-type stars,"A comprehensive model atom for Fe with more than 3000 energy levels is
presented. As a test and first application of this model atom, Fe abundances
are determined for the Sun and five stars with well determined stellar
parameters and high-quality observed spectra. Non-LTE leads to systematically
depleted total absorption in the Fe I lines and to positive abundance
corrections in agreement with the previous studies, however, the magnitude of
non-LTE effect is smaller compared to the earlier results. Non-LTE corrections
do not exceed 0.1 dex for the solar metallicity and mildly metal-deficient
stars, and they vary within 0.21 dex and 0.35 dex in the very metal-poor stars
HD 84937 and HD 122563, respectively, depending on the assumed efficiency of
collisions with hydrogen atoms. Based on the analysis of the Fe I/Fe II
ionization equilibrium in these two stars, we recommend to apply the Drawin
formalism in non-LTE studies of Fe with a scaling factor of 0.1. For the Fe II
lines, non-LTE corrections do not exceed 0.01 dex in absolute value. The solar
non-LTE abundance obtained from 54 Fe I lines is 7.56+-0.09 and the abundance
from 18 Fe II lines varies between 7.41+-0.11 and 7.56+-0.05 depending on the
source of the gf-values. Thus, gf-values available for the iron lines are not
accurate enough to pursue high-accuracy absolute abundance determinations.
Lines of Fe I give, on average, a 0.1 dex lower abundance compared to those of
Fe II lines for HD 61421 and HD 102870, even when applying a differential
analysis relative to the Sun. A disparity between Fe I and Fe II points to
problems of stellar atmosphere modelling or/and effective temperature
determination.",1101.4570v1
2011-01-25,On the Structure of Vacancy Ordered Superconducting Alkali Metal Iron Selenide,"With single crystal X-ray diffraction studies, we compare the structures of
three sample showing optimal superconductivity, K0.774(4)Fe1.613(2)Se2,
K0.738(6)Fe1.631(3)Se2 and Cs0.748(2)Fe1.626(1)Se2. All have an almost
identical ordered vacancy structure with a ({\sqrt}5 x {\sqrt}5 x 1) super
cell. The tetragonal unit cell, space group I4/m, possesses lattice parameters
at 250K of a = b = 8.729(2) {\AA} and c = 14.120(3) {\AA}, a = b = 8.7186(12)
{\AA} and c = 14.0853(19) {\AA} and at 295 K, a = b = 8.8617(16) {\AA} and c =
15.304(3) {\AA} for the three crystals, respectively. The structure contains
two iron sites; one is almost completely empty, whilst the other is fully
occupied. There are similarly two alkali metal sites that are occupied in the
range of 72.2(2) % to 85.3(3) %. The inclusion of alkali metals and the
presence of vacancies within the structure allows for considerable relaxation
of the FeSe4 tetrahedron, compared with members of the Fe(Te, Se, S) series,
and the resulting shift of the Se - F - Se bond angles to less distorted
geometry could be important in understanding the associated increase in the
superconducting transition temperature. The structure of these superconductors
distinguishes themselves from the structure of the non-superconducting phases
by an almost complete absence of Fe on the (0 0.5 0.25) site as well as lower
alkali metal occupancy that ensures an exact Fe2+ oxidation state, which are
clearly critical parameters in the promotion of superconductivity.",1101.4882v2
2011-01-25,A possible solution to the [alpha/Fe]-sigma problem in early type galaxies within a hierarchical galaxy formation model,"The most massive elliptical galaxies apparently formed the fastest, because
the ratio of alpha elements (such as oxygen) to iron is the smallest. In fact,
iron is mainly produced from type Ia supernovae on a timescale of ~ 0.1-1
billion years, while the alpha elements come from massive stars on timescales
of a few tens of million years (Matteucci 1994). Reproducing such a alpha/Fe
correlation has long been a severe problem for cosmological theories of galaxy
formation, which envisage massive galaxies to assemble gradually from smaller
progenitors, and to be characterized by a star formation history too much
extended towards late cosmic times. While it has recently become clear that
feedback from Active Galactic Nuclei (AGN) activity play a role in the late
quenching of star formation (e.g. Cattaneo et al. 2009), and that early star
formation history in the galaxy progenitors affect the alpha/Fe ratio (Calura &
Menci 2009), major mergers alone cannot enhance the star formation in the
high-redshift progenitors to the levels required to match the steepness of the
observed alpha/Fe correlation (Spolaor et al. 2010). Here we report that the
inclusion of the effects of fly-by 'harassments', that trigger lower level
starbursts, combined with the AGN quenching of the starburst activity,
considerably enhances the capability to account for the observed alpha/Fe ratio
in ellipticals within cosmological galaxy formation models . The critical
difference between the earlier work and the present result is the effect of
starbursts driven by fly-by encounters that would have been very common amongst
the high-redshift progenitors of massive galaxies and which would have boosted
star formation in the first 2 billion years after the Big Bang, combined with
quenching of the burst activity within the first 3-4 Gyr.",1101.4938v1
2011-04-26,On the driver of relativistic effects strength in Seyfert galaxies,"Spectroscopy of X-ray emission lines emitted in accretion discs around
supermassive black holes is one of the most powerful probes of the accretion
flow physics and geometry, while also providing in principle observational
constraints on the black hole spin.[...] We aim at determining the ultimate
physical driver of the strength of this relativistic reprocessing feature. We
first extend the hard X-ray flux-limited sample of Seyfert galaxies studied so
far (FERO, de la Calle Perez et al. 2010) to obscured objects up to a column
density N_H=6x10^23 atoms/cm/cm. We verify that none of the line properties
depends on the AGN optical classification, as expected from the Seyfert
unification scenarios. There is also no correlation between the accretion disc
inclination, as derived from formal fits of the line profiles, and the optical
type or host galaxy aspect angle, suggesting that the innermost regions of the
accretion disc and the host galaxy plane are not aligned. [...]. Data are not
sensitive enough to the detailed ionisation state of the line-emitting disc.
However, the lack of dependency of the line EW on either the luminosity or the
rest-frame centroid energy rules out that disc ionisation plays an important
role on the EW dynamical range in Seyferts. The dynamical range of the
relativistically broadened K-alpha iron line EW in nearby Seyferts appears to
be mainly determined by the properties of the innermost accretion flow. We
discuss several mechanisms (disc ionisation, disc truncation, aberration due to
a mildly relativistic outflowing corona) which can explain this. [...]
Observational data are still not in contradiction with scenarios invoking
different mechanisms for the spectral complexity around the iron line, most
notably the ""partial covering"" absorption scenario. (abridged).",1104.4918v1
2011-04-27,Spitzer spectra of evolved stars in omega Centauri and their low-metallicity dust production,"Dust production is explored around 14 metal-poor ([Fe/H] = -1.91 to -0.98)
giant stars in the Galactic globular cluster omega Centauri using new Spitzer
IRS spectra. This sample includes the cluster's post-AGB and carbon stars and
is thus the first representative spectral study of dust production in a
metal-poor ([Fe/H] < -1) population. Only the more metal rich stars V6 and V17
([Fe/H] = -1.08, -1.06) exhibit silicate emission, while the five other stars
with mid-infrared excess show only a featureless continuum which we argue is
caused by metallic iron dust grains. We examine the metallicity of V42, and
find it is likely part of the metal-rich population ([Fe/H] ~ -0.8). Aside from
the post-AGB star V1, we find no star from the cluster's bulk, metal-poor
([Fe/H] < -1.5) population - including the carbon stars - to be producing
detectable amounts of dust. We compare the dust production to the stars'
H-alpha line profiles obtained at the Magellan/Clay telescope at Las Campanas
Observatory, finding pulsation shocking in the strongest pulsators (V6, V17 and
V42), but evidence of outflow in all other stars. We conclude that the onset of
dust production does not signify a fundamental change in the material leaving
the star. Our data add to a growing body of evidence that metallic iron
dominates dust production in metal-poor, oxygen-rich stars, but that dust is
probably not the primary accelerant of winds in this mass-metallicity regime.",1104.5155v1
2011-05-16,The influence of non-isotropic scattering of thermal radiation on spectra of brown dwarfs and hot exoplanets,"(abridged) We calculate near-infrared thermal emission spectra using a
doubling-adding radiative transfer code, which includes scattering by clouds
and haze. Initial temperature profiles and cloud optical depths are taken from
the drift-phoenix brown dwarf model. As is well known, cloud particles change
the spectrum compared to when clouds are ignored. The clouds reduce fluxes in
the near-infrared spectrum and make it redder than for the clear sky case. We
also confirm that not including scattering in the spectral calculations can
result in errors on the spectra of many tens of percent, both in magnitude and
in variations with wavelength. This is especially apparent for particles that
are larger than the wavelength and only have little iron in them. Scattering
particles will show deeper absorption features than absorbing (e.g. iron)
particles and particle size will also affect the calculated infrared colours.
Large particles also tend to be strongly forward-scattering, and we show that
assuming isotropic scattering in this case also leads to very large errors in
the spectrum. Thus, care must be taken in the choice of radiative transfer
method for heat balance or spectral calculations when clouds are present in the
atmosphere. Besides the choice of radiative transfer method, the type of
particles that are predicted by models will change conclusions about e.g.
infrared colours and trace gas abundances. As a result, knowledge of the
scattering properties of the clouds is essential when deriving temperature
profiles or gas abundances from direct infrared observations of exoplanets or
brown dwarfs and from secondary eclipse measurements of transiting exoplanets,
since scattering clouds will change the depth of gas absorption features, among
other things. Thus, ignoring the presence of clouds can yield retrieved
properties that differ significantly from the real atmospheric properties.",1105.3062v2
2011-07-05,GRAVITAS : General Relativistic Astrophysics VIa Timing And Spectroscopy: An ESA M3 mission proposal,"GRAVITAS is an X-ray observatory, designed and optimised to address the ESA
Cosmic Vision theme of ""Matter under extreme conditions"". It was submitted as a
response to the call for M3 mission proposals. The concept centres around an
X-ray telescope of unprecedented effective area, which will focus radiation
emitted from close to the event horizon of black holes or the surface of
neutron stars. To reveal the nature and behaviour of matter in the most extreme
astrophysical environments, GRAVITAS targets a key feature in the X-ray spectra
of compact objects: the iron Kalpha line at ~6.5 keV. The energy, profile, and
variability of this emission line, and the properties of the surrounding
continuum emission, shaped by General Relativity (GR) effects, provide a unique
probe of gravity in its strong field limit. Among its prime targets are
hundreds of supermassive black holes in bright Active Galactic Nuclei (AGN),
which form the perfect laboratory to help understand the physical processes
behind black hole growth. Accretion plays a fundamental role in the shaping of
galaxies throughout cosmic time, via the process of feedback. Modest
(~sub-arcmin) spatial resolution would deliver the necessary sensitivity to
extend high quality X-ray spectroscopy of AGN to cosmologically-relevant
distances. Closer to home, ultra-high count rate capabilities and
sub-millisecond time resolution enable the study of GR effects and the equation
of state of dense matter in the brightest X-ray binaries in our own Galaxy,
using multiple probes, such as the broad iron line, the shape of the disk
continuum emission, quasi-periodic oscillations, reverberation mapping, and
X-ray burst oscillations. Despite its breakthrough capabilities, all enabling
technologies for GRAVITAS are already in a high state of readiness. It is based
on ultra light-weight X-ray optics and a focal plane detector using silicon
technology.",1107.0955v1
2011-08-04,Identifying a new intermediate-polar using XMM-Newton and INTEGRAL,"The bright X-ray source, 2XMMi J180438.7-145647 is fortunate to have long
baseline observations in INTEGRAL that compliment observations taken by other
missions. Optical spectroscopy of this object has suggested a distance of ~7
kpc and an identification with a low mass X-ray binary. We instead use the
X-ray data from 0.3-40 keV to identify the source as a bright intermediate
polar (IP) with an estimate for the white dwarf mass of~0.60 M_solar. This
identification is supported by the presence of an iron triplet, the component
lines of which are some of the strongest seen in IPs; and the signature of the
spin period of the white dwarf at ~24 mins. We note that the lack of broad-band
variability may suggest that this object is a stream-fed IP, similar in many
respects to the well studied IP, V2400 Oph. Phase-binning has allowed us to
create spectra corresponding to the peaks and troughs of the lightcurve from
which we determine that the spectra appear harder in the troughs, consistent
with the behaviour of other IPs binned on their spin periods. This work
strongly suggests a mis-identification in the optical due to the presence of
large columns of enshrouding material. We instead propose a distance to the
source of <2.5 kpc to be consistent with the luminosities of other IPs in the
dim, hard state. The relatively high flux of the source together with the
strength of the iron lines may, in future, allow the source to be used to
diagnose the properties of the shock heated plasma and the reflected component
of the emission.",1108.1105v1
2011-08-12,The High Energy view of the Broad Line Radio Galaxy 3C 111,"We present the analysis of Suzaku and XMM-Newton observations of the
broad-line radio galaxy (BLRG) 3C 111. Its high energy emission shows
variability, a harder continuum with respect to the radio quiet AGN population,
and weak reflection features. Suzaku found the source in a minimum flux level;
a comparison with the XMM-Newton data implies an increase of a factor of 2.5 in
the 0.5-10 keV flux, in the 6 months separating the two observations. The iron
K complex is detected in both datasets, with rather low equivalent width(s).
The intensity of the iron K complex does not respond to the change in continuum
flux. An ultra-fast, high-ionization outflowing gas is clearly detected in the
XIS data; the absorber is most likely unstable. Indeed, during the XMM-Newton
observation, which was 6 months after, the absorber was not detected. No clear
roll-over in the hard X-ray emission is detected, probably due to the emergence
of the jet as a dominant component in the hard X-ray band, as suggested by the
detection above ~ 100 keV with the GSO on-board Suzaku, although the present
data do not allow us to firmly constrain the relative contribution of the
different components. The fluxes observed by the gamma-ray satellites CGRO and
Fermi would be compatible with the putative jet component if peaking at
energies E ~ 100 MeV. In the X-ray band, the jet contribution to the continuum
starts to be significant only above 10 keV. If the detection of the jet
component in 3C 111 is confirmed, then its relative importance in the X-ray
energy band could explain the different observed properties in the high-energy
emission of BLRGs, which are otherwise similar in their other multiwavelength
properties. Comparison between X-ray and gamma-ray data taken at different
epochs suggests that the strong variability observed for 3C 111 is probably
driven by a change in the primary continuum.",1108.2609v1
2011-08-30,The Bulge Radial Velocity/Abundance Assay,"The Bulge Radial Velocity/Abundance Assay (BRAVA) has accomplished a survey
of 10,000 red giants in the Southern Galactic bulge, approximately spanning -8
deg. < l < +8 deg. and -3 deg. <b < -8 deg., a region within roughly 1 kpc from
the nucleus. We find that the Galactic bulge at b=-4 deg. displays a clear
departure from solid body rotation, and that the rotation field along the major
axis at b=-6 deg. and b=-8 deg is identical to that at lower latitude; this is
""cylindrical"" rotation, a hallmark observed in edge-on bars. Comparison of the
BRAVA dataset with an N-body bar shows that >90% of the bulge population is in
the bar, leaving little room for a ""classical"" bulge component. We also report
on the first iron abundance and composition measurements in the outer bulge, at
b=-8 deg. The iron abundance in this field falls on the trend of a suspected
gradient measured from high resolution spectroscopy of bulge clump stars.
Further, we find that the trends of [\alpha/Fe] vs [Fe/H] that characterize the
bulge at lower latitude are present 1 kpc from the nucleus, consistent with a
rapid (<1 Gyr) timescale for the formation of the bulge, even near its
boundary. Although the dynamics of the bulge are consistent with those of a
dynamically buckled N-body bar, the presence of an abundance gradient is not
compatible with purely dynamical processes; we propose that missing baryonic
physics is needed. We also report on the remarkable massive bulge globular
cluster Terzan 5, which has a bimodal abundance and composition distribution,
and is proposed as the remnant of a population of primordial building block
stellar systems that formed the bulge. Terzan 5 is presently a unique case, and
it is important to test whether the dissolution of systems similar to it
populated the bulge.",1108.6044v1
2011-09-01,Suzaku Observations of Iron K-lines from the Intracluster Medium of the Coma Cluster,"The Coma cluster was observed with an X-ray Imaging Spectrometer (XIS)
onboard Suzaku in six pointings, including the central X-ray peak region, the
14'west offset region, 30'and 34'north-west offset regions, and 44'and
60'south-west offset regions. Owing to its lower background level, Suzaku has
better sensitivity to Fe K-alpha lines than other satellites. Using precise Fe
line measurements, we studied the temperature structure, possible bulk motions,
and iron abundance distributions in the intracluster medium (ICM). The observed
spectra were well-represented by a single-temperature model, and two- or three-
temperature model did not improve chi-square substantially. The temperature,
derived from K-alpha line ratios of H-like and He-like Fe, agree with those
derived from the single-temperature model. Because the line ratio is a steep
function of temperature, the consistency supports the accuracy of temperature
measurements conducted with Suzaku. Within the 34'region, the redshift derived
from the central energy of the He-like Fe line is consistent with that from
optical observations, within a calibration error of 18 eV or 818 km/s in the
line of sight. This value is smaller than the sound velocity of ICM, which is
1500 km/s. The central energy of Fe lines at the 44'offset region around the
NGC 4839 subcluster is also consistent with those within the 34'region. These
results on the temperature and velocity structure suggest that the core of the
cluster is in a relaxed state, and non-thermal electrons relevant to the radio
halo are accelerated by intracluster turbulence rather than large-scale shocks.
Fe abundance is almost constant at 0.4 solar within the 34'region, and
decreases with radius. This value is slightly lower than those of other
clusters, which means the gas have been mixed well during a past merger
associated with the growth of the cluster.",1109.0154v2
2011-09-09,The Chemical Evolution of Globular Clusters - II. Metals and Fluorine,"In the first paper in this series, we proposed a new framework in which to
model the chemical evolution of globular clusters. This model, is predicated
upon the assumption that clusters form within an interstellar medium enriched
locally by the ejecta of a single Type Ia supernova and varying numbers of
asymptotic giant branch stars, superimposed on an ambient medium pre-enriched
by low-metallicity Type II supernovae. Paper I was concerned with the
application of this model to the observed abundances of several reactive
elements and so-called non-metals for three classical intermediate-metallicity
clusters, with the hallmark of the work being the successful recovery of many
of their well-known elemental and isotopic abundance anomalies. Here, we expand
upon our initial analysis by (a) applying the model to a much broader range of
metallicities (from the factor of three explored in Paper I, to now, a factor
of ~50; i.e., essentially, the full range of Galactic globular cluster
abundances, and (b) incorporating a broader suite of chemical species,
including a number of iron-peak isotopes, heavier alpha-elements, and fluorine.
While most empirical globular cluster abundance trends are reproduced, our
model would suggest the need for a higher production of Ca, Si, and Cu in
low-metallicity (or so-called ""prompt"") Type Ia supernovae than predicted in
current stellar models in order to reproduce the observed trends in NGC 6752,
and a factor of two reduction in carbon production from asymptotic giant branch
stars to explain the observed trends between carbon and nitrogen. Observations
of heavy-element isotopes produced primarily by Type Ia supernovae, including
those of titanium, iron, and nickel, could support/refute unequivocally our
proposed framework. Hydrodynamical simulations would be necessary to study its
viability from a dynamical point of view.",1109.1938v1
2011-09-21,NGC 5548: Lack of a Broad Fe K Line and Constraints on the Location of the Hard X-ray Source,"We present an analysis of the co-added and individual 0.7-40 keV spectra from
seven Suzaku observations of the Sy 1.5 galaxy NGC 5548 taken over a period of
eight weeks. We conclude that the source has a moderately ionized, three-zone
warm absorber, a power-law continuum, and exhibits contributions from cold,
distant reflection. Relativistic reflection signatures are not significantly
detected in the co-added data, and we place an upper limit on the equivalent
width of a relativistically broad Fe K line at EW \leq 26 eV at 90% confidence.
Thus NGC 5548 can be labeled an ""weak"" type-1 AGN in terms of its observed
inner disk reflection signatures, in contrast to sources with very broad,
strong iron lines such as MCG-6-30-15, which are likely much fewer in number.
We compare physical properties of NGC 5548 and MCG-6-30-15 that might explain
this difference in their reflection properties. Though there is some evidence
that NGC 5548 may harbor a truncated inner accretion disk, this evidence is
inconclusive, so we also consider light bending of the hard X-ray continuum
emission in order to explain the lack of relativistic reflection in our
observation. If the absence of a broad Fe K line is interpreted in the
light-bending context, we conclude that the source of the hard X-ray continuum
lies at <100 gravitational radii. We note, however, that light-bending models
must be expanded to include a broader range of physical parameter space in
order to adequately explain the spectral and timing properties of average AGN,
rather than just those with strong, broad iron lines.",1109.4651v1
2011-10-20,High Resolution XMM-Newton Spectroscopy of the Cooling Flow Cluster A3112,"We examine high signal to noise XMM-Newton European Photon Imaging Camera
(EPIC) and Reflection Grating Spectrometer (RGS) observations to determine the
physical characteristics of the gas in the cool core and outskirts of the
nearby rich cluster A3112. The XMM-Newton Extended Source Analysis Software
data reduction and background modeling methods were used to analyze the XMM-
Newton EPIC data. From the EPIC data we find that the iron and silicon
abundance gradients show significant increase towards the center of the cluster
while the oxygen abundance profile is centrally peaked but has a shallower
distribution than that of iron. The X-ray mass modeling is based on the
temperature and deprojected density distributions of the intra-cluster medium
determined from EPIC observations. The total mass of A3112 obeys the M-T
scaling relations found using XMM-Newton and Chandra observations of massive
clusters at R500. The gas mass fraction f_gas= 0.149^{+0.036}_{-0.032} at R500,
is consistent with the seven-year WMAP results. The comparisons of line fluxes
and flux limits on the Fe XVII and Fe XVIII lines obtained from high resolution
RGS spectra indicate that there is no spectral evidence for cooler gas
associated with the cluster with temperature below 1.0 keV in the central <38""
(\sim 52 kpc) region of A3112. High resolution RGS spectra also yield an upper
limit to the turbulent motions in compact core of A3112 (206 km/s). We find
that the energy contribution of turbulence to total energy is less than 6 per
cent. This upper limit is consistent with the amount of energy contribution
measured in recent high resolution simulations of relaxed galaxy clusters.",1110.4422v2
2011-11-11,Modelling of the ultraviolet and visual SED variability in the hot magnetic Ap star CU Vir,"The spectral energy distribution (SED) in chemically peculiar stars may be
significantly affected by their abundance anomalies. The observed SED
variations are usually assumed to be a result of inhomogeneous surface
distribution of chemical elements, flux redistribution and stellar rotation.
However, the direct evidence for this is still only scarce. We aim to identify
the processes that determine the SED and its variability in the UV and visual
spectral domains of the helium-weak star CU Vir. We used the model atmospheres
to obtain the emergent flux and predict the rotationally modulated flux
variability of the star. We show that most of the light variations in the vby
filters of the Stromgren photometric system are a result of the uneven surface
distribution of silicon, chromium, and iron. Our models are only able to
explain a part of the variability in the u filter, however. The observed UV
flux distribution is very well reproduced, and the models are able to explain
most of the observed features in the UV light curve. The variability observed
in the visible is merely a faint gleam of that in the UV. While the amplitude
of the light curves reaches only several hundredths of magnitude in the visual
domain, it reaches about 1 mag in the UV. The visual and UV light variability
of CU Vir is caused by the flux redistribution from the far UV to near UV and
visible regions, inhomogeneous distribution of the elements and stellar
rotation. Bound-free transitions of silicon and bound-bound transitions of iron
and chromium contribute the most to the flux redistribution. This mechanism can
explain most of the rotationally modulated light variations in the filters
centred on the Paschen continuum and on the UV continuum of the star CU Vir.
However, another mechanism(s) has to be invoked to fully explain the observed
light variations in the u filter and in the region 2000-2500 A.",1111.2746v1
2011-11-28,Dust in Historical Galactic Type Ia Supernova Remnants with Herschel,"The origin of interstellar dust in galaxies is poorly understood,
particularly the relative contributions from supernovae and the cool stellar
winds of low-intermediate mass stars. Here, we present Herschel PACS and SPIRE
photometry at 70-500um of the historical young supernova remnants: Kepler and
Tycho; both thought to be the remnants of Type Ia explosion events. We detect a
warm dust component in Kepler's remnant with T = 82K and mass 0.0031Msun; this
is spatially coincident with thermal X-ray emission optical knots and
filaments, consistent with the warm dust originating in the circumstellar
material swept up by the primary blast wave of the remnant. Similarly for
Tycho's remnant, we detect warm dust at 90K with mass 0.0086Msun. Comparing the
spatial distribution of the warm dust with X-rays from the ejecta and swept-up
medium, and Ha emission arising from the post-shock edge, we show that the warm
dust is swept up interstellar material. We find no evidence of a cool (25-50 K)
component of dust with mass >0.07Msun as observed in core-collapse remnants of
massive stars. Neither the warm or cold dust components detected here are
spatially coincident with supernova ejecta material. We compare the lack of
observed supernova dust with a theoretical model of dust formation in Type Ia
remnants which predicts dust masses of 0.088(0.017)Msun for ejecta expanding
into surrounding densities of 1(5)cm-3. The model predicts that silicon- and
carbon-rich dust grains will encounter the interior edge of the observed dust
emission at 400 years confirming that the majority of the warm dust originates
from swept up circumstellar or interstellar grains (for Kepler and Tycho
respectively). The lack of cold dust grains in the ejecta suggests that Type Ia
remnants do not produce substantial quantities of iron-rich dust grains and has
important consequences for the 'missing' iron mass observed in ejecta.",1111.6627v2
2011-12-23,Non-standard s process in low metallicity massive rotating stars,"Context. Rotation is known to affect the nucleosynthesis of light elements in
massive stars, mainly by rotation-induced mixing. In particular, rotation
boosts the primary nitrogen production. Models of rotating stars are able to
reproduce the nitrogen observed in low-Z halo stars. Aims. Here we present the
first grid of stellar models for rotating massive stars at low Z, where a full
s-process network is used to study the impact of rotation-induced mixing on the
nucleosynthesis of heavy elements. Methods. We used the Geneva stellar
evolution code that includes an enlarged reaction network with nuclear species
up to bismuth to calculate 25 M$_\odot$ models at three different Z and with
different initial rotation rates. Results. First, we confirm that
rotation-induced mixing leads to a production of primary $^{22}$Ne, which is
the main neutron source for the s process in massive stars. Therefore rotation
boosts the s process in massive stars at all Z. Second, the neutron-to-seed
ratio increases with decreasing Z in models including rotation, which leads to
the complete consumption of all iron seeds at Z < 1e-3 by the end of core
He-burning. Thus at low Z, the iron seeds are the main limitation for this
boosted s process. Third, as Z decreases, the production of elements up to the
Ba peak increases at the expense of the elements of the Sr peak. We studied the
impact of the initial rotation rate and of the uncertain
$^{17}$O$(\alpha,\gamma)$ rate (which strongly affects the neutron poison
strength of $^{16}$O) on our results. This study shows that rotating models can
produce significant amounts of elements up to Ba over a wide range of Z.
Fourth, compared to the He-core, the primary $^{22}$Ne production in the
He-shell is even higher (> 1% in mass fraction at all Z), which could open the
door for an explosive neutron capture nucleosynthesis in the He-shell, with a
primary neutron source.",1112.5548v1
2012-01-24,"Effective temperatures, rotational velocities, microturbulent velocities and abundances in the atmospheres of the Sun,. HD1835 and HD10700","We describe our procedure to determine effective temperatures, rotational
velocities, microturbulent velocities, and chemical abundances in the
atmospheres of Sun-like stars. We use independent determinations of iron
abundances using the fits to the observed Fe I and Fe II atomic absorption
lines. We choose the best solution from the fits to these spectral features for
the model atmosphere that provides the best confidence in the determined log
N(Fe), Vt, and vsini. First, we compute the abundance of iron for a set of
adopted microturbulent velocities. To determine the most self-consistent
effective temperature and microturbulent velocity in any star's atmosphere, we
used an additional constraint where we minimise the dependence of the derived
abundances of Fe I and Fe II on the excitation potential of the corresponding
lines. We analyse the spectra of the Sun and two well known solar type stars,
HD1835 and HD10700 to determine their abundances, microturbulent velocity and
rotational velocity. For the Sun abundances of elements obtained from the fits
of their absorption features agree well enough (+/- 0.1 dex) with the known
values for the Sun. We determined a rotational velocity of vsini = 1.6 +/- 0.3
km/s for the spectrum of the Sun as a star. For HD1835 the self-consistent
solution for Fe I and Fe II lines log N(Fe)=+0.2 was obtained with a model
atmosphere of 5807/4.47/+0.2 andmicroturbulent velocity Vt = 0.75 km/s, and
leads to vsini = 7.2 $\pm$ 0.5 km/s. For HD10700 the self-consistent solution
log N(Fe) = -4.93 was obtained using a model atmosphere of 5383/4.59/-0.6and
microturbulent velocity Vt = 0.5 km/s. The Fe I and Fe II lines give rise to a
vsini = 2.4 +/- 0.4 km/s. Using the Teff found from the ionisation equilibrium
parameters for all three stars, we found abundances of a number of other
elements: Ti, Ni, Ca, Si, Cr. ... Abriged.",1201.5099v2
2012-02-14,On The Effect of Giant Planets on the Scattering of Parent Bodies of Iron Meteorite from the Terrestrial Planet Region into the Asteroid Belt: A Concept Study,"In their model for the origin of the parent bodies of iron meteorites, Bottke
et al proposed differentiated planetesimals that were formed in the region of
1-2 AU during the first 1.5 Myr, as the parent bodies, and suggested that these
objects and their fragments were scattered into the asteroid belt as a result
of interactions with planetary embryos. Although viable, this model does not
include the effect of a giant planet that might have existed or been growing in
the outer regions. We present the results of a concept study where we have
examined the effect of a planetary body in the orbit of Jupiter on the early
scattering of planetesimals from terrestrial region into the asteroid belt. We
integrated the orbits of a large battery of planetesimals in a disk of
planetary embryos, and studied their evolutions for different values of the
mass of the planet. Results indicate that when the mass of the planet is
smaller than 10 Earth-masses, its effects on the interactions among
planetesimals and planetary embryos is negligible. However, when the planet
mass is between 10 and 50 Earth-masses, simulations point to a transitional
regime with ~50 Earth-mass being the value for which the perturbing effect of
the planet can no longer be ignored. Simulations also show that further
increase of the mass of the planet strongly reduces the efficiency of the
scattering of planetesimals from the terrestrial planet region into the
asteroid belt. We present the results of our simulations and discuss their
possible implications for the time of giant planet formation.",1202.2975v1
2012-03-08,Suzaku observations of the Hydra A cluster out to the virial radius,"We report Suzaku observations of the northern half of the Hydra A cluster out
to ~1.4 Mpc, reaching the virial radius. This is the first Suzaku observations
of a medium-size (kT ~3 keV) cluster out to the virial radius. Two observations
were conducted, north-west and north-east offsets, which continue in a filament
direction and a void direction of the large-scale structure of the Universe,
respectively. The X-ray emission and distribution of galaxies elongate in the
filament direction. The temperature profiles in the two directions are mostly
consistent with each other within the error bars and drop to 1.5 keV at 1.5
r_500. As observed by Suzaku in hot clusters, the entropy profile becomes
flatter beyond r_500, in disagreement with the r^1.1 relationship that is
expected from accretion shock heating models. When scaled with the average
intracluster medium (ICM) temperature, the entropy profiles of clusters
observed with Suzaku are universal and do not depend on system mass. The
hydrostatic mass values in the void and filament directions are in good
agreement, and the Navarro, Frenk, and White universal mass profile represents
the hydrostatic mass distribution up to ~ 2 r_500. Beyond r_500, the ratio of
gas mass to hydrostatic mass exceeds the result of the Wilkinson microwave
anisotropy probe, and at r_100, these ratios in the filament and void
directions reach 0.4 and 0.3, respectively. We discuss possible deviations from
hydrostatic equilibrium at cluster outskirts. We derived radial profiles of the
gasmass- to-light ratio and iron-mass-to-light ratio out to the virial radius.
Within r_500, the iron-mass-to-light ratio of the Hydra A cluster was compared
with those in other clusters observed with Suzaku.",1203.1700v4
2012-03-14,Barium abundance in red giants of NGC 6752. Non-local thermodynamic equilibrium and three-dimensional effects,"(Abridged) Aims: We study the effects related to departures from non-local
thermodynamic equilibrium (NLTE) and homogeneity in the atmospheres of red
giant stars in Galactic globular cluster NGC 6752, to assess their influence on
the formation of Ba II lines. Methods: One-dimensional (1D) local thermodynamic
equilibrium (LTE) and 1D NLTE barium abundances were derived using classical 1D
ATLAS stellar model atmospheres. The three-dimensional (3D) LTE abundances were
obtained for 8 red giants on the lower RGB, by adjusting their 1D LTE
abundances using 3D-1D abundance corrections, i.e., the differences between the
abundances obtained from the same spectral line using the 3D hydrodynamical
(CO5BOLD) and classical 1D (LHD) stellar model atmospheres. Results: The mean
1D barium-to-iron abundance ratios derived for 20 giants are <[Ba/Fe]>_{1D
NLTE} = 0.05 \pm0.06 (stat.) \pm0.08 (sys.). The 3D-1D abundance correction
obtained for 8 giants is small (~+0.05 dex), thus leads to only minor
adjustment when applied to the mean 1D NLTE barium-to-iron abundance ratio for
the 20 giants, <[Ba/Fe]>_{3D+NLTE} = 0.10 \pm0.06(stat.) \pm0.10(sys.). The
intrinsic abundance spread between the individual cluster stars is small and
can be explained in terms of uncertainties in the abundance determinations.
Conclusions: Deviations from LTE play an important role in the formation of
barium lines in the atmospheres of red giants studied here. The role of 3D
hydrodynamical effects should not be dismissed either, even if the obtained
3D-1D abundance corrections are small. This result is a consequence of subtle
fine-tuning of individual contributions from horizontal temperature
fluctuations and differences between the average temperature profiles in the 3D
and 1D model atmospheres: owing to the comparable size and opposite sign, their
contributions nearly cancel each other.",1203.3124v2
2012-03-20,Manganese in dwarf spheroidal galaxies,"We provide manganese abundances (corrected for the effect of the hyperfine
structure) for a large number of stars in the dwarf spheroidal galaxies
Sculptor and Fornax, and for a smaller number in the Carina and Sextans dSph
galaxies. Abundances had already been determined for a number of other elements
in these galaxies, including alpha and iron-peak ones, which allowed us to
build [Mn/Fe] and [Mn/alpha] versus [Fe/H] diagrams. The Mn abundances imply
sub-solar [Mn/Fe] ratios for the stars in all four galaxies examined. In
Sculptor, [Mn/Fe] stays roughly constant between [Fe/H]\sim -1.8 and -1.4 and
decreases at higher iron abundance. In Fornax, [Mn/Fe] does not vary in any
significant way with [Fe/H]. The relation between [Mn/alpha] and [Fe/H] for the
dSph galaxies is clearly systematically offset from that for the Milky Way,
which reflects the different star formation histories of the respective
galaxies. The [Mn/alpha] behavior can be interpreted as a result of the
metal-dependent Mn yields of type II and type Ia supernovae. We also computed
chemical evolution models for star formation histories matching those
determined empirically for Sculptor, Fornax, and Carina, and for the Mn yields
of SNe Ia, which were assumed to be either constant or variable with
metallicity. The observed [Mn/Fe] versus [Fe/H] relation in Sculptor, Fornax,
and Carina can be reproduced only by the chemical evolution models that include
a metallicity-dependent Mn yield from the SNe Ia.",1203.4491v2
2012-04-02,Correlated Gravitational Wave and Neutrino Signals from General-Relativistic Rapidly Rotating Iron Core Collapse,"We present results from a new set of 3D general-relativistic hydrodynamic
simulations of rotating iron core collapse. We assume octant symmetry and focus
on axisymmetric collapse, bounce, the early postbounce evolution, and the
associated gravitational wave (GW) and neutrino signals. We employ a
finite-temperature nuclear equation of state, parameterized electron capture in
the collapse phase, and a multi-species neutrino leakage scheme after bounce.
The latter captures the important effects of deleptonization, neutrino cooling
and heating and enables approximate predictions for the neutrino luminosities
in the early evolution after core bounce. We consider 12-solar-mass and
40-solar-mass presupernova models and systematically study the effects of (i)
rotation, (ii) progenitor structure, and (iii) postbounce neutrino leakage on
dynamics, GW, and, neutrino signals. We demonstrate, that the GW signal of
rapidly rotating core collapse is practically independent of progenitor mass
and precollapse structure. Moreover, we show that the effects of neutrino
leakage on the GW signal are strong only in nonrotating or slowly rotating
models in which GW emission is not dominated by inner core dynamics. In rapidly
rotating cores, core bounce of the centrifugally-deformed inner core excites
the fundamental quadrupole pulsation mode of the nascent protoneutron star. The
ensuing global oscillations (f~700-800 Hz) lead to pronounced oscillations in
the GW signal and correlated strong variations in the rising luminosities of
antineutrino and heavy-lepton neutrinos. We find these features in cores that
collapse to protoneutron stars with spin periods <~ 2.5 ms and rotational
energies sufficient to drive hyper-energetic core-collapse supernova
explosions. Hence, joint GW + neutrino observations of a core collapse event
could deliver strong evidence for or against rapid core rotation. [abridged]",1204.0512v2
2012-04-04,"The Suzaku X-ray spectrum of NGC 3147. Further insights on the best ""true"" Seyfert 2 galaxy candidate","NGC 3147 is so far the most convincing case of a ""true"" Seyfert 2 galaxy,
i.e. a source genuinely lacking the Broad Line Regions. We obtained a Suzaku
observation with the double aim to study in more detail the iron line complex,
and to check the Compton-thick hypothesis for the lack of observed optical
broad lines.
  The Suzaku XIS and HXD/PIN spectra of the source were analysed in detail. The
line complex is composed of at least two unresolved lines, one at about 6.45
keV and the other one at about 7 keV, most likely identified with Fe XVII/XIX,
the former, and Fe XXVI, the latter. The high-ionization line can originate
either in a photoionized matter or in an optically thin thermal plasma. In the
latter case, an unusually high temperature is implied. In the photoionized
model case, the large equivalent width can be explained either by an extreme
iron overabundance or by assuming that the source is Compton-thick. In the
Compton-thick hypothesis, however, the emission above 2 keV is mostly due to a
highly ionized reflector, contrary to what is usually found in Compton-thick
Seyfert 2s, where reflection from low ionized matter dominates. Moreover, the
source flux varied between the XMM-Newton and the Suzaku observations, taken
3.5 years apart, confirming previous findings and indicating that the size of
the emitting region must be smaller than a parsec.
  The hard X-ray spectrum is also inconclusive on the Compton-thick hypothesis.
Weighting the various arguments, a ""true"" Seyfert 2 nature of NGC 3147 seems to
be still the most likely explanation, even if the ""highly ionized reflector""
Compton-thick hypothesis cannot at present be formally rejected.",1204.0946v1
2012-04-24,Intrinsic crystal phase separation in antiferromagnetic superconductor RbyFe2-xSe2: a diffraction study,"The crystal and magnetic structures of the superconducting iron based
chalcogenides RbyFe2-xSe2 have been studied by means of single crystal
synchrotron x-ray and high resolution neutron powder diffraction in the
temperature range 2-570 K. The ground state of the crystal is an intrinsically
phase separated state with two distinct by symmetry phases. The main phase has
the iron vacancy ordered \surd5x\surd5 superstructure (I4/m space group) with
AFM ordered Fe spins. The minority phase does not have \surd5x\surd5-type of
ordering and has smaller in plane lattice constant a and larger tetragonal
c-axis and can be well described assuming the parent average vacancy disordered
structure (I4/mmm space group) with the refined stoichiometry
Rb0.60(5)(Fe1.10(5))Se)2. The minority phase amounts to 8-10% mass fraction.
The unit cell volume of the minority phase is 3.2% smaller than the one of the
main phase at T = 2 K and has quite different temperature dependence. The
minority phase transforms to the main vacancy ordered phase on heating above
the phase separation temperature T_P = 475 K. The spatial dimensions of the
phase domains strongly increase above TP from 1000 \AA\ to > 2500 \AA\ due to
the merging of the regions of the main phase that were separated by the second
phase at low temperatures. Additional annealing of the crystals at the
temperature T=488 K close to T_P for the long time drastically reduces the
amount of the minority phase.",1204.5449v3
2012-04-26,XMM-Newton observations of GX 13+1: correlation between photoionised absorption and broad line emission,"We analysed data from five XMM-Newton observations of GX 13+1 to investigate
the variability of the photo-ionised absorber present in this source. We fitted
EPIC and RGS spectra obtained from the ""least-variable"" intervals with a model
consisting of disc-blackbody and blackbody components together with a Gaussian
emission feature at ~6.55-6.7 keV modified by absorption due to cold and
photo-ionised material. We found a significant correlation between the hard,
~6-10 keV, flux, the ionisation and column density of the absorber and the
equivalent width of the broad iron line. We interpret the correlation in a
scenario in which a disc wind is thermally driven at large, ~10^{10} cm, radii
and the broad line results from reprocessed emission in the wind and/or hot
atmosphere. The breadth of the emission line is naturally explained by a
combination of scattering, recombination and fluorescence processes. We
attribute the variations in the absorption and emission along the orbital
period to the view of different parts of the wind, possibly located at slightly
different inclination angles. We constrain the inclination of GX 13+1 to be
between 60 and 80 degrees from the presence of strong absorption in the line of
sight, that obscures up to 80% of the total emission in one observation, and
the absence of eclipses. We conclude that the presence of a disc wind and/or a
hot atmosphere can explain the current observations of narrow absorption and
broad iron emission features in neutron star low mass X-ray binaries as a
class.",1204.5904v1
2012-05-30,Overabundance of alpha-elements in exoplanet host stars,"We present the results for a chemical abundance analysis between
planet-hosting and stars without planets for 12 refractory elements for a total
of 1111 nearby FGK dwarf stars observed within the context of the HARPS GTO
programs. Of these stars, 109 are known to harbour high-mass planetary
companions and 26 stars are hosting exclusively Neptunians and super-Earths. We
found that the [X/Fe] ratios for Mg, Al, Si, Sc, and Ti both for giant and
low-mass planet hosts are systematically higher than those of comparison stars
at low metallicities ([Fe/H] < from -0.2 to 0.1 dex depending on the element).
The most evident discrepancy between planet-hosting and stars without planets
is observed for Mg. Our data suggest that the planet incidence is greater among
the thick disk population than among the thin disk for mettallicities bellow
-0.3 dex. After examining the [alpha/Fe] trends of the planet host and non-host
samples we conclude that a certain chemical composition, and not the Galactic
birth place of the stars, is the determinating factor for that. The inspection
of the Galactic orbital parameters and kinematics of the planet-hosting stars
shows that Neptunian hosts tend to belong to the ""thicker"" disk compared to
their high-mass planet-hosting counterparts.We also found that Neptunian hosts
follow the distribution of high-alpha stars in the UW vs V velocities space,
but they are more enhanced in Mg than high-alpha stars without planetary
companions. Our results indicate that some metals other than iron may also have
an important contribution to planet formation if the amount of iron is low.
These results may provide strong constraints for the models of planet
formation, especially for planets with low mass.",1205.6670v2
2012-07-07,An upper limit on the sulphur abundance in HE 1327-2326,"Context: Star HE 1327-2326 is a unique object, with the lowest measured iron
abundance ([Fe/H] ~ -6) and a peculiar chemical composition that includes large
overabundances of C, N, and O with respect to iron. One important question is
whether the chemical abundances in this star reflect the chemical composition
of the gas cloud from which it was formed or if they have been severely
affected by other processes, such as dust-gas winnowing. Aims: We measure or
provide an upper limit to the abundance of the volatile element sulphur, which
can help to discriminate between the two scenarios. Methods: We observed HE
1327-2326 with the high resolution infra-red spectrograph CRIRES at the VLT to
observe the S I lines of Multiplet 3 at 1045 nm. Results: We do not detect the
S I line. A 3sigma$upper limit on the equivalent width (EW) of any line in our
spectrum is EW<0.66 pm. Using either one-dimensional static or
three-dimensional hydrodynamical model-atmospheres, this translates into a
robust upper limit of [S/H]<-2.6. Conclusions: This upper limit does not
provide conclusive evidence for or against dust-gas winnowing, and the evidence
coming from other elements (e.g., Na and Ti) is also inconclusive or
contradictory. The formation of dust in the atmosphere versus an origin of the
metals in a metal-poor supernova with extensive ""fall-back"" are not mutually
exclusive. It is possible that dust formation distorts the peculiar abundance
pattern created by a supernova with fall-back, thus the abundance ratios in HE
1327-2326 may be used to constrain the properties of the supernova(e) that
produced its metals, but with some caution.",1207.1806v3
2012-07-25,Rapid-response mode VLT/UVES spectroscopy of super iron-rich gas exposed to GRB 080310. Evidence of ionization in action and episodic star formation in the host,"We analyse high-resolution near-UV and optical spectra of the afterglow of
GRB 080310, obtained with the Very Large Telescope Ultraviolet and Visual
Echelle Spectrograph (VLT/UVES), to investigate the circumburst environment and
the interstellar medium of the gamma-ray burst (GRB) host galaxy. The VLT
rapid-response mode (RRM) enabled the observations to start only 13 minutes
after the Swift trigger and a series of four exposures to be collected before
dawn. A low neutral-hydrogen column-density (log N (HI) = 18.7) is measured at
the host-galaxy redshift of z = 2.42743. At this redshift, we also detect a
large number of resonance ground-state absorption lines (e.g., CII, MgII, AlII,
SiII, CrII, CIV, SiIV), as well as time-varying absorption from the
fine-structure levels of FeII. Time-varying absorption from a highly excited
FeIII energy level (7S3), giving rise to the so-called UV34 line triplet, is
also detected, for the first time in a GRB afterglow. The CrII ground-state and
all observed FeII energy levels are found to depopulate with time, whilst the
FeIII 7S3 level is increasingly populated. This absorption-line variability is
clear evidence of ionization by the GRB, which is for the first time
conclusively observed in a GRB afterglow spectrum. We derive ionic column
densities at each epoch of observations by fitting absorption lines with a
four-component Voigt-profile model. We perform CLOUDY photo-ionization
modelling of the expected pre-burst ionic column densities, to estimate that,
before the onset of the burst, [C/H] = -1.3 \pm 0.2, [O/H] < -0.8, [Si/H] =
-1.2 \pm 0.2, [Cr/H] = +0.7 \pm 0.2, and [Fe/H] = +0.2 \pm 0.2 for the
integrated line profile, indicating strong overabundances of iron and chromium.
For one of the components, we observe even more extreme ratios of [Si/Fe] \leq
-1.47 and [C/Fe] \leq -1.74. [abridged]",1207.6102v1
2012-08-14,The Golden Channel at a Neutrino Factory revisited: improved sensitivities from a Magnetised Iron Neutrino Detector,"This paper describes the performance and sensitivity to neutrino mixing
parameters of a Magnetised Iron Neutrino Detector (MIND) at a Neutrino Factory
with a neutrino beam created from the decay of 10 GeV muons. Specifically, it
is concerned with the ability of such a detector to detect muons of the
opposite sign to those stored (wrong-sign muons) while suppressing
contamination of the signal from the interactions of other neutrino species in
the beam. A new more realistic simulation and analysis, which improves the
efficiency of this detector at low energies, has been developed using the GENIE
neutrino event generator and the GEANT4 simulation toolkit. Low energy neutrino
events down to 1 GeV were selected, while reducing backgrounds to the $10^{-4}$
level. Signal efficiency plateaus of ~60% for $\nu_\mu$ and ~70% for
$\bar{\nu}_\mu$ events were achieved starting at ~5 GeV. Contamination from the
$\nu_\mu\rightarrow \nu_\tau$ oscillation channel was studied for the first
time and was found to be at the level between 1% and 4%. Full response matrices
are supplied for all the signal and background channels from 1 GeV to 10 GeV.
The sensitivity of an experiment involving a MIND detector of 100 ktonnes at
2000 km from the Neutrino Factory is calculated for the case of $\sin^2
2\theta_{13}\sim 10^{-1}$. For this value of $\theta_{13}$, the accuracy in the
measurement of the CP violating phase is estimated to be $\Delta
\delta_{CP}\sim 3^\circ - 5^\circ$, depending on the value of $\delta_{CP}$,
the CP coverage at $5\sigma$ is 85% and the mass hierarchy would be determined
with better than $5\sigma$ level for all values of $\delta_{CP}$.",1208.2735v2
2012-09-13,Solar Fe abundance and magnetic fields - Towards a consistent reference metallicity,"We investigate the impact on Fe abundance determination of including magnetic
flux in series of 3D radiation-MHD simulations of solar convection which we
used to synthesize spectral intensity profiles corresponding to disc centre. A
differential approach is used to quantify the changes in theoretical equivalent
width of a set of 28 iron spectral lines spanning a wide range in lambda,
excitation potential, oscillator strength, Land\'e factor, and formation
height. The lines were computed in LTE using the spectral synthesis code LILIA.
We used input magnetoconvection snapshots covering 50 minutes of solar
evolution and belonging to series having an average vertical magnetic flux
density of 0, 50, 100 and 200 G. For the relevant calculations we used the
Copenhagen Stagger code. The presence of magnetic fields causes both a direct
(Zeeman-broadening) effect on spectral lines with non-zero Land\'e factor and
an indirect effect on temperature-sensitive lines via a change in the
photospheric T-tau stratification. The corresponding correction in the
estimated atomic abundance ranges from a few hundredths of a dex up to |Delta
log(Fe)| ~ 0.15 dex, depending on the spectral line and on the amount of
average magnetic flux within the range of values we considered. The
Zeeman-broadening effect gains relatively more importance in the IR. The
largest modification to previous solar abundance determinations based on
visible spectral lines is instead due to the indirect effect, i.e., the
line-weakening caused by a warmer stratification on an optical depth scale. Our
results indicate that the average solar iron abundance obtained when using
magnetoconvection models can be 0.03-0.11 dex higher than when using the
simpler HD convection approach. We demonstrate that accounting for magnetic
flux is important in state-of-the-art solar photospheric abundance
determinations based on 3D simulations.",1209.2771v1
2012-10-02,X-ray spectroscopy of the ADC source X1822-371 with Chandra and XMM-Newton,"The eclipsing low-mass X-ray binary X1822-371 is the prototype of the
accretion disc corona (ADC) sources. We analyse two Chandra observations and
one XMM-Newton observation to study the discrete features and their variation
as a function of the orbital phase, deriving constraints on the temperature,
density, and location of the plasma responsible for emission lines. The HETGS
and XMM/Epic-pn observed X1822-371 for 140 and 50 ks, respectively. We
extracted an averaged spectrum and five spectra from five selected
orbital-phase intervals that are 0.04-0.25, 0.25-0.50, 0.50-0.75, 0.75-0.95,
and, finally, 0.95-1.04; the orbital phase zero corresponds to the eclipse
time. All spectra cover the energy band between 0.35 and 12 keV. We confirm the
presence of local neutral matter that partially covers the X-ray emitting
region; the equivalent hydrogen column is $5 \times 10^{22}$ cm$ ^{-2}$ and the
covered fraction is about 60-65%. We identify emission lines from highly
ionised elements, and a prominent fluorescence iron line associated with a
blending of FeI-FeXV resonant transitions. The transitions of He-like ions show
that the intercombination dominates over the forbidden and resonance lines. The
line fluxes are the highest during the orbital phases between 0.04 and 0.75. We
discuss the presence of an extended, optically thin corona with optical depth
of about 0.01 that scatters the X-ray photons from the innermost region into
the line of sight. The photoionised plasma producing most of the observed lines
is placed in the bulge at the outer radius of the disc distant from the central
source of $6 \times 10^{10}$ cm. The OVII and the fluorescence iron line are
probably produced in the photoionised surface of the disc at inner radii.
(Abridged)",1210.0874v1
2012-10-25,XMM-Newton observations of the Galactic Centre Region - I: The distribution of low-luminosity X-ray sources,"We exploit XMM-Newton archival data in a study of the extended X-ray emission
emanating from the Galactic Centre (GC) region. EPIC-pn and EPIC-MOS
observations, with a total exposure approaching 0.5 and 1 Ms respectively, were
used to create mosaiced images of a 100 pc x 100 pc region centred on Sgr A* in
four bands covering the 2-10 keV energy range. We have also constructed a set
of narrow-band images corresponding to the neutral iron fluorescence line at
6.4 keV and the K-shell lines at 6.7 keV and 6.9 keV from helium-like and
hydrogenic iron. We use a combination of spatial and spectral information to
decompose the GC emission into three distinct components. These comprise: the
emission from hard X-ray emitting unresolved point sources; the reflected
continuum and fluorescent line emission from dense molecular material; and the
soft diffuse emission from thermal plasma in the temperature range, kT ~
0.8-1.5 keV.
  We show that the unresolved-source component accounts for the bulk of the
6.7-keV and 6.9-keV line emission. We fit the observed X-ray surface brightness
distribution with an empirical 2-d model, which we then compare with a 3-d
mass-model prediction for the old stellar population in the GC. The X-ray
surface brightness falls-off more rapidly with angular offset from Sgr A* than
predicted. One interpretation is that the 2-10 keV X-ray emissivity increases
from 5 x 10^27 erg s^-1 Msun^-1 at 20' up to almost twice this value at 2'.
Alternatively, some refinement of the mass model may be required.
  The unresolved hard X-ray emitting source population, on the basis of
spectral comparisons, is most likely dominated by magnetic CVs. We use the
X-ray observations to set constraints on the number density of such sources.
Our analysis does not support the conjecture that a significant fraction of the
hard X-ray emission from the GC originates in very-hot diffuse thermal plasma.",1210.6808v1
2012-11-12,Theory of Quantum Phase Transition in Iron-based Superconductors with Half-Dirac Nodal Electron Fermi Surface,"The quantum phase transition in iron-based superconductors with 'half-Dirac'
node at the electron Fermi surface as a $T=0$ structural phase transition
described in terms of nematic order is discussed. An effective low energy
theory that describes half-Dirac nodal Fermions and their coupling to Ising
nematic order that describes the phase transition is derived and analyzed using
renormalization group (RG) study of the large-$N_f$ version of the theory. The
inherent absence of Lorentz invariance of the theory leads to RG flow structure
where the velocities $v_F$ and $v_\Delta$ at the paired half-Dirac nodes
($1\overline{1}$ and $2\overline{2}$) in general flow differently under RG,
implying that the nodal electron gap is deformed and the $C_4$ symmetry is
broken, explaining the structural (orthogonal to orthorhombic) phase transition
at the quantum critical point (QCP). The theory is found to have Gaussian fixed
point $\lambda^*=0, (v_{\Delta}/v_F)^*=0$ with stable flow lines toward it,
suggesting a second order nematic phase transition. Interpreting the
fermion-Ising nematic boson interaction as a decay process of nematic Ising
order parameter scalar field fluctuations into half-Dirac nodal fermions, I
find that the theory surprisingly behaves as systems with dynamical critical
exponent $z = 1$, reflecting undamped quantum critical dynamics and emergent
fully relativistic field theory arising from the non(fully)-relativistic field
theory and is direct consequence of $(v_{\Delta}/v_F)^*=0$ fixed point. The
nematic critical fluctuations lead to remarkable change to the spectral
function peak where at a critical point $\lambda_c$, directly related to
nematic QCP, the central spectral peak collapses and splits into satellite
spectral peaks around nodal point. The vanishing of the zero modes density of
states leads to the undamped $z=1$ quantum critical dynamics.",1211.2790v4
2012-12-04,An Examination of the Spectral Variability in NGC 1365 with Suzaku,"We present jointly analyzed data from three deep Suzaku observations of NGC
1365. These high signal-to-noise spectra enable us to examine the nature of
this variable, obscured AGN in unprecedented detail on timescales ranging from
hours to years. We find that, in addition to the power-law continuum and
absorption from ionized gas seen in most AGN, inner disk reflection and
variable absorption from neutral gas within the Broad Emission Line Region are
both necessary components in all three observations. We confirm the clumpy
nature of the cold absorbing gas, though we note that occultations of the inner
disk and corona are much more pronounced in the high-flux state (2008) than in
the low-flux state (2010) of the source. The onset and duration of the ""dips""
in the X-ray light curve in 2010 are both significantly longer than in 2008,
however, indicating that either the distance to the gas from the black hole is
larger, or that the nature of the gas has changed between epochs. We also note
significant variations in the power-law flux over timescales similar to the
cold absorber, both within and between the three observations. The warm
absorber does not vary significantly within observations, but does show
variations in column density of a factor of more than 10 on timescales less
than 2 weeks that seem unrelated to the changes in the continuum, reflection or
cold absorber. By assuming a uniform iron abundance for the reflection and
absorption, we have also established that an iron abundance of roughly 3.5
times the solar value is sufficient to model the broad-band spectrum without
invoking an additional partial-covering absorber. Such a measurement is
consistent with previous published constraints from the 2008 Suzaku observation
alone, and with results from other Seyfert AGN in the literature.",1212.0772v1
2012-12-06,Radiative cooling in collisionally and photo ionized plasmas,"We discuss recent improvements in the calculation of the radiative cooling in
both collisionally and photo ionized plasmas. We are extending the spectral
simulation code Cloudy so that as much as possible of the underlying atomic
data is taken from external databases, some created by others, some developed
by the Cloudy team. This paper focuses on recent changes in the treatment of
many stages of ionization of iron, and discusses its extensions to other
elements. The H-like and He-like ions are treated in the iso-electronic
approach described previously. Fe II is a special case treated with a large
model atom. Here we focus on Fe III through Fe XXIV, ions which are important
contributors to the radiative cooling of hot, 1e5 to 1e7 K, plasmas and for
X-ray spectroscopy. We use the Chianti atomic database to greatly expand the
number of transitions in the cooling function. Chianti only includes lines that
have atomic data computed by sophisticated methods. This limits the line list
to lower excitation, longer wavelength, transitions. We had previously included
lines from the Opacity Project database, which tends to include higher energy,
shorter wavelength, transitions. These were combined with various forms of the
g-bar approximation, a highly approximate method of estimating collision rates.
For several iron ions the two databases are almost entirely complementary. We
adopt a hybrid approach in which we use Chianti where possible, supplemented by
lines from the Opacity Project for shorter wavelength transitions. The total
cooling including the lightest thirty elements differs significantly from some
previous calculations.",1212.1233v1
2013-01-04,Optical properties of iron-based superconductor LiFeAs single crystal,"We have measured the reflectivity spectra of the iron based superconductor
LiFeAs (Tc = 17.6 K) in the temperature range from 4 to 300 K. In the
superconducting state (T < Tc), the clear opening of the optical absorption gap
was observed below 25 cm-1, indicating an isotropic full gap formation. In the
normal state (T > Tc), the optical conductivity spectra display a typical
metallic behavior with the Drude type spectra at low frequencies, but we found
that the introduction of the two Drude components best fits the data,
indicating the multiband nature of this superconductor. A theoretical analysis
of the low temperature data (T=4K < Tc) also suggests that two superconducting
gaps best fit the data and their values were estimated as {\Delta}1 = 1.59 meV
and {\Delta}2 = 3.15 meV, respectively. Using the Ferrell-Glover-Tinkham (FGT)
sum rule and dielectric function {\epsilon}1({\omega}), the superconducting
plasma frequency ({\omega}ps) is consistently estimated to be 6,665 cm-1,
implying that about 59 % of the free carriers in the normal state condenses
into the SC condensate. To investigate the various interband transition
processes (for {\omega} > 200 cm-1), we have also performed the local-density
approximation (LDA) band calculation and calculated the optical spectra of the
interband transitions. The theoretical results provided a qualitative agreement
with the experimental data below 4000 cm-1",1301.0694v2
2013-02-06,Octant sensitivity for large theta(13) in atmospheric and long baseline neutrino experiments,"One of the unknown parameters in neutrino oscillations is the octant of the
mixing angle theta_{23}. In this paper, we discuss the possibility of
determining the octant of theta_{23} in the long baseline experiments T2K and
NOvA in conjunction with future atmospheric neutrino detectors, in light of
non-zero value of theta_{13} measured by reactor experiments. We consider two
detector technologies for atmospheric neutrinos - magnetized iron calorimeter
and non-magnetized Liquid Argon Time Projection Chamber. We present the octant
sensitivity for T2K/NOvA and atmospheric neutrino experiments separately as
well as combined. For the long baseline experiments, a precise measurement of
theta_{13}, which can exclude degenerate solutions in the wrong octant,
increases the sensitivity drastically. For theta_{23} = 39^o and sin^2 2
theta_{13} = 0.1, at least ~2 sigma sensitivity can be achieved by T2K+NOvA for
all values of delta_{CP} for both normal and inverted hierarchy. For
atmospheric neutrinos, the moderately large value of theta_{13} measured in the
reactor experiments is conducive to octant sensitivity because of enhanced
matter effects. A magnetized iron detector can give a 2 sigma octant
sensitivity for 500 kT yr exposure for theta_{23} = 39^o, delta_{CP} = 0 and
normal hierarchy. This increases to 3 sigma for both hierarchies by combining
with T2K+NOvA. This is due to a preference of different theta_{23} values at
the minimum chi^2 by T2K/NOvA and atmospheric neutrino experiments. A Liquid
Argon detector for atmospheric neutrinos with the same exposure can give higher
octant sensitivity, due to the interplay of muon and electron contributions and
superior resolutions. We obtain a ~3 sigma sensitivity for theta_{23} = 39^o
for normal hierarchy. This increases to > ~4 sigma for all values of delta_{CP}
if combined with T2K+NOvA. For inverted hierarchy the combined sensitivity is
~3 sigma.",1302.1370v2
2013-02-13,Measuring Black Hole Spin using X-ray Reflection Spectroscopy,"I review the current status of X-ray reflection (a.k.a. broad iron line)
based black hole spin measurements. This is a powerful technique that allows us
to measure robust black hole spins across the mass range, from the stellar-mass
black holes in X-ray binaries to the supermassive black holes in active
galactic nuclei. After describing the basic assumptions of this approach, I lay
out the detailed methodology focusing on ""best practices"" that have been found
necessary to obtain robust results. Reflecting my own biases, this review is
slanted towards a discussion of supermassive black hole (SMBH) spin in active
galactic nuclei (AGN). Pulling together all of the available XMM-Newton and
Suzaku results from the literature that satisfy objective quality control
criteria, it is clear that a large fraction of SMBHs are rapidly-spinning,
although there are tentative hints of a more slowly spinning population at high
(M>5*10^7Msun) and low (M<2*10^6Msun) mass. I also engage in a brief review of
the spins of stellar-mass black holes in X-ray binaries. In general,
reflection-based and continuum-fitting based spin measures are in agreement,
although there remain two objects (GROJ1655-40 and 4U1543-475) for which that
is not true. I end this review by discussing the exciting frontier of
relativistic reverberation, particularly the discovery of broad iron line
reverberation in XMM-Newton data for the Seyfert galaxies NGC4151, NGC7314 and
MCG-5-23-16. As well as confirming the basic paradigm of relativistic disk
reflection, this detection of reverberation demonstrates that future large-area
X-ray observatories such as LOFT will make tremendous progress in studies of
strong gravity using relativistic reverberation in AGN.",1302.3260v2
2013-03-12,Fast and Furious: Shock Heated Gas as the Origin of Spatially Resolved Hard X-ray Emission in the Central 5 kpc of the Galaxy Merger NGC 6240,"We have obtained a deep, sub-arcsecond resolution X-ray image of the nuclear
region of the luminous galaxy merger NGC 6240 with Chandra, which resolves the
X-ray emission from the pair of active nuclei and the diffuse hot gas in great
detail. We detect extended hard X-ray emission from kT~6 keV (~70 million K)
hot gas over a spatial scale of 5 kpc, indicating the presence of fast shocks
with velocity of ~2200 km/s. For the first time we obtain the spatial
distribution of this highly ionized gas emitting FeXXV, which shows a
remarkable correspondence to the large scale morphology of H_2(1-0) S(1) line
emission and H\alpha filaments. Propagation of fast shocks originated in the
starburst driven wind into the ambient dense gas can account for this
morphological correspondence. With an observed L(0.5-8 keV)=5.3E+41 erg/s, the
diffuse hard X-ray emission is 100 times more luminous than that observed in
the classic starburst galaxy M82. Assuming a filling factor of 1% for the 70 MK
temperature gas, we estimate its total mass (M_{hot}=1.8E+8 Msun) and thermal
energy (E_{th}=6.5E+57 ergs). The total iron mass in the highly ionized plasma
is M_{Fe}=4.6E+5 Msun. Both the energetics and the iron mass in the hot gas are
consistent with the expected injection from the supernovae explosion during the
starburst that is commensurate with its high star formation rate. No evidence
for fluorescent Fe I emission is found in the CO filament connecting the two
nuclei.",1303.2980v2
2013-03-12,Lithium abundance in the metal-poor open cluster NGC 2243,"Lithium is a fundamental element for studying the mixing mechanisms acting in
the stellar interiors, for understanding the chemical evolution of the Galaxy
and the Big Bang nucleosynthesis. The study of Li in stars of open clusters
(hereafter OC) allows a detailed comparison with stellar evolutionary models
and permits us to trace its galactic evolution. The OC NGC 2243 is particularly
interesting because of its low metallicity ([Fe/H]=$-0.54 \pm0.10$ dex). We
measure the iron and lithium abundance in stars of the metal-poor OC NGC 2243.
The first aim is to determine whether the Li dip extends to such low
metallicities, the second is to compare the results of our Li analysis in this
OC with those present in 47 Tuc, a globular cluster of similar metallicity. We
performed a detailed analysis of high-resolution spectra obtained with the
multi-object facility FLAMES at the ESO VLT 8.2m telescope. Lithium abundance
was derived through line equivalent widths and the OSMARCS atmosphere models.
We determine a Li dip center of 1.06 $M_\odot$, which is much smaller than that
observed in solar metallicity and metal-rich clusters. This finding confirms
and strengthens the conclusion that the mass of the stars in the Li dip
strongly depends on stellar metallicity. The mean Li abundance of the cluster
is $\log n{\rm (Li)}=2.70$ dex, which is substantially higher than that
observed in 47 Tuc. We estimated an iron abundance of [Fe/H]=$-0.54 \pm0.10$
dex for NGC 2243, which is similar (within the errors) to previous findings.
The [$ \alpha$/Fe] content ranges from $0.00\pm0.14$ for Ca to $0.20\pm0.22$
for Ti, which is low when compared to thick disk stars and to Pop II stars, but
compatible with thin disk objects. We found a mean radial velocity of 61.9
$\pm$ 0.8 \kms for the cluster.",1303.3027v1
2013-04-27,"Environments of Strong / Ultrastrong, Ultraviolet Fe II Emitting Quasars","We have investigated the strength of ultraviolet Fe II emission from quasars
within the environments of Large Quasar Groups (LQGs) in comparison with
quasars elsewhere, for 1.1 <= <z_LQG> <= 1.7, using the DR7QSO catalogue of the
Sloan Digital Sky Survey. We use the Weymann et al. W2400 equivalent width,
defined between the rest-frame continuum-windows 2240-2255 and 2665-2695 Ang.,
as the measure of the UV Fe II emission. We find a significant shift of the
W2400 distribution to higher values for quasars within LQGs, predominantly for
those LQGs with 1.1 <= <z_LQG> <= 1.5. There is a tentative indication that the
shift to higher values increases with the quasar i magnitude. We find evidence
that within LQGs the ultrastrong emitters with W2400 >= 45 Ang. (more
precisely, ultrastrong-plus with W2400 >= 44 Ang.) have preferred
nearest-neighbour separations of ~ 30-50 Mpc to the adjacent quasar of any
W2400 strength. No such effect is seen for the ultrastrong emitters that are
not in LQGs. The possibilities for increasing the strength of the Fe II
emission appear to be iron abundance, Ly-alpha fluorescence, and
microturbulence, and probably all of these operate. The dense environment of
the LQGs may have led to an increased rate of star formation and an enhanced
abundance of iron in the nuclei of galaxies. Similarly the dense environment
may have led to more active blackholes and increased Ly-alpha fluorescence. The
preferred nearest-neighbour separation for the stronger emitters would appear
to suggest a dynamical component, such as microturbulence. In one particular
LQG, the Huge-LQG (the largest structure known in the early universe), six of
the seven strongest emitters very obviously form three pairings within the
total of 73 members.",1304.7396v2
2013-05-15,Dust input from AGB stars in the Large Magellanic Cloud,"The dust-forming population of AGB stars and their input to the interstellar
dust budget of the Large Magellanic Cloud (LMC) are studied with evolutionary
dust models with the main goals (1) to investigate how the amount and
composition of dust from AGB stars vary over galactic history; (2) to
characterise the mass and metallicity distribution of the present population of
AGB stars; (3) to quantify the contribution of AGB stars of different mass and
metallicity to the present stardust population in the interstellar medium
(ISM). We use models of the stardust lifecycle in the ISM developed and tested
for the Solar neighbourhood. The first global spatially resolved reconstruction
of the star formation history of the LMC from the Magellanic Clouds Photometric
Survey is employed to calculate the stellar populations in the LMC. The dust
input from AGB stars is dominated by carbon grains from stars with masses < 4
Msun almost over the entire history of the LMC. The production of silicate,
silicon carbide and iron dust is delayed until the ISM is enriched to about
half the present metallicity in the LMC. For the first time, theoretically
calculated dust production rates of AGB stars are compared to those derived
from IR observations of AGB stars for the entire galaxy. We find good agreement
within scatter of various observational estimates. We show that the majority of
silicate and iron grains in the present stardust population originate from a
small population of intermediate-mass stars consisting of only about 4% of the
total number of stars, whereas in the Solar neighbourhood they originate from
low-mass stars. With models of the lifecycle of stardust grains in the ISM we
confirm a large discrepancy between dust input from stars and the existing
interstellar dust mass in the LMC reported in Matsuura et al. 2009.",1305.3521v1
2013-06-05,"Chemical abundances of the Milky Way thick disk and stellar halo II.: sodium, iron-peak and neutron-capture elements","We present chemical abundance analyses of sodium, iron-peak and
neutron-capture elements for 97 kinematically selected thick disk, inner halo
and outer halo stars with metallicities -3.3<[Fe/H]<-0.5. The main aim of this
study is to examine chemical similarities and differences among metal-poor
stars belonging to these old Galactic components as a clue to determine their
early chemodynamical evolution. In our previous paper, we obtained abundances
of alpha elements by performing a one-dimensional LTE abundance analysis based
on the high-resolution (R~50000) spectra obtained with the Subaru/HDS. In this
paper, a similar analysis is performed to determine abundances of an additional
17 elements. We show that, in metallicities below [Fe/H]~-2, the abundance
ratios of many elements in the thick disk, inner halo, and outer halo
subsamples are largely similar. In contrast, in higher metallicities
([Fe/H]>-1.5), differences in some of the abundance ratios among the three
subsamples are identified. Specifically, the [Na/Fe], [Ni/Fe], [Cu/Fe], and
[Zn/Fe] ratios in the inner and outer halo subsamples are found to be lower
than those in the thick disk subsample. In contrast to what was observed for
[Mg/Fe] in our previous paper, [Eu/Fe] ratios are more enhanced in the two halo
subsamples rather than in the thick disk subsample. The observed distinct
chemical abundances of some elements between the thick disk and inner/outer
halo subsamples with [Fe/H]>-1.5 support the hypothesis that these components
formed through different mechanisms. In particular, our results favor the
scenario that the inner and outer halo components formed through an assembly of
multiple progenitor systems that experienced various degrees of chemical
enrichments, while the thick disk formed through rapid star formation with an
efficient mixing of chemical elements.",1306.0954v1
2013-06-09,Advanced burning stages and fate of 8-10 Mo stars,"The stellar mass range 8<M/Mo<12 corresponds to the most massive AGB stars
and the most numerous massive stars. It is host to a variety of supernova
progenitors and is therefore very important for galactic chemical evolution and
stellar population studies. In this paper, we study the transition from
super-AGB star to massive star and find that a propagating neon-oxygen burning
shell is common to both the most massive electron capture supernova (EC-SN)
progenitors and the lowest mass iron-core collapse supernova (FeCCSN)
progenitors. Of the models that ignite neon burning off-center, the 9.5Mo model
would evolve to an FeCCSN after the neon-burning shell propagates to the
center, as in previous studies. The neon-burning shell in the 8.8Mo model,
however, fails to reach the center as the URCA process and an extended (0.6 Mo)
region of low Ye (0.48) in the outer part of the core begin to dominate the
late evolution; the model evolves to an EC-SN. This is the first study to
follow the most massive EC-SN progenitors to collapse, representing an
evolutionary path to EC-SN in addition to that from SAGB stars undergoing
thermal pulses. We also present models of an 8.75Mo super-AGB star through its
entire thermal pulse phase until electron captures on 20Ne begin at its center
and of a 12Mo star up to the iron core collapse. We discuss key uncertainties
and how the different pathways to collapse affect the pre-supernova structure.
Finally, we compare our results to the observed neutron star mass distribution.",1306.2030v1
2013-06-10,X-ray Outflows and Super-Eddington Accretion in the Ultraluminous X-ray Source Holmberg IX X-1,"Studies of X-ray continuum emission and flux variability have not
conclusively revealed the nature of ultra-luminous X-ray sources (ULXs) at the
high-luminosity end of the distribution (those with Lx > 1e40 erg/s). These are
of particular interest because the luminosity requires either super-Eddington
accretion onto a black hole of mass ~10 Msun, or more standard accretion onto
an intermediate-mass black hole. Super-Eddington accretion models predict
strong outflowing winds, making atomic absorption lines a key diagnostic of the
nature of extreme ULXs. To search for such features, we have undertaken a long,
500 ks observing campaign on Holmberg IX X-1 with Suzaku. This is the most
sensitive dataset in the iron K bandpass for a bright, isolated ULX to date,
yet we find no statistically significant atomic features in either emission or
absorption; any undetected narrow features must have equivalent widths less
than 15-20 eV at 99% confidence. These limits are far below the >150 eV lines
expected if observed trends between mass inflow and outflow rates extend into
the super-Eddington regime, and in fact rule out the line strengths observed
from disk winds in a variety of sub-Eddington black holes. We therefore cannot
be viewing the central regions of Holmberg IX X-1 through any substantial
column of material, ruling out models of spherical super-Eddington accretion.
If Holmberg IX X-1 is a super-Eddington source, any associated outflow must
have an anisotropic geometry. Finally, the lack of iron emission suggests that
the stellar companion cannot be launching a strong wind, and that Holmberg IX
X-1 must primarily accrete via roche-lobe overflow.",1306.2317v1
2013-06-11,Thermal convection in Earth's inner core with phase change at its boundary,"Inner core translation, with solidification on one hemisphere and melting on
the other, provides a promising basis for understanding the hemispherical
dichotomy of the inner core, as well as the anomalous stable layer observed at
the base of the outer core - the F-layer - which might be sustained by
continuous melting of inner core material. In this paper, we study in details
the dynamics of inner core thermal convection when dynamically induced melting
and freezing of the inner core boundary (ICB) are taken into account. If the
inner core is unstably stratified, linear stability analysis and numerical
simulations consistently show that the translation mode dominates only if the
viscosity $\eta$ is large enough, with a critical viscosity value, of order $3
10^{18}$ Pas, depending on the ability of outer core convection to supply or
remove the latent heat of melting or solidification. If $\eta$ is smaller, the
dynamical effect of melting and freezing is small. Convection takes a more
classical form, with a one-cell axisymmetric mode at the onset and chaotic
plume convection at large Rayleigh number. [...] Thermal convection requires
that a superadiabatic temperature profile is maintained in the inner core,
which depends on a competition between extraction of the inner core internal
heat by conduction and cooling at the ICB. Inner core thermal convection
appears very likely with the low thermal conductivity value proposed by Stacey
& Davis (2007), but nearly impossible with the much higher thermal conductivity
recently put forward. We argue however that the formation of an iron-rich layer
above the ICB may have a positive feedback on inner core convection: it implies
that the inner core crystallized from an increasingly iron-rich liquid,
resulting in an unstable compositional stratification which could drive inner
core convection, perhaps even if the inner core is subadiabatic.",1306.2482v1
2013-06-25,Superorbital Phase-Resolved Analysis of SMC X-1,"The high-mass X-ray binary SMC X-1 is an eclipsing binary with an orbital
period of 3.89 d. This system exhibits a superorbital modulation with a period
varying between ~40 d and ~65 d. The instantaneous frequency and the
corresponding phase of the superorbital modulation can be obtained by a
recently developed time-frequency analysis technique, the Hilbert-Huang
transform (HHT). We present a phase-resolved analysis of both the spectra and
the orbital profiles with the superorbital phase derived from the HHT. The
X-ray spectra observed by the Proportional Counter Array onboard the Rossi
X-ray Timing Explorer are fitted well by a blackbody plus a Comptonized
component. The plasma optical depth, which is a good indicator of the
distribution of material along the line of sight, is significantly
anti-correlated with the flux detected at 2.5-25 keV. However, the relationship
between the plasma optical depth and the equivalent width of the iron line is
not monotonic: there is no significant correlation for fluxes higher than ~35
mCrab but clear positive correlation when the intensity is lower than ~20
mCrab. This indicates that the iron line production is dominated by different
regions of this binary system in different superorbital phases. To study the
dependence of the orbital profile on the superorbital phase, we obtained the
eclipse profiles by folding the All Sky Monitor light curve with the orbital
period for different superorbital states. A dip feature, similar to the
pre-eclipse dip in Her X-1, lying at orbital phase ~0.6-0.85, was discovered
during the superorbital transition state. This indicates that the accretion
disk has a bulge that absorbs considerable X-ray emission in the stream-disk
interaction region. The dip width is anti-correlated with the flux, and this
relation can be interpreted by the precessing tilted accretion disk scenario.",1306.5819v1
2013-07-30,New and updated stellar parameters for 71 evolved planet hosts. On the metallicity - giant planet connection,"It is still being debated whether the well-known metallicity - giant planet
correlation for dwarf stars is also valid for giant stars. For this reason,
having precise metallicities is very important. Different methods can provide
different results that lead to discrepancies in the analysis of planet hosts.
To study the impact of different analyses on the metallicity scale for evolved
stars, we compare different iron line lists to use in the atmospheric parameter
derivation of evolved stars. Therefore, we use a sample of 71 evolved stars
with planets. With these new homogeneous parameters, we revisit the metallicity
- giant planet connection for evolved stars. A spectroscopic analysis based on
Kurucz models in local thermodynamic equilibrium (LTE) was performed through
the MOOG code to derive the atmospheric parameters. Two different iron line
list sets were used, one built for cool FGK stars in general, and the other for
giant FGK stars. Masses were calculated through isochrone fitting, using the
Padova models. Kolmogorov-Smirnov tests (K-S tests) were then performed on the
metallicity distributions of various different samples of evolved stars and red
giants. All parameters compare well using a line list set, designed
specifically for cool and solar-like stars to provide more accurate
temperatures. All parameters derived with this line list set are preferred and
are thus adopted for future analysis. We find that evolved planet hosts are
more metal-poor than dwarf stars with giant planets. However, a bias in giant
stellar samples that are searched for planets is present. Because of a colour
cut-off, metal-rich low-gravity stars are left out of the samples, making it
hard to compare dwarf stars with giant stars. Furthermore, no metallicity
enhancement is found for red giants with planets ($\log g < 3.0$\,dex) with
respect to red giants without planets.",1307.7870v1
2013-08-07,Abundance gradients in spiral disks: is the gradient inversion at high redshift real?,"We compute the abundance gradients along the disk of the Milky Way by means
of the two-infall model: in particular, the gradients of oxygen and iron and
their temporal evolution. First, we explore the effects of several physical
processes which influence the formation and evolution of abundance gradients.
They are: i) the inside-out formation of the disk, ii) a threshold in the gas
density for star formation, iii) a variable star formation efficiency along the
disk, iv) radial flows and their speed, and v) different total surface mass
density (gas plus stars) distributions for the halo. We are able to reproduce
at best the present day gradients of oxygen and iron if we assume an inside-out
formation, no threshold gas density, a constant efficiency of star formation
along the disk and radial gas flows. It is particularly important the choice of
the velocity pattern for radial flows and the combination of this velocity
pattern with the surface mass density distribution in the halo. Having selected
the best model, we then explore the evolution of abundance gradients in time
and find that the gradients in general steepen in time and that at redshift z~3
there is a gradient inversion in the inner regions of the disk, in the sense
that at early epochs the oxygen abundance decreases toward the Galactic center.
This effect, which has been observed, is naturally produced by our models if an
inside-out formation of the disk and and a constant star formation efficiency
are assumed. The inversion is due to the fact that in the inside-out formation
a strong infall of primordial gas, contrasting chemical enrichment, is present
in the innermost disk regions at early times. The gradient inversion remains
also in the presence of radial flows, either with constant or variable speed in
time, and this is a new result.",1308.1549v1
2013-08-09,KASCADE-Grande measurements of energy spectra for elemental groups of cosmic rays,"The KASCADE-Grande experiment, located at KIT-Karlsruhe, Germany, consists of
a large scintillator array for measurements of charged particles, N_ch, and of
an array of shielded scintillation counters used for muon counting, N_mu.
KASCADE-Grande is optimized for cosmic ray measurements in the energy range 10
PeV to 1000 PeV, thereby enabling the verification of a knee in the iron
spectrum expected at approximately 100 PeV. Exploring the composition in this
energy range is of fundamental importance for understanding the transition from
galactic to extragalactic cosmic rays. Following earlier studies of elemental
spectra reconstructed in the knee energy range from KASCADE data, we have now
extended these measurements to beyond 100 PeV. By analysing the two-dimensional
shower size spectrum N_ch vs. N_mu, we reconstruct the energy spectra of
different mass groups by means of unfolding methods. The procedure and its
results, giving evidence for a knee-like structure in the spectrum of iron
nuclei, will be presented.",1308.2098v1
2013-08-09,S-process in low-mass extremely metal-poor stars,"Extremely metal-poor low-mass stars experience an ingestion of protons into
the helium-rich layer during the core He-flash, resulting in the production of
neutrons through the reactions
^{12}C(p,\gamma)^{13}N(\beta)^{13}C(\alpha,n)^{16}O. This is a potential site
for the production of s-process elements in extremely metal-poor stars not
occurring in more metal-rich counterparts. Observationally, the signatures of
s-process elements in the two most iron deficient stars observed to date,
HE1327-2326 & HE0107-5240, still await for an explanation. We investigate the
possibility that low-mass EMP stars could be the source of s-process elements
observed in extremely iron deficient stars, either as a result of
self-enrichment or in a binary scenario as the consequence of a mass transfer
episode. We present evolutionary and post-processing s-process calculations of
a 1Msun stellar model with metallicities Z=0, 10^{-8} and 10^{-7}. We assess
the sensitivity of nucleosynthesis results to uncertainties in the input
physics of the stellar models, particularly regarding the details of convective
mixing during the core He-flash. Our models provide the possibility of
explaining the C, O, Sr, and Ba abundance for the star HE0107-5240 as the
result of mass-transfer from a low-mass EMP star. The drawback of our model is
that if mass would be transferred before the primary star enters the AGB phase,
nitrogen would be overproduced and the ^{12}C/^{13}C abundance ratio would be
underproduced in comparison to the observed values. Our results show that
low-mass EMP stars cannot be ruled out as the companion stars that might have
polluted HE1327-2326 & HE0107-5240 and produced the observed s-process pattern.
However, more detailed studies of the core He-flash and the proton ingestion
episode are needed to determine the robustness of our predictions.",1308.2224v1
2013-08-12,Distinguishing $s^{\pm}$ and $s^{++}$ electron pairing symmetries by neutron spin resonance in superconducting NaFe$_{0.935}$Co$_{0.045}$As,"A determination of the superconducting (SC) electron pairing symmetry forms
the basis for establishing a microscopic mechansim for superconductivity. For
iron pnictide superconductors, the $s^\pm$-pairing symmetry theory predicts the
presence of a sharp neutron spin resonance at an energy below the sum of hole
and electron SC gap energies ($E\leq 2\Delta$) below $T_c$. On the other hand,
the $s^{++}$-pairing symmetry expects a broad spin excitation enhancement at an
energy above $2\Delta$ below $T_c$. Although the resonance has been observed in
iron pnictide superconductors at an energy below $2\Delta$ consistent with the
$s^\pm$-pairing symmetry, the mode has also be interpreted as arising from the
$s^{++}$-pairing symmetry with $E\ge 2\Delta$ due to its broad energy width and
the large uncertainty in determining the SC gaps. Here we use inelastic neutron
scattering to reveal a sharp resonance at E=7 meV in SC
NaFe$_{0.935}$Co$_{0.045}$As ($T_c = 18$ K). On warming towards $T_c$, the mode
energy hardly softens while its energy width increases rapidly. By comparing
with calculated spin-excitations spectra within the $s^{\pm}$ and
$s^{++}$-pairing symmetries, we conclude that the ground-state resonance in
NaFe$_{0.935}$Co$_{0.045}$As is only consistent with the $s^{\pm}$-pairing, and
is inconsistent with the $s^{++}$-pairing symmetry.",1308.2453v1
2013-08-12,3-D non-LTE radiative transfer effects in Fe I lines: II. Line formation in 3-D radiation hydrodynamic simulations,"We investigate the effects of horizontal radiative transfer (RT) a NLTE on
important diagnostic iron lines in a realistic 3-D HD simulation. Using a
multi-level atom we compute and compare widely used Fe I line profiles at 3
different levels of approximation (3-D NLTE, 1-D NLTE, LTE). We find that the
influence of horizontal RT is of the same order of magnitude as that of NLTE,
although spatially more localized. Also, depending on the temperature of the
surroundings, horizontal RT is found to weaken or strengthen spectral lines.
Line depths and equivalent width may differ by up to 20% against the
corresponding LTE value if 3-D RT is applied. Residual intensity contrasts in
LTE are found to be larger than those in 3-D NLTE by up to a factor of two.
When compared to 1-D NLTE, we find that horizontal RT weakens the contrast by
up to 30% almost independently of the angle of line of sight. While the CLV of
the 1-D and 3-D NLTE contrasts are of similar form, the LTE contrast CLV shows
a different run. The determination of temperatures by 1-D NLTE inversions of
spatially resolved observations may produce errors of up to 200 K if one
neglects 3-D RT. We find a linear correlation between the intensity difference
of 1-D and 3-D NLTE and a simple estimate of the temperature in the horizontal
environment of the line formation region. This correlation could be used to
coarsely correct for the effects of horizontal RT in inversions done in 1-D
NLTE. Horizontal RT is less important if one considers spatially averaged line
profiles because local line strengthening and weakening occur with similar
frequency in our HD atmosphere. Thus, the iron abundance is underestimated by
0.012 dex if calculated using 1-D NLTE RT. Since effects of horizontal RT are
largest for spatially resolved quantities, the use of 3-D RT is particularly
important for the interpretation of high spatial resolution observations.",1308.2490v1
2013-08-21,A High Resolution View of the Warm Absorber in the Quasar MR2251-178,"High resolution X-ray spectroscopy of the warm absorber in the nearby quasar,
MR2251-178 (z = 0.06398) is presented. The observations were carried out in
2011 using the Chandra High Energy Transmission Grating and the XMM-Newton
Reflection Grating Spectrometer, with net exposure times of approximately 400
ks each. A multitude of absorption lines from C to Fe are detected, revealing
at least 3 warm absorbing components ranging in ionization parameter from
log(\xi/erg cm s^-1) = 1-3 and with outflow velocities < 500 km/s. The lowest
ionization absorber appears to vary between the Chandra and XMM-Newton
observations, which implies a radial distance of between 9-17 pc from the black
hole. Several broad soft X-ray emission lines are strongly detected, most
notably from He-like Oxygen, with FWHM velocity widths of up to 10000 km/s,
consistent with an origin from Broad Line Region (BLR) clouds. In addition to
the warm absorber, gas partially covering the line of sight to the quasar
appears to be present, of typical column density N_H = 10^23 cm^-2. We suggest
that the partial covering absorber may arise from the same BLR clouds
responsible for the broad soft X-ray emission lines. Finally the presence of a
highly ionised outflow in the iron K band from both 2002 and 2011 Chandra HETG
observations appears to be confirmed, which has an outflow velocity of -15600
\pm 2400 km/s. However a partial covering origin for the iron K absorption
cannot be excluded, resulting from low ionization material with little or no
outflow velocity.",1308.4550v1
2013-09-13,The Stellar Abundances for Galactic Archaeology (SAGA) Database III - Analysis of Enrichment Histories for Elements and Two Modes of Star Formation during the Early Evolution of Milky Way,"We study the enrichment histories for nine elements, C, four alpha-elements
of Mg, Si, Ca, and Ti, Sc, and three iron-peak elements of Co, Ni, and Zn, by
using a large number of stellar data, collected by the Stellar Abundances for
Galactic Archaeology (SAGA) database. We find statistically significant
changes, or breaks, of the mean abundance ratios to iron at three metallicities
of [Fe/H]-1.8, -2.2, and -3.3. Across the first one, the mean abundance ratios
decrease with the metallicity by similar extents for all the elements with the
sufficient data. Across the latter two, downward trends with the metallicity
are also detected but for limited elements, C, Co, Zn, and possibly Sc, and for
two of Co and Zn, respectively. The breaks define four stellar populations with
the different abundance patters which are dominant in each metallicity range
divided by the breaks, Pop IIa, IIb, IIc, and IId in order of increasing
metallicity. We also explore their spatial distributions with the spectroscopic
distances to demonstrate that Pops IIa and IIb spread over the Galactic halo
while Pops IIc and IId are observed near the Galactic plane. In particular, Pop
IIc stars emerge around [Fe/H] -2.6 and coexist with Pop IIb stars, segregated
by the spatial distributions. Our results reveal two distinct modes of star
formation during the early stages of Galaxy formation, which are associated
with the variations of IMF and the spatial distribution of remnant low-mass
stars. For the two lower-metallicity populations, the enhancements of Zn and Co
indicate a high-mass and top-heavy IMF together with the statistics on the
carbon-enhanced stars. We discuss the relevance to the kinematically resolved
structures of the Galactic halo and the possible sites of these populations
within the framework of hierarchical structure formation scenario.",1309.3430v2
2013-09-17,Chemical gradients in the Milky Way from the RAVE data. I. Dwarf stars,"Aim: We aim at measuring the chemical gradients of the elements Mg, Al, Si,
and Fe along the Galactic radius to provide new constraints on the chemical
evolution models of the Galaxy and Galaxy models such as the Besancon model.
  Methods: We analysed three different samples selected from three independent
datasets: a sample of 19,962 dwarf stars selected from the RAVE database, a
sample of 10,616 dwarf stars selected from the Geneva-Copenhagen Survey (GCS)
dataset, and a mock sample (equivalent to the RAVE sample) created by using the
GALAXIA code, which is based on the Besancon model. We measured the chemical
gradients as functions of the guiding radius (Rg) at different distances from
the Galactic plane reached by the stars along their orbit (Zmax).
  Results: The chemical gradients of the RAVE and GCS samples are negative and
show consistent trends, although they are not equal: at Zmax<0.4 kpc and
4.5<Rg(kpc)<9.5, the iron gradient for the RAVE sample is d[Fe/H]/dRg=-0.065
dex kpc^{-1}, whereas for the GCS sample it is d[Fe/H]/dRg=-0.043 dex kpc^{-1}
with internal errors +-0.002 and +-0.004 dex kpc^{-1}, respectively. The
gradients of the RAVE and GCS samples become flatter at larger Zmax.
Conversely, the mock sample has a positive iron gradient of
d[Fe/H]/dRg=+0.053+-0.003 dex kpc^{-1} at Zmax<0.4 kpc and remains positive at
any Zmax. These positive and unrealistic values originate from the lack of
correlation between metallicity and tangential velocity in the Besancon model.
The discrepancies between the observational samples and the mock sample can be
reduced by i) decreasing the density, ii) decreasing the vertical velocity, and
iii) increasing the metallicity of the thick disc in the Besancon model.",1309.4279v1
2013-09-24,The magnetic and structural properties near the Lifshitz point in Fe1+xTe,"We construct a phase diagram of the parent compound Fe1+xTe as a function of
interstitial iron x in terms of the electronic, structural, and magnetic
properties. For a concentration of x < 10%, Fe1+xTe undergoes a ""semimetal"" to
metal transition at approximately 70 K that is also first-order and coincident
with a structural transition from a tetragonal to a monoclinic unit cell. For x
~ 14%, Fe1+xTe undergoes a second-order phase transition at approximately 58 K
corresponding to a ""semimetal"" to ""semimetal"" transition along with a
structural orthorhombic distortion. At a critical concentration of x ~ 11%,
Fe1+xTe undergoes two transitions: the higher temperature one is a second-order
transition to an orthorhombic phase with incommensurate magnetic ordering and
temperature-dependent propagation vector, while the lower temperature one
corresponds to nucleation of a monoclinic phase with a nearly commensurate
magnetic wavevector. While both structural and magnetic transitions display
similar critical behavior for x < 10% and near the critical concentration of x
~ 11%, samples with large interstitial iron concentrations show a marked
deviation between the critical response indicating a decoupling of the order
parameters. Analysis of temperature dependent inelastic neutron data reveals
incommensurate magnetic fluctuations throughout the Fe1+xTe phase diagram are
directly connected to the ""semiconductor""-like resistivity above T_N and
implicates scattering from spin fluctuations as the primary reason for the
semiconducting or poor metallic properties. The results suggest that doping
driven Fermi surface nesting maybe the origin of the gapless and incommensurate
spin response at large interstitial concentrations.",1309.6310v1
2013-10-09,Four new X-ray-selected supernova remnants in the Large Magellanic Cloud,"Aims: We present a detailed multi-wavelength study of four new supernova
remnants (SNRs) in the Large Magellanic Cloud (LMC). The objects were
identified as SNR candidates in X-ray observations performed during the survey
of the LMC with XMM-Newton.
  Methods: Data obained with XMM-Newton are used to investigate the
morphological and spectral features of the remnants in X-rays. We measure the
plasma conditions, look for supernova (SN) ejecta emission, and constrain some
of the SNR properties (e.g. age and ambient density). We supplement the X-ray
data with optical, infrared, and radio-continuum archival observations, which
allow us to understand the conditions resulting in the current appearance of
the remnants. Based on the spatially-resolved star formation history (SFH) of
the LMC together with the X-ray spectra, we attempt to type the supernovae that
created the remnants.
  Results: We confirm all four objects as SNRs, to which we assign the names
MCSNR J0508-6830, MCSNR J0511-6759, MCSNR J0514-6840, and MCSNR J0517-6759. In
the first two remnants, an X-ray bright plasma is surrounded by very faint [S
II] emission. The emission from the central plasma is dominated by Fe L-shell
lines, and the derived iron abundance is greatly in excess of solar. This
establishes their type Ia (i.e. thermonuclear) SN origin. They appear to be
more evolved versions of other Magellanic Cloud iron-rich SNRs which are
centrally-peaked in X-rays. From the two other remnants (MCSNR J0514-6840 and
MCSNR J0517-6759), we do not see ejecta emission. At all wavelengths at which
they are detected, the local environment plays a key role in their
observational appearance. We present evidence that MCSNR J0517-6759 is close to
and interacting with a molecular cloud, suggesting a massive progenitor.",1310.2569v1
2013-10-14,The Reflection Component from Cygnus X-1 in the Soft State Measured by NuSTAR and Suzaku,"The black hole binary Cygnus X-1 was observed in late-2012 with the Nuclear
Spectroscopic Telescope Array (NuSTAR) and Suzaku, providing spectral coverage
over the ~1-300 keV range. The source was in the soft state with a
multi-temperature blackbody, power-law, and reflection components along with
absorption from highly ionized material in the system. The high throughput of
NuSTAR allows for a very high quality measurement of the complex iron line
region as well as the rest of the reflection component. The iron line is
clearly broadened and is well-described by a relativistic blurring model,
providing an opportunity to constrain the black hole spin. Although the spin
constraint depends somewhat on which continuum model is used, we obtain a*>0.83
for all models that provide a good description of the spectrum. However, none
of our spectral fits give a disk inclination that is consistent with the most
recently reported binary values for Cyg X-1. This may indicate that there is a
>13 degree misalignment between the orbital plane and the inner accretion disk
(i.e., a warped accretion disk) or that there is missing physics in the
spectral models.",1310.3830v1
2013-10-16,Identification of a Jet-Driven Supernova Remnant in the Small Magellanic Cloud: Possible Evidence for the Enhancement of Bipolar Explosions at Low Metallicity,"Recent evidence has suggested that the supernova remnant (SNR) 0104-72.3 in
the Small Magellanic Cloud (SMC) may be the result of a prompt Type Ia SN based
on enhanced iron abundances and its association with a star-forming region. In
this paper, we present evidence that SNR 0104-72.3 arose from a jet-driven
bipolar core-collapse SN. Specifically, we use serendipitous Chandra X-ray
Observatory data of SNR 0104-72.3 taken due to its proximity to the calibration
source SNR E0102-72.3. We analyze 56 Advanced CCD Imaging Spectrometer (ACIS)
observations of SNR 0104-72.3 to produce imaging and spectra with an effective
exposure of 528.6 ks. We demonstrate that SNR 0104-72.3 is highly elliptical
relative to other nearby young SNRs, suggesting a core-collapse SN origin.
Furthermore, we compare ejecta abundances derived from spectral fits to
nucleosynthetic yields of Type Ia and core-collapse (CC) SNe, and we find that
the iron, neon, and silicon abundances are consistent with either a spherical
CC SN of a 18-20 solar mass progenitor or an aspherical CC SN of a 25 solar
mass progenitor. We show that the star-formation history at the site of SNR
0104-72.3 is also consistent with a CC origin. Given the bipolar morphology of
the SNR, we favor the aspherical CC SN scenario. This result may suggest
jet-driven SNe occur frequently in the low-metallicity environment of the SMC,
consistent with the observational and theoretical work on broad-line Type Ic
SNe and long-duration gamma-ray bursts.",1310.4498v2
2013-10-23,Functional Renormalization Group for multi-orbital Fermi Surface Instabilities,"Technological progress in material synthesis, as well as artificial
realization of condensed matter scenarios via ultra-cold atomic gases in
optical lattices or epitaxial growth of thin films, is opening the gate to
investigate a plethora of unprecedented strongly correlated electron systems.
In a large subclass thereof, a metallic state of layered electrons undergoes an
ordering transition below some temperature into unconventional states of matter
driven by electronic correlations, such as magnetism, superconductivity, or
other Fermi surface instabilities. While this type of phenomena has been a
well-established direction of research in condensed matter for decades, the
variety of today's accessible scenarios pose fundamental new challenges to
describe them. A core complication is the multi-orbital nature of the
low-energy electronic structure of these systems, such as the multi-d orbital
nature of electrons in iron pnictides and transition-metal oxides in general,
but also electronic states of matter on lattices with multiple sites per unit
cell such as the honeycomb or kagome lattice. In this review, we propagate the
functional renormalization group (FRG) as a suited approach to investigate
multi-orbital Fermi surface instabilities. The primary goal of the review is to
describe the FRG in explicit detail and render it accessible to everyone both
at a technical and intuitive level. Summarizing recent progress in the field of
multi-orbital Fermi surface instabilities, we illustrate how the unbiased
fashion by which the FRG treats all kinds of ordering tendencies guarantees an
adequate description of electronic phase diagrams and often allows to obtain
parameter trends of sufficient accuracy to make qualitative predictions for
experiments. This review includes detailed and illustrative illustrations of
magnetism and, in particular, superconductivity for the iron pnictides from the
viewpoint of FRG. Furthermore, it discusses candidate scenarios for topological
bulk singlet superconductivity and exotic particle-hole condensates on
hexagonal lattices such as sodium-doped cobaltates, graphene doped to van Hove
Filling, and the kagome Hubbard model. In total, the FRG promises to be one of
the most versatile and revealing numerical approaches to address unconventional
Fermi surface instabilities in future fields of condensed matter research.",1310.6191v1
2013-11-20,The curious time lags of PG 1244+026: Discovery of the iron K reverberation lag,"High-frequency iron K reverberation lags, where the red wing of the line
responds before the line centroid, are a robust signature of relativistic
reflection off the inner accretion disc. In this letter, we report the
discovery of the Fe K lag in PG 1244+026 from ~120 ks of data (1 orbit of the
XMM-Newton telescope). The amplitude of the lag with respect to the continuum
is 1000 s at a frequency of ~1e-4 Hz. We also find a possible
frequency-dependence of the line: as we probe higher frequencies (i.e. shorter
timescales from a smaller emitting region) the Fe K lag peaks at the red wing
of the line, while at lower frequencies (from a larger emitting region) we see
the dominant reflection lag from the rest frame line centroid. The mean energy
spectrum shows a strong soft excess, though interestingly, there is no
indication of a soft lag. Given that this source has radio emission and it has
little reported correlated variability between the soft excess and the hard
band, we explore one possible explanation in which the soft excess in this
source is dominated by the steep power-law like emission from a jet, and that a
corona (or base of the jet) irradiates the inner accretion disc, creating the
blurred reflection features evident in the spectrum and the lag. General
Relativistic ray-tracing models fit the Fe K lag well, with the best-fit giving
a compact X-ray source at a height of 5 gravitational radii and a black hole
mass of 1.3e7 Msun.",1311.5164v1
2013-12-08,On the kinematic separation of field and cluster stars across the Bulge globular NGC 6528,"We present deep and precise multi-band photometry of the Galactic Bulge
globular cluster NGC6528. The current dataset includes optical and
near-infrared images collected with ACS/WFC, WFC3/UVIS, and WFC3/IR on board
the Hubble Space Telescope. The images cover a time interval of almost ten
years and we have been able to carry out a proper-motion separation between
cluster and field stars. We performed a detailed comparison in the m_F814W,
m_F606W - m_F814W Color-Magnitude Diagram with two empirical calibrators
observed in the same bands. We found that NGC6528 is coeval with and more
metal-rich than 47Tuc. Moreover, it appears older and more metal-poor than the
super-metal-rich open cluster NGC6791. The current evidence is supported by
several diagnostics (red horizontal branch, red giant branch bump, shape of the
sub-giant branch, slope of the main sequence) that are minimally affected by
uncertainties in reddening and distance. We fit the optical observations with
theoretical isochrones based on a scaled-solar chemical mixture and found an
age of 11 +- 1 Gyr and an iron abundance slightly above solar ([Fe/H = +0.20).
The iron abundance and the old cluster age further support the recent
spectroscopic findings suggesting a rapid chemical enrichment of the Galactic
Bulge.",1312.2272v2
2013-12-16,Magnetic structure map for face-centered tetragonal iron: appearance of a new collinear spin structure,"For face-centered cubic (fcc) and tetragonal (fct) iron a large number of
magnetic configurations as a function of crystal structural parameters were
studied by means of density functional theory. The stability of magnetic
structures was defined by the magnetic re-orientation energy $\Delta
{E}^i_\text{reor}$ as the difference of the total energy of configuration $i$
and that of the fcc ferromagnetic state. The Cluster Expansion technique was
applied to several volumes deriving $\Delta {E}_\text{reor}$ for more than
90.000 collinear spin structures for each volume. A variety of structures with
promisingly low $\Delta {E}_\text{reor}$ were tetragonally distorted according
to a two-dimensional mesh defined by volume per atom and $c/a$ ratio of the
distortion. At each of the points on this mesh $\Delta E_\text{reor}$ of all
collinear structure were compared to results for non-collinear spin spirals
(SS) which were calculated for a grid of propagation directions. The lowest
$\Delta {E}_\text{reor}$ of all investigated spin structures then defined the
magnetic structure map spanned by volume per atom and $c/a$ ratio. Three local
minima were identified and for each of the minima SS were calculated on a fine
grid of propagation vectors. For the volume per atom of 10.6 \AA$^3$ and the
distortion range $0.94 \le c/a \le 1.01$ we found a new, surprisingly simple
collinear spin structure with four atoms per fct unit cell to be the most
stable one. This structure was called AFM/NM because it consists of two atoms
with anti-ferromagnetically ordered local moments of $\pm 1.8 \mu_\text{B}$ and
of two nonmagnetic atoms with zero local moment. It seems that the newly
detected AFM/NM structure explains a variety of puzzling experimental results.",1312.4313v2
2014-01-07,Superparamagnetic iron oxide polyacrylic acid coated γ-Fe2O3 nanoparticles does not affect kidney function but causes acute effect on the cardiovascular function in healthy mice,"This study describes the distribution of intravenously injected polyacrylic
acid (PAA) coated {\gamma}-Fe2O3 NPs (10 mg kg-1) at the organ, cellular and
subcellular levels in healthy BALB/cJ mice and in parallel addresses the
effects of NP injection on kidney function, blood pressure and vascular
contractility. Magnetic resonance imaging (MRI) and transmission electron
microscopy (TEM) showed accumulation of NPs in the liver within 1h after
intravenous infusion, accommodated by intracellular uptake in endothelial and
Kupffer cells with subsequent intracellular uptake in renal cells, particularly
the cytoplasm of the proximal tubule, in podocytes and mesangial cells. The
renofunctional effects of NPs were evaluated by arterial acid-base status and
measurements of glomerular filtration rate (GFR) after instrumentation with
chronically indwelling catheters. Arterial pH was 7.46 and 7.41 in mice 0.5 h
after injections of saline or NP, and did not change over the next 12h. In
addition, the injections of NP did not affect arterial PCO2 or [HCO3-] either.
Twenty-four and 96h after NP injections, the GFR averaged 11.0 and 13.0 ml
min-1 g-1, respectively, values which were statistically comparable with
controls (14.0 and 14.0 ml min-1 g-1). Mean arterial blood pressure (MAP)
decreased 12-24h after NP injections (111 vs 123 min-1) associated with a
decreased contractility of small mesenteric arteries revealed by myography to
characterise endothelial function. In conclusion, our study demonstrates that
accumulation of superparamagnetic iron oxide nanoparticles does not affect
kidney function in healthy mice but temporarily decreases blood pressure.",1401.1847v1
2014-02-12,Stokes $IQUV$ Magnetic Doppler Imaging of Ap stars II: Next Generation Magnetic Doppler Imaging of $α^2$ CVn,"We present updated magnetic field maps of the chemically peculiar B9p star
$\alpha^2$ CVn created using a series of time resolved observations obtained
using the high resolution spectropolarimeters ESPaDOnS and Narval. We compare
these new magnetic field maps with the original magnetic Doppler imaging maps
based on spectra recorded with the MuSiCoS spectropolarimeter and taken a
decade earlier. These new maps are inferred from line profiles in all four
Stokes parameters using the magnetic Doppler imaging code INVERS10. With the
addition of new lines exhibiting Stokes $IQUV$ signatures we have a unique
insight into how the derived magnetic surface structure may be affected by the
atomic lines chosen for inversion. We report new magnetic maps of $\alpha^2$
CVn created using strong iron lines (directly comparable to the published
MuSiCoS maps), weak iron lines and chromium lines, all of which yield a
magnetic field structure roughly consistent with that obtained previously.
  We then derive an updated magnetic structure map for $\alpha^2$ CVn based on
the complete sample of Fe and Cr lines, which we believe to produce a more
representative model of the magnetic topology of $\alpha^2$ CVn. In agreement
with the previous mapping, this new updated magnetic map shows a dipolar-like
field which has complex sub-structure which cannot be explained by a simple low
order multipolar geometry. Our new maps show that regardless of the atomic line
or species choice, the reconstructed magnetic field is consistent with that
published previously, suggesting that the reconstructed field is a realistic
representation of the magnetic field of $\alpha^2$ CVn. $\alpha^2$ CVn is the
first Ap star for which multiple, high resolution magnetic maps have been
derived, providing important observational evidence for the stability of both
the large and small-scale magnetic field.",1402.2938v1
2014-02-15,Revealing the location and structure of the accretion disk-wind in PDS456,"We present evidence for the rapid variability of the high velocity iron
K-shell absorption in the nearby ($z=0.184$) quasar PDS456. From a recent long
Suzaku observation in 2013 ($\sim1$Ms effective duration) we find that the the
equivalent width of iron K absorption increases by a factor of $\sim5$ during
the observation, increasing from $<105$eV within the first 100ks of the
observation, towards a maximum depth of $\sim500$eV near the end. The implied
outflow velocity of $\sim0.25$c is consistent with that claimed from earlier
(2007, 2011) Suzaku observations. The absorption varies on time-scales as short
as $\sim1$ week. We show that this variability can be equally well attributed
to either (i) an increase in column density, plausibly associated with a clumpy
time-variable outflow, or (ii) the decreasing ionization of a smooth
homogeneous outflow which is in photo-ionization equilibrium with the local
photon field. The variability allows a direct measure of absorber location,
which is constrained to within $r=200-3500$$\rm{r_{g}}$ of the black hole. Even
in the most conservative case the kinetic power of the outflow is $\gtrsim6\%$
of the Eddington luminosity, with a mass outflow rate in excess of $\sim40\%$
of the Eddington accretion rate. The wind momentum rate is directly equivalent
to the Eddington momentum rate which suggests that the flow may have been
accelerated by continuum-scattering during an episode of Eddington-limited
accretion.",1402.3700v2
2014-03-11,Broad iron emission line and kilohertz quasi-periodic oscillations in the neutron star system 4U 1636-53,"Both the broad iron (Fe) line and the frequency of the kilohertz
quasi-periodic oscillations (kHz QPOs) in neutron star low-mass X-ray binaries
(LMXBs) can potentially provide independent measures of the inner radius of the
accretion disc. We use XMM-Newton and simultaneous Rossi X-ray Timing Explorer
observations of the LMXB 4U 1636-53 to test this hypothesis. We study the
properties of the Fe-K emission line as a function of the spectral state of the
source and the frequency of the kHz QPOs. We find that the inner radius of the
accretion disc deduced from the frequency of the upper kHz QPO varies as a
function of the position of the source in the colour-colour diagram, in
accordance with previous work and with the standard scenario of accretion disc
geometry. On the contrary, the inner disc radius deduced from the profile of
the Fe line is not correlated with the spectral state of the source. The values
of the inner radius inferred from kHz QPOs and Fe lines, in four observations,
do not lead to a consistent value of the neutron star mass, regardless of the
model used to fit the Fe line. Our results suggest that either the kHz QPO or
the standard relativistic Fe line interpretation does not apply for this
system. Furthermore, the simultaneous detection of kHz QPOs and broad Fe lines
is difficult to reconcile with models in which the broadening of the Fe line is
due to the reprocessing of photons in an outflowing wind.",1403.2700v3
2014-04-14,"Interplane resistivity of underdoped single crystals (Ba$_{1-x}$K$_x$)Fe$_2$As$_2$, $0 \leq x<0.34$","Temperature-dependent inter-plane resistivity, $\rho _c(T)$, was measured in
hole-doped iron-arsenide superconductor (Ba$_{1-x}$K$_x$)Fe$_2$As$_2$ over a
doping range from parent compound to optimal doping $T_c\approx 38~K$, $0\leq x
\leq 0.34$. Measurements were undertaken on high-quality single crystals grown
from FeAs flux. The coupled magnetic/structural transition at $T_{SM}$ leads to
clear accelerated decrease of $\rho_c(T)$ on cooling in samples with $T_c
<$26~K ($x <0.25$). This decrease in hole-doped material is in notable contrast
to an increase in $\rho_c(T)$ in the electron-doped Ba(Fe$_{1-x}$Co$_x$)Fe
$_2$As$_2$ and iso-electron substituted BaFe$_2$(As$_{1-x}$P$_x$)$_2$. The
$T_{SM}$ decreases very sharply with doping, dropping from $T_s$=71~K to zero
on increase of $T_c$ from approximately 25 to 27~K. The $\rho_c(T)$ becomes
$T$-linear close to optimal doping. The broad crossover maximum in $\rho_c(T)$,
found in the parent BaFe$_2$As$_2$ at around $T_{max} \sim$200~K, shifts to
higher temperature $\sim$250~K with doping $x$=0.34. The maximum shows clear
correlation with the broad crossover feature found in the temperature-dependent
in-plane resistivity $\rho_a(T)$. The doping evolution of $T_{max}$ in
(Ba$_{1-x}$K$_x$)Fe$_2$As$_2$ is in notable contrast with both rapid
suppression of $T_{max}$ found in Ba(Fe$_{1-x}TM_x$)$_2$As$_2$
($TM$=Co,Rh,Ni,Pd) and its rapid increase BaFe$_2$(As$_{1-x}$P$_x$)$_2$. This
observation suggest that pseudogap features are much stronger in hole-doped
than in electron-doped iron-based superconductors, revealing significant
electron-hole doping asymmetry similar to the cuprates. This paper replaces:
cond-mat:1106.0533.",1404.3664v1
2014-06-04,New Fe I level energies and line identifications from stellar spectra,"The spectrum of the Fe I atom is critical to many areas of astrophysics and
beyond. Measurements of the energies of its high-lying levels remain woefully
incomplete, however, despite extensive analysis of ultraviolet laboratory iron
absorption spectra, optical laboratory iron emission spectra, and the solar
infrared spectrum. In this work we use as sources the high-resolution archival
absorption-line ultraviolet and optical spectra of stars, whose warm
temperatures favor moderate Fe I excitation. We derive the energy for a
particular upper level in Kurucz's semiempirical calculations by adopting a
trial value that yields the same wavelength for a given line predicted to be
about as strong as that of a strong unidentified spectral line observed in the
stellar spectra, then checking the new wavelengths of other strong predicted
transitions that share the same upper level for coincidence with other strong
observed unidentified lines. To date this analysis has provided the upper
energies of 66 Fe I levels. Many new level energies are higher than those
accessible to laboratory experiments; several exceed the Fe I ionization
energy. These levels provide new identifications for over two thousand
potentially detectable lines. Almost all of the new levels of odd parity
include UV lines that were detected but unclassified in laboratory Fe I
absorption spectra, providing an external check on the energy values. We
motivate and present the procedure, provide the resulting new level energies
and their uncertainties, list all the potentially detectable UV and optical new
Fe I line identifications and their gf-values, point out new lines of
astrophysical interest, and discuss the prospects for additional Fe I
energy-level determinations in the near future.",1406.0933v3
2014-06-16,Location and sizes of forsterite grains in protoplanetary disks: interpretation from the Herschel DIGIT programme,"The spectra of protoplanetary disks contain mid- and far- infrared emission
features produced by forsterite dust grains. The spectral features contain
information about the forsterite temperature, chemical composition and grain
size. We aim to characterize how the 23 and 69 micron features can be used to
constrain the physical locations of forsterite in disks. We check for
consistency between two independent forsterite temperature measurements: the
23/69 feature strength ratio and the shape of the 69 micron band. We performed
radiative transfer modeling to study the effect of disk properties to the
forsterite spectral features. Temperature-dependent forsterite opacities were
considered in self-consistent models to compute forsterite emission from
protoplanetary disks. Modelling grids are presented to study the effects of
grain size, disk gaps, radial mixing and optical depth to the forsterite
features. Independent temperature estimates derived from the 23/69 feature
strength ratio and the 69 micron band shape are most inconsistent for HD141569
and Oph IRS 48. A case study of the disk of HD141569 shows two solutions to fit
the forsterite spectrum. A model with T ~ 40 K, iron-rich (~0-1 % Fe) and 1
micron forsterite grains, and a model with warmer (T ~ 100 K), iron-free, and
larger (10 micron) grains. We find that for disks with low upper limits of the
69 micron feature (most notably in flat, self-shadowed disks), the forsterite
must be hot, and thus close to the star. We find no correlation between disk
gaps and the presence or absence of forsterite features. We argue that the 69
micron feature of the evolved transitional disks HD141569 and Oph IRS 48 is
most likely a tracer of larger (i.e. ~10 micron) forsterite grains.",1406.3951v1
2014-06-17,"New Detections of Arsenic, Selenium, and Other Heavy Elements in Two Metal-Poor Stars","We use the Space Telescope Imaging Spectrograph on board the Hubble Space
Telescope to obtain new high-quality spectra covering the 1900 to 2360 Angstrom
wavelength range for two metal-poor stars, HD 108317 and HD 128279. We derive
abundances of Cu II, Zn II, As I, Se I, Mo II, and Cd II, which have not been
detected previously in either star. Abundances derived for Ge I, Te I, Os II,
and Pt I confirm those derived from lines at longer wavelengths. We also derive
upper limits from the non-detection of W II, Hg II, Pb II, and Bi I. The mean
[As/Fe] ratio derived from these two stars and five others in the literature is
unchanged over the metallicity range -2.8 < [Fe/H] < -0.6, <[As/Fe]> = +0.28
+/- 0.14 (std. dev. = 0.36 dex). The mean [Se/Fe] ratio derived from these two
stars and six others in the literature is also constant, <[Se/Fe]> = +0.16 +/-
0.09 (std. dev. = 0.26 dex). The As and Se abundances are enhanced relative to
a simple extrapolation of the iron-peak abundances to higher masses, suggesting
that this mass region (75 < A < 82) may be the point at which a different
nucleosynthetic mechanism begins to dominate the quasi-equilibrium alpha-rich
freezeout of the iron peak. <[CuII/CuI]> = +0.56 +/- 0.23 in HD 108317 and HD
128279, and we infer that lines of Cu I may not be formed in local
thermodynamic equilibrium in these stars. The [Zn/Fe], [Mo/Fe], [Cd/Fe], and
[Os/Fe] ratios are also derived from neutral and ionized species, and each
ratio pair agrees within the mutual uncertainties, which range from 0.15 to
0.52 dex.",1406.4554v1
2014-06-20,Suzaku Observation of the Black Hole Binary 4U 1630--47 in the Very High State,"We report the results from an X-ray and near-infrared observation of the
Galactic black hole binary 4U 1630--47 in the very high state, performed with
{\it Suzaku} and IRSF around the peak of the 2012 September-October outburst.
The X-ray spectrum is approximated by a steep power law, with photon index of
3.2, identifying the source as being in the very high state. A more detailed
fit shows that the X-ray continuum is well described by a multi-color disc,
together with thermal and non-thermal Comptonization. The inner disc appears
slightly truncated by comparison with a previous high/soft state of this
source, even taking into account energetic coupling between the disc and
corona, although there are uncertainties due to the dust scattering correction.
The near-infrared fluxes are higher than the extrapolated disc model, showing
that there is a contribution from irradiation in the outer disk and/or the
companion star at these wavelengths. Our X-ray spectra do not show the Doppler
shifted iron emission lines indicating a baryonic jet which were seen four days
previously in an XMM-Newton observation, despite the source being in a similar
state. There are also no significant absorption lines from highly ionized irons
as are seen in the previous high/soft state data. We show that the increased
source luminosity is not enough on its own to make the wind so highly ionized
as to be undetectable. This shows that the disc wind has changed in terms of
its launch radius and/or density compared to the high/soft state.",1406.5512v1
2014-06-27,Chemical gradients in the Milky Way from the RAVE data. II. Giant stars,"We provide new constraints on the chemo-dynamical models of the Milky Way by
measuring the radial and vertical chemical gradients for the elements Mg, Al,
Si, Ti, and Fe in the Galactic disc and the gradient variations as a function
of the distance from the Galactic plane ($Z$). We selected a sample of giant
stars from the RAVE database using the gravity criterium 1.7$<$log g$<$2.8. We
created a RAVE mock sample with the Galaxia code based on the Besan\c con model
and selected a corresponding mock sample to compare the model with the observed
data. We measured the radial gradients and the vertical gradients as a function
of the distance from the Galactic plane $Z$ to study their variation across the
Galactic disc. The RAVE sample exhibits a negative radial gradient of
$d[Fe/H]/dR=-0.054$ dex kpc$^{-1}$ close to the Galactic plane ($|Z|<0.4$ kpc)
that becomes flatter for larger $|Z|$. Other elements follow the same trend
although with some variations from element to element. The mock sample has
radial gradients in fair agreement with the observed data. The variation of the
gradients with $Z$ shows that the Fe radial gradient of the RAVE sample has
little change in the range $|Z|\lesssim0.6$ kpc and then flattens. The iron
vertical gradient of the RAVE sample is slightly negative close to the Galactic
plane and steepens with $|Z|$. The mock sample exhibits an iron vertical
gradient that is always steeper than the RAVE sample. The mock sample also
shows an excess of metal-poor stars in the [Fe/H] distributions with respect to
the observed data. These discrepancies can be reduced by decreasing the number
of thick disc stars and increasing their average metallicity in the Besan\c con
model.",1406.7244v1
2014-07-21,Constraints on Core Collapse from the Black Hole Mass Function,"We model the observed black hole mass function under the assumption that
black hole formation is controlled by the compactness of the stellar core at
the time of collapse. Low compactness stars are more likely to explode as
supernovae and produce neutron stars, while high compactness stars are more
likely to be failed supernovae that produce black holes with the mass of the
helium core of the star. Using three sequences of stellar models and
marginalizing over a model for the completeness of the black hole mass
function, we find that the compactness xi(2.5) above which 50% of core
collapses produce black holes is xi(2.5)=0.24 (0.15 < xi(2.5) < 0.37) at 90%
confidence). While models with a sharp transition between successful and failed
explosions are always the most likely, the width of the transition between the
minimum compactness for black hole formation and the compactness above which
all core collapses produce black holes is not well constrained. The models also
predict that f=0.18 (0.09 < f < 0.39) of core collapses fail assuming a minimum
mass for core collapse of 8Msun. We tested four other criteria for black hole
formation based on xi(2.0) and xi(3.0), the compactnesses at enclosed masses of
2.0 or 3.0 rather than 2.5Msun, the mass of the iron core, and the mass inside
the oxygen burning shell. We found that xi(2.0) works as well as xi(2.5), while
the compactness xi(3.0) works significantly worse, as does using the iron core
mass or the mass enclosed by the oxygen burning shell. As expected from the
high compactness of 20-25Msun stars, black hole formation in this mass range
provides a natural explanation of the red supergiant problem.",1407.5622v1
2014-07-30,The NuSTAR spectrum of Mrk 335: Extreme relativistic effects within 2 gravitational radii of the event horizon?,"We present 3-50 keV NuSTAR observations of the AGN Mrk 335 in a very low flux
state. The spectrum is dominated by very strong features at the energies of the
iron line at 5-7 keV and Compton hump from 10-30 keV. The source is variable
during the observation, with the variability concentrated at low energies,
which suggesting either a relativistic reflection or a variable absorption
scenario. In this work we focus on the reflection interpretation, making use of
new relativistic reflection models that self consistently calculate the
reflection fraction, relativistic blurring and angle-dependent reflection
spectrum for different coronal heights to model the spectra. We find that the
spectra can be well fit with relativistic reflection, and that the lowest flux
state spectrum is described by reflection alone, suggesting the effects of
extreme light-bending occurring within ~2 gravitational radii of the event
horizon. The reflection fraction decreases sharply with increasing flux,
consistent with a point source moving up to above 10 Rg as the source
brightens. We constrain the spin parameter to greater than 0.9 at the 3 sigma
confidence level. By adding a spin-dependent upper limit on the reflection
fraction to our models, we demonstrate that this can be a powerful way of
constraining the spin parameter, particularly in reflection dominated states.
We also calculate a detailed emissivity profile for the iron line, and find
that it closely matches theoretical predictions for a compact source within a
few Rg of the black hole.",1407.8223v1
2014-09-08,Chemical tagging of the Ursa Major moving group: A northern selection of FGK stars,"Stellar kinematic groups are kinematical coherent groups of stars which might
share a common origin.These groups spread through the Galaxy over time due to
tidal effects caused by Galactic rotation and disc heating.However, the
chemical information survives these processes. The information provided by the
analysis of chemical elements can reveal the origin of these kinematic groups.
Here we investigate the origin of the stars that belong to the Ursa Major
Moving Group. We present high-resolution spectroscopic observations obtained
from three different spectrographs of kinematically selected FGK stars of the
Ursa Major moving group. Stellar atmospheric parameters (Teff, log(g), xi, and
[Fe/H]) were determined using our own automatic code (StePar) which makes use
of the sensitivity of iron equivalent widths measured in the spectra. We
critically compare the StePar results with other methods (Teff values derived
using the infrared flux method and log(g) values based on Hipparcos
parallaxes). We derived the chemical abundances of 20 elements, and their
[X/Fe] ratios of all stars in the sample. We perform a differential abundance
analysis with respect to a reference star of the UMa MG (HD115043). We have
also carried out a systematic comparison of the abundance pattern of the Ursa
Major MG and the Hyades SC with the thin disc stellar abundances. Our chemical
tagging analysis indicates that the Ursa Major MG is less affected by field
star contamination than other moving groups (such as the Hyades SC). We find a
roughly solar iron composition for the finally selected stars, whereas the
[X/Fe] ratios are roughly sub-solar except for super-solar Barium abundance.We
conclude that 29 out of 44 (i.e. 66 %) candidate stars share a similar chemical
composition. In addition, we find that the abundance pattern of the Ursa Major
MG might be marginally different from that of the Hyades SC.",1409.2348v1
2014-09-11,XMM-Newton observations reveal the disappearance of the wind in 4U 1630-47,"We report on XMM-Newton observations of the black hole X-ray binary 4U
1630-47 during its 2012-2013 outburst. The first five observations monitor the
source as its luminosity increases across the high-soft state of accretion. In
the sixth observation the source has made a transition to an ""anomalous"" state,
characterised by a significant contribution of electron scattering. A
thermally/radiatively driven disc wind is present in the first four
observations, which becomes more photoionised as the luminosity increases with
time. In the fifth observation, the wind is not observed any more as a
consequence of strong photoionisation and the low sensitivity of this
observation. This overall trend is then consistent with a fully ionised wind
causing the electron scattering characteristic of the anomalous state in the
sixth observation. A broad iron emission line co-exists with the absorption
features from the wind in the first four observations but is not visible in the
last two observations. We find that the changes in the state of the wind as
measured from modelling the absorption features with a self-consistent warm
absorber model are correlated to the changes in the broad iron line. When the
latter is modeled with a reflection component we find that the reflection
fraction decreases as the illumination increases. We propose that the changes
in both the absorption and broad emission lines are caused by the increasing
luminosity and temperature of the accretion disc along the soft state. Such
changes ultimately enable the transition to a state where the wind is fully
ionised and consequently Comptonisation plays a significant role.",1409.3406v2
2014-09-15,The origin of the most iron-poor star,"We investigate the origin of carbon-enhanced metal-poor (CEMP) stars starting
from the recently discovered $\rm [Fe/H]<-7.1$ star SMSS J031300 (Keller et al.
2014). We show that the elemental abundances observed on the surface of SMSS
J031300 can be well fit by the yields of faint, metal free, supernovae. Using
properly calibrated faint supernova explosion models, we study, for the first
time, the formation of dust grains in such carbon-rich, iron-poor supernova
ejecta. Calculations are performed assuming both unmixed and uniformly mixed
ejecta and taking into account the partial destruction by the supernova reverse
shock. We find that, due to the paucity of refractory elements beside carbon,
amorphous carbon is the only grain species to form, with carbon condensation
efficiencies that range between (0.15-0.84), resulting in dust yields in the
range (0.025-2.25)M$_{\odot}$. We follow the collapse and fragmentation of a
star forming cloud enriched by the products of these faint supernova explosions
and we explore the role played by fine structure line cooling and dust cooling.
We show that even if grain growth during the collapse has a minor effect of the
dust-to-gas ratio, due to C depletion into CO molecules at an early stage of
the collapse, the formation of CEMP low-mass stars, such as SMSS J031300, could
be triggered by dust cooling and fragmentation. A comparison between model
predictions and observations of a sample of C-normal and C-rich metal-poor
stars supports the idea that a single common pathway may be responsible for the
formation of the first low-mass stars.",1409.4424v2
2014-09-26,VLT/FLAMES spectroscopy of red giant branch stars in the Fornax dwarf spheroidal galaxy,"Fornax is one of the most massive dwarf spheroidal galaxies in the Local
Group. The Fornax field star population is dominated by intermediate age stars
but star formation was going on over almost its entire history. It has been
proposed that Fornax experienced a minor merger event. Despite recent progress,
only the high metallicity end of Fornax field stars ([Fe/H]>-1.2 dex) has been
sampled in larger number via high resolution spectroscopy. We want to better
understand the full chemical evolution of this galaxy by better sampling the
whole metallicity range, including more metal poor stars. We use the VLT-FLAMES
multi-fibre spectrograph in high-resolution mode to determine the abundances of
several alpha, iron-peak and neutron-capture elements in a sample of 47
individual Red Giant Branch stars in the Fornax dwarf spheroidal galaxy. We
combine these abundances with accurate age estimates derived from the age
probability distribution from the colour-magnitude diagram of Fornax. Similar
to other dwarf spheroidal galaxies, the old, metal-poor stars of Fornax are
typically alpha-rich while the young metal-rich stars are alpha-poor. In the
classical scenario of the time delay between SNe II and SNe Ia, we confirm that
SNe Ia started to contribute to the chemical enrichment at [Fe/H] between -2.0
and -1.8 dex. We find that the onset of SNe Ia took place between 12-10 Gyrs
ago. The high values of [Ba/Fe], [La/Fe] reflect the influence of SNe Ia and
AGB stars in the abundance pattern of the younger stellar population of Fornax.
Our findings of low [alpha/Fe] and enhanced [Eu/Mg] are compatible with an
initial mass function that lacks the most massive stars and with star formation
that kept going on throughout the whole history of Fornax. We find that massive
stars kept enriching the interstellar medium in alpha-elements, although they
were not the main contributor to the iron enrichment.",1409.7703v1
2014-10-03,Orbital occupancy and charge doping in iron-based superconductors,"Iron-based superconductors (FBS) comprise several families of compounds
having the same atomic building blocks for superconductivity, but large
discrepancies among their physical properties. A longstanding goal in the field
has been to decipher the key underlying factors controlling TC and the various
doping mechanisms. In FBS materials this is complicated immensely by the
different crystal and magnetic structures exhibited by the different families.
In this paper, using aberration-corrected scanning transmission electron
microscopy (STEM) coupled with electron energy loss spectroscopy (EELS), we
observe a universal behavior in the hole concentration and magnetic moment
across different families. All the parent materials have the same total number
of electrons in the Fe 3d bands; however, the local Fe magnetic moment varies
due to different orbital occupancy. Although the common understanding has been
that both long-range and local magnetic moments decrease with doping, we find
that, near the onset of superconductivity, the local magnetic moment increases
and shows a dome-like maximum near optimal doping, where no ordered magnetic
moment is present. In addition, we address a longstanding debate concerning how
Co substitutions induces superconductivity in the 122 arsenide family, showing
that the 3d band filling increases a function of doping. These new microscopic
insights into the properties of FBS demonstrate the importance of spin
fluctuations for the superconducting state, reveal changes in orbital occupancy
among different families of FBS, and confirm charge doping as one of the
mechanisms responsible for superconductivity in 122 arsenides.",1410.0971v1
2014-12-11,The 2D Distribution of Iron Rich Ejecta in the Remnant of SN 1885 in M31,"We present Hubble Space Telescope (HST) ultraviolet Fe I and Fe II images of
the remnant of Supernova 1885 (S And) which is observed in absorption against
the bulge of the Andromeda galaxy, M31. We compare these Fe I and Fe II
absorption line images to previous HST absorption images of S And, of which the
highest quality and theoretically cleanest is Ca II H & K. Because the remnant
is still in free expansion, these images provide a 2D look at the distribution
of iron synthesized in this probable Type Ia explosion, thus providing insights
and constraints for theoretical SN Ia models. The Fe I images show extended
absorption offset to the east from the remnant's center as defined by Ca II
images and is likely an ionization effect due to self-shielding. More
significant is the remnant's apparent Fe II distribution which consists of four
streams or plumes of Fe-rich material seen in absorption that extend from
remnant center out to about 10,000 km/s. This is in contrast to the remnant's
Ca II absorption, which is concentrated in a clumpy, roughly spherical shell at
1000 to 5000 km/s but which extends out to 12,500 km/s. The observed
distributions of Ca and Fe rich ejecta in the SN 1885 remnant are consistent
with delayed detonation white dwarf models. The largely spherical symmetry of
the Ca-rich layer argues against a highly anisotropic explosion as might result
from a violent merger of two white dwarfs.",1412.3815v3
2014-12-31,Strong Variability of Overlapping Iron Broad Absorption Lines in Five Radio-selected Quasars,"We present the variability study of broad absorption lines (BALs) in a
uniformly radio-selected sample of 28 BAL quasars using the archival data from
the FIRST Bright Quasar Survey (FBQS) and the Sloan Digital Sky Survey (SDSS),
as well as those obtained by ourselves, covering time scales $\sim 1-10$ years
in the quasar's rest-frame. To our surprise, 5 quasars showing strong
variations are all belong to a special subclass of overlapping iron low
ionization BAL (OFeLoBAL) quasars, however, other 4 non-overlapping FeLoBALs
(non-OFeLoBALs) are invariable except one case with weak optical depth change.
Meanwhile, we also find 6 typical variations of high-ionization and
low-ionization BALs in this BAL quasar sample. Photoionization models suggest
that OFeLoBALs are formed in a relative dense ($n_e>10^6$ cm$^{-3}$) outflows
at a distance from the subparsec to the dozens of parsecs from the continuum
source. They differ from those of non-OFeLoBALs, which are likely produced by
low-density gas, locating at a distance of hundreds to thousands parsecs. Thus,
OFeLoBALs and non-OFeLoBALs, i.e., FeLoBALs with/without strong BAL variations,
perhaps represent the bimodality of Fe II absorption, the former is located in
the active galactic nucleus environment rather than the host galaxy. We suggest
that high density and small distance are the necessary conditions that cause
OFeLoBALs. As suggested in the literature, strong BAL variability is possibly
due to variability of the covering factor of BAL regions caused by clouds
transiting across the line of sight rather than ionization variations.",1501.00091v3
2015-01-02,Determining the Mass of Kepler-78b With Nonparametric Gaussian Process Estimation,"Kepler-78b is a transiting planet that is 1.2 times the radius of Earth and
orbits a young, active K dwarf every 8 hours. The mass of Kepler-78b has been
independently reported by two teams based on radial velocity measurements using
the HIRES and HARPS-N spectrographs. Due to the active nature of the host star,
a stellar activity model is required to distinguish and isolate the planetary
signal in radial velocity data. Whereas previous studies tested parametric
stellar activity models, we modeled this system using nonparametric Gaussian
process (GP) regression. We produced a GP regression of relevant Kepler
photometry. We then use the posterior parameter distribution for our
photometric fit as a prior for our simultaneous GP + Keplerian orbit models of
the radial velocity datasets. We tested three simple kernel functions for our
GP regressions. Based on a Bayesian likelihood analysis, we selected a
quasi-periodic kernel model with GP hyperparameters coupled between the two RV
datasets, giving a Doppler amplitude of 1.86 $\pm$ 0.25 m s$^{-1}$ and
supporting our belief that the correlated noise we are modeling is
astrophysical. The corresponding mass of 1.87 $^{+0.27}_{-0.26}$ M$_{\oplus}$
is consistent with that measured in previous studies, and more robust due to
our nonparametric signal estimation. Based on our mass and the radius
measurement from transit photometry, Kepler-78b has a bulk density of
6.0$^{+1.9}_{-1.4}$ g cm$^{-3}$. We estimate that Kepler-78b is 32$\pm$26% iron
using a two-component rock-iron model. This is consistent with an Earth-like
composition, with uncertainty spanning Moon-like to Mercury-like compositions.",1501.00369v2
2015-01-05,Relationship between X-ray spectral index and X-ray Eddington ratio for Mrk 335 and Ark 564,"We present a comprehensive flux resolved spectral analysis of the bright
Narrow line Seyfert I AGNs, Mrk~335 and Ark~564 using observations by
XMM-Newton satellite. The mean and the flux resolved spectra are fitted by an
empirical model consisting of two Comptonization components, one for the low
energy soft excess and the other for the high energy power-law. A broad Iron
line and a couple of low energies edges are required to explain the spectra.
For Mrk~335, the 0.3 - 10 keV luminosity relative to the Eddington value,
L{$_{X}$}/L$_{Edd}$, varied from 0.002 to 0.06. The index variation can be
empirically described as $\Gamma$ = 0.6 log$_{10}$ L{$_{X}$}/L$_{Edd}$ + 3.0
for $0.005 < L{_{X}}/L_{Edd} < 0.04$. At $ L_{{X}}/L_{Edd} \sim 0.04$ the
spectral index changes and then continues to follow $\Gamma$ = 0.6 log$_{10}$
L$_{{X}}$/L$_{Edd}$ + 2.7, i.e. on a parallel track. We confirm that the result
is independent of the specific spectral model used by fitting the data in the 3
- 10 keV band by only a power-law and an Iron line. For Ark~564, the index
variation can be empirically described as $\Gamma$ = 0.2 log$_{10}$
L$_{{X}}$/L$_{Edd}$ + 2.7 with a significantly large scatter as compared to
Mrk~335. Our results indicate that for Mrk~335, there may be accretion disk
geometry changes which lead to different parallel tracks. These changes could
be related to structural changes in the corona or enhanced reflection at high
flux levels. There does not seem to be any homogeneous or universal
relationship for the X-ray index and luminosity for different AGNs or even for
the same AGN.",1501.00908v1
2015-01-08,Neutrino-driven supernova of a low-mass iron-core progenitor boosted by three-dimensional turbulent convection,"We present the first successful simulation of a neutrino-driven supernova
explosion in three dimensions (3D), using the Prometheus-Vertex code with an
axis-free Yin-Yang grid and a sophisticated treatment of three-flavor,
energy-dependent neutrino transport. The progenitor is a nonrotating,
zero-metallicity 9.6 Msun star with an iron core. While in spherical symmetry
outward shock acceleration sets in later than 300 ms after bounce, a successful
explosion starts at ~130 ms postbounce in two dimensions (2D). The 3D model
explodes at about the same time but with faster shock expansion than in 2D and
a more quickly increasing and roughly 10 percent higher explosion energy of
>10^50 erg. The more favorable explosion conditions in 3D are explained by
lower temperatures and thus reduced neutrino emission in the cooling layer
below the gain radius. This moves the gain radius inward and leads to a bigger
mass in the gain layer, whose larger recombination energy boosts the explosion
energy in 3D. These differences are caused by less coherent, less massive, and
less rapid convective downdrafts associated with postshock convection in 3D.
The less violent impact of these accretion downflows in the cooling layer
produces less shock heating and therefore diminishes energy losses by neutrino
emission. We thus have, for the first time, identified a reduced mass accretion
rate, lower infall velocities, and a smaller surface filling factor of
convective downdrafts as consequences of 3D postshock turbulence that
facilitate neutrino-driven explosions and strengthen them compared to the 2D
case.",1501.01961v2
2015-01-20,"Spectroscopic Abundances in the Open Cluster, NGC 6819","High-dispersion spectra of 333 stars in the open cluster NGC 6819, obtained
using the HYDRA spectrograph on the WIYN 3.5m telescope, have been analyzed to
determine the abundances of iron and other metals from lines in the 400 A
region surrounding the Li 6708 A line. Our spectra, with signal-to-noise per
pixel (SNR) ranging from 60 to 300, span the luminosity range from the tip of
the red giant branch to a point two magnitudes below the top of the cluster
turnoff. We derive radial and rotational velocities for all stars, as well as
[Fe/H] based on 17 iron lines, [Ca/H], [Si/H], and [Ni/H] in the 247 most
probable, single members of the cluster. Input temperature estimates for model
atmosphere analysis are provided by (B-V) colors merged from several sources,
with individual reddening corrections applied to each star relative to a
cluster mean of E(B-V) = 0.16. Extensive use is made of ROBOSPECT, an automatic
equivalent width measurement program; its effectiveness on large spectroscopic
samples is discussed. From the sample of likely single members, [Fe/H] = -0.03
+/- 0.06, where the error describes the median absolute deviation about the
sample median value, leading to an internal precision for the cluster below
0.01 dex. The final uncertainty in the cluster abundance is therefore dominated
by external systematics due to the temperature scale, surface gravity, and
microturbulent velocity, leading to [Fe/H] = -0.02 +/- 0.02 for a sub-sample
restricted to main sequence and turnoff stars. This result is consistent with
our recent intermediate-band photometric determination of a slightly subsolar
abundance for this cluster. [Ca/Fe], [Si/Fe], and [Ni/Fe] are determined to be
solar within the uncertainties. NGC 6819 has an abundance distribution typical
of solar metallicity thin disk stars in the solar neighborhood.",1501.04973v1
2015-01-26,A one-dimensional Chandrasekhar-mass delayed-detonation model for the broad-lined Type Ia supernova 2002bo,"We present 1D non-local thermodynamic equilibrium (non-LTE) time-dependent
radiative-transfer simulations of a Chandrasekhar-mass delayed-detonation model
which synthesizes 0.51 Msun of 56Ni, and confront our results to the Type Ia
supernova (SN Ia) 2002bo over the first 100 days of its evolution. Assuming
only homologous expansion, this same model reproduces the bolometric and
multi-band light curves, the secondary near-infrared (NIR) maxima, and the
optical and NIR spectra. The chemical stratification of our model qualitatively
agrees with previous inferences by Stehle et al., but reveals significant
quantitative differences for both iron-group and intermediate-mass elements. We
show that +/-0.1 Msun (i.e., +/-20 per cent) variations in 56Ni mass have a
modest impact on the bolometric and colour evolution of our model. One notable
exception is the U-band, where a larger abundance of iron-group elements
results in less opaque ejecta through ionization effects, our model with more
56Ni displaying a higher near-UV flux level. In the NIR range, such variations
in 56Ni mass affect the timing of the secondary maxima but not their magnitude,
in agreement with observational results. Moreover, the variation in the I, J,
and K_s magnitudes is less than 0.1 mag within ~10 days from bolometric
maximum, confirming the potential of NIR photometry of SNe Ia for cosmology.
Overall, the delayed-detonation mechanism in single Chandrasekhar-mass white
dwarf progenitors seems well suited for SN 2002bo and similar SNe Ia displaying
a broad Si II 6355 A line. Whatever multidimensional processes are at play
during the explosion leading to these events, they must conspire to produce an
ejecta comparable to our spherically-symmetric model.",1501.06583v2
2015-02-26,Suzaku broad-band spectrum of 4U 1705-44: Probing the Reflection component in the hard state,"Iron emission lines at 6.4-6.97 keV, identified with Kalpha radiative
transitions, are among the strongest discrete features in the X-ray band. These
are one of the most powerful probes to infer the properties of the plasma in
the innermost part of the accretion disk around a compact object. In this paper
we present a recent Suzaku observation, 100-ks effective exposure, of the atoll
source and X-ray burster 4U 1705-44, where we clearly detect signatures of a
reflection component which is distorted by the high-velocity motion in the
accretion disk. The reflection component consists of a broad iron line at about
6.4 keV and a Compton bump at high X-ray energies, around 20 keV. All these
features are consistently fitted with a reflection model, and we find that in
the hard state the smearing parameters are remarkably similar to those found in
a previous XMM-Newton observation performed in the soft state. In particular,
we find that the inner disk radius is Rin = 17 +/- 5 Rg (where Rg is the
Gravitational radius, GM/c^2), the emissivity dependence from the disk radius
is -2.5 +/- 0.5, the inclination angle with respect to the line of sight is i =
43 +/- 5 degrees, and the outer radius of the emitting region in the disk is
Rout > 200 Rg. We note that the accretion disk does not appear to be truncated
at large radii, although the source is in a hard state at about 3 % of the
Eddington luminosity for a neutron star. We also find evidence of a broad
emission line at low energies, at 3.03 +/- 0.03 keV, compatible with emission
from mildly ionized Argon (Ar XVI-XVII). Argon transitions are not included in
the self-consistent reflection models that we used and we therefore added an
extra component to our model to fit this feature. The low energy line appears
compatible with being smeared by the same inner disk parameters found for the
reflection component.",1502.07669v1
2015-02-26,The spin rate of pre-collapse stellar cores: wave-driven angular momentum transport in massive stars,"The core rotation rates of massive stars have a substantial impact on the
nature of core-collapse supernovae and their compact remnants. We demonstrate
that internal gravity waves (IGW), excited via envelope convection during a red
supergiant phase or during vigorous late time burning phases, can have a
significant impact on the rotation rate of the pre-SN core. In typical ($10 \,
M_\odot \lesssim M \lesssim 20 \, M_\odot$) supernova progenitors, IGW may
substantially spin down the core, leading to iron core rotation periods $P_{\rm
min,Fe} \gtrsim 30 \, {\rm s}$. Angular momentum (AM) conservation during the
supernova would entail minimum NS rotation periods of $P_{\rm min,NS} \gtrsim 3
\, {\rm ms}$. In most cases, the combined effects of magnetic torques and IGW
AM transport likely lead to substantially longer rotation periods. However, the
stochastic influx of AM delivered by IGW during shell burning phases inevitably
spin up a slowly rotating stellar core, leading to a maximum possible core
rotation period. We estimate maximum iron core rotation periods of $P_{\rm
max,Fe} \lesssim 5 \times 10^3 \, {\rm s}$ in typical core-collapse supernova
progenitors, and a corresponding spin period of $P_{\rm max, NS} \lesssim 500
\, {\rm ms}$ for newborn neutron stars. This is comparable to the typical birth
spin periods of most radio pulsars. Stochastic spin-up via IGW during shell
O/Si burning may thus determine the initial rotation rate of most neutron
stars. For a given progenitor, this theory predicts a Maxwellian distribution
in pre-collapse core rotation frequency that is uncorrelated with the spin of
the overlying envelope.",1502.07779v3
2015-03-09,"Gate-tuned Superconductor-Insulator transition in (Li,Fe)OHFeSe","The antiferromagnetic(AFM) insulator-superconductor transition has been
always a center of interest in the underlying physics of unconventional
superconductors. The quantum phase transition between Mott insulator with AFM
and superconductor can be induced by doping charge carriers in high-Tc cuprate
superconductors. For the best characterized organic superconductors of
k-(BEDT-TTF)2X (X=anion), a first order transition between AFM insulator and
superconductor can be tuned by applied external pressure or chemical pressure.
Also, the superconducting state can be directly developed from AFM insulator by
application of pressure in Cs3C60. The resemblance of these phase diagrams
hints a universal mechanism governing the unconventional superconductivity in
close proximity to AFM insulators. However, the superconductivity in iron-based
high-Tc superconductors evolves from an AFM bad metal by doping charge
carriers, and no superconductor-insulator transition has been observed so far.
Here, we report a first-order transition from superconductor to insulator with
a strong charge doping induced by ionic gating in the thin flakes of single
crystal (Li,Fe)OHFeSe. The Tc is continuously enhanced with electron doping by
ionic gating up to a maximum Tc of 43 K, and a striking
superconductor-insulator transition occurs just at the verge of optimal doping
with highest Tc. A novel phase diagram of temperature-gating voltage with the
superconductor-insulator transition is mapped out, indicating that the
superconductor -insulator transition is a common feature for unconventional
superconductivity. These results help to uncover the underlying physics of
iron-based superconductivity as well as the universal mechanism of high-Tc
superconductivity. Our finding also suggests that the gate-controlled strong
charge doping makes it possible to explore novel states of matter in a way
beyond traditional methods.",1503.02457v1
2015-03-12,On the alpha-element gradients of the Galactic thin disk using Cepheids,"We present new homogeneous measurements of Na, Al and three alpha-elements
(Mg, Si, Ca) for 75 Galactic Cepheids. The abundances are based on high
spectral resolution (R ~ 38,000) and high signal-to-noise ratio (S/N ~ 50-300)
spectra collected with UVES at ESO VLT. The current measurements were
complemented with Cepheid abundances either provided by our group (75) or
available in the literature, for a total of 439 Galactic Cepheids. Special
attention was given in providing a homogeneous abundance scale for these five
elements plus iron (Genovali et al. 2013, 2014). In addition, accurate
Galactocentric distances (RG) based on near-infrared photometry are also
available for all the Cepheids in the sample (Genovali et al. 2014). They cover
a large fraction of the Galactic thin disk (4.1 <= RG <= 18.4 kpc). We found
that the above five elements display well defined linear radial gradients and
modest standard deviations over the entire range of RG. Moreover, the
[element/Fe] abundance ratios are constant across the entire thin disk; only
the Ca radial distribution shows marginal evidence of a positive slope. These
results indicate that the chemical enrichment history of iron and of the quoted
five elements has been quite similar across the four quadrants of the Galactic
thin disk. The [element/Fe] ratios are also constant over the entire period
range. This empirical evidence indicates that the chemical enrichment of
Galactic Cepheids has also been very homogenous during the range in age that
they cover (~10-300 Myr). Once again, [Ca/Fe] vs. log(P) shows a (negative)
gradient, being underabundant among youngest Cepheids. Finally, we also found
that Cepheid abundances agree quite well with similar abundances for thin and
thick disk dwarf stars and they follow the typical Mg-Al and Na-O correlations.",1503.03758v1
2015-03-30,Electrochemical synthesis of highly ordered nanowires with a rectangular cross-section using an in-plane nanochannel array,"Rapid and reproducible assembly of aligned nanostructures on a wafer-scale is
a crucial, yet one of the most challenging tasks in the incorporation of
nanowires into integrated circuits. We present the synthesis of a periodic
nanochannel template designed for electrochemical growth of perfectly aligned,
rectangular nanowires over large areas. The nanowires can be electrically
contacted and characterized in situ using a pre-patterned multi-point
measurement platform. During the measurement the wires remain within a thick
oxide matrix providing protection against breaking and oxidation. We use laser
interference lithography, reactive ion etching and atomic layer deposition to
create cm-long parallel nanochannels with characteristic dimensions as small as
40 nm. In a showcase study pulsed electrodeposition of iron is carried out
creating rectangular shaped iron nanowires within the nanochannels. By design
of the device, the grown wires are in contact with an integrated electrode
system on both ends directly after the deposition. No further processing steps
are required for electrical characterization, minimizing the risk of damage and
oxidation. The developed nanowire measurement device allows for multi-probe
resistance measurements and can easily be adopted for transistor applications.
The guided, in-plane growth of electrodeposited nanowire arrays which are
tunable in size and density paves the way for the incorporation of nanowires
into a large variety of multifunctional devices.",1503.08597v1
2015-04-17,Electronic Structure and Superconductivity of FeSe-Related Superconductors,"The FeSe superconductor and its related systems have attracted much attention
in the iron-based superconductors owing to their simple crystal structure and
peculiar electronic and physical properties. The bulk FeSe superconductor has a
superconducting transition temperature (Tc) of ~8 K; it can be dramatically
enhanced to 37 K at high pressure. On the other hand, its cousin system, FeTe,
possesses a unique antiferromagnetic ground state but is non-superconducting.
Substitution of Se by Te in the FeSe superconductor results in an enhancement
of Tc up to 14.5 K and superconductivity can persist over a large composition
range in the Fe(Se,Te) system. Intercalation of the FeSe superconductor leads
to the discovery of the AxFe2-ySe2 (A=K, Cs and Tl) system that exhibits a Tc
higher than 30 K and a unique electronic structure of the superconducting
phase. The latest report of possible high temperature superconductivity in the
single-layer FeSe/SrTiO3 films with a Tc above 65 K has generated much
excitement in the community. This pioneering work opens a door for interface
superconductivity to explore for high Tc superconductors. The distinct
electronic structure and superconducting gap, layer-dependent behavior and
insulator-superconductor transition of the FeSe/SrTiO3 films provide critical
information in understanding the superconductivity mechanism of the iron-based
superconductors. In this paper, we present a brief review on the investigation
of the electronic structure and superconductivity of the FeSe superconductor
and related systems, with a particular focus on the FeSe films.",1504.04436v2
2015-05-20,Constraints on explosive silicon burning in core-collapse supernovae from measured Ni/Fe ratios,"Measurements of explosive nucleosynthesis yields in core-collapse supernovae
provide tests for explosion models. We investigate constraints on explosive
conditions derivable from measured amounts of nickel and iron after radioactive
decays using nucleosynthesis networks with parameterized thermodynamic
trajectories. The Ni/Fe ratio is for most regimes dominated by the production
ratio of 58Ni/(54Fe + 56Ni), which tends to grow with higher neutron excess and
with higher entropy. For SN 2012ec, a supernova that produced a Ni/Fe ratio of
$3.4\pm1.2$ times solar, we find that burning of a fuel with neutron excess
$\eta \approx 6\times 10^{-3}$ is required. Unless the progenitor metallicity
is over 5 times solar, the only layer in the progenitor with such a neutron
excess is the silicon shell. Supernovae producing large amounts of stable
nickel thus suggest that this deep-lying layer can be, at least partially,
ejected in the explosion. We find that common spherically symmetric models of
$M_{\rm ZAMS} \lesssim 13$ Msun stars exploding with a delay time of less than
one second ($M_{\rm cut} < 1.5$ Msun) are able to achieve such silicon-shell
ejection. Supernovae that produce solar or sub-solar Ni/Fe ratios, such as SN
1987A, must instead have burnt and ejected only oxygen-shell material, which
allows a lower limit to the mass cut to be set. Finally, we find that the
extreme Ni/Fe value of 60-75 times solar derived for the Crab cannot be
reproduced by any realistic-entropy burning outside the iron core, and
neutrino-neutronization obtained in electron-capture models remains the only
viable explanation.",1505.05323v1
2015-05-25,The Carina Project. VIII. The α-element abundances,"We have performed a new abundance analysis of Carina Red Giant (RG) stars
from spectroscopic data collected with UVES (high resolution) and
FLAMES/GIRAFFE (high and medium resolution) at ESO/VLT. The former sample
includes 44 RGs, while the latter consists of 65 (high) and ~800 (medium
resolution) RGs, covering a significant fraction of the galaxy's RG branch
(RGB), and red clump stars. To improve the abundance analysis at the faint
magnitude limit, the FLAMES/GIRAFFE data were divided into ten surface gravity
and effective temperature bins. The spectra of the stars belonging to the same
gravity/temperature bin were stacked. This approach allowed us to increase by
at least a factor of five the signal-to-noise ratio in the faint limit
(V>20.5mag). We took advantage of the new photometry index cU,B,I introduced by
Monelli et al. (2014), as an age and probably a metallicity indicator, to split
stars along the RGB. These two stellar populations display distinct [Fe/H] and
[Mg/H] distributions: their mean Fe abundances are -2.15$\pm$0.06dex
(sig=0.28), and -1.75$\pm$0.03dex (sig=0.21), respectively. The two iron
distributions differ at the 75% level. This supports preliminary results by
Lemasle et al. (2012) and by Monelli et al. (2014). Moreover, we found that the
old and intermediate-age stellar populations have mean [Mg/H] abundances of
-1.91$\pm$0.05dex (sig=0.22) and -1.35$\pm$0.03dex (sig=0.22); these differ at
the 83% level. Carina's {\alpha}-element abundances agree, within 1sigma, with
similar abundances for field Halo stars and for cluster (Galactic, Magellanic)
stars. The same outcome applies to nearby dwarf spheroidals and ultra-faint
dwarf galaxies, in the iron range covered by Carina stars. Finally, we found
evidence of a clear correlation between Na and O abundances, thus suggesting
that Carina's chemical enrichment history is quite different than in the
globular clusters.",1505.06597v2
2015-05-25,Twin peak HF QPOs as a spectral imprint of dual oscillation modes of accretion tori,"High frequency (millisecond) quasi-periodic oscillations (HF QPOs) are
observed in the X-ray power-density spectra of several microquasars and low
mass X-ray binaries. Two distinct QPO peaks, so-called twin peak QPOs, are
often detected simultaneously exhibiting their frequency ratio close or equal
to 3/2. Following the analytic theory and previous studies of observable
spectral signatures, we aim to model the twin peak QPOs as a spectral imprint
of specific dual oscillation regime defined by a combination of the lowest
radial and vertical oscillation mode of optically thick slender tori with
constant specific angular momentum. We examined power spectra and fluorescent
K$\alpha$ iron line profiles for two different simulation setups with the mode
frequency relations corresponding to the epicyclic resonance HF QPOs model and
modified relativistic precession QPOs model. We use relativistic ray-tracing
implemented in parallel simulation code LSDplus. In the background of the Kerr
spacetime geometry, we analyze the influence of the distant observer
inclination and the spin of the central compact object. Relativistic optical
projection of the oscillating slender torus is illustrated by images in false
colours related to the frequency shift. We show that performed simulations
yield power spectra with the pair of dominant peaks corresponding to the
frequencies of radial and vertical oscillation modes with the proper ratio
equal to 3/2 on a wide range of inclinations and spin values. We also discuss
exceptional cases of a very small and very high inclination as well as unstable
high spin relativistic precession-like configuration predicting constant
frequency ratio equal to 1/2. We demonstrate signifiant dependency of broadened
K$\alpha$ iron line profiles on the inclination of the distant observer.",1505.06673v1
2015-06-04,Systematic NLTE study of the -2.6 < [Fe/H] < 0.2 F and G dwarfs in the solar neighbourhood. I. Stellar atmosphere parameters,"We present atmospheric parameters for 51 nearby FG dwarfs uniformly
distributed over the -2.60 < [Fe/H] < +0.20 metallicity range that is suitable
for the Galactic chemical evolution research. Lines of iron, Fe I and Fe II,
were used to derive a homogeneous set of effective temperatures, surface
gravities, iron abundances, and microturbulence velocities. We used
high-resolution (R>60000) Shane/Hamilton and CFHT/ESPaDOnS observed spectra and
non-local thermodynamic equilibrium (NLTE) line formation for Fe I and Fe II in
the classical 1D model atmospheres. The spectroscopic method was tested with
the 20 benchmark stars, for which there are multiple measurements of the
infrared flux method (IRFM) Teff and their Hipparcos parallax error is < 10%.
We found NLTE abundances from lines of Fe I and Fe II to be consistent within
0.06 dex for every benchmark star, when applying a scaling factor of S_H = 0.5
to the Drawinian rates of inelastic Fe+H collisions. The obtained atmospheric
parameters were checked for each program star by comparing its position in the
log g-Teff plane with the theoretical evolutionary track in the Yi et al.
(2004) grid. Our final effective temperatures lie in between the T_IRFM scales
of Alonso et al. (1996) and Casagrande et al. (2011), with a mean difference of
+46 K and -51 K, respectively. NLTE leads to higher surface gravity compared
with that for LTE. The shift in log g is smaller than 0.1 dex for stars with
either [Fe/H] > -0.75, or Teff < 5750 K, or log g > 4.20. NLTE analysis is
crucial for the VMP turn-off and subgiant stars, for which the shift in log g
between NLTE and LTE can be up to 0.5 dex. The obtained atmospheric parameters
will be used in the forthcoming papers to determine NLTE abundances of
important astrophysical elements from lithium to europium and to improve
observational constraints on the chemo-dynamical models of the Galaxy
evolution.",1506.01621v1
2015-07-02,A Spectroscopic Analysis of the Galactic Globular Cluster NGC 6273 (M19),"A combined effort utilizing spectroscopy and photometry has revealed the
existence of a new globular cluster class. These ""anomalous"" clusters, which we
refer to as ""iron-complex"" clusters, are differentiated from normal clusters by
exhibiting large (>0.10 dex) intrinsic metallicity dispersions, complex
sub-giant branches, and correlated [Fe/H] and s-process enhancements. In order
to further investigate this phenomenon, we have measured radial velocities and
chemical abundances for red giant branch stars in the massive, but scarcely
studied, globular cluster NGC 6273. The velocities and abundances were
determined using high resolution (R~27,000) spectra obtained with the
Michigan/Magellan Fiber System (M2FS) and MSpec spectrograph on the
Magellan-Clay 6.5m telescope at Las Campanas Observatory. We find that NGC 6273
has an average heliocentric radial velocity of +144.49 km s^-1 (sigma=9.64 km
s^-1) and an extended metallicity distribution ([Fe/H]=-1.80 to -1.30) composed
of at least two distinct stellar populations. Although the two dominant
populations have similar [Na/Fe], [Al/Fe], and [alpha/Fe] abundance patterns,
the more metal-rich stars exhibit significant [La/Fe] enhancements. The [La/Eu]
data indicate that the increase in [La/Fe] is due to almost pure s-process
enrichment. A third more metal-rich population with low [X/Fe] ratios may also
be present. Therefore, NGC 6273 joins clusters such as omega centauri, M 2, M
22, and NGC 5286 as a new class of iron-complex clusters exhibiting complicated
star formation histories.",1507.00756v1
2015-08-07,"Spectrophotometry of asteroids 32 Pomona, 145 Adeona, 704 Interamnia, 779 Nina, 330825, and 2012 QG42 and laboratory study of possible analog samples","Six asteroids including two NEAs, one of which is PHA, accessible for
observation in September 2012 were investigated using a low-resolution
spectrophotometry in the range 0.35-0.90 um with the aim to study features of
their reflectance spectra. For the first time we discovered likely spectral
signs (as a maximum at 0.4-0.6 um in reflectance spectra) of simultaneous
sublimation activity and presence of a temporal coma on three primitive-type
main-belt asteroids, Adeona, Interamnia, and Nina, being at perihelion
distances or approaching to it. We suggest that such a cometary-like activity
may be a common phenomenon at the highest subsolar surface temperatures for C
and close type asteroids including considerable amounts of H2O and CO2 ices
beneath the surface. However, excavation of fresh ice at recent impact event(s)
could be an alternative explanation of the phenomenon. Similar absorption bands
centered at 0.38, 0.44 and 0.67-0.71 um registered in the reflectance spectra
of Adeona, Interamnia, and Nina clearly point to predominantly silicate surface
matter. To specify its content, we performed laboratory investigations of
ground samples of known carbonaceous chondrites (Orguel, Mighei, Murchison, and
Boriskino) and seven samples of low-iron Mg serpentines as possible analogs of
the asteroids. In particular, we found that the equivalent width of the band
centered at 0.44 um in reflectance spectra of the low-Fe serpentine samples has
a high correlation with content of Fe3+ (octahedral and tetrahedral). It means
that the absorption feature can be used as an indicator of ferric iron in
oxidized and hydrated low-Fe silicate compounds on asteroids (abridged).",1508.01690v1
2015-09-08,Identifying the best iron-peak and $α$-capture elements for chemical tagging: The impact of the number of lines on measured scatter,"The main goal of this work is to explore which elements carry the most
information about the birth origin of stars and as such that are best suited
for chemical tagging. We explored different techniques to minimize the effect
of outlier value lines in the abundances by using Ni abundances derived for
1111 FGK type stars.We evaluated how the limited number of spectral lines can
affect the final chemical abundance. Then we were able to make an efficient
even footing comparison of the [X/Fe] scatter between the elements that have
different number of observable spectral lines in the studied spectra. We found
that the most efficient way of calculating the average abundance of elements
when several spectral lines are available is to use a weighted mean (WM) where
as a weight we considered the distance from the median abundance. This method
can be effectively used without removing suspected outlier lines.We showed that
when the same number of lines is used to determine chemical abundances, the
[X/Fe] star-to-star scatter for iron group and $\alpha$-capture elements is
almost the same. On top of this, but at a lower level the largest scatter was
observed for Al and the smallest for Cr and Ni. We recommend caution when
comparing [X/Fe] scatters among elements that have a different number of
spectral lines available. A meaningful comparison is necessary to identify
elements that show the largest intrinsic scatter and can be thus used for
chemical tagging.",1509.02419v1
2015-09-08,Metallicity of Ca2Cu6P5 with Single and Double Copper-Pnictide Layers,"We report thermodynamic and transport properties, and also theoretical
calculations, for Cu-based compound Ca2Cu6P5 and compare with CaCu(2-x)P2. Both
materials have layers of edge-sharing copper pnictide tetrahedral CuP4, similar
to Fe-As and Fe-Se layers (with FeAs4, FeSe4) in the iron-based
superconductors. Despite the presence of this similar transition-metal pnictide
layer, we find that both Ca2Cu6P5 and CaCu(2-x)P2 have temperature-independent
magnetic susceptibility and show metallic behavior with no evidence of either
magnetic ordering or superconductivity down to 1.8 K. CaCu(2-x)P2 is slightly
off-stoichiometric, with delta = 0.14. Theoretical calculations suggest that
unlike Fe 3d-based magnetic materials with a large density of states (DOS) at
the Fermi surface, Cu have comparatively low DOS, with the majority of the 3d
spectral weight located well below Fermi level. The room-temperature
resistivity value of Ca2Cu6P5 is only 9 micro ohm-cm, due to a substantial
plasma frequency and an inferred electron-phonon coupling lambda of 0.073
(significantly smaller than that of metallic Cu). Also, microscopy result shows
that Cu-Cu distance along the c-axis within the double layers can be very short
(2.5 A), even shorter than metallic elemental copper bond (2.56 A). The value
of dp over dT for CaCu(2-x)P2 at 300 K is approximately three times larger than
in Ca2Cu6P5, which suggests the likelihood of stronger electron-phonon
coupling. This study shows that the details of Cu-P layers and bonding are
important for their transport characteristics. In addition, it emphasizes the
remarkable character of the DOS of '122' iron-based materials, despite much
structural similarities.",1509.02508v1
2015-09-14,Cool Core Clusters from Cosmological Simulations,"We present results obtained from a set of cosmological hydrodynamic
simulations of galaxy clusters, aimed at comparing predictions with
observational data on the diversity between cool-core (CC) and non-cool-core
(NCC) clusters. Our simulations include the effects of stellar and AGN feedback
and are based on an improved version of the smoothed particle hydrodynamics
code GADGET-3, which ameliorates gas mixing and better captures gas-dynamical
instabilities by including a suitable artificial thermal diffusion. In this
Letter, we focus our analysis on the entropy profiles, the primary diagnostic
we used to classify the degree of cool-coreness of clusters, and on the iron
profiles. In keeping with observations, our simulated clusters display a
variety of behaviors in entropy profiles: they range from steadily decreasing
profiles at small radii, characteristic of cool-core systems, to nearly flat
core isentropic profiles, characteristic of non-cool-core systems. Using
observational criteria to distinguish between the two classes of objects, we
find that they occur in similar proportions in both simulations and in
observations. Furthermore, we also find that simulated cool-core clusters have
profiles of iron abundance that are steeper than those of NCC clusters, which
is also in agreement with observational results. We show that the capability of
our simulations to generate a realistic cool-core structure in the cluster
population is due to AGN feedback and artificial thermal diffusion: their
combined action allows us to naturally distribute the energy extracted from
super-massive black holes and to compensate for the radiative losses of
low-entropy gas with short cooling time residing in the cluster core.",1509.04247v2
2015-09-29,Enrichment of r-process elements in dwarf spheroidal galaxies in chemo-dynamical evolution model,"The rapid neutron-capture process (r-process) is a major process to
synthesize elements heavier than iron, but the astrophysical site(s) of
r-process is not identified yet. Neutron star mergers (NSMs) are suggested to
be a major r-process site from nucleosynthesis studies. Previous chemical
evolution studies however require unlikely short merger time of NSMs to
reproduce the observed large star-to-star scatters in the abundance ratios of
r-process elements relative to iron, [Eu/Fe], of extremely metal-poor stars in
the Milky Way (MW) halo. This problem can be solved by considering chemical
evolution in dwarf spheroidal galaxies (dSphs) which would be building blocks
of the MW and have lower star formation efficiencies than the MW halo. We
demonstrate that enrichment of r-process elements in dSphs by NSMs using an
N-body/smoothed particle hydrodynamics code. Our high-resolution model
reproduces the observed [Eu/Fe] by NSMs with a merger time of 100 Myr when the
effect of metal mixing is taken into account. This is because metallicity is
not correlated with time up to ~ 300 Myr from the start of the simulation due
to low star formation efficiency in dSphs. We also confirm that this model is
consistent with observed properties of dSphs such as radial profiles and
metallicity distribution. The merger time and the Galactic rate of NSMs are
suggested to be <~ 300 Myr and ~ $10^{-4}$ yr$^{-1}$, which are consistent with
the values suggested by population synthesis and nucleosynthesis studies. This
study supports that NSMs are the major astrophysical site of r-process.",1509.08934v1
2015-10-07,Nanoanalytical TEM studies and micromagnetic modelling of Nd-Fe-B magnets,"We have analysed the influence of the microstructural features, such as
intergranular grain boundary (GB) phases and misalignment of the hard magnetic
grains, on the optimization of magnetization reversal processes in order to
improve the coercive field of Nd-Fe-B magnets. The microstructural model of the
grains and intergranular phases, which is used for theoretical simulations, has
been derived from a detailed nanoanalytical TEM/STEM study of a Dy/Tb free
magnet and a high coercive (Nd,Tb)-Fe-B magnet. Special attention is laid on
the EELS analysis of GB with a thickness ranging from 2 - 30 nm. This analysis
identified the majority of the GB phases to have about 50 -70 at.% of iron and
only a few GBs, which are connecting two nearby grain boundary junctions (GBj),
possess a similar chemical composition as the adjacent GBj with a low iron
content (< 10 at. %) and a high rare earth and oxygen content. Finite element
micromagnetic simulations have been carried out in order to study the influence
of internal demagnetizing fields determined by the microstructure on the
magnetization switching behaviour. Special emphasis was put on the influence of
the GB and their magnetic properties, due to their substantial influence on the
nucleation of reverse magnetic domains and the pinning of domain walls. The
strongest reduction of the coercive field is caused by GB with soft
ferromagnetic properties. Shielding the Nd-Fe-B grains from the nucleation
sites at the GBj with Dy or Tb shells, leads to an increase of the coercivity
from 2.5 to 3.6 T and 2.5 to 4.3 T, respectively.",1510.01958v2
2015-10-23,GIANO-TNG spectroscopy of red supergiants in the young star cluster RSGC3,"The Scutum complex in the inner disk of the Galaxy has a number of young star
clusters dominated by red supergiants that are heavily obscured by dust
extinction and observable only at infrared wavelengths. These clusters are
important tracers of the recent star formation and chemical enrichment history
in the inner Galaxy. During the technical commissioning and as a first science
verification of the GIANO spectrograph at the Telescopio Nazionale Galileo, we
secured high-resolution (R=50,000) near-infrared spectra of five red
supergiants in the young Scutum cluster RSGC3. Taking advantage of the full
YJHK spectral coverage of GIANO in a single exposure, we were able to measure
several tens of atomic and molecular lines that were suitable for determining
chemical abundances. By means of spectral synthesis and line equivalent width
measurements, we obtained abundances of Fe and iron-peak elements such as Ni,
Cr, and Cu, alpha (O, Mg, Si, Ca, Ti), other light elements (C, N, F, Na, Al,
and Sc), and some s-process elements (Y, Sr). We found average half-solar iron
abundances and solar-scaled [X/Fe] abundance patterns for most of the elements,
consistent with a thin-disk chemistry. We found depletion of [C/Fe] and
enhancement of [N/Fe], consistent with standard CN burning, and low 12C/13C
abundance ratios (between 9 and 11), which require extra-mixing processes in
the stellar interiors during the post-main sequence evolution. We also found
local standard of rest V(LSR)=106 km/s and heliocentric V(HEL)=90 km/s radial
velocities with a dispersion of 2.3 km/s. The inferred radial velocities,
abundances, and abundance patterns of RSGC3 are very similar to those
previously measured in the other two young clusters of the Scutum complex,
RSGC1 and RSGC2, suggesting a common kinematics and chemistry within the Scutum
complex.",1510.06870v1
2015-10-27,Subaru/HDS study of CH stars: elemental abundances for stellar neutron-capture process studies,"A comprehensive abundance analysis providing rare insight into the chemical
history of lead stars is still lacking. We present results from high resolution
(R ~ 50000), spectral analyses of three CH stars, HD 26, HD 198269, HD 224959,
and, a carbon star with a dusty envelope, HD 100764. Previous studies on these
objects are limited by both resolution and wavelength regions and the results
differ significantly from each other. We have undertaken to re-analyse the
chemical composition of these objects based on high resolution Subaru spectra
covering the wavelength regions 4020 to 6775 A,. Considering local
thermodynamic equilibrium and using model atmospheres, we have derived the
stellar parameters, the effective temperatures Teff, surface gravities log g,
and metallicities [Fe/H] for these objects. The derived parameters for HD 26,
HD 100764, HD 198269 and HD 224959 are (5000, 1.6, -1.13), (4750, 2.0 -0.86),
(4500, 1.5, -2.06) and (5050, 2.1, -2.44) respectively. The stars are found to
exhibit large enhancements of heavy elements relative to iron in conformity to
previous studies. Large enhancement of Pb with respect to iron is also
confirmed. Updates on the elemental abundances for several s-process elements
(Y, Zr, La, Ce, Nd, Sm, Pb) along with the first-time estimates of abundances
for a number of other heavy elements (Sr, Ba, Pr, Eu, Er, W) are reported. Our
analysis suggests that neutron-capture elements in HD 26 primarily originate in
s-process while the major contributions to the abundances of neutron-capture
elements in the more metal-poor objects HD 224959 and HD 198269 are from
r-process, possibly formed from materials that are pre-enriched with products
of r-process.",1510.07814v1
2015-11-11,Polarization of Magnetic Dipole Emission and Spinning Dust Emission from Magnetic Nanoparticles,"Magnetic dipole emission (MDE) from interstellar magnetic nanoparticles is an
important Galactic foreground in the microwave frequencies, and its
polarization level may pose great challenges for achieving reliable
measurements of cosmic microwave background (CMB) B-mode signal. To obtain
theoretical constraints on the polarization of MDE, we first compute the degree
of alignment of big silicate grains incorporated with magnetic inclusions. We
find that, in realistic conditions of the interstellar medium, thermally
rotating big grains with magnetic inclusions are weakly aligned and achieve
{\it alignment saturation} when the magnetic alignment rate becomes much faster
than the rotational damping rate. We then compute the degree of alignment for
free-flying magnetic nanoparticles, taking into account various interaction
processes of grains with the ambient gas and radiation field, including neutral
collisions, ion collisions, and infrared emission. We find that the rotational
damping by infrared emission can significantly decrease the degree of alignment
of small particles from the saturation level, whereas the excitation by ion
collisions can enhance the alignment of ultrasmall particles. Using the
computed degrees of alignment, we predict the polarization level of MDE from
free-flying magnetic nanoparticles to be rather low. Such a polarization level
is within the upper limits measured for anomalous microwave emission (AME),
which indicates that MDE from free-flying iron particles may not be ruled out
as a source of AME. We also quantify spinning dust emission from free-flying
iron nanoparticles with permanent magnetic moments and find that its emissivity
is one order of magnitude lower than that from spinning polycyclic aromatic
hydrocarbons (PAHs). Finally, we compute the polarization spectra of spinning
dust emission from PAHs for the different interstellar magnetic fields.",1511.03691v1
2015-12-25,Thermal evolution of antiferromagnetic correlations and tetrahedral bond angles in superconducting FeTe$_{1-x}$Se$_x$,"It has recently been demonstrated that dynamical magnetic correlations
measured by neutron scattering in iron chalcogenides can be described with
models of short-range correlations characterized by particular {choices of
four-spin plaquettes, where the appropriate choice changes as the} parent
material is doped towards superconductivity. Here we apply such models to
describe measured maps of magnetic scattering as a function of two-dimensional
wave vectors obtained for optimally superconducting crystals of
FeTe$_{1-x}$Se$_x$. We show that the characteristic antiferromagnetic wave
vector evolves from that of the bicollinear structure found in underdoped
chalcogenides (at high temperature) to that associated with the stripe
structure of antiferromagnetic iron arsenides (at low temperature); {these can
both be described with the same local plaquette, but with different
inter-plaquette correlations}. While the magnitude of the low-energy magnetic
spectral weight is substantial at all temperatures, it actually weakens
somewhat at low temperature, where the charge carriers become more itinerant.
The observed change in spin correlations is correlated with the dramatic drop
in the electronic scattering rate and the growth of the bulk nematic response
on cooling. Finally, we also present powder neutron diffraction results for
lattice parameters in FeTe$_{1-x}$Se$_x$ indicating that the tetrahedral bond
angle tends to increase towards the ideal value on cooling, in agreement with
the increased screening of the crystal field by more itinerant electrons and
the correspondingly smaller splitting of the Fe $3d$ orbitals.",1512.08036v2
2015-12-26,CALET: a high energy astroparticle physics experiment on the ISS,"CALET (CALorimetric Electron Telescope) is a high energy astroparticle
physics experiment planned for a long exposure mission aboard the International
Space Station (ISS) by the Japanese Aerospace Exploration Agency, in
collaboration with the Italian Space Agency (ASI) and NASA. The main science
goal is high precision measurements of the inclusive electron (+positron)
spectrum below 1 TeV and the exploration of the energy region above 1 TeV,
where the shape of the high end of the spectrum might unveil the presence of
nearby sources of acceleration. CALET has been designed to achieve a large
proton rejection capability (>10$^5$) with a fine grained imaging calorimeter
(IMC) followed by a total absorption calorimeter (TASC), for a total thickness
of 30 X$_{0}$ and 1.3 proton interaction length. With an excellent energy
resolution and a lower background contamination with respect to previous
experiments, CALET will search for possible spectral signatures of dark matter
with both electrons and gamma rays. CALET will also measure the high energy
spectra and relative abundance of cosmic nuclei from proton to iron and detect
trans-iron elements up to Z$\sim$40. The charge identification of individual
nuclear species is performed by a dedicated module (CHD) and by multiple dE/dx
measurements in the IMC. With a large exposure and high energy resolution,
CALET will be able to verify and complement the observations of CREAM, PAMELA
and AMS-02 on a possible deviation from a pure power-law of proton and He
spectra in the few hundred GeV region and to extend the study to the multi-TeV
region. CALET will also contribute to clarify the present experimental picture
on the energy dependence of the boron/carbon ratio, below and above 1 TeV/n,
thereby providing valuable information on cosmic-ray propagation in the galaxy.
Gamma-ray transients will be studied with a dedicated Gamma-ray Burst Monitor
(GBM).",1512.08059v1
2016-01-17,COSMIC-LAB: Unexpected Results from High-resolution Spectra of AGB Stars in Globular Clusters,"This thesis is aimed at clarifying one of the least studied phases of stellar
evolution: the asymptotic giant branch (AGB). Recent results obtained for
Galactic globular clusters (GCs) suggest that the AGB stage may contain crucial
information about the evolutionary history of exotic stars (Beccari et al.
2006) and multiple-populations (Campbell et al. 2013) in the parent cluster.
The thesis presents the analysis of a large sample of high-resolution spectra
of AGB stars in four Galactic GCs, acquired at the Very Large Telescope (ESO)
and the 2.2 meter telescope (MPG). The obtained results provide evidence of a
previously unknown physical mechanism affecting the neutral species of some
chemical elements in the atmosphere of most AGB stars: because of it, the
abundances derived from neutral lines are systematically underestimated, while
those measured from ionized lines remain unaffected. Such a behaviour exactly
corresponds to what expected in the case of non-local thermodynamic equilibrium
(NLTE) conditions in the star atmosphere. For this reason, in this work we
refer to it as ""NLTE effect"", with the caveat that this could be not the case.
In fact, the current NLTE models are unable to account for the observed effect,
thus demonstrating that either our comprehension of NLTE is not adequate
enough, or that some more complex physical phenomena are occurring in AGB
atmospheres. This effect has been found in all the investigated GCs. It affects
most (but not all) AGB stars and, in some cases, also some RGB stars. It is
particularly evident for iron and titanium lines (i.e., the elements providing
the largest number of both neutral and ionized lines). The deep understanding
of the detected phenomenon is of paramount importance since it has a huge
impact on the proper determination of GC chemistry and enrichment history (for
instance, it can mimic spurious iron spreads).",1601.04346v1
2016-01-21,High resolution spectroscopic analysis of seven giants in the bulge globular cluster NGC 6723,"Globular clusters associated with the Galactic bulge are important tracers of
stellar populations in the inner Galaxy. High resolution analysis of stars in
these clusters allows us to characterize them in terms of kinematics,
metallicity, and individual abundances, and to compare these fingerprints with
those characterizing field populations. We present iron and element ratios for
seven red giant stars in the globular cluster NGC~6723, based on high
resolution spectroscopy. High resolution spectra ($R\sim48~000$) of seven K
giants belonging to NGC 6723 were obtained with the FEROS spectrograph at the
MPG/ESO 2.2m telescope. Photospheric parameters were derived from $\sim130$ FeI
and FeII transitions. Abundance ratios were obtained from line-to-line spectrum
synthesis calculations on clean selected features. An intermediate metallicity
of [Fe/H]$=-0.98\pm0.08$ dex and a heliocentric radial velocity of
$v_{hel}=-96.6\pm1.3~km s^{-1}$ were found for NGC 6723. Alpha-element
abundances present enhancements of $[O/Fe]=0.29\pm0.18$ dex,
$[Mg/Fe]=0.23\pm0.10$ dex, $[Si/Fe]=0.36\pm0.05$ dex, and $[Ca/Fe]=0.30\pm0.07$
dex. Similar overabundance is found for the iron-peak Ti with
$[Ti/Fe]=0.24\pm0.09$ dex. Odd-Z elements Na and Al present abundances of
$[Na/Fe]=0.00\pm0.21$ dex and $[Al/Fe]=0.31\pm0.21$ dex, respectively. Finally,
the s-element Ba is also enhanced by $[Ba/Fe]=0.22\pm0.21$ dex. The enhancement
levels of NGC 6723 are comparable to those of other metal-intermediate bulge
globular clusters. In turn, these enhancement levels are compatible with the
abundance profiles displayed by bulge field stars at that metallicity. This
hints at a possible similar chemical evolution with globular clusters and the
metal-poor of the bulge going through an early prompt chemical enrichment.",1601.05736v1
2016-02-02,The initial abundance and distribution of 92Nb in the Solar System,"Niobium-92 is an extinct proton-rich nuclide, which decays to 92Zr with a
half-life of 37 Ma. This radionuclide potentially offers a unique opportunity
to determine the timescales of early Solar System processes and the site(s) of
nucleosynthesis for p-nuclei, once its initial abundance and distribution in
the Solar System are well established. Here we present internal Nb-Zr isochrons
for three basaltic achondrites with known U-Pb ages: the angrite NWA 4590, the
eucrite Agoult, and the ungrouped achondrite Ibitira. Our results show that the
relative Nb-Zr isochron ages of the three meteorites are consistent with the
time intervals obtained from the Pb-Pb chronometer for pyroxene and
plagioclase, indicating that 92Nb was homogeneously distributed among their
source regions. The Nb-Zr and Pb-Pb data for NWA 4590 yield the most reliable
and precise reference point for anchoring the Nb-Zr chronometer to the absolute
timescale: an initial 92Nb/93Nb ratio of $(1.4 \pm 0.5) \times 10^{-5}$ at
$4557.93 \pm 0.36$ Ma, which corresponds to a 92Nb/93Nb ratio of $(1.7 \pm 0.6)
\times 10^{-5}$ at the time of the Solar System formation. On the basis of this
new initial ratio, we demonstrate the capability of the Nb-Zr chronometer to
date early Solar System objects including troilite and rutile, such as iron and
stony-iron meteorites. Furthermore, we estimate a nucleosynthetic production
ratio of 92Nb to the p-nucleus 92Mo between 0.0015 and 0.035. This production
ratio, together with the solar abundances of other p-nuclei with similar
masses, can be best explained if these light p-nuclei were primarily
synthesized by photodisintegration reactions in Type Ia supernovae.",1602.00966v1
2016-03-02,Optimal Auctions for Negatively Correlated Items,"We consider the problem of designing revenue-optimal auctions for selling two
items and bidders' valuations are independent among bidders but negatively
correlated among items.
  In this paper, we obtain the closed-form optimal auction for this setting, by
directly addressing the two difficulties above. In particular, the first
difficulty is that when pointwise maximizing virtual surplus under
multi-dimensional feasibility (i.e., the Border feasibility), (1) neither the
optimal interim allocation is trivially monotone in the virtual value, (2) nor
the virtual value is monotone in the bidder's type. As a result, the optimal
interim allocations resulting from virtual surplus maximization no longer
guarantees BIC. To address (1), we prove a generalization of Border's theorem
and show that optimal interim allocation is indeed monotone in the virtual
value. To address (2), we adapt Myerson's ironing procedure to this setting by
redefining the (ironed) virtual value as a function of the lowest utility
point. The second difficulty, perhaps a more challenging one, is that the
lowest utility type in general is no longer at the endpoints of the type
interval. To address this difficulty, we show by construction that there exist
an allocation rule and an induced lowest utility type such that they form a
solution of the virtual surplus maximization and in the meanwhile guarantees
IIR. In the single bidder case, the optimal auction consists of a randomized
bundle menu and a deterministic bundle menu; while in the multiple bidder case,
the optimal auction is a randomization between two extreme mechanisms. The
optimal solutions of our setting can be implemented by a Bayesian IC and IR
auction, however, perhaps surprisingly, the revenue of this auction cannot be
achieved by any (dominant-strategy) IC and IR auction.",1603.00562v3
2016-03-04,The thermal instability of the warm absorber in NGC 3783,"We model the observed X-ray spectral continuum shape, ionic column densities,
and absorption measure distribution (AMD) of the warm absorber in the Seyfert
galaxy NGC 3783. We assume a photo-ionized medium with a uniform total
(gas+radiation) pressure. The irradiation causes the wind to be radiation
pressure compressed (RPC). We compare the observational characteristics derived
from the 900 ksec Chandra observation to radiative transfer computations in
pressure equilibrium using the radiative transfer code TITAN. We explore
different values of the ionization parameter xi of the incident flux and adjust
the hydrogen-equivalent column density, N_H0 of the warm absorber to match the
observed soft X-ray continuum. We derive theoretical column densities for a
broad range of ionic species of iron and neon and an AMD that we compare to the
observations. We find an extension of the degeneracy between xi and N_H0 for
the constant pressure models previously discussed for NGC 3783. Including the
ionic column densities of iron and neon in the comparison between observations
and data we conclude that a range of ionization parameters between 4000 and
8000 ergs cm/s is preferred. For the first time, we present theoretical AMD for
a constant pressure wind in NGC 3783 that correctly reproduces the observed
level and is in approximate agreement with the observational appearance of an
instability region. Using a variety of observational indicators, we confirm
that the X-ray outflow of NGC 3783 can be described as an RPC medium in
pressure equilibrium. The observed AMD agrees with a uniformly hot or a
uniformly cold thermal state. The measured ionic column densities suggest that
the wind tends to the uniformly cold thermal state. The occurrence of thermal
instability in the warm absorber model may depend on the computational method
and the spatial scale on which the radiative transfer is solved.",1603.01448v1
2016-03-11,Nonlinear and time-resolved optical study of the 112-type iron-based superconductor parent Ca$_{1-x}$La$_{x}$FeAs$_{2}$ across its structural phase transition,"The newly discovered 112-type ferropnictide superconductors contain chains of
As atoms that break the tetragonal symmetry between the $a$ and $b$ axes. This
feature eliminates the need for uniaxial strain that is usually required to
stabilize large single domains in the electronic nematic state that exists in
the vicinity of magnetic order in the iron-based superconductors. We report
detailed structural symmetry measurements of 112-type
Ca$_{0.73}$La$_{0.27}$FeAs$_{2}$ using rotational anisotropy optical second
harmonic generation. This technique is complementary to diffraction experiments
and enables a precise determination of the point group symmetry of a crystal.
By combining our measurements with density functional theory calculations, we
uncover a strong optical second harmonic response of bulk electric dipole
origin from the Fe and Ca $3d$-derived states that enables us to assign $C_2$
as the crystallographic point group. This makes the 112-type materials
high-temperature superconductors without a center of inversion, allowing for
the possible mixing of singlet and triplet Cooper pairs in the superconducting
state. We also perform pump-probe transient reflectivity experiments that
reveal a 4.6 THz phonon mode associated with the out-of-plane motion of As
atoms in the FeAs layers. We do not observe any suppression of the optical
second harmonic response or shift in the phonon frequency upon cooling through
the reported monoclinic-to-triclinic transition at 58 K. This allows us to
identify $C_1$ as the low-temperature crystallographic point group but suggests
that structural changes induced by long-range magnetic order are subtle and do
not significantly affect electronic states near the Fermi level.",1603.03785v1
2016-04-09,Reduced radiative conductivity of high and low spin FeO6 octahedra in the Earth's lower mantle,"The ability of Earths mantle to conduct heat by radiation is determined by
optical properties of mantle phases. Optical properties of mantle minerals at
high pressure are accessible through diamond anvil cell experiments, but
because of the extensive thermal radiation at T above 1000 K such studies are
limited to lower temperatures. Particularly uncertain is the
temperature-dependence of optical properties of lower mantle minerals across
the spin transition as the spin state itself is a strong function of
temperature. Here we use laser-heated DACs combined with a pulsed bright
supercontinuum laser probe and a synchronized time-gated detector to examine
optical properties of high and low spin ferrous iron at 45-73 GPa and to 1600 K
in FeO6, one of the most abundant building blocks in the mantle. Siderite
(FeCO3) is used as a model for FeO6-octahedra as it contains no ferric iron and
exhibits a sharp optically apparent spin transition at 44 GPa, simplifying data
interpretation. We find that the optical absorbance of low spin FeO6 is
substantially increased at 1000-1200 K due to the partially lifted Laporte
selection rule. The temperature-induced low to high spin transition, however,
results in a dramatic drop in absorbance of the FeO6-unit. The absorption edge
(Fe-O charge transfer) red-shifts (~ 1 cm-1/K) with increasing temperature and
at T above 1600 K becomes the dominant absorption mechanism in the visible
range, suppressing radiative conductivity. This implies that the radiative
conductivity of analogous FeO6-bearing minerals such as ferropericlase, the
second most abundant mineral in the Earths lower mantle, is substantially
reduced approaching the core-mantle boundary conditions. Finally, our results
emphasize that optical properties of mantle minerals probed at room temperature
are insufficient to model radiative thermal conductivity of planetary
interiors.",1604.02613v1
2016-04-11,Chemical abundances and kinematics of barium stars,"In this paper we present an homogeneous analysis of photospheric abundances
based on high-resolution spectroscopy of a sample of 182 barium stars and
candidates. We determined atmospheric parameters, spectroscopic distances,
stellar masses, ages, luminosities and scale height, radial velocities,
abundances of the Na, Al, $alpha$-elements, iron-peak elements, and s-process
elements Y, Zr, La, Ce, and Nd. We employed the local-thermodynamic-equilibrium
model atmospheres of Kurucz and the spectral analysis code {\sc moog}. We found
that the metallicities, the temperatures and the surface gravities for barium
stars can not be represented by a single gaussian distribution. The abundances
of $alpha$-elements and iron peak elements are similar to those of field giants
with the same metallicity. Sodium presents some degree of enrichment in more
evolved stars that could be attributed to the NeNa cycle. As expected, the
barium stars show overabundance of the elements created by the s-process. By
measuring the mean heavy-element abundance pattern as given by the ratio
[s/Fe], we found that the barium stars present several degrees of enrichment.
We also obtained the [hs/ls] ratio by measuring the photospheric abundances of
the Ba-peak and the Zr-peak elements. Our results indicated that the [s/Fe] and
the [hs/ls] ratios are strongly anti-correlated with the metallicity. Our
kinematical analysis showed that 90% of the barium stars belong to the thin
disk population. Based on their luminosities, none of the barium stars are
luminous enough to be an AGB star, nor to become self-enriched in the s-process
elements. Finally, we determined that the barium stars also follow an
age-metallicity relation.",1604.03031v1
2016-04-14,Discovery of Broad Soft X-ray Absorption Lines from the Quasar Wind in PDS 456,"High resolution soft X-ray spectroscopy of the prototype accretion disk wind
quasar, PDS 456, is presented. Here, the XMM-Newton RGS spectra are analyzed
from the large 2013-2014 XMM-Newton campaign, consisting of 5 observations of
approximately 100 ks in length. During the last observation (hereafter OBS. E),
the quasar is at a minimum flux level and broad absorption line profiles are
revealed in the soft X-ray band, with typical velocity widths of $\sigma_{\rm
v}\sim 10,000$ km s$^{-1}$. During a period of higher flux in the 3rd and 4th
observations (OBS. C and D, respectively), a very broad absorption trough is
also present above 1 keV. From fitting the absorption lines with models of
photoionized absorption spectra, the inferred outflow velocities lie in the
range $\sim 0.1-0.2c$. The absorption lines likely originate from He and H-like
neon and L-shell iron at these energies. Comparison with earlier archival data
of PDS 456 also reveals similar absorption structure near 1 keV in a 40 ks
observation in 2001, and generally the absorption lines appear most apparent
when the spectrum is more absorbed overall. The presence of the soft X-ray
broad absorption lines is also independently confirmed from an analysis of the
XMM-Newton EPIC spectra below 2 keV. We suggest that the soft X-ray absorption
profiles could be associated with a lower ionization and possibly clumpy phase
of the accretion disk wind, where the latter is known to be present in this
quasar from its well studied iron K absorption profile and where the wind
velocity reaches a typical value of 0.3$c$.",1604.04196v1
2016-04-22,Phase separation in iron chalcogenide superconductor Rb0.8+xFe1.6+ySe2 as seen by Raman light scattering and band structure calculations,"We report Raman light scattering in the phase separated superconducting
single crystal Rb0.77Fe1.61Se2 with Tc = 32 K. The spectra have been measured
in a wide temperature range 3K -500K. The observed phonon lines from the
majority vacancy ordered Rb2Fe4Se5 (245) antiferromagnetic phase with TN= 525 K
demonstrate modest anomalies in frequency, intensity and halfwidth at the
superconductive phase transition. We identify phonon lines from the minority
compressed Rb{\delta}Fe2Se2 (122) conductive phase. The superconducting gap
with dx2-y2 symmetry is also detected in our spectra. In the range 0-600 cm-1
we observed the low intensive but highly polarized B1g-type background which
becomes well structured under cooling. The possible magnetic or multiorbital
origin of this background has been discussed. We argue that phase separation in
M0.8+xFe1.6+ySe2 has pure magnetic origin. It occurs below Neel temperature
when iron magnetic moment achieves some critical magnitude. We state that there
is a spacer between the majority 245 and minority 122 phases. Using ab-initio
spin polarized band structure calculations we demonstrate that compressed
vacancy ordered Rb2Fe4Se5 phase can be conductive and therefore may serve as a
protective interface spacer between the pure metallic Rb{\delta}Fe2Se2 phase
and the insulating Rb2Fe4Se5 phase providing the percolative Josephson-junction
like superconductivity in the whole sample of Rb0.8+xFe1.6+ySe2 Our lattice
dynamics calculations show significant difference in the phonon spectra of the
conductive and insulating Rb2Fe4.Se5 phases.",1604.06825v1
2016-05-10,Cosmic-ray energy spectrum and composition up to the ankle - the case for a second Galactic component,"We have carried out a detailed study to understand the observed energy
spectrum and composition of cosmic rays with energies up to ~10^18 eV. Our
study shows that a single Galactic component with subsequent energy cut-offs in
the individual spectra of different elements, optimised to explain the observed
spectra below ~10^14 eV and the knee in the all-particle spectrum, cannot
explain the observed all-particle spectrum above ~2x10^16 eV. We discuss two
approaches for a second component of Galactic cosmic rays -- re-acceleration at
a Galactic wind termination shock, and supernova explosions of Wolf-Rayet
stars, and show that the latter scenario can explain almost all observed
features in the all-particle spectrum and the composition up to ~10^18 eV, when
combined with a canonical extra-galactic spectrum expected from strong radio
galaxies or a source population with similar cosmological evolution. In this
two-component Galactic model, the knee at ~ 3x10^15 eV and the second knee at
~10^17 eV in the all-particle spectrum are due to the cut-offs in the first and
second components, respectively. We also discuss several variations of the
extra-galactic component, from a minimal contribution to scenarios with a
significant component below the ankle (at ~4x10^18 eV), and find that
extra-galactic contributions in excess of regular source evolution are neither
indicated nor in conflict with the existing data. Our main result is that the
second Galactic component predicts a composition of Galactic cosmic rays at and
above the second knee that largely consists of helium or a mixture of helium
and CNO nuclei, with a weak or essentially vanishing iron fraction, in contrast
to most common assumptions. This prediction is in agreement with new
measurements from LOFAR and the Pierre Auger Observatory which indicate a
strong light component and a rather low iron fraction between ~10^17 and 10^18
eV.",1605.03111v2
2016-05-11,Broadband observations of the X-ray burster 4U 1705-44 with BeppoSAX,"4U 1705-44 is one of the most-studied type I X-ray burster and Atoll sources.
This source represents a perfect candidate to test different models proposed to
self-consistently track the physical changes occurring between different
spectral states because it shows clear spectral state transitions. The
broadband coverage, the sensitivity and energy resolution of the BeppoSAX
satellite offers the opportunity to disentangle the components that form the
total X-ray spectrum and to study their changes according to the spectral
state. Using two BeppoSAX observations carried out in August and October 2000,
respectively, for a total effective exposure time of about 100 ks, we study the
spectral evolution of the source from a soft to hard state. Energy spectra are
selected according to the source position in the color-color diagram (CCD)
Results. We succeeded in modeling the spectra of the source using a physical
self-consistent scenario for both the island and banana branches (the double
Comptonization scenario). The components observed are the soft Comptonization
and hard Comptonization, the blackbody, and a reflection component with a broad
iron line. When the source moves from the banana state to the island state, the
parameters of the two Comptonization components change significantly and the
blackbody component becomes too weak to be detected. We interpret the soft
Comptonization component as emission from the hot plasma surrounding the
neutron star, hard Comptonization as emission from the disk region, and the
blackbody component as emission from the inner accretion disk. The broad
feature in the iron line region is compatible with reflection from the inner
accretion disk.",1605.03366v1
2016-05-12,The Soft State of Cygnus X-1 Observed with NuSTAR: A Variable Corona and a Stable Inner Disk,"We present a multi-epoch hard X-ray analysis of Cygnus X-1 in its soft state
based on four observations with NuSTAR. Despite the basic similarity of the
observed spectra, there is clear spectral variability between epochs. To
investigate this variability, we construct a model incorporating both the
standard disk-corona continuum and relativistic reflection from the accretion
disk, based on prior NuSTAR work on Cygnus X-1, and apply this model to each
epoch independently. We find excellent consistency for the black hole spin, and
the iron abundance of the accretion disk, which are expected to remain constant
on observational timescales. In particular, we confirm that Cygnus X-1 hosts a
rapidly rotating black hole, 0.93<a*<0.96, in broad agreement with the majority
of prior studies of the relativistic disk reflection and constraints on the
spin obtained through studies of the thermal accretion disk continuum. Our work
also confirms the apparent misalignment between the inner disk and the orbital
plane of the binary system reported previously, finding the magnitude of this
warp to be ~10-15deg. This level of misalignment does not significantly change
(and may even improve) the agreement between our reflection results and the
thermal continuum results regarding the black hole spin. The spectral
variability observed by NuSTAR is dominated by the primary continuum, implying
variability in the temperature of the scattering electron plasma. Finally, we
consistently observe absorption from ionized iron at ~6.7 keV, which varies in
strength as a function of orbital phase in a manner consistent with the
absorbing material being an ionized phase of the focused stellar wind from the
supergiant companion star.",1605.03966v1
2016-06-02,A search for X-ray reprocessing echoes in the power spectral density functions of AGN,"We present the results of a detailed study of the X-ray power spectra density
(PSD) functions of twelve X-ray bright AGN, using almost all the archival
XMM-Newton data. The total net exposure of the EPIC-pn light curves is larger
than 350 ks in all cases (and exceeds 1 Ms in the case of 1H 0707-497). In a
physical scenario in which X-ray reflection occurs in the inner part of the
accretion disc of AGN, the X-ray reflection component should be a filtered echo
of the X-ray continuum signal and should be equal to the convolution of the
primary emission with the response function of the disc. Our primary objective
is to search for these reflection features in the 5-7 keV (iron line) and 0.5-1
keV (soft) bands, where the X-ray reflection fraction is expected to be
dominant. We fit to the observed periodograms two models: a simple bending
power law model (BPL) and a BPL model convolved with the transfer function of
the accretion disc assuming the lamp-post geometry and X-ray reflection from a
homogeneous disc. We do not find any significant features in the best-fitting
BPL model residuals either in individual PSDs in the iron band, soft and full
band (0.3-10 keV) or in the average PSD residuals of the brightest and more
variable sources (with similar black hole mass estimates). The typical
amplitude of the soft and full-band residuals is around 3-5 per cent. It is
possible that the expected general relativistic effects are not detected
because they are intrinsically lower than the uncertainty of the current PSDs,
even in the strong relativistic case in which X-ray reflection occurs on a disc
around a fast rotating black hole having an X-ray source very close above it.
However, we could place strong constrains to the X-ray reflection geometry with
the current data sets if we knew in advance the intrinsic shape of the X-ray
PSDs, particularly its high frequency slope.",1606.00844v1
2016-06-09,Ternary borides Nb$_7$Fe$_3$B$_8$ and Ta$_7$Fe$_3$B$_8$ with Kagome-type iron framework,"Two new ternary borides $TM$$_7$Fe$_3$B$_8$ ($TM$ = Nb, Ta) were synthesized
by high-temperature thermal treatment of samples obtained by arc-melting. This
new type of structure with space group $P$6/$mmm$, comprises $TM$ slabs
containing isolated planar hexagonal [B$_6$] rings and iron centered $TM$
columns in a Kagome type of arrangement. Chemical bonding analysis in
Nb$_7$Fe$_3$B$_8$ by means of the electron localizability approach reveals
two-center interactions forming the Kagome net of Fe and embedded B, while
weaker multicenter bonding present between this net and Nb atoms. Magnetic
susceptibility measurements reveal antiferromagnetic order below $T_N$ = 240 K
for Nb$_7$Fe$_3$B$_8$ and $T_N$ =265 K for Ta$_7$Fe$_3$B$_8$. Small remnant
magnetization below 0.01 $\mu_B$/f.u. is observed in the antiferromagnetic
state. The bulk nature of the magnetic transitions was confirmed by the
hyperfine splitting of the M\""o{\ss}bauer spectra, the sizable anomalies in the
specific heat capacity, and the kinks in the resistivity curves. The high-field
paramagnetic susceptibilities fitted by the Curie-Weiss law show effective
paramagnetic moments $\mu_{eff}$ about 3.1 $\mu_B$/Fe in both compounds. The
temperature dependence of the electrical resistivity also reveals metallic
character of both compounds. Density functional calculations corroborate the
metallic behaviour of both compounds and demonstrate the formation of a sizable
local magnetic moment on the Fe-sites. They indicate the presence of both
antiferro- and ferromagnetic interactions.",1606.03123v1
2016-08-02,Atomic-scale observation and manipulation of plaquette antiferromagnetic order in iron-based superconductor,"The symmetry requirement and the origin of magnetic orders coexisting with
superconductivity have been strongly debated issues of iron-based
superconductors (FeSCs). Observation of C$_4$-symmetric antiferromagnetism in
violation of the inter-band nesting condition of spin-density waves in
superconducting ground state will require significant change in our
understanding of the mechanism of FeSC. The superconducting material
Sr$_2$VO$_3$FeAs, a bulk version of monolayer FeSC in contact with a perovskite
layer with its magnetism (T$_N$ ~ 50 K) and superconductivity (T$_c$ ~ 37 K)
coexisting at parent state, has no reported structural orthorhombic distortion
and thus makes a perfect system to look for theoretically expected C$_4$
magnetisms. Based on variable temperature spin-polarized scanning tunneling
microscopy (SPSTM) with newly discovered imaging mechanism that removes the
static surface reconstruction (SR) pattern by fluctuating it rapidly with
spin-polarized tunneling current, we could visualize underlying C$_4$ symmetric
(2$\times$2) magnetic domains and its phase domain walls. We find that this
magnetic order is perfectly consistent with the plaquette antiferromagnetic
order in tetragonal Fe spin lattice expected from theories based on the
Heisenberg exchange interaction of local Fe moments and the quantum order by
disorder. The inconsistency of its modulation Q vectors from the nesting
condition also implies that the nesting-based C$_2$ symmetric magnetism is not
a unique prerequisite of high-T$_c$ FeSC. Furthermore, the plaquette
antiferromagnetic domain wall dynamics under the influence of small spin torque
effect of spin-polarized tunneling current are shown to be consistent with
theoretical simulation based on the extended Landau-Lifshitz-Gilbert equation.",1608.00884v3
2016-08-19,"Optical properties of $A$Fe$_\mathbf{2}$As$_\mathbf{2}$ ($A=\,$Ca, Sr, and Ba) single crystals","The detailed optical properties have been determined for the iron-based
materials $A$Fe$_2$As$_2$, where $A=\,$Ca, Sr, and Ba, for light polarized in
the iron-arsenic ($a-b$) planes over a wide frequency range, above and below
the magnetic and structural transitions at $T_N =$ 172, 195, and 138 K,
respectively. The real and imaginary parts of the complex conductivity are fit
simultaneously using two Drude terms in combination with a series of
oscillators. Above $T_N$, the free-carrier response consists of a weak, narrow
Drude term, and a strong, broad Drude term, both of which show only a weak
temperature dependence. Below $T_N$ there is a slight decrease of the plasma
frequency but a dramatic drop in the scattering rate for the narrow Drude term,
and for the broad Drude term there is a significant decrease in the plasma
frequency, while the decrease in the scattering rate, albeit significant, is
not as severe. The small values observed for the scattering rates for the
narrow Drude term for $T\ll{T_N}$ may be related to the Dirac cone-like
dispersion of the electronic bands. Below $T_N$ new features emerge in the
optical conductivity that are associated with the reconstruction Fermi surface
and the gapping of bands at $\Delta_1 \simeq$ 45 $-$ 80 meV, and $\Delta_2
\simeq$ 110 $-$ 210 meV. The reduction in the spectral weight associated with
the free carriers is captured by the gap structure, specifically, the spectral
weight from the narrow Drude term appears to be transferred into the low-energy
gap feature, while the missing weight from the broad term shifts to the
high-energy gap.",1608.05709v3
2016-09-16,A deep X-ray view of the bare AGN Ark 120. II. Evidence for Fe K emission transients,"We report on the results from a large observational campaign on the bare
Seyfert galaxy Ark 120, jointly carried out in 2014 with XMM-Newton, Chandra,
and NuSTAR. The fortunate line of sight to this source, devoid of any
significant absorbing material, provides an incomparably clean view to the
nuclear regions of an active galaxy. Here we focus on the analysis of the iron
fluorescence features, which form a composite emission pattern in the 6$-$7 keV
band. The prominent K$\alpha$ line from neutral iron at 6.4 keV is resolved in
the Chandra High-Energy Transmission Grating spectrum to a full-width at half
maximum of 4700$^{+2700}_{-1500}$ km s$^{-1}$, consistent with an origin from
the optical broad-line region. Excess components are detected on both sides of
the narrow K$\alpha$ line: the red one (6.0$-$6.3 keV) clearly varies in
strength in about one year, and hints at the presence of a broad, mildly
asymmetric line from the accretion disk; the blue one (6.5$-$7.0 keV), instead,
is likely a blend of different contributions, and appears to be constant when
integrated over long enough exposures. However, the Fe K excess emission map
computed over the 7.5 days of the XMM-Newton monitoring shows that both the red
and the blue features are actually highly variable on timescales of
$\sim$10$-$15 hours, suggesting that they might arise from short-lived hotspots
on the disk surface, located within a few tens of gravitational radii from the
central supermassive black hole and possibly illuminated by magnetic
reconnection events. Any alternative explanation would still require a highly
dynamic, inhomogeneous disk/coronal system, involving clumpiness and/or
instability.",1609.05210v1
2016-10-14,Elemental partitioning and isotopic fractionation of Zn between metal and silicate and geochemical estimation of the S content of the Earth's core,"Zinc metal-silicate fractionation provides experimental access to the
conditions of core formation and Zn has been used to estimate the S contents of
the Earth's core and of the bulk Earth, assuming that they share similar
volatility and that Zn was not partitioned into the Earth's core. We have
conducted a suite of partitioning experiments to characterize Zn metal-silicate
elemental and isotopic fractionation as a function of time, temperature, and
composition. Experiments were conducted at temperatures from 1473-2273K, with
run durations from 5-240 minutes for four starting materials. Chemical and
isotopic equilibrium is achieved within 10 minutes. Zinc metal-silicate
isotopic fractionation displays no resolvable dependence on temperature,
composition, or oxygen fugacity. Thus, the Zn isotopic composition of silicate
phases can be used as a proxy for bulk telluric bodies. Results from this study
and literature data were used to parameterize Zn metal-silicate partitioning as
a function of temperature, pressure, and redox state. Using this
parameterization and viable formation conditions, we have estimated a range of
Zn contents in the cores of iron meteorite parent bodies (i.e. iron meteorites)
of ~0.1-150 ppm, in good agreement with natural observations. We have
calculated the first geochemical estimates for the Zn contents of the Earth's
core and of the bulk Earth, at 242 +/-107 ppm and 114 +/-34 ppm (respectively),
that consider the slightly siderophile behavior of Zn and are therefore
significantly higher than previous estimates. Assuming similar volatility for S
and Zn, a chondritic S/Zn ratio, and considering our new estimates, we have
calculated a geochemical upper bound for the S content of the Earth's core of
6.3 +/-1.9 wt%. This indicates that S may be a major contributor to the density
deficit of the Earth's core or that the S/Zn ratio for the Earth is
non-chondritic.",1610.04463v1
2016-10-20,The Broadband Spectral Variability of Holmberg IX X-1,"We present results from four new broadband X-ray observations of the extreme
ultraluminous X-ray source Holmberg IX X-1 ($L_{\rm{X}} > 10^{40}$ erg/s),
performed by $Suzaku$ and $NuSTAR$ in coordination. Combined with the archival
data, we now have broadband observations of this remarkable source from six
separate epochs. Two of these new observations probe lower fluxes than seen
previously, allowing us to extend our knowledge of the broadband spectral
variability exhibited. The spectra are well fit by two thermal blackbody
components, which dominate the emission below 10 keV, as well as a steep
($\Gamma \sim 3.5$) powerlaw tail which dominates above $\sim$15 keV.
Remarkably, while the 0.3-10.0 keV flux varies by a factor of $\sim$3 between
all these epochs, the 15-40 keV flux varies by only $\sim$20%. Although the
spectral variability is strongest in the $\sim$1-10 keV band, both of the
thermal components are required to vary when all epochs are considered. We also
re-visit the search for iron absorption features, leveraging the high-energy
$NuSTAR$ data to improve our sensitivity to extreme velocity outflows in light
of the ultra-fast outflow recently detected in NGC 1313 X-1. Iron absorption
from a similar outflow along our line of sight can be ruled out in this case.
We discuss these results in the context of super-Eddington accretion models
that invoke a funnel-like geometry for the inner flow, and propose a scenario
in which we have an almost face-on view of a funnel that expands to larger
radii with increasing flux, resulting in an increasing degree of geometrical
collimation for the emission from intermediate temperature regions.",1610.06611v2
2016-10-21,Two Groups of Red Giants with Distinct Chemical Abundances in the Bulge Globular Cluster NGC 6553 Through the Eyes of APOGEE,"Multiple populations revealed in globular clusters (GCs) are important
windows to the formation and evolution of these stellar systems. The metal-rich
GCs in the Galactic bulge are an indispensable part of this picture, but the
high optical extinction in this region has prevented extensive research. In
this work, we use the high resolution near-infrared (NIR) spectroscopic data
from APOGEE to study the chemical abundances of NGC 6553, which is one of the
most metal-rich bulge GCs. We identify ten red giants as cluster members using
their positions, radial velocities, iron abundances, and NIR photometry. Our
sample stars show a mean radial velocity of $-0.14\pm5.47$ km s$^{-1}$, and a
mean [Fe/H] of $-0.15\pm 0.05$. We clearly separate two populations of stars in
C and N in this GC for the first time. NGC 6553 is the most metal-rich GC where
the multiple stellar population phenomenon is found until now. Substantial
chemical variations are also found in Na, O, and Al. However, the two
populations show similar Si, Ca, and iron-peak element abundances. Therefore,
we infer that the CNO, NeNa, and MgAl cycles have been activated, but the MgAl
cycle is too weak to show its effect on Mg. Type Ia and Type II supernovae do
not seem to have significantly polluted the second generation stars. Comparing
with other GC studies, NGC 6553 shows similar chemical variations as other
relatively metal-rich GCs. We also confront current GC formation theories with
our results, and suggest possible avenues for improvement in the models.",1610.06763v1
2016-10-24,Observations of the X-ray pulsar LMC X-4 with NuSTAR: limit on the magnetic field and tomography of the system in the fluorescent iron line,"We present results of the spectral and timing analysis of the X-ray pulsar
LMC X-4 with the NuSTAR observatory in the broad energy range 3-79 keV. Along
with the detailed analysis of the averaged source spectrum, the high-precision
pulse phased-resolved spectra were obtained for the first time. It has been
shown that the comptonization model gives the best approximation of the
obtained spectra. The evolution of its parameters was traced depending on the
pulse phase as well. The search for the possible cyclotron absorption line was
performed for all energy spectra in the 5-55 keV energy range. The obtained
upper limit for the depth of the cyclotron absorption line $\tau\simeq0.15$
($3\sigma$) indicates no cyclotron absorption line in this energy range, which
provides an estimate of the magnitude of the magnetic field on the surface of
the neutron star: $B < 3 \times 10^{11}$ G or $B > 6.5 \times 10^{12}$ G. The
latter one is agree with the estimate of the magnetic field obtained from the
analysis of the power spectrum of the pulsar: $B \sim 3 \times 10^{13}$ G.
Based on results of the pulse phase-resolved spectroscopy we revealed a delay
between maxima of the source emission and the equivalent width of the
fluorescent iron line. This delay can be apparently associated with the travel
time of photons between the emitting regions in the vicinity of the neutron
star and the relatively cold regions where this emission is reflected
(presumably, at the inflowing stream or at the place of an interaction of the
stream and the outer edge of the accretion disk).",1610.08092v1
2016-10-27,IC 3639 - A new bona fide Compton thick AGN unveiled by NuSTAR,"We analyse high-quality NuSTAR observations of the local (z = 0.011) Seyfert
2 active galactic nucleus (AGN) IC 3639, in conjunction with archival Suzaku
and Chandra data. This provides the first broadband X-ray spectral analysis of
the source, spanning nearly two decades in energy (0.5-30 keV). Previous X-ray
observations of the source below 10 keV indicated strong reflection/obscuration
on the basis of a pronounced iron fluorescence line at 6.4 keV. The hard X-ray
energy coverage of NuSTAR, together with self-consistent toroidal reprocessing
models, enables direct broadband constraints on the obscuring column density of
the source. We find the source to be heavily Compton-thick (CTK) with an
obscuring column in excess of $3.6\times10^{24}$ cm$^{-2}$, unconstrained at
the upper end. We further find an intrinsic 2-10 keV luminosity of
$\textrm{log}_{10}(L_{\textrm{2-10 keV}} \textrm{[erg s}^{-1}]) =
43.4^{+0.6}_{-1.1}$ to 90% confidence, almost 400 times the observed flux, and
consistent with various multi-wavelength diagnostics. Such a high intrinsic to
observed flux ratio in addition to an Fe-K$\alpha$ fluorescence line equivalent
width exceeding 2 keV is extreme amongst known bona fide CTK AGN, which we
suggest are both due to the high level of obscuration present around IC 3639.
Our study demonstrates that broadband spectroscopic modelling with NuSTAR
enables large corrections for obscuration to be carried out robustly, and
emphasises the need for improved modelling of AGN tori showing intense iron
fluorescence.",1610.08997v1
2016-11-04,Chemical trends in the Galactic Halo with APOGEE data,"The galaxy formation process in the $\Lambda$-Cold Dark Matter scenario can
be constrained from the analysis of stars in the Milky Way's halo system. We
examine the variation of chemical abundances in distant halo stars observed by
the Apache Point Galactic Evolution Experiment (APOGEE), as a function of
distance from the Galactic center ($r$) and iron abundance ([M/H]), in the
range 5 $\lesssim r \lesssim$ 30 kpc and $-2.5 <$ [M/H] $<$ 0.0. We perform a
statistical analysis of the abundance ratios derived by the APOGEE pipeline
(ASPCAP) and distances calculated by several approaches. Our analysis reveals
signatures of a different chemical enrichment between the inner and outer
regions of the halo, with a transition at about 15 kpc. The derived metallicity
distribution function exhibits two peaks, at [M/H] $\sim -1.5$ and $\sim -2.1$,
consistent with previously reported halo metallicity distributions. We obtain a
difference of $\sim 0.1$ dex for $\alpha$-element-to-iron ratios for stars at
$r > 15$ kpc and [M/H] $> -1.1$ (larger in the case of O, Mg and S) with
respect to the nearest halo stars. This result confirms previous claims for
low-$\alpha$ stars found at larger distances. Chemical differences in elements
with other nucleosynthetic origins (Ni, K, Na, and Al) are also detected. C and
N do not provide reliable information about the interstellar medium from which
stars formed because our sample comprises RGB and AGB stars and can experience
mixing of material to their surfaces.",1611.01249v1
2016-11-11,"Competing instabilities, orbital ordering and splitting of band degeneracies from a parquet renormalization group analysis of a 4-pocket model for iron-based superconductors: application to FeSe","We report the results of a parquet renormalization group (RG) study of
competing instabilities in the full 2D four pocket, three orbital low-energy
model for iron-based superconductors. We derive and analyze the RG flow of the
couplings, which describe all symmetry-allowed interactions between low-energy
fermions. Despite that the number of the couplings is large, we argue that
there are only two stable fixed trajectories of the RG flow and one weakly
unstable fixed trajectory with a single unstable direction. Each fixed
trajectory has a finite basin of attraction in the space of initial system
parameters. On the stable trajectories, either interactions involving only
$d_{xz}$ and $d_{yz}$ or only $d_{xy}$ orbital components on the electron
pockets dominate, while on the weakly unstable trajectory interactions
involving $d_{xz}$ ($d_{yz}$) and $d_{xy}$ orbital states on the electron
pockets remain comparable. The behavior along the two stable fixed trajectories
has been analyzed earlier [A.V. Chubukov, M. Khodas, and R.M. Fernandes,
arXiv:1602.05503]. Here we focus on the system behavior along the weakly
unstable trajectory and apply the results to FeSe. We find, based on the
analysis of susceptibilities along this trajectory, that the leading
instability upon lowering the temperature is towards a {\it three-component}
d-wave orbital nematic order. Two components are the differences between
fermionic densities on $d_{xz}$ and $d_{yz}$ orbitals on hole pockets and on
electron pockets, and the third one is the difference between the densities of
$d_{xy}$ orbitals on the two electron pockets. We argue that this order is
consistent with the splitting of band degeneracies, observed in recent
photoemission data on FeSe by A. Fedorov et al [arXiv:1606.03022].",1611.03912v1
2016-11-17,A Chemical Composition Survey of the Iron-Complex Globular Cluster NGC 6273 (M 19),"Recent observations have shown that a growing number of the most massive
Galactic globular clusters contain multiple populations of stars with different
[Fe/H] and neutron-capture element abundances. NGC 6273 has only recently been
recognized as a member of this ""iron-complex"" cluster class, and we provide
here a chemical and kinematic analysis of > 300 red giant branch (RGB) and
asymptotic giant branch (AGB) member stars using high resolution spectra
obtained with the Magellan-M2FS and VLT-FLAMES instruments. Multiple lines of
evidence indicate that NGC 6273 possesses an intrinsic metallicity spread that
ranges from about [Fe/H] = -2 to -1 dex, and may include at least three
populations with different [Fe/H] values. The three populations identified here
contain separate first (Na/Al-poor) and second (Na/Al-rich) generation stars,
but a Mg-Al anti-correlation may only be present in stars with [Fe/H] > -1.65.
The strong correlation between [La/Eu] and [Fe/H] suggests that the s-process
must have dominated the heavy element enrichment at higher metallicities. A
small group of stars with low [alpha/Fe] is identified and may have been
accreted from a former surrounding field star population. The cluster's large
abundance variations are coupled with a complex, extended, and multimodal blue
horizontal branch (HB). The HB morphology and chemical abundances suggest that
NGC 6273 may have an origin that is similar to omega Cen and M 54.",1611.05830v1
2017-01-04,A re-analysis of the NuSTAR and XMM-Newton broad-band spectrum of Ser~X-1,"Context: Ser X-1 is a well studied LMXB which clearly shows a broad iron
line. Recently, Miller et al. (2103) have presented broad-band, high quality
NuSTAR data of SerX-1.Using relativistically smeared self-consistent reflection
models, they find a value of R_in close to 1.0 R_ISCO (corresponding to 6 R_g),
and a low inclination angle, less than 10 deg. Aims: The aim of this paper is
to probe to what extent the choice of reflection and continuum models (and
uncertainties therein) can affect the conclusions about the disk parameters
inferred from the reflection component. To this aim we re-analyze all the
available public NuSTAR and XMM-Newton. Ser X-1 is a well studied source, its
spectrum has been observed by several instruments, and is therefore one of the
best sources for this study. Methods: We use slightly different continuum and
reflection models with respect to those adopted in literature for this source.
In particular we fit the iron line and other reflection features with
self-consistent reflection models as reflionx (with a power-law illuminating
continuum modified with a high energy cutoff to mimic the shape of the incident
Comptonization spectrum) and rfxconv. With these models we fit NuSTAR and
XMM-Newton spectra yielding consistent spectral results. Results: Our results
are in line with those already found by Miller et al. (2013) but less extreme.
In particular, we find the inner disk radius at about 13 R_g and an inclination
angle with respect to the line of sight of about 27 deg. We conclude that,
while the choice of the reflection model has little impact on the disk
parameters, as soon as a self-consistent model is used, the choice of the
continuum model can be important in the precise determination of the disk
parameters from the reflection component. Hence broad-band X-ray spectra are
highly preferable to constrain the continuum and disk parameters.",1701.01069v1
2017-01-22,Determination of robust metallicities for metal-rich red giant branch stars,"The study of the Milky Way relies on our ability to interpret the light from
stars correctly. This calls for a reinvestigation of how reliably we can
determine, e.g., iron abundances in such stars and how well they reproduce
those of dwarf stars. Here we explore robust ways to determine the iron content
of metal-rich giant stars. We aim to understand what biases and shortcomings
widely applied methods suffer from. In this study we are mainly concerned with
standard methods to analyse stellar spectra. This includes the analysis of
individual lines to determine stellar parameters, analysis of the broad wings
of certain lines (e.g., H$\alpha$ and calcium lines) to determine effective
temperature and surface gravity for the stars. For NGC 6528 we find that [Fe/H]
= $+0.04$ dex with a scatter of $\sigma=0.07$ dex, which gives an error in the
derived mean abundance of 0.02 dex. Our work has two important conclusions for
analysis of metal-rich red giant branch stars. 1) For spectra with S/N below
about 35 per reduced pixel [Fe/H] become too high, 2) Determination of $T_{\rm
eff}$ using the wings of the H$\alpha$ line results in [Fe/H] values about 0.1
dex higher than if excitational equilibrium is used. The last conclusion is
perhaps not surprising as we expect NLTE effect to become more prominent in
cooler stars and we can not use the the wings of the H$\alpha$ line to
determine $T_{\rm eff}$ for the cool stars in our sample. We therefore
recommend that in studies of metal-rich red giant stars care needs to be taken
to obtain sufficient calibration data in order to be able to also use the
cooler stars.",1701.06132v1
2017-03-05,Reliable estimation of prediction uncertainty for physico-chemical property models,"The predictions of parameteric property models and their uncertainties are
sensitive to systematic errors such as inconsistent reference data, parametric
model assumptions, or inadequate computational methods. Here, we discuss the
calibration of property models in the light of bootstrapping, a sampling method
akin to Bayesian inference that can be employed for identifying systematic
errors and for reliable estimation of the prediction uncertainty. We apply
bootstrapping to assess a linear property model linking the 57Fe Moessbauer
isomer shift to the contact electron density at the iron nucleus for a diverse
set of 44 molecular iron compounds. The contact electron density is calculated
with twelve density functionals across Jacob's ladder (PWLDA, BP86, BLYP, PW91,
PBE, M06-L, TPSS, B3LYP, B3PW91, PBE0, M06, TPSSh). We provide systematic-error
diagnostics and reliable, locally resolved uncertainties for isomer-shift
predictions. Pure and hybrid density functionals yield average prediction
uncertainties of 0.06-0.08 mm/s and 0.04-0.05 mm/s, respectively, the latter
being close to the average experimental uncertainty of 0.02 mm/s. Furthermore,
we show that both model parameters and prediction uncertainty depend
significantly on the composition and number of reference data points.
Accordingly, we suggest that rankings of density functionals based on
performance measures (e.g., the coefficient of correlation, r2, or the
root-mean-square error, RMSE) should not be inferred from a single data set.
This study presents the first statistically rigorous calibration analysis for
theoretical Moessbauer spectroscopy, which is of general applicability for
physico-chemical property models and not restricted to isomer-shift
predictions. We provide the statistically meaningful reference data set MIS39
and a new calibration of the isomer shift based on the PBE0 functional.",1703.01685v2
2017-08-03,Observations of the Ultraviolet-Bright Star Y453 in the Globular Cluster M4 (NGC 6121),"We present a spectral analysis of the UV-bright star Y453 in M4. Model fits
to the star's optical spectrum yield T_eff ~ 56,000 K. Fits to the star's FUV
spectrum, obtained with the Cosmic Origins Spectrograph (COS) on board the
Hubble Space Telescope, reveal it to be considerably hotter, with T_eff ~
72,000 K. We adopt T_eff = 72,000 +/- 2000 K and log g = 5.7 +/- 0.2 as our
best-fit parameters. Scaling the model spectrum to match the star's optical and
near-infrared magnitudes, we derive a mass M_* = 0.53 +/- 0.24 M_sun and
luminosity log L/L_sun = 2.84 +/- 0.05, consistent with the values expected of
an evolved star in a globular cluster. Comparing the star with post-horizontal
branch evolutionary tracks, we conclude that it most likely evolved from the
blue horizontal branch, departing the AGB before third dredge-up. It should
thus exhibit the abundance pattern (O-poor and Na-rich) characteristic of the
second-generation (SG) stars in M4. We derive the star's photospheric
abundances of He, C, N, O, Si, S, Ti, Cr, Fe, and Ni. CNO abundances are
roughly 0.25 dex greater than those of the cluster's SG stars, while the Si and
S abundances agree match the cluster values. Abundances of the iron-peak
elements (except for iron itself) are enhanced by 1 to 3 dex. Rather than
revealing the star's origin and evolution, this pattern reflects the combined
effects of diffusive and mechanical processes in the stellar atmosphere.",1708.01315v1
2017-09-04,Iron Snow in the Martian Core?,"The decline of Mars' global magnetic field some 3.8-4.1 billion years ago is
thought to reflect the demise of the dynamo that operated in its liquid core.
The dynamo was probably powered by planetary cooling and so its termination is
intimately tied to the thermochemical evolution and present-day physical state
of the Martian core. Bottom-up growth of a solid inner core, the
crystallization regime for Earth's core, has been found to produce a long-lived
dynamo leading to the suggestion that the Martian core remains entirely liquid
to this day. Motivated by the experimentally-determined increase in the Fe-S
liquidus temperature with decreasing pressure at Martian core conditions, we
investigate whether Mars' core could crystallize from the top down. We focus on
the ""iron snow"" regime, where newly-formed solid consists of pure Fe and is
therefore heavier than the liquid. We derive global energy and entropy
equations that describe the long-timescale thermal and magnetic history of the
core from a general theory for two-phase, two-component liquid mixtures,
assuming that the snow zone is in phase equilibrium and that all solid falls
out of the layer and remelts at each timestep. Formation of snow zones occurs
for a wide range of interior and thermal properties and depends critically on
the initial sulfur concentration, x0. Release of gravitational energy and
latent heat during growth of the snow zone do not generate sufficient entropy
to restart the dynamo unless the snow zone occupies at least 400 km of the
core. Snow zones can be 1.5-2 Gyrs old, though thermal stratification of the
uppermost core, not included in our model, likely delays onset. Models that
match the available magnetic and geodetic constraints have x0~10% and snow
zones that occupy approximately the top 100 km of the present-day Martian core.",1709.01100v1
2017-09-24,Fe I in the β Pictoris circumstellar gas disk I. Physical properties of the neutral iron gas,"The young planetary system {\beta} Pictoris is surrounded by a circumstellar
disk of dust and gas. Because both dust and gas have a lifetime shorter than
the system age, they need to be replenished continuously. The gas composition
is partly known, but its location and its origin are still a puzzle. The gas
source could be the exocomets (or so-called falling and evaporating bodies,
FEBs), which are observed as transient features in absorption lines of
refractory elements (Mg, Ca, and Fe) when they transit in front of the star at
several tens of stellar radii.
  Nearly 1700 high-resolution spectra of {\beta} Pictoris have been obtained
from 2003 to 2015 using the HARPS spectrograph. In these spectra, the
circumstellar disk is always detected as a stable component among the numerous
variable absorption signatures of transiting exocomets.
  Summing all the 1700 spectra allowed us to reach a signal-to-noise ratio
higher than 1000, which is an unprecedentedly high number for a {\beta}
Pictoris spectrum. It revealed many weak Fe I absorption lines of the
circumstellar gas in more than ten excited states. These weak lines bring new
information on the physical properties of the neutral iron gas in the
circumstellar disk. The population of the first excited levels follows a
Boltzmann distribution with a slope consistent with a gas temperature of about
1300 K; this temperature corresponds to a distance to the star of ~ 38 RStar
and implies a turbulence of {\xi} ~ 0.8 km/s.",1709.08170v1
2017-09-26,Near L-Edge Single and Multiple Photoionization of Singly Charged Iron Ions,"Absolute cross sections for m-fold photoionization (m=1,...,6) of Fe+ by a
single photon were measured employing the photon-ion merged-beams setup PIPE at
the PETRA III synchrotron light source, operated by DESY in Hamburg, Germany.
Photon energies were in the range 680-920 eV which covers the photoionization
resonances associated with 2p and 2s excitation to higher atomic shells as well
as the thresholds for 2p and 2s ionization. The corresponding resonance
positions were measured with an uncertainty of +- 0.2 eV. The cross section for
Fe+ photoabsorption is derived as the sum of the individually measured
cross-sections for m-fold ionization. Calculations of the Fe+ absorption cross
sections have been carried out using two different theoretical approaches,
Hartree-Fock including relativistic extensions and fully relativistic
Multi-Configuration Dirac Fock. Apart from overall energy shifts of up to about
3 eV, the theoretical cross sections are in good agreement with each other and
with the experimental results. In addition, the complex deexcitation cascades
after the creation of inner-shell holes in the Fe+ ion have been tracked on the
atomic fine-structure level. The corresponding theoretical results for the
product charge-state distributions are in much better agreement with the
experimental data than previously published configuration-average results. The
present experimental and theoretical results are valuable for opacity
calculations and are expected to pave the way to a more accurate determination
of the iron abundance in the interstellar medium.",1709.09092v1
2017-10-10,High-precision abundances of elements in Kepler LEGACY stars. Verification of trends with stellar age,"HARPS-N spectra with S/N > 250 and MARCS model atmospheres were used to
derive abundances of C, O, Na, Mg, Al, Si, Ca, Ti, Cr, Fe, Ni, Zn, and Y in ten
stars from the Kepler LEGACY sample (including the binary pair 16 Cyg A and B)
selected to have metallicities in the range -0.15 < [Fe/H] < +0.15 and ages
between 1 and 7 Gyr. Stellar gravities were obtained from seismic data and
effective temperatures were determined by comparing non-LTE iron abundances
derived from FeI and FeII lines. Available non-LTE corrections were also
applied when deriving abundances of the other elements. The results support the
[X/Fe]-age relations previously found for solar twins. [Mg/Fe], [Al/Fe], and
[Zn/Fe] decrease by ~0.1 dex over the lifetime of the Galactic thin disk due to
delayed contribution of iron from Type Ia supernovae relative to prompt
production of Mg, Al, and Zn in Type II supernovae. [Y/Mg] and [Y/Al], on the
other hand, increase by ~0.3 dex, which can be explained by an increasing
contribution of s-process elements from low-mass AGB stars as time goes on. The
trends of [C/Fe] and [O/Fe] are more complicated due to variations of the ratio
between refractory and volatile elements among stars of similar age. Two stars
with about the same age as the Sun show very different trends of [X/H] as a
function of elemental condensation temperature Tc and for 16 Cyg, the two
components have an abundance difference, which increases with Tc. These
anomalies may be connected to planet-star interactions.",1710.03544v1
2017-10-23,The velocity ellipsoid in the Galactic disc using Gaia DR1,"The stellar velocity ellipsoid of the solar neighbour is re-examined using
intermediate-old mono-abundances stellar groups with high quality chemistry
data together with parallaxes and proper motions from Gaia DR1. We find the
average velocity dispersion values for the three space velocity components for
the thin and thick disc of (\sigma_{U},\sigma_{V},\sigma_{W})_{thin} = (33 \pm
4, 28 \pm 2, 23 \pm 2) and (\sigma_{U},\sigma_{V},\sigma_{W})_{thick} = (57 \pm
6, 38 \pm 5, 37 \pm 4) km s^{-1}, respectively. The mean values of the ratio
between the semi-axes of the velocity ellipsoid for the thin disc are found to
be, \sigma_{V}/\sigma_{U} = 0.70 \pm 0.13 and \sigma_{W}/\sigma_{U} is 0.64 \pm
0.08, while for the thick disc \sigma_{V}/\sigma_{U} = 0.67 \pm 0.11 and
\sigma_{W}/\sigma_{U} is 0.66 \pm 0.11. Inputting these dispersions into the
linear Str\""omberg relation for the thin disc groups, we find the Sun's
velocity with respect to the LSR in Galactic rotation to be V_{\sun} = 13.9 \pm
3.4 km s^{-1}. A relation is found between the vertex deviation and the
chemical abundances for the thin disc, ranging from -5 to +40^{\circ} as
iron-abundance increases. For the thick disc we find a vertex deviation of
l_{uv} \sim -15^{\circ}. The tilt angle (l_{uw}) in the U-W plane for the thin
disc groups ranges from -10 to +15^\circ, but there is no evident relation
between l_{uw} and the mean abundances. However we find a weak relation for
l_{uw} as a function of iron abundances and \alpha-elements for most of the
groups in the thick disc, where the tilt angle decreases from -5 to -20^\circ
when [Fe/H] decreases and [\alpha/Fe] increases. The velocity anisotropy
parameter is independent of the chemical group abundances and its value is
nearly constant for both discs (\beta \sim 0.5), suggesting that the combined
disc is dynamically relaxed.",1710.08479v1
2017-11-06,K2-141 b: A 5-M$_\oplus$ super-Earth transiting a K7 V star every 6.7 hours,"We report on the discovery of K2-141 b (EPIC 246393474 b), an
ultra-short-period super-Earth on a 6.7-hour orbit transiting an active K7 V
star based on data from K2 campaign 12. We confirmed the planet's existence and
measured its mass with a series of follow-up observations: seeing-limited
MuSCAT imaging, NESSI high-resolution speckle observations, and FIES and HARPS
high-precision radial-velocity monitoring. K2-141 b has a mass of $5.31 \pm
0.46 $ $M_{\oplus}$ and radius of $1.54^{+0.10}_{-0.09}$ $R_{\oplus}$, yielding
a mean density of $8.00_{ - 1.45 } ^ { + 1.83 }$ $\mathrm{g\,cm^{-3}}$ and
suggesting a rocky-iron composition. Models indicate that iron cannot exceed
$\sim$70 % of the total mass. With an orbital period of only 6.7 hours, K2-141
b is the shortest-period planet known to date with a precisely determined mass.",1711.02097v2
2017-12-15,Interior Structures and Tidal Heating in the TRAPPIST-1 Planets,"With seven planets, the TRAPPIST-1 system has the largest number of
exoplanets discovered in a single system so far. The system is of
astrobiological interest, because three of its planets orbit in the habitable
zone of the ultracool M dwarf. Assuming the planets are composed of
non-compressible iron, rock, and H$_2$O, we determine possible interior
structures for each planet. To determine how much tidal heat may be dissipated
within each planet, we construct a tidal heat generation model using a single
uniform viscosity and rigidity for each planet based on the planet's
composition. With the exception of TRAPPIST-1c, all seven of the planets have
densities low enough to indicate the presence of significant H$_2$O in some
form. Planets b and c experience enough heating from planetary tides to
maintain magma oceans in their rock mantles; planet c may have eruptions of
silicate magma on its surface, which may be detectable with next-generation
instrumentation. Tidal heat fluxes on planets d, e, and f are lower, but are
still twenty times higher than Earth's mean heat flow. Planets d and e are the
most likely to be habitable. Planet d avoids the runaway greenhouse state if
its albedo is $\gtrsim$ 0.3. Determining the planet's masses within $\sim0.1$
to 0.5 Earth masses would confirm or rule out the presence of H$_2$O and/or
iron in each planet, and permit detailed models of heat production and
transport in each planet. Understanding the geodynamics of ice-rich planets f,
g, and h requires more sophisticated modeling that can self-consistently
balance heat production and transport in both rock and ice layers.",1712.05641v2
2018-01-16,The origin of ICM enrichment in the outskirts of present-day galaxy clusters from cosmological hydrodynamical simulations,"The uniformity of the intra-cluster medium (ICM) enrichment level in the
outskirts of nearby galaxy clusters suggests that chemical elements were
deposited and widely spread into the intergalactic medium before the cluster
formation. This observational evidence is supported by numerical findings from
cosmological hydrodynamical simulations, as presented in Biffi et al. (2017),
including the effect of thermal feedback from active galactic nuclei. Here, we
further investigate this picture, by tracing back in time the spatial origin
and metallicity evolution of the gas residing at z=0 in the outskirts of
simulated galaxy clusters. In these regions, we find a large distribution of
iron abundances, including a component of highly-enriched gas, already present
at z=2. At z>1, the gas in the present-day outskirts was distributed over tens
of virial radii from the the main cluster and had been already enriched within
high-redshift haloes. At z=2, about 40% of the most Fe-rich gas at z=0 was not
residing in any halo more massive than 1e11 Msun/h in the region and yet its
average iron abundance was already 0.4, w.r.t. the solar value by Anders &
Grevesse (1989). This confirms that the in situ enrichment of the ICM in the
outskirts of present-day clusters does not play a significant role, and its
uniform metal abundance is rather the consequence of the accretion of both
low-metallicity and pre-enriched (at z>2) gas, from the diffuse component and
through merging substructures. These findings do not depend on the mass of the
cluster nor on its core properties.",1801.05425v2
2018-03-07,Extracting a less model dependent cosmic ray composition from $X_\mathrm{max}$ distributions,"At higher energies the uncertainty in the estimated cosmic ray mass
composition, extracted from the observed distributions of the depth of shower
maximum $X_\text{max}$, is dominated by uncertainties in the hadronic
interaction models. Thus, the estimated composition depends strongly on the
particular model used for its interpretation. To reduce this model dependency
in the interpretation of the mass composition, we have developed a novel
approach which allows the adjustment of the normalisation levels of the proton
$<X_\text{max}>$ and $\sigma (X_\text{max})$ guided by real observations of
$X_\text{max}$ distributions. In this paper we describe the details of this
approach and present a study of its performance and its limitations. Using this
approach we extracted cosmic ray mass composition information from the
published Pierre Auger $X_\text{max}$ distributions. We have obtained a
consistent mass composition interpretation for Epos-LHC, QGSJetII-04 and
Sibyll2.3. Our fits suggest a composition consisting of predominantly iron.
Below $10^{18.8}$ eV, the small proportions of proton, helium and nitrogen
vary. Above $10^{18.8}$ eV, there is little proton or helium, and with
increasing energy the nitrogen component gradually gives way to the growing
iron component, which dominates at the highest energies. The fits suggest that
the normalisation level for proton $<X_\mathrm{max}>$ is much deeper than the
initial predictions of the hadronic interaction models. The fitted
normalisation level for proton $\sigma (X_\text{max})$ is also greater than the
model predictions. When fixing the expected normalisation of
$\sigma(X_\mathrm{max})$ to that suggested by the QGSJetII-04 model, a slightly
larger fraction of protons is obtained. These results remain sensitive to the
other model parameters that we keep fixed, such as the elongation rate and the
$<X_\text{max}>$ separation between p and Fe.",1803.02520v1
2018-03-23,Neutron-induced reactions in nuclear astrophysics,"The quest for the origin of the chemical elements, which we find in our body,
in our planet (Earth), in our star (Sun), or in our galaxy (Milky Way) could
only be resolved with a thorough understanding of the nuclear physics
properties of stable and unstable atomic nuclei. While the elements until iron
are either created during the big bang or during fusion reactions in stars,
most of the elements heavier than iron are produced via neutron-induced
reactions. Therefore, neutron capture cross sections of stable and unstable
isotopes are important. So far, time-of-flight or activation methods have been
applied very successfully, but these methods reach their limits once the
isotopes with half-lives shorter than a few months are of interest. A
combination of a radioactive beam facility, an ion storage ring and a high flux
reactor or a spallation source would allow a direct measurement of
neutron-induced reactions over a wide energy range of isotopes with half-lives
down to minutes. The idea is to measure neutron-induced reactions on
radioactive ions in inverse kinematics. This means, the radioactive ions will
pass through a neutron target. In order to efficiently use the rare nuclides as
well as to enhance the luminosity, the exotic nuclides can be stored in an ion
storage ring. The neutron target can be the core of a research reactor, where
one of the central fuel elements is replaced by the evacuated beam pipe of the
storage ring. Alternatively, a large moderator surrounding a spallation source
can be intersected by the beam pipe of an ion storage ring. Using particle
detectors and Schottky spectroscopy, most of the important neutron-induced
reactions, such as (n,$\gamma$), (n,p), (n,$\alpha$), (n,2n), or (n,f), could
be investigated.",1803.08678v1
2018-03-26,Distinct pressure evolution of coupled nematic and magnetic order in FeSe,"FeSe, despite being the structurally simplest compound in the family of
iron-based superconductors, shows an astoundingly rich interplay of physical
phenomena including nematicity and pressure-induced magnetism. Here, we present
a microscopic study of these two phenomena by high-energy x-ray diffraction and
time-domain M\""ossbauer spectroscopy on FeSe single crystals over a wide
temperature and pressure range. The topology of the pressure-temperature phase
diagram is a surprisingly close parallel to the well-known doping-temperature
phase diagram of BaFe2As2 generated through partial Fe/Co and Ba/Na
substitution. In FeSe with pressure p as a control parameter, the
magneto-structural ground state can be tuned from ""pure"" nematic - paramagnetic
with an orthorhombic lattice distortion - through a strongly coupled
magnetically ordered and orthorhombic state to a magnetically ordered state
without an orthorhombic lattice distortion. The magnetic hyperfine field
increases monotonically over a wide pressure range. However, the orthorhombic
distortion initially decreases under increasing pressure, but is stabilized by
cooperative coupling to the pressure-induced magnetic order. Close to the
reported maximum of the superconducting critical temperature Tc (occuring at p
= 6.8 GPa), the orthorhombic distortion suddenly disappears and FeSe remains
tetragonal down to the lowest temperature measured. Analysis of the structural
and magnetic order parameters suggests an independent origin of the structural
and magnetic ordering phenomena, and their cooperative coupling leads to the
similarity with the canonical phase diagram of iron pnictides.",1803.09449v1
2018-04-01,The 1.5 Ms Observing Campaign on IRAS 13224-3809: X-ray Spectral Analysis I,"We present a detailed spectral analysis of the recent 1.5\,Ms XMM-Newton
observing campaign on the narrow line Seyfert 1 galaxy IRAS~13224$-$3809, taken
simultaneously with 500\,ks of NuSTAR data. The X-ray lightcurve shows three
flux peaks, registering at about 100 times the minimum flux seen during the
campaign, and rapid variability with a time scale of kiloseconds. The spectra
are well fit with a primary powerlaw continuum, two relativistic-blurred
reflection components from the inner accretion disk with very high iron
abundance, and a simple blackbody-shaped model for the remaining soft excess.
The spectral variability is dominated by the power law continuum from a corona
region within a few gravitational radii from the black hole. Additionally,
blueshifted Ne \textsc{x}, Mg \textsc{xii}, Si \textsc{xiv} and S \textsc{xvi}
absorption lines are identified in the stacked low-flux spectrum, confirming
the presence of a highly ionized outflow with velocity up to $v= 0.267$ and
$0.225$\,c. We fit the absorption features with \texttt{xstar} models and find
a relatively constant velocity outflow through the whole observation. Finally,
we replace the \texttt{bbody} and supersolar abundance reflection models by
fitting the soft excess successfully with the extended reflection model
\texttt{relxillD}, which allows for higher densities than the standard
\texttt{relxill} model. This returns a disk electron density $n_{\rm
e}>10^{18.7}$\,cm$^{-3}$ and lowers the iron abundance from $Z_{\rm
Fe}=24^{+3}_{-4}Z_\odot$ with $n_{\rm e}\equiv10^{15}$\,cm$^{-3}$ to $Z_{\rm
Fe}=6.6^{+0.8}_{-2.1}Z_\odot$.",1804.00349v1
2018-04-08,A high-density relativistic reflection origin for the soft and hard X-ray excess emission from Mrk 1044,"We present the first results from a detailed spectral-timing analysis of a
long ($\sim$130 ks) XMM-Newton observation and quasi-simultaneous NuSTAR and
Swift observations of the highly-accreting narrow-line Seyfert 1 galaxy Mrk
1044. The broadband (0.3$-$50 keV) spectrum reveals the presence of a strong
soft X-ray excess emission below $\sim$1.5 keV, iron K$_{\alpha}$ emission
complex at $\sim$6$-$7 keV and a `Compton hump' at $\sim$15$-$30 keV. We find
that the relativistic reflection from a high-density accretion disc with a
broken power-law emissivity profile can simultaneously explain the soft X-ray
excess, highly ionized broad iron line and the Compton hump. At low frequencies
($[2-6]\times10^{-5}$ Hz), the power-law continuum dominated 1.5$-$5 keV band
lags behind the reflection dominated 0.3$-$1 keV band, which is explained with
a combination of propagation fluctuation and Comptonization processes, while at
higher frequencies ($[1-2]\times10^{-4}$ Hz), we detect a soft lag which is
interpreted as a signature of X-ray reverberation from the accretion disc. The
fractional root-mean-squared (rms) variability of the source decreases with
energy and is well described by two variable components: a less variable
relativistic disc reflection and a more variable direct coronal emission. Our
combined spectral-timing analyses suggest that the observed broadband X-ray
variability of Mrk~1044 is mainly driven by variations in the location or
geometry of the optically thin, hot corona.",1804.02703v2
2018-04-19,The Peculiar Atmospheric Chemistry of KELT-9b,"The atmospheric temperatures of the ultra-hot Jupiter KELT-9b straddle the
transition between gas giants and stars, and therefore between two
traditionally distinct regimes of atmospheric chemistry. Previous theoretical
studies assume the atmosphere of KELT-9b to be in chemical equilibrium. Despite
the high ultraviolet flux from KELT-9, we show using photochemical kinetics
calculations that the observable atmosphere of KELT-9b is predicted to be close
to chemical equilibrium, which greatly simplifies any theoretical
interpretation of its spectra. It also makes the atmosphere of KELT-9b, which
is expected to be cloudfree, a tightly constrained chemical system that lends
itself to a clean set of theoretical predictions. Due to the lower pressures
probed in transmission (compared to emission) spectroscopy, we predict the
abundance of water to vary by several orders of magnitude across the
atmospheric limb depending on temperature, which makes water a sensitive
thermometer. Carbon monoxide is predicted to be the dominant molecule under a
wide range of scenarios, rendering it a robust diagnostic of the metallicity
when analyzed in tandem with water. All of the other usual suspects (acetylene,
ammonia, carbon dioxide, hydrogen cyanide, methane) are predicted to be
subdominant at solar metallicity, while atomic oxygen, iron and magnesium are
predicted to have relative abundances as high as 1 part in 10,000. Neutral
atomic iron is predicted to be seen through a forest of optical and
near-infrared lines, which makes KELT-9b suitable for high-resolution
ground-based spectroscopy with HARPS-N or CARMENES. We summarize future
observational prospects of characterizing the atmosphere of KELT-9b.",1804.07137v3
2018-04-23,Metal Pollution of Low-Mass Population III Stars through Accretion of Interstellar Objects like `Oumuamua,"We calculate accretion mass of interstellar objects (ISOs) like `Oumuamua
onto low-mass population III stars (Pop.~III survivors), and estimate surface
pollution of Pop.~III survivors. An ISO number density estimated from the
discovery of `Oumuamua is so high ($\sim 0.2$~au$^{-3}$) that Pop.~III
survivors have chances at colliding with ISOs $\gtrsim 10^5$ times per $1$~Gyr.
`Oumuamua itself would be sublimated near Pop.~III survivors, since it has
small size, $\sim 100$~m. However, ISOs with size $\gtrsim 3$~km would reach
the Pop.~III survivor surfaces. Supposing an ISO cumulative number density with
size larger than $D$ is $n \propto D^{-\alpha}$, Pop.~III survivors can accrete
ISO mass $\gtrsim 10^{-16}M_\odot$, or ISO iron mass $\gtrsim 10^{-17}M_\odot$,
if $\alpha < 4$. This iron mass is larger than the accretion mass of
interstellar medium (ISM) by several orders of magnitude. Taking into account
material mixing in a convection zone of Pop.~III survivors, we obtain their
surface pollution is typically [Fe/H] $\lesssim -8$ in most cases, however the
surface pollution of Pop.~III survivors with $0.8M_\odot$ can be [Fe/H]
$\gtrsim -6$ because of the very shallow convective layer. If we apply to
Pop.III survivors located at the Galactocentric distance of 8 kpc, the
dependence of the metal pollustion is as follows. If $\alpha > 4$, Pop.~III
survivors have no chance at colliding with ISOs with $D \gtrsim 3$~km, and keep
metal-free. If $3 < \alpha < 4$, Pop.~III survivors would be most polluted by
ISOs up to [Fe/H] $\sim -7$. If $\alpha < 3$ up to $D \sim 10$~km, Pop.~III
survivors could hide in metal-poor stars so far discovered. Pop.~III survivors
would be more polluted with decreasing the Galactocentric distance. Although
the metal pollution depends on $\alpha$ and the Galactocentric distance, we
first show the importance of ISOs for the metal pollution of Pop.~III
survivors.",1804.08200v2
2018-05-02,"Electronic phase separation in iron selenide (Li, Fe)OHFeSe superconductor system","The phenomenon of phase separation into antiferromagnetic (AFM) and
superconducting (SC) or normal-state regions has great implication for the
origin of high-temperature (high-Tc) superconductivity. However, the occurrence
of an intrinsic antiferromagnetism above the Tc of (Li, Fe)OHFeSe
superconductor is questioned. Here we report a systematic study on a series of
(Li, Fe)OHFeSe single crystal samples with Tc up to ~41 K. We observe an
evident drop in the static magnetization at Tafm ~125 K, in some of the SC (Tc
< ~38 K, cell parameter c < ~9.27 {\AA}) and non-SC samples. We verify that
this AFM signal is intrinsic to (Li, Fe)OHFeSe. Thus, our observations indicate
mesoscopic-to-macroscopic coexistence of an AFM state with the normal (below
Tafm) or SC (below Tc) state in (Li, Fe)OHFeSe. We explain such coexistence by
electronic phase separation, similar to that in high-Tc cuprates and iron
arsenides. However, such an AFM signal can be absent in some other samples of
(Li, Fe)OHFeSe, particularly it is never observed in the SC samples of Tc > ~38
K, owing to a spatial scale of the phase separation too small for the
macroscopic magnetic probe. For this case, we propose a microscopic electronic
phase separation. It is suggested that the microscopic static phase separation
reaches vanishing point in high-Tc (Li, Fe)OHFeSe, by the occurrence of
two-dimensional AFM spin fluctuations below nearly the same temperature as Tafm
reported previously for a (Li, Fe)OHFeSe (Tc ~42 K) single crystal. A complete
phase diagram is thus established. Our study provides key information of the
underlying physics for high-Tc superconductivity.",1805.00688v1
2018-05-02,On a new and homogeneous metallicity scale for Galactic classical Cepheids - I. Physical parameters,"We gathered more than 1130 high-resolution optical spectra for more than 250
Galactic classical Cepheids. The spectra were collected with different optical
spectrographs: UVES at VLT, HARPS at 3.6m, FEROS at 2.2m MPG/ESO, and STELLA.
To improve the effective temperature estimates, we present more than 150 new
line depth ratio (LDR) calibrations that together with similar calibrations
already available in the literature allowed us to cover a broad range in
wavelength (between 5348 and 8427 angstrom) and in effective temperatures
(between 3500 and 7700 K). This means the unique opportunity to cover both the
hottest and coolest phases along the Cepheid pulsation cycle and to limit the
intrinsic error on individual measurements at the level of ~100 K. Thanks to
the high signal-to-noise ratio of individual spectra we identified and measured
hundreds of neutral and ionized lines of heavy elements, and in turn, have the
opportunity to trace the variation of both surface gravity and microturbulent
velocity along the pulsation cycle. The accuracy of the physical parameters and
the number of Fe I (more than one hundred) and Fe II (more than ten) lines
measured allowed us to estimate mean iron abundances with a precision better
than 0.1 dex. Here we focus on 14 calibrating Cepheids for which the current
spectra cover either the entire or a significant portion of the pulsation
cycle. The current estimates of the variation of the physical parameters along
the pulsation cycle and of the iron abundances agree quite well with similar
estimates available in the literature. Independent homogeneous estimates of
both physical parameters and metal abundances based on different approaches
that can constrain possible systematics are highly encouraged.",1805.00727v1
2018-05-09,Near-infrared spectral evolution of the Type Ia supernova 2014J in the nebular phase: implications for the progenitor system,"As the closest Type Ia supernova in decades, SN 2014J provides a unique
opportunity for detailed investigation into observational signatures of the
progenitor system and explosion mechanism in addition to burning product
distribution. We present a late-time near-infrared spectral series from
Gemini-N at $307-466$ days after the explosion. Following the $H$-band
evolution probes the distribution of radioactive iron group elements, the
extent of mixing, and presence of magnetic fields in the expanding ejecta.
Comparing the isolated $1.6440$ $\mu$m [Fe II] emission line with synthetic
models shows consistency with a Chandrasekhar-mass white dwarf of
$\rho_c=0.7\times10^9$ g cm${}^{-3}$ undergoing a delayed detonation. The ratio
of the flux in the neighboring $1.54$ $\mu$m emission feature to the flux in
the $1.6440$ $\mu$m feature shows evidence of some limited mixing of stable and
radioactive iron group elements in the central regions. Additionally, the
evolution of the $1.6440$ $\mu$m line shows an intriguing asymmetry. When
measuring line-width of this feature, the data show an increase in line width
not seen in the evolution of the synthetic spectra, corresponding to
$\approx1{,}000$ km s${}^{-1}$, which could be caused by a localized transition
to detonation producing asymmetric ionization in the ejecta. Using the
difference in width between the different epochs, an asymmetric component in
the central regions, corresponding to approximately the inner $2\times10^{-4}$
of white dwarf mass suggests an off-center ignition of the initial explosion
and hence of the kinematic center from the chemical center. Several additional
models investigated, including a He detonation and a merger, have difficulty
reproducing the features seen these spectra.",1805.03556v2
2018-05-18,Consistent Iron Abundances Derived from Neutral and Singly-Ionized Iron Lines in Ultraviolet and Optical Spectra of Six Warm Metal-Poor Stars,"Neutral Fe lines in metal-poor stars yield conflicting abundances depending
on whether and how deviations from local thermodynamic equilibrium (LTE) are
considered. We have collected new high resolution and high signal-to-noise
ultraviolet (UV) spectra of three warm dwarf stars with [Fe/H] = -2.9 with the
Space Telescope Imaging Spectrograph on the Hubble Space Telescope. We locate
archival UV spectra for three other warm dwarfs with [Fe/H] = -3.3, -2.2, and
-1.6, supplemented with optical spectra for all six stars. We calculate stellar
parameters using methods that are largely independent of the spectra, adopting
broadband photometry, color-temperature relations, Gaia parallaxes, and assumed
masses. We use the LTE line analysis code MOOG to derive Fe abundances from
hundreds of Fe I and Fe II lines with wavelengths from 2290 to 6430 Angstroms.
The [Fe/H] ratios derived separately from Fe I and Fe II lines agree in all six
stars, with [Fe II/H] - [Fe I/H] ranging from +0.00 +/- 0.07 to -0.12 +/- 0.09
dex, when strong lines and Fe I lines with lower excitation potential < 1.2 eV
are excluded. This constrains the extent of any deviations from LTE that may
occur within this parameter range. While our result confirms non-LTE
calculations for some warm, metal-poor dwarfs, it may not be generalizable to
more metal-poor dwarfs, where deviations from LTE are predicted to be larger.
We also investigate trends of systematically lower abundances derived from Fe I
lines in the Balmer continuum region (3100-3700 Angstroms), and we conclude
that no proposed explanation for this effect can fully account for the
observations presently available.",1805.07390v1
2018-05-30,A Recommendation Algorithm to Predict Giant Exoplanet Host Stars Using Stellar Elemental Abundances,"The presence of certain elements within a star, and by extension its planet,
strongly impacts the formation and evolution of the planetary system. The
positive correlation between a host star's iron-content and the presence of an
orbiting giant exoplanet has been confirmed; however, the importance of other
elements in predicting giant planet occurrence is less certain despite their
central role in shaping internal planetary structure. We designed and applied a
machine learning algorithm to the Hypatia Catalog (Hinkel et a. 2014) to
analyze the stellar abundance patterns of known host stars to determine those
elements important in identifying potential giant exoplanet host stars. We
analyzed a variety of different elements ensembles, namely volatiles,
lithophiles, siderophiles, and Fe. We show that the relative abundances of
oxygen, carbon, and sodium, in addition to iron, are influential indicators of
the presence of a giant planet. We demonstrate the predictive power of our
algorithm by analyzing stars with known giant planets and found that they had
median 75% prediction score. We present a list of ~350 stars with no currently
discovered planets that have a $\geq$90% prediction probability likelihood of
hosting a giant exoplanet. We investigated archival HARPS data and found
significant trends that HIP62345, HIP71803, and HIP10278 host long-period giant
planet companions with estimated minimum $M_p\sin(i)$ values of 3.7, 6.8, and
8.5 M$_{J}$, respectively. We anticipate that our findings will revolutionize
future target selection, the role that elements play in giant planet formation,
and the determination of giant planet interior structure models.",1805.12144v2
2018-06-12,Galactic Archeology with the AEGIS Survey: The Evolution of Carbon and Iron in the Galactic Halo,"Understanding the evolution of carbon and iron in the Milky Way's halo is of
importance because these two elements play crucial roles constraining star
formation, Galactic assembly, and chemical evolution in the early Universe.
Here, we explore the spatial distributions of carbonicity, [C/Fe], and
metallicity, [Fe/H], of the halo system based on medium-resolution ($R \sim$
1,300) spectroscopy of $\sim$58,000 stars in the Southern Hemisphere from the
AAOmega Evolution of Galactic Structure (AEGIS) survey. The AEGIS carbonicity
map exhibits a positive gradient with distance, as similarly found for the
Sloan Digital Sky Survey (SDSS) carbonicity map of Lee et al. The metallicity
map confirms that [Fe/H] decreases with distance, from the inner halo to the
outer halo. We also explore the formation and chemical-evolution history of the
halo by considering the populations of carbon-enhanced metal-poor (CEMP) stars
present in the AEGIS sample. The cumulative and differential frequencies of
CEMP-no stars (as classified by their characteristically lower levels of
absolute carbon abundance, $A$(C) $\leq$ 7.1 for sub-giants and giants)
increases with decreasing metallicity, and is \textit{substantially higher than
previous determinations} for CEMP stars as a whole. In contrast, that of
CEMP-$s$ stars (with higher $A$(C)), remains almost flat, at a value
$\sim$10\%, in the range $-\,4.0 \lesssim$ [Fe/H] $\lesssim-$2.0. The
distinctly different behaviors of the CEMP-no and CEMP-$s$ stars relieve the
tension with population-synthesis models assuming a binary mass-transfer
origin, which previously struggled to account for the higher reported
frequencies of CEMP stars, taken as a whole, at low metallicity.",1806.04738v1
2018-06-26,Modeling dust emission in PN IC 418,"We investigated the infrared (IR) dust emission from PN IC 418, using a
detailed model controlled by a previous determination of the stellar properties
and the characteristics of the photoionized nebula, keeping as free parameters
the dust types, amounts and distributions relative to the distance of the
central star. The model includes the ionized region and the neutral region
beyond the recombination front (Photodissociation region, or PDR), where the
[OI] and [CII] IR lines are formed. We succeeded in reproducing the observed
infrared emission from 2 to 200~\mm. The global energy budget is fitted by
summing up contributions from big grains of amorphous carbon located in the
neutral region and small graphite grains located in the ionized region (closer
to the central star).
  Two emission features seen at 11.5 and 30~\mm are also reproduced by assuming
them to be due to silicon carbide (SiC) and magnesium and iron sulfides
(Mg$_x$Fe$_{1-x}$S), respectively. For this, we needed to consider ellipsoidal
shapes for the grains to reproduce the wavelength distribution of the features.
  Some elements are depleted in the gaseous phase: Mg, Si, and S have sub-solar
abundances (-0.5 dex below solar by mass), while the abundance of C+N+O+Ne by
mass is close to solar. Adding the abundances of the elements present in the
dusty and gaseous forms leads to values closer to but not higher than solar,
confirming that the identification of the feature carriers is plausible. Iron
is strongly depleted (3 dex below solar) and the small amount present in dust
in our model is far from being enough to recover the solar value. A remaining
feature is found as a residue of the fitting process, between 12 and 25~\mm,
for which we do not have identification.",1806.10248v2
2018-11-02,NuSTAR and XMM-Newton broad-band spectrum of SAX J1808.4-3658 during its latest outburst in 2015,"The first discovered accreting millisecond pulsar, SAX J1808.4-3658, went
into X-ray outburst in April 2015. We triggered a 100 ks XMM-Newton ToO, taken
at the peak of the outburst, and a 55 ks NuSTAR ToO, performed four days apart.
We report here the results of a detailed spectral analysis of both the
XMM-Newton and NuSTAR spectra. While the XMM-Newton spectrum appears much
softer than in previous observations, the NuSTAR spectrum confirms the results
obtained with XMM-Newton during the 2008 outburst. We find clear evidence of a
broad iron line that we interpret as produced by reflection from the inner
accretion disk. For the first time, we use a self-consistent reflection model
to fit the reflection features in the NuSTAR spectrum; in this case we find a
statistically significant improvement of the fit with respect to a simple
Gaussian or diskline model to fit the iron line, implying that the reflection
continuum is also significantly detected. Despite the differences evident
between the XMM-Newton and NuSTAR spectra, the smearing best-fit parameters
found for these spectra are consistent with each other and are compatible with
previous results. In particular, we find an upper limit to the inner disk
radius of $\sim 12~R_g$. In all the cases, a high inclination angle
($>50^\circ$) of the system is required. This inclination angle, combined with
measurements of the radial velocity of the optical companion, results in a low
value for the neutron star mass ($<0.8\,M_\odot$), a result that deserves
further investigation.",1811.00940v1
2018-11-09,The chemical composition of planet building blocks as predicted by stellar population synthesis,"Future space missions will improve considerably our understanding of the
formation and history of planetary systems. Currently, observations show that
the presence of planetary companions is closely linked to the metallicity and
the chemical abundances of the host stars. We aim to build an integrated tool
to predict the planet building blocks composition as a function of the stellar
populations, for the interpretation of the ongoing and future large surveys. We
synthesize stellar populations with the Besan\c{c}on Galaxy model (BGM) which
includes stellar evolutionary tracks computed with the stellar evolution code
STAREVOL. We integrate to the BGM a simple stoichiometric model to determine
the expected composition of the planet building blocks. We determine the
expected PBB composition around FGK stars, for the four galactic populations
within the Milky Way. Our solar neighborhood simulations are in good agreement
with the recent results obtained with the HARPS survey for f_iron, f_w and the
heavy mass fraction f_Z. We present evidence of the clear dependence of f_iron
and f_w with the initial alpha abundances [\alpha/Fe] of the host star. We find
that the different initial [\alpha/Fe] distributions in the different galactic
populations lead to a bimodal distribution of PBB composition and to an
iron/water valley separating PBB with high and low iron/water mass fractions.
We linked host star abundances and expected PBB composition in an integrated
model of the Galaxy. Derived trends are an important step for statistical
analyses of expected planet properties. In particular, internal structure
models may use these results to derive statistical trends of rocky planets
properties, constrain habitability and prepare interpretation of on-going and
future large scale surveys of exoplanet search.",1811.04096v1
2018-11-22,Effect of PEG binder on gas sensitivity of ferric oxide films synthesized by spin coating and doctor blade methods,"Ferric oxide (Fe2O3) thin films were fabricated on amorphous nonconductive
and FTO conductive glass substrates starting from iron acetate nanoparticles by
the doctor blade and the spin coating techniques. Thin films of Fe2O3 with and
without the PEG binder were investigated. Films were subsequently annealed at
500 0C in air for 1 hour to crystallize the phase Fe2O3. The structural and
chemical properties of Fe2O3 thin films were determined using XRD and FTIR.
According to XRD, the single phase of Fe2O3 crystallized in the thin film after
annealing. The optical band gap of synthesized Fe2O3 thin films were determined
by UV-Visible spectrums. Gas sensitivity, respond time and recovery time of
Fe2O3 thin films were measured in 1000ppm of CO2 gas using AUTO LAB. Thin films
synthesized by the doctor blade method were thicker and more uniform than the
thin films prepared by the spin coating technique. Gas sensitivity of Fe2O3
films synthesized by the doctor blade method is slightly higher than that of
the films fabricated by the spin coating technique. Fe2O3 films with the PEG
binder posses a higher gas sensitivity, lower respond time and lower recovery
time compared to films without PEG binder. After adding the PEG binder, the
optical band gap of Fe2O3 thin films reduces. The reduction of the activation
energy is the reason for the improvement of the gas sensitivity after adding
the PEG. However, the peak positions of FTIR do not indicate any significant
change due to the adding of the PEG. Adding the binder increased the gas
sensitivity of iron oxide by 15.44%. Both FTIR and UV-Visible data confirm the
formation of Fe2O3 in the thin film.",1811.09614v1
2019-02-04,Quantum-critical scale invariance in a transition metal alloy,"Quantum-mechanical fluctuations between competing phases at $T=0$ induce
exotic finite-temperature collective excitations that are not described by the
standard Landau Fermi liquid framework. These excitations exhibit anomalous
temperature dependences, or non-Fermi liquid behavior, in the transport and
thermodynamic properties in the vicinity of a quantum critical point, and are
often intimately linked to the appearance of unconventional Cooper pairing as
observed in strongly correlated systems including the high-$T_c$ cuprate and
iron pnictide superconductors. The presence of superconductivity, however,
precludes direct access to the quantum critical point, and makes it difficult
to assess the role of quantum-critical fluctuations in shaping anomalous
finite-temperature physical properties. Here we report temperature-field scale
invariance of non-Fermi liquid thermodynamic, transport, and Hall quantities in
a non-superconducting iron-pnictide,
Ba(Fe$_{1/3}$Co$_{1/3}$Ni$_{1/3}$)$_{2}$As$_{2}$, indicative of quantum
criticality at zero temperature and zero applied magnetic field. Beyond a
linear in temperature resistivity, the hallmark signature of strong
quasiparticle scattering, we find the scattering rate that obeys a universal
scaling relation between temperature and applied magnetic fields down to the
lowest energy scales. Together with the dominance of hole-like carriers close
to the zero-temperature and zero-field limits, the scale invariance, isotropic
field response, and lack of applied pressure sensitivity suggests a unique
quantum critical system that does not drive a pairing instability.",1902.01034v3
2019-02-13,Spectral analysis of the barium central star of the planetary nebula Hen 2-39,"Barium stars are peculiar red giants characterized by an overabundance of
s-process elements along with an enrichment in carbon. These stars are
discovered in binaries with white dwarf companions. The more recently formed of
these stars are still surrounded by a planetary nebula. Precise abundance
determinations of the various s-process elements, especially, of the lightest,
short-lived radionuclide technetium will establish constraints for the
formation of s-process elements in asymptotic giant branch stars as well as
mass transfer through, for example, stellar wind, Roche-lobe overflow, and
common-envelope evolution. We performed a detailed spectral analysis of the
K-type subgiant central star of the planetary nebula Hen 2-39 based on
high-resolution optical spectra obtained with the Ultraviolet and Visual
Echelle Spectrograph at the Very Large Telescope using LTE model atmospheres.
We confirm the effective temperature of $T_\mathrm{eff} = 4350 \pm 150$ K for
the central star of the planetary nebula Hen 2-39. It has a photospheric carbon
enrichment of $[\mathrm{C/H}]= 0.36 \pm 0.08$ and a barium overabundance of
$[\mathrm{Ba/Fe}]= 1.8 \pm 0.5$. We find a deficiency for most of the
iron-group elements (calcium to iron) and establish an upper abundance limit
for technetium ($\log \epsilon_\mathrm{Tc} < 2.5$). The quality of the
available optical spectra is not sufficient to measure abundances of all
s-process elements accurately. Despite large uncertainties on the abundances as
well as on the model yields, the derived abundances are most consistent with a
progenitor mass in the range 1.75-3.00 $M_\odot$ and a metallicity of
$[\mathrm{Fe/H}]= -0.3 \pm 1.0$. This result leads to the conclusion that the
formation of such systems requires a relatively large mass transfer that is
most easily obtained via wind-Roche lobe overflow.",1902.04897v1
2019-03-01,Signature of Dispersing 1D Majorana Channels in an Iron-based Superconductor,"The possible realization of Majorana fermions as quasiparticle excitations in
condensed matter physics has created much excitement. Most recent studies have
focused on Majorana bound states which can serve as topological qubits. More
generally, akin to elementary particles, Majorana fermions can propagate and
display linear dispersion. These excitations have not yet been directly
observed, and can also be used for quantum information processing. One route to
realizing this is in a line junction between two phase-shifted superconductors
coupled to topological surface states. Recent theory indicates that in
iron-based superconductors, a particular type of crystalline defect, i.e., a
domain wall (DW) between two regions with a half-unit cell shift between them,
should create a $\pi$-phase shift in the superconducting order parameter.
Combined with recent data showing topological surface states in
FeSe$_x$Te$_{1-x}$ we find that this is the ideal system to realize helical
1D-dispersing Majorana modes. Here we report scanning tunneling spectroscopic
(STS) measurements of crystalline DWs in FeSe$_{0.45}$Te$_{0.55}$. By analyzing
large-area superconducting gap maps, we identify the gap in the topological
surface state, demonstrating that our sample is an effective Fu-Kane
proximitized topological system. We further locate DWs across which the atoms
shift by half a unit cell. STS data on these DWs reveal a flat density of
states inside the superconducting gap, a hallmark of linearly dispersing modes
in 1D. This unique signature is absent in DWs in the related superconductor,
FeSe which is not in the topological phase. Our combined data are consistent
with the observation of dispersing Majorana states at a $\pi$-phase shift DW in
a proximitized topological material.",1903.00515v4
2019-08-05,Spectral and orbital survey of medium-sized meteoroids,"We investigate the spectra, material properties, and orbital distribution of
millimeter- to decimeter-sized meteoroids. Our study aims to distinguish the
characteristics of populations of differently sized meteoroids and reveal the
heterogeneity of identified meteoroid streams. We verify the surprisingly large
ratio of pure iron meteoroids on asteroidal orbits detected among mm-sized
bodies. Emission spectra and multi-station meteor trajectories were collected
within the AMOS network observations. The sample is based on 202 meteors of -1
to -14 magnitude, corresponding to meteoroids of mm to dm sizes. Meteoroid
composition is studied by relative intensity ratios of Na, Mg, and Fe.
Heliocentric orbits, trajectory parameters, and material strengths inferred
from empirical $K_B$ and $P_E$ parameters were determined for 146 meteoroids.
An overall increase of Na content compared to the population of mm-sized
meteoroids was detected, reflecting weaker effects of space weathering
processes on larger meteoroids. We report a very low ratio of pure iron
meteoroids and the discovery of a new spectral group of Fe-rich meteors. The
majority of meteoroids on asteroidal orbits were found to be chondritic.
Thermal processes causing Na depletion and physical processes resulting in
Na-rich spectra are described and linked to characteristically increased
material strengths. Numerous major and minor shower meteors were identified in
our sample, revealing various degrees of heterogeneity within Halley-type,
ecliptical, and sungrazing meteoroid streams. Our results imply a scattered
composition of the fragments of comet 2P/Encke and 109P/Swift-Tuttle. The
largest disparities were detected within the $\alpha$-Capricornids and
$\delta$-Aquarids. We also find a spectral similarity between $\kappa$-Cygnids
and Taurids, which could imply a similar composition of the parent objects of
the two streams.",1908.01565v2
2019-08-08,High-$T_c$ Iron-phosphide Superconductivity Enhanced by Reemergent Antiferromagnetic Spin Fluctuations in (Sr$_4$Sc$_2$O$_6$)Fe$_2$(As$_{1-x}$P$_{x}$)$_2$ probed by NMR,"We report a systematic NMR study on
[Sr$_4$Sc$_2$O$_6$]Fe$_2$(As$_{1-x}$P$_x$)$_2$, for which the local lattice
parameters of the iron-pnictogen (Fe$Pn$) layer are similar to those of the
series LaFe(As$_{1-x'}$P$_{x'}$)O, which exhibit two segregated
antiferromagnetic (AFM) order phases, AFM1 at $x'$=0-0.2 and AFM2 at
$x'$=0.4-0.7. Our results revealed that the parent AFM1 phase at $x$=0
disappears at $x$=0.3-0.4, corresponding to a pnictogen height ($h_{pn}$) from
the Fe-plane of 1.3-1.32 \AA, which is similar to that of
LaFe(As$_{1-x'}$P$_{x'}$)O and various parent Fe-pnictides. By contrast, the
AFM2 order reported for LaFe(As$_{0.4}$P$_{0.6}$)O does not appear at
$x\sim$0.8, although the local lattice parameters of the Fe$Pn$ layer and the
microscopic electronic states are quite similar. Despite the absence of the
{\it static} AFM2 order, reemergent {\it dynamical} AFM spin fluctuations were
observed at approximately $x\sim$0.8, which can be attributed to the
instability of the AFM2 phase. We suggest this re-enhancement of AFM spin
fluctuations to play a significant role in enhancing the $T_c$ to 17 K for
$x$=0.8-1. Finally, we discuss the universality and diversity of the
complicated magnetic ground states from a microscopic point of view, including
the difference in the origins of the AFM1 and AFM2 phases, and their relations
with the high superconducting transitions in Fe-pnictides.",1908.02980v1
2019-08-09,"Abundances of alpha-Process Elements in Thin-Disk, Thick-Disk, and Halo Stars of the Galaxy: Non-LTE Analysis","The atmospheric parameters and abundances of Mg, Si, Ca, and Ti have been
determined for 20 stars using the Gaia DR2 parallaxes, high-resolution spectra,
and the non-local thermodynamic equilibrium (non-LTE) line formation modeling.
A sample of stars with homogeneous data on the abundances of alpha-process
elements has thus been increased to 94. It is shown that applying a non-LTE
approach and classical 1D atmospheric models with spectroscopically determined
surface gravities based on Fe~I and Fe~II lines yields reliable results.
Analysis of the full sample confirms the conclusions of earlier studies
indicating enhancements of Mg, Si, Ca, and Ti relative to Fe for halo and
thick-disk stars, and larger enhancements for the thick-disk stars compared to
the thin-disk stars of similar metallicities. The following new results are
obtained. The ratios [Mg/Fe], [Si/Fe], [Ca/Fe], and [Ti/Fe] in the thick disk
remain constant and similar to each other at the level 0.3 when [Fe/H] < -0.4,
and fall off when the metallicity becomes higher, suggesting the onset of the
production of iron in Type Ia supernovae. Halo stars have the same [alpha/Fe]
values independent of their distance (within ~ 8 kpc of the Sun), providing
evidence for a universal evolution of the abundances of alpha-process elements
in different parts of the Galaxy. The enhancements relative to iron for halo
stars are, on average, similar, at the level 0.3 dex, for Mg, Si, Ca, and Ti.
These data are important for constraining the nucleosynthesis models. The
star-to-star scatter of [alpha/Fe] increases for [Fe/H] < -2.6, while the
scatter of the ratios between the different alpha-process elements remains
small, possibly indicating incomplete mixing of nucleosynthesis products at the
epoch of the formation of these stars.",1908.03370v1
2019-09-16,An evolving broad iron line from the first Galactic ultraluminous X-ray pulsar Swift J0243.6+6124,"We present a spectral study of the ultraluminous Be/X-ray transient pulsar
Swift J0243.6+6124 using Neutron Star Interior Composition Explorer (NICER)
observations during the system's 2017--2018 giant outburst. The 1.2--10~keV
energy spectrum of the source can be approximated with an absorbed cut-off
power law model. We detect strong, luminosity-dependent emission lines in the
6--7 keV energy range. A narrow 6.42 keV line, observed in the sub-Eddington
regime, is seen to evolve into a broad Fe-line profile in the super-Eddington
regime. Other features are found at 6.67 and 6.97 keV in the Fe-line complex.
An asymmetric broad line profile, peaking at 6.67 keV, is possibly due to
Doppler effects and gravitational redshift. The 1.2--79 keV broadband spectrum
from NuSTAR and NICER observations at the outburst peak is well described by an
absorbed cut-off power law plus multiple Gaussian lines and a blackbody
component. Physical reflection models are also tested to probe the broad iron
line feature. Depending on the mass accretion rate, we found emission sites
that are evolving from ~5000 km to a range closer to the surface of the neutron
star. Our findings are discussed in the framework of the accretion disk and its
implication on the magnetic field, the presence of optically thick accretion
curtain in the magnetosphere, jet emission, and the massive, ultra-fast outflow
expected at super-Eddington accretion rates. We do not detect any signatures of
a cyclotron absorption line in the NICER or NuSTAR data.",1909.07338v1
2019-11-06,The Impact of Starbursts on Element Abundance Ratios,"We investigate the impact of bursts in star formation on the predictions of
one-zone chemical evolution models, adopting oxygen (O), iron (Fe), and
strontium (Sr), as representative $\alpha$, iron-peak, and s-process elements,
respectively. To this end, we develop the Versatile Integrator for Chemical
Evolution (VICE), a python package. Starbursts driven by a temporary boost of
gas accretion rate create loops in [O/Fe]-[Fe/H] evolutionary tracks and a peak
in the stellar [O/Fe] distribution at intermediate values. Bursts driven by a
temporary boost of star formation efficiency have a similar effect, and they
also produce a population of $\alpha$-deficient stars during the depressed star
formation phase that follows the burst. This $\alpha$-deficient population is
more prominent if the outflow rate is tied to a time-averaged star formation
rate (SFR) instead of the instantaneous SFR. Theoretical models of Sr
production predict a strong metallicity dependence of supernova and asymptotic
giant branch (AGB) star yields, though comparison to data suggests an
additional source that is nearly metallicity-independent. Evolution of [Sr/Fe]
and [Sr/O] during a starburst is complex because of the yield metallicity
dependence and the multiple timescales in play. Moderate amplitude (10-20\%)
sinusoidal oscillations in SFR produce loops in [O/Fe]-[Fe/H] tracks and
multiple peaks in [O/Fe] distributions, which could be one source of intrinsic
scatter in observed sequences. We investigate models that have a factor of ~2
enhancement of SFR at t = 12 Gyr, as suggest by some recent Milky Way
observations. A late episode of enhanced star formation could help explain the
existence of young stars with moderate $\alpha$-enhancements and the
surprisingly young median age found for solar metallicity stars in the solar
neighborhood, while also raising the possibility that this starburst has not
fully decayed.",1911.02598v1
2019-11-14,Stellar population astrophysics (SPA) with the TNG. Revisiting the metallicity of Praesepe (M44),"Open clusters exquisitely track the Galactic disc chemical properties and its
time evolution; a substantial number of studies and large spectroscopic surveys
focus mostly on the chemical content of relatively old clusters (age $\gtrsim$
1 Gyr). Interestingly, the less studied young counterpart populating the solar
surrounding has been found to be solar (at most), with a notable surprising
lack of young metal-rich objects. While there is wide consensus about the
moderately above-solar composition of the Hyades cluster, the metallicity of
Praesepe is still controversial. Recent studies suggest that these two clusters
share identical chemical composition and age, but this conclusion is disputed.
With the aim of reassessing the metallicity of Praesepe, and its difference (if
any) with the Hyades cluster, we present in this paper a spectroscopic
investigation of ten solar-type dwarf members. We exploited $GIARPS$ at the TNG
to acquire high-resolution, high-quality optical and near-IR spectra and
derived stellar parameters, metallicity ([Fe/H]), light elements, $\alpha$- and
iron-peak elements, by using a strictly differential (line-by-line) approach.
We also analysed in the very same way the solar spectrum and the Hyades solar
analogue HD 28099. Our findings suggest that Praesepe is more metal-rich than
the Hyades, at the level of $\Delta$[Fe/H]=+0.05$\pm$0.01 dex, with a mean
value of [Fe/H]=+0.21$\pm0.01$ dex. All the other elements scale with iron, as
expected. This result seems to reject the hypothesis of a common origin for
these two open clusters. Most importantly, Praesepe is currently the most
metal-rich, young open cluster living in the solar neighbourhood.",1911.06337v2
2020-01-15,Utilizing Essential Symmetry Breaking in Auxiliary-Field Quantum Monte Carlo: Application to the Spin Gaps of the C$_{36}$ Fullerene and an Iron Porphyrin Model Complex,"We present three distinct examples where phaseless auxiliary-field Quantum
Monte Carlo (ph-AFQMC) can be reliably performed with a single-determinant
trial wavefunction with essential symmetry breaking. We first utilized
essential time-reversal symmetry breaking with ph-AFQMC to compute the
triplet-singlet energy gap in the TS12 set. We found statistically better
performance of ph-AFQMC with complex-restricted orbitals than with
spin-unrestricted orbitals. We then showed the utilization of essential spin
symmetry breaking when computing the single-triplet gap of a known
biradicaloid, C$_{36}$. ph-AFQMC with spin-unrestricted Hartree-Fock
(ph-AFQMC+UHF) fails catastrophically even with spin-projection and predicts no
biradicaloid character. With approximate Brueckner orbitals obtained from
regularized orbital-optimized second-order M{\o}ller-Plesset perturbation
theory ($\kappa$-OOMP2), ph-AFQMC quantitatively captures strong biradicaloid
character of C$_{36}$. Lastly, we applied ph-AFQMC to the computation of the
quintet-triplet gap in a model iron porphyrin complex where brute-force methods
with a small active space fail to capture the triplet ground state. We show
unambiguously that neither triplet nor quintet is strongly correlated using
UHF, $\kappa$-OOMP2, and coupled-cluster with singles and doubles (CCSD)
performed on UHF and $\kappa$-OOMP2 orbitals. There is no essential symmetry
breaking in this problem. By virtue of this, we were able to perform
UHF+ph-AFQMC reliably with a cc-pVTZ basis set and predicted a triplet ground
state for this model geometry. The largest ph-AFQMC in this work correlated 186
electrons in 956 orbitals. Our work highlights the utility, scalability, and
accuracy of ph-AFQMC with a single determinant trial wavefunction with
essential symmetry breaking for systems mainly dominated by dynamical
correlation with little static correlation.",2001.05109v2
2020-04-23,Chandra High Energy Transmission Gratings Spectra of V3890 Sgr,"The recurrent nova (RN) V3890 Sgr was observed during the 7th day after the
onset of its most recent outburst, with the Chandra ACIS-S camera and High
Energy Transmission Gratings (HETG). A rich emission line spectrum was
detected, due to transitions of Fe-L and K-shell ions ranging from neon to
iron. The measured absorbed flux is $\approx 10^{-10}$ erg cm$^{-2}$ s$^{-1}$
in the 1.4-15 Angstrom range (0.77-8.86 keV). The line profiles are asymmetric,
blue-shifted and skewed towards the blue side, as if the ejecta moving towards
us are less absorbed than the receding ones. The full width at half maximum of
most emission lines is 1000-1200 km s$^{-1}$, with some extended blue wings.
The spectrum is thermal and consistent with a plasma in collisional ionization
equilibrium with column density 1.3 $\times 10^{22}$ cm$^{-2}$ and at least two
components at temperatures of about 1 keV and 4 keV, possibly a forward and a
reverse shock, or regions with differently mixed ejecta and red giant wind. The
spectrum is remarkably similar to the symbiotic RNe V745 Sco and RS Oph, but we
cannot distinguish whether the shocks occurred at a distance of few AU from the
red giant, or near the giant's photosphere, in a high density medium containing
only a small mass. The ratios of the flux in lines of aluminum, magnesium and
neon relative to the flux in lines of silicon and iron probably indicate a
carbon-oxygen white dwarf (CO WD).",2004.11263v2
2020-05-19,"ARES II: Characterising the Hot Jupiters WASP-127 b, WASP-79 b and WASP-62 b with HST","This paper presents the atmospheric characterisation of three large, gaseous
planets: WASP-127b, WASP-79b and WASP-62b. We analysed spectroscopic data
obtained with the G141 grism (1.088 - 1.68 $\mu$m) of the Wide Field Camera 3
(WFC3) onboard the Hubble Space Telescope (HST) using the Iraclis pipeline and
the TauREx3 retrieval code, both of which are publicly available. For WASP-127
b, which is the least dense planet discovered so far and is located in the
short-period Neptune desert, our retrieval results found strong water
absorption corresponding to an abundance of log(H$_2$O) =
-2.71$^{+0.78}_{-1.05}$, and absorption compatible with an iron hydride
abundance of log(FeH)=$-5.25^{+0.88}_{-1.10}$, with an extended cloudy
atmosphere. We also detected water vapour in the atmospheres of WASP-79 b and
WASP-62 b, with best-fit models indicating the presence of iron hydride, too.
We used the Atmospheric Detectability Index (ADI) as well as Bayesian log
evidence to quantify the strength of the detection and compared our results to
the hot Jupiter population study by Tsiaras et al. 2018. While all the planets
studied here are suitable targets for characterisation with upcoming facilities
such as the James Webb Space Telescope (JWST) and Ariel, WASP-127 b is of
particular interest due to its low density, and a thorough atmospheric study
would develop our understanding of planet formation and migration.",2005.09615v2
2020-05-29,"Cold, dry, windy, and UV irradiated -- surveying Mars relevant conditions in Ojos del Salado Volcano (Andes Mountains, Chile)","The Special Collection of papers in this issue of Astrobiology provide an
overview of the characteristics and potential for future exploration of the
Ojos del Salado volcano, located in the Andes Mountains in front of the Atacama
Desert in northern Chile. The main benefits of this site compared with others
are the combination of strong UV radiation, the presence of permafrost, and
geothermal activity within a dry terrain. The interaction between limited snow
events and wind results in snow patches buried under a dry soil surface. This
leads to ephemeral water streams that only flow duringdaytime hours. On this
volcano, which has the highest located subsurface temperature monitoring
systems reported to date, seasonal melting of the permafrost is followed by
fast percolation events. This is due to the high porosity of these soils. The
results are landforms that shaped by the strong winds. At this site, both
thermal springs and lakes (the latter arising from melting ice) provide
habitats for life; a 6480m high lake heated by volcanic activity shows both
warm and cold sediments that contain a number of different microbial species,
including psychrophiles. Where the permafrost melts, thawing ponds have formed
at 5900m that is dominated by populations of Bacteroidetes and Proteobacteria,
while in the pond sediments and the permafrost itself Acidobacteria,
Actinobacteria, Bacteroidetes, Patescibacteria, Proteobacteria, and
Verrucomicrobia are abundant. In turn, fumaroles show the presence of
acidophilic iron-oxidizers and iron-reducing species. In spite of the extreme
conditions reported at Ojos del Salado, this site is easily accessible.",2005.14450v1
2020-06-05,Chemically peculiar A and F stars with enhanced s-process and iron-peak elements: stellar radiative acceleration at work,"We present $\gtrsim 15,000$ metal-rich (${\rm [Fe/H]}>-0.2$dex) A and F stars
whose surface abundances deviate strongly from Solar abundance ratios and
cannot plausibly reflect their birth material composition. These stars are
identified by their high [Ba/Fe] abundance ratios (${\rm [Ba/Fe]}>1.0$dex) in
the LAMOST DR5 spectra analyzed by Xiang et al. (2019). They are almost
exclusively main sequence and subgiant stars with $T_{\rm eff}\gtrsim6300$K.
Their distribution in the Kiel diagram ($T_{\rm eff}$--$\log g$) traces a sharp
border at low temperatures along a roughly fixed-mass trajectory (around
$1.4M_\odot)$ that corresponds to an upper limit in convective envelope mass
fraction of around $10^{-4}$. Most of these stars exhibit distinctly enhanced
abundances of iron-peak elements (Cr, Mn, Fe, Ni) but depleted abundances of Mg
and Ca. Rotational velocity measurements from GALAH DR2 show that the majority
of these stars rotate slower than typical stars in an equivalent temperature
range. These characteristics suggest that they are related to the so-called
Am/Fm stars. Their abundance patterns are qualitatively consistent with the
predictions of stellar evolution models that incorporate radiative
acceleration, suggesting they are a consequence of stellar internal evolution
particularly involving the competition between gravitational settling and
radiative acceleration. These peculiar stars constitute 40% of the whole
population of stars with mass above 1.5$M_\odot$, affirming that ""peculiar""
photospheric abundances due to stellar evolution effects are a ubiquitous
phenomenon for these intermediate-mass stars. This large sample of Ba-enhanced
chemically peculiar A/F stars with individual element abundances provides the
statistics to test more stringently the mechanisms that alter the surface
abundances in stars with radiative envelopes.",2006.03329v1
2020-06-29,Impact of the returning radiation on the analysis of the reflection spectra of black holes,"A fraction of the electromagnetic radiation emitted from the surface of a
geometrically thin and optically thick accretion disk of a black hole returns
to the disk because of the strong light bending in the vicinity of the compact
object (returning radiation). While such radiation clearly affects the observed
spectrum of the source, it is often neglected in theoretical models. In the
present paper, we study the impact of the returning radiation on relativistic
reflection spectra. Assuming neutral material in the disk, we estimate the
systematic uncertainties on the measurement of the properties of the system
when we fit the data with a theoretical model that neglects the returning
radiation. Our NICER simulations show that the inclination angle of the disk
and the black hole spin parameter tend to be overestimated for low viewing
angles, while no clear bias is observed for high viewing angles. The iron
abundance of the disk is never overestimated. In the most extreme cases (in
particular, for maximally rotating black holes) the returning radiation
flattens the radial emissivity beyond a few gravitational radii. In such cases,
it also produces residuals that cannot be compensated by adjusting the
parameters of models neglecting the returning radiation. This may be an
important issue for interpretation of data from future X-ray missions (e.g.
Athena). When we simulate some observations with NuSTAR and we fit data above
10 keV, we find that some conclusions valid for the NICER simulations are not
true any longer (e.g., we can get a high iron abundance).",2006.15838v2
2020-07-02,Iron in X-COP: tracing enrichment in cluster outskirts with high accuracy abundance profiles,"We present the first metal abundance profiles for a representative sample of
massive clusters. Our measures extend to $R_{500}$ and are corrected for a
systematic error plaguing previous outskirt estimates. Our profiles flatten out
at large radii, admittedly not a new result, however the radial range and
representative nature of our sample extends its import well beyond previous
findings. We find no evidence of segregation between cool-core and
non-cool-core systems beyond $\sim 0.3 R_{500}$, implying that, as was found
for thermodynamic properties (Ghirardini et al, 2019), the physical state of
the core does not affect global cluster properties. Our mean abundance within
$R_{500}$ shows a very modest scatter, $< $15%, suggesting the enrichment
process must be quite similar in all these massive systems. This is a new
finding and has significant implications on feedback processes. Together with
results from thermodynamic properties presented in a previous X-COP paper, it
affords a coherent picture where feedback effects do not vary significantly
from one system to another. By combing ICM with stellar measurements we have
found the amount of Fe diffused in the ICM to be about ten times higher than
that locked in stars. Although our estimates suggest, with some strength, that
the measured iron mass in clusters is well in excess of the predicted one,
systematic errors prevent us from making a definitive statement. Further
advancements will only be possible when systematic uncertainties, principally
those associated to stellar masses, both within and beyond $R_{500}$, can be
reduced.",2007.01084v1
2020-07-21,Unveiling the Planet Population at Birth,"The radius distribution of small, close-in exoplanets has recently been shown
to be bimodal. The photoevaporation model predicted this bimodality. In the
photoevaporation scenario, some planets are completely stripped of their
primordial H/He atmospheres, whereas others retain them. Comparisons between
the photoevaporation model and observed planetary populations have the power to
unveil details of the planet population inaccessible by standard observations,
such as the core mass distribution and core composition. In this work, we
present a hierarchical inference analysis on the distribution of close-in
exoplanets using forward-models of photoevaporation evolution. We use this
model to constrain the planetary distributions for core composition, core mass
and initial atmospheric mass fraction. We find that the core-mass distribution
is peaked, with a peak-mass of $\sim 4$M$_\oplus$. The bulk core-composition is
consistent with a rock/iron mixture that is ice-poor and ``Earth-like''; the
spread in core-composition is found to be narrow ($\lesssim 16\%$ variation in
iron-mass fraction at the 2$\sigma$ level) and consistent with zero. This
result favours core formation in a water/ice poor environment. We find the
majority of planets accreted a H/He envelope with a typical mass fraction of
$\sim 4\%$; only a small fraction did not accrete large amounts of H/He and
were ``born-rocky''. We find four-times as many super-Earths were formed
through photoevaporation, as formed without a large H/He atmosphere. Finally,
we find core-accretion theory over-predicts the amount of H/He cores would have
accreted by a factor of $\sim 5$, pointing to additional mass-loss mechanisms
(e.g. ``boil-off'') or modifications to core-accretion theory.",2007.11006v2
2020-07-24,The Most Metal-poor Stars in the Inner Bulge,"The bulge is the oldest component of the Milky Way. Since numerous
simulations of Milky Way formation have predicted that the oldest stars at a
given metallicity are found on tightly bound orbits, the Galaxy's oldest stars
are likely metal-poor stars in the inner bulge with small apocenters (i.e.,
$R_{\mathrm{apo}}\lesssim4$ kpc). In the past, stars with these properties have
been impossible to find due to extreme reddening and extinction along the line
of sight to the inner bulge. We have used the mid-infrared metal-poor star
selection of Schlaufman & Casey (2014) on Spitzer/GLIMPSE data to overcome
these problems and target candidate inner bulge metal-poor giants for
moderate-resolution spectroscopy with AAT/AAOmega. We used those data to select
three confirmed metal-poor giants ($[\mathrm{Fe/H}]=-3.15,-2.56,-2.03$) for
follow-up high-resolution Magellan/MIKE spectroscopy. A comprehensive orbit
analysis using Gaia DR2 astrometry and our measured radial velocities confirms
that these stars are tightly bound inner bulge stars. We determine the
elemental abundances of each star and find high titanium and iron-peak
abundances relative to iron in our most metal-poor star. We propose that the
distinct abundance signature we detect is a product of nucleosynthesis in the
Chandrasekhar-mass thermonuclear supernova of a CO white dwarf accreting from a
helium star with a delay time of about 10 Myr. Even though chemical evolution
is expected to occur quickly in the bulge, the intense star formation in the
core of the nascent Milky Way was apparently able to produce at least one
Chandrasekhar-mass thermonuclear supernova progenitor before chemical evolution
advanced beyond $[\mathrm{Fe/H}]\sim-3$.",2007.12728v1
2021-02-01,Connecting the Light Curves of Type IIP Supernovae to the Properties of their Progenitors,"Observations of core-collapse supernovae (CCSNe) reveal a wealth of
information about the dynamics of the supernova ejecta and its composition but
very little direct information about the progenitor. Constraining properties of
the progenitor and the explosion requires coupling the observations with a
theoretical model of the explosion. Here, we begin with the CCSN simulations of
Couch et al 2020 ApJ 890 127, which use a non-parametric treatment of the
neutrino transport while also accounting for turbulence and convection. In this
work we use the SuperNova Explosion Code to evolve the CCSN hydrodynamics to
later times and compute bolometric light curves. Focusing on SNe IIP, we then
(1) directly compare the theoretical STIR explosions to observations and (2)
assess how properties of the progenitor's core can be estimated from optical
photometry in the plateau phase alone. First, the distribution of plateau
luminosities (L$_{50}$) and ejecta velocities achieved by our simulations is
similar to the observed distributions. Second, we fit our models to the light
curves and velocity evolution of some well-observed SNe. Third, we recover
well-known correlations, as well as the difficulty of connecting any one SN
property to zero-age main sequence mass. Finally, we show that there is a
usable, linear correlation between iron core mass and L$_{50}$ such that
optical photometry alone of SNe IIP can give us insights into the cores of
massive stars. Illustrating this by application to a few SNe, we find iron core
masses of 1.3-1.5 solar masses with typical errors of ~0.05 solar masses. Data
are publicly available online (\url{https://doi.org/10.5281/zenodo.6631964}).",2102.01118v2
2021-06-09,Turbulent transport of impurities in 3D devices,"A large diffusive turbulent contribution to the radial impurity transport in
Wendelstein 7-X (W7-X) plasmas has been experimentally inferred during the
first campaigns and numerically confirmed by means of gyrokinetic simulations
with the code stella. In general, the absence of strong impurity accumulation
during the initial W7-X campaigns is attributed to this diffusive term. In the
present work the diffusive contribution is also calculated in other stellarator
plasmas. In particular, the diffusion (D) and convection (V) coefficients of
carbon and iron impurities produced by ion-temperature-gradient (ITG)
turbulence are obtained for W7-X, LHD, TJ-II and NCSX. The results show that,
although the size of D and V can differ across the four devices, inward
convection is found for all of them. For W7-X, TJ-II and NCSX the two
coefficients are comparable and the turbulent peaking factor is surprisingly
similar. In LHD, appreciably weaker diffusive and convective impurity transport
and significantly larger turbulent peaking factor are predicted. All this
suggests that ITG turbulence, although not strongly, would lead to negative
impurity density gradients in stellarators. Then, considering mixed ITG/Trapped
Electron Mode (TEM) turbulence for the specific case of W7-X, it has been
quantitatively assessed to what degree pellet fueled reduced turbulence
scenarios feature reduced turbulent transport of impurities as well. The
results for trace iron impurities show that, although their turbulent transport
is not entirely suppressed, a significant reduction of V and a stronger
decrease of D are found. Although the diffusion is still above neoclassical
levels, the neoclassical convection would gain under such conditions a greater
specific weight on the dynamics of impurities in comparison with standard ECRH
scenarios.",2106.05017v2
2021-06-21,Correlations Among STM Observables in Disordered Unconventional Superconductors,"New developments in scanning tunneling spectroscopy now allow for the
spatially resolved measurement of the Josephson critical current $I_c$ between
a tip and a superconducting sample, a nearly direct measurement of the true
superconducting order parameter. However, it is unclear how these $I_c$
measurements are correlated with previous estimates of the spectral gap taken
from differential conductance measurements. In particular, recent such
experiments on an iron-based superconductor found almost no correlation between
$I_c$ and the spectral gap obtained from differential conductance $g=dI/dV$
spectra, reporting instead a more significant correlation between $I_c$ and the
the coherence-peak height. Here we point out that the correlation--or the lack
thereof--between these various quantities can be naturally explained by the
effect of disorder on unconventional superconductivity. Using large scale
numerical simulations of a BCS $d$-wave pair Hamiltonian with many-impurity
potentials, we observe that ""substitutional"" disorder models with weak
pointlike impurities lead to a situation in which the true superconducting
order parameter and $I_c$ are both uncorrelated with the spectral gap from
$dI/dV$ measurements and highly correlated with the coherence-peak heights. The
underlying mechanism appears to be the disorder-induced transfer of spectral
weight away from the coherence peaks. On the other hand, smooth impurity
potentials with a length scale larger than the lattice constant lead to a large
positive correlation between the true superconducting order parameter and the
spectral gap, in addition to a large correlation between the order parameter
and the coherence-peak height. We discuss the applicability of our results to
recent Josephson scanning tunneling spectroscopy experiments on iron-based and
cuprate high-temperature superconductors.",2106.11091v2
2021-06-24,X-ray Emission of the $γ$-ray Loud Young Radio Galaxy NGC 3894,"The radio source 1146+596 is hosted by an elliptical/S0 galaxy NGC\,3894,
with a low-luminosity active nucleus. The radio structure is compact,
suggesting a very young age of the jets in the system. Recently, the source has
been confirmed as a high-energy (HE, $>0.1$\,GeV) $\gamma$-ray emitter, in the
most recent accumulation of the {\it Fermi} Large Area Telescope (LAT) data.
Here we report on the analysis of the archival {\it Chandra} X-ray Observatory
data for the central part of the galaxy, consisting of a single 40\,ksec-long
exposure. We have found that the core spectrum is best fitted by a combination
of an ionized thermal plasma with the temperature of $\simeq 0.8$\,keV, and a
moderately absorbed power-law component (photon index $\Gamma = 1.4\pm 0.4$,
hydrogen column density $N_{\rm H}/10^{22}$\,cm$^{-2}$\,$= 2.4\pm 0.7$). We
have also detected the iron K$\alpha$ line at $6.5\pm 0.1$\,keV, with a large
equivalent width of EW\,$= 1.0_{-0.5}^{+0.9}$\,keV. Based on the simulations of
the {\it Chandra}'s Point Spread Function (PSF), we have concluded that, while
the soft thermal component is extended on the scale of the galaxy host, the
hard X-ray emission within the narrow photon energy range 6.0--7.0\,keV
originates within the unresolved core (effectively the central kpc radius). The
line is therefore indicative of the X-ray reflection from a cold neutral gas in
the central regions of NGC\,3894. We discuss the implications of our findings
in the context of the X-ray Baldwin effect. NGC\,3894 is the first young radio
galaxy detected in HE $\gamma$-rays with the iron K$\alpha$ line.",2106.13193v2
2021-06-30,The Inhomogeneity of Composition along the Magnetic Cloud Axis,"It is generally accepted that CMEs result from eruptions of magnetic flux
ropes, which are dubbed as magnetic clouds in interplanetary space. The
composition (including the ionic charge states and elemental abundances) is
determined prior to and/or during CME eruptions in the solar atmosphere, and
does not alter during magnetic cloud propagation to 1 AU and beyond. It has
been known that the composition is not uniform within a cross section
perpendicular to magnetic cloud axis, and the distribution of ionic charge
states within a cross section provides us an important clue to investigate the
formation and eruption processes of flux ropes due to the freeze-in effect. The
flux rope is a three dimensional magnetic structure intrinsically, and it
remains unclear whether the composition is uniform along the flux rope axis as
most magnetic clouds are only detected by one spacecraft. In this paper we
report a magnetic cloud that was observed by ACE near 1 AU on 1998 March 4--6
and Ulysses near 5.4 AU on March 24--28 sequentially. At these times, both
spacecraft were located around the ecliptic plane, and the latitudinal and
longitudinal separations between them were $\sim$2.2$^{\circ}$ and
$\sim$5.5$^{\circ}$, respectively. It provides us an excellent opportunity to
explore the axial inhomogeneity of flux rope composition, as both spacecraft
almost intersected the cloud center at different sites along its axis. Our
study shows that the average values of ionic charge states exhibit significant
difference along the axis for carbon, and the differences are relatively slight
but still obvious for charge states of oxygen and iron, as well as the
elemental abundances of iron and helium. Besides the means, the composition
profiles within the cloud measured by both spacecraft also exhibit some
discrepancies. We conclude that the inhomogeneity of composition exists along
the cloud axis.",2106.15834v1
2021-06-30,Spectroscopy and photometry of the least-massive Type-II globular clusters: NGC1261 AND NGC6934,"Recent work has revealed two classes of Globular Clusters (GCs), dubbed
Type-I and Type-II. Type-II GCs are characterized by a blue- and a red- red
giant branch composed of stars with different metallicities, often coupled with
distinct abundances in the slow-neutron capture elements (s-elements). Here we
continue the chemical tagging of Type-II GCs by adding the two least-massive
clusters of this class, NGC1261 and NGC6934. Based on both spectroscopy and
photometry, we find that red stars in NGC1261 are slightly enhanced in [Fe/H]
by ~0.1 dex and confirm that red stars of NGC 6934 are enhanced in iron by ~0.2
dex. Neither NGC1261 nor NGC6934 show internal variations in the s-elements,
which suggests a GC mass threshold for the occurrence of s-process enrichment.
We found a significant correlation between the additional Fe locked in the red
stars of Type-II GCs and the present-day mass of the cluster. Nevertheless,
most Type II GCs retained a small fraction of Fe produced by SNe II, lower than
the 2%; NGC6273, M54 and omega Centauri are remarkable exceptions. In the
appendix, we infer for the first time chemical abundances of Lanthanum, assumed
as representative of the s-elements, in M54, the GC located in the nucleus of
the Sagittarius dwarf galaxy. Red-sequence stars are marginally enhanced in
[La/Fe] by 0.10\pm0.06 dex, in contrast with the large [La/Fe] spread of most
Type II GCs. We suggest that different processes are responsible for the
enrichment in iron and s-elements in Type-II GCs.",2106.15978v1
2021-07-02,Ti I lines at 2.2 $μ$m as probes of the cool parts of sunspots,"The sunspot umbra harbors the coolest plasma on the solar surface due to the
presence of strong magnetic fields. The routinely used atomic lines to observe
the photosphere have weak signals in the umbra and are often swamped by
molecular lines. This makes it harder to infer the properties of the umbra,
especially in the darkest regions. The lines of the Ti I multiplet at 2.2
$\mu$m are formed mainly at temperatures $\le\!4500$ K and are not known to be
affected by molecular blends in sunspots. Since the first systematic
observations in the 1990's, these lines have been seldom observed due to the
instrumental challenges involved at these longer wavelengths. We revisit these
lines and investigate their formation in different solar features. We
synthesize the Ti I multiplet using a snapshot from 3D MHD simulation of a
sunspot and explore the properties of two of its lines in comparison with two
commonly used iron lines at 630.25 nm and $1.5648\,\mu$m. We find that the Ti I
lines have stronger signals than the Fe I lines in both intensity and
polarization in the sunspot umbra and in penumbral spines. They have little to
no signal in the penumbral filaments and the quiet Sun, at $\mu=1$. Their
strong and well-split profiles in the dark umbra are less affected by stray
light. Consequently, inside the sunspot it is easier to invert these lines and
to infer the atmospheric properties, compared to the iron lines. The Cryo-NIRSP
instrument at the DKIST will provide the first ever high resolution
observations in this wavelength range. In this preparatory study, we
demonstrate the unique temperature and magnetic sensitivities of the Ti
multiplet, by probing the Sun's coolest regions which are not favourable for
the formation of other commonly used spectral lines. We thus expect such
observations to advance our understanding of sunspot properties.",2107.01247v1
2022-07-23,Data Adaptive Regularization for Abdominal Quantitative Susceptibility Mapping,"Purpose: To improve repeatability and reproducibility across acquisition
parameters and reduce bias in quantitative susceptibility mapping (QSM) of the
liver, through development of an optimized regularized reconstruction algorithm
for abdominal QSM.
  Theory and Methods: An optimized approach to estimation of magnetic
susceptibility distribution is formulated as a constrained reconstruction
problem that incorporates estimates of the input data reliability and
anatomical priors available from chemical shift-encoded imaging. The proposed
data-adaptive method was evaluated with respect to bias, repeatability, and
reproducibility in a patient population with a wide range of liver iron
concentration (LIC). The proposed method was compared to the state-of-the-art
approach in liver QSM for two multi-echo SGRE protocols with different
acquisition parameters at 3T.
  Results: The data-adaptive method produced susceptibility maps with higher
subjective quality due to reduced shading artifacts. For both acquisition
protocols, higher linear correlation with both $R_2$ and $R_2^*$-based
measurements were observed for the data-adaptive method ($r^2=0.74/0.72$ for
$R_2$, $0.98/0.99$ for $R_2^*$) than the standard method ($r^2=0.62/0.67$ and
$0.84/0.91$). For both protocols, the data-adaptive method enabled better
test-retest repeatability (repeatability coefficients 0.14/0.14ppm for the
data-adaptive method, 0.26/0.31ppm for the standard method) and reproducibility
across protocols (reproducibility coefficient 0.25ppm vs 0.36ppm) than the
standard method.
  Conclusions: The proposed data-adaptive QSM algorithm may enable
quantification of liver iron concentration with improved
repeatability/reproducibility across different acquisition parameters as 3T.",2207.11416v1
2022-07-27,The breakdown of both strange metal and superconducting states at a pressure-induced quantum critical point in iron-pnictide superconductors,"The strange metal (SM) state, characterized by a linear-in-temperature
resistivity, is often seen in the normal state of high temperature
superconductors. It is believed that the SM state is one of the keys to
understand the underlying mechanism of high-Tc superconductivity. Here we
report the first observation of the concurrent breakdown of the SM normal state
and superconductivity at a pressure-induced quantum critical point in an
iron-pnictide superconductor, Ca10(Pt4As8)((Fe0.97Pt0.03)2As2)5. We find that,
upon suppressing the superconducting state by applying pressure, the power
exponent changes from 1 to 2, and the corresponding coefficient A, the slope of
the temperature-linear resistivity per FeAs layer, gradually diminishes. At a
critical pressure (12.5 GPa), A and Tc go to zero concurrently,where a quantum
phase transition (QPT) from a superconducting state with a SM normal state to a
non-superconducting Fermi liquid state takes place. Scaling analysis on the
results obtained from the pressurized 1048 superconductor reveals that A and Tc
have a positive relation, which exhibits a similarity with that is seen in
other chemically-doped unconventional superconductors, regardless of the type
of the tuning method (doping or pressurizing), the crystal structure, the bulk
or film superconductors and the nature of dopant. These results suggest that
there is a simple but powerful organizational principle of connecting the SM
normal state with the high-Tc superconductivity.",2207.13272v2
2017-05-29,Baby MIND: A magnetized segmented neutrino detector for the WAGASCI experiment,"T2K (Tokai-to-Kamioka) is a long-baseline neutrino experiment in Japan
designed to study various parameters of neutrino oscillations. A near detector
complex (ND280) is located 280~m downstream of the production target and
measures neutrino beam parameters before any oscillations occur. ND280's
measurements are used to predict the number and spectra of neutrinos in the
Super-Kamiokande detector at the distance of 295~km. The difference in the
target material between the far (water) and near (scintillator, hydrocarbon)
detectors leads to the main non-cancelling systematic uncertainty for the
oscillation analysis. In order to reduce this uncertainty a new
WAter-Grid-And-SCintillator detector (WAGASCI) has been developed. A magnetized
iron neutrino detector (Baby MIND) will be used to measure momentum and charge
identification of the outgoing muons from charged current interactions. The
Baby MIND modules are composed of magnetized iron plates and long plastic
scintillator bars read out at the both ends with wavelength shifting fibers and
silicon photomultipliers. The front-end electronics board has been developed to
perform the readout and digitization of the signals from the scintillator bars.
Detector elements were tested with cosmic rays and in the PS beam at CERN. The
obtained results are presented in this paper.",1705.10406v3
2017-06-15,"$η$ Carinae's Dusty Homunculus Nebula from Near-Infrared to Submillimeter Wavelengths: Mass, Composition, and Evidence for Fading Opacity","Infrared observations of the dusty, massive Homunculus Nebula around the
luminous blue variable $\eta$ Carinae are crucial to characterize the mass-loss
history and help constrain the mechanisms leading to the Great Eruption. We
present the 2.4 - 670 $\mu$m spectral energy distribution, constructed from
legacy ISO observations and new spectroscopy obtained with the {\em{Herschel
Space Observatory}}. Using radiative transfer modeling, we find that the two
best-fit dust models yield compositions which are consistent with CNO-processed
material, with iron, pyroxene and other metal-rich silicates, corundum, and
magnesium-iron sulfide in common. Spherical corundum grains are supported by
the good match to a narrow 20.2 $\mu$m feature. Our preferred model contains
nitrides AlN and Si$_3$N$_4$ in low abundances. Dust masses range from 0.25 to
0.44 $M_\odot$ but $M_{\rm{tot}} \ge$ 45 $M_\odot$ in both cases due to an
expected high Fe gas-to-dust ratio. The bulk of dust is within a 5$""$ $\times$
7$""$ central region. An additional compact feature is detected at 390 $\mu$m.
We obtain $L_{\rm{IR}}$ = 2.96 $\times$ 10$^6$ $L_\odot$, a 25\% decline from
an average of mid-IR photometric levels observed in 1971-1977. This indicates a
reduction in circumstellar extinction in conjunction with an increase in visual
brightness, allowing 25-40\% of optical and UV radiation to escape from the
central source. We also present an analysis of $^{12}$CO and $^{13}$CO $J =
5-4$ through $9-8$ lines, showing that the abundances are consistent with
expectations for CNO-processed material. The [$^{12}$C~{\sc{ii}}] line is
detected in absorption, which we suspect originates in foreground material at
very low excitation temperatures.",1706.05112v1
2017-06-29,"X-shooter spectroscopy of young stellar objects in Lupus: Lithium, iron, and barium elemental abundances","With the purpose of performing a homogeneous determination of elemental
abundances for members of the Lupus T association, we analyzed three chemical
elements: lithium, iron, and barium. The aims were: to derive the Li abundance
for ~90% of known class II stars in the Lupus I, II, III, IV clouds; to perform
chemical tagging of a region where few Fe abundance measurements have been
obtained in the past, and no determination of the Ba content has been done up
to now. We also investigated possible Ba enhancement, as this element has
become increasingly interesting in the last years following the evidence of Ba
over-abundance in young clusters, the origin of which is still unknown. Using
X-shooter@VLT, we analyzed the spectra of 89 cluster members, both class II and
III stars. We measured the strength of the Li line and derived the abundance of
this element through equivalent width measurements and curves of growth. For
six class II stars we also measured the Fe and Ba abundances using the spectral
synthesis and the code MOOG. The veiling contribution was taken into account
for all three elements. We find a dispersion in the strength of the Li line at
low Teff and identify three targets with severe Li depletion. The nuclear age
inferred for these highly Li-depleted stars is around 15 Myr, which exceeds the
isochronal one. As in other star-forming regions, no metal-rich members are
found in Lupus, giving support to a recent hypothesis that the Fe abundance
distribution of most of the nearby young regions could be the result of a
common and widespread star formation episode involving the Galactic thin disk.
We find that Ba is over-abundant by ~0.7 dex with respect to the Sun. Since
current theoretical models cannot reproduce this Ba abundance pattern, we
investigated whether this unusually large Ba content might be related to
effects due to stellar parameters, stellar activity, and accretion.",1706.09684v1
2018-02-02,Spectral Evidence for Amorphous Silicates in Least-processed CO Meteorites and Their Parent Bodies,"Least-processed carbonaceous chondrites (carbonaceous chondrites that have
experienced minimal aqueous alteration and thermal metamorphism) are
characterized by their predominately amorphous iron-rich silicate
interchondrule matrices and chondrule rims. The presence of abundant amorphous
material in a meteorite indicates that the parent body, or at least a region of
the parent body, experienced minimal processing since the time of accretion.
The CO chemical group of carbonaceous chondrites has a significant number of
these least-processed samples. We present visible/near-infrared and
mid-infrared spectra of eight least-processed CO meteorites (petrologic type
3.0-3.1). In the visible/near-infrared, these COs are characterized by a broad
weak feature that was first observed by Cloutis et al. (2012) to be at 1.3-um
and attributed to iron-rich amorphous silicate matrix materials. This feature
is observed to be centered at 1.4-um for terrestrially unweathered,
least-processed CO meteorites. At mid-infrared wavelengths, a 21-um feature,
consistent with Si-O vibrations of amorphous materials and glasses, is also
present. This spectral signature is absent in both the near- and mid-infrared
spectra of higher metamorphic grade COs because this material has
recrystallized as crystalline olivine. Furthermore, spectra of least-processed
primitive meteorites from other chemical groups (CRs, MET 00426 and QUE 99177,
and C2-ungrouped Acfer 094), also exhibit a 21-um feature. Thus, we conclude
that the 1.4- and 21-umm features are characteristic of primitive
least-processed meteorites from all chemical groups of carbonaceous chondrites.
Finally, we present an IRTF+SPeX observation of asteroid (93) Minerva that has
spectral similarities in the visible/near-infrared to the least-processed CO
carbonaceous chondrites. Minerva is likely the least-processed CO-like asteroid
observed to date.",1802.00830v1
2018-02-08,Orbital Origin of Extremely Anisotropic Superconducting Gap in Nematic Phase of FeSe Superconductor,"The iron-based superconductors are characterized by multiple-orbital physics
where all the five Fe 3$d$ orbitals get involved. The multiple-orbital nature
gives rise to various novel phenomena like orbital-selective Mott transition,
nematicity and orbital fluctuation that provide a new route for realizing
superconductivity. The complexity of multiple-orbital also asks to disentangle
the relationship between orbital, spin and nematicity, and to identify dominant
orbital ingredients that dictate superconductivity. The bulk FeSe
superconductor provides an ideal platform to address these issues because of
its simple crystal structure and unique coexistence of superconductivity and
nematicity. However, the orbital nature of the low energy electronic
excitations and its relation to the superconducting gap remain controversial.
Here we report direct observation of highly anisotropic Fermi surface and
extremely anisotropic superconducting gap in the nematic state of FeSe
superconductor by high resolution laser-based angle-resolved photoemission
measurements. We find that the low energy excitations of the entire hole pocket
at the Brillouin zone center are dominated by the single $d_{xz}$ orbital. The
superconducting gap exhibits an anti-correlation relation with the $d_{xz}$
spectral weight near the Fermi level, i.e., the gap size minimum (maximum)
corresponds to the maximum (minimum) of the $d_{xz}$ spectral weight along the
Fermi surface. These observations provide new insights in understanding the
orbital origin of the extremely anisotropic superconducting gap in FeSe
superconductor and the relation between nematicity and superconductivity in the
iron-based superconductors.",1802.02940v1
2018-02-13,Probing the use of spectroscopy to determine the meteoritic analogues of meteors,"Determining the source regions of meteorites is one of the major goals of
current research in planetary science. Whereas asteroid observations are
currently unable to pinpoint the source regions of most meteorite classes,
observations of meteors with camera networks and the subsequent recovery of the
meteorite may help make progress on this question. The main caveat of such an
approach, however, is that the recovery rate of meteorite falls is low,
implying that the meteoritic analogues of at least 80% of the observed falls
remain unknown.
  Aims: Spectroscopic observations of bolides may have the potential to
mitigate this problem by classifying the incoming material.
  Methods: To probe the use of spectroscopy to determine the meteoritic
analogues of bolides, we collected emission spectra in the visible range
(320-880nm) of five meteorite types (H,L,LL,CM,eucrite) acquired in atmospheric
entry-like conditions in a plasma wind tunnel at the University of Stuttgart
(Germany). A detailed spectral analysis including line identification and mass
ratio determinations (Mg/Fe,Na/Fe) was subsequently performed on all spectra.
  Results: Spectroscopy, via a simple line identification, allows us to
distinguish the main meteorite classes (chondrites, achondrites and irons) but
does not have the potential to distinguish for example an H from a CM
chondrite.
  Conclusions: The source location within the main belt of the different
meteorite classes (H, L, LL, CM, etc.) should continue to be investigated via
fireball observation networks. Spectroscopy of incoming bolides only marginally
helps precisely classify the incoming material (iron meteorites only). To reach
a statistically significant sample of recovered meteorites along with accurate
orbits (>100) within a reasonable time frame (10-20 years), the optimal
solution may be the spatial extension of existing fireball observation
networks.",1802.04699v2
2018-02-14,Hydrodynamical Neutron-star Kicks in Electron-capture Supernovae and Implications for the CRAB Supernova,"Neutron stars (NSs) obtain kicks of typically several 100 km/s at birth. The
gravitational tug-boat mechanism can explain these kicks as consequences of
asymmetric mass ejection during the supernova (SN) explosion. Support for this
hydrodynamic explanation is provided by observations of SN remnants with
associated NSs, which confirm the prediction that the bulk of the explosion
ejecta, in particular chemical elements between silicon and the iron group, are
dominantly expelled in the hemisphere opposite to the direction of the NS kick.
Here, we present a large set of two- and three-dimensional explosion
simulations of electron-capture SNe, considering explosion energies between
~3x10^49 erg and ~1.6x10^50 erg. We find that the fast acceleration of the SN
shock in the steep density gradient delimiting the O-Ne-Mg core of the
progenitor enables such a rapid expansion of neutrino-heated matter that the
growth of neutrino-driven convection freezes out quickly in a high-mode
spherical harmonics pattern. Since the corresponding momentum asymmetry of the
ejecta is very small and the gravitational acceleration by the fast-expanding
ejecta abates rapidly, the NS kick velocities are at most a few km/s. The
extremely low core compactness of O-Ne-Mg-core progenitors therefore favors
hydrodynamic NS kicks much below the ~160 km/s measured for the Crab pulsar.
This suggests either that the Crab Nebula is not the remnant of an
electron-capture SN, but of a low-mass iron-core progenitor, or that the Crab
pulsar was not accelerated by the gravitational tug-boat mechanism but received
its kick by a non-hydrodynamic mechanism such as, e.g., anisotropic neutrino
emission.",1802.05274v2
2018-02-21,Can the relativistic light bending model explain X-ray spectral variations of Seyfert galaxies?,"Many Seyfert galaxies are known to exhibit Fe-K broad emission line features
in their X-ray energy spectra. The observed lines have three distinct features;
(1) the line profiles are skewed and show significant low-energy tails, (2) the
Fe-K band have low variability, which produces a broad and deep dip in the
root-mean-square (rms) spectra, and (3) photons in this band have time lags
behind those in the adjacent energy bands with amplitudes of several $R_g/c$,
where $R_g$ is the gravitational radius. The ""relativistic light bending model""
is proposed to explain these observed features, where a compact X-ray source
(lamp post) above an extreme Kerr black hole illuminates the innermost area of
the accretion disc. In this paper, we critically examine the relativistic light
bending model by computing the rms spectra and the lag features using a
ray-tracing technique, when a lamp post moves vertically on the black hole spin
axis. As a result, we found that the observed deep rms dip requires that the
iron is extremely overabundant ($\gtrsim10$ solar), whereas the observed lag
amplitude is consistent with the normal iron abundance. Furthermore,
disappearance of the lag in the high-flux state requires a source height as
high as $\sim40\,R_g$, which contradicts the relativistically broad emission
line feature. Our simulations agree with the data that the reverberation
feature moves to lower frequencies with larger source height, however, if this
scenario is correct, the simulations predict detection of a clear Fe-K lag at
low frequencies, which is not constrained in the data. Therefore, we conclude
that the relativistic light bending model may not explain the characteristic
Fe-K spectral variations in Seyfert galaxies.",1802.07554v2
2018-02-21,Broad absorption line symbiotic stars: highly ionized species in the fast outflow from MWC 560,"In symbiotic binaries, jets and disk winds may be integral to the physics of
accretion onto white dwarfs from cool giants. The persistent outflow from
symbiotic star MWC 560 (=V694 Mon) is known to manifest as broad absorption
lines (BALs), most prominently at the Balmer transitions. We report the
detection of high-ionization BALs from C IV, Si IV, N V, and He II in
International Ultraviolet Explorer spectra obtained on 1990 April 29-30, when
an optical outburst temporarily erased the obscuring 'iron curtain' of
absorption troughs from Fe II and similar ions. The C IV and Si IV BALs reached
maximum radial velocities at least 1000 km/s higher than contemporaneous Mg II
and He II BALs; the same behaviors occur in the winds of quasars and
cataclysmic variables. An iron curtain lifts to unveil high-ionization BALs
during the P Cygni phase observed in some novae, suggesting by analogy a
temporary switch in MWC 560 from persistent outflow to discrete mass ejection.
At least three more symbiotic stars exhibit broad absorption with blue edges
faster than 1500 km/s; high-ionization BALs have been reported in AS 304
(=V4018 Sgr), while transient Balmer BALs have been reported in Z And and CH
Cyg. These BAL-producing fast outflows can have wider opening angles than has
been previously supposed. BAL symbiotics are short-timescale laboratories for
their giga-scale analogs, broad absorption line quasars (BALQSOs), which
display a similarly wide range of ionization states in their winds.",1802.07743v2
2018-02-28,Late metal-silicate separation on the IAB parent asteroid: Constraints from combined W and Pt isotopes and thermal modelling,"The short-lived $^{182}$Hf-$^{182}$W decay system is a powerful chronometer
for constraining the timing of metal-silicate separation and core formation in
planetesimals and planets. Neutron capture effects on W isotopes, however,
significantly hamper the application of this tool. In order to correct for
neutron capture effects, Pt isotopes have emerged as a reliable in-situ neutron
dosimeter. This study applies this method to IAB iron meteorites, in order to
constrain the timing of metal segregation on the IAB parent body. The
$\epsilon^{182}$W values obtained for the IAB iron meteorites range from -3.61
$\pm$ 0.10 to -2.73 $\pm$ 0.09. Correlating $\epsilon^{\mathrm{i}}$Pt with
$^{182}$W data yields a pre-neutron capture $^{182}$W of -2.90 $\pm$ 0.06. This
corresponds to a metal-silicate separation age of 6.0 $\pm$ 0.8 Ma after CAI
for the IAB parent body, and is interpreted to represent a body-wide melting
event. Later, between 10 and 14 Ma after CAI, an impact led to a catastrophic
break-up and subsequent reassembly of the parent body. Thermal models of the
interior evolution that are consistent with these estimates suggest that the
IAB parent body underwent metal-silicate separation as a result of internal
heating by short-lived radionuclides and accreted at around 1.4 $\pm$ 0.1 Ma
after CAIs with a radius of greater than 60 km.",1802.10421v1
2018-07-05,V902 Monocerotis: a likely disc-accreting intermediate polar,"Aims: We aim to confirm whether the eclipsing cataclysmic variable V902 Mon
is an Intermediate Polar, to characterise its X-ray spectrum and flux, and to
refine its orbital ephemeris and spin period. Methods: We performed
spectrographic observations of V902 Mon in 2016 with the 2.2m Calar Alto
telescope, and X-ray photometry and spectroscopy with XMM-Newton in October
2017. This data was supplemented by several years of AAVSO visual photometry.
Results: We have confirmed V902 Mon as an IP based on detecting the spin
period, with a value of 2,208s, at multiple epochs. Spectroscopy of the donor
star and Gaia parallax yield a distance of 3.5+1.3-0.9, kpc, suggesting an
X-ray luminosity one or two orders of magnitude lower than the 10^33 erg/s
typical of previously known IPs. The X-ray to optical flux ratio is also very
low. The inclination of the system is more than 79deg, with a most likely value
of around 82deg. We have refined the eclipse ephemeris, stable over 14,000
cycles. The Halpha line is present throughout the orbital cycle and is clearly
present during eclipse, suggesting an origin distant from the white dwarf, and
shows radial velocity variations at the orbital period. The amplitude and
overall recessional velocity seem inconsistent with an origin in the disc. The
\emph{XMM-Newton} observation reveals a partially absorbed plasma model typical
of magnetic CVs, with a fluorescent iron line at 6.4keV showing a large
equivalent width of 1.4keV. Conclusions: V902 Mon is an IP, and probably a
member of the hypothesized X-ray underluminous class of IPs. It is likely to be
a disc accretor, though the radial velocity behaviour of the Halpha line
remains puzzling. The large equivalent width of the fluorescent iron line, the
small FX/Fopt ratio, and the only marginal detection of X-ray eclipses suggests
that the X-ray emission arises from scattering.",1807.01981v1
2018-07-05,"Mineralogy, structure and habitability of carbon-enriched rocky exoplanets: A laboratory approach","Carbon-enriched rocky exoplanets have been proposed around dwarf stars as
well as around binary stars, white dwarfs and pulsars. However, the
mineralogical make up of such planets is poorly constrained. We performed
high-pressure high-temperature laboratory experiments ($P$ = 1$-$2 GPa, $T$ =
1523$-$1823 K) on carbon-enriched chemical mixtures to investigate the deep
interiors of Pluto- to Mars-size planets the upper mantles of larger planets.
  Our results show that these exoplanets, when fully-differentiated, comprise a
metallic core, a silicate mantle and a graphite layer on top of the silicate
mantle. The silicate mineralogy (olivine, orthopyroxene, clinopyroxene and
spinel) is largely unaffected by the amount of carbon. Metals are either two
immiscible iron-rich alloys (S-rich and S-poor) or a single iron-rich alloy in
the Fe-C-S system with immiscibility depending on the S/Fe ratio and core
pressure. Graphite is the dominant carbon-bearing phase at the conditions of
our experiments with no traces of silicon carbide or carbonates. If the bulk
carbon content is higher than needed to saturate the mantle and the core,
graphite would be in the form of an additional layer on top of the silicate
mantle assuming differentiation. For a thick enough graphite layer, diamonds
would form at the bottom of this layer due to high pressures.
  We model the interior structure of Kepler-37b and show that a mere 10 wt%
graphite layer would decrease its derived mass by 7%, suggesting future space
missions that determine both radius and mass of rocky exoplanets with
insignificant gaseous envelopes could provide quantitative limits on their
carbon content. Future observations of rocky exoplanets with graphite-rich
surfaces would show low albedos due to the low reflectance of graphite. The
absence of life-bearing elements other than carbon on the surface likely makes
them uninhabitable.",1807.02064v2
2018-07-10,X-shooting GRBs at high redshift: probing dust production history,"Evolved asymptotic giant branch (AGB) stars and Type Ia supernovae (SNe) are
important contributors to the elements that form dust in the interstellar
medium of galaxies, in particular, carbon and iron. However, they require at
least a Gyr to start producing these elements, therefore, a change in dust
quantity or properties may appear at high redshifts. In this work, we use
extinction of gamma-ray burst (GRB) afterglows as a tool to look for variations
in dust properties at z>3. We use a spectroscopically selected sample of GRB
afterglows observed with the VLT/X-shooter instrument to determine extinction
curves out to high redshifts. We present ten new z>3 X-shooter GRBs of which
six are dusty. Combining these with individual extinction curves of three
previously known z>3 GRBs, we find an average extinction curve consistent with
the SMC-Bar. A comparison with spectroscopically selected GRBs at all redshifts
indicates a drop in visual extinction (A_V) at z>3.5 with no moderate or high
extinction bursts. We check for observational bias using template spectra and
find that GRBs up to z~8 are detectable with X-shooter up to A_V~0.3 mag.
Although other biases are noted, a uniformly low dust content above z>3.5
indicates a real drop, suggesting a transition in dust properties and/or
available dust building blocks. The remarkable increase in dust content at
z<3.5 could arise due to carbon and possibly iron production by the first
carbon-rich AGB and Type Ia SNe, respectively. Alternatively, z>3.5 dust drop
could be the result of low stellar masses of GRB host galaxies.",1807.03597v1
2018-07-18,Optical dimming of RW Aur associated with an iron rich corona and exceptionally high absorbing column density,"RW Aur is a binary system composed of two young, low-mass stars. The primary,
RW Aur A, has undergone visual dimming events ($\Delta V =2-3$~mag) in 2011,
2014-16, and 2017-2018. Visual and IR observations indicate a gray absorber
that moved into the line-of-sight. This dimming is also associated with changes
in the outflow. In 2017, when the optical brightness was almost 2~mag below the
long-term average we triggered a Chandra observation to measure the absorbing
column density $N_\mathrm{H}$ and to constrain dust properties and the
gas-to-dust ratio of the absorber. In 2017, the X-ray spectrum is more absorbed
than it was in the optically bright state ($N_\mathrm{H} = (4\pm 1) \times
10^{23}\;\mathrm{cm}^{-2}$) and shows significantly more hot plasma than in
X-ray observations taken before. Also, a new emission feature at $6.63\pm0.02$
keV (statistic) $\pm0.02$ keV (systematic) appeared indicating an Fe abundance
an order of magnitude above Solar, in contrast with previous sub-Solar Fe
abundance measurements. Comparing X-ray absorbing column density $N_\mathrm{H}$
and optical extinction $A_V$, we find that either the gas-to-dust ratio in the
absorber is orders of magnitude higher than in the ISM or the absorber has
undergone significant dust evolution. Given the high column density coupled
with changes in the X-ray spectral shape, this absorber is probably located in
the inner disk. We speculate that a break-up of planetesimals or a terrestrial
planet could supply large grains causing gray absorption; some of these grains
would be accreted and enrich the stellar corona with iron which could explain
the inferred high abundance.",1807.06995v1
2018-07-25,APOGEE Data Releases 13 and 14: Stellar Parameter and Abundance Comparisons With Independent Analyses,"Data from the SDSS-IV / Apache Point Observatory Galactic Evolution
Experiment (APOGEE-2) have been released as part of SDSS Data Releases 13
(DR13) and 14 (DR14). These include high resolution H-band spectra, radial
velocities, and derived stellar parameters and abundances. DR13, released in
August 2016, contained APOGEE data for roughly 150,000 stars, and DR14,
released in August 2017, added about 110,000 more. Stellar parameters and
abundances have been derived with an automated pipeline, the APOGEE Stellar
Parameter and Chemical Abundance Pipeline (ASPCAP). We evaluate the performance
of this pipeline by comparing the derived stellar parameters and abundances to
those inferred from optical spectra and analysis for several hundred stars. For
most elements -- C, Na, Mg, Al, Si, S, Ca, Cr, Mn, Ni -- the DR14 ASPCAP
analysis have systematic differences with the comparisons samples of less than
0.05 dex (median), and random differences of less than 0.15 dex (standard
deviation). These differences are a combination of the uncertainties in both
the comparison samples as well as the ASPCAP-analysis. Compared to the
references, magnesium is the most accurate alpha-element derived by ASPCAP, and
shows a very clear thin/thick disk separation, while nickel is the most
accurate iron-peak element (besides iron).",1807.09784v1
2018-08-01,Nebular-phase spectra of superluminous supernovae: physical insights from observational and statistical properties,"We study the spectroscopic evolution of superluminous supernovae (SLSNe)
later than 100 days after maximum light. We present new data for Gaia16apd and
SN2017egm, and analyse these with a larger sample comprising 41 spectra of 12
events. The spectra become nebular within 2-4 $e$-folding times after light
curve peak, with the rate of spectroscopic evolution correlated to the light
curve timescale. Emission lines are identified with well-known transitions of
oxygen, calcium, magnesium, sodium and iron. SLSNe are differentiated from
other Type Ic SNe by a prominent O I $\lambda$7774 line and higher-ionisation
states of oxygen. The iron-dominated region around 5000 \AA\ is more similar to
broad-lined SNe Ic than to normal SNe Ic. Principal Component Analysis shows
that 5 `eigenspectra' capture 75% of the variance, while a clustering analysis
shows no clear evidence for multiple SLSN sub-classes. Line velocities are
5000--8000 km/s, and show stratification of the ejecta. O I $\lambda$7774
likely arises in a dense inner region that also produces calcium emission,
while [O I] $\lambda$6300 comes from further out until 300--400 days. The
luminosities of O I $\lambda$7774 and Ca II suggest significant clumping, in
agreement with previous studies. Ratios of [Ca II]$\lambda$7300/[O
I]$\lambda$6300 favour progenitors with relatively massive helium cores, likely
$\gtrsim 6$ M$_\odot$, though more modelling is required here. SLSNe with broad
light curves show the strongest [O I] $\lambda$6300, suggesting larger ejecta
masses. We show how the inferred velocity, density and ionisation structure
point to a central power source.",1808.00510v2
2018-10-24,Fe I in the Beta Pictoris circumstellar gas disk. II. The time variations in the iron circumstellar gas,"Beta Pictoris is a young planetary system surrounded by a debris disk of dust
and gas. The gas source of this disk could be exocomets (or 'falling and
evaporating bodies', FEBs), which produce refractory elements (Mg, Ca, Fe)
through sublimation of dust grains at several tens of stellar radii. Nearly
1700 high resolution spectra of Beta Pictoris have been obtained from 2003 to
2017 using the HARPS spectrograph. In paper I, we showed that a very high S/N
ratio allows the detection of many weak Fe I lines in more than ten excited
levels, and we derived the physical characteristics of the iron gas in the
disk. The measured temperature of the gas (~1300 K) suggested that it is
produced by evaporation of grains at about 0.3 au (38 Rstar) from the star.
Here we describe the yearly variations of the column densities of all Fe I
components (from both ground and excited levels). The drop in the Fe I ground
level column density after 2011 coincides with a drop in Fe I excited levels
column density, as well as in the Ca II doublet and a ground level Ca I line at
the same epoch. All drops are compatible together with
photoionisation-recombination equilibrium and Beta Pic like relative
abundances, in a medium at 1300 K and at 0.3 au from Beta Pictoris.
Interestingly, this warm medium does not correlate with the numerous exocomets
in the circumstellar environnement of this young star.",1810.10421v1
2019-01-17,Emergence of Superconductivity from Fully Incoherent Normal State in an Iron-Based Superconductor (Ba$_{0.6}$K$_{0.4}$)Fe$_2$As$_2$,"In unconventional superconductors, it is generally believed that
understanding the physical properties of the normal state is a pre-requisite
for understanding the superconductivity mechanism. In conventional
superconductors like niobium or lead, the normal state is a Fermi liquid with a
well-defined Fermi surface and well-defined quasipartcles along the Fermi
surface. Superconductivity is realized in this case by the Fermi surface
instability in the superconducting state and the formation and condensation of
the electron pairs (Cooper pairing). The high temperature cuprate
superconductors, on the other hand, represent another extreme case that
superconductivity can be realized in the underdoped region where there is
neither well-defined Fermi surface due to the pseudogap formation nor
quasiparticles near the antinodal regions in the normal state. Here we report a
novel scenario that superconductivity is realized in a system with well-defined
Fermi surface but without quasiparticles along the Fermi surface in the normal
state. High resolution laser-based angle-resolved photoemission measurements
have been performed on an optimally-doped iron-based superconductor
(Ba$_{0.6}$K$_{0.4}$)Fe$_2$As$_2$. We find that, while sharp superconducting
coherence peaks emerge in the superconducting state on the hole-like Fermi
surface sheets, no quasiparticle peak is present in the normal state. Its
electronic behaviours deviate strongly from a Fermi liquid system. The
superconducting gap of such a system exhibits an unusual temperature dependence
that it is nearly a constant in the superconducting state and abruptly closes
at T$_c$. These observations have provided a new platform to study
unconventional superconductivity in a non-Fermi liquid system.",1901.05693v1
2019-01-24,Anisotropic magnetic excitations and incipient Néel order in Ba(Fe$_{1-x}$Mn$_{x}$)$_{2}$As$_{2}$,"It is currently understood that high temperature superconductivity (SC) in
the transition metal $(M)$ substituted iron arsenides
Ba(Fe$_{1-x}$$M$$_{x}$)$_{2}$As$_{2}$ is promoted by magnetic excitations with
wave vectors $(\pi,0)$ or $(0,\pi)$. It is known that while a small amount of
Co substitution leads to SC, the same does not occur for Mn for any value of
$x$. In this work, magnetic excitations in the iron arsenides
Ba(Fe$_{1-x}$Mn$_{x}$)$_{2}$As$_{2}$ ($x=0.0$, $0.007$, $0.009$, $0.08$) are
investigated by means of Resonant Inelastic X rays Scattering (RIXS) at the Fe
$L_{3}$-edge, for momentum transfer $\boldsymbol{q}$ along the high symmetry
Brillouin zone $(\pi,0)$ and $(\pi,\pi)$ directions. It is shown that with
increasing Mn content ($x$), the excitations become anisotropic both in
dispersion and lineshape. Both effects are detected even for small values of
$x$, evidencing a cooperative phenomenon between the Mn impurities, that we
ascribe to emerging N\'eel order of the Mn spins. Moreover, for $x=0.08$, the
excitations along $\boldsymbol{q}\parallel(\pi,0)$ are strongly damped and
nearly non dispersive. This result suggests that phases of arsenides containing
local moments at the FeAs layers, as in Mn or Cr substituted phases, do not
support high temperature SC due to absence of the appropriate magnetic
excitations.",1901.08543v3
2019-04-09,CsMn$_4$As$_3$: A layered tetragonal transition-metal pnictide compound with antiferromagnetic ground state,"We report the synthesis and properties of a new layered tetragonal ternary
compound CsMn$_4$As$_3$ (structure: KCu$_4$S$_3$-type, space group: $P4/mmm$,
No. 123 and $Z = 2$). The material is a small band-gap semiconductor and
exhibits an antiferromagnetic ground state associated with Mn spins. The
compound exhibits a signature of a distinct magnetic moment canting event at
150(5)~K with a canting angle of $\approx 0.3^{\circ}$. Although, some features
of the magnetic characteristics of this new compound are qualitatively similar
to those of the related BaMn$_2$As$_2$, the underlying Mn sublattices of the
two materials are quite different. While the Mn square-lattice layers in
BaMn$_2$As$_2$ are equally spaced along the $c$-direction with the interlayer
distance $d_{\rm L\,Ba} = 6.7341(4)$ Ang., the Mn sublattice forms bilayers in
CsMn$_4$As$_3$ with the interlayer distance within a bilayer $d_{\rm L\,Cs} =
3.1661(6)$ Ang. and the distance between the two adjacent bilayers $d_{\rm B} =
7.290(6)$ Ang. This difference in the Mn sublattice is bound to significantly
alter the energy balance between the $J_{1}$, $J_{2}$ and $J_{c}$ exchange
interactions within the J1-J2-Jc model compared to that in BaMn$_2$As$_2$ and
the other related 122 compounds including the well-known iron-arsenide
superconductor parent compound BaFe$_2$As$_2$. Owing to the novelty of its
transition metal sublattice, this new addition to the family of tetragonal
materials related to the iron-based superconductors brings prospects for doping
and pressure studies in the search of new superconducting phases as well as
other exciting correlated-electron properties.",1904.04598v1
2019-04-09,Insulating Parent Phase and Distinct Doping Evolution to Superconductivity in Single-Layer FeSe/SrTiO3 Films,"The single-layer FeSe/SrTiO3 (FeSe/STO) films have attracted much attention
because of their simple crystal structure, distinct electronic structure and
record high superconducting transition temperature (Tc). The origin of the
dramatic Tc enhancement in single-layer FeSe/STO films and the dichotomy of
superconductivity between single-layer and multiple-layer FeSe/STO films are
still under debate. Here we report a comprehensive high resolution
angle-resolved photoemission spectroscopy and scanning tunneling
microscopy/spectroscopy measurements on the electronic structure evolution with
doping in single-layer and multiple-layer FeSe/STO films. We find that the
single-layer FeSe/STO films have a distinct parent phase and a route of doping
evolution to superconductivity that are fundamentally different from
multiple-layer FeSe/STO films. The parent phase of the single-layer FeSe/STO
films is insulating, and its doping evolution is very similar to that of doping
a Mott insulator in cuprate superconductors. In multiple-layer FeSe/STO films,
high-Tc superconductivity occurs by suppressing the nematic order in the parent
compound with electron doping. The single-layer FeSe/STO films represent the
first clear case in the iron-based superconductors that the parent compound is
an insulator. Our observations of the unique parent state and doping evolution
in the single-layer FeSe/STO films provide key insight in understanding its
record high-Tc superconductivity. They also provide a new route of realizing
superconductivity in iron-based superconductors that is common in high
temperature cuprate superconductors.",1904.04662v1
2019-06-19,Iron abundance distribution in the hot gas of merging galaxy clusters,"We present XMM-Newton/EPIC observations of six merging galaxy clusters and
study the distributions of their temperature, iron (Fe) abundance and
pseudo-entropy along the merging axis. For the first time, we focus
simultaneously, and in a comprehensive way, on the chemical and thermodynamic
properties of the freshly collided intracluster medium (ICM). The Fe
distribution of these clusters along the merging axis is found to be in good
agreement with the azimuthally-averaged Fe abundance profile in typical
non-cool-core clusters out to $r_{500}$. In addition to showing a moderate
central abundance peak, though less pronounced than in relaxed systems, the Fe
abundance flattens at large radii towards $\sim$0.2-0.3 $Z_\odot$. Although
this shallow metal distribution is in line with the idea that disturbed,
non-cool-core clusters originate from the merging of relaxed, cool-core
clusters, we find that in some cases, remnants of metal-rich and low entropy
cool cores can persist after major mergers. While we obtain a mild
anti-correlation between the Fe abundance and the pseudo-entropy in the (lower
entropy, $K$ = 200-500 keV cm$^2$) inner regions, no clear correlation is found
at (higher entropy, $K$ = 500-2300 keV cm$^2$) outer radii. The apparent
spatial abundance uniformity that we find at large radii is difficult to
explain through an efficient mixing of freshly injected metals, particularly in
systems for which the time since the merger is short. Instead, our results
provide important additional evidence in favour of the early enrichment
scenario - in which the bulk of the metals are released outside galaxies at $z$
> 2-3 - and extend it from cool-core and (moderate) non-cool-core clusters to a
few of the most disturbed merging clusters as well. These results constitute a
first step towards a deeper understanding of the chemical history of merging
clusters.",1906.08067v1
2019-07-02,Neutron star mergers and rare core-collapse supernovae as sources of r-process enrichment in simulated galaxies,"We use cosmological, magnetohydrodynamical simulations of Milky Way-mass
galaxies from the Auriga project to study their enrichment with rapid neutron
capture (r-process) elements. We implement a variety of enrichment models from
both binary neutron star mergers and rare core-collapse supernovae. We focus on
the abundances of (extremely) metal-poor stars, most of which were formed
during the first ~Gyr of the Universe in external galaxies and later accreted
onto the main galaxy. We find that the majority of metal-poor stars are
r-process enriched in all our enrichment models. Neutron star merger models
result in a median r-process abundance ratio which increases with metallicity,
whereas the median trend in rare core-collapse supernova models is
approximately flat. The scatter in r-process abundance increases for models
with longer delay times or lower rates of r-process producing events. Our
results are nearly perfectly converged, in part due to the mixing of gas
between mesh cells in the simulations. Additionally, different Milky Way-mass
galaxies show only small variation in their respective r-process abundance
ratios. Current (sparse and potentially biased) observations of metal-poor
stars in the Milky Way seem to prefer rare core-collapse supernovae over
neutron star mergers as the dominant source of r-process elements at low
metallicity, but we discuss possible caveats to our models. Dwarf galaxies
which experience a single r-process event early in their history show highly
enhanced r-process abundances at low metallicity, which is seen both in
observations and in our simulations. We also find that the elements produced in
a single event are mixed with ~10^8 Msun of gas relatively quickly,
distributing the r-process elements over a large region.",1907.01557v2
2019-07-17,Heavy metals in intermediate He-rich hot subdwarfs: The chemical composition of HZ44 and HD127493,"Hot subluminous stars can be spectroscopically classified as subdwarf B (sdB)
and O (sdO) stars. While the latter are predominantly hydrogen deficient, the
former are mostly helium deficient. The atmospheres of most sdOs are almost
devoid of hydrogen, whereas a small group of hot subdwarf stars of mixed H/He
composition exists, showing extreme metal abundance anomalies. Whether such
intermediate helium-rich (iHe) subdwarf stars provide an evolutionary link
between the dominant classes is an open question. The presence of strong Ge,
Sn, and Pb lines in the UV spectrum of HZ$\,$44 suggests a strong enrichment of
heavy elements in this iHe-sdO star and calls for a detailed quantitative
spectral analysis focusing on trans-iron elements. Non-LTE model atmospheres
calculated with TLUSTY are combined with high-quality optical, UV and FUV
spectra of HZ$\,$44 and its hotter sibling HD$\,$127493 to determine their
atmospheric parameters and metal abundance patterns. By collecting atomic data
from literature we succeeded to determine abundances of 29 metals in HZ$\,$44,
including the trans-iron elements Ga, Ge, As, Se, Zr, Sn, and Pb and provide
upper limits for 10 other metals. This makes it the best described hot subdwarf
in terms of chemical composition. For HD$\,$127493 the abundance of 15 metals,
including Ga, Ge, and Pb and upper limits for another 16 metals were derived.
Heavy elements turn out to be overabundant by one to four orders of magnitude
with respect to the Sun. Zr and Pb are among the most enriched elements. The C,
N, and O abundance for both stars can be explained by nucleosynthesis of
hydrogen burning in the CNO cycle along with their helium enrichment. On the
other hand, the heavy-element anomalies are unlikely to be caused by
nucleosynthesis. Instead diffusion processes are evoked with radiative
levitation overcoming gravitational settlement of the heavy elements.",1907.07781v1
2019-07-29,Turbulence and Rotation in Solar-Type Stars,"Stellar spectra with a high resolution of 115000 obtained with the HARPS
spectrograph provide an opportunity to examine turbulence velocities and their
depth distributions in the photosphere of stars. Fourier analysis was performed
for 17 iron lines in the spectra of 13 stars with an effective temperature of
4900--6200 K and a logarithm of surface gravity of 3.9--5.0 as well as in the
spectrum of the Sun as a star. Models of stellar atmospheres were taken from
the MARCS database. The standard concept of isotropic Gaussian microturbulence
was assumed in this study. A satisfactory fit between the synthesized profiles
of spectral lines and observational data verified the reliability of the
Fourier method. The most likely estimates of turbulence velocities, the
rotation velocity, and the iron abundance and their photospheric depth
distribution profiles were obtained as a result. Microturbulence does not vary
to any significant degree with depth, while macroturbulence has a marked depth
dependence. The macroturbulence velocity increases with depth in the stellar
atmosphere. The higher the effective temperature of a star and the stronger the
surface gravity, the steeper the expected macroturbulence gradient. The mean
macroturbulence velocity increases for stars with higher temperatures, weaker
gravity, and faster rotation. The mean macro- and microturbulence velocities
are correlated with each other and with the rotation velocity in the examined
stars. The ratio between the macroturbulence velocity and the rotation velocity
in solar-type stars varies from 1 (the hottest stars) to 1.7 (the coolest
stars). The age dependence of the rotation velocity is more pronounced than
that of the velocity of macroturbulent motions.",1907.12241v1
2019-10-07,Optical and photoemission investigation of structural and magnetic transitions in the iron-based superconductor Sr$_\mathbf{0.67}$Na$_\mathbf{0.33}$Fe$_\mathbf{2}$As$_\mathbf{2}$,"We report the temperature-dependent optical conductivity and ARPES studies of
the iron-based superconductor (SC) Sr$_{0.67}$Na$_{0.33}$Fe$_2$As$_2$ in the
high-temperature tetragonal paramagnetic phase; below the structural and
magnetic transitions at $T_{\rm N}\simeq$125 K in the orthorhombic
spin-density-wave (SDW)-like phase, and $T_r\simeq$42 K in the reentrant
tetragonal double-Q magnetic phase where both charge and SDW order exist; and
below the SC transition at $T_c\simeq$10 K. The free-carrier component in the
optical conductivity is described by two Drude contributions; one strong and
broad, the other weak and narrow. The broad Drude component decreases
dramatically below $T_{\rm N}$ and $T_r$, with much of its strength being
transferred to a bound excitation in the mid-infrared, while the narrow Drude
component shows no anomalies at either of the transitions, actually increasing
in strength at low temperature while narrowing dramatically. The behavior of an
infrared-active mode suggests zone-folding below $T_r$. Below $T_c$ the
dramatic decrease in the low-frequency optical conductivity signals the
formation of a SC energy gap. ARPES reveals hole-like bands at the center of
the Brillouin zone (BZ), with both electron- and hole-like bands at the
corners. Below $T_{\rm N}$, the hole pockets at the center of the BZ decrease
in size, consistent with the behavior of the broad Drude component; while below
$T_r$ the electron-like bands shift and split, giving rise to a low-energy
excitation in the optical conductivity at ~20 meV. The magnetic states, with
resulting SDW and charge-SDW order, respectively, lead to a significant
reconstruction of the Fermi surface that has profound implications for the
transport originating from the electron and hole pockets, but appears to have
relatively little impact on the SC in this material.",1910.02927v2
2019-10-28,Type Ia Supernova Explosions from Hybrid Carbon-Oxygen-Neon White Dwarf Progenitors That Have Mixed During Cooling,"The creation of ""hybrid"" white dwarfs, made of a C-O core within a O-Ne shell
has been proposed, and studies indicate that ignition in the C-rich central
region makes these viable progenitors for thermonuclear (type Ia) supernovae.
Recent work found that the C-O core is mixed with the surrounding O-Ne as the
white dwarf cools prior to accretion, which results in lower central C
fractions in the massive progenitor than previously assumed. To further
investigate the efficacy of hybrid white dwarfs as progenitors of thermonuclear
supernovae, we performed simulations of thermonuclear supernovae from a new
series of hybrid progenitors that include the effects of mixing during cooling.
The progenitor white dwarf model was constructed with the one-dimensional
stellar evolution code MESA and represented a star evolved through the phase of
unstable interior mixing followed by accretion until it reached conditions for
the ignition of carbon burning. This MESA model was then mapped to a
two-dimensional initial condition for explosions simulated with FLASH. For
comparison, similar simulations were performed for a traditional C-O progenitor
white dwarf. By comparing the yields of the explosions, we find that, as with
earlier studies, the lower C abundance in the hybrid progenitor compared to the
traditional C-O progenitor leads to a lower average yield of 56Ni. Although the
unmixed hybrid WD showed a similar decrement also in total iron group yield,
the mixed case does not and produces a smaller fraction of iron group elements
in the form of 56Ni. We attribute this to the higher central density required
for ignition and the location, center or off-center, of deflagration ignition.",1910.12403v1
2019-12-15,The influence of NLTE effects in Fe I lines on an inverted atmosphere I. 6301 A and 6302 A lines formed in 1D NLTE,"Ultraviolet over-ionisation of iron atoms in the solar atmosphere leads to
deviations in their level populations from the Saha-Boltzmann statistics. This
causes their line profiles to form in Non-Local Thermodynamic Equilibrium
(NLTE) conditions. While inverting such profiles to determine atmospheric
parameters, the NLTE effects are often neglected and deviations from LTE are
compensated for by tweaking other quantities. We investigate how the routinely
employed LTE inversion of iron lines formed in NLTE under- or over-estimates
atmospheric quantities such as temperature (T), line-of-sight velocity (v_LOS),
magnetic field strength (B) and inclination (gamma) while the previous papers
have focused mainly on T. We synthesize the Stokes profiles of Fe I 6301.5 A
and 6302.5 A lines in both LTE and NLTE using a snapshot of a 3D MHD
simulation. The profiles are then inverted in LTE. By considering the
atmosphere inferred from inversion of LTE profiles to be the fiducial model, we
compare atmosphere from the inversion of NLTE profiles with it. Any differences
observed are attributed to NLTE effects. Neglecting the NLTE effects introduces
errors in the inverted atmosphere. While the errors in T can go up to 13%, in
v_LOS and B the errors can be as high as 50% or more. We find these errors to
be present at all three inversion nodes. Importantly, they survive degradation
from spatial averaging of the profiles. We give an overview of how the neglect
of NLTE effects influences the values of T, v_LOS, B and gamma determined by
inverting Fe I 6300 A line pair, as observed, e.g., by Hinode. Errors are found
at the sites of granules, intergranular lanes, magnetic elements, basically in
every region susceptible to NLTE effects. For an accurate determination of
atmospheric quantities and their stratification, it is therefore important to
take account of NLTE effects.",1912.07007v2
2020-03-06,Studying the Reflection Spectra of the New Black Hole X-ray Binary Candidate MAXI J1631-479 Observed by NuSTAR: A Variable Broad Iron Line Profile,"We present results from the Nuclear Spectroscopic Telescope Array (NuSTAR)
observations of the new black hole X-ray binary candidate MAXI J1631-479 at two
epochs during its 2018-2019 outburst, which caught the source in a disk
dominant state and a power-law dominant state. Strong relativistic disk
reflection features are clearly detected, displaying significant variations in
the shape and strength of the broad iron emission line between the two states.
Spectral modeling of the reflection spectra reveals that the inner radius of
the optically-thick accretion disk evolves from $<1.9$ $r_{\rm g}$ to $12\pm1$
$r_{\rm g}$ (statistical errors at 90% confidence level) from the disk dominant
to the power-law dominant state. Assuming in the former case that the inner
disk radius is consistent with being at the ISCO, we estimate a black hole spin
of $a^*>0.94$. Given that the bolometric luminosity is similar in the two
states, our results indicate that the disk truncation observed in MAXI
J1631-479 in the power-law dominant state is unlikely to be driven by a global
variation in the accretion rate. We propose that it may instead arise from
local instabilities in the inner edge of the accretion disk at high accretion
rates. In addition, we find an absorption feature in the spectra centered at
$7.33\pm0.03$ keV during the disk dominant state, which is evidence for a rare
case that an extremely fast disk wind ($v_{\rm out}=0.067^{+0.001}_{-0.004}~c$)
is observed in a low-inclination black hole binary, with the viewing angle of
$29\pm1^{\circ}$ as determined by the reflection modeling.",2003.03465v1
2020-08-04,The infancy of core-collapse supernova remnants,"We present 3D hydrodynamic simulations of neutrino-driven supernovae (SNe)
with the PROMETHEUS-HOTB code, evolving the asymmetrically expanding ejecta
from shock breakout until they reach the homologous expansion phase after
roughly one year. Our calculations continue the simulations for two red
supergiant (RSG) and two blue supergiant (BSG) progenitors by Wongwathanarat et
al., who investigated the growth of explosion asymmetries produced by
hydrodynamic instabilities during the first second of the explosion and their
later fragmentation by Rayleigh-Taylor instabilities. We focus on the late time
acceleration and inflation of the ejecta caused by the heating due to the
radioactive decay of $^{56}$Ni to $^{56}$Fe and by a new outward-moving shock,
which forms when the reverse shock from the He/H-shell interface compresses the
central part of the ejecta. The mean velocities of the iron-rich ejecta
increase between 100 km/s and 350 km/s ($\sim$8-30\%), and the fastest one
percent of the iron accelerates by up to $\sim$1000 km/s ($\sim$20-25\%). This
'Ni-bubble effect', known from 1D models, accelerates the bulk of the nickel in
our 3D models and causes an inflation of the initially overdense Ni-rich
clumps, which leads to underdense, extended fingers, enveloped by overdense
skins of compressed surrounding matter. We also provide volume and surface
filling factors as well as a spherical harmonics analysis to characterize the
spectrum of Ni-clump sizes quantitatively. Three of our four models give volume
filling factors larger than 0.3, consistent with what is suggested for SN 1987A
by observations.",2008.01763v2
2020-08-13,On the detection of surface spin freezing in iron oxide nanoparticles and its long-term evolution under ambient oxidation,"Exchange bias effects linked to surface spin freezing (SSF) are commonly
found in iron oxide nanoparticles, while signatures of SSF in low-field
temperature-dependent magnetization curves have been much less frequently
reported. Here, we present magnetic properties of dense assemblies of
similar-sized (~ 8 nm diameter) particles synthesized by a magnetite (sample
S1) and a maghemite (sample S2) method, and the influence of long-term (4-year)
sample aging under ambient conditions on these properties. The size of the
exchange bias field of the different sample (fresh or aged) states is found to
correlate with (a) whether a low-temperature hump feature signaling the SSF
transition is detected in out-of-phase ac susceptibility or zero-field-cooled
(ZFC) dc magnetization recorded at low field and with (b) the prominence of
irreversibility between FC and ZFC curves recorded at high field. Sample S1
displays a lower magnetization than S2, and it is in S1 where the largest SSF
effects are found. These effects are significantly weakened by aging but remain
larger than the SSF effects in S2, where the influence of aging is considerably
smaller. A non-saturating component due to spin disorder in S1 also weakens
with aging, accompanied by, we infer, an increase in the superspin and the
radius of the ordered nanoparticle cores. X-ray diffraction and M\""ossbauer
spectroscopy provide indication of maghemite-like stoichiometry in both aged
samples as well as thicker disordered particle shells in aged-S1 relative to
aged-S2 (crystallographically-disordered and spin-disordered according to
diffraction and M\""ossbauer, respectively). The pronounced diminution in SSF
effects with aging in S1 is attributed to a (long-term) transition, caused by
ambient oxidation, from magnetite-like to maghemite-like stoichiometry, and a
concomitant softening of the spin-disordered shell anisotropy...",2008.05874v1
2020-08-31,"Structural, magnetic and electronic properties of CaBaCo4-xMxO7 (M= Fe, Zn)","The effect of substituting iron and zinc for cobalt in CaBaCo$_4$O$_7$ has
been investigated using neutron diffraction and x-ray absorption spectroscopy.
The orthorhombic distortion present in the parent compound CaBaCo$_4$O$_7$
decreases with increasing the content of either Fe or Zn. The samples
CaBaCo$_3$ZnO$_7$ and CaBaCo$_{4-x}$Fe$_x$O$_7$ with $x \leq 1.5$ are
metrically hexagonal but much better refinements in the neutron diffraction
patterns are obtained using an orthorhombic unit cell. The two types of
substitution have opposite effects on the structural and magnetic properties.
Fe atoms preferentially occupy the sites at the triangular layer. Thus, the
replacement of Co by Fe supresses the ferrimagnetic ordering and
CaBaCo$_{4-x}$Fe$_x$O$_7$ samples are antiferromagnetically ordered with a new
propagation vector k=(1/3,0,0). However, the Zn atoms prefer occupying the
Kagome layer, which is very detrimental for the long range magnetic
interactions giving rise to a magnetic glass. The oxidation state of iron and
zinc is found to be 3+ and 2+, respectively, independently of the content.
Therefore, the average Co oxidation state changes accordingly with the
Fe$^{3+}$ or Zn$^{2+}$ doping. Also, x-ray absorption spectroscopy data
confirms the different preferential occupation for both Fe and Zn cations. The
combined information obtained by neutron diffraction and x-ray absorption
spectroscopy indicates that cobalt atoms can be either in a fluctuating
Co$^{2+}$/Co$^{3+}$ valence state or, alternatively, Co$^{2+}$ and Co$^{3+}$
ions being randomly distributed in the lattice. These results explain the
occurrence of local disorder in the CoO$_4$ tetrahedra obtained by EXAFS. An
anomaly in the lattice parameters and an increase in the local disorder is
observed only at the ferrimagnetic transition for CaBaCo$_4$O$_7$ revealing the
occurrence of local magneto-elastic coupling.",2008.13649v1
2020-10-14,"The X-SHOOTER/ALMA sample of Quasars in the Epoch of Reionization. I. NIR spectral modeling, iron enrichment and broad emission line properties","We present X-SHOOTER near-infrared spectroscopy of a large sample of 38
luminous ($M_{1450}=-29.0$ to $-24.4$) quasars at $5.78<z<7.54$, which have
complementary CII observations from ALMA. This X-SHOOTER/ALMA sample provides
us with the most comprehensive view of reionization-era quasars to date,
allowing us to connect the quasar properties with those of its host galaxy. In
this work we introduce the sample, discuss data reduction and spectral fitting,
and present an analysis of the broad emission line properties. The measured
FeII/MgII flux ratio suggests that the broad line regions of all quasars in the
sample are already enriched in iron. We also find the MgII line to be on
average blueshifted with respect to the CII redshift with a median of
$-391\,\rm{km}\,\rm{s}^{-1}$. A significant correlation between the MgII-CII
and CIV-CII velocity shifts indicates a common physical origin. Furthermore, we
frequently detect large CIV-MgII emission line velocity blueshifts in our
sample with a median value of $-1848\,\rm{km}\,\rm{s}^{-1}$. While we find all
other broad emission line properties not to be evolving with redshift, the
median CIV-MgII blueshift is much larger than found in low-redshift,
luminosity-matched quasars ($-800\,\rm{km}\,\rm{s}^{-1}$). Dividing our sample
into two redshift bins, we confirm an increase of the average CIV-MgII
blueshift with increasing redshift. Future observations of the rest-frame
optical spectrum with the James Webb Space Telescope will be instrumental in
further constraining the possible evolution of quasar properties in the epoch
of reionization.",2010.06902v1
2020-10-21,Composition and origin of L5 Trojan asteroids of Mars: Insights from spectroscopy,"We investigate the mineralogy of L5 Martian Trojan asteroids via reflectance
spectroscopy, in particular (101429) 1998 $\mbox{VF}_{31}$, the only L5 Trojan
that does not belong to the Eureka family (Christou, 2013). We find that this
asteroid most likely belongs to the Bus-Demeo S-complex, in agreement with
Rivkin et al. (2007) and obtain good spectral matches with Sq- or S-type
asteroids, the lunar surface and of Martian and lunar meteorites. Mixture
fitting to spectral endmembers suggests a surface abundance of Mg-rich
orthopyroxene and iron metal or, alternatively, a mixture of plagioclase and
metal with a small amount of Mg-poor orthopyroxene. The metallic component may
be part of the intrinsic mineral makeup of the asteroid or an indication of
extreme space weathering.
  We discuss several origin scenarios for (101429). The asteroid could be
related to iron-rich primitive achondrites (Rivkin et al.), may have originated
as impact ejecta from Mars - as proposed recently for the Eureka family
asteroids (Polishook et al., 2017) - or could be a relic fragment of the Moon's
original solid crust. If, on the other hand, (101429) is a relatively recent
addition to the Martian Trojan clouds (Christou et al., 2020), its origin is
probably traced to high-inclination asteroid families in the Inner Main Belt.
  For the olivine-dominated Eureka family, we find that the two smaller
asteroids are more spectrally similar to one another than to (5261) Eureka.
Spectral profiles of all three asteroids are closely similar shortward of
$\sim$0.7$\mu$m but diverge at longer wavelengths. For the two smaller
asteroids in particular, we find the spectra are virtually identical up to
$0.8$$\mu$m. We attribute spectral differences in the near-IR region to
differences in either: degree of space weathering, olivine chemical composition
and/or regolith grain size.",2010.10947v1
2020-10-29,Spectroscopic Evidence of Superconductivity Pairing at 83 K in Single-Layer FeSe/SrTiO3 Films,"Single-layer FeSe films grown on the SrTiO3 substrate (FeSe/STO) have
attracted much attention because of their possible record-high superconducting
critical temperature Tc and distinct electronic structures in iron-based
superconductors. However, it has been under debate on how high its Tc can
really reach due to the inconsistency of the results obtained from the
transport, magnetic and spectroscopic measurements. Here we report
spectroscopic evidence of superconductivity pairing at 83 K in single-layer
FeSe/STO films. By preparing high-quality single-layer FeSe/STO films, we
observe for the first time strong superconductivity-induced Bogoliubov
back-bending bands that extend to rather high binding energy ~100 meV by
high-resolution angle-resolved photoemission measurements. The Bogoliubov
back-bending band provides a new definitive benchmark of superconductivity
pairing that is directly observed up to 83 K in the single-layer FeSe/STO
films. Moreover, we find that the superconductivity pairing state can be
further divided into two temperature regions of 64-83 K and below 64 K. We
propose the 64-83 K region may be attributed to superconductivity fluctuation
while the region below 64 K corresponds to the realization of long-range
superconducting phase coherence. These results indicate that either Tc as high
as 83 K is achievable in iron-based superconductors, or there is a pseudogap
formation from superconductivity fluctuation in single-layer FeSe/STO films.",2010.15362v1
2020-11-03,Discovery of a Fast Iron Low-ionization Outflow in the Early Evolution of the Nearby Tidal Disruption Event AT2019qiz,"We report the results of ultraviolet (UV) and optical photometric and
spectroscopic analysis of the tidal disruption event (TDE) AT2019qiz. Our
follow-up observations started $<$10 days after the source began to brighten in
the optical and lasted for a period of six months. Our late-time host-dominated
spectrum indicates that the host galaxy likely harbors a weak active galactic
nucleus. The initial {\it Hubble Space Telescope (HST)} spectrum of AT2019qiz
exhibits an iron and low-ionization broad absorption line (FeLoBAL) system that
is seen for the first time in a TDE. This spectrum also bears a striking
resemblance to that of Gaia16apd, a superluminous supernova. Our observations
provide insights into the outflow properties in TDEs and show evidence for a
connection between TDEs and engine-powered supernovae at early phase, as
originally suggested in Metzger & Stone (2016). In a time frame of 50 days, the
UV spectra of AT2019qiz started to resemble previous TDEs with only
high-ionization BALs. The change in UV spectral signatures is accompanied by a
decrease in the outflow velocity, which began at $15,000$ km s$^{-1}$ and
decelerated to $\sim10,000$ km s$^{-1}$. A similar evolution in the H$\alpha$
emission line width further supports the speculation that the broad Balmer
emission lines are formed in TDE outflows. In addition, we detect narrow
absorption features on top of the FeLoBAL signatures in the early HST UV
spectrum of AT2019qiz. The measured HI column density corresponds to a
Lyman-limit system whereas the metal absorption lines, such as NV, CIV, FeII,
and MgII, are likely probing the circumnuclear gas and interstellar medium in
the host galaxy.",2011.01593v2
2020-11-15,Three-dimensional Supernova Models Provide New Insights into the Origins of Stardust,"We present the isotope yields of two post-explosion, three-dimensional 15
$M_\odot$ core-collapse supernova models, 15S and 15A, and compare them to the
carbon, nitrogen, silicon, aluminum, sulfur, calcium, titanium, iron, and
nickel isotopic compositions of SiC stardust. We find that these core-collapse
supernova models predict similar carbon and nitrogen compositions to SiC X
grains and grains with $^{12}$C/$^{13}$C $<$ 20 and $^{14}$N/$^{15}$N $<$ 60,
which we will hereafter refer to as SiC 'D' grains. Material from the interior
of a 15 $M_\odot$ explosion reaches high enough temperatures shortly after core
collapse to produce the large enrichments of $^{13}$C and $^{15}$N necessary to
replicate the compositions of SiC D grains. The innermost ejecta in a
core-collapse supernova is operating in the neutrino-driven regime and
undergoes fast proton capture after being heated by the supernova shockwave.
Both 3-D models predict 0.3 $<$ $^{26}$Al/$^{27}$Al $<$ 1.5, comparable to the
ratios seen in SiC X, C, and D grains. Models 15S and 15A, in general, predict
very large anomalies in calcium isotopes but do compare qualitatively with the
SiC X grain measurements that show $^{44}$Ca and $^{43}$Ca excesses. The
titanium isotopic compositions of SiC X grains are well reproduced. The models
predict $^{57}$Fe excesses and depletions that are observed in SiC X grains,
and in addition predict accurately the $^{60}$Ni/$^{58}$Ni,
$^{61}$Ni/$^{58}$Ni, and $^{62}$Ni/$^{58}$Ni ratios in SiC X grains, as a
result of fast neutron captures initiated by the propagation of the supernova
shockwave. Finally, symmetry has a noticeable effect on the production of
silicon, sulfur, and iron isotopes in the SN ejecta.",2011.07459v2
2020-11-25,Light Quantum Control of Persisting Higgs Modes in Iron-Based Superconductors,"The Higgs mechanism, i.e., spontaneous symmetry breaking of the quantum
vacuum, is a cross-disciplinary principle, universal for understanding dark
energy, antimatter and quantum materials, from superconductivity to magnetism.
Yet, Higgs modes in one-band superconductors (SCs) are currently under debate
due to their competition with charge-density fluctuations. A distinct Higgs
mode, controllable by terahertz (THz) laser pulses, can arise in multi-band,
unconventional SCs via strong {\em interband} Coulomb interaction, but is yet
to be accessed. Here we both discover and demonstrate quantum control of such
collective mode in iron-based high-temperature superconductors. Using
two-pulse, phase coherent THz spectroscopy, we observe a tunable and coherent
2$\Delta_{\mathrm{SC}}$ amplitude oscillation of the complex order parameter in
such SC with coupled lower and upper bands. The nonlinear dependence of the
amplitude mode oscillations on the THz driving fields is distinct from any
one-band and conventional SC results: we observe a large nonlinear change of
resonance strength, yet with a persisting mode frequency. We argue that this
result provides compelling evidence for a transient coupling between the
electron and hole amplitude modes via strong interband coherent interaction. To
support this scenario, we perform quantum kinetic modeling of a hybrid Higgs
mechanism without invoking extra disorder or phonons. In addition to
distinguishing between collective modes and charge fluctuations, the light
quantum control of multiband SCs can be extended to probe and manipulate
many-body entanglement and hidden symmetries in different quantum materials.",2011.13036v2
2020-11-27,XMM-Newton observations of the extremely X-ray luminous quasar CFHQS J142952+544717=SRGE J142952.1+544716 at redshift z=6.18,"We present results from a 20 ks XMM-Newton DDT observation of the radio-load
quasar CFHQS J142952+544717 at z=6.18, whose extreme X-ray luminosity was
recently revealed by the SRG/eROSITA telescope in the course of its first
all-sky survey. The quasar has been confidently detected with a total of $\sim
1400$ net counts in the 0.2-10 keV energy band (1.4 to 72 keV in the object's
rest frame). Its measured spectrum is unusually soft and can be described by an
absorbed power-law model with a photon index of $\Gamma = 2.5\pm0.2$. There are
no signs of a high-energy cutoff or reflected component, with an 90 % upper
limit on the fluorescence iron K$\alpha$ equivalent width of $\approx 290$ eV
and the corresponding upper limit on the iron K-edge absorption depth of 0.6.
We have detected, at the $> 95\%$ confidence level, an excess absorption above
the Galactic value, corresponding to a column density $N_H= 3\pm2 \times
10^{22}$ cm$^{-2}$ of material located at z=6.18. The intrinsic luminosity of
CFHQS J142952+544717 in the 1.4 to 72 keV energy band is found to be
$5.5_{-0.6}^{+0.8} \times 10^{46}$ erg s$^{-1}$. We did not detect
statistically significant flux changes between two SRG scans and the XMM-Newton
observation, spanning over $\sim 7.5$ months, implying that the quasar remained
at this extremely high luminosity level for at least a month in its rest frame.
We put forward the hypothesis that the extreme X-ray properties of CFHQS
J142952+544717 are associated with inverse Compton scattering of cosmic
microwave background photons (at z=6.18) in its relativistic jets.",2011.13724v2
2020-12-02,Synthesis and Characterization of Sodium Iron Antimonate Na2FeSbO5 One-Dimensional Antiferromagnetic Chain Compound with a Spin Glass Ground State,"A new oxide, sodium iron antimonate, Na2FeSbO5, was synthesized and
structurally characterized, and its static and dynamic magnetic properties were
comprehensively studied both experimentally by dc and ac magnetic
susceptibility, magnetization, specific heat, electron spin resonance (ESR) and
Moessbauer measurements, and theoretically by density functional calculations.
The resulting single-crystal structure (a = 15.6991(9) A; b = 5.3323 (4) A; c =
10.8875(6) A; S.G. Pbna) consists of edge-shared SbO6 octahedral chains, which
alternate with vertex-linked, magnetically active FeO4 tetrahedral chains. The
57Fe Moessbauer spectra confirmed the presence of high-spin Fe3+ (3d5) ions in
a distorted tetrahedral oxygen coordination. The magnetic susceptibility and
specific heat data show the absence of a long-range magnetic ordering in
Na2FeSbO5 down to 2 K, but ac magnetic susceptibility unambigously demonstrates
spin-glass-type behavior with a unique two-step freezing at Tf1 about 80 K and
Tf2 about 35 K. Magnetic hyperfine splitting of 57Fe Moessbauer spectra was
observed below T* about 104 K (Tf1 < T*). The spectra just below T* (Tf1 < T <
T*) exhibit a relaxation behavior caused by critical spin fluctuations,
indicating the existence of short-range correlations. The stochastic model of
ionic spin relaxation was used to account for the shape of the Moessbauer
spectra below the freezing temperature. A complex slow dynamics is further
supported by ESR data revealing two different absorption modes presumably
related to ordered and disordered segments of spin chains. The data imply a
spin-cluster ground state for Na2FeSbO5.",2012.01106v1
2021-01-02,Influence of NLTE effects in Fe I lines on inverted atmosphere II. 6301 A and 6302 A lines formed in 3DNLTE,"This paper forms the second part of our study on how the neglect of NLTE
conditions in the formation of Fe I 6301.5 A and the 6302.5 A lines influences
the atmosphere obtained by inverting their profiles in LTE. The main cause of
NLTE effects is the line opacity deficit due to the excess ionization of the Fe
I atoms by the UV photons in the Sun. In the first paper, the above
photospheric lines were assumed to have formed in 1DNLTE and the effects of
horizontal radiation transfer (RT) were neglected. In the present paper, the
iron lines are computed in 3DNLTE. We investigate the influence of horizontal
RT on the inverted atmosphere and how it can enhance or reduce the errors due
to the neglect of 1DNLTE effects. The iron lines are computed in LTE, 1DNLTE
and 3DNLTE. They all are inverted using an LTE inversion code. The atmosphere
from the inversion of LTE profiles is taken as the reference model. The test
atmospheres from the inversion of 1DNLTE and 3DNLTE profiles are compared with
it. The differences between models are analysed and correspondingly attributed
to NLTE and 3D effects. The effects of horizontal RT are evident in regions
surrounded by strong horizontal gradients in temperature. In some regions, the
3D effects enhance the 1DNLTE effects while in some, they weaken. The errors
due to neglecting the 3D effects are less than 5% in temperature while the
errors are mostly less than 20% in both velocity and magnetic field strength.
These errors are found to survive spatial and spectral degradation. The neglect
of horizontal RT is found to introduce errors in the derived atmosphere. How
large the errors are depends on how strong the local horizontal gradients are
in temperature. Compared to the 1DNLTE effect, the 3D effects are more
localised to specific regions in the atmosphere and overall less dominant.",2101.00506v1
2021-01-24,Exploring the diversity of double detonation explosions for type Ia supernovae: Effects of the post-explosion helium shell composition,"The detonation of a helium shell on top of a carbon-oxygen white dwarf has
been argued as a potential explosion mechanism for type Ia supernovae (SNe~Ia).
The ash produced during helium shell burning can lead to light curves and
spectra that are inconsistent with normal SNe~Ia, but may be viable for some
objects showing a light curve bump within the days following explosion. We
present a series of radiative transfer models designed to mimic predictions
from double detonation explosion models. We consider a range of core and shell
masses, and systematically explore multiple post-explosion compositions for the
helium shell. We find that a variety of luminosities and timescales for early
light curve bumps result from those models with shells containing $^{56}$Ni,
$^{52}$Fe, or $^{48}$Cr. Comparing our models to SNe~Ia with light curve bumps,
we find that these models can reproduce the shapes of almost all of the bumps
observed, but only those objects with red colours around maximum light ($B-V
\gtrsim 1$) are well matched throughout their evolution. Consistent with
previous works, we also show that those models in which the shell does not
contain iron-group elements provide good agreement with normal SNe~Ia of
different luminosities from shortly after explosion up to maximum light. While
our models do not amount to positive evidence in favour of the double
detonation scenario, we show that provided the helium shell ash does not
contain iron-group elements, it may be viable for a wide range of normal
SNe~Ia.",2101.09792v1
2021-03-12,Chemical analysis of the Bulge Globular Cluster NGC 6553,"Globular Clusters are among the oldest objects in the Galaxy, thus their
researchers are key to understanding the processes of evolution and formation
that the galaxy has experienced in early stages. Spectroscopic studies allow us
to carry out detailed analyzes on the chemical composition of Globular
Clusters. The aim of our research is to perform a detailed analysis of chemical
abundances to a sample of stars of the Bulge Globular Cluster NGC 6553, in
order to determine chemical patterns that allow us to appreciate the phenomenon
of Multiple Population in one of the most metal-rich Globular Clusters in the
Galaxy. This analysis is being carried out with data obtained by FLAMES/GIRAFFE
spectrograph, VVV Survey and DR2 of Gaia Mission. We analyzed 20 Red Horizontal
Branch Stars, being the first extensive spectroscopic abundance analysis for
this cluster and measured 8 chemical elements (O, Na, Mg, Si, Ca, Ti, Cr and
Ni), deriving a mean iron content of $[Fe/H] = -0.10\pm0.01$ and a mean of
$[\alpha/Fe] = 0.21\pm0.02$, considering Mg, Si, Ca and Ti (errors on the
mean). We found a significant spread in the content of Na but a small or
negligible in O. We did not find an intrinsic variation in the content of
$\alpha$ and iron-peak elements, showing a good agreement with the trend of the
Bulge field stars, suggesting a similar origin and evolution.",2103.07014v1
2021-04-03,Genuine Electronic Structure and Superconducting Gap Structure in (Ba$_{0.6}$K$_{0.4}$)Fe$_{2}$As$_{2}$ Superconductor,"The electronic structure and superconducting gap structure are prerequisites
to establish microscopic theories in understanding the superconductivity
mechanism of iron-based superconductors. However, even for the most extensively
studied optimally-doped (Ba$_{0.6}$K$_{0.4}$)Fe$_2$As$_2$, there remain
outstanding controversies on its electronic structure and superconducting gap
structure. Here we resolve these issues by carrying out high-resolution
angle-resolved photoemission spectroscopy (ARPES) measurements on the
optimally-doped (Ba$_{0.6}$K$_{0.4}$)Fe$_2$As$_2$ superconductor using both
Helium lamp and laser light sources. Our results indicate the ""flat band""
feature observed around the Brillouin zone center in the superconducting state
originates from the combined effect of the superconductivity-induced band
back-bending and the folding of a band from the zone corner to the center. We
found direct evidence of the band folding between the zone corner and the
center in both the normal and superconducting state. Our resolution of the
origin of the flat band makes it possible to assign the three hole-like bands
around the zone center and determine their superconducting gap correctly.
Around the zone corner, we observe a tiny electron-like band and an M-shaped
band simultaneously in both the normal and superconducting states. The obtained
gap size for the bands around the zone corner ($\sim$5.5 meV) is significantly
smaller than all the previous ARPES measurements. Our results establish a new
superconducting gap structure around the zone corner and resolve a number of
prominent controversies concerning the electronic structure and superconducting
gap structure in the optimally-doped (Ba$_{0.6}$K$_{0.4}$)Fe$_2$As$_2$. They
provide new insights in examining and establishing theories in understanding
superconductivity mechanism in iron-based superconductors.",2104.01407v1
2021-05-04,"The Effect of Geometry, Spin and Orbital Optimization in Achieving Accurate, Fully-Correlated Results for Iron-Sulfur Cubanes","Iron-sulfur clusters comprise an important functional motif of the catalytic
centers of biological systems, capable of enabling important chemical
transformations at ambient conditions. This remarkable capability derives from
a notoriously complex electronic structure that is characterized by a high
density of states that is sensitive to geometric changes. The spectral
sensitivity to subtle geometric changes has received little attention from
fully-correlated calculations, owing partly to the exceptional computational
complexity for treating these large and correlated systems accurately. To
provide insight into this aspect, we report the first Complete Active Space
Self Consistent Field (CASSCF) calculations for different geometries of
cubane-based clusters using two complementary, fully-correlated solvers:
spin-pure Adaptive Sampling Configuration Interaction (ASCI) and Density Matrix
Renormalization Group (DMRG). We find that the previously established picture
of a double-exchange driven magnetic structure, with minute energy gaps (< 1
mHa) between consecutive spin states, has a weak dependence on the underlying
geometry. However, the spin gap between the lowest singlet and the highest spin
states is strongly geometry dependent, changing by an order of magnitude upon
slight deformations that are still within biologically relevant parameters. The
CASSCF orbital optimization procedure, using active spaces as large as 86
electrons in 52 orbitals, was found to reduce this gap by a factor of two
compared to typical mean-field orbital approaches. Our results clearly
demonstrate the need for performing highly correlated calculations to unveil
the challenging electronic structure of these complex catalytic centers.",2105.01754v2
2021-05-10,Cloud busting: enstatite and quartz clouds in the atmosphere of 2M2224-0158,"We present the most detailed data-driven exploration of cloud opacity in a
substellar object to-date. We have tested over 60 combinations of cloud
composition and structure, particle size distribution, scattering model, and
gas phase composition assumptions against archival $1-15 {\rm \mu m}$
spectroscopy for the unusually red L4.5~dwarf 2MASSW~J2224438-015852 using the
Brewster retrieval framework. We find that, within our framework, a model that
includes enstatite and quartz cloud layers at shallow pressures, combined with
a deep iron cloud deck fits the data best. This models assumes a Hansen
distribution for particle sizes for each cloud, and Mie scattering. We
retrieved particle effective radii of $\log_{10} a {\rm (\mu m)} =
-1.41^{+0.18}_{-0.17}$ for enstatite, $-0.44^{+0.04}_{-0.20}$ for quartz, and
$-0.77^{+0.05}_{-0.06}$ for iron. Our inferred cloud column densities suggest
${\rm (Mg/Si)} = 0.69^{+0.06}_{-0.08}$ if there are no other sinks for
magnesium or silicon. Models that include forsterite alongside, or in place of,
these cloud species are strongly rejected in favour of the above combination.
We estimate a radius of $0.75 \pm 0.02$ Rjup, which is considerably smaller
than predicted by evolutionary models for a field age object with the
luminosity of 2M2224-0158. Models which assume vertically constant gas
fractions are consistently preferred over models that assume thermochemical
equilibrium. From our retrieved gas fractions we infer ${\rm [M/H]} =
+0.38^{+0.07}_{-0.06}$ and ${\rm C/O} = 0.83^{+0.06}_{-0.07}$. Both these
values are towards the upper end of the stellar distribution in the Solar
neighbourhood, and are mutually consistent in this context. A composition
toward the extremes of the local distribution is consistent with this target
being an outlier in the ultracool dwarf population.",2105.04268v1
2021-05-13,Near-Room-Temperature Ferromagnetic Behavior of Single-Atom-Thick 2D Iron in Nanolaminated Ternary MAX Phases,"Two dimensional (2D) ferromagnetic materials have attracted much attention in
the fields of condensed matter physics and materials science, but their
synthesis is still a challenge given their limitations on structural stability
and susceptibility to oxidization. MAX phases nanolaminated ternary carbides or
nitrides possess a unique crystal structure in which single-atom-thick A
sublayers are interleaved by two dimensional MX slabs, providing nanostructured
templates for designing 2D ferromagnetic materials if the non-magnetic A
sublayers can be substituted replaced by magnetic elements. Here, we report
three new ternary magnetic MAX phases (Ta2FeC, Ti2FeN and Nb2FeC) with A
sublayers of single-atom-thick 2D iron through an isomorphous replacement
reaction of MAX precursors (Ta2AlC, Ti2AlN and Nb2AlC) with a Lewis acid salts
(FeCl2). All these MAX phases exhibit ferromagnetic (FM) behavior. The Curie
temperature (Tc) of Ta2FeC and Nb2FeC MAX phase are 281 K and 291 K,
respectively, i.e. close to room temperature. The saturation magnetization of
these ternary magnetic MAX phases is almost two orders of magnitude higher than
that of V2(Sn,Fe)C MAX phase whose A-site is partial substituted by Fe.
Theoretical calculations on magnetic orderings of spin moments of Fe atoms in
these nanolaminated magnetic MAX phases reveal that the magnetism can be mainly
ascribed to intralayer exchange interaction of the 2D Fe atomic layers. Owning
to the richness in composition of MAX phases, there is a large compositional
space for constructing functional single-atom-thick 2D layers in materials
using these nanolaminated templates.",2105.06139v1
2021-05-26,Magnetic Particle Spectroscopy (MPS) with One-stage Lock-in Implementation for Magnetic Bioassays with Improved Sensitivities,"In recent years, magnetic particle spectroscopy (MPS) has become a highly
sensitive and versatile sensing technique for quantitative bioassays. It relies
on the dynamic magnetic responses of magnetic nanoparticles (MNPs) for the
detection of target analytes in liquid phase. There are many research studies
reporting the application of MPS for detecting a variety of analytes including
viruses, toxins, and nucleic acids, etc. Herein, we report a modified version
of MPS platform with the addition of a one-stage lock-in design to remove the
feedthrough signals induced by external driving magnetic fields, thus capturing
only MNP responses for improved system sensitivity. This one-stage lock-in MPS
system is able to detect as low as 781 ng multi-core Nanomag50 iron oxide MNPs
(micromod Partikeltechnologie GmbH) and 78 ng single-core SHB30 iron oxide MNPs
(Ocean NanoTech). In addition, using a streptavidin-biotin binding system as a
proof-of-concept, we show that these single-core SHB30 MNPs can be used for
Brownian relaxation-based bioassays while the multi-core Nanomag50 cannot be
used. The effects of MNP amount on the concentration dependent response
profiles for detecting streptavidin was also investigated. Results show that by
using lower concentration/amount of MNPs, concentration-response curves shift
to lower concentration/amount of target analytes. This lower
concentrationresponse indicates the possibility of improved bioassay
sensitivities by using lower amounts of MNPs.",2105.12718v1
2021-09-13,The stellar mass versus stellar metallicity relation of star-forming galaxies at $1.6\le z\le3.0$ and implications for the evolution of the $α$-enhancement,"We measure the relationship between stellar mass and stellar metallicity, the
stellar mass--metallicity relation (MZR), for 1336 star-forming galaxies at
$1.6\le z\le3.0$ (<z>=2.2) using rest-frame far-ultraviolet spectra from the
zCOSMOS-deep survey. High signal-to-noise composite spectra containing stellar
absorption features are fit with population synthesis model spectra of a range
of metallicity. We find stellar metallicities, which mostly reflect iron
abundances, scaling as
$(Z_{Fe,\ast}/Z_{Fe,\odot})=-(0.81\pm0.01)+(0.32+0.03)\log(M_\ast/10^{10}M_\odot)$
across the mass range of $10^9\lesssim M_\ast/M_\odot\lesssim10^{11}$, being
$\approx6\times$ lower than seen locally at the same masses. The instantaneous
oxygen-to-iron ratio ($\alpha$-enhancement) inferred using the gas-phase oxygen
MZRs, is on average found to be [O/Fe]$\approx0.47$, being higher than the
local [O/Fe]$\approx0$. The observed changes in [O/Fe] and [Fe/H] are
reproduced in simple flow-through gas-regulator models with steady
star-formation histories (SFHs) that follow the evolving main sequence. Our
models show that the [O/Fe] is determined almost entirely by the instantaneous
specific star formation rate alone while being independent of the SFHs, mass,
and the gas-regulation characteristics of the systems. We find that the
locations of $\sim10^{10}M_\odot$ galaxies at z~2 in the [O/Fe]--metallicity
planes are in remarkable agreement with the sequence of low-metallicity
thick-disk stars in our Galaxy. This manifests a beautiful concordance between
the results of Galactic archaeology and observations of high-redshift Milky Way
progenitors. However, there remains a question of how and when the old
metal-rich, low-$\alpha$/Fe stars seen in the bulge had formed by z~2 because
such a stellar population is not seen in our data and difficult to explain in
the context of our models.",2109.06044v1
2021-09-28,Stable nickel production in Type Ia supernovae: A smoking gun for the progenitor mass?,"At present, there are strong indications that white dwarf (WD) stars with
masses well below the Chandrasekhar limit (MCh ~ 1.4 Msun) contribute a
significant fraction of SN Ia progenitors. The relative fraction of stable
iron-group elements synthesized in the explosion has been suggested as a
possible discriminant between MCh and sub-MCh events. In particular, it is
thought that the higher-density ejecta of MCh WDs, which favours the synthesis
of stable isotopes of nickel, results in prominent [Ni II] lines in late-time
spectra. We study the explosive nucleosynthesis of stable nickel in SNe Ia
resulting from MCh and sub-MCh progenitors. We explore the potential for lines
of [Ni II] at 7378 \AA\ and 1.94 microns in late-time spectra to serve as a
diagnostic of the exploding WD mass, using nonlocal thermodynamic equilibrium
radiative-transfer simulations with the CMFGEN code. We find that the radiative
proton-capture reaction 57Co(p,gamma)58Ni is the dominant production mode for
58Ni in both MCh and sub-MCh models, while the alpha-capture reaction on 54Fe
has a negligible impact on the final 58Ni yield. More importantly, we
demonstrate that the lack of [Ni II] lines in late-time spectra of sub-MCh
events is not always due to an under-abundance of stable Ni; rather, it results
from the higher ionization of Ni in the inner ejecta. Conversely, the strong
[Ni II] lines predicted in our 1D MCh models are completely suppressed when
56Ni is sufficiently mixed with the innermost layers, which are rich in stable
iron-group elements. [Ni II] lines in late-time SN Ia spectra have a complex
dependency on the abundance of stable Ni, which limits their use in
distinguishing among MCh and sub-MCh progenitors. However, we argue that a
low-luminosity SN Ia displaying strong [Ni II] lines would most likely result
from a Chandrasekhar-mass progenitor. [Abridged]",2109.13840v3
2021-10-17,The iron and oxygen content of LMC Classical Cepheids and its implications for the Extragalactic Distance Scale and Hubble constant,"Classical Cepheids are primary distance indicators and a crucial stepping
stone to determining the present-day Hubble constant Ho to the precision and
accuracy required to constrain apparent deviations from the LCDM Concordance
Cosmological Model. We have measured the iron and oxygen abundances of of 89
Cepheids in the LMC, one of the anchors of the local Distance Scale,
quadrupling the prior sample and including 68 of the 70 Cepheids used to
constrain Ho by the SH0ES program. The goal is to constrain the extent to which
the Cepheid luminosity is influenced by their chemical composition, an
important contributor to the uncertainty on the determination of the Ho itself
and a critical factor in the internal consistency of the distance ladder. We
have derived stellar parameters and abundances from a self-consistent
spectroscopic analysis based on Equivalent Width of absorption lines. The
[Fe/H] distribution of LMC Cepheids is a single Gaussian with a mean of
-0.4079+-0.003 dex (0.1 dex systematic uncertainty) and sigma 0.076+-0.003 dex.
The latter is fully compatible with the measurement error and supports the low
dispersion of 0.069 mag seen in the NIR HST LMC period-luminosity relation. The
uniformity of the abundance has the important consequence that the LMC Cepheids
alone cannot provide any meaningful constraint on the dependence of the Cepheid
Period-Luminosity relation on chemical composition at any wavelength. This
revises a prior claim based on a small sample of 22 LMC Cepheids that there was
little dependence (or uncertainty) between composition and NIR luminosity, a
conclusion which would produce a conflict between anchors of the distance
ladder with different mean abundance. The chemical homogeneity of the LMC
Cepheid population makes it an ideal environment to calibrate the metallicity
dependence between the more metal poor SMC and metal rich Milky Way and
NGC4258.",2110.08860v2
2022-01-05,Phase-resolved spectroscopy of a quasi-periodic oscillation in the black hole X-ray binary GRS 1915+105 with NICER and NuSTAR,"Quasi-periodic oscillations (QPOs) are often present in the X-ray flux from
accreting stellar-mass black holes (BHs). If they are due to relativistic
(Lense-Thirring) precession of an inner accretion flow which is misaligned with
the disc, the iron emission line caused by irradiation of the disc by the inner
flow will rock systematically between red and blue shifted during each QPO
cycle. Here we conduct phase-resolved spectroscopy of a $\sim2.2$ Hz type-C QPO
from the BH X-ray binary GRS 1915+105, observed simultaneously with NICER and
NuSTAR. We apply a tomographic model in order to constrain the QPO
phase-dependent illumination profile of the disc. We detect the predicted QPO
phase-dependent shifts of the iron line centroid energy, with our best fit
featuring an asymmetric illumination profile ($>2{\sigma}$ confidence). The
observed line energy shifts can alternatively be explained by the spiral
density waves of the accretion-ejection instability model. However we
additionally measure a significant ($>3{\sigma}$) modulation in reflection
fraction, strongly favouring a geometric QPO origin. We infer that the disc is
misaligned with previously observed jet ejections, which is consistent with the
model of a truncated disc with an inner precessing hot flow. However our
inferred disc inner radius is small ($r_\text{in}{\sim} 1.4 GM/c^2$). For this
disc inner radius, Lense-Thirring precession cannot reproduce the observed QPO
frequency. In fact, this disc inner radius is incompatible with the predictions
of all well-studied QPO models in the literature.",2201.01765v1
2022-01-24,Formation of Zn and Pb sulfides in a redox-sensitive modern system due to high atmospheric fallout,"The study shows that the air-derived metal enrichment (up to 2.3 g Zn kg-1,
1.1 g Pb kg-1, and 62 mg Cd kg-1) is retained in a thin layer (~30 cm) around
10-15 cm below the peat surface. A combination of focused ion beam (FIB)
technology and scanning (SEM) and transmission (TEM) electron microscopy
reveals that micrometric spheroids are most characteristic for ZnS and
(Zn,Cd)S, although the sulfides readily form pseudomorphs after different plant
tissues resulting in much larger aggregates. The aggregates have a complex
polycrystalline sphalerite structure much more advanced than typically obtained
during low-temperature synthesis or observed in other modern occurrences. Platy
highly-disordered radially-aggregated submicrometre crystals develop within the
time constraints of several decades in the cold (~15{\deg}C) and acid (pH
3.4-4.4) peat. The less abundant Pb sulfides occur as submicron cube-like
crystals between ZnS or as flat irregular or square patches on plant root
macrofossils. All PbS are crystalline and defect-free. Pb ion complexation with
dissolved and solid organic matter is probably responsible for the low number
and equilibrium shape of PbS crystals. Iron is absent in the authigenic sulfide
mineralization and occurs entirely as organically bound ferric iron (Fe3+), as
revealed by Mossbauer spectroscopy. The different affinity of metals to organic
matter enhances the precipitation of Zn and Cd as sulfides over Pb and Fe. Our
findings demonstrate that human activities lead to the formation of
near-surface stratiform metal sulfide accumulations in peat, and the polluted
sites can be of use to understand and reconstruct ancient ore deposits' genesis
and mechanisms of formation.",2201.09552v1
2022-02-14,Giant Impact onto a Vesta-Like Asteroid and Formation of Mesosiderites through Mixing of Metallic Core and Surface Crust,"Mesosiderites are a type of stony-iron meteorites composed of a mixture of
silicates and Fe-Ni metals. The mesosiderite silicates and metals are
considered to have originated from the crust and metal core, respectively, of a
differentiated asteroid. In contrast, mesosiderites rarely contain the olivine
that is mainly included in a mantle. Although a giant impact onto a
differentiated asteroid is considered to be a probable mechanism to mix crust
and metal materials to form mesosiderites, it is not obvious how such a giant
impact can form mesosiderite-like materials without including mantle materials.
We conducted numerical simulations of giant impacts onto differentiated
asteroids, using the smoothed particle hydrodynamics method, to investigate the
detailed distribution of mixed materials on the resultant bodies. For the
internal structure of a target body, we used a thin-crust model derived from
the magma ocean crystallization model of the asteroid Vesta and a thick-crust
and a large-core model suggested from the proximity observation of Vesta by the
Dawn probe. In the simulations with the former model, excavation of the metal
core requires nearly catastrophic impacts and mantle is exposed over large
surface areas. Thus, stony-iron materials produced on its surface are likely to
include mantle materials and it is difficult to produce mesosiderite-like
materials. Conversely, in the simulations with the latter model, mantle
materials are exposed only at impact sites, even when the impacts excavate the
metal core, and the formation of a surface with little mantle material and the
formation of mesosiderite-like materials are possible. Therefore, our
simulations suggest that an internal structure with a thick crust and a large
core is more likely as a mesosiderite parent body rather than the thin-crust
internal structure inferred from the conventional magma ocean model.",2202.06486v1
2022-02-16,"Spin Seebeck effect in iron oxide thin films: Effects of phase transition, phase coexistence, and surface magnetism","Understanding impacts of phase transition, phase coexistence, and surface
magnetism on the longitudinal spin Seebeck effect (LSSE) in a magnetic system
is essential to manipulate the spin to charge current conversion efficiency for
spincaloritronic applications. We aim to elucidate these effects by performing
a comprehensive study of the temperature dependence of LSSE in biphase iron
oxide (BPIO = alpha-Fe2O3 + Fe3O4) thin films grown on Si (100) and Al2O3 (111)
substrates. A combination of temperature-dependent anomalous Nernst effect
(ANE) and electrical resistivity measurements show that the contribution of ANE
from the BPIO layer is negligible compared to the intrinsic LSSE in the
Si/BPIO/Pt heterostructure even at room temperature. Below the Verwey
transition of the Fe3O4 phase, the total signal across BPIO/Pt is dominated by
the LSSE. Noticeable changes in the intrinsic LSSE signal for both Si/BPIO/Pt
and Al2O3/BPIO/Pt heterostructures around the Verwey transition of the Fe3O4
phase and the antiferromagnetic (AFM) Morin transition of the alpha-Fe2O3 phase
are observed. The LSSE signal for Si/BPIO/Pt is found to be almost two times
greater than that for Al2O3/BPIO/Pt, an opposite trend is observed for the
saturation magnetization though. Magnetic force microscopy reveals the higher
density of surface magnetic moments of the Si/BPIO film compared to the
Al2O3/BPIO film, which underscores a dominant role of interfacial magnetism on
the LSSE signal and thereby explains the larger LSSE for Si/BPIO/Pt.",2202.07910v1
2022-02-16,A new and homogeneous metallicity scale for Galactic classical Cepheids II. The abundance of iron and alpha elements,"Classical Cepheids are the most popular distance indicators and tracers of
young stellar populations. The key advantage is that they are bright and they
can be easily identified in Local Group and Local Volume galaxies. Their
evolutionary and pulsation properties depend on their chemical abundances. The
main aim of this investigation is to perform a new and accurate abundance
analysis of two tens of calibrating Galactic Cepheids using high spectral
resolution (R$\sim$40,000-115,000) and high S/N spectra ($\sim$400) covering
the entire pulsation cycle. We focus our attention on possible systematics
affecting the estimate of atmospheric parameters and elemental abundances along
the pulsation cycle. We cleaned the line list by using atomic transition
parameters based on laboratory measurements and by removing lines that are
either blended or display abundance variations along the pulsation cycle. The
spectroscopic approach that we developed brings forward small dispersions in
the variation of the atmospheric parameters ($\sigma$($T_{\rm eff}$)$\sim$50 K,
$\sigma$($\log{g}$)$\sim$0.2 dex, and $\sigma$($\xi$)$\sim$0.2 km/s) and in the
abundance of both iron ($\lesssim$ 0.05 dex) and alpha elements ($\lesssim$0.10
dex) over the entire pulsation cycle. We also provide new and accurate
effective temperature templates by splitting the calibrating Cepheids into four
different period bins, ranging from short to long periods. For each period bin,
we performed an analytical fit with Fourier series providing $\theta =
5040/{T_{\rm eff}}$ as a function of the pulsation phase. The current findings
are a good viaticum to trace the chemical enrichment of the Galactic thin disk
by using classical Cepheids and a fundamental stepping stone for further
investigations into the more metal-poor regime typical of Magellanic Cepheids.",2202.07945v1
2022-03-01,Low-luminosity type IIP supernovae: SN 2005cs and SN 2020cxd as very low-energy iron core-collapse explosions,"SN 2020cxd is a representative of the family of low-energy, underluminous
Type IIP supernovae (SNe), whose observations and analysis were recently
reported by Yang et al. (2021). Here we re-evaluate the observational data for
the diagnostic SN properties by employing the hydrodynamic explosion model of a
9 MSun red supergiant progenitor with an iron core and a pre-collapse mass of
8.75 Msun. The explosion of the star was obtained by the neutrino-driven
mechanism in a fully self-consistent simulation in three dimensions (3D).
Multi-band light curves and photospheric velocities for the plateau phase are
computed with the one-dimensional radiation-hydrodynamics code STELLA, applied
to the spherically averaged 3D explosion model as well as spherisized radial
profiles in different directions of the 3D model. We find that the overall
evolution of the bolometric light curve, duration of the plateau phase, and
basic properties of the multi-band emission can be well reproduced by our SN
model with its explosion energy of only 0.7x10^50 erg and an ejecta mass of 7.4
Msun. These values are considerably lower than the previously reported numbers,
but they are compatible with those needed to explain the fundamental
observational properties of the prototype low-luminosity SN 2005cs. Because of
the good compatibility of our photospheric velocities with line velocities
determined for SN 2005cs, we conclude that the line velocities of SN 2020cxd
are probably overestimated by up to a factor of about 3. The evolution of the
line velocities of SN 2005cs compared to photospheric velocities in different
explosion directions might point to intrinsic asymmetries in the SN ejecta.",2203.00473v2
2022-03-06,Coupling between the accreting corona and the relativistic jet in the micro quasar GRS 1915+105,"GRS 1915+105 was the first stellar-mass black-hole in our Galaxy to display a
superluminal radio jet, similar to those observed in active galactic nuclei
with a supermassive black hole at the centre. It has been proposed that the
radio emission in GRS 1915+105 is fed by instabilities in the accretion disc by
which the inner parts of the accretion flow is ejected in the jet. Here we show
that there is a significant correlation between: (i) the radio flux, coming
from the jet, and the flux of the iron emission line, coming from the disc and,
(ii) the temperature of the corona that produces the high-energy part of the
X-ray spectrum via inverse Compton scattering and the amplitude of a
high-frequency variability component coming from the innermost part of the
accretion flow. At the same time, the radio flux and the flux of the iron line
are strongly anti-correlated with the temperature of the X-ray corona and the
amplitude of the high-frequency variability component. These correlations
persist over ~10 years, despite the highly variable X-ray and radio properties
of the source in that period. Our findings provide, for the first time,
incontrovertible evidence that the energy that powers this black-hole system
can be directed either to the X-ray corona or the jet. When this energy is used
to power the corona, raising its temperature, there is less energy left to fuel
the jet and the radio flux drops, and vice versa. These facts, plus the
modelling of the variability in this source show conclusively that in GRS
1915+105 the X-ray corona morphs into the jet.",2203.02963v1
2022-03-07,"The in situ origin of the globular cluster NGC 6388 from abundances of Sc, V, and Zn of a large sample of stars","Chemical tagging of globular clusters (GCs) is often done using abundances of
alpha-elements. The iron-peak elements Sc, V, and in particular Zn were
proposed as an alternative to alpha-elements to tag accreted GCs in the
metal-rich regime, where the dwarf galaxy Sagittarius and its GCs show
peculiarly marked under-abundances of these heavier species with respect to
Milky Way stars. A handful of stars in NGC 6388 was used to suggest an accreted
origin for this GC, contradicting the results from dynamics. We tested the
efficiency of the iron-peak method by using large samples of stars in NGC 6388,
compared to thousands of field stars in the disc and the bulge of the Milky
Way. Our abundance ratios of Sc (185 stars) and V (35 stars) for NGC 6388 are
within about 1.5 sigma from the average for the field stars with a similar
metallicity, and they are in perfect agreement for Zn (31 stars), claimed to be
the most sensitive element concerning the accretion pattern. Moreover, the
chemo-dynamical plots, coupled to the bifurcated age-metallicity relation of
GCs in the Galaxy, clearly rule out any association of NGC 6388 to the groups
of accreted GCs. Using a large set of GC abundances from the literature, we
also show that the new method with Sc, V, and Zn seems to be efficient in
picking up GCs related to the Sagittarius dwarf galaxy. Whether this is also
generally true for accreted GCs seems to be less evident, and it should be
verified with larger and homogeneous samples of stars both in the field and in
GCs.",2203.03645v1
2022-03-22,Co-loading of doxorubicin and iron oxide nanocubes in polycaprolactone fibers for combining Magneto-Thermal and chemotherapeutic effects on cancer cells,"Among the strategies to fight cancer, multi-therapeutic approaches are
considered as a wise choice to put in place multiple weapons to suppress
tumors. In this work, to combine chemotherapeutic effects to magnetic
hyperthermia when using biocompatible scaffolds, we have established an
electrospinning method to produce nanofibers of polycaprolactone loaded with
magnetic nanoparticles as heat mediators to be selectively activated under
alternating magnetic field and doxorubicin as a chemotherapeutic drug.
Production of the fibers was investigated with iron oxide nanoparticles of
peculiar cubic shape (at 15 and 23 nm in cube edges) as they provide benchmark
heat performance under clinical magnetic hyperthermia conditions. With 23 nm
nanocubes when included into the fibers, an arrangement in chains was obtained.
This linear configuration of magnetic nanoparticles resemble that of the
magnetosomes, produced by magnetotactic bacteria, and our magnetic fibers
exhibited remarkable heating effects as the magnetosomes. Magnetic fiber
scaffolds showed excellent biocompatibility on fibroblast cells when missing
the chemotherapeutic agent and when not exposed to magnetic hyperthermia as
shown by viability assays. On the contrary, the fibers containing both magnetic
nanocubes and doxorubicin showed significant cytotoxic effects on cervical
cancer cells following the exposure to magnetic hyperthermia. Notably, these
tests were conducted at magnetic hyperthermia field conditions of clinical use.
As here shown, on the doxorubicin sensitive cervical cancer cells, the
combination of heat damage by magnetic hyperthermia with enhanced diffusion of
doxorubicin at therapeutic temperature are responsible for a more effective
oncotherapy.",2203.12380v1
2022-03-23,Prospects of measuring a metallicity trend and spread in globular clusters from low-resolution spectroscopy,"The metallicity spread, or the metallicity trend along the evolutionary
sequence of a globular cluster, is a rich source of information to help
understand the cluster physics (e.g. multiple populations) and stellar physics
(e.g. atomic diffusion). Low-resolution integral-field-unit spectroscopy in the
optical with the MUSE is an attractive prospect if it can provide these
diagnostics because it allows us to extract spectra of a large fraction of the
cluster stars. We investigate the possibilities of full-spectrum fitting to
derive stellar parameters and chemical abundances at low spectral resolution
(R~2000). We reanalysed 1584 MUSE spectra of 1061 stars above the turn-off of
NGC 6397 using FERRE and employing two different synthetic libraries. We derive
the equivalent iron abundance \fehe for fixed values of \afe. We find that (i)
the interpolation schema and grid mesh are not critical for the precision,
metallicity spread, and trend; (ii) with the two grids, \fehe increases by ~0.2
dex along the sub-giant branch, starting from the turn-off of the main
sequence; (iii) restricting the wavelength range to the optical decreases the
precision significantly; and (iv) the precision obtained with the synthetic
libraries is lower than the precision obtained previously with empirical
libraries. Full-spectrum fitting provides reproducible results that are robust
to the choice of the reference grid of synthetic spectra and to the details of
the analysis. The \fehe increase along the sub-giant branch is in stark
contrast with the nearly constant iron abundance previously found with
empirical libraries. The precision of the measurements (0.05 dex on \fehe) is
currently not sufficient to assess the intrinsic chemical abundance spreads,
but this may change with deeper observations. Improvements of the synthetic
spectra are still needed to deliver the full possibilities of full-spectrum
fitting.",2203.12685v1
2022-03-30,The p-process in exploding rotating massive stars,"The p-process nucleosynthesis can explain proton-rich isotopes that are
heavier than iron, which are observed in the Solar System, but discrepancies
still persist and important questions concerning the astrophysical site(s) of
the p-process remain unanswered. We investigate how the p-process operates in
exploding rotating massive stars that have experienced an enhanced s-process
nucleosynthesis during their life through rotational mixing. We computed 25
$M_{\odot}$ stellar models at a metallicity of $Z=10^{-3}$ with different
initial rotation velocities and rates for the uncertain
$^{17}$O($\alpha$,$\gamma$)$^{21}$Ne reaction. The nucleosynthesis calculation,
followed with a network of 737 isotopes, was coupled to stellar evolution, and
the p-process nucleosynthesis was calculated in post-processing during both the
final evolutionary stages and spherical explosions of various energies. In our
models, the p-nuclides are mainly synthesized during the explosion, but not
much during the ultimate hydrostatic burning stages. The p-process yields
mostly depend on the initial number of trans-iron seeds, which in turn depend
on the initial rotation. We found that the impact of rotation on the p-process
is comparable to the impact of rotation on the s-process. From no to fast
rotation, the s-process yields of nuclides with mass number $A<140$ increase by
$3-4$ dex, and so do the p-process yields. Fast rotation with a lower
$^{17}$O($\alpha,\gamma$) rate significantly produces s- and p-nuclides with
$A\geq140$. Our results suggest that the contribution of core-collapse
supernovae from massive stars to the solar (and Galactic) p-nuclei has been
underestimated in the past, and more specifically, that the contribution from
massive stars with sub-solar metallicities may even dominate. A more detailed
study including stellar models with a wide range of masses and metallicities
remains to be performed.",2203.16380v1
2022-04-11,The GAPS Programme at TNG XXXIII. HARPS-N detects multiple atomic species in emission from the dayside of KELT-20b,"The detection of lines in emission in planetary atmospheres provides direct
evidence of temperature inversion. We confirm the trend of ultra-hot Jupiters
orbiting A-type stars showing temperature inversions on their daysides, by
detecting metals emission lines in the dayside of KELT-20b. We first detect the
planetary emission by using the G2 stellar mask of the HARPS-N pipeline, which
is mainly composed of neutral iron lines, as a template. Using neutral iron
templates, we perform a retrieval of the atmospheric temperature-pressure
profile of the planet, confirming a thermal inversion. Then we create models of
planetary emission of different species using the retrieved inverted
temperature-pressure profile. By using the cross-correlation technique, we
detect FeI, FeII and CrI at signal-to-noise ratio levels of 7.1, 3.9 and 3.6,
respectively. The latter is detected for the first time in emission in the
atmosphere of an exoplanet. Contrary to FeI, FeII and CrI are detected only
after the occultation and not before, hinting for different atmospheric
properties in view on the pre- and post- occultation orbital phases. A further
retrieval of the temperature-pressure profile performed independently on the
pre- and post- occultation phases, while not highly significant, points to a
steeper thermal inversion in the post-occultation.",2204.04948v1
2022-05-19,Nuclear Weak Rates and Nuclear Weak Processes in Stars,"Nuclear weak rates in stellar environments are obtained by shell-model
calculations including Gamow-Teller (GT) and spin-dipole transitions, and
applied to nuclear weak processes in stars. The important roles of accurate
weak rates for the study of astrophysical processes are pointed out. The weak
rates in $sd$-shell are used to study the evolution of ONeMg cores in stars
with 8-10 M$_{\odot}$. Cooling of the core by nuclear Urca processes, and the
heating by double e-captures on $^{20}$Ne are studied. Especially, the
e-capture rates for a second-forbidden transition in $^{20}$Ne are evaluated
with the multipole expansion method of Walecka and
Behrens-B$\ddot{\mbox{u}}$hring, and the final fate of the cores, core-collapse
or thermonuclear explosion, are discussed. The weak rates in $pf$-shell are
applied to nucleosynthesis of iron-group elements in Type Ia supernovae. The
over-production problem of neutron-rich iron isotopes compared with the solar
abundances is now reduced to be within a factor of two. The weak rates for
nuclear Urca pair with $A$=31 in the island of inversion are evaluated with the
effective interaction obtained by the extended Kuo-Krenciglowa method. The
transition strengths and e-capture rates in $^{78}$Ni, important for
core-collapse processes, are evaluated with the $pf$-$sdg$ shell, and compared
with those obtained by the random-phase-approximation and an effective rate
formula. $\beta$-decay rates of $N$ =126 isotones are evaluated with both the
GT and first-forbidden transitions. The half-lives are found to be shorter than
those obtained by standard models. Neutrino-nucleus reaction cross sections on
$^{13}$C, $^{16}$O and $^{40}$Ar are obtained with new shell-model
Hamiltonians. Implications on nucleosynthesis, neutrino detection, neutrino
oscillations and neutrino mass hierarchy are discussed.",2205.09262v2
2022-06-29,Does the Fe L-shell blend bias abundance measurements in intermediate-temperature clusters?,"In intermediate-temperature (T = 2.5 - 4.5 keV) galaxy clusters, abundance
measurements are almost-equally driven by Fe K and L transitions, at $\sim$ 6.7
keV and 0.9 - 1.3 keV, respectively. While K-shell-derived measurements are
considered reliable, the resolution of the currently available instrumentation,
as well as our current knowledge of the atomic processes, makes the modelling
of the L-line complex challenging, resulting in potential biases for abundance
measurements. In this work, we study systematics related to the modelling of
the Fe L-line complex that may influence iron-abundance measurements in the
intermediate-temperature range. To this aim, we select a sample of three bright
galaxy clusters, with long XMM-Newton observations available and temperature in
the 2.5 - 4.5 keV range. We fit spectra extracted from concentric rings with
APEC and APEC+APEC models, by alternatively excluding the L and K bands, and
derive the fractional difference of the metal abundances, $\Delta Z/Z$, as
indication of the consistency between K- and L-shell-derived measurements. The
$\Delta Z/Z$ distribution is then studied as a function of the cluster radius,
ring temperature and X-ray flux. The L-induced systematics, measured through an
individual fit of each MOS and pn spectrum, remain constant at a 5 - 6% value
in the whole 2.5 - 4.5 keV temperature range. Conversely, a joint fit of MOS
and pn spectra leads to a slight excess of 1 - 2% in the above estimate. No
significant dependence on the ring X-ray flux is highlighted. The measured 5 -
8% value indicates a modest contribution of the systematics to the derived iron
abundances, giving confidence for future measurements. To date, these findings
represent the best-achievable estimate of the systematics in analysis, while
future microcalorimeters will significantly improve our understanding of the
atomic processes underlying the Fe L emissions.",2206.14827v1
2022-08-08,The chemical abundance pattern of the extremely metal-poor thin disk star 2MASS J1808-5104 and its origins,"We present a high-resolution ($R\sim35,000$), high signal-to-noise
($S/N=350$) Magellan/MIKE spectrum of the bright extremely metal-poor star
2MASS~J1808$-$5104. We find [Fe/H] = $-$4.01 (spectroscopic LTE stellar
parameters), [Fe/H] = $-$3.8 (photometric stellar parameters), [Fe/H] = $-$3.7
(spectroscopic NLTE stellar parameters). We measured a carbon-to-iron ratio of
$\mbox{[C/Fe]}= 0.38$ from the CH G-band. J1808$-$5104 is thus not
carbon-enhanced, contrary to many other stars with similarly low iron
abundances. We also determine, for the first time, a barium abundance
($\mbox{[Ba/Fe]} =-0.78$), and obtain a significantly reduced upper limit for
the nitrogen abundance ([N/Fe]$ < - 0.2$). J1808$-$5104 has low ratio of
$\mbox{[Sr/Ba]}=-0.17$, which is consistent with that of stars in ultra-faint
dwarf galaxies. We also fit the abundance pattern of J1808$-$5104 with
nucleosynthesis yields from a grid of Population\,III supernova models. There
is a good fit to the abundance pattern which suggests J1808$-$5104 originated
from gas enriched by a single massive supernova with a high explosion energy of
E $=10\times10^{51}$\,erg and a progenitor stellar mass of
M$=29.5$\,M$_{\odot}$. Interestingly, J1808$-$5104 is a member of the Galactic
thin disk, as confirmed by our detailed kinematic analysis and calculated
stellar actions and velocities. Finally, we also established the orbital
history of J1808$-$5104 using our time-dependent Galactic potential the
\texttt{ORIENT}. J1808$-$5104 appears to have a stable quasi-circular orbit and
been largely confined to the thin disk. This unique orbital history, the star's
very old age ($\sim13.5$\,Gyr), and the low [C/Fe] and [Sr/Ba] ratios suggest
that J1808$-$5104 may have formed at the earliest epoch of the hierarchical
assembly of the Milky Way, and it is most likely associated with the primordial
thin disk.",2208.03891v1
2022-09-02,An intermediate polar candidate toward the Galactic plane,"For the past decade, it has been suggested that intermediate polars (IPs), a
subclass of magnetic cataclysmic variables (CVs), are one of the main
contributors to the hard diffuse X-ray emission from the Galactic center (GC)
and Galactic ridge. In our ongoing \emph{XMM-Newton} survey of the central
region of the Galactic disk ($20^\circ\times2^\circ$), we detected a persistent
IP candidate, $1.7^\circ$ away from the GC. In this work, we better
characterize the behavior of this source by looking at the new and archival
XMM-Newton data. We performed a detailed X-ray spectral modeling of the source.
Furthermore, we searched for X-ray pulsations in the light curve as well as its
counterpart at other wavelengths. The XMM-Newton spectrum (0.8--10 keV) of the
source is described by a partial covering collisionally ionized diffuse gas
with plasma temperature $kT=15.7^{+20.9}_{-3.6}$ keV. In addition, the spectrum
shows the presence of iron lines at $E=6.44$, 6.65, and 6.92 keV with
equivalent widths of $194^{+89}_{-70}$, $115^{+79}_{-75}$, and $98^{+93}_{-74}$
eV, respectively. The X-ray light curve shows a coherent modulation with a
period of $P=432.44\pm0.36$ s, which we infer is the spin period of the white
dwarf. The white dwarf mass estimated from fitting a physical model to the
spectrum results in $M_{\rm WD}=1.05^{+0.16}_{-0.21}\ M_{\odot}$. We were able
to find a likely optical counterpart in the Gaia catalog with a G magnitude of
19.26, and the distance to the source derived from the measured Gaia parallax
is $\sim$4.3 kpc. We provide an improved source localization with subarcsec
accuracy. The spectral modeling of the source indicates the presence of
intervening circumstellar gas, which absorbs the soft X-ray photons. The
measured equivalent width of the iron lines and the detection of the spin
period in the light curve are consistent with those from IPs.",2209.00970v1
2022-09-12,53Mn-53Cr chronology and ε54Cr-Δ17O genealogy of Erg Chech 002: the oldest andesite in the Solar System,"The meteorite sample Erg Chech (EC) 002 is the oldest felsic igneous rock
from the Solar System analysed to date and provides a unique opportunity to
study the formation of felsic crusts on differentiated protoplanets immediately
after metal-silicate equilibration or core formation. The extinct 53Mn-53Cr
chronometer provides chronological constraints on the formation of EC 002 by
applying the isochron approach using chromite, metal-silicate-sulphide and
whole-rock fractions as well as ""leachates"" obtained by sequential digestion of
a bulk sample. Assuming a chondritic evolution of its parent body, a 53Cr/52Cr
model age is also obtained from the chromite fraction. The 53Mn-53Cr isochron
age of 1.73 (+/-) 0.96 Ma (anchored to D'Orbigny angirte) and the chromite
model age constrained between 1.46 (-0.68/+0.78) and 2.18 (-1.06/+1.32) Ma
after the formation of calcium-aluminium-rich inclusions (CAIs) agree with the
26Al-26Mg ages (anchored to CAIs) reported in previous studies. This indicates
rapid cooling of EC 002 that allowed near-contemporaneous closure of multiple
isotope systems. Additionally, excess in the neutron-rich 54Cr (nucleosynthetic
anomalies) combined with mass-independent isotope variations of 17O provide
genealogical constraints on the accretion region of the EC 002 parent body. The
54Cr and 17O isotope compositions of EC 002 confirm its origin in the
""non-carbonaceous"" reservoir and overlap with the vestoid material NWA 12217
and anomalous eucrite EET 92023. This indicates a common feeding zone during
accretion in the protoplanetary disk between the source of EC 002 and vestoids.
The enigmatic origin of iron meteorites remains still unresolved as EC 002,
which is more like a differentiated crust, has an isotope composition that does
not match known irons meteorite groups that were once planetesimal cores.",2209.05381v1
2022-09-13,The Puzzle of Meteoritic Minerals Heideite and Brezinaite; Are they Iron-based Superconductors? Are they Technosignatures?,"Transition metal sulfides (Fe, V)3S4 and (Fe, Ti)3S4, with the monoclinic
Cr3S4 type structure have been studied for a long time, itinerant magnetism in
form of Spin density waves (SDW) have been found in these systems with
different features as evidenced by 57Fe Mossbauer Spectroscopy, there is an
intricate relationship between the proportion of Fe, V and Ti atoms, the degree
of commensurability of the SDW and the magnetic transition temperature. These
sulfides have no natural occurrence on Earth and some of these phases were
detected as minerals in meteorites; the mineral Heideite in the Bustee and
Kaidun meteorites, with minor proportion of Cr atoms leading to the general
formula (Fe, Cr)1+x (Ti, Fe)2S4, and the mineral Brezinaite in the Tucson
meteorite, with minor proportion of Fe atoms and traces of V, Ti and Mn atoms,
leading to the formula (Cr2.65Fe0.20V0.09Ti0.06Mn0.04)3.04S4. In this critical
review of the experimental literature, we discuss the issues that these
meteoritic minerals are structurally sensitive to the method of synthesis, and
so is their magnetic behavior, especially in the presence of minor and trace
elements. This discussion could shed light on our knowledge in Solid State
Physics and Planetary Science; these meteoritic minerals are promising
candidates for iron-based superconductors because of three clues: they are
layered structures, they undergo a transition to SDW with variable degree of
commensurability and the minor and trace elements could act as dopants and
hence suppress the SDW giving rise to superconductivity. On the other side, the
genesis of these meteoritic minerals could require controlled and sophisticated
process not easily found in nature. So, it is important to be open-minded and
even provocative to consider the following question: Are these meteoritic
minerals samples of Extraterrestrial Technosignatures?",2209.05679v1
2022-10-11,Ironing the folds: The phase space chevrons of a GSE-like merger as a dark matter subhalo detector,"Recent work uncovered features in the phase space of the Milky Way's stellar
halo which may be attributed to the last major merger. When stellar material
from a satellite is accreted onto its host, it phase mixes and appears finely
substructured in phase space. For a high-eccentricity merger, this substructure
most clearly manifests as numerous wrapping chevrons in $(v_r, r)$ space,
corresponding to stripes in $(E, \theta_r)$ space. We introduce the idea of
using this substructure as an alternative subhalo detector to cold stellar
streams. We simulate an N-body merger akin to the GSE and assess the impact of
subhaloes on these chevrons. We examine how their deformation depends on the
mass, pericentre, and number of subhaloes. To quantify the impact of
perturbers, we utilise the appearance of chevrons in $(E, \theta_r)$ space to
introduce a new quantity -- the ironing parameter. We show that: (1) a single
flyby of a massive ($\sim 10^{10}$ M$_{\odot}$) subhalo with pericentre
comparable to, or within, the shell's apocentre smooths out the substructure,
(2) a single flyby of a low mass ($\lesssim 10^8$ M$_{\odot}$) has negligible
effect, (3) multiple flybys of subhalos derived from a subhalo mass function
between $10^7-10^{10}$ M$_{\odot}$ cause significant damage if deep within the
potential, (4) the effects of known perturbers (e.g. Sagittarius) should be
detectable and offer constraints on their initial mass. The sensitivity to the
populations of subhaloes suggests that we should be able to place an upper
limit on the Milky Way's subhalo mass function.",2210.05679v2
2022-10-13,"TOI-561 b: A Low Density Ultra-Short Period ""Rocky"" Planet around a Metal-Poor Star","TOI-561 is a galactic thick disk star hosting an ultra-short period (0.45 day
orbit) planet with a radius of 1.37 R$_{\oplus}$, making it one of the most
metal-poor ([Fe/H] = -0.41) and oldest ($\sim$10 Gyr) sites where an
Earth-sized planet has been found. We present new simultaneous radial velocity
measurements (RVs) from Gemini-N/MAROON-X and Keck/HIRES, which we combined
with literature RVs to derive a mass of M$_{b}$=2.24 $\pm$ 0.20 M$_{\oplus}$.
We also used two new Sectors of TESS photometry to improve the radius
determination, finding R$_{b}$=$1.37 \pm 0.04 R_\oplus$, and confirming that
TOI-561 b is one of the lowest-density super-Earths measured to date ($\rho_b$=
4.8 $\pm$ 0.5 g/cm$^{3}$). This density is consistent with an iron-poor rocky
composition reflective of the host star's iron and rock-building element
abundances; however, it is also consistent with a low-density planet with a
volatile envelope. The equilibrium temperature of the planet ($\sim$2300 K)
suggests that this envelope would likely be composed of high mean molecular
weight species, such as water vapor, carbon dioxide, or silicate vapor, and is
likely not primordial. We also demonstrate that the composition determination
is sensitive to the choice of stellar parameters, and that further measurements
are needed to determine if TOI-561 b is a bare rocky planet, a rocky planet
with an optically thin atmosphere, or a rare example of a non-primordial
envelope on a planet with a radius smaller than 1.5 R$_{\oplus}$.",2210.06665v3
2022-10-14,The homogeneity of chemical abundances in H II regions of the Magellanic Clouds,"We use very deep spectra obtained with the Ultraviolet-Visual Echelle
Spectrograph at the Very Large Telescope to derive physical conditions and
chemical abundances of four H II regions of the Large Magellanic Cloud (LMC)
and four H II regions of the Small Magellanic Cloud (SMC). The observations
cover the spectral range 3100-10400 \A with a spectral resolution of
$\Delta\lambda\ge\lambda/11600$, and we measure 95-225 emission lines in each
object. We derive ionic and total abundances of O, N, S, Ne, Ar, Cl, and Fe
using collisionally excited lines. We find average values of
$12+\log(\mbox{O/H})=8.37$ in the LMC and $8.01$ in the SMC, with standard
deviations of $\sigma=0.03$ and 0.02~dex, respectively. The S/O, Ne/O, Ar/O,
and Cl/O abundance ratios are very similar in both clouds, with
$\sigma=0.02$-0.03~dex, which indicates that the chemical elements are well
mixed in the interstellar medium of each galaxy. The LMC is enhanced in N/O by
$\sim0.20$~dex with respect to the SMC, and the dispersions in N/O,
$\sigma=0.05$~dex in each cloud, are larger than those found for the other
elements. The derived standard deviations would be much larger for all the
abundance ratios, up to 0.20~dex for N/O, if previous spectra of these objects
were used to perform the analysis. Finally, we find a wide range of iron
depletions in both clouds, with more than 90 per cent of the iron atoms
deposited onto dust grains in most objects.",2210.07460v1
2022-11-11,"The unaltered pulsar: GRO J1750-27, a super-critical X-ray neutron star that does not blink an eye","When accreting X-ray pulsars (XRPs) undergo bright X-ray outbursts, their
luminosity-dependent spectral and timing features can be analysed in detail.
The XRP GRO J1750-27 recently underwent one of such episodes, during which it
was observed with $NuSTAR$ and monitored with $NICER$. Such a data set is
rarely available, as it samples the outburst over more than a month at a
luminosity that is always exceeding ${\sim}5\times10^{37}\,$erg/s. This value
is larger than the typical critical luminosity value, where a radiative shock
is formed above the neutron star's surface. Our data analysis of the joint
spectra returns a highly ($N_H\sim(5-8)\times10^{22}\,$cm$^{-2}$) absorbed
spectrum showing a K$\alpha$ iron line, a soft blackbody component likely
originating from the inner edge of the accretion disk, and confirms the
discovery of one of the deepest cyclotron lines, at a centroid energy of
${\sim}44\,$keV corresponding to a magnetic field strength of
$4.7\times10^{12}\,$G. This value is independently supported by the best-fit
physical model for spectral formation in accreting XRPs which, in agreement
with recent findings, favours a distance of $14$ kpc and also reflects a
bulk-Comptonization dominated accretion flow. Contrary to theoretical
expectations and observational evidence from other similar sources, the pulse
profiles as observed by $NICER$ through the outburst raise, peak and decay
remain remarkably steady. The $NICER$ spectrum, including the iron K$\alpha$
line best-fit parameters, also remain almost unchanged at all probed outburst
stages, similar to the pulsed fraction behaviour. We argue that all these
phenomena are linked and interpret them as resulting from a saturation effect
of the accretion column's emission, which occurs in the high-luminosity regime.",2211.06367v2
2022-12-01,Three dimensional magnetorotational core-collapse supernova explosions of a 39 solar mass progenitor star,"We perform three-dimensional simulations of magnetorotational supernovae
using a $39\,M_{\odot}$ progenitor star with two different initial magnetic
field strengths of $10^{10}$ G and $10^{12}$ G in the core. Both models rapidly
undergo shock revival and their explosion energies asymptote within a few
hundred milliseconds to values of $\gtrsim 2\times10^{51}$ erg after
conservatively correcting for the binding energy of the envelope. Magnetically
collimated, non-relativistic jets form in both models, though the jets are
subject to non-axisymmetric instabilities. The jets do not appear crucial for
driving the explosion, as they only emerge once the shock has already expanded
considerably. Our simulations predict moderate neutron star kicks of about
$150\, \mathrm{km}\,\mathrm{s}^{-1}$, no spin-kick alignment, and rapid early
spin-down that would result in birth periods of about $20\, \mathrm{ms}$, too
slow to power an energetic gamma-ray burst jet. More than $0.2\,M_\odot$ of
iron-group material are ejected, but we estimate that the mass of ejected
$^{56}\mathrm{Ni}$ will be considerably smaller as the bulk of this material is
neutron-rich. Explosive burning does not contribute appreciable amounts of
$^{56}\mathrm{Ni}$ because the burned material originates from the slightly
neutron-rich silicon shell. The iron-group ejecta also show no pronounced
bipolar geometry by the end of the simulations. The models thus do not
immediately fit the characteristics of observed hypernovae, but may be
representative of other transients with moderately high explosion energies. The
gravitational-wave emission reaches high frequencies of up to 2000 Hz and
amplitudes of over 100 cm. The gravitational-wave emission is detectable out to
distances of $\sim4$ Mpc in the planned Cosmic Explorer detector.",2212.00200v3
2022-12-12,Systematic Broad-band X-ray Study of super-Eddington Accretion onto Supermassive Black Holes. I. X-ray Continuum,"We present the first systematic broad-band X-ray study of super-Eddington
accretion onto SMBHs with simultaneous {\it NuSTAR} and {\it XMM-Newton} or
{\it Swift}/XRT observations of a sample of 8 super-Eddington accreting AGN
with Eddington ratio $1<\lambda_{\rm Edd}<426$. We find that the SEAMBHs show a
steep primary continuum slope as expected for sources accreting in the super
Eddington regime, mostly dominated by relativistic reflection. The Iron
K$\alpha$ emission lines of the sources of our sample show relativistic
broadening. In addition the equivalent widths of the narrow components of the
Iron K$\alpha$ lines follow the 'X-ray Baldwin' effect, also known as the
'Iwasawa-Taniguchi' effect. We found a statistically significant correlation
between the photon-index of the primary power-law and the Eddington ratio,
consistent with past studies. Moreover, as expected for super-Eddington
sources, the median value of the reflection fraction of the sources we analysed
is a factor $\sim 2$ higher than the median reflection fraction value of the
type\,1 AGN from the BASS sample. We are able to estimate the coronal
temperature for three sources of our sample: Mrk\,382 ($kT_e=7.8$\,keV),
PG\,0026+129 ($kT_e=39$\,keV) and IRAS\,04416+1215 ($kT_e=3$\,keV). Looking at
the position of the SEAMBHs sources of our sample in the
compactness-temperature diagram it appears that in super-Eddington AGN, as for
lower Eddington ratio AGN, the X-ray corona is controlled by pair production
and annihilation.",2212.06183v1
2022-12-15,Non-trivial band topology and orbital-selective electronic nematicity in a new titanium-based kagome superconductor,"Electronic nematicity that spontaneously breaks rotational symmetry has been
shown as a generic phenomenon in correlated quantum systems including
high-temperature superconductors and the AV3Sb5 (A = K, Rb, Cs) family with a
kagome network. Identifying the driving force has been a central challenge for
understanding nematicity. In iron-based superconductors, the problem is
complicated because the spin, orbital and lattice degrees of freedom are
intimately coupled. In vanadium-based kagome superconductors AV3Sb5, the
electronic nematicity exhibits an intriguing entanglement with the charge
density wave order (CDW), making understanding its origin difficult. Recently,
a new family of titanium-based kagome superconductors ATi3Bi5 has been
synthesized. In sharp contrast to its vanadium-based counterpart, the
electronic nematicity occurs in the absence of CDW. ATi3Bi5 provides a new
window to explore the mechanism of electronic nematicity and its interplay with
the orbital degree of freedom. Here, we combine polarization-dependent
angle-resolved photoemission spectroscopy with density functional theory to
directly reveal the band topology and orbital characters of the multi-orbital
RbTi3Bi5. The promising coexistence of flat bands, type-II Dirac nodal line and
nontrivial Z2 topological states is identified in RbTi3Bi5. Remarkably, our
study clearly unveils the orbital character change along the G-M and G-K
directions, implying a strong intrinsic inter-orbital coupling in the Ti-based
kagome metals, reminiscent of iron-based superconductors. Furthermore,
doping-dependent measurements directly uncover the orbital-selective features
in the kagome bands, which can be well explained by the d-p hybridization. The
suggested d-p hybridization, in collaboration with the inter-orbital coupling,
could account for the electronic nematicity in ATi3Bi5.",2212.07958v1
2023-01-20,The chemical DNA of the Magellanic Clouds -- I. The chemical composition of 206 Small Magellanic Cloud red giant stars,"We present the chemical composition of 206 red giant branch stars members of
the Small Magellanic Cloud (SMC) using optical, high-resolution spectra
collected with the multi-object spectrograph FLAMES-GIRAFFE at the ESO Very
Large Telescope. This sample includes stars in three fields located in
different positions within the parent galaxy. We analysed the main groups of
elements, namely light- (Na), alpha- (O, Mg, Si, Ca, Ti), iron-peak (Sc, V, Fe,
Ni, Cu) and s-process elements (Zr, Ba, La). The metallicity distribution of
the sample displays a main peak around [Fe/H] ~ -1 dex and a weak metal-poor
tail. However, the three fields display [Fe/H] distributions different with
each other, in particular a difference of 0.2 dex is found between the mean
metallicities of the two most internal fields.The fraction of metal-poor stars
increases significantly (from ~1 to ~20%) from the innermost fields to the most
external one, likely reflecting an age gradient in the SMC. Also, we found a
hint of possible chemically/kinematic distinct substructures. The SMC stars
have abundance ratios clearly distinct with respect to the Milky Way stars, in
particular for the elements produced by massive stars (like Na, $\alpha$ and
most iron-peak elements) that have abundance ratios systematically lower than
those measured in our Galaxy. This points out that the massive stars
contributed less to the chemical enrichment of the SMC with respect to the
Milky Way, according to the low star formation rate expected for this galaxy.
Finally, we identified small systematic differences in the abundances of some
elements (Na, Ti, V and Zr) in the two innermost fields, suggesting that the
chemical enrichment history in the SMC has been not uniform.",2301.08758v1
2023-01-30,The Hubble/STIS Near-ultraviolet Transmission Spectrum of HD 189733b,"The benchmark hot Jupiter HD 189733b has been a key target to lay out the
foundations of comparative planetology for giant exoplanets. As such, HD
189733b has been extensively studied across the electromagnetic spectrum. Here,
we report the observation and analysis of three transit light curves of HD
189733b obtained with {\Hubble}/STIS in the near ultraviolet, the last
remaining unexplored spectral window to be probed with present-day
instrumentation for this planet. The NUV is a unique window for atmospheric
mass-loss studies owing to the strong resonance lines and large photospheric
flux. Overall, from a low-resolution analysis ($R=50$) we found that the
planet's near-ultraviolet spectrum is well characterized by a relatively flat
baseline, consistent with the optical-infrared transmission, plus two regions
at $\sim$2350 and $\sim$2600 {\AA} that exhibit a broad and significant excess
absorption above the continuum. From an analysis at a higher resolution
($R=4700$), we found that the transit depths at the core of the magnesium
resonance lines are consistent with the surrounding continuum. We discarded the
presence of \ion{Mg}{ii} absorption in the upper atmosphere at a
$\sim$2--4$\sigma$ confidence level, whereas we could place no significant
constraint for \ion{Mg}{i} absorption. These broad absorption features coincide
with the expected location of \ion{Fe}{ii} bands; however, solar-abundance
hydrodynamic models of the upper atmosphere are not able to reproduce the
amplitude of these features with iron absorption. Such scenario would require a
combination of little to no iron condensation in the lower-atmosphere,
super-solar metallicities, and a mechanism to enhance the absorption features
(such as zonal wind broadening). The true nature of this feature remains to be
confirmed.",2301.13025v1
2023-01-30,A Catalog of 71 Coronal Line Galaxies in MaNGA: [NeV] is an Effective AGN Tracer,"Despite the importance of AGN in galaxy evolution, accurate AGN
identification is often challenging, as common AGN diagnostics can be confused
by contributions from star formation and other effects (e.g.,
Baldwin-Phillips-Terlevich diagrams). However, one promising avenue for
identifying AGNs are ``coronal emission lines"" (``CLs""), which are highly
ionized species of gas with ionization potentials $\ge$ 100 eV. These CLs may
serve as excellent signatures for the strong ionizing continuum of AGN. To
determine if CLs are in fact strong AGN tracers, we assemble and analyze the
largest catalog of optical CL galaxies using the Sloan Digital Sky Survey's
Mapping Nearby Galaxies at Apache Point Observatory (MaNGA) catalog. We detect
CL emission in 71 MaNGA galaxies, out of the 10,010 unique galaxies from the
final MaNGA catalog, with $\ge$ 5$\sigma$ confidence. In our sample, we measure
[NeV]$\lambda$3347, $\lambda$3427, [FeVII]$\lambda$3586, $\lambda$3760,
$\lambda$6086, and [FeX]$\lambda$6374 emission and crossmatch the CL galaxies
with a catalog of AGNs that were confirmed with broad line, X-ray, IR, and
radio observations. We find that [NeV] emission, compared to [FeVII] and [FeX]
emission, is best at identifying high luminosity AGN. Moreover, we find that
the CL galaxies with the least dust extinction yield the most iron CL
detections. We posit that the bulk of the iron CLs are destroyed by dust grains
in the galaxies with the highest [OIII] luminosities in our sample, and that
AGN in the galaxies with low [OIII] luminosities are possibly too weak to be
detected using traditional techniques.",2301.13322v1
2023-02-09,Chaotic winds from a dying world: a one-dimensional map for evolving atmospheres,"Planets which are smaller than Mercury and heated to sublimation temperatures
of $\sim$2000 K lose mass catastrophically in dusty evaporative winds. The
winds are observed to gust and recede largely without pattern; transit depths
from the Kepler mission vary randomly from orbit to orbit by up to a factor of
10 or more. We explain how chaotic outflows may arise by constructing a map for
the wind mass-loss rate as a function of time. The map is built on three
statements: (1) The wind mass-loss rate scales in proportion to the surface
equilibrium vapor pressure, rising exponentially with ground temperature. (2)
Because the wind takes a finite time to escape the planet's gravity well, the
surface mass-loss rate at any time determines the wind optical depth at a later
time -- the atmosphere has hysteresis. (3) The ground temperature increases
with optical depth (greenhouse effect) when the atmosphere is optically thin,
and decreases with optical depth when the atmosphere is optically thick
(nuclear winter). Statement (3) follows from how dust condenses in the face of
intense stellar irradiation. As discussed recently, condensates initially naked
before the star must be silicate-rich and iron-poor, staying cool enough for
condensation by absorbing weakly in the visible and emitting strongly in the
infrared. Later, when grains are numerous enough to self-shield from starlight,
they may accrete more iron and reverse their visible-to-infrared opacity ratio.
Depending on parameters, the map for the wind can regularly boom and bust
between a greenhouse and a nuclear winter, or erupt into chaos. Lyapunov times
are measured in orbital periods, the time for the wind to turn by Coriolis
forces away from the planet's dayside, out of the Hill sphere.",2302.04898v2
2023-03-02,"Concurrent Ferromagnetism and Superconductivity in Fe(Te,Se) van der Waals Josephson Junctions","Ferromagnetism and superconductivity are two key ingredients to create
non-Abelian quasiparticle excitations that are expected as building blocks to
construct topological quantum computers. Adversely, ferromagnetism and
superconductivity are typically also two hostile orderings competing to align
spins in different configurations, making the material design and experimental
implementation extremely challenging. Recently, iron-based superconductor
Fe(Te,Se) has emerged as a connate topological superconductor (TSC), which
differentiates itself from other hybrid TSCs by self-proximitizing its Dirac
surface states with bulk superconductivity. So far, the efforts to search for
Majorana states in this material are prevalently focused on spectroscopy
techniques. In this paper, we present the global transport signature of
interfacial magnetism coexisting with superconductivity. Time-reversal symmetry
breaking superconducting states are confirmed through device level transport
measurements for the first time in a van der Waals (vdW) Josephson junction
structure. Magnetic hysteresis is observed in this device scheme, which only
appears below the superconducting critical temperature, leading to potential
Fulde-Ferrell (FF) superconducting pairing mechanisms. The 0-{\pi} phase mixing
in the Fraunhofer patterns pinpoints the ferromagnetic state dwelling on the
surface. Furthermore, a stochastic field-free superconducting diode effect also
confirms the spontaneous time-reversal symmetry breaking which reflects the
behavior of the ferromagnetism. Our work paves a new way to explore topological
superconductivity in iron-based superconductors for future high Tc
fault-tolerant qubit implementations from a device perspective.",2303.00966v2
2023-03-19,$\rm Li_x(C_5H_5N)_yFe_{2-z}Se_2$: a defect resilient expanded-lattice high-temperature superconductor,"Two-dimensional iron-chalcogenide intercalates display a remarkable
correlation of the interlayer spacing with the enhancement of the
superconducting critical temperature ($T_c$). In this work, synchrotron x-ray
absorption ($XAS$, at Fe and Se K edges) and emission ($XES$) spectroscopies,
allow to discuss how the important rise of $T_c$ (44 K) in the molecule
intercalated $\rm Li_x(C_5H_5N)_yFe_{2-z}Se_2$ relates to the electronic and
local structure changes felt by the inorganic host upon doping ($x$). $XES$
shows that widely-separated layers of edge-sharing $\rm FeSe_4$ tetrahedra,
carry low-spin moieties with a local Fe magnetic moment slightly reduced
compared to the parent $\beta$-$\rm Fe_{2-z}Se_2$. Pre-edge $XAS$ advises on
the progressively reduced mixing of metal $3d-4p$ states upon lithiation.
Doping-mediated local lattice modifications, probed by conventional
$T_c$-optimization measures (cf. anion height and $FeSe_4$ tetrahedra
regularity), become less relevant when layers are spaced far away. On the basis
of extended x-ray absorption fine structure, such distortions are compensated
by a softer Fe-network that relates to Fe-site vacancies, alleviating
electron-lattice correlations and superconductivity. Density functional theory
($DFT$) guided modification of isolated $\rm Fe_{2-z}Se_2$ ($z$, vacant sites)
planes, resembling the host layers, identify that Fe-site deficiency occurs at
low energy cost, giving rise to stretched Fe-sheets, in accord with
experiments. The robust high-$T_c$ in $\rm Li_x(C_5H_5N)_yFe_{2-z}Se_2$, arises
from the interplay of electron donating spacers and the iron-selenide layers
tolerance to defect chemistry, a tool to favorably tune its Fermi surface
properties.",2303.10716v1
2023-05-02,Lunar Mantle Structure and Composition Inferred From Apollo 12 -- Explorer 35 Electromagnetic Sounding,"Constraints on the interior of the Moon have been derived from its inductive
response, principally as measured by the magnetic transfer function (TF)
between the distantly orbiting Explorer 35 satellite and the Apollo 12 surface
station. The most successful prior studies used a dataset spanning 0.01-1 mHz,
so the lunar response could be modeled as a simple dipole. However, earlier
efforts also produced transfer functions up to 40 mHz. The smaller
electromagnetic skin depth at higher frequency would better resolve the
uppermost mantle-where key information about primitive lunar evolution may
still be preserved-but requires a multipole treatment. I compute new profiles
of electrical conductivity vs depth using both low- and high-frequency ranges
of published Apollo-Explorer TFs. Using the low-frequency data, I derive
temperature profiles at depths >400 km (<1 mHz) consistent with conductive heat
loss and expectations of the iron (and possibly water) content of the mantle.
The near-constant iron fraction (Mg# 81 +/- 10) could imply efficient mixing
due to now-defunct convection. Alternatively, incomplete overturn of
gravitationally unstable magma-ocean cumulates could have left a heterogeneous
distribution of minerals at hundred-km scales that are not resolved by
electromagnetic sounding. A third explanation is that the electromagnetically
probed region may be the initial equilibrium crystallization in a mantle that
did not buoyantly overturn. In contrast, the high-frequency data produced
higher conductivities than expected, requiring unrealistically low Mg# or high
water content. Either the published transfer functions >> 1 mHz are incorrect,
or the TF multipole method at the Moon is unreliable. Future electromagnetic
sounding using the magnetotelluric method can operate up to 100s Hz and is
largely insensitive to multipole effects, resolving structure to 100 km or
less.",2305.01462v2
2023-05-24,Modeling the chemical enrichment history of the Bulge Fossil Fragment Terzan 5,"Terzan 5 is a heavily obscured stellar system located in the inner Galaxy. It
has been postulated to be a stellar relic, a Bulge Fossil Fragment witnessing
the complex history of the assembly of the Milky Way bulge. In this paper, we
follow the chemical enrichment of a set of putative progenitors of Terzan 5 to
assess whether the chemical properties of this cluster fit within a formation
scenario in which it is the remnant of a primordial building block of the
bulge. We can explain the metallicity distribution function and the runs of
different element-to-iron abundance ratios as functions of [Fe/H] derived from
optical-infrared spectroscopy of giant stars in Terzan 5, by assuming that the
cluster experienced two major star formation bursts separated by a long
quiescent phase. We further predict that the most metal-rich stars in Terzan 5
are moderately He-enhanced and a large spread of He abundances in the cluster,
Y = 0.26-0.335. We conclude that current observations fit within a formation
scenario in which Terzan 5 originated from a pristine, or slightly
metal-enriched, gas clump about one order of magnitude more massive than its
present-day mass. Losses of gas and stars played a major role in shaping Terzan
5 the way we see it now. The iron content of the youngest stellar population is
better explained if the white dwarfs that give rise to type Ia supernovae (the
main Fe factories) sink towards the cluster center, rather than being stripped
by the strong tidal forces exerted by the Milky Way in the outer regions.",2305.15355v1
2023-06-07,2021 occultations and transits of Linus orbiting (22) Kalliope: I. Polygonal and `cliptracing' algorithm,"The satellite Linus orbiting the main-belt asteroid (22) Kalliope exhibited
occultation and transit events in late 2021. A photometric campaign was
organized and observations were taken by the TRAPPIST-South, SPECULOOS-Artemis,
OWL-Net, and BOAO telescopes, with the goal to constrain models of this system.
Our dynamical model is complex, with multipoles (up to the order $\ell = 2$),
internal tides, and external tides. The model was constrained by astrometry
(spanning 2001--2021), occultations, adaptive-optics imaging, calibrated
photometry, as well as relative photometry. Our photometric model was
substantially improved. A new precise (${<}\,0.1\,{\rm mmag}$) light curve
algorithm was implemented, based on polygon intersections, which are computed
exactly -- by including partial eclipses and partial visibility of polygons.
Moreover, we implemented a `cliptracing' algorithm, based again on polygon
intersections, in which partial contributions to individual pixels are computed
exactly. Both synthetic light curves and synthetic images are then very smooth.
Based on our combined solution, we confirmed the size of Linus, $(28\pm
1)\,{\rm km}$. However, this solution exhibits some tension between the light
curves and the PISCO speckle-interferometry dataset. In most solutions, Linus
is darker than Kalliope, with the albedos $A_{\rm w} = 0.40$ vs. $0.44$. This
is confirmed on deconvolved images. A~detailed revision of astrometric data
allowed us to revise also the $J_2 \equiv -C_{20}$ value of Kalliope. Most
importantly, a~homogeneous body is excluded. For a differentiated body, two
solutions exist: low-oblateness ($C_{20} \simeq -0.12$), with a~spherical iron
core, and alternatively, high-oblateness ($C_{20} \simeq -0.22$) with an
elongated iron core. These correspond to the low- and high-energy collisions,
respectively, studied by means of SPH simulations in our previous work.",2306.04768v1
2023-07-04,Packed bed thermal energy storage for waste heat recovery in the iron and steel industry: An experimental study on powder hold-up and pressure drop,"Waste heat recovery in the energy intensive industry is one of the most
important measures for the mitigation of climate change. The utilization of
just a fraction of the theoretically available waste heat potential would lead
to a significant reduction of the primary energy consumption and hence a
reduction of greenhouse gas emissions. The present study examines the
integration of a packed bed thermal energy storage for waste heat recovery in
the iron and steel industry. Along with the highly fluctuating availability of
excess heat the main difficulty of waste heat recovery in industrial processes
is the high amount of powder that is transported by the hot exhaust gases.
Therefore, investigations focus on the pressure drop and powder hold-up in a
packed bed thermal energy storage that is operated with a gas-powder two phase
exhaust gas as heat transfer fluid with the ultimate goal to assess its
suitability and robustness under such challenging operational conditions. The
results indicate, that 98 % of the powder that is introduced into the system
with the heat transfer fluid during charging accumulates in the packed bed.
Remarkably, most of the powder hold-up in the packed bed is concentrated near
the surface at which the heat transfer fluid enters the packed bed. When
reversing the flow direction of the heat transfer fluid to discharge the
storage with a clean single phase gas, this gas is not contaminated with the
powder that has been accumulated in previous charging periods. Further, the
radial distribution of the powder hold-up in the packed bed is observed to be
even which indicates that there is no risk of random flow channel formation
that could affect the thermal performance (storage capacity, thermal power
rate) of the system. The results reinforce the great potential of packed bed
thermal energy storage systems for waste heat recovery in the energy intensive
industry.",2307.01585v2
2023-07-10,The individual abundance distributions of disc stars across birth radii in GALAH,"Individual abundances in the Milky Way disc record stellar birth properties
(e.g. age, birth radius ($R_{\rm birth}$)) and capture the diversity of the
star-forming environments over time. Assuming an analytical relationship
between ([Fe/H], [$\alpha$/Fe]) and $R_{\rm birth}$, we examine the
distributions of individual abundances [X/Fe] of elements C, O, Mg, Si, Ca
($\alpha$), Al (odd-z), Mn (iron-peak), Y, and Ba (neutron-capture) for stars
in the Milky Way. We want to understand how these elements might differentiate
environments across the disc. We assign tracks of $R_{\rm birth}$ in the
[$\alpha$/Fe] vs. [Fe/H] plane as informed by expectations from simulations for
$\sim 59,000$ GALAH stars in the solar neighborhood ($R\sim7-9$ kpc) which also
have inferred ages. Our formalism for $R_{\rm birth}$ shows that older stars
($\sim$10 Gyrs) have a $R_{\rm birth}$ distribution with smaller mean values
(i.e., $\bar{R}_{\mbox{birth}}$$\sim5\pm0.8$ kpc) compared to younger stars
($\sim6$ Gyrs; $\bar{R}_{\mbox{birth}}$$\sim10\pm1.5$ kpc), for a given [Fe/H],
consistent with inside-out growth. The $\alpha$-, odd-z, and iron-peak element
abundances decrease as a function of $R_{\rm birth}$, whereas the
neutron-capture abundances increase. The $R_{\rm birth}$-[Fe/H] gradient we
measure is steeper compared to the present-day gradient (-0.067 dex/kpc vs
-0.058 dex/kpc), which we also find true for $R_{\rm birth}$-[X/Fe] gradients.
These results (i) showcase the feasibility of relating the birth radius of
stars to their element abundances, (ii) the abundance gradients across $R_{\rm
birth}$ are steeper than those over current radius, and (iii) offer an
observational comparison to expectations on element abundance distributions
from hydrodynamical simulations.",2307.04724v1
2023-07-11,"Dynamics of orbital degrees of freedom probed via isotope $^{121,123}$ Sb nuclear quadrupole moments in Sb-substituted iron-pnictide superconductors","Isotope $^{121,123}$Sb nuclei with large electric quadrupole moments are
applied to investigate the dynamics of orbital degrees of freedom in
Sb-substituted iron(Fe)-based compounds. In the parent compound
LaFe(As$_{0.6}$Sb$_{0.4}$)O, the nuclear spin relaxation rate
$^{121,123}(T_{1}^{-1})$ at $^{121,123}$Sb sites was enhanced at structural
transition temperature ($T_{s}\sim$ 135 K), which is higher than N\'eel
temperature ($T_{\rm N}\sim$125 K). The isotope ratio
$^{123}(T_{1}^{-1})/^{121}(T_{1}^{-1})$ indicates that the electric quadrupole
relaxation due to the dynamical electric field gradient at Sb site increases
significantly toward $T_{s}$. It is attributed to the critically enhanced
nematic fluctuations of stripe-type arrangement of Fe-$3d_{xz}$ (or $3d_{yz}$)
orbitals. In the lightly electron-doped superconducting (SC) compound
LaFe(As$_{0.7}$Sb$_{0.3}$)(O$_{0.9}$F$_{0.1}$), the nematic fluctuations are
largely suppressed in comparison with the case of the parent compound, however,
it remains a small enhancement below 80 K down to the $T_c$($\sim$ 20 K). The
results indicate that the fluctuations from both the spin and orbital degrees
of freedom on the $3d_{xz}$(or $3d_{yz}$) orbitals can be seen in lightly
electron-doped SC state of LaFeAsO-based compounds. We emphasize that isotope
$^{121,123}$Sb quadrupole moments are sensitive local probe to identify the
dynamics of orbital degrees of freedom in Fe-pnictides, which provides with a
new opportunity to discuss the microscopic correlation between the
superconductivity and both nematic and spin fluctuations simultaneously even in
the polycrystalline samples.",2307.05112v1
2023-07-11,The Dependence of Iron-rich Metal-poor Star Occurrence on Galactic Environment Supports an Origin in Thermonuclear Supernova Nucleosynthesis,"It has been suggested that a class of chemically peculiar metal-poor stars
called iron-rich metal-poor (IRMP) stars formed from molecular cores with metal
contents dominated by thermonuclear supernova nucleosynthesis. If this
interpretation is accurate, then IRMP stars should be more common in
environments where thermonuclear supernovae were important contributors to
chemical evolution. Conversely, IRMP stars should be less common in
environments where thermonuclear supernovae were not important contributors to
chemical evolution. At constant $[\text{Fe/H}] \lesssim -1$, the Milky Way's
satellite classical dwarf spheroidal (dSph) galaxies and the Magellanic Clouds
have lower $[\text{$\alpha$/Fe}]$ than the Milky Way field and globular cluster
populations. This difference is thought to demonstrate the importance of
thermonuclear supernova nucleosynthesis for the chemical evolution of the Milky
Way's satellite classical dSph galaxies and the Magellanic Clouds. We use data
from the Sloan Digital Sky Survey (SDSS) Apache Point Observatory Galactic
Evolution Experiment (APOGEE) and Gaia to infer the occurrence of IRMP stars in
the Milky Way's satellite classical dSph galaxies $\eta_{\text{dSph}}$ and the
Magellanic Clouds $\eta_{\text{Mag}}$ as well as in the Milky Way field
$\eta_{\text{MWF}}$ and globular cluster populations $\eta_{\text{MWGC}}$. In
order of decreasing occurrence, we find
$\eta_{\text{dSph}}=0.07_{-0.02}^{+0.02}$,
$\eta_{\text{Mag}}=0.037_{-0.006}^{+0.007}$,
$\eta_{\text{MWF}}=0.0013_{-0.0005}^{+0.0006}$, and a 1-$\sigma$ upper limit
$\eta_{\text{MWGC}}<0.00057$. These occurrences support the inference that IRMP
stars formed in environments dominated by thermonuclear supernova
nucleosynthesis and that the time lag between the formation of the first and
second stellar generations in globular clusters was longer than the
thermonuclear supernova delay time.",2307.05669v2
2023-07-31,Effects of Grain Magnetic Properties and Grain Growth on Synthetic Dust Polarization of MHD Simulations in Protostellar Environments,"Thermal dust polarization is a powerful tool to probe magnetic fields
($\textbf{B}$) and grain properties. However, a systematic study of the
dependence of dust polarization on grain properties in protostellar
environments is not yet available. In this paper, we post-process a non-ideal
MHD simulation of a collapsing protostellar core with our updated POLARIS code
to study in detail the effects of iron inclusions and grain growth on thermal
dust polarization. We found that superparamagnetic (SPM) grains can produce
high polarization degree of $p \sim 10-40\%$ beyond $\sim 500$ au from the
protostar because of their efficient alignment by magnetically enhanced
Radiative Torque mechanism. The magnetic field tangling by turbulence in the
envelope causes the decrease in $p$ with increasing emission intensity $I$ as
$p\propto I^{\alpha}$ with the slope $\alpha \sim -0.3$. But within 500 au, SPM
grains tend to have inefficient internal alignment (IA) and be aligned with
$\textbf{B}$ by RATs only, producing lower $p \sim 1\%$ and a steeper slope of
$\alpha \sim -0.6$. For paramagnetic (PM) grains, the alignment loss of grains
above $1\mu m$ in the inner $\sim 200$ au produces $p << 1\%$ and the
polarization hole with $\alpha \sim -0.9$. Grain growth can increase $p$ in the
envelope for SPM grains, but cause stronger depolarization for SPM grains in
the inner $\sim 500$ au and for PM grains in the entire protostellar core.
Finally, we found the increase of polarization angle dispersion function $S$
with iron inclusions and grain growth, implying the dependence of B-field
strength measured using the DCF technique on grain alignment and grain
properties.",2307.16829v2
2023-08-02,Numerical modeling of thermal dust polarization from aligned grains in the envelope of evolved stars with updated POLARIS,"Magnetic fields are thought to influence the formation and evolution of
evolved star envelopes. Thermal dust polarization from magnetically aligned
grains is potentially a powerful tool for probing magnetic fields and dust
properties in these circumstellar environments. In this paper, we present
numerical modeling of thermal dust polarization from the envelope of IK Tau
using the magnetically enhanced radiative torque (MRAT) alignment theory
implemented in our updated POLARIS code. Due to the strong stellar radiation
field, the minimum size required for RAT alignment of silicate grains is $\sim
0.005 - 0.05\,\rm\mu m$. Additionally, ordinary paramagnetic grains can achieve
perfect alignment by MRAT in the inner regions of $r < 500\,\rm au$ due to
stronger magnetic fields of $B\sim 10$ mG - 1G, producing thermal dust
polarization degree of $\sim 10\,\%$. The polarization degree can be enhanced
to $\sim 20-40\%$ for grains with embedded iron inclusions. We also find that
the magnetic field geometry affects the alignment size and the resulting
polarization degree due to the projection effect in the plane-of-sky. We also
study the spectrum of polarized thermal dust emission and find the increased
polarization degree toward $\lambda > 50\,\rm\mu m$ due to the alignment of
small grains by MRAT. Furthermore, we investigate the impact of rotational
disruption by RATs (RAT-D) and find the RAT-D effect cause a decrease in the
dust polarization fraction. Finally, we compare our numerical results with
available polarization data observed by SOFIA/HAWC+ for constraining dust
properties, suggesting grains are unlikely to have embedded iron clusters and
might have slightly elongated shapes. Our modeling results suggest further
observational studies at far-infrared/sub-millimeter wavelengths to understand
the properties of magnetic fields and dust in AGB envelopes.",2308.01215v1
2023-08-02,"Oxygen, sulfur, and iron radial abundance gradients of classical Cepheids across the Galactic thin disk","Classical Cepheids (CCs) are solid distance indicators and tracers of young
stellar populations. Our aim is to provide iron, oxygen, and sulfur abundances
for the largest and most homogeneous sample of Galactic CCs ever analyzed. The
current sample covers a wide range in Galactocentric distances (RG), pulsation
modes and periods. High-resolution and high S/N spectra collected with
different spectrographs were adopted to estimate the atmospheric parameters.
Individual distances are based on Gaia trigonometric parallaxes or on
near-infrared Period-Luminosity relations. We found that Fe and alpha-element
radial gradients based on CCs display a well-defined change in the slope for RG
larger than 12 kpc. Radial gradients based on open clusters, covering a wide
range in age, display similar trends, meaning that the flattening in the outer
disk is an intrinsic feature of the radial gradients since it is independent of
age. Empirical evidence indicates that the radial gradient for S is steeper
than for Fe. The difference in the slope is a factor of two in the linear fit.
We also found that S is, on average, under-abundant compared with O. We
performed a detailed comparison with Galactic chemical evolution models and we
found that a constant Star Formation Efficiency for RG larger than 12 kpc takes
account for the flattening in both Fe and alpha-elements. To further constrain
the impact that predicted S yields for massive stars have on radial gradients,
we adopted a ""toy model"" and we found that the flattening in the outermost
regions requires a decrease of a factor of four in the current S predictions.
Sulfur photospheric abundances, compared with other alpha-elements, have the
key advantage of being a volatile element. Therefore, stellar S abundances can
be directly compared with nebular S abundances in external galaxies.",2308.01928v1
2023-08-29,Planet formation throughout the Milky Way: Planet populations in the context of Galactic chemical evolution,"As stellar compositions evolve over time in the Milky Way, so will the
resulting planet populations. In order to place planet formation in the context
of Galactic chemical evolution, we make use of a large ($N = 5\,325$) stellar
sample representing the thin and thick discs, defined chemically, and the halo,
and we simulate planet formation by pebble accretion around these stars. We
build a chemical model of their protoplanetary discs, taking into account the
relevant chemical transitions between vapour and refractory minerals, in order
to track the resulting compositions of formed planets. We find that the masses
of our synthetic planets increase on average with increasing stellar
metallicity [Fe/H] and that giant planets and super-Earths are most common
around thin-disc ($\alpha$-poor) stars since these stars have an overall higher
budget of solid particles. Giant planets are found to be very rare
($\lesssim$1\%) around thick-disc ($\alpha$-rich) stars and nearly non-existent
around halo stars. This indicates that the planet population is more diverse
for more metal-rich stars in the thin disc. Water-rich planets are less common
around low-metallicity stars since their low metallicity prohibits efficient
growth beyond the water ice line. If we allow water to oxidise iron in the
protoplanetary disc, this results in decreasing core mass fractions with
increasing [Fe/H]. Excluding iron oxidation from our condensation model instead
results in higher core mass fractions, in better agreement with the core-mass
fraction of Earth, that increase with increasing [Fe/H]. Our work demonstrates
how the Galactic chemical evolution and stellar parameters, such as stellar
mass and chemical composition, can shape the resulting planet population.",2308.15504v1
2023-09-11,The Scale of Stellar Yields: Implications of the Measured Mean Iron Yield of Core Collapse Supernovae,"The scale of alpha-element yields is difficult to predict from theory because
of uncertainties in massive star evolution, supernova physics, and black hole
formation, and it is difficult to constrain empirically because the impact of
higher yields can be compensated by greater metal loss in galactic winds. We
use a recent measurement of the mean iron yield of core collapse supernovae
(CCSN) by Rodriguez et al. (RMN23), $\bar{y}_{\rm Fe}^{\rm cc} =0.058 \pm 0.007
M_\odot$, to infer the scale of alpha-element yields by assuming that the
plateau of [alpha/Fe] abundance ratios observed in low metallicity stars
represents the yield ratio of CCSN. For a Kroupa IMF and a plateau at
[alpha/Fe]=0.45, we find that the population-averaged yields of O and Mg per
unit mass of star formation are about equal to the mass fractions of these
elements in the sun. The inferred O and Fe yields agree with predictions of the
Sukhbold et al. (2016) CCSN models assuming their Z9.6+N20 neutrino-driven
engine, a scenario in which many progenitors with $M<40M_\odot$ implode to
black holes rather than exploding. The yields are lower than assumed in some
models of galactic chemical evolution (GCE) and the galaxy mass-metallicity
relation, reducing the level of outflows needed to match observed abundances.
For straightforward assumptions, we find that one-zone GCE models with
mass-loading factor $\eta\approx 0.6$ evolve to solar metallicity at late
times. By requiring that models reach [alpha/Fe]=0 at late times, and assuming
a mean Fe yield of $0.7M_\odot$ per Type Ia supernova, we infer a Hubble-time
integrated SNIa rate of $1.1\times 10^{-3} M_\odot^{-1}$, compatible with
estimates from supernova surveys. The RMN23 measurement provides one of the few
empirical anchors for the absolute scale of nucleosynthetic yields, with
wide-ranging implications for stellar and galactic astrophysics.",2309.05719v1
2023-10-11,Absence of topological Hall effect in Fe$_x$Rh$_{100-x}$ epitaxial films: revisiting their phase diagram,"A series of Fe$_x$Rh$_{100-x}$ ($30 \leq x \leq 57$) films were epitaxially
grown using magnetron sputtering, and were systematically studied by
magnetization-, electrical resistivity-, and Hall resistivity measurements.
After optimizing the growth conditions, phase-pure Fe$_{x}$Rh$_{100-x}$ films
were obtained, and their magnetic phase diagram was revisited. The
ferromagnetic (FM) to antiferromagnetic (AFM) transition is limited at narrow
Fe-contents with $48 \leq x \leq 54$ in the bulk Fe$_x$Rh$_{100-x}$ alloys. By
contrast, the FM-AFM transition in the Fe$_x$Rh$_{100-x}$ films is extended to
cover a much wider $x$ range between 33 % and 53 %, whose critical temperature
slightly decreases as increasing the Fe-content. The resistivity jump and
magnetization drop at the FM-AFM transition are much more significant in the
Fe$_x$Rh$_{100-x}$ films with $\sim$50 % Fe-content than in the Fe-deficient
films, the latter have a large amount of paramagnetic phase. The
magnetoresistivity (MR) is rather weak and positive in the AFM state, while it
becomes negative when the FM phase shows up, and a giant MR appears in the
mixed FM- and AFM states. The Hall resistivity is dominated by the ordinary
Hall effect in the AFM state, while in the mixed state or high-temperature FM
state, the anomalous Hall effect takes over. The absence of topological Hall
resistivity in Fe$_{x}$Rh$_{100-x}$ films with various Fe-contents implies that
the previously observed topological Hall effect is most likely extrinsic. We
propose that the anomalous Hall effect caused by the FM iron moments at the
interfaces nicely explains the hump-like anomaly in the Hall resistivity. Our
systematic investigations may offer valuable insights into the spintronics
based on iron-rhodium alloys.",2310.07140v1
2023-10-19,Potential Lifshitz transition at optimal substitution in nematic pnictide Ba$_{1-x}$Sr$_x$Ni$_2$As$_2$,"BaNi$_2$As$_2$ is a structural analog of the pnictide superconductor
BaFe$_2$As$_2$, which, like the iron-based superconductors, hosts a variety of
ordered phases including charge density waves (CDWs), electronic nematicity,
and superconductivity. Upon isovalent Sr substitution on the Ba site, the
charge and nematic orders are suppressed, followed by a sixfold enhancement of
the superconducting transition temperature ($T_c$). To understand the
mechanisms responsible for enhancement of $T_c$, we present high-resolution
angle-resolved photoemission spectroscopy (ARPES) measurements of the
Ba$_{1-x}$Sr$_{x}$Ni$_2$As$_2$ series, which agree well with our density
functional theory (DFT) calculations throughout the substitution range.
Analysis of our ARPES-validated DFT results indicates a Lifshitz transition and
reasonably nested electron and hole Fermi pockets near optimal substitution
where $T_c$ is maximum. These nested pockets host Ni $d_{xz}$/$d_{yz}$ orbital
compositions, which we associate with the enhancement of nematic fluctuations,
revealing unexpected connections to the iron-pnictide superconductors. This
gives credence to a scenario in which nematic fluctuations drive an enhanced
$T_c$.",2310.13163v1
2023-10-31,First spectroscopic investigation of Anomalous Cepheid variables,"Anomalous Cepheids (ACEPs) are intermediate mass metal-poor pulsators mostly
discovered in dwarf galaxies of the Local Group. However, recent Galactic
surveys, including the Gaia DR3, found a few hundreds of ACEPs in the Milky
Way. Their origin is not well understood. We aim to investigate the origin and
evolution of Galactic ACEPs by studying for the first time the chemical
composition of their atmospheres. We used UVES@VLT to obtain high-resolution
spectra for a sample of 9 ACEPs belonging to the Galactic halo. We derived the
abundances of 12 elements, including C, Na, Mg, Si, Ca, Sc, Ti, Cr, Fe, Ni, Y,
and Ba. We complemented these data with literature abundances for an additional
three ACEPs that were previously incorrectly classified as type II Cepheids,
thus increasing the sample to a total of 12 stars. All the investigated ACEPs
have an iron abundance [Fe/H]$<-1.5$ dex as expected from theoretical
predictions for these pulsators. The abundance ratios of the different elements
to iron show that the ACEP's chemical composition is generally consistent with
that of the Galactic halo field stars, except the Sodium, which is found
overabundant in 9 out of the 11 ACEPs where it was measured, in close
similarity with second-generation stars in the Galactic Globular Clusters. The
same comparison with dwarf and ultra-faint satellites of the Milky Way reveals
more differences than similarities so it is unlikely that the bulk of Galactic
ACEPs originated in such a kind of galaxies which subsequently dissolved in the
Galactic halo. The principal finding of this work is the unexpected
overabundance of Sodium in ACEPs. We explored several hypotheses to explain
this feature, finding that the most promising scenario is the evolution of
low-mass stars in a binary system with either mass transfer or merging.
Detailed modelling is needed to confirm this hypothesis.",2310.20503v1
2023-11-08,A self-synthesized origin of heavy metals in hot subdwarf stars?,"Some He-rich hot subdwarf stars (He-sdOBs) present high abundances of
trans-iron elements, such as Sr, Y, Zr and Pb. Diffusion processes are
important in hot subdwarf stars, and it is thought that the high abundances of
heavy elements in these stars are due to the action of radiative levitation.
However, during the formation of He-sdOBs, hydrogen can be ingested into the
convective zone driven by the He-core flash. It is known that episodes in which
protons are being ingested into He-burning convective zones can lead to
neutron-capture processes and the formation of heavy elements. In this work we
aim to explore for the first time if neutron-capture processes can occur in
late He-core flashes happening in the cores of the progenitors of He-sdOBs. We
compute a detailed evolutionary model of a stripped red-giant star with a
stellar evolution code with a nuclear network comprising 32 isotopes. Then we
post-process the stellar models in the phase of He and H burning with a
post-processing nucleosynthesis code with a nuclear network of 1190 species
that allows us to follow the neutron-capture processes in detail. We find the
occurrence of neutron-capture processes in our model, with neutron densities
reaching a value of $\sim5\times10^{12}\,{\rm cm}^{-3}$. We find that the
trans-iron elements are enhanced in the surface by 1 to 2 dex as compared to
initial compositions. Moreover, the relative abundance pattern $[{\rm
X}_i/\rm{Fe}]$ produced by neutron-capture processes closely resembles those
observed in some He-sdOBs, hinting at a possible self-synthesized origin of the
heavy elements in these stars. We conclude that intermediate neutron-capture
processes can occur during a proton ingestion event in the He-core flash of
stripped red-giant stars. This mechanism offers a natural channel to produce
the heavy elements observed in some of the He-sdOBs.",2311.04700v1
2023-12-07,Interface-Induced Superconductivity in Magnetic Topological Insulator-Iron Chalcogenide Heterostructures,"When two different electronic materials are brought together, the resultant
interface often shows unexpected quantum phenomena, including interfacial
superconductivity and Fu-Kane topological superconductivity (TSC). Here, we use
molecular beam epitaxy (MBE) to synthesize heterostructures formed by stacking
together two magnetic materials, a ferromagnetic topological insulator (TI) and
an antiferromagnetic iron chalcogenide (FeTe). We discover emergent
interface-induced superconductivity in these heterostructures and demonstrate
the trifecta occurrence of superconductivity, ferromagnetism, and topological
band structure in the magnetic TI layer, the three essential ingredients of
chiral TSC. The unusual coexistence of ferromagnetism and superconductivity can
be attributed to the high upper critical magnetic field that exceeds the Pauli
paramagnetic limit for conventional superconductors at low temperatures. The
magnetic TI/FeTe heterostructures with robust superconductivity and atomically
sharp interfaces provide an ideal wafer-scale platform for the exploration of
chiral TSC and Majorana physics, constituting an important step toward scalable
topological quantum computation.",2312.04353v1
2023-12-08,"The Heavy Metal Survey: The Evolution of Stellar Metallicities, Abundance Ratios, and Ages of Massive Quiescent Galaxies Since z~2","We present the elemental abundances and ages of 19 massive quiescent galaxies
at $z\sim1.4$ and $z\sim2.1$ from the Keck Heavy Metal Survey. The ultra-deep
LRIS and MOSFIRE spectra were modeled using a full-spectrum stellar population
fitting code with variable abundance patterns. The galaxies have iron
abundances between [Fe/H] = -0.5 and -0.1 dex, with typical values of $-0.2$
[$-0.3$] at $z\sim1.4$ [$z\sim2.1$]. We also find a tentative
$\log\sigma_v$-[Fe/H] relation at $z\sim1.4$. The magnesium-to-iron ratios span
[Mg/Fe] = 0.1--0.6 dex, with typical values of $0.3$ [$0.5$] dex at $z\sim1.4$
[$z\sim2.1$]. The ages imply formation redshifts of $z_{\rm form}=2-8$.
Compared to quiescent galaxies at lower redshifts, we find [Fe/H] was $\sim0.2$
dex lower at $z=1.4-2.1$. We find no evolution in [Mg/Fe] out to $z\sim1.4$,
though the $z\sim2.1$ galaxies are $0.2$ dex enhanced compared to $z=0-0.7$. A
comparison of these results to a chemical evolution model indicates that
galaxies at higher redshift form at progressively earlier epochs and over
shorter star-formation timescales, with the $z\sim2.1$ galaxies forming the
bulk of their stars over 150 Myr at $z_{\rm form}\sim4$. This evolution cannot
be solely attributed to an increased number of quiescent galaxies at later
times; several Heavy Metal galaxies have extreme chemical properties not found
in massive galaxies at $z\sim0.0-0.7$. Thus, the chemical properties of
individual galaxies must evolve over time. Minor mergers also cannot fully
account for this evolution as they cannot increase [Fe/H], particularly in
galaxy centers. Consequently, the build-up of massive quiescent galaxies since
$z\sim2.1$ may require further mechanisms such as major mergers and/or central
star formation.",2312.05307v1
2023-12-12,Abundances of iron-peak elements in accreted and in situ born Galactic halo stars,"Previous work on the abundances of C, O, Na, Mg, Si, Ca, Ti, Cr, Mn, Fe, Ni,
Cu, and Zn in low-alpha (accreted) and high-alpha (in situ born) halo stars is
extended to include the abundances of Sc, V, and Co, enabling us to study the
nucleosynthesis of all iron-peak elements along with the lighter elements. The
Sc, V, and Co abundances were determined from a 1D MARCS model-atmosphere
analysis of equivalent widths of atomic lines in high signal-to-noise, high
resolution spectra assuming local thermodynamic equilibrium (LTE). In addition,
new 3D and/or non-LTE calculations were used to correct the 1D LTE abundances
for several elements including consistent 3D non-LTE calculations for Mg. The
two populations of accreted and in situ born stars are well separated in
diagrams showing [Sc/Fe], [V/Fe], and [Co/Fe] as a function of [Fe/H]. The
[X/Mg] versus [Mg/H] trends for high-alpha and low-alpha stars were used to
determine the yields of core-collapse and Type Ia supernovae. The largest Type
Ia contribution occurs for Cr, Mn, and Fe, whereas Cu is a pure core-collapse
element. Sc, Ti, V, Co, Ni, and Zn represent intermediate cases. A comparison
with yields calculated for supernova models shows poor agreement for the
core-collapse yields. The Ia yields suggest that sub-Chandrasekhar-mass Type Ia
supernovae provide a dominant contribution to the chemical evolution of the
host galaxies of the low-alpha stars. A substructure in the abundances and
kinematics of the low-alpha stars suggests that they arise from at least two
different satellite accretion events, Gaia-Sausage-Enceladus and Thamnos.",2312.07768v1
2023-12-20,On the Origin of the X-ray Emission in Heavily Obscured Compact Radio Sources,"X-ray continuum emission of active galactic nuclei (AGNs) may be reflected by
circumnuclear dusty tori, producing prominent fluorescence iron lines at X-ray
frequencies. Here we discuss the broad-band emission of three radio-loud AGN
belonging to the class of compact symmetric objects (CSOs), with detected
narrow Fe\,K$\alpha$ lines. CSOs have newly-born radio jets, forming compact
radio lobes with projected linear sizes of the order of a few to hundreds of
parsecs. We model the radio--to--$\gamma$-ray spectra of compact lobes in
{J1407+2827}, J1511+0518, and {J2022+6137}, which are among the nearest and the
youngest CSOs known to date, and are characterized by an intrinsic X-ray
absorbing column density of $N_{\rm H} > 10^{23}$\,cm$^{-2}$. In addition to
the archival data, we analyze the newly acquired \chandra\ X-ray Observatory
and Sub-Millimeter Array (SMA) observations, and also refine the $\gamma$-ray
upper limits from the \fermi\ Large Area Telescope (LAT) monitoring. The new
\chandra\ data exclude the presence of the extended X-ray emission components
on scales larger than $1.5^{\prime \prime}$. The SMA data unveil a correlation
of the spectral index of the electron distribution in the lobes and $N_{\rm
H}$, which can explain the $\gamma$-ray quietness of heavily obscured CSOs.
Based on our modeling, we argue that the inverse-Compton emission of compact
radio lobes may account for the intrinsic X-ray continuum in all these sources.
Furthermore, we propose that the observed iron lines may be produced by a
reflection of the lobes' continuum from the surrounding cold dust.",2312.13418v2
2024-01-10,Nematic quantum disordered state in FeSe,"The unusual quantum-disordered magnetic ground state intertwined with
superconductivity and electronic nematicity in FeSe has been a research focus
in iron-based superconductors. However, the intrinsic spin excitations across
the entire Brillouin zone in detwinned FeSe, which forms the basis for a
microscopic understanding of the magnetic state and superconductivity, remain
to be determined. Here, we use inelastic neutron scattering to map out the spin
excitations of FeSe dewtinned with a uniaxial-strain device. We find that the
stripe spin excitations (Q=(1, 0)/(0, 1)) exhibit the $C_2$ symmetry up to
$E\approx120$ meV, while the N{\'e}el spin excitations (Q=(1, 1)) retain their
$C_4$ symmetry in the nematic state. The temperature dependence of the
difference in the spin excitations at Q=(1, 0) and (0, 1) for temperatures
above the structural phase transition unambiguously shows the establishment of
the nematic quantum disordered state. The similarity of the N\'eel excitations
in FeSe and NaFeAs suggests that the N\'eel excitations are driven by the
enhanced electron correlations in the $3d_{xy}$ orbital. By determining the key
features of the stripe excitations and fitting their dispersions using a
Heisenberg Hamiltonian with biquadratic interaction ($J_1$-$K$-$J_2$), we
establish a spin-interaction phase diagram and conclude that FeSe is close to a
crossover region between the antiferroquadrupolar, N\'eel, and stripe ordering
regimes. The results provide an experimental basis for establishing a
microscopic theoretical model to describe the origin and intertwining of the
emergent orders in iron-based superconductors.",2401.05092v1
2024-01-17,Aperture and Resolution Effects on Ultraviolet Star-Forming Properties: Insights from Local Galaxies and Implications for High-Redshift Observations,"We present an analysis of the effects of spectral resolution and aperture
scales on derived galaxy properties using far-ultraviolet (FUV) spectra of
local star-forming galaxies from the International Ultraviolet Explorer (R~250,
FOV~10""x20"") and Cosmic Origins Spectrograph on the Hubble Space Telescope
(R~15,000, FOV~2.5""). Using these spectra, we measured FUV luminosities,
spectral slopes, dust attenuation, and equivalent widths. We find that galaxies
with one dominant stellar cluster have FUV properties that are independent of
aperture size, while galaxies with multiple bright clusters are sensitive to
the total light fraction captured by the aperture. Additionally, we find
significant correlations between the strength of stellar and interstellar
absorption-lines and metallicity, indicating metallicity-dependent line-driven
stellar winds and interstellar macroscopic gas flows shape the stellar and
interstellar spectral lines, respectively. The observed line-strength versus
metallicity relation of stellar-wind lines agrees with the prediction of
population synthesis models for young starbursts. In particular, measurements
of the strong stellar CIV 1548,1550 line provide an opportunity to determine
stellar abundances as a complement to gas-phase abundances. We provide a
relation between the equivalent width of the CIV line and the oxygen abundance
of the galaxy. We discuss this relation in terms of the stellar-wind properties
of massive stars. As the driving lines in stellar winds are mostly ionized iron
species, the CIV line may eventually offer a method to probe
alpha-element-to-iron ratios in star-forming galaxies once consistent models
with non-solar abundance ratios are available. These results have important
implications for the galaxy-scale, low-resolution observations of high-redshift
galaxies from JWST (R~100-3,500).",2401.08971v1
2024-02-09,High-Resolution X-Ray Spectroscopy of Interstellar Iron Toward Cygnus X-1 and GX 339-4,"We present a high-resolution spectral study of Fe L-shell extinction by the
diffuse interstellar medium (ISM) in the direction of the X-ray binaries Cygnus
X-1 and GX 339-4, using the XMM-Newton reflection grating spectrometer. The
majority of interstellar Fe is suspected to condense into dust grains in the
diffuse ISM, but the compounds formed from this process are unknown. Here, we
use the laboratory cross sections from Kortright & Kim (2000) and Lee et al.
(2009) to model the absorption and scattering profiles of metallic Fe, and the
crystalline compounds fayalite (Fe$_2$SiO$_4$), ferrous sulfate (FeSO$_4$),
hematite ($\alpha$-Fe$_2$O$_3$), and lepidocrocite ($\gamma$-FeOOH), which have
oxidation states ranging from Fe$^{0}$ to Fe$^{3+}$. We find that the observed
Fe L-shell features are systematically offset in energy from the laboratory
measurements. An examination of over two dozen published measurements of Fe
L-shell absorption finds a 1-2 eV scatter in energy positions of the L-shell
features. Motivated by this, we fit for the best energy-scale shift
simultaneously with the fine structure of the Fe L-shell extinction cross
sections. Hematite and lepidocrocite provide the best fits ($\approx +1.1$ eV
shift), followed by fayalite ($\approx +1.8$ eV shift). However, fayalite is
disfavored, based on the implied abundances and knowledge of ISM silicates
gained by infrared astronomical observations and meteoritic studies. We
conclude that iron oxides in the Fe$^{3+}$ oxidation state are good candidates
for Fe-bearing dust. To verify this, new absolute photoabsorption measurements
are needed on an energy scale accurate to better than 0.2 eV.",2402.06726v1
2024-02-28,Elastocaloric evidence for a multicomponent superconductor stabilized within the nematic state in Ba(Fe$_{1-x}$Co$_x$)$_2$As$_2$,"The iron-based high-$T_c$ superconductors exhibit rich phase diagrams with
intertwined phases, including magnetism, nematicity and superconductivity. The
superconducting $T_c$ in many of these materials is maximized in the regime of
strong nematic fluctuations, making the role of nematicity in influencing the
superconductivity a topic of intense research. Here, we use the AC
elastocaloric effect (ECE) to map out the phase diagram of
Ba(Fe$_{1-x}$Co$_x$)$_2$As$_2$ near optimal doping. The ECE signature at $T_c$
on the overdoped side, where superconductivity condenses without any nematic
order, is quantitatively consistent with other thermodynamic probes that
indicate a single-component superconducting state. In contrast, on the slightly
underdoped side, where superconductivity condenses within the nematic phase,
ECE reveals a second thermodynamic transition proximate to and below $T_c$. We
rule out magnetism and re-entrant tetragonality as the origin of this
transition, and find that our observations strongly suggest a phase transition
into a multicomponent superconducting state. This implies the existence of a
sub-dominant pairing instability that competes strongly with the dominant
$s^\pm$ instability. Our results thus motivate a re-examination of the pairing
state and its interplay with nematicity in this extensively studied iron-based
superconductor, while also demonstrating the power of ECE in uncovering
strain-tuned phase diagrams of quantum materials.",2402.17945v1
2024-02-28,METAL-Z: Measuring dust depletion in low metalicity dwarf galaxies,"The cycling of metals between interstellar gas and dust is a critical aspect
of the baryon cycle of galaxies, yet our understanding of this process is
limited. This study focuses on understanding dust depletion effects in the low
metallicity regime (< 20% Zo) typical of cosmic noon. Using medium-resolution
UV spectroscopy from the COS onboard the Hubble Space Telescope, gas-phase
abundances and depletions of iron and sulfur were derived toward 18 sightlines
in local dwarf galaxies IC 1613 and Sextans A. The results show that the
depletion of Fe and S is consistent with that found in the Milky Way, LMC and
SMC. The depletion level of Fe increases with gas column density, indicating
dust growth in the interstellar medium (ISM). The level of Fe depletion
decreases with decreasing metallicity, resulting in the fraction of iron in gas
ranging from 3% in the MW to 9% in IC 1613 and ~19% in Sextans A. The
dust-to-gas and dust-to-metal ratios (D/G, D/M) for these dwarf galaxies were
estimated based on the MW relations between the depletion of Fe and other
elements. The study finds that D/G decreases only slightly sub-linearly with
metallicity, with D/M decreasing from 0.41 +/- 0.05 in the MW to 0.11 +/- 0.11
at 0.10 Zo (at log N(H) = 21 cm-2). The trend of D/G vs. metallicity using
depletion in local systems is similar to that inferred in Damped Ly-alpha
systems from abundance ratios but lies higher than the trend inferred from FIR
measurements in nearby galaxies.",2402.18733v1
2024-03-07,"Effects of mechanical stress, chemical potential, and coverage on hydrogen solubility during hydrogen enhanced decohesion of ferritic steel grain boundaries: A first-principles study","Hydrogen enhanced decohesion (HEDE) is one of the many mechanisms of hydrogen
embrittlement, a phenomenon which severely impacts structural materials such as
iron and iron alloys. Grain boundaries (GBs) play a critical role in this
mechanism, where they can provide trapping sites or act as hydrogen diffusion
pathways. The interaction of H with GBs and other crystallographic defects, and
thus the solubility and distribution of H in the microstructure, depends on the
concentration, chemical potential and local stress. Therefore, for a
quantitative assessment of HEDE, a generalized solution energy in conjunction
with the cohesive strength as a function of hydrogen coverage is needed. In
this work, we carry out density functional theory calculations to investigate
the influence of H on the decohesion of the $\Sigma$5(310)[001] and
$\Sigma$3(112)[1$\bar{1}$0] symmetrical tilt GBs in bcc Fe, as examples for
open and close-packed GB structures. A method to identify the segregation sites
at the GB plane is proposed. The results indicate that at higher local
concentrations, H leads to a significant reduction of the cohesive strength of
the GB planes, significantly more pronounced at the $\Sigma$5 than at the
$\Sigma$3 GB. Interestingly, at finite stress the $\Sigma$3 GB becomes more
favorable for H solution, as opposed to the case of zero stress, where the
$\Sigma$5 GB is more attractive. This suggests that under certain conditions
stresses in the microstructure can lead to a re-distribution of H to the
stronger grain boundary, which opens a new path to designing H-resistant
microstructures. To round up our study, we investigate the effects of typical
alloying elements in ferritic steel, C, V, Cr and Mn, on the solubility of H
and the strength of the GBs.",2403.04741v1
2024-03-20,A Gap in the Densities of Small Planets Orbiting M Dwarfs: Rigorous Statistical Confirmation Using the Open-source Code RhoPop,"Using mass-radius-composition models, small planets ($\mathrm{R}\lesssim 2
\mathrm{R_\oplus}$) are typically classified into three types: iron-rich,
nominally Earth-like, and those with solid/liquid water and/or atmosphere.
These classes are generally expected to be variations within a compositional
continuum. Recently, however, Luque & Pall\'e observed that potentially
Earth-like planets around M dwarfs are separated from a lower-density
population by a density gap. Meanwhile, the results of Adibekyan et al. hint
that iron-rich planets around FGK stars are also a distinct population. It
therefore remains unclear whether small planets represent a continuum or
multiple distinct populations. Differentiating the nature of these populations
will help constrain potential formation mechanisms. We present the RhoPop
software for identifying small-planet populations. RhoPop employs mixture
models in a hierarchical framework and a nested sampler for parameter and
evidence estimates. Using RhoPop, we confirm the two populations of Luque &
Pall\'e with $>4\sigma$ significance. The intrinsic scatter in the Earth-like
subpopulation is roughly half that expected based on stellar abundance
variations in local FGK stars, perhaps implying M dwarfs have a smaller spread
in the major rock-building elements (Fe, Mg, Si) than FGK stars. We apply
RhoPop to the Adibekyan et al. sample and find no evidence of more than one
population. We estimate the sample size required to resolve a population of
planets with Mercury-like compositions from those with Earth-like compositions
for various mass-radius precisions. Only 16 planets are needed when
$\sigma_{M_p} = 5\%$ and $\sigma_{R_p} = 1\%$. At $\sigma_{M_p} = 10\%$ and
$\sigma_{R_p} = 2.5\%$, however, over 154 planets are needed, an order of
magnitude increase.",2403.13961v1
1993-04-06,Element Diffusion in the Solar Interior,"We study the diffusion of helium and other heavy elements in the solar
interior by solving exactly the set of flow equations developed by Burgers for
a multi-component fluid, including the residual heat-flow terms. No
approximation is made concerning the relative concentrations and no restriction
is placed on the number of elements considered. We give improved diffusion
velocities for hydrogen, helium, oxygen and iron, in the analytic form derived
previously by Bahcall and Loeb. These expressions for the diffusion velocities
are simple to program in stellar evolution codes and are expected to be
accurate to $\sim 15\%$. Our complete treatment of element diffusion can be
directly incorporated in a standard stellar evolution code by means of an
exportable subroutine, but, for convenience, we also give simple analytical
fits to our numerical results.",9304005v1
1994-04-20,Analysis of the 3d6 4s(6D)4f-5g Supermultiplet of Fe I in Laboratory and Solar Infrared Spectra,"The combined laboratory and solar analysis of the highly-excited
subconfigurations 4f and 5g of Fe I has allowed us to classify 87 lines of the
4f-5g supermultiplet in the spectral region 2545-2585 cm-1. The level structure
of these JK-coupled configurations is predicted by semiempirical calculations
and the quadrupolic approximation. Semiempirical gf-values have been calculated
and are compared to gf values derived from the solar spectrum. The solar
analysis has shown that these lines, which should be much less sensitive than
lower excitation lines to departures from LTE and to temperature uncertainties,
lead to a solar abundance of iron which is consistent with the meteoritic value
(A_Fe = 7.51).",9404050v1
1995-03-03,"The First Second of a Type-II Supernova: Convection, Accretion, and Shock Propagation","One- and two-dimensional hydrodynamical simulations of neutrino-driven
supernova explosions are discussed. The simulations cover the phase between the
stagnation of the prompt shock and about one second after core bounce.
Systematic variation of the neutrino fluxes from the neutrino sphere shows that
the explosion energy, explosion time scale, initial mass of the protoneutron
star, and explosive nucleosynthesis of iron-group elements depend sensitively
on the strength of the neutrino heating during the first few 100 ms after shock
formation. Convective overturn in the neutrino-heated region behind the shock
is a crucial help for the explosion only in a narrow window of neutrino
luminosities. Here powerful explosions can be obtained only in the
multi-dimensional case. For higher core-neutrino fluxes also spherically
symmetrical models yield energetic explosions, while for lower luminosities
even with convection no strong explosions occur.",9503015v1
1995-04-03,COOLING FLOW MODELS OF THE X--RAY EMISSION AND TEMPERATURE PROFILES FOR A SAMPLE OF ELLIPTICAL GALAXIES,"A simple spherically-symmetric, steady-state, cooling-flow description with
gas loss (following Sarazin \& Ashe 1989), within galaxy models constrained by
radially extended stellar dynamical data, is shown to provide generally
reasonable fits to the existing data on X-ray emission profiles and
temperatures for a set of bright elliptical galaxies in Virgo and Fornax. Three
free parameters are needed to specify the model: the external mass flux, the
external pressure, and a dimensionless factor, which regulates the mass
deposition rate along the flow. Three different assumptions on the supernova
rate have been considered. A moderate value for the supernova rate in
elliptical galaxies is found to be preferred. Confining pressures of
$p_{ext}\sim4\div15\times10^3\kelvin$ cm$^{-3}$ and significant accretion rates
of external material, up to $4\msolar/\yr$, are suggested by our models. A
possible correlation between $L_X/L_B$ and the iron abundance in the gas inside
ellipticals is pointed out.",9504002v2
1995-05-18,X-RAY OUTBURST OF THE PECULIAR SEYFERT GALAXY IC 3599,"We report optical, soft X-ray, and UV observations of the peculiar Seyfert
galaxy IC 3599 using data obtained with ROSAT and IUE. Most remarkably, we
discovered a rapid decrease of the X-ray flux by a factor of about 100 within
one year and a more gradual decrease thereafter. The X-ray spectrum of IC 3599
was soft at flux maximum and became even softer as the flux decreased.
Simultaneously with the late decrease of the X-ray flux, we observed a decrease
in the strength of highly ionized optical iron lines. We discuss several
explanations for this behaviour including an accretion disk instability and
tidal disruption of a star orbiting a central massive black hole.",9505085v1
1995-10-19,Model Atmospheres for Low Field Neutron Stars,"We compute model atmospheres and emergent spectra for low field (B<10^10 G)
neutron stars, using new opacity and equation of state data from the OPAL
project. These computations, incorporating improved treatments of flux
transport and convective stability, provide spectra for hydrogen, solar
abundance and iron atmospheres. We compare our results to high field magnetic
atmospheres, available only for hydrogen. An application to apparently thermal
flux from the low field millisecond pulsar PSR J0437--4715 shows that H
atmospheres fit substantially better than Fe models. We comment on extension to
high fields and the implication of these results for neutron star luminosities
and radii.",9510094v2
1995-11-22,Metal Enhancements in the X-ray Gas around Central Cluster Galaxies,"The X-ray emission by hot gas around the central galaxies of galaxy clusters
is commonly modeled assuming the existence of steady-state, multiphase cooling
flows. The inflowing gas will be chemically enriched by type Ia supernovae and
stellar mass loss occurring in the outer parts of the central galaxy. This may
give rise to a substantial metallicity enhancement towards the center, whose
amplitude is proportional to the ratio of the central galaxy luminosity to the
mass inflow rate. The metallicity of the hotter phases is expected to be higher
than that of the colder, denser phases. The metallicity profile expected for
the Centaurus cluster is in good agreement with the iron abundance gradient
recently inferred from ASCA measurements (Fukazawa et al. 1994). However,
current data do not rule out alternative models where cooling is balanced by
some heat source. In either case, the enhancement expected from injection by
type Ia supernovae is roughly as observed. Most of this work is described in
more detail in Reisenegger, Miralda-Escud\'e, \& Waxman (1996;
astro-ph/9511044).",9511105v1
1995-12-12,The first simultaneous X-ray/gamma-ray observations of Cyg X-1 by Ginga and OSSE,"We present the results of 4 simultaneous observations of Cygnus X-1 by Ginga
and OSSE. The X-ray/gamma-ray spectra can be described by an intrinsic
continuum and a component due to Compton reflection including an iron K-alpha
line. The intrinsic spectrum at X-ray energies is a power-law with a photon
spectral index of Gamma=1.6. The intrinsic gamma-ray spectrum can be
phenomenologically described by either a power-law without cutoff up to 150
keV, and an exponential cutoff above that energy, or by an exponentially cutoff
power law and a second hard component.",9512073v1
1996-05-10,The Compton Mirror in NGC 4151,"We show that the sharp cutoff in the hard X-ray spectrum of NGC 4151, unusual
for Seyfert 1 galaxies, can be reconciled with the average Seyfert 1 spectrum
if we assume that the central source is completely hidden from our line of
sight by the thick part of the accretion disk or by the broad emission line
clouds. The observed X-ray radiation is produced by scattering of the Seyfert
1-type spectrum in the higher, cooler parts of the accretion disk corona, or in
a wind. A sharp cutoff appears as a result of the Compton recoil effect. This
model naturally explains a discrepancy regarding the inclination of the central
source, inferred to be low (face-on) from observations of the iron $K\alpha$
emission line, but inferred to be high on the basis of optical and UV
observations.",9605052v1
1996-07-08,Physical Conditions in Low Ionization Regions of the Orion Nebula,"We reexamine the spectroscopic underpinnings of recent suggestions that [O I]
and [Fe II] lines from the Orion H II region are produced in gas where the
iron-carrying grains have been destroyed and the electron density is
surprisingly high. Our new observations show that previous detections of [O I]
5577 were dominated by telluric emission. Our limits are consistent with a
moderate density (10^4 cm^{-3}) photoionized gas. We show that a previously
proposed model of the Orion H II region reproduces the observed [O I] and [Fe
II] spectrum. These lines are fully consistent with formation in a dusty region
of moderate density.",9607045v1
1996-08-19,Scattering of X-ray emission lines by the neutral and molecular hydrogen in the Sun's atmosphere and in the vicinity of active galactic nuclei and compact sources,"In many astrophysical objects an account for scattering of the X-ray
fluorescent and resonance lines of iron ions by the electrons, bound in atomic
and molecular hydrogen is important. Specific distortions of the scattered line
profile spectrum appear in comparison with scattering by free electrons.
Analysis of scattered line spectra may provide information on the ionization
state, helium abundance and geometry of scattering media in the vicinity of
AGNs, compact X-ray sources and on the surface of X-ray flaring stars and the
Sun.",9608114v1
1996-10-09,Galaxy evolution: the effect of dark matter on the chemical evolution of ellipticals and galaxy clusters,"In this paper we discuss the chemical evolution of elliptical galaxies and
its consequences on the evolution of the intracluster medium (ICM). We use
chemical evolution models taking into account dark matter halos and compare the
results with previous models where dark matter was not considered. In
particular, we examine the evolution of the abundances of some relevant heavy
elements such as oxygen, magnesium and iron and conclude that models including
dark matter halos and an initial mass function (IMF) containing more massive
stars than the Salpeter (1955) IMF, better reproduce the observed abundances of
Mg and Fe both in the stellar populations and in the ICM (ASCA results). We
also discuss the origin of gas in galaxy clusters and conclude that most of it
should have a primordial origin.",9610059v1
1996-10-11,Spallation of Iron in Black Hole Accretion Flows,"In the local Galactic interstellar medium there is approximate energy
equipartition between cosmic rays, magnetic fields and radiation. If this holds
in the central regions of AGN, in particular Seyfert galaxies, then consideral
nuclear spallation of Fe occurs, resulting in enhanced abundances of the sub-Fe
elements Ti, V, Cr and Mn. These elements produce a cluster of X-ray
flourescence lines at energies just below the 6.4 keV Fe-K$\alpha$ line. It is
suggested that the red wings on the Fe lines observed with ASCA from various
Seyfert AGN are due to the unresolved line emission from these elements. Future
observations with more sensitive X-ray instruments should resolve these lines.
The estimated gamma ray emission from nuclear deexcitation and neutral pion
production is calculated and found to be below the sensitivities of any current
instruments. However, very luminous nearby Seyferts displaying Fe lines with
red wings would have $>100$ MeV continuum emission detectable by future
instruments such as GLAST.",9610081v1
1996-10-29,Comment on a paper by M. A. Bautista ``Atomic data from the Iron Project. XVI. Photoionization cross sections and oscillator strengths for Fe V'',"Recently, Bautista (1996, A&AS, 119, 105) reported new calculations of
photoionization cross sections for Fe V, and compared them with the earlier
results of Reilman & Manson (1979, ApJS, 40, 815) and Verner et al. (1993,
Atomic Data Nucl. Data Tables, 55, 233). Bautista claimed that beyond 10 Ry the
new cross sections ``converge well toward the results by Reilman and Manson'',
whereas ``the calculations by Verner et al. still underestimate the cross
section by almost factor of two''. We show that Bautista erroneously compared
the total (summed over shells) cross sections from Reilman & Manson with the
partial 3d-shell cross sections from Verner et al. Actually, the total cross
sections from Verner et al. and Reilman & Manson agree within 3% at all
energies.",9610244v1
1996-11-13,Galactic Drips and How to Stop Them!,"The temperature of hot interstellar gas at large radii in elliptical galaxies
can be lower than the mean galactic virial temperature. If so, a nonlinear
cooling wave can form in the hot interstellar gas and propagate slowly toward
the galactic core. If the cooling wave survives hydrodynamic instabilities, it
can intermittently deposit cold gas within about 15 effective radii. For a
bright elliptical the total mass deposited in this manner can approach 10^10
solar masses. The cold gas that drips out at large galactic radii may account
for the young stellar populations and extended gas at $\sim 10^4$ K observed in
many ellipticals, features that are often attributed to galactic mergers.
Galactic drips are expected in relatively isolated (field) ellipticals provided
(i) the galactic stellar velocity ellipsoids are radially oriented at large
galactic radii and (ii) the current Type Ia supernova rate is sufficiently
small to be consistent with interstellar iron abundances found in recent X-ray
studies. Galactic drips are surpressed in ellipticals located within clusters
of galaxies; when the pressure in the ambient cluster gas exceeds that in the
outer parts of the galactic interstellar medium, some cluster gas flows into
the galaxy which surpresses the drips.",9611096v1
1996-11-29,Ultraviolet Light from Old Stellar Populations,"We consider the general theoretical problem of ultraviolet light from old
stellar populations (t > 2 Gyr), and the interpretation of galaxy spectra at
short wavelengths (lamda < 3200A) The sources believed to be responsible for
the observed `ultraviolet upturn phenomenon' (UVX) are Post-AGB (P-AGB),
extreme horizontal branch (EHB) and AGB-Manque (AGBM) stars. The production of
EHB stars depends on mass loss on the red giant branch, which is poorly
understood, making the far-UV flux problematical as an indicator of the gross
properties, such as the age, of a given galaxy. We discuss the current state of
the comparison between theory and observation for the UVX phenomenon, and
revisit the interpretation of the well-known UVX-Mg2 correlation. In
particular, we draw attention to the fact that the UVX appears not to be
correlated with indices that measure the iron abundance, which has implications
for models that explain the UV-Mg2 correlation as an abundance-driven effect.
Finally, we note the potential utility of ultraviolet observations in
distinguishing age and metallicity from galaxy spectral energy distributions.",9612008v1
1996-12-19,The Great Annihilator 1E1740.7-2942: Molecular cloud connection and coronal structure,"Using 12CO and 13CO observations we present column density maps of the
molecular cloud (V = -135 km/s) in the direction of 1E1740.7-2942. Hydrogen
column densities of the cloud scatter between (3.5 - 11) 10**22 cm-2, depending
on the method used. From this we conclude, deriving first a simple analytic
formula, that despite of the weakness of the iron fluorescent 6.4 keV line
(Churazov et al. 1996), the source may lie inside the cloud, or at least close
to its edge. The combined ASCA/BATSE spectrum from September 1993 and 1994 can
be modelled with a two-phase accretion disc corona model, where the hot region
is detached from the cold disc. Geometrically, the hot phase can be interpreted
e.g. as a number of active regions (magnetic loops) above the disc, or as a
spherical hot cloud around the central object.",9612194v1
1997-01-08,The ASCA X-ray spectrum of the powerful radio galaxy 3C109,"We report the results from an ASCA X-ray observation of the powerful Broad
Line Radio Galaxy, 3C109. The ASCA spectra confirm our earlier ROSAT detection
of intrinsic X-ray absorption associated with the source. The absorbing
material obscures a central engine of quasar-like luminosity. The luminosity is
variable, having dropped by a factor of two since the ROSAT observations 4
years before. The ASCA data also provide evidence for a broad iron emission
line from the source, with an intrinsic FWHM of ~ 120,000 km/s. Interpreting
the line as fluorescent emission from the inner parts of an accretion disk, we
can constrain the inclination of the disk to be $> 35$ degree, and the inner
radius of the disk to be $< 70$ Schwarzschild radii. Our results support
unified schemes for active galaxies, and demonstrate a remarkable similarity
between the X-ray properties of this powerful radio source, and those of lower
luminosity, Seyfert 1 galaxies.",9701033v1
1997-01-22,General relativistic effects in the neutrino-driven wind and r-process nucleosynthesis,"We discuss general relativistic effects in the steady-state neutrino-driven
``wind'' which may arise from nascent neutron stars. In particular, we
generalize previous analytic estimates of the entropy per baryon $S$, the mass
outflow rate $\dot M$, and the dynamical expansion time scale $\tau_{dyn}$. We
show that $S$ increases and $\tau_{dyn}$ decreases with increasing values of
the mass-to-radius ratio describing the supernova core. Both of these trends
indicate that a more compact core will lead to a higher number of neutrons per
iron peak seed nucleus. Such an enhancement in the neutron-to-seed ratio may be
required for successful r-process nucleosynthesis in neutrino-heated supernova
ejecta.",9701178v1
1997-04-18,Gamma rays and neutrinos from the Crab Nebula produced by pulsar accelerated nuclei,"We investigate the consequences of the acceleration of heavy nuclei (e.g.
iron nuclei) by the Crab pulsar. Accelerated nuclei can photodisintegrate in
collisions with soft photons produced in the pulsar's outer gap, injecting
energetic neutrons which decay either inside or outside the Crab Nebula. The
protons from neutron decay inside the nebula are trapped by the Crab Nebula
magnetic field, and accumulate inside the nebula producing gamma-rays and
neutrinos in collisions with the matter in the nebula. Neutrons decaying
outside the Crab Nebula contribute to the Galactic cosmic rays. We compute the
expected fluxes of gamma-rays and neutrinos, and find that our model could
account for the observed emission at high energies and may be tested by
searching for high energy neutrinos with future neutrino telescopes currently
in the design stage.",9704186v1
1997-05-08,Spectropolarimetry of FIRST 0840+3633,"We present Keck spectropolarimetry of a rare ``Iron Lo-BALQSO,'' FIRST
0840+3633. The continuum is 4% polarized near 2000 angstroms rest-frame, but
falls to 2% at longer wavelengths, and maintains a relatively constant position
angle of 50 degrees. The emission lines are unpolarized. The polarization
increases up to 8% in the low-ionization absorption troughs of Mg II 2800 and
Al III 1860. The polarization and its position angle vary in a complicated
manner across the metastable Fe II absorption lines, suggesting that more than
one mechanism is at work or that the system geometry is complex.",9705053v1
1997-05-12,Physical Conditions of the Coronal Line Region in Seyfert Galaxies,"The launch of the Infrared Space Observatory and new atomic data have opened
a window to the study of high ionization gas in active galactic nuclei (AGN).
We present the results of a large number of photoionization simulations of the
``coronal line'' region in AGN, employing new atomic data from the Opacity and
Iron Projects. Our grid of line emission spans 8 orders of magnitude in gas
density and 14 orders of magnitude in ionizing flux in an effort to identify
the optimal conditions in which these lines form. We show that coronal lines
form at distances from just outside the broad line region to ~400L_{43.5}^{1/2}
pc, in gas with ionization parameter -2.0 < log U(H) < 0.75, corresponding to
gas densities of 10$^2$ to 10$^{8.5}$ cm$^{-3}$, with electron temperatures
~12,000K -- 150,000K. A large range of distances from the central source
implies significant line width variation among the coronal lines. We identify
several line ratios which could be used to measure relative abundances, and we
use these to show that the coronal line gas is likely to be dust free.",9705082v1
1997-06-02,Decoupled Nuclei and Nuclear Polar Rings in Regular Spiral Galaxies. NGC 2841,"The Sb galaxy NGC 2841 was observed at the 6 m telescope of SAO RAS with the
Multi-Pupil Field Spectrograph and at the 1 m telescope of SAO RAS with the
long-slit spectrograph. An unresolved nucleus of NGC 2841 is shown to be
chemically decoupled both in magnesium and in iron with abundance break
estimates of 0.36 dex for Mg and 0.6 dex for Fe; an abundance gradient in the
bulge is seen only in the magnesium index and is typical for early-type disk
galaxies. The rotation axis of the nuclear ionized gas in NGC 2841 is
orthogonal to that of the central stellar population; an existence of a bulge
stellar component with decoupled rotation momentum in the radius range 5"" -12""
is suspected. A possible scenario for the origin of the unusual central
structure in NGC 2841 is proposed.",9706003v1
1997-06-07,X-ray detections of weak Seyfert2's with BeppoSAX,"We report the detection in the X rays of two weak Seyfert2's (NGC3393 and
NGC4941) with the Italian-Dutch satellite BeppoSAX. These are among the first
sources observed in a sample of 12 Seyfert2's which are being studied within
the BeppoSAX core program, in an effort to probe the putative torus at high
X-ray energies, calibrate an isotropic luminosity indicator for absorbed
nuclei, and determine the distribution of torus thicknesses, Nh. Both a Compton
thick spectrum, with a reflected power law and a large equivalent width iron
line, and a Compton thin spectrum, with the intrinsic power law transmitted
through a large column density absorber, provide acceptable fits to both
sources, with some preference for the latter model in the case of NGC4941. The
high initial detection rate in our program points to a large final X-ray
sample.",9706070v1
1997-07-08,Detailed NLTE Model Atmospheres for Novae during Outburst: I. New Theoretical Results,"We present new detailed NLTE calculations for model atmospheres of novae
during outburst. This fully self-consistent NLTE treatment for a number of
model atoms includes 3922 NLTE levels and 47061 NLTE primary transitions. We
discuss the implication of departures from LTE for the strengths of the lines
in nova spectra. The new results show that our large set of NLTE lines
constitute the majority of the total line blanketing opacity in nova
atmospheres. Although we include LTE background lines, their effect are small
on the model structures and on the synthetic spectra. We demonstrate that the
assumption of LTE leads to incorrect synthetic spectra and that NLTE
calculations are required for reliably modeling nova spectra. In addition, we
show that detailed NLTE treatment for a number of ionization stages of iron
changes the results of previous calculations and improve the fit to observed
nova spectra.",9707104v1
1997-07-22,Spectropolarimetry of FIRST BAL QSOs,"We present Keck spectropolarimetry of two rare low-ionization broad
absorption line (BAL) QSOs, FIRST J084044.5+363328 and FIRST J155633.8+351758,
that also exhibit narrow absorption lines from metastable excited levels of Fe
II (``Iron Lo-BALs''). These QSOs were discovered in optical follow-ups to a
deep radio survey; FIRST J155633.8+351758 is radio-loud, the first BAL QSO so
identified. FIRST J084044.5+363328 is highly polarized and exhibits many
features found in other BAL QSOs, and the polarization and its position angle
vary in a complicated manner across the metastable Fe II absorption lines,
suggesting that more than one mechanism is at work, or that the system geometry
is complex. FIRST J155633.8+351758 may be the most highly polarized BAL QSO
known, and exhibits other unusual polarization properties compared to other
highly polarized BAL QSOs. Currently available data cannot yet discriminate
among the possible lines of sight to BAL QSOs (edge-on, pole-on, or random).",9707238v1
1997-07-22,"A Second UV ""Light Bulb"" behind the SN 1006 Remnant","A point X-ray source located 9 arcmin northeast of the center of SN~1006 has
been spectroscopically identified as a background QSO, with a redshift of
0.335. The object is moderately bright, with magnitude V=18.3. If its
ultraviolet spectrum is typical of low-z quasars, this object will be a second
(after the Schweizer-Middleditch star) source to use for absorption
spectroscopy of material within SN 1006. Absorption spectra provide a unique
probe for unshocked ejecta within this supernova remnant, and can possibly
solve the long-standing problem of ""missing"" iron in the remnants of Type Ia
supernovae.",9707247v1
1997-08-25,ASCA observations of type-2 Seyfert Galaxies. III. Orientation and X-ray Absorption,"We discuss the spectral properties of a sample of type-2 Seyfert galaxies
based upon the analysis of \asca data. In this paper we consider the sources
for which the X-ray spectra appear to be dominated by the nuclear continuum,
transmitted through a large column of absorbing material. We find that both
Seyfert-2 galaxies and NELGs show iron K$\alpha$ line profiles indicative of
reprocessing of nuclear X-rays in a face-on accretion disk. Such line profiles
are also observed in Seyfert-1 galaxies. This result is contrary to unification
models, which would predict the inner regions of Seyfert-2 galaxies to be
observed edge-on. This raises some questions as to the orientation of the
circumnuclear absorber. If the observed differences between Seyfert type-1 and
type-2 galaxies, and NELGs are not due to differences in the orientation of the
absorbing material, then we suggest that differences in dust composition and
grain size, and in the density of the circumnuclear gas could be of primary
importance.",9708231v1
1997-09-02,New Measurement of Metal Abundance in the Elliptical Galaxy NGC 4636 with Asca,"High quality X-ray spectra of NGC 4636 are obtained with ASCA. Theoretical
models are found unable to reproduce the data in the Fe-L line region. Spectral
data above 1.4 keV indicate that Mg to Si abundance ratio is $\sim 1$ solar.
Assuming that the abundance ratios among $\alpha$-elements are the same with
the solar ratios, spectral fit with increased systematic error in the 0.4--1.6
keV range gives abundances of $\alpha$-elements and Fe to be both $\sim$ 1
solar by taking one solar of Fe to be 3.24$\times 10^{-5}$ by number. These new
abundance results solve discrepancy between stellar and hot-gas metallicity,
but still a low supernova rate is implied. We also detect strong abundance
gradients for both $\alpha$-elements and iron in a similar fashion. The
abundance is $\sim 1$ solar within $4'$, and decreases outerwards down to
$0.2\sim 0.3$ solar at $10'$ from the galaxy center. Dilution due to an
extended hot gas is suggested.",9709009v1
1997-09-22,Discovery of a Large-Scale Abundance Gradient in the Cluster of Galaxies AWM7 with ASCA,"A large-scale gradient in the metal abundance has been detected with ASCA
from an X-ray bright cluster of galaxies AWM7. The metal abundance shows a peak
of 0.5 solar at the center and smoothly declines to <~ 0.2 solar at a radius of
500 kpc. The gas temperature is found to be constant at 3.8 keV. The radial
distribution of iron can be fit with a beta-model with beta ~ 0.8 assuming the
same core radius (115 kpc) as that of the intracluster medium. The metal
distribution in AWM7 suggests that the gas injected from galaxies is not
efficiently mixed in the cluster space and traces the distribution of galaxies.",9709208v1
1997-10-17,The IntraCluster Medium: An Invariant Stellar IMF,"Evidence supporting the hypothesis of an invariant stellar Initial Mass
Function is strong and varied. The intra-cluster medium in rich clusters of
galaxies is one of the few contrary locations where recent interpretations of
the chemical abundances have favoured an IMF that is biased towards massive
stars, compared to the `normal' IMF. This interpretation hinges upon the
neglect of Type Ia supernovae to the ICM enrichment, and a particular choice of
the nucleosynthesis yields of Type II supernovae. We demonstrate here that when
one adopts yields determined empirically from observations of Galactic stars,
rather than the uncertain model yields, a self-consistent picture may be
obtained with an invariant stellar IMF, and about half of the iron in the ICM
being produced by Type Ia supernovae.",9710195v1
1997-11-14,Cygnus X-1: X-ray Emission Mechanism and Geometry,"We summarize recent observations of Cyg X-1 during its 1996 state transition.
The results favor an emission geometry with a central optically thin corona
surrounded by an optically thick, geometrically thin accretion disk. As the
soft state is approached, the inner edge of the disk moves closer to the black
hole, and the corona shrinks, perhaps due to more efficient cooling. Soft
X-rays are from the innermost disk, and inverse-Comptionization by the corona
appears to be responsible for the hard X-ray emission. Both Compton reflection
and an iron emission line have been observed in both states. They are likely to
originate in the inner region of the disk. Also briefly discussed is the
theoretical effort to simultaneously model the observed spectral and temporal
X-ray properties of Cyg X-1.",9711166v1
1997-11-19,Line emission from an accretion disk around black hole: effects of the disk structure,"The observed iron K-alpha fluorescence lines in Seyfert galaxies provide
strong evidence for an accretion disk near a supermassive black hole as a
source of the line emission. Previous studies of line emission have considered
only geometrically thin disks, where the gas moves along geodesics in the
equatorial plane of a black hole. Here we extend this work to include effects
on line profiles from finite disk thickness, radial accretion flow and
turbulence. We adopt the Novikov-Thorne solution, and find that within this
framework, turbulent broadening is the most significant effect. The most
prominent changes in the skewed, double-horned line profiles is a substantial
reduction in the maximum flux at both red and blue peaks. We show that at the
present level of signal-to-noise in X-ray spectra, proper treatment of the
actual structure of the accretion disk can change estimates of the inclination
angle of the disk. Thus these effects will be important for future detailed
modeling of high quality observational data.",9711214v1
1997-11-20,High Energy Break and Reflection Features in the Seyfert Galaxy MCG+8-11-11,"We present the results from ASCA and OSSE simultaneous observations of the
Seyfert 1.5 galaxy MCG+8-11-11 performed in August-September 1995. The ASCA
observations indicate a modest flux increase (20%) in 3 days, possibly
correlated to a softening of the 0.6-9 keV spectrum. The spectrum is well
described by a hard power law (Gamma=1.64) absorbed by a column density
slightly larger than the Galactic value, with an iron line at 6.4 keV of EW=400
eV. The simultaneous OSSE data are characterized by a much softer power law
with photon index Gamma=3.0, strongly suggesting the presence of a spectral
break in the hard X/soft gamma-ray band. A joint fit to OSSE and ASCA data
clearly shows an exponential cut-off at about 300 keV, and strong reflection
component. MCG+8-11-11 features a spectral break in the underlying continuum
unambiguously. This, together with the inferred low compactness of this source,
favours thermal or quasi-thermal electron Comptonization in a structured Corona
as the leading process of high energy radiation production.",9711242v1
1997-11-29,Wide-Band X-Ray Spectra and Images of the Starburst Galaxy M82,"The ASCA results of the starburst galaxy M82 are presented. The X-rays in the
0.5--10 keV band exhibit a thin thermal spectrum with emission lines from
highly ionized magnesium, silicon, and sulfur, as well as a hard tail extending
to higher than 10keV energy. The soft X-rays are spatially extended, while the
hard X-rays show an unresolved point-like structure with possible a long-term
flux variability. The flux ratio of the emission lines and the spatially
extended structure in the low-energy band indicate that at least
two-temperature thin thermal plasmas are present. The abundances of the oxygen,
neon, magnesium, silicon, sulfur, and iron in the thin thermal plasmas are
found to be significantly lower than the cosmic value. Neither type-Ia nor
type-II supernova explosions can reproduce the observed abundance ratio. The
origin of the unresolved hard X-rays is uncertain, but is probably an obscured
low-luminosity AGN.",9712002v1
1997-12-17,BeppoSAX observations of 3C 273,"We present preliminary results of BeppoSAX AO1 observations of 3C 273
performed in January 1997. We also present a close comparison with data
obtained during the satellite SVP, in July 1996. On average, the AO1 flux is
about a factor 2 higher than the flux detected during the SVP, and roughly on
the middle of the historical X-ray flux range. Power law fits with galactic
absorption to all observations yield spectral indices in the range 1.53-1.6,
with the spectrum extending from 0.2 to at least up to 200 keV without any
significant slope change. The broad band spectrum appears basically
featureless, marking a clear difference from the SVP data, where an absorption
feature at low energy and a fluorescence iron emission line are present. The
lack of cold/warm matter signatures in our data may indicate that, at this
""high"" level of luminosity, the featureless continuum produced in a
relativistic jet overwhelms any thermal and/or reprocessing component, while
the two components were at least comparable during the ""low"" state of July
1996.",9712234v1
1997-12-18,1H0419-577: a two-state Seyfert Galaxy?,"The preliminary results of the BeppoSAX observation of the radio-quiet AGN
1H0419-577 are presented. Despite its broad line optical spectrum, the
intermediate X-ray spectrum (i.e. 2--10 keV) is flatter than typically observed
in Seyfert 1s and no iron line is significantly detected. Even more
intriguingly, a 1992 ROSAT pointed observation suggests a dramatic (~ 1) change
in the spectral shape for E < 2 keV. Such behavior is briefly discussed in the
framework of our current understanding of Comptonization scenarios in the
nuclear regions of radio-quiet AGN.",9712248v1
1998-01-27,A Comparison of Cosmic Ray Composition Measurements at the Highest Energies,"In recent years the Fly's Eye and Akeno groups have presented analyses of the
cosmic ray mass composition at energies above 10^17 eV. While the analysis of
the Fly's Eye group points to a likely change in mass composition from heavy to
light at energies above 10^18 eV, the Akeno analysis favours an unchanging
composition. However, the two groups base their conclusions on simulations
using quite different hadronic models. Here we present a comparison of the
experiments using the same hadronic model and find that the agreement between
the experiments is much improved. Under this model, both experiments measure a
composition rich in iron around 10^17 eV which becomes lighter at higher
energies. However, the agreement is not complete, which indicates scope for
improvement of the interaction model, or perhaps the need for a re-examination
of the experimental results.",9801260v2
1998-02-08,Can Stellar Yields Accurately Constrain the Upper Limit to the Initial Mass Function?,"Recent determinations of the upper mass limit to the local initial mass
function (IMF) claim a value of m(upper)=50+/-10 solar masses, based upon
direct comparisons of the observed oxygen and iron abundances in metal-poor
stars with the predicted stellar yields from Type II supernovae (SNe). An
unappreciated uncertainty in these analyses is the input physics intrinsic to
each SNe grid, and its effect upon stellar nucleosynthesis. We demonstrate how
such uncertainties, coupled with the uncertain metal-poor halo star
normalization, while allowing us to set a lower bound to m(upper) of
approximately 40 solar masses, nullifies any attempt at constraining the upper
bound.",9802091v1
1998-02-11,ASCA Measurements of Silicon and Iron Abundances in the Intracluster Medium,"We analyzed the ASCA X-ray data of 40 nearby clusters of galaxies, whose
intracluster-medium temperature distributes in the range of 0.9--10 keV. We
measured the Si and Fe abundances of the intracluster medium, spatially
averaging over each cluster, but excluding the central $\sim 0.15 h_{50}^{-1}$
Mpc region in order to avoid any possible abundance gradients and complex
temperature structures. The Fe abundances of these clusters are 0.2--0.3 solar,
with only weak dependence on the temperature of the intracluster medium, hence
on the cluster richness. In contrast, the Si abundance is observed to increase
from 0.3 to 0.6--0.7 solar from the poorer to richer clusters. These results
suggest that the supernovae of both type-Ia and type-II significantly
contribute to the metal enrichment of the intracluster medium, with the
relative contribution of type-II supernovae increasing towards richer clusters.
We suggest a possibility that a considerable fraction of type-II supernova
products escaped from poorer systems.",9802126v1
1998-02-13,Intracluster Medium Abundances Revisited,"We examine the origin of heavy elements in the intracluster medium (ICM) of
galaxy clusters, concentrating upon the roles played by supernovae (SNe) Types
Ia and II. The most accurately determined elemental abundances, Si and Fe,
imply a mild predominance of Type II SNe as the source of ICM Fe, contributing
approximately 60-80% of its total (and approximately 100% of the
alpha-elements). (Currently) intractable uncertainties in measuring X-ray
alpha-element ICM abundances, the initial mass function (IMF), and stellar
evolution ingredients, make a more precise determination of the Ia:II ICM iron
``ratio'' impossible.",9802172v1
1998-02-26,ASCA spectroscopy of the luminous infrared galaxy NGC6240: X-ray emission from a starburst and a buried active nucleus,"We present an X-ray spectral study of the prototype far-infrared galaxy
NGC6240 from ASCA. The soft X-ray spectrum (below 2 keV) shows clear signatures
of thermal emission well described with a multi-temperature optically-thin
plasma, which probably originates in a powerful starburst. Strong hard X-ray
emission is also detected with ASCA and its spectrum above 3 keV is extremely
flat with a prominent iron K line complex, very similar to that seen in the
Seyfert 2 galaxy NGC1068 but about an order of magnitude more luminous
[L(3-10keV)=1.4E42 erg/s]. The hard X-ray spectrum indicates that only
reflected X-rays of an active galactic nucleus (AGN) buried in a heavy
obscuration [N(H)>2E24 cm-2] are visible. This is evidence for an AGN in
NGC6240 emitting possibly at a quasar luminosity and suggests its significant
contribution to the far-infrared luminosity.",9802336v1
1998-03-31,"IRAS 06562-0337, The Iron Clad Nebula: A New Young Star Cluster","IRAS 06562-0337 has been the recent subject of a classic debate:
proto-planetary nebula or young stellar object? We present the first 2 micron
image of IRAS 06562-0337, which reveals an extended diffuse nebula containing
approximately 70 stars inside a 30 arcsec radius around a bright, possibly
resolved, central object. The derived stellar luminosity function is consistent
with that expected from a single coeval population, and the brightness of the
nebulosity is consistent with the predicted flux of unresolved low-mass stars.
The stars and nebulosity are spatially coincident with strong CO line emission.
We therefore identify IRAS 06562-0337 as a new young star cluster embedded in
its placental molecular cloud. The central object is likely a Herbig Be star, M
approx 20 M_sun, which may be seen in reflection. We present medium resolution,
high S/N, 1997 epoch optical spectra of the central object. Comparison with
previously published spectra shows new evidence for time variable permitted and
forbidden line emission, including SiII, FeII, [FeII], and [OI]. We suggest the
origin is a dynamic stellar wind in the extended, stratified atmosphere of the
massive central star in IRAS 06562-0337.",9803345v1
1998-05-06,Doppler Imaging of Ap Stars,"Doppler imaging, a technique which inverts spectral line profile variations
of an Ap star into a two-dimensional abundance maps, provides new observational
constraints on diffusion mechanism in the presence of a global magnetic field.
A programme is presented here with the aim to obtain abundance distributions of
at least five elements on each star, in order to study how different diffusion
processes act under influence of a stellar magnetic field. The importance of
this multi-element approach is demonstrated, by presenting the abundance maps
of helium, magnesium, silicon, chromium and iron for the magnetic B9pSi star CU
Virginis.",9805065v1
1998-05-15,X-ray spectroscopy of the broad line radio galaxy 3C111,"We present an ASCA observation of the broad line radio galaxy 3C111. The
X-ray spectrum is well described by a model consisting of a
photoelectrically-absorbed power-law form. The inferred absorbing column
density is significantly greater than expected on the basis of 21-cm
measurements of Galactic HI. Whilst this may be due intrinsic absorption from a
circumnuclear torus or highly warped accretion disk, inhomogeneities and
molecular gas within the foreground giant molecular cloud may also be
responsible for some of this excess absorption. We also claim a marginal
detection of a broad iron Ka line which is well explained as being a
fluorescent line originating from the central regions of a
radiatively-efficient accretion disk. This line appears weak in comparison to
those found in (radio-quiet) Seyfert nuclei. We briefly discuss the
implications of this fact.",9805217v1
1998-05-26,The stellar population of the decoupled nucleus in M 31,"The results of a spectroscopic and photometric investigation of the central
region of M 31 are presented. An analysis of absorption-index radial profiles
involving magnesium, calcium, and iron lines has shown that the unresolved
nucleus of M 31 is distinct by its increased metallicity; unexpectedly, among
two nuclei of M 31, it is the faintest one located exactly in the dynamical
center of the galaxy (and dynamically decoupled) which is chemically distinct.
The Balmer absorption line H-beta has been included into the analysis to
disentangle metallicity and age effects; an age difference by a factor 3 is
detected between stellar populations of the nucleus and of the bulge, the
nucleus being younger. The morphological analysis of CCD images has revealed
the presence of a nuclear stellar-gaseous disk with a radius of some 100 pc,
the gas component of which looks non-stationary, well inside the bulge of M 31.",9805318v1
1998-05-29,Quasi-periodic oscillations discovered in the new X-ray pulsar XTE J1858+034,"We report the discovery of low frequency quasi-periodic oscillations centered
at 0.11 Hz in the newly discovered 221 s X-ray pulsar XTE J1858+034. Among
about 30 known transient X-ray pulsars this is the sixth source in which QPOs
have been observed. If the QPOs are produced because of inhomogeneities in the
accretion disk at the magnetospheric boundary, the low frequency of the QPOs
indicate a large magnetosphere for this pulsar. Both the Keplerian frequency
model and the beat frequency model are applicable for production of QPOs in
this source. The QPOs and regular pulsations are found to be stronger at higher
energy which favours the beat frequency model. The magnetic field of the pulsar
is calculated as a function of its distance. The energy spectrum is found to be
very hard, consisting of two components, a cut-off power law and an iron
fluorescence line.",9805366v1
1998-06-03,Heavy obscuration in X-ray weak AGNs,"We present observations in the 0.1-100 keV spectral band of 8 Seyfert 2
galaxies, obtained by means of BeppoSAX. These sources were selected according
to their [OIII] optical emission line flux, to avoid biases against obscuration
on the pc scale. All sources were detected. All of them are weak X-ray
emitters, and most of them are characterized by prominent iron lines at 6.4-7
keV (EW > 500 eV) and by a flat continuum, indicative of heavy obscuration
along our line of sight (N_H > 10^25 cm^-2 in most cases). These results 1)
provide further evidence in favor of the unified scenario, and 2) indicate that
the average obscuration of type 2 AGNs is very likely much higher than deduced
by former X-ray surveys. These findings have important implications for the
synthesis of the X-ray background.",9806055v2
1998-06-10,Line Emission from an Accretion Disk around a Black hole: Effects of Disk Structure,"The observed iron K-alpha fluorescence lines in Seyfert-1 galaxies provide
strong evidence for an accretion disk near a supermassive black hole as a
source of the line emission. These lines serve as powerful probes for examining
the structure of inner regions of accretion disks. Previous studies of line
emission have considered geometrically thin disks only, where the gas moves
along geodesics in the equatorial plane of a black hole. Here we extend this
work to consider effects on line profiles from finite disk thickness, radial
accretion flow and turbulence. We adopt the Novikov and Thorne (1973) solution,
and find that within this framework, turbulent broadening is the dominant new
effect. The most prominent change in the skewed, double-horned line profiles is
a substantial reduction in the maximum flux at both red and blue peaks. The
effect is most pronounced when the inclination angle is large, and when the
accretion rate is high. Thus, the effects discussed here may be important for
future detailed modeling of high quality observational data.",9806134v1
1998-06-17,The hidden X-ray Seyfert nucleus in 3C 273: BeppoSAX results,"We present the results of BeppoSAX AO1 Core Program observations of 3C~273
performed in Jan. 1997 and compare them in detail with data obtained during the
satellite Science Verification Phase (SVP), in Jul. 1996. Though a power law is
an acceptable representation of the data in the whole 0.1-200 keV range, there
is indication of a steepening of the spectrum as the energy increases. Our data
mark a difference with respect to the SVP data, where a steeper power law below
0.5 keV, an absorption feature at 0.6 keV, and a more prominent fluorescence
iron line have been found. The weakening of cold/warm matter signatures in our
data with respect to the SVP ones may indicate that, at higher luminosities,
the featureless continuum produced in a relativistic jet overwhelms any thermal
and/or reprocessed radiation, while the two components were almost comparable
during the lower state of Jul. 1996. We conclude that this radio--loud source
shows evidence not only for thermal disk--like emission, but also substantial
reprocessing of X-rays onto cold matter.",9806229v2
1998-06-22,A New Dual-Component Photoionization Model for the Narrow Emission-Line Regions in Active Galactic Nuclei,"Having found that type 1 Seyfert nuclei have excess [FeVII]6087 emission with
respect to type 2s, Murayama & Taniguchi have proposed that the high-ionization
nuclear emission-line region (HINER) traced by the [FeVII]6087 emission resides
in the inner wall of dusty tori. The covering factor of the torus is usually
large (e.g., ~ 0.9). Further, electron density in the tori (e.g., ~ 10^7-10^8
cm-3) is considered to be higher significantly than that (e.g., ~ 10^3-10^4
cm^-3) in the narrow-line region (NLR). Therefore it is expected that the torus
emission contributes to the majority of the higher-ionization emission lines.
Taking this HINER component into account, we have constructed new
dual-component (i.e., a typical NLR with a HINER torus) photoionization models.
Comparison of our model with the observations show that that if the torus
emission contributes ~ 10 % of the NLR emission, our dual-component model can
explain the observed high [FeVII]6087/[OIII]5007 intensity ratios of the
Seyfert 1s without invoking any unusual assumptions (e.g., the overabundance of
iron).",9806287v1
1998-07-02,Contribution of Type Ia and Type II Supernovae for Intra-Cluster Medium Enrichment,"The origin of the chemical composition of the intracluster medium (ICM) is
discussed in this paper. In particular, the contribution from Type Ia
supernovae (SNe Ia) to the ICM enrichment is shown to exist by adopting the
fitting formulas which have been used in the analysis of the solar system
abundances. Our analysis means that we can use the frequency of SNe Ia relative
to SNe II as the better measure than $M_{Fe, SN Ia}/M_{Fe, total}$ for
estimating the contribution of SNe Ia. Moreover, the chemical compositions of
ICMs are shown to be similar to that of the solar system abundances. We can
also reproduce the sulfur/iron abundance ratio within a factor of 2, which
means that the abundance problem of sulfur needs not to be emphasized too
strongly. We need more precise observations to conclude whether ICMs really
suffer the shortage problem of sulfur or not.",9807022v1
1998-07-21,The swan song: the disappearance of the nucleus of NGC 4051 and the echo of its past glory,"BeppoSAX observed the low-luminous Seyfert 1 Galaxy NGC4051 in a ultra-dim
X-ray state. The 2-10 keV flux (1.26 x 10^{-12} erg/cm^2/s) was about 20 times
fainter than its historical average value, and remained steady along the whole
observation (~2.3 days). The observed flat spectrum (\Gamma ~ 0.8) and intense
iron line (EW ~600 eV) are best explained assuming that the active nucleus has
switched off, leaving only a residual reflection component visible.",9807213v2
1998-08-14,Redshift determination in the X-ray band of gamma-ray bursts,"If gamma-ray bursts originate in dense stellar forming regions, the
interstellar material can imprint detectable absorption features on the
observed X-ray spectrum. Such features can be detected by existing and planned
X-ray satellites, as long as the X-ray afterglow is observed after a few
minutes from the burst. If the column density of the interstellar material
exceeds ~10^{23} cm^{-2} there exists the possibility to detect the K_alpha
fluorescent iron line, which should be visible for more than one year, long
after the X-ray afterglow continuum has faded away. Detection of these X-ray
features will make possible the determination of the redshift of gamma-ray
bursts even when their optical afterglow is severely dimmed by extinction.",9808156v1
1998-09-04,Age Dating of a High-Redshift QSO B1422+231 at Z=3.62 and its Cosmological Implications,"The observed Fe II(UV+optical)/Mg II lambda lambda 2796,2804 flux ratio from
a gravitationally lensed quasar B1422+231 at z=3.62 is interpreted in terms of
detailed modeling of photoionization and chemical enrichment in the broad-line
region (BLR) of the host galaxy. The delayed iron enrichment by Type Ia
supernovae is used as a cosmic clock. Our standard model, which matches the Fe
II/Mg II ratio, requires the age of 1.5 Gyr for B1422+231 with a lower bound of
1.3 Gyr, which exceeds the expansion age of the Einstein-de Sitter Omega_0=1
universe at a redshift of 3.62 for any value of the Hubble constant in the
currently accepted range, H_0=60-80 km,s^{-1},Mpc^{-1}. This problem of an age
discrepancy at z=3.62 can be unraveled in a low-density Omega_0<0.2 universe,
either with or without a cosmological constant, depending on the allowable
redshift range of galaxy formation. However, whether the cosmological constant
is a required option in modern cosmology awaits a thorough understanding of
line transfer processes in the BLRs.",9809047v1
1998-09-08,ASCA Observations of the Seyfert 2 Galaxy NGC 7582: An Obscured and Scattered View of the Hidden Nucleus,"ASCA observations of the Seyfert 2 galaxy NGC 7582 revealed it was highly
variable on the timescale of $\sim2\times10^4$ s in the hard X-ray (2-10 keV)
band, while the soft X-ray (0.5-2 keV) flux remained constant during the
observations.
  The spectral analysis suggests that this object is seen through an obscuring
torus with the thickness of N$_{\rm H}\sim1.0\times 10^{23}\rm cm^{-2}$. The
hard X-ray is an absorbed direct continuum from a hidden Seyfert 1 nucleus; the
soft X-ray is dominated by the scattered central continuum from an extended
spatial region. Thus we have an obscured/absorbed and a scattered view of this
source as expected from the unification model for Seyfert galaxies.
  More interestingly, the inferred X-ray column was observed to increase by
$\sim4\times10^{22} \rm cm^{-2}$ from 1994 to 1996, suggesting a ``patchy''
torus structure, namely the torus might be composed of many individual clouds.
The observed iron line feature near 6.4 keV with the equivalent width of 170 eV
is also consistent with the picture of the transmission of nuclear X-ray
continuum through a non-uniform torus.",9809086v1
1998-09-14,Detection of a cyclotron line and its second harmonic in 4U1907+09,"We report the detection of a cyclotron absorption line and its second
harmonic in the average spectrum of the high mass X-ray binary 4U1907+09
observed by the BeppoSAX satellite on 1997 September 27 and 28. The broad band
spectral capability of BeppoSAX allowed a good determination of the continuum
against which the two absorption features are evident at ~ 19 and ~ 39 keV.
Correcting for the gravitational redshift of a ~ 1.4 solar mass neutron star,
the inferred surface magnetic field strength is B = 2.1 10E12 G that is typical
for this kind of systems. We also detected an iron emission line at ~ 6.4 keV,
with an equivalent width of ~ 60 eV.",9809167v1
1998-09-20,Emission-Line Probes of Circumnuclear Dust in AGNs,"Emission lines that trace elements subject to strong depletion onto grains
provide a means for probing the dust content of AGNs. Examples include infrared
[FeII] and optical [CaII] lines. The excitation mechanisms underlying the
[FeII] lines remain controversial, resulting in related disagreement over the
gas-phase abundance of iron in Seyfert narrow-line regions. In this
contribution we emphasize the utility of the [CaII] lines as a consistency test
for claims of grain destruction affecting the [FeII] lines. A search for [CaII]
emission in NGC 1068 at a location of strongest [FeII] emission along the radio
jet yields a strong upper limit, but no detection. This result suggests that
grains survive largely intact in a region that otherwise shows strong evidence
of shock processing.",9809247v1
1998-10-05,Core Collapse Supernovae --- Theory between Achievements and New Challenges,"Multi-dimensional hydrodynamic simulations of the post-bounce evolution of
collapsed stellar iron cores have demonstrated that convective overturn between
the stalled shock and the neutrinosphere can have an important effect on the
neutrino-driven explosion mechanism. Whether a model yields a successful
explosion or not, however, still depends on the power of neutrino energy
deposition behind the stalled shock. The neutrino interaction with the stellar
gas in the ``hot bubble'' also determines the duration of the shock stagnation
phase, the explosion energy, and the composition of the neutrino-heated
supernova ejecta. More accurate models require a more precise calculation of
the neutrino luminosities and spectra and of the angular distributions of the
neutrinos in the heating region. Therefore it is necessary to improve the
numerical treatment of the neutrino transport, to develop a better
understanding of the neutrino opacities of the dense nuclear medium, and to
take into account convective processes {\it inside} the newly formed neutron
star.",9810058v1
1998-10-22,On the possibility that rotation causes latitudinal abundance variations in stars,"The effect of rotation of a star on the distribution of chemical species in
radiative zones is discussed. Gravity darkening generates a large radiative
force on heavy element ions which is directed toward the equatorial plane.
Taking iron as an example, it is shown that this force may produce drift
velocities similar to, and larger than, the typical velocities of bulk motion
due to meridional circulation. This potentially allows large chemical abundance
inhomogeneities to build up across a meridian over the lifetime of the star --
particularly near the equatorial plane. This enhancement may be significantly
reduced if the mass loss of the star is strongly metallicity dependent, in
which case the mass-loss rate may be enhanced in the equatorial plane.",9810360v1
1998-10-22,Calibrator Design for the COBE Far Infrared Absolute Spectrophotometer (FIRAS),"The photometric errors of the external calibrator for the FIRAS instrument on
the COBE are smaller than the measurement errors on the cosmic microwave
background (CMBR) spectrum (typically 0.02 MJy/sr, 1 sigma), and smaller than
0.01% of the peak brightness of the CMBR. The calibrator is a re-entrant cone,
shaped like a trumpet mute, made of Eccosorb iron-loaded epoxy. It fills the
entire beam of the instrument and is the source of its accuracy. Its known
errors are caused by reflections, temperature gradients, and leakage through
the material and around the edge. Estimates and limits are given for all known
error sources. Improvements in understanding the temperature measurements of
the calibrator allow an improved CMBR temperature determination of 2.725 +/-
0.002 K.",9810373v1
1998-11-03,"Microwave Emission by Dust: Mechanisms, Properties and Prospects for ISM Studies","I review my work with Bruce Draine on dust emissivity at microwave
frequencies (3 cm - 3 mm). This emissivity explains the recently detected
""anomalous"" component of the galactic foreground emission. Both small (a<0.001
micron) and large grains contribute to this emission. Small grains have
electric dipole moments and emit while they rotate; the microwave emission of
large grains is mostly due to magneto-dipole radiation. Most efficient
magneto-dipole emitters are strongly magnetic, e.g. ferrimagnetic or
ferromagnetic, materials. The relative role of the two mechanisms can be
established through observations of microwave emissivity from dark clouds. New
microwave window is a window of opportunity for interstellar studies. Magnetic
fields inside dark clouds may be successfully studied via microwave
polarization. Microwave emissivity constrains the abundance of strongly
magnetic materials. For instance, the available data at 90 GHz indicate that
not more than 5% of interstellar Fe is in the form of metallic iron grains or
inclusions (e.g., in ``GEMS''). Future missions, e.g. MAP and PLANCK, will
bring a wealth of microwave data that can be successfully used to study ISM.
Such a study would be appreciated by cosmologists who franticly try to remove
all foregrounds from their data.",9811043v1
1998-11-16,BeppoSAX confirms extreme relativistic effects in the X-ray spectrum of MCG-6-30-15,"We report the first simultaneous measure of the X-ray broadband (0.1--200
keV) continuum and of the iron K-alpha fluorescent line profile in the Seyfert
1 galaxy MCG-6-30-15. Our data confirms the ASCA detection of a skewed and
redshifted line profile (Tanaka et al. 1995). The most straightforward
explanation is that the line photons are emitted in the innermost regions of a
X-ray illuminated relativistic disk. The line Equivalent Width (~200 eV) is
perfectly consistent with the expected value for solar abundances, given the
observed amount of Compton reflection. We report also the discovery of a
cut-off in the nuclear primary emission at the energy of ~160 keV.",9811246v1
1998-11-25,Enrichment of the Intracluster Medium,"The relevance of galaxies of different luminosity and mass for the chemical
enrichment of the intracluster medium (ICM) is analysed. For this purpose, I
adopt the composite luminosity function of cluster galaxies from Trentham
(1998), which exhibits a significant rise at the very faint end. The model -
adopting a universal Salpeter IMF - is calibrated on reproducing the
M_Fe/L_tot, M_Fe/M_*, and alpha/Fe ratios observed in clusters. Although the
contribution to total luminosity and ICM metals peaks around L* galaxies (M*
approx -20), faint objects with M_B>-18 still provide at least 30 per cent of
the metals present in the ICM. In consistency with the solar alpha/Fe ratios
determined by {ASCA}, the model predicts that 60 per cent of the ICM iron comes
from Type Ia supernovae. The predicted slope of the relation between
intracluster gas mass and cluster luminosity emerges shallower than the
observed one, indicating that the fraction of primordial gas increases with
cluster richness.",9811409v1
1998-12-16,ASCA Observations of GRO J1744-28,"We report the ASCA results of the bursting X-ray pulsar \gro, which was
observed in February 1996 and March 1997. The source flux in the 2--10 keV band
was $2.0\times10^{-8}$ erg/sec/cm$^2$ in 1996 and $5.0\times10^{-9}$
erg/sec/cm$^2$ in 1997. We detected 12 and 17 Type II bursts during the two
observations with mean bursting intervals of about 27 min and 37 min. Each
burst is followed by an intensity dip with the depleted flux depending on the
burst fluence. The energy spectra are approximated by an absorbed power law
with additional structure around 6--7 keV\@. Constant absorption column,
$(5-6)\times10^{22}$ cm$^{-2}$, independent of the observation dates and
emission phases (persistent, burst and dip) is interpreted as an interstellar
absorption. The source may be actually located near the Galactic center, at a
distance of 8.5 kpc. The structure in the energy spectrum at 6--7 keV is most
probably due to iron and maybe reproduced by a disk line model with additional
broadening mechanism.",9812298v1
1999-01-11,RXTE Observations of the X-ray Pulsar XTE J1855-026 - a Possible New Supergiant System,"A new X-ray source, XTE J1855-026, was discovered during RXTE scans along the
galactic plane. The source shows pulsations at a period of 361 s and also
modulation at a period of 6.1 days which we interpret as the orbital period of
the system. The X-ray spectrum above ~3 keV can be fitted with an absorbed
power law model with a high-energy cut-off, and an iron emission line at
approximately 6.4 keV. We interpret these results as indicating that XTE
J1855-026 is likely to consist of a neutron star accreting from the wind of an
O or B supergiant primary. A less likely interpretation is that XTE J1855-026
is instead a Be/neutron star binary, in which case it would have the shortest
known orbital period for such a system.",9901125v1
1999-02-15,Role of disk galaxies in the chemical enrichment of the intracluster medium,"Elliptical galaxies are often assumed to be the primary source of heavy
elements in the intracluster medium (ICM), with the contribution of other
morphological types being negligible. In this paper we argue that a role of
spiral galaxies in the chemical evolution of the ICM is also important. This
statement rests upon our recent calculations of the heavy element loss from a
disk galaxy through the hot steady-state galactic wind and dust grains
expulsion by stellar radiation pressure. We show that a typical disk galaxy is
nearly as effective in enriching the ICM as an elliptical galaxy of the same
mass. Having estimated the oxygen and iron loss from a single galaxy, we
integrate them over the galactic mass spectrum. We show that the ""effective""
loss (per unit luminosity) from spiral galaxies is comparable to the loss from
ellipticals. The dominant role of early-type galaxies in rich clusters is
caused by that they outnumber spirals.",9902202v1
1999-02-23,X-ray reflection spectra from ionized slabs,"X-ray reflection spectra are an important component in the X-ray spectra of
many active galactic nuclei and Galactic black hole candidates. It is likely
that reflection takes place from highly ionized surfaces of the accretion disc
in some cases. This can lead to strong Comptonization of the emergent iron, and
other, absorption and emission features. We present such reflection spectra
here, computed in a self-consistent manner with the method described by Ross
and Fabian. In particular we emphasise the range where the ionization parameter
(the flux to density ratio) \xi is around and above 10^4. Such spectra may be
relevant to the observed spectral features found in black hole candidates such
as Cygnus X-1 in the low/hard state.",9902325v1
1999-02-25,Microwave Emission from Galactic Dust Grains,"Observations of the cosmic microwave background have revealed a component of
10-60 GHz emission from the Galaxy which correlates with 100-140um emission
from interstellar dust but has an intensity much greater than expected for the
low-frequency tail of the ""electric dipole vibrational"" emission peaking at
\~130um. This ""anomalous emission"" is more than can be accounted for by
dust-correlated free-free emission. The anomalous emission could be due in part
to magnetic dipole emission from thermal fluctuations of the magnetization
within interstellar dust grains, but only if a substantial fraction of the Fe
in interstellar dust resides in magnetic materials such as metallic iron or
magnetite. The observed anomalous emission is probably due primarily to
electric dipole radiation from spinning ultrasmall interstellar dust grains.
This rotational emission is expected to be partially polarized. From the
standpoint of minimizing confusion with non-CBR foregrounds, 60-120 GHz appears
to be the optimal frequency window.",9902356v1
1999-03-10,Heavy nuclei at the end of the cosmic ray spectrum?,"We provide an account of the possible acceleration of iron nuclei up to
energies $\sim300$ EeV in the nearby, metally-rich starburst galaxy NGC 253. It
is suggested that particles can escape from the nuclear region with energies of
$\sim10^{15}$ eV and then could be reaccelerated at the terminal shock of the
galactic superwind generated by the starburst, avoiding in this way the
photodisintegration expected if the nuclei were accelerated in the central
region of high photon density. We have also made estimates of the expected
arrival spectrum, which displays a strong dependency with the energy cutoff at
the source.",9903145v3
1999-03-29,Striking Photospheric Abundance Anomalies in Blue Horizontal-Branch Stars in Globular Cluster M13,"High-resolution optical spectra of thirteen blue horizontal-branch (BHB)
stars in the globular cluster M13 show enormous deviations in element
abundances from the expected cluster metallicity. In the hotter stars (T_eff >
12000 K), helium is depleted by factors of 10 to 100 below solar, while iron is
enhanced to three times the solar abundance, two orders of magnitude above the
canonical metallicity [Fe/H] ~= -1.5 dex for this globular cluster. Nitrogen,
phosphorus, and chromium exhibit even more pronounced enhancements, and other
metals are also mildly overabundant, with the exception of magnesium, which
stays very near the expected cluster metallicity. These photospheric anomalies
are most likely due to diffusion --- gravitational settling of helium, and
radiative levitation of the other elements --- in the stable radiative
atmospheres of these hot stars. The effects of these mechanisms may have some
impact on the photometric morphology of the cluster's horizontal branch and on
estimates of its age and distance.",9903437v1
1999-04-13,An RXTE Observation of NGC 6300: a new bright Compton reflection Dominated Seyfert 2 Galaxy,"Scanning and pointed RXTE observations of the nearby Seyfert 2 galaxy NGC
6300 reveal that it is a source of hard X-ray continuum and large equivalent
width Fe K$\alpha$ emission. These properties are characteristic of
Compton-reflection dominated Seyfert 2 galaxies. The continuum can be modeled
as Compton-reflection; subsolar iron abundance is required and a high
inclination preferred. However, the poor energy resolution of RXTE means that
this description is not unique, and the continuum can also be modeled using a
``dual absorber'', i.e. a sum of absorbed power laws. Observations with higher
energy resolution detectors will cleanly discriminate between these two models.
Optical observations support the Compton-reflection dominated interpretation as
$L_X/L_{[OIII]}$ is low. NGC 6300 is notable because with $F_{2-10}\approx 6.4
\times 10^{-12} ergs cm^{-2} s^{-1}$, it is the second brightest such object
known.",9904155v1
1999-04-14,Comparison between predicted and empirical DV(Bump -HB) in Galactic Globular Clusters,"We present observational estimates of DV(Bump-HB) in a sample of 28 Galactic
Globular Clusters (GGCs) observed by HST. The photometric accuracy and the
sizable number of stars measured in each cluster allowed us to single out the
RGB Bump both in metal-poor and in metal-rich GGCs. Empirical values are
compared with homogeneous theoretical predictions which account for both H and
He burning phases over a wide range of metal abundances (0.0001 < Z < 0.02). We
found that, within current observational uncertainties on both iron and
$\alpha$-element abundances, theory and observations are in very good
agreement, provided that the metallicity scale by Carretta & Gratton (1997) as
extended by Cohen et al. (1999) is adopted. Interesting enough, we also found
that both theoretical and observed values show a change in the slope of the
DV(Bump-HB)-[M/H] relation toward higher metal contents.",9904183v1
1999-04-26,A BeppoSAX observation of the massive X-ray binary 4U1700-37,"A 0.5-200 keV BeppoSAX spectrum of the non-pulsating high-mass X-ray binary
4U1700-37 is presented. The spectrum is well characterized by the standard
accreting pulsar model of an absorbed power-law with a photon index of 1.07
+0.02 -0.03, sharply modified by an exponential cutoff above 5.9 +/- 0.2 keV.
The e-folding energy of the cutoff is 23.9 +/-0.5 keV. A soft bremsstrahlung
component with a temperature of 0.2 +/- 0.1 keV is also required, together with
a narrow iron line at 6.5 keV. Both continuum components are absorbed by a
column of (5.1 +/- 0.2) x 10E22 atom/cm2. There is some evidence for the
presence of a broad cyclotron absorption feature at ~37 keV, although we cannot
exclude the possibility that this is due to an incorrect modeling of the
continuum, or instrumental effects. The hypothesis that the compact object is a
neutron star rather than a black hole seems most likely.",9904349v1
1999-05-05,Gamma Doradus Stars: Defining a New Class of Pulsating Variables,"In this paper we describe a new class of pulsating stars, the prototype of
which is the bright, early, F-type dwarf, Gamma Doradus. These stars typically
have between 1 and 5 periods ranging from 0.4 to 3 days with photometric
amplitudes up to 0.1 in Johnson V. The mechanism for these observed variations
is high-order, low-degree, non-radial, gravity-mode pulsation. Gamma Doradus
stars exhibit variability on a time scale that is an order of magnitude slower
than Delta Scuti stars. They may offer additional insight into stellar physics
when they are better understood (e.g., they may represent the cool portion of
an ""iron opacity instability strip"" currently formed by the Beta Cephei stars,
the SPB stars, and the subdwarf B stars; they may also offer insight into the
presence of g-modes in solar-like stars).",9905042v1
1999-05-20,The rp Process Ashes from Stable Nuclear Burning on an Accreting Neutron Star,"We calculate the nucleosynthesis during stable nuclear burning on an
accreting neutron star. This is appropriate for weakly magnetic neutron stars
accreting at near-Eddington rates in low mass X-ray binaries, and for most
accreting X-ray pulsars. We show that the nuclear burning proceeds via the
rapid proton capture process (rp process), and makes nuclei far beyond the iron
group. The final mixture of nuclei consists of elements with a range of masses
between approximately A=60 and A=100. The average nuclear mass of the ashes is
set by the extent of helium burning via (alpha,p) reactions, and depends on the
local accretion rate.
  Our results imply that the crust of these accreting neutron stars is made
from a complex mixture of heavy nuclei, with important implications for its
thermal, electrical and structural properties. A crustal lattice as impure as
our results suggest will have a conductivity set mostly by impurity scattering,
allowing more rapid Ohmic diffusion of magnetic fields than previously
estimated.",9905274v1
1999-05-26,X-ray and radio observations of RX J1826.2-1450/LS 5039,"RX J1826.2-1450/LS 5039 has been recently proposed to be a radio emitting
high mass X-ray binary. In this paper, we present an analysis of its X-ray
timing and spectroscopic properties using different instruments on board the
RXTE satellite. The timing analysis indicates the absence of pulsed or periodic
emission on time scales of 0.02-2000 s and 2-200 d, respectively. The source
spectrum is well represented by a power-law model, plus a Gaussian component
describing a strong iron line at 6.6 keV. Significant emission is seen up to 30
keV, and no exponential cut-off at high energy is required. We also study the
radio properties of the system according to the GBI-NASA Monitoring Program. RX
J1826.2-1450/LS 5039 continues to display moderate radio variability with a
clearly non-thermal spectral index. No strong radio outbursts have been
detected after several months.",9905344v1
1999-06-09,A Method of Mass Measurement in Black Hole Binaries Using Timing and High Resolution X-ray Spectroscopy,"In X-ray binaries, several percent of the compact object luminosity is
intercepted by the surface of the normal companion and re-radiated through
Compton reflection and the K-fluorescence. This reflected emission follows the
variability of the compact object with a delay approximately equal to the
orbital radius divided by the speed of light. This provides the possibility of
measuring the orbital radius and thus substantially refining the compact object
mass determination compared to using optical data alone. We demonstrate that it
may be feasible to measure the time delay between the direct and reflected
emission using cross-correlation of the light curves observed near the Kalpha
line and above the K-edge of neutral iron. In the case of Cyg X-1, the time
delay measurement is feasible with a 300--1000 ksec observation by a telescope
with a 1000 cm^2 effective area near 6.4 keV and with a ~5eV energy resolution.
With longer exposures, it may be possible to obtain mass constraints even if an
X-ray source in the binary system lacks an optical counterpart.",9906170v1
1999-07-08,An Ultraviolet Fe II Image of SN 1885 in M31,"Ultraviolet imaging of the remnant of Supernova 1885 in M31 with the Hubble
Space Telescope using the F255W filter on the WFPC2 reveals a dark spot of Fe
II absorption at the remnant's known position in the bulge of M31. The diameter
of the absorbing spot is 0""55 +- 0""15, slightly smaller than, but consistent
with, the 0""70 +- 0""05 diameter measured in the higher quality WFPC2 Ca II
absorption image previously reported by us. The measured ratio of flux inside
to outside SNR 1885 in the Fe II image is 0.24 +- 0.17, consistent with the
ratio 0.33 +- 0.04 expected on the basis of a model fit to the previously
obtained near-UV FOS spectrum. The observed depth of Fe II absorption suggests
that Fe II is fully saturated, with an iron mass in the range M_Fe = 0.1-1.0
Msun. Besides Fe, ion species Mg I, Mg II, and Mn I probably make some
contribution to the absorption from the SN 1885 remnant in the F255W image.",9907102v1
1999-07-14,X-ray dependencies on luminosity in AGN,"Several X-ray properties of active galactic nuclei depend, or appear to
depend, on their luminosity. It has long been suggested that alpha o-x, the
X-ray ``loudness'' decreases with luminosity. There never has been a
satisfactory explanation of this observational claim, and the statistical
soundness of the result has been disputed. The earliest systematic studies of
the X-ray variability of AGN showed that these properties also depend on
luminosity. In particular, the normalization of the power spectrum, or
alternatively the the variability amplitude, are anti-correlated with
luminosity. Most recently, tentative evidence from Ginga for an X-ray Baldwin
effect - a decrease in the iron K-alpha equivalent width with luminosity - has
been confirmed and extended by ASCA. The new data show that the reduction in
strength is accompanied by changes in profile. These results will be described
and their interpretation discussed.",9907192v1
1999-07-15,Stroemgren photometry of globular clusters: M55 & M22,"We present Stroemgren CCD photometry for the two galactic globular clusters
M55 (NGC 6809) and M22 (NGC 6656). We find average Stroemgren metallicities of
-1.71 dex for M55 and -1.62 dex for M22. The determination of metal abundances
in cluster giants with the Stroemgren m1 index in comparison with spectroscopic
data from Briley et al. (1993) and Norris & Freeman (1982, 1983) shows that M55
and M22 have different distributions of cyanogen strengths. In M55, no CN
abundance variations are visible among the giant-branch stars. In striking
contrast, a large dispersion of cyanogen strengths is seen in M22. For M22 we
find patchily distributed variations in the foreground reddening of
E(B-V)=0.07, which explain the colour dispersion among the giant-branch stars.
There is no evidence for a spread in iron within M22 since the variations in m1
are dominated by the large range in CN abundances, as already found by
Anthony-Twarog et al. (1995). The difference between M55 and M22 may resemble
the difference in integral CN band strength between M31 globular clusters and
the galactic system. The colour-magnitude diagram of M55 shows the presence of
a population of 56 blue-straggler stars that are more centrally concentrated
than the red giant-branch stars.",9907200v1
1999-07-15,Fitting the spectrum of the X-ray background: the effects of high metallicity absorption,"Recent work by Risaliti et al.(1999) suggests that more than half of all
Seyfert 2 galaxies in the local universe are Compton-thick (N_H > 10^24 cm^-2).
This has implications for AGN synthesis models for the X-ray background (XRB),
the flexibility of which for the inclusion of large numbers of high-z type 2
sources we examine here. We highlight the importance of Compton down-scattering
in determining the individual source spectra and the fit to the XRB spectrum,
and demonstrate how parameter space opens up considerably if a super-solar iron
abundance is assumed for the absorbing material. This is illustrated with a
model which satisfies the present constraints, but which predicts substantial
numbers of type 2 source at the faint flux levels soon to be probed for the
first time by the Chandra and XMM missions. We demonstrate also how a strong
negative K-correction facilitates the detection of sources with 10^~24 < N_H <
10^25 cm^-2 out to the highest redshifts at which they could plausibly exist.",9907204v1
1999-07-27,Testing Narrow-line Seyfert 1 scenarios with photoionization models,"Narrow Line Seyfert 1 (NLSy1) galaxies have recently received a lot of
attention due to their unusual optical--X-ray properties which are not yet well
understood. Photoionization models of the circum-nuclear emission/absorption
regions allow to investigate scenarios to explain the main characteristics of
NLSy1s, i.e., (i) extremely steep X-ray spectra within the ROSAT energy range,
(ii) narrow Balmer lines and (iii) weak forbidden lines except for some
relatively strong high-ionization iron lines. Here, we focus on (iii). In
particular, we study the influence of different EUV - soft-X-ray spectral
shapes (a giant soft excess, a steep X-ray powerlaw, presence of a warm
absorber) and NLR cloud properties on the predicted optical emission-line
ratios. The calculations were carried out with Ferland's code Cloudy.",9907373v1
1999-08-06,Iron K-alpha line profiles driven by non-axisymmetric illumination,"Previous calculations of Fe K-alpha line profiles are based on axisymmetric
emissivity laws. In this paper, we show line profiles driven by non-axial
symmetric illumination which results from an off-axis X-ray point source. We
find that source location and motion have significant effects on the red wing
and blue horn of the line profiles. The disk region under the source will
receive more flux, which is the most important factor to affect the line
profiles. We suggest that at least part of the variation in Fe K-alpha line
profiles is caused by the motion of X-ray sources. Future observations of Fe
K-alpha line profiles will provide more information about the distribution and
motion of the X-ray sources around black holes, and hence the underlying
physics.",9908079v1
1999-08-24,GRB: A Signature of Phase Transition to QGP?,"It is suggested that the inner energetic engine of Gamma ray burst (GRB) may
be the result of the transition of normal hadron to quark-gluon plasma (QGP) in
rapidly-rotating and spin-down newborn neutron star. When such a nascent
neutron star slows down through dipole electromagnetic and quadruple
gravitational radiation, the increasing center density may reach the QCD
transition density, i.e., 5-10 nuclear density. Such kind of energy release
from the phase transition would be responsible for GRB and its possible beaming
effect. The relative dense gaseous environment of GRB location and the iron
line observed in the X-ray afterglow support this idea. Some predictions in
this model are given. keywords: Gamma-ray Bursts, Supernova, Quark-gluon plasma",9908262v1
1999-09-27,"Blue Horizontal--Branch Stars: The ""Jump"" in Stromgren u, Low Gravities, and Radiative Levitation of Metals","We study the ``jump'' in the blue horizontal--branch (BHB) distribution first
detected by Grundahl et al. (1998) in the Galactic globular cluster (GC) M13.
On the basis of Stromgren photometry for a sample of fourteen GC's we show
that: 1) The jump is best characterized as a systematic shift, on a (u, u-y)
color-magnitude diagram, from canonical zero-age HB (ZAHB) models, in the sense
that the stars appear brighter and/or hotter than the models; 2) the jump is a
ubiquitous phenomenon, ocurring over the temperature range 11,500 < Teff <
20,000K; 3) An analogous feature is present in (log g, log Teff) diagrams --
indicating a common physical origin for the two phenomena; 4) The physical
mechanism responsible for the jump phenomenon is most likely radiative
levitation of iron and other",9909448v1
1999-09-30,NLTE Model Atmospheres for Central Stars of Planetary Nebulae,"Present observational techniques provide stellar spectra with high resolution
at a high signal-to-noise ratio over the complete wavelength range -- from the
far infrared to the X-ray.
  NLTE effects are particularly important for hot stars, hence the use of
reliable NLTE stellar model atmosphere fluxes is required for an adequate
spectral analysis.
  State-of-the-art NLTE model atmospheres include the metal-line blanketing of
millions of lines of all elements from hydrogen up to the iron-group elements
and thus permit precise analyses of extremely hot compact stars, e.g. central
stars of planetary nebulae, PG 1159 stars, white dwarfs, and neutron stars.
Their careful spectroscopic study is of great interest in several branches of
modern astrophysics, e.g. stellar and galactic evolution, and interstellar
matter.",9909507v1
1999-10-04,X-ray spectral components from a broad band BeppoSAX observation of the Seyfert galaxy IC 4329A,"From the spectral analysis of a broadband (0.1-200 keV) BeppoSAX observation
of the Seyfert 1 galaxy IC 4329A, the main results obtained are: a) the amount
of reflection, together with the intensity of the iron K line, indicate a
geometry with a solid angle substantially less than 2pi; b) the power law is
affected by a cut off with e-folding energy about 270 keV, the fourth
individual object so far where this property has been firmly detected; c) two
absorption features at about 0.7 and 1 keV are found, the first corresponding
to a blend of O vi and O vii, the other to a combination of FeL and NeK edges.
Compared to an earlier ASCA observation, when the source was 30% fainter, the
values of both the relative amount of reflection and the warm absorber
ionization degree are significantly lower: the comparison is suggestive of
sizeable delay effects in this object, due to geometrical factors in the
reflection, and to relaxation to equilibrium states in the ionization of the
absorber.",9910054v1
1999-10-14,The nature of the hard X-ray power-law tail in M87,"Spatially-resolved spectroscopy of the elliptical galaxy M87 with the MECS
instrument on board BeppoSAX demonstrates that the hard X-ray power-law tail,
originally discovered by ASCA (Matsumoto et al 1996; Allen et al. 1999),
originates in the innermost 2'. Our results are consistent with it being
produced in an Accretion Dominated Flow, although a substantial jet
contribution cannot be ruled out. An origin from a Seyfert-like nucleus is
disfavored by our data. As a by-product of this result, we present an analysis
of the thermal emission coming from the center of the Virgo cluster, which
exhibits a strong positive radial temperature gradient, along with a radial
decrease of the iron abundance.",9910271v1
1999-10-20,The r-Process Enriched Low Metallicity Giant HD 115444,"New high resolution, very high signal-to-noise spectra of ultra-metal-poor
(UMP) giant stars HD 115444 and HD 122563 have been gathered with the
High-Resolution Echelle Spectrometer of the McDonald Observatory 2.7m
Telescope. With these spectra, line identification and model atmosphere
analyses have been conducted, emphasizing the neutron-capture elements. Twenty
elements with Z > 30 have been identified in the spectrum of HD 115444. This
star is known to have overabundances of the neutron-capture elements, but it
has lacked a detailed analysis necessary to compare with nucleosynthesis
predictions. The new study features a line-by-line differential abundance
comparison of HD 115444 with the bright, well-studied halo giant HD 122563. For
HD 115444, the overall metallicity is [Fe/H]~ -3.0. The abundances of the light
and iron-peak elements generally show the same pattern as other UMP stars (e.g.
overdeficiencies of manganese and chromium, overabundances of cobalt), but the
differential analysis indicates several nucleosynthesis signatures that are
unique to each star.",9910376v1
1999-10-27,Metallicity distribution of bulge planetary nebulae and the [O/Fe] x [Fe/H] relation,"The O/H metallicity distribution of different samples of planetary nebulae in
the bulge of the Milky Way and M31 are compared. O/H abundances are converted
into [Fe/H] metallicity by the use of theoretical [O/Fe] x [Fe/H] relationships
both for the bulge and the solar neighbourhood. It is found that these
relationships imply an offset of [Fe/H] abundances by a factor up to 0.5 dex
for bulge nebulae. Systematic errors in the O/H abundances as suggested by some
recent recombination line work, ON cycling and statistical uncertainties are
unable to explain the observed offset, suggesting that the adopted relationship
for the bulge probably overestimates the oxygen enhancement relative to iron.",9910496v1
1999-11-01,Effects of Kerr Spacetime on Spectral Features from X-Ray Illuminated Accretion Discs,"We performed detailed calculations of the relativistic effects acting on both
the reflection continuum and the iron line from accretion discs around rotating
black holes. Fully relativistic transfer of both illuminating and reprocessed
photons has been considered in Kerr spacetime. We calculated overall spectra,
line profiles and integral quantities, and present their dependences on the
black hole angular momentum.
  We show that the observed EW of the lines is substantially enlarged when the
black hole rotates rapidly and/or the source of illumination is near above the
hole. Therefore, such calculations provide a way to distinguish among different
models of the central source.",9910562v1
1999-11-05,Pulsar Kick and Asymmetric Iron Velocity Distribution in SN 1987A,"We have investigated the relation of the direction of the momentum among the
matter, neutrino, and proto-neutron star in a collapse-driven supernova in
order to discuss the pulsar kick. In particular, we have investigated the
effects of the pulsar motion on the explosion, which are neglected in the
previous study. As a result, it is suggested that the direction of the total
momentum of the matter and neutrino is opposite to that of the momentum of the
proto-neutron star in the asymmetric explosion models. This is because the
center of the explosion deviates from the center of the progenitor due to the
pulsar motion. This picture is common among the asymmetric explosion models. So
if we assume that the pulsar motion is caused by an asymmetric supernova
explosion, the neutron star born in SN 1987A, which has not been found yet,
will be moving in the southern part of the remnant. In other words, if we can
find one neutron star in SN 1987A on the south part of the remnant, asymmetric
explosion models will be supported by the observation better than the binary
models.",9911077v2
1999-12-03,"The Type Ib/c Supernova, Gamma-Ray Burst, Soft Gamma-Ray Repeater, Magnetar Connection","The polarization of core-collapse supernovae shows that many if not all of
these explosions must be strongly bi-polar. The most obvious way to produce
this axial symmetry is by the imposition of a jet as an intrinsic part of the
explosion process. These jets could arise by MHD processes in the formation of
pulsars and be especially strong in the case of magnetars. The jets will blow
iron-peak material out along the axes and other elements from the progenitor
along the equator, a very different composition structure than pictured in
simple spherical ""onion skin"" models. In extreme cases, these processes could
lead to the production of gamma-ray bursts powered by strong Poynting flux.",9912080v2
1999-12-07,Spectral analysis of four multi mode pulsating sdB stars,"Four members of the new class of pulsating sdB stars are analysed from Keck
HIRES spectra using NLTE and LTE model atmospheres. Atmospheric parameters
(Teff, log g, log(He/H)), metal abundances and rotational velocities are
determined. Balmer line fitting is found to be consistent with the helium
ionization equilibrium for PG1605+072 but not so for PG1219+534 indicating that
systematic errors in the model atmosphere analysis of the latter have been
underestimated previously. All stars are found to be helium deficient probably
due to diffusion. The metals are also depleted with the notable exception of
iron which is solar to within error limits in all four stars, confirming
predictions from diffusion calculations of Charpinet et al. (1997). While three
of them are slow rotator's (vsini < 10km/s), PG1605+072 displays considerable
rotation (vsini = 39km/s, P<8.7h) and is predicted to evolve into an unusually
fast rotating white dwarf. This nicely confirms a prediction by Kawaler (1999)
who deduced a rotation velocity of 130km/s from the power spectrum of the
pulsations which implies a low inclination angle of the rotation axis.",9912133v1
2000-01-18,Implications of Abundance Gradients in Intracluster Gas,"Analysis of spatially resolved ASCA spectra of the intracluster gas in Abell
496 confirms that metal abundances increase toward the center. We also find
spatial gradients in several abundance ratios, indicating that the fraction of
iron from SN Ia increases toward the cluster center. The dominant metal
enrichment mechanism near the cluster center must therefore be different than
in the outer parts. We show that ram pressure stripping of gas from cluster
galaxies cannot account for the central abundance enhancement. We suggest that
two successive stages of galactic winds contaminate intracluster gas:
protogalactic winds driven by SN II, followed by less energetic winds driven by
SN Ia, which have longer lived progenitors than SN II. The less energetic
secondary wind from a cD galaxy may be suppressed, due to its location at the
cluster center, leading to the observed central enhancement of SN Ia ejecta.",0001304v1
2000-01-25,X-Ray Afterglows of Gamma-Ray Bursts,"The afterglow emission has become the main stream of Gamma-Ray burst research
since its discovery three years ago. With the distance-scale enigma solved, the
study of the late-time GRB emission is now the most promising approach to
disclose the origin of these explosions and their relationship with the
environment of the host galaxy in the early phase of the Universe. In this
contribution I will review X-ray observations and their implication on our
undertstanding on the GRB phenomenon. These measurements are providing a direct
probe into the nature of the progenitor and a measurement of the GRB beaming
properties, crucial to establish the total energy output. Some evidence of iron
lines connects the GRB explosion with massive progenitors, thence with
star-forming regions. Furthermore a comparison of the spectral properties with
the temporal evolution indicates that the fireball expansion should not be - on
average - highly collimated, with a jet angle $>10 \deg$.",0001436v1
2000-01-27,LiBeB Production and Associated Astrophysical Sites,"The various modes of spallative LiBeB production are summarized, and
classified according to their dependence or independence on the abundance of
medium heavy elements (CNO) illustrated by that of oxygen in the interstellar
medium.
  The predictions of the models are confronted to the available observational
correlations (Be, B vs O). Clearly, a primary mechanism should lead to a slope
one in the lg(Be/H) vs [O/H] plot and a secondary mechanism to a slope two. Due
to the ambiguity of the O data, another criterion, based on energetics, can
help us to select an adequate model. A purely secondary origin in the very
early Galaxy is much more energy demanding than a primary one. Indeed,
magnesium seems to be a possible surrogate of oxygen and iron since i) it is
spectroscopically more easy to cope with and ii) its nucleosynthetic yield is
independent of the mass cut and does not depend on metallicity.",0001474v1
2000-02-08,The hard X-ray properties of the Seyfert nucleus in NGC 1365,"We present BeppoSAX observations of the Seyfert 1.8 galaxy NGC1365 in the
0.1--100 keV range. The source was 6 times brighter than during an ASCA
observation 3 years earlier. The 4--10 keV flux is highly variable during the
BeppoSAX observation, while the soft (0.1-4 keV) emission is constant within
the errors. Both a cold and a warm reflector and a cold absorber are required
to explain the observed spectrum. The comparison between ASCA and BeppoSAX
spectra strongly suggests that the circumnuclear material has a more complex
structure than a simple homogeneous torus, with quite different absorbing gas
columns along different lines of sight. A broad iron K_alpha line is also
present in the spectrum, with the peak energy significantly redshifted. This
can be explained by means of a relativistic disk line model. Alternatively, a
warm absorption Fe line system with N_H ~ 10^23 cm^(-2) could account for the
observed line profile.",0002169v1
2000-03-02,Gamma-loud quasars: a view with BeppoSAX,"We present $Beppo$SAX observations of the $\gamma $-ray emitting quasars
0836+710, 1510-089 and 2230+114. All the objects have been detected in the PDS
up to 100 keV and have extremely flat power-law spectra above 2 keV ($\alpha
_x$=0.3--0.5). 0836+710 shows absorption higher than the galactic value and
marginal evidence for the presence of the redshifted 6.4 keV Iron line.
1510-089 shows a spectral break around 1 keV, with the low energy spectrum
steeper ($\alpha_l$=1.6) than the high energy power-law ($\alpha_h$=0.3). The
data are discussed in the light of current Inverse Compton models for the high
energy emission.",0003019v1
2000-03-13,Grain Survival in Supernova Remnants and Herbig-Haro Objects,"By using the flux ratio [FeII]8617/[OI]6300, we demonstrate that most of the
interstellar dust grains survive in shocks associated with supernova remnants
and Herbig-Haro objects. The [FeII]/[OI] flux ratio is sensitive to the
gas-phase Fe/O abundance ratio, but is insensitive to the ionization state,
temperature, and density of the gas. We calculate the [FeII]/[OI] flux ratio in
shocks, and compare the results with the observational data. When only 20% of
iron is in the gas phase, the models reproduce most successfully the
observations. This finding is in conflict with the current consensus that
shocks destroy almost all the grains and 100% of metals are in the gas phase.
We comment on previous works on grain destruction, and discuss why grains are
not destroyed in shocks.",0003170v1
2000-03-27,Massive Stars in the Range $\rm 13-25 M_\odot$: Evolution and Nucleosynthesis. II. the Solar Metallicity Models,"We present the evolutionary properties of a set of massive stellar models
(namely 13, 15, 20 and 25 $\rm M_\odot$) from the main sequence phase up to the
onset of the iron core collapse. All these models have initial solar chemical
composition, i.e. Y=0.285 and Z=0.02. A 179 isotope network, extending from
neutron up to $\rm ^{68}Zn$ and fully coupled to the evolutionary code has been
adopted from the Carbon burning onward. Our results are compared, whenever
possible, to similar computations available in literature.",0003401v1
2000-04-03,The Absolute Abundance of Iron in the Solar Corona,"We present a measurement of the abundance of Fe relative to H in the solar
corona using a technique which differs from previous spectroscopic and solar
wind measurements. Our method combines EUV line data from the CDS spectrometer
on SOHO with thermal bremsstrahlung radio data from the VLA. The coronal Fe
abundance is derived by equating the thermal bremsstrahlung radio emission
calculated from the EUV Fe line data to that observed with the VLA, treating
the Fe/H abundance as the sole unknown. We apply this technique to a compact
cool active region and find Fe/H
  = 1.56 x 10^{-4}, or about 4 times its value in the solar photosphere.
Uncertainties in the CDS radiometric calibration, the VLA intensity
measurements, the atomic parameters, and the assumptions made in the spectral
analysis yield net uncertainties of order 20%. This result implies that low
first ionization potential elements such as Fe are enhanced in the solar corona
relative to photospheric values.",0004007v1
2000-04-25,Non-LTE Abundances and Consequences for the Evolution of the alpha elements in the Galaxy,"Abundances of alpha-elements such as Ca and Mg in disk and halo stars are
usually derived from equivalent widths lines measured on high resolution
spectra, and assuming Local Thermodynamic Equilibrium (LTE) . In this paper, we
present non-LTE differential abundances derived by computing the statistical
equilibrium of CaI and MgI atoms, using high resolution equivalent widths
available in the literature for 252 dwarf to subgiant stars. These non-LTE
abundances combined with recent determination of non-LTE abundances of iron,
seem to remove the dispersion of the [Ca/Fe] and [Mg/Fe] ratios in the galactic
halo and disk phases, revealing new and surprising structures. These results
have important consequences for chemical evolution models of the Galaxy. In
addition, non-LTE abundance ratios for stars belonging to the M92 cluster
apparently have the same behavior. More high resolution observations, mainly of
globular clusters, are urgently needed to confirm our results.",0004337v1
2000-05-04,Oscillating structure of γ-bursts and their possible origin,"As it is well-known that the hydrodinamic collapse of the massive star iron
core should lead to the production of a hot neutron star. The assumption is
made that the thermonuclear burning of the envelope matter, accreting onto the
hot neutron star, can proceed in the oscillatoric regime (analogously to that
happens during heat explosion of the carbon-oxigene cores of stars with smaller
masses). Local density oscillations in the vicinity of the neutron star surface
can generate shock waves, in which the stratification of the electron-positron
plasma from the rest of the matter can happen due to the light preasure. In the
case of the spherically symmetric collapse of the compact star it can lead to
the production of the expanding relativistic fireball shells with
characteristic oscillation time of ~ 10^{-2} s, observed in the cosmological
\gamma-bursts (GRB), can occur. It is pointed out that nonrotating massive
Wolf-Rayet's (WR) stars could be the source for the GRB, whose collapses,
according to a number of observations, can happen without any noticeable
ejection of the envelope.",0005078v1
2000-05-04,Composition of UHE Cosmic Ray Primaries,"Project GRAND presents results on the atomic composition of primary cosmic
rays. This is accomplished by determining the average height of primary
particles that cause extensive air showers detected by Project GRAND. Particles
with a larger cross sectional area, such as iron nuclei, are likely to start an
extensive air shower higher in the atmosphere whereas protons, with a smaller
cross section, would pass through more air before interacting and thus start
showers at lower heights. Such heights can be determined by extrapolating
identified muon tracks backward (upward) to determine their height of origin
(Gress et al., 1997). Since muons are from the top, hadronic part of the
shower, they are a good estimator for the beginning of the shower. The data for
this study were taken during the previous year with 20 million shower events.",0005089v1
2000-05-08,X-ray Continuum Slope and X-ray Spectral Features in NLS1 Galaxies,"The idea that some of the unusual features in the X-ray spectra of
Narrow-Line Seyfert 1 galaxies (NLS1s) are due to the steep X-ray continuum is
tested by comparing photoionization model calculations with various observed
properties of Seyfert 1 galaxies. A meaningful comparison must involve the
careful use of the right X-ray ionization parameter, designated here U(oxygen).
When this is done, it is found that the strength of the continuum absorption
features is insensitive to the exact slope of the 0.1-50 keV continuum. It is
also shown that the complex of iron L-shell lines near 1 keV can produce strong
absorption and emission features, depending on the gas distribution and line
widths. While this may explain some unusual X-ray features in AGN, the
predicted intensity of the features do not distinguish NLS1 from broader line
sources. Finally, acceleration of highly ionized gas, by X-ray radiation
pressure, is also not sensitive to the exact slope of the X-ray continuum.",0005142v1
2000-05-08,The Fe II problem in NLS1s,"For more than twenty years, strong Fe II emission lines have been observed in
Active Galactic Nuclei and in particular in Narrow Line Seyfert 1 galaxies. A
quick overview of the observations and of the models proposed to interpret the
Fe II spectrum is given. The influence of atomic data and of physical
parameters are discussed, and it is shown that the strengths of the Fe II lines
cannot be explained in the framework of photoionization models. A non-radiative
heating, for instance due to shocks, with an overabundance of iron, can help to
solve the problem. A comparison with other objects emitting intense Fe II lines
favors also the presence of strong outflows and shocks. We suggest some issues
in the context of AGN evolution.",0005153v1
2000-05-08,X-ray reprocessing in Narrow-Line Seyfert 1 Galaxies: Ton S180 and Ark 564,"We present the results of spectral analysis of the ASCA data for the
Narrow-Line Seyfert 1 galaxy (NLS1) Ton S180 and simultaneous ASCA and RXTE
data modelling for the NLS1 Ark 564. We model both the primary and reflected
continuum as well as the iron K alpha line, the energy of which depends on the
ionization state of the reprocessor. We show that the reprocessing matter is
mildly ionized, and we find the soft to hard luminosity ratio to be about 2.5.
The accretion rate approximately corresponds to the Eddington limit value.",0005156v1
2000-05-08,Modelling of the X-ray broad absorption features in Narrow-Line Seyfert 1s,"We investigate the origin of the broad absorption features detected near
1-1.4 keV in several Narrow Line Seyfert 1 galaxies, by modelling the absorbing
medium with various physical parameters, using the ionization code PEGAS. The
observed properties of the X-ray absorption features can be reproduced by
taking into account the peculiar soft X-ray excess which is well fitted by a
blackbody plus an underlying power law. We equally stress that the emission
coming from the absorbing medium (related to the covering factor) has a strong
influence on the resulting X-ray spectrum, in particular on the apparent
position and depth of the absorption features. A non-solar iron abundance may
be required to explain the observed deep absorption. We also investigate the
influence of an additional collisional ionization process (hybrid case) on the
predicted absorption features.",0005169v1
2000-05-08,"Studies of the high luminosity quasar, PDS 456","X-ray and multi-wavelength observations of the most luminous known local
(z<0.3) AGN, the recently discovered radio-quiet quasar PDS 456, are presented.
The spectral energy distribution shows that PDS 456 has a bolometric luminosity
of 1e47 erg/s, peaking in the UV. The X-ray spectrum obtained by ASCA and RXTE
shows considerable complexity. The most striking feature observed is a deep,
highly-ionised, iron K edge (8.7 keV, rest-frame), originating via reprocessing
from highly ionised material, possibly the inner accretion disk. PDS 456 was
found to be remarkably variable for its luminosity; in one flare the X-ray flux
doubled in just about 15 ksec. If confirmed this would be an unprecedented
event in a high-luminosity source, with a light-crossing time corresponding to
about 2RS. The implications are that either flaring occurs within the very
central regions, or else that PDS 456 is a super-Eddington or relativistically
beamed system.",0005175v1
2000-06-02,Equilibrium configurations of relativistic White Dwarfs,"The Feynman-Metropolis-Teller treatment for compressed atoms is here
reconsidered in the framework of the relativistic generalised Fermi-Thomas
model, obtained by Ruffini et al. Physical properties of a zero temperature
plasma is thus investigated and the resulting equation of state, which keeps
into account quantum, relativistic and electromagnetic effects, is applied to
the study of equilibrium configurations of relativistic White Dwarfs.
  It is shown that numerical evaluation of such configuration leads, for the
same central density $\rho_c$, to smaller values of radius R and of mass M than
in the classical works of Chandrasekhar and Salpeter, the deviations being most
marked at the lowest densities (up to 30% from the
  Chandrasekhar model and 10% from the Salpeter one for $\rho_c \sim
10^6g/cm^3$, corresponding to $M \sim 0.2 M_{\odot}$).
  At high densities we considered the occurrence of inverse beta decays, whose
effect is to introduce gravitational instability of the configurations. We
consequently find the maximum mass of White Dwarfs, which, for an Oxygen and an
Iron WD, is respectively $1.365 M_{\odot}$ and $1.063 M_{\odot}$.",0006036v1
2000-06-03,Analysis of Four A-F Supergiants in M31 from Keck HIRES Spectroscopy,"The first stellar abundances in M31 are presented, based on Keck I HIRES
spectroscopy and model atmospheres analyses of three A-F supergiants, 41-2368,
41-3712, and A-207. We also present the preliminary analysis of a fourth star,
41-3654. We find that the stellar oxygen abundances are in good agreement with
those determined from nebular studies, even though the stars do {\it not} show
a clear radial gradient in oxygen. The uncertainties in the stellar abundances
are smaller than the range in the nebular results, making these stars ideal
objects for further studies of the distribution of oxygen in M31. We show that
the stars can be used to study the abundance distributions of other elements as
well, including iron-group and heavier elements.
  The A-F supergiants also provide direct information on the metallicity and
reddening of nearby Cepheid stars. We have examined the metallicity and
reddening assumptions used for Cepheids within 1' of our targets and noted the
differences from values used in the literature.",0006046v1
2000-06-20,The Effect of Diffusion on Pulsations of Stars on the Upper Main Sequence. delta Scuti and Metallic A Stars,"Recent dramatic improvements in the modeling of abundance evolution due to
diffusion in A stars have been achieved with the help of monochromatic opacity
tables from the OPAL group. An important result in the context of stellar
pulsations is the substantial helium abundance shown to be left over in the
driving region of delta Scuti-type pulsations in chemically peculiar Am stars.
An accurate opacity profile in the entire stellar envelope including the full
effect of heavy elements is also now available for the first time.
  Pulsations are shown to be excluded for young Am stars but occur naturally
when these stars evolve off the ZAMS. The predicted variable metallic A stars
all lie towards the red edge of the instability strip, in qualitative agreement
with the observed variable delta Delphini and mild Am stars.
  Results show little direct excitation from iron-peak elements in A-type
stars. The main abundance effect is due to the settling of helium, along with a
marginal effect due to the enhancement of hydrogen.",0006272v1
2000-06-23,The Metallicity Distribution Function of Red Giants in the LMC,"We report new metallicity determinations for 39 red giants in a 220 square
arcminute region, 1.8 degrees southwest of the bar of the Large Magellanic
Cloud. These abundance measurements are based on spectroscopy of the Ca II
infrared triplet. The metallicity distribution function (MDF) shows a strong
peak at [Fe/H] = -0.57 +/- 0.04. Half the red giants in our field fall within
the range -0.83 < [Fe/H] < -0.41. We find a striking contrast in the shape of
the MDF below [Fe/H] < -1 between our inner disk field and the distant outer
field studied by Olszewski (1993). Our field-star MDF seems similar to that of
the intermediate-age (1-3 Gyr) star clusters. We have also obtained abundance
estimates using Stromgren photometry for ~1000 red giants in the same field.
The Stromgren measurements, which are sensitive to a combination of cyanogen
and iron lines, correlate well with the Ca II measurements, but a
metallicity-dependent offset is found (abridged).",0006327v1
2000-07-05,Face-on galaxies NGC 524 and NGC 6340: chemically decoupled nuclei and inclined circumnuclear disks,"Central regions of the early-type disk galaxies NGC 524 and NGC 6340 have
been investigated with the Multi-Pupil Field Spectrograph at the 6m telescope
of the Special Astrophysical Observatory of the Russian Academy of Sciences. I
confirm the existence of chemically distinct stellar nuclei in these galaxies
which have been claimed earlier. The metallicity differences which are found
between the nuclei and the bulges, 0.5 - 1.0 kpc from the centers, reach 0.5 -
0.6 dex. Both nuclei are magnesium overabundant, but the bulges have different
magnesium-to-iron ratios: it is solar in NGC 6340 and the same as the nuclear
one in NGC 524. The kinematical and morphological analyses reveal the existence
of inclined central disks in these galaxies. In NGC 524 the central disk
consists of stars, dust, and ionized gas; its extension may be as large as up
to R=3 kpc, and it is inclined by more than 20 deg to the global galactic
plane. In NGC 6340 only a gaseous polar disk with the radius less than 500 pc
is detected.",0007051v1
2000-07-06,Galaxy Mergers: A Search for Chemical Signatures,"We have gathered high resolution echelle spectra for more than two dozen
high-velocity metal-poor field stars, including BD+80 245, a star previously
known to have extremely low [alpha/Fe] abundances, as well as G4-36, a new
low-alpha star with unusually large [Ni/ Fe]. In this kinematically selected
sample, other chemically anomalous stars have also been uncovered. In addition
to deriving the alpha-element abundances, we have also analysed iron-group and
s-process elements. Not only does chemical substructure exist in the halo, but
the chemical anomalies are not all the same within all elemental groups.",0007065v1
2000-07-17,Compton-Thick X-ray Absorption in the Seyfert Galaxies Tololo 0109-383 and ESO 138-G1,"We present analyses of the ASCA X-ray spectra of two Seyfert galaxies, Tololo
0109-383 and ESO 138-G1. In both cases, spectral fitting reveals two
statistically acceptable continuum models: Compton reflection and partial
covering. Both spectra have strong iron K-alpha lines, with equivalent widths
greater than 1.5 keV. These large equivalent widths are suggestive of heavier
obscuration than that directly indicated by the partial-covering models
(approximately 2 x 10^23 cm^-2), with the actual column densities being
`Compton-thick' (i.e. N_H > 1.5 x 10^24 cm^-2). We use the hard X-ray/[O III]
flux correlation for Seyferts and data from the literature to provide
additional support for this hypothesis. Since Tololo 0109-383 is known to have
optical type 1 characteristics such as broad Balmer line components and Fe II
emission, this result marks it as a notable object.",0007237v2
2000-07-21,Probing Dense Matter in the cores of AGN: Observations with RXTE and ASCA,"Preliminary results from an X-ray spectral study of Seyfert 1 galaxies with
ASCA and RXTE are presented. From an analysis of X-ray reprocessing features of
Compton reflection and Fe K-alpha fluorescence, it is found that iron line
strength is not necessarily a good predictor of the amount of reflection. The
variability properties of Fe K-alpha and reflection do not necessarily scale
together and substantial decoupling of the behavior of the reprocessed flux
with respect to continuum variability is common. Such trends suggest the
presence of multiple and/or complex regions of dense matter in AGN cores and
that standard accretion disk models drastically oversimplify reality.",0007327v1
2000-07-27,Presupernova collapse models with improved weak-interaction rates,"Improved values for stellar weak interaction rates have been recently
calculated based upon a large shell model diagonalization. Using these new
rates (for both beta decay and electron capture), we have examined the
presupernova evolution of massive stars in the range 15-40 Msun. Comparing our
new models with a standard set of presupernova models by Woosley and Weaver, we
find significantly larger values for the electron-to-baryon ratio Ye at the
onset of collapse and iron core masses reduced by approximately 0.1 Msun. The
inclusion of beta-decay accounts for roughly half of the revisions, while the
other half is a consequence of the improved nuclear physics. These changes will
have important consequences for nucleosynthesis and the supernova explosion
mechanism.",0007412v1
2000-08-04,On the peculiar X-ray properties of the bright nearby radio-quiet quasar PDS456,"BeppoSAX and ASCA observations of the nearby (z=0.184), high-luminosity,
radio-quiet quasar PDS456 are presented. The X-ray spectrum is characterized by
a prominent ionized edge at 8-9 keV (originally discovered by RXTE, Reeves et
al. 2000) and by a soft excess below 1.5 keV. The lack of any significant iron
K alpha emission line suggests for the edge an origin from line-of-sight
material rather than from reflection from a highly ionized accretion disc. The
hard X-ray continuum is indeed well modelled by transmission through a
highly-ionized medium with a large column density (N_H warm = 4.5 x 10^24
cm^-2) plus an additional cold absorber with a lower column density (N_H cold =
2.7 x 10^22 cm^-2).",0008090v1
2000-08-22,"Interstellar X-ray Absorption Spectroscopy of Oxygen, Neon, and Iron with the Chandra LETGS Spectrum of X0614+091","We find resolved interstellar O K, Ne K, and Fe L absorption spectra in the
Chandra Low Energy Transmission Grating Spectrometer spectrum of the low mass
X-ray binary X0614+091. We measure the column densities in O and Ne, and find
direct spectroscopic constraints on the chemical state of the interstellar O.
These measurements probably probe a low-density line of sight through the
Galaxy and we discuss the results in the context of our knowledge of the
properties of interstellar matter in regions between the spiral arms.",0008349v1
2000-08-23,Strangeness in Neutron Stars,"It is generally agreed on that the tremendous densities reached in the
centers of neutron stars provide a high-pressure environment in which numerous
novel particles processes are likely to compete with each other. These
processes range from the generation of hyperons to quark deconfinement to the
formation of kaon condensates and H-matter. There are theoretical suggestions
of even more exotic processes inside neutron stars, such as the formation of
absolutely stable strange quark matter, a configuration of matter even more
stable than the most stable atomic nucleus, iron. In the latter event, neutron
stars would be largely composed of pure quark matter, eventually enveloped in a
thin nuclear crust. No matter which physical processes are actually realized
inside neutron stars, each one leads to fingerprints, some more pronounced than
others though, in the observable stellar quantities. This feature combined with
the unprecedented progress in observational astronomy, which allows us to see
vistas with remarkable clarity that previously were only imagined, renders
neutron stars to nearly ideal probes for a wide range of physical studies,
including the role of strangeness in dense matter.",0008376v1
2000-09-27,Unusual Properties of X-Ray Emission near the Galactic Center,"The X-ray spectrum in a $1^{\circ}\times1^{\circ}$ region of the Galactic
center observed with the ASCA satellite is examined in detail, following the
first report by Koyama et al. (1996, AAA 65.155.208). The observed spectrum
contains prominent emission lines from helium-like and hydrogen-like ions of
various elements, and is essentially the same all over the region. If the
observed spectrum is thermal emission from hot plasmas, it requires
multi-temperature plasma components, each at a different degree of ionization
and with a different amount of absorption. The absence of adiabatic cooling and
of systematic changes in the degree of ionization over the region is against
the Galactic center origin of hot plasmas. A significant broadening of the
helium-like and hydrogen-like iron K-lines is confirmed. The line width
corresponds to a rms velocity of $\sim3300$ km~s$^{-1}$, which far exceeds the
sound velocity in a plasma of $kT\sim14$ keV measured with the Ginga satellite.
These facts cast doubt on a thermal origin of the observed X-ray emission.",0009445v1
2000-09-29,The beryllium abundance in the very metal-poor halo star G 64-12 from VLT/UVES observations,"We report on a new spectroscopic analysis of the very metal deficient star G
64-12 ([Fe/H]=-3.3), aimed at determining, for the first time, its Be content.
The spectra were observed during the Science Verification of UVES, the ESO VLT
Ultraviolet and Visible Echelle Spectrograph. The high resolution (~48,000) and
high S/N (~130 per pixel) achieved at the wavelengths of the BeII resonance
doublet allowed an accurate determination of its abundance: log N(Be/H) =
-13.10 +/- 0.15 dex. The Be abundance is significantly higher than expected
from previous measurements of Be in stars of similar metallicity (3D and NLTE
corrections acting to make a slightly higher value than an LTE analysis). When
compared to iron, the high [Be/Fe] ratio thus found may suggest a flattening in
the beryllium evolutionary trend at the lowest metallicity end or the presence
of dispersion at early epochs of galactic evolution.",0009482v1
2000-10-06,ASCA Observation of an X-Ray-Luminous Active Nucleus in Markarian 231,"We have obtained a moderately long (100 kilosecond) ASCA observation of the
Seyfert 1 galaxy Markarian 231, the most luminous of the local ultraluminous
infrared galaxy (ULIRG) population. In the best-fitting model we do not see the
X-ray source directly; the spectrum consists of a scattered power-law component
and a reflection component, both of which have been absorbed by a column N_H
\approx 3 X 10^(22)/cm^2. About 3/4 of the observed hard X-rays arise from the
scattered component, reducing the equivalent width of the iron K alpha line.
The implied ratio of 1-10 keV X-ray luminosity to bolometric luminosity,
L_x/L_bol \sim 2%, is typical of Sy 1 galaxies and radio-quiet QSOs of
comparable bolometric luminosities, and indicates that the bolometric
luminosity is dominated by the AGN. Our estimate of the X-ray luminosity also
moves Mrk 231 in line with the correlations found for AGN with extremely strong
Fe II emission. A second source separated by about 2 arcminutes is also clearly
detected, and contributes about 25% of the total flux.",0010125v1
2000-10-13,Iron K-alpha Emission from a Decaying Magnetar Model of Gamma-Ray Bursts,"The recent report of X-ray Fe features in the afterglow of the gamma-ray
burst GRB 991216 may provide important clues for identifying the nature of its
progenitor and constraining the burst mechanism. We argue that the strong line
emission can be attributed to the interaction of a continuing (but decaying)
post-burst relativistic outflow from the central engine with the progenitor
stellar envelope at distances less than a light-hour. Only a small mass of Fe
is then required, which could have been readily produced by the star itself.",0010258v1
2000-11-09,"Population synthesis of neutron stars, strange (quark) stars and black holes","We compute and present the distribution in mass of single and binary neutron
stars, strange stars, and black holes. The calculations were performed using a
stellar population synthesis code. We follow all phases of single and binary
evolution, starting from a ZAMS binary and ending in the creation of one
compact object (neutron star, black hole, strange star) and a white dwarf, or
two compact objects (single or binary). We assume that neutron stars are formed
in the collapse of iron/nickel cores in the mass range M0 < M < M1, quark stars
in the range M1 < M < M2, and black holes for core masses M > M2 and find that
the population of quark stars can easily be as large as the population of black
holes, even if there is only a small mass window for their formation.",0011183v1
2000-11-14,The 2000 outburst of the recurrent nova CI Aquilae: optical spectroscopy,"We present low- and medium resolution spectra of the recurrent nova CI
Aquilae taken at 14 epochs in May and June, 2000. The overall appearance is
similar to other U Sco-type recurrent novae (U Sco, V394 CrA). Medium
resolution (R=7000-10000) hydrogen and iron profiles suggest an early expansion
velocity of 2000-2500 km/s. The H\alpha evolution is followed from Dt = -0.6 d
to +53 d, starting from a nearly Gaussian shape to a double peaked profile
through strong P-Cyg profiles. The interstellar component of the sodium D line
and two diffuse interstellar bands put constraints on the interstellar
reddening which is estimated to be E(B-V)=0.85\pm0.3. The available visual and
CCD-V observations are used to determine t0,t2 and t3. The resulting parameters
are: t0=2451669.5\pm0.1, t2=30\pm1 d, t3=36\pm1 d. The recent lightcurve is
found to be generally similar to that observed in 1917 with departures as large
as 1-2 mag in certain phases. This behaviour is also typical for the U Sco
subclass.",0011270v1
2000-11-28,Chandra detection of reflected X-ray emission from the type 2 QSO in IRAS 09104+4109,"We present X-ray imaging spectroscopy of the extremely luminous infrared
galaxy IRAS 09104+4109 (z=0.442) obtained with the Chandra X-ray Observatory.
With the arcsec resolution of Chandra, an unresolved source at the nucleus is
separated from the surrounding cluster emission. A strong iron K line at 6.4
keV on a very hard continuum is detected from the nuclear source, rendering
IRAS 09104+4109 the most distant reflection-dominated X-ray source known.
Combined with the BeppoSAX detection of the excess hard X-ray emission, it
provides further strong support to the presence of a hidden X-ray source of
quasar luminosity in this infrared galaxy. Also seen is a faint linear
structure to the North, which coincides with the main radio jet. An X-ray
deficit in the corresponding region suggests an interaction between the cluster
medium and the jet driven by the active nucleus.",0011518v1
2000-12-01,The Seyfert-Starburst Connection in X-rays. I. The Data,"We analyze X-ray spectra and images of a sample of Seyfert 2 galaxies that
unambiguously contain starbursts, based on their optical and UV
characteristics. Although all sample members contain active galactic nuclei
(AGNs), supermassive black holes or other related processes at the galactic
centers alone cannot account for the total X-ray emission in all instances.
Eleven of the twelve observed galaxies are significantly resolved with the
ROSAT HRI, while six of the eight sources observed with the lower-resolution
PSPC also appear extended on larger scales. The X-ray emission is extended on
physical scales of 10 kpc and greater, which we attribute to starburst-driven
outflows and supernova-heating of the interstellar medium. Spectrally, a
physically-motivated composite model of the X-ray emission that includes a
heavily absorbed (N_H > 10^{23} cm^{-2}) nuclear component (the AGN), power-law
like scattered AGN flux, and a thermal starburst describes this sample well.
Half the sample exhibit iron K alpha lines, which are typical of AGNs.",0012035v1
2000-12-05,Chandra--ASCA--RXTE observations of the micro-quasar GRS 1915+105,"A Chandra AO1 30ks HETGS observation of the X-ray transient micro-quasar GRS
1915+105 reveals absorption edges and faint line emission over the HETG energy
range. We find from a preliminary analysis evidence for prominent neutral K
edges associated with iron, silicon, magnesium, and tentatively sulphur. The
column densities assuming solar abundances are consistent with ~ few x $10^{22}
cm^{-2}$ in excess of the Galactic value, and may point to surrounding cold
material associated with GRS 1915+105. Neutral Fe K$\alpha$ emission, and
ionized absorption from Fe XXV and Fe XXVI are resolved. We limit our
discussion to the Chandra results.",0012111v1
2000-12-17,Stellar spectroscopy far beyond the Local Group,"Multi-object spectroscopic observations of blue supergiants in NGC 3621, a
spiral galaxy at a distance of 6.7 Mpc, carried out with the ESO VLT and FORS
are presented. We demonstrate the feasibility of quantitative stellar
spectroscopy at distances approaching a ten-fold increase over previous
investigations by determining chemical composition, stellar parameters,
reddening, extinction and wind properties of one of our targets, a supergiant
of spectral type A1 Ia located in the outskirts of NGC 3621. The metallicity
(determined from iron group elements) is reduced by a factor of two relative to
the sun in qualitative agreement with results from previous abundance studies
based on H II region oxygen emission lines. Reddening and extinction are E(B-V)
= 0.12 and Av = 0.37, respectively, mostly caused by the galactic foreground.
Comparing stellar wind momentum and absolute V magnitude with galactic and M31
counterparts we confirm the potential of the wind momentum-luminosity
relationship as an alternative tool to estimate extragalactic distances.",0012372v1
2001-02-15,Ionized Iron Lines in X-ray Reflection Spectra,"We present results from new calculations of the X-ray reflection spectrum
from ionized accretion discs. These computations improve on our previous models
by including the condition of hydrostatic balance in the vertical direction,
following the work of Nayakshin, Kazanas & Kallman. We find that an ionized Fe
K$\alpha$ line is prominent in the reflection spectra for a wide variety of
physical conditions. The results hold for both gas and radiation pressure
dominated discs and when the metal abundances have been varied.",0102268v2
2001-03-11,Contribution of nuclei accelerated by gamma-ray pulsars to cosmic rays in the Galaxy,"We consider the galactic population of gamma-ray pulsars as possible sources
of cosmic rays at and just above the ``knee'' in the observed cosmic ray
spectrum at $10^{15}$--$10^{16}$ eV. We suggest that iron nuclei may be
accelerated in the outer gaps of pulsars, and then suffer partial
photo-disintegration in the non-thermal radiation fields of the outer gaps. As
a result, protons, neutrons, and surviving heavier nuclei are injected into the
expanding supernova remnant. We compute the spectra of nuclei escaping from
supernova remnants into the interstellar medium, taking into account the
observed population of radio pulsars.
  Our calculations, which include a realistic model for acceleration and
propagation of nuclei in pulsar magnetospheres and supernova remnants, predict
that heavy nuclei accelerated directly by gamma-ray pulsars could contribute
about 20% of the observed cosmic rays in the knee region. Such a contribution
of heavy nuclei to the cosmic ray spectrum at the knee can significantly
increase the average value of $<\ln A>$ with increasing energy as is suggested
by recent observations.",0103160v1
2001-03-14,"The Early Formation, Evolution and Age of the Neutron-Capture Elements in the Early Galaxy","Abundance observations indicate the presence of rapid-neutron capture (i.e.,
r-process) elements in old Galactic halo and globular cluster stars. These
observations demonstrate that the earliest generations of stars in the Galaxy,
responsible for neutron-capture synthesis and the progenitors of the halo
stars, were rapidly evolving. Abundance comparisons among several halo stars
show that the heaviest neutron-capture elements (including Ba and heavier) are
consistent with a scaled solar system r-process abundance distribution, while
the lighter such elements do not conform to the solar pattern. These
comparisons suggest two r-process sites or at least two different sets of
astrophysical conditions. The large star-to-star scatter observed in the
neutron-capture/iron ratios at low metallicities -- which disappears with
increasing [Fe/H] -- suggests an early, chemically unmixed and inhomogeneous
Galaxy. The stellar abundances indicate a change from the r-process to the slow
neutron capture (i.e., s-) process at higher metallicities in the Galaxy. The
detection of thorium in halo and globular cluster stars offers a promising,
independent age-dating technique that can put lower limits on the age of the
Galaxy.",0103222v1
2001-03-26,A hard X-ray constraint on the presence of an AGN in the ultra-luminous infrared galaxy Arp220,"We present X-ray results on the ultraluminous infrared galaxy Arp220 obtained
with BeppoSAX. The X-ray emission up to 10 keV is detected. No significant
signal is detected with the PDS detector in the higher energy band. The 2-10
keV emission has a hard spectrum (photon-index of 1.7), similar to M82, and a
luminosity of 1e41 erg/s. A population of X-ray binaries may be a major source
of this X-ray emission. The upper limit of an iron K line equivalent width at
6.4 keV is ~600 eV. This observation imposes so far the tightest constraint on
an active nucleus if present in Arp220. We find that a column density of X-ray
absorption must exceed 10**25 cm-2 for an obscured active nucleus to be
significant in the energetics, and the covering factor of the absorption should
be almost unity. The underluminous soft X-ray starburst emission may need a
good explanation, if the bolometric luminosity is primarily powered by a
starburst.",0103417v1
2001-03-26,Precipitating Condensation Clouds in Substellar Atmospheres,"We present a method to calculate vertical profiles of particle size
distributions in condensation clouds of giant planets and brown dwarfs. The
method assumes a balance between turbulent diffusion and sedimentation in
horizontally uniform cloud decks. Calculations for the Jovian ammonia cloud are
compared with results from previous methods. An adjustable parameter describing
the efficiency of sedimentation allows the new model to span the range of
predictions made by previous models. Calculations for the Jovian ammonia cloud
are consistent with observations. Example calculations are provided for water,
silicate, and iron clouds on brown dwarfs and on a cool extrasolar giant
planet. We find that precipitating cloud decks naturally account for the
characteristic trends seen in the spectra and colors of L- and T-type ultracool
dwarfs.",0103423v2
2001-04-10,Oxygen Abundances in Metal-Poor Stars (-2.2 < [Fe/H] < -1.2) from Infrared OH lines,"Infrared OH lines at 1.55 - 1.56 um in the H-band were obtained with the
Phoenix high-resolution spectrograph at the 2.1m telescope of the Kitt Peak
National Observatory for a sample of 14 metal-poor stars. Detailed analyses of
the sample stars have been carried out, deriving stellar parameters based on
two methods: (a) spectroscopic parameters; (b) IRFM effective temperatures,
trigonometric gravities and metallicities from Fe II lines. The Fe I lines
present in the H-band region observed showed to be well fitted by the stellar
parameters within $\Delta$[Fe/H] < 0.15 dex. The oxygen abundances were derived
from fits of spectrum synthesis calculations to the infrared OH lines. CO lines
in the H- and K-bands were obtained for a subsample in order to determine their
carbon abundances. Adopting the spectroscopic parameters a mean oxygen-to-iron
ratio of [O/Fe] ~ +0.52 is obtained, whereas using the IRFM temperatures,
Hipparcos gravities and [FeII/H], [O/Fe] ~ +0.25 is found. A mean of the two
methods gives a final value of [O/Fe] ~ +0.4 for the metallicity range -2.2 <
[Fe/H] < -1.2 of the sample metal-poor stars.",0104184v1
2001-04-11,Evolution of Lithium-Beryllium-Boron and Oxygen in the early Galaxy,"Oxygen is a much better evolutionary index than iron to describe the history
of Lithium-Beryllium-Boron (LiBeB) since it is the main producer of these light
elements at least in the early Galaxy. The O-Fe relation is crucial to the
determination of the exact physical process responsible for the LiBeB
production. At low metallicity, if [O/Fe] vs [Fe/H] is flat, then the
production mode is independent of the interstellar metallicity, BeB is
proportional to oxygen, i.e. is of primary nature. If not, the production mode
is function of the progressive enrichment in O of the interstellar medium, BeB
varies rather as the square of O, i.e. is of secondary nature. In the first
case, fast nuclei enriched into He, C and O injected by supernovae and
accelerated in surrounding superbubbles would explain the primary trend.
  In the second case, the main spallative agent would be the standard galactic
cosmic rays. Calculated nucleosynthetic yields of massive stars, estimates of
the energy cost of production of beryllium nuclei, and above all recent
observations reported in this meeting seem to favor the primary mechanism, at
least in the early Galaxy.",0104194v1
2001-04-12,NLTE Synthetic Spectral Fits to the Type Ia Supernova 1994D in NGC 4526,"We have fit the normal, well observed, Type Ia Supernova (SN Ia) SN 1994D
with non-LTE spectra of the deflagration model W7. We find that well before
maximum luminosity W7 fits the optical spectra of SN 1994D. After maximum
brightness the quality of the fits weakens as the spectrum forms in a core rich
in iron peak elements. We show the basic structure of W7 is likely to be
representative of the typical SN Ia. We have shown that like W7, the typical SN
Ia has a layer of unburned C+O composition at v > 15000 \kmps, followed by
layers of C-burned and O-burned material with a density structure similar to
W7. We present UVOIR (UBVRIJKH) synthetic photometry and colors and compare
with observation. We have computed the distance to the host galaxy, NGC 4526,
obtaining a distance modulus of \mu = 30.8 \pm 0.3. We discuss further
application of this direct measurement of SNe Ia distances. We also discuss
some simple modifications to W7 that could improve the quality of the fits to
the observations.",0104225v1
2001-04-17,A Search for Fine Structure of the Knee in EAS Size Spectra,"28 size spectra of extensive air showers from 7 different experiments are
analysed consistently. They are fitted by adjusting either 4 or 5 parameters:
knee position, power law exponents above and below the knee, overall intensity
and, in addition, a parameter describing the smoothness of the bend. The
residuals are then normalized to the same knee position and averaged. When 5
parameters are employed no systematic deviation from a single smooth knee is
apparent at the 1% level up to a factor of 4 above the knee. At larger shower
sizes a moderately significant deviation can be seen whose shape and position
are compatible with a second knee caused by iron group nuclei.",0104282v1
2001-06-04,Ionisation Structure in Accretion Shocks with a Composite Cooling Function,"We have investigated the ionisation structure of the post-shock regions of
magnetic cataclysmic variables using an analytic density and temperature
structure model in which effects due to bremsstrahlung and cyclotron cooling
are considered. We find that in the majority of the shock-heated region where
H- and He-like lines of the heavy elements are emitted, the
collisional-ionisation and corona-condition approximations are justified. We
have calculated the line emissivity and ionisation profiles for Iron as a
function of height within the post-shock flow. For low-mass white dwarfs, line
emission takes place near the shock. For high-mass white dwarfs, most of the
line emission takes place in regions well below the shock and hence it is less
sensitive to the shock temperature. Thus, the line ratios are useful to
determine the white-dwarf masses for the low-mass white dwarfs, but the method
is less reliable when the white dwarfs are massive. Line spectra can, however,
be used to map the hydrodynamic structure of the post-shock accretion flow.",0106052v1
2001-06-04,L-dwarf variability: Magnetic star spots or non-uniform clouds?,"The recent discovery of photometric variations in L dwarfs has opened a
discussion on the cause of the variations. We argue against the existence of
magnetic spots in these atmospheres and favor the idea that non-uniform
condensate coverage (i.e. clouds) is responsible for the variations. The
magnetic Reynolds number (Rm) in the atmosphere of L dwarfs, which describes
how well the gas couples with the magnetic field, is too small (<<1) to support
the formation of magnetic spots. In constrast silicate and iron clouds form in
the photospheres of L dwarfs. Inhomogeneities in such cloud decks can plausibly
produce the observed photometric variations. Further evidence in support of
clouds is the tendency for variable L dwarfs to be bluer in J-Ks than the
average L dwarf of a given spectral type. This color effect is expected if
clear holes appear in an otherwise uniform cloud layer.",0106062v1
2001-06-06,The nebular spectra of the hypernova SN 1998bw and evidence for asymmetry,"The nebular spectra of the energetic Type Ic supernova SN1998bw (hypernova)
are studied. The transition to the nebular phase occurred at an epoch of about
100 days after outburst, which is assumed to coincide with GRB980425. Early in
the nebular epoch the spectra show the characteristics of a typical SN Ic
spectrum, with strong lines of [OI], CaII and MgI], and lines of [FeII].
However, the [FeII] lines are unusually strong for a SN Ic. Also, lines of
different elements have different widths, indicating different expansion
velocities. In particular, iron appears to expand more rapidly than oxygen.
Furthermore, the [OI] nebular lines decline more slowly than the [FeII] ones,
signalling deposition of gamma-rays in a slowly-moving O-dominated region.
These facts suggest that the explosion was aspherical. The absence of [FeIII]
nebular lines can be understood if the ejecta are significantly clumped. A
schematic picture of what this very unusual stellar explosion may have looked
like is presented.",0106095v1
2001-06-12,The Stellar Parameters and Evolutionary State of the Primary in the d'-Symbiotic System StH\alpha190,"We report on a high-resolution, spectroscopic stellar parameter and abundance
analysis of a d' symbiotic star: the yellow component of StH\alpha190. This
star has recently been discovered, and confirmed here, to be a rapidly rotating
(vsini=100 km/s) subgiant, or giant, that exhibits radial-velocity variations
of probably at least 40 km/s, indicating the presence of a companion (a white
dwarf star). It is found that the cool stellar component has Teff=5300K and log
g=3.0. The iron and calcium abundances are close to solar, however, barium is
overabundant, relative to Fe and Ca, by about +0.5 dex. The barium enhancement
reflects mass-transfer of s-process enriched material when the current white
dwarf was an asymptotic giant branch (AGB) star. The past and future evolution
of this binary system depends critically on its current orbital period, which
is not yet known. Concerted and frequent radial-velocity measurements are
needed to provide crucial physical constraints to this d' symbiotic system.",0106215v1
2001-06-13,ASCA observations of massive medium-distant clusters of galaxies. II,"We have selected seven medium-distant clusters of galaxies (z ~ 0.1 - 0.3)
for multi-wavelength observations with the goal of investigating their
dynamical state. Following Paper I (Pierre et al. 1999) which reported the ASCA
results about two of them, we present here the analysis of the ASCA
observations of the other five clusters; RXJ1023.8-2715 (A3444),
RXJ1031.6-2607, RXJ1050.5-0236 (A1111), RXJ1203.2-2131(A1451), and
RXJ1314.5-2517. Except for RXJ1031.6, whose X-ray emission turned out to be
dominated by an AGN, the ASCA spectra are well fitted by a one-temperature thin
thermal plasma model. We compare the temperature-luminosity relation of our
clusters with that of nearby ones (z<0.1). Two clusters, RXJ1050.5 and
RXJ1023.8, show larger luminosities than the bulk of clusters at similar
temperatures, which suggests the presence of a cooling flow. The temperature
vs. iron-abundance relationship of our sample is consistent with that of nearby
clusters.",0106248v1
2001-06-19,Bremsstrahlung of Flavor-Degenerate Pairs by Neutrinos in the Nuclear Field,"Neutrino Bremsstrahlung of flavor-degenerate pairs in the field of a nucleus
is of potential importance for neutrino astrophysics and is representative of a
class of processes connecting leptonic electroweak sectors to real or virtual
photons. We focus on first generation flavor production by both electron and
muon neutrinos and present Standard Model cross sections and distributions for
lead and iron nuclei. The results (of order 10-41 cm2 for electron neutrino -
lead collisions at 100 MeV) have been fitted to empirical formulae that can be
used to estimate backgrounds to neutrino detection experiments and flux
normalizations. A compact form of the matrix element obtained by analytic
reduction is used to explain the distributions. The V-A limits of the cross
sections are shown to agree with published work from the pre-neutral current
era. Event signatures and the possible roles of these processes in stellar and
laboratory neutrino physics are discussed. Cross sections are compared with
those for neutrino-electron scattering for neutrino spectra corresponding to
typical supernovae temperatures.",0106317v2
2001-06-19,The K-alpha complex of He-like iron with dielectronic satellites,"It is shown that the dielectronic satellites (DES) dominate X-ray spectral
formation in the 6.7 keV K-alpha complex of Fe XXV at temperatures below that
of maximum abundance in collisional ionization equilibrium T_m. Owing to their
extreme temperature sensitivity the DES are excellent spectral diagnostics for
T < T_m in photoionized, colllisional, or hybrid plasmas; whereas the
forbidden, intercombination, and resonance lines of Fe XXV are not. A
diagnostic line ratio GD(T) is defined including the DES and the lines, with
parameters from new relativistic atomic calculations. The DES absorption
resonance strengths may be obtained from differential oscillator strengths to
possibly yield the Fe XXIV/Fe XXV column densities. The DES contribution to
highly ionized Fe should be of interest for models of redward broadening of
K-alpha features, ionized accretion discs, accretion flows, and K-alpha
temporal-temperature variability in AGN.",0106330v1
2001-07-05,Spectral Indices of Stars at Super-solar Regime,"We derived Lick narrow-band indices for 139 candidate super metal-rich stars
of different luminosity class previously studied in Malagnini et al. (2000).
Indices include Iron Fe50, Fe52, Fe53, and Magnesium Mgb and Mg2 features. By
comparing observations with Kurucz' synthetic model atmospheres, no evidence is
found for non-standard Mg vs. Fe relative abundance (i.e. [Mg/Fe]~ 0, on the
average, for our sample). A comparison with the Worthey et al.(1994) and
Buzzoni et al.(1992, 1994) fitting function predictions for [Fe/H] > 0 is
performed and briefly discussed.",0107105v1
2001-07-06,In-flight performances of SilEye-2 Experiment and cosmic ray abundances inside space station Mir,"Cosmic ray measurements performed with the instrument SilEye-2 on Mir space
station are presented. SilEye-2 is a silicon detector telescope for the study
of the causes of Light Flashes perception by astronauts. As a stand-alone
device, it monitors in the short and long term the radiation composition inside
Mir. The cosmic ray detector consists of an array of 6 active silicon strip
detectors which allow nuclear identification of cosmic rays up to Iron. The
device was operational for more than 1000 hours in the years 1998-2000,
measuring also several Solar Particle Events. In this work we present the
in-flight performance of the instrument and nuclear abundance data from Boron
to Silicon above ~150 MeV/n inside Mir.",0107128v1
2001-07-13,BeppoSAX observations of the Narrow-Line Seyfert 1 galaxy RX J1702.5+3247,"We report optical, radio and X-ray observations of the Narrow-Line Seyfert 1
galaxy RX J1702.5+3247. The soft (0.1-2 keV) X-ray flux, measured by BeppoSAX,
is characterized by strong variability on short time scales (< 500 sec). The
most extreme amplitude variations require a radiative efficiency exceeding the
maximum for a Kerr black hole, implying the presence of relativistic effects. A
comparison with archival ROSAT data reveals long term temporal and spectral
variability. The 0.1-10 keV spectrum is equally well fitted either by an
ionized reflection disk model, or by a broken power law plus a Gaussian line,
consistent with a hydrogen-like iron line at 6.97 keV from a highly ionized
accretion disk.",0107240v1
2001-07-18,A Possible Emission Feature in an X-ray Afterglow of GRB970828 as a Radiative Recombination Edge,"A gamma-ray burst of 28 August 1997 was localized by the All-Sky Monitor on
the Rossi XTE satellite and its coordinates were promptly disseminated. An ASCA
followup started 1.17 days after the burst as a Target of Opportunity
Observation and detected an X-ray afterglow. The spectral data displayed a hump
around ~5 keV and an absorption column of 7.1 x 10^21 cm^{-2}. This hump
structure is likely a recombination edge of iron in the vicinity of the source,
taking account of the redshift z = 0.9578 found for the likely host galaxy of
the associated radio flare. Radiative Recombination edge and Continuum model
can interpret the spectrum from highly ionized plasma in a non equilibrium
ionization state. The absorption could be also due to the medium presumably in
the vicinity of the GRB.",0107331v1
2001-08-28,"Neutrinos from Early-Phase, Pulsar-Driven Supernovae","Neutron stars, just after their formation, are surrounded by expanding,
dense, and very hot envelopes which radiate thermal photons. Iron nuclei can be
accelerated in the wind zones of such energetic pulsars to very high energies.
These nuclei photo-disintegrate and their products lose energy efficiently in
collisions with thermal photons and with the matter of the envelope, mainly via
pion production. When the temperature of the radiation inside the envelope of
the supernova drops below $\sim 3\times 10^6$ K, these pions decay before
losing energy and produce high energy neutrinos. We estimate the flux of muon
neutrinos emitted during such an early phase of the pulsar - supernova envelope
interaction. We find that a 1 km$^2$ neutrino detector should be able to detect
neutrinos above 1 TeV within about one year after the explosion from a
supernova in our Galaxy. This result holds if these pulsars are able to
efficiently accelerate nuclei to energies $\sim 10^{20}$ eV, as postulated
recently by some authors for models of Galactic acceleration of the extremely
high energy cosmic rays (EHE CRs).",0108447v2
2001-09-07,"X-ray Spectra and Light Curves of AR Lac: Temperature Structure, Abundances, and Variability","We observed AR Lac, an eclipsing RS CVn binary star, with the Chandra High
Energy Grating Spectrometer for a total of 100 ks divided into six intervals
covering both quadratures and eclipses. We repeated observations at each phase.
At least two flares were seen, in which the flux increased by factors of two
and four. The flares occurred near eclipse phases and compromised detection of
eclipse modulation. The quadrature fluxes were the most stable, but they also
show non-repeating trends. Quadrature line profiles are broadened relative to
eclipse profiles, presumably due to orbital velocity Doppler shifted emission
from each binary component. The spectrum appears to be iron poor and neon rich,
similar to HR 1099, but not as extreme as II Pegasi. We will examine line
strengths, widths, and positions vs. phase, and present preliminary
differential emission measure models and abundance determinations using the
APED emissivity database.
  This work is supported by NASA contract NAS8-38249 (HETG) and SAO SV1-61010
(CXC) to MIT.",0109120v1
2001-09-10,A multivariate study of mass composition for simulated showers at the Auger South Observatory,"The output parameters from the ground array of the Auger South observatory,
were simulated for the typical instrumental and environmental conditions at its
Malarg\""ue site using the code sample-sim. Extensive air showers started by
photons, protons and iron nuclei at the top of the atmosphere were used as
triggers. The study utilized the air shower simulation code Aires with both
QGSJet and Sibyll hadronic interaction models. A total of 1850 showers were
used to produce more than 35,000 different ground events. We report here on the
results of a multivariate analysis approach, including principal component
analysis and neural networks, to the development of new primary composition
diagnostics.",0109140v1
2001-09-18,Inclinations and black hole masses of Seyfert 1 galaxies,"A tight correlation of black hole mass and central velocity dispersion has
been found recently for both active and quiescent galaxies. By applying this
correlation, we develop a simple method to derive the inclination angles for a
sample of 11 Seyfert 1 galaxies that have both measured central velocity
dispersions and black hole masses estimated by reverberation mapping. These
angles, with a mean value of 36 degree that agrees well with the result
obtained by fitting the iron K$\alpha$ lines of Seyfert 1s observed with ASCA,
provide further support to the orientation-dependent unification scheme of AGN.
A positive correlation of the inclinations with observed FWHMs of H$\beta$ line
and a possible anti-correlation with the nuclear radio-loudness have been
found. We conclude that more accurate knowledge on inclinations and broad line
region dynamics is needed to improve the black hole mass determination of AGN
with the reverberation mapping technique.",0109283v1
2001-09-19,Soft X-Ray Absorption by Fe$^{0+}$ to Fe$^{15+}$ in Active Galactic Nuclei,"A full set of calculations is presented for inner-shell n = 2 to 3
photoexcitation of the 16 iron charge states: Fe I through Fe XVI. The blend of
the numerous absorption lines arising from these excitations (mainly 2p - 3d)
forms an unresolved transition array (UTA), which has been recently identified
as a prominent feature between 16 - 17 \AA in the soft X-ray spectra of active
galactic nuclei (AGN). Despite the blending within charge-states, the ample
separation between the individual-ion features enables precise diagnostics of
the ionization range in the absorbing medium. Column density and turbulent
velocity diagnostics are also possible, albeit to a lesser accuracy. An
abbreviated set of atomic parameters useful for modeling the Fe 2p - 3d UTA is
given. It is shown that the effects of accompanying photoexcitation to higher
levels ($n \ge$ 4), as well as the associated photoionization edges, may also
be relevant to AGN spectra.",0109314v1
2001-09-21,The Chandra LETGS high resolution X-ray spectrum of the isolated neutron star RX J1856.5-3754,"We present the Chandra LETGS X-ray spectrum of the nearby (~60 pc) neutron
star RX J1856.5-3754. Detailed spectral analysis of the combined X-ray and
optical data rules out the nonmagnetic neutron star atmosphere models with
hydrogen, helium, iron and solar compositions. We also conclude that strongly
magnetized atmosphere models are unable to represent the data. The data can be
explained with a two-component blackbody model. The harder component with
temperature of kT_bb~63 eV and a radius R_bb~2.2 km of the emitting region well
fits the X-ray data and can be interpreted as radiation from a hot region on
the star's surface.",0109374v1
2001-09-28,Molybdenum Evidence for Inherited Planetary Scale Isotope Heterogeneity of the Protosolar Nebula,"Isotope anomalies provide important information about early solar system
evolution. Here we report molybdenum isotope abundances determined in samples
of various meteorite classes. There is no fractionation of molybdenum isotopes
in our sample set within 0.1 permil and no contribution from the extinct
radionuclide 97Tc at mass 97 (97Tc/92Mo<3E-6). Instead, we observe clear
anomalies in bulk iron meteorites, mesosiderites, pallasites, and chondrites
characterized by a coupled excess in p- and r- or a mirror deficit in s-process
nuclides (Mo-HL). This large scale isotope heterogeneity of the solar system
observed for molybdenum must have been inherited from the interstellar
environment where the sun was born, illustrating the concept of ``cosmic
chemical memory''. The presence of molybdenum anomalies is used to discuss the
filiation between planetesimals.",0109549v1
2001-10-08,Abundances and Kinematics of Field Stars II: Kinematics and Abundance Relationships,"As an investigation of the origin of ``$\alpha$-poor'' halo stars, we analyze
kinematic and abundance data for 73 intermediate metallicity stars ($-1 >$
[Fe/H] $\geq -2$) selected from Paper I of this series. We find evidence for a
connection between the kinematics and the enhancement of certain
element-to-iron ([X/Fe]) ratios in these stars. Statistically significant
correlations were found between [X/Fe] and galactic rest-frame velocities
(\vrf{}) for Na, Mg, Al, Si, Ca and Ni, with marginally significant
correlations existing for Ti and Y as well. We also find that the [X/Fe] ratios
for these elements all correlate with a similar level of significance with
[Na/Fe]. Finally, we compare the abundances of these halo stars against those
of stars in nearby dSph galaxies. We find significant differences between the
abundance ratios in the dSph stars and halo stars of similar metallicity. From
this result, it is unlikely that the halo stars in the solar neighborhood,
including even the ``$\alpha$-poor'' stars, were once members of disrupted dSph
galaxies similar to those studied to date.",0110164v1
2001-11-01,Extremely Weak Reflection Features in the X-ray Spectrum of XTE J1118+480: Possible Evidence for X-ray-Emitting Jets?,"We have simultaneously fit Chandra and RXTE spectra of the Galactic black
hole XTE J1118+480 with three models for X-ray reflection. We explored a range
of accretion disc ionizations (log(xi)=1-4; xi=L_X/nR^{2}) and iron abundances
(0.10-1.00). Our fits with the constant density ionized disc models of Ross &
Fabian indicate that less than 0.5 per cent (90 per cent confidence
upper-limit) of the observed flux is reflected. Fits with the ""pexrav"" of model
Magdziarz & Zdziarski indicate that the two-dimensional solid angle (Omega/2pi)
subtended by the disc relative to a central source of incident hard X-rays is
0.01 +0.06 -0.01. A combination of the high inclination (i=81 degrees),
Comptonization, and bulk velocities may each contribute to the low reflection
fractions we have measured. The results are also consistent with extended jets
being the source of the hard X-ray flux, as the disc would then represent a
small solid angle as seen from the emission region.",0111027v2
2001-11-02,Evidence for Accretion: High-Resolution X-ray Spectroscopy of the Classical T Tauri Star TW Hydrae,"We present high resolution X-ray spectra of the X-ray bright classical T
Tauri star, TW Hydrae, covering the wavelength range of 1.5-25 AA. The
differential emission measure derived from fluxes of temperature-sensitive
emission lines shows a plasma with a sharply peaked temperature distribution,
peaking at log T = 6.5. Abundance anomalies are apparent, with iron very
deficient relative to oxygen, while neon is enhanced relative to oxygen.
Density-sensitive line ratios of Ne IX and O VII indicate densities near log
n_e = 13. A flare with rapid (~1 ks) rise time was detected during our 48 ksec
observation; however, based on analysis of the emission-line spectrum during
quiescent and flaring states, the derived plasma parameters do not appear
strongly time-dependent. The inferred plasma temperature distribution and
densities are consistent with a model in which the bulk of the X-ray emission
from TW Hya is generated via mass accretion from its circumstellar disk.
Assuming accretion powers the X-ray emission, our results for log n_e suggest
an accretion rate of ~10^{-8} M_sun yr^{-1}.",0111049v1
2001-11-02,Disclosing the true nature of the Sy 2 galaxy NGC 3281: one more Compton-thick source,"We present the BeppoSAX broad-band X-ray spectrum of the Seyfert 2 galaxy NGC
3281. The source high-energy spectrum is characterized by the nuclear
transmitted component, with an absorbing column density of about 2 10^24 cm^-2,
while the MECS spectrum is reflection-dominated, with a prominent (EW about
0.5-1.2 keV) iron K_alpha emission line. The source is detected at only the 5
sigma significance level in the LECS band, because of the strong obscuration
which hampers at low energies the direct view of the active nucleus harbored in
NGC 3281. BeppoSAX results are consistent with the scenario where NGC 3281 is
inclined more than 60 degrees with respect to the line-of-sight. Combining the
N_H value obtained from the present X-ray analysis with the A_V measurement, a
N_H/A_V about 50 times the Galactic value is derived.",0111056v1
2001-11-15,Millions of Single Cloud Weak MgII Systems,"We report on a population of absorption systems selected by the presence of
very weak Mg II doublets. A sub-population of these systems are iron enriched
and have near solar metallicities. This would indicated advanced stages (i.e.
few Gyr) of in situ star formation within the absorbing structures. From
photoionization modeling, we infer low ionization fractions of f(HI/H)~0.01,
and gas densities of ~0.1 cm^-3. Since the maximum HI column densities are
\~10^17 cm^-2, the inferred cloud sizes are ~10 pc. From their redshift number
densities, this implies that their co-moving spatial density outnumbers normal
bright galaxies by a factor of a few million.",0111315v1
2001-11-21,Chandra Grating Observations of Seyfert 1 Galaxies,"We present new results from a Chandra HETG observation of NGC 5548 and give a
comparison of absorption and emission features found in other Seyfert 1
galaxies using Chandra grating observations. Deep soft X-ray edges are seen in
Mkn 509 and NGC 3783, consistent with ASCA data. In NGC 5548 and NGC 4501 the
edges are weak but consistent with the low column densities. We show that the
detection of a narrow, probably non-disk, component of the iron line is very
common. However, just as importantly, it is not detected in some cases. We show
the effect of removing this narrow component from the ASCA Fe-K line profile in
NGC 4151, revealing the underlying true shape of the relativistic Fe-K line
component.",0111428v1
2001-12-17,Spectral properties of the Narrow-Line Seyfert 1 Quasar PG1211+143,"We propose a theoretical model to explain the spectrum of the quasar
PG1211+143 emitted in the Optical/X-ray bands. In particular, we suggest that
the inner accretion disk may develop a warm, optically thick skin, which
produces a profound emission feature observed in the soft X-ray band. This is
well modelled with the Comptonized black body emission.
  The same warm, mildly ionized medium may also be responsible for the hard
X-ray reflection and the presence of the iron $K_{\alpha}$ line. However, in
our model it still remains an open question, whether the seed photons for
Comptonization come from the cold accretion disc or from the hotter plasma.
High resolution spectroscopy available through the Chandra and XMM data may
provide now an independent test of the physical conditions in the Comptonizing
and reflecting warm skin.",0112387v1
2002-01-24,Inner-shell 1s - 2p Soft X-ray Absorption Lines,"The HULLAC atomic code is used to compute wavelengths and oscillator
strengths for the 1s - np inner-shell absorption lines in Li-like to F-like
ions of neon, magnesium, aluminum, silicon, sulfur, argon, calcium, and iron.
Many of these lines are expected to be observed in Chandra and XMM-Newton
high-resolution X-ray spectra of active galaxies. The new atomic data are
incorporated in the ION code for spectral modeling of photoionized plasmas. The
calculated spectra are subsequently compared with the spectrum of NGC 3783 and
show very good agreement. The usefulness of these lines as diagnostics for the
ionization state, column densities, and velocities in line-of-sight
photoionized gas is called attention to.",0201416v1
2002-01-28,Theoretical Uncertainties in the Subgiant--Mass Age Relation and the Absolute Age of Omega Cen,"The theoretical uncertainties in the calibration of the relationship between
the subgiant mass and age in metal-poor stars are investigated using a Monte
Carlo approach. Assuming that the mass and iron abundance of a subgiant star
are known exactly, uncertainties in the input physics used to construct stellar
evolution models and isochrones lead to a Gaussian 1-sigma uncertainty of
+/-2.9% in the derived ages. The theoretical error budget is dominated by the
uncertainties in the calculated opacities.
  Observations of detached double lined eclipsing binary OGLEGC-17 in the
globular cluster Omega Cen have found that the primary is on the subgiant
branch with a mass of M = 0.809+/-0.012 M_sun and [Fe/H]= -2.29+/-0.15 (Kaluzny
et al. 2001). Combining the theoretical uncertainties with the observational
errors leads to an age for OGLEGC-17 of 11.10+/-0.67 Gyr. The one-sided, 95%
lower limit to the age of OGLEGC-17 is 10.06 Gyr, while the one-sided, 95%
upper limit is 12.27 Gyr.",0201443v1
2002-01-31,XMM-Newton EPIC observations of Her X-1,"We present spin-resolved X-ray data of the neutron star binary Her X-1. We
find evidence that the Iron line at 6.4 keV originates from the same location
as the blackbody X-ray component. The line width and energy varies over both
the spin period and the 35 day precession period. We also find that the
correlation between the soft and hard X-ray light curves varies over the 35 day
period.",0201526v1
2002-02-04,The s-process in rotating AGB stars,"We discuss the occurrence of the s-process during the radiative interpulse
phase of rotating AGB stars. Due to differential rotation, protons are mixed
into C12-rich layers after thermal pulses, in the course of the so called third
dredge up episode. We follow the time evolution of key isotope abundances in
the relevant layers with a post-processing code which includes time dependant
mixing and nucleosynthesis. In rotating AGB models, the mixing persists during
the entire interpulse phase due to the steep gradient of angular velocity at
the envelope-core interface. As the layers containing protons and C12, which
are formed this way, become hotter, a C13-pocket is formed in a natural way.
However, in this situation also N14 is formed and spread over the entire
C13-pocket. We include the neutron consuming N14(n,p) reaction in our network
and determine to what extent it reduces the production of trans-iron elements.
We propose that rotation may be responsible for the spread of efficiencies of
the C13 neutron source as required by observations.",0202067v1
2002-02-04,Discovery of complex narrow X-ray absorption features from the low-mass X-ray binary GX13+1 with XMM-Newton,"We report the detection of a complex of narrow X-ray absorption features from
the low-mass X-ray binary GX13+1 during 3 XMM-Newton observations in 2000 March
and April. The features are consistent with being due to resonant scattering of
the K_alpha and K_beta lines of He- and H-like iron (Fe xxv and Fe xxvi) and
H-like calcium (Ca xx) K_alpha. Only the Fe xxvi K_alpha line has been
previously observed from GX13+1. Due to the closeness in energy the Fe xxv and
Fe xxvi K_beta features may also be ascribed to Nixxvii and Nixxviii K_alpha,
respectively. We also find evidence for the presence of a deep (tau~0.2) Fe xxv
absorption edge at 8.83 keV. The equivalent widths of the lines do not show any
obvious variation on a timescale of a few days suggesting that the absorbing
material is a stable feature of the system and present during a range of
orbital phases.",0202077v1
2002-02-19,Atomic Processes in Planetary Nebulae,"A hot central star illuminating the surrounding ionized H II region usually
produces very rich atomic spectra resulting from basic atomic processes:
photoionization, electron-ion recombination, bound-bound radiative transitions,
and collisional excitation of ions. Precise diagnostics of nebular spectra
depend on accurate atomic parameters for these processes. Latest developments
in theoretical computations are described, especially under two international
collaborations known as the Opacity Project (OP) and the Iron Project (IP),
that have yielded accurate and large-scale data for photoionization cross
sections, transition probabilities, and collision strengths for electron impact
excitation of most astrophysically abundant ions. As an extension of the two
projects, a self-consistent and unified theoretical treatment of
photoionization and electron-ion recombination has been developed where both
the radiative and the dielectronic recombination processes are considered in an
unified manner. Results from the Ohio State atomic-astrophysics group, and from
the OP and IP collaborations, are presented. A description of the electronic
web-interactive database, TIPTOPBASE, with the OP and the IP data, and a
compilation of recommended data for effective collision strengths, is given.",0202343v1
2002-02-27,Long Term Spectral Variability of Seyfert Galaxies from RXTE Color-Flux Diagrams,"We present results from RXTE data obtained during a systematic monitoring
program of four Seyfert galaxies (NGC5548, NGC5506, MCG-6-30-15 and NGC4051).
We studied the variability of three hardness ratios derived from the light
curves in four energy bands. All the objects show similar spectral variations
in all ratios. In order to interpret the results we computed the hardness
ratios corresponding to a simple spectral model of a power law plus iron line
plus reflection component, considering two possibilities: a)variations with
constant line equivalent width and reflection parameter R and b) variations
with constant line and reflection flux. The overall, mean observed trends can
be explained by spectral slope variations and a constant flux Fe line and
reflection component, although the existence of a line component which is
variable on short time scales cannot be excluded. Finally, we find that the
data are not consistent with an increase of R with flux for individual sources,
indicating that, as a single source varies, softer spectra do not correspond to
larger R values.",0202498v1
2002-03-10,Mass Composition of Cosmic Rays in the Range 2 x 10^17 - 3 x 10^18 Measured with Haverah Park Array,"At the Haverah Park Array a number of air shower observables were measured
that are relevant to the determination of the mass composition of cosmic rays.
In this paper we discuss measurements of the risetime of signals in large area
water-Cherenkov detectors and of the lateral distribution function of the
water-Cherenkov signal. The former are used to demonstrate that the CORSIKA
code, using the QGSJET98 model, gives an adequate description of the data with
a low sensitivity, in this energy range, to assumptions about primary mass. By
contrast the lateral distribution is sufficiently well measured that there is
mass sensitivity. We argue that in the range 0.2-1.0 EeV the data are well
represented with a bi-modal composition of 34+-2 % protons and the rest iron.
We also discuss the systematic errors induced by the choice of hadronic model.",0203150v1
2002-03-13,Reprocessing of X-rays in AGN. I. Plane parallel geometry -- test of pressure equilibrium,"We present a model of the vertical stratification and the spectra of an
irradiated medium under the assumption of constant pressure. Such a solution
has properties intermediate between constant density models and hydrostatic
equilibrium models, and it may represent a flattened configuration of gas
clumps accreting onto the central black hole. Such a medium develops a hot
skin, thicker than hydrostatic models, but thinner than constant density
models, under comparable irradiation. The range of theoretical values of the
alpha_ox index is comparable to those from hydrostatic models and both are
close to the observed values for Seyfert galaxies but lower than in quasars.
The amount of X-ray Compton reflection is consistent with the observed range.
The characteristic property of the model is a frequently multicomponent iron K
alpha line.",0203202v1
2002-03-15,Chandra Observations of the Gravitational Potential Structure in Abell 1060,"We present results from a Chandra observation of Abell 1060, the nearby
cluster of galaxies. The ACIS-I image shows that the central cusp-like
structure, previously seen from PSPC, is caused mainly by an emission from the
central elliptical galaxy NGC 3311. We confirmed that the central region is
remarkably isothermal with a temperature of 3.2 keV, based on the spectral fits
for fine pixels. An extended region in the northeast of NGC 3311 indicates high
iron abundance. The surface brightness profile excluding the central galaxy,
NGC 3311, can be fitted only by a double beta model, with core radii about 40
and 140 kpc, out to a radius of about 200 kpc. This suggests that the
gravitational potential in Abell 1060 consists of 2 components.",0203244v1
2002-03-18,X-Ray Spectroscopy of Gamma-Ray Bursts,"Observational evidence of iron absorption and emission lines in X-ray spectra
of Gamma-Ray Bursts is quite compelling. I will briefly review the results,
summarize different models and describe the connection with massive progenitors
in star-forming regions implied by these results. This link is also supported
by measurements of the X-ray absorbing gas in several GRB's, with column
density consistent with that of Giant Molecular Clouds harbouring
star-formation in our Galaxy, as well as by evidences gathered in other
wavelengths. However, the volume density inferred by the fireball-jet model is
much lower than typical of a GMC, and I will confront this with the alternative
explanation of fireball expansion in a high dense medium, outlining the
problems that both models have at present. Finally I will briefly summarize
some results on dark GRB's, and describe the prospects of high resolution X-ray
spectroscopy in getting closer to the central environment of GRB, and far in
the Early Universe by using GRB as beacons to probe star and galaxy formation.",0203275v1
2002-03-20,Lyman-break galaxies: are they young spheroids?,"We have compared the results from a model for the chemical evolution of an
elliptical galaxy with initial luminous mass of 2x10^10 M_sun and effective
radius of 2 kpc with the recent abundance determinations for the Lyman-break
galaxy MS 1512-cB58 at a redshift z=2.7276. After correcting the iron abundance
determination for the presence of dust we concluded that the observed [Si/Fe],
[Mg/Fe], [N/Fe] are consistent with our model when a galactic age between 20
and 35 Myr is assumed. Moreover, the [N/O] ratio also suggests the same age.
This age is in very good agreement with other independent studies based on the
analysis of the spectral energy distribution suggesting that this object is
younger than 35 Myr. Therefore, we suggest that MS 1512-cB58 is a truly young
normal elliptical galaxy experiencing its main episode of star formation and
galactic wind.",0203329v1
2002-03-22,Iron abundance in HII regions,"Optical CCD spectra are used to determine the Fe abundances at several
positions inside seven bright Galactic HII regions. The observed [FeIII] line
ratios are compared with the predictions of different sets of collision
strengths and transition probabilities for this ion to select the atomic data
providing the best fit to the observations. The values found for the Fe++ and
Fe+ abundances, along with ionization correction factors for the contribution
of Fe3+, obtained from available grids of photoionized models, imply that the
Fe/O ratio in the ionized gas is between 2% and 30% of solar. The Fe abundances
derived for each area are correlated both with the degree of ionization and the
colour excess. A possible explanation is suggested, namely the presence of a
population of small grains, probably originating from the fragmentation of
larger grains. These small grains would release Fe atoms into the gas after the
absorption of energetic photons; the small grains surviving this destruction
process would be swept out of the ionized region by the action of radiation
pressure or stellar winds. An indication of a further and more efficient
destruction agent is given by the high Fe abundance derived for a position
sampling the optical jet H399 in M20, where dust destruction due to shock waves
has presumably taken place.",0203394v1
2002-03-26,New Members of the Cluster Family in Nearby Lenticulars,"Using spectra obtained with the Keck I telescope we have demonstrated
conclusively that the faint (23<V<24 mag.) and unusually extended objects we
discovered in HST images of the lenticular galaxies, NGC 1023 and NGC 3384, are
star clusters associated with their respective galaxies. In the case of NGC
1023 we were further able to establish that these objects are old (>7--8 Gyr),
moderately metal-rich ([Fe/H]=-0.58+/-0.24) and, having a system rotation curve
which is very similar to that of the host galaxy, are associated with the
lenticular disk. Alpha-element to iron abundance ratios are highly supersolar
with [alpha/Fe] between +0.3 and +0.6. With moderately high metallicities and
luminosities, and effective radii in the range 7--15 pc (compared to the 2--3
pc sizes typical of normal globular and open clusters), this population of
clusters has no known analog in the Milky Way or elsewhere in the Local Group.",0203454v2
2002-04-10,The broad band X-ray spectrum of the black hole candidate GRS1758-258,"We present the results of a BeppoSAX observation of the black hole candidate
GRS1758-258 carried out in 1997, while the source was in its low/hard state.
The X-ray spectrum, simultaneously observed over the broad energy range from
0.1 to 200 keV, can be well described by a Comptonized emission model with
electron temperature kT_e = 31.4 keV and optical depth of 4.0 (spherical
geometry), although a cut-off power-law and a reflection model cannot be
excluded. Additionally, a broad iron line at 6.4 keV with equivalent width EW =
67 eV has been marginally detected. The 0.1-200 keV luminosity is 1.4x10^37
erg/s for an assumed distance of 8 kpc. The soft and hard luminosities are such
that the source falls inside the so-called ""burster box"". No evidence for a
soft excess is present.",0204176v1
2002-05-02,An unusual iron Lo-BAL quasar detected by ISOCAM,"We report the discovery of an unusual low--ionization broad absorption line
quasar at z=1.776 which exhibits absorption lines from many excited states of
Feii. This member of the rare class of 'FeLoBAL' quasars was serendipitously
found in a mid-infrared (MIR) survey of distant clusters carried out with the
ISOCAM camera. ISO J005645.1-273816 has a high MIR to UV luminosity ratio,
suggesting a strong dust obscuration plus emission from very hot dust. This
characteristic makes MIR surveys particularly efficient at detecting LoBAL
quasars.",0205022v1
2002-05-17,Rotation and activity in the solar-metallicity open cluster NGC2516,"We report new measures of radial velocities and rotation rates (v sin i) for
51 F and early-G stars in the open cluster NGC2516, and combine these with
previously published data. From high signal-to-noise spectra of two stars, we
show that NGC2516 has a relative iron abundance with respect to the Pleiades of
delta([Fe/H])= +0.04 +/- 0.07 at the canonical reddening of E(B - V) = 0.12, in
contrast to previous photometric studies that placed the cluster 0.2 to 0.4 dex
below solar. We construct a color-magnitude diagram based on radial velocity
members, and explore the sensitivity of photometric determinations of the
metallicity and distance to assumed values of the reddening. For a metal
abundance near solar, the Hipparcos distance to NGC2516 is probably
underestimated. Finally, we show that the distribution of rotation rates and
X-ray emission does not differ greatly from that of the Pleiades, when
allowance is made for the somewhat older age of NGC2516.",0205300v1
2002-06-10,On the formation of inner vacuum gaps in radio pulsars,"The problem of formation of the Ruderman-Sutherland type inner vacuum gap in
neutron stars with ${\bf\Omega}\cdot{\bf B}<0$ is considered. It is argued by
means of the condition $T_i/T_s>1$ (where $T_i$ is the critical temperature
above which $^{56}_{26}$Fe ions will not be bound at the surface and $T_s$ is
the actual temperature of the polar cap surface heated by the back-flow of
relativistic electrons) that the inner vacuum gap can form, provided that the
actual surface magnetic field is extremaly strong ($B_s\gtrsim 10^{13}$ G) and
curved (${\cal R}<10^6$ cm), irrespective of the value of dipolar component
measured from the pulsar spin down rate. Calculations are carried out for
pulsars with drifting subpulses and/or periodic intensity modulations, in which
the existence of the quasi steady vacuum gap discharging via ${\bf E}\times{\bf
B}$ drifting sparks is almost unavoidable. Using different pair-production
mechanisms and different estimates of the cohesive energies of surface iron
ions, we show that it is easier to form the vacuum gap controlled by the
resonant inverse Compton scaterring seed photons than by the curvature
radiation seed photons.",0206141v1
2002-06-11,Multiple X-ray reflection from ionized slabs,"Multiple reflection of X-rays may be important when an accretion disc and its
hot corona have a complicated geometry, or if returning radiation due to
gravitational light bending is important, or in emission from a funnel such as
proposed in some gamma-ray burst models. We simulate the effects of multiple
reflection by modifying the boundary condition for an X-ray illuminated slab.
Multiple reflection makes the soft X-ray spectrum steeper (softer) and
strengthens broad emission and absorption features, especially the K-shell
features of iron. This may be important in explaining the spectra of sources
such as the Narrow-Line Seyfert 1 galaxy 1H0707-495.",0206170v1
2002-07-01,XMM-Newton observations of MR Vel/RX J0925.7-4758,"We report on XMM-Newton observations of the galactic supersoft X-ray source
RX J0925.7-4758. The RGS spectrum exhibits a wealth of spectral features from
iron and oxygen. XMM-Newton data confirm the finding of previous Chandra
HETGS/MEG observations that NLTE models of hot white dwarf atmospheres fail to
represent the complex spectrum. There are clear evidences for P Cygni profiles
with wind velocities of up to 2000 km/s. Small flux variations with time scales
larger than 1000s are present. The strongest power is at ~ 0.21d, a period
close to that seen in V band optical light curves. A detailed analysis of the
associated changes in the RGS and EPIC pn spectra hint at a mostly grey
mechanism suggesting a variation of the visibility of the white dwarf due to
occulting material in the accretion disk. Finally, we detect radial velocity
changes of 173 +/- 47 km/s between two RGS observations obtained half an
orbital cycle apart. The amplitude of the RGS velocity shift is consistent with
that of the optical He II 4686 and thus supports the idea that most of the He
II optical line emission arises from the accretion disk.",0207004v1
2002-06-29,Discovery of an ionized Fe-K edge in the z=3.91 Broad Absorption Line Quasar APM 08279+5255 with XMM-Newton,"Recent XMM-Newton observations of the high-redshift, lensed, broad absorption
line (BAL) quasi-stellar object APM 08279+5255, one of the most luminous
objects in the universe, allowed the detection of a high column density
absorber ($N_H \approx 10^{23}$ cm$^{-2}$) in the form of a K-shell absorption
edge of significantly ionized iron (Fe XV - XVIII) and corresponding ionized
lower-energy absorption. Our findings confirm a basic prediction of
phenomenological geometry models for the BAL outflow and can constrain the size
of the absorbing region. The Fe/O abundance of the absorbing material is
significantly higher than solar (Fe/O = 2-5), giving interesting constraints on
the gas enrichment history in the early Universe.",0207005v1
2002-07-12,Reflection at large distance from the central engine in Seyfert 1s,"We consider the possibility that most of the reflection component, observed
in the hard X-ray spectra of Seyfert galaxies, could be formed on an extended
medium, at large distance from the central source of primary radiation (e.g. on
a torus). Then, the reflector cannot respond to the rapid fluctuations of the
primary source. The observed reflected flux is controlled by the time-averaged
primary spectrum rather than the instantaneous (observed) one. We show that
this effect strongly influences the spectral fit parameters derived under the
assumption of a reflection component consistent with the primary radiation. We
find that a pivoting primary power-law spectrum with a nearly constant
Comptonised luminosity may account for the reported correlation between the
reflection amplitude R and the spectral index Gamma, and simultaneously
produces an iron line EW that is nearly independent of Gamma. We emphasize the
effects of the modelling of the primary component on the determination of the
reflection amplitude, and show that in NGC 5548, when these effects are taken
into account, the RXTE data are consistent with the reflection features being
produced mainly at large distance from the central source.",0207269v1
2002-07-15,On the Structure of the Iron K-Edge,"It is shown that the commonly held view of a sharp Fe K edge must be modified
if the decay pathways of the series of resonances converging to the K
thresholds are adequately taken into account. These resonances display damped
Lorentzian profiles of nearly constant widths that are smeared to impose
continuity across the threshold. By modeling the effects of K damping on
opacities, it is found that the broadening of the K edge grows with the
ionization level of the plasma and that the appearance at high ionization of a
localized absorption feature at 7.2 keV is identified as the K-beta unresolved
transition array.",0207324v2
2002-07-18,Mrk 1014: An AGN Dominated ULIRG at X-rays,"In this paper we report on an XMM-Newton observation of the ultraluminous
infrared QSO Mrk 1014. The X-ray observation reveals a power-law dominated
(photon index of about 2.2) spectrum with a slight excess in the soft energy
range. AGN and starburst emission models fit the soft excess emission equally
well, however, the most plausible explanation is an AGN component as the
starburst model parameter, temperature and luminosity, appear physically
unrealistic. The mean luminosity of Mrk 1014 is about 2 times 10^44 erg s^-1.
We have also observed excess emission at energies greater than 5 keV. This
feature could be attributed to a broadened and redshifted iron complex, but
deeper observations are required to constrain its origin. The light curve shows
small scale variability over the 11 ks observation. There is no evidence of
intrinsic absorption in Mrk 1014. The X-ray observations support the notion of
an AGN dominated central engine. We establish the need for a longer observation
to constrain more precisely the nature of the X-ray components.",0207378v1
2002-08-01,"Chemical Composition of the Carbon-rich, Extremely Metal-Poor Star CS 29498--043: A New Class of Extremely Metal-Poor Stars with Excesses of Magnesium and Silicon","We analyze a high-resolution, high signal-to-noise spectrum of the
carbon-rich, extremely metal-poor star CS29498-043, obtained with the Subaru
Telescope High Dispersion Spectrograph. We find its iron abundance is extremely
low ([Fe/H] = -3.7), placing it among the few stars known with [Fe/H] < -3.5,
while Mg and Si are significantly overabundant ([Mg/Fe] = +1.8, and [Si/Fe] =
+1.1) compared with stars of similar metallicity without carbon excess.
Overabundances of N and Al were also found. These characteristics are similar
to the carbon-rich, extremely metal-poor star CS22949-037. Though the sample is
small, our discovery of CS29498-043 suggests the existence of a class of
extremely metal-poor stars with large excesses of C, N, Mg, and Si.",0208019v1
2002-08-02,Using Cepheids to determine the galactic abundance gradient. III.First results for the outer disc,"As a continuation of our previous work, which concerned the radial abundance
distribution in the galactic disc over the distances 4-10 kpc this paper
presents the first results on the metallicicty in the outer disc (RG > 10 kpc).
Based on high-resolution spectra obtained for 19 distant Cepheids we sampled
galactocentric distances from 10 to 12 kpc. Combined with the results of our
previous work on the inner and middle parts of the galactic disc, the present
data enable one to study the structure of the radial abundance distribution
over a large baseline. In particular, we find indications of a discontinuity in
the radial abundance distribution for iron as well as a number of the other
elements. The discontinuity is seen at a galactocentric distance RG = 10 kpc.
This finding supports the results reported earlier by Twarog et al. (1997).",0208056v1
2002-08-09,Elemental Abundances and Ionization States within the Local Interstellar Cloud Derived from HST and FUSE Observations of the Capella Line of Sight,"We use ultraviolet spectra of Capella from the Hubble Space Telescope (HST)
and Far Ultraviolet Spectroscopic Explorer (FUSE) satellites to study
interstellar absorption lines from the Local Interstellar Cloud (LIC).
Measurements of these lines are used to empirically determine the ionization
states of carbon, nitrogen, and silicon in the LIC, for comparison with the
predictions of theoretical photoionization models. We find that the observed
ionization states are consistent with previously published photoionization
predictions. Total abundances are determined for the elements mentioned above,
and others, for comparison with solar abundances. Magnesium, aluminum, silicon,
and iron are all depleted by at least a factor of 10 toward Capella. The
abundances of carbon, nitrogen, and oxygen are essentially solar, although the
error bars are large enough to also allow depletions of about a factor of 2 for
these elements.",0208214v1
2002-08-25,A new measurement of zinc metallicity in a DLA at z=3.35,"We present chemical abundance measurements in the z_abs=3.35045 Damped
Lyman-alpha (DLA) system observed in the UVES spectrum of the BAL quasar BR
1117-1329. We measure a neutral hydrogen column density N(HI)=6.9+/-1.7*10^{20}
atoms/cm2 and derive mean abundances relative to solar: [Si/H] = -1.26+/-0.13,
[Fe/H]=-1.51+/-0.13, [Ni/H]=-1.57+/-0.13, [Cr/H]=-1.36+/-0.13,
[Zn/H]=-1.18+/-0.13, [Al/H]>-1.25, [O/H]>-1.25 and [N/H]<-2.24. This is the
third measurement of Zn, an element mildly depleted onto dust grain, at
z_abs>3. The iron to zinc and chromium to zinc ratios, [Fe/Zn]=-0.33+/-0.05 and
[Cr/Zn]=-0.18+/-0.05 demonstrate that the absorber has a low dust content. The
nitrogen ratio [N/Si]<-0.98 suggests that the ``secondary'' N production
process is taking place in this DLA. Finally, this absorber does not seem to
present a convincing alpha-enhancement as shown by the alpha over Fe-peak
element ratios: [Si/Fe]=0.25+/-0.06, [Si/Cr]=0.10+/-0.06 and
[Si/Zn]=-0.08+/-0.06.",0208450v1
2002-09-05,X-ray spectroscopy of Eta Carinae with XMM-Newton,"We present XMM-Newton observations of the luminous star Eta Carinae,
including a high resolution soft X-ray spectrum of the surrounding nebula
obtained with the Reflection Grating Spectrometer. The EPIC image of the field
around Eta Car shows many early-type stars and diffuse emission from hot,
shocked gas. The EPIC spectrum of the star is similar to that observed in
previous X-ray observations, and requires two temperature components. The RGS
spectrum of the surrounding nebula shows K-shell emission lines from hydrogen-
and helium-like nitrogen and neon and L-shell lines from iron, but little or no
emission from oxygen. The observed emission lines are not consistent with a
single temperature, but the range of temperatures observed is not large,
spanning ~0.15-0.6 keV. We obtain upper limits for oxygen line emission and
derive a lower limit of N/O > 9. This is consistent with previous abundance
determinations for the ejecta of Eta Car, and with theoretical models for the
evolution of massive, rotating stars.",0209087v2
2002-09-11,Ultra-High Energy Heavy Nuclei Propagation in Extragalactic Magnetic Fields,"We extend existing work on the propagation of ultra-high energy cosmic rays
in extragalactic magnetic fields to a possible component of heavy nuclei,
taking into account photodisintegration, pion production, and creation of e+e-
pairs. We focus on the influence of the magnetic field on the spectrum and
chemical composition of observed ultra-high energy cosmic rays. We apply our
simulations to the scenarios proposed by Anchordoqui et al, in which Iron
nuclei are accelerated in nearby starburst galaxies, and show that it is in
marginal agreement with the data. We also show that it is highly unlikely to
detect He nuclei from M87 at the highest energies observed $\sim3 10^{20} $eV
as required for the scenario of Ahn et al. in which the highest energy cosmic
rays originate from M87 and are deflected in a Parker spiral Galactic magnetic
field.",0209192v1
2002-09-12,A Chandra observation of the H2O megamaser IC2560,"A short Chandra ACIS-S observation of the Seyfert 2 galaxy IC 2560, which
hosts a luminous nuclear water megamaser, shows: 1) the X-ray emission is
extended; 2) the X-ray spectrum shows emission features in the soft (E<2 keV)
X-ray band; this is the major component of the extended emission; and 3) a very
strong (EW~3.6 keV) iron K line at 6.4 keV on a flat continuum. This last
feature clearly indicates that the X-ray source is hidden behind Compton-thick
obscuration, so that the intrinsic hard X-ray luminosity must be much higher
than observed, probably close to ~3e42 erg/s. We briefly discuss the
implications for powering of the maser emission and the central source.",0209245v1
2002-10-08,Spectral Features and Masses in the PeV Region,"An analysis is made of the masses and spectral features for cosmic rays in
the PeV region, insofar as they have a bearing on the problem of the
interaction of cosmic ray particles. In our Single Source Model we identified
two 'peaks' seen in a summary of the world's data on primary spectra, and
claimed that they are probably due to oxygen and iron nuclei from a local,
recent supernova. In the present work we examine other possible mass
assignments. We conclude that of the other possibilities only Helium and Oxygen
(instead of O and Fe) has much chance of success; the original suggestion is
still preferred, however. Concerning our location with respect to the SNR
shell, the analysis suggests that we are close to it - probably just inside.",0210192v1
2002-10-18,The Chemistry of Extragalactic Globular Clusters,"We present preliminary results of VLT/FORS spectroscopy of globular clusters
in nearby early-type galaxies. Our project aims at studying the chemistry and
determine the ages of globular cluster (sub-)populations. First results
indicate that the different galaxies host from little to significant
intermediate-age populations, and that the latter have alpha-element over iron
ratios closer to solar than the old population that show an alpha-element
enhancement similar to the diffuse stellar light.",0210419v1
2002-10-21,Globular Clusters in nearby Galaxy Cluster,"The discovery of a large population of intra-cluster star clusters in the
central region of the Hydra I and Centaurus galaxy clusters is presented. Based
on deep VLT photometry (V,I), many star clusters have been identified not only
around the early-type galaxies, but also in the intra-cluster field, as far as
250 kpc from the galaxy centres. These intra-cluster globulars are
predominantly blue, with a siginificant fraction being even bluer than the
metal-poor halo clusters around massive galaxies. When interpreted as a
metallicity effect they would have iron abundances around [Fe/H] = -2 dex.
However, they might also be relatively young clusters which could have formed
in tidal tails during recent interactions of the central galaxies.",0210466v1
2002-11-11,Stationary models of relativistic magnetohydrodynamic jets,"Highly relativistic jets are most probably driven by strong magnetic fields
and are launched from the accretion disk surrounding a central black hole. In
this paper we review some of our recent results considering the two-dimensional
magnetic field structure and the dynamics of collimating relativistic jets.
Applying the stationarity assumption enables us to calculate global solutions
of the relevant MHD equations. We discuss solutions of the Grad-Shafranov
equation obtained in a general relativistic context applying the 3+1 formalism
for Kerr geometry. These solutions extend from the inner light surface around
the Kerr black hole to the asymptotic regime of a cylindrically collimated jet
with a finite radius. In a further step, we include differential rotation of
the foot points of the field lines. Considering the general relativistic MHD
wind equation, we investigate the dynamics of the collimating jet, in
particular the effects of Kerr metric on the acceleration. Temperature and
density follow a power law. Having at hand a relativistic MHD jet solution, we
calculate the thermal optically thin X-ray spectrum for the innermost hot part
of the jet. Doppler shift and boosting is taken into account. For microquasars
we obtain a jet X-ray luminosity 10^33 erg/s. Iron emission lines are clearly
visible.",0211233v1
2002-11-20,Quiet Sun magnetic fields at high spatial resolution,"We present spectro-polarimetric observations of Inter-Network magnetic fields
at the solar disk center. A Fabry-Perot spectrometer was used to scan the two
Fe I lines at 6301.5 A and 6302.5 A. High spatial resolution (0.5"")
magnetograms were obtained after speckle reconstruction. The patches with
magnetic fields above noise cover approximately 45% of the observed area. Such
large coverage renders a mean unsigned magnetic flux density of some 20 G (or
20 Mx/cm^2), which exceeds all previous measurements. Magnetic signals occur
predominantly in intergranular spaces. The systematic difference between the
flux densities measured in the two iron lines leads to the conclusion that,
typically, we detect structures with intrinsic field strengths larger than 1kG
occupying only 2% of the surface.",0211454v1
2002-12-16,Status of the KASCADE-Grande Experiment,"The status and capabilities of the KASCADE-Grande extensive air shower
experiment are presented. The installation is located at Forschungszentrum
Karlsruhe and comprises a large collecting area (0.5 km^2) electromagnetic
array (Grande) operated jointly with the existing KASCADE detectors.
KASCADE-Grande will cover the primary energy range 10^16 eV < E_0 < 10^18 eV
overlapping with KASCADE around 10^16 eV, thus providing continuous information
on the primary energy and mass of cosmic rays from 3x10^14 eV up to 10^18 eV.
The major goal of the measurements is the unambiguous observation of the``iron
knee'' expected in the cosmic ray spectrum at E_k^{Fe} ~ 10^17 eV.",0212347v1
2003-01-09,"An XMM-Newton observation of the Narrow Line Seyfert 1 Galaxy, Markarian 896","XMM-Newton observations of the NLS1 Markarian 896 are presented. Over the
2-10 keV band, an iron emission line, close to 6.4 keV, is seen. The line is
just resolved and has an equivalent width of ~170 eV. The broad-band spectrum
is well modelled by a power law slope of gamma ~ 2.03, together with two
blackbody components to fit the soft X-ray excess. Using a more physical
two-temperature Comptonisation model, a good fit is obtained for an input
photon distribution of kT ~ 60eV and Comptonising electron temperatures of ~0.3
and 200 keV. The soft excess cannot be explained purely through the
reprocessing of a hard X-ray continuum by an ionised disc reflector.",0301152v1
2003-01-17,On the Progenitor of Supernova 2001du in NGC 1365,"Hubble Space Telescope (HST) WFPC2 archival images obtained years prior to
the explosion of the Type II-plateau supernova (SN) 2001du in NGC 1365
previously have been analyzed to isolate the progenitor star. The SN site was
located using precise astrometry applied to the HST images, with significant
uncertainty, leaving three possible progenitor candidates. Images of the fading
SN have recently become publicly available in the HST archive, allowing us to
pinpoint the SN's exact location on the pre-explosion images. We show that the
SN occurred in very close proximity to one of the blue candidate stars, but we
argue that this star is not the actual progenitor. Instead, the progenitor was
not detected on the pre-SN images, and we constrain the progenitor's mass to be
less than 13 (+7, -4) Msuns. This is consistent with previous constraints on
the progenitor masses of other Type II-plateau supernovae (SNe), suggesting
that such SNe arise from the iron core collapse of massive stars at the lower
extreme of the possible mass range.",0301346v2
2003-01-17,"Supernovae, Gamma-Ray Bursts, and Stellar Rotation","One of the most dramatic possible consequences of stellar rotation is its
influence on stellar death, particularly of massive stars. If the angular
momentum of the iron core when it collapses is such as to produce a neutron
star with a period of 5 ms or less, rotation will have important consequences
for the supernova explosion mechanism. Still shorter periods, corresponding to
a neutron star rotating at break up, are required for the progenitors of
gamma-ray bursts (GRBs). Current stellar models, while providing an excess of
angular momentum to pulsars, still fall short of what is needed to make GRBs.
The possibility of slowing young neutron stars in ordinary supernovae by a
combination of neutrino-powered winds and the propeller mechanism is discussed.
The fall back of slowly moving ejecta during the first day of the supernova may
be critical. GRBs, on the other hand, probably require stellar mergers for
their production and perhaps less efficient mass loss and magnetic torques than
estimated thus far.",0301373v1
2003-01-27,The nature of the absorbing torus in compact Radio Galaxies,"We present BeppoSAX observations of the two radio galaxies PKS 1934-63 and S5
1946+708. Strong Iron Kalpha lines are detected in both objects indicating that
the two sources are absorbed by column densities higher than 10^24 cm^(-2).
  Combining radio continuum, HI absorption and X-ray data we can constrain the
physical state and the dimensions of the absorber. We find that the putative
obscuring torus is molecular and located at a distance higher than 20 pc from
the center in S5 1946+70. In PKS 1934-63 no radio nucleus has been observed. If
this is due to free-free absorption a radius of only a few pc is inferred.
Since the Kalpha lines have been detected only at 90% confidence, we also
discuss the implications if they would be not as strong as found from our data.
  From our results it appears that the combination of hard X-ray data and
spatially resolved HI absorption measurements provides a powerful diagnostic
for conditions in the absorbing ``torus''.",0301522v1
2003-02-07,Parallel Universes,"I survey physics theories involving parallel universes, which form a natural
four-level hierarchy of multiverses allowing progressively greater diversity.
  Level I: A generic prediction of inflation is an infinite ergodic universe,
which contains Hubble volumes realizing all initial conditions - including an
identical copy of you about 10^{10^29} meters away.
  Level II: In chaotic inflation, other thermalized regions may have different
effective physical constants, dimensionality and particle content.
  Level III: In unitary quantum mechanics, other branches of the wavefunction
add nothing qualitatively new, which is ironic given that this level has
historically been the most controversial.
  Level IV: Other mathematical structures give different fundamental equations
of physics. The key question is not whether parallel universes exist (Level I
is the uncontroversial cosmological concordance model), but how many levels
there are. I discuss how multiverse models can be falsified and argue that
there is a severe ""measure problem"" that must be solved to make testable
predictions at levels II-IV.",0302131v1
2003-02-11,A search for X-ray variability in the open cluster NGC 2516,"We present the results of a search for X-ray variability in the galactic open
cluster NGC 2516. This cluster has been observed on 8 occasions using
XMM-Newton making it an excellent target for such a study. We find 4 sources
which show significant variability, implying the detection of one significantly
variable source every 25ksec. All sources exhibit spectra which can be fitted
using an absorbed one or two temperature thermal plasma model. The brightest of
these flares also show a prominent Iron line near ~7.0keV. All 4 sources lie
near the observed main sequence of NGC 2516 suggesting they are cluster
members. We propose that at least 3 of the 4 objects are RS CVn systems. We
compare the properties of the brightest flare with those of solar flares.",0302200v1
2003-02-28,X-ray spectral evolution of low-mass X-ray binary GX 349+2,"We present the results of a systematic investigation of spectral evolution in
the Z source GX 349+2, using data obtained during 1998 with
Proportional-Counter-Array (PCA) on-board the RXTE satellite. The source traced
a extended normal branch (NB) and flaring branch (FB) in the color-color
diagram (CD) and hardness-intensity diagram (HID) during these observations.
The spectra at different positions of Z-track were best fitted by a model
consisting of a disk blackbody and a comptonized spectrum. A broad (gaussian)
iron line at $\sim 6.7$ keV is also required to improve the fit. The spectral
parameters showed a systematic and significant variation with the position
along the Z-track. The evolution in spectral parameters is discussed in the
view of increasing mass accretion rate scenario, proposed to explain the motion
of Z sources in the CD and HID.",0302581v2
2003-03-18,Iron Emission in z~6 QSOs,"We have obtained low-resolution near infrared spectra of three QSOs at 5.7 <
z < 6.3 using the NICMOS instrument of the Hubble Space Telescope. The spectra
cover the rest-frame ultraviolet emission of the objects between lambda_rest ~
1600A - 2800A. The Fe II emission-line complex at 2500A is clearly detected in
two of the objects, and possibly detected in the third. The strength of this
complex and the ratio of its integrated flux to that of Mg II lambda 2800 are
comparable to values measured for QSOs at lower redshifts, and are consistent
with Fe/Mg abundance ratios near or above the solar value. There thus appears
to be no evolution of QSO metallicity to z~6. Our results suggest that massive,
chemically enriched galaxies formed within 1 Gyr of the Big Bang. If this
chemical enrichment was produced by Type Ia supernovae, then the progenitor
stars formed at z ~ 20 +/- 10, in agreement with recent estimates based on the
cosmic microwave background. These results also support models of an
evolutionary link between star formation, the growth of supermassive black
holes and nuclear activity.",0303424v1
2003-03-19,Absorption spectra of Fe L-lines in Seyfert 1 galaxies,"Absorption L-lines of iron ions are observed, in absorption, in spectra of
Seyfert 1 galaxies by the new generation of X-ray satellites: Chandra (NASA)
and XMM-Newton (ESA). Lines associated to Fe23+ to Fe17+ are well resolved.
Whereas, those corresponding to Fe16+ to Fe6+ are unresolved. Forbidden
transitions of the Fe16+ to Fe6+ ions were previously observed, for the same
objects, in the visible and infra-red regions, showing that the plasma had a
low density. To interpret X-ray, visible and infra-red data, astrophysical
models assume an extended absorbing medium of very low density surrounding an
intense X-ray source. We have calculated atomic data (wavelengths, radiative
and autoionization rates) for n=2 to n'=3-4 transitions and used them to
construct refined synthetic spectra of the unresolved part of the L-line
spectra.",0303435v1
2003-03-20,A grid of synthetic ionizing spectra for very hot compact stars from NLTE model atmospheres,"The precise analysis of properties of planetary nebulae is strongly dependent
on good models for the stellar ionizing spectrum. Observations in the UV -
X-ray wavelength range as well as NLTE model atmosphere calculations of spectra
of their exciting stars have shown that neither blackbody fluxes nor ""standard""
NLTE atmosphere models which are composed out of hydrogen and helium only are
good approximations. Strong differences between synthetic spectra from these
compared to observed spectra at energies higher than 54 eV (He II ground state)
can be ascribed to the neglect of metal-line blanketing.
  Realistic modeling of the emergent fluxes of hot stars in the UV - X-ray
wavelength range requires metal-line blanketed NLTE model atmospheres which
include all elements from hydrogen up to the iron-group. For this purpose, we
present a grid (solar and halo abundance ratios) of metal-line blanketed NLTE
model atmosphere fluxes which covers the parameter range of central stars of
planetary nebulae.",0303464v1
2003-03-28,The properties of the absorbing and line emitting material in IGR J16318-4848,"We have performed a detailed analysis of the XMM-Newton observation of IGR
J16318-4848, to study the properties of the matter responsible for the
obscuration and for the emission of Fe and Ni lines. Even if the line of sight
material has a column density of about 2x10^24 cm^-2, from the Fe Kalpha line
EW and Compton Shoulder we argue that the matter should have an average column
density of a few x10^23 cm^-2, along with a covering factor of about 0.1-0.2.
The iron Kalpha line varies on time scales as short as 1000 s, implying a size
of the emitting region smaller than about 3x10^13 cm. The flux of the line
roughly follows the variations of the continuum, but not exactly, suggesting a
variation of the geometrical properties of the emitting region on similar time
scales.",0303626v1
2003-04-02,Binary Blue Metal-Poor Stars: Evidence for AGB Mass Transfer,"We present new abundance analyses of six blue metal-poor (BMP) stars with
very low iron abundances ([Fe/H] < -2), based on new high resolution echelle
spectra. Three are spectroscopic binaries and three have constant radial
velocities. The chemical compositions of these two groups are very different,
as the binary BMP stars have large enhancements of carbon and neutron-capture
elements that are products of s-process nucleosynthesis. One star, CS
29497-030, has an extreme enhancement of lead, [Pb/Fe] = +3.7, the largest
abundance in any star yet discovered. It probably also has an oxygen
overabundance compared to the other BMP stars of our sample. The binary BMP
stars must have attained their status via mass transfer during the asymptotic
giant branch (AGB) evolutions of their companion stars, which are now unseen
and most likely are compact objects. We have not found any examples of AGB mass
transfer among BMP binaries with [Fe/H] > -2.",0304064v1
2003-04-03,Induced Formation of Primordial Low-Mass Stars,"We show that the explosion of the first supernovae can trigger low-mass star
formation via gravitational fragmentation of the supernova-driven gas shell. If
the shell mass does not exceed the host galaxy gas mass, all explosions with
energies E_SN > 10^{51} erg can lead to shell fragmentation. However, the
minimum ambient density required to induce such fragmentation is much larger,
n_0 > 300 cm^{-3}, for Type II supernovae than for pair-instability ones, which
can induce star formation even at lower ambient densities. The typical mass of
the unstable fragments is 10^{4-7} Msun; their density is in the range
110-6x10^7 cm{-3}. Fragments have a metallicity strictly lower than 10^{-2.6}
Zsun and large values of the gravitational-to-pressure force ratio f ~ 8. Based
on these findings, we conclude that the second generation of stars produced by
such self-propagating star formation is predominantly constituted by low-mass,
long-living, extremely metal-poor (or even metal-free, if mixing is suppressed)
stars. We discuss the implications of such results for Pop III star formation
scenarios and for the most iron-poor halo star HE0107-5240.",0304074v2
2003-04-04,Metastable strange matter and compact quark stars,"Strange quark matter in beta equilibrium at high densities is studied in a
quark confinement model. Two equations of state are dynamically generated for
the {\it same} set of model parameters used to describe the nucleon: one
corresponds to a chiral restored phase with almost massless quarks and the
other to a chiral broken phase. The chiral symmetric phase saturates at around
five times the nuclear matter density. Using the equation of state for this
phase, compact bare quark stars are obtained with radii and masses in the
ranges $R\sim 5 - 8$ km and $M\sim M_\odot$. The energy per baryon number
decreases very slowly from the center of the star to the periphery, remaining
above the corresponding values for the iron or the nuclear matter, even at the
edge. Our results point out that strange quark matter at very high densities
may not be absolutely stable and the existence of an energy barrier between the
two phases may prevent the compact quarks stars to decay to hybrid stars.",0304096v1
2003-04-14,Low-Mass Relics of Early Star Formation,"The earliest stars to form in the Universe were the first sources of light,
heat and metals after the Big Bang. The products of their evolution will have
had a profound impact on subsequent generations of stars. Recent studies of
primordial star formation have shown that, in the absence of metals (elements
heavier than helium), the formation of stars with masses 100 times that of the
Sun would have been strongly favoured, and that low-mass stars could not have
formed before a minimum level of metal enrichment had been reached. The value
of this minimum level is very uncertain, but is likely to be between 10^{-6}
and 10^{-4} that of the Sun. Here we show that the recent discovery of the most
iron-poor star known indicates the presence of dust in extremely
low-metallicity gas, and that this dust is crucial for the formation of
lower-mass second-generation stars that could survive until today. The dust
provides a pathway for cooling the gas that leads to fragmentation of the
precursor molecular cloud into smaller clumps, which become the lower-mass
stars.",0304254v1
2003-04-15,Detailed Analysis of Nearby Bulgelike Dwarf Stars III. Alpha and Heavy-element abundances,"The present sample of nearby bulgelike dwarf stars has kinematics and
metallicities characteristic of a probable inner disk or bulge origin. Ages
derived by using isochrones give 10-11 Gyr for these stars and metallicities
are in the range -0.80< [Fe/H]< +0.40. We calculate stellar parameters from
spectroscopic data, and chemical abundances of Mg, Si, Ca, Ti, La, Ba, Y, Zr
and Eu are derived by using spectrum synthesis.
  We found that [alpha-elements/Fe] show different patterns depending on the
element. Si, Ca and Ti-to-iron ratios decline smoothly for increasing
metallicities, and follow essentially the disk pattern. O and Mg, products of
massive supernovae, and also the r-process element Eu, are overabundant
relative to disk stars, showing a steeper decline for metallicities [Fe/H] >
-0.3 dex. [s-elements/Fe] roughly track the solar values with no apparent trend
with metallicity for [Fe/H] < 0, showing subsolar values for the metal rich
stars. Both kinematical and chemical properties of the bulgelike stars indicate
a distinct identity of this population when compared to disk stars.",0304282v2
2003-04-23,How did the metals in a giant star originate?,"The chemical composition of stars with extremely low metal contents (taking
``metals'' to mean all elements other than hydrogen and helium) provides us
with information on the masses of the stars that produced the first metals.
Such a direct connection is not possible, however, if the surface of the star
has been polluted by enriched material, either dredged from the star's interior
or transferred from a companion star. Here we argue that, in the case of
HE0107-5240 (ref. 1), the most iron poor star known, the oxygen abundance could
be a discriminant: a ratio of [O/Fe] exceeding +3.5 would favour a pristine
origin of metals, whereas an [O/Fe] ratio of less than +3 would favour the
pollution hypothesis. Using this criterion, we suggest how the required
information on oxygen abundance might be obtained.",0304415v1
2003-05-12,Stellar Abundances in Dwarf Irregular Galaxies,"Dwarf irregular galaxies appear to have undergone very slow chemical
evolution since they have low nebular abundances, but have had ongoing star
formation over the past 15 Gyr. They are too distant for red giant abundance
analyses to examine the details of their chemical evolution, however the
isolated, bright blue supergiants do allow us to determine their present-day
iron abundances to compare with both stellar and nebular alpha-element results.
The [alpha/Fe] ratios in four Local Group dwarf irregular galaxies (NGC6822,
WLM, Sextans A, and GR 8) all appear to have solar ratios regardless of the
differences in their metallicities and star formation histories. Surprisingly,
WLM's stellar metallicity is three times higher than the nebular oxygen
abundance. We compare the [alpha/Fe] ratios in the dwarf irregulars to those
from recent analyses of red giant branch stars in dwarf spheroidal galaxies,
and also to damped Ly-alpha systems, and discuss these in the context of model
predictions.",0305188v1
2003-05-19,A BeppoSAX observation of MKN6,"We have used the BeppoSAX satellite to study the broad band (0.5-100 keV)
X-ray spectrum of the Seyfert 1.5 galaxy MKN6. The source is characterized by a
power law of Gamma=1.7 [+0.08, -0.07] and there is no strong evidence for
either a reflection bump or a high energy cut-off. We have detected a narrow
iron line at 6.4 keV (rest frame) with an equivalent width of 98 [+33, -35] eV.
MKN6 also exhibits strong and complex absorption. At least two components (NH_1
=1.34 [+0.4,-0.4] x 10^(22) cm^(-2) and NH_2 = 4.18 [+2.2, -1.3] x 10^(22)
cm^(-2)) are present and they both partially cover the source with covering
fractions of ~90% and ~50% respectively. Comparison with a previous ASCA
observation indicates that in both absorbing columns the NH is variable over a
2 year timescale, while the covering fractions are constant over the same
amount of time. The state of each absorber is cold or mildly photoionized. The
Broad Line Region (BLR) is suggested as the possible location for this complex
absorption.",0305329v1
2003-05-20,An Estimate Of The Primary Mass Of Cosmic Rays At $10^{18}$ eV As Inferred From Volcano Ranch Data,"Accurate measurements of the lateral distribution of extensive air showers
produced by cosmic rays of energy greater than $10^{17}$ eV were made in the
1970s by Linsley. At the time, the state of knowledge about the best hadronic
interaction model to use to describe such data prevented conclusions about the
cosmic ray mass from being drawn. We have used a modern model, {\sc qgsjet98},
to infer the primary mass from these data, using the very careful records left
by Linsley. We find that at a median energy of $10^{18}$ eV, the data are well
described by an iron-dominated composition (88 $\pm$ 6(stat) $\pm$ 18 (syst))%.
We discuss the systematic errors in this estimate that arise from model
uncertainties and from the range of energies used in the work of Linsley. These
data are used with the permission of the late John Linsley to whom this work is
dedicated.",0305351v1
2003-05-23,Metal Rich Stars in omega Centauri,"I present some preliminary results from a high-resolution spectroscopic
observing campaign conducted with UVES at the ESO VLT, devoted to the study of
the newly discovered, metal-rich red giant branch (RGB-a) in omega Centauri. In
particular, I derive and discuss accurate abundances of iron-peak elements,
alpha-elements and s-process elements. The main results discussed in this
contribution are: (i) the RGB-a is the most metal-rich component of the RGB
stellar mix in omega Cen, with [Fe/H]=-0.62+/-0.06; (ii) the RGB-a has a lower
alpha-enhancement compared to the other red giants, possibly due to SNe type Ia
pollution and (iii) the s-process elements overabundance of the RGB-a is
similar to that of the other red giants in omega Cen, and unusually high for
globular cluster stars, due to pollution by low mass AGB stars.",0305449v1
2003-05-26,XMM-Newton study of the persistent X-ray source 1E1743.1-2843 located in the Galactic Center direction,"We report the results of an XMM-Newton observation of the persistent X-ray
source 1E1743.1-2843, located in the Galactic Center (GC) direction. We
determine the position of the source at alpha_J2000=17h46m21.0s,
delta_J2000=-28deg43'44"" (with an uncertainty of 1.5""), which is the most
accurate to date, and will enable cross-identifications at other wavelengths.
The source was bright during this observation (L_2-10keV ~ 2.7 x 10^36
d^2_10kpc erg/s for a power-law continuum), with no significant variability. We
propose that 1E1743.1-2843 may be explained in terms of a black hole candidate
in a low/hard state. There is an indication that the source exhibits different
states from a comparison of our results with previous observations (e.g.,
ART-P, BeppoSAX). However, the present spectral analysis does not rule out the
hypothesis of a neutron star low-mass X-ray binary as suggested previously. If
1E1743.1-2843 is actually located in the GC region, we might expect to observe
significant 6.4keV fluorescent iron line emission from nearby molecular clouds
(e.g., GCM+0.25+0.01).",0305489v1
2003-06-05,Where was the Iron Synthesized in Cassiopeia A?,"We investigate the properties of Fe-rich knots on the east limb of the
Cassiopeia A supernova remnant using observations with Chandra/ACIS and
analysis methods developed in a companion paper. We use the fitted ionization
age and electron temperature of the knots to constrain the ejecta density
profile and the Lagrangian mass coordinates of the knots. Fe-rich knots which
also have strong emission from Si, S, Ar, and Ca are clustered around mass
coordinates q~0.35-0.4 in the shocked ejecta; for ejecta mass 2M_sun, this
places the knots 0.7-0.8 M_sun out from the center (or 2-2.1 M_sun, allowing
for a 1.3 M_sun compact object). We also find an Fe clump that is evidently
devoid of line emission from lower mass elements, as would be expected if it
were the product of alpha-rich freeze out; the mass coordinate of this clump is
similar to those of the other Fe knots.",0306120v1
2003-06-09,An AGN Sample with High X-ray-to-optical Flux Ratio from RASS II.Optical Emission Line Properties of Seyfert 1 Type AGN,"This work studies the optical emission line properties of a sample of 155
low-redshift bright X-ray selected ROSAT Seyfert~1 type AGN for which adequate
signal-to-noise ratio spectroscopic observations are available. We measured
emission line properties by performing multi-component fits to the emission
line profiles, covering the effect of blended iron emission. We also obtained
continuum parameters, including 250eV X-ray luminosities derived from the ROSAT
database. In addition, the measured properties are gathered for a correlation
analysis, which confirms the well-known relations between the strengths of
Fe~II, [O III] emission and the X-ray slope. We also detect striking
correlations between H$\beta$ redshift (or blueshift), flux ratios of Fe `II to
H$\beta$ broad component and [O III] to H$\beta$ narrow component. These trends
are most likely driven by the Eddington ratio.",0306169v1
2003-06-12,Long Term X-ray Variability in GX13+1: Energy Dependent Periodic Modulation,"A search is made for periodic modulation in the X-ray flux from the low mass
X-ray binary GX13+1 using Rossi X-ray Timing Explorer All Sky Monitor data
collected over a period of almost seven years. From a filtered data set, which
excludes measurements with exceptionally large error bars and so maximizes
signal to noise, modulation is found at a period of 24.065 +/- 0.018 days. The
modulation is most clearly detectable at high energies (5 - 12 keV). Spectral
changes are revealed as a modulation in hardness ratio on the 24 day period and
there is a phase shift between the modulation in the 5 - 12 keV energy band
compared to the 1.5 - 5 keV band. The high-energy spectrum of GX13+1 is unusual
in displaying both emission and absorption iron line features and it is
speculated that the peculiar spectral and timing properties may be connected.",0306262v1
2003-06-13,Delayed soft X-ray emission lines in the afterglow of GRB 030227,"Strong, delayed X-ray line emission is detected in the afterglow of GRB
030227, appearing near the end of the XMM-Newton observation, nearly twenty
hours after the burst. The observed flux in the lines, not simply the
equivalent width, sharply increases from an undetectable level (<1.7e-14
erg/cm^2/s, 3 sigma) to 4.1e-14 erg/cm^2/s in the final 9.7 ks. The line
emission alone has nearly twice as many detected photons as any previous
detection of X-ray lines. The lines correspond well to hydrogen and/or
helium-like emission from Mg, Si, S, Ar and Ca at a redshift z=1.39. There is
no evidence for Fe, Co or Ni--the ultimate iron abundance must be less than a
tenth that of the lighter metals. If the supernova and GRB events are nearly
simultaneous there must be continuing, sporadic power output after the GRB of a
luminosity >~5e46 erg/s, exceeding all but the most powerful quasars.",0306284v2
2003-06-16,Modeling of iron K lines: radiative and Auger decay data for Fe II-Fe IX,"A detailed analysis of the radiative and Auger de-excitation channels of
K-shell vacancy states in Fe II-Fe IX has been carried out. Level energies,
wavelengths, A-values, Auger rates and fluorescence yields have been calculated
for the lowest fine-structure levels populated by photoionization of the ground
state of the parent ion. Different branching ratios, namely
K-alpha_2/K-alpha_1, K-beta/K-alpha, KLM/KLL, KMM/KLL, and the total K-shell
fluorescence yields, omega_K, obtained in the present work have been compared
with other theoretical data and solid-state measurements, finding good general
agreement with the latter. The K-alpha_2/K-alpha_1 ratio is found to be
sensitive to the excitation mechanism. From these comparisons it has been
possible to estimate an accuracy of ~10% for the present transition
probabilities.",0306321v2
2003-06-27,The Chemical Composition and Gas-to-Dust Mass Ratio of Nearby Interstellar Matter,"Recent results on nearby interstellar gas and interstellar byproducts within
the solar system are used to select among the equilibrium radiative transfer
models of the nearest interstellar material of Slavin and Frisch (2002).
Assuming O/H~400 ppm, Models 2 and 8 are found to yield good fits to available
data on local interstellar material, and pickup ions and anomalous cosmic rays
inside of the heliosphere, with the exception of Ne. For these models, the
density of interstellar gas at the entry point to the heliosphere is n(HI)~0.20
/cc and n(e-)~0.1 /cc. These models suggest the chemical composition of the
nearby ISM is ~60--70% subsolar if S is undepleted (where HI and HII must be
included for abundance calculations). Gas-to-dust mass ratios of 178-183 for
solar abundances, or 611-657 for 70% solar abundances are found. The percentage
of the dust mass that is carried by iron is directly correlated with the
gas-to-dust mass ratio implying an Fe-rich grain core remains after grain
destruction.",0306590v2
2003-07-08,The Chemistry of Galaxy Clusters,"From X-ray observations of galaxy clusters one derives the mass of the
intracluster medium along with its chemical composition. Optical/infrared
observations are used to estimate the mass of the stellar components of
galaxies, along with their chemical composition and age. This review shows that
when combining all this information, several interesting inferences can be
drawn, including: (1) galaxies lose more metals than they retain; (2) clusters
and the general field have converted the same fraction of baryons into stars,
hence the metallicity of the $z = 0$ Universe as a whole has to be nearly the
same we see in clusters, $\sim$1/3 solar; (3) for the same reason, the thermal
content of the intergalactic medium is expected to be nearly the same as the
preheating energy of clusters; (4) a strong increase of the Type Ia supernova
(SN) rate with lookback time is predicted if SNe Ia produce a major fraction of
cosmic iron; (5) the global metallicity of the $z\approx 3$ Universe was
already $\sim$1/10 solar; and (6) the Milky Way disk formed out of material
that was pre-enriched to $\sim$1/10 solar by the bulge stellar population.",0307146v1
2003-07-09,Nitrogen Abundances in High-z DLAs,"Determination of chemical abundances for elements produced mainly by Type I
SNae and intermediate mass stars in high redshift DLAs probes the early
chemical build-up on time-scales comparable with their production. Nitrogen
shows a peculiar behaviour never detected before in any other class of objects.
For [N/H] < -3 there is a plateau with [N/Si]= -1.45(\pm 0.05). We interpret
this as empirical evidence for primary N production by massive stars in young
systems where AGB stars have not yet had time to make their contribution. The
plateau provides the observational integrated yields for N production by
massive stars which are theoretically rather uncertain. High N/Si and solar
[alpha/iron-peak] ratios are observed at high redshift and place at an earlier
epoch the onset of star formation. On the other hand, low N/Si, i.e. young
objects, are observed also at relatively low redshifts. These evidences suggest
that DLAs started to be formed at a very early epoch but their formation has
been extended up to later times.",0307173v1
2003-07-30,"On the origin of HE0107-5240, the most iron deficient star presently known","We show that the ""puzzling"" chemical composition observed in the extremely
metal poor star HE0107-5240 may be naturally explained by the concurrent
pollution of at least two supernovae. In the simplest possible model a
supernova of quite low mass (~15 Msun), underwent a ""normal"" explosion and
ejected ~0.06 Msun of 56Ni while a second one was massive enough (~35 Msun) to
experience a strong fall back that locked in a compact remnant all the
carbon-oxygen core. In a more general scenario, the pristine gas clouds were
polluted by one or more supernovae of relatively low mass (less than ~25 Msun).
The successive explosion of a quite massive star experiencing an extended fall
back would have largely raised the abundances of the light elements in its
close neighborhood.",0307527v1
2003-08-15,Stellar pollution and [Fe/H] in the Hyades,"The Hyades open cluster presents a unique laboratory for planet formation and
stellar pollution studies because all of the stars have essentially the same
age and were born from the same cloud of gas. Furthermore, with an age of
roughly 650 Myr most of the intermediate and low mass stars are on the main
sequence. Given these assumptions, the accretion of metal rich material onto
the surface of a star during and shortly after the formation of planetary
systems should be evident via the enhanced metallicity of the star. Building on
previous work, stellar evolution models which include the effects of stellar
pollution are applied to the Hyades. The results of several Monte Carlo
simulations, in which the amount of accreted material is drawn at random from a
Gaussian distribution with standard deviation equal to half the mean, are
presented. An effective temperature-[Fe/H] relation is produced and compared to
recent observations. The theoretical predictions presented in this letter will
be useful in future searches for evidence of stellar pollution due to planet
formation. It is concluded that stellar pollution effects at the mean level of
>=2 Earth masses of iron are ruled out by current observational data.",0308268v1
2003-08-20,The chemical composition of a mild barium star HD202109,"We present the result of chemical abundances of a mild barium star HD202109
(zeta Cyg) determined from the analysis of spectrum obtained by using a 2-m
telescope at the Peak Terskol Observatory and a high-resolution spectrometer
with R=80,000, signal to noise ratio >100. We also present the atmospheric
parameters of the star determined by using various methods including iron-line
abundance analysis. For line identifications, we use whole-range synthetic
spectra computed by using the Kurucz database and the latest lists of spectral
lines. Among the determined abundances of 51 elements, those of P, S, K, Cu,
Zn, Ge, Rb, Sr, Nb, Mo, Ru, Rh, Pd, In, Sm, Gd, Tb, Dy, Er, Tm, Hf, Os, Ir, Pt,
Tl, and Pb have not been previously known. Under the assumption that the
overabundance pattern of Ba stars is due to wind-accretion process, adding
information of more element abundances enables one to show that the heavy
element overabundances of HD202109 can be explained with the wind accretion
scenario model.",0308337v2
2003-08-20,Rosseland and Planck Mean Opacities for Protoplanetary Discs,"In this paper, we present mean gas and dust opacities relevant to the
physical conditions typical of protoplanetary discs. As the principal absorber
for temperatures below ~1,500 K, we consider spherical and aggregate dust
particles of various sizes, chemical structure, and porosity, consisting of
ice, organics, troilite, silicates, and iron. For higher temperatures, ions,
atoms, molecules, and electrons are included as the main opacity sources.
Rosseland and Planck mean opacities are calculated for temperatures between 5 K
and 10,000 K and gas densities ranging from 10^{-18} g/ccm to 10^{-7} g/ccm.
The dependence on the adopted model of dust grains is investigated. We compare
our results with recent opacity tables and show how different opacity models
affect the calculated hydrodynamical structure of accretion discs.",0308344v1
2003-08-21,Sgr A East and its surroundings observed in X-rays,"We report the results of an XMM-Newton observation of Sgr A East and its
surroundings. The X-ray spectrum of Sgr A East is well represented with a
two-temperature plasma model with temperatures of ~1 and ~4 keV. Only the iron
abundance shows clear spatial variation; it concentrates in the core of Sgr A
East. The derived plasma parameters suggest that Sgr A East originated in a
single supernova. Around Sgr A East, there is a broad distribution of hard
X-ray emission with a superimposed soft excess component extending away from
the location of Sgr A East both above and below the plane. We discuss the
nature of these structures as well as the close vicinity of Sgr A*.",0308373v1
2003-08-27,3EG J2027+3429 another Blazar behind the Galactic Plane,"We report on the association of an X-ray source (WGA J2025.1+3342),
serendipitously found with BeppoSAX in two separate observations, with the
unidentified EGRET source 3EG J2027+3429. The source is detected from 1 keV up
to about 100 keV, has a flat (0.6-1.5) spectrum and is highly variable both in
intensity and shape. The data indicate marginal evidence for an iron line in
the source rest frame. The overall X-ray luminosity is 4 10^{45} erg s^{-1}
typical of a quasar. The X-ray source is coincident in radio with a bright
object characterized by a flat spectrum over the band 0.3-10 GHz while in
optical it is identified with a quasar at redshift 0.22. All available data
indicate a SED compatible with a low frequency peaked or red blazar type
object. This identification is interesting because this is the second blazar
found behind the galactic plane in the direction of the Cygnus region.",0308473v1
2003-08-28,On the filling factor of emitting material in the upper atmosphere of Epsilon Eri (K2 V),"The emission measure distribution in the upper transition region and corona
of Epsilon Eri is derived from observed emission line fluxes. Theoretical
emission measure distributions are calculated assuming that the radiation
losses are balanced by the net conductive flux. We discuss how the area factor
of the emitting regions as a function of temperature can be derived from a
comparison between these emission measure distributions. It is found that the
filling factor varies from ~0.2 in the mid transition region to ~1.0 in the
inner corona. The sensitivity of these results to the adopted ion fractions,
the iron abundance and other parameters is discussed. The area factors found
are qualitatively similar to the observed structure of the solar atmosphere,
and can be used to constrain two-component models of the chromosphere. Given
further observations, the method could be applied to investigate the trends in
filling factors with indicators of stellar activity.",0308502v1
2003-09-01,Fe II lifetimes and transition probabilities,"Fe II radiative lifetimes were measured applying the time-resolved nonlinear
laser-induced fluoresence technique. We investigated 21 levels of up to 47000
1/cm. The uncertainties are typically 2-3%. The lifetimes provide an improved
absolute scale to our branching fractions which were measured with a Fourier
transform spectrometer and a high-resolution grating spectrometer and which
have been published earlier. We report absolute transition probabilities of 140
Fe II lines in the wavelength range 220-780 nm. The overall uncertainties are
estimated to be 6% for the strong and up to 26% for the weak transitions. The
results are compared with recent experimental data from the literature. Our
large set of accurate data can be used for a reliability check of theoretical
data calculated for iron abundances in astrophysical plasmas.",0309023v3
2003-09-16,XMM-Newton Observations of the Perseus Cluster II: Evidence for Gas Motions in the Core,"The 5-9 keV spectrum of the inner ~100 kpc of the Perseus cluster measured by
XMM-Newton can be well described by an optically thin plasma emission model as
predicted by the APEC code, without any need for invoking a strong Ni
overabundance or the effects of resonant scattering. For the strongest 6.7 keV
line of He-like iron, the optical depth of the cluster, calculated using
observed density, temperature and abundance profiles, is of order 3. The lack
of evidence for resonant scattering effects implies gas motion in the core with
a range in velocities of at least half of the sound velocity. If this motion
has the character of small scale turbulence, then its dissipation would provide
enough energy to compensate for radiative cooling of the gas. The activity of
the supermassive black hole at the center of the cluster may be the driving
force of the gas motion.",0309427v1
2003-09-18,Inferring the coronal flaring patterns in AGN from reverberation maps,"The relativistically broadened iron K-alpha line at 6.4 keV observed in the
Seyfert 1 galaxy MCG-6-30-15 has provided a probe of the strong-gravity
environment near a black hole, in particular suggesting that it is rapidly
spinning. An important variable in such analyses is the geometry of the
illuminating source. We present a new technique which constrains this geometry
based on the spectral line shape, based on a model of discrete, point-like
flaring regions in the X-ray corona. We apply it to simulated reverberation
maps and give examples of successful reconstructions of complex coronal flaring
patterns. For time-averaged spectral lines the problem is highly degenerate,
and so its inversion more challenging. We quantify this degeneracy and give a
measure of the spatial accuracy of the method in this case, before checking
that it is consistent with the existing picture of MCG-6-30-15 by applying it
to recent data from XMM-Newton.",0309518v2
2003-09-29,A common trend in the chemical evolution of Local Group dwarf spheroidals and Damped Ly-alpha systems,"We compare chemical abundances of Local Group dwarf spheroidals, obtained
from recent UVES/VLT observations, and of high redshift Damped Lyman alpha
systems (DLAs), corrected for dust effects. We focus, in particular, on the
abundance ratio between alpha-capture elements and iron, alpha/Fe, a well known
indicator of chemical evolution. Comparison of the data in the plane alpha/Fe
versus Fe/H shows a remarkable similarity between the dwarf spheroidals and the
DLAs, suggestive of a common trend in their chemical evolution. At any given
metallicity these two distinct types of astronomical targets show alpha/Fe
ratios systematically lower than those of Milky Way stars. In terms of chemical
evolution models, this suggests that, on average, dSph galaxies and DLA systems
are characterized by lower, or more episodic, star formation rates than the
Milky Way.",0309765v1
2003-10-06,A new population of X-ray transients in the Galactic Centre,"A comparison of the XMM-Newton and Chandra Galactic Centre (GC) Surveys has
revealed two faint X-ray transients with contrasting properties. The X-ray
spectrum of XMM J174544-2913.0 shows a strong iron line with an equivalent
width of ~2 keV, whereas that of XMM J174457-2850.3 is characterised by a very
hard continuum with photon index ~1.0. The X-ray flux of both sources varied by
more than 2 orders of magnitude over a period of months with a peak X-ray
luminosity of 5 x 10^34 erg/s. We discuss the nature of these peculiar sources.",0310140v1
2003-10-06,Emission Line Properties of AGN from a post-COSTAR FOS HST Spectral Atlas,"This paper joins a series compiling consistent emission line measurements of
large AGN spectral databases, useful for reliable statistical studies of
emission line properties. It is preceded by emission line measurements of 993
spectra from the Large Bright Quasar Survey (Forster et al. 2001) and 174
spectra of AGN obtained from the Faint Object Spectrograph (FOS) on HST prior
to the installation of COSTAR (Kuraszkiewicz et al. 2002). This time we
concentrate on 220 spectra obtained with the FOS after the installation of
COSTAR, completing the emission line analysis of all FOS archival spectra. We
use the same automated technique as in previous papers, which accounts for
Galactic extinction, models blended optical and UV iron emission, includes
Galactic and intrinsic absorption lines and models emission lines using
multiple Gaussians. We present UV and optical emission line parameters
(equivalent widths, fluxes, FWHM, line positions) for a large number (28) of
emission lines including upper limits for undetected lines. Further scientific
analyses will be presented in subsequent papers.",0310165v1
2003-10-08,Determination of the calorimetric energy in extensive air showers,"The contribution of different components of an air shower to the total energy
deposit in the atmosphere, for different angles and primary particles, was
studied using the CORSIKA air shower simulation code. The amount of missing
energy, parameterized in terms of the calorimetric energy, was calculated. The
results show that this parameterization varies less than 1% with angle or
observation level. The dependence with the primary mass is less than 5% and,
with the high energy hadronic interaction model, less than 2%. The systematic
error introduced by the use of just one parameterization of the missing energy
correction function, for an equal mixture of proton and iron at 45deg, was
calculated to be below 3%. We estimate the statistical error due to
shower-to-shower fluctuations to be about 1%.",0310234v3
2003-10-21,Coronal abundances from high-resolution X-ray data: The case of Algol,"We discuss the determination of elemental abundances from high resolution
X-ray data. We emphasize the need for an accurate determination of the
underlying temperature structure and advocate the use of a line ratio method
which allows us to utilize, first, the strongest lines observed in the X-ray
spectra, and second, lines that span a rather wide temperature range. We point
out the need to use continuous emission measure distributions and show via
example that modeling in terms of individual temperature components yields
errors of more than 50%. We stress the need to derive differential emission
measure distributions based on physical assumptions and considerations. We
apply our methods to the Chandra LETGS spectrum of Algol and show that nitrogen
is considerably enhanced compared to cosmic abundances by a factor of 2 while
carbon is depleted by at least a factor of 25. Iron, silicon, and magnesium,
are all depleted compared to cosmic abundances, while the noble gas neon has
the relatively highest abundance.",0310594v1
2003-10-21,The Formation of the First Low-Mass Stars From Gas With Low Carbon and Oxygen Abundances,"The first stars in the Universe are predicted to have been much more massive
than the Sun. Gravitational condensation accompanied by cooling of the
primordial gas due to molecular hydrogen, yields a minimum fragmentation scale
of a few hundred solar masses. Numerical simulations indicate that once a gas
clump acquires this mass, it undergoes a slow, quasi-hydrostatic contraction
without further fragmentation. Here we show that as soon as the primordial gas
- left over from the Big Bang - is enriched by supernovae to a carbon or oxygen
abundance as small as ~0.01-0.1% of that found in the Sun, cooling by
singly-ionized carbon or neutral oxygen can lead to the formation of low-mass
stars. This mechanism naturally accommodates the discovery of solar mass stars
with unusually low (10^{-5.3} of the solar value) iron abundance but with a
high (10^{-1.3} solar) carbon abundance. The minimum stellar mass at early
epochs is partially regulated by the temperature of the cosmic microwave
background. The derived critical abundances can be used to identify those
metal-poor stars in our Milky Way galaxy with elemental patterns imprinted by
the first supernovae.",0310622v1
2003-10-22,Accretion and Outflow in the AGN and Starburst of NGC 5135,"Observations of the Seyfert 2 and starburst galaxy NGC 5135 with the Chandra
X-ray Observatory demonstrate that both of these phenomena contribute
significantly to its X-ray emission. We spatially isolate the active galactic
nucleus (AGN) and demonstrate that it is entirely obscured by column density
N_H > 10^{24} cm^{-2}, detectable in the Chandra bandpass only as a strongly
reprocessed, weak continuum and a prominent iron K alpha emission line with
equivalent width of 2.4 keV. Most of the soft X-ray emission, both near the AGN
and extending over several-kpc spatial scales, is collisionally-excited plasma.
We attribute this thermal emission to stellar processes. The AGN dominates the
X-ray emission only at energies above 4 keV. In the spectral energy
distribution that extends to far-infrared wavelengths, nearly all of the
emergent luminosity below 10 keV is attributable to star formation, not the
AGN.",0310669v1
2003-10-27,Oxygen trends in the Galactic thin and thick disks,"We present oxygen abundances for 72 F and G dwarf stars in the solar
neighbourhood. Using the kinematics of the stars we divide them into two
sub-samples with space velocities that are typical for the thick and thin
disks, respectively. The metallicities of the stars range from [Fe/H] = -0.9 to
+0.4 and we use the derived oxygen abundances of the stars to: (1) perform a
differential study of the oxygen trends in the thin and the thick disk; (2) to
follow the trend of oxygen in the thin disk to the highest metallicities. We
analyze the forbidden oxygen lines at 6300 {\AA} and 6363 {\AA} as well as the
(NLTE afflicted) triplet lines around 7774 {\AA}. For the forbidden line at
6300 A we have spectra of very high S/N (>400) and resolution (R=215 000). This
has enabled a very accurate modeling of the oxygen line and the blending Ni
lines. The high internal accuracy in our determination of the oxygen abundances
from this line is reflected in the very tight trends we find for oxygen
relative to iron........",0310741v1
2003-10-29,Luminosity and Redshift Dependence of Quasar Spectral Properties,"Using a large sample of quasar spectra from the SDSS, we examine the
composite spectral trends of quasars as functions of both redshift and
luminosity, independently of one another. Aside from the well known Baldwin
effect (BE) -- the decrease of line equivalent width with luminosity -- the
average spectral properties are remarkably similar. Host galaxy contamination
and the BE are the primary causes for apparent changes in the average spectral
slope of the quasars. The BE is detected for most emission lines, including the
Balmer lines, but with several exceptions including NV1240A. Emission line
shifts of several lines are associated with the BE. The BE is mainly a function
of luminosity, but also partly a function of redshift in that line equivalent
widths become stronger with redshift. Some of the complex iron features change
with redshift, particularly near the small blue bump region.",0310840v1
2003-10-30,Hints of star fomation at z>6: the chemical abundances of the DLA system in the QSO BRI 1202-0725 (z_abs = 4.383),"The Damped Ly-alpha (DLA) absorber at redshift z_abs=4.383 observed toward
QSO BRI 1202-0725 is studied by means of high resolution (FWHM ~ 7 km/s)
VLT-UVES spectra. We refine a previously determined Si abundance and derive
with confidence abundances for C, N and O which are poorly known in DLAs. The
[O/Fe] ratio is ~0.6, but we cannot establish if iron is partially locked into
dust grains. The [C/Fe]=0.08 \pm 0.13 and [Si/C]=0.31 \pm 0.07. [N/O] and
[N/Si] are about -1, which is consistent with the majority of DLAs. This value
is much larger than the one observed for the DLA toward QSO J0307-4945 at
z_abs= 4.466. The current interpretation of the bimodal distribution of N
abundances in DLAs implies that large [N/alpha] values correspond to relatively
old systems. Adopting a scale time of 500 Myrs for full N production by
intermediate mass stars, the onset of star formation in our DLA took place
already at redshift z> 6.",0310866v1
2003-11-26,Evolution and nucleosynthesis of primordial low mass stars,"We discuss in detail the evolutionary properties of low mass stars M< 1
M(Solar) having metallicity lower than Z=10^(-6) from the pre- main sequence up
to (almost) the end of the Asymptotic Giant Branch phase. We also discuss the
possibility that the large [C,N/Fe] observed on the surface of the most Iron
poor star presently known, HE0107-5240, may be attributed to the autopollution
induced by the penetration of the He convective shell into the H rich mantle
during the He core flash of a low mass, very low metallicity star. On the basis
of a quite detailed analysis, we conclude that the autopollution scenario
cannot be responsible for the observed chemical composition of HE0107-5240.",0311580v1
2003-12-05,XMM-Newton observations of 3C 273,"A series of nine XMM-Newton observations of the radio-loud quasar 3C 273 are
presented, concentrating mainly on the soft excess. Although most of the
individual observations do not show evidence for iron emission, co-adding them
reveals a weak, broad line (EW ~ 56 eV). The soft excess component is found to
vary, confirming previous work, and can be well fitted with multiple blackbody
components, with temperatures ranging between ~40 and ~330 eV, together with a
power-law. Alternatively, a Comptonisation model also provides a good fit, with
a mean electron temperature of ~350 eV, although this value is higher when the
soft excess is more luminous over the 0.5-10 keV energy band. In the RGS
spectrum of 3C 273, a strong detection of the OVII He-alpha absorption line at
zero redshift is made; this may originate in warm gas in the local
intergalactic medium, consistent with the findings of both Fang et al. (2003)
and Rasmussen et al. (2003).",0312148v1
2003-12-17,Doppler broadening of the iron line and R-Gamma correlation in black hole binaries,"RXTE/PCA observations of several black hole X-ray binaries in the low
spectral state revealed a tight correlation between spectral parameters and
characteristic frequencies of variability of X-ray flux. In particular, the
amplitude of reflection increases and the slope of Comptonized radiation
steepens as the noise frequencies increase. The data also suggest that there is
a correlated increase of the width of the Fe fluorescent line, probably related
to the Doppler broadening of the reflection features. Moreover, the width of
the line seems to follow DeltaE/E ~ nu_qpo^{1/3} law. If confirmed with higher
energy resolution observations, this result will have significant impact on the
models of the accretion flow and on our understanding of the nature of
characteristic frequencies of variability in X-ray binaries. In particular, it
will lend support to the truncated disk picture, confirming that the spectral
variations are indeed related to changes of the position of the inner disk
boundary and that characteristic variability frequencies are proportional to
the Keplerian frequency at the inner boundary of the accretion disk.",0312445v1
2003-12-18,Atomic and Molecular Data for Stellar Physics: Former Successes and Future Challenges,"This review highlights current (and future) hot topics in astrophysics where
atomic or molecular input data are (or will be) essential, with special
emphasis on topics relating to nucleosynthesis and cosmochemistry.
  We first discuss issues (like the abundances of oxygen and iron in the Sun,
and that of lithium in post-AGB stars) where the use of poor-quality atomic or
molecular data have led to spurious astrophysical puzzles which sparked fancy
astrophysical models or theories. We then address issues where the advent of
new instruments (like the ultraviolet high-resolution spectrographs--GHRS
onboard HST, Keck-HRS or VLT-UVES--or future infrared satellites) calls for new
and accurate atomic or molecular data.",0312486v1
2003-12-23,Gamma-Ray Bursts observed by XMM-Newton,"Analysis of observations with XMM-Newton have made a significant contribution
to the study of Gamma-ray Burst (GRB) X-ray afterglows. The effective area,
bandpass and resolution of the EPIC instrument permit the study of a wide
variety of spectral features. In particular, strong, time-dependent, soft X-ray
emission lines have been discovered in some bursts. The emission mechanism and
energy source for these lines pose major problems for the current generation of
GRB models. Other GRBs have intrinsic absorption, possibly related to the
environment around the progenitor, or possible iron emission lines similar to
those seen in GRBs observed with BeppoSAX. Further XMM-Newton observations of
GRBs discovered by the Swift satellite should help unlock the origin of the GRB
phenomenon over the next few years.",0312602v1
2004-01-09,The Evolution of the Accretion Disk around 4U 1820-30 During a Superburst,"Accretion from a disk onto a collapsed, relativistic star -- a neutron star
or black hole -- is the mechanism widely believed to be responsible for the
emission from compact X-ray binaries. Because of the extreme spatial resolution
required, it is not yet possible to directly observe the evolution or dynamics
of the inner parts of the accretion disk where general relativistic effects are
dominant. Here, we use the bright X-ray emission from a superburst on the
surface of the neutron star 4U 1820-30 as a spotlight to illuminate the disk
surface. The X-rays cause iron atoms in the disk to fluoresce, allowing a
determination of the ionization state, covering factor and inner radius of the
disk over the course of the burst. The time-resolved spectral fitting shows
that the inner region of the disk is disrupted by the burst, possibly being
heated into a thicker, more tenuous flow, before recovering its previous form
in ~1000 s. This marks the first instance that the evolution of the inner
regions of an accretion disk has been observed in real-time.",0401154v1
2004-01-14,Abundances of neutron-capture elements in the Hot Extreme-Helium Stars V1920 Cygni and HD 124448,"Analysis of HST STIS ultraviolet spectra of two hot extreme helium stars
(EHes): V1920 Cyg and HD 124448 provide the first measurements of abundances of
neutron-capture elements for EHes. Although the two stars have similar
abundances for elements up through the iron-group, they differ strikingly in
their abundances of heavier elements: V1920 Cyg is enriched by a factor of 30
in light neutron-capture elements (Y/Fe, Zr/Fe) relative to HD 124448. These
differences in abundances of neutron-capture elements among EHes mirrors that
exhibited by the RCrB stars, and is evidence supporting the view that there is
an evolutionary connection between these two groups of hydrogen-deficient
stars. Also, the abundances of Y and Zr in V1920 Cyg provide evidence that at
least one EHe star went through a s-process synthesis episode in its earlier
evolution.",0401263v1
2004-01-15,INTEGRAL observations of the transient source IGR J19140+098,"IGR J19140+098 was discovered during the early INTEGRAL observations of
GRS1915+105 in March 2003. The following observations by INTEGRAL and RXTE show
significant variability on various time scales from 100s to 1ks, but no
pulsations. The ISGRI spectra show strong spectral variability in the 20-80keV
range. Combined JEMX_2-ISGRI spectra are well fitted by a power-law and a
thermal emission model with a rather high temperature. RXTE data also reveal an
apparently broad ionised iron line not detected in earlier INTEGRAL
observations. These results are compatible with a galactic X-ray binary source.",0401308v1
2004-01-25,Propagation of electromagnetic waves in space plasma,"Coherent Raman Effect on Incoherent Light (CREIL), shifts the frequencies of
normally incoherent light without any blurring of the images or altering the
order of the spectra. CREIL operates in gases having quadrupolar resonances in
the megaherz range, and it is easily confused with Doppler effects. When CREIL
is taken into account, the propagation of light in cosmic low pressure gases
involves a complex combination of absorptions and frequency shifts. Current
star theory predicts very bright accreting neutron stars. These should be
small, very hot objects surrounded by dirty atomic hydrogen. CREIL predicts
spectra for these stars that have exactly the characteristics found in the
spectra of the quasars. The intrinsic redshifting in the extended photosphere
of Quasars as defined by CREIL events drastically reduces both the size and
distance to quasars, and clearly identifies the missing neutron stars as
quasar-like objects. A full interpretation of quasar spectra does not require
jets, dark matter, a variation of the fine structure constant, or an early
synthesis of iron. CREIL is useful in explaining other astrophysical problems,
such as redshifting proportional to the path of light through the corona of the
Sun. CREIL radiation transfers may explain the blueshifting of radio signals
from Pioneer 10 and 11.",0401529v1
2004-02-05,Timing and spectral studies of the transient X-ray pulsar EXO 053109-6609.2 with ASCA and Beppo-SAX,"We report timing and spectral properties of the transient Be X-ray pulsar EXO
053109--6609.2 studied using observations made with the ASCA and BeppoSAX
observatories. Though there must have been at least one spin-down episode of
the pulsar since its discovery, the new pulse period measurements show a
monotonic spin-up trend since 1996. The pulse profile is found to have marginal
energy dependence. There is also evidence for strong luminosity dependence of
the pulse profile, a single peaked profile at low luminosity that changes to a
double peaked profile at high luminosity. This suggests a change in the
accretion pattern at certain luminosity level. The X-ray spectrum is found to
consist of a simple power-law with photon index in the range of 0.4--0.8. At
high intensity level the spectrum also shows presence of weak iron emission
line.",0402127v1
2004-02-10,Implications of the central metal abundance peak in cooling core clusters of galaxies,"Recent XMM-Newton observations of clusters of galaxies have provided detailed
information on the distribution of heavy elements in the central regions of
clusters with cooling cores providing strong evidence that most of these metals
come from recent SN type Ia. In this paper we compile information on the
cumulative mass profiles of iron, the most important metallicity tracer. We
find that long enrichment times (larger than 5 Gyr) are necessary to produce
the central abundance peaks. Classical cooling flows, a strongly convective
intracluster medium, and a complete metal mixing by cluster mergers would
destroy the observed abundance peaks too rapidly. Thus the observations set
strong constraints on cluster evolution models requiring that the cooling cores
in clusters are preserved over very long times. We further conclude from the
observations that the innermost part of the intracluster medium is most
probably dominated by gas originating predominantly from stellar mass loss of
the cD galaxy.",0402216v1
2004-02-13,Models for extremely metal-poor halo stars,"Two alternative scenarios concerning the origin and evolution of extremely
metal-poor halo stars are investigated. The first one assumes that the stars
have been completely metal-free initially and produced observed carbon and
nitrogen overabundances during the peculiar core helium flash typical for
low-mass Population-III stars. The second scenario assumes that the initial
composition resulted from a mixture of primordial material with ejecta from a
single primordial supernovae. Both scenarios are shown to have problems in
reproducing C, N, and O abundances simultaneously, and both disagree with
observed 12C/13C-ratios,though in different directions. We concentrate on the
most iron-poor, carbon-rich object of this class, HE0107-5240, and conclude
that the second scenario presently offers the more promising approach to
understand these objects, in particular because evolutionary tracks match
observations very well.",0402334v1
2004-02-26,A Far-UV Spectroscopic Analysis of the Central Star of the Planetary Nebula Longmore 1,"We have performed a non-LTE spectroscopic analysis using far-UV and UV data
of the central star of the planetary nebula K1-26 (Longmore 1), and found Teff
= 120+/-10 kK, logg = 6.7 +0.3/-0.7, and y = 0.10. The temperature is
significantly hotter than previous results based on optical line analyses,
highlighting the importance of analyzing the spectra of such hot objects at
shorter wavelengths. The spectra show metal lines (from, e.g, carbon, oxygen,
sulfur, and iron). The signatures of most elements can be fit adequately using
solar abundances, confirming the classification of Longmore 1 as a high gravity
O(H) object. Adopting a distance of 800 pc, we derive R = 0.04 Rsun, L = 250
Lsun, and M = 0.6 Msun. This places the object on the white dwarf cooling
sequence of the evolutionary tracks with an age of ~= 65 kyr.",0402653v1
2004-03-01,An XMM-Newton study of the RGH 80 galaxy group,"We present an X-ray study of the galaxy group RGH 80, observed by XMM-Newton.
The X-ray emission of the gas is detected out to ~ 462h^{-1}_{50} kpc,
corresponding to ~ 0.45 r_{200}. The group is relatively gas rich and luminous
with respect to its temperature of 1.01 +/- 0.01 keV. Using the deprojected
spectral analysis, we find that the temperature peaks at ~ 1.3 keV around
0.11r_{200}, and then decreases inwards to 0.83 keV at the center and outwards
to ~ 70% of the peak value at large radii. Within the central ~ 60 kpc of the
group where the gas cooling time is less than the Hubble time, two-temperature
model with temperatures of 0.82 and 1.51 keV and the Galactic absorption gives
the best fit of the spectra, with ~ 20% volume occupied by the cool component.
We also derive the gas entropy distribution, which is consistent with the
prediction of cooling and/or internal heating models. Furthermore, the
abundances of O, Mg, Si, S, and Fe decrease monotonically with radius. With the
observed abundance ratio pattern, we estimate that ~ 85% or ~ 72% of the iron
mass is contributed by SN Ia, depending on the adopted SN II models.",0403026v1
2004-03-10,Hydra Observations of Aluminum Abundances in the Red Giants of the Globular Clusters M80 and NGC 6752,"Aluminum and other metal abundances were determined in 21 red giants in the
globular clusters NGC 6752 and M80 as part of a larger study to determine
whether the aluminum distribution on the red giant branch is related to the
second parameter effect that causes clusters of similar metallicity to display
different horizontal branch morphologies. The observations were obtained of the
Al I lines near 6700 Angstroms with the CTIO Blanco 4-m telescope and Hydra
multi-object spectrograph. The spectra have a resolving power of 18000 or 9400,
with typical S/N ratios of 100-200. Mean [Fe/H] values obtained from the
spectra are -1.58 for NGC 6752 and -1.73 for M80; this represents the first
spectroscopic iron abundance determination for M80. Both NGC 6752 and M80
display a spread in aluminum abundance, with mean [Al/Fe] ratios of +0.51 and
+0.37, respectively. No trend in the variation of the mean Al abundance with
position on the giant branch is discernible in either cluster with our small
sample.",0403263v1
2004-03-17,Chemical Abundances in the Secondary Star in the Black Hole Binary A0620-00,"Using a high resolution spectrum of the secondary star in the black hole
binary A0620-00, we have derived the stellar parameters and veiling caused by
the accretion disk in a consistent way. We have used a chi^2 minimization
procedure to explore a grid of 800 000 LTE synthetic spectra computed for a
plausible range of both stellar and veiling parameters. Adopting the best model
parameters found, we have determined atmospheric abundances of Fe, Ca, Ti, Ni
and Al. The Fe abundance of the star is [Fe/H]=0.14 +- 0.20. Except for Ca, we
found the other elements moderately over-abundant as compared with stars in the
solar neighborhood of similar iron content. Taking into account the small
orbital separation, the mass transfer rate and the mass of the convection zone
of the secondary star, a comparison with element yields in supernova explosion
models suggests a possible explosive event with a mass cut comparable to the
current mass of the compact object. We have also analyzed the Li abundance,
which is unusually high for a star of this spectral type and relatively low
mass.",0403402v1
2004-04-02,The first broad-band persistent X-ray spectrum of the dipping low mass X-ray binary EXO 0748-676,"We report on the results of a BeppoSAX observation of the dipping LMXRB EXO
0748-676 performed in 2000 November. This is the first simultaneous observation
of this source over the 0.1-100 keV energy range. The persistent spectrum is
complex and shows a soft excess, which requires the inclusion of an ionized
absorber (with a sub-solar abundance of iron). A cutoff power-law is a good fit
to the high energy part of the spectrum, with a photon index of 1.3 and a
cutoff around 50 keV. The 0.1-100 keV luminosity is 8.2E36 erg/s.",0404038v1
2004-04-02,The complex X-ray spectrum of NGC 4507,"XMM-Newton and Chandra/HETG spectra of the Compton-thin (NH 4x10^{23}
cm^{-2}) Seyfert 2 galaxy, NGC 4507, are analyzed and discussed. The main
results are: a) the soft X-ray emission is rich in emission lines; an (at
least) two--zone photoionization region is required to explain the large range
of ionization states. b) The 6.4 keV iron line is likely emitted from
Compton-thick matter, implying the presence of two circumnuclear cold regions,
one Compton-thick (the emitter), one Compton-thin (the cold absorber). c)
Evidence of an Fe xxv absorption line is found in the Chandra/HETG spectrum.
The column density of the ionized absorber is estimated to be a few x10^{22}
cm^{-2}.",0404050v1
2004-04-16,Revealing the nature of the highly obscured galactic source IGR J16318-4848,"The X-ray source IGR J16318-4848 was the first source discovered by INTEGRAL
on 2003, January 29. We carried out optical and near-infrared (NIR)
observations at the European Southern Observatory (ESO La Silla) in the course
of a Target of Opportunity (ToO) programme. We discovered the optical
counterpart and confirmed an already proposed NIR candidate. NIR spectroscopy
revealed a large amount of emission lines, including forbidden iron lines and
P-Cygni profiles. The spectral energy distribution of the source points towards
a high luminosity and a high temperature, with an absorption greater than the
interstellar absorption, but two orders of magnitude lower than the X-ray
absorption. We show that the source is an High Mass X-ray binary (HMXB) at a
distance between ~1 and 6 kpc, the mass donor being an early-type star,
probably a sgB[e] star, surrounded by a rich and absorbing circumstellar
material. This would make the second High Mass X-ray Binary (HMXB) with a
sgB[e] star after CI Cam, indicating that a new class of strongly absorbed
X-ray binaries is being unveiled by INTEGRAL.",0404332v1
2004-04-19,Central Stars of Planetary Nebulae in the Large Magellanic Cloud: A Far-UV Spectroscopic Analysis,"We observed seven central stars of planetary nebulae (CSPN) in the Large
Magellanic Cloud (LMC) with the Far Ultraviolet Spectroscopic Explorer (FUSE),
and performed a model-based analysis of these spectra in conjunction with
Hubble Space Telescope (HST) spectra in the UV and optical range to determine
the stellar and nebular parameters. Most of the objects show wind features, and
they have effective temperatures ranging from 38 to 60 kK with mass-loss rates
of ~= 5x10^-8 Msun/yr. Five of the objects have typical LMC abundances. One
object (SMP LMC 61) is a [WC4] star, and we fit its spectra with He/C/O-rich
abundances typical of the [WC] class, and find its atmosphere to be
iron-deficient. Most objects have very hot (T ~> 2000 K) molecular hydrogen in
their nebulae, which may indicate a shocked environment. One of these (SMP LMC
62) also displays OVI 1032-38 nebular emission lines, rarely observed in PN.",0404367v1
2004-04-30,A look with BeppoSAX at the low-luminosity Galactic X-ray source 4U 2206+54,"A pointed observation of the low-luminosity galactic source 4U 2206+54 was
carried out in November 1998 with BeppoSAX. The light curve of 4U 2206+54 shows
erratic variability on a timescale of about 1 hour; neither hardness variations
nor time periodicities are detected throughout this 67 ks long observation.
Thanks to the wide spectral coverage capabilities of BeppoSAX we could observe
the source X-ray continuum over three energy decades, from 0.6 to 60 keV. The
spectrum could be equally well fitted either with a blackbody plus
Comptonization or with a high energy cutoff power law. No iron emission around
6.5 keV was detected, while a tentative detection of a cyclotron resonant
feature in absorption is presented. Comparison of the present BeppoSAX data
with the information available in the literature for this source suggests that
4U 2206+54 is a close binary system in which a (possibly magnetized) NS is
accreting from the companion star wind.",0404603v2
2004-05-04,Galactic Evolution of Nitrogen,"We present detailed spectroscopic analysis of nitrogen abundances in 31
unevolved metal-poor stars analysed by spectral synthesis of the near-UV NH
band at 3360 A observed at high resolution with various telescopes. We found
that [N/Fe] scales with that of iron in the metallicity range -3.1 < [Fe/H] <0
with the slope 0.01+-0.02. Furthermore, we derive uniform and accurate (N/O)
ratios using oxygen abundances from near-UV OH lines obtained in our previous
studies. We find that a primary component of nitrogen is required to explain
the observations. The NH lines are discovered in the VLT/UVES spectra of the
very metal-poor subdwarfs G64-12 and LP815-43 indicating that these stars are N
rich. The results are compared with theoretical models and observations of
extragalactic HII regions and Damped Ly$\alpha$ systems. This is the first
direct comparison of the (N/O) ratios in these objects with those in Galactic
stars.",0405049v1
2004-05-07,Partial Covering Interpretation of the X-Ray Spectrum of the NLS1 1H 0707-495,"The X-ray spectrum of 1H 0707-495 obtained with XMM-Newton showing a deep
flux drop at ~7 keV (Boller et al. 2002) is studied based on the partial
covering concept. The previously inferred extreme iron overabundance can be
reduced down to ~3x solar if the hard component gradually steepens at high
energies. The spectral shape supports that 1H 0707-495 is an AGN analogue of
the galactic black-hole binaries in the soft state. Interpreting the soft
excess as the emission from an optically-thick disk, the minimum black hole
mass M is estimated to be 2 x 10^6 solar masses from the intrinsic luminosity
corrected for partial covering. Based on the slim disk model, the observed disk
temperature implies that the luminosity is close to the Eddington limit. The
rapid and large flux variations with little change in the spectral shape can
also be explained, if not all, as due to changes in the partial covering
fraction. Partial covering may account for the large variability
characteristics of NLS1.",0405158v1
2004-05-13,Outflows in Regions of Star Formation,"The high spatial and spectral resolution offered by the new generation of
infrared spectrometers at ESO is optimally suited for the observational study
of outflows from young stellar objects. Models of interstellar shock waves
would benefit from observations of spectrally resolved line profiles. This
applies also to attempts of measuring the rotation rates of jets very close to
their driving source, which in general suffer considerable extinction.
Observations of forbidden lines of ionised iron, [Fe II], could be used to
accomplish this. The possibility of using rotational lines of molecular
hydrogen, H2, to study the temporal evolution of outflow and disk gas is
discussed. Similarly, high resolution IR observations of fluorescent water
lines, H2O, open up the possibility to access outflow and disk water.",0405248v1
2004-05-13,Isothermal Shock Formation in Non-Equatorial Accretion Flows around Kerr Black Holes,"We explore isothermal shock formation in non-equatorial, adiabatic accretion
flows onto a rotating black hole, with possible application to some active
galactic nuclei (AGNs). The isothermal shock jump conditions as well as the
regularity condition, previously developed for one-dimensional (1D) flows in
the equatorial plane, are extended to two-dimensional (2D), non-equatorial
flows, to explore possible geometrical effects. The basic hydrodynamic
equations with these conditions are self-consistently solved in the context of
general relativity to explore the formation of stable isothermal shocks. We
find that strong shocks are formed in various locations above the equatorial
plane, especially around a rapidly-rotating black hole with the prograde flows
(rather than a Schwarzschild black hole). The retrograde flows are generally
found to develop weaker shocks. The energy dissipation across the shock in the
hot non-equatorial flows above the cooler accretion disk may offer an
attractive illuminating source for the reprocessed features, such as the iron
fluorescence lines, which are often observed in some AGNs.",0405269v1
2004-05-26,Nucleosynthesis inside Gamma-Ray Burst Accretion Disks,"We investigate nucleosynthesis inside both a gamma-ray burst accretion disk
and a wind launched from an inner region of the disk using one-dimensional
models of the disk and wind and a nuclear reaction network. Far from a central
black hole, the composition of accreting gas is taken to be that of an O-rich
layer of a massive star before core collapse. We find that the disk consists of
five layers characterized by dominant elements: O16, Si28, Fe54 (and Ni56),
He4, and nucleons, and the individual layers shift inward with keeping the
overall profiles of compositions as the accretion rate decreases. Ni56 are
abundantly ejected through the wind from the inner region of the disk with the
electron fraction \simeq 0.5. In addition to iron group, elements heavier than
Cu, in particular Cu63 and Zn64, are massively produced through the wind.
Various neutron-rich nuclei can be also produced in the wind from neutron-rich
regions of the disk, though the estimated yields have large uncertainties.",0405510v1
2004-05-28,Stars as thermonuclear reactors: their fuels and ashes,"Atomic nuclei are transformed into each other in the cosmos by nuclear
reactions inside stars: -- the process of nucleosynthesis. The basic concepts
of determining nuclear reaction rates inside stars and how they manage to burn
their fuel so slowly most of the time are discussed. Thermonuclear reactions
involving protons in the hydrostatic burning of hydrogen in stars are discussed
first. This is followed by triple alpha reactions in the helium burning stage
and the issues of survival of carbon and oxygen in red giant stars connected
with nuclear structure of oxygen and neon. Advanced stages of nuclear burning
in quiescent reactions involving carbon, neon, oxygen and silicon are
discussed. The role of neutron induced reactions in nucleosynthesis beyond iron
is discussed briefly, as also the experimental detection of neutrinos from SN
1987A which confirmed broadly the ideas concerning gravitational collapse
leading to a supernova.",0405568v1
2004-06-05,"Fe II and Mg II in Luminous, Intermediate-Redshift Narrow-line Seyfert 1 Galaxies from the Sloan Digital Sky Survey","We present results from analysis of spectra from a sample of ~900 quasars
from the Sloan Digital Sky Survey. These objects were selected for their
intermediate redshift (1.2<z<1.8), placing MgII and UV FeII in the optical band
pass, relatively narrow MgII lines, and moderately good signal-to-noise-ratio
spectra. Using a maximum likelihood analysis, we discovered that there is a
significant dispersion in the FeII/MgII ratios in the sample. Using
simulations, we demonstrate that this range, and corresponding correlation
between FeII equivalent width and FeII/MgII ratio, are primarily a consequence
of a larger dispersion of FeII equivalent width (EW) relative to MgII EW. This
larger dispersion in FeII EW could be a consequence of a range in iron
abundance, or in a range of FeII excitation. The latter possibility is
supported by evidence that objects with weak (zero) CII]\lambda 2325 equivalent
width are likely to have large FeII/MgII ratios. We discuss physical effects
that could produce a range of FeII/MgII ratio.",0406137v2
2004-06-09,An Observation of the Intermediate Polar XY Arietis with Chandra,"Chandra serendipitously observed the eclipsing (80 deg < i < 84 deg)
intermediate polar, XY Arietis (=H0253+193), in two separate but continuous
observations five weeks apart. XY Ari was in a quiescent state during both
observations. We pursue the study of phase-resolved spectra for this system
focusing on the Fe K lines. From the combined and separate data sets, we
readily detect emission lines of iron near 6.4, 6.7, and 6.9 keV at better than
99% significance in contrast to previous results. We confirm the orbit-phased
sinusoidal absorption column behavior first observed with Ginga as well as a
sinusoid-like behavior as a function of spin phase. The presence of the 6.4,
6.7, and 6.9 keV lines requires different ionization states with xi <2 (6.4
keV) and xi \sim$3.5-4 (6.7 and 6.9 keV) that must vary with phase. We also
detect emission lines at 3.25, 4.8, and 5.4 keV that are not instrumental in
origin. The 4.8 keV line may be identified as Ca XIX (4.832 keV) and the 3.25
keV line may be Ar I K, but the 5.4 keV line has no obvious identification.",0406245v1
2004-06-29,A New Contributor to Chemical Evolution in High-Redshift Galaxies,"The recent discovery of a new population of stars exhibiting unusual
elemental abundance patterns characterized by enhanced Ti to Ga elements and
low alpha and n-capture elements suggests the contribution of a new class of
supernovae, probably a kind of Type Ia supernovae associated with close binary
evolution. The role of these supernovae in chemical evolution is negligible in
normal galaxies that undergo moderate star formation such as our own. Thus,
while the frequency of occurrence would be too low to detect in low-redshift
galaxies, it may represent a prominent population in high-redshift objects such
as early epoch massive elliptical galaxies and QSOs. The chemical contributor
of this proposed type of supernovae in combination with recognized supernovae
is shown to be compatible with the recent observational features in the distant
universe, successfully reproducing the Type II supernovae-like abundance
pattern with enhancement of Ga and Ge in the gas of newborn massive galaxies
and high iron abundances in QSOs even at redshifts of around 6.",0406636v1
2004-07-03,Beyond the iron group: heavy metals in hot subdwarfs,"We report the discovery of strong photospheric resonance lines of Ga III, Ge
IV, Sn IV and Pb IV in the UV spectra of more than two dozen sdB and sdOB stars
at temperatures ranging from 22000 K to 40000 K. Lines of other heavy elements
are also detected, however in these cases more atomic data are needed. Based on
these discoveries, we present a hypothesis to explain the apparent lack of
silicon in sdB stars hotter than ~32000 K. The existence of triply ionised Ge,
Sn, and Pb suggests that rather than silicon sinking deep into the photosphere,
it is removed from the star in a fractionated stellar wind. This hypothesis
provides a challenge to diffusion models of sdB stars.",0407067v1
2004-07-07,A possible feature of thermal matter in relativistic jets of radio-loud quasars,"It has been suggested that relativistic jets in quasars may contain a
considerable amount of thermal matter. In this paper, we explore the
possibility that the K-alpha line from the thermal matter may appear at tens of
keV due to a high Doppler blue-shift. In the jet comoving frame, the energy
density of photons originally emitted by the accretion disk and reflected off
the broad line region clouds dominates over that of photons of other origin. We
discuss the photoionization states of the thermal matter and find that the
irons elements are neutral. The high metallicity in quasars enhances the
possibility to detect the thermal matter in the relativistic jet in some
radio-loud quasars. A highly Doppler blue-shifted K-alpha line may be detected.
We make a rediction for 3C 273, in which the K-alpha line luminosity might be
of the order $3.0\times 10^{44}$ erg/s with an equivalent width of 2.4 keV.
Such a line could be detected in a future mission.",0407123v1
2004-07-08,Optical and near infrared observations of SN 1998bu,"Infrared and optical spectra of SN 1998bu at an age of one year after
explosion are presented. The data show evidence for the radioactive decay of
56Co to 56Fe, long assumed to be the powering source for the supernova light
curve past maximum light. The spectra provide direct evidence for at least 0.4
solar masses of iron being present in the ejecta of the supernova. The fits to
the data also show that the widths of the emission lines increase with time.
Photometric measurements in the H-band show that the supernova is not fading
during the observation period. This is consistent with theoretical
expectations.",0407177v1
2004-07-21,X-ray binaries and their descendants: binary radio pulsars; evidence for three classes of neutron stars?,"An important recent discovery by Pfahl et al. (2002) is that there are two
classes of Be X-ray binaries: one with orbits of small eccentricity (<0.25), in
which the neutron stars received hardly any kick velocity at birth and a class
with substantial orbital eccentricities, in which the neutron stars received a
kick velocity of order 100 km/s at birth. Also many of the double neutron stars
(5 out of 7) have a low orbital eccentricity (0.09 to 0.27), which indicates
that their second-born neutron stars received hardly any velocity kick at
birth. These second-born neutron stars tend to have low masses (1.25 to 1.35
Msun). It is proposed that the low-mass, low-kick neutron stars are formed by
the electron capture of degenerate O-Ne-Mg cores of stars with initial masses
below about 12-14 Msun, while the high-kick neutron stars originated from the
photo-disintegration collapse of the iron cores of stars which started out with
masses larger than this limit. The latter group may be further subdivided into
two classes of different mass.",0407451v1
2004-07-23,Neutrinos from microquasars,"The jets of microquasars with high-mass stellar companions are exposed to the
dense matter field of the stellar wind as well as to the photon densities found
in the surrounding medium. Photopion and proton-proton interactions could then
lead to copious production of neutrinos. In this work, we analyze the hadronic
microquasar model, particularly in what concerns to the neutrino production.
Limits to this kind of models using data from AMANDA-II are established. New
constraints are also imposed upon specific microquasar models based on
photopion processes. These are very restrictive particularly for the case of
SS433, a microquasar for which the presence of accelerated hadrons has been
already inferred from iron X-ray line observations.",0407494v1
2004-07-27,The isolated elliptical NGC 4555 observed with Chandra,"We present analysis of a Chandra observation of the elliptical galaxy NGC
4555. The galaxy lies in a very low density environment, either isolated from
all galaxies of similar mass or on the outskirts of a group. Despite this, NGC
4555 has a large gaseous halo, extending to ~60 kpc. We find the mean gas
temperature to be ~0.95 keV and the Iron abundance to be ~0.5 solar. We model
the surface brightness, temperature and abundance distribution of the halo and
use these results to estimate parameters such as the entropy and cooling time
of the gas, and the total gravitational mass of the galaxy. In contrast to
recent results showing that moderate luminosity ellipticals contain relatively
small quantities of dark matter, our results show that NGC 4555 has a massive
dark halo and large mass-to-light ratio (56.8 [+34.2,-35.8] solar at 50 kpc,
42.7 [+14.6,-21.2] solar at 5 effective radii, 1 sigma errors). We discuss this
disparity and consider possible mechanisms by which galaxies might reduce their
dark matter content.",0407552v1
2004-08-03,The Influence of Reaction Rates on the Final p-Abundances,"The astrophysical p-process is responsible for the origin of the proton rich
nuclei,which are heavier than iron. A huge network involving thousands of
reaction rates is necessary to calculate the final p-abundances. But not all
rates included in the network have a strong influence on the p-nuclei
abundances. The p-process was investigated using a full nuclear reaction
network for a type II supernovae explosion when the shock front passes through
the O/Ne layer. Calculations were done with a multi-layer model adopting the
seed of a pre-explosion evolution of a 25 mass star. In extensive simulations
we investigated the impact of single reaction rates on the final p-abundances.
The results are important for the strategy of future experiments in this field.",0408060v1
2004-08-26,The narrow-line quasar NAB 0205+024 observed with XMM-Newton,"The XMM-Newton observation of the narrow-line quasar NAB 0205+024 reveals
three striking differences since it was last observed in the X-rays with ASCA.
Firstly, the 2-10 keV power-law is notably steeper. Secondly, a hard X-ray
flare is detected, very similar to that seen in I Zw 1. Thirdly, a strong and
broad emission feature is detected with the bulk of its emission redward of 6.4
keV, and extending down to ~5 keV in the rest frame. The most likely
explanation for the broad feature is neutral iron emission emitted from a
narrow annulus of an accretion disc close to the black hole. The hard X-ray
flare could be the mechanism which illuminates this region of the disc,
allowing for the emission line to be detected. The combination of effects can
be understood in terms of the `thundercloud' model proposed by Merloni &
Fabian.",0408507v1
2004-09-13,Flux and energy modulation of redshifted iron emission in NGC3516: implications for the black hole mass,"We report the tentative detection of the modulation of a transient,
redshifted Fe Kalpha emission feature in the X-ray spectrum of the Seyfert
galaxy NGC3516. The detection of the spectral feature at 6.1 keV, in addition
to a stable 6.4 keV line, has been reported previously. We find on re-analysing
the XMM-Newton data that the feature varies systematically in flux at intervals
of 25 ks. The peak moves in energy between 5.7 keV and 6.5 keV. The spectral
evolution of the feature agrees with Fe K emission arising from a spot on the
accretion disc, illuminated by a corotating flare located at a radius of (7-16)
rg, modulated by Doppler and gravitational effects as the flare orbits around
the black hole. Combining the orbital timescale and the location of the
orbiting flare, the mass of the black hole is estimated to be (1-5)e+7 Msun,
which is in good agreement with values obtained from other techniques.",0409293v1
2004-09-14,Cosmogenic Neutrinos from Ultra-High Energy Nuclei,"We calculate the flux of neutrinos generated by the propagation of ultra-high
energy iron over cosmological distances and show that even if ultra-high energy
cosmic rays are composed of heavy nuclei, a significant flux of high-energy
neutrinos should be present throughout the universe. The resulting neutrino
flux has a new peak at $\sim 10^{14} eV$ generated by neutron decay and
reproduces the double peak structure due to photopion production at higher
energies ($\sim 10^{18}$ eV). Depending on the maximum energy and cosmological
evolution of extremely high energy cosmic accelerators the generated neutrino
flux can be detected by future experiments.",0409316v2
2004-09-22,Thorium-rich halo star HD221170: further evidence against the universality of the r-process,"We report the abundance determination in the atmosphere of the bright halo
star HD221170. The spectra were taken with the Terskol Observatory's 2.0-m
telescope with a resolution R=45000 and signal-to-noise ratio up to 250 in the
wavelength region 3638-10275 \AA. The adopted atmospheric parameters correspond
to an effective temperature \Tef=4475 K, a surface gravity \lgg=1.0, a
microturbulent velocity \vmi=1.7 \kms, and a macroturbulent velocity \vma=4
\kms. The abundances of 43 chemical elements were determined with the method of
spectrum synthesis. The large overabundances (by 1 dex relative to iron) of
elements with Z$>38$ are shown to follow the same pattern as the solar
r-abundances. The present HD221170 analysis confirms the non-universality of
the r-process, or more exactly the observation that the astrophysical sites
hosting the r-process do not always lead to a unique relative abundance
distribution for the bulk Ba to Hg elements, the Pb-peak elements, and the
actinides.",0409547v1
2004-09-24,Three-Dimensional Delayed-Detonation Model of Type Ia Supernova,"We study a Type Ia supernova explosion using large-scale three-dimensional
numerical simulations based on reactive fluid dynamics with a simplified
mechanism for nuclear reactions and energy release. The initial deflagration
stage of the explosion involves a subsonic turbulent thermonuclear flame
propagating in the gravitational field of an expanding white dwarf. The
deflagration produces an inhomogeneous mixture of unburned carbon and oxygen
with intermediate-mass and iron-group elements in central parts of the star.
During the subsequent detonation stage, a supersonic detonation wave propagates
through the material unburned by the deflagration. The total energy released in
this delayed-detonation process, (1.3-1.6)x10^51 ergs, is consistent with a
typical range of kinetic energies obtained from observations. In contrast to
the deflagration model that releases only about 0.6x10^51 ergs, the
delayed-detonation model does not leave carbon, oxygen, and intermediate-mass
elements in central parts of a white dwarf. This removes the key disagreement
between three-dimensional simulations and observations, and makes a delayed
detonation the mostly likely mechanism for Type Ia supernova explosions.",0409598v1
2004-09-26,The Low X-Ray State of LS 5039 / RX J1826.2-1450,"Recent XMM-Newton and Chandra observations of the high mass X-ray binary LS
5039 / RX J1826.2-1450 caught the source in a faint X-ray state. In contrast
with previous RXTE observations, we fail to detect any evidence of iron line
emission. We also fail to detect X-ray pulsations. The X-ray spectrum can be
well fitted by a simple powerlaw, slightly harder than in previous
observations, and does not require the presence of any additional disk or
blackbody component. XMM-Newton data imply an X-ray photoelectric absorption
($N_{\rm H} \sim 7 \times 10^{21}$ cm$^{-2}$) consistent with optical
reddening, indicating that no strong local absorption occurs at the time of
these observations. We discuss possible source emission mechanisms and
hypotheses on the nature of the compact object, giving particular emphasis to
the young pulsar scenario.",0409608v1
2004-09-27,A puzzling event during the X-ray emission of the binary system GX 1+4,"We report on a long X-ray observation of the slow-rotating binary pulsar GX
1+4. BeppoSAX observed, in the 0.1-200 keV energy range, an event in which the
source flux dropped for almost a day, and then recovered. During this event
only the high-energy emission was found to be pulsed and the pulsations were
shifted in phase of ~0.2 . The spectrum during the event was well fitted by a
Compton-reflection model. A broad iron line at ~6.55 keV was present outside of
the event, where instead two narrow emission lines at ~6.47 keV and ~7.05 keV
were detected. The pulse profile was highly variable as a function of both
energy and time. We interpret this low-flux event as an occultation of the
direct X-ray emission, due to the increase of a torus-like accretion disk; we
then discuss similarities between this source and the recently discovered
highly absorbed INTEGRAL sources.",0409626v3
2004-09-29,Fluorescence photons produced in air by extensive air showers,"The air fluorescence technique has long been used to detect extensive air
showers and to reconstruct its geometry and energy. The fluorescence photon
yield of an electron in air is of main importance in the reconstruction
procedure. Historically, the fluorescence yield used in the reconstruction of
the showers is approximated at all energies by that of an electron with kinetic
energy of 80 MeV, because these are the most abundant in a shower.
  In this paper, we calculate the fluorescence yield taking into account the
energy spectrum of electrons in showers initiated by proton and iron nuclei as
a function of height. We compare our results with previous calculations based
on mono energetic electrons (80 MeV) and a difference in excess of 8% is found.
Finally, the influence of a more realistic fluorescence yield in the shower
energy reconstruction is also discussed.",0409727v1
2004-10-05,Black Hole Spin in AGN and GBHCs,"We discuss constraints on black hole spin and spin-related astrophysics as
derived from X-ray spectroscopy. After a brief discussion about the robustness
with which X-ray spectroscopy can be used to probe strong gravity, we summarize
how these techniques can constrain black hole spin. In particular, we highlight
XMM-Newton studies of the Seyfert galaxy MCG-6-30-15 and the stellar-mass black
hole GX339-4. The broad X-ray iron line profile, together with reasonable and
general astrophysical assumptions, allow a non-rotating black hole to be
rejected in both of these sources. If we make the stronger assertion of no
emission from within the innermost stable circular orbit, the MCG-6-30-15 data
constrain the dimensionless spin parameter to be a>0.93. Furthermore, these
XMM-Newton data are already providing evidence for exotic spin-related
astrophysics in the central regions of this object. We conclude with a
discussion of the impact that Constellation-X will have on the study of strong
gravity and black hole spin.",0410116v1
2004-10-08,Magnetorotational supernovae,"We present the results of 2D simulations of the magnetorotational model of a
supernova explosion. After the core collapse the core consists of rapidly a
rotating proto-neutron star and a differentially rotating envelope. The
toroidal part of the magnetic energy generated by the differential rotation
grows linearly with time at the initial stage of the evolution of the magnetic
field. The linear growth of the toroidal magnetic field is terminated by the
development of magnetohydrodynamic instability, leading to drastic acceleration
in the growth of magnetic energy. At the moment when the magnetic pressure
becomes comparable with the gas pressure at the periphery of the proto-neutron
star $\sim 10-15$km from the star centre the MHD compression wave appears and
goes through the envelope of the collapsed iron core. It transforms soon to the
fast MHD shock and produces a supernova explosion. Our simulations give the
energy of the explosion $0.6\cdot 10^{51}$ ergs. The amount of the mass ejected
by the explosion is $\sim 0.14M_\odot$. The implicit numerical method, based on
the Lagrangian triangular grid of variable structure, was used for the
simulations.",0410234v2
2004-10-19,Metallicity measurements using atomic lines in M and K dwarf stars,"We report the first survey of chemical abundances in M and K dwarf stars
using atomic absorption lines in high resolution spectra. We have measured Fe
and Ti abundances in 35 M and K dwarf stars using equivalent widths measured
from (lambda / Delta lambda) = 33,000 spectra. Our analysis takes advantage of
recent improvements in model atmospheres of low-temperature dwarf stars. The
stars have temperatures between 3300 and 4700 K, with most cooler than 4100 K.
They cover an iron abundance range of -2.44 < [Fe/H] < +0.16. Our measurements
show [Ti/Fe] decreasing with increasing [Fe/H], a trend similar to that
measured for warmer stars where abundance analysis techniques have been tested
more thoroughly. This study is a step toward the observational calibration of
procedures to estimate the metallicity of low-mass dwarf stars using
photometric and low-resolution spectral indices.",0410452v1
2004-10-22,Is the interstellar gas of starburst galaxies well mixed?,"The extent to which the ISM in galaxies is well mixed is not yet settled.
Measured metal abundances in the diffuse neutral gas of star--forming gas--rich
dwarf galaxies are deficient with respect to that of the ionized gas. The
reasons, if real, are not clear and need to be based on firm grounds. Far-UV
spectroscopy of giant HII regions such as NGC604 in the spiral galaxy M33 using
FUSE allows us to investigate possible systematic errors in the metallicity
derivation. We still find underabundances of nitrogen, oxygen, argon, and iron
in the neutral phase by a factor of~6. This could either be explained by the
presence of less chemically evolved gas pockets in the sightlines or by dense
clouds out of which HIIregions form. Those could be more metallic than the
diffuse medium.",0410528v1
2004-10-29,On the primary particle type of the most energetic Fly's Eye event,"The longitudinal profile of the 320 EeV event observed by the Fly's Eye
experiment is analysed. A method of testing the hypothesis of a specific
primary particle type is described. Results for different particle types are
summarized. For hadronic primaries between proton and iron nuclei, the
discrepancy between observed and simulated profiles is in the range of 0.6-1.0
sigma for two different hadronic interaction models investigated. For primary
photons, the discrepancy is 1.5sigma assuming a standard extrapolation of the
photonuclear cross-section with energy. Larger values of the cross-section at
highest energies make primary photon showers more similar to hadron-initiated
events. The influence of varying the extrapolation of the photonuclear
cross-section is studied.",0410739v1
2004-11-08,The Metallicity dependence of the Cepheid Period-Luminosity relation: methodology and results,"We present the results of an observational campaign undertaken to assess the
influence of the iron content on the Cepheid Period-Luminosity relation. Our
data indicate that this dependence is not well represented by a simple linear
relation. Rather, the behaviour is markedly non monotonic, with the correction
peaking at about solar metallicity and declining for higher and lower values of
[Fe/H].",0411190v1
2004-11-10,High Resolution Spectroscopy of 4U 1728-34 from a Simultaneous Chandra-RXTE Observation,"We report on a simultaneous Chandra and RossiXTE observation of the LMXB
atoll bursting source 4U 1728-34 performed on 2002 March 3-5. We fitted the
1.2-35 keV continuum spectrum with a blackbody plus a Comptonized component. An
overabundance of Si by a factor of ~2 with respect to Solar abundance is
required for a satisfactory fit. Large residuals at 6-10 keV can be fitted by a
broad (FWHM ~ 1.6 keV) Gaussian emission line, or, alternatively, by absorption
edges associated with Fe I and Fe XXV at ~7.1 keV and ~9 keV, respectively. In
this interpretation, we find no evidence of a broad, or narrow Fe Kalpha line,
between 6 and 7 keV. We tested our alternative modeling of the iron Kalpha
region by reanalyzing a previous BeppoSAX observation of 4U 1728-34, finding a
general agreement with our new spectral model.",0411270v2
2004-11-15,XMM-Newton observations of the Lockman Hole: III. A relativistic Fe line in the mean X-ray spectra of type-1 and type-2 AGN,"Using the 770 ksec XMM-Newton survey of the Lockman Hole field in combination
with extensive optical identifications of the AGN population, we derive an
average rest-frame spectrum of AGN types-1 and 2. The most prominent feature in
the averaged spectrum is a strong fluorescent Fe line. In both type-1 and
type-2 AGN, a clear relativistic line profile is rev ealed. A laor line profile
with an inner disk radius smaller than the last stabl e orbit of a
Schwarzschild black hole is most consistent with the data, indicati ng that the
average supermassive black hole has significant spin. Equivalent wid ths of the
broad relativistic lines range between 400--600 eV. We used the disk reflection
model to compare the observed strength of the line with the amplitude of the
reflection component, concluding that to consistently describe the observations
the average iron abundance should be about three times the solar value.",0411340v2
2004-11-25,Muons with E_th >= 1 Gev and Mass Composition in the Energy Range 10^{18}-10^{20} ev Observed by Yakutsk Eas Array,"The ratio of the muon flux density to charged particle flux density at
distances of 300 and 600 m from the shower axis ($\rhom(300)/\rhos(300)$ and
$\rhom(600)/\rhos(600)$) is measured. In addition, the energy dependence of
$\rhom(1000)$ is analysed for showers with energies above $10^{18}$ eV. A
comparison between the experimental data and calculations performed with the
QGSJET model is given for the cases of primary proton, iron nucleus and gamma-
ray. We conclude that the showers with $\E\ge3\times10^{18}$ eV can be formed
by light nuclei with a pronounced fraction of protons and helium nuclei. It is
not excluded however that a small part of showers with energies above $10^{19}$
eV could be initiated by primary gamma-rays.",0411683v2
2004-12-03,Stellar Evolution with Enriched Surface Convection Zones I. General Effects of Planet Consumption,"Abundance analyses of stars with planets have revealed that their
metallicities are enhanced relative to field stars. Such a trend was originally
suggested to be due to accretion of iron-rich planetary material. Based on this
assumption, we have developed a stellar evolution code to model stars with
non-uniform metallicity distributions. We have calculated ``polluted'' stellar
evolution tracks for stars with M=0.9-1.2 M_sun. Our models encompass a range
of initial metal content from Z=0.01 to 0.03, and include metallicity
enhancements within the stellar convection zone corresponding to
Delta-Z=0.005-0.03. We find that the primary effects of metal enhancement on
stellar structure and evolution are expansion of the convection zone and
downward shift of effective temperature. In addition, we have computed the
surface metallicities expected for stars of different mass for fixed quantities
of pollution; there appears to be no correlation with present observational
data on the metallicities of stars known to harbor planets.",0412104v2
2004-12-09,XMM-Newton observation of 4U 1543-475: the X-ray spectrum of a stellar-mass black-hole at low luminosity,"We report the results of an observation of the galactic black-hole binary 4U
1543-475 performed by XMM-Newton on 2002 August 18, about two months after the
start of an outburst detected by Rossi-XTE. Despite the relatively low flux of
the source, corresponding to a luminosity Lx ~ 4x10^34 erg/s (i.e. about
10^(-5) times the Eddington luminosity), we could obtain a good quality
spectrum thanks to the high throughput of the XMM-Newton EPIC instrument. The
spectrum is well fit by a power law with photon index 1.9-2 without any
evidence for iron emission lines or for thermal emission from an accretion
disk. We could estimate an upper-limit on the disk bolometric luminosity as a
function of the colour temperature: it is always lower than ~10^33 erg/s, i.e.
less than 10 % of the source total luminosity. Finally, we evaluated that the
disk colour temperature must satisy the condition kTcol<0.25 keV in order to
obtain an acceptable value for the disk inner radius.",0412209v1
2004-12-15,The XMM-Newton spectrum of the high-z optically-obscured QSO RX J1343.4+0001: a classic radio quiet QSO,"We present a 30 ks XMM-Newton observation of the z = 2.35 Type II radio quiet
quasar RX J1343.4+0001. These data provide the first good quality X-ray
spectrum for this object. We measured a continuum slope Gamma = 1.85+/-0.10
with only an upper limit on the column density of the absorbing material of
Nh(z) <~ 10^22 cm^-2 as well as an Fe Kalpha emission line at the 3 sigma
confidence level. We do not find therefore a highly absorbed object nor a truly
flat spectrum as suggested on the basis of previous less sensitive ROSAT and
ASCA measurements. The Nh(z) upper limit is fully consistent with the optical
extinction 3 <A_V <10 inferred from IR observations. The Fe Kalpha line is
consistent with fluorescence from neutral iron and, noteworthy, is one of the
most distant observed so far. The X-ray spectral properties of RX J1343.4+0001
agree well with the steep continuum slope (Gamma ~ 1.9) being independent of
increasing redshift and luminosity as inferred by X-ray studies of large
samples of RQ QSOs.",0412360v1
2004-12-15,Determining the grain composition of the interstellar medium with high resolution X-ray spectroscopy,"We investigate the ability of high resolution X-ray spectroscopy to directly
probe the grain composition of the interstellar medium. Using iron K-edge
experimental data of likely ISM dust candidates taken at the National
Synchrotron Light Source at Brookhaven National Laboratory and the Advanced
Photon Source at Argonne National Laboratory, we explore the prospects for
determining the chemical composition of astrophysical dust and discuss a
technique for doing so. Focusing on the capabilities of the AstroE2 XRS
micro-calorimeters, we assess the limiting effects of spectral resolution and
noise for detecting significant X-ray absorption fine structure signal in
astrophysical environments containing dust. We find that given sufficient
signal, the resolution of the XRS will allow us to definitively distinguish gas
from dust phase absorption, and certain chemical compositions.",0412393v1
2004-12-16,The Metallicity of Post-T Tauri Stars: A preliminary approach to the understanding of the metal enrichment of stars harboring planets,"The metallicity of young low mass Post-T Tauri stars in coeval associations
is practically unknown. This work is the beginning of a systematic measurement
of these metallicities based on high resolution spectra of low rotating members
of these associations. Here, we present an application by examining the
behavior of the Iron abundance with stellar mass and temperature of some
members of an association 30 Myr old. This will test the possibility of
explaining the high metallic content of stars with planets by means of
injection of planetesimals during this early stage of evolution.",0412398v1
2004-12-19,Extreme Test of Quantum Theory with Black Holes,"We propose an extreme test of quantum theory using astrophysical black holes
and entangled photons from atomic cascades. The identification of a cascade
emission close to a black-hole event horizon would allow us to observe photons
entangled with partners that have fallen behind the horizon. The experiment
involves testing the characteristic cos^2(theta) modulation of photon
transmission through a pair of polarisers at relative angle theta (Malus' law).
For single photons, Malus' law is a remarkable feature of quantum theory: it is
equivalent to expectation additivity for incompatible observables, and is
generically violated for hidden-variables theories with nonstandard probability
distributions. An experiment with entangled states straddling an event horizon
is motivated by the Hawking information loss puzzle, as well as on general
grounds. In principle, one could test the currently observed X-ray photons in
iron lines from black-hole accretion discs. However, only a small fraction
(~0.6%) have cascade partners, and current X-ray polarimetry does not permit
successive measurements on a single X-ray photon. A realisable experiment
requires the identification of an appropriate cascade in a more convenient
frequency band.",0412503v1
2005-01-20,Superfluidity in the Solar Interior: Implications for Solar Eruptions and Climate,"Efforts to understand unusual weather or abrupt changes in climate have been
plagued by deficiencies of the standard solar model (SSM). While it assumes
that our primary source of energy began as a homogeneous ball of hydrogen (H)
with a steady, well-behaved H-fusion reactor at its core, observations instead
reveal a very heterogeneous, dynamic Sun. As examples, the upward acceleration
and departure of H+ ions from the surface of the quiet Sun and abrupt climatic
changes, including geomagnetic reversals and periodic magnetic storms that
eject material from the solar surface are not explained by the SSM. The present
magnetic fields are probably deep-seated remnants of very ancient origin. These
could have been generated from two mechanisms. These are: a) Bose-Einstein
condensation of iron-rich, zero-spin material into a rotating, superfluid,
superconductor surrounding the solar core and/or b) superfluidity and quantized
vortices in nucleon-paired Fermions at the core.",0501441v1
2005-01-31,New Elemental Abundances for V1974 Cygni,"We present a new analysis of existing optical and ultraviolet spectra of the
ONeMg nova V1974 Cygni 1992. Using these data and the photoionization code
Cloudy, we have determined the physical parameters and elemental abundances for
this nova. Many of the previous studies of this nova have made use of incorrect
analyses and hence a new study was required. Our results show that the ejecta
are enhanced, relative to solar, in helium, nitrogen, oxygen, neon, magnesium
and iron. Carbon was found to be subsolar. We find an ejected mass of ~2x10e-4
solar masses. Our model results fit well with observations taken at IR, radio,
sub-millimeter and X-ray wavelengths.",0501648v1
2005-02-28,Nuclear Astrophysics,"Nuclear physics has a long and productive history of application to
astrophysics which continues today. Advances in the accuracy and breadth of
astrophysical data and theory drive the need for better experimental and
theoretical understanding of the underlying nuclear physics. This paper will
review some of the scenarios where nuclear physics plays an important role,
including Big Bang Nucleosynthesis, neutrino production by our sun,
nucleosynthesis in novae, the creation of elements heavier than iron, and
neutron stars. Big-bang nucleosynthesis is concerned with the formation of
elements with A <= 7 in the early Universe; the primary nuclear physics inputs
required are few-nucleon reaction cross sections. The nucleosynthesis of
heavier elements involves a variety of proton-, alpha-, neutron-, and
photon-induced reactions, coupled with radioactive decay. The advent of
radioactive ion beam facilities has opened an important new avenue for studying
these processes, as many involve radioactive species. Nuclear physics also
plays an important role in neutron stars: both the nuclear equation of state
and cooling processes involving neutrino emission play a very important role.
Recent developments and also the interplay between nuclear physics and
astrophysics will be highlighted.",0502588v1
2005-03-08,One-armed Spiral Instability in a Low T/|W| Postbounce Supernova Core,"A three-dimensional, Newtonian hydrodynamic technique is used to follow the
postbounce phase of a stellar core collapse event. For realistic initial data
we have employed post core-bounce snapshots of the iron core of a 20 solar mass
star. The models exhibit strong differential rotation but have centrally
condensed density stratifications. We demonstrate for the first time that such
postbounce cores are subject to a so-called low-T/|W| nonaxisymmetric
instability and, in particular, can become dynamically unstable to an m=1 -
dominated spiral mode at T/|W| ~ 0.08. We calculate the gravitational wave
emission by the instability and find that the emitted waves may be detectable
by current and future GW observatories from anywhere in the Milky Way.",0503187v2
2005-03-23,Abundance trends in kinematical groups of the Milky Way's disk,"We have compiled a large catalogue of metallicities and abundance ratios from
the literature in order to investigate abundance trends of several alpha and
iron peak elements in the thin disk and the thick disk of the Galaxy. The
catalogue includes 743 stars with abundances of Fe, O, Mg, Ca, Ti, Si, Na, Ni
and Al in the metallicity range -1.30 < [Fe/H] < +0.50. We have checked that
systematic differences between abundances measured in the different studies
were lower than random errors before combining them. Accurate distances and
proper motions from Hipparcos, and radial velocities from several sources have
been retreived for 639 stars and their velocities (U,V,W) and galactic orbits
have been computed. Ages of 322 stars have been estimated with the Bayesian
method of isochrone fitting developped by Pont & Eyer (2004). Two samples
kinematically representative of the thin and thick disks have been selected,
taking into account the Hercules stream which is intermediate in kinematics,
but with a probable dynamical origin. [Abridged...]",0503498v1
2005-03-30,X-ray line tomography of AGN-induced motion in clusters of galaxies,"The thermal broadening of emission lines of heavy ions is small enough such
that Doppler shifts due to bulk motions may be detected with the next
generation of X-ray observatories. This opens up the possibility to study gas
velocities in the intra-cluster medium. Here we study the effect of bulk
motions induced by a central active galactic nucleus (AGN) on the emission
lines around the FeXXV complex. We have modelled the evolution of AGN-induced
bubbles in a realistic cosmological framework and studied the resulting FeXXV
line profiles. We found that in clusters with AGN feedback, motions induced by
the inflation of bubbles and their buoyant rise lead to distinct features in
the iron emission lines that are detectable with a spectral resolution of about
10 eV. These observations will help to determine the mechanical energy that
resides in the bubbles and thereby the kinetic luminosity of the AGN.",0503656v2
2005-03-30,On the fine structure of the sunspot penumbrae. II. The nature of the Evershed flow,"We investigate the fine structure of the sunspot penumbra by means of a model
that allows for a flux tube in horizontal pressure balance with the magnetic
background atmosphere in which it is embedded. We apply this model to
spectropolarimetric observations of two neutral iron lines at 1.56 $\mu$m and
invert several radial cuts in the penumbra of the same sunspot at two different
heliocentric angles. In the inner part of the penumbra we find hot flux tubes
that are somewhat inclined to the horizontal. They become gradually more
horizontal and cooler with increasing radial distance. This is accompanied by
an increase in the velocity of the plasma and a decrease of the gas pressure
difference between flux tube and the background component. At large radial
distances the flow speed exceeds the critical speed and evidence is found for
the formation of a shock front. These results are in good agreement with
simulations of the penumbral fine structure and provide strong support for the
siphon flow as the physical mechanism driving the Evershed flow.",0503677v1
2005-04-12,The temperature structure in the core of Sersic 159-03,"We present results from a new 120 ks XMM-Newton observation of the cluster of
galaxies Sersic 159-03. In this paper we focus on the high-resolution X-ray
spectra obtained with the Reflection Grating Spectrometer (RGS). The spectra
allow us to constrain the temperature structure in the core of the cluster and
determine the emission measure distribution as a function of temperature. We
also fit the line widths of mainly oxygen and iron lines.",0504262v1
2005-05-06,Dust Scattering in Miras R Car and RR Sco resolved by optical interferometric polarimetry,"We present optical interferometric polarimetry measurements of the Mira-like
variables R Car and RR Sco, using the Sydney University Stellar Interferometer.
By making visibility measurements in two perpendicular polarisations, the
relatively low-surface brightness light scattered by atmospheric dust could be
spatially separated from the bright Mira photospheric flux. This is the first
reported successful use of long-baseline optical interferometric polarimetry.
Observations were able to place constraints on the distribution of
circumstellar material in R Car and RR Sco. The inner radius of dust formation
for both stars was found to be less than 3 stellar radii: much closer than the
expected innermost stable location for commonly-assumed astrophysical ``dirty
silicate'' dust in these systems (silicate dust with a significant iron
content). A model with the dust distributed over a shell which is geometrically
thin compared to the stellar radius was preferred over an outflow. We propose
dust components whose chemistry and opacity properties enable survival at these
extreme inner radii.",0505112v1
2005-05-14,"Family ties: abundances in Terzan 7, a Sgr dSph globular cluster","We study the chemical composition of 5 giant stars in the globular cluster
Terzan 7 associated with the Sagittarius dwarf spheroidal galaxy (Sgr dSph),
based on high resolution UVES-VLT spectra. We confirm the metallicity found by
previous high resolution investigations: [Fe/H] ~ -0.6. We also show that this
cluster displays the same low alpha-element to iron ratio found in Sgr dSph
field stars of similar metallicity, as well as the same low Ni/Fe ratio. These
chemical signatures are characteristic of the Sgr dSph system, and appear to be
shared both by the globular cluster Pal 12, which was most likely stripped from
Sgr by tidal interaction, and by Pal 5, which may also have belonged in the
past to the Sgr dSph system. Intriguingly even globular cluster Ruprecht 106,
although not associated to Sgr, displays similar characteristics.",0505307v1
2005-05-19,Early star formation in the Galaxy from beryllium and oxygen abundances,"We investigate the evolution of the star formation rate in the early Galaxy
using beryllium and oxygen abundances in metal poor stars. Specifically, we
show that stars belonging to two previously identified kinematical classes (the
so-called ``accretion'' and ``dissipative'' populations) are neatly separated
in the [O/Fe] vs. Log(Be/H) diagram. The dissipative population follows the
predictions of our model of Galactic evolution for the thick disk component,
suggesting that the formation of this stellar population occurred on a
timescale significantly longer (by a factor ~5-10) than the accretion
component. The latter shows a large scatter in the [O/Fe] vs. Log(Be/H)
diagram, probably resulting from the inhomogeneous enrichment in oxygen and
iron of the protogalactic gas. Despite the limitation of the sample, the data
suggest that the combined use of products of spallation reactions (like
beryllium) and elemental ratios of stellar nucleosynthesis products (like
[O/Fe]) can constrain theoretical models for the formation and early evolution
of our Galaxy.",0505396v1
2005-06-20,Nitrogen-deficient and iron-rich associated absorbers with oversolar metallicities towards the quasar HE0141-3932,"HE0141-3932 (zem=1.80) is a bright blue radio-quite quasar which reveals an
emission line spectrum with an unusually weak Ly-alpha line. In addition, large
redshift differences (Delta z=0.05) are observed between high ionization and
low ionization emission lines. Absorption systems identified at z=1.78, 1.71,
and 1.68 show mild oversolar metallicities (Z ~= 1-2Zsolar) and can be
attributed to the associated gas clouds ejected from the circumnuclear region.
The joint analysis of the emission and absorption lines leads to the conclusion
that this quasar is seen almost pole-on. Its apparent luminosity may be Doppler
boosted by ~10 times. The absorbing gas shows high abundance of Fe, Mg, and Al
([Fe, Mg, Al/C] ~= 0.15+/-0.10) along with underabundance of N ([N/C]<=-0.5).
This abundance pattern is at variance with current chemical evolution models of
QSOs predicting [N/C]>0 and [Fe/C]<0 at Z ~ Zsolar. Full details of this work
are given in Reimers et al. (2005).",0506446v1
2005-06-24,Kappa-mechanism excitation of retrograde mixed modes in rotating B-type stars,"I examine the stability of retrograde mixed modes in rotating B-type stars.
These modes can be regarded as a hybrid between the Rossby modes that arise
from conservation of vorticity, and the Poincare modes that are gravity waves
modified by the Coriolis force. Using a non-adiabatic pulsation code based
around the traditional approximation, I find that the modes are unstable in
mid- to late-B type stars, due to the same iron-bump opacity mechanism usually
associated with SPB and $\beta$ Cep stars. At one half of the critical rotation
rate, the instability for $m=1...4$ modes spans the spectral types B4 to A0.
Inertial-frame periods of the unstable modes range from 100 days down to a
fraction of a day, while normalized growth rates can reach in excess of
$10^{-5}$.
  I discuss the relevance of these findings to SPB and pulsating Be stars, and
to the putative Maia class of variable star. I also outline some of the
questions raised by this discovery of a wholly-new class of pulsational
instability in early-type stars.",0506580v3
2005-06-25,The Ital-FLAMES survey of the Sagittarius dwarf Spheroidal galaxy. I. Chemical abundances of bright RGB stars,"We present iron and $\alpha$ element (Mg, Ca, Ti) abundances for a sample of
15 Red Giant Branch stars belonging to the main body of the Sagittarius dwarf
Spheroidal galaxy. Abundances have been obtained from spectra collected using
the high resolution spectrograph FLAMES-UVES mounted at the VLT. Stars of our
sample have a mean metallicity of [Fe/H]=-0.41$\pm$0.20 with a metal poor tail
extending to [Fe/H]=-1.52. The $\alpha$ element abundance ratios are slightly
subsolar for metallicities higher than [Fe/H]\gtsima-1, suggesting a slow star
formation rate. The [$\alpha$/Fe] of stars having [Fe/H]$<$-1 are compatible to
what observed in Milky Way stars of comparable metallicity.",0506622v2
2005-07-08,The relativistic shift of narrow spectral features from black-hole accretion discs,"Transient spectral features have been discovered in the X-ray spectra of
Active Galactic Nuclei, mostly in the 5--7 keV energy range. Several
interpretations were proposed for the origin of these features. We examined a
model of Doppler boosted blue horns of the iron line originating from a spot in
a black hole accretion disc, taking into account different approximations of
general relativistic light rays and the resulting shift of energy of photons.
We provide a practical formula for the blue horn energy of an intrinsically
narrow line and assess its accuracy by comparing the approximation against an
exact value, predicted under the assumption of a planar accretion disc. The
most accurate approximation provides excellent agreement with the spot orbital
radius down to the marginally stable orbit of a non-rotating black hole.",0507196v1
2005-07-08,Probing the outer edge of an accretion disk: A Her X-1 turn-on observed with RXTE,"We present the analysis of Rossi X-ray Timing Explorer (RXTE) observations of
the turn-on phase of a 35 day cycle of the X-ray binary Her X-1. During the
early phases of the turn-on, the energy spectrum is composed of X-rays
scattered into the line of sight plus heavily absorbed X-rays. The energy
spectra in the 3-17 keV range can be described by a partial covering model,
where one of the components is influenced by photoelectric absorption and
Thomson scattering in cold material plus an iron emission line at 6.5 keV. In
this paper we show the evolution of spectral parameters as well as the
evolution of the pulse profile during the turn-on. We describe this evolution
using Monte Carlo simulations which self-consistently describe the evolution of
the X-ray pulse profile and of the energy spectrum.",0507198v1
2005-07-14,Heavy element abundances in DAO white dwarfs measured from FUSE data,"We present heavy element abundance measurements for 16 DAO white dwarfs,
determined from Far-Ultraviolet Spectroscopic Explorer {FUSE} spectra. Evidence
of absorption by heavy elements was found in the spectra of all the objects.
Measurements were made using models that adopted the temperatures, gravities
and helium abundances determined from both optical and FUSE data by Good et al.
(2004). Despite the different evolutionary paths that the types of DAO white
dwarfs are thought to evolve through, their abundances were not found to vary
significantly, apart from for the silicon abundances. Abundances measured when
the FUSE derived values of temperature, gravity and helium abundance were
adopted were, in general, a factor 1-10 higher than those determined when the
optical measure of those parameters was used. Satisfactory fits to the
absorption lines were achieved in approximately equal number. The models that
used the FUSE determined parameters seemed better at reproducing the strength
of the nitrogen and iron lines, while for oxygen, the optical parameters were
better.",0507341v1
2005-07-19,The Type Ia Supernova Rate,"We explore the idea that the Type Ia supernovae (SNe Ia) rate consists of two
components: a prompt piece that is proportional to the star formation rate
(SFR) and an extended piece that is proportional to the total stellar mass. We
fit the parameters of this model to the local observations of Mannucci and
collaborators and then study its impact on three important problems. On cosmic
scales, the model reproduces the observed SNe Ia rate density below z=1, and
predicts that it will track the measured SFR density at higher redshift,
reaching a value of 1-3.5 X 10^-4 per yr per Mpc^3 at z=2. In galaxy clusters,
a large prompt contribution helps explain the iron content of the intracluster
medium. Within the Galaxy, the model reproduces the observed stellar [O/Fe]
abundance ratios if we allow a short (approximately 0.7 Gyr) delay in the
prompt component. Ongoing medium-redshift SN surveys will yield more accurate
parameters for our model",0507456v2
2005-07-20,UHECR Composition Measurements Using the HiRes-II Detector,"While stereo measurements of extensive air showers allow a more precise
determination of the depth of shower maximum and hence the composition of
UHECR's, monocular measurements allow one to go much lower in energy. Since the
composition of UHECR seems to constant throughout the HiRes stereo energy range
but changing just below it, this is not a trivial lowering of the energy
threshold. We fit the observed Xmax distribution to a combination of expected
proton and iron Xmax distributions, using two different interaction models, to
determine the relative fraction of light and heavy components throughout the
HiRes monocular energy range. Using a two component fit allows both the mean
Xmax and the width of the Xmax distribution to contribute composition
measurement and allows us to deal with the Xmax acceptance bias caused by
limited elevation coverage. An updated analysis from a larger data set will be
presented in Pune.",0507483v1
2005-07-27,Gamma-Rays from Single Lobe Supernova Explosions,"Multi-dimensional simulations of the neutrino-driven mechanism behind
core-collapse supernovae have long shown that the explosions from this
mechanism would be asymmetric. Recently, detailed core-collapse simulations
have shown that the explosion may be strongest in a single direction. We
present a suite of simulations modeling these ``single-lobe'' supernova
explosions of a 15 solar mass red supergiant star, focusing on the effect these
asymmetries have on the gamma-ray emission and the mixing in the explosion. We
discuss how asymmetries in the explosion mechanism might explain many of the
observed ``asymmetries'' of supernovae, focusing on features of both supernova
1987A and the Cas A supernova remnant. In particular, we show that single-lobe
explosions provide a promising solution to the redshifted iron lines of
supernova 1987A. We also show that the extent of mixing for explosive burning
products depends sensitively on the angular profile of the velocity asymmetry
and can be much more extensive than previously assumed.",0507651v1
2005-08-10,Relativistic outflow in CXO CDFS J033260.0-274748,"In this letter we report the detection of a strong and extremely blueshifted
X-ray absorption feature in the 1 Ms Chandra spectrum of CXO CDFS
J033260.0-274748, a quasar at z = 2.579 with L_2-10keV ~ 4x10^44 ergs/s. The
broad absorption feature at ~ 6.3 keV in the observed frame can be fitted
either as an absorption edge at 20.9 keV or as a broad absorption line at 22.2
keV rest frame. The absorber has to be extremely ionized with an ionization
parameter \xi ~ 10^4, and a high column density N_H >5x10^23 cm^-2. We reject
the possibility of a statistical or instrumental artifact. The most likely
interpretation is an extremely blueshifted broad absorption line or absorption
edge, due to H or He--like iron in a relativistic jet-like outflow with bulk
velocity of ~ 0.7-0.8 c. Similar relativistic outflows have been reported in
the X-ray spectra of several other AGNs in the past few years.",0508225v1
2005-08-19,The magnetic structure of neutron stars and their surface-to-core temperature relation,"We study the relation between the mean effective surface temperature T_s and
the internal temperature T_b for magnetic neutron stars, assuming that the
magnetic field near the surface has a presumably small-scale structure. The
heavy-element (iron) and light-element (accreted) heat-blanketing envelopes are
considered, and the results are compared with the case of a dipole magnetic
field. We argue that the difference in the T_b(T_s)-relation for different
magnetic configurations is always much smaller than a possible difference
caused by variations of the chemical composition in the envelope.",0508415v2
2005-08-29,Highly ionized iron absorption lines from outflowing gas in the X-ray spectrum of NGC 1365,"We present the discovery of four absorption lines in the X-ray spectrum of
the Seyfert Galaxy NGC 1365, at energies between 6.7 and 8.3 keV. The lines are
detected with high statistical confidence (from >20sigma for the strongest to
\~4sigma for the weakest) in two XMM-Newton observations 60 ksec long. We also
detect the same lines, with lower signal-to-noise (but still >2sigma for each
line) in two previous shorter (~10 ksec) XMM observations. The spectral
analysis identifies these features as FeXXV and FeXXVI Kalpha and Kbeta lines,
outflowing with velocities varying between ~1000 to ~5000 km/s among the
observations. These are the highest quality detections of such lines so far.
The high equivalent widths (EW(Kalpha)~100 eV) and the Kalpha/Kbeta ratios
imply that the lines are due to absorption of the AGN continuum by a highly
ionized gas with column density N_H~5x10^23 cm^{-2}",0508608v1
2005-09-07,An Observationally Motivated Framework for AGN Heating of Cluster Cores,"The cooling-flow problem is a long-standing puzzle that has received
considerable recent attention, in part because the mechanism that quenches
cooling flows in galaxy clusters is likely to be the same mechanism that
sharply truncates the high end of the galaxy luminosity function. Most of the
recent models for halting cooling in clusters have focused on AGN heating, but
the actual heating mechanism has remained mysterious. Here we present a
framework for AGN heating derived from a Chandra survey of gas entropy profiles
within cluster cores. This set of observations strongly suggests that the inner
parts of cluster cores are shock-heated every ~10^8 years by intermittent AGN
outbursts, driven by a kinetic power output of ~ 10^45 erg/sec and lasting at
least 10^7 years. Beyond ~30 kpc these shocks decay to sound waves, releasing
buoyant bubbles that heat the core's outer parts. Between heating episodes,
cooling causes the core to relax toward an asymptotic pure-cooling profile. The
density distribution in this asymptotic profile is sufficiently peaked that the
AGN shock does not cause a core entropy inversion, allowing the cluster core to
retain a strong iron abundance gradient, as observed.",0509176v1
2005-09-09,A Comparison of the Chemical Evolutionary Histories of the Galactic Thin Disk and Thick Disk Stellar Populations,"We have studied 23 long-lived G dwarfs that belong to the thin disk and thick
disk stellar populations. Abundances have been derived for 24 elements: O, Na,
Mg, Al, Si, Ca, Ti, Sc, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Sr, Y, Zr, Ba, La, Ce,
Nd, and Eu. We find that the behavior of [alpha/Fe] and [Eu/Fe] vs. [Fe/H] are
quite different for the two populations. As has long been known, the thin disk
O, Mg, Si, Ca, and Ti ratios are enhanced relative to iron at the lowest
metallicities, and decline toward solar values as [Fe/H] rises above -1.0. For
the thick disk, the decline in [alpha/Fe] and [Eu/Fe] does not begin at [Fe/H]
= -1.0, but at -0.4. Other elements share this behavior, including Sc, Co, and
Zn, suggesting that at least in the chemical enrichment history of the thick
disk, these elements were manufactured in similar-mass stars. Combining our
results for the oldest and longest-lived stars with prior work, we find clear
signs for an independent origin for the Galactic thick disk. (Abridged)",0509267v1
2005-09-13,Formation of the First Stars,"How and when did the first generation of stars form at the end of the cosmic
dark ages? Quite generically, within variants of the cold dark matter model of
cosmological structure formation, the first sources of light are expected to
form in ~ 10^{6} M_sun dark matter potential wells at redshifts z > 20. I
discuss the physical processes that govern the formation of the first stars.
These so-called Population~III stars are predicted to be predominantly very
massive, and to have contributed significantly to the early reionization of the
intergalactic medium. Such an early reionization epoch is inferred from the
recent measurement of the Thomson optical depth by the {\it WMAP} satellite. I
address the importance of heavy elements in bringing about the transition from
an early star formation mode dominated by massive stars, to the familiar mode
dominated by low mass stars, at later times, and present possible observational
probes. This transition could have been gradual, giving rise to an
intermediate-mass population of still virtually metal-free stars (``Population
II.5''). These stars could have given rise to the peculiar class of black-hole
forming supernovae inferred from the abundance pattern of extremely iron-poor
stars.",0509354v1
2005-09-15,Evolution of Galaxies and the Tully-Fisher Relation,"We study the evolution of the [O/Fe]-[Fe/H] relation and the dependence of
the iron abundance on distance from the galactic plane z in a one-zone model
for a disk galaxy, starting from the beginning of star formation (Wiebe98). We
obtain good agreement with the observational data, including, for the first
time, agreement for the [Fe/H]-z relation out to heights of 16 kpc. We also
study the influence of the presence of dark matter in the galaxies on the
star-formation rate. Comparison of the observed luminosity of the Galaxy with
the model prediction places constraints on the fractional mass of dark matter,
which cannot be much larger than the fractional mass of visible matter, at
least within the assumed radius of the Galaxy, 20 kpc. We studied the evolution
of disk galaxies with various masses, which should obey the Tully-Fisher
relation, M \propto R^2. The Tully-Fisher relation can be explained as a
combination of a selection effect related to the observed surface brightnesses
of galaxies with large radii and the conditions for the formation for
elliptical galaxies.",0509423v2
2005-09-16,Analysis of extensive air showers with the hybrid code SENECA,"The ultrahigh energy tail of the cosmic ray spectrum has been explored with
unprecedented detail. For this reason, new experiments are exerting a severe
pressure on extensive air shower modeling. Detailed fast codes are in need in
order to extract and understand the richness of information now available. In
this sense we explore the potential of SENECA, an efficient hybrid
tridimensional simulation code, as a valid practical alternative to full Monte
Carlo simulations of extensive air showers generated by ultrahigh energy cosmic
rays. We discuss the influence of this approach on the main longitudinal
characteristics of proton, iron nucleus and gamma induced air showers for
different hadronic interaction models. We also show the comparisons of our
predictions with those of CORSIKA code.",0509503v1
2005-09-20,Acceptance of fluorescence detectors and its implication in energy spectrum inference at the highest energies,"Along the years HiRes and AGASA experiments have explored the fluorescence
and the ground array experimental techniques to measure extensive air showers,
being both essential to investigate the ultra-high energy cosmic rays. However,
such Collaborations have published contradictory energy spectra for energies
above the GZK cut-off. In this article, we investigate the acceptance of
fluorescence telescopes to different primary particles at the highest energies.
Using CORSIKA and CONEX shower simulations without and with the new
pre-showering scheme, which allows photons to interact in the Earth magnetic
field, we estimate the aperture of the HiRes-I telescope for gammas, iron
nuclei and protons primaries as a function of the number of simulated events
and primary energy. We also investigate the possibility that systematic
differences in shower development for hadrons and gammas could mask or distort
vital features of the cosmic ray energy spectrum at energies above the
photo-pion production threshold. The impact of these effects on the true
acceptance of a fluorescence detector is analyzed in the context of top-down
production models.",0509597v1
2005-09-28,An abundance analysis of the symbiotic star CH Cyg,"The photospheric abundances for the cool component of the symbiotic star CH
Cyg were calculated for the first time using high-resolution near-infrared
spectra and the method of of standard LTE analysis and atmospheric models. The
iron abundance for CH Cyg was found to be solar, [Fe/H] = 0.0+/-0.19. The
atmospheric parameters and metallicity for CH Cyg are found to be approximately
equal to those for nearby field M7 giants. The calculated [C/H] = -0.15, [N/H]
= +0.16, [O/H] = -0.07, and the isotopic ratios of 12C/13C and 16O/17O are
close to the mean values for single M giants that have experienced the first
dredge-up. A reasonable explanation for the absence of barium star-like
chemical peculiarities seems to be the high metallicity of CH Cyg. The emission
line technique was explored for estimating CNO ratios in the wind of the giant.",0509852v1
2005-10-07,Dust obscuration of DLA galaxies,"We show that the extinction of quasar absorbers increases exponentially with
the logarithmic column density of any volatile metal (e.g. zinc), with a
charateristic turning point above which the quasars are severely dimmed. We
derive the relation between extinction, HI column density, metallicity and
fraction of iron in dust in Damped Lyman alpha (DLA) systems. We use this
relation to estimate the effect of dust obscuration on the statistical
distributions of N(HI) and metallicity measured in magnitude-limited surveys of
DLAs. In the redshift range where the measurements of zinc column densities
have sufficient statistics (1.8 </= z </= 3) we find that the obscuration bias
affects the shapes of the observed distributions. The metallicity distribution
is particularly affected by the bias, which hampers the detection of DLA
galaxies with near solar metallicity. Our results perfectly reproduce, without
tuning the dust parameters, the DLA observational threshold log N(ZnII) </~
13.15 found by Boisse' and collaborators in 1998, in terms of a rapid rise of
the obscuration. Our predictions of the effects of the bias on the statistics
of DLAs are consistent with observational results obtained from unbiased
surveys of radio-selected quasars.",0510216v1
2005-10-14,Thermonuclear supernova simulations with stochastic ignition,"We apply an ad hoc model for dynamical ignition in three-dimensional
numerical simulations of thermonuclear supernovae assuming pure deflagrations.
The model makes use of the statistical description of temperature fluctuations
in the pre-supernova core proposed by Wunsch & Woosley (2004). Randomness in
time is implemented by means of a Poisson process. We are able to vary the
explosion energy and nucleosynthesis depending on the free parameter of the
model which controls the rapidity of the ignition process. However, beyond a
certain threshold, the strength of the explosion saturates and the outcome
appears to be robust with respect to number of ignitions. In the most energetic
explosions, we find about 0.75 solar masses of iron group elements. Other than
in simulations with simultaneous multi-spot ignition, the amount of unburned
carbon and oxygen at radial velocities of a few 1000 km/s tends to be reduced
for an ever increasing number of ignition events and, accordingly, more
pronounced layering results.",0510427v1
2005-10-18,The Chemical Composition of Cepheids in the Milky Way and the Magellanic Clouds,"We have measured the elemental abundances of 68 Galactic and Magellanic
Cepheids from FEROS and UVES high-resolution and high signal-to-noise spectra
in order to establish the influence of the chemical composition on the
properties of these stars (see Romaniello et al. 2005). Here we describe the
robust analytical procedure we have developed to accurately determine them. The
resulting iron abundances span a range between ~ -0.80 dex for stars in the
Small Magellanic Cloud and ~ +0.20 dex for the most metal-rich ones in the
Galaxy. While the average values for each galaxy are in good agreement with
non-pulsating stars of similar age, Cepheids display a significant spread. Thus
it is fundamental to measure the metallicity of individual stars.",0510514v1
2005-10-19,On the fine structure of the sunspot penumbrae. III The vertical extension of penumbral filaments,"In this paper we study the fine structure of the penumbra as inferred from
the uncombed model (flux tube embedded in a magnetic surrounding) when applied
to penumbral spectropolarimetric data from the neutral iron lines at 6300 \AA.
The inversion infers very similar radial dependences in the physical quantities
(LOS velocity, magnetic field strength etc) as those obtained from the
inversion of the Fe I 1.56 $\mu$m lines. In addition, the large Stokes $V$ area
asymmetry exhibited by the visible lines helps to constrain the size of the
penumbral flux tubes. As we demonstrate here, the uncombed model is able to
reproduce the area asymmetry with striking accuracy, returning flux tubes as
thick as 100-300 kilometers in the vertical direction, in good agreement with
previous investigations.",0510586v1
2005-10-27,Phase-resolved spectroscopy of the helium dwarf nova 'SN 2003aw' in quiescence,"High time resolution spectroscopic observations of the ultra-compact helium
dwarf nova 'SN 2003aw' in its quiescent state at V=20.5 reveal its orbital
period at 2027.8 +/- 0.5 seconds or 33.80 minutes. Together with the
photometric 'superhump' period of 2041.5 +/- 0.5 seconds, this implies a mass
ratio q of 0.036. We compare both the average and time-resolved spectra of 'SN
2003aw' and SDSS J124058.03-015919.2. Both show a DB white dwarf spectrum plus
an optically thin, helium-dominated accretion disc. 'SN 2003aw' distinguishes
itself from the SDSS source by its strong calcium H & K emission lines,
suggesting higher abundances of heavy metals than the SDSS source. The silicon
and iron emission lines observed in the SDSS source are about twice as strong
in 'SN 2003aw'. The peculiar 'double bright spot' accretion disc feature seen
in the SDSS source is also present in time-resolved spectra of 'SN 2003aw',
albeit much weaker.",0510767v1
2005-11-17,X-ray reflections on AGN,"X-ray reflection generates much of the spectral complexity in the X-ray
spectra of AGN. It is argued that strong relativistic blurring of the
reflection spectrum should commonly be expected from objects accreting at a
high Eddington rate. The good agreement found between the local density in
massive black holes and the energy density in quasar and AGN light requires
that the accretion which built massive black holes was radiatively efficient,
involving thin discs extending within 6 gravitational radii. The soft excess
found in the spectra of many AGN can be explained by X-ray reflection when such
blurring is included in the spectral analysis. Some of the continuum
variability and in particular the puzzling variability of the broad iron line
can be explained by the strong light bending expected in the region immediately
around a black hole. Progress in understanding this behaviour in the brightest
sources can be made now with long observations using instruments on XMM-Newton
and Suzaku. Future missions like Xeus and Con-X, with large collecting areas,
are required to expand the range of accessible objects and to make
reverberation studies possible.",0511537v1
2005-12-15,The mass of cosmic rays above 1017 eV,"Interpretation of the energy spectrum and arrival distribution of cosmic rays
is complicated by lack of knowledge of the nature of the primaries. We review
claims for the mass composition above 1017 eV where it can be determined only
indirectly from air-shower observables. Difficulties in comparisons between
data arise because, inevitably, a set of measurements is interpreted using the
best model of hadronic interactions available at the time of analysis. We
discuss the situation and conclude that the evidence for a proton-dominated
mass composition, even at the highest energies, is unconvincing. However, it
may be that there are consistent differences between mass measurements from
optical techniques and those based upon other shower observables. We also find
that iron nuclei of ultra high energy can probably escape from the galaxies
that host GRBs, possible cosmic ray accelerators. The accelerators must lie
nearby.",0512408v1
2005-12-16,Lateral distribution of Cherenkov light in extensive air showers at high mountain altitude produced by different primary particles in wide energy range,"The general aim of this work is to obtain the lateral distribution of
atmospheric Cherenkov light in extensive air showers produced by different
primary particles precisely by. protons, Helium, Iron, Oxygen, Carbon,
Nitrogen, Calcium, Silicon and gamma quanta in wide energy range at high
mountain observation level of Chacaltaya cosmic ray station. The simulations
are divided generally in two energy ranges 10GeV-10 TeV and 10 TeV-10 PeV. One
large detector has been used for simulations, the aim being to reduce the
statistical fluctuations of the obtained characteristics. The shape of the
obtained lateral distributions of Cherenkov light in extensive air showers is
discussed and the scientific potential for solution of different problems as
well.",0512432v1
2005-12-16,INTEGRAL and RXTE Observations of Centaurus A,"INTEGRAL and RXTE performed three simultaneous observations of the nearby
radio galaxy Cen A in 2003 March, 2004 January, and 2004 February with the
goals of investigating the geometry and emission processes via the
spectral/temporal variability of the X-ray/low energy gamma ray flux, and
intercalibration of the INTEGRAL instruments with respect to those on RXTE.
When combined with earlier archival RXTE results, we find the power law
continuum flux and the line-of-sight column depth varied independently, and the
iron line flux was essentially unchanging. Taking X-ray spectral measurements
from satellite missions since 1970 into account, we discover a variability in
the column depth between 1.0x10^23 cm^-2 and 1.5x10^23 cm^-2, and suggest that
variations in the edge of a warped accretion disk viewed nearly edge-on might
be the cause.",0512451v1
2005-12-20,An Overview of Extremely Large Telescopes Projects,"IAU Symposium 232 allows a snapshot of ELTs at a stage when design work in
several critical mass projects has been seriously underway for two to three
years. The status and som eof the main initial design choices are reviewed for
the North American Giant Magellan Telescope (GMT) and the Thirty Meter
Telescope (TMT) projects and the European Euro50 and the Overwhelmingly Large
(OWL) projects. All the projects are drawing from the same ""basket"" of science
requirements, although each project has somewhat different ambitions. The role
of the project offices in creating the balance between project scope, timeline
and cost, the ""iron triangle"" of project management, is emphasized with the OWL
project providing a striking demonstration at this meeting. There is a
reasonable case that the very broad range of science would be most effectively
undertaken on several complementary telescopes.",0512499v1
2005-12-21,The Oxygen Abundance of HE 1327-2326,"From a newly obtained VLT/UVES spectrum we have determined the oxygen
abundance of HE 1327-2326, the most iron-poor star known to date. UV-OH lines
yield a 1D LTE abundance of [O/Fe]_OH = 3.7 (subgiant case) and [O/Fe]_OH = 3.4
(dwarf case). Using a correction of -1.0 dex to account for 3D effects on OH
line formation, the abundances are lowered to [O/Fe] = 2.8 and [O/Fe] = 2.5,
respectively, which we adopt. Without 3D corrections, the UV-OH based abundance
would be in disagreement with the upper limits derived from the OI triplet
lines: [O/Fe]_trip < 2.8 (subgiant) and [O/Fe]_trip < 3.0 (dwarf). We also
correct the previously determined carbon and nitrogen abundances for 3D
effects. Knowledge of the O abundance of HE 1327-2326 has implications for the
interpretation of its abundance pattern. A large O abundance is in accordance
with HE 1327-2326 being an early Population II star which formed from material
chemically enriched by a first generation supernova. Our derived abundances,
however, do not exclude other possibilities such as a Population III scenario.",0512543v1
2006-01-08,Excitation of g modes in Wolf-Rayet stars by a deep opacity bump,"We examine the stability of l=1 and l=2 g modes in a pair of nitrogen-rich
Wolf-Rayet stellar models characterized by differing hydrogen abundances. We
find that modes with intermediate radial orders are destabilized by a kappa
mechanism operating on an opacity bump at an envelope temperature log T ~ 6.25.
This `deep opacity bump' is due primarily to L-shell bound-free transitions of
iron. Periods of the unstable modes span ~ 11-21 hr in the model containing
some hydrogen, and ~ 3-12 hr in the hydrogen-depleted model. Based on the
latter finding, we suggest that self-excited g modes may be the source of the
9.8 hr-periodic variation of WR 123 recently reported by Lefevre et al. (2005).",0601154v2
2006-01-18,Observable Effects of Dust Formation in Dynamic Atmospheres of M-type Mira Variables,"The formation of dust with temperature-dependent non-grey opacity is
considered in a series of self-consistent model atmospheres at different phases
of an O-rich Mira variable of mass 1.2 $M_\odot$. Photometric and
interferometric properties of these models are predicted under different
physical assumptions regarding the dust formation. The iron content of the
initial silicate that forms and the availability of grain nuclei are found to
be critical parameters that affect the observable properties. In particular,
parameters were found where dust would form at 2-3 times the average continuum
photospheric radius. This work provides a consistent physical explanation for
the larger apparent size of Mira variables at wavelengths shorter than 1 $\mu$m
than that predicted by dust free fundamental-mode pulsation models.",0601383v1
2006-02-21,Tracing gas motions in the Centaurus Cluster,"We apply the stochastic model of iron transport developed by Rebusco et. al.
(2005) to the Centaurus cluster. Using this model, we find that an effective
diffusion coefficient D in the range 2x10^28 - 4x10^28 cm^2 s^-1 can
approximately reproduce the observed abundance distribution. Reproducing the
flat central profile and sharp drop around 30-70 kpc, however, requires a
diffusion coefficient that drops rapidly with radius so that D > 4x10^28 cm^2
s^-1 only inside about 25 kpc. Assuming that all transport is due to
fully-developed turbulence, which is also responsible for offsetting cooling in
the cluster core, we calculate the length and velocity scales of energy
injection. These length scales are found to be up to a factor of ~ 10 larger
than expected if the turbulence is due to the inflation and rising of a bubble.
We also calculate the turbulent thermal conductivity and find it is unlikely to
be significant in preventing cooling.",0602466v1
2006-02-25,Luminosity dependent study of the High Mass X-ray Binary Pulsar 4U~0114+65 with ASCA,"Here we report the spectral characteristics of the high and low states of the
pulsar 4U~0114+65 and examine the change in the parameters of the spectral
model. A power law and a photoelectric absorption by material along the line of
sight together with a high energy cut-off suffice to describe the continuum
spectrum in both the states. A fluorescence iron line at $\sim$6.4 keV is
present in the high as well as in the low state, though it is less intense in
the latter. The photon index, cut-off energy and e-folding energy values hardly
show any discernible change over the states. We compare these spectral
characteristics as observed with ASCA to that with other satellites. We also
compare the spectral characteristics of 4U~0114+650 with other X-ray sources
which show intensity variation at different time scales.",0602558v1
2006-03-03,Metallicity structure in X-ray bright galaxy groups,"Using Chandra X-ray data of a sample of 15 X-ray bright galaxy groups, we
present preliminary results of a coherent study of the radial distribution of
metal abundances in the hot gas in groups. The iron content in group outskirts
is found to be lower than in clusters by a factor of ~2, despite showing mean
levels in the central regions comparable to those of clusters. The abundance
profiles are used to constrain the contribution from supernovae type Ia and II
to the chemical enrichment and thermal energy of the intragroup medium at
different group radii. The results suggest a scenario in which a substantial
fraction of the chemical enrichment of groups took place in filaments prior to
group collapse.",0603085v1
2006-03-16,Yields of Population III Supernovae and the Abundance Patterns of Extremely Metal-Poor Stars,"The abundance patterns of extremely metal-poor (EMP) stars provide us with
important information on nucleosynthesis in supernovae (SNe) formed in a Pop
III or EMP environment, and thus on the nature of the first stars in the
Universe. We review nucleosynthesis yields of various types of those SNe,
focusing on core-collapse (black-hole-forming) SNe with various progenitor
masses, explosion energies (including Hypernovae), and asphericity. We discuss
the implications of the observed trends in the abundance ratios among iron-peak
elements, and the large C/Fe ratio observed in certain EMP stars with
particular attention to recently discovered hyper metal-poor (HMP) stars. We
show that the abundance pattern of the HMP stars with [Fe/H] < -5 and other EMP
stars are in good accord with those of black-hole-forming supernovae, but not
pair-instability supernovae. This suggests that black-hole-forming supernovae
made important contributions to the early Galactic (and cosmic) chemical
evolution. Finally we discuss the nature of First (Pop III) Stars.",0603433v1
2006-04-01,Chemical abundances in LMC stellar populations I. The Inner disk sample Based on observations collected at the VLT UT2 telescope,"The advent of the new class 8 meters telescopes allows for the first time the
detailed study of numerous stars of galaxies other than our own. The Large
Magellanic Cloud is one of the most interesting targets due to its proximity
and its relatively face-on disk, permitting to separate populations pertaining
to the different structures of the galaxy. We have used FLAMES (the Fibre Large
Array Multi Element Spectrograph) at the VLT-UT2 telescope to obtain spectra of
a large sample of stars from the Inner Disk of the LMC, $\sim$2 kpc from the
center of the galaxy. We investigate the chemical abundances of iron-peak
elements, heavy and light $s$-process elements, Cu, Na, Sc and
$\alpha$-elements for a sample of red giant stars. Metallicities for the sample
stars range from [Fe/H] = $-$1.76 to $-$0.02. LMC inner disk stars show a
definitely different chemical pattern when compared to galactic stars of the
same metallicity.",0604009v2
2006-04-03,Abundance analysis of cool extreme helium star: LSS 3378,"Abundance analysis of the cool extreme helium (EHe) star LSS 3378 is
presented. The abundance analysis is done using LTE line formation and LTE
model atmospheres constructed for EHe stars.
  The atmosphere of LSS 3378 shows evidence of H-burning, He-burning, and
s-process nucleosynthesis. The derived abundances of iron-peak and
alpha-elements indicate absence of selective fractionation or any other
processes that can distort chemical composition of these elements. Hence, the
Fe abundance (log epsilon(Fe) = 6.1) is adopted as an initial metallicity
indicator. The measured abundances of LSS 3378 are compared with those of R
Coronae Borealis (RCB) stars and with rest of the EHe stars as a group.",0604023v1
2006-04-03,High resolution infrared spectroscopy of the old open cluster NGC6791,"We report abundance analysis for 6 M giant members of the old open cluster
NGC6791, based on infrared spectroscopy (1.5-1.8 micron) at R=25,000, using the
NIRSPEC spectrograph at the Keck II telescope. We find the iron abundance
<[Fe/H]>= +0.35 +/- 0.02$, confirming the super solar metallicity of this
cluster derived from optical medium-high resolution spectroscopy. We also
measure C, O and other alpha element abundances, finding roughly solar
[alpha/Fe] and <[C/Fe]> = -0.35. Our approach constrains [O/Fe] especially
well, based on the measurement of a number of OH lines near 1.6micron; we find
[O/Fe]=-0.07 +/-0.03. The Solar alpha enhancement is in contrast to the
composition of similar stars in the Galactic bulge. We also find low
12C/13C~10, confirming the presence of extra-mixing processes during the red
giant phase of evolution, up to super solar metallicities.",0604030v1
2006-04-13,The flow field in the sunspot canopy,"We investigate the flow field in the sunspot canopy using simultaneous Stokes
vector spectropolarimetry of three sunspots ($\theta$ = 27, 50, 75 deg) and
their surroundings in visible (630.15 and 630.25 nm) and near infrared (1564.8
and 1565.2 nm) neutral iron lines.} {To calibrate the Doppler shifts, we
compare an absolute velocity calibration using the telluric $O_2$-line at
630.20 nm and a relative velocity calibration using the Doppler shift of Stokes
V profiles in the umbra under the assumption that the umbra is at rest. Both
methods yield the same result within the calibration uncertainties (~150 m/s).
We study the radial dependence of Stokes V profiles in the directions of disk
center and limb side. Maps of Stokes V profile shifts, polarity, amplitude
asymmetry, field strength and magnetic field azimuth provide strong evidence
for the presence of a magnetic canopy and for the existence of a radial outflow
in the canopy. Our findings indicate that the Evershed flow does not cease
abruptly at the white-light spot boundary, but that at least a part of the
penumbral Evershed flow continues into the magnetic canopy.",0604301v1
2006-04-27,"Resonance scattering, absorption and off-centre abundance peaks in clusters of galaxies","A possible explanation for the central abundance dips found from
spatially-resolved X-ray spectroscopy of several groups and clusters of
galaxies is resonance scattering. A number of the prominent iron emission lines
are resonance lines. We construct a unique spectral model which takes account
of resonance scattering for several thousand resonance lines, projection
effects, photoelectric absorption, and allows direct spectral fitting. We apply
our model to Chandra observations of two clusters with pronounced central
abundance dips, Centaurus and Abell 2199. The results show that the effect of
resonance scattering on emission from the centre of the cluster can be as much
as 30 per cent for the Fe-K resonance lines, and 10 per cent for several Fe-L
lines, if turbulence is low. The change to the metallicities obtained by
fitting low resolution CCD spectra is at most 10 per cent. Accounting for
resonance scattering does not remove the central dip. Allowing for internal
absorption within the Centaurus significantly improves the quality of the fits,
indicating the presence of absorbing material within the inner 40 kpc of NGC
4696.",0604575v1
2006-05-04,Variable iron-line emission near the black hole of Markarian 766,"We investigate the link between ionised Fe X-ray line emission and continuum
emission in the bright nearby AGN, Mrk 766. A new long (433 ks) XMM-Newton
observation is analysed, together with archival data from 2000 and 2001. The
contribution from ionised line emission is measured and its time variations on
short (5-20 ks) timescales are correlated with the continuum emission. The
ionised line flux is found to be highly variable and to be strongly correlated
with the continuum flux, demonstrating an origin for the ionised line emission
that is co-located with the continuum emission. Most likely the emission is
ionised reflection from the accretion disc within a few A.U. of the central
black hole, and its detection marks the first time that such an origin has been
identified other than by fitting to spectral line profiles. Future observations
may be able to measure a time lag and hence achieve reverberation mapping of
AGN at X-ray energies.",0605130v1
2006-06-13,Unveiling the nature of the highly absorbed X-ray source SAXJ1748.2-2808 with XMM-Newton,"We report on the results of an EPIC XMM-Newton observation of the faint
source SAXJ1748.2-2808 and the surrounding field. This source was discovered
during the BeppoSAX Galactic center survey performed in 1997-1998. A spatial
analysis resulted in the detection of 31 sources within the EPIC field of view.
SAXJ1748.2-2808 is clearly resolved into 2 sources in EPIC images with the
brighter contributing almost 80% of the 2-10keV flux. Spectral fits to this
main source are consistent with an absorbed power-law with a photon index of
1.4+/-0.5 and absorption equivalent to 14E22cm-2 together with an iron line at
6.6+/-0.2 keV with an equivalent width of ~780eV. The significantly better
statistics of the XMM-Newton observation, compared with BeppoSAX,allows to
exclude a thermal nature for the X-ray emission. A comparison with other
observations of SAXJ1748.2-2808 does not reveal any evidence for spectral or
intensity long-term variability. Based on these properties we propose that the
source is a low-luminosity high-mass X-ray binary located in the Galactic
center region.",0606307v1
2006-06-27,"Outgassing of Ordinary Chondritic Material and Some of its Implications for the Chemistry of Asteroids, Planets, and Satellites","We used chemical equilibrium calculations to model thermal outgassing of
ordinary chondritic material as a function of temperature, pressure, and bulk
compositions and use our results to discuss outgassing on asteroids and the
early Earth. The calculations include ~1,000 solids and gases of the elements
Al, C, Ca, Cl, Co, Cr, F, Fe, H, K, Mg, Mn, N, Na, Ni, O, P, S, Si, and Ti. The
major outgassed volatiles from ordinary chondritic material are CH4, H2, H2O,
N2, and NH3(the latter at conditions where hydrous minerals form). Contrary to
widely held assumptions, CO is never the major C-bearing gas during ordinary
chondrite metamorphism. The calculated oxygen fugacity (partial pressure) of
ordinary chondritic material is close to that of the quartz-fayalite-iron (QFI)
buffer. Our results are insensitive to variable total pressure, variable
volatile element abundances, and kinetic inhibition of C and N dissolution in
Fe metal. Our results predict that Earth's early atmosphere contained CH4, H2,
H2O, N2, and NH3; similar to that used in Miller-Urey synthesis of organic
compounds.",0606671v1
2006-06-27,They Came From the Deep in the Supernova: The Origin of TiC and Metal Subgrains in Presolar Graphite Grains,"A new formation scenario for TiC and Fe,Ni-metal inclusions in presolar
graphite grains of supernova origin is described. The mineralogy and chemistry
require condensation of (Fe,Ni)-titanides from Fe, Ni, and Ti-rich gaseous
ejecta, subsequent carburization to make TiC and metal, and encapsulation into
graphite. Titanides only condense if Si is depleted relative to heavier mass
elements, which requires alpha-rich freeze-out and a deep mass-cut for the
supernova ejecta. This Si-poor core material must remain unmixed with other
supernova zones until the titanides condensed. This can be accomplished by
transport of core ejecta in bipolar jets through the major expanding supernova
zone ejecta. If the jets stall in regions dominated by C-rich ejecta such as
C-He zone where graphite condenses, thermochemically favored in situ
carburization of the titanides - either before or during encapsulation into
condensing graphite - leads to a TiC and metal composite. This scenario agrees
with theoretical models and observations of asymmetric core collapse in
supernovae that are associated with bipolar jets loaded with iron-peak
elements.",0606673v1
2006-07-03,Sulphur abundances in disk stars as determined from the forbidden 10821 A [SI] line,"Aims: In this paper we aim to study the chemical evolution of sulphur in the
galactic disk, using a new optimal abundance indicator: the [SI] line at 10821
A. Similar to the optimal oxygen indicators, the [OI] lines, the [SI] line has
the virtues of being less sensitive to the assumed temperatures of the stars
investigated and of likely being less prone to non-LTE effects than other
tracers. Methods: High-resolution, near-infrared spectra of the [SI] line are
recorded using the Phoenix spectrometer on the Gemini South telescope. The
analysis is based on 1D, LTE model atmospheres using a homogeneous set of
stellar parameters. Results: The 10821 A [SI] line is suitable for an abundance
analysis of disk stars, and the sulphur abundances derived from it are
consistent with abundances derived from other tracers. We corroborate that, for
disk stars, the trend of sulphur-to-iron ratios with metallicity is similar to
that found for other alpha elements, supporting the idea of a common
nucleosynthetic origin.",0607017v1
2006-07-06,Enrichment in the Centaurus cluster of galaxies,"We perform a detailed spatially-resolved, spectroscopic, analysis of the core
of the Centaurus cluster of galaxies using a deep Chandra X-ray observation and
XMM-Newton data. The Centaurus cluster core has particularly high metallicity,
upto twice Solar values, and we measure the abundances of Fe, O, Ne, Mg, Si, S,
Ar, Ca and Ni. We map the distribution of these elements in many spatial
regions,and create radial profiles to the east and west of the centre. The
ratios of the most robustly determined elements to iron are consistent with
Solar ratios, indicating that there has been enrichment by both Type Ia and
Type II supernovae. For a normal initial stellar mass function it represents
the products of about 4x10^10 solar masses of star formation. This star
formation can have occured either continuously at a rate of 5 solar masses per
year for the past 8 Gyr or more,or was part of the formation of the central
galaxy at earlier times. Either conclusion requires that the inner core of the
Centaurus cluster has not suffered a major disruption within the past 8 Gyr, or
even longer.",0607113v1
2006-07-11,Atomic and Molecular Opacities for Brown Dwarf and Giant Planet Atmospheres,"We present a comprehensive description of the theory and practice of opacity
calculations from the infrared to the ultraviolet needed to generate models of
the atmospheres of brown dwarfs and extrasolar giant planets. Methods for using
existing line lists and spectroscopic databases in disparate formats are
presented and plots of the resulting absorptive opacities versus wavelength for
the most important molecules and atoms at representative temperature/pressure
points are provided. Electronic, ro-vibrational, bound-free, bound-bound,
free-free, and collision-induced transitions and monochromatic opacities are
derived, discussed, and analyzed. The species addressed include the alkali
metals, iron, heavy metal oxides, metal hydrides, $H_2$, $H_2O$, $CH_4$, $CO$,
$NH_3$, $H_2S$, $PH_3$, and representative grains. [Abridged]",0607211v4
2006-07-13,The puzzling abundance pattern of HD134439 and HD134440,"Abundances of 18 elements are determined for the common proper-motion pair,
HD134439 and HD134440, which shows high [Mn/Fe] and low [\alpha/Fe] ratios as
compared to normal halo stars. Moreover, puzzling abundances are indicated from
elements whose origins are normally considered to be from the same
nucleosynthesis history. Particularly, we have found that [Mg/Fe] and [Si/Fe]
are lower than [Ca/Fe] and [Ti/Fe] by 0.1-0.3 dex. When elemental abundances
are interpreted in term of their condensation temperatures (Tc), obvious trends
of [X/Fe] vs. Tc for alpha elements and probably iron-peak elements as well are
shown. The hypothesis that these stars have formed from a dusty environment in
dSph galaxy provides a solution to the puzzling abundance pattern.",0607287v1
2006-08-03,The intergalactic propagation of ultra-high energy cosmic ray nuclei,"We investigate the propagation of ultra-high energy cosmic ray nuclei (A =
1-56) from cosmologically distant sources through the cosmic radiation
backgrounds. Various models for the injected composition and spectrum and of
the cosmic infra-red background are studied using updated photo-disintegration
cross-sections. The observational data on the spectrum and the composition of
ultra-high energy cosmic rays are jointly consistent with a model where all of
the injected primary cosmic rays are iron nuclei (or a mixture of heavy and
light nuclei).",0608085v4
2006-08-16,Pinning Down Gravitational Settling,"We analyse high-resolution archival UVES data of turnoff and subgiant stars
in the nearby globular cluster NGC 6397 ([Fe/H] = -2). Balmer-profile analyses
are performed to derive reddening-free effective temperatures. Due to the
limited S/N and uncertainties related to blaze removal, we find the data
quality insufficient to exclude the existence of gravitational settling. If the
newly derived effective temperatures are taken as a basis for an abundance
analysis, the photospheric iron (Fe II) abundance in the turnoff stars is 0.11
dex lower than in the (well-mixed) subgiants.",0608338v1
2006-08-16,Sensitivity of p-Process Nucleosynthesis to Nuclear Reaction Rates in a 25 Solar Mass Supernova Model,"The astrophysical p process, which is responsible for the origin of the
proton rich stable nuclei heavier than iron, was investigated using a full
nuclear reaction network for a type II supernova explosion when the shock front
passes through the O/Ne layer. Calculations were performed with a multi-layer
model adopting the seed of a pre-explosion evolution of a 25 solar mass star.
The reaction flux was calculated to determine the main reaction path and
branching points responsible for synthesizing the proton rich nuclei. In order
to investigate the impact of nuclear reaction rates on the predicted p-process
abundances, extensive simulations with different sets of collectively and
individually modified neutron-, proton-, alpha-capture and photodisintegration
rates have been performed. These results are not only relevant to explore the
nuclear physics related uncertainties in p-process calculations but are also
important for identifying the strategy and planning of future experiments.",0608341v1
2006-08-31,Galactic chemical evolution: Carbon through Zinc,"We calculate the evolution of heavy element abundances from C to Zn in the
solar neighborhood adopting our new nucleosynthesis yields. Our yields are
calculated for wide ranges of metallicity (Z=0-Z_\odot) and the explosion
energy (normal supernovae and hypernovae), based on the light curve and spectra
fitting of individual supernovae. The elemental abundance ratios are in good
agreement with observations. Among the alpha-elements, O, Mg, Si, S, and Ca
show a plateau at [Fe/H] < -1, while Ti is underabundant overall. The observed
abundance of Zn ([Zn/Fe] ~ 0) can be explained only by the high energy
explosion models, which requires a large contribution of hypernovae. The
observed decrease in the odd-Z elements (Na, Al, and Cu) toward low [Fe/H] is
reproduced by the metallicity effect on nucleosynthesis. The iron-peak elements
(Cr, Mn, Co, and Ni) are consistent with the observed mean values at -2.5 <
[Fe/H] < -1$, and the observed trend at the lower metallicity can be explained
by the energy effect. We also show the abundance ratios and the metallicity
distribution functions of the Galactic bulge, halo, and thick disk. Our results
suggest that the formation timescale of the thick disk is ~ 1-3 Gyr.",0608688v1
2006-09-01,Oxygen abundances in the Galactic Bulge: evidence for fast chemical enrichment,"AIMS: We spectroscopically characterize the Galactic Bulge to infer its star
formation timescale, compared to the other Galactic components, through the
chemical signature on its individual stars.
  METHODS: We derived iron and oxygen abundances for 50 K giants in four fields
towards the Galactic bulge. High resolution (R=45,000) spectra for the target
stars were collected with FLAMES-UVES at the VLT.
  RESULTS: Oxygen, as measured from the forbidden line at 6300 \AA, shows a
well-defined trend with [Fe/H], with [O/Fe] higher in bulge stars than in thick
disk ones, which were known to be more oxygen enhanced than thin disk stars.
  CONCLUSIONS: These results support a scenario in which the bulge formed
before and more rapidly than the disk, and therefore the MW bulge can be
regarded as a prototypical old spheroid, with a formation history similar to
that of early-type (elliptical) galaxies.",0609052v2
2006-09-06,The Supernova -- Gamma-Ray Burst Connection,"Observations show that at least some gamma-ray bursts (GRBs) happen
simultaneously with core-collapse supernovae (SNe), thus linking by a common
thread nature's two grandest explosions. We review here the growing evidence
for and theoretical implications of this association, and conclude that most
long-duration soft-spectrum GRBs are accompanied by massive stellar explosions
(GRB-SNe). The kinetic energy and luminosity of well-studied GRB-SNe appear to
be greater than those of ordinary SNe, but evidence exists, even in a limited
sample, for considerable diversity. The existing sample also suggests that most
of the energy in the explosion is contained in nonrelativistic ejecta
(producing the supernova) rather than in the relativistic jets responsible for
making the burst and its afterglow. Neither all SNe, nor even all SNe of Type
Ibc produce GRBs. The degree of differential rotation in the collapsing iron
core of massive stars when they die may be what makes the difference.",0609142v1
2006-09-14,The Formation of the Double Pulsar PSR J0737-3039A/B,"Recent timing observations of the double pulsar J0737-3039A/B have shown that
its transverse velocity is extremely low, only 10 km/s, and nearly in the Plane
of the Galaxy. With this new information, we rigorously re-examine the history
and formation of this system, determining estimates of the pre-supernova
companion mass, supernova kick and misalignment angle between the pre- and
post-supernova orbital planes. We find that the progenitor to the recently
formed `B' pulsar was probably less than 2 MSun, lending credence to
suggestions that this object may not have formed in a normal supernova
involving the collapse of an iron core. At the same time, the supernova kick
was likely non-zero. A comparison to the history of the double-neutron-star
binary B1534+12 suggests a range of possible parameters for the progenitors of
these systems, which should be taken into account in future binary population
syntheses and in predictions of the rate and spatial distribution of short
gamma-ray burst events.",0609416v2
2006-09-19,On the Origin of the Type Ia Supernova Width-Luminosity Relation,"Brighter Type Ia supernovae (SNe Ia) have broader, more slowly declining
B-band light curves than dimmer SNe Ia. We study the physical origin of this
width-luminosity relation (WLR) using detailed radiative transfer calculations
of Chandrasekhar mass SN Ia models. We find that the luminosity dependence of
the diffusion time (emphasized in previous studies) is in fact of secondary
relevance in understanding the model WLR. Instead, the essential physics
involves the luminosity dependence of the spectroscopic/color evolution of SNe
Ia. Following maximum-light, the SN colors are increasingly affected by the
development of numerous Fe II/Co II lines which blanket the B-band and, at the
same time, increase the emissivity at longer wavelengths. Because dimmer SNe Ia
are generally cooler, they experience an earlier onset of Fe III to Fe II
recombination in the iron-group rich layers of ejecta, resulting in a more
rapid evolution of the SN colors to the red. The faster B-band decline rate of
dimmer SNe Ia thus reflects their faster ionization evolution.",0609540v1
2006-09-23,Theoretical aspects of relativistic spectral features,"The inner parts of black-hole accretion discs shine in X-rays which can be
monitored and the observed spectra can be used to trace strong gravitational
fields in the place of emission and along paths of light rays. This paper
summarizes several aspects of how the spectral features are influenced by
relativistic effects. We focus our attention onto variable and broad emission
lines, origin of which can be attributed to the presence of orbiting patterns
-- spots and spiral waves in the disc. We point out that the observed spectrum
can determine parameters of the central black hole provided the intrinsic local
emissivity is constrained by theoretical models.",0609645v1
2006-09-27,The XMM-Newton RGS spectrum of the high luminosity Seyfert 1 galaxy Markarian 509,"We present a detailed analysis of the soft X-ray spectrum of the Seyfert 1
galaxy Markarian 509 taken with the XMM-Newton Reflection Grating Spectrometer.
An underlying power-law continuum and three warm absorber phases provide a good
fit to the data along with a number of broad and narrow emission lines. Our
three warm absorber phases each have different ionization parameters and column
densities. We identify a low ionization, log xi=0.89, high outflow velocity
phase producing an Fe M-shell UTA feature along with absorption from O VI and N
VI. There is an intermediate phase, log xi=2.14, showing absorption from H-like
carbon and nitrogen and He-like neon and oxygen. The third, high ionization,
log xi=3.26, low outflow velocity phase contains absorption from O VIII, Ne X
and highly ionized iron. All phases are blueshifted with respect to the
systemic velocity with flow velocities ranging from -60km/s to -510km/s. The
observed broad emission features have an RMS velocity of ~8000km/s for the C VI
and O VII lines.",0609746v1
2006-09-29,On SN 2003fg: The Probable Super-Chandrasekhar-Mass SN Ia,"Howell et al. have reported the discovery of SN Ia SN 2003fg (SNLS-03D3bb)
and conclude that SN 2003fg is very likely a super-Chandrasekhar-mass SN Ia
perhaps with a mass of order 2 solar masses. Their work is the first strong
evidence that has been presented for a super-Chandrasekhar SN Ia. We have
performed an analysis of the SN 2003fg data using the Yoon & Langer binding
energy formula for a rotating super-Chandrasekhar-mass white dwarf (also used
by Howell et al.) included in a simple model of SNe Ia (which we call the SSC
model for Simple Super-Chandrasekhar model for SNe Ia) which assumes
spherically symmetric ejecta and relies on the approximations of an exponential
density profile for SN Ia ejecta and of a sharp boundary of the SN Ia
iron-peak-element core. Our results support the conclusion of Howell et al.: SN
2003fg is very probably super-Chandrasekhar and probably has mass of order 2
solar masses.",0609804v3
2006-10-13,r-Process Enhanced Halo Stars,"Abundance observations indicate the presence of rapid-neutron capture (i.e.,
r-process) elements in old Galactic halo and globular cluster stars. These
observations provide insight into the nature of the earliest generations of
stars in the Galaxy -- the progenitors of the halo stars -- responsible for
neutron-capture synthesis of the heavy elements. The large star-to-star scatter
observed in the abundances of neutron-capture element/iron ratios at low
metallicities -- which diminishes with increasing metallicity or [Fe/H] --
suggests the formation of these heavy elements (presumably from certain types
of supernovae) was rare in the early Galaxy. The stellar abundances also
indicate a change from the r-process to the slow neutron capture (i.e., s-)
process at higher metallicities in the Galaxy and provide insight into Galactic
chemical evolution. Finally, the detection of thorium and uranium in halo and
globular cluster stars offers an independent age-dating technique that can put
lower limits on the age of the Galaxy, and hence the Universe.",0610412v1
2006-10-27,Computation of the Fourier parameters of RR Lyrae stars by template fitting,"Due to the importance of accurate Fourier parameters, we devise a method that
is more appropriate for deriving these parameters on low-quality data than the
traditional Fourier fitting. Based on the accurate light curves of 248
fundamental mode RR Lyrae stars, we test the power of a full-fetched
implementation of the template method in the computation of the Fourier
decomposition. The applicability of the method is demonstrated also on datasets
of filter passbands different from that of the template set. We examine in more
detail the question of the estimation of Fourier- based iron abundance [Fe/H]
and average brightness. We get, for example, for light curves sampled randomly
in 30 data points with sigma=0.03 mag observational noise that optimized direct
Fourier fits yield sigma_[Fe/H]=0.33, whereas the template fits result in
sigma_[Fe/H]=0.18. Tests made on the RR Lyrae database of the Large Magellanic
Cloud (LMC) of the Optical Gravitational Lensing Experiment (OGLE) support the
applicability of the method on real photometric time series. These tests also
show that the dominant part of error in estimating the average brightness comes
from other sources, most probably from crowding effects, even for under-sampled
light curves.",0610823v1
2006-11-01,Amplification and variability of the AGN X-ray emission due to microlensing,"We consider the contribution of microlensing to the AGN Fe K$\alpha$ line and
X-ray continuum amplification and variation. To investigate the variability of
the line and X-ray continuum, we studied the effects of microlensing on quasar
X-ray spectra produced by crossing of a microlensing pattern across a standard
relativistic accretion disk. To describe the disk emission we used a ray
tracing method considering both metrics, Schwarzschild and Kerr. We found that
the Fe K$\alpha$ and continuum may experience significant amplification by a
microlensing event (even for microlenses of very small mass). Also, we
investigate a contribution of microlensing to the X-ray variability of
high-redshifted QSOs, finding that cosmologically distributed deflector may
contribute significantly to the X-ray variability of high-redshifted QSOs
(z>2).",0611016v1
2006-11-23,Two Disk Components from a Gas Rich Disk-Disk Merger,"We employ N-body, smoothed particle hydrodynamical simulations, including
detailed treatment of chemical enrichment, to follow a gas-rich merger which
results in a galaxy with disk morphology. We trace the kinematic, structural
and chemical properties of stars formed before, during, and after the merger.
We show that such a merger produces two exponential disk components, with the
older, hotter component having a scale-length 20% larger than the
later-forming, cold disk. Rapid star formation during the merger quickly
enriches the protogalactic gas reservoir, resulting in high metallicities of
the forming stars. These stars form from gas largely polluted by Type II
supernovae, which form rapidly in the merger-induced starburst. After the
merger, a thin disk forms from gas which has had time to be polluted by Type Ia
supernovae. Abundance trends are plotted, and we examine the proposal that
increased star formation during gas-rich mergers may explain the high
alpha-to-iron abundance ratios which exist in the relatively high-metallicity
thick disk component of the Milky Way.",0611748v1
2006-11-28,XMM-Newton study of 0.012<z<0.024 groups. I: Overview of the IGM thermodynamics,"We study the thermodynamic properties of the hot gas in a sample of groups in
the 0.012-0.024 redshift range, using XMM-Newton observations. We present
measurements of temperature, entropy, pressure and iron abundance.
Non-parametric fits are used to derive the mean properties of the sample and to
study dispersion in the values of entropy and pressure. The scaling of the
entropy at 0.2r500 matches well the results of Ponman et al. (2003). However,
compared to cool clusters, the groups in our sample reveal larger entropy at
inner radii and a substantially flatter slope in the entropy in the outskirts,
compared to both the prediction of pure gravitational heating and to
observations of clusters. This difference corresponds to the systematically
flatter group surface brightness profiles, reported previously. The scaled
pressure profiles can be well approximated with a Sersic model with n=4. We
find that groups exhibit a systematically larger dispersion in pressure,
compared to clusters of galaxies, while the dispersion in entropy is similar.",0611846v2
2006-11-28,The Two-dimensional XMM-Newton Group Survey: z<0.012 groups,"We present the results of the 2-dimensional XMM-Newton Group Survey (2dXGS),
an archival study of nearby galaxy groups. In this paper we consider eleven
nearby systems (z<0.012) in Mulchaey et al. (2003), which span a broad range in
X-ray luminosity from 10^40 to 10^43 ergs/s. We measure the iron abundance and
temperature distribution in these systems and derive pressure and entropy maps.
We find statistically significant evidence for structure in the entropy and
pressure of the gas component of seven groups on the 10-20% level. The
XMM-Newton data for the three groups with best statistics also suggest patchy
metalicity distributions within the central 20--50 kpc of the brightest group
galaxy, probed with 2-10 kpc resolution. This provides insights into the
processes associated with thermalization of the stellar mass loss. Analysis of
the global properties of the groups reveals a subclass of X-ray faint groups,
which are characterized by both higher entropy and lower pressure. We suggest
that the merger history of the central elliptical is responsible for both the
source and the observed thermodynamical properties of the hot gas of the X-ray
faint groups.",0611858v1
2006-12-12,Search for narrow energy-shifted lines in XMM-Newton AGN spectra,"The detection of X-ray narrow spectral features in the 5-7 keV band is
becoming increasingly more common in AGN observations, thanks to the
capabilities of current X-ray satellites. Such lines, both in emission and in
absorption, are mostly interpreted as arising from Iron atoms. When observed
with some displacement from their rest frame position, these lines carry the
potential to study the motion of circumnuclear gas in AGN, providing a
diagnostic of the effects of the gravitational field of the central black hole.
These narrow features have been often found with marginal statistical
significance. We are carrying on a systematic search for narrow features using
spectra of bright type 1 AGNs available in the XMM-Newton archive. The aim of
this work is to characterise the occurrence of the narrow features phenomenon
on a large sample of objects and to estimate the significance of the features
through Monte Carlo simulations. The project and preliminary results are
presented.",0612317v1
2006-12-15,Non-LTE Models for Neutron Star Atmospheres and Supernova-Fallback Disks,"We describe our recent progress in modeling supernova-fallback disks and
neutron star (NS) atmospheres.
  We present a first detailed spectrum synthesis calculation of a SN-fallback
disk composed of iron. We assume a thin disk with a radial structure described
by the alpha-disk model. The vertical structure and emission spectrum are
computed self-consistently by solving the structure equations simultaneously
with the radiation transfer equations under non-LTE conditions. We describe the
properties of a specific disk model and discuss various effects on the emergent
UV/optical spectrum.
  We investigate Compton scattering effects on the thermal spectrum of NSs. In
addition, we constructed a new generation of metal line-blanketed non-LTE model
atmospheres for NSs. It is compared to X-ray burst spectra of EXO0748-676. It
is possible that the gravitational redshift, deduced from absorption lines, is
lower (z=0.24) than hitherto assumed (z=0.35). Accordingly, this would result
in NS mass and radius lower limits of M>1.63Msun and R>13.8 km.",0612425v1
2006-12-28,Heating of Heavy Ions by Interplanetary Coronal Mass Ejection (ICME) Driven Collisionless Shocks,"Shock heating and particle acceleration processes are some of the most
fundamental physical phenomena of plasma physics with countless applications in
laboratory physics, space physics, and astrophysics. This study is motivated by
previous observations of non-thermal heating of heavy ions in astrophysical
shocks (Korreck et al. 2004). Here, we focus on shocks driven by Interplanetary
Coronal Mass Ejections (ICMEs) which heat the solar wind and accelerate
particles. This study focuses specifically on the heating of heavy ions caused
by these shocks. Previous studies have focused only on the two dynamically
dominant species, H+ and He2+ . This study utilizes thermal properties measured
by the Solar Wind Ion Composition Spectrometer (SWICS) aboard the Advanced
Composition Explorer (ACE) spacecraft to examine heavy ion heating. This
instrument provides data for many heavy ions not previously available for
detailed study, such as Oxygen (O6+, O7+), Carbon (C5+, C6+), and Iron (Fe10+).
The ion heating is found to depend critically on the upstream plasma",0612767v1
2007-01-05,Ruling out a massive-assymptoic giant-branch star as the progenitor of supernova 2005cs,"We calculate the predicted UBVRIJHK absolute magnitudes for models of
supernova progenitors and apply the result to the case of supernova 2005cs. We
agree with previous results that the initial mass of the star was of low,
around 6 to 8 M(sun). However such stars are thought to go through second
dredge-up to become AGB stars. We show that had this occurred to the progenitor
of 2005cs it would have been observed in JHK pre-explosion images. The
progenitor was not detected in these bands and therefore we conclude that it
was not an AGB star. Furthermore if some AGB stars do produce supernovae they
will have a clear signature in pre-explosion near-infrared images.
Electron-capture supernovae are thought to occur in AGB stars, hence the
implication is that 2005cs was not an electron-capture supernova but was the
collapse of an iron core.",0701152v1
2007-01-07,Modeling the X-ray fractional variability spectrum of Active Galactic Nuclei using multiple flares,"Using Monte-Carlo simulations of X-ray flare distributions across the
accretion disk of active galactic nuclei (AGN), we obtain modeling results for
the energy-dependent fractional variability amplitude. Referring to previous
results of this model, we illustrate the relation between the shape of the
point-to-point fractional variability spectrum, F_pp, and the time-integrated
spectral energy distribution, F_E. The results confirm that the spectral shape
and variability of the iron Kalpha line are dominated by the flares closest to
the disk center.",0701164v1
2007-01-07,Ultrahigh energy cosmic rays as heavy nuclei from cluster accretion shocks,"Large-scale accretion shocks around massive clusters of galaxies, generically
expected in the cold dark matter scenario of cosmological structure formation,
are shown to be plausible sources of the observed ultrahigh energy cosmic rays
(UHECRs) by accelerating a mixture of heavy nuclei including the iron group
elements. Current observations can be explained if the source composition at
injection for the heavier nuclei is somewhat enhanced from simple expectations
for the accreting gas. The proposed picture should be clearly testable by
current and upcoming facilities in the near future through characteristic
features in the UHECR spectrum, composition and anisotropy, in particular the
rapid increase of the average mass composition with energy from $10^{19}$ to
$10^{20}$ eV.",0701167v3
2007-01-14,Interstellar Iron and Silicon Depletions in Translucent Sight Lines,"We report interstellar FeII and SiII column densities toward six translucent
sight lines (A_V >~ 1) observed with the Space Telescope Imaging Spectrograph
(STIS). The abundances were determined from the absorption of SiII] at 2335
Angstroms, and several weak Fe transitions including the first reported
detections of the 2234 Angstrom line. We derive an empirical f-value for the
FeII 2234 Angstrom transition of log(f lambda) = -1.54 +/- 0.05. The observed
sight lines sample a variety of extinction characteristics as indicated by
their R_V values, which range from 2.6 - 5.8. The dust-phase abundances of both
Si and Fe are positively correlated with the small-grain population (effective
radii smaller than a few hundred micron) toward the targets. The physical
conditions along the sight lines suggest that this relationship may be due to
differences in the survival of small particles in some interstellar
environments. The chemical composition of the small grains could either
resemble dust mantles or be silicate rich.",0701408v1
2007-01-19,Exploring the X-ray spectral variability of MCG-6-30-15 with XMM-Newton,"We present a study of the spectral variability of the Seyfert I galaxy
MCG-6-30-15 based on the two long XMM-Newton observations from 2000 and 2001.
The X-ray spectrum and variability properties of the 2001 data have previously
been well described with a two-component model consisting of a variable power
law and a much less variable reflection component, containing a broad
relativistic iron line from the accretion disc around a rapidly rotating Kerr
black hole. The lack of variability of the reflection component has been
interpreted as an effect of strong gravitational light bending very close to
the central black hole. Using an improved reflection model, we fit the
two-component model to time-resolved spectra of both observations. Assuming
that the photon index of the power law is constant we reconfirm the old result
and show that this does not depend on the time-scale of the analysis.",0701567v1
2007-01-20,The origin of the ankle,"The differential intensity of cosmic radiation shows a sequence of
depressions referred to as ""knees"" in a large energy band above 10^15 eV. The
global depression entailed in the complete spectrum with respect to the
extrapolated intensity based on low energy data amounts to a maximum factor of
8, occurring at 5 x 10^18 eV, where flux measurements exhibit a relative
minimum, referred to as the ""ankle"". It is demonstrated by a full simulation of
cosmic ray trajectories in the Galaxy that the intensity minimum around the
ankle energy is primarily due to the nuclear interactions of the cosmic ions
with the interstellar matter and to the galactic magnetic field. ""Ankles""
signal the onset energies of the rectilinear propagation in the Milky Way at
the Earth, being for example, 4 x 10^18 eV for helium and 6 x 10^19 eV for
iron. The ankle, in spite of its notable importance at the Earth, is a local
perturbation of the universal spectrum which, between the knee and the ankle,
decreases by a round factor 10^9, regaining its unperturbed status above 10^19
eV.",0701593v1
2007-01-23,INTEGRAL Observations of the Vela Region Focusing on Vela X-1,"The Vela region has been observed for 1.7 Ms in November 2005 by the INTEGRAL
satellite. We present preliminary spectral and temporal results of Vela X-1, an
eclipsing neutron star hosted in a wind-accreting high-mass X-ray binary
system. Using data from ISGRI, SPI and JEM-X, we firmly confirm the existence
of cyclotron resonant scattering features (CRSF) at ~27 keV and ~54 keV,
implying a neutron-star magnetic field of ~3 10^12 Gauss, and the presence of
an iron emission line at ~6.5 keV. During two strong flares those parameters
remained unchanged. Furthermore we measure the neutron-star spin period of
283.6 s, indicating a still constant trend.",0701641v1
2007-01-26,First ground based measurement of atmospheric Cherenkov light from cosmic rays,"A recently proposed novel technique for the detection of cosmic rays with
arrays of Imaging Atmospheric Cherenkov Telescopes is applied to data from the
High Energy Stereoscopic System (H.E.S.S.). The method relies on the ground
based detection of Cherenkov light emitted from the primary particle prior to
its first interaction in the atmosphere. The charge of the primary particle (Z)
can be estimated from the intensity of this light, since it is proportional to
Z$^2$. Using H.E.S.S. data, an energy spectrum for cosmic-ray iron nuclei in
the energy range 13--200 TeV is derived. The reconstructed spectrum is
consistent with previous direct measurements and is one of the most precise so
far in this energy range.",0701766v1
2007-03-10,Constraining global parameters of accreting black holes by modeling magnetic flares,"We present modeling results for the reprocessed radiation expected from
magnetic flares above AGN accretion disks. Relativistic corrections for the
orbital motion of the flare and for the curved space-time in the vicinity of
the black hole are taken into account. We investigate the local emission
spectra, as seen in a frame co-orbiting with the disk, and the observed spectra
at infinity. We investigate long-term flares at different orbital phases and
short-term flares for various global parameters of the accreting black hole.
Particular emphasis is put on the relation between the iron Kalpha line and the
Compton hump as these two features can be simultaneously observed by the Suzaku
satellite and later by Simbol-X.",0703240v1
2007-03-14,Absorption Measure Distribution of the Outflow in IRAS 13349+2438: Direct Observation of Thermal Instability?,"We analyze the Chandra X-ray spectrum obtained with the HETGS grating
spectrometer of IRAS 13349+2438, which has one of the richest absorption
spectra of a quasar outflow. Absorption from almost all charge states of Fe is
detected. This allows for a detailed reconstruction of the absorption measure
distribution (AMD), which we define as the continuous distribution of column
density as a function of ionization parameter. We find a double peaked AMD for
IRAS 13349+2438 with a total (ionized) column density of N_H = (1.2 +- 0.3)*
10^{22} cm^-2} assuming solar iron abundance. For comparison, we perform a
similar analysis on the well studied HETGS spectrum of NGC 3783. Both sources
feature a deep minimum in column density consistent with no absorption from gas
at temperatures of 4.5 < log T < 5 (K). We interpret the minima as
observational evidence for thermal instability in this temperature regime.",0703351v1
2007-03-14,Delayed detonations in full-star models of Type Ia supernova explosions,"Aims: We present the first full-star three-dimensional explosion simulations
of thermonuclear supernovae including parameterized deflagration-to-detonation
transitions that occur once the flame enters the distributed burning regime.
Methods: Treating the propagation of both the deflagration and the detonation
waves in a common front-tracking approach, the detonation is prevented from
crossing ash regions. Results: Our criterion triggers the detonation wave at
the outer edge of the deflagration flame and consequently it has to sweep
around the complex structure and to compete with expansion. Despite the impeded
detonation propagation, the obtained explosions show reasonable agreement with
global quantities of observed type Ia supernovae. By igniting the flame in
different numbers of kernels around the center of the exploding white dwarf, we
set up three different models shifting the emphasis from the deflagration phase
to the detonation phase. The resulting explosion energies and iron group
element productions cover a large part of the diversity of type Ia supernovae.
Conclusions: Flame-driven deflagration-to-detonation transitions, if
hypothetical, remain a possibility deserving further investigation.",0703378v1
2007-03-19,Stokes diagnostics of simulated solar magneto-convection,"We present results of synthetic spectro-polarimetric diagnostics of radiative
MHD simulations of solar surface convection with magnetic fields. Stokes
profiles of Zeeman-sensitive lines of neutral iron in the visible and infrared
spectral ranges emerging from the simulated atmosphere have been calculated in
order to study their relation to the relevant physical quantities and compare
with observational results. We have analyzed the dependence of the Stokes-I
line strength and width as well as of the Stokes-V signal and asymmetries on
the magnetic field strength. Furthermore, we have evaluated the correspondence
between the actual velocities in the simulation with values determined from the
Stokes-I (Doppler shift of the centre of gravity) and Stokes-V profiles
(zero-crossing shift). We confirm that the line weakening in strong magnetic
fields results from a higher temperature (at equal optical depth) in the
magnetic flux concentrations. We also confirm that considerable Stokes-V
asymmetries originate in the peripheral parts of strong magnetic flux
concentrations, where the line of sight cuts through the magnetopause of the
expanding flux concentration into the surrounding convective donwflow.",0703490v1
2007-03-22,Statistical methods applied to composition studies of ultrahigh energy cosmic rays,"The mass composition of high energy cosmic rays above $10^{17}$ eV is a
crucial issue to solve some open questions in astrophysics such as the
acceleration and propagation mechanisms. Unfortunately, the standard procedures
to identify the primary particle of a cosmic ray shower have low efficiency
mainly due to large fluctuations and limited experimental observables. We
present a statistical method for composition studies based on several
measurable features of the longitudinal development of the CR shower such as
$N_{max}$, $X_{max}$, asymmetry, skewness and kurtosis. Principal component
analysis (PCA) was used to evaluate the relevance of each parameter in the
representation of the overall shower features and a linear discriminant
analysis (LDA) was used to combine the different parameters to maximize the
discrimination between different particle showers. The new parameter from LDA
provides a separation between primary gammas, proton and iron nuclei better
than the procedures based on $X_{max}$ only. The method proposed here was
successfully tested in the energy range from $10^{17}$ to $10^{20}$ eV even
when limitations of shower track length were included in order to simulate the
field of view of fluorescence telescopes.",0703582v1
1993-05-11,Electronic Structure and Bonding in Epitaxially Stabilized Cubic Iron Silicides,"We present an ab initio full-potential linearized augmented plane-wave
(FLAPW) study of the structural and electronic properties of the two bulk
unstable compounds FeSi (CsCl structure) and FeSi$_2$ (CaF$_2$ structure) which
have recently been grown by molecular beam epitaxy on Si(111). We obtain
equilibrium bulk lattice constants of 2.72 \AA\ and 5.32 \AA\ for FeSi and
FeSi$_2$, respectively. The density of states (DOS) of FeSi agrees well with
experiment, and shows metallic behavior. In agreement with a previous
calculation the DOS of FeSi$_2$ shows a large density of $d$-states at the
Fermi level, explaining the instability of the bulk phase. The electron charge
distributions reveal a small charge transfer from Si to Fe atomic spheres in
both compounds. While in FeSi the Fe-Si bond is indeed partially ionic, we show
that in FeSi$_2$ the electron distribution corresponds to a covalent charge
accumulation in the Fe-Si bond region. The reversed order of $d$-bands in FeSi
with respect to FeSi$_2$ is understood in terms of crystal field splitting and
Fe-Fe nearest neighbor $dd$-interactions in the CsCl structure, and a strong Si
$p$/Fe $d$ bonding in the fluorite structure, respectively.",9305007v1
1994-06-06,Volume Effect in the Landau Theory of Martensitic Phase Transitions in Cubic Crystals,"An effect of the volume change upon proper ferroelastic (martensitic) phase
transitions in cubic crystals is considered. Corresponding terms in the
Ginzburg-Landau expansion of the Gibbs free energy are analyzed for the first-
as well as second-order phase transitions from cubic to tetragonal lattice
under the action of uniaxial and hydrostatic pressure. The pressure effect on
the critical temperature as well as on the phase transition anomalies of
isothermal compressibility and linear thermal expansion coefficient are studied
and recent experimental data on thermal expansion anomalies in V$_3$Si, In-Tl
and Ni-Al are discussed. The non-linearity of thermal expansion leads to the
special relation between the shear strain and volume change as a result of the
elastic energy minimization. This phenomenon can provide the transformation
from FCC lattice to BCC one, observed in the iron alloys.",9406030v2
1995-08-26,Magnetic Properties of Epitaxial and Polycrystalline Fe/Si Multilayers,"Fe/Si multilayers with antiferromagnetic interlayer coupling have been grown
via ion-beam sputtering on both glass and single-crystal substrates. High-angle
x-ray diffraction measurements show that both sets of films have narrow Fe
peaks, implying a large crystallite size and crystalline iron silicide spacer
layers. Low-angle x-ray diffraction measurements show that films grown on glass
have rougher interfaces than those grown on single-crystal substrates. The
multilayers grown on glass have a larger remanent magnetization than the
multilayers grown on single-crystal substrates. The observation of
magnetocrystalline anisotropy in hysteresis loops and $(hkl)$ peaks in x-ray
diffraction demonstrates that the films grown on MgO and Ge are epitaxial. The
smaller remanent magnetization in Fe/Si multilayers with better layering
suggests that the remanence is not an intrinsic property.",9508117v1
1995-12-18,Soft X-ray Fluorescence Study of Buried Silicides in Antiferromagnetically Coupled Fe/Si Multilayer,"Soft x-ray fluorescence spectroscopy has been employed to obtain information
about the Si-derived valence band states of Fe/Si multilayers. The valence band
spectra are quite different for films with and without antiferromagnetic
interlayer exchange coupling, demonstrating that these multilayers have
different silicide phases in their spacer layers. Comparison with previously
published fluorescence data on bulk iron silicides shows that the Fe
concentration in the silicide spacer layers is substantial. Near-edge x-ray
absorption data on antiferromagnetically coupled multilayers in combination
with the fluorescence data demonstrate unambiguously that the silicide spacer
layer in these films is metallic. These results on the electronic structure of
buried layers in a multilayer film exemplify the wide range of experiments made
possible by new high-brightness synchrotron sources.",9512126v1
1996-09-11,Exchange Coupling Between Iron Layers Separated by BCC Copper,"The exchange coupling between Fe layers separated by BCC Cu is calculated for
Fe/Cu/Fe (001) trilayers. It is shown that the coupling is basically regulated
by three extrema of the bulk BCC Cu Fermi surface. The contributions from those
extrema are all of the same order of magnitude, but that associated with the
``belly'' at the $\Gamma$-point dominates. The calculated temperature
dependence of the coupling varies considerably with spacer layer thickness.
Individually, the amplitudes of these extrema contribution decrease with
temperature, each according to a different rate. Such an effect may cause an
actual increase of coupling with temperature for some Cu thicknesses.",9609104v1
1997-06-04,Monte Carlo Simulation of Magnetization Reversal in Fe Sesquilayers on W(110),"Iron sesquilayers grown at room temperature on W(110) exhibit a pronounced
coercivity maximum near a coverage of 1.5 atomic monolayers. On lattices which
faithfully reproduce the morphology of the real films, a kinetic Ising model is
utilized to simulate the domain-wall motion. Simulations reveal that the
dynamics is dominated by the second-layer islands, which act as pinning
centers. The simulated dependencies of the coercivity on the film coverage, as
well as on the temperature and the frequency of the applied field, are very
similar to those measured in experiments. Unlike previous micromagnetic models,
the presented approach provides insight into the dynamics of the domain-wall
motion and clearly reveals the role of thermal fluctuations.",9706036v2
1998-01-07,Monte Carlo simulation of magnetization reversal via domain-wall motion in Fe sesquilayers on W(110),"Iron sesquilayers are ultrathin films with coverages between one and two
atomic monolayers. They consist of an almost defect-free monolayer with compact
islands of a second atomic layer on top. This variation of the film thickness
results in a strong interaction between domain walls and the island structure.
It makes these systems an ideal laboratory to study the dynamics of domain
walls driven by weak external fields. We present computer simulations which
provide insight into the role of the thermally activated nucleation processes
by which a driven domain wall overcomes the obstacles created by the islands.",9801052v1
1998-04-03,First principles simulations of liquid Fe-S under Earth's core conditions,"First principles electronic structure calculations, based upon density
functional theory within the generalized gradient approximation and ultra-soft
Vanderbilt pseudopotentials, have been used to simulate a liquid alloy of iron
and sulfur at Earth's core conditions. We have used a sulfur concentration of
$\approx 12 % $wt, in line with the maximum recent estimates of the sulfur
abundance in the Earth's outer core. The analysis of the structural, dynamical
and electronic structure properties has been used to report on the effect of
the sulfur impurities on the behavior of the liquid. Although pure sulfur is
known to form chains in the liquid phase, we have not found any tendency
towards polymerization in our liquid simulation. Rather, a net S-S repulsion is
evident, and we propose an explanation for this effect in terms of the
electronic structure. The inspection of the dynamical properties of the system
suggests that the sulfur impurities have a negligible effect on the viscosity
of Earth's liquid core.",9804035v1
1998-05-10,Assisted Tunneling in Ferromagnetic Junctions and Half-Metallic Oxides,"Different mechanisms of spin-dependent tunneling are analyzed with respect to
their role in tunnel magnetoresistance (TMR). Microscopic calculation within a
realistic model shows that direct tunneling in iron group systems leads to
about a 30% change in resistance, which is close but lower than experimentally
observed values. The larger observed values of the tunnel magnetoresistance
(TMR) might be a result of tunneling involving surface polarized states. It is
found that tunneling via resonant defect states in the barrier radically
decreases the TMR by order of magnitude. One-magnon emission is shown to reduce
the TMR, whereas phonons increase the effect. The inclusion of both magnons and
phonons reasonably explains an unusual bias dependence of the TMR. The model
presented here is applied qualitatively to half-metallics with 100% spin
polarization, where one-magnon processes are suppressed and the change in
resistance in the absence of spin-mixing on impurities may be arbitrarily
large. Even in the case of imperfect magnetic configurations, the resistance
change can be a few 1000 percent. Examples of half-metallic systems are
CrO2/TiO2 and CrO2/RuO2.",9805114v1
1998-07-14,The hematite (alpha-Fe_2 O_3) (0001) surface: evidence for domains of distinct chemistry,"Using spin-density functional theory we investigated various possible
structures of the hematite (0001) surface. Depending on the ambient oxygen
partial pressure, two geometries are found to be particularly stable under
thermal equilibrium: one being terminated by iron and the other by oxygen. Both
exhibit huge surface relaxations (-57 % for the Fe- and -79 % for the
O-termination) with important consequences for the surface electronic and
magnetic properties. With scanning tunneling microscopy we observe two
different surface terminations coexisting on single crystalline alpha-Fe_2 O_3
(0001) films, which were prepared in high oxygen pressures.",9807202v1
1998-08-08,The Influence of the Bulk Density on the Intergranular Properties of YBa2Cu3-xFexOy (0<x<0.01) Ceramics,"The influence of the bulk density of YBa2Cu3-xFexOy (0 < x < 0.01) ceramics
on the intergranular superconducting (SC) properties was studied using the
temperature dependence of AC magnetic susceptibility measurements. It was found
that the simultaneous variation of the sample's density and the iron impurity
concentration does not influence effectively the onset temperature of the
superconducting state Tc(on). While only increasing of the sample's density
shifts the intergranular hysteresis losses peak temperature Tm(J) to the lower
values which connects with the decreasing of the Josephson magnetic vortices
pinning role. It was established that the shielding capability and Tm(J)
display a plateau with X in the 0.003 < X < 0..007 region which is due to the
monotonous decrease of the sample's density. It was shown that the shielding
capability at the T=78K for the sample with 3.8g/cm3 is two times higher than
that for the sample with the density of 5.0g/cm3. The possible interpretations
of the observed results are discussed.",9808086v1
1998-10-28,"Interplay of Chemical Bonding and Magnetism in Fe_4N, Fe_3N, Fe_2N","Using spin density functional theory we have carried out a comparative study
of chemical bonding and magnetism in Fe_4N, Fe_3N and Fe_2N. All of these
compounds form close packed Fe lattices, while N occupies octahedral
interstitial positions. High spin fcc Fe and hypothetical FeN with rock salt
structure have been included in our study as reference systems. We find strong,
covalent Fe-N bonds as a result of a substantial \sigma-type p-d hybridisation,
with some charge transfer to N. Those Fe d orbitals which contribute to the p-d
bonds, do no longer participate in the exchange splitting of the Fe d bands.
Because of the large exchange fields, the majority spin d bands are always
fully occupied, while the minority spin d bands are close to half-filling, thus
optimizing the Fe d-d covalent bonding. As a consequence, in good approximation
the individual Fe moments decrease in steps of 0.5 \mu_B from fcc iron (2.7
\mu_B) via Fe_4N (2.7 and 1.97 mu_B}), \chem{Fe_3N} (1.99 \mu_B) to \zeta -
Fe_2N (1.43 \mu_B).",9810383v1
1998-12-16,Superconducting and Magnetic Properties of Nb/Pd_1-xFe_x/Nb Triple Layers,"The superconducting and magnetic properties of Nb/Pd_1-xFe_x/Nb triple layers
with constant Nb layer thickness d_Nb=200 A and different interlayer
thicknesses are investigated. The thickness dependence of the magnetization and
of the superconducting transition temperature shows that for small iron
concentration x the Pd_1-xFe_x layer is likely to be in the paramagnetic state
for very thin films whereas ferromagnetic order is established for x>=0.13. The
parallel critical field B_c2II(T) exhibits a crossover from two-dimensional
(2D) behavior where the Nb films are coupled across the interlayer, towards a
2D behavior of coupled Nb films with increasing d_PdFe or x. This 2D-2D
crossover allows a determination of the penetration depth xi_F of Cooper pairs
into the Pd_1-xFe_x layer as a function of x. For samples with a ferromagnetic
interlayer xi_ is found to be independent of x.",9812278v1
1999-11-24,Kinetics of moisture absorption in mixtures for iron foundry,"The moisture absorption in granulated materials used in foundry technologies
is analyzed. The absorption process has a diffusive behavior mainly. A simple
experimental technique, in which the wet weight increment was recorded as the
experimental parameter and an analytic method with computing procedure to find
the parameters characterizing the process was used. The determination of these
parameters by traditional methods is a very difficult task so, very refined and
expensive trials are needed. The fitting of the model permits to determine the
diffusion coefficient and the moisture concentration in the separation surface
between the sample and the environment. The concentration profiles are
established for different times. Finally, the possibility of occurrence of
superimposed diffusive processes in some materials is analyzed and the
diffusion coefficient and the amount of moisture incorporated by each process
are calculated.",9911400v1
2000-04-18,"Metallic and nonmetallic double perovskites: A case study of A$_2$FeReO$_6$ (A= Ca, Sr, Ba)","We have investigated the structure and electronic properties of ferrimagnetic
double perovskites, A2FeReO6 (A= Ca, Sr, Ba). The A=Ba phase is cubic (Fm3m)
and metallic, while the A=Ca phase is monoclinic (P21/n) and nonmetallic.
  57Fe Mossbauer spectroscopy shows that iron is present mainly in the
high-spin (S=5/2) Fe3+ state in the Ca compound, while it occurs in an
intermediate state between high-spin Fe2+ and Fe3+ in the Ba compound. It is
argued that a direct Re t2g - Re t2g interaction is the main cause for the
metallic character of the Ba compound; the high covalency of Ca-O bonds and the
monoclinic distortion (which lifts the degeneracy of t2g states) seem to
disrupt the Re-Re interaction in the case of the Ca compound, making it
non-metallic for the same electron count.",0004315v1
2000-05-05,Analysis of Dislocation Mechanism for Melting of Elements: Pressure Dependence,"In the framework of melting as a dislocation-mediated phase transition we
derive an equation for the pressure dependence of the melting temperatures of
the elements valid up to pressures of order their ambient bulk moduli. Melting
curves are calculated for Al, Mg, Ni, Pb, the iron group (Fe, Ru, Os), the
chromium group (Cr, Mo, W), the copper group (Cu, Ag, Au), noble gases (Ne, Ar,
Kr, Xe, Rn), and six actinides (Am, Cm, Np, Pa, Th, U). These calculated
melting curves are in good agreement with existing data. We also discuss the
apparent equivalence of our melting relation and the Lindemann criterion, and
the lack of the rigorous proof of their equivalence. We show that the would-be
mathematical equivalence of both formulas must manifest itself in a new
relation between the Gr\""{u}neisen constant, bulk and shear moduli, and the
pressure derivative of the shear modulus.",0005118v1
2000-05-29,Electronic and Magnetic Properties of Febr2,"Electronic and magnetic (e-m) properties of FeBr2 have been surprisingly well
described as originating from the Fe2+ ions and their fine electronic
structure. The fine electronic structure have been evaluated taking into
account the spin-orbit (s-o) coupling, crystal-field and inter-site
spin-dependent interactions. The required magnetic doublet ground state with an
excited singlet at D=2.8 meV results from the trigonal distortion. This effect
of the trigonal distortion and a large magnetic moment of iron, of 4.4 mB, can
be theoretically derived provided the s-o coupling is correctly taking into
account. The obtained good agreement with experimental data indicates on
extremaly strong correlations of the six 3d electrons in the Fe2+ ion yielding
their full localization and the insulating state. These calculations show that
for the meaningful analysis of e-m properties of FeBr2 the spin-orbit coupling
is essentially important and that the orbital moment (0.74 mB) is largely
unquenched (by the off-cubic trigonal distortion in the presence of the
spin-orbit coupling).",0005502v1
2000-08-08,Influence of carbon and nitrogen on electronic structure and hyperfine interactions in fcc iron-based alloys,"Carbon and nitrogen austenites, modeled by Fe8N and Fe8C superstructures are
studied by full-potential LAPW method. Structure parameters, electronic and
magnetic properties as well as hyperfine interaction parameters are obtained.
Calculations prove that Fe-C austenite can be successfully modeled by ordered
Fe8C superstructure. The results show that chemical Fe-C bond in Fe8C has
higher covalent part than in Fe8N. Detailed analysis of electric field gradient
formation for both systems is performed. The calculation of electric field
gradient allow us to carry out a good interpretation of Moessbauer spectra for
Fe-C and Fe-N systems.",0008129v1
2000-11-23,Magnetization in Molecular Iron Rings,"The organometallic ring molecules Fe_6 and Fe_10 are leading examples of a
class of nanoscopic molecular magnets, which have been of intense recent
interest both for their intrinsic magnetic properties and as candidates for the
observation of macroscopic quantum coherent phenomena. Torque magnetometry
experiments have been performed to measure the magnetization in single crystals
of both systems. We provide a detailed interpretation of these results, with a
view to full characterization of the material parameters. We present both the
most accurate numerical simulations performed to date for ring molecules, using
Exact Diagonalization and Density Matrix Renormalization Group techniques, and
a semiclassical description for purposes of comparison. The results permit
quantitative analysis of the variation of critical fields with angle, of the
nature and height of magnetization and torque steps, and of the width and
rounding of the plateau regions in both quantities.",0011403v1
2001-01-31,Langevin Simulation of Thermally Activated Magnetization Reversal in Nanoscale Pillars,"Numerical solutions of the Landau-Lifshitz-Gilbert micromagnetic model
incorporating thermal fluctuations and dipole-dipole interactions (calculated
by the Fast Multipole Method) are presented for systems composed of nanoscale
iron pillars of dimension 9 nm x 9 nm x 150 nm. Hysteresis loops generated
under sinusoidally varying fields are obtained, while the coercive field is
estimated to be 1979 $\pm$ 14 Oe using linear field sweeps at T=0 K. Thermal
effects are essential to the relaxation of magnetization trapped in a
metastable orientation, such as happens after a rapid reversal of an external
magnetic field less than the coercive value. The distribution of switching
times is compared to a simple analytic theory that describes reversal with
nucleation at the ends of the nanomagnets. Results are also presented for
arrays of nanomagnets oriented perpendicular to a flat substrate. Even at a
separation of 300 nm, where the field from neighboring pillars is only $\sim$ 1
Oe, the interactions have a significant effect on the switching of the magnets.",0101477v2
2001-09-28,Density functional simulation of small Fe nanoparticles,"We calculate from first principles the electronic structure, relaxation and
magnetic moments in small Fe particles, applying the numerical local orbitals
method in combination with norm-conserving pseudopotentials. The accuracy of
the method in describing elastic properties and magnetic phase diagrams is
tested by comparing benchmark results for different phases of crystalline iron
to those obtained by an all-electron method. Our calculations for the
bipyramidal Fe_5 cluster qualitatively and quantitatively confirm previous
plane-wave results that predicted a non-collinear magnetic structure. For
larger bcc-related (Fe_35) and fcc-related (Fe_38, Fe_43, Fe_62) particles, a
larger inward relaxation of outer shells has been found in all cases,
accompanied by an increase of local magnetic moments on the surface to beyond 3
mu_B.",0109540v2
2001-10-09,Decay of spin-Peierls state in CuGeO3:Fe. The case of a strong disorder,"Influence of doping by iron impurity on spin-Peierls state in CuGeO3 is
studied. ESR measurements for the frequency/temperature domain 60-450 GHz/
1.8-300 K and specific heat data obtained for the interval 6-20 K show that
insertion of 1% of Fe completely destroy both spin-Peierls and
antiferromagnetic orders. Damping of long-range magnetic order is accompanied
by onset at T<20 K of power asymptotics for magnetic susceptibility
chi~T^-alpha and magnetic part of specific heat cm~T^(1-alpha), with the index
alpha=0.35-0.37. This effect is characteristic to the limit of strong disorder
for doped CuGeO3 and may reflect formation of the Griffiths phase at low
temperatures in CuGeO3:Fe.",0110177v1
2001-11-27,Complementary approaches to the ab initio calculation of melting properties,"Several research groups have recently reported {\em ab initio} calculations
of the melting properties of metals based on density functional theory, but
there have been unexpectedly large disagreements between results obtained by
different approaches. We analyze the relations between the two main approaches,
based on calculation of the free energies of solid and liquid and on direct
simulation of the two coexisting phases. Although both approaches rely on the
use of classical reference systems consisting of parameterized empirical
interaction models, we point out that in the free energy approach the final
results are independent of the reference system, whereas in the current form of
the coexistence approach they depend on it. We present a scheme for correcting
the predictions of the coexistence approach for differences between the
reference and {\em ab initio} systems. To illustrate the practical operation of
the scheme, we present calculations of the high-pressure melting properties of
iron using the corrected coexistence approach, which agree closely with earlier
results from the free energy approach. A quantitative assessment is also given
of finite-size errors, which we show can be reduced to a negligible size.",0111510v1
2001-12-03,Electron correlation effects and ferromagnetism in Iron,"Electron correlation effects in Fe are analyzed using a first principles
LCAO-scheme. In our approach, we first use a local orbital DFT-LDA solution to
introduce a Hubbard Hamiltonian without fitting parameters. In a second step,
we introduce a many-body solution to this Hamiltonian using a DMF
approximation. Our analysis shows that magnetism in Fe is an effect associated
with the first atomic Hund's rule. Moreover, we also find important correlation
effects in the Fe-spin polarized DOS. The photoemision spectra is explained
using a value of U_eff as large as 4 eV, provided the satellite peaks appearing
around 3-5 eV below the Fermi energy are interpreted appropriately.",0112038v1
2001-12-07,Proton Spin Relaxation Induced by Quantum Tunneling in Fe8 Molecular Nanomagnet,"The spin-lattice relaxation rate $T_{1}^{-1}$ and NMR spectra of $^1$H in
single crystal molecular magnets of Fe8 have been measured down to 15 mK. The
relaxation rate $T_1^{-1}$ shows a strong temperature dependence down to 400
mK. The relaxation is well explained in terms of the thermal transition of the
iron state between the discreet energy levels of the total spin S=10. The
relaxation time $T_1$ becomes temperature independent below 300 mK and is
longer than 100 s. In this temperature region stepwise recovery of the
$^1$H-NMR signal after saturation was observed depending on the return field of
the sweep field. This phenomenon is attributed to resonant quantum tunneling at
the fields where levels cross and is discussed in terms of the Landau-Zener
transition.",0112111v1
2002-08-01,Magnetic shape-memory effects in La2-xSrxCuO4 crystals,"The magnetic field affects the motion of electrons and the orientation of
spins in solids, but it is believed to have little impact on the crystal
structure. This common perception has been challenged recently by ferromagnetic
shape-memory alloys, where the spin-lattice coupling is so strong that
crystallographic axes even in a fixed sample are forced to rotate, following
the direction of moments. One would, however, least expect any structural
change to be induced in antiferromagnets where spins are antiparallel and give
no net moment. Here we report on such unexpected magnetic shape-memory effects
that take place ironically in one of the best-studied 2D antiferromagnets,
La2-xSrxCuO4 (LSCO). We find that lightly-doped LSCO crystals tend to align
their b axis along the magnetic field, and if the crystal orientation is fixed,
this alignment occurs through the generation and motion of crystallographic
twin boundaries. Both resistivity and magnetic susceptibility exhibit curious
switching and memory effects induced by the crystal-axes rotation; moreover,
clear kinks moving over the crystal surfaces allow one to watch the crystal
rearrangement directly with a microscope or even bare eyes.",0208013v1
2002-08-12,"Fe/V and Fe/Co (001) superlattices: growth, anisotropy, magnetisation and magnetoresistance","Some physical properties of bcc Fe/V and Fe/Co (001) superlattices are
reviewed. The dependence of the magnetic anisotropy on the in-plane strain
introduced by the lattice mismatch between Fe and V is measured and compared to
a theoretical derivation. The dependence of the magnetic anisotropy (and
saturation magnetisation) on the layer thickness ratio Fe/Co is measured and a
value for the anisotropy of bcc Co is derived from extrapolation. The
interlayer exchange coupling of Fe/V superlattices is studied as a function of
the layer thickness V (constant Fe thickness) and layer thickness of Fe
(constant V thickness). A region of antiferromagnetic coupling and GMR is found
for V thicknesses 12-14 monolayers. However, surprisingly, a 'cutoff' of the
antiferromagnetic coupling and GMR is found when the iron layer thickness
exceeds about 10 monolayers.",0208229v1
2002-08-22,"Spin fluctuations, electron-phonon coupling and superconductivity in near-magnetic elementary metals; Fe,Co,Ni and Pd","An investigation of possibilities for superconductivity mediated by spin
fluctuations in some elementary metals is motivated by the recent discovery of
superconductivity in the hcp high-pressure phase of iron.
  The electronic structure, the electron-phonon coupling ($\lambda_{ph}$) and
the coupling due to spin-fluctuations ($\lambda_{sf}$) are calculated for
different phases and different volumes for four elementary metals. The results
show that such possibilities are best for systems near, but on the non-magnetic
side of, a magnetic instability. Fcc Ni, which show stable magnetism over a
wide pressure range, is not interesting in this respect. Ferro- and
antiferro-magnetic fluctuations in hcp Fe contribute to a relatively strong
coupling in the pressure range where superconductivity is observed. The absence
of fluctuations at large q-vectors makes fcc Pd only moderately interesting
despite its large exchange enhancement for q=0. Fcc Co at high pressure ($\sim$
0.5 Mbar) behaves as an improved version of Pd, where the fluctuations extend
to larger q. The estimations of T$_C$, which reproduce the experimental
situation in Fe quite well, suggest a measurable T$_C$ for the high-pressure
phase of fcc Co, while the estimate is lower for the ambient-pressure phase of
fcc Pd.",0208424v1
2002-08-30,Itinerant Ferromagnetism in the Periodic Anderson Model,"We introduce a novel mechanism for itinerant ferromagnetism, based on a
simple two-band model. The model includes an uncorrelated and dispersive band
hybridized with a second band which is narrow and correlated. The simplest
Hamiltonian containing these ingredients is the Periodic Anderson Model (PAM).
Using quantum Monte Carlo and analytical methods, we show that the PAM and an
extension of it contain the new mechanism and exhibit a non-saturated
ferromagnetic ground state in the intermediate valence regime. We propose that
the mechanism, which does not assume an intra atomic Hund's coupling, is
present in both the iron group and in some f electron compounds like
Ce(Rh_{1-x} Ru_x)_3 B_2, La_x Ce_{1-x} Rh_3 B_2 and the uranium
monochalcogenides US, USe, and UTe.",0208604v1
2002-11-25,Calculation of thermal expansion coefficient of Fe/sub 3/Al with the addition of transition metal elements,"The addition of transition metal elements can significantly modify physical
properties of intermetalic compounds. We studied the influence of Molybdenum
and Vanadium additives on thermal expansion coefficient (CTE) of Fe/sub 3/Al
and FeAl over the wide range of temperatures. The site preference of both
transition metals was determined by full-potential LMTO method within the
grandcanonical formalism. At low temperatures CTEs were found directly from the
FP-LMTO calculations by incorporating them into the Debye model of a solid. The
obtained thermal expansion for pure Fe/sub 3/Al and FeAl is within 10% of its
experimentally measured values. At high temperatures we performed molecular
dynamics simulations based on our many-body atomistic potentials. The
parameters were fitted to reproduce the total energy of a crystal under various
types of deformations obtained by FP-LMTO method and were tested with respect
to different structures and vacancy formation energies. Our calculations show
that addition of V decreases the CTEs of both iron-aluminides, while the
addition of Mo makes Fe/sub 3/Al DO3 structure unstable.",0211569v1
2002-12-17,Anomalous temperature dependence of the dephasing time in mesoscopic Kondo wires,"We present measurements of the magnetoconductance of long and narrow quasi
one-dimensional gold wires containing magnetic iron impurities in a temperature
range extending from $15 $mK to $4.2 $K. The dephasing rate extracted from the
weak antilocalisation shows a pronounced plateau in a temperature region of
$300 $mK - $800 $mK, associated with the phase breaking due to the Kondo
effect. Below the Kondo temperature the dephasing rate decreases linearly with
temperature, in contradiction with standard Fermi-liquid theory. Our data
suggest that the formation of a spin glass due to the interactions between the
magnetic moments are responsible for the observed anomalous temperature
dependence.",0212420v1
2003-01-22,Tunneling splitting of magnetic levels in Fe8 detected by 1H NMR cross relaxation,"Measurements of proton NMR and the spin lattice relaxation rate 1/T1 in the
octanuclear iron (III) cluster [Fe8(N3C6H15)6O2(OH)12][Br8 9H2O], in short Fe8,
have been performed at 1.5 K in a powder sample aligned along the main
anisotropy z axis, as a function of a transverse magnetic field (i.e.,
perpendicular to the main easy axis z). A big enhancement of 1/T1 is observed
over a wide range of fields (2.5-5 T), which can be attributed to the tunneling
dynamics; in fact, when the tunneling splitting of the pairwise degenerate
m=+-10 states of the Fe8 molecule becomes equal to the proton Larmor frequency
a very effective spin lattice relaxation channel for the nuclei is opened. The
experimental results are explained satisfactorily by considering the
distribution of tunneling splitting resulting from the distribution of the
angles in the hard xy plane for the aligned powder, and the results of the
direct diagonalization of the model Hamiltonian.",0301415v1
2003-02-13,"Properties of superconducting MgB_2 wires: ""in-situ"" versus ""ex-situ"" reaction technique","We have fabricated a series of iron-sheathed superconducting wires prepared
by the powder-in-tube technique from (MgB_2)_{1-x}:(Mg+2B)_x initial powder
mixtures taken with different proportions, so that x varies from 0 to 1. It
turned out that ""ex-situ"" prepared wire (x = 0) has considerable disadvantages
compared to all the other wires in which ""in-situ"" assisted (0 < x < 1) or pure
""in-situ"" (x = 1) preparation was used due to weaker inter-grain connectivity.
As a result, higher critical current densities J_c were measured over the
entire range of applied magnetic fields B_a for all the samples with x > 0.
Pinning of vortices in MgB_2 wires is shown to be due to grain boundaries.
J_c(B_a) behavior is governed by an interplay between the transparency of grain
boundaries and the amount of ""pinning"" grain boundaries. Differences between
thermo-magnetic flux-jump instabilities in the samples and a possible threat to
practical applications are also discussed.",0302249v1
2003-03-07,Macroscopic and Microscopic Investigation on the History Dependence of the Mechanical Behaviour of Powders,"As an example for history dependent mechanical behaviour of cohesive powders
experiments and computer simulations of uniaxial consolidation are compared.
Some samples were precompacted transversally to the consolidation direction and
hence had a different history. The experiments were done with two carbonyl iron
powders, for which the average particle diameters differed by a factor of ca.
2. Whereas the particle diameter was the only characteristic length in the
simulations, the evaluation of the experimental data indicates that at least a
second characteristic length must be present.",0303132v1
2003-05-19,Andreev bound states in normal and ferromagnet/high-Tc superconducting tunnel junctions,"Ag/BSCCO and Fe/Ag/BSCCO planar tunnel junctions were constructed in order to
study experimentally the effect of an exchange potential on the spin polarized
current transported through Andreev bound states appearing at the interface
with a superconductor with broken time reversal pairing symmetry. The zero bias
conductance peak (ZBCP) resulting from the Andreev bound states (ABS) is split
into two symmetric peaks shifted at finite energies when the counterlectrode is
normal. Four asymmetric peaks are observed when the ferromagnetic spin
polarized charge reservoir is added, due to the combined effect of a
spin-filtering exchange energy in the barrier, which is a spin dependent
phenomenon, and the spin independent effect of a broken time reversal symmetry
(BTRS). The polarization in the iron layer leads to asymmetry. Due to the shift
of ABS peaks to finite energies, the conductance at zero energy behaves as
predicted by recent theoretical developments for pure d-wave junctions without
Andreev reflections.",0305446v1
2003-06-11,Electron Coherence in Mesoscopic Kondo Wires,"We present measurements of the magnetoresistance of long and narrow quasi
one-dimensional gold wires containing magnetic iron impurities. The electron
phase coherence time extracted from the weak antilocalisation shows a
pronounced plateau in a temperature region of 300 mK - 800 mK, associated with
the phase breaking due to the Kondo effect. Below the Kondo temperature, the
phase coherence time increases, as expected in the framework of Kondo physics.
At much lower temperatures, the phase coherence time saturates again, in
contradiction with standard Fermi liquid theory. In the same temperature
regime, the resistivity curve displays a characteristic maximum at zero
magnetic field, associated with the formation of a spin glass state. We argue
that the interactions between the magnetic moments are responsible for the low
temperature saturation of the phase coherence time.",0306276v1
2003-09-17,"Iron and molybdenum valences in double-perovskite (Sr,Nd)2FeMoO6: electron-doping effect","Double perovskite, (Sr1-xNdx)2FeMoO6, was doped with electrons through
partial substitution of divalent Sr by trivalent Nd (0 < x < 0.2). The Fe
valence and the degree of B-site order were probed by 57Fe Mossbauer
spectroscopy. Replacing Sr by Nd increased the fraction of Fe and Mo atoms
occupying wrong sites, i.e. antisite disorder. It had very little effect on the
Fe valence: a small but visible increase in the isomer shift was seen for the
mixed-valent FeII/III atoms occupying the right site indicating a slight
movement towards divalency of these atoms, which was more than counterbalanced
by the increase in the fraction of antisite Fe atoms with III valence state. It
is therefore argued that the bulk of the electron doping is received by
antisite Mo atoms, which - being surrounded by six MoV/VI atoms - prefer the
lower IV/V valence state. Thus under Nd substitution, the charge-neutrality
requirement inflicts a lattice disorder such that low-valent MoIV/V can exist.",0309394v1
2003-11-21,First-principle molecular dynamics with ultrasoft pseudopotentials: parallel implementation and application to extended bio-inorganic system,"We present a plane-wave ultrasoft pseudopotential implementation of
first-principle molecular dynamics, which is well suited to model large
molecular systems containing transition metal centers. We describe an efficient
strategy for parallelization that includes special features to deal with the
augmented charge in the contest of Vanderbilt's ultrasoft pseudopotentials. We
also discuss a simple approach to model molecular systems with a net charge
and/or large dipole/quadrupole moments. We present test applications to
manganese and iron porphyrins representative of a large class of biologically
relevant metallorganic systems. Our results show that accurate
Density-Functional Theory calculations on systems with several hundred atoms
are feasible with access to moderate computational resources.",0311507v1
2004-01-28,Importance of Thermal Disorder on the Properties of Alloys: Origin of Paramagnetism and Structural Anomalies in Iron-Aluminum,"The bcc-based Fe_{1-x}Al_{x} exhibit interesting magnetic and anomalous
structural properties as a function of composition and sample processing
conditions arising from thermal or off-stoichiometric chemical disorder, and,
although well studied, these properties are not understood. In stoichiometric
B2 FeAl, including the effects of partial long-range order (i.e., thermal
antisites), we find the observed paramagnetic response (with non-zero local
moments), in contrast to past investigations which find ferromagnetism based on
local density approximation (LDA) to density functional theory or which find a
non-magnetic state from LDA+U, both of which are inconsistent with experiment.
Moreover, from this magneto-chemical coupling, we are able to determine the
origins of the lattice constant anomalies found in Fe_{1-x}Al_{x} for x=25-50,
as observed from various processing conditions.",0401587v1
2004-01-30,Magnetoelectric Effects in Ferromagnetic Metal-Piezoelectric Oxide Layered Structures,"Frequency dependence of magnetoelectric (ME) coupling is investigated in
trilayers of ferromagnetic alloy and piezoelectric lead zirconate titanate
(PZT). The ferromagnetic phases studied include permendur, a soft magnet with
high magnetostriction, iron, nickel, and cobalt. Low frequency data on ME
voltage coefficient versus bias magnetic field indicate strong coupling only
for trilayers with permendure or Ni. Measurements of frequency dependence of ME
voltage reveal a giant ME coupling at electromechanical resonance. The ME
interactions for transverse fields is an order of magnitude stronger than for
longitudinal fields. The maximum voltage coefficient of 90 V/cm Oe at resonance
is measured for samples with nickel or permendure and is three orders of
magnitude higher than low-frequency values.",0401648v1
2004-04-15,Evidence for crossed Andreev reflection in superconductor-ferromagnet hybrid structures,"We have measured the non-local resistance of aluminum-iron spin-valve
structures fabricated by e-beam lithography and shadow evaporation. The sample
geometry consists of an aluminum bar with two or more ferromagnetic wires
forming point contacts to the aluminum at varying distances from each other. In
the normal state of aluminum, we observe a spin-valve signal which allows us to
control the relative orientation of the magnetizations of the ferromagnetic
contacts. In the superconducting state, at low temperatures and excitation
voltages well below the gap, we observe a spin-dependent non-local resistance
which decays on a smaller length scale than the normal-state spin-valve signal.
The sign, magnitude and decay length of this signal is consistent with
predictions made for crossed Andreev reflection (CAR).",0404360v2
2004-04-27,Phase Separation in Li$_x$FePO$_4$ Induced by Correlation Effects,"We report on a significant failure of LDA and GGA to reproduce the phase
stability and thermodynamics of mixed-valence Li$_x$FePO$_4$ compounds.
Experimentally, Li$_x$FePO$_4$ compositions ($0 \leq x \leq 1$) are known to be
unstable and phase separate into Li FePO$_4$ and FePO$_4$. However,
first-principles calculations with LDA/GGA yield energetically favorable
intermediate compounds an d hence no phase separation. This qualitative failure
of LDA/GGA seems to have its origin in the LDA/GGA self-interaction which de
localizes charge over the mixed-valence Fe ions, and is corrected by explicitly
considering correlation effects in this material. This is demonstrated with
LDA+U calculations which correctly predict phase separation in Li$_x$FePO$_4$
for $U-J \gtrsim 3.5$eV. T he origin of the destabilization of intermediate
compounds is identified as electron localization and charge ordering at
different iron sites. Introduction of correlation also yields more accurate
electrochemical reaction energies between FePO$_4$/Li$_x$FePO$_ 4$ and
Li/Li$^+$ electrodes.",0404631v2
2004-05-02,Spin Dynamics and Multiple Reflections in Ferromagnetic Film in Contact with Normal Metal Layers,"Spin dynamics of a metallic ferromagnetic film imbedded between normal metal
layers is studied using the spin-pumping theory of Tserkovnyak et al. [Phys.
Rev. Lett. 88, 117601 (2002)]. The scattering matrix for this structure is
obtained using a spin-dependent potential with quantum well in the
ferromagnetic region. Owing to multiple reflections in the well, the excess
Gilbert damping and the gyromagnetic ratio exhibit quantum oscillations as a
function of the thickness of the ferromagnetic film. The wavelength of the
oscillations is given by the depth of the quantum well. For iron film imbedded
between gold layers, the amplitude of the oscillations of the Gilbert damping
is in an order of magnitude agreement with the damping observed by Urban et al.
[Phys. Rev. Lett. 87, 217204 (2001)]. The results are compared with the linear
response theory of Mills [Phys. Rev. B 68, 0144419 (2003)].",0405020v1
2004-05-06,Theory of Metal-Insulator Transition in PrRu4P12 and PrFe4P12,"All symmetry allowed couplings between the 4f^2-electron ground state doublet
of trivalent praseodymium in PrRu4P12 and PrFe4P12 and displacements of the
phosphorus, iron or ruthenium ions are considered. Two types of displacements
can change the crystal lattice from body-centred cubic to simple orthorhombic
or to simple cubic. The first type lowers the point group symmetry from
tetrahedral to orthorhombic, while the second type leaves it unchanged, with
corresponding space group reductions Im3 --> Pmmm and Im3 --> Pm3 respectively.
In former case, the lower point-group symmetry splits the degeneracy of the
4f^2 doublet into states with opposite quadrupole moment, which then leads to
anti-quadrupolar ordering, as in PrFe4P12. Either kind of displacement may
conspire with nesting of the Fermi surface to cause the metal-insulator or
partial metal-insulator transition observed in PrFe4P12 and PrRu4P12. We
investigate this scenario using band-structure calculations, and it is found
that displacements of the phosphorus ions in PrRu4P12 (with space group
reduction Im3 --> Pm3) open a gap everywhere on the Fermi surface.",0405127v1
2004-05-07,A linear response approach to the calculation of the effective interaction parameters in the LDA+U method,"In this work we reexamine the LDA+U method of Anisimov and coworkers in the
framework of a plane-wave pseudopotential approach. A simplified
rotational-invariant formulation is adopted. The calculation of the Hubbard U
entering the expression of the functional is discussed and a linear response
approach is proposed that is internally consistent with the chosen definition
for the occupation matrix of the relevant localized orbitals. In this way we
obtain a scheme whose functionality should not depend strongly on the
particular implementation of the model in ab-initio calculations. We
demonstrate the accuracy of the method, computing structural and electronic
properties of a few systems including transition and rare-earth correlated
metals, transition metal monoxides and iron-silicate.",0405160v1
2004-05-10,Self-assembly of iron nanoclusters on the Fe3O4(111) superstructured surface,"We report on the self-organized growth of a regular array of Fe nanoclusters
on a nanopatterned magnetite surface. Under oxidizing preparation conditions
the (111) surface of magnetite exhibits a regular superstructure with
three-fold symmetry and a 42 A periodicity. This superstructure represents an
oxygen terminated (111) surface, which is reconstructed to form a periodically
strained surface. This strain patterned surface has been used as a template for
the growth of an ultrathin metal film. A Fe film of 0.5 A thickness was
deposited on the substrate at room temperature. Fe nanoclusters are formed on
top of the surface superstructure creating a regular array with the period of
the superstructure. We also demonstrate that at least the initial stage of Fe
growth occurs in two-dimensional mode. In the areas of the surface where the
strain pattern is not formed, random nucleation of Fe was observed.",0405201v2
2004-06-24,Resonant magnetic X-ray scattering spectra in SDW Cr -- ab initio study -----,"Using ab-initio band structure calculation based on the local density
approximation, Cr K-edge resonant X-ray magnetic scattering spectra are
analyzed in the spin density wave (SDW) state of chromium. We perform band
structure calculation, assuming an ideal bcc lattice structure with the lattice
constant observed at the spin-flip temperature T_{SF} and a commensurate SDW
state with the propagation vector close to the observed value at T_{SF}. Taking
account of the spin-orbit interaction, we obtain the orbital moment on each Cr
site induced in proportion to the local spin moment, which is quite small, at
most a tenth of those in nickel or iron. In spite of the tiny 3d orbital
moment, the orbital polarization is found to have large fluctuations as a
function of energy. We obtain the scattering intensity at the Cr K-edge on the
SDW magnetic Bragg spot, which shows resonant enhancement in good agreement
with the experiment. The 3d orbital polarization is found to be highly
correlated with the intensity of the resonant main peak, indicating that the 4p
orbital polarization is mainly induced by the 3d orbital polarization through
the p-d hybridization.",0406576v1
2004-09-15,Effect of Nano Scale Fe Doping on Superconducting Properties of MgB2,"Iron is an important sheath material for fabrication of MgB2 wires. However,
the effect of Fe doping on the superconducting properties of MgB2 remains
controversial. In this work, we present results of nano-scale Fe particle
doping in to MgB2. The Fe doping experiments were performed using both bulk and
thin film form. It was found that Fe doping did not affect the lattice
parameters of MgB2, as evidenced by the lack of change in the XRD peak
positions for MgB2. Because of the high reactivity of nano-scale Fe particles,
Fe doping is largely in the form of FeB at low doping level while Fe2B was
detected at 10wt% doping by both XRD and TEM. There is no evidence for Fe
substitution for Mg. The transition temperature decreased modestly with
increasing Fe doping levels. The Jc(H) performance was severely depressed at
above 3wt% doping level. The detrimental effect of nano-scale Fe doping on both
Tc and Jc(H) is attributable to the grain decoupling as a result of magnetic
scattering of Fe-containing dopants at grain boundaries.",0409408v1
2004-10-17,Low-temperature anomaly in heat capacity due to overlapping the spectrums in molecular crystals,"Investigations of dynamic and thermodynamic properties for a molecular
crystal tris-hexafluoroacetylacetonate-iron $Fe(O_2C_5HF_6)_3$ are presented.
Heat capacity $C_p(T)$ has been measured by adiabatic calorimetry method in the
temperature range $4.8-321 K$. An anomaly with a maximum at $T_c = 44.6 K$ has
been discovered. Intermolecular vibrations spectrum was calculated by lattice
dynamics method in quasiharmonic approximation. Intramolecular frequencies are
found by solving the Schr\""odinger equation in approach of small harmonic
oscillations. In the frequency interval $\approx 30-70 cm^{-1}$ overlapping the
spectrums intra- and intermolecular oscillations has been found. The good
agreement for calculated and experimental $C_p(T)$ occurred to be possible for
two sets of the force constants. These sets describe two phases above and below
$T_c$. The difference between phases is connected with freezing of rotation
$CF_3$ groups. It has been concluded that the interaction between different
modes leads to phase transition and anomaly in heat capacity.",0410428v1
2004-11-27,Point defect dynamics in bcc metals,"We present an analysis of the time evolution of self-interstitial atom and
vacancy (point defect) populations in pure bcc metals under constant
irradiation flux conditions. Mean-field rate equations are developed in
parallel to a kinetic Monte Carlo (kMC) model. When only considering the
elementary processes of defect production, defect migration, recombination and
absorption at sinks, the kMC model and rate equations are shown to be
equivalent and the time evolution of the point defect populations is analyzed
using simple scaling arguments. We show that the typically large mismatch of
the rates of interstitial and vacancy migration in bcc metals can lead to a
vacancy population that grows as the square root of time. The vacancy cluster
size distribution under both irreversible and reversible attachment can be
described by a simple exponential function. We also consider the effect of
highly mobile interstitial clusters and apply the model with parameters
appropriate for vanadium and $\alpha-$iron.",0411680v1
2004-12-23,Modeling truncated hemoglobin vibrational dynamics,"We present a study on the near equilibrium dynamics of two small proteins in
the family of truncated hemoglobins, developed under the framework of a
Gaussian network approach. Effective beta carbon atoms are taken into account
besides C-alphas for all residues but glycines in the coarse-graining
procedure, without leading to an increase in the degrees of freedom
(betaGaussian Model). Normalized covariance matrix and deformation along
slowest modes with collective character are analyzed, pointing out
anti-correlations between functionally relevant sites for the proteins under
study. In particular we underline the functional motions of an extended
tunnel-cavity system running inside the protein matrix, which provide a pathway
for small ligands binding with the iron in the heme group. We give a rough
estimate of the order of magnitude of the relaxation times of the slowest two
overdamped modes and compare results with previous studies on globins.",0412661v2
2005-02-23,Charge order in Fe2OBO3: An LSDA+U study,"Charge ordering in the low-temperature monoclinic structure of iron oxoborate
(Fe2OBO3) is investigated using the local spin density approximation (LSDA)+U
method. While the difference between t_{2g} minority occupancies of Fe^{2+} and
Fe^{3+} cations is large and gives direct evidence for charge ordering, the
static ""screening"" is so effective that the total 3d charge separation is
rather small. The occupied Fe^{2+} and Fe^{3+} cations are ordered alternately
within the chain which is infinite along the a-direction. The charge order
obtained by LSDA+U is consistent with observed enlargement of the \beta angle.
An analysis of the exchange interaction parameters demonstrates the
predominance of the interribbon exchange interactions which determine the whole
L-type ferrimagnetic spin structure.",0502555v1
2005-03-07,Thermal enhancement of the antiferromagnetic exchange coupling between Fe epilayers separated by a crystalline ZnSe spacer,"We have put into evidence the existence of an antiferromagnetic coupling
between iron epilayers separated by a ZnSe crystalline semiconductor. The
effect has been observed for ZnSe spacers thinner than 4 nm at
room-temperature. The coupling constant increases linearly with temperature
with a constant slope of ~5.5x 10-9 J/m2K. The mechanisms that may explain such
exchange interaction are discussed in the manuscript. It results that
thermally-induced effective exchange coupling mediated by spin-dependent on and
off resonant tunnelling of electrons via localized mid-gap defect states in the
ZnSe spacer layer appears to be the most plausible mechanism to induce the
antiferromagnetic coupling.",0503148v1
2005-03-14,Gutzwiller-Correlated Wave Functions: Application to Ferromagnetic Nickel,"Ferromagnetic Nickel is the most celebrated iron group metal with pronounced
discrepancies between the experimental electronic properties and predictions of
density functional theories. In this work, we show in detail that the recently
developed multi-band Gutzwiller theory provides a very good description of the
quasi-particle band structure of nickel. We obtain the correct exchange
splittings and we reproduce the experimental Fermi-surface topology. The
correct (111)-direction of the magnetic easy axis and the right order of
magnitude of the magnetic anisotropy are found. Our theory also reproduces the
experimentally observed change of the Fermi-surface topology when the magnetic
moment is oriented along the (001)-axis. In addition to the numerical study, we
give an analytical derivation for a much larger class of variational
wave-functions than in previous investigations. In particular, we cover cases
of superconductivity in multi-band lattice systems.",0503332v1
2005-03-15,Direct evidence of the orbital contribution to the magnetic moment in AA'FeReO6 double perovskites,"Spin and orbital magnetic moments of Re in AA'FeReO6 double perovskites (A,A'
= Ba, Sr, Ca) have been directly probed employing XMCD spectroscopy at the Re
L2,3-edges. A considerable orbital magnetic moment is observed in all the
studied compounds despite octahedral coordination. Relative orbital to spin
contribution per Re atom rises with lattice distortion from mL/mS = -0.28 to
-0.34 for AA'=Ba2FeReO6 and Ca2FeReO6, respectively. A preliminary XMCD
measurements at the Fe L2,3-edges reveals also a significant orbital moment of
iron in Ca2FeReO6. The relation of the results to the magnetic properties of
the compounds is discussed.",0503358v1
2005-04-13,Growth Mechanisms and Oxidation-Resistance of Gold-Coated Iron Nanoparticles,"We report the chemical synthesis of Fe-core/Au-shell nanoparticles by a
reverse micelle method, and the investigation of their growth mechanisms and
oxidation-resistant characteristics. The core-shell structure and the presence
of the Fe & Au phases have been confirmed by transmission electron microscopy,
energy dispersive spectroscopy, X-ray diffraction, Mossbauer spectroscopy, and
inductively coupled plasma techniques. Additionally, atomic-resolution
Z-contrast imaging and electron energy loss spectroscopy (EELS) in a scanning
transmission electron microscope (STEM) have been used to study details of the
growth processes. The Au-shell grows by nucleating on the Fe-core surface
before coalescing. The magnetic moments of such nanoparticles, in the loose
powder form, decrease over time due to oxidation. The less than ideal
oxidation-resistance of the Au shell may have been caused by the rough Au
surfaces. However, in the pressed pellet form, electrical transport
measurements show that the particles are fairly stable, as the resistance of
the pellet does not change appreciably over time.",0504314v1
2005-04-26,Theoretical estimates for proton-NMR spin-lattice relaxation rates of heterometallic spin rings,"Heterometallic molecular chromium wheels are fascinating new magnetic
materials. We reexamine the available experimental susceptibility data on MCr7
wheels in terms of a simple isotropic Heisenberg Hamiltonian for M=Fe, Ni, Cu,
and Zn and find in that FeCr7 needs to be described with an iron-chromium
exchange that is different from all other cases. In a second step we model the
behavior of the proton spin lattice relaxation rate as a function of applied
magnetic field for low temperatures as it is measured in Nuclear Magnetic
Resonance (NMR) experiments. It appears that CuCr7 and NiCr7 show an
unexpectedly reduced relaxation rate at certain level crossings.",0504658v2
2005-07-06,Partially ferromagnetic electromagnet for trapping and cooling neutral atoms to quantum degeneracy,"We have developed a compact partially ferromagnetic electromagnet to produce
a Ioffe-Pritchard trap for neutral atoms. Our structure permits strong magnetic
confinement with low power consumption. Compared to the previous iron-core
electromagnet, it allows for easy compensation of remnant fields and very high
stability, along with cost-effective realization and compactness. We describe
and characterize our apparatus and demonstrate trapping and cooling of Rb 87
atoms to quantum degeneracy. Pure Bose-Einstein condensates containing 10^6
atoms are routinely realized on a half-minute cycle. In addition we test the
stability of the magnetic trap by producing atom lasers.",0507129v2
2005-08-19,Spin-waves in antiferromagnetic single crystal LiFePO$_4$,"Spin-wave dispersions in the antiferromagnetic state of single crystal
LiFePO$_4$ were determined by inelastic neutron scattering measurements. The
dispersion curves measured from the (010) reflection along both {\it a}$^\ast$
and {\it b}$^\ast$ reciprocal-space directions reflect the anisotropic coupling
of the layered Fe$^{2+}$ (S = 2) spin-system. The spin-wave dispersion curves
were theoretically modeled using linear spin-wave theory by including in the
spin-Hamiltonian in-plane nearest- and next-nearest-neighbor interactions ({\it
J}$_1$ and {\it J}$_2$), inter-plane nearest-neighbor interactions ({\it
J}$_\bot$) and a single-ion anisotropy ({\it D}). A weak (010) magnetic peak
was observed in elastic neutron scattering studies of the same crystal
indicating that the ground state of the staggered iron moments is not along
(010) direction, as previously reported from polycrystalline samples studies,
but slightly rotated away from this axis.",0508480v1
2005-08-27,Raman spectroscopy and field emission measurements on catalytically grown carbon nanotubes,"We used microcontact printing to pattern a silicon surface with an
iron-containing catalytic solution. Multi-wall carbon nanotubes were
subsequently grown on the patterned areas by chemical vapor deposition at
temperatures between 650 and 1000C. We demonstrate that the diameter of the
catalytically grown multi-wall nanotubes increases with the deposition
temperature. Raman spectroscopy has been used to investigate the crystalline
character of the obtained structures and it is found that the fraction of the
nano-crystalline shell increases with the temperatures. The measurement of the
field emission properties shows a correlation between the tube diameter and the
emission field values.",0508657v2
2005-09-14,Magnetic ordering in trigonal chain compounds,"We present electronic structure calculations for the one-dimensional magnetic
chain compounds Ca_3CoRhO_6 and Ca_3FeRhO_6. The calculations are based on
density functional theory and the local density approximation. We use the
augmented spherical wave (ASW) method. The observed alternation of low- and
high-spin states along the Co-Rh and Fe-Rh chains is related to differences in
the oxygen coordination of the transition metal sites. Due to strong
hybridization the O 2p states are polarized, giving rise to extended localized
magnetic moments centered at the high-spin sites. Strong metal-metal overlap
along the chains leads to a substantial contribution of the low-spin Rh
4d_{3z^2-r^2} orbitals to the exchange coupling of the extended moments.
Interestingly, this mechanism holds for both compounds, even though the
coupling is ferromagnetic for the cobalt and antiferromagnetic for the iron
compound. However, our results allow to understand the different types of
coupling from the filling dependence of the electronic properties.",0509374v1
2005-10-27,High spin polarization in the ferromagnetic filled skutterudites KFe4Sb12 and NaFe4Sb12,"The spin polarization of ferromagnetic alkali-metal iron antimonides KFe4Sb12
and NaFe4Sb12 is studied by point-contact Andreev reflection using
superconducting Nb and Pb tips. From these measurements an intrinsic transport
spin polarization Pt of 67% and 60% for the K and Na compound, respectively, is
inferred which establishes these materials as a new class of highly spin
polarized ferromagnets. The results are in accord with band structure
calculations within the local spin density approximation (LSDA) that predict
nearly 100% spin polarization in the density of states. We discuss the impact
of calculated Fermi velocities and spin fluctuations on Pt.",0510736v1
2005-11-21,"Electronic structure study by means of X-ray spectroscopy and theoretical calculations of the ""ferric star"" single molecule magnet","The electronic structure of the single molecule magnet system
M[Fe(L)2]3*4CHCl3 (M=Fe,Cr; L=CH3N(CH2CH2O)2) has been studied using X-ray
photoelectron spectroscopy, X-ray absorption spectroscopy, soft X-ray emission
spectroscopy, and density functional calculations. There is good agreement
between theoretical calculations and experimental data. The valence band mainly
consists of three bands between 2 eV and 30 eV. Both theory and experiments
show that the top of the valence band is dominated by the hybridization between
Fe 3d and O 2p bands. From the shape of the Fe 2p spectra it is argued that Fe
in the molecule is most likely in the 2+ charge state. Its neighboring atoms
(O,N) exhibit a magnetic polarisation yielding effective spin S=5/2 per iron
atom, giving a high spin state molecule with a total S=5 effective spin for the
case of M = Fe.",0511522v2
2006-02-08,Investigation of the presence of charge order in magnetite by measurement of the spin wave spectrum,"Inelastic neutron scattering results on magnetite (Fe3O4) show a large
splitting in the acoustic spin wave branch, producing a 7 meV gap midway to the
Brillouin zone boundary at q = (0,0,1/2) and E = 43 meV. The splitting occurs
below the Verwey transition temperature, where a metal-insulator transition
occurs simultaneously with a structural transformation, supposedly caused by
the charge ordering on the iron sublattice. The wavevector (0,0,1/2)
corresponds to the superlattice peak in the low symmetry structure. The
dependence of the magnetic superexchange on changes in the crystal structure
and ionic configurations that occur below the Verwey transition affect the spin
wave dispersion. To better understand the origin of the observed splitting, we
have constructed a series of Heisenberg models intended to reproduce the
pairwise variation of the magnetic superexchange arising from both small
crystalline distortions and charge ordering. We find that none of the models
studied predicts the observed splitting, whose origin may arise from
charge-density wave formation or magnetoelastic coupling.",0602214v1
2006-02-15,A spin triplet supercurrent through the half-metallic ferromagnet CrO2,"In general, conventional superconductivity should not occur in a ferromagnet,
though it has been seen in iron under pressure. Moreover, theory predicts that
the current is always carried by pairs of electrons in a spin singlet state, so
conventional superconductivity decays very rapidly when in contact with a
ferromagnet, which normally prohibits the existence of singlet pairs. It has
been predicted that this rapid spatial decay would not occur when spin triplet
superconductivity could be induced in the ferromagnet. Here we report a
Josephson supercurrent through the strong ferromagnet CrO2, from which we infer
that it is a spin triplet supercurrent. Our experimental setup is different
from those envisaged in the earlier predictions, but we conclude that the
underlying physical explanation for our result is a conversion from spin
singlet to spin triplets at the interface. The supercurrent can be switched
with the direction of the magnetization, analogous to spin valve transistors,
and therefore could enable magnetization-controlled Josephson junctions.",0602359v1
2006-02-16,Ferromagnetic resonance in systems with competing uniaxial and cubic anisotropies,"We develop a model for ferromagnetic resonance in systems with competing
uniaxial and cubic anisotropies. This model applies to (i) magnetic materials
with both uniaxial and cubic anisotropies, and (ii) magnetic nanoparticles with
effective core and surface anisotropies; We numerically compute the resonance
frequency as a function of the field and the resonance field as a function of
the direction of the applied field for an arbitrary ratio of cubic-to-uniaxial
anisotropy. We also provide some approximate analytical expressions in the case
of weak cubic anisotropy. We propose a method that uses these expressions for
estimating the uniaxial and cubic anisotropy constants, and for determining the
relative orientation of the cubic anisotropy axes with respect to the crystal
principle axes. This method is applicable to the analysis of experimental data
of resonance type measurements for which we give a worked example of an iron
thin film with mixed anisotropy.",0602369v3
2006-02-18,Scaling Behavior of Portevin-Le Chatelier Effect,"The scaling behavior of the Portevin-Le Chatelier (PLC) effect is studied by
deforming a substitutional alloy, Al-2.5%Mg and an interstitial alloy, low
carbon steel (0.15%C, 0.33%Mn, 0.04%P, 0.05%S, 0.15%Si and rest Iron) at room
temperature for a wide range of strain rates. To reveal the exact scaling
nature, the time series data of true stress vs. time, obtained during the
tensile deformation (corrected for drift due to strain hardening by polynomial
fitting method), are analyzed by two complementary methods: the standard
deviation analysis and the diffusion entropy analysis. From these analyses we
could establish that in the entire span of strain rates, PLC effect showed Levy
walk type of scaling property.",0602436v1
2006-06-27,Fe adatoms along Bi lines on H/Si(001): Patterning atomic magnetic chains,"The stability, electronic and magnetic properties of Fe atoms adsorbed on the
self-assembled Bi-dimer lines nanostructure on the H/Si(001) surface are
addressed by spin-density functional calculations. Our results show that Fe
adatoms are much more stable on sites closer to the Bi nanolines being able to
form one-dimensional atomic arrays. The most stable structure occurs on a
missing dimer line aside the Bi dimers, which corresponds to an array with
distances between Fe adatoms of about 8 Ang. In this array the irons are
coupled antiferromagnetically with spin magnetic moment of about 1.5 Bohr
magnetons per Fe atom, whereas the coupling exchange interactions is found to
be of 14.4 meV. We also estimate a large magnetic anisotropy energy for the Fe
adatom of about 3 meV/atom. In addition, the electronic band structure of the
Fe array at the most stable structure shows a magnetic half-metal behavior.",0606707v2
2006-08-14,Thermal relaxation of magnetic clusters in amorphous Hf_{57}Fe_{43} alloy,"The magnetization processes in binary magnetic/nonmagnetic amorphous alloy
Hf_{57}Fe_{43} are investigated by the detailed measurements of magnetic
hysteresis loops, temperature dependence of magnetization, relaxation of
magnetization and magnetic ac susceptibility, including a nonlinear term.
Blocking of magnetic moments at lower temperatures is accompanied with the slow
relaxation of magnetization and magnetic hysteresis loops. All of the observed
properties are explained with the superparamagnetic behaviour of the single
domain magnetic clusters inside the nonmagnetic host, their blocking by the
anisotropy barriers and thermal fluctuation over the barriers accompanied by
relaxation of magnetization. From magnetic viscosity analysis based on thermal
relaxation over the anisotropy barriers it is found out that magnetic clusters
occupy the characteristic volume from 25 up to 200 nm3 . The validity of the
superparamagnetic model of Hf_{57}Fe_{43} is based on the concentration of iron
in the Hf_{100-x}Fe_{43} system that is just below the threshold for the long
range magnetic ordering. This work throws more light on magnetic behaviour of
other amorphous alloys, too.",0608307v3
2006-09-15,Surfactant effects in monodisperse magnetite nanoparticles of controlled size,"Monodisperse magnetite Fe3O4 nanoparticles of controlled size within 6 and 20
nm in diameter were synthesized by thermal decomposition of an iron organic
precursor in an organic medium. Particles were coated with oleic acid. For all
samples studied, saturation magnetization Ms reaches the expected value for
bulk magnetite, in contrast to results in small particle systems for which Ms
is usually much smaller due to surface spin disorder. The coercive field for
the 6 nm particles is also similar to that of bulk magnetite. Both results
suggest that the oleic acid molecules covalently bonded to the nanoparticle
surface yield a strong reduction in the surface spin disorder. However,
although the saturated state may be similar, the approach to saturation is
different and, in particular, the high-field differential susceptibility is one
order of magnitude larger than in bulk materials. The relevance of these
results in biomedical applications is discussed.",0609384v1
2006-10-18,A new type of temperature driven reorientation transition in magnetic thin films,"We present a new type of temperature driven spin reorientation transition
(SRT) in thin films. It can occur when the lattice and the shape anisotropy
favor different easy directions of the magnetization. Due to different
temperature dependencies of the two contributions the effective anisotropy may
change its sign and thus the direction of the magnetization as a function of
temperature may change. Contrary to the well-known reorientation transition
caused by competing surface and bulk anisotropy contributions the reorientation
that we discuss is also found in film systems with a uniform lattice
anisotropy. The results of our theoretical model study may have experimental
relevance for film systems with positive lattice anisotropy, as e.g. thin iron
films grown on copper.",0610504v1
2006-11-09,New ultrasmall iron-oxide nanoparticles with high magnetisation as potential T1-MRI contrast agents for Molecular Imaging,"Here we report on the synthesis of very small gamma-Fe2O3 nanoparticles (5
nm) presenting very narrow particle size distribution and exceptionally high
saturation magnetisation. The synthesis has been carried out in an organic
medium with subsequent transfer to an aqueous solution at physiological pH. The
structural and magnetic properties were kept unaltered after the solvent
exchange. NMR relaxometric measurements show the potential of these particles
as specific reporters for magnetic resonance molecular imaging.",0611243v1
2006-12-10,Substituting the main group element in cobalt - iron based Heusler alloys: Co$_2$FeAl$_{1-x}$Si$_x$,"This work reports about electronic structure calculations for the Heusler
compound Co$_2$FeAl$_{1-x}$Si$_x$. Particular emphasis was put on the role of
the main group element in this compound. The substitution of Al by Si leads to
an increase of the number of valence electrons with increasing Si content and
may be seen as electron-doping. Self-consistent electronic structure
calculations were performed to investigate the consequences of the electron
doping for the magnetic properties. The series Co$_2$FeAl$_{1-x}$Si$_x$ is
found to exhibit half-metallic ferromagnetism and the magnetic moment follows
the Slater-Pauling rule. It is shown that the electron-doping stabilises the
gap in the minority states for $x=0.5$.",0612241v1
2006-12-23,Magnetic phase diagram of Ce2Fe17,"Rare-earth-based permanent-magnet materials rich in iron have relatively low
ferromagnetic ordering temperatures. This is believed to be due to the presence
of antiferromagnetic exchange interactions, besides the ferromagnetic
interactions responsible for the magnetic order. The magnetic properties of
Ce2Fe17 are anomalous. Instead of ferromagnetic, it is antiferromagnetic, and
instead of one ordering temperature, it shows two, at the Neel temperature TN ~
208 K and at TT ~ 124 K. Ce2Fe17, doped by 0.5% Ta, also shows two ordering
temperatures, one to an antiferromagnetic phase, at TN ~ 214 K, and one to a
ferromagnetic phase, at T0 ~ 75 K. In order to clarify this behavior,
single-crystalline samples were prepared by solution growth, and characterized
by electron microscopy, single crystal x-ray diffraction, temperature-dependent
specific heat, and magnetic field and temperature-dependent electrical
resistivity and magnetization. From these measurements, magnetic H-T phase
diagrams were determined for both Ta-doped Ce2Fe17 and undoped Ce2Fe17. These
phase diagrams can be very well described in terms of a theory that gives
magnetic phase diagrams of systems with competing antiferro- and
ferromagnetism.",0612603v1
2007-01-02,Resonant soft x-ray magnetic scattering from the 4f and 3d electrons in DyFe(4)Al(8),"Soft x-ray resonant scattering has been used to examine the charge and
magnetic interactions in the cycloidal antiferromagnetic compound \dyfeal. By
tuning to the Dy $M_4$ and $M_5$ absorption edges and the Fe L(2) and L(3)
absorption edges we can directly observe the behavior of the Dy 4f and Fe 3d
electron shells. Magnetic satellites surrounding the (110) Bragg peak were
observed below 60 K. The diffraction peaks display a complex spectra at the Dy
M(5) edge, indicative of a split 4f electron band. This is in contrast to a
simple resonance observed at the Fe L(3) absorption edge, which probes the Fe
3d electron shell. Temperature dependant measurements detail the ordering of
the magnetic moments on both the iron and the dysprosium antiferromagnetic
cycloids. The ratio between the intensities of the Dy M(4) and M(5) remained
constant throughout the temperature range, in contrast to a previous study
conducted at the Dy L(2,3) edges. Our results demonstrate the ability of soft
x-ray diffraction to separate the individual magnetic components in complicated
multi-element magnetic structures.",0701034v1
2007-01-26,Use of Superparamagnetic Nanoparticle/Block Copolymer Electrostatic Complexes as Contrast Agents in Magnetic Resonance Imaging,"During the past years we have investigated the complexation between
nanocolloids and oppositely charged polymers. The nanocolloids examined were
ionic surfactant micelles and inorganic oxide nanoparticles. For the polymers,
we used homopolyelectrolytes and block copolymers with linear and comb
architectures. In general, the attractive interactions between oppositely
charged species are strong and as such, the simple mixing of solutions
containing dispersed constituents yield to a precipitation, or to a phase
separation. We have developed means to control the electrostatically-driven
attractions and to preserve the stability of the mixed solution. With these
approaches, we designed novel core-shell nanostructures, e.g. as those obtained
with polymers and iron oxide superparamagnetic nanoparticles. In this
presentation, we show that electrostatic complexation can be used to tailor new
functionalized nanoparticles and we provide examples related to biomedical
applications in the domain of contrast agents for Magnetic Resonance Imaging.",0701663v1
2007-02-23,Spectral and Fermi surface properties from Wannier interpolation,"We present an efficient first-principles approach for calculating Fermi
surface averages and spectral properties of solids, and use it to compute the
low-field Hall coefficient of several cubic metals and the magnetic circular
dichroism of iron. The first step is to perform a conventional first-principles
calculation and store the low-lying Bloch functions evaluated on a uniform grid
of k-points in the Brillouin zone. We then map those states onto a set of
maximally-localized Wannier functions, and evaluate the matrix elements of the
Hamiltonian and the other needed operators between the Wannier orbitals, thus
setting up an ``exact tight-binding model.'' In this compact representation the
k-space quantities are evaluated inexpensively using a generalized
Slater-Koster interpolation. Because of the strong localization of the Wannier
orbitals in real space, the smoothness and accuracy of the k-space
interpolation increases rapidly with the number of grid points originally used
to construct the Wannier functions. This allows k-space integrals to be
performed with ab-initio accuracy at low cost. In the Wannier representation,
band gradients, effective masses, and other k-derivatives needed for transport
and optical coefficients can be evaluated analytically, producing numerically
stable results even at band crossings and near weak avoided crossings.",0702554v1
2007-03-15,Theoretical introduction to express way of the complex determination of the thermophysical parameters of metals,"A method to measure thermophysical characteristics (TPC) of conductive
materials is described. The method is based upon controlled bulk (e.g., Ohmic)
heating and measurement of the averaged over the volume of a sample temperature
and the temperature of the surface of a sample. To measure averaged over a
sample volume temperature a dilatometric technique could be used and surface
temperature could be measured by x-ray method. This allows one to avoid
distortion of the temperature field by the thermocouples and directly takes
into account heat losses from the surface of a sample. The treatment of the
experimental data should be based upon theoretical calculations presented in
this paper. The measured values of the averaged over the volume of a sample
temperature and a surface temperature allow for the calculation of TPC of the
material. The experimental data obtained on the iron-based materials prove the
high accuracy of the described approach [1-3].",0703392v2
1999-01-15,The Atmospheric Neutrino Flavor Ratio from a 3.9 Fiducial Kiloton-Year Exposure of Soudan 2,"We report a measurement of the atmospheric neutrino flavor ratio, R, using a
sample of quasi-elastic neutrino interactions occurring in an iron medium. The
flavor ratio (tracks/showers) of atmospheric neutrinos in a 3.9 fiducial
kiloton-year exposure of Soudan 2 is 0.64 +- 0.11 (stat.) +- 0.06 (syst.) of
that expected. Important aspects of our main analysis have been checked by
carrying out two independent, alternative analyses; one is based upon automated
scanning, the other uses a multivariate approach for background subtraction.
Similar results are found by all three approaches.",9901024v1
1999-12-14,Longitudinal Hadronic Shower Development in a Combined Calorimeter,"This work is devoted to the experimental study of the longitudinal hadronic
shower development in the ATLAS barrel combined prototype calorimeter
consisting of the lead-liquid argon electromagnetic part and the
iron-scintillator hadronic part. The results have been obtained on the basis of
the 1996 combined test beam data which have been taken on the H8 beam of the
CERN SPS, with the pion beams of 10, 20, 40, 50, 80, 100, 150 and 300 GeV/c.
The degree of description of generally accepted Bock parameterization of the
longitudinal shower development has been investigated. It is shown that this
parameterization does not give satisfactory description for this combined
calorimeter. Some modification of this parameterization, in which the e/h
ratios of the compartments of the combined calorimeter are used, is suggested
and compared with the experimental data. The agreement between such
parameterization and the experimental data is demonstrated.",9912028v1
2000-01-05,"Search for Nucleon Decay with Final States l+ eta, nubar eta, and nubar pi+,0 Using Soudan 2","We have searched for nucleon decay into five two-body final states using a
4.4 kiloton-year fiducial exposure of the Soudan 2 iron tracking calorimeter.
For proton decay into the fully visible final states mu+ eta and e+ eta, we
observe zero and one event, respectively, that satisfy our search criteria for
nucleon decay. The lifetime lower limits (tau/B) thus implied are 89 x 10^30
years and 81 x 10^30 years at 90% confidence level. For neutron decay into
nubar eta, we obtain the lifetime lower limit 71 x 10^30 years. Limits are also
reported for neutron decay into nubar pi0, and for proton decay into nubar pi+.",0001015v1
2000-01-13,Neutrino Oscillation Appearance Experiment using Nuclear Emulsion and Magnetized Iron,"This report describes an apparatus that could be used to measure both the
identity and charge of an outgoing lepton in a charged current neutrino
interaction. This capability in a massive detector would allow the most
comprehensive set of neutrino oscillation physics measurements. By measuring
the six observable transitions between initial and final state neutrinos, one
would be able to measure all elements of the neutrino mixing matrix, as well as
search for CP violation, and matter effects. If the measured matrix is not
unitary, then one would also have an unambiguous determination of sterile
neutrinos. Emulsion is considered as the tracking medium, and different
techniques are discussed for the application of a magnetic field.",0001035v1
2000-04-06,Hadron Energy Reconstruction for the ATLAS Barrel Prototype Combined Calorimeter in the Framework of the Non-parametrical Method,"Hadron energy reconstruction for the Atlas barrel prototype combined
calorimeter, consisting of the lead-liquid argon electromagnetic part and the
iron-scintillator hadronic part, in the framework of the non-parametrical
method has been fulfilled. This method uses only the known e/h ratios and the
electron calibration constants and does not require the determination of any
parameters by a minimization technique and can be used for the fast energy
reconstruction in the first level trigger. The obtained reconstruction of the
mean values of energies is within $\pm 1%$ and the fractional energy resolution
is $[(58\pm3)% \sqrt{GeV}/\sqrt{E}+(2.5\pm0.3)%]\oplus (1.7\pm0.2) GeV/E$. The
obtained value of the e/h ratio for electromagnetic compartment of the combined
calorimeter is $1.74\pm0.04$ and agrees with the prediction that $e/h > 1.7$
for this electromagnetic calorimeter. The results of the study of the
longitudinal hadronic shower development are presented. The data have been
taken in the H8 beam line of the CERN SPS using pions of 10 -- 300 GeV.",0004009v1
2001-04-02,Hadron Energy Reconstruction for the ATLAS Calorimetry in the Framework of the Non-parametrical Method,"This paper discusses hadron energy reconstruction for the ATLAS barrel
prototype combined calorimeter (consisting of a lead-liquid argon
electromagnetic part and an iron-scintillator hadronic part) in the framework
of the non-parametrical method. The non-parametrical method utilizes only the
known $e/h$ ratios and the electron calibration constants and does not require
the determination of any parameters by a minimization technique. Thus, this
technique lends itself to an easy use in a first level trigger. The
reconstructed mean values of the hadron energies are within $\pm 1%$ of the
true values and the fractional energy resolution is $[(58\pm3)%
/\sqrt{E}+(2.5\pm0.3)%]\oplus (1.7\pm0.2)/E$. The value of the $e/h$ ratio
obtained for the electromagnetic compartment of the combined calorimeter is
$1.74\pm0.04$ and agrees with the prediction that $e/h > 1.7$ for this
electromagnetic calorimeter. Results of a study of the longitudinal hadronic
shower development are also presented. The data have been taken in the H8 beam
line of the CERN SPS using pions of energies from 10 to 300 GeV.",0104002v2
2001-04-11,New calibrations and time stability of the response of the INTERCAST CR-39,"We present new calibrations of different production batches (from 1989 to
1999) of the INTERCAST CR-39, using the BNL-AGS 1 A GeV iron beam. The
comparison with previous results, obtained with the 158 A GeV lead beam from
the CERN-SPS shows that, while each production batch has a different
calibration curve (mainly due to minor differences in the production
conditions), the aging effect is negligible. We also tested the dependence of
the CR-39 response from the time elapsed between exposure and analysis (fading
effect). The fading effect, if present, is less than 10%. It may be compatible
with the experimental uncertainties on the bulk etching rate vB.",0104022v1
2001-05-22,Extraction of R=sigma_L/sigma_T from CCFR Neutrino and Antinetrino Differential Cross Sections,"We report on the extraction of R=sigam_L/sigma_T from CCFR neutrino and
antineutrino-Iron differential cross sections. R as measured in neutrno
scattering is in agreement with $R$ as measured in muon and electron
scattering. All data on R for Q2 > 1 GeV2 are in agreement with a NNLO QCD
calculation which uses NNLO PDFs and includes target mass effects. We report on
the first measurements of R in the low x and Q2 < 1 GeV2 region (where an
anomalous large rise in R for nuclear targets has been observed by the HERMES
collaboration).",0105067v1
2002-11-07,Design and test results of the AMS RICH detector,"The AMS-02 detector will operate for at least 3 years on the International
Space Station, measuring cosmic ray spectra at about 400 km above sea level
over a wide range of geomagnetic latitude.
  The proximity focusing ring imaging \v{C}erenkov counter of AMS-02 will
measure the particle velocity $\beta$ with $\approx 0.1%$ uncertainty, making
possible to discriminate Beryllium isotopes up to about 15 GeV/nucl. In
addition its charge measurement will allow to study the elemental composition
of cosmic rays up to Iron. A prototype of the RICH detector was tested with
cosmic rays and on a ion beam accelerated by SPS, at CERN (October 2002).",0211018v1
2006-07-31,Machine-Related Backgrounds in the SiD Detector at ILC,"With a multi-stage collimation system and magnetic iron spoilers in the
tunnel, the background particle fluxes on the ILC detector can be substantially
reduced. At the same time, beam-halo interactions with collimators and
protective masks in the beam delivery system create fluxes of muons and other
secondary particles which can still exceed the tolerable levels for some of the
ILC sub-detectors. Results of modeling of such backgrounds in comparison to
those from the e+ e- interactions are presented in this paper for the SiD
detector.",0608001v1
1992-11-19,Recent Work on Standard Solar Models,"Recent results on standard solar models are reviewed. I shall summarize
briefly three of the themes that I stressed at the Neutrino '92 Conference: 1)
Different solar model codes give the same answers when the same input data are
used; 2) Improved calculations of standard solar models include helium
diffusion, the Livermore radiative opacity, the meteoritic iron abundance, and
a variety of other corrections; and 3) There are a few basic rules that should
be followed in using standard solar models. At the Neutrino '92 Conference, I
reviewed in more detail the recent work on standard solar models by Marc
Pinsonneault and myself. This work has by now appeared in print (Rev. Mod.
Phys. 64, 885, 1992, hereafter Paper I, and ApJ Letters, 69, 717, 1992, Paper
II). Therefore, there is no need for me to repeat the details here.",9211280v1
1997-09-09,Neutrino-photon reactions in astrophysics and cosmology,"At energies above the threshold for $W$ production the process $\nu \gamma
\to l W^+$ is competive with $\nu \nu$ scattering at the same center of mass
energies. In a cosmological setting, absorption of ultra high energy neutrinos
by the microwave photon background is comparable to absorption by the neutrino
background. In passing through matter, the process $\nu \to l W^+$ will occur
in the coulomb field of nuclei. For iron, the interaction rate per nucleon is
roughly 20% of the charge current cross-section. The related process,
$\anti\nu_e e^- \to \gamma W^-$ dominates $\anti\nu_e e^-$ scattering for about
a decade in energy above the resonance for $W$ production.",9709290v1
1997-12-07,Off-shell Corrections and Moments of the Deep Inelastic Nuclear Structure Functions,"We present an improved method for handling off-shell effects in deep
inelastic nuclear scattering. With a firm understanding of the effects of the
nuclear wave function, including these off-shell corrections as well as binding
and nucleon-nucleon correlations, we can begin to examine the role of QCD in
nuclei through an analysis of the moments of the nuclear structure function.
Our analysis is aimed at extracting the Q^2 dependence of the moments of the
nucleon structure function by using the recent high x world Iron data and by
properly removing nuclear effects from the perturbative contribution. In
addition, we compare quantitatively the behavior of the extracted moments with
a simple O(1/Q^2) phenomenological form and we determine the mass term for this
parametrization.",9712286v1
1998-05-07,Measurement of Atmospheric Neutrino Oscillations with a High-Density Detector,"We propose an experiment to test the hypothesis that the reported anomaly on
atmospheric neutrino fluxes is due to nu_mu <-> nu_x oscillations. It will rely
both on a disappearance technique, exploiting the method of the dependence of
the event rate on L/E, which was recently shown to be effective for detection
of neutrino oscillation and measurement of the oscillation parameters, and on
an appearance technique, looking for an excess of muon-less events at high
energy produced by upward-going tau neutrinos. The detector will consist of
iron planes interleaved by limited streamer tubes. The total mass will be about
30 kt. The possibility of recuperating most of the instrumentation from
existing detectors allows to avoid R&D phases and to reduce construction time.
In four years of data taking, this experiment will be sensitive to oscillations
nu_mu <-> nu_x with Delta m^2 > 10^-4 eV^2 and a mixing near to maximal, and
answer the question whether nu_x is a sterile or a tau neutrino.",9805249v2
2000-12-13,CP-violation in 3- and 4-family at the Neutrino Factory,"The leptonic CP-violating phase $\delta$ can be measured with a Neutrino
Factory with $2 \times 10^{20} $ useful muons per year, if the solar neutrino
problem is solved by the LMA-MSW solution, with $\Delta m_{12}^2 \ge 2 \times
10^{-5}$ eV$^2$ (in this analysis a 40 kT magnetized iron detector is
considered, taking into account its efficiencies and backgrounds). If LSND is
confirmed, CP-violating phenomena in four-family scenarios can be most easily
addressed with a small 1 kT detector at $L = \cal O$(10) km (no detailed
analysis of the detector efficiencies and backgrounds has been performed in
this case).",0012153v1
2000-12-27,Propagation of Muons and Taus at High Energies,"The photonuclear contribution to charged lepton energy loss has been
re-evaluated taking into account HERA results on real and virtual photon
interactions with nucleons. With large $Q^2$ processes incorporated, the
average muon range in rock for muon energies of $10^9$ GeV is reduced by only
5% as compared with the standard treatment. We have calculated the tau energy
loss for energies up to $10^9$ GeV taking into consideration the decay of the
tau. A Monte Carlo evaluation of tau survival probability and range show that
at energies below $10^7-10^8$ GeV, depending on the material, only tau decays
are important. At higher energies the tau energy losses are significant,
reducing the survival probability of the tau. We show that the average range
for tau is shorter than its decay length and reduce to 17 km in water for an
incident tau energy of $10^9$ GeV, as compared with its decay length of 49 km
at that energy. In iron, the average tau range is 4.7 km for the same incident
energy.",0012350v1
2001-07-27,Extragalactic Sources for Ultra High Energy Cosmic Ray Nuclei,"In this article we examine the hypothesis that the highest energy cosmic rays
are complex nuclei from extragalactic sources. Under reasonable physical
assumptions, we show that the nearby metally rich starburst galaxies (M82 and
NGC 253) can produce all the events observed above the ankle. This requires
diffusion of particles below $10^{20}$ eV in extragalactic magnetic fields $B
\approx 15$ nG. Above $10^{19}$ eV, the model predicts the presence of
significant fluxes of medium mass and heavy nuclei with small rate of change of
composition. Notwithstanding, the most salient feature of the
starburst-hypothesis is a slight anisotropy induced by iron debris just before
the spectrum-cutoff.",0107287v4
2002-06-04,The silver channel at the Neutrino Factory,"We notice that looking for $\nu_e \to \nu_\tau$ at the same time as $\nu_e
\to \nu_\mu$ oscillations could significantly help to reduce the errors in the
leptonic CP-violating phase $\delta$ measurement. We show how the $\nu_e \to
\nu_\mu$ (``golden'') and $\nu_e \to \nu_\tau$ (``silver'') transitions
observed at an OPERA-like 2 Kton lead-emulsion detector at L = 732 Km, in
combination with the $\nu_e \to \nu_\mu$ transitions observed at a 40 Kton
magnetized iron detector with a baseline of L = 3000 Km, strongly reduce the
so-called $(\theta_{13}, \delta)$ ambiguity. We also show how a moderate
increase in the OPERA-like detector mass (4 Kton instead of 2 Kton) completely
eliminates the clone regions even for small values of $\theta_{13}$.",0206034v1
2002-07-12,Possible Studies of Parton Distribution Functions at JHF,"We discuss possible studies of parton distribution functions (PDFs) in the
nucleon and nuclei at the Japan Hadron Facility (JHF). First, the PDFs could be
investigated by the 50 GeV primary proton facility. The distributions at medium
x are determined, for example, by Drell-Yan measurements. Second, there are
feasibility studies to propose a neutrino factory within the 50 GeV proton
ring. If such an intensive high-energy neutrino facility is built, neutrino
reactions should be able to provide valuable information on the PDFs, whereas
the current structure functions have been measured mainly for neutrino-iron
reactions.",0207151v1
2002-09-18,Modified Paschos-Wolfenstein relation and extraction of weak mixing angle sin^2 theta_W,"The NuTeV collaboration reported anomalously large weak mixing angle sin^2
theta_W in comparison with the standard model prediction. Neutrino and
antineutrino charged- and neutral-current events are analyzed for extracting
sin^2 theta_W. Although the Paschos-Wolfenstein relation is not directly used
in the analysis, it plays an important role in the determination. Noting that
the target nucleus, iron, is not an isoscalar nucleus, we derive a
leading-order expression for a modified Paschos-Wolfenstein relation for
nuclei, which may have neutron excess. Then, using charge and baryon-number
conservations for nuclei, we discuss a nuclear correction in the sin^2 theta_W
determination. It is noteworthy that nuclear modifications are different
between valence up- and down-quark distributions. We show this difference
effect on the NuTeV sin^2 theta_W deviation.",0209200v2
2003-01-18,Charge Symmetry Violating Contributions to Neutrino Reactions,"The NuTeV group has measured charged and neutral current reactions for
neutrinos on iron targets. Ratios of these cross sections provide an
independent measurement of the Weinberg angle. The NuTeV value for sin^2
theta_W is three standard deviations larger than the value measured in other
electroweak processes. By reviewing theoretical estimates of parton charge
symmetry violation (CSV), we study CSV contributions to the NuTeV measurement.
We conclude that charge symmetry violating effects should remove roughly 30% of
the discrepancy between the NuTeV result and other determinations of sin^2
theta_W.",0301147v3
2003-05-16,The synergy of the golden and silver channels at the Neutrino Factory,"We deepen the study of the so-called ``silver channel'' $\nu_e \to \nu_\tau$
\cite{Donini:2002rm} and of its relevance to solve some of the ambiguities that
can arise in the simultaneous measurement of $(\theta_{13},\delta)$ at the
Neutrino Factory by presenting in full detail the characteristics of the
considered OPERA-like detector and the experimental treatment of the different
backgrounds and signals. Furthermore, we perform a detailed study of the
systematic errors associated both with the OPERA-like and the magnetized-iron
detectors and their effects on the sensitivity. Finally, we also apply a
refined statistical analysis of the simulated events based on the frequentist
approach.",0305185v1
2003-06-06,"Supernova Neutrinos, Neutrino Oscillations, and the Mass of the Progenitor Star","We investigate the initial progenitor mass dependence of the early-phase
neutrino signal from supernovae taking neutrino oscillations into account. The
early-phase analysis has advantages in that it is not affected by the time
evolution of the density structure of the star due to shock propagation or
whether the remnant is a neutron star or a black hole. The initial mass affects
the evolution of the massive star and its presupernova structure, which is
important for two reasons when considering the neutrino signal. First, the
density profile of the mantle affects the dynamics of neutrino oscillation in
supernova. Second, the final iron core structure determines the features of the
neutrino burst, i.e., the luminosity and the average energy. We find that both
effects are rather small. This is desirable when we try to extract information
on neutrino parameters from future supernova-neutrino observations. Although
the uncertainty due to the progenitor mass is not small for intermediate
$\theta_{13}$ ($10^{-5} \lesssim \sin^{2}{2 \theta_{13}} \lesssim 10^{-3}$), we
can, nevertheless, determine the character of the mass hierarchy and whether
$\theta_{13}$ is very large or very small.",0306056v1
2003-07-08,Nuclear modification of structure functions in lepton scattering,"We discuss nuclear structure functions in lepton scattering including
neutrino reactions. First, the determination of nuclear parton distribution
functions is explained by using the data of electron and muon deep inelastic
scattering and those of Drell-Yan processes. Second, NuTeV sin^2 theta_W
anomaly is discussed by focusing on nuclear corrections in the iron target.
Third, we show that the HERMES effect, which indicates nuclear modification of
the longitudinal-transverse structure function ratio, should exist at large x
with small Q^2 in spite of recent experimental denials at small x.",0307105v1
2004-10-19,Detecting matter effects in long baseline experiments,"Experiments strongly suggest that the flavour mixing responsible for the
atmospheric neutrino anomaly is very close to being maximal. Thus, it is of
great theoretical as well as experimental importance to measure any possible
deviation from maximality. In this context, we reexamine the effects of matter
interactions in long baseline neutrino oscillation experiments. Contrary to
popular belief, the muon neutrino survival probability is shown to be quite
sensitive to matter effects. Moreover, for moderately long baselines, the
difference between the survival probilities for $\nu_\mu$ and $\bar\nu_\mu$ is
shown to be large and sensitive to the deviation of $|U_{\mu 3}|$ from
maximality. Performing a realistic analysis, we demonstrate that a muon-storage
ring $\nu$-source alongwith an iron calorimeter detector can measure such
deviations. (Contrary to recent claims, this is not so for the NuMI--{\sc
minos} experiment.) We also discuss the possible correlation in measuring
$U_{\mu 3}$ and $U_{e3}$ in such experiment.",0410266v1
2004-12-20,Nuclear modification difference between u_v and d_v distributions and its relation to NuTeV sin^2 theta_W anomaly,"We investigate a possible nuclear correction to the NuTeV measurement of the
weak-mixing angle sin^2 theta_W. In particular, a nuclear modification
difference between u_v and d_v distributions contributes to the NuTeV
measurement with the iron target. First, the modification differenceis
determined by a chi^2 analysis so as to reproduce nuclear data on the structure
function F_2 and Drell-Yan processes. Then, taking the NuTeV kinematics into
account, we calculate a contribution to the sin^2 theta_W determination. In
addition, its uncertainty is estimated by the Hessian method. Although the
uncertainty becomes comparable to the NuTeV deviation, the effect is not large
enough to explain the whole NuTeV sin^2 theta_W anomaly at this stage. However,
it is difficult to determine such a nuclear modification difference, so that we
need further investigations on the difference and its effect on the NuTeV
anomaly.",0412284v2
2005-11-10,Perspectives for a neutrino program based on the upgrades of the CERN accelerator complex,"In this paper, we discuss the possibilities offered to neutrino physics by
the upgrades of the CERN accelerator complex. Emphasis is on the physics reach
of a medium $\gamma$ (350-580) $\beta$-beam that fully exploits the
improvements in the CERN accelerator complex for the luminosity/energy upgrade
of the LHC. We show that, this design not only profits of the ongoing efforts
for the upgrades of the LHC, but also leverage out the existing infrastructures
of the LNGS underground laboratory. Furthermore, given the involved high
neutrino energies, above 1 GeV, a non-magnetized iron detector could
efficiently exploit the neutrino beam.
  We show that the performance of this complex for what concerns the discovery
of the CP violation in the leptonic sector, in case $\theta_{13}$ is discovered
by Phase I experiments, is comparable with the current baseline design based on
a gigantic water Cherenkov at Frejus. Furthermore, this complex has also some
sensitivity to the neutrino mass hierarchy.",0511134v2
2006-09-25,Probing Lepton Number Violating Interactions with Beta-beams,"We show that a detector placed near a beta-beam storage ring can probe lepton
number violating interactions, as predicted by supersymmetric theories with
R-parity non-conservation. In the presence of such interactions, nu_tau can be
produced during beta-decay leading to tau leptons through weak interactions.
Alternatively, electron neutrinos from beta-decay of radioactive ions can
produce tau leptons in a nearby detector through these interactions. The muons
from the decay of these tau leptons can be readily identified in a small iron
calorimeter detector and will signal violation of R-parity.",0609252v2
2006-10-16,The mass hierarchy with atmospheric neutrinos at INO,"We study the neutrino mass hierarchy at the magnetized Iron CALorimeter
(ICAL) detector at India-based Neutrino Observatory with atmospheric neutrino
events generated by the Monte Carlo event generator Nuance. We judicially
choose the observables so that the possible systematic uncertainties can be
reduced. The resolution as a function of both energy and zenith angle
simultaneously is obtained for neutrinos and anti-neutrinos separately from
thousand years un-oscillated atmospheric neutrino events at ICAL to migrate
number of events from neutrino energy and zenith angle bins to muon energy and
zenith angle bins. The resonance ranges in terms of directly measurable
quantities like muon energy and zenith angle are found using this resolution
function at different input values of $\theta_{13}$. Then, the marginalized
$\chi^2$s are studied for different input values of $\theta_{13}$ with its
resonance ranges taking input data in muon energy and zenith angle bins.
Finally, we find that the mass hierarchy can be explored up to a lower value of
$\theta_{13}\approx 5^\circ$ with confidence level $>$ 95% in this set up.",0610196v3
2006-10-25,Neutrino mass hierarchy and $θ_{13}$ with a magic baseline beta-beam experiment,"We underscore the physics advantage of an experiment where neutrinos produced
in a beta-beam facility at CERN are observed in a large magnetized iron
calorimeter (ICAL) at the India-based Neutrino Observatory (INO). The CERN-INO
distance is close to the so-called ""magic"" baseline which helps evade some of
the parameter degeneracies and allows for a better measurement of the neutrino
mass hierarchy and $\theta_{13}$. We expound the possibility of using
radioactive $^8B$ and $^{8}Li$ as the source isotopes for the $\nue$ and
$\anue$ beta-beam, respectively, and show that very good sensitivity to both
the mass hierarchy and $\theta_{13}$ is possible with a boost $\gamma$ in the
250-500 ballpark.",0610333v2
2007-02-18,A GEANT-based study of atmospheric neutrino oscillation parameters at INO,"We have studied the dependence of the allowed space of the atmospheric
neutrino oscillation parameters on the time of exposure for a magnetized Iron
CALorimeter (ICAL) detector at the India-based Neutrino Observatory (INO). We
have performed a Monte Carlo simulation for a 50 kTon ICAL detector generating
events by the neutrino generator NUANCE and simulating the detector response by
GEANT. A chi-square analysis for the ratio of the up-going and down-going
neutrinos as a function of $L/E$ is performed and the allowed regions at 90%
and 99% CL are displayed. These results are found to be better than the current
experimental results of MINOS and Super-K. The possibilities of further
improvement have also been discussed.",0702180v3
2007-03-20,Neutrino hierarchy from CP-blind observables with high density magnetized detectors,"High density magnetized detectors are well suited to exploit the outstanding
purity and intensities of novel neutrino sources like Neutrino Factories and
Beta Beams. They can also provide independent measurements of leptonic mixing
parameters through the observation of atmospheric muon-neutrinos. In this
paper, we discuss the combination of these observables from a multi-kton iron
detector and a high energy Beta Beam; in particular, we demonstrate that even
with moderate detector granularities the neutrino mass hierarchy can be
determined for $\theta_{13}$ values greater than 4$^\circ$.",0703209v3
1996-08-18,M-Theory (the Theory Formerly Known as Strings),"Superunification underwent a major paradigm shift in 1984 when
eleven-dimensional supergravity was knocked off its pedestal by ten-dimensional
superstrings. This last year has witnessed a new shift of equal proportions:
perturbative ten-dimensional superstrings have in their turn been superseded by
a new non-perturbative theory called {\it $M$-theory}, which describes
supermembranes and superfivebranes, which subsumes all five consistent string
theories and whose low energy limit is, ironically, eleven-dimensional
supergravity. In particular, six-dimensional string/string duality follows from
membrane/fivebrane duality by compactifying $M$-theory on $S^1/Z_2 \times K3$
(heterotic/heterotic duality) or $S^1 \times K3$ (Type $IIA$/heterotic duality)
or $S^1/Z_2 \times T^4$ (heterotic/Type $IIA$ duality) or $S^1 \times T^4$
(Type $IIA$/Type $IIA$ duality).",9608117v3
2002-10-03,Critical analyses of order parameter and phase transitions at high density in Gross-Neveu model,"By critical analyses of the order parameter of symmetry breaking, we have
researched the phase transitions at high density in D=2 and D=3 Gross-Neveu
(GN) model and shown that the gap equation obeyed by the dynamical fermion mass
has the same effectivenesss as the effective potentials for such analyses of
all the second order and some special first order phase transitions. In the
meantime we also further ironed out a theoretical divergence and proven that in
D=3 GN model a first order phase transition does occur in the case of zero
temperature and finite chemical potential.",0210023v3
1999-10-18,A high-precision polarimeter,"We have built a polarimeter in order to measure the electron beam
polarization in hall C at JLAB. Using a superconducting solenoid to drive the
pure-iron target foil into saturation, and a symmetrical setup to detect the
Moller electrons in coincidence, we achieve an accuracy of <1%. This sets a new
standard for Moller polarimeters.",9910013v1
2002-11-25,The Single-Particle Structure of Neutron-Rich Nuclei of Astrophysical Interest at the Ornl Hribf,"The rapid nuetron-capture process (r process) produces roughly half of the
elements heavier than iron. The path and abundances produced are uncertain,
however, because of the lack of nuclear strucure information on important
neutron-rich nuclei. We are studying nuclei on or near the r-process path via
single-nucleon transfer reactions on neutron-rich radioactive beams at ORNL's
Holifield Radioactive Ion Beam Facility (HRIBF). Owing to the difficulties in
studying these reactions in inverse kinematics, a variety of experimental
approaches are being developed. We present the experimental methods and initial
results.",0211027v1
2003-07-11,"Low-Q scaling, duality, and the EMC effect","High energy lepton scattering has been the primary tool for mapping out the
quark distributions of nucleons and nuclei. Data on the proton and deuteron
have shown that there is a fundamental connection between the low and high
energy regimes, referred to as quark-hadron duality. We present the results of
similar studies to more carefully examine scaling, duality, and in particular
the EMC effect in nuclei. We extract nuclear modifications to the structure
function in the resonance region, and for the first time demonstrate that
nuclear effects in the resonance region are identical to those measured in deep
inelastic scattering. With the improved precision of the data at large $x$, we
for the first time observe that the large-x crossover point appears to occur at
lower $x$ values in carbon than in iron or gold.",0307012v3
2005-11-28,Cosmogenic activation of Germanium and its reduction for low background experiments,"Production of $^{60}$Co and $^{68}$Ge from stable isotopes of Germanium by
nuclear active component of cosmic rays is a principal background source for a
new generation of $^{76}$Ge double beta decay experiments like GERDA and
Majorana. The biggest amount of cosmogenic activity is expected to be produced
during transportation of either enriched material or already grown crystal.
  In this letter properties and feasibility of a movable iron shield are
discussed. Activation reduction factor of about 10 is predicted by simulations
with SHIELD code for a simple cylindrical configuration. It is sufficient for
GERDA Phase II background requirements. Possibility of further increase of
reduction factor and physical limitations are considered. Importance of
activation reduction during Germanium purification and detector manufacturing
is emphasized.",0511049v1
2006-04-06,Level density of $^{56}$Fe and low-energy enhancement of $γ$-strength function,"The $^{55}$Mn$(d,n)^{56}$Fe differential cross section is measured at $E_d=7$
MeV\@. The $^{56}$Fe level density obtained from neutron evaporation spectra is
compared to the level density extracted from the
$^{57}$Fe$(^3$He,$\alpha\gamma)^{56}$Fe reaction by the Oslo-type technique.
Good agreement is found between the level densities determined by the two
methods. With the level density function obtained from the neutron evaporation
spectra, the $^{56}$Fe $\gamma$-strength function is also determined from the
first-generation $\gamma$ matrix of the Oslo experiment. The good agreement
between the past and present results for the $\gamma$-strength function
supports the validity of both methods and is consistent with the low-energy
enhancement of the $\gamma$ strength below $\sim 4$ MeV first discovered by the
Oslo method in iron and molybdenum isotopes.",0604002v1
1996-01-30,Temperature Dependence of Pair Correlations in Nuclei in the Iron-Region,"We use the shell model Monte Carlo approach to study thermal properties and
pair correlations in $^{54,56,58}$Fe and in $^{56}$Cr. The calculations are
performed with the modified Kuo-Brown interaction in the complete $1p0f$ model
space. We find generally that the proton-proton and neutron-neutron $J=0$
pairing correlations, which dominate the ground state properties of even-even
nuclei, vanish at temperatures around 1 MeV. This pairing phase transition is
accompanied by a rapid increase in the moment of inertia and a partial
unquenching of the M1 strength. We find that the M1 strength totally unquenches
at higher temperatures, related to the vanishing of isoscalar proton-neutron
correlations, which persist to higher temperatures than the pairing between
like nucleons. The Gamow-Teller strength is also correlated to the isoscalar
proton-neutron pairing and hence also unquenches at a temperature larger than
that of the pairing phase transition.",9601047v1
1997-11-21,Approximate Treatment of Lepton Distortion in Charged-Current Neutrino Scattering from Nuclei,"The partial-wave expansion used to treat the distortion of scattered
electrons by the nuclear Coulomb field is simpler and considerably less
time-consuming when applied to the production of muons and electrons by low and
intermediate-energy neutrinos. For angle-integrated cross sections, however, a
modification of the ""effective-momentum-transfer"" approximation seems to work
so well that for muons the full distorted-wave treatment is usually
unnecessary, even at kinetic energies as low as an MeV and in nuclei as heavy
as lead. The method does not work as well for electron production at low
energies, but there a Fermi function usually proves adequate. Scattering of
electron-neutrinos from muon decay on iodine and of atmospheric neutrinos on
iron are discussed in light of these results.",9711045v1
1998-01-08,Electron capture on iron group nuclei,"We present Gamow-Teller strength distributions from shell model Monte Carlo
studies of fp-shell nuclei that may play an important role in the pre-collapse
evolution of supernovae. We then use these strength distributions to calculate
the electron-capture cross sections and rates in the zero-momentum transfer
limit. We also discuss the thermal behavior of the cross sections. We find
large differences in these cross sections and rates when compared to the naive
single-particle estimates. These differences need to be taken into account for
improved modeling of the early stages of type II supernova evolution.",9801012v1
1998-03-11,Shell model calculation of the beta- and beta+ partial halflifes of 54Mn and other unique second forbidden beta decays,"The nucleus 54Mn has been observed in cosmic rays. In astrophysical
environments it is fully stripped of its atomic electrons and its decay is
dominated by the beta- branch to the 54Fe ground state. Application of 54Mn
based chronometer to study the confinement of the iron group cosmic rays
requires knowledge of the corresponding halflife, but its measurement is
impossible at the present time. However, the branching ratio for the related
beta+ decay of 54Mn was determined recently. We use the shell model with only a
minimal truncation and calculate both beta+ and beta- decay rates of 54Mn. Good
agreement for the beta+ branch suggests that the calculated partial halflife of
the beta- decay, (4.94 \pm 0.06) x 10^5 years, should be reliable. However,
this halflife is noticeably shorter than the range 1-2 x 10^6 y indicated by
the fit based on the 54Mn abundance in cosmic rays. We also evaluate other
known unique second forbidden beta decays from the nuclear p and sd shells
(10Be, 22Na, and two decay branches of 26Al) and show that the shell model can
describe them with reasonable accuracy as well.",9803032v1
2000-03-08,Level Densities by Particle-Number Reprojection Monte Carlo Methods,"A particle-number reprojection method is applied in the framework of the
shell model Monte Carlo approach to calculate level densities for a family of
nuclei using Monte Carlo sampling for a single nucleus. In particular we can
also calculate level densities of odd-even and odd-odd nuclei despite a new
sign problem introduced by the projection on an odd number of particles. The
method is applied to level densities in the iron region using the complete
$pf+g_{9/2}$-shell. The single-particle level density parameter $a$ and the
backshift parameter $\Delta$ are extracted by fitting the microscopically
calculated level densities to the backshifted Bethe formula. We find good
agreement with experimental level densities with no adjustable parameters in
the microscopic calculations. The parameter $a$ is found to vary smoothly with
mass and does not show odd-even effects. The calculated backshift parameter
$\Delta$ displays an odd-even staggering effect versus mass and is in better
agreement with the experimental data than are the empirical values.",0003015v1
2002-08-12,Liquid-Gas Phase Transition of Supernova Matter and Its Relation to Nucleosynthesis,"We investigate the liquid-gas phase transition of dense matter in supernova
explosion by the relativistic mean field approach and fragment based
statistical model. The boiling temperature is found to be high (T_{boil} >= 0.7
MeV for rho_B >= 10^{-7} fm^{-3}), and adiabatic paths are shown to go across
the boundary of coexisting region even with high entropy. This suggests that
materials experienced phase transition can be ejected to outside. We calculated
fragment mass and isotope distribution around the boiling point. We found that
heavy elements at the iron, the first, second, and third peaks of r-process are
abundantly formed at rho_B = 10^{-7}, 10^{-5}, 10^{-3} and 10^{-2} fm^{-3},
respectively.",0208020v1
2002-11-08,Nuclear Reactions Important in Alpha-Rich Freezeouts,"The alpha-rich freezeout from equilibrium occurs during the core-collapse
explosion of a massive star when the supernova shock wave passes through the
Si-rich shell of the star. The nuclei are heated to high temperature and broken
down into nucleons and alpha particles. These subsequently reassemble as the
material expands and cools, thereby producing new heavy nuclei, including a
number of important supernova observables. In this paper we introduce two
web-based applications. The first displays the results of a reaction-rate
sensitivity study of alpha-rich freezeout yields. The second allows the
interested reader to run paramaterized explosive silicon burning calculations
in which the user inputs his own parameters. These tools are intended to aid in
the identification of nuclear reaction rates important for experimental study.
We then analyze several iron-group isotopes (59Ni, 57Co, 56Co, and 55Fe) in
terms of their roles as observables and examine the reaction rates that are
important in their production.",0211022v1
2003-03-18,Nuclear level statistics: extending the shell model theory to higher temperatures,"The Shell Model Monte Carlo (SMMC) approach has been applied to calculate
level densities and partition functions to temperatures up to ~ 1.5 - 2 MeV,
with the maximal temperature limited by the size of the configuration space.
Here we develop an extension of the theory that can be used to higher
temperatures, taking into account the large configuration space that is needed.
We first examine the configuration space limitation using an
independent-particle model that includes both bound states and the continuum.
The larger configuration space is then combined with the SMMC under the
assumption that the effects on the partition function are factorizable. The
method is demonstrated for nuclei in the iron region, extending the calculated
partition functions and level densities up to T ~ 4 MeV. We find that the
back-shifted Bethe formula has a much larger range of validity than was
suspected from previous theory. The present theory also shows more clearly the
effects of the pairing phase transition on the heat capacity.",0303040v1
2005-06-17,Charged Lepton Production from Iron Induced by Atmospheric Neutrinos,"The charged current lepton production induced by neutrinos in $^{56}Fe$
nuclei has been studied. The calculations have been done for the quasielastic
as well as the inelastic reactions assuming $\Delta$ dominance and take into
account the effect of Pauli blocking, Fermi motion and the renormalization of
weak transition strengths in the nuclear medium. The quasielastic production
cross section for lepton production are found to be strongly reduced due to
nuclear effects while there is about 10% reduction in the inelastic cross
sections in the absence of the final state interactions of the pions. The
numerical results for the momentum and angular distributions of the leptons
averaged over the various atmospheric neutrino spectra at the Soudan and
Gransasso sites have been presented. The effect of nuclear model dependence and
the atmospheric flux dependence on the relative yield of ${\mu}$ to e has been
studied and discussed.",0506057v1
2005-08-13,The nuclear moment of inertia and spin distribution of nuclear levels,"We introduce a simple model to calculate the nuclear moment of inertia at
finite temperature. This moment of inertia describes the spin distribution of
nuclear levels in the framework of the spin-cutoff model. Our model is based on
a deformed single-particle Hamiltonian with pairing interaction and takes into
account fluctuations in the pairing gap. We derive a formula for the moment of
inertia at finite temperature that generalizes the Belyaev formula for zero
temperature. We show that a number-parity projection explains the strong
odd-even effects observed in shell model Monte Carlo studies of the nuclear
moment of inertia in the iron region.",0508027v1
2000-08-18,An ECR hydrogen negative ion source at CEA/Saclay: preliminary results,"The development of a high intensity negative ion source is part of a
considerably larger activity presently undergoing at CEA Saclay in the field of
high intensity linear accelerators. Preliminary studies toward the construction
of a 2.45 GHz ECR H- ion source have been performed for few months. This new
test bench takes advantage of our experience on the French high intensity
proton source SILHI. In the new source, the high-energy electrons created in
the ECR zone are trapped by a dipole magnetic filter. A rectangular 200 mm long
plasma chamber and an intermediate iron shield are used to minimize the
magnetic field in the extraction region. A second magnetic filter separates
electrons and negative ions in a 10 kV extraction system. To reduce the
electron/H- ratio, the plasma electrode is slightly polarized. The design
allows future evolutions such as cesium injection, higher energy extraction and
plasma diagnostics. The installation of the source is now in progress. The
first helium plasma has been produced for few weeks to verify the electron
separator behavior. The design, computations and the first results of the
source are presented.",0008143v1
2003-05-09,The particle-in-cell model for ab initio thermodynamics: implications for the elastic anisotropy of the Earth's inner core,"We assess the quantitative accuracy of the particle-in-cell (PIC)
approximation used in recent ab initio predictions of the thermodynamic
properties of hexagonal-close-packed iron at the conditions of the Earth's
inner core. The assessment is made by comparing PIC predictions for a range of
thermodynamic properties with the results of more exact calculations that avoid
the PIC approximation. It is shown that PIC gives very accurate results for
some properties, but that it gives an incorrect treatment of anharmonic lattice
vibrations. In addition, our assessment does not support recent PIC-based
predictions that the hexagonal c/a ratio increases strongly with increasing
temperature, and we point out that this casts doubt on a proposed
re-interpretation of the elastic anisotropy of the inner core.",0305033v2
2004-11-19,New applications of Equinox code for real-time plasma equilibrium and profile reconstruction for tokamaks,"Recent development of real-time equilibrium code Equinox [1] using a
fixed-point algorithm [2] allow major plasma magnetic parameters to be
identified in real-time, using rigorous analytical method. The code relies on
the boundary flux code providing flux values on the first wall of vacuum
vessel. By means of least-square minimization of differences between magnetic
field obtained from previous solution and the next measurements the code
identifies the source term of the non-linear Grad-Shafranov equation [3]. The
strict use of analytical equations together with a flexible algorithm offers an
opportunity to include new measurements into stable magnetic equilibrium code
and compare the results directly between several tokamaks while maintaining the
same physical model (i.e. no iron model is necessary inside the equilibrium
code). The successful implementation of this equilibrium code for JET and Tore
Supra have been already published [1], in this paper, we show the preliminary
results of predictive runs of the Equinox code using the ITER geometry.",0411181v1
2006-01-04,Simulation Studies of Delta-ray Backgrounds in a Compton-Scatter Transition Radiation Detector,"In order to evaluate the response to cosmic-ray nuclei of a Compton-Scatter
Transition Radiation Detector in the proposed ACCESS space-based mission, a
hybrid Monte Carlo simulation using GEANT3 and an external transition radiation
(TR) generator routine was constructed. This simulation was employed to study
the effects of delta-ray production induced by high-energy nuclei and to
maximize the ratio of TR to delta-ray background. The results demonstrate the
ability of a Compton-Scatter Transition Radiation Detector to measure nuclei
from boron to iron up to Lorentz factors ~ 10^5 taking into account the steeply
falling power-law cosmic ray spectra.",0601020v1
2006-11-22,Efficient Degradation and Expression Prioritization with Small RNAs,"We build a simple model for feedback systems involving small RNA (sRNA)
molecules based on the iron metabolism system in the bacterium E. coli, and
compare it with the corresponding system in H. pylori which uses purely
transcriptional regulation. This reveals several unique features of sRNA based
regulation that could be exploited by cells. Firstly, we show that sRNA
regulation can maintain a smaller turnover of target mRNAs than transcriptional
regulation, without sacrificing the speed of response to external shocks.
Secondly, we propose that a single sRNA can prioritize the usage of different
target mRNAs. This suggests that sRNA regulation would be more common in more
complex systems which need to co-regulate many mRNAs efficiently.",0611069v3
2007-04-06,Millimeter-Thick Single-Walled Carbon Nanotube Forests: Hidden Role of Catalyst Support,"A parametric study of so-called ""super growth"" of single-walled carbon
nanotubes(SWNTs) was done by using combinatorial libraries of iron/aluminum
oxide catalysts. Millimeter-thick forests of nanotubes grew within 10 min, and
those grown by using catalysts with a thin Fe layer (about 0.5 nm) were SWNTs.
Although nanotube forests grew under a wide range of reaction conditions such
as gas composition and temperature, the window for SWNT was narrow. Fe
catalysts rapidly grew nanotubes only when supported on aluminum oxide.
Aluminum oxide, which is a well-known catalyst in hydrocarbon reforming, plays
an essential role in enhancing the nanotube growth rates.",0704.0915v1
2007-04-11,Physical parameters of evolved stars in clusters and in the field from line-depth ratios,"We present a high-resolution spectroscopic analysis of two samples of evolved
stars selected in the field and in the intermediate-age open cluster IC 4651,
for which detailed measurements of chemical composition were made in the last
few years. Applying the Gray's method based on ratios of line depths, we
determine the effective temperature and compare our results with previous ones
obtained by means of the curves of growth of iron lines. The knowledge of the
temperature enables us to estimate other fundamental stellar parameters, such
as color excess, age, and mass.",0704.1462v1
2007-04-13,"Spectrum of cosmic rays, produced in supernova remnants","Nonlinear kinetic theory of cosmic ray (CR) acceleration in supernova
remnants is employed to calculate CR spectra. The magnetic field in SNRs is
assumed to be significantly amplified by the efficiently accelerating nuclear
CR component. It is shown that the calculated CR spectra agree in a
satisfactory way with the existing measurements up to the energy $10^{17}$ eV.
The power law spectrum of protons extends up to the energy $3\times 10^{15}$ eV
with a subsequent exponential cutoff. It gives a natural explanation for the
observed knee in the Galactic CR spectrum. The maximum energy of the
accelerated nuclei is proportional to their charge number $Z$. Therefore the
break in the Galactic CR spectrum is the result of the contribution of
progressively heavier species in the overall CR spectrum so that at $10^{17}$
eV the CR spectrum is dominated by iron group nuclei. It is shown that this
component plus a suitably chosen extragalactic CR component can give a
consistent description for the entire Galactic CR spectrum.",0704.1715v1
2007-04-16,Single pion electro-- and neutrinoproduction on heavy targets,"We present a calculation of single pion electroproduction cross sections on
heavy targets in the kinematic region of the Delta(1232) resonance. Final state
interactions of the pions are taken into account using the pion multiple
scattering model of Adler, Nussinov and Paschos (ANP model). For
electroproduction and neutral current reactions we obtain results for carbon,
oxygen, argon and iron targets and find a significant reduction of the
W-spectra for pi^0 as compared to the free nucleon case. On the other hand, the
charged pion spectra are only little affected by final state interactions.
Measurements of such cross sections with the CLAS detector at JLAB could help
to improve our understanding of pion rescattering effects and serve as
important/valuable input for calculations of single pion neutrinoproduction on
heavy targets relevant for current and future long baseline neutrino
experiments. Two ratios, in Eq. (3.8) and (3.10), will test important
properties of the model.",0704.1991v1
2007-04-17,Maximum Entropy for Gravitational Wave Data Analysis: Inferring the Physical Parameters of Core-Collapse Supernovae,"The gravitational wave signal arising from the collapsing iron core of a Type
II supernova progenitor star carries with it the imprint of the progenitor's
mass, rotation rate, degree of differential rotation, and the bounce depth.
Here, we show how to infer the gravitational radiation waveform of a core
collapse event from noisy observations in a network of two or more LIGO-like
gravitational wave detectors and, from the recovered signal, constrain these
source properties. Using these techniques, predictions from recent core
collapse modeling efforts, and the LIGO performance during its S4 science run,
we also show that gravitational wave observations by LIGO might have been
sufficient to provide reasonable estimates of the progenitor mass, angular
momentum and differential angular momentum, and depth of the core at bounce,
for a rotating core collapse event at a distance of a few kpc.",0704.2157v2
2007-05-09,Quark-nova explosion inside a collapsar: application to Gamma Ray Bursts,"If a quark-nova occurs inside a collapsar, the interaction between the
quark-nova ejecta (relativistic iron-rich chunks) and the collapsar envelope,
leads to features indicative of those observed in Gamma Ray Bursts. The
quark-nova ejecta collides with the stellar envelope creating an outward moving
cap
  (Gamma ~ 1-10) above the polar funnel. Prompt gamma-ray burst emission from
internal shocks in relativistic jets (following accretion onto the quark star)
become visible after the cap becomes optically thin. Model features include:
(i) precursor activity (optical, X-ray, gamma-ray), (ii) prompt gamma-ray
emission, and (iii) afterglow emission. We discuss SN-less long duration GRBs,
short hard GRBs (including association and non-association with star forming
regions), dark GRBs, the energetic X-ray flares detected in Swift GRBs, and the
near-simultaneous optical and gamma-ray prompt emission observed in GRBs in the
context of our model.",0705.1240v3
2007-05-17,Applications of nanoparticles of gamma Fe2O3 for hyperthermia in E.coli by Nd:YAG laser,"The paper explores the use of nanoparticles of gamma Fe2O3 for hyperthermia
treatment of living organisms by absorption of 1064 nm radiations from Nd:YAG
laser. Escherichia coli cells have been used as the model system for
demonstrating the effect wherein lysine is used as an interface between the
cell walls and the nanoparticles. Scanning Electron Microscopic observations
have, exclusively, proved that attachment of nanoparticles of iron oxide along
with lysine alone is responsible for absorption of above radiations. The
quantitative estimation has been provided by growth rate measurements and
protein assessment of the cells. The nanoparticles of gamma Fe2O3 were
synthesized by DC arc plasma assisted gas phase condensation.",0705.2523v1
2007-05-21,Room temperature spin polarized magnetic semiconductor,"Alternating layers of granular Iron (Fe) and Titanium dioxide
(TiO$_{2-\delta}$) were deposited on (100) Lanthanum aluminate (LaAlO$_3$)
substrates in low oxygen chamber pressure using a controlled pulsed laser
ablation deposition technique. The total thickness of the film was about 200
nm. The films show ferromagnetic behavior for temperatures ranging from 4 to
$400 ^oK$. The layered film structure was characterized as p-type magnetic
semiconductor at $300 ^oK$ with a carrier density of the order of $10^{20}
/cm^3$. The undoped pure TiO$_{2-\delta}$ film was characterized as an n-type
magnetic semiconductor. The hole carriers were excited at the interface between
the granular Fe and TiO$_{2-\delta}$ layers similar to holes excited in the
metal/n-type semiconductor interface commonly observed in
Metal-Oxide-Semiconductor (MOS) devices. The holes at the interface were
polarized in an applied magnetic field raising the possibility that these
granular MOS structures can be utilized for practical spintronic device
applications.",0705.2993v1
2007-05-30,Epitaxial thin films of multiferroic Bi2FeCrO6 with B-site cationic order,"Epitaxial thin films of Bi2FeCrO6 have been synthesized by pulsed laser
deposition on SrRuO3 on (100)- and (111)-oriented SrTiO3 substrates. Detailed
X-ray diffraction and cross-section transmission electron microscopy analysis
revealed a double perovskite crystal structure of the Bi2FeCrO6 epitaxial films
very similar to that of BiFeO3 along with a particularly noteworthy Fe3+/Cr3+
cation ordering along the [111] direction. The films contain no detectable
magnetic iron oxide impurities and have the correct cationic average
stoichiometry throughout their thickness. They however exhibit a slight
modulation in the Fe and Cr compositions forming complementary stripe patterns,
suggesting minor local excess or depletion of Fe and Cr. The epitaxial BFCO
films exhibit good ferroelectric and piezoelectric properties, in addition to
magnetic properties at room temperature, as well as an unexpected
crystallographic orientation dependence of their room temperature magnetic
properties. Our results qualitatively confirm the predictions made using the
ab-initio calculations: the double-perovskite structure of Bi2FeCrO6 films
exhibit a Fe3+/Cr3+ cation ordering and good multiferroic properties, along
with the unpredicted existence of magnetic ordering at room temperature.",0705.4390v1
2007-06-04,Sum-rules for electron energy-loss near-edge spectra,"We derive four sum-rule expressions for spectra measured in electron
energy-loss near edge structure experiments. These sum-rules permit the
determination spin and orbital magnetic moments, spin-orbit interaction and
number of states, analogously to the sum rules of x-ray magnetic circular
dichroism. The derivation of the sum-rules is based on dynamical electron
diffraction theory and the properties of the mixed dynamic form-factor. The
accuracy of the sum-rules is tested by a complete evaluation of the thickness
dependent electron energy-loss spectra for iron, cobalt, and nickel crystals.
We find that the sum-rules reproduce both spin and orbital moments with very
good accuracy. Our results provide a foundation for the use of the energy loss
magnetic chiral dichroism technique as a quantitative probe of element specific
magnetic properties.",0706.0402v2
2007-06-14,Molecular opacities for low-mass metal-poor AGB stars undergoing the Third Dredge Up,"The concomitant overabundances of C, N and s-process elements are commonly
ascribed to the complex interplay of nucleosynthesis, mixing and mass loss
taking place in Asymptotic Giant Branch stars. At low metallicity, the
enhancement of C and/or N may be up to 1000 times larger than the original iron
content and significantly affects the stellar structure and its evolution. For
this reason, the interpretation of the already available and still growing
amount of data concerning C-rich metal-poor stars belonging to our Galaxy as
well as to dwarf spheroidal galaxies would require reliable AGB stellar models
for low and very low metallicities. In this paper we address the question of
calculation and use of appropriate opacity coefficients, which take into
account the C enhancement caused by the third dredge up. A possible N
enhancement, caused by the cool bottom process or by the engulfment of protons
into the convective zone generated by a thermal pulse and the subsequent huge
third dredge up, is also considered. Basing on up-to-date stellar models, we
illustrate the changes induced by the use of these opacity on the physical and
chemical properties expected for these stars.",0706.2100v1
2007-06-18,The Spectrum of the Black Hole X-ray Nova V404 Cygni in Quiescence as Measured by XMM-Newton,"We present XMM observations of the black hole X-ray nova V404 Cygni in
quiescence. Its quiescent spectrum can be best fitted by a simple power-law
with slope 2. The spectra are consistent with that expected for the
advection-dominated accretion flow (ADAF). V404 Cyg was roughly equal in
luminosity compared to the previous observation of Chandra. We see variability
of a factor of 4 during the observation. We find no evidence for the presence
of fluorescent or H-like/He-like iron emission, with upper limits of 52 eV and
110 eV respectively. The limit on the fluorescent emission is improved by a
factor of 15 over the previous estimate, and the restriction on H-like/He-like
emission is lower than predicted from models by a factor of roughly 2.",0706.2652v1
2007-06-20,"Optical spectroscopy of RU Cam, a pulsating carbon star","We analysed the high resolution spectra of a RU Cam, classified as W Vir type
star. The atmospheric parameters of RU Cam were estimated Teff=5250K and log
g=1.0. The hydrogen deficiency of RU Cam was not confirmed. The iron abundance,
[Fe/H]=-0.37, is close to the solar one. Abundances of most other elements are
also close to normal. We found considerable excesses of carbon and nitrogen:
[C/Fe]=+0.98, [N/Fe]=+0.60. The carbon to oxygen ratio is C/O$\ge$1. The carbon
isotopic abundance ratio is equal to C^12/C^13=4.5. For sodium a moderate
overabundance Na/Fe=+0.55 was obtained. For two moments of observations we
found close heliocentric velocity values, Vr=-21.7+/-0.8 and -23.1+/-1.0 km/s.
Both spectra contain a peculiar feature - an emission component of NaI doublet
which location agrees with the radial velocity from the bulk of metallic lines.
For our two observing moments we found no dependence of radial velocities on
the formation depth or on excitation energy for metallic lines.",0706.2969v1
2007-06-20,Neutrino-driven explosions twenty years after SN1987A,"The neutrino-heating mechanism remains a viable possibility for the cause of
the explosion in a wide mass range of supernova progenitors. This is
demonstrated by recent two-dimensional hydrodynamic simulations with detailed,
energy-dependent neutrino transport. Neutrino-driven explosions were not only
found for stars in the range of 8-10 solar masses with ONeMg cores and in case
of the iron core collapse of a progenitor with 11 solar masses, but also for a
``typical'' progenitor model of 15 solar masses. For such more massive stars,
however, the explosion occurs significantly later than so far thought, and is
crucially supported by large-amplitude bipolar oscillations due to the
nonradial standing accretion shock instability (SASI), whose low (dipole and
quadrupole) modes can develop large growth rates in conditions where convective
instability is damped or even suppressed. The dominance of low-mode deformation
at the time of shock revival has been recognized as a possible explanation of
large pulsar kicks and of large-scale mixing phenomena observed in supernovae
like SN 1987A.",0706.3056v1
2007-07-18,Charge Order Superstructure with Integer Iron Valence in Fe2OBO3,"Solution-grown single crystals of Fe2OBO3 were characterized by specific
heat, Mossbauer spectroscopy, and x-ray diffraction. A peak in the specific
heat at 340 K indicates the onset of charge order. Evidence for a doubling of
the unit cell at low temperature is presented. Combining structural refinement
of diffraction data and Mossbauer spectra, domains with diagonal charge order
are established. Bond-valence-sum analysis indicates integer valence states of
the Fe ions in the charge ordered phase, suggesting Fe2OBO3 is the clearest
example of ionic charge order so far.",0707.2743v1
2007-07-27,Magnetic Field Generation in Planets and Satellites by Natural Nuclear Fission Reactors,"One of the most fundamental problems in physics has been to understand the
nature of the mechanism that generates the geomagnetic field and the magnetic
fields of other planets and satellites. For decades, the dynamo mechanism,
thought to be responsible for generating the geomagnetic field and other
planetary magnetic fields, has been ascribed to convection in each planet's
iron-alloy core. Recently, I described the problems inherent in Earth-core
convection and proposed instead that the geomagnetic field is produced by a
dynamo mechanism involving convection, not in the fluid core, but in the
electrically conductive, fluid, fission-product sub-shell of a natural nuclear
fission reactor at the center of the Earth, called the georeactor. Here I set
forth in detail the commonality in the Solar System of the matter like that of
the inside of the Earth, which is my basis for generalizing the concept of
planetary magnetic field generation by natural planetocentric nuclear fission
reactors.",0707.4161v4
2007-08-01,Abundances on the Main Sequence of Omega Centauri,"Abundance ratios of carbon, nitrogen and strontium relative to iron,
calculated using spectrum synthesis techniques, are given for a sample of main
sequence and turnoff stars that belong to the globular cluster omega Centauri.
The variations of carbon, nitrogen and/or strontium show several different
abundance patterns as a function of [Fe/H]. The source of the
enhancements/depletions in carbon, nitrogen and/or strontium may be enrichment
from asymptotic giant branch stars of low (1--3 solar masses) and intermediate
(3--8 solar masses) mass. Massive rotating stars which produce excess nitrogen
without carbon and oxygen overabundances may also play a role. These abundances
enable different contributors to be considered and incorporated into the
evolutionary picture of omega Cen.",0708.0096v1
2007-08-01,The 4th Concept Detector for the International Linear Collider,"The 4th Concept detector presently being designed for the International
Linear Collider introduces several innovations in order to achieve the
necessary experimental goal of a detecter that is 2-to-10 times better than the
already excellent SLC and LEP detectors. We introduce a dual-readout
calorimeter system, a cluster counting drift chamber, and a second solenoid to
return the magnetic flux without iron. We discuss particle identification,
momentum and energy resolutions, and the machine-detector interface that
together offer the possibility of a very high-performance detector for
e^+e^-physics up to $\sqrt{s} = 1$ TeV.",0708.0142v2
2007-08-01,First-principles thermal equation of state and thermoelasticity for hcp Fe under high pressures,"We investigate the equation of state and elastic properties of nonmagnetic
hcp iron at high pressures and high temperatures using the first principles
linear response linear-muffin-tin-orbital method in the generalized-gradient
approximation. We calculate the Helmholtz free energy as a function of volume,
temperature, and volume-constrained strain, including the electronic excitation
contributions from band structures and lattice vibrational contributions from
quasi-harmonic lattice dynamics. We perform detailed investigations on the
behavior of elastic moduli and equation of state properties as a function of
temperature and pressure, including the pressure-volume equation of state, bulk
modulus, the thermal expansion coefficient, the Gruneisen ratio, and the shock
Hugoniots. A detailed comparison has been made with available experimental
measurements and theoretical predictions.",0708.0183v1
2007-08-03,Strong spin-orbit induced Gilbert damping and g-shift in iron-platinum nanoparticles,"The shape of ferromagnetic resonance spectra of highly dispersed, chemically
disordered Fe_{0.2}Pt_{0.8} nanospheres is perfectly described by the solution
of the Landau-Lifshitz-Gilbert (LLG) equation excluding effects by crystalline
anisotropy and superparamagnetic fluctuations. Upon decreasing temperature, the
LLG damping $\alpha(T)$ and a negative g-shift, g(T)-g_0, increase proportional
to the particle magnetic moments determined from the Langevin analysis of the
magnetization isotherms. These novel features are explained by the scattering
of the $q \to 0$ magnon from an electron-hole (e/h) pair mediated by the
spin-orbit coupling, while the sd-exchange can be ruled out. The large
saturation values, $\alpha(0)=0.76$ and $g(0)/g_0-1=-0.37$, indicate the
dominance of an overdamped 1 meV e/h-pair which seems to originate from the
discrete levels of the itinerant electrons in the d_p=3 nm nanoparticles.",0708.0463v1
2007-08-06,Emission Lines in X-ray Spectra of Clusters of Galaxies,"Emission lines in X-ray spectra of clusters of galaxies reveal the presence
of heavy elements in the diffuse hot plasma (the Intra Cluster Medium, or ICM)
in virial equilibrium in the dark matter potential well. The relatively simple
physical state of the ICM allows us to estimate, with good accuracy, its
thermodynamical properties and chemical abundances. These measures put strong
constraints on the interaction processes between the galaxies and the
surrounding medium, and have significant impact on models of galaxy formation
as well. This field is rapidly evolving thanks to the X-ray satellites Chandra
and XMM-Newton. Among the most relevant progresses in the last years, we
briefly discuss the nature of cool cores and the measure of the Iron abundance
in high redshift clusters. Future X-ray missions with bolometers promise to
provide a substantial step forward to a more comprehensive understanding of the
complex physics of the ICM.",0708.0674v1
2007-08-29,A Deep Chandra Observation of Kepler's Supernova Remnant: A Type Ia Event with Circumstellar Interaction,"We present initial results of a 750 ks Chandra observation of the remnant of
Kepler's supernova of AD 1604. The strength and prominence of iron emission,
together with the absence of O-rich ejecta, demonstrate that Kepler resulted
from a thermonuclear supernova, even though evidence for circumstellar
interaction is also strong. We have analyzed spectra of over 100 small regions,
and find that they fall into three classes. (1) The vast majority show Fe L
emission between 0.7 and 1 keV and Si and S K alpha emission; we associate
these with shocked ejecta. A few of these are found at or beyond the mean blast
wave radius. (2) A very few regions show solar O/Fe abundance rations; these we
associate with shocked circumstellar medium (CSM). Otherwise O is scarce. (3) A
few regions are dominated by continuum, probably synchrotron radiation.
Finally, we find no central point source, with a limit about 100 times fainter
than the central object in Cas A. The evidence that the blast wave is
interacting with CSM may indicate a Ia explosion in a more massive progenitor.",0708.3858v1
2007-08-31,Stellar Models and Yields of Asymptotic Giant Branch Stars,"We present stellar yields calculated from detailed models of low and
intermediate-mass asymptotic giant branch (AGB) stars. We evolve models with a
range of mass from 1 to 6Msun, and initial metallicities from solar to 1/200th
of the solar metallicity. Each model was evolved from the zero age main
sequence to near the end of the thermally-pulsing AGB phase, and through all
intermediate phases including the core He-flash for stars initially less
massive than 2.5Msun. For each mass and metallicity, we provide tables
containing structural details of the stellar models during the TP-AGB phase,
and tables of the stellar yields for 74 species from hydrogen through to
sulphur, and for a small number of iron-group nuclei. All tables are available
for download. Our results have many applications including use in population
synthesis studies and the chemical evolution of galaxies and stellar systems,
and for comparison to the composition of AGB and post-AGB stars and planetary
nebulae.",0708.4385v2
2007-09-03,X-ray reflection in accreting stellar-mass black hole systems,"The X-ray spectra of accreting stellar-mass black hole systems exhibit
spectral features due to reflection, especially broad iron K alpha emission
lines. We investigate the reflection by the accretion disc that can be expected
in the high/soft state of such a system. First, we perform a self-consistent
calculation of the reflection that results from illumination of a hot, inner
portion of the disc with its atmosphere in hydrostatic equilibrium. Then we
present reflection spectra for a range of illumination strengths and disc
temperatures under the assumption of a constant-density atmosphere. Reflection
by a hot accretion disc differs in important ways from that of a much cooler
disc, such as that expected in an active galactic nucleus.",0709.0270v1
2007-09-21,"Self-assembly of polymers or copolymers and ferrofluids leading to either 1-d, 2-d or 3-d aggregates decorated with magnetic nanoparticles","A novel type of hybrid colloids is presented, based on the association of
several polymeric systems and ferrofluids. On the one hand, we use inorganic
nanoparticles made of magnetic iron oxide prepared at the LI2C, which response
to a magnetic field of low intensity. On the other hand the organic part is
made either of long linear polyacrylamide chains or of mesoscopic structures
(vesicles and micelles) self-assembled from amphiphile
polybutadiene-b-poly(glutamic acid) di-block copolymers, which conformation is
pH-sensitive.",0709.3514v1
2007-09-25,The Burst Spectra of EXO 0748-676 during a Long 2003 XMM-Newton Observation,"Gravitationally redshifted absorption lines from highly ionized iron have
been previously identified in the burst spectra of the neutron star in EXO
0748-676. To repeat this detection we obtained a long, nearly 600 ks
observation of the source with XMM-Newton in 2003. The spectral features seen
in the burst spectra from the initial data are not reproduced in the burst
spectra from this new data. In this paper we present the spectra from the 2003
observations and discuss the sensitivity of the absorption structure to changes
in the photospheric conditions.",0709.4062v1
2007-10-10,The control of iron oxidation state during FeO and olivine crystal growth,"Crystal growth experiments (micro-pulling down or Czochralski methods,
respectively) and DTA/TG measurements with Fe2+ containing olivines
(fayalite--forsterite solid solution) and with FeO (wustite) are performed. For
both substances the oxygen partial pressure p_O2 of the growth atmosphere had
to be adjusted within the stability region of Fe2+ for all temperatures ranging
from room temperature to the melting point. The formation of Fe3+ (Fe3O4,
Fe2O3) had to be avoided. The adjustment of p_O2 could be obtained by a mixture
of argon, carbon dioxide and carbon monoxide. Thermodynamic equilibrium
calculations show, that mixtures of an inert gas (e.g. argon) with another gas
or gas mixture that supplies oxygen at elevated temperature (e.g. CO2/CO) are
superior to the use of inert gases with constant oxygen admixture. The reason
is that the Ar/CO2/CO mixture adjusts its oxygen concentration with temperature
in a way similar to that needed for the stabilization of Fe2+.",0710.2050v1
2007-10-11,RXTE confirmation of the Intermediate Polar status of Swift J0732.5-1331,"Aims. We intend to establish the X-ray properties of Swift J0732.5-1331 and
therefore confirm its status as an intermediate polar. Method. We analysed
36,240 s of X-ray data from RXTE. Frequency analysis was used to constrain
temporal variations and spectral analysis used to characterise the emission and
absorption properties. Results. The X-ray spin period is confirmed to be
512.4(3) s with a strong first harmonic. No modulation is detected at the
candidate orbital period of 5.6 h, but a coherent modulation is present at the
candidate 11.3 h period. The spectrum is consistent with a 37 keV
bremsstrahlung continuum with an iron line at 6.4 keV absorbed by an equivalent
hydrogen column density of around 10^22 atoms cm^-2. Conclusions. Swift
J0732-1331 is confirmed to be an intermediate polar.",0710.2248v1
2007-10-23,"NGC3147: a ""true"" Seyfert 2 without the broad-line region","We report on simultaneous optical and X-ray observations of the Seyfert
galaxy, NGC3147. The XMM-Newton spectrum shows that the source is unabsorbed in
the X-rays ($N_H<5\times10^{20}$ cm$^{-2}$). On the other hand, no broad lines
are present in the optical spectrum. The origin of this optical/X-rays
misclassification (with respect to the Unification Model) cannot be attributed
to variability, since the observations in the two bands are simultaneous.
Moreover, a Compton-thick nature of the object can be rejected on the basis of
the low equivalent width of the iron K$\alpha$ line ($\simeq130$ eV) and the
large ratio between the 2-10 keV and the [OIII] fluxes. It seems therefore
inescapable to conclude that NGC3147 intrinsically lacks the Broad Line Region
(BLR), making it the first ""true"" Seyfert 2.",0710.4226v1
2007-10-24,Magnetic tight-binding and the iron-chromium enthalpy anomaly,"We describe a self consistent magnetic tight-binding theory based in an
expansion of the Hohenberg-Kohn density functional to second order, about a non
spin polarised reference density. We show how a first order expansion about a
density having a trial input magnetic moment leads to the Stoner--Slater rigid
band model. We employ a simple set of tight-binding parameters that accurately
describes electronic structure and energetics, and show these to be
transferable between first row transition metals and their alloys. We make a
number of calculations of the electronic structure of dilute Cr impurities in
Fe which we compare with results using the local spin density approximation.
The rigid band model provides a powerful means for interpreting complex
magnetic configurations in alloys; using this approach we are able to advance a
simple and readily understood explanation for the observed anomaly in the
enthalpy of mixing.",0710.4399v1
2007-10-25,Ocean Planet or Thick Atmosphere: On the Mass-Radius Relationship for Solid Exoplanets with Massive Atmospheres,"The bulk composition of an exoplanet is commonly inferred from its average
density. For small planets, however, the average density is not unique within
the range of compositions. Variations of a number of important planetary
parameters--which are difficult or impossible to constrain from measurements
alone--produce planets with the same average densities but widely varying bulk
compositions. We find that adding a gas envelope equivalent to 0.1%-10% of the
mass of a solid planet causes the radius to increase 5-60% above its gas-free
value. A planet with a given mass and radius might have substantial water ice
content (a so-called ocean planet) or alternatively a large rocky-iron core and
some H and/or He. For example, a wide variety of compositions can explain the
observed radius of GJ 436b, although all models require some H/He. We conclude
that the identification of water worlds based on the mass-radius relationship
alone is impossible unless a significant gas layer can be ruled out by other
means.",0710.4941v1
2007-10-31,XMM-Newton Detection of a Compton-thick AGN in the 1-Jy ULIRG/LINER F04103-2838,"We report on the detection of Fe Kalpha emission in F04103$-$2838, an
ultraluminous infrared galaxy (ULIRG; log[L$_{\rm IR}$/L$_\odot$] $\ge$ 12)
that is optically classified as a LINER. Previous {\it Chandra} observations
suggested the presence of both a starburst and an AGN in this source. A deeper
($\sim$20 ksec) {\it XMM-Newton} spectrum reveals an Fe Kalpha line at rest
frame energy $\sim$6.4 keV, consistent with cold neutral iron. The best-fit
spectral model indicates the Fe Kalpha line has an equivalent width of
$\sim$1.6 keV. The hard X-ray emission is dominated by a Compton-thick AGN with
intrinsic 0.2--10 keV luminosity $\sim10^{44}$ ergs s$^{-1}$, while the soft
X-ray emission is from $\sim$0.1 keV gas attributed to the starburst. The X-ray
spectrum of this source bears a striking resemblance to that of the archetypal
luminous infrared galaxy NGC 6240 despite differences in merger state and
infrared properties.",0711.0002v1
2007-11-01,Magnetic resonance in iron oxide nanoparticles: quantum features and effect of size,"In order to better understand the transition from quantum to classical
behavior in spin system, electron magnetic resonance (EMR) is studied in
suspensions of superparamagnetic magnetite nanoparticles with an average
diameter of ~ 9 nm and analyzed in comparison with the results obtained in the
maghemite particles of smaller size (~ 5 nm). It is shown that both types of
particles demonstrate common EMR behavior, including special features such as
the temperature-dependent narrow spectral component and multiple-quantum
transitions. These features are common for small quantum systems and not
expected in classical case. The relative intensity of these signals rapidly
decreases with cooling or increase of particle size, marking gradual transition
to the classical FMR behavior.",0711.0168v1
2007-11-07,Ultrahigh energy cosmic rays as heavy nuclei from cluster accretion shocks,"Large-scale accretion shocks around massive clusters of galaxies, generically
expected in hierarchical scenarios of cosmological structure formation, are
shown to be potential sources of the observed ultrahigh energy cosmic rays
(UHECRs) by accelerating a mixture of heavy nuclei including the iron group
elements. Current observations can be explained if the source composition at
injection for the heavier nuclei is somewhat enhanced from simple expectations
for the accreting gas. The proposed picture should be testable by current and
upcoming facilities in the near future through characteristic features in the
UHECR spectrum, composition and anisotropy. The associated X-ray and gamma-ray
signatures are also briefly discussed.",0711.1027v1
2007-11-12,Low temperature dephasing in irradiated metallic wires,"We present phase coherence time measurements in quasi-one-dimensional Ag
wires implanted with Ag$^{+}$ ions with an energy of $100 keV$. The
measurements have been carried out in the temperature range from $100 mK$ up to
$10 K$; this has to be compared with the Kondo temperature of iron in silver,
i.e. $T_{K}^{Ag/Fe} \approx 4 K$, used in recent experiments on dephasing in
Kondo systems\cite{mallet_prl_06,birge_prl_06}. We show that the phase
coherence time is not affected by the implantation procedure, clearly proving
that ion implantation process by itself \emph{does not lead to any extra
dephasing} at low temperature.",0711.1810v2
2007-11-19,The MINERvA Neutrino Interaction Experiment,"The MINERvA neutrino interaction experiment in the NuMI beam at Fermilab will
measure several aspects of neutrino interactions in the few GeV energy region.
We will make cross section and form factor measurements using a fine-grained
fully active scintillator (CH) target, and also investigate nuclear effects on
neutrino interactions as well as hadron rescattering using integral nuclear
targets made of helium, carbon, iron, and lead. We will improve or add to
existing measurements and address some specific questions that are important
for current and upcoming neutrino oscillation experiments. This paper reports
on the progress toward the design, construction, and calibration of the
detector, which we expect will get its first neutrino beam in 2009.",0711.3029v1
2007-11-20,Beyond 1D: spectral line formation with 3D hydrodynamical model atmospheres of red giants,"We present the results of realistic, 3D, hydrodynamical, simulations of
surface convection in red giant stars with varying effective temperatures and
metallicities. We use the convection simulations as time-dependent,
hydrodynamical, model atmospheres to compute spectral line profiles for a
number of ions and molecules under the assumption of local thermodynamic
equilibrium (LTE). We compare the results with the predictions of line
formation calculations based on 1D, hydrostatic, model stellar atmospheres in
order to estimate the impact of 3D models on the derivation of elemental
abundances. We find large negative 3D-1D LTE abundance corrections (typically
-0.5 to -1 dex) for weak low-excitation lines from molecules and neutral
species in the very low metallicity cases. Finally, we discuss the extent of
departures from LTE in the case of neutral iron spectral line formation.",0711.3186v1
2007-11-22,"Stroemgren metallicity calibration: the m1, b-y relation","We performed a new calibration of the Stroemgren metallicity index m1 based
on the b-y color of cluster red giant stars. The current
Metallicity-Index-Color relation is not linear in the color range 0.40 < b-y <
1.0, but provides iron abundances of cluster and field red giants with an
accuracy of ~ 0.25 dex.",0711.3534v1
2007-11-29,Magnetoelectric Effects on Composite Nano Granular $Fe/TiO_{2-δ}$ Films,"Employing a new experimental technique to measure magnetoelectric response
functions, we have measured the magnetoelectric effect in composite films of
nano granular metallic iron in anatase titanium dioxide at temperatures below
50 K. A magnetoelectric resistance is defined as the ratio of a transverse
voltage to bias current as a function of the magnetic field. In contrast to the
anomalous Hall resistance measured above 50 K, the magnetoelectic resistance
below 50 K is significantly larger and exhibits an even symmetry with respect
to magnetic field reversal $H\to -H$. The measurement technique required
attached electrodes in the plane of the film composite in order to measure
voltage as a function of bias current and external magnetic field. To our
knowledge, the composite films are unique in terms of showing magnetoelectric
effects at low temperatures, $<$ 50 K, and anomalous Hall effects at high
temperatures, $>$ 50 K.",0711.4776v1
2007-12-03,Temporal evolution of magnetic elements,"We study the structure and evolution of the magnetic field of the quiet Sun
by investigating weak spectro-polarimetric signals. To this end, we observed a
quiet region close to the disk center with the German VTT in Tenerife, July 07,
2006. We recorded 38 scans of the same area. Each scan was eight arcsec wide
and observed within about 100 seconds. We used POLIS to simultaneously observe
Stokes profiles of the neutral iron lines at 630.15 and 630.25 nm, the Stokes-I
profile of the Ca II H line at 396.8 nm, and a continuum speckle channel at 500
nm. We witness two examples of magnetic flux cancellation of small-scale
opposite-polarity patches, followed by an enhanced chromospheric emission. In
each case, the two opposite-polarity patches gradually became smaller and,
within a few minutes, the smaller one completely disappeared. The larger patch
also diminished significantly. We provide evidence for a cancellation scenario
in the photosphere which leaves minor traces at the chromospheric level.",0712.0234v1
2007-12-05,"$θ_{13}$, $δ$ and the neutrino mass hierarchy at a $γ=350$ double baseline Li/B $β$-Beam","We consider a $\beta$-Beam facility where $^8$Li and $^8$B ions are
accelerated at $\gamma = 350$, accumulated in a 10 Km storage ring and let
decay, so as to produce intense $\bar \nu_e$ and $\nu_e$ beams. These beams
illuminate two iron detectors located at $L \simeq 2000$ Km and $L \simeq 7000$
Km, respectively. The physics potential of this setup is analysed in full
detail as a function of the flux. We find that, for the highest flux ($10
\times 10^{18}$ ion decays per year per baseline), the sensitivity to
$\theta_{13}$ reaches $\sin^2 2 \theta_{13} \geq 2 \times10^{-4}$; the sign of
the atmospheric mass difference can be identified, regardless of the true
hierarchy, for $\sin^2 2 \theta_{13} \geq 4\times10^{-4}$; and, CP-violation
can be discovered in 70% of the $\delta$-parameter space for $\sin^2 2
\theta_{13} \geq 10^{-3}$, having some sensitivity to CP-violation down to
$\sin^2 2 \theta_{13} \geq 10^{-4}$ for $|\delta| \sim 90^\circ$.",0712.0796v3
2007-12-06,Editorial: Statistics and forensic science,"Forensic science is usually taken to mean the application of a broad spectrum
of scientific tools to answer questions of interest to the legal system.
Despite such popular television series as CSI: Crime Scene Investigation and
its spinoffs--CSI: Miami and CSI: New York--on which the forensic scientists
use the latest high-tech scientific tools to identify the perpetrator of a
crime and always in under an hour, forensic science is under assault, in the
public media, popular magazines [Talbot (2007), Toobin (2007)] and in the
scientific literature [Kennedy (2003), Saks and Koehler (2005)]. Ironically,
this growing controversy over forensic science has occurred precisely at the
time that DNA evidence has become the ``gold standard'' in the courts, leading
to the overturning of hundreds of convictions many of which were based on
clearly less credible forensic evidence, including eyewitness testimony [Berger
(2006)].",0712.0974v1
2007-12-16,Evidence of magnetic field wrapping around penumbral filaments,"We employ high-spatial resolution spectropolarimetric observations from the
Solar Optical Telescope on-board the Hinode spacecraft to investigate the fine
structure of the penumbral magnetic fields. The Stokes vector of two neutral
iron lines at 630 nm is inverted at every spatial pixel to retrieve the
depth-dependence of the magnetic field vector, line-of-sight velocity and
thermodynamic parameters. We show that the azimuthal angle of the magnetic
field vector has opposite sign on both sides above the penumbral filaments.
This is consistent with the wrapping of an inclined field around the horizontal
filaments. The wrapping effect is stronger for filaments with larger horizontal
extensions. In addition, we find that the external magnetic field can penetrate
into the intraspines, leading to non-radial magnetic fields inside them. These
findings shed some light on the controversial small-scale structure of the
sunspot penumbra.",0712.2548v1
2007-12-18,Defect-induced ferromagnetism in fullerenes,"Based on the ab initio electronic structure calculations the picture of
ferromagnetism in polimerized C60 is proposed which seems to explain the whole
set of controversial experimental data. We have demonstrated that, in contrast
with cubic fullerene, in rhombohedral C60 the segregation of iron atoms is
energetically unprofitable which is a strong argument in favor of intrinsic
character of carbon ferromagnetism which can be caused by vacancies with
unpaired magnetic electrons. It is shown that: (i) energy formation of the
vacancies in the rhombohedral phase of C60 is essentially smaller than in the
cubic phase, (ii) there is a strong ferromagnetic exchange interactions between
carbon cages containing the vacancies, and (iii) the fusion of the magnetic
vacancies into nonmagnetic bivacancy is energetically profitable. The latter
can explain a fragility of the ferromagnetism.",0712.2928v2
2007-12-18,Metallicity estimates of Galactic Cepheids based on Walraven photometry,"We present new empirical and theoretical calibrations of two photometric
metallicity indices based on Walraven photometry. The empirical calibration
relies on a sample of 48 Cepheids for which iron abundances based on high
resolution spectra are available in the literature. They cover a broad range in
metal abundance (-0.5 < [Fe/H] < +0.5) and the intrinsic accuracy of the
Metallicity Index Color (MIC) relations is better than 0.2 dex. The theoretical
calibration relies on a homogeneous set of scaled-solar evolutionary tracks for
intermediate-mass stars and on pulsation predictions concerning the topology of
the instability strip. The metal content of the adopted evolutionary tracks
ranges from Z=0.001 to Z=0.03 and the intrinsic accuracy of the MIC relations
is better than 0.1 dex.",0712.3006v1
2007-12-20,Determining element abundances of [WC]-type Central Stars for probing stellar evolution and nucleosynthesis,"[WC]-type CSPNs are hydrogen-deficient Central Stars of Planetary Nebulae
showing strong stellar winds and a carbon-rich chemistry. We have analyzed new
high-resolution spectra of [WC]-type CSPNs with the Potsdam Wolf-Rayet (PoWR)
non-LTE expanding atmosphere models, using upgraded model atoms and atomic
data. Previous analyses are repeated on the basis of the current models which
account for iron-line blanketing. We especially focus on determining the
chemical composition, including some trace elements like nitrogen which are of
key importance for understanding the evolutionary origin of the
hydrogen-deficient Central Stars.",0712.3453v1
2007-12-21,Criteria for mixing rules application for inhomogeneous astrophysical grains,"The analysis presented in this paper verifies which of the mixing rules are
best for real components of interstellar dust in possible wide range of
wavelengths.The DDA method with elements of different components with various
volume fractions has been used. We have considered 6 materials: ice, amorphous
carbon, graphite, SiC, silicates and iron, and the following mixing rules:
Maxwell-Garnett, Bruggeman, Looyenga, Hanay and Lichtenecker which must satisfy
rigorous bounds. The porous materials have also been considered. We have
assumed simplified spatial distribution, shape and size of inclusions. The
criteria given by \citet{draine1988} have been used to determine the range of
wavelengths for the considered mixtures in order to calculate the ${\rm
Q_{ext}}$ using the DDA. From all chosen mixing rules for the examined
materials in majority of cases (13 out of 20) the best results have been
obtained using the Lichtenecker mixing rule. In 5 cases this rule is better for
some volume fraction of inclusions.",0712.3796v3
2008-01-01,A Self-Consistent NLTE-Spectra Synthesis Model of FeLoBAL QSOs,"We present detailed radiative transfer spectral synthesis models for the Iron
Low Ionization Broad Absorption Line (FeLoBAL) active galactic nuclei (AGN)
FIRST J121442.3+280329 and ISO J005645.1-273816. Detailed NLTE spectral
synthesis with a spherically symmetric outflow reproduces the observed spectra
very well across a large wavelength range. While exact spherical symmetry is
probably not required, our model fits are of high quality and thus very large
covering fractions are strongly implied by our results. We constrain the
kinetic energy and mass in the ejecta and discuss their implications on the
accretion rate. Our results support the idea that FeLoBALs may be an
evolutionary stage in the development of more ``ordinary'' QSOs.",0801.0321v2
2008-01-03,Spin orbit precession damping in transition metal ferromagnets,"We provide a simple explanation, based on an effective field, for the
precession damping rate due to the spin-orbit interaction. Previous effective
field treatments of spin-orbit damping include only variations of the state
energies with respect to the magnetization direction, an effect referred to as
the breathing Fermi surface. Treating the interaction of the rotating spins
with the orbits as a perturbation, we include also changes in the state
populations in the effective field. In order to investigate the quantitative
differences between the damping rates of iron, cobalt, and nickel, we compute
the dependence of the damping rate on the density of states and the spin-orbit
parameter. There is a strong correlation between the density of states and the
damping rate. The intraband terms of the damping rate depend on the spin-orbit
parameter cubed while the interband terms are proportional to the spin-orbit
parameter squared. However, the spectrum of band gaps is also an important
quantity and does not appear to depend in a simple way on material parameters.",0801.0549v1
2008-01-04,Could the Ultra Metal-poor Stars be Chemically Peculiar and Not Related to the First Stars?,"Chemically peculiar stars define a class of stars that show unusual elemental
abundances due to stellar photospheric effects and not due to natal variations.
In this paper, we compare the elemental abundance patterns of the ultra
metal-poor stars with metallicities [Fe/H] $\sim -5 $ to those of a subclass of
chemically peculiar stars. These include post-AGB stars, RV Tauri variable
stars, and the Lambda Bootis stars, which range in mass, age, binarity, and
evolutionary status, yet can have iron abundance determinations as low as
[Fe/H] $\sim -5$. These chemical peculiarities are interpreted as due to the
separation of gas and dust beyond the stellar surface, followed by the
accretion of dust depleted-gas. Contrary to this, the elemental abundances in
the ultra metal-poor stars are thought to represent yields of the most
metal-poor supernova and, therefore, observationally constrain the earliest
stages of chemical evolution in the Universe. The abundance of the elements in
the photospheres of the ultra metal-poor stars appear to be related to the
condensation temperature of that element; if so, then their CNO abundances
suggest true metallicities of [X/H]~ -2 to -4, rather than their present
metallicities of [Fe/H] < -5.",0801.0752v1
2008-01-14,The Effects of Mass Loss on the Evolution of Chemical Abundances in Fm Stars,"Self-consistent stellar models including all effects of atomic diffusion and
radiative accelerations as well as mass loss are evolved from the pre main
sequence for stars of 1.35-1.5, M$_{\odot}$ at solar metallicity (Z=0.02). A
mass loss rate similar to the solar mass loss rate is sufficient to reproduce
observations of the star $\tau$UMa. We discuss the effect of mass loss on the
iron convection zone that naturally appears beneath the main hydrogen
convection zone of these stars. We also find that the effects of mass loss can
be distinguished from those caused by turbulence, but are nevertheless able to
explain the particularities of the AmFm phenomenon.",0801.2122v1
2008-01-16,Observing the strong gravity regime of accreting black holes with Simbol-X,"The X-ray reflection features of irradiated accretion disks around black
holes enable us to probe the effects of strong gravity. We investigate to which
precision the reflection signs, i.e. the iron K-line and the Comptonized hump,
can be observed with Simbol-X for nearby Seyfert galaxies. The simulations
presented include accurate computations of the local reprocessed spectra and
modifications due to general relativistic effects in the vicinity of the black
hole. We discuss the impact of global black hole parameters and of the
irradiation pattern of the disk on the resulting spectra as they will be
detected by the Simbol-X mission.",0801.2450v2
2008-01-17,Abundances of Planetary Nebula NGC2392,"The spectra of the planetary nebula NGC2392 is reanalysed using spectral
measurements made in the mid-infrared with the Spitzer Space Telescope. The aim
is to determine the chemical composition of this object. We also make use of
IUE and ground based spectra. Abundances determined from the mid-infrared
lines, which are insensitive to electron temperature, are used as the basis for
the determination of the composition, which are found to differ somewhat from
earlier results. The abundances found, especially the low value of helium and
oxygen, indicate that the central star was originally of rather low mass.
Abundances of phosphorus, iron, silicon and chlorine have been determined for
the first time in this nebula. The variation of electron temperature in this
nebula is very clear reaching quite high values close to the center. The
temperature of the central star is discussed in the light of the high observed
stages of ionization. The nebular information indicates the spectrum of the
star deviates considerably from a blackbody.",0801.2767v1
2008-01-18,Spectra of W$^{39+}$-W$^{47+}$ in the 12 nm to 20 nm region observed with an EBIT light source,"We observed spectra of highly ionized tungsten in the extreme ultraviolet
with an electron beam ion trap (EBIT) and a grazing incidence spectrometer at
the National Institute of Standards and Technology. Stages of ionization were
distinguished by varying the energy of the electron beam between 2.1 keV and
4.3 keV and correlating the energies with spectral line emergence. The spectra
were calibrated by reference lines of highly ionized iron produced in the EBIT.
Identification of the observed lines was aided by collisional-radiative
modeling of the EBIT plasma. Good quantitative agreement was obtained between
the modeling results and the experimental observations. Our line
identifications complement recent results for W$^{40+}$-W$^{45+}$ observed in a
tokamak plasma by P\""{u}tterich {\it et al} (\jpb {\bf 38}, 3071, 2005). For
most lines we agree with their assignment of ionization stage. Additionally, we
present new identifications for some allowed and forbidden lines of W$^{39+}$,
W$^{44+}$, W$^{46+}$, and W$^{47+}$. The uncertainties of our wavelengths range
from 0.002 nm to 0.010 nm.",0801.2817v1
2008-01-24,"Accretion discs, coronae and jets in black hole binaries: prospects for Simbol-X","The phenomenology of accretion disc, coronnae and jets in X-ray binaries is
rather well established. However the structure of the accretion flow in the
various spectral states is still debated and the connection between the hot
flow and compact jet is far from being understood. Simbol-X should address
these two important questions in several ways. First, it will provide us with
the capability of producing high sensivity, broad band spectra and therefore
constrain simultaneously the shape and luminosity of all spectral components
(iron line, reflection bump, thermal disc and comptonised emission) which in
turn provides information on the geometry of the accretion flow. It will also
determine the exact contribution of jets to the X-ray band both in bright and
quiescent states. Finally it will shed new lights on the underlying mechanisms
triggering spectral state transitions by allowing us to follow in exquisite
details the rapid spectral evolution and its correlation with the radio jet
emission during those transitions.",0801.3767v1
2008-01-30,X-ray Emissions from Three-dimensional Magnetohydrodynamic Coronal Accretion Flows,"We calculate the radiation spectrum and its time variability of the black
hole accretion disk-corona system based on the three-dimensional
magnetohydrodynamic simulation. In explaining the spectral properties of active
galactic nuclei (AGNs), it is often assumed that they consist of a
geometrically thin, optically thick disk and hot, optically thin corona
surrounding the thin disk. As for a model of the corona, we adopt the
simulation data of three-dimensional, non-radiative MHD accretion flows
calculated by Kato and coworkers, while for a thin disk we assume a standard
type disk. We perform Monte Carlo radiative transfer simulations in the corona,
taking into account the Compton scattering of soft photons from the thin disk
by hot thermal electrons and coronal irradiation heating of the thin disk,
which emits blackbody radiation. By adjusting the density parameter of the MHD
coronal flow, we can produce the emergent spectra which are consistent with
those of typical Seyfert galaxies. Moreover, we find rapid time variability in
X-ray emission spectra, originating from the density fluctuation produced by
the magnetorotational instability in the MHD corona. The features of reflection
component including iron fluorescent line emission are also briefly discussed.",0801.4613v1
2008-01-30,Cosmic Ray Velocity and Electric Charge Measurements in the AMS experiment,"The Alpha Magnetic Spectrometer (AMS) is a particle physics detector designed
to measure charged cosmic ray spectra with energies up to the TeV region and
with high energy photon detection capability up to few hundred GeV. It will be
installed on the International Space Station (ISS) in 2008 and will operate for
more than three years. Due to its large acceptance, the flight duration and the
state-of-art of particle identification techniques, AMS will have a remarkable
sensitivity on antimatter and dark matter searches. The addition of different
detector systems provide AMS with complementary and redundant electric charge
and velocity measurements. The velocity of singly charged particles is expected
to be measured with a precision of 0.1% and charge separation up to iron is
attainable. The AMS capability of measuring a large range of electric charges
and accurate velocities, will largely contribute to a better understanding of
cosmic ray production, acceleration and propagation mechanisms in the galaxy.",0801.4656v1
2008-02-06,Chandra unveils a binary Active Galactic Nucleus in Mrk463,"We analyse Chandra, XMM-Newton and HST data of the double-nucleus
Ultraluminous Infrared Galaxy (ULIRG), Mrk463. The Chandra detection of two
luminous ($\mathrm{L}_\mathrm{2-10 keV}=1.5\times10^{43}$ and
$3.8\times10^{42}$ erg cm$^{-2}$ s$^{-1}$), unresolved nuclei in Mrk~463
indicates that this galaxy hosts a binary AGN, with a projected separation of
$\simeq3.8$ kpc ($3.83\pm0.01$ arcsec). While the East nucleus was already
known to be a Seyfert 2 (and this is further confirmed by our Chandra detection
of a neutral iron line), this is the first unambiguous evidence in favour of
the AGN nature of the West nucleus. Mrk463 is therefore the clearest case so
far for a binary AGN, after NGC6240.",0802.0825v1
2008-02-12,Detection of supernovae neutrinos with neutrino-iron scattering,"The $\nu_e-^{56}$Fe cross section is evaluated in the projected quasiparticle
random phase approximation (PQRPA). This model solves the puzzle observed in
RPA for nuclei with mass around $^{12}$C, because it is the only RPA model that
treats the Pauli principle correctly. The cross sections as a function of the
incident neutrino energy are compared with recent theoretical calculations of
similar models. The average cross section weighted with the flux spectrum
yields a good agreement with the experimental data. The expected number of
events in the detection of supernova neutrinos is calculated for the LVD
detector leading to an upper limit for the electron neutrino energy of
particular importance in this experiment",0802.1553v2
2008-02-12,Giant orbital moments are responsible for the anisotropic magnetoresistance of atomic contacts,"We study here, both experimentally and theoretically, the anisotropy of
magnetoresistance in atomic contacts. Our measurements on iron break junctions
reveal an abrupt and hysteretic switch between two conductance levels when a
large applied field is continuously rotated. We show that this behaviour stems
from the coexistence of two metastable electronic states which result from the
anisotropy of electronic interactions responsible for the enhancement of
orbital magnetization. In both states giant orbital moments appear on the low
coordinated central atom in a realistic contact geometry. However they differ
by their orientation, parallel or perpendicular, with respect to the axis of
the contact. Our explanation is totally at variance with the usual model based
on the band structure of a monatomic linear chain, which we argue cannot be
applied to 3d ferromagnetic metals.",0802.1595v1
2008-02-12,Electronic transport in iron atomic contacts: from the infinite wire to realistic geometries,"We present a theoretical study of spin polarized transport in Fe atomic
contacts using a self-consistent tight-binding Hamiltonian in a non-orthogonal
$s$, $p$ and $d$ basis set, the spin-polarization being obtained from a
non-collinear Stoner-like model and the transmission probability from the
Fisher-Lee formula. The behaviour of an infinite perfect Fe wire is compared
with that of an infinite chain presenting geometric defects or magnetic walls
and with that of a finite chain connected to infinite one-dimensional or
three-dimensional leads. In the presence of defects or contacts the
transmission probability of $d$ electrons is much more affected than that of
$s$ electrons, in particular, contact effects may suppress some transmission
channels. It is shown that the behaviour of an infinite wire is never obtained
even in the limit of long chains connected to electrodes. The introduction of
the spin-orbit coupling term in the Hamiltonian enables us to calculate the
anisotropy of the magneto-resistance. Finally whereas the variation of the
magneto-resistance as a function of the magnetization direction is step-like
for an infinite wire, it becomes smooth in the presence of defects or contacts.",0802.1598v1
2008-02-28,On the Cepheid Metallicity Dichotomy,"With the aid of stellar atmosphere models, we derive iron abundances [Fe/H]
from the OGLE B, V, I photometry on the Magellanic Cloud Cepheids. We show that
in both clouds the average metallicities of the first overtone variables are
lower than those of the fundamental ones (by ~0.2 and ~0.3 dex in the LMC and
SMC, respectively). Consequently, there is a correlation between the overall
[Fe/H] and luminosity; the lower luminosity stars tend to be also of lower
metallicity. These metallicity dependencies are concordant with the ones
derived for the two types of double-mode Cepheids from pulsation theory. Yet
another support of this dichotomy comes from the evolution theories that
require lower metallicities for blue-looping low-luminosity stars than for
high-luminosity ones. We also comment on the possibility of using
period-luminosity-color relations to derive more accurate metallicities.",0802.4166v1
2008-03-04,Magneto-Dielectric phenomena in charge and spin frustrated system of layered iron oxide,"Dielectric and magnetic phenomena in spin and charge frustrated system RFe2O4
(R is a rare-earth metal ion) are studied. An electronic model for charge, spin
and orbital degrees in a pair of triangular-lattice planes is derived. We
analyze this model by utilizing the mean-field approximation and the
Monte-Carlo simulation in a finite size cluster. A three fold-type charge
ordered structure with charge imbalance between the planes is stabilized in
finite temperatures. This polar charge order is reinforced by spin ordering of
Fe ions. This novel magneto-dielectric phenomenon is caused by spin frustration
and charge-spin coupling in the exchange interaction. We show cross-correlation
effect in magnetic- and electric-field responses. Oxygen deficiency effect as
an impurity effect in a frustrated charge-spin coupled system is also examined.",0803.0394v1
2008-03-04,Light Vector Mesons in the Nuclear Medium,"The light vector mesons ($\rho$, $\omega$, and $\phi$) were produced in
deuterium, carbon, titanium, and iron targets in a search for possible
in-medium modifications to the properties of the $\rho$ meson at normal nuclear
densities and zero temperature. The vector mesons were detected with the CEBAF
Large Acceptance Spectrometer (CLAS) via their decays to $e^{+}e^{-}$. The rare
leptonic decay was chosen to reduce final-state interactions. A combinatorial
background was subtracted from the invariant mass spectra using a
well-established event-mixing technique. The $\rho$ meson mass spectrum was
extracted after the $\omega$ and $\phi$ signals were removed in a nearly
model-independent way. Comparisons were made between the $\rho$ mass spectra
from the heavy targets ($A > 2$) with the mass spectrum extracted from the
deuterium target. With respect to the $\rho$-meson mass, we obtain a small
shift compatible with zero. Also, we measure widths consistent with standard
nuclear many-body effects such as collisional broadening and Fermi motion.",0803.0492v1
2008-03-05,Hall effect and magnetoresistance in the normal state of the superconductor LaO$_{0.9}$F$_{0.1-x}$FeAs,"By using a two-step method, we successfully synthesized the iron based new
superconductor LaO$_{0.9}$F$_{0.1-x}$FeAs. The Hall effect and
magnetoresistance were measured in wide temperature region. A negative Hall
coefficient R_H has been found implying a dominant conduction by electron-like
charge carriers in this material. The charge carrier density determined at 100K
is about 9.8E20 cm-3, which is close to the cuprate superconductors. It is
further found that the magnetoresistance does not follow the Kohler's law.
Meanwhile, the Hall coefficient, the resistivity at 0T, and magnetoresistance
all have an anomalous property at about 240K, which may be induced by the
multi-band effect or by some exotic scattering mechanism.",0803.0623v3
2008-03-06,Properties of the ultraviolet flux of type Ia supernovae: an analysis with synthetic spectra of SN 2001ep and SN 2001eh,"The spectral properties of type Ia supernovae in the ultraviolet (UV) are
investigated using the early-time spectra of SN 2001ep and SN 2001eh obtained
using the Hubble Space Telescope (HST). A series of spectral models is computed
with a Monte Carlo spectral synthesis code, and the dependence of the UV flux
on the elemental abundances and the density gradient in the outer layers of the
ejecta is tested. A large fraction of the UV flux is formed by reverse
fluorescence scattering of photons from red to blue wavelengths. This process,
combined with ionization shifts due to enhanced line blocking, can lead to a
stronger UV flux as the iron-group abundance in the outer layers is increased,
contrary to previous claims.",0803.0871v2
2008-03-06,Tight-Binding Theory of Manganese and Iron Oxides,"The electronic structure is found to be understandable in terms of free-atom
term values and universal interorbital coupling parameters, since
self-consistent tight-binding calculations indicate that Coulomb shifts of the
d-state energies are small. Special-point averages over the bands are seen to
be equivalent to treatment of local octahedral clusters. The cohesive energy
per manganese for MnO, Mn2O3, and MnO2, in which manganese exists in valence
states Mn2+, Mn3+, and Mn4+, is very nearly the same and dominated by the
transfer of manganese s electrons to oxygen p states. There are small
corrections, one eV per Mn in all cases, from couplings of minority-spin
states. Transferring one majority-spin electron from an upper cluster state to
a nonbonding oxygen state adds 1.67 eV to the cohesion for Mn2O3, and two
transfers adds twice that for MnO2 . The electronic and magnetic properties are
consistent with this description and appear to be understandable in terms of
the same parameters.",0803.0994v1
2008-03-17,Point-Contact Spectroscopy of Iron-Based Layered Superconductor LaO$_{0.9}$F$_{0.1-δ}$FeAs,"We present point-contact spectroscopy data for junctions between a normal
metal and the newly discovered F-doped superconductor
LaO$_{0.9}$F$_{0.1-\delta}$FeAs (F-LaOFeAs). A zero-bias conductance peak was
observed and its shape and magnitude suggests the presence of Andreev bound
states at the surface of F-LaOFeAs, which provides a possible evidence of an
unconventional pairing symmetry with a nodal gap function. The maximum gap
value $\Delta_0\approx3.9\pm0.7$meV was determined from the measured spectra,
in good agreement with the recent experiments on specific heat and lower
critical field.",0803.2405v3
2008-03-20,Bimodality in low luminosity E and S0 galaxies,"Stellar population characteristics are presented for a sample of low
luminosity early-type galaxies (LLEs) in order to compare them with their more
luminous counterparts. Long-slit spectra of a sample of 10 LLEs were taken with
the ESO New Technology Telescope, selected for their low luminosities. Line
strengths were measured on the Lick standard system. Lick indices for these
LLEs were correlated with velocity dispersion (sigma), alongside published data
for a variety of Hubble types. The LLEs were found to fall below an
extrapolation of the correlation for luminous ellipticals and were consistent
with the locations of spiral bulges in plots of line strengths versus sigma.
Luminosity weighted average ages, metallicities and abundance ratios were
estimated from chi-squared fitting of 19 Lick indices to predictions from
simple stellar population models. The LLEs appear younger than luminous
ellipticals and of comparable ages to spiral bulges. These LLEs show a bimodal
metallicity distribution, consisting of a low metallicity group (possibly
misclassified dwarf spheroidal galaxies) and a high metallicity group (similar
to spiral bulges). Finally, they have low alpha-element to iron-peak abundance
ratios indicative of slow, extended star formation.",0803.3025v1
2008-03-22,Iron-based layered superconductor LaO$_{1-x}$F$_x$FeAs: an antiferromagnetic semimetal,"We have studied the newly found superconductor compound LaO$_{1-x}$F$_x$FeAs
through the first-principles density functional theory calculations. We find
that the parent compound LaOFeAs is a quasi-2-dimensional antiferromgnetic
semimetal with most carriers being electrons and with a magnetic moment of
$2.3\mu_B$ located around each Fe atom on the Fe-Fe square lattice. Furthermore
this is a commensurate antiferromagnetic spin density wave due to the Fermi
surface nesting, which is robust against the F-doping. The observed
superconduction happens on the Fe-Fe antiferromagnetic layer, suggesting a new
superconductivity mechanism, mediated by the spin fluctuations. An abrupt
change on the Hall measurement is further predicted for the parent compound
LaOFeAs.",0803.3286v1
2008-03-23,Unconventional pairing originating from disconnected Fermi surfaces in superconducting LaFeAsO$_{1-x}$F$_x$},"For a newly discovered iron-based high $T_c$ superconductor
LaFeAsO$_{1-x}$F$_x$, we have constructed a minimal model, where inclusion of
all the five Fe $d$ bands is found to be necessary. Random-phase approximation
is applied to the model to investigate the origin of superconductivity. We
conclude that the multiple spin fluctuation modes arising from the nesting
across the disconnected Fermi surfaces realize an extended s-wave pairing,
while d-wave pairing can also be another candidate.",0803.3325v2
2008-03-24,Fast Variability of Nonthermal X-Ray Emission in Cassiopeia A: Probing Electron Acceleration in Reverse-Shocked Ejecta,"Recent discovery of the year-scale variability in the synchrotron X-ray
emission of the supernova remnant (SNR) RX J1713.7-3946 has initiated our study
of multi-epoch X-ray images and spectra of the young SNR Cassiopeia A based on
the Chandra archive data taken in 2000, 2002, and 2004. We have found
year-scale time variations in the X-ray intensity for a number of X-ray
filaments or knots associated with the reverse-shocked regions. The X-ray
spectra of the variable filaments are characterized by a featureless continuum,
and described by a power law with a photon index within 1.9-2.3. The upper
limits on the iron K-line equivalent width are 110 eV, which favors a
synchrotron origin of the X-ray emission. The characteristic variability
timescale of 4 yr can be explained by the effects of fast synchrotron cooling
and diffusive shock acceleration with a plausible magnetic field of 1 mG. The
X-ray variability provides a new effective way of studying particle
acceleration at supernova shocks.",0803.3410v1
2008-03-24,Atomic Processes in Planetary Nebulae and H II Regions,"Spectroscopic studies of Planetary Nebulae (PNe) and H {\sc ii} regions have
driven much development in atomic physics. In the last few years the
combination of a generation of powerful observatories, the development of ever
more sophisticated spectral modeling codes, and large efforts on mass
production of high quality atomic data have led to important progress in our
understanding of the atomic spectra of such astronomical objects. In this paper
I review such progress, including evaluations of atomic data by comparisons
with nebular spectra, detection of spectral lines from most iron-peak elements
and n-capture elements, observations of hyperfine emission lines and analysis
of isotopic abundances, fluorescent processes, and new techniques for
diagnosing physical conditions based on recombination spectra. The review is
directed toward atomic physicists and spectroscopists trying to establish the
current status of the atomic data and models and to know the main standing
issues.",0803.3457v1
2008-03-25,The effect of rotation on the abundances of the chemical elements of the A-type stars in the Praesepe cluster,"We study how chemical abundances of late B-, A- and early F-type stars evolve
with time, and we search for correlations between the abundance of chemical
elements and other stellar parameters, such as effective temperature and Vsini.
We have observed a large number of B-, A- and F-type stars belonging to open
clusters of different ages. In this paper we concentrate on the Praesepe
cluster (log t = 8.85), for which we have obtained high resolution, high
signal-to-noise ratio spectra of sixteen normal A- and F-type stars and one Am
star, using the SOPHIE spectrograph of the Observatoire de Haute-Provence. For
all the observed stars, we have derived fundamental parameters and chemical
abundances. In addition, we discuss another eight Am stars belonging to the
same cluster, for which the abundance analysis had been presented in a previous
paper. We find a strong correlation between peculiarity of Am stars and Vsini.
The abundance of the elements underabundant in Am stars increases with Vsini,
while it decreases for the overabundant elements. Chemical abundances of
various elements appear correlated with the iron abundance.",0803.3540v1
2008-03-26,Realistic calculations of nuclear disappearance lifetimes induced by neutron-antineutron oscillations,"Realistic calculations of nuclear disappearance lifetimes induced by
neutron-antineutron oscillations are reported for oxygen and iron, using
antineutron nuclear potentials derived from a recent comprehensive analysis of
antiproton atomic X-ray and radiochemical data. A lower limit of 3.3 x 10E8 s
on the neutron-antineutron oscillation time is derived from the
Super-Kamiokande I new lower limit of 1.77 x 10E32 yr on the neutron lifetime
in oxygen. Antineutron scattering lengths in carbon and nickel, needed in trap
experiments using ultracold neutrons, are calculated from updated antinucleon
optical potentials at threshold, with results shown to be largely model
independent.",0803.3696v3
2008-03-29,Superconductivity at 52 K in iron-based F-doped layered quaternary compound Pr[O1-xFx]FeAs,"Since the discovery of copper oxide superconductor in 1986 [1], extensive
efforts have been devoted to the search of new high-Tc superconducting
materials, especially high-Tc systems other than cuprates. The recently
discovered quaternary superconductor La[O1-xFx]FeAs with the superconducting
critical transition Tc of 26 K [2], which has a much simple layered structure
compared with cuprates, has attracted quick enthusiasm and is going to become a
new high-Tc system [3-6]. Here we report the discovery of bulk
superconductivity in the praseodymium-arsenide oxides Pr[O1-xFx]FeAs with an
onset drop of resistivity as high as 52 K, and the unambiguous zero-resistivity
and Meissner transition at low temperature, which will place these quaternary
compounds to another high-Tc superconducting system explicitly.",0803.4283v1
2008-04-01,Structural identification of cubic iron-oxide nanocrystal mixtures: X-ray powder diffraction versus quasi-kinematic transmission electron microscopy,"Two novel (and proprietary) strategies for the structural identification of a
nanocrystal from either a single high-resolution (HR) transmission electron
microscopy (TEM) image or a single precession electron diffraction pattern are
proposed and their advantages discussed in comparison to structural
fingerprinting from powder X-ray diffraction patterns. Simulations for cubic
magnetite and maghemite nanocrystals are used as examples. This is an expanded
and updated version of a conference paper that has been published in Suppl.
Proc. of TMS 2008, 137th Annual Meeting & Exhibition, Volume 1, Materials
Processing and Properties, pp. 25-32.",0804.0063v1
2008-04-06,"Mott State and Quantum Critical Points in Rare-Earth Oxypnictides $RO_{1-x}F_xFeAs$ ($R=La, Sm, Nd, Pr, Ce$)","We investigate the magnetic phase diagram of the newly discovered iron-based
high temperature oxypnictide superconductors of the type RO$_{1-x}$F$_x $FeAs,
with rare earths R=La, Sm, Nd, Pr and Ce by means of {\it ab initio} SGGA and
SGGA+U density functional computations. We find undoped LaOFeAs to be a Mott
insulator when incorporating electronic correlations via SGGA+U for any
physically relevant value of $U$. The doped compounds are according to SGGA
conductors with a transition from an antiferromagnetic to a non-magnetic state
at a hole doping of concentration $x_c$=0.075 for R=Nd, Pr and at electron
doping $x_c$=0.25 for Ce and 0.6 for Sm. Superconductivity in these rare-earth
oxypnictides thus appears in the vicinity of a magnetic quantum critical point
where electronic correlations are expected to play an important role because of
the vicinity of a Mott insulating state at zero doping.",0804.0866v3
2008-04-07,The Wall and The Ball: A Study of Domain Referent Spreadsheet Errors,"The Cell Error Rate in simple spreadsheets averages about 2% to 5%. This CER
has been measured in domain free environments. This paper compares the CERs
occurring in domain free and applied domain tasks. The applied domain task
requires the application of simple linear algebra to a costing problem. The
results show that domain referent knowledge influences participants' approaches
to spreadsheet creation and spreadsheet usage. The conclusion is that
spreadsheet error making is influenced by domain knowledge and domain
perception. Qualitative findings also suggest that spreadsheet error making is
a part of overall human behaviour, and ought to be analyzed against this wider
canvas.",0804.0943v1
2008-04-10,Theory of magnetic excitations in iron-based layered superconductors,"Based on the effective four-band model we analyze the spin response in the
normal and superconducting states of the Fe-pnictide superconductors. While the
normal state spin excitations are dominated by the continuum of the
interorbital antiferromagnetic fluctuations and the intraband spin density wave
fluctuations, the unconventional superconductivity yields different feedback.
The resonance peak in form of the well-defined spin exciton occurs {\it only}
for the interband scattering at the antiferromagnetic momentum ${\bf Q}_{AFM}$
for the $s_\pm$ (extended s-wave) superconducting order parameter and it
disappears rapidly for ${\bf q} < {\bf Q}_{AFM}$. The resonance feature is
extremely weak for the $d_{x^2 -y^2}$-wave order parameter due to specific
Fermi surface topology of these compounds. The essential difference between
$s_\pm$-wave and $d_{x^2 -y^2}$-wave symmetries for the magnetic excitations
can be used for experimental determination of the superconducting wave function
symmetry.",0804.1793v2
2008-04-16,Superconductivity and Phase Diagram in the Iron-based Arsenic-oxides ReFeAsO1-delta (Re = rare earth metal) without F-Doping,"Here we report a new class of superconductors prepared by high pressure
synthesis in the quaternary family ReFeAsO1-delta (Re = Sm, Nd, Pr, Ce, La)
without fluorine doping. The onset superconducting critical temperature (Tc) in
these compounds increases with the reduction of Re atom size, and the highest
Tc obtained so far is 55 K in SmFeAsO1-delta. For the NdFeAsO1-delta system
with different oxygen concentration a dome-shaped phase diagram was found.",0804.2582v3
2008-04-21,Probing protoneutron star density profile from neutrino signals,"Supernovae of Type II is a phenomenon that occurs at the end of evolution of
massive stars when the iron core of the star exceeds a mass limit. After
collapse of the core under gravity the shock wave alone does not succeed in
expelling the mass of the star and in this sense the role of neutrinos is the
most important mechanism to do so. During the emission of neutrinos flavor
conversion is possible, related the phenomenon of oscillations, which however
depends directly on the particular density profile of the medium. In this paper
we present results of numerical simulations of neutrino flavor conversion in
protoneutron stars and after collapse. The probabilities of survival for a
given flavor in a complete three-flavors framework is estimated through an
algorithm which conserves unitarity to a high degree of accuracy. The
sensitivity of the results to the different adopted models for the protoneutron
star structure is examined in detail demonstrating how the neutrino signal
could be used to check the validity of models.",0804.3247v1
2008-04-23,Superconductivity at 53.5 K in GdFeAsO1-delta,"Here we report the fabrication and superconductivity of the iron-based
arsenic-oxide GdFeAsO1-delta compound with oxygen-deficiency, which has an
onset resistivity transition temperature at 53.5 K. This material has a same
crystal structure as the newly discovered high-Tc ReFeAsO1-delta family (Re =
rare earth metal) and a further reduced crystal lattice, while the Tc starts to
decrease compared with the SmFeAsO1-delta system.",0804.3727v3
2008-04-28,Thorium-doping induced superconductivity up to 56 K in Gd1-xThxFeAsO,"Following the discovery of superconductivity in an iron-based arsenide
LaO1-xFxFeAs with a superconducting transition temperature (Tc) of 26 K[1], Tc
was pushed up surprisingly to above 40 K by either applying pressure[2] or
replacing La with Sm[3], Ce[4], Nd[5] and Pr[6]. The maximum Tc has climbed to
55 K, observed in SmO1-xFxFeAs[7, 8] and SmFeAsO1-x[9]. The value of Tc was
found to increase with decreasing lattice parameters in LnFeAsO1-xFx (Ln stands
for the lanthanide elements) at an apparently optimal doping level. However,
the F- doping in GdFeAsO is particularly difficult[10,11] due to the lattice
mismatch between the Gd2O2 layers and Fe2As2 layers. Here we report observation
of superconductivity with Tc as high as 56 K by the Th4+ substitution for Gd3+
in GdFeAsO. The incorporation of relatively large Th4+ ions relaxes the lattice
mismatch, hence induces the high temperature superconductivity.",0804.4290v2
2008-05-02,Commensurate Spin Density Wave in LaOFeAs: A Local Probe Study,"We present a detailed study on the magnetic order in the undoped mother
compound LaOFeAs of the recently discovered Fe-based superconductor
LaO$_{1-x}$F$_x$FeAs. In particular, we present local probe measurements of the
magnetic properties of LaOFeAs by means of $^{57}$Fe M\""ossbauer spectroscopy
and muon spin relaxation in zero external field along with magnetization and
resistivity studies. These experiments prove a commensurate static magnetic
order with a strongly reduced ordered moment of 0.25(5) $\mu_B$ at the iron
site below T_N = 138 K, well separated from a structural phase transition at
T_N = 156 K. The temperature dependence of the sublattice magnetization is
determined and compared to theory. Using a four-band spin density wave model
both, the size of the order parameter and the quick saturation below T_N are
reproduced.",0805.0264v2
2008-05-06,Flux-lattice melting in LaO$_{1-x}$F$_{x}$FeAs: first-principles prediction,"We report the theoretical study of the flux-lattice melting in the novel
iron-based superconductor $LaO_{0.9}F_{0.1}FeAs$ and
$LaO_{0.925}F_{0.075}FeAs$. Using the Hypernetted-Chain closure and an
efficient algorithm, we calculate the two-dimensional one-component plasma pair
distribution functions, static structure factors and direct correlation
functions at various temperatures. The Hansen-Verlet freezing criterion is
shown to be valid for vortex-liquid freezing in type-II superconductors.
Flux-lattice meting lines for $LaO_{0.9}F_{0.1}FeAs$ and
$LaO_{0.925}F_{0.075}FeAs$ are predicted through the combination of the density
functional theory and the mean-field substrate approach.",0805.0632v2
2008-05-06,Pulsation-Initiated Mass Loss in Luminous Blue Variables: A Parameter Study,"Luminous blue variables (LBVs) are characterized by semi-periodic episodes of
enhanced mass-loss, or outburst. The cause of these outbursts has thus far been
a mystery. One explanation is that they are initiated by kappa-effect
pulsations in the atmosphere caused by an increase in luminosity at
temperatures near the so-called ``iron bump'' (T ~ 200,000 K), where the Fe
opacity suddenly increases. Due to a lag in the onset of convection, this
luminosity can build until it exceeds the Eddington limit locally, seeding
pulsations and possibly driving some mass from the star. We present some
preliminary results from a parameter study focusing on the conditions necessary
to trigger normal S-Dor type (as opposed to extreme eta-Car type) outbursts. We
find that as Y increases or Z decreases, the pulsational amplitude decreases
and outburst-like behavior, indicated by a large, sudden increase in
photospheric velocity, becomes likes likely.",0805.0764v1
2008-05-07,Processing and Characterization of Precision Microparts from Nickel-based Materials,"The objective of this research was to study the influence of electroplating
parameters on electrodeposit characteristics for the production of nickel (Ni)
and nickel-iron (Ni-Fe) microparts by photoelectroforming. The research focused
on the most relevant parameter for industry, which is the current density,
because it determines the process time and the consumed energy. The results of
the Ni and Ni-Fe characterisations can be divided into two aspects closely
linked with each other ; the morphology and the hardness.",0805.0866v1
2008-05-09,Evidence for electromagnetic granularity in the polycrystalline iron-based superconductor LaO0.89F0.11FeAs,"The new rare-earth arsenate superconductors are layered, low carrier density
compounds with many similarities to the high-Tc cuprates. An important question
is whether they also exhibit weak-coupling across randomly oriented
grain-boundaries. In this work we show considerable evidence for such
weak-coupling by study of the dependence of magnetization in bulk and powdered
samples. Bulk sample magnetization curves show very little hysteresis while
remanent magnetization shows almost no sample size dependence, even after
powdering. We conclude that these samples exhibit substantial electromagnetic
granularity on a scale approximating the grain size, though we cannot yet
determine whether this is intrinsic or extrinsic.",0805.1282v1
2008-05-12,MOST detects SPBe pulsations in HD 127756 & HD 217543: Asteroseismic rotation rates independent of vsini,"The MOST (Microvariability and Oscillations of Stars) satellite has
discovered SPBe (Slowly Pulsating Be) oscillations in the stars HD 127756
(B1/B2 Vne) and HD 217543 (B3 Vpe). For HD 127756, 30 significant frequencies
are identified from 31 days of nearly continuous photometry; for HD 217543, up
to 40 significant frequencies from 26 days of data. In both cases, the
oscillations fall into three distinct frequency ranges, consistent with models
of the stars. The variations are caused by nonradial g-modes (and possibly
r-modes) distorted by rapid rotation and excited by the opacity mechanism near
the iron opacity bump. A comparison of pulsation models and observed frequency
groups yields a rotation frequency for each star, independently of vsini. The
rotation rates of these stars, as well as those of the SPBe stars previously
discovered by MOST, HD 163868 and $\beta$ CMi, are all close to their critical
values.",0805.1720v1
2008-05-14,Intrinsic Properties of Stoichiometric LaOFeP,"DC and ac magnetization, resistivity, specific heat, and neutron diffraction
data reveal that stoichiometric LaOFeP is metallic and non-superconducting
above T = 0.35 K, with gamma = 12.5 mJ/mol*K. Neutron diffraction data at room
temperature and T = 10 K are well described by the stoichiometric, tetragonal
ZrCuSiAs structure and show no signs of structural distortions or long range
magnetic ordering, to an estimated detectability limit of 0.07 uB/Fe. We
propose a model, based on the shape of the iron-pnictide tetrahedron, that
explains the differences between LaOFeP and LaOFeAs, the parent compound of the
recently discovered high-Tc oxyarsenides, which, in contrast, shows both
structural and spin density wave (SDW) transitions.",0805.2149v1
2008-05-14,Theory of the Magnetic Moment in Iron Pnictides,"We show that the combined effects of spin-orbit, monoclinic distortion, and
p-d hybridization in tetrahedrally coordinated Fe in LaOFeAs invalidates the
naive Hund's rule filling of the Fe d-levels. The two highest occupied levels
have one electron each but as a result of the p-d hybridization have very
different on-site repulsions. As a result, electrons in the upper level are
more itinerant while those in the lower level are more localized. It is the
xy-projection of the spin in the lower level that orders antiferromagnetically
as the z-components of the spins in the two levels is shown to be vanishingly
small in the ground state. The resulting magnetic moment is highly anisotropic
with an in-plane value of $0.25-0.35\mu_B$ per Fe and a z-projection of
$0.06\mu_B$, both of which are in agreement with experiment. As a consequence,
we arrive the minimal model that describes the electronic properties of
LaOFeAs.",0805.2167v2
2008-05-14,"MuSR studies of RE(O,F)FeAs (RE = La, Nd, Ce) and LaOFeP systems: possible incommensurate/stripe magnetism and superfluid density","Muon spin relaxation (MuSR) measurements in iron oxy-pnictide systems have
revealed: (1) commensurate long-range order in undoped LaOFeAs; (2) Bessel
function line shape in La(O0.97F0.03)FeAs which indicates possible
incommensurate or stripe magnetism; (3) anomalous weak magnetism existing in
superconducting LaOFeP, Ce(O0.84F0.16)FeAs, and Nd(O0.88F0.12)FeAs but absent
in superconducting La(O0.92F0.08)FeAs; and (4) scaling of superfluid density
and Tc in the Ce, La, and Nd-FeAs superconductors following a nearly linear
relationship found in cuprates.",0805.2186v1
2008-05-19,Suzaku Observation of Group of Galaxies NGC 507: Temperature and Metal Distributions in the Intra-cluster Medium,"Temperature and abundance distributions of the intra-cluster medium (ICM) in
the NGC 507 group of galaxies were studied with Suzaku. Observed concentric
annular spectra were well-represented by a two temperature model for ICM, and
we found steeper abundance gradients for Mg, Si, S, and Fe compared with O in
the central region. Abundance ratios of alpha-elements to iron were found to be
similar to those in other groups and poor clusters. We calculated metal
mass-to-light ratios for Fe, O and Mg (IMLR, OMLR, MMLR) for NGC 507, and
values for different systems were compared. Hotter and richer systems tend to
show higher values of IMLR, OMLR, and MMLR. OMLR and MMLR were measured to an
outer region for the first time with Suzaku, while IMLR was consistent with
that with ASCA. We also looked into 2-dimensional map of the hardness ratio,
but found no significant deviation from the circular symmetry.",0805.2771v1
2008-05-19,Impact of impellers on the axisymmetric magnetic mode in the VKS2 dynamo experiment,"In the VKS2 (von K\'arm\'an Sodium 2) successful dynamo experiment of
September 2006, the magnetic field that was observed showed a strong
axisymmetric component, implying that non axisymmetric components of the flow
field were acting. By modeling the induction effect of the spiraling flow
between the blades of the impellers in a kinematic dynamo code, we find that
the axisymmetric magnetic mode is excited and becomes dominant in the vicinity
of the dynamo threshold. % The control parameters are the magnetic Reynolds
number of the mean flow, the coefficient measuring the induction effect,
$\alpha$, and the type of boundary conditions (vacuum for steel impellers and
normal field for soft iron impellers). We show that using realistic values of
$\alpha$, the observed critical magnetic Reynolds number, $Rm^c \approx 32$,
can be reached easily with ferromagnetic boundary conditions. We conjecture
that the dynamo action achieved in this experiment may not be related to the
turbulence in the bulk of the flow, but rather to the alpha effect induced by
the impellers.",0805.2805v2
2008-05-19,Electromagnetic properties and electronic structure of iron-based layered superconductor LaOFeP,"Structural, electronic, and magnetic properties of undoped and aliovalent-ion
(Ca, F)-doped LaOFeP, which undergo superconducting transitions at transition
temperatures (Tc) 4-7 K [Kamihara et al, J. Am. Chem. Soc. 128, 10012, (2006)],
were investigated. Tc of the samples varied from 2.4 to 5.5 K in the undoped
samples, and was increased up to ~7 K by Ca- and F-doping. The Tc increases are
correlated with a decrease in the lattice volume. LaOFeP exhibits paramagnetism
in the normal conducting state. Photoemission spectroscopy combined with
first-principle band calculations clarified that Fe 3d (dz2 + (dxz, dyz))
orbitals hybridized with P 3p to form a Fermi surface. The band calculations
also suggest that the 3d electron of the Fe in LaOFeP is basically in the
low-spin configuration, and that the spin moment of LaOFeP is almost quenched,
leading to the paramagnetism of the itinerant electrons.",0805.2983v1
2008-05-21,A Numerical Renormalization Group Study of the Superconducting and Spin Density Wave Instabilities in MFeAsO$_{1-x}$F$_x$ Compounds,"We apply the fermion renormalization group method, implemented numerically by
Honerkamp et.al., to a two-band model of FeAs-based materials. At half filling
we find the $(\pi,0)$ or $(0,\pi)$ spin density wave order and a sub-dominant
superconducting pairing tendency. Due to a topological reason, the spin density
wave gap has nodes on the fermi surfaces. Away from half filling we find an
unconventional s-wave and a sub-dominant $d_{x^2-y^2}$ pairing instability. The
former has $s$ symmetry around the hole fermi surface but exhibits
$s+d_{x^2-y^2}$ symmetry around the electron pockets where the 90 degree
rotation is broken. The pairing mechanism is inter-pocket pair hopping.
Interestingly, the same interaction also drives the antiferromagnetism.",0805.3343v3
2008-05-22,Pseudogap Value in the Energy Spectrum of LaOFeAs: Fixed Spin Moment Treatment,"The experimental data available up to date in literature corresponding to the
paramagnetic - spin density wave transition in nonsuperconducting LaOFeAs are
discussed. In particular, we pay attention that upon spin density wave
transition there is a relative decrease of the density of states on the Fermi
level and a pseudogap formation. The values of these quantities are not
properly described in frames of the density functional theory. The agreement of
them with experimental estimations becomes more accurate with the use of fixed
spin moment procedure when iron spin moment is set to experimental value.
Strong electron correlations which are not included into the present
calculation scheme may lead both to the decrease of spin moment and
renormalization of energy spectrum in the vicinity of the Fermi level for
correct description of discussed characteristics.",0805.3453v1
2008-05-22,The Araucaria Project: the Local Group Galaxy WLM--Distance and metallicity from quantitative spectroscopy of blue Supergiants,"The quantitative analysis of low resolution spectra of A and B supergiants is
used to determine a distance modulus of 24.99 +/- 0.10 mag (995 +/- 46 Kpc) to
the Local Group galaxy WLM. The analysis yields stellar effective temperatures
and gravities, which provide a distance through the Flux weighted
Gravity--Luminosity Relationship (FGLR). Our distance is 0.07 mag larger than
the most recent results based on Cepheids and the tip of the RGB. This
difference is within the 1-sigma overlap of the typical uncertainties quoted in
these photometric investigations. In addition, non-LTE spectral synthesis of
the rich metal line spectra (mostly iron, chromium and titanium) of the A
supergiants is carried out, which allows the determination of stellar
metallicities. An average metallicity of -0.87 +/- 0.06 dex with respect to
solar metallicity is found.",0805.3555v1
2008-05-30,Chemical Abundances in 35 Metal-Poor Stars. I. Basic Data,"We carried out a homogeneous abundance study for various elements, including
$\alpha$-elements, iron peak elements and $n$-capture elements for 35
metal-poor stars with a wide metallicity range
($-3.0\lesssim$[Fe/H]$\lesssim-0.5$). High-resolution ($R\simeq30$k), high
signal-to-noise($S/N\geq110$) spectra with a wavelength range of 3800 to 10500
\AA using the Bohyunsan Optical Echelle Spectrograph (BOES). Equivalent widths
were measured by means of the Gaussian-fitting method for numerous isolated
weak lines of elements. Atmospheric parameters were determined by a
self-consistent LTE analysis technique using Fe I and Fe II lines. In this
study, we present the EWs of lines and atmospheric parameters for 35 metal-poor
stars.",0805.4663v1
2008-06-03,Critical Fields and Anisotropy of NdO0.82F0.18FeAs Single Crystals,"The newly discovered iron-based superconductors have stimulated enormous
interests in the field of superconductivity. Since the new superconductor is a
layered system, the anisotropy is a parameter with the first priority to know.
Meanwhile any relevant message about the critical fields (upper critical field
and irreversibility line) are essentially important. By using flux method, we
have successfully grown the single crystals NdO0.82F0.18FeAs at ambient
pressure. Resistive measurements reveal a surprising discovery that the
anisotropy \Gamma = (mc/mab)^{1/2} is below 5, which is much smaller than the
theoretically calculated results. The data measured up to 400 K show a
continuing curved feature which prevents a conjectured linear behavior for an
unconventional metal. The upper critical fields determined based on the
Werthamer-Helfand-Hohenberg formula are H_{c2}^{H||ab}(T=0 K) = 304 T and
H_{c2}^{H||c}(T=0 K)=62-70 T, indicating a very encouraging application of the
new superconductors.",0806.0532v1
2008-06-04,Symmetry of superconducting states with two orbitals on a tetragonal lattice: application to $LaO_{1-x}F_{x}FeAs$,"We use group theory to classify the superconducting states of systems with
two orbitals on a tetragonal lattice. The orbital part of the superconducting
gap function can be either symmetric or anti-symmetric. For the orbital
symmetric state, the parity is even for spin singlet and odd for spin triplet;
for the orbital anti-symmetric state, the parity is odd for spin singlet and
even for spin triplet. The gap basis functions are obtained with the use of the
group chain scheme by taking into account the spin-orbit coupling. In the weak
pairing limit, the orbital anti-symmetric state is only stable for the
degenerate orbitals. Possible application to iron-based superconductivity is
discussed.",0806.0712v3
2008-06-04,Electronic structure of oxygen-free 38K superconductor Ba1-xKxFe2As2 in comparison with BaFe2As2 from first principles,"Based on first-principles FLAPW-GGA calculation, we have investigated
electronic structure of newly discovered oxygen-free 38K superconductor
Ba1-xKxFe2As2 in comparison with parent phase - tetragonal ternary iron
arsenide BaFe2As2. The density of states, magnetic properties, near-Fermi bands
compositions, together with Sommerfeld coefficients and molar Pauli
paramagnetic susceptibility are evaluated. The results allow us to classify
these systems as quasi-two-dimensional ionic metals, where the conduction is
strongly anisotropic, only happening on the (Fe-As) layers. According to our
calculations, at the hole doping of BaFe2As2 the density of states at the Fermi
level grows, and this can be a possible factor of occurrence of
superconductivity for Ba1-xKxFe2As2. On the other hand, Ba1-xKxFe2As2 lays at
the border of magnetic instability and the pairing interactions might involve
magnetic or orbital fluctuations.",0806.0750v1
2008-06-04,Valence band and core level photoemission spectros-copy of LaFeAsO$_{1-x}$F$_{x}$,"We have investigated the electronic structure of LaFeAsO$_{1-x}$F$_{x}$ (x =
0; 0.1; 0.2) by angle-integrated photoemission spectroscopy and local density
approximation (LDA) based band structure calculations. The valence band
consists of a low energy peak at E = -0.25 eV and a broad structure around E =
-5 eV in qualitative agreement with LDA. From the photon energy dependence of
these peaks we conclude that the former derives almost exclusively from Fe 3d
states. This constitutes experimental evidence for the strong iron character of
the relevant states in a broad window around EF and confirms theoretical
predictions.",0806.0833v2
2008-06-06,Superconductivity in hole-doped (Sr$_{1-x}$K$_x$)Fe$_2$As$_2$,"A series of layered (Sr$_{1-x}$K$_x$)Fe$_2$As$_2$ compounds with nominal x=0
to 0.40 are synthesized by solid state reaction method. Similar to other parent
compounds of iron-based pnictide superconductors, the pure SrFe$_2$As$_2$ shows
a strong resistivity anomaly near 210 K, which was ascribed to the
spin-density-wave instability. The anomaly temperature is much higher than
those observed in LaOFeAs and BaFe$_2$As$_2$, the two prototype parent
compounds with ZrCuSiAs- and ThCr$_2$Si$_2$-type structures. K-doping strongly
suppresses this anomaly and induces superconductivity. Like in the case of
K-doped BaFe$_2$As$_2$, sharp superconducting transitions at T$_c\sim$38 K was
observed. We performed the Hall coefficient measurement, and confirmed that the
dominant carriers are hole-type. The carrier density is enhanced by a factor of
3 in comparison to F-doped LaOFeAs superconductor.",0806.1209v1
2008-06-09,Non-LTE Spectral Analysis of Extremely Hot Post-AGB Stars: Constraints for Evolutionary Theory,"Spectral analysis by means of Non-LTE model-atmosphere techniques has arrived
at a high level of sophistication: fully line-blanketed model atmospheres which
consider opacities of all elements from H to Ni allow the reliable
determination of photospheric parameters of hot, compact stars. Such models
provide a crucial test of stellar evolutionary theory: recent abundance
determinations of trace elements like, e.g., F, Ne, Mg, P, S, Ar, Fe, and Ni
are suited to investigate on AGB nucleosynthesis. E.g., the strong Fe depletion
found in hydrogen-deficient post-AGB stars is a clear indication of an
efficient s-process on the AGB where Fe is transformed into Ni or even heavier
trans iron-group elements. We present results of recent spectral analyses based
on high-resolution UV observations of hot stars.",0806.1432v1
2008-06-16,Structural and magnetic phase diagram of CeFeAsO1-xFx and its relationship to high-temperature superconductivity,"We use neutron scattering to study the structural and magnetic phase
transitions in the iron pnictides CeFeAsO1-xFx as the system is tuned from a
semimetal to a high-transition-temperature (high-Tc) superconductor through
Fluorine (F) doping x. In the undoped state, CeFeAsO develops a structural
lattice distortion followed by a stripe like commensurate antiferromagnetic
order with decreasing temperature. With increasing Fluorine doping, the
structural phase transition decreases gradually while the antiferromagnetic
order is suppressed before the appearance of superconductivity, resulting an
electronic phase diagram remarkably similar to that of the high-Tc copper
oxides. Comparison of the structural evolution of CeFeAsO1-xFx with other
Fe-based superconductors reveals that the effective electronic band width
decreases systematically for materials with higher Tc. The results suggest that
electron correlation effects are important for the mechanism of high-Tc
superconductivity in these Fe pnictides.",0806.2528v1
2008-06-16,Antiferromagnetic transition in EuFe$_2$As$_2$: A possible parent compound for superconductors,"Ternary iron arsenide EuFe$_2$As$_2$ with ThCr$_2$Si$_2$-type structure has
been studied by magnetic susceptibility, resistivity, thermopower, Hall and
specific heat measurements. The compound undergoes two magnetic phase
transitions at about 200 K and 20 K, respectively. The former was found to be
accompanied with a slight drop in magnetic susceptibility (after subtracting
the Curie-Weiss paramagnetic contribution), a rapid decrease in resistivity, a
large jump in thermopower and a sharp peak in specific heat with decreasing
temperature, all of which point to a spin-density-wave-like antiferromagnetic
transition. The latter was proposed to be associated with an A-type
antiferromagnetic ordering of Eu$^{2+}$ moments. Comparing with the physical
properties of the iso-structural compounds BaFe$_2$As$_2$ and SrFe$_2$As$_2$,
we expect that superconductivity could be induced in EuFe$_2$As$_2$ through
appropriate doping.",0806.2591v2
2008-06-16,Electronic structure and exotic exchange splitting in spin-density-wave states of BaFe$_2$As$_2$,"The magnetic properties in the parent compounds are often intimately related
to the microscopic mechanism of superconductivity. Here we report the first
direct measurements on the electronic structure of a parent compound of the
newly discovered iron-based superconductor, BaFe$_2$As$_2$, which provides a
foundation for further studies. We show that the energy of the spin density
wave (SDW) in BaFe$_2$As$_2$ is lowered through exotic exchange splitting of
the band structure, rather than Fermi surface nesting of itinerant electrons.
This clearly demonstrates that a metallic SDW state could be solely induced by
interactions of local magnetic moments, resembling the nature of
antiferromagnetic order in cuprate parent compounds.",0806.2627v2
2008-06-22,Thermodynamic properties of Ba1-xMxFe2As2 (M = La and K),"The specific heat $C(T)$ of BaFe$_2$As$_2$ single crystal, electron-doped
Ba$_{0.7}$La$_{0.3}$Fe$_2$As$_2$ and hole-doped Ba$_{0.5}$K$_{0.5}$Fe$_2$As$_2$
polycrystals were measured. For undoped BaFe$_2$As$_2$ single crystal, a very
sharp specific heat peak was observed at 136 K. This is attributed to the
structural and antiferromagnetic transitions occurring at the same temperature.
$C(T)$ of the electron-doped non-superconducting
Ba$_{0.7}$La$_{0.3}$Fe$_2$As$_2$ also shows a small peak at 120 K, indicating a
similar but weaker structural/antiferromagnetic transition. For the hole-doped
superconducting Ba$_{0.5}$K$_{0.5}$Fe$_2$As$_2$, a clear peak of $C/T$ was
observed at $T_c$ = 36 K, which is the highest peak seen at superconducting
transition for iron-based high-$T_c$ superconductors so far. The electronic
specific heat coefficient $\gamma$ and Debye temperature $\Theta_D$ of these
compounds were obtained from the low temperature data.",0806.3573v2
2008-06-24,Electronic Structure and Electron Correlation in LaFeAsO_{1-x}F_x and LaFePO_{1-x}F_x,"Photoemission spectroscopy is used to investigate the electronic structure of
the newly discovered iron-based superconductors LaFeAsO_{1-x}F_x and
LaFePO_{1-x}F_x. Line shapes of the Fe 2p core-level spectra suggest an
itinerant character of Fe 3d electrons. The valence-band spectra are generally
consistent with band-structure calculations except for the shifts of Fe
3d-derived peaks toward the Fermi level. From spectra taken in the Fe 3p -> 3d
core-absorption region, we have obtained the experimental Fe 3d partial density
of states, and explained it in terms of a band-structure calculation with a
phenomenological self-energy correction, yielding a mass renormalization factor
of ~< 2.",0806.3860v1
2008-06-26,High Energy Observations of AGN Jets and their Future Prospects,"In next five years, dramatic progress is anticipated for the AGN studies, as
we have two important missions to observe celestial sources in the high energy
regime: GLAST and Suzaku. In this talk, I will summarize recent highlights in
studies of AGN jets, focusing on the high-sensitivity X-ray observations that
may shed new light on the forthcoming GLAST era. I will especially present some
examples from most recent Suzaku observations of blazars, which provides
important hints for the shock acceleration in sub-pc scale jets, as well as
particle content in jets. Then I will focus on the neutral iron-line feature
observed in some broad line radio galaxies, as a probe of jet launching and/or
the disk-jet connection. Finally, I will discuss new results of large scale
(kpc to Mpc) jets recently resolved with Chandra X-ray observatory.
Simultaneous monitoring observations in various wavelengths will be
particularly valuable for variable blazar sources, allowing the cross
correlations of time series as well as detailed modeling of the spectral
evolution between the X-ray and gamma-ray energy bands. Possible impacts of
these new observations across the electromagnetic spectrum on various spatial
scales are discussed to challenge the long-standing mystery of AGN jet sources.",0806.4240v1
2008-07-03,Coulomb Parameter U and Correlation Strength in LaFeAsO,"First principles constrained density functional theory scheme in Wannier
functions formalism has been used to calculate Coulomb repulsion U and Hund's
exchange J parameters for iron 3d electrons in LaFeAsO. Results strongly depend
on the basis set used in calculations: when O-2p, As-4p, and Fe-3d orbitals and
corresponding bands are included, computation results in U=3-4 eV, however,
with the basis set restricted to Fe-3d orbitals and bands only, computation
gives parameters corresponding to F^0=0.8 eV, J=0.5 eV. LDA+DMFT (the Local
Density Approximation combined with the Dynamical Mean-Field Theory)
calculation with this parameters results in weakly correlated electronic
structure that is in agreement with X-ray experimental spectra.",0807.0547v1
2008-07-04,Pressure Effect on Superconductivity of Iron-based Arsenic-oxide ReFeAsO0.85 (Re=Sm and Nd),"Here we report pressure effect on superconducting transition temperature (Tc)
of ReFeAsO0.85 (Re= Sm and Nd) system without fluorine doping. In-situ
measurements under high pressure showed that Tc of the two compounds decrease
monotonously over the pressure range investigated. The pressure coefficients
dTc/dP in SmFeAsO0.85 and Nd FeAsO0.85 were different, revealing the important
influence of the deformation in layers on Tc. Theoretical calculations
suggested that the electron density of states decrease with increasing
pressure, following the same trend of experimental data.",0807.0675v2
2008-07-06,Momentum dependence of the superconducting gap in NdFeAsO1-xFx single crystals measured by angle resolved photoemission spectroscopy,"We use angle resolved photoemission spectroscopy (ARPES) to study the
momentum dependence of the superconducting gap in NdFeAsO1-xFx single crystals.
We find that the Gamma hole pocket is fully gapped below the superconducting
transition temperature. The value of the superconducting gap is 15 +- 1.5 meV
and its anisotropy around the hole pocket is smaller than 20% of this value.
This is consistent with an isotropic or anisotropic s-wave symmetry of the
order parameter or exotic d-wave symmetry with nodes located off the Fermi
surface sheets. This is a significant departure from the situation in the
cuprates, pointing to possibility that the superconductivity in the iron
arsenic based system arises from a different mechanism.",0807.0815v1
2008-07-07,Optical spectroscopy of superconducting Ba{0.55}K{0.45}Fe2As2: evidence for strong coupling to low energy bosons,"Optical spectroscopy on single crystals of the new iron arsenide
superconductor Ba{0.55}K{0.45}Fe2As2 shows that the infrared spectrum consists
of two major components: a strong metallic Drude band and a well separated mid
infrared absorption centered at 0.7 eV. It is difficult to separate the two
components unambiguously but several fits of Lorentzian peaks suggest a model
with a Drude peak having a plasma frequency of 1.8 to 2.1 eV and a midinfrared
peak with a plasma frequency of 2.5 eV. In contrast to the cuprate
superconductors the scattering rate obtained from the extended Drude model
saturates at 150 meV as compared to 500 meV for a typical cuprate. Detailed
analysis of the frequency dependent scattering rate shows that the charge
carriers interact with broad bosonic spectrum with a peak at 25 meV and a
coupling constant lambda =approx 2 at low temperature. As the temperature
increases this coupling weakens to lambda=0.6 at ambient temperature. This
suggests a bosonic spectrum that is similar to what is seen in the lower Tc
cuprates.",0807.1040v1
2008-07-08,Possibility of Unconventional Pairing Due to Coulomb Interaction in Fe-Based Pnictide Superconductors: Perturbative Analysis of Multi-Band Hubbard Models,"Possibility of unconventional pairing due to Coulomb interaction in
iron-pnictide superconductors is studied by applying a perturbative approach to
realistic 2- and 5-band Hubbard models. The linearized Eliashberg equation is
solved by expanding the effective pairing interaction perturbatively up to
third order in the on-site Coulomb integrals. The numerical results for the
5-band model suggest that the eigenvalues of the Eliashberg equation are
sufficiently large to explain the actual high Tc for realistic values of
Coulomb interaction and the most probable pairing state is spin-singlet s-wave
without any nodes just on the Fermi surfaces, although the superconducting
order parameter changes its sign between the small Fermi pockets. On the other
hand the 2-band model is quite insufficient to explain the actual high Tc.",0807.1168v2
2008-07-09,The chemical evolution of Manganese in different stellar systems,"Aims. To model the chemical evolution of manganese relative to iron in three
different stellar systems: the solar neighbourhood, the Galactic bulge and the
Sagittarius dwarf spheroidal galaxy, and compare our results with the recent
and homogeneous observational data. Methods. We adopt three chemical evolution
models well able to reproduce the main properties of the solar vicinity, the
galactic Bulge and the Sagittarius dwarf spheroidal. Then, we compare different
stellar yields in order to identify the best set to match the observational
data in these systems. Results. We compute the evolution of manganese in the
three systems and we find that in order to reproduce simultaneously the [Mn/Fe]
versus [Fe/H] in the Galactic bulge, the solar neighbourhood and Sagittarius,
the type Ia SN Mn yield must be metallicity-dependent. Conclusions. We conclude
that the different histories of star formation in the three systems are not
enough to reproduce the different behaviour of the [Mn/Fe] ratio, unlike the
situation for [alpha/Fe]; rather, it is necessary to invoke
metallicity-dependent type Ia SN Mn yields, as originally suggested by
McWilliam, Rich & Smecker-Hane in 2003.",0807.1463v1
2008-07-09,Lattice and magnetic instabilities in CaFe2As2: A single crystal neutron diffraction study,"Neutron diffraction measurements of a high quality single crystal of CaFe2As2
are reported. A sharp transition was observed between the high temperature
tetragonal and low temperature orthorhombic structures at TS = 172.5K (on
cooling) and 173.5K (on warming). Coincident with the structural transition we
observe a rapid, but continuous, ordering of the Fe moments, in a commensurate
antiferromagnetic structure is observed, with a saturated moment of
0.80(5)muB/Fe directed along the orthorhombic a-axis. The hysteresis of the
structural transition is 1K between cooling and warming and is consistent with
previous thermodynamic, transport and single crystal x-ray studies. The
temperature onset of magnetic ordering shifts rigidly with the structural
transition providing the clearest evidence to date of the coupling between the
structural and magnetic transitions in this material and the broader class of
iron arsenides.",0807.1525v3
2008-07-10,"Structural Chemistry, Spin Order, and the Distinction Between the Cuprate and Pnictide High-Temperature Superconductors","In the cuprate and iron-pnictide systems, valence changes induce
high-temperature superconductivity while the local structural chemistry and
local spin order both independently generate the attractive interactions
responsible for the high transition temperature. We argue that together they
favor d-wave singlet superconductivity in the cuprates but s-wave singlet in
the pnictides. This difference arises from the existence of a large on-site
repulsion between carriers in the cuprates largely absent in the pnictides.
Fluorine is responsible for raising Tc significantly in some pnictides and in
the cuprates to 155K-168K, the highest achieved at ambient pressure. We propose
an experimental procedure for finding and fabricating the fluorinated cuprate
phase having that exceptional property.",0807.1673v5
2008-07-15,Physical and kinematical properties of the X-ray absorber in the broad absorption line quasar APM 08279+5255,"We have re-analyzed the X-ray spectra of the gravitational lensed
high-redshift BAL QSO APM 08279+5255, observed with the XMM-Newton and Chandra
observatories. Previous studies (Hasinger et al. 2002; Chartas et al. 2002)
detected unusual, highly-ionized iron absorption features, but differed in
their interpretation of these features, regarding the kinematical and
ionization structure. We seek one physical model that can be successfully
applied to both observations. For the first time we have performed detailed
photoionization modeling on the X-ray spectrum of APM 08279+5255. The absorbing
gas in APM 08279+5255 can be represented by a two-absorbers model with column
densities N_H(1)~7x10^{22} cm^-2, N_H(2)~6x10^{22} cm^-2, and ionization
parameters logxi(1)~1.5 and logxi(2)~3, with one of them (the high-ionization
component) outflowing at v~0.18(\pm 0.01)c, carrying large amount of gas out of
the system. We find that the Chandra spectrum of APM 08279+5255 requires the
same Fe/O ratio overabundance (previously) indicated by the XMM-Newton
observation, showing that both absorber components underwent similar chemical
evolution and/or have similar origin.",0807.2372v1
2008-07-16,Columnar magnetic structure coupled with orthorhombic distortion in the antiferromagnetic iron arsenide SrFe$_2$As$_2$,"Neutron powder diffraction experiments were carried out on polycrystalline
SrFe$_2$As$_2$ in order to determine the magnetic structure and its
relationship with the crystallographic one. Below $T_0$=205 K, magnetic
reflections appear simultaneously with the onset of the orthorhombic
distortion. From a detailed Rietveld analysis, the magnetic propagation vector
of SrFe$_2$As$_2$ is determined to be {\textit{\textbf{q}}}=(1 0 1); the
coupling of Fe moments is antiferromagnetic along the longer $a$ direction
within the Fe-As layer, and the interlayer coupling is antiferromagnetic as
well. The size of the Fe magnetic moment is deduced to be 1.01(3) ${\mu}_{\rm
B}$ with an orientation parallel to the a-axis. The temperature dependence of
the magnetic moment shows excellent agreement with not only that of the muon
precession frequency but also with that of the structural distortion, revealing
the strong coupling of the columnar magnetic order and the structural
distortion in SrFe$_2$As$_2$.",0807.2608v1
2008-07-18,Pressure-induced volume-collapsed tetragonal phase of CaFe2As2 as seen via neutron scattering,"Recent investigations of the superconducting iron-arsenide families have
highlighted the role of pressure, be it chemical or mechanical, in fostering
superconductivity. Here we report that CaFe2As2 undergoes a pressure-induced
transition to a non-magnetic, volume ""collapsed"" tetragonal phase, which
becomes superconducting at lower temperature. Spin-polarized total-energy
calculations on the collapsed structure reveal that the magnetic Fe moment
itself collapses, consistent with the absence of magnetic order in neutron
diffraction.",0807.3032v3
2008-07-20,Electronic structure of LaFe1-xCoxAsO from first principle calculations,"Based on the first-principles calculations, we have investigated the
geometry, binding properties, density of states and band structures of the
novel superconductor LaFe1-xCoxAsO and its parent compounds with the ZrCuSiAs
structure. We demonstrate that La-O bond and TM-As (TM=Fe or Co) bond are both
strongly covalent, while the LaO and TMAs layers have an almost ionic
interaction through the Bader charge analysis. Partial substitution of iron
with cobalt modify the Fermi level from a steep edge to a flat slope, which
explains why in this system Co doping suppresses the spin density wave (SDW)
transition.",0807.3153v2
2008-07-24,Evidence for Strong Itinerant Spin Fluctuations in the Normal State of CeFeAsO(0.89)F(0.11) Iron-Oxypnictides,"The electronic structure in the normal state of CeFeAsO0.89F0.11 oxypnictide
superconductors has been investigated with x-ray absorption and photoemission
spectroscopy. All the data exhibit signatures of Fe d-electron itinerancy.
Exchange multiplets appearing in the Fe 3s core level indicate the presence of
itinerant spin fluctuations. These findings suggest that the underlying physics
and the origin of superconductivity in these materials are likely to be quite
different from those of the cuprate high-temperature superconductors. These
materials provide opportunities for elucidating the role of magnetic
fluctuations in high-temperature superconductivity.",0807.3781v2
2008-07-24,Modeling UX Ursae Majoris: An abundance of challenges,"We present a system model for optical and far UV spectra of the nova-like
variable UX UMa involving a white dwarf, secondary star, gas stream, hot spot
and accretion disk using our code BINSYN and based on an initially adopted
system distance. Calculated SED intensity data successfully fit successive
tomographically-extracted annuli longward of the Balmer limit but require a
postulated `iron curtain' shortward of the Balmer limit that is applied to the
annulus section closest to the secondary star, while postulated recombination
emission fills in the model SED shortward of the Balmer limit and is applied to
the annulus section more remote from the secondary star. The same model fits
$UBV$ 1954 light curves by Walker and Herbig. Fits to $HST$ $FOS$ spectra are
approximate but require assumed time-variable changes in the SED. Comparable
effects, possibly involving variable absorption, afflict $FUSE$ spectra.",0807.3920v1
2008-07-25,Superconductivity and Crystal Structures of (Ba1-xKx)Fe2As2 (x = 0 - 1),"We report on doping dependencies of structural parameters and superconducting
transition temperatures in the solid solution (Ba1-xKx)Fe2As2. As the main
effect of doping on the crystal structure, we find linear decreasing As-Fe-As
bond angles and Fe-Fe distances, equivalent to an elongation of the FeAs4
tetrahedra along [001]. The structural changes are intimately coupled to the
electronic states at the Fermi level, because the most relevant Fe-3dx2-y2
orbitals are strongly affected by the As-Fe-As bond angle. Superconductivity is
present over the whole doping range in (Ba1-xKx)Fe2As2 with a maximum Tc of 38
K at x ~ 0.4. The superconducting transitions in the orthorhombic compounds
(Ba0.9K0.1)Fe2As2 (Tc ~ 3 K) and (Ba0.8K0.2)Fe2As2 (Tc ~ 25 K) is strong
evidence for the coexistence of superconductivity with the structurally
distorted and potentially magnetically ordered state in the BaFe2As2 family of
iron arsenide superconductors.",0807.4096v2
2008-07-28,Superconductivity at 27 K in tetragonal FeSe under high pressure,"A huge enhancement of the superconducting transition temperature Tc was
observed in tetragonal FeSe superconductor under high pressure. The onset
temperature became as high as 27 K at 1.48 GPa and the pressure coefficient
showed a huge value of 9.1 K/GPa. The upper critical field Hc2 was estimated to
be ~ 72 T at 1.48 GPa. Because of the high Hc2, FeSe system may be a candidate
for application as superconducting wire rods. Moreover, the investigation of
superconductivity on simple structured FeSe may provide important clues to the
mechanism of superconductivity in iron-based superconductors.",0807.4315v2
2008-07-29,Anisotropic pairing in the iron pnictides,"We determine the anisotropy of the spin fluctuation induced pairing gap on
the Fermi surface of the FeAs based superconductors as function of the exchange
and Hund's coupling $J_{H}$. We find that for sufficiently large $J_{H}$,
nearly commensurate magnetic fluctuations yield a fully gapped
$s^{\pm}$-pairing state with small anisotropy of the gap amplitude on each
Fermi surface sheet, but significant variations of the gap amplitude for
different sheets of the Fermi surface. In particular, we obtain the large
variation of the gap amplitude on different Fermi surface sheets, as seen in
ARPES experiments. For smaller values of Hund's coupling incommensurate
magnetic fluctuations yield an $s^{\pm}$-pairing state with line nodes. Such a
state is also possible once the anisotropy of the material is reduced and three
dimensional effects come into play.",0807.4566v2
2008-07-31,Evidence for Unconventional Superconductivity in Arsenic-Free Iron-Based Superconductor FeSe : A ^77Se-NMR Study,"We report the results of $^{77}$Se--nuclear magnetic resonance (NMR) in
$\alpha$-FeSe, which exhibits a similar crystal structure to the
LaFeAsO$_{1-x}$F$_x$ superconductor and shows superconductivity at 8 K. The
nuclear-spin lattice relaxation rate $1/T_1$ shows $T^3$ behavior below the
superconducting transition temperature $T_c$ without a coherence peak. The
$T_1T=$ const. behavior, indicative of the Fermi liquid state, can be seen in a
wide temperature range above $T_c$. The superconductivity in $\alpha$-FeSe is
also an unconventional one as well as LaFeAsO$_{1-x}$F$_x$ and related
materials. The FeAs layer is not essential for the occurrence of the
unconventional superconductivity.",0808.0040v3
2008-08-03,Magnetic and Transport Studies on Electron-doped CeFeAsO1-xFx Superconductor,"The magnetic and transport behaviors of cerium substituted iron oxy-arsenide
superconductor with x = 0.1 to 0.4 fluoride (F) doping have been investigated
in this report. Temperature dependent susceptibility and resistivity
measurements showed the 0.1 F-doped sample (CeFeAsO0.9F0.1) has a
superconducting transition temperature (Tc) of around 30 K. With increasing
doping beyond x = 0.2 Tc saturates to around 40 K. Temperature dependent
susceptibility measured in different magnetic fields for the under-doped sample
showed Meissner effect in low field and the diamagnetism is still visible up to
1 Tesla, with an obvious magnetic transition below 5 K, perhaps originating
from magnetic ordering of the rare earth cerium. The corresponding field
dependent resistance versus temperature measurements indicated a broadening of
less than 3 K for Tc at mid-point by increasing the field to 5 Tesla indicating
rather low anisotropy. An estimated upper critical field of more than 48 Tesla
and accordingly an estimated maximum coherence length of 2.6 nm were obtained
confirming the high upper critical field with a short coherence length for this
superconductor.",0808.0296v1
2008-08-04,Tellurium substitution effect on superconductivity of the alpha-phase Iron Selenide,"We have carried out a systematic study of the PbO-type compound
FeSe_{1-x}Te_x (x = 0~1), where Te substitution effect on superconductivity is
investigated. It is found that superconducting transition temperature reaches a
maximum of Tc=15.2K at about 50% Te substitution. The pressure-enhanced Tc of
FeSe0.5Te0.5 is more than 10 times larger than that of FeSe. Interestingly,
FeTe is no longer superconducting. A low temperature structural distortion
changes FeTe from triclinic symmetry to orthorhombic symmetry. We believe that
this structural change breaks the magnetic symmetry and suppresses
superconductivity in FeTe.",0808.0474v2
2008-08-06,The correlation of black hole mass with metallicity index of host spheroid,"We investigate the correlation between the mass of the supermassive black
holes (SMBHs) and metal abundance, using existing data sets. The SMBH mass
$M_{bh}$ is well correlated with integrated stellar feature of Mgb. For 28
galaxies, the best-fit $M_{bh}$-Mgb relation has a small scatter, which is an
equivalent level with other well-known relation, such as a correlation between
the stellar velocity dispersion and the mass. An averaged iron index $<$Fe$>$
also positively correlates with $M_{bh}$, but the best-fit $M_{bh}$-$<$Fe$>$
relation has a larger scatter. The difference comes from the synthesis and
evolution mechanisms, and may be important for the SMBH and star formation
history in the host spheroid.",0808.0769v1
2008-08-06,Granularity and vortex dynamics in LaO_0.92F_0.08FeAs as probed by harmonics of the AC magnetic susceptibility,"Fundamental and higher harmonics of the AC magnetic susceptibility have been
measured on a LaO_0.92F_0.08FeAs sample as a function of the temperature, at
various amplitudes and frequencies of the AC magnetic field, with a small
superimposed DC field parallel to the AC field. The granularity of the sample
has been investigated and the inter-grain and intra-grain contributions have
been clearly individuated looking at both the first and third harmonics. The
vortex dynamics has been also analyzed, and a comparison with the magnetic
behavior of both the MgB_2 and the cuprate superconductors has been performed.
Some vortex dissipative phenomena, i.e. the thermally activated flux flow and
the flux creep, have been detected in the presented measurements, similar to
what obtained on YBCO. Nevertheless, although the general behavior is similar,
several differences have been also evidenced between these different classes of
superconductors, mainly in the third harmonics. We infer that different vortex
dynamics have to be included into the analysis of the magnetic response in this
iron-based new material.",0808.0804v1
2008-08-10,59-Co and 75-As NMR Investigation of Electron-Doped High Tc Superconductor BaFe(1.8)Co(0.2)As(2) (Tc = 22K),"We report an NMR investigation of the superconductivity in BaFe(2)As(2)
induced by Co doping (Tc=22K). We demonstrate that Co atoms form an alloy with
Fe atoms and donate carriers without creating localized moments. Our finding
strongly suggests that the underlying physics of iron-pnictide superconductors
is quite different from the widely accepted physical picture of high Tc
cuprates as doped Mott insulators. We also show a crossover of electronic
properties into a low temperature pseudo-gap phase with a pseudo-gap Delta
560K, where chi(spin) constant and resisitivty T. The NMR Knight shift below Tc
decreases for both along the c-axis and ab-plane, and is consistent with the
singlet pairing scenario.",0808.1420v2
2008-08-12,Magnetism Driven by Anion Vacancies in Superconducting $α$--FeSe$_{1-x}$,"To study the microscopic electronic and magnetic interactions in the
substoichiometric iron chalcogenide FeSe$_{1-x}$ which is observed to
superconduct at x~1/8 up to $T_c$=27 K, we use first principles methods to
study the Se vacancy in this nearly magnetic FeSe system. The vacancy forms a
ferrimagnetic cluster of eight Fe atoms, which for the ordered x=1/8 alloy
leads to half metallic conduction. Similar magnetic clusters are obtained for
FeTe$_{1-x}$ and for BaFe$_2$As$_2$ with an As vacancy, although neither of
these are half metallic. Based on fixed spin density results, we suggest the
low energy excitations in FeSe$_{1-x}$ are antiparamagnon-like with short
correlation length.",0808.1733v2
2008-08-13,Jet modification in 200 AGeV Au-Au collisions,"The computation of hard processes in hadronic collisions is a major success
of perturbative Quantum Chromodynamics. The environment of heavy-ion collisions
offers the opportunity to embed such hard processes into a soft medium which is
created simultaneously and study the medium-induced modifications. On the level
of single high transverse momentum hadrons, a reduction in yield, the so-called
quenching is observed. However, on the level of jets, the energy-momentum flux
carried by hadrons is conserved, i.e. the effect of the medium is a
redistribution of energy and momentum, and statements about quenching of jets
can only be made for specific cuts used to identify the jet. In this paper, we
present a baseline computation for the expected modification of the
longitudinal momentum distribution in jets by the medium created in 200 AGeV
Au-Au collisions given a realistic set of experimental cuts used to identify
jets in a heavy-iron environment. For this purpose, we use a Monte-Carlo code
developed to simulate in-medium shower evolution following a hard process and a
3-d hydrodynamical evolution to simulate the soft medium.",0808.1803v1
2008-08-13,Ranges of Atmospheric Mass and Composition of Super Earth Exoplanets,"Terrestrial-like exoplanets may obtain atmospheres from three primary
sources: Capture of nebular gases, degassing during accretion, and degassing
from subsequent tectonic activity. Here we model degassing during accretion to
estimate the range of atmospheric mass and composition on exoplanets ranging
from 1 to 30 Earth masses. We use bulk compositions drawn from primitive and
differentiated meteorite compositions. Degassing alone can create a wide range
of masses of planetary atmospheres, ranging from less than a percent of the
planet's total mass up to ~6 mass% of hydrogen, ~20 mass% of water, and/or ~5
mass% of carbon compounds. Hydrogen-rich atmospheres can be outgassed as a
result of oxidizing metallic iron with water, and excess water and carbon can
produce atmospheres through simple degassing. As a byproduct of our atmospheric
outgassing models we find that modest initial water contents (10 mass% of the
planet and above) create planets with deep surface liquid water oceans soon
after accretion is complete.",0808.1909v1
2008-08-17,Spin Dynamics in Iron-based Layered Superconductor (La_{0.87}Ca_{0.13})FePO Revealed by ^{31}P and ^{139}La NMR Studies,"We report ^{31}P and ^{139}La NMR studies of (La_{0.87}Ca_{0.13})FePO, which
is a family member of the recently discovered superconductor
LaFeAs(O_{1-x}F_x). In the normal state, Knight shift and $1/T_1T$ show that a
Fermi-liquid state with moderate ferromagnetic fluctuations emerges below 30K.
  From 1/T_1T of ^{31}P and ^{139}La, quasi-two dimensional electronic
structure is suggested, in which the FeP layer is more conductive than the LaO
layer. In the superconducting (SC) state, although a clear Meissner signal was
observed, 1/T_1T increases below T_c, in contrast to a decrease of 1/T_1T due
to the opening of a SC gap, suggesting that novel low-energy spin dynamics
develop in the SC state.",0808.2293v1
2008-08-20,Correlation effects of exchange splitting and coexistence of spin-density-wave and superconductivity in single crystalline Sr1-xKxFe2As2,"The nature of spin-density wave and its relation with superconductivity are
crucial issues in the newly discovered Fe-based high temperature
superconductors. Particularly it is unclear whether the superconducting phase
and spin density wave (SDW) are truly exclusive from each other as suggested by
certain experiments. With angle resolved photoemission spectroscopy, we here
report exchange splittings of the band structures in Sr1-xKxFe2As2
(x=0,0.1,0.2), and the non-rigid-band behaviors of the splitting. Our data on
single crystalline superconducting samples unambiguously prove that SDW and
superconductivity could coexist in iron-pnictides.",0808.2738v1
2008-08-20,Superconducting Properties of Two-Orbital t-t'-J-J' Models,"Motivated by the recent contradiction of the superconducting pairing symmetry
in the angle-resolved photoemission spectra (ARPES) and the nuclear magnetic
resonance (NMR) data in the FeAs superconductors, we present the theoretical
results on the phase diagram, the temperature dependent Fermi surfaces in
normal state, the ARPES character of quasiparticles and the spin-lattice
relaxation 1/T$_{1}$ of the two-orbital t-t$^{'}$-J-J$^{'}$ models. Our results
show that most of the properties observed in iron-based superconductors could
be comprehensively understood in the present scenario qualitatively, indicating
that the pairing symmetry of the ironpnictides is anisotropic nodeless s-wave,
mainly originating from the band structures and the Fermi surface topology.",0808.2763v2
2008-08-21,High energy spin excitations in BaFe2As2,"We report neutron scattering measurements of cooperative spin excitations in
antiferromagnetically ordered BaFe2As2, the parent phase of an iron pnictide
superconductor. The data extend up to ~100meV and show that the spin excitation
spectrum is sharp and highly dispersive. By fitting the spectrum to a linear
spin-wave model we estimate the magnon bandwidth to be in the region of 0.17eV.
The large characteristic spin fluctuation energy suggests that magnetism could
play a role in the formation of the superconducting state.",0808.2836v2
2008-08-26,Impurity suppression of the critical temperature in the iron-based superconductors,"We study the impurity suppression of the critical temperature $T_c$ of the
FeAs superconductors theoretically based on the the $\pm$s-wave pairing state
of a two band model. The effects of non-magnetic and magnetic impurities are
studied with the $\mathcal{T}$-matrix approximation, which can continuously
treat impurity scattering from weak to strong coupling limit. We found that
both magnetic and non-magnetic impurities suppress $T_c$ with a rate that is
practically indistinguishable from the standard d-wave case despite a possibly
large difference of the positive and negative s-wave order parameter (OP)
magnitudes. This is because the density of states enters together with the OP
magnitude for the scattering process.",0808.3473v2
2008-08-28,Orbital Selective Superconductivity in Two-Orbital Asymmetric t-J Models,"We present the zero-temperature superconducting (SC) ground states of the
two-orbital asymmetric $t-J$ model on a square lattice by means of the
auxiliary-boson approach. Besides the two-gap SC phase, we find an orbital
selective SC (OSSC) phase, which is simultaneously SC in one orbit and normal
in another orbit. The novel OSSC phase is stable only for sufficient asymmetric
degree in orbital space and doping concentration. The pairing symmetry of the
SC phase is s-wave-like in most doping regime, against the d-wave symmetry of
the single-orbital $t-J$ model in a square lattice. The implication of the
present scenario on multi-orbital heavy fermion and iron-based superconductors
is also discussed.",0808.3809v1
2008-09-02,Near-Infrared Photometry of Four Stellar Clusters in the Small Magellanic Cloud,"We present high-quality J, H and K photometry of four Small Magellanic Cloud
stellar clusters with intermediate ages in the 1-7 Gyr range (namely NGC 339,
361, 416 and 419) . We obtained deep Color-Magnitude Diagrams to study the
evolved sequences and providing a detailed census of the Red Giant Branch
(RGB), Asymptotic Giant Branch (AGB) and Carbon star populations in each
cluster and their contribution to the total cluster light. We find that in the
5-7 Gyr old clusters AGB stars account for ~6 % of the total light in K-band,
Carbon stars are lacking and RGB stars account for ~45 % of the total
bolometric luminosity. These empirical findings are in good agreement with the
theoretical predictions. Finally, we derived photometric metallicities computed
by using the properties of the RGB and finding an iron content of [Fe/H]=-1.18,
-1.08, -0.99 and -0.96 dex for NGC 339, 361, 416 and 419 respectively.",0809.0495v1
2008-09-10,Kramers degeneracy in a magnetic field and Zeeman spin-orbit coupling in antiferromagnets,"In this article, I analyze the symmetries and degeneracies of electron
eigenstates in a commensurate collinear antiferromagnet. In a magnetic field
transverse to the staggered magnetization, a hidden anti-unitary symmetry
protects double degeneracy of the Bloch eigenstates at a special set of
momenta. In addition to this `Kramers degeneracy' subset, the manifold of
momenta, labeling the doubly degenerate Bloch states in the Brillouin zone, may
also contain an `accidental degeneracy' subset, that is not protected by
symmetry and that may change its shape under perturbation. These degeneracies
give rise to a substantial momentum dependence of the transverse g-factor in
the Zeeman coupling, turning the latter into a spin-orbit interaction.
  I discuss a number of materials, where Zeeman spin-orbit coupling is likely
to be present, and outline the simplest properties and experimental
consequences of this interaction, that may be relevant to systems from chromium
to borocarbides, cuprates, hexaborides, iron pnictides, as well as organic and
heavy fermion conductors.",0809.1893v3
2008-09-13,Chemical Abundances from the Continuum,"The calculation of solar absolute fluxes in the near-UV is revisited,
discussing in some detail recent updates in theoretical calculations of
bound-free opacity from metals. Modest changes in the abundances of elements
such as Mg and the iron-peak elements have a significant impact on the
atmospheric structure, and therefore self-consistent calculations are
necessary. With small adjustments to the solar photospheric composition, we are
able to reproduce fairly well the observed solar fluxes between 200 and 270 nm,
and between 300 and 420 nm, but find too much absorption in the 270-290 nm
window. A comparison between our reference 1D model and a 3D time-dependent
hydrodynamical simulation indicates that the continuum flux is only weakly
sensitive to 3D effects, with corrections reaching <10% in the near-UV, and <2%
in the optical.",0809.2364v1
2008-09-15,Role of covalent Fe-As bonding in the magnetic moment formation and exchange mechanisms in iron-pnictide superconductors,"The electronic origin of the huge magnetostructural effect in layered Fe-As
compounds is elucidated using LiFeAs as a prototype. The crucial feature of
these materials is the strong covalent bonding between Fe and As, which tends
to suppress the exchange splitting. The bonding-antibonding splitting is very
sensitive to the distance between Fe and As nuclei. We argue that the fragile
interplay between bonding and magnetism is universal for this family of
compounds. The exchange interaction is analyzed in real space, along with its
correlation with covalency and doping. The range of interaction and itinerancy
increase as the Fe-As distance is decreased. Superexchange makes a large
antiferromagnetic contribution to the nearest-neighbor coupling, which develops
large anisotropy when the local moment is not too small. This anisotropy is
very sensitive to doping.",0809.2586v3
2008-09-19,An ab-initio calculation of the core-level x-ray photoemission spectra -Fe 3s- and 1s-core levels-,"We develop a method of the ab-initio calculation for the core-level x-ray
photoemission spectroscopy (XPS). By calculating one-electron states in the
presence of core-hole potential, excited states are constructed by distributing
electrons on these one-electron states. The overlap integrals between the
excited states and the ground state are evaluated by using the wavefunctions
with and without the core-hole potential, and finally the XPS spectra are
obtained. Implementing the procedure, we obtain the spin-resolved 3s-core XPS
spectra in ferromagnetic iron without any adjustable parameters, in good
agreement with the experiment. The spectral shapes are quite different for
different spin channels. We explain the behavior in terms of the difference in
the one-electron states screening the core-hole potential.",0809.3296v1
2008-09-23,Ab initio exchange interactions and magnetic properties of Gd2Fe17 iron sublattice: rhombohedral vs. hexagonal phases,"In the framework of the LSDA+U method electronic structure and magnetic
properties of the intermetallic compound Gd2Fe17 for both rhombohedral and
hexagonal phases have been calculated. On top of that, ab initio exchange
interaction parameters within the Fe sublattice for all present nearest and
some next nearest Fe ions have been obtained. It was found that for the first
coordination sphere direct exchange interaction is ferromagnetic. For the
second coordination sphere indirect exchange interaction is observed to be
weaker and of antiferromagnetic type. Employing the theoretical values of
exchange parameters Curie temperatures Tc of both hexagonal and rhombohedral
phases of Gd2Fe17 within Weiss mean-field theory were estimated. Obtained
values of Tc and its increase going from the hexagonal to rhombohedral crystal
structure of Gd2Fe17 agree well with experiment. Also for both structures
LSDA+U computed values of total magnetic moment coincide with experimental
ones.",0809.3905v2
2008-10-01,Anomalous behavior of the Debye temperature in Fe-rich Fe-Cr alloys,"Debye temperature, $\Theta_D$, of Fe-rich Fe$_{100-x}$Cr$_x$ disordered
alloys with $0\le x \le 22.3$ was determined from the temperature dependence of
the central shift of M\""ossbauer spectra recorded in the temperature range of
60 -- 300 K. Its compositional dependence shows a maximum at $x \approx 5$ with
a relative increase of $\sim 30$% compared to a pure iron. The composition at
which the effect occurs correlates well with that at which several other
quantities, e. g. the Curie temperature and the spin-wave stiffness
coefficient, $D_0$, show their maxima, but the enhancement of $\Theta_D$ is
significantly greater and comparable with the enhancement of the hyperfine
field (spin-density of itinerant $s$-like electrons) in the studied system. The
results suggest that the electron-phonon interaction is important in this alloy
system.",0810.0123v1
2008-10-01,Pressure effects on the electron-doped high Tc superconductor BaFe(2-x)Co(x)As(2),"Application of pressures or electron-doping through Co substitution into Fe
sites transforms the itinerant antiferromagnet BaFe(2)As(2) into a
superconductor with the Tc exceeding 20K. We carried out systematic transport
measurements of BaFe(2-x)Co(x)As(2) superconductors in pressures up to 2.5GPa,
and elucidate the interplay between the effects of electron-doping and
pressures. For the underdoped sample with nominal composition x = 0.08,
application of pressure strongly suppresses a magnetic instability while
enhancing Tc by nearly a factor of two from 11K to 21K. In contrast, the
optimally doped x=0.20 sample shows very little enhancement of Tc=22K under
applied pressure. Our results strongly suggest that the proximity to a magnetic
instability is the key to the mechanism of superconductivity in iron-pnictides.",0810.0287v1
2008-10-01,NMR measurements of intrinsic spin susceptibility in LaFeAsO(0.9)F(0.1),"We will probe the intrinsic behavior of spin susceptibility chi_(spin) in the
LaFeAsO(1-x)F(x) superconductor (x ~ 0.1, Tc ~ 27K) using 19-F and 75-As NMR
techniques. Our new results firmly establish the pseudo-gap behavior with
Delta_(PG)/kB ~ 140K. The estimated magnitude of chi_(spin) at 290K,
~1.8x10^(-4) [emu/mol-Fe], is approximately twice larger than that in high Tc
cuprates. We also show that chi_(spin) levels off below ~50K down to Tc.",0810.0305v1
2008-10-06,Pairing State with a time-reversal symmetry breaking in FeAs based superconductors,"We investigate the competition between the extended $s_{\pm}$-wave and
$d_{x^2-y^2}$-wave pairing order parameters in the iron-based superconductors.
Because of the frustrating pairing interactions among the electron and the hole
fermi pockets, a time reversal symmetry breaking $s+id$ pairing state could be
favored. We analyze this pairing state within the Ginzburg-Landau theory, and
explore the experimental consequences. In such a state, spatial inhomogeneity
induces supercurrent near a non-magnetic impurity and the corners of a square
sample. The resonance mode between the $s_{\pm}$ and $d_{x^2-y^2}$-wave order
parameters can be detected through the $B_{1g}$-Raman spectroscopy.",0810.0887v3
2008-10-06,Scanning Tunneling Spectroscopy and Vortex Imaging in the Iron-Pnictide Superconductor BaFe$_{1.8}$Co$_{0.2}$As$_2$,"We present an atomic resolution scanning tunneling spectroscopy study of
superconducting BaFe$_{1.8}$Co$_{0.2}$As$_2$ single crystals in magnetic fields
up to $9 \text{Tesla}$. At zero field, a single gap with coherence peaks at
$\overline{\Delta}=6.25 \text{meV}$ is observed in the density of states. At $9
\text{T}$ and $6 \text{T}$, we image a disordered vortex lattice, consistent
with isotropic, single flux quantum vortices. Vortex locations are uncorrelated
with strong scattering surface impurities, demonstrating bulk pinning. The
vortex-induced sub-gap density of states fits an exponential decay from the
vortex center, from which we extract a coherence length $\xi=27.6\pm 2.9
\text{\AA}$, corresponding to an upper critical field $H_{c2}=43 \text{T}$.",0810.1048v2
2008-10-08,Dielectric anomalies induced by different mechanisms in Pb(Fe1/2Nb1/2)1-xTixO3 single crystals,"We investigated the dielectric properties of Pb(Fe1/2Nb1/2)1-xTixO3 single
crystals below room temperature. Two dielectric anomalies were detected in
sample A while only one was detected in sample B in the temperature range
90~300 K. A Debye-like relaxation with strong frequency dispersion was detected
in both samples. The pre-edge XAFS suggests that this dielectric anomaly is
induced by the hopping conductivity between Fe2+ and Fe3+. The EXAFS results
give us a clear picture of the local structure of iron ions. The weak frequency
dependent dielectric anomaly only observed in sample A is supposed to be due to
the dipole glass behavior.",0810.1346v3
2008-10-08,Interband superconductivity: contrasts between BCS and Eliashberg theory,"The newly discovered iron pnictide superconductors apparently present an
unusual case of interband-channel pairing superconductivity. Here we show that,
in the limit where the pairing occurs within the interband channel, several
surprising effects occur quite naturally and generally: different
density-of-states on the two bands lead to several unusual properties,
including a gap ratio which behaves inversely to the ratio of
density-of-states; the weak-coupling limit of the Eliashberg and the BCS
theory, commonly taken as equivalent, in fact predict qualitatively different
dependence of the $\Delta_{1}/\Delta_{2}$ and $\Delta/T_{c}$ ratios on coupling
constants. We show analytically that these effects follow directly from the
interband character of superconductivity. Our results show that in the
interband-only pairing model the maximal gap ratio is $\sqrt{N_{2}/N_{1}}$ as
strong-coupling effects act only to reduce this ratio. This suggests that if
the large experimentally reported gap ratios (up to a factor 2) are correct,
the pairing mechanism must include more intraband interaction than is usually
assumed.",0810.1476v1
2008-10-09,Muon-spin rotation study of the in-plane magnetic penetration depth of FeSe_0.85: evidence for nodeless superconductivity,"The in-plane magnetic penetration depth \lambda_{ab} of the iron selenide
superconductor with the nominal composition FeSe_0.85 was studied by means of
muon-spin rotation. The measurements of \lambda_{ab}^{-2}(T) are inconsistent
with the presence of nodes in the gap as well as with a simple isotropic s-wave
type of the order parameter, but can be equally well described within a two-gap
(s+s) and an anisotropic s-wave gap picture. This implies that the
superconducting energy gap in FeSe_0.85 contains no nodes.",0810.1716v1
2008-10-09,Kondo decoherence: finding the right spin model for iron impurities in gold and silver,"We exploit the decoherence of electrons due to magnetic impurities, studied
via weak localization, to resolve a longstanding question concerning the
classic Kondo systems of Fe impurities in the noble metals gold and silver:
which Kondo-type model yields a realistic description of the relevant multiple
bands, spin and orbital degrees of freedom? Previous studies suggest a fully
screened spin $S$ Kondo model, but the value of $S$ remained ambiguous. We
perform density functional theory calculations that suggest $S = 3/2$. We also
compare previous and new measurements of both the resistivity and decoherence
rate in quasi 1-dimensional wires to numerical renormalization group
predictions for $S=1/2,1$ and 3/2, finding excellent agreement for $S=3/2$.",0810.1771v2
2008-10-10,Inverse Raman Scattering in Silicon,"Stimulated Raman scattering is a well-known nonlinear process that can be
harnessed to produce optical gain in a wide variety of media. This effect has
been used to produce the first silicon-based lasers and high-gain amplifiers.
Interestingly, the Raman effect can also produce intensity-dependent nonlinear
loss through a corollary process known as inverse Raman scattering (IRS). Here,
we demonstrate IRS in silicon--a process that is substantially modified by the
presence of optically-generated free carriers--achieving attenuation levels >15
dB with a pump intensity of 4 GW/cm^2. Ironically, we find that free-carrier
absorption, the detrimental effect that suppresses other nonlinear effects in
silicon, actually facilitates IRS by delaying the onset of contamination from
coherent anti-Stokes Raman scattering. The carriers allow significant IRS
attenuation over a wide intensity range. Silicon-based IRS could be used to
produce chip-scale wavelength-division multiplexers, optical signal inverters,
and fast optical switches.",0810.1939v1
2008-10-14,SrFeAsF as a parent compound for iron pnictide superconductors,"We have successfully synthesized the fluo-arsenide SrFeAsF, a new parent
phase with the ZrCuAsSi structure. The temperature dependence of resistivity
and dc magnetization both reveal an anomaly at about T_{an} = 173 K, which may
correspond to the structural and/or Spin-Density-Wave (SDW) transition. Strong
Hall effect and magnetoresistance were observed below T_{an}. Interestingly,
the Hall coefficient R_H is positive below T_{an}, which is opposite to the
cases in the two parent phases of FeAs-based systems known so far, i.e.,
LnFeAsO (Ln = rare earth elements) and (Ba, Sr)Fe_2As_2 where the Hall
coefficient R_H is negative. This strongly suggests that the gapping to the
Fermi surfaces induced by the SDW order is more complex than we believed before
that it removes the density of states on some Fermi pockets and leaves one of
the electron pockets less-gapped or un-gapped. Our data clearly show that it is
possible for the parent phase to have electron-like or hole-like charge
carriers.",0810.2475v2
2008-10-15,On the origin of microturbulence in hot stars,"We present results from the first extensive study of convection zones in the
envelopes of hot massive stars, which are caused by opacity peaks associated
with iron and helium ionization. These convective regions can be located very
close to the stellar surface. Recent observations of microturbulence in massive
stars from the VLT-Flames survey are in good agreement with our predictions
concerning the occurrence and the strength of sub-surface convection in hot
stars. We argue further that convection close to the surface may trigger
clumping at the base of the stellar wind of massive stars.",0810.2546v1
2008-10-17,Band Structure and Fermi Surface of an Extremely Overdoped Iron-Based Superconductor KFe2As2,"We have performed high-resolution angle-resolved photoemission spectroscopy
on heavily overdoped KFe_2As_2 (transition temperature (Tc = 3 K). We observed
several renormalized bands near the Fermi level with a renormalization factor
of 2-4. While the Fermi surface (FS) around the Brillouin-zone center is
qualitatively similar to that of optimally-doped Ba_{1-x}K_xFe_2As_2 (x = 0.4;
Tc = 37 K), the FS topology around the zone corner (M point) is markedly
different: the two electron FS pockets are completely absent due to excess of
hole doping. This result indicates that the electronic states around the M
point play an important role in the high-Tc superconductivity of
Ba$_{1-x}$K$_x$Fe$_2$As$_2$ and suggests that the interband scattering via the
antiferromagnetic wave vector essentially controls the Tc value in the
overdoped region.",0810.3047v1
2008-10-19,Cosmic Ray Results from the IceTop Air Shower Array,"We report on the first results obtained with the IceTop air shower array on
the cosmic ray energy spectrum and mass composition in the range of 1 PeV to 80
PeV. IceTop is the surface detector of the IceCube neutrino telescope currently
under construction at the South Pole. A high sensitivity to the primary mass
composition was observed by reconstructing showers at different zenith angles.
Assuming only protons or iron nuclei as primary particles yields significantly
different energy spectra for different zenith angle ranges, while only models
with mixed composition, like the poly-gonato model, lead to the expected
isotropic flux. The prospects of composition measurements with different,
alternative methods using the full IceCube detector are also discussed.",0810.3409v1
2008-10-20,Systematic ^{75}As NMR study of the dependence of low-lying excitations on F doping in the iron oxypnictide LaFeAs(O_{1-x}F_{x}),"We report systematic $^{75}$As NMR studies on LaFeAs(O$_{1-x}$F$_{x}$) ($0\le
x\le0.14$). At $x=0.04$ near the phase boundary, from resistivity, spin-lattice
relaxation rate $1/T_1$, and NMR spectrum measurements, we found weak magnetic
order at $T_N\simeq 30$ K. Antiferromagnetic (AFM) fluctuations proved through
$1/T_1$ are suppressed significantly with F-doping, and pseudogap behavior
without pronounced AFM fluctuations is observed at $x=0.11$ where $T_c$ is
maximum. This significant suppression of $1/T_1T$ upon F-doping while $T_c$
remains nearly unchanged suggests that low-energy AFM fluctuations probed with
$^{75}$As NMR do not play a crucial role in the superconductivity.",0810.3569v2
2008-10-23,The Age and Metallicity of the Bootes I System,"We present Washington photometry of a field central to the Bootes I dwarf
spheroidal galaxy, which was discovered as a stellar overdensity in the Sloan
Digital Sky Survey (DR5). We show that the Washington filters are much more
effective than the Sloan filters in separating the metal-poor turn-off stars in
the dwarf galaxy from the foreground stars. We detect 165 objects in the field,
and statistically determine that just over 40% of the objects are non-members.
Our statistical analysis mostly agrees with radial velocity measurements of the
brighter stars. We find that that there is a distinct main-sequence turn-off
and subgiant branch, where there is some evidence of a spread in chemical
abundance. Any evidence of an age spread is limited to a few billion years. The
brightest 7 Bootes I members give a (photometric-color derived) weighted mean
iron-abundance of [Fe/H]=-2.1+/-0.4, and the best-fit isochrone is the 14.1
Gyr, Z=0.0002 model, with DM=19.11 and E(B-V)=0.02.",0810.4353v1
2008-10-25,Detection of Hard X-Rays from the Compton-Thick Seyfert 2 Galaxy NGC 2273 with Suzaku,"We have obtained a broad-band spectrum of the Compton-thick Seyfert 2 galaxy
NGC 2273 with Suzaku. The spectrum reveals the first detection of hard X-rays
above ~10 keV from NGC 2273. The broad-band spectrum is well represented by a
three-component model, accompanied by both a strong iron Ka line with an
equivalent width of ~ 1.8 keV and several weak lines. The three-component model
consists of a soft component, a reflection component from cold matter, and an
absorbed power-law component. The soft component can be represented by thin
thermal emission with kT~0.56 keV or by a scattered component with a scattering
fraction of 0.4%. Fixing the photon indices of the power law and reflection
components at 1.9, we found that the power law component, heavily absorbed by
gas with a column density of ~1.5x10^24 cm^-2, has an intrinsic 2-10 keV
luminosity of ~1.7x10^42 erg/s. We also apply a reflection model based on a
Monte Carlo simulation, assuming a simple torus geometry. We found that the
model fits the broad band spectrum well, and we place some tentative
constraints on the geometry of the putative torus in NGC2273.",0810.4570v1
2008-10-26,Development of Glass Resistive Plate Chambers for INO,"The India-based Neutrino Observatory (INO) collaboration is planning to build
a massive 50kton magnetised Iron Calorimeter (ICAL) detector, to study
atmospheric neutrinos and to make precision measurements of the parameters
related to neutrino oscillations. Glass Resistive Plate Chambers (RPCs) of
about 2m X 2m in size are going to be used as active elements for the ICAL
detector. We have fabricated a large number of glass RPC prototypes of 1m X 1m
in size and have studied their performance and long term stability. In the
process, we have developed and produced a number of materials and components
required for fabrication of RPCs. We have also designed and optimised a number
of fabrication and quality control procedures for assembling the gas gaps. In
this paper we will review our activities towards development of glass RPCs for
the INO ICAL detector and will present results of the characterisation studies
of the RPCs.",0810.4693v1
2008-10-27,Anisotropic itinerant magnetism and spin fluctuations in BaFe2As2: A neutron scattering study,"Neutron scattering measurements were performed to investigate magnetic
excitations in a single-crystal sample of the ternary iron arsenide BaFe2As2, a
parent compound of a recently discovered family of Fe-based superconductors. In
the ordered state, we observe low energy spin-wave excitations with a gap
energy of 9.8(4) meV. The in-plane spin-wave velocity v_ab and out-of-plane
spin-wave velocity v_c measured at 12 meV are 280(150) and 57(7) meV A,
respectively. At high energy, we observe anisotropic scattering centered at the
antiferromagnetic wave vectors. This scattering indicates two-dimensional spin
dynamics, which possibly exist inside the Stoner continuum. At T_N=136(1) K,
the gap closes, and quasi-elastic scattering is observed above T_N, indicative
of short-range spin fluctuations. In the paramagnetic state, the scattering
intensity along the L direction becomes ""rodlike,"" characteristic of
uncorrelated out-of-plane spins, attesting to the two-dimensionality of the
system.",0810.4790v2
2008-10-31,The minimum stellar metallicity observable in the Galaxy,"The first stars fundamentally transformed the early Universe through their
production of energetic radiation and the first heavy chemical elements. The
impact on cosmic evolution sensitively depends on their initial mass function
(IMF), which can be empirically constrained through detailed studies of
ancient, metal-poor halo stars in our Galaxy. We compare the lowest magnesium
and iron abundances measured in Galactic halo stars with theoretical
predictions for the minimum stellar enrichment provided by Population III stars
under the assumption of a top-heavy IMF. To demonstrate that abundances
measured in metal-poor stars reflect the chemical conditions at their
formation, and that they can thus be used to derive constraints on the
primordial IMF, we carry out a detailed kinematic analysis of a large sample of
metal-poor stars drawn from the SDSS survey. We assess whether interstellar
accretion has altered their surface abundances. We find that accretion is
generally negligible, even at the extremely low levels where the primordial IMF
can be tested. We conclude that the majority of the first stars were very
massive, but had likely masses below ~140 M.",0811.0020v1
2008-10-31,"Anisotropy, Itineracy, and Magnetic Frustration in High-Tc Iron Pnictides","Using first-principle density functional theory calculations combined with
insight from a tight-binding representation, dynamical mean field theory, and
linear response theory, we have extensively investigated the electronic
structures and magnetic interactions of nine ferropnictides representing three
different structural classes. The calculated magnetic interactions are found to
be short-range, and the nearest ($J_{1a}$) and next-nearest ($J_{2}$) exchange
constants follow the universal trend of J_{1a}/2J_{2}\sim 1, despite their
itinerant origin and extreme sensitivity to the z-position of As. These results
bear on the discussion of itineracy versus magnetic frustration as the key
factor in stabilizing the superconducting ground state. The calculated spin
wave dispersions show strong magnetic anisotropy in the Fe plane, in contrast
to cuprates.",0811.0034v3
2008-11-05,Superconductivity at 56 K in Samarium-doped SrFeAsF,"We synthesized the samples Sr$_{1-x}$Sm$_x$FFeAs with ZrCuSiAs-type
structure. These samples were characterized by resistivity and susceptibility.
It is found that substitution of rare earth metal for alkaline earth metal in
this system suppresses the anomaly in resistivity and induces
superconductivity. Superconductivity at 56 K in nominal composition
Sr$_{0.5}$Sm$_{0.5}$FFeAs is realized, indicating that the superconducting
transition temperatures in the iron arsenide fluorides can reach as high as
that in oxypnictides with the same structure.",0811.0761v3
2008-11-06,Resolution-dependent mechanisms for bimodal switching-time distributions in simulated Fe nanopillars,"We study the magnetization-switching statistics following reversal of the
applied field for three separate computational models representing the same
physical system, an iron nanopillar. The primary difference between the models
is the resolution of the computational lattice and, consequently, the intrinsic
parameters that must be rescaled to retain similarity to the physical system.
Considering the first-passage time to zero for the magnetization component in
the longitudinal (easy-axis) direction, we look for applied fields that result
in bimodal distributions of this time for each system and compare the results
to the experimental system. We observe that the relevant fluctuations leading
to bimodal distributions are different for each lattice resolution and result
in magnetization-switching behavior that is unique to each computational model.
Correct model resolution is thus essential for obtaining reliable numerical
results for the system dynamics.",0811.1028v1
2008-11-07,Substitution Effects on FeSe Superconductor,"We have investigated the effect of atomic substitutions in the FeSe system,
which exhibits the simplest crystal structure among the iron-based
superconductors. An enhancement of the superconducting transition temperature
Tc was observed with the substitution of S or Te for Se; the Tc increased with
S substitution by up to 20 %, and also increased with Te substitution up to 75
%. In contrast, Co or Ni substitutions for the Fe site significantly suppressed
superconductivity. In this work we present a detailed description of the
substitution technique employed to determine Tc in the FeSe system.",0811.1123v3
2008-11-10,Strong short-range magnetic order in a frustrated FCC lattice and its possible role in the iron structural transformation,"We investigate magnetic properties of a frustrated Heisenberg antiferromagnet
with a face-centered cubic (FCC) lattice and exchange interactions between the
nearest- and next-nearest neighbours, J1 and J2. In a collinear phase with the
wave vector Q = (pi,pi,pi) the equations of the self-consistent spin-wave
theory for the sublattice magnetization and the average short range order
parameter are obtained and numerically solved. The dependence of the Neel
temperature T_N on the ratio J2/J1 is obtained. It is shown, that at strong
enough frustration there is a wide temperature region above T_N with strong
short range magnetic order. Application of this result to description of
structural phase transition between alpha and gamma-phase of Fe is considered.",0811.1472v1
2008-11-10,The XMM-Newton long look of NGC 1365: uncovering of the obscured X-ray source,"We present an analysis of the extreme obscuration variability observed during
an XMM-Newton 5-days continuous monitoring of the AGN in NGC 1365. The source
was in a reflection-dominated state in the first ~1.5 days, then a strong
increase of the 7-10 keV emission was observed in ~10 hours, followed by a
symmetric decrease. The spectral analysis of the different states clearly shows
that this variation is due to an uncovering of the X-ray source. From this
observation we estimate a size of the X-ray source D_S<10^13 cm, a distance of
the obscuring clouds R~10^16 cm and a density n~10^11 cm^{-3}. These values
suggest that the X-ray absorption/reflection originate from the broad line
region clouds. This is also supported by the resolved width of the iron narrow
Kalpha emission line, consistent with the width of the broad Hbeta line.",0811.1594v2
2008-11-12,CERN-INO magical Beta-beam experiment: A high precision probe for neutrino parameters,"This talk is an attempt to underscore in detail the physics reach of an
experimental set-up where neutrinos produced in a beta-beam facility at CERN
would be observed in the proposed large magnetized iron calorimeter detector
(ICAL) at the India-based Neutrino Observatory (INO). The ""magical"" CERN-INO
beta-beam set-up offers an excellent avenue to use the ""Golden"" channel ($\nu_e
\to \nu_{\mu}$) oscillation probability for a simultaneous determination of the
neutrino mass ordering and $\theta_{13}$ avoiding the impact of the CP phase
$\delta_{CP}$ on these measurements. With Lorentz boost $\gamma=650$ and
irrespective of the true value of $\delta_{CP}$, the neutrino mass hierarchy
could be determined at $3\sigma$ C.L. if $\sin^22\theta_{13}{\rm {(true)}} >
5.6 \times 10^{-4}$ and we can expect an unambiguous signal for $\theta_{13}$
at $3\sigma$ C.L. if $\sin^22\theta_{13}{\rm {(true)}} > 5.1 \times 10^{-4}$
independent of the true neutrino mass hierarchy.",0811.1822v1
2008-11-12,X-Ray Reflection Nebulae with Large Equivalent Widths of Neutral Iron Ka Line in the Sgr C Region,"This paper reports on the first results of the Suzaku observation in the Sgr
C region. We detected four diffuse clumps with strong line emission at 6.4keV,
Ka from neutral or low-ionized Fe. One of them, M359.38-0.00, is newly
discovered with Suzaku. The X-ray spectra of the two bright clumps,
M359.43-0.07 and M359.47-0.15, after subtracting the Galactic center diffuse
X-ray emission (GCDX), exhibit strong Ka line from FeI with large equivalent
widths (EWs) of 2.0-2.2keV and clear Kb of FeI. The GCDX in the Sgr C region is
composed of the 6.4keV- and 6.7keV-associated components. These are
phenomenologically decomposed by taking relations between EWs of the 6.4keV and
6.7keV lines. Then the former EWs against the associated continuum in the
bright clump regions are estimated to be 2.4(+2.3_-0.7)keV. Since the two
different approaches give similar large EWs of 2keV, we strongly suggest that
the 6.4keV clumps in the Sgr C region are due to X-ray reflection/fluorescence
(the X-ray reflection nebulae).",0811.1830v1
2008-11-12,Bond analysis of cobalt and iron based skutterudites: elongated lanthanum bonds in LaFe4P12,"Motivated by the possibility of further improving the thermoelectric
properties of skutterudites we investigate charge transfer and bonding in this
class of materials using density functional calculations. Results for the CoP3,
CoSb3, LaFe4P12 and the hypothetical FeP3 compounds are presented using the
procrystal as the non-binding reference. Spherical integration and Bader
analysis are performed to illustrate charge transfer differences between these
compounds. The results are in good qualitative agreement with simple
electronegativity considerations. The calculations confirm that the transition
metal-pnictogen and the pnictogen-pnictogen bonds are covalent, while the
filler atom-pnictogen bond is of a more polar and complex nature. The success
of the ""rattling"" cage as phonon inhibitor is explained by a unique
semi-correlated bonding scheme between lanthanum and phosphorus. Elongated
bonds along the crystal axes surrounds the lanthanum ion and generate a
dodecahedra grid. Vibrations along the crystal axes are then closely connected
to and scatter from the phosphorus rings. In the other directions, a more
uncorrelated vibration is possible. This duality widens the phonon dampening
possibilities.",0811.1889v1
2008-11-14,"Metallicities for 13 nearby open clusters from high-resolution spectroscopy of dwarf and giant stars. Stellar metallicity, stellar mass, and giant planets","We present a study of accurate stellar parameters and iron abundances for 39
giants and 16 dwarfs in the 13 open clusters IC2714, IC4651, IC4756, NGC2360,
NGC2423, NGC2447 (M93), NGC2539, NGC2682 (M67), NGC3114, NGC3680, NGC4349,
NGC5822, NGC6633. The analysis was done using a set of high-resolution and
high-S/N spectra obtained with the UVES spectrograph (VLT). These clusters are
currently being searched for planets using precise radial velocities. For all
the clusters, the derived average metallicities are close to solar.
Interestingly, the values derived seem to depend on the line-list used. This
dependence and its implications for the study of chemical abundances in giants
stars are discussed. We show that a careful choice of the lines may be crucial
for the derivation of metallicities for giant stars on the same metallicity
scale as those derived for dwarfs. Finally, we discuss the implications of the
derived abundances for the metallicity- and mass-giant planet correlation. We
conclude that a good knowledge of the two parameters is necessary to correctly
disentangle their influence on the formation of giant planets.",0811.2392v1
2008-11-16,Solar neutrinos and the solar composition problem,"Standard solar models (SSM) are facing nowadays a new puzzle: the solar
composition problem. New determinations of solar metal abundances lead SSM
calculations to conflict with helioseismological measurements, showing
discrepancies that extend from the convection zone to the solar core and can
not be easily assigned to deficiencies in the modelling of the solar convection
zone. We present updated solar neutrino fluxes and uncertainties for two SSM
with high (old) and low (new) solar metallicity determinations. The
uncertainties in iron and carbon abundances are the largest contribution to the
uncertainties of the solar neutrino fluxes. The uncertainty on the ^14N+p ->
^15O+g rate is the largest of the non-composition uncertainties to the CNO
neutrino fluxes. We propose an independent method to help identify which SSM is
the correct one. Present neutrino data can not distinguish the solar neutrino
predictions of both models but ongoing measurements can help to solve the
puzzle.",0811.2424v1
2008-11-16,The Absence of Superconductivity in Single Phase CaFe2As2 under Hydrostatic Pressure,"Recent high-pressure studies found that superconductivity can be achieved
under very low pressure in the parent iron arsenide compound CaFe2As2, although
details of the sharpness and temperature of transitions vary between liquid
medium and gas medium measurements. To better understand this issue, we
performed high-pressure susceptibility and transport studies on CaFe2As2, using
helium as the pressure medium. The signatures of the transitions to the
low-temperature orthorhombic and collapsed tetragonal phase remained
exceptionally sharp and no signature of bulk superconductivity was found under
our hydrostatic conditions. Our results suggest that phase separation and
superconductivity in CaFe2As2 are induced by non-hydrostatic conditions
associated with the frozen liquid media.",0811.2554v2
2008-11-19,The location and kinematics of the coronal-line emitting regions in AGN,"We use the photoionisation code Cloudy to determine both the location and the
kinematics of the optical forbidden, high ionisation line (hereafter, FHIL)
emitting gas in the narrow line Seyfert 1 galaxy Ark 564. The results of our
models are compared with the observed properties of these emission lines to
produce a physical model that is used to explain both the kinematics and the
source of this gas. The main features of this model are that the FHIL emitting
gas is launched from the putative dusty torus and is quickly accelerated to its
terminal velocity of a few hundred km/s. Iron-carrying grains are destroyed
during this initial acceleration. This velocity is maintained by a balance
between radiative forces and gravity in this super-Eddington source. Eventually
the outflow is slowed at large radii by the gravitational forces of and
interactions with the host galaxy. In this model, FHIL emission traces the
transition between the AGN and bulge zones of influence.",0811.3204v1
2008-11-20,A critical re-examination of resonant soft x-ray Bragg forbidden reflections in magnetite,"Magnetite, Fe$_3$O$_4$, displays a highly complex low temperature crystal
structure that may be charge and orbitally ordered. Many of the recent
experimental claims of such ordering rely on resonant soft x-ray diffraction at
the oxygen K and iron L edges. We have re-examined this system and undertaken
soft x-ray diffraction experiments on a high-quality single crystal. Contrary
to previous claims in the literature, we show that the intensity observed at
the Bragg forbidden (001/2)$_c$ reflection can be explained purely in terms of
the low-temperature structural displacements around the resonant atoms. This
does not necessarily mean that magnetite is not charge or orbitally ordered,
but rather that the present sensitivity of resonant soft x-ray experiments does
not allow conclusive demonstration of such ordering.",0811.3350v2
2008-11-22,75As-NMR studies on La FeAsO1-xFx (x=0.14) under a pressure of 3GPa,"75As-nuclear magnetic resonance (NMR) on an iron-based superconductor
LaFeAsO1-xFx (x=0.14) was performed under a pressure of 3GPa. Enhancement of
superconducting transition temperature Tc was confirmed from the relaxation
rate 1/T1; Tc goes up to 40K by applying pressure up to 3GPa. 1/T1T, which is
temperature independent just above Tc and gives a measure of the density of
states (DOS) at the Fermi energy, enhances by applying pressure. These facts
suggest that the increase of the DOS leads to the enhancement of Tc. On the
other hand, anomalous behavior of 1/T1T observed at high temperatures is
suppressed by applying pressure.",0811.3672v3
2008-11-26,Ironing out primordial temperature fluctuations with polarisation: optimal detection of cosmic structure imprints,"Secondary anisotropies of the cosmic microwave background (CMB) can be
detected by using the cross-correlation between the large-scale structure (LSS)
and the CMB temperature fluctuations. In such studies, chance correlations of
primordial CMB fluctuations with the LSS are the main source of uncertainty. We
present a method for reducing this noise by exploiting information contained in
the polarisation of CMB photons. The method is described in general terms and
then applied to our recently proposed optimal method for measuring the
integrated Sachs-Wolfe (ISW) effect. We obtain an expected signal-to-noise
ratio of up to 8.5. This corresponds to an enhancement of the signal-to-noise
by 23 per cent as compared to the standard method for ISW detection, and by 16
per cent w.r.t. our recently proposed method, both for the best-case scenario
of having perfect (noiseless) CMB and LSS data.",0811.4433v2
2008-11-27,"A unified theory for the cuprates, iron-based and similar superconducting systems: non-Fermi-liquid to Fermi-liquid crossover, low-energy and waterfall anomalies","A unified theory is outlined for the cuprates, Fe-based, and related
superconductors. Their low-energy excitations are approached in terms of
auxiliary particles representing combinations of atomic-like electron
configurations, and the introduction of a Lagrange Bose field enables their
treatment as bosons or fermions. This theory correctly describes the observed
phase diagram of the cuprates, including the non-Fermi-liquid to FL crossover
in the normal state, the existence of Fermi arcs below T^* and of ""marginal-FL""
behavior above it. The anomalous behavior of numerous physical quantities is
accounted for, including kink- and waterfall-like spectral features, the drop
in the scattering rates below T^* and more radically below T_c, and an
effective increase in the density of carriers with T and \omega, reflected in
transport, optical and other properties. Also is explained the correspondence
between T_c, the resonance-mode energy, and the increase in the gap below T_c.",0811.4561v1
2008-11-27,Two-dimensional magnetism in the pnictide superconductor parent material SrFeAsF probed by muon-spin relaxation,"We report muon-spin relaxation measurements on SrFeAsF, which is the parent
compound of a newly discovered iron-arsenic-fluoride based series of
superconducting materials. We find that this material has very similar magnetic
properties to LaFeAsO, such as separated magnetic and structural transitions
(TN = 120 K, Ts = 175 K), contrasting with SrFe2As2 where they are coincident.
The muon oscillation frequencies fall away very sharply at TN, which suggests
that the magnetic exchange between the layers is weaker than in comparable
oxypnictide compounds. This is consistent with our specific heat measurements,
which find that the entropy change S = 0.05 J/mol/K largely occurs at the
structural transition and there is no anomaly at TN.",0811.4598v1
2008-11-30,Andreev Bound states as a phase sensitive probe of the pairing symmetry of the iron pnictide superconductors,"A leading contender for the pairing symmetry in the Fe-pnictide high
temperature superconductors is extended s-wave $s_\pm$, a nodeless state in
which the pairing changes sign between Fermi surfaces. Verifying such a pairing
symmetry requires a special phase sensitive probe that is also momentum
selective. We show that the sign structure of $s_\pm$ pairing leads to surface
Andreev bound states at the sample edge. In the clean limit they only occur
when the edge is along the nearest neighbor Fe-Fe bond, but not for a diagonal
edge or a surface orthogonal to the c-axis. In contrast to d-wave Andreev bound
states, they are not at zero energy and, in general, do not produce a zero bias
tunneling peak. Consequences for tunneling measurements are derived, within a
simplified two band model and also for a more realistic five band model.",0812.0015v1
2008-11-28,Small RNAs Establish Delays and Temporal Thresholds in Gene Expression,"Non-coding RNAs are crucial regulators of gene expression in prokaryotes and
eukaryotes, but it remains poorly understood how they affect the dynamics of
transcriptional networks. We analyzed the temporal characteristics of the
cyanobacterial iron stress response by mathematical modeling and quantitative
experimental analyses, and focused on the role of a recently discovered small
non-coding RNA, IsrR. We found that IsrR is responsible for a pronounced delay
in the accumulation of isiA mRNA encoding the late-phase stress protein, IsiA,
and that it ensures a rapid decline in isiA levels once external stress
triggers are removed. These kinetic properties allow the system to selectively
respond to sustained (as opposed to transient) stimuli, and thus establish a
temporal threshold, which prevents energetically costly IsiA accumulation under
short-term stress conditions. Biological information is frequently encoded in
the quantitative aspects of intracellular signals (e.g., amplitude and
duration). Our simulations reveal that competitive inhibition and regulated
degradation allow intracellular regulatory networks to efficiently discriminate
between transient and sustained inputs.",0812.0025v1
2008-12-01,Near-degeneracy of several pairing channels in multiorbital models for the Fe-pnictides,"Weak-coupling approaches to the pairing problem in the iron pnictide
superconductors have predicted a wide variety of superconducting ground states.
We argue here that this is due both to the inadequacy of certain approximations
to the effective low-energy band structure, and to the natural near-degeneracy
of different pairing channels in superconductors with many distinct Fermi
surface sheets. In particular, we review attempts to construct two-orbital
effective band models, the argument for their fundamental inconsistency with
the symmetry of these materials, and the comparison of the dynamical
susceptibilities in two- and five-orbital models. We then present results for
the magnetic properties, pairing interactions, and pairing instabilities within
a five-orbital Random Phase Approximation model. We discuss the robustness of
these results for different dopings, interaction strengths, and variations in
band structure. Within the parameter space explored, an anisotropic,
sign-changing s-wave state and a d_x2-y2 state are nearly degenerate, due to
the near nesting of Fermi surface sheets.",0812.0343v2
2008-12-04,Medium Effects in rho-Meson Photoproduction,"We compute dilepton invariant mass spectra from the decays of rho mesons
produced by photon reactions off nuclei. Our calculations employ a realistic
model for the rho photoproduction amplitude on the nucleon which provides fair
agreement with measured cross sections. Medium effects are implemented via an
earlier constructed rho propagator based on hadronic many-body theory. At
incoming photon energies of 1.5 -3 GeV as used by the CLAS experiment at JLAB,
the average density probed for iron targets is estimated at about half
saturation density. At the pertinent rho-meson 3-momenta the predicted medium
effects on the rho propagator are rather moderate. The resulting dilepton
spectra approximately agree with recent CLAS data.",0812.0987v3
2008-12-09,Insular superconductivity in Co-doped iron pnictide CaFe$_{1-x}$Co$_x$AsF,"The presence of macroscopic phase separation between the superconducting and
magnetic phases in \cfcaf is demonstrated by muon spin rotation (muSR)
measurements conducted across their phase boundaries (x=0.05-0.15). The
magnetic phase tends to retain the high transition temperature (T_m > T_c),
while Co-doping induces strong randomness. The volumetric fraction of
superconducting phase is nearly proportional to the Co content $x$ with
constant superfluid density. These observations suggest the formation of
superconducting ""islands"" (or domains) associated with Co ions in the
Fe$_2$As$_2$ layers, indicating a very short coherence length.",0812.1670v3
2008-12-10,Disk reflection signatures in the spectrum of the bright Z-source GX 340+0,"We present the preliminary results of a 50 ks long XMM-Newton observation of
the bright Z-source GX 340+0. In this Letter we focus on the study of a broad
asymmetric emission line in the Fe K alpha energy band, whose shape is clearly
resolved and compatible with a relativistically smeared profile arising from
reflection on a hot accretion disk extending close to the central accreting
neutron star. By combining temporal and spectral analysis, we are able to
follow the evolution of the source along its Horizontal Branch. However,
despite a significant change in the continuum emission and luminosity, the line
profile does not show any strong correlated variation. This broad line is
produced by recombination of highly ionized iron (Fe XXV) at an inferred inner
radius close to 13 gravitational radii while the fit requires a high value for
the outer disk radius. The inclination of the source is extremely well
constrained at 35 deg, while the emissivity index is -2.50.",0812.1974v1
2008-12-11,Full Gap Superconductivity in Ba$_{0.6}$K$_{0.4}$Fe$_2$As$_2$ Probed by Muon Spin Rotation,"Superfluid density ($n_s$) in the mixed state of an iron pnictide
superconductor Ba$_{0.6}$K$_{0.4}$Fe$_2$As$_2$ is determined by muon spin
rotation for a sample with optimal doping ($x=0.4$). The temperature dependence
of $n_s$ is perfectly reproduced by the conventional BCS model for s-wave
paring, where the order parameter can be either a single-gap with
$\Delta=8.35(6)$ meV [$2\Delta/k_BT_c=5.09(4)$], or double-gap structure with
$\Delta_1=12$ meV (fixed) [$2\Delta_1/k_BT_c=7.3$] and $\Delta_2=6.8(3)$ meV
[$2\Delta_2/k_BT_c=4.1(2)$]. The latter is consistent with the recent result of
angle-resolved photo-emssion spectroscopy. The large gap parameters
($2\Delta/k_BT_c$) indicate extremely strong coupling of carriers to bosons
that mediate the Cooper pairing.",0812.2069v2
2008-12-11,Impurity-induced in-gap state and Tc in sign-reversing s-wave superconductors: analysis of iron oxypnictide superconductors,"The sign-reversing fully gapped superconducting state, which is expected to
be realized in oxypnictide superconductors, can be prominently affected by
nonmagnetic impurities due to the interband scattering of Cooper pairs. We
study this problem based on the isotropic two-band BCS model: In oxypnictide
superconductors, the interband impurity scattering $I'$ is not equal to the
intraband one $I$. In the Born scattering regime, the reduction in Tc is
sizable and the impurity-induced density of states (DOS) is prominent if $I\sim
I'$, due to the interband scattering. Although impurity-induced DOS can yield a
power-law temperature dependence in $1/T_1$, a sizable suppression in Tc is
inevitably accompanied. In the unitary scattering regime, in contrast, impurity
effect is very small for both Tc and DOS except at $I=I'$. By comparing theory
and experiments, we expect that the degree of anisotropy in the $s_\pm$-wave
gap function strongly depends on compounds.",0812.2100v2
2008-12-11,Quantum and classical structures in nondeterminstic computation,"In categorical quantum mechanics, classical structures characterize the
classical interfaces of quantum resources on one hand, while on the other hand
giving rise to some quantum phenomena. In the standard Hilbert space model of
quantum theories, classical structures over a space correspond to its
orthonormal bases. In the present paper, we show that classical structures in
the category of relations correspond to biproducts of abelian groups. Although
relations are, of course, not an interesting model of quantum computation, this
result has some interesting computational interpretations. If relations are
viewed as denotations of nondeterministic programs, it uncovers a wide variety
of non-standard quantum structures in this familiar area of classical
computation. Ironically, it also opens up a version of what in philosophy of
quantum mechanics would be called an ontic-epistemic gap, as it provides no
direct interface to these nonstandard quantum structures.",0812.2266v3
2008-12-15,Microscopic origin of pressure-induced phase transitions in iron-pnictide $AFe_2As_2$ superconductors: an {ab initio} molecular-dynamics study,"Using {\it ab initio} molecular dynamics we investigate the electronic and
lattice structure of $A$Fe$_2$As$_2$ ($A$=Ca, Sr, Ba) under pressure. We find
that the structural phase transition (orthorhombic to tetragonal symmetry) is
always accompanied by a magnetic phase transition in all the compounds, while
the nature of the transitions is different for the three systems. Our
calculations explain the origin of the existence of a collapsed tetragonal
phase in CaFe$_2$As$_2$ and its absence in BaFe$_2$As$_2$. We argue that
changes of the Fermi surface nesting features dominate the phase transition
under pressure rather than spin frustration or a Kondo scenario. The
consequences for superconductivity are discussed.",0812.2920v3
2008-12-16,Anomalous Hall effect in granular ferromagnetic metals and effects of weak localization,"We theoretically investigate the anomalous Hall effect in a system of
dense-packed ferromagnetic grains in the metallic regime. Using the formalism
recently developed for the conventional Hall effect in granular metals, we
calculate the residual anomalous Hall conductivity $\sigma_{xy}$ and
resistivity $\rho_{xy}$ and weak localization corrections to them for both
skew-scattering and side-jump mechanisms. We find that, unlike for
homogeneously disordered metals, the scaling relation between $\rho_{xy}$ and
the longitudinal resistivity $\rho_{xx}$ does not hold. The weak localization
corrections, however, are found to be in agreement with those for homogeneous
metals. We discuss recent experimental data on the anomalous Hall effect in
polycrystalline iron films in view of the obtained results.",0812.3085v2
2008-12-18,"Observation of the Josephson effect in Pb/(Ba,K)Fe2As2 single crystal junctions","We have fabricated c-axis Josephson junctions on single crystals of
(Ba,K)Fe2As2 by using Pb as the counter electrode in two geometries, planar and
point contact. Junctions in both geometries show resistively shunted junction
I-V curves below the Tc of the counter electrode. Microwave induced steps were
observed in the I-V curves, and the critical currents are suppressed with an
in-plane magnetic field in a manner consistent with the small junction limit.
ICRN products of up to 0.3 mV have been observed in these junctions at 4.2 K.
The observation of Josephson coupling along the c-axis between (Ba,K)Fe2As2 and
a conventional superconductor suggests the existence of a s-wave
superconducting order parameter in this class of iron pnictide superconductors.",0812.3605v2
2008-12-21,Suppression of antiferromagnetic spin fluctuations in the collapsed tetragonal phase of CaFe2As2,"Inelastic neutron scattering measurements of CaFe2As2 under applied
hydrostatic pressure show that the antiferromagnetic spin fluctuations observed
in the ambient pressure, paramagnetic, tetragonal (T) phase are strongly
suppressed, if not absent, in the collapsed tetragonal (cT) phase. These
results are consistent with a quenched Fe moment in the cT phase and the strong
decrease in resistivity observed upon crossing the boundary from the T to cT
phase. The suppression or absence of static antiferromagnetic order and dynamic
spin fluctuations in the non-superconducting cT phase supports the notion of a
coupling between spin fluctuations and superconductivity in the iron arsenides.",0812.4056v1
2008-12-22,Electronic structure of heavily electron-doped BaFe$_{1.7}$Co$_{0.3}$As$_2$ studied by angle-resolved photoemission,"We have performed high-resolution angle-resolved photoemission spectroscopy
on heavily electron-doped non-superconducting (SC)
BaFe$_{1.7}$Co$_{0.3}$As$_2$. We find that the two hole Fermi surface pockets
at the zone center observed in the hole-doped superconducting
Ba$_{0.6}$K$_{0.4}$Fe$_2$As$_2$ are absent or very small in this compound,
while the two electron pockets at the M point significantly expand due to
electron doping by the Co substitution. Comparison of the Fermi surface between
non-SC and SC samples indicates that the coexistence of hole and electron
pockets connected via the antiferromagnetic wave vector is essential in
realizing the mechanism of superconductivity in the iron-based superconductors.",0812.4111v3
2008-12-29,Superconducting properties of the oxygen-vacant iron oxyarsenide TbFeAsO1-x from underdoped to overdoped compositions,"A wide-range doping was achieved by a high-pressure method for TbFeAsO1-x
from ""under doped"" to ""over doped"" superconducting compositions throughout the
optimized superconductivity (Tc of 44 K). Tc vs. lattice constant shows a
dome-shaped feature, while Tc vs. the lattice constant likely follows a unique
empirical curve over the doping range. The relatively large amount of oxygen
vacancies up to 0.3 per the formula unit was introduced possibly because of the
smaller replacement Tb than the other Ln (rare-earth element) in the LnFeAsO1-x
system.",0812.4907v2
2009-01-01,75As NMR Study of Hole-Doped Superconductor Ba1-xKxFe2As2 (Tc = 38K),"We report the 75As nuclear magnetic resonance (NMR) measurement of the
hole-doped superconductor Ba1-xKxFe2As2 with different lattice parameters and
different superconducting volume fractions (Tc = 38K). 75As-NMR spectra
revealed that the magnetically ordered and superconducting phases are
microscopically separated. The spin-lattice relaxation rate 1/T1 in the normal
state reflects the existence of a large two-dimensional antiferromagnetic spin
fluctuation. The 1/T1 in the superconducting state down to the lowest
measurement temperature T varies close to T^3. In addition, it exhibits no
coherence peak just below Tc. This shows a T dependence similar to those of
other iron pnictides.",0901.0177v2
2009-01-02,Electronic structure and Magnetism in BaMn$_2$As$_2$ and BaMn$_2$Sb$_2$,"We study the properties of ThCr$_2$Si$_2$ structure BaMn$_2$As$_2$ and
BaMn$_2$Sb$_2$ using density functional calculations of the electronic and
magnetic as well experimental measurements on single crystal samples of
BaMn$_2$As$_2$. These materials are local moment magnets with moderate band gap
antiferromagnetic semiconducting ground states. The electronic structures show
substantial Mn - pnictogen hybridization, which stabilizes an intermediate spin
configuration for the nominally $d^5$ Mn. The results are discussed in the
context of possible thermoelectric applications and the relationship with the
corresponding iron / cobalt / nickel compounds Ba(Fe,Co,Ni)$_2$As$_2$.",0901.0272v2
2009-01-09,Fermi surface topology and low-lying quasiparticle structure of magnetically ordered Fe1+xTe,"We report the first photoemission study of Fe1+xTe - the host compound of the
newly discovered iron-chalcogenide superconductors. Our results reveal a pair
of nearly electron- hole compensated Fermi pockets, strong Fermi velocity
renormalization and an absence of a spin-density-wave gap. A shadow hole pocket
is observed at the ""X""-point of the Brillouin zone which is consistent with a
long-range ordered magneto-structural groundstate. No signature of Fermi
surface nesting instability associated with Q= pi(1/2, 1/2) is observed. Our
results collectively reveal that the Fe1+xTe series is dramatically different
from the undoped phases of the high Tc pnictides and likely harbor unusual
mechanism for superconductivity and quantum magnetic order.",0901.1299v1
2009-01-11,Theory of tunnelling into a multi-band superconductor: decoherence and interference,"By an exact formulation of tunnelling into a multi-band superconductor in
terms of Green's functions, we demonstrate that the multi-band feature of the
iron-based superconductors can lead to novel interference between Andreev
reflections and decoherence effect of quasi-particles to Andreev reflections in
a tunnelling junction. These effects depend on the relative sign of the gaps
for s-wave pairing, and the sign of the Fermi velocities also matters for
tunnelling along the nodal direction of d-wave gaps. Experimental probe of such
effects could determine both the pairing symmetry and the relative sign of the
gaps on different bands.",0901.1419v2
2009-01-14,Plasma focus based repetitive source of fusion neutrons and hard x-rays,"A plasma focus device capable of operating at 0.2 pulses per second during
several minutes is used as a source of hard x-rays and fast neutrons. An
experimental demonstration of the use of the neutrons emissions for radiation
probing of hydrogenated substances is presented, showing a particular
application in detecting water concentrations differences in the proximity of
the device by elastic scattering. Moreover, the device produces ultrashort hard
x-rays pulses useful for introspective images of small objects, static or in
fast motion, suitable for the identification of internal submillimetric
defects. Clear images of metallic objects shielded by several millimeters iron
walls are shown.",0901.2007v1
2009-01-16,Star Formation in HII Galaxies. Properties of the ionized gas,"We propose a methodology to perform a self-consistent analysis of the
physical properties of the emitting gas of HII galaxies adequate to the data
that can be obtained with the XXI century technology. This methodology requires
the production and calibration of empirical relations between the different
line temperatures that should superseed currently used ones based on very
simple, and poorly tested, photo-ionization model sequences. Then, these
observations are analysed applying a methodology designed to obtain accurate
elemental abundances of oxygen, sulphur, nitrogen, neon, argon and iron in the
ionsied gas. Four electron temperatures and one electron density are derived
from the observed forbidden line ratios using the five-level atom
approximation. For our best objects errors of 1% in T([OIII]), 3% in T([OII])
and 5% in T([SIII]) are achieved with a resulting accuracy between 5 and 9% in
total oxygen abundances, O/H. These accuracies are expected to improve as
better calibrations based on more precise measurements, both on electron
temperatures and densities, are produced.",0901.2465v1
2009-01-19,NMR Studies on the Superconducting Symmetry of Iron Pnictide Systems,"NMR longitudinal relaxation rates 1/T1 and Knight shifts K have been measured
for superconducting samples of LaFe1-yCoyAsO1-xFx with y=0.0 and 0.0075 and for
a nonsuperconducting metallic sample with y=0.1, where the x values are always
fixed at 0.11. The temperature (T) dependence the relaxation rates 1/T1 of the
superconducting samples has been found to be markedly different from the
behavior 1/T1 T^(2.5-3.0) reported by many groups in the entire T range
measured (from the temperature immediately below the superconducting transition
temperature Tc down to (0.1-0.2)Tc). The nonexistence of the coherence peak has
also been found. Based on the results of the measurements and other kinds of
existing data, arguments are presented on the superconducting symmetry of the
Fe pnictide systems, where the several points which cannot be easily understood
by existing theories, are pointed out. Results of the measurements on the
nonsuperconducting metallic samples are also presented.",0901.2830v1
2009-01-20,Broad relativistic iron emission line observed in SAX J1808.4-3658,"During the September-October 2008 outburst of the accreting millisecond
pulsar SAX J1808.4-3658, the source was observed by both Suzaku and XMM-Newton
approximately 1 day apart. Spectral analysis reveals a broad relativistic Fe
K-alpha emission line which is present in both data-sets, as has recently been
reported for other neutron star low-mass X-ray binaries. The properties of the
Fe K line observed during each observation are very similar. From modeling the
Fe line, we determine the inner accretion disk radius to be 13.2 +/- 2.5
GM/c^2. The inner disk radius measured from the Fe K line suggests that the
accretion disk is not very receded in the island state. If the inner disk (as
measured by the Fe line) is truncated at the magnetospheric radius this implies
a magnetic field strength of ~3E8 G at the magnetic poles, consistent with
other independent estimates.",0901.3142v2
2009-01-21,Superconductivity up to 30 K in the vicinity of quantum critical point in BaFe$_{2}$(As$_{1-x}$P$_{x}$)$_{2}$,"We report bulk superconductivity induced by an isovalent doping of phosphorus
in BaFe$_{2}$(As$_{1-x}$P$_{x}$)$_{2}$. The P-for-As substitution results in
shrinkage of lattice, especially for the FeAs block layers. The resistivity
anomaly associated with the spin-density-wave (SDW) transition in the undoped
compound is gradually suppressed by the P doping. Superconductivity with the
maximum $T_c$ of 30 K emerges at $x$=0.32, coinciding with a magnetic quantum
critical point (QCP) which is evidenced by the disappearance of SDW order and
the linear temperature-dependent resistivity in the normal state. The $T_c$
values were found to decrease with further P doping, and no superconductivity
was observed down to 2 K for $x\geq$ 0.77. The appearance of superconductivity
in the vicinity of QCP hints to the superconductivity mechanism in iron-based
arsenides.",0901.3227v2
2009-01-26,RXTE confirmation of the intermediate polar status of IGR J15094-6649,"Aims. To establish the X-ray properties of the intermediate polar candidate
IGR J15094-6649 and therefore confirm its inclusion into the class.
  Methods. 42 856 s of X-ray data from RXTE was analysed. Frequency analysis
was used to constrain temporal variations and spectral analysis used to
characterise the emission and absorption properties.
  Results. A spin period of 809.7+-0.6 s is present, revealed as a complex
pulse profile whose modulation depth decreases with increasing X-ray energy.
The spectrum is well fitted by either a 19+-4 keV Bremsstrahlung or
Gamma=1.8+-0.1 power law, with an iron emission line feature and significant
absorption in each case.
  Conclusions. IGR J15094-6649 is confirmed to be an intermediate polar.",0901.3983v1
2009-01-28,Chemical evolution of the galactic bulge: single and double infall models,"Recent work has produced a wealth of data concerning the chemical evolution
of the galactic bulge, both for stars and nebulae. Present theoretical models
generally adopt a limited range of such constraints, frequently using a single
chemical element (usually iron), which is not enough to describe it
unambiguously. In this work, we take into account constraints involving as many
chemical elements as possible, basically obtained from bulge nebulae and stars.
Our main goal is to show that different scenarios can describe, at least
partially, the abundance distribution and several distance-independent
correlationss for these objects. Three classes of models were developed. The
first is a one-zone, single-infall model, the second is a one-zone,
double-infall model and the third is a multizone, double infall model. We show
that a one-zone model with a single infall episode is able to reproduce some of
the observational data, but the best results are achieved using a multizone,
double infall model.",0901.4382v1
2009-02-06,"Superconductivity, magnetism and crystal chemistry of Ba1-xKxFe2As2","BaFe2As2 is the parent compound of the '122' iron arsenide superconductors
and crystallizes with the tetragonal ThCr2Si2 type structure, space group
I4/mmm. A spin density wave transition at 140 K is accompanied by a symmetry
reduction to space group Fmmm and simultaneously by antiferromagnetic ordering.
Hole-doping induces superconductivity in Ba1-xKxFe2As2 with a maximum Tc of 38
K at x = 0.4. The upper critical fields approach 75 T with rather small
anisotropy of Hc2. At low potassium concentrations (x <= 0.2),
superconductivity apparently co-exists with the orthorhombic distorted and
magnetically ordered phase. At doping levels x >= 0.3, the structural
distortion and antiferromagnetic ordering is completely suppressed and the Tc
is maximized. No magnetically ordered domains could be detected in optimally
doped Ba1-xKxFe2As2 (x >= 0.3) by 57Fe-Moessbauer spectroscopy in contrast muSR
results obtained with single crystals. The magnetic hyperfine interactions
investigated by 57Fe Moessbauer spectroscopy are discussed and compared to the
ZrCuSiAs-type materials.",0902.1085v1
2009-02-07,Superconducting fluctuations in the reversible magnetization of the iron-pnictide $Ba_{1-x}K_xFe_2As_2$,"We report on isofield magnetization curves obtained as a function of
temperature in two single crystals of $Ba_{1-x}K_xFe_2As_2$ with
superconducting transition temperature $T_c$=28K and 32.7 K. Results obtained
for fields above 20 kOe show a well defined rounding effect on the reversible
region extending 1-3 K above $T_c(H)$ masking the transition. This rounding
appears to be due to three-dimensional critical fluctuations, as the higher
field curves obey a well know scaling law for this type of critical
fluctuations. We also analysed the asymptotic behavior of $\sqrt M$vs.T curves
in the reversible region which probes the shape of the gap near $T_c(H)$.
Results of the analysis suggests that phase fluctuations are important in
$Ba_{1-x}K_xFe_2As_2$ which is consistent with nodes in the gap.",0902.1252v2
2009-02-10,Enhancement of electronic anomalies in iron-substituted La_2-x_Sr_x_Cu_1-y_Fe_y_O_4_ around x=0.22,"We have measured the temperature dependences of Rho and Chi for
Fe-substituted La_2-x_Sr_x_Cu_1-y_Fe_y_O_4_ in the overdoped regime, in order
to investigate Fe-substitution effects on electronic properties around x=0.22.
  From the Rho measurements, it has been found around x=0.22 that the values of
Rho are large at room temperature and that Rho exhibits a pronounced upturn at
low temperatures. Moreover, from the Rho and Chi measurements, it has been
found that T_c_ is anomalously depressed around x=0.22. These results indicate
that the electronic anomalies around x=0.22 are enhanced by Fe substitution,
which might be related to the development of stripe correlations by Fe
substitution.",0902.1618v1
2009-02-10,The Role of Dust Clouds in the Atmospheres of Brown Dwarfs,"The new spectroscopic classes, L and T, are defined by the role of dust
clouds in their atmospheres, the former by their presence and the latter by
their removal and near absence. Moreover, the M to L and L to T transitions are
intimately tied to the condensation and character of silicate and iron grains,
and the associated clouds play pivotal roles in the colors and spectra of such
brown dwarfs. Spanning the effective temperature range from $\sim$2200 K to
$\sim$600 K, these objects are being found in abundance and are a new arena in
which condensation chemistry and the optical properties of grains is assuming
astronomical importance. In this short paper, I summarize the role played by
such refractories in determining the properties of these ""stars"" and the
complexities of their theoretical treatment.",0902.1777v1
2009-02-13,Growth and Superconductivity of FeSex Crystals,"Iron selenide (FeSex) crystals with lateral dimensions up to millimeters were
grown via a vapor self-transport method. The crystals consist of the dominant
alpha - phase with trace amounts of beta- phase as identified by powder x-ray
diffraction. With four-probe resistance measurements we obtained a
zero-resistance critical temperature of 7.5 K and a superconducting onset
transition temperature of up to 11.8 K in zero magnetic field as well as an
anisotropy of 1.5 +- 0.1 for the critical field. Magnetization measurements on
individual crystals reveal the co-existence of superconductivity and
ferromagnetism.",0902.2240v1
2009-02-14,"ARPES studies of the electronic structure of LaOFe(P,As)","We report a comparison study of LaOFeP and LaOFeAs, two parent compounds of
recently discovered iron-pnictide superconductors, using angle-resolved
photoemission spectroscopy. Both systems exhibit some common features that are
very different from well-studied cuprates. In addition, important differences
have also been observed between these two ferrooxypnictides. For LaOFeP,
quantitative agreement can be found between our photoemission data and the LDA
band structure calculations, suggesting that a weak coupling approach based on
an itinerant ground state may be more appropriate for understanding this new
superconducting compound. In contrast, the agreement between LDA calculations
and experiments in LaOFeAs is relatively poor, as highlighted by the unexpected
Fermi surface topology around (pi,pi). Further investigations are required for
a comprehensive understanding of the electronic structure of LaOFeAs and
related compounds.",0902.2503v1
2009-02-18,"Ultra High Energy Cosmic Ray, Neutrino, and Photon Propagation and the Multi-Messenger Approach","The propagation of UHECR nuclei for A=1 (protons) to A=56 (iron) from
cosmological sources through extragalactic space is discussed in the first
lecture. This is followed in the second and third lectures by a consideration
of the generation and propagation of secondary particles produced via the UHECR
loss interactions. In the second lecture we focus on the generation of the
diffuse cosmogenic UHE-neutrino flux. In the third lecture we investigate the
arriving flux of UHE-photon flux at Earth. In the final lecture the results of
the previous lectures are put together in order to provide new insights into
UHECR sources. The first of these providing a means with which to investigate
the local population of UHECR sources through the measurement of the UHECR
spectrum and their photon fraction at Earth. The second of these providing
contraints on the UHECR source radiation fields through the possible
observation at Earth of UHECR nuclei.",0902.3012v1
2009-02-18,Doppler-Broadened Iron X-ray Lines from Tycho's Supernova Remnant,"We use \suzaku observations to measure the spatial variation of the Fe
K$\alpha$ line with radius in the \tycho supernova remnant. The Fe line widths
show a significant decrease from a FWHM value of 210 eV at the center to 130 eV
at the rim. Over the same radial range the line center energy remains nearly
constant. These observations are consistent with a scenario in which the shell
of Fe-emitting ejecta in \tycho is expanding at speeds of 2800--3350 km
s$^{-1}$. The minimum line width we measure is still a factor of two larger
than expected from a single component plasma emission model. If thermal Doppler
broadening is the dominant additional source of broadening, we infer an ion
temperature of $(1--3) \times 10^{10}$ K.",0902.3049v1
2009-02-23,Why Does Undoped FeSe Become A High Tc Superconductor Under Pressure?,"Unlike the parent phases of the iron-arsenide high Tc superconductors,
undoped FeSe is not magnetically ordered and exhibits superconductivity with
Tc~9K. Equally surprising is the fact that applied pressure dramatically
enhances the modest Tc to ~37K. We investigate the electronic properties of
FeSe using 77Se NMR to search for the key to the superconducting mechanism. We
demonstrate that the electronic properties of FeSe are very similar to those of
electron-doped FeAs superconductors, and that antiferromagnetic spin
fluctuations are strongly enhanced near Tc. Furthermore, applied pressure
enhances spin fluctuations. Our findings suggest a link between spin
fluctuations and the superconducting mechanism in FeSe.",0902.3832v2
2009-02-23,Superconductivity at 22.3 K in SrFe2-xIrxAs2,"By substituting the Fe with the 5d-transition metal Ir in SrFe2As2, we have
successfully synthesized the superconductor SrFe2-xIrxAs2 with Tc = 22.3 K at x
= 0.5. X-ray diffraction indicates that the material has formed the
ThCr2Si2-type structure with a space group I4/mmm. The temperature dependence
of resistivity and dc magnetization both reveal sharp superconducting
transitions at around 22 K. An estimate on the diamagnetization signal reveals
a high Meissner shielding volume. Interestingly, the normal state resistivity
exhibits a roughly linear behavior up to 300 K. The superconducting transitions
at different magnetic fields were also measured yielding a slope of -dHc2/dT =
3.8 T/K near Tc. Using the Werthamer-Helfand-Hohenberg (WHH) formula, the upper
critical field at zero K is found to be about 58 T. Counting the possible
number of electrons doped into the system in SrFe2-xIrxAs2, we argue that the
superconductivity in the Ir-doped system is different from the Co-doped case,
which should add more ingredients to the underlying physics of the iron
pnictide superconductors.",0902.3957v2
2009-02-24,Thermal instability in X-ray photoionized media in Active Galactic Nuclei: II. Role of the thermal conduction in warm absorber,"A photoionized gas under constant pressure can display a thermal instability,
with three or more solutions for possible thermal equilibrium. A unique
solution of the structure of the irradiated medium is obtained only if electron
conduction is considered. The subject of our study is to estimate how the
effect of thermal conduction affects the structure and transmitted spectrum of
the warm absorber computed by solving radiative transfer with the code TITAN.
We developed a new computational mode for the code TITAN to obtain several
solutions for a given external conditions and we test a posteriori which
solution is the closest one to the required integral condition based on
conduction. We demonstrate that the automatic mode of the code TITAN provides
the solution to the radiative transfer which is generally consistent with the
estimated exact solution within a few per cent accuracy, with larger errors for
some line intensities (up to 20 per cent) for iron lines at intermediate
ionization state.",0902.4083v1
2009-02-24,"Frontiers of the physics of dense plasmas and planetary interiors: experiments, theory, applications","Recent developments of dynamic x-ray characterization experiments of dense
matter are reviewed, with particular emphasis on conditions relevant to
interiors of terrestrial and gas giant planets. These studies include
characterization of compressed states of matter in light elements by x-ray
scattering and imaging of shocked iron by radiography. Several applications of
this work are examined. These include the structure of massive ""Super Earth""
terrestrial planets around other stars, the 40 known extrasolar gas giants with
measured masses and radii, and Jupiter itself, which serves as the benchmark
for giant planets.",0902.4115v1
2009-02-24,Heating and cooling of magnetars with accreted envelopes,"We study the thermal structure and evolution of magnetars as cooling neutron
stars with a phenomenological heat source in an internal layer. We focus on the
effect of magnetized (B > 10^{14} G) non-accreted and accreted outermost
envelopes composed of different elements, from iron to hydrogen or helium. We
discuss a combined effect of thermal conduction and neutrino emission in the
outer neutron star crust and calculate the cooling of magnetars with a dipole
magnetic field for various locations of the heat layer, heat rates and magnetic
field strengths. Combined effects of strong magnetic fields and light-element
composition simplify the interpretation of magnetars in our model: these
effects allow one to interpret observations assuming less extreme (therefore,
more realistic) heating. Massive magnetars, with fast neutrino cooling in their
cores, can have higher thermal surface luminosity.",0902.4213v1
2009-02-26,Tricritical Points and Liquid-Solid Critical Lines,"Tricritical points separate continuous and discontinuous symmetry breaking
transitions. They occur in a variety of physical systems and their mathematical
models. A tricritical point is used to determine a liquid-solid phase
transition line in the pressure-temperature plane [Aitta, J. Stat. Mech.,
2006]. Excellent experimental agreement has been obtained for iron, the
material having the most high pressure data. This allows extrapolation to much
higher pressures and temperatures than available experimentally. One can
predict the temperature at the liquid-solid boundary in the core of the Earth
where the pressure is 329 GPa. Light matter, present as impurities in the core
fluid, is found to generate about a 600 K reduction of this temperature.",0902.4578v1
2009-02-27,Looking outside the Galaxy: the discovery of chemical anomalies in 3 old Large Magellanic Cloud clusters,"By using the multifiber spectrograph FLAMES mounted at the ESO-VLT, we have
obtained high-resolution spectra for 18 giant stars, belonging to 3 old
globular clusters of the Large Magellanic Cloud (namely NGC 1786, 2210 and
2257). While stars in each cluster showed quite homogeneous iron content,
within a few cents of dex (the mean values being Fe/H]= -1.75+-0.01 dex,
-1.65+-0.02 dex and -1.95+-0.02 dex for NGC 1786, 2210 and 2257, respectively),
we have detected significant inhomogeneities for the [Na/Fe], [Al/Fe], [O/Fe]
and [Mg/Fe] abundance ratios, with evidence of [O/Fe] vs [Na/Fe] and [Mg/Fe] vs
[Al/Fe] anticorrelations. The trends detected nicely agree with those observed
in Galactic Globular Clusters, suggesting that such abundance anomalies are
ubiquitous features of old stellar systems and they do not depend on the parent
galaxy environment. In NGC 1786 we also detected two extreme O-poor, Na-rich
stars. This is the first time that a firm signature of extreme chemical
abundance anomalies has been found in an extragalactic stellar cluster.",0902.4778v1
2009-02-27,The superconductor KxSr(1-x)Fe2As2: Normal state and superconducting properties,"The normal state and superconducting properties are investigated in the phase
diagram of K_xSr_{1-x}Fe_2As_2 for 0<x<1. The ground state upper critical
field, H_{c2}(0), is extrapolated from magnetic field dependent resistivity
measurements. H_{c2}(0) scales with the critical temperature, T_c, of the
superconducting transition. In the normal state the Seebeck coefficient is
shown to experience a dramatic change near a critical substitution of x=0.3.
This is associated with the formation of a spin density wave state above the
superconducting transition temperature. The results provide strong evidence for
the reconstruction of the Fermi surface with the onset of magnetic order.",0903.0013v1
2009-03-09,Cohesive and magnetic properties of grain boundaries in bcc Fe with Cr additions,"Structural, cohesive, and magnetic properties of two symmetric $\Sigma3(111)$
and $\Sigma5(210)$ tilt grain boundaries (GBs) in pure bcc Fe and in dilute
FeCr alloys are studied from first principles. Different concentration and
position of Cr solute atoms are considered. We found that Cr atoms placed in
the GB interstice enhance the cohesion by 0.5-1.2 J/m$^2$. Substitutional Cr in
the layers adjacent to the boundary shows anisotropic effect on the GB
cohesion: it is neutral when placed in the (111) oriented Fe grains, and
enhances cohesion (by 0.5 J/m$^2$) when substituted in the boundary layer of
the (210) grains. The strengthening effect of the Cr solute is dominated by the
chemical component of the adhesive binding energy. Our calculations show that
unlike the free iron surfaces, Cr impurities segregate to the boundaries of the
Fe grains. The magnetic moments on GB atoms are substantially changed and their
variation correlates with the corresponding relaxation pattern of the GB
planes. The moments on Cr additions are 2-4 times enhanced in comparison with
that in a Cr crystal and are antiparallel to the moments on the Fe atoms.",0903.1618v2
2009-03-12,Pressure evolution of low-temperature crystal structure and bonding of 37 K $T_c$ FeSe superconductor,"FeSe with the PbO structure is a key member of the family of new high-$T_c$
iron pnictide and chalcogenide superconductors, as while it possesses the basic
layered structural motif of edge-sharing distorted FeSe$_4$ tetrahedra, it
lacks interleaved ion spacers or charge-reservoir layers. We find that
application of hydrostatic pressure first rapidly increases $T_c$ which attains
a broad maximum of 37 K at $\sim$7 GPa (this is one of the highest $T_c$ ever
reported for a binary solid) before decreasing to 6 K upon further compression
to $\sim$14 GPa. Complementary synchrotron X-ray diffraction at 16 K was used
to measure the low-temperature isothermal compressibility of $\alpha$-FeSe,
revealing an extremely soft solid with a bulk modulus, $K_0$ = 30.7(1.1) GPa
and strong bonding anisotropy between inter- and intra-layer directions that
transforms to the more densely packed $\beta$-polymorph above $\sim$9 GPa. The
non-monotonic $T_c$($P$) behavior of FeSe coincides with drastic anomalies in
the pressure evolution of the interlayer spacing, pointing to the key role of
this structural feature in modulating the electronic properties.",0903.2204v1
2009-03-12,Universal relation between magnetic resonance and superconducting gap in unconventional superconductors,"Unconventional superconductors such as the high-transition temperature
cuprates, heavy-fermion systems and iron arsenide-based compounds exhibit
antiferromagnetic fluctuations that are dominated by a resonance, a collective
spin-one excitation mode in the superconducting state. Here we demonstrate the
existence of a universal linear relation, $Er \propto 2\Delta$, between the
magnetic resonance energy (Er) and the superconducting pairing gap ($\Delta$),
spanning two orders of magnitude in energy. This relation is valid for
materials that range from being close to the Mott-insulating limit to being on
the border of itinerant magnetism. Since the common excitonic picture of the
resonance has not led to such universality, our observation suggests a much
deeper connection between antiferromagnetic fluctuations and unconventional
superconductivity.",0903.2291v1
2009-03-13,The nature of the magnetic and structural phase transitions in BaFe$_{2}$As$_{2}$,"We present the results of an investigation of both the magnetic and
structural phase transitions in a high quality single crystalline sample of the
undoped, iron pnictide compound BaFe$_2$As$_2$. Both phase transitions are
characterized via neutron diffraction measurements which reveal simultaneous,
continuous magnetic and structural orderings with no evidence of hysteresis,
consistent with a single second order phase transition. The onset of long-range
antiferromagnetic order can be described by a simple power law dependence
$\phi(T)^2\propto(1-\frac{T}{T_N})^{2\beta}$ with $\beta=0.103\pm0.018$; a
value near the $\beta=0.125$ expected for a two-dimensional Ising system.
Biquadratic coupling between the structural and magnetic order parameters is
also inferred along with evidence of three-dimensional critical scattering in
this system.",0903.2430v2
2009-03-23,On Estimating the Flux of the Brightest Cosmic Ray Source above 57x10^18 eV,"The sources of ultra-high energy cosmic rays are not yet known. However, the
discovery of anisotropic cosmic rays above 57x10^18 eV by the Pierre Auger
Observatory suggests that a direct source detection may soon be possible. The
near-future prospects for such a measurement are heavily dependent on the flux
of the brightest source. In this work, we show that the flux of the brightest
source above 57x10^18 eV is expected to comprise 10% or more of the total flux
if two general conditions are true. The conditions are: 1.) the source objects
are associated with galaxies other than the Milky Way and its closest
neighbors, and 2.) the cosmic ray particles are protons or heavy nuclei such as
iron and the Greisen-Zatsepin-Kuz'min effect is occurring. The Pierre Auger
Observatory collects approximately 23 events above 57x10^18 eV per year.
Therefore, it is plausible that, over the course of several years, tens of
cosmic rays from a single source will be detected.",0903.3981v1
2009-03-24,Timescale Resolved Spectroscopy of Cyg X-1,"We propose the timescale-resolved spectroscopy (TRS) as a new method to
combine the timing and spectral study. TRS is based on the time domain power
spectrum and reflects the variable amplitudes of spectral components on
different timescales. We produce the TRS with the RXTE PCA data for Cyg X-1 and
studied the spectral parameters (the power law photon index and the equivalent
width of the iron fluorescent line) as a function of timescale. The results of
TRS and frequency-resolved spectra (FRS) have been compared, and similarities
have been found for the two methods with the identical motivations. We also
discover the correspondences between the evolution of photon index with
timescale and the evolution of the equivalent width with timescale. The
observations can be divided into three types according to the correspondences
and different type is connected with different spectral state.",0903.4118v1
2009-03-25,Three- to Two-Dimensional Transition of the Electronic Structure in CaFe2As2 - parent compound for an iron arsenic high temperature superconductor,"We use angle-resolved photoemission spectroscopy (ARPES) to study the
electronic properties of CaFe2As2 - parent compound of a pnictide
superconductor. We find that the structural and magnetic transition is
accompanied by a three- to two-dimensional (3D-2D) crossover in the electronic
structure. Above the transition temperature (Ts) Fermi surfaces around Gamma
and X points are cylindrical and quasi-2D. Below Ts the former becomes a 3D
ellipsoid, while the latter remains quasi-2D. This finding strongly suggests
that low dimensionality plays an important role in understanding the
superconducting mechanism in pnictides.",0903.4388v1
2009-03-26,Superconductivity induced by ruthenium substitution in an iron arsenide: investigation of SrFe2-xRuxAs2 (0 <= x <= 2),"The magnetism in SrFe2As2 can be suppressed by electron doping through a
small substitution of Fe by Co or Ni, giving way to superconductivity. We
demonstrate that a massive substitution of Fe by isovalent ruthenium similarly
suppresses the magnetic ordering in SrFe2-xRuxAs2 and leads to bulk
superconductivity for 0.6 <= x <= 0.8. Magnetization, electrical resistivity,
and specific heat data show Tc up to approx 20K. Detailed structural
investigations reveal a strong decrease of the lattice parameter ratio c/a with
increasing x. DFT band structure calculations are in line with the observation
that the magnetic order in SrFe2-xRuxAs2 is only destabilized for large x.",0903.4668v2
2009-03-27,The electronic structure of LiFeAs and NaFeAs probed by resonant inelastic x-ray scattering spectra,"Results of resonant inelastic X-ray scattering (RIXS) measurements at Fe
L-edges and electronic structure calculations of LiFeAs and NaFeAs are
presented. Both experiment and theory show that in the vicinity of the Fermi
energy, the density of states is dominated by contributions from Fe 3d-states.
The comparison of Fe L2,3 non-resonant and resonant (excited at L2-threshold)
X-ray emission spectra with spectra of LaOFeAs and CaFe2As2 show a great
similarity in energy and I(L2)/I(L3) intensity ratio. The I(L2)/I(L3) intensity
ratio of all FeAs-based superconductors is found to be more similar to metallic
Fe than to correlated FeO. Basing on these measurements we conclude that
iron-based superconductors are weakly or moderately correlated systems.",0903.4901v2
2009-03-29,Anisotropic spin fluctuations and multiple superconducting gaps in hole-doped Ba_0.7K_0.3Fe_2As_2: NMR in a single crystal,"We report the first ^{75}As-NMR study on a single crystal of the hole-doped
iron-pnictide superconductor Ba_{0.7}K_{0.3}Fe_2As_{2} (T_c = 31.5 K). We find
that the Fe antiferromagnetic spin fluctuations are anisotropic and are weaker
compared to underdoped copper-oxides or cobalt-oxide superconductors. The spin
lattice relaxation rate 1/T_1 decreases below T_c with no coherence peak and
shows a step-wise variation at low temperatures, which is indicative of
multiple superconducting gaps, as in the electron-doped
Pr(La)FeAsO$_{1-x}$F$_{x}$. Furthermore, no evidence was obtained for a
microscopic coexistence of a long-range magnetic and superconductivity.",0903.5098v2
2009-04-06,Redshift Evolution in the Iron Abundance of the Intracluster Medium,"Clusters of galaxies provide a closed box within which one can determine the
chemical evolution of the gaseous baryons with cosmic time. We studied this
metallicity evolution in the hot X-ray emitting baryons through an analysis of
XMM-Newton observations of 29 galaxy clusters in the redshift range 0.3 < z <
1.3. Taken alone, this data set does not show evidence for significant
evolution. However, when we also include a comparable sample of 115 clusters
observed with Chandra (Maughan et al. 2008) and a lower redshift sample of 70
clusters observed with XMM at z < 0.3 (Snowden et al. 2008), there is
definitive evidence for a decrease in the metallicity. This decrease is
approximately a factor of two from z = 0 to z \approx 1, over which we find a
least-squares best-fit line Z(z) / Z_{\odot} = (0.46 \pm 0.05) - (0.38 \pm
0.03)z. The greatest uncertainty in the evolution comes from poorly constrained
metallicities in the highest redshift bin.",0904.1007v1
2009-04-06,Is There a Dark Matter Signal in the Galactic Positron Annihilation Radiation?,"Assuming Galactic positrons do not go far before annhilating, a difference
between the observed 511 keV annihilation flux distribution and that of
positron production, expected from beta-plus decay in Galactic iron
nucleosynthesis, was evoked as evidence of a new source and a signal of dark
matter. We show, however, that the dark mater sources can not account for the
observed positronium fraction without extensive propagation. Yet with such
propagation, standard nucleosynthetic sources can fully account for the spatial
differences and the positronium fraction, leaving no signal for dark mater to
explain.",0904.1025v3
2009-04-09,Evaluating the locality of intrinsic precession damping in transition metals,"The Landau-Lifshitz-Gilbert damping parameter is typically assumed to be a
local quantity, independent of magnetic configuration. To test the validity of
this assumption we calculate the precession damping rate of small amplitude
non-uniform mode magnons in iron, cobalt, and nickel. At scattering rates
expected near and above room temperature, little change in the damping rate is
found as the magnon wavelength is decreased from infinity to a length shorter
than features probed in recent experiments. This result indicates that
non-local effects due to the presence of weakly non-uniform modes, expected in
real devices, should not appreciably affect the dynamic response of the element
at typical operating temperatures. Conversely, at scattering rates expected in
very pure samples around cryogenic temperatures, non-local effects result in an
order of magnitude decrease in damping rates for magnons with wavelengths
commensurate with domain wall widths. While this low temperature result is
likely of little practical importance, it provides an experimentally testable
prediction of the non-local contribution of the spin-orbit torque-correlation
model of precession damping. None of these results exhibit strong dependence on
the magnon propagation direction.",0904.1455v1
2009-04-11,Three-band s+- Eliashberg theory and the superconducting gaps of iron pnictides,"The experimental critical temperatures and gap values of the superconducting
pnictides of both the 1111 and 122 families can be simultaneously reproduced
within the Eliashberg theory by using a three-band model where the dominant
role is played by interband interactions and the order parameter undergoes a
sigh reversal between hole and electron bands (s+- wave symmetry). High values
of the electron-boson coupling constants and small typical boson energies (in
agreement with experiments) are necessary to obtain the values of all the gaps
and to correctly reproduce their temperature dependence.",0904.1808v2
2009-04-14,Optimizing the flux coupling between a nanoSQUID and a magnetic particle using atomic force microscope nanolithography,"We present results of Niobium based SQUID magnetometers for which the
weak-links are engineered by the local oxidation of thin films using an Atomic
Force Microscope (AFM). Firstly, we show that this technique allows the
creation of variable thickness bridges with 10 nm lateral resolution. Precise
control of the weak-link milling is offered by the possibility to realtime
monitor weak-link conductance. Such a process is shown to enhance the magnetic
field modulation hence the sensitivity of the magnetometer. Secondly, AFM
lithography is used to provide a precise alignment of NanoSQUID weak-links with
respect to a ferromagnetic iron dot. The magnetization switching of the
near-field coupled particle is studied as a junction of the applied magnetic
field direction.",0904.2100v1
2009-04-14,The Electronic Phase Diagram of the Iron-based High Tc Superconductor Ba(Fe(1-x)Co(x))2As2 Under Hydrostatic Pressure (0 < x <0.099),"We report comprehensive resistivity measurements of single crystalline
samples of the Ba(Fe(1-x)Co(x))2As2 high Tc superconductor under hydrostatic
pressure up to 2.75 GPa and over a broad concentration range, 0 < x < 0.099. We
show that application of pressure progressively suppresses the SDW transition
temperature, T_SDW, in the underdoped regime. There is no sign of
pressure-induced superconductivity in the undoped BaFe2As2 down to 1.8 K, but
applied pressure dramatically enhances Tc in the underdoped regime. The effect
of pressure on Tc is very small in the optimally and overdoped regimes. As a
consequence, the dome of the superconducting phase extends to x 0.02 under
pressure. We discuss the implications of our findings in the context of a
possible quantum phase transition between the SDW and superconducting phases.",0904.2215v1
2009-04-17,Relativistically broadened iron line in the SUZAKU observation of the neutron star X-ray binary 4U 1705-44,"The X-ray spectra of accreting compact objects often exhibit discrete
emission features associated with fluorescent emission in the accretion disk,
the strongest of which is the Fe Kalpha fluorescence line at 6.4--6.97keV.
These reflection features are amongst the best tools in the study of the inner
region of accretion flow around a compact object. Here we report on three
Suzaku observations of the neutron star X-ray binary 4U1705-44 where a broad,
skewed Fe Kalpha emission line is clearly visible above the continuum. By using
a relativistically-blurred reflection model we find that in 4U1705-44 the inner
disk radius extends down to rin=10.5^{+1.0}_{-1.7} GM/c^2 and is at an angle of
29.8^{+1.1}_{-1.0} degrees to the line of sight. Furthermore, we find that the
level of ionisation in the surface layers of the accretion disk changes by two
orders of magnitude between the three observations, however the inner radius
obtained from the line profile remains stable.",0904.2747v1
2009-04-19,First-principles study of the effect of Fe impurities in MgO at geophysically relevant pressures,"The self-interaction corrected local spin density (SIC-LSD) formalism and the
standard GGA treatment of the exchange-correlation energy have been applied to
study the collapse of the magnetic moment of Fe impurities in MgO. The system
Mg_{1-x}Fe_xO is believed to be the second most abundant mineral in the Earth's
lower mantle.
  We confirm the experimentally found increase of the critical pressure upon
iron concentration. Our calculations using standard GGA for a fixed Fe
concentration show that different arrangements of Fe atoms can remarkably shift
the transition pressure of the high spin (HS) to low spin (LS) transition. This
could explain the experimentally found broad transition regions. Our results
indicate that the HS-LS transition in Mg$_{1-x}Fe_xO is first order. We find
that SIC-LSD fails to predict the divalent Fe configuration as the lowest
energy configuration and discuss possible reasons for it.",0904.2901v1
2009-04-24,Effect of electron-doping on spin excitations of underdoped BaFe$_{1.96}$Ni$_{0.04}$As$_{2}$,"We use neutron scattering to study magnetic order and spin excitations in
BaFe$_{1.96}$Ni$_{0.04}$As$_{2}$. On cooling, the system first changes the
lattice symmetry from tetragonal to orthoromhbic near $\sim$97 K, and then
orders antiferromagnetically at $T_N=91$ K before developing weak
superconductivity below $\sim$15 K. Although superconductivity appears to
co-exist with static antiferromagnetic order from transport and neutron
diffraction measurement, inelastic neutron scattering experiments reveal that
magnetic excitations do not respond to superconductivity. Instead, the effect
of electron-doping is to reduce the c-axis exchange coupling in BaFe$_2$As$_2$
and induce quasi two-dimensional spin excitations. These results suggest that
transition from three-dimensional spin waves to two-dimensional spin
excitations by electron-doping is important for the separated
structural/magnetic phase transitions and high-temperature superconductivity in
iron arsenides.",0904.3775v1
2009-04-24,Microscopic origin of magnetism and magnetic interactions in ferropnictides,"One year after their initial discovery, two schools of thought have
crystallized regarding the electronic structure and magnetic properties of
ferropnictide systems. One postulates that these are itinerant weakly
correlated metallic systems that become magnetic by virtue of spin-Peierls type
transition due to near-nesting between the hole and the electron Fermi surface
pockets. The other argues these materials are strongly or at least moderately
correlated, the electrons are considerably localized and close to a
Mott-Hubbard transition, with the local magnetic moments interacting via
short-range superexchange. In this paper we argue that neither picture is fully
correct. The systems are moderately correlated, but with correlations driven by
Hund's rule coupling rather than by the on-site Hubbard repulsion. The iron
moments are largely local, driven by Hund's intra-atomic exchange.
Superexchange is not operative and the interactions between the Fe moments are
considerably long-range and driven mostly by one-electron energies of all
occupied states.",0904.3857v1
2009-04-24,Efficacy of surface error corrections to density functional theory calculations of vacancy formation energy in transition metals,"We calculate properties like equilibrium lattice parameter, bulk modulus and
monovacancy formation energy for nickel (Ni), iron (Fe) and chromium (Cr) using
Kohn-Sham density functional theory (DFT). We compare relative performance of
local density approximation (LDA) and generalized gradient approximation (GGA)
for predicting such physical properties for these metals. We also make a
relative study between two different flavors of GGA exchange correlation
functional, namely, PW91 and PBE. These calculations show that there is a
discrepancy between DFT calculations and experimental data. In order to
understand this discrepancy in the calculation of vacancy formation energy, we
introduce a correction for the surface intrinsic error corresponding to an
exchange correlation functional using the scheme implemented by Mattsson et al.
[Phys. Rev. B 73, 195123 (2006)] and compare the effectiveness of the
correction scheme for Al and the 3d-transition metals.",0904.3859v2
2009-04-27,The 13C Pocket in Low Mass AGB Stars,"It is well known that thermally pulsing Asymptotic Giant Branch stars with
low mass play a relevant role in the chemical evolution. They have synthesized
about 30% of the galactic carbon and provide an important contribution to the
nucleosynthesis of heavy elements (A>80). The relevant nucleosynthesis site is
the He-rich intermediate zone (less than 10^{-2} Msun), where
alpha(2alpha,gamma)12C reactions and slow neutron captures on seed nuclei
essentially iron) take place. A key ingredient is the interplay between nuclear
processes and convective mixing. It is the partial overlap of internal and
external convective zones that allows the dredge-up of the material enriched in
C and heavy elements. We review the progresses made in the last 50 years in the
comprehension of the s process in AGB stars, with special attention to the
identification of the main neutron sources and to the particular physical
conditions allowing this important nucleosynthesis.",0904.4163v1
2009-04-27,Fermi liquid state and enhanced electron correlations in the new iron pnictide CaFe$_4$As$_3$,"The newly discovered CaFe$_4$As$_3$ system displays low-temperature Fermi
liquid behavior, with enhanced electron-electron correlations. At high
temperatures, the magnetic susceptibility shows Curie-Weiss behavior, with a
large temperature-independent contribution. Antiferromagnetic ordering is
observed below T$_N$ = (88.0 $\pm$ 1.0) K, possibly via a spin density wave
(SDW) transition. A remarkably sharp drop in resistivity occurs below T$_2$ =
(26.4 $\pm$ 1.0) K, correlated with a similarly abrupt increase in the
susceptibility, but no visible feature in the specific heat. The electronic
specific heat coefficient $\gamma$ at low temperatures is close to 0.02 J
mol$^{-1}_{Fe}$ K$^{-2}$, but a higher value for $\gamma$ ($\sim$0.08 J
mol$^{-1}_{Fe}$ K$^{-2}$ can be inferred from a linear C$ / $T \textit{vs.}
T$^2$ just above T$_2$. The Kadowaki-Woods ratio A$/\gamma^2$ = 55$*10^{-5}$
$\mu \Omega$cm mol$^2$ K$^2 $mJ$^{-2}$ is nearly two orders of magnitude larger
than that of heavy fermions.",0904.4188v1
2009-04-29,Can mass loss and overshooting prevent the excitation of g-modes in blue supergiants?,"Thanks to their past history on the main sequence phase, supergiant massive
stars develop a convective shell around the helium core. This intermediate
convective zone (ICZ) plays an essential role in governing which g-modes are
excited. Indeed a strong radiative damping occurs in the high density radiative
core but the ICZ acts as a barrier preventing the propagation of some g-modes
into the core. These g-modes can thus be excited in supergiant stars by the
kappa-mechanism in the superficial layers due to the opacity bump of iron, at
log T=5.2. However massive stars are submitted to various complex phenomena
such as rotation, magnetic fields, semiconvection, mass loss, overshooting.
Each of these phenomena exerts a significant effect on the evolution and some
of them could prevent the onset of the convective zone. We develop a numerical
method which allows us to select the reflected, thus the potentially excited,
modes only. We study different cases in order to show that mass loss and
overshooting, in a large enough amount, reduce the extent of the ICZ and are
unfavourable to the excitation of g-modes.",0904.4641v1
2009-05-04,Low Temperature Crystal Structure and 57Fe Moessbauer Spectroscopy of Sr3Sc2O5Fe2As2,"The crystal structure of the layered iron arsenide Sr3Sc2O5Fe2As2 was
determined between 300 and 10 K. The lattice parameters of the tetragonal cell
decrease anisotropically according to delta(c)/c : delta(a)/a = 4.2, which
results in a slight flattening of the As-Fe-As bond angle within the FeAs
layers. No indication of a structural instability could be detected. 57Fe
Moessbauer spectroscopic data show a single signal at 4.2, 77, and 298 K,
respectively, subjected to quadrupole splitting. The isomer shift increases
from 0.36(1) mm/s at 298 K to 0.49(1) mm/s at 4.2 K. No indication for magnetic
ordering was found.",0905.0337v1
2009-05-05,Structural and magnetic phase transitions in Na$_{1-δ}$FeAs,"We use neutron scattering to study the spin and lattice structures of single
crystal and powder samples of Na$_{1-\delta}$FeAs ($T_c = 23$ K). On cooling
from room temperature, the system goes through a series of phase transitions:
first changing the crystal symmetry from tetragonal to orthorhombic at 49 K,
then ordering antiferromagnetically with a spin structure similar to that of
LaFeAsO and a small moment (0.09$\pm$0.04 $\mu_B$), and finally becoming
superconducting below about 23 K. These results confirm that antiferromagnetic
order is ubiquitous for the parent compounds of the iron arsenide
superconductors, and suggest that the separated structural and magnetic phase
transition temperatures are due to the reduction in the c-axis exchange
coupling of the system.",0905.0525v1
2009-05-08,The Multiverse Hierarchy,"I survey physics theories involving parallel universes, arguing that they
form a natural four-level hierarchy of multiverses allowing progressively
greater diversity. Level I: A generic prediction of inflation is an infinite
ergodic universe, which contains Hubble volumes realizing all initial
conditions -- including an identical copy of you about 10^(10^29)m away. Level
II: In chaotic inflation, other thermalized regions may have different physical
constants, dimensionality and particle content. Level III: In unitary quantum
mechanics, other branches of the wavefunction add nothing qualitatively new,
which is ironic given that this level has historically been the most
controversial. Level IV: Other mathematical structures give different
fundamental equations of physics. The key question is not whether parallel
universes exist (Level I is the uncontroversial cosmological concordance
model), but how many levels there are. I discuss how multiverse models can be
falsified and argue that there is a severe ""measure problem"" that must be
solved to make testable predictions at levels II-IV.",0905.1283v1
2009-05-12,Capture and Indirect Detection of Inelastic Dark Matter,"We compute the capture rate for Dark Matter in the Sun for models where the
dominant interaction with nuclei is inelastic -- the Dark Matter up-scatters to
a nearby dark ""partner"" state with a small splitting of order a 100 keV. Such
models have previously been shown to be compatible with DAMA/LIBRA data, as
well as data from all other direct detection experiments. The kinematics of
inelastic Dark Matter ensures that the dominant contribution to capture occurs
from scattering off of iron. We give a prediction for neutrino rates for
current and future neutrino telescopes based on the results from current direct
detection experiments. Current bounds from Super--Kamiokande and IceCube-22
significantly constrain these models, assuming annihilations are into two-body
Standard Model final states, such as W+W-, t-tbar, b-bbar or tau+tau-.
Annihilations into first and second generation quarks and leptons are generally
allowed, as are annihilations into new force carriers which decay dominantly
into e+e-, mu+mu- and pi+pi-.",0905.1847v2
2009-05-12,Strong-coupling Spin-singlet Superconductivity with Multiple Full Gaps in Hole-doped Ba$_{0.6}$K$_{0.4}$Fe$_2$As$_2$ Probed by Fe-NMR,"We present $^{57}$Fe-NMR measurements of the novel normal and
superconducting-state characteristics of the iron-arsenide superconductor
Ba$_{0.6}$K$_{0.4}$Fe$_2$As$_2$ ($T_c$ = 38 K). In the normal state, the
measured Knight shift and nuclear spin-lattice relaxation rate $(1/T_1)$
demonstrate the development of wave-number ($q$)-dependent spin fluctuations,
except at $q$ = 0, which may originate from the nesting across the disconnected
Fermi surfaces. In the superconducting state, the spin component in the
$^{57}$Fe-Knight shift decreases to almost zero at low temperatures, evidencing
a spin-singlet superconducting state. The $^{57}$Fe-$1/T_1$ results are totally
consistent with a $s^\pm$-wave model with multiple full gaps, regardless of
doping with either electrons or holes.",0905.1896v1
2009-05-16,Strong electron-electron correlation and weak localization in CeO_{0.9}F_{0.1}Fe_{1-x}Co_xAs,"Electron-doping of the semimetal (CeOFeAs) by either fluorine (max Tc ~ 43
K)or cobalt (max Tc ~ 11 K) leads to superconductivity. Here we show the effect
of transition metal (Co) substitution at the iron site on the superconducting
properties of CeO0.9F0.1FeAs (Tc ~38 K)to understand the interplay of charge
carriers in both the rare earth-oxygen and Fe-As layers. Simultaneous doping of
equivalent number of charge carriers in both layers leads to a Tc of 9.8 K
which is lower than the Tc obtained when either the conducting layer (CeAs) or
charge reservoir layer (CeO) is individually doped. This suggests a clear
interplay between the two layers to control the superconductivity. The
resistivity shows a T2 dependence (T >>Tc) which indicates strong
electron-electron correlation. Hall coefficient and thermoelectric power
indicate increased carrier concentration with cobalt doping in CeO0.9F0.1FeAs.
The rf penetration depth both for CeO0.9F0.1Fe0.95Co0.05As and CeO0.9F0.1FeAs
show an exponential temperature dependence with a gap value of ~ 1.6 and 1.9
meV. A resistance minimum is observed in the normal state near Tc which also
shows negative magnetoresistance and provides evidence for the onset of weak
localization.",0905.2679v1
2009-05-19,The fourth Dimension,"In different passages of his dialogues, Plato showed deep
mathematically-based physical insights. Regrettably most readers overlooked the
respective statements, or they utterly did not understand those hints since
they were full of philological fallacious terms. Respectable translators
misinterpreted such statements and therefore Plato's respective remarks were
not recognized as substantial knowledge. Furthermore, Plato often supplemented
such basic remarks by diffusely veiled and varied allusions that were often
ironically hidden somewhere in his dialogues by inconspicuous double meanings.
However, this mode of intentionally coded discrete communication was generally
not understood because such irony is not to everyone's taste. However, the
attempts to reconstruct Plato's system on the basis of admittedly individually
interpreted double meanings lead to a conclusive mathematical-physical cyclical
system of dimensions. Additionally it was possible to assign Plato's system of
philosophical ideas analogously to this cyclical system. Plato took the
verifiability of the mathematical-physical results as proof of the system of
his ideas and finally as proof of his ethical creed, the unconditional trust in
the 'all surmounting Good.'",0905.3048v2
2009-05-19,Testing astrophysical models for the PAMELA positron excess with cosmic ray nuclei,"The excess in the positron fraction reported by the PAMELA collaboration has
been interpreted as due to annihilation or decay of dark matter in the Galaxy.
More prosaically, it has been ascribed to direct production of positrons by
nearby pulsars, or due to pion production during stochastic acceleration of
hadronic cosmic rays in nearby sources. We point out that measurements of
secondary nuclei produced by cosmic ray spallation can discriminate between
these possibilities. New data on the titanium-to-iron ratio from the ATIC-2
experiment support the hadronic source model above and enable a prediction to
be made for the boron-to-carbon ratio at energies above 100 GeV. Presently, all
cosmic ray data are consistent with the positron excess being astrophysical in
origin.",0905.3152v3
2009-05-19,Surface Geometric and Electronic Structure of BaFe2As2(001),"BaFe2As2 exhibits properties characteristic of the parent compounds of the
newly discovered iron (Fe)-based high-TC superconductors. By combining the real
space imaging of scanning tunneling microscopy/spectroscopy (STM/S) with
momentum space quantitative Low Energy Electron Diffraction (LEED) we have
identified the surface plane of cleaved BaFe2As2 crystals as the As terminated
Fe-As layer - the plane where superconductivity occurs. LEED and STM/S data on
the BaFe2As2(001) surface indicate an ordered arsenic (As) - terminated
metallic surface without reconstruction or lattice distortion. It is surprising
that the STM images the different Fe-As orbitals associated with the
orthorhombic structure, not the As atoms in the surface plane.",0905.3194v1
2009-05-20,Accelerated search kinetics mediated by redox reactions of DNA repair enzymes,"A Charge Transport (CT) mechanism has been proposed in several papers (e.g.,
Yavin, et al. PNAS, v102 3546 (2005)) to explain the localization of Base
Excision Repair (BER) enzymes to lesions on DNA. The CT mechanism relies on
redox reactions of iron-sulfur cofactors that modify the enzyme's binding
affinity. These redox reactions are mediated by the DNA strand and involve the
exchange of electrons between BER enzymes along DNA. We propose a mathematical
model that incorporates enzyme binding/unbinding, electron transport, and
enzyme diffusion along DNA. Analysis of our model within a range of parameter
values suggests that the redox reactions can increase desorption of BER enzymes
not already bound to their targets, allowing the enzymes to be recycled, thus
accelerating the overall search process. This acceleration mechanism is most
effective when enzyme copy numbers and enzyme diffusivity along the DNA are
small. Under such conditions, we find that CT BER enzymes find their targets
more quickly than simple ""passive"" enzymes that simply attach to the DNA
without desorbing.",0905.3211v1
2009-05-20,Topological change of the Fermi surface in ternary iron-pnictides with reduced c/a ratio: A dHvA study of CaFe2P2,"We report a de Haas-van Alphen effect study of the Fermi surface of CaFe2P2
using low temperature torque magnetometry up to 45 T. This system is a close
structural analogue of the collapsed tetragonal non-magnetic phase of CaFe2As2.
We find the Fermi surface of CaFe2P2 to differ from other related ternary
phosphides in that its topology is highly dispersive in the c-axis, being
three-dimensional in character and with identical mass enhancement on both
electron and hole pockets (~1.5). The dramatic change in topology of the Fermi
surface suggests that in a state with reduced (c/a) ratio, when bonding between
pnictogen layers becomes important, the Fermi surface sheets are unlikely to be
nested.",0905.3305v1
2009-05-20,Looking for pulsations in HgMn stars through CoRoT lightcurves,"HgMn Chemically Peculiar stars are among the quietest stars of the
main-sequence. However, according to theoretical predictions, these stars could
have pulsations related to the very strong overabundances of iron peak
elements, which are produced by atomic diffusion in upper layers. Such
pulsations have never been detected from ground based observations.
  Our aim is to search for signatures of pulsations in HgMn stars using the
high quality lightcurves provided by the CoRoT satellite.
  We identified three faint stars (V>12), from VLT-GIRAFFE multiobject
spectrograph survey in a field which was planned for observation by CoRoT. They
present the typical characteristics of HgMn stars. They were observed by the
CoRoT satellite during the long run (131 days) which started from the 24th of
October 2007, with the exoplanets CCD's (Additional Programme). In the present
work, we present the analysis of the ground based spectra of these three stars
and the analysis of the corresponding CoRoT lightcurves.
  Two of these three HgMn candidates show low amplitude (less than 1.6 mmag)
periodic variations (4.3 and 2.53 days respectively, with harmonics) which are
compatible with periods predicted by theoretical models.",0905.3340v1
2009-05-29,Ferromagnetic resonance linewidth in ultrathin films with perpendicular magnetic anisotropy,"Transition metal ferromagnetic films with perpendicular magnetic anisotropy
(PMA) have ferromagnetic resonance (FMR) linewidths that are one order of
magnitude larger than soft magnetic materials, such as pure iron (Fe) and
permalloy (NiFe) thin films. A broadband FMR setup has been used to investigate
the origin of the enhanced linewidth in Ni$|$Co multilayer films with PMA. The
FMR linewidth depends linearly on frequency for perpendicular applied fields
and increases significantly when the magnetization is rotated into the film
plane. Irradiation of the film with Helium ions decreases the PMA and the
distribution of PMA parameters. This leads to a great reduction of the FMR
linewidth for in-plane magnetization. These results suggest that fluctuations
in PMA lead to a large two magnon scattering contribution to the linewidth for
in-plane magnetization and establish that the Gilbert damping is enhanced in
such materials ($\alpha \approx 0.04$, compared to $\alpha \approx 0.002$ for
pure Fe).",0905.4779v2
2009-05-31,Nodeless superconducting gap in electron-doped BaFe$_{1.9}$Ni$_{0.1}$As$_2$ probed by quasiparticle heat transport,"The in-plane thermal conductivity $\kappa$ of electron-doped iron-arsenide
superconductor BaFe$_{1.9}$Ni$_{0.1}$As$_2$ ($T_c$ = 20.3 K) single crystal was
measured down to 70 mK. In zero field, the absence of a residual linear term
$\kappa_0/T$ at $ T \to 0$ is strong evidence for nodeless superconducting gap.
In magnetic field, $\kappa_0/T$ shows a slow field dependence up to $H$ = 14.5
T ($\approx$ 30% $H_{c_2}$). This is consistent with the superconducting gap
structure demonstrated by angle-resolved photoemission spectroscopy experiments
in BaFe$_{1.85}$Co$_{0.15}$As$_2$ ($T_c$ = 25.5 K), where isotropic
superconducting gaps with similar size on hole and electron pockets were
observed.",0906.0138v2
2009-06-01,$π$-junction to probe antiphase s-wave pairing in iron pnictide superconductors,"Josephson junctions between a $FeAs$-based superconductor with antiphase
s-wave pairing and a conventional s-wave superconductor are studied. The
translational invariance in a planar junction between a single crystal pnictide
and an aluminum metal greatly enhances the relative weight of electron pockets
in the pnictide to the critical current. In a wide doping region of the
pnictide, a planar and a point contact junctions have opposite phases, which
can be used to design a tri-junction ring with $\pi$ phase to probe the
antiphase pairing.",0906.0169v3
2009-06-04,Neutrino deuteron reaction in the heating mechanism of core-collapse supernovae,"We examine a potential role of the neutrino deuteron reactions in the
mechanism of supernova explosion by evaluating the energy transfer cross
section for the neutrino heating. We calculate the energy loss rate due to the
neutrino absorptions through the charged-current process as well as the
neutrino scattering through the neutral-current process. In so doing, we adopt
a detailed evaluation of cross sections for the neutrino deuteron reactions
with the phenomenological Lagrangian approach. We find the energy transfer
cross section for the deuteron is larger than those for $^{3}$H, $^{3}$He and
$^{4}$He for neutrino temperatures (T$_\nu$ $\sim 4$ MeV) relevant to supernova
core. Because of the low energy threshold for the deuteron breakup, the energy
transfer rate rapidly increases from low temperature, T$_\nu$ $\sim 1$ MeV.
This suggests that the neutrino deuteron reactions may contribute effectively
to the heating mechanism during the dissociation of irons into light elements
and nucleons in the shocked material of supernova core.",0906.0856v1
2009-06-09,"Fabrication of the iron-based superconducting wire using Fe(Se, Te)","We have fabricated the Fe(Se, Te) superconducting wire by a special process
based on a powder-in-tube method. The pure Fe tube plays the role of not only
the sheath but also the raw material for synthesizing the superconducting
phases. We succeeded in observing zero resistivity current on the
current-voltage measurements for the Fe(Se, Te) wire. Introduction of the
pinning centers and fabricating a multi-core wire will enhance the critical
current density for the next step.",0906.1636v2
2009-06-09,Particle Propagation in the Galactic Center and Spatial Distribution of Non-Thermal X-rays,"We showed that if the non-thermal emission from the Galactic center in the
range 14-40 keV is due to inverse bremsstrahlung emission of subrelativistic
protons, their interactions with hot and cold fractions of the interstellar
medium are equally important. Our estimation show that about 30% of the total
non-thermal flux from the GC in the range 14-40 keV is generated in regions of
cold gas while the rest is produced by proton interaction with hot plasma. From
the spatial distribution of 6.7 keV iron line we concluded the spatial
distribution of hot plasma is strongly non-uniform that should be taken into
account in analysis of protons propagation in the GC. From the Suzaku data we
got independent estimates for the diffusion coefficient of subrelativistic
protons in the GC, which was in the range $ 10^{26} - 10^{27}$ cm$^2$s$^{-1}$",0906.1712v1
2009-06-10,"Superconductivity in SmFe1-xMxAsO (M = Co, Rh, Ir)","In this paper we report the comparative study of superconductivity by 3d
(Co), 4d (Rh), 5d (Ir) element doping in SmFeAsO. X-ray diffraction patterns
indicate that the material has formed the ZrCuSiAs-type structure with a space
group P4/nmm. It is found that the antiferromagnetic spin-density-wave (SDW)
order in the parent compounds is rapidly suppressed by Co, Rh, and Ir doping,
and superconductivity emerges. Both electrical resistance and magnetization
measurements show superconductivity up to around 10 K in SmFe1-xMxAsO (M = Co,
Rh, Ir). Co, Rh and Ir locate in the same column in the periodic table of
elements but have different electronic band structure, so comparative study
would add more ingredients to the underlying physics of the iron-based
superconductors.",0906.1898v1
2009-06-10,Spectroscopic Imaging Scanning Tunneling Microscopy as a Probe of Orbital Structures and Ordering,"Unlike charge and spin, the orbital degree of freedom of electrons in
transition metal oxides is difficult to detect. We present the theoretical
study of a new detection method in metallic orbitally active systems by
analyzing the quasiparticle scattering interference (QPI) pattern of the
spectroscopic imaging scanning tunneling spectroscopy, which is sensitive to
orbital structures and orbital ordering. The QPIs for the $d_{xz}$ and
$d_{yz}$-orbital bands in the $t_{2g}$-orbital systems show a characteristic
stripe-like feature as a consequence of their quasi-one-dimensional nature,
which is robust against orbital hybridization. With the occurrence of orbital
ordering proposed in Sr$_3$Ru$_2$O$_7$ and iron-pnictides, the stripe-like QPI
patterns exhibit nematic distortion breaking the $C_4$-symmetry.",0906.1973v3
2009-06-10,Cosmic-ray origin in OB associations and preferential acceleration of refractory elements: Evidence from abundances of elements 26Fe through 34Se,"We report abundances of elements from 26Fe to 34Se in the cosmic radiation
measured during fifty days of exposure of the Trans-Iron Galactic Element
Recorder (TIGER) balloon-borne instrument. These observations add support to
the concept that the bulk of cosmic-ray acceleration takes place in OB
associations, and they further support cosmic-ray acceleration models in which
elements present in interstellar grains are accelerated preferentially compared
with those found in interstellar gas.",0906.2021v1
2009-06-19,Homogeneous vs. inhomogeneous coexistence of magnetic order and superconductivity probed by NMR in Co and K doped iron pnictides,"In Ba(Fe0.95Co0.05)2As2 all of the 75As NMR intensity at the paramagnetic
resonance position vanishes abruptly below Tonset(SDW)=56 K, indicating that
magnetic (spin density wave) order is present in all of the sample volume,
despite bulk superconductivity below Tc=15 K. The two phases thus coexist
homogeneously at the microscopic scale. In Ba0.6K0.4Fe2As2, on the other hand,
the signal loss below Tonset(SDW)~75 K is not complete, revealing that magnetic
order is bound to finite-size areas of the sample, while the remaining NMR
signal shows a clear superconducting response below Tc=37 K. Thus, the two
phases are not homogeneously mixed, at least for this potassium concentration.
For both samples, spatial electronic and/or magnetic inhomogeneity is shown to
characterize the NMR properties in the normal state.",0906.3708v1
2009-06-26,Differential stellar population models: how to reliably measure [Fe/H] and [alpha/Fe] in galaxies,"We present differential stellar population models, which allow improved
determinations of the ages, iron and alpha-element abundances of old stellar
populations from spectral fitting. These new models are calibrated at solar
abundances using the predictions from classical, semi-empirical stellar
population models. We then use the predictive power of fully synthetic models
to compute predictions for different [Fe/H] and [alpha/Fe]. We show that these
new differential models provide remarkably accurate fits to the integrated
optical spectra of the bulge globular clusters NGC6528 and NGC6553, and that
the inferred [Fe/H] and [alpha/Fe] agree with values derived elsewhere from
stellar photometry and spectroscopy. The analysis of a small sample of SDSS
early-type galaxies further confirms that our alpha-enhanced models provide a
better fit to the spectra of massive ellipticals than the solar-scaled ones.
Our approach opens new opportunities for precision measurements of abundance
ratios in galaxies.",0906.5000v1
2009-06-29,Upper critical fields of the 11-system iron-chalcogenide superconductor FeSe$_{0.25}$Te$_{0.75}$,"We have performed electrical resistivity measurements of a polycrystalline
sample of FeSe$_{0.25}$Te$_{0.75}$, which exhibits superconductivity at $T_{\rm
c} \sim 14$ K, in magnetic fields up to 55 T to determine the upper critical
field $\mu_{0}H_{\rm c2}$. In this compound, very large slopes of
$\mu_{0}H_{\rm c2}$ at the onset, the mid-point, the zero-resistivity
temperatures on superconductivity are determined to be -13.7, -10.1, and -6.9
T/K, respectively. The observed $\mu_{0}H_{\rm c2}(T)$s of this compound are
considerably smaller than those expected from the Werthamer-Helfand-Hohenberg
model, manifesting the Pauli limiting behavior. These results suggest that this
compound has a large Maki parameter, but it is smaller than that calculated for
a weak-coupling superconductor, indicating a large superconducting gap of this
compound as a strong-coupling superconductor.",0906.5248v1
2009-06-30,Fermi surface topology and low-lying quasiparticle dynamics of parent Fe$_{1+x}$Te/Se Superconductor by orbital-polarization resolved ARPES,"We report the first photoemission study of Fe$_{1+x}$Te - the host compound
of the newly discovered iron-chalcogenide superconductors (maximum T$_c$ $\sim$
27K). Our results reveal a pair of nearly electron-hole compensated Fermi
pockets, strong Fermi velocity renormalization and an absence of a
spin-density-wave gap. A shadow hole pocket is observed at the X-point of the
Brillouin zone which is consistent with a long-range ordered magneto-structural
groundstate. No signature of Fermi surface nesting instability associated with
Q=($\pi$/2, $\pi$/2) is observed. Our results collectively reveal that the
Fe$_{1+x}$Te series is dramatically different from the high T$_{c}$ pnictides
and likely harbor unusual mechanism for superconductivity and magnetic order.",0906.5392v1
2009-06-30,Disorder-sensitive superconductivity in the iron silicide Lu$_2$Fe$_3$Si$_5$ studied by the Lu-site substitutions,"We studied effect of non-magnetic and magnetic impurities on
superconductivity in Lu$_2$Fe$_3$Si$_5$ by small amount substitution of the Lu
site, which investigated structural, magnetic, and electrical properties of
non-magnetic (Lu$_{1-x}$Sc$_x$)$_2$Fe$_3$Si$_5$,
(Lu$_{1-x}$Y$_x$)$_2$Fe$_3$Si$_5$, and magnetic
(Lu$_{1-x}$Dy$_x$)$_2$Fe$_3$Si$_5$. The rapid depression of $T_c$ by
non-magnetic impurities in accordance with the increase of residual resistivity
reveals the strong pair breaking dominated by disorder. We provide compelling
evidence for the sign reversal of the superconducting order parameter in
Lu$_2$Fe$_3$Si$_5$.",0906.5569v1
2009-07-01,Chemical Compositions of Kinematically Selected Outer Halo Stars,"Chemical abundances of 26 metal-poor dwarfs and giants are determined from
high-resolution and high signal-to-noise ratio spectra obtained with
Subaru/HDS. The sample is selected so that most of the objects have outer-halo
kinematics. Self-consistent atmospheric parameters were determined by an
iterative procedure based on spectroscopic analysis. Abundances of 13 elements,
including $\alpha$-elements (Mg, Si, Ca, Ti), odd-Z light elements (Na, Sc),
iron-peak elements (Cr, Mn, Fe, Ni, Zn) and neutron-capture elements (Y, Ba),
are determined by two independent data reduction and LTE analysis procedures,
confirming the consistency of the stellar parameters and abundances results. We
find a decreasing trend of [$\alpha$/Fe] with increasing [Fe/H] for the range
of $-3.5 <$ [Fe/H]$ < -1$, as found by Stephens and Boesgaard (2002). [Zn/Fe]
values of most objects in our sample are slightly lower than the bulk of halo
stars previously studied. These results are discussed as possible chemical
properties of the outer halo in the Galaxy.",0907.0076v2
2009-07-03,"Atomically-flat, chemically-stable, superconducting epitaxial thin film of iron-based superconductor, cobalt-doped BaFe$_2$As$_2$","Epitaxial growth of Fe-based superconductors such as Co-doped SrFe$_2$As$_2$
(SrFe$_2$As$_2$:Co) was reported recently, but has still insufficient
properties for device application because they have rough surfaces and are
decomposed by reactions with water vapor in an ambient atmosphere. This letter
reports that epitaxial films of Co-doped BaFe$_2$As$_2$ grown at 700 oC show
the onset superconducting transition tempearture of 20 K. The transition is
sharper than those observed on the SrFe$_2$As$_2$:Co films, which would
originate from their improved crystallinity. These films also have
atomically-flat surfaces with steps-and-terraces structures and exhibit
chemical stability against exposure to water vapor.",0907.0666v1
2009-07-07,Phase diagram of the PrFeAsO$_{1-x}$F$_{x}$ superconductor,"The electronic phase diagram of PrFeAsO$_{1-x}$F$_{x}$ (0$\leq$x$\leq$0.225)
has been determined using synchrotron X-ray powder diffraction, magnetization
and resistivity measurements. The structural transition temperature is
suppressed from 154 K to $\approx$120 K and the magnetic phase transitions of
both iron and praseodymium ions are completely suppressed by x$\approx$0.08
fluorine doping, coinciding with the emergence of superconductivity. The
optimal doping is x$\approx$0.15 when T$_{C}$=47 K, while the maximum
solubility of fluorine in PrFeAsO$_{1-x}$F$_{x}$ is reached around x=0.22. The
structural, magnetic and superconducting phase diagram is presented.",0907.1308v1
2009-07-15,Quark matter under strong magnetic fields in the su(3) Nambu-Jona-Lasinio Model,"In the present work we use the mean field approximation to investigate quark
matter described by the su(3) Nambu-Jona-Lasinio model subject to a strong
magnetic field. We consider two cases: pure quark matter and quark matter in
beta-equilibrium possibly present in magnetars. The results are compared with
the ones obtained with the su(2) version of the model. The energy per baryon of
magnetized quark matter becomes more bound than nuclear matter made of iron
nuclei, for B around 2x10^(19)G. When the su(3) NJL model is applied to stellar
matter, the maximum mass configurations are always above 1.45 solar masses and
may be as high as 1.86 solar masses for a central magnetic field of 5x10^(18)G.
These numbers are within the masses of observed neutron stars.",0907.2607v1
2009-07-15,Driving and damping mechanisms in hybrid pressure-gravity modes pulsators,"We study the energetic aspects of hybrid pressure-gravity modes pulsations.
The case of hybrid beta Cephei-SPB pulsators is considered with special
attention. In addition to the already known sensitivity of the driving
mechanism to the heavy elements mixture (mainly the iron abundance), we show
that the characteristics of the propagation and evanescent regions play also a
major role, determining the extension of the stable gap in the frequency domain
between the unstable low order pressure and high order gravity modes. Finally,
we consider the case of hybrid delta Sct-gamma Dor pulsators.",0907.2636v1
2009-07-16,Lattice distortion and magnetic quantum phase transition in CeFeAs(1-x)P(x)O,"We use neutron scattering to show that replacing the larger arsenic with
smaller phosphorus in CeFeAs(1-x)P(x)O simultaneously suppresses the AF order
and orthorhombic distortion near x = 0.4, providing evidence for a magnetic
quantum critical point. Furthermore, we find that the pnictogen height in iron
arsenide is an important controlling parameter for their electronic and
magnetic properties, and may play an important role in electron pairing and
superconductivity.",0907.2853v1
2009-07-17,"Phase diagram of CeFeAs$_{1-x}$P$_{x}$O obtained from electric resistivity, magnetization, and specific heat measurements","We performed a systematic study on the properties of CeFeAs$_{1-x}$P$_{x}$O
($0\leq x\leq 1$) by electrical resistivity, magnetization and specific heat
measurements. The c-axis lattice constant decreases significantly with
increasing P content, suggesting a remarkable chemical pressure. The Fe-3d
electrons show the enhanced metallic behavior upon P-doping and undergo a
magnetic quantum phase transition around $x \approx 0.4$. Meanwhile, the Ce-4f
electrons develop a ferromagnetic order near the same doping level. The
ferromagnetic order is vanishingly small around $x=0.9$. The data suggest a
heavy-fermion-like behavior as $x\geq 0.95$. No superconductivity is observed
down to 2 K. Our results show the ferromagnetic ordered state as an
intermediate phase intruding between the antiferromagnetic bad metal and the
nonmagnetic heavy fermion metal and support the cerium-containing iron
pnictides as a unique layered Kondo lattice system.",0907.2961v2
2009-07-21,Discrimination of mass hierarchy with atmospheric neutrinos at a magnetized muon detector,"We have studied the mass hierarchy with atmospheric neutrinos considering the
muon energy and zenith angle of the event at the magnetized iron calorimeter
detector. For $\chi^2$ analysis we have migrated the number of events from
neutrino energy and zenith angle bins to muon energy and zenith angle bins
using the two-dimensional energy-angle correlated resolution functions. The
binning of data is made in two-dimensional grids of $\log_{10} E - L^{0.4}$
plane to get a better reflection of the oscillation pattern in the $\chi^2$
analysis. Then the $\chi^2$ is marginalized considering all possible systematic
uncertainties of the atmospheric neutrino flux and cross section. The effects
of the ranges of oscillation parameters on the marginalization are also
studied. The lower limit of the range of $\theta_{13}$ for marginalization is
found to be very crucial in determining the sensitivity of hierarchy for a
given $\theta_{13}$. Finally, we show that one can discriminate atmospheric
neutrino mass hierarchy at $>$90% C.L. if the lower limit of $\theta_{13} \ge
5^\circ$.",0907.3540v3
2009-07-21,The Dependency of the Cepheid Period-Luminosity Relation on Chemical Composition,"The dependency of the Cepheid Period-Luminosity Relation on chemical
composition at different wavelengths is assessed via direct detailed abundance
analysis of Galactic and Magellanic Cepheids, as derived from high resolution,
high signal-to-noise spectra. Our measurements span one order of magnitude in
iron content and allow to rule out at the ~ 9 sigma level the universality of
the Period-Luminosity Relation in the V band, with metal rich stars being
fainter than metal poor ones by ~0.3 mag. The dependency is less pronounced in
the K band. Its magnitude and statistical significance decisively depend on
detailed distance measurements to individual stars, as inferred via the
Infrared Surface Brightness Method.",0907.3655v2
2009-07-23,Prospects of measuring the leptonic CP phase with atmospheric neutrinos,"We have studied the prospects of measuring the CP violating phase with
atmospheric neutrinos at a large magnetized iron calorimeter detector
considering the muons (directly measurable) of the neutrino events generated by
a MonteCarlo event generator Nuance. The effect of $\theta_{13}$ and
$\delta_{CP}$ appears dominantly neither in atmospheric neutrino oscillation
nor in solar neutrino oscillation, but appears as subleading in both cases.
These are observable in range of $E \sim 1$ GeV for atmospheric neutrino, where
solar and atmospheric oscillation couple. In this regime, the quasi-elastic
events dominate and the energy resolution is very good, but the angular
resolution is very poor. Unlike beam experiments this poor angular resolution
acts against its measurements. However, we find that one can be able to
distinguish $\delta_{CP}\approx 0^\circ$ and $180^\circ$ at 90% confidence
level. We find no significant sensitivity for $\delta_{CP}\approx 90^\circ$ or
$270^\circ$.",0907.3978v2
2009-07-24,In-situ fabrication of cobalt-doped SrFe2As2 thin films by using pulsed laser deposition with excimer laser,"The remarkably high superconducting transition temperature and upper critical
field of iron(Fe)-based layered superconductors, despite ferromagnetic material
base, open the prospect for superconducting electronics. However, success in
superconducting electronics has been limited because of difficulties in
fabricating high-quality thin films. We report the growth of high-quality
c-axis-oriented cobalt(Co)-doped SrFe2As2 thin films with bulk
superconductivity by using an in-situ pulsed laser deposition technique with a
248-nm-wavelength KrF excimer laser and an arsenic(As)-rich phase target. The
temperature and field dependences of the magnetization showing strong
diamagnetism and transport critical current density with superior Jc-H
performance are reported. These results provide necessary information for
practical applications of Fe-based superconductors.",0907.4227v1
2009-07-31,A new surface parameter for composition studies at high energies,"A new family of parameters intended for composition studies is presented.
They make exclusive use of surface data combining the information from the
total signal at each triggered detector and the array geometry. We perform an
analytical study of these composition estimators in order to assess their
reliability, stability and possible optimization. The influence of the
different slopes of the proton and Iron lateral distribution function on the
discrimination power of the estimators is also studied. Additionally, the
stability of the parameter in face of a possible underestimation of the size of
the muon component by the shower simulation codes, as it is suggested by
experimental evidence, is also studied.",0907.5480v1
2009-07-31,The cleavage surface of the BaFe_(2-x)Co_(x)As_(2) and Fe_(y)Se_(1-x)Te_(x) superconductors: from diversity to simplicity,"We elucidate the termination surface of cleaved single crystals of the
BaFe_(2-x)Co_(x)As_(2) and Fe_(y)Se_(1-x)Te_(x) families of the high
temperature iron based superconductors. By combining scanning tunneling
microscopic data with low energy electron diffraction we prove that the
termination layer of the Ba122 systems is a remnant of the Ba layer, which
exhibits a complex diversity of ordered and disordered structures. The observed
surface topographies and their accompanying superstructure reflections in
electron diffraction depend on the cleavage temperature. In stark contrast,
Fe_(y)Se_(1-x)Te_(x) possesses only a single termination structure - that of
the tetragonally ordered Se_(1-x)Te_(x) layer.",0907.5544v1
2009-07-31,Magnetism and superconductivity in single crystals $Eu_{1-x}Sr_xFe_{2-y}Co_{y}As_2$,"We systematically studied the transport properties of single crystals of
$Eu_{1-x}Sr_xFe_{2-y}$Co$_{y}As_2$. Co doping can suppress the spin-density
wave (SDW) ordering and induces a superconducting transition, but a resistivity
reentrance due to the antiferromagnetic ordering of $Eu^{2+}$ spins is
observed, indicating the competition between antiferromagnetism (AFM) and
superconductivity. It is striking that the resistivity reentrance can be
completely suppressed by external magnetic field (H) because a metamagnetic
transition from antiferromagnetism to ferromagnetism for $Eu^{2+}$ spins is
induced by magnetic field. Superconductivity without resistivity reentrance
shows up by partial substitution of Eu$^{2+}$ with non-magnetic Sr$^{2+}$ to
completely destroy the AFM ordering of $Eu^{2+}$ spins. These results suggest
that the antiferromagnetism destroys the superconductivity, while the
ferromagnetism can coexist with the superconductivity in the iron-based
high-$T_c$ superconductors.",0907.5547v1
2009-08-05,^{31}P and ^{75}As NMR evidence for a residual density of states at zero energy in superconducting BaFe_2(As_{0.67}P_{0.33})_2,"^{31}P and ^{75}As NMR measurements were performed in superconducting
BaFe_2(As_{0.67}P_{0.33})_2 with T_c = 30 K. The nuclear-spin-lattice
relaxation rate T_1^{-1} and the Knight shift in the normal state indicate the
development of antiferromagnetic fluctuations, and T_1^{-1} in the
superconducting (SC) state decreases without a coherence peak just below T_c,
as observed in (Ba_{1-x}K_{x})Fe_2As_2. In contrast to other iron arsenide
superconductors, the T_1^{-1} \propto T behavior is observed below 4K,
indicating the presence of a residual density of states at zero energy. Our
results suggest that strikingly different SC gaps appear in
BaFe_2(As_{1-x}P_{x})_2 despite a comparable T_c value, an analogous phase
diagram, and similar Fermi surfaces to (Ba_{1-x}K_{x})Fe_2As_2.",0908.0625v2
2009-08-05,Krylov implementation of the hybridization expansion impurity solver and application to 5-orbital models,"We present an implementation of the hybridization expansion impurity solver
which employs sparse matrix exact-diagonalization techniques to compute the
time evolution of the local Hamiltonian. This method avoids computationally
expensive matrix-matrix multiplications and becomes advantageous over the
conventional implementation for models with 5 or more orbitals. In particular,
this method will allow the systematic investigation of 7-orbital systems
(lanthanide and actinide compounds) within single-site dynamical mean field
theory. We illustrate the power and usefulness of our approach with dynamical
mean field results for a 5-orbital model which captures some aspects of the
physics of the iron based superconductors.",0908.0681v2
2009-08-12,The Inner Rim Structures of Protoplanetary Discs,"The inner boundary of protoplanetary discs is structured by the dramatic
opacity changes at the transition from the dust-containing to a dust-free zone.
This paper explores the variety and limits of inner rim structures in passively
heated dusty discs. For this study, we implemented detailed sublimation physics
in a fast Monte Carlo radiative transfer code. We show that the inner rim in
dusty discs is not an infinitely sharp wall but a diffuse region which may be
narrow or wide. Furthermore, high surface densities and large silicate grains
as well as iron and corundum grains decrease the rim radius, from a 2.2AU
radius for small silicates around a 47 Solar luminosity Herbig Ae star
typically to 0.4AU and as close as 0.2AU. A passive disc with grain growth and
a diverse dust composition must thus have a small inner rim radius. Finally, an
analytical expression is presented for the rim location as a function of dust,
disc and stellar properties.",0908.1692v3
2009-08-20,Evidence for Nodal superconductivity in Sr$_{2}$ScFePO$_{3}$,"Point contact Andreev reflection spectra have been taken as a function of
temperature and magnetic field on the polycrystalline form of the newly
discovered iron-based superconductor Sr2ScFePO3. A zero bias conductance peak
which disappears at the superconducting transition temperature, dominates all
of the spectra. Data taken in high magnetic fields show that this feature
survives until 7T at 2K and a flattening of the feature is observed in some
contacts. Here we inspect whether these observations can be interpreted within
a d-wave, or nodal order parameter framework which would be consistent with the
recent theoretical model where the height of the P in the Fe-P-Fe plane is key
to the symmetry of the superconductivity. However, in polycrystalline samples
care must be taken when examining Andreev spectra to eliminate or take into
account artefacts associated with the possible effects of Josephson junctions
and random alignment of grains.",0908.2902v2
2009-08-21,Magnetic structure of EuFe2As2 determined by single crystal neutron diffraction,"Among various parent compounds of iron pnictide superconductors, EuFe2As2
stands out due to the presence of both spin density wave of Fe and
antiferromagnetic ordering (AFM) of the localized Eu2+ moment. Single crystal
neutron diffraction studies have been carried out to determine the magnetic
structure of this compound and to investigate the coupling of two magnetic
sublattices. Long range AFM ordering of Fe and Eu spins was observed below 190
K and 19 K, respectively. The ordering of Fe2+ moments is associated with the
wave vector k = (1,0,1) and it takes place at the same temperature as the
tetragonal to orthorhombic structural phase transition, which indicates the
strong coupling between structural and magnetic components. The ordering of Eu
moment is associated with the wave vector k = (0,0,1). While both Fe and Eu
spins are aligned along the long a axis as experimentally determined, our
studies suggest a weak coupling between the Fe and Eu magnetism.",0908.3142v1
2009-08-24,The two-dimensional frustrated Heisenberg model on the orthorhombic lattice,"We discuss new high-field magnetization data recently obtained by Tsirlin et
al. for layered vanadium phosphates in the framework of the square-lattice
model. Our predictions for the saturation fields compare exceptionally well to
the experimental findings, and the strong bending of the curves below
saturation agrees very well with the experimental field dependence. Furthermore
we discuss the remarkably good agreement of the frustrated Heisenberg model on
the square lattice in spite of the fact that the compounds described with this
model actually have a lower crystallographic symmetry. We present results from
our calculations on the thermodynamics of the model on the orthorhombic (i.e.,
rectangular) lattice, in particular the temperature dependence of the magnetic
susceptibility. This analysis also sheds light on the discussion of magnetic
frustration and anisotropy of a class of iron pnictide parent compounds, where
several alternative suggestions for the magnetic exchange models were proposed.",0908.3442v1
2009-09-02,A study of nuclear effect in $F_3$ structure function in the deep inelastic $ν(\barν)$ reactions in nuclei,"We study nuclear effect in the $F^A_3(x)$ structure function in the deep
inelastic neutrino reactions on iron by taking into account Fermi motion,
binding, target mass correction, shadowing and anti-shadowing corrections.
Calculations have been done in a local density approximation using relativistic
nuclear spectral functions which include nucleon correlations for nuclear
matter. Results for $F^A_3(x)$ have been compared with the results reported at
NuTeV and also with some of the older experiments reported in the literature.",0909.0360v1
2009-09-02,Nuclear EMC Effect in a Statistical Model,"A simple statistical model in terms of light-front kinematic variables is
used to explain the nuclear EMC effect in the range $x \in [0.2,~0.7]$, which
was constructed by us previously to calculate the parton distribution functions
(PDFs) of the nucleon. Here, we treat the temperature $T$ as a parameter of the
atomic number $A$, and get reasonable results in agreement with the
experimental data. Our results show that the larger $A$, the lower $T$ thus the
bigger volume $V$, and these features are consistent with other models.
Moreover, we give the predictions of the quark distribution ratios,
\emph{i.e.}, $q^A(x) / q^D(x)$, $\bar{q}^A(x) / \bar{q}^D(x)$, and $s^A(x) /
s^D(x)$, and also the gluon ratio $g^A(x) / g^D(x)$ for iron as an example. The
predictions are different from those by other models, thus experiments aiming
at measuring the parton ratios of antiquarks, strange quarks, and gluons can
provide a discrimination of different models.",0909.0454v1
2009-09-03,Observation of Dirac Cone Electronic Dispersion in BaFe2As2,"We performed an angle-resolved photoemission spectroscopy study of BaFe2As2,
which is the parent compound of the so-called 122 phase of the iron-pnictide
high-temperature superconductors. We reveal the existence of a Dirac cone in
the electronic structure of this material below the spin-density-wave
temperature, which is responsible for small spots of high photoemission
intensity at the Fermi level. Our analysis suggests that the cone is slightly
anisotropic and its apex is located very near the Fermi level, leading to tiny
Fermi surface pockets. Moreover, the bands forming the cone show an anisotropic
leading edge gap away from the cone that suggests a nodal spin-density-wave
description.",0909.0574v1
2009-09-04,"Unconventional electronic reconstruction in undoped (Ba,Sr)Fe$_2$As$_2$ across the spin density wave transition","Through a systematic high resolution angle-resolved photoemission study of
the iron pnictide compounds (Ba,Sr)Fe$_2$As$_2$, we show that the electronic
structures of these compounds are significantly reconstructed across the spin
density wave ordering, which cannot be described by a simple folding scenario
of conventional density wave ordering. Moreover, we find that LDA calculations
with an incorporated suppressed magnetic moment of 0.5$\mu_{\tiny{\textrm{B}}}$
can match well the details in the reconstructed electronic structure,
suggesting that the nature of magnetism in the pnictides is more itinerant than
local, while the origin of suppressed magnetic moment remains an important
issue for future investigations.",0909.0831v1
2009-09-04,Inelastic X-ray Scattering Study of superconducting SmFeAs(O$_{1-x}$F$_{y}$) Single Crystals: Evidence for Strong Momentum-Dependent Doping-Induced Renormalizations of Optical Phonons,"We report inelastic x-ray scattering experiments on the lattice dynamics in
SmFeAsO and superconducting SmFeAsO$_{0.6}$F$_{0.35}$ single crystals.
Particular attention was paid to the dispersions along the [100] direction of
three optical modes close to 23 meV, polarized out of the FeAs planes.
Remarkably, two of these modes are strongly renormalized upon fluorine doping.
These results provide significant insight into the energy and momentum
dependence of the coupling of the lattice to the electron system and underline
the importance of spin-phonon coupling in the superconducting iron-pnictides.",0909.0913v2
2009-09-04,Intrinsic pinning on structural domains in underdoped single crystals of Ba(Fe$_{1-x}$Co$_x$)$_2$As$_2$,"Critical current density was studied in single crystals of
Ba(Fe$_{1-x}$Co$_x$)$_2$As$_2$ for the values of $x$ spanning the entire doping
phase diagram. A noticeable enhancement was found for slightly underdoped
crystals with the peak at $x = 0.058$. Using a combination of polarized-light
imaging, x-ray diffraction and magnetic measurements we associate this behavior
with the intrinsic pinning on structural domains in the orthorhombic phase.
Domain walls extend throughout the sample thickness in the direction of
vortices and act as extended pinning centers. With the increasing $x$ domain
structure becomes more intertwined and fine due to a decrease of the
orthorhombic distortion. This results in the energy landscape with maze-like
spatial modulations favorable for pinning. This finding shows that iron-based
pnictide superconductors, characterized by high values of the transition
temperature, high upper critical fields, and low anisotropy may intrinsically
have relatively high critical current densities.",0909.0923v3
2009-09-04,X-raying the Winds of Luminous Active Galaxies,"We briefly describe some recent observational results, mainly at X-ray
wavelengths, on the winds of luminous active galactic nuclei (AGNs). These
winds likely play a significant role in galaxy feedback. Topics covered include
(1) Relations between X-ray and UV absorption in Broad Absorption Line (BAL)
and mini-BAL quasars; (2) X-ray absorption in radio-loud BAL quasars; and (3)
Evidence for relativistic iron K BALs in the X-ray spectra of a few bright
quasars. We also mention some key outstanding problems and prospects for future
advances; e.g., with the International X-ray Observatory (IXO).",0909.0958v1
2009-09-11,"The double life of electrons in magnetic iron pnictides, as revealed by NMR","We present a phenomenological, two-fluid approach to understanding the
magnetic excitations in Fe pnictides, in which a paramagnetic fluid with
gapless, incoherent particle-hole excitations coexists with an
antiferromagnetic fluid with gapped, coherent spin wave excitations. We show
that this two-fluid phenomenology provides an excellent quantitative
description of NMR data for magnetic ""122"" pnictides, and argue that it finds a
natural justification in LSDA and spin density wave calculations. We further
use this phenomenology to estimate the maximum renormalisation of the ordered
moment that can follow from low-energy spin fluctuations in Fe pnictides. We
find that this is too small to account for the discrepancy between ab intio
calculations and neutron scattering measurements.",0909.2207v4
2009-09-12,Nuclear effects in neutrino-nucleus DIS,"We explain the current status of nuclear parton distribution functions in
connection with neutrino-nucleus interactions. Neutrino deep inelastic
scattering (DIS) measurements have been done for heavy nuclear targets such as
iron and lead. In order to extract structure functions of the nucleon, one
needs to remove nuclear effects from the data. However, recent studies indicate
that there are inconsistencies in nuclear modifications between charged-lepton
and neutrino scattering measurements. Nuclear medium effects could be also an
origin for the NuTeV anomaly in the weak-mixing angle. In addition, the
modifications could affect neutrino-oscillation experiments because some DIS
events of neutrino-oxygen nucleus interactions are contained. On the other
hand, the nuclear medium effects themselves are interesting and important for
describing nuclei in terms of quark and gluon degrees of freedom.",0909.2329v1
2009-09-15,Theory of Andreev reflection in a two-orbital model of iron-pnictide superconductors,"A recently developed theory for the problem of Andreev reflection between a
normal metal (N) and a multiband superconductor (MBS) assumes that the incident
wave from the normal metal is coherently transmitted through several bands
inside the superconductor. Such splitting of the probability amplitude into
several channels is the analogue of a quantum waveguide. Thus, the appropriate
matching conditions for the wave function at the N/MBS interface are derived
from an extension of quantum waveguide theory. Interference effects between the
transmitted waves inside the superconductor manifest themselves in the
conductance. We provide results for a FeAs superconductor, in the framework of
a recently proposed effective two-band model and two recently proposed gap
symmetries: in the sign-reversed s-wave ($\Delta\cos(k_x)\cos(k_y)$) scenario
resonant transmission through surface Andreev bound states (ABS) at nonzero
energy is found as well as destructive interference effects that produce zeros
in the conductance; in the extended s-wave ($\Delta[\cos(k_x)+\cos(k_y)]$)
scenario no ABS at finite energy are found.",0909.2826v1
2009-09-16,"Electronic band structure, phonon spectrum, and elastic properties of LaOFeAs","We present results of ab-initio calculations of the electronic band
structure, lattice dynamical properties, and elastic constants of LaOFeAs, the
parent compound of the recently discovered superconducting iron-oxypnictide
(LaO1-xFxFeAs). The total and partial electronic density of states (EDOS) of
the undoped LaOFeAs (in the insulating or metallic state) are extracted from
the electronic band structure. The phonon dispersion and the phonon density of
states (PDOS) are also studied. Possible implications of the band structure,
EDOS, and PDOS of LaOFeAs on the eventual appearance of high-Tc
superconductivity upon carrier doping are discussed. The values of various
independent elastic constants for both insulating and metallic states are
estimated and discussed.",0909.2914v2
2009-09-16,Calculation of stellar electron-capture cross sections on nuclei based on microscopic Skyrme functionals,"A fully self-consistent microscopic framework for evaluation of nuclear
weak-interaction rates at finite temperature is introduced, based on Skyrme
functionals. The single-nucleon basis and the corresponding thermal occupation
factors of the initial nuclear state are determined in the finite-temperature
Skyrme Hartree-Fock model, and charge-exchange transitions to excited states
are computed using the finite-temperature RPA. Effective interactions are
implemented self-consistently: both the finite-temperature single-nucleon
Hartree-Fock equations and the matrix equations of RPA are based on the same
Skyrme energy density functional. Using a representative set of Skyrme
functionals, the model is applied in the calculation of stellar
electron-capture cross sections for selected nuclei in the iron mass group and
for neutron-rich Ge isotopes.",0909.3070v1
2009-09-17,Bulk electronic structure of optimally doped Ba(Fe$_{1-x}$Co$_{x}$)$_2$As$_2$,"We report high-resolution, bulk Compton scattering measurements unveiling the
Fermi surface of an optimally-doped iron-arsenide superconductor,
Ba(Fe$_{0.93}$Co$_{0.07}$)$_2$As$_2$. Our measurements are in agreement with
first-principles calculations of the electronic structure, revealing both the
$X$-centered electron pockets and the $\Gamma$-centered hole pockets. Moreover,
our data are consistent with the strong three-dimensionality of one of these
sheets that has been predicted by electronic structure calculations at the
local-density-approximation-minimum As position. Complementary calculations of
the noninteracting susceptibility, $\chi_0({\bf q}, \omega)$, suggest that the
broad peak that develops due to interband Fermi-surface nesting, and which has
motivated several theories of superconductivity in this class of material,
survives the measured three dimensionality of the Fermi surface in this family.",0909.3194v2
2009-09-25,Modelling hybrid Beta Cephei/SPB pulsations: Gamma Pegasi,"Recent photometric and spectroscopic observations of the hybrid variable
Gamma Pegasi (Handler et al. 2009, Handler 2009) revealed 6 frequencies of the
SPB type and 8 of the Beta Cep type pulsations. Standard seismic models, which
have been constructed with OPAL (Iglesias & Rogers 1996) and OP (Seaton 2005)
opacities by fitting three frequencies (those of the radial fundamental and two
dipole modes), do not reproduce the frequency range of observed pulsations and
do not fit the observed individual frequencies with a satisfactory accuracy. We
argue that better fitting can be achieved with opacity enhancements, over the
OP data, by about 20-50 percent around the opacity bumps produced by excited
ions of the iron-group elements at temperatures of about 200 000 K (Z bump) and
2 million K (Deep Opacity Bump).",0909.4643v1
2009-09-29,Weak anisotropy of the superconducting upper critical field in Fe1.11Te0.6Se0.4 single crystals,"We have determined the resistive upper critical field Hc2 for single crystals
of the superconductor Fe1.11Te0.6Se0.4 using pulsed magnetic fields of up to
60T. A rather high zero-temperature upper critical field of mu0Hc2(0) approx
47T is obtained, in spite of the relatively low superconducting transition
temperature (Tc approx 14K). Moreover, Hc2 follows an unusual temperature
dependence, becoming almost independent of the magnetic field orientation as
the temperature T=0. We suggest that the isotropic superconductivity in
Fe1.11Te0.6Se0.4 is a consequence of its three-dimensional Fermi-surface
topology. An analogous result was obtained for (Ba,K)Fe2As2, indicating that
all layered iron-based superconductors exhibit generic behavior that is
significantly different from that of the high-Tc cuprates.",0909.5328v1
2009-09-30,He and Ne ages of large presolar silicon carbide grains: Solving the recoil problem,"Knowledge about the age of presolar grains provides important insights into
Galactic chemical evolution and the dynamics of grain formation and destruction
processes in the Galaxy. Determination from the abundance of cosmic ray
interaction products is straightforward, but in the past has suffered from
uncertainties in correcting for recoil losses of spallation products. The
problem is less serious in a class of large (tens of micrometer) grains. We
describe the correction procedure and summarise results for He and Ne ages of
presolar SiC ""Jumbo"" grains that range from close to zero to ~850 Myr, with the
majority being less than 200 Myr. We also discuss the possibility of extending
our approach to the majority of smaller SiC grains and explore possible
contributions from trapping of cosmic rays.",0909.5532v1
2009-10-01,Pressure-driven phase transitions in correlated systems,"Motivated by recent experimental measurements on pressure-driven phase
transitions in Mott-insulators as well as the new iron pnictide
superconductors, we show that first principles Car-Parrinello molecular
dynamics calculations are a powerful method to describe the microscopic origin
of such transitions. We present results for (i) the pressure-induced insulator
to metal phase transition in the prototypical Mott insulator TiOCl as well as
(ii) the pressure-induced structural and magnetic phase transitions in the
family of correlated metals $A$Fe$_2$As$_2$ ($A$=Ca,Sr,Ba). Comparison of our
predictions with existing experimental results yields very good agreement.",0910.0158v1
2009-10-05,Isotope shifts and hyperfine structure of the Fe I 372 nm resonance line,"We report measurements of the isotope shifts of the $3d^64s^2 a ^5D_4 -
3d^64s4p z ^5F_5^o$ Fe I resonance line at 372 nm between all four stable
isotopes $^{54}$Fe, $^{56}$Fe, $^{57}$Fe, and $^{58}$Fe, as well as the
complete hyperfine structure of that line for $^{57}$Fe, the only stable
isotope having a non-zero nuclear spin. The field and specific mass shift
coefficients of the transition have been derived from the data, as well as the
experimental value for the hyperfine structure magnetic dipole coupling
constant $A$ of the excited state of the transition in $^{57}$Fe: $A(3d^64s4p z
^5F_5^o) = 81.69(86)$ MHz. The measurements were done by means of Doppler-free
laser saturated-absorption spectroscopy in a Fe-Ar hollow cathode using both
natural and enriched iron samples. The measured isotope shifts and hyperfine
constants are reported with uncertainties at the percent level.",0910.0479v1
2009-10-05,First-principles thermal equation of state and thermoelasticity of hcp Fe at high pressures,"We investigate the equation of state and elastic properties of hcp iron at
high pressures and high temperatures using first principles linear response
linear-muffin-tin-orbital method in the generalized-gradient approximation. We
calculate the Helmholtz free energy as a function of volume, temperature, and
volume-conserving strains, including the electronic excitation contributions
from band structures and lattice vibrational contributions from quasi-harmonic
lattice dynamics. We perform detailed investigations on the behavior of elastic
moduli and equation of state properties as functions of temperature and
pressure, including the pressure-volume equation of state, bulk modulus, the
thermal expansion coefficient, the Gruneisen ratio, and the shock Hugoniot.
Detailed comparison has been made with available experimental measurements and
theoretical predictions.",0910.0884v1
2009-10-06,Band and momentum dependent electron dynamics in superconducting ${\rm Ba(Fe_{1-x}Co_{x})_2As_2}$ as seen via electronic Raman scattering,"We present details of carrier properties in high quality ${\rm
Ba(Fe_{1-x}Co_{x})_2As_2}$ single crystals obtained from electronic Raman
scattering. The experiments indicate a strong band and momentum anisotropy of
the electron dynamics above and below the superconducting transition
highlighting the importance of complex band-dependent interactions. The
presence of low energy spectral weight deep in the superconducting state
suggests a gap with accidental nodes which may be lifted by doping and/or
impurity scattering. When combined with other measurements, our observation of
band and momentum dependent carrier dynamics indicate that the iron arsenides
may have several competing superconducting ground states.",0910.0898v2
2009-10-09,On the influence of high energy electron populations on metal abundance estimates in galaxy groups and clusters,"Spectral line emissivities have usually been calculated for a Maxwellian
electron distribution. But many theoretical works on galaxy groups and clusters
and on the solar corona suggest to consider modified Maxwellian electron
distribution functions to fit observed X-ray spectra. Here we examine the
influence of high energy electron populations on measurements of metal
abundances. A generalized approach which was proposed in the paper by Prokhorov
et al. (2009) is used to calculate the line emissivities for a modified
Maxwellian distribution. We study metal abundances in galaxy groups and
clusters where hard X-ray excess emission was observed. We found that for
modified Maxwellian distributions the argon abundance decreases for the HCG 62
group, the iron abundance decreases for the Centaurus cluster and the oxygen
abundance decreases for the solar corona with respect to the case of a
Maxwellian distribution. Therefore, metal abundance measurements are a
promising tool to test the presence of high energy electron populations.",0910.1640v1
2009-10-14,Electron correlation and spin density wave order in iron pnictides,"We study the correlation effects on the electronic structure and spin density
wave order in Fe-pnictides. Using the multiorbital Hubbard model and Gutzwiller
projection, we show that nonperturbative correlation effects are essential to
stabilize the metallic spin density wave phase for the intermediate correlation
strengths appropriate for pnictides. We find that the ordered moments depend
sensitively on the Hund's rule coupling $J$ but weakly on the intraorbital
Coulomb repulsion $U$, varying from $0.3\mu_B$ to $1.5\mu_B$ in the range
$J=0.3\sim0.8$ eV for $U=3\sim4$ eV. We obtain the phase diagram and discuss
the effects of orbital order and electron doping, the evolution of the Fermi
surface topology with the ordered moment, and compare to recent experiments.",0910.2707v2
2009-10-15,Single vortex structure in two models of iron pnictide $s^\pm$ superconductivity,"The structure of a single vortex in a FeAs superconductor is studied in the
framework of two formulations of superconductivity for the recently proposed
sign-reversed $s$ wave ($s^\pm$) scenario: {\it (i)} a continuum model taking
into account the existence of an electron and a hole band with a repulsive
local interaction between the two; {\it (ii)} a lattice tight-binding model
with two orbitals per unit cell and a next-nearest-neighbour attractive
interaction. In the first model, the local density of states (LDOS) at the
vortex centre, as a function of energy, exhibits a peak at the Fermi level,
while in the second model such LDOS peak is deviated from the Fermi level and
its energy depends on band filling. An impurity located outside the vortex core
has little effect on the LDOS peak, but an impurity close to the vortex core
can almost suppress it and modify its position.",0910.2879v1
2009-10-19,New approach to primary mass composition analysis with simultaneous use of ground and fluorescence detectors data,"We study the possibility to reconstruct primary mass composition with the use
of combinations of basic shower characteristics, measured in hybrid
experiments, such as depth of shower maximum from fluorescence side and signal
in water Cherenkov tanks or in plastic scintillators from the ground side. To
optimize discrimination performance of shower observables combinations we apply
Fisher's discriminant analysis and give statistical estimates of separation of
the obtained distributions on Fisher variables for proton and iron primaries.
At the final stage we apply Multiparametric Topological Analysis to these
distributions to extract composition from prepared mixtures with known
fractions of showers from different primary particles. It is shown, that due to
high sensitivity of water tanks to muons, combination of signal in them with
$\xmax$ looks especially promising for mass composition analysis, provided the
energy is determined from longitudinal shower profile.",0910.3520v1
2009-10-22,About the strength of correlation effects in the electronic structure of iron,"The strength of electronic correlation effects in the spin-dependent
electronic structure of ferromagnetic bcc Fe(110) has been investigated by
means of spin and angle-resolved photoemission spectroscopy. The experimental
results are compared to theoretical calculations within the three-body
scattering approximation and within the dynamical mean-field theory, together
with one-step model calculations of the photoemission process. This comparison
indicates that the present state of the art many-body calculations, although
improving the description of correlation effects in Fe, give too small mass
renormalizations and scattering rates thus demanding more refined many-body
theories including non-local fluctuations.",0910.4360v1
2009-10-29,Surprising Metallicity of a Newly Discovered M79 Post-AGB Star,"A detailed chemical composition analysis based on a high-resolution
(R=35,000) CCD spectrum is presented for a newly discovered post-AGB star in
the globular cluster M79 for the first time. The elemental abundance results of
M79 Post-AGB star are found to be [C/Fe]=-0.7, [O/Fe]=+1.4, [alpha-
process/Fe]=0.5, and [s-process/Fe]=-0.1. The surprising result is that the
iron abundance of the star is apparently about 0.6 dex less than that of the
cluster's red giants as reported by published studies including a recent
high-resolution spectroscopic analysis by Carretta and colleagues.",0910.5567v1
2009-10-29,Simulation of a flux emergence event and comparison with observations by Hinode,"We study the observational signature of flux emergence in the photosphere
using synthetic data from a 3D MHD simulation of the emergence of a twisted
flux tube. Several stages in the emergence process are considered. At every
stage we compute synthetic Stokes spectra of the two iron lines Fe I 6301.5
{\AA} and Fe I 6302.5 {\AA} and degrade the data to the spatial and spectral
resolution of Hinode's SOT/SP. Then, following observational practice, we apply
Milne-Eddington-type inversions to the synthetic spectra in order to retrieve
various atmospheric parameters and compare the results with recent Hinode
observations. During the emergence sequence, the spectral lines sample
different parts of the rising flux tube, revealing its twisted structure. The
horizontal component of the magnetic field retrieved from the simulations is
close to the observed values. The flattening of the flux tube in the
photosphere is caused by radiative cooling, which slows down the ascent of the
tube to the upper solar atmosphere. Consistent with the observations, the
rising magnetized plasma produces a blue shift of the spectral lines during a
large part of the emergence sequence.",0910.5737v1
2009-11-04,Solar-like oscillations in massive main-sequence stars. I. Asteroseismic signatures of the driving and damping regions,"Motivated by the recent detection of stochastically excited modes in the
massive star V1449 Aql (Belkacem et al., 2009b), already known to be a $\beta$
Cephei, we theoretically investigate the driving by turbulent convection. By
using a full non-adiabatic computation of the damping rates, together with a
computation of the energy injection rates, we provide an estimate of the
amplitudes of modes excited by both the convective region induced by the iron
opacity bump and the convective core. Despite uncertainties in the dynamical
properties of such convective regions, we demonstrate that both are able to
efficiently excite $p$ modes above the CoRoT observational threshold and the
solar amplitudes. In addition, we emphasise the potential asteroseismic
diagnostics provided by each convective region, which we hope will help to
identify the one responsible for solar-like oscillations, and to give
constraints on this convective zone. A forthcoming work will be dedicated to an
extended investigation of the likelihood of solar-like oscillations across the
Hertzsprung-Russell diagram.",0911.0908v1
2009-11-05,Ultra-High Energy Cosmic-Ray Acceleration in the Jet of Centaurus A,"We evaluate the achievable maximum energy of nuclei diffusively accelerated
by shock wave in the jet of Cen A, based on an updated model involving the
stochastic magnetic fields that are responsible for recent synchrotron X-ray
measurements. For the maximum energy analysis, conceivable energy constraints
from spatiotemporal scales are systematically considered for the jet-wide
including discrete X-ray knots. We find that in the inner region within ~1
arcmin from galactic core, which includes knots AX and BX, proton and iron
nucleus can be accelerated to 10^{19}-10^{20} and 10^{21} eV (10-100 EeV and
ZeV) ranges, respectively. The upper cutoff energy of the very energetic
neutrinos produced via photopion interaction is also provided. These are
essential for identifying the acceleration site of the ultra-high energy cosmic
ray detected in the Pierre Auger Observatory, which signifies the arrival from
nearby galaxies including Cen A.",0911.0921v1
2009-11-09,Role of dipole-dipole interactions in multiple quantum transitions in magnetic nanoparticles,"In order to better understand the origin of multiple quantum transitions
observed in superparamagnetic nanoparticles, electron magnetic resonance (EMR)
studies have been performed on iron oxide nanoparticles assembled inside the
anodic alumina membrane. The positions of both the main resonance and
""forbidden"" (double-quantum, 2Q) transitions observed at the half-field
demonstrate the characteristic angular dependence with the line shifts
proportional to 3cos2q-1, where q is the angle between the channel axis and
external magnetic field B. This result can be attributed to the interparticle
dipole-dipole interactions within elongated aggregates inside the channels. The
angular dependence of the 2Q intensity is found to be proportional to
sin2qcos2q, that is consistent with the predictions of quantum-mechanical
calculations with the account for the mixing of states by non-secular
inter-particle dipole-dipole interactions. Good agreement is demonstrated
between different kinds of measurements (magnetization curves, line shifts and
2Q intensity), evidencing applicability of the quantum approach to the
magnetization dynamics of superparamagnetic objects.",0911.1752v1
2009-11-11,Gravitational Lensing by Black Holes,"We review the theoretical aspects of gravitational lensing by black holes,
and discuss the perspectives for realistic observations. We will first treat
lensing by spherically symmetric black holes, in which the formation of
infinite sequences of higher order images emerges in the clearest way. We will
then consider the effects of the spin of the black hole, with the formation of
giant higher order caustics and multiple images. Finally, we will consider the
perspectives for observations of black hole lensing, from the detection of
secondary images of stellar sources and spots on the accretion disk to the
interpretation of iron K-lines and direct imaging of the shadow of the black
hole.",0911.2187v2
2009-11-13,An Unusually Fast-Evolving Supernova,"Analyses of supernovae (SNe) have revealed two main types of progenitors:
exploding white dwarfs and collapsing massive stars. We present SN2002bj, which
stands out as different from any SN reported to date. Its light curve rises and
declines very rapidly, yet reaches a peak intrinsic brightness greater than -18
mag. A spectrum obtained 7 days after discovery shows the presence of helium
and intermediate-mass elements, yet no clear hydrogen or iron-peak elements.
The spectrum only barely resembles that of a Type Ia supernova, with added
carbon and helium. Its properties suggest that SN2002bj may be representative
of a class of progenitors that previously has been only hypothesized: a helium
detonation on a white dwarf, ejecting a small envelope of material. New surveys
should find many such objects, despite their scarcity.",0911.2699v1
2009-11-16,Effects of nematic fluctuations on the elastic properties of iron arsenide superconductors,"We demonstrate that the changes in the elastic properties of the FeAs
systems, as seen in our resonant ultrasound spectroscopy data, can be naturally
understood in terms of fluctuations of emerging nematic degrees of freedom.
Both the softening of the lattice in the normal, tetragonal phase as well as
its hardening in the superconducting phase are consistently described by our
model. Our results confirm the view that structural order is induced by
magnetic fluctuations.",0911.3084v2
2009-11-18,Thermonuclear explosions of rapidly rotating white dwarfs - II. Detonations,"Context: Superluminous type Ia supernovae (SNe Ia) may be explained by
super-Chandrasekhar-mass explosions of rapidly rotating white dwarfs (WDs). In
a preceding paper, we showed that the deflagration scenario applied to rapidly
rotating WDs generates explosions that cannot explain the majority of SNe Ia.
Aims: Rotation of the progenitor star allows super-Chandrasekhar-mass WDs to
form that have a shallower density stratification. We use simple estimates of
the production of intermediate and iron group elements in pure detonations of
rapidly rotating WDs to assess their viability in explaining rare SNe Ia.
Methods: We numerically construct WDs in hydrostatic equilibrium that rotate
according to a variety of rotation laws. The explosion products are estimated
by considering the density stratification and by evaluating the result of
hydrodynamics simulations. Results: We show that a significant amount of
intermediate mass elements is produced for theoretically motivated rotation
laws, even for prompt detonations of WDs. Conclusions: Rapidly rotating WDs
that detonate may provide an explanation of rare superluminous SNe Ia in terms
of both burning species and explosion kinematics.",0911.3545v1
2009-11-18,Suzaku broadband spectroscopy of Swift J1753.5-0127 in the Low-Hard State,"We present Suzaku observations of the Galactic black hole candidate Swift
J1753.5-0127 in the low-hard state. The broadband coverage of Suzaku enables us
to detect the source over the energy range 0.6 -- 250 keV. The broadband
spectrum (2 -- 250 keV) is found to be consistent with a simple power-law
(gamma \sim 1.63). In agreement with previous observations of this system, a
significant excess of soft X-ray flux is detected consistent with the presence
of a cool accretion disc. Estimates of the disc inner radius infer a value
consistent with the ISCO (R_{in} \lesssim 6 R_g, for certain values of, e.g.
N_H, i), although we cannot conclusively rule out the presence of an accretion
disc truncated at larger radii (R_{in} \sim 10 - 50 R_g). A weak,
relativistically-broadened iron line is also detected, in addition to disc
reflection at higher energy. However, the iron-K line profile favours an inner
radius larger than the ISCO (R _{in} \sim 10 - 20 R_g). The implications of
these observations for models of the accretion flow in the low-hard state are
discussed.",0911.3642v1
2009-11-19,"Comparison of Ab initio Low-Energy Models for LaFePO, LaFeAsO, BaFe2As2, LiFeAs, FeSe and FeTe: Electron Correlation and Covalency","Effective low-energy Hamiltonians for several different families of
iron-based superconductors are compared after deriving them from the
downfolding scheme based on first-principles calculations. Systematic
dependences of the derived model parameters on the families are elucidated,
many of which are understood from the systematic variation of the covalency
between Fe-3d and pnictogen-/chalcogen-p orbitals.",0911.3705v2
2009-11-19,Metallicity gradients in the Milky Way,"Radial metallicity gradients are observed in the disks of the Milky Way and
in several other spiral galaxies. In the case of the Milky Way, many objects
can be used to determine the gradients, such as HII regions, B stars, Cepheids,
open clusters and planetary nebulae. Several elements can be studied, such as
oxygen, sulphur, neon, and argon in photoionized nebulae, and iron and other
elements in cepheids, open clusters and stars. As a consequence, the number of
observational characteristics inferred from the study of abundance gradients is
very large, so that in the past few years they have become one of the main
observational constraints of chemical evolution models. In this paper, we
present some recent observational evidences of abundance gradients based on
several classes of objects. We will focus on (i) the magnitude of the
gradients, (ii) the space variations, and (iii) the evidences of a time
variation of the abundance gradients. Some comments on recent theoretical
models are also given, in an effort to highlight their predictions concerning
abundance gradients and their variations.",0911.3763v1
2009-11-19,Magnetic Anistropy due to the Casimir Effect,"We consider the Casimir interaction between a ferromagnetic and a
non-magnetic mirror, and show how the Casimir effect gives rise to a magnetic
anisotropy in the ferromagnetic layer. The anisotropy is out-of-plane if the
non-magnetic plate is optically isotropic. If the non-magnetic plate shows a
uniaxial optical anisotropy (with optical axis in the plate plane), we find an
in-plane magnetic anisotropy. In both cases, the energetically most favorable
magnetization orientation is given by the competition between polar,
longitudinal and transverse contributions to the magneto-optical Kerr effect,
and will therefore depend on the interplate distance. Numerical results will be
presented for a magnetic plate made out of iron, and non-magnetic plates of
gold (optically isotropic), quartz, calcite and barium titanate (all uniaxially
birefringent).",0911.3854v1
2009-11-19,In-plane electronic anisotropy in underdoped Ba(Fe$_{1-x}$Co$_x$)$_2$As$_2$ revealed by detwinning in a magnetic field,"We present results of angle-dependent magnetoresistance measurements and
direct optical images of underdoped Ba(Fe$_{1-x}$Co$_x$)$_2$As$_2$ which reveal
partial detwinning by action of a 14T magnetic field. Driven by a substantial
magneto-elastic coupling, this result provides evidence for an electronic
origin of the lattice distortion in underdoped iron pnictides. The observed
anisotropy in these partially detwinned samples implies a substantial in-plane
electronic anisotropy in the broken symmetry state, with a smaller resistivity
along the antiferromagnetic ordering direction.",0911.3878v1
2009-11-21,Spectroscopic Study of $^{75}$As and $^{139}$La NMR on Layered Structure Ferromagnet LaCoAsO,"$^{75}$As and $^{139}$La field-swept NMR spectra were obtained for the novel
weakly itinerant ferromagnet LaCoAsO with 2D layered structure above the Curie
temperature of 55 K. By analyzing NMR spectra, temperature dependences of
Knight shift $K$ and nuclear quadrupole resonance frequency $\nu_Q$ were
obtained successfully for each nucleus. We confirmed from the so-called
$K$-$\chi$ plots that the macroscopic magnetization of our {LaCoAsO} powder
sample is intrinsic and does not contain the contribution from impurity phases.
We estimated hyperfine coupling constants from the slope of $K$-$\chi$ plots
and compared to that of iron-arsenide superconductor.",0911.4166v2
2009-11-24,Incommensurate itinerant antiferromagnetic excitations and spin resonance in the FeTe$_{0.6}$Se$_{0.4}$ superconductor,"We report on inelastic neutron scattering measurements that find
incommensurate itinerant like magnetic excitations in the normal state of
superconducting FeTe$_{0.6}$Se$_{0.4}$ (\Tc=14K) at wave-vector
$\mathbf{Q}_{inc}=(1/2\pm\epsilon,1/2\mp\epsilon)$ with $\epsilon$=0.09(1). In
the superconducting state only the lower energy part of the spectrum shows
significant changes by the formation of a gap and a magnetic resonance that
follows the dispersion of the normal state excitations. We use a four band
model to describe the Fermi surface topology of iron-based superconductors with
the extended $s(\pm)$ symmetry and find that it qualitatively captures the
salient features of these data.",0911.4713v1
2009-11-24,Stellar Parameters for a Sample of Stars with Planets,"The study of chemical abundances in stars with planets is an important
ingredient for the models of formation and evolution of planetary systems. In
order to determine accurate abundances, it is crucial to have a reliable set of
atmospheric parameters. In this work, we describe the homogeneous determination
of effective temperatures, surface gravities and iron abundances for a large
sample of stars with planets as well as a control sample of stars without giant
planets. Our results indicate that the metallicity distribution of the stars
with planets is more metal rich by ~ 0.13 dex than the control sample stars.",0911.4723v1
2009-11-30,Disorder Induced Effects on the Critical Current Density of Iron Pnictide BaFe_1.8 Co_0.2 As_2 single crystals,"Investigating the role of disorder in superconductors is an essential part of
characterizing the fundamental superconducting properties as well as assessing
potential applications of the material. In most cases, the information
available on the defect matrix is poor, making such studies difficult, but the
situation can be improved by introducing defects in a controlled way, as
provided by neutron irradiation. In this work, we analyze the effects of
neutron irradiation on a Ba(Fe$_{1-x}$Co$_x$)$_2$As$_2$ single crystal. We
mainly concentrate on the magnetic properties which were determined by
magnetometry. Introducing disorder by neutron irradiation leads to significant
effects on both the reversible and the irreversible magnetic properties, such
as the transition temperature, the upper critical field, the anisotropy, and
the critical current density. The results are discussed in detail by comparing
them with the properties in the unirradiated state.",0911.5582v1
2009-12-07,Direct observation of a nodeless superconducting energy gap in the optical conductivity of iron-pnictides,"The temperature-dependent optical reflectivity and complex transmissivity of
an epitaxially grown Ba(Fe$_{0.9}$Co$_{0.1}$)$_2$As$_2$ thin film were measured
and the optical conductivity and permittivity evaluated over a wide frequency
range. The opening of the superconducting gap $2\Delta_0 = 3.7$ meV below
$T_c\approx 20$ K is {\em directly} observed by a completely vanishing optical
conductivity. The temperature and frequency dependent electrodynamic properties
of Ba(Fe$_{0.9}$Co$_{0.1}$)$_2$As$_2$ in the superconducting state agree well
with the BCS predictions with no nodes in the order parameter. The spectral
weight of the condensate $1.94\times 10^7 {\rm cm}^{-2}$ corresponds to a
London penetration depth $\lambda_L=3600$ \AA.",0912.1256v1
2009-12-08,The possible feature of the energy spectrum of the primary cosmic rays at ultra-high energies,"The energies of the most energetic extensive air showers observed at the
Yakutsk array have been estimated with help of the all detectors readings
instead of using of the standard procedure with a parameter s(600). The energy
of the most energetic extensive air shower observed at the Yakutsk array
happened to be 200, 200, 180 and 165 EeV with the values of the Xi**2 function
per one degree of freedom 0.9, 1., 0.9 and 1.1 for the primary protons and
helium, oxygen and iron nuclei accordingly.",0912.1473v1
2009-12-10,"Interplay between charge-order, ferroelectricity and ferroelasticity: tungsten bronze structures as a playground for multiferroicity","Large electron-electron Coulomb-interactions in correlated systems can lead
to a periodic arrangement of localized electrons, the so called ""charge-order"".
The latter is here proposed as a driving force behind ferroelectricity in iron
fluoride K0.6FeF3. By means of density functional theory, we propose different
non-centrosymmetric d5/d6 charge-ordering patterns, each giving rise to
polarization along different crystallographic axes and with different
magnitudes. Accordingly, we introduce the concept of ""ferroelectric anistropy""
(peculiar to improper ferroelectrics with polarization induced by electronic
degrees of freedom), denoting the small energy difference between competing
charge-ordered states that might be stabilized upon electrical field-cooling.
Moreover, we suggest a novel type of charge-order-induced ferroelasticity:
first-principles simulations predict a monoclinic distortion to be driven by a
specific charge-ordering pattern, which, in turn, unambiguously determines the
direction of ferroelectric polarization. K0.6FeF3 therefore emerges as a
prototypical compound, in which the intimately coupled electronic and
structural degrees of freedom result in a manifest and peculiar
multiferroicity.",0912.1960v1
2009-12-10,Superconductivity at 31 K in 111 type iron arsenide superconductor NaxFeAs induced by pressure,"The effect of pressure on superconductivity of 111 type NaxFeAs is
investigated through temperature dependent electrical resistance measurement in
a diamond anvil cell. The superconducting transition temperature (Tc) increases
from 26 K to a maximum 31 K as the pressure increases from ambient to 3 GPa.
Further increasing pressure suppresses Tc drastically. The behavior of pressure
tuned Tc in NaxFeAs is much different from that in LixFeAs, although they have
the same Cu2Sb type structure",0912.2025v1
2009-12-10,Towards a consistent picture for quasi-1D organic superconductors,"The electrical resistivity of the quasi-1D organic superconductor (TMTSF)2PF6
was recently measured at low temperature from the critical pressure needed to
suppress the spin-density-wave state up to a pressure where superconductivity
has almost disappeared. This data revealed a direct correlation between the
onset of superconductivity at Tc and the strength of a non-Fermi-liquid linear
term in the normal-state resistivity, going as r(T) = r0 + AT + BT2 at low
temperature, so that A goes to 0 as Tc goes to 0. Here we show that the
contribution of low-frequency antiferromagnetic fluctuations to the
spin-lattice relaxation rate is also correlated with this non-Fermi-liquid term
AT in the resistivity. These correlations suggest that anomalous scattering and
pairing have a common origin, both rooted in the low-frequency
antiferromagnetic fluctuations measured by NMR. A similar situation may also
prevail in the recently-discovered iron-pnictide superconductors.",0912.2049v1
2009-12-12,Two types of s-wave pairing due to magnetic and orbital fluctuations in the two-dimensional 16-band d-p model for iron-based superconductors,"We study superconductivity in the two-dimensional 16-band d-p model extracted
from a tight-binding fit to the band structure of LaFeAsO, using the random
phase approximation. When the intraorbital repulsion U is larger than the
interorbital one U', an extended s-wave (s+--wave) pairing with sign reversal
of order parameter is mediated by antiferromagnetic spin fluctuations, while
when U<U' another kind of s-wave (s++-wave) pairing without sign reversal is
mediated by ferro-orbital fluctuations. The s++-wave pairing is enhanced due to
the electron-phonon coupling and then can be expanded over the realistic
parameter region with U>U'.",0912.2392v4
2009-12-15,Superconductivity at 23 K in Pt doped BaFe2As2 single crystals,"We report superconductivity in single crystals of the new iron-pnictide
system BaFe1.9Pt0.1As2 grown by a self-flux solution method and characterized
via x-ray, transport, magnetic and thermodynamic measurements. The magnetic
ordering associated with a structural transition at 140 K present in BaFe2As2
is completely suppressed by substitution of 5% Fe with Pt and superconductivity
is induced at a critical temperature Tc=23 K. Full diamagnetic screening in the
magnetic susceptibility and a jump in the specific heat at Tc confirm the bulk
nature of the superconducting phase. All properties of the superconducting
state including transition temperature Tc, the lower critical field Hc1=200 mT,
upper critical field Hc2~65 T, and the slope dHc2/dT are comparable in value to
the those found in other transition-metal-substituted BaFe2As2 series,
indicating the robust nature of superconductivity induced by substitution of
Group VIII elements.",0912.2752v2
2009-12-15,Quadratic X-ray magneto-optical effect in reflection at the M-edges of 3d transition metals,"We have observed a quadratic x-ray magneto-optical effect in near-normal
incidence reflection at the M-edges of iron. The effect appears as the
magnetically induced rotation of ca. 0.1$ degrees of the polarization plane of
linearly polarized x-ray radiation upon reflection. A comparison of the
measured rotation spectrum with results from x-ray magnetic linear dichroism
data demonstrates that this is the first observation of the Schaefer-Hubert
effect in the x-ray regime. Ab initio density-functional theory calculations
reveal that hybridization effects of the 3p core states necessarely need to be
considered when interpreting experimental data. The discovered magneto-x-ray
effect holds promise for future ultrafast and element-selective studies of
ferromagnetic as well as antiferromagnetic materials.",0912.2867v1
2009-12-16,Coupling of spin and orbital excitations in the iron-based superconductor FeSe(0.5)Te(0.5),"We present a combined analysis of neutron scattering and photoemission
measurements on superconducting FeSe(0.5)Te(0.5). The low-energy magnetic
excitations disperse only in the direction transverse to the characteristic
wave vector (1/2,0,0), whereas the electronic Fermi surface near (1/2,0,0)
appears to consist of four incommensurate pockets. While the spin resonance
occurs at an incommensurate wave vector compatible with nesting, neither
spin-wave nor Fermi-surface-nesting models can describe the magnetic
dispersion. We propose that a coupling of spin and orbital correlations is key
to explaining this behavior. If correct, it follows that these nematic
fluctuations are involved in the resonance and could be relevant to the pairing
mechanism.",0912.3205v2
2009-12-17,"Droplet-like Fermi surfaces in the anti-ferromagnetic phase of EuFe$_2$As$_2$, an Fe-pnictide superconductor parent compound","Using angle resolved photoemission it is shown that the low lying electronic
states of the iron pnictide parent compound EuFe$_2$As$_2$ are strongly
modified in the magnetically ordered, low temperature, orthorhombic state
compared to the tetragonal, paramagnetic case above the spin density wave
transition temperature. Back-folded bands, reflected in the orthorhombic/
anti-ferromagnetic Brillouin zone boundary hybridize strongly with the
non-folded states, leading to the opening of energy gaps. As a direct
consequence, the large Fermi surfaces of the tetragonal phase fragment, the low
temperature Fermi surface being comprised of small droplets, built up of
electron and hole-like sections. These high resolution ARPES data are therefore
in keeping with quantum oscillation and optical data from other undoped
pnictide parent compounds.",0912.3434v1
2009-12-18,Elastic isotropy of hcp-Fe under Earth core conditions,"Our first-principles calculations show that both the compressional and shear
waves of hcp-Fe become elastically isotropic under the high temperatures of
Earth inner core conditions, with the variation in sound velocities along
different angles from the c axis within 1%. We computed the thermoelasticity at
high pressures and temperatures from quasiharmonic linear response
linear-muffin-tin-orbital calculations in the generalized-gradient
approximation. The calculated anisotropic shape and magnitude in hcp-Fe at
ambient temperature agree well with previous first-principles predictions, and
the anisotropic effects show strong temperature dependences. This implies that
other mechanisms, rather than the preferential alignment of the hcp-Fe crystal
along the Earth rotation axis, account for the seismic P-wave travel time
anomalies. Either the inner core is not hcp iron, and/or the seismologically
observed anisotropy is caused by inhomogeneity, i.e. multiple phases.",0912.3587v1
2009-12-18,The crystal structure of FeSe0.44Te0.56,"The crystal structure of the superconductor FeSe0.44Te0.56 was redetermined
by high-resolution X-ray single crystal diffraction at 173 K (anti-PbO-type,
P4/nmm, a=3.7996(2), c=5.9895(6) A, R1=0.022, wR2=0.041, 173 F^2).
Significantly different z-coordinates of tellurium and selenium at the 2c site
are clearly discernible and were refined to z_Te=0.2868(3) and z_Se=0.2468(7).
Thus the chalcogen heights differ by 0.24 A and the Fe-Se bonds are by 0.154 A
shorter than the Fe-Te bonds, while three independent (Te,Se)-Fe-(Te,Se) bond
angles occur. An elevated U33 displacement parameter of the iron atom is
suggestive of a slightly puckered Fe layer resulting from different
combinations of Se or Te neighbors. Such strong disorder underlines the
robustness of superconductivity against structural randomness and has not yet
been considered in theoretical studies of this system.",0912.3706v2
2009-12-21,Electronic Ferroelectricity and Frustration,"Beyond a conventional classification of ferroelectricity, there is a class of
materials where electronic degrees of freedom and electronic interactions are
directly responsible for electric polarization and ferroelectric transition.
This is termed electronic ferroelectricity. In this article, we review
electronic ferroelectricity from a view point of frustration. Experimental and
theoretical examinations in spin driven ferroelectric materials, recently
termed multiferroics, are introduced. Spin frustration caused by competing
magnetic interactions is of prime importance for this type of ferroelectricity.
Charge driven ferroelectricity where electronic charge order induces electric
polarization is reviewed. In particular, exotic dielectric and
magneto-dielectric properties in layered iron oxides are focused on. Through a
number of recent experimental and theoretical researches, charge fluctuation
due to frustrated geometry plays essential roles on electronic ferroelectricity
in this compound.",0912.4083v1
2009-12-28,Volovik effect in the $\pm$s-wave state for the iron-based superconductors,"We studied the field dependencies of specific heat coefficient $\gamma(H) =
\lim_{T \rightarrow 0} C(T,H)/T $ and thermal conductivity coefficient $\lim_{T
\rightarrow 0} \kappa(T ,H)/T$ of the $\pm$s-wave state in the mixed state. We
found that it is a generic feature of the two band s-wave state with the
unequal sizes of gaps, small $\Delta_S$ and large $\Delta_L$, that Doppler
shift of the quasiparticle excitations (Volovik effect) creates a finite
density of states, on the extended states outside of vortex cores, proportional
to $H$ in contrast to the $\sqrt{H}$ dependence of the d-wave state. Impurity
scattering effect on the $\pm$s-wave state, however, makes this generic
$H$-linear dependence sublinear approaching to the $\sqrt{H}$ behavior. Our
calculations of $\lim_{T \rightarrow 0} \kappa(T ,H)/T$ successfully fit the
experimental data of Ba(Fe$_{1-x}$Co$_x )_2$ As$_2$ with different Co-doping
$x$ by systematically varying the gap size ratio $R= |\Delta_S | / |\Delta_L
|$. We also resolve the dilemma of a substantial value of $\gamma(H \rightarrow
0)$ but almost zero value of $\lim_{T \rightarrow 0} \kappa(T ,H \rightarrow
0)/T$, observed in experiments.",0912.5049v2
2009-12-27,"Observation of intertwined Fermi surface topology, orbital parity symmetries and electronic interactions in iron arsenide superconductors","We present a polarization and topology resolved study of the low energy band
structure in optimally doped superconducting Ba0.6K0.4Fe2As2 using angle
resolved photoemission spectroscopy. Polarization-contrasted measurements allow
us to identify and trace all low energy bands expected in models, revealing
unexpected symmetry breaking and a surprisingly intertwined Fermi surface
topology of hole-like bands near the Brillouin zone center. Band structure
correlations across the Gamma-M spin fluctuation wavevector are compared with
the superconducting gap anisotropy which suggest a partial scenario for
spin-mediated interband instability contributing to superconductivity in the
hole doped regime.",0912.5089v1
2009-12-29,"The quite complex ""Simple Stellar Populations"" of Globular Clusters","There is compelling observational evidence that globular clusters (GCs) are
quite complex objects. A growing body of photometric results indicate that the
evolutionary sequences are not simply isochrones in the observational plane -as
believed until a few years ago- from the main sequence, to the subgiant, giant,
and horizontal branches. The strongest indication of complexity comes however
from the chemistry, from internal dispersion in iron abundance in a few cases,
and in light elements (C, N, O, Na, Mg, Al, etc.) in all GCs. This universality
means that the complexity is intrinsic to the GCs and is most probably related
to their formation mechanisms. The extent of the variations in light elements
abundances is dependent on the GC mass, but mass is not the only modulating
factor; metallicity, age, and possibly orbit can play a role. Finally, one of
the many consequences of this new way of looking at GCs is that their stars may
show different He contents.",0912.5280v1
2010-01-05,Magnetic frustration in an iron based Cairo pentagonal lattice,"The Fe3+ lattice in the Bi2Fe4O9 compound is found to materialize the first
analogue of a magnetic pentagonal lattice. Due to its odd number of bonds per
elemental brick, this lattice, subject to first neighbor antiferromagnetic
interactions, is prone to geometric frustration. The Bi2Fe4O9 magnetic
properties have been investigated by macroscopic magnetic measurements and
neutron diffraction. The observed non-collinear magnetic arrangement is related
to the one stabilized on a perfect tiling as obtained from a mean field
analysis with direct space magnetic configurations calculations. The
peculiarity of this structure arises from the complex connectivity of the
pentagonal lattice, a novel feature compared to the well-known case of
triangle-based lattices.",1001.0710v1
2010-01-10,Chemical composition of stellar populations in Omega Centauri,"We derive abundances of Fe, Na, O, and s-elements from GIRAFFE@VLT spectra
for more than 200 red giant stars in the Milky Way satellite Omega Centauri.
Our preliminary results are that: (i) we confirm that Omega Centauri exibiths
large star-to-star metallicity variations ($\sim$ 1.4 dex); (ii) the
metallicity distribution reveals the presence of at least five stellar
populations with different [Fe/H]; (iii) a clear Na-O anticorrelation is
clearly observed for the metal-poor and metal-intermediate populations while
apparently the anticorrelation disappears for the most metal-rich populations.
Interestingly the Na level grows with iron.",1001.1500v1
2010-01-11,Measurement of neutron star parameters: a review of methods for low-mass X-ray binaries,"Measurement of at least three independent parameters, for example, mass,
radius and spin frequency, of a neutron star is probably the only way to
understand the nature of its supranuclear core matter. Such a measurement is
extremely difficult because of various systematic uncertainties. The lack of
knowledge of several system parameter values gives rise to such systematics.
Low-mass X-ray binaries, which contain neutron stars, provide a number of
methods to constrain the stellar parameters. Joint application of these methods
has a great potential to significantly reduce the systematic uncertainties, and
hence to measure three independent neutron star parameters accurately. Here we
review the methods based on (1) thermonuclear X-ray bursts; (2)
accretion-powered millisecond-period pulsations; (3) kilohertz quasi-periodic
oscillations; (4) broad relativistic iron lines; (5) quiescent emissions; and
(6) binary orbital motions.",1001.1642v1
2010-01-17,The Interior Dynamics of Water Planets,"The ever-expanding catalog of detected super-Earths calls for theoretical
studies of their properties in the case of a substantial water layer. This work
considers such water planets with a range of masses and water mass fractions (2
to 5 M_Earth, 0.02% to 50% H2 O). First, we model the thermal and dynamical
structure of the near-surface for icy and oceanic surfaces, finding separate
regimes where the planet is expected to maintain a subsurface liquid ocean and
where it is expected to exhibit ice tectonics. Newly discovered exoplanets may
be placed into one of these regimes given estimates of surface temperature,
heat flux, and gravity. Second, we construct a parameterized convection model
for the underlying ice mantle of higher ice phases, finding that materials
released from the silicate iron core should traverse the ice mantle on the
timescale of 0.1 to 100 megayears. We present the dependence of the overturn
times of the ice mantle and the planetary radius on total mass and water mass
fraction. Finally, we discuss the implications of these internal processes on
atmospheric observables.",1001.2890v1
2010-01-18,The metal-insulator transition and lattice distortion in semiconductors,"A relation between the energy of an elementary `insulating' excitation
corresponding to the metal-insulator transition and the bandgap width in a
semiconductor is obtained. An effect of atomic relaxation on the temperature
and pressure dependence of the bandgap width is considered. It is shown that
the metal-insulator transition in a semiconductor causes a weak rhombohedral or
monoclinic distortion in the case of a diamond and zincblende structure and a
weak tetragonal or orthorhombic distortion in the case of a rocksalt structure.
A change in the bandgap associated with a ferroelectric (antiferroelectric)
transition in a semiconductor is also obtained.",1001.3061v3
2010-01-19,Theory of Normal State Pseudogap Behavior in FeSe(1-x)$Te(x),"The normal state of the recently discovered Iron Selenide (FeSe)-based
superconductors shows a range of inexplicable features. Along with bad-metallic
resistivity, characteristic pseudogap features and proximity to insulating
states, reminiscent of the underdoped high-Tc cuprates, mark these systems as
strongly correlated non-Fermi Liquid metals. Here, using the first-principles
LDA+DMFT method, we show how strong multi-orbital correlation-induced
orbital-selective Mott-like physics leads to an orthogonality catastrophe
underpinning these inexplicable incoherent features. Excellent agreement with a
range of resistivity and Seebeck data strongly support our proposal. We discuss
pseudogap regime microscopically, along with implications for the nature of the
instability at lower T, and propose that related systems could be of use in
thermoelectric devices.",1001.3273v1
2010-01-20,Fermi surface and mass enhancement in KFe$_2$As$_2$ from de Haas-van Alphen effect measurements,"We report on a band structure calculation and de Haas-van Alphen measurements
of KFe$_2$As$_2$. Three cylindrical Fermi surfaces are found. Effective masses
of electrons range from 6 to 18$m_e$, $m_e$ being the free electron mass.
Remarkable discrepancies between the calculated and observed Fermi surface
areas and the large mass enhancement ($\gtrsim 3$) highlight the importance of
electronic correlations in determining the electronic structures of iron
pnicitide superconductors.",1001.3441v2
2010-01-26,Gap structure in the electron-doped Iron-Arsenide Superconductor Ba(Fe0.92Co0.08)2As2: low-temperature specific heat study,"We report the field and temperature dependence of the low-temperature
specific heat down to 400 mK and in magnetic fields up to 9 T of the
electron-doped Ba(Fe0.92Co0.08)2As2 superconductor. Using the phonon specific
heat obtained from pure BaFe2As2 we find the normal state Sommerfeld
coefficient to be 18 mJ/mol.K^2 and a condensation energy of 1.27 J/mol. The
temperature dependence of the electronic specific heat clearly indicate the
presence of the low-energy excitations in the system. The magnetic field
variation of field-induced specific heat cannot be described by single clean s-
or d-wave models. Rather, the data require an anisotropic gap scenario which
may or may not have nodes. We discuss the implications of these results.",1001.4564v1
2010-01-27,"Coupled structural and magnetic properties of ferric fluoride nanostructures: part II, a Monte-Carlo Heisenberg study","We present a numerical study of the magnetic structure of nanostructured iron
fluoride, using the Monte-Carlo-Metropolis simulated annealing technique and a
classical Heisenberg Hamiltonian with a superexchange angle dependence. The
parameters are adjusted on experimental results, and the atomic structure and
topology taken from a previous atomistic model of grain boundaries in the same
system. We find perfect antiferromagnetic crystalline grains and a disordered
magnetic configuration (speromagnetic like) at the grain boundary, in agreement
with experimental findings. Both the lowest magnetic energy and the rate of
magnetic frustration are found to be dependent on the relative disorientation
of crystalline grains, i.e. on the cationic topology. By simulating hysteresis
loops, we find that the magnetization rotation is not spatially uniform. We
conclude on possible extensions of the model.",1001.4959v1
2010-01-27,Coupled structural and magnetic properties of ferric fluoride nanostructures part I: a Metropolis atomistic study,"A modified Metropolis atomistic simulation is proposed to model the structure
of grain boundaries (GBs) and interfaces in ionic nanostructured systems and is
applied to the magnetically interesting case of iron trifluoride (FeF3). We
chose long-range interatomic potentials adjusted on experimental results, and
adapted a previously established Monte Carlo scheme consisting of various
modifications of the simulated annealing/ Metropolis algorithm. Atomic
structures of twisted and tilted GBs as a function of the relative
disorientation of the grains have been achieved yielding close to
experimentally measured properties. This approach takes into account the
structure of the grains far from the interface in order to constrain the
relative orientation of the grains, without any periodic boundary conditions.
One concludes that a long-range coulombic falloff of the interatomic potentials
is necessary to obtain GB structures presenting a correct local topology but
with a smooth transition from crystalline to amorphous states. The structural
features are finally discussed in terms of topological aspects and local
magnetic structure.",1001.4971v2
2010-01-27,A real-space effective c-axis lattice constant theory of superconductivity,"Based on the recent developed real-space picture of superconductivity, we
study the stability of the superconducting vortex lattices in layered
superconductors. It is shown that the effective c-axis lattice constant play a
significant role in promoting the superconducting transition temperature in
these materials. An unified expression Tc(max)=10c*-28 can be applied to
estimate the highest possible Tc(max) for a given layered superconductor with
an effective c-axis lattice constant c*. For the newly discovered iron-based
superconductors, our results suggest that their Tc cannot exceed 60K, 50K and
40K for the 1111, 21311 and 122 series, respectively. In the case of
copper-based oxide superconductors, it seems that the highest Tc can reach
about 161K without applying of the external pressure. In our theoretical
framework, we could interpret the experimental results of the completely
different superconducting transition temperatures obtained in two very similar
cuprate superconductors (La{2-x}Ba{x}CuO{4} of 40K and
Sr{2-x}Ba{x}CuO{3+\delta} of 98K). In addition, the physical reason why the
superconductivity does not occur in noble metals (like gold, silver and copper)
is discussed. Finally, we argue that the metallic hydrogen cannot exhibit
superconductivity at room temperature, it even cannot be a superconductor at
any low temperature.",1001.5067v1
2010-01-28,EC 11481-2303 - A Peculiar Subdwarf OB Star Revisited,"EC 11481-2303 is a peculiar, hot, high-gravity pre-white dwarf. Previous
optical spectroscopy revealed that it is a sdOB star with an effective
temperature (Teff) of 41790 K, a surface gravity log(g)= 5.84, and He/H = 0.014
by number. We present an on-going spectral analysis by means of non-LTE
model-atmosphere techniques based on high-resolution, high-S/N optical
(VLT-UVES) and ultraviolet (FUSE, IUE) observations. We are able to reproduce
the optical and UV observations simultaneously with a chemically homogeneous
NLTE model atmosphere with a significantly higher effective temperature and
lower He abundance (Teff = 55000 K, log (g) = 5.8, and He / H = 0.0025 by
number). While C, N, and O appear less than 0.15 times solar, the iron-group
abundance is strongly enhanced by at least a factor of ten.",1001.5115v1
2010-01-29,Strong correlation and massive spectral-weight redistribution induced spin density wave in a-Fe1.06Te,"The electronic structure of a-Fe1.06Te is studied with angle-resolved
photoemission spectroscopy. We show that there is substantial spectral weight
around Gamma and X, and lineshapes are intrinsically incoherent in the
paramagnetic state. The magnetic transition is characterized by a massive
spectral-weight transfer over an energy range as large as the band width, which
even exhibits a hysteresis loop that marks the strong first order transition.
Coherent quasiparticles emerge in the magnetically ordered state due to
decreased spin fluctuations, which account for the change of transport
properties from insulating behavior to metallic behavior. Our observation
demonstrates that Fe1.06Te distinguishes itself from other iron-based systems
with more local characters and much stronger interactions among different
degrees of freedom, and how a spin density wave is formed in the presence of
strong correlation.",1001.5327v1
2010-02-01,Statistics of subgap states in $s_\pm$ superconductors,"There is strong support in favor of an unusual $s_{\pm}$ superconducting
state in the new iron-based superconductors, in which the gap parameter has
opposite signs in different bands. In this case scattering between different
bands by impurities has a pair-breaking effect and introduces states inside the
gap. We studied the statistics of disorder-induced subgap states in $s_{\pm}$
superconductors due to collective effects of impurities. Numerically solving
the two-band Bogolyubov equations, we explored the behavior of the density of
states and localization length. We located the mobility edge separating the
localized and delocalized states for the 3D case and the crossover between the
weak and strong localization regimes for the 2D case. We found that the widely
used self-consistent T-matrix approximation is not very accurate in describing
subgap states.",1002.0363v1
2010-02-02,Structural and Magnetic Properties of Co1-xFexSr2YCu2O7 compounds,"Here we study the structural and magnetic properties of the CoFeSr2YCu2O7
compound with x = 0.0 to 1.0. X-ray diffraction patterns and simulated data
obtained from Rietveld refinement of the same indicate that the iron ion
replacement in CoFeSr2YCu2O7 induces a change in crystal structure. The
orthorhombic Ima2 space group structure of Co-1212 changes to tetragonal P4/mmm
with increasing Fe ion. The XPS studies reveal that both Co and Fe ions are in
mixed states for the former and in case of later.Although none of the studied
as synthesized samples in CoFeSr2YCu2O7 are superconducting, the interesting
structural changes in terms of their crystallisation space groups and the weak
magnetism highlights the rich solid state chemistry of this class of materials.",1002.0402v2
2010-02-02,"Comparative study on the thermoelectric effect of parent oxypnictides La$T$AsO ($T$ = Fe, Ni)","The thermopower and Nernst effect were investigated for undoped parent
compounds LaFeAsO and LaNiAsO. Both thermopower and Nernst signal in iron-based
LaFeAsO are significantly larger than those in nickel-based LaNiAsO.
Furthermore, abrupt changes in both thermopower and Nernst effect are observed
below the structural phase transition temperature and spin-density wave (SDW)
type antiferromagnetic (AFM) order temperature in Fe-based LaFeAsO. On the
other hand, Nernst effect is very small in the Ni-based LaNiAsO and it is
weakly temperature-dependent, reminiscent of the case in normal metals. We
suggest that the effect of SDW order on the spin scattering rate should play an
important role in the anomalous temperature dependence of Hall effect and
Nernst effect in LaFeAsO. The contrast behavior between the LaFeAsO and LaNiAsO
systems implies that the LaFeAsO system is fundamentally different from the
LaNiAsO system and this may provide clues to the mechanism of high $T_c$
superconductivity in the Fe-based systems.",1002.0417v1
2010-02-03,Orbital Symmetry of Ba(Fe1-xCox)2As2 Superconductors Probed with X-ray Absorption Spectroscopy,"The orbital symmetries of electron doped iron-arsenide superconductors
Ba(Fe1-xCox)2As2 have been measured with x-ray absorption spectroscopy. The
data reveal signatures of Fe d electron itinerancy, weak electronic
correlations, and a high degree of Fe-As hybridization related to the bonding
topology of the Fe dxz+yz states, which are found to contribute substantially
at the Fermi level. The energies and detailed orbital character of Fe and As
derived unoccupied s and d states are found to be in remarkably good agreement
with the predictions of standard density functional theory.",1002.0769v2
2010-02-04,Magnetic excitations in ferro-pnictide materials controlled by a quantum critical point into hidden order,"The two-orbital J1-J2 model that describes a square lattice of frustrated
spin-1 iron atoms is analyzed within the linear spin-wave approximation and by
exact diagonalization over a 4x4 cluster. A quantum critical point (QCP) is
identified that separates hidden magnetic order at weak Hund's rule coupling
from a commensurate spins density wave (cSDW) at strong Hund's rule coupling.
Although the moment for cSDW order is small at the QCP, the critical linear
spin-wave spectrum shows strong low-energy excitations centered at the
wavenumbers that correspond to cSDW order. These disperse anisotropically. A
fit to the magnetic excitation spectrum of ferro-pnictide materials obtained
recently by inelastic neutron scattering measurements notably accounts for the
absence of softening at the wavenumber that corresponds to Neel order.",1002.0891v3
2010-02-05,Incommensurate spin-density wave and magnetic lock-in transition in CaFe4As3,"The magnetic structure for the newly discovered iron-arsenide compound
\CaFeAs has been studied by neutron powder diffraction. Long-range magnetic
order is detected below 85K, with an incommensurate modulation described by the
propagation vector k=(0,$\delta$,0), $\delta\sim$ 0.39. Below $\sim$ 25K, our
measurements detect a first-order phase transition where $\delta$ locks into
the commensurate value 3/8. A model of the magnetic structure is proposed for
both temperature regimes, based on Rietveld refinements of the powder data and
symmetry considerations. The structures correspond to longitudinal
spin-density-waves with magnetic moments directed along the \textit{b}-axis. A
Landau analysis captures the change in thermodynamic quantities observed at the
two magnetic transitions, in particular the drop in resistivity at the lock-in
transition.",1002.1336v1
2010-02-07,Proposal to determine the Fermi-surface topology of a doped iron-based superconductor using bulk-sensitive Fourier-transform Compton scattering,"We have carried out first-principles calculations of the Compton scattering
spectra to demonstrate that the filling of the hole Fermi surface in
LaO$_{1-x}$F$_{x}$FeAs produces a distinct signature in the Fourier transformed
Compton spectrum when the momentum transfer vector lies along the [100]
direction. We thus show how the critical concentration $x_c$, where hole Fermi
surface pieces are filled up and the superconductivity mediated by
antiferromagnetic spin fluctuations is expected to be suppressed, can be
obtained in a bulk-sensitive manner.",1002.1483v1
2010-02-08,A Triplet Resonance in Superconducting FeSe0.4Te0.6,"From heavy fermions to cuprates and iron pnictides, a spin resonance is a
staple of nearly magnetic superconductors. Possible explanations include a
two-particle bound state or loss of magnon damping in the superconductor. While
both scenarios suggest a central role for magnetic fluctuations, distinguishing
them is important to identify the right theoretical framework and to guide the
search for higher temperature superconductors. Using inelastic neutron
scattering technique, we show that the spin resonance in optimally doped
Fe(Se,Te) splits into three peaks in a high magnetic field, a signature of a
two-particle triplet bound state",1002.1617v2
2010-02-08,Determination of the Nature of the Tetragonal to Orthorhombic Phase Transition in SrFe_2As_2 by Measurement of the Local Order Parameter,"SrFe2As2 is the end-member for a series of iron-pnictide superconductors and
has a tetragonal-to-orthorhombic phase transition near 200 K. Previous
macroscopic measurements to determine the nature of the transition gave
seemingly inconsistent results so we use electron microscopy to monitor the
local order parameter showing that the transformation is first order and that
the orthorhombic phase grows as needle domains. This suggests the transition
occurs via the passage of transformation dislocations, explaining the apparent
inconsistencies. This mechanism may be common to similar transitions.",1002.1639v2
2010-02-09,High Resolution X-Ray Spectroscopy of SN 1987A: Monitoring with XMM-Newton,"We report the results of our XMM-Newton monitoring of SN 1987A. The ongoing
propagation of the supernova blast wave through the inner circumstellar ring
caused a drastic increase in X-ray luminosity during the last years, enabling
detailed high resolution X-ray spectroscopy with the Reflection Grating
Spectrometer. The observations can be used to follow the detailed evolution of
the arising supernova remnant. The fluxes and broadening of the numerous
emission lines seen in the dispersed spectra provide information on the
evolution of the X-ray emitting plasma and its dynamics. These were analyzed in
combination with the EPIC-pn spectra, which allow a precise determination of
the higher temperature plasma. We modeled individual emission lines and fitted
plasma emission models. Especially from the observations between 2003 and 2007
we can see a significant evolution of the plasma parameters and a deceleration
of the radial velocity of the lower temperature plasma regions. We found an
indication (3-sigma-level) of an iron K feature in the co-added EPIC-pn
spectra. The comparison with Chandra grating observations in 2004 yields a
clear temporal coherence of the spectral evolution and the sudden deceleration
of the expansion velocity seen in X-ray images ~6100 days after the explosion.",1002.1865v1
2010-02-11,Numerical Forecast of the Melting and Thermal Histories of Particles Injected in a Plasma Jet,"This work presents the numerical simulation of the melting process of a
particle injected in a plasma jet. The plasma process is nowadays applied to
produce thin coatings on metal mechanical components with the aim of improving
the surface resistance to different phenomena such as corrosion, temperature or
wear. In this work we studied the heat transfer including phase-change of a
bi-layer particle composed of a metallic iron core coated with ceramic alumina,
inside a plasma jet. The model accounted for the environmental conditions along
the particle path. The numerical simulation of this problem was performed via a
temperature-based phase-change finite element formulation. The results obtained
with this methodology satisfactorily described the melting process of the
particle. Particularly, the results of the present work illustrate the phase
change evolution in a bi-layer particle during its motion in the plasma jet.
Moreover, the numerical trends agreed with those previously reported in the
literature and computed with a finite volume enthalpy based formulation.",1002.2370v1
2010-02-12,Electron-phonon coupling and charge gap in spin-density-wave iron-pnictides from quasiparticle relaxation dynamics,"We investigate the quasiparticle relaxation and low-energy electronic
structure in undoped SrFe_2As_2 exhibiting spin-density wave (SDW) ordering
using optical pump-probe femtosecond spectroscopy. A remarkable critical
slowing down of the quasiparticle relaxation dynamics at the SDW transition
temperature T_SDW = 200K is observed. From temperature dependence of the
transient reflectivity amplitude we determine the SDW-state charge gap
magnitude, 2Delta_SDW/k_BT_SDW=7.2+-1. The second moment of the Eliashberg
function, lambda<(hbar omega)^2>=110+-10meV^2, determined from the relaxation
time above T_SDW, is similar to SmFeAsO and BaFe_2As_2 indicating a rather
small electron phonon coupling constant unless the electron-phonon spectral
function (alpha^2F(omega) is strongly enhanced in the low-energy phonon region.",1002.2582v1
2010-02-17,Scaling relations in anisotropic superconductors with strong pair-breaking,"Following the work of Abrikosov and Gor'kov on the pair-breaking effects, one
can derive the temperature dependencies of the electronic specific heat
$C_s/T=\gamma^\prime+\mu T^2$ (with the jump at the superconducting transition
$\Delta C \propto T_c^3$) for materials with zero Fermi surface average of the
order parameter $<\Delta>=0$ (e.g. d-wave) or for those with $<\Delta> \ll
\Delta_{max}$ (e.g., $\pm s$ of iron-pnictides) in the presence of strong
pair-breaking. Moreover, the London penetration depth satisfies
$\lambda^{-2}=\lambda_0^{-2}(1-T^2/T_c^2)$ (or $\lambda -\lambda_0=\beta T^2 $
at low temperatures) and the slope of the upper critical field near $T_c$ is
$H_{c2}^\prime \propto T_c$. Remarkably simple relations between these at first
sight unrelated quantities take place: $\mu \lambda_0^2
T_c^3/|H_{c2}^\prime|=3\phi_0/8\pi^2$ and $\Delta C \beta^2
  T_c^4/|H_{c2,c}^\prime| = \phi_0/16\pi^2 $ are universal constants. The
prediction is checked on two samples of Ba(Fe$_{1-x}$Co$_{x}$)$_2$As$_2$ and on
CeCoIn$_5$ for which the data needed are available.",1002.3390v1
2010-02-19,"Dielectronic recombination data for astrophysical applications: Plasma rate-coefficients for Fe^q+ (q=7-10, 13-22) and Ni^25+ ions from storage-ring experiments","This review summarizes the present status of an ongoing experimental effort
to provide reliable rate coefficients for dielectronic recombination of highly
charged iron ions for the modeling of astrophysical and other plasmas. The
experimental work has been carried out over more than a decade at the heavy-ion
storage-ring TSR of the Max-Planck-Institute for Nuclear Physics in Heidelberg,
Germany. The experimental and data reduction procedures are outlined. The role
of previously disregarded processes such as fine-structure core excitations and
trielectronic recombination is highlighted. Plasma rate coefficients for
dielectronic recombination of Fe^q+ ions (q=7-10, 13-22) and Ni^25+ are
presented graphically and in a simple parameterized form allowing for easy use
in plasma modeling codes. It is concluded that storage-ring experiments are
presently the only source for reliable low-temperature dielectronic
recombination rate-coefficients of complex ions.",1002.3678v1
2010-02-25,Signatures of pressure induced superconductivity in insulating Bi2212,"We have performed several high pressure electrical resistance experiments on
Bi1.98Sr2.06Y0.68Cu2O8, an insulating parent compound of the high-Tc Bi2212
family of copper oxide superconductors. We find a resistive anomaly, a downturn
at low temperature, that onsets with applied pressure in the 20-40 kbar range.
Through both resistance and magnetoresistance measurements, we identify this
anomaly as a signature of induced superconductivity. Resistance to higher
pressures decreases Tc, giving a maximum of 10 K. The higher pressure
measurements exhibit a strong sensitivity to the hydrostaticity of the pressure
environment. We make comparisons to the pressure induced superconductivity now
ubiquitous in the iron arsenides.",1002.4672v1
2010-02-26,Significant reduction of electronic correlations upon isovalent Ru substitution of BaFe2As2,"We present a detailed investigation of Ba(Fe0.65Ru0.35)2As2 by transport
measurements and Angle Resolved photoemission spectroscopy. We observe that Fe
and Ru orbitals hybridize to form a coherent electronic structure and that Ru
does not induce doping. The number of holes and electrons, deduced from the
area of the Fermi Surface pockets, are both about twice larger than in
BaFe2As2. The contribution of both carriers to the transport is evidenced by a
change of sign of the Hall coefficient with decreasing temperature. Fermi
velocities increase significantly with respect to BaFe2As2, suggesting a
significant reduction of correlation effects. This may be a key to understand
the appearance of superconductivity at the expense of magnetism in undoped iron
pnictides.",1002.4952v2
2010-02-28,Low-temperature synthesis of SmFeAsO0.7F0.3 wires with high transport critical current density,"Ag-sheathed SmFeAsO0.7F0.3 (Sm-1111) superconducting wires were prepared by a
one-step solid state reaction at temperatures as low as 850~900C, instead of
commonly used temperatures of 1150~1250C. The X-ray diffraction pattern of the
as-sintered samples is well indexed on the basis of tetragonal ZrCuSiAs-type
structure. We characterized transport critical current density Jc of the
SmFeAsO0.7F0.3 wires in increasing and subsequently decreasing fields, by a
resistive four-probe method. A transport Jc as high as ~1300 A/cm^2 at 4.2 K
and self field has been observed for the first time in Sm-1111 type
polycrystalline superconductors. The Jc also shows a rapid depression in small
applied fields as well as a magnetic-history dependence, indicating weak-linked
grain boundaries. The low-temperature synthesis method can be very beneficial
to fabricating the RE-1111 iron oxynictides in a convenient and safe way.",1003.0153v1
2010-03-04,Medium Modifications of the Rho Meson in Nuclear Photoproduction,"We extend our recent study of dilepton invariant-mass spectra from the decays
of rho mesons produced by photon reactions off nuclei. We specifically focus on
experimental spectra as recently measured by the CLAS Collaboration at the
Thomas Jefferson National Accelerator Facility using carbon and iron nuclei.
Building on our earlier work we broaden our description to a larger set of
observables in order to identify sensitivities to the medium effects predicted
by microscopic calculations of the rho spectral function. We compute mass
spectra for several target nuclei and study the spectral shape as a function of
the 3-momentum of the outgoing lepton pair. We also compute the so-called
nuclear transparency ratio which provides an alternative means (and thus
consistency check) of estimating the inelastic rho width in the cold nuclear
medium.",1003.0910v2
2010-03-04,Comparative study of transport and magnetic Jc in the polycrystalline iron-based superconductor NdFeAsO{0.88}F{0.12},"Polycrystalline NdFeAsO0.88F0.12 superconductors prepared by high pressure
(HP) and ambient pressure (AP) method were comparatively studied by
magnetization and transport measurements. Upper critical field (Hc2),
irreversibility field (Hirr) and the anisotropy parameter were estimated from
resistance transition curves. The broadening of transition width was observed,
and ascribed to both Hc2 anisotropy and superconductivity inhomogeneity of
samples. Magnetic hysteresis loops (MHLs) in low fields were measured to detect
the trace of weak-link behavior. The reclosed hysteresis loops in low fields
manifest that there are weak-links in both samples. Magnetization critical
current density Jcm were derived from MHLs. High-pressure synthesized sample
shows higher Jcm. However, by means of direct transport I-V measurements,
transport critical current density Jct was very low. The Jct values for two
samples are comparable. Large discrepancies between Jcm and Jct also indicate
that there are weak-links in both samples. The relative mechanism is discussed
in detail.",1003.0946v2
2010-03-11,Superconductivity and spin-density-waves in multi-band metals,"We present a detailed description of two-band quasi-2D metals with s-wave
superconducting (SC) and antiferromagnetic spin-density wave (SDW)
correlations. We present a general approach and use it to investigate the
influence of the difference between the shapes and the areas of the two Fermi
surfaces on the phase diagram. In particular, we determine the conditions for
the co-existence of SC and SDW orders at different temperatures and dopings. We
argue that a conventional s-wave SC order co-exists with SDW order only at very
low $T$ and in a very tiny range of parameters. An extended s-wave
superconductivity, for which SC gap changes sign between the two bands,
co-exists with antiferromagnetic SDW over a much wider range of parameters and
temperatures, but even for this SC order the regions of SDW and SC can still be
separated by a first order transition. We show that the co-existence range
becomes larger if SDW order is incommensurate. We apply our results to
iron-based pnictide materials, in some of which co-existence of SDW and SC
orders has been detected.",1003.2389v2
2010-03-14,Site-dependent NMR Spin-lattice Relaxation in the Superconducting State of an Iron Pnictide Superconductor,"In a conventional superconductor, the spin-lattice relaxation rate on all
nuclei should have the same temperature dependence below Tc. We performed
$^{23}$Na, $^{75}$As, and $^{59}$Co NMR studies on single crystals of
NaFe0.95Co0.05As, and found that spin-lattice relaxation rates show very
different temperature dependent power-law behavior on three sites. We propose
that such site-dependent behavior is due to the facts that the superconductor
has two gaps of very different sizes. The power-law exponent of each nucleus is
affected by the strength of the hyperfine coupling to the small gap. We also
found that the large superconducting gap on the cobalt site is smaller than on
other two sites. It suggests a local suppression of the superconducting gap on
the dopant site.",1003.2775v1
2010-03-19,Leaving the ISCO: the inner edge of a black-hole accretion disk at various luminosities,"The ""radiation inner edge"" of an accretion disk is defined as the inner
boundary of the region from which most of the luminosity emerges. Similarly,
the ""reflection edge"" is the smallest radius capable of producing a significant
X-ray reflection of the fluorescent iron line. For black hole accretion disks
with very sub-Eddington luminosities these and all other ""inner edges"" locate
at ISCO. Thus, in this case, one may rightly consider ISCO as the unique inner
edge of the black hole accretion disk. However, even for moderate luminosities,
there is no such unique inner edge as differently defined edges locate at
different places. Several of them are significantly closer to the black hole
than ISCO. The differences grow with the increasing luminosity. For nearly
Eddington luminosities, they are so huge that the notion of the inner edge
losses all practical significance.",1003.3887v1
2010-03-24,Broad Balmer-line Absorption in SDSS J172341.10+555340.5,"I present the discovery of Balmer-line absorption from H alpha to H9 in iron
low-ionizaton broad absorption line (FeLoBAL) quasar, SDSS~J172341.10+555340.5
by near-infrared spectroscopy with the Cooled Infrared Spectrograph and Camera
for OHS (CISCO) attached to the Subaru telescope. The redshift of the
Balmer-line absorption troughs is 2.0530 +/- 0.0003, and it is blueshifted by
5370 km s^{-1} from the Balmer emission lines. It is more than $4000$ km s^{-1}
blueshifted from the previously known UV absorption lines. I detect relatively
strong (EW_rest=20A) [O III] emission lines which are similar to those found in
other broad absorption line quasars with Balmer-line absorption. I derived a
column density of neutral hydrogen of 5.2x10^{17} cm^{-2} by using the curve of
growth and taking account of Ly alpha trapping. I searched for UV absorption
lines which have the same redshift with Balmer-line absorption. I found Al II}
and Fe III absorption lines at z=2.053 which correspond to previously
unidentified absorption lines, and the presence of other blended troughs that
were difficult to identify.",1003.4622v2
2010-03-26,Evolution of the optical spectrum with doping in iron pnictides Ba(Fe1-xCox)2As2,"We investigated the optical spectrum of Ba(Fe1-xCox)2As2 single crystals with
various doping levels. It is found that the low-energy optical conductivity
spectrum of this system can be decomposed into two components: a sharp Drude
term and a broad ""incoherent"" term. For the compounds showing magnetic order, a
gap appears predominantly in the ""incoherent"" component, while an s-wave like
superconducting gap opens in both components for highly doped compounds. The
Drude weight steadily increases as doping proceeds, consistent with electron
doping in this system. On the other hand, the ""incoherent"" spectral weight is
almost doping independent, but its spectral feature is intimately connected
with the magnetism. We demonstrate that the presence of two distinct components
in the optical spectrum well explains the doping and temperature dependences of
the dc resistivity.",1003.5038v1
2010-03-27,Weak-Coupling Theory for Multiband Superconductivity Induced by Jahn-Teller Phonons,"Emergence of superconductivity in a two-band system coupled with breathing
and Jahn-Teller phonons is discussed in a weak-coupling limit. With the use of
a standard quantum mechanical procedure, the phonon-mediated attraction is
derived. From the analysis of the model including such attraction, a BCS-like
formula for a superconducting transition temperature $T_{\rm c}$ is obtained.
When only the breathing phonon is considered, $T_{\rm c}$ is the same as that
of the one-band model. On the other hand, when Jahn-Teller phonons are active,
$T_{\rm c}$ is significantly enhanced by the interband attraction even within
the weak-coupling limit. Relevance of the present result to actual materials
such as iron pnictides is briefly commented.",1003.5274v1
2010-03-30,Influence of magnetism on the superconducting properties of iron-based superconductor NdFeAsO0.88F0.12,"Both DC and AC magnetization measurements were performed on the
NdFeAsO0.88F0.12 superconductor to investigate the influence of magnetism on
the superconducting properties of this system. The crossover of the ZFC and FC
magnetic susceptibility curves under 7.5KOe was observed. The imaginary
component of the first harmonics of the AC magnetic susceptibility, increases
with the increasing DC field below 10K and shows frequency dependency under
7.5KOe at low temperature. The paramagnetism of Nd3+ ions tilts the magnetic
hysteresis loops and broadens the hysteresis width. After correction for the
paramagnetism, the field and temperature dependence of intrinsic Jcm was
obtained and compared with the experimentally obtained total Jcm. The origin of
the abnormal behavior of magnetization was investigated and attributed to a
magnetic background, which was speculated to be caused by the spin-glass state.
However, this magnetic background does not affect the flux pinning properties
in this sample. The related mechanism was discussed.",1003.5807v2
2010-03-31,Evidence for superconducting gap nodes in the zone-centered hole bands of KFe2As2 from magnetic penetration-depth measurements,"Among the iron-based pnictide superconductors the material KFe$_2$As$_2$ is
unusual in that its Fermi surface does not consist of quasi-nested electron and
hole pockets. Here we report measurements of the temperature dependent London
penetration depth of very clean crystals of this compound with residual
resistivity ratio $>1200$. We show that the superfluid density at low
temperatures exhibits a strong linear-in-temperature dependence which implies
that there are line nodes in the energy gap on the large zone-centered hole
sheets. The results indicate that KFe$_2$As$_2$ is an unconventional
superconductor with strong electron correlations.",1003.6022v2
2010-04-02,Performance of the MIND detector at a Neutrino Factory using realistic muon reconstruction,"A Neutrino Factory producing an intense beam composed of nu_e(nubar_e) and
nubar_mu(nu_mu) from muon decays has been shown to have the greatest
sensitivity to the two currently unmeasured neutrino mixing parameters,
theta_13 and delta_CP . Using the `wrong-sign muon' signal to measure nu_e to
nu_mu(nubar_e to nubar_mu) oscillations in a 50 ktonne Magnetised Iron Neutrino
Detector (MIND) sensitivity to delta_CP could be maintained down to small
values of theta_13. However, the detector efficiencies used in previous studies
were calculated assuming perfect pattern recognition. In this paper, MIND is
re-assessed taking into account, for the first time, a realistic pattern
recognition for the muon candidate. Reoptimisation of the analysis utilises a
combination of methods, including a multivariate analysis similar to the one
used in MINOS, to maintain high efficiency while suppressing backgrounds,
ensuring that the signal selection efficiency and the background levels are
comparable or better than the ones in previous analyses.",1004.0358v1
2010-04-09,No anomalous spin fluctuation in optimally doped and overdoped iron-based oxypnictide superconductors LaFeAsO$_{1-x}$F$_x$ probed by muon spin relaxation,"Zero field and longitudinal field muon spin relaxation measurements have been
performed in optimally doped and overdoped superconductors LaFeAsO$_{1-x}$F$_x$
in order to investigate the magnetic fluctuation over a wide range of
temperature and longitudinal field. We have observed no sign of magnetic
fluctuation against temperature in the muons' time window (10$^{-5}\sim$
10$^{-9}$s). Considering the current results and other results, i.e., spin
fluctuation observed by neutron scattering, pseudogap-like behaviors by NMR and
photoemission spectroscopy, it is suggested that not only the spin fluctuation
but also the multiband character with several different orbital contributions
at the Fermi surface may play an important role in the superconducting pairing
mechanism of LaFeAsO$_{1-x}$F$_x$.",1004.1589v1
2010-04-12,Density of Phonon States in Superconducting FeSe as a Function of Temperature and Pressure,"The temperature and pressure dependence of the partial density of phonon
states of iron atoms in superconducting Fe1.01Se was studied by 57Fe nuclear
inelastic scattering (NIS). The high energy resolution allows for a detailed
observation of spectral properties. A sharpening of the optical phonon modes
and shift of all spectral features towards higher energies by ~4% with
decreasing temperature from 296 K to 10 K was found. However, no detectable
change at the tetragonal - orthorhombic phase transition around 100 K was
observed. Application of a pressure of 6.7 GPa, connected with an increase of
the superconducting temperature from 8 K to 34 K, results in an increase of the
optical phonon mode energies at 296 K by ~12%, and an even more pronounced
increase for the lowest-lying transversal acoustic mode. Despite these strong
pressure-induced modifications of the phonon-DOS we conclude that the
pronounced increase of Tc in Fe1.01Se with pressure cannot be described in the
framework of classical electron-phonon coupling. This result suggests the
importance of spin fluctuations to the observed superconductivity.",1004.2007v1
2010-04-13,Dissipationless Anomalous Hall Current in $Fe_{100-x}(SiO_2)_x$ Films,"The observation of dissipationless anomalous Hall current is one of the
experimental evidences to confirm the intrinsic origin of anomalous Hall
effect. To study the origin of anomalous Hall effect in iron,
Fe$_{100-x}$(SiO$_{2}$)$_{x}$ granular films with volume fraction of SiO$_{2}$
0\le x \le 40.51 were fabricated using co-sputtering. Hall and longitudinal
resistivities were measured in the temperature range 5 to 350 K with magnetic
fields up to 5 Tesla. As x increased from 0 to 40.51, the anomalous Hall
resistivity and longitudinal resistivity increased about 4 and 3 orders in
magnitude, respectively. Analysis of the results revealed that the normalized
anomalous Hall conductivity is a constant for all the samples, the evidence of
dissipationless anomalous Hall current in Fe.",1004.2105v1
2010-04-13,Heat treatment effects on the superconducting properties of Ag-doped SrKFeAs compound,"The superconducting properties of polycrystalline Sr0.6K0.4Fe2As2 were
strongly influenced by Ag doping (Supercond. Sci. Technol. 23 (2010) 025027).
Ag addition is mainly dominated by silver diffusing, so the annealing process
is one of the essential factors to achieve high quality Ag doped
Sr0.6K0.4Fe2As2. In this paper, the optimal annealing conditions were studied
for Ag doped Sr0.6K0.4Fe2As2 bulks prepared by a one-step solid reaction
method. It is found that the annealing temperature has a strong influence on
the superconducting properties, especially on the critical current density Jc.
As a result, higher heat treatment temperature (~900C) is helpful in diffusing
Ag and reducing the impurity phase gathered together to improve the grain
connectivity. In contrast, low-temperature sintering is counterproductive for
Ag doped samples. These results clearly suggest that annealing at ~900C is
necessary for obtaining high Jc Ag-doped samples.",1004.2137v2
2010-04-17,Structural and superconducting properties in LaFeAs1-xSbxO1-yFy,"We report the antimony (Sb) doping effect in a prototype system of iron-based
supercon-ductors LaFeAsO1-yFy (y=0, 0.1, 0.15). X-ray powder diffraction
indicates that the lattice pa-rameters increase with Sb content within the
doping limit. Rietveld structural refinements show that, with the partial
substitution of Sb for As, while the thickness of the Fe2As2 layers increases
significantly, that of the La2O2 layers shrinks simultaneously. So a negative
chemical pressure is indeed ""applied"" to the superconducting-active Fe2As2
layers, in con-trast to the effect of positive chemical pressure by the
phosphorus doping. Electrical resis-tance and magnetic susceptibility
measurements indicate that, while the Sb doping hardly influences the SDW
anomaly in LaFeAsO, it recovers SDW order for the optimally-doped sample of
y=0.1. In the meantime, the superconducting transition temperature can be
raised up to 30 K in LaFeAs1-xSbxO1-yFy with x=0.1 and y=0.15. The Sb doping
effects are discussed in term of both J1-J2 model and Fermi Surface (FS)
nesting scenario.",1004.2940v1
2010-04-21,Precise determination of muon and electromagnetic shower contents from shower universality property,"We consider two new aspects of Extensive Air Shower development universality
allowing to make accurate estimation of muon and electromagnetic (EM) shower
contents in two independent ways. In the first case, to get muon (or EM) signal
in water Cherenkov tanks or in scintillator detectors it is enough to know the
vertical depth of shower maximum and the total signal in the ground detector.
In the second case, the EM signal can be calculated from the primary particle
energy and the zenith angle. In both cases the parametrizations of muon and EM
signals are almost independent on primary particle nature, energy and zenith
angle. Implications of the considered properties for mass composition and
hadronic interaction studies are briefly discussed. The present study is
performed on 28000 of proton, oxygen and iron showers, generated with CORSIKA
6.735 for $E^{-1}$ spectrum in the energy range log(E/eV)=18.5-20.0 and
uniformly distributed in cos^2(theta) in zenith angle interval theta=0-65
degrees for QGSJET II/Fluka interaction models.",1004.3673v1
2010-04-21,A minimal Beta Beam with high-Q ions to address CP violation in the leptonic sector,"In this paper we consider a Beta Beam setup that tries to leverage at most
existing European facilities: i.e. a setup that takes advantage of facilities
at CERN to boost high-Q ions (8Li and 8B) aiming at a far detector located at L
= 732 Km in the Gran Sasso Underground Laboratory. The average neutrino energy
for 8Li and 8B ions boosted at \gamma ~ 100 is in the range E_\nu = [1,2] GeV,
high enough to use a large iron detector of the MINOS type at the far site. We
perform, then, a study of the neutrino and antineutrino fluxes needed to
measure a CP-violating phase delta in a significant part of the parameter
space. In particular, for theta_13 > 3 deg, if an antineutrino flux of 3 10^19
useful 8Li decays per year is achievable, we find that delta can be measured in
60% of the parameter space with 6 10^18 useful 8B decays per year.",1004.3773v2
2010-04-27,Orbital-weight redistribution triggered by spin order in the pnictides,"The one-particle spectral function and its orbital composition are
investigated in a three-orbital model for the undoped parent compounds of the
iron-based superconductors. In the realistic parameter regime, where results
best fit experimental data, it is observed that the magnetization in the xz and
yz orbitals are markedly different and the Fermi surface presents mostly xz
character, as recently observed in photoemission experiments [T. Shimojima et
al., Phys. Rev. Lett. 104, 057002 (2010)]. Since the ferro-orbital order in
this regime is at most a few percent, these results are mainly driven by the
magnetic order. An analogous analysis for a five-orbital model leads to similar
conclusions.",1004.4803v2
2010-05-03,Collective spin mode in a multi-component system of coupled itinerant and localized electrons,"We study collective spin excitations of a magnetically ordered state in a
multi-component system composed of both itinerant electrons and local moments.
Here the induced spin-density-wave (SDW) ordering of itinerant electrons and
the collinear antiferromangetic (AF) ordering of local moments are locked
together via a Hund's rule coupling. We show that the Goldstone theorem still
holds at the RPA level with the gapless spin wave protected inside the small
SDW gap of itinerant electrons, which, however, is fragile in the presence of
ion-anisotropy. A gapped out-of-phase spin mode extending over a much wider
energy scale above the SDW gap is found to be more robust against the
ion-anisotropy, which is mainly contributed by the local moment fluctuations.
While the scattering between the Goldstone mode and itinerant electrons
diminishes within the SDW gap, the out-of-phase mode will strongly interact
with itinerant electrons and thus dominate the spin and charge dynamics in such
an ordered phase. Possible relevance of such a model to the iron-pnictides will
be also discussed.",1005.0421v1
2010-05-04,Competition between Ferrimagnetism and Magnetic Frustration in Zinc Substituted YBaFe4O7,"The substitution of zinc for iron in YBaFe4O7 has allowed the oxide series
YBaFe4-xZnxO7, with 0.40 < x < 1.50, belonging to the ""114"" structural family
to be synthesized. These oxides crystallize in the hexagonal symmetry (P63mc),
as opposed to the cubic symmetry (F-43m) of YBaFe4O7. Importantly, the d.c.
magnetization shows that the zinc substitution induces ferrimagnetism, in
contrast to the spin glass behaviour of YBaFe4O7. Moreover, a.c. susceptibility
measurements demonstrate that concomitantly these oxides exhibit a spin glass
or a cluster glass behaviour, which increases at the expense of ferrimagnetism,
as the zinc content is increased. This competition between ferrimagnetism and
magnetic frustration is interpreted in terms of lifting of the geometric
frustration, inducing the magnetic ordering, and of cationic disordering, which
favours the glassy state.",1005.0480v1
2010-05-04,Magnetic ordering and dense Kondo behaviour in EuFe$_{2}$P$_{2}$,"Ternary iron phosphide EuFe$_2$P$_2$ with ThCr$_2$Si$_2$-type structure has
been systematically studied by the measurements of crystal structure,
magnetization, M\""{o}ssbauer effect, transport properties and specific heat.
The structural refinement result confirms no direct P-P covalent bonding. The
M\""{o}ssbauer spectra indicate no magnetic moment for the Fe atoms and, that
the Eu ions are divalent in the whole temperatures, carrying local moments of
$S$=7/2. The Eu$^{2+}$ spins order ferromagnetically at $T_C$=29.5 K, followed
by a possible helimagnetic ordering below $T_{HM}$=26 K, where the Eu$^{2+}$
moments tilt a little from the c-axis. External magnetic field increases $T_C$
gradually, but suppresses $T_{HM}$ rapidly. (Magneto)resistivity data indicate
characteristic dense Kondo behaviour above the Curie temperature. The result is
discussed in terms of the interplay between intersite RKKY and intrasite Kondo
interactions.",1005.0516v2
2010-05-06,"Chemical composition of the old globular clusters NGC 1786, NGC 2210 and NGC 2257 in the Large Magellanic Cloud","This paper presents the chemical abundance analysis of a sample of 18 giant
stars in 3 old globular clusters in the Large Magellanic Cloud, namely NGC
1786, NGC 2210 and NGC 2257. The derived iron content is [Fe/H]= --1.75+-0.01
dex (sigma= 0.02 dex), --1.65+-0.02 dex (sigma= 0.04 dex) and --1.95+-0.02 dex
(sigma= 0.04 dex) for NGC 1786, NGC 2210 and NGC 2257, respectively. All the
clusters exhibit similar abundance ratios, with enhanced values (+0.30 dex) of
[alpha/Fe], consistent with the Galactic Halo stars, thus indicating that these
clusters have formed from a gas enriched by Type II SNe. We also found evidence
that r-process are the main channel of production of the measured neutron
capture elements (Y, Ba, La, Nd, Ce and Eu). In particular the quite large
enhancement of [Eu/Fe] (+0.70 dex) found in these old clusters clearly
indicates a relevant efficiency of the r-process mechanism in the LMC
environment.",1005.0964v1
2010-05-10,23Na and 75As NMR Studies on NaFeAs0.8P0.2 Single Crystals,"We report our $^{23}$Na and $^{75}$As NMR studies on isovalent
phosphorus-doped NaFeAs$_{0.8}$P$_{0.2}$ ($T_c=$ 33 K) single crystals. Our
data suggest a dramatic enhancement of the electron density of states on the
Fermi surface, and a large residual electron density of state below $T_c$.
However, evidence of antiferromagnetic spin fluctuations is shown by the
spin-lattice relaxation rate. The penetration depth, revealed from $^{23}$Na
NMR linewidth, follows the universal Uemura relation in iron pnictides. These
observations suggest that the correlation effects are still important for the
superconductivity in the phosphorus doped sample, although the Fermi surface is
probably significantly changed upon doping.",1005.1448v2
2010-05-12,Transfer of optical spectral weight in magnetically ordered superconductors,"We show that, in antiferromagnetic superconductors, the optical spectral
weight transferred to low frequencies below the superconducting transition
temperature originates from energies that can be much larger than twice the
superconducting gap $\Delta$. This contrasts to non-magnetic superconductors,
where the optical spectrum is suppressed only for frequencies below $2\Delta$.
In particular, we demonstrate that the superfluid condensate of the
magnetically ordered superconductor is not only due to states of the
magnetically reconstructed Fermi surface, but is enhanced by transfer of
spectral weight from the mid infrared peak generated by the spin density wave
gap. We apply our results to the iron arsenide superconductors, addressing the
decrease of the zero-temperature superfluid density in the doping regime where
magnetism coexists with unconventional superconductivity.",1005.2174v3
2010-05-17,Cooperative effects of Coulomb and electron-phonon interactions in the two-dimensional 16-band d-p model for iron-based superconductors,"We study the electronic states and the superconductivity in the
two-dimensional 16-band d-p model coupled with A1g, B1g and Eg local phonons
and obtain the rich phase diagram including the magnetic, charge and orbital
ordered phases on the parameter plane of the Coulomb and electron-phonon
interactions. When the electron-phonon interaction is dominant, the charge
fluctuations induce the s++ wave superconductivity, while when the Coulomb
interaction is dominant, the magnetic fluctuations induce the s+- wave
superconductivity. Remarkably, the orbital fluctuations are enhanced due to the
cooperative effects of the Coulomb and electron-phonon interactions and induce
the s++ wave and the nodal s+- wave superconductivities.",1005.2814v2
2010-05-17,Electron-Hole Asymmetry in Superconductivity of Pnictides Originated from the Observed Rigid Chemical Potential Shift,"We have performed a systematic photoemission study of the chemical potential
shift as a function of carrier doping in a pnictide system based on
BaFe$_2$As$_2$. The experimentally determined chemical potential shift is
consistent with the prediction of a rigid band shift picture by the
renormalized first-principle band calculations. This leads to an electron-hole
asymmetry (EHA) in the Fermi surface (FS) nesting condition due to different
effective masses for different FS sheets, which can be calculated from the
Lindhard function of susceptibility. This built-in EHA from the band structure,
which matches well with observed asymmetric superconducting domes in the phase
diagram, strongly supports FS near-nesting driven superconductivity in the iron
pnictides.",1005.2966v1
2010-05-18,Superconductivity induced by doping Rh in CaFe2-xRhxAs2,"In this paper we report the synthesis of iron-based superconductors
CaFe2-xRhxAs2 using one-step solid state reaction method, which crystallizes in
the ThCr2Si2-type structure with a space group I4/mmm. The systematic evolution
of the lattice constants demonstrates that the Fe ions are successfully
replaced by the Rh. By increasing the doping content of Rh, the
spin-density-wave (SDW) transition in the parent compound is suppressed and
superconductivity emerges. The maximum superconducting transition temperature
is found at 18.5 K with the doping level of x = 0.15. The temperature
dependence of DC magnetization confirms superconducting transitions at around
15 K. The general phase diagram was obtained and found to be similar to the
case of Rh-doping Sr122 system. Our results explicitly demonstrate the
feasibility of inducing superconductivity in Ca122 compounds by higher
d-orbital electrons doping, however, different Rh-doping effect between FeAs122
compounds and FeAs1111 systems still remains an open question.",1005.3172v2
2010-05-20,Distinct high-T transitions in underdoped Ba$_{1-x}$K$_{x}$Fe$_{2}$As$_{2}$,"In contrast to the simultaneous structural and magnetic first order phase
transition $T_{0}$ previously reported, our detailed investigation on an
underdoped Ba$_{0.84}$K$_{0.16}$Fe$_{2}$As$_{2}$ single crystal unambiguously
revealed that the transitions are not concomitant. The tetragonal ($\tau$:
I4/mmm) - orthorhombic ($\vartheta$: Fmmm) structural transition occurs at
$T_{S}\simeq$ 110 K, followed by an adjacent antiferromagnetic (AFM) transition
at $T_{N}\simeq$ 102 K. Hysteresis and coexistence of the $\tau$ and
$\vartheta$ phases over a finite temperature range observed in our NMR
experiments confirm the first order character of the structural transition and
provide evidence that both $T_{S}$ and $T_{N}$ are strongly correlated. Our
data also show that superconductivity (SC) develops in the $\vartheta$ phase
below $T_{c}$ = 20 K and coexists with long range AFM. This new observation,
$T_{S}\neq T_{N}$, firmly establishes another similarity between the hole-doped
BaFe$_{2}$As$_{2}$ via K substitution and the electron-doped iron-arsenide
superconductors.",1005.3718v1
2010-05-21,Microscopic Study of the Superconducting State of the Iron Pnictide RbFe_2As_2,"A study of the temperature and field dependence of the penetration depth
\lambda of the superconductor RbFe_2As_2 (T_c=2.52 K) was carried out by means
of muon-spin rotation measurements. In addition to the zero temperature value
of the penetration depth \lambda(0)=267(5) nm, a determination of the upper
critical field B_c2(0)=2.6(2) T was obtained. The temperature dependence of the
superconducting carrier concentration is discussed within the framework of a
multi-gap scenario. Compared to the other ""122"" systems which exhibit much
higher Fermi level, a strong reduction of the large gap BCS ratio 2\Delta/k_B
T_c is observed. This is interpreted as a consequence of the absence of
interband processes. Indications of possible pair-breaking effect are also
discussed.",1005.3989v3
2010-05-23,Inelastic x-ray scattering investigations of lattice dynamics in SmFeAsO$_{1-x}$F$_y$ superconductors,"We report measurements of the phonon density of states as measured with
inelastic x-ray scattering in SmFeAsO$_{1-x}$F$_y$ powders. An unexpected
strong renormalization of phonon branches around 23 meV is observed as fluorine
is substituted for oxygen. Phonon dispersion measurements on
SmFeAsO$_{1-x}$F$_y$ single crystals allow us to identify the 21 meV A$_{1g}$
in-phase (Sm,As) and the 26 meV B$_{1g}$ (Fe,O) modes to be responsible for
this renormalization, and may reveal unusual electron-phonon coupling through
the spin channel in iron-based superconductors.",1005.4165v1
2010-05-24,The Puzzle of High Temperature Superconductivity in Layered Iron Pnictides and Chalcogenides,"The response of the worldwide scientific community to the discovery in 2008
of superconductivity at Tc = 26 K in the Fe-based compound LaFeAsO_{1-x}F_x has
been very enthusiastic. In short order, other Fe-based superconductors with the
same or related crystal structures were discovered with Tc up to 56 K. Many
experiments were carried out and theories formulated to try to understand the
basic properties of these new materials and the mechanism for Tc. In this
selective critical review of the experimental literature, we distill some of
this extensive body of work, and discuss relationships between different types
of experiments on these materials with reference to theoretical concepts and
models. The experimental normal-state properties are emphasized, and within
these the electronic and magnetic properties because of the likelihood of an
electronic/magnetic mechanism for superconductivity in these materials.",1005.4392v2
2010-05-26,"RXTE observations of the 1A 1118-61 in an outburst, and the discovery of a cyclotron line","We present the analysis of RXTE monitoring data obtained during the January
2009 outburst of the hard X-ray transient 1A 1118-61. Using these observations
the broadband (3.5-120 keV) spectrum of the source was measured for the first
time ever. We have found that the broadband continuum spectrum of the source is
similar to other accreting pulsars and is well described by several
conventionally used phenomenological models. We have discovered that regardless
of the applied continuum model, a prominent broad absorption feature at ~55 keV
is observed. We interpret this feature as a cyclotron resonance scattering
feature (CRSF). The observed CRSF energy is one of the highest known and
corresponds to a magnetic field of B~4.8 x 10^12 G in the scattering region.
Our data also indicate the presence of an iron emission line presence that has
not been previously reported for 1A 1118-61. Timing properties of the source,
including a strong spin-up, were found to be similar to those observed by
CGRO/BATSE during the previous outburst, but the broadband capabilities of RXTE
reveal a more complicated energy dependency of the pulse-profile.",1005.4782v1
2010-05-26,Probing CPT violation in neutrino oscillation: A three flavor analysis,"We have studied $CPT$ violation in neutrino oscillation considering three
flavor framework with matter effect. We have constructed a new way to find the
oscillation probability incorporating $CPT$ violating terms without any
approximation. Then $CPT$ violation with atmospheric neutrinos for a magnetized
iron calorimeter detector considering the muons (directly measurable with high
resolution) of the charge current events has been studied for zero and nonzero
$\theta_{13}$ values. It is found that a potential bound of $\delta b_{32}
\lapp 6\times 10^{-24}$ GeV at 99% CL can be obtained with 1 Mton.year exposure
of this detector; and unlike neutrino beam experiments, there is no possibility
to generate `fake' $CPT$ violation due to matter effect with atmospheric
neutrinos. The advantages of atmospheric neutrinos to discriminate $CPT$
violation from CP violation and nonstandard interactions are also discussed.",1005.4851v3
2010-05-27,Milne-Eddington inversion of the Fe I line pair at 630~nm,"The iron lines at 630.15 and 630.25 nm are often used to determine the
physical conditions of the solar photosphere. A common approach is to invert
them simultaneously under the Milne-Eddington approximation. The same
thermodynamic parameters are employed for the two lines, except for their
opacities, which are assumed to have a constant ratio. We aim at investigating
the validity of this assumption, since the two lines are not exactly the same.
We use magnetohydrodynamic simulations of the quiet Sun to examine the behavior
of the ME thermodynamic parameters and their influence on the retrieval of
vector magnetic fields and flow velocities. Our analysis shows that the two
lines can be coupled and inverted simultaneously using the same thermodynamic
parameters and a constant opacity ratio. The inversion of two lines is
significantly more accurate than single-line inversions because of the larger
number of observables.",1005.5013v2
2010-05-29,{\it Ab initio} calculations of magnetic structure and lattice dynamics of Fe/Pt multilayers,"The magnetization distribution, its energetic characterization by the
interlayer coupling constants and lattice dynamics of (001)-oriented Fe/Pt
multilayers are investigated using density functional theory combined with the
direct method to determine phonon frequencies. It is found that ferromagnetic
order between consecutive Fe layers is favoured, with the enhanced magnetic
moments at the interface. The bilinear and biquadratic coupling coefficients
between Fe layers are shown to saturate fast with increasing thickness of
nonmagnetic Pt layers which separate them. The phonon calculations demonstrate
a rather strong dependence of partial iron phonon densities of states on the
actual position of Fe monolayer in the multilayer structure.",1005.5454v1
2010-06-02,X-ray reflected spectra from accretion disk models. I. Constant density atmospheres,"We present new models for illuminated accretion disks, their structure and
reprocessed emission. We consider the effects of incident X-rays on the surface
of an accretion disk by solving simultaneously the equations of radiative
transfer, energy balance and ionization equilibrium over a large range of
column densities. We assume plane-parallel geometry and azimuthal symmetry,
such that each calculation corresponds to a ring at a given distance from the
central object. Our models include recent and complete atomic data for K-shell
processes of the iron and oxygen isonuclear sequences. We examine the effect on
the spectrum of fluorescent K$\alpha$ line emission and absorption in the
emitted spectrum. We also explore the dependence of the spectrum on the
strength of the incident X-rays and other input parameters, and discuss the
importance of Comptonization on the emitted spectrum.",1006.0485v1
2010-06-03,Unusual Nernst effect and spin density wave precursors in superconducting $\rm\bf LaFeAsO_{1-x}F_x$,"The Nernst effect has recently proven as a sensitive probe for detecting
unusual normal state properties of unconventional superconductors. Here we
present a systematic study of the Nernst effect of the iron pnictide
superconductor \laf with a particular focus on its evolution upon doping. For
the parent compound we observe a huge negative Nernst coefficient accompanied
with a severe violation of the Sondheimer cancellation in the spin density wave
(SDW) ordered state. Surprisingly, an unusual and enhanced Nernst signal is
also found at underdoping ($x=0.05$) despite the presence of bulk
superconductivity and the absence of static magnetic order, strongly suggestive
of SDW precursors at $T\lesssim150$ K. A more conventional normal state Nernst
response is observed at optimal doping ($x=0.1$) where it is rather featureless
with a more complete Sondheimer cancellation.",1006.0715v1
2010-06-04,Surface-driven electronic structure in LaFeAsO studied by angle resolved photoemission spectroscopy,"We measured the electronic structure of an iron arsenic parent compound
LaFeAsO using angle resolved photoemission spectroscopy (ARPES). By comparing
with a full-potential Linear Augmented PlaneWave calculation we show that the
extra large Gamma hole pocket measured via ARPES comes from electronic
structure at the sample surface. Based on this we discuss the strong
polarization dependence of the band structure and a temperature-dependent
hole-like band around the M point. The two phenomena give additional evidences
for the existence of the surface-driven electronic structure.",1006.0929v1
2010-06-09,"Comment on ""Symmetries and Interaction Coefficients of Kelvin waves"" [arXiv:1005.4575] by Lebedev and L'vov","We comment on the claim by Lebedev and L'vov [arXiv:1005.4575] that the
symmetry with respect to a tilt of a quantized vortex line does not yet
prohibit coupling between Kelvin waves and the large-scale slope of the line.
Ironically, the counterexample of an effective scattering vertex in the local
induction approximation (LIA) attempted by Lebedev and L'vov invalidates their
logic all by itself being a notoriously known example of how symmetries impose
stringent constraints on kelvon kinetics---not only the coupling in question
but the kinetics in general are absent within LIA. We further explain that the
mistake arises from confusing symmetry properties of a specific mathematical
representation in terms of the canonical vortex position field w(z) = x(z) +
iy(z), which explicitly breaks the tilt symmetry due to an arbitrary choice of
the z-axis, with those of the real physical system recovered in final
expressions.",1006.1789v2
2010-06-11,Thermal nuclear pairing within the self-consistent quasiparticle RPA,"The self-consistent quasiparticle RPA (SCQRPA) is constructed to study the
effects of fluctuations on pairing properties in nuclei at finite temperature
and z-projection M of angular momentum. Particle-number projection (PNP) is
taken into account within the Lipkin-Nogami method. Several issues such as the
smoothing of superfluid-normal phase transition, thermally assisted pairing in
hot rotating nuclei, extraction of the nuclear pairing gap using an improved
odd-even mass difference are discussed. A novel approach of embedding the PNP
SCQRPA eigenvalues in the canonical and microcanonical ensembles is proposed
and applied to describe the recent empirical thermodynamic quantities for iron,
molybdenum, dysprosium, and ytterbium isotopes.",1006.2201v1
2010-06-15,Angular resolved specific heat in iron-based superconductors: the case for nodeless extended $s$-wave gap,"We consider the variation of the field-induced component of the specific heat
$C({\bf H})$ with the direction of the applied field in $Fe-$pnictides within
quasi-classical Doppler-shift approximation, with special emphasis to recent
experiments on FeSe$_{0.4}$Te$_{0.6}$ [Zheng et al., arXiv:1004.2236]. We show
that for extended $s-$wave gap with no nodes, $C({\bf H})$ has $\cos 4 \phi$
component, where $\phi$ is the angle between ${\bf H}$ and the direction
between hole and electron Fermi surfaces. The maxima of $C({\bf H})$ are at
$\pi/4$, $3\pi/4$, etc. if the applied field is smaller than $H_0 \leq 1T$, and
at $\phi =0, \pi/2$, etc. if the applied field is larger than $H_0$. The
angle-dependence of $C({\bf H})$, the positions of the maxima, and the relative
magnitude of the oscillating component are consistent with the experiments
performed in the field of $9T >> H_0$. We show that the observed $\cos 4 \phi$
variation does not hold if the $s-$wave gap has accidental nodes along the two
electron Fermi surfaces.",1006.3091v1
2010-06-17,Homogeneous Cu-Fe super saturated solid solutions prepared by severe plastic deformation,"A Cu-Fe nanocomposite containing 50 nm thick iron filaments dispersed in a
copper matrix was processed by torsion under high pressure at various strain
rates and temperatures. The resulting nanostructures were characterized by
transmission electron microscopy, atom probe tomography and M\""ossbauer
spectrometry. It is shown that alpha-Fe filaments are dissolved during severe
plastic deformation leading to the formation of a homogeneous supersaturated
solid solution of about 12 at.% Fe in fcc Cu. The dissolution rate is
proportional to the total plastic strain but is not very sensitive to the
strain rate. Similar results were found for samples processed at liquid
nitrogen temperature. APT data revealed asymmetric composition gradients
resulting from the deformation induced intermixing. On the basis of these
experimental data, the formation of the supersaturated solid solutions is
discussed",1006.3433v1
2010-06-17,Competition of local-moment ferromagnetism and superconductivity in Co-substituted EuFe2As2,"In contrast to SrFe2As2, where only the iron possesses a magnetic moment, in
EuFe2As2 an additional large, local magnetic moment is carried by Eu2+. Like
SrFe2As2, EuFe2As2 exhibits a spin-density wave transition at high
temperatures, but in addition the magnetic moments of the Eu2+ order at around
20 K. The interplay of pressure-induced superconductivity and the Eu2+ order
leads to a behavior which is reminiscent of re-entrant superconductivity as it
was observed, for example, in the ternary Chevrel phases or in the rare-earth
nickel borocarbides. Here, we study the delicate interplay of the ordering of
the Eu2+ moments and superconductivity in EuFe1.9Co0.1As2, where application of
external pressure makes it possible to sensitively tune the ratio of the
magnetic (T_C) and the superconducting (T_{c,onset}) critical temperatures. We
find that superconductivity disappears once T_C > T_{c,onset}.",1006.3471v1
2010-06-17,Ultrafast transient response and electron-phonon coupling in the iron-pnictide superconductor Ba(Fe(1-x)Co(x))2As2,"The transient response of Ba(Fe(1-x)Co(x))2As2, x=0.08 was studied by
pump-probe optical reflectivity. After ultrafast photoexcitation, hot electrons
were found to relax with two different characteristic times, indicating the
presence of two distinct decay channels: a faster one, of less than 1 ps in the
considered pump fluence range, and a slower one, corresponding to lattice
thermalization and lasting ~6 ps. Our analysis indicates that the fast
relaxation should be attributed to preferential scattering of the electrons
with only a subset of the lattice vibration modes, with a second moment of the
Eliashberg function lambda(omega^2)~64 meV^2. The simultaneous excitation of a
strong fully symmetric A(1g) optical phonon corroborates this conclusion and
makes it possible to deduce the value of lambda~0.12. This small value for the
electron-phonon coupling confirms that a phonon mediated process cannot be the
only mechanism leading to the formation of superconducting pairs in this family
of pnictides.",1006.3490v2
2010-06-20,Out-of-plane momentum and symmetry dependent superconducting gap in Ba0.6K0.4Fe2As2,"The three-dimensional band structure and superconducting gap of
Ba0.6K0.4Fe2As2 are studied with high-resolution angle-resolved photoemission
spectroscopy. In contrast to previous results, we have identified three
hole-like Fermi surfaces near the zone center with sizable out-of-plane or kz
dispersion. The superconducting gap on certain Fermi surface shows significant
kz-dependence. Moreover, we found that the superconducting gap sizes are
different at the same Fermi momentum for two bands with different spatial
symmetries (one odd, one even). Our results provide further information on the
rich superconducting gap structure in iron pnictides, and a distinct test for
theories.",1006.3936v1
2010-06-30,BaFe2As2 Surface Domains and Domain Walls: Mirroring the Bulk Spin Structure,"High-resolution scanning tunneling microscopy (STM) measurements on
BaFe2As2-one of the parent compounds of the iron-based superconductors-reveals
a (1x1) As-terminated unit cell on the (001) surface. However, there are
significant differences of the surface unit cell compared to the bulk: only one
of the two As atoms in the unit cell is imaged and domain walls between
different (1x1) regions display a C2 symmetry at the surface. It should have
been C2v if the STM image reflected the geometric structure of the surface or
the orthorhombic bulk. The inequivalent As atoms and the bias dependence of the
domain walls indicate that the origin of the STM image is primarily electronic
not geometric. We argue that the surface electronic topography mirrors the bulk
spin structure of BaFe2As2, via strong orbital-spin coupling.",1006.5907v1
2010-07-05,Impact of the Spin Density Wave Order on the Superconducting Gap of Ba(Fe$_{1-x}$Co$_x$)$_2$As$_2$,"We report a doping dependent electronic Raman scattering measurements on
iron-pnictide superconductor Ba(Fe$_{1-x}$Co$_x$)$_2$As$_2$ single crystals. A
strongly anisotropic gap is found at optimal doping for x=0.065 with
$\Delta_{max}\sim 5\Delta_{min}$. Upon entering the coexistence region between
superconducting (SC) and spin-density-wave (SDW) orders, the effective pairing
energy scale is strongly reduced. Our results are interpreted in terms of a
competition between SC and SDW orders for electronic state at the Fermi level.
Our findings advocate for a strong connection between the SC and SDW gaps
anisotropies which are both linked to interband interactions.",1007.0720v2
2010-07-07,Magnetisation distribution in the tetragonal phase of BaFe2As2,"We have determined the spatial distribution of the magnetisation induced by a
field of 9 T in the tetragonal phase of BaFe2As2 using polarised neutron
diffraction. Magnetic structure factors derived from the polarisation
dependence of the intensities of Bragg reflections were used to make a maximum
entropy reconstruction of the distribution projected on the 110 plane. The
reconstruction shows clearly that the magnetisation is confined to the region
around the iron atoms and that there is no significant magnetisation associated
with either the As or Ba atoms. The distribution of magnetisation around the Fe
atom is significantly non-spherical with a shape which is extended in the <111>
directions in the projection. These results show that the electrons which give
rise to the paramagnetic susceptibility are confined to the Fe atoms their
distribution suggests that they occupy 3d t_2g type orbitals with about 60% in
those of xy symmetry.",1007.1116v2
2010-07-12,Atomic data and spectral model for Fe III,"We present new atomic data (radiative transitions rates and collision
strengths) from large scale calculations and a non-LTE spectral model for Fe
III. This model is in very good agreement with observed astronomical emission
spectra, in contrast with previous models that yield large discrepancies with
observations. The present atomic computations employ a combination of atomic
physics methods, e.g. relativistic Hatree-Fock, the Thomas-Fermi-Dirac
potential, and Dirac-Fock computation of A-values and R-matrix with
intermediate coupling frame transformation and Dirac R-matrix. We study the
advantages and shortcomings of each method. It is found that the Dirac R-matrix
collision strengths yield excellent agreement with observations, much improved
over previously available models. By contrast, the transformation of
LS-coupling R-matrix fails to yield accurate effective collision strengths at
around 10^4 K, despite using very large configuration expansions, due to the
limited treatment of spin-orbit effects in the near threshold resonances of the
collision strengths. The present work demonstrates that accurate atomic data
for low ionization iron-peak species is now within reach.",1007.1960v1
2010-07-13,Doping evolution of superconducting gaps and electronic densities of states in Ba(Fe1-xCox)2As2 iron pnictides,"An extensive calorimetric study of the normal- and superconducting-state
properties of Ba(Fe1-xCox)2As2 is presented for 0 < x < 0.2. The normal-state
Sommerfeld coefficient increases (decreases) with Co doping for x < 0.06 (x >
0.06), which illustrates the strong competition between magnetism and
superconductivity to monopolize the Fermi surface in the underdoped region and
the filling of the hole bands for overdoped Ba(Fe1-xCox)2As2. All
superconducting samples exhibit a residual electronic density of states of
unknown origin in the zero-temperature limit, which is minimal at optimal
doping but increases to the normal-state value in the strongly under- and
over-doped regions. The remaining specific heat in the superconducting state is
well described using a two-band model with isotropic s-wave superconducting
gaps.",1007.2218v1
2010-07-14,Comparative study of the electronic structures of Fe3O4 and Fe2SiO4,"The electronic properties of two spinels Fe$_3$O$_4$ and Fe$_2$SiO$_4$ are
studied by the density functional theory. The local Coulomb repulsion $U$ and
the Hund's exchange $J$ between the $3d$ electrons on iron are included. For
$U=0$, both spinels are half-metals, with the minority $t_{2g}$ states at the
Fermi level. Magnetite remains a metal in a cubic phase even at large values of
$U$. The metal-insulator transition is induced by the $X_3$ phonon, which
lowers the total energy and stabilizes the charge-orbital ordering.
Fe$_2$SiO$_4$ transforms to a Mott insulating state for $U>2$ eV with a gap
$\Delta_g\sim U$. The antiferromagnetic interactions induce the tetragonal
distortion, which releases the geometrical frustration and stabilizes the
long-range order. The differences of electronic structures in the high-symmetry
cubic phases and the distorted low-symmetry phases of both spinels are
discussed.",1007.2340v1
2010-07-17,Pressure-induced changes in the magnetic and valence state of EuFe2As2,"We present the results of electrical resistivity, ac specific heat, magnetic
susceptibility, X-ray absorption spectroscopy (XAS) and X-ray magnetic circular
dichroism (XMCD) of the ternary iron arsenide EuFe2As2 single crystal under
pressure. Applying pressure leads to a continuous suppression of the
antiferromagnetism associated with Fe moments and the antiferromagnetic
transition temperature becomes zero in the vicinity of a critical pressure Pc
~2.5-2.7 GPa. Pressure-induced re-entrant superconductivity, which is highly
sensitive to the homogeneity of the pressure, only appears in the narrow
pressure region in the vicinity of Pc due to the competition between
superconductivity and the antiferromagnetic ordering of Eu2+ moments. The
antiferromagnetic state of Eu2+ moments changes to the ferromagnetic state
above 6 GPa. We also found that the ferromagnetic order is suppressed with
further increasing pressure, which is connected with a valence change of Eu
ions.",1007.2889v2
2010-07-21,"Electronic structure, spin state, and magnetism of the square-lattice Mott insulator La2Co2Se2O3 from first principles","Electronic and magnetic structures of the newly synthesized cobalt
oxyselenide La2Co2Se2O3 (structurally similar to the superconducting iron
pnictides) are studied through density functional calculations. The obtained
results show that this material is a Mott insulator, and that it has a very
stable Co2+ high-spin ground state with a t2g-like orbital ordering, which is
substantiated by the calculated crystal-field excitation energies. The square
lattice of the Co2+ spins is found to have a strong antiferro (a weak ferro)
magnetic coupling for the second nearest neighbors (2nn) via O (Se2) and an
intermediate antiferro one for the 1nn, with the strength ratio about 10:1:3.
The present results account for the available experimental data of magnetism,
and the prediction of a planar frustrated (2x2) antiferromagnetic structure
would motivate a new experiment.",1007.3697v1
2010-07-28,Nodes in the Order Parameter of Superconducting Iron Pnictides Observed by Infrared Spectroscopy,"The temperature and frequency dependences of the conductivity are derived
from optical reflection and transmission measurements of electron doped
BaFe$_2$As$_2$ crystals and films. The data is consistent with gap nodes or
possibly a very small gap in the crossover region between these two
possibilities. This can arise when one of the several pockets known to exist in
these systems has extended s-wave gap symmetry with an anisotropic piece
canceling or nearly so the isotropic part in some momentum direction.
Alternatively, a node can be lifted by impurity scattering which reduces
anisotropy. We find that the smaller gap on the hole pocket at the $\Gamma$
point in the Brillouin zone is isotropic s-wave while the electron pocket at
the $M$ point has a larger gap which is anisotropic and falls in the crossover
region.",1007.5215v1
2010-07-29,BaFe_{1.8}Co_{0.2}As_2 thin film hybrid Josephson junctions,"Josephson junctions with iron pnictides open the way for fundamental
experiments on superconductivity in these materials and their application in
superconducting devices. Here, we present hybrid Josephson junctions with a
BaFe_{1.8}Co_{0.2}As_2 thin film electrode, an Au barrier and a PbIn counter
electrode. The junctions show RSJ-like current-voltage characteristics up to
the critical temperature of the counter electrode of about 7.2K. The
temperature dependence of the critical current, IC, does not show an
Ambegaokar-Baratoff behavior. Well-pronounced Shapiro steps are observed at
microwave frequencies of 10-18GHz. Assuming an excess current, I_ex, of 200
{\mu}A at 4.2K we get an effective I_C R_N product of 6 {\mu}V.",1007.5252v2
2010-07-30,Reversible shift in the superconducting transition for La1.85Sr0.15CuO4 and BaFe1.8Co0.2As2 using piezoelectric substrates,"The use of piezoelectric substrates enables a dynamic observation of strain
dependent properties of functional materials. Based on studies with
La1.85Sr0.15CuO4 we extended this approach to the iron arsenic superconductors
represented by BaFe2-xCoxAs2 to investigate strain driven changes in detail. We
demonstrate that epitaxial thin films can be prepared on
(001)Pb(Mg1/3Nb2/3)0.72Ti0.28O3 substrates using pulsed laser deposition. The
structural as well as the electric properties of the grown films were
characterized in detail. A reversible shift of the superconducting transition
of 0.44 K for La1.85Sr0.15CuO4 and 0.2 K for BaFe1.8Co0.2As2 was observed
applying a biaxial strain of 0.022% and 0.017% respectively.",1007.5454v1
2010-08-02,A Search for Defect Related Ferromagnetism in SrTiO$_3$,"Room temperature ferromagnetic hysteresis is observed in commercial SrTiO$_3$
substrates purchased from a variety of suppliers. It is shown that the
ferromagnetic signal comes from the unpolished surfaces. Surface impurity
phases cannot be detected using either x-ray diffraction or energy dispersive
x-ray spectra on the unpolished surfaces. However, a possible correlation
between surface disorder (xray diffraction peak linewidth) and ferromagnetism
is observed. Ar ion bombardment (10keV-90 keV) can be used to produce surface
layer disorder but is not found to induce ferromagnetism. Annealing of the
substrates at temperatures ranging from 600 to 1100 $^\circ$C is found to alter
the hysteresis curves differently depending on whether the annealing is
performed in air or in vacuum. Identical annealing behaviour is observed if the
substrates are artificially spiked with iron. This suggests that the
ferromagnetic hysteresis of as purchased SrTiO$_3$ could be due to Fe
contamination of the unpolished surfaces. In addition, it is shown that no
ferromagnetism is observed in samples that contain $10^{19}-10^{21}$ cm$^{-3}$
of oxygen vacancies if all the faces are polished.",1008.0299v1
2010-08-02,Iron substitution in NdCoAsO: crystal structure and magnetic phase diagram,"The effects of replacing small amounts of Co with Fe in NdCoAsO are reported.
Polycrystalline materials with compositions NdCo1-xFexAsO (x = 0.05, 0.10,
0.15, and 0.20) are studied and the results compared to previous reports for
NdCoAsO. Rietveld analysis of powder x-ray diffraction data shows that as Fe
replaces Co on the transition metal (T) site, the T-As distance increases, and
the As tetrahedra surrounding the T-site become more regular. Electrical
resistivity and magnetization measurements indicate that the three magnetic
phase transitions in NdCoAsO are suppressed as Co is replaced by Fe, and these
transitions are not observed above 1.8 K for x = 0.20. Based on these results,
the magnetic phase diagram for the Co-rich side of the NdCoAsO-NdFeAsO system
is constructed.",1008.0304v2
2010-08-05,Reciprocal Relations Between Kinetic Curves,"We study coupled irreversible processes. For linear or linearized kinetics
with microreversibility, $\dot{x}=Kx$, the kinetic operator $K$ is symmetric in
the entropic inner product. This form of Onsager's reciprocal relations implies
that the shift in time, $\exp (Kt)$, is also a symmetric operator. This
generates the reciprocity relations between the kinetic curves. For example,
for the Master equation, if we start the process from the $i$th pure state and
measure the probability $p_j(t)$ of the $j$th state ($j\neq i$), and,
similarly, measure $p_i(t)$ for the process, which starts at the $j$th pure
state, then the ratio of these two probabilities $p_j(t)/p_i(t)$ is constant in
time and coincides with the ratio of the equilibrium probabilities. We study
similar and more general reciprocal relations between the kinetic curves. The
experimental evidence provided as an example is from the reversible water gas
shift reaction over iron oxide catalyst. The experimental data are obtained
using Temporal Analysis of Products (TAP) pulse-response studies. These offer
excellent confirmation within the experimental error.",1008.1056v2
2010-08-09,Transport properties of iron-based FeTe0.5Se0.5 superconducting wire,"FeTe0.5Se0.5 superconducting wires have been fabricated using ex-situ PIT
method with an Fe sheath. Among the other FeAs-based superconductor,
FeTe0.5Se0.5 has great advantage for application due to binary composition and
less toxic. Surprisingly, superconducting current was observed in the
as-fabricated wire without any heat treatments. Zero resistivity and transport
critical current density (Jc) were 3.2 K and 2.8 A/cm2, respectively. In
addition, by annealing at 200 degC for 2 h, critical temperature Tczero and Jc
were enhanced up to 9.1 K, and 64.1 A/cm2, respectively. This suggests that the
grain connectivity was improved by heat treatment, and superconducting property
of FeTe0.5Se0.5 wire was enhanced.",1008.1447v3
2010-08-13,'Genesis': A takeover from field-responsive matter?,"Cairns-Smith (2008) has argued for a pre-Darwinian era, with a simpler basis
for life's functioning via primitive ""crystal genes"" (information transfer,
kinetic control on metabolic reactions). At the other extreme, guided by the
structural similarity of clusters in early-evolved enzymes to iron-sulphide
minerals like greigite, the hydrothermal mound scenario of Russell and
coworkers (1994) presents how non-equilibrium forces rooted in geochemistry
could be extrapolated to understand the metabolic functioning of living
systems. The informational vs metabolic aspects of life in these respective
scenarios can be linked together via a framboid-based theory of Sawlowicz
(2000), as these assemblies typically form in colloidal environments. In this
background, we consider the ramifications of a magnetic rock field on the mound
scenario, asking if soft matter assemblies are compatible with a coherent
order.",1008.2362v1
2010-08-16,Superconductivity at 28.3 and 17.1 K in (Ca4Al2O6-y)(Fe2Pn2) (Pn = As and P),"We have successfully synthesized (Ca4Al2O6-y)(Fe2Pn2) (Pn = As and P)
(Al-42622(Pn)) using high-pressure synthesis technique. Al-42622(Pn) exhibit
superconductivity for both Pn = As and P with the transition temperatures of
28.3 K and 17.1 K, respectively. The a-lattice parameters of Al-42622(Pn) (a =
3.713 {\AA} and 3.692 {\AA} for Pn = As and P, respectively) are smallest among
the iron-pnictide superconductors. Correspondingly, Al-42622(As) has the
smallest As-Fe-As bond angle (102.1 {\deg}) and the largest As distance from
the Fe planes (1.500 {\AA}).",1008.2586v3
2010-08-19,Nodeless two-gap superconductivity in stoichiometric iron pnictide LiFeAs,"The variations of in- and inter- plane London penetration depths,
$\Delta\lambda(T)$, were measured using a tunnel diode resonator in single
crystals of the intrinsic pnictide superconductor LiFeAs. This compound appears
to be in the clean limit with a residual resistivity of 4 ($T\to0$) to 8
($T_c$) $\mu \Omega\cdot$cm and $RRR$ of 65 to 35, respectively. The superfluid
density, $\rho_s(T)=\lambda^2(0)/\lambda^2(T)$, is well described by the
self-consistent two-gap $\gamma-$model. Together with the previous data, our
results support the universal evolution of the superconducting gap from
nodeless to nodal upon departure from optimal doping. We also conclude that
pairbreaking scattering plays an important role in the deviation of the
low-temperature behavior of $\lambda(T)$ from exponential in Fe-based
compounds.",1008.3251v3
2010-08-19,The Lateral Distribution Function of Coherent Radio Emission from Extensive Air Showers; Determining the Chemical Composition of Cosmic Rays,"The lateral distribution function (LDF) for coherent electromagnetic
radiation from air showers initiated by ultra-high-energy cosmic rays is
calculated using a macroscopic description. A new expression is derived to
calculate the coherent radio pulse at small distances from the observer. It is
shown that for small distances to the shower axis the shape of the electric
pulse is determined by the `pancake' function, describing the longitudinal
distribution of charged particles within the shower front, while for large
distances the pulse is determined by the shower profile. This reflects in a
different scaling of the LDF at small and at large distances. As a first
application we calculate the LDF for proton- and iron-induced showers and we
show that this offers a very sensitive measure to discriminate between these
two. We show that due to interference between the geo-magnetic and the
charge-excess contributions the intensity pattern of the radiation is not
circular symmetric.",1008.3308v1
2010-08-20,Two-band BCS superconductivity in Ba(Fe0.9Co0.1)2As2,"The conductivity and permittivity optical spectra of iron-pnictide
Ba(Fe0.9Co0.1)2As2 film (Tc=20 K) are analyzed. In the superconducting state,
at all temperatures up to Tc the temperature dependences of the magnetic field
penetration depth and of the superconducting condensate density are well
described within the generalized two-band BCS model with intraband and
interband pairing interactions considered. It is shown that the smaller
superconducting energy gap 2{\Delta} = 3.7 meV develops in the electronic
subsystem while the larger gap 2{\Delta} >= 7 meV opens in the hole subsystem.
The normal state parameters (plasma frequencies and scattering rates) of
electron and hole conduction bands are determined. At all temperatures the
obtained data are consistent with the results of electronic photoemission
experiments on Ba(Fe1-x Cox)2As2.",1008.3473v3
2010-08-23,Testing the No-Hair Theorem with Observations of Black Holes in the Electromagnetic Spectrum,"According to the no-hair theorem, astrophysical black holes are uniquely
described by their mass and spin. In this paper, we review a new framework for
testing the no-hair hypothesis with observations in the electromagnetic
spectrum. The approach is formulated in terms of a Kerr-like spacetime
containing a quadrupole moment that is independent of both mass and spin. If
the no-hair theorem is correct, then any deviation from the Kerr metric
quadrupole has to be zero. We show how upcoming VLBI imaging observations of
Sgr A* as well as spectroscopic observations of iron lines from accreting black
holes with IXO may lead to the first astrophysical test of the no-hair theorem.",1008.3902v2
2010-08-29,Fermiology of Sr4V2O6Fe2As2: Quasi-Nested Fe vs Mott-Insulating V Orbitals,"We have performed an angle-resolved photoemission spectroscopy study of a new
iron-based superconductor Sr4V2O6Fe2As2. While V 3d orbitals are found to be in
a Mott insulator state and show an incoherent peak at ~ 1 eV below the Fermi
level, the dispersive Fe 3d bands form several hole- and electron-like Fermi
surfaces (FSs), some of which are quasi-nested by the (pi, 0) wave vector. This
differs from the local density approximation (LDA) calculations, which predict
non-nested FSs for this material. However, LDA+U with a large effective Hubbard
energy U on V 3d electrons can reproduce the experimental observation
reasonably well. The observed fermiology in superconducting Sr4V2O6Fe2As2
strongly supports that (pi, 0) interband scattering between quasi-nested FSs is
indispensable to superconductivity in pnictides.",1008.4905v1
2010-08-30,X-ray absorption by Broad Line Region Clouds in Mrk 766,"We present a new analysis of a 9-day long XMM-Newton monitoring of the Narrow
Line Seyfert 1 galaxy Mrk 766. We show that the strong changes in spectral
shape which occurred during this observation can be interpreted as due to Broad
Line Region clouds crossing the line of sight to the X-ray source. Within the
occultation scenario, the spectral and temporal analysis of the eclipses
provides precise estimates of the geometrical structure, location and physical
properties of the absorbing clouds. In particular, we show that these clouds
have cores with column densities of at least a few 10^23 cm^-2 and velocities
in the plane of the sky of the order of thousands km/s. The three different
eclipses monitored by XMM-Newton suggest a broad range in cloud velocities (by
a factor ~4-5). Moreover, two iron absorption lines clearly associated with
each eclipse suggest the presence of highly ionized gas around the obscuring
clouds, and an outflow component of the velocity spanning from 3,000 to 15,000
km/s",1008.5067v1
2010-09-02,Association of oxygen vacancies with impurity metal ions in lead titanate,"Thermodynamic, structural and electronic properties of isolated copper and
iron atoms as well as their complexes with oxygen vacancies in tetragonal lead
titanate are investigated by means of first principles calculations. Both
dopants exhibit a strong chemical driving force for the formation of M_Ti-V_O
(M = Cu, Fe) defect associates. The most stable configurations corresponds to a
local dipole aligned along the tetragonal axis parallel to the spontaneous
polarization. Local spin moments are obtained and the calculated spin densities
are discussed. The calculations provide a simple and consistent explanation for
the experimental findings. The results are discussed in the context of models
for degradation of ferroelectric materials.",1009.0552v1
2010-09-10,Nucleosynthesis in the Stellar Systems omega Cen and M22,"The stellar system omega Centauri is well known for the large range in
abundance among its member stars. Recent work has indicated that the globular
cluster M22 (NGC 6656) also possesses an internal abundance range, albeit
substantially smaller than that in omega Cen. Here we compare, as a function of
[Fe/H], element-to-iron ratios in the two systems for a number of different
elements using data from abundance analyses of red giant branch stars. It
appears that the nucleosynthetic enrichment processes were very similar in
these two systems despite the substantial difference in total mass.",1009.1955v1
2010-09-10,Antiferromagnetic Critical Fluctuations in BaFe$_2$As$_2$,"Magnetic correlations near the magneto-structural phase transition in the
bilayer iron pnictide parent compound, BaFe$_2$As$_2$, are measured. In close
proximity to the antiferromagnetic phase transition in BaFe$_2$As$_2$, a
crossover to three dimensional critical behavior is anticipated and has been
preliminarily observed. Here we report complementary measurements of
two-dimensional magnetic fluctuations over a broad temperature range about
T$_N$. The potential role of two-dimensional critical fluctuations in the
magnetic phase behavior of BaFe$_2$As$_2$ and their evolution near the
anticipated crossover to three dimensional critical behavior and long-range
order are discussed.",1009.2116v1
2010-09-17,"Existence, character and origin of surface-related bands in the high temperature iron pnictide superconductor BaFe_{2-x}Co_{x}As_{2}","Low energy electron diffraction (LEED) experiments, LEED simulations and
finite slab density functional calculations are combined to study the cleavage
surface of Co doped BaFe_{2-x}Co_{x}As_{2} (x = 0.1, 0.17). We demonstrate that
the energy dependence of the LEED data can only be understood from a
terminating 1/2 Ba layer accompanied by distortions of the underlying
As-Fe_2-As block. As a result, surface related Fe 3d states are present in the
electronic structure, which we identify in angle resolved photoemission
experiments. The close proximity of the surface-related states to the bulk
bands inevitably leads to broadening of the ARPES signals, which excludes the
use of the BaFe_{2-x}Co_{x}As_{2} system for accurate determination of
self-energies using ARPES.",1009.3493v1
2010-09-20,Electronic Structure Calculation by First Principles for Strongly Correlated Electron Systems,"Recent trends of ab initio studies and progress in methodologies for
electronic structure calculations of strongly correlated electron systems are
discussed. The interest for developing efficient methods is motivated by recent
discoveries and characterizations of strongly correlated electron materials and
by requirements for understanding mechanisms of intriguing phenomena beyond a
single-particle picture. A three-stage scheme is developed as renormalized
multi-scale solvers (RMS) utilizing the hierarchical electronic structure in
the energy space. It provides us with an ab initio downfolding of the global
band structure into low-energy effective models followed by low-energy solvers
for the models. The RMS method is illustrated with examples of several
materials. In particular, we overview cases such as dynamics of semiconductors,
transition metals and its compounds including iron-based superconductors and
perovskite oxides, as well as organic conductors of kappa-ET type.",1009.3851v1
2010-09-21,Single Crystal Growth and Characterization of the Iron-Based Superconductor KFe2As2 Synthesized by KAs Flux Method,"Centimeter sized platelet single crystals of KFe2As2 were grown using a
self-flux method. An encapsulation technique using commercial stainless steel
container allowed the stable crystal growth lasting for more than 2 weeks.
Ternary K-Fe-As systems with various starting compositions were examined to
determine the optimal growth conditions. Employment of KAs flux led to the
growth of large single crystals with the typical size of as large as 15 mm x 10
mm x 0.4 mm. The grown crystals exhibit sharp superconducting transition at 3.4
K with the transition width 0.2 K, as well as the very large residual
resistivity ratio exceeding 450, evidencing the good sample quality.",1009.4002v1
2010-09-22,An ARPES view on the high-Tc problem: phonons vs spin-fluctuations,"We review the search for a mediator of high-Tc superconductivity focusing on
ARPES experiment. In case of HTSC cuprates, we summarize and discuss a
consistent view of electronic interactions that provides natural explanation of
both the origin of the pseudogap state and the mechanism for high temperature
superconductivity. Within this scenario, the spin-fluctuations play a decisive
role in formation of the fermionic excitation spectrum in the normal state and
are sufficient to explain the high transition temperatures to the
superconducting state while the pseudogap phenomenon is a consequence of a
Peierls-type intrinsic instability of electronic system to formation of an
incommensurate density wave. On the other hand, a similar analysis being
applied to the iron pnictides reveals especially strong electron-phonon
coupling that suggests important role of phonons for high-Tc superconductivity
in pnictides.",1009.4336v1
2010-09-30,Mobility analysis of FeTe thin films,"The Hall effect is investigated in detail for nonsuperconducting and
superconducting FeTe thin films. The Hall coefficient commonly exhibits a sign
reversal from positive in a high-temperature paramagnetic state to negative in
a low-temperature antiferromagnetic state. Phenomenological analysis by a
simple two-band Drude model indicates that hole mobility is significantly
suppressed in the antiferromagnetic state. When suppression of the hole
mobility is insufficient, superconductivity shows up in FeTe. This result
strongly suggests that the itinerancy in both hole and electron channels is the
essential factor for the occurrence of superconductivity in iron chalcogenide
superconductors.",1009.6035v2
2010-10-07,A past capture event at Sagittarius A* inferred from the fluorescent X-ray emission of Sagittarius B clouds,"The fluorescent X-ray emission from neutral iron in the molecular clouds (Sgr
B) indicates that the clouds are being irradiated by an external X-ray source.
The source is probably associated with the Galactic central black hole (Sgr
A*), which triggered a bright outburst one hundred years ago. We suggest that
such an outburst could be due to a partial capture of a star by Sgr A*, during
which a jet was generated. By constraining the observed flux and the time
variability ($\sim$ 10 years) of the Sgr B's fluorescent emission, we find that
the shock produced by the interaction of the jet with the dense interstellar
medium represents a plausible candidate for the X-ray source emission.",1010.1312v1
2010-10-10,Electronic structure of BaNi$_2$As$_2$,"BaNi$_2$As$_2$, with a first order phase transition around 131 K, is studied
by the angle-resolved photoemission spectroscopy. The measured electronic
structure is compared to the local density approximation calculations,
revealing similar large electronlike bands around $\bar{M}$ and differences
along $\bar{\Gamma}$-$\bar{X}$. We further show that the electronic structure
of BaNi$_2$As$_2$ is distinct from that of the sibling iron pnictides.
Particularly, there is no signature of band folding, indicating no collinear
SDW related magnetic ordering. Moreover, across the strong first order phase
transition, the band shift exhibits a hysteresis, which is directly related to
the significant lattice distortion in BaNi$_2$As$_2$.",1010.1905v2
2010-10-14,Macroscopic quantum tunneling in multigap superconducting Josephson junctions: Escape rate enhancement via quantum fluctuations of Josephson-Leggett mode,"We theoretically study the macroscopic quantum tunneling (MQT) in a hetero
Josephson junction formed by a conventional single-gap superconductor and a
multi-gap one such as ${MgB}_{2}$ and iron-based superconductors. In such a
Josephson junction more than one phase differences are defined. We clarify the
quantum dynamics of the phase differences and construct a theory for the MQT in
the multi-gap Josephson junctions. The dynamics of the phase differences are
strongly affected by the Josephson-Leggett mode, which is the out-of-phase
oscillation mode of the phase differences. The escape rate is calculated in
terms of the effective action renormalized by the Josephson-Leggett mode. It is
shown that the escape rate is drastically enhanced when the frequency of the
Josephson-Leggett mode is less than the Josephson-plasma frequency.",1010.2804v2
2010-10-12,Revealing the degree of magnetic frustration by non-magnetic impurities,"Imaging the magnetic fields around a non-magnetic impurity can provide a
clear benchmark for quantifying the degree of magnetic frustration. Focusing on
the strongly frustrated $J_1$-$J_2$ model and the spatially anisotropic
$J_{1a}$-$J_{1b}$-$J_2$ model, very distinct low energy behaviors reflect
different levels of magnetic frustration. In the $J_1$-$J_2$ model, bound
magnons appear trapped near the impurity in the ground state and strongly
reduce the ordered moments for sites proximal to the impurity. In contrast,
local moments in the $J_{1a}$-$J_{1b}$-$J_2$ model are enhanced on the impurity
neighboring sites. These theoretical predictions can be probed by experiments
such as nuclear magnetic resonance and scanning tunneling microscopy, and the
results can elucidate the role of frustration in antiferromagnets and help
narrow the possible models to understand magnetism in the iron pnictdies.",1010.2917v2
2010-10-14,Theory of Orbital Nematicity in Underdoped Iron Arsenides,"Recent finding of an {\it unusual} in-plane resistivity anisotropy in the
underdoped 122-family at high temperature ($T$) suggests an orbital nematic
(ON) order, posing a challenge to extant theories. The {\it sign} of the
anisotropy contradicts expectations from weakly correlated as well as pure
spin-only nematic views. Here, we show how such an ON order with accompanying
structural distortion arises from {\it residual}, intersite and inter-orbital
two-body interactions in an incoherent ""bad metal"" close to Mottness.
Enhancement of orbital-selective incoherence is shown to be necessary for
understanding transport anisotropy. Our results suggest that ON order, with
subsequent antiferromagnetic order might be the {\it primary} competitor to
superconductivity in Fe arsenides.",1010.2940v1
2010-10-19,Pressure versus concentration tuning of the superconductivity in Ba(Fe(1-x)Cox)2As2,"In the iron arsenide compound BaFe2As2, superconductivity can be induced
either by a variation of its chemical composition, e.g., by replacing Fe with
Co, or by a reduction of the unit-cell volume through the application of
hydrostatic pressure p. In contrast to chemical substitutions, pressure is
expected to introduce no additional disorder into the lattice. We compare the
two routes to superconductivity by measuring the p dependence of the
superconducting transition temperature Tc of Ba(Fe(1-x)Cox)2As2 single crystals
with different Co content x. We find that Tc(p) of underdoped and overdoped
samples increases and decreases, respectively, tracking quantitatively the
Tc(x) dependence. To clarify to which extent the superconductivity relies on
distinct structural features we analyze the crystal structure as a function of
x and compare the results with that of BaFe2As2 under pressure.",1010.3863v1
2010-10-22,Double resonance Raman study of disorder in CVD-grown single-walled carbon nanotubes,"Single-walled carbon nanotubes (SWNTs) with varying degrees of disorder were
investigated using multiple-excitation Raman spectroscopy. The lattice disorder
was imparted into the nanotubes by the addition of varying amounts of sulfur to
the iron catalyst in a thermal chemical vapor deposition process. Changes in
the intensities of peaks occurring due to a double resonance Raman process were
studied. The intensity of the disorder-induced D band increased with a decrease
in the sulfur content. Upon post-synthesis heat treatment, the double resonance
process got quenched due to defect healing. The second order G' band and iTOLA
bands exhibited a two-peak structure, of which one of the peaks is relatively
more sensitive to defects and decreased in intensity with heat treatment.",1010.4714v2
2010-10-25,"Macroscopic Model of Geomagnetic-Radiation from Air Showers, II","The generic properties of the emission of coherent radiation from a moving
charge distribution are discussed. The general structure of the charge and
current distributions in an extensive air shower are derived. These are
subsequently used to develop a very intuitive picture for the properties of the
emitted radio pulse. Using this picture can be seen that the structure of the
pulse is a direct reflection of the shower profile. At higher frequencies the
emission is suppressed because the wavelength is shorter than the important
length scale in the shower. It is shown that radio emission can be used to
distinguish proton and iron induced air showers.",1010.5268v1
2010-10-31,On the Progenitors of Core-Collapse Supernovae,"Theory holds that a star born with an initial mass between about 8 and 140
times the mass of the Sun will end its life through the catastrophic
gravitational collapse of its iron core to a neutron star or black hole. This
core collapse process is thought to usually be accompanied by the ejection of
the star's envelope as a supernova. This established theory is now being tested
observationally, with over three dozen core-collapse supernovae having had the
properties of their progenitor stars directly measured through the examination
of high-resolution images taken prior to the explosion. Here I review what has
been learned from these studies and briefly examine the potential impact on
stellar evolution theory, the existence of ""failed supernovae"", and our
understanding of the core-collapse explosion mechanism.",1011.0203v1
2010-11-03,Importance of Fermi surface topology for high temperature superconductivity in electron-doped iron arsenic superconductors,"We used angle resolved photoemission spectroscopy and thermoelectric power to
study the poorly explored, highly overdoped side of the phase diagram of
Ba(Fe1-xCox)2As2 high temperature superconductor. Our data demonstrate that
several Lifshitz transitions - topological changes of the Fermi surface - occur
for large x. Tc starts to decrease with doping when the cylindrical, central
hole pocket changes to ellipsoids centering at the Z point, and goes to zero
before these ellipsoids disappear around x = 0.2. Changes in thermoelectric
power occur at similar x-values. Beyond this doping level the central pocket
changes to electron-like and superconductivity does not exist. Our observations
reveal the crucial importance of the underlying Fermiology in this class of
materials. A necessary condition for superconductivity is the presence of the
central hole pockets rather than perfect nesting between central and corner
pockets.",1011.0980v2
2010-11-04,Electronic Structure Studies of Detwinned BaFe$_2$As$_2$ by Photoemission,"We performed angle resolved photoelectron spectroscopy (ARPES) studies on
mechanically detwinned BaFe2As2. We observe clear band dispersions and the
shapes and characters of the Fermi surfaces are identified. Shapes of the two
hole pockets around the {\Gamma}-point are found to be consistent with the
Fermi surface topology predicted in the orbital ordered states. Dirac-cone like
band dispersions near the {\Gamma}-point are clearly identified as
theoretically predicted. At the X-point, split bands remain intact in spite of
detwinning, barring twinning origin of the bands. The observed band dispersions
are compared with calculated band structures. With a magnetic moment of 0.2 ?B
per iron atom, there is a good agreement between the calculation and
experiment.",1011.1112v2
2010-11-06,The Elemental Abundance Distributions of Milky Way Satellite Galaxies,"The chemical compositions of the stars in Milky Way (MW) satellite galaxies
reveals the history of gas flows and star formation (SF) intensity. This talk
presented a Keck/DEIMOS spectroscopic survey of the Fe, Mg, Si, Ca, and Ti
abundances of nearly 3000 red giants in eight MW dwarf satellites. The
metallicity and alpha-to-iron ratio distributions obey the following trends:
(1) The more luminous galaxies are more metal-rich, indicating that they
retained gas more efficiently than the less luminous galaxies. (2) The shapes
of the metallicity distributions of the more luminous galaxies require gas
infall during their SF lifetimes. (3) At [Fe/H] < -1.5, [alpha/Fe] falls
monotonically with increasing [Fe/H] in all MW satellites. One interpretation
of these trends is that the SF timescale in any MW satellite is long enough
that Type Ia supernovae exploded for nearly the entire SF lifetime.",1011.1530v1
2010-11-08,Consistent model of magnetism in ferropnictides,"The discovery of superconductivity in LaFeAsO introduced the ferropnictides
as a major new class of superconducting compounds with critical temperatures
second only to cuprates. The presence of magnetic iron makes ferropnictides
radically different from cuprates. Antiferromagnetism of the parent compounds
strongly suggests that superconductivity and magnetism are closely related.
However, the character of magnetic interactions and spin fluctuations in
ferropnictides, in spite of vigorous efforts, has until now resisted
understanding within any conventional model of magnetism. Here we show that the
most puzzling features can be naturally reconciled within a rather simple
effective spin model with biquadratic interactions, which is consistent with
electronic structure calculations. By going beyond the Heisenberg model, this
description explains numerous experimentally observed properties, including the
peculiarities of the spin wave spectrum, thin domain walls, crossover from
first to second order phase transition under doping in some compounds, and
offers new insight in the occurrence of the nematic phase above the
antiferromagnetic phase transition.",1011.1715v2
2010-11-11,Evidence for electromagnetic granularity in polycrystalline Sm1111 iron-pnictides with enhanced phase purity,"We prepared polycrystalline SmFeAsO1-xFx (Sm1111) bulk samples by sintering
and hot isostatic pressing (HIP) in order to study the effects of phase purity
and relative density on the intergranular current density. Sintered and HIPped
Sm1111 samples are denser with fewer impurity phases, such as SmOF and the
grain boundary wetting phase, FeAs. We found quite complex magnetization
behavior due to variations of both the inter and intragranular current
densities. Removing porosity and reducing second phase content enhanced the
intergranular current density, but HIPping reduced Tc and the intragranular
current density, due to loss of fluorine and reduction of Tc. We believe that
the HIPped samples are amongst the purest polycrystalline 1111 samples yet
made. However, their intergranular current densities are still small, providing
further evidence that polycrystalline pnictides, like polycrystalline cuprates,
are intrinsically granular.",1011.2547v1
2010-11-11,Baryonic Bound State of Vortices in Multicomponent Superconductors,"We construct a bound state of three 1/3-quantized Josephson coupled vortices
in three-component superconductors with intrinsic Josephson couplings, which
may be relevant with regard to iron-based superconductors. We find a Y-shaped
junction of three domain walls connecting the three vortices, resembling the
baryonic bound state of three quarks in QCD. The appearance of the Y-junction
(but not a Delta-junction) implies that in both cases of superconductors and
QCD, the bound state is described by a genuine three-body interaction (but not
by the sum of two-body interactions). We also discuss a
confinement/deconfinement phase transition.",1011.2552v2
2010-11-11,Origin of the Ultrahigh-Energy Cosmic Rays and their Spectral Break,"The energy spectrum, composition and arrival directions of ultrahigh energy
cosmic rays (UHECRs) with energy above the cosmic ray ankle, measured by the
Pierre Auger Observatory, are inconsistent if their origin is assumed to be
extragalactic. Their observed properties, however, are those expected from
UHECRs accelerated by the highly relativistic jets emitted in Galactic gamma
ray bursts, most of which are beamed away from Earth. If this alternative
interpretation is correct, the observed break in the energy spectrum of UHECRs
around 50 EeV is not the Greisen-Zatsepin-Kuzmin cutoff but the energy
threshold for free escape of ultrahigh energy iron cosmic rays from the Galaxy
and above their respective free-escape threshold-energies, UHECR nuclei should
point back to their Galactic sources or their remnants rather than to active
galactic nuclei (AGN) within the GZK horizon.",1011.2672v2
2010-11-16,Itinerant Spin Excitations in SrFe2As2 Measured by Inelastic Neutron Scattering,"We report inelastic neutron scattering measurements of the magnetic
excitations in SrFe2As2, the parent of a family of iron-based superconductors.
The data extend throughout the Brillouin zone and up to energies of ~260meV. An
analysis with the local-moment J_1-J2 model implies very different in-plane
nearest-neighbor exchange parameters along the $a$ and $b$ directions, both in
the orthorhombic and tetragonal phases. However, the spectrum calculated from
the J1-J2 model deviates significantly from our data. We show that the
qualitative features that cannot be described by the J1-J2 model are readily
explained by calculations from a 5-band itinerant mean-field model.",1011.3831v2
2010-11-17,A Ray-Tracing Algorithm for Spinning Compact Object Spacetimes with Arbitrary Quadrupole Moments. I. Quasi-Kerr Black Holes,"We describe a new numerical algorithm for ray tracing in the external
spacetimes of spinning compact objects characterized by arbitrary quadrupole
moments. Such spacetimes describe non-Kerr vacuum solutions that can be used to
test the no-hair theorem in conjunction with observations of accreting black
holes. They are also appropriate for neutron stars with spin frequencies in the
300-600 Hz range, which are typical of the bursting sources in low-mass X-ray
binaries. We use our algorithm to show that allowing for the quadrupole moment
of the spacetime to take arbitrary values leads to observable effects in the
profiles of relativistic broadened fluorescent iron lines from geometrically
thin accretion disks.",1011.4078v1
2010-11-19,Spin canting as a result of the competition between stripes and spirals in cuprates,"Based on the extended Hubbard model we calculate the energy of stripe and
spiral ground states. We find that uniform spirals get favored by a large
$t'/t$ ratio but are unstable at small doping towards stripes and checkerboard
textures with spin canting. The structure of these inhomogeneities also depends
on t'/t and the associated spin currents may induce a small lattice distortion
associated with local dipole moments. We discuss a new kind of stripe which
appears as a domain wall of the antiferromagnetic (AF) order parameter with a
fractional change of the phase of the AF order. For large |t'/t| spirals can be
stabilized under certain conditions in the overdoped regime which may explain
the elastic incommensurate magnetic response recently observed in iron-codoped
Bi2201 materials.",1011.4447v1
2010-11-19,The AGB population of NGC 6822,"The metallicity gradient and the stellar distribution within the Local Group
dwarf galaxy NGC 6822 has been studied photometrically using asymptotic branch
stars (AGB). In order to study the stellar and metallicity distribution, the
carbon- and oxygen-rich AGB stars have been isolated using deep high-quality
near-infrared UKIRT photometry. The ratio between them, the C/M ratio, has been
used to derive the [Fe/H] abundance within the galaxy. The [Fe/H] abundance and
stellar distribution were analysed as a function of galactic radius. A mean C/M
ratio of 0.288 +/- 0.014 has been found which corresponds to an iron abundance
of [Fe/H] =-1.14 +/-0.08 dex, with variations in the north and south, as well
as at larger galactocentric distances. Variations in the magnitude of the tip
of the red giant branch has also been detected.",1011.4464v1
2010-11-22,Orbital occupation and magnetic moments of tetrahedrally coordinated iron in CaBaFe4O7,"CaBaFe4O7 is a mixed-valent transition metal oxide having both Fe2+ and Fe3+
ions in tetrahedral coordination. Here we characterize its magnetic properties
by magnetization measurements and investigate its local electronic structure
using soft x-ray absorption spectroscopy at the Fe L2,3 edges, in combination
with multiplet cluster and spin-resolved band structure calculations. We found
that the Fe2+ ion in the unusual tetrahedral coordination is Jahn-Teller active
with the high-spin e^2 (up) t2^3 (up) e^1 (down) configuration having a
x^2-y^2-like electron for the minority spin. We deduce that there is an
appreciable orbital moment of about L_z=0.36 caused by multiplet interactions,
thereby explaining the observed magnetic anisotropy. CaBaFe4O7, a member of the
'114' oxide family, offers new opportunities to explore charge, orbital and
spin physics in transition metal oxides.",1011.4818v1
2010-12-03,Magnetic and electrical properties and carrier doping effects on the Fe-based host compound Sr4Sc2Fe2As2O6,"Additional charge carriers were introduced to the iron oxyarsenide
Sr4Sc2Fe2As2O6 under a high-pressure condition, followed by measurements of
electrical resistivity, Hall coefficient, and magnetic susceptibility. The host
compound Sr4Sc2Fe2As2O6 shows metallic conductivity down to ~200 K and turns to
show a semiconducting-like conductivity accompanied by a positive
magneto-resistance (22% at 70 kOe). Although the carrier density is comparable
at 300 K (5.9x1021 cm-3) with that of the other Fe-based superconductors, no
superconductivity appears down to 2 K. This is primarily because the net
carrier density decreases over 3 orders of magnitude on cooling and
additionally a possible magnetic order at ~120 K prevents carriers from
pairing. The properties were altered largely by introducing the additional
carriers.",1012.0616v1
2010-12-10,Density functional study of orbital-selective magnetism in FeAs-based superconductors,"We performed spin-polarized density functional calculations of
lanthanide-series (Ln) iron oxypnictides LnFeAsO (Ln=La, Ce, Pr, Nd, Sm, and
Gd) with constrained Fe magnetic moments, finding that in-plane dxy and
out-of-plane dyz orbital characters are preferred for small Fe magnetic
moments. Comparison of LnFeAsO compounds shows that the antiferromagnetism
(AFM) from the Fe dxy orbital is itinerantly driven by orbital-dependent
Fermi-surface nesting while AFM from the Fe dyz orbital is driven by
superexchange mechanism. The Fe magnetic moments of the two orbital characters
show different coupling strengths to Fermi-surface electrons
orbital-selectively, suggesting that they may play different roles in
superconductivity and in AFM, and making d orbital characters of the magnetic
moment resolvable by measuring the electronic structures.",1012.2224v2
2010-12-10,Defect driven ferroelectricity and magnetism in nanocrystalline KTaO3,"Nominally pure nanocrystalline KTaO3 was thoroughly investigated by
micro-Raman and magnetic resonance spectroscopic techniques. In all samples the
defect driven ferroelectricity and magnetism are registered. Both ordering
states are suggested to appear due to the iron atoms and oxygen vacancies. The
concentration of defects was estimated to be 0.04 and 0.06-0.1 mole %,
respectively. Note that undoped single crystals of KTaO3 are nonmagnetic and
have never exhibited ferromagnetic properties. The results enable us to refer a
nanosized KTa(Fe)O3 to the class of multiferroics and assume that it could
perform the magnetoelectric effect at T<29 K. It was also established that the
critical concentration of impurity defects necessary to provoke the appearance
of the new phase states in the material strongly correlates with the size of
the particle; as the size of the particle decreases, the critical concentration
decreases as well.",1012.2295v1
2010-12-10,The Curie temperature and exchange energy between two sublattices in half-metallic greigite Fe3S4,"High-temperature magnetic measurements have been carried out in
hydrothermally synthesized greigite (Fe3S4). We show that the Curie temperature
of greigite is significantly lower than that for its iron oxide counterpart
Fe3O4. The lower TC value (about 677 K) of greigite is in quantitative
agreement with that calculated using the exchange energy (3.25 meV) and the
spin values of the two sublattices, which are inferred from the neutron and
magnetization data of high-quality pure greigite samples. We further show that,
with an effective on-site Hubbard energy Ueff = 1.16 eV, the lattice constant
and two sublattice spins predicted from ab initio density-function theory are
in nearly perfect agreement with the measured values. The parameter Ueff = 1.16
eV ensures Fe3S4 to be an excellent half-metallic material for spintronic
applications.",1012.2364v1
2010-12-12,Thermal effects on neutrino-nucleus inelastic scattering in stellar environments,"Thermal effects for inelastic neutrino-nucleus scattering off even-even
nuclei in the iron region are studied. Allowed and first-forbidden
contributions to the cross sections are calculated within the quasiparticle
random phase approximation, extended to finite temperatures within the
Thermo-Field-Dynamics formalism. The GT$_0$ strength distribution at finite
temperatures is calculated for the sample nucleus $^{54}$Fe. The
neutral-current neutrino-nucleus inelastic cross section is calculated for
relevant temperatures during the supernova core collapse. The thermal
population of the excited states significantly enhances the cross section at
low neutrino energies. In agreement with studies using a large scale
shell-model approach the enhancement is mainly due to neutrino up-scattering at
finite temperatures.",1012.2543v1
2010-12-13,Distinct electronic nematicities between electron and hole underdoped iron pnictides,"We systematically investigated the in-plane resistivity anisotropy of
electron-underdoped $EuFe_{2-x}Co_xAs_2$ and $BaFe_{2-x}Co_xAs_2$, and
hole-underdoped $Ba_{1-x}K_xFe_2As_2$. Large in-plane resistivity anisotropy
was found in the former samples, while {\it tiny} in-plane resistivity
anisotropy was detected in the latter ones. When it is detected, the anisotropy
starts above the structural transition temperature and increases smoothly
through it. As the temperature is lowered further, the anisotropy takes a
dramatic enhancement through the magnetic transition temperature. We found that
the anisotropy is universally tied to the presence of non-Fermi liquid T-linear
behavior of resistivity. Our results demonstrate that the nematic state is
caused by electronic degrees of freedom, and the microscopic orbital
involvement in magnetically ordered state must be fundamentally different
between the hole and electron doped materials.",1012.2731v1
2010-12-14,A detailed spectroscopic analysis of the open cluster NGC 5460,"Within the context of a large project aimed at studying early F-, A- and late
B-type stars we present the abundance analysis of the photospheres of 21
members of the open cluster NGC 5460, an intermediate age cluster (logt ~ 8.2)
previously unstudied with spectroscopy. Our study is based on medium and high
resolution spectra obtained with the FLAMES instrument of the ESO/VLT. We show
that cluster members have a nearly solar metallicity, and that there is
evidence that the abundances of magnesium and iron are correlated with the
effective temperature, exhibiting a maximum around Teff=10500 K. No
correlations are found between abundances and projected equatorial velocity,
except for marginal evidence of barium being more abundant in slower than in
faster rotating stars. We discovered two He-weak stars, and a binary system
where the hotter component is a HgMn star. We provide new estimates for the
cluster distance (720 +/- 50 pc), age (logt = 8.2 +/- 0.1), and mean radial
velocity (-17.9 +/- 5.2 km/s).",1012.3050v1
2010-12-16,Fabrication and some properties of biaxially aligned Sr0.6K0.4Fe2As2 superconductors by processing in high magnetic field,"We fabricated the c axis and ab-plane biaxially aligned Sr0.6K0.4Fe2As2
superconductor using a two-step magnetic field procedure. The effect of
magnetic fields on the structure and superconducting properties of
Sr0.6K0.4Fe2As2 has been investigated by using X-ray diffraction and magnetic
measurements. The degree of orientation of the samples was about 0.39 for the c
axis and 0.51 for ab-plane orientation, as evaluated from the Lotgering factor
of X-ray diffraction. This technology might be useful in a variety of potential
applications, including preparing iron based superconducting bulks and wires
with high critical currents.",1012.3572v1
2010-12-16,Synthesis and crystal growth of Cs0.8(FeSe0.98)2: a new iron-based superconductor with Tc=27K,"We report on the synthesis of large single crystals of a new FeSe-layer
superconductor Cs0.8(FeSe0.98)2. X-ray powder diffraction, neutron
powder-diffraction and magnetization measurements have been used to compare the
crystal structure and the magnetic properties of Cs0.8(FeSe0.98)2 with those of
the recently discovered potassium intercalated system KxFe2Se2. The new
compound Cs0.8(FeSe0.98)2 shows a slightly lower superconducting transition
temperature (Tc=27.4 K) in comparison to 29.5 in K0.8(FeSe0.98)2). The volume
of the crystal unit cell increases by replacing K by Cs - the c-parameter grows
from 14.1353(13) {\AA} to 15.2846(11) {\AA}. For the so far known alkali metal
intercalated layered compounds (K0.8Fe2Se2 and Cs0.8(FeSe0.98)2) the Tc
dependence on the anion height (distance between Fe-layers and Se-layers) was
found to be analogous to those reported for As-containing Fe-superconductors
and Fe(Se1-xChx), where Ch=Te, S.",1012.3637v1
2010-12-22,Explosive nucleosynthesis in core-collapse supernovae,"The specific mechanism and astrophysical site for the production of half of
the elements heavier than iron via rapid neutron capture (r-process) remains to
be found. In order to reproduce the abundances of the solar system and of the
old halo stars, at least two components are required: the heavy r-process
nuclei (A>130) and the weak r-process which correspond to the lighter heavy
nuclei (A<130). In this work, we present nucleosynthesis studies based on
trajectories of hydrodynamical simulations for core-collapse supernovae and
their subsequent neutrino-driven winds. We show that the weak r-process
elements can be produced in neutrino-driven winds and we relate their
abundances to the neutrino emission from the nascent neutron star. Based on the
latest hydrodynamical simulations, heavy r-process elements cannot be
synthesized in the neutrino-driven winds. However, by artificially increasing
the wind entropy, elements up to A=195 can be made. In this way one can mimic
the general behavior of an ejecta where the r-process occurs. We use this to
study the impact of the nuclear physics input (nuclear masses, neutron capture
cross sections, and beta-delayed neutron emission) and of the long-time
dynamical evolution on the final abundances.",1012.4917v1
2010-12-23,Non-collinear spin-density wave antiferromagnetism in FeAs,"We present the magnetic structure of the itinerant monoarsenide, FeAs, with
the B31 structure. Powder neutron diffraction confirms incommensurate modulated
magnetism with wavevector $\mathbf{q} = (0.395\pm0.001)\mathbf{c}^*$ at 4 K,
but cannot distinguish between a simple spiral and a collinear spin-density
wave structure. Polarized single crystal diffraction confirms that the
structure is best described as a non-collinear spin-density wave arising from a
combination of itinerant and localized behavior with spin amplitude along the
b-axis direction being (15 $\pm$ 5)% larger than in the a-direction.
Furthermore, the propagation vector is temperature dependence, and the
magnetization near the critical point indicates a two-dimensional Heisenberg
system. The nature of the magnetism in the simplest iron arsenide is of
fundamental importance in understanding the interplay between localized and
itinerant magnetism and superconductivity.",1012.5311v2
2010-12-27,Electronic Structure of KFe$_2$Se$_2$ from First Principles Calculations,"Electronic structure and magnetic properties for iron-selenide KFe$_2$Se$_2$
are studied by first-principles calculations. The ground state is stripe-like
antiferromagnetic with calculated 2.26 $\mu_B$ magnetic moment on Fe atoms; and
the $J_1$, $J_2$ coupling strengths are calculated to be 0.038 eV and 0.029 eV.
The states around $E_F$ are dominated by the Fe-3d orbitals which hybridize
noticeably to the Se-4p orbitals. While the band structure of KFe$_2$Se$_2$ is
similar to a heavily electron-doped BaFe$_2$As$_2$ or FeSe system, the Fermi
surface of KFe$_2$Se$_2$ is much closer to \fs11 system since the electron
sheets around $M$ is symmetric with respect to $x$-$y$ exchange. These
features, as well as the absence of Fermi surface nesting, suggest that the
parental KFe$_2$Se$_2$ could be regarded as an electron over-doped 11 system
with possible local moment magnetism.",1012.5621v2
2010-12-29,"Electronic structures and magnetic orders of Fe-vacancies ordered ternary iron selenides TlFe$_{1.5}$Se$_2$ and AFe$_{1.5}$Se$_2$ (A=K, Rb, or Cs)","By the first-principles electronic structure calculations, we find that the
ground state of the Fe-vacancies ordered TlFe$_{1.5}$Se$_2$ is a
quasi-two-dimensional collinear antiferromagnetic semiconductor with an energy
gap of 94 meV, in agreement with experimental measurements. This
antiferromagnetic order is driven by the Se-bridged antiferromagnetic
superexchange interactions between Fe moments. Similarly, we find that crystals
AFe$_{1.5}$Se$_2$ (A=K, Rb, or Cs) are also antiferromagnetic semiconductors
but with a zero-gap semiconducting state or semimetallic state nearly
degenerated with the ground states. Thus rich physical properties and phase
diagrams are expected.",1012.6015v2
2011-01-10,Monopolelike probes for quantitative magnetic force microscopy: calibration and application,"A local magnetization measurement was performed with a Magnetic Force
Microscope (MFM) to determine magnetization in domains of an exchange coupled
[Co/Pt]/Co/Ru multilayer with predominant perpendicular anisotropy. The
quantitative MFM measurements were conducted with an iron filled carbon
nanotube tip, which is shown to behave like a monopole. As a result we
determined an additional in-plane magnetization component of the multilayer,
which is explained by estimating the effective permeability of the sample
within the \mu*-method.",1101.1804v1
2011-01-10,Latest results from the Pierre Auger Observatory,"Recent results obtained with the Pierre Auger Observatory are described.
These include measurements of the spectrum, anisotropies and composition of
ultra-high energy cosmic rays. The ankle of the spectrum is measured at
$4\times 10^{18}$~eV and a suppression above $3\times 10^{19}$~eV consistent
with the GZK effect is observed. At energies above $5.5\times 10^{19}$~eV a
correlation with the distribution of nearby extragalactic objects is found,
including an excess around the direction of Centaurus~A, the nearest radio loud
active galaxy. Measurements of the depth of shower maximum and its fluctuations
suggest a gradual change in the average mass of the primary cosmic rays (under
standard extrapolations of hadronic interaction models), being the results
consistent with a light composition consisting mostly of protons at few$\times
10^{18}$~eV and approaching the expectations from iron nuclei at $4\times
10^{19}$~eV. Upper bounds on the photon fraction and the neutrino fluxes are
also obtained.",1101.1825v1
2011-01-10,Coexistence of Magnetism and Superconductivity in the Iron-based Compound Cs_0.8(FeSe_0.98)_2,"We report on muon-spin rotation/relaxation (\muSR), electrical resistivity,
magnetization and differential scanning calorimetry measurements performed on a
high-quality single crystal of Cs_0.8(FeSe_0.98)_2. Whereas our transport and
magnetization data confirm the bulk character of the superconducting state
below T_c = 28.5(2)K, the \muSR data indicate that the system is {\it magnetic}
below T_N = 478.5(3)K, where a first-order transition occurs. The first-order
character of the magnetic transition is confirmed by differential scanning
calorimetry data. Taken all together, these data indicate in
Cs_0.8(FeSe_0.98)_2 a microscopic coexistence between the superconducting phase
and a strong magnetic phase. The observed ratio between T_N and T_c is the
highest one reported to date for a magnetic superconductor.",1101.1873v3
2011-01-12,[O/Fe] Estimates for Carbon-Enhanced Metal-Poor Stars from Near-IR Spectroscopy,"We report on oxygen abundances determined from medium-resolution near-IR
spectroscopy for a sample of 57 carbon-enhanced metal-poor (CEMP) stars
selected from the Hamburg/ESO survey. The majority of our program stars exhibit
oxygen-to-iron ratios in the range +0.5 < [O/Fe]< +2.0. The [O/Fe] values for
this sample are statistically compared to available high-resolution estimates
for known CEMP stars, as well as to high-resolution estimates for a set of
carbon-normal metal-poor stars. Carbon, nitrogen, and oxygen abundance patterns
for a sub-sample of these stars are compared to yield predictions for very
metal-poor asymptotic giant-branch abundances in the recent literature. We find
that the majority of our sample exhibit patterns that are consistent with
previously studied CEMP stars having s-process-element enhancements, and thus
have very likely been polluted by carbon- and oxygen-enhanced material
transferred from a metal-poor asymptotic giant-branch companion.",1101.2260v1
2011-01-21,A biotic cosmos demystified?,"Oceanic planets formed by type Ia supernovae become spectacularly abundant as
stars cease to shine. However, the timing may not be altogether inappropriate.
Neutrino annihilation might thermally regulate iron-cored water-worlds,
sustaining habitable subglacial oceans. If dark matter and dark energy decay to
neutrinos, the universe could support life for ~ 10^23 years. Civilisations
surmounting the arduous process of hereditary genetics soon discern the biotic
nature of the cosmos and accept their role within it. An infrastructure guards
against the spread of rogue colonists. Recruited colonists could harness the
available energy for the benefit of life with stupendous efficiency, providing
unmistakeable evidence of cosmological optimisation. The anthropic
coincidences, inhospitable aspects of the current universe and Fermi's paradox
would all be illuminated. Semiconductors sensitive to a neutrinoelectric effect
offer a laboratory test of the planetary heating mechanism.",1101.4172v3
2011-01-26,A Near-Infrared Search for Silicates in Jovian Trojan Asteroids,"We obtained near-infrared (0.8 - 2.5 micron) spectra of seven Jovian Trojan
asteroids that have been formerly reported to show silicate-like absorption
features near 1 micron. Our sample includes the Trojan (1172) Aneas, which is
one of three Trojans known to possess a comet-like 10 micron emission feature,
indicative of fine-grained silicates. Our observations show that all seven
Trojans appear featureless in high signal-to-noise ratio spectra. The
simultaneous absence of the 1 micron band and presence of the 10 micron
emission can be understood if the silicates on (1172) Aneas are iron-poor.
  In addition, we present near infrared observations of five optically grey
Trojans, including three objects from the collisionally produced Eurybates
family. The five grey Trojans appear featureless in the near infrared with no
diagnostic absorption features. The near infrared spectrum of Eurybates can be
best fitted with the spectrum of a CM2 carbonaceous chondrite, which hints that
the C-type Eurybates family members may have experienced aqueous alteration.",1101.5167v1
2011-01-30,Controlling electrostatic co-assembly using ion-containing copolymers : from surfactants to nanoparticles,"In this review, we address the issue of the electrostatic complexation
between charged-neutral diblock copolymers and oppositely charged nanocolloids.
We show that nanocolloids such as surfactant micelles and iron oxide magnetic
nanoparticles share similar properties when mixed with charged-neutral
diblocks. Above a critical charge ratio, core-shell hierarchical structures
form spontaneously under direct mixing conditions. The core-shell structures
are identified by a combination of small-angle scattering techniques and
transmission electron microscopy. The formation of multi-level objects is
driven by the electrostatic attraction between opposite charges and by the
release of the condensed counterions. Alternative mixing processes inspired
from molecular biology are also described. The protocols applied here consist
in screening the electrostatic interactions of the mixed dispersions, and then
removing the salt progressively as example by dialysis. With these techniques,
the oppositely charged species are intimately mixed before they can interact,
and their association is monitored by the desalting kinetics. As a result,
sphere- and rod-like aggregates with remarkable superparamagnetic and stability
properties are obtained. These findings are discussed in the light of a new
paradigm which deals with the possibility to use inorganic nanoparticles as
building blocks for the design and fabrication of supracolloidal assemblies
with enhanced functionalities.",1101.5821v1
2011-01-31,Template assisted self-assembly of individual and clusters of magnetic nanoparticles,"The deliberate control over the spatial arrangement of nanostructures is the
desired goal for many applications as e.g. in data storage, plasmonics or
sensor arrays. Here we present a novel method to assist the self-assembly
process of magnetic nanoparticles. The method makes use of nanostructured
aluminum templates obtained after anodization of aluminum disks and the
subsequent growth and removal of the newly formed alumina layer, resulting in a
regular honeycomb type array of hexagonally shaped valleys. The iron oxide
nanoparticles, 20 nm in diameter, are spin coated onto the nanostructured
templates. Depending on the size, each hexagon site can host up to 30
nanoparticles. These nanoparticles form clusters of different arrangements
within the valleys, such as collars, chains, and hexagonally closed islands.
Ultimately, it is possible to isolate individual nanoparticles. The strengths
of magnetic interaction between particles in a cluster is probed using the
memory effect known from the coupled state in superspin glass systems.",1101.5899v1
2011-01-31,Metastable $π$-junction between an s$_\pm$-wave and an s-wave superconductor,"We examine a contact between a superconductor whose order parameter changes
sign across the Brillioun zone, and an ordinary, uniform-sign superconductor.
Within a Ginzburg-Landau type model, we find that if the the barrier between
the two superconductors is not too high, the frustration of the Josephson
coupling between different portions of the Fermi surface across the contact can
lead to surprising consequences. These include time-reversal symmetry breaking
at the interface and unusual energy-phase relations with multiple local minima.
We propose this mechanism as a possible explanation for the half-integer flux
quantum transitions in composite niobium--iron pnictide superconducting loops,
which were discovered in a recent experiment [Chen et al., Nature Phys.
\textbf{6},260 (2010)].",1102.0042v3
2011-02-01,Ab initio study of the modification of elastic properties of alpha-iron by hydrostatic strain and by hydrogen interstitials,"The effect of hydrostatic strain and of interstitial hydrogen on the elastic
properties of $\alpha$-iron is investigated using \textit{ab initio}
density-functional theory calculations. We find that the cubic elastic
constants and the polycrystalline elastic moduli to a good approximation
decrease linearly with increasing hydrogen concentration. This net strength
reduction can be partitioned into a strengthening electronic effect which is
overcome by a softening volumetric effect. The calculated hydrogen-dependent
elastic constants are used to determine the polycrystalline elastic moduli and
anisotropic elastic shear moduli. For the key slip planes in $\alpha$-iron,
$[1\bar{1}0]$ and $[11\bar{2}]$, we find a shear modulus reduction of
approximately 1.6% per at.% H.",1102.0187v1
2011-02-02,Hall effect of FeTe and Fe(Se_1-x_Te_x_) thin films,"The Hall effect is investigated in thin-film samples of iron-chalcogenide
superconductors in detail. The Hall coefficient (RH) of FeTe and Fe(Se1-xTex)
exhibits a similar positive value around 300 K, indicating that the
high-temperature normal state is dominated by hole-channel transport. FeTe
exhibits a sign reversal from positive to negative across the transition to the
low-temperature antiferromagnetic state, indicating the occurrence of drastic
reconstruction in the band structure. The mobility analysis using the carrier
density theoretically calculated reveals that the mobility of holes is strongly
suppressed to zero, and hence the electric transport looks to be dominated by
electrons. The Se substitution to Te suppresses the antiferromagnetic
long-range order and induces superconductivity instead. The similar mobility
analysis for Fe(Se0.4Te0.6) and Fe(Se0.5Te0.5) thin films shows that the
mobility of electrons increases with decreasing temperature even in the
paramagnetic state, and keeps sufficiently high values down to the
superconducting transition temperature. From the comparison between FeTe and
Fe(Se1-xTex), it is suggested that the coexistence of 'itinerant' carriers both
in electron and hole channels is indispensable for the occurrence of
superconductivity.",1102.0332v1
2011-02-07,Nanoscale phase separation of antiferromagnetic order and superconductivity in K$_{0.75}$Fe$_{1.75}$Se$_2$,"We report an in-plane optical spectroscopy study on the iron-selenide
superconductor K$_{0.75}$Fe$_{1.75}$Se$_2$. The measurement revealed the
development of a sharp reflectance edge below T$_c$ at frequency much smaller
than the superconducting energy gap on a relatively incoherent electronic
background, a phenomenon which was not seen in any other Fe-based
superconductors so far investigated. Furthermore, the feature could be
noticeably suppressed and shifted to lower frequency by a moderate magnetic
field. Our analysis indicates that this edge structure arises from the
development of a Josephson-coupling plasmon in the superconducting condensate.
Together with the transmission electron microscopy analysis, our study yields
compelling evidence for the presence of nanoscale phase separation between
superconductivity and magnetism. The results also enable us to understand
various seemingly controversial experimental data probed from different
techniques.",1102.1381v4
2011-02-08,Neutron Repulsion,"Earth is connected gravitationally, magnetically and electrically to its heat
source - a neutron star that is obscured from view by waste products in the
photosphere. Neutron repulsion is like the hot filament in an incandescent
light bulb. Excited neutrons are emitted from the solar core and decay into
hydrogen that glows in the photosphere like a frosted light bulb. Neutron
repulsion was recognized in nuclear rest mass data in 2000 as the overlooked
source of energy, the keystone of an arch that locked together these puzzling
space-age observations: 1.) Excess 136Xe accompanied primordial helium in the
stellar debris that formed the solar system (Fig. 1); 2.) The Sun formed on the
supernova core (Fig. 2); 3.) Waste products from the core pass through an
iron-rich mantle, selectively carrying lighter elements and lighter isotopes of
each element into the photosphere (Figs. 3-4); and 4.) Neutron repulsion powers
the Sun and sustains life (Figs. 5-7). Together these findings offer a
framework for understanding how: a.) The Sun generates and releases neutrinos,
energy and solar-wind hydrogen and helium; b.) An inhabitable planet formed and
life evolved around an ordinary-looking star; c.) Continuous climate change -
induced by cyclic changes in gravitational interactions of the Sun's energetic
core with planets - has favored survival by adaptation.",1102.1499v1
2011-02-09,Quasiparticle interference in antiferromagnetic parent compounds of Fe-based superconductors,"Recently reported quasiparticle interference imaging in underdoped
Ca(Fe{1-x}Co{x})_2As{2} shows pronounced C{2} asymmetry that is interpreted as
an indication of an electronic nematic phase with a unidirectional electron
band, dispersive predominantly along the $b$-axis of this orthorhombic
material. On the other hand, even more recent transport measurements on
untwinned samples show near isotropy of the resistivity in the $ab$ plane, with
slightly larger conductivity along a (and not b). We show that in fact both
sets of data are consistent with the calculated ab initio Fermi surfaces, which
has a decisively broken C_{4}, and yet similar Fermi velocity in both
directions. This reconciles completely the apparent contradiction between the
conclusions of the STM and the transport experiments.",1102.1930v1
2011-02-11,Towards an ideal graphene-based spin-filter,"The Fe$_3$O$_4$(111)/graphene/Ni(111) trilayer is proposed to be used as an
ideal spin-filtering sandwich where the half-metallic properties of magnetite
are used. Thin magnetite layers on graphene/Ni(111) were prepared via
successive oxidation of thin iron layer predeposited on graphene/Ni(111) and
formed system was investigated by means of low-energy electron diffraction
(LEED) and photoelectron spectroscopy (PES) of core levels as well as valence
band. The electronic structure and structural quality of the graphene film
sandwiched between two ferromagnetic layers remains unchanged upon magnetite
formation as confirmed by LEED and PES data.",1102.2367v1
2011-02-11,Pressure cycle of superconducting Cs0.8Fe2Se2: a transport study,"We report measurements of the temperature and pressure dependence of the
electrical resistivity of single crystalline iron-based chalcogenide
Cs0.8Fe2Se2. In this material superconductivity Tc~30K develops from a normal
state with extremely large resistivity. At ambient pressure a large ""hump"" in
the resistivity is observed around 200K. Under pressure, the resistivity
decreases by two orders of magnitude, concomitant with a sudden Tc suppression
around p~8GPa. Even at 9GPa a metallic resistivity state is not recovered, and
the {\rho}(T) ""hump"" is still detected. A comparison of the data measured upon
increasing and decreasing the external pressure leads us to suggest that
superconductivity is not related to this hump.",1102.2464v2
2011-02-14,Common Crystalline and Magnetic Structure of superconducting A2Fe4Se5,"Single crystal neutron diffraction study has been performed on new
superconductor A2Fe4Se5, where A = Cs, K, (Tl,Rb) and (Tl,K), and the same Fe
vacancy ordered crystal structure and the same block checkerboard
antiferromagne tic order recently discovered in the K2Fe4Se5 superconductor are
observed. Thus, all known alkali metal and/or Tl intercalated iron selenide
superconductors share common crystalline and magnetic structure. Investigation
on electronic process in these new superconductors, for which a different
electronic structure from those in previous Fe-based high-Tc superconductors is
emerging, now has a valid structural and magnetic framework.",1102.2882v2
2011-02-16,Elastic properties and inter-atomic bonding in new superconductor KFe2Se2 from first principles calculations,"Very recently (November, 2010, PRB, 82, 180520R) the first 122-like ternary
superconductor KxFe2Se2 with enhanced TC ~ 31K has been discovered. This
finding has stimulated much activity in search of related materials and
triggered the intense studies of their properties. Indeed already in 2010-2011
the superconductivity (TC ~ 27-33K) was also found in the series of new
synthesized 122 phases such as CsxFe2Se2, RbxFe2Se2, (TlK)xFeySe2 etc. which
have formed today the new family of superconducting iron-based materials
without toxic As. Here, using the ab initio FLAPW-GGA method we have predicted
for the first time the elastic properties for KFe2Se2 and discussed their
interplay with inter-atomic bonding for this system. Our data reveal that the
examined phase is relatively soft material. In addition, this system is
mechanically stable, adopts considerable elastic anisotropy, and demonstrates
brittleness. These conclusions agree with the bonding picture for KFe2Se2,
where the inter-atomic bonding is highly anisotropic and includes ionic,
covalent and metallic contributions.",1102.3248v1
2011-02-17,"Anomalous optical phonons in FeTe pnictides: spin state, magnetic order, and lattice anharmonicity","Polarized Raman-scattering spectra of non-superconducting, single-crystalline
FeTe are investigated as function of temperature. We have found a relation
between the magnitude of ordered magnetic moments and the linewidth of A1g
phonons at low temperatures. This relation is attributed to the intermediate
spin state (S=1) and the orbital degeneracy of the Fe ions. Spin-phonon
coupling constants have been estimated based on microscopic modeling using
density-functional theory and analysis of the local spin density. Our
observations show the importance of orbital degrees of freedom for the Fe-based
superconductors with large ordered magnetic moments, while small magnetic
moment of Fe ions in some iron pnictides reflects the low spin state of Fe ions
in those systems.",1102.3688v1
2011-02-23,Absence of Tunneling Character in c-axis Transport of SmFeAsO0.85 Single Crystals,"We made electrical transport measurements along the c-axis of SmFeAsO0.85
single crystals, in both three- and four-terminal configurations, focusing on
examining the possible formation of Josephson coupling between FeAs
superconducting layers. Anisotropic bulk superconductivity was observed along
the c-axis, but without Josephson coupling, as confirmed by the absence of both
the hysteresis in current-voltage curves and the modulation of the critical
current by the in-plane magnetic fields. The variation of the critical currents
for different magnetic-field directions gives the anisotropy ratio of 5. This
three-dimensional electronic structure of our iron pnictide superconductors is
in clear contrast to the two-dimensional one observed in the cuprate
superconductors, another stacked superconducting system.",1102.4645v1
2011-02-23,On the nature of spectral line broadening in solar coronal dimmings,"We analyze the profiles of iron emission lines observed in solar coronal
dimmings associated with coronal mass ejections, using the EUV Imaging
Spectrometer on board Hinode. We quantify line profile distortions with
empirical coefficients (asymmetry and peakedness) that compare the fitted
Gaussian to the data. We find that the apparent line broadenings reported in
previous studies are likely to be caused by inhomogeneities of flow velocities
along the line of sight, or at scales smaller than the resolution scale, or by
velocity fluctuations during the exposure time. The increase in the amplitude
of Alfv\'en waves cannot, alone, explain the observed features. A
double-Gaussian fit of the line profiles shows that, both for dimmings and
active region loops, one component is nearly at rest while the second component
presents a larger Doppler shift than that derived from a single-Gaussian fit.",1102.4745v1
2011-02-24,Angle-resolved photoemission spectroscopy study of PrFeAsO_{0.7}: Dependence of the electronic structure on the pnictogen height,"We have performed an angle-resolved photoemission spectroscopy (ARPES) study
of the iron-based superconductor PrFeAsO_{0.7} and examined the Fermi surfaces
and band dispersions near the Fermi level. Heavily hole-doped electronic states
have been observed due to the polar nature of the cleaved surfaces.
Nevertheless, we have found that the ARPES spectra basically agree with band
dispersions calculated in the local density approximation (LDA) if the
bandwidth is reduced by a factor of ~2.5 and then the chemical potential is
lowered by ~70 meV. Comparison with previous ARPES results on LaFePO reveals
that the energy positions of the d_{3z^2-r^2}- and d_{yz,zx}-derived bands are
considerably different between the two materials, which we attribute to the
different pnictogen height as predicted by the LDA calculation.",1102.4907v1
2011-02-25,Thermal evolution of Pt-rich FePt/Fe3O4 heterodimers studied using x-ray absorption near edge spectroscopy,"FePt/Fe3O4 nanoparticles can be used as building blocks to obtain, upon
thermal annealing, magnetic nanocomposites with combined magnetic properties.
Although the pre- and post-annealed samples are usually well characterized, a
detailed investigation during annealing is necessary to reveal the role of
intermediate processes to produce a desirable composite. We present an
alternative method using in situ XANES to investigate the thermal evolution of
oleic acid and oleylamine coated Pt-rich FePt/Fe3O4 heterodimers. As the
temperature increases, a progressive reduction of Fe3O4 to FeO occurs helped by
the thermolysis of the surfactants; while above 550 K Fe3Pt starts to be
formed. At 840 K an abrupt increase of FeO further drives the phase
transformation to stabilize the iron platinum soft phase. Thus, the Fe3O4
reduction acts as catalyst that promotes the Fe and Pt interdiffusion between
the Pt-rich FePt and Fe3O4/FeO to form Fe3Pt instead of exchange coupled
FePt/Fe3O4 with hard magnetic properties. In addition, the role of the
interface of the heterodimer ends is discussed. The pre- and post-annealed
samples were also characterized by TEM, XRD, EXAFS, magnetometry and
M\""ossbauer spectroscopy.",1102.5321v1
2011-03-01,Time-Reversal-Symmetry-Broken Superconductivity Induced by Frustrated Inter-Component Couplings,"Superconductivity is associated with spontaneously broken gauge symmetry. In
some exotic superconductors the time-reversal symmetry is broken as well,
accompanied with internal magnetic field. A time-reversal symmetry broken
(TRSB) superconductivity without internal magnetic field involved can be
induced by frustrated inter-component couplings, which becomes a realistic
issue recently due to the discovery of iron-pnictide superconductors. Here we
derive stability condition for this novel TRSB state using the Ginzburg-Landau
(GL) theory. We find that there are multiple divergent coherence lengths, and
that this novel superconductivity cannot be categorized by the GL number into
type I or type II. We reveal that the critical Josephson current of a
constriction junction between two bulk superconductors of different chiralities
is suppressed significantly from that for same chirality. This effect provides
a unique way to verify experimentally this brand new superconductivity.",1103.0123v2
2011-03-02,Fresnel aperture diffraction: a phase-sensitive probe for superconducting pairing symmetry,"Fresnel single aperture diffraction (FSAD) is proposed as a phase-sensitive
probe for pairing symmetry and Fermi surface of a superconductor. We consider
electrons injected, through a small aperture, into a thin superconducting (SC)
layer. It is shown that in case of SC gap symmetry
$\Delta(-k_x,\mathbf{k}_\parallel)=\Delta(k_x,\mathbf{k}_\parallel)$ with $k_x$
and $\mathbf{k}_\parallel$ respectively the normal and parallel component of
electron Fermi wavevector, quasiparticle FSAD pattern developed at the image
plane is zeroth-order minimum if $k_x x=n\pi$ ($n$ is an integer and $x$ is SC
layer thickness). In contrast, if
$\Delta(-k_x,\mathbf{k}_\parallel)=-\Delta(k_x, \mathbf{k}_\parallel)$, the
corresponding FSAD pattern is zeroth-order maximum. Observable consequences are
discussed for iron-based superconductors of complex multi-band pairings.",1103.0424v1
2011-03-04,Nodal gap structure of BaFe_2(As_{1-x}P_x)_2 from angle-resolved thermal conductivity in a magnetic field,"The structure of the superconducting order parameter in the iron-pnictide
superconductor BaFe$_2$(As$_{0.67}$P$_{0.33}$)$_2$ ($T_c=31$\,K) with line
nodes is studied by the angle-resolved thermal conductivity measurements in a
magnetic field rotated within the basal plane. We find that the thermal
conductivity displays distinct fourfold oscillations with minima when the field
is directed at $\pm45^\circ$ with respect to the tetragonal a-axis. We discuss
possible gap structures that can account for the data, and conclude that the
observed results are most consistent with the closed nodal loops located at the
flat parts of the electron Fermi surface with high Fermi velocity.",1103.0885v2
2011-03-06,"Basic design and engineering of normal-conducting, iron-dominated electromagnets","The intention of this course is to provide guidance and tools necessary to
carry out an analytical design of a simple accelerator magnet. Basic concepts
and magnet types will be explained as well as important aspects which should be
considered before starting the actual design phase. The central part of this
course is dedicated to describing how to develop a basic magnet design.
Subjects like the layout of the magnetic circuit, the excitation coils, and the
cooling circuits will be discussed. A short introduction to materials for the
yoke and coil construction and a brief summary about cost estimates for magnets
will complete this topic.",1103.1119v1
2011-03-07,Stable magnetostructural coupling with tunable magnetoresponsive effects in hexagonal phase-transition ferromagnets,"The magnetostructural coupling between the structural and the magnetic
transition plays a crucial role in magnetoresponsive effects in a
martensitic-transition system. A combination of various magnetoresponsive
effects based on this coupling may facilitate the multifunctional applications
of a host material. Here, we demonstrate a possibility to obtain a stable
magnetostructural coupling in a broad temperature window from 350 to 70 K,
showing tunable magnetoresponsive effects, based on simultaneous manipulation
of the phase stability and the magnetic structure by suitable chemical
substitution of iron in MnNiGe. The resultant MnNiGe:Fe exhibits a
magnetic-field-induced martensitic transition from paramagnetic austenite to
ferromagnetic martensite, featuring (i) a large volume increase, (ii) a
distinct magnetization change, (iii) small thermal hysteresis and (iv) a giant
negative magnetocaloric effect. The results indicate that stable
magnetostructural coupling is accessible in hexagonal phase-transition systems
to attain the magnetoresponsive effects with broad tunability.",1103.1313v2
2011-03-12,Varying Eu$^{2+}$ magnetic order in EuFe$_2$As$_2$ by chemical pressure,"Among iron 122 pnictide superconductors, the EuFe$_2$As$_2$ series draws
particular interest because, in addition to superconductivity or the long-range
spin-density-wave order in the Fe subsystem, the localized Eu$^{2+}$ magnetic
moments order at low temperatures. Here we present a novel scheme of how the
spins align in the Eu compounds when pressure varies the coupling; we explain
magnetization measurements on EuFe$_2$(As$_{1-x}$P$_x$)$_2$ single crystals as
well as other observations of the Eu$^{2+}$ ordering previously reported in
literature. The magnetic moments of the Eu$^{2+}$ ions are slightly canted even
in the parent compound EuFe$_2$As$_2$, yielding a ferromagnetic contribution
along the $c$-direction that becomes stronger with pressure. Reducing the
interlayer distance even further, the antiferromagnetic coupling of the $ab$
planes finally turns ferromagnetic.",1103.2446v1
2011-03-15,Oxygen hyperstoichiometric hexagonal ferrite CaBaFe4O7+δ(δ \approx 0.14) : coexistence of ferrimagnetism and spin glass behavior,"An oxygen hyperstoichiometric ferrite CaBaFe4O7+\delta (\delta \approx 0.14)
has been synthesized using ""soft"" reduction of CaBaFe4O8. Like the oxygen
stoichiometric ferrimagnet CaBaFe4O7, this oxide also keeps the hexagonal
symmetry (space group: P63mc), and exhibits the same high Curie temperature of
270 K. However, the introduction of extra oxygen into the system weakens the
ferrimagnetic interaction significantly at the cost of increased magnetic
frustration at low temperature. Moreover, this canonical spin glass (Tg ~ 166
K) exhibits an intriguing cross-over from de Almeida-Thouless type to
Gabay-Toulouse type critical line in the field temperature plane above a
certain field strength, which can be identified as the anisotropy field. Domain
wall pinning is also observed below 110 K. These results are interpreted on the
basis of cationic disordering on the iron sites.",1103.2939v1
2011-03-15,Calorimetric Evidence of Strong-Coupling Multiband Superconductivity in Fe(Te0.57Se0.43) Single Crystal,"We have investigated the specific heat of optimally-doped iron chalcogenide
superconductor Fe(Te0.57Se0.43) with a high-quality single crystal sample. The
electronic specific heat Ce of this sample has been successfully separated from
the phonon contribution using the specific heat of a non-superconducting sample
(Fe0.90Cu0.10)(Te0.57Se0.43) as a reference. The normal state Sommerfeld
coefficient gamma_n of the superconducting sample is found to be ~ 26.6 mJ/mol
K^2, indicating intermediate electronic correlation. The temperature dependence
of Ce in the superconducting state can be best fitted using a double-gap model
with 2Delta_s(0)/kBTc = 3.92 and 2Delta_l(0)/kBTc = 5.84. The large gap
magnitudes derived from fitting, as well as the large specific heat jump of
Delta_Ce(Tc)/gamma_n*Tc ~ 2.11, indicate strong-coupling superconductivity.
Furthermore, the magnetic field dependence of specific heat shows strong
evidence for multiband superconductivity.",1103.2961v1
2011-03-16,"Point-contact study of ReFeAs(1-x)Fx (Re=La, Sm) superconducting films","Point-contact (PC) Andreev-reflection (AR) measurements of the
superconducting gap in iron-oxipnictide ReFeAsO_{1-x}F_x (Re=La, Sm) films have
been carried out. The value of the gap is distributed in the range 2\Delta
\simeq 5-10 meV (for Re=Sm) with a maximum in the distribution around 6 meV.
Temperature dependence of the gap \Delta(T) can be fitted well by BCS curve
giving reduced gap ratio 2\Delta /kT_c^*\simeq 3.5 (here T_c^* is the critical
temperature from the BCS fit). At the same time, an expected second larger gap
feature was difficult to resolve distinctly on the AR spectra making
determination reliability of the second gap detection questionable. Possible
reasons for this and the origin of other features like clear-cut asymmetry in
the AR spectra and current regime in PCs are discussed.",1103.3157v1
2011-03-18,Composition of Transiting and Transiting-only super-Earths,"The relatively recent detections of the first three transiting super-Earths
mark the beginning of a subfield within exoplanets that is both fruitful and
challenging. The first step into characterizing these objects is to infer their
composition given the degenerate character of the problem. The calculations
show that Kepler-10b has a composition between an Earth-like and a Mercury-like
(enriched in iron) composition. In contrast, GJ 1214b is too large to be solid,
and has to have a volatile envelope. Lastly, while three of the four reported
mass estimates of CoRoT-7b allow for a rocky composition, one forbids it and
can only be reconciled with significant amounts of water vapor. In addition to
these three transiting low-mass planets, there are now more than one thousand
Kepler planets with only measured radius. Even without a mass measurement
(""transiting-only"") it is still possible to place constraints on the amount of
volatile content of the highly-irradiated planets, as their envelopes, if
present, are flared. Using Kepler-9d as an example, we estimate its water
vapor, or hydrogen and helium content to be less than 50% or 0.1% by mass
respectively.",1103.3725v1
2011-03-25,"A temporal study of oxygen-rich pulsating variable AGB star, T Cep: Investigation on dust formation and dust properties","Pulsation is believed to be the leading cause of dusty mass loss from
Asymptotic Giant Branch (AGB) stars. We present a temporal study of T Cep, a
long-period Mira variable, using seven ISO SWS spectra, covering a 16-month
period over a single pulsation cycle. The observed spectral dust features
change over the pulsation cycle of this Mira. In general, the overall apparent
changes in spectral features can be attributed to changes in the dust
temperature, resulting from the intrinsic pulsation cycle of the central star.
However, not all feature changes are so easily explained. Based on direct
comparison with laboratory spectra of several potential minerals, the dust is
best explained by crystalline iron-rich silicates. These findings contradict
the currently favored dust formation hypotheses.",1103.5040v1
2011-03-27,Spin-filtering and Disorder Induced Giant Magnetoresistance in Carbon Nanotubes: Ab Initio Calculations,"Nitrogen-doped carbon nanotubes can provide reactive sites on the
porphyrin-like defects. It's well known that many porphyrins have transition
metal atoms, and we have explored transition metal atoms bonded to those
porphyrin-like defects in N-doped carbon nanotubes. The electronic structure
and transport are analyzed by means of a combination of density functional
theory and recursive Green's functions methods. The results determined the Heme
B-like defect (an iron atom bonded to four nitrogens) as the most stable and
with a higher polarization current for a single defect. With randomly
positioned Heme B-defects in a few hundred nanometers long nanotubes the
polarization reaches near 100% meaning an effective spin filter. A disorder
induced magnetoresistance effect is also observed in those long nanotubes,
values as high as 20000% are calculated with non-magnectic eletrodes.",1103.5177v2
2011-03-30,Biaxially textured cobalt-doped BaFe2As2 films with high critical current density over 1 MA/cm2 on MgO-buffered metal-tape flexible substrates,"High critical current densities (Jc) > 1 MA/cm2 were realized in cobalt-doped
BaFe2As2 (BaFe2As2:Co) films on flexible metal substrates with
biaxially-textured MgO base-layers fabricated by an ion-beam assisted
deposition technique. The BaFe2As2:Co films showed small in-plane crystalline
misorientations (delta fai BaFe2As2:Co) of ~3o regardless of doubly larger
misorientaions of the MgO base-layers (delta fai MgO = 7.3o), and exhibited
high self-field Jc up to 3.5 MA/cm2 at 2 K. These values are comparable to that
on MgO single crystals and the highest Jc among iron pnictide superconducting
tapes and wires ever reported. High in-field Jc suggests the existence of
c-axis correlated vortex pinning centers.",1103.5815v2
2011-04-04,Epitaxial growth of FeSe$_{0.5}$Te$_{0.5}$ thin films on CaF$_2$ substrates with high critical current density,"In-situ epitaxial growth of FeSe$_{0.5}$Te$_{0.5}$ thin films is demonstrated
on a non-oxide substrate CaF$_2$. Structural analysis reveals that compressive
stress is moderately added to 36-nm thick FeSe$_{0.5}$Te$_{0.5}$, which pushes
up the critical temperature above 15 K, showing higher values than that of bulk
crystals. Critical current density at $T$ = 4.5 K reaches 5.9 x 10$^4$
Acm$^{-2}$ at $\mu_0H$ = 10 T, and 4.2 x 10$^4$ Acm$^{-2}$ at $\mu_0H$ = 14 T.
These results indicate that fluoride substrates have high potential for the
growth of iron-based superconductors in comparison with popular oxide
substrates.",1104.0477v2
2011-04-04,The NLTE Barium Abundance in Dwarf Stars in the Metallicity Range of -1 < [Fe/H] < +0.3,"We present the results of determination of the barium abundance considering
the non-LTE (NLTE) effects in 172 dwarf stars in the metallicity range of -1<
[Fe/H] <+0.3, assigned to different Galactic substructures by kinematic
criteria. We used a model of the Ba atom with 31 levels of Ba I and 101 levels
of Ba II. The atmosphere models for the investigated stars were computed using
the ATLAS9 code modified by new opacity distribution functions. The NLTE
profiles of the unblended Ba II (4554 A, 5853 A, 6496 A) were computed and then
compared to those observed. The line 6141 A was also used, but with an
allowance for its correlation with the iron line. The average barium abundances
in the thin and thick discs are 0.01 +/- 0.08 and -0.03 +/- 0.07, respectively.
The comparison to the calculations of the Galactic chemical evolution by
Serminato et al. (2009) was conducted. The trend obtained for the Ba abundance
versus [Fe/H] suggests a complex barium production process in the thin and
thick discs.",1104.0534v1
2011-04-05,Incommensurate spin-density wave order in electron-doped BaFe2As2 superconductors,"Neutron diffraction studies of Ba(Fe[1-x]Co[x])2As2 reveal that commensurate
antiferromagnetic order gives way to incommensurate magnetic order for Co
compositions between 0.056 < x < 0.06. The incommensurability has the form of a
small transverse splitting (0, +-e, 0) from the nominal commensurate
antiferromagnetic propagation vector Q[AFM] = (1, 0, 1) (in orthorhombic
notation) where e = 0.02-0.03 and is composition dependent. The results are
consistent with the formation of a spin-density wave driven by Fermi surface
nesting of electron and hole pockets and confirm the itinerant nature of
magnetism in the iron arsenide superconductors.",1104.0717v1
2011-04-08,Magnetic nanocomposites at microwave frequencies,"Most conventional magnetic materials used in the electronic devices are
ferrites, which are composed of micrometer-size grains. But ferrites have small
saturation magnetization, therefore the performance at GHz frequencies is
rather poor. That is why functionalized nanocomposites comprising magnetic
nanoparticles (e.g. Fe, Co) with dimensions ranging from a few nm to 100 nm,
and embedded in dielectric matrices (e.g. silicon oxide, aluminium oxide) have
a significant potential for the electronics industry. When the size of the
nanoparticles is smaller than the critical size for multidomain formation,
these nanocomposites can be regarded as an ensemble of particles in
single-domain states and the losses (due for example to eddy currents) are
expected to be relatively small. Here we review the theory of magnetism in such
materials, and we present a novel measurement method used for the
characterization of the electromagnetic properties of composites with
nanomagnetic insertions. We also present a few experimental results obtained on
composites consisting of iron nanoparticles in a dielectric matrix.",1104.1535v1
2011-04-11,Collinear to Anti-collinear Quantum Phase Transition by Vacancies,"We study static vacancies in the collinear magnetic phase of a frustrated
Heisenberg $J_1$-$J_2$ model. It is found that vacancies can rapidly suppress
the collinear antiferromagnetic state (CAFM)and generate a new magnetic phase,
an anti-collinear magnetic phase (A-CAFM), due to magnetic frustration. We
investigate the quantum phase transition between these two states by studying a
variety of vacancy superlattices. We argue that the anti-collinear magnetic
phase can exist in iron-based superconductors in the absence of any preceding
structural transitions and an observation of this novel phase will
unambiguously resolve the relation between the magnetic and structural
transitions in these materials.",1104.1848v2
2011-04-12,"Reply to ""Comment on 'Isotope effect in multi-band and multi-channel attractive systems and inverse isotope effect in iron-based superconductors'""","The Comment insists on the following: in our model it is assumed that the
effective interactions have specific energy ranges within the single band with
a cutoff at \omega_1 for the phononic part and a range from \omega_1 to
\omega_2 in the AF channel. Our reply is that we assume that V_i(k,k')\neq 0 if
|\xi_k|<\omega_i and |\xi_{k'}|<\omega_i, and otherwise V_i(k,k')= 0 (i=1,2),
as stated in our paper. This is the model of BCS type with two attractive
interactions, and this assumption is the characteristic of the BCS
approximation. The claim ""the integration limits have been modified such that
the AF channel mediated pairing sets in where the ph-channel pairing terminates
and is limited at an energy given by \omega_j=\omega_{AF}"" in the Comment is
wrong. We describe the model and the method to solve the gap equation in more
detail.",1104.2146v1
2011-03-26,Parametrization for Cherenkov light lateral distribution function in Extensive Air Showers,"The simulation of the Cherenkov light lateral distribution function (LDF) in
Extensive Air Showers (EAS) was perfomed with the CORSIKA code in the energy
range 10^13-10^16 eV for configuration of the Tunka-25 EAS array. On the basis
of this simulation we obtained sets of approximating functions for primary
protons, iron nuclei and gamma-quanta for zenith angles Theta<=20. The
comparison of the calculated Cherenkov light LDF with that measured with the
Tunka-25 array has shown an opportunity of primary particle identification and
definition of its energy around the ""knee"".",1104.2510v1
2011-04-15,The effect of hydrogen on the magnetic properties of FeV superlattice,"The electronic and magnetic structures of a hydrogenated and hydrogen free
superlattice of 3 iron monolayers and 9 vanadium monolayers are studied using
the first principle full-potential augmented-plane-wave method as implemented
in WIEN2k package. The volume, the total energy and the magnetic moments of the
system are studied versus the hydrogen positions at the octahedral sites within
the superlattice and also versus the filling of the vanadium octahedral
location by hydrogen atoms. It is found that the hydrogen locations at the
interior of vanadium layer are energetically more favourable. The local Fe
magnetic moment and the average magnetic moment per supercell are found to
increase as the H position moves towards the Fe-V interface. On the other hand,
the average magnetic moment per supercell is found to initially decrease up to
filling by 3 H atoms and then increases afterwards. To our knowledge, this is
the first reporting on the increase in the computed magnetic moment with
hydrogenation. These trends of magnetic moments are attributed to the volume
changes resulting from hydrogenation and not to electronic hydrogen-metal
interaction.",1104.2965v1
2011-04-18,A new composition-sensitive parameter for Ultra-High Energy Cosmic Rays,"A new family of parameters intended for composition studies in cosmic ray
surface array detectors is proposed. The application of this technique to
different array layout designs has been analyzed. The parameters make exclusive
use of surface data combining the information from the total signal at each
triggered detector and the array geometry. They are sensitive to the combined
effects of the different muon and electromagnetic components on the lateral
distribution function of proton and iron initiated showers at any given primary
energy. Analytical and numerical studies have been performed in order to assess
the reliability, stability and optimization of these parameters. Experimental
uncertainties, the underestimation of the muon component in the shower
simulation codes, intrinsic fluctuations and reconstruction errors are
considered and discussed in a quantitative way. The potential discrimination
power of these parameters, under realistic experimental conditions, is compared
on a simplified, albeit quantitative way, with that expected from other surface
and fluorescence estimators.",1104.3399v1
2011-04-22,Modelling the Broad-band Spectra of MCG-6-30-15 with a Relativistic Reflection Model,"The spectrum of the bright Seyfert I galaxy MCG-6-30-15 shows a broad Fe
K-alpha emission line, generally interpreted to originate very close to the
central black hole which must then have a high spin. The observed X-ray
variability is driven by a powerlaw component, with little variability found in
the iron line energy band. The disconnection of continuum and line variability
may be a consequence of strong gravitational light bending. The X-ray spectrum
of MCG-6-30-15 is however complex, strongly modified at soft X-ray energies by
warm absorbers, which some workers have extended to build an
absorption-dominated model of the whole source behaviour. The absorption model
interprets the whole X-ray spectrum without a relativistic reflection component
and attributes most variability to the warm absorbers. We re-examine the
XMM-Newton, Chandra and Suzaku data taken in 2001, 2004 and 2006, respectively,
and construct a model consisting of several warm absorbers confirmed by
spectral analysis, together with a relativistically blurred reflection
component that explains both the soft and hard excesses as well. The model
works well on data from all epochs, demonstrating that the reflection model
provides a consistent interpretation of the broadband spectrum of MCG-6-30-15.",1104.4483v1
2011-04-27,Study of the X-ray/gamma source AX J1910.7+0917 and three newly discovered INTEGRAL sources,"AX J1910.7+0917 is a still unidentified source discovered with ASCA and
observed more recently with IBIS/ISGRI, mainly noticeable for its rather hard
spectrum. We analyzed all the public available data on this source, and we took
advantage of the recent improvements performed in the INTEGRAL data analysis
software to fully exploit the IBIS/ISGRI data. In the data collected from
INTEGRAL, XMM-Newton, Chandra and ASCA the source is clearly variable. The
spectrum can be modelled as an absorbed powerlaw (NH~6x10^22 cm^-2, Gamma=1.5)
with an iron line at 6.4 keV. The present data still do not allow for a unique
classification of the source. In the IBIS/ISGRI field of view around AX
J1910.7+0917, we discovered three new sources: IGR J19173+0747, IGR J19294+1327
and IGR J19149+1036, where the latter is positionally coincident with the
Einstein source 2E 1912.5+1031. For the first two sources we report results
obtained from follow-up observations carried out with Swift/XRT.",1104.5102v1
2011-04-28,Electronic inhomogeneity in a Kondo lattice,"Inhomogeneous electronic states resulting from entangled spin, charge, and
lattice degrees of freedom are hallmarks of strongly correlated electron
materials; such behavior has been observed in many classes of d-electron
materials, including the high-Tc copper-oxide superconductors, manganites, and
most recently the iron-pnictide superconductors. The complexity generated by
competing phases in these materials constitutes a considerable theoretical
challenge-one that still defies a complete description. Here, we report a new
manifestation of electronic inhomogeneity in a strongly correlated f-electron
system, using CeCoIn5 as an example. A thermodynamic analysis of its
superconductivity, combined with nuclear quadrupole resonance measurements,
shows that nonmagnetic impurities (Y, La, Yb, Th, Hg and Sn) locally suppress
unconventional superconductivity, generating an inhomogeneous electronic ""Swiss
cheese"" due to disrupted periodicity of the Kondo lattice. Our analysis may be
generalized to include related systems, suggesting that electronic
inhomogeneity should be considered broadly in Kondo lattice materials.",1104.5457v1
2011-04-29,Evolution of correlation strength in KxFe(2-y)Se2 superconductor doped with S,"We report the evolution of thermal transport properties of iron-based
superconductor K$_x$Fe$_{2-y}$Se$_2$ with sulfur substitution at Se sites.
Sulfur doping suppresses the superconducting $T_c$ as well as the Seebeck
coefficient. The Seebeck coefficient of all crystals in the low temperature
range can be described very well by diffusive thermoelectric response model.
The zero-temperature extrapolated value of Seebeck coefficient divided by
temperature $S/T$ gradually decreases from $-0.48 \mu V/K^2$ to a very small
value $\sim$ 0.03 $\mu$V/K$^2$ where $T_c$ is completely suppressed. The normal
state electron Sommerfeld term ($\gamma_n$) of specific heat also decreases
with the increase of sulfur content. The dcrease of $S/T$ and $\gamma_n$
reflects a suppression of the density of states at the Fermi energy, or a
change in the Fermi surface that would induce the suppression of correlation
strength.",1104.5711v1
2011-04-30,Magnetic hydrogels derived from polysaccharides with improved specific power absorption: potential devices for remotely triggered drug delivery,"We report on novel ferrogels derived from polysaccharides (sodium alginate
and chitosan) with embedded iron oxide nanoparticles synthesized in situ and
their combination with thermally responsive poly (N-isopropylacrylamide) for
externally-driven drug release using AC magnetic fields. Samples were
characterized by Raman spectroscopy, transmission electron microscopy (TEM) and
magnetic measurements. The obtained nanoparticles were found to be of ca. 10 nm
average size, showing magnetic properties very close to those of the bulk
material. The thermal response was measured by power absorption experiments,
finding specific power absorption (SPA) values between 100-300 W/g, which was
enough for attaining the lower critical solution temperature (LCST) of the
polymeric matrix within few minutes. This fast response makes these materials
good candidates for externally controlled drug release.",1105.0075v1
2011-05-11,"Systematics of the temperature-dependent inter-plane resistivity in Ba(Fe$_{1-x}$T$_x$)$_2$As$_2$ with T= Rh, Ni, and Pd","Temperature-dependent inter-plane resistivity, $\rho_c(T)$, was measured
systematically as a function of transition metal substitution in the
iron-arsenide superconductors Ba(Fe$_{1-x}$T$_x$)$_2$As$_2$, $T$= Ni, Pd, Rh.
The data are compared with the behavior found in
Ba(Fe$_{1-x}$Co$_x$)$_2$As$_2$, revealing resistive signatures of pseudogap. In
all compounds we find resistivity crossover at a characteristic pseudogap
temperature $T^*$ from non-metallic to metallic temperature dependence on
cooling. Suppression of $T^*$ proceeds very similar in cases of Ni and Pd
doping and much faster than in similar cases of Co and Rh doping. In cases of
Co and Rh doping an additional minimum in the temperature-dependent $\rho_c$
emerges for high dopings, when superconductivity is completely suppressed.
These features are consistent with the existence of a charge gap covering part
of the Fermi surface. The part of the Fermi surface affected by this gap is
notably larger for Ni and Pd doped compositions than in Co and Rh doped
compounds.",1105.2277v1
2011-05-13,Scaling of nascent nodes in extended s-wave superconductors,"We analyze the low-energy properties of superconductors near the onset of
accidental nodes, i.e. zeroes of the gap function not enforced by symmetry. The
existence of such nodes has been motivated by recent experiments suggesting a
transition between nodeless and nodal superconductivity in iron-based
compounds. We find that the low-temperature behavior of the penetration depth,
the specific heat, and the NMR spin-lattice relaxation rate are determined by
the scaling properties of a quantum critical point associated with the nascent
nodes. Although the power-law exponents are insensitive to weak short-range
electronic interactions, they can be significantly altered by the curvature of
the Fermi surface or by the three-dimensional character of the gap.
Consequently, the behavior of macroscopic quantities near the onset of nodes
can be used as a criterion to determine the nodal structure of the gap
function.",1105.2785v2
2011-05-17,Superconductivity and ferromagnetism in EuFe$_{2}$(As$_{1-x}$P$_{x}$)$_{2}$,"Superconductivity and ferromagnetism are two antagonistic cooperative
phenomena, which makes it difficult for them to coexist. Here we demonstrate
experimentally that they do coexist in EuFe$_{2}$(As$_{1-x}$P$_{x}$)$_{2}$ with
$0.2\leq x\leq0.4$, in which superconductivity is associated with Fe-3$d$
electrons and ferromagnetism comes from the long-range ordering of Eu-4$f$
moments via Ruderman-Kittel-Kasuya-Yosida (RKKY) interactions. The coexistence
is featured by large saturated ferromagnetic moments, high and comparable
superconducting and magnetic transition temperatures, and broad coexistence
ranges in temperature and field. We ascribe this unusual phenomenon to the
robustness of superconductivity as well as the multi-orbital characters of iron
pnictides.",1105.3255v1
2011-05-17,Effective Ex-Situ Fabrication of F-Doped SmFeAsO Wire for High Transport Critical Current Density,"We demonstrate the fabrication of superconducting SmFeAsO1-xFx (Sm-1111)
wires by using the ex-situ powder-in-tube technique. Sm-1111 powder and a
binder composed of SmF3, samarium arsenide, and iron arsenide were used to
synthesize the superconducting core. Although the F content of Sm-1111 is
reduced in the process of ex-situ fabrication, the binder compensates by
sufficiently supplementing the F content, thereby preventing a decrease in the
superconducting transition temperature and a shrinkage of the superconducting
volume fraction. Thus, in the superconducting Sm-1111 wire with the binder, the
transport critical current density reaches the highest value of ~4 kA/cm2 at
4.2 K.",1105.3342v2
2011-05-19,High energy pseudogap and its evolution with doping in Fe-based superconductors as revealed by optical spectroscopy,"We report optical spectroscopic measurements on electron- and hole-doped
BaFe2As2. We show that the compounds in the normal state are not simple metals.
The optical conductivity spectra contain, in addition to the free carrier
response at low frequency, a temperature-dependent gap-like suppression at
rather high energy scale near 0.6 eV. This suppression evolves with the
As-Fe-As bond angle induced by electron- or hole-doping. Furthermore, the
feature becomes much weaker in the Fe-chalcogenide compounds. We elaborate that
the feature is caused by the strong Hund's rule coupling effect between the
itinerant electrons and localized electron moment arising from the multiple Fe
3d orbitals. Our experiments demonstrate the coexistence of itinerant and
localized electrons in iron-based compounds, which would then lead to a more
comprehensive picture about the metallic magnetism in the materials.",1105.3939v1
2011-05-20,Neutrino Probes of the Nature of Light Dark Matter,"Dark matter particles gravitationally trapped inside the Sun may annihilate
into Standard Model particles, producing a flux of neutrinos. The prospects of
detecting these neutrinos in future multi-\kton{} neutrino detectors designed
for other physics searches are explored here. We study the capabilities of a
34/100 \kton{} liquid argon detector and a 100 \kton{} magnetized iron
calorimeter detector. These detectors are expected to determine the energy and
the direction of the incoming neutrino with unprecedented precision allowing
for tests of the dark matter nature at very low dark matter masses, in the
range of 5-50 GeV. By suppressing the atmospheric background with angular cuts,
these techniques would be sensitive to dark matter - nucleon spin dependent
cross sections at the fb level, reaching down to a few ab for the most
favorable annihilation channels and detector technology.",1105.4077v2
2011-05-26,Phosphor induced significant hole-doping in ferropnictide superconductor BaFe2(As(1-x)Px)2,"The superconductivity in high temperature superconductors ordinarily arises
when doped with hetero-valent ions that introduce charge carriers. However, in
ferropnictides, ""iso-valent"" doping, which is generally believed not to
introduce charge carriers, can induce superconductivity as well. Moreover,
unlike other ferropnictides, the superconducting gap in BaFe2(As1-xPx)2 has
been found to contain nodal lines. The exact nature of the ""iso-valent"" doping
and nodal gap here are key open issues in building a comprehensive picture of
the iron-based high temperature superconductors. With angle-resolved
photoemission spectroscopy (ARPES), we found that the phosphor substitution in
BaFe2(As1-xPx)2 induces sizable amount of holes into the hole Fermi surfaces,
while the dxy-originated band is relatively intact. This overturns the previous
common belief of ""iso-valent"" doping, explains why the phase diagram of
BaFe2(As1-xPx)2 is similar to those of the holedoped compounds, and rules out
theories that explain the nodal gap based on vanishing dxy hole pocket.",1105.5242v1
2011-05-27,Orbitally resolved lifetimes in Ba(Fe0.92Co0.08)2As2 measured by ARPES,"Despite many ARPES investigations of iron pnictides, the structure of the
electron pockets is still poorly understood. By combining ARPES measurements in
different experimental configurations, we clearly resolve their elliptic shape.
Comparison with band calculation identify a deep electron band with the dxy
orbital and a shallow electron band along the perpendicular ellipse axis with
the dxz/dyz orbitals. We find that, for both electron and hole bands, the
lifetimes associated with dxy are longer than for dxz/dyz. This suggests that
the two types of orbitals play different roles in the electronic properties and
that their relative weight is a key parameter to determine the ground state.",1105.5604v2
2011-05-31,Micromagnetic study of flux-closure states in Fe dots using quantitative Lorentz Microscopy,"A micromagnetic study of epitaxial micron-sized iron dots is reported through
the analysis of Fresnel contrast in Lorentz Microscopy. Their use is reviewed
and developed through analysis of various magnetic structures in such dots.
Simple Landau configuration is used to investigate various aspects of
asymmetric Bloch domain walls. The experimental width of such a complex wall is
first derived and its value is discussed with the help of micromagnetic
simulations. Combination of these two approaches enables us to define what is
really extracted when estimating asymmetric wall width in Lorentz Microscopy.
Moreover, quantitative data on the magnetization inside the dot is retrieved
using phase retrieval as well as new informations on the degrees of freedom of
such walls. Finally, it is shown how the existence and the propagation of a
surface vortex can be characterized and monitored. This demonstrates the
ability to reach a magnetic sensitivity a priori hidden in Fresnel contrast,
based on an original image treatment and backed-up by the evaluation of
contrasts obtained from micromagnetic simulations.",1105.6295v2
2011-06-05,Novel Insulating Magnetism in Vacancy-Ordered K2Fe4Se5,"We unveil the novel physical origin of the insulating block checkerboard
antiferromagnetism in vacancy-ordered K2Fe4Se5. Our first-principles electronic
structure analysis reveals its incompatibility with a simple Fermi-surface
nesting or Mott insulator scenario, and suggests the picture of coexisting
itinerant and localized electronic states. Consistently, we demonstrate that it
can be unified with the metallic collinear or bicollinear antiferromagnetism of
the vacancy-free parent compounds LaOFeAs, BaFe2As2, or FeTe in the
spin-fermion model. These results indicate that the blocking effects of Hund's
rule coupling and the resulting electron correlation are crucial to the
electronic and magnetic structures of iron-based superconductors.",1106.0881v2
2011-06-06,Correlation of high temperature X-ray photoemission spectral features and conductivity of epitaxially strained (La0.8Sr0.2)0.95Ni0.2Fe0.8O3/SrTiO3(110),"Reversible and irreversible discontinuities at around 573 K and 823 K in the
electric conductivity of a strained 175 nm thin film of
(La0.8Sr0.2)0.95Ni0.2Fe0.8O3-{\delta} grown by pulsed laser deposition on
SrTiO3 (110) are reflected by valence band changes as monitored in
photoemission and oxygen K-edge x-ray absorption spectra. The irreversible jump
at 823 K is attributed to depletion of doped electron holes and reduction of
Fe4+ to Fe3+, as evidenced by oxygen and iron core level soft x-ray
spectroscopy, and possibly of a chemical origin, whereas the reversible jump at
573 K possibly originates from structural changes.",1106.1024v1
2011-06-06,Fe-resonant valence band photoemission and oxygen NEXAFS study on La1-xSrxFe0.75Ni0.25O3-δ,"Iron resonant valance band photoemission spectra of Sr substituted
LaFe0.75Ni0.25 O3-{\delta} have been recorded across the Fe 2p - 3d absorption
threshold to obtain Fe specific spectral information on the 3d projected
partial density of states. Comparison with La1-xSrxFeO3 resonant VB PES
literature data suggests that substitution of Fe by Ni forms electron holes
which are mainly O 2p character. Substitution of La by Sr increases the hole
concentration to an extent that the eg structure vanishes. The variation of the
eg and t2g structures is paralleled by the changes in the electrical
conductivity.",1106.1086v1
2011-06-07,Analysis of interdiffusion between SmFeAsO0.92F0.08 and metals for ex situ fabrication of superconducting wire,"We demonstrate the fabrication of superconducting SmFeAsO1-xFx (Sm-1111)
wires by using the ex-situ powder-in-tube technique. Sm-1111 powder and a
binder composed of SmF3, samarium arsenide, and iron arsenide were used to
synthesize the superconducting core. Although the F content of Sm-1111 is
reduced in the process of ex-situ fabrication, the binder compensates by
sufficiently supplementing the F content, thereby preventing a decrease in the
superconducting transition temperature and a shrinking of the superconducting
volume fraction. Thus, in the superconducting Sm-1111 wire with the binder, the
transport critical current density reaches the highest value of ~4000 A/cm2 at
4.2 K.",1106.1328v2
2011-06-11,Fish-tail and vortex dynamics in Ni doped iron-pnictide BaFe{1.82}Ni_{0.18}As_2,"We study the vortex-dynamics of a BaFe{1.82}Ni_{0.18}As_2 crystal with Tc = 8
K, by measuring flux-creep over the second magnetisation (or fish-tail) peak
for both H//c-axis and H//ab planes. Magnetic relaxation data show an
anomalously long initial stage of relaxation, lasting approximately10 minutes
for H//c-axis and 2-3 min for H//ab, resembling a transient effect with a lower
relaxation rate, which is followed by the usual log(time) relaxation.
Interestingly, study of the relaxation rate R vs H for both stages of
relaxation and for both field directions, are featureless over the field range
associated with the fish-tail. The same trend was confirmed by plotting R vs T
obtained from flux-creep data measured as a function of temperature for a fixed
field (H//$c-axis). A plot of the activation energy U(M,T) calculated from the
time relaxation of the magnetisation at a fixed field also shows a smooth
behavior further supporting the view that the fish-tail peak is not associated
with a crossover in vortex pinning regime within the collective pinning
scenario.",1106.2248v2
2011-06-17,A Three-Dimensional Tight-Binding Model and Magnetic Instability of KFe2e2,"For a newly discovered iron-based high T_c superconducting parent material
KFe2Se2, we present an effective three-dimensional five-orbital tight-binding
model by fitting the band structures. The three t2g-symmetry orbitals of the
five Fe 3d orbitals mainly contribute to the electron-like Fermi surface, in
agreement with recent angle-resolved photoemission spectroscopy experiments. To
understand the groundstate magnetic structure, the two- and three-dimensional
dynamical spin susceptibilities within the random phase approximation are
investigated. It obviously shows a sharp peak at wave vector $\mathbf{Q}$
$\thicksim$ ($\pi$, $\pi$), indicating the magnetic instability of {\it
N$\acute{e}$el}-type antiferromagnetic rather than ($\pi$/2, $\pi$/2)-type
antiferromagnetic ordering. While along $\emph{c}$ axis, it exhibits a
ferromagnetic coupling between the nearest neighboring FeSe layers. The
difference between the present results and the experimental observation in
KxFe2-ySe2 is attributed to the presence of Fe vacancy in the latter.",1106.3485v1
2011-06-21,Antiferromagnetic Spin Fluctuations and Unconventional Nodeless Superconductivity in an Iron-based New Superconductor (Ca_4Al_2O_{6-y})(Fe_2As_2):75As-NQR Study,"We report 75As-nuclear quadrupole resonance (NQR) studies on
(Ca_4Al_2O_{6-y})(Fe_2As_2) with Tc=27K, which unravel unique normal-state
properties and point to unconventional nodeless superconductivity (SC).
Measurement of nuclear-spin-relaxation rate 1/T_1 has revealed a significant
development of two dimensional (2D) antiferromagnetic (AFM) spin fluctuations
down to Tc, in association with the fact that FeAs layers with the smallest
As-Fe-As bond angle are well separated by thick perovskite-type blocking layer.
Below Tc, the temperature dependence of 1/T_1 without any trace of the
coherence peak is well accounted for by an s(+-)-wave multiple gaps model. From
the fact that Tc=27K in this compound is comparable to Tc=28K in the
optimally-doped LaFeAsO_{1-y} in which AFM spin fluctuations are not dominant,
we remark that AFM spin fluctuations are not a unique factor for enhancing Tc
among existing Fe-based superconductors, but a condition for optimizing SC
should be addressed from the lattice structure point of view.",1106.4105v1
2011-06-22,Evidence for conventional superconductivity in SrPd2Ge2,"Electronic structure of SrPd2Ge2 single crystals is studied by angle-resolved
photoemission spectroscopy (ARPES), scanning tunneling spectroscopy (STS) and
band-structure calculations within the local-density approximation (LDA). The
STS measurements show single s-wave superconducting energy gap \Delta(0) = 0.5
meV. Photon-energy dependence of the observed Fermi surface reveals a strongly
three-dimensional character of the corresponding electronic bands. By comparing
the experimentally measured and calculated Fermi velocities a renormalization
factor of 0.95 is obtained, which is much smaller than typical values reported
in Fe-based superconductors. We ascribe such an unusually low band
renormalization to the different orbital character of the conduction electrons
and using ARPES and STS data argue that SrPd2Ge2 is likely to be a conventional
superconductor, which makes it clearly distinct from isostructural iron
pnictide superconductors of the ""122"" family.",1106.4585v1
2011-06-26,Anisotropic two-orbital Hubbard model: single-site versus cluster dynamical mean-field theory,"The anisotropic two-orbital Hubbard model with different bandwidths and
degrees of frustration in each orbital is investigated in the framework of both
single-site dynamical mean-field theory (DMFT) as well as its cluster extension
(DCA) for clusters up to four sites combined with a continuous-time quantum
Monte Carlo algorithm. This model shows a rich phase diagram which includes the
appearance of orbital selective phase transitions, non-Fermi liquid behavior as
well as antiferromagnetic metallic states. We discuss the advantages and
drawbacks of employing the single-site DMFT with respect to DCA and the
consequences for the physical picture obtained out of these calculations.
Finally, we argue that such a minimal model may be of relevance to understand
the nature of the antiferromagnetic metallic state in the iron-pnictide
superconductors as well as the origin of the small staggered magnetization
observed in these systems.",1106.5255v1
2011-06-27,"Comment on ""Infrared signature of the superconducting gap symmetry in iron-arsenide superconductors"", Y. M. Dai et al. arXiv:1106.4430","Y. M. Dai et al. in their recent work arXiv:1106.4430 presented a
reflectivity study of the in-plance optical conductivity of a
$\textrm{Ba}_{0.6}\textrm{K}_{0.4}\textrm{Fe}_2\textrm{As}_2$ (BKFA)
superconductor with $T_{\textrm{c}}\approx39K$. The single crystals used in
this study are of high quality and the measurements are rather accurate. The
authors analyzed the optical conductivity of BKFA in the framework of the
Mattis-Bardeen theory and the BCS theory of superconductivity. This analysis,
however, generates a series of severe contradictions with a large body of
experimental data obtained with multiple probes as well as misuses both the
Mattis-Bardeen and the BCS theories of superconductivity beyond their
approximation regions.",1106.5343v1
2011-06-27,Nodal superconductivity in Ba(Fe$_{1-x}$Ru$_x$)$_2$As$_2$ induced by isovalent Ru substitution,"We present the ultra-low-temperature heat transport study of an iron-based
superconductor Ba(Fe$_{0.64}$Ru$_{0.36}$)$_2$As$_2$ ($T_c$ = 20.2 K), in which
the superconductivity is induced by isovalent Ru substitution. In zero field we
find a large residual linear term $\kappa_0/T$, more than 40% of the
normal-state value. At low field, the $\kappa_0/T$ shows an $H^{1/2}$
dependence. These provide strong evidences for nodes in the superconducting gap
of Ba(Fe$_{0.64}$Ru$_{0.36}$)$_2$As$_2$, which mimics that in another
isovalently substituted superconductor BaFe$_2$(As$_{1-x}$P$_x$)$_2$. Our
results show that the isovalent Ru substitution can also induce nodal
superconductivity in BaFe$_2$As$_2$, as P does, and they may have the same
origin. We further compare them with other two nodal superconductors LaFePO and
LiFeP.",1106.5417v2
2011-06-29,Suzaku Discovery of a Hard Component Varying Independently of the Power-Law Emission in MCG-6-30-15,"Focusing on hard X-ray variability, we reanalyzed Suzaku data of Type I
Seyfert galaxy MCG-6-30-15 obtained in 2006. Intensity-sorted spectroscopy and
a principal component analysis consistently revealed a very hard component that
varies independently of the dominant power-law emission. Although the exact
nature of this hard component is not yet identified, it can be modeled as a
power-law with a photon index ~2 affected by a partial covering absorption, or
as a thermal Comptonization emission with a relatively large optical depth.
When this component is included in the fitting model, the time-averaged 2.5-55
keV spectrum of MCG-6-30-15 can be reproduced successfully by invoking a mildly
broadened iron line with its emission region located at > 8 times the
gravitational radii from the central black hole, and a moderate reflection with
a covering fraction of ~3.4. This result implies that the solution of a highly
spinning black hole in MCG-6-30-15, obtained by Miniutti et al. (2007, PASJ,
59, S315) using the same Suzaku data, is a model dependent result.",1106.5872v1
2011-07-02,Nanoscale phase separation in the iron chalcogenide superconductor K0.8Fe1.6Se2 as seen via scanning nanofocused x-ray diffraction,"Advanced synchrotron radiation focusing down to a size of 300 nm has been
used to visualize nanoscale phase separation in the K0.8Fe1.6Se2
superconducting system using scanning nanofocus single-crystal X-ray
diffraction. The results show an intrinsic phase separation in K0.8Fe1.6Se2
single crystals at T< 520 K, revealing coexistence of i) a magnetic phase
characterized by an expanded lattice with superstructures due to Fe vacancy
ordering and ii) a non-magnetic phase with an in-plane compressed lattice. The
spatial distribution of the two phases at 300 K shows a frustrated or arrested
nature of the phase separation. The space-resolved imaging of the phase
separation permitted us to provide a direct evidence of nanophase domains
smaller than 300 nm and different micrometer-sized regions with percolating
magnetic or nonmagnetic domains forming a multiscale complex network of the two
phases.",1107.0412v2
2011-07-03,Linear decrease of critical temperature with increasing Zn substitution in the iron-based superconductor BaFe1.89-2xZn2xCo0.11As2,"The nonmagnetic impurity effect is studied on the Fe-based BaFe1.89Co0.11As2
superconductor (Tc = 25 K) with Zn substitution for Fe up to 8 at. %, which is
achieved by means of high-pressure and high-temperature heating. Tc decreases
almost linearly with increasing the Zn content and disappears at ~8 atomic %,
being different in the shared phenomenology of the early Zn doping studies,
where Tc decreases little. The Tc decreasing rate, however, remains much lower
(3.63 K/%) than what is expected for the s(+-)-wave model, implying the model
is unlikely. Another symmetry model such as the non-sign reversal s-wave model
may better account for the result.",1107.0423v1
2011-07-04,London Penetration Depth in Iron - based Superconductors,"Measurements of London penetration depth are a sensitive tool to study
multi-band superconductivity and it has provided several important insights to
the behavior of Fe-based superconductors. We first briefly review the
""experimentalist - friendly"" self-consistent Eilenberger model that relates the
measurable superfluid density and structure of superconducting gaps. Then we
focus on the \BaFe -derived materials, for which the results are consistent
with 1) two distinct superconducting gaps; 2) development of strong in-plane
gap anisotropy with the departure from the optimal doping; 3) appearance of gap
nodes along the $c-$direction in a highly overdoped regime; 4) significant
pair-breaking, presumably due to charge doping; 5) fully gapped (exponential)
intrinsic behavior at the optimal doping if scattering is removed (probed in
the ""self-doped"" stoichiometric LiFeAs); 6) competition between magnetically
ordered state and superconductivity, which do coexist in the underdoped
compounds. Overall, it appears that while there are common trends in the
behavior of Fe-based superconductors, the gap structure is non-universal and is
sensitive to the doping level. It is plausible that the rich variety of
possible gap structures within the general $s_{\pm}$ framework is responsible
for the observed behavior.",1107.0675v1
2011-07-04,Enhancement of the Superconducting Transition Temperature under Pressure in Rare-Earth Doped Ca$_{1-x}$La$_x$Fe$_2$As$_2$ (x=0.27),"We report measurements of the pressure dependence of the superconducting
transition temperature T_c in single crystal samples of the rare-earth doped
superconductor Ca$_{0.73}$La$_{0.27}$Fe$_2$As$_2$. We track T_c with two
techniques, via in-plane resistivity measurements and with a resonant tunnel
diode oscillator circuit which is sensitive to the skin depth. We show that
initially T_c rises steeply with pressure, forming a superconducting dome with
a maximum T_c of ~44 K at 20 kbar. We discuss this observation in the context
of other electron-doped iron pnictide superconductors, and conclude that the
application of pressure offers an independent way to tune T_c in this system.",1107.0689v1
2011-07-05,Massless Leggett Mode in Three-band Superconductors with Time-Reversal-Symmetry Breaking,"The Leggett mode associated with out-of-phase oscillations of superconducting
phase in multi-band superconductors usually is heavy due to the interband
coupling, which makes its excitation and detection difficult. We report on the
existence of a massless Leggett mode in three-band superconductors with
time-reversal-symmetry-breaking (TRSB). The mass of the Leggett mode is small
close to the TRSB transition and vanishes at the transition point, and thus
locates within the smallest superconducting energy gap, which makes it stable
and detectable. The mass of the Leggett mode can be measured by Raman
spectroscopy. The thermodynamic consequences of this massless mode and possible
realization in iron-based superconductors are also discussed.",1107.0814v2
2011-07-05,Evidence for filamentary superconductivity nucleated at antiphase domain walls in antiferromagnetic CaFe$_2$As$_2$,"Resistivity, magnetization and microscopic $^{75}$As nuclear magnetic
resonance (NMR) measurements in the antiferromagnetically ordered state of the
iron-based superconductor parent material CaFe$_2$As$_2$ exhibit anomalous
features that are consistent with the collective freezing of domain walls.
Below $T^*\approx 10$ K, the resistivity exhibits a peak and downturn, the bulk
magnetization exhibits a sharp increase, and $^{75}$As NMR measurements reveal
the presence of slow fluctuations of the hyperfine field. These features in
both the charge and spin response are strongly field dependent, are fully
suppressed by $H^*\approx 15$ T, and suggest the presence of filamentary
superconductivity nucleated at the antiphase domain walls in this material.",1107.0904v2
2011-07-07,"56Ni, Explosive Nucleosynthesis, and SNe Ia Diversity","The origin of the iron-group elements titanium to zinc in nature is
understood to occur under explosive burning conditions in both Type Ia
(thermonuclear) and Type II (core collapse) supernovae. In these dynamic
environments, the most abundant product is found to be 56Ni ({\tau} = 8.5 days)
that decays through 56Co ({\tau} = 111.5 days) to 56Fe. For the case of SNe Ia,
the peak luminosities are proportional to the mass ejected in the form of 56Ni.
It follows that the diversity of SNe Ia reflected in the range of peak
luminosity provides a direct measure of the mass of 56Ni ejected. In this
contribution, we identify and briefly discuss the factors that can influence
the 56Ni mass and use both observations and theory to quantify their impact. We
address specifically the variations in different stellar populations and
possible distinctions with respect to SNe Ia progenitors.",1107.1278v1
2011-07-07,"Synthesis, crystal structure and magnetism of beta-Fe1.00(2)Se1.00(3) single crystals","Understanding iron based superconductors requires high quality impurity free
single crystals. So far they have been elusive for beta-FeSe and extraction of
intrinsic materials properties has been compromised by several magnetic
impurity phases. Herein we report synchrotron - clean beta-FeSe superconducting
single crystals grown via LiCl/CsCl flux method. Phase purity yields evidence
for a defect induced weak ferromagnetism that coexists with superconductivity
below Tc. In contrast to Fe1+yTe - based superconductors, our results reveal
that the interstitial Fe(2) site is not occupied and that all contribution to
density of states at the Fermi level must come from in-plane Fe(1).",1107.1496v1
2011-07-09,Pairing mechanism in multiband superconductors,"We investigate pairing mechanism in multiband superconductors. To put our
feet on firm ground, unbiased renormalization group analysis is carried out for
iron-based superconductors. It is quite remarkable that, after integrating out
quantum fluctuations, the renormalization-group flows agree exceedingly well
with a mean-field Hamiltonian where interband pair hopping plays an essential
role. Through interband pair hopping, electrons can overcome the repulsive
interaction between them and form resonating Cooper pairs between different
bands. Unlike the conventional superconductors, the pairing mechanism in
multiband superconductors is resonating pair hopping between different bands,
just like the resonating chemical bonds in benzene. The effective mean-field
Hamiltonian spots a small parameter dictating the critical temperature and also
explains how interband pair hopping always enahnces spin fluctuations at the
nesting momentum connecting the Fermi surfaces. In short, no attractive glue is
needed and resonating interband pair hopping is the key to Cooper pair
formation in unconventional superconductors. Implications to cuprates and
related issues are also discussed at the end.",1107.1796v2
2011-07-11,Fermi-surface reconstruction involving two Van Hove singularities across the antiferromagnetic transition in BaFe2As2,"We report an angle-resolved photoemission study of BaFe2As2, a parent
compound of iron-based superconductors. Low-energy tunable excitation photons
have allowed the first observation of a saddle-point singularity at the Z
point, as well as the Gamma point. With antiferromagnetic ordering, both of
these two van Hove singularities come down below the Fermi energy, leading to a
topological change in the innermost Fermi surface around the kz axis from
cylindrical to tear-shaped, as expected from first-principles calculation.
These singularities may provide an additional instability for the Fermi surface
of the superconductors derived from BaFe2As2.",1107.1960v2
2011-07-11,The need for a local source of UHE CR nuclei,"Recent results of the Pierre Auger (Auger) fluorescence detectors indicate an
increasingly heavy composition of ultra-high energy (UHE) cosmic rays (CRs).
Assuming that this trend continues up to the highest energies observed by the
Auger surface detectors we derive the constraints this places on the local
source distribution of UHE CR nuclei. Utilizing an analytic description of UHE
CR propagation we derive the expected spectra and composition for a wide range
of source emission spectra. We find that sources of intermediate-to-heavy
nuclei are consistent with the observed spectra and composition data above the
ankle. This consistency requires the presence of nearby sources within 60 Mpc
and 80 Mpc for silicon and iron only sources, respectively. The necessity of
these local sources becomes even more compelling in the presence nano-Gauss
local extragalactic magnetic fields.",1107.2055v2
2011-07-11,New Indivisible Geoscience Paradigm,"Earth's interior, I posit, is like one of the rare, oxygen-starved ""enstatite
chondrite"" meteorites (and unlike a more-oxidized ""ordinary chondrite"" as has
been believed for seventy years). Laboratory-analyzed enstatite-chondrite
samples are comparable to having-in-hand impossibleto- gather deep-Earth
samples. Enstatite-chondrite formation in oxygen-starved conditions caused
oxygen-loving elements to occur, in part, as non-oxides in their iron-alloy.
Observations, consistent with solar abundance and behavior of chemical
elements, lead me to a new interpretation of: (1) Earth's early formation as a
Jupiter-like gas-giant, (2) its decompressionpowered surface geology, (3)
Earth's internal composition, and (4) a natural, planetocentric nuclear-fission
reactor as source of both the geomagnetic field and energy channeled to surface
""hot-spots"". I present a unified vision of Earth formation and concomitant
dynamics that explains in a logical and causally related way: (1) fluid
Earth-core formation without wholeplanet melting, and (2) the myriad
measurements and observations, previously attributed to ""plate tectonics"", but
without necessitating mantle convection.",1107.2149v1
2011-07-13,The MOLDY short-range molecular dynamics package,"We describe a parallelised version of the MOLDY molecular dynamics program.
This Fortran code is aimed at systems which may be described by short-range
potentials and specifically those which may be addressed with the embedded atom
method. This includes a wide range of transition metals and alloys. MOLDY
provides a range of options in terms of the molecular dynamics ensemble used
and the boundary conditions which may be applied. A number of standard
potentials are provided, and the modular structure of the code allows new
potentials to be added easily. The code is parallelised using OpenMP and can
therefore be run on shared memory systems, including modern multicore
processors. Particular attention is paid to the updates required in the main
force loop, where synchronisation is often required in OpenMP implementations
of molecular dynamics. We examine the performance of the parallel code in
detail and give some examples of applications to realistic problems, including
the dynamic compression of copper and carbon migration in an iron-carbon alloy.",1107.2619v1
2011-07-14,"Successive transition from superconducting to antiferromagnetic phase in (Ca_6(Al, Ti)_4O_y)Fe_2As_2 studied via ^{75}As and ^{27}Al NMR","An unusual successive phase transition from superconducting (SC) to
antiferromagnetic (AF) phases was discovered via ^{75}As and ^{27}Al nuclear
magnetic resonance (NMR) in (Fe_2As_2)(Ca_6(Al, Ti)_4O_y) with four (Al, Ti)O
layers intercalated between FeAs planes. Although the spatially-uniform AF
ordering is clearly visible from ^{27}Al spectra, the ordered moments are very
small and the low-frequency fluctuation is much suppressed, contrary to
existing pnictides with localized magnetic elements. Furthermore, the
temperature (T) dependence of the fluctuation at both nuclei is very similar
throughout the entire temperature range. These facts suggest that some
hybridization between Ti and Fe orbitals induces a uniform electronic state
within FeAs and (Al, Ti)O layers accompanied by the SC and AF transitions. The
iron-based pnictide with Ti-doped blocking layers is the first high-T_c
compound having metallic blocking layers.",1107.2765v2
2011-07-15,Satellites and large doping- and temperature-dependence of electronic properties in hole-doped BaFe2As2,"Over the last years, superconductivity has been discovered in several
families of iron-based compounds. Despite intense research, even basic
electronic properties of these materials, such as Fermi surfaces, effective
electron masses, or orbital characters are still subject to debate. Here, we
address an issue that has not been considered before, namely the consequences
of dynamical screening of the Coulomb interactions among Fe-d electrons. We
demonstrate its importance not only for correlation satellites seen in
photoemission spectroscopy, but also for the low-energy electronic structure.
From our analysis of the normal phase of BaFe2As2 emerges the picture of a
strongly correlated compound with strongly doping- and temperature-dependent
properties. In the hole overdoped regime, an incoherent metal is found, while
Fermi-liquid behavior is recovered in the undoped compound. At optimal doping,
the self-energy exhibits an unusual square-root energy dependence which leads
to strong band renormalizations near the Fermi level.",1107.3128v1
2011-07-21,A de Haas-van Alphen study of the Fermi surfaces of superconducting LiFeP and LiFeAs,"We report a de Haas-van Alphen (dHvA) oscillation study of the 111 iron
pnictide superconductors LiFeAs with T_c ~18K and LiFeP with T_c~5K. We find
that for both compounds the Fermi surface topology is in good agreement with
density functional band-structure calculations and shows quasi-nested electron
and hole bands. The effective masses generally show significant enhancement, up
to ~3 for LiFeP and ~5 for LiFeAs. However, one hole Fermi surface in LiFeP
shows a very small enhancement, as compared with its other sheets. This
difference probably results from k-dependent coupling to spin fluctuations and
may be the origin of the different nodal and nodeless superconducting gap
structures in LiFeP and LiFeAs respectively.",1107.4375v2
2011-07-22,The Chemical and Dynamical Evolution of Isolated Dwarf Galaxies,"Using a suite of simulations (Governato et al. 2010) which successfully
produce bulgeless (dwarf) disk galaxies, we provide an analysis of their
associated cold interstellar media (ISM) and stellar chemical abundance
patterns. A preliminary comparison with observations is undertaken, in order to
assess whether the properties of the cold gas and chemistry of the stellar
components are recovered successfully. To this end, we have extracted the
radial and vertical gas density profiles, neutral hydrogen velocity dispersion,
and the power spectrum of structure within the ISM. We complement this analysis
of the cold gas with a brief examination of the simulations' metallicity
distribution functions and the distribution of alpha-elements-to-iron.",1107.4538v1
2011-07-25,Uncertainties in modeling low-energy neutrino induced reactions on iron group nuclei,"Charged-current neutrino-nucleus cross sections for 54,56Fe and 58,60Ni are
calculated and compared using frameworks based on relativistic and Skyrme
energy density functionals, and the shell model. The current theoretical
uncertainties in modeling neutrino-nucleus cross sections are assessed in
relation to the predicted Gamow-Teller transition strength and available data,
multipole decomposition of the cross sections, and cross sections averaged over
the Michel flux and Fermi-Dirac distribution. Employing different microscopic
approaches and models, the DAR neutrino-56Fe cross section and its theoretical
uncertainty are estimated: <sigma>_th=(258+-57) 10^{-42} cm^2, in very good
agreement with the experimental value: <sigma>_exp=(256+-108+-43) 10^{-42}
cm^2.",1107.4872v2
2011-08-01,Propagation of Ultrahigh Energy Nuclei in the Magnetic Field of our Galaxy,"In this work, we present detailed simulations for propagation of ultra-high
energy (UHE) heavy nuclei, with E > 60 EeV, within recent Galactic Magnetic
Field (GMF) models. We investigate the impacts of the regular and turbulent
components of the GMF. We show that with UHE heavy nuclei, there is no
one-to-one correspondence between the arrival directions of cosmic rays (CR)
measured at Earth and the direction of their extragalactic sources. Sources can
have several distorted images on the sky. We compute images of galaxy clusters
and of the supergalactic plane in recent GMF models and show the challenges,
and possibilities, of ""UHECR astronomy"" with heavy nuclei. Finally, we present
a quantitative study of the impact of the GMF on the (de-)magnification of
source fluxes, due to magnetic lensing effects. We find that for 60 EeV iron
nuclei, sources located in up to about one fifth of the sky would have their
fluxes so strongly demagnified that they would not be detectable at Earth, even
by the next generation of UHECR experiments.",1108.0362v2
2011-08-01,"Critical fields, thermally-activated transport and critical current density of beta-FeSe single crystals","We present critical fields, thermally-activated flux flow (TAFF) and critical
current density of tetragonal phase beta-FeSe single crystals. The upper
critical fields Hc2(T) for H||(101) and H\bot(101) are nearly isotropic and are
likely governed by Pauli limiting process. The obtained large Ginzburg-Landau
parameter k \sim 72.3(2) indicates that beta-FeSe is a type-II superconductor
with smaller penetration depth than in Fe(Te,Se). The resistivity below Tc
follows Arrhenius TAFF behavior. For both field directions below 30 kOe single
vortex pinning is dominant whereas collective creep becomes important above 30
kOe. The critical current density Jc from M-H loops for H||(101) is about five
times larger than for H\bot(101), yet much smaller than in other iron-based
superconductors.",1108.0407v1
2011-08-02,Spin fluctuations and unconventional pairing in KFe$_2$As$_2$,"We study the relation between the spin fluctuation and superconductivity in
an heavily hole doped end material KFe$_2$As$_2$. We construct a five orbital
model by approximately unfolding the Brillouin zone of the three dimensional
ten orbital model obtained from first principles calculation. By applying the
random phase approximation, we obtain the spin susceptibility and solve the
linearized Eliashberg equation. The incommensurate spin fluctuation observed
experimentally is understood as originating from interband interactions, where
the multiorbital nature of the band structure results in an electron-hole
asymmetry of the incommensurability in the whole iron-based superconductor
family. As for superconductivity, s-wave and d-wave pairings are found to be in
close competition, where the sign change in the gap function in the former is
driven by the incommensurate spin fluctuations. We raise several possible
explanations for the nodes in the superconducting gap of KFe$_2$As$_2$ observed
experimentally.",1108.0657v2
2011-08-02,What controls the phase diagram and superconductivity in Ru substituted BaFe$_2$As$_2$?,"We use high resolution angle-resolved photoemission to study the electronic
structure of the iron based high-temperature superconductors
Ba(Fe$_{1-x}$Ru$_x$)$_2$As$_2$ as a function of Ru concentration. We find that
substitution of Ru for Fe is isoelectronic, i. e., it does not change the value
of the chemical potential. More interestingly, there are no measured,
significant changes in the shape of the Fermi surface or in the Fermi velocity
over a wide range of substitution levels ($0<x<0.55$). Given that the
suppression of the antiferromagnetic and structural phase has been associated
with the emergence of the superconducting state, Ru substitution must achieve
this via a mechanism that does not involve changes of the Fermi surface. We
speculate that this mechanism relies on magnetic dilution which leads to the
reduction of the effective Stoner enhancement.",1108.0711v2
2011-08-03,Planar hybrid superconductor-normal metal-superconductor thin film junctions based on BaFe1.8Co0.2As2,"To investigate the transport properties of iron based superconductors, we
prepared planar hybrid superconductor-normal metal-superconductor (SNS') thin
film junctions with BaFe1.8Co0.2As2 as base electrode. As counter electrode we
used a lead indium alloy, while the normal metal layer was formed by thin gold
films. Temperature dependent measurements of the electrical conductivity were
strongly influenced by the properties of the electrodes. We developed a
junction structure that allows us to characterize the electrodes, too,
including the behavior of their normal state resistance in order to correct
their influences on the conduction spectra. The corrected conductivity of the
junction was described within an extended BTK-model and shows a behavior
dominated by Andreev reflexion.",1108.0851v2
2011-08-04,$β$-decay of key titanium isotopes in stellar environment,"Amongst iron regime nuclei, $\beta$-decay rates on titanium isotopes are
considered to be important during the late phases of evolution of massive
stars. The key $\beta$-decay isotopes during presupernova evolution were
searched from available literature and a microscopic calculation of the decay
rates were performed using the proton-neutron quasiparticle random phase
approximation (pn-QRPA) theory. As per earlier simulation results electron
capture and $\beta$-decay on certain isotopes of titanium are considered to be
important for the presupernova evolution of massive stars. Earlier the stellar
electron capture rates and neutrino energy loss rates due to relevant titanium
isotopes were presented. In this paper we finally present the $\beta$-decay
rates of key titanium isotopes in stellar environment. The results are also
compared against previous calculations. The pn-QRPA $\beta$-decay rates are
bigger at high stellar temperatures and smaller at high stellar densities
compared to the large scale shell model results. This study can prove useful
for the core-collapse simulators.",1108.1026v1
2011-08-08,Conceptual design of 20 T dipoles for high-energy LHC,"Availability of 20 T operational field dipole magnets would open the way for
a 16.5 TeV beam energy accelerator in the LHC tunnel. Here we discuss the main
issues related to the magnet design of this extremely challenging dipole: main
constraints, superconductor choice, coil lay-out, iron, forces and stresses,
and field quality. A tentative cost estimate is also given. The present
technology, based on Nb-Ti and now near to be extended to Nb3Sn superconductor,
would allow reaching 15 T operational field. To reach 20 T, HTS conductors
capable to carry 400 A/mm2 at 15-20 T under transverse stress of 150-200 MPa
are an essential element.",1108.1619v1
2011-08-08,"Synthesis, crystal and magnetic structure of iron selenide BaFe2Se3 with possible superconductivity at Tc=11K","We report on synthesis of single crystals of BaFe2Se3 and study of their
crystal and magnetic structures by means of synchrotron single crystal X-ray
and neutron powder diffraction. The crystal structure has orthorhombic symmetry
and consists of double chains of FeSe4 edge connected tetrahedra intercalated
by barium. Below 240 K long range block-spin checkerboard antiferromagnetic
(AFM) order is developed. The magnetic structure is similar to one observed in
A0.8Fe1.6Se2 (A=K, Rb or Cs) superconductors. The crystals exhibit a transition
to the diamagnetic state with an onset transition temperature of Tc ~11 K.
Though we observe FeSe as an impurity phase (<0.8% mass fraction) the
diamagnetism unlikely can be attributed to the FeSe-superconductor which has
Tc\approx8.5K.",1108.1670v3
2011-08-11,Chemical abundances and kinematics of a sample of metal-rich barium stars,"We determined the atmospheric parameters and abundance pattern for a sample
of metal-rich barium stars. We used high-resolution optical spectroscopy.
Atmospheric parameters and abundances were determined using the local
thermodynamic equilibrium atmosphere models of Kurucz and the spectral analysis
code MOOG. We show that the stars have enhancement factors, [s/Fe], from 0.25
to 1.16. Their abundance pattern of the Na, Al, alpha-elements, and iron group
elements as well as their kinematical properties are similar to the
characteristics of the other metal-rich and super metal-rich stars already
analyzed. We conclude that metal-rich barium stars do not belong to the bulge
population. We also show that metal-rich barium stars are useful targets for
probing the s-process enrichment in high-metallicity environments.",1108.2500v1
2011-08-12,Nuclear medium effects in $ν/\barν$-A DIS,"Nuclear medium effects in the weak structure functions $F_2(x,Q^2)$ and
$F_3(x,Q^2)$ have been studied for deep inelastic neutrino/antineutrino
reactions in iron nucleus by taking into account Fermi motion, binding, pion
and rho meson cloud contributions, target mass correction, shadowing and
anti-shadowing corrections. The calculations have been performed in a local
density approximation using relativistic nuclear spectral functions which
include nucleon correlations. Using these structure functions we have obtained
the ratio $R_{F2,F3}^A(x,Q^2)= \frac{2F_{2,3}^A(x,Q^2)}{AF_{2,3}^D(x,Q^2)}$,
the differential scattering cross section $\frac{1}{E}\frac{d^2\sigma}{dxdy}$
and the total scattering cross section $\sigma$. The results of our numerical
calculations in $^{56}Fe$ are compared with the experimental results of NuTeV
and CDHSW collaborations.",1108.2564v1
2011-08-17,A minimum single-band model for low-energy excitations in superconducting K$_x$Fe$_2$Se$_2$,"We propose a minimum single-band model for the newly discovered iron-based
superconducting K$_x$Fe$_2$Se$_2$. Our model is found to be numerically
consistent with the five-orbital model at low energies. Based on our model and
the random phase approximation, we study the spin fluctuation and the pairing
symmetry of superconducting gap function. The $(\pi/2,\pi/2)$ spin excitation
and the $d_{x^2-y^2}$ pairing symmetry are revealed. All of the results can
well be understood in terms of the interplay between the Fermi surface topology
and the local spin interaction, providing a sound picture to explain why the
superconducting transition temperature is as high as to be comparable to those
in pnictides and some cuprates. A common origin of superconductivity is
elucidated for this compound and other high-T$_c$ materials.",1108.3491v1
2011-08-17,Proximity fingerprint of s+- superconductivity,"We suggest a straightforward and unambiguous test to identify possible
opposite signs of superconducting order parameter in different bands proposed
for iron-based superconductors (s+- state). We consider proximity effect in a
weakly coupled sandwich composed of a s+- superconductor and thin layer of
s-wave superconductor. In such system the s-wave order parameter is coupled
differently with different s+- gaps and it typically aligns with one of these
gaps. This forces the other s+- gap to be anti-aligned with the s-wave gap. In
such situation the aligned band induces a peak in the s-wave density of states
(DoS), while the anti-aligned band induces a dip. Observation of such
contact-induced negative feature in the s-wave DoS would provide a definite
proof for s+- superconductivity.",1108.3515v3
2011-08-22,Block Spin Magnetic Phase Transition of A$_y$Fe$_{1.6}$Se$_2$ Under High Pressure,"We predict an unconventional magnetic ground state in A$_y$Fe$_{1.6}$Se$_2$
with $\sqrt{5}\times\sqrt{5}$ Fe-vacancy superstructure under hydraulic
external pressure based on first-principles simulations. While the Fe-vacancy
ordering persists up to at least $\sim $ 12GPa, the magnetic ground state goes
at $\sim$10GPa from the BS-AFM phase to a N{\'e}el-FM phase, a ferromagnetic
arrangement of a ""{\it{N{\'e}el cluster}}"". The new magnetic phase is metallic,
and the BS-AFM to N{\'e}el-FM phase transition is accompanied by a sizable
structural change. The two distinct magnetic phases can be understood within
the extended $J_1$-$J_2$ Heisenberg model by assuming a pressure-tuned
competition between the intrablock and interblock nearest-neighbor couplings of
iron moments.",1108.4322v2
2011-08-23,Unconventional multiband superconductivity with nodes in single-crystalline SrFe2(As_0.65P_0.35)2 as seen via 31P-NMR and specific heat,"We report 31P-NMR and specific heat measurements on an iron (Fe)-based
superconductor SrFe2(As0.65P0.35)2 with Tc=26 K, which have revealed the
development of antiferromagnetic correlations in the normal state and the
unconventional superconductivity(SC) with nodal gap dominated by the gapless
low-lying quasiparticle excitations. The results are consistently argued with
an unconventional multiband SC state with the gap-size ratio of different bands
being significantly large; the large full gaps in s\pm-wave state keep Tc high,
whereas a small gap with a nodal-structure causes gapless feature under
magnetic field. The present results will develop an insight into the strong
material dependence of SC-gap structure in Fe-based superconductors.",1108.4480v2
2011-08-24,In vitro toxicity and uptake of magnetic nanorods,"In this paper we investigate the internalization and cytotoxicity of
nanostructured materials having the form of elongated rods, with diameter of
200 nm and lengths 1 - 10 {\mu}m. The rods were made from the controlled
aggregation of sub-10 nm iron oxide nanoparticles. Recently, we have shown that
the nanorods inherited the superparamagnetic property of the particles. These
rods can actually be moved by the application of an external magnetic field.
Here we evaluate the in vitro toxicity of the magnetic nanorods by using MTT
assays on NIH/3T3 mouse fibroblasts. The toxicity assays revealed that the
nanorods are biocompatible, as exposed cells remained 100% viable relative to
controls over a period of a few days. Optical microscopy allow to visualize the
rods inside the cells and to determine their number per cell. Roughly 1/3 of
the total incubated rods were uptaken by the fibroblasts.",1108.4773v1
2011-08-25,XHIP: An Extended Hipparcos Compilation,"We present the Extended Hipparcos Compilation (XHIP), a database of all stars
in the New Reduction of the Hipparcos Catalog extensively cross-referenced with
data from a broad survey of presently available sources. The resulting
collection uniquely assigns 116,096 spectral classifications, 46,392 radial
velocities, and 18,549 homogenized iron abundances [Fe/H] to Hipparcos stars.
Stellar classifications from SIMBAD, indications of multiplicity from CCDM or
WDS, stellar ages from the Geneva-Copenhagen Survey III, supplemental
photometry from 2MASS and SIMBAD, and identifications of exoplanet host stars
are also included. Parameters for solar encounters and Galactic orbits are
calculated for a kinematically complete subset. Kinetic bias is found to be
minimal. Our compilation is available through the Centre de Donn\'ees
astronomiques de Strasbourg (CDS) as Catalog V/137B.",1108.4971v2
2011-08-30,X-ray evidence for the accretion disc-outflow connection in 3C 111,"We present the spectral analysis of three Suzaku XIS observations of 3C 111
requested to monitor the predicted variability of its ultra-fast outflow on ~7
days time-scales. We detect an ionized iron emission line in the first
observation and a blue-shifted absorption line in the second, when the flux is
~30% higher. The location of the material is constrained at <0.006pc from the
variability. Detailed modelling support an identification with ionized
reflection off the accretion disc at ~20-100r_g from the black hole and a
highly ionized and massive ultra-fast outflow with velocity ~0.1c,
respectively. The outflow is most probably accelerated by radiation pressure,
but additional magnetic thrust can not be excluded. The measured high outflow
rate and mechanical energy support the claims that disc outflows may have a
significant feedback role. This work provides the first direct evidence for an
accretion disc-outflow connection in a radio-loud AGN, possibly linked also to
the jet activity.",1108.6095v1
2011-09-07,Probing the Order Parameter of Superconducting LiFeAs using Pb/LiFeAs and Au/LiFeAs Point-Contact Spectroscopy,"We have fabricated c-axis point contact junctions between high-quality LiFeAs
single crystals and Pb or Au tips in order to study the nature of the
superconducting order parameter of LiFeAs, one of the few stoichiometric
iron-based superconductors. The observation of the Josephson current in c-axis
junctions with a conventional s-wave superconductor as the counterelectrode
indicates that the pairing symmetry in LiFeAs is not pure d-wave or pure
spin-triplet p-wave. A superconducting gap is clearly observed in point contact
Andreev reflection measurements performed on both Pb/LiFeAs and Au/LiFeAs
junctions. The conductance spectra can be well described by the
Blonder-Tinkham-Klapwijk model with a lifetime broadening term, resulting in a
gap value of \approx 1.6 meV (2{\Delta}/kBTC \approx 2.2).",1109.1537v2
2011-09-09,Microscopically derived Ginzburg-Landau theory for magnetic order in the iron pnictides,"We examine the competition of the observed stripe spin density wave (SDW)
with other commensurate and incommensurate SDW phases in a two-band model of
the pnictides. Starting from this microscopic model, we rigorously derive an
expansion of the free energy in terms of the different order parameters at the
mean-field level. We show that three distinct commensurate SDW states are
possible and study their appearance as a function of the doping and the
electronic structure. We show that the stripe phase is generally present, but
its extent in the phase diagram depends strongly upon the number of hole Fermi
pockets that are nested with the electron Fermi pockets. Electron pockets
competing for the same portion of a hole pocket play a crucial role. We discuss
the relevance of our results for the antiferromagnetism of the pnictides.",1109.2071v2
2011-09-09,"Competing superconducting, magnetic and charge orderings in the AF Heisenberg-Kondo lattice with Dirac electrons","Many recently discovered advanced materials, such as high-Tc cuprates, iron
pnictides and several heavy-fermions, exhibit a rich phase diagram suggesting
the presence of different competing interactions that would lead to various
types of ordering. Nevertheless, there is not yet a clear unifying picture
allowing the understanding of the detailed mechanisms that generate such
competing interactions. Having such a picture, however, could quite well be at
the very roots of the requirements for understanding high-Tc superconductivity
in cuprates and pnictides, for instance. In this work we consider the
antiferromagnetic (AF) Heisenberg-Kondo lattice, consisting of localized spins
with AF exchange interactions between nearest neighbors on a square lattice and
itinerant electrons, which undergo a magnetic Kondo interaction with the
localized spins, but are otherwise non-interacting. Using the Schwinger-boson
(CP$^1$) formalism and assuming the electrons are Dirac-like, we integrate on
the localized degrees of freedom thereby obtaining the effective interaction
among the itinerant electrons. This contains a BCS-like superconducting term, a
Nambu-Jona-Lasinio-like, charge gap term and a Ising and Heisenberg-like
magnetic terms. All these four competing interactions, therefore are generated
by the original Kondo magnetic interaction.",1109.2151v1
2011-09-12,Central stars of planetary nebulae: The white dwarf connection,"This paper is focused on the transition phase between central stars and white
dwarfs, i.e. objects in the effective temperature range 100,000 - 200,000 K. We
confine our review to hydrogen-deficient stars because the common H-rich
objects are subject of the paper by Ziegler et al. in these proceedings. We
address the claimed iron-deficiency in PG1159 stars and [WC] central stars. The
discovery of new Ne VII and Ne VIII lines in PG1159 stars suggests that the
identification of O VII and O VIII lines that are used for spectral
classification of [WCE] stars is wrong. We then present evidence for two
distinct post-AGB evolutionary sequences for H-deficient stars based on
abundance analyses of the He-dominated O(He) stars and the hot DO white dwarf
KPD0005+5106. Finally, we report on evidence for an H-deficient post-super AGB
evolution sequence represented by the hottest known, carbon/oxygen-atmosphere
white dwarf H1504+65 and the recently discovered carbon-atmosphere ""hot DQ""
white dwarfs.",1109.2391v1
2011-09-12,Spatial and Temporal Variations of the Diffuse Iron 6.4 keV Line in the Galactic Center Region,"We analyze the diffuse Fe I K-alpha line generated in the diffuse
interstellar molecular hydrogen by primary photons or subrelativistic protons
injected by Sagittarius (Sgr) A*. We showed that unlike emission from compact
molecular clouds, this emission can be permanently observed in the directions
of the Galactic center. We conclude that the diffuse emission of 6.4 keV line
observed at present is probably due to Fe I K-alpha vacancy production by
primary photons if the X-ray luminosity of Sgr A* was about Lx ~ 10^39-10^40
erg/s. In principle these data can also be described in the framework of the
model when the 6.4 keV line emission is generated by subrelativistic protons
generated by accretion onto the central black hole but in this case extreme
parameters of this model are necessary.",1109.2614v1
2011-09-14,Long- to short-range magnetic order in fluorine-doped CeFeAsO,"The evolution of the antiferromagnetic order parameter in CeFeAsO_{1-x}F_{x}
as a function of the fluorine content x was investigated primarily via
zero-field muon-spin spectroscopy. The long-range magnetic order observed in
the undoped compound gradually turns into a short-range order at x=0.04,
seemingly accompanied/induced by a drastic reduction of the magnetic moment of
the iron ions. Superconductivity appears upon a further increase in doping
(x>0.04) when, unlike in the cuprates, the Fe magnetic moments become even
weaker. The resulting phase diagram evidences the presence of a crossover
region, where the superconducting and the magnetic order parameters coexist on
a nanoscopic range.",1109.3170v1
2011-09-19,Mechanism of Cooper-pairing in layered high temperature superconductors,"In this study, the pairing mechanism for layered HTS materials based on
attraction between electrons from adjacent layers is proposed. Initially, each
layer has expanded Fermi sphere owing to ridged geometry. When the two layers
are close enough for tunneling, it becomes energetically advantageous to form
correlated quantum states (CQS), reducing the Fermi sphere volume. Cooper
pairs, comprising inter-tunneling electrons, occupy the CQS. The image force is
responsible for the electron-electron attraction. Pair-binding energy and the
corresponding effective mass vary in a wide range. At T>0, some heavy pairs do
not condense. Such pairs are responsible for pseudogap. Light pairs get Bose
condensed and are responsible for superconductivity. The proposed mechanism
provides clarification of superconductivity in cuprates, iron based
superconductors and LSCO/LCO interfaces. It provides explanation of two energy
gaps and two characteristic temperatures in layered superconducting materials.
It also provides clarification on the Fermi surface pockets, anisotropy of
charge transport in pseudogap state, and other properties of HTS materials. The
pseudogap, estimated within the model, fits the experimental values for the
two-layer cuprates, such as YBCO, Bi2212, Tl2212, and Hg1212.",1109.3978v1
2011-09-19,Magnetic nanocomposites: new methodology for micromagnetic modeling and SANS experiments,"A new methodology for micromagnetic simulations of magnetic nanocomposites is
presented. The methodology is especially suitable for simulations of two-phase
composites consisting of magnetically hard inclusions in a soft magnetic matrix
phase. The proposed technique allows to avoid the unnecessary discretization of
the 'hard' inclusions (these are normally in a single-domain state), but
enables an arbitrary fine discretization of the 'soft' phase. The method is
applied to the determination of the equilibrium magnetization state of an
iron-based nanocomposite from the Nanoperm (FeZrBCu) family of alloys and to
the calculation of the corresponding small-angle neutron scattering (SANS)
cross-section. For this highly interesting material, the results of our
simulations exhibit a remarkable agreement with the nontrivial 'clover-leaf'
SANS cross-sections observed experimentally (A. Michels et al., Phys. Rev. B,
v. 74, 134407 (2006)).",1109.4075v1
2011-09-20,Fundamental Parameters and Chemical Composition of Arcturus,"We derive a self-consistent set of atmospheric parameters and abundances of
17 elements for the red giant star Arcturus: Teff = 4286+/-30 K, logg =
1.66+/-0.05, and [Fe/H] = -0.52+/-0.04. The effective temperature was
determined using model atmosphere fits to the observed spectral energy
distribution from the blue to the mid-infrared (0.44 to 10 um). The surface
gravity was calculated using the trigonometric parallax of the star and stellar
evolution models. A differential abundance analysis relative to the solar
spectrum allowed us to derive iron abundances from equivalent width
measurements of 37 FeI and 9 FeII lines, unblended in the spectra of both
Arcturus and the Sun; the [Fe/H] value adopted is derived from FeI lines. We
also determine the mass, radius, and age of Arcturus: M = 1.08+/-0.06 Msun, R =
25.4+/-0.2 Rsun, and t = 7.1(+1.5/-1.2) Gyr. Finally, abundances of the
following elements are measured from an equivalent width analysis of atomic
features: C, O, Na, Mg, Al, Si, K, Ca, Sc, Ti, V, Cr, Mn, Co, Ni, and Zn. We
find the chemical composition of Arcturus typical of that of a local thick-disk
star, consistent with its kinematics.",1109.4425v1
2011-09-21,RKKY interaction in SDW phase of iron-based superconductors,"Using the multiband model we analyze the Ruderman-Kittel-Kasuya-Yosida (RKKY)
interaction between the magnetic impurities in layered ferropnictide
superconductors. In the normal state the interaction is spin isotropic and is
dominated by the nesting features of the electron and hole bands separated by
the antiferromagnetic momentum, ${\bf Q}_{AF}$. In the AF state the RKKY
interaction maps into an effective anisotropic XXZ-type Heisenberg exchange
model. The anisotropy originates from the breaking of the spin-rotational
symmetry induced by the AF order and its strength depends on the size of the AF
gap and the structure of the folded Fermi surface. We discuss our results in
connection to the recent experiments.",1109.4643v1
2011-09-23,Friedel-like Oscillations from Interstitial Iron in Superconducting Fe1+yTe0.62Se0.38,"Using polarized and unpolarized neutron scattering we show that interstitial
Fe in superconducting Fe_{1+y}Te_{1-x}Se_x induces a magnetic Friedel-like
oscillation that diffracts at Q_(in-plane)=(1/2,0) and involves >50 neighboring
Fe sites. The interstitial >2 mu_B moment is surrounded by compensating
ferromagnetic four spin clusters that may seed double stripe ordering in
Fe_{1+y}Te. A semi-metallic 5-band model with (1/2,1/2) Fermi surface nesting
and four fold symmetric super-exchange between interstitial Fe and two in-plane
nearest neighbors largely accounts for the observed diffraction.",1109.5196v1
2011-10-06,Energy and Xmax reconstruction of hadron-initiated showers in surface arrays,"The current methods to determine the primary energy in surface arrays are
different when dealing with hadron or photon initiated showers. In this work,
we adapt a method previously developed for photon-initiated showers to hadron
primaries. We determine the Monte Carlo parametrizations that relate the
surface energy estimator and the maximum of shower development for both, proton
and Iron primaries. Using for each primary their own set of calibration curves,
which is of course impossible in practice, we show that the energy could be
inferred with a negligible bias and 12% resolution. However, we show that a
mixed calibration could also be performed, including both type of primaries,
such that the bias still remains low and the achieved resolution is around 15%.
In addition, the method allows the simultaneous determination of Xmax in pure
surface arrays with resolution better than 7%.",1110.1179v1
2011-10-07,Direct observation of the influence of the FeAs4 tetrahedron on superconductivity and antiferromagnetic correlations in Sr2VO3FeAs,"We measure the pressure dependence of the electrical resistivity and the
crystal structure of iron superconductor Sr2VO3FeAs. Below ~10 GPa the
structure compresses but remains undeformed, with regular FeAs4 tetrahedrons,
and a constant Tc. Beyond 10GPa, the tetrahedron strongly distorts, while Tc
goes gradually to zero. Band structure calculations of the undistorted
structure show multiple nesting features that hinder the development of an
antiferromagnetic ground state (AF), allowing the appearance of
superconductivity. The deformation of the tetrahedra that breaks band
degeneracy degrades multiple nesting, thus favouring one particular AF state at
the expense of Tc.",1110.1559v1
2011-10-11,Spin Glass and Semiconducting Behavior in 1D BaFe2-δSe3 Crystals,"We investigate the physical properties and electronic structure of
BaFe2-{\delta}Se3 crystals, which were grown out of tellurium flux. The crystal
structure of the compound, an iron-deficient derivative of the ThCr2Si2-type,
is built upon edge-shared FeSe4 tetrahedra fused into double chains. The
semiconducting BaFe2-{\delta}Se3 with {\delta} \approx 0.2 ({\rho}295K = 0.18
{\Omega}\cdotcm and Eg = 0.30 eV) does not order magnetically, however there is
evidence for short-range magnetic correlations of spin glass type (Tf \approx
50 K) in magnetization, heat capacity and neutron diffraction results. A
one-third substitution of selenium with sulfur leads to a slightly higher
electrical conductivity ({\rho}295K = 0.11 {\Omega}\cdotcm and Eg = 0.22 eV)
and a lower spin glass freezing temperature (Tf \approx 15 K), corroborating
with higher electrical conductivity reported for BaFe2S3. According to the
electronic structure calculations, BaFe2Se3 can be considered as a
one-dimensional ladder structure with a weak interchain coupling.",1110.2439v1
2011-10-17,MINERvA Status and Event Reconstruction,"MINERvA (Main INjector ExpeRiment v-A) is a few-GeV neutrino scattering
experiment that began taking data in the NuMI beam at Fermilab (FNAL) in the
Fall of 2009. MINERvA employs a fine-grained detector, with an eight ton active
target region composed of plastic scintillator. It also uses nuclear targets
composed of carbon, iron, and lead placed upstream of the active region to
measure v-A dependence. The experiment will provide important inputs for
neutrino oscillation experiments and a pure weak probe of nuclear structure. We
offer a set of initial kinematic distributions of interest and provide a
summary of current operations and event reconstruction status. Contribution to
NUFACT 11, XIIIth International Workshop on Neutrino Factories, Super beams and
Beta beams, 1-6 August 2011, CERN and University of Geneva .",1110.3727v1
2011-10-21,Magnetic properties of spin diluted iron pnictides from muSR and NMR in LaFe1-xRuxAsO,"The effect of isoelectronic substitutions on the microscopic properties of
LaFe1-xRuxAsO, for 0< x< 0.8, has been investigated by means of muSR and 139La
NMR. It was found that Ru substitution causes a progressive reduction of the
N\`eel temperature (T_N) and of the magnetic order parameter without leading to
the onset of superconductivity. The temperature dependence of 139La nuclear
spin-lattice relaxation rate 1/T_1 can be suitably described within a two-band
model. One band giving rise to the spin density wave ground-state, while the
other one is characterized by weakly correlated electrons. Fe for Ru
substitution yields to a progressive decrease of the density of states at the
Fermi level close to the one derived from band structure calculations. The
reduction of T_N with doping follows the predictions of the J_1-J_2 model on a
square lattice, which appears to be an effective framework to describe the
magnetic properties of the spin density wave ground-state.",1110.4812v1
2011-10-25,Optical conductivity of superconducting K{0.8}Fe{2-y}Se2 single crystals: Evidence for a Josephson-coupled phase,"The optical properties of the iron-chalcogenide superconductor
K{0.8}Fe{2-y}Se2, with a critical temperature Tc = 31 K, have been measured
over a wide frequency range in the a-b planes above and below Tc. The
conductivity is incoherent at room temperature, but becomes coherent
(Drude-like) at T ~ Tc; however, R_\Box ~ 64 k-Ohm, well above the threshold
for the superconductor-insulator transition at R_\Box = h/4e^2 ~ 6.9 k-Ohm.
Below Tc, the superfluid density \rho_{s0} ~ 48 x 10^3 cm^{-2} places this
material on the scaling line \rho_{s0}/8 ~ 4.4 \sigma_{dc} Tc, but in a region
associated with Josephson coupling, suggesting this material is inhomogeneous
and constitutes a Josephson phase.",1110.5529v2
2011-10-25,Ba{1-x}KxMn2As2: An Antiferromagnetic Local-Moment Metal,"The compound BaMn2As2 with the tetragonal ThCr2Si2 structure is a
local-moment antiferromagnetic insulator with a Neel temperature TN = 625 K and
a large ordered moment mu = 3.9 mu_B/Mn. We demonstrate that this compound can
be driven metallic by partial substitution of Ba by K, while retaining the same
crystal and antiferromagnetic structures together with nearly the same high TN
and large mu. Ba_{1-x}K_xMn2As2 is thus the first metallic ThCr2Si2-type
MAs-based system containing local 3d transition metal M magnetic moments, with
consequences for the ongoing debate about the local moment versus itinerant
pictures of the FeAs-based superconductors and parent compounds. The
Ba_{1-x}K_xMn2As2 class of compounds also forms a bridge between the layered
iron pnictides and cuprates and may be useful to test theories of high Tc
superconductivity.",1110.5546v2
2011-10-26,"Correlation-enhanced electron-phonon coupling: Applications of GW and screened hybrid functional to bismuthates, chloronitrides, and other high Tc superconductors","We show that the electron-phonon coupling (EPC) in many materials can be
significantly underestimated by the standard density functional theory (DFT) in
the local density approximation (LDA) due to large non-local correlation
effects. We present a simple yet efficient methodology to evaluate the
realistic EPC going beyond LDA by using more advanced and accurate GW and
screened hybrid functional DFT approaches. The corrections we propose explain
the extraordinarily high superconducting temperatures that are observed in two
distinct classes of compounds-the bismuthates and the transition metal
chloronitrides, thus solving a thirty-year-old puzzle. Our work calls for the
critically reevaluation of the EPC of certain phonon modes in many other
materials such as cuprates and iron-based superconductors. The proposed
methodology can be used to design new correlation-enhanced high temperature
superconductors and other functional materials involving electron-phonon
interaction.",1110.5751v2
2011-10-26,High transport critical current densities in textured Fe-sheathed Sr1-xKxFe2As2+Sn superconducting tapes,"We report the realization of grain alignment in Sn-added Sr1-xKxFe2As2
superconducting tapes prepared by ex-situ powder-in-tube method. At 4.2 K, high
transport critical current densities Jc of 2.5x10^4 A/cm^2 (Ic = 180 A) in
self-field and 3.5x10^3 A/cm^2 (Ic = 25.5 A) in 10 T have been measured. These
values are the highest ever reported so far for Fe-based superconducting wires
and tapes. We believe the superior Jc in our tape samples are due to well
textured grains and strengthened intergrain coupling achieved by Sn addition.
Our results demonstrated an encouraging prospect for application of iron based
superconductors.",1110.5784v2
2011-11-03,Effect of tensile stress on the in-plane resistivity anisotropy in BaFe2As2,"The effect of uniaxial tensile stress and the resultant strain on the
structural/magnetic transition in the parent compound of the iron arsenide
superconductor, BaFe$_2$As$_2$, is characterized by temperature-dependent
electrical resistivity, x-ray diffraction and quantitative polarized light
imaging. We show that strain induces a measurable uniaxial structural
distortion above the first-order magnetic transition and significantly smears
the structural transition. This response is different from that found in
another parent compound, SrFe$_2$As$_2$, where the coupled structural and
magnetic transitions are strongly first order. This difference in the
structural responses explains the in-plain resistivity anisotropy above the
transition in BaFe$_2$As$_2$. This conclusion is supported by the
Ginzburg-Landau - type phenomenological model for the effect of the uniaxial
strain on the resistivity anisotropy.",1111.0997v1
2011-11-03,Doping - dependent superconducting gap anisotropy in the two-dimensional 10-3-8 pnictide Ca$_{10}$(Pt$_3$As$_8$)[(Fe$_{1-x}$Pt$_{x}$)$_2$As$_2$]$_5$,"The characteristic features of
Ca$_{10}$(Pt$_3$As$_8$)[(Fe$_{1-x}$Pt$_x$)$_2$As$_2$]$_5$ (""10-3-8"")
superconductor are relatively high anisotropy and a clear separation of
superconductivity and structural/magnetic transitions, which allows studying
the superconducting gap without complications due to the coexisting order
parameters. The London penetration depth, measured in underdoped single
crystals of 10-3-8 ($x =$ 0.028, 0.041, 0.042, and 0.097), shows behavior
remarkably similar to other Fe-based superconductors, exhibiting robust
power-law, $\Delta \lambda(T) = A T^n$. The exponent $n$ decreases from 2.36
($x =$ 0.097, close to optimal doping) to 1.7 ($x =$ 0.028, a heavily
underdoped composition), suggesting that the superconducting gap becomes more
anisotropic at the dome edge. A similar trend is found in low-anisotropy
superconductors based on BaFe$_2$As$_2$ (""122""), implying that it is an
intrinsic property of superconductivity in iron pnictides, unrelated to the
coexistence of magnetic order and superconductivity or the anisotropy of the
normal state. Overall this doping dependence is consistent with $s_{\pm}$
pairing competing with intra-band repulsion.",1111.1003v1
2011-11-07,Effects of correlation in LiFeAs,"We discuss the role of electronic correlations in the iron-based
superconductor LiFeAs by studying the effects on band structure, mass
enhancements, and Fermi surface in the framework of density functional theory
combined with dynamical mean field theory calculations. We conclude that LiFeAs
shows characteristics of a moderately correlated metal and that the strength of
correlations is mainly controlled by the value of the Hund's rule coupling J.
The hole pockets of the Fermi surface show a distinctive change in form and
size with implications for the nesting properties. Our calculations are in good
agreement with recent angle-resolved photoemission spectroscopy and de Haas-van
Alphen experiments.",1111.1620v2
2011-11-08,Superconducting proximity effect to the block antiferromagnetism in K$_{y}$Fe$_{2-x}$Se$_{2}$,"Recent discovery of superconducting (SC) ternary iron selenides has block
antiferromagentic (AFM) long range order. Many experiments show possible
mesoscopic phase separation of the superconductivity and antiferromagnetism,
while the neutron experiment reveals a sizable suppression of magnetic moment
due to the superconductivity indicating a possible phase coexistence. Here we
propose that the observed suppression of the magnetic moment may be explained
due to the proximity effect within a phase separation scenario. We use a
two-orbital model to study the proximity effect on a layer of block AFM state
induced by neighboring SC layers via an interlayer tunneling mechanism. We
argue that the proximity effect in ternary Fe-selenides should be large because
of the large interlayer coupling and weak electron correlation. The result of
our mean field theory is compared with the neutron experiments
semi-quantitatively. The suppression of the magnetic moment due to the SC
proximity effect is found to be more pronounced in the d-wave superconductivity
and may be enhanced by the frustrated structure of the block AFM state.",1111.1860v1
2011-11-08,A Bayesian approach to magnetic moment determination using muSR,"A significant challenge in zero-field muSR experiments arises from the
uncertainty in the muon site. It is possible to calculate the dipole field (and
hence precession frequency nu) at any particular site given the magnetic moment
mu and magnetic structure. One can also evaluate f(nu), the probability
distribution function of nu assuming that the muon site can be anywhere within
the unit cell with equal probability, excluding physically forbidden sites.
Since nu is obtained from experiment, what we would like to know is g(mu|nu),
the probability density function of mu given the observed nu. This can be
obtained from our calculated f(nu/mu) using Bayes' theorem. We describe an
approach to this problem which we have used to extract information about real
systems including a low-moment osmate compound, a family of molecular magnets,
and an iron-arsenide compound.",1111.1980v1
2011-11-09,Effect of uniaxial strain on the structural and magnetic phase transitions in BaFe$_2$As$_2$,"We report neutron scattering experiments probing the influence of uniaxial
strain on both the magnetic and structural order parameters in the parent iron
pnictide compound, BaFe$_2$As$_2$. Our data show that modest strain fields
along the in-plane orthorhombic b-axis can affect significant changes in phase
behavior simultaneous to the removal of structural twinning effects. As a
result, we demonstrate in BaFe$_2$As$_2$ samples detwinned via uniaxial strain
that the in-plane C$_4$ symmetry is broken by \textit{both} the structural
lattice distortion \textit{and} long-range spin ordering at temperatures far
above the nominal (strain-free), phase transition temperatures. Surprising
changes in the magnetic order parameter of this system under relatively small
strain fields also suggest the inherent presence of magnetic domains
fluctuating above the strain-free ordering temperature in this material.",1111.2326v2
2011-11-14,VLT/X-shooter observations and the chemical composition of cool white dwarfs,"We present a model atmosphere analysis of cool hydrogen-rich white dwarfs
observed at the Very Large Telescope (VLT) with the X-shooter spectrograph. The
intermediate-dispersion and high signal-to-noise ratio of the spectra allowed
us to conduct a detailed analysis of hydrogen and heavy element line profiles.
In particular, we tested various prescriptions for hydrogen Balmer line
broadening parameters and determined the effective temperature and surface
gravity of each star. Three objects (NLTT 1675, 6390 and 11393) show the
presence of heavy elements (Mg, Al, Ca, or Fe). Our abundance analysis revealed
a relatively high iron to calcium ratio in NLTT 1675 and NLTT 6390. We also
present an analysis of spectropolarimetric data obtained at the VLT using the
focal reducer and low dispersion spectrograph (FORS) and we established strict
upper limits on the magnetic field strengths in three of the DAZ white dwarfs
and determined the longitudinal magnetic field strength in the DAZ NLTT 10480.
The class of DAZ white dwarfs comprises objects that are possibly accreting
material from their immediate circumstellar environment and the present study
contributes in establishing class properties.",1111.3250v1
2011-11-14,Quantised orbital angular momentum transfer and magnetic dichroism in the interaction of electron vortices with matter,"Following the very recent experimental realisation of electron vortices, we
consider their interaction with matter, in particular the transfer of orbital
angular momentum in the context of electron energy loss spectroscopy, and the
recently observed dichroism in thin film magnetised iron samples. We show here
that orbital angular momentum exchange does indeed occur between electron
vortices and the internal electronic-type motion, as well as center of mass
motion of atoms in the electric dipole approximation. This contrasts with the
case of optical vortices where such transfer only occurs in transitions
involving multipoles higher than the dipole. The physical basis of the observed
dichroism is explained.",1111.3259v2
2011-11-15,Unconventional Anisotropic s-Wave Superconducting Gaps of LiFeAs Iron-Pnictide Superconductor,"We have performed high-resolution angle-resolved photoemission spectroscopy
on Fe-based superconductor LiFeAs (Tc = 18 K). We reveal multiple nodeless
superconducting (SC) gaps with 2D/kBTc ratios varying from 2.8 to 6.4,
depending on the Fermi surface (FS). We also succeeded in directly observing a
gap anisotropy along the FS with magnitude up to ~30 %. The anisotropy is
four-fold symmetric with an antiphase between the hole and electron FSs,
suggesting complex anisotropic interactions for the SC pairing. The observed
momentum dependence of the SC gap offers an excellent opportunity to
investigate the underlying pairing mechanism.",1111.3496v2
2011-11-16,Metamagnetic Behavior and Kondo Breakdown in Heavy-Fermion CeFePO,"We report that nonmagnetic heavy-fermion (HF) iron oxypnictide CeFePO with
two-dimensional XY-type anisotropy shows a metamagnetic behavior at the
metamagnetic field H_M \simeq 4 T perpendicular to the c-axis and that a
critical behavior is observed around H_M. Although the magnetic character is
entirely different from that in other Ce-based HF metamagnets, H_M in these
metamagnets is linearly proportional to the inverse of the effective mass, or
to the temperature where the susceptibility shows a peak. This finding suggests
that H_M is a magnetic field breaking the local Kondo singlet, and the critical
behavior around H_M is driven by the Kondo breakdown accompanied by the
Fermi-surface instability.",1111.3749v3
2011-11-18,Magnetoelastic coupling in iron,"Exchange interactions in {\alpha}- and {\gamma}-Fe are investigated within an
ab-initio spin spiral approach. We have performed total energy calculations for
different magnetic structures as a function of lattice distortions, related
with various cell volumes and the Bain tetragonal deformations. The effective
exchange parameters in {\gamma}-Fe are very sensitive to the lattice
distortions, leading to the ferromagnetic ground state for the tetragonal
deformation or increase of the volume cell. At the same time, the
magnetic-structure-independent part of the total energy changes very slowly
with the tetragonal deformations. The computational results demonstrate a
strong mutual dependence of crystal and magnetic structures in Fe and explain
the observable ""anti-Invar"" behavior of thermal expansion coefficient in
{\gamma}-Fe.",1111.4432v1
2011-11-21,Dissipative electro-elastic network model of protein electrostatics,"We propose a dissipative electro-elastic network model (DENM) to describe the
dynamics and statistics of electrostatic fluctuations at active sites of
proteins. The model combines the harmonic network of residue beads with
overdamped dynamics of the normal modes of the network characterized by two
friction coefficients. The electrostatic component is introduced to the model
through atomic charges of the protein force field. The overall effect of the
electrostatic fluctuations of the network is recorded through the
frequency-dependent response functions of the electrostatic potential and
electric field at the active site. We also consider the dynamics of
displacements of individual residues in the network and the dynamics of
distances between pairs of residues. The model is tested against loss spectra
of residue displacements and the electrostatic potential and electric field at
the heme's iron from all-atom molecular dynamics simulations of three hydrated
globular proteins.",1111.4726v1
2011-11-21,Pairing Glue Activation in Cuprates within the Quantum Critical Regime,"A grand challenge in many-body quantum physics is to explain the apparent
connection between quantum criticality and high-temperature superconductivity
in the cuprates and similar systems, such as the iron pnictides and
chalcogenides. Here we argue that the quantum-critical regime plays an
essential role in activating a strong-pairing mechanism: although pairing
bosons create a symmetry-breaking instability which suppresses pairing, the
combination of these broken-symmetry states within the critical regime can
restore this symmetry for the paired quasiparticles. This condition is shown to
be met within a large-U ansatz. A hidden quantum phase transition then arises
between a Fermi-liquid and a non-Fermi-liquid broken-symmetry striped state,
and a critical regime in which the broken-symmetry states are combined.",1111.5033v3
2011-11-17,About a possible path towards the reverse engineering of quantum mechanics,"An out of the box intellectual path exploring the foundations of quantum
mechanics is discussed in some detail, in order to clarify why a possibly
different way to look at the relevant fundamental questions can be identified
and can support further research. Two key concepts arise. (1) Einstein critics
to quantum mechanics could be taken seriously, but ironically, in order to
really do so, one would have to take seriously also some of Lorentz critics to
special relativity - both in a possibly more modern way; such interconnection
possibly having been a blocking factor to openly discuss some of the cross
implications of alternative views about quantum mechanics to date. (2) The
probabilistic interpretation is a by-product of (a) quantum evolution
equations, (b) conservation laws for the combination of measuring system and
measured object and (c) persistency of calibration of the measuring system - as
such there is no intellectual conflict whatsoever between hidden variables
theories and probabilistic interpretation, provided we consider multicomponent
hidden variable models and we allow for the existence of an underlying network.
The implications of such concepts, in particular for the development of a
microscopic quantisation program, are heuristically discussed or preliminarily
explored.",1111.5215v1
2011-11-24,Interplay between superconductivity and antiferromagnetism in some iron-pnictide single crystals studied by $^{57}$Fe Mössbauer spectroscopy,"We have performed detailed $^{57}$Fe M\""ossbauer spectroscopy measurements on
Ba$_{0.78}$K$_{0.22}$Fe$_2$As$_2$ and BaFe$_{2-x}$Ni$_x$As$_2$ single crystal
mosaics showing antiferromagnetic ordering below $T_N$ with superconductivity
below $T_C$. Analysis of the M\""ossbauer spectra shows a decrease in the
magnetic hyperfine (hf) field but no change in the magnetic volume fraction
below $T_C$. This clearly indicates the coexistence of magnetism and
superconductivity in these compounds. The decrease in the magnetic hf field
below $T_C$ depends on the difference between $T_N$ and $T_C$, being the
largest for $T_N$ close to $T_C$. Two different explanations for this
observation are given. We also find that the non-magnetic volume fraction below
$T_N$ correlates with the Ni doping $x$, being large for high $T_C$ and small
for high $T_N$.",1111.5853v1
2011-11-28,Phase diagram and oxygen annealing effect of FeTe1-xSex iron-based superconductor,"Phase diagrams of as-grown and O2-annealed FeTe1-xSex determined from
magnetic susceptibility measurement were obtained. For as-grown samples, the
antiferromagnetic order was fully suppressed in the range region x \geq 0.15,
and weak superconductivity appeared when x \geq 0.1. Beginning at x = 0.5, weak
superconductivity was found to evolve into bulk superconductivity.
Interestingly, for O2-annealed samples, complete suppression of magnetic order
and the occurrence of bulk superconductivity were observed when x \geq 0.1. We
found that O2-annealing induces bulk superconductivity for FeTe1-xSex. Oxygen
probably plays a key role in the suppression of the magnetic order and the
appearance of bulk superconductivity.",1111.6472v3
2011-12-01,Detailed abundances for M giants in two inner bulge fields from Infrared Spectroscopy,"We report abundance analysis for 30 M giant stars in two inner Galactic bulge
fields at (l,b)=(0,-1.75) deg and at (l,b)=(1,-2.65) deg, based on R=25,000
infrared spectroscopy from 1.5-1.8um using NIRSPEC at the Keck II telescope. We
find iron abundances of <[Fe/H]>=-0.16 +/- 0.03 dex with a 1-sigma dispersion
of 0.12 +/- 0.02 and <[Fe/H]>=-0.21 +/- 0.02 dex, with a 1-sigma dispersion of
0.09+/- 0.016 for the (l,b)=(0,-1.75) and (l,b)=(1,-2.65) deg fields,
respectively. In agreement with all prior studies, we find enhanced [alpha/Fe]
of +0.3 dex. We confirm the lack of any major vertical abundance or composition
gradient in the innermost ~600 pc between Baade's window and 150 pc from the
Galactic plane. We also confirm that the known enhancement of alpha elements
observed between 500 and 1000 pc from the nucleus is also present over the
volume of the inner bulge and may therefore be presumed to be a general
characteristic of bulge/bar stars within 1 kpc of the Galactic Center.",1112.0306v1
2011-12-08,Photovoltaic Effect on Molecule Coupled Ferromagnetic Films of a Magnetic Tunnel Junction,"Economical solar energy conversion to electricity can be boosted by the
discovery of fundamentally new photovoltaic mechanism, and a suitable system to
realize it with commonly available materials like iron (Fe) and nickel (Ni).
This paper reports the observation of photovoltaic effect on a molecular
spintronics device, composed of magnetic tunnel junction (MTJ) and
organometallic molecular clusters (OMCs). A prefabricated MTJ with exposed side
edges, after enabling the bridging of OMC channels between its two
ferromagnetic films, exhibited following phenomenon (i) dramatic increase in
exchange coupling, (ii) 3-6 orders current suppression and (iii) photovoltaic
effect. This paper focuses on the photovoltaic effect. Control experiments on
isolated ferromagnetic films suggested that OMCs neither affected the magnetic
properties nor produced any photovoltaic effect; photovoltaic effect was only
observed on the ferromagnetic films serving as magnetic electrodes in a MTJ.
Present paper invites further investigation of the similar photovoltaic effect
on other combinations of MTJs and promising magnetic molecules, like single
molecular magnets, organometallic clusters and porphyrins. This research can
lead to mass producible and economical spin photovoltaic devices.",1112.1879v2
2011-12-10,Existence of Orbital Order and its Fluctuation in Ba(Fe$_{1-x}$Co$_x$)$_2$As$_2$ Revealed by X-ray Absorption Spectroscopy,"We performed temperature dependent X-ray linear dichroism (XLD) experiments
on an iron pnictide system, Ba(Fe$_{1-x}$Co$_x$)$_2$As$_2$ with $x$=0.00 and
0.05, to experimentally verify existence of orbital ordering (OO). We observed
clear XLD in polarization dependent X-ray absorption spectra of Fe $L$ edges.
By exploiting the difference in the temperature dependent behaviors, we were
able to separate OO and structure contributions to XLD. The observed OO signal
indicates different occupation numbers for $d_{yz}$ and $d_{zx}$ orbitals and
supports existence of a ferro-OO. The results are also consistent with the
theoretical prediction. Moreover, we find substantial OO signal above the
transition temperature, which suggests that OO fluctuation exists well above
the transition temperature.",1112.2243v1
2011-12-20,A Constructive Approach to Reduced-Form Auctions with Applications to Multi-Item Mechanism Design,"We provide a constructive proof of Border's theorem [Bor91, HR15a] and its
generalization to reduced-form auctions with asymmetric bidders [Bor07, MV10,
CKM13]. Given a reduced form, we identify a subset of Border constraints that
are necessary and sufficient to determine its feasibility. Importantly, the
number of these constraints is linear in the total number of bidder types. In
addition, we provide a characterization result showing that every feasible
reduced form can be induced by an ex-post allocation rule that is a
distribution over ironings of the same total ordering of the union of all
bidders' types.
  We show how to leverage our results for single-item reduced forms to design
auctions with heterogeneous items and asymmetric bidders with valuations that
are additive over items. Appealing to our constructive Border's theorem, we
obtain polynomial-time algorithms for computing the revenue-optimal auction.
Appealing to our characterization of feasible reduced forms, we characterize
feasible multi-item allocation rules.",1112.4572v2
2011-12-20,Observation of Multiple Superconducting Gaps in the Infrared Reflectivity Spectra of Ba(Fe0.9Co0.1)2As2,"The results of infrared reflectivity measurements for the iron-based
high-temperature superconductor Ba(Fe0.9Co0.1)2As2 are reported. The
reflectivity is found to be close to unity at frequencies w lower than 2Delta/h
(2Delta is the superconducting gap and h is Planck's constant). This is
evidence for the s+/- or s+/+ symmetry of the superconducting order parameter
in the studied compound. The infrared reflectivity spectra of
Ba(Fe0.9Co0.1)2As2 manifest opening of several superconducting gaps at
temperatures lower than critical Tc.",1112.4636v2
2011-12-21,"Optical properties and electronic structure of multiferroic hexagonal orthoferrites RFeO3 (R=Ho, Er, Lu)","We report on optical studies of the thin films of multiferroic hexagonal
(P.G. 6mm) rare-earth orthoferrites RFeO3 (R=Ho, Er, Lu) grown epitaxially on a
(111)-surface of ZrO2(Y2O3) substrate. The optical absorption study in the
range of 0.6-5.6 eV shows that the films are transparent below 1.9 eV; above
this energy four broad intense absorption bands are distinguished. The
absorption spectra are analyzed taking into account the unusual fivefold
coordination of the Fe(3+) ion. Temperature dependence of the optical
absorption at 4.9 eV shows anomaly at 124 K, which we attribute to magnetic
ordering of iron sublattices.",1112.5102v3
2011-12-26,Surface properties of the clean and Au/Pd covered Fe$_3$O$_4$(111): a DFT and DFT+$U$ study,"The spin-density functional theory (DFT) and DFT+$U$ with Hubbard $U$ term
accounting for on-site Coulomb interactions were applied to investigate
structure, stability, and electronic properties of different terminations of
the Fe$_3$O$_4$(111) surface. All terminations of the ferrimagnetic
Fe$_3$O$_4$(111) surface exhibit very large (up to 90%) relaxations of the
first four interlayer distances, decreasing with the oxide layer depth. Our
calculations predict the iron terminated surface to be most stable in a wide
range of the accessible values of the oxygen chemical potential. The adsorption
of Au and Pd on two stable Fe- and O-terminated surfaces is studied. Our
results show that Pd binds stronger than Au both to the Fe- and O-terminated
surface. DFT+$U$ gives stronger bonding than DFT. The bonding of both
adsorbates to the O-terminated magnetite surface is by 1.5-2.5 eV stronger than
to the Fe-terminated surface.",1112.5827v1
2011-12-28,Possibility of Horizontal Line Node in KFe$_2$As$_2$ Probed by Muon Spin Rotation,"The anisotropy and temperature dependence of the magnetic field penetration
depth in the iron-based superconductor KFe$_2$As$_2$ have been measured down to
20 mK by means of muon spin rotation. We have observed that the flux-line
lattice forms triangular symmetry when we applied the field parallel to c-axis,
suggesting the interaction between vortices should be isotropic. The
temperature dependence of the penetration depth observd with an applied field
parallel and perpendicular to c-axis are different. These results can be
accounted for by a superconducting gap function with a horizontal line node in
the basal plane.",1112.6078v1
2011-12-29,Phenomenology of Neutrino Oscillations at the Neutrino Factory,"We consider the prospects for a neutrino factory to measure mixing angles,
the CP violating phase and mass-squared differences by detecting wrong-charged
muons arising from the chain \mu^+ to \nu_e to \nu_\mu\ to \mu^- and the
right-charged muons coming from the chain \mu^+ to \bar{\nu}_\mu\ to
\bar{\nu}_\mu\ to \mu^+ (similar to \mu^- chains), where \nu_e to \nu_\mu\ and
\bar{\nu}_\mu\ to \bar{\nu}_\mu\ are neutrino oscillation channels through a
long baseline. First, we perform the baseline and energy optimization of the
neutrino factory including the latest simulation results from the magnetized
iron neutrino detector (MIND). Second, we study physics with near detectors and
consider the treatment of systematic errors including cross section errors,
flux errors, and background uncertainties. Third, the effects of one additional
massive sterile neutrino are investigated in the context of near and far
detector combinations.",1112.6259v1
2012-01-04,"KxFe2-ySe2 single crystals: Floating-zone growth, Transport and Structural properties","Single crystals of superconducting KxFe2-ySe2 have been grown with the
optical floating-zone technique under application of 8 bar of argon pressure.
We found that large and high quality single crystals with dimensions of
~\varnothing6 \times 10 mm could be obtained at the termination of the grown
ingot through quenching, while the remaining part of the ingot decomposed.
As-grown single crystals commonly represent an intergrowth of two sets of the
c-axis characterized by slightly different lattice constants. Single crystal of
K0.80Fe1.81Se2 shows a superconducting transition at Tc = 31.6 K, leading to a
near 100% expulsion of the external magnetic field in magnetization
measurements. On the other hand, neutron-diffraction data indicate that
superconductivity in the sample coexists with a iron-vacancy superstructure and
static antiferromagnetic order. The anisotropic ratio of the upper critical
field Hc2 for both H//c and H//ab configurations is \sim3.46.",1201.0902v1
2012-01-04,A new candidate for probing Population III nucleosynthesis with carbon-enhanced damped Lyman-alpha systems,"We report the identification of a very metal-poor damped Lyman-alpha system
(DLA) at z_abs = 3.067295 that is modestly carbon-enhanced, with an iron
abundance of ~1/700 solar ([Fe/H] = -2.84) and [C,O/Fe] ~ +0.6. Such an
abundance pattern is likely to be the result of nucleosynthesis by massive
stars. On the basis of 17 metal absorption lines, we derive a 2 sigma upper
limit on the DLA's kinetic temperature of T_DLA <= 4700 K, which is broadly
consistent with the range of spin temperature estimates for DLAs at this
redshift and metallicity. While the best-fitting abundance pattern shows the
expected hallmarks of Population III nucleosynthesis, models of high-mass
Population II stars can match the abundance pattern almost as well. We discuss
current limitations in distinguishing between these two scenarios and the
marked improvement in identifying the remnants of Population III stars expected
from the forthcoming generation of 30-metre class telescopes.",1201.1004v2
2012-01-05,Metallicities for 6 nearby open clusters from high-resolution spectra of giant stars. [Fe/H] values for a planet search sample,"We present a study of the stellar parameters and iron abundances of 18 giant
stars in 6 open clusters. The analysis was based on high-resolution and
high-S/N spectra obtained with the UVES spectrograph (VLT-UT2). The results
complement our previous study where 13 clusters were already analyzed. The
total sample of 18 clusters is part of a program to search for planets around
giant stars. The results show that the 18 clusters cover a metallicity range
between -0.23 and +0.23 dex. Together with the derivation of the stellar
masses, these metallicities will allow the metallicity and mass effects to be
disentangled when analyzing the frequency of planets as a function of these
stellar parameters.",1201.1108v1
2012-01-09,A General Mechanism for Orbital Selective Phase Transitions,"Based on the analysis of a two-orbital Hubbard model within a mean-field
approach, we propose a mechanism for an orbital selective phase transition
(OSPT) where coexistence of localized and itinerant electrons can be realized.
We show that this OSPT exists both at and near half filling even in the absence
of crystal field splittings or when bandwidths, orbital degeneracies and
magnetic states are equal for both orbitals provided the orbitals have
different band dispersions. Such conditions should be generally satisfied in
many materials. We find that this OSPT is not sensitive to the strength of
Hund's rule coupling and that heavy doping favors the collinear
antiferromagnetic state over the OSPT. We discuss our results in relation to
the iron pnictides.",1201.1689v2
2012-01-19,"Impact of microstructure, temperature and strain ratio on energy-based low- cycle fatigue life prediction models for TiAl alloys","In this paper, two fatigue lifetime prediction models are tested on TiAl
intermetallic using results from uniaxial low-cycle fatigue tests. Both
assessments are based on dissipated energy but one of them considers a
hydrostatic pressure correction. This work allows to confirm, on this kind of
material, the linear nature, already noticed on silicon molybdenum cast iron,
TiNi shape memory alloy and 304L stainless steel, of dissipated energy,
corrected or not with hydrostatic pressure, according to the number of cycles
to failure. This study also highlights that, firstly, the dissipated energy
model is here more adequate to estimate low-cycle fatigue life and that,
secondly, intrinsic parameters like microstructure as well as extrinsic
parameters like temperature or strain ratio have an impact on prediction
results.",1201.4084v1
2012-01-20,Magnetic origin of chemical balance in alloyed Fe-Cr stainless steels: first-principles and Ising model study,"Iron-chromium forms the basis of most of the stainless steel grades in the
markets. Recently new insights into the physical and chemical properties of
Fe-Cr based alloys have been obtained. Some of the new results are quite
unexpected and call for further investigations. The present study addresses the
magnetic contribution in the atomic driving forces behind the chemical
composition in Fe-Cr alloyed with Al, Ti, V, Mn, Co, Ni, and Mo. Using the ab
initio exact muffin-tin orbitals method and an Ising-type spin model, it is
found that the magnetic moment of the solute atom combined with the induced
changes in the magnetic moments of the host atoms form the main framework in
determining the mixing energy and chemical potentials of low-Cr Fe-Cr based
alloys. The results obtained in the present work are related to tuning of the
microstructure and corrosion protection of low-Cr steels.",1201.4336v1
2012-01-23,Influence of the magnetoelectric coupling on the electric field induced magnetization reversal in a composite non-strained multiferroic chain,"We study theoretically the multiferroic dynamics in a composite
one-dimensional system consisting of BaTiO3 multiferroically coupled to an iron
chain. The method treats the magnetization and the polarization as
thermodynamic quantities describable via a combination of the Landau-Lifshits-
Gilbert and the Ginzburg-Landau dynamics coupled via an additional term in the
total free energy density. This term stems from the multiferroic interaction at
the interface. For a wide range of strengths of this coupling we predict the
possibility of obtaining a well-developed hysteresis in the ferromagnetic part
of the system induced by an external electric field. The dependence of the
reversal modes on the electric field frequency is also investigated and we
predict a considerable stability of the magnetization reversal for frequencies
in the range of 0.5 - 12 [GHz].",1201.4740v1
2012-01-24,Electronic Orders in the Verwey Structure of Magnetite,"Electronic structure calculations of the Verwey ground state of magnetite,
Fe3O4, using density functional theory with treatment of on-site Coulomb
interactions (DFT+U scheme) are reported. These calculations use the
recently-published experimental crystal structure coordinates for magnetite in
the monoclinic space group Cc. The computed density distribution for minority
spin electron states close to the Fermi level demonstrates that charge order
and Fe2+-orbital order are present at the B-type lattice sites to a
first-approximation. However, Fe2+/Fe3+ charge differences are diminished
through weak bonding interactions of the Fe2+-states to specific pairs of
neighboring iron sites that create linear, three-B-atom trimeron units that may
be regarded as 'orbital molecules'. Trimerons are ordered evenly along most Fe
atom chains in the Verwey structure, but more complex interactions are observed
within one chain.",1201.5106v2
2012-01-25,Effect of impurities on growth and morphology of cementite nanowires,"Effects of doping on morphology of iron carbide (cementite) nanowires have
been explored by first principle electronic structure calculations. We examined
the role of several realistic impurities (Si, Mn, V, P and S) in the formation
energies of the cementite nanowires with different sizes and morphologies. It
is shown that the presence of the impurities decreases the formation energy and
can switch the preferable axis of the cementite nanowire growth. The conditions
of the formation and decomposition of cementite nanowires in steels are also
discussed.",1201.5327v2
2012-01-26,Infrared emissivity spectroscopy of a soda-lime silicate glass up to the melt,"The short-range structure of an iron doped soda-lime glass was investigated
by infrared emissivity spectroscopy from room temperature up to the melt.
Quantitative information on the distribution of the Q^n tetrahedral units was
obtained by fitting the emissivity spectra using a dielectric function model
(DFM). The DFM is based on causal Gaussian bands, associated with the
stretching motions of the silicate tetrahedra. The changes in the absorption
modes are related to the activation of a dynamical disorder that continuously
increases with temperature. The obtained Q^n speciation at room temperature is
in good agreement with the magic-angle spinning nuclear magnetic resonance (MAS
NMR) study. The distribution of the tetrahedral species undergoes slight
changes with temperature, except during glass crystallization where Q^4 units
increases, with a slight augmentation of Q^2 and Q^4 units in the melt. These
results demonstrate the potentiality of infrared spectroscopy in the
quantitative analysis of the polymerization degree of glasses and melts.",1201.5676v1
2012-01-27,The effects of Vanadium on the strength of a bcc Fe Σ3(111)[1-10] grain boundary,"The effects of micro-alloying element, vanadium, on a bcc Fe \Sigma
3(111)[1-10] symmetric tilt grain boundary strength are studied using density
functional theory calculations. The lowest energy configuration of the grain
boundary structure are obtained from the first-principles calculations. The
substitutional and interstitial point defect formation energies of vanadium in
the grain boundary are compared. The substitutional defect is prefered to
interstitial one. The segregation energies of vanadium onto the grain boundary
and its fractured surfaces are computed. The cohesive energy calculation of the
grain boundary with and without vanadium show that vanadium strengthen the bcc
iron \Sigma 3(111)[1-10] grain boundary.",1201.5915v1
2012-02-01,Theory of High-Tc Superconductivity: Transition Temperature,"It is demonstrated that the transition temperature (Tc) of high-Tc
superconductors is determined by their layered crystal structure, bond lengths,
valency properties of the ions, and Coulomb coupling between electronic bands
in adjacent, spatially separated layers. Analysis of 31 high-Tc materials
(cuprates, ruthenates, rutheno-cuprates, iron pnictides, organics) yields the
universal relationship for optimal compounds, kBTc0 = {\beta}/\ell{\zeta},
where \ell is related to the mean spacing between interacting charges in the
layers, {\zeta} is the distance between interacting electronic layers, {\beta}
is a universal constant and Tc0 is the optimal transition temperature
(determined to within an uncertainty of +/- 1.4 K by this relationship).
Non-optimum compounds, in which sample degradation is evident, e.g. by
broadened superconducting transitions and diminished Meissner fractions,
typically exhibit reduced Tc < Tc0. It is shown that Tc0 may be obtained from
an average of Coulomb interaction forces between the two layers.",1202.0306v1
2012-02-03,Experimental and theoretical electronic structure of EuRh2As2,"The Fermi surfaces (FS's) and band dispersions of EuRh2As2 have been
investigated using angle-resolved photoemission spectroscopy. The results in
the high-temperature paramagnetic state are in good agreement with the full
potential linearized augmented plane wave calculations, especially in the
context of the shape of the two-dimensional FS's and band dispersion around the
Gamma (0,0) and X (pi,pi) points. Interesting changes in band folding are
predicted by the theoretical calculations below the magnetic transition
temperature Tn=47K. However, by comparing the FS's measured at 60K and 40K, we
did not observe any signature of this transition at the Fermi energy indicating
a very weak coupling of the electrons to the ordered magnetic moments or strong
fluctuations. Furthermore, the FS does not change across the temperature (~
25K) where changes are observed in the Hall coefficient. Notably, the Fermi
surface deviates drastically from the usual FS of the superconducting
iron-based AFe2As2 parent compounds, including the absence of nesting between
the Gamma and X FS pockets.",1202.0744v1
2012-02-12,Theory of High-Tc Superconductivity: Accurate Predictions of Tc,"The superconducting transition temperatures of high-Tc compounds based on
copper, iron, ruthenium and certain organic molecules are discovered to be
dependent on bond lengths, ionic valences, and Coulomb coupling between
electronic bands in adjacent, spatially separated layers [1]. Optimal
transition temperature, denoted as T_c0, is given by the universal expression
$k_BT_c0 = e^2 \Lambda / \ell\zeta$; $\ell$ is the spacing between interacting
charges within the layers, \zeta is the distance between interacting layers and
\Lambda is a universal constant, equal to about twice the reduced electron
Compton wavelength (suggesting that Compton scattering plays a role in
pairing). Non-optimum compounds in which sample degradation is evident
typically exhibit Tc < T_c0. For the 31+ optimum compounds tested, the
theoretical and experimental T_c0 agree statistically to within +/- 1.4 K. The
elemental high Tc building block comprises two adjacent and spatially separated
charge layers; the factor e^2/\zeta arises from Coulomb forces between them.
The theoretical charge structure representing a room-temperature superconductor
is also presented.",1202.2480v2
2012-02-16,Orbital Selective Magnetism in the Spin-Ladder Iron Selenides Ba$_{1-x}$K$_{x}$Fe$_2$Se$_3$,"Here we show that the 2.80(8) {\mu}B/Fe block antiferromagnetic order of
BaFe2Se3 transforms into stripe antiferromagnetic order in KFe2Se3 with a
decrease in moment to 2.1(1) {\mu}B/Fe. This reduction is larger than expected
from the change in electron count from Ba$^{2+}$ to K$^{+}$, and occurs with
the loss of the displacements of Fe atoms from ideal positions in the ladders,
as found by neutron pair distribution function analysis. Intermediate
compositions remain insulating, and magnetic susceptibility measurements show a
suppression of magnetic order and probable formation of a spin-glass. Together,
these results imply an orbital-dependent selection of magnetic versus bonded
behavior, driven by relative bandwidths and fillings.",1202.3676v2
2012-02-19,High $T_c$ superconductivity at the FeSe/SrTiO$_3$ Interface,"In a recent experiment the superconducting gap of a single unit cell thick
FeSe film on SrTiO$_3$ substrate is observed by scanning tunneling spectroscopy
and angle-resolved photoemission spectroscopy. The value of the superconducting
gap is much larger than that of the bulk FeSe under ambient pressure. In this
paper we study the effects of screening due to the ferroelectric phonons on
Cooper pairing. We conclude it can significantly enhance the energy scale of
Cooper pairing and even change the pairing symmetry. Our results also raise
some concerns on whether phonons can be completely ignored for bulk iron-based
superconductors.",1202.4141v2
2012-02-20,"Observation of superconductivity at 30 K~46 K in AxFe2Se2 (A = Li, Na, Ba, Sr, Ca, Yb, and Eu)","New iron selenide superconductors by intercalating smaller-sized alkali
metals (Li, Na) and alkaline earths using high-temperature routes have been
pursued ever since the discovery of superconductivity at about 30 K in KFe2Se2,
but all have failed so far. Here we demonstrate that a series of
superconductors with enhanced Tc=30~46 K can be obtained by intercalating
metals, Li, Na, Ba, Sr, Ca, Yb, and Eu in between FeSe layers by the
ammonothermal method at room temperature. Analysis on their powder X-ray
diffraction patterns reveals that all the main phases can be indexed based on
body-centered tetragonal lattices with a~3.755-3.831 {\AA} while c~15.99-20.54
{\AA}. Resistivities show the corresponding sharp transitions at 45 K and 39 K
for NaFe2Se2 and Ba0.8Fe2Se2, respectively, confirming their bulk
superconductivity. These findings provide a new starting point for studying the
properties of these superconductors and an effective synthetic route for the
exploration of new superconductors as well.",1202.4340v2
2012-02-20,Antiferromagnetic Domain Wall Engineering in Chromium Films,"We have engineered an antiferromagnetic domain wall by utilizing a magnetic
frustration effect of a thin iron cap layer deposited on a chromium film.
Through lithography and wet etching we selectively remove areas of the Fe cap
layer to form a patterned ferromagnetic mask over the Cr film. Removing the Fe
locally removes magnetic frustration in user-defined regions of the Cr film. We
present x-ray microdiffraction microscopy results confirming the formation of a
90{\deg} spin-density wave propagation domain wall in Cr. This domain wall
nucleates at the boundary defined by our Fe mask.",1202.4401v1
2012-02-21,A first-principles investigation on the effects of magnetism on the Bain transformation of $α$-phase FeNi systems,"The effects of magnetism on the Bain transformation of $\alpha$-phase FeNi
systems are investigated by using the full potential linearized augmented plane
wave (FLAPW) method based on the generalized gradient approximation (GGA). We
found that Ni impurity in bcc Fe increases the lattice constant in
ferromagnetic (FM) states, but not in the nonmagnetic (NM) states. The shear
modulus $G$ and Young's modulus $E$ of bcc Fe are also increased by raising the
concentration of nickel. All the compositions considered show high shear
anisotropy and the ratio of the bulk to shear modulus is greater than 1.75
implying ductility. The mean sound velocities in the $[100]$ directions are
greater than in the $[110]$ directions. The Bain transformation, which is a
component of martensitic transformation, has also been studied to reveal that
Ni$_{x}$Fe$_{1-x}$ alloys are elastically unstable in the NM states, but not so
in the FM states. The electronic structures explain these results in terms of
the density of states at the Fermi level. It is evident that magnetism cannot
be neglected when dealing with the Bain transformation in iron and its alloys.",1202.4726v1
2012-02-23,Tuning magnetism in FeAs-based materials via tetrahedral structure,"Resistivity, magnetic susceptibility, neutron scattering and x-ray
crystallography measurements were used to study the evolution of magnetic order
and crystallographic structure in single-crystal samples of the Ba1-xSrxFe2As2
and Sr1-yCayFe2As2 series. A non-monotonic dependence of the magnetic ordering
temperature T0 on chemical pressure is compared to the progression of the
antiferromagnetic staggered moment, characteristics of the ordering transition
and structural parameters to reveal a distinct relationship between the
magnetic energy scale and the tetrahedral bond angle, even far above T0. In
Sr1-yCayFe2As2, an abrupt drop in T0 precisely at the Ca concentration where
the tetrahedral structure approaches the ideal geometry indicates a strong
coupling between the orbital bonding structure and the stabilization of
magnetic order, providing strong constraints on the nature of magnetism in the
iron-arsenide superconducting parent compounds.",1202.5324v2
2012-02-24,Block magnetism coupled with local distortion in the iron-based spin-ladder compound BaFe2Se3,"Magnetism in the insulating BaFe$_2$Se$_3$ was examined through
susceptibility, specific heat, resistivity and neutron diffraction
measurements. After formation of a short-range magnetic correlation, a
long-range ordering was observed below $T_{\rm N}\sim 255$ K. The transition is
obscured by bulk properties. Magnetic moments ($\parallel a$) are arranged to
form a Fe$_4$ ferromagnetic unit, and each Fe$_4$ stacks antiferromagnetically.
This block magnetism is of the third type among magnetic structures of ferrous
materials. The magnetic ordering drives unusually large distortion via
magnetoelastic coupling.",1202.5371v1
2012-02-24,Nanoscale layering of antiferromagnetic and superconducting phases in Rb2Fe4Se5,"We studied phase separation in a single-crystalline antiferromagnetic
superconductor Rb2Fe4Se5 (RFS) using a combination of scattering-type scanning
near-field optical microscopy (s-SNOM) and low-energy muon spin rotation
(LE-\mu SR). We demonstrate that the antiferromagnetic and superconducting
phases segregate into nanometer-thick layers perpendicular to the iron-selenide
planes, while the characteristic in-plane size of the metallic domains reaches
10 \mu m. By means of LE-\mu SR we further show that in a 40-nm thick surface
layer the ordered antiferromagnetic moment is drastically reduced, while the
volume fraction of the paramagnetic phase is significantly enhanced over its
bulk value. Self-organization into a quasiregular heterostructure indicates an
intimate connection between the modulated superconducting and antiferromagnetic
phases.",1202.5446v2
2012-02-28,"Conductance of non-ballistic point contacts in hybrid systems ""normal metal/superconductor"" Cu/Mo-C and Cu/LaOFFeAs","We consider the shape of the curves of ""Andreev"" conductance of non-ballistic
point contact NS heterosystems depending on the bias voltage at the contact.
The obtained shape of those curves is caused by the contribution from the
mechanism of coherent scattering by impurities which doubles the scattering
cross section. The behavior of generalized and differential conductance is
compared for ballistic and non-ballistic transport regimes. The criteria are
considered allowing one to discriminate between those regimes with the
corresponding conduction curves similar in appearance. The analysis is extended
to the case of non-ballistic transport in NS point contacts with exotic
superconductors, molybdenum carbide Mo-C and oxypnictide
La[O$_{1-x}$F$_{x}$]FeAs from a group of iron-based superconductors.",1202.6173v1
2012-03-01,Macroscopic phase segregation in superconducting K0.73Fe1.67Se2 as seen by muon spin rotation and infrared spectroscopy,"Using muon spin rotation (\muSR) and infrared spectroscopy we investigated
the recently discovered superconductor K0.73Fe1.67Se2 with Tc = 32 K. We show
that the combined data can be consistently described in terms of a
macroscopically phase segregated state with a matrix of ~88% volume fraction
that is insulating and strongly magnetic and inclusions with a ~12% volume
fraction which are metallic, superconducting and non-magnetic. The electronic
properties of the latter, in terms of the normal state plasma frequency and the
superconducting condensate density, appear to be similar as in other iron
selenide or arsenide superconductors.",1203.0286v2
2012-03-03,Extension of the Wu-Jing equation of state (EOS) for highly porous materials: calculations to validate and compare the thermoelectron model,"In order to verify and validate the newly developed thermoelectron equation
of state (EOS) model that is based on the Wu-Jing (W-J) EOS, calculations of
shock compression behavior have been made on five different porous metals-iron,
copper, lead, tungsten, and aluminum-which are commonly used as standards. The
model was used to calculate the Hugoniot, shock temperature, sound velocity,
and unloading isentrope for these materials and comparisons were made to
previous calculations and available data. Based on these comparisons, it is
felt that the model provides information in good agreement with the
corresponding experimental and theoretical data published previously. This
suggests that the new model can satisfactorily describe the properties of
shocked porous materials over a wide range of pressure and porosity.",1203.0619v1
2012-03-07,The interplay of electron doping and chemical pressure in Ba(Fe(1-y)Coy)2(As(1-x)Px)2,"The effects of internal chemical pressure on electron doped iron arsenide
superconductors are studied in the series Ba(Fe(1-y)Coy)2(As(1-x)Px)2.
Combinations of both dopants induce superconductivity also in such areas where
only one would not suffice, and can likewise move the system into an overdoped
state, while no higher critical temperature than 31 K in BaFe2(As(1-x)Px)2 was
found. The phase diagram gives no evidence of holes in BaFe2(As(1-x)Px)2 as
suggested by recent photoemission experiments. Chemical and physical pressure
act similarly in Ba(Fe(1-y)Coy)2(As(1-x)Px)2, but our data reveal that the most
important control parameter is the length of the Fe-As bond and not the unit
cell volume. This emphasizes that differences between chemical and physical
pressure which manifest oneself as the non-linear reduction of the Fe-As
distance in BaFe2(As(1-x)Px)2 are strongly linked to the superconducting
properties also in the Co doped compounds.",1203.1459v1
2012-03-12,Suppression of Superconductivity by Twin Boundaries in FeSe,"Low-temperature scanning tunneling microscopy and spectroscopy are employed
to investigate twin boundaries in stoichiometric FeSe films grown by molecular
beam epitaxy. Twin boundaries can be unambiguously identified by imaging the
90{\deg} change in the orientation of local electronic dimers from Fe site
impurities on either side. Twin boundaries run at approximately 45{\deg} to the
Fe-Fe bond directions, and noticeably suppress the superconducting gap, in
contrast with the recent experimental and theoretical findings in other iron
pnictides. Furthermore, vortices appear to accumulate on twin boundaries,
consistent with the degraded superconductivity there. The variation in
superconductivity is likely caused by the increased Se height in the vicinity
of twin boundaries, providing the first local evidence for the importance of
this height to the mechanism of superconductivity.",1203.2629v2
2012-03-13,Coexistence and competition of the short-range incommensurate antiferromagnetic order with superconductivity in BaFe2-xNixAs2,"Superconductivity in the iron pnictides develops near antiferromagnetism, and
the antiferromagnetic (AF) phase appears to overlap with the superconducting
phase in some materials such as BaFe2-xTxAs2 (where T = Co or Ni). Here we use
neutron scattering to demonstrate that genuine long-range AF order and
superconductivity do not coexist in BaFe2-xNixAs2 near optimal
superconductivity. In addition, we find a first-order-like AF to
superconductivity phase transition with no evidence for a magnetic quantum
critical point. Instead, the data reveal that incommensurate short-range AF
order coexists and competes with superconductivity, where the AF spin
correlation length is comparable to the superconducting coherence length.",1203.2759v2
2012-03-17,Magnetic Phase Transition and Relaxation Effects in LiFePO4,"We report the observation of para - antiferromagnetic transition at ~ 50 K in
lithium iron phosphate, LiFePO4 through DC magnetization and M\""ossbauer
spectroscopy. The Ferrous ion Fe2+ (3d6, 5D) in LiFePO4 exhibits relaxation
effects with a relaxation frequency ~1.076 \times 10(rise to 7) s-1 at 300 K.
The temperature dependence of the frequency suggests the origin of the
relaxation is spin-lattice type. The quadrupole splitting at low temperatures
indicates the excited orbital states mix strongly to the orbital doublet ground
state via spin-orbit coupling. Modified molecular field model analysis yields a
saturation value for hyperfine field ~125 kOe. The anomaly in magnetization and
M\""ossbauer parameters below 27 K may be ascribed to contribution of orbital
angular momentum. The high value of the asymmetry parameter ({\eta} ~ 0.8) of
the electric field gradient obtained in the antiferromagnetic regime indicates
a strongly distorted octahedral oxygen neighbourhood for the ferrous sites.",1203.3863v2
2012-03-19,Antiferromagnetic Order and Superconductivity in Sr4(Mg0.5-xTi0.5+x)2O6Fe2As2 with Electron Doping: 75As-NMR Study,"We report an 75As-NMR study on iron (Fe)-based superconductors with thick
perovskitetype blocking layers Sr4(Mg0.5-xTi0.5+x)2O6Fe2As2 with x=0 and 0.2.
We have found that antiferromagnetic (AFM) order takes place when x=0, and
superconductivity (SC) emerges below Tc=36 K when x=0.2. These results reveal
that the Fe-pnictides with thick perovskitetype blocks also undergo an
evolution from the AFM order to the SC by doping electron carriers into FeAs
planes through the chemical substitution of Ti+4 ions for Mg+2 ions, analogous
to the F-substitution in LaFeAsO compound. The reason why the Tc=36 K when
x=0.2 being higher than the optimally electron-doped LaFeAsO with Tc=27 K
relates to the fact that the local tetrahedron structure of FeAs4 is optimized
for the onset of SC.",1203.4190v1
2012-03-20,Phase soliton and pairing symmetry of a two-band superconductor: Role of the proximity effect,"We suggest a mechanism which promotes the existence of a phase soliton --
topological defect formed in the relative phase of superconducting gaps of a
two-band superconductor with s+- type of pairing. This mechanism exploits the
proximity effect with a conventional s-wave superconductor which favors the
alignment of the phases of the two-band superconductor which, in the case of
s+- pairing, are pi-shifted in the absence of proximity. In the case of a
strong proximity such effect can be used to reduce soliton's energy below the
energy of a soliton-free state thus making the soliton thermodynamically
stable. Based on this observation we consider an experimental setup, applicable
both for stable and metastable solitons, which can be used to distinguish
between s+- and s++ types of pairing in the iron-based multiband
superconductors.",1203.4554v3
2012-03-25,First Principles Calculation of Helical Spin Order in Iron Perovskite SrFeO3 and BaFeO3,"Motivated by recent discovery of ferromagnetism in cubic perovskite BaFeO3
under small magnetic field, we investigate spin order in BaFeO3 and
isostructual SrFeO3 by the first principles calculation. The on-site Coulomb
and exchange interactions are necessary for the helical spin order consistent
with experiments. SrFeO3 exhibits stable G-type helical order, while A- and
G-type helical orders in BaFeO3 are almost degenerate at short propagating
vector with tiny energetic barrier with respect to ferromagnetic spin order,
explaining ferromagnetism under small field. The results are consistent with
model calculation where negative charge-transfer energy is explicitly taken
into account.",1203.5470v1
2012-03-26,Probing the role of Co substitution in the electronic structure of iron-pnictides,"The role of Co substitution in the low-energy electronic structure of
Ca(Fe$_{0.944}$Co$_{0.056}$)$_2$As$_2$ is investigated by resonant
photoemission spectroscopy and density functional theory. The Co 3d-state
center-of-mass is observed at 250 meV higher binding energy than Fe's,
indicating that Co posses one extra valence electron, and that Fe and Co are in
the same 2+ oxidation state. Yet, significant Co character is detected for the
Bloch wavefunctions at the chemical potential, revealing that the Co 3d
electrons are part of the Fermi sea determining the Fermi surface. This
establishes the complex role of Co substitution in CaFe2As2, and the inadequacy
of a rigid-band shift description.",1203.5814v1
2012-03-28,Opening of the superconducting gap in the hole pockets of Ba(Fe(1-x)Co(x))2As2 as seen via Angle-Resolved PhotoElectron Spectroscopy,"We present an Angle-Resolved PhotoElectron Spectroscopy study of the changes
in the electronic structure of electron doped Ba(Fe(1-x)Co(x))2As2 across the
superconducting phase transition. By changing the polarization of the incoming
light, we were able to observe the opening of the gap for the inner hole pocket
alpha, and to compare its behavior with the outer hole-like band beta.
Measurements along high symmetry directions show that the behavior of beta is
consistent with an isotropic gap opening, while slight anisotropies are
detected for the inner band alpha. The implications of these results for the
s+/- symmetry of the superconducting order parameter are discussed, in relation
to the nature of the different iron orbitals contributing to the electronic
structure of this multiband system.",1203.6194v2
2012-04-02,Abrupt change in the energy gap of superconducting Ba1-xKxFe2As2 single crystals with hole doping,"We performed a Laser angle-resolved photoemission spectroscopy (ARPES) study
on a wide doping range of Ba1-xKxFe2As2 (BaK) and precisely determined the
doping evolution of the superconducting (SC) gaps in this compound. The gap
size of the outer hole Fermi surface (FS) sheet around the Brillioun zone (BZ)
center shows an abrupt drop with overdoping (for x > 0.6) while the inner and
middle FS gaps roughly scale with Tc. This is accompanied by the simultaneous
disappearance of the electron FS sheet with similar orbital character at the BZ
corner. These results browse the different contributions of X2-Y2 and XZ/YZ
orbitals to superconductivity in BaK and can be hardly completely reproduced by
the available theories on iron-based superconductors.",1204.0326v1
2012-04-02,Quantum critical point for stripe order: An organizing principle of cuprate superconductivity,"A spin density-wave quantum critical point (QCP) is the central organizing
principle of organic, iron-pnictide, heavy-fermion and electron-doped cuprate
superconductors. It accounts for the superconducting Tc dome, the
non-Fermi-liquid resistivity, and the Fermi-surface reconstruction. Outside the
magnetically ordered phase above the QCP, scattering and pairing decrease in
parallel as the system moves away from the QCP. Here we argue that a similar
scenario, based on a stripe-order QCP, is a central organizing principle of
hole-doped cuprate superconductors. Key properties of Eu-LSCO, Nd-LSCO and YBCO
are naturally unified, including stripe order itself, its QCP, Fermi-surface
reconstruction, the linear-T resistivity, and the nematic character of the
pseudogap phase.",1204.0490v1
2012-04-03,A photonic crystal cavity-optical fiber tip nanoparticle sensor for biomedical applications,"We present a sensor capable of detecting solution-based nanoparticles using
an optical fiber tip functionalized with a photonic crystal cavity. When sensor
tips are retracted from a nanoparticle solution after being submerged, we find
that a combination of convective fluid forces and optically-induced trapping
cause an aggregation of nanoparticles to form directly on cavity surfaces. A
simple readout of quantum dot photoluminescence coupled to the optical fiber
shows that nanoparticle presence and concentration can be detected through
modified cavity properties. Our sensor can detect both gold and iron oxide
nanoparticles and can be utilized for molecular sensing applications in
biomedicine.",1204.0818v1
2012-04-05,"Gaseous Material Orbiting the Polluted, Dusty White Dwarf HE1349-2305","We present new spectroscopic observations of the polluted, dusty,
helium-dominated atmosphere white dwarf star HE1349-2305. Optical spectroscopy
reveals weak CaII infrared triplet emission indicating that metallic gas debris
orbits and is accreted by the white dwarf. Atmospheric abundances are measured
for magnesium and silicon while upper limits for iron and oxygen are derived
from the available optical spectroscopy. HE1349-2305 is the first gas
disk-hosting white dwarf star identified amongst previously known polluted
white dwarfs. Further characterization of the parent body polluting this star
will require ultraviolet spectroscopy.",1204.1132v1
2012-04-04,Rare earth substitution in lattice-tuned Sr0.3Ca0.7Fe2As2 solid solutions,"The effects of aliovalent rare earth substitution on the physical properties
of Sr0.3Ca0.7Fe2As2 solid solutions are explored. Electrical transport,
magnetic susceptibility and structural characterization data as a function of
La substitution into (Sr_1-y_Ca_y)_1-x_La_x_Fe2As2 single crystals confirm the
ability to suppress the antiferromagnetic ordering temperature from 200 K in
the undoped compound down to 100 K approaching the solubility limit of La.
Despite up to ~30% La substitution, the persistence of magnetic order and lack
of any signature of superconductivity above 10 K present a contrasting phase
diagram to that of Ca1-xLaxFe2As2, indicating that the suppression of magnetic
order is necessary to induce the high-temperature superconducting phase
observed in Ca1-xLaxFe2As2.",1204.1335v2
2012-04-08,Two successive field-induced spin-flop transitions in single-crystalline CaCo$_{2}$As$_{2}$,"CaCo$_{2}$As$_{2}$, a ThCr$_{2}$Si$_{2}$-structure compound, undergoes an
antiferromagnetic transition at \emph{T$_{N}$}=76K with the magnetic moments
being aligned parallel to the \emph{c} axis. Electronic transport measurement
reveals that the coupling between conducting carriers and magnetic order in
CaCo$_{2}$As$_{2}$ is much weaker comparing to the parent compounds of iron
pnictide. Applying magnetic field along \emph{c} axis induces two successive
spin-flop transitions in its magnetic state. The magnetization saturation
behaviors with \emph{\textbf{H}$\parallel$c} and \emph{\textbf{H}$\parallel$ab}
at 10K indicate that the antiferromagnetic coupling along \emph{c} direction is
very weak. The interlayer antiferromagntic coupling constant \emph{J$_{c}$} is
estimated to be about 2 meV.",1204.1736v1
2012-04-09,Measurement of The Broad Line Region Size in a Luminous MACHO Quasar,"We measure the broad emission line region (BLR) size of a luminous, L~1E47
erg/s, high-z quasar using broadband photometric reverberation mapping. To this
end, we analyze ~7.5 years of photometric data for MACHO 13.6805.324 (z~1.72)
in the B and R MACHO bands and find a time delay of 180+/-40 days in the rest
frame of the object. Given the spectral-variability properties of high-z
quasars, we associate this lag with the rest-UV iron emission blends. Our
findings are consistent with a simple extrapolation of the BLR size-luminosity
relation in local active galactic nuclei to the more luminous, high-z quasar
population. Long-term spectroscopic monitoring of MACHO 13.6805.324 may be able
to directly measure the line-to-continuum time-delay and test our findings.",1204.1862v1
2012-04-19,Plasma Pressure Driven Asymmetric Supernovae and Highly Collimated Gamma-Ray Bursts,"During the process of collapse of a massive star, a cavity is generated
between the central iron core and an outer stellar envelope. The dynamics of
this cavity, filled with plasma and magnetic field of the rapidly rotating
proto-magnetar's magnetosphere, is believed to be very relevant in
understanding supernovae and gamma-ray bursts. The interactions of the
pressurized conducting plasma and the magnetic fields are described by a set of
magnetohydrodynamic (MHD) equations with poloidal and toroidal plasma flows not
aligned with magnetic fields. A sequence of MHD equilibria in response to the
increasing plasma pressure in the cavity, by continuous filling from the
rotating magnetosphere, is solved to account for asymmetric supernovae, highly
collimated gamma-ray burst jets, and also active galactic nucleus plasma torus.
It is shown that the magnetosphere of the central compact star is likely the
central engine of supernova and gamma-ray burst by feeding them plasma,
magnetic energy, and rotational energy.",1204.4360v2
2012-04-23,Importance of correlation effects in hcp iron revealed by a pressure-induced electronic topological transition,"We discover that hcp phases of Fe and Fe0.9Ni0.1 undergo an electronic
topological transition at pressures of about 40 GPa. This topological change of
the Fermi surface manifests itself through anomalous behavior of the Debye
sound velocity, c/a lattice parameter ratio and M\""ossbauer center shift
observed in our experiments. First-principles simulations within the dynamic
mean field approach demonstrate that the transition is induced by many-electron
effects. It is absent in one-electron calculations and represents a clear
signature of correlation effects in hcp Fe.",1204.5130v1
2012-05-03,Generalized joint density of states and its application to exploring the pairing symmetry of superconductors,"We introduce a generalized joint density of states (GJDOS), which
incorporates the coherent factor into the JDOS, to study quasiparticle
interference (QPI) in superconductors. The intimate relation between the
Fourier-transformed local density of states and GJDOS is revealed: they corre-
spond respectively to the real and imaginary parts of a generalized
impurity-response function, and particularly share the same angular factors and
singular boundaries, as seen from our approximate analytic results for d-wave
superconductors. Remarkably, our numerical GJDOS analysis agrees well with the
QPI patten of d-wave cuprates and s\pm-wave iron-based superconductors.
Moreover, we illustrate that the present GJDOS scenario can uncover the sign
features of the superconducting gap and thus can be used to explore the
possible pairing symmetry of the KxFe2-ySe2 superconductors.",1205.0598v1
2012-05-03,Quenched Fe Moment in the Collapsed Tetragonal Phase of Ca$_{1-x}$Pr$_{x}$Fe$_2$As$_2$,"We report $^{75}$As NMR studies on single crystals of rare-earth doped iron
pnictides superconductor Ca$_{1-x}$Pr$_{x}$Fe$_{2}$As$_{2}$ ($x$=0.075 and
0.15). The $^{75}$As spectra show a chemical pressure effect with doping and a
first order structure transition to the collapsed tetragonal phase upon
cooling. A sharp drop of the Knight shift is seen below the structural
transition, whereas $1/T_1$ is strongly enhanced at low-temperatures. These
evidences indicate quenching of Fe local magnetism and short-range ordering of
Pr$^{3+}$ moment in the collapsed tetragonal phase. The quenched Fe moment
through structure collapse suggests a strong interplay of structure and
magnetism, which is important for understanding the nature of the collapsed
tetragonal phase.",1205.0604v1
2012-05-09,Pseudo-potentials based first-principles approach to the magneto-optical Kerr effect: from metals to the inclusion of local fields and excitonic effects,"We propose a first-principles scheme for the description of the
magneto-optical kerr effect within density functional theory (DFT). Though the
computation of Kerr parameters is often done within DFT, starting from the
conductivity or the dielectric tensor, there is no formal justification to this
choice.
  As a first steps, using as reference materials iron, cobalt and nickel we
show that pseudo-potential based calculations give accurate predictions. Then
we derive a formal expression for the full dielectric tensor in terms of the
density-density correlation function. The derived equation is exact in systems
with an electronic gap, with the possible exception of Chern insulators, and
whenever the time reversal symmetry holds and can be used as a starting point
for the inclusion of local fields and excitonic effects within time-dependent
DFT for such systems.
  In case of metals instead we show that, starting from the density-density
correlation function, the term which describes the anomalous Hall effect is
neglected giving a wrong conductivity.",1205.1994v3
2012-05-14,Isotope shifts and hyperfine structure of the Fe I 373.7 nm resonance line,"We report measurements of the isotope shifts of the 3d6 4s2 a 5D3 - 3d6 4s4p
z 5F4o FeI resonance line at 373.7 nm between all four stable isotopes 54Fe,
56Fe, 57Fe and 58Fe, as well as the complete hyperfine structure of that line
for 57Fe, the only stable isotope having a non-zero nuclear spin. The field and
specific mass shift coefficients of the transition have been derived from the
data, as well as the experimental value for the hyperfine structure magnetic
dipole coupling constant A of the excited state of the transition in 57Fe :
A(3d6 4s4p z 5F4o) = 68.21(69) MHz. The measurements were carried out by means
of high-resolution Doppler-free laser saturated absorption spectroscopy in a
Fe-Ar hollow cathode discharge cell using both natural and enriched iron
samples. The measured isotope shifts and hyperfine constants are reported with
uncertainties at the percent level.",1205.3146v1
2012-05-17,Interstellar Dust Close to the Sun,"The low density interstellar medium (ISM) close to the Sun and inside of the
heliosphere provides a unique laboratory for studying interstellar dust grains.
Grain characteristics in the nearby ISM are obtained from observations of
interstellar gas and dust inside of the heliosphere and the interstellar gas
towards nearby stars. Comparison between the gas composition and solar
abundances suggests that grains are dominated by olivines and possibly some
form of iron oxide. Measurements of the interstellar Ne/O ratio by the
Interstellar Boundary Explorer spacecraft indicate that a high fraction of
interstellar oxygen in the ISM must be depleted onto dust grains. Local
interstellar abundances are consistent with grain destruction in ~150 km/s
interstellar shocks, provided that the carbonaceous component is hydrogenated
amorphous carbon and carbon abundances are correct. Variations in relative
abundances of refractories in gas suggest variations in the history of grain
destruction in nearby ISM. The large observed grains, > 1 micron, may indicate
a nearby reservoir of denser ISM. Theoretical three-dimensional models of the
interaction between interstellar dust grains and the solar wind predict that
plumes of about 0.18 micron dust grains form around the heliosphere.",1205.4017v1
2012-05-19,Iron spin-reorientation transition in NdFeAsO,"The low-temperature magnetic structure of NdFeAsO has been revisited using
neutron powder diffraction and symmetry analysis using the Sarah
representational analysis program. Four magnetic models with one magnetic
variable for each of the Nd and Fe sublattices were tested. The best fit was
obtained using a model with Fe moments pointing along the c-direction, and Nd
moments along the a-direction. This signals a significant interplay between
rare-earth and transition metal magnetism, which results in a
spin-reorientation of the Fe sublattice upon ordering of the Nd moments. All
models that fit the data well, including collinear models with more than one
magnetic variable per sublattice, were found to have an Fe moment of 0.5 BM and
a Nd moment of 0.9 BM, demonstrating that the low-temperature Fe moment is not
substantially enhanced compared to the spin-density wave (SDW) state.",1205.4312v1
2012-05-22,Theory of nonequilibrium dynamics of multiband superconductors,"We study the nonequilibrium dynamics of multiband BCS superconductors
subjected to ultrashort pump pulses. Using density-matrix theory, the time
evolution of the Bogoliubov quasiparticle densities and the superconducting
order parameters are computed as a function of pump pulse frequency, duration,
and intensity. Focusing on two-band superconductors, we consider two different
model systems. The first one, relevant for iron-based superconductors,
describes two-band superconductors with a repulsive interband interaction
$V_{12}$ which is much larger than the intraband pairing terms. The second
model, relevant for MgB$_2$, deals with the opposite limit where the intraband
interactions are dominant and the interband pair scattering $V_{12}$ is weak
but attractive. For ultrashort pump pulses, both of these models exhibit a
nonadiabatic behavior which is characterized by oscillations of the
superconducting order parameters. We find that for nonvanishing $V_{12}$, the
superconducting gap on each band exhibits two oscillatory frequencies which are
determined by the long-time asymptotic values of the gaps. The relative
strength of these two frequency components depends sensitively on the magnitude
of the interband interaction $V_{12}$.",1205.4861v2
2012-05-23,Bulk electronic structure of superconducting LaRu2P2 single crystals measured by soft x-ray angle-resolved photoemission spectroscopy,"We present a soft X-ray angle-resolved photoemission spectroscopy (SX-ARPES)
study of the stoichiometric pnictide superconductor LaRu2P2. The observed
electronic structure is in good agreement with density functional theory (DFT)
calculations. However, it is significantly different from its counterpart in
high-temperature superconducting Fe-pnictides. In particular the bandwidth
renormalization present in the Fe-pnictides (~2 - 3) is negligible in LaRu2P2
even though the mass enhancement is similar in both systems. Our results
suggest that the superconductivity in LaRu2P2 has a different origin with
respect to the iron pnictides. Finally we demonstrate that the increased
probing depth of SX-ARPES, compared to the widely used ultraviolet ARPES, is
essential in determining the bulk electronic structure in the experiment.",1205.5216v1
2012-05-23,Electronic phase diagram of disordered Co doped BaFe2As2,"Superconducting and normal state transport properties in iron pnictides are
sensitive to disorder and impurity scattering. By investigation of
Ba(Fe1-xCox)2As2 thin films with varying Co concentration, we demonstrate that
in the dirty limit the superconducting dome in the electronic phase diagram of
Ba(Fe1-xCox)2As2 shifts towards lower doping concentrations, which differs
significantly from observations in single crystals. We show that especially in
the underdoped regime superconducting transition temperatures higher than 27 K
are possible.",1205.5219v3
2012-05-25,Superconductivity at Tc = 44 K in LixFe2Se2(NH3)y,"Following a recent proposal by Burrard-Lucas et al. [unpublished, arXiv:
1203.5046] we intercalated FeSe by Li in liquid ammonia. We report on the
synthesis of new LixFe2Se2(NH3)y phases as well as on their magnetic and
superconducting properties. We suggest that the superconducting properties of
these new hybride materials appear not to be influenced by the presence of
electronically-innocent Li(NH2) salt moieties. Indeed, high onset temperatures
of 44 K and shielding fractions of almost 80% were only obtained in samples
containing exclusively Lix(NH3)y moieties acting simultaneously as electron
donors and spacer units. The c-axis of the new intercalated phases is strongly
enhanced when compared to the alkali-metal intercalated iron selenides
A1-xFe2-ySe2 with A = K, Rb, Cs, Tl with T c = 32 K.",1205.5731v1
2012-05-31,Superconducting Fluctuations and Anomalous Phonon Renormalization much above superconducting transition temperature in Ca4Al2O5.7Fe2As2,"Raman studies on Ca4Al2O5.7Fe2As2 superconductor in the temperature range of
5 K to 300 K, covering the superconducting transition temperature Tc ~ 28.3 K,
reveal that the Raman mode at ~ 230 cm-1 shows a sharp jump in frequency by ~ 2
% and linewidth increases by ~ 175 % at To ~ 60 K. Below To, anomalous
softening of the mode frequency and a large decrease by ~ 10 cm-1 in the
linewidth is observed. These precursor effects at T0 (~ 2Tc) are attributed to
significant superconducting fluctuations, possibly enhanced due to reduced
dimensionality arising from weaked coupling between the well separated (~ 15
{\AA}) Fe-As layers in the unit cell. A large blue-shift of the mode frequency
between 300 K to 60 K (~7%) indicates strong spin-phonon coupling in this
superconductor.",1205.7033v1
2012-06-03,Importance of many body effects in the kernel of hemoglobin for ligand binding,"We propose a mechanism for binding of diatomic ligands to heme based on a
dynamical orbital selection process. This scenario may be described as bonding
determined by local valence fluctuations. We support this model using
linear-scaling first-principles calculations, in combination with dynamical
mean-field theory, applied to heme, the kernel of the hemoglobin metalloprotein
central to human respiration. We find that variations in Hund's exchange
coupling induce a reduction of the iron 3d density, with a concomitant increase
of valence fluctuations. We discuss the comparison between our computed optical
absorption spectra and experimental data, our picture accounting for the
observation of optical transitions in the infrared regime, and how the Hund's
coupling reduces, by a factor of five, the strong imbalance in the binding
energies of heme with CO and O_2 ligands.",1206.0412v2
2012-06-08,Substituent Effects on the Spin-Transition Temperature in Complexes with Tris(pyrazolyl) Ligands,"Iron (II) complexes with substituted tris(pyrazolyl) ligands, which exhibit a
thermally driven transition from a low-spin state at low temperatures to a
high-spin state at elevated temperatures, have been studied by M\""ossbauer
spectroscopy and magnetic susceptibility measurements. From the observed
spectra the molar high-spin fraction and the transition temperature have been
extracted. All substituents, except for bromine, lead to a decrease of the
transition temperature. Density functional calculations have been carried out
to compare the experimentally observed shifts of the transition temperature
with those derived from theory.",1206.1883v1
2012-06-10,Anomalous impurity effects in the iron-based superconductor KFe$_2$As$_2$,"High-quality K(Fe$_{1-x}$Co$_x$)$_2$As$_2$ single crystals have been grown by
using KAs flux method. Instead of increasing the superconducting transition
temperature $T_{\rm c}$ through electron doping, we find that Co impurities
rapidly suppress $T_{\rm c}$ down to zero at only $x \approx$ 0.04. Such an
effective suppression of $T_{\rm c}$ by impurities is quite different from that
observed in Ba$_{0.5}$K$_{0.5}$Fe$_2$As$_2$ with multiple nodeless
superconducting gaps. Thermal conductivity measurements in zero field show that
the residual linear term $\kappa_0/T$ only change slightly with $3.4\%$ Co
doping, despite the sharp increase of scattering rate. The implications of
these anomalous impurity effects are discussed.",1206.2030v3
2012-06-11,Diffusion of hydrogen within idealised grains of bcc-Fe: A kinetic Monte Carlo study,"Structural defects in materials such as vacancies, grain boundaries, and
dislocations may trap hydrogen and a local accumulation of hydrogen at these
defects can lead to the degradation of the materials properties. An important
aspect in obtaining insight into hydrogen induced embrittlement on the
atomistic level is to understand the diffusion of hydrogen in these materials.
In our study we employ kinetic Monte Carlo (kMC) simulations to investigate
hydrogen diffusion in bcc iron within different microstructures. All input data
to the kMC model, such as available sites, solution energies, and diffusion
barriers are obtained from first-principles calculations. We find that hydrogen
mainly diffuses within the interface region with an overall diffusivity that is
lower than in pure bcc-Fe bulk. The concentration dependence of the diffusion
coefficient is strongly non-linear and the diffusion coefficient may even
decrease with increasing hydrogen concentration. To describe the macroscopic
diffusion coefficient we derive an analytic expression as a function of
hydrogen concentration and temperature which is in excellent agreement with our
numerical results for idealised microstructures.",1206.2314v1
2012-06-12,Electric field control of magnetic exchange coupling,"Electric control of magnetism is a vision which drives intense research on
magnetic semiconductors and multiferroics. Recently, also ultrathin metallic
films were reported to show magnetoelectric effects at room temperature. Here
we demonstrate much stronger effects by exploiting reduction/oxidation
reactions in a naturally grown oxide layer exchange coupled to an underlying
ferromagnet. For the exemplarily studied FePt/iron oxide composite in an
electrolyte, a large and reversible change of magnetization and anisotropy is
obtained. The principle can be transferred to various metal/oxide combinations.
It represents a novel approach towards multifunctionality.",1206.2467v3
2012-06-13,Mn local moments prevent superconductivity in iron-pnictides Ba(Fe 1-x Mn x)2As2,"75As nuclear magnetic resonance (NMR) experiments were performed on
Ba(Fe1-xMnx)2As2 (xMn = 2.5%, 5% and 12%) single crystals. The Fe layer
magnetic susceptibility far from Mn atoms is probed by the75As NMR line shift
and is found similar to that of BaFe2As2, implying that Mn does not induce
charge doping. A satellite line associated with the Mn nearest neighbours
(n.n.) of 75As displays a Curie-Weiss shift which demonstrates that Mn carries
a local magnetic moment. This is confirmed by the main line broadening typical
of a RKKY-like Mn-induced staggered spin polarization. The Mn moment is due to
the localization of the additional Mn hole. These findings explain why Mn does
not induce superconductivity in the pnictides contrary to other dopants such as
Co, Ni, Ru or K.",1206.2741v2
2012-06-15,Pressure-induced changes of the vibrational modes of spin-crossover complexes studied by nuclear resonance scattering of synchrotron radiation,"Nuclear inelastic scattering (NIS) spectra were recorded for the
spin-crossover complexes STP and ETP (STP =
[Fe(1,1,1-trisf[N-(2-pyridylmethyl)-N-methylamino]methylg- ethane)](ClO4)2 and
ETP =
[Fe(1,1,1-trisf[N-(2-pyridylmethyl)-N-methylamino]methylg-butane)](ClO4)2) at
30 K and at room temperature and also at ambient pressure and applied pressure
(up to 2.6 GPa). Spin transition from the high-spin (HS) to the low-spin (LS)
state was observed by lowering temperature and also by applying pressure at
room temperature and has been assigned to the hardening of iron-bond stretching
modes due to the smaller volume in the LS isomer.",1206.3451v1
2012-06-20,Evolution of band structure from optimally doped to heavily overdoped Co-substituted NaFeAs,"Using angle-resolved photoemission spectroscopy, we studied the electronic
structure of NaFe$_{1-x}$Co$_x$As from an optimally doped superconducting
compound ($x=0.028$) to a heavily overdoped non-superconducting one
($x=0.109$). Similar to the case of ""122"" type iron pnictides, our data suggest
that Co dopant in NaFe$_{1-x}$Co$_x$As supplies extra charge carriers and
shifts the Fermi level accordingly. In the $x=0.109$ compound, the hole-like
bands around the zone center $\Gamma$ move to deeper binding energies and an
electron pocket appears instead. The overall band renormalization remains
basically the same throughout the doping range we studied, suggesting that the
local magnetic/electronic correlations are not affected by carrier doping. We
speculate that a balance between itinerant properties of mobile carriers and
local interactions may play an important role for the superconductivity.",1206.4402v1
2012-06-27,BaFe2Se2O as an Iron-Based Mott Insulator with Antiferromagnetic Order,"A new compound with a quasi-two-dimensional array of FeSe3O tetrahedra and an
orthorombic structure, namely BaFe2Se2O, has been successfully fabricated.
Experimental results show that this compound is an insulator and has an
antiferromagnetic (AF) transition at 240 K. Band structure calculation reveals
the narrowing of Fe 3d bands near the Fermi energy, which leads to the
localization of magnetism and the Mott insulating behavior. The large distances
between the Fe atoms perhaps are responsible for the characters. Linear
response calculation further indicates a strong in-plane AF exchange $J$, this
can account for the enhanced magnetic susceptibility (which has a maximum at
about 450 K) above the Neel temperature.",1206.6154v3
2012-06-27,Effect of Ru susbstitution on atomic displacements in the layered SmFe_{1-x}Ru_xAsO_{0.85}F_{0.15} superconductor,"The effect of Ru substitution on the local structure of layered
SmFe$_{1-x}$Ru$_x$AsO$_{0.85}$F$_{0.15}$ superconductor has been studied by As
$K$- and Sm $L_3$ - edges x-ray-absorption spectroscopy. The extended
x-ray-absorption fine-structure measurements reveal distinct Fe-As and Ru-As
bondlengths in the Ru substituted samples with the latter being $\sim$0.03 \AA\
longer. Local disorder induced by the Ru substitution is mainly confined to the
FeAs layer while the SmO spacer layer sustains a relative order, consistent
with the x-ray-absorption near-edge structure spectra. The results suggest
that, in addition to the order/disorder in the active active iron-arsenide
layer, its coupling to the rare-earth\textminus oxygen spacer layer needs to be
considered for describing the electronic properties of these layered
superconductors.",1206.6526v1
2012-06-29,Ferromagnetism and superconductivity in P-doped CeFeAsO,"We report on superconductivity in CeFeAs1-xPxO and the possible coexistence
with Ce- ferromagnetism (FM) in a small homogeneity range around x = 30% with
ordering temperatures of T_SC = T_C = 4K. The antiferromagnetic (AFM) ordering
temperature of Fe at this critical concentration is suppressed to T^N_Fe ~ 40K
and does not shift to lower temperatures with further increase of the P
concentration. Therefore, a quantum-critical-point scenario with T^N_Fe -> 0K
which is widely discussed for the iron based superconductors can be excluded
for this alloy series. Surprisingly, thermal expansion and X-ray powder
diffraction indicate the absence of an orthorhombic distortion despite clear
evidence for short range AFM Fe-ordering from muon-spin-rotation measurements.
Furthermore, we discovered the formation of a sharp electron spin resonance
signal unambiguously connected with the emergence of FM ordering.",1206.7088v2
2012-07-02,"Germanium, Arsenic, and Selenium Abundances in Metal-Poor Stars","The elements germanium (Ge, Z=32), arsenic (As, Z=33), and selenium (Se,
Z=34) span the transition from charged-particle or explosive synthesis of the
iron-group elements to neutron-capture synthesis of heavier elements. Among
these three elements, only the chemical evolution of germanium has been studied
previously. Here we use archive observations made with the Space Telescope
Imaging Spectrograph on board the Hubble Space Telescope and observations from
several ground-based facilities to study the chemical enrichment histories of
seven stars with metallicities -2.6 < [Fe/H] < -0.4. We perform a standard
abundance analysis of germanium, arsenic, selenium, and several other elements
produced by neutron-capture reactions. When combined with previous derivations
of germanium abundances in metal-poor stars, our sample reveals an increase in
the [Ge/Fe] ratios at higher metallicities. This could mark the onset of the
weak s-process contribution to germanium. In contrast, the [As/Fe] and [Se/Fe]
ratios remain roughly constant. These data do not directly indicate the origin
of germanium, arsenic, and selenium at low metallicity, but they suggest that
the weak and main components of the s-process are not likely sources.",1207.0518v1
2012-07-03,Updated Atomic Data and Calculations for X-ray Spectroscopy,"We describe the latest release of AtomDB, version 2.0.2, a database of atomic
data and a plasma modeling code with a focus on X-ray astronomy. This release
includes several major updates to the fundamental atomic structure and process
data held within AtomDB, incorporating new ionization balance data,
state-selective recombination data, and updated collisional excitation data for
many ions, including the iron L-shell ions from Fe$^{+16}$ to Fe$^{+23}$ and
all of the hydrogen- and helium-like sequences. We also describe some of the
effects that these changes have on calculated emission and diagnostic line
ratios, such as changes in the temperature implied by the He-like G-ratios of
up to a factor of 2.",1207.0576v1
2012-07-05,Spin reorientation in TlFe1.6Se2 with complete vacancy ordering,"The relationship between vacancy ordering and magnetism in TlFe1.6Se2 has
been investigated via single crystal neutron diffraction, nuclear forward
scattering, and transmission electron microscopy. The examination of chemically
and structurally homogenous crystals allows the true ground state to be
revealed, which is characterized by Fe moments lying in the ab-plane below
100K. This is in sharp contrast to crystals containing regions of order and
disorder, where a competition between c-axis and ab-plane orientations of the
moments is observed. The properties of partially-disordered TlFe1.6Se2 are
therefore not associated with solely the ordered or disordered regions. This
contrasts the viewpoint that phase separation results in independent physical
properties in intercalated iron selenides, suggesting a coupling between
ordered and disordered regions may play an important role in the
superconducting analogues.",1207.1318v2
2012-07-06,Two-band superconductivity featuring different anisotropies in the ternary iron silicide Lu$_{2}$Fe$_{3}$Si$_{5}$,"We report detailed studies of the upper critical field and low-temperature
specific heat in the two-gap superconductor Lu$_{2}$Fe$_{3}$Si$_{5}$. The
anisotropy of the upper critical field suggests that the active band is
quasi-one-dimensional. Low-temperature specific heat in magnetic fields reveals
that the virtual $H_{c2}$ in the passive band is almost isotropic. These
results strongly indicate that the two bands have two different anisotropies,
similar to the typical two-gap superconductor MgB$_{2}$, and their interplay
may be essential to the two-gap superconductivity in Lu$_{2}$Fe$_{3}$Si$_{5}$.",1207.1502v1
2012-07-08,Emergent Phases of Nodeless and Nodal Superconductivity Separated by Antiferromagnetic Order in Iron-based Superconductor (Ca4Al2O6)Fe2(As1-xPx)2: 75As- and 31P-NMR Studies,"We report $^{31}$P- and $^{75}$As-NMR studies on
(Ca$_4$Al$_2$O$_{6}$)Fe$_2$(As$_{1-x}$P$_x$)$_2$ with an isovalent substitution
of P for As. We present the novel evolution of emergent phases that the
nodeless superconductivity (SC) in 0$\le x \le$0.4 and the nodal one around
$x$=1 are intimately separated by the onset of a commensurate stripe-type
antiferromagnetic (AFM) order in 0.5$\le x \le$ 0.95, as an isovalent
substitution of P for As decreases a pnictogen height $h_{Pn}$ measured from
the Fe plane. It is demonstrated that the AFM order takes place under a
condition of 1.32\AA$\le h_{Pn} \le$1.42\AA, which is also the case for other
Fe-pnictides with the Fe$^{2+}$ state in (Fe$Pn$)$^{-}$ layers. This novel
phase evolution with the variation in $h_{Pn}$ points to the importance of
electron correlation for the emergence of SC as well as AFM order.",1207.1920v2
2012-07-09,Time-Dependent Density Diagnostics of Solar Flare Plasmas Using SDO/EVE,"Temporally-resolved electron density measurements of solar flare plasmas are
presented using data from the EUV Variability Experiment (EVE) onboard the
Solar Dynamics Observatory (SDO). The EVE spectral range contains emission
lines formed between 10^4-10^7 K, including transitions from highly ionized
iron (>10 MK). Using three density-sensitive Fe XXI ratios, peak electron
densities of 10^(11.2)-10^(12.1) cm^(-3) were found during four X-class flares.
While previous measurements of densities at such high temperatures were made at
only one point during a flaring event, EVE now allows the temporal evolution of
these high-temperature densities to be determined at 10 s cadence. A comparison
with GOES data revealed that the peak of the density time profiles for each
line ratio correlated well with that of the emission measure time profile for
each of the events studied.",1207.1990v1
2012-07-10,Magnetism in parent Fe-chalcogenides: quantum fluctuations select a plaquette order,"We analyze magnetic order in iron-chalcogenide Fe$_{1+y}$Te -- the parent
compound of high-temperature superconductor Fe$_{1+y}$Te$_{1-x}$Se$_x$. Neutron
scattering experiments show that magnetic order in this material contains
components with momentum $Q_1=(\pi/2, \pi/2)$ and $Q_2 =(\pi/2, -\pi/2)$ in
Fe-only Brillouin zone. The actual spin order depends on the interplay between
these two components. Previous works argued that spin order is a single-$Q$
state (either $Q_1$ or $Q_2$). Such an order breaks rotational $C_4$ symmetry
and order spins into a double diagonal stripe. We show that quantum
fluctuations actually select another order -- a double $Q$ plaquette state with
equal weight of $Q_1$ and $Q_2$ components, which preserves $C_4$ symmetry but
breaks $Z_4$ translational symmetry. We argue that the plaquette state is
consistent with recent neutron scattering experiments on Fe$_{1+y}$Te.",1207.2201v2
2012-07-16,CVD Synthesis of Small-Diameter Single Walled Carbon Nanotubes on Silicon,"A simple process for chemical vapor deposition of ultra SD single wall carbon
nanotubes has been developed. In this process, an iron nitrate nonahydrate
solution in isopropyl alcohol with a concentration of 400 ug/mlit was used to
catalyze nanoparticles formation on an oxidized silicon wafer. The oxide on the
substrate was made of a thick layer of wet oxide sandwiched between tow thin
layers of dry oxide. The process results in semiconducting single-walled carbon
nanotubes (SWNTs) with diameter of less than 0.7nm and more than 1ev band gap
energy, which are amongst the smallest diameters of SWNTs ever reported.",1207.3555v1
2012-07-16,Infrared Measurement of the Pseudogap in P-Doped and Co-Doped BaFe2As2 High-Temperature Superconductors,"We report on infrared studies of charge dynamics in a prototypical pnictide
system: the BaFe2As2 family. Our experiments have identified hallmarks of the
pseudogap state in the BaFe2As2 system that mirror the spectroscopic
manifestations of the pseudogap in the cuprates. The magnitude of the infrared
pseudogap is in accord with that of the spin-density-wave gap of the parent
compound. By monitoring the superconducting gap of both P- and Co-doped
compounds, we find that the infrared pseudogap is unrelated to
superconductivity. The appearance of the pseudogap is found to correlate with
the evolution of the antiferromagnetic fluctuations associated with the
spin-density-wave instability. The strong-coupling analysis of infrared data
further reveals the interdependence between the magnetism and the pseudogap in
the iron pnictides.",1207.3567v1
2012-07-17,"Magneto-elastically coupled structural, magnetic and superconducting order parameters in BaFe$_{2}$(As$_{1-x}$P$_{x}$)$_{2}$","We measure the transport properties of mechanically strained single crystals
of BaFe$_{2}$(As$_{1-x}$P$_{x}$)$_{2}$ over a wide range of $x$. The N\'eel
transition is extremely sensitive to stress and this sensitivity increases as
optimal doping is approached, even though the transition itself is strongly
suppressed. Furthermore, we observe significant changes in the superconducting
transition temperature with applied strain, which mirror changes as a function
of the composition $x$. These experiments are a direct illustration of the
intimate coupling between different degrees of freedom in iron-based
superconductors, revealing the importance of magneto-elastic coupling to the
magnetic and superconducting transition temperatures.",1207.3858v1
2012-07-17,Non-Fermi Liquid behavior at the Orbital Ordering Quantum Critical Point in the Two-Orbital Model,"The critical behavior of a two-orbital model with degenerate $d_{xz}$ and
$d_{yz}$ orbitals is investigated by multidimensional bosonization. We find
that the corresponding bosonic theory has an overdamped collective mode with
dynamical exponent $z=3$, which appears to be a general feature of a
two-orbital model and becomes the dominant fluctuation in the vicinity of the
orbital-ordering quantum critical point. Since the very existence of this $z=3$
overdamped collective mode induces non-Fermi liquid behavior near the quantum
critical point, we conclude that a two-orbital model generally has a sizable
area in the phase diagram showing non-Fermi liquid behavior. Furthermore, we
show that the bosonic theory resembles the continuous model near the d-wave
Pomeranchuk instability, suggesting that orbital order in a two-orbital model
is identical to nematic order in a continuous model. Our results can be applied
to systems with degenerate $d_{xz}$ and $d_{yz}$ orbitals such as iron-based
superconductors and bilayer strontium ruthenates Sr$_3$Ru$_2$O$_7$.",1207.4206v2
2012-07-18,Bound States of Defects in Superconducting LiFeAs Studied by Scanning Tunneling Spectroscopy,"Defects in LiFeAs are studied by scanning tunneling microscopy (STM) and
spectroscopy (STS). Topographic images of the five predominant defects allow
the identification of their position within the lattice. The most commonly
observed defect is associated with an Fe site and does not break the local
lattice symmetry, exhibiting a bound state near the edge of the smaller gap in
this multi-gap superconductor. Three other common defects, including one also
on an Fe site, are observed to break local lattice symmetry and are
pair-breaking indicated by clear in-gap bound states, in addition to states
near the smaller gap edge. STS maps reveal complex, extended real-space bound
state patterns, including one with a chiral distribution of the local density
of states (LDOS). The multiple bound state resonances observed within the gaps
and at the inner gap edge are consistent with theoretical predictions for
s$^{\pm}$ gap symmetry proposed for LiFeAs and other iron pnictides.",1207.4249v2
2012-07-18,Detection of Iron Kα Emission from a Complete Sample of Submillimeter Galaxies,"We present an X-ray stacking analysis of a sample of 38 submillimeter
galaxies with <z>=2.6 discovered at >4{\sigma} significance in the Lockman Hole
North with the MAMBO array. We find a 5{\sigma} detection in the stacked soft
band (0.5-2.0 keV) image, and no significant detection in the hard band (2.0-8
keV). We also perform rest-frame spectral stacking based on spectroscopic and
photometric redshifts and find a ~4{\sigma} detection of Fe K{\alpha} emission
with an equivalent width of EW>1 keV. The centroid of the Fe K{\alpha} emission
lies near 6.7 keV, indicating a possible contribution from highly ionized Fe
XXV or Fe XXVI; there is also a slight indication that the line emission is
more spatially extended than the X-ray continuum. This is the first X-ray
analysis of a complete, flux-limited sample of SMGs with statistically robust
radio counterparts.",1207.4486v1
2012-07-27,Evidence for a cos(4\varphi) Modulation of the Superconducting Energy Gap of Optimally Doped FeTe_{0.6}Se_{0.4} Single Crystals Using Laser Angle-Resolved Photoemission Spectroscopy,"We study the superconducting(SC)-gap anisotropy of the \Gamma-centered hole
Fermi surface in optimally doped FeTe_{0.6}Se_{0.4} (T_c = 14.5 K), using
laser-excited angle-resolved photoemission spectroscopy (ARPES). We observe
sharp superconducting coherence peaks at T = 2.5 K. In contrast to earlier
ARPES studies but consistent with thermodynamic results, the momentum
dependence shows a \cos(4\varphi) modulation of the SC-gap anisotropy. The
observed SC-gap anisotropy strongly indicates that the pairing interaction is
not a conventional phonon-mediated isotropic one. Instead, the results suggest
the importance of second-nearest-neighbor electronic interactions between the
iron sites in the framework of s_\pm-wave superconductivity.",1207.6571v3
2012-07-28,Self-doping effect and possible antiferromagnetism at titanium-layers in the iron-based superconductor Ba$_2$Ti$_2$Fe$_2$As$_4$O,"The electronic structure of Ba$_2$Ti$_2$Fe$_2$As$_4$O, a newly discovered
superconductor, is investigated using first-principles calculations based on
local density approximations. Multiple Fermi surface sheets originating from
Ti-3$d$ and Fe-3$d$ states are present corresponding to the conducting
Ti$_2$As$_2$O and Fe$_2$As$_2$ layers respectively. Compared with
BaFe$_2$As$_2$, sizeable changes in the related Fermi surface sheets indicate
significant electron transfer (about 0.12$e$) from Ti to Fe, which suppresses
the stripe-like antiferromagnetism at the Fe sites and simultaneously induces
superconductivity. Our calculations also suggest that an additional
N\'{e}el-type antiferromagnetic instability at the Ti sites is relatively
robust against the electron transfer, which accounts for the anomaly at 125 K
in the superconducting Ba$_2$Ti$_2$Fe$_2$As$_4$O.",1207.6705v1
2012-07-29,Dynamic approach to finite-temperature magnetic phase transitions in the extended J1- J2 model with vacancy order,"The recently discovered iron-based superconductors A$_{y}$Fe$_{2-x}$Se$_{2}$
($A$=K, Rb, Cs, Tl) show a long-range antiferromagnetic order with an
unexpected high transition temperature $T_N \sim 550$ K and a unique $\sqrt{5}
\times \sqrt{5}$ vacancy order. Taking the extended $J_1$-$J_2$ model as a
minimal model, we investigate the finite-temperature magnetic phase transitions
in a square lattice with a $\sqrt{5} \times \sqrt{5}$ vacancy superstructure by
using large-scale Monte Carlo simulations. By the parallel tempering technique,
the block spin checkerboard and stripe antiferromagnetic states are detected to
be the groundstates for three representative sets of model parameters. The
short-time dynamic approach is applied to accurately determine the critical
temperature as well as the static and dynamic exponents. Our results indicate
that the dramatic enhancement of the critical temperature as observed in
experiments should be mainly due to a combination effect of the vacancy order
and the block lattice contraction.",1207.6740v3
2012-07-29,Quantum Criticality Stabilizes High T_c Superconductivity Against Competing Symmetry-Breaking Instabilities,"The occurrence of high-T_c superconductivity in systems including the
cuprates and the iron-based superconductors, is known to coincide with the
existence of anomalous normal-state properties which have been associated with
quantum criticality. We argue here that this observation results from the fact
that quantum criticality can allow the occurrence of very-strong-coupling
superconductivity by preventing its suppression due to competing
symmetry-breaking instabilities. Treating the electrons through a large-U
ansatz yields their separation into boson quasiparticles which are directly
involved in the formation of these instabilities, represented as their Bose
condensates, and charge-carrying fermion quasiparticles which are affected by
them indirectly. Within the critical regime, condensates corresponding to the
different broken-symmetry states are combined; consequently their negative
effect on the pairing of the fermions is strongly diminished, enabling high-T_c
superconductivity to occur. The observed phase diagram of the hole-doped
cuprates then derives from a hidden T=0 quantum phase transition between a
Fermi-liquid and a non-Fermi-liquid broken-symmetry striped state. The
pseudogap range within this diagram is found to include two distinct regimes,
with partial pairing occurring in one of them.",1207.6789v1
2012-08-06,Spin-state Crossover Model for the Magnetism of Iron Pnictides,"We propose a minimal model describing magnetic behavior of Fe-based
superconductors. The key ingredient of the model is a dynamical mixing of
quasi-degenerate spin states of Fe2+ ion by intersite electron hoppings,
resulting in an effective local spin Seff. The moments Seff tend to form
singlet pairs, and may condense into a spin nematic phase due to the emergent
biquadratic exchange couplings. The long-range ordered part m of Seff varies
widely, 0<=m<=Seff, but magnon spectra are universal and scale with Seff,
resolving the puzzle of large but fluctuating Fe-moments. Unusual temperature
dependences of a local moment and spin susceptibility are also explained.",1208.1197v3
2012-08-07,Anisotropic electrical resistivity of LaFeAsO: evidence for electronic nematicity,"Single crystals of LaFeAsO were successfully grown out of KI flux.
Temperature dependent electrical resistivity was measured with current flow
along the basal plane, \rho_perpend(T), as well as with current flow along the
crystallographic c-axis, \rho_parallel(T), the latter one utilizing electron
beam lithography and argon ion beam milling. The anisotropy ratio was found to
lie between \rho_parallel/\rho_perpend = 20 - 200. The measurement of
\rho_perpend(T) was performed with current flow along the tetragonal [1 0 0]
direction and along the [1 1 0] direction and revealed a clear in-plane
anisotropy already at T \leq 175 K. This is significantly above the
orthorhombic distortion at T_0 = 147 K and indicates the formation of an
electron nematic phase. Magnetic susceptibility and electrical resistivity give
evidence for a change of the magnetic structure of the iron atoms from
antiferromagnetic to ferromagnetic arrangement along the c-axis at T^\ast = 11
K.",1208.1480v3
2012-08-11,Suppression of backward scattering of Dirac fermions in iron pnictides Ba(Fe$_{1-x}$Ru$_x$As)$_2$,"We report electronic transport of Dirac cones when Fe is replaced by Ru,
which has an isoelectronic electron configuration to Fe, using single crystals
of Ba(Fe$_{1-x}$Ru$_x$As)$_2$. The electronic transport of parabolic bands is
shown to be suppressed by scattering due to the crystal lattice distortion and
the impurity effect of Ru, while that of the Dirac cone is not significantly
reduced due to the intrinsic character of Dirac cones. It is clearly shown from
magnetoresistance and Hall coefficient measurements that the inverse of average
mobility, proportional to cyclotron effective mass, develops as the square root
of the carrier number (n) of the Dirac cones. This is the unique character of
the Dirac cone linear dispersion relationship. Scattering of Ru on the Dirac
cones is discussed in terms of the estimated mean free path using experimental
parameters.",1208.2328v2
2012-08-13,Specific Heat Discontinuity DeltaC vs Tc in Annealed Ba(Fe1-xCox)2As2,"The low temperature specific heat of annealed single crystal samples of
Ba(Fe1-xCox)2As2 with compositions spanning the entire superconducting phase
diagram was measured. Effort was made to discover the best annealing schedule
to maximize Tc and minimize transition width in these samples. Values of
deltaC/Tc normalized to 100% superconducting volume fractions varied
proportionally to Tc^alpha. Within a rather narrow error bar of +-0.15, the
exponent alpha was the same (approximately 2) over a range of compositions
(0.055 < x < 0.15) around the optimal concentration, x=0.08, where Tc is the
maximum in the phase diagram. Thus, whether the superconductivity was
coexistent with magnetism (underdoped) or not (overdoped) did not affect the
non-BCS variation (alpha nearly 2 instead of 0.8-0.9 for BCS superconductors)
of deltaC/Tc with Tc. The annealed samples in the present work, with increased
deltaC/Tc and Tc values compared to previous results for the Ba(Fe1-xCox)2As2
alloy system, suggest that the intrinsic value of the exponent alpha for the
iron superconductors, when the samples are annealed, with fewer defects, may
indeed be even further from the BCS value of 0.8-0.9 than previously thought.",1208.2492v1
2012-08-16,"Filamentary superconductivity across the phase diagram of Ba(Fe,Co)$_2$As$_2$","We show magnetotransport results on Ba(Fe$_{1-x}$Co$_x$)$_2$As$_2$ ($0.0 \leq
x \leq 0.13$) single crystals. We identify the low temperature resistance step
at 23 K in the parent compound with the onset of filamentary superconductivity
(FLSC), which is suppressed by an applied magnetic field in a similar manner to
the suppression of bulk superconductivity (SC) in doped samples. FLSC is found
to persist across the phase diagram until the long range antiferromagnetic
order is completely suppressed. A significant suppression of FLSC occurs for
$0.02<x<0.04$, the doping concentration where bulk SC emerges. Based on these
results and the recent report of an electronic anisotropy maximum for 0.02
$\leq x \leq$ 0.04 [Science 329, 824 (2010)], we speculate that, besides spin
fluctuations, orbital fluctuations may also play an important role in the
emergence of SC in iron-based superconductors.",1208.3352v1
2012-08-17,Anisotropic resistivity of Na$_{1-δ}$Fe$_{1-x}$Co$_x$As,"Temperature-dependent resistivity is studied in single crystals of
iron-arsenide superconductor Na$_{1-\delta}$Fe$_{1-x}$Co$_x$As for electrical
current directions along, $\rho_a (T)$, and transverse, $\rho_c (T)$, to the
Fe-As layers. Doping with Co increases stability of this compound to reaction
with the environment and suppresses numerous features in both $\rho_a(T)$ and
$\rho_c(T)$ compared to the stoichiometric NaFeAs. Evolution of $\rho_a (T)$
with $x$ follows a universal trend observed in other pnictide superconductors,
exhibiting a $T$-linear temperature dependence close to the optimal doping and
development of $T^2$ dependence upon further doping. $\rho_c (T)$ in parent
compound shows a non - monotonic behavior with a crossover from non-metallic
resistivity increase on cooling from room temperature down to $\sim$ 80 K to a
metallic decrease below this temperature. Both $\rho_a (T)$ and $\rho_c (T)$
show several correlated crossover - like features at $T>$ 80 K. Despite a
general trend towards more metallic behavior of inter - plane resistivity in
Co-doped samples, the temperature of the crossover from insulating to metallic
behavior (80 K) does not change much with doping.",1208.3646v1
2012-08-21,"Contrast of LiFeAs with isostructural, isoelectronic, and non-superconducting MgFeGe","Stoichiometric LiFeAs at ambient pressure is an 18 K superconductor while
isoelectronic MgFeGe is not, despite their extremely similar electronic
structures. To investigate possible sources of this distinctively different
superconducting behavior, we quantify the differences using first principles
density functional theory, establishing first that the Fe total 3d occupations
are identical in the two compounds. Individual 3d orbital occupations also
differ very little ($\sim 0.01$). The differences in Fermi surfaces (FSs) do
not seem significant; however a redistribution of bands just above the Fermi
level does represent a possibly significant distinction. Because the bands and
FSs of LiFeAs are less in agreement with experiment than for other
iron-pnictides, we study the effects of additional exchange-correlations
effects beyond GGA (the generalized gradient approximation) by applying the
modified Becke-Johnson potential (mBJ) exchange potential, which gives much
improved bandgaps in insulators compared to GGA and might be useful for
semimetals such as the Fe-based superconductors. Overall, we conclude that the
mBJ corrections do not improve the description of LiFeAs as compared to
experiment.",1208.4180v2
2012-08-22,Chandra grating spectroscopy of three hot white dwarfs,"High-resolution soft X-ray spectroscopic observations of single hot white
dwarfs are scarce. With the Chandra Low-Energy Transmission Grating, we have
observed two white dwarfs, one is of spectral type DA (LB 1919) and the other
is a non-DA of spectral type PG1159 (PG 1520+525). The spectra of both stars
are analyzed, together with an archival Chandra spectrum of another DA white
dwarf (GD 246). The soft X-ray spectra of the two DA white dwarfs are
investigated in order to study the effect of gravitational settling and
radiative levitation of metals in their photospheres. LB 1919 is of interest
because it has a significantly lower metallicity than DAs with otherwise
similar atmospheric parameters. GD 246 is the only white dwarf known that shows
identifiable individual iron lines in the soft X-ray range. For the PG1159
star, a precise effective temperature determination is performed in order to
confine the position of the blue edge of the GW Vir instability region in the
HRD. (abridged)",1208.4478v1
2012-08-24,Superconductivity Appears in the Vicinity of an Insulating-Like Behavior in CeO$_{1-x}$F$_{x}$BiS$_{2}$,"Resistive and magnetization properties have been measured in BiS$_2$-based
samples CeO$_{1-x}$F$_{x}$BiS$_{2}$ with a systematic substitution of O with F
(0 $<$ x $<$ 0.6). In contrast to the band structure calculations, it is found
that the parent phase of CeOBiS$_2$ is a bad metal, instead of an band
insulator. By doping electrons into the system, it is surprising to find that
superconductivity appears together with an insulating normal state. This
evolution is clearly different from the cuprate and the iron pnictide systems,
and is interpreted as approaching the von Hove singularity. Furthermore,
ferromagnetism which may arise from the Ce moments, has been observed in the
low temperature region in all samples, suggesting the co-existence of
superconductivity and ferromagnetism in the superconducting samples.",1208.5000v1
2012-08-25,"Glassy Transition in the Vortex Lattice of Ba(Fe0.93Rh0.07)2As2 superconductor, probed by NMR and ac-susceptibility","By using Nuclear Magnetic Resonance and ac-susceptibility, the characteristic
correlation times for the vortex dynamics, in an iron-based superconductor,
have been derived. Upon cooling, the vortex dynamics displays a crossover
consistent with a vortex glass transition. The correlation times, in the fast
motions regime, merge onto a universal curve which is fit by the Vogel-Fulcher
law, rather than by an Arrhenius law. Moreover, the pinning barrier shows a
weak dependence on the magnetic field which can be heuristically justified
within a fragile glass scenario. In addition, the glass freezing temperatures
obtained by the two techniques merge onto the de Almeida-Thouless line. Finally
the phase diagram for the mixed phase has been derived.",1208.5142v4
2012-08-28,Alternative route to charge density wave formation in multiband systems,"Charge and spin density waves, periodic modulations of the electron and
magnetization densities, respectively, are among the most abundant and
non-trivial low-temperature ordered phases in condensed matter. The ordering
direction is widely believed to result from the Fermi surface topology.
However, several recent studies indicate that this common view needs to be
supplemented. Here, we show how an enhanced electron-lattice interaction can
contribute to or even determine the selection of the ordering vector in the
model charge density wave system ErTe3. Our joint experimental and theoretical
study allows us to establish a relation between the selection rules of the
electronic light scattering spectra and the enhanced electron-phonon coupling
in the vicinity of band degeneracy points. This alternative proposal for charge
density wave formation may be of general relevance for driving phase
transitions into other broken-symmetry ground states, particularly in multiband
systems such as the iron based superconductors.",1208.5701v2
2012-08-31,Comparison of Gamow-Teller strengths in the random phase approximation,"The Gamow-Teller response is astrophysically important for a number of
nuclides, particularly around iron. The random phase approximation (RPA) is an
efficient way to generate strength distributions. In order to better understand
both theoretical systematics and uncertainties, we compare the Gamow-Teller
strength distributions for a suite of nuclides and for a suite of interactions,
including semi-realistic interactions in the $1p$-$0f$ space with the RPA and a
separable multi-shell interaction in the quasi-particle RPA. We also compare
with experimental results for GT$_-$ on ${54}$Fe.",1208.6538v2
2012-09-03,"Growth and characterization of n-type electron-induced ferromagnetic semiconductor (In,Fe)As","We show that by introducing isoelectronic iron (Fe) magnetic impurities and
Beryllium (Be) double-donor atoms into InAs, it is possible to grow a n-type
ferromagnetic semiconductor (FMS) with the ability to control ferromagnetism by
both Fe and independent carrier doping by low-temperature molecular-beam
epitaxy. We demonstrate that (In,Fe)As doped with electrons behaves as an
n-type electron-induced FMS. This achievement opens the way to realize novel
spin-devices such as spin light-emitting diodes or spin field-effect
transistors, as well as helps understand the mechanism of carrier-mediated
ferromagnetism in FMSs.",1209.0250v1
2012-09-05,A 57Fe Mössbauer Study Of Local Structure And Spin Arrangements In Antiferromagnetic NaFeAs,"Detailed 57Fe M\""ossbauer spectroscopy measurements on superconducting NaFeAs
powder crystals have been performed. The 57Fe spectra recorded in the
paramagnetic temperature range (T > TN \approx 46 +/- 2 K) were discussed
supposing Fe2+ ions are located in distorted tetrahedral (FeAs4) polyhedra. Our
results reveal that the structural transition (TS \approx 55 K) has a weak
effect on the electronic structure of iron atoms while the development of the
antiferromagnetic order (T =< TN) induces a redistribution of the charge at
57Fe nuclei. In the low-temperature range, the spectra show a diffuse resonance
absorption structure which evidences for the existence of a continuous
distribution of hyperfine fields HFe at 57Fe nuclei. The shape of these spectra
can be related to the formation of a microdomain structure or phase separation.
Analysis of the resulting distributions p(HFe) has shown that the M\""ossbauer
spectra give consistent and physically reasonable 57Fe hyperfine parameters
over the whole temperature range.",1209.0924v2
2012-09-05,High resolution reddening map in the direction of the stellar system Terzan 5,"We have used optical images acquired with the Hubble Space Telescope to
construct the first high-resolution extinction map in the direction of Terzan
5, a peculiar stellar system in the inner bulge of our Galaxy. The map has a
spatial resolution of 8"" X 8"", over a total FoV of 200"" X 200"". The absorption
clouds show a patchy structure on a typical scale of 20"" and extinction
variations as large as delta E(B-V) = 0.67 mag, especially in the direction of
the center of the system. These correspond to an absolute color excess ranging
from E(B-V)=2.15 mag, up to 2.82 mag. After the correction for differential
reddening, two distinct red giant branches become clearly visible in the color
magnitude diagram of Terzan 5 and they well correspond to the two
sub-populations with different iron abundances recently discovered in this
system.",1209.0990v1
2012-09-10,The reawakening of the sleeping X-ray pulsar XTE J1946+274,"We report on a series of outbursts of the high mass X-ray binary XTE
J1946+274 in 2010/2011 as observed with INTEGRAL, RXTE, and Swift. We discuss
possible mechanisms resulting in the extraordinary outburst behavior of this
source. The X-ray spectra can be described by standard phenomenological models,
enhanced by an absorption feature of unknown origin at about 10 keV and a
narrow iron K alpha fluorescence line at 6.4 keV, which are variable in flux
and pulse phase. We find possible evidence for the presence of a cyclotron
resonance scattering feature at about 25 keV at the 93% level. The presence of
a strong cyclotron line at 35 keV seen in data from the source's 1998 outburst
and confirmed by a reanalysis of these data can be excluded. This result
indicates that the cyclotron line feature in XTE J1946+274 is variable between
individual outbursts.",1209.1918v1
2012-09-11,The stratified evolution of a cool star,"A low mass star usually experiences stratification and abundance anomalies
during its evolution. A 0.95 solar mass star with a metallicity Z = 0.004 is
followed from the main-sequence to the Horizontal Branch (HB). On the
main-sequence the larger effects of stratification may come from accretion as
was suggested in relation to metallicity and planet formation. As it evolves
through the giant branch, stratification appears around the hydrogen burning
shell. It may create hydrodynamic instabilities and be related to abundance
anomalies on the giant branch. After the He flash the star evolves to the HB.
If it loses enough mass, it ends up a hot HB star (or in the field an sdB star)
with effective temperatures larger than 11000 K. All sdB stars are observed to
have an approximately solar iron abundance whatever their original metallicity,
implying overabundances by factors of up to 100. So should the 0.95 solar mass
star. How its internal hydrodynamic properties on the main sequence may
influence its fate on the HB is currently uncertain.",1209.2403v1
2012-09-18,Impurity states in multiband s-wave superconductors: analysis of iron pnictides,"We examine the effect of a single, non-magnetic impurity in a multiband,
extended s-wave superconductor allowing for anisotropy of the gaps on the Fermi
surfaces. We derive analytic expressions for the Green's functions in the
continuum and analyse the conditions for the existence of sharp
impurity-induced resonant states. Underlying band structure is more relevant
for the multiband than for single band case, and mismatch between the bands
generically makes the formation of the impurity states less likely in the
physical regime of parameters. We confirm these conclusions by numerically
solving the impurity problem in a tight-binding parameterization of the bands
relevant to pnictide superconductors.",1209.3835v2
2012-09-21,Engineering Study of Sector Magnet for the Daedalus Experiment,"The Daedalus experiment seeks to evaluate neutrino scattering effects that go
beyond the standard model. Modular accelerators are employed to produce 800 MeV
proton beams at the megawatt power level directed toward a target, producing
neutrinos. The Superconducting Ring Cyclotron (SRC) consists of identical
sectors (currently 6) of superconducting dipole magnets with iron return
frames. The Daedalus Collaboration has produced a conceptual design for the
magnet, which, after several iterations, is the current best design that
achieves the physics requirements of the experiment. The Technology and
Engineering Division (T&ED) of the MIT Plasma Science and Fusion Center was
awarded with a contract by the Daedalus team to further develop the magnet
conceptual design. The resulting Engineering Study is reported here.",1209.4886v1
2012-09-25,Study of The Abundance Patterns in The Metal-Poor Stellar Stream,"The chemical abundances of the metal-poor stars in the stellar stream provide
important information for setting constraints on models of neutron-capture
processes. The study of these stars could give us a better understanding of
r-process nucleosynthesis and chemical composition of the early Galaxy. Using
the updated main r-process and weak r-process patterns, we fit abundances in
the stellar stream stars. The weak r-process component coefficients are almost
constant for the sample stars, including r-rich stars, which means that both
weak r-process and Fe are produced as primary elements from SNeII and their
yields have nearly a constant mass fraction. The difference between the stream
stars and r-rich stars is obvious. For the stream stars, that the increase
trend in the main r-process component coefficients as metallicity increases
means the gradual increase in the production of main r-process elements
relative to iron. This behavior implies that the masses of progenitors for the
main r-process are smaller than those of the weak r-process. Furthermore, we
find metal-poor stream star HD 237846 is a weak r-process star.",1209.5505v1
2012-09-25,Structural phase transition below 250 K in superconducting K$_{0.75}$Fe$_{1.75}$Se$_{2}$,"Vibrational properties of iron-chalcogenide superconductor
K$_{0.75}$Fe$_{1.75}$Se$_{2}$ with $T_{c}\sim$ 30 K have been measured by Raman
and optical spectroscopies over temperature range of 3-300 K. Sample undergoes
\textit{I4/m} $\to $ \textit{I4} structural phase transition accompanied by
loss of inversion symmetry at $T_{1}$, below 250 K, observed as appearance of
new fully-symmetric Raman mode at $\sim$ 165 cm$^{-1}$. Small vibration mode
anomalies are also observed at $T_{2}\sim$ 160 K. From first-principles
vibrational analysis of antiferromagnetic K$_{0.8}$Fe$_{1.6}$Se$_{2}$ utilizing
pseudopotentials all observed Raman and infrared modes have been assigned and
the displacement patterns of the new Raman mode identified as involving
predominantly the Se atoms.",1209.5718v1
2012-10-02,Graphene as a reversible spin manipulator of molecular magnets,"One of the primary objectives in molecular nano-spintronics is to manipulate
the spin states of organic molecules with a d-electron center, by suitable
external means. In this letter, we demonstrate by first principles density
functional calculations, as well as second order perturbation thoery, that a
strain induced change of the spin state, from S=1 $\to$ S=2, takes place for an
iron porphyrin (FeP) molecule deposited at a divacancy site in a graphene
lattice. The process is reversible in a sense that the application of tensile
or compressive strains in the graphene lattice can stabilize FeP in different
spin states, each with a unique saturation moment and easy axis orientation.
The effect is brought about by a change in Fe-N bond length in FeP, which
influences the molecular level diagram as well as the interaction between the C
atoms of the graphene layer and the molecular orbitals of FeP.",1210.0666v1
2012-10-03,Atomically Controlled Epitaxial Growth of Single-Crystalline Germanium Films on a Metallic Silicide,"We demonstrate high-quality epitaxial germanium (Ge) films on a metallic
silicide, Fe3Si, grown directly on a Ge(111) substrate. Using molecular beam
epitaxy techniques, we can obtain an artificially controlled arrangement of
silicon (Si) or iron (Fe) atoms at the surface on Fe3Si(111). The Si-terminated
Fe3Si(111) surface enables us to grow two-dimensional epitaxial Ge films,
whereas the Fe-terminated one causes the three-dimensional epitaxial growth of
Ge films. The high-quality Ge grown on the Si-terminated surface has almost no
strain, meaning that the Ge films are not grown on the low-temperature-grown Si
buffer layer but on the lattice matched metallic Fe3Si. This study will open a
new way for vertical-type Ge-channel transistors with metallic source/drain
contacts.",1210.1027v1
2012-10-05,Thermodynamics of Ising Spins on the Star Lattice,"There is a new class of two-dimensional magnetic materials polymeric iron
(III) acetate fabricated recently in which Fe ions form a star lattice. We
study the thermodynamics of Ising spins on the star lattice with exact analytic
method and Monte Carlo simulations. Mapping the star lattice to the honeycomb
lattice, we obtain the partition function for the system with asymmetric
interactions. The free energy, internal energy, specific heat, entropy and
susceptibility are presented, which can be used to determine the sign of the
interactions in the real materials. Moreover, we find the rich phase diagrams
of the system as a function of interactions, temperature and external magnetic
field. For frustrated interactions without external field, the ground state is
disordered (spin liquid) with residual entropy 1.522 per unit cell. When a weak
field is applied, the system enters a ferrimagnetic phase with residual entropy
ln4 per unit cell.",1210.1675v1
2012-10-08,Microwave absorption study of pinning regimes in $\bf Ba(Fe_{1-x}Co_x)_2As_2$ single crystals,"Magnetic field dependent modulated microwave absorption (MMWA) measurements
have been carried out to investigate vortex pinning effects in single crystals
of the iron-based high-Tc superconductor Ba(Fe_{1-x}Co_x)_2As_2 with three
different cobalt doping levels of x = 0.07, 0.09, and 0.11. The dependence of
the MMWA hysteresis loops on temperature, magnetic field, and Co-concentration
have been measured and analyzed using a theoretical model of microwave
absorption in superconductors. The analysis reveals that in an underdoped
crystal (x = 0.07) the so called \dtc-pinning due to magnetically ordered
regions defines the temperature dependence of the critical current density,
while in the optimally doped (x = 0.09) and overdoped (x = 0.11) samples the
pinning is governed by structural imperfections due to inhomogeneous
distribution of cobalt dopant and has the so called \delta-l character.",1210.2309v1
2012-10-09,"Spin Wave Excitations in AFe$_{1.5}$Se$_2$ (A=K, Tl): Analytical Study","We have analytically solved the spin wave excitations for the intercalated
ternary iron-selenide AFe$_{1.5}$Se$_2$ (A=K, Tl) in the $4\times 2$ collinear
antiferromagnetic order. It is found that there are one acoustic branch
(gapless Goldstone mode) and two gapful optical branches of spin wave
excitations with each in double degeneracy. By examining the non-imaginary
excitation frequency condition, we can determine the corresponding phase
boundary. The exchange couplings between Fe moments in AFe$_{1.5}$Se$_2$ are
derived based on the first-principles total energy calculations. The Fe spin is
found to be $S=3/2$ through computing the antiferromagnetic quantum
fluctuation. And it is further found that a very small spin-orientation
anisotropy can remarkably suppress the antiferromagnetic quantum fluctuation.
The spin dynamical structure factors are calculated and discussed in
association with neutron inelastic scattering experiment.",1210.2668v1
2012-10-11,Recent developments in the shell model Monte Carlo approach to nuclei,"The shell model Monte Carlo (SMMC) approach provides a powerful method for
the microscopic calculation of statistical and collective nuclear properties in
model spaces that are many orders of magnitude larger than those that can be
treated by conventional methods. We discuss recent applications of the method
to describe the emergence of collectivity in the framework of the
configuration-interaction shell model and the crossover from vibrational to
rotational collectivity in families of rare-earth nuclei. We have calculated
state densities of these rare-earth nuclei and find their collective
enhancement factors to be correlated with the pairing and shape phase
transitions. We also discuss an accurate method to calculate the ground-state
energy of odd-even and odd-odd nuclei, circumventing the sign problem that
originates in the projection on an odd number of particles. We have applied
this method to calculate pairing gaps in families of isotopes in the iron
region.",1210.3102v1
2012-10-11,Thermopower of the Correlated Narrow Gap Semiconductor FeSi and Comparison to RuSi,"Iron based narrow gap semiconductors such as FeSi, FeSb2, or FeGa3 have
received a lot of attention because they exhibit a large thermopower, as well
as striking similarities to heavy fermion Kondo insulators. Many proposals have
been advanced, however, lacking quantitative methodologies applied to this
problem, a consensus remained elusive to date. Here, we employ realistic
many-body calculations to elucidate the impact of electronic correlation
effects on FeSi. Our methodology accounts for all substantial anomalies
observed in FeSi: the metallization, the lack of conservation of spectral
weight in optical spectroscopy, and the Curie susceptibility. In particular we
find a very good agreement for the anomalous thermoelectric power. Validated by
this congruence with experiment, we further discuss a new physical picture of
the microscopic nature of the insulator-to-metal crossover. Indeed, we find the
suppression of the Seebeck coefficient to be driven by correlation induced
incoherence. Finally, we compare FeSi to its iso-structural and iso-electronic
homologue RuSi, and predict that partially substituted Fe(1-x)Ru(x)Si will
exhibit an increased thermopower at intermediate temperatures.",1210.3379v1
2012-10-17,Ferromagnetic Quantum Critical Point in Heavy-Fermion Iron Oxypnictide Ce(Ru$_{1-x}$Fe$_x$)PO,"We have performed ^{31}P-NMR measurements on Ce(Ru_{1-x}Fe_{x})PO in order to
investigate ferromagnetic (FM) quantum criticality, since heavy-fermion (HF)
ferromagnet CeRuPO with a two-dimensional structure turns to a HF paramagnet by
an isovalent Fe-substitution for Ru. We found that Ce(Ru_{0.15}Fe_{0.85})PO
shows critical fluctuations down to \sim 0.3 K, as well as the continuous
suppression of Curie temperature and the ordered moments by the
Fe-substitution. These experimental results suggest the presence of a FM
quantum critical point (QCP) at x \sim 0.86, which is a rare example among
itinerant ferromagnets. In addition, we point out that the critical behaviors
in Ce(Ru_{0.15}Fe_{0.85})PO share the similarity with those in YbRh_{2}Si_{2},
where the local criticality of $f$ electrons has been discussed. We reveal that
Ce(Ru_{1-x}Fe_{x})PO is a new system to study FM quantum criticality in HF
compounds.",1210.4604v1
2012-10-17,The spectrum of Fe II,"The spectrum of singly-ionized iron (Fe II) has been recorded using
high-resolution Fourier transform and grating spectroscopy over the wavelength
range 900 {\AA} to 5.5 {\mu}m. The spectra were observed in high-current
continuous and pulsed hollow cathode discharges using Fourier transform (FT)
spectrometers at the Kitt Peak National Observatory, Tucson, AZ and Imperial
College, London and with the 10.7 m Normal Incidence Spectrograph at the
National Institute of Standards and Technology. Roughly 12 900 lines were
classified using 1027 energy levels of Fe II that were optimized to measured
wavenumbers. The wavenumber uncertainties of lines in the FT spectra range from
10-4 cm-1 for strong lines around 4 {\mu}m to 0.05 cm-1 for weaker lines around
1500 {\AA}. The wavelength uncertainty of lines in the grating spectra is 0.005
{\AA}. The ionization energy of (130 655.4+-0.4) cm-1 was estimated from the
3d6(5D)5g and 3d6(5D)6h levels.",1210.4773v1
2012-10-19,Unique phase diagram with narrow superconducting dome in EuFe$_2$(As$_{1-x}$P$_x$)$_2$ due to Eu$^{2+}$ local magnetic moments,"The interplay between superconductivity and Eu$ ^{2+}$ magnetic moments in
EuFe$_2$(As$_{1-x}$P$_x$)$_2$ is studied by electrical resistivity measurements
under hydrostatic pressure on $x=0.13$ and $x=0.18$ single crystals. We can map
hydrostatic pressure to chemical pressure $x$ and show, that superconductivity
is confined to a very narrow range $0.18\leq x \leq 0.23$ in the phase diagram,
beyond which ferromagnetic (FM) Eu ordering suppresses superconductivity. The
change from antiferro- to FM Eu ordering at the latter concentration coincides
with a Lifshitz transition and the complete depression of iron magnetic order.",1210.5440v2
2012-10-26,Bulk properties and electronic structure of PuFeAsO,"Here we present bulk property measurements and electronic structure
calculations for PuFeAsO, an actinide analogue of the iron-based rare-earth
superconductors RFeAsO. Magnetic susceptibility and heat capacity data suggest
the occurrence of an antiferromagnetic transition at TN=50 K. No further
anomalies have been observed down to 2 K, the minimum temperature that we have
been able to achieve. Structural measurements indicate that PuFeAsO, with its
more localized 5f electrons, bears a stronger resemblance to the RFeAsO
compounds with larger R ions, than NpFeAsO does.",1210.7251v1
2012-10-28,Observation of charge accumulation and onsite Coulomb repulsion at transition metal impurities in the iron pnictides,"We report a combined valence band photoemission and Auger spectroscopy study
of single crystalline Ca(Fe,Co)2As2 and Ba(Fe,TM)2As2 with TM=Ni or Cu. The
valence band photoemission data show directly that the TM-states move to higher
binding energies with increasing atomic number, contributing less and less to
the states close to the Fermi level. Furthermore, the 3d8 final state of the
LVV Auger decay, which is observed for Ni and Cu, unambiguously reveals the
accumulation of charge at these impurities. We also show that the onsite
Coulomb interaction on the impurity strongly increases when moving from Co over
Ni to Cu. Our results quantify the impurity potentials and imply that the
superconducting state is robust against impurity scattering.",1210.7483v1
2012-10-30,Physical parameters of three field RR Lyrae stars,"Str\""omgren $uvby-\beta$ photometry of the stars classified as RR Lyrae stars
RU Piscium, SS Piscium and TU Ursae Majoris has been used to estimate their
iron abundance, temperature, gravity and absolute magnitude. The stability of
the pulsating period is discussed. The nature of SS Psc as a RRc or a HADS is
addressed. The reddening of each star is estimated from the Str\""omgren colour
indices and reddening sky maps. The results of three approaches to the
determination of [Fe/H], $T_{\rm eff}$ and $\log(g)$ are discussed: Fourier
light curve decomposition, the Preston $\Delta S$ index and the theoretical
grids on the $(b-y)_o - c_1{_o}$ plane.",1210.7886v1
2012-10-31,Theory and Simulation of the diffusion of kinks on dislocations in bcc metals,"Isolated kinks on thermally fluctuating (1/2)<111> screw, <100> edge and
(1/2)<111> edge dislocations in bcc iron are simulated under zero stress
conditions using molecular dynamics (MD). Kinks are seen to perform stochastic
motion in a potential landscape that depends on the dislocation character and
geometry, and their motion provides fresh insight into the coupling of
dislocations to a heat bath. The kink formation energy, migration barrier and
friction parameter are deduced from the simulations. A discrete
Frenkel-Kontorova-Langevin (FKL) model is able to reproduce the coarse grained
data from MD at a fraction of the computational cost, without assuming an a
priori temperature dependence beyond the fluctuation-dissipation theorem.
Analytic results reveal that discreteness effects play an essential r\^ole in
thermally activated dislocation glide, revealing the existence of a crucial
intermediate length scale between molecular and dislocation dynamics. The model
is used to investigate dislocation motion under the vanishingly small stress
levels found in the evolution of dislocation microstructures in irradiated
materials.",1210.8327v2
2012-11-02,One-step theory of fcc-bcc martensitic transformation,"Martensitic transformation in steels is responsible for their very high
strength and has thus been studied for more than one century since the first
works of Martens. However, there is not yet simple physical theory. A rigorous
classification of the crystallographic subgroupoids (packets) of the KS
variants and the continuity between the KS, NW and Pitsch variants are
introduced to represent the crystallographic intricacy associated to the
martensite transformation. From this analysis, a new simple theory based on
Pitsch distortion is proposed. The distortion respects the hard sphere packing
of the iron atoms and implies the existence of a neutral line along the close
packed directions. Its principal strains are 0, -5.8 and +15.5 %, well below
the +12, +12 and -20 % values of the Bain distortion. Martensite variants
nucleate by Pitsch distortion in an austenitic matrix continuously deformed by
the transformation. The martensite variants grow by the same Pitsch distortion;
they are locally in Pitsch orientation, and therefore are gradually oriented
inside the deformation field of austenite leading to the continuum of
orientations including KS and NW. Many observations reported in literature can
now be re-interpreted.",1211.0495v1
2012-11-02,Polarized neutron reflectometry study of Fe16N2 with Giant Saturation Magnetization prepared by N Inter-diffusion in Annealed Fe-N Thin Films,"We report a synthesis route to grow iron nitride thin films with giant
saturation magnetization (Ms) through an N inter-diffusion process. By post
annealing Fe/Fe-N structured films grown on GaAs(001) substrates, nitrogen
diffuses from the over-doped amorphous-like Fe-N layer into strained
crystalline Fe layer and facilitates the development of metastable Fe16N2
phase. As explored by polarized neutron reflectometry, the depth-dependent Ms
profile can be well described by a model with the presence of a giant Ms up to
2360 emu/cm3 at near-substrate interface, corresponding to the strained regions
of these annealed films. This is much larger than the currently known limit
(Fe65Co35 with Ms \sim 1900 emu/cm3). The present synthesis method can be used
to develop writer materials for future magnetic recording application.",1211.0551v1
2012-11-06,Calculation of the transport critical current density of c-axis textured 122 iron-based superconductors,"The c-axis textured Sr1-xKxFe2As2 tapes produced by cold rolling and
post-annealing, could carry a high super-current over 2*104 A/cm2. However, the
magnitude is far from its maximum, because of the current obstacles associated
with various defects in the material. To predict the maximal transport critical
current density, we modeled the current paths in a c-axis textured polycrystal
as a three-dimensional flow network, and calculated the maximum flow with the
Ford-Fulkerson algorithm. It indicates that a much higher super-current of
about 2*105 A/cm2 could be achieved in an ideal c-axis textured K-doped 122
polycrystal. The dependences of transport Jc on density, content of invalid
boundary and grain size and shape were also studied. The results imply that,
over 30% of the grain boundaries in the reported c-axis textured Sr1-xKxFe2As2
tapes may act as current obstacles, and the large ratio of width to thickness
was expected to be the most favorable grain shape for high transport Jc in
c-axis textured 122 superconducting tapes.",1211.1141v1
2012-11-06,Anisotropies and Homogeneities of Superconducting Properties in Iron-Platinum-Arsenide Ca10(Pt3As8)(Fe1.79Pt0.21As2)5,"We report a study on the anisotropy of superconducting properties in single
crystalline Ca10(Pt4-{\delta}As8)(Fe1.79Pt0.21As2)5 with Tc ~13.6 K. Under a
field of 5 Oe, the sample reaches fully-diamagnetic state at ~10 K for H//c,
and ~8 K for H//ab, indicating the presence of slight inhomogeneities. The
magnetization measurements reveal fish-tail effect in the hysteresis loop for
both H//c and H//ab. Averaged critical current densities at low magnetic fields
along the c-axis and ab-plane Jc(H//c) and Jc(H//ab) at 5 K are estimated to be
0.9*10^5 and 0.7*10^5 A/cm2, respectively. Resistive transitions under magnetic
field show broadening, which is consistent with a relatively large anisotropy
of upper critical field. Magneto-optical images reveal homogenous current flow
within the ab-plane.",1211.1221v2
2012-11-08,Effects of nuclear medium and nonisoscalarity in extracting $sin^2θ_W$ using Paschos-Wolfenstein relation,"We study the nuclear medium effects and nonisoscalarity correction in the
extraction of weak mixing angle sin$^2\theta_W$ using Paschos-Wolfenstein (PW)
relation. The calculations are performed for the iron nucleus. The results are
discussed along with the experimental result inferred by NuTeV collaboration.
The nuclear medium effects like Fermi motion, binding, shadowing and
antishadowing corrections and pion and rho meson cloud contributions have been
taken into account. Calculations have been performed in the local density
approximation using a relativistic nuclear spectral function which includes
nucleon correlations. These studies may be useful for the ongoing MINER$\nu$A
experiment as well as for the proposed NuSOnG experiment.",1211.1817v2
2012-11-08,Constraints of the compactness of the isolated neutron stars via X-ray phase-resolved spectroscopy,"A model with a condensed iron surface and partially ionized hydrogen-thin
atmosphere allows us to fit simultaneously the observed general spectral shape
and the broad absorption feature (observed at 0.3 keV) in different spin phases
of the isolated neutron star RBS 1223. We constrain some physical properties of
the X-ray emitting areas, i.e. the temperatures (Tpole1 ~ 105eV, Tpole2 ~99eV),
magnetic field strengths Bpole1 ~ Bpole2 ~ 8.6x10^13G) at the poles, and their
distribution parameters (a1 ~ 0.61, a2 ~ 0.29, indicating an absence of strong
toroidal magnetic field component). In addition, we are able to place some
constraints on the geometry of the emerging X-ray emission and the
gravitational redshift (z ~0.16+0.03-0.01) of the isolated neutron star RBS
1223.",1211.1842v2
2012-11-08,Closing the Window on Strongly Interacting Dark Matter,"Constraints are placed on the spin-independent interaction cross section of
dark matter with regular matter by refining two methods. First, dark
matter--cosmic ray interactions are considered, wherein cosmic ray protons
collide with dark matter to contribute to the gamma ray sky. This constraint is
developed using the NFW and Moore dark matter density profiles and new data
from the Fermi gamma ray space telescope. Second, the Earth capture scenario is
considered, wherein particles that are captured self-annihilate at Earth's
center, thus adding to its internal heat flow. The constraint presented here is
developed based on analysis of the drift time of dark matter particles through
Earth, modeled as a core composed of iron and a mantle composed of oxygen with
linear density gradients between layers. An analysis of the cosmic ray
constraint (which rules out dark matter--regular matter interaction cross
sections greater than its value) shows that it overlaps significantly with the
Earth drift time constraint (which rules out cross sections smaller than its
value), closing the window on strongly interacting dark matter particles up to
a mass of about 10^{17} GeV when combined with other exclusions.",1211.1951v1
2012-11-12,An orbital-selective spin liquid in a frustrated heavy fermion spinel LiV$_2$O$_4$,"The pronounced enhancement of the effective mass is the primary phenomenon
associated with strongly correlated electrons. In the presence of local
moments, the large effective mass is thought to arise from Kondo coupling, the
interaction between itinerant and localised electrons. However, in d electron
systems, the origin is not clear because of the competing Hund's rule coupling.
Here we experimentally address the microscopic origin for the heaviest d
fermion in a vanadium spinel LiV2O4 having geometrical frustration. Utilising
orbital-selective 51V NMR, we elucidate the orbital-dependent local moment that
exhibits no long-range magnetic order despite persistent antiferromagnetic
correlations. A frustrated spin liquid, Hund-coupled to itinerant electrons,
has a crucial role in forming heavy fermions with large residual entropy. Our
method is important for the microscopic observation of the orbital-selective
localisation in a wide range of materials including iron pnictides, cobaltates,
manganites, and ruthnates.",1211.2844v1
2012-11-14,Are There Any Stars Lacking Neutron-Capture Elements? Evidence from Strontium and Barium,"The cosmic dispersion in the abundances of the heavy elements strontium and
barium in halo stars is well known. Strontium and barium are detected in most
cool, metal-poor giants, but are these elements always detectable? To identify
stars that could be considered probable candidates for lacking these elements,
I examine the stellar abundance data available in the literature for 1148 field
stars and 226 stars in dwarf galaxies, 776 of which have metallicities lower
than [Fe/H]<-2.0. Strontium or barium have been detected in all field, globular
cluster, and dwarf galaxy environments studied. All upper limits are consistent
with the lowest detected ratios of [Sr/H] and [Ba/H]. The frequent appearance
of these elements raises the intriguing prospect that at least one kind of
neutron-capture reaction operates as often as the nucleosynthesis mechanisms
that produce lighter elements, like magnesium, calcium, or iron, although the
yields of heavy elements may be more variable.",1211.3427v1
2012-11-15,"Annealing, acid, and alcoholic beverage effects on Fe1+yTe0.6Se0.4","We have systematically investigated and compared different methods to induce
superconductivity in iron chalcogenide Fe1+yTe0.6Se0.4 including annealing in
vacuum, N2, O2, I2 atmosphere, and immersing samples into acid and alcoholic
beverages. Vacuum and N2 annealing are proved to be ineffective to induce
superconductivity in Fe1+yTe0.6Se0.4 single crystal. O2 and I2 annealing, acid
and alcoholic beverages can induce superconductivity by oxidizing the excess Fe
in the sample. Superconductivity in O2 annealed sample is in bulk nature, while
I2, acid and alcoholic beverages can only induce superconductivity near the
surface. By comparing different effects of O2, I2, acid and alcoholic
beverages, we propose a scenario to explain how the superconductivity is
induced in the non-superconducting as-grown Fe1+yTe0.6Se0.4.",1211.3491v1
2012-11-16,Bicrystalline Grain Boundary and Hybrid SNS Junctions Based on Ba-122 Thin Films,"To investigate the properties of iron-based superconductors, we examined
different kinds of Josephson junctions using Co-doped Ba-122 thin films. Based
on bicrystalline SrTiO3 substrates we prepared grain boundary (GB) junctions,
which showed clear Josephson effects. We present electrical measurements at
varying temperatures and magnetic fields. Furthermore, we prepared hybrid
junctions using thin film technique. Confined by a Ba-122 base electrode (S)
and a PbIn counter electrode (S') two different geometries of hybrid junctions
are formed: a planar SNS' junction with a gold barrier (N) in between and an
edge-type junction with an interface-engineered barrier. All three kinds of
junctions showed asymmetric resistively shunted junction-like (RSJ) behavior
with ICRN products of 20.2 /mu V (GB junctions), 18.4 /mu V (planar SNS'
junctions) and 12.3 /mu V (edge-type junctions), respectively. An excess
current could be observed at all junctions.",1211.3879v1
2012-11-27,Theoretical spectroscopy of realistic condensed matter systems,"This thesis is devoted to ab initio calculations of ground and excited state
properties of different systems within density functional theory and time
dependent density functional theory. From the numerical point of view we
implemented an original method in the DP code to calculate the independent
particle response function. Moreover, we generalized the DP code to the spin
degree of freedom in order to study the magnetic properties of realistic
condensed matter systems. We studied reflectance anisotropy and energy loss
spectra of a clean and oxidized surface, and we performed an analysis of the
origin of the main spectral features. Thanks to the comparison between
experimental and theoretical energy loss spectra, we roule out the p(2x1)
reconstruction for the Si(100) surface. Moreover, in the case of a simple BeH
molecule we evidenced the problem of correctly describing the excitation
spectra for open shell systems within the TDDFT framework. In the second part
of the thesis, we presented the study of the optical properties of magnetic
systems such as FeS2, CoS2 or NiS2, interesting materials for possible
technological applications in the growing field of spintronics. Within this
context we calculated ground state properties and optical condictivity of BCC
bulk iron, for which we found a nice agreement with available experimental
data.",1211.6270v1
2012-11-28,Stability of xenon oxides at high pressures,"Xenon, which is quite inert under ambient conditions, may become reactive
under pressure. The possibility of formation of stable xenon oxides and
silicates in the interior of the Earth could explain the atmospheric missing
xenon paradox. Using the ab initio evolutionary algorithm, we predict the
thermodynamical stabilization of Xe-O compounds at high pressures (XeO, XeO2
and XeO3 at pressures above 83, 102 and 114 GPa, respectively). Our
calculations indicate large charge transfer in these oxides, suggesting that
large electronegativity difference and pressure are the key factors favoring
the formation of xenon compounds. Xenon compounds in the Earth's mantle,
however, cannot directly explain the missing xenon paradox: xenon oxides are
unstable in equilibrium with metallic iron in the Earth's lower mantle, while
xenon silicates are predicted to spontaneously decompose at all mantle
pressures (<136 GPa). This does not preclude Xe atoms from being retained in
defects of mantle silicates and oxides.",1211.6520v2
2012-11-28,Nonlocal optical generation of spin and charge currents on the surface of magnetic insulators using total absorption and surface plasmons,"We study the nonlocal spin and charge current generation in a finite metallic
element on the surface of magnetic insulators such as \tcb{yttrium iron garnet}
due to the absorption of the magnetic surface plasmon (MSP). Whereas a surface
plasmon is completely reflected by a metal, \tcb{an} MSP \tcb{can be} absorbed
\tcb{due to the absence of backward states}. The \tcb{injection of} MSP
generates a voltage in the longitudinal direction parallel to the wave vector,
\tcb{with the voltage} proportional to input power. If the metal is a
ferromagnet, a spin current can also be \tcb{induced} in the longitudinal
direction. Our \tcb{results provide a way to improve upon} integrated circuits
of spintronics and spin wave logic devices.",1211.6716v1
2012-12-02,Lateral spin injection and detection through electrodeposited Fe/GaAs contacts,"Efforts to achieve efficient injection of spin-polarized electrons into a
semiconductor, a key prerequisite for developing electronics that exploit the
electron's spin degree of freedom, have so far met with limited success. Here
we report experimental studies of lateral spin injection and detection through
electrodeposited Fe/GaAs tunnel contacts. We demonstrate spin injection
efficiencies two orders of magnitude higher than for state-of-the-art contacts
fabricated via ultra-high-vacuum methods, including those with MgO or Al2O3
tunnel barriers. To account for this enhancement, we propose that an iron oxide
layer that forms at the Fe/GaAs interface during electrodeposition, being
magnetic, acts as a tunnel barrier with a spin-dependent height, presenting
quantum spin transport calculations for such systems. This serendipitous
discovery of greatly enhanced efficiency of spin injection into GaAs via
electrodeposited contacts introduces a promising new direction for the
development of practical semiconductor spintronic devices.",1212.0258v1
2012-12-11,Red Supergiant Stars as Cosmic Abundance Probes: II. NLTE Effects in J-band Silicon Lines,"Medium resolution J-band spectroscopy of individual red supergiant stars is a
promising tool to investigate the chemical composition of the young stellar
population in star forming galaxies. As a continuation of recent work on iron
and titanium, detailed non-LTE calculations are presented to investigate the
influence of NLTE on the formation of silicon lines in the J-band spectra of
red supergiants. Substantial effects are found resulting in significantly
stronger absorption lines of neutral silicon in non-LTE. As a consequence,
silicon abundances determined in non-LTE are significantly smaller than in LTE
with the non-LTE abundance corrections varying smoothly between -0.4 dex to
-0.1 dex for effective temperatures between 3400K to 4400K. The effects are
largest at low metallicity. The physical reasons behind the non-LTE effects and
the consequences for extragalactic J-band abundance studies are discussed.",1212.2649v1
2012-12-14,Forward and inverse problems in fundamental and applied magnetohydrodynamics,"This Minireview summarizes the recent efforts to solve forward and inverse
problems as they occur in different branches of fundamental and applied
magnetohydrodynamics. As for the forward problem, the main focus is on the
numerical treatment of induction processes, including self-excitation of
magnetic fields in non-spherical domains and/or under the influence of
non-homogeneous material parameters. As an important application of the
developed numerical schemes, the functioning of the von-K\'{a}rm\'{a}n-sodium
(VKS) dynamo experiment is shown to depend crucially on the presence of
soft-iron impellers. As for the inverse problem, the main focus is on the
mathematical background and some first practical applications of the
Contactless Inductive Flow Tomography (CIFT), in which flow induced magnetic
field perturbations are utilized for the reconstruction of the velocity field.
The promises of CIFT for flow field monitoring in the continuous casting of
steel are substantiated by results obtained at a test rig with a low melting
liquid metal. While CIFT is presently restricted to flows with low magnetic
Reynolds numbers, some selected problems of non-linear inverse dynamo theory,
with possible application to geo- and astrophysics, are also discussed.",1212.3447v1
2012-12-15,Calibration Systems of the ATLAS Tile Calorimeter,"TileCal is the hadronic calorimeter covering the most central region of the
ATLAS experiment at the LHC. This sampling calorimeter uses iron plates as
absorber and plastic scintillating tiles as the active material. A
multi-faceted calibration system allows to monitor and equalize the calorimeter
response at each stage of the signal production, from scintillation light to
digitization. This calibration system is based on signal generation from
different sources: a Cs radioactive source, laser light, charge injection and
minimum bias events produced in proton-proton collisions. A brief description
of the different TileCal calibration systems is given and the latest results on
their performance in terms of calibration factors, linearity and stability are
presented.",1212.3676v1
2012-12-16,Wetting dynamics on lyophilic solid surfaces patterned by lyophobic islands,"A theory for wetting of structured solid surfaces is developed, based on the
delta-comb periodic potential. It possesses two matching parameters: the
effective line tension and the friction coefficient on the three-phase contact
line at the surface. The theory is validated on the dynamics of spreading of
liquid zinc droplets on morphologically patterned zinkophilic iron surface by
means of square patterns of zinkophobic aluminum oxide. It is found that the
effective line tension is negative and it has essential contribution to the
dynamics of spreading. Thus, the theoretical analysis shows that the presence
of lyophobic patterns situated on lyophilic surface makes the latter completely
wettable, i.e. no equilibrium contact angle on such surface exists making the
droplet spread completely in form of thin liquid layer on the patterned
surface.",1212.3791v4
2012-12-18,Time Reversal Invariant Topological Superconductivity and Majorana Kramers Pairs,"We propose a feasible route to engineer one and two dimensional time reversal
invariant (TRI) topological superconductors (SC) via proximity effects between
nodeless extended s wave iron-based SC and semiconductors with large Rashba
spin-orbit interactions. At the boundary of a TRI topological SC, there emerges
a Kramers pair of Majorana edge (bound) states. For a Josephson pi-junction we
predict a Majorana quartet that is protected by mirror symmetry and leads to a
mirror fractional Josephson effect. We analyze the evolution of Majorana pair
in Zeeman fields, as the SC undergoes a symmetry class change as well as
topological phase transitions, providing an experimental signature in tunneling
spectroscopy. We briefly discuss the realization of this mechanism in candidate
materials and the possibility of using s and d wave SC and weak topological
insulators.",1212.4232v2
2012-12-18,Experimental realization of dynamo action: present status and prospects,"In the last decades, the experimental study of dynamo action has made great
progress. However, after the dynamo experiments in Karlsruhe and Riga, the
von-Karman-Sodium (VKS) dynamo is only the third facility that has been able to
demonstrate fluid flow driven self-generation of magnetic fields in a
laboratory experiment. Further progress in the experimental examination of
dynamo action is expected from the planned precession driven dynamo experiment
that will be designed in the framework of the liquid sodium facility DRESDYN
(DREsden Sodium facility for DYNamo and thermohydraulic studies).
  In this paper, we briefly present numerical models of the VKS dynamo that
demonstrate the close relation between the axisymmetric field observed in that
experiment and the soft iron material used for the flow driving impellers. We
further show recent results of preparatory water experiments and design studies
related to the precession dynamo and delineate the scientific prospects for the
final set-up.",1212.4331v1
2012-12-21,Structural and magnetic phase transitions in triclinic Ca10(FeAs)10(Pt3As8),"We report the structural and magnetic phase transitions of triclinic
Ca10(FeAs)10(Pt3As8). High-resolution X-ray powder diffraction reveals
splitting of the in-plane (a,b) lattice parameters at Ts ~ 120 K.
Platinum-doping weakens the distortion and shifts the transition temperature to
80 K in Ca10(Fe1-xPt_xAs)10(Pt3As8) with x = 0.03. muSR experiments show the
onset of magnetic order near Ts and a broad magnetic phase transition. No
symmetry breaking is associated to the structural transition in
Ca10(FeAs)10(Pt3As8) in contrast to the other parent compounds of iron arsenide
superconductors.",1212.5531v1
2012-12-24,Fabrication and transport properties of Sr0.6K0.4Fe2As2 multifilamentary superconducting wires,"Seven-core Ag/Fe sheathed Sr0.6K0.4Fe2As2 (Sr-122) superconducting wires were
produced by the ex situ powder-in-tube (PIT) method. The relationship between
the cold-work deformation process and the superconducting properties of wires
were systematically studied. It was found that flat rolling can efficiently
increase the density of the superconducting core and largely improve the
transport critical current density (Jc) of as-drawn wires. The Jc of the best
sample achieved 21.1 kA/cm^2 at 4.2 K in self field, and showed very weak
magnetic field dependence in high fields. Our result suggested a promising
future of multifilamentary iron-based superconductors in practical application.",1212.5873v1
2012-12-24,Spin-state transition in the Fe-pnictides,"We report a Fe K\beta x-ray emission spectroscopy study of local magnetic
moments in the rare-earth doped iron pnictide Ca_{1-x}RE_xFe_2As_2 (RE=La, Pr,
and Nd). In all samples studied the size of the Fe local moment is found to
decrease significantly with temperature and goes from ~0.9 \mu_B at T = 300 K
to ~0.45 \mu_B at T = 70 K. In the collapsed tetragonal (cT) phase of Nd- and
Pr-doped samples (T<70K) the local moment is quenched, while the moment remains
unchanged for the La-doped sample, which does not show lattice collapse. Our
results show that Ca_{1-x}RE_xFe_2As_2 (RE= Pr and Nd) exhibits a spin-state
transition and provide direct evidence for a non-magnetic Fe^{2+} ion in the
cT-phase, as predicted by Yildirim. We argue that the gradual change of the the
spin-state over a wide temperature range reveals the importance of multiorbital
physics, in particular the competition between the crystal field split Fe 3d
orbitals and the Hund's rule coupling.",1212.5925v1
2013-01-02,Discovery of the first Super-Lithium rich Beat Cepheid: V371 Per,"Four high-resolution spectra of the double-mode Cepheid V371 Per, obtained
for the first time, showed the presence of the abnormally strong Li I 6707.76 A
line. Our analysis of the light element abundances indicates that the star did
not go through the evolutionary dredge-up stage. Large distance from the
galactic plane and the low metallicity suggest that V371 Per may belong to the
thick disc (or to the halo) of the Galaxy, which is consistent with its low
metallicity [Fe/H]=-0.42 and the enhancement of the alpha- and s-elements
relative to iron. Line splitting is observed in one of the spectra, which can
be due to the non-radial pulsations.",1301.0199v1
2013-01-03,Pair Breaking Caused by Magnetic Impurities in the High-T$_\text{C}$ Superconductor Bi$_{2.1}$Sr$_{1.9}$Ca(Cu$_{1-x}$Fe$_{x}$)$_{2}$O$_{y}$,"Conventional superconductivity is robust against the addition of impurities
unless the impurities are magnetic in which case superconductivity is quickly
suppressed. Here we present a study of the cuprate superconductor
Bi$_2$Sr$_2$Ca$_1$Cu$_2$O$_{8+\delta}$ that is intentionally doped with the
magnetic impurity, Fe. Through the use of our Tomographic Density of States
(TDoS) technique, we find that while the superconducting gap magnitude is
essentially unaffected by the inclusion of iron, the onset of
superconductivity, T$_{C}$, and the pair-breaking rate are strongly dependent
and correlated. These findings suggest that, in the cuprates, the pair-breaking
rate is critical to the determination of T$_{C}$ and that magnetic impurities
do not disrupt the strength of pairing but rather the lifetime of the pairs.",1301.0521v2
2013-01-11,Perspectives of the disproportionation driven superconductivity in strongly correlated 3d compounds,"Disproportionation in 3d compounds can give rise to an unconventional
electron-hole Bose liquid with a very rich phase diagram from a Bose metal,
charge ordering insulator to an inhomogeneous Bose superfluid. Optimal
conditions for the disproportionation driven high-T_c superconductivity are
shown to realize only for several Jahn-Teller d^n configurations that permit
the formation of well defined local composite bosons. These are the high-spin
d^4, low-spin d^7, and d^9 configurations given the octahedral crystal field,
and the d^1, high-spin d^6 configurations given the tetrahedral crystal field.
The disproportionation reaction has a peculiar anti-Jahn- Teller character
lifting the bare orbital degeneracy. Superconductivity in the d^4 and d^6
systems at variance with d^1, d^7, and d^9 systems implies an unavoidable
coexistence of the spin-triplet composite bosons and a magnetic lattice. We
argue that unconventional high-T_c superconductivity observed in quasi-2D
cuprates with tetragonally distorted CuO_6 octahedra and iron-based layered
pnictides/chalcogenides with tetrahedrally coordinated Fe^2+ ions can be a key
argument supporting the disproportionation scenario is at work in these
compounds.",1301.2395v1
2013-01-11,Terzan 5: a Fossil Remnant of the Galactic Bulge,"Terzan 5 is a stellar system located in the Galactic Bulge, at a distance of
5.9 kpc. Recent discoveries show that it hosts two stellar populations with
different iron abundance ({\Delta}[Fe/H]=0.5). Such a large difference has been
measured only in {\omega} Centauri in the Galactic halo. Moreover no
anticorrelation is observed in Terzan 5, hence it is not a genuine globular
cluster. The observed chemical patterns are strikingly similar to those
observed in the Bulge stars. This suggests that Terzan 5 is a remnant fragment
of the Galactic bulge.",1301.2436v1
2013-01-16,NGC5694: another extra-galactic globular cluster,"We discuss the chemical composition of six giant stars of the outer Halo
globular cluster NGC5694, through the analysis of UVES@FLAMES high-resolution
spectra. The cluster has an average iron content [Fe/H]=--1.83+-0.01,
solar-scaled [alpha/Fe] ratios and a very low Ba abundance
([Ba/Fe]=--0.71+-0.06). These anomalous abundance patterns are different from
those observed in other Halo globular clusters but similar to those of the
metal-poor stars in typical dwarf spheroidal galaxies. These findings suggest
an extra-galactic origin for NGC5694, likely from a dwarf spheroidal galaxy.",1301.3606v1
2013-01-21,Nanoscale Surface Element Identification and Dopant Homogeneity in the High-$T_c$ Superconductor Pr$_x$Ca$_{1-x}$Fe$_2$As$_2$,"We use scanning tunneling microscopy to determine the surface structure and
dopant distribution in Pr$_x$Ca$_{1-x}$Fe$_2$As$_2$, the highest-$T_c$ member
of the 122 family of iron-based superconductors. We identify the cleaved
surface termination by mapping the local tunneling barrier height, related to
the work function. We image the individual Pr dopants responsible for
superconductivity, and show that they do not cluster, but in fact repel each
other at short length scales. We therefore suggest that the low volume fraction
high-$T_c$ superconducting phase is unlikely to originate from Pr
inhomogeneity.",1301.4942v2
2013-01-22,Quasi-two-dimensional non-collinear magnetism in the Mott insulator Sr$_2$F$_2$Fe$_2$OS$_2$,"The magnetism of Sr$_2$F$_2$Fe$_2$OS$_2$ was examined through neutron powder
diffraction and thermodynamic and transport measurements. Quasi-two-dimensional
magnetic order develops below $T_N$ = 106(2) K with an in-plane correlation
length exceeding 310 \AA\ and an out-of-plane correlation length of just 17(3)
\AA. The data are consistent with a two-k structure with $k_1$ = (1/2, 0, 1/2)
and $k_2$ = (0, 1/2, 1/2) and an ordered moment of 3.3(1) $\mu_B$ oriented
along the in-plane components of k. This structure is composed of orthogonal
AFM chains intersecting at super-exchange mediating O sites. Density Functional
Theory (DFT) also points to this structure and a narrower Fe 3d band than for
the iron pnictides from which electronic correlations produce a Mott insulator.",1301.5056v1
2013-01-23,"Nodal superconductivity in isovalently substituted SrFe$_2$(As$_{1-x}$P$_{x}$)$_2$ pnictide superconductor at the optimal doping, $x=$0.35","Temperature-dependent London penetration depth, $\lambda(T)$, was measured in
optimally - doped, $x=$0.35, as-grown ($T_c \approx$25 K,
RRR=$\rho(300K)/\rho(T_c)$=4.5) and annealed ($T_c \approx$35 K, RRR=6.4)
single crystals of SrFe$_2$(As$_{1-x}$P$_{x}$)$_2$ iron - based superconductor.
Annealing increases the RRR and decreases the absolute value of the London
penetration depth from $\lambda(0) = 300 \pm 10$ nm in as-grown sample to
$\lambda(0) = 275 \pm 10$ nm. At low temperatures, $\lambda(T) \sim T$
indicating superconducting gap with line nodes. Analysis of the full -
temperature range superfluid density is consistent with the line nodes, but
differs from the simple single - gap $d-$wave. The observed behavior is very
similar to that of BaFe$_2$(As$_{1-x}$P$_{x}$)$_2$, showing that isovalently
substituted pnictides are inherently different from the charge - doped
materials.",1301.5622v1
2013-01-24,"Superconductivity, Antiferromagnetism, and Neutron Scattering","High-temperature superconductivity in both the copper-oxide and the
iron-pnictide/chalcogenide systems occurs in close proximity to
antiferromagnetically ordered states. Neutron scattering has been an essential
technique for characterizing the spin correlations in the antiferromagnetic
phases and for demonstrating how the spin fluctuations persist in the
superconductors. While the nature of the spin correlations in the
superconductors remains controversial, the neutron scattering measurements of
magnetic excitations over broad ranges of energy and momentum transfer provide
important constraints on the theoretical options. We present an overview of the
neutron scattering work on high-temperature superconductors and discuss some of
the outstanding issues.",1301.5888v1
2013-01-25,Upper critical field of isoelectron substituted SrFe$_2$(As$_{1-x}$P$_x$)$_2$,"The upper critical field $H_{c2}$ of optimally doped iron-based
superconductor SrFe$_{2}$(As$_{1-x}$P$_{x}$)$_{2}$ ($x$ = 0.35, $T_c$ = 25 K)
was measured as a function of temperature down to 1.6 K for two principal
directions of magnetic field $H \parallel c$ and $H \parallel a$. Measurements
were performed in pulsed magnetic fields up to 65 T using a tunnel-diode
resonator technique on as-grown and heavy-ion irradiated single crystals, with
columnar defect density corresponding to a matching field $B\phi$ = 25 T. The
$H_{c2,c}(T)$ is close to $T$-linear, while clear saturation is observed for
$H_{c2,a}(T)$, leading to a strongly temperature dependent anisotropy parameter
$\gamma$. The linear shape of $H_{c2,c}(T)$ is very similar to that observed in
nodal KFe$_2$As$_2$ but very different from full-gap LiFeAs. Irradiation does
not introduce any additional features on $H_{c2}(T)$ line corresponding to the
matching field. Instead, it suppresses uniformly both $T_c$ and $H_{c2}$,
keeping their ratio constant.",1301.6142v1
2013-01-27,Angular-dependent upper critical field of overdoped Ba(Fe$_{1-x}$Ni$_x$)$_2$As$_2$,"In-plane resistivity measurements as a function of temperature, magnetic
field and its orientation with respect to the crystallographic $ab-$plane were
used to study the upper critical field, $H_{c2}$, of two overdoped compositions
of the iron-based superconductor Ba(Fe$_{1-x}$Ni$_x$)$_2$As$_2$, $x=$0.054 and
$x$=0.072. Measurements were performed using precise alignment (with accuracy
less than 0.1$^o$) of magnetic field with respect to the Fe-As-plane. The
dependence of the $H_{c2}$ on angle $\theta$ between the field and the
$ab$-plane was measured in isothermal conditions in a broad temperature range.
We found that the shape of $H_{c2}(\theta)$, clearly deviates from
Ginzburg-Landau functional form.",1301.6396v1
2013-02-02,Rethinking Globular Cluster Formation,"This paper is aimed at emphasizing some of the main hints, constraints and
difficulties we currently have in trying to understand how globular clusters
formed, along with their multiple stellar generations, an issue that must be
regarded as intimately connected to the formation process itself. Thus, the
topics that are addressed include i) the required mass of the progenitor, ii)
how to form new stars in an environment already crowded by a previous stellar
generation, iii) how photometry and spectroscopy appear to suggest different
formation processes for second generation stars, iv) whether dilution with
pristine material may (or may not) be necessary for the formation of second
generations, v) why the few clusters with multiple iron abundances are after
all not so different from those that are homogeneous, and finally vi) why
special environmental conditions may not be necessary for the formation of
globular clusters with multiple stellar generations.",1302.0329v1
2013-02-04,Ferromagnetic Quantum Critical Point Induced by Tuning the Magnetic Dimensionality of the Heavy-Fermion Iron Oxypnictide Ce(Ru$_{1-x}$Fe$_x$)PO,"We have performed 31P-NMR measurements of the c-axis-aligned poly-crystal
Ce(Ru1-xFex)PO with a two-dimensional layered structure in order to understand
the origin of TCurie suppression by Fe substitution. The variation in the
magnetic-fluctuation character with respect to x is investigated from the
in-plane and out-of plane fluctuations and the relationship between the static
spin susceptibility and the in-plane fluctuation. It was found that
three-dimensional ferromagnetic (FM) correlations are dominant and give rise to
the FM ordering in CeRuPO. The out-of-plane fluctuations are significantly
suppressed with increasing x, and it was revealed that the FM fluctuations
become two dimensional near a FM quantum critical point (QCP). Our NMR results
strongly suggest that a unique FM QCP in Ce(Ru1-xFex)PO is induced by the
suppression of the magnetic correlations along the c-axis, which is a different
mechanism from that presumed in heavy-fermion compounds.",1302.0578v2
2013-02-05,Type II superconductivity in SrPd2Ge2,"Previous investigations have shown that SrPd2Ge2, a compound isostructural
with ""122"" iron pnictides but iron- and pnictogen-free, is a conventional
superconductor with a single s-wave energy gap and a strongly three-dimensional
electronic structure. In this work we reveal the Abrikosov vortex lattice
formed in SrPd2Ge2 when exposed to magnetic field by means of scanning
tunneling microscopy and spectroscopy. Moreover, by examining the differential
conductance spectra across a vortex and estimating the upper and lower critical
magnetic fields by tunneling spectroscopy and local magnetization measurements,
we show that SrPd2Ge2 is a strong type II superconductor with \kappa >>
sqrt(2). Also, we compare the differential conductance spectra in various
magnetic fields to the pair breaking model of Maki - de Gennes for dirty limit
type II superconductor in the gapless region. This way we demonstrate that the
type II superconductivity is induced by the sample being in the dirty limit,
while in the clean limit it would be a type I superconductor with \kappa\ <<
sqrt(2), in concordance with our previous study (T. Kim et al., Phys. Rev. B
85, (2012)).",1302.1022v1
2013-02-06,Gap Symmetry and Stability Analysis in the Multi-Orbital Fe-Based Superconductors,"The iron-based superconductors allow for a zoo of possible order parameters
due to their orbital degrees of freedom. These order parameters are often
written in an orbital basis, as this allows to distinguish their different
symmetry. Unlike in standard single-band superconductors, where electrons of
the same band - and hence, energy - are paired, a general order parameter in
such a multi-orbital system also contains pairing of electrons belonging to
different bands. As this corresponds to pairing of electrons of different
energy, such order parameters are energetically less stable. Here, we present a
simple criterion for a stability analysis of the orbital part of the gap
function based on the basic principle that electrons of equal energy are paired
in the superconducting state. This not only allows to find the most stable
states, but also to identify the terms in a (tight-binding) Hamiltonian
suppressing any given superconducting state. Our approach thus allows to
identify the minimal Hamiltonian necessary to compare competing instabilities.",1302.1468v2
2013-02-07,Evidence of Strong Correlations and Coherence-Incoherence Crossover in the Iron Pnictide Superconductor KFe2As2,"Using resistivity, heat-capacity, thermal-expansion, and susceptibility
measurements we study the normal-state behavior of KFe2As2. We find that both
the Sommerfeld coefficient gamma = 103 mJ mol-1 K-2 and the Pauli
susceptibility chi = 4x10-4 are strongly enhanced, which confirm the existence
of heavy quasiparticles inferred from previous de Haas-van Alphen and ARPES
experiments. We discuss this large enhancement using a Gutzwiller slave-boson
mean-field calculation, which reveals the proximity of KFe2As2 to an
orbital-selective Mott transition. The temperature dependence of the magnetic
susceptibility and the thermal expansion provide strong experimental evidence
for the existence of a coherence-incoherence crossover, similar to what is
found in heavy fermion and ruthenate compounds, due to Hund's coupling between
orbitals.",1302.1696v1
2013-02-13,Ligand field parameters and the ground state of Fe(II) phthalocyanine,"A judicious analysis of previously published experimental data leads one to
conclude that the ground state of iron(II) phthalocyanine is an orbitally
degenerate spin triplet $a_{1g}^2 e_g^{\uparrow\downarrow\uparrow}
b_{2g}^{\uparrow}$ ($^3E_g$). The ligand field parameters, in relation to
Racah's $C$, are approximately as follows: $B_{20}/C=0.84$, $B_{40}/C=0.0074$.
The uniqueness of this result is demonstrated by means of a special diagram in
the $B_{20}/C-B_{40}/C$ plane (under additional conditions that
$B_{44}/B_{40}=35/3$ and $B/C=0.227$). The system is in a strong-ligand-field
regime, which enables the use of single-determinant techniques corrected for
correlations within the 3d shell of Fe.",1302.3023v2
2013-02-13,Nucleosynthesis in the gamma-ray burst accretion disks and associated outflows,"We investigate nucleosynthesis inside the gamma-ray burst (GRB) accretion
disks formed by the Type II collapsars and outflows launched from these disks.
We deal with accretion disks having relatively low accretion rates: 0.001 M_sun
s^{-1} <~ Mdot <~ 0.01 M_sun s^{-1} and hence they are predominantly advection
dominated. We report the synthesis of several unusual nuclei like 31P, 39K,
43Sc, 35Cl and various isotopes of titanium, vanadium, chromium, manganese and
copper in the disk. We also confirm that isotopes of iron, cobalt, nickel,
argon, calcium, sulphur and silicon get synthesized in the disk, as shown by
previous authors. Much of these heavy elements thus synthesized are ejected
from the disk and survive in the outflows. Indeed, emission lines of many of
these heavy elements have been observed in the X-ray afterglows of several
GRBs.",1302.3067v1
2013-02-13,Unconventional Superconductivity,"A brief review of unconventional superconductivity is given, stretching from
the halcyon days of helium-3 to the modern world of Majorana fermions. Along
the way, we will encounter such strange beasts as heavy fermion
superconductors, cuprates, and their iron-based cousins. Emphasis will be put
on the fact that in almost all cases, an accepted microscopic theory has yet to
emerge. This is attributed to the difficulty of constructing a theory of
superconductivity outside the Migdal-Eliashberg framework.",1302.3176v2
2013-02-15,PARSEC: A Parametrized Simulation Engine for Ultra-High Energy Cosmic Ray Protons,"We present a new simulation engine for fast generation of ultra-high energy
cosmic ray data based on parametrizations of common assumptions of UHECR origin
and propagation. Implemented are deflections in unstructured turbulent
extragalactic fields, energy losses for protons due to photo-pion production
and electron-pair production, as well as effects from the expansion of the
universe. Additionally, a simple model to estimate propagation effects from
iron nuclei is included. Deflections in galactic magnetic fields are included
using a matrix approach with precalculated lenses generated from backtracked
cosmic rays. The PARSEC program is based on object oriented programming
paradigms enabling users to extend the implemented models and is steerable with
a graphical user interface.",1302.3761v2
2013-02-19,"Effect of magnetism on kinetics of ""gamma""-""alpha"" transformation and pattern formation in iron","Kinetics of polymorphous ""gamma""-""alfa"" transformation in Fe is studied
numerically within a model taking into account both lattice and magnetic
degrees of freedom, based on first-principle calculations of the total energy
for different magnetic states. It is shown that magnetoelastic phenomena,
namely, a strong sensitivity of the potential relief along the Bain deformation
path to the magnetic state, are crucial for the picture of the transformation.
With the temperature increase, a scenario of the phase transformation evolves
from a homogeneous lattice instability at T<Ms (Ms is the temperature of the
beginning of the martensitic transformation) to the growth and nucleation of
embryos of the new phase at T>Ms. In the latter case, a stage of formation of a
tweed-like structure occurs, with a strong short-range order and slow
interphase fluctuations.",1302.4643v2
2013-02-20,"Non-metallic, non-Fermi-liquid resistivity of FeCrAs from 0 to 17 GPa","An unusual, non-metallic resistivity of the 111 iron-pnictide compound FeCrAs
is shown to be relatively unchanged under pressures of up to 17 GPa. Combined
with our previous finding that this non-metallic behaviour persists from at
least 80 mK to 800 K, this shows that the non-metallic phase is exceptionally
robust. Antiferromagnetic order, with a Neel temperature T_N ~ 125 K at ambient
pressure, is suppressed at a rate of 7.1 +/- 0.1 K/GPa, falling to below 50 K
at 10 GPa. We conclude that formation of a spin-density wave gap at T_N does
not play an important role in the non-metallic resistivity of FeCrAs at low
temperatures.",1302.4791v1
2013-02-20,Transport signatures of spatially modulated electronic nematic phases,"Electronic nematic phases are broadly characterized by spontaneously broken
rotational symmetry. Although they have been widely recognized in the context
of high temperature cuprates, bilayer ruthenates, and iron-based
superconductors, the focus so far has been exclusively on the uniform nematic
phase. Recently, however, it was proposed that on a square lattice a nematic
instability in the d-wave charge channel could lead to a spatially modulated
nematic state, where the modulation vector q is determined by the relative
location of the Fermi level to the van Hove singularity. Interestingly, this
finite-q nematic phase has also been identified as an additional leading
instability that is as strong as the superconducting instability near the onset
of spin density wave order. Here we study the electrical conductivity tensor in
the modulated nematic phase for a general modulation vector. Our results can be
used to identify modulated nematic phases in correlated materials.",1302.5117v1
2013-02-21,Superconductivity induced by U-doping in the SmFeAsO system,"Through partial substitution of Sm by U in SmFeAsO, a different member of the
family of iron-based superconductors was successfully synthesized. X-ray
diffraction measurements show that the lattice constants along the a and c axes
are both squeezed through U doping, indicating a successful substitution of U
at the Sm site. The parent compound shows a strong resistivity anomaly near 150
K, associated with spin-density-wave instability.U doping suppresses this
instability and leads to a transition to the superconducting state at
temperatures up to 49 K. Magnetic measurements confirm the bulk
superconductivity in this system. For the sample with a doping level of x =
0.2, the external magnetic field suppresses the onset temperature very slowly,
indicating a rather high upper critical field. In addition, the Hall effect
measurements show that U clearly dopes electrons into the material.",1302.5155v1
2013-02-28,Synthesis of New Layered Oxypnictides Sr2CrO2(FeAs)2,"We successfully synthesized new layered iron oxypnictide Sr2CrO2(FeAs)2 by
solid-state-reaction techniques. This is the first report on the Fe-substituted
Sr2Mn3As2O2-type oxypnictides to our knowledge. A pellet of stoichiometric
mixtures of SrO, Cr and FeAs wrapped with tantalum foil was sintered at
900{\deg}C for 96 h. Results of x-ray diffraction measurement and Rietveld
refinements show that the structure of the sample belongs to the space group of
I4/mmm with the lattice constants of a = 3.9948(1) {\AA} and c = 18.447(1)
{\AA}. Temperature dependence of the resistivity for Sr2CrO2(FeAs)2 shows
semiconductor-like behavior. Additionally, the sample does not exhibit
superconducting transition in measurements of resistivity and magnetization
even in the low temperature down to 3 K.",1302.7196v1
2013-03-01,Expanded Iron UTA spectra -- probing the thermal stability limits in AGN clouds,"The Fe unresolved transition array (UTAs) produce prominent features in the
15-17?A wavelength range in the spectra of Active Galactic Nuclei (AGN). Here
we present new calculations of the energies and oscillator strengths of inner-
shell lines from Fe XIV, Fe XV, and Fe XVI. These are crucial ions since they
are dominant at inflection points in the gas thermal stability curve, and UTA
excitation followed by autoionization is an important ionization mechanism for
these species. We incorporate these, and data reported in previous papers, into
the plasma simulation code Cloudy. This updated physics is subsequently
employed to reconsider the thermally stable phases in absorbing media in Active
Galactic Nuclei. We show how the absorption profile of the Fe XIV UTA depends
on density, due to the changing populations of levels within the ground
configuration.",1303.0316v1
2013-03-07,Longitudinal magnetoresistance in Co-doped BaFe2As2 and LiFeAs single crystals: Interplay between spin fluctuations and charge transport in iron-pnictides,"The longitudinal in-plane magnetoresistance (LMR) has been measured in
different Ba(Fe_(1-x)Co_x)2As2 single crystals and in LiFeAs. For all these
compounds, we find a negative LMR in the paramagnetic phase whose magnitude
increases as H^2. We show that this negative LMR can be readily explained in
terms of suppression of the spin fluctuations by the magnetic field. In the
Co-doped samples, the absolute value of the LMR coefficient is found to
decrease with doping content in the paramagnetic phase. The analysis of its T
dependence in an itinerant nearly antiferromagnetic Fermi liquid model
evidences that the LMR displays a qualitative change of T variation with
increasing Co content. The latter occurs at optimal doping for which the
antiferromagnetic ground state is suppressed. The same type of analysis for the
negative LMR measured in LiFeAs suggests that this compound is on the verge of
magnetism.",1303.1677v2
2013-03-07,Studies of homogeneous precipitation in very dilute iron-coper alloys using kinetic Monte Carlo simulations and statistical theory of nucleation,"Kinetics of homogeneous nucleation and growth of copper precipitates under
electron irradiation of Fe_{1-x}Cu_x alloys at concentrations x from 0.06 at.%
to 0.4 at.% and temperatures T from 290 to 450C is studied using the kinetic
Monte Carlo (KMC) simulations and the statistical theory of nucleation (STN).
The conventional assumption about the similarity of mechanisms of precipitation
under electron irradiation and during thermal aging is adopted. The
earlier-developed ab initio model of interactions in Fe-Cu alloys is used for
both the KMC simulations and the STN calculations. Values of the nucleation
barrier F_c and the prefactor J_0 in the Zeldovich-Volmer relation for the
nucleation rate J are calculated for a number of concentrations and
temperatures. For the dilute alloys with x less then 0.2%, the STN and the KMC
results for the nucleation barrier F_c do virtually coincide with each other,
which seems to confirm a high reliability of the STN for this problem. The STN
calculations are also used to estimate the temperature dependencies of
concentrations which correspond to the homogeneous or the heterogeneous
precipitation limit and both dependencies are found to be rather sharp.",1303.1753v1
2013-03-08,Heat capacity jump at Tc and pressure derivatives of superconducting transition temperature in the Ba1-xKxFe2As2 (0.2 < x < 1.0) series,"We present the evolution of the initial (up to ~ 10 kbar) hydrostatic,
pressure dependencies of Tc and of the ambient pressure jump in the heat
capacity associated with the superconducting transition as a function of K -
doping in the Ba1-xKxFe2As2 family of iron-based superconductors. The pressure
derivatives show weak but distinct anomaly near x ~ 0.7. In the same
concentration region Delta Cp at Tc deviates from the Delta Cp ~ T^3 scaling
found for most BaFe2As2 - based superconductors. These results are consistent
with a Lifshitz transition, and possible significant modification of the
superconducting state, occurring near x ~ 0.7.",1303.2010v1
2013-03-11,The Reach of INO for Atmospheric Neutrino Oscillation Parameters,"The India-based Neutrino Observatory (INO) will host a 50 kt magnetized iron
calorimeter (ICAL@INO) for the study of atmospheric neutrinos. Using the
detector resolutions and efficiencies obtained by the INO collaboration from a
full-detector GEANT4-based simulation, we determine the reach of this
experiment for the measurement of the atmospheric neutrino mixing parameters
($\sin^2 \theta_{23}$ and $|\Delta m_{32}^2 |$). We also explore the
sensitivity of this experiment to the deviation of $\theta_{23}$ from maximal
mixing, and its octant.",1303.2534v2
2013-03-11,"Individual Alpha Elements, C, N, and Ba in Early Type Galaxies","Spectral data on early type galaxies is analyzed for chemical abundance with
an emphasis on obtaining detailed abundances for the elements O and Si in
addition to C, N, Na, Mg, Ca, Fe, and Ba. The abundance trends with velocity
dispersion fit preconceptions based upon previous Mg conclusions, namely that
larger galaxies have a higher alpha element to iron peak ratio indicative of a
higher ratio of Type II to Type Ia supernova products. The heaviest alpha
elements, Ca and Ti, do not participate in this trend, although this fact does
not necessarily alter the basic picture given the uncertainties in
nucleosynthetic yields. Elements that likely have significant contributions
from intermediate-mass stars, namely C, N, and Ba, also gain ground relative to
Fe in massive galaxies at a modest level, with the Ba conclusion uncertain from
our data alone.",1303.2603v1
2013-03-13,A Ni-Fe Layered Double Hydroxide-Carbon Nanotube Complex for Water Oxidation,"Highly active, durable and cost-effective electrocatalysts for water
oxidation to evolve oxygen gas hold a key to a range of renewable energy
solutions including water splitting and rechargeable metal-air batteries. Here,
we report the synthesis of ultrathin nickel iron layered double hydroxide
nanoplates on mildly oxidized multi-walled carbon nanotubes. Incorporation of
Fe into the nickel hydroxide induced the formation of NiFe-layered double
hydroxide. The nanoplates were covalently attached to a network of nanotubes,
affording excellent electrical wiring to the nanoplates. The ultra-thin Ni-Fe
layered double hydroxide nanoplates/carbon nanotube complex was found to
exhibit unusually high electro-catalytic activity and stability for oxygen
evolution and outperformed commercial precious metal Ir catalysts.",1303.3308v2
2013-03-14,Quasiparticle mass enhancement close to the quantum critical point in BaFe$_2$(As$_{1-x}$P$_x$)$_2$,"We report a combined study of the specific heat and de Haas-van Alphen effect
in the iron-pnictide superconductor BaFe$_2$(As$_{1-x}$P$_x$)$_2$. Our data
when combined with results for the magnetic penetration depth give compelling
evidence for the existence of a quantum critical point (QCP) close to $x=0.30$
which affects the majority of the Fermi surface by enhancing the quasiparticle
mass. The results show that the sharp peak in the inverse superfluid density
seen in this system results from a strong increase in the quasiparticle mass at
the QCP.",1303.3396v2
2013-03-14,Investigation of charge states and multiferroicity in Fe-doped h-YMnO3,"Polycrystalline YMn1-xFexO3 (YMFO_x) (0 <= x <= 0.1) compounds have been
prepared in single phase and characterized by synchrotron X-ray diffraction,
X-ray absorption near edge spectroscopy, magnetization, and dielectric
measurements. Iron-substitution in hexagonal YMnO3 causes intra-lattice changes
exceeding those of the lattice cell. XANES provide mixed-valence Mn3+/Mn4+ and
Fe4+ charge states in these manganites, consistent with the observed decrease
of the effective magnetic moment with Fe-doping. Magnetization M(T) evidence
antiferromagnetic (AFM) ordering of the specimens with little weak
ferromagnetism, and the metrices of exchange interaction suppress with
Fe-doping, attributed to the lengthening of the Mn-O planar bond lengths.
Dielectric {\epsilon}'(T) results showing highly doping-dependent anomaly at
T_N indicate linear magneto-electric coupling.",1303.3398v2
2013-03-15,Phase diagram and superconductivity at 58.1 K in α-FeAs free SmFeAsO1-xFx,"The Phase diagram of SmFeAsO1-xFx in terms of x is exhibited in this study.
SmFeAsO1-xFx from x = 0 to x = 0.3 were prepared by low temperature sintering
with slow cooling. The low temperature sintering suppresses the formation of
the amorphous FeAs, which is inevitably produced as an impurity by using high
temperature sintering. Moreover, slow cooling is effective to obtain the high
fluorine concentration. The compositional change from feedstock composition is
quite small after this synthesis. We can reproducibly observe a record
superconducting transition for an iron based superconductor at 58.1 K. This
achievement of a high superconducting transition is due to the success in a
large amount of fluorine substitution. A shrinking of the a lattice parameter
caused by fluorine substitution is observed and the substitutional rate of
fluorine changes at x =0.16.",1303.3725v2
2013-03-17,Two-dimensional magnetic interactions in LaFeAsO,"Inelastic neutron scattering measurements demonstrate that the magnetic
interactions in antiferromagnetic LaFeAsO are two-dimensional. Spin wave
velocities within the Fe layer and the magnitude of the spin gap are similar to
the \textit{A}Fe$_2$As$_2$ based materials. However, the ratio of interlayer
and intralayer exchange is found to be less than $\sim 10^{-4}$ in LaFeAsO,
very similar to the cuprates, and $\sim$ 100 times smaller than that found in
\textit{A}Fe$_2$As$_2$ compounds. The results suggest that the effective
dimensionality of the magnetic system is highly variable in the parent
compounds of the iron arsenides and weak 3-D interactions may limit the maximum
attainable superconducting $T_{c}$.",1303.4033v1
2013-03-19,<3D> NLTE line formation in the atmospheres of red supergiants,"Red supergiants with their enormous brightness at J-band are ideal probes of
cosmic chemical composition. It is therefore crucial to have realistic models
of radiative transfer in their atmospheres, which will permit determination of
abundances accurate to 0.15 dex, the precision attainable with future telescope
facilities in galaxies as distant as tens of Mpc. Here, we study the effects of
non-local thermodynamic equilibrium (NLTE) on the formation of iron, titanium,
and silicon lines, which dominate J-band spectra of red supergiants. It is
shown that the NLTE radiative transfer models enable accurate derivation of
metallicity and effective temperature in the J-band. We also discuss
consequences for RSG spectrum synthesis in different spectral windows,
including the heavily TiO-blanketed optical region, and atmospheric structure.
We then touch upon challenges of NLTE integration with new generation of 3D
hydrodynamical RSG models and present the first calculations of NLTE spectra
with the mean 3D model of Betelgeuse.",1303.4768v1
2013-03-24,Determination of $sin^{2}θ_W$ using $ν(\barν)$-Nucleus scattering,"We have studied nonisoscalarity and medium effects in the extraction of weak
mixing angle using Paschos and Wolfenstein relation in the iron nucleus.
Paschos and Wolfenstein(PW) relation is valid for an isoscalar target. We have
modified the PW relation for nonisoscalar target as well as incorporated the
medium effects like Pauli blocking, Fermi motion, nuclear binding energy and
pion rho cloud contributions. In our calculations we have used the relativistic
nuclear spectral function which includes nucleon correlations. Finally local
density approximation is applied to translate the numerical results to the
finite nuclei. We have studied the dependence of $sin^{2}\theta_W$ on Bjorken
variables $x$ and $y$, four momentum transfer square ($Q^2$), energy of the
neutrino and antineutrino, and effect of excess neutrons over protons in the
nuclear target.",1303.5928v1
2013-03-29,An analytically tractable model of bad metals,"We discuss a model Kondo-type Hamiltonian representing an analytically
tractable version of the model used by Yin {\it et.al.}, Phys. Rev. B{\bf 86},
2399 (2012) to explain the non-Fermi liquid behavior of iron chalcogenides and
ruthenates in an intermediate energy range. We consider a regime where a
complete screening of the local degrees of freedom proceeds in two stages
described by two characteristic energy scales $T_K^{orb} >> E_0$. The first
scale marks a screening of the orbital degrees of freedom and the second one
marks a crossover to the regime with coherent propagation of quasiparticles. We
present analytical results for the specific heat and magnetic susceptibility at
$T << T_K^{orb}$.",1303.7448v2
2013-04-04,"On Euler's ""Misleading Induction"", Andrews' ""Fix"", and How to Fully Automate them","One of the greatest experimental mathematicians of all time was also one of
the greatest mathematicians of all time, the great Leonhard Euler. Usually he
had an uncanny intuition on how many ""special cases"" one needs before one can
formulate a plausible conjecture, but one time he was ""almost fooled"", only to
find out that his conjecture was premature.
  In 1990, George Andrews found a way to ""correct"" Euler. Here we show how to
generate, AUTOMATICALLY, rigorously-proved Euler-Andrews Style formulas, that
enables one to generate Euler-style ""cautionary tales"" about the ""danger"" of
using naive empirical induction. Ironically, the way we prove the Andrews-style
corrections is empirical! But in order to turn the empirical proof into a
full-fledged rigorous proof, we must make sure that we check sufficiently many
(but still not that many!) special cases.",1304.1226v1
2013-04-04,Ab-initio prediction of magnetoelectricity in infinite-layer CaFeO2 and MgFeO2,"Density functional based simulations are employed to explore magnetoelectric
effects in iron-based oxides, showing a unique layered structure. We
theoretically predict CaFeO2 to be a promising magnetoelectric, showing
magnetically-controlled large electric polarization, possibly even above room
temperature. The cross coupling between magnetic and dipolar degrees of freedom
needs, as main ingredients, Fe-site spin-orbit coupling and a spin-dependent O
p - Fe d hybridization, along with structural constraints related to the
non-centrosymmetric point group and the peculiar geometry characterized by
""flattened"" FeO4 tetrahedrons. In order to enhance magnetoelectric effects, we
performed a materials-design leading to a novel and optimized system, MgFeO2,
where the larger O4 tetrahedral distortion leads to a stronger polarization.",1304.1228v2
2013-04-04,Revisiting the hardening of the cosmic-ray energy spectrum at TeV energies,"Measurements of cosmic rays by experiments such as ATIC, CREAM, and PAMELA
indicate a hardening of the cosmic-ray energy spectrum at TeV energies. In our
recent work (Thoudam & H\""orandel 2012a), we showed that the hardening can be
due to the effect of nearby supernova remnants. We showed it for the case of
proton and helium. In this paper, we present an improved and detailed version
of our previous work, and extend our study to heavier cosmic-ray species such
as boron, carbon, oxygen, and iron nuclei. Unlike our previous study, the
present work involves a detailed calculation of the background cosmic rays and
follows a consistent treatment of cosmic-ray source parameters between the
background and the nearby components. Moreover, we also present a detailed
comparison of our results on the secondary-to-primary ratios, secondary
spectra, and the diffuse gamma-ray spectrum with the results expected from
other existing models, which can be checked by future measurements at high
energies.",1304.1400v2
2013-04-09,Upper critical field of high quality single crystals of KFe$_2$As$_2$,"Measurements of temperature-dependent in-plane resistivity, $\rho(T)$, were
used to determine the upper critical field and its anisotropy in high quality
single crystals of stoichiometric iron arsenide superconductor KFe$_2$As$_2$.
The crystals were characterized by residual resistivity ratio,
$\rho(300K)/\rho(0)$ up to 3000 and resistive transition midpoint temperature,
$T_c$=3.8 K, significantly higher than in previous studies on the same
material. We find increased $H_{c2}(T)$ for both directions of the magnetic
field, which scale with the increased $T_c$. This unusual linear $H_{c2}(T_c)$
scaling is not expected for orbital limiting mechanism of the upper critical
field in clean materials.",1304.2689v1
2013-04-10,Large room-temperature magnetoresistance in lateral organic spin valves fabricated by in-situ shadow evaporation,"We report the successful fabrication of lateral organic spin valves with a
channel length in the sub $100\,nm$ regime. The fabication process is based on
in-situ shadow evaporation under UHV conditions and therefore yields clean and
oxygen-free interfaces between the ferromagnetic metallic electrodes and the
organic semiconductor. The spin valve devices consist of Nickel and Cobalt-iron
electrodes and the high mobility \emph{n}-type organic semiconductor
$N,N'$-bis(heptafluorobutyl)-$3,4:9,10$-perylene diimide. Our studies comprise
fundamental investigations of the process' and materials' suitability for the
fabrication of lateral spin valve devices as well as magnetotransport
measurements at room temperature. The best devices exhibit a magnetoresistance
of up to $50\,%$, the largest value for room temperature reported so far.",1304.2911v2
2013-04-10,Finite temperature and pressure molecular dynamics for BaFe2As2,"We study the temperature and pressure dependence of the structural and
electronic properties of the iron pnictide superconductor BaFe2As2. We use
density functional theory based Born-Oppenheimer molecular dynamics simulations
to investigate the system at temperatures from T=5 K to 150 K and pressures
from P=0 GPa to 30 GPa. When increasing the pressure at low temperature, we
find the two transitions from an orthorhombic to a tetragonal and to a
collapsed tetragonal structure that are also observed in zero temperature
structure relaxations and in experiment. However, these transitions are
considerably smeared out at finite temperature, whereas the critical pressure
for the first transition increases with temperature. We also analyze the
electronic structure of BaFe2As2 at finite temperature and work out differences
between the time averaged band structure and Fermi surface at finite
temperature compared to the known zero temperature results. Our results should
be helpful for resolving some open issues in experimental reports for BaFe2As2
under high pressure.",1304.3039v1
2013-04-12,"Effect of Vacuum Annealing on Superconductivity in Fe(Se,Te) Single Crystals","The effect of vacuum annealing on superconductivity is investigated in
Fe(Se,Te) single crystals. It is found that superconductivity is not enhanced
by annealing under high vacuum (~ 10^(-3) Pa) or by annealing in a sealed
evacuated quartz tube. In a moderate vacuum atmosphere (~ 1 Pa), iron oxide
layers are found to show up on sample surfaces, which would draw excess Fe out
of the crystal. Thus, it is suggested that remanent oxygen effectively works to
remove excess Fe from the matrix of Fe(Se,Te) crystals, resulting improvement
of superconducting transition temperature. Our transport measurements suggest
that the excess Fe scatters the carriers on electron- and hole-type channels in
a different manner. We discuss how the mobility of two types of carriers
correlate with superconductivity. Since both the electron and hole bands are
important for the occurrence of superconductivity, excess Fe would suppress
superconductivity mainly due to strong scattering of electrons.",1304.3590v1
2013-04-14,Peculiarities of performance of the spin valve for the superconducting current,"The spin valve effect for the superconducting current based on the
superconductor/ferromagnet proximity effect has been studied for a
CoO_x/Fe1/Cu/Fe2/Cu/Pb multilayer. The magnitude of the effect $\Delta T_c$ =
T_c^{AP} - T_c^{P}, where T_c^{P} and T_c^{AP} are the superconducting
transition temperatures for the parallel (P) and antiparallel (AP) orientation
of magnetizations, respectively, has been measured for different thicknesses of
the Fe1 layer d_{Fe1}. The obtained dependence of the effect on d_{Fe1} reveals
that $\Delta T_c$ can be increased in comparison with the case of a
half-infinite Fe1 layer considered by the previous theory. A maximum of the
spin valve effect occurs at d_{Fe1} ~ d_{Fe2}. At the optimal value of d_{Fe1},
almost full switching from the normal to the superconducting state when
changing the mutual orientation of magnetizations of the iron layers Fe1 and
Fe2 from P to AP is demonstrated.",1304.3939v1
2013-04-23,Low-energy bound states at interfaces between superconducting and block antiferromagnet regions in KxFe{2-y}Se2,"The high-Tc alkali doped iron selenide superconductors KxFe{2-y}Se2 have been
recently shown to be intrinsically phase separated into Fe vacancy ordered
block antiferromagnetic regions and superconducting regions at low
temperatures. In this work, we use a microscopic five orbital Hubbard model to
obtain the electronic low-energy states near the interfaces between block
antiferromagnets and superconductors. It is found that abundant low-energy
in-gap bound states exist near such interfaces irrespective of whether the
superconductor has d- or s-wave pairing symmetry. By contrast, it is shown how
nonmagnetic scattering planes can provide a natural means to distinguish
between these two leading pairing instabilities of the KxFe{2-y}Se2 materials.",1304.6424v1
2013-04-24,Thermodynamic Observation of a Vortex Melting Transition in the Fe-based Superconductor Ba0.5K0.5Fe2As2,"In cuprate high-temperature superconductors the small coherence lengths and
high transition termperatures result in strong thermal fluctuations, which
render the superconducting transition in applied magnetic fields into a wide
continuous crossover. A state with zero resistance is found only below the
vortex melting transition, which occurs well below the onset of superconducting
correlations. Here we investigate the vortex phase diagram of the novel
Fe-based superconductor in form of a high-quality single crystal of
Ba0.5K0.5Fe2As2, using three different experimental probes (specific heat,
thermal expansion and magnetization). We find clear thermodynamic signatures of
a vortex melting transition, which shows that the thermal fluctuations in
applied magnetic fields also have a considerable impact on the superconducting
properties of iron-based superconductors.",1304.6464v1
2013-04-26,Direct microscopic calculations of nuclear level densities in the shell model Monte Carlo approach,"Nuclear level densities are crucial for estimating statistical nuclear
reaction rates. The shell model Monte Carlo method is a powerful approach for
microscopic calculation of state densities in very large model spaces. However,
these state densities include the spin degeneracy of each energy level, whereas
experiments often measure level densities in which each level is counted just
once. To enable the direct comparison of theory with experiments, we introduce
a method to calculate directly the level density in the shell model Monte Carlo
approach. The method employs a projection on the minimal absolute value of the
magnetic quantum number. We apply the method to nuclei in the iron region as
well as the strongly deformed rare-earth nucleus $^{162}$Dy. We find very good
agreement with experimental data including level counting at low energies,
charged particle spectra and Oslo method at intermediate energies, neutron and
proton resonance data, and Ericson's fluctuation analysis at higher excitation
energies.",1304.7258v1
2013-04-28,Temperature dependent local atomic displacements in Ru substituted SmFe_{1-x}Ru_{x}AsO_{0.85}F_{0.15} superconductors,"Local structure of SmFe$_{1-x}$Ru$_x$AsO$_{0.85}$F$_{0.15}$ ($x$ = 0.0, 0.05,
0.25 and 0.5) superconductors has been investigated by temperature dependent As
$K$-edge extended x-ray absorption fine structure. The effect of Ru
substitution remains confined to the iron-arsenide layer but neither the static
disorder nor the Fe-As bond strength suffers any change for $x \le$ 0.25. With
further Ru substitution the static disorder increases while the Fe-As bond
strength remains unchanged. Also, the Ru-As distance ($\sim$2.42 \AA),
different from the Fe-As distance ($\sim$2.39 \AA), does not show any change in
its force constant with the Ru substitution. These observations suggest that
the SmFe$_{1-x}$Ru$_x$AsO$_{0.85}$F$_{0.15}$ system breaks down to coexisting
local electronic phases on isoelectric substitution in the active FeAs layer.",1304.7416v1
2013-05-01,"Nanotube caps on Ni, Fe, and NiFe nano particles: A path to chirality selective growth","Carbon nanotubes have properties depending on the arrangement of carbon atoms
on the tube walls, called chirality. Also it has been tried to grow nanotubes
of only one chirality for more than a decade it is still not possible today. A
narrowing of the distribution of chiralities, however, which is a first step
towards chirality control, has been observed for the growth of nanotubes on
catalysts composed of nickel and iron. In this paper, we have calculated
carbon-metal bond energies, adhesion energies and charge distributions of
carbon nanotube caps on Ni, Fe and NiFe alloy clusters using density functional
theory. A growth model using the calculated energies was able to reproduce the
experimental data of the nanotube growth on the alloy catalysts. The electronic
charge was found to be redistributed from the catalyst particles to the edges
of the nanotube caps in dependence of the chiral angles of the caps increasing
the reactivity of the edge atoms. Our study develops an explanation for the
chirality enrichment in the carbon nanotube growth on alloy catalyst particles.",1305.0145v1
2013-05-06,Dzyaloshinsky-Moriya driven helical-butterfly structure in Ba3NbFe3Si2O14,"We have used soft x-ray magnetic diffraction at the Fe3+ L2,3 edges to
examine to what extent the Dzyaloshinsky-Moriya interaction in Ba3NbFe3Si2O14
influences its low temperature magnetic structure. A modulated component of the
moments along the c-axis is present, adding to the previously proposed helical
magnetic configuration of co-planar moments in the a,b-plane. This leads to a
helical-butterfly structure and suggests that both the multi-axial in-plane and
the uniform out-of-plane Dzyaloshinsky-Moriya vectors are relevant. A non zero
orbital magnetic signal is also observed at the oxygen K edge, which reflects
the surprisingly strong hybridization between iron 3d and oxygen 2p states,
given the nominal spherical symmetry of the Fe3+ half filled shell.",1305.1160v1
2013-05-06,Analysis of a carbon dimer bound to a vacancy in iron using density functional theory and a new tight binding model,"Recent density functional theory (DFT) calculations by Foerst et al. have
predicted that vacancies in both low and high carbon steels have a carbon dimer
bound to them. This is likely to change the thinking of metallurgists in the
kinetics of the development of microstructures. While the notion of a C2
molecule bound to a vacancy in Fe will potentially assume a central importance
in the atomistic modeling of steels, neither a recent tight binding (TB) model
nor existing classical interatomic potentials can account for it. Here we
present a new TB model for C in Fe, based on our earlier work for H in Fe,
which correctly predicts the structure and energetics of the carbon dimer at a
vacancy in Fe. Moreover the model is capable of dealing with both concentrated
and dilute limits of carbon in both bcc-Fe and fcc-Fe as comparisons with DFT
show. We use both DFT and TB to make a detailed analysis of the dimer and to
come to an understanding as to what governs the choice of its curious
orientation within the vacancy.",1305.1171v1
2013-05-08,"Nematic State of the Pnictides Stabilized by the Interplay Between Spin, Orbital, and Lattice Degrees of Freedom","The nematic state of the iron-based superconductors is studied in the undoped
limit of the three-orbital ($xz$, $yz$, $xy$) spin-fermion model via the
introduction of lattice degrees of freedom. Monte Carlo simulations show that
in order to stabilize the experimentally observed lattice distortion and
nematic order, and to reproduce photoemission experiments, {\it both} the
spin-lattice and orbital-lattice couplings are needed. The interplay between
their respective coupling strengths regulates the separation between the
structural and N\'eel transition temperatures. Experimental results for the
temperature dependence of the resistivity anisotropy and the angle-resolved
photoemission (ARPES) orbital spectral weight are reproduced by the present
numerical simulations.",1305.1879v1
2013-05-10,Theory of superconductivity in a three-orbital model of Sr$_2$RuO$_4$,"In conventional and high transition temperature copper oxide and iron
pnictide superconductors, the Cooper pairs all have even parity. As a rare
exception, Sr$_2$RuO$_4$ is the first prime candidate for topological chiral
p-wave superconductivity, which has time-reversal breaking odd-parity Cooper
pairs known to exist before only in the neutral superfluid $^3$He. However,
there are several key unresolved issues hampering the microscopic description
of the unconventional superconductivity. Spin fluctuations at both large and
small wavevectors are present in experiments, but how they arise and drive
superconductivity is not yet clear. Spontaneous edge current is expected but
not observed conclusively. Specific experiments point to highly band- and/or
momentum-dependent energy gaps for quasiparticle excitations in the
superconducting state. Here, by comprehensive functional renormalization group
calculations with all relevant bands, we disentangle the various competing
possibilities. In particular we show the small wavevector spin fluctuations,
driven by a single two-dimensional band, trigger p-wave superconductivity with
quasi-nodal energy gaps.",1305.2317v2
2013-05-10,Implementation of non-equilibrium vertex corrections in KKR: transport through disordered layers,"The theoretical description of modern nanoelectronic devices requires a
quantum mechanical treatment and often involves disorder, e.g. form alloys.
Therefore, the ab initio theory of transport using non-equilibrium Green's
functions is extended to the case of disorder described by the coherent
potential approximation. This requires the calculation of non-equilibrium
vertex corrections. We implement the vertex corrections in a
Korringa-Kohn-Rostoker multiple scattering scheme. In order to verify our
implementation and to demonstrate the accuracy and applicability we investigate
a system of an iron-cobalt alloy layer embedded in copper. The results obtained
with the coherent potential approximation are compared to supercell
calculations. It turns out that vertex corrections play an important role for
this system.",1305.2399v1
2013-05-14,Spectral matching for abundances of 848 stars of the giant branches of the globular cluster ω Centauri,"We present the effective temperatures, surface gravities and abundances of
iron, carbon and barium of 848 giant branch stars, of which 557 also have
well-defined nitrogen abundances, of the globular cluster {\omega} Centauri.
This work used photometric sources and lower resolution spectra for this
abundance analysis. Spectral indices were used to estimate the oxygen abundance
of the stars, leading to a determination of whether a particular star was
oxygen-rich or oxygen-poor.
  The 557-star subset was analyzed in the context of evolutionary groups, with
four broad groups identified. These groups suggest that there were at least
four main four periods of star formation in the cluster. The exact order of
these star formation events is not yet understood.
  These results compare well with those found at higher resolution and show the
value of more extensive lower resolution spectral surveys. They also highlight
the need for large samples of stars when working with a complex object like
{\omega} Cen.",1305.3059v2
2013-05-15,Design and Performance Analysis of a 2.5 MW-Class HTS Synchronous Motor for Ship Propulsion,"The development of cryogenic technology and high temperature superconducting
(HTS) materials has seen continued interest worldwide in the development of HTS
machines since the late 1980s. In this paper, the authors present a conceptual
design of a 2.5 MW class synchronous motor. The structure of the motor is
specified and the motor performance is analyzed via a three-dimensional model
using the finite element method (FEM). Rotor optimization is carried out to
decrease the harmonic components in the air gap field generated by HTS tapes.
Based on the results of this 3D simulation, the determination of the operating
conditions and load angle is discussed with consideration to the HTS material
properties. The economic viability of air-core and iron-core designs is
compared. The results show that this type of HTS machine has the potential to
achieve an economic, efficient and effective machine design, which operates at
a low load angle, and this design process provides a practical way to simulate
and analyze the performance of such machines.",1305.3590v3
2013-05-18,Estimation of Lateral Distribution Function in Extensive Air Showers by Using AIRES Simulation System,"In this work the estimation of the lateral distribution function in Extensive
Air showers was performed by using a system for air shower simulations which is
called AIRES version 2.6 for different hadronic models like (QGSJET99, SIBYLL
and SIBYLL1.6). The simulation was fulfilled in the high energy range
(10^15-10^19 eV) for different primary particles like (gamma, protons and iron
nuclei) for vertical showers. This simulation can be used to reconstruct the
type and energy of the particle that generated Extensive Air showers for
charged particles that registered with different arrays.",1305.4628v2
2013-05-30,Guided self-assembly of magnetic beads for biomedical applications,"Micromagnetic beads are widely used in biomedical applications for cell
separation, drug delivery, and hypothermia cancer treatment. Here we propose to
use self-organized magnetic bead structures which accumulate on fixed magnetic
seeding points to isolate circulating tumor cells. The analysis of circulating
tumor cells is an emerging tool for cancer biology research and clinical cancer
management including the detection, diagnosis and monitoring of cancer.
Microfluidic chips for isolating circulating tumor cells use either affinity,
size or density capturing methods. We combine multiphysics simulation
techniques to understand the microscopic behavior of magnetic beads interacting
with Nickel accumulation points used in lab-on-chip technologies. Our proposed
chip technology offers the possibility to combine affinity and size capturing
with special antibody-coated bead arrangements using a magnetic gradient field
created by Neodymium Iron Boron permanent magnets. The multiscale simulation
environment combines magnetic field computation, fluid dynamics and discrete
particle dynamics.",1305.7072v1
2013-06-03,Review on Superconducting Materials,"Short review of the topical comprehension of the superconductor materials
classes Cuprate High-Temperature Superconductors, other oxide superconductors,
Iron-based Superconductors, Heavy-Fermion Superconductors, Nitride
Superconductors, Organic and other Carbon-based Superconductors and Boride and
Borocarbide Superconductors, featuring their present theoretical understanding
and their aspects with respect to technical applications.",1306.0429v2
2013-06-05,Magnetic chains: From self-buckling to self-assembly,"Spherical neodymium-iron-boron magnets are perman-ent magnets that can be
assembled into a variety of structures due to their high magnetic strength. A
one-dimensional chain of these magnets responds to mechanical loadings in a
manner reminiscent of an elastic rod. We investigate the macroscopic mechanical
properties of assemblies of ferromagnetic spheres by considering chains, rings,
and chiral cylinders of magnets. Based on energy estimates and simple
experiments, we introduce an effective magnetic bending stiffness for a chain
of magnets and show that, used in conjunction with classic results for elastic
rods, it provides excellent estimates for the buckling and vibration dynamics
of magnetic chains. We then use this estimate to understand the dynamic
self-assembly of a cylinder from an initially straight chain of magnets.",1306.1014v2
2013-06-07,Negative Magnetoresistance and Spin Filtering of Spin-Coupled Diiron-Oxo Clusters,"Spin dependent transport has been investigated for an {\it open shell
singlet} diiron-oxo cluster. Currents and magnetoresistances have been studied,
as a function of spin state, within the non-equilibrium Green's function
approach. The applied bias can be used for tuning the sign of the observed
magnetoresistance. A colossal magnetoresistance ratio has been determined, on
the order of to 6000$%$, for hydrogen anchoring. Applied biases lower than 0.3
V, in conjunction with sulfur anchoring, induce a negative magnetoresistance
due to lowering of the anchor-scatterer tunneling barrier. In addition, the
diiron-oxo cluster displays nearly perfect spin filtering for parallel
alignment of the iron magnetic moments due to energetic proximity, relative to
the Fermi level, of its highest occupied molecular orbitals.",1306.1588v2
2013-06-07,Free energy generalization of the Peierls potential in iron,"In body-centered cubic (bcc) crystals, ${1}{2}111$ screw dislocations exhibit
high intrinsic lattice friction as a consequence of their non-planar core
structure, which results in a periodic energy landscape known as the Peierls
potential, $U_P$. The main features determining plastic flow, including its
stress and temperature dependences, can be derived directly from this
potential, hence its importance. In this Letter, we use thermodynamic
integration to provide a full thermodynamic extension of $U_P$ for bcc Fe. We
compute the Peierls free energy path as a function of stress and temperature
and show that the critical stress vanishes at 700K, supplying the qualitative
elements that explain plastic behavior in the athermal limit.",1306.1633v4
2013-06-11,Discovery of high-frequency iron K lags in Ark 564 and Mrk 335,"We use archival XMM-Newton observations of Ark 564 and Mrk 335 to calculate
the frequency dependent time-lags for these two well-studied sources. We
discover high-frequency Fe K lags in both sources, indicating that the red wing
of the line precedes the rest frame energy by roughly 100 s and 150 s for Ark
564 and Mrk 335, respectively. Including these two new sources, Fe K
reverberation lags have been observed in seven Seyfert galaxies. We examine the
low-frequency lag-energy spectrum, which is smooth, and shows no feature of
reverberation, as would be expected if the low-frequency lags were produced by
distant reflection off circumnuclear material. The clear differences in the low
and high frequency lag-energy spectra indicate that the lags are produced by
two distinct physical processes. Finally, we find that the amplitude of the Fe
K lag scales with black hole mass for these seven sources, consistent with a
relativistic reflection model where the lag is the light travel delay
associated with reflection of continuum photons off the inner disc.",1306.2551v1
2013-06-11,Effect of pressure cycling on Iron: Signatures of an electronic instability and unconventional superconductivity,"High pressure electrical resistivity and x-ray diffraction experiments have
been performed on Fe single crystals. The crystallographic investigation
provides direct evidence that in the martensitic $bcc \rightarrow hcp$
transition at 14 GPa the $\lbrace 110\rbrace_{bcc}$ become the $\lbrace
002\rbrace_{hcp}$ directions. During a pressure cycle, resistivity shows a
broad hysteresis of 6.5 GPa, whereas superconductivity, observed between 13 and
31 GPa, remains unaffected. Upon increasing pressure an electronic instability,
probably a quantum critical point, is observed at around 19 GPa and, close to
this pressure, the superconducting $T_{c}$ and the isothermal resistivity
($0<T<300\,$K) attain maximum values. In the superconducting pressure domain,
the exponent $n = 5/3$ of the temperature power law of resistivity and its
prefactor, which mimics $T_{c}$, indicate that ferromagnetic fluctuations may
provide the glue for the Cooper pairs, yielding unconventional
superconductivity.",1306.2587v1
2013-06-11,Nature of the bad metallic behavior of Fe_{1.06}Te inferred from its evolution in the magnetic state,"We investigate with angle resolved photoelectron spectroscopy the change of
the Fermi Surface (FS) and the main bands from the paramagnetic (PM) state to
the antiferromagnetic (AFM) occurring below 72 K in Fe_{1.06}Te. The evolution
is completely different from that observed in iron-pnictides as nesting is
absent. The AFM state is a rather good metal, in agreement with our magnetic
band structure calculation. On the other hand, the PM state is very anomalous
with a large pseudogap on the electron pocket that closes in the AFM state. We
discuss this behavior in connection with spin fluctuations existing above the
magnetic transition and the correlations predicted in the spin-freezing regime
of the incoherent metallic state.",1306.2603v2
2013-06-12,Hybrid deterministic/stochastic algorithm for large sets of rate equations,"We propose a hybrid algorithm for the time integration of large sets of rate
equations coupled by a relatively small number of degrees of freedom. A subset
containing fast degrees of freedom evolves deterministically, while the rest of
the variables evolves stochastically. The emphasis is put on the coupling
between the two subsets, in order to achieve both accuracy and efficiency. The
algorithm is tested on the problem of nucleation, growth and coarsening of
clusters of defects in iron, treated by the formalism of cluster dynamics. We
show that it is possible to obtain results indistinguishable from fully
deterministic and fully stochastic calculations, while speeding up
significantly the computations with respect to these two cases.",1306.2817v1
2013-06-18,Of Substitution and Doping: Spatial and Electronic Structure in Fe Pnictides,"A highly intriguing aspect in iron-pnictide superconductors is the
composition-dependent electronic structure, in particular the question if and
how charge carriers are introduced to the system upon substitution of Ba by
alkali metals or of Fe by other transition metals, TM. We report on a
systematic study of spatial structure and electronic states by x-ray
diffraction and x-ray absorption on a large number of compositions in the
(Ba,K)(Fe,TM)2As2 family. The coherent combination of detailed structural
information with an in-depth analysis of the electronic structure allows us to
sensitively disentangle (charge-carrier) ""doping"" effects from ""substitutional""
effects. Results include a doping character that is site-decoupled, as well as
TM 3d energy-level schemes that exhibit non-standard level sequences and even
t2-e level crossings. Our study indicates that doping per se seems to play a
lesser role than expected for pnictide superconductivity and magnetism.",1306.4222v2
2013-06-18,Electronic Raman scattering from orbital nematic fluctuations,"We compute Raman scattering intensities via the lowest-order coupling to the
bosonic propagator associated with orbital nematic fluctuations in a minimal
model for iron pnictides. The model consists of two bands on a square lattice
exhibiting four Fermi pockets and a transition from the normal to a nematic
state. It is shown that the orbital fluctuations produce in the B1g channel
strong quasi-elastic light scattering around the nematic critical temperature
Tn, both above and below Tn. This holds for the A1g symmetry only below Tn
whereas no low-energy scattering from orbital fluctuations is found in the B2g
symmetry. Due to the nematic distortion the electron pocket at the X-point may
disappear at low temperatures. Such a Lifshitz transition causes in the B2g
spectrum a large upward shift of spectral weight in the high energy region
whereas no effect is seen in the other symmetries.",1306.4267v1
2013-06-18,Complex state induced by impurities in multiband superconductors,"We study the role of impurities in a two-band superconductor, and elucidate
the nature of the recently predicted transition from s_{+-} state to s_{++}
state induced by interband impurity scattering. Using a Ginzburg-Landau theory,
derived from microscopic equations, we demonstrate that close to T_c this
transition is necessarily a direct one, but deeper in the superconducting state
an intermediate complex state appears. This state has a distinct order
parameter, which breaks the time-reversal symmetry, and is separated from the
s_{+-} and s_{++} states by phase transitions. Based on our results, we suggest
a phase diagram for systems with weak repulsive interband pairing, and discuss
its relevance to iron-based superconductors.",1306.4268v2
2013-06-18,Interplay of the electronic and lattice degrees of freedom in A_{1-x}Fe_{2-y}Se_{2} superconductors under pressure,"The local structure and electronic properties of Rb$_{1-x}$Fe$_{2-y}$Se$_2$
are investigated by means of site selective polarized x-ray absorption
spectroscopy at the iron and selenium K-edges as a function of pressure. A
combination of dispersive geometry and novel nanodiamond anvil pressure-cell
has permitted to reveal a step-like decrease in the Fe-Se bond distance at
$p\simeq11$ GPa. The position of the Fe K-edge pre-peak, which is directly
related to the position of the chemical potential, remains nearly constant
until $\sim6$ GPa, followed by an increase until $p\simeq 11$ GPa. Here, as in
the local structure, a step-like decrease of the chemical potential is seen.
Thus, the present results provide compelling evidence that the origin of the
reemerging superconductivity in $A_{1-x}$Fe$_{2-y}$Se$_2$ in vicinity of a
quantum critical transition is caused mainly by the changes in the electronic
structure.",1306.4305v1
2013-06-18,Measurement of the elastoresistivity coefficients of the underdoped iron-arsenide Ba(Fe$_{0.975}$Co$_{0.025}$)$_2$As$_2$,"A new method is presented for measuring terms in the elastoresistivity tensor
$m_{ij}$ of single crystal samples with tetragonal symmetry. The technique is
applied to a representative underdoped Fe-arsenide,
Ba(Fe$_{0.975}$Co$_{0.025}$)$_2$As$_2$, revealing an anomalously large and
anisotropic elastoresistance in comparison to simple metals. The $m_{66}$
coefficient follows a Curie-Weiss temperature dependence, providing direct
evidence that the tetragonal-to-orthorhombic structural phase transition that
occurs at $T_s$ = 97.5 K in this material is not the result of a true-proper
ferro-elastic transition. Rather, the material suffers a pseudo-proper
transition for which the lattice strain is not the primary order parameter.",1306.4377v2
2013-06-20,Chiral properties of hematite (α-Fe2O3) inferred from resonant Bragg diffraction using circularly polarized x-rays,"Chiral properties of the two phases - collinear motif (below Morin transition
temperature, TM=250 K) and canted motif (above TM) - of magnetically ordered
hematite ({\alpha}-Fe2O3) have been identified in single crystal resonant x-ray
Bragg diffraction, using circular polarized incident x-rays tuned near the iron
K-edge. Magneto-electric multipoles, including an anapole, fully characterize
the high-temperature canted phase, whereas the low-temperature collinear phase
supports both parity-odd and parity-even multipoles that are time-odd. Orbital
angular momentum accompanies the collinear motif, while it is conspicuously
absent with the canted motif. Intensities have been successfully confronted
with analytic expressions derived from an atomic model fully compliant with
chemical and magnetic structures. Values of Fe atomic multipoles previously
derived from independent experimental data, are shown to be completely
trustworthy.",1306.4923v1
2013-06-24,Pseudogap Formation and Quantum Phase Transition in Strongly-Correlated Electron Systems,"Pseudogap formation is an ubiquitous phenomena in strongly-correlated
superconductors, for example cuprates, heavy-fermion superconductors, and iron
pnictides. As the system is cooled, an energy gap opens in the excitation
spectrum before entering the superconducting phase. The origin of formation and
the relevancy to the superconductivity remains unclear, which is the most
challenging problem in condensed matter physics. Here, using the cuprate as a
model, we demonstrate that the formation of pseudogap is due to a massive gauge
interaction between electrons, where the mass of the gauge boson, determining
the interaction length scale, is the consequence of the remnant
antiferromagnetic fluctuation inherited from the parent compounds. Extracting
from experimental data, we predict that there is a quantum phase transition
belonging to the 2D XY universality class at the critical doping where
pseudogap transition vanishes.",1306.5498v4
2013-06-25,Orbital-Selective Mottness in KxFe2-ySe2 Superconductors Revealed by Pump-Probe Spectroscopy,"We report transient optical signatures of the orbital-selective Mottness in
superconducting KxFe2-ySe2 crystals by using dual-color pump-probe
spectroscopy. Besides multi-exponential decay recovery dynamics of
photo-induced quasiparticles, a damped oscillatory component due to coherent
acoustic phonons emerges when the superconducting phase is suppressed by
increasing the temperature or excitation power. The oscillatory component
diminishes with significant enhancement of a slow decay component upon raising
temperature to 150-160 K. These results are in consistence with the picture of
orbital-selective Mott phase transition, indicating a vital role played by
electron correlation in the iron-based superconductors.",1306.5817v1
2013-06-25,Collision-Induced Dissociation Studies on Fe(O2)n+ (n=1-6) Clusters: Application of a New Technique Based on Crossed Molecular Beams,"Gas-phase oxygen-rich iron oxide clusters Fe(O2)n+ (n=1-6), are produced in a
molecular beam apparatus. Their stability and structure are investigated by
measuring the fragmentation cross sections from collision-induced-dissociation
experiments. For this purpose, two different techniques have been employed. The
first one relies on the measurement of the fragments resulting after
collisional activation and subsequent dissociation of mass selected cluster
ions in a molecular beam passing through a cell filled with noble gas atoms.
The second one is a new approach that we introduce and is based on crossed
molecular beams to measure the fragmentation cross sections, in a more
efficient manner without mass selection of the individual clusters. The cross
sections obtained with the different techniques are compared with each other as
well as with theoretical ones resulting from the application of a simple
geometrical projection model. Finally, the general trends observed are compared
with results for other Fe-molecule clusters available in the literature.",1306.5902v1
2013-06-25,The influence of oxygen and hydrogen adsorption on the magnetic structure of the ultrathin iron film on the Ir(001) surface,"We present a detailed ab initio study of the electronic structure and
magnetic order of an Fe monolayer on the Ir(001) surface covered by adsorbed
oxygen and hydrogen. The results are compared to the clean Fe/Ir(001) system,
where recent intensive studies indicated a strong tendency towards an
antiferromagnetic order and complex magnetic structures. The adsorption of an
oxygen overlayer significantly increases interlayer distance between the Fe
layer and the Ir substrate, while the effect of hydrogen is much weaker. We
show that the adsorption of oxygen (and also of hydrogen) leads to a p(2$\times
$1) antiferromagnetic order of the Fe moments, which is also supported by an
investigation based on a disordered local moment state. Simulated scanning
tunneling images using the simple Tersoff-Hamann model hint that the proposed
p(2$\times $1) antiferromagnetic order could be detected even by non-magnetic
tips.",1306.5925v1
2013-06-25,The Effect of Hydrogen Adsorption on the Magnetic Properties of a Surface Nanocluster of Iron,"The effect of hydrogen adsorption on the magnetic properties of an Fe$_3$
cluster immersed in a Cu(111) surface has been calculated using densifty
functional theory and the results used to parametrize an Alexander-Anderson
model which takes into account the interaction of d-electrons with itinerant
electrons. A number of adatom configurations containing one to seven H-atoms
were analyzed. The sequential addition of hydrogen atoms is found to
monotonically reduce the total magnetic moment of the cluster with the effect
being strongest when the H-atoms sit at low coordinated sites. Decomposition of
the charge density indicates a transfer of 0.4 electrons to each of the H-atoms
from both the Fe-atoms and from the copper substrate, irrespective of
adsorption site and coverage. The magnetic moment of only the nearest neighbor
Fe-atoms is reduced and mainly due to increased population of minority spin
d-states. This can be modeled by increased indirect coupling of d-states via
the conduction s-band in the Alexander-Anderson model.",1306.5999v1
2013-07-04,Prediction of phonon-mediated high temperature superconductivity in stoichiometric Li$_2$B$_3$C,"The discovery of superconductivity in Magnesium Diborate (MgB$_2$) has
stimulated great interest in the search of new superconductors with similar
lattice structures. Unlike cuprate or iron-based superconductors, MgB$_2$ is
indisputably a phonon-mediated high temperature superconductor. The emergence
of high temperature superconductivity in this material results from the strong
coupling between the boron $\sigma$-bonding electrons around the Fermi level
and the bond-stretching optical phonon modes. Here we show, based on the
first-principles calculations, that Li$_2$B$_3$C is such a good candidate of
superconductor whose superconducting transition temperature (T$_c$) might be
even higher than MgB$_2$. Li$_2$B$_3$C consists of alternating graphene-like
boron-carbon layers and boron-boron layers with intercalated lithium atoms
between them. Similar to MgB$_2$, Li$_2$B$_3$C is inherently metallic and
possesses two $\sigma$- and two $\pi$-electron bands around the Fermi energy.
The superconducting pairs are glued predominately by the strong interaction
between boron $\sigma$-bonding electrons and various optical phonon modes.",1307.1323v1
2013-07-04,"""Anti-glitches"" in the Quark-Nova model for AXPs","In the Quark-Nova model, AXPs are quark stars surrounded by a degenerate
iron-rich Keplerian ring (a few stellar radii away). AXP bursts are caused by
accretion of chunks from the inner edge of the ring following magnetic field
penetration. For bright bursts, the inner disk is prone to radiation induced
warping which can tilt it into counter-rotation (i.e. retrograde). For AXP
1E2259+586, the 2002 burst satisfies the condition for the formation of a
retrograde inner ring. We hypothesize the 2002 burst reversed the inner ring
setting the scene for the 2012 outburst and ""anti-glitch"" when the retrograde
inner ring was suddenly accreted leading to the basic observed properties of
the 2012 event.",1307.1386v2
2013-07-07,Andreev Reflection Like Enhancement Above Bulk $T_c$ in Electron Underdoped Iron Arsenides,"We use point contact spectroscopy (PCS) to probe the superconducting
properties of electron doped $\rm{Ba(Fe_{1-x}Co_x)_2As_2}$ ($\rm{x = 0.05,
0.055, 0.07, 0.08}$) and hole doped $\rm{Ba_{0.8}K_{0.2}Fe_2As_2}$. PCS
directly probes the low energy density of states via Andreev reflection,
revealing two distinct superconducting gaps in both compound families. Apart
from the electron underdoped $\rm{Ba(Fe_{1-x}Co_{x})_2As_2}$, the excess
current due to Andreev reflection for the compounds follows the typical BCS
temperature dependence. For underdoped $\rm{Ba(Fe_{1-x}Co_{x})_2As_2}$, the
temperature dependence of the excess current deviates from that of BCS,
developing a tail at higher temperatures and surviving above bulk $T_c$.
Possible explanations for this anomalous behavior are explored.",1307.1908v1
2013-07-10,Kondo-like mass enhancement of Dirac fermion in iron pnictides Ba(Fe$_{1-x}$Mn$_x$As)$_2$,"The effect of Mn substitution, acting as a magnetic impurity for Fe, on the
Dirac cone was investigated in Ba(Fe$_{1-x}$Mn$_x$As)$_2$. Both
magnetoresistance and Hall resistivity studies clearly indicate that the
cyclotron effective mass ($m^{\ast}$) of the Dirac cone is anomalously enhanced
at low temperatures by the impurity, although its evolution as a function of
carrier number proceeds in a conventional manner at higher temperatures.
Kondo-like band renormalization induced by the magnetic impurity scattering is
suggested as an explanation for this, and the anomalous mass enhancement of the
Dirac fermions is discussed.",1307.2813v3
2013-07-11,Progressive slowing down of spin fluctuations in underdoped LaFeAsO$_{1-x}$F$_x$,"The evolution of low-energy spin dynamics in the iron-based superconductor
LaFeAsO$_{1-x}$F$_x$ was studied over a broad doping, temperature, and magnetic
field range (x = 0 - 0.15, T up to 480K, H up to 30T) by means of As nuclear
magnetic resonance (NMR). An enhanced spin-lattice relaxation rate divided by
temperature, 1/T1T, in underdoped superconducting samples (x = 0.045, 0.05 and
0.075) suggests the presence of antiferromagnetic spin fluctuations, which are
strongly reduced in optimally-doped (x = 0.10) and completely absent in
overdoped (x = 0.15) samples. In contrast to previous analysis, Curie-Weiss
fits are shown to be insufficient to describe the data over the whole
temperature range. Instead, a BPP-type model is used to describe the occurrence
of a peak in 1/T1T clearly above the superconducting transition, reflecting a
progressive slowing down of the spin fluctuations down to the superconducting
phase transition.",1307.3138v1
2013-07-12,$B_{1g}$-like pairing states in two-leg ladder iron superconductors,"Motivated by the recent report of superconductivity in Fe-based ladder
materials, we study the pairing state of a multi-orbital t-J model defined on
two-leg ladders using the standard mean-field theory. We find that the
superconducting order parameters change sign between the $d_{xz}$ and $d_{yz}$
orbitals in most of the phase diagram. By analogy with the two-dimensional Fe
planes, we conclude that the leading pairing channel of this state belongs to
the $B_{1g}$ symmetry class, which is distinct from the common $s_{\pm}$ gap
with the $A_{1g}$ symmetry. By smoothly interpolating from planes into ladders,
we show that a first-order transition occurs between these two competing phases
when the dimension of the system is reduced.",1307.3309v2
2013-07-12,Electron-capture supernovae as sources of 60Fe,"We investigate the nucleosynthesis of the radionuclide 60Fe in
electron-capture supernovae (ECSNe). The nucleosynthetic results are based on a
self-consistent, two-dimensional simulation of an ECSN as well as models in
which the densities are systematically increased by some factors (low-entropy
models). 60Fe is found to be appreciably made in neutron-rich ejecta during the
nuclear quasi-equilibrium phase with greater amounts being produced in the
lower-entropy models. Our results, combining them with the yields of
core-collapse supernovae (CCSNe) in the literature, suggest that ECSNe account
for at least 4-30% of live 60Fe in the Milky Way. ECSNe co-produce neutron-rich
isotopes, 48Ca, 50Ti, 54Cr, some light trans-iron elements, and possibly weak
r-process elements including some radionuclides such as 93Zr, 99Tc, and 107Pd,
whose association with 60Fe might have been imprinted in primitive meteorites
or in the deep ocean crust on the Earth.",1307.3319v2
2013-07-12,Electronic effects in high-energy radiation damage in iron,"Electronic effects are believed to be important in high--energy radiation
damage processes where high electronic temperature is expected, yet their
effects are not currently understood. Here, we perform molecular dynamics
simulations of high-energy collision cascades in $\alpha$-iron using the
coupled two-temperature molecular dynamics (2T-MD) model that incorporates both
effects of electronic stopping and electron-ion interaction. We subsequently
compare it with the model employing the electronic stopping only, and find
several interesting novel insights. The 2T-MD results in both decreased damage
production in the thermal spike and faster relaxation of the damage at short
times. Notably, the 2T-MD model gives a similar amount of the final damage at
longer times, which we interpret to be the result of two competing effects:
smaller amount of short-time damage and shorter time available for damage
recovery.",1307.3385v2
2013-07-12,Artificially engineered superlattices of pnictide superconductor,"Significant progress has been achieved in fabricating high quality bulk and
thinfilm iron-based superconductors. In particular, artificial layered pnictide
superlattices offer the possibility of tailoring the superconducting properties
and understanding the mechanism of the superconductivity itself. For high field
applications, large critical current densities (Jc) and irreversibility fields
(Hirr) are indispensable along all crystal directions. On the other hand, the
development of superconducting devices such as tunnel junctions requires
multilayered heterostructures. Here we show that artificially engineered
undoped Ba-122 / Co doped Ba-122 compositionally modulated superlattices
produce ab-aligned nanoparticle arrays. These layer and self-assemble along
c-axis aligned defects, and combine to produce very large Jc and Hirr
enhancements over a wide angular range. We also demonstrate a structurally
modulated SrTiO3 (STO) / Co doped Ba-122 superlattice with sharp interfaces.
Success in superlattice fabrication involving pnictides will aid the progress
of heterostructured systems exhibiting novel interfacial phenomena and device
applications.",1307.3576v1
2013-07-17,Growth modes of nanoparticle superlattice thin films,"We report about the fabrication and characterization of iron oxide
nanoparticle thin film superlattices. The formation into different film
morphologies is controlled by tuning the particle plus solvent-to-substrate
interaction. It turns out that the wetting vs. dewetting properties of the
solvent before the self-assembly process during solvent evaporation plays a
major role to determine the resulting film morphology. In addition to layerwise
growth also three-dimensional mesocrystalline growth is evidenced. The
understanding of the mechanisms ruling nanoparticle self-assembly represents an
important step toward the fabrication of novel materials with tailored optical,
magnetic or electrical transport properties.",1307.4693v4
2013-07-19,Microstructure and Structural Phase Transitions in Iron-Based Superconductors,"Crystal structures and microstructural features, such as structural phase
transitions, defect structures, chemical and structural inhomogeneities, are
known to have profound effects on the physical properties of superconducting
materials. Recently, a large amount of works on the structural properties of
Fe-based high-Tc superconductors have been published. This review article will
mainly focus on typical microstructural features in samples that have been well
characterized by physical measurements. (a) Certain common structural features
are discussed. In particular, crystal structural features for different
superconducting families, local structural distortions in the Fe2Pn2 (Pn=P, As,
Sb) or Fe2Ch2 (Ch=S, Se, Te) blocks, and structural transformations in the 122
system. (b) In FeTe(Se) (11-family), the superconductivity, chemical and
structural inhomogeneities are investigated and discussed in correlation with
superconductivity. (c) In K0.8Fe1.6+xSe2 system, we focus on typical compounds
with emphasis on Fe-vacancy order and phase separations. The microstructural
features in other superconducting materials are also briefly discussed.",1307.5112v1
2013-07-24,Role of Dirac cones in magnetotransport properties of REFeAsO (RE=rare earth) oxypnictides,"In this work we study the effect of the rare earth element in iron
oxypnictides of composition REFeAsO (RE=rare earth). On one hand we carry out
Density Functional Theory calculations of the band structure, which evidence
the multiband character of these compounds and the presence of Dirac cones
along the Y-{\Gamma} and Z-R directions of the reciprocal space. On the other
hand, we explore transport behavior by means of resistivity, Hall resistance
and magnetoresistance measurements, which confirm the dominant role of Dirac
cones. By combining our theoretical and experimental approaches, we extract
information on effective masses, scattering rates and Fermi velocities for
different rare earth elements.",1307.6352v1
2013-07-26,N-Body Simulation of the Formation of the Earth-Moon System from a Single Giant Impact,"The giant impact hypothesis is the dominant theory of how the Earth-Moon
system was formed. Models have been created that can produce a disk of debris
with the proper mass and composition to create our Moon. Models have also been
created which start with a disk of debris that eventually coalesces into a
Moon. To date, no model has been created that produces a stable Earth-Moon
system in a single simulation. Here we combine two recently published ideas in
this field, along with a new gravity-centered model, and generate such a
simulation. In addition, we show how the method can produce a heterogeneous,
iron-deficient Moon made of mantle material from both colliding bodies, and a
resultant Earth whose equatorial plane is significantly tilted off the ecliptic
plane. The accuracy of the simulation adds credence to the theory that our Moon
was born from the violent union of two heavenly bodies.",1307.7062v1
2013-07-26,Ferro-orbital ordering transition in iron telluride Fe$_{1+y}$Te,"Fe$_{1+y}$Te with $y \lesssim 0.05$ exhibits a first-order phase transition
on cooling to a state with a lowered structural symmetry, bicollinear
antiferromagnetic order, and metallic conductivity, $d\rho/dT > 0$. Here, we
study samples with $y = 0.09(1)$, where the frustration effects of the
interstitial Fe decouple different orders, leading to a sequence of
transitions. While the lattice distortion is closely followed by
\emph{incommensurate} magnetic order, the development of \emph{bicollinear}
order and metallic electronic coherence is uniquely associated with a separate
hysteretic first-order transition, at a markedly lower temperature, to a phase
with dramatically enhanced bond-order wave (BOW) order. The BOW state suggests
ferro-orbital ordering, where electronic delocalization in ferromagnetic zigzag
chains decreases local spin and results in metallic transport.",1307.7162v2
2013-07-26,Linear magnetoconductivity in multiband spin-density-wave metals with nonideal nesting,"In several parent iron-pnictide compounds the resistivity has an extended
range of linear magnetic field dependence. We argue that there is a simple and
natural explanation of this behavior. Spin density wave transition leads to
Fermi-surface reconstruction corresponding to strong modification of the
electronic spectrum near the nesting points. It is difficult for quasiparticles
to pass through these points during their orbital motion in magnetic field,
because they must turn sharply. As the area of the Fermi surface affected by
the nesting points increases proportionally to magnetic field, this mechanism
leads to the linear magnetoresistance. The crossover between the quadratic and
linear regimes takes place at the field scale set by the SDW gap and scattering
rate.",1307.7184v3
2013-07-29,Simple concentration-dependent pair interaction model for large-scale simulations of Fe-Cr alloys,"This work is motivated by the need for large-scale simulations to extract
physical information on the iron-chromium system that is a binary model alloy
for ferritic steels used or proposed in many nuclear applications. From
first-principles calculations and the experimental critical temperature we
build a new energetic rigid lattice model based on pair interactions with
concentration and temperature dependence. Density functional theory
calculations in both norm-conserving and projector augmented-wave approaches
have been performed. A thorough comparison of these two different ab initio
techniques leads to a robust parametrization of the Fe-Cr Hamiltonian.
Mean-field approximations and Monte Carlo calculations are then used to account
for temperature effects. The predictions of the model are in agreement with the
most recent phase diagram at all temperatures and compositions. The solubility
of Cr in Fe below 700 K remains in the range of about 6 to 12%. It reproduces
the transition between the ordering and demixing tendency and the spinodal
decomposition limits are also in agreement with the values given in the
literature.",1307.7561v1
2013-08-02,"Effect of heavy-ion irradiation on London penetration depth in over-doped Ba(Fe,Co)2As2","Irradiation with 1.4 GeV $^{208}$Pb ions was used to induce artificial
disorder in single crystals of iron-arsenide superconductor
Ba(Fe$_{1-x}$Co$_x$)$_2$As$_2$ and to study its effect on the
temperature-dependent London penetration depth and transport properties. Study
was undertaken on overdoped single crystals with $x$=0.108 and $x$=0.127
characterized by notable modulation of the superconducting gap. Irradiation
with doses 2.22$\times10^{11}$$\textit{d}$/cm$^2$ and
2.4$\times10^{11}$$\textit{d}$/cm$^2$, corresponding to the matching fields of
$B_{\phi} = $6 T and 6.5 T, respectively, suppresses the superconducting $T_c$
by approximately 0.3 to 1 K. The variation of the low-temperature penetration
depth in both pristine and irradiated samples is well described by the
power-law, $\Delta \lambda (T)=AT^n$. Irradiation increases the magnitude of
the pre-factor $A$ and decreases the exponent $n$, similar to the effect of
irradiation in optimally doped samples. This finding supports universal
$s_{\pm}$ pairing in Ba(Fe$_{1-x}$Co$_x$)$_2$As$_2$ compounds for the whole Co
doping range.",1308.0537v1
2013-08-10,Impurity effects on electronic transport in ferropnictide superconductors,"Effects of impurities and disorder on transport properties by electronic
quasiparticles in superconducting iron pnictides are theoretically considered.
The most prominent new features compared to the case of pure material should
appear at high enough impurity concentration when a specific narrow band of
conducting quasiparticle states can develop within the superconducting gap,
around the position of localized impurity level by a single impurity center.
The predicted specific threshold effects in the frequency dependent optical
conductivity and temperature dependent thermal conductivity and also in Seebeck
and Peltier coefficients can have interesting potentialities for practical
applications.",1308.2351v3
2013-08-13,Strain effects on the electronic structure of the FeSe0.5Te0.5 superconductor,"The electronic structure of the strained FeSe0.5Te0.5 superconductor has been
investigated from first principles. Our calculation results indicate that the
influence of hydrostatic, biaxial or uniaxial compressive stress on the density
of states at the Fermi level is insignificant. The overall shape of the
Fermi-surface (FS) nesting function for FeSe0.5Te0.5 at ambient pressure
resembles that of its parent compound, FeSe, but under the ab-plane compressive
strain. In these two systems, changes of their FSs under various stress
conditions are qualitatively almost the same. However, in FeSe0.5Te0.5 the
intensity of the perfect Q=(0.5,0.5)*(2\pi/a) nesting vector is more
diminished. These findings are in good agreement with former experimental data
and support the idea of spin-fluctuation mediated superconductivity in iron
chalcogenides.",1308.2949v1
2013-08-15,Magnetic Phase Diagram of a Five-Orbital Hubbard Model in the Real-Space Hartree Fock Approximation Varying the Electronic Density,"Using the real-space Hartree Fock approximation, the magnetic phase diagram
of a five-orbital Hubbard model for the iron-based superconductors is studied
varying the electronic density $n$ in the range from 5 to 7 electrons per
transition metal atom. The Hubbard interaction $U$ is also varied, at a fixed
Hund coupling $J/U=0.25$. Several qualitative trends and a variety of competing
magnetic states are observed. At $n$=5, a robust G-type antiferromagnetic
insulator is found, in agreement with experimental results for BaMn$_2$As$_2$.
As $n$ increases away from 5, magnetic states with an increasing number of
nearest-neighbors ferromagnetic links become energetically stable. This
includes the well-known C-type antiferromagnetic state at $n$=6, the E-phase
known to exist in FeTe, and also a variety of novel states not found yet
experimentally, some of them involving blocks of ferromagnetically oriented
spins. Regions of phase separation, as in Mn-oxides, have also been detected.
Comparison with previous theoretical investigations indicate that these
qualitative trends may be generic characteristics of phase diagrams of
multiorbital Hubbard models.",1308.3426v1
2013-08-16,Quantum Criticality in Electron-doped BaFe_{2-x}Ni_xAs_2,"A quantum critical point (QCP) is a point in a system's phase diagram at
which an order is completely suppressed at absolute zero temperature (T). The
presence of a quantum critical point manifests itself in the finite-T physical
properties, and often gives rise to new states of matter. Superconductivity in
the cuprates and in heavy fermion materials is believed by many to be mediated
by fluctuations associated with a quantum critical point. In the
recently-discovered iron-pnictide high temperature superconductors, it is
unknown whether a QCP exists or not in a carrier-doped system. Here we report
transport and nuclear magnetic resonance (NMR) measurements on
BaFe_{2-x}Ni_xAs_2 (0 =< x =< 0.17). We find two critical points at x_{c1} =
0.10 and x_{c2} = 0.14. The electrical resistivity follows \rho = \rho_0 +
A*T^n, with n = 1 around x_{c1} and another minimal n = 1.1 at x_{c2}. By NMR
measurements, we identity x_{c1} to be a magnetic QCP and suggest that x_{c2}
is a new type of QCP associated with a nematic structural phase transition. Our
results suggest that the superconductivity in carrier-doped pnictides is
closely linked to the quantum criticality.",1308.3539v1
2013-08-18,Spin excitation anisotropy as a probe of orbital ordering in the paramagnetic tetragonal phase of superconducting BaFe1.904Ni0.096As2,"We use polarized neutron scattering to demonstrate that in-plane spin
excitations in electron doped superconducting BaFe1.904Ni0.096As2 (Tc=19.8 K)
change from isotropic to anisotropic in the tetragonal phase well above the
antiferromagnetic (AF) ordering and tetragonal-to-orthorhombic lattice
distortion temperatures (Tn=Ts=33 K) without an uniaxial pressure. While the
anisotropic spin excitations are not sensitive to the AF order and
tetragonal-to-orthorhombic lattice distortion, superconductivity induces
further anisotropy for spin excitations along the [1,1,0] and [1,-1,0]
directions. These results indicate that the spin excitation anisotropy is a
probe of the electronic anisotropy or orbital ordering in the tetragonal phase
of iron pnictides.",1308.3858v1
2013-08-19,"The Origin of HVS17, an Unbound Main Sequence B Star at 50 kpc","We analyze Keck ESI spectroscopy of HVS17, a B-type star traveling with a
Galactic rest frame radial velocity of +445 km/s in the outer halo of the Milky
Way. HVS17 has the projected rotation of a main sequence B star and is
chemically peculiar, with solar iron abundance and sub-solar alpha abundance.
Comparing measured T_eff and logg with stellar evolution tracks implies that
HVS17 is a 3.91 +-0.09 Msun, 153 +-9 Myr old star at a Galactocentric distance
of r=48.5 +-4.6 kpc. The time between its formation and ejection significantly
exceeds 10 Myr and thus is difficult to reconcile with any Galactic disk
runaway scenario involving massive stars. The observations are consistent, on
the other hand, with a hypervelocity star ejection from the Galactic center. We
show that Gaia proper motion measurements will easily discriminate between a
disk and Galactic center origin, thus allowing us to use HVS17 as a test
particle to probe the shape of the Milky Way's dark matter halo.",1308.4181v1
2013-08-20,Spatial Inhomogeneity of the Superconducting Gap and Order Parameter in FeSe_{0.4}Te_{0.6},"We have performed a low temperature scanning tunneling microscopy and
spectroscopy study of the iron chalcogenide superconductor FeSe_{0.4}Te_{0.6}
with T_{C}~14 K. Spatially resolved measurements of the superconducting gap
reveal substantial inhomogeneity on a nanometer length scale. Analysis of the
structure of the gap seen in tunneling spectra by comparison with calculated
spectra for different superconducting order parameters (s-wave, d-wave, and
anisotropic s-wave) yields the best agreement for an order parameter with
anisotropic s-wave symmetry with an anisotropy of ~40%. The temperature
dependence of the superconducting gap observed in places with large and small
gap size indicates that it is indeed the superconducting transition temperature
which is inhomogeneous. The temperature dependence of the gap size is
substantially larger than would be expected from BCS theory. An analysis of the
local gap size in relation with the local chemical composition shows almost no
correlation with the local concentration of Se-/Te-atoms at the surface.",1308.4339v1
2013-08-22,A Precision Measurement of Charm Dimuon Production in Neutrino Interactions from the NOMAD Experiment,"We present our new measurement of the cross-section for charm dimuon
production in neutrino-iron interactions based upon the full statistics
collected by the NOMAD experiment. After background subtraction we observe
15,344 charm dimuon events, providing the largest sample currently available.
The analysis exploits the large inclusive charged current sample - about
$9\times 10^6$ events after all analysis cuts - and the high resolution NOMAD
detector to constrain the total systematic uncertainty on the ratio of charm
dimuon to inclusive Charged Current (CC) cross-sections to $\sim 2%$. We also
perform a fit to the NOMAD data to extract the charm production parameters and
the strange quark sea content of the nucleon within the NLO QCD approximation.
We obtain a value of $m_c(m_c)=1.159\pm0.075$ GeV/c$^2$ for the running mass of
the charm quark in the $\bar{\rm MS}$ scheme and a strange quark sea
suppression factor of $\kappa_s = 0.591 \pm 0.019$ at $Q^2=20$ GeV$^2$/c$^2$.",1308.4750v1
2013-08-27,Origin of Dust around V1309 Sco,"The origin of dust grains in the interstellar medium is still open problem.
\cite{Nicholls2013} found the presence of a significant amount of dust around
V1309 Sco which maybe originate from the merger of a contact binary. We
investigate the origin of dust around V1309 Sco, and suggest that these dust
grains are efficiently produced in the binary-merger ejecta. By means of
\emph{AGBDUST} code, we estimate that $\sim 5.2\times10^{-4} M_\odot$ of dust
grains are produced, and their radii are $\sim 10^{-5}$ cm. These dust grains
mainly are composed of silicate and iron grains. Because the mass of the
binary-merger ejecta is very small, the contribution of dust produced by
binary-merger ejecta to the overall dust production in the interstellar medium
is negligible. However, it is the most important that the discovery of a
significant amount of dust around V1309 Sco offers a direct support for the
idea---common-envelope ejecta provides an ideal environment for dust formation
and growth. Therefore, we confirm that common-envelope ejecta can be important
source of cosmic dust.",1308.5735v1
2013-08-27,Calculating Time Lags From Unevenly-Sampled Light Curves,"Timing techniques offer powerful tools to study dynamical astrophysical
phenomena. In the X-ray band, they offer the potential of probing accretion
physics down to the event horizon. Recent work has used frequency and
energy-dependent time lags as a tool for studying relativistic reverberation
around the black holes in several Seyfert galaxies. This was achieved thanks to
the evenly-sampled light curves obtained using XMM-Newton. Continuous-sampled
data is however not always available and standard Fourier techniques are not
applicable. Here, building on the work of Miller et al. (2010), we discuss and
use a maximum likelihood method to obtain frequency-dependent lags that takes
into account light curve gaps. Instead of calculating the lag directly, the
method estimates the most likely lag values at a particular frequency given two
observed light curves. We use Monte Carlo simulations to assess the method's
applicability, and use it to obtain lag-energy spectra from Suzaku data for two
objects, NGC 4151 and MCG-5-23-16, that had previously shown signatures of iron
K reverberation. The lags obtained are consistent with those calculated using
standard methods using XMM-Newton data.",1308.5852v1
2013-08-28,Tunneling spectroscopy for probing orbital anisotropy in iron pnictides,"Using realistic multi-orbital tight-binding Hamiltonians and the T-matrix
formalism, we explore the effects of a non-magnetic impurity on the local
density of states in Fe-based compounds. We show that scanning tunneling
spectroscopy (STS) has very specific anisotropic signatures that track the
evolution of orbital splitting (OS) and antiferromagnetic gaps. Both
anisotropies exhibit two patterns that split in energy with decreasing
temperature, but for OS these two patterns map onto each other under 90 degree
rotation. STS experiments that observe these signatures should expose the
underlying magnetic and orbital order as a function of temperature across
various phase transitions.",1308.6248v2
2013-08-30,Why is the superconducting Tc so high in rare-earth-doped CaFe2As2?,"In rare-earth doped single crystalline CaFe2As2, the mysterious small volume
fraction which superconducts up to 49 K, much higher than the bulk Tc ~ 30s K,
has prompted a long search for a hidden variable that could enhance the Tc by
more than 30% in iron-based superconductors of the same structure. Here we
report a chemical, structural, and magnetic study of CaFe2As2 systematically
doped with La, Ce, Pr, and Nd. Coincident with the high Tc phase, we find
extreme magnetic anisotropy, accompanied by an unexpected doping-independent Tc
and equally unexpected superparamagnetic clusters associated with As vacancies.
These observations lead us to conjecture that the tantalizing Tc enhancement
may be associated with naturally occurring chemical interfaces and may thus
provide a new paradigm in the search for superconductors with higher Tc.",1309.0034v2
2013-09-08,Evidence of unconventional low-frequency dynamics in the normal phase of Ba(Fe1-xRhx)2As2 iron-based supercondutors,"This work presents 75As NMR spin echo decay rate (1/T2) measurements in
Ba(Fe1-xRhx)2As2 superconductors, for 0.041 < x < 0.094. It is shown that 1/T2
increases upon cooling, in the normal phase, suggesting the onset of an
unconventional very low-frequency activated dynamic. The correlation times of
the fluctuations and their energy barriers are derived. The motion is favored
at large Rh content, while it is hindered by the application of a magnetic
field perpendicular to the FeAs layers. The same dynamic is observed in the
spin-lattice relaxation rate, in a quantitatively consistent manner. These
results are discussed in the light of nematic fluctuations involving domain
wall motion. The analogies with the behaviour observed in the cuprates are also
outlined.",1309.1936v1
2013-09-11,"Concepts relating magnetic interactions, intertwined electronic orders and strongly correlated superconductivity","Unconventional superconductivity (SC) is said to occur when Cooper pair
formation is dominated by repulsive electron-electron interactions, so that the
symmetry of the pair wavefunction is other than isotropic s-wave. The strong,
on-site, repulsive electron-electron interactions that are the proximate cause
of such superconductivity are more typically drivers of commensurate magnetism.
Indeed, it is the suppression of commensurate antiferromagnetism (AF) that
usually allows this type of unconventional superconductivity to emerge.
Importantly, however, intervening between these AF and SC phases, intertwined
electronic ordered phases of an unexpected nature are frequently discovered.
For this reason, it has been extremely difficult to distinguish the microscopic
essence of the correlated superconductivity from the often spectacular
phenomenology of the intertwined phases. Here we introduce a model conceptual
framework within which to understand the relationship between antiferromagnetic
electron-electron interactions, intertwined ordered phases and correlated
superconductivity. We demonstrate its effectiveness in simultaneously
explaining the consequences of antiferromagnetic interactions for the
copper-based, iron-based and heavy-fermion superconductors, as well as for
their quite distinct intertwined phases.",1309.2719v1
2013-09-12,Low-energy interband transitions in the infrared response of Ba(Fe1-xCox)2As2,"We studied the doping and temperature (T) dependence of the infrared (IR)
response of Ba(Fe1-xCox)2As2 single crystals. We show that a weak band around
1000 cm-1, that was previously interpreted in terms of interaction of the
charge carriers with magnetic excitations or of a pseudogap, is rather related
to low-energy interband transitions. Specifically, we show that this band
exhibits a similar doping and T-dependence as the hole pockets seen by angle
resolved photoemission spectroscopy (ARPES). Notably, we find that it vanishes
as a function of doping near the critical point where superconductivity is
suppressed in the overdoped regime. Our IR data thus provide bulk specific
information (complementary to the surface sensitive ARPES) for a Lifshitz
transition. Our IR data also reveal a second low-energy band around 2300 cm-1
which further emphasizes the necessity to consider the multiband nature of
these iron arsenides in the analysis of the optical response.",1309.3198v1
2013-09-13,The lateral shower age parameter as an estimator of chemical composition,"We explore the feasibility of estimating primary cosmic ray composition at
ultra high energies from the study of lateral age parameter of Extensive Air
Showers (EAS) at ground level. Using different types of lateral distribution
functions, we fit the particle density of simulated EAS to find the lateral age
parameter. We discuss the chemical composition calculating the merit factor for
each parameter distribution. The analysis considers three different primary
particles (proton, iron and gamma), four different zenith angles (0{\deg},
15{\deg}, 30{\deg} and 45{\deg}) and three primary energies (10^{17.25} eV,
10^{17.50} eV and 10^{17.75} eV).",1309.3536v1
2013-09-17,Strongly Correlated Materials,"Strongly correlated materials are profoundly affected by the repulsive
electron-electron interaction. This stands in contrast to many commonly used
materials such as silicon and aluminum, whose properties are comparatively
unaffected by the Coulomb repulsion. Correlated materials often have remarkable
properties and transitions between distinct, competing phases with dramatically
different electronic and magnetic orders. These rich phenomena are fascinating
from the basic science perspective and offer possibilities for technological
applications. This article looks at these materials through the lens of
research performed at Rice University. Topics examined include: Quantum phase
transitions and quantum criticality in ""heavy fermion"" materials and the iron
pnictide high temperature superconductors; computational ab initio methods to
examine strongly correlated materials and their interface with analytical
theory techniques; layered dichalcogenides as example correlated materials with
rich phases (charge density waves, superconductivity, hard ferromagnetism) that
may be tuned by composition, pressure, and magnetic field; and nanostructure
methods applied to the correlated oxides VO2 and Fe3O4, where metal-insulator
transitions can be manipulated by doping at the nanoscale or driving the system
out of equilibrium. We conclude with a discussion of the exciting prospects for
this class of materials.",1309.4473v1
2013-09-23,Interactions of Cosmic Rays in the Atmosphere: Growth Curves Revisited,"Measurements of cosmic-ray abundances on balloons are affected by
interactions in the residual atmosphere above the balloon. Corrections for such
interactions are particularly important for observations of rare secondary
particles such as boron, antiprotons and positrons. These corrections can
either be calculated if the relevant cross sections in the atmosphere are
known, or may be empirically determined by extrapolation of the ""growth
curves"", i. e. the individual particle intensities as functions of atmospheric
depth. The growth-curve technique is particularly attractive for long-duration
balloon flights where the periodic daily altitude variations permit rather
precise determinations of the corresponding particle intensity variations. We
determine growth curves for nuclei from boron (Z=5) to iron (Z=26), using data
from the 2006 Arctic balloon flight of the TRACER detector for cosmic-ray
nuclei, and we compare the growth curves with predictions from published cross
section values. In general, good agreement is observed. We then study the
boron/carbon abundance ratio and derive a simple and energy-independent
correction term for this ratio. We emphasize that the growth-curve technique
can be developed further to provide highly accurate tests of published
interaction cross section values.",1309.5739v1
2013-09-26,The polluted atmosphere of the white dwarf NLTT 25792 and the diversity of circumstellar environments,"We present an analysis of X-Shooter spectra of the polluted, hydrogen-rich
white dwarf NLTT 25792. The spectra show strong lines of calcium (Ca H&K,
near-infrared calcium triplet, and Ca I 4226 and numerous lines of iron along
with magnesium and aluminum lines from which we draw the abundance pattern.
Moreover, the photospheric Ca H&K lines are possibly blended with a
circumstellar component shifted by -20 km/s relative to the photosphere. A
comparison with a sample of four white dwarfs with similar parameters show
considerable variations in their abundance patterns, particularly in the
calcium to magnesium abundance ratio that varies by a factor of five within
this sample. The observed variations, even after accounting for diffusion
effects, imply similar variations in the putative accretion source. Also, we
find that silicon and sodium are significantly underabundant in the atmosphere
of NLTT 25792, a fact that may offer some clues on the nature of the accretion
source.",1309.6804v1
2013-09-27,Unusual pressure effects on the superconductivity of indirectly electron-doped (Ba1-xLax)Fe2As2 epitaxial films,"Applying an external pressure to indirectly electron-doped 122-type
(Ba1-xLax)Fe2As2 epitaxial films enhances the superconducting critical
temperature (Tc) up to 30.3 K. Different from the other family compounds, the
Tc is enhanced not only in the under-doped region but also in the optimally
doped and over-doped regions. Narrowing of the superconducting transition width
and an increase in the carrier density take place simultaneously in the whole
doping region, except at the heavily over-doped limit. This characteristic is
unique to and observed only in (Ba1-xLax)Fe2As2, in which the La doping is
stabilized via non-equilibrium growth of the vapor phase epitaxy, among the
122-type iron-based superconductors, AFe2As2 (A = Ba, Sr, and Ca).",1309.7100v2
2013-09-27,Beating the superparamagnetic size limit of nanoparticles on a ferroelectric substrate,"When decreasing the size of nanoscale magnetic particles their magnetization
becomes vulnerable to thermal fluctuations as approaching the superparamgnetic
limit, hindering thus applications relying on a stable magnetization. Here, we
show theoretically that a magnetoelectric coupling to a ferroelectric substrate
renders possible the realization of substantially smaller nano clusters with
thermally stable magnetization. For an estimate of cluster size we perform
calculations with realistic material parameters for iron nano particles on
ferroelectric BaTiO3 substrate. We find, steering the polarization of BaTiO3
with electric fields affects the magnetism of the deposited magnetic clusters.
These findings point to a qualitatively new class of superparamagnetic
composites.",1309.7136v1
2013-09-27,Inelastic neutron scattering study of crystal field excitations of Nd3+ in NdFeAsO,"Inelastic neutron scattering experiments were performed to investigate the
crystalline electric field (CEF) excitations of Nd3+ (J = 9/2) in the iron
pnictide NdFeAsO. The crystal field level structures for both the
high-temperature paramagnetic phase and the low-temperature antiferromagnetic
phase of NdFeAsO are constructed. The variation of CEF excitations of Nd3+
reflects not only the change of local symmetry but also the change of magnetic
ordered state of the Fe sublattice. By analyzing the crystal field interaction
with a crystal field Hamiltonian, the crystal field parameters are obtained. It
was found that the sign of the fourth and sixth-order crystal field parameters
change upon the magnetic phase transition at 140 K, which may be due to the
variation of exchange interactions between the 4f and conduction electrons.",1309.7323v1
2013-09-29,Coupled magnetic and ferroelectric excitations in PbFe_{1/2}Nb_{1/2}O_{3},"A neutron scattering investigation of the magnetoelectric coupling in
PbFe_{1/2}Nb_{1/2}O_{3} (PFN) has been undertaken. Ferroelectric order occurs
below 400 K, as evidenced by the softening with temperature and subsequent
recovery of the zone center transverse optic phonon mode energy (\hbar
\Omega_{0}). Over the same temperature range, magnetic correlations become
resolution limited on a terahertz energy scale. In contrast to the behavior of
nonmagnetic disordered ferroelectrics (namely Pb(Mg,Zn)_{1/3}Nb_{2/3}O_{3}), we
report the observation of a strong deviation from linearity in the temperature
dependence of (\hbar \Omega_{0})^{2}. This deviation is compensated by a
corresponding change in the energy scale of the magnetic excitations, as probed
through the first moment of the inelastic response. The coupling between the
short-range ferroelectric and antiferromagnetic correlations is consistent with
calculations showing that the ferroelectricity is driven by the displacement of
the body centered iron site, illustrating the multiferroic nature of magnetic
lead based relaxors in the dynamical regime.",1309.7587v1
2013-09-29,Strongly enhanced current densities in Sr0.6K0.4Fe2As2 superconducting tapes,"Improving transport current has been the primary issue for practical
application of superconducting wires and tapes. However, the porous nature of
powder-in-tube (PIT) processed iron-based superconducting tapes is thought to
be one of the important reasons for the low Jc values. In this work, the
superconducting core density of ex-situ Sr0.6K0.4Fe2As2 tapes was significantly
improved by employing a simple hot pressing as an alternative route for final
sintering. At 4.2 K, the transport Jc values showed excellent values of
5.1x10^4 A/cm^2 at 10 T and 4.3x10^4 A/cm^2 at 14 T, respectively, which attain
the Jc level desired for practical applications. Moreover, the Jc values
exhibited extremely weak magnetic field dependence. These results clearly
demonstrate that PIT pnictide wire conductors are very promising for high field
magnet applications.",1309.7618v2
2013-10-02,Chemical Abundances of RR Lyrae Type C Star AS162158,"We report the first extensive model atmosphere and detailed chemical
abundance study of eight RR Lyrae variable stars of c subclass throughout their
pulsation cycles. Atmospheric parameters effective temperature, surface
gravity, microturbulent velocity, and metallicity have been derived. Spectra
for this abundace analysis have been obtained with the echelle spectrograph of
100-inch du Pont telescope at Las Campanas Observatory. We have found
metallicities and element abundance ratios to be constant within observational
uncertainties at all phases of all stars. Moreover, the $\alpha$-element and
Fe-group abundance ratios with respect to iron are consistent with other
horizontal-branch members (RRab, blue and red non-variables). The [Fe/H] values
of these eight RRc stars have been used to anchor the metallicity scale of a
much larger sample of RRc stars obtained with low S/N ""snapshot"" spectra.",1310.0580v1
2013-10-04,In-plane spin excitation anisotropy in the paramagnetic phase of NaFeAs,"We use unpolarized and polarized inelastic neutron scattering to study
low-energy spin excitations in NaFeAs, which exhibits a
tetragonal-to-orthorhombic lattice distortion at $T_s\approx 58$ K followed by
a collinear antiferromagnetic (AF) order below $T_N\approx 45$ K. In the AF
ordered state ($T<T_N$), spin waves are entirely c-axis polarized below
$\sim$10 meV, exhibiting a gap of $\sim4$ meV at the AF zone center and
disperse to $\sim$7 meV near the c-axis AF zone boundary. On warming to the
paramagnetic state with orthorhombic lattice distortion ($T_N<T<T_s$), spin
excitations become anisotropic within the FeAs plane. Upon further warming to
the paramagnetic tetragonal state ($T>T_s$), spin excitations become more
isotropic. Since similar magnetic anisotropy is also observed in the
paramagnetic tetragonal phase of superconducting
BaFe$_{1.904}$Ni$_{0.096}$As$_2$, our results suggest that the spin excitation
anisotropy in superconducting iron pnictides originates from similar anisotropy
already present in their parent compounds.",1310.1143v1
2013-10-09,Spin resonance in AFe2Se2 with s-wave pairing symmetry,"We study spin resonance in the superconducting state of recently discovered
alkali-intercalated iron selenide materials A_xFe_(2-y)Se_2 (A=K,Rb,Cs) in
which the Fermi surface has only electron pockets. Recent angle-resolved
photoemission spectroscopy (ARPES) studies [M. Xu et al., Phys. Rev. B 85,
220504(R) (2012)] were interpreted as strong evidence for s-wave gap in these
materials, while the observation of the resonance peak in neutron scattering
measurements [G. Friemel et al., Phys. Rev. B 85, 140511 (2012)] suggests that
the gap must have different signs at Fermi surface points connected by the
momentum at which the resonance has been observed. We consider recently
proposed unconventional s+- superconducting state of A_xFe_(2-y)Se_2 with
superconducting gap changing sign between the hybridized electron pockets. We
argue that such a state supports a spin resonance. We compute the dynamical
structure factor and show that it is consistent with the results of inelastic
neutron scattering.",1310.2334v2
2013-10-10,Strange Inter-layer Properties of $Ba(Fe_{1-x}Co_x)2As_2$ Appearing in Ultrasonic Measurements,"We have investigated the elastic constant C33 of Ba(Fe1-xCox)2As2 with eight
different Co concentrations by ultrasonic measurement. We found remarkable
elastic anomalies near the quantum critical point. We have studied them by
measuring the electrical resistivity, heat capacity, and ultrasonic attenuation
in addition to the elastic constant. These results have revealed that the
inter-layer three-dimensional properties appearing in C33 to be possibly
originated from the magnetic character of these materials. Our data about the
elastic constant C33 highlight the importance of controlling the c-axis length
in the emergence of superconductivity in iron-based superconductors.",1310.2681v1
2013-10-11,Enhanced superconductivity and evidence for novel pairing in single-layer FeSe on SrTiO3 thin film under large tensile strain,"Single-layer FeSe films with extremely expanded in-plane lattice constant of
3.99A are fabricated by epitaxially growing FeSe/Nb:SrTiO3/KTaO3
heterostructures, and studied by in situ angle-resolved photoemission
spectroscopy. Two elliptical electron pockets at the Brillion zone corner are
resolved with negligible hybridization between them, indicating the symmetry of
the low energy electronic structure remains intact as a free-standing
single-layer FeSe, although it is on a substrate. The superconducting gap
closes at a record high temperature of 70K for the iron based superconductors.
Intriguingly, the superconducting gap distribution is anisotropic but nodeless
around the electron pockets, with minima at the crossings of the two pockets.
Our results put strong constraints on the current theories, and support the
coexistence of both even and odd parity spin-singlet pairing channels as
classified by the lattice symmetry.",1310.3060v1
2013-10-20,Impurity effects in Cu$_2$O,"The doping of wide gap semiconductors is an interesting problem both from the
scientific and technological point of view. A well known example of this
problem is the doping of Cu$_2$O. The only element which has produced an order
of magnitude increase in the conductivity of Cu$_2$O bulk samples is chlorine,
as previously reported by us and others. However the solar cells produced with
this material do not show any improvement in performances because of the
reduction in the minority carrier diffusion length. In this paper we
investigate the effect of other impurities in order to check their possible use
as dopants and to assess their effects on the minority carrier diffusion
length. Seven impurities have been introduced by evaporation on the starting
copper sheet before the oxidation used to produce Cu$_2$O: chromium (Cr), iron
(Fe), silver (Ag), silicon (Si), sodium (Na), sulfur (S) and phosphorus (P).
The experiments show that a 20 ppm of concentration of these dopants does not
give any relevant effect neither on the resistivity, nor on the mobility. The
effect on minority carrier diffusion length is also negligible except for
sodium which produces a slight degradation of the samples.",1310.5341v1
2013-10-22,Point defect modeling in materials: coupling ab initio and elasticity approaches,"Modeling point defects at an atomic scale requires careful treatment of the
long-range atomic relaxations. This elastic field can strongly affect point
defect properties calculated in atomistic simulations because of the finite
size of the system under study. This is an important restriction for ab initio
methods which are limited to a few hundred atoms. We propose an original
approach coupling ab initio calculations and linear elasticity theory to obtain
the properties of an isolated point defect for reduced supercell sizes. The
reliability and benefit of our approach are demonstrated for three problematic
cases: the self-interstitial in zirconium, clusters of self-interstitials in
iron, and the neutral vacancy in silicon.",1310.5799v1
2013-10-22,Nucleosynthesis inside accretion disks and outflows formed during core collapse of massive stars,"We investigate nucleosynthesis inside the gamma-ray burst (GRB) accretion
disks and in the outflows launched from these disks mainly in the context of
Type II collapsars. We report the synthesis of several unusual nuclei like 31P,
39K, 43Sc, 35Cl and various isotopes of titanium, vanadium, chromium, manganese
and copper in the disk. We also confirm the presence of iron-group and
alpha-elements in the disk, as shown by previous authors. Much of these heavy
elements thus synthesized are ejected from the disk and survive in the
outflows. While emission lines of several of these elements have been observed
in the X-ray afterglows of GRBs by BeppoSAX, Chandra, XMM-Newton etc., Swift
seems to have not found these lines yet.",1310.5911v1
2013-10-22,Large low-temperature magnetoresistance in SrFe2As2 single crystals,"We present the first report on a large low-temperature magnetoresistance (MR)
of more than 1600% in a SrFe2As2 single crystal and 1300% in a low-energy Ca
ion-implanted SrFe2As2 single crystal that occurs before the emergence of
crystallographic strain-induced bulk superconductivity arising from a sample
aging effect. In accordance to band structure calculations from literature,
which consitently show more than 2 bands are involved in the transport, we have
modeled this large MR at high fields using a 3-carrier scenario rather than
solely on quantum linear MR model generally used to explain the MR in
iron-pnictides. At and below 20 K the large MR may be due to 3-carrier
transport in an inhomogeneous state where there are superconducting and
metallic regions.",1310.6071v1
2013-10-28,Principle of Maximum Entanglement Entropy and Local Physics of Correlated many-body Electron-Systems,"We argue that, because of the quantum-entanglement, the local physics of the
strongly-correlated materials at zero temperature is described in very good
approximation by a simple generalized Gibbs distribution, which depends on a
relatively small number local quantum thermodynamical potentials. We
demonstrate that our statement is exact in certain limits, and we perform
numerical calculations of the iron compounds FeSe and FeTe and of the elemental
cerium by employing the Gutzwiller Approximation (GA) that strongly support our
theory in general.",1310.7520v2
2013-10-28,Enhanced Superconductivity on the Tetragonal Lattice in FeSe under Hydrostatic Pressure,"Superconductivity under pressure in FeSe ($T_{\rm c}$$\sim$7.5 K) has been
investigated using single-crystal specimens through the measurements of DC
magnetization and electrical resistivity. A characteristic three-step increase
in $T_{\rm c}$ has been found under hydrostatic pressure up to $\sim$34 K above
7 GPa. The structural transition from a tetragonal phase to an orthorhombic
phase ($T_{\rm s}$$\sim$87 K) is found to disappear at $P$$\sim$2.3 GPa, above
which $T_{\rm c}$ increases rapidly, suggesting that the superconductivity is
enhanced by the tetragonal environment. Under non-hydrostatic pressure, the
increase in $T_{\rm c}$ is suppressed and the superconductive volume fraction
is considerably reduced above 2 GPa, probably owing to the breaking of the
tetragonal lattice symmetry by the uniaxial stress. The intimate correlation
between the enhanced (suppressed) superconductivity and the tetragonality
(orthorhombicity) in the phase diagram is a common feature of FeSe and other
iron-pnictide superconductors.",1310.7546v3
2013-11-01,New Li-Ethylenediamine-Intercalated Superconductor Li$_x$(C$_2$H$_8$N$_2$)$_y$Fe$_{2-z}$Se$_2$ with $T_c$ = 45 K,"A new iron-based superconductor Li$_x$(C$_2$H$_8$N$_2$)$_y$Fe$_{2-z}$Se$_2$
with $T_c$ = 45 K has successfully been synthesized via intercalation of
dissolved lithium metal in ethylenediamine. The distance between neighboring Fe
layers is 10.37 {\AA} and much larger than those of FeSe with $T_c$ = 8 K and
K$_x$Fe$_2$Se$_2$ with $T_c$ ~ 30 K. It seems that the high-$T_c$ of
Li$_x$(C$_2$H$_8$N$_2$)$_y$Fe$_{2-z}$Se$_2$ is caused by the possible
two-dimensional electronic structure due to the large $c$-axis length.",1311.0141v1
2013-11-03,s-wave pairing in the optimally-doped LaO0.5F0.5BiS2 superconductor,"We report on the magnetic and superconducting properties of LaO0.5F0.5BiS2 by
means of zero- (ZF) and transverse-field (TF) muon-spin spectroscopy
measurements (uSR). Contrary to previous results on iron-based superconductors,
measurements in zero field demonstrate the absence of magnetically ordered
phases. TF-uSR data give access to the superfluid density, which shows a marked
2D character with a dominant s-wave temperature behavior. The field dependence
of the magnetic penetration depth confirms this finding and further suggests
the presence of an anisotropic superconducting gap.",1311.0457v2
2013-11-03,Magnetization distribution and orbital moment in the non-Superconducting Chalcogenide Compound K0.8Fe1.6Se2,"We have used polarized and unpolarized neutron diffraction to determine the
spatial distribution of the magnetization density induced by a magnetic field
of 9 T in the tetragonal phase of K0.8Fe1.6Se2. The maximum entropy
reconstruction shows clearly that most of the magnetization is confined to the
region around the iron atoms whereas there is no significant magnetization
associated with either Se or K atoms. The distribution of magnetization around
the Fe atom is slightly nonspherical with a shape which is extended along the
[0 0 1] direction in the projection. Multipolar refinement results show that
the electrons which give rise to the paramagnetic susceptibility are confined
to the Fe atoms and their distribution suggests that they occupy 3d t2g-type
orbitals with around 66% in those of xz/yz symmetry. Detail modeling of the
magnetic form factor indicates the presence of an orbital moment to the total
paramagnetic moment of Fe2+",1311.0492v1
2013-11-04,An extended Heitler-Matthews model for the full hadronic cascade in cosmic air showers,"The Heitler-Matthews model for hadronic air showers will be extended to all
the generations of electromagnetic subshowers in the hadronic cascade. The
analysis is outlined in detail for showers initiated by primary protons. For
showers initiated by iron primaries the part of the analysis is given for as
far as it differs from the analysis for a primary proton. Predictions for
shower sizes and the depth of maximum shower size are compared with results of
Monte Carlo simulations. The depth of maximum as it follows from the
extrapolation of the Heitler-Matthews model restricted to the first generation
of electromagnetic subshowers is too small with respect to Monte Carlo
predictions. It is shown that the inclusion of all the generations of
electromagnetic subshowers leads to smaller predictions for the depth of
maximum and to smaller predictions for the elongation rate. The discrepancy
between discrete model predictions and Monte Carlo predictions for the depth of
maximum can therefore not be explained from the number of generations that is
taken into consideration. An alternative explanation will be proposed.",1311.0642v3
2013-11-06,On the Sodium versus Iron Correlation in Late B-Type Stars,"With an aim to study whether the close correlation between [Na/H] and [Fe/H]
recently found in A-type stars further persists in the regime of B-type stars,
the abundances of Na were determined for 30 selected sharp-lined late B-type
stars (10000K < T_eff < 14000K) from the Na I 5890/5896 doublet. These Na
abundances were then compared with the O and Fe abundances (derived from the O
I 6156-8 and Fe II 6147/6149 lines) showing anti-correlated peculiarities. It
turned out that, unlike the case of A-type stars, [Na/H] is roughly constant at
a slightly subsolar level ([Na/H] ~ -0.2 (+/-0.2)) without any significant
correlation with [Fe/H] which shows considerable dispersion ranging from ~ -0.6
to ~ +1.0. This may serve as an important observational constraint for
understanding the abundance peculiarities along with the physical mechanism of
atomic diffusion in upper main-sequence stars of late A through late B-type
including Am and HgMn stars.",1311.1260v1
2013-11-06,Enhanced Superconductivity up to 43 K by P/Sb Doping of Ca1-xLaxFeAs2,"The effects of isovalent doping on the superconducting transition temperature
Tc in novel 112-type iron arsenide Ca1-xLaxFeAs2 were studied by conducting
measurements of electrical resistivity rho and magnetization M. P or Sb doping
strongly enhances Tc: P-doped Ca0.84La0.16FeAs2 and Sb-doped Ca0.85La0.15FeAs2
exhibited Tc of 41 and 43 K, respectively, while Ca0.85La0.15FeAs2 without P/Sb
exhibited Tc = 35 K. These observations will give a hint for further enhancing
Tc of rare-earth doped Ca-Fe-As systems.",1311.1269v2
2013-11-06,Superconductivity in Ca10(Ir4As8)(Fe2As2)5 with Square-Planar Coordination of Iridium,"We report the unprecedented square-planar coordination of iridium in the iron
iridium arsenide Ca10(Ir4As8)(Fe2As2)5. This material experiences
superconductivity at 16 K. X-ray photoemission spectroscopy and first-
principles band calculation suggest Ir(II) oxidation state, which yields
electrically conductive Ir4As8 layers. Such metallic spacer layers are thought
to enhance the interlayer coupling of Fe2As2, in which superconductivity
emerges, thus offering a way to control the superconducting transition
temperature.",1311.1280v1
2013-11-07,"The Terzan 5 puzzle: discovery of a third, metal-poor component","We report on the discovery of 3 metal-poor giant stars in Terzan 5, a complex
stellar system in the the Galactic bulge, known to have two populations at
[Fe/H]=-0.25 and +0.3. For these 3 stars we present new echelle spectra
obtained with NIRSPEC at Keck II, which confirm their radial velocity
membership and provide average [Fe/H]=-0.79 dex iron abundance and
[alpha/Fe]=+0.36 dex enhancement. This new population extends the metallicity
range of Terzan~5 0.5 dex more metal poor, and it has properties consistent
with having formed from a gas polluted by core collapse supernovae.",1311.1706v1
2013-11-09,Formation of Nanofoam carbon and re-emergence of Superconductivity in compressed CaC6,"Pressure can tune material's electronic properties and control its quantum
state, making some systems present disconnected superconducting region as
observed in iron chalcogenides and heavy fermion CeCu2Si2. For CaC6
superconductor (Tc of 11.5 K), applying pressure first Tc increases and then
suppresses and the superconductivity of this compound is eventually disappeared
at about 18 GPa. Here, we report a theoretical finding of the re-emergence of
superconductivity in heavily compressed CaC6. The predicted phase III (space
group Pmmn) with formation of carbon nanofoam is found to be stable at wide
pressure range with a Tc up to 14.7 K at 78 GPa. Diamond-like carbon structure
is adhered to the phase IV (Cmcm) for compressed CaC6 after 126 GPa, which has
bad metallic behavior, indicating again departure from superconductivity.
Re-emerged superconductivity in compressed CaC6 paves a new way to design
new-type superconductor by inserting metal into nanoporous host lattice.",1311.2184v2
2013-11-12,Unconventional sign-changing superconductivity near quantum criticality in YFe$_2$Ge$_2$,"I present the results of first principles calculations of the electronic
structure and magnetic interactions for the recently discovered superconductor
YFe$_2$Ge$_2$ and use them to identify the nature of superconductivity and
quantum criticality in this compound. I find that the Fe $3d$ derived states
near the Fermi level show a rich structure with the presence of both linearly
dispersive and heavy bands. The Fermi surface exhibits nesting between hole and
electron sheets that manifests as a peak in the susceptibility at $(1/2,1/2)$.
I propose that the superconductivity in this compound is mediated by
antiferromagnetic spin fluctuations associated with this peak resulting in a
$s_\pm$ state similar to the previously discovered iron-based superconductors.
I also find that various magnetic orderings are almost degenerate in energy,
which indicates that the proximity to quantum criticality is due to competing
magnetic interactions.",1311.2922v1
2013-11-20,Polarization-Dependent Three-Dimensional Angle-Resolved Photoemission Spectroscopy of BaFe$_{1.8}$Co$_{0.2}$As$_{2}$,"We performed polarization- and photon-energy-dependent angle-resolved
photoemission spectroscopy of a slightly overdoped iron pnictide
superconductor, BaFe$_{1.8}$Co$_{0.2}$As$_{2}$, to clarify the
three-dimensional electronic structure including its orbital characters at the
Brillouin zone center. Two hole Fermi surfaces (FSs) with $d_{xz/yz}$ and
$d_{xy/x^2-y^2}$ orbitals were observed but $d_{z^2}$ hole FS, which has nodes
according to a theory of the spin-fluctuation superconductivity mechanism, did
not appear. These results suggest that no node will appear at hole FSs at the
zone center.",1311.4990v1
2013-11-20,X-ray time delays in the Narrow Line Seyfert 1 galaxy PG 1244+026,"We analyse the X-ray time-lags in the Narrow Line Seyfert 1 (NLS1) galaxy PG
1244+026 ($M_{\rm BH}\sim 10^7 M_{\rm sun}$, $L/L_{\rm Edd}\sim 1$). The time
delay between the soft (0.3--0.7~keV) and harder (1.2--4.0~keV) variations
shows shows the well established switch from hard lags at low frequencies to
soft lags at high frequencies. The low frequency hard lags are qualitatively
consistent with the propagation of fluctuations model, with some long-timescale
response of the reflection component. The high frequency soft lag appears to
extend over a wide frequency band, that we divide this into two narrow
frequency ranges, and examine the lag as a function of energy for each of
these. At high frequencies the soft excess emission is delayed with respect to
the harder energy bands, without any corresponding strong, hard X-ray
reflection signature. At even higher frequencies a soft lag is seen at the
softest energies, as well as tentative evidence for an iron K$\alpha$
reverberation signal. These results point to the importance of reprocessing as
well as reflection in determining the lags in NLS1s.",1311.5165v2
2013-11-21,"L4Fe2As2Te1-xO4-yFy (L = Pr, Sm, Gd): a layered oxypnictide superconductor with Tc up to 45 K","The synthesis, structural and physical properties of iron lanthanide
oxypnictide superconductors, L4Fe2As2Te1-xO4 (L = Pr, Sm, Gd), with transition
temperature at ~ 25 K are reported. Single crystals have been grown at high
pressure using cubic anvil technique. The crystal structure consists of layers
of L2O2 tetrahedra separated by alternating layers of chains of Te and of
Fe2As2 tetrahedra: -L2O2-Te-L2O2-Fe2As2-L2O2-Te-L2O2- (space group: I4/mmm, a ~
4.0, c ~ 29.6 {\AA}). Substitution of oxygen by fluorine increases the critical
temperature, e.g. in Gd4Fe2As2Te1-xOyF4-y up to 45 K. Magnetic torque
measurements reveal an anisotropy of the penetration depths of ~31.",1311.5437v2
2013-11-22,Magnetic phase transitions and superconductivity in strained FeTe,"The influence of hydrostatic pressure and ab-plane strain on the magnetic
structure of FeTe is investigated from first principles. The results of
calculations reveal a phase transition from antiferromagnetic double-stripe
ordering at ambient pressure to ferromagnetic ordering at 2 GPa, or under
compressive strain reducing the lattice parameter a by about 3%. In turn, a
tensile strain of less than 2% induces the phase transition to
antiferromagnetic single-stripe ordering. It corresponds to the superconducting
FeTe thin films, thereby confirming that the superconducting state is
positively linked to single-stripe antiferromagnetic fluctuations. Both types
of transition indicate that the position of Te atoms in the crystal is crucial
for the magnetic and superconducting properties of iron chalcogenides.",1311.5732v1
2013-11-22,Coherent emission of $γ$ quanta by synchrotron radiation excited nuclei: geometry of nearly backward scattering,"A possibility of further development of Synchrotron M\""{o}ssbauer Source
(SMS) of $^{57}$Fe 14.4 keV radiation is considered. The principles and
detailed description of the SMS device is given in Refs. Phys. Rev. A 84,
053851 (2011) G. V. Smirnov et al, J. Synchrotron Rad., v. 19, 559 (2012) V.
Potapkin et al. The perfect crystal of Iron Borate, FeBO$_{3}$, is the central
element of this device. The coherent nuclear fluorescence of IB crystal
illuminated by synchrotron radiation produces the sharply directed beam of 14.4
keV M\""{o}ssbauer radiation from the crystal set at the pure nuclear Bragg
reflection. Up to now the low angle scattering geometry was used for generation
of the coherent $\gamma $ radiation. The analysis performed in the present
paper shows that the source of about two times larger power can be obtained
when nearly backward scattering geometry is employed. This result can be
efficiently applied in development of high resolution spectroscopy using
synchrotron radiation.",1311.5771v1
2013-11-24,Temperature and high strain rate dependence of tensile deformation behavior in single crystal iron from dislocation dynamics simulations,"We conduct dislocation dynamics (DD) simulations of Fe periodic single
crystals under tensile load at several high strain rates and temperatures. The
simulations are enabled by the recent development of temperature-dependent
dislocation mobility relations obtained from atomistic calculations. The
plastic evolution in the simulations is governed by rapid initial dislocation
multiplication, followed by a saturation of the flow stress when the
subpopulation of slow plastic carriers becomes stabilized by dislocation
annihilation. Above 500 K, edge dislocations coexist with screw dislocations
and contribute proportionaly to the value of the flow stress. The DD
simulations are used to interpret shock-loading experiments in Fe in terms of
the relative importance of different strengthening mechanisms. We find that in
the $10^4$-to-$10^6$ s$^{-1}$ strain rate regime, work hardening explains the
hardening of shock-loaded bulk Fe crystals.",1311.6173v1
2013-11-26,Field Measurement for Superconducting Magnets of ADS Injector I,"The superconducting solenoid magnet prototype for ADS injection-I had been
fabricated in Beijing Qihuan Mechanical and Electric Engineer Company and
tested in Haerbin Institute of Technology (HIT) in Nov, 2012. Batch magnet
production was processed after some major revision from the magnet prototype,
they include: removing off the perm-alloy shield, extending the iron yoke,
using thin superconducting cable, etc. The first one of the batch magnets was
tested in the vertical Dewar in HIT in Sept. 2013. Field measurement was
carried out at the same time by the measurement platform that seated on the top
of the vertical Dewar. This paper will present the field measurement system
design, measurement results and discussion on the residual field from the
persistent current effect.",1311.6596v1
2013-11-28,From supernovae to neutron stars,"The gravitational collapse, bounce, the explosion of an iron core of an 11.2
$M_{\odot}$ star is simulated by two-dimensional neutrino-radiation
hydrodynamic code. The explosion is driven by the neutrino heating aided by
multi-dimensional hydrodynamic effects such as the convection. Following the
explosion phase, we continue the simulation focusing on the thermal evolution
of the protoneutron star up to $\sim$70 s when the crust of the neutron star is
formed using one-dimensional simulation. We find that the crust forms at
high-density region ($\rho\sim10^{14}$ g cm$^{-3}$) and it would proceed from
inside to outside. This is the first self-consistent simulation that
successfully follows from the collapse phase to the protoneutron star cooling
phase based on the multi-dimensional hydrodynamic simulation.",1311.7249v2
2013-12-01,Chemical Bonding in Aqueous Ferrocyanide: Experimental and Theoretical X-ray Spectroscopic Study,"Resonant inelastic X-ray scattering (RIXS) and X-ray absorption (XA)
experiments at the iron L- and nitrogen K-edge are combined with high-level
first principles restricted active space self-consistent field (RASSCF)
calculations for a systematic investigation of the nature of the chemical bond
in potassium ferrocyanide in aqueous solution. The atom- and site-specific RIXS
excitations allow for direct observation of ligand-to-metal (Fe L-edge) and
metal-to-ligand (N K-edge) charge transfer bands and thereby evidence for
strong {\sigma}-donation and {\pi}-back-donation. The effects are identified by
comparing experimental and simulated spectra related to both the unoccupied and
occupied molecular orbitals in solution.",1312.0236v1
2013-12-04,Ray-tracing in pseudo-complex General Relativity,"Motivated by possible observations of the black hole candidate in the center
of our galaxy and the galaxy M87, ray-tracing methods are applied to both
standard General Relativity (GR) and a recently proposed extension, the
pseudo-complex General Relativity (pc-GR). The correction terms due to the
investigated pc-GR model lead to slower orbital motions close to massive
objects. Also the concept of an innermost stable circular orbit (ISCO) is
modified for the pc-GR model, allowing particles to get closer to the central
object for most values of the spin parameter $a$ than in GR. Thus, the
accretion disk, surrounding a massive object, is brighter in pc-GR than in GR.
Iron K$\alpha$ emission line profiles are also calculated as those are good
observables for regions of strong gravity. Differences between the two theories
are pointed out.",1312.1170v2
2013-12-09,Point contact spectroscopy in Fe-based superconductors: recent advancements and future challenges,"Iron-based superconductors (FeSC) present an unprecedented variety of
features both in the superconducting and in the normal state. Different
families differ in the value of the critical temperature, in the shape of the
Fermi surface, in the existence or absence of quasi-nesting conditions, in the
range of doping in which the antiferromagnetic (AFM) and the superconducting
phase coexist and in the structure of the order parameter in the reciprocal
space, and so on. In this paper the most important results of point-contact
spectroscopy (PCS) in Fe-based superconductors are reviewed, and the most
recent advances are described with the aim to discuss the future perspectives
and challenges of this spectroscopic technique in the characterization of the
superconducting properties of these complex compounds. One of the main
challenges, faced so far only by a few researchers in the PCS field, is to
fully explore the phase diagram of these materials, as a function of doping or
pressure, to understand the interplay between superconductivity and magnetism,
the effect of intrinsic or extrinsic inhomogeneities, the role of spin
fluctuations (SFs) in the pairing, the symmetry and the structure of the order
parameter(s).",1312.2527v1
2013-12-10,On the origin of variable structures in the winds of hot luminous stars,"Examination of the temporal variability properties of several strong optical
recombination lines in a large sample of Galactic Wolf-Rayet (WR) stars reveals
possible trends, especially in the more homogeneous WC than the diverse WN
subtypes, of increasing wind variability with cooler subtypes. This could imply
that a serious contender for the driver of the variations is stochastic,
magnetic subsurface convection associated with the 170 kK partial-ionization
zone of iron, which should occupy a deeper and larger zone of greater mass in
cooler WR subtypes. This empirical evidence suggests that the heretofore
proposed ubiquitous driver of wind variability, radiative instabilities, may
not be the only mechanism playing a role in the stochastic multiple
small-scaled structures seen in the winds of hot luminous stars. In addition to
small-scale stochastic behaviour, subsurface convection guided by a global
magnetic field with localized emerging loops may also be at the origin of the
large-scale corotating interaction regions as seen frequently in O stars and
occasionally in the winds of their descendant WR stars.",1312.2864v1
2013-12-10,Spectrum splitting of bimagnon excitations in a spatially frustrated Heisenberg antiferromagnet revealed by resonant inelastic x-ray scattering,"We perform a comprehensive analysis of the bimagnon resonant inelastic x-ray
scattering (RIXS) intensity spectra of the spatially frustrated Jx-Jy-J2
Heisenberg model on a square lattice in both the antiferromagnetic and the
collinear antiferromagnetic phase. We study the model for strong frustration
and significant spatial anisotropy to highlight the key signatures of RIXS
spectrum splitting which may be experimentally discernible. Based on an
interacting spin wave theory study within the ladder approximation
Bethe-Salpeter scheme, we find the appearance of a robust two-peak structure
over a wide range of the transferred momenta in both magnetically ordered
phases. The unfrustrated model has a single-peak structure with a two-peak
splitting originating due to spatial anisotropy and frustrated interactions.
Our predicted two-peak structure from both magnetically ordered regime can be
realized in iron pnictides.",1312.2876v2
2013-12-12,Impact of electronic correlations on the equation of state and transport in $ε$-Fe,"We have obtained the equilibrium volumes, bulk moduli, equations of state of
the ferromagnetic cubic $\alpha$ and paramagnetic hexagonal $\epsilon$ phases
of iron in close agreement with experiment using an ab initio dynamical
mean-field theory approach. The local dynamical correlations are shown to be
crucial for a successful description of the ground-state properties of
paramagnetic $\epsilon$-Fe. Moreover, they enhance the effective mass of the
quasiparticles and reduce their lifetimes across the $\alpha \to \epsilon$
transition leading to a step-wise increase of the resistivity, as observed in
experiment. The calculated magnitude of the jump is significantly
underestimated, which points to non-local correlations. The implications of our
results for the superconductivity and non-Fermi-liquid behavior of
$\epsilon$-Fe are discussed.",1312.3654v1
2013-12-13,Phosphorus in the Young Supernova Remnant Cassiopeia A,"Phosphorus ($^{31}$P), which is essential for life, is thought to be
synthesized in massive stars and dispersed into interstellar space when these
stars explode as supernovae (SNe). Here we report on near-infrared
spectroscopic observations of the young SN remnant Cassiopeia A, which show
that the abundance ratio of phosphorus to the major nucleosynthetic product
iron ($^{56}$Fe) in SN material is up to 100 times the average ratio of the
Milky Way, confirming that phosphorus is produced in SNe. The observed range is
compatible with predictions from SN nucleosynthetic models but not with the
scenario in which the chemical elements in the inner SN layers are completely
mixed by hydrodynamic instabilities during the explosion.",1312.3807v1
2013-12-16,Optical conductivity of nodal metals,"Fermi liquid theory is remarkably successful in describing the transport and
optical properties of metals; at frequencies higher than the scattering rate,
the optical conductivity adopts the well-known power law behavior
$\sigma_1(\omega) \propto \omega^{-2}$. We have observed an unusual non-Fermi
liquid response $\sigma_1(\omega) \propto \omega^{-1\pm 0.2}$ in the ground
states of several cuprate and iron-based materials which undergo electronic or
magnetic phase transitions resulting in dramatically reduced or nodal Fermi
surfaces. The identification of an inverse (or fractional) power-law behavior
in the residual optical conductivity now permits the removal of this
contribution, revealing the direct transitions across the gap and allowing the
nature of the electron-boson coupling to be probed. The non-Fermi liquid
behavior in these systems may be the result of a common Fermi surface topology
of Dirac cone-like features in the electronic dispersion.",1312.4466v1
2013-12-20,Ultrafast modulation of the chemical potential in BaFe$_2$As$_2$ by coherent phonons,"Time- and angle-resolved extreme ultraviolet photoemission spectroscopy is
used to study the electronic structure dynamics in BaFe$_2$As$_2$ around the
high-symmetry points $\Gamma$ and $M$. A global oscillation of the Fermi level
at the frequency of the $A_{1g}$(As) phonon mode is observed. It is argued that
this behavior reflects a modulation of the effective chemical potential in the
photoexcited surface region that arises from the high sensitivity of the band
structure near the Fermi level to the $A_{1g}$ phonon mode combined with a low
electron diffusivity perpendicular to the layers. The results establish a novel
way to tune the electronic properties of iron pnictides: coherent control of
the effective chemical potential. The results further suggest that the
equilibration time for the effective chemical potential needs to be considered
in the ultrafast electronic structure dynamics of materials with weak
interlayer coupling.",1312.6025v1
2013-12-23,Heat capacity jump at T_c and pressure derivatives of superconducting transition temperature in the Ba(1-x)NaxFe2As2 (0.1 <= x <= 0.9) series,"We present the evolution of the initial (up to ~ 10 kbar) hydrostatic,
pressure dependencies of T_c and of the ambient pressure jump in the heat
capacity associated with the superconducting transition as a function of Na -
doping in the Ba(1-x)NaxFe2As2 family of iron-based superconductors. For Na
concentrations 0.15 <= x <= 0.9, the jump in specific heat at T_c, Delta C_p,
follows the Delta C_p ~ T^3 scaling found for most BaFe2As2 - based
superconductors. Pressure dependencies are non-monotonic for x = 0.2 and x =
0.24. For other Na concentrations T_c decreases under pressure in almost linear
fashion. The anomalous behavior of the x = 0.2 and x = 0.24 samples under
pressure are possibly due to the crossing of the phase boundaries of the narrow
antiferromagnetic tetragonal phase, unique for the Ba(1-x)NaxFe2As2 series,
with the application of pressure.",1312.6705v1
2014-01-07,The polluted atmospheres of cool white dwarfs and the magnetic field connection,"We present an analysis of X-Shooter spectra of the polluted hydrogen-rich
white dwarfs (DAZ) NLTT 888 and NLTT 53908. The spectra of NLTT 53908 show
strong, Zeeman-split calcium lines (CaII H&K and Ca I $\lambda 4226$) and the
star appears to be a close relative of the polluted magnetic white dwarf (DAZH)
NLTT 10480, while the spectra of NLTT 888 show narrow lines of calcium and
iron. A comparison of the DAZ NLTT 888 and the DAZH NLTT 53908 with other class
members illustrates the diversity of environment and formation circumstances
surrounding these objects. In particular, we find that the incidence of
magnetism in old, polluted white dwarfs significantly exceeds that found in the
general white dwarf population which suggests an hypothetical link between a
crowded planetary system and magnetic field generation.",1401.1249v1
2014-01-10,The Iron K Line Profile of IRAS 18325-5926,"IRAS 18325-5926 is an X-ray bright, Compton-thin, type-2 Seyfert galaxy and
it was the first Seyfert 2 in which the presence of a broad Fe K-alpha emission
line was claimed. However, although the structure of the Fe line appears broad,
there is tentative evidence that it may comprise multiple lines. Nevertheless,
previous analyses have only consisted of fitting standalone broad components to
the Fe K band. Here, we have analyzed all available X-ray CCD data from Suzaku,
XMM-Newton and ASCA to fully investigate the nature of the emission complex by
testing broad-band physical models and alternative hypotheses. We find that
both a model consisting of broad, blurred reflection from an ionized accretion
disc and a model consisting of cold, neutral reflection plus narrow emission
lines from highly-ionized photoionized gas (log \xi = 3.5) offer statistically
comparable fits to the data although the true reality of the Fe line cannot
currently be determined with existing data. However, it is hoped that better
quality data and improved photon statistics in the Fe K band will allow a more
robust distinction between models to be made.",1401.2420v1
2014-01-14,Ipopv2: Photoionization of Ni XIV -- a test case,"Several years ago, M. Asplund and coauthors (2004) proposed a revision of the
Solar composition. The use of this new prescription for Solar abundances in
standard stellar models generated a strong disagreement between the predictions
and the observations of Solar observables. Many claimed that the Standard Solar
Model (SSM) was faulty, and more specifically the opacities used in such
models. As a result, activities around the stellar opacities were boosted. New
experiments (J. Bailey at Sandia on Z-Pinch, The OPAC consortium at LULI200) to
measure directly absorbtion coefficients have been realized or are underway.
Several theoretical groups (CEA-OPAS, Los Alamos Nat. Lab., CEA-SCORCG, The
Opacity Project - The Iron Project (IPOPv2)) have started new sets of
calculations using different approaches and codes. While the new results seem
to confirm the good quality of the opacities used in SSM, it remains important
to improve and complement the data currently available. We present recent
results in the case of the photoionization cross sections for Ni XIV (Ni13+ )
from IPOPv2 and possible implications on stellar modelling.",1401.3122v1
2014-01-16,Terzan 5: a pristine fragment of the Galactic Bulge?,"Terzan 5 is a stellar system located in the inner Bulge of the Galaxy and has
been historically catalogued as a globular cluster. However, recent photometric
(Ferraro et al. 2009) and spectroscopic (Origlia et al. 2011; Origlia et al.
2013) investigations have shown that it hosts at least three stellar
populations with different iron abundances (with a total spread of
Delta[Fe/H]>1 dex) thus demonstrating that Terzan 5 is not a genuine globular
cluster. In addition, the striking similarity between the chemical patterns of
this system and those of its surrounding environment, the Galactic Bulge, from
the point of view of both the metallicity distribution and the alpha-element
enrichment, suggests that Terzan 5 could be a pristine fragment of the Bulge
itself.",1401.3962v1
2014-01-20,Total and Partial Fragmentation Cross-Section of 500 MeV/nucleon Carbon Ions on Different Target Materials,"By using an experimental setup based on thin and thick double-sided
microstrip silicon detectors, it has been possible to identify the
fragmentation products due to the interaction of very high energy primary ions
on different targets. Here we report total and partial cross-sections measured
at GSI (Gesellschaft fur Schwerionenforschung), Darmstadt, for 500 MeV/n energy
$^{12}C$ beam incident on water (in flasks), polyethylene, lucite, silicon
carbide, graphite, aluminium, copper, iron, tin, tantalum and lead targets. The
results are compared to the predictions of GEANT4 (v4.9.4) and FLUKA (v11.2)
Monte Carlo simulation programs.",1401.4897v1
2014-01-21,Tunable VUV laser based spectrometer for Angle Resolved Photoemission Spectroscopy (ARPES),"We have developed an angle-resolved photoemission spectrometer with tunable
VUV laser as a photon source. The photon source is based on the fourth harmonic
generation of a near IR beam from a Ti:sapphire laser pumped by a CW green
laser and tunable between 5.3eV and 7eV. The most important part of the set-up
is a compact, vacuum enclosed fourth harmonic generator based on KBBF crystals,
grown hydrothermally in the US. This source can deliver a photon flux of over
10^14 photons/s. We demonstrate that this energy range is sufficient to measure
the kz dispersion in an iron arsenic high temperature superconductor, which was
previously only possible at synchrotron facilities.",1401.5404v1
2014-01-21,Dramatic Changes in the Electronic Structure Upon Transition to the Collapsed Tetragonal Phase in CaFe2As2,"We use angle-resolved photoemission spectroscopy (ARPES) and density
functional theory (DFT) calculations to study the electronic structure of
CaFe$_2$As$_2$ in previously unexplored collapsed tetragonal (CT) phase. This
unusual phase of the iron arsenic high temperature superconductors was hard to
measure as it exists only under pressure. By inducing internal strain, via the
post growth, thermal treatment of the single crystals, we were able to
stabilize the CT phase at ambient-pressure. We find significant differences in
the Fermi surface topology and band dispersion data from the more common
orthorhombic-antiferromagnetic or tetragonal-paramagnetic phases, consistent
with electronic structure calculations. The top of the hole bands sinks below
the Fermi level, which destroys the nesting present in parent phases. The
absence of nesting in this phase along with apparent loss of Fe magnetic
moment, are now clearly experimentally correlated with the lack of
superconductivity in this phase.",1401.5416v1
2014-01-22,The effect of exceptionally high fluorine doping on the anisotropy of single crystalline SmFeAsO1-xFx,"We succeeded in growing single crystalline SmFeAsO1-xFx with exceptionally
high fluorine concentration by using a CsCl flux method. Comparing to
conventional flux methods, this method can introduce about double the amount of
fluorine into the oxygen site. The obtained single crystal shows the highest
superconducting transition temperature (Tc = 57.5 K) in single crystalline iron
pnictides. In addition, the residual resistivity ratio (RRR) is almost three
times as large as that of previously reported single crystals. This suggests
that our single crystals are suitable for investigation of the intrinsic
superconducting properties since they have few defects and impurities. Using
both the Werthamer-Helfand-Hohenberg model and the effective mass model, we
demonstrated that a higher fluorine concentration suppresses the anisotropic
superconductivity of SmFeAsO1-xFx.",1401.5611v2
2014-01-28,Phase Transformation Dynamics in Porous Battery Electrodes,"Porous electrodes composed of multiphase active materials are widely used in
Li-ion batteries, but their dynamics are poorly understood. Two-phase models
are largely empirical, and no models exist for three or more phases. Using a
modified porous electrode theory based on non-equilibrium thermodynamics, we
show that experimental phase behavior can be accurately predicted from free
energy models, without artificially placing phase boundaries or fitting the
open circuit voltage. First, we simulate lithium intercalation in porous iron
phosphate, a popular two-phase cathode, and show that the zero-current voltage
gap, sloping voltage plateau and under-estimated exchange currents all result
from size-dependent nucleation and mosaic instability. Next, we simulate porous
graphite, the standard anode with three stable phases, and reproduce
experimentally observed fronts of color-changing phase transformations. These
results provide a framework for physics-based design and control for
electrochemical systems with complex thermodynamics.",1401.7072v2
2014-01-29,The poisoning effect of Mn in LaFe(1-x)Mn(x)AsO(0.89)F(0.11): unveiling a quantum critical point in the phase diagram of iron-based superconductors,"A superconducting-to-magnetic transition is reported for
LaFe$_{1-x}$Mn$_x$AsO$_{0.89}$F$_{0.11}$ where a per thousand amount of Mn
impurities is dispersed. By employing local spectroscopic techniques like muon
spin rotation (muSR) and nuclear quadrupole resonance (NQR) on compounds with
Mn contents ranging from x=0.025% to x=0.75%, we find that the electronic
properties are extremely sensitive to the Mn impurities. In fact, a small
amount of Mn as low as 0.2% suppresses superconductivity completely. Static
magnetism, involving the FeAs planes, is observed to arise for x > 0.1% and
becomes further enhanced upon increasing Mn substitution. Also a progressive
increase of low energy spin fluctuations, leading to an enhancement of the NQR
spin-lattice relaxation rate 1/T1, is observed upon Mn substitution. The
analysis of 1/T1 for the sample closest to the the crossover between
superconductivity and magnetism (x = 0.2%) points towards the presence of an
antiferromagnetic quantum critical point around that doping level.",1401.7576v1
2014-01-30,Electronic structure of BaNi$_2$P$_2$ observed by angle-resolved photoemission spectroscopy,"We have performed an angle-resolved photoemission spectroscopy (ARPES) study
of BaNi$_2$P$_2$ which shows a superconducting transition at $T_c$ $\sim$ 2.5
K. We observed hole and electron Fermi surfaces (FSs) around the Brillouin zone
center and corner, respectively, and the shapes of the hole FSs dramatically
changed with photon energy, indicating strong three-dimensionality. The
observed FSs are consistent with band-structure calculation and de Haas-van
Alphen measurements. The mass enhancement factors estimated in the normal state
were $m^*$/$m_b$ $\leq$ 2, indicating weak electron correlation compared to
typical iron-pnictide superconductors. An electron-like Fermi surface around
the Z point was observed in contrast with BaNi$_2$As$_2$ and may be related to
the higher $T_c$ of BaNi$_2$P$_2$.",1401.7897v2
2014-01-31,A global cloud map of the nearest known brown dwarf,"Brown dwarfs -- substellar bodies more massive than planets but not massive
enough to initiate the sustained hydrogen fusion that powers self-luminous
stars -- are born hot and slowly cool as they age. As they cool below about
2,300 K, liquid or crystalline particles composed of calcium aluminates,
silicates and iron condense into atmospheric 'dust', which disappears at still
cooler temperatures (around 1,300 K). Models to explain this dust dispersal
include both an abrupt sinking of the entire cloud deck into the deep, unob-
servable atmosphere and breakup of the cloud into scattered patches (as seen on
Jupiter and Saturn). Thus far, observations of brown dwarfs have been limited
to globally integrated measurements, which can reveal surface inhomogeneities
but cannot unambiguously resolve surface features. Here we report a
two-dimensional map of a brown dwarf's surface that allows identification of
large-scale bright and dark features, indicative of patchy clouds.",1401.8145v1
2014-02-01,Phase stability and Nucleation effect upon Iron addition to SmCo5 bulk magnets,"Change in structure and magnetic properties of SmCo5-xFex permanent magnets
for different values of x ranging from 0 to 2 have been studied. Structural
investigation from X-ray diffraction (XRD) patterns confirms the hexagonal
CaCu5-type structure of the SmCo5-xFex ribbons for 0<x<2. The decrease in
angular position of the diffraction peaks points to the lattice expansion due
to the substitution of Co atoms by larger Fe atoms. Mixture of phases occurs
for x>2 and has been confirmed by both XRD studies and magnetic measurements.
Nucleation effect induced by the additive Fe enhances the coercivity (Hc)up to
27 kOe which is much larger than 4.5 kOe obtained for pure SmCo5.",1402.0138v1
2014-02-03,Hemispherical Parker waves driven by thermal shear in planetary dynamos,"Planetary and stellar magnetic fields are thought to be sustained by helical
motions ($\alpha$-effect) and, if present, differential rotation
($\Omega$-effect). In the Sun, the strong differential rotation in the
tachocline is responsible for an efficient $\Omega$-effect creating a strong
axisymmetric azimuthal magnetic field. This is a prerequisite for Parker dynamo
waves that may be responsible for the solar cycle. In the liquid iron cores of
terrestrial planets, the Coriolis force organizes convection into columns with
a strong helical flow component. These likely dominate magnetic field
generation while the $\Omega$-effect is of secondary importance. Here we use
numerical simulations to show that the planetary dynamo scenario may change
when the heat flux through the outer boundary is higher in one hemisphere than
in the other. A hemispherical dynamo is promoted that is dominated by fierce
thermal wind responsible for a strong $\Omega$-effect. As a consequence Parker
dynamo waves are excited equivalent to those predicted for the Sun. They obey
the same dispersion relation and propagation characteristics. We suggest that
Parker waves may therefore also play a role in planetary dynamos for all
scenarios where zonal flows become an important part of convective motions.",1402.0343v1
2014-02-06,Temperature-induced Change in the Fermi Surface Topology in the Spin Density Wave Phase of Sr(Fe$_{1-x}$Co$_x$)$_2$As$_2$,"We report electronic Raman scattering measurements of
Sr(Fe$_{1-x}$Co$_x$)$_2$As$_2$ single crystals in their magnetic - Spin Density
Wave (SDW) phase. The spectra display multiple, polarization-resolved SDW gaps
as expected in a band-folding itinerant picture for a multiband system. The
temperature dependence of the SDW gaps reveals an unusual evolution of the
reconstructed electronic structure with at least one gap being activated only
well below the magnetic SDW transition $T_N$. A comparison with temperature
dependent Hall measurements allows us to assign this activated behavior to a
change in the Fermi surface topology deep in the SDW phase, which we attribute
to the disappearance of a hole-like Fermi pocket. Our results highlight the
strong sensitivity of the low energy electronic structure to temperature in
iron-arsenide superconductors.",1402.1422v2
2014-02-07,Signatures of superconducting and pseudogap phases in ultrafast transient reflectivity of Ca(Fe0.927Co0.073)2As2,"We present femtosecond time-resolved pump-probe spectroscopic studies of a
pseudogap (PG) along with the superconducting (SC) gap in an overdoped iron
pnictide Ca(Fe0.927Co0.073)2As2. It is seen that the temperature evolution of
the photoexcited quasiparticle (QP) relaxation dynamics, coherently excited
A1g-symmetric optical phonon and two acoustic phonon dynamics behave
anomalously in the vicinity of the superconducting transition temperature Tc. A
continuous change in the sign of the experimentally measured transient
differential reflectivity Delta_R/R signal at the zero time-delay between the
pump and probe pulses at a temperature of ~200 K is inferred as an evidence of
the emergence of the PG phase around that temperature. This behavior is
independent of the pump photon energy and occurs for crystals without the spin
density wave phase transition.",1402.1627v1
2014-02-07,Suzaku Discovery of Fe K-Shell Line from the O-Rich SNR G292.0+1.8,"We report the Suzaku/XIS results of the Galactic oxygen-rich supernova
remnant (SNR), G292.0+1.8, a remnant of a core-collapse supernova. The X-ray
spectrum of G292.0+1.8 consists of two type plasmas, one is in collisional
ionization equilibrium (CIE) and the other is in non-equilibrium ionization
(NEI). The CIE plasma has nearly solar abundances, and hence would be
originated from the circumstellar and interstellar mediums. The NEI plasma has
super-solar abundances, and the abundance pattern indicates that the plasma
originates from the supernova ejecta with a main sequence of 30-35 Msolar. Iron
K-shell line at energy of 6.6 keV is detected for the first time in the NEI
plasma.",1402.1633v1
2014-02-12,Electron Impact Ionization of Stored Highly Charged Ions,"Accurate cross section data for electron impact ionization (EII) are needed
in order to interpret the spectra of collisionally ionized plasmas both in
astrophysics and in the laboratory. Models and spectroscopic diagnostics of
such plasmas rely on accurate ionization balance calculations, which depend, in
turn, on the underlying rates for EII and electron-ion recombination. EII
measurements have been carried out using the TSR storage ring located at the
Max-Planck-Institut fuer Kernphysik in Heidelberg, Germany. Storage ring
measurements are largely free of metastable contamination, resulting in
unambiguous EII data, unlike what is encountered with other experimental
geometries. As it is impractical to perform experiments for every ion, theory
must provide the bulk of the necessary EII data. In order to guide theory, TSR
experiments have focused on providing at least one measurement for every
isoelectronic sequence. EII data have been measured for ions from 13
isoelectronic sequences: Li-like silicon and chlorine, Be-like sulfur, B-like
magnesium, and F-like through K-like iron. These experimental results provide
an important benchmark for EII theory.",1402.2964v1
2014-02-21,Enhancement of Superconducting Transition Temperature Due to Antiferromagnetic Spin Fluctuations in Iron-pnictides LaFe(As_{1-x}P_x)(O_{1-y}F_y) : 31P-NMR Studies,"Systematic P-NMR studies on LaFe(As_{1-x}P_x)(O_{1-y}F_y) with y=0.05 and 0.1
have revealed that the antiferromagnetic spin fluctuations (AFMSFs) at low
energies are markedly enhanced around x=0.6 and 0.4, respectively, and as a
result, Tc exhibits respective peaks at 24 K and 27 K against the
P-substitution for As. This result demonstrates that the AFMSFs are responsible
for the increase in Tc for LaFe(As_{1-x}P_x)(O_{1-y}F_y) as a primary mediator
of the Cooper pairing. From a systematic comparison of AFMSFs with a series of
(La_{1-z}Y_z)FeAsO_{\delta} compounds in which Tc reaches 50 K for z=0.95, we
remark that a moderate development of AFMSFs causes the Tc to increase up to 50
K under the condition that the local lattice parameters of FeAs tetrahedron
approaches those of the regular tetrahedron. We propose that the T_c of
Fe-pnictides exceeding 50 K is maximized under an intimate collaboration of the
AFMSFs and other factors originating from the optimization of the local
structure.",1402.5220v1
2014-03-02,Transport in multiband systems with hot spots on the Fermi surface: Forward-scattering corrections,"Multiband models with hot spots are of current interest partly because of
their relevance for the iron-based superconductors. In these materials, the
momentum-dependent scattering off spin fluctuations and the ellipticity of the
electron Fermi pockets are responsible for anisotropy of the lifetimes of
excitations around the Fermi surface. The deep minima of the lifetimes---the
so-called hot spots---have been assumed to contribute little to the transport
as is indeed predicted by a simple relaxation-time approach. Calculating
forward-scattering corrections to this approximation, we find that the
effective transport times are much more isotropic than the lifetimes and that,
therefore, the hot spots contribute to the transport even in the case of strong
spin-fluctuation scattering. We discuss this effect on the basis of an
analytical solution of the Boltzmann equation and calculate numerically the
temperature and doping dependence of the resistivity and the Hall, Seebeck, and
Nernst coefficients.",1403.0144v2
2014-03-02,Heat transport in RbFe2As2 single crystal: evidence for nodal superconducting gap,"The in-plane thermal conductivity of iron-based superconductor RbFe$_2$As$_2$
single crystal ($T_c \approx$ 2.1 K) was measured down to 100 mK. In zero
field, the observation of a significant residual linear term $\kappa_0/T$ =
0.65 mW K$^{-2}$ cm$^{-1}$ provides clear evidence for nodal superdonducting
gap. The field dependence of $\kappa_0/T$ is similar to that of its sister
compound CsFe$_2$As$_2$ with comparable residual resistivity $\rho_0$, and lies
between the dirty and clean KFe$_2$As$_2$. These results suggest that the
(K,Rb,Cs)Fe$_2$As$_2$ serial superconductors have a common nodal gap structure.",1403.0191v3
2014-03-02,Nodeless superconducting gaps in Ca$_{10}$(Pt$_{4-δ}$As$_8$)((Fe$_{1-x}$Pt$_{x}$)$_2$As$_2$)$_5$ probed by quasiparticle heat transport,"The in-plane thermal conductivity of iron-based superconductor
Ca$_{10}$(Pt$_{4-\delta}$As$_8$)((Fe$_{1-x}$Pt$_{x}$)$_2$As$_2$)$_5$ single
crystal (``10-4-8"", $T_c$ = 22 K) was measured down to 80 mK. In zero field,
the residual linear term $\kappa_0/T$ is negligible, suggesting nodeless
superconducting gaps in this multiband compound. In magnetic fields,
$\kappa_0/T$ increases rapidly, which mimics those of multiband superconductor
NbSe$_2$ and LuNi$_2$B$_2$C with highly anisotropic gap. Such a field
dependence of $\kappa_0/T$ is an evidence for multiple superconducting gaps
with quite different magnitudes or highly anisotropic gap. Comparing with the
London penetration depth results of
Ca$_{10}$(Pt$_3$As$_8$)((Fe$_{1-x}$Pt$_{x}$)$_2$As$_2$)$_5$ (``10-3-8"")
compound, the 10-4-8 and 10-3-8 compounds may have similar superconducting gap
structure.",1403.0194v1
2014-03-04,Tunnel diode oscillator measurements of the upper critical magnetic field of FeTe0:5Se0:5,"Temperature dependence of the upper critical magnetic field (Hc2) of single
crystalline FeTe0.5Se0.5 (Tc = 14.5 K) have been determined by tunnel diode
oscillator-based measurements in magnetic fields of up to 55 T and temperatures
down to 1.6 K. The Werthamer-Helfand-Hohenberg model accounts for the data for
magnetic field applied both parallel (H || ab) and perpendicular (H || c) to
the iron conducting plane, in line with a single band superconductivity.
Whereas Pauli pair breaking is negligible for H || c, Pauli contribution is
evidenced for H || ab with Maki parameter alpha= 1.4, corresponding to Pauli
field HP = 79 T. As a result, the Hc2 anisotropy (= Habc2 /Hcc2) which is
already rather small at Tc (gamma = 1.6) further decreases as the temperature
decreases and becomes smaller than 1 at liquid helium temperatures.",1403.0844v1
2014-03-05,Design and demonstration of a quasi-monoenergetic neutron source,"The design of a neutron source capable of producing 24 and 70 keV neutron
beams with narrow energy spread is presented. The source exploits
near-threshold kinematics of the $^{7}$Li(p,n)$^{7}$Be reaction while taking
advantage of the interference `notches' found in the scattering cross-sections
of iron. The design was implemented and characterized at the Center for
Accelerator Mass Spectrometry at Lawrence Livermore National Laboratory.
Alternative filters such as vanadium and manganese are also explored and the
possibility of studying the response of different materials to low-energy
nuclear recoils using the resultant neutron beams is discussed.",1403.1285v2
2014-03-08,"High critical-current density with less anisotropy in BaFe2(As,P)2 epitaxial thin films: Effect of intentionally grown c-axis vortex-pinning centers","We report herein a high and isotropic critical-current density Jc for
BaFe2(As,P)2 epitaxial films. The isotropy of Jc with respect to the
magnetic-field direction was improved significantly by decreasing the film
growth rate to 2.2 {\AA}/s. The low growth rate served to preferentially align
dislocations along the c-axis, which work well as c-axis vortex-pinning
centers. Because of the intentional introduction of effective pinning, the
absolute Jc at 9 T was larger than that obtained for other iron-based
superconductors and conventional alloy superconducting wires.",1403.1947v2
2014-03-08,Challenges in nucleosynthesis of trans-iron elements,"Nucleosynthesis beyond Fe poses additional challenges not encountered when
studying astrophysical processes involving light nuclei. Astrophysical sites
and conditions are not well known for some of the processes involved. On the
nuclear physics side, different approaches are required, both in theory and
experiment. The main differences and most important considerations are
presented for a selection of nucleosynthesis processes and reactions,
specifically the $s$-, $r$-, $\gamma$-, and $\nu p$-processes. Among the
discussed issues are uncertainties in sites and production conditions, the
difference between laboratory and stellar rates, reaction mechanisms, important
transitions, thermal population of excited states, and uncertainty estimates
for stellar rates. The utility and limitations of indirect experimental
approaches are also addressed. The presentation should not be viewed as
confining the discussed problems to the specific processes. The intention is to
generally introduce the concepts and possible pitfalls along with some
examples. Similar problems may apply to further astrophysical processes
involving nuclei from the Fe region upward and/or at high plasma temperatures.
The framework and strategies presented here are intended to aid the conception
of future experimental and theoretical approaches.",1403.2015v1
2014-03-11,Chemical abundance analysis of symbiotic giants. I. RW Hya and SY Mus,"The study of symbiotic systems is of considerable importance in our
understanding of binary system stellar evolution in systems where mass loss or
transfer takes place. Elemental abundances are of special significance since
they can be used to track mass exchange. However, there are few symbiotic
giants for which the abundances are fairly well determined. Here we present for
the first time a detailed analysis of the chemical composition for the giants
in the RW Hya and SY Mus systems. The analysis is based on high resolution (R
50000), high S/N, near-IR spectra. Spectrum synthesis employing standard LTE
analysis and atmosphere models was used to obtain photospheric abundances of
CNO and elements around the iron peak (Sc, Ti, Fe, and Ni). Our analysis
reveals a significantly sub-solar metallicity, [Fe/H]-0.75}, for the RW Hya
giant confirming its membership in the Galactic halo population and a
near-solar metallicity for the SY Mus giant. The very low 12C/13C isotopic
ratios, 6-10, derived for both objects indicate that the giants have
experienced the first dredge-up",1403.2659v1
2014-03-22,Neutron Reactions in Astrophysics,"The quest for the origin of matter in the Universe had been the subject of
philosophical and theological debates over the history of mankind, but
quantitative answers could be found only by the scientific achievements of the
last century. A first important step on this way was the development of
spectral analysis by Kirchhoff and Bunsen in the middle of the 19$^{\rm th}$
century, which provided first insight in the chemical composition of the sun
and the stars. The energy source of the stars and the related processes of
nucleosynthesis, however, could be revealed only with the discoveries of
nuclear physics. A final breakthrough came eventually with the compilation of
elemental and isotopic abundances in the solar system, which are reflecting the
various nucleosynthetic processes in detail.
  This review is focusing on the mass region above iron, where the formation of
the elements is dominated by neutron capture, mainly in the slow ($s$) and
rapid ($r$) processes. Following a brief historic account and a sketch of the
relevant astrophysical models, emphasis is put on the nuclear physics input,
where status and perspectives of experimental approaches are presented in some
detail, complemented by the indispensable role of theory.",1403.5670v1
2014-03-24,Dust formation in macronovae,"We examine dust formation in macronovae (as known as kilonovae), which are
the bright ejecta of neutron star binary mergers and one of the leading sites
of r-process nucleosynthesis. We find that dust grains of r-process elements
are difficult to form because of the low number density of the r-process atoms,
while carbon or elements lighter than irons can condense into dust if they are
abundant, in light of the first macronova candidate associated with GRB
130603B. Dust grains absorb emission from ejecta with opacity even greater than
that of the r-process elements, and re-emit photons at infrared wavelengths.
Such dust emission can potentially account for the macronova without r-process
nucleosynthesis as an alternative model. This dust scenario predicts a more
featureless spectrum than the r-process model and day-scale
optical-to-ultraviolet emission.",1403.5872v2
2014-03-26,Photoconductivity and photo-detection response of multiferroic bismuth iron oxide,"We report visible light detection with in-plane BiFeO3 (BFO) thin films grown
on pre-patterned inter-digital electrodes. In-plane configured BFO film
displayed photocurrents with a 40:1 photo-to-dark-current ratio and improved
photo-sensing ability for >15000 s (4 hrs) under small bias voltage (42V).
Nearly sixty percent of the photo-induced charge carriers decay in 1.0 s and
follow a double-exponential decay model. At 373 K the effect of light does not
significantly increase the dark current, probably due to reduced mobility.
Sub-bandgap weak monochromatic light (1 mw/cm2) shows one fold increase in
photo-charge carriers.",1403.6748v1
2014-03-26,Simulating a two-dimensional frustrated spin system with fermionic resonating-valence-bond states,"The frustrated Heisenberg $J_{1}-J_{2}$ model on a square lattice is
numerically investigated by variational Monte Carlo simulations. We propose a
antiferromagnetic fermion resonating-valence-bond (AF-fRVB) state that has
ability to examine the entire phase diagram in the $J_{1}-J_{2}$ model. Two
phase transition points, the second order around $J_{2}/J_{1}=0.45$ and the
first order around $J_{2}/J_{1}=0.6$, can be extracted more clearly than the
conventional bosonic RVB state. At the maximally frustrated point
($J_{2}/J_{1}=0.5$), the AF-fRVB state shows the variational ground-state
energy in the thermodynamic limit very close to the one estimated by the
projected entangled pair state at the largest bond dimension available. On the
other hand, in the frustrated regime $0.4\lesssim J_{2}/J_{1}\leq0.5$, AF-fRVB
states with $s_{+-}$ (using the terminology in the field of iron-based
superconductors) and $d_{xy}$ pairing symmetries are degenerate in the
thermodynamic limit, implying the existence of gapless Dirac excitations in the
spinon spectrum.",1403.6879v1
2014-03-30,Scattering of electron vortex beams on a magnetic crystal: towards atomic resolution magnetic measurements,"Use of electron vortex beams (EVB), that is convergent electron beams
carrying an orbital angular momentum (OAM), is a novel development in the field
of transmission electron microscopy. They should allow measurement of
element-specific magnetic properties of thin crystals using electron magnetic
circular dichroism (EMCD)---a phenomenon similar to the x-ray magnetic circular
dichroism. Recently it has been shown computationally that EVBs can detect
magnetic signal in a scanning mode only at atomic resolution. In this follow-up
work we explore in detail the elastic and inelastic scattering properties of
EVBs on crystals, as a function of beam diameter, initial OAM, acceleration
voltage and beam displacement from an atomic column. We suggest that for a 10
nm layer of bcc iron oriented along (001) zone axis an optimal configuration
for a detection of EMCD is an EVB with OAM of $1\hbar$ and a diameter of 1.6
\AA, acceleration voltage 200 keV and an annular detector with inner and outer
diameters of $G$ and $5G$, respectively, where $\mathbf{G}=(100)$.",1403.7730v1
2014-03-31,Strain effects on electronic structure and superconductivity in the iron telluride,"The influence of tensile strain in the ab-plane on crystal and electronic
structure of FeTe has been studied ab initio. In superconducting FeSe the Fermi
surface nesting with a vector q~(0.5,0.5)(2\pi /a) is believed to be crucial
for rising superconductivity mediated by spin-fluctuations. The results
presented here indicate that tensile-strained FeTe also exhibits such
conditions. Furthermore, the Fermi surface changes, related to the increase of
the lattice parameter a of this telluride, are opposite to analogous effects
reported for FeSe. Since a recently reported transition from the double-stripe
to the single-stripe magnetic order in FeTe under tensile strain in the
ab-plane is associated with an occurence of superconductivity in corresponding
thin films, these findings allow for drawing a consistent picture of
superconductivity in FeSe(1-x)Te(x) systems, in general.",1403.8005v2
2014-04-02,Spurious peaks arising from multiple scattering events involving cryostat walls in inelastic neutron scattering,"Well defined peaks with energies of about 18 meV have been observed in a
variety of inelastic neutron scattering experiments on single crystals as well
as on powders of iron-based superconductors and their parent compounds using
either the triple-axis or the time-of-flight technique. They can easily be
mistaken for signatures of real excitations. We have found that they are due to
multiple scattering events involving primarily walls of the sample environment.
Hence, they are particularly troublesome in experiments using very small
samples as have been used with recently developed high intensity neutron
spectrometers. It will be discussed what needs to be done to reduce the
unwanted scattering to a minimum.",1404.0522v2
2014-04-03,Charge Transfer Kinetics at the Solid-Solid Interface in Porous Electrodes,"Interfacial charge transfer is widely assumed to obey Butler-Volmer kinetics.
For certain liquid-solid interfaces, Marcus-Hush-Chidsey theory is more
accurate and predictive, but it has not been applied to porous electrodes. Here
we report a simple method to extract the charge transfer rates in carbon-coated
LiFePO4 porous electrodes from chronoamperometry experiments, obtaining curved
Tafel plots that contradict the Butler-Volmer equation but fit the
Marcus-Hush-Chidsey prediction over a range of temperatures. The fitted
reorganization energy matches the Born solvation energy for electron transfer
from carbon to the iron redox site. The kinetics are thus limited by electron
transfer at the solid-solid (carbon-LixFePO4) interface, rather than by ion
transfer at the liquid-solid interface, as previously assumed. The proposed
experimental method generalizes Chidsey's method for phase-transforming
particles and porous electrodes, and the results show the need to incorporate
Marcus kinetics in modeling batteries and other electrochemical systems.",1404.0859v1
2014-04-03,Fermi-Surface Reconstruction and Complex Phase Equilibria in CaFe$_{2}$As$_{2}$,"Fermi-surface topology governs the relationship between magnetism and
superconductivity in iron-based materials. Using low-temperature transport,
angle-resolved photoemission, and x-ray diffraction we show unambiguous
evidence of large Fermi surface reconstruction in CaFe$_{2}$As$_{2}$ at
magnetic spin-density-wave and nonmagnetic collapsed-tetragonal ($cT$)
transitions. For the $cT$ transition, the change in the Fermi surface topology
has a different character with no contribution from the hole part of the Fermi
surface. In addition, the results suggest that the pressure effect in
CaFe$_{2}$As$_{2}$ is mainly leading to a rigid-band-like change of the valence
electronic structure. We discuss these results and their implications for
magnetism and superconductivity in this material.",1404.1095v1
2014-04-07,Fingerprints of Galactic Loop I on the Cosmic Microwave Background,"We investigate possible imprints of galactic foreground structures such as
the ""radio loops"" in the derived maps of the cosmic microwave background.
Surprisingly there is evidence for these not only at radio frequencies through
their synchrotron radiation, but also at microwave frequencies where emission
by dust dominates. This suggests the mechanism is magnetic dipole radiation
from dust grains enriched by metallic iron or ferrimagnetic materials. This new
foreground we have identified is present at high galactic latitudes, and
potentially dominates over the expected $B$-mode polarization signal due to
primordial gravitational waves from inflation.",1404.1899v3
2014-04-09,Zinc abundances of planetary nebulae,"Zinc is a useful surrogate element for measuring Fe/H as, unlike iron, it is
not depleted in the gas phase media. Zn/H and O/Zn ratios have been derived
using the [Zn IV] emission line at 3.625um for a sample of nine Galactic
planetary nebulae, seven of which are based upon new observations using the
VLT. Based on photoionization models, O/O++ is the most reliable ionisation
correction factor for zinc that can readily be determined from optical emission
lines, with an estimated accuracy of 10% or better for all targets in our
sample. The majority of the sample is found to be sub-solar in [Zn/H]. [O/Zn]
in half of the sample is found to be consistent with Solar within
uncertainties, whereas the remaining half are enhanced in [O/Zn]. [Zn/H] and
[O/Zn] as functions of Galactocentric distance have been investigated and there
is little evidence to support a trend in either case.",1404.2524v1
2014-04-10,Synthesis and physical properties of Ca1-xRExFeAs2 with RE = La ~ Gd,"Synthesis of a series of layered iron arsenides Ca1-xRExFeAs2 (112) was
attempted by heating at 1000 C under a high-pressure of 2 GPa. The 112 phase
successfully forms with RE = La, Ce, Nd, Sm, Eu and Gd, while Tb, Dy and Ho
substituted and RE free samples does not contain the 112 phase. The Ce, Nd, Sm,
Eu and Gd doped Ca1-xRExFeAs2 are new compounds. All of them exhibit
superconducting transition except for the Ce doped sample. The behaviour of the
critical temperature, with the RE ionic radii have been investigated.",1404.2738v1
2014-04-24,Superconductivity driven by the screening of long-distance Coulomb interaction,"The pair-fluctuation contribution reduces the electrostatic screening length
in superconductivity as compared to the normal state. When a conductor
possesses a static background charge distribution, superconductivity arises
even in the absence of an explicit pairing interaction, such that the Coulomb
repulsion is reduced and the total energy is lowered. We demonstrate that the
superconducting gap increases with increased background charge at first, after
which the mixing of the Higgs and plasma modes suppresses superconductivity in
the pseudogap phase. This indicates that the mechanism may be relevant to the
cuprates and iron pnictides. When the background charge is identified with the
incoherent component of optical conductivity in the cuprates, our results
reproduce the shape, size and position of the superconducting dome with zero
free parameters. A superconducting critical temperature of about 1000 K is
possible in ion-doped conductors.",1404.6292v1
2014-04-25,An all-electrical torque differential magnetometer operating under ambient conditions,"An all-electrical torque differential magnetometry (also known as cantilever
magnetometry) setup employing piezoelectric quartz tuning forks is
demonstrated. The magnetometer can be operated under ambient conditions as well
as low temperatures and pressures. It extends the allowed specimen mass range
up to several 10 $\mu$g without any significant reduction in the sensitivity.
Operation under ambient conditions and a simple all-electrical design of the
magnetometer should allow for an easy integration with other experimental
setups. The uniaxial magnetic anisotropy of a 25 $\mu$m diameter iron wire,
measured under ambient conditions with a high signal to noise ratio, was found
to be in good agreement with its literature value. Further applications of the
technique are discussed.",1404.6341v2
2014-05-02,Spectral line broadening in magnetized black holes,"We consider weakly magnetized non-rotating black holes. In the presence of a
regular magnetic field the motion of charged particles in the vicinity of a
black hole is modified. As a result, the position of the innermost stable
circular orbit (ISCO) becomes closer to the horizon. When the Lorentz force is
repulsive (directed from the black hole) the ISCO radius can reach the
gravitational radius. In the process of accretion charged particles (ions) of
the accreting matter can be accumulated near their ISCO, while neutral
particles fall down to the black hole after they reach $6M$ radius. The sharp
spectral line Fe K$\alpha$, emitted by iron ions at such orbits, is broadened
when the emission is registered by a distant observer. In this paper we study
this broadening effect and discuss how one can extract information concerning
the strength of the magnetic field from the observed spectrum.",1405.0510v3
2014-05-06,Evolution from incoherent to coherent electronic states and its implications to superconductivity in FeTe1-xSex,"We have performed systematic angle-resolved photoemission spectroscopy
(ARPES) of iron-chalcogenide superconductor FeTe1-xSex to elucidate the
electronic states relevant to the superconductivity. While the Fermi-surface
shape is nearly independent of x, we found that the ARPES spectral line shape
shows prominent x dependence. A broad ARPES spectrum characterized by a small
quasiparticle weight at x = 0, indicative of incoherent electronic states,
becomes progressively sharper with increasing x, and a well-defined
quasiparticle peak appears around x = 0.45 where bulk superconductivity is
realized. The present result suggests the evolution from incoherent to coherent
electronic states and its close relationship to the emergence of
superconductivity.",1405.1172v1
2014-05-05,Mathematical Modeling on Open Limestone Channel,"Acid mine drainage (AMD) is the outflow of acidic water from metal mines or
coal mines. When exposed to air and water, metal sulfides from the deposits of
the mines are oxidized and produce acid, metal ions and sulfate, which lower
the pH value of the water. An open limestone channel (OLC) is a passive and low
cost way to neutralize AMD. The dissolution of calcium into the water increases
the pH value of the solution. A differential equation model is numerically
solved to predict the variation of concentration of each species in the OLC
solution. The diffusion of Calcium due to iron precipitates is modeled by a
linear equation. The results give the variation of pH value and the
concentration of Calcium.",1405.1338v1
2014-05-08,Effect of nominal substitution of transition metals for excess Fe in Fe_{1+x}Se superconductor,"Taking cue from the increase in the superconducting transition temperature
(Tc) of Fe1+xSe via nominal (2 wt%) substitution of Cr instead of excess Fe, we
have now extended our study with nominal substitution (<=5 wt%) with other
transition metals (Ni, Co, Fe, Mn, Cr, V and Ti) in place of excess iron. The
Tc is found to increase (maximum ~11 K) or get suppressed depending on the
substituted transition metal. Our studies indicate that the superconducting
transition temperature depends on various parameters like the ionic size of the
transition metal, its magnetic moment as well as the amount of hexagonal phase
present as impurity.",1405.2050v3
2014-05-13,Magnetism and superconductivity in Sr$_2$VFeAsO$_3$ revealed by $^{75}$As- and $^{51}$V-NMR under elevated pressures,"We report $^{75}$As- and $^{51}$V-nuclear magnetic resonance (NMR)
measurements on the iron-based superconductor Sr$_2$VFeAsO$_3$ with alternating
stacks structure. We find that the $^{75}$As nuclear spin-spin relaxation rate
($1/T_2$) shows a pronounced peak at $T_N$ = 165 K, below which the resonance
peak shifts to a higher frequency due to the onset of an internal magnetic
field. The $^{51}$V spectrum does not shift, but is broadened below $T_N$. We
conclude that the Fe electrons oder antiferromagnetically below $T_N$ with a
magnetic moment $m_{Fe}$ $\sim$ 0.4 $\mu_B$. Application of external pressure
up to 2.4 GPa reduces $T_N$ in a rate of $-$40 K/GPa, and enhances the
superconducting transition temperature $T_c$ in a rate of 2 K/GPa. The
pressure-temperature phase diagram for Sr$_2$VFeAsO$_3$ shows that
superconductivity coexists with antiferromagnetism over a wide pressure range
with an unprecedented high $T_c$ up to 36.5 K.",1405.3048v1
2014-05-15,Nuclear Target Cross Section Ratios at MINERvA,"Measurements of $\nu_{\mu}$ inclusive charged-current cross section ratios on
carbon, iron, and lead relative to scintillator are presented. Data for the
analysis were collected by the fine-grained MINERvA detector in the NuMI
beamline at Fermilab. This is the first direct measurement of nuclear
dependence in neutrino scattering. The ratios show a depletion at low Bjorken
$x$ and enhancement at large $x$, both of which increase with the nucleon
number of the target. The data exhibit trends not found in GENIE, a standard
neutrino-nucleus event generator, or alternative models of nuclear modification
to inelastic structure functions.",1405.3960v1
2014-05-19,Neutron Scattering Measurements of Spatially Anisotropic Magnetic Exchange Interactions in Semiconducting K0.85Fe1.54Se2 (TN=280 K),"We use neutron scattering to study the spin excitations associated with the
stripe antiferromagnetic (AFM) order in semiconducting
K$_{0.85}$Fe$_{1.54}$Se$_2$ ($T_N$=$280$ K). We show that the spin wave spectra
can be accurately described by an effective Heisenberg Hamiltonian with highly
anisotropic in-plane couplings at $T$= $5$ K. At high temperature ($T$= $300$
K) above $T_N$, short range magnetic correlation with anisotropic correlation
lengths are observed. Our results suggest that, despite the dramatic difference
in the Fermi surface topology, the in-plane anisotropic magnetic couplings are
a fundamental property of the iron based compounds; this implies that their
antiferromagnetism may originate from local strong correlation effects rather
than weak coupling Fermi surface nesting.",1405.4737v1
2014-05-19,Multiferroic Iron Oxide Thin Films at Room-Temperature,"In spite of being highly relevant for the development of a new generation of
information storage devices, not many single-phase materials displaying
magnetic and ferroelectric orders above room temperature are known. Moreover,
these uncommon materials typically display insignificant values of the remanent
moment in one of the ferroic orders or are complex multicomponent oxides which
will be very challenging to integrate in devices. Here we report on the
strategy to stabilize the metastable epsilon-Fe2O3 in thin film form, and we
show that besides its already known ferrimagnetic nature, the films are also
ferroelectric at 300 K with a remanent polarization of 1 microC/cm2. The film
polarization shows long retention times and can be switched under small applied
voltages. These characteristics make of epsilon-Fe2O3 the first single-ion
transition-metal oxide which is ferro(ferri)magnetic and ferroelectric at room
temperature. The simple composition of this new multiferroic oxide and the
discovery of a robust path for its thin film growth may boost the exploitation
of epsilon-Fe2O3 in novel devices.",1405.4909v1
2014-05-22,Layered water Cherenkov detector for the study of ultra high energy cosmic rays,"We present a new design for the water Cherenkov detectors that are in use in
various cosmic ray observatories. This novel design can provide a significant
improvement in the independent measurement of the muonic and electromagnetic
component of extensive air showers. From such multi-component data an event by
event classification of the primary cosmic ray mass becomes possible. According
to popular hadronic interaction models, such as EPOS-LHC or QGSJetII-04, the
discriminating power between iron and hydrogen primaries reaches Fisher values
of $\sim$ 2 or above for energies in excess of $10^{19}$ eV with a detector
array layout similar to that of the Pierre Auger Observatory.",1405.5699v1
2014-05-25,Theory of Point Contact Spectroscopy in Correlated Materials,"We develop a microscopic theory for the point-contact conductance between a
metalic electrode and a strongly correlated material using the non-equilibrium
Schwinger-Kadanoff-Baym-Keldysh formalism. We explicitly show that in the
classical limit, contact size shorter than the scattering length of the system,
the microscopic model can be reduced to an effective model with transfer matrix
elements that conserve in-plane momentum. We find that the conductance $dI/dV$
is proportional to the {\it effective density of states}, that is, the
integrated single-particle spectral function $A(\omega=eV)$ over the whole
Brillouin zone. From this conclusion, we are able to establish the conditions
under which a non-Fermi liquid metal exhibits a zero-bias peak in the
conductance. This finding is discussed in the context of recent point-contact
spectroscopy on the iron pnictides and chalcogenides which has exhibited a
zero-bias conductance peak.",1405.6357v2
2014-05-25,CaFeAs$_2$: a Staggered Intercalation of Quantum Spin Hall and High Temperature Superconductivity,"We predict that CaFeAs$_2$, a newly discovered iron-based high temperature
(T$_c$) superconductor, is a staggered intercalation compound that integrates
topological quantum spin hall (QSH) and superconductivity (SC). CaFeAs$_2$ has
a structure with staggered CaAs and FeAs layers. While the FeAs layers are
known to be responsible for high T$_c$ superconductivity, we show that with
spin orbital coupling each CaAs layer is a $Z_{2}$ topologically nontrivial
two-dimensional QSH insulator and the bulk is a 3-dimensional weak topological
insulator. In the superconducting state, the edge states in the CaAs layer are
natural 1D topological superconductors. The staggered intercalation of QSH and
SC provides us an unique opportunity to realize and explore novel physics, such
as Majorana modes and Majorana Fermions chains.",1405.6401v2
2014-05-28,Contactless measurement of nonlinear conductivity in the radio-frequency range,"We have developed a system for contactless measurement of nonlinear
conductivity in the radio-frequency band, and over a wide temperature range. A
non-resonant circuit is used to electrically excite the sample, and the induced
signal is detected by a resonant circuit whose natural frequency matches higher
harmonics of the excitation. A simple modification of the probe allows
non-resonant detection suitable for stronger signals. Two measurement
procedures are proposed that allow significant excitation power variation, up
to 150 W. The apparatus has been validated trough the measurement of the
nonlinear response at the superconducting transition of a high-Tc
superconductor, and the nematic transition of an iron pnictide.",1405.7282v1
2014-05-31,Point contact spectroscopy in the superconducting and normal state of $\mathrm{NaFe_{1-\textit{x}}Co_\textit{x}As}$,"We use point contact spectroscopy to probe the superconducting and normal
state properties of the iron-based superconductor
$\rm{NaFe_{1-\textit{x}}Co_{\textit{x}}As}$ with $\rm{\textit{x} = 0, 0.02,
0.06}$. Andreev spectra corresponding to multiple superconducting gaps are
detected in the superconducting phase. For $\rm{\textit{x} = 0.02}$, a broad
conductance enhancement around zero bias voltage is detected in both the normal
and the superconducting phase. Such a feature is not present in the
$\rm{\textit{x} = 0.06}$ samples. We suspect that this enhancement is caused by
orbital fluctuations, as previously detected in underdoped
$\rm{Ba(Fe_{1-\textit{x}}Co_\textit{x})_2As_2}$ (Phys. Rev. B 85, 214515
(2012)). Occasionally, the superconducting phase shows a distinct asymmetric
conductance feature instead of Andreev reflection. We discuss the possible
origins of this feature. NaFeAs (the parent compound) grown by two different
techniques is probed. Melt-grown NaFeAs shows a normal state conductance
enhancement. On the other hand, at low temperatures, flux-grown NaFeAs shows a
sharp dip in the conductance at zero bias voltage. The compounds are very
reactive in air and the different spectra are likely a reflection of their
different oxidation and purity levels.",1406.0038v1
2014-06-01,Hydrogen-Activation Mechanism of [Fe] Hydrogenase Revealed by Multi-Scale Modeling,"When investigating the mode of hydrogen activation by [Fe] hydrogenases, not
only the chemical reactivity at the active site is of importance but also the
large-scale conformational change between the so-called open and closed
conformations, which leads to a special spatial arrangement of substrate and
iron cofactor. To study H2 activation, a complete model of the solvated and
cofactor-bound enzyme in complex with the substrate methenyl-H4MPT+ was
constructed. Both the closed and open conformations were simulated with
classical molecular dynamics on the 100 ns time scale.
Quantum-mechanics/molecular-mechanics calculations on snapshots then revealed
the features of the active site that enable the facile H2 cleavage. The
hydroxyl group of the pyridinol ligand can easily be deprotonated. With the
deprotonated hydroxyl group and the structural arrangement in the closed
conformation, H2 coordinated to the Fe center is subject to an ionic and
orbital push-pull effect and can be rapidly cleaved with a concerted hydride
transfer to methenyl-H4MPT+. An intermediary hydride species is not formed.",1406.0166v1
2014-06-04,Observation of strong electron pairing on bands without Fermi surfaces in LiFe1-xCoxAs,"In conventional BCS superconductors, the quantum condensation of
superconducting electron pairs is understood as a Fermi surface (FS)
instability, in which the low-energy electrons are paired by attractive
interactions. Whether this explanation is still valid in high-Tc
superconductors such as cuprates and iron-based superconductors remains an open
question. In particular, a fundamentally different picture of the electron
pairs, which are believed to be formed locally by repulsive interactions, may
prevail. Here we report a high-resolution angle-resolved photoemission
spectroscopy study on LiFe1-xCoxAs. We reveal a large and robust
superconducting (SC) gap on a band sinking below the Fermi energy upon Co
substitution. The observed FS-free SC order is also the largest over the
momentum space, which rules out a proximity effect origin and indicates that
the SC order parameter is not tied to the FS as a result of a FS instability.",1406.0983v2
2014-06-04,Anomalous Nernst and Hall effects in magnetized platinum and palladium,"We study the anomalous Nernst effect (ANE) and anomalous Hall effect (AHE) in
proximity-induced ferromagnetic palladium and platinum which is widely used in
spintronics, within the Berry phase formalism based on the relativistic band
structure calculations. We find that both the anomalous Hall ($\sigma_{xy}^A$)
and Nernst ($\alpha_{xy}^A$) conductivities can be related to the spin Hall
conductivity ($\sigma_{xy}^S$) and band exchange-splitting ($\Delta_{ex}$) by
relations $\sigma_{xy}^A =\Delta_{ex}\frac{e}{\hbar}\sigma_{xy}^S(E_F)'$ and
$\alpha_{xy}^A =
-\frac{\pi^2}{3}\frac{k_B^2T\Delta_{ex}}{\hbar}\sigma_{xy}^s(\mu)""$,
respectively. In particular, these relations would predict that the
$\sigma_{xy}^A$ in the magnetized Pt (Pd) would be positive (negative) since
the $\sigma_{xy}^S(E_F)'$ is positive (negative). Furthermore, both
$\sigma_{xy}^A$ and $\alpha_{xy}^A$ are approximately proportional to the
induced spin magnetic moment ($m_s$) because the $\Delta_{ex}$ is a linear
function of $m_s$. Using the reported $m_s$ in the magnetized Pt and Pd, we
predict that the intrinsic anomalous Nernst conductivity (ANC) in the magnetic
platinum and palladium would be gigantic, being up to ten times larger than,
e.g., iron, while the intrinsic anomalous Hall conductivity (AHC) would also be
significant.",1406.1029v1
2014-06-09,Magnetic and orbital instabilities in a lattice of SU(4) organometallic Kondo complexes,"Motivated by experiments of scanning tunneling spectroscopy (STS) on
self-assembled networks of iron(II)-phtalocyanine (FePc) molecules deposited on
a clean Au(111) surface [FePc/Au(111)] and its explanation in terms of the
extension of the impurity SU(4) Anderson model to the lattice in the Kondo
regime, we study the competition between the Kondo effect and the
magneto-orbital interactions occurring in FePc/Au(111). We explore the quantum
phases and critical points of the model using a large-$N$ slave-boson method in
the mean-field approximation. The SU(4) symmetry in the impurity appears as a
combination of the usual spin and an orbital pseudospin arising from the
degenerate $3d_{xz}$ and $3d_{yz}$ orbitals in the Fe atom. In the case of the
lattice, our results show that the additional orbital degrees of freedom
crucially modify the low-temperature phase diagram, and induce new types of
orbital interactions among the Fe atoms, which can potentially stabilize exotic
quantum phases with magnetic and orbital order. The dominant instability
corresponds to spin ferromagnetic and orbital antiferromagnetic order.",1406.2347v1
2014-06-11,ARPES experiment in fermiology of quasi-2D metals (Review Article),"Angle resolved photoemission spectroscopy (ARPES) enables direct observation
of the Fermi surface and underlying electronic structure of crystals---the
basic concepts to describe all the electronic properties of solids and to
understand the key electronic interactions involved. The method is the most
effective to study quasi-2D metals, to which the subjects of almost all hot
problems in modern condensed matter physics have happened to belong. This has
forced incredibly the development of the ARPES method which we face now. The
aim of this paper is to introduce to the reader the state-of-the-art ARPES,
reviewing the results of its application to such topical problems as high
temperature superconductivity in cuprates and iron based superconductors, and
electronic ordering in the transition metal dichalcogenides and manganites.",1406.2948v1
2014-06-14,Critical Behavior of the SDW Transition in Underdoped Ba(Fe1-xCox)2As2 (x <=0.05): 75As NMR Investigation,"We investigate the nature of the SDW (Spin Density Wave) transition in the
underdoped regime of an iron-based high Tc superconductor Ba(Fe1-xCox)2As2 by
75As NMR, with primary focus on a composition with x = 0.02 (T_SDW = 99 K).We
demonstrate that critical slowing down toward the three dimensional SDW
transition sets in at the tetragonal to orthorhombic structural phase
transition, Ts = 105 K, suggesting strong interplay between structural
distortion and spin correlations. In the critical regime between Ts and T_SDW,
the dynamical structure factor of electron spins S(q,Wn) measured with the
longitudinal NMR relaxation rate 1/T1 exhibits a divergent behavior obeying a
power law, 1/T1~S(q, Wn)~(T/T_SDW-1)^a with the critical exponent a ~ 0.33.",1406.3734v1
2014-06-16,Search for Magnetic Monopole using ICAL at INO,"Sub-relativistic magnetic monopoles are predicted from the GUT era by theory.
To date there have been no confirmed observations of such exotic particles. The
Iron CALorimeter (ICAL) at India-based Neutrino Observatory (INO) aims to
measure the neutrino oscillation parameters precisely. As it is a tracking
detector there is also the possibility of detecting magnetic monopoles in the
sub-relativistic region. Using ICAL the magnetic monopole event is
characterised by the large time intervals of upto 30 microsec between the
signals in successive layers of the active detectors. The aim of this study is
to identify the sensitivity of ICAL for a particle carrying magnetic charge in
the mass range from 10^{5} to 10^{17} GeV with beta ranging from 10^{-5} to 9 x
10^{-1} for ICAL at INO. A similar study has also been carried out for the ICAL
prototype which will be placed overground. Due to the rock cover of
approximately 1.3 km, ICAL at INO will not be able to place bounds on the flux
of the lower mass magnetic monopoles. This mass region is however addressed by
the prototype ICAL.",1406.3938v1
2014-06-16,An air-cooled Litz wire coil for measuring the high frequency hysteresis loops of magnetic samples : a useful setup for magnetic hyperthermia applications,"A low-cost and simple setup for measuring the high-frequency hysteresis loops
of magnetic samples is described. An AMF in the range 6-100 kHz with amplitude
up to 80 mT is produced by a Litz wire coil. The latter is air-cooled using a
forced-air approach so no water flow is required to run the setup.
High-frequency hysteresis loops are measured using a system of pick-up coils
and numerical integration of signals. Reproducible measurements are obtained in
the frequency range of 6-56 kHz. Measurement examples on ferrite cylinders and
on iron oxide nanoparticle ferrofluids are shown. Comparison with other
measurement methods of the hysteresis loop area (complex susceptibility,
quasi-static hysteresis loops and calorific measurements) is provided and shows
the coherency of the results obtained with this setup. This setup is well
adapted to the magnetic characterization of colloidal solutions of MNPs for
magnetic hyperthermia applications.",1406.4013v1
2014-06-16,Infrared dichroism of gold nanorods controlled using a magnetically addressable mesophase,"Gold nanorods have unique optical properties, which make them promising
candidates for building nano-structured materials using a ""bottom-up"" strategy.
We formulate stable bulk materials with anisotropic optical properties by
inserting gold and iron oxide nanorods within a lamellar mesophase.
Quantitative measurements of the order parameter by modelling the absorbance
spectra show that the medium is macroscopically aligned in a direction defined
by an external magnetic field. Under field, the system exhibits significant
absorption dichroism in the infrared range, at the position of the longitudinal
plasmon peak of the gold nanorods (about 1200 nm), indicating strong
confinement of these particles within the water layers of the lamellar phase.
This approach can yield soft and addressable optical elements.",1406.4014v1
2014-06-21,The Deaths of Very Massive Stars,"The theory underlying the evolution and death of stars heavier than 10 Msun
on the main sequence is reviewed with an emphasis upon stars much heavier than
30 Msun. These are stars that, in the absence of substantial mass loss, are
expected to either produce black holes when they die, or, for helium cores
heavier than about 35 Msun, encounter the pair instability. A wide variety of
outcomes is possible depending upon the initial composition of the star, its
rotation rate, and the physics used to model its evolution. These heavier stars
can produce some of the brightest supernovae in the universe, but also some of
the faintest. They can make gamma-ray bursts or collapse without a whimper.
Their nucleosynthesis can range from just CNO to a broad range of elements up
to the iron group. Though rare nowadays, they probably played a
disproportionate role in shaping the evolution of the universe following the
formation of its first stars.",1406.5657v1
2014-06-22,Variation of the X-ray non-thermal emission in the Arches cloud,"The origin of the iron fluorescent line at 6.4 keV from an extended region
surrounding the Arches cluster is debated and the non-variability of this
emission up to 2009 has favored the low-energy cosmic-ray origin over a
possible irradiation by hard X-rays. By probing the variability of the Arches
cloud non-thermal emission in the most recent years, including a deep
observation in 2012, we intend to discriminate between the two competing
scenarios. We perform a spectral fit of XMM-Newton observations collected from
2000 to 2013 in order to build the Arches cloud lightcurve corresponding to
both the neutral Fe Kalpha line and the X-ray continuum emissions. We reveal a
30% flux drop in 2012, detected with more than 4 sigma significance for both
components. This implies that a large fraction of the studied non-thermal
emission is due to the reflection of an X-ray transient source.",1406.5727v1
2014-06-22,Putnam looks at quantum mechanics (again and again),"Hilary Putnam (1965, 2005) has argued that from a realist perspective,
quantum mechanics stands in need of an interpretation. Ironically, this
hypothesis may appear vulnerable against arguments drawing on Putnam's own
work. Nancy Cartwright (2005) has urged that his 1962 essay on the meaning of
theoretical terms suggests that quantum mechanics needs no interpretation and
thus stands in tension with his claim of three years later. She furthermore
contends that this conflict should be resolved in favour of the earlier work,
as quantum mechanics, like all successful theories, does not need an
interpretation. The first part of this essay deflates both of these objections.
The second part addresses and evaluates Putnam's own assessments of the main
interpretative options available in 1965 and 2005. Although we may disagree on
some aspects, his pessimistic conclusion will come out largely unscathed, and,
in fact, enhanced. I will close by briefly stating the historical relevance of
this work.",1406.5737v1
2014-06-23,"Phonon Anomalies, Orbital-Ordering and Electronic Raman Scattering in iron-pnictide Ca(Fe0.97Co0.03)2As2: Temperature-dependent Raman Study","We report inelastic light scattering studies on Ca(Fe0.97Co0.03)2As2 in a
wide spectral range of 120-5200 cm-1 from 5K to 300K, covering the tetragonal
to orthorhombic structural transition as well as magnetic transition at Tsm ~
160K. The mode frequencies of two first-order Raman modes B1g and Eg, both
involving displacement of Fe atoms, show sharp increase below Tsm.
Concomitantly, the linewidths of all the first-order Raman modes show anomalous
broadening below Tsm, attributed to strong spin-phonon coupling. The high
frequency modes observed between 400-1200 cm-1 are attributed to the electronic
Raman scattering involving the crystal field levels of d-orbitals of Fe2+. The
splitting between xz and yz d-orbital levels is shown to be ~ 25 meV which
increases as temperature decreases below Tsm. A broad Raman band observed at ~
3200 cm-1 is assigned to two-magnon excitation of the itinerant Fe 3d
antiferromagnet.",1406.5844v1
2014-06-30,Interplay of magnetism and superconductivity in EuFe$_{2}$(As$_{1-x}$P$_{x}$)$_{2}$ single crystals probed by muon spin rotation and ${}^{57}$Fe Mössbauer spectroscopy,"We present our results of a local probe study on
EuFe$_{2}$(As$_{1-x}$P$_{x}$)$_{2}$ single crystals with $x$=0.13, 0.19 and
0.28 by means of muon spin rotation and ${}^{57}$Fe M\""ossbauer spectroscopy.
We focus our discussion on the sample with $x$=0.19 viz. at the optimal
substitution level, where bulk superconductivity ($T_{\text{SC}}=28$ K) sets in
above static europium order ($T^{\text{Eu}}=20$K) but well below the onset of
the iron antiferromagnetic (AFM) transition ($\sim$100 K). We find enhanced
spin dynamics in the Fe sublattice closely above $T_{\text{SC}}$ and propose
that these are related to enhanced Eu fluctuations due to the evident coupling
of both sublattices observed in our experiments.",1406.7715v1
2014-06-30,Theoretical Analysis of Bayesian Optimisation with Unknown Gaussian Process Hyper-Parameters,"Bayesian optimisation has gained great popularity as a tool for optimising
the parameters of machine learning algorithms and models. Somewhat ironically,
setting up the hyper-parameters of Bayesian optimisation methods is notoriously
hard. While reasonable practical solutions have been advanced, they can often
fail to find the best optima. Surprisingly, there is little theoretical
analysis of this crucial problem in the literature. To address this, we derive
a cumulative regret bound for Bayesian optimisation with Gaussian processes and
unknown kernel hyper-parameters in the stochastic setting. The bound, which
applies to the expected improvement acquisition function and sub-Gaussian
observation noise, provides us with guidelines on how to design hyper-parameter
estimation methods. A simple simulation demonstrates the importance of
following these guidelines.",1406.7758v1
2014-07-01,Emergent defect states as a source of resistivity anisotropy in the nematic phase of iron pnictides,"We consider the role of potential scatterers in the nematic phase of Fe-based
superconductors above the transition temperature to the (pi,0) magnetic state
but below the orthorhombic structural transition. The anisotropic spin
fluctuations in this region can be frozen by disorder, to create elongated
magnetic droplets whose anisotropy grows as the magnetic transition is
approached. Such states act as strong anisotropic defect potentials which
scatter with much higher probability perpendicular to their length than
parallel, although the actual crystal symmetry breaking is tiny. We calculate
the scattering potentials, relaxation rates, and conductivity in this region,
and show that such emergent defect states are essential for the transport
anisotropy observed in experiments.",1407.0117v1
2014-07-01,Anomalous ideal tensile strength of ferromagnetic Fe and Fe-rich alloys,"Within the same failure mode, iron has the lowest ideal tensile strength
among the transition metals crystallizing in the body-centered cubic structure.
Here, we demonstrate that this anomalously low strength of Fe originates partly
from magnetism and is reflected in unexpected alloying effects in dilute
Fe(\emph{M}) (\emph{M} = Al, V, Cr, Mn, Co, Ni) binaries. We employ the
structural energy difference and the magnetic pressure to disentangle the
magnetic effect on the ideal tensile strength from the chemical effect. We find
that the investigated solutes strongly alter the magnetic response of the Fe
host from the weak towards a stronger ferromagnetic behavior, which is
explained based on single-particle band energies.",1407.0289v1
2014-07-03,The electronic structure of Co-substituted $\textrm{Fe}\textrm{Se}$ superconductor probed by soft X-ray spectroscopy and density functional theory,"We study the crystalline and electronic properties of the
$\textrm{Fe}_{1-x}\textrm{Co}_x\textrm{Se}$ system ($x=0$, 0.25, 0.5, 0.75, and
1.0) using X-ray diffraction, X-ray spectroscopy and density functional theory.
We show that the introduction of Co $3d$ states in FeSe relaxes the bond
strengths and induces a structural transition from tetragonal to hexagonal
whose crossover takes place at $x\approx0.38$. This structural transition in
turn modifies the magnetic order which can be related to the spin state. Using
resonant inelastic X-ray spectroscopy we estimate the spin state of the system;
FeSe is found to be in a high spin state (S=2), but Fe is reduced to a low spin
state upon Co substitution of $x \le 0.25$, well below the structural
transition. Finally, we show evidence that FeSe is a moderately correlated
system but the introduction of Co into the host lattice weakens the correlation
strength for $x\ge0.25$. These novel findings are important to unravel the
mechanisms responsible for the superconducting state in iron-chalcogenide
superconductors.",1407.0746v1
2014-07-03,"A Tale of Three Galaxies: Anomalous Dust Properties in IRASF10398+1455, IRASF21013-0739 and SDSSJ0808+3948","On a galactic scale the 9.7um silicate emission is usually only seen in type
1 active galactic nuclei (AGNs). They usually also display a flat emission
continuum at ~5--8um and the absence of polycyclic aromatic hydrocarbon (PAH)
emission bands. In contrast, starburst galaxies, luminous infrared (IR)
galaxies (LIRGs), and ultraluminous IR galaxies (ULIRGs) exhibit a red 5--8um
emission continuum, strong 10um and 18um silicate absorption features, and
strong PAH emission bands. Here we report the detection of anomalous dust
properties by Spitzer/Infrared Spectrograph in three galaxies (IRASF10398+1455,
IRASF21013-0739 and SDSSJ0808+3948) which are characterized by the simultaneous
detection of a red 5--8um emission continuum, the 9.7 and 18um silicate
emission features as well as strong PAH emission bands. These apparently
contradictory dust IR emission properties are discussed in terms of iron-poor
silicate composition, carbon dust deficit, small grain size and low dust
temperature in the young AGN phase of these three galaxies.",1407.0914v3
2014-07-03,"Superconductivity by rare earth doping in the 1038-type compounds (Ca$_{1-x}$RE$_x$)$_{10}$(FeAs)$_{10}$(Pt$_3$As$_8$) with RE = Y, La-Nd, Sm-Lu","We report superconductivity in polycrystalline samples of the 1038-type
compounds (Ca$_{1-x}$RE$_x$)$_{10}$(FeAs)$_{10}$(Pt$_3$As$_8$) up to T$_c$ = 35
K with RE = Y, La-Nd, Sm, Gd-Lu. The critical temperatures are independent of
the trivalent rare earth element used, yielding an universal T$_c$($x$) phase
diagram for electron doping in all these systems. The absence of
superconductivity in Eu$^{2+}$ doped samples, as well as the close resemblance
of (Ca$_{1-x}$RE$_x$)$_{10}$(FeAs)$_{10}$(Pt$_3$As$_8$) to the 1048 compound
substantiate that the electron doping scenario in the RE-1038 and 1048 phases
is completely analogous to other iron-based superconductors with simpler
crystal structures.",1407.1007v1
2014-07-05,Self-organized electronic superlattices in layered materials,"We show that in layered systems with electronic phase separation tendency,
the long-range Coulomb interaction can drive the spontaneous formation of
unidirectional superlattices of electronic charge in a completely homogeneous
crystalline background. In this self-organized electronic heterostructure, the
ratio among the number of crystalline planes in the minority and majority
electronic phases corresponds to Farey fractions with the superlattice period
controlled by the background charge density and the frustrating Coulomb
interaction strength. The phase diagram displays Arnold tongues obeying a
modified Farey tree hierarchy and a devil's staircase typical of systems with
frustration among different scales. We further discuss the competition of these
electronic superlattices, recently observed in iron-based superconductors and
mixed valence compounds, with in-plane electronically modulated phases.",1407.1378v1
2014-07-10,NMR investigation of spin correlations in BaCo2As2,"We use NMR techniques to investigate the magnetic properties of BaCo2As2
single crystals, the non-superconducting end member of the Co-substituted
iron-pnictide high Tc superconductor Ba(Fe1-xCox)2As2 with x = 1. We present
75As NMR evidence for enhancement of low frequency spin fluctuations below ~
100 K. This enhancement is accompanied by that of static uniform spin
susceptibility at the wave vector q = 0, suggesting that the primary channel of
the spin correlations is ferromagnetic rather than antiferromagnetic.
Comparison between the NMR Knight shift 75K and bulk susceptibility chi(bulk)
data uncovers the presence of two separate components of spin susceptibility
with distinct temperature dependences, presumably because multiple electronic
bands crossing the Fermi energy play different roles in the electronic
properties of BaCo2As2.",1407.2750v1
2014-07-13,Accurate bare susceptibilities from full-potential $\textit{ab initio}$ calculations,"Electronic susceptibilities are a very popular tool to study electronic and
magnetic properties of materials, both in experiment and theory. Unfortunately,
the numerical evaluation of even the bare susceptibility, which depends on the
computation of matrix elements and sums over energy bands, is very
work-intensive and therefore various approximations have been introduced to
speed up the calculations. We present a reliable and efficient implementation
to compute static as well as dynamic bare susceptibilities based on
full-potential density functional theory (DFT) calculations. Based on the exact
results we will assess the accuracy of replacing the matrix elements with a
constant and the impact of truncating the sum over the energy bands. Results
will be given for representative and topical materials, such as Cr, a classical
transition metal, as well as for FeSe and LaFeAsO, examples of iron-based
superconductors.",1407.3444v2
2014-07-14,Observation of pseudogap-like feature above Tc in LiFeAs and (Ba0.6K0.4)Fe2As2 by ultrafast optical measurement,"We utilize ultrafast optical measurement to study the quasiparticle
relaxation in stoichiometric LiFeAs and nearly optimally doped (BaK)Fe2As2
crystals. According to our temperature-dependent studies of LiFeAs, we have
observed pseudogap-like feature at onset temperature of ~ 55 K, which is above
Tc = 15 K. In addition, the onset temperature of pseudogap ~90K was also
observed in Ba0.6K0.4Fe2As2 (Tc = 36 K). Our findings seem implying that the
pseudogap feature, which is due to antiferromagnetic fluctuations, is universal
for the largely studied 11, 111, 122, and 1111 iron-based superconductors.",1407.3539v1
2014-07-16,The Effect of Doppler Broadening on the $6.3 \ PeV$ $W^-$ Resonance in $\barν_e e^-$ Collisions,"We calculate the Doppler broadening of the $W^-$ resonance produced in
$\bar{\nu}_e e^-$ collisions of cosmic anti-neutrinos with $E_{\nu}\approx 6.3
\ PeV$ with electrons in atoms up to Iron. Revisiting this issue is prompted by
recent observations of PeV neutrinos by Ice-Cube. Despite its poor energy
resolution, the $20\%$ Doppler broadening of the resonance due to electronic
motions can produce observable effects via non-linear neutrino absorption near
the resonance. The attendant suppression of the peak cross section allows
$\bar{\nu}_e$ to travel correspondingly longer distances. While this effect is
unlikely to be directly detected in the near future, it may facilitate
terrestrial tomography at depths of $\sim 10 \ km$, complementing deeper
explorations using the more frequent nuclear interactions at lower energies.",1407.4415v1
2014-07-17,Spatial ordering of nano-dislocation loops in ion-irradiated materials,"Defect microstructures formed in ion-irradiated metals, for example iron or
tungsten, often exhibit patterns of spatially ordered nano-scale dislocation
loops. We show that such ordered dislocation loop structures may form
spontaneously as a result of Brownian motion of loops, biased by the
angular-dependent elastic interaction between the loops. Patterns of spatially
ordered loops form once the local density of loops produced by ion irradiation
exceeds a critical threshold value.",1407.4683v1
2014-07-18,Estimating R-Process Yields from Abundances of the Metal-Poor Stars,"The chemical abundances of metal-poor stars provide important clues to
explore stellar formation history and set significant constraints on models of
the r-process. In this work, we find that the abundance patterns of the light
and iron group elements of the main r-process stars are very close to those of
the weak r-process stars. Based on a detailed abundance comparison, we find
that the weak r-process occurs in supernovae with a progenitor mass range of
$\sim11-26M_{\odot}$. Using the SN yields given by Heger & Woosley and the
abundances of the weak r-process stars, the weak r-process yields are derived.
The SNe with a progenitor mass range of $15M_{\odot}<M<26M_{\odot}$ are the
main sites of the weak r-process and their contributions are larger than 80%.
Using the abundance ratios of the weak r-process and the main r-process in the
solar system, the average yields of the main r-process are estimated. The
observed correlations of the [neutron-capture/Eu] versus [Eu/Fe] can be
explained by mixing of the two r-process abundances in various fractions.",1407.4878v1
2014-07-22,Orbital Selective Mott Transition Induced by Orbitals with Distinct Noninteracting Densities of States,"By applying dynamical mean-field theory in combination with exact
diagonalization at zero temperature to a half-filled Hubbard model with two
orbitals having distinct noninteracting densities of states, we show that an
orbital selective Mott transition (OSMT) will take place even without crystal
field splitting, differences in bandwidth and orbital degeneracy. We find that
formation of local spin triplet states followed by a two-stage breakdown of the
Kondo effect, rather than decoupling of charge degrees of freedom among
different orbitals, is the underlying physics for the OSMT. The relevance of
our findings to Ca$_{2-x}$Sr$_x$RuO$_4$ and the iron-based superconductors is
discussed, and a decent candidate to detect such an origin for the OSMT is
proposed.",1407.5795v1
2014-07-31,Improving the Scalability of DPWS-Based Networked Infrastructures,"The Devices Profile for Web Services (DPWS) specification enables seamless
discovery, configuration, and interoperability of networked devices in various
settings, ranging from home automation and multimedia to manufacturing
equipment and data centers. Unfortunately, the sheer simplicity of event
notification mechanisms that makes it fit for resource-constrained devices,
makes it hard to scale to large infrastructures with more stringent
dependability requirements, ironically, where self-configuration would be most
useful. In this report, we address this challenge with a proposal to integrate
gossip-based dissemination in DPWS, thus maintaining compatibility with
original assumptions of the specification, and avoiding a centralized
configuration server or custom black-box middleware components. In detail, we
show how our approach provides an evolutionary and non-intrusive solution to
the scalability limitations of DPWS and experimentally evaluate it with an
implementation based on the the Web Services for Devices (WS4D) Java Multi
Edition DPWS Stack (JMEDS).",1407.8546v1
2014-08-02,"Synthesis and post-annealing effects of alkaline-metal-ethylenediamine-intercalated superconductors Ax(C2H8N2)yFe2-zSe2 (A = Li, Na) with Tc = 45 K","New iron-based intercalation superconductors Ax(C2H8N2)yFe2-zSe2 (A = Li, Na)
with Tc = 45 K have successfully been synthesized via intercalation of
dissolved alkaline metal in ethylenediamine. The c-axis lengths of
Ax(C2H8N2)yFe2-zSe2 (A = Li, Na) are 20.74(7) {\AA} and 21.9(1) {\AA},
respectively, and are about 50 % larger than that of KxFe2Se2, indicating that
not only alkaline metal but also ethylenediamine is intercalated between the
Se-Se layers of FeSe. It seems that the high-Tc of Ax(C2H8N2)yFe2-zSe2 (A = Li,
Na) is caused by the possible two-dimensional electronic structure due to the
large c-axis length. Through the post-annealing in an evacuated glass tube, it
has been found that Tc decreases with increasing post-annealing temperature and
that deintercalation of EDA from the as-intercalated sample takes place at low
temperatures below 250 {\deg}C.",1408.0346v1
2014-08-06,Permanent magnet with MgB2 bulk superconductor,"Superconductors with persistent zero-resistance currents serve as permanent
magnets for high-field applications requiring a strong and stable magnetic
field, such as magnetic resonance imaging (MRI). The recent global helium
shortage has quickened research into high-temperature superconductors (HTSs)
materials that can be used without conventional liquid-helium cooling to 4.2 K.
Herein, we demonstrate that 40-K-class metallic HTS magnesium diboride (MgB2)
makes an excellent permanent bulk magnet, maintaining 3 T at 20 K for 1 week
with an extremely high stability (<0.1 ppm/h). The magnetic field trapped in
this magnet is uniformly distributed, as for single-crystalline
neodymium-iron-boron. Magnetic hysteresis loop of the MgB2 permanent bulk
magnet was detrmined. Because MgB2 is a simple-binary-line compound that does
not contain rare-earth metals, polycrystalline bulk material can be
industrially fabricated at low cost and with high yield to serve as strong
magnets that are compatible with conventional compact cryocoolers, making MgB2
bulks promising for the next generation of Tesla-class permanent-magnet
applications.",1408.1277v1
2014-08-08,Orbital-driven nematicity in FeSe,"A very fundamental and unconventional characteristic of superconductivity in
iron-based materials is that it occurs in the vicinity of {\it two} other
instabilities. Apart from a tendency towards magnetic order, these Fe-based
systems have a propensity for nematic ordering: a lowering of the rotational
symmetry while time-reversal invariance is preserved. Setting the stage for
superconductivity, it is heavily debated whether the nematic symmetry breaking
is driven by lattice, orbital or spin degrees of freedom. Here we report a very
clear splitting of NMR resonance lines in FeSe at $T_{nem}$ = 91K, far above
superconducting $T_c$ of 9.3 K. The splitting occurs for magnetic fields
perpendicular to the Fe-planes and has the temperature dependence of a
Landau-type order-parameter. Spin-lattice relaxation rates are not affected at
$T_{nem}$, which unequivocally establishes orbital degrees of freedom as
driving the nematic order. We demonstrate that superconductivity competes with
the emerging nematicity.",1408.1875v3
2014-08-09,Stellar origin of the 182Hf cosmochronometer and the presolar history of solar system matter,"Among the short-lived radioactive nuclei inferred to be present in the early
solar system via meteoritic analyses, there are several heavier than iron whose
stellar origin has been poorly understood. In particular, the abundances
inferred for 182Hf (half-life = 8.9 million years) and 129I (half-life = 15.7
million years) are in disagreement with each other if both nuclei are produced
by the rapid neutron-capture process. Here, we demonstrate that contrary to
previous assumption, the slow neutron-capture process in asymptotic giant
branch stars produces 182Hf. This has allowed us to date the last rapid and
slow neutron-capture events that contaminated the solar system material at
roughly 100 million years and 30 million years, respectively, before the
formation of the Sun.",1408.2050v1
2014-08-12,Nematic spin correlations in the tetragonal state of uniaxial strained BaFe2-xNixAs2,"Understanding the microscopic origins of electronic phases in high-transition
temperature (high-Tc) superconductors is important for elucidating the
mechanism of superconductivity. In the paramagnetic tetragonal phase of
BaFe2-xTxAs2 (where T is Co or Ni) iron pnictides, an in-plane resistivity
anisotropy has been observed. Here we use inelastic neutron scattering to show
that low-energy spin excitations in these materials change from four-fold
symmetric to two-fold symmetric at temperatures corresponding to the onset of
the in-plane resistivity anisotropy. Because resistivity and spin excitation
anisotropies both vanish near optimal superconductivity, we conclude that they
are likely intimately connected.",1408.2756v1
2014-08-13,Dynamical correlations and screened exchange on the experimental bench: spectral properties of the cobalt pnictide BaCo2As2,"Understanding the Fermi surface and low-energy excitations of iron or cobalt
pnictides is crucial for assessing electronic instabilities such as magnetic or
superconducting states. Here, we propose and implement a new approach to
compute the low-energy properties of correlated electron materials, taking into
account both screened exchange beyond the local density approximation and local
dynamical correlations. The scheme allows us to resolve the puzzle of BaCo2As2,
for which standard electronic structure techniques predict a ferromagnetic
instability not observed in nature.",1408.3136v2
2014-08-14,Role of magnetic degrees of freedom in a scenario of phase transformations in steel,"The diversity of mesostructures formed in steel at cooling from a
high-temperature austenite (""gamma"") phase is determined by the interplay of
shear reconstructions of crystal lattice and diffusion of carbon. Combining
first-principles calculations with large-scale phase-field simulations we
demonstrate a decisive role of magnetic degrees of freedom in the formation of
energy relief along the Bain path of ""gamma""-""alpha"" transformation and, thus,
in this interplay. We show that there is the main factor, namely, the magnetic
state of iron and its evolution with temperature which controls the change in
character of the transformation. Based on the computational results we propose
a simple model which reproduces, in good agreement with experiment, the most
important curves of the phase transformation in Fe-C, namely, the lines
relevant to a start of ferrite, bainite, and martensite transformations.
Phase-field simulations within the model describe qualitatively typical
patterns at these transformations.",1408.3275v2
2014-08-17,Interaction between multi components vortices at arbitrary distances using a variational method in the Ginzburg-Landau theory,"We study the interaction between the vortices in multi components
superconductors based on the Jacobs and Rebbi variation method using
Ginzburg-Landau theory. With one condensation, we get attraction interaction
between the vortices for type I and repulsion for type II superconductors. With
two condensation states such as Mg B_{2} superconductors the behavior is quite
different. There is attraction at large distances and repulsion when the
vortices are close to each other. A stability point at distance
2.7/{\lambda}_{1} is obtained. In the case of three condensation states such as
iron based superconductors,we see different behavior depending on penetration
depth and correlation length. The formation energy of a vortex with three
condensation states is larger than the one with one condensation state with
comparable penetration and correlation length. We obtain two stability points
for the superconductors with three condensation states.",1408.3834v2
2014-08-19,Anomalous Superconducting-Gap Structure of Slightly Overdoped Ba(Fe$_{1-x}$Co$_{x}$)$_{2}$As$_{2}$,"We observed the anisotropic superconducting-gap (SC-gap) structure of a
slightly overdoped superconductor, Ba(Fe$_{1-x}$Co$_{x}$)$_{2}$As$_{2}$
($x=0.1$), using three-dimensional (3D) angle-resolved photoemission
spectroscopy. Two hole Fermi surfaces (FSs) observed at the Brillouin zone
center and an inner electron FS at the zone corner showed a nearly isotropic SC
gap in 3D momentum space. However, the outer electron FS showed an anisotropic
SC gap with nodes or gap minima around the M and A points. The different
anisotropies obtained the SC gap between the outer and inner electron FSs
cannot be expected from all theoretical predictions with spin fluctuation,
orbital fluctuation, and both competition. Our results provide a new insight
into the SC mechanisms of iron pnictide superconductors.",1408.4260v1
2014-08-25,"Ground state, collective mode, phase soliton and vortex in multiband superconductors","This article reviews theoretical and experimental work on the novel physics
in multiband superconductors. Multiband superconductors are characterized by
multiple superconducting energy gaps in different bands with interaction
between Cooper pairs in these bands. The discovery of prominent multiband
superconductors $\mathrm{MgB_2}$ and later iron-based superconductors has
triggered enormous interests in multiband superconductors. Most recently
discovered superconductors exhibit multiband features. The multiband
superconductors possess novel properties that are not shared by their
single-band counterpart. Examples include the time-reversal symmetry broken
state in multiband superconductors with frustrated interband couplings, the
collective oscillation of number of Cooper pairs between different bands, known
as the Leggett mode, the phase soliton and fractional vortex, which are the
main focus of this review. This review presents a survey of a wide range of
theoretical exploration and experimental investigations of novel physics in
multiband superconductors. Vast information derived from these studies is shown
to highlight unusual and unique properties of multiband superconductors, and to
reveal the challenges and opportunities in the research on the multiband
superconductivity.",1408.5938v2
2014-08-26,Measurement of the Velocity of the Neutrino with MINOS,"The MINOS experiment uses a beam of predominantly muon-type neutrinos
generated using protons from the Main Injector at Fermilab in Batavia, IL, and
travelling 735 km through the Earth to a disused iron mine in Soudan, MN. The
10{\mu}s-long beam pulse contains fine time structure which allows a precise
measurement of the neutrino time of flight to be made. The time structure of
the parent proton pulse is measured in the beamline after extraction from the
Main Injector, and neutrino interactions are timestamped at the Fermilab site
in the Near Detector (ND), and at the Soudan site in the Far Detector (FD).
Small, transportable auxiliary detectors, consisting of scintillator planes and
associated readout electronics, are used to measure the relative latency
between the two large detectors. Time at each location is measured with respect
to HP5071A Cesium clocks, and time is transferred using GPS Precise Point
Positioning (PPP) solutions for the clock offset at each location. We describe
the timing calibration of the detectors and derive a measurement of the
neutrino velocity, based on data from March and April 2012. We discuss the
prospects for further improvements that would yield a still more accurate
result.",1408.6267v1
2014-08-29,The spin of the black hole 4U 1543-47,"We present a new analysis of Rossi X-ray Timing Explorer observations of the
2002 outburst of the transient X-ray nova 4U 1543-47. We focus on observations
in the High/Soft state, and attempt to measure the spin of the black hole by
simultaneously fitting the thermal disk continuum and by modeling the broadened
iron k-shell emission lines and additional blurred reflection features.
Previous works have found that use of these methods individually returns
contradictory values for the dimensionless spin parameter a* =cJ/GM^2. We find
that when used in conjunction with each other, a moderate spin is obtained
(a*=0.43 +0.22 -0.31) that is actually consistent with both other values within
errors. We discuss limitations of our analysis, systematic uncertainties, and
implications of this measurement, and compare our result to those previously
claimed for 4U 1543-47.",1408.7028v1
2014-09-01,Magnetic structure of the Eu2+ moments in superconducting EuFe2(As1-xPx)2 with x = 0.19,"The magnetic structure of the Eu2+ moments in the superconducting
EuFe2(As1-xPx)2 sample with x = 0.19 has been determined using neutron
scattering. We conclude that the Eu2+ moments are aligned along the c direction
below T_C = 19.0(1) K with an ordered moment of 6.6(2) mu_B in the
superconducting state. An impurity phase similar to the underdoped phase exists
within the bulk sample which orders antiferromagnetically below T_N = 17.0(2)
K. We found no indication of iron magnetic order, nor any incommensurate
magnetic order of the Eu2+ moments in the sample.",1409.0432v1
2014-09-07,Quantum Monte Carlo study of the $S_4$ symmetric microscopic model for iron-based superconductors,"The $S_4$ symmetric microscopic model with two iso-spin components has been
studied via constrained-path quantum Monte Carlo simulation. Our results
demonstrate a stable $(\pi,0)$ or $(0,\pi)$ magnetic order which is
significantly enhanced on increasing both the Coulomb repulsion $U$ and Hund's
coupling strength $J$. Also, our simulation indicates that the magnetic order
tends to be in an orthomagnetic one, in which the nearest-neighbour magnetic
moment are orthogonal to each other, rather than in a collinear
antiferromagnetic state. Interestingly, when the system is doped away from half
filling, the magnetic order is obviously elevated in the low doping density,
and then significantly suppressed when more electrons are introduced.
Meanwhile, we find that an $A_{1g}$ $s_{\pm}$-wave pairing dominates all the
singlet nearest-neighbour pairings, and is significantly enhanced via electron
doping.",1409.2075v1
2014-09-08,The sensitivity of the ICAL detector at India-based Neutrino Observatory to neutrino oscillation parameters,"The India-based Neutrino Observatory (INO) will host a 50 kt magnetized iron
calorimeter (ICAL) detector that will be able to detect muon tracks and hadron
showers produced by Charged-Current muon neutrino interactions in the detector.
The ICAL experiment will be able to determine the precision of atmospheric
neutrino mixing parameters and neutrino mass hierarchy using atmospheric muon
neutrinos through earth matter effect. In this paper, we report on the
sensitivity for the atmospheric neutrino mixing parameters
($\sin^{2}\theta_{23}$ and $|\Delta m^{2}_{32}|$) for the ICAL detector using
the reconstructed neutrino energy and muon direction as observables. We apply
realistic resolutions and efficiencies obtained by the ICAL collaboration with
a GEANT4-based simulation to reconstruct neutrino energy and muon direction.
Our study shows that using neutrino energy and muon direction as observables
for a $\chi^{2}$ analysis, ICAL detector can measure $\sin^{2}\theta_{23}$ and
$|\Delta m^{2}_{32}|$ with 13% and 4% uncertainties at 1$\sigma$ confidence
level for 10 years of exposure.",1409.2231v1
2014-09-09,Anomalous density of states in multiband superconductors near Lifshitz transition,"We consider a multiband metal with deep primary bands and a shallow secondary
one. In the normal state the system undergoes Lifshitz transition when the
bottom of the shallow band crosses the Fermi level. In the superconducting
state Cooper pairing in the shallow band is induced by the deep ones. As a
result, the density of electrons in the shallow band remains finite even when
the bottom of the band is above the Fermi level. We study the density of states
in the system and find qualitatively different behaviors on the two sides of
the Lifshitz transition. On one side of the transition the density of states
diverges at the energy equal to the induced gap, whereas on the other side it
vanishes. We argue that this physical picture describes the recently measured
gap structure in shallow bands of iron pnictides and selenides.",1409.2807v2
2014-09-09,The diversity of quasars unified by accretion and orientation,"Quasars are rapidly accreting supermassive black holes at the center of
massive galaxies. They display a broad range of properties across all
wavelengths, reflecting the diversity in the physical conditions of the regions
close to the central engine. These properties, however, are not random, but
form well-defined trends. The dominant trend is known as Eigenvector 1, where
many properties correlate with the strength of optical iron and [OIII]
emission. The main physical driver of Eigenvector 1 has long been suspected to
be the quasar luminosity normalized by the mass of the hole (the Eddington
ratio), an important quantity of the black hole accretion process. But a
definitive proof has been missing. Here we report an analysis of archival data
that reveals that Eddington ratio indeed drives Eigenvector 1. We also find
that orientation plays a significant role in determining the observed
kinematics of the gas, implying a flattened, disklike geometry for the
fast-moving clouds close to the hole. Our results show that most of the
diversity of quasar phenomenology can be unified with two simple quantities,
Eddington ratio and orientation.",1409.2887v1
2014-09-10,Theoretical investigation of the electronic and magnetic properties of the orthorhombic phase of Ba(Fe$_{1-x}$Co$_x$)$_2$As$_2$,"We present a comprehensive study on the low-temperature orthorhombic phase of
Ba(Fe$_{1-x}$Co$_x$)$_2$As$_2$ based on the Korringa-Kohn-Rostoker-Green
function approach. Using this bandstructure method in combination with the
coherent potential approximation alloy theory we are able to investigate the
evolution of the magnetic and electronic properties of this prototype iron
pnictide for arbitrary concentrations $x$, while dealing with the chemical
disorder without uncontrolled simplifications by using solely a rigid band
shift or the virtual crystal approximation. We discuss the development of the
site resolved magnetic moments for the experimentally observed stripe
antiferromagnetic order together with the strong electronic anisotropy of the
Fermi surface and compare it with angle-resolved photoemission spectroscopy
measurements of detwinned crystals. We furthermore calculate magnetic exchange
coupling parameters $J_{ij}$ and use them for Monte-Carlo simulations on the
basis of the classical Heisenberg model to get an insight on the temperature
dependence of the magnetic ordering on the cobalt concentration.",1409.3099v1
2014-09-10,On the Raman O VI and related lines in classical novae,"We critically examine the recent claimed detection of Raman scattered O VI at
around 6830\AA\ in the iron curtain stage spectra of the classical CO nova V339
Del. The observed line variations are compatible in profile and timing of
emission line strength with an excited state transition of neutral carbon. Line
formation in classical nova ejecta is physically very different from that in
symbiotic binaries, in which the O VI emission line is formed within the wind
of the companion red giant at low differential velocity. The ejecta velocity
and density structure prevent the scattering from producing analogous features.
There might , however, be a broadband spectropolarimetric signature of the
Raman process and also Rayleigh scattering at some stage in the expansion. We
show that the neutral carbon spectrum, hitherto under-exploited for novae, is
especially useful as a probe of the structure of the ejecta during the early,
optically thick stages of the expansion",1409.3240v1
2014-09-11,Effects of applied strain on radiation damage generation in body-centered cubic iron,"Radiation damage in body-centered cubic (BCC) Fe has been extensively studied
by computer simulations to quantify effects of temperature, impinging particle
energy, and the presence of extrinsic particles. However, limited investigation
has been conducted into the effects of mechanical stresses and strain. In a
reactor environment, structural materials are often mechanically strained, and
an expanded understanding of how this strain affects the generation of defects
may be important for predicting microstructural evolution and damage
accumulation under such conditions. In this study, we have performed molecular
dynamics simulations in which various types of homogeneous strains are applied
to BCC Fe and the effect on defect generation is examined. It is found that
volume-conserving shear strains yield no statistically significant variations
in the stable number of defects created via cascades in BCC Fe. However,
strains that result in volume changes are found to produce significant effects
on defect generation.",1409.3519v2
2014-09-13,Coexistence of 3d-ferromagnetism and superconductivity in [(Li(1-x)Fex)OH](Fe(1-y)Liy)Se,"Superconducting [(Li(1-x)Fex)OH](Fe(1-y)Liy)Se (x ~ 0.2, y ~ 0.08) was
synthesized by hydrothermal methods and structurally characterized by single
crystal X-ray diffraction. The crystal structure contains anti-PbO type
(Fe(1-y)Liy)Se layers separated by layers of (Li(1-x)Fex)OH. Electrical
resistivity and magnetic susceptibility measurements reveal superconductivity
at 43 K. An anomaly in the diamagnetic shielding indicates ferromagnetic
ordering near 10 K while superconductivity is retained. The ferromagnetism
emerges from the iron atoms in the (Li(1-x)Fex)OH layer. Isothermal
magnetization measurements confirm the superposition of ferromagnetic with
superconducting hysteresis. The internal ferromagnetic field is larger than the
lower, but smaller than the upper critical field of the superconductor, which
gives evidence for a spontaneous vortex phase where both orders coexist.
57Fe-M\""ossbauer spectra, 7Li-NMR spectra, and muSR experiments consistently
support this rare situation, especially in a bulk material where magnetism
emerges from a 3d-element.",1409.3982v1
2014-09-14,Soft striped magnetic fluctuations competing with superconductivity in Fe_{1+x}Te,"Neutron spectroscopy is used to investigate the magnetic fluctuations in
Fe_{1+x}Te - a parent compound of chalcogenide superconductors. Incommensurate
""stripe-like"" excitations soften with increased interstitial iron
concentration. The energy crossover from incommensurate to stripy fluctuations
defines an apparent hour-glass dispersion. Application of sum rules of neutron
scattering find that the integrated intensity is inconsistent with an S=1
Fe^{2+} ground state and significantly less than S=2 predicted from weak
crystal field arguments pointing towards the Fe^{2+} being in a superposition
of orbital states. The results suggest that a highly anisotropic order competes
with superconductivity in chalcogenide systems.",1409.4051v1
2014-09-16,Inverse problem for extragalactic transport of ultra-high energy cosmic rays,"The energy spectra and composition of ultra-high energy cosmic rays are
changing in a course of propagation in the expanding Universe filled with
background radiation. We developed a numerical code for solution of inverse
problem for cosmic-ray transport equations that allows the determination of
average source spectra of different nuclei from the cosmic ray spectra observed
at the Earth. Employing this approach, the injection spectra of protons and
Iron nuclei in extragalactic sources are found assuming that only these species
are accelerated at the source. The data from the Auger experiment and the
combined data from the Telescope Array + HiRes experiments are used to
illustrate the method.",1409.4654v4
2014-09-17,Increased magnetocrystalline anisotropy in epitaxial Fe-Co-C thin films with spontaneous strain,"Rare earth free alloys are in focus of permanent magnet research since the
accessibility of the elements needed for nowadays conventional magnets is
limited. Tetragonally strained iron-cobalt (Fe-Co) has attracted large interest
as promising candidate due to theoretical calculations. In experiments,
however, the applied strain quickly relaxes with increasing film thickness and
hampers stabilization of a strong magnetocrystalline anisotropy. In our study
we show that already 2 at% of carbon substantially reduce the lattice
relaxation leading to the formation of a spontaneously strained phase with 3 %
tetragonal distortion. In these strained
(Fe$_{0.4}$Co$_{0.6}$)$_{0.98}$C$_{0.02}$ films, a magnetocrystalline
anisotropy above 0.4 MJ/m$^3$ is observed while the large polarization of 2.1 T
is maintained. Compared to binary Fe-Co this is a remarkable improvement of the
intrinsic magnetic properties. In this paper, we relate our experimental work
to theoretical studies of strained Fe-Co-C and find a very good agreement.",1409.4952v1
2014-09-25,Characterisation of Glass Electrodes and RPC Detectors for $INO-ICAL$ Experiment,"India-based Neutrino Observatory (INO) is a planned neutrino experiment to be
build up in southern part of India.The INO observatory will host a 51 kton Iron
Calorimeter (ICAL) detector to detect atmospheric neutrinos. Resistive Plate
Chamber (RPC) has been chosen as the active detector element for the ICAL
experiment. The ICAL experiment will consist of about 28,000 RPC's of dimension
$2~m\times 2~m$, divided into three modules. The experiment is planned to take
data at least for 20 years from its start date. Due to the large number of RPC
needed for ICAL experiment and the long lifetime of the experiment, it is
necessary to carry out detailed $R\&D$ to optimise each and every parameter of
the detector performance. We report on the performance studies carried out on
the RPC's made with these electrodes, and finally compare the detector
performance with that of the material properties to optimise the detector
parameters.",1409.7184v1
2014-09-26,Superconducting gap structure of BaFe_2(As_{1-x}P_{x})_2,"We present a study of the superconducting gap structure in the iron-pnictide
series BaFe2(As1-xPx)2. By measuring the variation of the specific heat as a
function of temperature and magnetic field we are able to determine the number
and Fermi surface location of the nodes in the superconducting gap. In
particular, from measurements of the variation of the specific heat as the
magnetic field is rotated in the ab plane of the sample we conclude that the
nodes are in the [110] directions. Then from a quantitative analysis of the
temperature and field dependence of the specific heat we further conclude that
nodes exists on all Fermi surface sheets.",1409.7523v1
2014-09-30,Observation of an electron band above the Fermi level in FeTe$_{0.55}$Se$_{0.45}$ from \emph{in-situ} surface doping,"We used \emph{in-situ} potassium (K) evaporation to dope the surface of the
iron-based superconductor FeTe$_{0.55}$Se$_{0.45}$. The systematic study of the
bands near the Fermi level confirms that electrons are doped into the system,
allowing us to tune the Fermi level of this material and to access otherwise
unoccupied electronic states. In particular, we observe an electron band
located above the Fermi level before doping that shares similarities with a
small three-dimensional pocket observed in the cousin, heavily-electron-doped
KFe$_{2-x}$Se$_2$ compound.",1409.8383v2
2014-09-30,Testing non-standard neutrino matter interactions in atmospheric neutrino propagation,"We study the effects of non-standard interactions on the oscillation pattern
of atmospheric neutrinos. We use neutrino oscillograms as our main tool to
infer the role of non-standard interactions (NSI) parameters at the probability
level in the energy range, $E \in [1,20]$ GeV and zenith angle range, $\cos
\theta \in [-1,0]$. We compute the event rates for atmospheric neutrino events
in presence of NSI parameters in the energy range $E \in [1,10]$ GeV for two
different detector configurations - a magnetized iron calorimeter and an
unmagnetized liquid Argon time projection chamber which have different
sensitivities to NSI parameters due to their complementary characteristics. As
an application, we discuss how NSI parameter, $\epsilon_{\mu\tau}$ impacts the
determination of the correct octant of $\theta_{23}$.",1409.8472v2
2014-10-02,Observation of Majorana Fermions in Ferromagnetic Atomic Chains on a Superconductor,"Majorana fermions are predicted to localize at the edge of a topological
superconductor, a state of matter that can form when a ferromagnetic system is
placed in proximity to a conventional superconductor with strong spin-orbit
interaction. With the goal of realizing a one-dimensional topological
superconductor, we have fabricated ferromagnetic iron (Fe) atomic chains on the
surface of superconducting lead (Pb). Using high-resolution spectroscopic
imaging techniques, we show that the onset of superconductivity, which gaps the
electronic density of states in the bulk of the Fe chains, is accompanied by
the appearance of zero energy end states. This spatially resolved signature
provides strong evidence, corroborated by other observations, for the formation
of a topological phase and edge-bound Majorana fermions in our atomic chains.",1410.0682v1
2014-10-03,Unexpected impact of magnetic disorder on multiband superconductivity,"We analyze how the magnetic disorder affects the properties of the two-band
$s_\pm$ and $s_{++}$ models, which are subject of hot discussions regarding
iron-based superconductors and other multiband systems like MgB$_2$. We show
that there are several cases when the transition temperature $T_c$ is not fully
suppressed by magnetic impurities in contrast to the Abrikosov-Gor'kov theory,
but a saturation of $T_c$ takes place in the regime of strong disorder. These
cases are: (1) the purely interband impurity scattering, (2) the unitary
scattering limit. We show that in the former case the $s_\pm$ gap is preserved,
while the $s_{++}$ state transforms into the $s_\pm$ state with increasing
magnetic disorder. For the case (2), the gap structure remains intact.",1410.0832v2
2014-10-13,[$α$/Fe] Abundances of Four Outer M 31 Halo Stars,"We present alpha element to iron abundance ratios, [$\alpha$/Fe], for four
stars in the outer stellar halo of the Andromeda Galaxy (M 31). The stars were
identified as high-likelihood field halo stars by Gilbert et al. (2012) and lie
at projected distances between 70 and 140 kpc from M 31's center. These are the
first alpha abundances measured for a halo star in a galaxy beyond the Milky
Way. The stars range in metallicity between [Fe/H]= -2.2 and [Fe/H]= -1.4. The
sample's average [$\alpha$/Fe] ratio is +0.20+/-0.20. The best-fit average
value is elevated above solar which is consistent with rapid chemical
enrichment from Type II supernovae. The mean [$\alpha$/Fe] ratio of our M31
outer halo sample agrees (within the uncertainties) with that of Milky Way
inner/outer halo stars that have a comparable range of [Fe/H].",1410.3475v1
2014-10-17,Influence of Electron-Impact Multiple Ionization on Equilibrium and Dynamic Charge State Distributions: A Case Study Using Iron,"We describe the influence of electron-impact multiple ionization (EIMI) on
the ionization balance of collisionally ionized plasmas. We are unaware of any
previous ionization balance calculations that have included EIMI, which is
usually assumed to be unimportant. Here, we incorporate EIMI cross-section data
into calculations of both equilibrium and non-equilibrium charge-state
distributions (CSDs). For equilibrium CSDs, we find that EIMI has only a small
effect and can usually be ignored. However, for non-equilibrium plasmas the
influence of EIMI can be important. In particular, we find that for plasmas in
which the temperature oscillates there are significant differences in the CSD
when including versus neglecting EIMI. These results have implications for
modeling and spectroscopy of impulsively heated plasmas, such as nanoflare
heating of the solar corona.",1410.4850v1
2014-10-20,Sensitivity for detection of decay of dark matter particle using ICAL at INO,"We report on the simulation studies on the possibility of dark matter
particle (DMP) decaying into leptonic modes. While not much is known about the
properties of dark matter particles except through their gravitational effect,
it has been recently conjectured that the so called ""anomalous Kolar Events""
observed some decades ago may be due to the decay of unstable dark matter
particles (M.V.N. Murthy and G.Rajasekaran, Pramana, {\bf 82}, 609 (2014)). The
aim of this study is to see if this conjecture can be verified at the proposed
Iron Calorimeter (ICAL) detector at INO. We study the possible decay to
leptonic modes which may be seen in this detector with some modifications. For
the purposes of simulation we assume that each channel saturates the decay
width for the mass ranging from $1-50 \rm{GeV/c^2}$. The aim is not only to
investigate the decay signatures, but also, more generally, to establish lower
bounds on the life time of DMP even if no such decay takes place.",1410.5182v1
2014-10-21,Possible superconductivity in Sr$_{2}$IrO$_{4}$ probed by quasiparticle interference,"Based on the possible superconducting (SC) pairing symmetries recently
proposed, the quasiparticle interference (QPI) patterns in electron- and
hole-doped Sr$_{2}$IrO$_{4}$ are theoretically investigated. In the
electron-doped case, the QPI spectra can be explained based on a model similar
to the octet model of the cuprates while in the hole-doped case, both the Fermi
surface topology and the sign of the SC order parameter resemble those of the
iron pnictides and there exists a QPI vector resulting from the interpocket
scattering between the electron and hole pockets. In both cases, the evolution
of the QPI vectors with energy and their behaviors in the nonmagnetic and
magnetic impurity scattering cases can well be explained based on the evolution
of the constant-energy contours and the sign structure of the SC order
parameter. The QPI spectra presented in this paper can be compared with future
scanning tunneling microscopy experiments to test whether there are SC phases
in electron- and hole-doped Sr$_{2}$IrO$_{4}$ and what the pairing symmetry is.",1410.5512v2
2014-10-23,Superconductivity and phase instability of NH3-free Na-intercalated FeSe1-zSz,"The discovery of ThCr2Si2-type AxFe2-ySe2 (A = K, Rb, Cs and Tl) with Tc ~
30K make much progress in iron-based superconducting field, but their
multiple-phase separations are disadvantageous for understanding the origin. On
the other hand, for small alkali metals, studies on (Li,Na)FeCu(S,Se)2 and
NaFe2-{\delta}S2 shows that these compounds possess CaAl2Si2-type structure,
implying that ThCr2Si2-type structure is unstable for small alkali-metal
intercalated FeSe under high-temperature. Here we report a new intercalate
Na0.65(1)Fe1.93(1)Se2 with Tc ~ 37 K, synthesized by low-temperature
ammonothermal method. The notable finding is that the Na0.65(1)Fe1.93(1)Se2
shows a ThCr2Si2-type structure, which is the first instance of small-sized
alkali metal intercalates without NH3 co-intercalation. Besides, the NH3-poor
Na0.80(4)(NH3)0.60Fe1.86(1)Se2 and NH3-rich phase with Tcs at 45 K and 42 K are
identified by tuning the concentration of Na-NH3 solutions. The modulation of
interlayer spacing reveals the versatile evolution of structural stability and
superconductivity in these intercalates.",1410.6385v1
2014-10-27,Charge Dynamics in a Correlated Fermion System on a Geometrically Frustrated Lattice,"Charge dynamics in an interacting fermionic model on a geometrically
frustrated lattice are examined. We analyze a spinless fermion model on a
paired triangular lattice, an electronic model for layered iron oxides, in zero
and finite temperatures by the exact diagonalization methods. We focus on the
two charge ordered (CO) phases, termed CO_1/2 and CO_1/3, which, respectively,
are realized by the inter-site Coulomb interaction and the quantum/thermal
fluctuations. The optical spectra in CO_1/3 show multiple components and their
low-energy weights are survived even below the ordering temperature (T_CO).
Changes of the dynamical charge correlation below T_CO in CO_1/3 are weakly
momentum dependent, in sharply contrast to CO_1/2. These characteristic
dynamics in CO_1/3 are attributable to the charge frustration effects, and
reproduce some aspects of the recent experimental optical and x-ray scattering
spectra.",1410.7218v1
2014-10-27,Eight billion asteroids in the Oort cloud,"The Oort cloud is usually thought of as a collection of icy comets inhabiting
the outer reaches of the Solar system, but this picture is incomplete. We use
simulations of the formation of the Oort cloud to show that ~4% of the small
bodies in the Oort cloud should have formed within 2.5 au of the Sun, and hence
be ice-free rock-iron bodies. If we assume these Oort cloud asteroids have the
same size distribution as their cometary counterparts, the Large Synoptic
Survey Telescope should find roughly a dozen Oort cloud asteroids during ten
years of operations. Measurement of the asteroid fraction within the Oort cloud
can serve as an excellent test of the Solar system's formation and dynamical
history. Oort cloud asteroids could be of particular concern as impact hazards
as their high mass density, high impact velocity, and low visibility make them
both hard to detect and hard to divert or destroy. However, they should be a
rare class of object, and we estimate globally catastrophic collisions should
only occur about once per billion years.",1410.7403v1
2014-10-28,Unified picture of the doping dependence of superconducting transition temperatures in alkali metal/ammonia intercalated FeSe,"In the recently synthesized Li$_x$(NH$_2$)$_y$(NH$_3$)$_z$Fe$_2$Se$_2$ family
of iron chalcogenides a molecular spacer consisting of lithium ions, lithium
amide and ammonia separates layers of FeSe. It has been shown that upon
variation of the chemical composition of the spacer layer, superconducting
transition temperatures can reach $T_c\sim 44 \mathrm{K}$, but the relative
importance of the layer separation and effective doping to the $T_c$
enhancement is currently unclear. Using state of the art band structure
unfolding techniques, we construct eight-orbital models from ab-initio density
functional theory calculations for these materials. Within an RPA
spin-fluctuation approach, we show that the electron doping enhances the
superconducting pairing, which is of $s_\pm$-symmetry and explain the
experimentally observed limit to $T_c$ in the molecular spacer intercalated
FeSe class of materials.",1410.7565v3
2014-10-30,Detection of Neutral Phosphorus in the Near Ultraviolet Spectra of Late-Type Stars,"We report the detection of several absorption lines of neutral phosphorus (P,
Z=15) in archival near ultraviolet spectra obtained with the Space Telescope
Imaging Spectrograph on board the Hubble Space Telescope. We derive phosphorus
abundances or interesting upper limits in 14 late-type stars with metallicities
spanning -3.8<[Fe/H]<-0.1. Previously, phosphorus had only been studied in
Galactic stars with -1.0<[Fe/H]<+0.3. Iron lines reveal abundance offsets
between the optical and ultraviolet regions, and we discuss and apply a
correction factor to account for this offset. In stars with [Fe/H]>-1.0, the
[P/Fe] ratio decreases toward the solar value with increasing metallicity, in
agreement with previous observational studies. In stars with [Fe/H]<-1.0,
<[P/Fe]>=+0.04+/-0.10, which overlaps with the [P/Fe] ratios found in several
high-redshift damped Lyman-alpha systems. This behavior hints at a primary
origin in massive stars.",1410.8539v1
2014-11-01,Glide-Plane Symmetry and Superconducting Gap Structure of Iron-Based Superconductors,"We consider the effect of glide-plane symmetry of the Fe-pnictogen/chalcogen
layer in Fe-based superconductors on pairing in spin fluctuation models. Recent
theories have proposed that so-called $\eta$-pairing states with nonzero total
momentum can be realized and possess exotic properties such as odd parity spin
singlet symmetry and time-reversal symmetry breaking. Here we show that $\eta$
pairing is inevitable when there is orbital weight at the Fermi level from
orbitals with even and odd mirror reflection symmetry in $z$; however, by
explicit calculation, we conclude that the gap function that appears in
observable quantities is identical to that found in earlier, 1 Fe per unit cell
pseudocrystal momentum calculations.",1411.0070v2
2014-11-04,In-plane magnetic field vs. temperature phase diagram of a quasi-2D frustrated multiband superconductor,"Motivated by the recent discovery of iron-based superconductors, with high
critical temperatures and multiple bands crossing the Fermi level, we address
the conditions for the presence of chiral superconducting phases configurations
in the in-plane magnetic field vs. temperature phase diagram of a quasi-2D
frustrated three-band superconductor. Due to Zeeman splitting, the coupled
superconducting gap equations present a complex set of solutions. For weak
interband couplings, chiral configurations are only attained in a narrow strip
of the in-plane magnetic field vs. temperature phase diagram. This strip of
chiral states becomes narrower and disappears at low temperatures, giving way
to a first-order transition between non-chiral superconducting states. For
stronger interband couplings, the chiral strip is much broader, if the
interband couplings are approximately equal; otherwise, the chiral region is
expected to be completely absent of the phase diagram.",1411.0937v2
2014-11-12,Spontaneous Breakdown of Time-Reversal Symmetry Induced by Thermal Fluctuations,"In systems with broken $U(1)$ symmetry, such as superfluids, superconductors
or magnets, the symmetry restoration is driven by proliferation of topological
defects in the form of vortex loops. Here we discuss that in certain systems
the proliferation of topological defects can, by contrast, lead to the
breakdown of an additional symmetry. As a particular example we demonstrate
that this effect should take place in $s+is$ superconductors, which are widely
discussed in connection with the Iron-based materials. In these systems a
vortex excitation can create a ""bubble"" of fluctuating $Z_2$ order parameter.
Thermal excitation of vortices then leads to breakdown of $Z_2$ time-reversal
symmetry when the temperature is increased.",1411.3202v2
2014-11-14,The impact of global nuclear mass model uncertainties on $r$-process abundance predictions,"Rapid neutron capture or `$r$-process' nucleosynthesis may be responsible for
half the production of heavy elements above iron on the periodic table. Masses
are one of the most important nuclear physics ingredients that go into
calculations of $r$-process nucleosynthesis as they enter into the calculations
of reaction rates, decay rates, branching ratios and Q-values. We explore the
impact of uncertainties in three nuclear mass models on $r$-process abundances
by performing global monte carlo simulations. We show that root-mean-square
(rms) errors of current mass models are large so that current $r$-process
predictions are insufficient in predicting features found in solar residuals
and in $r$-process enhanced metal poor stars. We conclude that the reduction of
global rms errors below $100$ keV will allow for more robust $r$-process
predictions.",1411.3973v1
2014-11-14,A mini review on NiFe-based materials as highly active oxygen evolution reaction electrocatalysts,"Oxygen evolution reaction (OER) electrolysis, as an important reaction
involved in water splitting and rechargeable metal-air battery, has attracted
increasing attention for clean energy generation and efficient energy storage.
Nickel/iron (NiFe)-based compounds have been known as active OER catalysts
since the last century, and renewed interest has been witnessed in recent years
on developing advanced NiFe-based materials for better activity and stability.
In this review, we present the early discovery and recent progress on
NiFe-based OER electrocatalysts in terms of chemical properties, synthetic
methodologies and catalytic performances. The advantages and disadvantages of
each class of NiFe-based compounds are summarized, including NiFe alloys,
electro-deposited films and layered-double hydroxide nanoplates. Some
mechanistic studies of the active phase of NiFe-based compounds are introduced
and discussed to give insight into the nature of active catalytic site, which
could facilitate further improving NiFe based OER electrocatalysts. Finally,
some applications of NiFe-based compounds for OER are described, including the
development of electrolyzer operating with a single AAA battery with voltage
below 1.5V and high performance rechargeable Zn-air batteries.",1411.4677v1
2014-11-19,Stability and magnetization of free-standing and graphene-embedded iron membranes,"Inspired by recent experimental realizations of monolayer Fe membranes in
graphene perforations, we perform ab initio calculations of Fe monolayers and
membranes embedded in graphene in order to assess their structural stability
and magnetization. We demonstrate that monolayer Fe has a larger spin
magnetization per atom than bulk Fe and that Fe membranes embedded in graphene
exhibit spin magnetization comparable to monolayer Fe. We find that
free-standing monolayer Fe is structurally more stable in a triangular lattice
compared to both square and honeycomb lattices. This is contradictory to the
experimental observation that the embedded Fe membranes form a square lattice.
However, we find that embedded Fe membranes in graphene perforations can be
more stable in the square lattice configuration compared to the triangular. In
addition, we find that the square lattice has a lower edge formation energy,
which means that the square Fe lattice may be favored during formation of the
membrane.",1411.5193v1
2014-11-19,Structural ${γ\textrm{-}\varepsilon}$ phase transition in Fe-Mn alloys from CPA+DMFT approach,"We present a computational scheme for total energy calculations of disordered
alloys with strong electronic correlations. It employs the coherent potential
approximation combined with the dynamical mean-field theory and allows one to
study the structural transformations. The material-specific Hamiltonians in the
Wannier function basis are obtained by density functional theory. The proposed
computational scheme is applied to study the ${\gamma\textrm{-}\varepsilon}$
structural transition in paramagnetic Fe-Mn alloys for Mn content from 10 to 20
at. %. The electronic correlations are found to play a crucial role in this
transition. The calculated transition temperature decreases with increasing Mn
content and is in a good agreement with experiment. We demonstrate that in
contrast to the ${\alpha\textrm{-}\gamma}$ transition in pure iron, the
${\gamma\textrm{-}\varepsilon}$ transition in Fe-Mn alloys is driven by a
combination of kinetic and Coulomb energies. The latter is found to be
responsible for the decrease of the ${\gamma\textrm{-}\varepsilon}$ transition
temperature with Mn content.",1411.5356v3
2014-11-19,Interplay between Kondo effect and Ruderman-Kittel-Kasuya-Yosida interaction,"The interplay between the Ruderman-Kittel-Kasuya-Yosida (RKKY) interaction
and the Kondo effect is expected to provide the driving force for the emergence
of many phenomena in strongly correlated electron materials. Two magnetic
impurities in a metal are the smallest possible system containing all these
ingredients and define a bottom up approach towards a long term understanding
of concentrated / dense systems. Here we report on the experimental and
theoretical investigation of iron dimers buried below a Cu(100) surface by
means of low temperature scanning tunnelling spectroscopy (STS) combined with
density functional theory (DFT) and numerical renormalization group (NRG)
calculations. The Kondo effect, in particular the width of the Abrikosov-Suhl
resonance, is strongly altered or even suppressed due to magnetic coupling
between the impurities. It oscillates as function of dimer separation revealing
that it is related to the RKKY interaction mediated by the conduction
electrons. Simulations based on density functional theory support this concept
showing the same oscillation period and trends in the coupling strength as
found in the experiment.",1411.5388v1
2014-11-25,Quantum critical elasticity,"We discuss elastic instabilities of the atomic crystal lattice at zero
temperature. Due to long-range shear forces of the solid, at such transitions
the phonon velocities vanish, if at all, only along certain crystallographic
directions, and, consequently, the critical phonon fluctuations are suppressed
to a lower dimensional manifold and governed by a Gaussian fixed-point. In case
of symmetry-breaking elastic transitions, a characteristic critical phonon
thermodynamics arises that is found, e.g., to violate Debye's $T^3$-law for the
specific heat. We point out that quantum critical elasticity is triggered
whenever a critical soft mode couples linearly to the strain tensor. In
particular, this is relevant for the electronic Ising-nematic quantum phase
transition in a tetragonal crystal as discussed in the context of certain
cuprates, ruthenates and iron-based superconductors.",1411.6925v3
2014-11-26,Effect of bombarding steel with Xe$^+$ ions on the surface nanostructure and on pulsed plasma nitriding process,"The modification of steel (AISI 316L and AISI 4140) surface morphology and
underlying inter-crystalline grains strain due to Xe$^+$ ion bombardment are
reported to affect nitrogen diffusion after a pulsed plasma nitriding process.
The ion bombardment induces regular nanometric patterns and increases the
roughness of the material surface. The strain induced by the noble gas
bombardment is observed in depths which are orders of magnitude larger than the
projectiles' stopping distance. The pre-bombarded samples show peculiar
microstructures formed in the nitrided layers, modifying the in-depth hardness
profile. Unlike the double nitrided layer normally obtained in austenitic
stainless steel by pulsed plasma nitriding process, the Xe$^+$ pre-bombardment
treatment leads to a single thick compact layer. In nitrided pre-bombarded AISI
4140 steel, the diffusion zone shows long iron nitride needle-shaped
precipitates, while in non-pre-bombarded samples finer precipitates are
distributed in the material.",1411.7281v1
2014-11-27,Competing superconducting and magnetic order parameters and field-induced magnetism in electron doped Ba(Fe$_{1-x}$Co$_{x}$)$_{2}$As$_{2}$,"We have studied the magnetic and superconducting properties of
Ba(Fe$_{0.95}$Co$_{0.05}$)$_{2}$As$_{2}$ as a function of temperature and
external magnetic field using neutron scattering and muon spin rotation. Below
the superconducting transition temperature the magnetic and superconducting
order parameters coexist and compete. A magnetic field can significantly
enhance the magnetic scattering in the superconducting state, roughly doubling
the Bragg intensity at 13.5 T. We perform a microscopic modelling of the data
by use of a five-band Hamiltonian relevant to iron pnictides. In the
superconducting state, vortices can slow down and freeze spin fluctuations
locally. When such regions couple they result in a long-range ordered
antiferromagnetic phase producing the enhanced magnetic elastic scattering in
agreement with experiments.",1411.7506v1
2014-12-09,An extreme gravitationally redshifted iron line at 4.8 keV in Mrk 876,"X-ray spectral lines at unforeseen energies are important because they can
shed light on the extreme physical conditions of the environment around the
supermassive black holes of active galactic nuclei (AGN). Mrk 876 displays such
a line at 4.8 keV rest-frame energy. A possible interpretation of its origin
can be found in the hotspot scenario. In this scenario the primary radiation
from a flare in the hot corona of an AGN illuminates a limited portion of the
accretion disk that emits by fluorescence. In this context the line can
represent an extreme gravitationally redshifted Fe line originating on the
accretion disk below 6 gravitational radii from a rotating supermassive black
hole. The correct estimate of the line significance requires a dedicated
approach. Based on an existing rigorous approach, we have performed extensive
Monte Carlo simulations. We determine that the line is a real feature at ~99
confidence level.",1412.3112v1
2014-12-10,M{ö}ssbauer characterization of an unusual high-spin side-on peroxo-Fe3+ species in the active site of superoxide reductase from Desulfoarculus Baarsii. Density functional calculations on related models,"Superoxide reductase (SOR) is an Fe protein that catalyzes the reduction of
superoxide to give H(2)O(2). Recently, the mutation of the Glu47 residue into
alanine (E47A) in the active site of SOR from Desulfoarculus baarsii has
allowed the stabilization of an iron-peroxo species when quickly reacted with
H(2)O(2) [Math{\'e} et al. (2002) J. Am. Chem. Soc. 124, 4966-4967]. To further
investigate this non-heme peroxo-iron species, we have carried out a
M{\""o}ssbauer study of the (57)Fe-enriched E47A SOR from D. baarsii reacted
quickly with H(2)O(2). Considering the M{\""o}ssbauer data, we conclude, in
conjunction with the other spectroscopic data available and with the results of
density functional calculations on related models, that this species
corresponds to a high-spin side-on peroxo-Fe(3+) complex. This is one of the
first examples of such a species in a biological system for which M{\""o}ssbauer
parameters are now available: delta(/Fe) = 0.54 (1) mm/s, DeltaE(Q) = -0.80 (5)
mm/s, and the asymmetry parameter eta = 0.60 (5) mm/s. The M{\""o}ssbauer and
spin Hamiltonian parameters have been evaluated on a model from the side-on
peroxo complex (model 2) issued from the oxidized iron center in SOR from
Pyrococcus furiosus, for which structural data are available in the literature
[Yeh et al. (2000) Biochemistry 39, 2499-2508]. For comparison, similar
calculations have been carried out on a model derived from 2 (model 3), where
the [CH(3)-S](1)(-) group has been replaced by the neutral [NH(3)](0) group
[Neese and Solomon (1998) J. Am. Chem. Soc. 120, 12829-12848]. Both models 2
and 3 contain a formally high-spin Fe(3+) ion (i.e., with empty minority spin
orbitals). We found, however, a significant fraction (approximately 0.6 for 2,
approximately 0.8 for 3) of spin (equivalently charge) spread over two occupied
(minority spin) orbitals. The quadrupole splitting value for 2 is found to be
negative and matches quite well the experimental value. The computed quadrupole
tensors are rhombic in the case of 2 and axial in the case of 3. This
difference originates directly from the presence of the thiolate ligand in 2. A
correlation between experimental isomer shifts for Fe(3+) mononuclear complexes
with computed electron densities at the iron nucleus has been built and used to
evaluate the isomer shift values for 2 and 3 (0.56 and 0.63 mm/s,
respectively). A significant increase of isomer shift value is found upon going
from a methylthiolate to a nitrogen ligand for the Fe(3+) ion, consistent with
covalency effects due to the presence of the axial thiolate ligand. Considering
that the isomer shift value for 3 is likely to be in the 0.61-0.65 mm/s range
[Horner et al. (2002) Eur. J. Inorg. Chem., 3278-3283], the isomer shift value
for a high-spin eta(2)-O(2) Fe(3+) complex with an axial thiolate group can be
estimated to be in the 0.54-0.58 mm/s range. The occurrence of a side-on peroxo
intermediate in SOR is discussed in relation to the recent data published for a
side-on peroxo-Fe(3+) species in another biological system [Karlsson et al.
(2003) Science 299, 1039-1042].",1412.3293v1
2014-12-10,Topological Characters in Fe(Te$_{1-x}$Se$_x$) thin films,"We investigate topological properties in the Fe(Te,Se) thin films. We find
that the single layer FeTe$_{1-x}$Se$_x$ has nontrivial $Z_2$ topological
invariance which originates from the parity exchange at $\Gamma$ point of
Brillouin zone. The nontrivial topology is mainly controlled by the Te(Se)
height. Adjusting the height, which can be realized as function of $x$ in
FeTe$_{1-x}$Se$_x$, can drive a topological phase transition. In a bulk
material, the two dimensional $Z_2$ topology invariance is extended to a strong
three-dimensional one. In a thin film, we predict that the topological
invariance oscillates with the number of layers. The results can also be
applied to iron-pnictides. Our research establishes FeTe$_{1-x}$Se$_x$ as a
unique system to integrate high T$_c$ superconductivity and topological
properties in a single electronic structure.",1412.3375v1
2014-12-11,Transition-Metal Substitutions in Iron Chalcogenides,"The $ab$-plane resistivity and Hall effect are studied in
Fe$_{1-y}$M$_y$Te$_{0.65}$Se$_{0.35}$ single crystals doped with two transition
metal elements, M = Co or Ni, over a wide doping range, $0 \leq y \leq 0.2$.
The superconducting transition temperature, $T_{c}$, reaches zero for Co at $y
\simeq 0.14$ and for Ni at $y \simeq 0.032$, while the resistivity at the
$T_{c}$ onset increases weakly with Co doping, and strongly with Ni doping. The
Hall coefficient $R_H$, positive for $y$ = 0, remains so at high temperatures
for all $y$, while it changes sign to negative at low $T$ for $y > 0.135$ (Co)
and $y > 0.06$ (Ni). The analysis based on a two band model suggests that at
high $T$ residual hole pockets survive the doping, but holes get localized upon
the lowering of $T$, so that the effect of the electron doping on the transport
becomes evident. The suppression of the $T_c$ by Co impurity is related to
electron doping, while in case of the Ni impurity strong electron localization
most likely contributes to fast decrease of the $T_c$.",1412.3599v1
2014-12-15,The hard X-ray spectrum of NGC 5506 as seen by NuSTAR,"NuSTAR observed the bright Compton-thin, narrow line Seyfert 1 galaxy, NGC
5506, for about 56 ks. In agreement with past observations, the spectrum is
well fit by a power law with Gamma~1.9, a distant reflection component and
narrow ionized iron lines. A relativistically blurred reflection component is
not required by the data. When an exponential high energy cutoff is added to
the power law, a value of 720(+130,-190) keV (90% confidence level) is found.
Even allowing for systematic uncertainties, we find a 3 sigma lower limit to
the high-energy cutoff of 350 keV, the highest lower limit to the cutoff energy
found so far in an AGN by NuSTAR.",1412.4541v1
2014-12-19,[(Li0.8Fe0.2)OH]FeS and the ferromagnetic superconductors [(Li0.8Fe0.2)OH]Fe(S1-xSex) (0<x<1),"[(Li0.8Fe0.2)OH]FeS and the series [(Li0.8Fe0.2)OH]Fe(S1-xSex) (0<x<1) were
synthesized by hydrothermal methods and characterized by X-ray single crystal
and powder diffraction, EDX and chemical analysis. Selenium-rich compounds show
the coexistence of magnetic ordering with superconductivity known from the pure
selenium compound. Sulphur doping decreases the critical temperature through
chemical pressure until superconductivity is completely absent in
[(Li0.8Fe0.2)OH]FeS, while the ferromagnetism in the [(Li0.8Fe0.2)OH] layers
persists. The Li:Fe ratio in the hydroxide layer, and thus the charge transfer
of 0.2 electrons from the hydroxide to the iron chalcogenide layers remains
unchanged in [(Li0.8Fe0.2)OH]Fe(S1-xSex), which indicates that the chemical
pressure effect of the smaller sulphide ions impedes superconductivity in
[(Li0.8Fe0.2)OH]FeS",1412.6475v1
2014-12-19,Red Supergiant Stars as Cosmic Abundance Probes. III. NLTE effects in J-band Magnesium lines,"Non-LTE calculations for Mg I in red supergiant stellar atmospheres are
presented to investigate the importance of non-LTE for the formation of Mg I
lines in the NIR J-band. Recent work using medium resolution spectroscopy of
atomic lines in the J-band of individual red supergiant stars has demonstrated
that technique is a very promising tool to investigate the chemical composition
of the young stellar population in star forming galaxies. As in previous work,
where non-LTE effects were studied for iron, titanium and silicon, substantial
effects are found resulting in significantly stronger Mg I absorption lines.
For the quantitative spectral analysis the non-LTE effects lead to magnesium
abundances significantly smaller than in LTE with the non-LTE abundance
corrections varying smoothly between -0.4 dex and -0.1 dex for effective
temperatures between 3400 K and 4400 K. We discuss the physical reasons of the
non-LTE effects and the consequences for extragalactic J-band abundance studies
using individual red supergiants in the young massive galactic double cluster h
and chi Persei.",1412.6527v2
2014-12-22,Superconductivity-induced reentrance of orthorhombic distortion in Ba1-xKxFe2As2,"Detailed knowledge of the phase diagram and the nature of the competing
magnetic and superconducting phases is imperative for an understanding of the
physics of iron-based superconductivity. Here, we show using thermodynamic
probes that the phase diagram of the first discovered, and highest Tc, 122-type
material, Ba1-xKxFe2As2 is in fact much richer than previously reported. Inside
the usual stripe-type magnetic order with C2-symmetry, we find a small pocket
of a tetragonal, C4-symmetric phase, which surprisingly reverts back to the
C2-phase at or slightly below the superconducting transition. This re-entrance
to a low-temperature orthorhombic state induced by superconductivity is
discussed in terms of competition of the two magnetic phases with
superconductivity and is illustrated by the measured changes in the electronic
entropy of the system. Using our thermodynamic data, we make predictions about
how the phase diagram of these competing orders will change under pressure.",1412.7038v2
2014-12-23,Tuning the magnetic anisotropy of single molecules,"The magnetism of single atoms and molecules is governed by the atomic scale
environment. In general, the reduced symmetry of the surrounding splits the $d$
states and aligns the magnetic moment along certain favorable directions. Here,
we show that we can reversibly modify the magnetocrystalline anisotropy by
manipulating the environment of single iron(II) porphyrin molecules adsorbed on
Pb(111) with the tip of a scanning tunneling microscope. When we decrease the
tip--molecule distance, we first observe a small increase followed by an
exponential decrease of the axial anisotropy on the molecules. This is in
contrast to the monotonous increase observed earlier for the same molecule with
an additional axial Cl ligand. We ascribe the changes in the anisotropy of both
species to a deformation of the molecules in the presence of the attractive
force of the tip, which leads to a change in the $d$ level alignment. These
experiments demonstrate the feasibility of a precise tuning of the magnetic
anisotropy of an individual molecule by mechanical control.",1412.7454v2
2014-12-30,GPU-based acceleration of free energy calculations in solid state physics,"Obtaining a thermodynamically accurate phase diagram through numerical
calculations is a computationally expensive problem that is crucially important
to understanding the complex phenomena of solid state physics, such as
superconductivity. In this work we show how this type of analysis can be
significantly accelerated through the use of modern GPUs. We illustrate this
with a concrete example of free energy calculation in multi-band iron-based
superconductors, known to exhibit a superconducting state with oscillating
order parameter. Our approach can also be used for classical BCS-type
superconductors. With a customized algorithm and compiler tuning we are able to
achieve a 19x speedup compared to the CPU (119x compared to a single CPU core),
reducing calculation time from minutes to mere seconds, enabling the analysis
of larger systems and the elimination of finite size effects.",1412.8754v2
2014-12-31,"La$_2$O$_3$Fe$_2$Se$_2$, a Mott insulator on the brink of orbital-selective metalization","La$_2$O$_3$Fe$_2$Se$_2$ can be explained in terms of Mott localization in
sharp contrast with the metallic behavior of FeSe and other parent parent
compounds of iron superconductors. We demonstrate that the key ingredient that
makes La$_2$O$_3$Fe$_2$Se$_2$ a Mott insulator, rather than a correlated metal
dominated by the Hund's coupling is the enhanced crystal-field splitting,
accompanied by a smaller orbital-resolved kinetic energy. The strong deviation
from orbital degeneracy introduced by the crystal-field splitting also pushes
this materials close to an orbital-selective Mott transition. We predict that
either doping or uniaxial external pressure can drive the material into an
orbital-selective Mott state, where only one or few orbitals are metallized
while the others remain insulating.",1501.00118v1
2015-01-02,Mott-Kondo Insulator Behavior in the Iron Oxychalcogenides,"We perform a combined experimental-theoretical study of the
Fe-oxychalcogenides (FeO$\emph{Ch}$) series
La$_{2}$O$_{2}$Fe$_{2}$O\emph{M}$_{2}$ (\emph{M}=S, Se), which is the latest
among the Fe-based materials with the potential \ to show unconventional
high-T$_{c}$ superconductivity (HTSC). A combination of incoherent Hubbard
features in X-ray absorption (XAS) and resonant inelastic X-ray scattering
(RIXS) spectra, as well as resitivity data, reveal that the parent
FeO$\emph{Ch}$ are correlation-driven insulators. To uncover microscopics
underlying these findings, we perform local density
approximation-plus-dynamical mean field theory (LDA+DMFT) calculations that
unravel a Mott-Kondo insulating state. Based upon good agreement between theory
and a range of data, we propose that FeO$\emph{Ch}$ may constitute a new, ideal
testing ground to explore HTSC arising from a strange metal proximate to a
novel selective-Mott quantum criticality.",1501.00332v1
2015-01-02,"Magnetism in Quasi-One-Dimensional A$_2$Cr$_3$As$_3$ (A=K,Rb) superconductors","We predict that the recently discovered quasi-one dimensional
superconductors, A$_2$Cr$_3$As$_3$(A=K,Rb), possess strong frustrated magnetic
fluctuations and are nearby a novel in-out co-planar magnetic ground state. The
frustrated magnetism is very sensitive to c-axis lattice constant and can thus
be suppressed by increasing pressure. Our results qualitatively explain strong
non-Fermi liquid behaviors observed in the normal state of the superconductors
as the intertwining between the magnetism and superconductivity can create a
large quantum critical region in quasi-one dimensional systems and also suggest
that the materials share similar phase diagrams and superconducting mechanism
with other unconventional superconductors, such as cuprates and iron-based
superconductors.",1501.00412v2
2015-01-03,Single Phase Synthesis and Room temperature Neutron Diffraction Studies on Multiferroic PbFe0.5Nb0.5O3,"The Lead-iron-niobate, (PbFe0.5Nb0.5O3 or PFN) was synthesized by low
temperature sintering Single Step / Solid State Reaction Method. The 700 C / 2
hrs calcined powder was sintered at 1050 C / 1 hr. The sintered pellets were
characterized through X-Ray Diffraction and Neutron Diffraction at room
temperature. It is found from the XRD pattern that the materials is in single
phase with no traces of pyrochlore phase. It was also confirmed from the
neutron diffraction pattern, the structure of PFN to be monoclinic, belongs to
space group C m. Structural studies has been carried out by refining the
obtained neutron diffraction data by Reitveld refinement method using Full Prof
Program. The neutron diffraction pattern at 290K (near room temperature) was
selected to refine the structure. The Lattice parameters obtained are; a =
5.6709 A, b = 5.6732, c = 4.0136 and {\alpha} = 90, \b{eta} = 89.881, {\gamma}
= 90.000. The P-E measurements showed hysteretic behavior with high remnant
polarization.",1501.00553v1
2015-01-05,Nematicity and quantum paramagnetism in FeSe,"In common with other iron-based high temperature superconductors, FeSe
exhibits a transition to a ``nematic'' phase below 90Kelvin in which the
crystal rotation symmetry is spontaneously broken. However, the absence of
strong low-frequency magnetic fluctuations near or above the transition has
been interpreted as implying the primacy of orbital ordering. In contrast, we
establish that quantum fluctuations of spin-1 local moments with strongly
frustrated exchange interactions can lead to a nematic quantum paramagnetic
phase consistent with the observations in FeSe. We show that this phase is a
fundamental expression of the existence of a Berry's phase associated with the
topological defects of a N\'eel antiferromagnet, in a manner analogous to that
which gives rise to valence bond crystal order for spin 1/2 systems. We present
an exactly solvable model realizing the nematic quantum paramagnetic phase,
discuss its relation with the spin-1 $J_1-J_2$ model, and construct a field
theory of the Landau-forbidden transition between the N\'eel state and this
nematic quantum paramagnet.",1501.00844v2
2015-01-05,A novel platform for two-dimensional chiral topological superconductivity,"We show that the surface of an $s$-wave superconductor decorated with a
two-dimensional lattice of magnetic impurities can exhibit chiral topological
superconductivity. If impurities order ferromagnetically and the
superconducting surface supports a sufficiently strong Rashba-type spin-orbit
coupling, Shiba sub-gap states at impurity locations can hybridize into
Bogoliubov bands with non-vanishing, sometimes large, Chern number $C$. This
topological superconductor supports $C$ chiral Majorana edge modes. We
construct phase diagrams for model two-dimensional superconductors, accessing
the dilute and dense magnetic impurity limits analytically and the intermediate
regime numerically. To address potential experimental systems, we identify
stable configurations of ferromagnetic iron atoms on the Pb (111) surface and
conclude that ferromagnetic adatoms on Pb surfaces can provide a versatile
platform for two-dimensional topological superconductivity.",1501.00999v1
2015-01-07,Pulse radiolysis studies on superoxide reductase from Treponema pallidum,"Superoxide reductases (SORs) are small metalloenzymes, which catalyze
reduction of O2*- to H2O2. The reaction of the enzyme from Treponema pallidum
with superoxide was studied by pulse radiolysis methods. The first step is an
extremely fast bi-molecular reaction of the ferrous center with O2, with a rate
constant of 6 x 10 (8) M(-1) s(-1). A first intermediate is formed which is
converted to a second one with a slower rate constant of 4800 s(-1). This
latter value is 10 times higher than the corresponding one previously reported
in the case of SOR from Desulfoarculus baarsii. The reconstituted spectra for
the two intermediates are consistent with formation of transient iron-peroxide
species.",1501.01443v1
2015-01-07,The flavin reductase ActVB from Streptomyces coelicolor: characterization of the electron transferase activity of the flavoprotein form,"The flavin reductase ActVB is involved in the last step of actinorhodin
biosynthesis in Streptomyces coelicolor. Although ActVB can be isolated with
some FMN bound, this form was not involved in the flavin reductase activity. By
studying the ferric reductase activity of ActVB, we show that its FMN-bound
form exhibits a proper enzymatic activity of reduction of iron complexes by
NADH. This shows that ActVB active site exhibits a dual property with regard to
the FMN. It can use it as a substrate that goes in and off the active site or
as a cofactor to provide an electron transferase activity to the polypeptide.",1501.01465v1
2015-01-07,Identification of iron(III) peroxo species in the active site of the superoxide reductase SOR from Desulfoarculus baarsii,"The active site of superoxide reductase SOR consists of an Fe2+ center in an
unusual [His4 Cys1] square-pyramidal geometry. It specifically reduces
superoxide to produce H2O2. Here, we have reacted the SOR from Desulfoarculus
baarsii directly with H2O2. We have found that its active site can transiently
stabilize an Fe3+-peroxo species that we have spectroscopically characterized
by resonance Raman. The mutation of the strictly conserved Glu47 into alanine
results in a stabilization of this Fe3+-peroxo species, when compared to the
wild-type form. These data support the hypothesis that the reaction of SOR
proceeds through such a Fe3+-peroxo intermediate. This also suggests that Glu47
might serve to help H2O2 release during the reaction with superoxide.",1501.01470v1
2015-01-07,Maximum screening fields of superconducting multilayer structures,"It is shown that a multilayer comprised of alternating thin superconducting
and insulating layers on a thick substrate can fully screen the applied
magnetic field exceeding the superheating fields $H_s$ of both the
superconducting layers and the substrate, the maximum Meissner field is
achieved at an optimum multilayer thickness. For instance, a dirty layer of
thickness $\sim 0.1\; \mu$m at the Nb surface could increase $H_s\simeq 240$ mT
of a clean Nb up to $H_s\simeq 290$ mT. Optimized multilayers of Nb$_3$Sn, NbN,
some of the iron pnictides, or alloyed Nb deposited onto the surface of the Nb
resonator cavities could potentially double the rf breakdown field, pushing the
peak accelerating electric fields above 100 MV/m while protecting the cavity
from dendritic thermomagnetic avalanches caused by local penetration of
vortices.",1501.01512v1
2015-01-08,Sulfurization of Iron in the Dynamic Solar Nebula and Implications for Planetary Compositions,"One explanation for the enhanced ratio of volatiles to hydrogen in Jupiter's
atmosphere compared to a a gas of solar composition is that the planet accreted
volatile-bearing clathrates during its formation. Models, however, suggest that
S would be over abundant if clathrates were the primary carrier of Jupiter's
volatiles. This led to the suggestion that S was depleted in the outer nebula
due to the formation troilite (FeS). Here, this depletion is quantitatively
explored by modeling the coupled dynamical and chemical evolution of Fe grains
in the solar nebula. It is found that disks that undergo rapid radial expansion
from an initially compact state may allow sufficient production of FeS and
carry H$_{2}$S-depleted gas outward where ices would form, providing the
conditions needed for S-depleted clathrates to form. However, this expansion
would also carry FeS grains to this region, which could also be incorporated
into planetesimals. Thus for clathrates to be a viable source of volatiles,
models must account for the presence of both H$_{2}$S in FeS in the outer solar
nebula.",1501.01878v1
2015-01-09,Study of the chemical composition of high energy cosmic rays using the muon LDF of EAS between $10^{17.25}$ eV and $10^{17.75}$ eV,"We explore the feasibility of estimating primary cosmic ray composition at
high energies from the study of two parameters of Extensive Air Showers (EAS)
at ground and underground level with Monte Carlo simulations using the new EPOS
and QGSJETII hadronic models tuned with LHC data. Namely, the slope and density
at a given distance of the muon lateral distribution function are analysed in
this work. The power to discriminate primary masses is quantified in terms of
merit factor for each parameter. The analysis considers three different primary
particles (proton, iron and gamma), four different zenith angles (0$^{\circ}$,
15$^{\circ}$, 30$^{\circ}$ and 45$^{\circ}$) and primary energies of
$10^{17.25}$ eV, $10^{17.50}$ eV and $10^{17.75}$ eV.",1501.02217v1
2015-01-11,Hidden Order as a Source of Interface Superconductivity,"Interfacial superconductivity is observed in a variety of heterostructures
composed of different materials including superconducting and
nonsuperconducting (at appropriate doping and temperatures) cuprates and
iron-based pnictides. The origin of this superconductivity remains in many
cases unclear. Here, we propose a general mechanism of interfacial
superconductivity for systems with competing order parameters. We assume that
parameters characterizing the material allow formation of another order like
charge- or spin-density wave competing and prevailing superconductivity in the
bulk (hidden superconductivity). Diffusive electron scattering on the interface
results in a suppression of this order and releasing the superconductivity. Our
theory is based on the use of Ginzburg--Landau equations applicable to a broad
class of systems. We demonstrate that the local superconductivity appears in
the vicinity of the interface and the spatial dependence of the superconducting
order parameter~$\Delta(x)$ is described by the Gross--Pitaevskii equation.
Solving this equation we obtain quantized values of temperature and doping
levels at which~$\Delta(x)$ appears. Remarkably, the local superconductivity
shows up even in the case when the rival order is only slightly suppressed and
may arise also on the surface of the sample (surface superconductivity).",1501.02505v2
2015-01-16,Slow magnetic fluctuations and superconductivity in fluorine-doped NdFeAsO,"Among the widely studied superconducting iron-pnictide compounds belonging to
the Ln1111 family (with Ln a lanthanide), a systematic investigation of the
crossover region between the superconducting and the antiferromagnetic phase
for the Ln = Nd case has been missing. We fill this gap by focusing on the
intermediate doping regime of NdFeAsO(1-x)F(x) by means of dc-magnetometry and
muon-spin spectroscopy measurements. The long-range order we detect at low
fluorine doping is replaced by short-range magnetic interactions at x = 0.08,
where also superconductivity appears. In this case, longitudinal-field
muon-spin spectroscopy experiments show clear evidence of slow magnetic
fluctuations that disappear at low temperatures. This fluctuating component is
ascribed to the glassy-like character of the magnetically ordered phase of
NdFeAsO at intermediate fluorine doping.",1501.04005v1
2015-01-19,Raman scattering in superconducting NdO1-xFxBiS2 crystals,"The recently discovered layered BiS2-based superconductors have attracted a
great deal of interest due to their structural similarity to cuprate and
iron-pnictide superconductors. We have performed Raman scattering measurements
on two superconducting crystals NdO0.5F0.5BiS2 (Tc = 4.5 K) and NdO0.7F0.3BiS2
(Tc = 4.8 K). The observed Raman phonon modes are assigned with the aid of
first-principles calculations. The asymmetrical phonon mode around 118 cm-1
reveals a small electron-phonon (e-ph) coupling constant 0.16, which is
insufficient to generate superconductivity at ~ 4.5 K. In the Raman spectra
there exists a clear temperature-dependent hump around 100 cm-1, which can be
well understood in term of inter-band vertical transitions around Fermi
surface. The transitions get boosted when the particular rectangular-like Fermi
surface meets band splitting caused by spin-orbit coupling. It enables a unique
and quantitative insight into the band splitting.",1501.04453v2
2015-01-20,Shape optimization of an electric motor subject to nonlinear magnetostatics,"The goal of this paper is to improve the performance of an electric motor by
modifying the geometry of a specific part of the iron core of its rotor. To be
more precise, the objective is to smooth the rotation pattern of the rotor. A
shape optimization problem is formulated by introducing a tracking-type cost
functional to match a desired rotation pattern. The magnetic field generated by
permanent magnets is modeled by a nonlinear partial differential equation of
magnetostatics. The shape sensitivity analysis is rigorously performed for the
nonlinear problem by means of a new shape-Lagrangian formulation adapted to
nonlinear problems.",1501.04752v1
2015-01-25,Sensorless Battery Internal Temperature Estimation using a Kalman Filter with Impedance Measurement,"This study presents a method of estimating battery cell core and surface
temperature using a thermal model coupled with electrical impedance
measurement, rather than using direct surface temperature measurements. This is
advantageous over previous methods of estimating temperature from impedance,
which only estimate the average internal temperature. The performance of the
method is demonstrated experimentally on a 2.3 Ah lithium-ion iron phosphate
cell fitted with surface and core thermocouples for validation. An extended
Kalman filter, consisting of a reduced order thermal model coupled with
current, voltage and impedance measurements, is shown to accurately predict
core and surface temperatures for a current excitation profile based on a
vehicle drive cycle. A dual extended Kalman filter (DEKF) based on the same
thermal model and impedance measurement input is capable of estimating the
convection coefficient at the cell surface when the latter is unknown. The
performance of the DEKF using impedance as the measurement input is comparable
to an equivalent dual Kalman filter using a conventional surface temperature
sensor as measurement input.",1501.06160v1
2015-01-26,Measurement of the chemical composition of the ultra-high-energy cosmic rays with the Pierre Auger Observatory,"The Pierre Auger Observatory infers the chemical composition of
ultra-high-energy cosmic rays through two independent detection techniques. The
Fluorescence Detector (FD) measures the longitudinal profile of high energy air
showers and can determine the depth of the shower maximum $X_{max}$, which is
sensitive to the chemical composition of the primary cosmic rays. Additionally,
measurements by the Surface Detector (SD) provide independent experimental
observables based on the muonic shower component to analyze the chemical
composition. We present the results for the $X_{max}$ distributions and the
mass composition results measured by the FD and the SD for the energies $E \geq
10^{18}$\,eV. The data will be compared with the expectations for proton and
iron primaries according to different hadronic interaction models.",1501.06325v1
2015-01-28,The Bubble-like Interior of the Core-Collapse Supernova Remnant Cassiopeia A,"The death of massive stars is believed to involve aspheric explosions
initiated by the collapse of an iron core. The specifics of how these
catastrophic explosions proceed remain uncertain due, in part, to limited
observational constraints on various processes that can introduce asymmetries
deep inside the star. Here we present near-infrared observations of the young
Milky Way supernova remnant Cassiopeia A, descendant of a type IIb
core-collapse explosion, and a three-dimensional map of its interior, unshocked
ejecta. The remnant's interior has a bubble-like morphology that smoothly
connects to and helps explain the multi-ringed structures seen in the remnant's
bright reverse shocked main shell of expanding debris. This internal structure
may have originated from turbulent mixing processes that encouraged the
development of outwardly expanding plumes of radioactive 56Ni-rich ejecta. If
this is true, substantial amounts of its decay product, 56Fe, may still reside
in these interior cavities.",1501.07283v1
2015-02-02,Cold condensation of dust in the ISM,"The condensation of complex silicates with pyroxene and olivine composition
at conditions prevailing in molecular clouds has been experimentally studied.
For this purpose, molecular species comprising refractory elements were forced
to accrete on cold substrates representing the cold surfaces of surviving dust
grains in the interstellar medium. The efficient formation of amorphous and
homogeneous magnesium iron silicates at temperatures of about 12 K has been
monitored by IR spectroscopy. The gaseous precursors of such condensation
processes in the interstellar medium are formed by erosion of dust grains in
supernova shock waves. In the laboratory, we have evaporated glassy silicate
dust analogs and embedded the released species in neon ice matrices that have
been studied spectroscopically to identify the molecular precursors of the
condensing solid silicates. A sound coincidence between the 10 micron band of
the interstellar silicates and the 10 micron band of the low-temperature
siliceous condensates can be noted.",1502.00388v1
2015-02-04,Is inner core seismic anisotropy a marker of plastic flow of cubic iron?,"This paper investigates whether observations of seismic anisotropy are
compatible with a cubic structure of the inner core Fe alloy. We assume that
anisotropy is the result of plastic deformation within a large scale flow
induced by preferred growth at the inner core equator. Based on elastic moduli
from the literature, bcc- or fcc-Fe produce seismic anisotropy well below
seismic observations ($\textless{}0.4\%$). A Monte-Carlo approach allows us to
generalize this result to any form of elastic anisotropy in a cubic system.
Within our model, inner core global anisotropy is not compatible with a cubic
structure of Fe alloy. Hence, if the inner core material is indeed cubic, large
scale coherent anisotropic structures, incompatible with plastic deformation
induced by large scale flow, must be present.",1502.01270v1
2015-02-05,Code intercomparison and benchmark for muon fluence and absorbed dose induced by an 18-GeV electron beam after massive iron shielding,"In 1974, Nelson, Kase, and Svenson published an experimental investigation on
muon shielding using the SLAC high energy LINAC. They measured muon fluence and
absorbed dose induced by a 18 GeV electron beam hitting a copper/water beam
dump and attenuated in a thick steel shielding. In their paper, they compared
the results with the theoretical mode ls available at the time. In order to
compare their experimental results with present model calculations, we use the
modern transport Monte Carlo codes MARS15, FLUKA2011 and GEANT4 to model the
experimental setup and run simulations. The results will then be compared
between the codes, and with the SLAC data.",1502.01681v1
2015-02-18,UV spectra of iron-doped carbon clusters FeC_n n = 3-6,"Electronic transitions of jet-cooled FeC$_n$ clusters ($n = 3 - 6$) were
measured between 230 and 300 nm by a mass-resolved 1+1 resonant two-photon
ionization technique. Rotational profiles were simulated based on previous
calculations of ground state geometries and compared to experimental
observations. Reasonable agreement is found for the planar fan-like structure
of FeC$_3$. The FeC$_4$ data indicate a shorter distance between the Fe atom
and the bent C$_4$ unit of the fan. The transitions are suggested to be
$^{3}$A$_{2} \leftarrow ^{3}$B$_{1}$ for FeC$_3$ and $^{5}$A$_{1} \leftarrow
^{5}$A$_{1}$ for FeC$_4$. In contrast to the predicted C$_{\infty \text{v}}$
geometry, non-linear FeC$_5$ is apparently observed. Line width broadening
prevents analysis of the FeC$_6$ spectrum.",1502.05310v1
2015-02-19,Low 60Fe abundance in Semarkona and Sahara 99555,"Iron-60 (t1/2=2.62 Myr) is a short-lived nuclide that can help constrain the
astrophysical context of solar system formation and date early solar system
events. A high abundance of 60Fe (60Fe/56Fe= 4x10-7) was reported by in situ
techniques in some chondrules from the LL3.00 Semarkona meteorite, which was
taken as evidence that a supernova exploded in the vicinity of the birthplace
of the Sun. However, our previous MC-ICPMS measurements of a wide range of
meteoritic materials, including chondrules, showed that 60Fe was present in the
early solar system at a much lower level (60Fe/56Fe=10-8). The reason for the
discrepancy is unknown but only two Semarkona chondrules were measured by
MC-ICPMS and these had Fe/Ni ratios below ~2x chondritic. Here, we show that
the initial 60Fe/56Fe ratio in Semarkona chondrules with Fe/Ni ratios up to
~24x chondritic is 5.4x10-9. We also establish the initial 60Fe/56Fe ratio at
the time of crystallization of the Sahara 99555 angrite, a chronological
anchor, to be 1.97x10-9. These results demonstrate that the initial abundance
of 60Fe at solar system birth was low, corresponding to an initial 60Fe/56Fe
ratio of 1.01x10-8.",1502.05611v1
2015-02-20,Magnetic and Dielectric Properties of Multiferroic BiFeO3 Nanoparticles Synthesized by a Novel Citrate Combustion Method,"Single phase BiFeO3 nanoparticles have been successfully synthesized for the
first time by a novel citrate combustion method without using any solvent. Well
mixed metal nitrates along with citric acid which is used as fuel combust to
give BiFeO3 nanoparticles after annealing. These particles are single phase in
nature and crystallize in the rhombohedral distorted perovskite structure
(space group-R3c) which has been confirmed by the Rietveld refinement of the
room temperature powder x-ray diffraction data. Nearly spherical particles of
average particle size 47 nm have been seen from transmission electron
micrograph. Room temperature magnetic hysteresis measurement shows weak
ferromagnetism though the magnetization does not saturate upto 1.75 T applied
field. The coercive field value is calculated to be 180 Oe which is 3 times
higher than that prepared by solvent free combustion method using Glycine. 57Fe
M\""ossbauer spectrum can be fitted with a sextet corresponding to single
magnetic state of hyperfine field about 49.5 T corresponding to Fe3+ state of
the iron atom. The dielectric relaxation and ac conductivity as a function of
frequency have been discussed. High dielectric permittivity has not been found
in these nanoparticles like other reported BiFeO3 ceramics.",1502.05797v1
2015-02-21,Spin liquid polymorphism in a correlated electron system on the threshold of superconductivity,"We report neutron scattering measurements, which reveal spin-liquid
polymorphism in a '11' iron chalcogenide superconductor, a poorly-metallic
magnetic FeTe tuned towards superconductivity by substitution of a small amount
of Tellurium with iso-electronic Sulphur. We observe liquid-like magnetic
dynamics, which is described by a competition of two phases with different
local structure, whose relative abundance depends on temperature. One is the
ferromagnetic (FM) plaquette phase observed in the non-superconducting FeTe,
which preserves the C$_4$ symmetry of the underlying square lattice and is
favored at high temperatures. The other is the antiferromagnetic plaquette
phase with broken C$_4$ symmetry, which emerges with doping and is predominant
at low temperatures. These findings suggest a first-order liquid-liquid phase
transition in the electronic spin system of FeTe$_{1-x}$(S,Se)$_x$. We thus
discover remarkable new physics of competing spin liquid polymorphs in a
correlated electron system approaching superconductivity. Our results
facilitate an understanding of large swaths of recent experimental data in
unconventional superconductors.",1502.06051v1
2015-02-25,HD188112: Supernova Ia progenitor?,"HD188112 is an extremely low mass white dwarf in a close binary system.
According to a previous study, the mass of HD188112 is $\sim$0.24 Msun and a
lower limit of 0.73 Msun could be put for the mass of its unseen companion, a
compact degenarate object. We used HST STIS spectra to measure the rotational
broadening of UV metallic lines in HD188112, in order to put tighter
constraints on the mass of its companion. By assuming that the system in is
synchronous rotation, we derive a companion mass between 1.05 and 1.25 Msun. We
also measure abundances for magnesium, silicon, and iron, respectively log
$N$(X)/$N$(H) = $-$6.40, $-$7.25, and $-$5.81. The radial velocities measured
from the UV spectra are found to be in very good agreement with the prediction
based on the orbital parameters derived in the previous study made a decade
ago.",1502.07096v1
2015-02-25,Electron capture cross sections for stellar nucleosynthesis,"In the first stage of this work, we perform detailed calculations for the
cross sections of the electron capture on nuclei under laboratory conditions.
Towards this aim we exploit the advantages of a refined version of the
proton-neutron quasi-particle random-phase approximation (pn-QRPA) and carry
out state-by-state evaluations of the rates of exclusive processes that lead to
any of the accessible transitions within the chosen model space. In the second
stage of our present study, we translate the above mentioned $e^-$-capture
cross sections to the stellar environment ones by inserting the temperature
dependence through a Maxwell-Boltzmann distribution describing the stellar
electron gas. As a concrete nuclear target we use the $^{66}Zn$ isotope, which
belongs to the iron group nuclei and plays prominent role in stellar
nucleosynthesis at core collapse supernovae environment.",1502.07225v1
2015-02-27,Doping evolution of antiferromagnetism and transport properties in the non-superconducting BaFe2-2xNixCrxAs2,"We report elastic neutron scattering and transport measurements on the Ni and
Cr equivalently doped iron pnictide BaFe$_{2-2x}$Ni$_{x}$Cr$_{x}$As$_{2}$.
Compared with the electron-doped BaFe$_{2-x}$Ni$_{x}$As$_{2}$, the long-range
antiferromagnetic (AF) order in BaFe$_{2-2x}$Ni$_{x}$Cr$_{x}$As$_{2}$ is
gradually suppressed with vanishing ordered moment and N\'{e}el temperature
near $x= 0.20$ without the appearance of superconductivity. A detailed analysis
on the transport properties of BaFe$_{2-x}$Ni$_{x}$As and
BaFe$_{2-2x}$Ni$_{x}$Cr$_{x}$As$_{2}$ suggests that the non-Fermi-liquid
behavior associated with the linear resistivity as a function of temperature
may not correspond to the disappearance of the static AF order. From the
temperature dependence of the resistivity in overdoped compounds without static
AF order, we find that the transport properties are actually affected by Cr
impurity scattering, which may induce a metal-to-insulator crossover in highly
doped BaFe$_{1.7-y}$Ni$_{0.3}$Cr$_{y}$As$_{2}$.",1502.07950v1
2015-02-27,Is HE 0436-4717 Anemic? A deep look at a bare Seyfert 1 galaxy,"A multi-epoch, multi-instrument analysis of the Seyfert 1 galaxy HE 0436-4717
is conducted using optical to X-ray data from XMM-Newton and Swift (including
the BAT). Fitting of the UV-to-X-ray spectral energy distribution shows little
evidence of extinction and the X-ray spectral analysis does not confirm
previous reports of deep absorption edges from OVIII. HE 0436-4717 is a ""bare""
Seyfert with negligible line-of-sight absorption making it ideal to study the
central X-ray emitting region. Three scenarios were considered to describe the
X-ray data: partial covering absorption, blurred reflection, and soft
Comptonization. All three interpretations describe the 0.5-10.0 keV spectra
well. Extrapolating the models to 100 keV results in poorer fits for the the
partial covering model. When also considering the rapid variability during one
of the XMM-Newton observations, the blurred reflection model appears to
describe all the observations in the most self-consistent manner. If adopted,
the blurred reflection model requires a very low iron abundance in HE
0436-4717. We consider the possibilities that this is an artifact of the
fitting process, but it appears possible that it is intrinsic to the object.",1502.07958v1
2015-03-03,Magnetic Fields of Uranus and Neptune: Metallic Fluid Hydrogen,"The magnetic fields of the Ice Giant Planets Uranus and Neptune (U/N) are
unique in the solar system. Based on a substantial database measured on Earth
for representative planetary fluids at representative dynamic pressures up to
200 GPa (2 Mbar) and a few 1000 K, the complex magnetic fields of U/N are (i)
probably made primarily by degenerate metallic fluid H (MFH) at or near the
crossover from the H-He envelopes to Ice cores at ~100 GPa (Mbar) pressures and
normalized radii of ~90% of the radii of U/N; (ii) because those magnetic
fields are made relatively close to the surfaces of U/N, non-dipolar fields can
be expected; (iii) the Ice cores are most probably a heterogeneous fluid
mixture of H, N, O, C, Fe/Ni and silicate-oxides and their mutual reaction
products at high pressures and temperatures,as discussed elsewhere. Ironically,
there is probably little nebular Ice in the Ice Giant Planets.",1503.01042v2
2015-03-06,NMR evidence for inhomogeneous glassy behavior driven by nematic fluctuations in iron arsenide superconductors,"We present $^{75}$As nuclear magnetic resonance spin-lattice and spin-spin
relaxation rate data in Ba(Fe$_{1-x}$Co$_x$)$_2$As$_2$ and
Ba(Fe$_{1-x}$Cu$_x$)$_2$As$_2$ as a function of temperature, doping and
magnetic field. The relaxation curves exhibit a broad distribution of
relaxation rates, consistent with inhomogeneous glassy behavior up to 100 K.
The doping and temperature response of the width of the dynamical heterogeneity
is similar to that of the nematic susceptibility measured by elastoresistance
measurements. We argue that quenched random fields which couple to the nematic
order give rise to a nematic glass that is reflected in the spin dynamics.",1503.01844v2
2015-03-09,Buffer Aided Relaying Improves Both Throughput and End-to-End Delay,"Buffer aided relaying has recently attracted a lot of attention due to the
improvement in the system throughput. However, a side effect usually deemed is
that buffering at relay nodes results in the increase in packet delays. In this
paper, we study the effect of buffering relays on the end-to-end delay of
users' data, from the time they arrive at source until delivery to the
destination. We use simple discussions to provide an insight on the overall
waiting time of the packets in the system. By studying the Bernoulli
distributed channel conditions, and using intuitive generalizations, we
conclude that the use of buffers at relays improves not only throughput, but
ironically the end-to-end delay as well. Computer simulations in the settings
of practical systems confirm the above results.",1503.02348v1
2015-03-09,Itinerancy enhanced quantum fluctuation of magnetic moments in iron-based superconductors,"We investigate the influence of itinerant carriers on dynamics and
fluctuation of local moments in Fe-based superconductors, via linear spin-wave
analysis of a spin-fermion model containing both itinerant and local degrees of
freedom. Surprisingly against the common lore, instead of enhancing the
($\pi$,0) order, itinerant carriers with well nested Fermi surfaces is found to
induce significant amount of \textit{spatial} and temporal quantum fluctuation
that leads to the observed small ordered moment. Interestingly, the underlying
mechanism is shown to be intra-pocket nesting-associated long-range coupling,
rather than the previously believed ferromagnetic double-exchange effect. This
challenges the validity of ferromagnetically compensated first-neighbor
coupling reported from short-range fitting to the experimental dispersion,
which turns out to result instead from the ferro-orbital order that is also
found instrumental in stabilizing the magnetic order.",1503.02653v1
2015-03-12,Anomalous phonon redshift in K-doped BaFe2As2 iron pnictides,"The effect of K, Co and P dopings on the lattice dynamics in the
BaFe$_2$As$_2$ system is studied by infrared spectroscopy. We focus on the
phonon at $\sim$ 253 cm$^{-1}$, the highest energy in-plane infrared-active
Fe-As mode in BaFe$_2$As$_2$. Our studies show that the Co and P dopings lead
to a blue shift of this phonon in frequency, which can be simply interpreted by
the change of lattice parameters induced by doping. In sharp contrast, an
unusual red shift of the same mode was observed in the K-doped compound, at
odds with the above explanation. This anomalous behavior in K-doped
BaFe$_2$As$_2$ is more likely associated with the coupling between lattice
vibrations and other channels, such as charge or spin. This coupling scenario
is also supported by the asymmetric line shape and intensity growth of the
phonon in the K-doped compound.",1503.03838v1
2015-03-13,MMonCa: An Object Kinetic Monte Carlo simulator for damage irradiation evolution and defect diffusion,"In this work we introduce the Object Kinetic Monte Carlo (OKMC) simulator
MMonCa and simulate the defect evolution in three different materials. We start
by explaining the theory of OKMC and showing some details of how such theory is
implemented by creating generic structures and algorithms in the objects that
we want to simulate. Then we successfully reproduce simulated results for
defect evolution in iron, silicon and tungsten using our simulator and compare
with available experimental data and similar simulations. The comparisons
validate MMonCa showing that it is powerful and flexible enough to be
customized and used to study the damage evolution of defects in a wide range of
solid materials.",1503.03987v1
2015-03-13,Microscopic Parameters from High-Resolution Specific Heat Measurements on Overdoped BaFe$_{2}$(As$_{1-x}$P$_{x}$)$_{2}$ Single Crystals,"We investigate the electronic specific heat of overdoped
BaFe$_{2}$(As$_{1-x}$P$_{x}$)$_{2}$ single crystals in the superconducting
state using high-resolution nanocalorimetry. From the measurements, we extract
the doping dependence of the condensation energy, superconducting gap $\Delta$,
and related microscopic parameters. We find that the anomalous scaling of the
specific heat jump $\Delta C \propto T_{\mathrm{c}}^3$, found in many
iron-based superconductors, in this system originates from a
$T_\mathrm{c}$-dependent ratio $\Delta/k_\mathrm{B}T_\mathrm{c}$ in combination
with a doping-dependent density of states $N(\varepsilon_\mathrm{F})$. A clear
enhancement is seen in the effective mass $m^{*}$ as the composition approaches
the value that has been associated with a quantum critical point at optimum
doping. However, a simultaneous increase in the superconducting carrier
concentration $n_\mathrm{s}$ maintains the superfluid density, yielding an
apparent penetration depth $\lambda$ that decreases with increasing
$T_\mathrm{c}$ without sharp divergence at the quantum critical point. Uemura
scaling indicates that $T_\mathrm{c}$ is governed by the Fermi temperature
$T_\mathrm{F}$ for this multi-band system.",1503.04088v1
2015-03-18,Super-Hydrophobic Multi-Walled Carbon Nanotube Coatings for Stainless Steel,"We have taken advantage of the native surface roughness and the iron content
of AISI 316 stainless steel to direct grow multi-walled carbon nanotube (MWCNT)
random networks by chemical vapor deposition (CVD) at low-temperature ($<
1000^{\circ}$C), without the addition of any external catalysts or
time-consuming pre-treatments. In this way, super-hydrophobic MWCNT films on
stainless steel sheets were obtained, exhibiting high contact angle values
($154^{\circ}$) and high adhesion force (high contact angle hysteresis).
Furthermore, the investigation of MWCNT films at scanning electron microscopy
(SEM) reveals a two-fold hierarchical morphology of the MWCNT random networks
made of hydrophilic carbonaceous nanostructures on the tip of hydrophobic
MWCNTs. Owing to the Salvinia effect, the hydrophobic and hydrophilic composite
surface of the MWCNT films supplies a stationary super-hydrophobic coating for
conductive stainless steel. This biomimetical inspired surface not only may
prevent corrosion and fouling but also could provide low-friction and
drag-reduction.",1503.05482v1
2015-03-20,"Collapse of the magnetic moment under pressure of AFe$_2$ (A = Y, Zr, Lu and Hf) in the cubic Laves phase","The electronic structures of four Laves phase iron compounds (e.g. YFe$_2$,
ZrFe$_2$, LuFe$_2$ and HfFe$_2$) have been calculated by the state-of-the-art
full potential electronic structure code. The magnetic moments collapse under
hydrostatic pressure. This feature is found to be universal in these materials.
Its electronic origin is provided by the sharp peaks in the density of states
near the Fermi level. It is shown that a first order quantum phase transition
can be expected under pressure in Y(Zr, or Lu)Fe$_2$, while a second order one
in HfFe$_2$. The bonding characteristics are discussed to elucidate the
equilibrium lattice constant variation. The large spontaneous volume
magnetostriction gives one of the most important character of these compounds.
Invar anomalies in these compounds can be partly explained by the current work
when the fast continuous magnetic moment decrease at the decrease of the
lattice constant was properly considered. This work may remind the
experimentalists of these ""old"" compounds and exploration of the quantum
properties under high pressures are greatly encouraged.",1503.06017v1
2015-03-25,Fractional Flux Plateau in Magnetization Curve of Multicomponent Superconductor Loop,"Time-reversal symmetry (TRS) may be broken in superconductors with three or
more condensates interacting repulsively, yielding two degenerate states
specified by chirality of gap functions. We consider a loop of such
superconductor with two halves occupied by the two states with opposite
chiralities. Fractional flux plateaus are found in magnetization curve
associated with free-energy minima, where the two domain walls between the two
halves accommodate different inter-component phase kinks leading to finite
winding numbers in a part of the whole condensates around the loop. Fractional
flux plateaus form pairs with their heights related to the flux quantum {\Phi}0
= hc/2e. This phenomenon is a clear evidence of time-reversal symmetry broken
(TRSB) superconductivity, which in a general point of view provides a novel
chance to explore relative phase difference, phase kink and soliton in
ubiquitous multi-component superconductivity such as that in iron pnicitides.",1503.07267v3
2015-03-26,Quantitative analysis of magnetic spin and orbital moments from an oxidized iron (1 1 0) surface using electron magnetic circular dichroism,"Understanding the ramifications of reduced crystalline symmetry on magnetic
behavior is a critical step in improving our understanding of nanoscale and
interfacial magnetism. However, investigations of such effects are often
controversial largely due to the challenges inherent in directly correlating
nanoscale stoichiometry and structure to magnetic behavior. Here, we describe
how to use Transmission Electron Microscope (TEM) to obtain Electron Magnetic
Circular Dichroism (EMCD) signals as a function of scattering angle to locally
probe the magnetic behavior of thin oxide layers grown on an Fe (1 1 0)
surface. Experiments and simulations both reveal a strong dependence of the
magnetic orbital to spin ratio on its scattering vector in reciprocal space. We
exploit this variation to extract the magnetic properties of the oxide cladding
layer, showing that it locally may exhibit an enhanced orbital to spin moment
ratio. This finding is supported here by both spatially and angularly resolved
EMCD measurements, opening up the way for compelling investigations into how
magnetic properties are affected by nanoscale features.",1503.07681v2
2015-03-28,Nearly-critical spin and charge fluctuations in KFe2As2 observed by high-pressure NMR,"We report a high-pressure 75As NMR study on the heavily hole-doped iron
pnictide superconductor KFe2As2 (Tc~3.8 K). The low-energy spin fluctuations
are found to decrease with applied pressure up to 2 GPa, but then increase
again, changing in lockstep with the pressure-induced evolution of Tc. Their
diverging nature suggests close proximity to a magnetic quantum critical point
at a negative pressure of P~-0.6 GPa. Above 2.4 GPa, the 75As satellite spectra
split below 40 K, indicating a breaking of As site symmetry and an incipient
charge order. These pressure-controlled phenomena demonstrate the presence of
nearly-critical fluctuations in both spin and charge, providing essential input
for the origin of superconductivity.",1503.08298v1
2015-03-31,Theory of excitations and dielectric response at a spin-orbital quantum critical point,"Despite possessing a local spin $2$ moment on the iron site and a Curie-Weiss
temperature of $45K$, the A site spinel FeSc$_2$S$_4$ does not magnetically
order down to 50mK. Previous theoretical work by Chen and Balents advanced an
explanation for this observation in the form of the ""$J_2$-$\lambda$"" model
which places FeSc$_2$S$_4$ close to a quantum critical point on the disordered
side of a quantum phase transition between a N\'{e}el ordered phase and a
""Spin-Orbital Liquid"" in which spins and orbitals are entangled, quenching the
magnetization. We present new theoretical studies of the optical properties of
the $J_2$-$\lambda$ model, including a computation of the dispersion relation
for the quasiparticle excitations and the form of the collective response to
electric field. We argue that the latter directly probes a low energy
excitation continuum characteristic of quantum criticality, and that our
results reinforce the consistency of this model with experiment.",1503.08887v2
2015-03-31,Ultrafast near infrared photoinduced absorption in a multiferroic single crystal of bismuth ferrite,"We studied the ultrafast third-order optical nonlinearity in a single crystal
of multiferroic bismuth ferrite (BiFeO3) in the near-infrared range of 0.5-1.0
eV, where the material is fundamentally transparent,at room temperature. With
pump pulses at 1.55 eV, which is off-resonant to the strong inter-band charge
transfer (CT) transition, we observed instantaneous transient absorption with
pencil-like temporal profile originating from the two-photon CT transition from
the oxygen 2p to the iron 3p levels. In contrast, under pumping with 3.10-eV
photons, the pencil-like absorption change was not observed but decay profiles
showed longer time constants. Although the two-photon absorption coefficient is
estimated to be 1.5 cm/GW, which is ten (hundred) times smaller than that of
two(one)-dimensional cuprates, it is larger than those of common semiconductors
such as ZnSe and GaAs at the optical communication wavelength.",1503.08976v1
2015-03-31,BeppoSAX observations of GRO J1744-28,"We present an analysis of BeppoSAX observations of the unique transient
bursting X-ray pulsar GRO J1744-28. The observations took place in March 1997
during the decay phase of the outburst. We find that the persistent broadband
X-ray continuum of the source is consistent with a cutoff power law typical for
the accreting pulsars. We also detect the fluorescence iron line at 6.7 keV and
an absorption feature at ~4.5 keV, which we interpret as a cyclotron line. The
corresponding magnetic field strength in the line forming region is ~3.7 x
10^11 G. Neither line is detected in the spectra of the bursts. However,
additional soft thermal component with kT ~2 keV was required to describe the
burst spectrum. We briefly discuss the nature of this component and argue that
among other possibilities it might be connected with thermonuclear flashes at
the neutron star surface which accompany the accretion-powered bursts in the
source.",1503.09020v1
2015-04-01,Possible Field-Temperature Phase Diagrams of Two-Band Superconductors with Paramagnetic Pair-Breaking,"Possible field-temperature superconducting (SC) phase diagrams in two-band
quasi-two-dimensional materials with a strong paramagnetic pair-breaking (PPB)
are considered theoretically. Attention is paid to the case under a magnetic
field $perpendicular$ to the SC layers and to essential differences from the
counterpart in the ordinary single-band material. It is found by examining the
$H_{c2}(T)$ curve and the vortex lattices to be realized close to $H_{c2}$ that
a PPB-induced SC phase with a spatial modulation parallel to the field tends to
occur more easily than in the single-band case, and that a crisscrossing vortex
lattice proposed previously can occur in place of the conventional
Fulde-Ferrell-Larkin-Ovchinnikov state within a parameter range. The relevance
of the obtained results to FeSe and other iron-based superconductors is
discussed.",1504.00112v2
2015-04-06,Quantifying the complex permittivity and permeability of magnetic nanoparticles,"The complex permittivity and permeability of superparamagnetic iron-oxide
nanoparticles has been quantified using a circular waveguide assembly with a
static magnetic field to align the nanoparticle's magnetization. The high
sensitivity of the measurement provides the precise resonant feature of
nanoparticles. The complex permeability in the vicinity of ferromagnetic
resonance (FMR) is in agreement with the nanoparticle's measured magnetization
via conventional magnetometry. A rigorous and self-consistent measure of
complex permittivities and permeabilities of nanoparticles is crucial to
ascertain accurately the dielectric behaviour as well as the frequency response
of nanoparticle magnetization, necessary ingredients when designing and
optimizing magnetic nanoparticles for biomedical applications.",1504.01404v1
2015-04-09,Plain s-wave superconductivity in single-layer FeSe on SrTiO3 probed by scanning tunneling microscopy,"Single-layer FeSe film on SrTiO3(001) was recently found to be the champion
of interfacial superconducting systems, with a much enhanced superconductivity
than the bulk iron-based superconductors. Its superconducting mechanism is of
great interest. Although the film has a simple Fermi surface topology, its
pairing symmetry is unsettled. Here by using low-temperature scanning tunneling
microscopy (STM), we systematically investigated the superconductivity of
single-layer FeSe/SrTiO3(001) films. We observed fully gapped tunneling
spectrum and magnetic vortex lattice in the film. Quasi-particle interference
(QPI) patterns reveal scatterings between and within the electron pockets, and
put constraints on possible pairing symmetries. By introducing impurity atoms
onto the sample, we show that the magnetic impurities (Cr, Mn) can locally
suppress the superconductivity but the non-magnetic impurities (Zn, Ag and K)
cannot. Our results indicate that single-layer FeSe/SrTiO3 has a plain s-wave
paring symmetry whose order parameter has the same phase on all Fermi surface
sections.",1504.02185v1
2015-04-09,Spectropolarimetrically accurate magnetohydrostatic sunspot model for forward modelling in helioseismology,"We present a technique to construct a spectropolarimetrically accurate
magneto-hydrostatic model of a large-scale solar magnetic field concentration,
mimicking a sunspot. Using the constructed model we perform a simulation of
acoustic wave propagation, conversion and absorption in the solar interior and
photosphere with the sunspot embedded into it. With the $6173\mathrm{\AA}$
magnetically sensitive photospheric absorption line of neutral iron, we
calculate observable quantities such as continuum intensities, Doppler
velocities, as well as full Stokes vector for the simulation at various
positions at the solar disk, and analyse the influence of non-locality of
radiative transport in the solar photosphere on helioseismic measurements.
Bisector shapes were used to perform multi-height observations. The differences
in acoustic power at different heights within the line formation region at
different positions at the solar disk were simulated and characterised. An
increase in acoustic power in the simulated observations of the sunspot umbra
away from the solar disk centre was confirmed as the slow magneto-acoustic
wave.",1504.02189v1
2015-04-09,The origin of nematic order in FeSe,"The origin of the 90 K nematic transition in the chalcogenide FeSe, which
displays no magnetic order down to T=0, remains a major puzzle for a unifying
theory for the iron-based superconductors. We analyze this problem in light of
recent experimental data which reveal very small Fermi pockets in this
material. We show that the smallness of the Fermi energy leads to a
near-degeneracy between magnetic fluctuations and fluctuations in the
charge-current density-wave channel. While the two fluctuation modes cooperate
to promote the same preemptive Ising-nematic order, they compete for primary
order. We argue that this explains why in FeSe the nematic order emerges when
the magnetic correlation length is smaller than in other Fe-based materials,
and why no magnetism is observed. We discuss how pressure lifts this
near-degeneracy, resulting in a non-monotonic dependence of the nematic
transition with pressure, in agreement with experiments.",1504.02315v1
2015-04-11,Magnetic Nanorods Confined in a Lamellar Lyotropic Phase,"The dilute lamellar phase of the nonionic surfactant C$_{12}$EO$_5$ was doped
with goethite (iron oxide) nanorods up to a fraction of 5 vol. %. The
interaction between the inclusions and the host phase was studied by polarized
optical microscopy (with or without an applied magnetic field) and by
small-angle X-ray scattering. We find that, when the orientation of the
nanorods is modified using the magnetic field, the texture of the lamellar
phase changes accordingly; one can thus induce a homeotropic-planar
reorientation transition. On the other hand, the lamellar phase induces an
attractive interaction between the nanorods. In more concentrated lamellar
phases (under stronger confinement) the particles form aggregates. This
behavior is not encountered for a similar system doped with spherical
particles, emphasizing the role of particle shape in the interaction between
doping particles and the host phase.",1504.02879v1
2015-04-15,Single Vortex Pinning and Penetration Depth in Superconducting NdFeAsO$_{1-x}$F$_x$,"We use a magnetic force microscope (MFM) to investigate single vortex pinning
and penetration depth in NdFeAsO$_{1-x}$F$_x$, one of the highest-$T_c$
iron-based superconductors. In fields up to 20 Gauss, we observe a disordered
vortex arrangement, implying that the pinning forces are stronger than the
vortex-vortex interactions. We measure the typical force to depin a single
vortex, $F_{\mathrm{depin}} \simeq 4.5$ pN, corresponding to a critical current
up to $J_c \simeq 7 \times 10^5$ A/cm$^2$. Furthermore, our MFM measurements
allow the first local and absolute determination of the superconducting
in-plane penetration depth in NdFeAsO$_{1-x}$F$_x$, $\lambda_{ab}=320 \pm 60$
nm, which is larger than previous bulk measurements.",1504.04045v1
2015-04-16,Origin of the Higher-$T_\rm{c}$ Phase in the K$_x$Fe$_{2-y}$Se$_2$ System,"Single crystals of K$_x$Fe$_{2-y}$Se$_2$ are prepared by quenching at various
temperatures. The crystals obtained at higher quenching temperatures have a
surface morphology with mesh-like texture. They show a sharp superconducting
transition at $T_\rm{c}$ ~32 K with a large shielding volume fraction. On the
other hand, the crystals prepared without quenching show an onset
superconducting transition at ~44 K and a zero resistivity around ~33 K, and
they possess island-like regions on the surface with a larger amount of Fe
incorporation. In-situ high-temperature single crystal X-ray diffraction
measurements tell us the Fe-vacancy ordered phase is generated at a temperature
region around 270 {\deg}C via iron diffusion. The creation of this Fe-vacancy
ordered phase may become a driving force of the growth of the higher $T_\rm{c}$
phase. The superconductivity at ~44 K is attributed to a metallic phase with no
Fe-vacancy.",1504.04197v2
2015-04-17,Structural analysis of superconducting dipole prototype for HIAF,"The High Intensity Heavy-Ion Accelerator Facility is a new project in the
Institute of Modern Physics. The dipole magnets of all rings are conceived as
fast cycled superconducting magnet with high magnetic field and large gap, the
warm iron and superconducting coil structure (superferric) is adopted. The
reasonable structure design of coil and cryostat is very important for reliable
operation. Based on the finite element software ANSYS, the mechanical analysis
of electromagnetic stress, the thermal stress in the cooling down and the
stress in the pumping are showed in detail. According to the analysis result,
the supporter structure is the key problem of coil system. With reasonable
support's structure design, the stress and the deformation of coil structure
can be reduced effectively, which ensure the stable operation of
superconducting coil system.",1504.04468v1
2015-04-21,Fast Luminous Blue Transients from Newborn Black Holes,"Newborn black holes in collapsing massive stars can be accompanied by a
fallback disk. The accretion rate is typically super-Eddington and strong disk
outflows are expected. Such outflows could be directly observed in some failed
explosions of compact (blue supergiants or Wolf-Rayet stars) progenitors, and
may be more common than long-duration gamma-ray bursts. Using an analytical
model, we show that the fallback disk outflows produce blue UV-optical
transients with a peak bolometric luminosity of ~10^(42-43) erg s^-1 (peak
R-band absolute AB magnitudes of -16 to -18) and an emission duration of ~ a
few to ~ 10 days. The spectra are likely dominated intermediate mass elements,
but will lack much radioactive nuclei and iron-group elements. The above
properties are broadly consistent with some of the rapid blue transients
detected by Pan-STARRS and PTF. This scenario can be distinguished from
alternative models using radio observations within a few years after the
optical peak.",1504.05582v1
2015-04-26,Amplitude modes and dynamic coexistence of competing orders in multicomponent superconductors,"We study the nonequilibrium dynamics of an electronic model with competing
spin-density-wave and unconventional superconductivity in the context of iron
pnictides. Focusing on the collisionless regime, we find that magnetic and
superconducting order parameters may coexist dynamically after a sudden quench,
even though the equilibrium thermodynamic state supports only one order
parameter. We consider various initial conditions concomitant with the phase
diagram and in a certain regime identify different oscillatory amplitude modes
with incommensurate frequencies for magnetic and superconducting responses. At
the technical level we solve the equations of motion for the electronic Green's
functions and self-consistency conditions by reducing the problem to a closed
set of Bloch equations in a pseudospin representation. For certain quench
scenarios the nonadiabatic dynamics of the pairing amplitude is completely
integrable and in principle can be found exactly.",1504.06874v2
2015-04-28,Single Photon Level Study of Microwave Properties of Lithium Niobate at milli-Kelvin Temperatures,"Properties of doped and natural impurities in Lithium Niobate single crystals
are studied using the Whispering Gallery Mode method at low temperatures as a
function of magnetic field. The study reveals considerable coupling of
microwave photon modes to the Fe$^{3+}$ spin ensemble in iron-doped and
non-doped crystals. The $S=5/2$ structure of the Fe$^{3+}$ impurities
demonstrate Zero Field Splittings of $11.21$ and $20.96$ GHz, significant
asymmetry of the Zeeman lines and additional lines with anomalous
$\text{g}$-factors of $1.37$ and $3.95$. Also, interactions between different
transitions of the Fe$^{3+}$ ion is observed. An additional ion impurity
ensemble with a splitting of about $1.7$ GHz is shown to couple to the
dominating Fe$^{3+}$ spins and the effect on $Q$-factors of microwave photon
modes due to the Fe$^{3+}$ ion ensemble is also demonstrated. Measurements down
to less than one photon level are made with a loss tangent of order $10^{-5}$
determined.",1504.07352v1
2015-04-28,Phase diagram of the isovalent phosphorous-substituted 122-type iron pnictides,"Recent experiments demonstrated that isovalent doping system gives the
similar phase diagram as the heterovalent doped cases. For example, with the
phosphorous (P)-doping, the magnetic order in
BaFe$_{2}$(As$_{1-x}$P$_{x}$)$_{2}$ compound is first suppressed, then the
superconductivity dome emerges to an extended doping region but eventually it
disappears at large $x$. With the help of a minimal two-orbital model for both
BaFe$_{2}$As$_{2}$ and BaFe$_{2}$P$_{2}$, together with the self-consistent
lattice Bogoliubov-de Gennes (BdG) equation, we calculate the phase diagram
against the P content $x$ in which the doped isovalent P-atoms are treated as
impurities. We show that our numerical results can qualitatively compare with
the experimental measurements.",1504.07539v1
2015-04-30,Ab initio calculation of Spin-Polarized Low-Energy Electron Diffraction Pattern for the systems Fe(001) and Fe(001)-p(1x1)-O,"The construction of a multi-channel vector spin polarimeter requires the
development of a new detector type, which works as a spin polarizing mirror
with high reflectivity and asymmetry properties to guarantee for a high figure
of merit. Technical realizations are found by spin polarized electron
scattering from a surface at low energies. A very promising candidate for such
a detector suitable material consists of an oxygen passivated iron surface, as
for example a Fe(001)-p(1x1)-O surface. We investigate in detail the electronic
structure of this adsorbate system and calculate the corresponding
spin-polarized low-energy electron scattering. Our theoretical study is based
on the fully relativistic SPRKKR-method in the framework of density functional
theory. Furthermore, we use the local spin-density approximation in combination
with dynamical mean field theory to determine the electronic structure of
Fe(001)-p(1x1)-O and demonstrate that a significant impact of correlation
effects occurs in the calculated figure of merit.",1504.08198v2
2015-04-30,TITUS: An Intermediate Distance Detector for the Hyper-Kamiokande Neutrino Beam,"The Tokai Intermediate Tank with Unoscillated Spectrum (TITUS) detector is a
proposed addition to the Hyper-Kamiokande (HK) experiment located approximately
2 km from the J-PARC neutrino beam. The design consists of a 2 kton Gadolinium
(Gd) doped water Cherenkov detector, surrounded by a magnetized iron detector
designed to range-out muons. The target material and location are chosen so
that the neutrino interactions and beam spectrum at TITUS will match those of
HK. Including a 0.1% Gd concentration allows for neutrino/antineutrino
discrimination via neutron tagging. The primary goal of TITUS is to directly
measure the neutrino flux and make cross-section measurements that reduce the
systematic uncertainty of the long-baseline oscillation physics program at HK
and enhance its sensitivity to CP violation. TITUS can also be used for physics
unrelated to the J-PARC beam, functioning as an independent detector for
supernova neutrino bursts and measuring the neutron rate to improve HK proton
decay searches.",1504.08272v2
2015-05-05,Formation depths of Fraunhofer lines,"We have summed up our investigations performed in 1970--1993. The main task
of this paper is clearly to show processes of formation of spectral lines as
well as their distinction by validity and by location. For 503 photospheric
lines of various chemical elements in the wavelength range 300--1000 nm we list
in Table the average formation depths of the line depression and the line
emission for the line centre and on the half-width of the line, the average
formation depths of the continuum emission as well as the effective widths of
the layer of the line depression formation. Dependence of average depths of
line depression formation on excitation potential, equivalent widths, and
central line depth are demonstrated by iron lines.",1505.00975v1
2015-05-06,Tetragonal magnetic phase in Ba$_{1-x}$K$_x$Fe$_2$As$_2$ from x-ray and neutron diffraction,"Combined neutron and x-ray diffraction experiments demonstrate the formation
of a low-temperature minority tetragonal phase in
Ba$_{0.76}$K$_{0.24}$Fe$_2$As$_2$ in addition to the majority magnetic,
orthorhombic phase. A coincident enhancement in the magnetic ($\frac{1}{2}$
$\frac{1}{2}$ 1) peaks shows that this minority phase is of the same type that
was observed in Ba$_{1-x}$Na$_x$Fe$_2$As$_2$ ($0.24 \leq x \leq 0.28$), in
which the magnetic moments reorient along the $c$-axis. This is evidence that
the tetragonal magnetic phase is a universal feature of the hole-doped
iron-based superconductors.",1505.01433v1
2015-05-11,Two-dimensional Cs-vacancy superstructure in iron-based superconductor $Cs_{0.8}Fe_{1.6}Se_2$,"Single crystal neutron diffraction is combined with synchrotron x-ray
scattering to identify the different superlattice phases present in
$Cs_{0.8}Fe_{1.6}Se_2$. A combination of single crystal refinements and first
principles modelling are used to provide structural solutions for the
$\sqrt{5}\times\sqrt{5}$ and $\sqrt{2}\times\sqrt{2}$ superlattice phases. The
$\sqrt{5}\times\sqrt{5}$ superlattice structure is predominantly composed of
ordered Fe vacancies and Fe distortions, whereas the $\sqrt{2}\times\sqrt{2}$
superlattice is composed of ordered Cs vacancies. The Cs vacancies only order
within the plane, causing Bragg rods in reciprocal space. By mapping x-ray
diffraction measurements with narrow spatial resolution over the surface of the
sample, the structural domain pattern was determined, consistent with the
notion of a majority antiferromagnetic $\sqrt{5}\times\sqrt{5}$ phase and a
superconducting $\sqrt{2}\times\sqrt{2}$ phase.",1505.02527v1
2015-05-11,"Interplay of structure, magnetism, and superconductivity in Se substituted iron telluride with excess Fe","We investigated the evolution of the temperature-composition phase diagram of
Fe$_{1+y}$Te upon Se substitution. In particular, the effect of Se substitution
on the two-step, coupled magneto-structural transition in Fe$_{1+y}$Te single
crystals is investigated. To this end, the nominal Fe excess was kept at $y$ =
0.12. For low Se concentrations, the two magneto-structural transitions
displayed a tendency to merge. In spite of the high Fe-content,
superconductivity emerges for Se concentrations, $x \geq$ 0.1. We present a
temperature-composition phase diagram to demonstrate the interplay of
structure, magnetism, and superconductivity in these ternary Fe chalcogenides.",1505.02542v1
2015-05-14,Nucleosynthesis in a Primordial Supernova: Carbon and Oxygen Abundances in SMSS J031300.36-670839.31,"SMSS J031300.36-670839.3 (hereafter SM0313-6708) is a sub-giant halo star,
with no detectable Fe lines and large overabundances of C and Mg relative to
Ca. We obtained VLT-UVES spectra extending to 3060 Angstroms showing strong OH
A-X band lines enabling an oxygen abundance to be derived. The OH A-X band
lines in SM0313-6708 are much stronger than the CH C-X band lines. Spectrum
synthesis fits indicate an [O/C] ratio of 0.02 +- 0.175. Our high S/N UVES data
also enabled us to lower the Fe abundance limit to [Fe/H]{3D},NLTE < -7.52 (3
sigma). These data support our previous suggestion that the star formed from
the iron-poor ejecta of a single massive star Population III supernova.",1505.03756v2
2015-05-16,"Glide reflection symmetry, Brillouin zone folding and superconducting pairing for the $P4/nmm$ space group","Motivated by the studies of the superconducting pairing states in the
iron-based superconductors, we analyze the effects of Brillouin zone folding
procedure from a space group symmetry perspective for a general class of
materials with the $P4/nmm$ space group. The Brillouin zone folding amounts to
working with an effective one-Fe unit cell, instead of the crystallographic
two-Fe unit cell. We show that the folding procedure can be justified by the
validity of a glide reflection symmetry throughout the crystallographic
Brillouin zone and by the existence of a minimal double degeneracy along the
edges of the latter. We also demonstrate how the folding procedure fails when a
local spin-orbit coupling is included although the latter does not break any of
the space group symmetries of the bare Hamiltonian. In light of these general
symmetry considerations, we further discuss the implications of the glide
reflection symmetry for the superconducting pairing in an effective
multi-orbital $t-J_{1}-J_{2}$ model. We find that the $P4/nmm$ space group
symmetry allows only pairing states with even parity under the glide reflection
and zero total momentum.",1505.04227v2
2015-05-17,Palladium and silver abundances in stars with [Fe/H] > -2.6,"Palladium (Pd) and silver (Ag) are the key elements for probing the weak
component in the rapid neutron-capture process (r-process) of stellar
nucleosynthesis. We performed a detailed analysis of the high-resolution and
high signal-to-noise ratio near-UV spectra from the archive of HIRES on the
Keck telescope, UVES on the VLT, and HDS on the Subaru Telescope, to determine
the Pd and Ag abundances of 95 stars. This sample covers a wide metallicity
range with -2.6 $\lesssim$ [Fe/H] $\lesssim$ +0.1, and most of them are dwarfs.
The plane-parallel LTE MAFAGS-OS model atmosphere was adopted, and the spectral
synthesis method was used to derive the Pd and Ag abundances from Pd I
{\lambda} 3404 {\AA} and Ag I {\lambda} 3280/3382 {\AA} lines. We found that
both elements are enhanced in metal-poor stars, and their ratios to iron show
flat trends at -0.6 < [Fe/H] < +0.1. The abundance ratios of [Ag/H] and [Pd/H]
are well correlated over the whole abundance range. This implies that Pd and Ag
have similar formation mechanisms during the Galactic evolution.",1505.04356v1
2015-05-19,Electronic nematic susceptibility of iron-based superconductors,"We review our recent experimental results on the electronic nematic phase in
electron- and hole-doped BaFe$_2$As$_2$ and FeSe. The nematic susceptibility is
extracted from shear-modulus data (obtained using a three-point-bending method
in a capacitance dilatometer) using Landau theory and is compared to the
nematic susceptibility obtained from elastoresistivity and Raman data. FeSe is
particularly interesting in this context, because of a large nematic, i.e., a
structurally distorted but paramagnetic, region in its phase diagram. Scaling
of the nematic susceptibility with the spin lattice relaxation rate from NMR,
as predicted by the spin-nematic theory, is found in both electron- and
hole-doped BaFe$_2$As$_2$, but not in FeSe. The intricate relationship of the
nematic susceptibility to spin and orbital degrees of freedom is discussed.",1505.05120v1
2015-05-22,Probing Atomic Structure and Majorana Wavefunctions in Mono-Atomic Fe-chains on Superconducting Pb-Surface,"Motivated by the striking promise of quantum computation, Majorana bound
states (MBSs) in solid-state systems have attracted wide attention in recent
years. In particular, the wavefunction localization of MBSs is a key feature
and crucial for their future implementation as qubits. Here, we investigate the
spatial and electronic characteristics of topological superconducting chains of
iron atoms on the surface of Pb(110) by combining scanning tunneling microscopy
(STM) and atomic force microscopy (AFM). We demonstrate that the Fe chains are
mono-atomic, structured in a linear fashion, and exhibit zero-bias conductance
peaks at their ends which we interprete as signature for a Majorana bound
state. Spatially resolved conductance maps of the atomic chains reveal that the
MBSs are well localized at the chain ends (below 25 nm), with two localization
lengths as predicted by theory. Our observation lends strong support to use
MBSs in Fe chains as qubits for quantum computing devices.",1505.06078v2
2015-05-22,Indications of Negative Evolution for the Sources of the Highest Energy Cosmic Rays,"Using recent measurements of the spectrum and chemical composition of the
highest energy cosmic rays, we consider the sources of these particles. We find
that the data strongly prefers models in which the sources of the ultra-high
energy cosmic rays inject predominantly intermediate mass nuclei, with
comparatively few protons or heavy nuclei, such as iron or silicon. If the
number density of sources per comoving volume does not evolve with redshift,
the injected spectrum must be very hard ($\alpha\simeq 1$) in order to fit the
spectrum observed at Earth. Such a hard spectral index would be surprising and
difficult to accommodate theoretically. In contrast, much softer spectral
indices, consistent with the predictions of Fermi acceleration ($\alpha\simeq
2$), are favored in models with negative source evolution. With this
theoretical bias, these observations thus favor models in which the sources of
the highest energy cosmic rays are preferentially located within the
low-redshift universe.",1505.06090v2
2015-05-25,Bandwidth and Electron Correlation-Tuned Superconductivity in Rb$_{0.8}$Fe$_{2}$(Se$_{1-z}$S$_z$)$_2$,"We present a systematic angle-resolved photoemission spectroscopy study of
the substitution-dependence of the electronic structure of
Rb$_{0.8}$Fe$_{2}$(Se$_{1-z}$S$_z$)$_2$ (z = 0, 0.5, 1), where
superconductivity is continuously suppressed into a metallic phase. Going from
the non-superconducting Rb$_{0.8}$Fe$_{2}$(Se$_{1-z}$S$_z$)$_2$ to
superconducting Rb$_{0.8}$Fe$_{2}$Se$_2$, we observe little change of the Fermi
surface topology, but a reduction of the overall bandwidth by a factor of 2 as
well as an increase of the orbital-dependent renormalization in the $d_{xy}$
orbital. Hence for these heavily electron-doped iron chalcogenides, we have
identified electron correlation as explicitly manifested in the quasiparticle
bandwidth to be the important tuning parameter for superconductivity, and that
moderate correlation is essential to achieving high $T_C$.",1505.06636v2
2015-05-25,Magnetic Ground State of an Individual Fe2+ Ion in Strained Semiconductor Nanostructure,"We investigate spin properties of a Fe2+ dopant, known for having single
nondegenerate ground state in bulk host semiconductor. Due to zero magnetic
moment such a ground state is of little use for spintronics and solotronics. We
show that this well-established picture of Fe2+ spin configuration can be
contradicted by subjecting the Fe2+ ion to sufficiently high strain, e.g.,
resulting from lattice mismatched epitaxial heterostructures. Our analysis
reveals that high strain induces qualitative change in the ion energy spectrum
and results in doubly degenerate ground state with spin projection Sz=+/-2. An
experimental proof of this concept is demonstrated using a new system: an
epitaxial quantum dot containing individual Fe2+ ion. Magnetic character of the
Fe2+ ground state in a CdSe/ZnSe dot is revealed in photoluminescence
experiments by exploiting a coupling between a confined exciton and the single
iron impurity.",1505.06763v1
2015-05-27,Energy and Direction Estimation of Neutrinos in muonless events at ICAL,"In this paper, we study events without identifiable muon tracks in the Iron
Calorimeter detector at the India-based Neutrino Observatory. Such events are
dominated by high energy (E$_\nu>$1 GeV) $\nu_e$ charged current interactions,
which have been studied only in a few experiments so far. The charged
particles, produced in these neutrino interactions, give rise to a set of hits
in the detector. We attempt to reconstruct the energy and the direction of the
neutrino in such events. We study the energy distribution for a given pattern
of hits of these events and find that the Landau distribution provides a good
fit. % The parameters of the fit can be correlated to the energy of the
neutrino. We define two kinematic variables based on the hit distribution and
use them to determine the cosine of the polar angle of the neutrino direction
($\cos \theta$). There is a moderate correlation between these variables and
the $\cos \theta$. These provide us enough information to prepare calibration
charts for looking up the energy and direction of the incident neutrino.",1505.07295v1
2015-05-28,Properties of AGN coronae in the NuSTAR era,"The focussing optics of NuSTAR have enabled high signal-to-noise spectra to
be obtained from many X-ray bright Active Galactic Nuclei (AGN) and Galactic
Black Hole Binaries (BHB). Spectral modelling then allows robust
characterization of the spectral index and upper energy cutoff of the coronal
power-law continuum, after accounting for reflection and absorption effects.
Spectral-timing studies, such as reverberation and broad iron line fitting, of
these sources yield coronal sizes, often showing them to be small and in the
range of 3 to 10 gravitational radii in size. Our results indicate that coronae
are hot and radiatively compact, lying close to the boundary of the region in
the compactness - temperature diagram which is forbidden due to runaway pair
production. The coincidence suggests that pair production and annihilation are
essential ingredients in the coronae of AGN and BHB and that they control the
shape of the observed spectra.",1505.07603v1
2015-05-28,Se content $x$ dependence of electron correlation strength in Fe$_{1+y}$Te$_{1-x}$Se$_{x}$,"The iron chalcogenide Fe$_{1+y}$Te$_{1-x}$Se$_{x}$ on the Te-rich side is
known to exhibit the strongest electron correlations among the Fe-based
superconductors, and is non-superconducting for $x$ < 0.1. In order to
understand the origin of such behaviors, we have performed ARPES studies of
Fe$_{1+y}$Te$_{1-x}$Se$_{x}$ ($x$ = 0, 0.1, 0.2, and 0.4). The obtained mass
renormalization factors for different energy bands are qualitatively consistent
with DFT + DMFT calculations. Our results provide evidence for strong orbital
dependence of mass renormalization, and systematic data which help us to
resolve inconsistencies with other experimental data. The unusually strong
orbital dependence of mass renormalization in Te-rich
Fe$_{1+y}$Te$_{1-x}$Se$_{x}$ arises from the dominant contribution to the Fermi
surface of the $d_{xy}$ band, which is the most strongly correlated and may
contribute to the suppression of superconductivity.",1505.07637v1
2015-05-30,Large increase of the anisotropy factor in the overdoped region of Ba(Fe$_{1-x}$Ni$_x$)$_2$As$_2$ as probed by fluctuation spectroscopy,"We study the diamagnetism induced by thermal fluctuations above the
superconducting transition of the iron pnictide Ba(Fe$_{1-x}$Ni$_x$)$_2$As$_2$
with different doping levels. The measurements are performed with magnetic
fields up to 7 T applied in the two main crystal directions. These data provide
double information: first, they confirm at a quantitative level the
applicability to these materials of a 3D-anisotropic Ginzburg-Landau approach
valid in the finite field regime. Then, they allow to determine the
doping-level dependence of the in-plane coherence length and of the
superconducting anisotropy factor, $\gamma$. Our results provide a stringent
confirmation of the large increase of $\gamma$ with the doping level, as
recently proposed from magnetoresistivity measurements. The implications of the
applicability of the model used to a multiband superconductor are discussed.",1506.00170v1
2015-06-04,"Exploring the feasibility of Fe(Se,Te) conductors by ex-situ Powder-in-Tube method","In this work, the feasibility condition of Powder-In-Tube (PIT) processed
wires of Fe(Se,Te) superconductor has been investigated. We faced several
technical issues that are extensively described and discussed. In particular,
we tested different metals and alloys as external sheaths (Cu, Ag, Nb, Ta, Ni,
Fe, cupronickel, brass) concluding that the only sheath that does not affect
substantially the Fe(Se,Te) phase is Fe. On the other hand, Fe sheath
introduces excess iron in the Fe(Se,Te) phase, which affects the
superconducting properties; we investigated the effects of the thermal
treatments and of the powder composition in order to avoid it. The maximum Jc
value obtained in our samples is 4*10^2 A/cm2, comparable to other published
values of PIT conductors of the 11 family. We conclude that the fabrication of
Fe(Se,Te) wires by PIT method is quite challenging and other approaches should
be developed.",1506.01630v1
2015-06-09,Optical observations of a SN 2002cx-like peculiar supernova SN 2013en in UGC 11369,"We present optical observations of a SN 2002cx-like supernova SN 2013en in
UGC 11369, spanning from a phase near maximum light (t= +1 d) to t= +60 d with
respect to the R-band maximum. Adopting a distance modulus of mu=34.11 +/- 0.15
mag and a total extinction (host galaxy+Milky Way) of $A_V \sim1.5$ mag, we
found that SN 2013en peaked at $M(R)\sim -18.6$ mag, which is underluminous
compared to the normal SNe Ia. The near maximum spectra show lines of Si II, Fe
II, Fe III, Cr II, Ca II and other intermediate-mass and iron group elements
which all have lower expansion velocities (i.e., ~ 6000 km/s). The photometric
and spectroscopic evolution of SN 2013en is remarkably similar to those of SN
2002cx and SN 2005hk, suggesting that they are likely to be generated from a
similar progenitor scenario or explosion mechanism.",1506.02845v1
2015-06-09,"Synthesis, Crystal Structure and Magnetism of Eu3Sc2O5Fe2As2","The iron arsenide Eu3Fe2O5Fe2As2 was synthesized at 1173-1373 K in a
resistance furnace and characterized by X-ray powder diffraction with Rietveld
analysis: Sr3Fe2O5Cu2S2-type, I4/mmm, a = 406.40(1) pm, c = 2646.9(1) pm.
Layers of edge-sharing FeAs4/4 tetrahedra are separated by perovskite-like
oxide blocks. No structural transition occurs in the temperature range from 10
to 300 K. Magnetic measurements have revealed Curie-Weiss behavior with an
effective magnetic moment of 7.79 muB per europium atom in agreement with the
theoretical value of 7.94 muB for Eu2+. A drop in the magnetic susceptibility
at 5 K indicates possible antiferromagnetic ordering. 151Eu and 57Fe
M\""ossbauer spectroscopic measurements have confirmed a beginning cooperative
magnetic phenomenon by showing significantly broadened spectra at 4.8 K
compared to those at 78 K.",1506.02925v1
2015-06-10,Interaction of discrete breathers with primary lattice defects in bcc Fe,"The interaction of discrete breathers with the primary lattice defects in
transition metals such as vacancy, dislocation, and surface is analyzed on the
example of bcc iron employing atomistic simulations. Scattering of discrete
breathers on the lattice defects induces localized atomic excitations, with
intensity and relaxation time depending on the defect structure and breather
kinetic energy. The dissipation of the intrinsic breather energy due to the
scattering is computed and analyzed. It is concluded that the
breather-to-defect energy transfer may stipulate the activation of the lattice
defects causing unexpected athermal effects such as enhanced mass transfer or
electroplasticity, already experimentally reported but so far not fully
understood at the atomic-scale level.",1506.03507v1
2015-06-12,Near-field microwave imaging of inhomogeneous K$_x$Fe$_y$Se$_2$: separation of topographic and electric features,"It is important for modern scanning microwave microscopes to overcome the
effect of the surface roughness. Here, we report microwave conductivity imaging
of the phase-separated iron chalcogenide K$_x$Fe$_y$Se$_2$ ($x=0.8$,
$y=1.6$-$2$), in which electric conductivity-induced contrast is distinguished
from topography-induced contrast using a combination of a scanning tunneling
microscope and a scanning microwave microscope (STM-SMM). We observed the
characteristic modulation of the local electric property that originates from
the mesoscopic phase separation of the metallic and semiconducting phases in
two different scanning modes: constant current (CC) mode and constant $Q$ (CQ)
mode. In particular, CQ scanning is useful because we obtain a qualitative
image in which the topographic contrast is largely eliminated without
degradation of the spatial resolution.",1506.03911v1
2015-06-17,"Giant enhancement in critical current density, up to a hundredfold, in superconducting NaFe0.97Co0.03As single crystals under hydrostatic pressure","Tremendous efforts towards improvement in the critical current density (Jc)
of iron based superconductors (FeSCs), especially at relatively low
temperatures and magnetic fields, have been made so far through different
methods, resulting in real progress. Jc at high temperatures in high fields
still needs to be further improved, however, in order to meet the requirements
of practical applications. Here, we demonstrate a simple approach to achieve
this. Hydrostatic pressure can significantly enhance Jc in NaFe0.97Co0.03As
single crystals by at least tenfold at low field and more than a hundredfold at
high fields. Significant enhancement in the in-field performance of
NaFe0.97Co0.03As single crystal in terms of pinning force density (Fp) is found
at high pressures. At high fields, the Fp is over 20 and 80 times higher than
under ambient pressure at12K and 14K, respectively, at P=1GPa. We believe that
the Co-doped NaFeAs compounds are very exciting and deserve to be more
intensively investigated. Finally, it is worthwhile to say that by using
hydrostatic pressure, we can achieve more milestones in terms of high Jc values
in different superconductors.",1506.05183v1
2015-06-17,Local spin-density-wave order inside vortex cores in multiband superconductors,"Coexistence of antiferromagnetic order with superconductivity in many
families of newly discovered iron-based superconductors has renewed interest to
this old problem. Due to competition between the two types of order, one can
expect appearance of the antiferromagnetism inside the cores of the vortices
generated by the external magnetic field. The structure of a vortex in type II
superconductors holds significant importance from the theoretical and the
application points of view. Here we consider the internal vortex structure in a
two-band s$_\pm$ superconductor near a spin-density-wave instability. We treat
the problem in a completely self-consistent manner within the quasiclassical
Eilenberger formalism. We study the structure of the s$_\pm$ superconducting
order and magnetic field-induced spin-density-wave order near an isolated
vortex. We examine the effect of this spin-density-wave state inside the vortex
cores on the local density of states.",1506.05440v2
2015-06-26,Correlated electron behavior of metalorganic molecules: insights from density functional theory combined with many-body effects using exact diagonalization,"A proper theoretical description of electronic structure of the 3d orbitals
in the metal centers of functional metalorganics is a challenging problem. In
this letter, we apply density functional theory and an exact diagonalization
method in a many body approach to study the ground state electronic
configuration of an iron porphyrin (FeP) molecule. Our study reveals that
dynamical correlation effects are important, and FeP is a potential candidate
for realizing a spin crossover due to a subtle balance of crystal field
effects, on-site Coulomb repulsion and hybridization between the Fe d-orbitals
and ligand N p-states. The mechanism of switching between two close lying
electronic configurations of Fe-d orbitals is shown. We discuss the generality
of the suggested approach and the possibility to properly describe the
electronic structure and related low energy physics of the whole class of
correlated metal centered organometallic molecules.",1506.07973v1
2015-06-29,Neutrino-driven explosions of ultra-stripped type Ic supernovae generating binary neutron stars,"We study explosion characteristics of ultra-stripped supernovae (SNe), which
are candidates of SNe generating binary neutron stars (NSs). As a first step,
we perform stellar evolutionary simulations of bare carbon-oxygen cores of mass
from 1.45 to 2.0 $M_\odot$ until the iron cores become unstable and start
collapsing. We then perform axisymmetric hydrodynamics simulations with
spectral neutrino transport using these stellar evolution outcomes as initial
conditions. All models exhibit successful explosions driven by neutrino
heating. The diagnostic explosion energy, ejecta mass, Ni mass, and NS mass are
typically $\sim 10^{50}$ erg, $\sim 0.1 M_\odot$, $\sim 0.01M_\odot$, and
$\approx 1.3 M_\odot$, which are compatible with observations of
rapidly-evolving and luminous transient such as SN 2005ek. We also find that
the ultra-stripped SN is a candidate for producing the secondary low-mass NS in
the observed compact binary NSs like PSR J0737-3039.",1506.08827v2
2015-07-01,Onset of the Meissner effect at 65 K in FeSe thin film grown on Nb doped SrTiO3 substrate,"We report the Meissner effect studies on an FeSe thin film grown on Nb doped
SrTiO3 substrate by molecular beam epitaxy. Two-coil mutual inductance
measurement clearly demonstrates the onset of diamagnetic screening at 65 K,
which is consistent with the gap opening temperature determined by previous
angle resolved photoemission spectroscopy results. The applied magnetic field
causes a broadening of the superconducting transition near the onset
temperature, which is the typical behavior for quasi-two-dimensional
superconductors. Our results provide direct evidence that FeSe thin film grown
on Nb doped SrTiO3 substrate has an onset TC ~ 65 K, which is the highest among
all iron based superconductors discovered so far.",1507.00129v2
2015-07-06,Isotope shifts and hyperfine structure of the laser cooling Fe I 358-nm line,"We report on the measurement of the isotope shifts of the $3d^74s \,\, a \,
{}^5\!F_5 - 3d^74p \,\, z \, {}^5\!G^o_6$ Fe~I line at 358~nm between all four
stable isotopes ${}^{54}$Fe, ${}^{56}$Fe, ${}^{57}$Fe and ${}^{58}$Fe, as well
as the hyperfine structure of that line for ${}^{57}$Fe, the only stable
isotope having a nonzero nuclear spin. This line is of primary importance for
laser cooling applications. In addition, an experimental value of the field and
specific mass shift coefficients of the transition is reported as well as the
hyperfine structure magnetic dipole coupling constant $A$ of the transition
excited state in $^{57}$Fe, namely $A(3d^74p \,\, z \, {}^5\!G^o_6)=31.241(48)$
MHz. The measurements were carried out by means of laser-induced fluorescence
spectroscopy performed on an isotope-enriched iron atomic beam. All measured
frequency shifts are reported with uncertainties below the third percent level.",1507.01498v1
2015-07-07,New Superconductivity Dome in LaFeAsO$_{1-x}$F$_{x}$ Accompanied by Structural Transition,"High temperature superconductivity is often found in the vicinity of
antiferromagnetism. This is also true in LaFeAsO$_{1-x}$F$_{x}$ ($x \leq$ 0.2)
and many other iron-based superconductors, which leads to proposals that
superconductivity is mediated by fluctuations associated with the nearby
magnetism. Here we report the discovery of a new superconductivity dome without
low-energy magnetic fluctuations in LaFeAsO$_{1-x}$F$_{x}$ with 0.25$\leq x
\leq$0.75, where the maximal critical temperature $T_c$ at $x_{opt}$ =
0.5$\sim$0.55 is even higher than that at $x \leq$ 0.2. By nuclear magnetic
resonance and Transmission Electron Microscopy, we show that a C4 rotation
symmetry-breaking structural transition takes place for $x>$ 0.5 above $T_c$.
Our results point to a new paradigm of high temperature superconductivity.",1507.01750v2
2015-07-08,Towards quantifying the role of exact exchange in predictions of transition metal complex properties,"We estimate the prediction sensitivity with respect to Hartree-Fock exchange
in approximate density functionals for representative Fe(II) and Fe(III)
octahedral complexes. Based on the observation that the range of parameters
spanned by the most widely-employed functionals is relatively narrow, we
compute electronic structure property and spin-state orderings across a
relatively broad range of Hartree-Fock exchange (0-50%) ratios. For the entire
range considered, we consistently observe linear relationships between
spin-state ordering that differ only based on the element of the direct ligand
and thus may be broadly employed as measures of functional sensitivity in
predictions of organometallic compounds. The role Hartree-Fock exchange in
hybrid functionals is often assumed to play is to correct self-interaction
error-driven electron delocalization (e.g. from transition metal centers to
neighboring ligands). Surprisingly, we instead observe that increasing
Hartree-Fock exchange reduces charge on iron centers, corresponding to
effective delocalization of charge to ligands, thus challenging notions of the
role of Hartree-Fock exchange in shifting predictions of spin-state ordering.",1507.02261v1
2015-07-11,End states and subgap structure in proximity-coupled chains of magnetic adatoms,"A recent experiment [Nadj-Perge et al., Science 346, 602 (2014)] provides
evidence for Majorana zero modes in iron (Fe) chains on the superconducting
Pb(110) surface. Here, we study this system by scanning tunneling microscopy
using superconducting tips. This high-resolution technique resolves a rich
subgap structure, including zero-energy excitations in some chains. We compare
the symmetry properties of the data under voltage reversal against theoretical
expectations and provide evidence that the putative Majorana signature overlaps
with a previously unresolved low-energy resonance. Interpreting the data within
a Majorana framework suggests that the topological gap is significantly smaller
than previously believed. Aided by model calculations, we also analyze
higher-energy features of the subgap spectrum and their relation to high-bias
peaks which we associate with the Fe d-bands.",1507.03104v2
2015-07-13,Localized High Frequency Electrodynamic Behavior of Optimally-doped Ba(Fe$_{1-x}$Co$_x$)$_2$As$_2$ Single Crystal films,"Localized high frequency (several GHz) electrodynamic properties of a high
quality epitaxial, single-crystal Iron-Pnicitde Ba(Fe$_{1-x}$Co$_x$)$_2$As$_2$
thin film near optimal doping (x=0.08) are measured under a localized and
strong RF magnetic field, created by a near-field microwave microscope. Two
reflection electrodynamic measurements, including linear and the third harmonic
responses, are performed to understand the electromagnetic properties of
Ba(Fe$_{1-x}$Co$_x$)$_2$As$_2$. Our measurement results show that
Ba(Fe$_{1-x}$Co$_x$)$_2$As$_2$ has have a wide superconducting transition width
and may have a multi-gap nature. In addition, based on the $1/T^2$ dependence
of the third harmonics signal at lower temperature,
Ba(Fe$_{1-x}$Co$_x$)$_2$As$_2$ shows the possibility of nodal behavior.",1507.03318v1
2015-07-14,Observational consequences of turbulent pressure in the envelopes of massive stars,"The major mass fraction of the envelope of hot luminous stars is radiatively
stable. However, the partial ionisation of hydrogen, helium and iron gives rise
to extended sub-surface convection zones in all of them. In this work, we
investigate the effect of the pressure induced by the turbulent motion in these
zones based on the mixing length theory, and search for observable
consequences. We find that the turbulent pressure fraction can amount up to ~5%
in OB supergiants, and to ~30% in cooler supergiants. The resulting structural
changes are, however, not significantly affecting the evolutionary tracks
compared to previous calculations. Instead, a comparison of macroturbulent
velocities derived from high quality spectra of OB stars with the turbulent
pressure fraction obtained in corresponding stellar models reveals a strong
correlation of these two quantities. We discuss a possible physical connection,
and conclude that turbulent pressure fluctuations may drive high-order
oscillations, which - as conjectured earlier - manifest themselves as
macroturbulence in the photospheres of hot luminous stars.",1507.03988v1
2015-07-15,Neutron investigation of the magnetic scattering in an iron-based ferromagnetic superconductor,"Neutron diffraction and small angle scattering experiments have been carried
out on the double-isotopic polycrystalline sample (7Li0.82Fe0.18OD)FeSe.
Profile refinements of the diffraction data establish the composition and
reveal an essentially single phase material with lattice parameters of a=
3.7827 {\AA} and c= 9.1277 {\AA} at 4 K, in the ferromagnetic-superconductor
regime, with a bulk superconducting transition of TC = 18 K. Small angle
neutron scattering (SANS) measurements in zero applied field reveal the onset
of ferromagnetic order below TF ~ 12.5 K, with a wave vector and temperature
dependence consistent with an inhomogeneous ferromagnet of spontaneous vortices
or domains in a mixed state. No oscillatory long range ordered magnetic state
is observed. Field dependent measurements establish a separate component of
magnetic scattering from the vortex lattice, which occurs at the expected wave
vector. The temperature dependence of the vortex scattering does not indicate
any contribution from the ferromagnetism, consistent with diffraction data that
indicate that the ordered ferromagnetic moment is quite small.",1507.04311v1
2015-07-16,Strong quantum effects in an almost classical antiferromagnet on a kagome lattice,"Two ubiquitous features of frustrated spin systems stand out: massive
degeneracy of their ground states and flat, or dispersionless, excitation
branches. In real materials, the former is frequently lifted by secondary
interactions or quantum fluctuations, in favor of an ordered or spin-liquid
state, but the latter often survive. We demonstrate that flat modes may
precipitate remarkably strong quantum effects even in the systems that are
otherwise written off as almost entirely classical. The resultant spectral
features should be reminiscent of the quasiparticle breakdown in quantum
systems, only here the effect is strongly amplified by the flatness of
spin-excitation branches, leading to the damping that is not vanishingly small
even at $S\!\gg\!1$. We provide a theoretical analysis of excitation spectrum
of the $S=5/2$ iron-jarosite to illustrate our findings and to suggest further
studies of this and other frustrated spin systems.",1507.04738v2
2015-07-21,Edge states and local electronic structure around an adsorbed impurity in a topological superconductor,"Recently topological superconducting states has attracted a lot of interest.
In this work, we consider a topo- logical superconductor with $Z_2$ topological
mirror order [1] and s$\pm$-wave superconducting pairing symmetry, within a
two-orbital model originally designed for iron-based superconductivity [2]. We
predict the existence of gapless edge states. We also study the local
electronic structure around an adsorbed interstitial magnetic impurity in the
system, and find the existence of low-energy in-gap bound states even with a
weak spin polar- ization on the impurity. We also discuss the relevance of our
results to the recent STM experiment on Fe(Te,Se) compound with adsorbed Fe
impurity [3], for which our density functional calculations show the Fe
impurity is spin polarized.",1507.05904v1